Lieselot Hemeryck

Increased oxidative and nitrosative reactions during digestion could contribute to the association between well-done red meat consumption and colorectal cancer

Uncured and nitrite-cured pork were subjected, raw, cooked (65 °C, 15 min) or overcooked (90 °C, 30 min), to an in vitro digestion model, which includes mouth, stomach, duodenum, and colon phases. Heating of uncured meat resulted in a pronounced increase in lipid and protein oxidation products throughout digestion. Nitrite-curing had an antioxidant effect during digestion, but this effect disappeared when the meat was overcooked, resulting in up to ninefold higher 4-hydroxy-2-nonenal concentrations compared with digested nitrite-cured raw and cooked pork. Colonic digesta contained significantly higher concentrations of the NOC-specific DNA adduct O(6)-carboxy-methylguanine when pork underwent a more intense heating procedure, independent of nitrite-curing, depending strongly on the fecal inoculum used. Since processed meats are usually nitrite-cured, the present study suggests that overcooking processed meat is likely to result in the formation of genotoxic compounds during digestion and should, therefore, be avoided.

O6-carboxymethylguanine DNA adduct formation and lipid peroxidation upon in vitro gastrointestinal digestion of haem-rich meat

SCOPE Epidemiological and clinical studies have demonstrated that the consumption of red haem-rich meat may contribute to the risk of colorectal cancer. Two hypotheses have been put forward to explain this causal relationship, i.e. N-nitroso compound (NOC) formation and lipid peroxidation (LPO). METHODS AND RESULTS In this study, the NOC-derived DNA adduct O(6)-carboxymethylguanine (O(6)-CMG) and the LPO product malondialdehyde (MDA) were measured in individual in vitro gastrointestinal digestions of meat types varying in haem content (beef, pork, chicken). While MDA formation peaked during the in vitro small intestinal digestion, alkylation and concomitant DNA adduct formation was observed in seven (out of 15) individual colonic digestions using separate faecal inocula. From those, two haem-rich meat digestions demonstrated a significantly higher O(6)-CMG formation (p < 0.05). MDA concentrations proved to be positively correlated (p < 0.0004) with haem content of digested meat. The addition of myoglobin, a haem-containing protein, to the digestive simulation showed a dose-response association with O(6)-CMG (p = 0.004) and MDA (p = 0.008) formation. CONCLUSION The results suggest the haem-iron involvement for both the LPO and NOC pathway during meat digestion. Moreover, results unambiguously demonstrate that DNA adduct formation is very prone to inter-individual variation, suggesting a person-dependent susceptibility to colorectal cancer development following haem-rich meat consumption.

Mass spectrometric mapping of the DNA adductome as a means to study genotoxin exposure, metabolism, and effect

Covalent binding of endo- or exogenous chemicals to DNA results in the formation of DNA adducts which are reflective of exposure of the human body to DNA-damaging molecules and their metabolic pathways. The study of DNA adduct types and levels in human tissue therefore offers an interesting tool in several fields of research, including toxicology and cancer epidemiology. Over the years, a range of techniques and methods have been developed to study the formation of endo- and exogenous DNA adducts. However, for the simultaneous detection, identification and quantification of both known and unknown DNA adducts, mass spectrometry (MS) is deemed to be the most promising technique. In this perspective, we focus on the analysis of multiple DNA adducts within a sample with the emphasis on untargeted analysis. The advantageous use of MS methodologies for DNA adductome mapping is discussed comprehensively with relevant field examples. In addition, several aspects of study design, sample pretreatment, and analysis are addressed as these factors significantly affect the reliability of DNA adductomics studies.

DNA adduct profiling of in vitro colonic meat digests to map red vs. white meat genotoxicity

The consumption of red meat has been linked to an increased colorectal cancer (CRC) risk. One of the major hypotheses states that heme iron (present in red meat) stimulates the formation of genotoxic N-nitroso compounds (NOCs) and lipid peroxidation products (LPOs). By means of DNA adductomics, chemically induced DNA adduct formation can be mapped in relation to e.g. dietary exposures. In this study, this state-of-the-art methodology was used to investigate alkylation and (lipid per)oxidation induced DNA adduct formation in in vitro red vs. white meat digests. In doing so, 90 alkylation and (lipid per)oxidation induced DNA adduct types could be (tentatively) identified. Overall, 12 NOC- and/or LPO-related DNA adduct types, i.e. dimethyl-T (or ethyl-T), hydroxymethyl-T, tetramethyl-T, methylguanine (MeG), guanidinohydantoin, hydroxybutyl-C, hydroxymethylhydantoin, malondialdehyde-x3-C, O6-carboxymethylguanine, hydroxyethyl-T, carboxyethyl-T and 3,N4-etheno-C were singled out as potential heme-rich meat digestion markers. The retrieval of these DNA adduct markers is in support of the heme, NOC and LPO hypotheses, suggesting that DNA adduct formation may indeed contribute to red meat related CRC risk.

DNA adductomics to study the genotoxic effects of red meat consumption with and without added animal fat in rats

Digestion of red and processed meat has been linked to the formation of genotoxic N-nitroso compounds (NOCs) and lipid peroxidation products (LPOs) in the gut. In this study, rats were fed a meat based diet to compare the possible genotoxic effects of red vs. white meat, and the interfering role of dietary fat. To this purpose, liver, duodenum and colon DNA adductomes were analyzed with UHPLC-HRMS. The results demonstrate that the consumed meat type alters the DNA adductome; the levels of 22 different DNA adduct types significantly increased upon the consumption of beef (compared to chicken) and/or lard supplemented beef or chicken. Furthermore, the chemical constitution of the retrieved DNA adducts hint at a direct link with an increase in NOCs and LPOs upon red (and processed) meat digestion, supporting the current hypotheses on the causal link between red and processed meat consumption and the development of colorectal cancer.