The Toxic Responses Of The Polychaete (periereis Nuntia Savigy) To The Benzo[a]pyrene

Benzo[a]Pyrene (B(a)P) is one of polycyclic aromatic hydrocarbons (PAHs), which are widely distributed and persistent in the aquatic environment. This contaminant has been shown to be genotoxic, endocrine-toxic, imuno-toxic, nerve-toxic, teratogenic and carcinogenic to a broad range of organisms. Data to date show that the level of B(a)P in the sediment has been in a high level that may pose threats to the deposit-feeders such as polychaetes. Polychaetes such as sandworms play an important role on the marine food chain in terms of their great contribution to the material cycling and energy flowing of the marine ecosystem. However, the studies about the toxicity of B(a)P to these animals are very limited until now. In the present study, we employed the sandworm Periereis nuntia Savigy, one of the most common benthic polychaetes in Chinese coastal area, as the model to stduy the potential effects of B(a)P on deposit-feeders. The sandworms Periereis nuntia Savigy were exposed to 2.5μg/L and 50μg/L B(a)P for 14 days, and samples were then collected for analysis of lipid peroxidation, antioxidative enzymes, detoxification enzymes, DNA damage, apoptosis and histological changes etc.. The mechanisms laid behind were also discussed.The results showed that both concentrations of B(a)P caused significant increase in lipid peroxidation compared the DMSO treated group (P<0.01). The antioxidative enzymes, including SOD, GSH-PX and GST were also enhanced significantly in both exposure groups (P<0.05). GSH concentration (P<0.01) decreased significantly in both exposure groups.The quantitative PCR results showed that the levels of CYP450 genes, including CYP2u, CYP3A and CYP4A, which played important roles in phase I detoxification, were all significantly induced in the 2.5μg/L B(a)P exposed group (P<0.01), which were 23.3-, 23.5- and 1203-folds to the control, respectively. However, in the 50μg/L B(a)P exposed group, these three enzymes were less induced compared to the low concentration group and no significant increases or decreases were observed. There was no significant changes detected in the level of CYP4B gene for both exposure groups, which might imply that the CYP4B gene and its coded protein is not involved in the detoxification of B(a)P in the sandworms. GST activity, which was orientated in the phase II detoxification, was induced significantly (P<0.01) only in the 2.5μg/L B(a)P exposed group but not in the 50μg/L exposure group. The Tunnel assay and DNA laddering were employed to detect the DNA damage in this study. The results of Tunnel assay showed that there were only a little apoptotic cells in the lower concentration (2.5μg/L B(a)P), while a lot of in the higher (50μg/L B(a)P). All of the apoptotic cells were found to occur in the celom. DNA laddering results showed that there were lots of DNA fragments which could be seen clearly through the gel in the 50μg/L B(a)P, though no clear 180-DNA-ladderring, while there was fragments recorded in the lower concentration group(2.5μg/L B(a)P). In addition, two of important apoptosis genes, caspase 8 and PDCD 10 were analyzed through the quantitative Real-Time PCR. Data showed that the level of both genes were all significantly induced in the lower concentration (2.5μg/L B(a)P), but there were no changes in the higher concentration group (50μg/L B(a)P).For the histological examination, after 14 days B(a)P exposure, there were some obvious changes in the outer muscle layers (longitudinal muscle) and celom cells, detected by regular HE-dyeing of histopathology analysis. In the 2.5μg/L B(a)P exposed group, the outer muscle layers became thicker clearly compared to the control, while there was no difference in the inner muscle layers. Most of the celom cells broke up, and the inclusion was released, whereas some cells agglomerated to be a big cell-cluster. In the 50μg/L B(a)P exposed group, the outer muscle layers were surrounded by several annulations, and the layer became thicker significantly. All of the celom cells broke up, and the the inclusion was released into the celom which gathered up to be a amylaceous fabric and no cell clusters were obeserved.This was the first time to use the polychaete Periereis nuntia Savigy to detect the potential effects of B(a)P on the marine deposit-feeding invertebrates. After 14 days B(a)P exposure, there were some obvious toxic performances on the polychaete Periereis nuntia Savigy. As intake of the B(a)P, a series of metabolites were produced, resulting in generation of some reactive oxygen species, such as O2-, H2O2 , HO·and so on, which was indicated by some obvious oxidative damages, e.g. lipid peroxidation in this study. The significant increase of antioxidative enzyme systems (SOD, CAT, GSH, GR, GSH-PX); the significant induction of detoxification systems, such as the molecular levels of CYP450s of phase I and the GST activity of the phase II; finally, the oxidative damage of DNA and the appearance of apoptosis; of course, there were some obvious damage to the celom cells and issues. The results here laid basic foundation for possible future's marine biomonitoring by using polychaetes.