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- Svensson, Susanne, 1964, et al.
(author)
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Analysis of the importance of lipid breakdown for elimination of okadaic acid (diarrhetic shellfish toxin) in mussels, Mytilus edulis: results from a field study and a laboratory experiment
- 2004
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In: Aquatic Toxicology. - : Elsevier BV. - 0166-445X. ; 66:4, s. 405-418
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Journal article (peer-reviewed)abstract
- Okadaic acid (OA) is a lipophilic phycotoxin, which accumulates in the digestive organs of mussels and may cause diarrhetic shellfish poisoning (DSP) in humans. Depuration of toxic mussels is a potential option for the shellfish industry to increase the availability of marketable mussels. To develop cost-effective deputation methods for DSP toxins, knowledge about the environmental conditions and physiological processes regulating the rate of depuration is essential. In this paper, the importance of lipid breakdown for elimination of OA in mussels was investigated by performing a field study and a manipulative laboratory experiment. First, total lipid content and concurrent concentration of OA in the digestive glands of farmed blue mussels, Mytilus edulis, was analysed on a monthly basis from January to June 2000. A significant positive correlation between levels of OA and lipid content was observed between January and March, when lipid levels were showing a decreasing trend. This supported a previously proposed model that breakdown of lipid stores may affect the release and elimination of this lipophilic toxin. To test this causal model, a laboratory experiment was performed. Mussels containing OA were exposed to experimental treatments (increased seawater temperature and/or food limitation) for 24 days in order to increase the energy requirements and need to use lipids as an energy source. It was predicted that mussels exposed to these treatments would have a faster elimination rate of OA compared to feeding mussels kept in ambient seawater temperature. The results showed that lipid content was significantly reduced in mussels exposed to an increased water temperature (24 degreesC) compared to ambient temperature (18 degreesC). The amount of lipids was not affected by food limitation. Although lipid content was-reduced in 24 degreesC, the rate of depuration of OA was not faster for mussels in this treatment and no correlation was detected between lipid content and, OA. Depuration rates were very similar for all treatments and followed an exponential decrease relationship (t(1/2) = 8 days). Thus, the proposed model that lipid breakdown affects the mechanism of elimination of OA was not supported. Nevertheless, the observed rates of depuration provide useful information and a potential predictive too] for large-scale depuration methods of mussels. The difficulties to influence the rate of depuration of this toxin by changing the environmental conditions suggest that processes, insensitive to short-term manipulation of the external environment, regulate depuration of OA. (C) 2003 Elsevier B.V. All rights reserved.
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| 2. |
- Svensson, Susanne, 1964, et al.
(author)
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Mussel blood cells, resistant to the cytotoxic effects of okadaic acid, do not express cell membrane p-glycoprotein activity (multixenobiotic resistance)
- 2003
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In: Aquatic Toxicology. - 0166-445X. ; 65:1, s. 27-37
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Journal article (peer-reviewed)abstract
- Okadaic acid (OA) is a dinoflagellate toxin, accumulating in shellfish and causing diarrhetic shellfish poisoning (DSP) in humans. OA is a highly cytotoxic agent in most cell lines because of its inhibiting properties of protein phosphatases. So far, the cytotoxicity of OA in mussels, the main vectors of DSP, has not been investigated. In this paper, the viability of mussel (Mytilus edulis) blood cells incubated in 10 nM-1 muM OA was studied. After 72 It of exposure, viability was reduced to 54% in 1 muM OA compared with 88% in control cells. This yielded a LC50 of > 1 muM for OA, which is 30-1000-times higher compared with other cell types. It was hypothesised that P-glycoprotein (p-gp) activity (multixenobiotic resistance, MXR) contributed to the resistance to OA. Vincristine and rhodamine B was used as p-gp substrates and verapamil or staurosporine (ST) as inhibitors of p-gp transport. However, no indications of cell membrane p-gp activity were detected. Instead, experimental observations led to the conclusion that a MXR transport system was present within lysosomal membranes. Various concentrations of OA did not affect the dynamics of vincristine in blood cells. As a positive control for the assay, p-gp activity was measured in mussel gill tissue. The efflux of rhodamine B was reduced by verapamil, which is, considered evidence for cell membrane p-gp activity, thus the accuracy of the method was confirmed. Rhodamine B efflux was also reduced by OA in gill tissue, which suggested that OA is either a competitive substrate or inhibitor of p-gp activity. When the volume of the lysosomal compartment was measured in blood cells pre-exposed to OA, a significant increase was detected compared with control cells. It was proposed that uptake and storage of OA within the lysosomal system might protect mussel blood cells from the cytotoxic effects of this compound. (C) 2003 Elsevier B.V. All rights reserved.
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