Alcohol and Colorectal Cancer: The Role of Alcohol Dehydrogenase 1C Polymorphism

[Alcohol as a health risk: new recommendations for dealing with alcohol]

BACKGROUND

Chronic alcohol consumption is related to more than 200 disorders. Up until now, limits for low-risk use of alcohol were 24 g/ day for men and 12 g/ day for women. Recent epidemiologic studies have shown that any alcohol may be harmful.

AIM

The aim of this review is to reassess the health risk of alcohol.

RESULTS

There is a linear relationship between the amount of alcohol consumed and mortality risk. No risk-free dose of alcohol exists. However, health risk varies not only with the amount of alcohol consumed but also with target organs, as well as individual genetic and non-genetic factors such as smoking, medication use, exposure to environmental toxins, and pre-existing disease that deteriorates with alcohol use. High-risk groups for the damaging effect of alcohol include children and adolescents, old people, and women. Diseases that are affected by alcohol even at a low dose include arterial hypertension, cardiac arrhythmia (extrasystole, arterial fibrillation), some liver diseases (non-alcoholic fatty liver disease, hepatitis C, porphyria) as well as breast cancer. For these disorders, a threshold of low risk does not exist. Finally, in addition to breast cancer, alcohol is a risk factor for cancer of the oral cavity, the larynx, pharynx, oesophagus, liver, and colorectum. During pregnancy alcohol is completely forbidden.

CONCLUSION

There is no such thing as a risk-free dose of alcohol.

Dynamic Alterations to Hepatic MicroRNA-29a in Response to Long-Term High-Fat Diet and EtOH Feeding

MicroRNA-29a (miR-29a) is a well characterized fibro-inflammatory molecule and its aberrant expression is linked to a variety of pathological liver conditions. The long-term effects of a high-fat diet (HFD) in combination with different levels of EtOH consumption on miR-29a expression and liver pathobiology are unknown. Mice at 8 weeks of age were divided into five groups (calorie-matched diet plus water (CMD) as a control group, HFD plus water (HFD) as a liver disease group, HFD plus 2% EtOH (HFD + 2% E), HFD + 10% E, and HFD + 20% E as intervention groups) and fed for 4, 13, 26, or 39 weeks. At each time point, analyses were performed for liver weight/body weight (BW) ratio, AST/ALT ratio, as well as liver histology assessments, which included inflammation, estimated fat deposition, lipid area, and fibrosis. Hepatic miR-29a was measured and correlations with phenotypic traits were determined. Four-week feeding produced no differences between the groups on all collected phenotypic traits or miR-29a expression, while significant effects were observed after 13 weeks, with EtOH concentration-specific induction of miR-29a. A turning point for most of the collected traits was apparent at 26 weeks, and miR-29a was significantly down-regulated with increasing liver injury. Overall, miR-29a up-regulation was associated with a lower liver/BW ratio, fat deposition, inflammation, and fibrosis, suggesting a protective role of miR-29a against liver disease progression. A HFD plus increasing concentrations of EtOH produces progressive adverse effects on the liver, with no evidence of beneficial effects of low-dose EtOH consumption. Moreover, miR-29a up-regulation is associated with less severe liver injury.

Alcohol Consumption, HDL-Cholesterol and Incidence of Colon and Rectal Cancer: A Prospective Cohort Study Including 250,010 Participants

Aims

Alcohol consumption has been linked to colorectal cancer (CRC) and also to the high-density lipoprotein cholesterol level (HDL-C). HDL-C has been associated with the incidence of CRC. The aim of this study was to investigate the association between self-reported alcohol consumption, HDL-C and incidence of CRC, separately for the two sites.

Methods

Altogether, 250,010 participants in Norwegian surveys have been followed-up for an average of 18 years with respect to a first-time outcome of colon or rectal cancer. During follow-up, 3023 and 1439 colon and rectal cancers were registered.

Results

For men, the HR per 1 drink per day was 1.05 with 95% confidence interval (0.98–1.12) for colon and 1.08 (1.02–1.15) for rectal cancer. The corresponding figures for women were 1.03 (0.97–1.10) and 1.05 (1.00–1.10). There was a positive association between alcohol consumption and HDL-C. HDL-C was inversely associated with colon cancer in men (0.74 (0.62–0.89) per 1 mmol/l) and positively associated with rectal cancer, although not statistically significant (1.15 (0.92–1.44). A robust regression that assigned weights to each observation and exclusion of weights ≤ 0.1 increased the HRs per 1 drink per day and decreased the HR per 1 mmol/l for colon cancer. The associations with rectal cancer remained unchanged.

Conclusion

Our results support a positive association between alcohol consumption and colon and rectal cancer, most pronounced for rectal cancer. Considering the positive relation between alcohol consumption and HDL-C, the inverse association between HDL-C and colon cancer in men remains unsettled.

Alcohol Use and Gastrointestinal Cancer Risk

Background

Alcohol use is an important and potentially modifiable risk factor for gastrointestinal cancers. The more and the longer a person drinks, the higher the risk of cancer becomes. Even modest use of alcohol may increase cancer risk; 100 g of alcohol per week or less is currently considered to be the limit of low-risk use.

Gastrointestinal Cancer Risk

Alcohol is causally associated with oesophageal squamous cell cancer, gastric cancer, hepatocellular carcinoma, colorectal cancer, and most likely also with pancreatic cancer. Alcohol when combined with tobacco smoking or excess body weight can act synergistically to cause gastrointestinal cancer. Exposure to alcohol may have contributed to the recent incidence increases of early-onset gastrointestinal cancers in some Western countries.

Conclusions

People with long-term risky alcohol use should be encouraged to join cancer screening programmes. Alcohol cessation appears to be effective in reducing the alcohol-induced, increased cancer risk.

Ethanol-Mediated Stress Promotes Autophagic Survival and Aggressiveness of Colon Cancer Cells via Activation of Nrf2/HO-1 Pathway

Epidemiological studies suggest that chronic alcohol consumption is a lifestyle risk factor strongly associated with colorectal cancer development and progression. The aim of the present study was to examine the effect of ethanol (EtOH) on survival and progression of three different colon cancer cell lines (HCT116, HT29, and Caco-2). Our data showed that EtOH induces oxidative and endoplasmic reticulum (ER) stress, as demonstrated by reactive oxygen species (ROS) and ER stress markers Grp78, ATF6, PERK and, CHOP increase. Moreover, EtOH triggers an autophagic response which is accompanied by the upregulation of beclin, LC3-II, ATG7, and p62 proteins. The addition of the antioxidant N-acetylcysteine significantly prevents autophagy, suggesting that autophagy is triggered by oxidative stress as a prosurvival response. EtOH treatment also upregulates the antioxidant enzymes SOD, catalase, and heme oxygenase (HO-1) and promotes the nuclear translocation of both Nrf2 and HO-1. Interestingly, EtOH also upregulates the levels of matrix metalloproteases (MMP2 and MMP9) and VEGF. Nrf2 silencing or preventing HO-1 nuclear translocation by the protease inhibitor E64d abrogates the EtOH-induced increase in the antioxidant enzyme levels as well as the migration markers. Taken together, our results suggest that EtOH mediates both the activation of Nrf2 and HO-1 to sustain colon cancer cell survival, thus leading to the acquisition of a more aggressive phenotype.

Alcohol intake, ADH1B and ADH1C genotypes, and the risk of colorectal cancer by sex and subsite in the Netherlands Cohort Study

The alcohol-colorectal cancer (CRC) association may differ by sex and ADH1B and ADH1C genotypes. ADH enzymes oxidize ethanol to acetaldehyde, both of which are human carcinogens. The Netherlands Cohort Study includes 120 852 participants, aged 55-69 years at baseline (1986), and has 20.3 years follow-up (case-cohort: nsubcohort = 4774; ncases = 4597). The baseline questionnaire included questions on alcohol intake at baseline and 5 years before. Using toenail DNA, available for ~75% of the cohort, we successfully genotyped six ADH1B and six ADH1C SNPs (nsubcohort = 3897; ncases = 3558). Sex- and subsite-specific Cox hazard ratios and 95% confidence intervals for CRC were estimated comparing alcohol categories, genotypes within drinkers and alcohol categories within genotype strata. We used a dominant genetic model and adjusted for multiple testing. Alcohol intake increased CRC risk in both sexes, though in women only in the (proximal) colon when in excess of 30 g/day. In male drinkers, ADH1B rs4147536 increased (distal) colon cancer risk. In female drinkers, ADH1C rs283415 increased proximal colon cancer risk. ADH1B rs3811802 and ADH1C rs4147542 decreased CRC risk in heavy (>30 g/day) and stable drinkers (compared to 5 years before baseline), respectively. Rs3811802 and rs4147542 significantly modified the alcohol-colon cancer association in women (Pfor interaction = 0.004 and 0.02, respectively). A difference in associations between genotype strata was generally clearer in men than women. In conclusion, men showed increased CRC risks across subsites and alcohol intake levels, while only colon cancer risk was increased in women at heavy intake levels. ADH1B rs3811802 and ADH1C rs4147542 significantly modified the alcohol-colon cancer association in women.

Alcohol, microbiome, life style influence alcohol and non-alcoholic organ damage

This paper is based upon the "8th Charles Lieber's Satellite Symposium" organized by Manuela G. Neuman at the Research Society on Alcoholism Annual Meeting, on June 25, 2016 at New Orleans, Louisiana, USA. The integrative symposium investigated different aspects of alcohol-induced liver disease (ALD) as well as non-alcohol-induced liver disease (NAFLD) and possible repair. We revealed the basic aspects of alcohol metabolism that may be responsible for the development of liver disease as well as the factors that determine the amount, frequency and which type of alcohol misuse leads to liver and gastrointestinal diseases. We aimed to (1) describe the immuno-pathology of ALD, (2) examine the role of genetics in the development of alcoholic hepatitis (ASH) and NAFLD, (3) propose diagnostic markers of ASH and non-alcoholic steatohepatitis (NASH), (4) examine age and ethnic differences as well as analyze the validity of some models, (5) develop common research tools and biomarkers to study alcohol-induced effects, 6) examine the role of alcohol in oral health and colon and gastrointestinal cancer and (7) focus on factors that aggravate the severity of organ-damage. The present review includes pre-clinical, translational and clinical research that characterizes ALD and NAFLD. Strong clinical and experimental evidence lead to recognition of the key toxic role of alcohol in the pathogenesis of ALD with simple fatty infiltrations and chronic alcoholic hepatitis with hepatic fibrosis or cirrhosis. These latter stages may also be associated with a number of cellular and histological changes, including the presence of Mallory's hyaline, megamitochondria, or perivenular and perisinusoidal fibrosis. Genetic polymorphisms of ethanol metabolizing enzymes and cytochrome p450 (CYP) 2E1 activation may change the severity of ASH and NASH. Other risk factors such as its co-morbidities with chronic viral hepatitis in the presence or absence of human deficiency virus were discussed. Dysregulation of metabolism, as a result of ethanol exposure, in the intestine leads to colon carcinogenesis. The hepatotoxic effects of ethanol undermine the contribution of malnutrition to the liver injury. Dietary interventions such as micro and macronutrients, as well as changes to the microbiota have been suggested. The clinical aspects of NASH, as part of the metabolic syndrome in the aging population, have been presented. The symposium addressed mechanisms and biomarkers of alcohol induced damage to different organs, as well as the role of the microbiome in this dialog. The microbiota regulates and acts as a key element in harmonizing immune responses at intestinal mucosal surfaces. It is known that microbiota is an inducer of proinflammatory T helper 17 cells and regulatory T cells in the intestine. The signals at the sites of inflammation mediate recruitment and differentiation in order to remove inflammatory inducers and promote tissue homeostasis restoration. The change in the intestinal microbiota also influences the change in obesity and regresses the liver steatosis. Evidence on the positive role of moderate alcohol consumption on heart and metabolic diseases as well on reducing steatosis have been looked up. Moreover nutrition as a therapeutic intervention in alcoholic liver disease has been discussed. In addition to the original data, we searched the literature (2008-2016) for the latest publication on the described subjects. In order to obtain the updated data we used the usual engines (Pub Med and Google Scholar). The intention of the eighth symposia was to advance the international profile of the biological research on alcoholism. We also wish to further our mission of leading the forum to progress the science and practice of translational research in alcoholism.

Possible Mechanisms of Ethanol-Mediated Colorectal Carcinogenesis: The Role of Cytochrome P4502E1, Etheno-DNA Adducts, and the Anti-Apoptotic Protein Mcl-1

BACKGROUND

Chronic alcohol consumption is a risk factor for colorectal cancer. The mechanisms by which ethanol (EtOH) exerts its carcinogenic effect on the colorectal mucosa are not clear and may include oxidative stress with the action of reactive oxygen species (ROS) generated through EtOH metabolism via cytochrome P4502E1 (CYP2E1) leading to carcinogenic etheno-DNA adducts. ROS may also induce apoptosis. However, the effect of chronic EtOH consumption on CYP2E1, etheno-DNA adducts as well as anti-apoptotic proteins in the colorectal mucosa of heavy drinkers without colorectal inflammation is still not known.

METHODS

Rectal biopsies from 32 alcoholics (>60 g EtOH/d) and from 12 controls (<20 g EtOH/d) were histologically examined, and immunohistochemistry for CYP2E1 and etheno-DNA adducts was performed. Apoptosis (cleaved PARP) as well as anti-apoptotic proteins including Bcl-x_L , Bcl-2, and Mcl-1 were immunohistochemically determined.

RESULTS

No significant difference in mucosal CYP2E1 or etheno-DNA adducts was observed between alcoholics and control patients. However, CYP2E1 and etheno-DNA adducts correlated significantly when both groups were combined (p < 0.001). In addition, although apoptosis was found not to be significantly affected by EtOH, the anti-apoptotic protein Mcl-1, but neither Bcl-x_L nor Bcl-2, was found to be significantly increased in heavy drinkers as compared to controls (p = 0.014).

CONCLUSIONS

Although colorectal CYP2E1 was not found to be significantly increased in alcoholics, CYP2E1 correlated overall with the level of etheno-DNA adducts in the colorectal mucosa, which identifies CYP2E1 as an important factor in colorectal carcinogenesis. Most importantly, however, is the up-regulation of the anti-apoptotic protein Mcl-1 in heavy drinkers counteracting apoptosis and possibly stimulating cancer development.

Effect of chronic alcohol consumption on the development and progression of non-alcoholic fatty liver disease (NAFLD)

A number of epidemiologic studies show a protective effect of light to moderate daily alcohol consumption on the development of non-alcoholic fatty liver disease (NAFLD). Although these small amounts of ethanol may prevent fatty liver, they may also be a risk factor for other diseases such as breast and colon cancer. Those individuals who have underlying hepatic steatosis or non-alcoholic steatohepatitis (NASH) should not use ethanol chronically since the data available at present do not support a beneficial effect of alcohol in this situation. Especially overweight and obese individuals may be more susceptible towards alcohol even at moderate doses. Animal experiments show a negative effect of ethanol on liver histology in either dietary or genetic NASH models. In addition, patients with NASH reveal a significant increased risk for hepatocellular cancer (HCC) even with social alcohol consumption. Thus, subjects with underlying NASH should abstain from alcohol at any amounts.

Moderate Alcohol Consumption and Colorectal Cancer Risk

BACKGROUND

Heavy alcohol drinking is a risk factor for colorectal cancer (CRC); previous studies have shown a linear dose-dependent association between alcohol intake and CRC. However, some studies suggest that moderate alcohol consumption may have a protective effect, similar to that seen in cardiovascular disease. Other factors may interact with alcohol and contribute additional risk for CRC. We aimed to determine the association between moderate alcohol consumption, limited to 30 g of alcohol per day, by beverage type on CRC risk and to assess the effects of other factors that interact with alcohol to influence CRC risk.

METHODS

The PubMed database was used to find articles published between 2008 and 2014 related to alcohol and CRC. Twenty-one relevant articles were evaluated and summarized, including 11 articles reporting on CRC risk associated with moderate intake and 10 articles focusing on genetic interactions associated with alcohol and CRC risk.

RESULTS

The association between alcohol and increased risk for CRC was found when intakes exceeded 30 g/d alcohol. Nonsignificant results were consistently reported for intakes <30 g/d. Additional risks for CRC were found to be related to obesity and folate status for regular alcohol consumers. Some significant results suggest that the development of CRC is dependent on the interaction of gene and environment.

CONCLUSIONS

The association between the amount of alcohol consumed and the incidence of CRC was not significant at moderate intake levels. Moderate alcohol consumption was associated with a reduced CRC risk in study populations with greater adherence to a Mediterranean diet, where wine contributed substantially to the alcoholic beverage consumed. Other factors such as obesity, folate deficiency, and genetic susceptibility may contribute additional CRC risk for those consuming alcohol. To minimize CRC risk, appropriate recommendations should encourage intakes below 30 g of alcohol each day.

The role of reactive oxygen species (ROS) and cytochrome P-450 2E1 in the generation of carcinogenic etheno-DNA adducts

Exocyclic etheno-DNA adducts are mutagenic and carcinogenic and are formed by the reaction of lipidperoxidation (LPO) products such as 4-hydoxynonenal or malondialdehyde with DNA bases. LPO products are generated either via inflammation driven oxidative stress or via the induction of cytochrome P-450 2E1 (CYP2E1). In the liver CYP2E1 is induced by various compounds including free fatty acids, acetone and ethanol. Increased levels of CYP2E1 and thus, oxidative stress are observed in the liver of patients with non-alcoholic steatohepatitis (NASH) as well as in the chronic alcoholic. In addition, chronic ethanol ingestion also increases CYP2E1 in the mucosa of the oesophagus and colon. In all these tissues CYP2E1 correlates significantly with the levels of carcinogenic etheno-DNA adducts. In contrast, in patients with non-alcoholic steatohepatitis (NASH) hepatic etheno-DNA adducts do not correlate with CYP2E1 indicating that in NASH etheno-DNA adducts formation is predominately driven by inflammation rather than by CYP2E1 induction. Since etheno-DNA adducts are strong mutagens producing various types of base pair substitution mutations as well as other types of genetic damage, it is strongly believed that they are involved in ethanol mediated carcinogenesis primarily driven by the induction of CYP2E1.

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Cytochrome P-450 2E1 is induced following chronic ethanol ingestion.

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CYP2E1 correlates with carcinogenic etheno-DNA formation.

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CYP2E1 and oxidative stress are important mechanisms in alcohol mediated carcinogenesis in the liver, undefined and colon.

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In NASH hepatic etheno-DNA adducts occur but possible due to inflammation.

The role of reactive oxygen species (ROS) and cytochrome P-450 2E1 in the generation of carcinogenic etheno-DNA adducts

Exocyclic etheno-DNA adducts are mutagenic and carcinogenic and are formed by the reaction of lipidperoxidation (LPO) products such as 4-hydoxynonenal or malondialdehyde with DNA bases. LPO products are generated either via inflammation driven oxidative stress or via the induction of cytochrome P-450 2E1 (CYP2E1). In the liver CYP2E1 is induced by various compounds including free fatty acids, acetone and ethanol. Increased levels of CYP2E1 and thus, oxidative stress are observed in the liver of patients with non-alcoholic steatohepatitis (NASH) as well as in the chronic alcoholic. In addition, chronic ethanol ingestion also increases CYP2E1 in the mucosa of the oesophagus and colon. In all these tissues CYP2E1 correlates significantly with the levels of carcinogenic etheno-DNA adducts. In contrast, in patients with non-alcoholic steatohepatitis (NASH) hepatic etheno-DNA adducts do not correlate with CYP2E1 indicating that in NASH etheno-DNA adducts formation is predominately driven by inflammation rather than by CYP2E1 induction. Since etheno-DNA adducts are strong mutagens producing various types of base pair substitution mutations as well as other types of genetic damage, it is strongly believed that they are involved in ethanol mediated carcinogenesis primarily driven by the induction of CYP2E1.

Epidemiology and pathophysiology of alcohol and breast cancer: Update 2012

AIMS

To update epidemiological data on alcohol and breast cancer, with special emphasis on light alcohol consumption, and to review mechanisms of alcohol mediated mammary carcinogenesis.

METHODS

For epidemiological data, in November 2011 we performed a literature search in various bibliographic databases, and we conducted a meta-analysis of data on light alcohol drinking. Relevant mechanistic studies were also reviewed to November 2011.

RESULTS

A significant increase of the order of 4% in the risk of breast cancer is already present at intakes of up to one alcoholic drink/day. Heavy alcohol consumption, defined as three or more drinks/day, is associated with an increased risk by 40-50%. This translates into up to 5% of breast cancers attributable to alcohol in northern Europe and North America for a total of approximately 50,000 alcohol-attributable cases of breast cancer worldwide. Up to 1-2% of breast cancers in Europe and North America are attributable to light drinking alone, given its larger prevalence in most female populations when compared with heavy drinking. Alcohol increases estrogen levels, and estrogens may exert its carcinogenic effect on breast tissue either via the ER or directly. Other mechanisms may include acetaldehyde, oxidative stress, epigenetic changes due to a disturbed methyl transfer and decreased retinoic acid concentrations associated with an altered cell cycle.

CONCLUSIONS

Women should not exceed one drink/day, and women at elevated risk for breast cancer should avoid alcohol or consume alcohol occasionally only.

Expression pattern, ethanol-metabolizing activities, and cellular localization of alcohol and aldehyde dehydrogenases in human large bowel: association of the functional polymorphisms of ADH and ALDH genes with hemorrhoids and colorectal cancer

Alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) are principal enzymes responsible for metabolism of ethanol. Functional polymorphisms of ADH1B, ADH1C, and ALDH2 genes occur among racial populations. The goal of this study was to systematically determine the functional expressions and cellular localization of ADHs and ALDHs in human rectal mucosa, the lesions of adenocarcinoma and hemorrhoid, and the genetic association of allelic variations of ADH and ALDH with large bowel disorders. Twenty-one surgical specimens of rectal adenocarcinoma and the adjacent normal mucosa, including 16 paired tissues of rectal tumor, normal mucosae of rectum and sigmoid colon from the same individuals, and 18 surgical mixed hemorrhoid specimens and leukocyte DNA samples from 103 colorectal cancer patients, 67 hemorrhoid patients, and 545 control subjects recruited in previous study, were investigated. The isozyme/allozyme expression patterns of ADH and ALDH were identified by isoelectric focusing and the activities were assayed spectrophotometrically. The protein contents of ADH/ALDH isozymes were determined by immunoblotting using the corresponding purified class-specific antibodies; the cellular activity and protein localizations were detected by immunohistochemistry and histochemistry, respectively. Genotypes of ADH1B, ADH1C, and ALDH2 were determined by polymerase chain reaction-restriction fragment length polymorphisms. At 33mM ethanol, pH 7.5, the activity of ADH1C*1/1 phenotypes exhibited 87% higher than that of the ADH1C*1/*2 phenotypes in normal rectal mucosa. The activity of ALDH2-active phenotypes of rectal mucosa was 33% greater than ALDH2-inactive phenotypes at 200μM acetaldehyde. The protein contents in normal rectal mucosa were in the following order: ADH1>ALDH2>ADH3≈ALDH1A1, whereas those of ADH2, ADH4, and ALDH3A1 were fairly low. Both activity and content of ADH1 were significantly decreased in rectal tumors, whereas the ALDH activity remained unchanged. The ADH activity was also significantly reduced in hemorrhoids. ADH4 and ALDH3A1 were uniquely expressed in the squamous epithelium of anus at anorectal junctions. The allele frequencies of ADH1C*1 and ALDH2*2 were significantly higher in colorectal cancer and that of ALDH2*2 also significantly greater in hemorrhoids. In conclusion, ADH and ALDH isozymes are differentially expressed in mucosal cells of rectum and anus. The results suggest that acetaldehyde, an immediate metabolite of ethanol, may play an etiological role in pathogenesis of large bowel diseases.

Colorectal adenoma to carcinoma progression is accompanied by changes in gene expression associated with ageing, chromosomal instability, and fatty acid metabolism

Background

Colorectal cancer develops in a multi-step manner from normal epithelium, through a pre-malignant lesion (so-called adenoma), into a malignant lesion (carcinoma), which invades surrounding tissues and eventually can spread systemically (metastasis). It is estimated that only about 5% of adenomas do progress to a carcinoma.

Aim

The present study aimed to unravel the biology of adenoma to carcinoma progression by mRNA expression profiling, and to identify candidate biomarkers for adenomas that are truly at high risk of progression.

Methods

Genome-wide mRNA expression profiles were obtained from a series of 37 colorectal adenomas and 31 colorectal carcinomas using oligonucleotide microarrays. Differentially expressed genes were validated in an independent colorectal gene expression data set. Gene Set Enrichment Analysis (GSEA) was used to identify altered expression of sets of genes associated with specific biological processes, in order to better understand the biology of colorectal adenoma to carcinoma progression.

Results

mRNA expression of 248 genes was significantly different, of which 96 were upregulated and 152 downregulated in carcinomas compared to adenomas. Classification of adenomas and carcinomas using the expression of these genes showed to be very accurate, also when tested in an independent expression data set. Gene-sets associated with ageing (which is related to senescence) and chromosomal instability were upregulated, and a gene-set associated with fatty acid metabolism was downregulated in carcinomas compared to adenomas. Moreover, gene-sets associated with chromosomal location revealed chromosome 4q22 loss and chromosome 20q gain of gene-set expression as being relevant in this progression.

Concluding remark

These data are consistent with the notion that adenomas and carcinomas are distinct biological entities. Disruption of specific biological processes like senescence (ageing), maintenance of chromosomal instability and altered metabolism, are key factors in the progression from adenoma to carcinoma.

Electronic supplementary material

The online version of this article (doi:10.1007/s13402-011-0065-1) contains supplementary material, which is available to authorized users.

Maternal alcohol consumption, alcohol metabolism genes, and the risk of oral clefts: a population-based case-control study in Norway, 1996-2001

Heavy maternal alcohol consumption during early pregnancy increases the risk of oral clefts, but little is known about how genetic variation in alcohol metabolism affects this association. Variants in the alcohol dehydrogenase 1C (ADH1C) gene may modify the association between alcohol and clefts. In a population-based case-control study carried out in Norway (1996-2001), the authors examined the association between maternal alcohol consumption and risk of oral clefts according to mother and infant ADH1C haplotypes encoding fast or slow alcohol-metabolizing phenotypes. Subjects were 483 infants with oral cleft malformations and 503 control infants and their mothers, randomly selected from all other livebirths taking place during the same period. Mothers who consumed 5 or more alcoholic drinks per sitting during the first trimester of pregnancy had an elevated risk of oral cleft in their offspring (odds ratio (OR) = 2.6, 95% confidence interval (CI): 1.4, 4.7). This increased risk was evident only in mothers or children who carried the ADH1C haplotype associated with reduced alcohol metabolism (OR= 3.0, 95% CI: 1.4, 6.8). There was no evidence of alcohol-related risk when both mother and infant carried only the rapid-metabolism ADH1C variant (OR = 0.9, 95% CI: 0.2, 4.1). The teratogenic effect of alcohol may depend on the genetic capacity of the mother and fetus to metabolize alcohol.

Acetaldehyde as a common denominator and cumulative carcinogen in digestive tract cancers

The key issue in cancer prevention is the identification of specific aetiologic factors. Acetaldehyde, the first metabolite of ethanol oxidation, is carcinogenic in animals. ADH and ALDH2 gene mutations provide an exceptional human model to estimate the long-term effects of acetaldehyde exposure in man. These models provide strong evidence for the local carcinogenic potential of acetaldehyde also in humans. Ethanol is metabolized to acetaldehyde by both mucosal and microbial enzymes. Many microbes produce acetaldehyde from ethanol, but their capacity to eliminate acetaldehyde is low, which leads to the accumulation of acetaldehyde in saliva during an alcohol challenge. Acetaldehyde is the most abundant carcinogen in tobacco smoke, and it readily dissolves into saliva during smoking. Fermented food and many alcoholic beverages can also contain significant amounts of acetaldehyde. Thus acetaldehyde, derived from mucosal or microbial oxidation of ethanol, tobacco smoke, and/or diet, appears to act as a cumulative carcinogen in the upper digestive tract of humans. The evidence strongly suggests the importance of world-wide screening of acetaldehyde and ethanol levels in many beverages and foodstuffs, as well as an urgent need for regulatory measures and consumer guidance. Screening of the risk groups with enhanced acetaldehyde exposure, e.g. people with ADH and ALDH2 gene polymorphisms and hypochlorhydric atrophic gastritis, should also be seriously considered. Most importantly, the GRAS (generally regarded as safe) status of acetaldehyde, which allows it to be used as a food additive, should be re-evaluated, and the classification of acetaldehyde as a carcinogen should be upgraded.

Acetaldehyde as an underestimated risk factor for cancer development: role of genetics in ethanol metabolism

Chronic ethanol consumption is a strong risk factor for the development of certain types of cancer including those of the upper aerodigestive tract, the liver, the large intestine and the female breast. Multiple mechanisms are involved in alcohol-mediated carcinogenesis. Among those the action of acetaldehyde (AA), the first metabolite of ethanol oxidation is of particular interest. AA is toxic, mutagenic and carcinogenic in animal experiments. AA binds to DNA and forms carcinogenic adducts. Direct evidence of the role of AA in alcohol-associated carcinogenesis derived from genetic linkage studies in alcoholics. Polymorphisms or mutations of genes coding for AA generation or detoxifying enzymes resulting in elevated AA concentrations are associated with increased cancer risk. Approximately 40% of Japanese, Koreans or Chinese carry the AA dehydrogenase 2*2 (ALDH2*2) allele in its heterozygous form. This allele codes for an ALDH2 enzyme with little activity leading to high AA concentrations after the consumption of even small amounts of alcohol. When individuals with this allele consume ethanol chronically, a significant increased risk for upper alimentary tract and colorectal cancer is noted. In Caucasians, alcohol dehydrogenase 1C*1 (ADH1C*1) allele encodes for an ADH isoenzyme which produces 2.5 times more AA than the corresponding allele ADH1C*2. In studies with moderate to high alcohol intake, ADH1C*1 allele frequency and rate of homozygosity was found to be significantly associated with an increased risk for cancer of the upper aerodigestive tract, the liver, the colon and the female breast. These studies underline the important role of acetaldehyde in ethanol-mediated carcinogenesis.