In vivo binding of 1-nitropyrene to albumin in the rat

Human risk assessment from exposure to nitropolynuclear aromatic hydrocarbons (NO2-PAH) has not been clearly defined, despite the widespread occurrence of such agents in the environment and their possible involvement in the etiology of some human cancers. This study was conducted since methods to determine exposure to and uptake of metabolically activated NO2-PAH are lacking. 1-Nitropyrene (1-NP), the most abundant and most extensively studied NO2-PAH, was found to bind to rat albumin at a level of 0.04 +/- 0.01% (mean +/- SD, n = 3) of the dose administered by gavage; the binding was linear over five orders of magnitude (P < 0.01). The adducts cleared at a rate (half-life = 60 h) similar to that of the unmodified rat albumin. Chromatographic analysis revealed that albumin adducts could be resolved further into a major and a minor component. Mild acid hydrolysis of the major 1-NP-albumin adduct yielded phenolic derivatives that, when subjected to acetylation, produced a material with a mass spectrum similar to that of a synthetically prepared mixture, consisting of more than one isomer, 1-acetylamino-X,Y-diacetoxypyrenes (chromatographic separation of the individual isomers was not achieved). Thus, this phenolic material that is released upon the acid treatment of albumin adducts may be a suitable indicator(s) for monitoring exposure to and metabolic activation of 1-NP.