Metabolic Transformation Of Paralytic Shellfish Toxins By Bivalve Molluscs And Their Physiological And Biochemical Responses

In recent years, harmful algal blooms (HABs) frequently occur in coastal watersworldwide, especially the frequency and scale of toxic algal blooms are risingobviously. Phycotoxins, as a kind of new micro-pollutants, are transferred into shellfishbodies and transformed to complex shellfish toxins, which potentially threatens thesustainable development of shellfish aquaculture and health of consumers. Paralyticshellfish toxins (PST) are a kind of shellfish toxins characterized by high toxicity, widedistribution, and many derivatives, which have caused poisoning incidents, victims,and huge economic losses for many times. Thus, PST is a required monitoring item forshellfish export trade. Rencently, some new compounds (such as M1-4) are detected inshellfish contaminated by PST-producing dinoflagellate. They are hydroxyl ordihydroxy derivatives of PST at C11site, which are considered as metabolicintermediates or products in detoxification process due to relatively low toxicity. Thisdiscovery provides a new target for interpreting metabolic profiling of PST in shellfish,and points out a direction for metabolomic study on shellfish toxins.In this thesis, these metabolites were focused as targets, and scallop Patinopectenyessoensis and mussel Mytilus galloprovincialis were selected as model organisms.Components of PST and responses of antioxidant enzymes were monitored inshellfishes fed with PST-producing algae in laboratory. Meanwhile the mixtures of PSTand digestive gland tissues of shellfish were incubated in order to explore the metabolicpathways of PST in shellfish and its influencing factors. Some original data andtheoretical basis will be accumulated for developing rapid detoxification technologyand antidote for PST toxins. It is very significant to support the sustainabledevelopment of shellfish aquaculture and to protect consumer health.The results of PST-accumulating and depurating experiments for mussels fed with ATHK algae showed that: M1and M5metabolites were detected in the digestive glandtissue of mussel after feeding1day, and M3, M4, M7metabolites were also detectedin the following period. It is the first time to testify that these metabolites will beproduced in mussels after they eat PST-producing alage. And it is hypothesized thatmussel can quickly discharge these metabolites in order to improve the efficiency ofdetoxification. At the same time, the transformation of β epimer to α epimer (such asC2â†'C1,C4â†'C3), and the reduction reaction of hydroxyl group at N1site (such asGTX6-GTX5) were found in the digestive gland of mussel, but no degradation of N-sulfcarbamoyl group occurred in the experimental period. Meanwhile, it ishypothesized that the derivatives with hydroxy group at N1site may be discharged easyby mussel.The results of incubation experiments for PST and digestive gland tissues ofshellfish showed that: no obvious transformation of PST components and no newmetabolites were found in all incubating mixtures with PST standard toxins and toxinextract of ATHK algae. The digestive gland tissue of mussel demonstrated slightlystronger ability than that of scallop for catalyzing PST transformation. Addingglutathione reductase to the digestive gland tissues of shellfish could promote theconversion of N-sulfcarbamoyl toxins from α epimer to β epimer (C1â†'C2). Comparedwith scallop, addition of glutathione reductase to the digestive gland tissue of musselcan obviously promote the conversion of ammonia acyl toxins from α epimer to βepimer (GTX1â†'GTX4, GTX2â†'GTX3).The results of simulating experiments of scallops and mussels fed on Alexandriumtamarense (ATHK) with low density (about600cells/mL) showed that: reactiveoxygen species (ROS) were produced in both muscle and digestive gland tissues, andthe concentration of ROS in muscle tissue was significantly higher than that in digestivegland tissue; while the malondialdehyde (MDA) as the product of lipid peroxidationwas mainly produced in digestive gland tissue. The catalase (CAT) activity was notactivated, meanwhile the superoxide dismutase (SOD) was activated after a slightinhibition, and the ROS was mainly removed by the antioxidant enzymes such asglutathione peroxidase (GSH-Px), glutathione reductase (GR) and glutathione S- transferase (GSTs) in scallop tissues. However, the SOD and CAT enzymes wereactivated successively to remove ROS, and the activity of GSH-Px, GR and GSTsenzymes did not change obviously in mussel tissues. Therefore, the responses ofantioxidant enzyme system to PST toxins showed some differences between scallopand mussel fed with the PST-producing algae with low density.