Aquatic Toxicology 69 (2004) 35–49 Characterization and profiling of hepatic cytochromes P450 and phase II xenobiotic-metabolizing enzymes in beluga whales (Delphinapterus leucas) from the St. Lawrence River Estuary and the Canadian Arctic Melissa A. McKinney a , Augustine Arukwe b , Sylvain De Guise c , Daniel Martineau d , Pierre Béland e , André Dallaire d , Stéphane Lair d , Michel Lebeuf f , Robert J. Letcher a,∗ a Great Lakes Institute for Environmental Research, University of Windsor, Windsor, Ont., Canada N9B 3P4 b Norwegian University of Science and Technology, Trondheim NO-7491, Norway c Department of Pathobiology, University of Connecticut, Storrs, CT 06269, USA d Département de Microbiologie et Pathologie, Faculté de Médecine Vétérinaire, Université de Montréal, Saint-Hyacinthe, Que., Canada J2S 7C6 e St. Lawrence National Institute of Ecotoxicology, 5040 Mentana, Montreal, Que., Canada H2J 3C3 f Department of Fisheries and Oceans Canada, Institut Maurice-Lamontagne, Mont-Joli, Que., Canada G5H 3Z4 Received 4 July 2003; received in revised form 11 March 2004; accepted 15 April 2004 Abstract Cytochromes P450 (CYP, phase I) and conjugating (phase II) enzymes can be induced by and influence the toxicokinetics (metabolism) and toxicity of xenobiotic contaminants in exposed organisms. Beluga whale (Delphinapterus leucas) from the endangered St. Lawrence (SL) River Estuary population exhibit deleterious health effects and various severe pathologies that have been associated with contaminant exposure. In contrast, such effects (e.g. reproductive and immunological impairment) are generally less frequent in less exposed populations in the Canadian Arctic (CA). In the present study, opportunistic sampling resulted in the collection immediately after death of liver tissue from a single female neonate SL beluga (SL6) and male and female CA beluga (n = 10) from the Arviat region of western Hudson Bay, in addition to sampling of stranded carcasses of male and female SL beluga (n = 5) at least 12h postmortem. We immunologically characterized cross-reactive proteins of hepatic microsomal CYP1A, CYP2B, CYP3A, CYP2E, epoxide hydrolase (EH) and uridine diphosphoglucuronosyl trans- ferase (UDPGT) isozymes. Cross-reactive proteins were found in all SL and CA beluga using anti-rat CYP1A1, anti-rainbow trout CYP3A, anti-human CYP2E1, anti-rabbit EH and anti-human UDPGT1A1 polyclonal antibodies (Abs), whereas faintly cross-reactive CYP2B proteins were only found in SL6 and the CA samples using an anti-rabbit CYP2B1 Ab. In corresponding catalytic activity assessments, only SL6 and all CA beluga microsomal samples exhibited CYP1A-mediated 7-ethoxyresorufin O-deethylase (EROD) activity (51–260 pmol/mg/min), CYP3A-mediated activity (113–899 pmol/mg/min) based on the forma- tion of 6-hydroxytestosterone using a testosterone hydroxylase assay, and UDPGT activity (830–4956 pmol/mg/min) based on 1-naphthylglucuronide formation. The marginal cross-reactivity with the anti-CYP2B1 Ab and lack of catalytically measurable ∗ Corresponding author. Tel.: +1-519-253-3000x3753; fax: +1-519-971-3616. E-mail address: letcher@uwindsor.ca (R.J. Letcher). 0166-445X/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.aquatox.2004.04.010