**1. Introduction**

[94] Yu, M. W., Lien, J. P., Chiu, Y. H., et al. (1997). Effect of aflatoxin metabolism and DNA adduct formation on hepatocellular carcinoma among chronic hepatitis B carri‐

[95] Zhang, Y. J., Ahsan, H., Chen, Y., et al. (2002). High frequency of promoter hyperme‐ thylation of RASSFIA and p16 and its relationship to aflatoxin B1-DNA adducts in

human hepatocellular carcinoma. *Mol Carcinog*, 35, 85-92.

ers in Taiwan. *J Hepatol*, 27, 320-330.

238 Aflatoxins - Recent Advances and Future Prospects

Aflatoxins are a group of naturally occurring carcinogens that are known to contaminate dif‐ ferent human and animal food stuffs. Aflatoxins are poisonous by-products from soil-borne fungus *Aspergillus*, which is responsible for the decomposition of plant materials [1-9]. The occurrence of aflatoxins foods and food products vary with geographic location, agricultural and agronomic practices. The susceptibility of food product to fungal attack occurs during pre-harvest, transportation, storage, and processing of the foods [1, 2, 4, 6, 9, 10]. The prob‐ lem of aflatoxin contamination of the food products is a common problem in tropical and subtropical regions of the world especially in the developing countries such as the sub-Sa‐ haran countries with poor practices and where the environmental conditions of warm tem‐ peratures and humidity favors the growth fungi [1, 2, 4, 6, 9, 10]. The various food products contaminated with aflatoxins include cereals like maize, sorghum, pearl millet, rice and wheat; oilseeds such as groundnut, soybean, sunflower and cotton; spices like chillies, black pepper, coriander, turmeric and zinger; tree nuts such as almonds, pistachio, walnuts and coconut; and milk and milk products [11]. The aflatoxins were initially isolated and identi‐ fied as the causative agent in Turkey X disease that caused necrosis of the liver in 1960 and over 100,000 turkeys died in England and USA and the death was attributed to the con‐ sumption of a mould-contaminated peanut meal [2, 6, 9, 12, 13]. Very high concentrations of aflatoxins are most often found in nutritive seeds such as maize, nuts and cereal grains in Africa and rice in China and Southeast Asia [2, 6, 9, 12-14].

© 2013 Bbosa et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Bbosa et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


**Table 1.** Summary of the major aflatoxins produced by the *Aspergillus* species of Moulds

Aflatoxins are a group of approximately 20 related fungal metabolites produced primarily by the fungi *Aspergillus flavus* and *A. parasiticus* [15-18]. Aflatoxins belongs to a group of di‐ furanocoumarins that are classified into two broad groups according to their chemical struc‐ ture and they include the difurocoumarocyclopentenone series (AFB1, AFB2, AFB2A, AFM1, AFM2, AFM2A and aflatoxicol) and the difurocoumarolactone series (AFG1, AFG2, AFG2A, AFGM1, AFGM2, AFGM2A and AFB3) [15-19], (Table 1 and figure 1).

**Figure 1.** Structures of the major aflatoxins B1, B2, G1, G2, M1, M2, B2A and G2A (Adopted from Reddy, 2012)[16]

The four major naturally known aflatoxins produced by the *Aspergillus* species of mold in‐ clude AFB1, AFB2, AFG1 and AFG2 where the "B" and "G" refer to the blue and green fluo‐ rescent colors produced under UV light on thin layer chromatography plates, while the subscript numbers 1 and 2 indicate major and minor compounds, respectively. Whereas the B designation of aflatoxins B1 and B2 result from the exhibition of blue fluorescence under UV-light, while the G designation refers to the yellow-green fluorescence of the relevant structures under UV-light [2, 6, 9, 12, 13]. The metabolic products of aflatoxins, M1 and M2 were first isolated from milk of lactating animals fed on Moldy grains contaminated with aflatoxin hence, the M designation [2, 4]. These toxins have closely similar structures (Figure 1) and form a unique group of highly oxygenated, naturally occurring heterocyclic com‐

Review of the Biological and Health Effects of Aflatoxins on Body Organs and Body Systems

http://dx.doi.org/10.5772/51201

241

Review of the Biological and Health Effects of Aflatoxins on Body Organs and Body Systems http://dx.doi.org/10.5772/51201 241

**Difuranocoumarins Type of aflatoxin** *Aspergillus specie(s)*

Aflatoxin B2a (AFB2a) *A. flavus*

Aflatoxin M2A (AFM2A) Metabolite of AFM2

Aflatoxicol M1 Metabolite of AFM1

Aflatoxin G2A (AFG2A) Metabolite of AFG2

Aflatoxin GM2 (AFGM2) Metabolite of AFG2 AFGM2A Metabolite of AFGM2

Aflatoxin B3 (AFB3) *Aspergillus* species not defined

Aflatrem *A. flavus, A. minisclerotigenes*

Aflatoxins are a group of approximately 20 related fungal metabolites produced primarily by the fungi *Aspergillus flavus* and *A. parasiticus* [15-18]. Aflatoxins belongs to a group of di‐ furanocoumarins that are classified into two broad groups according to their chemical struc‐ ture and they include the difurocoumarocyclopentenone series (AFB1, AFB2, AFB2A, AFM1, AFM2, AFM2A and aflatoxicol) and the difurocoumarolactone series (AFG1, AFG2, AFG2A,

Aflatoxin Q1 (AFQ1) Major metabolite of AFB1 in in vitro liver preparations of other higher vertebrates

Aflatoxin GM1 (AFG1) *A. flavus*

Parasiticol (P) *A. flavus*

Aspertoxin *A. flavus*

**Table 1.** Summary of the major aflatoxins produced by the *Aspergillus* species of Moulds

AFGM1, AFGM2, AFGM2A and AFB3) [15-19], (Table 1 and figure 1).

Aflatoxicol (AFL) *A. flavus*, metabolite of AFB1

Aflatoxin B1 (AFB1) *A. flavus, A. arachidicola, A. bombycis, A.*

*venezuelensis* Aflatoxin B2 (AFB2) *A. arachidicola, A. flavus, A. minisclerotigenes, A. nomius, A. parasiticus*

Aflatoxin M1 (AFM1) *A. flavus, A. parasiticus*; metabolite of aflatoxin B1 in

Aflatoxin M2 (AFM2) Metabolite of aflatoxin B2 in milk of cattle fed on contaminated foods

Aflatoxin G1 (AFG1) *A. arachidicola, A. flavus, A. minisclerotigenes, A. nomius, A. Parasiticus* Aflatoxin G2 (AFG2) *A. arachidicola, A. flavus, A. minisclerotigenes, A. nomius, A. parasiticus*

*minisclerotigenes, A. nomius, A. ochraceoroseus, A. parasiticus, A. pseudotamarii, A. rambellii, Emericella*

humans and animals and comes from a mother's milk

Difurocoumarocyclopenten

240 Aflatoxins - Recent Advances and Future Prospects

**Difurocoumarolactone**

**series**

one series

**Figure 1.** Structures of the major aflatoxins B1, B2, G1, G2, M1, M2, B2A and G2A (Adopted from Reddy, 2012)[16]

The four major naturally known aflatoxins produced by the *Aspergillus* species of mold in‐ clude AFB1, AFB2, AFG1 and AFG2 where the "B" and "G" refer to the blue and green fluo‐ rescent colors produced under UV light on thin layer chromatography plates, while the subscript numbers 1 and 2 indicate major and minor compounds, respectively. Whereas the B designation of aflatoxins B1 and B2 result from the exhibition of blue fluorescence under UV-light, while the G designation refers to the yellow-green fluorescence of the relevant structures under UV-light [2, 6, 9, 12, 13]. The metabolic products of aflatoxins, M1 and M2 were first isolated from milk of lactating animals fed on Moldy grains contaminated with aflatoxin hence, the M designation [2, 4]. These toxins have closely similar structures (Figure 1) and form a unique group of highly oxygenated, naturally occurring heterocyclic com‐ pounds. Aflatoxins B2 and G2 were established as the dihydroxy derivatives of B1 and G1, respectively. Whereas, aflatoxin M1 is 4-hydroxy aflatoxin B1 and aflatoxin M2 is 4-dihy‐ droxy aflatoxin B2. Of the four major aflatoxins (B1, B2, G1 and G2), G2 occurs in high quanti‐ ties though less toxic while AFB1 is the most toxic of all the aflatoxin. The World Health Organization (WHO) classifies AFB1 as a class 1 carcinogen [4, 6, 9, 18]. The aflatoxins dis‐ play potency of toxicity, carcinogenicity, mutagenicity in the order of AFB1> AFG1> AFB2> AFG2 [15-19]. The extent of toxicity depends on the organ affected especially the liver. The lethal toxicity of aflatoxin B1 varies in different animals from extremely susceptible (Sheep, Rat, Dog) to resistant species (Monkey, Chicken, Mouse). However, there are no toxicity in humans though epidemiological data from studies in Africa, South Africa, South East Asia and India implicate aflatoxins in the incidence of liver cancer especially the hepatobiliary carcinoma and death of children due to malnutrition, kwashiorkor and marasmus [20, 21]. Aflatoxins have been associated with various diseases like aflatoxicosis and other health problems in humans, livestock and domestic animals globally.

AFQ1, a less toxic detoxification metabolite. The CYP3A5 metabolizes AFB1 mainly to the *exo-*epoxide and some AFQ1 [29]. However, polymorphism studies with CYP3A5 have indi‐ cated that, this enzyme isoform is not expressed by most people especially in Africans [28]. Studies in Gambian children showed that aflatoxin cross the placenta and transported to the fetus and the new born where they can cause detrimental effects [28]. The CYP3A7 is a ma‐ jor CYP450 enzyme isoform in human fetal liver and metabolizes AFB1 to the 8, 9- epoxide

Review of the Biological and Health Effects of Aflatoxins on Body Organs and Body Systems

http://dx.doi.org/10.5772/51201

243

The epoxidation of AFB1 to the exo-8, 9-epoxide is a critical step in the genotoxic pathway of this carcinogen. The binding of AFB1 to DNA and DNA adduction by AFB1 exo-8,9 epoxide has been reported to cause a functional changes of DNA conformation [31].The epoxide is highly unstable and binds with high affinity to guanine bases in DNA to form afltoxin-N7 guanine [32]. The aflatoxin-N7-guanine has been shown to be capable of forming guanine (purine) to thymine (pyrimidine) transversion mutations in DNA and hence affecting the p53 suppressor gene in the cell cycle [33, 34]. The p53 gene is important in preventing cell cycle progression when there are DNA mutations, or signaling apoptosis. The mutations have been reported to affect some base pair locations more than others especially in the third base of codon 249 of the p53 gene in the region corresponding to the DNA binding do‐ main of the corresponding protein [13, 34]and this appears to be more susceptible to aflatox‐ in-mediated mutations than nearby bases [35]. AFB1 induces the transversion of base G to base T in the third position of codon 249 and similar mutations have been observed in hepa‐ tocellular carcinoma (HCC) in high AFB1 contaminated food in regions in East Asia and Af‐

Epoxide hydrolase and glutathione-S-transferase (GST) are both involved in hepatic detoxi‐ fication of activated AFB1, but the GST-catalyzed conjugation of glutathione to AFB1-8,9-ep‐ oxides is thought to play the most important role in preventing epoxide binding to target macromolecules like DNA and various cell proteins [38]. Glutathione pathway is reported to play a vital role in the detoxification of AFB1 [39, 40]. The AFB1 8,9 *exo* and *endo*epoxides are conjugated by glutathione to form AFB-mercapturate and the reaction is catalyzed by gluta‐ thione S-transferase (GST) [39, 40]. The glutathione-aflatoxin conjugate is transported from the cells with an ATP-dependent multidrug-resistance protein through an accelerated proc‐ ess [39]. Despite a preference for conjugating the more mutagenic AFB1 exo-epoxide isomer, the relatively low capacity for GST-catalyzed detoxification of bio-activated AFB1 in lung may be an important factor in the susceptibility of the lung to AFB1 toxicity [4, 8, 41].The *exo* and *endo* epoxide can also be converted non-enzymatically to AFB1-8,9-dihydrodiol which in turn can slowly undergo a base-catalysed ring opening reaction to a dialdehyde phenolate ion [27]. AFB1 dialdehyde can form Schiff bases with lysine residues in serum albumin form‐ ing aflatoxin-albumin complex [42]. Also the aflatoxin dialdehyde are reduced to a dialcohol in a NADPH-dependent catalyzed reaction by aflatoxin aldehyde reductase (AFAR) [43]. However the guanine alkylation by aflatoxin B1 produces *exo*-8,9-epoxide which is the reac‐ tive form and a carcinogen to the liver and the reaction is more than 2000 times more effi‐

that may cause fetal defects to the developing fetus [30].

cient in DNA than in aqueous solution [44], (Figure 2).

rica [34, 36, 37].
