Metabolism mycotoxins, effect

Contamination occurs primarily in wheat, barley, rye, and maize. Type A trichothecenes include mainly T-2 toxin, HT-2, and diacetoxyscirpenol (DAS) mycotoxins of the group B include mainly 4-deoxynivalenol (DON), commonly known as vomitoxin, and nivalenol (NIV). Toxic effects include nausea, vomiting, visual disorder, vertigo, throat irritation, and feed refusal in farm animals. The most toxic is T-2, followed by DAS and NIV, with DON being the least toxic in acute toxicity studies but the most widespread in grains worldwide and therefore the most studied. Issues related to chemical and physical data, occurrence, toxicity, absorption, distribution, and metabolism of trichothecenes are reviewed in WHO (89) and IARC (34). Physicochemical data for some selected Fusarium toxins is given by Sydenham et al. (90). The molecular structures of the main trichothecenes are shown in Fig. 9. 

Hayes, J.R. (1985) Effect of Nutrition on the Metabolism and Toxicity of Mycotoxins. This Volume. 

Swanson, S.P., Corley, R.A. (1989). The distribution, metabolism and excretion of trichothecene mycotoxins. In Trichothecene Mycotoxicosis Physiological Effects, Vol. 1 (V.R. Beasley, ed.), pp. 37-61. CRC Press, Boca Raton, FL. 

Molds also produce complex products of secondary metabolism. These secondary metabolites include chemicals used to ensure that the molds maintain their niche within their current habitat. These chemicals may suppress the growth of bacteria or other molds (antibiotic effect), or may be toxic to other eukaryotic cells (mycotoxic effect),. Mycotoxins may function as inhibitors of DNA, RNA, and protein synthesis. The production of secondary metabolites... 

Compared with some of the other mycotoxins such as aflatoxin, the trichothecenes do not appear to require metabolic activation to exert their biological activity.50 After direct dermal application or oral ingestion, the trichothecene mycotoxins can cause rapid irritation to the skin or intestinal mucosa. In cell-free systems or single cells in culture, these mycotoxins cause a rapid inhibition of protein synthesis and polyribosomal disaggregation.35 47 50 Thus, we can postulate that the trichothecene mycotoxins have molecular capability of direct reaction with cellular components. Despite this direct effect, it is possible to measure the toxicokinetics and the metabolism of the trichothecene mycotoxins. 

Mycotoxins are by-products of fungal metabolism. A wide variety of fungi produce substances that produce adverse health effects in animals and humans, but mycotoxin production is most commonly associated with the terrestrial filamentous fungi called molds. T-2 mycotoxin is one of a family of nearly 150 toxins produced by Fusarium and related fungi... 

Hennig, A., Fink-Gremmels, J. Leistner, L. (1991) Mutagenicity and effects of ochratoxin A on the frequency of sister chromatid exchange after metabolic activation. In Castegnaro, M., Plestina, R., Dirheimer, G., Chemozemsky, I.N. Bartsch, H., eds. Mycotoxins, endemic nephropathy and urinary tract tumours. Lyon, France, International Agency for Research on Cancer, pp. 255-260 (IARC Scientific Publications No. 115). 

Diets rich in fibre have been shown to overcome the toxicity of zearalenone (Smith, 1980a), a uterotropic Fusarium mycotoxin. Alfalfa was particularly effective and has been shown to alter zearalenone metabolism (Smith, 1980b James and Smith, 1982). 

These general principles will now be illustrated from secondary metabolic pathways leading to acknowledged mycotoxins. We can summarize them in the statement that under conditions which are optimal for its growth a fungus will display little or none of its potential for secondary biosynthesis, but under suboptimal conditions (and with minor genetic changes that have the same effect) the precise pattern of secondary metabolism elicited will depend both on the prior history of the culture and on its current environmental conditions. 

---