Division of Environmental Health Sciences and Masonic Cancer Center, University of Minnesota, Minneapolis, Minnesota 55455, USA.
Drug Metab Dispos. 2012 Mar;40(3):596-601. doi: 10.1124/dmd.111.043679. Epub 2011 Dec 20.
Furan is a liver toxicant and carcinogen in rodents. It is classified as a possible human carcinogen, but the human health effects of furan exposure remain unknown. The oxidation of furan by cytochrome P450 (P450) enzymes is necessary for furan toxicity. The product of this reaction is the reactive α,β-unsaturated dialdehyde, cis-2-butene-1,4-dial (BDA). To determine whether human liver microsomes metabolize furan to BDA, a liquid chromatography/tandem mass spectrometry method was developed to detect and quantify BDA by trapping this reactive metabolite with N-acetyl-l-cysteine (NAC) and N-acetyl-l-lysine (NAL). Reaction of NAC and NAL with BDA generates N-acetyl-S-[1-(5-acetylamino-5-carboxypentyl)-1H-pyrrol-3-yl]-l-cysteine (NAC-BDA-NAL). Formation of NAC-BDA-NAL was quantified in 21 different human liver microsomal preparations. The levels of metabolism were comparable to that observed in F-344 rat and B6C3F1 mouse liver microsomes, two species known to be sensitive to furan-induced toxicity. Studies with recombinant human liver P450s indicated that CYP2E1 is the most active human liver furan oxidase. The activity of CYP2E1 as measured by p-nitrophenol hydroxylase activity was correlated to the extent of NAC-BDA-NAL formation in human liver microsomes. The formation of NAC-BDA-NAL was blocked by CYP2E1 inhibitors but not other P450 inhibitors. These results suggest that humans are capable of oxidizing furan to its toxic metabolite, BDA, at rates comparable to those of species sensitive to furan exposure. Therefore, humans may be susceptible to furan's toxic effects.
呋喃是一种肝脏毒物和啮齿动物致癌物。它被归类为可能的人类致癌物，但呋喃暴露对人类健康的影响尚不清楚。细胞色素 P450（P450）酶对呋喃的氧化是呋喃毒性所必需的。该反应的产物是反应性α，β-不饱和二醛，顺式-2-丁烯-1,4-二醛（BDA）。为了确定人肝微粒体是否将呋喃代谢为 BDA，开发了一种液相色谱/串联质谱法，通过用 N-乙酰-l-半胱氨酸（NAC）和 N-乙酰-l-赖氨酸（NAL）捕获这种反应性代谢物来检测和定量 BDA。NAC 和 NAL 与 BDA 的反应生成 N-乙酰-S-[1-（5-乙酰氨基-5-羧基戊基）-1H-吡咯-3-基]-l-半胱氨酸（NAC-BDA-NAL）。在 21 种不同的人肝微粒体制剂中定量测定了 NAC-BDA-NAL 的形成。代谢水平与 F-344 大鼠和 B6C3F1 小鼠肝微粒体观察到的水平相当，这两种物种已知对呋喃诱导的毒性敏感。用重组人肝 P450 进行的研究表明，CYP2E1 是最活跃的人肝呋喃氧化酶。用对硝基苯酚羟化酶活性测定的 CYP2E1 活性与 NAC-BDA-NAL 在人肝微粒体中的形成程度相关。NAC-BDA-NAL 的形成被 CYP2E1 抑制剂阻断，但其他 P450 抑制剂则没有。这些结果表明，人类能够以与对呋喃暴露敏感的物种相当的速率将呋喃氧化为其毒性代谢物 BDA。因此，人类可能易受呋喃的毒性影响。
