Peffley D M, Gayen A K, Morand O H
Department of Pharmacology and Molecular Biology, Finch University of Health Sciences-The Chicago Medical School, IL, USA.
Biochem Pharmacol. 1998 Aug 15;56(4):439-49. doi: 10.1016/s0006-2952(98)00083-5.
In vivo inhibition of 2,3-oxidosqualene:lanosterol cyclase (OSC, E.C. 5.4.99.7)--the enzyme which catalyzes the cyclization of monooxidosqualene to lanosterol--does not result in elevated 3-hydroxy-3-methylglutaryl CoA reductase (HMGR) activity. This trait is attributed to increased levels of oxysterols, produced upon partial inhibition of OSC, that suppress HMGR and other sterol-responsive genes. The OSC inhibitor [4'-(6-allyl-ethyl-amino-hexyloxy)-2'-fluoro-phenyl]-(4-bromopheny l)-methanone (Ro 48-8071) was shown earlier to lower low-density lipoprotein (LDL) cholesterol in hamsters with no increase in hepatic HMGR, in contrast to simvastatin. To delineate the regulatory mechanism(s) by which Ro 48-8071 reduces cholesterol synthesis without raising HMGR levels, Syrian hamster C100 cells were incubated with either Ro 48-8071 or simvastatin, and their effects on cholesterol synthesis and LDL uptake, as well as on HMGR mRNA levels and rates of synthesis, were determined. Using RNase protection and radioimmunoprecipitation assays, we found that, in the absence of LDL in the culture medium, both HMGR mRNA levels and synthesis were reduced with concentrations of Ro 48-8071 inhibiting cholesterol synthesis by 50-75%, whereas LDL uptake was either reduced or unchanged. In contrast, simvastatin, at concentrations inhibiting cholesterol synthesis by the same 50-75%, increased both HMGR mRNA levels and synthesis, as well as LDL uptake. In the presence of LDL, HMGR mRNA levels and synthesis along with LDL uptake were little affected after incubation with Ro 48-8071. Still, simvastatin markedly increased both HMGR mRNA levels and synthesis in cells incubated in the presence of LDL, leaving LDL uptake unaffected. These data suggest that inhibition of OSC by Ro 48-8071 results in an indirect down-regulation of HMGR mRNA levels and synthesis.
体内抑制2,3-氧化角鲨烯：羊毛甾醇环化酶（OSC，E.C. 5.4.99.7）——催化单氧化角鲨烯环化生成羊毛甾醇的酶——不会导致3-羟基-3-甲基戊二酰辅酶A还原酶（HMGR）活性升高。这一特性归因于部分抑制OSC后产生的氧化甾醇水平升高，其可抑制HMGR和其他甾醇反应性基因。与辛伐他汀相反，OSC抑制剂[4'-(6-烯丙基-乙基-氨基-己氧基)-2'-氟-苯基]-(4-溴苯基)-甲酮（Ro 48-8071）早前被证明可降低仓鼠的低密度脂蛋白（LDL）胆固醇，而不会增加肝脏HMGR。为了阐明Ro 48-8071降低胆固醇合成而不提高HMGR水平的调节机制，将叙利亚仓鼠C100细胞与Ro 48-8071或辛伐他汀一起孵育，并测定它们对胆固醇合成和LDL摄取以及对HMGR mRNA水平和合成速率的影响。使用核糖核酸酶保护和放射免疫沉淀分析，我们发现，在培养基中不存在LDL的情况下，Ro 48-8071浓度抑制胆固醇合成50-75%时，HMGR mRNA水平和合成均降低，而LDL摄取要么降低要么不变。相反，辛伐他汀在抑制胆固醇合成50-75%的浓度下，增加了HMGR mRNA水平和合成以及LDL摄取。在存在LDL的情况下，与Ro 48-8071孵育后，HMGR mRNA水平和合成以及LDL摄取几乎没有受到影响。然而，辛伐他汀在存在LDL的情况下孵育的细胞中显著增加了HMGR mRNA水平和合成，而LDL摄取不受影响。这些数据表明，Ro 48-8071对OSC的抑制导致HMGR mRNA水平和合成的间接下调。
