Abstract
Purpose :
The early stages of Age-related Macular Degeneration (AMD) are characterized, among other things, by the accumulation of lipofuscin in the retinal pigment epithelium cells and by the death of these cells. The main component of lipofuscin, A2E, efficiently absorbs high-energy visible light (HEV, 400-500 nm). Two modes of action are currently suggested in the literature to explain cell dysfunctions in the retina following exposure to HEV. One of them is that A2E could act as a detergent and disrupt the integrity of the membranes because of its amphiphilic properties. Our goal was to assess the photo-toxicity of HEV light on the cytoplasmic membranes that interact with A2E.
Methods :
A2E was synthesized and its stability in different solvents and under several light conditions was assessed by UV-visible spectroscopy and high pressure liquid chromatography (HPLC). Langmuir monolayers was used as a membrane model to evaluate the disorder due to A2E and its photo-irradiated product in the presence of different lipids found in physiological membranes. A surface tensiometer allowed to gather information on the perturbation of A2E and photo-irradiated A2E through the determination of two binding parameters.
Results :
Highly pure A2E was stable for more than one day in black condition, allowing to carry out binding measurements with the membrane model. Higher values of the two binding parameters were observed with lipids composed of phosphocholine head group, compared to other head groups. Even higher binding parameters were observed in the presence of lysobisphosphatidic acid (LBPA) which is specifically found in lysosome. Regarding the acidic environment of lysosomes, our study of the influence of the pH revealed that pH 5 was more favorable to A2E binding than pH 7. Finally, the photo-irradiation of A2E led to atypical trends where the membrane binding was independent of lipid concentrations, suggesting a different membrane behavior of A2E in the presence of HEV.
Conclusions :
These data highlighted the binding preference of A2E for specific lipids, as LBPA, under certain specific conditions, as acidic pH, and the behavioral difference of A2E and its photo-irradiated product. This project provides a better understanding of the influence of light to the eye and its eventual involvement in AMD, disease for which no treatment is currently available for the dry form, responsible for 80% of cases.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.