NMN supplementation prevents vascular senescence in experimental diabetic retinopathy

Abstract

Purpose : Microvascular dysfunction contributes to diabetic retinopathy (DR). Our previous studies have shown that hyperglycemia promotes retinal vascular stress-induced premature senescence (SIPS). This effect is associated with loss of nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme in the nicotinamide adenine dinucleotide (NAD+) salvage pathway, converting nicotinamide to nicotinamide mononucleotide (NMN) and enabling NAD+ biosynthesis. Here we have investigated whether exogenous supplementation of NMN could override the effects of hyperglycemia in lowering NAD+ levels and could prevent retinal vascular senescence in a rat model of type I diabetes.

Methods : Rats were made diabetic by intravenous injection of streptozotocin (60mg/Kg). Two weeks after the onset of hyperglycemia (250mg/dl or more) half of the diabetic rats was fed with NMN (100mg/Kg, daily). Six weeks after the starting of the treatment, rats were sacrificed and processed for different molecular and morphological analyses. Hematoxylin/eosin staining was used for histopathological evaluation and morphometric analysis of retinal sections. Immunohistochemistry was used to assess reactive oxygen species formation (DHE). Western blotting was used to measure NAMPT levels and of senescence and oxidative stress markers and to assess albumin vascular extravasation. NAD+ was measured with a colorimentric assay.

Results : In diabetic rats we found signficant decreased levels of NAMPT and NAD+. Treatments with NMN prevented NAD+ loss without rescuing NAMPT expression. Furthermore, NMN significantly decreased diabetes-induced up-regulation of reactive oxygen species and levels of the oxidative stress markers 4-HNE and nitrotyrosine. Furthermore, we found that NMN supplementation in diabetic rats halted the expression of senescence markers evoking the occurrence of SIPS. These normalizing effects of NMN on the retinal vasculature, were further confirmed by the results of this treatment in preventing diabetes –induced albumin extravasation, as sign of vascular hyperpermeability, in diabetic rats.

Conclusions : Our studies suggest that alterations of the NAMPT-NAD+ axis affects the retinal vasculature in diabetes and support the use of NMN supplementation in preserving retinal vascular function in DR.

This is a 2020 ARVO Annual Meeting abstract.