Suitability of the MTT-based cytotoxicity assay to detect okadaic acid contamination of mussels

Effects of methanolic extract and fractions from Litsea cubeba bark on the production of inflammatory mediators in RAW264.7 cells

Both the methanolic extract and its fractions (0.01 mg/ml) from Litsea cubeba bark were found to inhibit NO and PGE2 production in LPS-activated RAW264.7 macrophages without significant cytotoxicity at less than 0.01 mg/ml concentration. Moreover, L. cubeba bark extract and its fractions significantly decreased the activity of myeloperoxidase catalyzing oxidation of chloride to HOCl and O2- production was reduced by methanol extract (0.05 mg/ml), chloroform fraction (0.025-0.05 mg/ml) and butanol fraction (0.005 mg/ml). These findings suggest that L. cubeba is beneficial for inflammatory conditions and may contain compound(s) with anti-inflammatory properties.

Immunomodulating Activities of Polysaccharides Isolated fromPanax ginseng

Panax ginseng C.A. Meyer has been traditionally used for the prevention and treatment of various chronic diseases and infections. Ginseng marc is a fibrous and insoluble by-product remaining after the extraction process of ginseng. In this research an extrusion process was employed to disintegrate the insoluble ginseng marc structure, and water-soluble ginseng marc polysaccharide (GMP) was isolated. GMP was examined for immunomodulatory effects in murine peritoneal macrophages. GMP significantly increased the lysosomal phosphatase activity and the phagocytic index of peritoneal macrophages (P<.05). The peritoneal macrophages treated with GMP also produced significantly more H(2)O(2) and nitrite than the control without GMP treatment (P<.05). In addition, GMP (100 microg/mL) significantly increased the cell viability of peritoneal macrophages (P<.05). These results suggest that GMP is an effective nonspecific immunomodulatory agent, and its immunostimulating effects may be due to its ability to stimulate the production of reactive oxygen intermediates.

Immune cell stimulating activity of mucopolysaccharide isolated from yam (Dioscorea batatas)

Mucopolysaccharide (YMP) of yam (Dioscorea batatas Decne) was tested for immunomodulatory activity in vitro. We examined the effect of YMP on the viability, cell-mediated cytotoxicity and IFN-gamma secretion of splenic lymphocytes. The cytotoxic activity of mouse splenocyte against leukemia cell was increased in the presence of YMP (10 microg/ml). However, YMP (10 microg/ml) did not affect the viability of splenocytes. The production of IFN-gamma was significantly increased in the YMP treated splenocytes, suggesting that YMP may induce cell-mediated immune responses. The effects of YMP on phagocytic activity were studied in relation to uptaking capacity and lysosomal phosphatase activity of the mouse peritoneal macrophages in vitro. YMP (50 microg/ml) was found to increase uptaking capacity and lysosomal phosphatase activity of peritoneal macrophages. In addition, YMP (10-100 microg/ml) significantly increased the viability of peritoneal macrophages (P<0.05). The data obtained demonstrate that the YMP may be used as sources of immunoactive polysaccharides.

Mussel blood cells, resistant to the cytotoxic effects of okadaic acid, do not express cell membrane p-glycoprotein activity (multixenobiotic resistance)

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 microM OA was studied. After 72 h of exposure, viability was reduced to 54% in 1 microM OA compared with 88% in control cells. This yielded a LC50 of >1 microM 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.

Development of a F actin-based live-cell fluorimetric microplate assay for diarrhetic shellfish toxins

A new cytotoxicity assay for detection and quantitation of diarrhetic shellfish toxins (DSP) is presented. This assay is based upon fluorimetric determination of F-actin depolymerization induced by okadaic acid (OA)-class compounds in the BE(2)-M17 neuroblastoma cell line. No interferences were observed with other marine toxins such as saxitoxin, domoic acid, or yessotoxin, thus indicating a good specificity of the assay as expected by the direct relationship between protein phosphatase inhibition and cytoskeletal changes. The proposed method is rapid (<2h) and shows a linear response in the range of 50-300 nM OA. The detection limit of the assay for crude methanolic extracts of bivalves lies between 0.2 and 1.0 microg OA per gram of digestive glands, depending on the type of samples (fresh or canned), thus being similar to that of the mouse bioassay. The performance of this assay has been evaluated by comparative analysis of 32 toxic mussel samples by the F-actin assay, mouse bioassay, HPLC and PP2A inhibition assay. Results obtained by the F-actin method showed no differences with HPLC and significant correlation with PP2A inhibition assay (r(2)=0.71). No false negative results were obtained with this new cell assay, which also showed optimum reproducibility.

Fluorescent microplate cell assay to measure uptake and metabolism of glucose in normal human lung fibroblasts

This is the first report of a fluorimetric microplate assay to assess glucose uptake and metabolism in eukaryotic cells. The assay was carried out incubating normal human lung fibroblasts in the wells of microtiter trays with a fluorescent D-glucose derivative, 2-N-7-(nitrobenz-2-oxa-1,3-diazol-4-yl)amino-2-deoxy-D-glucose (2-NBDG). This dye could be incorporated by glucose transporting systems in living cells. Substrate uptake was determined by analysing the data obtained with a fluorescence microplate reader. Variables studied in the development of the assay included dye concentration and incubation period. We found that this cell assay is very sensitive, reproducible, provides fast results and graphical display of data. It requires small sample volumes and allows handling of a large number of samples simultaneously. Okadaic acid was used to assess this microplate assay in the field of cytotoxicity. This diarrhetic shellfish toxin is a tumour promoter and a specific inhibitor of protein phosphatases 1 and 2A. The exposition of cells to okadaic acid (0.1 nM-1 microM) at different time intervals causes a decrease in intracellular glucose (40-50% over controls). Results obtained with okadaic acid are the starting point to evaluate application of the method to routine toxicity probes.

A cytotoxicity assay for the detection and differentiation of two families of shellfish toxins

There is an urgent need for an alternative to the mouse bioassay for the detection of algal toxins in shellfish on both analytical and animal welfare grounds. Several alternative methodologies have been described, but have not gained widespread acceptance to date, because each assay measures only one or a small number of related phycotoxins out of the increasing range that needs to be detected. A simple cytotoxicity assay using either the HepG2 or ECV-304 cell lines is described with two end-point measurements, which can detect and distinguish between two unrelated classes of phycotoxins. Morphological examination following 3h exposure to the sample enables the detection of the diarrhetic shellfish poisons, including okadaic acid and related toxins. Viability testing using MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide), following 24h exposure of the same cells to the sample, reveals a second class of toxin, which is most probably the newly-described toxin, azaspiracid. This assay should play an important role in shellfish monitoring in the future.

Aquatic biotoxins: design and implementation of seafood safety monitoring programs

Naturally occurring toxicants are usually odorless, tasteless, and generally undetectable by any simple chemical test. Various programs have been established that are effective in reducing risks associated with these toxicants in food. These programs include setting regulatory limits, monitoring susceptible commodities for toxin levels, and using decontamination procedures. Bioassays have been used traditionally to monitor suspect products. All traditional bioassays, however, have one common disadvantage, i.e., the lack of specificity for individual toxins. The lack of available reference standards for specific toxins has also hampered implementation of monitoring programs. Utilizing the knowledge gained with regulatory monitoring and decontamination programs for other toxins, e.g., aflatoxin, similar seafood safety programs can be developed for aquatic biotoxins that will reduce risks and hazards associated with the contaminant to practicable levels and help to preserve an adequate food supply. Research is needed in several areas identified in this article. International cooperation has an important role in achieving these essential elements. Global programs will help in the adequate management of risks associated with aquatic biotoxins. To have an effective monitoring program, it is necessary to define precisely the local needs for information in a short or long time range. It is necessary to have basic knowledge about the biological, chemical, and physical conditions as well as temporal and geographic variations within the region of interest (2). Regardless of the overall success of fish/shellfish toxin monitoring plans, emergencies will occur. Therefore, contingency plans should be developed so there will be no misunderstanding of what actions to take (148). In general, however, the structure of the program must be kept as simple as possible to facilitate fast and uncomplicated flow of information among the various organizations and individuals involved (2). Public health and safety requires the removal of any toxic shellfish from the market, within practicability, and closure of any suspect harvest area. It should be important to remember that economic value of the fish or shellfish resource is always secondary to public health and safety (148).