Changes in lipid peroxide level in retinal pigment epithelial cells in vitro upon addition of linoleic acids or linoleic acid hydroperoxides under varying concentrations of oxygen

We previously observed the presence of autofluorescent lipofuscin or its like in retinal pigment epithelial (RPE) cells, which were incubated with linoleic acid hydroperoxides (LHP). We studied the effect of oxygen on the level of lipid peroxides in RPE cells in the presence of linoleic acids (LA) or LHP The level of lipid peroxides in these cells was determined by use of the thiobarbituric acid-reactive substance (TEARS), which responded to oxygen concentrations qualitatively, and a linear regression analysis. Multiple linear regression analysis disclosed that treatment with LA for 24 hr resulted in detectable increase in the level of TEARS in the cells, whereas treatment with LA or LHP for 48 hr caused detectable decrease. Stepwise linear regression analysis showed that the level of TEARS decreased in an oxygen-tension dependent manner in the cells incubated with LA for 48 hr. Thus, it was shown that short-term incubation with LA increased the level of TEARS in the cells and that LA decreased its level in an oxygen-tension dependent manner. For these results, the postulation was made that the prolonged auto-oxidation of LA caused production of lipofuscin-like materials, a complex of lipid peroxides and proteins that were insoluble in SDS and acetic acid solution.