Hepatic CYP1A enzymes in fish as a biomarker of water pollution

Abstract

Poly aromatic hydrocarbon (PAR) and polychlorinated biphenyl (PCB) compounds are widespread contaminants in the aquatic environment. Induction of hepatic cytochrome P450 1A (CYP1A) enzymes in fish have been used as a biomarker to detect exposure to PAH and to a certain extent PCB-like compounds. In the present study, Chinook salmon (Oncorynchus tschawytscha) were used as an animal model (i) to examine the induction of liver cytochrome CYP1A enzymes by β-napthoflavone (BNF) and Araclor 1254 (Laboratory studies), and (ii) to evaluate the feasibility of using CYP1A induction as an early warning indicator of PAH and/or PCB contamination in waterways (Field studies). Measurement of ethoxyresorufin-O-deethylase (EROD) and aryl hydrocarbon hydroxylase (AHH) enzyme activities in fish liver microsomes were used to monitor CYP1A enzyme activity.

Optimal conditions for salmon husbandry in laboratory studies were established. Laboratory experiments were carried out in plastic water tanks with a continuous water supply from 2 trickle towers and a holding tank. Fish received BNF and Aroclor via IP injection and diets. The IP doses for BNF and Aroclor were 13 and 120 mg/kg body weight, respectively. Fish were sacrificed 4 and 7 days post injection. P450 content, AHH and EROD activities were significantly higher in BNF and Aroclor groups compared to the corresponding controls.

BNF and Aroclor were given to fish via the diet at a rate of 20 and 40 mg/kg body weight. The fish were sacrificed 2 and 4 weeks after exposure to the chemicals. Both AHH and EROD activities in all treatment groups were higher than the corresponding control groups. Trends of CYP1A induction following BNF and Aroclor administration via diets were similar to induction via IF injection. However, the magnitude of induction was lower.

An increase in CYP1A enzyme activity in response to BNF or Aroclor uptake by Chinook salmon has not previously been published. Although both AHH and EROD activities were elevated following exposure to BNF and Aroclor, EROD appeared to be a more sensitive indicator of CYP1A activity than AHH.

Due to a variety of reasons outlined in the thesis, only a limited number of field trials were conducted. Fish were caged in 4 rivers in and around Christchurch. Although interpretation of field trials were difficult due to a lack of 'proper controls', elevated CYP1A enzyme activities in fish at one of the sites (Hanmer) give reasons for concern in terms of organic pollution of this particular waterway. More data are required from a variety of sites if this technique is to be used by agencies to monitor the environment for ecotoxicological risk. Results presented here indicate that measurement of EROD enzyme is a more sensitive early warning indicator of water pollution by PAH's and PCB's than AHH.