Biological markers of exposure to benzene: 5-phenylcysteine in albumin

Abstract

Results of experiments in our laboratory have shown that benzene is metabolized by animals in part to an intermediate that binds to cysteine groups in hemoglobin to form the adduct S-phenylcysteine (SPC). These results suggested that SPC in hemoglobin may be an effective biological marker for exposure to benzene. However, we could not detect SPC in the globin of humans occupationally exposed to benzene concentrations as high as 28 p.p.m. for 8 h/day, 5 days/week. As another approach, we examined the binding of benzene to cysteine groups of a different blood protein, albumin. To facilitate the process, a new method for the precipitative isolation of albumin from plasma was also developed. The isolated albumin was analyzed for SPC by isotope dilution GC-MS. We used this approach to measure SPC in the albumin of F344/N rats exposed by gavage to 0-10,000 mumol/kg benzene. Amounts of albumin-associated SPC increased as a function of dose, followed by a leveling off in the amount of SPC seen at doses greater than 1000 mumol/kg. Levels of SPC were measured in humans occupationally exposed to average concentrations of 0, 4.4, 8.4 and 23 p.p.m. benzene 8 h/day, 5 days/week. Of nine controls, seven had levels of SPC below the limit of detection (0.1 pmol SPC/mg albumin). SPC increased in the exposed groups linearly, giving a statistically significant slope (P less than 0.001) of 0.044 +/- 0.008 pmol/mg albumin/p.p.m. with an intercept of 0.135 +/- 0.095 pmol/mg albumin. From this study, we conclude that SPC in albumin may prove useful as a biomarker for benzene exposure.

Interphase cytogenetics of workers exposed to benzene.

“…Urine samples were immediately aliquoted and frozen on dry ice, and stored at -70°C. Urinary phenol was measured using a modification of a previously described isotope dilution gas chromatography-mass spectroscopy (GC-MS) assay, which employed a 13C-label analog of phenol as the internal standard (27) …”

S-phenylcysteine in albumin as a benzene biomarker.

“…All other reagents were acquired from Aldrich and were of > 99% purity. Globin was isolated from the red blood cells as previously described (1). The isolation process frees the heme group from the globin protein.…”

“…We have measured the formation of SPC in albumin in workers after benzene exposure (1) and levels of SPC in humans occupationally exposed to average concentrations of 0, 4.4, 8.4, and 23.1 ppm benzene 8 hr/day, 5 days/week. SPC increased linearly in the exposed group, giving a statistically significant slope (p < 0.00 1) of 0.044 ± 0.008 pmol/(mg albumin x ppm), with an intercept of 0.135 ± 0.095 pmol/mg albumin.…”

The Use of Protein Adducts to Investigate the Disposition of Reactive Metabolites of Benzene

“…This Environmental Health Perspectives * Vol 104, Supplement 6 * December 1996 m is interesting because, although BO is capable of reacting with macromolecules, we currently have only a very sketchy understanding of the disposition of BO in vivo and SPC could provide an important avenue for such inquiries. Bechtold et al (12,14) also postulated that there should be much lower background levels of BO adducts than BQ adducts, thus making SPC in Hb or albumin more specific markers of benzene exposure.…”