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Cytochrome P450 1A as a biomarker of contaminant exposure in free-ranging marine mammals Miller, Kelsey A.


Marine mammals are exposed to high concentrations of organochlorine contaminants that have been linked to adverse health effects. Hepatic cytochrome P450 1A (CYP1A) is a widely used biomarker of organochlorine exposure. CYP1A catalyzes the biotransformation of xenobiotic compounds and is specifically induced by planar aromatic and halogenated hydrocarbons. CYP1A analysis has traditionally involved harvesting liver samples from dead animals. However, because of legal and ethical constraints, the use of liver for biomarker studies in free-ranging marine mammals has become increasingly unacceptable. The objective of this study was to determine whether CYP1A in skin biopsies, obtained using minimally-invasive techniques, could be used as a biomarker of organochlorine exposure in wild harbour seals and killer whales. This study consisted of three groups: (1) 20 free-ranging harbour seal pups were captured in southern British Columbia (BC) and temporarily housed in captivity. Skin-blubber and liver biopsies were collected, and three seals were orally treated with B-naphthoflavone (BNF), a known CYP1A inducer. (2) Skin-blubber biopsies were collected in the field from 42 seals (pups and adults) in BC and Washington State. (3) Skin-blubber biopsies were collected from 13 free-ranging killer whales in BC. CYP1A enzyme activity and protein levels were quantified in both liver and skin biopsies from seals using the ethoxyresorufin O-deethylase (EROD) and immunoblot assays, respectively. Cutaneous CYP1A expression was near the detection limit and did not correlate with hepatic CYP1A. However, in both tissues, CYP1A protein levels were induced by BNF treatment, and CYP1A expression increased during three weeks in captivity. Hepatic CYP1A expression correlated with blubber contaminant levels, and cutaneous CYP1A protein levels were higher in pups from Washington State than in pups from BC. EROD activity was not detected in killer whale skin, though a possible CYP1A protein band was detected by immunoblot analysis. In this study, CYP1A was quantified in small liver and skin biopsies obtained from free-ranging marine mammals using minimally-invasive methods. However, further studies are needed to validate the use of CYP1A as a biomarker of organochlorine exposure in marine mammal skin.

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