In vitro metabolism of benzo[a]pyrene-7,8-dihydrodiol and dibenzo[def,p]chrysene-11,12 diol in rodent and human hepatic microsomes

Journal Article · Sat Jan 21 00:00:00 EST 2017 · Toxicology Letters

DOI:https://doi.org/10.1016/j.toxlet.2017.01.008· OSTI ID:1342760

Smith, Jordan N. ^[1]; Mehinagic, Denis ^[1]; Nag, Subhasree ^[1]; Crowell, Susan R. ^[2]; Corley, Richard A. ^[1]

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1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
2. Genentech, South San Francisco, CA (United States)

Polycyclic aromatic hydrocarbons (PAHs) are contaminants that are ubiquitously found in the environment, produced through combustion of organic matter or petrochemicals, and many of which are procarcinogens. The prototypic PAH, benzo[a]pyrene (B[a]P) and the highly carcinogenic dibenzo[def,p]chrysene (DBC) are metabolically activated by isoforms of the P450 enzyme superfamily producing benzo[a]pyrene-7,8-dihydrodiol (B[a]P diol), dibenzo[def,p]chrysene-11,12 diol (DBC diol). Each of these diols can be further metabolized by cytochrome P450 enzymes to highly reactive diol-epoxide metabolites that readily react with DNA or by phase II conjugation facilitating excretion. To complement prior in vitro metabolism studies with parent B[a]P and DBC, both phase I metabolism and phase II glucuronidation of B[a]P diol and DBC diol were measured in this paper in hepatic microsomes from female B6129SF1/J mice, male Sprague-Dawley rats, and female humans. Metabolic parameters, including intrinsic clearance and Michaelis-Menten kinetics were calculated from substrate depletion data. Mice and rats demonstrated similar B[a]P diol phase I metabolic rates. Compared to rodents, human phase I metabolism of B[a]P diol demonstrated lower overall metabolic capacity, lower intrinsic clearance at higher substrate concentrations (>0.14 μM), and higher intrinsic clearance at lower substrate concentrations (<0.07 μM). Rates of DBC diol metabolism did not saturate in mice or humans and were highest overall in mice. Higher affinity constants and lower capacities were observed for DBC diol glucuronidation compared to B[a]P diol glucuronidation; however, intrinsic clearance values for these compounds were consistent within each species. Finally, kinetic parameters reported here will be used to extend physiologically based pharmacokinetic (PBPK) models to include the disposition of B[a]P and DBC metabolites in animal models and humans to support future human health risk assessments.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE; National Inst. of Health (NIH) (United States)
• Contributing Organization: Genentech, South San Francisco, CA (United States)
• Grant/Contract Number: AC05-76RL01830; P42 ES016465
• OSTI ID: 1342760
• Report Number(s): PNNL-SA-121283; PII: S0378427417300085
• Journal Information: Toxicology Letters, Vol. 269; ISSN 0378-4274
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
60 APPLIED LIFE SCIENCES
Benzo[a]pyrene
Dibenzo[def
p]chrysene
Polycyclic aromatic hydrocarbons
PAH