Modulation of the rod outer segment aerobic metabolism diminishes the production of radicals due to light absorption

Abstract

PurposeOxidative stress is a primary risk factor for inflammatory and degenerative retinopathies. Irradiation with blue light of eye explants was shown to cause an oxidative stress, higher in the rod outer segment (OS) than in the inner limb, ultimately impairing the extra‐mitochondrial aerobic metabolism of the OS. Here, to establish a correlation between the energy metabolism and phototransduction, the aerobic metabolism of purified bovine rod OS was assayed in function of exposure to either ambient or dim light.MethodsIsolated bovine rod OS, purified by Fycoll/sucrose gradient were utilized. Production of Reactive Oxygen Intermediates (ROI) was evaluated by citofluorimetry, with dihydrorhodamine 123 (DHR) probe; ATP synthesis and oxygen consumption were assayed by luminometry or oximetry, respectively. When necessary, isolated OS were preincubated with 30 μM Resveratrol, for 15 min, or 5 mM Metformin, for 2 h.ResultsUpon exposure to ambient light for 1 h, a significant increase in oxygen consumption as well as ATP synthetic ability by rod OS was observed, along with a consistent ROI production, with respect to dim light, i.e. the physiological rod conditions. Pretreatment with resveratrol, inhibitor of F1Fo‐ATP synthase, or metformin, inhibitor of the respiratory complex I, significantly diminished the ROI production in vitro.ConclusionsData show for the first time the relationship between light and the rod OS metabolism. A production of ROI by the OS in vitro was also observed, positively correlating to light exposure. A beneficial effect of metformin and resveratrol was found, as modulators of ROI production, consistently with their inhibitory action on the complexes I and V of respiration, respectively. Data shed new light on the prevention of the cone loss secondary to rod damage due to oxidative stress.