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Properties and regional expression of a CYP3A-like protein in channel catfish intestine

Författare och institution:
M. O. James (-); Z. Lou (-); L. Rowland-Faux (-); Malin C. Celander (Zoologiska institutionen)
Publicerad i:
Aquatic Toxicology, 72 ( 4 ) s. 361-371
Artikel, refereegranskad vetenskaplig
Sammanfattning (abstract):
Biotransformation in the intestine may influence the bioavailability and toxicity of ingested xenobiotics. The objective of this study was to examine the expression and catalytic properties of a constitutive cytochrome P450 (CYP) 3A-like protein along the intestine of channel catfish, Ictalurus punctatus. Fish were maintained on commercial chow or nutritionally complete semi-purified diets. Polyclonal antibodies generated against rainbow trout CYP3A proteins reacted strongly with catfish washed intestinal microsomes on Western blots showing a major protein band with MW of 59 kDa. In catfish maintained on a standard chow diet, the expression of this protein was higher in the proximal segment (0.101 ± 0.031 units/mg protein, mean ± S.D., n = 4) than in the distal part (0.032 ± 0.023 units/mg protein). Microsomal testosterone 6β-hydroxylation activity was monitored as the catalytic indicator of CYP3A, and was higher in proximal than distal catfish intestine (263 ± 80.3 and 88.6 ± 15.6 pmol/min/mg protein for proximal and distal, respectively, mean S.D., n = 4). CYP3A protein levels and testosterone 6β-hydroxylation activities were lower in microsomes from the proximal segment of intestine from catfish maintained on a semi-purified diet, compared with commercial chow, but again the proximal intestine had higher CYP3A and 6β-hydroxylase activities than distal intestine. Testosterone 6β-hydroxylase activities in all samples correlated with the CYP3A protein levels, r(2) = 0.8. Testosterone 6β-hydroxylation was inhibited by specific CYP3A inhibitors, ketoconazole (IC50 = 0.02 μ M) and erythromycin (IC50 = 41 μ M), as well as general CYP inhibitors, metyrapone (IC50 = 2.8 μ M) and SKF-525A (IC50 = 25 μ M). There was evidence for the involvement of CYP3A in the mono-oxygenation of benzo(a)pyrene and of (-)-benzo(a)pyrene-7,8-dihydrodiol in intestinal microsomes from catfish maintained on the semi-purified diet. Mono-oxygenation of both substrates was increased in a concentration-dependent manner by in vitro addition of a-naphthoflavone. Benzo(a)pyrene hydroxylase activities were higher in proximal than in distal intestine; 3.72 ± 0.77 pmol/min/mg protein, mean ± S.D., n = 5 and 1.45 ± 0.42 in these respective segments. The results of this study strongly suggest that CYP3A is important in the first pass metabolism of dietary xenobiotics in untreated fish. © 2005 Elsevier B.V. All rights reserved.
Ämne (baseras på Högskoleverkets indelning av forskningsämnen):
Biologiska vetenskaper
cytochrome p450, cyp3a, testosterone 6 beta-hydroxylase, ahh, (-)-benzo(alpha)pyrene-7,8-dihydrodiol, cyp inhibitors, trout cytochrome p450s, rainbow-trout, ictalurus-punctatus, fundulus-heteroclitus, teleost fish, liver, metabolism, benzo(a)pyrene, inhibitors, biotransformation
Postens nummer:
Posten skapad:
2007-07-27 11:20

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