Sterol 27-hydroxylase acts on 7-ketocholesterol in human atherosclerotic lesions and macrophages in culture

27-Hydroxycholesterol (27OH) is the major oxysterol in human atheroscleroti c lesions, followed by 7-ketocholesterol (7K), Whereas 7K probably originat es nonenzymically, 27OH arises by the action of sterol 27-hydroxylase, a cy tochrome P450 enzyme expressed at particularly high levels in the macrophag e and proposed to represent an important pathway by which macrophages elimi nate excess cholesterol, We hypothesized and here show that 27-hydroxylated 7-ketocholesterol (27OH-7K) is present in human lesions, probably generate d by the action of sterol 27-hydroxylase on 7K. Moreover, [SH]27OH-7K was p roduced by human monocyte-derived macrophages (HMDMs) supplied with [H-3]7K but not in HMDMs from a patient with cerebrotendinous xanthomatosis (CTX) shown to have a splice-junction mutation of sterol 27-hydroxylase. Whereas [H-3]27OH-7K was predominantly secreted into the medium, [H-3]-27OH formed from [H-3] cholesterol was mostly cell-associated. The majority of supplied [H-3]7K was metabolized beyond 27OH-7K to aqueous-soluble products (appare ntly bile acids derived from the sterol 27-hydroxylase pathway). Metabolism to aqueous-soluble products was ablated by a sterol 27-hydroxylase inhibit or and absent in CTX cells. Sterol 27-hydroxylase therefore appears to repr esent an important pathway by which macrophages eliminate not only choleste rol but also oxysterols such as 7K, The fact that 7K (and cholesterol) stil l accumulates in lesions and foam cells indicates that this pathway may be perturbed in atherosclerosis and affords a new opportunity for the developm ent of therapeutic strategies to regress atherosclerotic lesions.