Comparative Studies Of Pollutioninduced Microsomal Nadph-Dependent Cytochrome P-450 Monooxygenase Enzyme Complex Of Til Apia Species

A B S T R A C T

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.

X

x i

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.