DN is a common diabetic complication that threatens the health and lives of diabetic patients. Unfortunately, most diabetic patients cannot obtain good treatment effects with routine therapies. Growing evidence has suggested that LDP may be a potential adjuvant or alternative medicine for DN[8–11]. However, the detailed mechanism of action remains obscure. As a relatively new approach in drug discovery, network pharmacology can illustrate the interaction between diseases, drugs, and targets[35, 36]. To some extent, the characteristics of network pharmacology coincide with the "multi-compounds, multi-targets, and multi-pathways" theory of traditional Chinese medicinal formula. Therefore, we explored the mechanism of action of the Chinese medicine formula LDP as an adjuvant treatment of DN through a network pharmacology approach. Moreover, the inner links between LDP and DN were further verified via molecular docking. The present study improves the understanding of the molecular mechanism of LDN in treating DN, which is of great importance for further basic research and clinical application.
Based on the results of network analysis, quercetin, kaempferol, beta-sitosterol, diosgenin, and stigmasterol can be defined as the crucial compounds of LDP in treating DN. It is reported that quercetin could inhibit inflammatory cell infiltration, alleviate renal oxidative stress injury, relieve the pathological damage of the kidney, and improve renal function in DN[37]. Kaempferol has anti-inflammatory, antioxidant, and anti-fibrotic properties in DN[38, 39]. Beta-sitosterol has been identified as a potential herbal nutraceutical for DN because it has anti-inflammatory, lipid-lowering, antioxidant and anti-diabetic activities[40]. Diosgenin plays a protective role in DN through lowering oxidative stress and inflammation[41]. Stigmasterol has the function of regulating glucose metabolism[42]. These main LDP compounds collectively exert anti-inflammation, antioxidant, anti-fibrotic, anti-hyperglycemic, and anti-hyperlipidemic effects which can form a pharmacological basis for the anti-DN function of LDP.
Through the PPI network analysis, JUN, MAPK8, AKT1, EGF, TP53, VEGFA, MMP9, MAPK1, and TNF were the key targets of LDP in treating DN. These targets are mainly connected with inflammation, vascular permeability, and oxidative stress. In some ways, this is consistent with the disease characteristics and pathogenesis of DN. To further reveal LDP's possible anti-DN molecular mechanism, we conducted molecular docking of 9 key targets with their corresponding active compounds. Study results have shown that the nine key targets have an excellent ability to bind their related active compounds in LDP. Among them, JUN, MAKP1, and AKT1 had a more stable binding ability than others. A recent study showed that c-Jun could be progressively elevated, and it could activate the expression of TGFβ1 via ross-activation and auto-regulation during renal fibrosis in DN[43]. MAPK1 can increase many inflammatory and adhesion factors in glomerular cells and exacerbate the damage in the pathological state of DN[44]. AKT1 is closely associated with the immune regulation and inflammation reaction of DN. It plays a vital role in basement membrane thickening, mesangial proliferation, and podocyte injury[45].
GO functional enrichment analysis of the 131 common targets was carried out (Fig. 6A ). The 10 most meaningful enriched BP terms were principally associate with apoptosis, response to oxygen levels, and response to lipopolysaccharide. Related research demonstrated that the initiation and progression of DN are closely associated with apoptosis, oxidative stress, and lipopolysaccharide level[46, 47]. MF terms mainly included transcription factor binding, protein homodimerization activity, cytokine receptor binding, and antioxidant activity. The targets primarily enriched in the above MF terms were JUN, TNF, VEGFA, SOD1, DPP4, and AKT1. They are principally included in inflammatory regulation, immune response, and oxidative stress. Inflammation and immune response play essential roles in the progression of DN[48]. CC terms were mainly enriched in membrane raft, protein kinase complex, extracellular matrix, transcription factor complex, and vesicle lumen. The key targets, such as TNF, MAPK1, and VEGFA, were included in these terms. These finds indicated that DN is very complex, and the LDP could be used to treat DN by interfering with various molecular functions and cellular components.
Associated with GO enrichment analysis, we found out that the main pathways of LDP on DN might be the AGE-RAGE signaling pathway and IL-17 signaling pathway based on the enrichment results of KEGG. As we all know, the AGE-RAGE signaling pathway is of great significance to diabetic complications. The upregulation of AGEs levels and RAGE expression can aggravate the progression of DN[49]. When the kidney is subjected to long-term stimulation of glycosylation of reducing sugars, the AGEs are gradually accumulated and increase the risk of extracellular matrix migration, renal tubular dysfunction, and glomerular proliferative lesion. Further, AGEs can bind to RAGE receptors to cause chronic inflammation reaction, oxidative stress, kidney tissue damage, and the loss of kidney function[50]. Sharma et al. have reported that AGE-RAGE interaction promotes DN's progression because of the release of fibronectin, TGF-β, and inflammatory cytokines[51]. If the IL-17 pathway is activated in many kidney diseases, it can promote inflammatory cytokines[52]. Inflammatory cytokines can cause glomerulosclerosis and kidney tissue damage in DN via inflammatory response[53]. Mohamed et al. have shown that low-dose recombinant IL-17 might prevent and reverse DN[54].
To some extent, our results are supported by the previous studies, which made them more reliable. However, there are also some limitations in this study. For example, it is difficult to ensure that the drug's active ingredients are identical to those absorbed into the patient's bloodstream; We are still vague about the interaction effects of different nodes in the network analysis; The functions and pathways highly researched may cause departures from expected results. Thus, further experimental and clinical studies are warranted to verify our theoretical prediction.