Brown A J, Watts G F, Burnett J R, Dean R T, Jessup W
Cell Biology Group, Heart Research Institute, Sydney 2050, Australia.
J Biol Chem. 2000 Sep 8;275(36):27627-33. doi: 10.1074/jbc.M004060200.
27-Hydroxycholesterol (27OH) is the major oxysterol in human atherosclerotic lesions, followed by 7-ketocholesterol (7K). Whereas 7K probably originates nonenzymically, 27OH arises by the action of sterol 27-hydroxylase, a cytochrome P450 enzyme expressed at particularly high levels in the macrophage and proposed to represent an important pathway by which macrophages eliminate excess cholesterol. We hypothesized and here show that 27-hydroxylated 7-ketocholesterol (270H-7K) is present in human lesions, probably generated by the action of sterol 27-hydroxylase on 7K. Moreover, [(3)H]27OH-7K was produced by human monocyte-derived macrophages (HMDMs) supplied with [(3)H]7K but not in HMDMs from a patient with cerebrotendinous xanthomatosis (CTX) shown to have a splice-junction mutation of sterol 27-hydroxylase. Whereas [(3)H]27OH-7K was predominantly secreted into the medium, [(3)H]-27OH formed from [(3)H]-cholesterol was mostly cell-associated. The majority of supplied [(3)H]7K was metabolized beyond 27OH-7K to aqueous-soluble products (apparently bile acids derived from the sterol 27-hydroxylase pathway). Metabolism to aqueous-soluble products was ablated by a sterol 27-hydroxylase inhibitor and absent in CTX cells. Sterol 27-hydroxylase therefore appears to represent an important pathway by which macrophages eliminate not only cholesterol but also oxysterols such as 7K. The fact that 7K (and cholesterol) still accumulates in lesions and foam cells indicates that this pathway may be perturbed in atherosclerosis and affords a new opportunity for the development of therapeutic strategies to regress atherosclerotic lesions.
27-羟基胆固醇（27OH）是人类动脉粥样硬化病变中的主要氧化甾醇，其次是7-酮胆固醇（7K）。7K可能非酶促产生，而27OH则由甾醇27-羟化酶作用产生，该酶是一种细胞色素P450酶，在巨噬细胞中表达水平特别高，被认为是巨噬细胞清除过量胆固醇的重要途径。我们提出假设并在此表明，27-羟基化的7-酮胆固醇（27OH-7K）存在于人类病变中，可能是由甾醇27-羟化酶对7K的作用产生的。此外，给予[³H]7K的人单核细胞衍生巨噬细胞（HMDM）产生了[³H]27OH-7K，但来自脑腱性黄瘤病（CTX）患者的HMDM未产生，该患者显示甾醇27-羟化酶存在剪接连接突变。[³H]27OH-7K主要分泌到培养基中，而由[³H]胆固醇形成的[³H]-27OH大多与细胞相关。大部分给予的[³H]7K代谢超过27OH-7K生成水溶性产物（显然是来自甾醇27-羟化酶途径的胆汁酸）。用甾醇27-羟化酶抑制剂可消除向水溶性产物的代谢，且CTX细胞中不存在这种代谢。因此，甾醇27-羟化酶似乎代表了巨噬细胞不仅清除胆固醇而且清除诸如7K等氧化甾醇的重要途径。7K（和胆固醇）仍在病变和泡沫细胞中积累这一事实表明，该途径在动脉粥样硬化中可能受到干扰，并为开发使动脉粥样硬化病变消退的治疗策略提供了新机会。
