Measurement of individual aflatoxin exposure among people having different risk to primary hepatocellular carcinoma.

The establishment of the carcinogenic role of aflatoxins has been impeded by the lack of suitable tests to measure individual exposure for long-term studies. It was shown that the use of immuno-concentration followed by high pressure liquid chromatography (HPLC) or immunoassay can regularly detect aflatoxins down to pg/ml in fluids including urine. Aflatoxin M1 (AFM1) in free form was identified as the major metabolite in urine suitable for use as an approximate dosimetric indicator of recent exposure to aflatoxin B1 (AFB1). A panel of monoclonal antibodies of IgG class were developed in the murine system against AFB1 and/or AFM1. Their affinity constants are at the level of 10(8)-10(9) L/mol, and they are suitable for use in either effective immuno-concentration or in high sensitivity immunoassays. It was shown in a high risk area of liver cancer (Qidong of China) that 10% or more of the local inhabitants had a urinary output of AFM1 one or two orders of magnitude higher than that of Beijing people, especially during the wet seasons. The ingestion of AFB1 among these local people was estimated to exceed 1 mg/year. The major source came from contaminated corn and rice, but local alcoholic beverages also contributed. The increased excretion of AFM1 was more pronounced in patients with chronic active hepatitis. This observation of very low AFM1 content in urine of a significant percentage of local people implies their food storage practices may offer a feasible method for such prevention. The value and possible problems in conducting long-term studies on primary prevention are discussed.