Extraction recoveries and stability of diarrhetic shellfish poisoning (DSP) toxins in naturally contaminated samples

Histopathological alterations induced by marine environmental pollutants on the bivalve Cerastoderma glaucum (Bruguière 1789) from Temsah Lake, Suez Canal, Egypt

Bivalves are considered a main consumed matrix for coastal communities worldwide and classified as hyperaccumulators of pollutants. The present study aims to determine some micro-organisms, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and okadaic acid (OA) levels in Cerastoderma glaucum collected from Temsah Lake, Egypt, and their induction through histopathological damage and caspase-3 protein expression. During the autumn, it was found different types of biological and chemical pollutants, especially benzo[a]pyrene (BaP) that accumulated in C. glaucum soft tissues and exceeded the safety limit for shellfish consumption. Dioxin-like PCB3 was predominant in C. glaucum soft tissues during autumn, but the total levels of PCBs in these tissues have not exceeded the permissible limit. Chlorophyll-a (Chl. a), nutrient concentrations, and Prorocentrum lima dinoflagellates in the water significantly increased during autumn. High P. lima abundance was confirmed by high OA in the soft tissues during this season compared to the other seasons. The measured contaminants may render C. glaucum more susceptible to bacterial and fungal infections. The autumn season showed a significant increase in the colony-forming units (CFU). C. glaucum showed calcification abnormalities and adhering of abnormal brown organic material to the inner surface of the shell valves, which was related to poor water conditions and Vibrio infection. Damages or injuries on gills and digestive gland tissues indicated an impact of the pollutants on C. glaucum. Also, high expressions of caspase-3 were recorded in these tissues during all the seasons. So, C. glaucum cockles, collected from Temsah Lake, may induce serious diseases to consumers, especially when eaten raw or insufficient cooking.

Response of fatty acids and lipid metabolism enzymes during accumulation, depuration and esterification of diarrhetic shellfish toxins in mussels (Mytilus galloprovincialis)

Bivalve mollusks accumulate diarrhetic shellfish toxins (DSTs) from toxigenic microalgae, thus posing a threat to human health by acting as a vector of toxins to consumers. In bivalves, free forms of DSTs can be esterified with fatty acids at the C-7 site to form acyl esters (DTX3), presumably a detoxification mechanism for bivalves. However, the effects of esterification of DSTs on fatty acid metabolism in mollusks remain poorly understood. In this study, mussels (Mytilus galloprovincialis) were fed the DST-producing dinoflagellate Prorocentrum lima for 10 days followed by an additional 10-days depuration in filtered seawater to track the variation in quantity and composition of DST acyl esters and fatty acids. A variety of esters of okadaic acid (OA) and dinophysistoxin-1 (DTX1) were mainly formed in the digestive gland (DG), although trace amounts of esters also appeared in muscle tissue. A large relative amount of OA (60%-84%) and DTX1 (80%-92%) was esterified to DTX3 in the visceral mass (referred to as digestive gland, DG), and the major ester acyl chains were C16:0, C16:1, C18:0, C18:1, C20:1 and C20:2. The DG and muscle tissues showed pronounced differences in fatty acid content and composition during both feeding and depuration periods. In the DG, fatty acid content gradually decreased in parallel with increasing accumulation and esterification of DSTs. The decline in fatty acids was accelerated during depuration without food. This reduction in the content of important polyunsaturated fatty acids, especially docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), would lead to a reduction in the nutritional value of mussels. Enzymes involved in lipid metabolism, including acetyl-coenzyme A carboxylase (ACC), fatty acid synthase (FAS), lipoprotein lipase (LPL) and hepatic lipase (HL), were actively involved in the metabolism of fatty acids in the DG, whereas their activities were weak in muscle tissue during the feeding period. This study helps to improve the understanding of interactions between the esterification of DSTs and fatty acid dynamics in bivalve mollusks.

Saxitoxins and okadaic acid group: accumulation and distribution in invertebrate marine vectors from Southern Chile

Harmful algae blooms (HABs) are the main source of marine toxins in the aquatic environment surrounding the austral fjords in Chile. Huichas Island (Aysén) has an history of HABs spanning more than 30 years, but there is limited investigation of the bioaccumulation of marine toxins in the bivalves and gastropods from the Region of Aysén. In this study, bivalves (Mytilus chilenses, Choromytilus chorus, Aulacomya ater, Gari solida, Tagelus dombeii and Venus antiqua) and carnivorous gastropods (Argobuccinum ranelliformes and Concholepas concholepas) were collected from 28 sites. Researchers analysed the accumulation of STX-group toxins using a LC with a derivatisation post column (LC-PCOX), while lipophilic toxins (OA-group, azapiracids, pectenotoxins and yessotoxins) were analysed using LC-MS/MS with electrospray ionisation (+/-) in visceral (hepatopancreas) and non-visceral tissues (mantle, adductor muscle, gills and foot). Levels of STX-group and OA-group toxins varied among individuals from the same site. Among all tissue samples, the highest concentrations of STX-group toxins were noted in the hepatopancreas in V. antiqua (95 ± 0.1 μg STX-eq 100 g(-1)), T. dombeii (148 ± 1.4 μg STX-eq 100 g(-1)) and G. solida (3232 ± 5.2 μg STX-eq 100 g(-1); p < 0.05); in the adductor muscle in M. chilensis (2495 ± 6.4 μg STX-eq 100 g(-1); p < 0.05) and in the foot in C. concholepas (81 ± 0.7 μg STX-eq 100 g(-1)) and T. dombeii (114 ± 1.2 μg STX-eq 100 g(-1)). The highest variability of toxins was detected in G. solida, where high levels of carbamate derivatives were identified (GTXs, neoSTX and STX). In addition to the detected hydrophilic toxins, OA-group toxins were detected (OA and DTX-1) with an average ratio of ≈1:1. The highest levels of OA-group toxins were in the foot of C. concholepas, with levels of 400.3 ± 3.6 μg OA eq kg(-1) (p < 0.05) and with a toxic profile composed of 90% OA. A wide range of OA-group toxins was detected in M. chilensis with a toxicity < 80 μg OA eq kg(-1), but with 74% of those toxins detected in the adductor muscle. In all evaluated species, there was no detection of lipophilic toxins associated with biotransformation in molluscs and carnivorous gastropods. In addition, the STX-group and OA-group toxin concentrations in shellfish was not associated with the presence of HAB. The ranking of toxin concentration in the tissues of most species was: digestive glands > mantle > adductor muscle for the STX-group toxins and foot > digestive gland for the OA-group toxins. These results gave a better understanding of the variability and compartmentalisation of STX-group and OA-group toxins in different bivalve and gastropod species from the south of Chile, and the analyses determined that tissues could play an important role in the biotransformation of STX-group toxins and the retention of OA-group toxins.

Production of monoclonal antibody and application in indirect competitive ELISA for detecting okadaic acid and dinophytoxin-1 in seafood

BACKGROUND, AIM, AND SCOPE

Okadaic acid (OA) and analogues of dinophysistoxin (DTX) are key diarrheic shellfish poisoning (DSP) toxins, which possibly arouse DSP symptoms by consuming the contaminated shellfish. Because of the stable toxicity in high temperature and the long-term carcinogenicity, the outbreaks of DSP related to consumption of bivalve mollusks contaminated by DSP toxins pose a hazard to public health. Therefore, it is worth developing a fast and reliable analytical method for the detection of OA and analogues in shellfish. In this paper, an indirect competitive enzyme-linked immunosorbent assay (ELISA) (icELISA) for detecting OA and DTX-1 in seafood was developed based on monoclonal antibody (McAb).

METHODS

The OA was conjugated to human immunoglobulin G (IgG) and bovine serum albumin (BSA) by the active ester method as the immune antigen and the detective antigen. The spleen cells from BALB/c mice immunized with OA-IgG were fused with SP2/0 myeloma cells. A hybridoma cell line, which secreted McAb against OA, was selected by "limiting dilution" cloning. An icELISA was developed based on immobilized conjugate (OA-BSA) competing the McAb with the free OA in seafood sample.

RESULTS

A hybridoma cell line, which secreted IgG1 subclass monoclonal antibody (McAb) against OA, was selected. The IC(50) of the McAb for OA and dinophytoxin-1 (DTX-1) were 4.40 and 3.89 ng/mL, respectively. Based on the McAb, an indirect competitive ELISA for detection of OA and DTX-1 in seafood was developed. The regression equation was y = 54.713x - 25.879 with a coefficient correlation of R (2) = 0.9729. The linear range and the limit of detection were 0.4-12.5 and 0.45 ng/mL, respectively. The average recovery of OA and DTX-1 spiked shellfish was 82.29% with the coefficient of variation of 7.67%.

CONCLUSION

The developed icELISA is a fast, sensitive, and convenient assay for detecting of total amount of OA and DTX-1 in seafood.

A mussel tissue certified reference material for multiple phycotoxins. Part 3: homogeneity and stability

A candidate certified reference material (CRM) for multiple shellfish toxins (domoic acid, okadaic acid and dinophysistoxins, pectenotoxins, yessotoxin, azaspiracids and spirolides) has been prepared as a freeze-dried powder from mussel tissues (Mytilus edulis). Along with the certified values, the most important characteristics for a reference material to be fit-for-purpose are homogeneity and stability. Acceptable between-bottle homogeneity was found for this CRM. Within-bottle homogeneity was assessed using domoic acid, and it was shown that repeated subsampling of the CRM can be performed precisely down to 0.35 g. Both short- and long-term stability studies carried out under isochronous conditions demonstrated excellent stability of the various toxins present in the material. While degradation of some analytes was observed at +60°C in short-term studies, it was determined that shipping at ambient temperature is adequate. No instability was detected in long-term stability studies, and it was shown that the material can be held at +18°C safely for up to 1 year. To guarantee stability of the CRM over its lifetime the stock will be maintained at -20°C. The results of the homogeneity and stability testing show that CRM-FDMT1 is appropriate for its intended use in quality assurance and quality control of shellfish toxin analysis methods.