Aldehyde dehydrogenase 2 and glutathione S-transferase M 1 polymorphisms in relation to the risk for oral cancer in Japanese drinkers

Can gene therapy be used to prevent cancer? Gene therapy for aldehyde dehydrogenase 2 deficiency

Approximately 8% of the world population and 35-45% of East Asians are carriers of the hereditary disorder aldehyde dehydrogenase 2 (ALDH2) deficiency. ALDH2 plays a central role in the liver to metabolize ethanol. With the common E487K variant, there is a deficiency of ALDH2 function; when ethanol is consumed, there is a systemic accumulation of acetaldehyde, an intermediate product in ethanol metabolism. In ALDH2-deficient individuals, ethanol consumption acutely causes the "Alcohol Flushing Syndrome" with facial flushing, tachycardia, nausea, and headaches. With chronic alcohol consumption, ALDH2 deficiency is associated with a variety of disorders, including a remarkably high risk for aerodigestive tract cancers. Acetaldehyde is a known carcinogen. The epidemiologic data relating to the association of ALDH2 deficiency and cancer risk are striking: ALDH2 homozygotes who are moderate-to-heavy consumers of ethanol have a 7-12-fold increased risk for esophageal cancer, making ALDH2 deficiency the most common hereditary disorder associated with an increased cancer risk. In this review, we summarize the genetics and biochemistry of ALDH2, the epidemiology of cancer risk associated with ALDH2 deficiency, the metabolic consequences of ethanol consumption associated with ALDH2 deficiency, and gene therapy strategies to correct ALDH2 deficiency and its associated cancer risk. With the goal of reducing the risk of aerodigestive tract cancers, in the context that ALDH2 is a hereditary disorder and ALDH2 functions primarily in the liver, ALDH2 deficiency is an ideal target for the application of adeno-associated virus-mediated liver-directed gene therapy to prevent cancer.

Association Between the Aldehyde Dehydrogenase-2 rs671 G>A Polymorphism and Head and Neck Cancer Susceptibility: A Meta-Analysis in East Asians

BACKGROUND

Aldehyde dehydrogenase-2 (ALDH2) plays an important role in the alcohol detoxification and acetaldehyde metabolism. Published studies have demonstrated some inconsistent associations between ALDH2 rs671 G>A polymorphism and head and neck cancer (HNC) risk.

METHODS

A meta-analysis was performed to provide pooled data on the association between the ALDH2 rs671 G>A polymorphism and HNC risk. Electronic databases were searched to identify relevant studies. Odds ratios and 95% confidence intervals (CIs) were used to examine the pooled effect size of each genetic model. In addition, heterogeneity test, accumulative analysis, sensitivity analysis, and publication bias were conducted to test the statistical power.

RESULTS

Thirteen publications (14 independent case-control studies) involving 10,939 subjects were selected. The stratified analysis indicated that both light/moderated drinking (e.g., GA vs. GG: OR = 1.47, 95% CI = 1.16 to 1.86, p < 0.01, I²  = 81.1%) and heavy drinking would increase HNC risk with rs671 G>A mutation (e.g., GA vs. GG: OR = 2.30, 95% CI = 1.11 to 4.77, p = 0.03, I²  = 81.9%).

CONCLUSIONS

In summary, this meta-analysis suggested that the ALDH2 rs671 G>A polymorphism may play an important synergistic effect in the pathogenesis of HNC development in East Asians.

Facial flushing after alcohol intake as a predictor for a high risk of synchronous or metachronous cancer of the upper gastrointestinal tract

Background

In Japan, there has been a lot of reports showing an association between facial flushing after light alcohol consumption and heterozygosity for inactive aldehyde dehydrogenase-2 (ALDH2). Persons with inactive ALDH2 may have a higher risk of alcohol-related oral, pharyngeal and esophageal cancers, compared with those with wild-type ALDH2. The purpose of this study was to examine whether flushers with oral or pharyngeal squamous cell carcinoma have an increased risk of synchronous or metachronous cancer of the upper gastrointestinal (UGI) tract.

Methods

A retrospective study was performed by medical chart review and through a questionnaire sent to 285 patients treated for oral and pharyngeal cancer. Responses were obtained from 150 patients (52.6%), who were classified as flushers or non-flushers, smokers (≥20 pack-year; 1 pack-years = number of cigarettes/20 per day) or non-smokers, and drinkers (≥14 units of alcohol consumption per week; 1 unit = 22 g) or non-drinkers. Relationships of these factors with occurrence of second primary cancers (SPCs) in the UGI tract were investigated.

Results

In Kaplan-Meier analysis, there was a significantly higher rate of SPC at 5 years in flushers and drinkers, but no relationship with smoking. In multivariate analyses, a history of flushing was significantly associated with SPC in the UGI tract (HR 2.64, 95% CI 1.25-5.52, P = 0.0109), but not with smoking or alcohol consumption.

Conclusions

A simple interview on history of facial flushing after alcohol intake can be useful for identifying patients at high risk for synchronous or metachronous cancers of the UGI tract.

Associations between aldehyde dehydrogenase 2 (ALDH2) rs671 genetic polymorphisms, lifestyles and hypertension risk in Chinese Han people

Hypertension is a multiple factor disease which was influenced by gene, environment, and lifestyle. Several studies confirmed that the ALDH2 rs671 polymorphism is associated with hypertension. However, the evidence remains inconclusive. Whether lifestyle affects blood pressure in different genotype groups have not been clarified, either. The subjects were adult Chinese Han people who received health examination in the period from December 2014 to December 2015. Detection of the ALDH2 r671 polymorphism was determined by polymerase chain reaction. Lifestyle data were collected using self-administered questionnaires. Basic characteristics and fasting venous blood sample were collected at baseline. 4018 subjects were eligible for participation.The frequencies of the ALDH2 rs671 genotype were 68.67% (GG), 28.67%(GL), 2.66%(LL), respectively. Pepole who harbored the L allele were less likely to develop incident hypertension. There was a significant association between food frequency and hypertension in the L genotype group. Fried food intake was significantly increased the risk of hypertension in the L genotype group. Our study suggested that ALDH2 rs671 L-genotypes are protective factors for hypertension in Han Chinese. Consumption of fried food accelerated the development of hypertension in individuals with poor metabolism of acetaldehyde.

ALDH2-deficiency as genetic epidemiologic and biochemical model for the carcinogenicity of acetaldehyde

Humans are cumulatively exposed to acetaldehyde from various sources including alcoholic beverages, tobacco smoke, foods and beverages. The genetic-epidemiologic and biochemical evidence in ALDH2-deficient humans provides strong evidence for the causal relationship between acetaldehyde-exposure due to alcohol consumption and cancer of the upper digestive tract. The risk assessment has so far relied on thresholds based on animal toxicology with lower one-sided confidence limit of the benchmark dose values (BMDL) typically ranging between 11 and 63 mg/kg bodyweight (bw)/day dependent on species and endpoint. The animal data is problematic for regulatory toxicology for various reasons (lack in study quality, problems in animal models and appropriateness of endpoints - especially cancer - for transfer to humans). In this study, data from genetic epidemiologic and biochemical studies are reviewed. The increase in the daily exposure dose to acetaldehyde in alcohol-consuming ALDH2-deficients vs. ALDH2-actives was about twofold. The acetaldehyde increase due to ALDH2 inactivity was calculated to be 6.7 μg/kg bw/day for heavy drinkers, which is associated with odds ratios of up to 7 for head and neck as well as oesophageal cancer. Previous animal toxicology based risk assessments may have underestimated the risk of acetaldehyde. Risk assessments of acetaldehyde need to be revised using this updated evidence.

Prognostic Value of Drinking Status and Aldehyde Dehydrogenase 2 Polymorphism in Patients With Head and Neck Squamous Cell Carcinoma

Background

The association between alcohol drinking, aldehyde dehydrogenase 2 (ALDH2) polymorphism, and survival in patients with head and neck squamous cell carcinoma (HNSCC) remains unclear.

Methods

We performed a retrospective cohort study of 267 HNSCC patients at Aichi Cancer Center. Of these, 65 patients (24%) were non-drinkers, 104 (39%) were light drinkers (ethanol <46 g or <5 days/week), 46 (17%) were moderate drinkers (ethanol intake 46–68 g/day and ≥5 days/week), and 52 (20%) were heavy drinkers (ethanol intake ≥69 g and ≥5 days/week). The prognostic value of pre-treatment drinking status and ALDH2 polymorphism was investigated using multivariate proportional hazard models.

Results

Drinking status was associated with disease-free survival (DFS) in HNSCC patients, with marginal statistical significance (5-year DFS: 67.9% [95% confidence interval {CI}, 53.8–78.4%] for non-drinkers, 57.6% [95% CI, 47.4–66.6%] for light drinkers, 46.1% [95% CI, 30.8–60.1%] for moderate drinkers, and 43.5% [95% CI, 29.3–56.9%] for heavy drinkers; P = 0.088). However, this association lost significance when multivariate analyses were adjusted for established prognostic factors. ALDH2 genotype was not significantly associated with DFS in HNSCC patients (5-year DFS: 85.7% [95% CI, 53.9–96.2%] for Lys/Lys, 56.2% [95% CI, 47.4–64.1%] for Glu/Lys, and 50.5% [95% CI, 40.3–59.7%] for Glu/Glu; P = 0.154). After stratification by ALDH2 genotype, we observed a significant positive dose-response relationship between drinking status and DFS in HNSCC patients with ALDH2 Glu/Glu (P_trend = 0.029).

Conclusions

In this study, we identified a significant positive dose-response relationship between pre-treatment drinking status and DFS in HNSCC patients with ALDH2 Glu/Glu. To confirm this association, further study is warranted.

Association of CYP1A1 and GSTM1 Polymorphisms With Oral Cancer Susceptibility: A Meta-Analysis

Our meta-analysis was aimed to evaluate the association of CYP1A1 and glutathione-S-transferase M1 (GSTM1) polymorphisms with oral cancer susceptibility.The related articles were searched in PubMed, Embase, and CNKI databases. Fifty eligible studies were included in our meta-analysis. Odds ratios (ORs) with 95% confidence intervals (CIs) were used to evaluate the relationship of CYP1A1 (rs4646903 and rs1048943) and GSTM1 polymorphisms with oral cancer risk. A random-effects model or fixed-effects model was employed depending on the heterogeneity.In overall analysis, CYP1A1 rs4646903 polymorphism was associated with the risk of oral cancer (CC vs TT: OR 1.65, 95% CI 1.33-2.05; CC vs TC+TT: OR 1.77, 95% CI 1.48-2.11; C vs T: OR 1.17, 95% CI 1.07-1.28), whereas rs1048943 showed no obvious association with oral cancer susceptibility. Moreover, subgroup analysis by ethnicity demonstrated that rs4646903 and rs1048943 both related with increased risk of oral cancer in Asians. Moreover, the analysis based on source of control suggested that rs4646903 could increase the risk for oral cancer in both population- and hospital-based populations, whereas no remarkable relationship of rs1048943 with oral cancer susceptibility was observed. For GSTM1 gene, null genotype appeared to be a risk factor for oral cancer (null vs present: OR 1.23, 95% CI 1.12-1.34), which was also proved in the subgroup analysis.The results demonstrated that CYP1A1 rs4646903 and null genotype of GSTM1 polymorphisms might serve as risk factors for oral cancer.

Tag single nucleotide polymorphisms of alcohol-metabolizing enzymes modify the risk of upper aerodigestive tract cancers: HapMap database analysis

Although alcohol is associated with higher upper aerodigestive tract (UADT) cancer risk, only a small fraction of alcoholics develop cancers. There is a lack of evidence proving the association of tag single nucleotide polymorphisms of alcohol-metabolizing enzymes with cancer risk. The aim of this study was to determine the association of these genetic polymorphisms with UADT cancer risk in a Chinese population. It was a hospital-based case-control candidate gene study. The databases of the International HapMap Project were searched for haplotype tag single nucleotide polymorphisms of the genes alcohol dehydrogenase (ADH)1B, ADH1C, and aldehyde dehydrogenase (ALDH)2. The genotyping was performed by the Sequenom MassARRAY system. Totally, 120 head and neck squamous cell carcinoma, 138 esophageal squamous cell carcinoma patients, and 276 age- and gender-matched subjects were enrolled between June 2008 and June 2010.Minor alleles of ADH1B (rs1229984) and ALDH2(rs671) were not only associated with the risk of UADT cancers (odds ratio [OR] [95% confidence interval, CI]: 3.53 [2.14-5.80] and 2.59 [1.79-3.75], respectively) but also potentiated the carcinogenic effects of alcohol (OR [95% CI]: 53.44 [25.21-113.29] and 70.08 [33.65-145.95], respectively). Similar effects were observed for head/neck and esophageal cancer subgroups. Multivariate logistic regression analysis identified four significant risk factors, including habitual use of cigarettes, alcohol, betel quid, and lower body mass index (P < 0.001). The haplotypes GAGC (OR 1.61, 95% CI 1.08-2.40, P = 0.018) and CCAATG (OR 1.69, 95% CI 1.24-2.30, P < 0.001) on chromosomes 4 and 12, respectively, were associated with higher cancer risk. These findings suggested that risk allele or haplotype carriers who consume alcohol and other carcinogens should be advised to undergo endoscopy screening. The information can be used to determine the degree of susceptibility of each subject and can be combined with other environmental factors, like carcinogen consumption, in the screening analysis.

GSTM1 null polymorphisms and oral cancer risk: a meta-analysis

Many studies have examined the association between the GSTM1 null gene polymorphism and oral cancer risk in various populations, but their results have been inconsistent. To assess this relationship more precisely, a meta-analysis was performed. The PubMed and Embase databases were searched for case-control studies published up to May 2013. Data were extracted and pooled odds ratio (OR) with 95% confidence intervals (CI) were calculated. Ultimately, 39 studies, comprising of 4,704 oral cancer cases and 7,090 controls, were included. Overall, for null versus present, the pooled OR was 1.29 (95% CI = 1.20-1.40), and the heterogeneity was found in all studies. In the stratified analysis by ethnicity, significant risks were found among Asians (OR = 1.39, 95% CI = 1.27-1.53; P = 0.000 for heterogeneity), but not in Caucasians (OR = 0.99, 95% CI = 0.83-1.18; P = 0.677 for heterogeneity). In conclusion, this meta-analysis demonstrates that the GSTM1 null gene polymorphism may be an increased risk of oral cancer in Asians but not in Caucasians.

Multi-susceptibility genes associated with the risk of the development stages of esophageal squamous cell cancer in Feicheng County

BACKGROUND

The purpose of this study was to evaluate the association of multi-genotype polymorphisms with the stepwise progression of esophageal squamous cell cancer (ESCC) and the possibility of predicting those at higher risk.

METHODS

A total of 1,004 subjects were recruited from Feicheng County, China, between Jan. 2004 and Dec. 2007 and examined by endoscopy for esophageal lesions. These subjects included 270 patients with basal cell hyperplasia (BCH), 262 patients with esophageal squamous cell dysplasia (ESCD), 226 patients with ESCC, and 246 controls with Lugol-voiding area but diagnosed as having normal esophageal squamous epithelial cells by histopathology. The genotypes for CYP2E1 G1259C, hOGG1 C326G, MTHFR C677T, MPO G463A, and ALDH2 allele genes were identified in blood samples collected from all participants.

RESULTS

The alleles ALDH2 and MTHFR C677T were critical for determining individual susceptibility to esophageal cancer. Compared to the ALDH 1*1 genotype, the ALDH 2*2 genotype was significantly associated with increased risks of BCH, ESCD, and ESCC. However, the TT genotype of MTHFR C677T only increased the risk of ESCC. Further analysis revealed that the combination of the high-risk genotypes 2*2/1*2 of ALDH 2 and TT/TC of MTHFR C677T increased the risk of BCH by 4.0 fold, of ESCD by 3.7 fold, and ESSC by 8.72 fold. The generalized odds ratio (ORG) of the two combined genotypes was 1.83 (95%CI: 1.55-2.16), indicating a strong genetic association with the risk of carcinogenic progression in the esophagus.

CONCLUSIONS

The study demonstrated that the genotypes ALDH2*2 and MTHFR 677TT conferred elevated risk for developing esophageal carcinoma and that the two susceptibility genotypes combined to synergistically increase the risk.

Multi-susceptibility genes associated with the risk of the development stages of esophageal squamous cell cancer in Feicheng County

Background

The purpose of this study was to evaluate the association of multi-genotype polymorphisms with the stepwise progression of esophageal squamous cell cancer (ESCC) and the possibility of predicting those at higher risk.

Methods

A total of 1,004 subjects were recruited from Feicheng County, China, between Jan. 2004 and Dec. 2007 and examined by endoscopy for esophageal lesions. These subjects included 270 patients with basal cell hyperplasia (BCH), 262 patients with esophageal squamous cell dysplasia (ESCD), 226 patients with ESCC, and 246 controls with Lugol-voiding area but diagnosed as having normal esophageal squamous epithelial cells by histopathology. The genotypes for CYP2E1 G1259C, hOGG1 C326G, MTHFR C677T, MPO G463A, and ALDH2 allele genes were identified in blood samples collected from all participants.

Results

The alleles ALDH2 and MTHFR C677T were critical for determining individual susceptibility to esophageal cancer. Compared to the ALDH 1*1 genotype, the ALDH 2*2 genotype was significantly associated with increased risks of BCH, ESCD, and ESCC. However, the TT genotype of MTHFR C677T only increased the risk of ESCC. Further analysis revealed that the combination of the high-risk genotypes 2*2/1*2 of ALDH 2 and TT/TC of MTHFR C677T increased the risk of BCH by 4.0 fold, of ESCD by 3.7 fold, and ESSC by 8.72 fold. The generalized odds ratio (OR_G) of the two combined genotypes was 1.83 (95%CI: 1.55-2.16), indicating a strong genetic association with the risk of carcinogenic progression in the esophagus.

Conclusions

The study demonstrated that the genotypes ALDH2*2 and MTHFR 677TT conferred elevated risk for developing esophageal carcinoma and that the two susceptibility genotypes combined to synergistically increase the risk.

Alcohol and aldehyde dehydrogenase polymorphisms and a new strategy for prevention and screening for cancer in the upper aerodigestive tract in East Asians

The ethanol in alcoholic beverages and the acetaldehyde associated with alcohol consumption are Group 1 human carcinogens (WHO, International Agency for Research on Cancer). The combination of alcohol consumption, tobacco smoking, the inactive heterozygous aldehyde dehydrogenase-2 genotype (ALDH2*1/*2) and the less-active homozygous alcohol dehydrogenase-1B genotype (ADH1B*1/*1) increases the risk of squamous cell carcinoma (SCC) in the upper aerodigestive tract (UADT) in a multiplicative fashion in East Asians. In addition to being exposed to locally high levels of ethanol, the UADT is exposed to a very high concentration of acetaldehyde from a variety of sources, including that as an ingredient of alcoholic beverages per se and that found in tobacco smoke; acetaldehyde is also produced by salivary microorganisms and mucosal enzymes and is present as blood acetaldehyde. The inefficient degradation of acetaldehyde by weakly expressed ALDH2 in the UADT may be cri! tical to the local accumulation of acetaldehyde, especially in ALDH2*1/*2 carriers. ADH1B*1/*1 carriers tend to experience less intense alcohol flushing and are highly susceptible to heavy drinking and alcoholism. Heavy drinking by persons with the less-active ADH1B*1/*1 leads to longer exposure of the UADT to salivary ethanol and acetaldehyde. The ALDH2*1/*2 genotype is a very strong predictor of synchronous and metachronous multiple SCCs in the UADT. High red cell mean corpuscular volume (MCV), esophageal dysplasia, and melanosis in the UADT, all of which are frequently found in ALDH2*1/*2 drinkers, are useful for identifying high-risk individuals. We invented a simple flushing questionnaire that enables prediction of the ALDH2 phenotype. New health appraisal models that include ALDH2 genotype, the simple flushing questionnaire, or MCV are powerful tools for devising a new strategy for prevention and screening for UADT cancer in East Asians.

Glutathione S-transferase M1 (GSTM1) and glutathione S-transferase T1 (GSTT1) null polymorphisms, smoking, and their interaction in oral cancer: a HuGE review and meta-analysis

The association between glutathione S-transferase M1 (GSTM1) and glutathione S-transferase T1 (GSTT1) null polymorphisms and oral cancer is not consistent across studies, and data on their interaction with smoking in oral cancer are lacking. The authors systematically searched PubMed and SciVerse Scopus for case-control studies examining the association between null genotypes of the GSTM1 and GSTT1 genes and oral cancer. Twenty-eight case-control studies published in English were identified. Summary odds ratios were derived via random-effects models. The summary odds ratio for the GSTM1 null genotype was 1.43 in Asians (95% confidence interval (CI): 1.14, 1.78; P < 0.01, I (2) = 73%) and 0.98 in Caucasians (95% CI: 0.76, 1.28; P = 0.91, I (2) = 0%). Case-only analysis of 6 studies (552 cases) showed an inverse multiplicative interaction between GSTM1 null polymorphisms and smoking (ever/high levels of smoking vs. never/low levels) (odds ratio (OR) = 0.51, 95% CI: 0.32, 0.82; P = 0.01, I (2) = 34%). The GSTT1 null genotype was not significantly associated with oral cancer in Asians (OR = 1.07, 95% CI: 0.82, 1.38; P = 0.63, I (2) = 65%) or Caucasians (OR = 1.04, 95% CI: 0.41, 2.65; P = 0.93, I (2) = 55%). In conclusion, the GSTM1 null genotype may be associated with a higher risk of oral cancer in Asians but not in Caucasians, and this effect may be modified by smoking status. The GSTT1 null genotype may not be associated with oral cancer.

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.

Inhibition of hepatic mitochondrial aldehyde dehydrogenase by carbon tetrachloride through JNK-mediated phosphorylation

The aim of this study was to investigate the mechanism of inhibition of mitochondrial aldehyde dehydrogenase (ALDH2) by carbon tetrachloride (CCl(4)). CCl(4) administration caused marked hepatocyte ballooning and necrosis in the pericentral region. CCl(4) also inhibited hepatic ALDH2 activity in a time-dependent manner without altering the protein level, suggesting ALDH2 inhibition through covalent modifications such as phosphorylation by JNK. To demonstrate phosphorylation, the isoelectric point (pI) of ALDH2 in CCl(4)-exposed rats was compared to that of untreated controls. Immunoblot analysis revealed that immunoreactive ALDH2 bands in CCl(4)-exposed rats were shifted to acidic pI ranges on two-dimensional electrophoresis (2-DE) gels. Incubation with alkaline phosphatase significantly restored the suppressed ALDH2 activity with a concurrent alkaline pI shift of the ALDH2 spots. Both JNK and activated JNK were translocated to mitochondria after CCl(4) exposure. In addition, incubation with catalytically active JNK led to significant inhibition of ALDH2 activity, with an acidic pI shift on 2-DE gels. Furthermore, immunoprecipitation followed by immunoblot analysis with anti-phospho-Ser-Pro antibody revealed phosphorylation of a Ser residue(s) of ALDH2. These results collectively indicate a novel underlying mechanism by which CCl(4) exposure activates JNK, which translocates to mitochondria and phosphorylates ALDH2, contributing to inhibition of ALDH2 activity accompanied by decreased cellular defense capacity and increased lipid peroxidation.

Oral cancer and polymorphism of ethanol metabolising genes

Oral cancer is the sixth most common cancer worldwide and a major health problem in some parts of the world. Epidemiological studies have shown that habitual alcohol consumption could be a risk factor in oral carcinogenesis, although the true involvement of alcohol is unknown. Via alcohol dehydrogenase (ADH) and cytochrome P450 oxidase (CYP) alcohol is metabolized to acetaldehyde, a highly toxic compound, which plays an important role in carcinogenesis. Subsequently, and during the metabolizing process, acetaldehyde becomes acetate by acetaldehyde dehydrogenase (ALDH). Therefore, acetaldehyde levels are determined mainly by the action of ADH, CYP and ALDH. Recently, several studies have found that certain polymorphisms of genes encoding these enzymes confer a higher or lower metabolic activity and therefore different risk for certain malignancies such as oral cancer. In this review, we analyze the polymorphisms of alcohol metabolising enzymes in relation susceptibility to an oral cancer.

ALDH2 genetic polymorphism and the risk of type II diabetes mellitus in CAD patients

The prevalence of type II diabetes mellitus (T2DM) in coronary artery disease (CAD) patients has been steadily increasing, especially in East Asian countries. Although many studies have suggested that certain genetic variants may predispose to the development of T2DM, very few studies investigated the genetic link with T2DM in CAD patients of East Asia. In this study, we investigated the relationship between Glu504Lys polymorphism in the acetaldehyde dehydrogenase 2 (ALDH2) gene, a key enzyme of alcohol metabolism, and the risk of having T2DM in Chinese Han CAD patients. We enrolled 542 CAD patients (180 women and 362 men) and 309 CAD-/DM- subjects (152 women and 157 men). T2DM was confirmed in 47.4% of CAD patients. Logistic and linear regression analyses showed that ALDH2 mutant genotypes ((*)1/(*)2 and (*)2/(*)2) were an independent risk factor for both T2DM in female CAD patients, even after controlling for alcohol consumption (OR=1.95, P=0.043), and fasting plasma glucose (FPG) in CAD-/DM- women (P=0.015), whereas the association with FPG disappeared after controlling for high-sensitivity C-reactive protein, a classic inflammatory biomarker. However, there was no relationship between the ALDH2 genetic polymorphism and T2DM or FPG in men. These findings suggest that the ALDH2 polymorphism is associated with an increased risk of T2DM in female CAD patients, and this association could be causal on the basis of the association between the polymorphism and FPG, which is partly explained by an increased inflammatory status. These findings will benefit the screening and treatment of a high-risk population in East Asians.

Aldehyde dehydrogenase 2 and head and neck cancer: a meta-analysis implementing a Mendelian randomization approach

Alcohol drinking at high doses is a risk factor for head and neck cancer, and exposure to acetaldehyde, the principle metabolite of alcohol, is supposed to account for the increased risk. Individuals homozygous for the 2 variant allele of aldehyde dehydrogenase 2 (ALDH2) are unable to metabolize acetaldehyde, which prevents them from alcohol drinking, whereas 1 2 have 6-fold higher blood acetaldehyde concentration postalcohol consumption with respect to 1 1. According to the concept of Mendelian randomization, because this polymorphism is distributed randomly during gamete formation, its association with head and neck cancer should be not confounded by smoking. We carried out a meta-analysis of ALDH2 and head and neck cancer searching for relevant studies on Medline and Embase up to January 31, 2008, and investigated the consistency between the expected odds ratio (OR) among drinkers from the largest pooled analysis among never smokers and the observed OR from this meta-analysis by an interaction test. Six studies were selected (945 cases, 2,917 controls). The OR of head and neck cancer among 2 2 was 0.53 [95% confidence interval (95% CI), 0.28-1.00] relative to 1 1 and 1.83 (95% CI, 1.21-2.77) among 1 2. The expected OR for head and neck cancer due to alcohol intake among 1 1 was 1.38 (95% CI, 0.88-2.17) and the observed OR among 1 1 compared with 2*2 from this meta-analysis was 1.88 (95% CI, 1.00-3.57; P for interaction = 0.43). Besides showing the effectiveness of the Mendelian randomization approach, these findings support the theory that alcohol increases head and neck cancer risk through the carcinogenic action of acetaldehyde.

An assessment of potential cancer risk following occupational exposure to ethanol

Recognition of the carcinogenic properties of ethanol has resulted from comprehensive evidence regarding the effect of consumption of alcohol; indeed, ethanol in alcoholic beverages is now considered a Group 1 carcinogen by the International Agency for Research on Cancer. However, there is little information on the effects of ethanol following exposure via the occupationally relevant routes of inhalation and dermal exposure. This review therefore focuses on these exposure routes, to assess potential carcinogenic risk associated with occupational exposure to ethanol. Inhalatory exposure at the current occupational exposure limit (OEL) for the United Kingdom (1000 ppm ethanol over an 8-h shift) was estimated to be equivalent to ingestion of 10 g ethanol (approximately 1 glass of alcohol) per day. However, in the occupational setting the dose-rate delivery of this amount of ethanol is low, allowing for its rapid and effective elimination, for the majority of individuals. Similarly, while dermal absorption in an occupational setting could potentially add to overall body ethanol burden, additional carcinogenic risk of such exposure is considered negligible. Thus, on balance, there appears little cause to suppose occupational exposure at or below the current OEL associates with any appreciable increase in risk of cancer. However, available occupational exposure data to confirm this view are currently limited. It is also suggested that adoption of a more flexible classification regime, considering risk in the context of hazard and exposure (such as that adopted by the German MAK commission), would represent an improvement over traditional occupational risk assessment practices.

CYP1A1, mEH, and GSTM1 Polymophisms and Risk of Oral and Pharyngeal Cancer: A Spanish Case-Control Study

Background. Genetic polymorphisms of drug metabolizing enzymes involved in the detoxification pathways of carcinogenic substances may influence cancer risk. Methods. Case-control study that investigates the relationship between CYP1A1 Ile/Val, exon 4 mEH, and GSTM1 null genetic polymorphism and the risk of oral and pharyngeal cancer examining the interaction between these genes, tobacco, and alcohol. 92 incident cases and 130 consecutive hospital-based controls have been included. Results. No significant associations were found for any of the genotypes assessed. The estimated risk was slightly elevated in subjects with the wild type of the mEH gene and the null GSTM1 genotype. For exon 4 mEH heterozygous polymorphism, the risk was slightly lower for heavy smokers than for light smokers. The inverse association was observed for the GSTM1 null genotype. Conclusions. The results suggest that exon 4 mEH and GSTM1 null polymorphisms might influence oral and pharyngeal cancer.

Meta-analysis and pooled analysis of GSTM1 and CYP1A1 polymorphisms and oral and pharyngeal cancers: a HuGE-GSEC review

The association of GSTM1 and CYP1A1 polymorphisms and oral and pharyngeal cancers was assessed through a meta-analysis of published case-control studies and a pooled analysis of both published and unpublished case-control studies from the Genetic Susceptibility to Environmental Carcinogens database (http://www.upci.upmc.edu/research/ccps/ccontrol/index.html ). Thirty publications used in the meta-analysis included a total of 7783 subjects (3177 cases and 4606 controls); 21 datasets, 9397 subjects (3130 cases and 6267 controls) were included in the pooled analysis. The GSTM1 deletion was 2-fold more likely to occur in African American and African cases than controls (odds ratio: 1.7, 95% confidence interval: 0.9-3.3), although this was not observed among whites (odds ratio: 1.0, 95% confidence interval: 0.9-1.1). The meta-analysis and pooled analysis showed a significant association between oral and pharyngeal cancer and the CYP1A1 MspI homozygous variant (meta-ORm2/m2: 1.9, 95% confidence interval: 1.4-2.7; Pooled ORm2m2: 2.0, 95% confidence interval: 1.3-3.1; ORm1m2 or [infi]m2m2: 1.3, 95% confidence interval: 1.1-1.6). The association was present for the CYP1A1 (exon 7) polymorphism (ORVal/Val: 2.2, 95% confidence interval: 1.1-4.5) in ever smokers. A joint effect was observed for GSTM1 homozygous deletion and the CYP1A1 m1m2 variant on cancer risk. Our findings suggest that tobacco use and genetic factors play a significant role in oral and pharyngeal cancer.

Epidemiology of carcinogen metabolism genes and risk of squamous cell carcinoma of the head and neck

The risk association between tobacco and alcohol use with squamous cell carcinoma of the head and neck (SCCHN) is well recognized. However, clearly not all individuals who smoke or drink develop SCCHN. Individual genetic susceptibility differences in carcinogen-metabolizing enzyme function, mutagen sensitivity, apoptosis, and chromosomal aberrations either alone or in combination have been theorized to modify the risk of SCCHN. Nearly all carcinogens and procarcinogens require activation by metabolizing enzymes. Similarly, detoxifying enzymes exist and deactivate carcinogens as well as their intermediate by-products. Together these enzymes are termed xenobiotic-metabolizing enzymes; genetic polymorphisms of these enzymes can modify an individual's response to carcinogens and hence the carcinogenic potential of such exposures. In this review, we explore the available evidence in recent literature regarding the risk association between SCCHN and various xenobiotic-metabolizing enzymes, including cytochrome P450s, glutathione S-transferases, N-acetyltransferases, NAD(P)H:quinone oxidoreductase 1, alcohol dehydrogenase, and aldehyde dehydrogenase.

Susceptibility to lung cancer and genetic polymorphisms in the alcohol metabolite-related enzymes alcohol dehydrogenase 3, aldehyde dehydrogenase 2, and cytochrome P450 2E1 in the Japanese population

BACKGROUND

It is believed that acetaldehyde plays an important role in alcohol-related carcinogenesis; although current epidemiologic studies have provided inconsistent findings on the association between alcohol consumption and the risk of lung cancer.

METHODS

To clarify the hypothesis that genetic polymorphisms in alcohol-metabolizing enzymes may influence susceptibility to lung cancer, the authors conducted a hospital-based case-control study and examined genetic polymorphisms in the alcohol dehydrogenase 3, aldehyde dehydrogenase 2 (ALDH(2)), and cytochrome P450 2E1 genes in 505 patients with histologically confirmed lung cancer and in a group of 256 noncancer controls who provided complete cigarette and alcohol consumption histories. Genotyping was conducted by polymerase chain reaction-restriction fragment-length polymorphism assay.

RESULTS

A significant association was noted between alcohol consumption and lung cancer risk. Thus, using the median value for the controls as the cut-off point, the odds ratios (OR) for light and heavy drinkers were 1.76 and 1.95, respectively (P for trend = .012), compared with nondrinkers. In addition, there was a significant trend toward increased risk of lung cancer in drinkers with ALDH(2) variant alleles (P for trend <.0001). The adjusted OR for heavy drinkers was 6.15 compared with nondrinkers. Regarding associations between histologic type and genotypes, the ALDH(2) variant allele was significantly less common in patients who had adenocarcinoma compared with controls.

CONCLUSIONS

The current observations suggested a positive association between alcohol consumption and the risk of lung cancer: Drinking may increase the risk, especially among individuals who have the variant ALDH(2) alleles.

Gene-gene and gene-environment interactions between alcohol drinking habit and polymorphisms in alcohol-metabolizing enzyme genes and the risk of head and neck cancer in Japan

Alcohol consumption is a strong risk factor for squamous cell carcinoma of the head and neck (SCCHN). The genetic polymorphisms aldehyde dehydrogenase2 (ALDH2) Glu487Lys and alcohol dehydrogenase 2 (ADH2) His47Arg, which have a strong impact on alcohol metabolism, are common in the Japanese population. To clarify the significance of these polymorphisms in SCCHN carcinogenesis, we conducted a matched case-control study with 239 incident SCCHN subjects and 716 non-cancer controls. Both ADH2 Arg/Arg and ALDH2 Glu/Lys were found to be independently associated with increased risk, with odds ratios (OR) of 2.67 (95% confidence interval [CI] 1.51-4.57) and 1.66 (95% CI 1.20-2.31), respectively. Further, compared with subjects having both ADH2 His/His and ALDH2 Glu/Glu, the adjusted OR and its 95% CI for those with both ADH2 Arg/Arg and ALDH2 Glu/Lys was 5.00 (2.32-10.71) in all subjects. This combination effect was evident in heavy drinkers (OR 11.3, 95% CI 2.97-43.3) but not in moderate or non-drinkers. Statistically significant gene-environment interactions between the two polymorphisms and drinking level were seen (ADH2 P = 0.035, ALDH2, P = 0.013). Furthermore, we also found a statistically significant gene-gene interaction between the two polymorphisms (P = 0.042). In conclusion, this case-control study showed a significantly increased risk of SCCHN in subjects with the ADH2 Arg/Arg and ALDH2 Glu/Lys polymorphisms in a Japanese population. In addition, our results also demonstrated that this risk was associated with significant gene-gene interactions between ADH2 and ALDH2 polymorphisms, as well as gene-environment interactions between these polymorphisms and alcohol drinking.

GSTM1 polymorphism and oral leukoplakia

BACKGROUND

Molecular epidemiological studies have now provided evidence that an individual susceptibility to cancer is mediated by genetic and environmental factors. Genetic polymorphisms have been described for enzymes involved in the metabolism of tobacco carcinogens and cancer risk is determined by the degree of expression and/or activity of enzymes involved in carcinogen activation or deactivation. The objective of this study was to investigate the GSTM1 null polymorphism and the risk for oral leukoplakia in individuals with tobacco-smoking habit in a Brazilian population.

METHODS

A total of 52 tobacco-smoking patients with oral leukoplakia and 52 tobacco-smoking controls were recruited in a Brazilian population. The GSTM1 genotypes were studied by polymerase chain reaction-based methods.

RESULTS

The frequency of the GSTM1 null genotype in the group with oral leukoplakia (57.7%) was statistically different from the controls (34.6%; OR: 2.57, 95% CI: 1.16-5.69, P < 0.05). The stratification of the samples according to the level of dysplasia showed increased prevalence of GSTM1 null genotype on lesions with moderate/severe histological dysplasia (68.2%) compared with the control group (31.9%). This difference was statistically significant (OR: 4.59, 95% CI: 1.29-16.33, P < 0.05).

CONCLUSION

In conclusion, the GSTM1 null genotype may increase the risk for oral leukoplakia development.

GSTM1 polymorphism and oral squamous cell carcinoma

We investigated the frequency of the GSTM1 genotypes in 70 Brazilian patients with oral squamous cell carcinoma (OSCC) and 82 age-sex matched controls. The GSTM1 genotypes were studied by PCR-based methods. The frequency of male patients with OSCC and null for the GSTM1 (70.5%) was statistically different from the male patients from the control group (48.5%) (Odds Ratio, OR=2.53, 95% CI=1.22-5.24, P<0.05). The frequency of the GSTM1 null genotype (0/0) in the group with OSCC (65.7%) was statistically different from the controls (48.7%) (OR=2.01, 95% CI=1.04-3.88, P<0.05). The prevalence of GSTM1 deficiency (null) was significantly higher for patients with oral cancer of the floor of the mouth (OR=3.67, 95% CI=1.11-12.11, P<0.05). In conclusion, the GSTM1 null genotype may increase the risk for OSCC development.

Population distribution of aldehyde dehydrogenase-2 genetic polymorphism: implications for risk assessment

The role of genetic polymorphisms in modulating xenobiotic metabolism and susceptibility to cancer and other health effects has been suggested in numerous studies. However, risk assessments have generally not used this information to characterize population variability or adjust risks for susceptible subgroups. This paper focuses upon the aldehyde dehydrogenase-2 (ALDH2) system because it exemplifies the pivotal role genetic polymorphisms can play in determining enzyme function and susceptibility. Allelic variants in ALDH2 cause decreased ability to clear acetaldehyde and other aldehyde substrates, with homozygous variants (ALDH2*2/2) having no activity and heterozygotes (ALDH2*1/2) having intermediate activity relative to the predominant wild type (ALDH2*1/1). These polymorphisms are associated with increased buildup of acetaldehyde following ethanol ingestion and increased immediate symptoms (flushing syndrome) and long-term cancer risks. We have used Monte Carlo simulation to characterize the population distribution of ALDH2 allelic variants and inter-individual variability in aldehyde internal dose. The nonfunctional allele is rare in most populations, but is common in Asians such that 40% are heterozygotes and 5% are homozygote variants. The ratio of the 95th or 99th percentiles of the Asian population compared to the median of the U.S. population is 14- to 26-fold, a variability factor that is larger than the default pharmacokinetic uncertainty factor (3.2-fold) commonly used in risk assessment. Approaches are described for using ALDH2 population distributions in physiologically based pharmacokinetic-Monte Carlo refinements of risk assessments for xenobiotics which are metabolized to aldehyde intermediates (e.g., ethanol, toluene, ethylene glycol monomethyl ether).

Oral cancer research with an emphasis on genomic analysis

Ablative surgery has been a standard procedure for many years, but during the past few years there has been a significant improvement in our understanding of invasion and metastasis in oral cancer. Each procedure has to be planned individually. Before surgery, every attempt must have been made to arrive at a proper diagnosis, including the exact nature and aggressiveness of the tumor and an analysis of the patient's genetic background. These procedures and the prognosis will be discussed.

High-dose vitamin therapy stimulates variant enzymes with decreased coenzyme binding affinity (increased K(m)): relevance to genetic disease and polymorphisms

As many as one-third of mutations in a gene result in the corresponding enzyme having an increased Michaelis constant, or K(m), (decreased binding affinity) for a coenzyme, resulting in a lower rate of reaction. About 50 human genetic dis-eases due to defective enzymes can be remedied or ameliorated by the administration of high doses of the vitamin component of the corresponding coenzyme, which at least partially restores enzymatic activity. Several single-nucleotide polymorphisms, in which the variant amino acid reduces coenzyme binding and thus enzymatic activity, are likely to be remediable by raising cellular concentrations of the cofactor through high-dose vitamin therapy. Some examples include the alanine-to-valine substitution at codon 222 (Ala222-->Val) [DNA: C-to-T substitution at nucleo-tide 677 (677C-->T)] in methylenetetrahydrofolate reductase (NADPH) and the cofactor FAD (in relation to cardiovascular disease, migraines, and rages), the Pro187-->Ser (DNA: 609C-->T) mutation in NAD(P):quinone oxidoreductase 1 [NAD(P)H dehy-drogenase (quinone)] and FAD (in relation to cancer), the Ala44-->Gly (DNA: 131C-->G) mutation in glucose-6-phosphate 1-dehydrogenase and NADP (in relation to favism and hemolytic anemia), and the Glu487-->Lys mutation (present in one-half of Asians) in aldehyde dehydrogenase (NAD + ) and NAD (in relation to alcohol intolerance, Alzheimer disease, and cancer).

Proteomic alterations of the variants of human aldehyde dehydrogenase isozymes correlate with hepatocellular carcinoma

To develop novel markers for hepatocellular carcinomas (HCC), 10 cases were analyzed by 2-dimensional electrophoresis (2DE) and matrix-assisted laser desorption ionization mass spectrometry. Results were compared to those of paired adjacent nontumorous liver tissues. Comparative analysis of the respective spot patterns in 2DE revealed that 3 variants of class 3 aldehyde dehydrogenase (ALDH-3) newly appeared while 2 variants of ALDH-2 diminished to undetectable levels in HCC. However, 4 ALDH-1 variants with different pIs remained unaffected. This pattern of concomitant appearance and disappearance of ALDH-3 and ALDH-2 variants was consistently observed in all HCC tissues. Our results suggest that alterations of ALDH isozyme variants may be closely correlated to HCC and that proteomic analysis of these proteins might be a novel approach to identify the molecular events in detail during hepatocarcinogenesis.

The role of acetaldehyde in the actions of alcohol (update 2000)

BACKGROUND

Recent advances in the field of acetaldehyde (AcH) research have raised the need for a comprehensive review on the role of AcH in the actions of alcohol. This update is an attempt to summarize the available AcH research.

METHODS

The descriptive part of this article covers not only recent research but also the development of the field. Special emphasis is placed on mechanistic analyses, new hypotheses, and conclusions.

RESULTS

Elevated AcH during alcohol intoxication causes alcohol sensitivity, which involves vasodilation associated with increased skin temperature, subjective feelings of hotness and facial flushing, increased heart and respiration rate, lowered blood pressure, sensation of dry mouth or throat associated with bronchoconstriction and allergy reactions, nausea and headache, and also reinforcing reactions like euphoria. These effects seem to involve catecholamine, opiate peptide, prostaglandin, histamine, and/or kinin mechanisms. The contribution of AcH to the pathological consequences of chronic alcohol intake is well established for different forms of cancer in the digestive tract and the upper airways. AcH seems to play a role in the etiology of liver cirrhosis. AcH may have a role in other pathological developments, which include brain damage, cardiomyopathy, pancreatitis, and fetal alcohol syndrome. AcH creates both unpleasant aversive reactions that protect against excessive alcohol drinking and euphoric sensations that may reinforce alcohol drinking. The protective effect of AcH may be used in future treatments that involve gene therapy with or without liver transplantation.

CONCLUSIONS

AcH plays a role in most of the actions of alcohol. The individual variability in these AcH-mediated actions will depend on the genetic polymorphism, not only for the alcohol and AcH-metabolizing enzymes but also for the target sites for AcH actions. The subtle balance between aversive and reinforcing, protecting and promoting factors will determine the overall behavioral and pathological developments.

Alcohol and upper gastrointestinal tract cancer: the role of local acetaldehyde production

Alcohol is, together with tobacco smoke, the main cause for upper GI tract cancer in industrialized countries. However, the tumour-promoting effects of alcohol intake are poorly understood and alcohol itself is not carcinogenic in the animal model. There is increasing evidence that alcohol metabolism, rather than the alcohol itself, generates carcinogenic and cell-toxic compounds. Acetaldehyde, first metabolite of ethanol, is highly toxic, mutagenic and carcinogenic. Polymorphisms in the genes coding for enzymes responsible for acetaldehyde accumulation and detoxification have been associated with an increased cancer risk. Acetaldehyde can also be produced in the mucosa and by the physiological microflora. This review summarizes the scientific evidence that alcohol intake leads to a local production of acetaldehyde. It describes the role of the oral microflora, the mucosa and the salivary glands in this process and shows that local acetaldehyde production from ethanol may contribute to the carcinogenesis of alcohol intake in the upper GI tract.

The role of acetaldehyde in the actions of alcohol (update 2000)

BACKGROUND

Recent advances in the field of acetaldehyde (AcH) research have raised the need for a comprehensive review on the role of AcH in the actions of alcohol. This update is an attempt to summarize the available AcH research.

METHODS

The descriptive part of this article covers not only recent research but also the development of the field. Special emphasis is placed on mechanistic analyses, new hypotheses, and conclusions.

RESULTS

Elevated AcH during alcohol intoxication causes alcohol sensitivity, which involves vasodilation associated with increased skin temperature, subjective feelings of hotness and facial flushing, increased heart and respiration rate, lowered blood pressure, sensation of dry mouth or throat associated with bronchoconstriction and allergy reactions, nausea and headache, and also reinforcing reactions like euphoria. These effects seem to involve catecholamine, opiate peptide, prostaglandin, histamine, and/or kinin mechanisms. The contribution of AcH to the pathological consequences of chronic alcohol intake is well established for different forms of cancer in the digestive tract and the upper airways. AcH seems to play a role in the etiology of liver cirrhosis. AcH may have a role in other pathological developments, which include brain damage, cardiomyopathy, pancreatitis, and fetal alcohol syndrome. AcH creates both unpleasant aversive reactions that protect against excessive alcohol drinking and euphoric sensations that may reinforce alcohol drinking. The protective effect of AcH may be used in future treatments that involve gene therapy with or without liver transplantation.

CONCLUSIONS

AcH plays a role in most of the actions of alcohol. The individual variability in these AcH-mediated actions will depend on the genetic polymorphism, not only for the alcohol and AcH-metabolizing enzymes but also for the target sites for AcH actions. The subtle balance between aversive and reinforcing, protecting and promoting factors will determine the overall behavioral and pathological developments.

Metabolizing enzyme genotype and risk for upper aerodigestive tract cancer

Genetic polymorphisms are associated with a number of enzymes involved in the metabolism of carcinogens important in the induction of upper aerodigestive tract cancer. It has been suggested that such polymorphisms may be linked to cancer susceptibility. Using a case-control molecular epidemiologic approach, the association between many of these genetic polymorphisms and susceptibility to upper aerodigestive tract cancer has been investigated in numerous studies. In this review, we summarize the findings of these studies, analyzing potential associations with upper aerodigestive tract cancer risk in terms of gene:environment interactions, genotype-induced functional defects in enzyme activity and/or expression, and the influence of race on these associations.