Abstract
Polycyclic aromatic hydrocarbons (PAHs) and metals are often environmental cocontaminants, yet there have been relatively few studies of combined effects of PAHs and metals on cytochrome P450 (P450)-catalyzed metabolism. We examined the effects of NaAsO2 in combination with benzo[a]pyrene (BAP) on CYP1A1 and CYP1B1 in T-47D human breast cancer cells by using estrogen metabolism as a probe of their activities. Exposure to BAP caused elevated rates of the 2- and 4-hydroxylation pathways of estrogen metabolism, indicating induction of both CYP1A1, an estradiol 2-hydroxylase, and CYP1B1, an estradiol 4-hydroxylase. BAP-induced metabolism peaked 9 to 16 h after exposure and returned to near-basal levels by 48 h. Concentration-response studies showed maximal induction of the 2- and 4-hydroxylation pathways at 3 μM BAP; higher levels caused reduced rates of metabolism due to inhibition of CYP1A1 and CYP1B1. NaAsO2 caused pronounced decreases in the induction of CYP1A1 and CYP1B1 by 3 μM BAP because cotreatment with 10 μM NaAsO2 inhibited the rates of the 2- and 4-hydroxylation pathways by 86 and 92%, respectively. Western immunoblots showed diminished levels of BAP-induced CYP1A1 by coexposure to NaAsO2. The levels of the CYP1A1 and CYP1B1 mRNAs induced by BAP were not significantly affected by coexposure to NaAsO2; however, heme oxygenase 1 mRNA levels were markedly induced by coexposure to BAP and NaAsO2. These results indicate a post-transcriptional inhibitory effect of arsenite on the expression of CYP1A1 and CYP1B1 in T-47D cells, possibly resulting from reduced heme availability.
Footnotes
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This research was supported by the U.S. Environmental Protection Agency's Science to Achieve Results program through Grant R827180010 and by U.S. Public Health Service Grants CA81243 and ES04913. Although the research described in this article has been funded in part by the U.S. Environmental Protection Agency's STAR program, it has not been subjected to the agency's required peer and policy review and therefore does not necessarily reflect the views of the agency, and no official endorsement should be inferred. N.L., who is affiliated with the Division of Environmental Health, Department of Preventive Medicine, Jiangxi Medical College, Nanchang, China, is grateful to the World Health Organization for support.
- Abbreviations used are::
- PAH
- polycyclic aromatic hydrocarbon
- BAP
- benzo[a]pyrene
- P450
- cytochrome P450
- AhR
- aromatic hydrocarbon receptor
- E2
- 17β-estradiol
- OHE2
- hydroxyestradiol
- MeOE2
- methoxyestradiol
- DMSO
- dimethyl sulfoxide
- RT-PCR
- reverse transcription-polymerase chain reaction
- GAPDH
- glyceraldehyde-3-phosphate dehydrogenase
- PCR
- polymerase chain reaction
- HO-1
- heme oxygenase 1
- TCDD
- 2,3,7,8-tetrachlorodibenzo-p-dioxin
- CPR
- NADPH-cytochrome P450 reductase
- MTT
- 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide
- Received May 15, 2001.
- Accepted November 30, 2001.
- The American Society for Pharmacology and Experimental Therapeutics
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