Transcriptional and catalytic responses of antioxidant and biotransformation pathways in mussels, Mytilus galloprovincialis, exposed to chemical mixtures.

tAntioxidant and biotransformation pathways are widely studied in marine organisms exposed to envi-ronmental stressors. However, mechanisms of responses and links between different intracellular levelsare not always easy to elucidate and conflicting results are frequently observed between molecular andenzymatic data. In this study, transcriptional and catalytic responses of antioxidant and biotransforma-tion parameters were analyzed after a 4-week exposure of a marine invertebrate, Mytilus galloprovincialis,to chemical mixtures from low polluted and highly polluted sediments. A significant, dose-dependentbioaccumulation was observed for polycyclic aromatic hydrocarbons, especially low molecular weightcompounds. Among antioxidant defences, catalase and glutathione peroxidases did not exhibit variationsin enzymatic activity, while the corresponding gene transcriptions were up- and down-regulated, respec-tively; unchanged mRNA levels of superoxide dismutase confirmed the non-synchronous pathways ofvariations for such antioxidants. Biotransformation responses also revealed inconsistent trends betweentranscriptional and catalytic variations of glutathione S-transferases, and a significant increase in mRNAlevels for cytochrome P450 3A1. The overall results indicated that transcriptional responses might be sen-sitive but do not necessarily correspond to functional changes, being more useful as “exposure” ratherthan “effect” biomarkers. Data on gene transcription and catalytic activities should be carefully inter-preted when assessing the impact of chemical pollutants and additional studies are needed on modulationof post-transcriptional mechanisms by environmental stressors.