Muconaldehyde formation from 14C-benzene in a hydroxyl radical generating system

Abstract

It has recently been proposed that muconaldehyde, a six carbon, α, β-unsaturated dialdehyde, may be a hematotoxic metabolite of benzene. The present studies indicate that trans-muconaldehyde is formed from benzene in vitro in a hydroxyl radical (·OH) generating system containing ascorbate, ferrous sulfate and EDTA in phosphate buffer, pH 6.7.Muconaldehyde formed from benzene in the ·OH generating system was identified by trapping it with thiobarbituric acid (TBA), which results in the formation of an adduct with a 495 nm absorption maximum and a 510 nm fluorescence emission maximum. These maxima were identical to those observed after reacting authentic trans, trans-muconaldehyde with TBA. This finding was supported by thin layer chromatography and solid phase extraction studies. In those studies benzene-derived muconaldehyde cochromatographed with the muconaldehyde/TBA standard. Analyses of the products from the ·OH generating system using high performance liquid chromatography (HPLC) confirm that trans,trans-muconaldehyde is a product of benzene ring fission. Regardledd of whether or not TBA was used for trapping, samples from the ·OH system incubated with benzene contained a peak which cochromatographed with the mucunaldehyde standard. The radioactivity profile of fractions collected during HPLC analysis demonstrates 14C-benzene to be the source of the trans,trans-muconaldehyde. The role of hydroxyl radicals in the formation of muconaldehyde was investigated by using dimethyl sulfoxide, mannitol, and ethanol as ·OH scavengers. These scavengers, at concentrations of 10 and 100 mM, were found to cause a dose-dependent decrease in the formation of muconaldehyde. This work indicates that benzene ring opening occurs in a chemical hydroxyl radical generating system, and results in the formation of a product which has the spectral and chromatographic characteristics of trans,trans-muconaldehyde.