Effects of Light on Skin Lipid Metabolism

The effects of light on in vitro skin lipid metabolism were examined. Fresh human skin specimens were irradiated with a Xenon lamp at a level equivalent to 10 x the minimal erythema dose. After irradiation the skin specimens were incubated 6 hours in the presence of 14 C-acetate. Total lipids were extracted and the levels of acetate incorporation determined. The total lipid free sterol, neutrol fat, and phospholipid fractions exhibited lower levels of incorporation in irradiated skin than did those from nonirradiated controls. Parallel studies on skin obtained from swine indicated that reduced levels of incorporation of acetate into the various classed of lipids were the results of altered synthesis and not due to reduced isotope uptake, increased lipid breakdown, or direct effects of light per se, on the lipid moieties. Further studies with human skin demonstrated that the light susceptible site of sterol synthesis lies along the biosynthetic pathway between acetate and meyalonate. The data suggest that light interferes with sterol synthesis prior to acetyl CoA and probably involves acetate activation or the availability of substantia, acetyl CoA pools.