Quantification of (7S,8R)-dihydroxy-(9R,10S)-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene adducts in human serum albumin by laser-induced fluorescence: Implications for the in vivo metabolism of benzo[a]pyrene

The ubiquitous environmental carcinogen benzo[a]pyrene (BaP) is metabolized in vivo in humans to its ultimate carcinogenic form of 7,8-dihydroxy-9,10- epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE). Mouse skin tumorigenicity s tudies indicate that the (7R,8S,9S,10R) enantiomer of BPDE, (7R,8S)-dihydro xy-(9S,10R)-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene [(7R,SS,9S,10R)BPDE], i s a potent tumor initiator, whereas the (7S,8R,9R,10S) enantiomer of BPDE, (7S,8R)-dihydroxy-(9R,10S)-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene [(7S,8R, 9R,10S)-BPDE], may act as a tumor promoter. In vitro experiments have shown that human liver microsomes are capable of metabolizing BaP to both the (7 R,8S,9S,10R) and (7S,8R,9R,10S) enantiomers of BPDE. However, the metabolis m of BaP to (7S,8R,9R,10S)-BPDE has not been demonstrated in humans in vivo . The adducts formed between human serum albumin (HSA) and the (7S,8R,9R,10R) and (7R,8S,9S,10R) enantiomers of BPDE have been described previously. (7S ,8R,9R,10S)-BPDE forms a stable adduct at histidine(146) of HSA, whereas (7 R,8S,9R,10R)-BPDE forms a relatively unstable ester adduct at aspartate(187 ) or glutamate(188) of HSA. Using high-performance liquid chromatography wi th laser-induced fluorescence (LIF) detector, we quantified the level of (7 S,8R,9R,10S)-BPDE adducts at histidine(146) in HSA isolated from 63 healthy males who were population control subjects for an ongoing case-control stu dy of bladder cancer. By design, roughly half of the participants were life long nonsmokers (n = 35), whereas the remaining 28 participants were curren t smokers of varying intensities. HP-BPDE adducts were detected in 60 of th e 63 samples (95%) by HPLC-LIF. Adduct levels ranged from undetectable (<0. 04 fmol/mg HSA) to 0.77 fmol/mg HSA. The samples had a mean and median (7S, 8R,9R,10S)-BPDE-HSA adduct level of 0.22 and 0.16 fmol of adduct/mg albumin , respectively. Mean adduct levels did not differ between smokers and nonsm okers (P = 0.72). Occupational exposure to polycyclic aromatic hydrocarbons was unrelated to adduct level (P = 0.62). Intake frequencies of two food i tems showed statistically significant associations with adduct levels. Cons umption of sweet potatoes was negatively related to adduct level (P 0.029), whereas intake of grapefruit juice was positively related to adduct level (P = 0.045). None of the three indices of residential ambient air pollution under study showed a statistically significant association with adduct lev els.