Acrylamide: Consideration of species differences and nonlinear processes in estimating risk and safety for human ingestion

Dietary exposure to acrylamide and breast cancer risk: results from the NutriNet-Santé cohort

BACKGROUND

Acrylamide is classified as a probable human carcinogen by the International Agency for Research on Cancer but epidemiologic evidence on the carcinogenicity of acrylamide from dietary sources is limited.

OBJECTIVES

This study aimed to investigate the associations between dietary acrylamide and breast cancer risk in the NutriNet-Santé cohort, accounting for menopausal and hormone receptor status.

METHODS

This prospective cohort study included 80,597 French females (mean ± SD age at baseline: 40.8 ± 14 y) during a mean ± SD follow-up of 8.8 ± 2.3 y. Acrylamide intake was evaluated using repeated 24-h dietary records (n ± SD = 5.5 ± 3.0), linked to a comprehensive food composition database. Associations between acrylamide intake and breast cancer risk (overall, premenopausal, and postmenopausal) were assessed by Cox hazard models adjusted for known risk factors (sociodemographic, anthropometric, lifestyle, medical history, and nutritional factors).

RESULTS

The mean ± SD dietary acrylamide intake was 30.1 ± 21.9 µg/d (main contributors: coffee, potato fries and chips, pastries, cakes, bread). During follow-up, 1016 first incident breast cancer cases were diagnosed (431 premenopausal, 585 postmenopausal). A borderline significant positive association was observed between dietary acrylamide exposure and breast cancer risk overall (HR for quartile 4 compared with 1: 1.21; 95% CI: 1.00, 1.47) and a positive association was observed with premenopausal cancer (HRQ4vs.Q1: 1.40; 95% CI: 1.04, 1.88). Restricted cubic spline analyses suggested evidence for nonlinearity of these associations, with higher HRs for intermediate (quartile 2) and high (quartile 4) exposures. Receptor-specific analyses revealed positive associations with estrogen receptor-positive breast cancer (total and premenopausal). Acrylamide intake was not associated with postmenopausal breast cancer.

CONCLUSIONS

Results from this large prospective cohort study suggest a positive association between dietary acrylamide and breast cancer risk, especially in premenopausal females, and provide new insights that support continued mitigation strategies to reduce the content of acrylamide in food.This trial was registered at clinicaltrials.gov as NCT03335644.

The construction and application of physiologically based toxicokinetic models for acrylamide, glycidamide and their biomarkers in rats and humans

Acrylamide (AA), a class 2A probable carcinogen to humans classified by the International Agency for Research on Cancer, has attracted extensive attention worldwide since it was widely used in industrial and domestic water treatment and detected in thermal processing foods. The metabolic adducts of AA and its primary metabolite glycidamide (GA) have been served as biomonitoring markers of AA intake, but the physiologically based toxicokinetics (PBTK) models to estimate internal dosimetry still remain unclear. An updated PBTK model for AA, GA and their metabolic biomarkers in rats and humans was developed and extended with time-course datasets from both literatures and our experiments. With adjustments to the model parameters, linear regression correlation coefficient (R²) between the fitting values and the validation datasets of rats and humans was greater than 0.76. The current model fits well with the experimental datasets of urinary N-acetyl-S-(2-carbamoylethyl)-l-cysteine (AAMA) and (N-(R,S)-acetyl-S-(carbamoyl-2-hydroxyethyl)-l-cysteine) (GAMA) of rats exposed to AA from 0.1 to 50 mg/kg b.w. and humans exposed to AA from 0.0005 to 0.020 mg/kg b.w., indicating the robustness of the current models. Parameters for adduct of AA with N-terminal valine of hemoglobin (AAVal) were extended to humans and validated. Kinetic parameters for rats were assessed and validated based upon fit to the experimental datasets for liver N3-(2-carbamoyl-2-hydroxyethyl)-adenine (N3-GA-Ade) and N7-(2-carbamoyl-2-hydroxyethyl)-guanine (N7-GA-Gua) adducts. Compared with the previous model, the developed model included the correlation between AA intake and its mercapturic acid adducts, AAMA and GAMA, in a larger dose range with new experimental data, and parameters for AAVal, N3-GA-Ade and N7-GA-Gua were improved and verified. The current multi-component PBTK models provide a superior foundation for the estimation of short-term to medium and long-term intake levels of human exposure to AA.

Acrylamide-induced Changes of Granulopoiesis in Porcine Bone Marrow

Introduction

Due to the widely documented and diverse toxic effects of acrylamide, the authors decided to evaluate the impact of high and low doses of this compound on the process of granulopoiesis in porcine bone marrow.

Material and Methods

The experiment was conducted on 15 Danish Landrace pigs at the age of 8 weeks. The animals were randomly assigned into three equal groups (n = 5). Control animals received empty gelatine capsules as placebo. Animals in the first experimental group (the LD group) received a low dose of acrylamide of 0.5 μg/kg b.w./day, and animals in the second experimental group (the HD group) received a tenfold higher dose of acrylamide of 5 μg/kg b.w./day. Placebo and acrylamide capsules were administered with feed every morning for 28 days. Bone marrow was collected into tubes without an anticoagulant twice - before the first capsule administration (day 0) and on the 28^th day of the study. After drying and staining, bone marrow smears were subjected to detailed cytological evaluation under a light microscope.

Results

Changes in cell morphology, i.e. degenerative changes in the cellular nuclei, were observed in both experimental groups. Both low and high doses of acrylamide decreased the number of segmented eosinophils, neutrophilic and segmented metamyelocytes, neutrophils, as well as basophils and basophilic metamyelocytes.

Conclusion

Acrylamide at doses of 0.5 μg/kg b.w./day and 5 μg/kg b.w./day clearly influences porcine granulopoiesis.

Characterization of primary glutathione conjugates with acrylamide and glycidamide: Toxicokinetic studies in Sprague Dawley rats treated with acrylamide

Acrylamide (AA) is classified as a probable human carcinogen and is ubiquitous in foods processed at high temperatures. The carcinogenicity of AA has been attributed to its active metabolite, glycidamide (GA). Both AA and GA can spontaneously or enzymatically conjugate with glutathione (GSH) to form their corresponding GSH conjugates. Profiling AA-glutathione conjugate (AA-GSH) and GA-glutathione conjugates (2 isomers: GA2-GSH and GA3-GSH) in serum would better illustrate AA detoxification compared with urinary metabolite analysis. However, the lack of AA-, GA2, and GA3-GSH study remains a critical data gap. Our study aimed to investigate the toxicokinetics of AA-, GA2-and GA3-GSH in Sprague Dawley rats treated with 0.1 mg/kg, 1.0 mg/kg, or 5.0 mg/kg AA. Blood samples were collected for LC-MS/MS analysis of the GSH conjugate products. Within 24 h of treatment, we observed rapid formation, elimination, and linear kinetics of AA-, GA2-and GA3-GSH. The ∑GA-GSH AUC/AA-GSH AUC ratios were 0.14-0.29, similar to ∑GA/AA AUC in serum but different from ∑GA/AA-derived urinary mercapturic acids in rodents. Our analysis of AA- and GA-GSHs values represents direct detoxification of AA and GA in vivo. This study advances our understanding of sex and inter-species differences in AA detoxification and may refine the existing kinetic models for a more relevant risk extrapolation.

The Influence of High and Low Doses of Acrylamide on Porcine Erythropoiesis

Introduction

Due to the widespread occurrence of acrylamide in the environment, its likely carcinogen status, and the suitability of the pig model as a human analogue, the authors decided to evaluate the impact of high and low doses of this compound on the processes of erythropoiesis in swine bone marrow.

Material and Methods

The experiment was carried out on Danish Landrace pigs at the age of eight weeks and body weight about 20 kg. The animals were divided into three equal groups consisting of five pigs in each. Control animals received empty gelatin capsules (placebos). Animals from the first experimental group received a low dose of acrylamide of 0.5 μg/kg b.w./day (> 99% purity; Sigma-Aldrich, Poland), and animals from the second experimental group received a dose 10 times higher. Placebos and acrylamide capsules were administered with feed every morning for 28 days. After anaesthetisation of the animals, bone marrow from the femur was collected into tubes without an anticoagulant on days 0 and 28. After drying and staining, bone marrow smears were subjected to detailed cytological evaluation using a light microscope.

Results

This study showed that high and low doses of acrylamide affected the process of porcine erythropoiesis. The cytotoxic effect of acrylamide on this process was demonstrated in a change of the polychromatic erythroblasts/normochromatic erythroblasts ratio.

Conclusion

Both doses of acrylamide caused a decrease in the number of ortho- and polychromatic erythroblasts.

Exposure assessment of process-related contaminants in food by biomarker monitoring

Exposure assessment is a fundamental part of the risk assessment paradigm, but can often present a number of challenges and uncertainties. This is especially the case for process contaminants formed during the processing, e.g. heating of food, since they are in part highly reactive and/or volatile, thus making exposure assessment by analysing contents in food unreliable. New approaches are therefore required to accurately assess consumer exposure and thus better inform the risk assessment. Such novel approaches may include the use of biomarkers, physiologically based kinetic (PBK) modelling-facilitated reverse dosimetry, and/or duplicate diet studies. This review focuses on the state of the art with respect to the use of biomarkers of exposure for the process contaminants acrylamide, 3-MCPD esters, glycidyl esters, furan and acrolein. From the overview presented, it becomes clear that the field of assessing human exposure to process-related contaminants in food by biomarker monitoring is promising and strongly developing. The current state of the art as well as the existing data gaps and challenges for the future were defined. They include (1) using PBK modelling and duplicate diet studies to establish, preferably in humans, correlations between external exposure and biomarkers; (2) elucidation of the possible endogenous formation of the process-related contaminants and the resulting biomarker levels; (3) the influence of inter-individual variations and how to include that in the biomarker-based exposure predictions; (4) the correction for confounding factors; (5) the value of the different biomarkers in relation to exposure scenario's and risk assessment, and (6) the possibilities of novel methodologies. In spite of these challenges it can be concluded that biomarker-based exposure assessment provides a unique opportunity to more accurately assess consumer exposure to process-related contaminants in food and thus to better inform risk assessment.

Effectiveness of selenium on acrylamide toxicity to retina

AIM

To investigate the hematological parameters, biochemical and electrophysiological role of acrylamide (ACR) in the retina and to assess whether selenium (Se) has protective potential in experimental oral intoxication with ACR.

METHODS

Sixty Wistar age matched-albino rats (3mo) weighing 195-230 g comprised of both sex were divided into 4 groups. Group I served as the control one in which animals take saline; group II was animals administrated ACR in dose of 15 mg/kg body weight per day for 28d; group III was animals received ACR then additionally Se (0.1 mg/kg body weight) for 28d; and group IV was animals received Se only (0.1 mg/kg body weight) for 28d. Blood analysis and serum trace element levels (Fe, Cu, and Zn) were measured. The electroretinogram (ERG) was recorded, the levels of malondialdehyde (MDA) and glutathione peroxidase (GSH-Px) in the retinal tissues were determined. Moreover the regulation of ion channels such as calcium, sodium and potassium were studied. All measurements were done for all groups after 28d.

RESULTS

Administration of ACR in group II caused a significant decrease (P<0.05) in hemoglobin (Hb), red blood cells (RBCs), hematocrit (HCT), white blood cells (WBCs) and lymphocyte of rats. A significant decrease (P<0.05) in Zn level, and alkaline phosphatase enzyme was observed compared to control. ERG which is a reflection of the electric activity in the retina; a- and-b wave amplitudes in ACR group had a reduction of 40% and 20% respectively. These changes accompanied by significant increases (P<0.05) in MDA level in the ACR group, in contrast with GSH-Px which is significant decreased (P<0.05). Moreover sodium and calcium were significant increased but potassium was significant decreased (P<0.05) compared to control group. There were no significant differences between group III (treated with Se) and control in all hematological parameter. Also serum trace elements levels (Cu, Fe and Zn), alkaline phosphatase enzyme and electric activity of the retina didn't change compared to control due to Se treatment.

CONCLUSION

This study provides evidence for the protective effect of Se on acrylamide induced toxicity by reducing oxidative stress.

Negligible colon cancer risk from food-borne acrylamide exposure in male F344 rats and nude (nu/nu) mice-bearing human colon tumor xenografts

Acrylamide, a possible human carcinogen, is formed in certain carbohydrate-rich foods processed at high temperature. We evaluated if dietary acrylamide, at doses (0.5, 1.0 or 2.0 mg/kg diet) reflecting upper levels found in human foods, modulated colon tumorigenesis in two rodent models. Male F344 rats were randomized to receive diets without (control) or with acrylamide. 2-weeks later, rats in each group received two weekly subcutaneous injections of either azoxymethane (AOM) or saline, and were killed 20 weeks post-injections; colons were assessed for tumors. Male athymic nude (nu/nu) mice bearing HT-29 human colon adenocarcinoma cells-derived tumor xenografts received diets without (control) or with acrylamide; tumor growth was monitored and mice were killed 4 weeks later. In the F344 rat study, no tumors were found in the colons of the saline-injected rats. However, the colon tumor incidence was 54.2% and 66.7% in the control and the 2 mg/kg acrylamide-treated AOM-injected groups, respectively. While tumor multiplicity was similar across all diet groups, tumor size and burden were higher in the 2 mg/kg acrylamide group compared to the AOM control. These results suggest that acrylamide by itself is not a "complete carcinogen", but acts as a "co-carcinogen" by exacerbating the effects of AOM. The nude mouse study indicated no differences in the growth of human colon tumor xenografts between acrylamide-treated and control mice, suggesting that acrylamide does not aid in the progression of established tumors. Hence, food-borne acrylamide at levels comparable to those found in human foods is neither an independent carcinogen nor a tumor promoter in the colon. However, our results characterize a potential hazard of acrylamide as a colon co-carcinogen in association with known and possibly other environmental tumor initiators/promoters.

Metabolite identification of a new tyrosine kinase inhibitor, HM781-36B, and a pharmacokinetic study by liquid chromatography/tandem mass spectrometry

RATIONALE

HM781-36B (1-[4-[4-(3,4-dichloro-2-fluorophenylamino)-7-methoxyquinazolin-6-yloxy]-piperidin-1-yl]prop-2-en-1-one hydrochloride) is a new anticancer drug to treat advanced solid tumors in clinical trial. In order to understand the behavior of HM781-36B in vitro and in vivo we validated an analytical method for HM781-36B and its major metabolites in plasma.

METHODS

In vivo and in vitro metabolism of HM781-36B was studied in dog plasma, urine and feces as well as using human and dog liver microsomes with extraction by ethyl acetate or methyl tert-butyl ether, respectively, and successfully separated by high-performance liquid chromatography diode-array detection mass spectrometry (HPLC-DAD/MS). Ten metabolites were identified by LC/ESI-ion trap mass spectrometry (MS, MS(2) , MS(3) and MRM) and LC/Q-TOF-MS/MS for exact mass measurement. For accurate characterization of the major metabolites, authentic standards (M1, M2, M4, and M10) were synthesized.

RESULTS

Ten metabolites of HM781-36B in an in vitro mixture were separated and identified by LC/ESI-MS(n) . The MS/MS spectral patterns of the parent drug and metabolites exhibited two characteristic ions (A- and B-type ions) attributed to the cleavage of the ether bond between the piperidine ring and the quinazoline ring, providing important information on the site of chemical conversion during the metabolism. Six hydroxylated derivatives including dehalogenation and demethylation, two N-oxide forms, a demethylated form and de-acryloylpiperideine metabolites were observed.

CONCLUSIONS

The LC/ESI-ion trap MS(n) technique was effective in obtaining structural information and yielded diagnostic ions for the identification of diverse metabolites. The multiple metabolic pathways of HM781-36B were suggested in in vitro and in vivo samples and the dihydroxylation (M1) and demethylation (M2) appeared to be the major metabolites.

Acrylamide hemoglobin adduct levels and ovarian cancer risk: a nested case-control study

BACKGROUND

Acrylamide is a probable human carcinogen formed during cooking of starchy foods. Two large prospective cohort studies of dietary acrylamide intake and ovarian cancer risk observed a positive association, although two other studies reported no association.

METHODS

We measured acrylamide exposure using red blood cell acrylamide and glycidamide hemoglobin adducts among women in two large prospective cohorts: the Nurses' Health Study and Nurses' Health Study II. Between blood collection and 2010, we identified 263 incident cases of epithelial ovarian cancer, matching two controls per case. We used logistic regression models to examine the association between acrylamide exposure and ovarian cancer risk, adjusting for matching factors, family history of ovarian cancer, tubal ligation, oral contraceptive use, body mass index, parity, alcohol intake, smoking, physical activity, and caffeine intake.

RESULTS

The multivariate-adjusted relative risk (RR) of ovarian cancer comparing the highest versus lowest tertile of total acrylamide adducts was 0.79 (95% CI, 0.50-1.24, P trend = 0.08). The comparable RR of ovarian cancer among non-smokers at blood draw was 0.85 (95% CI, 0.57-1.27, P trend = 0.14). The association did not differ by tumor histology (serous invasive versus not), P for heterogeneity = 0.86. Individual adduct types (acrylamide or glycidamide) were not associated with risk.

CONCLUSIONS

We observed no evidence that acrylamide exposure as measured by adducts to hemoglobin is associated with an increased risk of ovarian cancer.

IMPACT

Our finding indicates that acrylamide intake may not increase risk of ovarian cancer.

Critical review of dose-response options for F344 rat mammary tumors for acrylamide - additional insights based on mode of action

Previous risk assessment reviews analyzed the potential for dietary acrylamide to increase breast cancer risk. Here, we critically review acrylamide animal bioassay data on mammary tumors for human relevance. We applied a systematic evaluation using reasonable standards of scientific certainty and a systematic weight of evidence (WOE) approach to evaluate several hypothesized modes of action (MOA), including (1) genotoxicity related to glycidamide formation and oxidative stress, (2) endocrine effects due to age-related hyperprolactinemia or secondary to neurotoxicity, and (3) epigenetic effects. We conclude that the appropriate approach for low-dose extrapolation of the rat mammary tumors can be narrowed to two options: (1) linear low-dose extrapolation (i.e., based on a MOA of mutagenicity from direct DNA interaction) from a point of departure (POD) for the combined incidence of adenomas and adenocarcinomas, since these tumor types are related; or (2) non-linear extrapolation, using uncertainty factors to estimate a Reference Dose (RfD) from a POD for tumor promotion derived using the combined fibroadenoma, adenoma and adenocarcinoma data. Non-linear extrapolation is used in the latter approach because these combined tumor types are unlikely to be exclusively caused by mutagenicity. Comparison of the WOE for each alternative MOA indicates that a non-linear approach (option 2) is more appropriate for evaluation of acrylamide-induced mammary tumors; a linear approach (option 1) is shown for comparison.

Development of a physiologically-based toxicokinetic model of acrylamide and glycidamide in rats and humans

Physiologically-based toxicokinetic ("pharmacokinetic") (PBPK or PBTK) modeling can be used as a tool to compare internal doses of acrylamide (AA) and its metabolite glycidamide (GA) in humans and rats. An earlier PBTK model for AA and GA in rats was refined and extended to humans based on new data. With adjustments to the previous parameters, excellent fits to a majority of the data for male Fisher 344 rats were obtained. Kinetic parameters for the human model were estimated based on fit to available human data for urinary metabolites of AA, and levels of hemoglobin adducts of AA and GA measured in studies in which human volunteers ingested known doses of AA. The simulations conducted with the rat and human models predicted that rats and humans ingesting comparable levels of AA (in mg/kg day) would have similar levels of GA in blood and tissues. This finding stands in contrast to the default approach that assumes a 3.2-fold increase in human risk due to pharmacokinetic differences between rats and humans. This model was used in a companion paper to estimate safe levels of ingested AA.

Towards a human-on-chip: culturing multiple cell types on a chip with compartmentalized microenvironments

We have developed a multi-channel 3D microfluidic cell culture system (multi-channel 3D-microFCCS) with compartmentalized microenvironments for potential application in human drug screening. To this end, the multi-channel 3D-microFCCS was designed for culturing different 3D cellular aggregates simultaneously to mimic multiple organs in the body. Four human cell types (C3A, A549, HK-2 and HPA) were chosen to represent the liver, lung, kidney and the adipose tissue, respectively. Cellular functions were optimized by supplementing the common medium with growth factors. However, TGF-beta1 was found to enhance A549 functions but inhibit C3A functions. Therefore, TGF-beta1 was specifically controlled-released inside the A549 compartment by means of gelatin microspheres mixed with cells, thus creating a cell-specific microenvironment. The function of A549 cells was enhanced while the functions of C3A, HK-2 and HPA cells were uncompromised, demonstrating the limited cross-talk between cell culture compartments similar to the in vivo situation. Such a multi-channel 3D-microFCCS could be potentially used to supplement or even replace animal models in drug screening.