3-MCPD as contaminant in processed foods: State of knowledge and remaining challenges.

3-Chloro-1,2-propanediol (3-MCPD) and its fatty acid esters (FE) are present as contaminants in different processed foods. Based on the available toxicological data the potential risk of 3-MCPD and its FE to human health was assessed by risk assessment authorities, including the European Food Safety Authority (EFSA). Considering the available data, EFSA concluded that 3-MCPD is a non-genotoxic compound exhibiting secondary carcinogenic effects in rodents. A tolerable daily intake of 2 µg/kg body weight and day was derived by EFSA for free and ester-bound 3-MCPD in 2018. However, there are still different pending issues that have remained unclear until now. Here, we summarize the current knowledge regarding 3-MCPD and its FE with a focus on pending issues regarding exposure assessment via biomarkers as well as the identification of (toxic) metabolites formed after exposure to FE of 3-MCPD and their modes of action.

Absorption and metabolism of 3-MCPD in hepatic and renal cell lines.

3-Monochloropropane-1,2-diol (3-MCPD) fatty acid esters are process contaminants mainly formed during the refinement of vegetable oils. Gastrointestinal hydrolysis yields free 3-MCPD, which is resorbed into the body. In long-term rat studies, 3-MCPD caused renal and testicular neoplasms. 3-MCPD metabolism via ß-chlorolactic acid has been postulated to underlie the toxic effects of 3-MCPD. Various efforts are ongoing to characterize the toxicological mode of action of 3-MCPD using in vitro systems. Published results suggest a very low sensitivity of cell cultures in vitro, as compared to 3-MCPD levels causing toxic effects in vivo. The insensitivity of in vitro systems raises the question to which extent 3-MCPD is absorbed and metabolized in vitro. We therefore analyzed cytotoxicity, absorption and metabolism of 3-MCPD and its metabolite ß-chlorolactic acid in renal and hepatic cells. Cytotoxicity tests using up to 100 mM 3-MCPD confirmed the low sensitivity of human and rat cell lines towards 3-MCPD toxicity. Furthermore, absorption and metabolism of 3-MCPD examined via GC-MS and LC-MS/MS were only observed to a minor degree, and 3-MCPD was also not converted by a metabolizing system (S9 fraction). In conclusion, our data indicate that current in vitro models are not well suited for studying 3-MCPD metabolism and toxicity.

Effects of 2-MCPD on oxidative stress in different organs of male mice.

2-Monochloropropane-1,3-diol (2-MCPD) and its isomer 3-monochloropropane-1,2-diol (3-MCPD) are widespread food contaminants. 3-MCPD has been classified as a non-genotoxic carcinogen, whereas very limited toxicological data are available for 2-MCPD. Animal studies indicate that heart and skeletal muscle are target organs of 2-MCPD. Oxidative stress may play a role in this process, and the potential of 3-MCPD to induce oxidative stress in vivo has already been demonstrated. To investigate the potential of 2-MCPD to induce oxidative stress in vivo, a 28-day oral feeding study in male HOTT reporter mice was conducted. This mouse model allows monitoring substance-induced oxidative stress in various target organs on the basis of Hmox1 promoter activation. Repeated daily doses of up to 100 mg 2-MCPD/kg body weight did not result in substantial toxicity. Furthermore, the highest dose of 2-MCPD had only minor effects on oxidative stress in kidney and testes, whereas brain, heart and skeletal muscle were not affected. Additionally, 2-MCPD caused only mild changes in the expression of Nrf2-dependent genes and only slightly affected the redox status of the redox-sensor protein DJ-1. Thus, the data indicate that 2-MCPD, in contrast to its isomer 3-MCPD, does not lead to a considerable induction of oxidative stress in male mice.

Correlation between 3-MCPD-induced organ toxicity and oxidative stress response in male mice.

3-Chloro-1,2-propanediol (3-MCPD) is a food contaminant which has been classified as a non-genotoxic carcinogen (category 2B). Previous studies suggested that oxidative stress might play a role in 3-MCPD toxicity. To elucidate the impact of 3-MCPD-mediated organ toxicity in more detail, transgenic reporter mice were employed which contain a lacZ reporter under the control of the heme oxygenase 1 (Hmox1) promoter which is responsive to oxidative stress. The mice received daily doses of up to 100 mg/kg body weight 3-MCPD per day in a 28-day feeding study. Subsequently, tissue slices from different organs were subjected to X-Gal staining as the readout for lacZ gene expression. A dose-dependent increase of blue stain was observed in mouse kidney that was exclusively visible in the renal cortex but not in the renal medulla. Moreover, blue-stained regions were detected in the basal membrane of the seminiferous tubules in testes and also in specific brain regions (cerebellum, midbrain and pons). Notably, gene expression of a number of Nrf2-dependent target genes except Hmox1 was not severely affected by 3-MCPD. In all three organs, however, the amount of irreversibly oxidized DJ-1 protein, which is a biomarker for oxidative stress, was significantly increased already by low doses of 3-MCPD.

[Heat-induced contaminants in foodstuffs : Acrylamide, furan, and fatty acid esters of monochloropropanediols and glycidol]. / Erhitzungsbedingte Kontaminanten in Lebensmitteln : Acrylamid, Furan und Fettsäureester von Monochlorpropandiolen und Glycidol.

The production and preparation of foodstuffs may entail at high temperatures the generation of undesirable, potentially harmful compounds. Among the best investigated heat-induced contaminants are acrylamide, furan, and the fatty acid esters of glycidol and the monochloropropanediols. This article presents the main insights into the formation, toxicology, and exposure of these compounds. Acrylamide and glycidol were characterized as carcinogens with a genotoxic mechanism in animal experiments. Their content in foods should be minimized. For 3­monochloropropanediol (3-MCPD), a tolerable daily intake can be derived. In contrast, a complete risk assessment is currently not possible for furan and 2­MCPD owing to insufficient data.Many other heat-induced substances in foodstuffs were identified in addition to the compounds mentioned above, but for most no data on their toxicological properties and human exposure is available. Therefore, no risk assessment can currently be undertaken for these compounds. To prioritize this large number of compounds according to their possible hazard potential, it is reasonable to utilize computer modeling programs for the prediction of defined toxicological endpoints based on the molecular chemical structures. However, substances classed as a priority must be further investigated with regard to the toxicology and quantification of the food content of these compounds to allow a meaningful risk assessment.