Formation of N-7-(2-carbamoyl-2-hydroxyethyl)guanine in DNA of the mouse and the rat following intraperitoneal administration of [14C]acrylamide.
ABSTRACT Acrylamide is an alkylating agent which reacts very slowly in direct reactions with DNA and is negative in the Ames test, but is carcinogenic in mice and rats. In order to explain the cancer-initiating properties of acrylamide we have studied DNA adduct formation in vitro with a metabolizing system and in vivo in mice and rats following i.p. administration of 14C-labeled acrylamide. A major adduct found in both species was N-7-(2-carbamoyl-2-hydroxy-ethyl)guanine, formed by reaction of the DNA with the epoxide metabolite glycidamide. The levels of this adduct were similar in the different organs of the two rodent species, which supports the notion that glycidamide is relatively evenly distributed among tissues and that the organ-specificity in acrylamide carcinogenesis cannot be explained by a selective accumulation of the DNA-reactive metabolite in target organs.
- SourceAvailable from: Joana P Miranda[show abstract] [hide abstract]
ABSTRACT: Acrylamide (AA) is a well-known industrial chemical classified as a probable human carcinogen. Benign and malignant tumours at different sites, including the mammary gland, have been reported in rodents exposed to AA. This xenobiotic is also formed in many carbohydrate-rich foods prepared at high temperatures. For this reason, AA is an issue of concern in terms of human cancer risk. The epoxide glycidamide (GA) is thought to be the ultimate genotoxic AA metabolite. Despite extensive experimental and epidemiological data focused on AA-induced breast cancer, there is still lack of information on the deleterious effects induced by GA in mammary cells. The work reported here addresses the characterisation and modulation of cytotoxicity, generation of reactive oxygen species, formation of micronuclei (MN) and quantification of specific GA-DNA adducts in human MCF10A epithelial cells exposed to GA. The results show that GA significantly induces MN, impairs cell proliferation kinetics and decreases cell viability at high concentrations by mechanisms not involving oxidative stress. KU55933, an inhibitor of ataxia telangiectasia mutated kinase, enhanced the cytotoxicity of GA (P < 0.05), supporting a role of this enzyme in regulating the repair of GA-induced DNA lesions. Moreover, even at low GA levels, N7-GA-Gua adducts were generated in a linear dose-response manner in MCF10A cells. These results confirm that human mammary cells are susceptible to GA toxicity and reinforce the need for additional studies to clarify the potential correlation between dietary AA exposure and breast cancer risk in human populations.Mutagenesis 11/2013; 28(6):721-9. · 3.50 Impact Factor
- [show abstract] [hide abstract]
ABSTRACT: Acrylamide (AA), classified as class 2A carcinogen (probably carcinogenic to humans) by the International Agency for Research on Cancer (IARC), is formed during heating of food from reducing carbohydrates and asparagine by Maillard reaction chemistry. After dietary uptake, AA is in part metabolically converted into the proximate genotoxic phase I metabolite glycidamide (GA). GA reacts with nucleophilic base positions in DNA, primarily forming N7-(2-carbamoyl-2-hydroxyethyl)guanine (N7-GA-Gua) adducts. In a competing phase II biotransformation pathway AA, as well as its phase I metabolite GA, is coupled to glutathione (GSH). The GSH coupling products are further biotransformed and excreted via urine as mercapturic acids (MA), N-acetyl-S-(2-carbamoylethyl)cysteine (AAMA), and N-acetyl-S-(2-hydroxy-2-carbamoylethyl)cysteine (GAMA). In the present study, hepatic biotransformation pathways and DNA adduct formation were studied in primary rat hepatocytes, incubated with AA (0.2-2,000 μM) for up to 24 h. Contents of AA-GSH, GA, AAMA, and GAMA were measured in the cell culture medium after solid phase extraction (SPE). N7-GA-Gua adducts in DNA of hepatocytes were determined by HPLC-ESI-MS/MS after lysis of the cells and neutral thermal hydrolysis. Formation of AA-GSH was linear with AA concentration and incubation time and became detectable already at 0.2 μM (4 h). In contrast to AA, GA was not detected before 16 h incubation at 10-fold higher AA concentration (2 μM). In summary, the rate of AA-GSH formation was found to be about 1.5-3 times higher than that of GA formation. N7-GA-Gua adducts were found only at the highest AA concentration tested (2,000 μM).Archives of Toxicology 04/2013; · 5.22 Impact Factor
- [show abstract] [hide abstract]
ABSTRACT: Acrylamide (AA), a probable human carcinogen, is present in high-temperature-processed foods, and has frequently been detected in humans worldwide. In the present study, the levels of a major AA metabolite, N-acetyl-S-(2-carbamoylethyl)-cysteine (AAMA) were measured in urine samples collected in two separate events with 3d interval from Korean children (n=31, 10-13years old), and their diets were surveyed for 4d period prior to the second urine sampling. Daily AA intake was estimated from AAMA urinary levels and the influence of food consumption on urinary AAMA levels was investigated. The concentrations of metabolite AAMA in urine ranged between 15.4 and 196.3ng/mL, with a median level of 68.1ng/mL, and the levels varied by day considerably even in a given child. Children who were exposed to environmental smoke at home exhibited significantly higher levels of AAMA in urine, suggesting the importance of passive smoking as a source of AA exposure among children. Median (95th percentile) values of daily AA intake in Korean children were 1.04 (2.47)μg/kgbodyweight/day, which is higher than those reported elsewhere. After adjustment for gender, body mass index, and smoking status of family members, the consumptions of cracker and chocolate were identified to be significantly associated with the concentrations of AAMA in urine. The result of this study will provide information useful for developing public health and safety management for AA.Science of The Total Environment 04/2013; 456-457C:17-23. · 3.26 Impact Factor