MIRI is a pathological process that occurs when blood flow is restored to the ischaemic myocardial tissue while causing stress injury. Myocardial I/R injury is associated with severe clinical manifestations leading to a high incidence of cardiac insufficiency and heart failure[11]. There are no effective methods to reduce MI/RI, so early intervention is particularly important, and TCM has unique advantages in this regard[12]. However, due to the multi-component and multi-target nature of Chinese medicine, the mechanism of traditional pharmacological methods in the treatment of MI/RI is still difficult to be fully elucidated. Therefore, in this study, we first validated the efficacy of SSNX through animal experiments, and then investigated the potential mechanism of SSNX intervention in MIRI through network pharmacology. In addition, molecular docking methods and further target validation demonstrated that the protective effects of SSNX on MIRI in miniature pigs, possibly through the inhibition of mitophagy.
The animal experiments demonstrated that SSNX significantly improved cardiac function and attenuated myocardial I/R injury, improved myocardial histopathological structure and reduced myocardial fibrosis in MIRI miniature pigs. To further explore the potential mechanism, we obtained 75 potential targets of SSNX for the treatment of MIRI by network pharmacology. Additionally, the KEGG results offer a relatively complete and macroscopic mechanistic picture of SSNX for the treatment of MIRI. To further explore more specific mechanisms, we analysed modularly by the MCODE algorithm. The results of the analysis grouped the potential targets into five clusters representing different functions, and we selected cluster 2 for subsequent studies. Enrichment analysis of cluster 2 suggested that the key mechanism of SSNX for MIRI may be related to mitophagy. Interestingly, the molecular docking results also further confirm this idea.
According to the molecular docking results, ginsenoside Rg1, Rb1 and Rb3 displayed good binding to mitophagy-related proteins, with the best binding to FUNDC1. Subsequently, the literature was queried to see if these three key compounds could treat MI/RI by modulating mitophagy. Research showed that Ginsenoside Rg1 significantly improved cardiac remodelling in left anterior descending coronary artery ligated mice, as evidenced by a reduction in cardiac fibrosis accompanied by an improvement in cardiac function. The mechanism was that ginsenoside Rg1 significantly increased mitochondrial formation, improved cardiac mitochondrial damage and enhanced SIRT1/PINK1/Parkin-mediated mitophagy during cardiac remodelling[13] However, the effects of the other two active components on mitophagy have not been investigated, and therefore further experimental validation of the above monomers is required to reveal their effects and mechanisms.
Based on the above predicted results, we further understood the effect of SSNX on the function of mitochondria. Transmission electron microscopy observed that SSNX significantly improved mitochondrial morphology. Interestingly, SSNX not only protected mitochondrial morphology, but also protected mitochondrial function by increasing myocardial ATP content and maintaining mitochondrial membrane potential. It is suggested that SSNX may protect mitochondrial function and morphology, which in turn interferes with MI/RI. Based on these results, we further verified whether SSNX could affect mitophagy
Autophagy is a metabolic process that degrades macromolecules and can degrade damaged organelles within cells, specific macromolecules, as well as invading viruses and bacteria[14]. Mitophagy is a type of autophagy that occurs in the mitochondria and is a key process for detecting mitochondrial function and removing damaged or unwanted mitochondria[15]. On the one hand, moderate mitophagy removes damaged or aged mitochondria from the cell, which helps to maintain intracellular homeostasis, achieve mitochondrial renewal and prevent further myocardial damage; on the other hand, over-activated mitophagy increases cell death and aggravates I/R damage[16]. In our experiments, mitophagy was excessively enhanced in the MI/RI miniature pigs model, as evidenced by abnormal mitochondrial structure, reduced ATP production, impaired MMP and a significant increase in mitophagy-related proteins.
Mitophagy is mainly divided into ubiquitin-dependent and non-ubiquitin-dependent receptor pathways, of which PINK1/Parkin is the most typical and is a key pathway regulating mitophagy[17]. Under normal conditions, PINK1 crosses the mitochondrial membrane to enter the mitochondria for degradation, but when the mitochondria are damaged, PINK1 transit into the mitochondria is blocked and accumulates in the outer mitochondrial membrane, which in turn activates Parkin, phosphorylates Parkin and promotes the activation of Parkin E3 ubiquitinylated ligase, which completes the activation of Parkin to recruit junction proteins for the mitochondria that need to be degraded, after which the junction protein LIR is activated with the help of the activated Parkin then binds to LC3 and mediates mitophagy through the LIR structure of the junction protein[18]. A variety of receptor proteins, in addition to PINK1/Parkin, are located in the outer mitochondrial membrane and interact with LC3 through the LIR motif to start mitochondrial autophagy. These proteins include FUNDC1, BNIP3, and NIX. FUNDC1 is an important receptor protein located in the outer mitochondrial membrane, and when mitochondria are damaged, the LIR motif in FUNDC1 activates mitophagy by molecularly docking with LC3 protein through hydrophobic interaction[19]. BNIP3 is located in the outer mitochondrial membrane and contains a transmembrane domain with the C-terminus inserted into the outer mitochondrial membrane and the N-terminal storm in the cytoplasm. BNIP3 relies on the direct action of the transmembrane domain LC3 to mediate the onset of mitophagy[20]. In the MI/RI miniature pig model, SSNX treatment resulted in a significant reduction in FUNDC1 and BNIP3. These results suggest that SSNX can prevent MIRI by inhibiting the PINK1/Parkin pathway and FUNDC1 and BNIP3 receptor-mediated mitophagy.
In summary, network pharmacology and animal experiments demonstrated that SSNX can effectively reduce myocardial I/R injury and protect mitochondrial structure and function, and its effects may be achieved by inhibiting mitophagy. Furthermore, according to the molecular docking results, ginsenoside Rg1, ginsenoside Rb1 and ginsenoside Rb2 are key components associated with mitophagy. The results of this study provide preclinical evidence for SSNX in the treatment of MI/RI and provide a more novel perspective for the treatment of MI/RI with Chinese herbal medicine.