The circadian clock plays a role in many biological processes, yet very little is known about its role in metabolism of drugs and carcinogens. The purpose of this study was to define the impact of circadian rhythms on benzo-a-pyrene (BaP) metabolism in the mouse mammary gland and develop a circadian in vitro model for investigating changes in BaP metabolism resulting from cross-talk between the molecular clock and aryl hydrocarbon receptor. Female 129sv mice (12 weeks old) received a single gavage dose of 50 mg/kg BaP at either noon or midnight, and mammary tissues were isolated 4 or 24 hours later. BaP-induced Cyp1a1 and Cyp1b1 mRNA levels were higher 4 hours after dosing at noon than at midnight and this corresponded with parallel changes in Per gene expression. In our in vitro model, we dosed MCF10A mammary cells at different times after serum shock to study how time of day shifts drug metabolism in cells. Analysis of CYP1A1 and CYP1B1 gene expression showed the maximum enzyme-induced metabolism response 12 and 20 hours after shock, as determined by EROD activity, metabolism of BaP and formation of DNA-BaP adducts. The pattern of PER, BMAL and AhR-induced CYP gene expression and BaP metabolism was similar to BaP-induced Cyp1A1 and Cyp1B1 and molecular clock gene expression in mouse mammary gland. These studies indicate time of day exposure influences BaP metabolism in mouse mammary gland and describes an in vitro model that can be used to investigate the circadian influence on the metabolism of carcinogens.
- The American Society for Pharmacology and Experimental Therapeutics