Abstract
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.
Footnotes
This work was supported by the National Institutes of Health National Institute of Environmental Health Sciences [Grant ES-10577]. All liquid chromatography/tandem mass spectrometry work was performed in the Masonic Cancer Center Analytical Biochemical Core facility, which is supported by the National Institutes of Health National Cancer Institute [Grant CA-77598].
Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
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The online version of this article (available at http://dmd.aspetjournals.org) contains supplemental material.
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ABBREVIATIONS:
- P450
- cytochrome P450
- BDA
- cis-2-butene-1,4-dial
- NAC
- N-acetyl cysteine
- HPLC
- high-performance liquid chromatography
- NAL
- N-acetyl lysine
- MS
- mass spectrometry
- NAC-BDA-NAL
- N-acetyl-S-[1-(5-acetylamino-5-carboxypentyl)-1H-pyrrol-3-yl]-l-cysteine
- NAC-BDA-[13C615N2]NAL
- [13C615N2]N-acetyl-S-[1-(5-acetylamino-5-carboxypentyl)-1H-pyrrol-3-yl]-l-cysteine
- LC-MS/MS
- liquid chromatography/tandem mass spectrometry.
- Received November 3, 2011.
- Accepted December 20, 2011.
- Copyright © 2012 by The American Society for Pharmacology and Experimental Therapeutics
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