Biomarkers of Aflatoxin Exposure and Its Relationship with the Hepatocellular Carcinoma

Abstract

Mycotoxins are secondary metabolites produced by fungi that grow naturally in foodstuffs. They are able to generate a wide variety of toxic effects in vertebrates, including men (Coulombe, 1991). Toxigenic fungi may contaminate foodstuffs in the most different phases of production and processing, from cultivation to transport and storage. Mycotoxins show high chemical stability and may persist in the foodstuff even after fungi were removed by common manufacturing and packaging processes (Chu, 1991). Diseases caused by mycotoxins are called mycotoxicoses. They are diffuse syndromes that cause lesions mainly in organs such as liver, kidneys, epithelial tissue (skin and mucous membranes) and central nervous system, depending on the type of the toxin. Two or more toxins may also occur simultaneously, leading to intensified toxic effects on the susceptible organism (Orsi et al., 2007). Aflatoxins are mycotoxins produced by fungi in the genus Aspergillus, species A. flavus, A. parasiticus and A. nomius (Moss, 1998). These fungi are distributed worldwide, and their optimal growth conditions are relative humidity of 80-85% and temperature around 30oC (Coulombe, 1991). Nowadays, 18 similar compounds are called aflatoxins. However, the most important in medical terms are types B1, B2, G1 e G2 (Coulombe, 1991). Aflatoxin B1 (AFB1), besides being the most frequently found in plant substrates, has the greatest toxigenic power. Aflatoxins B2 (AFB2), G1 (AFG1) and G2 (AFG2) have about 50, 20 and 10% of AFB1 toxigenic power, respectively (Leeson et al., 1995). AFB1 is a genotoxic compound, and is considered to be one of the most potent natural mutagens. Liver carcinogenesis is the most important effect of chronic aflatoxin exposure. This toxicity has been widely demonstrated – mainly in relation to AFB1 in many animal species, including fish, birds, rodents, carnivores and primates (Busby & Wogan, 1984). Based on available studies, the International Agency for Research on Cancer (IARC) concluded, in 1987, that there was enough evidence to classify AFB1 in Group 1 human carcinogen (Rothschild, 1992) One of the most important aspects in risk analysis of chemical substances is to determine the degree of human exposure (World Health Organization [WHO], 2002), a particularly difficult task for contaminants present in foodstuffs. However, it is possible to indirectly estimate the degree of exposure based on data on consumption of contaminated foodstuffs, and on the average occurrence of the toxin. In this estimation, the degree of exposure is