Ethylmorphine N-demethylase activity as a marker for cytochrome P450 CYP3A activity in rat hepatic microsomes |
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| Affiliation: | 1. Department of Radiology, Faculty of Medicine, Khon Kaen University, Khon Kaen 40002, Thailand;2. Department of Parasitology, Faculty of Medicine, Khon Kaen University, Khon Kaen 40002, Thailand;3. Department of Pathology, Faculty of Medicine, Khon Kaen University, Khon Kaen 40002, Thailand;4. Graduate School, Faculty of Veterinary Medicine, Khon Kaen University, Khon Kaen 40002, Thailand;5. Department of Veterinary Anatomy, Faculty of Veterinary Medicine, Khon Kaen University, Khon Kaen 40002, Thailand;6. Department of Veterinary Pathobiology, Faculty of Veterinary Medicine, Khon Kaen University, Khon Kaen 40002, Thailand;7. Department of Microbiology, Immunology & Tropical Medicine, Research Center for Neglected Diseases of Poverty, School of Medicine and Health Sciences, George Washington University, Washington, DC 20037, United States;8. WHO Collaborating Centre for Research and Control of Opisthorchiasis (Southeast Asian liver fluke disease), Khon Kaen University, Khon Kaen 40002, Thailand;1. HOPLITE Research Group, Department of Pathology and Microbiology, AVC-UPEI, Charlottetown, PE C1A 4P3, Canada;2. Center for Biomedical Research, University of Victoria, Victoria, BC V8W 2Y2, Canada;3. Pacific Biological Research Station, Fisheries and Oceans, Nanaimo, BC V9T 6N7, Canada;4. Cargill, Cargill Innovation Center, Dirdal, Norway |
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| Abstract: | ![]()
The purpose of this study was to evaluate the selectivity and sensitivity of ethylmorphine N-demethylase (EMD) as an indicator of chemically-induced cytochrome P450 CYP3A activity in liver microsomes of rats following treatment with selective enzyme inducers. Male and female Sprague–Dawley (CD®) rats were dosed with either pregnenolone-16α-carbonitrile (PCN; 50 mg/kg per day for 5 days), phenobarbital (PB; 100 mg/kg per day for 4 days), beta-naphthoflavone (βNF; 100 mg/kg per day for 3 days), clofibrate (CF; 300 mg/kg per day for 14 days), isoniazid (ISO; 100 mg/kg per day for 3 days), or dexamethasone (DEX; 50 mg/kg per day for 4 days). Microsomes were isolated, frozen and subsequently assayed for protein, cytochrome P450 content and EMD activity. In males, significant elevations (P<0.01) in EMD activity were observed in microsomes from PB-, DEX- and PCN-dosed animals compared with untreated controls. Microsomes from ISO- and βNF-dosed males showed a reduction (P<0.05) in EMD activity when compared with control microsomes, and CF was without effect. In females, EMD activities were significantly increased in microsomes from PCN, DEX and PB-dosed but not βNF, ISO, or CF-dosed animals. As expected on the basis of sex-related differences in gene expression, EMD activities in untreated animals were considerably higher in males than females, attributable to constitutive CYP3A and CYP2C11 activities. The selectivity of EMD for induced CYP3A was confirmed on the basis of inhibition studies with selected steroid substrates of CYP3A, polyclonal anti-CYP3A1 antibodies and triacetyloleandomycin (TAO), a selective inhibitor of CYP3A. In conclusion, for both sexes, the greatest elevations (≈3–13-fold) in EMD activity were observed in microsomes from rats dosed with DEX, a potent archetypal inducer with lesser but significant increases noted for PCN and PB, indicating that EMD is a reliable indicator of induced rat hepatic cytochrome P450 CYP3A activity. |
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