Lipofuscin Can Be Eliminated From Retinal Pigment Epithelium After Drug Treatment

Abstract

Purpose: : Lipofuscin is a pigment that is formed in tissues with high oxidative stress. It is generally believed that the gradual accumulation of this pigment is the constant sign of ageing and that the retinal pigment epithelial (RPE) cells could not eliminate their lipofuscin during life. In a pre-clinical study involving 66 monkeys and focused on a new treatment for acid-related diseases, we discovered that the oral administration of tetrahydropyridoethers (THPE) leads to a significant removal of lipofuscin from RPE cells. The aim of this study was to confirm this observation in cultures of human aged RPE cells.

Methods: : The human RPE cells were obtained from seven organ donors aged between 36 and 75 years. The cells were incubated with different concentrations of a THPE compound or vehicle. Changes in pigmentation were regularly observed by light, fluorescence and electron microscopy till 36 days. Cell viability and phagocytic activity were tested as well.

Results: : We previously showed that after exposure to THPE, RPE cells of monkeys lose lipofuscin. These in vivo experiments indicated that lipofuscin granules, melanosomes as well as melanolipofuscin granules were released to macrophages. These were frequently present and were located between the Bruch’s membrane and the RPE or in the subretinal space.The cultured RPE cells showed 100% survival at THPE concentrations up to 0.25 mM, whereas most of the cells died within days at 0.5 mM. Instead of the grainy yellow-golden lipofuscin autofluoerescence, a diffuse white-bluish glow appeared in the RPE cells indicating degradation of lipofuscin under the influence of the THPE compound. Pigment granules containing lipofuscin disappeared completely in an increasing portion of the cultured cells.The RPE cells regained their ability to phagocytose after THPE-induced removal of lipofuscin. Depending on the degree of lipofuscin loss, phagocytic activity increased by 10 to 20 times compared to controls.

Conclusions: : The present study demonstrates that the dogma that lipofuscin can not be removed from RPE cells has not be perpetuated any more. Our finding that removal of lipofuscin is possible has great implication for the treatment of lipofuscin-related diseases, in particular the dry age-related macular degeneration.

Keywords: ipofuscin • age-related macular degeneration • retinal pigment epithelium