24(S),25-epoxycholesterol--a potential friend.

According to current concepts, oxysterols are the physiological mediators of a number of cholesterolinduced metabolic effects (for a review, see Bjorkhem et al1). Most of the evidence for this is however still indirect, and there is a discrepancy between the great number of studies demonstrating potent effects of oxysterols under in vitro conditions and the few studies consistent with a regulatory effect in vivo. Oxysterol binding proteins and receptors are doubtless of regulatory importance in cholesterol turnover, but the physiological ligand(s) to the proteins have not yet been defined with certainty. In this issue of Arteriosclerosis, Thrombosis, and Vascular Biology, the article by Wong et al2 gives strong support for the contention that the oxysterol 24(S),25-epoxycholesterol, an efficient activator of the nuclear receptor LXR in vitro, is an important mediator of statin-induced effects on cholesterol homeostasis in THP-1 macrophages.