STEROL 27-HYDROXYLASE - HIGH-LEVELS OF ACTIVITY IN VASCULAR ENDOTHELIUM

Sterol 27-hydroxylase activity in bovine aortic endothelial (BAE) cell s in culture has been compared with that in HepG2 cells and in Chinese hamster ovary (CHO) cells using identical culture conditions. The tot al enzyme activity of BAE cells (3.0 nmol/72 h per mg cell protein) wa s comparable with that of HepG2 cells (4.0 nmol/72 h per mg protein) a nd both values were significantly greater than that in CHO cells (0.00 2 nmol/72 h per mg protein). The enzyme was identified in the mitochon dria extracted from BAE cells by Western blotting using an antibody of proven specificity, and its metabolites 27-hydroxycholesterol and 3 b eta-hydroxy-5-cholestenoic acid were identified by mass spectrum analy sis. The presence of the enzyme in endothelium provides a mechanism fo r preventing accumulation of intracellular cholesterol by initiating a pathway of bile acid synthesis different from that initiated by 7 alp ha-hydroxylation of cholesterol in the liver.