Abstract
Humans are exposed to a variety of natural and man-made environmental agents. It has been estimated by Hemminiki and Vainio (1984) that humans ingest approximately 1 μg dimethylnitrosamine (DMNA) per day. Lawley (1989) estimates that the fraction of DNA guanine methylated at the O6 position by DMNA is about 3 × 10-9 or 10 O6-methylguanine (MeGua) molecules per genome containing 1.2 × 1010 DNA nucleotides. A study by Umbenhauer et al., (1985) directly measured the amounts of O6-MeGua in the DNA of a non-exposed population and one exposed to DMNA in their diet. The level of O6-MeGua in the tissue samples obtained from half of the non-exposed and the majority of exposed individuals assayed were below the detection limit (100 O6-MeGua in molecules per genome) of the assay. The remaining non-exposed individuals exhibited 116 to 176 molecules per genome, while the exposed population exhibited significantly higher values between 236 and 664 O6-MeGuae molecules per genome. Although it is very difficult to relate the actual daily ingestion of the DMNA with daily adduct formation, these and other (Poirier, 1984; Perera et al., 1987; Manchester et al., 1988) data demonstrate that human exposure to chemical agents can cause the formation of detectable levels of DNA damage. One characteristic of all of these studies is the large inter-individual variation in the levels of DNA adduct detected.