Cholesterol 7-hydroperoxides in rat skin as a marker for lipid peroxidation.

Concentrations of cholesterol 7alpha- and 7beta-hydroperoxides (Ch 7-OOHs) in the skin of rats were determined by HPLC with a chemiluminescence detector. We demonstrated that (a) the concentrations of Ch 7-OOHs in rat skin were highly correlated with rat age (r = 0.929; N = 51, 1 to 55 weeks old), (b) the concentrations of Ch 7-OOHs in the skin of rats in an ambient light room were not significantly different from those found in rats kept in a dark room for 12 weeks, and (c) lipid peroxidation in vitro induced by ADP-Fe2+ caused an increase in the concentrations of Ch 7-OOHs in homogenates of rat skin. These results indicated that levels of Ch 7-OOHs in skin might be a good marker for aging of rats and might be independent of housing illumination, thus a good marker for endogenous lipid peroxidation. Furthermore, we observed that ultraviolet light B (UVB) irradiation markedly enhanced the concentrations of Ch 7-OOHs in the skin of rats in vivo depending on the duration of the irradiation, and the increases in Ch 7-OOHs were inhibited by radical scavengers, i.e. tocopherols. Therefore, it was suggested that the levels of Ch 7-OOHs in the skin could also be a good marker for UVB-dependent lipid peroxidation.