Monooxygenase activities in carp as biochemical markers of pollution by polycyclic and polyhalogenated aromatic hydrocarbons: choice of substrates and effects of temperature, gender and capture stress

Abstract

Cytochrome P450-dependent monooxygenase activities (7-ethoxyresorufin, 7-pentoxyresorufin and 7-ethoxycoumarin O-dealkylases and aminopyrine N-demethylase) were measured in hepatopancreatic microsomes of carp collected in one control and one polychlorinated biphenyl- and polycyclic aromatic hydrocarbon-polluted ponds in the Czech Republic. The magnitudes of responses of monooxygenase activities to the exposure to polycyclic and polyhalogenated aromatic compounds (PAC), namely polycyclic aromatic hydrocarbons and polychlorinated biphenyls, and effects of other factors including ambient temperature and stress associated with reduction of water volume at capture were assessed. An increase of the level of 7-ethoxyresorufin O-deethylase (EROD) i.e. the specific monooxygenase activity mediated by the cytochrome P4501A (CYP1A) isoenzymes, was the most sensitive biochemical marker of environmental pollution and exposure to PAC. Carp hepatic 7-pentoxyresorufin O-depentylase (PROD) was unsuitable as a specific indicator of elevation of cytochrome P4502B-like isoenzymes (and thus as a biomarker of presence of CYP2B-type of inducers e.g. organochlorine pesticides) due to a probable inducibility by CYP1A inducers. PROD, unlike aminopyrine N-demethylase, another mammalian CYP2B-dependent activity which was not increased by exposure to PAC, was strongly inhibited by CYP1A inhibitors, α-naphthoflavone and 9-hydroxyellipticine. The respective dose-response curves were related to the EROD inhibition. Chloramphenicol, an inhibitor of CYP2B enzymes. inhibited both activities only weakly or not at all. Adaptation of carp to lower ambient temperatures and to the stress associated with reduction of water volume and subsequent capture by netting proved to highly significantly inhibit levels of EROD and PROD activities. Summer appeared to be the most suitable season for the biochemical monitoring of contamination. Activity of 7-ethoxycoumarin O-deethylase (ECOD) was also markedly induced by PAC, but the enzyme was less responsive than the EROD activity. The ECOD activity was not significantly influenced by ambient temperature or by stress associated with capture and removal of fish. This probably reflected a modulation of partly different CYP enzymes other than EROD. Unlike in ECOD, the results confirmed the high specificity and sensitivity of induction of CYP1A-dependent EROD activity in carp (PAC in environmental exposure levels affected EROD highly significantly).