Effect of epigallocatechin gallat on sciatic nerve in diabetic neuropathic pain model: The role of TRPV1 channel

Diabetic neuropathic pain (DNP) is a significant complication of diabetes. Epigallocatechin Gallate (EGCG) has been reported to have antioxidant, anti-inflammatory, anti-carcinogenic, neurodegeneration preventive and diabetes risk reduction properties. In our literature research, no study was found on the effect of EGCG on the role of the TRPV1 channel in the process of sciatic nerve damage in the streptozotocin (STZ)-induced DNP model. To investigate whether EGCG has therapeutic properties in the DNP model, rats were divided into four groups (n=7): Control, EGCG, DNP, and DNP+EGCG. On the first day of the study (day 0), STZ (45 mg/kg intraperitoneal) was administered to DNP and DNP+EGCG groups. Blood glucose levels of all groups were measured on the 3rd day of the study. Diabetes was proven to have occurred in rats in DNP and DNP+EGCG groups. Afterwards, EGCG was administered intragastrically at 20/mg/kg/day for 14 days in the EGCG, DNP+EGCG groups. During the study (days 0, 3, 8, 14, 17), mean weight change, blood glucose levels, hot plate and tail dipping tests were performed. At the end of the study, sciatic nerve samples were analysed by stereological, histopathological and immunohistochemistry (IHC) methods. The data obtained showed that the hot plate and tail immersion test times were significantly shorter in the DNP group compared to the control and EGCG groups. It was determined that the DNP+EGCG hot plate and tail immersion test times were longer than the control group. As a result of the analysis using Hematoxylin-Eosin and Toluidine Blue stains, sciatic nerves in the control and EGCG groups were observed in normal histological structure, while axonal degeneration was detected in the DNP group. DNP+EGCG was found to have less degeneration in axons compared to DNP. When IHC findings were evaluated, intense TRPV1 and INOS expression was observed in the DNP group, while low TRPV1 and INOS expression was observed in the Control, EGCG, and DNP+EGCG groups. As a result of stereological analysis, no statistically significant difference was found between the groups. The results of the study showed that EGCG treatment may modulate pain tolerance, stabilize blood glucose levels, alleviate the deterioration in the sciatic nerve, and decrease the increased TRPV1 and INOS expressions by inhibiting the mechanisms causing damage in streptozotocin-induced DNP model. This suggested that EGCG may be a potential therapeutic agent against DNP.