Comparative study of the catalytic activity and proteinic expression of cytochrome P4501A (CYP1A) in suckermouth armored catfishes (Loricariidae) and tilapias (Cichlidae) / Estudo comparativo da atividade catalítica e expressão protéica do citocromo P4501A (CYP1A) em cascudos (Loricariidae) e tilápias (Cichlidae)

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

The cytochrome P450 (CYP) superfamily plays important roles in the biotransformation of xenobiotic and endogenous compounds. The CYP1A subfamily is well conserved in vertebrates and has been found in all jawed fish studied to date. In a previous study, we had found that suckermouth armored catfishes of the Loricariidae family (Hyposthomus luetkeni and H.affinis) did not show ethoxy-resorufin-O-deethylase (EROD) activity in liver microsomes. Since EROD is a marker of CYP1A catalytic activity in vertebrates, this unexpected finding prompted us to investigate in depth the CYP system of loricariid catfishes, particularly the CYP1A subfamily. In this study, we compared the capacities of suckermouth armored catfishes (Loricariidae), Nile tilapias (Oreochromis niloticus, Cichlidae) and mice (Swiss Webster), control and treated with CYP1A-inducing agents (50 mg/kg ip ßnaphthoflavone, BNF, and 7-12 dimethyl-benzoanthracene, DMBA) to: i - catalyze several activities that are known to be catalyzed by CYPs, ii - express CYP1A protein in liver tissue and iii activate the pro-mutagen DMBA. In liver microsomes of tilapias and mice, constitutive activities of EROD, and of other alkoxy-resorufin-O-dealkylases (XROD: MROD, PROD and BROD) were found. In the two species, activities of these monooxygenases were induced after treatment with BNF and DMBA. In suckermouth armored catfishes (control and induced) no XROD activities were noted. In liver microsomes of suckermouth catfishes and mice, the ethoxycoumarin-deethylase activity (ECOD) was found to be approximately fivefold the ECOD activity recorded in tilapias. CYP1A apparently did not take part in the catalysis of ECOD reaction in the two fish species. Results also showed that two antibodies against- fish CYP1A recognized liver microsomal proteins with a CYP-compatible molecular weight in induced tilapias and mice. These putative CYP1A proteins, however, were not consistently detected in suckermouth catfish liver microsomes. Taken together, findings from this study suggested that, in contrast to tilapias and mice, suckermouth catfishes do not show CYP1A catalytic activity and do not express, or do express only tiny amounts of constitutive CYP1A proteins in the liver. Although not showing CYP1A catalytic activity in the liver, armored suckermouth catfishes were able to convert the pro-mutagen DMBA into its genotoxic metabolites, a metabolic activation usually mediated by CYP1 family enzymes, in particular, CYP1A and 1B.

ASSUNTO(S)

tilapia sistema enzimático do citocromo p-450 translocador nuclear receptor aril hidrocarboneto peixes aryl hydrocarbon receptor nuclear translocator xenobióticos animais tilápia cytochrome p-450 enzyme system ecosystem estudo comparativo ciencias biologicas xenobiotics ecossistema fishes camundongos

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