Induction of cytochrome P450 1A1 expression in captive river otters fed Prudhoe Bay crude oil: evaluation by immunohistochemistry and quantitative RT-PCR

Numerous studies have explored the relationships between exposure to a vari ety of environmental contaminants, such as polycyclic aromatic hydrocarbons , and induction of cytochrome P450 1A (CYP1A) in different vertebrates. Few controlled studies, however, simulated chronic long-term exposure with rep eated non-lethal sampling of the same individuals, which should better repr esent repeated exposure incidents in animals inhabiting polluted areas. In this study, we investigated the effects of chronic exposure to crude oil on levels of CYP1A1 in endothelial cells of skin biopsies and peripheral mono nuclear blood cells in captive river otters (Lontra canadensis) using repea ted sampling of the same individuals. We hypothesized that ingestion of oil would result in an increase in levels of CYP1A1 in both targets, and predi cted that the relationship between prolonged exposure and expression of CYP 1A1 would reach a plateau indicative of continuous detoxification of hydroc arbons. Fifteen wild-caught male otters were acclimated to captivity, and t hen fed diets containing no oil (control) or diets containing weathered cru de oil at 5 mg day(-1) kg(-1) body weight (low-dose) and 50 mg day(-1) kg(- 1) body weight (high-dose), at the Alaska Sealife Center in Seward, Alaska, USA. Expression of CYP1A1 was assessed with immunohistochemical analysis o f CYP1A1 protein in skin biopsies and by quantitative RT-PCR analysis of CY P1A1 mRNA in mononuclear blood cells. Both assays revealed a decrease betwe en capture and the transfer to captivity, indicating that the enclosure at the Alaska Sealife Center, and the food we offered to the otters were free of potential inducers of CYP1A1. During the exposure period, increases in C YP1A1 expression were registered by both techniques, followed by a decline in CYP1A1 after oil administration ended. Levels of endothelial CYP1A1 in t he high-dose group were comparable to those recorded for wild river otters in PWS in 1996 and 1997. Levels of CPY1A1 mRNA in mononuclear blood cells, however, were well below levels recorded for river otters in Prince William Sound, and no correlation was detected between values obtained from the tw o methods. Thus, our results from this longitudinal study with repeated sam pling of the same individuals provide support for the use of cytochrome P45 0 1A1 as a biomarker for hydrocarbon exposure. Nonetheless, our results als o suggest that the induction process of CYP1A1 may be complicated and inter acting with other processes in vivo. Such interactions may obscure our abil ity to describe specific, quantitative, predictable, dose-response relation ships between exposure to hydrocarbons and induction of CYP1A1, which are r equired of reliable biomarkers. Evaluations of such interactions based on t heoretical physiological models in live-animals merit further investigation .