Effects of feeding Alexandrium tamarense, a paralytic shellfish toxin producer, on antioxidant enzymes in scallops (Patinopecten yessoensis) and mussels (Mytilus galloprovincialis)

• Scallops and mussels were fed with PST-producing algae Alexandrium tamarense.
• Variation of ROS and response of antioxidant enzymes were monitored in shellfish.
• SOD activity was inhibited, and CAT activity was not stimulated in scallops.
• Both SOD and CAT activities in tissues of mussels were induced to remove ROS.
• Similar dynamic fluctuations of GSH-Px activity were found in both bivalves.

Contamination of molluscan bivalves with paralytic shellfish toxins (PST) is a frequent occurrence worldwide. Paralytic shellfish poisoning (PSP) events seriously threaten consumers' health and shellfish economy. It is worthwhile to investigate the dynamic response of antioxidant enzymes to PST accumulated by bivalves, since this will help us explore the mechanisms for accumulation and biotransformation of PST in shellfish. In this study, scallops (Patinopecten yessoensis) and mussels (Mytilus galloprovincialis) were fed in the laboratory with Alexandrium tamarense (ATHK), a PST-producing dinoflagellate. Dynamic variations of reactive oxygen species (ROS) and antioxidant enzymes including superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6) and glutathione peroxidase (GSH-Px, EC 1.11.1.9) were monitored in the muscle and digestive gland of experimental shellfish. Results showed that ROS was quickly generated and then disappeared in the tissues of scallop and mussel in the PST-accumulating and depurating periods, and that different response of antioxidant enzymes to ROS occurred in the two different bivalves. SOD activity was obviously inhibited in the tissues of scallop, while the CAT activity was not stimulated by the toxic bait in scallop. However, both SOD and CAT activities were induced in the tissues of mussel to effectively scavenge superoxide anion free radical and H2O2. Similar dynamic fluctuation of GSH-Px activity was also stimulated to remove H2O2 or other superoxide compounds in the tissues of both bivalves, which was hypothetically modulated by the depletion and regeneration of glutathione. Only GSH-Px enzyme was induced to remove ROS in scallop, but all SOD, CAT, and GSH-Px enzymes were stimulated to avoid oxidative stress in mussel. The species specific response of antioxidant enzymes between scallop and mussel fed with toxic A. tamarense has been described here for the first time.