Inhibitory Action of Antidiabetic Drugs on the Free Radical Production by the Rod Outer Segment Ectopic Aerobic Metabolism.

Silvia Ravera,Davide Maggi,Federico Caicci,Alessandra Puddu,Paolo Degan,Carlo E Traverso,Isabella Panfoli,Massimo Nicolò,Lucia Manni

doi:10.3390/antiox9111133

Abstract

Rod outer segments (OS) express the FoF1-ATP synthase and the respiratory chain, conducting an ectopic aerobic metabolism that produces free radicals in vitro. Diabetic retinopathy, a leading cause of vision loss, is associated with oxidative stress in the outer retina. Since metformin and glibenclamide, two anti-type 2 diabetes drugs, target the respiratory complexes, we studied the effect of these two drugs, individually or in association, on the free radical production in purified bovine rod OS. ATP synthesis, oxygen consumption, and oxidative stress production were assayed by luminometry, oximetry and flow cytometry, respectively. The expression of FoF1-ATP synthase was studied by immunogold electron microscopy. Metformin had a hormetic effect on the OS complex I and ATP synthetic activities, being stimulatory at concentrations below 1 mM, and inhibitory above. Glibenclamide inhibited complexes I and III, as well as ATP production in a concentration-dependent manner. Maximal concentrations of both drugs inhibited the ROI production by the light-exposed OS. Data, consistent with the delaying effect of these drugs on the onset of diabetic retinopathy, suggest that a combination of the two drugs at the beginning of the treatment might reduce the oxidative stress production helping the endogenous antioxidant defences in avoiding retinal damage.

Highlights

Genetic and environmental factors are involved in the pathogenesis of Type 2 diabetes mellitus (T2D), which is characterized by high blood glucose levels and insulin resistance in target organs [1]
Two anti-type 2 diabetes drugs, target the respiratory complexes, we studied the effect of these two drugs, individually or in association, on the free radical production in purified bovine rod outer segments (OS)
The oxidative stress in the outer retina may not solely depend on the mitochondrial oxidative phosphorylation (OxPhos), and on an extramitochondrial aerobic metabolism [14] functionally expressed in the OS [15,18], as confirmed by the transmission electron microscopy (TEM) immunogold analysis reported in Figure 1, showing the ectopic expression of ATP synthase in the OS

Summary

Introduction

Genetic and environmental factors are involved in the pathogenesis of Type 2 diabetes mellitus (T2D), which is characterized by high blood glucose levels and insulin resistance in target organs [1]. In T2D, hyperglycemia and unbalanced oxidative stress determine both macro- and micro-vascular damage, bearing multifactorial pathogenesis. The most common ocular T2D complication is diabetic retinopathy (DR) [3,4], characterized by changes in the retinal microcirculation and neuronal damage. It has been observed that retinal neurons are damaged in the early stages of DR [5]. Neurodegeneration is an early manifestation of DR associated with oxidative stress [6]. It was demonstrated that oxidative stress in early DR is restricted to photoreceptors [7]. Oxidative stress plays a central role in other retinal degenerations, including age-related macular degeneration (AMD) [8], generally characterized by a photoreceptor and retinal pigmented epithelium (RPE) oxidative damage

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