Identification and Pathway Mapping of Furan Target Proteins Reveal Mitochondrial Energy Production and Redox Regulation as Critical Targets of Furan Toxicity

Abstract

Furan, a heat-generated food contaminant, is hepatotoxic and carcinogenic in rodents. Furan is oxidized by cytochrome P450 2E1 to cis-2-butene-1,4-dial, a chemically reactive α,β-unsaturated dialdehyde, which has been identified as the key toxic metabolite of furan based on its ability to interact with tissue nucleophiles. In addition to genotoxicity, sustained cytotoxicity mediated through covalent binding of cis-2-butene-1,4-dial to critical target proteins is thought to play a key role in furan carcinogenicity. To identify putative protein targets of reactive furan metabolites, male F344/N rats (n = 5 per dose) were administered a single dose of [3,4-(14)C]-furan (20 mCi/mmol) at doses associated with hepatotoxicity following long-term exposure (0.1 and 2 mg/kg body weight [bw]). Liver proteins were separated by two-dimensional gel electrophoresis and protein spots carrying radiolabel were located by fluorography. In total, 83 discrete protein spots containing (14)C were consistently detected in livers of animals given [3,4-(14)C]-furan at 2.0 mg/kg bw, accounting for 4-5% of the proteome covered by our analyses. Protein spots were excised and digested in gel with trypsin for identification by protein mass spectrometry. Protein database search and subsequent pathway mapping identified 61 proteins localized predominantly in the cytosol and mitochondria, including structural proteins, mitochondrial enzymes involved in glucose metabolism, mitochondrial β-oxidation, and adenosine triphosphate synthesis, and proteins that participate in the maintenance of redox homeostasis and protein folding. Collectively, our data suggest that functional loss of several individual proteins and interference with pathways, most notably mitochondrial energy production, redox regulation, and protein folding, may combine to disrupt cell homeostasis and cause hepatocyte cell death.

Live‐Cell Studies of p300/CBP Histone Acetyltransferase Activity and Inhibition

“…In addition to a possible contribution to C646 fluorescence, furan rings in general are sometimes associated with pharmacokinetic liabilities. [14] Structure-based modeling studies with p300 HAT domain had suggested that the furan replacement would be tolerated. The synthesis of C107 followed a route developed for C646 in which a benzaldeyde building block was used in place of the corresponding furanyl aldehyde (see Supporting Information for complete chemical characterization).…”

Furan-induced hepatotoxic and hematologic changes in diabetic rats: the protective role of lycopene

“…Humans may be exposed to it through consumption of thermally treated foods (1). Furan is also found in cigarette smoke and engine exhausts (2).…”

“…Furan is also found in cigarette smoke and engine exhausts (2). It is also hepatotoxic and carcinogenic in animals; high incidence of cancers has been observed in animals, even at the lowest dose treated (1). Due to the prevalent use of furan, it is important to determine its toxic effects on organisms.…”

Low dose assessment of the carcinogenicity of furan in male F344/N Nctr rats in a 2-year gavage study

“…Extensive binding of furan to proteins has been demonstrated in rats treated with furan, with the highest levels being detected in the liver (Burka et al ., 1991). Substantial hepatic protein binding has been detected at doses as low as 0.1 mg furan/kg BW, with the binding increasing 10-fold at 2 mg/kg BW (Moro et al ., 2012b). Mass spectral analyses indicated that the targeted proteins were localized primarily in the cytosol and mitochondria, with fewer furan-modified nuclear proteins being detected.…”

“…The incidences of these lesions tended to become significant at only the highest dose of 2 mg furan/kg BW, which is probably a reflection of the fact that much higher levels of furan-protein binding are detected in the liver as compared to other organs (Burka et al ., 1991; Moro et al ., 2012b). …”