DISCUSSION
As a progressive ophthalmopathy, DR was resulted from pathological alterations mediated by long-term accumulations of hyperglycemia in the retina of DM patients (Nawaz, Rezzola, 2019). Several treatment approaches, such as physiotherapy and drug therapy, have been demonstrated to be able to alleviate DR (Pardue and Allen, 2018). A previous finding has suggested that phytoestrogens such as biochanin A could play a therapeutic role in DR treatment (Mehrabadi, Salemi, 2018). By establishing a STZ model in rats, the current study explored the potential roles of CMS and SIRT1 in oxidative stress, inflammatory response, and cell apoptosis of retinal cells, and got the conclusion that CMS induced the activation of SIRT1 and effectively inhibited oxidative stress, inflammatory response, as well as cell apoptosis in rats with DR.
Initially, based on our findings, SIRT1 was expressed at a low level in rats with DR. SIRT1, as a nuclear protein, was found to regulate inflammation and apoptosis as well as other metabolic pathways through deacetylation of histones, non-histones and transcription factors (Kowluru, Santos, 2014a). Consistent with our study, Li et al.also demonstrated that SIRT1 was down-regulated in the endothelial cells of STZ-induced diabetic mice and enhancing SIRT1 could increase resistance to oxidative stress and inhibit diabetic vascular endothelial dysfunction (Li, Kim, 2016). In addition, activation of retinal SIRT1 was reported to protect the retina from damage in the diabetic milieu (Maghbooli, Emamgholipour, 2018).
Next, the relationship between CMS and SIRT1 in mice with DR was studied. We proved that SIRT1 was activated by CMS, indicating that the functions of CMS on DR might be associated with SIRT1. Furthermore, our study found that CMS inhibited oxidative stress and inflammatory response in rats in with DR through the activation of SIRT1, indicated by decreased levels of ROS, MDA, iNOS, NO, increased level of SOD, and reduced levels of inflammatory factors. Induction of ROS production was proved to be one of the major reasons for retinal cell death in DR by mitochondrial dysfunction (Pearsall, Cheng, 2019). It was reported that increased levels of MDA, NO and decreased iNOS, SOD levels were found in the DM-model rats, blocking of which would contribute to enhanced anti-oxidation (Long, Yu, 2012). DR was related to elevated release of pro-inflammatory cytokines including IL-1β, IL-6 and TNF-α (Gao, Li, 2017, Sharma, Purohit, 2015). A previous study demonstrated that CMS inhibited production of hydrogen peroxide-induced ROS, lipid peroxidation, and prevented reduction of intracellular glutathione levels and SOD activity (Jeon, Seo, 2012). Besides, CMS has been observed to prevent IL-1β-induced catabolic effects by inhibiting inflammation and inflammatory cytokines in chondrocytes (You, Cho, 2017). Furthermore, enhanced SIRT1 was associated with reduced oxidative stress and ameliorated DR (Kowluru, Santos, 2014b). In addition, activated SIRT1 was proved to down-regulate pro-inflammatory cytokines, inhibit oxidative stress and cell inflammation, thereby improve DR (Karbasforooshan and Karimi, 2018).
Furthermore, we proved that CMS suppressed apoptosis of retinal cells, thereby ameliorated DR through the activation of SIRT1, as supported by reduced levels of Cyt-C, Caspase-3. Phytoestrogens, including CMS, genistein, and daidzein, were reported to suppress apoptosis by working with 17β-estradiol (Schmidt, Michna, 2005). Genistein, for example, inhibited chemical hypoxia-induced cell apoptosis by suppressing the mitochondrial apoptotic pathway and level of Caspase-3 (Shi, Zhang, 2019). What’s more, activated SIRT1 together with silenced protein arginine methyltransferases was involved in suppressing the oxidative stress-induced apoptosis of retinal pigment epithelial cells in DR, as supported by reduced level of Caspase-3 (Kim, Park, 2015). Moreover, another study also proved that activation of SIRT1 was related to inhibited HG-induced apoptosis and inflammation cytokines production in DR (Tong, Peng, 2019). Collectively, our study suggested that CMS might be an important reagent for DR treatment, which regulated the pathogenesis of DR by activating SIRT1.
In summary, we have proved that CMS could inhibit oxidative stress, inflammatory response, and cell apoptosis in rats with DR through the activation of SIRT1, which may have potentially important therapeutic implications in the treatment of oxidative stress and inflammatory response in patients suffering from DR.