SULFITE ENHANCEMENT OF DIOLEPOXIDE MUTAGENICITY - THE ROLE OF ALTERED GLUTATHIONE METABOLISM
SULFITE ENHANCEMENT OF DIOLEPOXIDE MUTAGENICITY - THE ROLE OF ALTERED GLUTATHIONE METABOLISM
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DOI：
10.1093/carcin/11.9.1635
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发表时间：
1990-09-01
期刊：
影响因子：
4.7
通讯作者：
ADAMS, KS
中科院分区：
文献类型：
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作者：
REED, GA;RYAN, MJ;ADAMS, KS
二氧化硫是大鼠和仓鼠呼吸道中苯并[a]芘的致癌物质。二氧化硫在生理条件下以亚硫酸根离子的形式存在。亚硫酸盐增强鼠伤寒沙门氏菌中 (.+-.-7r,8t-二羟基-9t,-10t-环氧-7,8,9,10-四氢苯并[a]芘 (抗-BPDE)) 和 7r,8t-二羟基-9c10c-环氧-7,8,9,10-四氢苯并[a]芘 (syn-BPDE) 的诱变效力菌株 TA98 和 TA100。当亚硫酸盐浓度在 1 至 20 mM 之间时，观察到二烯环氧化合物致突变性的增强，并且两种二烯环氧化合物的浓度依赖性是相同的。致突变性的半最大增强发生在.apprx。 5 mM 亚硫酸盐。在这些条件下，亚硫酸盐对细菌既无毒，也无致突变性。二醇环氧化物致突变性的增强需要在添加二醇环氧化物之前将细菌暴露于亚硫酸盐。同时添加亚硫酸盐和二醇环氧化合物显着降低增强效果，并且在二醇环氧化合物15分钟后添加实际上消除了该效果。这与亚硫酸盐用于提高通过二醇环氧化物修饰DNA的过程的效率相一致，而不是在DNA加合物形成后产生一些作用。通过使用 [3H]anti-BPDE 测定亚硫酸盐对 TA98 致突变性和 DNA 结合的影响，为这一假设提供了直接证据。在添加标记诱变剂之前，将细菌暴露于 10 mM 亚硫酸盐中 5 分钟，与没有亚硫酸盐的平行培养相比，DNA 结合水平增加了 170%。还观察到致突变性相应增加。由于亚硫酸盐可以影响谷胱甘肽/谷胱甘肽-S-转移酶系统（针对 BPDE 的主要细胞防御系统），因此确定了亚硫酸盐对沙门氏菌中这些途径的影响。当用 N-乙酰氧基-2-乙酰氨基芴（一种不被谷胱甘肽清除的直接作用诱变剂）处理菌株 TA98 时，事先向细菌中添加 10 mM 亚硫酸盐对最终的活力或致突变性没有影响。对细菌谷胱甘肽水平的评估表明，10 mM 亚硫酸盐处理导致共底物浓度降低 82%。然而，我们在任何孵化中都无法检测到二烯环氧丙烷-谷胱甘肽缀合物。此外，亚硫酸盐的存在导致以磺酸盐衍生物的形式显着捕获二醇环氧化物。基于这些数据，我们得出结论，谷胱甘肽的消耗确实在增强鼠伤寒沙门氏菌中二醇环氧化物致突变性方面发挥了作用。然而，我们无法在这些系统中检测 BPDE-谷胱甘肽缀合物，并且在这些孵育中观察到新型亚硫酸盐依赖性 BPDE 衍生产物，表明谷胱甘肽消耗可能不是涉及增强效果的唯一机制。
Sulfur dioxide is a cocarcinogen for benzo[a]pyrene in the respiratory tract of rats and hamsters. Sulfur dioxide exists under physiological conditions as the sulfite ion. Sulfite enhances the mutagenic potency of (.+-.-7r,8t-dihydroxy-9t,-10t-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (anti-BPDE)) and 7r,8t-dihydroxy-9c10c-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (syn-BPDE) in Salmonella typhimurium strains TA98 and TA100. This enhancement of diolepoxide mutagenicity is observed with sulfite concentrations between 1 and 20 mM, and the concentration dependence is identical for the two diolepoxides. Half-maximal enhancement of mutagenicity occurs at .apprx. 5 mM sulfite. Sulfite is neither toxic nor mutagenic to the bacteria under these conditions. The enhancement of diolepoxide mutagenicity requires that the bacteria be exposed to sulfite prior to the addition of the diolepoxide. Simultaneous addition of sulfite and diolepoxide significantly decreases the enhancing effect, and addition 15 min after the diolepoxide virtually abolishes the effect. This is consistent with sulfite serving to increase the efficiency of processes leading to DNA modification by the diolepoxides, rather than some effect subsequent to DNA adduct formation. Direct evidence for this hypothesis was provided by determining the effect of sulfite on mutagenicity and DNA binding in TA98 using [3H]anti-BPDE. Exposure of the bacteria to 10 mM sulfite for 5 min prior to the addition of the labeled mutagen led to as much as 170% increase in DNA binding levels relative to parallel incubations without sulfite. Corresponding increases in mutagenicity were seen as well. As sulfite can affect the glutathione/glutathione-S-transferase systems, the primary cellular defense against BPDE, the effect of sulfite on these pathways in Salmonella was determined. When strain TA98 was treated with N-acetoxy-2-acetamidofluorene, a direct-acting mutagen not scavenged by glutathione, prior addition of 10 mM sulfite to the bacteria had no effect on resultant viability or mutagenicity. Assessment of the bacterial glutathione levels revealed that 10 mM sulfite treatment results in an 82% decrease in the concentration of the cosubstrate. We were, however, unable to detect diolepoxide-glutathione conjugates in any of our incubations. Moreover, the presence of sulfite leads to significnt trapping of the diolepoxide in the form of sulfonate derivatives. Based on these data, we conclude that the depletion of glutathione does indeed play a role in the enhancement of diolepoxide mutagenicity in S. typhimurium. Our inability to detect BPDE-glutathione conjugates in these systems, however, and the observation of novel sulfite-dependent BPDE-derived products in these incubations, suggests that glutathione depletion may not be the only mechanism involved in the enhancing effect.