1. Introduction
Due to the intense efforts made by clinicians and researchers, only one human infection, “smallpox”, has been successfully eradicated from the world [
1]. However, the recent outburst of a new type of pneumonia caused by a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) [
2] is not likely to disappear from the globe completely, even after the quick development of a sustainable vaccine. This indicates one certain thing: that the world needs novel treatment plans and possible therapeutic interventions to combat the highly infectious disease (COVID-19), no matter what else happens next.
In late December 2019, a life-threatening contagious disease with unknown etiology was first reported in Wuhan, Hubei province, China [
3]. Although infectious disease experts identified the new coronavirus (SARS-CoV-2) spread from the animal host, concerns remained over how the first person might have been infected [
4]. Viral genomics and epidemiological studies evidenced that the animal-to-human shifted SARS-CoV-2 can rapidly transmit from one person to another through interaction or respiratory droplets [
5,
6]. Hence, the World Health Organization (WHO) initially declared a global emergency on 22 January 2020, as the Wuhan coronavirus spread. On 20 August 2020, the Center for Systems Science and Engineering (CSSE) at Johns Hopkins University reported a health crisis with intensifying global case numbers (22,260,000) and fatalities [
7,
8]. COVID-19 predominantly attacks the respiratory system, even though other organ systems are compromised. Lower respiratory tract infection (LRTI) associated with fever, shortness of breath, and dry cough were reported as the symptoms with the first case from Wuhan, China [
9]. Additionally, muscle aches, chills, sore throat, runny nose, headache, and chest pain were observed [
10]. Currently, COVID-19 symptoms are similar to pneumonia, though a significant number of COVID-19 infected cases are asymptomatic, which can affect others as silent spread [
11]. Importantly, patients with underlying diseases, such as asthma, diabetes, and hypertension, are more susceptible to COVID-19 [
12,
13].
A report suggests that around 40% of those infected with SARS-CoV-2 might remain asymptomatic and thus, the transmission might carry a greater risk than expected [
11]. At present, endeavors to develop medications for COVID-19 by repositioning existing drugs have been pursued, as well as vaccine development. However, the efforts have been hampered by the lack of scientific evidence on how COVID-19 attacks human hosts [
14]. On the other hand, phytochemicals have always played a pivotal role in providing potential therapy against diverse diseases [
15], including fighting a mutant coronavirus [
16]. From folk remedy times, medicinal plants provided many outstanding bioactive compounds, which led to great drug discoveries, such as aspirin from
Salix, taxol from
Taxus brevifolia, and artemisinin from
Artemisia annua [
17,
18,
19]. During the 2003 SARS outbreak, a series of Chinese herbal treatments were effectively implemented to control the pandemic situation [
20], and even now, the Chinese government impulses traditional remedies aimed at COVID-19 prevention. According to the state administration of traditional Chinese medicine (TMC), 85.2% of the country’s COVID-19 patients (total: 60,107) until 17 February 2020 had been recovered with the treatment of TMC [
21]. Although researchers race to develop a vaccine, the rigorous validation of traditional medicine for identifying the wide-spectrum antiviral active components can also be a viable way to control the COVID 19 disease. Therefore, an attempt to explore novel antiviral compounds with the underlying mechanism of action should not be halted.
Korean traditional medicine literature, “Donguibogam”, established about 400 years ago, illustrates that
Panax Ginseng C.A. Meyer (PGCAM) is a very potent herbal plant with multiple pharmacological activities, particularly strengthening the immune system against some pathogens [
22]. According to an experiment, ginseng interrupted cellular oxidative damage induced by a respiratory syncytial virus (RSV) and downregulated pro-inflammatory gene expression level induced by RSV in the human alveolar epithelial cell [
23]. Additionally, potential bioactive compounds of ginseng extracts, including ginsenoside derivatives (Rg1, Rg3, Rb1, Rb2, Rb3, Re, Rd, Rh2) and compound K, are renowned for therapeutic efficacy against several infectious diseases [
24]. However, the major drawback of these compounds is their high molecular weight and low bioavailability; even the absorption and transportation rate of intact ginsenosides and their metabolites from the intestines are very poor [
25]. In addition, some reports studied via Caco-2 permeability assay indicated the low permeability of ginsenoside derivatives (<2.59 ± 0.17·10
−7 cm/s) and compound K (<8.65·10
−7 cm/s) [
26,
27]. It is evident that low permeable compounds have poor bioavailability profiles, which do not reach the intended biological system; thus, therapeutic efficacy is not well consistent [
28]. Therefore, these findings suggest that the pharmacological value of low molecular weight compounds (LMWCs) in ginseng should be strengthened to provide therapeutic evidence against immune dysfunction, especially in treating COVID-19 infection during an urgent pandemic outbreak.
Network pharmacology (NP), a new paradigm and combined analytical system, can efficiently explore the interaction networking of diverse factors, such as ligands, protein targets, diseases, and genes [
29]. NP can unveil the target prediction and mechanism of drug action with a multidimensional perspective, which highlights shifting of the approach from “one target, one ligand” to “multiple targets, multivariate therapeutics” [
30]. Importantly, it widely contributes to drug discovery by providing 40% of the recent active candidates with successful clinical evidence [
31]. Currently, network pharmacology has been utilized broadly to decipher bioactive compounds and mechanisms of phytochemicals against diverse diseases [
32]. In this research, we implemented network pharmacology to analyze LMWCs and mechanisms of PGCAM against COVID-19. Firstly, LMWCs in PGCAM were identified using browsing literature and public database and then filtered through Lipinski’s rule for drug-likeness compounds. Afterwards, genes that interacted with selected compounds or COVID-19-related genes were screened using public databases, and the overlapping genes between compounds and COVID-19 target genes were identified. Thirdly, KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway enrichment analysis of overlapping genes was employed to explore the molecular mechanisms of PGCAM against COVID-19. Finally, the potential bioactive compounds and key genes of PGCAM against COVID-19 were selected by analyzing the binding affinity energy in virtual mode. The overall workflow is presented in
Figure 1.
3. Discussion
Compounds–genes network indicated that the clinical efficacy of PGCAM on COVID-19-associated genes was directly involved in 27 genes. Of these, both RELA and NFKB1 genes were more significant genes than any other kind of genes. On top of that, based on the pathway enrichment, the PI3K-Akt signaling pathway is found as the topmost mechanism of PGCAM against COVID-19. Accordingly, the docking score through virtual screening on the six genes related to the PI3K-Akt signaling pathway suggested that five bioactive compounds (paeonol, frutinone A, nepetin, ramalic acid, trifolirhizin) were considered the most significant compounds of PGCAM against COVID-19. Meanwhile, the consequence of the KEGG pathway enrichment analysis of 27 genes might be an anti-COVID mechanism. The relationships of 28 signaling pathways with anti-virus properties were discussed as follows.
PPAR signaling pathway: Triggered PPAR-α regulates immunity of cytoplasmic DNA, blocks interferon production, and boosts vulnerability to viral infection [
33].
MAPK (
Mitogen-Activated Protein Kinase) signaling pathway: Virus-infected cells cause severe reactions that activate the MAPK signaling cascades to shield from virus attack. They can also be used by viruses to facilitate viral replication [
34]. Furthermore, the p38 MAPK signaling pathway is a potent inflammatory pathway in lung and heart damage in COVID-19 patients [
35].
ErbB signaling pathway: A great number of prime oncogenic virus infections are associated with ErbB signaling pathway. The Hepatitis B Virus(HBV) also induces overexpression of the Epidermal Growth Factor Receptor (EGFR) gene and protein [
34,
36,
37,
38].
RAS signaling pathway: Inhibition of RAS can curtail tissue damage severity in COVID-19 patients. Additionally, ACE (Angiotensin-converting enzyme) blockers cause a reduction in the response of the RAS system [
39].
cAMP signaling pathway: cAMPs might have a viral-resistant effect by curbing viral replication and interrupting viral entry. On the other hand, they might have an inimical role by decreasing HIV antiviral immune responses, thus halting the removal of the virus and causing T cell malfunction [
40].
Chemokine signaling pathway: Elevation of chemokines (CXCL10 and CXCL8) is clinically characteristic of COVID-19 infection. Moreover, its expression level indicated different clinical acuteness among the COVID-19 patients [
41].
NF-κB signaling pathway: Activation of NF-κB signaling pathway shows acute inflammation induced after SARS-CoV attack, and NF-κB blockers are favorable antivirals in the disorder caused by COVID-19 [
42].
HIF-1 signaling pathway: HIF-1α expression supports SARS-CoV-2 replication and sustainability, and it intensifies the cytokine production level in monocytes [
43].
FOXO signaling pathway: Reduction of FOXO3 in T cells interrupted apoptosis, elevated multifunction of CD8 cells, and enhanced viral control [
44].
Sphingolipid signaling pathway: Sphingolipids play a major protective role in the lungs against pulmonary and lung damage, and the control of their pathways may provide effective and improved therapeutic tactics [
45]. Regulation of sphingolipids can be very advantageous and can have an effect on anti-inflammation, preservation of neuronal integrity, and anti-coagulant effects [
46,
47]. All of these favorable features might be utilized to counterbalance the involved disorders of COVID-19 [
48].
PI3K-Akt signaling pathway: Activating of PI3K-Akt signaling is an important mechanism to prolong viral replication in both acute and constant infection, thus, virus-infected Vero E6 cells are activated by PI3K-Akt pathway [
49,
50].
AMPK signaling pathway: In both HBV and HBC viral infections, the AMPK activation is advantageous, but in others, such as the Ebola virus, dengue virus, and even human cytomegaloviral infections, AMPK plays a counteracting role [
51].
Wnt signaling pathway: Controlling Wnt signaling could be a critical process in affecting the sustainability of viral pathogenesis [
52].
Toll-like receptor signaling pathway: TLR-7 agonists may inhibit the onset of acute COVID-19 in indicative patients and synergy effects with antiviral treatment [
53].
NOD-like receptor signaling pathway: NLRs may regulate inflammatory response via NF-κB inhibition and block the viral defense system via interaction with mitochondrial antiviral-signaling protein (MAVS) [
54].
RIG-I-like receptor signaling pathway: A report shows that SARS-CoV-2 ORF6 blocks RIG-I-like receptor signaling pathway, thus leading to the interruption of the host’s innate immune system [
55].
JAK/STAT signaling pathway: JAK/STAT pathway is linked to the induction of multiple molecular immune pathways. The interruption of this pathway may lead to the blockade of several cellular responses [
56].
IL-17 signaling pathway: IL-17 blockers are immunologically probable as a strategy to inhibit severe respiratory symptoms in COVID-19 patients [
57].
T cell receptor signaling pathway: It remains uncertain whether T cell responses are beneficial or detrimental in COVID-19, and whether T cell responses have minimal or maximal effects in COVID-19 infection [
58].
B cell receptor signaling pathway: B cells have a crucial role in fighting viral infections; however, B cells are triggered after viral infection and before the production of immunoglobulin G (IgG) [
59].
TNF signaling pathway: Anti-TNFα monoclonal antibodies are likely to weaken inflammatory disorders occurring in COVID-19 infection, lessening the release of other inflammatory-aggravating triggers [
60].
Neutrophin signaling pathway: A report shows that neurofilament light chain (NfL)—a biomarker of astrocytic and neuronal damage—was elevated in the blood of patients with COVID-19 [
61]. It is evident that COVID-19 infection might dampen the neurological signaling pathway.
GnRH signaling pathway: When viral infections disturb the Blood–Brain Barrier (BBB), circulating immune cells, such as B and T cells, monocytes, and granulocytes, can enter the brain parenchyma to produce cytokines, and thus, it might be able to negatively alter the functions of GnRH neurons [
62].
Prolactin signaling pathway: Patients with HIV have a higher prolactin amount compared to the healthy. Additionally, prolactin is considered as a cytokine in its response in the immune system [
63,
64].
Adipocytokine signaling pathway: Adipose tissue can react to proinflammatory inducement triggered in the lung through systemic circulation adipocytokines and other inflammatory factors [
65].
Relaxin signaling pathway: The dysfunction of the relaxin signaling pathway might bring respiratory disorders recognized in COVID-19 patients. Moreover, SARS-CoV-2 NSP7 protein renders relaxin receptors very much weaker [
66].
AGE-RAGE signaling pathway in diabetic complications: AGE-RAGE can also act as an innate immune sensor, including in respiratory viruses. As a consequence, the blocking of RAGE curtails the inflammatory level and progression of cardiovascular diseases [
67].
Epithelial cell signaling in
Helicobacter pylori infection:
Helicobacter pylori downregulates T and B cell signaling to initiate the immune system [
68]. It is obvious that COVID-19 patients with
Helicobacter pylori might be vulnerable to inflammatory responses.
Based on the pathway enrichment analysis, both RELA and NFKB1 were considered as hub genes in PGCAM against COVID-19. Two genes of each were directly enriched in 21 out of 28 signaling pathways by the PI3K-Akt signaling pathway, indicating that PI3K-Akt signaling pathway might be a hub signaling pathway in PGCAM against COVID-19. The other four genes (IL6, MCL1, VEGFA, and IL2) directly related to the PI3K-Akt signaling pathway might be the significant genes to exert synergistic effects against COVID-19. Liu et al. [
69] showed that inhibition of both RELA and/or NFKB1 reduces cytokine secretion and thus alleviates inflammation severity. A report specified that MCL-1 inhibition in mitochondrial membrane stimulates BAX, Cytochrome C, Caspase-9, and Caspase-3, and thus it leads to cell death [
70,
71]. Noticeably, a report indicated that vascular endothelial growth factor A (VEGFA) was inhibited by angiotensin-converting enzyme 2 (ACE2) and upregulated by the attack of COVID-19, since COVID-19 interrupts the expression of ACE2. Consequently, VEGFA elevates vascular permeability and aggravation of endothelial damage [
72]. Most recently, it has been reported that a higher level of both IL-2 and IL-6 was detected in COVID-19 patients [
73]. Endothelial cell inflammation is also a major severity in COVID-19 infection, and its unmanageable cytokine production in tissues and cells aggravates severe immune reaction, which is defined as “cytokine storm”, resulting in worsening pneumonia. On top of that, the inhibition of six genes (RELA, NFKB1, IL6, MCL1, VEGFA, and IL2) associated with the PI3K-Akt signaling pathway contributes to the anti-proinflammation, anti-vascular permeability, and pro-apoptosis against COVID-19.
Therefore, the key mechanism of PGCAM against COVID-19 might be to block inflammation and vascular permeability, and trigger pro-apoptosis in tissues and/or cells by inactivating the PI3K-Akt signaling pathway.
5. Conclusions
The efficiency of LMWCs extracted from PGCAM and their anti-COVID-19 mechanisms were firstly analyzed by using network pharmacology. The findings of this research indicated that potential bioactive compounds are paenol, frutinone A, ramalic acid, nepetin, and trifolirhizin, and the target genes are RELA, NFKB1, MCL1, VEGFA, IL2, and IL6 of PGCAM against COVID-19. The mechanism(s) of PGCAM against COVID-19 might be inhibited inflammation, vascular permeability, and induction of cell apoptosis against COVID-19 by inactivating the PI3K-Akt signaling pathway. This research provides a scientific indication to support the therapeutic effect of PGCAM on COVID-19, and thus, the proper application of five bioactive compounds against COVID-19 might have potential synergistic effects, such as anti-inflammation, anti-vascular permeability, and pro-apoptosis of the infected cells to prevent COVID-19 vulnerability.
Still, there are also limitations to our analysis. The incompleteness of the herbal natural products database, COVID-19-related genes and protein–protein interaction network might bring bias about target gene findings. Moreover, our approach is dependent on GSEA analysis and molecular docking simulation, either agonist or antagonist. Thus, our predicted result would need to be further improved, through in vitro and in vivo.
The current study did not verify the LMWCs of PGCAM, whose efficacy needs to be validated via clinical test. However, our approach is a holistic perspective and integrated gene–compound interaction, which might be good and promising hints against COVID-19.
Finally, our analysis did not consider the target gene expression level practically after treatment of the selected compounds, which should be implemented in the future.