Sildenafil ameliorates long term peripheral neuropathy in type II diabetic mice.

Lei Wang,Yi Zhang,Michael Chopp,Alexandra Szalad,Longfei Jia,Xuerong Lu,Zheng Gang Zhang,Ruilan Zhang,Li Zhang,Mei Lu,Julie A Chowen

doi:10.1371/journal.pone.0118134

Abstract

Diabetic peripheral neuropathy is a common complication of long-standing diabetes mellitus. To mimic clinical trials in which patients with diabetes enrolled have advanced peripheral neuropathy, we investigated the effect of sildenafil, a specific inhibitor of phosphodiesterase type 5 enzyme, on long term peripheral neuropathy in middle aged male mice with type II diabetes. Treatment of diabetic mice (BKS.Cg-m+/+Leprdb/J, db/db) at age 36 weeks with sildenafil significantly increased functional blood vessels and regional blood flow in the sciatic nerve, concurrently with augmentation of intra-epidermal nerve fiber density in the skin and myelinated axons in the sciatic nerve. Functional analysis showed that the sildenafil treatment considerably improved motor and sensory conduction velocities in the sciatic nerve and peripheral thermal stimulus sensitivity compared with the saline treatment. In vitro studies showed that mouse dermal endothelial cells (MDE) cultured under high glucose levels exhibited significant down regulation of angiopoietin 1 (Ang1) expression and reduction of capillary-like tube formation, which were completely reversed by sildenafil. In addition, incubation of dorsal root ganglia (DRG) neurons with conditioned medium harvested from MDE under high glucose levels suppressed neurite outgrowth, where as conditional medium harvested from MDE treated with sildenafil under high glucose levels did not inhibit neurite outgrowth of DRG neurons. Moreover, blockage of the Ang1 receptor, Tie2, with a neutralized antibody against Tie2 abolished the beneficial effect of sildenafil on tube formation and neurite outgrowth. Collectively, our data indicate that sildenafil has a therapeutic effect on long term peripheral neuropathy of middle aged diabetic mice and that improvement of neurovascular dysfunction by sildenafil likely contributes to the amelioration of nerve function. The Ang1/Tie2 signaling pathway may play an important role in these restorative processes.

Highlights

Diabetic peripheral neuropathy is a common complication of diabetes
To examine the therapeutic effect of sildenafil on db/db mice with long-term peripheral neuropathy, sildenafil was administered at a dose of 10 mg/kg to male db/db mice at middle age of 36 weeks, and treated daily for 8 consecutive weeks, and the mice were sacrificed at age 44 weeks
We found that sildenafil treatment significantly improved diabetes—reduced motor and sensory conducting velocity (MCV and sensory nerve conduction velocity (SCV)) in the sciatic nerve measured by electrophysiological tests (Fig. 1A, B)

Summary

Introduction

Diabetic peripheral neuropathy is a common complication of diabetes. There is a compelling need to develop therapeutic approaches for diabetic peripheral neuropathy. Sildenafil Ameliorates Long Term Diabetic Neuropathy numerous reagents have been validated in experimental diabetic peripheral neuropathy, clinical trials show that the majority of them do not achieve clinical benefits for treatment of diabetic peripheral neuropathy [1,2]. We previously demonstrated that hyperglycemia upregulated PDE5 expression, and suppression of PDE5 by sildenafil increased cGMP levels and significantly ameliorated peripheral neuropathy in diabetic mice [9]. It is not known whether the therapeutic effect of sildenafil can be achieved in diabetic mice with long term peripheral neuropathy, because diabetic mice used in our previous study were relatively young, i.e.16 weeks old. To mimic the clinical situation, in the present study, we treated 36 week old diabetic mice with sildenafil

Methods

Results

Conclusion