CHROMIUM TOXICITY: REDUCTIVE ACTIVATION BY HUMAN ENZYMES

接触铬(铬)化合物，可通过 职业暴露或环境，与广泛的 一系列毒性影响，包括对内脏的严重损害 并增加某些癌症的发病率。细胞内 通过活性中间体将六价铬还原为三价铬， 被认为在细胞毒性、致突变性和 六价铬化合物的致癌性关于铬(VI)还原的研究 主要集中在净化化学品或啮齿动物的作用机制上 组织，但我们已经确定啮齿动物的某些方面 研究不能轻易地推论到人类身上。我们进行了一次 初步实验确定人类微粒体酶是否可以 生成一种活性铬中间体，铬(V)。ESR波谱 在77K下采集的数据清楚地显示了铬(V)的产生(明显 抗坏血酸介导的还原过程中的g值为1.98的信号 六价铬的含量。一种跨越不同的铬(V)信号的浅而宽的信号 在抗坏血酸介导的铬(V)还原过程中也可见； 奇怪的是，这种宽广的信号(峰间宽度约为750 G)类似于Luo等人报道的一种铬(IV)络合物。这个 这一宽泛信号的特征与 具有两个未配对的d电子的过渡金属，尽管更远 需要进行分析才能最终得出其真实性质。 在人对铬(VI)的还原过程中，铬(V)也很明显 肝脏微粒体。在将范围从4000G扩展到100G后， 观察到g=198系的不对称性。小得多的铬(V)信号 是在使用预煮的微粒子时看到的；这可能是由于 暴露在NADPH生成系统中60分钟，如NADPH 一种已知的铬(VI)的还原剂，尽管其速度比它慢得多 由微粒体酶催化。NADPH发电系统已经被 以前显示生成少量容易检测到的铬(V) 由ESR提供。相对的铬(V)信号强度表明 预煮微粒子的信号仅为活性微粒子的43% 微粒体与铬(V)的生成。尽管这些实验是 在没有氧气的情况下进行，一些铬的强度可能不 表示产生的铬(V)的绝对量，而不是相对的量 在特定实验条件下的“稳态”水平。

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.