Lipofuscin granules and melanosomes from human retinal pigment epithelium have opposite roles in photooxidation of cardiolipin

The influence of lipofuscin granules and melanosomes from human retinal pig ment epithelium on the light-induced photooxidation of cardiolipin liposome s and the generation of superoxide radicals was studied. Lipofuscin granule s were able to stimulate, while melanosomes inhibited, the cardiolipin phot ooxidation. The visible light irradiation of both melanosomes and lipofusci n granules generated superoxide radicals with mean rates of 1.5 nmole/min/1 0(7) and 38 nmole/min/10(7) granules, accordingly. However, melanosomes but not lipofuscin granules reacted readily with superoxide radicals. Moreover , the rate constant of degradation of superoxide radicals in the presence o f melanosomes was about five orders of magnitude higher than the rate const ant of its photogeneration. Therefore, we propose that melanosomes in retin al pigment epithelium cells have a photoprotective role whereas lipofuscin granules may stimulate photodestructive reactions.