Zhang J, Akwa Y, el-Etr M, Baulieu E E, Sjövall J
Department of Medical Biochemistry and Biophysics, Karolinska Institute, Stockholm, Sweden.
Biochem J. 1997 Feb 15;322 ( Pt 1)(Pt 1):175-84. doi: 10.1042/bj3220175.
The metabolism of 27-, 25- and 24-hydroxycholesterol in cultures of rat astrocytes, Schwann cells and neurons was studied. 27- and 25-Hydroxycholesterol, but not 24-hydroxycholesterol, underwent 7 alpha-hydroxylation with subsequent oxidation to 7 alpha-hydroxy-3-oxo-delta 4 steroids in all three cell types. When cells were incubated for 24 h with 0.28 nmol of 27-hydroxycholesterol in 10 ml of medium, the rates of conversion into 7 alpha-hydroxylated metabolites were 0.21, 0.12 and 0.02 nmol/24 h per 10(6) cells in the media of astrocytes, Schwann cells and neurons respectively. The corresponding values for 25-hydroxycholesterol were 0.26, 0.16 and 0.04. A minor fraction of 27-hydroxycholesterol and its 7 alpha-hydroxylated metabolites was oxidized to 3 beta-hydroxy-5-cholestenoic acid. 3 beta, 7 alpha-dihydroxy-5-cholestenoic acid and 7 alpha-hydroxy-3-oxo-4-cholestenoic acid. In addition to the two hydroxycholesterols, other 3 beta-hydroxy-delta 4 steroids, dehydro-epiandrosterone, pregnenolone, 3 beta-hydroxy-5-cholestenoic acid and 3 beta-hydroxy-5-cholenoic acid underwent 7 alpha-hydroxylation. Competitive experiments did not distinguish between the presence of one or several 7 alpha-hydroxylases. In astrocyte incubations, 27-hydroxycholesterol also underwent 25-hydroxylation, and 12% of its metabolites carried a 25-hydroxy group. 25-Hydroxylation of added 24-hydroxycholesterol was also observed in the astrocyte incubations, as was the formation of 7 alpha, 25-dihydroxy-4-cholesten-3-one, 25-hydroxycholesterol and 7 alpha, 25-dihydroxycholesterol from endogenous precursor(s). Our study indicates that side-chain oxygenated cholesterol can undergo metabolic transformations that may be of importance for cholesterol homoeostasis in the brain.
研究了大鼠星形胶质细胞、雪旺氏细胞和神经元培养物中27-、25-和24-羟基胆固醇的代谢情况。27-和25-羟基胆固醇，而非24-羟基胆固醇，在所有三种细胞类型中都经历了7α-羟基化，随后氧化为7α-羟基-3-氧代-δ4类固醇。当细胞在含有0.28 nmol 27-羟基胆固醇的10 ml培养基中孵育24小时时，在星形胶质细胞、雪旺氏细胞和神经元培养基中，每10(6)个细胞转化为7α-羟基化代谢物的速率分别为0.21、0.12和0.02 nmol/24小时。25-羟基胆固醇的相应值分别为0.26、0.16和0.04。一小部分27-羟基胆固醇及其7α-羟基化代谢物被氧化为3β-羟基-5-胆甾烯酸、3β,7α-二羟基-5-胆甾烯酸和7α-羟基-3-氧代-4-胆甾烯酸。除了这两种羟基胆固醇外，其他3β-羟基-δ4类固醇、脱氢表雄酮、孕烯醇酮、3β-羟基-5-胆甾烯酸和3β-羟基-5-胆烯酸也经历了7α-羟基化。竞争性实验无法区分是存在一种还是几种7α-羟化酶。在星形胶质细胞孵育中，27-羟基胆固醇还经历了25-羟基化，其代谢物中有12%带有25-羟基。在星形胶质细胞孵育中也观察到添加的24-羟基胆固醇的25-羟基化，以及由内源性前体形成7α,25-二羟基-4-胆甾烯-3-酮、25-羟基胆固醇和7α,25-二羟基胆固醇。我们的研究表明，侧链氧化的胆固醇可以进行代谢转化，这可能对大脑中的胆固醇稳态很重要。
