3. Discussion
Many substances found in nature, referred to as secondary metabolites, are derived from plants and have been used for millennia to create new therapeutics. In general, the phytochemical investigation of
Globularia alypum revealed the presence of significant amounts of various chemical components, while the present work is aimed at analyzing the aqueous extracts of leaves of
G alypum using the HPLC-DAD method for detecting the characteristic peak values and their functional groups. HPLC analysis revealed different characteristic peak values with various functional constituents in the extracts. The identified chemicals in Tunisian GA extracts have never been reported. The examined extracts were different from those in the results of other researchers working on Tunisian aqueous
G. alypum species. Indeed, the phenolic fraction of
Globularia alypum aqueous extract (GAAE) from the northwest of Tunisia is dominated by iridoids and secoiridoids with an abundance of serratoside, as demonstrated by Hajji et al. utilizing HPLC-PDA/ESI-MS analysis. They demonstrated the detection of three more flavonoids. Phellamurin comes in third, after quercetin glucoside and gallo-catechin as the primary ingredients. Verbascoside constituted the majority of GAAE’s composition [
10]. Furthermore, since the aqueous extracts of Bouriche et al. include distinct components, their study can be cited. In fact, the authors noted that the aqueous extracts of
G. alypum that were collected in June 2010 from Sétif, in Eastern Algeria, showed the presence of flavonoids and phenolic acids according to the HPLC-TOF/MS analysis. The glycoside flavonoids diosmin, rutin, and scutellarin are present in significant concentrations in these extracts, with naringin and quercetin-3-β-D-glucoside having the highest concentrations. Additionally, they disclosed that of the identified phenolic acids, there was a high cinnamic acid concentration together with protocatechuic acid [
14]. The variations observed in the phenolic profiles of aqueous extracts derived from diverse sources may be attributed to growth and environmental factors such as soil composition, altitude, rainfall, and climate, as well as the distinct methods employed to ascertain this composition. These elements may have a direct impact on the composition of chemical components. Given their high phenolic component content, our obtained extracts will probably show a range of biological activity [
13]. For instance, Calvin et al. reveled that nepetin isolated from
Eupatorium arnottianum (EA) was investigated in the TPA mouse ear edema and was found to be active. Nepetin reduced the TPA mouse ear edema and inhibited the NF kappaB induction as it is a major component of the EA extract [
15]. Moreover, Boubaker et al. showed that isorhamnetin 3-O-rutinoside promotes apoptosis of human myelogenous erythroleukaemia cells [
16]. Furthermore, as far as we know, few studies have been conducted to determine the phenolic composition of aqueous extracts of
Globularia alypum in Tunisia. The evaluation of these extracts is very limited; only few plants have been evaluated to date, and no data have been described before to determine the polyphenol composition of decoction or infusion extracts. Almost all the available studies in the literature reported mostly on methanolic extracts or essential oils.
Nowadays, due to safety concerns for synthetic antioxidants, there is an increasing demand for natural antioxidants [
16]. Herbs are great sources of antioxidants due to their natural antioxidant components, especially for food preservation. The results shown in this study revealed that aqueous extracts of
G. alypum leaves showed important antioxidant activities and that this effect was in a dose-dependent relationship. Regarding antioxidant activity, it has been previously reported that phenolic compounds such as flavonoids, phenolic acid, and tannins contribute considerably to the antioxidant activity in medicinal plants [
17]. Our extract contained the highest-level nepetin-7-O-glucoside. It has been reported that this molecule exhibits several pharmacological effects, including anti-inflammatory and antioxidant activities [
15]. In addition, isorhamnetin 3-O-rutinoside is a flavonoid glycoside that exerts an antioxidant effect [
16]. Our results are also in compliance with a study conducted by Jrah et al., who showed that aqueous extract of
G. alypum showed the highest antioxidant capacity with a value of 8.9 mM TE and 4.5 mM TE by FRAP and the Reducing Power (RP) method, respectively [
17]. It is interesting to note that our findings imply that our extracts have noticeably more antioxidant activity than other nearby plants. For instance, according to ABTS and β-carotene assays,
G. alypum obtained from Oueslatia Kairouan in central Tunisia showed antioxidant activity at IC 50 = 0.89 and 0.42 mg/mL, respectively [
18]. On the other hand, 0.04 and 0.15 mg/mL were sufficient to enhance the same impact. Additionally, a study conducted in January 2016 in Batna, Algeria examined the antioxidant activity of
G. alypum collected from Ain Zaatot. Two methods were used to quantify this activity: the ferric reducing antioxidant power (FRAP) and the DPPH radical scavenging assay. The data obtained indicated that
G. alypum exhibited significant concentrations of scavenging activity: IC50 223.04 ± 0.73 to 85.37 ± 1.48 µg/mL and EC50 0.31 ± 0.01 to 0.68 ± 0.19 mg/mL [
19]. The variety seen in the antioxidant activities of G. alypum might likely be explained by the experimental setup, the methods employed, and the utilization of plants from various geographical regions. It is important to mention that aqueous extracts of
G. alypum showed an effect on colonic antioxidant enzyme activity. A study conducted by Hajji et al. showed that GA collected from Northwest of Tunisia had a significant decrease in superoxide dismutase (SOD) and gluthation peroxidase (GPx) activities in the colon of AA-intoxicated animals compared to the controls, whereas GAAE (100, 200 and 400 mg/Kg, b.w.) or sulfasalazine (100 mg/Kg, b.w.) pretreatment over seven days significantly protected against this depletion when compared to the colitis group (
p < 0.05) [
10]. In the same context, a recent study of Hajji et al. proved that GAAE regenerates antioxidant enzymes after depletion under LOP administration enzyme levels showed depletion when treated only with LOP. However, administration of yohimbine regenerates antioxidant enzyme levels. GAAE also significantly increased SOD and GPx levels in a dose-dependent manner (400 mg/kg) [
13]. The results of a second Algerian investigation demonstrated that
G. alypum methanolic and aqueous extracts, which were obtained in June 2010 from Sétif in Eastern Algeria, could chelate ferrous ions in a concentration-dependent way. In contrast to the methanolic extract, the aqueous extract displayed more activity. In total, 52.69 μg/mL and 148.15 μg/mL, respectively, were the IC50 values. Compared to the results obtained with EDTA, the standard chelator, which produced an IC50 value of 5.97 μg/mL, this activity was less significant [
14]. We draw the conclusion that the primary cause of the phenolic components of GA’s antioxidant activity is their redox characteristics, which enable them to function as singlet oxygen quenchers, hydrogen donors, and reducing agents [
20]. A metallic chelating potential might also exist in them [
21].
According to WHO, 0.3–1% of the world population is affected by rheumatoid arthritis (RA), and among them females are three times more prone to the disease compared to males [
22]. RA is a chronic, inflammatory, and systemic autoimmune disease [
23]. Therapeutic agents against arthritis such as analgesics and NSAIDS reduce inflammation and joint destruction in either acute or chronic RA patients [
24]. On the other hand, gastrointestinal ulcers, cardiovascular complications, myelosuppression, hepatic fibrosis, stomatitis, cirrhosis, nephrotoxicity, pulmonary toxicity, immunological reactions, and local injection-site reactions are among the long-term dangers associated with medication use. Furthermore, increased expenses and adverse effects, such as elevated chances of infections and miscarriages, necessitate ongoing surveillance [
24]. As a result, fresh strategies are created to preserve the harmony between these possible hazards and recognized advantages [
25]. Safer and more effective medications are currently being created from oriental sources for the treatment of RA. To lessen these negative effects and boost the positive effects, a wide range of herbal extracts and products, including polyherbal formulations, are created [
24]. A review conducted by Choudhary et al. reported that about 485 plant species would have a promising anti-arthritic activity in humans. Cross-validation of information regarding the ethnic proof of historically used anti-arthritic plants was conducted using a variety of journal articles and reviews [
26]. As far as we know, no such review has examined the relationship between the plant family, components utilized, and dosage form and the anti-arthritic properties of the plants. According to these data, the Papilonaceae family of plants has a higher concentration of plants with anti-arthritic action. Of these sections, leaves have been utilized most frequently in oil dose form to treat arthritis [
26]. The used extracts in this study showed that aqueous extracts of
G. alypum had an important anti-arthritic activity. In light of our knowledge, the evaluation of anti-arthritic activity of
G. alypum is extremely limited. Only a little data relating to this activity have been reported. For instance, Friscic et al. showed that 50 μg/mL of aqueous extracts of
G. alypum inhibited COX-1 activity and that this inhibition reached 51.3% (
G. alypum) in the TMPD assay and 40.6% in the PGE2 assay. The authors also showed that the results obtained for
G. alypum are comparable to those reported for the methanolic leaf (GAME) (5.33%) and the flower extract (61.05%) of the same species tested at a 33 μg/mL concentration using the TMPD assay [
27]. Another study reported that the treatment of animals with GAME produced a significant decrease in the inflammatory cells; however, slight improvements in edema tissue were observed in the reference group. The authors explained that this anti-inflammatory effect of GAME may be equally related to its cinnamic acid content [
28]. Additionally, they demonstrated that the outcomes for
G. alypum are similar to those reported for the same species’ methanolic leaf (GAME) (5.33%) and flower extract (61.05%) when examined using the TMPD assay at a dose of 33 μg/mL [
27]. Another study found that offering GAME to rats resulted in a considerable reduction in inflammatory cells, although the reference group’s edema tissue showed only modest reductions. The authors clarified that GAME’s anti-inflammatory properties might be equally attributed to the amount of cinnamic acids it contains [
28].
To select plant extracts with potential antitumor properties for future bio-related studies, cytotoxicity screening models provide important preliminary data [
17]. To date, no reports have been found in the literature on the evaluation of the cytotoxicity of aqueous leaves extracts, as performed in this study. The present study examined, for the first time, the ability of AGAL to inhibit cancer cell proliferation, which is known to be the most promising route to treat cancer. The infusion extract presented a higher anti-proliferative effect with an IC50 = 50 µg/mL. This result can be explained by the richness of this extract of active molecules, especially ferulic acid (
Figure 3). In fact, the study of Ekowati et al. performed in 2020 demonstrated that ferulic acid showed anticancer potential by suppressing angiogenesis and causing inhibition of melanoma growth in a xenograft model [
29]. Comparing our result with the study of Friscic et al. [
27], we distinguished that our extract has the lowest antiproliferative effect (IC
50 = 50 and 231.43 µg/mL). In addition, no research has been performed previously to evaluate the anti-proliferative activity of aqueous extract.
Nowadays, many researchers around the world are working on plant extracts to develop new antimicrobial agents with enhanced safety and efficiency [
15,
16,
17,
18,
19]. The prime objective of ethnopharmacology is to identify plants for medicinal importance with minimal side effects. Additionally, active compounds from the plant extracts with antibacterial activity can be transformed into possible medication. Research to develop efficient and accessible medication from active plant compounds in the interest of public health is the need of the present world. The present in vitro experimental study explored the antibacterial effect of aqueous extracts of
G. alypum leaves against
Pseudomonas aeruginosa,
Salmonella enterica subsp.
enterica serovar Typhimurium,
Escherichia coli, and
Staphylococcus aureus. The tested stains exhibited sensitivity to the extract, according to the results.
S. aureus had the strongest effect, with a minimum inhibitory concentration (MIC) of 6.25 mg/mL and a zone of inhibition measuring 24 mm. The discussion is limited because, although the anti-arthritic effect of
G. alypum aqueous extracts has been previously described, no research has been conducted to characterize its antibacterial activity. The limited information that is currently available on this activity, however, mostly reports on the antibacterial action of organic extracts [
30]. For instance, we previously reported that sonication-obtained extracts of
G. alypum demonstrated a noteworthy antibacterial effect on
S. aureus, exhibiting a zone of inhibition of 14.5 mm that aligns with our actual study. However, these methanolic extracts demonstrated no effect against the remaining strains tested [
31]. In addition to other water-soluble components that were naturally present in the plant material, Nayak et al. speculated that the anionic components, such as chlorides, thiocyanate, sulfates, and nitrate, may be responsible for the antibacterial action of aqueous extracts [
32].
Since polyphenols, tannins, and flavonoids are often produced by plants and are involved in their defense against microbial infections, their presence in plant extracts may account for the antibacterial activity. Interestingly, Nepetin-7-Glucoside, a flavonoid and glycoside, is highly abundant in our extract [
33]. Furthermore, trans-ferulic acid (TFA), which is abundant in the aqueous extract, possesses a variety of pharmacological qualities, such as antifungal and antibacterial activities [
34].
In compliance with several other studies, the results obtained in this study showed that Gram-positive bacteria are more susceptible to plant extracts than Gram-negative bacteria. These differences may be related to the cell wall composition of bacteria. In fact, the cell wall of Gram-positive bacteria is single layered, whereas that of Gram-negative cells is multilayered [
35]. Moreover, our extract also inhibited Gram-negative bacteria. This can be explained by the fact that Gram-negative bacteria have a hydrophilic membrane due to the presence of lipopolysaccharides, and thus, a small hydrophilic molecule can pass through the outer membrane as it was reported in several studies [
35]. On the contrary, lipophilic compounds and macromolecules can pass through this outer membrane. Therefore, understanding of the permeation properties of the outer membrane of the microorganisms is essential to know about the antibacterial activity of a solute [
35].
Extracellular polysaccharides (EPS) are a complex matrix of microorganisms that link to one another to form biofilms. These biofilms can shield cells from antibacterial agents and decrease their antibacterial effectiveness [
36]. Since adhesion affects the biofilm’s eventual development and maturity, it is the initial and most important stage in the formation of a biofilm [
37]. Naturally occurring bacteria that produce biofilms are the main source of many illnesses in both humans and animals [
38]. Bacterial biofilms can also result in major issues for the food business. These days, a lot of research has been conducted with the aim to create benign antibiofilm agents because they do not eventually induce medication resistance [
39]. In the current study, an antimicrobial assay showed that our extracts displayed an antibiofilm activity especially against
S. aureus. To the best of our knowledge, no prior information has been provided regarding the antibiofilm activity of
G. alypum, and this is the first time that it has been documented. Furthermore, our investigation demonstrated that
G. alypum extract exhibited clear antibiofilm efficacy against
S. aureus biofilms at doses equal to or lower than the 1/4 MIC threshold. Many phytochemicals found in medicinal plants, including flavonoids, glycosides, tannic acid, phenolics, and chlorogenic acid, have the ability to suppress or completely eliminate biofilms by preventing the growth of bacteria that produce them, rupturing the polysaccharides in extracellular polymer (EPS), destroying the integrity of the bacteria’s membrane, preventing the activity of enzymes linked to biofilm formation, rupturing the fibrils that allow bacteria adherence to one another, suppressing the expression of genes related to biofilms, or suppressing the quorum-sensing system [
40,
41,
42].
G. alypum contain more than a dozen chemical constituents, including the following flavonoids: cafeic acid, trans-ferrulic acid, Verbascoside, Nepetin-7-Glucoside, Isorhamnetin-3-O-Rutinoside and other chemical constituents. We hypothesize that the combined action of
G. alypum’s phytoconstituents, particularly the abundant flavonoids and ferrulic acid that have demonstrated both biofilm and antibacterial activity, may be responsible for both the suppression of biofilm formation and antibacterial activity. Nevertheless, a thorough explanation of the precise mechanisms at play is still required. We already demonstrated the high ferulic acid content of our extracts. One of the most prevalent phenolic acids in natural species is ferulic acid (AF), also known as 3-(4-hy-droxy-3-methoxyphenyl)-2-propenoic acid, a secondary metabolite that is a member of the phenolic chemical class [
43]. After indirect studies demonstrated that ferulic acid had a high antibacterial activity against
L. monocytogenes [
44], the examination of ferulic acid’s antimicrobial potential was proposed. The study of Pinheiro and his collaborators demonstrated that ferulic acid derivatives inhibit
Staphylococcus aureus [
45].