Quievryn George, Messer Joseph, Zhitkovich Anatoly
Department of Pathology and Laboratory Medicine, Brown University, 70 Ship Street, Room 507, Providence RI 02912, USA.
Carcinogenesis. 2006 Nov;27(11):2316-21. doi: 10.1093/carcin/bgl076. Epub 2006 May 19.
Recent epidemiological and risk assessment studies have found a very high risk of lung cancer among chromium(VI)-exposed workers even at permissible levels of exposure. However, mechanistic views on the key genotoxic role of transient Cr(V) intermediates were more consistent with the threshold or highly non-linear (heavy dose) models of genetic damage by intracellular Cr(VI). In this work, we examined the production of mutagenic DNA lesions during metabolism of Cr(VI) by its dominant reducer ascorbate (vitamin C) under conditions promoting increased yield of transient Cr forms. We found that slow reductive activation of Cr(VI) by limited concentrations of ascorbate resulted in a greater yield of DCFH-oxidizing Cr intermediates but these species were unable to cause DNA strand breaks. Cr(VI)-ascorbate reactions generated a high number of Cr-DNA adducts that were responsible for all mutagenic responses detected in Cr(VI)-treated pSP189 shuttle plasmids following their replication in human cells. Mutagenicity of DNA damage resulting from the reactions with increased stability of Cr intermediates was approximately four times lower relative to the conditions lacking detectable Cr(V) formation. Unlike other reactions, slow reduction of Cr(VI) with ascorbate produced Cr-DNA adducts that were more resistant to dissociation by chelators, suggesting multicoordinate binding of Cr(III) to DNA. Overall, our findings do not support the possibility that increased Cr(V) formation at depleted ascorbate levels modeling heavy dose exposures causes higher levels of mutagenic DNA damage.
近期的流行病学和风险评估研究发现，即使在允许的接触水平下，接触六价铬的工人患肺癌的风险也非常高。然而，关于瞬态五价铬中间体关键遗传毒性作用的机制观点，与细胞内六价铬遗传损伤的阈值或高度非线性（高剂量）模型更为一致。在这项工作中，我们研究了在促进瞬态铬形态产量增加的条件下，六价铬通过其主要还原剂抗坏血酸（维生素C）代谢过程中诱变DNA损伤的产生情况。我们发现，有限浓度的抗坏血酸对六价铬的缓慢还原活化导致二氯荧光素（DCFH）氧化铬中间体的产量更高，但这些物质无法导致DNA链断裂。六价铬-抗坏血酸反应产生了大量的铬-DNA加合物，这些加合物是在经六价铬处理的pSP189穿梭质粒在人类细胞中复制后检测到的所有诱变反应的原因。与缺乏可检测到的五价铬形成的条件相比，由于铬中间体稳定性增加的反应导致的DNA损伤的诱变性大约低四倍。与其他反应不同，抗坏血酸对六价铬的缓慢还原产生的铬-DNA加合物更耐螯合剂解离，这表明三价铬与DNA的多配位结合。总体而言，我们的研究结果不支持在模拟高剂量暴露的抗坏血酸水平降低时五价铬形成增加会导致更高水平诱变DNA损伤的可能性。
