Incorporation of phytosterols in human keratinocytes: Consequences on UVA-induced lipid peroxidation and calcium ionophore-induced prostaglandin release

We have designed experimental conditions allowing the replacement of 50% of cholesterol of human keratinocytes (SVK14 line) with sitosterol or stigmasterol without affecting cellular viability. We have investigated the influence of incorporating phytosterol on the ultraviolet-A-induced formation of lipid-peroxidation products (thiobarbituric reactive substances (TBARS)) in these cells. Our results show that ultraviolet-A-induced lipid peroxidation depends on the nature of the phytosterol. Sitosterol induces a significant decrease (−30%) of TBARS relative to the control whereas stigmasterol markedly increases lipid peroxidation (+70%). We have also studied the effect of plant sterols on prostaglandin release by using the Ca2+ ionophore A23187 as an in vitro model of the inflammation induced by UVA radiation. We show that in the presence of 50% of phytosterol (particularly stigmasterol), the release of prostaglandin (6-ketoPG1α, PGE2) is increased compared to untreated cells. This pro-inflammatory effect of phytosterols is correlated with a loss of the regulation of the intracellular Ca2+ concentration.