A review of the toxicology of acrylamide

Abstract

Acrylamide (ACR) is a chemical used in many industries around the world and more recently was found to form naturally in foods cooked at high temperatures. Acrylamide was shown to be a neurotoxicant, reproductive toxicant, and carcinogen in animal species. Only the neurotoxic effects were observed in humans and only at high levels of exposure in occupational settings. The mechanism underlying neurotoxic effects of ACR may be basic to the other toxic effects seen in animals. This mechanism involves interference with the kinesin-related motor proteins in nerve cells or with fusion proteins in the formation of vesicles at the nerve terminus and eventual cell death. Neurotoxicity and resulting behavioral changes can affect reproductive performance of ACR-exposed laboratory animals with resulting decreased reproductive performance. Further, the kinesin motor proteins are important in sperm motility, which could alter reproduction parameters. Effects on kinesin proteins could also explain some of the genotoxic effects on ACR. These proteins form the spindle fibers in the nucleus that function in the separation of chromosomes during cell division. This could explain the clastogenic effects of the chemical noted in a number of tests for genotoxicity and assays for germ cell damage. Other mechanisms underlying ACR-induced carcinogenesis or nerve toxicity are likely related to an affinity for sulfhydryl groups on proteins. Binding of the sulfhydryl groups could inactive proteins/enzymes involved in DNA repair and other critical cell functions. Direct interaction with DNA may or may not be a major mechanism for cancer induction in animals. The DNA adducts that form do not correlate with tumor sites and ACR is mostly negative in gene mutation assays except at high doses that may not be achievable in the diet. All epidemiologic studies fail to show any increased risk of cancer from either high-level occupational exposure or the low levels found in the diet. In fact, two of the epidemiologic studies show a decrease in cancer of the large bowel. A number of risk assessment studies were performed to estimate increased cancer risk. The results of these studies are highly variable depending on the model. There is universal consensus among international food safety groups in all countries that examined the issue of ACR in the diet that not enough information is available at this time to make informed decisions on which to base any regulatory action. Too little is known about levels of this chemical in different foods and the potential risk from dietary exposure. Avoidance of foods containing ACR would result in worse health issues from an unbalanced diet or pathogens from under cooked foods. There is some consensus that low levels of ACR in the diet are not a concern for neurotoxicity or reproductive toxicity in humans, although further research is need to study the long-term, low-level cumulative effects on the nervous system. Any relationship to cancer risk from dietary exposure is hypothetical at this point and awaits more definitive studies.