Hidaka Y, Hotta H, Nagata Y, Iwasawa Y, Horie M, Kamei T
Central Research Laboratories, Banyu Pharmaceutical Co., Ltd., Tokyo, Japan.
J Biol Chem. 1991 Jul 15;266(20):13171-7.
We have reported previously that NB-598 competitively inhibits human squalene epoxidase and strongly inhibits cholesterol synthesis from [14C]acetate in cultured cells. Furthermore, multiple oral administration of NB-598 decreased serum cholesterol levels in dogs (Horie, M., Tsuchiya, Y., Hayashi, M., Iida, Y., Iwasawa, Y., Nagata, Y., Sawasaki, Y., Fukuzumi, H., Kitani, K., and Kamei, T. (1990) J. Biol. Chem. 265, 18075-18078). In the present study, the effects of NB-598 on 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase and low-density-lipoprotein (LDL) receptor were examined using a human hepatoma cell line Hep G2. Incubation of Hep G2 cells with NB-598 for 18 h increased HMG-CoA reductase activity in a dose-dependent manner. However, the increase in activity induced by NB-598 was lower than that induced by L-654,969 (a potent HMG-CoA reductase inhibitor), although NB-598 inhibited cholesterol synthesis more potently than L-654,969. On the other hand, HMG-CoA reductase mRNA was increased to the same extent by both inhibitors. These results demonstrate that NB-598 does not inhibit the synthesis of non-sterol derivative(s) of mevalonate, which regulate HMG-CoA reductase activity at the post-transcriptional level. NB-598 increased the binding of 125I-LDL to Hep G2 cells. LDL receptor mRNA was also induced by NB-598. In the presence of LDL or cycloheximide, NB-598 did not increase LDL receptor activity. These results demonstrate that the induction of LDL receptor activity by NB-598 is due to increases in mRNA and protein through the inhibition of cholesterol synthesis at the squalene epoxidase step. From these observations, squalene epoxidase inhibitor is expected to be highly effective in the treatment of hypercholesterolemia and also is very useful as a research tool for studying the regulation of cholesterol metabolism.
我们之前报道过，NB-598可竞争性抑制人鲨烯环氧酶，并强烈抑制培养细胞中由[14C]乙酸盐合成胆固醇的过程。此外，多次口服NB-598可降低犬类的血清胆固醇水平（堀江，M.，土屋，Y.，林，M.，饭田，Y.，岩泽，Y.，永田，Y.，笹崎，Y.，深津，H.，北谷，K.，及龟井，T.（1990年）《生物化学杂志》265卷，18075 - 18078页）。在本研究中，使用人肝癌细胞系Hep G2检测了NB-598对3-羟基-3-甲基戊二酰辅酶A（HMG-CoA）还原酶和低密度脂蛋白（LDL）受体的影响。用NB-598孵育Hep G2细胞18小时，HMG-CoA还原酶活性呈剂量依赖性增加。然而，NB-598诱导的活性增加低于L-654,969（一种强效HMG-CoA还原酶抑制剂）诱导的增加，尽管NB-598比L-654,969更有效地抑制胆固醇合成。另一方面，两种抑制剂使HMG-CoA还原酶mRNA增加的程度相同。这些结果表明NB-598不抑制甲羟戊酸非甾醇衍生物的合成，后者在转录后水平调节HMG-CoA还原酶活性。NB-598增加了125I-LDL与Hep G2细胞的结合。NB-598还诱导了LDL受体mRNA的表达。在存在LDL或环己酰亚胺的情况下，NB-598未增加LDL受体活性。这些结果表明，NB-598诱导LDL受体活性是由于通过在鲨烯环氧酶步骤抑制胆固醇合成，从而使mRNA和蛋白质增加。基于这些观察结果，鲨烯环氧酶抑制剂有望在高胆固醇血症的治疗中非常有效，并且作为研究胆固醇代谢调节的研究工具也非常有用。
