DNA DAMAGE AND MERCAPTURIC ACID EXCRETION AFTER LOW DOSE ORAL APPLICATION OF ACRYLAMIDE TO RATS
Acrylamide (AA), classified as a genotoxic carcinogen (IARC, group 2A), is formed by thermal treatment of food. The margin of exposure (MOE) of AA, representing the distance between the bench mark dose associated with 10% tumor incidence in rats and the estimated average human exposure, is considered to be low and of human health concern. After uptake, AA is activated in the liver by CYP450 2E1, generating the genotoxic epoxide 2,3-epoxy-propanamide (glycidamide, GA). GA damages DNA by forming covalent adducts, primarily at N7 of guanine (N7-GA-Gua). AA and its genotoxic metabolite GA are, however, also conjugated to glutathione and excreted via urine as mercapturic acids (MA), namely N-acetyl-S-(2-carbamoylethyl)-cysteine (AAMA), and N-acetyl-S-(2-hydroxy-2-carbamoylethyl)-cysteine (GAMA). Urinary MA excretion is used to monitor exposure. In a comprehensive dose-response study, female Sprague Dawley (SD) rats on an AA free diet were gavaged with AA in aqueous solution, at single doses of 0.1-10,000µg/kg bw. Formation of urinary MAs and of N7-GA-Gua DNA adducts in liver, kidney and lung was measured 16h after application. Untreated controls were found to excrete about 0.8nmol MA. Since the animals had ingested at best 0.4nmol AA/d with their diet, this was suggestive for some background endogenous formation of AA. At the lowest dosage (0.1µg AA/kg bw), N7-GA-Gua adducts above the limit of detection (LOD, 0.2adducts/108 nucleotides) were not detected in any organ tested. At 1µg/kg bw, enhanced adduct levels were found in kidney (around 1adduct/108 nucleotides) and lung (<1adduct/108 nucleotides), not in liver. At 10 and 100µg/kg bw, adducts were found in all three organs, at levels not significantly different to those found at 1µgAA/kg bw (about 1-2adducts/108 nucleotides), thus not exhibiting a dose-response relationship. In summary, the results allow to conclude that exposure to single doses of AA in the range of human dietary exposure leads to N7-GA-Gua adduct levels in tissues of SD rats at the low end of background DNA lesions of various origin in human and rat tissues.This study was supported by ISIC, the Institute for Scientific Information on Coffee.