Vasopeptidase inhibitor ilepatril (AVE7688) prevents obesity- and diabetes-induced neuropathy in C57Bl/6J mice

Abstract

Previously we demonstrated that inhibition of neutral endopeptidase (NEP), a protease that degrades vaso- and neuro-active peptides, and angiotensin converting enzyme (ACE) with a vasopeptidase inhibitor improves vascular and neural function in diabetic rat models. The purpose of this study was to determine whether inhibition of NEP and ACE or deletion of NEP provides protection from nerve impairment caused by diabetes or diet induced obesity (DIO). To determine the role of NEP and ACE inhibition in neuropathy related to insulin-deficient diabetes or DIO we used C57Bl/6J mice treated with AVE7688, a vasopeptidase inhibitor, or NEP deficient (-/-) mice. Mice at 12 weeks of age were fed a high fat diet for 12 weeks or were diabetic for duration of 12 weeks following a single injection of high dose streptozotocin. Both a prevention and intervention protocol was used for AVE7688 treatment. Glucose utilization was impaired in DIO C57Bl/6J and NEP -/- mice. However, treating DIO C57Bl/6J or NEP -/- mice with AVE7688 improved glucose tolerance. Thermal hypoalgesia and nerve conduction slowing were present in both streptozotocin-diabetic and DIO C57Bl/6J mice but not in AVE7688 treated C57Bl/6J mice or NEP -/- mice exposed to either streptozotocin-induced diabetes or a high fat diet. Intraepidermal nerve fiber (IENF) profiles were decreased in the hindpaw of C57Bl/6J diabetic or DIO mice and this improved when the mice were treated with AVE7688. IENF profiles were not decreased in diabetic or DIO NEP (-/-) mice. These studies suggest that NEP plays a role in regulating nerve function in insulin-deficient diabetes and DIO.

Figure 1

Glucose utilization curve for C57Bl/6J (A) and neutral endopeptidase (NEP −/−) deficient (B) mice fed a normal or high fat containing diet for 12 weeks. Data are the mean ± standard error of the mean in mg/dl. The area under the curve (AUC) was significantly different p < 0.01 for high fat fed mice vs. control for both C57Bl/6J and NEP −/− mice. There was no significant difference for AUC between mice fed a high fat diet containing AVE7688 and control or high fat fed mice. The number of mice in each group was the same as shown in Table 1.

Figure 2

Motor and sensory nerve conduction velocity for C57Bl/6J mice. Study groups included mice fed a normal diet with or without AVE7688 for 12 weeks (Control), streptozotocin-induced diabetes duration 12 weeks treated with or without AVE7688, or fed a high fat containing diet with or without AVE7688 for 12 weeks. Data are the mean ± standard error of the mean. The numbers of mice in each group was the same as shown in Table 1. *, p < 0.05 versus control; +, p < 0.05 versus untreated mice for respective group

Figure 3

Motor and sensory nerve conduction velocity for neutral endopeptidase deficient (NEP −/−) mice. Study groups included mice fed a normal diet with or without AVE7688 for 12 weeks (Control), streptozotocin-induced diabetes duration 12 weeks, or fed a high fat containing diet with or without AVE7688 for 12 weeks. Data are the mean ± standard error of the mean. The numbers of mice in each group was the same as shown in Table 1.

Figure 4

Thermal response latency in the hindpaw for C57Bl/6J (A) and neutral endopeptidase (NEP −/−) deficient (B) mice. Study groups were the same as described in Figures 2 and 3 for C57Bl/6J and NEP −/− mice, respectively. Data are the mean ± standard error of the mean. The numbers of animals for each group are the same as described in Table 1. *, p < 0.05 versus control; +, p < 0.05 versus untreated mice for respective group

Figure 5

Intraepidermal nerve fiber profiles in the hindpaw of C57Bl/6J (B) and neutral endopeptidase (NEP −/−) deficient (C) mice. Illustration (A) is a representation of intraepidermal nerve fiber profiles in the hindpaw of a C57Bl/6J mouse. The scale bar represents 50 μm and the arrows identify individual nerve fibers. Study groups were the same as described in Figures 2 and 3 for C57Bl/6J and NEP −/− mice, respectively. Data are presented as the mean ± SEM intraepidermal nerve fiber profiles per mm. The number of mice in each group was the same as shown in Table 1. *, p < 0.05 versus control; +, p < 0.05 versus untreated mice for respective group