Comparative Studies of Pollution Induced Microsomal Nadph-Dependent Cytochrome P-450 Monooxygenase Enzyme Complex of Tilapia Species

Abstract

The baseline levels of hepatic microsomal proteins of cytochrome P-450 monooxygenase enzyme complex of two economically important tilapia species, Oreochromis! niloticus and Seratherodon. galilaeus. Were measured and compared with the levels of the enzyme in O. niloticus injected with J5-naphthoflavone (fl-NF) a classical inducer of cytochrome P-4501A isozyme, and O. niloticus exposed to effluents from Akosombo Textiles Limited (ATL-E). This was done in order to find out if this enzyme complex could be used as a biomarker to determine the ATL effluent effects on the fish species in the Volta Lake into which the effluent is discharged. The relationship between exposure to the pollutants and the health status of the fishes was assessed by measuring two biological indices - condition factor (CF) and liver I somatic index (LSI). Total protein concentration was determined by the Folin-Lowry method. The activities of NADPH cytochrome P -450 reductase, a component of the monooxygenase enzyme complex, were measured using reduction of exogenous cytochrome c. Cytochrome P-450 enzyme activity was measured using ethoxyresorufin-O-deethylase (EROD) assay which indicates specifically the induction of cytochrome P-4501A isozyme. The results indicate no relationship between the exposure to the pollutants, ATL-E and fi-NF, and the CF (one of the biological indices). On the other hand, there was a relationship between exposure to ATL-E and the health status of the fish expressed as liver somatic index (LSI). The results further indicate that the total microsomal protein concentration and the total cytochrome P-450 reductase activity of $. Galilaeus were 2-fold and 1.5-fold higher than the values in Q. niloticus. The total microsomal protein concentration of the ATL-E controls, that is fishes at Konkontekope, showed a significant increase relative to the aquarial fi-NF controls. In spite of the higher protein concentration of the ATL-E control fishes over the aquarial controls, there was no difference in their total reductase activity. Both types of control fishes as well as the S- ealilaeus did not show any response to the EROD assay indicating the absence of cytochrome P-4501A isozyme in the microsomal proteins induced. There was a significant increase in the total microsomal protein concentration of test fishes over their controls. Microsomes from fishes exposed to the ATL effluent showed increases in the total NADPH cytochrome P-450 reductase activity compared to their controls, unlike the microsomes from fishes injected with fl-NF. However, microsomes prepared from both 13-NF-injected and ATL-E exposed fishes responded to the EROD assay indicating the presence of cytochrome P-4501A isozyme induction by these pollutants. The induction of total NADPH cytochrome P-450 reductase by the factory effluent suggests that the xenoorganics in the factory effluent could belong to the PB-type or the third type of inducers. That the cytochrome P-4501A protein was induced by the factory effluent, as evidenced by the positive response to EROD assay, indicates that the effluent contains the 3-methylcholanthrene type of inducers. This study h^s indicated that the effluent from the Akosombo Textiles Limited contains a mixture of inducers - the 3-MC type, the PB-type and the third type. The three types of inducers may act synergistically to promote the induction exhibited. The molecular weight(s) of the monooxygenase isozymes induced by both BNF and ATL-E were resolved electrophoretically on 10% SDS-PAG. The BNF and ATL-E exposed fishes were found to induce protein isozymes with similar electrophoretic mobilities with an approximate molecular weight of 53,700 daltons.