Abstract
To better understand the effect of Paralytic Shellfish Toxins (PSTs) accumulation in the digestive gland of the Pacific oyster, Crassostrea gigas, we experimentally exposed individual oysters for 48 h to a PSTs producer, the dinoflagellate Alexandrium catenella. In comparison to the effect of the non-toxic Alexandrium tamarense, on the eight apoptotic related genes tested, Bax and BI.1 were significantly upregulated in oysters exposed 48 h to A. catenella. Among the five detoxification related genes tested, the expression of cytochrome P450 (CYP1A) was shown to be correlated with toxin concentration in the digestive gland of oysters exposed to the toxic dinoflagellate. Beside this, we observed a significant increase in ROS production, a decrease in caspase-3/7 activity and normal percentage of apoptotic cells in this tissue. Taken together, these results suggest a feedback mechanism, which may occur in the digestive gland where BI.1 could play a key role in preventing the induction of apoptosis by PSTs. Moreover, the expression of CYP1A, Bax and BI.1 were found to be significantly correlated to the occurrence of natural toxic events, suggesting that the expression of these genes together could be used as biomarker to assess the biological responses of oysters to stress caused by PSTs.
Highlights
The Pacific oyster Crassostreas gigas, like many other bivalve mollusks, is a filter feeder that consumes microphytoplankton, including toxic dinoflagellates when they occurred
Glutathione S-transferase belongs to a large super-family of multi-functional enzymes primary involved in cellular detoxification by catalyzing the nucleophilic attack by glutathione (GSH) on electrophilic compounds with a wide range of endogenous and xenobiotic agents, including environmental toxins and oxidative stress products [22,23,24,25,26,27]
We previously demonstrated that exposure of oysters to toxic A. catenella induces apoptosis of circulating hemocytes even though Bax and executioner caspases were over-expressed before apoptosis occurred [20]
Summary
The Pacific oyster Crassostreas gigas, like many other bivalve mollusks, is a filter feeder that consumes microphytoplankton, including toxic dinoflagellates when they occurred. Toxins (PSTs) are naturally produced by some cyanobacteria and a number of toxic dinoflagellate species including Alexandrium catenella, Alexandrium minutum, Alexandrium tamarense, Pyrodinium bahamense and Gymnodinium catenatum [1,2,3]. Saxitoxin is one of the most potent and deadly toxins in the world and was shown to be a highly selective blocker of Na+ channels in excitable cells, thereby affecting nerve impulse generation [4] and can lead, in extreme cases, to human death [5]. PSTs. When concentration exceeds the sanitary threshold (800 μg saxitoxin equiv/kg wet weights) farms are closed resulting in economic losses [6]
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