Therapeutic Capabilities of Triterpenes and Triterpenoids in Immune and Inflammatory Processes: A Review

Abstract

Plant-derived secondary metabolites such as triterpenes and triterpenoids are present in a wide range of plant species. These compounds are particularly attractive due to their extensive range of biological properties and potential applications as intermediates in the synthesis of novel pharmacologically promising medications. Saponins, which are glycosylated triterpenoids found in nature, exhibit the same properties. At this point, the effectiveness of saponins as an anti-inflammatory medication has been verified. This review article examines the primary connections between immune responses and anti-inflammatory activity, focusing specifically on the correlation between triterpenes and triterpenoids. These connections have been investigated in various cell models, as well as in vitro and in vivo studies. The present research provides a comprehensive overview of the current understanding of the therapeutic capabilities of triterpenes and triterpenoids in immune and inflammatory processes. It also highlights emerging standards and their potential utilization in pharmaceutical and clinical settings.

1. Introduction

Bioactive compounds are present in various plant materials and are categorized into several classes, including terpenoids, alkaloids and other nitrogen-containing compounds, organosulfur compounds, and phenolics [1,2]. Bioactive compounds are natural primary and secondary metabolites obtained from different plant parts, including leaves, stems, roots, seeds, flowers, and fruits. These compounds can be recovered through various extraction methods [3,4]. The demand for these compounds has risen due to their perception as natural and safe for use in various industries, including cosmetics, food, agriculture, and pharmaceuticals [5]. Bioactive compounds exhibit a broad range of health-promoting properties in humans and animals. These properties include antibacterial, antimicrobial, anti-inflammatory, anti-aging, and anticancer effects [1,6].

Triterpenes, along with sterols, are isoprenoids that are synthesized via the mevalonate pathway [7]. Triterpenes are a type of secondary metabolite comprising 30 carbon atoms that are generated through the conjunction of six isoprene units. Through the process of cyclization and oxidation of two units with 15 carbon atoms each, squalene or similar acyclic 30-carbon precursors can be produced [8]. Approximately 20,000 triterpenes have been identified in nature, with a significant number existing in their unbound state. Other compounds could be found as glycosides (saponins) or in other forms. The main natural triterpenes are cyclic derivatives and can be classified based on the number of rings in their structures. Figure 1 illustrates typical structures of triterpenes and triterpenoids. In this regard, the majority of C30 derivatives fall into two categories: tetracyclic (lanostanes, euphanes, tirucallanes, cucurbitanes, dammaranes, and baccharenes) or pentacyclic (cycloartanes, ursanes, oleananes, lupanes, friedelanes, hopanes, and serratanes) derivatives, as also stated by Thimmappa et al. [7]. Cyclic triterpenes have the ability to undergo additional conversion into a range of metabolites such as steroids, saponins, limonoids, and other chemically related compounds [9]. However, triterpenic molecules are highly hydrophobic, which severely limits their use as effective pharmacological agents. Currently, one of the most common ways to increase triterpenic potency and bioavailability is chemical modification. Typically, this necessitates elevated temperature and pH levels, the utilization of expensive reagents, and the introduction of protective groups to the reactive centers of the molecule [10,11,12,13]. Due to the preceding factors, there is a search for plant-derived compounds that can be used as an alternative or complementary approach to antibiotic treatment. These compounds may also have the ability to prevent the formation of biofilms or aid in the complete removal of existing biofilms. Recently, there has been a growing fascination with pentacyclic triterpenes. Polycyclic organic compounds derived from plants are utilized in traditional phytotherapy for their diverse range of beneficial therapeutic qualities [14]. Preclinical investigations have demonstrated that triterpenes exhibit a diverse array of pharmacological actions such as anticancer, antioxidant, anti-inflammatory, anti-atherosclerotic, antiviral, hepatoprotective, and immunomodulatory activity [8,15].

Terpenoids, commonly referred to as terpenes, are widely recognized for their antioxidant properties [1]. Out of the terpene-based group, triterpenes are considered to possess neuroprotective properties [16]. Triterpenoids are triterpenes that contain heteroatoms, typically oxygen, and they are complex organic compounds composed of 30 carbon atoms arranged in five 6-carbon rings, each with various substituents. This triterpene group is produced through the cytosolic mevalonate route from acetyl-CoA, which is transformed into active isoprene units. Terpenoids are formed by the condensation of six molecules of activated isoprene [17]. They are most frequently found in the peels of fruits, leaves, and the bark of plants [18]. Their primary physiological function is to protect against the detrimental impacts of bacteria and insects [18]. Triterpenoids represent a class of chemicals that is found in many different plants, and they have a wide range of structures. They have attracted interest due to their pharmacological properties [19]. The biosynthesis of isoprenoids/terpenoids is important for living organisms, agriculture, and industry [20]. Natural products are crucial for the identification of numerous potentially bioactive medications due to a substantial body of research that showcases their analgesic, hepatoprotective, anti-inflammatory, antibacterial, antioxidant, and antiallodynic properties.

Natural compounds, such as polyphenols and triterpenic compounds, have been utilized in traditional medicine and continue to be employed today because of their bioactive properties [21]. The pharmacological actions of many triterpenoids have been linked to the significant functional groups present in the ring structure, such as the hydroxyl group, which has been attributed to the numerous pharmacological effects found for certain pentacyclic triterpenoids, such as their anticancer properties [22]. Additional research revealed that the functions of hydroxylated pentacyclic triterpenoids are greatly influenced by the quantity of hydroxyl groups present in rings C1–C6. This was observed in chemically altered 18β-glycyrrhetinic acid, which is an oleanane-type triterpenoid [23]. Terpenes obtained from plants have also been linked to therapeutic benefits such as anticancer and anti-inflammatory properties [24], along with the capacity to overcome treatment resistance and inhibit cancer migration [22,25]. Triterpenoids possess a diverse array of biological properties, such as anticancer, antiangiogenic, anti-inflammatory, antiviral, antioxidant, antidiabetic, antihyperlipidemic, antibacterial, hepatoprotective, and cardioprotective effects, among others. Thus, the majority of triterpenoids have significant biological activity while maintaining a low level of toxicity, suggesting their potential as a substitute for conventional chemotherapeutic agents [18,26]. Despite the recent reviews of Biswas et al. [27] and Bildziukevich et al. [28], in which the biosynthesis and pharmacological properties of triterpenoid saponins were presented, the authors believe that a further in-depth examination of the anti-inflammatory effects of triterpenes and triterpenoids from leaf extracts could shed more light on their value for the pharmaceutical sector.

2. Biosynthetic Pathways of Triterpenes and Triterpenoids

Plants synthesize triterpenes through complex and intricate biosynthetic pathways, as seen in Figure 2. The triterpenes that have been identified and studied are all constructed using a triterpene core, which is formed by six isopentenyl pyrophosphate (IPP) precursors derived from the mevalonate pathway [29]. IPP is partially converted into the allylic isomer dimethylallyl pyrophosphate by IPP isomerase. Then, two IPP molecules and one allylic isomer dimethylallyl pyrophosphate molecule combine to create farnesyl pyrophosphate by prenyltransferase, which serves as the fundamental unit for various terpene pathways dependent on the mevalonate pathway. These pathways include the production of tri- and sesquiterpenes [30]. The initial and crucial stage in the process of triterpene biosynthesis involves the merging of two farnesyl pyrophosphate molecules through the action of squalene synthase, resulting in the formation of the first triterpene compound, known as squalene. Subsequently, this molecule undergoes activation through epoxidation by a squalene epoxidase, leading to the synthesis of 2,3-oxidosqualene [29,31].

The initial branch in triterpene biosynthesis occurs when 2,3-oxidosqualene is converted into various triterpene backbones through cyclization by oxidosqualene cyclase enzymes. This process results in over a hundred different triterpene structures, including cycloartenol for main sterol synthesis and α-amyrin for specialized triterpenes (Figure 1). The cyclization process is initiated by the protonation of an epoxy group, which is then followed by the cyclization and rearrangement of carbocation species [32]. The process is ultimately halted either by deprotonation or the addition of water [29]. The structures produced are then modified through oxidations facilitated by cytochrome P450 enzymes, thereby increasing their variability in both structure and biological function [29,33,34]. Ultimately, triterpenes have the potential to undergo modifications by the addition of sugars, sugar chains, or other chemical groups to the activated carbons. Glycosylated triterpenes are commonly known as triterpene saponins.

Triterpenoids are synthesized from plants through two different pathways, the methylerythritol 4-phosphate/deoxyxylulose 5-phosphate pathway and the mevalonate pathway [35]. This pathway has been studied by examining the genes involved in the biosynthesis of terpenoids [20,36]. Isoprenoids are generated from IPP and its isomer, allylic dimethylallyl pyrophosphate, which are C5 building blocks synthesized through the isoprenoid route. This pathway produces both primary and secondary metabolites. IPP and dimethylallyl pyrophosphate are produced through the mevalonate and methylerythritol 4-phosphate/deoxyxylulose 5-phosphate pathways [37].

3. Methodology

The methodology included the general approach of the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA, Berlin, Germany) 2020 statement [38], as illustrated in Figure 3. This study employed electronic databases, including Science Direct and Scopus, to perform an extensive search for research studies related to the anti-inflammatory properties of triterpenes and triterpenoids derived from plant leaf extracts. The search for articles published between 2019 and 2024 that satisfied the review criteria was conducted using the following terms: (“plant” OR “plants”) AND (“leaf” OR “leaves”) AND (“extract” OR “extracts” OR “extraction”) AND (“triterpene” OR “triterpenoid”) AND (“anti-inflammatory” OR “antiinflammatory”). Publications were included by using the above inclusion criteria, with limitation only to research papers, from which the full text and references that were recognized as possibly relevant were collected. The number of papers retrieved was 200, of which 159 were removed due to not being relevant to the topic. For instance, studies including other plant parts or materials (i.e., roots, seeds, pomace, and pulp) or conducting experiments other than inflammation-related assays were excluded from the present review. In addition, review papers that were mistakenly classified as research papers were been excluded.

4. Extraction of Targeted Compounds

The initial stage in obtaining targeted natural compounds from their original sources is extraction. Solvent extraction methods such as maceration, hydrodistillation, and Soxhlet extraction are all procedures that are based on the same principle, which involves the diffusion of natural compounds from a solid plant matrix into a liquid phase. A number of cycles carried out successively within these laborious protocols ensure the thoroughness of the extractions [1]. However, a large amount of energy is required for the release of the preferred compound in some methods, which involve using greater temperatures or mechanical forces. It should be noted that several green techniques could also be employed for that reason. When extracting compounds of interest from their natural sources, “green” extraction methods aim to minimize negative impacts on the environment and the use of harmful solvents. Compared to conventional extraction techniques, these approaches offer several benefits, such as a shorter extraction times, smaller volumes of harmful organic solvents, a greater extraction yield, and the ability to automate the process for greater reproducibility while consuming less energy [39]. These techniques include accelerated solvent extraction, microwave-assisted extraction, ultrasound-assisted extraction, pulsed electric field extraction, and enzyme-assisted extraction [40]. The extraction process can be made more effective with any solvent that increases solubility and diffusivity in the aforementioned processes. Solvents with polarity values close to those of the solute are more likely to dissolve the natural compounds effectively, according to the law of miscibility and similarity. When it comes to solvent extraction for phytochemical research, alcohols, acetone, water, and ethyl acetate are some of the frequently used solvents [41].

5. Anti-Inflammatory Activity of Triterpenes and Triterpenoids

Inflammation is a normal response of the human body to several detrimental stimuli, including physical injury, noxious chemicals, and microorganisms. The inflammatory response is triggered by a sequence of external and internal signals that arise from mechanical, chemical, or biological tissue injury [42]. Inflammation is strongly linked to the initiation and progression of numerous significant illnesses. It is primarily characterized by local redness, swelling, pain, edema, and an increase in temperature due to reactions in the vascular system. If recurrent acute inflammatory events are not resolved, they can result in chronic inflammatory diseases such as arthritis [43], colitis [44], or asthma [45]. These conditions are linked to irreversible tissue damage and an increased risk of developing cardiovascular disease [46], cancer [47], rheumatoid arthritis [48], and osteoporosis [49]. Chronic inflammation encompasses debilitating autoimmune disorders characterized by intense inflammation [50] and resulting in significant tissue impairment. Pro-inflammatory cytokines, including tumor necrosis factor-α (TNF-α) [51], interleukin (IL)-6 [52], and IL-1 beta [53], are present for extended durations in chronic inflammatory diseases. Inflammation arises from a persistent immunological response involving pro-inflammatory macrophages, microglia, and neutrophils [54], as well as cytokines secreted by several cell types, including endothelial cells, oligodendrocytes, and fibroblasts [55]. The mechanism by which inflammatory disorders occur is an intricate network of interrelated processes. Numerous enzymes and components participate in cellular signaling networks. Drug treatment can often improve inflammatory responses by inhibiting the generation or release of inflammatory mediators [42]. The clinical management of inflammation involves the use of two primary categories of medications, nonsteroidal anti-inflammatory drugs and steroidal anti-inflammatory drugs [42,56,57].

Anti-inflammatory activity is a frequently attributed biological activity of natural triterpenes [9]. Recently, several studies have highlighted the anti-inflammatory activity of ursane-type triterpenes, especially ursolic acid [58,59,60]. Therefore, ursane-type triterpenes can be investigated as candidates for the treatment of diseases associated with neuroinflammation. From this viewpoint, interesting results of experimental models have been obtained for the treatment of multiple sclerosis through the effect of ursolic acid on immunomodulation and neuronal repair by direct remyelination in the chronic progressive stage of the disease, for which there is currently no effective therapy [61]. However, recent data suggest that ursolic acid may have negative consequences, including toxicity, in certain situations [62]. This raises concerns about the concentration and resolution of its toxicity.

Triterpenes possessing an oleanane structure are believed to have much higher activity compared to those with an ursane backbone [63]. Moreover, the inclusion of a keto group at C3 and carboxyl groups at C17 in the oleanane skeleton, along with the augmentation of the quantity of oxygenated functional groups in other locations, amplifies the anti-inflammatory activity [9,63]. Furthermore, a comparison of anti-inflammatory evidence for both oleanolic and moronic acids indicated that the latter demonstrates greater promise. In accordance with a preliminary study on the association between structure and activity, it is suggested that the presence of a Δ¹⁸ double bond at the C13–C18 ring may be the cause of this activity.

5.1. Leaf Extracts Containing Triterpenes

5.1.1. Membrane Stability Assay on Triterpenes

Bolaji et al. [64] investigated leaf extracts from Euphorbia graminae plants for the presence of phytochemical components. The ground leaves were first macerated in methanol and then vacuum treated. Among other compounds, triterpenes were identified in the phytochemical analysis. A membrane stabilization assay was employed to assess anti-inflammatory activity. Membrane stabilization has been recognized as a mechanism through which specific medicinal plants confer anti-inflammatory effects. Due to the stability of the membrane, after inflammation, serum proteins are prevented from leaking into the tissues during the period of increased permeability, as stated by Fujiati et al. [65]. The mechanism of a plant extract’s anti-inflammatory activity can be measured by its ability to inhibit hypotonicity impact via membrane stabilization in red blood cells. To this end, after incubation at 56 °C for 30 min, stressed bovine red blood cells exhibited enhanced protection after treatment with leaf extracts, achieving 100% stability at lower concentrations (0.05−0.15 μg/mL), in contrast to the positive control treated with the anti-inflammatory drug diclofenac, which reached a plateau at 20% stability. At a higher concentration of 1.0 μg/mL, a plateau of 30% membrane stability was observed, whereas diclofenac yielded approximately 80% membrane stability. Studies indicate that saponins (i.e., triterpene glycosides) can bind to macromolecules on cell membranes, obstructing the interaction of inflammatory agents with these regions. This intriguing discovery warrants further investigation using fractions of leaf extract to isolate the triterpenes exhibiting anti-inflammatory properties.

5.1.2. Protein Inhibition Assay on Triterpenes

An aromatic tree native to North America and adapted to Brazil, Liquidambar styraciflua L. is commonly called the sweet gum or alligator tree. Its leaves are often employed to alleviate gastrointestinal issues, scratches, and coughs. Mancarz et al. [66] evaluated the chemical composition and biological efficacy of extracts obtained from the aerial portions of L. styraciflua L. A hydroalcoholic mixture was employed for the extraction of ground leaves. The authors identified triterpenes only by phytochemical analysis in several fractions. To assess anti-inflammatory activity, a hyaluronidase enzyme inhibition assay was used. One type of inflammatory process involves the hydrolysis of hyaluronic acid by the enzyme hyaluronidase, which causes edema and other inflammatory symptoms by degrading the extracellular matrix and increasing tissue permeability. Many pathophysiological processes require hyaluronidase, and inflammation is linked to numerous chronic diseases. Various fractions of the extract were acquired using chloroform, n-hexane, butanol, ethyl acetate, and water. A commercial propolis extract (positive control) exhibited a 50% inhibition concentration (IC₅₀) value of 32.13 mg/mL in hyaluronidase enzyme. The IC₅₀ values for the aqueous extract (75.32 mg/mL), ethyl acetate fraction (59.57 mg/mL), butanol fraction (51.29 mg/mL), and hydroalcoholic fraction (49.13 mg/mL) indicated that the hydroalcoholic fraction displayed the closest value to propolis extract and was the most desirable fraction. The remaining fractions of n-hexane and chloroform were deemed to lack significant inhibitory activity and were excluded from subsequent investigations. Consequently, additional anti-inflammatory investigations on the percentage of inhibition activity were conducted. At a concentration of 100 mg/mL, propolis extract attained approximately 98% inhibition, while the hydroalcoholic fraction reached around 83%, indicating its potential as an anti-inflammatory agent for possible application in the pharmaceutical industry. Nonetheless, the terpene composition must be elucidated alongside the in vivo activity to enhance understanding of the anti-inflammatory properties of this chemical class.

5.1.3. In Vivo Assays on Triterpenes

Regarding the treatment of snakebite envenomation, only the use of antivenom has been approved in Colombia. Since the antivenom effectively neutralizes systemic effects but is ineffective against local effects, complications may arise. In contrast, for basic medical needs, people living in rural areas often turn to plants that are both common and easy to reach. Piper auritum is one of these plants that has long been revered by the indigenous peoples of Chocó and Antioquia. An alcoholic extract from the leaves of P. auritum was tested for its anti-edema effects on mice as part of the research conducted by Rengifo-Rios et al. [67]. Soxhlet extraction was conducted for 48 h to prepare the extract. The right leg of each mice was injected with venom, followed by the administration of the alcoholic extract in the same leg. The National Institute of Health anti-edema serum was utilized as the positive control, with the effective dose 50 (ED₅₀) assessed. The findings indicated that the National Institute of Health serum exhibited an ED₅₀ value of 1.36 mL/mg of venom, while the alcoholic P. auritum extract demonstrated an ED₅₀ value of 1.78 mL/mg of venom, suggesting a value comparable to the positive control. The authors assert that the triterpenes present in the plant may underlie the extract’s anti-edematous properties, as these compounds exhibit anti-myonecrotic activity by forming covalent bonds with toxins, particularly phospholipases A₂. However, they emphasize that to gain a comprehensive understanding of the extract’s efficacy, it is essential to isolate and analyze its constituents.

Most African countries have a long history of using Ficus asperifolia to treat inflammatory diseases. The exploration of the anti-inflammatory properties of a methanolic leaf extract from F. asperifolia was the aim of the study by Abdullahi et al. [68]. Phytochemical and acute toxicity tests were performed on the extract. The extract was evaluated at doses of 250−1000 mg/kg for its anti-inflammatory properties through carrageenan-induced paw edema and acetic acid-induced writhing in mouse models. The median lethal dose (LD₅₀) of F. asperifolia, when administered intraperitoneally, was established at 3800 mg/kg. In comparison to the control group, the group administered piroxicam, the positive control, at 1000 mg/kg exhibited reduced writhing behavior by ~21%, achieving a plateau of ~35% after 6 h. Similarly, at a dosage of 1000 mg/kg of the extract, the outcomes were comparable to those of the anti-inflammatory medication, exhibiting a peak activity level above 50% inhibition of pain. The methanolic leaf extract of F. asperifolia demonstrated potential anti-inflammatory properties, with the authors identifying the presence of triterpenes; however, further elucidation of their anti-inflammatory activity could be achieved through isolation.

Traditional Peruvian medicine involves the use of the plant Encelia canescens Lam, which has anti-inflammatory activity. The study by Fernández-Flores et al. [69] was aimed to determine whether an ethanolic extract of E. canescens leaves could protect levels of mouse albumin, total protein, and malondialdehyde (MDA) in a 1% carrageenan-induced air pouch model. Three different concentrations of E. canescens were tested (100, 250, and 500 mg/kg) compared to 2 mg/kg of dexamethasone, a National Institute of Health (NIH) serum. The results showed that the extract had dose-dependent effects on the three biochemical parameters, all of which exhibited significant differences (p < 0.05) compared to the control group. In addition, 500 mg/kg of extract was more effective than 2 mg/kg of dexamethasone in the albumin denaturation assay (achieving 1.01 compared to 1.21 g/dL) and in the MDA assay (1.24 versus 1.44 nmol/L). Comparable values were observed in the total protein assay, with both anti-inflammatory agents achieving ~3.6 g/dL. Terpenes may reduce inflammation by stabilizing lysosomes. These lysosomes contain proteases and hydrolytic enzymes that cause inflammatory chemical mediators. When inflammation occurs, these lysosomes disintegrate, causing damage and other inflammatory phenomena. The histological analysis of E. canescens’s anti-inflammatory effects revealed that, in healthy tissue, inflammation did not appear as a layer of flattened cells overlaying loose vascular connective tissue. Upon observing inflammatory changes such as leukocyte infiltration and edema, the lining layer of flattened cells in the carrageenan 1% group showed an increase in macrophages and fibroblasts. Reduced leukocyte migration and MDA concentration were associated with the anti-inflammatory efficacy of the 500 mg/kg extract. Nevertheless, it is still not known how chemical composition relates to anti-inflammatory activity, so such investigations could shed more light on this aspect.

Research into the compounds and anti-inflammatory properties of Morinda citrifolia (noni) leaf extract was conducted in a study by Ly et al. [70]. Dried leaves were extracted with 70% ethanol at 60 °C, and a protein denaturation assay was utilized for anti-inflammatory activity measurement. The results demonstrated that noni leaves contained coumarins, triterpenes, tannins, alkaloids, saponins, and flavonoids. In terms of concentration-dependent anti-inflammatory activity, the noni leaf extract showed the following values: 12.18% (at 20 mg/L), 34.06% (at 40 mg/L), 45.79% (at 60 mg/L), 52.75% (at 80 mg/L), and 60.90% (at 100 mg/L). In comparison to that for ascorbic acid (168.81 mg/L), the IC₅₀ value for inhibiting protein denaturation with noni leaf extract was lower, at 70.21 mg/L. After eleven days of treatment, noni leaf extract aided in wound healing in mice by decreasing wound area and increasing histological regeneration. When applied to rabbit skin, noni leaf extract produced negligible skin swelling, suggesting a promising anti-inflammatory effect. However, further in vivo studies are required to support this evidence.

The Ammoides pusilla plant is a medicinally significant species with a long history of use in traditional medicinal practices. A study by Belkhodja et al. [71] included an in vivo anti-inflammatory potential assessment of A. pusilla leaves and the determination of its value in the treatment of a severe disease that affects the stability of articular cartilage and bone structure. Dried leaves were extracted with boiling water for 15 min. The phytochemical analysis of the extract revealed that it was abundant in polyphenols (~22 mg/g of extract), including flavonoids, tannins, coumarins, anthocyanins, and triterpenes. Rheumatoid arthritis led to unique swelling in the paw. The measurement of this edema was performed in mice to assess anti-inflammatory activity. When tested on mice with Freund’s adjuvant-induced rheumatoid arthritis, the anti-inflammatory activity data demonstrated that the aqueous A. pusilla-infused extract may have promising antiarthritic effects. The treated mice (preventive or curative) had stable body weights compared to arthritic mice, which lost 5 g from an initial weight of ~35 g. In addition, the thickness of edema decreased from 5.56 to 2.59 mm for the curative group and from 4.76 to 2.51 mm for the preventive group when 250 mg/kg of the aqueous extract of A. pusilla was administered orally, as compared to the reference medicine (diclofenac). Edema, a sign of inflammation, decreased in volume with 20 mg/kg of diclofenac, with the average thickness decreasing from 5.67 mm to 2.71 mm. The authors attributed these anti-inflammatory effects to triterpenes that were present in the extract as inflammation-reducing mediators. A class of medications known as nonsteroidal anti-inflammatory drugs has shown promise in the treatment of edema and pain by blocking cyclooxygenase-1 and cyclooxygenase-2 (COX-1 and COX-2). As an alternative chemical for inflammation prevention, the aqueous extract of A. pusilla is thus of great therapeutic interest, as it provides a cure for edema.

Table 1. Anti-inflammatory effects of plant leaf extracts and identification of the main triterpenes.

Sample	Triterpene	Anti-Inflammatory Effect	Ref.
E. graminae	Triterpenes determined through non-specific colorimetric techniques	30% membrane stability from the extract, ~80% membrane stability from diclofenac	[64]
L. styraciflua L		Aqueous extract IC50 values (75.32 mg/mL), ethyl acetate fraction (59.57 mg/mL), butanol fraction (51.29 mg/mL), and hydroalcoholic fraction (49.13 mg/mL), compared to propolis IC50 value of 32.13 mg/mL in hyaluronidase inhibition assay	[66]
P. auritum		Antivenom and anti-inflammatory activities at 500 mg/kg better than those of NIH serum dexamethasone when used at 2 mg/kg in an albumin denaturation assay	[67]
F. asperifolia		Comparable activity to piroxicam, achieving >50% pain inhibition	[68]
E. canescens Lam		Albumin denaturation assay: 500 mg/kg of extract achieved 1.01 compared to 1.21 g/dL that 2 mg/kg for dexamethasone	[69]
M. citrifolia		IC50: higher protein denaturation activity (70.21 mg/L) than ascorbic acid (168.81 mg/L)	[70]
A. pusilla		Edema reduced from 5.56 to 2.59 mm in the curative group and from 4.76 to 2.51 mm in the preventive group at 250 mg/kg of the aqueous extract of A. pusilla	[71]

IC₅₀: 50% inhibitory concentration; NIH: National Institute of Health.

provides a brief review of non-specific triterpenes and their anti-inflammatory activity. The authors employed a non-specific colorimetric approach to detect the presence of triterpenes in the mentioned investigations. Identification techniques for the chemical composition of the extracts could clarify their anti-inflammatory properties.

5.2. Leaf Extracts Containing Triterpenoids and Saponins

5.2.1. Protein and NO Inhibition Assays on Triterpenoids and Saponins

An investigation by Anjum et al. [72] aimed to assess the biological activities and qualitative and quantitative chemical composition of an ethyl acetate extract of Ardisia solanacea Roxb. from the Tarai region of Uttarakhand. The Soxhlet method was employed to obtain extracts from the plant, utilizing ethyl acetate as the solvent. Oils, resins, diterpenes, triterpenoids, carbohydrates, and alkaloids were among the many bioactive components identified by qualitative GC-MS analysis. It was also possible to quantify the triterpenoid α-amyrenone. Anti-inflammatory activity was assessed through a protein denaturation assay. The leaf extract’s anti-inflammatory activity was assessed in comparison to that of diclofenac, which served as the positive control. Diclofenac had an IB₅₀ value of 2.80 μg/mL in the protein denaturation assay (i.e., meaning 50% inhibition of the denaturation of proteins), whereas the ethyl acetate leaf extract of A. solanacea had strong anti-inflammatory properties, with an IB₅₀ value of 3.13 μg/mL. Further in vivo studies could provide evidence of whether the plant is safe for use in the pharmaceutical industry.

Fractionation is a highly effective method for assessing the anti-inflammatory properties of specific chemical compounds, as it is highly effective for their separation and, thus, for their separate study. The process is typically conducted using the column chromatography technique with solvents of appropriate polarity. Aro et al. [73] conducted a study to examine the anti-inflammatory properties of acetone leaf extracts from Oxyanthus speciosus subsp. stenocarpus. The main objective was to reduce chronic inflammatory diseases, such as tuberculosis. The air-dried leaves were extracted with acetone, and the extract was evaporated in vacuo. Hexane, ethyl acetate, and methanol were utilized for the fractionation. The results indicated that the fraction containing the triterpenoid rotundic acid exhibited a significant anti-inflammatory effect. Nitric oxide (NO) production in lipopolysaccharide (LPS)-activated RAW 264.7 macrophages ranging from 2.39 to 0.48 μM was achieved within the concentration range of 3.12–25 μg/mL. In comparison, the fractions of the carotenoid lutein ranged from 1.98 to 0.14 μM, while the fraction of the flavonoid quercetin ranged from 2.50 to 0.35 μM. This research explored the anti-inflammatory efficacy of certain component fractions as regulators of cellular redox potential. Rotundic acid showed encouraging outcomes as a therapeutic agent against tuberculosis, as evidenced by its efficacy both in vitro and intracellularly in macrophages. However, further investigation is required to analyze its bioavailability, its effects in vivo, and its mechanism of action.

The leaves of Nyctanthes arbor-tristis contain betulinic acid, a lupane-type triterpenoid that had never been reported before but was studied by Karan et al. and exhibited strong anti-inflammatory properties [74]. The ground leaf powder was extracted with methanol and fractionated with water, n-butanol, and ethyl acetate. The bioactivity-guided fractionation method was used for the first time to isolate betulinic acid from an ethyl acetate leaf extract of N. arbor-tristis. The betulinic acid structure was determined through several spectroscopic analyses, including nuclear magnetic resonance, Fourier-transform infrared spectroscopy, and high-resolution mass spectrometry. It demonstrated excellent anti-inflammatory properties, with IC₅₀ values of 10.34 μg/mL for COX-1, which had two levels of enzyme (i.e., 10 μL of enzyme referred to as COX-1). The other IC₅₀ values were 12.92 μg/mL for COX-2, 15.53 μg/mL for 5-lipoxygenase assay (5-LOX), 15.21 μg/mL for NO production, and 16.65 μg/mL for TNF-α in RAW 264.7 cells. As a positive control for the inhibition of COX-1, COX-2, and 5-LOX, boswellic acid was used at a concentration of 50 μg/mL. It achieved 97.36, 94.32, and 92.64 μg/mL values for COX-1, COX-2, and 5-LOX, respectively. For NO production and TNF-α, dexamethasone was used at a concentration of 15 μg/mL. Both drugs achieved higher than 95% inhibition in each assay (i.e., 97.99 and 98.34%, respectively), whereas several subfractions of ethyl acetate extract achieved 3.35–92.20% in all assays, with subfraction 7 being the most preferable. It could be concluded that betulinic acid acts as a promising anti-inflammatory agent; however, in vivo assays would confirm this outcome.

Globally, Ziziphus plants are renowned for their medicinal and nutritional value, although their complete chemical composition has not yet been disclosed. A study by Sakna et al. [75] examined the anti-inflammatory properties of Ziziphus mauritana, Z. spina-christi, and Z. jujuba methanolic leaf extracts. To this end, 80% methanol was used for the extraction process. Several triterpenoids were identified through the liquid chromatography–mass spectrometry method, such as ceanothic acid, isoceanothic acid, apiceanothic acid, and epigouanic acid. However, the total triterpenoids were expressed photometrically as ursolic acid equivalents (UAE). A COX-1 assay was used to measure anti-inflammatory activity, with a commercially available selective cyclooxygenase inhibitor (SC-560) achieving 65.71% inhibition at the same concentration as the extracts (10 mg/mL). The results showed promising anti-inflammatory activity determined through % COX-1 inhibition of Z. mauritiana (90.34), Z. spina-christi (89.31), and Z. jujuba (76.87). It was observed that the first two extracts exhibited the highest inhibition, with no statistical differences (p > 0.05). However, it should be highlighted that Z. mauritiana had 30% less triterpenoid content when compared to Z. spina-christi (224.15 mg UAE/g extract) but had comparable anti-inflammatory activity. The authors report that this activity was probably caused by the presence of triterpenoids. Z. jujuba also recorded the lowest amount of triterpenoids (146.12 mg UAE/g extract). However, the authors state that these findings were merely suggestive. Subsequent comprehensive investigations of Ziziphus leaf extracts in living organisms or, preferably, studies focusing on individual, isolated compounds, are necessary to establish more definitive conclusions. In addition, studies could include more cultivars of the Ziziphus plant to shed more light on the anti-inflammatory properties of this plant.

A methanolic extract from the leaves of Calophyllum inophyllum with substantial anti-inflammatory effects in vitro was the subject that Van Than et al. [76] investigated. Dried leaves were extracted with methanol and fractionated with dichloromethane, ethyl acetate, and n-hexane through column chromatography. The authors investigated the inhibition of NO production and cytokine production in RAW 264.7 cells when stimulated with lipopolysaccharide from these compounds. From the total of twelve compounds, two new compounds with coumaroyl ester structures were identified as terpenoids and had comparable IC₅₀ values to the positive control dexamethasone (0.012 μM). Compounds 1 and 2 achieved 2.44 and 7.00 μM, respectively. Compound 9 achieved 15.46 μM, and all remaining compounds exhibited >50 μM IC₅₀ values. The two specific compounds also revealed effectiveness in deteriorating abnormal inflammation responses, as they lowered concentrations of interleukin (IL)-1β and TNF-α at concentrations of 5 and 10 μM in a dose-dependent way. For instance, IL-1β concentration was reduced from >300 to ~200 and ~100 pg/mL at concentrations of 5 and 10 μM of compound 1, respectively. A similar reduction was observed for compound 2. Regarding TNF-α, a reduction from 250 to 200 and 150 pg/mL was noticed when concentrations of 5 and 10 μM of both compounds were administered. In the case of prostaglandin E₂ (PGE2) and IL-6, neither compound affected the concentration of these two substances. As for NO production, it was significantly reduced to a comparable level to that achieved with dexamethasone. It was also revealed that compound 1 inhibited the phosphorylation of IκB, which led to a decrease in the nuclear translocation of nuclear factor κ light-chain enhancer of activated B cells (NF-κB) when treated at 10 μM, whereas compound 2 did not show any significant effects at this concentration. Hence, the E-coumaroyl ester triterpenoid, rather than the Z-coumaroyl ester triterpenoid, may be responsible for NF-κB inhibition activation by CIL, which is in line with its NO inhibitory effect. The anti-inflammatory effects of C. inophyllum extract may be attributed to these compounds, which are active phytochemical components. Further in vivo studies could support these findings and provide evidence for a novel anti-inflammatory extract for the pharmaceutical industry.

Some interesting research studies involve the discovery of novel triterpenic compounds (vide infra). To start with, Tai et al. [77] explored the anti-inflammatory activity of Syzygium bullockii leaf extract by using a NO production inhibition assay. The methanolic extract was further partitioned with solvents of ranging polarities (i.e., ethyl acetate, dichloromethane, and n-hexane). Seventeen compounds in total were identified in the methanolic S. bullockii extract, wherein terpenoids syzygiumursanolide C, chebuloside II, and three undescribed compounds (i.e., syzybullosides A–C) were isolated. The results showed that the identified compounds had an IC₅₀ range of 1.30–13.70 μM in NO production inhibition using lipopolysaccharide-activated RAW 264.7 cells. The three unknown compounds showed values of 6.93–13.61 μM, whereas the positive control N^G-monomethyl-L-arginine (L-NMMA) had a value of 33.8 μM. The compounds showed promising anti-inflammatory activity, which could be further supported with additional experiments.

Vinh et al. [78] explored a total of 23 triterpenoid saponins, including two novel compounds (12 and 15), that were isolated from an ethanol extract of Stauntonia hexaphylla leaves. NO production and cytokine production assays were used to determine the anti-inflammatory activities of the isolated saponins. With an IC₅₀ value of 0.59 μM in the NO production assay, compound 13 showed the strongest inhibitory effect when compared to that of the positive control dexamethasone at 0.13 μM. Compounds 1 and 3 also achieved values of 1.82 and 16.65 μM, while the remaining compounds had values >50 μM. The two compounds were also used at a concentration of 1–10 μM to examine the inhibitory effects on LPS-stimulated RAW 264.7 cells. Both compounds led to the concentration-related inhibition of pro-inflammatory cytokines. Specifically, compound 13 inhibited the protein expression of NO synthase and COX-2 in LPS-activated RAW 264.7 cells, along with NO, IL-1β, IL-6, and PGE2 but not TNF-α secretion. The authors used structure–activity relationships to investigate the chemical byproducts of these isolated chemicals. The findings raised the possibility that compound 13, derived from S. hexaphylla, could have anti-inflammatory properties. This study presented the first in-depth analysis of saponins derived from S. hexaphylla leaves. Applying screening criteria for anti-inflammatory extracts and performing in vivo experiments could lead to more comprehensive results about saponins’ mechanism of action.

Capparis L. (Capparaceae) is cultivated globally. Traditional medicine practitioners have long relied on capers to alleviate a wide range of symptoms, including rheumatism, kidney, and liver issues. The goal of Gazioglu et al. [79] was to identify the anti-inflammatory activity of Capparis ovata extracts. C. ovata leaves were extracted with dichloromethane/hexane (1:1), and the structure of eight identified compounds was studied with spectroscopic methods. The compounds were tested at concentrations ranging from 12 to 26 μM against the production of inflammatory cytokines in SH-SY5Y human cell lines. Well-known triterpenoids such as oleanolic acid, β-sitosterol, ursolic acid, bismethyl-octylphthalate, and stigmast-5,22-dien-3-β-myristate were identified in this extract. Interestingly, the treatment of SH-SY5Y cells with 26 μM of compound 1 (i.e., a novel triterpenoid ester named olean-12-en-28-ol, 3b-pentacosanoate), as the lethal dose to 10% of cells treated (i.e., EC₁₀), reduced mRNA expression levels of chemokine (C-X-C motif) ligand 9 (i.e., CXCL9) (19.36-fold), CXCL10 (8.14-fold), and TNF (18.69) compared to those in the control group. This research showed that triterpenoids extracted from C. ovata have anti-inflammatory properties. It was discovered that compounds 1 and 3 (i.e., oleanolic acid) showed great promise as therapeutic agents for the treatment of inflammatory diseases.

Menopausal discomfort and intestinal hemorrhage have both been alleviated with the use of Osmanthus fragrans var. aurantiacus. A methanolic leaf extract was generated by Jeong et al. [80], and the extracted compounds were isolated through a fractionation procedure utilizing water, n-hexane, ethyl acetate, and n-butanol. The authors identified four triterpenoids, namely, 3-O-trans-p-coumaroyltormentic acid (1), 3β-trans-p-coumaroyloxy-2α-hydroxyl-urs-12-en-28-oic acid (2), 3-β-cis-p-coumaroyloxy-2α-hydroxyl-urs-12-en-28-oic acid (3), and 3-O-cis-coumaroylmaslinic acid (4). The anti-inflammatory activity was examined through NO production inhibition in RAW 264.7 cells with the ethyl acetate fraction, which was found to be the most preferable. The four compounds showed dose-dependent NO production inhibition using concentrations of 1−10 μM and were compared with the positive control curcumin (10−100 μM). The results revealed that compound 2 at 10 μM exhibited the greatest inhibition (>80%), while curcumin at 100 μM led to ~50% inhibition. Moreover, the levels of LPS-stimulated protein, COX-2, NF-κB, and phosphorylated extracellular regulated kinase (pERK) 1/2 were significantly decreased by compounds 2–4 according to Western blotting. Specifically, compound 2 at 10 μM had the greatest inhibitory effect (~50%) on the phosphorylation of ERK 1/2 at a 0.5 relative density of pERK/ERK through Western blot analysis, whereas the highest value of LPS-stimulated cells was ~1.2. Interestingly, levels of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, and IL-8 were reduced in LPS-induced macrophages and colonic epithelial cells under exposure to compounds 2–4. The study suggested that these compounds extracted from O. fragrans var. aurantiacus leaves could be useful in preventing and treating inflammatory bowel disease. However, further evidence for the identified triterpenoids could be provided by prospective in vivo experiments. The medicinal application of O. fragrans var. aurantiacus in the treatment of inflammation-related disorders has made it an increasingly popular commodity in China and Korea [80]. Meanwhile, new research has shown that O. fragrans var. aurantiacus possesses anti-inflammatory properties, which could make it an effective anticancer agent. This is particularly true in colorectal cancer, where inflammation plays a key role in the progression and evolution of the disease [81]. Considering the above information, Han et al. [82] aimed to study O. fragrans var. aurantiacus for its possible effects on colorectal cancer by examining its anti-proliferative and pro-apoptotic characteristics. Using two sonication cycles of ~2 h each, the dried leaves were immersed in ethanol for the extraction process. Following the procedure previously outlined by Jeong et al. [80], the extracts were fractionated using n-hexane, ethyl acetate, n-butanol, and water. Ethyl acetate fractions were selected to be reanalyzed. Maslinic acid and corosolic acid are two triterpenoids that the authors identified, and they are thought to be anticancer compounds for colorectal cancer. In two colorectal cancer cell lines (HCT 116 and HT29), the ethyl acetate fraction at a concentration of 100 μg/mL considerably decreased p65 and ERK phosphorylation levels without impacting protein expression levels. However, at a lower concentration of 50 μg/mL, the fraction primarily decreased inhibitor of nuclear factor kappa α (i.e., Iκ-Bα) phosphorylation in HT29 cells. Furthermore, the COX-2 gene, which is implicated in the mediation of inflammation-related cancer pathways, was shown to have its expression reduced in colorectal cancer cells by the ethyl acetate leaf fraction. The COX-2 gene is a downstream target of NF-B and ERK1/2 that mediates inflammation-related carcinogenic pathways. Taken together, these findings point to the fact that the ethyl acetate fraction of O. fragrans leaves inhibits the NF-κB and mitogen-activated protein kinase (MAPK)-ERK pathways, which in turn cause colorectal cancer cells to undergo apoptosis. The above results were validated since the measured IC₅₀ values from the two specific compounds were ~30 μg/mL, and no cytotoxic effects were observed. In addition, normal human colon cells showed a ~30% decrease in cell viability at 20 μg/mL. The findings highlight that the two triterpenoids induce colorectal cancer cell death, with corosolic acid being more potent in this activity and demonstrating the anti-inflammatory and anticancer characteristics of O. fragrans var. aurantiacusin leaves.

Cecropia pachystachya, one of the species of the Urticaceae family, is widely used in South America as a folk medicine due to its pain-relieving properties. Its bioactive compounds can exert anti-inflammatory activity by halting the production of inflammatory mediators from immune cells. To this end, Daga et al. [83] investigated an extract obtained with the supercritical CO₂ technique as a medication for Chagas disease, a zoonotic infection with which millions of people are affected every year. NO inhibition is an essential assay to assess the inflammation process [84], wherein lipopolysaccharide is administered as a pro-inflammatory stimulus control to RAW 264.7 macrophages. The results showed that NO production was reduced from ~20 to ~5 μM when a 300 μg/mL C. pachystachya extract was used. Ursolic acid was proposed to be responsible for the anti-inflammatory activity of C. pachystachya extract, a trend that has also been supported by Ahmad et al. [85].

In South China, Cyclocarya paliurus is often used for the treatment and prevention of inflammatory disorders. However, no active anti-inflammatory compounds have been identified, despite the fact that research on the anti-inflammatory effects of C. paliurus leaves has been reported. To this end, Liu et al. [86] explored the anti-inflammatory effects of an ethanolic C. paliurus leaf extract and identified its anti-inflammatory compounds by using RAW 264.7 cells to build a bioactivity-guided identification model. The extract was fractionated with polyethylene, ethyl acetate, water, and n-butanol. The structures of 18 dammarane triterpenoid saponins were identified with spectroscopic methods and determined after isolating the active fraction. Among these, 11 were newly discovered 3,4-seco-dammarane triterpenoid saponins (1–11). The IC₅₀ values for compounds 7, 8, 10, and 11 varied from 8.23−11.23 μM, indicating a strong inhibition of NO production. The most preferable fraction was that of ethyl acetate at 80 μg/mL, which achieved comparable inhibition to the positive control dexamethasone (~90%). The release of TNF-α, PGE2, and IL-6 in RAW 264.7 cells activated by lipopolysaccharide was considerably reduced by these four compounds in a concentration-dependent way. Indeed, the highest concentration of the above compounds found in the extract (i.e., 40 μM) achieved a substantial decrease compared to values in untreated cells in TNF-α expression (~60 from ~375 pg/mL), in PGE2 (~60 from ~140 pg/mL), and in IL-6 (~120 from ~410 pg/mL) cytokine expression. In addition, the activities of COX-2 (from ~0.7 to ~0.15 COX-2–β-actin ratio), iNOS (from ~0.55 to ~0.25 iNOS–β-actin ratio), and NF-κB/p65 (from ~0.7 to ~0.3 NF-κB/p65–β-actin ratio) were reduced by compound 7 at a 20 μM concentration. Further in vivo investigation is warranted because the results indicate that 3,4-seco-dammarane triterpenoid saponins have the potential to be used as anti-inflammatory drugs.

Luo et al. [87] isolated four new tetracyclic triterpenoids from Jatropha gossypiifolia ethanolic leaf extract (1−4) through thorough spectroscopic analyses. The extracts were suspended in water and fractionated with petroleum ether. Compounds named jagabeoeuphols A–C (1−3) are uncommon triterpenoids of the 19 (10 → 9)abeo-euphane type that have a Δ⁵⁽¹⁰⁾ group and a 7,8-epoxide moiety, while jagoseuphone A (4) is a common euphane-type triterpenoid. NO production in RAW 264.7 cells stimulated by LPS assistance was examined to study the inhibitory effects of terpenoid compounds. Only compound 4 showed a substantial inhibitory effect, with an IC₅₀ value of 20.1 μM, whereas the positive control quercetin had a value of 16.8 μM. The other three compounds had significantly higher (p < 0.05) IC₅₀ values (>50 μM). Further in vitro and preferably in vivo assays could lead to clearer insights into the relationship between the structure and anti-inflammatory activity of these triterpenoids, especially the uncommon ones (1−3).

Three known triterpenoids (ternstroenols) were isolated from the leaves of Ternstroemia cherryi from the Australian rainforest via chromatographic separation in a study by Singh et al. [88]. The dried leaves were extracted with n-hexane, ethyl acetate, methanol, ethanol, and water. The ethanolic extract was found to be the most preferable for the anti-inflammatory assay. Extensive spectroscopic analysis, chemical derivatization, and degradation assays were used to determine the ternstroenol structures. The extracts showed an IC₅₀ value of 0.72–3.70 μM for NO production in RAW 264.7 macrophages activated by LPS and interferon-γ (IFN-γ). Further in vivo studies could shed more light on the anti-inflammatory activity of this leaf extract, as the authors mainly described the structure of five novel compounds in the T. cherryi fruit extract.

A wide variety of Southeast Asian countries produce Citrus hystrix. The anti-inflammatory properties of this leaf extract have been examined by Buakaew et al. [89]. Few details are known about the leaves’ anti-inflammatory and anti-inflammasome capabilities, however. The purpose of this research was to examine how C. hystrix leaves influence the nucleotide-binding domain, leucine-rich repeat-containing family, pyrin domain-containing-3, and nuclear factor κ light-chain enhancer of activated B cells (i.e., NLRP3 and NF-κB, respectively) signaling pathways. Three crude extracts were obtained from the C. hystrix leaves through a sequential extraction process using hexane, ethyl acetate, and 95% ethanol. The extract was fractionated with organic solvents of varying polarities, generating six fractions. Spectroscopic methods were used to identify and confirm the structure of the active compound lupeol, which was fractionated from the ethanolic extract using chromatographic techniques. The lupeol fraction, along with the ethanolic extract, both suppressed the expression of inflammasome genes and NF-κB proteins and considerably decreased the secretion of pro-inflammatory cytokines. Indeed, IL-1β, IL-6, and TNF-α were significantly reduced with either the lupeol fraction at 25 μg/mL or the ethanolic C. hystrix extract at 1.5 or 2.5 μg/mL in a dose-dependent way. The positive control, dexamethasone, was administered at 0.1 nM and was the most effective anti-inflammatory agent of all, except for the NF-κB1 cytokine and nitric oxide synthase 2 (NOS2). In both cases, dexamethasone and the two extracts achieved a two- and one-and-a-half-fold decrease in these cytokines compared to the control group. The results suggested that the triterpenoid lupeol found in C. hystrix leaves could lead to the discovery of new anti-inflammatory and anti-inflammasome agents.

A novel ursane-type triterpenoid that decreases nitrite levels in LPS-stimulated macrophages was examined in an additional investigation of Centella asiatica leaf extracts by Chianese et al. [90]. Using 90% ethanol at 70 °C, the authors extracted dried C. asiatica leaves. Multiple fractionations utilizing a 50% hydroacetonic solution, hexane, n-butanol, and methanol were performed to isolate compounds identified as madecassoside (1), terminoloside (2), and isomadecassoside (3). The compounds were tested for the inhibition of NO production in the J774A1 cell medium. At the highest concentration of 50 μM, the first two compounds induced a decrease from ~19 to 15 μM in nitrites. Isomadecassoside was also efficient, as it lowered nitrates from ~18 to 14 μM. Many phytochemical analyses on C. asiatica leaves were performed; however, none of them included isomadecassoside, despite its similarity in molecular formula and chromatographic behavior to compounds (1) and (2). It appears that all three of these compounds have nearly the same nitrite reduction potential, with isomadecassoside displaying comparable or even superior activity to madecassoside.

The anti-inflammatory activity and accumulation of corosolic (CA), ursolic (UA), and oleanolic (OA) acids were examined in chloroform extracts from Prunus padus leaves in a study by Magiera et al. [91]. The compounds were identified and measured through chromatographic methods. The total levels of these compounds at different times of harvest ranged from 1.41 to 4.54 mg/g DW in leaves. The concentration-dependent inhibition of pro-inflammatory enzymes (lipoxygenase and hyaluronidase) by the plant extracts was correlated with the levels and activity of pure triterpenoid acids, particularly corosolic and ursolic acids, according to their activity parameters. The comparison of the results with positive controls (heparin, indomethacin, dexamethasone) may lend credence to traditional medicine’s claims about P. padus’s use in anti-inflammatory treatments. The pure triterpenoid fractions, including the most active CA, showed similar potency toward both enzymes (IC₅₀: 14.3–22.2 μg/U for LOX and 12.6–18.1 μg/U for HYAL), but the extracts were more effective LOX inhibitors (IC₅₀: 10.5–12.8 μg/U) than HYAL inhibitors (IC₅₀: 19.3–22.0 μg/U). It is worth noting that the LOX assay showed lower activities of the triterpenoids compared to those of the extracts. This finding could indicate a potential synergy between the triterpenoids and other components of the extracts. To fully understand the plant’s beneficial effects on reducing inflammation progression and any potential toxicity, additional in vivo research is needed.

Inflammatory disorder, epilepsy, diarrhea, pain, and anemia treatments are some of the traditional uses of Waltheria indica L. in Africa, South America, and Hawaii. The purpose of the research by Termer et al. [92] was to quantify the secondary metabolite composition of W. indica. There was a correlation between the type and quantity of secondary metabolites and the extract’s activity when tested for COX-2 inhibition. The authors observed that the extract composition and the COX-2 enzymatic inhibitory activity were affected by the extraction parameters. Water, ethanol, methanol, and ethyl acetate were used as solvents at temperatures ranging from 30 to 90 °C in a procedure including accelerated solvent extraction, where high temperatures and pressures (i.e., 1460 psi) were applied. Triterpenoid saponins ranged from 47.3 to 214.8 mg of oleanolic acid equivalents per gram of dried weight, based on the solvent used. The COX-2 enzyme was inhibited to a lesser extent by the ethanolic extract at 30 °C and the ethyl acetate extract at 90 °C, with a 37.7% and 38.9% inhibition rate, respectively. In contrast, the methanolic and aqueous extracts exhibited a 21.9% and 9.2% inhibition rate, respectively. The amount of triterpenoid saponins in the extracts was proportional to their COX-2 inhibitory activity. The saponin concentration was directly proportional to the increase in COX-2 inhibition. The study showed that extracts of W. indica inhibit the key inflammatory enzyme COX effectively; however, in vivo studies are required.

The Brazilian Unified Public Health System strongly favors the anti-inflammatory agent Varronia curassavica, a vital medicinal plant in Brazil. At the same time, essential oil extracted from V. curassavica leaves is among the most marketed products in Brazil. To this end, Moro et al. [93] investigated the anti-inflammatory activity of ethanolic extracts of V. curassavica leaves with inhibition assays (phospholipase A₂, COX-1, and COX-2) after further fractionation using several solvents and mixtures (i.e., hexane, ethyl acetate, and methanol). The isolated triterpenoid cordialin A was evaluated for its effectiveness by comparing it to two controls: diclofenac (a positive control) and thioetheramide (a negative control); all three substances were tested at the same concentration (10.0–100.0 μg/mL). The results showed that the inhibition of phospholipase A₂ (2.8–10.3%), COX-1 (8.3–27.2%), and COX-2 (3.3–22.2%) was observed with ascending concentrations of cordialin A. This compound had greater anti-inflammatory activity than flavonoid brickellin; however, the authors stated that neither compound exhibited anti-inflammatory activity.

Over twenty unknown isolated triterpenoids identified as brujavanoids A–U from a methanolic extract of Brucea javanica leaves (1–21) were investigated by Hu et al. [94]. An LPS-activated RAW 264.7 cell model was used to assess the anti-inflammatory effects of all the isolated compounds. In RAW 264.7 cells activated by LPS, the most active one, brujavanoid E (5), inhibited the nuclear translocation of NF-κB p65 and suppressed the transcriptional expression of common pro-inflammatory mediators. This compound had the lowest IC₅₀ value of all 27 identified at 4.1 μM, lower than the positive control dexamethasone (9.2 μM). B. javanica offers a fresh opportunity to discover anti-inflammatory agents thanks to its structural diversity and bioactivity. However, further in vivo assays could shed more light on the safety of this extract.

Camellia japonica is among the most valuable species of the Theaceae family, as it provides great economic value and has high-added-value bioactive compounds. Triterpenoid saponins, or tea saponins, are one kind of bioactive compound found in Camellia species at ~10% w/w of dry weight. Phytochemical research on C. japonica is necessary since its chemical profile is the building block of its industrial use. To this end, Liu et al. [95] provided aqueous C. japonica leaf extracts, which were fractionated in order to comprehensively identify the triterpenoid compounds of the specific plant. The fractions were evaluated for their anti-inflammatory activity through NO production inhibition assays in RAW 264.7 cells. The authors annotated thirty-eight triterpenoids through the use of molecular networking, half of them being potentially novel compounds. They identified 13 compounds through spectroscopic techniques, 6 of them being the known camellioside A, camellioside B, camellioside E, camellioside G, 3β,17β-dihydroxy-16-oxo-28-norolean-12-en-3-O-β-D-glucopyranosyl-(1→2)-O-β-D-galactopyranosyl-(1→3)-O-[6-O-acetyl-β-D galactopyranosyl-(1→3)]-β-D-glucopyranosiduronic acid, and 3β,16α,17β-trihydroxy-28-norolean-12-en-3-O-β-D-glucopyranosyl-(1→2)-O-β-D-galactopyranosyl-(1→3)-O-[β-D-galactopyranosy-(1→2)]-β-D-glucopyranosiduronic acid. The six known compounds showed substantial anti-inflammatory activity, since at 25 μM, they achieved inhibition rates of 3.21–37.99%, whereas the positive control L-NMMA achieved 57.04% at 50 μM. Specifically, an unknown compound reached the highest inhibition rate, while camellioside B (31.31%) and camellioside A (28.96%) showed promising results.

5.2.2. In Vivo Assays on Triterpenoids and Saponins

One traditional remedy for skin inflammatory disorders is Tabernaemontana catharinensis, commonly described as snakeskin. The leaves were macerated in 70% ethanol for 10 days at room temperature. To validate the topical anti-inflammatory properties of T. catharinensis leaves, the study conducted by Camponogara et al. [96] examined the therapeutic efficacy of a crude extract and its various constituents using a mouse model of irritant contact dermatitis using the ear edema assay through Croton oil exposure. A qualitative phytochemical study of snakeskin crude extract and n-butanol, dichloromethane, and ethyl acetate fractions was performed using a chromatographic technique, with the triterpenoids ehretiolide, oleanolic acid, and oleanonic acid being identified in ethyl acetate and dichloromethane fractions. Applying croton oil to the skin caused a significant increase in ear thickness in mice, with a maximum effect of ~144 μm noticed 6 h after treatment. In contrast, applying the crude extract did not cause any change in the ear thickness of mice (~23 μm). The extract and its fractions were applied at concentrations of 0.001–10 μg/ear and showed a dose-dependent reduction in acute ear edema caused by croton oil. The inhibitory dose 50% (ID₅₀) values for the snakeskin extract and its fractions were 0.006 μg/ear for crude extract and 0.061, 0.002, and 0.001 μg/ear for dichloromethane, n-butanol, and ethyl acetate fractions, respectively. By applying 10 μg/ear, maximum inhibition (100%) was achieved by crude extract and the positive control dexamethasone. Fractions of dichloromethane (~85%), ethyl acetate (~86%), and n-butanol (~83%) indicated promising anti-inflammatory activities. Inflammatory illnesses may be amenable to treatment with formulations containing snakeskin leaf extracts. Since snakeskin leaves decreased inflammatory parameters in a croton oil-induced irritating contact dermatitis model, it is feasible for them to be used in the pharmaceutical industry.

A study of another Miconia species was conducted by Gatis-Carrazzoni et al. [97] to examine Miconia minutiflora (Bonpl) leaf extract’s anti-inflammatory properties. Ground powder was extracted through maceration with methanol for 48 h, with the extract being finally evaporated. The phytochemical profile was determined through the chromatographic technique. Anti-inflammatory activity was examined through carrageenan and acetic acid-induced vascular permeability in male and female mice. All tested concentrations of M. minutiflora methanol extract (i.e., 50–200 mg/kg) demonstrated anti-inflammatory activity. Myrianthic acid and arjunolic acid were identified in the extract. With a 70% inhibitory effect on leukocyte migration, the methanolic extract at a dose of 100 mg/kg demonstrated the highest level of activity at 5.36 × 10⁶ polymorphonuclear leukocytes (PMNLs) per milliliter. The positive control indomethacin was administered at 5 mg/kg and had an activity of 6.54 × 10⁶ PMNL/mL. The effects of the extracts were not dependent on dosage. Regarding carrageenan-induced edema, carrageenan was injected subplantarically and induced paw edema promptly. At concentrations of 100 and 200 mg/kg, M. minutiflora extract decreased the edema and had similar anti-inflammatory activity to the positive control indomethacin, reaching ~80 μg/mL by Evans blue staining (1%). Compared to that of the control group, all the above injections significantly decreased the volume of edema at all timepoints evaluated. A myeloperoxidase activity assay was performed to assess the anti-inflammatory activity associated with neutrophil abundance in the subplantar tissue. Methanolic extracts and indomethacin decreased the activity of myeloperoxidase (MPO) in the plantar region of animals displaying edema, with a mean optical density (mOD) of 0.256 and 0.866 mOD/tissue, respectively, in comparison to the control value of 1.197 mOD/tissue. After inducing peritoneal capillary permeability with acetic acid in mice, methanolic extract inhibited the effect statistically significantly (p < 0.001) and did not demonstrate a dose-dependent inhibitory effect. The results were similar to those for the carrageenan-induced edema, as the peritoneal capillary permeability was significantly inhibited by indomethacin at a dose of 5 mg/kg and by methanolic extracts of 100 and 200 mg/kg at ~90 μg/mL based on Evans blue staining (1%). In contrast to the control treatment (vehicle), methanolic M. minutiflora extract demonstrated efficacy in impeding cell migration into the pleural cavity in carrageenan-induced pleurisy. At a dose of 100 mg/kg, the methanol extract of M. minutiflora inhibited polymorphonuclear cell migration by 62%. In conclusion, the anti-inflammatory activity of M. minutiflora leaf extract was evidenced through multiple assays. However, fractionation to examine the impact of triterpenoids could shed more light on the investigation.

Immune dysregulation is the primary cause of many disorders. Atopic dermatitis (AD) is a chronic inflammatory skin disease that may occur from immune dysregulation. This disorder was the focus of an investigation by Lee et al. [98], who explored the anti-inflammatory properties of C. asiatica (CA) ethanol leaf extract. The main bioactive triterpenoids in the plant, which are asiatic acid, asiaticoside, madecassic acid, and madecassoside, are responsible for its medicinal properties. This study was the first to use both in vitro and in vivo models to show that CA had pharmacological effects on skin inflammation caused by DNCB. In inflammation-stimulated human epidermal keratinocytes (HaCaT) cells, treatment with the extract inhibited the expression of IL-6 and TNF-α in a dose-dependent manner through interferon-γ (IFN-γ)- and TNF-α-induced inflammation. A mouse model of atopic dermatitis was established with the administration of 2,4-dinitrochlorobenzene. In the AD mouse model, two forms of treatment were used. One was an oral dose of 200 mg/kg/d (AD + CA-200), and the other was a topical application of 80 μg/cm² (AD + CA-80). Interestingly, there was a significant decrease in mast cell infiltration in the ear tissue of the groups that were treated with CA. Moreover, in both the AD + CA-80 and AD + CA-200 groups, there was a decrease in the expression of IL-6 in mast cells and in the levels of various pathogenic cytokines like TNF-α, IL-4, IL-5, IL-6, IL-10, IL-17, the inducible isoform of NO synthase (iNOS), COX-2, and CXCL9. The authors found that CA regulates the allergic inflammation of the skin through its pharmacological role and signaling mechanism. This supports the hypothesis that CA could be developed as a therapeutic agent for AD. According to the authors, CA successfully decreases inflammation and restores immunological equilibrium by blocking p38 mitogen-activated protein kinase signaling. However, to confirm CA’s anti-atopic dermatitis effects on human skin, additional clinical trials are necessary. In addition, investigations with the isolated compounds madecassoside, asiaticoside, madecassic acid, and asiatic acid could provide strong evidence for CA extract to be made publicly available to the pharmaceutical industry.

A popular species of Miconia (Melastomataceae) native to South and Central America is Miconia albicans. Pain, inflammation, and other infections can all be alleviated with the help of M. albicans leaf extracts. Aqueous M. albicans leaf extracts were prepared with boiling water by Dembogurski et al. [99] to study their anti-inflammatory activities and components. The triterpenoid O-hexosyl was one of several components identified by the authors. To investigate its anti-inflammatory effect, two assays were employed: the carrageenan-induced paw edema assay and the leukocyte influx assay. An hour prior to injecting carrageenan, three groups of mice were treated with different substances: saline water (vehicle), 15 mg/kg of indomethacin (positive control), or 256 mg/kg of M. albicans extract. Carrageenan’s 55.5% reduction in paw edema after 240 min was comparable to indomethacin’s 66.6% reduction. Furthermore, 4 h following the injection of carrageenan, the leukocyte influx in the abdominal cavity was recorded at 4238 cells/mm³. Both indomethacin (1438 cells/mm³) and M. albicans aqueous extract (1488 cells/mm³) reduced leukocyte influx, while saline solution (2100 cells/mm³) and indomethacin (66 and 65%, respectively) had little effect. A reduction in leukocyte influx was observed for saline solution (2100 cells/mm³), indomethacin (1438 cells/mm³), and M. albicans aqueous extract (1488 cells/mm³), indicating 66 and 65% reductions for the latter two medications, respectively.

Fibrosis of the liver develops as a result of chronic liver disease and is marked by an overabundance of fibrillary collagen. A study by Chang et al. [100] explored bitter melon leaf triterpenoid-enriched extract (TEE) and how it could protect mice against carbon tetrachloride-induced liver fibrosis. Dried bitter melon leaves were extracted with ethanol, and the crude extract was fractionated. Among the compounds, 24-O-acetyl-cimigenol-3-O-β-D-xylopyranoside was the most abundant, followed by methyl lucidenate P, 25-O-acetyl cimigenol-3-O-β-D-galactoside, and asperosaponin VI. Five fractions were generated, but the first four were discarded, so that TEE was produced. One week prior to beginning carbon tetrachloride administration and for the duration of the experiment, male mice were administered 100 or 150 mg/kg of TEE orally once a day. Mice were administered carbon tetrachloride intraperitoneally for nine weeks. The aspartate (AST) and alanine transaminase activities (ALT) induced in the serum by carbon tetrachloride were found to be decreased when TEE supplementation was administered. Specifically, ALT in the control group treated with carbon tetrachloride decreased from ~130 to 60–70 U/L when either TEE at 100 or 150 mg/kg or silymarin at 200 mg/kg was previously delivered to mice. Similar results were obtained for AST, where a decrease from ~80 to ~40 U/L was noticed. Statistically insignificant (p > 0.05) values were observed in AST and ALT assays between TEE at both concentrations and silymarin. It was proven that transdermal endothelial growth factor (TEE) could alleviate liver fibrosis by controlling the secretion of inflammatory cytokines and the expression of α-smooth muscle actin (α-SMA) in the liver, thus decreasing the buildup of collagen. The triterpenoid-enriched fraction of wild bitter melon leaf extract may represent a promising candidate for the prevention of liver fibrosis, according to these findings. An acetonic extract produced from the leaves of Sapium lateriflorum contained ten compounds, one of which was a novel acyl triterpenoid with anti-inflammatory properties, 3β-palmitoyloxy-1β,11α-dihydroxy-olean-12-ene (1). Other triterpenoids were also found, such as 3β-palmitoyloxy olean-12-ene (2), lupeyl palmitate (3), 3β-palmitoyloxy-11-oxo-olean-12-ene (5), and 6’-O-palmitoyl 3-O-β-sitosteryl-β-D-glucopyranoside (9). Novillo et al. [101] fractionated the extract, and the compounds showed negligible cytotoxic effects; they were also tested for their anti-inflammatory properties in mouse models of ear and paw edema caused by TPA and carrageenan, respectively. The novel compound (1) had significant anti-inflammatory properties comparable to those of indomethacin and was significantly better than the other compounds, according to the results. Indeed, at a dose of 0.1 μmol/ear, it achieved 68.76% inhibition, whereas indomethacin achieved 78.76% inhibition (2.88 mg) in TPA-induced ear edema. This activity was attributed to the hydroxyl at C-11. The anti-inflammatory activity could be explained by potential molecular mechanisms, according to docking studies of olean-12-ene’s 3β-palmitoyloxy esters with NF-κB and COX-2 receptors. In carrageenan-induced ear edema, it was revealed that the results were also comparable to those of indomethacin. At a dose of 31.6 mg/kg, compound (1) achieved 0.040 mL of edema volume, similar to 0.034 mL when 7.5 mg/kg of indomethacin was applied. The research indicates that the novel triterpenoid (1) could be a promising anti-inflammatory agent.

Momordica charantia L. leaves may alleviate conditions associated with inflammation. However, their safety profile is still unknown, and it is not known which components in their extracts have anti-inflammatory or harmful effects. A study by Chou et al. [102] examined the cytotoxicity, anti-inflammatory effects, and underlying mechanisms of the characteristic cucurbitane-type triterpenoid species found in the leaves of M. charantia L. Air-dried leaves were extracted with methanol at room temperature. Momordicines I, II, and IV and (23E) 3β,7β,25-trihydroxycucurbita-5,23-dien-19-al (TCD), four structurally related triterpenoids, were extracted and isolated from the triterpenoid-rich fractions of M. charantia leaf extracts. Normal cells were cytotoxically affected by momordicine I, while momordicine II was less toxic, and there were no discernible negative effects on cell growth for momordicine IV or TCD. In both in vitro and in vivo assays, TCD reduced inflammation. Incorporating 40 µM of TCD considerably reduced iNOS expression from 1 to ~0.2 regarding relative band intensity of iNOS/actin compared to that of the control group through Western blot analysis. Ear edema improved after TCD administration. All three tested doses of TCD (250, 500, and 750 µg/ear) considerably decreased the amount of ear edema in mice 4, 16, and 24 h following TPA stimulation in a dose-dependent way from ~45 to 30 μm of ear thickness compared to ~50 μm in the TPA control group. Indomethacin had effects similar to those of 500 and 750 µg/ear TCD on reducing ear inflammation. One possible anti-inflammatory mechanism is that TCD inhibits the differentiation of RAW 264.7 cells into pro-inflammatory cells resembling macrophages, which is induced by LPS. IKK/NF-κB, which was activated by LPS, was inhibited by TCD, according to the findings. A future investigation into the extract’s safety could be a reasonable goal for developing an extraction protocol that can increase TCD content while decreasing momordicine content. Further information about leaf extracts with anti-inflammatory activity due to triterpenoid compounds is provided in

Table 2. Anti-inflammatory effects of plant leaf extracts and identification of the main triterpenoids.

Sample	Triterpenoid	Anti-Inflammatory Effect	Ref.
A. solanacea Roxb.	α-Amyrenone	Ethyl acetate extract had an IB50 value of 3.13 μg/mL in the protein denaturation assay compared to 2.80 μg/mL for diclofenac	[72]
O. speciosus subsp. stenocarpus	Rotundic acid	Extract concentrations of 3.12−25 μg/mL achieved 2.39−0.48 μM NO production inhibition	[73]
N. arbor-tristis	Betulinic acid	IC50: COX-1 (10.34 μg/mL), COX-2 (12.92 μg/mL), 5-LOX (15.53 μg/mL), NO (15.21 μg/mL), TNF-α (16.65 μg/mL)	[74]
Z. mauritana	Ceanothic acid, isoceanothic acid, apiceanothic acid, and epigouanic acid	% COX-1 inhibition of Z. Mauritiana (90.34), Z. Spina-Christi (89.31), and Z. Jujuba (76.87)	[75]
Z. spina-christi
Z. jujuba
C. inophyllum	Twelve unknown triterpenoids	Compounds (1) and (2) had 2.44 and 7.00 μM IC50 values compared to dexamethasone (0.012 μM) against cytokine production in RAW 264.7 cells	[76]
S. bullockii	Six triterpenoid glycosides, including an unknown compound (syzybulloside A)	IC50 values of 6.93–11.58 μM for triterpenoids (1–6) against NO production in RAW 264.7 cells	[77]
S. hexaphylla	Twenty-three triterpenoid saponins, two of them novel	Compound (13) had an IC50 value of 0.59 μM compared to 0.13 μM for dexamethasone against NO production	[78]
Cappars ovata	Oleanolic acid, β-sitosterol, ursolic acid, bismethyl-octylphthalate, stigmast-5,22-dien-3-β-myristate, and the novel compound olean-12-en-28ol, 3b-pentacosanoate (1)	Compound (1) reduced the mRNA Expression of CXCL9 (19.36-fold), CXCL10 (8.14-fold), and TNF (18.69) compared to that in the control group	[79]
O. fragrans var. aurantiacus	3-O-trans-p-coumaroyltormentic acid (1), 3β-trans-p-coumaroyloxy-2α-hydroxyl-urs-12-en-28-oic acid (2), 3-β-cis-p-coumaroyloxy-2α-hydroxyl-urs-12-en-28-oic acid (3), and 3-O-cis-coumaroylmaslinic acid (4)	Compounds (2−4) decreased the levels of LPS-stimulated cytokines COX-2, NF-κB, and phosphorylated extracellular regulated kinase (pERK)1/2	[80]
	Maslinic acid, corosolic acid	In both HCT116 and HT29 cell lines, the phosphorylation levels of p65, Iκ-Bα, and ERK were considerably reduced by the ethyl acetate fraction (at 50 and 100 μg/mL, respectively); however, corosolic acid had stronger anticancer activity	[82]
C. pachystachya	Ursolic acid, pomolic acid	NO production in RAW 246.7 macrophages decreased from ~20 to ~5 μM using 300 μg/mL extract	[83]
C. paliurus	Eighteen dammarane triterpenoid saponins	IC50 values for compounds (7), (8), (10), and (11) ranged from 8.23 to 11.23 μM for NO inhibition; ethyl acetate extract at 80 μg/mL decreased TNF-α, PGE2, IL-6, COX-2, iNOS, and NF-κB/p65 expression	[86]
J. gossypiifolia	Unknown jagabeoeuphols A–C (1−3) and jagoseuphone A (4), a common euphane-type triterpenoid	Compound (4): lower IC50 value (20.1 μM) than the positive control quercetin (16.8 μM) for NO production inhibition	[87]
T. cherryi	Three ternstroenols	IC50 value of 0.72−3.70 μM against NO production in RAW 264.7 macrophages activated with LPS and IFN-γ	[88]
C. hystrix	Lupeol	At 25 μg/mL, IL-1β, IL-6, and TNF-α were significantly reduced with either a lupeol fraction or with ethanolic C. hystrix extract at 1.5 or 2.5 μg/mL	[89]
C. asiatica	Asiatic acid, asiaticoside, madecassic acid, and madecassoside	Decrease in the expression of cytokines TNF-α, IL-4, IL-5, IL-6, IL-10, IL-17, iNOS, COX-2, and CXCL9	[98]
	Madecassoside (1), terminoloside (2), and isomadecassoside (3)	At 50 μM, compounds (1) and (2) decreased from NO production from ~19 to 15 μM; compound (3) lowered NO production from ~18 to 14 μM	[90]
P. padus	Corosolic (CA), ursolic (UA), and oleanolic (OA)acids	CA fraction: IC50 value 14.3–22.2 μg/U for LOX and 12.6–18.1 μg/U for HYAL); the extracts were more effective LOX inhibitors (IC50: 10.5–12.8 μg/U) than HYAL inhibitors (IC50: 19.3–22.0 μg/U)	[91]
W. indica	Triterpenoid saponins expressed as oleanolic acid equivalents	Ethanolic and ethyl acetate extracts achieved 37.7% and 38.9% inhibition of COX-2	[92]
V. curassavica	Cordialin A	Inhibition of phospholipase A2 (2.8–10.3%), COX-1 (8.3–27.2%), and COX-2 (3.3–22.2%) at a concentration range of 10.0–100.0 μg/mL	[93]
B. javanica	27 triterpenoids named brujavanoids A–U	Brujavanoid E had a lower IC50 value compared to dexamethasone (4.1 and 9.2 μM, respectively) in the NO production inhibition assay	[94]
C. japonica	Unknown, camellioside B, and camellioside A	The three triterpenoids achieved 37.99, 31.31, and 28.96% NO production inhibition at a 25 μM concentration	[95]
T. catharinensis	Ehretiolide, oleanolic acid, and oleanonic acid	ID50 values for ear edema ranged from 0.001 to 0.0061 μg/ear for fractions	[96]
M. minutiflora	Myrianthic acid, arjunolic acid	Methanolic extract achieved 5.36 × 106 PMNL/mL compared to indomethacin 5 mg/kg (6.54 × 106 PMNL/mL); ~80 μg/mL decreased edema at 100 or 200 mg/kg of extract	[97]
M. albicans	O-hexosyl triterpenoid	Reduction in leukocytes by 65% (compared to 66% for indomethacin) and paw edema by 55.5% (compared to 66.6% for indomethacin) from carrageenan induction	[99]
Bitter melon	24-O-acetyl-cimigenol-3-O-β-D-xylopyranoside as the most abundant, methyl lucidenate P, 25-O-acetyl cimigenol-3-O-β-D-galactoside, and asperosaponin VI	Triterpenoid-rich extract: ALT decreased from ~130 to 60−70 U/L; AST decreased from ~80 to ~40 U/L	[100]
S. lateriflorum	Ten triterpenoids, one of which is novel (3β-palmitoyloxy-1β,11α-dihydroxy-olean-12-ene) (1)	0.1 μmol/ear of compound (1) achieved 68.76% inhibition, indomethacin 78.76% in TPA-induced ear edema; 31.6 mg/kg of compound (1) achieved a 0.040 mL edema volume (0.034 mL when 7.5 mg/kg of indomethacin was used)	[101]
M. charantia	Momordicines I, II, and IV and (23E) 3β,7β,25-trihydroxycucurbita-5,23-dien-19-al (TCD)	40 µM TCD reduced iNOS expression from 1 to ~0.2 iNOS/actin compared to the control group. Regarding the TPA control group, TCD at 250, 500, or 750 µg/ear decreased ear edema in mice after 4, 16, and 24 h from ~45 to 30 μm of ear thickness compared to ~50 μm in the control group, comparable to indomethacin	[102]

ALT: alanine transaminase; AST: aspartate transaminase; COX: cyclooxygenase; CXCL: chemokine (C-X-C motif) ligand; HYAL: hyaluronidase; IB₅₀: 50% inhibition of the denaturation of protein; IC₅₀: 50% inhibitory concentration; ID₅₀: 50% inhibitory dose; IFN: interferon; IL: interleukin; iNOS: inducible isoform of nitric oxide; LOX: lipoxygenase; LPS: lipopolysaccharide; MAPK: mitogen-activated protein kinase; NF-κB: nuclear factor κ light-chain enhancer of activated B cells; NO: nitric oxide; pERK: phosphorylated extracellular regulated kinase; PMNL: polymorphonuclear leukocyte; TCD: (23E) 3β,7β,25-trihydroxycucurbita-5,23-dien-19-al; TNF: tumor necrosis factor; TPA: tetradecanoylphorbol-13-acetate.

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6. Limitations

Extensive research has explored the association between triterpenes and triterpenoids and their potential anti-inflammatory activity. However, there is a lack of fractionation and in vivo or in vitro laboratory testing to substantiate these findings. Most researchers isolated and identified compounds from extracts and simply attributed their medicinal properties to these compounds based on the literature. In addition, there are studies in which the qualitative identification of extracts has been carried out and medicinal activity is simply attributed to specific groups of compounds. To advance the development of leaf extract preparation from plants of pharmacological interest, it would be advisable to conduct more in vitro and in vivo tests after the fractionation of the extract and isolation of specific compounds.

7. Conclusions and Future Perspectives

Triterpenes and triterpenoids are secondary metabolites of plant origin. Due to their complex chemical structures, they have attracted interest as potential therapeutic agents against various diseases. Their most studied potential action is anti-inflammatory. Several studies indicate that plant leaf extracts rich in triterpenes or triterpenoids have anti-inflammatory activity both in vivo and in vitro. So far, the anti-inflammatory activity of triterpenoids appears to be stronger than that of triterpenes.

Given the chemical similarity between many bioactive triterpenes and steroidal anti-inflammatory compounds, these natural products have the potential to serve as a foundation for the identification of novel prototypes in the search for new medication development. However, additional investigations are needed to ascertain the clinical efficacy of these compounds. Triterpenes should be examined more thoroughly for their potential pharmacological activity. These studies should include various in vivo experiments, the determination of pharmacokinetic and pharmacodynamic parameters, the assessment of acute toxicity, and the examination of potential adverse effects such as herb–drug interactions. Furthermore, efforts should be made to enhance the biological activity and bioavailability of these chemicals through structural alterations. These modifications could include the development and synthesis of new derivatives, improvement of water solubility, and encapsulation in carriers such as nanostructures.