title: Inhibition of CYP1A enzymes by alpha-naphthoflavone causes both synergism and antagonism of retene toxicity to rainbow trout (Oncorhynchus mykiss).
abstract: Retene (7-isopropyl-1-methyl phenanthrene) is a polycyclic aromatic hydrocarbon (PAH), that causes dioxin-like toxicity to early life stages of fish, including increased rates of mortality, developmental defects characterized as blue sac disease (BSD), and induction of CYP1A enzymes. This study determined whether toxicity is associated with retene, or with its metabolism by CYP1A enzymes to hydroxylated derivatives. Larval rainbow trout (Oncorhynchus mykiss) were co-exposed to four concentrations of waterborne retene and four concentrations of waterborne alpha-naphthoflavone (ANF), a compound that antagonizes CYP1A induction and inhibits oxygenation reactions. The prevalence of mortality and BSD increased in an exposure-dependent manner for larvae exposed to retene alone. Tissue concentrations of CYP1A protein and retene metabolites also increased, but no un-metabolized retene (i.e., the parent compound) was measurable. At low concentrations of ANF, toxicity increased dramatically, while tissue concentrations of polar hydroxylated metabolites of retene decreased, and concentrations of less polar metabolites, and of parent retene, increased. At the highest concentration of ANF, retene toxicity was eliminated, and parent retene was the predominant form in tissue; no concentration of ANF was toxic by itself. The inhibition of retene hydroxylation and toxicity by ANF suggests that toxicity was caused by specific retene metabolites, and not by parent retene. The potentiation of retene toxicity at low concentrations of ANF, and the antagonism at high concentrations is a unique, non-linear interaction based on modulating CYP1A enzyme activity and retene metabolism. It demonstrates that effects on fish of different complex mixtures of hydrocarbons may not be easily predicted.
authors.affiliation: School of Environmental Studies, Queen's University, Kingston, Ont., Canada K7L 3N6. hodsonp@biology.queensu.ca
authors.forename: Peter V
authors.initials: PV
authors.lastname: Hodson
authors.forename: Kashif
authors.initials: K
authors.lastname: Qureshi
authors.forename: Cameron A J
authors.initials: CA
authors.lastname: Noble
authors.forename: Parveen
authors.initials: P
authors.lastname: Akhtar
authors.forename: R Stephen
authors.initials: RS
authors.lastname: Brown
mesh_terms: D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000187:drug effects*; D001571:Benzoflavones / Q000494:pharmacology*; D015153:Blotting, Western / Q000662:veterinary; D002851:Chromatography, High Pressure Liquid / Q000662:veterinary; D019363:Cytochrome P-450 CYP1A1 / Q000187:drug effects / Q000378:metabolism; D004347:Drug Interactions; D004790:Enzyme Induction / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005393:Fish Diseases / Q000473:pathology; D007814:Larva / Q000737:chemistry / Q000187:drug effects; D000432:Methanol / Q000494:pharmacology; D017686:Oncorhynchus mykiss; D010616:Phenanthrenes / Q000032:analysis / Q000378:metabolism / Q000633:toxicity*; D014874:Water Pollutants, Chemical / Q000378:metabolism / Q000633:toxicity*
chemical_list: D001571:Benzoflavones; D004791:Enzyme Inhibitors; D010616:Phenanthrenes; D014874:Water Pollutants, Chemical; C447880:retene; C011512:alpha-naphthoflavone; D001189:Aryl Hydrocarbon Hydroxylases; D019363:Cytochrome P-450 CYP1A1; D000432:Methanol