Molecular mechanisms of alcohol-mediated carcinogenesis

The epidemiology and pathogenesis of neoplasia in the small intestine

PURPOSE

The mucosa of the small intestine encompasses about 90% of the luminal surface area of the digestive system, but only 2% of the total annual gastrointestinal cancer incidence in the United States.

METHODS

The remarkable contrast in age-standardized cancer incidence between the small and large intestine has been reviewed with respect to the cell type patterns, demographic features, and molecular characteristics of neoplasms.

RESULTS

Particularly noteworthy is the predominance of adenocarcinoma in the colon, which exceeds 98% of the total incidence by cell type, in contrast to that of 30% to 40% in the small intestine, resulting in an age-standardized ratio of rates exceeding 50-fold. The prevalence of adenomas and carcinomas is most prominent in the duodenum and proximal jejunum. The positive correlation in global incidence rates of small and large intestinal neoplasms and the reciprocal increases in risk of second primary adenocarcinomas suggest that there are common environmental risk factors. The pathophysiology of Crohn inflammatory bowel disease and the elevated risk of adenocarcinoma demonstrate the significance of the impaired integrity of the mucosal barrier and of aberrant immune responses to luminal indigenous and potentially pathogenic microorganisms.

CONCLUSION

In advancing a putative mechanism for the contrasting mucosal susceptibilities of the small and large intestine, substantial differences are underscored in the diverse taxonomy, concentration and metabolic activity of anaerobic organisms, rate of intestinal transit, changing pH, and the enterohepatic recycling and metabolism of bile acids. Experimental and epidemiologic studies are cited that suggest that the changing microecology, particularly in the colon, is associated with enhanced metabolic activation of ingested and endogenously formed procarcinogenic substrates.

p53 Mutations in carcinoma of the esophagus and gastroesophageal junction

BACKGROUND

Recent studies suggested p53 mutations as a prognostic factor. Tumors of the esophagus and gastroesophageal (GE) junction show raising incidence with a general poor prognosis.

METHODS

p53 Mutational spectra in 103 patients (68 squamous cell carcinoma/SCC and 35 adenocarcinoma/AC) were compared to clinical and pathologic data.

RESULTS AND CONCLUSIONS

p53 Mutations were found in 26 of 68 SSC (38.2%) and in 12 of 35 AC (34.5%). We only found G > T transversions in smokers with SCC. The survival of patients was not affected by p53 mutational status. In our study, the frequency and mutational spectrum of mutant p53 is similar in both histological types without prognostic relevance.

Increased formation of gastric N(2)-ethylidene-2'-deoxyguanosine DNA adducts in aldehyde dehydrogenase-2 knockout mice treated with ethanol

We analyzed an acetaldehyde-derived DNA adduct, N(2)-ethylidene-2'-deoxyguanosine (N(2)-Eti-dG) in stomach DNA of aldehyde dehydrogenase (Aldh)-2-knockout mice that were fed with alcohol to determine effects of alcohol consumption and Aldh2 genotype on the level of DNA damage in stomach. Aldh2-active(+/+), heterozygote(+/-) and knockout(-/-) mice were fed 20% ethanol for 5 weeks, then the level of N(2)-Eti-dG in stomach was determined by liquid chromatography tandem mass spectrometry. The average N(2)-Eti-dG level in DNA from untreated mice was not significantly different among Aldh2 genotypes (2.0-3.1 adducts/10(7) bases), however, the average N(2)-Eti-dG level in DNA from ethanol-treated mice was 4.8+/-2.6 adducts/10(7) bases in Aldh2+/+ mice, 7.9+/-1.1 adducts/10(7) bases in Aldh2+/- mice, and 48.6+/-12.0 adducts/10(7) bases in Aldh2-/- mice, respectively. Our data clearly showed that alcohol drinking caused DNA damage in stomach, which was Aldh2 genotype-dependent in this experimental animal model. This result suggests that heavy-alcohol drinking and Aldh2 deficiency might be risk factors of stomach cancer.

N2-ethyldeoxyguanosine as a potential biomarker for assessing effects of alcohol consumption on DNA

Head and neck cancers are causally related to alcohol consumption, but the underlying mechanisms are unclear. Ethanol is metabolized to acetaldehyde, an experimental carcinogen. Quantitation of the major DNA adduct of acetaldehyde, N2-ethylidenedeoxyguanosine, in human tissues could help to elucidate the mechanism of alcohol carcinogenicity. We applied a quantitative method for the analysis of this adduct, measured as the NaBH3CN reduction product N2-ethyldeoxyguanosine (N2-ethyl-dGuo) by liquid chromatography-electrospray ionization-tandem mass spectrometry-selected reaction monitoring, on DNA (0.04 +/- 0.03 mg) isolated from blood collected from control subjects recruited from two studies conducted in different areas of Europe between 1999 and 2005. The group selected from the first study (n = 127) included alcohol drinkers and abstainers while the group from the second study (n = 50) included only heavy drinkers. N2-ethyl-dGuo was detected in all DNA samples. After adjusting for potential confounders, in the first study, drinkers showed a higher level of N2-ethyl-dGuo (5,270 +/- 8,770 fmol/micromol dGuo) compared with nondrinkers (2,690 +/- 3040 fmol/micromol dGuo; P = 0.04). A significant trend according to dose was observed in both studies (P = 0.02 and 0.04, respectively). Taking into account the amount of alcohol consumption, adduct levels were higher in younger compared with older subjects (P = 0.01), whereas no differences were observed comparing men with women. These results show the feasibility of quantifying N2-ethyl-dGuo in small-volume blood samples and are consistent with the hypothesis that ethanol contributes to carcinogenesis through DNA adducts formation.

Impact of alcohol consumption with polymorphisms in alcohol-metabolizing enzymes on pancreatic cancer risk in Japanese

The putative impact of alcohol on pancreatic cancer (PC) risk remains controversial. Here, we conducted a case-control study in Japanese to assess the impact of alcohol in conjunction with polymorphisms in alcohol-metabolizing enzymes. Cases were 160 patients with pancreatic cancer at Aichi Cancer Center, Nagoya, Japan. Two control groups of 800 age- and sex-matched non-cancer subjects each were independently selected. The impact of alcohol and polymorphisms in aldehyde dehydrogenase 2 (ALDH2) Glu504Lys, alcohol dehydrogenase (ADH) 1B His48Arg, and ADH1C Arg272Gln on PC risk was examined with multivariate analysis adjusted for potential confounders to estimate odds ratios (ORs) and 95% confidence intervals (CIs). Results showed no independent impact of alcohol or genotype on PC risk except former drinking. To avoid reverse causation, former drinkers were excluded in further analyses. In the analysis of the combined effects of alcohol consumption and genotype, significant impact of alcohol was seen for those subjects with ALDH2 Lys+ allele, ADH1B His/His, or ADH1C Arg/Arg (trend P = 0.077, 0.003, or 0.020, respectively), each of which is associated with a high concentration or rapid production of acetaldehyde. Analysis of genotype combinations showed that ‘ever drinking’ with both ADH1B His/His and ALDH2 Lys + was the most potent risk factor for PC relative to ‘never drinkers’ with both ADH1B His/His and ALDH2 Glu/Glu [OR (95% CI); 4.09 (1.30–12.85)]. These results indicate that alcohol has an impact on PC risk when the effects of alcohol consumption and metabolism are combined. Acetaldehyde may be involved in the mechanisms underlying PC development.

Vitamins B2, B6, and B12 and risk of new colorectal adenomas in a randomized trial of aspirin use and folic acid supplementation

BACKGROUND

Folate, other vitamin B cofactors, and genes involved in folate-mediated one-carbon metabolism all may play important roles in colorectal neoplasia. In this study, we examined the associations between dietary and circulating plasma levels of vitamins B(2), B(6), and B(12) and risk colorectal adenomas.

METHODS

The Aspirin/Folate Polyp Prevention Study is a randomized clinical trial of folic acid supplementation and incidence of new colorectal adenomas in individuals with a history of adenomas (n = 1,084). Diet and supplement use were ascertained through a food frequency questionnaire administered at baseline. Blood collected at baseline was used to determine plasma B-vitamin levels. We used generalized linear regression to estimate risk ratios (RR) and 95% confidence intervals (95% CI) as measures of association.

RESULTS

We found a borderline significant inverse association with plasma B(6) [pyridoxal 5'-phosphate (PLP)] and adenoma risk (adjusted RR Q4 versus Q1, 0.78; 95% CI, 0.61-1.00; P(trend) = 0.08). This association was not modified by folic acid supplementation or plasma folate. However, the protective association of PLP with adenoma risk was observed only among subjects who did not drink alcohol (P(interaction) = 0.03). Plasma B(2) (riboflavin) was inversely associated with risk of advanced lesions (adjusted RR Q4 versus Q1, 0.51; 95% CI, 0.26-0.99; P(trend) = 0.12). No significant associations were observed between adenoma risk and plasma vitamin B(12) or dietary intake of vitamin B(2) and B(6). When we examined specific gene-B-vitamin interactions, we observed a possible interaction between methylenetetrahydrofolate reductase -C677T and plasma B(2) on risk of all adenomas.

CONCLUSION

Our results suggest that high levels of PLP and B(2) may protect against colorectal adenomas.

Mouse models in liver cancer research: A review of current literature

Primary liver cancer remains one of the most lethal malignancies worldwide. Due to differences in prevalence of etiological factors the incidence of primary liver cancer varies among the world, with a peak in East-Asia. As this disease is still lethal in most of the cases, research has to be done to improve our understanding of the disease, offering insights for possible treatment options. For this purpose, animal models are widely used, especially mouse models. In this review, we describe the different types of mouse models used in liver cancer research, with emphasis on genetically engineered mice used in this field. We focus on hepatocellular carcinoma (HCC), as this is by far the most common type of primary liver cancer, accounting for 70%-85% of cases.

New concepts in the pathogenesis of alcoholic liver disease

Alcoholic liver disease still represents an important cause for death and disability in most well-developed countries and is becoming a leading cause of disease in developing countries. It is now increasingly clear that, besides the formation of acetaldehyde, alcohol effects on the liver include oxidative stress, disturbances in methionine metabolism, endoplasmic reticulum stress, inflammatory/immune responses and adipokine imbalances. This article will discuss the most recent findings on the mechanisms by which alcohol abuse causes hepatic steatosis and steatohepatitis, and now it contributes to the progression of fibrosis. Although still incomplete, these data shed new light on the multifactorial pathogenesis of alcoholic liver disease and open new possibilities in the understanding of how gender and genetic factors can influence disease progression.

Safety evaluation of topical applications of ethanol on the skin and inside the oral cavity

Ethanol is widely used in all kinds of products with direct exposure to the human skin (e.g. medicinal products like hand disinfectants in occupational settings, cosmetics like hairsprays or mouthwashes, pharmaceutical preparations, and many household products). Contradictory evidence about the safety of such topical applications of the alcohol can be found in the scientific literature, yet an up-to-date risk assessment of ethanol application on the skin and inside the oral cavity is currently lacking.The first and foremost concerns of topical ethanol applications for public health are its carcinogenic effects, as there is unambiguous evidence for the carcinogenicity of ethanol orally consumed in the form of alcoholic beverages. So far there is a lack of evidence to associate topical ethanol use with an increased risk of skin cancer. Limited and conflicting epidemiological evidence is available on the link between the use of ethanol in the oral cavity in the form of mouthwashes or mouthrinses and oral cancer. Some studies pointed to an increased risk of oral cancer due to locally produced acetaldehyde, operating via a similar mechanism to that found after alcoholic beverage ingestion.In addition, topically applied ethanol acts as a skin penetration enhancer and may facilitate the transdermal absorption of xenobiotics (e.g. carcinogenic contaminants in cosmetic formulations). Ethanol use is associated with skin irritation or contact dermatitis, especially in humans with an aldehyde dehydrogenase (ALDH) deficiency.After regular application of ethanol on the skin (e.g. in the form of hand disinfectants) relatively low but measurable blood concentrations of ethanol and its metabolite acetaldehyde may occur, which are, however, below acute toxic levels. Only in children, especially through lacerated skin, can percutaneous toxicity occur.As there might be industry bias in many studies about the safety of topical ethanol applications, as well as a general lack of scientific research on the long-term effects, there is a requirement for independent studies on this topic. The research focus should be set on the chronic toxic effects of ethanol and acetaldehyde at the point of impact, with special regard to children and individuals with genetic deficiencies in ethanol metabolism.

Synergistic premalignant effects of chronic ethanol exposure and insulin receptor substrate-1 overexpression in liver

AIM

Insulin receptor substrate, type 1 (IRS-1) transmits growth and survival signals, and is overexpressed in more than 90% of hepatocellular carcinomas (HCCs). However, experimental overexpression of IRS-1 in the liver was found not to be sufficient to cause HCC. Since chronic alcohol abuse is a risk factor for HCC, we evaluated potential interactions between IRS-1 overexpression and chronic ethanol exposure by assessing premalignant alterations in gene expression.

METHODS

Wild-type (wt) or IRS-1 transgenic (Tg) mice, constitutively overexpressing the human (h) transgene in the liver, were pair-fed isocaloric liquid diets containing 0% or 24% ethanol for 8 weeks. The livers were used for histopathologic study and gene expression analysis, focusing on insulin, insulin-like growth factor (IGF) and wingless (WNT)-Frizzled (FZD) pathways, given their known roles in HCC.

RESULTS

In wt mice, chronic ethanol exposure caused hepatocellular microsteatosis with focal chronic inflammation, reduced expression of proliferating cell nuclear antigen (PCNA) and increased expression of IGF-I and IGF-I receptor. In hIRS-1 Tg mice, chronic ethanol exposure caused hepatic micro- and macrosteatosis, focal chronic inflammation, apoptosis and disordered lobular architecture. These effects of ethanol in hIRS-1 Tg mice were associated with significantly increased expression of IGF-II, insulin, IRS-4, aspartyl-asparaginyl beta hydroxylase (AAH), WNT-1 and FZD 7, as occurs in HCC.

CONCLUSION

In otherwise normal liver, chronic ethanol exposure mainly causes liver injury and inflammation with impaired DNA synthesis. In contrast, in the context of hIRS-1 overexpression, chronic ethanol exposure may serve as a cofactor in the pathogenesis of HCC by promoting expression of growth factors, receptors and signaling molecules known to be associated with hepatocellular transformation.

Interplay between oxidative stress and immunity in the progression of alcohol-mediated liver injury

Inflammation is recognized increasingly as having an important role in the pathogenesis of alcoholic liver disease (ALD). Nonetheless, the mechanisms by which alcohol maintains hepatic inflammation are still characterized incompletely. Several studies have demonstrated that ethanol-induced oxidative stress promotes immune responses in ALD by stimulating both humoral and cellular reactions against liver proteins adducted to hydroxyethyl free radicals and several lipid peroxidation products. Moreover, ALD patients have autoantibodies targeting cytochrome P4502E1 and oxidized phospholipids. In both chronic alcohol-fed rats and heavy drinkers, the elevation of IgG against lipid peroxidation-derived antigens is associated with tumor necrosis factor-alpha production and the severity of liver inflammation. On this basis, we propose that allo- and autoimmune reactions associated with oxidative stress might contribute to fueling hepatic inflammation in ALD.

Age, alcohol metabolism and liver disease

PURPOSE OF REVIEW

Alcohol consumption among the elderly has increased. Alcohol metabolism changes with age and the elderly are more sensitive to the toxic effects; this increased consumption is therefore of great clinical relevance.

RECENT FINDINGS

Metabolism of ethanol changes with advancing age because activity of the enzymes involved, such as alcohol and acetaldehyde dehydrogenase and cytochrome P-4502E1, diminish with age. The water distribution volume also decreases with age. Both lead to increased blood concentrations of ethanol. Also, elderly people take more drugs, and ethanol and these drugs may interact; therefore, alcohol consumption can modify serum drug concentrations and their toxicity. Finally, elderly people may suffer more frequently from other types of liver disease, and alcohol may exacerbate these.

SUMMARY

Over recent decades alcohol consumption has increased among those who are older than 65 years. Alcohol is more toxic in the ageing organism because of changes in its metabolism, distribution and elimination, which lead to central nervous system effects at lower levels of intake; also, ageing organs such as brain and liver are more sensitive to the toxicity of alcohol. For these reasons, alcohol should be used in moderation, especially among those of older age.