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Dose dependent effects of Benzo[a]pyrene
(BaP) on cytochrome P4501A (CYP1A), glutathione-
S-transferase (GST) and fluorescent aromatic compounds
(FACs) metabolites biomarker responses
were studied in African sharptooth catfish (Clarias
gariepinus) following 24 h of waterborne exposures.
Based on biomass of C. gariepinus in different tanks,
BaP concentrations of 1.60, 3.44, and 18.21 lg/L that
corresponded to 0.5, 1.0, and 5.0 mg/kg body weight
were used. Significant induction of EROD activities
in gill filaments was observed at all doses and the accumulation of FACs metabolites in bile was significantly
different between groups. Accumulation of
FACs metabolites in bile strongly correlated
(r2 = 0.99) with BaP doses. Hepatic EROD activities
were undetectable and no effect on GST activities
was observed. The highest dose of BaP from the dose
dependent study was further studied to assess the
interactive and temporal responses of C. gariepinus
on CYP1A, GST, and FACs metabolites biomarkers
following exposure to either BaP alone, 17a-ethynylestradiol
(EE2) alone or a combination of both
compounds at concentrations of 54.17 lg/L for BaP,
51.38 lg/L for EE2 and 54.44 lg/L for each of both
compounds. Based on biomass in each tank, these
concentrations corresponded to 5 mg/kg body weight.
While a group of six fish was sacrificed on day 0 from
the control tank only, other groups of six fish were
sacrificed after 1, 3, and 6 days of exposure from the
control and exposed groups. Maximum induction of
gill filament and hepatic EROD activities was observed
after 1 day of exposure. Both EROD activities
in gill filaments and liver were significantly induced
by exposure to BaP alone or co-administration with
EE2. Gill filament EROD induction was significantly
inhibited (50%) by co-administration of BaP and EE2
compared to administration of BaP alone. Levels of
FACs in bile for BaP and BaP + EE2 exposed groups
were significantly different from the control at all
doses and time points. A significant induction of GST
activities was observed in fish exposed to BaP and
BaP + EE2 after 3 days. Exposure to EE2 alone
caused significant induction of this enzyme after day
6. This study reports for the first time the significant
antagonistic influence of EE2 on BaP in gills of fish
following waterborne exposures. The results also indicate that chemical mixtures may affect biomarker
responses differently from compounds administered
alone and that the sensitivity of CYP1A to interactive
chemicals is different in gills and liver. |
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