Effects of polyphenolic phytochemicals on ectopic oxidative phosphorylation in rod outer segments

BACKGROUND AND PURPOSE The rod outer segments (OS) of the retina are specialized organelles where phototransduction takes place. The mitochondrial electron transport complexes I–IV, cytochrome c and FoF1-ATP synthase are functionally expressed in the OS disks. Here, we have studied the effect of some polyphenolic compounds acting as inhibitors of mitochondrial ATPase/synthase activity on the OS ectopic FoF1- ATP synthase. The mechanism of apoptosis in the OS was also investigated studying the expression of cytochrome c, caspase 9 and 3 and Apaf-1. EXPERIMENTAL APPROACH We prepared OS from fresh bovine retinae. Semi-quantitative Western blotting, confocal and electron microscopy, and cytofluorimetry were used along with biochemical analyses such as oximetry, ATP synthesis and hydrolysis. KEY RESULTS Resveratrol and curcumin plus piperine inhibited ATP synthesis and oxygen consumption in the OS. Epigallocatechin gallate and quercetin inhibited ATP hydrolysis and oxygen consumption in the OS. Malondialdehyde and hydrogen peroxide were produced in respiring OS in the presence of substrates. Cytochrome c was located inside the disk membranes. Procaspase 9 and 3, as well as Apaf-1 were expressed in the OS. CONCLUSIONS AND IMPLICATIONS These polyphenolic phytochemicals modulated the FoF1-ATP synthase activity of the the OS reducing production of reactive oxygen intermediates by the OS ectopic electron transport chain. Polyphenols decrease membrane peroxidation and cytochrome c release from disks, preventing the induction of caspase-dependent apoptosis in the OS Such effects are relevant in the design of protection against functional impairment of the OS following oxidative stress from exposure to intense illumination.