Beta-naphthoflavone-inducedCYP1A expression in the guppy Jenynsia multidentata: Time-dependent response, anesthetic MS-222 effect and fin analysis.

Abstract Cytochrome P450 1A (CYP1A) expression in fish is used as a biomarker of exposure to organic contaminants, such PAHs, PCBs and dioxins, in the aquatic environment. South American guppy fish Jenynsia multidentata were exposed to the prototypical aryl hydrocarbon receptor (AHR) agonist beta-naphthoflavone (BNF; 1 μM) and the fins were biopsied to characterize different aspects of CYP1A induction. RTq-PCR was used to quantify CYP1A mRNA levels in fish tissues. CYP1A induction in the gill, liver and anal fin (gonopodium) occurred within the first hour of waterborne exposure to BNF and persisted throughout 2, 4, 8, 24, 48 and 96 h compared to controls (DMSO vehicle; p CYP1A mRNA level at 4 h (∼34-fold over control). Basal CYP1A mRNA levels and its induction following BNF exposure were not affected by administration of a chemical anesthetic (fish immersion in 100 mg l −1 MS-222 for 2–5 min) in the gill, liver, gonopodium, dorsal or tail fin ( p ex vivo assay, in which small pieces of biopsied fins were exposed to BNF for 4 h, high CYP1A induction was observed in the tail and gonopodium (∼49-fold and ∼69-fold, respectively) but not in the dorsal fin compared to controls. To our knowledge, this is the first study to show that a 1 h waterborne exposure to an AHR agonist is sufficient to cause CYP1A induction in fish organs and fins. The present study added new information to the field regarding the use of MS-222 as an anesthetic on fish and the analysis of biopsied fins as an alternative non-lethal ex vivo assay for evaluating the CYP1A biomarker in fish. This observation could be useful for planning fish toxicological bioassays and biomonitoring studies on the aquatic environments in South America.