Metabolic activation and inactivation of food carcinogens 5-hydroxymethylfurfural and furfuryl alcohol in humans, mice and rats
Final Report Abstract
5-Hydroxymethylfurfural (HMF) and furfuryl alcohol (FFA) are moderately potent rodent carcinogens which are formed by heat- and acid-catalyzed reactions of carbohydrates. The margins between carcinogenic doses in animal studies and the estimated dietary human intake are small. Sulfotransferases (SULT) catalyze the turnover of HMF and FFA to DNA-reactive sulfate esters. If the carcinogenicity is based on this genotoxic mechanism, the low margin of exposure indicates a high human risk. It is also possible that humans are more sensitive to the exposure of HMF and FFA due to differences of SULT expression in humans and rodents. We studied the sulfo conjugation HMF and FFA by individual SULT forms of different species. The results supported the hypothesis that HMF and FFA are sulfo conjugated not only in mice but also in the human body. Human SULT1A1 was about as effective as the orthologue in mouse, the species in which carcinogenic effects of HMF (liver) and FFA (kidney) were observed. However, the in vitro data of sulfo conjugation do not allow inferring carcinogenic risks in particular species and tissues due to various unknown parameters. For example, a comprehensive overview about SULT expression in different organisms is lacking. Hence, HMF sulfo conjugation and oxidative detoxification was studied in individual tissues (liver, kidney, lung and colon) of humans, mice and rats. The results indicated that HMF sulfo conjugation was most substantial in the liver of female mice, the target tissue for HMF-induced neoplastic effects, and that humans may be less sensitive regarding HMF sulfo conjugation compared to the rodent models. This finding supports the impression that the carcinogenic risk resulting from human dietary exposure to HMF may be of minor importance. Mass spectrometric methods for the detection of DNA adducts of FFA and HMF were developed. The FFA-related adduct N2-((furan-2-yl)methyl)-2'-deoxyguanosine (N2-MFdG) was detected in DNA samples from FFA-treated animals. An equimolar dose of HMF did not lead to formation of detectable adduct levels in mice. The bioactivation of FFA was studied in vivo by the tissue distribution of N2-MF-dG in DNA samples from different FFA-treated transgenic mice strains, which were either deficient of endogenous Sult1a1 or Sult1d1 or which expressed hSULT1A1/1A2. The Sult1a1 knockout lowered the N2-MF-dG levels in the liver and the colon by two-thirds. In contrast, the reduction of adduct levels due to Sult1d1 knockout was small. The N2-MF-dG levels detected in hSULT1A1/1A2-expressing mice were higher than those in wild type mice supporting the hypothesis that FFA is converted to the mutagenic 2-sulfoxymethylfuran also in the human body. In this context, we also studied the indirect genotoxicity of ethanol resulting from competitive inhibition of alcohol dehydrogenases (ADHs) and aldehyde dehydrogenases (ALDHs). The saturation of the oxidative pathways caused by the moderate dose of 1.6 g ethanol/kg body weight increased the genotoxicity related to FFA exposure in mice. Thus, regular ethanol consumption may increase the effects of other genotoxins, which depend on the detoxification by ADH and ALDH in humans. At this stage of the project it became increasingly clear that human HMF exposure may be harmless. Thus, we focused the development of a human biomarker on FFA. Due to the limited time frame we were not able to investigate the potential use of FFA adducts in human DNA or the urinary mercapturic acid of FFA as biomarkers. Currently, we develop a mass spectrometric method for the quantification of the FFA-related hemoglobin adduct N-methylfuranyl-Val-fluorescein-thiohydantoin, which is released by Edman degradation. The mass spectrometric method will be applied to analyze the adduct levels in blood samples of FFA-treated mice and of human volunteers. This study is in progress. The basic goal of the project was to comprehend HMF and FFA bioactivation and detoxification in mice and rats, the animal models of carcinogenicity studies, and in humans. An improvement of assessing the respective human exposure risk was sought. Our data allow for some cautious conclusions. Various results indicate that human HMF exposure may be harmless. High doses of around 100 mg HMF/kg body weight but also of 100 mg SMF/kg body weight did not lead to detectable levels of DNA adducts in mice. Also, HMF-related DNA adducts were not detected in human tissue samples. It is of note, that the carcinogenic effect in the 2-year bioassay was restricted to the formation of hepatic adenoma in female mice, which is a weak indication with questionable significance. Our in vitro experiments in hepatic tissue preparation further showed that female mice are more sensitive regarding HMF sulfo conjugation compared to humans. In summary, the risk resulting from human dietary HMF exposure is expected to be small. Several observations indicated that the mutagenic effect of FFA may be more important than that of HMF. First, equimolar doses of FFA and HMF led to detectable adduct levels in FFA- but not in HMF-treated mice. Second, we detected N2-MFdG in DNA samples of human lung and to a lesser extend in human liver, kidney and colon. These data are indicators for the effect of FFA, however, risk assessment for human FFA exposure is not supported. Without valid estimation of FFA intake and of oral carcinogenicity in rodent models FFA risk assessment remains speculative.
Publications
- (2014) Bioactivation of food genotoxicants 5-hydroxymethylfurfural and furfuryl alcohol by sulfotransferases from human, mouse and rat: a comparative study. Arch. Toxicol.
Sachse, B., Meinl, W., Sommer, Y., Glatt, H., Seidel, A., Monien, B. H.
(See online at https://doi.org/10.1007/s00204-014-1392-6) - (2014) The effect of knockout of Sulfotransferases 1a1 and 1d1 and of transgenic human Sulfotransferases 1A1/1A2 on the formation of DNA adducts from furfuryl alcohol in mouse models. Carcinogenesis 35, 2339-2345
Sachse, B., Meinl, W., Glatt, H., Monien, B. H.
(See online at https://doi.org/10.1093/carcin/bgu152) - (2015). Simultaneous detection of multiple DNA adducts in human lung samples by isotope-dilution UPLC-MS/MS, Anal. Chem. 87, 641-648
Monien, B. H., Schumacher, F., Herrmann, K., Glatt, H., Turesky, R. J., Chesné, C.
(See online at https://doi.org/10.1021/ac503803m) - Ethanol and 4-methylpyrazole increase DNA adduct formation of furfuryl alcohol in FVB/N wild-type mice and in mice expressing human Sulfotransferases 1A1/1A2. Carcinogenesis, Volume 37, Issue 3, 1 March 2016, Pages 314–319
Sachse, B., Meinl, W., Glatt, H., Monien, B. H.
(See online at https://doi.org/10.1093/carcin/bgw006)
