Gastritis, a general digestive system disease resulting from a variety of factors, is a type of infectious or autoimmune inflammation characterized by gastric mucosal damage [30]. At present, the first-line drugs for gastritis therapy are antibiotics and proton pump inhibitors, but these drugs are not sufficiently specific to this disease and have serious side effects [31, 32]. In addition, the nonsteroidal anti-inflammatory drugs (NSAIDs) commonly used in the clinic to reduce inflammation can easily cause gastric mucosal damage and subsequently induce peptic ulcers [33]. Significantly, long-term chronic inflammation of the gastric mucosa might lead to atrophy of the mucosa and glands and could even develop into gastric cancer [34]. Therefore, it is necessary to find safer and more effective drugs from natural drugs for the treatment of gastritis. TCM prescriptions have gradually developed through the processing of compatible Chinese herbal medicines according to long-term and rich experiences. TCMs are characterized by the synergistic effect of multiple components, and their advantages lie in long-lasting efficacy, mild medicinal properties, nourishing effects, and outstanding effects on the treatment of chronic diseases [35]. XSLJP is a complex TCM prescription with a complicated mechanism that remains unelucidated. Clearly exploring the mechanism of XSLJP and reasonably adjusting the drug dosage according to the drug characteristics will improve the application of XSLJP in the clinical treatment of gastritis.
Active components and corresponding targets of XSLJP in the treatment of gastritis
In this study, 26 potential targets of XSLJP in the treatment of gastritis were identified (Table 1), and 21 of these were verified by literature mining using the PubMed database, which demonstrated the reliability and validity of this study. In addition, molecular docking simulations demonstrated that the remaining five targets can be well docked with some of the active components of XSLJP (Table 5S and Fig. 3), which suggests that the 26 key targets are likely the main targets of XSLJP in the treatment of gastritis. Subsequently, we analyzed the topological parameters of these 26 targets according to their PPI diagram (Fig. 4) and obtained eight targets with a high degree of interaction (Table 2), and these eight targets, namely, TP53, IL6, PTGS2, STAT3, JUN, FOS, EGFR, and HIF1A, might be the key targets of XSLJP in the treatment of gastritis.
To date, most of the active components of XSLJP have been confirmed to have biological activity and various pharmacological effects. The interactions between different active components in a TCM preparation exert a therapeutic effect as a whole, and the preparation must have certain key active components that exert the major pharmacological effects. According to the ‘drug-compound-common target’ network (Fig. 5), we identified 12 potential key active components of XSLJP with a degree higher than 6 (Table 3). The targets related to these 12 key active components are consistent with 24 of the 26 potential targets of XSLJP in the treatment of gastritis (Table 1), which demonstrates that these 12 key active components are likely the key active components of XSLJP in the treatment of gastritis.
Based on the abovementioned identifications, flexible docking simulations between the 12 key active components and the eight key targets were conducted to further explore their mode of interactions. The results showed that all 12 key active components and eight key targets had good docking scores (Table 4) with satisfactory docking postures (Fig. 6 and Fig. 7). Moreover, according to the docking score results, a heatmap was drawn to show the correlation between the key components and key targets (Fig. 10). As shown in the figure, four key active components, namely, glycitein, formononetin, glepidotin A and licochalcone α, had relatively better docking scores with most of the eight hub targets. These findings are particularly interesting because they provide novel ideas as described below for further studies of this TCM medicine, including biological experimental verification, XSLIP prescription adjustment and single-component Western medicine development.
Potential key signaling pathways involved in the mechanisms of XSLJP in the treatment of gastritis
In our study, the GO biological function analysis (Table 6 and Fig. 9) showed that the abovementioned targets are related to a variety of biological processes, including positive regulation of transcription from the RNA polymerase II promoter and positive regulation of transcription. In addition, the KEGG enrichment analysis (Table 5 and Fig. 8) revealed that these targets are involved in infectious disease pathways and immune inflammatory pathways, among other pathways. These results indicate that the mechanism of XSLJP in the treatment of gastritis might be related to these extensive and intricate signaling pathways.
Figure 11 shows a schematic diagram of the possible mechanism of XSLJP based on the 26 common targets and their main enriched signals. In the figure, the boxes represent the corresponding proteins encoded by the gene targets, and the green and yellow boxes represent the experimentally verified targets and the key targets, respectively. The schematic diagram shows the positions of the proteins encoded by the 26 genes in the signal pathways and their upstream and downstream relationships. On the one hand, Fig. 11 shows the existence of several target clusters, and these are mainly concentrated in the TNF, JAK/STAT, MAPK (ERK/JNK/p38), p53 and NO/VEGF signaling pathways. On the other hand, most of the predicted targets of the active components are closely related to immune regulation and influence various inflammatory cytokines, including IL-1β, IL-6/8/10/12, TNF-α, COX-2, iNOS, NO, TGF-β, NF-κB, and IFN-γ, to regulate the immune process of the body. The following discussion will focus on the key active components, the key targets and their corresponding signaling pathways related to XSLJP in the treatment of gastritis.
XSLJP and the TNF signaling pathway
Figure 1S shows detailed information on the TNF signaling pathway. TNF-α can be regulated by some gene promoters, such as NF-κB, c-Jun, and AP1, and subsequently induces apoptosis by TNF-α family proteins, such as FasL, TNF-α and TRAIL, whose expression is mediated by linker proteins containing death domains, such as FADD [36]. By mediating linker proteins without the death domain, such as TRAF, TNF-α can induce Toll-like receptor (TLR), IL-1 receptor (IL1R) or other members of the TNF family to activate NF-κB, JNK, p38 and other downstream signaling pathways [36]. Due to its pivotal location with respect to the TLR downstream signaling pathway, NF-κB can induce chemotactic granulocytes and macrophages, increase capillary permeability and cause lymphocyte infiltration to participate in the early immune response and inflammatory reaction by initiating target genes to express inflammatory factors, such as TNF-α, IL-1/6/8/12 and IFN [37]. The activation of this pathway can not only directly stimulate the synthesis of ICAF and IL-1 to promote cell adhesion, proliferation and inflammation but also indirectly stimulate other cells to produce vascular growth factor and promote angiogenesis and the apoptosis of transformed cells [38]. Formononetin, naringenin, berberine and other active components of XSLJP can regulate the expression of TNF, IL-1B, IL-10 and other cytokines in the TNF signaling pathway. For instance, formononetin can reduce intracellular calcium, restrict the activation of NF-κB, the phosphorylation of its upstream protein IκKα and the activity of caspase-1, and further inhibit the release of histamine and the secretion of TNF-α, IL-1β and IL-6, which ultimately results in the exertion of antioxidant, anti-inflammatory, proapoptotic and antitumor activities [39]. Naringenin can reduce the lung injury of mice with mycoplasma pneumonia to exhibit anti-inflammatory activity by inhibiting the expression of autophagy-mediated proinflammatory cytokines, such as IL-6, IL-1β, TNF-α and TGF-β, as well as pulmonary fibrosis [36]. Berberine can significantly inhibit the expression of IL-6 and TNF-α in human HK-2 cells damaged by palmitic acid (PA) and can attenuate PA-induced lipotoxicity through the PPAR-α pathway [40]. In addition, our calculations revealed that glepidotin A showed the best docking to IL-6 with the lowest docking energy, which suggests that glepidotin A might exert a series of downstream biological effects by binding with the IL-6 protein to mediate its protein expression level and biological function, but this hypothesis needs to be verified by future experiments. It is worth noting that glepidotin A can also combine tightly with all seven other hub targets, particularly PTGS2, JUN and FOS, with very low docking energies, which implies that this compound might significantly contribute to pill therapy for gastritis and has the potential to be developed into a single component-multiple target agent.
XSLJP and the JAK/STAT signaling pathway
Figure 2S shows detailed information on the JAK/STAT signaling pathway. Cytokines such as STAT3, CCL2, IFN-α/β/γ, IL-6/10 and MMP-9 can activate the JAK/STAT signaling pathway in host cells [41]. These cytokines can phosphorylate JAK to activate STAT3, which can enter the cell nucleus and further combine with its target gene promoters to stimulate transcription [41]. STAT3 protein plays an important role in selectively inducing and maintaining the oncogenic inflammatory microenvironment at the beginning of malignant transformation and cancer development [42]. In addition, activated JAKs can also upregulate the expression of STAT3 via the Grb2/mTOR or Grb2/Ras/Raf/MEK/p-ERK/TF pathways [43]. As a crucial activator of STAT3 [44], IL-6 can indirectly promote the production of the proinflammatory factor CCL2 in monocytes to drive downstream Ca2+ signal transduction and thereby lead to enhanced expression of MMP-9, which can degrade a variety of extracellular matrix components and further promote tumor cell infiltration and metastasis [45]. In addition, CCL2 can trigger the secretion of CCL2/CCR2 to promote and maintain the generation of an immunosuppressive microenvironment [45]. IL-10, a major immunomodulatory cytokine, can activate STAT3 phosphorylation directly in a positive feedback manner due to the STAT3 binding site in its promoter after JAK activation [45, 46]. IL-10 can also downregulate the production of IL-12 and the expression of costimulatory molecules in macrophages and thereby reduces the generation of the Th1 response [47]. Ergosterol peroxide (EP), nobiletin, naringenin and other active components of XSLJP can affect the expression of cytokines in the JAK/STAT signaling pathway, such as STAT3, CCL2, IFN-α/β/γ, IL-6/10 and MMP-9. For instance, EP can significantly inhibit the phosphorylation of STAT3 and the expression and secretion of VEGF-C, and as a result, EP can counteract tumor angiogenesis and thereby suppress ovarian tumor growth[48]. Similarly, by reducing the activity and expression of STAT3, nobiletin can inhibit the angiogenesis of CD36-dependent breast cancer cells [49] and estrogen receptor-positive (ER+) breast cancer cells [50]. In addition, nobiletin can significantly and dose-dependently inhibit the secretion of inflammatory mediators such as NO, TNF-α and CCL2 in a coculture of adipocytes and macrophages [51]. Another active component, naringenin, can upregulate the expression of IL-6/10/18R1/18RAP, MMP-2/-3/-9, IFG1R and BCL2 and thus exerts anti-inflammatory and regenerative effects in degenerated human NP cells [52]. As demonstrated by our calculations, licochalcone α, in addition to glepidotin A as described above, exhibits high binding affinity to the active pocket of STAT3, which pending experimental verification, suggests that licochalcone α might combine with STAT3 and inhibit the expression of STAT3 or the biological effects of STAT3 against gastritis.
XSLJP and the MAPK (ERK/JNK/p38) signaling pathway
Figure 3S shows detailed information on the MAPK (ERK/JNK/p38) signaling pathway. Activation of the ERK1/2 pathway mainly amplifies the signal, whereas activation of the p38 pathway induces the expression of IL-1β/6/8, TNF-α, COX-2, iNOS, and prostaglandins, which participate in the proliferation and differentiation of immune cells [53, 54]. In the JNK/SAPK pathway, JNK can be activated by cytokines such as VEGF, IFN-α, IL-1, TRAF2, TGF-β and TNF-α and can then be phosphorylated and incorporated into the nucleus through the MAPK cascade reaction to act on downstream transcription factors such as c-Jun, c-Fos, AP-1, Elk1, p53, c-Myc, and Smad4 [53–55]. In the presence of IL-6, TGFβ1 drives the differentiation of T helper 17 (Th17) cells and then promotes further inflammation and enhances autoimmune conditions [56]. After binding to epidermal growth factor (EGF) and other ligands, EGFR autophosphorylates and stimulates Ras protein, which triggers gene transcription and control cell proliferation, differentiation and survival by activating signaling pathways such as the MAPK and PI3K/Akt pathways [57]. When the gastric mucosa is injured, the expression of EGFR in gastric parietal cells and related tissues is significantly increased [58], which might enhance the expression or activity of EGFR downstream signaling molecules such as ERK2, MEK1, AP1 and plasma membrane RTK [57]. In addition, EGFR can activate STAT3 and induce a series of biological effects downstream of STAT3, as discussed above discussion. Berberine, formononetin, and other active components of XSLJP can affect the expression of TGFB1, IL-6, TNF, EGFR and other cytokines in the MAPK signaling pathway. For instance, berberine can greatly reduce the expression of EGFR, further inhibit the phosphorylation of Raf, MEK and ERK, and thereby induce glioblastoma senescence [59]. Formononetin, another key component, has been identified as an EGFR inhibitor that can inhibit the tumor growth of nonsmall cell lung cancer through the EGFR/Akt/Mcl-1 pathway [60]. In this study, naringenin was the best-docked compound to TGFB1 in the LibDock mode (Table 5S), which suggests that this compound might directly bind to TGFB1, but its induction of the expression of TGFB1 and further downstream effects on gastritis need to be verified by biological experiments. In addition, glycitein exhibited significant binding affinity within the active site of EGFR, c-Jun and c-Fos, which suggests that glycitein might also target these three proteins to inhibit the expression of EGFR and the downstream transcription factors c-Jun and c-Fos or influence its downstream biological effects in gastritis therapy, but these effects remain to be confirmed by further experiments.
XSLJP and the p53 signaling pathway
Figure 4S shows detailed information on the p53 signaling pathway. As a key node in the p53 signaling pathway, p53, a transcription factor, can interact with a variety of functional proteins to induce a series of biological effects, such as blocking the cell cycle, promoting apoptosis, repairing DNA and inhibiting tumor angiogenesis and inflammation [61]. As an important downstream protein of p53 and a cyclin-dependent protein kinase inhibitor, p21 can bind to a series of cyclin-CDK complexes to inhibit the activity of corresponding protein kinases and thereby affects the phosphorylation of its downstream protein, interferes with the transcriptional regulation of CDK/cyclin complexes and ultimately causes cell cycle arrest [62, 63]. Moreover, the p53 protein triggers cell apoptosis unless it applies its own exonuclease activity to repair damaged DNA by forming a complex with p21 and GADD45 [64]. Under most conditions, regulated by the p53 protein concurrently with the apoptotic protein Bax, Bcl-2 exerts an anti-apoptotic effect by preventing the release of apoptosis-forming factors such as cytochrome C from the mitochondria, regulating the transcription factors NF-κB, AP-1, CRE and NFAT by blocking their entry into the nucleus, and thereby jointly promoting apoptosis [65]. Di-n-butyl phthalate, atractylenolide II, naringenin, berberine and other active components of XSLJP can affect the expression of p53, Bcl-2, and other cytokines in the p53 signaling pathway. For instance, di-n-butyl phthalate can effectively induce the apoptosis of mouse osteoblasts through the downstream effect mediated by p53 activation [66]. Atractylenolide II can decrease the expression of CDK2, p-AKT, p-ERK and Bcl-2, increase the phosphorylation of p38 and p53, p21 and p27, and further activate caspase-3/-8/-9, which results in the induction of G1 cell cycle arrest and apoptosis in B16 melanoma cells [67]. Naringenin can upregulate the expression of IL6/10, MMP-2/-3/-9 and Bcl-2 and downregulate the expression of IL1A and CASP3 in degenerated human nucleus pulposus cells, and thus, this compound exhibits anti-inflammatory and regenerative effects [52]. Berberine can trigger the release of cytochrome C from the mitochondrial membrane space into the cytoplasm, significantly increase the expression of caspase-3/-7/-9, cleaved PARP and Bax and reduce that of Bcl-2, which ultimately results in activation of the apoptotic pathway [68]. Among the key predicted components identified in this study, berberine exhibited low binding energies with TP53, which suggests that berberine might affect a series of downstream biological effects by binding to the p53 protein to induce apoptosis in gastritis cells, but this hypothesis needs to be verified by further experiments.
XSLJP and the NO/VEGF signaling pathway
Figure 5S shows detailed information on the NO/VEGF signaling pathway. COX-1 encoded by the PTGS1 gene mainly exists in normal tissue cells and is responsible for the production of endogenous prostaglandins (PGs) involved in mucosal protection, whereas COX-2 encoded by the PTGS2 gene is generally expressed in inflammatory environments and cancer tissues rather than normal tissues [69]. In most cases of inflammation and cancer, COX-2 and NF-κB are often activated simultaneously, whereas inactivated EGFR triggers the EGFR signaling pathway through negative feedback to promote cancer cell proliferation [70]. Inflammatory factors such as NF-κB, IL-6/-8, and IFN-γ exert a certain therapeutic effect on gastric ulcers by stimulating inflammatory cells to express iNOS and produce NO, and the enhancement of this compounds might promote the protection of mucosal glycoproteins and reduce oxidative stress, which is speculated to be the therapeutic mechanism for gastric ulcers [71]. Under hypoxic conditions, an increase in HIF-1, a cell hypoxia receptor molecule encoded by the HIF1A gene, can stimulate the activation of VEGF, a basic factor for vascular growth regulation, and stimulate angiogenesis to promote oxygen delivery [72]. Berberine, mairin, nobiletin, licochalcone α, and other active components of XSLJP can affect the expression of COX-1/2 and iNOS in the NO/VEGF signaling pathway. For instance, berberine can downregulate the expression of HIF-1α and VEGF, inhibit the phosphorylation of Akt and ERK, and suppress the growth of NSCLC cells through main pathways, such as NF-κB/COX-2, HIF-1α/VEGF, PI3K/Akt, and RAR/MEK/ERK [68]. Mairin can inhibit the expression and transcriptional activity of HIF-1α under hypoxic conditions, inhibit the nuclear accumulation of STAT3 and the expression of key factors such as VEGF, and protect against angiogenesis in hypoxic PC-3 prostate cells [73]. Nobiletin can reduce the expression of NF-κB and HIF-1α and the phosphorylation of Akt in both PC-3 and DU-145 cells and further downregulate the expression of VEGF and c-Myc respectively to suppress the viability of these two cell lines [74]. Licochalcone α exerts a strong inhibitory effect on the production of thromboxane A2, arachidonic acid and collagen-induced platelet aggregation and thereby inhibits the expression of COX-1 and COX-2 against inflammation [75]. Among the key predicted components identified in this study, formononetin showed good binding affinity to both PTGS2, Jun and HIF1A, which suggests that formononetin is likely to integrate with these proteins to affect their expression level or induce their downstream function in suppressing the inflammatory process in gastritis. However, the existence of a direct interaction between this active component and its target proteins remains to be further verified by experiments.
The pharmacological effects of active components in TCM prescriptions are complementary to each other. As shown in Fig. 2 and Fig. 3, the following finding was obtained for all the targets, regardless of their experimental verification: either one active component corresponds to multiple targets or multiple components act on the same target, which indicates that the TCM prescription XSLJP treats gastritis through a multitarget and multichannel approach. Attentionally, the signaling pathways mainly included the TNF, JAK/STAT, MAPK, p53 and NO/VEGF signaling pathways, and the regulation of some active compounds on these pathways had been verified, which indicates the scientificity and reliability of this study. Notably, this study showed that the core active ingredients glepidotin A, licochalcone α, glycitein, berberine and formononetin interact with most of the core targets at the optimal level, which implies the importance of these core active ingredients in gastritis therapy, but the interaction between these compounds and core targets requires experimental verification. As indicated by the discussion above, this research has the potential to provide basic ideas for and guide follow-up studies on the mechanism of XSLJP in the treatment of gastritis.
Outlook/Prospects
In addition to exploring the mechanism of XSLJP in the treatment of gastritis, our research can also provide certain reference ideas for the future optimization of prescription compositions, dosage adjustment, clinical applications and the adjustment of combination schemes. For example, lauric acid, an active component in Codonopsis, possesses antibacterial, anti-inflammatory and anticancer properties [76, 77] but might also cause inflammation [78]. In addition, from a broad perspective, this study found that certain active components might exert a wide range of pharmacological effects by targeting multiple targets, as shown in Fig. 2 and Fig. 3, which provides a theoretical basis for the streamlining of TCM prescriptions. The heat map clearly shows the likely mutual interaction between key components and hub targets determined by molecular docking, which provides a clue for the optimization of prescription compositions in the development of multitarget TCM medicines.
The focus of this research was to explore the mechanism of XSLJP in the treatment of gastritis, but as observed in many studies, inflammatory conditions can promote cancerous development, which in turn induces an inflammatory microenvironment that is more conducive to cancer progression [79]. Normal gastric cells often undergo inflammation after being invaded by infectious Helicobacter pylori and further develop chronic inflammation, which might deteriorate into gastric cancer if no treatments are applied in time and properly. The correlation between gastritis and gastric cancer is obvious because gastritis meets the characteristics of cancer-related inflammation regarding specific inflammatory mediators, including cytokines and chemokines [79]. The above-described analysis on predicting targets of the active components of XSLJP and their related pathways confirms the importance of cytokines and chemokines in gastritis drug therapy. Therefore, our study also indicates that XSLJP might have the potential to be further studied for the treatment of gastric cancer.