Comparison of cytotoxicity and thin-layer chromatography methods for detection of mycotoxins

The use of isolated human lymphocytes in mycotoxin cytotoxicity testing

The cytotoxicity of selected mycotoxins against isolated human lymphocytes was investigated, as a means of detecting mycotoxins in extracts derived from cereal samples. The methodology was based on the ability of viable cells to reduce methyl tetrazolium bromide to a purple formazan dye that could be quantitated by spectrophometric means and hence give a measure of the cytotoxicity of added substances. The results showed that there was good correlation with the occurrence of identified mycotoxins with only a minimum of false positives. For example, of the 13 samples of barley or barley derivatives that were positive for the mycotoxins, fumonisin B(1) (FB1) deoxynivalenol (DON) and ochratoxin A (OTA), all gave positive cytotoxicity responses. Two samples negative for mycotoxins gave no cytotoxicity responses. There was little variation between the results for lymphocytes drawn from the same healthy volunteer on three different occasions. Furthermore, for two of the mycotoxins tested (FB1 and DON) it was possible to correlate general levels of mycotoxins present to the cytotoxic response of the lymphocytes but not for OTA, where it was concluded that interfering substances prevented direct correlation. It was concluded that this method was suited for general application as it could handle relatively high number of samples in a short period of time.

The incidence of fungi and mycotoxins in South Africa wheat and wheat-based products

This investigation was undertaken to survey the fungal and mycotoxin contamination of South African wheat ranging from that growing in the field to processed wheat products. Samples of wheat were taken from various growing areas in South Africa and screened for fungi and mycotoxins, using a range of methodologies, including chromatography, immunoaffinity/fluorimetry, and cytotoxicity testing. Similar samples were taken from supermarkets and retail outlets in South Africa and analyzed in a similar manner. The result showed that a range of fungi and mycotoxins could be detected in wheat in all these sample types. The major fungal contaminants were Fusarium spp. and their attendant mycotoxins, in particular deoxynivalenol, which is in keeping with the observations made in the rest of the world. An interesting observation was that samples of wheat taken from the field with heavy Fusarium contamination were contaminated with fumonisin B1, which is not normally associated with this crop. Of more concern were the low but persistent levels of mycotoxins and fungi in wheat-based products sold directly to the public.

Cytotoxicity assays for mycotoxins produced by Fusarium strains: a review

Mycotoxins are naturally occurring toxic secondary metabolites of fungi that may be present in food and feed. Several of these mycotoxins have been associated with human and animal diseases. Fusarium species, found worldwide in cereals and other food types for human and animal consumption, are the most important toxigenic fungi in northern temperate regions. The overall economical loss and the detrimental health effects in humans and animals of mycotoxin contamination are enormous and therefore, rapid screening methods will form an important tool in the protection of humans and animals as well as to minimize economical losses by early detection. An overview of methods for the determination of cytotoxicity and the application of such bioassays to screen solid fungal cultures, cereals, respectively, food/feedstuffs for the presence and toxic potential of Fusarium mycotoxins is presented. Various cell lines including different endpoints of toxicity using vertebrate cells and the predictive value of the in vitro assays are reviewed. Bioassays are compared with existing chemical analytical methods and the possibilities and limitations of such systems are discussed. The review is based on 149 references.

Cytotoxicity of four trichothecenes evaluated by three colorimetric bioassays

The application of cell culture technique for screening of low concentrations of Fusarium mycotoxins was examined. Three colorimetric bioassays were used to determine the cytotoxicity of the trichothecenes T-2 toxin (T-2), HT-2 toxin (HT-2), deoxynivalenol (DON) and nivalenol (NIV) to 3T3 mouse fibroblasts (3T3 cells). The bioassays assess DNA synthesis (incorporation of 5-bromo-2'-deoxyuridine; BrdU), metabolic activity (cleavage of 3-(4,5-dimethyltiazol-2-yl)-2,5-diphenyltetrazolium bromide; MTT) and cell membrane damage (release of lactate dehydrogenase; LDH), respectively. The BrdU bioassay was the most sensitive and the IC50 values (50% response compared to untreated cells) of T-2, HT-2, DON and NIV were 4.6, 13, 263 and 365 ng/ml, respectively. At the same toxin concentrations used in the BrdU bioassay, only T-2 and HT-2 were toxic enough to obtain IC50 values using the MTT bioassay. The IC50 values for T-2 and HT-2 were 12 and 68 ng/ml, respectively. When determined by the LDH bioassay, the IC50 values of T-2 and HT-2 were 18 and 42 ng/ml, respectively. At the tested concentrations, DON and NIV had a minor effect on the 3T3 cells when evaluated by the MTT and LDH bioassays. The BrdU bioassay in combination with 3T3 cells was found to be a suitable method for determination of trichothecene-induced toxicity at low concentrations.

Highly sensitive protein translation assay for trichothecene toxicity in airborne particulates: comparison with cytotoxicity assays

Screening assays for environmental mycotoxins in bulk samples currently use cytotoxicity in cell cultures, but their application to air particulate samples often lacks sensitivity and specificity for fungal spores. An assay based on inhibition of protein synthesis using translation of firefly luciferase in a rabbit reticulocyte system has been developed for the detection of trichothecene mycotoxins found in the spores of toxigenic fungi. Ethanol extracts of air particulates trapped on polycarbonate filters are ultrafiltered and applied at several dilutions to a translation reaction mixture. The activity of translated luciferase is measured directly in a luminometer, eliminating the need for radioisotopes and time-consuming sample processing. Parallel standard curves using a commercially available trichothecene provide for expression of the results in T-2 toxin equivalents per cubic meter of air. The assay can be completed in 2 h and is readily applicable to multiple samples. Comparison to the 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide cytotoxicity assay indicates a 400-fold increase in sensitivity of trichothecene detection in addition to a much higher specificity for these toxins. Initial field testing indicates a strong correlation between the measured level of toxicity and the presence of toxigenic fungi detected with microbiological methods. In conclusion, this luciferase translation assay offers a rapid and highly sensitive and specific method for quantitative detection of trichothecene mycotoxin activity in air particulate samples.

Cytotoxicity of mycotoxins evaluated by the MTT-cell culture assay

The application of a modified colorimetric bioassay for the evaluation of the biological effects of mycotoxins is reported. Using three different monolayer cell lines (swine kidney, Madin Darby canine kidney, HeLa) the influence of nine different mycotoxins on the cellular methylthiazoltetrazolium (MTT)-cleavage activity was evaluated. The yellow tetrazolium salt MTT is converted by mitochondrial dehydrogenases of metabolically active cells to an insoluble purple formazan product, which was then solubilized with dimethylsulfoxide. The optical density of this homogeneous solution was suitable for a precise spectrophotometric measurement by a plate reader at a wavelength of 510 nm. Nine mycotoxins were simultaneously tested in all three cell lines, from which the swine kidney cell line proved to be the most sensitive. The effects of additional 35 mycotoxins were therefore tested using swine kidney monolayers as target cells. A total of 28 toxins of the 44 mycotoxins tested proved to be cytotoxic in the MTT-bioassay. Most of them belong to the group of trichothecene mycotoxins. Concentrations ranged between 0.01 micrograms and 100 micrograms/ml of cell culture medium. The MTT cleavage assay was found to be a quick (24 hours) and easy to perform system for the evaluation of the biological activity of many different mycotoxins and may also provide a useful tool for the testing of a large variety of sample materials.

Investigation on the toxicity of fungi from rootstock snacks

Chicken embryo bioassay was used to monitor the toxicity of extracts from rootstock snack samples during a 210-day storage period. Results show that the relative toxicity values which were initially very low increased significantly as from 120th day (when 32% mortality was recorded) up till the last day when 73% was obtained. Toxicity of extracts from axenic cultures of 12 fungal species isolated from the snack samples was also determined. The strains of Aspergillus chevalieri, Rhizopus nigricans and Rhizopus sp investigated were nontoxic. A. niger, A. flavus, A. fumigatus, Penicillium chrysogenum, A. parasiticus, P. citrinum, A. ochraceus, Fusarium monifilorme and A. candidus were found to be toxic in decreasing order of potency as recorded after 30 days of growth at room temperature on substrate of 0.90 water activity level. Trends in the moisture content levels, pH and the incidence of fungal growth on the snack samples were also studied. Results suggest that storage for a period not exceeding 90 days and maintenance of safe moisture level would control mould growth and the associated mycotoxins in the snack.

The use of tissue culture for the detection of mycotoxins

After incubation with 20 different mycotoxin standards and extracts from fungi and feed stuffs, fluorescent flow cytometry was used to measure viability of NS-1 cells and compared to microscopic assessment of cytotoxicity on stained HEp-11 monolayers. Both methods gave essentially the same results but the cytometric analysis offered a more quantitative approach and was particularly appropriate in the screening of extracts containing fats. The potential uses of a cytotoxic test in the analysis of feed stuffs and fungal extracts for the presence of mycotoxins are discussed.

An appraisal of bioassay methods for the detection of mycotoxins—a review

The literature on bioassay methods for mycotoxin detection has been reviewed. An outline of the range of bioassay methods is given and the role of cytotoxicity tests in particular has been emphasized.

The cytotoxicity of T-2 toxin and related 12,13-epoxytrichothecenes to Adriamycin-sensitive and -resistant P388 leukemia cells

The cytotoxicity of T-2 toxin and related trichothecenes was studied in Adriamycin-sensitive and -resistant P388 leukemia cells in vitro. The structure-activity relationship indicated that a free hydroxyl in the C-3 position contributed to the activity. Free hydroxyls at the 4, 8, and 15 positions interfered with the activity, and their estrification resulted in improved cytotoxicity. The cytotoxic activity of these trichothecenes did not seem to be related to their degree of lipophilicity. Adriamycin-resistant P388 cells were cross-resistant to the trichothecenes, and this resistance could be circumvented by verapamil.

Repetitive hit-and-run fluoroimmunoassay for T-2 toxin

A monoclonal antibody for T-2 toxin is converted to a Fab'-fluorescein derivative. The latter is specifically complexed onto a T-2 agarose gel. Fifteen successive doses of T-2 ranging from 1 to 50 ng are then repetitively and linearly detected using a column packed with a small volume (0.2 ml) of this gel without recharging with Fab'-fluorescein. For these assays the effluent from the column is monitored with a spectrofluorometer.

Structure-function relationships of 12,13-epoxytrichothecene mycotoxins in cell culture: comparison to whole animal lethality

Nineteen 12,13-epoxytrichothecene mycotoxins were tested for their relative capabilities to inhibit protein synthesis in Vero cells and rat spleen lymphocytes. Although the lymphocytes were generally more sensitive to the mycotoxins, good correlation existed between the relative potencies of the various trichothecenes in the two cell systems. The most potent mycotoxins (T-2, verrucarin A and roridin A) have acetyl side groups on, or a hydrocarbon chain between, carbons 4 and 15 of the basic ring structure. Loss of side groups from either of these positions or an isovaleryl group at carbon 8 resulted in reduced protein synthesis inhibition (T-2 to HT-2, neosolaniol or diacetoxyscirpenol). Any combination of loss from all three positions (T-2 triol, T-2 tetraol, 15-monoacetyl DAS, scirpentriol, fusarenon X and deoxynivalenol) further weakens their effect. Reduction of the hydroxyl groups to hydroxides, forming verrucarol and deoxyverrucarol, reduced their effectiveness by over a thousand-fold compared to the most potent mycotoxins. Addition of side groups resulted in reduced effectiveness only when an acetyl group was added to the carbon 3 position of T-2 (acetyl T-2) and deoxynivalenol (3-acetyl deoxynivalenol) or on substitution of an epoxide across the 9,10 carbons of diacetoxyscirpenol (beta-epoxide DAS). Effects of combining these and other mycotoxins were additive and showed no synergism or competition for binding to the active site. When in vitro effects of the mycotoxins were compared with results from whole animal lethality tests, several of the trichothecenes were weak inhibitors of protein synthesis in vitro but had in vivo toxicities similar to that of T-2 toxin. Thus, the in vitro cell response of a given trichothecene is not always an accurate predictor of toxicity in whole animals.