Types and Metabolism of Aflatoxins

Aflatoxins (from the Latin name of the fungus Aspergillus flavus + toxin) are a group of mycotoxins produced primarily by two types of mold: Aspergillus flavus and Aspergillus parasiticus. Aflatoxins are also produced by other fungi of the same family such as Aspergillus nomius and Aspergillus niger. These naturally occurring toxins are found in several types of food crops which include peanuts, walnuts, almonds, pistachios, pecans, cottonseed, corn, and millet. Several different types of aflatoxins of related chemical structures are known.1

Aflatoxins are secondary metabolites of fungi that were discovered in agricultural commodities in 1960s. Secondary metabolites are substances produced by living cells that are not essential for the growth of the producing organism. Aflatoxins were originally identified in peanut meal that killed turkeys. It was later discovered that animals exposed to the toxin exhibited increased tumor formation, especially in the liver.

Fungi Producing Aflatoxins

Aspergillus flavus is common and widespread in nature and is most often found when certain grains are grown under stressful conditions such as drought. The mold occurs in soil, decaying vegetation, hay and grains undergoing microbiological deterioration and invades all types of organic substances. Favorable conditions include high humidity and temperature.

Aflatoxin inhibits the production of natural killer cells involved in the immune surveillance for elimination of tumor cells. The compromised immune system has been linked to aflatoxin exposure and subsequent viral infections.1

Types of Aflatoxins

The common types of aflatoxins produced are B1, B2, G1, and G2. Aflatoxin B1 is the most common and toxic of this class and is classified by IARC (international Agency for Research on Cancer) as human carcinogen. Its chemical name is 2,3,6a 9a-tetrahydro-4-methoxycyclopenta[c]furo[2,3-h][1][benzopyran-1,11-dione.2 In addition, there are other types of aflatoxins, namely M1 and M2 have been reported as contaminants of food, especially of milk.

Aflatoxin Metabolism

Following intake, aflatoxins are metabolized into a variety of products such as aflatoxicol, aflatoxin Q1, aflatoxin P1, and aflatoxin M1 in the liver by cytochrome P450 group of enzymes. In addition, another metabolite, called aflatoxin 8,9 epoxide, can be formed, which can induce DNA mutations ultimately leading to hepatic carcinoma.3



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Toxic Effects on Humans and Animals

Aflatoxicosis in animals can be acute and chronic. Acute cases are characterized by severe liver damage, whereas liver cirrhosis, liver cancer and DNA damage occur in chronic toxicity. Chronic intake of aflatoxin in animals can lead to poor food intake and weight loss.3

Signs and Symptoms of Aflatoxin Acute Effects

Most of aflatoxin affects are chronic. A brief exposure to aflatoxins however, may produce a wide range of acute effects that may very within the species, age, sex, nutritional condition, and the dose. Some symptoms of acute effect of aflatoxin exposure in humans arising from ingestion of contaminated nuts are vomiting, abdominal pain, and pulmonary edema. High exposure may cause convulsions, coma and death.2

Treatment of Aflatoxicosis

Avoidance of food containing aflatoxins is the primary measure. Once exposed, there is a risk of future cancer; there is no treatment to prevent this. For an acute exposure, amphotericin B and itraconazole may be helpful.4


References

  1. Handbook of Applied Mycology (Handbook of Applied Mycology, Vol. 5). Arora
  2. A comprehensive guide to the hazardous properties of chemical substances. Pradyot Patnaik
  3. Handbook of nutrition and food. Carolyn D. Berdanier, Johanna T. Dwyer, Elaine B. Feldman
  4. Introduction to weapons of mass destruction. Roland E. Langford


 

 


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