Contreras L M, Vivas J, Urbina J A
Laboratorio de Química Biológica, Instituto Venezolano de Investigaciones Científicas, Escuela de Biología, Facultad de Ciencias, Universidad Central de Venezuela, Caracas, Venezuela.
Biochem Pharmacol. 1997 Mar 7;53(5):697-704. doi: 10.1016/s0006-2952(96)00903-3.
The accepted mechanism for the antiproliferative effects of sterol biosynthesis inhibitors (SBI) against the protozoan parasite Trypanosoma (Schizotrypanum) cruzi, the causative agent of Chagas' disease, is the depletion of specific parasite sterols that are essential growth factors and cannot be replaced by cholesterol, the main sterol present in the vertebrate host. However, the precise metabolic roles of these specific parasite sterols are unknown. We approached this problem by subjecting T. cruzi epimastigotes to two types of SBI, inhibitors of sterol C-14 demethylase and delta 24(25) methyl transferase, and investigating the modification of lipid composition and enzyme activities in the plasma membranes of the parasite. We found in purified plasma membrane from SBI-treated cells that, together with the expected changes in the sterol composition, there was also an inversion of the phosphatidylcholine (PC) to phosphatidylethanolamine (PE) ratio and a large increase in the content of saturated fatty acids esterified to phospholipids. The modification of the phospholipid headgroup composition correlated with a 70% reduction in the specific activity of the membrane-bound PC-PE-N-methyl transferase SBI-treated cells; it was shown that this inhibition was not due to a direct effect of the drug on the enzyme. Finally, the specific activity of the Mg(2+)-dependent, vanadate-sensitive ATPase present in the membranes was also inhibited by ca. 50% in SBI-treated cells. The results suggest that one of the primary effects of the depletion of endogenous sterols induced by SBI in T. cruzi is a modification of the cellular phospholipid composition as a consequence of a reduced activity of PE-PC-N-methyl transferase and probably of the acyl delta 9 and delta 6 desaturases; this, in turn, could affect the activity of other enzymatic and transport proteins.
甾醇生物合成抑制剂（SBI）对恰加斯病病原体原生动物寄生虫克氏锥虫（裂殖锥虫）具有抗增殖作用，公认的机制是特定寄生虫甾醇的消耗，这些甾醇是必需的生长因子，无法被脊椎动物宿主中存在的主要甾醇胆固醇替代。然而，这些特定寄生虫甾醇的确切代谢作用尚不清楚。我们通过用两种类型的SBI（甾醇C-14脱甲基酶抑制剂和δ24(25)甲基转移酶抑制剂）处理克氏锥虫前鞭毛体，并研究寄生虫质膜中脂质组成和酶活性的变化来解决这个问题。我们在经SBI处理的细胞的纯化质膜中发现，除了甾醇组成的预期变化外，磷脂酰胆碱（PC）与磷脂酰乙醇胺（PE）的比例也发生了倒置，并且酯化到磷脂上的饱和脂肪酸含量大幅增加。磷脂头部基团组成的改变与经SBI处理的细胞膜结合PC-PE-N-甲基转移酶的比活性降低70%相关；结果表明，这种抑制不是由于药物对该酶的直接作用。最后，膜中存在的Mg(2+)依赖性、钒酸盐敏感的ATP酶的比活性在经SBI处理的细胞中也被抑制了约50%。结果表明，SBI诱导的克氏锥虫内源性甾醇消耗的主要作用之一是细胞磷脂组成的改变，这是由于PE-PC-N-甲基转移酶以及可能的酰基δ9和δ6去饱和酶活性降低所致；反过来，这可能会影响其他酶和转运蛋白的活性。
