Effect of apple peel extract on diabetes-induced peripheral neuropathy and wound injury

Diabetic peripheral neuropathy (DPN) affects up to 50 % diabetic patients. Moreover, uncontrolled diabetes associated with impaired wound healing. The present study was aimed at exploring the effect of apple peel extract (APE) on type 2 diabetes (T2D)-induced DPN and delayed wound healing.

In adult male Sprague-Dawley rats on high-fat diet, a single low dose streptozotocin (STZ, 35 mg/kg) was administered via intraperitoneal route to induce T2D. Plantar test using Hargreaves apparatus was used to evaluate the DPN. Six different groups of rats were treated orally with saline (naïve control and DPN control), APE (100, 200 and 400 mg/kg) and gabapentin (30 mg/kg) daily for 7 consecutive days and thermal paw withdrawal latency (PWL) was measured. To elucidate the underlying antioxidant effect of APE, the catalase (CAT), glutathione (GSH) and malonaldehyde (MDA) levels were measured. To evaluate the wound healing potential of APE, excision ischemic open wound model was used. Six different groups of rats were applied with 2 % gum acacia (naïve control and diabetic control), 1 % silver sulfadiazine (SSD) cream and APE cream (5, 10 and 20 %) twice daily for 28 days. Dry connective tissue parameters like hydroxyproline and hexosamine were also measured to further confirm the wound healing activity.

Diabetes produced thermal hyperalgesia in rats with a significant decrease in PWL as compared to naive controls indicating induction of DPN. APE and gabapentin significantly improved PWL in diabetic animals. Biochemical analysis revealed a significant improvement in oxidative stress parameters such as catalase, GSH and MDA. Wound closure was significantly more after day 15 of topical application of APE and SSD as compared to control group. APE significantly increased hydroxyproline and hexosamine levels as compared to standard cream. Moreover, histopathology revealed that, topical application of APE cream showed an enhanced healing process.

On the basis of the findings, we conclude that APE has a potential to be used as a therapeutic intervention for the management of DPN and delayed wound healing in the diabetic condition.