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.