A comparison of the binding and distribution of benzo[a]pyrene in human and rat serum

Uptake and distribution of benzo[a]pyrene (B[a]P) in human and rat serum were studied by incubation, gel filtration and ultracentrifugation. A maximum uptake of 230 and 120 micrograms B[a]P/ml was found for human and rat serum, respectively. Of the B[a]P uptake about 1% was irreversibly bound to serum constituents from both species. The uptake of B[a]P by the lipoproteins was 90-95% and 80-85% for human and rat serum, respectively, the remainder being bound to albumin. In human serum B[a]P was mainly associated with low density lipoproteins (44-47%) while in rat serum with high density lipoproteins (40-54%). However, the distribution of B[a]P between the different lipoprotein fractions showed a high correlation with the concentration of cholesterol for both species. The present results demonstrate a serum uptake capacity of B[a]P for both species which exceeds any known occupational exposure. The extensive association between B[a]P and lipoproteins may have implications for the availability of B[a]P for metabolizing organs, an area which should be further investigated. As far as the total serum uptake and distribution of B[a]P are concerned, the rat seems to be an acceptable animal model for extrapolation of in vivo results to man.