The study design was divided into three processes, including the general network pharmacology process (P1) and the two improved processes (P2 and P3). Using this approach 20 core compounds and 6 core targets were predicted, among which 4 active compounds (quercetin, naringenin, liquiritigenin, and licoisoflavanone) and 2 targets (SYK and JAK2), were associated with SARS-CoV-2 infection, as confirmed by previous studies. Furthermore, after ADMET and molecular docking analysis, two new active compounds were identified: vestitol was identified in P1 and glabrone was jointly identified in processes P2 and P3. In addition, 2 new targets were also predicted, among which PTEN was identified in P2, and MAP3K8 were identified in P3. In addition, this study also revealed the signaling pathways of P53, cAMP, and NF-kB.
Considering the 4 active compounds (quercetin, naringenin, liquiritigenin, and licoisoflavanone), their potential roles in the treatment of COVID-19 have been demonstrated in previous studies. Quercetin has anti-inflammatory, antiviral and anticoagulant effects [47]. Naringenin also induces anti-inflammatory and antiviral activity [48]. As a flavonoid with anticancer, antioxidant, hepatoprotective, immune regulatory, and antiplatelet aggregation properties, liquiritigenin has served as a therapy for COVID-19 [49]. Licoisoflavanone is an isoflavonoid compound that plays a role in the reduction of antiviral, cytokine storms, prevention of ARDS and multi-organ damage, and reduction of the severity of inflammatory diseases [50].
Previous studies have also indicated that SYK and JAK2 may serve as target proteins related to SARS-CoV-2. SYK has been reported to regulate signal transduction pathways implicated in these complications associated with COVID-19 [51]. JAK2 involves in M2 macrophage polarisation, inflammatory response, pulmonary fibrosis, and thrombosis by activating STAT3, a signal transduction and transcriptional activator [52]. Furthermore, the SYK inhibitor (fostamatinib) [51] and the JAK2 inhibitor (fedratinib) [53], evaluated in clinical studies, are highly effective in the prevention and treatment of COVID-19.
The examples given above demonstrate the important roles of the 4 active compounds and 3 targets in COVID-19, identified in our analysis, and confirmed by previous studies, suggesting the usefulness of our model in the prediction of active compounds and targets. In fact, we also identified 2 new compounds (vestitol and glabrone) and 2 new targets (PTEN and MAP3K8) that have not yet been demonstrated to be directly associated with the treatment of COVID-19, but have been attested to have a role in the treatment of COVID-19-related diseases (e.g. hepatitis B, influenza A virus).
Many related studies have shown that vestitol can achieve an anti-inflammatory effect by inhibiting the NF-kB signaling pathway and has shown to be a considerable promising new anti-inflammatory agent [54]. Glabrone can achieve an antioxidant activity by modulating the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway and an anti-inflammatory effect by regulating the NF-kB signaling pathway [55]. Meanwhile, an antiviral activity was demonstrated by cytopathic effect (CPE) inhibition assays targeting the influenza A virus [56].
The two new targets identified using our approach, including PTEN and MAP3K8, are potentially key targets for the treatment of COVID-19. Studies have shown that PTEN plays a crucial role in the SARS-CoV infection, which was revealed by analysising the Rreactome pathway, through activate dendritic cells, produce hyperactive B-cells and uncontrolled T-cells, and secrete proinflammatory cytokines. Therefore, similar to SARS-CoV infection, PTEN can regulate several Reactome pathways and immune responses in COVID-19[57]. MAP3K8 participates in the pulmonary fibrotic response and the lung inflammatory response. An increasing number of studies have also highlighted the significance of MAP3K8 in suppressing lung inflammation and fibrosis (the main symptom of COVID-19) [58].
Finally, in terms of the signaling pathway, the P53, cAMP, and NF-kB signaling pathways, discovered by using KEGG pathway analysis, are involved in inflammation, immunomodulation and infection. The P53 signaling pathway is a pathway known to influence immune responses [59]. Furthermore, p53, an intrinsic host restriction factor of SARS-CoV-2, can reduce virus production [60]. the cAMP signaling pathway is the most important signaling pathway in EG pathway enrichment, and EG could also act on the PI3K-Akt, JAK-STAT and chemokine signaling pathways, thus reducing responses such as inflammation and apoptosis [34]. In turn, the NF-kB signaling pathway, considered as an inflammation center [61], induces various target genes in inflammatory diseases [62, 63], as well as regulates cytokine storm syndromes and immunosuppression [64, 65].