Comparative Metabolism of Furan in Rodent and Human Cryopreserved Hepatocytes

Abstract

Furan is a liver toxicant and carcinogen in rodents. Although humans are most likely exposed to furan through a variety of sources, the effect of furan exposure on human health is still unknown. In rodents, furan requires metabolism to exert its toxic effects. The initial product of the cytochrome P450 2E1-catalyzed oxidation is a reactive a,b-unsaturated dialdehyde, cis-2-butene-1,4-dial (BDA). BDA is toxic and mutagenic and consequently is considered responsible for the toxic effects of furan. The urinary metabolites of furan in rats are derived from the reaction of BDA with cellular nucleophiles, and precursors to these metabolites are detected in furan-exposed hepatocytes. Many of these precursors are 2-(S-glutathionyl) butanedial-amine cross-links in which the amines are amino acids and polyamines. Because these metabolites are derived from the reaction of BDA with cellular nucleophiles, their levels are a measure of the internal dose of this reactive metabolite. To compare the ability of human hepatocytes to convert furan to the same metabolites as rodent hepatocytes, furan was incubated with cryopreserved human and rodent hepatocytes. A semiquantitative liquid chromatography with tandem mass spectrometry assay was developed for a number of the previously characterized furan metabolites. Qualitative and semiquantitative analysis of the metabolites demonstrated that furan is metabolized in a similar manner in all three species. These results indicate that humans may be susceptible to the toxic effects of furan.

Abundant Rodent Furan-Derived Urinary Metabolites Are Associated with Tobacco Smoke Exposure in Humans

“…The acetylated BDA-lysine compound 1 was the most abundant furan metabolite detected in the human samples, consistent with the observation that this direct reaction product was the dominant BDA-derived metabolite of furan in human hepatocytes. 17 The sulfoxide metabolite 3 was the second most abundant BDA-derived reaction product detected in most of the human samples; however, sulfide 2 was more abundant than the sulfoxide 3 in some of the samples. The latter case occurred more frequently in the Asian cohort samples and was not associated with smoking status.…”

“…The total sum of cysteine-BDA-lysine derived metabolites ( 2 – 5 ) was less than the BDA-lysine metabolite 1 . This finding was somewhat surprising given that studies in rat hepatocytes indicated that the formation of glutathione-BDA-lysine metabolites occurred to a much greater extent than metabolite 1 ; 3,17 glutathione-BDA-lysine is likely a major precursor to metabolites 2 – 5 . 3,17 A likely explanation for this discrepancy is that we are not accounting for all of the cysteine-BDA-lysine-derived metabolites reported in rat urine.…”

“…This finding was somewhat surprising given that studies in rat hepatocytes indicated that the formation of glutathione-BDA-lysine metabolites occurred to a much greater extent than metabolite 1 ; 3,17 glutathione-BDA-lysine is likely a major precursor to metabolites 2 – 5 . 3,17 A likely explanation for this discrepancy is that we are not accounting for all of the cysteine-BDA-lysine-derived metabolites reported in rat urine. The cysteine derivative can be metabolized by sequentially by β-lysase, S -methyltransferase and sulfur oxidases, respectively, whereas the lysine residue can undergo oxidative deamination.…”

“…This is consistent with our previous observations of the relative formation of metabolite 1 and glutathione-BDA-lysine in mouse hepatocytes. 17 The higher levels of metabolites 2 and 3 in the urine of mice relative to rats indicate that the cysteine and lysine residues of the cross-link are less susceptible to further metabolism in mice. Analysis by ion trap mass spectrometry indicated that the metabolic profile of furan metabolites in mice was much simpler than that observed for rats and there was little evidence of any further metabolism of the cysteine and lysine portions of this cross-link beyond acetylation of the lysine residue and S -oxidation (data not shown).…”

Cytochrome P450–Mediated Metabolic Activation of Diosbulbin B

“…Similar cyclic molecules derived from cis-enedial and GSH were previously documented (Chen et al, 1995;Peterson et al, 2005Peterson et al, , 2011Gates et al, 2014). In addition, we performed a separate microsomal incubation in which GSH was replaced with NAC, and no such metabolite formed by the intramolecular cyclization occurring in the GSH-fortified incubation was detected.…”