Confinement stress and starvation modulate the induction of EROD activity after dietary exposure to PCB 126 in the Mozambique tilapia (Oreochromis mossambicus)

Polychlorinated biphenyls (PCBs) are environmental pollutants, accumulating in the food chain and inducing cytochrome P450 1A (CYP P450 1A) monooxygenase enzymes. This study aimed to investigate the influence of dietary PCB 126 exposure on cytochrome P4501A-associated enzyme activities in head kidney, liver, gill and intestine of unstressed and stressed tilapia (Oreochromis mossambicus) before and after starvation. Fish were fed diets containing 0 μg (control), 0.5 μg (low) or 50 μg (high) PCB126 per kg body weight per day for 7 days. After the PCB-exposure each treatment group was sampled directly, or was subsequently exposed to confinement stress. Replicate groups remained undisturbed, starved for 3 weeks and were thereafter sampled directly or after confinement. Catalytic activity of CYP P4501A was determined as 7-ethoxyresorufin-O-deethylase (EROD) activity. Directly after PCB exposure and after starvation, EROD activities in liver, gill and head kidney increased with higher PCB dose. Intestinal EROD activities were not detectable at any sampling point. Confinement, known to evoke a stress response increased EROD activities in livers (only directly after PCB exposure) and in head kidneys (directly after PCB exposure and after starvation) but only in fish fed the low PCB-diet. We suggest that stressing tilapia induces EROD activities at non-saturating PCB concentrations and that this effect is more pronounced in nourished than in starved fish. These data show that the cytochrome P450 1A response to toxicants in fish is also influenced by non-chemical factors. This should be considered when EROD activities are used as a biomarker for environmental monitoring studies. This revised version was published online in August 2006 with corrections to the Cover Date.     

Acute effects of benzo[a]pyrene on liver phase I and II enzymes,and DNA damage on sea bream <Emphasis Type="Italic">Sparus aurata</Emphasis>

In the present study biotransformation and detoxification responses to acute exposure to the polycyclic aromatic hydrocarbons benzo[a]pyrene (B[a]P) were investigated in the liver of Sparus aurata (sea bream). Sexually immature gilthead sea bream were treated by intraperitoneal injection of B[a]P (20 mg kg⁻¹) for 6, 12, 24, and 48 h. B[a]P accumulation was quantified in sea bream liver by mean of gas phase chromatography (GPC-MS) after the various exposure periods. The following biological responses were measured: (1) ethoxyresorufin-O-deethylase (EROD) activity, as a phase I biotransformation parameter; (2) liver glutathione S-transferase (GST) activity as a phase II conjugation enzyme. DNA damage was assessed over time using the single-cell gel electrophoresis comet assay. B[a]P bioaccumulation in the liver resulted in a biphasic curve with an increasing uptake up to 5.55 ± 0.67 μg g⁻¹ dry weight after only 6 h exposure and 4.67 ± 0.68 μg g⁻¹ dry weight after 48 h exposure. EROD activity showed a nonsymmetrical bell-shaped kinetic with a maximum at 24 h and lower but significant activities at 12 and 48 h with respect to control animals. Hepatic GST activities were only significant after 48 h exposure. Comet assay showed an increase in liver cells DNA damage with a maximum after 48 h exposure reaching up to 12.17 %DNA in the tail.