Trichothecenes

Fungi produce a large number of metabolites that are not essential for life, but may provide the fungus with an ecological advantage in certain environments. Such metabolites are referred to as secondary metabolites. Fungal secondary metabolites include plant growth regulators (gibberellins), pharmaceutically useful compounds (penicillin, lovastatin), pigments (carotenoids), and mycotoxins (trichothecenes, fumonisins, aflatoxin, ochratoxins).

Mycotoxins may accumulate in infected crop plants, and upon ingestion, lead to the development of diseases (mycotoxicoses) in humans and animals.2 Among the most toxic are the trichothecenes which have various detrimental effects on eukaryotic cells including interference with protein production, disruption of nucleic acid synthesis and induction of apoptosis (cell death).3 Exposure to trichothecenes toxins in animals can cause feed refusal, immunological problems, vomiting, skin dermatitis, hemorrhagic lesions, abortion and death. In plants they cause chlorosis, inhibition of root elongation, and dwarfism.2

Barley

Trichothecenes are a family of over 200 toxins. They are small molecules that can move passively across cell membranes. They are easily absorbed, allowing for a rapid effect. Trichothecene mycotoxins are categorized into several types and the type B trichothecene group includes deoxynivaelnol (DON), nivalenol (NIV), and their derivatives, having a relatively low toxicity compared with type A trichothecenes, such as T-2 or HT-2 toxins, but the toxicity varies with differences in cell type or species.4 Exposure to T-2 toxin increases susceptibility to infections from Candida, Cryptococcus, Mycobacterium, Listeria and Salmonella.6 A number of the molds that are plant pathogens produce trichothecene mycotoxins including Fusarium, Myrothecium, Spicellum, Stachybotrys, Cephalosporium, Trichoderma, and Trichothecium.



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Barley is a widespread crop that ranks fourth among the world’s cereals for the importance of its contribution to feed and food production. About 80%–90% of barley grain yield is earmarked for livestock feed and about 10% is transformed into malt for many brewing, distilling and baking products. The fungal spores can in fact be carried through the malting process and affect both the beer quality and safety. Recently, T-2 and HT-2 toxins, two of the most toxic members of type-A trichothecenesin, were detected in malting barley grown in Italy. The malt contamination with Fusarium is now recognized by uncontrolled escape of wet foam when opening a beer bottle. This is not caused by high temperature or shaking, but is caused by the presence of fungal hydrophobins, proteins produced by Fusarium and other filamentous fungi.7

Deoxynivalenol (DON) is the major mycotoxin produced by Fusarium fungi in grains. It is also know as vomitoxin due to his strong emetic effects after consumption, because it is transported into the brain, where it runs dopaminergic receptors. DON is probably the best known and most common contaminant of grains and their subsequent products. One of the most important physicochemical property of DON is its ability to withstand high temperatures, which is the risk of its occurrence in food. However, DON levels are reduced in cooked pasta and noodles because of leaching into the cooking water. Potential impact of DON on human health may occur after ingestion of contaminated foods from oats, barley, wheat, corn or other grains. DON was detected also in buckwheat, sorghum, popcorn and other foods for human consumption, such as flour, bread, noodles, beer and malt.1 Food and feed contaminated with DON pose a health risk to humans and livestock. The ingestion of DON with contaminated food leads to reduced immunity, anemia, headache, nausea, and abdominal pain as well as alimentary toxic aleukia (absence of leukocytes from blood), a condition characterized by vomiting, diarrhea, anemia, dermatitis, gastrointestinal necrosis and can be lethal, particularly in immune-suppressed persons.5

Over the past 15–20 years, toxic mold exposure has become hazardous and frequent. It has been demonstrated that mycotoxins can be detected in human blood and in animal tissue. Recently aflatoxin B1 was found in adolescents in China, which may impose substantial risk for liver cancer in adulthood. Trichothecenes as well as ochratoxins A and B can be measured in urine as a screening test which can assist the physician to determine what the best mode of therapy would be.

Although the majority of trichothecenes contribute to crop disease and mycotoxicoses, they have also been considered as antibiotics and antileukemics. However, the mechanism of action of the trichothecene compounds, with regard to any of their toxicological effects is not well understood.3

References

  1. Deoxynivalenol and its toxicity
  2. Trichothecenes: From Simple to Complex Mycotoxins
  3. Current and Future Experimental Strategies for Structural Analysis of Trichothecene Mycotoxins-A Prospectus
  4. Phytotoxicity Evaluation of Type B Trichothecenes Using a Chlamydomonas reinhardtii Model System
  5. Biological detoxification of the mycotoxin deoxynivalenol and its use in genetically engineered crops and feed additives
  6. Clinical Environmental Health and Toxic Exposures. John Burke Sullivan, Gary R. Krieger
  7. Morcia C, Tumino G, Ghizzoni R, et al. Occurrence of Fusarium langsethiae and T-2 and HT-2 Toxins in Italian Malting Barley. Brera C, ed. Toxins. 2016;8(8):247. doi:10.3390/toxins8080247.

 

 


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