Miller L R, Pascal R A, Schroepfer G J
J Biol Chem. 1981 Aug 10;256(15):8085-91.
14 alpha-Hydroxymethyl-5 alpha-cholest-7-ene-3 beta, 15 alpha-diol and 14 alpha-hydroxymethyl-5 alpha-cholest-6-ene-3 beta, 15 alpha-diol have been shown to be potent inhibitors of the synthesis of digitonin-precipitable sterols in mouse L-cells and in primary cultures of fetal mouse liver cells and to cause a reduction in the levels of activity of 3-hydroxy-3-methylglutaryl-CoA reductase in the same cells (Schroepfer, G. J., Jr., Parish, E. J., Pascal, R. A., Jr., and Kandutsch, A. A. (1980) J. Lipid Res. 21, 571-584). In the present study, we have found that both sterols have a second, but distinct, site of action, distal to the formation of mevalonic acid. 14 alpha-Hydroxymethyl-5 alpha-cholest-7-ene-3 beta, 15 alpha-diol has been found to be a potent inhibitor of the synthesis of digitonin-precipitable sterols from labeled mevalonate in cell-free preparations of rat liver. This inhibition was accompanied by a striking accumulation of labeled lanosterol and 24,25-dihydrolanosterol. The latter sterols were fully characterized by the results of chromatographic and co-crystallization experiments. In contrast, 14 alpha-hydroxymethyl-5 alpha-cholest-6-ene-3 beta, 15 alpha-diol had only a slight effect on the synthesis of digitonin-precipitable sterols from labeled mevalonate in cell-free rat liver preparations. The delta 6-3 beta, 15 alpha, 32-triol had no apparent effect on the metabolism of lanosterol and 24,25-dihydrolanosterol but caused a substantial accumulation of labeled 5 alpha-cholest-8-en-3 beta-ol which was fully characterized by the results of chromatographic and co-crystallization experiments. These findings are compatible with a specific inhibition of the metabolism of lanosterol and 24,25-dihydrolanosterol by the delta 7-3 beta, 15 alpha, 32-triol and a specific inhibition of the delta 8 leads to delta 7 isomerase by the delta 6-3 beta, 15 alpha, 32-triol. [2,4]3H]14 alpha-Hydroxymethyl-5 alpha-cholest-7-ene-3 beta, 15 alpha-diol, prepared by chemical synthesis, was not convertible to cholesterol upon incubation, under aerobic conditions, with a cell-free homogenate preparation of rat liver. The labeled delta 7-3 beta, 15 alpha, 32-triol was, however, metabolized to several polar compounds.
14α-羟甲基-5α-胆甾-7-烯-3β,15α-二醇和14α-羟甲基-5α-胆甾-6-烯-3β,15α-二醇已被证明是小鼠L细胞和胎鼠肝细胞原代培养物中洋地黄皂苷可沉淀甾醇合成的有效抑制剂，并能使相同细胞中3-羟基-3-甲基戊二酰辅酶A还原酶的活性水平降低（施罗普费尔，G.J.，小，帕里什，E.J.，帕斯卡，R.A.，小，和坎杜奇，A.A.（1980年）《脂质研究杂志》21，571 - 584）。在本研究中，我们发现这两种甾醇都有第二个但不同的作用位点，在甲羟戊酸形成的远端。已发现14α-羟甲基-5α-胆甾-7-烯-3β,15α-二醇是大鼠肝脏无细胞制剂中由标记甲羟戊酸合成洋地黄皂苷可沉淀甾醇的有效抑制剂。这种抑制伴随着标记羊毛甾醇和24,25-二氢羊毛甾醇的显著积累。通过色谱和共结晶实验结果对后一种甾醇进行了全面表征。相比之下，14α-羟甲基-5α-胆甾-6-烯-3β,15α-二醇对大鼠肝脏无细胞制剂中由标记甲羟戊酸合成洋地黄皂苷可沉淀甾醇只有轻微影响。δ6-3β,15α,32-三醇对羊毛甾醇和24,25-二氢羊毛甾醇的代谢没有明显影响，但导致标记的5α-胆甾-8-烯-3β-醇大量积累，通过色谱和共结晶实验结果对其进行了全面表征。这些发现与δ7-3β,15α,32-三醇对羊毛甾醇和24,25-二氢羊毛甾醇代谢的特异性抑制以及δ6-3β,15α,32-三醇对δ8向δ7异构酶的特异性抑制相一致。通过化学合成制备的[2,4]³H]14α-羟甲基-5α-胆甾-7-烯-3β,15α-二醇在有氧条件下与大鼠肝脏无细胞匀浆制剂一起孵育时不能转化为胆固醇。然而，标记的δ7-3β,15α,32-三醇被代谢为几种极性化合物。
