Mycotoxins as Causal Factors of Diseases in Humans

Mycotoxicological research in South Africa 1910-2011

The British mycologist, I.B. Pole-Evans, was appointed as the first South African government mycologist in 1905 following the Anglo-Boer War (1899-1902). The Onderstepoort Veterinary Research Institute was founded in 1908 with the Swiss veterinarian, Arnold Theiler, as the first director. Thus, the stage was set for the commencement of mycotoxicological research when the Union of South Africa came into being in 1910. The first accounts of this pioneering research appeared in the 'Seventh and eight reports of the Director of Veterinary Research, Union of South Africa. 1918' in which D.T. Mitchell reported on the experimental reproduction of the neurotoxic syndrome, diplodiosis, in cattle with pure cultures of Stenocarpella maydis (= Diplodia zea) isolated by P.A. Van der Bijl and grown on sterile maize kernels. This is the first report of the experimental reproduction of a veterinary mycotoxicosis with a pure culture of a fungus in South Africa and possibly in the world. This seminal research was followed by a great deal of multidisciplinary research on veterinary mycotoxicoses as well as human syndromes in which fungal toxins are suspected to be involved, taxonomy of mycotoxigenic fungi and chemistry of mycotoxins in South Africa. The mycotoxicoses studied in South Africa include the following (more or less in chronological order): diplodiosis, Paspalum staggers, aflatoxicosis, human hepatocellular carcinoma, ochratoxicosis, lupinosis, facial eczema, tremorgenic mycotoxicosis, hyperoestrogenism, stachybotryotoxicosis, ergotism, leukoencephalomalacia and human oesophageal cancer. A major breakthrough in mycotoxicological research was made in South Africa in 1988 with the isolation and chemical characterisation of the carcinogenic fumonisins produced by Fusarium verticillioides in maize. Current research at the PROMEC Unit of the South African Medical Research Council on the risk assessment of fumonisins and intervention methods to reduce fumonisin intake by rural populations on a maize staple diet is highlighted. This paper concludes with a selected list of mycotoxicological publications by South African mycologists/plant pathologists, veterinarians and chemists/biochemists.

Selective enrichment of ochratoxin A using human serum albumin bound magnetic beads as the concentrating probes for capillary electrophoresis/electrospray ionization-mass spectrometric analysis

Ochratoxin A (OTA) is a toxicant commonly present in many food products. Conventionally, immuno-affinity analysis is applied to rapidly screen the presence of OTA in food. However, antibodies are expensive. In this study, we present a new approach for selectively enriching OTA from aqueous samples using human serum albumin (HSA) bound magnetic beads as the affinity probes, followed by the analysis of CE/ESI-MS. In addition to demonstrating the feasibility of using the affinity probes to concentrate OTA, we also propose a rapid concentration and elution method for extraction, that is, OTA are extracted from aqueous samples by pipetting the samples in and out of a sample vial for 1 min followed by elution with pipetting for another minute. On the basis of the magnetic property, the affinity magnetic probe-target species could be rapidly isolated from the solution during the process of extraction and elution by magnetic separation. CE/ESI-MS, coupled by the electrodeless/sheathless interface, is used for the analysis of the samples. As this method features speed and cost-effectiveness, it is suitable for the purpose of rapid screening. In fact, the lowest detection limit for OTA is approximately 4 x 10(-3) mg/L.

Mycotoxins in infant cereal foods from the Canadian retail market

Three hundred and sixty-three samples of cereal-based infant foods were collected from the Canadian retail marketplace over 3 years. The samples included oat-, barley-, soy-, and rice-based infant cereals, mixed-grain infant cereals, teething biscuits, creamed corn, and soy-based formulas. Samples were analysed for targeted mycotoxins (deoxynivalenol, nivalenol, HT-2 toxin, zearalenone, ochratoxin A, fumonisins B(1) and B(2), and five ergot alkaloids). Soy-based cereals (which usually contain corn) exhibited the highest incidences of deoxynivalenol (100%), zearalenone (46%) and fumonisins (75%). Overall, deoxynivalenol was the most frequently detected mycotoxin--it was detected in 63% of samples analysed. Survey results demonstrated the regular occurrence of multiple mycotoxins in cereal-based infant foods.

Interaction of ochratoxin A with human serum albumin. Binding sites localized by competitive interactions with the native protein and its recombinant fragments

Competitive interactions of ochratoxin A (OTA) and several other acidic compounds were utilized to gain insight into the localization of binding sites and the nature of binding interactions between anionic species and human serum albumin (HSA). Depolarization of OTA fluorescence in the presence of a competing anion was used to quantify ligand-protein interactions. The results obtained were rationalized in terms of OTA displacement from its major binding site. Based on their ability to displace OTA, two distinct groups of the anionic ligands were revealed. The first group contained structurally diverse compounds that shared a common binding site in subdomain IIA (Sudlow Site I). The second group consisted of three non-steroidal anti-inflammatory drugs, which showed much lower affinity to Site I than the OTA dianion. The major site for these drugs was located in domain III. Fluorescence spectroscopy measurements of OTA, warfarin (WAR) and naproxen (NAP) complexes with recombinant proteins corresponding to the domains of HSA (D1-D3) revealed binding to all domains but with different affinities. The binding constants for OTA and WAR decreased in the series D2z.Gt;D3>D1. In contrast, NAP showed the most favorable interaction with D3 and comparable affinities to the two remaining domains. The OTA binding constant for D2, 7.9 x 10(5) M(-1), was smaller than the largest constant for HSA by a factor of approximately 7. The binding constant for OTA with D3, 1.1 x 10(5) M(-1), was very close to that of the secondary binding site for HSA.

Mycotoxin detoxication of animal feed by different adsorbents

The contamination of animal feed with mycotoxins represents a worldwide problem for farmers. These toxins originate from molds whose growth on living and stored plants is almost unavoidable particularly under moist conditions. Mycotoxin-containing feed can cause serious diseases in farm animals resulting in suffering and even death and thus can cause substantial economic losses. The most applied method for protecting animals against mycotoxicosis is the utilization of adsorbents mixed with the feed which are supposed to bind the mycotoxins efficiently in the gastro-intestinal tract. Aluminosilicates are the preferred adsorbents, followed by activated charcoal and special polymers. The efficiency of mycotoxin binders, however, differs considerably depending mainly on the chemical structure of both the adsorbent and the toxin. This review describes the most important types of adsorbents and the respective mechanisms of adsorption. Data of the in vitro and in vivo efficacy of detoxication are given.