SIRT1 Activation by Polydatin Alleviates Oxidative Damage and Elevates Mitochondrial Biogenesis in Experimental Diabetic Neuropathy

Mitochondrial dysfunction has been implicated as a one of the major factors linked to the development of painful diabetic neuropathy (DN). Several studies have demonstrated that sirtuin (SIRT1) activation recuperates nerve function by activating mitochondrial biogenesis. Polydatin, a resveratrol glycoside, has been explored to improve mitochondrial function via SIRT1 activation. However, the neuroprotective effects of polydatin in DN remain elusive. In this study, polydatin (25 and 50 mg/kg, oral) was administered for last 2 weeks of 8-week study to diabetic Sprague-Dawley rats weighing 250-300 g (post 6-weeks of streptozotocin 55 mg/kg, intraperitoneal). Treatment with polydatin significantly attenuated mechanical and thermal hyperalgesia in diabetic rats. Treated diabetic rats also showed improvement in motor/sensory nerve conduction velocities and nerve blood flow. For in vitro studies, Neuro2a cells were exposed to high-glucose (30 mM) condition to simulate short-term hyperglycemia. Polydatin was evaluated for its role in SIRT1 and Nrf2 activation at a dose of 5, 10, and 20 mu M concentrations. Polydatin exposure normalized the mitochondrial superoxides, membrane potentials and improved neurite outgrowth in high-glucose-exposed Neuro2a cells. Increased SIRT1 activation by polydatin resulted in peroxisome proliferator activated receptor-gamma coactivator-1 alpha (PGC-1 alpha) directed mitochondrial biogenesis. SIRT1 activation also facilitated Nrf2-directed antioxidant signaling. Study results inferred that decline in mitochondrial biogenesis and oxidative function in diabetic rats and high-glucose-exposed Neuro2a cells, could be counteracted by polydatin administration, postulated via enhancing SIRT1 and Nrf2 axis.