Transcriptional and biochemical analysis of antioxidant enzymes in the mussel Mytilus galloprovincialis during experimental exposures to the toxic dinoflagellate Prorocentrum lima

- DSP toxins are produced by HABs of Dinophysis and Prorocentrum dinoflagellates, being mainly accumulated by marine organisms.
- Bivalves display resistance to DSP toxins, but little is known about the protective mechanism observed in these organisms.
- This work studies the expression and biochemical activities of antioxidant enzymes in the mussel Mytilus galloprovincialis.
- Results show a down-regulation of these genes which is counterbalanced by the up-regulation of other antioxidant genes.
- Activity analyses reveal high antioxidant activity levels along with reduced lipid peroxidation.

The genotoxic and cytotoxic effects of Diarrhetic Shellfish Poisoning (DSP) toxins have been widely investigated in bivalve molluscs, representing the main vectors of these compounds in the Atlantic coast of Europe. DSP toxins are produced by Harmful Algal Blooms (HABs) of Dinophysis and Prorocentrum dinoflagellates, being subsequently accumulated by marine organisms and biomagnified throughout trophic webs. Yet, bivalves display increased resistance to the harmful effects of these toxins during HAB episodes. While previous reports have suggested that such resilience might be the result of an increased activity in the bivalve antioxidant system, very little is still known about the specific mechanism underlying the protective effect observed in these organisms. The present work aims to fill this gap by studying transcriptional expression levels and biochemical activities of antioxidant enzymes in different tissues the mussel Mytilus galloprovincialis during experimental exposures to DSP toxins produced by the dinoflagellate Prorocentrum lima. Results are consistent with the presence of a compensatory mechanism involving a down-regulation in the expression of specific genes encoding antioxidant enzymes [i.e., SuperOxide Dismutase (SOD) and CATalase (CAT)] which is counterbalanced by the up-regulation of other antioxidant genes such as Glutathione S-Transferase pi-1 (GST-pi) and Selenium-dependent Glutathione PeroXidase (Se-GPx), respectively. Enzymatic activity analyses mirror gene expression results, revealing high antioxidant activity levels (consistent with a protective role for the antioxidant system) along with reduced lipid peroxidation (increasing the defense against oxidative stress).