Investigation of absorption, metabolism kinetics and DNA-binding of intratracheally administered benzo[a]pyrene in the isolated, perfused rat lung: a comparative study between microcrystalline and particulate adsorbed benzo[a]pyrene

Benzo[a]pyrene (B[a]P) adsorbed onto urban air particles (UAP) or in microcrystalline form (MCr) was administered intratracheally to the isolated perfused lung in doses of 100 and 1.5 micrograms. The appearance rate constant calculated for B[a]P release to the perfusate buffer was significantly lower for B[a]P administered adsorbed onto UAP (0.007 +/- 0.002 min-1) compared to the microcrystalline preparation (0.051 +/- 0.030 min-1). A classical two-compartmental model fitted well to the elimination of B[a]P from the perfusate buffer, after administration in solution to the buffer reservoir; C = 24 e-0.05t + 14 e-0.01t (pmol/ml). The concentration of polar metabolites in the perfusion buffer, at the end of experiments was approx. 9-fold higher for lungs administered the microcrystalline preparation compared to UAP at 1.5 microgram doses. At the 100 microgram dose level, the difference between preparations was only 2-fold, the data indicating that enzyme saturation might be important at the high dose level. With regard to the metabolite pattern, adsorption of B[a]P onto urban air particles caused a relative increase in the formation of B[a]P-9,10-dihydrodiol, whereas the relative formation rate for phenols was decreased. The absolute levels of B[a]P metabolites covalently bound to DNA was significantly higher in lungs given the MCr preparation compared to the UAP. When calculated as the amount metabolites bound, in relation to the total amount polar metabolites at the end of perfusion, however, the UAP preparation was significantly more efficient to enhance the production of DNA binding metabolites; 2.62 +/- 0.59 X 10(-5) vs. 1.33 +/- 0.21 X 10(-5) (pmol covalently DNA-bound metabolites/mg DNA/pmol metabolites formed). The results indicate that urban air particles may exert a cocarcinogenic effect with polynuclear aromatic hydrocarbons by increasing the pulmonary residence time for the carcinogenic hydrocarbon and/or alter the metabolite pattern in a way that enhances the covalent binding of metabolites to DNA.