A central role for heme iron in colon carcinogenesis associated with red meat intake

Synthesis and in vitro characterization of the genotoxic, mutagenic and cell-transforming potential of nitrosylated heme

Data from epidemiological studies suggest that consumption of red and processed meat is a factor contributing to colorectal carcinogenesis. Red meat contains high amounts of heme, which in turn can be converted to its nitrosylated form, NO-heme, when adding nitrite-containing curing salt to meat. NO-heme might contribute to colorectal cancer formation by causing gene mutations and could thereby be responsible for the association of (processed) red meat consumption with intestinal cancer. Up to now, neither in vitro nor in vivo studies characterizing the mutagenic and cell transforming potential of NO-heme have been published due to the fact that the pure compound is not readily available. Therefore, in the present study, an already existing synthesis protocol was modified to yield, for the first time, purified NO-heme. Thereafter, newly synthesized NO-heme was chemically characterized and used in various in vitro approaches at dietary concentrations to determine whether it can lead to DNA damage and malignant cell transformation. While NO-heme led to a significant dose-dependent increase in the number of DNA strand breaks in the comet assay and was mutagenic in the HPRT assay, this compound tested negative in the Ames test and failed to induce malignant cell transformation in the BALB/c 3T3 cell transformation assay. Interestingly, the non-nitrosylated heme control showed similar effects, but was additionally able to induce malignant transformation in BALB/c 3T3 murine fibroblasts. Taken together, these results suggest that it is the heme molecule rather than the NO moiety which is involved in driving red meat-associated carcinogenesis.

The Relation between Red Meat and Whole-Grain Intake and the Colonic Mucosal Barrier: A Cross-Sectional Study

The Colonic Mucosal Barrier (CMB) is the site of interaction between the human body and the colonic microbiota. The mucus is the outer part of the CMB and is considered as the front-line defense of the colon. It separates the host epithelial lining from the colonic content, and it has previously been linked to health and diseases. In this study, we assessed the relationship between red meat and whole-grain intake and (1) the thickness of the colonic mucus (2) the expression of the predominant mucin gene in the human colon (MUC2). Patients referred to colonoscopy at the University Hospital of Southern Denmark- Sonderjylland were enrolled between June 2017 and December 2018, and lifestyle data was collected in a cross-sectional study design. Colonic biopsies, blood, urine, and fecal samples were collected. The colonic mucus and bacteria were visualized by immunostaining and fluorescence in situ hybridization techniques. We found a thinner mucus was associated with high red meat intake. Similarly, the results suggested a thinner mucus was associated with high whole-grain intake, albeit to a lesser extent than red meat. This is the first study assessing the association between red meat and whole-grain intake and the colonic mucus in humans. This study is approved by the Danish Ethics Committee (S-20160124) and the Danish Data Protecting Agency (2008-58-035). A study protocol was registered at clinical trials.gov under NCT04235348.

Inulin and milk mineral fortification of a pork sausage exhibits distinct effects on the microbiome and biochemical activity in the gut of healthy rats

This study investigated inulin and calcium-rich milk mineral incorporation into a pork sausage in order to examine the effects on microbiome and biochemical activity in the gastrointestinal tract upon ingestion. Rats (n = 48) were fed one of four sausages; a pork sausage enriched with 1) inulin (6.0%) and milk mineral (3%), 2) inulin (6.0%), 3) milk mineral (3%) or 4) control sausages without enrichment. NMR-based metabolomics revealed that inulin-enrichment increased the fecal concentration of short-chain fatty acids (SCFAs). Milk mineral-enrichment also increased SCFA concentrations, although less pronounced. In addition, milk mineral reduced the concentration of nitroso compounds in feces and small intestinal content. Combined enrichment with both inulin and milk mineral showed no cumulative effect on SCFA formation and seemed to oppose the milk mineral-induced reduction of nitroso compound formation. 16S rRNA gene amplicon sequencing indicated that alterations of the gut microbiome contributed to the observed effects.

Meat and colorectal cancer in Middle Eastern and North African countries: update of literature review

Background

This review discusses the findings from epidemiological studies that have examined the possible role of meat and colorectal cancer (CRC) risk in Middle Eastern and North African (MENA) countries.

Methods

We conducted a literature search in the PubMed, Clinical Trials, Google Scholar, Science Direct, and Cochrane databases for observational studies that investigated the association between meat and CRC risk in adults from the MENA region.

Results

Eleven studies were included in this review. For red meat overall, significant associations were found. Regarding beef meat intake, the study included found controversial results with OR = 0.18 (95% CI 0.03–0.09). A positive association was observed between chicken and CRC risk, at OR = 2.52 (95% CI 1.33–4.77) to OR = 4.00 (95% CI 1.53–10.41) to OR = 15.32 (95% CI 3.28–71.45). A significant association was observed between processed meat intake and CRC risk, OR = 9.08 (95% CI 1.02–80.58).

Conclusion

This is the first literature review which illustrated the association between meat consumption and CRC risk in MENA region. We concluded that these studies included in this review have been controversial and not sufficient to establish a clear relationship between CRC and meat consumption in the MENA region. Further studies are necessary to be carried out in this region, with a larger sample size and submit to rigorous criteria. This review will help researchers to improve the quality of future studies about the association between CRC and nutritional diet in general and meat in particular.

Nitrates/Nitrites in Food-Risk for Nitrosative Stress and Benefits

In the context of impact on human health, nitrite/nitrate and related nitrogen species such as nitric oxide (NO) are a matter of increasing scientific controversy. An increase in the content of reactive nitrogen species may result in nitrosative stress-a deleterious process, which can be an important mediator of damage to cell structures, including lipids, membranes, proteins and DNA. Nitrates and nitrites are widespread in the environment and occur naturally in foods of plant origin as a part of the nitrogen cycle. Additionally, these compounds are used as additives to improve food quality and protect against microbial contamination and chemical changes. Some vegetables such as raw spinach, beets, celery and lettuce are considered to contain high concentrations of nitrates. Due to the high consumption of vegetables, they have been identified as the primary source of nitrates in the human diet. Processed meats are another source of nitrites in our diet because the meat industry uses nitrates/nitrites as additives in the meat curing process. Although the vast majority of consumed nitrates and nitrites come from natural vegetables and fruits rather than food additives, there is currently a great deal of consumer pressure for the production of meat products free of or with reduced quantities of these compounds. This is because, for years, the cancer risks of nitrates/nitrites have been considered, since they potentially convert into the nitrosamines that have carcinogenic effects. This has resulted in the development and rapid expansion of meat products processed with plant-derived nitrates as nitrite alternatives in meat products. On the other hand, recently, these two ions have been discussed as essential nutrients which allow nitric oxide production and thus help cardiovascular health. Thus, this manuscript reviews the main sources of dietary exposure to nitrates and nitrites, metabolism of nitrites/nitrates, and health concerns related to dietary nitrites/nitrates, with particular emphasis on the effect on nitrosative stress, the role of nitrites/nitrates in meat products and alternatives to these additives used in meat products.

Adherence to the Dietary Approaches to Stop Hypertension (DASH) dietary pattern reduces the risk of colorectal cancer: A systematic review and meta-analysis

BACKGROUND & AIMS

Colorectal cancer (CRC) has become a major concern due to industrialization and dietary changes generated by it. Many of the components of the DASH (Dietary Approach to Stop Hypertension) diet are associated with the risk of CRC. However, the relationship between DASH dietary pattern and CRC has not been studied yet in a systematic review and meta-analysis. The present study was conducted to review the studies investigating the relationship between DASH diet and the risk of CRC.

METHODS

PubMed and Scopus search engines were searched to find relevant publications from inception up to September 2019. All the observational studies that addressed the association between DASH diet and CRC were included in the systematic review and meta-analysis. All the steps including data base search, screening, and data extraction were carried out by two researchers, independently.

RESULTS

Eight studies included in this systematic review and 5 studies (out of 8 studies included in the systematic review) were included in the meta-analysis. Combining 12 effects sizes from 5 studies, a significant inverse association between adherence to the DASH diet and risk of CRC was found (RR: 0.80; 95% CI: 0.74, 0.85). Based on the result of this study, individuals with greater adherence to DASH diet had 20% lower risk of CRC.

CONCLUSION

The current study demonstrates that the risk of CRC is negatively associated with the adherence to the DASH dietary pattern.

The Multifaceted Role of Heme in Cancer

Heme, an iron-containing porphyrin, is of vital importance for cells due to its involvement in several biological processes, including oxygen transport, energy production and drug metabolism. Besides these vital functions, heme also bears toxic properties and, therefore, the amount of heme inside the cells must be tightly regulated. Similarly, heme intake from dietary sources is strictly controlled to meet body requirements. The multifaceted nature of heme renders it a best candidate molecule exploited/controlled by tumor cells in order to modulate their energetic metabolism, to interact with the microenvironment and to sustain proliferation and survival. The present review summarizes the literature on heme and cancer, emphasizing the importance to consider heme as a prominent player in different aspects of tumor onset and progression.

Global Profiling of Toxicologically Relevant Metabolites in Urine: Case Study of Reactive Aldehydes

Among the numerous unknown metabolites representative of our exposure, focusing on toxic compounds should provide more relevant data to link exposure and health. For that purpose, we developed and applied a global method using data independent acquisition (DIA) in mass spectrometry to profile specifically electrophilic compounds originating metabolites. These compounds are most of the time toxic, due to their chemical reactivity toward nucleophilic sites present in biomacromolecules. The main line of cellular defense against these electrophilic molecules is conjugation to glutathione, then metabolization into mercapturic acid conjugates (MACs). Interestingly, MACs display a characteristic neutral loss in MS/MS experiments that makes it possible to detect all the metabolites displaying this characteristic loss, thanks to the DIA mode, and therefore to highlight the corresponding reactive metabolites. As a proof of concept, our workflow was applied to the toxicological issue of the oxidation of dietary polyunsaturated fatty acids, leading in particular to the formation of toxic alkenals, which lead to MACs upon glutathione conjugation and metabolization. By this way, dozens of MACs were detected and identified. Interestingly, multivariate statistical analyses carried out only on extracted HRMS signals of MACs yield a better characterization of the studied groups compared to results obtained from a classic untargeted metabolomics approach.

Biomarkers of meat and seafood intake: an extensive literature review

Meat, including fish and shellfish, represents a valuable constituent of most balanced diets. Consumption of different types of meat and fish has been associated with both beneficial and adverse health effects. While white meats and fish are generally associated with positive health outcomes, red and especially processed meats have been associated with colorectal cancer and other diseases. The contribution of these foods to the development or prevention of chronic diseases is still not fully elucidated. One of the main problems is the difficulty in properly evaluating meat intake, as the existing self-reporting tools for dietary assessment may be imprecise and therefore affected by systematic and random errors. Dietary biomarkers measured in biological fluids have been proposed as possible objective measurements of the actual intake of specific foods and as a support for classical assessment methods. Good biomarkers for meat intake should reflect total dietary intake of meat, independent of source or processing and should be able to differentiate meat consumption from that of other protein-rich foods; alternatively, meat intake biomarkers should be specific to each of the different meat sources (e.g., red vs. white; fish, bird, or mammal) and/or cooking methods. In this paper, we present a systematic investigation of the scientific literature while providing a comprehensive overview of the possible biomarker(s) for the intake of different types of meat, including fish and shellfish, and processed and heated meats according to published guidelines for biomarker reviews (BFIrev). The most promising biomarkers are further validated for their usefulness for dietary assessment by published validation criteria.

Fecal microbiome as determinant of the effect of diet on colorectal cancer risk: comparison of meat-based versus pesco-vegetarian diets (the MeaTIc study)

Background

Convincing evidence suggests that the risk of colorectal cancer (CRC) is increased by the typical Western diet characterized by high consumption of red and processed meat. In addition, some epidemiological studies suggest a reduction in the risk of CRC associated with fish consumption. The role of the gut microbiome in this diet-associated risk is not well understood.

Methods/design

This is a randomized parallel open clinical trial comprising a total of 150 clinically healthy subjects randomly assigned to three groups: a meat-based diet of which 4 portions per week are red meat (1 portion = 150 g), 3 portions per week are processed meat (1 portion = 50 g), and 1 portion per week is poultry (1 portion = 150 g), for a total amount of 900 g per week of meat and derivatives; a meat-based diet supplemented with alpha-tocopherol; and a pesco-vegetarian diet excluding fresh and processed meat and poultry, but which includes 3 portions per week of fish for a total amount of 450 g per week. Each intervention will last 3 months. The three diets will be isocaloric and of three different sizes according to specific energy requirements. Anthropometric measurements, body composition, and blood and fecal samples will be obtained from each participant at the beginning and end of each intervention phase. The measure of the primary outcome will be the change from baseline in DNA damage induced by fecal water using the comet assay in a cellular model. Secondary outcome measures will be changes in the profile of fecal microbiomes, global fecal and urinary peroxidation markers, and neoplastic biomarkers.

Discussion

Although epidemiological data support the promoting role of meat and the possible protective role of fish in colon carcinogenesis, no study has directly compared dietary profiles characterized by the presence of these two food groups and the role of the gut microbiome in these diet-associated CRC risks. This study will test the effect of these dietary profiles on validated CRC risk biomarkers.

Trial registration

ClinicalTrials.gov, NCT03416777. Registered on 3 May 2018.

Mechanism of colorectal carcinogenesis triggered by heme iron from red meat

Colorectal cancer (CRC) is one of the major tumor entities worldwide, with an increasing incidence in younger people. CRC formation is causally linked to various genetic, life-style and dietary risk factors. Among the ladder, the consumption of red meat has emerged as important risk factor contributing to CRC. A large body of evidence shows that heme iron is the critical component of red meat, which promotes colorectal carcinogenesis. In this review, we describe the uptake and cellular fate of both heme and inorganic iron in intestinal epithelial cells. Next, an overview on the DNA damaging properties of heme iron is provided, highlighting the DNA adducts relevant for CRC etiology. Moreover, heme triggered mechanisms leading to colonic hyperproliferation are presented, which are intimately linked to changes in the intestinal microbiota induced by heme. A special focus was set on the impact of heme iron on innate and adaptive immune cells, which could be relevant in the context of CRC. Finally, we recapitulate in vivo studies providing evidence for the tumor-promoting potential of dietary heme iron. Altogether, heme iron affects numerous key pathways involved in the pathogenesis of CRC.

A Review of the In Vivo Evidence Investigating the Role of Nitrite Exposure from Processed Meat Consumption in the Development of Colorectal Cancer

The World Cancer Research Fund (WCRF) 2007 stated that the consumption of processed meat is a convincing cause of colorectal cancer (CRC), and therefore, the public should avoid it entirely. Sodium nitrite has emerged as a putative candidate responsible for the CRC-inducing effects of processed meats. Sodium nitrite is purported to prevent the growth of Clostridium botulinum and other food-spoiling bacteria, but recent, contradictory peer-reviewed evidence has emerged, leading to media reports questioning the necessity of nitrite addition. To date, eleven preclinical studies have investigated the effect of consuming nitrite/nitrite-containing meat on the development of CRC, but the results do not provide an overall consensus. A sizable number of human clinical studies have investigated the relationship between processed meat consumption and CRC risk with widely varying results. The unique approach of the present literature review was to include analysis that limited the human studies to those involving only nitrite-containing meat. The majority of these studies reported that nitrite-containing processed meat was associated with increased CRC risk. Nitrite consumption can lead to the formation of N-nitroso compounds (NOC), some of which are carcinogenic. Therefore, this focused perspective based on the current body of evidence links the consumption of meat containing nitrites and CRC risk.

A Prospective Analysis of Red and Processed Meat Consumption and Risk of Colorectal Cancer in Women

BACKGROUND

Red and processed meats have been implicated as risk factors in the development of colorectal cancer in U.S. women, but associations with cooking practices are less well established.

METHODS

Data are from the Sister Study, a cohort of women ages 35 to 74 years from the United States and Puerto Rico who have a sister diagnosed with breast cancer. Red and processed meat consumption, meat cooking practices, and intake of common meat products were collected at baseline using self-administered questionnaires (N = 48,704). Multivariable HRs (HR_adj) and 95% confidence intervals (95% CI) were estimated.

RESULTS

During a median 8.7 years' follow-up (range <1-12.7 years), 216 colorectal cancer cases were diagnosed. In categorical analyses, an increased risk of colorectal cancer was seen in the highest quartile of processed meat consumption compared with the lowest [HR_adj = 1.52 (95% CI, 1.01-2.30); P _trend = 0.02], and for specific meat products, including breakfast sausages [HR_adj = 1.85 (95% CI, 1.30-2.64)] and bacon [HR_adj = 1.46 (95% CI, 1.01-2.11)]. The HR_adj for the highest quartile of red meat consumption was 1.04 (95% CI, 0.68-1.60), and little evidence of association was observed for cooking practices or doneness of red meat. We observed positive associations with specific red meat products when cooking methods were considered, for example, grilled/barbequed steaks [HR_adj = 2.23 (95% CI, 1.20-4.14)] and hamburgers [HR_adj = 1.98 (95% CI, 1.00-3.91)].

CONCLUSIONS

Higher reported daily intake of processed meats and consumption of barbecued/grilled red meat products were associated with increased risk of colorectal cancer in women.

IMPACT

Variability in colorectal risk risk by meat type and cooking method should be considered when evaluating meat consumption.

Meat subtypes and colorectal cancer risk: A pooled analysis of 6 cohort studies in Japan

Red meat and processed meat have been suggested to increase risk of colorectal cancer (CRC), especially colon cancer. However, it remains unclear whether these associations differ according to meat subtypes or colon subsites. The present study addressed this issue by undertaking a pooled analysis of large population-based cohort studies in Japan: 5 studies comprising 232 403 participants (5694 CRC cases) for analysis based on frequency of meat intake, and 2 studies comprising 123 635 participants (3550 CRC cases) for analysis based on intake quantity. Study-specific hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using the Cox proportional hazards model and then pooled using the random effect model. Comparing the highest vs lowest quartile, beef intake was associated with an increased risk of colon cancer in women (pooled HR 1.20; 95% CI, 1.01-1.44) and distal colon cancer (DCC) risk in men (pooled HR 1.30; 95% CI, 1.05-1.61). Frequent intake of pork was associated with an increased risk of distal colon cancer in women (pooled HR 1.44; 95% CI, 1.10-1.87) for "3 times/wk or more" vs "less than 1 time/wk". Frequent intake of processed red meat was associated with an increased risk of colon cancer in women (pooled HR 1.39; 95% CI, 0.97-2.00; P trend = .04) for "almost every day" vs "less than 1 time/wk". No association was observed for chicken consumption. The present findings support that intake of beef, pork (women only), and processed red meat (women only) might be associated with a higher risk of colon (distal colon) cancer in Japanese.

Consumption of meat, traditional and modern processed meat and colorectal cancer risk among the Moroccan population: A large-scale case-control study

The current study aimed to investigate the relationship between red and white meat subtypes, processed meat (divided into traditional "Khlii, Kaddid" and industrially processed meat) and colorectal cancer (CRC) risk, considering CRC subsites, in Moroccan adults. A case-control study was conducted including 2,906 matched case-control pairs recruited from the five largest university hospitals in Morocco. Dietary data were collected through a validated Food Frequency Questionnaire (FFQ). Multivariable odds ratios (OR) and 95% confidence intervals (CI), for the association of CRC risk with meat consumption (high vs. low intake), were estimated using conditional logistic regression models, adjusted for relevant confounding variables. Overall, consumption of red meat was positively associated with colon cancer and CRC risk (OR = 1.23, 95% CI = 1.05-1.44; OR = 1.14, 95% CI = 1.02-1.27), respectively. In contrast, no significant association was observed between the consumption of red meat and rectal cancer risk (OR = 1.05, 95% = 0.90-1.23). Interestingly, while processed meat from industrial processes was positively associated with colon cancer, rectal cancer and CRC (OR = 1.61, 95% CI = 1.27-2.04; OR = 1.73, 95% CI = 1.34-2.23; OR = 1.67, 95% CI = 1.41-1.98), processed meat prepared using traditional methods was inversely associated with colon cancer and CRC risk (OR = 0.74, 95% CI = 0.57-0.98; OR = 0.77, 95% CI = 0.64-0.93), respectively. Furthermore, positive associations were observed between poultry intake and colon cancer risk among men (OR = 1.27, 95% CI = 1.01-1.59). Our study showed similar associations between the consumption of red meat and CRC risk in Morocco as in developed countries, while inverse associations were found for traditionally processed meat products. This is the first study to investigate the differential effects of traditional vs. westernized processed meat products in a developing country. Other studies are needed to confirm these findings and to understand the physiological pathways underlying these associations.

Estimation of the Burden of Iron Deficiency Anemia in France from Iron Intake: Methodological Approach

: Dietary iron deficiency (ID) is the first nutritional deficiency in the world, in terms of disability adjusted life years (DALY). This nutritional deficiency may lead to anemia, especially among children, adolescents, and adult women. The aim of this study was to build an original probabilistic model to quantitatively assess the ID, the iron deficiency anemia (IDA) and the subsequent health burden in France expressed in DALY, per age class and gender. The model considered the distribution of absorbed iron intake, the iron requirement distribution established by the European Food Safety Authority and the iron status in France. Uncertainty due to lack of data and variability due to biological diversity were taken into account and separated using a second-order Monte Carlo procedure. A total of 1290 (95% CI = 1230-1350) IDA cases corresponding to 16 (95% CI = 11-20) DALY were estimated per 100,000 individuals per year. The major contributors to IDA burden were menstruating females aged from 25 to 44 years old. Then, a consumption scenario was built with ground beef as intake, an increase in red meat consumption to 100 g/d would not eliminate entirely the IDA burden. The quantitative methodology applied here for France could be reused for other populations.

Identifying labelling and marketing advantages of nutrients in minced beef meat: A case study

In 2006, the European Commission approved nutrition and health claim regulations of foods to stimulate healthier choices. To document how commercial, minced beef meat complied with regulations, meat samples from 72 carcasses were analysed. These samples were a source of niacin (B3), pyridoxine (B6), phosphorus and iron (cow meat only), and a rich source of protein, monounsaturated fat, vitamin B12 and zinc. A potential exists for establishing beef meat as a source of vitamin K, iron and selenium. The meat's nutrient relevance for young women when ingesting 150 g of raw beef mince/day was estimated. Increased levels of riboflavin (B2), pantothenic acid (B5), iron and selenium beyond presently observed, would better support this group's recommended nutrient intake. If the bioactivity of 25-OH-vitamin D3 could be used in calculations, vitamin D3 in the minced meat would add positively to the intake of vitamin D3 that was 49% of the recommended intake.

Red Meat-Derived Nitroso Compounds, Lipid Peroxidation Products and Colorectal Cancer

About 20 years ago, the research group of Sheila Anne Bingham in Cambridge, UK, showed for the first time that volunteers consuming large amounts of red meat excrete high amounts of nitroso compounds via feces. In the meantime, it has been demonstrated that heme leads to the enhanced formation of nitroso compounds in the gastrointestinal tract and that the main nitroso compounds formed in the gastrointestinal tract are S-nitrosothiols and the nitrosyl heme. Moreover, it has been postulated that these endogenously formed nitroso compounds may alkylate guanine at the O⁶-position, resulting in the formation of the promutagenic DNA lesions O⁶-methylguanine and O⁶-carboxymethylguanine, which, if not repaired (in time), could lead to gene mutations and, subsequently to the development of colorectal cancer. Alternatively, it has been postulated that heme iron could contribute to colorectal carcinogenesis by inducing lipid peroxidation. In the present review, the evidence supporting the above-mentioned hypotheses will be presented.

Red and processed meat consumption and esophageal cancer risk: a systematic review and meta-analysis

BACKGROUND

The associations between red and processed meat consumption and esophageal cancer risk remain inconclusive. We performed a systematic review and meta-analysis to analyze these associations.

METHODS

We searched PubMed and EMBASE to identify studies published between the databases' dates of inception and May 2019.

RESULTS

We ultimately selected 33 eligible studies for analysis. We found that the summary relative risks for the associations between meat consumption and esophageal cancer risk were positive for the case-control studies (P < 0.05), but negative for the cohort studies included in the analysis (P > 0.05). Subtype analysis indicated that red and processed meat consumption was not associated with the risks of esophageal adenocarcinoma (P > 0.05) and esophageal squamous cell carcinoma (P > 0.05) in the cohort studies.

CONCLUSIONS

We found case-control but not cohort studies to associate consumption of red and processed meat with the risk of esophageal cancer. Further large prospective studies are needed to validate these findings.

Iron and Cancer

This review explores the multifaceted role that iron has in cancer biology. Epidemiological studies have demonstrated an association between excess iron and increased cancer incidence and risk, while experimental studies have implicated iron in cancer initiation, tumor growth, and metastasis. The roles of iron in proliferation, metabolism, and metastasis underpin the association of iron with tumor growth and progression. Cancer cells exhibit an iron-seeking phenotype achieved through dysregulation of iron metabolic proteins. These changes are mediated, at least in part, by oncogenes and tumor suppressors. The dependence of cancer cells on iron has implications in a number of cell death pathways, including ferroptosis, an iron-dependent form of cell death. Uniquely, both iron excess and iron depletion can be utilized in anticancer therapies. Investigating the efficacy of these therapeutic approaches is an area of active research that promises substantial clinical impact.

Haem iron reshapes colonic luminal environment: impact on mucosal homeostasis and microbiome through aldehyde formation

BACKGROUND

The World Health Organization classified processed and red meat consumption as "carcinogenic" and "probably carcinogenic", respectively, to humans. Haem iron from meat plays a role in the promotion of colorectal cancer in rodent models, in association with enhanced luminal lipoperoxidation and subsequent formation of aldehydes. Here, we investigated the short-term effects of this haem-induced lipoperoxidation on mucosal and luminal gut homeostasis including microbiome in F344 male rats fed with a haem-enriched diet (1.5 μmol/g) 14-21 days.

RESULTS

Changes in permeability, inflammation, and genotoxicity observed in the mucosal colonic barrier correlated with luminal haem and lipoperoxidation markers. Trapping of luminal haem-induced aldehydes normalised cellular genotoxicity, permeability, and ROS formation on a colon epithelial cell line. Addition of calcium carbonate (2%) to the haem-enriched diet allowed the luminal haem to be trapped in vivo and counteracted these haem-induced physiological traits. Similar covariations of faecal metabolites and bacterial taxa according to haem-induced lipoperoxidation were identified.

CONCLUSIONS

This integrated approach provides an overview of haem-induced modulations of the main actors in the colonic barrier. All alterations were closely linked to haem-induced lipoperoxidation, which is associated with red meat-induced colorectal cancer risk.

The interaction of Hemin and Sestrin2 modulates oxidative stress and colon tumor growth

Several large epidemiological and animal studies demonstrate a direct correlation between dietary heme iron intake and/or systemic iron levels and cancer risk in several cancers including colorectal cancer (CRC). However, the precise mechanisms for how heme iron contributes to CRC and how cancer cells respond to heme iron-induced stress are still unclear. Previously we have shown that one of the stress-inducible proteins, Sestrin2 (SESN2), is a novel tumor suppressor in colon by limiting endoplasmic reticulum stress and mammalian target of rapamycin complex 1 (mTORC1) signaling and tumor growth. But the relationship between heme iron and SESN2, especially in the context of colon carcinogenesis, was not investigated previously. Here, we found that hemin dose-dependently increased SESN2 expression in an oxidative stress and nuclear factor (erythroid-derived 2)-like 2 (NFE2L2, NRF2)-dependent manner. Since SESN2 overexpression reduced hemin-induced oxidative stress, SESN2 could be an important target of NRF2 exerting antioxidant function. Indeed, expression of several oxidative stress responsive proteins such as NRF2 and its target genes was reduced by SESN2. Although we formerly reported that SESN2 expression was reduced after p53 mutation in colon tumors, mouse colon tumors, which have intact p53 and NRF2, induced SESN2 expression in response to iron stimulus. Although SESN2 overexpression decreased murine colon tumor cell growth both in vitro and in vivo, it rendered colon cancer cells more resistant to hemin-induced apoptosis and therefore promoted tumor growth during hemin treatment. Taken together, although SESN2 generally suppresses tumorigenesis, it can produce tumor-promoting role in iron-rich environment by suppressing oxidative stress-associated cancer cell death.

Combined Consumption of Beef-Based Cooked Mince and Sucrose Stimulates Oxidative Stress, Cardiac Hypertrophy, and Colonic Outgrowth of Desulfovibrionaceae in Rats

SCOPE

High red meat and sucrose consumption increases the epidemiological risk for chronic diseases. Mechanistic hypotheses include alterations in oxidative status, gut microbiome, fat deposition, and low-grade inflammation.

METHODS AND RESULTS

For 2 weeks, 40 rats consumed a diet high in white or red meat (chicken-based or beef-based cooked mince, respectively), and containing corn starch or sucrose in a 2 × 2 factorial design. Lard was mixed with lean chicken or beef to obtain comparable dietary fatty acid profiles. Beef (vs chicken)-fed rats had higher lipid oxidation products (malondialdehyde, 4-hydroxy-2-nonenal, and hexanal) in stomach content and blood, and lower blood glutathione. Sucrose (vs corn starch)-fed rats showed increased blood lipid oxidation products and glutathione peroxidase activity, higher liver weight and malondialdehyde concentrations, and mesenterial and retroperitoneal fat accumulation. Beef-sucrose-fed rats had increased cardiac weight, suggesting pathophysiological effects on the cardiovascular system. The colonic microbiome of beef-sucrose-fed rats showed an outgrowth of the sulfate-reducing family of the Desulfovibrionaceae, and lower abundance of the Lactobacillus genus, indicating intestinal dysbiosis. Blood C-reactive protein, a marker for inflammation, was not different among groups.

CONCLUSIONS

Consumption of a cooked beef-based meat product with sucrose increased oxidative stress parameters and promoted cardiac hypertrophy and intestinal dysbiosis.

Essential roles of mitochondrial and heme function in lung cancer bioenergetics and tumorigenesis

Contrary to Warburg’s hypothesis, mitochondrial oxidative phosphorylation (OXPHOS) contributes significantly to fueling cancer cells. Several recent studies have demonstrated that radiotherapy-resistant and chemotherapy-resistant cancer cells depend on OXPHOS for survival and progression. Several cancers exhibit an increased risk in association with heme intake. Mitochondria are widely known to carry out oxidative phosphorylation. In addition, mitochondria are also involved in heme synthesis. Heme serves as a prosthetic group for several proteins that constitute the complexes of mitochondrial electron transport chain. Therefore, heme plays a pivotal role in OXPHOS and oxygen consumption. Further, lung cancer cells exhibit heme accumulation and require heme for proliferation and invasion in vitro. Abnormalities in mitochondrial biogenesis and mutations are implicated in cancer. This review delves into mitochondrial OXPHOS and lesser explored area of heme metabolism in lung cancer.

Recommendation-based dietary indexes and risk of colorectal cancer in the Nurses' Health Study and Health Professionals Follow-up Study

Background

Many dietary indexes exist for chronic disease prevention, but the optimal dietary pattern for colorectal cancer prevention is unknown.

Objective

We sought to determine associations between adherence to various dietary indexes and incident colorectal cancer in 2 prospective cohort studies.

Design

We followed 78,012 women in the Nurses' Health Study and 46,695 men in the Health Professionals Follow-up Study from 1986 and 1988, respectively, until 2012. We created dietary index scores for the Dietary Approaches to Stop Hypertension (DASH) diet, Alternative Mediterranean Diet (AMED), and Alternative Healthy Eating Index-2010 (AHEI-2010) and used Cox regression to estimate HRs and 95% CIs for risk of colorectal cancer (CRC) and by anatomic subsite. We also conducted latency analyses to examine associations between diet and CRC risk during different windows of exposure. We conducted analyses in men and women separately, and subsequently pooled these results in a random-effects meta-analysis.

Results

We documented 2690 colorectal cancer cases. Pooled multivariable HRs for colorectal cancer risk comparing the highest to lowest quintile of diet scores were 0.89 (95% CI: 0.74, 1.08; P-trend = 0.10) for DASH, 0.89 (95% CI: 0.73, 1.10; P-trend = 0.31) for AMED, and 0.95 (95% CI: 0.83, 1.09; P-trend = 0.56) for AHEI-2010 (P-heterogeneity ≥ 0.07 for all). In sex-specific analyses, we observed stronger associations in men for all dietary indexes (DASH: multivariable HR = 0.81, 95% CI: 0.66, 0.98; P-trend = 0.003; AMED: multivariable HR = 0.80, 95% CI: 0.65, 0.98; P-trend = 0.02; AHEI-2010: multivariable HR = 0.88, 95% CI: 0.72, 1.07; P-trend = 0.04) than in women (multivariable HRs range from 0.98 to 1.01).

Conclusions

Adherence to the DASH, AMED, and AHEI-2010 diets was inversely associated with colorectal cancer risk in men. These diets were not associated with colorectal cancer risk in women. This observational study was registered at http://www.clinicaltrials.gov as NCT03364582.

Mechanistic Evidence for Red Meat and Processed Meat Intake and Cancer Risk: A Follow-up on the International Agency for Research on Cancer Evaluation of 2015

The Working Group of the International Agency for Research on Cancer classified the consumption of processed meat as carcinogenic to humans (Group 1), and classified red meat as probably carcinogenic to humans (Group 2A); consumption of both meat types is associated with an increased risk of colorectal cancer. These classifications are based on a compilation of epidemiology data and mechanistic evidence from animal and human studies. The curing of meats with nitrite can produce carcinogenic N-nitroso compounds (NOCs), and the smoking of meat produces polycyclic aromatic hydrocarbons (PAHs). The high-temperature cooking of meat also produces carcinogenic heterocyclic aromatic amines (HAAs). The ingestion of heme from meat can catalyze the formation of NOCs and lipid peroxidation products (LPOs) in the digestive tract. Many of these chemicals form DNA adducts, some of which can induce mutations and initiate carcinogenesis. Another recent hypothesis is that N-glycolylneuraminic acid, a non-human sialic acid sugar present in red meat, becomes incorporated in the cell membrane, triggering the immune response with associated inflammation and reactive oxygen species, which can contribute to DNA damage, tumor promotion, and cancer. The mechanisms by which these chemicals in meat induce DNA damage, and the impact of dietary and host factors that influence the biological potency of these chemicals are highlighted in this updated report.

Soil is a key factor influencing gut microbiota and its effect is comparable to that exerted by diet for mice

Exposure to an unsanitary environment increases the diversity and alters the composition of gut microbiota. To identify the key element in the unsanitary environment responsible for this phenomenon, we investigated the effect and the extent by which the soil in our environment influenced the composition of gut microbiota. Results show that adding unsterile or sterile soil to bedding, either before birth or after weaning, influences significantly the composition of mice gut microbiota. Specifically, unsterile soil increases the richness and biodiversity of gut microbiota. Interestingly, based on UniFrac distance analysis of 16S rRNA sequences, the impact of soil on gut microbiota is comparable to that exerted by diet. These findings provide a potential new strategy for intervening on the human gut microbial community and preventing disease.

Suggestion for a subdivision of processed meat products on the Danish market based on their content of carcinogenic compounds

Carcinogenic effects in humans are ascribed to processed meat by organisations such as International Agency for Research on Cancer, World Cancer Research Fund and American Institute for Cancer Research. However, the term 'processed meat' covers a heterogenic group of products whose content of potential hazards differ considerably. To improve estimates of associations between processed meat intake and cancer risk we investigated ways to divide processed meat into subgroups that more precisely reflects its carcinogenic characteristics. We collected ingredient lists and declarations of salt content for >1000 processed meat products on the Danish market and combined the information with knowledge related to processing parameters. Some compounds that could affect the products' carcinogenic characteristics, alone or in combination, were evaluated and compared for 12 types of processed meat products, and we suggest subgrouping of processed meat with similar level of carcinogenic potential, which could improve the understanding of the cancer risk associated with processed meat intake in scientific human studies.

Association between red and processed meat intake and colorectal adenoma incidence and recurrence: a systematic review and meta-analysis

The associations between red and processed meat intake and colorectal adenoma (CRA) incidence and recurrence are inconclusive. We performed a systematic review and meta-analysis to analysis these associations. We conducted a systematic search of PubMed, EMBASE and Web of Science up to December 2016. The relative risks (RRs) and 95% confidence intervals (CIs) were assessed. Subgroup analyses, dose-response-analyses, subtype analyses and analyses of CRA locations were also conducted. Twenty-seven studies that involved 208,117 participants and 19,150 cases met criteria. The RRs of the highest versus lowest intakes for CRA incidence were 1.23 (1.15–1.31) for red meat and 1.15 (1.07–1.24) for processed meat. Dose-response analyses for meat per 100 g/day yielded the results were consistent with the original analyses, with 1.14 (1.07–1.20) for red meat and 1.27 (1.03–1.50) for processed meat. Additionally, there were no associations between red and processed meat intake and CRA recurrence, including total CRA (P > 0.05), advanced CRA (P > 0.05) and multiple CRA (P > 0.05). In conclusion, our findings support the hypothesis that red and processed meat intake was associated with an increased CRA incidence but not for CRA recurrence.

Association between a pro plant-based dietary score and cancer risk in the prospective NutriNet-santé cohort

Diverse plant products (e.g. fruits, vegetables, legumes) are associated with decreased cancer risk at several locations while red and processed meat were found to increase cancer risk. A pro plant-based dietary score reflecting the relative contribution of consumed plant vs animal products was developed, and was associated with lower overall mortality, type 2 diabetes and cardiovascular disease risk, among omnivorous adults. For the first time, we investigated the prospective associations between this pro plant-based dietary score and cancer risk. This study included 42,544 men and women of the French NutriNet-Santé prospective cohort (2009-2016) aged ≥45 years who completed at least three 24-hr-dietary records during the first year of follow-up. The risk of developing cancer was compared across sex-specific tertiles of pro plant-based dietary score by multivariable Cox models. In total, 1,591 first primary incident cancer cases were diagnosed during follow-up, among which 487 breast, 243 prostate, 198 digestive and 68 lung cancers. A higher pro plant-based dietary score was associated with decreased risks of overall (HR_t3vs.t1 =0.85; 95% CI 0.76, 0.97; P_trend =0.02), digestive (HR_t3vs.t1 =0.68; 95% CI 0.47; 0.99; P_trend  = 0.04) and lung (HR_t3vs.t1 =0.47; 95% CI 0.25, 0.90; P_trend =0.02) cancer, though no substantial associations were found for breast or prostate cancers. This large cohort study supports a beneficial role of higher intakes of plant-based products along with lower intakes of animal products, within a balanced omnivorous diet, regarding primary cancer prevention. These results are consistent with mechanistic evidence from experimental studies.

Isotopic labelling for the characterisation of HNE-sequestering agents in plant-based extracts and its application for the identification of anthocyanidins in black rice with giant embryo

Reactive carbonyl species (RCS) are cytotoxic molecules that originate from lipid peroxidation and sugar oxidation. Natural derivatives can be an attractive source of potential RCS scavenger. However, the lack of analytical methods to screen and identify bioactive compounds contained in complex matrices has hindered their identification. The sequestering actions of various rice extracts on RCS have been determined using ubiquitin and 4-hydroxy-2-nonenal (HNE) as a protein and RCS model, respectively. Black rice with giant embryo extract was found to be the most effective among various rice varieties. The identification of bioactive compounds was then carried out by an isotopic signature profile method using the characteristic isotopic ion cluster generated by the mixture of HNE: ²H₅-HNE mixed at a 1:1 stoichiometric ratio. An in-house database was used to obtain the structures of the possible bioactive components. The identified compounds were further confirmed as HNE sequestering agents through HPLC-UV analysis.

Molecular mechanisms of the preventable causes of cancer in the United States

Annually, there are 1.6 million new cases of cancer and nearly 600,000 cancer deaths in the United States alone. The public health burden associated with these numbers has motivated enormous research efforts into understanding the root causes of cancer. These efforts have led to the recognition that between 40% and 45% of cancers are associated with preventable risk factors and, importantly, have identified specific molecular mechanisms by which these exposures modify human physiology to induce or promote cancer. The increasingly refined knowledge of these mechanisms, which we summarize here, emphasizes the need for greater efforts toward primary cancer prevention through mitigation of modifiable risk factors. It also suggests exploitable avenues for improved secondary prevention (which includes the development of therapeutics designed for cancer interception and enhanced techniques for noninvasive screening and early detection) based on detailed knowledge of early neoplastic pathobiology. Such efforts would complement the current emphasis on the development of therapeutic approaches to treat established cancers and are likely to result in far greater gains in reducing morbidity and mortality.

Targeting Colon Luminal Lipid Peroxidation Limits Colon Carcinogenesis Associated with Red Meat Consumption

Red meat is probably carcinogenic to humans (WHO/IARC class 2A), in part through heme iron-induced lipoperoxidation. Here, we investigated whether red meat promotes carcinogenesis in rodents and modulates associated biomarkers in volunteers, speculating that an antioxidant marinade could suppress these effects via limitation of the heme induced lipid peroxidation. We gave marinated or non-marinated beef with various degrees of cooking to azoxymethane-initiated rats, Min mice, and human volunteers (crossover study). Mucin-depleted foci were scored in rats, adenoma in Min mice. Biomarkers of lipoperoxidation were measured in the feces and urine of rats, mice, and volunteers. The organoleptic properties of marinated meat were tested. Fresh beef increased colon carcinogenesis and lipoperoxidation in rats and mice and lipoperoxidation in humans. Without an adverse organoleptic effect on meat, marinade normalized peroxidation biomarkers in rat and mouse feces, reduced peroxidation in human feces and reduced the number of Mucin-depleted foci in rats and adenoma in female Min mice. This could lead to protective strategies to decrease the colorectal cancer burden associated with red meat consumption. Cancer Prev Res; 11(9); 569-80. ©2018 AACR.

Red meat and colon cancer: A review of mechanistic evidence for heme in the context of risk assessment methodology

On October 26, 2015, IARC published a summary of their findings regarding the association of cancer with consumption of red meat or processed meat (IARC 2015; The Lancet Oncology 2015). The Working Group concluded that there is limited evidence in human beings for carcinogenicity from the consumption of red meat and inadequate evidence in experimental animals for the carcinogenicity of consumption of red meat. Nevertheless, the working group concluded that there is strong mechanistic evidence by which ingestion of red meat can be linked to human colorectal cancer and assigned red meat to Group 2A "probably carcinogenic to humans". The Working Group cited supporting mechanistic evidence for multiple meat components, including those formed from meat processing, such as N-nitroso compounds (NOC) and heterocyclic aromatic amines, and the endogenous compound, heme iron. The mechanism of action for each of these components is different and so it is critical to evaluate the evidence for each component separately. Consequently, this review critically examined studies that investigated mechanistic evidence associated with heme iron to assess the weight of the evidence associating exposure to red meat with colorectal cancer. The evidence from in vitro studies utilized conditions that are not necessarily relevant for a normal dietary intake and thus do not provide sufficient evidence that heme exposure from typical red meat consumption would increase the risk of colon cancer. Animal studies utilized models that tested promotion of preneoplastic conditions utilizing diets low in calcium, high in fat combined with exaggerations of heme exposure that in many instances represented intakes that were orders of magnitude above normal dietary consumption of red meat. Finally, clinical evidence suggests that the type of NOC found after ingestion of red meat in humans consists mainly of nitrosyl iron and nitrosothiols, products that have profoundly different chemistries from certain N-nitroso species which have been shown to be tumorigenic through the formation of DNA adducts. In conclusion, the methodologies employed in current studies of heme have not provided sufficient documentation that the mechanisms studied would contribute to an increased risk of promotion of preneoplasia or colon cancer at usual dietary intakes of red meat in the context of a normal diet.

Red and processed meat consumption and gastric cancer risk: a systematic review and meta-analysis

The associations between red and processed meat consumption and gastric cancer risk have remained inconclusive. We performed a systematic review and meta-analysis to analyze these associations. We searched PubMed and EMBASE to identify studies published from inception through October 2016. Subtype analyses of gastric cancer (gastric cardia adenocarcinoma and gastric non-cardiac adenocarcinoma) and dose-response analyses were performed. We finally selected 42 eligible studies. The summary relative risks of highest versus lowest consumption were positive for case-control studies with 1.67 (1.36-2.05) for red meat and 1.76 (1.51-2.05) for processed meat, but negative for cohort studies with 1.14 (0.97-1.34) for red meat and 1.23 (0.98-1.55) for processed meat. Subtype analyses of cohort studies suggested null results for gastric cardia adenocarcinoma (red meat, P = 0.79; processed meat, P = 0.89) and gastric non-cardiac adenocarcinoma (red meat, P = 0.12; processed meat, P = 0.12). In conclusion, the present analysis suggested null results between red and processed meat consumption and gastric cancer risk in cohort studies, although case-control studies yielded positive associations. Further well-designed prospective studies are needed to validate these findings.

Development and validation of an ultra high performance liquid chromatography-electrospray tandem mass spectrometry method using selective derivatisation, for the quantification of two reactive aldehydes produced by lipid peroxidation, HNE (4-hydroxy-2(E)-nonenal) and HHE (4-hydroxy-2(E)-hexenal) in faecal water

Red or processed meat rich diets have been shown to be associated with an elevated risk of colorectal cancer (CRC). One major hypothesis involves dietary heme iron which induces lipid peroxidation. The quantification of the resulting reactive aldehydes (e.g. HNE and HHE) in the colon lumen is therefore of great concern since these compounds are known for their cytotoxic and genotoxic properties. UHPLC-ESI-MS/MS method has been developed and validated for HNE and HHE quantification in rat faeces. Samples were derivatised using a brominated reagent (BBHA) in presence of pre-synthesized deuterated internal standards (HNE-d11/HHE-d5), extracted by solid phase extraction, and then analysed by LC-positive ESI-MS/MS (MRM) on a TSQ Vantage mass spectrometer. The use of BBHA allowed the efficient stabilisation of the unstable and reactive hydroxy-alkenals HNE and HHE. The MRM method allowed selective detection of HNE and HHE on the basis of characteristic transitions monitored from both the 79 and 81 bromine isotopic peaks. This method was validated according to the European Medicines Agency (EMEA) guidelines, by determining selectivity, sensitivity, linearity, carry-over effect, recovery, matrix effect, repeatability, trueness and intermediate precision. The performance of the method enabled the quantification of HNE and HHE in concentrations 0.10-0.15 μM in faecal water. Results are presented on the application to the quantification of HNE and HHE in different faecal waters obtained from faeces of rats fed diets with various fatty acid compositions thus corresponding to different pro-oxidative features.

Meat intake, cooking methods and doneness and risk of colorectal tumours in the Spanish multicase-control study (MCC-Spain)

PURPOSE

Although there is convincing evidence that red and processed meat intake increases the risk of colorectal cancer (CRC), the potential role of meat cooking practices has not been established yet and could partly explain the current heterogeneity of results among studies. Therefore, we aimed to investigate the association between meat consumption and cooking practices and the risk of CRC in a population-based case-control study.

METHODS

A total of 1671 CRC cases and 3095 controls recruited in Spain between September 2008 and December 2013 completing a food frequency questionnaire with a meat-specific module were included in the analyses. Odds ratios (OR) and confidence intervals (CI) were estimated by logistic regression models adjusted for known confounders.

RESULTS

Total meat intake was associated with increased risk of CRC (OR T3-T1 1.41; 95% CI 1.19-1.67; p trend < 0.001), and similar associations were found for white, red and processed/cured/organ meat. Rare-cooked meat preference was associated with low risk of CRC in red meat (ORrare vs. medium 0.66; 95% CI 0.51-0.85) and total meat (ORrare vs. medium 0.56; 95% CI 0.37-0.86) consumers, these associations being stronger in women than in men. Griddle-grilled/barbecued meat was associated with an increased CRC risk (total meat: OR 1.45; 95% CI 1.13-1.87). Stewing (OR 1.25; 95% CI 1.04-1.51) and oven-baking (OR 1.18; 95% CI 1.00-1.40) were associated with increased CRC risk of white, but not red, meat.

CONCLUSIONS

Our study supports an association of white, red, processed/cured/organ and total meat intake with an increased risk of CRC. Moreover, our study showed that cooking practices can modulate such risk.

Probabilistic estimates of heterocyclic amines and polycyclic aromatic hydrocarbons concentrations in meats and breads applicable to exposure assessments

Random effect meta-regressions were constructed to estimate concentrations of two heterocyclic amines (HCA) and eight polycyclic aromatic hydrocarbons (PAH) in meat and breads. Eighteen HCA studies and nine PAH studies of food concentration were assembled. Concentration was computed for beef, poultry, pork, and seafood, and bread. Fixed effect predictors included cooking time, form of the food, cooking method, interaction between form and cooking method, temperature at which the food was cooked, fuel of the flame source, percentage of fat, and other elements. Meat type was significant to all HCAs but only three of the PAHs. Cooking method or an interaction between cooking method and food form was significant in all the overall models for each compound, and 80% of models created for stratifications of the data based on meat type. Improvement on compilations such as the Computerized Heterocyclic Amines Resource for Research in Epidemiology of Disease (CHARRED) database comes from inclusion of additional studies, PAH compounds, more generalizable food categories, more cooking methods (such as smoking), and addition of seafood. Meta-regression allows parameters to be estimated with separation of between-study heterogeneity, and extrapolation of exposures to more foods. Resulting uncertainty estimates are useful in a probabilistic exposure assessment.

Dietary iron intake and breast cancer risk: modulation by an antioxidant supplementation

Experimental results suggested that iron-induced lipid peroxidation may explain the direct associations observed between red/processed meat intakes and colorectal and breast cancer risk. However, epidemiological evidence is lacking. Thus, we investigated the association between dietary iron intake and breast cancer risk, and its potential modulation by an antioxidant supplementation and lipid intake. This prospective study included 4646 women from the SU.VI.MAX trial (daily low-dose antioxidants vs. placebo). 188 incident breast cancers were diagnosed (median follow-up=12.6y). Dietary iron intake was assessed using repeated 24h dietary records. Multivariable Cox proportional hazards models were computed. Dietary iron intake was associated with an increased breast cancer risk (HRT3vs.T1=1.67 (1.02-2.71), P-trend=0.04). This association was observed in the placebo group (HRT3vs.T1=2.80 (1.42-5.54), P-trend=0.003), but not in the antioxidant-supplemented group (P-trend=0.7, P-interaction=0.1). Besides, in the placebo group, the increased breast cancer risk associated with dietary iron intake was more specifically observed in women with higher lipid intake (P-trend=0.046). These findings suggest that dietary iron intake may be associated with an increased breast cancer risk, especially in women who did not received antioxidants during the trial and who consumed more lipids. This supports the experimental results suggesting that breast cancer risk may be increased by iron-induced lipid peroxidation.

Environmental contributions to gastrointestinal and liver cancer in the Asia-Pacific region

In the Asia-Pacific region, gastric, colorectal, and hepatocellular (liver) cancer show substantial regional variation in incidence consistent with the presence of important environmental factors. For gastric cancer, global incidence is concentrated in Asia with substantially higher rates in East Asia than in South-East Asia and Australia. The differences in incidence rates for gastric cancer in the Asia-Pacific region may be due, in part, to differences in the prevalence of Helicobacter pylori infection and the prevalence of H. pylori virulence factors. Smoking is also correlated with gastric cancer risk and is responsible for the highest population attributable fraction among men in East Asia. Colorectal cancer has increased rapidly in incidence to become the third most common digestive cancer in Asia. According to cohort studies in Asia, smoking, alcohol use, obesity, and physical inactivity increase the risk of colorectal cancer. Unlike West Asia, East Asia and Australia have high incidence rates for colorectal cancer that correlates to a high Human Development Index and a high prevalence of alcohol consumption and obesity. Liver cancer is the second most common digestive cancer in Asia. The high incidence of liver cancer in East Asia and South-East Asia is concordant with the high prevalence of hepatitis B virus and hepatitis C virus infection. Other important risk factors include alcohol use, smoking, and diabetes. The identification of the earlier and other environmental factors (currently under investigation) is central to the development and implementation of effective cancer control programs for the region.

Enhancement of colon carcinogenesis by the combination of indole-3 carbinol and synbiotics in hemin-fed rats

The risk of developing colorectal cancer (CRC) could be associated with red and processed meat intake. Experimental data supports that hemin iron, found abundantly in red meat, promotes CRC in mice and rats, while indole-3 carbinol (I3C) and synbiotics (syn) exert anti-carcinogenic activities in most studies of colon carcinogenesis. This study aimed to investigate the modifying effects of I3C and syn (inulin + Bifidobacterium lactis), given separately or together, on dimethylhidrazine (DMH)-induced colon carcinogenesis in hemin-fed rats. All animals were given four subcutaneous DMH injections and then, two weeks after carcinogen exposure, they began a basal diet containing hemin, hemin + I3C, hemin + syn, or hemin + I3C + syn for 23 weeks. The combination of I3C + syn significantly increased fecal water genotoxicity, tumor volume and invasiveness when compared to the hemin-fed control group. The groups fed I3C or syn alone had a significant reduction in the number of preneoplastic aberrant crypt foci (ACF) lesions compared to the hemin-fed group. Dietary I3C also reduced fecal water genotoxicity. Gene expression analysis of colorectal tumors demonstrated that the combination of dietary I3C + syn increased transcript levels for Raf1 and decreased tumor progression and invasiveness related to the genes Cdh1 and Appl1. This analysis also revealed that the Tnf and Cdh1 genes were significantly up- and down-regulated, respectively, in tumors of rats that received I3C, in comparison with the hemin-fed group. These findings reveal that the joint administration of I3C and syn enhanced the development of colon tumors induced by DMH in hemin-fed rats, while they potentially reduced ACF development when given alone.

Red and processed meat intake and cancer risk: Results from the prospective NutriNet-Santé cohort study

The International Agency for Research on Cancer (WHO-IARC) classified red meat and processed meat as probably carcinogenic and carcinogenic for humans, respectively. These conclusions were mainly based on studies concerning colorectal cancer, but scientific evidence is still limited for other cancer locations. In this study, we investigated the prospective associations between red and processed meat intakes and overall, breast, and prostate cancer risk. This prospective study included 61,476 men and women of the French NutriNet-Santé cohort (2009-2015) aged ≥35 y and who completed at least three 24 hrs dietary records during the first year of follow-up. The risk of developing cancer was compared across sex-specific quintiles of red and processed meat intakes by multivariable Cox models. 1,609 first primary incident cancer cases were diagnosed during follow-up, among which 544 breast cancers and 222 prostate cancers. Red meat intake was associated with increased risk of overall cancers [HR_Q5vs.Q1 =1.31 (1.10-1.55), p_trend  = 0.01) and breast cancer (HR_Q5vs.Q1  = 1.83 (1.33-2.51), p_trend  = 0.002]. The latter association was observed in both premenopausal [HR_Q5vs.Q1 =2.04 (1.03-4.06)] and postmenopausal women [HR_Q5vs.Q1 =1.79 (1.26-2.55)]. No association was observed between red meat intake and prostate cancer risk. Processed meat intake was relatively low in this study (cut-offs for the 5th quintile = 46 g/d in men and 29 g/d in women) and was not associated with overall, breast or prostate cancer risk. This large cohort study suggested that red meat may be involved carcinogenesis at several cancer locations (other than colon-rectum), in particular breast cancer. These results are consistent with mechanistic evidence from experimental studies.

4-Hydroxynonenal metabolites and adducts in pre-carcinogenic conditions and cancer

4-hydroxy-2-nonenal (HNE) is an amazing reactive compound, originating from lipid peroxidation within cells but also in food and considered as a "second messenger" of oxidative stress. Due to its chemical features, HNE is able to make covalent links with DNA, proteins and lipids. The aim of this review is to give a comprehensive summary of the chemical properties of HNE and of the consequences of its reactivity in relation to cancer development. The formation of exocyclic etheno-and propano-adducts and genotoxic effects are addressed. The adduction to cellular proteins and the repercussions on the regulation of cell signaling pathways involved in cancer development are reviewed, notably on the Nrf2/Keap1/ARE pathway. The metabolic pathways leading to the inactivation/elimination or, on the contrary, to the bioactivation of HNE are considered. A special focus is given on the link between HNE and colorectal cancer development, due to its occurrence in foodstuffs and in the digestive lumen, during digestion.