209
RNA. At the molecular level, aflatoxins impart their effect either interfering with
DNA replication or transcription of messenger RNA into protein. Clifford et al.
(1967) revealed that the administration of a single dose of aflatoxin (7 mg/kg body
weight) resulted in slow development of periportal necrosis. Hepatic enzymes were
released into the serum after 48 h of poisoning. This was followed by a rise in serum
phosphatase activity and bilirubin concentration. Shortly after this study, it was
revealed (Clifford et al. 1967) that the biochemical changes underlying the development of liver necrosis in the rat after administration of AFB1 were initiated by the
toxin interacting with DNA. This interaction prevented the RNA polymerase transcribing the DNA and inhibited the formation of mRNA. The failure of mRNA
formation resulted in an inhibition in protein synthesis that they considered to be the
cause of the liver necrosis. They compared interactions of AFB1, AFG1, and AFG2
with DNA. Raney et al. (1993) studied the binding of AFB1 to DNA and DNA
adduction by corresponding epoxide. Their results demonstrated that duplex structure favors adduct formation. Adduct yields were compared for A, B, and Z form of
DNA helices. About 12 times less adduct was produced from the A-form helix when
compared with the B form, while no adduct was produced from a Z-form duplex.
They concluded that reaction of AFB1-8,9-epoxide with DNA proceeds via an
intercalated transition state complex only with the B form of the double helix.
Aflatoxin binds with lysine component of serum albumin resulting in the formation of lysine AFB1 (Sabbioni 1990). Ch’ih et al. (1993) investigated the nuclear
translocation of AFB1-protein complex. The in vitro binding of 3[H] AFB1 to various proteins was studied by equilibrium dialysis. It was reported that at 23 °C, 3[H]
AFB1 binding activity (mMol/mole) decreased as follows: pyruvate
kinase > albumin- NLS > albumin > carbonic anhydrase > RNase > histone. The
nuclear translocation and activation of AFB1 and AFB1 protein complexes were
investigated using isolated rat liver nuclei in the presence of an ATP and NADPH
regenerating system (Mishra and Das 2003).
12.9.5 Occurrence of Aflatoxin
AFs may contaminate a wide variety of agricultural commodities, especially if they
have high carbohydrate and/or fat contents. Cereals and all products derived from
cereals represent a risk for the consumers, because these products are very sensitive
to AF contamination (Anthony et al. 2012; Hashemi et al. 2014).
Aflatoxins are carcinogenic compounds, and their presence in food is a major
food-related health issue. Aflatoxins are commonly found in foodstuffs such as
groundnuts, wine, and maize and feed products such as wheat. Maize has the highest risk of aflatoxin contamination among cereals in the European Union, which has
limited its presence to 4 l g kg
−1
in maize foodstuff (Verheecke et al. 2014).
12 Fungal Mycotoxins
RNA. At the molecular level, aflatoxins impart their effect either interfering with
DNA replication or transcription of messenger RNA into protein. Clifford et al.
(1967) revealed that the administration of a single dose of aflatoxin (7 mg/kg body
weight) resulted in slow development of periportal necrosis. Hepatic enzymes were
released into the serum after 48 h of poisoning. This was followed by a rise in serum
phosphatase activity and bilirubin concentration. Shortly after this study, it was
revealed (Clifford et al. 1967) that the biochemical changes underlying the development of liver necrosis in the rat after administration of AFB1 were initiated by the
toxin interacting with DNA. This interaction prevented the RNA polymerase transcribing the DNA and inhibited the formation of mRNA. The failure of mRNA
formation resulted in an inhibition in protein synthesis that they considered to be the
cause of the liver necrosis. They compared interactions of AFB1, AFG1, and AFG2
with DNA. Raney et al. (1993) studied the binding of AFB1 to DNA and DNA
adduction by corresponding epoxide. Their results demonstrated that duplex structure favors adduct formation. Adduct yields were compared for A, B, and Z form of
DNA helices. About 12 times less adduct was produced from the A-form helix when
compared with the B form, while no adduct was produced from a Z-form duplex.
They concluded that reaction of AFB1-8,9-epoxide with DNA proceeds via an
intercalated transition state complex only with the B form of the double helix.
Aflatoxin binds with lysine component of serum albumin resulting in the formation of lysine AFB1 (Sabbioni 1990). Ch’ih et al. (1993) investigated the nuclear
translocation of AFB1-protein complex. The in vitro binding of 3[H] AFB1 to various proteins was studied by equilibrium dialysis. It was reported that at 23 °C, 3[H]
AFB1 binding activity (mMol/mole) decreased as follows: pyruvate
kinase > albumin- NLS > albumin > carbonic anhydrase > RNase > histone. The
nuclear translocation and activation of AFB1 and AFB1 protein complexes were
investigated using isolated rat liver nuclei in the presence of an ATP and NADPH
regenerating system (Mishra and Das 2003).
12.9.5 Occurrence of Aflatoxin
AFs may contaminate a wide variety of agricultural commodities, especially if they
have high carbohydrate and/or fat contents. Cereals and all products derived from
cereals represent a risk for the consumers, because these products are very sensitive
to AF contamination (Anthony et al. 2012; Hashemi et al. 2014).
Aflatoxins are carcinogenic compounds, and their presence in food is a major
food-related health issue. Aflatoxins are commonly found in foodstuffs such as
groundnuts, wine, and maize and feed products such as wheat. Maize has the highest risk of aflatoxin contamination among cereals in the European Union, which has
limited its presence to 4 l g kg
−1
in maize foodstuff (Verheecke et al. 2014).
12 Fungal Mycotoxins