Tue. Sep 17th, 2019

Mycotoxins (Fungal Toxins)

4 min read
Mycotoxins are defined as natural products from molds that evoke a toxic response when introduced in low concentrations to vertebrates. These are toxic compounds produced as metabolic products by some molds. They are products of secondary metabolism of molds i.e. part of metabolism that is not essential for cell growth and maintenance of basic cell functions.

Mycotoxin (Greek: Mykes, Mukos- Fungus, Toxikon-Poison).

Mycotoxins are defined as natural products from molds that evoke a toxic response when introduced in low concentrations to vertebrates. These are toxic compounds produced as metabolic products by some molds.

All mycotoxins are low-molecular-weight natural products (i.e., small molecules) produced as secondary metabolites by filamentous fungi. These metabolites constitute a toxigenically and chemically heterogeneous assemblage that are grouped together.

Most fungi are aerobic and are ubiquitous in occurrence in extremely small quantities due to minute size of pores. They consume organic matters when humidity and temperature are sufficient (has saprophytic nutrition) and under favorable conditions, proliferate into colonies, producing mycotoxins at higher concentration.

They are products of secondary metabolism of molds i.e. part of metabolism that is not essential for cell growth and maintenance of basic cell functions. The actual function for production of these toxins are not known but they may be in part, used for chemical warfare thus, providing some advantage to survive in the environment.

Molds can produce mycotoxins on food items such as fruits, nuts, cereals etc. Growth of molds can occur either before, during and after harvest, storage on/in food under warm, damp and humid conditions. Most of them are chemically stable and survive food processing.

As these toxic metabolites weakens the receiving hosts, fungus may use them as a strategy to better environment for further proliferation.  The production of toxins depends on the surrounding intrinsic and extrinsic environments and the toxins vary greatly in their severity, depending on the organism infected and its susceptibility, metabolism, and defense mechanisms.

There are several hundred different mycotoxins that has been identified. However, most common mycotoxin that pose a concern to human health and livestock includes aflatoxins, patulin, fumonisins, ochratoxin A, deoxynivalenol etc.  Exposure to mycotoxins can happen either directly by eating infected food or indirectly from animals that are fed contaminated feed, in particular from milk.

They can cause variety of health effects and pose serious threat to humans, animals, cattles etc. The effects ranges from acute poisoning to long term effects such as cancer, immunodeficiency and even death.

 

Mode of actions of Mycotoxins

Effect on energy production:
• Inhibit certain enzymes involved in Krebs’ cycle.
• Moniliformin, a toxin of Fusarium, inhibits the oxidation of pyruvate and a-ketoglutarate.
• It also causes disturbances in intracellular osmoregulation.

Inhibition in synthesis of DNA, RNA, proteins and immune systems:
• Inhibition in these macromolecules lead to cell death.
• Aflatoxin B1 inhibits DNA synthesis in liver cells.
• Ochratoxin A inhibits the activity of phenylalanyl – tRNA synthetase which is required in the first step of protein synthesis.
• Also reduces the renal mRNA coding for certain enzymes such as phosphoenolpyruvate carboxylase.

 

Effects on Nervous Systems
• Mycotoxins causing paralysis and inhibition in respiratory system e.g. citrioviridin. They kill nerve cells disrupting energy supply as they inhibit ATPase activity.
• Mycotoxins inducing trembling in animals e.g. fumitremorgin A, penitrem A. They alter functional states of neurotansmitters and disrupt nervous system.
• Mycotoxins causing vomiting in animals e.g. vomitoxins such as trichothecenes. They act on chemoreceptor trigger zone in medulla oblongata and change the biogenic amines.

 

Effects on Hormones’ Activities:
• Aflatoxin B1 binds covalently with acceptor sites of chromatin and thus, reduces the nuclear acceptor sites of hormone-receptor complexes.

Carcinogenic Effects:
• Aflatoxins, B1, and G1, and sterigmatocystin versicolorin A, luteoskyrin are known as carcinogenic mycotoxins.

 

Effects on Reproductive Systems:
•Zearalenone causes embryonic death and inhibition of development in swines.
•Ergot ingestion may cause abortion in animals.
•Ergot is also associated with reduced weight gain and milk production in animals.

 

However, because of their pharmacological activity, some mycotoxins or mycotoxin derivatives have found use as antibiotics, growth promotants, and other kinds of drugs; still others have been implicated as chemical warfare agents.

While all mycotoxins are of fungal origin, not all toxic compounds produced by fungi are called mycotoxins.

Minimization of risk from mycotoxins

  • Inspect whole grains (especially corn, sorghum, wheat, rice), dried figs and nuts such as peanuts, pistachio, almond, walnut, coconut which are regularly contaminated with aflatoxins for evidence of mold, and discard any that look moldy, discoloured, or shriveled.
  • Avoid damage of grains before and during drying, and in storage, as damaged grain is more prone to invasion of molds and therefore mycotoxin contamination.
  • Buy grains and nuts as fresh as possible.
  • Proper storage of foods – kept free of insects, dry, and not too warm.
  •  Reduction of storage time- Do not keep foods for extended periods of time before being used.
  • Ensure a diverse diet – this not only helps to reduce mycotoxins exposure, but also improves nutrition.

 

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