Trichothecenes mycotoxins - potent human poisons

Trichothecenes

Trichothecenes are a group of very potent toxic chemical compounds produced mainly by Fusarium, Trichoderma, Myrothecium, Stachybotyrs and other less common moulds. Scientists have to this date identified approximately 60 toxins belonging to this large group. Not all trichothecenes are acutely toxic to humans but some of them, such as T-2 toxin, are so toxic that they have been used by military as biological weapons.

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Trichothecenes mycotoxins have a long and well documented history of poisoning people and animals. They have cause major damages in the farming industry mainly due to animal feeding on grains contaminated by moulds. They are commonly found as food and feed contaminants, and consumption of these mycotoxins can result in alimentary haemorrhage and vomiting and direct contact causes dermatitis.

Trichothecenes in homes

Because trichothecenes are non volatile chemical compounds they are not naturally present in the indoor air in their free form. However, they are contained in mould spores and parts of mould bodies (hyphaes) which can be present in the indoor air in substantial concentrations. Trichothecenes have been found in aerosolised spores, so inhalation of aerosols containing high spore concentrations is a potential health hazard. T-2, diacetoxyscirpenol, T-2 tetraol and roridine A, and have been detected in the dust from office ventilation systems.

Trichothecenes mycotoxins have been shown to be very stable in air and light. They stability in natural environment exceeds several weeks. Some of the most toxic ones are stable under high temperatures so cooking will not destroy them. One of the most toxic T-2 toxin can withstand temperature of 260 C before is deactivated and destroyed _{(Trusal, 1985; Wannemacher and Wiener, 1997)}. Trichothecenes toxins can be inactivated with 3-5 % hypochlorite solutions _{(Wannemacher and Wiener, 1997)}. The toxins are soluble in water only with difficulties but are readily dissolved in chemical solvents such as DMSO, glucol, acetone and other organic solvents and chloroform. They have a peppery odour and negligible vapour pressure.

People are most likely to become exposed to these toxins during renovations or refurbishment of buildings with history of water damage of mould growth. Symptoms of exposure trichothecenes mycotoxins include headaches, dizziness, vertigo, fatigue, tachycardia, salivation, fever and skin damage. In recent literature exposure to trichothecenes mycotoxins have been implicated in syndromes of ill health commonly described as "sick building syndrome".

Chemistry

Chemically trichothecenes contain a common 12,13-epoxytrichothene skeleton and an olefinic bond with various side chain substitutions. Trichothecenes can be chemically classified in two distinct groups: macrocylic or nonmacrocyclic compounds. The division is based on the presence or absence of a macrocylic ester or an ester-ether connection between carbon atom 4 and carbon atom 15 in the chain. The nonmacrocylic trichothecenes can be further sub-classified into individual subgroups: type-A, where carbon atom 8 has a hydrogen or ester type chain attached . Toxins belongin gto this group includediacetoxyscirpeno, neosolanio and T-2 toxin.The second subgroup, type-B, has a ketone attached to the main atomic chain. This group include mycotoxins such as nivalenol, fusarenon-x, and deoxynivalenol. Fusarium mould in is considered clinically the most important mould genus responsible for production of nonmacrocylic trichothecenes.

Alkaline reagents can hydrolyse trichothecenes mycotoxins which contain an ester group. Hydrolysis is carried out to the main parent alcohol of that particular toxin. Trichothecenes are thus chemically stable and can persist for long periods once formed.

Effect of trichothecenes on human body

Many of the toxic effects of trichothecenes are not fully understood but the knowledge of their effects on humans is rapidly expanding. They are known to inhibit protein synthesis, DNA synthesis, impair of ribosome function, inhibit of mitochondrial protein synthesis, inducing of reparable single strand breaks in DNA and immunosuppression thus allowing secondary and opportunistic bacterial infections. It is also suspected from causing delayed hypersensitivity.

Alimentary toxic aleukia (ATA) is the most well recognised human trichothecene mycotoxicosis. It is known that the T-2 toxin was involved in large numbe rof cases of so called alimentary toxic aleukia. The toxins was responsible for widespread disease and number of toxin related deaths. Exposure to trichothecenes mycotoxins for prolonged periods of time can often result in skin rashes, which can later develop into necrotic lesions. Many outbreaks of acute human diseases involving nausea, vomiting, gastrointestinal upset, dizziness, diarrhoea and headache have occurred particularly in Asia and these outbreaks have been attributed to the consumption of Fusarium-contaminated grain.