Peterson A R, Peterson H, Spears C P, Trosko J E, Sevanian A
Institute for Toxicology, University of Southern California, School of Pharmacy, Los Angeles 90033.
Mutat Res. 1988 Oct;203(5):355-66. doi: 10.1016/0165-1161(88)90032-5.
The uptake, metabolism and alkylating properties of the diastereomeric cholesterol epoxides were studied using Chinese hamster lung fibroblasts (V79 cells). Specific emphasis is given to the comparative cyto- and geno-toxic effects of cholesterol 5 beta,6 beta-epoxide (beta CE) and cholesterol 5 alpha,6 alpha-epoxide (alpha CE) and data are provided for the first time indicating that beta CE can induce more 6-thioguanine-resistant cells than alpha CE. Cholesterol 5 beta,6 beta-epoxide induced colonies of cells resistant to 6-thioguanine at 2-3-fold the frequencies observed with the alpha-isomer, but neither compound produced ouabain-resistant colonies. The cytotoxicity (LD50) of alpha CE was estimated to be 45-50 microM whereas beta CE displayed an LD50 of 25-29 microM. Inhibition of DNA synthesis (IC50) was observed over the same dose ranges as the LD50 for each epoxide isomer. The epoxides were assimilated by cells to an equal extent, however, beta CE was metabolized to cholestane 3 beta,5 alpha-6 beta-triol twice as rapidly as the alpha-isomer. Both epoxides reacted with 4-(4'-nitrobenzyl)-pyridine to a similar extent, and with identical nucleophilic selectivity at pH 7.4, but their alkylating activity was estimated on this basis to be two orders of magnitude less than methyl methanesulfonate. Binding experiments with the DNA or cultured V79 cells or with calf-thymus DNA indicated that interactions were noncovalent and DNA binding did not correlate with the potency of the epoxides to induce the 6-thioguanine-resistant phenotype. Our results could be interpreted as indicating that both cholesterol epoxide isomers are weak mutagens or that they might induce some epigenetic event repressing the hypoxanthine guanine-phosphoribosyltransferase gene. The similarity of the epoxides' alkylating activity and their DNA-binding properties are inconsistent with their different potencies in inducing the 6-thioguanine-resistant phenotype, suggesting that the mechanism leading to this phenotype is not necessarily the result of DNA alkylation.
利用中国仓鼠肺成纤维细胞（V79细胞）研究了非对映体胆固醇环氧化物的摄取、代谢及烷基化特性。重点比较了胆固醇5β,6β - 环氧化物（βCE）和胆固醇5α,6α - 环氧化物（αCE）的细胞毒性和遗传毒性，首次提供的数据表明βCE比αCE能诱导更多对6 - 硫代鸟嘌呤耐药的细胞。胆固醇5β,6β - 环氧化物诱导的对6 - 硫代鸟嘌呤耐药的细胞集落频率是α异构体的2 - 3倍，但两种化合物均未产生对哇巴因耐药的集落。αCE的细胞毒性（LD50）估计为45 - 50μM，而βCE的LD50为25 - 29μM。在与每种环氧化物异构体的LD50相同的剂量范围内观察到DNA合成抑制（IC50）。两种环氧化物被细胞同化的程度相同，然而，βCE代谢为胆甾烷3β,5α - 6β - 三醇的速度是α异构体的两倍。两种环氧化物与4 - （4'-硝基苄基）吡啶的反应程度相似，在pH 7.4时具有相同的亲核选择性，但据此估计它们的烷基化活性比甲磺酸甲酯低两个数量级。用DNA或培养的V79细胞或小牛胸腺DNA进行的结合实验表明，相互作用是非共价的，且DNA结合与环氧化物诱导6 - 硫代鸟嘌呤耐药表型的能力无关。我们的结果可以解释为表明两种胆固醇环氧化物异构体都是弱诱变剂，或者它们可能诱导一些表观遗传事件抑制次黄嘌呤鸟嘌呤磷酸核糖转移酶基因。环氧化物的烷基化活性及其DNA结合特性的相似性与它们诱导6 - 硫代鸟嘌呤耐药表型的不同能力不一致，这表明导致该表型的机制不一定是DNA烷基化的结果。
