According to the theory of TCM, CAD belongs to the category of “chest pain” or “heartache”, the main treatment is promoting blood circulation to remove blood stasis [18]. The pathogenesis of CAD in TCM is the syndrome of deficiency in origin and excess in superficiality. Deficiency in origin is the deficiency of yin-yang and qi-blood, and excess in superficiality is the interaction of phlegm, blood stasis, Qi stagnation and cold coagulation [19]. Since CAD lasts longer, blockage of the Qi and blood may cause cardiovascular ischemia, hypoxia and necrosis, so as to aggravate the severity of diseases [20]. Moreover, the blockage of Qi and blood can also produce many harmful products, including blood lipids, blood clots and so on [21]. Thus, approaches that recovery the cardiovascular patency are extremely crucial in the treatment of CAD.
Previous studies have shown that many components of TCM play a therapeutic role in CAD through autophagic pathway. For example, Han J et al. [22] have found that when human umbilical vein endothelial cells are subjected to oxidative stress, curcumin can induce autophagy through FOXO1 signaling pathway and protect vascular endothelial cells from oxidative stress. Similarly, in the mouse model of acute myocardial infarction, polydatin can activate Sirt3, up-regulate autophagic flux of myocardial cells and improve mitochondrial dysfunction, so as to protect myocardial cells from myocardial infarction injury [23]. Hu J et al. [24] have found that in the model of myocardial infarction, luteolin can up-regulate autophagic flux of myocardial cells and improve mitochondrial viability through Mst1 inhibitor, so as to alleviate myocardial dysfunction. Contrary to the cardiovascular protection by inducing autophagy, some Chinese medicines can also inhibit the excessive expression of autophagy. For instance, Huang Z et al. [25] have found that berberine can alleviate myocardial ischemia-reperfusion injury (IRI) by inhibiting the over-expression of autophagy-related proteins (SIRT1, BNIP3 and Beclin-1). Additional reports have demonstrated that danshensu can inhibit IRI-induced excessive autophagy through activating mTOR signaling pathway and reduce cell apoptosis, so as to alleviate myocardial cells IRI and improve cardiac function [26]. Thus, It can be seen that autophagy plays a role of “double-edged sword” in cardiovascular diseases: in the early stage of the disease, induction of autophagy is protective due to less damage. When the cardiovascular system continues to be invaded by damaging factors, the disease can worsen to the late stage. At this moment, the disease also has an autophagic effect, while the induction of autophagy may cause autophagic cell death.
In the present study, 107 Sal-related targets, 241 Sir (autophagy agonist)-related targets, 100 CQ (autophagy inhibitor)-related targets, and 576 CAD-related targets were obtained from the public databases. Integrating potential targets of three compounds with those of CAD revealed exactly 36 therapeutic targets. Based on the topological analysis of PPI network, the top 5 core targets were selected, consisting of GAPDH, CASP3, MTOR, VEGFA, and EGFR. GO functional analysis showed that the role of active compounds (Sal, Sir and CQ) in CAD was related to many biological processes, including serine/threonine-protein kinase activity, endopeptidase activity, L-cysteine endopeptidase activity, response to oxidative stress, cellular response to chemical stress, response to reactive oxygen species, response to UV and so on. KEGG signaling pathway enrichment technology retrieved many related pathways from these core targets, such as inflammation, lipid response, oxidative stress, autophagy, apoptosis, diabetic cardiomyopathy, estrogen signaling pathway and so on. Apparently, those three compounds may be used to treat CAD via autophagic pathway. Meanwhile, this fact implies that both induction and inhibition of autophagy seem to be beneficial for CAD, which is consistent with the concept of previous literature. To verify 5 key proteins of GAPDH, CASP3, MTOR, VEGFA, and EGFR, we respectively imported them into the online tool AutoDock Vina, we found that the three active compounds all had good binding ability with the selected targets. It not only suggests that these compounds can regulate autophagy in a multi-target and multi-channel manner, thus affecting the occurrence and development of CAD, but also suggests that they may be important potential targets for the treatment of CAD, so as to provide novel ideas for succeeding researches.
Among those 5 core targets, CASP3 (Caspase-3), a member of the cysteine protease family, is a downstream protein in the apoptosis pathway and an apoptotic enzyme that functions through the death receptor and mitochondrial pathways [27]. Previous studies have found a significant increase in Caspase-3 expression in the models of CAD rats [28], while the expression of Caspase-3 is decreased through the treatment of PCI [29], which demonstrates that Caspase-3-mediated apoptosis may be an important molecular mechanism of CAD. mTOR is a serine/threonine protein kinase that belongs to the phosphatidylinositol 3 kinase (PI3K) [30]. There are two different sub-types of mTORC1 and mTORC2. mTORC1 is involved in the synthesis of proteins, controlling ribosome biogenesis, inhibiting autophagy, regulating the biological activity of mitochondria and regulating cell cycle [31]. mTORC2 is mainly involved in the regulation of apoptosis and proliferation, maintaining cytoskeleton structure and polarity [32]. Studies have shown that PI3K/Akt/mTORC1 and AMPK/mTORC1 signaling pathways play important roles in the progression of coronary atherosclerosis [33]. The PI3K/Akt/mTORC1 pathway is involved in the proliferation and migration of vascular smooth muscle cells during coronary atherosclerosis. Activated vascular smooth muscle cells may promote the progression of atherosclerotic plaques [34], inhibition of the PI3K/Akt/mTORC1 signaling pathway not only promotes autophagy in macrophages and stabilizes arteriosclerosis plaques [35], but also inhibits the damage of endothelial cells and delays the progression of coronary arteriosclerosis [36]. Thus, inhibition of the PI3K/Akt/mTORC1 signaling pathway can effectively enhance autophagy, attenuate lipid metabolic disorders, and reduce plaque area [35]. Similarly, inhibition of AMPK/mTORC1 signaling pathway effectively prevents vascular smooth muscle cells proliferation and intimal thickening, activates autophagy in endothelial cells, and delays endothelial cells senescence [37, 38]. However, the platelet-derived growth factors-induced vascular smooth muscle cells proliferation via inhibition of mTORC1/S6K pathway is not associated with AMPK [39]. VEGFA is a member of the VEGF family, also known as vascular endothelial factor A, which plays an important role in angiogenesis and endothelial cell growth. It can induce proliferation and migration of endothelial cells and induce vascular permeability, which are necessary for physiological and pathological angiogenesis [40]. Studies have shown that VEGFA can bind to VEGFR-2 in the endothelial membrane under the condition of myocardial ischemia and hypoxia, and induce new capillary in the infarcted area and promote the establishment of collateral circulation in the ischemic peripheral tissues through multiple approaches (including SRC, Raf-mek, PI3K-Akt and DII4-Notch pathways), so as to improve the function of heart [41–44]. It is also reported that the cardiac function of rats with acute myocardial infarction tends to improve after the introduction of VEGFA [45]. Moreover, Shi ZZ et al. [46] have found that in coronary artery disease, HIF-1α expression is stable and binds to the VEGFA gene in the nucleus, so as to activate the HIF-1α/VEGFA pathway, which promotes angiogenesis and improves myocardial ischemia. EGFR is the expression product of c-erbB1 (a proto-oncogene), and a member of the human epidermal growth factor (HER) family. It is mainly distributed in vascular epithelial cells and can interfere the growth, differentiation and proliferation of vascular epithelial cells through RAS/RAF/MEK/MAPK and PI3K/PDK1/Akt pathways [47, 48]. EGFR-specific binding to ligand (EGF) promotes ROS formation in the cardiovascular system and contributes to cardiovascular system [49]. Moreover, Li WX et al. [50] have found that EGFR may be a therapeutic target for obesity-related cardiovascular diseases, which is associated with myocardial inflammation, fibrosis, apoptosis and dysfunction. According to the literature review, these 5 core targets are closely related to the occurrence and development of cardiovascular diseases, which is also consistent with the results of network pharmacological analysis.
Subsequently, based on the analysis results of network pharmacology, we investigated the role of Sal in CAD through cell experiments, focusing on the autophagic pathway. Moreover, in order to evaluate the efficacy via autophagic pathway, we seclected autophagy agonist (Sir) and autophagy inhibitor (CQ) as the autophagic control group. Due to the pathogenesis of CAD, which indirectly triggered cardiovascular hypoxia, the cardiomyocytes (H9C2) were exposed to CoCl2, so as to induce cells hypoxia. In order to evaluate whether the film was successfully made, we used the Hypoxia-inducible factor (HIF-1α) as a standard. More and more evidences have shown that HIF-1α signaling pathway plays an essential role in the process of hypoxia. Under the condition of hypoxia, the organism produces a series of compensatory regulation to resistance the low-oxygen stress, among which HIF-1α is the critical transcriptional regulator of hypoxia-induced regulation, so as to mediate the process of cell growh, proliferation, migration, apoptosis and autophagy [51–53]. Meanwhile, HIF-1α is also the critical molecule in many physiological and pathological regulation. HIF-1α is expressed under the condition of normoxia, but HIF-1α protein can be rapidly degraded by the pathway of intracellular oxygen-dependent ubiquitin protease, and can only be stably expressed under the condition of hypoxia [54, 55]. Cheng JK et al. [56] have found that the SENP1/HIF-1α signaling pathway enables the stable expression of HIF-1α, and the lack of erythropoietin in SENP1-depleted mouse embryos can cause severe ischemia. Tian H et al. [57] have found that chronic hypoxia induces the increased expression of SUMO-1, degradation of SENP1 protein, increase of desumoylation-modified HIF-1α, and increase of HIF-1α stability and transcriptional activity in the wall of pulmonary arterioles of mice, so as to cause hypoxic pulmonary hypertension (HPH). Other studies have shown that VEGF is an important target gene of HIF-1α transcriptional activation, and the expression of VEGF is regulated by HIF-1α. Under the condition of hypoxia, HIF-1α can improve hypoxia by promoting VEGF and its receptor 1, increasing vascular permeability and inducing angiogenesis. The levels of HIF-1α and VEGF are significantly increased in patients with acute exacerbation of high altitude pulmonary heart disease, and are negatively correlated with arterial partial pressure of oxygen, and prolonged hypoxemia can cause pulmonary hypertension and pulmonary vascular remodeling, which suggesting that HIF-1α/VEGF signaling pathway may be an important factor in the high altitude heart disease [58]. Thus, it be seen that HIF-1α not only plays a regulatory role in hypoxia stress, but also its related signaling pathways are closely associated with the occurrence and development of diseases. Following treatment with Sal for 24 h in CoCl2-exposed H9C2 cells, we found that Sal could not only induce cells autophagy, but also reverse the CoCl2-caused injury, which suggested that autophagy may play a protective role in this process. However, further studies showed that Sal-mediated autophagy was not always beneficial to H9C2 cells. When H9C2 cells were treated with CoCl2 for 12 h, Sal-mediated autophagy does not reverse this chemical damage, and accelerates the procedure of cell death, suggesting that autophagy may exist a function of assisting injury. Thus, autophagy plays different roles at different stages of injury, which is consistent with our analysis of network pharmacology.
However, there are still some limitations for this study. On the one hand, the network pharmacology research relies more on various existing databases, but the sifted condition of compounds in databases may not be accurate enough. On the other hand, the screened active ingredients may exist the difference of those actually absorbed in the blood of patients with CAD. Due to the accuracy and reliability of the data have a great impact on the predicted results, it is extremely necessary to further verify the reliability and quality of the predicted results and optimize the screening criteria of the TCM database, so as to improve network pharmacology research. Hence, further experiment in vivo and clinical verification of the effect of Sal on heart and blood vessels is demanded to validate theoretical predictions.