Abstract
Pyridine (PY) effects on rat hepatic cytochromes P450 (CYP) 3A1 and 3A2 expression were examined at the levels of metabolic activity, protein, and mRNA and were compared with those of CYP2B1/2 and CYP2E1. CYP3A metabolic activity as well as CYP3A protein and mRNA levels increased following treatment of rats with PY. CYP3A1 and CYP3A2 were differentially affected by PY treatment in terms of induction levels, dose dependence, and stability of mRNA. CYP3A1 mRNA levels maximally increased ∼42-fold after PY treatment, whereas CYP3A2 mRNA level increased ∼4-fold. Moreover, CYP3A1 mRNA levels decreased more rapidly than those of CYP3A2 as determined following inhibition of transcription with actinomycin D or cordycepin. Treatment of rats with PY resulted in a dose-dependent increase in CYP3A1, CYP3A2, and CYP2B1/2B2 protein levels. In contrast to the effects of PY treatment on CYP3A1 and 2B, CYP2E1 protein levels increased in the absence of a concomitant increase in CYP2E1 mRNA levels. Treatment of rats with PY at 200 mg/kg/day for 3 days increased both protein and mRNA levels of CYP3A2, whereas treatment with higher than 200 mg/kg/day for 3 days increased CYP3A2 protein levels without an increase in CYP3A2 mRNA levels. These data demonstrated that PY regulates the various CYPs examined in this study at different levels of expression and that PY regulates CYP3A1 expression through transcriptional activation and CYP3A2 expression through transcriptional and post-transcriptional activation at a low- and high-dose PY treatment, respectively.
Footnotes
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Send reprint requests to: Raymond F. Novak, Wayne State University, Institute of Environmental Health Sciences, 2727 Second Ave., Room 4000, Detroit, MI. E-mail: raymond.novak{at}wayne.edu
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This research was supported by National Institutes of Health Grants ES05577 (H.K.), CA16954 (P.F.H.), CA44353 and ES00267 (F.P.G.), and ES03656 (R.F.N.).
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↵2 CYP3A1 was the first rat CYP3A form cloned and has been reported to be at very low levels in both males and females but is highly induced in response to dexamethasone. CYP3A23 is a recent addition to the rat CYP3A subfamily and is 98.6% identical to CYP3A1 (Kirita and Matsubara, 1993; Komori and Oda, 1994), and it may be that earlier studies describing the expression of CYP3A1 may have been measuring CYP3A23. In a study using reverse transcriptase-polymerase chain reaction to detect the various CYP3A forms, CYP3A23 was found to be regulated in a manner similar to that reported previously for CYP3A1, but no CYP3A1 was detected, even though three different PCR primer combinations were tested (Mahnke et al., 1997). Since the oligomeric probe sequence previously believed to be specific for CYP3A1 (Kirita and Matsubara, 1993) is derived from a region that is completely conserved in CYP3A23, our data pertinent to CYP3A1 mRNA expression may also reflect CYP3A23 expression.
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↵3 The NCBI BLAST search result was as of May 25, 2000.
- Abbreviations used are::
- PY
- pyridine
- PB
- phenobarbital
- DEX
- dexamethasone
- CYP
- cytochrome P450
- PAGE
- polyacrylamide gel electrophoresis
- Mab
- monoclonal antibody
- Received August 1, 2000.
- Accepted August 12, 2000.
- The American Society for Pharmacology and Experimental Therapeutics
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Differential Induction of Rat Hepatic Cytochromes P450 3A1, 3A2, 2B1, 2B2, and 2E1 in Response to Pyridine Treatment
