CHROMIUM TOXICITY: REDUCTIVE ACTIVATION BY HUMAN ENZYMES

铬毒性：人体酶的还原激活

• 批准号: 6307855
• 负责人: CHARLES R MYERS
• 金额: $ 1.13万
• 依托单位: MEDICAL COLLEGE OF WISCONSIN
• 依托单位国家: 美国
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-03-01 至 2001-02-28
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6307855
• 关键词: Mammalia; bioengineering /biomedical engineering; biological products; biomaterials; biomedical resource; environmental toxicology; enzymes; hematology

Exposure to chromium (Cr) compounds, which can occur through occupational exposure or the environment, is associated with a wide array of toxic effects, including serious damage to internal organs and increased incidence of certain cancers. The intracellular reductive metabolism of Cr(VI) to Cr(III), via reactive intermediates, is thought to play a key role in the cytotoxicity, mutagenicity, and carcinogenicity of Cr(VI) compounds. Studies on Cr(VI) reduction have largely focused on the mechanisms by purified chemicals or rodent tissues, but we have determined that certain aspects of the rodent studies cannot be readily extrapolated to humans. We conducted a preliminary experiment to determine if human microsomal enzymes could generate one of the reactive Cr intermediates, Cr(V). ESR spectra collected at 77 K clearly showed the production of Cr(V) (distinct signal with g value of 1.98) during the ascorbate-mediated reduction of Cr(VI). A shallow, broad signal spanning the distinct Cr(V) signal was also seen during the ascorbate-mediated reduction of Cr(V); curiously, this broad signal (peak-to-peak width of approximately 750 G) resembles that for a Cr(IV) complex reported by Luo et al. The features of this broad signal are consistent with those of a transition metal with two unpaired d electrons, although further analysis would be required to definitively conclude its true nature. Cr(V) was also clearly evident during the reduction of Cr(VI) by human hepatic microsomes. Upon expansion of the range from 4000 G to 100 G, asymmetry in the g=198 line was observed. A much smaller Cr(V) signal was seen when pre-boiled microsomes were used; this was probably due to the exposure to the NADPH-generating system for 60 min, as NADPH is a known reductant of Cr(VI) although at a much slower rate than that catalyzed by microsomal enzymes. NADPH-generating systems have been previously shown to generate small amounts of Cr(V) readily detectable by ESR. The relative Cr(V) signal intensities indicate that the signal with pre-boiled microsomes was only 43% of that with active microsomes in generating Cr(V). Although these experiments were conducted in the absence of O2, some of the Cr intensities may not represent absolute amounts of Cr(V) produced, but rather relative "steady-state" levels under the specific experimental conditions.

暴露于铬（Cr）化合物，这可能发生在 职业暴露或环境，与广泛的 一系列毒性作用，包括对内脏器官的严重损害 以及某些癌症的发病率增加。 细胞内 Cr（VI）通过活性中间体还原代谢为Cr（III）， 被认为在细胞毒性、致突变性和 Cr（VI）化合物的致癌性。 关于Cr（VI）还原的研究 主要集中在纯化的化学品或啮齿动物的机制 组织，但我们已经确定，啮齿动物的某些方面， 研究不能轻易地外推到人类身上。 我们进行了一项 初步实验，以确定人类微粒体酶是否可以 生成反应性Cr中间体之一Cr（V）。 ESR谱 在77 K下收集的样品清楚地显示了Cr（V）的产生（明显的 g值为1.98的信号） Cr（VI）。 一个浅而宽的信号，跨越不同的Cr（V）信号 在抗坏血酸介导的Cr（V）还原过程中也观察到; 奇怪的是，该宽信号（峰-峰宽度约为750 G）类似于由Luo等人报道的Cr（IV）络合物。 这种广泛信号的特征与 具有两个未配对d电子的过渡金属，尽管进一步 需要进行分析，才能最终确定其真实性质。 Cr（V）在人血还原Cr（VI）过程中也明显存在 肝微粒体 当范围从4000 G扩展到100 G时， 观察到g=198线的不对称性。 一个小得多的Cr（V）信号 当使用预煮沸的微粒体时观察到;这可能是由于 暴露于NADPH生成系统60分钟，因为NADPH 一种已知的Cr（VI）还原剂，尽管其速率比 由微粒体酶催化 NADPH生成系统已经被 先前显示产生少量Cr（V），易于检测 的ESR。 相对Cr（V）信号强度表明， 预煮微粒体信号仅为活性微粒体的43 微粒体产生Cr（V）。 虽然这些实验 在不存在O2的情况下进行，一些Cr强度可能不 表示产生的Cr（V）的绝对量，而是相对量。 在特定实验条件下的“稳态”水平。