Effects of alkylphenols on CYP1A and CYP3A expression in first spawning Atlantic cod ( Gadus morhua)

• Published in: Aquatic toxicology Vol. 67; no. 4; pp. 303 - 313
• Main Authors: Hasselberg, Linda, Meier, Sonnich, Svardal, Asbjørn, Hegelund, Tove, Celander, Malin C
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 12.05.2004; Elsevier Science
• Subjects: Agnatha. Pisces; Alkylphenols; Animal, plant and microbial ecology; Animals; Applied ecology; Aryl Hydrocarbon Hydroxylases - metabolism; Atlantic Ocean; Biological and medical sciences; Biological Sciences; Biologiska vetenskaper; Coumarins; CYP1A; CYP3A; Cytochrome P-450 CYP1A1 - metabolism; Cytochrome P-450 CYP3A; Cytochrome P450; Dose-Response Relationship, Drug; Ecotoxicology, biological effects of pollution; Effects of pollution and side effects of pesticides on vertebrates; Estradiol; Female; Fish; Fishes - metabolism; Fishes - physiology; Fluorescence; Fundamental and applied biological sciences. Psychology; Gadus morhua; Gene Expression Regulation - drug effects; Immunoblotting; in-vitro; liver; Male; Marine; marine fish; nonylphenol; Oncorhynchus mykiss; Oxidoreductases, N-Demethylating - metabolism; Phenols - toxicity; pregnane-x-receptor; rainbow-trout; salmon salmo-salar; Sex Factors; Stenotomus chrysops; trout oncorhynchus-mykiss; vitellogenin synthesis; Water Pollutants, Chemical - toxicity; Atlantic Ocean; CYP3A; EROD; CYP1A; Cytochrome P450; Alkylphenols; Fish; AhR; PXR; ER; Estradiol; BFC; Ecotoxicology; Toxicity; Spawning; Oil industry; Aquatic environment; Reproduction; Vertebrata; Pisces; Marine platform; Water pollution; Biological effect; Produced water; Gadus morhua
• ISSN: 0166-445X; 1879-1514
• DOI: 10.1016/j.aquatox.2003.12.007

Alkylphenols are continuously released into the ocean as a result of offshore oil production. Alkylphenols, including 4- tert-butylphenol (C 4), 4 n-pentylphenol (C 5), 4 n-hexylphenol (C 6), and 4 n-heptylphenol (C 7), up to 237 ppb concentrations, have been detected in produced water from oil platforms. Previous studies have shown that alkylphenols induce vitellogenesis in fish. Atlantic cod ( Gadus morhua) of both sexes were force-fed with various doses ranging between 0.02 and 80 ppm of a mixture of alkylphenols (C 4:C 5:C 6:C 7 ratio 1:1:1:1) or 5 ppm 17β-estradiol. We investigated effects on hepatic CYP1A and CYP3A protein expression in protein blots, using antibodies against scup ( Stenotomus chrysops) CYP1A1 and rainbow trout ( Oncorhynchus mykiss) CYP3A. There was a sexually dimorphic expression of CYP1A and CYP3A protein levels, with females expressing higher levels than males. Treatment of male Atlantic cod with 17β-estradiol resulted in increased CYP1A and CYP3A protein levels. Exposure to alkylphenols resulted in a dose-dependent increase of CYP1A and CYP3A protein expression in males, but not in females. However, this increase of CYP1A protein levels was not reflected on the CYP1A-mediated ethoxyresorufin- O-deethylase (EROD) activity, implying that alkylphenols inhibited the CYP1A enzyme activity in vivo. In vitro inhibition studies with pooled liver microsomes from Atlantic cod confirmed that the alkylphenols mixture efficiently inhibited the CYP1A activity (IC 50=10 μM), although the inhibitory effect of each individual alkylphenol varied. The IC 50 values for each individual alkylphenol on the CYP1A activity were, in a descending order of magnitude: [C 7>C 6>C 5⪢C 4], ranging from 12 to 300 μM with decreased length of the 4-alkyl chain. The effect of alkylphenols on the CYP3A activity in vitro in liver microsomes also was investigated, using the fluorescent 7-benzyloxy-4-[trifluoromethyl]-coumarin (BFC) as a diagnostic CYP3A substrate. The alkylphenol mixture inhibited CYP3A activity with IC 50 value at 100 μM. The IC 50 values for each individual alkylphenol on CYP3A activity were, in a descending order of magnitude: [C 5>C 6>C 7>C 4], ranging between 60 and 250 μM. Taken together, our results show that the alkylphenol mixture and 17β-estradiol resulted in elevated hepatic CYP1A and CYP3A expression in male Atlantic cod. The alkylphenol mixture strongly inhibited CYP1A activities, whereas it weakly inhibited CYP3A activity in Atlantic cod liver microsomes in vitro. In addition, 17β-estradiol was a weak inhibitor of CYP3A activity (IC 50=75 μM) and did not notably inhibit the CYP1A activity in vitro.