Toxicokinetics of acrylamide in primary rat hepatocytes: coupling to glutathione is faster than conversion to glycidamide.

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).

N7-glycidamide-guanine DNA adduct formation by orally ingested acrylamide in rats: a dose-response study encompassing human diet-related exposure levels.

Acrylamide (AA) is formed during the heating of food and is classified as a genotoxic carcinogen. The margin of exposure (MOE), 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 of concern. After ingestion, AA is converted by P450 into the genotoxic epoxide glycidamide (GA). GA forms DNA adducts, primarily at N7 of guanine (N7-GA-Gua). We performed a dose-response study with AA in female Sprague-Dawley (SD) rats. AA was given orally in a single dosage of 0.1-10 000 µg/kg bw. The formation of urinary mercapturic acids and of N7-GA-Gua DNA adducts in liver, kidney, and lung was measured 16 h after application. A mean of 37.0 ± 11.5% of a given AA dose was found as mercapturic acids (MAs) in urine. MA excretion in urine of untreated controls indicated some background exposure from endogenous AA. N7-GA-Gua adduct formation was not detectable in any organ tested at 0.1 µg AA/kg bw. At a dose of 1 µg/kg bw, adducts were found in kidney (around 1 adduct/10(8) nucleotides) and lung (below 1 adduct/10(8) nucleotides) but not in liver. At 10, respectively, 100 µg/kg bw, adducts were found in all three organs, at levels close to those found at 1 µg AA/kg, covering a range of about 1-2 adducts/10(8) nucleotides. As compared to DNA adduct levels from electrophilic genotoxic agents of various origin found in human tissues, N7-GA-Gua adduct levels within the dose range of 0.1-100 µg AA/kg bw were at the low end of this human background. We propose to take the background level of DNA lesions in humans more into consideration when doing risk assessment of food-borne genotoxic carcinogens.

Profiling of mercapturic acids of acrolein and acrylamide in human urine after consumption of potato crisps.

SCOPE: Acrolein (AC) and acrylamide (AA) are food contaminants generated by heat treatment. We studied human exposure after consumption of potato crisps by monitoring excretion of mercapturic acids (MAs) in urine. METHODS AND RESULTS: MA excretion was monitored in human urine collected up to 72 h after ingestion of a test meal of experimental (study 1: 1 mg AA/150 g) or commercially available (study 2: 44 µg AA plus 4.6 µg AC/175 g) potato crisps. MA contents were analysed after purification via SPE using HPLC-ESI-MS/MS. On the basis of the area under the curve values of MAs excreted in urine, the total excretion of AC-related MAs exceeded that of AA-related MAs up to 12 times in study 1 and up to four times in study 2. Remarkably, AC content of potato crisps of study 2 was found to be only about 1/10 the AA content, as determined by isotope dilution headspace GC/MS. CONCLUSION: Our results indicate substantially higher exposure to AC from potato crisps than to AA. Total AC in such foods may encompass bioavailable AC forms not detected by headspace GC/MS. Both findings may also apply to other heat processed foods.