Aflatoxins
Aflatoxins are naturally occurring
bis-furanocoumarin compounds produced by the fungus Aspergillus flavus (and related species: A. parasiticus), and occur as contaminants of several nuts, grains,
and seeds, such as peanuts, cottonseed, rye, barley, corn, etc. They are
composed of highly substituted coumarin compounds that contain a fused
dihydrofurofuran configuration. A dozen or more of these compounds have been
identified: Aflatoxin, Aflatoxin B1, Aflatoxin B2,
Aflatoxin B2a, Aflatoxin B3, Aflatoxin G1,
Aflatoxin G2, Aflatoxin G2a, Aflatoxin M1,
Aflatoxin M2, Aflatoxin P, and Aflatoxin T2. The
aflatoxins are highly fluorescent. The “B” refers to blue, the “G” signifies
green fluorescence, while “M” aflatoxins are fungal metabolites present in
milk, and “T” compounds are found in tobacco. Most of them are associated with
various types of liver damage. Aflatoxin B1 is a potent hepatotoxin
and carcinogen.
Consumption of dietary aflatoxins
varies from 10 to 200 ng/kg/day, though the recommended maximum daily intake
should be less than 50 ng/kg/day.
Aflatoxins are usually encountered
in the context of chronic exposure, via food intake or secondary to the
handling of food-stuffs. Aflatoxins have been incriminated in the pathogenesis
of the following conditions:
■■ Hepatitis,
fatty liver, cirrhosis
■■ Hepatocellular
carcinoma
■■ Hepatic failure
■■ Reye’s
syndrome
■■ Kwashiorkor.
Aflatoxins
accumulate in the presence of liver disease, and the association with hepatic cancer is confounded by the
occurrence of hepatitis-B. The latter is not only a risk factor for liver
cancer, but may also impair excretion of aflatoxins, causing further liver
injury and DNA damage. Thus, it must be admitted that in these conditions it is
not clear whether aflatoxin is a primary cause of the disease, is an incidental
product which accumulates secondary to the disease process, or is a
contrib-uting cause in association with other factors.
Aflatoxins can be detected in body
fluids and tissues by RIA and ELISA. HPLC with fluorescence detection has also
been used to detect and quantify aflatoxins in blood or tissue. Elevation of
serum alkaline phosphatase is a good indicator of aflatoxin toxicity. In one
study, there was a significant correla-tion between urinary levels of
aflatoxins and the presence of hepatitis B surface antigen in serum, with risk
of an increased incidence of heptatocellular carcinoma.
Treatment is mostly supportive. In
one experimental study involving ducklings which were given 5 micrograms of
aflatoxin and 50 mg of turmeric for 14 days, increased weight gain was seen
compared to controls. Almost complete reversal of fatty changes, granular
degeneration, and necrosis was observed. Antioxidants such as vitamin A have
been shown in vitro to inhibit aflatoxin-induced DNA adduct formation.
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