Monitoring of individual human exposure to aflatoxins (AF) and N‐nitrosamines (NNO) by immunoassays

Highly sensitive immunoassays have been used to quantitate aflatoxins (AF) and N‐nitrosamines (NNO) in human body fluids and tissues, respectively. This approach was taken in order to quantitate environmental exposure to these agents at an individual level to facilitate the investigation of their role in the etiology of human cancer. In order to analyse AF in human urine, an immunopurification step has been developed by using AF‐specific antibody bound to AH‐Sepharose 4B gel in a small (4‐ml gel volume) affinity column prior to enzyme‐linked immunosorbent assay (ELISA). The ELISA can be used to quantitate aflatoxin B 1 (AFB 1 ) over the range 0.01 ng/ml to 10 ng/ml and the assay system has been validated by using human urine samples spiked with AFB 1 over this concentration range. In addition, 29 urine samples from the Philippines have been analysed and found to contain a range of levels from zero to 4.25 ng/ml AFB 1 equivalent with a mean of 0.875 ng/ml. This compared with a mean of 0.066 ng/ml AFB 1 equivalent in samples from France. Radioimmunoassay of O 6 ‐methyldeoxyguanosine (O 6 ‐medG) has been performed on human oesophageal and cardiac stomach mucosal DNA from tissue samples obtained during surgery in Linxian County, People's Republic of China, an area of high risk for both oesophageal and stomach cancer. Using the methodology described and having 1 mg of hydrolyzed DNA allows the detection of approximately 25 fmol O 6 medG per mg DNA. Of the 37 tissue samples analyzed from Linxian County, 17 samples had levels of O 6 ‐medG ranging from 15 to 50 fmol/mg DNA, ten showed higher levels up to 160 fmol/mg DNA, and the remaining ten samples were below the limit of detection. For comparison, 12 tissue samples were obtained from hospitals in Europe and all showed levels below 45 fmol O 6 ‐medG/mg DNA with seven below the limit of detection. All tissue samples from Linxian county showed normal levels of O 6 ‐alkylguanine DNA alkyltransferase when compared to levels in other parts of the world. The approaches described appear promising for assessing the role of AFB 1 in the etiology of human liver cancer and of nitrosamines as possible causative agents in oesophageal or stomach cancer.