Abstract
Heme oxygenase (HO-1), the rate-limiting enzyme in the physiological breakdown of heme, is ubiquitous, and its expression can be increased by arsenite [As(III)], and similar other stimuli that induce cellular oxidative stress. Interestingly, it has been shown that the As(III)-induced HO-1 is inversely correlated with a decrease in cytochromes P450 (P450s) activity; however, the direct role for HO-1 in the inhibition of P450 enzymes remains unknown. Our results showed that As(III) at a concentration of 5 μM decreased the constitutive and inducible expression of CYP1A1, CYP1A2, CYP3A23, and CYP3A2 at the mRNA, protein, and catalytic activity levels. Moreover, As(III) decreased the nuclear accumulation of aryl hydrocarbon receptor (AhR) and pregnane X receptor without increasing their degradation. As(III) also increased the binding of cytosolic AhR to heat shock protein 90 and hepatitis B virus X-associated protein 2. In the presence of 2,3,7,8-tetrachlorodibenzo-p-dioxin as an inducer for CYP1A and rifampin as an inducer for CYP3A, As(III) decreased the enzymatic activity of the four P450s more than it decreased their mRNA or protein expression levels. It is noteworthy that treatment with the competitive HO-1 inhibitor, tin-mesoporphyrin, or supplementing external heme partially reversed the As(III)-mediated decrease in activities of the four P450s. In conclusion, the current study provides the first evidence that As(III) decreases CYP1A1, CYP1A2, CYP3A23, and CYP3A2 expression in freshly isolated rat primary hepatocytes. Furthermore, inhibiting the As(III)-mediated induction of HO-1 partially restores the enzymatic activity of these P450s that was initially decreased by As(III), confirming the direct role of HO-1 in the inhibition of P450s.
Footnotes
This work was supported by Natural Sciences and Engineering Research Council of Canada [Discovery Grant RGPIN 250139-07]. A.A.-M. is the recipient of an Alberta Innovates Technology Futures Graduate Scholarship.
Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
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ABBREVIATIONS:
- P450
- cytochrome P450
- AhR
- aryl hydrocarbon receptor
- Hsp90
- heat shock protein 90
- XAP2
- hepatitis B virus X-associated protein 2
- TCDD
- 2,3,7,8-tetrachlorodibenzo-p-dioxin
- ARNT
- aryl hydrocarbon receptor nuclear translocator
- XRE
- xenobiotic response element
- PXR
- pregnane X receptor
- CAR
- constitutive androstane receptor
- Rif
- rifampin
- RXRα
- retinoid X receptor α
- As(III)
- arsenite
- HO-1
- heme oxygenase-1
- MTT
- 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium
- DMEM
- Dulbecco's modified Eagle's medium
- DFB
- [3-[(3,4-difluorobenzyl)oxy]-5,5-dimethyl-4-[4-(methylsulfonyl)phenyl]furan-2(5H)-one]
- DFH
- [3-hydroxy-5,5-dimethyl-4-[4-(methylsulfonyl)phenyl]furan-2(5H)-one]
- GAPDH
- glyceraldehyde-3-phosphate dehydrogenase
- DMSO
- dimethylsulfoxide
- PCR
- polymerase chain reaction
- RT-PCR
- reverse transcription-polymerase chain reaction
- EROD
- 7-ethoxyresorufin O-deethylase
- MROD
- 7-methoxyresorufin O-deethylase
- EMSA
- electrophoretic mobility shift assay
- SnMP
- tin mesoporphyrin
- CT
- cycle threshold.
- Received August 29, 2011.
- Accepted December 8, 2011.
- Copyright © 2012 by The American Society for Pharmacology and Experimental Therapeutics
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