In recent years, network pharmacology is developing rapidly as a new discipline. Network pharmacology is the statistical analysis of high-throughput omics data and component-target-disease-pathway interactions based on virtual computer and network database retrieva [12]. Network pharmacology can explore the mechanism of action of single component and multi-component of TCM, providing a special and novel approach for the study of TCM [13].
The global incidence of diabetes is rapidly increasing, bringing heavy mental pressure and economic burden to individuals, families and society [14]. The existing western drugs for the treatment of diabetes include insulin, metformin, sulfonylureas, nateglinide, thiazolidinediones, DDP-4 inhibitors, GLP-1 receptor agonists, glycosidase inhibitors and SLGT-2 inhibitors, etc. Although the hypoglycemic effect is relatively rapid and obvious, they treat the symptoms but not the root cause and have large side effects. TCM has become a potential drug for the treatment of diabetes due to its advantages of safety, effectiveness, economy and practicality [6].
Diabetes belongs to the category of “consumptive thirst (Xiaoke)” in TCM, and its basic pathogenesis is Qi deficiency and blood stasis [15]. Radix Astragali (RA), Radix Puerariae (RP), Radix Trichosanthis (RT) and Radix Rehmanniae (RR) are four TCMs commonly used in the treatment of diabetes. RA has the effect of Yiqi Wenyang, and is one of the single drugs frequently used in the treatment of diabetes and its complications, and plays a leading role in the treatment of diabetes, diabetic nephropathy and diabetic cardiovascular complications [16]. Clearing heat and dampness, nourishing and coordinating are also the main functions of TCM in the treatment of diabetes. RR has the effects of clearing heat and cooling blood, nourishing Yin and producing fluid; RT has the effects of clearing heat and removing fire, and RP has the effects of engendering liquid and allaying thirst [17]. In this study, Astragali-Rehmanniaeare (RAR) can play the role of nourishing Qi and nourishing Yin, and Puerariae-Trichosanthis (RPT) can achieve the effect of engendering liquid and allaying thirst to treat diabetes. The 8-week SD rats experiment showed that compared with the model group, the blood glucose of RAR group and RPT group had a significant downward trend and the hypoglycemic effect was better than that of metformin group. However, the mechanism of RAR and RPT in the treatment of diabetes is still unclear, this study is the first to explore the mechanism of these four drugs in the treatment of diabetes.
Through the network pharmacological analysis, the core active components of Astragali-Rehmanniaeare (RAR) and Puerariae-Trichosanthis (RPT) in the treatment of diabetes are quercetin, daidzein, kaempferol, puerarin, formononetin and so on. The core targets include PTGS2, AKT1, PIK3CA, TNF, NOS3, MAPK1, etc. The biological pathway of RAR and RPT in the treatment of diabetes mainly acts on PI3K-Akt signaling pathway and insulin resistance pathway. Quercetin and kaempferol are the active components of Radix Astragali (RA). Many studies have shown that quercetin is a promising drug target for the treatment of diabetes and its complications. Quercetin has various anti-hyperglycemia mechanisms, such as enhancing insulin sensitivity, promoting glycogen synthesis, inhibiting α-glucosidase activity and improving insulin resistance [18]. High fat diet or obesity can reduce glucose uptake in skeletal muscle. Quercetin enhances glucose uptake in skeletal muscle by acting on glucose transport and insulin receptor signaling, thereby improving glucose utilization [19]. Kaempferol can enhance lipolysis and counter high fatty acid and impaired glucose uptake, glycogen synthesis, AMPK activity, and glucose transporter (GLUT4) expression [20]. Daidzein and puerarin are the active components of Radix Puerariae (RP), and studies have shown that daidzein can inhibit the activity of glucosidase [21]. Puerarin can enhance the insulin sensitivity of diabetic rats, and can up-regulate the expression of PI3K, Akt and AMPK to promote glucose transport. At the same time, puerarin can also increase the glucose utilization rate of dexamethasone-induced adipocyte 3T3-L1 insulin resistance model and improve insulin resistance [22, 23]. Formononetin is the common active component of RA and RP, which has anti-apoptosis, anti-inflammatory, antioxidant and other pharmacological effects [24, 25]. Related studies have shown that formononetin can reduce blood glucose, improve insulin resistance and reduce oxidative stress [26].
PI3K/AKT signaling pathway plays an important role in regulating cell growth, proliferation, survival, transcription and protein synthesis pathways [27]. Phosphatidyl inositol 3-kinase (PI3K) is an important kinase of phosphoinositol and inositol. Activation of PI3K can further promote the activation of Akt, and the phosphorylation of activated Akt can activate or inhibit its downstream target proteins, and then regulates apoptosis-related proteins Bax and Bcl-2 to inhibit cell apoptosis through PI3K/Akt signaling pathway [28]. RAC-alpha serine /threonine-protein kinase 1 (AKT1), as one of the Akt kinases, is involved in the regulation of cell proliferation, survival, metabolism and angiogenesis, and can induce glucose transport to regulate glucose uptake, so as to regulate diabetes mellitus and its complications [29]. Akt plays an important role in regulating insulin-dependent metabolic responses. Activation of Akt can regulate glucose uptake and lipid metabolism, but Akt overexpression can lead to elevated blood glucose and induce insulin resistance [30–33]. The results of animal experiments in this study showed that the Akt level of Astragali-Rehmanniaeare (RAR) group and Puerariae-Trichosanthis (RPT) group was significantly higher than that of the control group but lower than that of the model group, indicating that RAR and RPT treated diabetes by improving the PI3K/Akt signaling pathway, which was consistent with the results of network pharmacological studies. Compared with the model group, the HOMA-IR value of the RPT group was significantly decreased, and the HOMA-β value of the RAR group was significantly increased. It suggests that RPT has the function of improving insulin resistance, while RAR has the function of improving islet β-cell. As we all know, the mechanism of diabetes is insulin resistance and β-cell dysfunction, but few drugs can improve both at the same time. Therefore, we predicted that the combination of these four drugs can improve both insulin resistance and islet β-cell function. Relevant animal validation experiments will be followed up in the future.