The use of monoclonal antibody affinity columns for assessing DNA damage and repair following exposure to aflatoxin B₁

Primary hepatocellular carcinoma is one of the most lethal and common cancers in the world. It is particularly prevalent on the continents of Africa and Asia. A number of epidemiological studies have associated the exposure status of people to aflatoxin B₁ as being important in the etiology of liver cancer. However, to date these studies have relied upon the criteria of presumptive intake data, rather than relying upon quantitative analyses of aflatoxin-DNA adduct and metabolite content obtained by monitoring biological fluids from exposed people. Information obtained by monitoring exposed individuals for specific DNA adducts and metabolites will define the pharmacokinetics of aflatoxin B₁ in people, thereby facilitating risk assessments. We have developed monoclonal antibodies specific for aflatoxin metabolites, especially the DNA adducts. These monoclonal antibodies are used in solid phase immunoassays for the preparative purification of these aflatoxin derivatives from biological fluids. These methods in conjunction with other analytical procedures have resulted in the development of rapid protocols used to quantitatively measure aflatoxins in urine obtained from people dietarily exposed to this carcinogen. The people examined live in the Gambia and high liver cancer regions in the People's Republic of China. We have recently completed a pilot study in China where we have now begun to identify the pharmacokinetic parameters associated with chronic exposure of aflatoxin B₁ in the diet. Despite the development of these new technologies, we must continue to define animal model systems which can be used to interpret the human data. Our work using animal models based on the differential effects of ethoxyquin on the kinetics of aflatoxin-DNA adducts and gamma glutamyl transpeptidase-positive foci formation indicate that the direct linear extrapolation of total adduct content in target tissues to dose may be inappropriate to assign risk to people (or rats). However, our findings do support the concept that measurement of the major, rapidly excised AFB₁-N⁷-Gua adduct in tissues and fluids is an appropriate dosimeter for estimating exposure status and risk in individuals consuming this mycotoxin. Further studies employing different classes of modifiers of aflatoxin carcinogenesis in rodent models should better define the relationships between hepatic and urinary levels of AFB₁-N⁷-Gua and susceptibility to neoplasia.