Indications for the involvement of a CYP3A-like iso-enzyme in the metabolism of chlorobornane (Toxaphene®) congeners in seals from inhibition studies with liver microsomes
| Autor: | Jan P. Boon, Anders Goksøyr, Cecile M. van Hezik, Henk-Jan de Geus, Wilma E. Lewis, Robert J. Letcher, P.G. Wester |
|---|---|
| Rok vydání: | 2001 |
| Předmět: |
Insecticides
Antifungal Agents Chromatography Gas Seals Earless Health Toxicology and Mutagenesis Blotting Western Cytochrome P450 Antineoplastic Agents In Vitro Techniques Aquatic Science Biology Isozyme Catalysis chemistry.chemical_compound Cytochrome P-450 Enzyme System Cytochrome P-450 CYP3A Animals Cytochrome P-450 Enzyme Inhibitors Ellipticines Netherlands Institute for Fisheries Research Enzyme Inhibitors Antibodies Blocking Biotransformation Inhibition Toxaphene chemistry.chemical_classification Seals Aldrin Oxidoreductases N-Demethylating Stereoisomerism Metabolism Isoenzymes Ketoconazole Enzyme Enantiomers chemistry Biochemistry Rijksinstituut voor Visserijonderzoek Microsomes Liver biology.protein Microsome Female Aryl Hydrocarbon Hydroxylases Xenobiotic |
| Zdroj: | Aquatic Toxicology 51 (2001) 3 Aquatic Toxicology, 51(3), 319-333 |
| ISSN: | 0166-445X |
| Popis: | The different isoforms of the cytochrome P450 (CYP) system can metabolise a suite of classes of lipophilic, anthropogenic compounds. The bioaccumulative potential as well as the toxicity of xenobiotics may be significantly altered in the process. To compare the metabolic ability of different wildlife species, it is important to identify the different iso-enzymes of CYP, which are responsible for the metabolism of different classes of compounds. This can be achieved with in vitro incubation assays. In the present study, preparations of hepatic microsomes of a harbour seal (Phoca vitulina) and a grey seal (Halichoerus grypus) demonstrated that the chlorobornane (CHB) congeners CHB-32 and -62 were metabolised enzymatically to their hydroxylated derivatives. These derivatives were partially characterised by their NCI mass-spectra. Inhibition studies were carried out to identify the specific CYP isoform(s) responsible for the metabolism of CHB-32 and -62. Ketoconazole has been shown to inhibit CYP3A enzymes in human and rat studies. In this study, ketoconazole caused concentration-dependent inhibition of metabolism of CHB-32 and -62, reaching 80% at the 1.0 microM treatment level. Ellipticine (1.0 microM), which has been shown to inhibit CYP1A1/2, also inhibited CHB-32 and -62 metabolism in the microsomes of grey seal, but to a much lower degree of less than 10 and 24%, respectively. In the same experiment the metabolism of 4,4'-dichlorobiphenyl was already inhibited 70% by ellipticine treatment at the same concentration. This non-ortho substituted PCB congener can easily attain a planar molecular configuration, and therefore served as a model CYP1A substrate. Inhibition of chlorobornane metabolism was not observed after the addition of goat anti-rat CYP2B antibodies or Aldrin, which is a model CYP2B substrate in rat. Cautious interpretation is advised for results obtained with so-called selective competitive inhibitors. Regardless, these studies indicated for the first time the possible involvement a CYP3A isoform in the mediation of chlorobornane metabolism in seals. The immunochemical cross-reactivity of mouse, rabbit or sheep anti-rat antibodies in the hepatic microsomes of harbour seal confirmed the presence of CYP1A1/2, CYP1A1, CYP2B1/2, CYP3A and CYP4A isoenzymes. Enantioselective metabolism by the microsomes of harbour seal was observed for both CHB-32 and -62. Stereochemical preferences of biotransformation enzymes can have an influence on the environmental distribution of both enantiomers of optically active compounds. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|
Full Text from ScienceDirect