S-phenylcysteine formation in hemoglobin as a biological exposure index to benzene

Benzene is metabolized to intermediates that bind to hemoglobin, forming adducts. These hemoglobin adducts may be usable as biomarkers of exposure. In this paper, we describe the development of a gas chromatography/mass spectroscopy assay for quantitating the binding of the benzene metabolite, benzene oxide, to cysteine groups in hemoglobin. We used this assay to study the hemoglobin adduct, S-phenylcysteine (SPC), in the blood of rats and mice exposed to benzene either by inhalation or by gavage. We were able to detect SPC in the hemoglobin of exposed rats and mice, to show the linearity of the exposure dose-response relationship, and to establish the sensitivity limits of this assay. For the same exposure regime, rats showed considerably higher levels of SPC than did mice. As yet, we have not been able to detect SPC in the globin of humans occupationally exposed to benzene. We attempted to determine whether the SPC found in hemoglobin originated from the metabolism of benzene within or outside of the red blood cell. We hypothesized that the greatest red blood cell metabolism would be associated with peripheral reticulocytes, which retain high metabolic capacity. After exposing rats to benzene, we isolated the red blood cells and used discontinuous Percoll gradients to fractionate them into age groups. No differences in SPC levels were found among any of the fractions, suggesting that the SPC found in globin originates from the metabolism of benzene to benzene oxide in a location external to the red blood cell. To our knowledge, this is the first demonstration of the nonenzymatic binding of the benzene metabolite, benzene oxide, to protein.(ABSTRACT TRUNCATED AT 250 WORDS)