Molecular Dosimetry of Urinary Aflatoxin-DNA Adducts in People Living in Guangxi Autonomous Region, People's Republic of China

TLDR: The relationship between dietary intake of aflatoxins and the excretion of the major aflatoxin-DNA adduct and other metabolites into the urine of chronically exposed people was explored and there was no positive statistical association between exposure in the diet and a flatoxin P1 excretion, despite aflat toxin P1 being quantitatively a major metabolite.

Abstract: Hepatocellular carcinoma is one of the five leading human cancers causing at least 250,000 deaths each year. One of the major risk factors for this disease is exposure to dietary aflatoxins, and the development of appropriate molecular dosimetry biomarkers would facilitate the identification of individuals at risk. This study was undertaken to explore the relationship between dietary intake of aflatoxins and the excretion of the major aflatoxin-DNA adduct and other metabolites into the urine of chronically exposed people. The following protocol was developed for this investigation in Guangxi Autonomous Region, People's Republic of China, where the diets of 30 males and 12 females (ages, 25–64 years) were monitored for 1 week and aflatoxin intake levels determined each day. Starting on the fourth day, total urine volumes were obtained in consecutive 12-h fractions for 3 or 4 days. High performance liquid chromatography and competitive radioimmunoassay analyses were done on each of the urine samples, and the relationships between excretion of total aflatoxin metabolites, aflatoxin- N7 -guanine, aflatoxin M1, aflatoxin P1, and aflatoxin B1, and aflatoxin B1 intake values were determined. The average intake of aflatoxin B1 by men was 48.4 μg/day, giving a total mean exposure during the study period of 276.8 μg. The average daily intake by women was 77.4 μg/day, resulting in a total average exposure during the 7-day period of 542.6 μg aflatoxin B1. Initial efforts to characterize aflatoxin metabolites in urine samples were with an analysis by competitive radioimmunoassay. The analysis by linear regression of the association between aflatoxin B1 intake/day and total aflatoxin metabolite excretion/day showed a correlation coefficient of only 0.26. These findings stimulated the immunoaffinity/analytical high performance liquid chromatography analysis for individual metabolites. When the data were analyzed by linear regression analysis, the aflatoxin N7 -guanine excretion and aflatoxin B1 intake from the previous day showed a correlation coefficient of 0.65 and P < 0.000001. Similar analysis for aflatoxin M1 resulted in a correlation coefficient of 0.55 and P < 0.00001, whereas there was no positive statistical association between exposure in the diet and aflatoxin P1 excretion, despite aflatoxin P1 being quantitatively a major metabolite. Analysis of the total aflatoxin- N7 -guanine excretion in the urine during the complete collection period plotted against the total aflatoxin B1 exposure in the diet for each of the individuals, smoothing the day to day variations, revealed a correlation coefficient of 0.80 and P < 0.0000001. Given this analysis, it is clear that a summation of excretion and exposure status provides a stronger association between exposure and a molecular dosimetry marker than was seen in prior statistical analyses. These findings support the concept that quantitation of the aflatoxin- N7 -guanine adduct in urine is a good biomarker for aflatoxin B1 exposures.