Aflatoxin metabolism in humans: detection of metabolites and nucleic acid adducts in urine by affinity chromatography.

Abstract

A high-affinity IgM monoclonal antibody specific for aflatoxins was covalently bound to Sepharose 4B and used as a preparative column to isolate aflatoxin derivatives from the urine of people and experimental animals who had been exposed to the carcinogen environmentally or under laboratory conditions. Aflatoxin levels were quantified by radioimmunoassay and high-performance liquid chromatography after elution from the afinity column. In studies on rats injected with ["'C]aflatoxin Bl, we identified the major aflatoxin-DNA adduct, 2,3-dihydro-2-(N7-guanyl)-3-hydroxyaflatoxin B1 (AFBl-N7-Gua), and the oxidative metabolites Ml and P1 as the major aflatoxin species present in the urine. When this methodology was applied to human urine samples obtained from people from the Guangxi Province of China exposed to aflatoxin B1 through dietary contamination, the aflatoxin metabolites detected were also AFB1-N7-Gua and aflatoxins Ml and Pl. Therefore, affinity chromatography using a monoclonal antibody represents a useful and rapid technique with which to isolate this carcinogen and its metabolites in biochemical epidemiology and for subsequent quantitative measurements, providing exposure information that can be used for risk assessment.The aflatoxins are highly carcinogenic agents consistently found as contaminants in human food supplies in many areas of the world and epidemiologically linked to increased incidence of human liver cancer in Asia and Africa [see Busby and Wogan (ref. complex procedures used to purify the aflatoxins prior to analysis have seriously limited the application of these approaches in large-scale epidemiologic studies.A major objective of our work has been the development of rapid, noninvasive screening procedures for assessing the exposure of humans to environmentally occurring carcinogens. Useful protocols require the ability to quantify chemical carcinogens and their metabolites, especially DNA and protein adducts, in readily accessible compartments, such as urine and serum. We have been developing these monitoring techniques through immunoassays using monoclonal antibodies (8-10). These antibodies have proven to be useful analytical tools for quantifying the aflatoxins in biological fluids and also for use with affinity chromatography matrices as preparative tools to isolate aflatoxins from biological fluids (10). We report here results of initial applications of these techniques to the analysis of human urine obtained from people environmentally exposed to AFB1 in their diet and also of urine of rats injected with AFB1. These preparative and analytical procedures permit rapid measurement of aflatoxins in complex biological fluids under conditions that can be applied to large numbers of samples collected in epidemiologic surveys seeking to evaluate aflatoxin exposure as a risk factor for liver cancer in man.

Genome-scale mutational signatures of aflatoxin in cells, mice, and human tumors

“…Partly, this is because peripheral biochemical markers of aflatoxin exposure, such as aflatoxinalbumin or urinary aflatoxin-DNA adducts reflect recent exposure. This makes it difficult to assess the strength of the association between the R249S mutation and long-term aflatoxin exposure (Groopman et al 1985;Wild et al 1986;Egner et al 2006). …”

Epidemiologic Approaches to Assessing Human Cancer Risk from Consuming Aquatic Food Resources from Chemically Contaminated Water

“…Detection of cellular carcinogen-DNA adducts in humans by highly specific antibodies has also been accomplished for a few agents and holds some promise for use as an epidemiologic end point (76). Detection of adducts in urine resulting from DNA repair processes has also been successful, although those who excrete the adducts may arguably be at lower risk because of their obvious DNA repair competency (77). Chemicals that alter DNA may also alter proteins.…”

DNA adducts as exposure biomarkers and indicators of cancer risk.

“…Atomic absorbance spectrometry is used for cisplatin (80,81) and electrochemical detection is used for oxidative DNA damage (82,83 dosimetry of aflatoxin exposure, 42 individuals in the Guanxi region of China (89) were studied. A portion of the actual food consumed was assayed for aflatoxin content and urinary output was assayed for excretion of aflatoxin B1-N7-guanine by both males and females (37,90). The dosimetry data showed an excellent correlation between dietary aflatoxin intake and urinary adduct excretion (91 …”