The Role of Epidemiology in Understanding the Relationship between Dietary Acrylamide and Cancer Risk in Humans

Interactions between dietary acrylamide intake and genes for ovarian cancer risk

Some epidemiological studies observed a positive association between dietary acrylamide intake and ovarian cancer risk but the causality needs to be substantiated. By analyzing gene-acrylamide interactions for ovarian cancer risk for the first time, we aimed to contribute to this. The prospective Netherlands Cohort Study on diet and cancer includes 62,573 women, aged 55–69 years. At baseline in 1986, a random subcohort of 2589 women was sampled from the total cohort for a case cohort analysis approach. Dietary acrylamide intake of subcohort members and ovarian cancer cases (n = 252, based on 20.3 years of follow-up) was assessed with a food frequency questionnaire. We selected single nucleotide polymorphisms (SNPs) in genes in acrylamide metabolism and in genes involved in the possible mechanisms of acrylamide-induced carcinogenesis (effects on sex steroid systems, oxidative stress and DNA damage). Genotyping was done on DNA from toenails through Agena’s MassARRAY iPLEX platform. Multiplicative interaction between acrylamide intake and SNPs was assessed with Cox proportional hazards analysis. Among the results for 57 SNPs and 2 gene deletions, there were no statistically significant interactions between acrylamide and gene variants after adjustment for multiple testing. However, there were several nominally statistically significant interactions between acrylamide intake and SNPs in the HSD3B1/B2 gene cluster: (rs4659175 (p interaction = 0.04), rs10923823 (p interaction = 0.06) and its proxy rs7546652 (p interaction = 0.05), rs1047303 (p interaction = 0.005), and rs6428830 (p interaction = 0.05). Although in need of confirmation, results of this study suggest that acrylamide may cause ovarian cancer through effects on sex hormones.

The influence of single nucleotide polymorphisms on the association between dietary acrylamide intake and endometrial cancer risk

It is unclear whether the association between dietary acrylamide intake and endometrial cancer risk as observed in some epidemiological studies reflects a causal relationship. We aimed at clarifying the causality by analyzing acrylamide-gene interactions for endometrial cancer risk. The prospective Netherlands Cohort Study on diet and cancer includes 62,573 women, aged 55–69 years. At baseline, a random subcohort of 2589 women was selected for a case cohort analysis approach. Acrylamide intake of subcohort members and endometrial cancer cases (n = 315) was assessed with a food frequency questionnaire. Single nucleotide polymorphisms (SNPs) in genes in acrylamide metabolism, sex steroid systems, oxidative stress and DNA repair were assessed through a MassARRAY iPLEX Platform. Interaction between acrylamide and SNPs was assessed with Cox proportional hazards analysis, based on 11.3 years of follow-up. Among the results for 57 SNPs and 2 gene deletions, there were no statistically significant interactions after adjustment for multiple testing. However, there were nominally statistically significant interactions for SNPs in acrylamide-metabolizing enzymes: CYP2E1 (rs915906 and rs2480258) and the deletions of GSTM1 and GSTT1. Although in need of confirmation, the interactions between acrylamide intake and CYP2E1 SNPs contribute to the evidence for a causal relationship between acrylamide and endometrial cancer risk.

A prospective study on dietary acrylamide intake and the risk for breast, endometrial, and ovarian cancers

BACKGROUND

Acrylamide is a probable human carcinogen formed during cooking of many common foods. Epidemiologic studies on acrylamide and breast cancer risk have been null; however, positive associations with ovarian and endometrial cancers have been reported. We studied acrylamide intake and risk for breast, endometrial, and ovarian cancers in a prospective cohort study.

METHODS

We assessed acrylamide intake among 88,672 women in the Nurses' Health Study using food frequency questionnaires administered every 4 years. Between 1980 and 2006, we identified 6,301 cases of invasive breast cancer, 484 cases of invasive endometrial adenocarcinoma, and 416 cases of epithelial ovarian cancer. We used Cox proportional hazards models to study the association between acrylamide and cancer risk.

RESULTS

We found no association between acrylamide intake and breast cancer overall or according to estrogen and progesterone receptor status. We found an increased risk for endometrial cancer among high acrylamide consumers (adjusted relative risk for highest versus lowest quintile = 1.41; 95% CI, 1.01-1.97; P for trend = 0.03). We observed a nonsignificant suggestion of increased risk for ovarian cancer overall (relative risk, 1.25; 95% CI, 0.88-1.77; P trend = 0.12), with a significantly increased risk for serous tumors (relative risk, 1.58; 95% CI, 0.99-2.52; P trend = 0.04). Associations did not differ by smoking status.

CONCLUSIONS

We observed no association between acrylamide and breast cancer. Risk for endometrial cancer and possibly ovarian cancer was greater among high acrylamide consumers.

IMPACT

This is the second prospective study to report positive associations with endometrial and ovarian cancers. These associations should be further evaluated to inform public health policy.

Acrylamide-induced nerve terminal damage: relevance to neurotoxic and neurodegenerative mechanisms

Acrylamide (ACR) has demonstrable neurotoxic effects in animals and humans that stem from its chemical behavior as a soft electrophilic alpha,beta-unsaturated carbonyl compound. Evidence is presented that the nerve terminal is a primary site of ACR action and that inhibition of neurotransmission mediates the development of neurological deficits. At the mechanistic level, recent proteomic, neurochemical, and kinetic data are considered, which suggest that ACR inhibits neurotransmission by disrupting presynaptic nitric oxide (NO) signaling. Nerve-terminal damage likely mediates the neurological complications that accompany the occupational exposure of humans to ACR. In addition, the proposed molecular mechanism of synaptotoxicity has substantial implications for the pathogenesis of Alzheimer's disease and other neurodegenerative conditions that involve neuronal oxidative stress and the secondary endogenous generation of acrolein and other conjugated carbonyl chemicals.

Using dietary exposure and physiologically based pharmacokinetic/pharmacodynamic modeling in human risk extrapolations for acrylamide toxicity

The discovery of acrylamide (AA) in many common cooked starchy foods has presented significant challenges to toxicologists, food scientists, and national regulatory and public health organizations because of the potential for producing neurotoxicity and cancer. This paper reviews some of the underlying experimental bases for AA toxicity and earlier risk assessments. Then, dietary exposure modeling is used to estimate probable AA intake in the U.S. population, and physiologically based pharmacokinetic/pharmacodynamic (PBPK/PD) modeling is used to integrate the findings of rodent neurotoxicity and cancer into estimates of risks from human AA exposure through the diet. The goal of these modeling techniques is to reduce the uncertainty inherent in extrapolating toxicological findings across species and dose by comparing common exposure biomarkers. PBPK/PD modeling estimated population-based lifetime excess cancer risks from average AA consumption in the diet in the range of 1-4 x 10 (-4); however, modeling did not support a link between dietary AA exposure and human neurotoxicity because marginal exposure ratios were 50-300 lower than in rodents. In addition, dietary exposure modeling suggests that because AA is found in so many common foods, even big changes in concentration for single foods or groups of foods would probably have a small impact on overall population-based intake and risk. These results suggest that a more holistic analysis of dietary cancer risks may be appropriate, by which potential risks from AA should be considered in conjunction with other risks and benefits from foods.

Acrylamide intake through diet and human cancer risk

More than one-third of the calories consumed by U.S. and European populations contain acrylamide, a substance classified as a "probable human carcinogen" based on laboratory data. Thus, it is a public health concern to evaluate whether intake of acrylamide at levels found in the food supply is an important cancer risk factor. Mean dietary intake of acrylamide in adults averages 0.5 microg/kg of body weight per day, whereas intake is higher among children. Several epidemiological studies examining the relationship between dietary intake of acrylamide and cancers of the colon, rectum, kidney, bladder, and breast have been undertaken. These studies found no association between intake of specific foods containing acrylamide and risk of these cancers. Moreover, there was no relationship between estimated acrylamide intake in the diet and cancer risk. Results of this research are compared with other epidemiological studies, and the findings are examined in the context of data from animal models. The importance of epidemiological studies to establish the public health risk associated with acrylamide in food is discussed, as are the limitations and future directions of such studies.

Carbohydrates and cancer: an overview of the epidemiological evidence

OBJECTIVE

To assess the epidemiological evidence on dietary carbohydrates and the risk of developing cancer.

METHOD

Review of published studies, concentrating on recent systematic reviews, meta-analyses and large prospective studies.

CONCLUSIONS

Carbohydrates have not been intensively investigated in epidemiological studies of diet and cancer. There is a moderately large amount of data on the possible association between dietary fibre and the risk for colorectal cancer; the results of studies have varied and no firm conclusion can be drawn, but the available data suggest that high intakes of dietary fibre possibly reduce the risk for colorectal cancer. There are also limited data which suggest that high intakes of sucrose might increase the risk for colorectal cancer and that high intakes of lactose might increase the risk for ovarian cancer. For other components of carbohydrates and other types of cancer, the available data are too sparse to draw even tentative conclusions. Further research is needed on the possible associations of carbohydrates with cancer risk.

Acrylamide, an in vivo thyroid carcinogenic agent, induces DNA damage in rat thyroid cell lines and primary cultures

Chronic treatment of rats with acrylamide induces various tumors among which thyroid tumors are the most frequent. The aim of the present study was to develop an in vitro model of acrylamide action on thyroid cells to allow the investigation of the mechanism of this tumorigenic action. The first part of the study considered as targets, characteristics of thyroid metabolism, which could explain the thyroid specificity of acrylamide action: the cAMP mitogenic effect and the important H2O2 generation by thyroid cells. However, acrylamide did not modulate H2O2 or cAMP generation in the thyroid cell models studied. No effect on thyroid cell proliferation was observed in the rat thyroid cell line FRTL5. On the other hand, as shown by the comet assay, acrylamide induced DNA damage, as the positive control H2O2 in the PC Cl3 and FRTL5 rat thyroid cell lines, as well as in thyroid cell primary cultures. The absence of effect of acrylamide on H2AX histone phosphorylation suggests that this effect does not reflect the induction of DNA double strand breaks. DNA damage leads to the generation of mutations. It is proposed that such mutations could play a role in the carcinogenic effect of acrylamide. The mechanism of this effect can now be studied in this in vitro model.