Aldehyde Dehydrogenase 2 (ALDH2) Polymorphism and the Risk of Alcoholic Liver Cirrhosis among East Asians: A Meta-Analysis

How does alcohol use impact morbidity and mortality of liver cirrhosis? A systematic review and dose-response meta-analysis

BACKGROUND

Alcohol consumption is the most important risk factor responsible for the disease burden of liver cirrhosis (LC). Estimates of risk relationships available usually neither distinguish between different causes such as alcohol-related LC or hepatitis-related LC, nor differentiate between morbidity and mortality as outcome. We aimed to address this research gap and identify dose-response relationships between alcohol consumption and LC, by cause and outcome.

METHODS

A systematic review using PubMed/Medline and Embase was conducted, identifying studies that reported an association between level of alcohol use and LC. Meta-regression models were used to estimate the dose-response relationships and control for heterogeneity.

RESULTS

Totally, 44 studies, and 1 secondary data source, with a total of 5,122,534 participants and 15,150 cases were included. Non-linear dose-response relationships were identified, attenuated for higher levels of consumption. For morbidity, drinking 25 g/day was associated with a RR of 1.81 (95% CI 1.68-1.94) compared to lifetime abstention; 50 g/day and 100 g/day corresponded to 3.54 (95% CI 3.29-3.81) and 8.15 (95% CI 7.46-8.91), respectively. For mortality, for 25 g/day, a RR of 2.65 (95% CI 2.22-3.16); for 50 g/day, a RR of 6.83 (95% CI 5.84-7.97); for 100 g/day, a RR of 16.38 (95% CI 13.81-19.42) were identified. A higher risk for alcohol-related and all-cause LC as compared to hepatitis C-related LC was found.

CONCLUSION

Our results demonstrated higher acceleration for mortality compared to morbidity. The current findings will inform the way we quantify the burden due to LC attributable to alcohol use.

Alcohol drinking and risks of liver cancer and non-neoplastic chronic liver diseases in China: a 10-year prospective study of 0.5 million adults

BACKGROUND

Alcohol consumption is an important risk factor for hepatic neoplastic and non-neoplastic diseases. Questions remain, however, about the relevance to disease risk of drinking patterns and alcohol tolerability, which differ appreciably between Chinese and Western populations.

METHODS

The prospective China Kadoorie Biobank included 512,715 adults (41% men) aged 30-79 years recruited from ten areas during 2004-2008, recording alcohol intake, drinking patterns, and other characteristics. After median 10 years' follow-up, 2531 incident liver cancer, 2040 liver cirrhosis, 260 alcoholic liver disease (ALD), and 1262 non-alcoholic fatty liver disease (NAFLD) cases were recorded among 492,643 participants without prior cancer or chronic liver disease at baseline. Cox regression was used to estimate adjusted hazard ratios (HR) relating alcohol intake and drinking patterns to each disease.

RESULTS

Overall, 33% of men and 2% of women drank alcohol regularly (i.e. at least weekly) at baseline. Among male current regular drinkers, alcohol consumption showed positive dose-response associations with risks of several major chronic liver diseases, with HRs per 280 g/week (i.e. around four drinks/day) higher usual alcohol intake of 1.44 (95% CI 1.23-1.69) for liver cancer (n = 547), 1.83 (1.60-2.09) for liver cirrhosis (n = 388), 2.01 (1.77-2.28) for ALD (n = 200), 1.71 (1.35-2.16) for NAFLD (n = 198), and 1.52 (1.40-1.64) for total liver disease (n = 1775). The association with ALD appeared stronger among men reporting flushing (i.e., with low alcohol tolerance). After adjustment for the total amount of weekly alcohol consumption, daily drinkers had significantly increased risk of ALD (2.15, 1.40-3.31) compared with non-daily drinkers, and drinking without meals was associated with significantly greater risks of liver cancer (1.32, 1.01-1.72), liver cirrhosis (1.37, 1.02-1.85), and ALD (1.60, 1.09-2.33) compared with drinking with meals. Female current regular drinkers had significantly higher risk of ALD, but not other liver diseases, than female abstainers.

CONCLUSIONS

In Chinese men, alcohol intake was associated with significantly increased risks of several major chronic liver diseases, and certain drinking patterns (e.g. drinking daily, drinking without meals) may further exacerbate the disease risks.

Association between Alcohol Consumption and Serum Cortisol Levels: a Mendelian Randomization Study

BACKGROUND

Several studies have reported conflicting results regarding the relationship between alcohol consumption and cortisol levels. However, the causality between alcohol consumption and cortisol levels has not been evaluated.

METHODS

This study examined 8,922 participants from the Dong-gu Study. The aldehyde dehydrogenase 2 (ALDH2) rs671 polymorphism was used as an instrumental variable for alcohol consumption. The association between the genetically predicted alcohol consumption and cortisol level was evaluated with Mendelian randomization (MR) using two-stage least squares regression.

RESULTS

Alcohol consumption was positively associated with the serum cortisol level in both sexes in the observational analysis. In the MR analysis, the genetically predicted alcohol consumption was positively related to the cortisol level in men, with cortisol levels increasing by 0.18 μg/dL per drink per day. However, there was no relationship in women in the MR analysis.

CONCLUSION

The predicted alcohol consumption according to the ALDH2 rs671 polymorphism was positively related to the cortisol levels, suggesting a causal relationship between alcohol consumption and cortisol levels.

Role of ALDH2 in Hepatic Disorders: Gene Polymorphism and Disease Pathogenesis

Aldehyde dehydrogenase 2 (ALDH2) is a key enzyme of alcohol metabolism and it is involved in the cellular mechanism of alcohol liver disease. ALDH2 gene mutations exist in about 8% of the world's population, with the incidence reaching 45% in East Asia. The mutations will result in impairment of enzyme activity and accumulation of acetaldehyde, facilitating the progression of other liver diseases, including non-alcoholic fatty liver diseases, viral hepatitis and hepatocellular carcinoma, through adduct formation and inflammatory responses. In this review, we seek to summarize recent research progress on the correlation between ALDH2 gene polymorphism and multiple liver diseases, with an attempt to provide clues for better understanding of the disease mechanism and for strategy making.

Aldehyde Dehydrogenase, Liver Disease and Cancer

Acetaldehyde dehydrogenase 2 (ALDH2) is the key enzyme responsible for metabolism of the alcohol metabolite acetaldehyde in the liver. In addition to conversion of the acetaldehyde molecule, ALDH is also involved in other cellular functions. Recently, many studies have investigated the involvement of ALDH expression in viral hepatitis, alcoholic liver disease (ALD), non-alcoholic fatty liver disease (NAFLD), liver fibrosis, and liver cancer. Notably, ALDH2 expression has been linked with liver cancer risk, as well as pathogenesis and prognosis, and has emerged as a promising therapeutic target. Of note, approximately 8% of the world's population, and approximately 30-40% of the population in East Asia carry an inactive ALDH2 gene. This review summarizes new progress in understanding tissue-specific acetaldehyde metabolism by ALDH2 as well as the association of ALDH2 gene polymorphisms with liver disease and cancer. New research directions emerging in the field are also briefly discussed.

Polymorphisms in alcohol dehydrogenase (ADH1) and cytochrome p450 2E1 (CYP2E1) genes in patients with cirrhosis and/or hepatocellular carcinoma

Introduction: One of the most important risk factors for hepatocellular carcinoma (HCC) is alcohol consumption: Studies in different populations suggest that the risk of liver disease could be associated with genetic variants of the enzymes involved in alcohol metabolism, such as alcohol dehydrogenase (ADH) and cytochrome P450 CYP2E1. Objective: To identify and characterize the allelic variants of ADH1B, ADH1C and CYP2E1 genes in Colombian patients with cirrhosis and/or HCC. Materials and methods: We included samples from patients attending the hepatology unit between 2005-2007 and 2014-2016 of a hospital in Medellin. Samples were genotyped using PCR-RFLP. We compared the results with two control groups and the 1000 Genomes Project database. Results: We collected 97 samples from patients with a diagnosis of cirrhosis and/or HCC. The two main risk factors were chronic alcohol consumption (18.6%) and cholangiopathies (17.5%). The most frequent genotypes in the study population were ADH1B*1/1 (82%), ADH1C*1/1 (59%), and CYP2E1*C/C (84%). Conclusions: This first study of polymorphisms in Colombian patients diagnosed with cirrhosis and/or HCC showed genotypes ADH1B*1/1, ADH1C*1/1 and CYP2E1*C/C as the most frequent. We found no significant differences in the genotype frequency between cases and controls. Further studies are necessary to explore the association between polymorphisms and the risk of end-stage liver disease from alcohol consumption.

Aldehyde dehydrogenase 2 activation ameliorates CCl4 -induced chronic liver fibrosis in mice by up-regulating Nrf2/HO-1 antioxidant pathway

Mitochondrial aldehyde dehydrogenase 2 (ALDH2) is critical in the pathogenesis of alcoholic liver cirrhosis. However, the effect of ALHD2 on liver fibrosis remains to be further elucidated. This study aimed to demonstrate whether ALDH2 regulates carbon tetrachloride (CCl₄)‐induced liver fibrosis and to investigate the efficacy of Alda‐1, a specific activator of ALDH2, on attenuating liver fibrosis. ALDH2 expression was increased after chronic CCl₄ exposure. ALDH2 deficiency accentuated CCl₄‐induced liver fibrosis in mice, accompanied by increased expression of collagen 1α1, α‐SMA and TIMP‐1. Moreover, ALDH2 knockout triggered more ROS generation, hepatocyte apoptosis and impaired mitophagy after CCl₄ treatment. In cultured HSC‐T6 cells, ALDH2 knockdown by transfecting with lentivirus vector increased ROS generation and α‐SMA expression in an in vitro hepatocyte fibrosis model using TGF‐β1. ALDH2 overexpression by lentivirus or activation by Alda‐1 administration partly reversed the effect of TGF‐β1, whereas ALDH2 knockdown totally blocked the protective effect of Alda‐1. Furthermore, Alda‐1 administration protected against liver fibrosis in vivo, which might be mediated through up‐regulation of Nrf2/HO‐1 cascade and activation of Parkin‐related mitophagy. These findings indicate that ALDH2 deficiency aggravated CCl₄‐induced hepatic fibrosis through ROS overproduction, increased apoptosis and mitochondrial damage, whereas ALDH2 activation through Alda‐1 administration alleviated hepatic fibrosis partly through activation of the Nrf2/HO‐1 antioxidant pathway and Parkin‐related mitophagy, which indicate ALDH2 as a promising anti‐fibrotic target and Alda‐1 as a potential therapeutic agent in treating CCl₄‐induced liver fibrosis.

ADH1B, ALDH2, GSTM1 and GSTT1 Gene Polymorphic Frequencies among Alcoholics and Controls in the Arcadian Population of Central India

Background: Epidemiological research has highlighted the global burden of primary liver cancer cases due to alcohol consumption, even in a low consumption country like India. Alcohol detoxification is governed by ADH1B, ALDH2, GSTM1 and GSTT1 genes that encode functional enzymes which are coordinated with each other to remove highly toxic metabolites i.e. acetaldehyde as well as reactive oxygen species generated through detoxification processes. Some communities in the population appears to be at greater risk for development of the liver cancer due to genetic predispositions. Methods: The aim of this study was to screen the arcadian population of central India in order to investigate and compare the genotype distribution and allele frequencies of alcohol metabolizing genes (ADH1B, ALDH2, GSTM1 and GSTT1) in both alcoholic (N=121) and control (N=145) healthy subjects. The gene polymorphism analysis was conducted using PCR and RFLP methods. Results: The allele frequency of ALDH2 *1 was 0.79 and of ALDH2*2 was 0.21 (OR:1.12; CI (95%): 0.74-1.71). The null allele frequency for GSTM1 was 0.28 (OR:0.85; CI (95%): 0.50-1.46) and for GSTT1 was 0.20 (OR:1.93; CI (95%): 1.05-3.55). No gene polymorphism for ADH1B was not observed. The total prevalence of polymorphisms was 3.38% for ALDH2, GSTM1 and GSTT1. Conclusion: The results of this study suggested that individuals of the Central India population under study are at risk for liver disorders due to ALDH2, GSTM1 and GSTT1 gene polymorphisms. This results may have significance for prevention of alcohol dependence, alcoholic liver disorders and the likelihood of liver cancer.

Alcohol Consumption, Aldehyde Dehydrogenase 2 Gene Polymorphisms, and Cardiovascular Health in Korea

Alcohol consumption is a serious health issue in Korea in terms of the amount consumed and the behavior related to its consumption. Aldehyde dehydrogenase 2 (ALDH2) is a key enzyme in alcohol metabolism that degrades acetaldehyde to nontoxic acetic acid. The enzyme is coded by the ALDH2 gene, which is commonly polymorphic in East Asian populations. A point mutation in the ALDH2 gene (the rs671 allele) yields an inactive form of ALDH2 that causes acetaldehyde accumulation in the body after alcohol consumption, thereby inhibiting normal alcohol metabolism. Individuals who are homozygous for polymorphism in ALDH2 tend to refrain from drinking alcohol, decreasing their chances of developing alcoholism and exposure to the associated risks. Mendelian randomization (MR) studies have demonstrated that alcohol consumption predicted by ALDH2 genotype is causally related to cardiovascular risks. Moreover, recent MR studies suggest that the ALDH2 variant has mechanistic effects on some disease outcomes or mortality through increased blood levels of acetaldehyde, showing differences therein between heterozygotes (ALDH2*2*2) and homozygotes (ALDH2*1*2) in those who consume alcohol. Accordingly, consideration of ALDH2 genotype in alcohol prevention programs is warranted. In conclusion, strategies that incorporate genetic information and provide an evidential basis from which to help people make informed decisions on alcohol consumption are urgently required.

Wuweizi protects against liver cirrhosis by promoting endogenous stem cell proliferation

AIM: To investigate the mechanism for Wuweizi to treat liver cirrhosis.

METHODS: A rat model of liver cirrhosis was developed with CCl₄. Rats were randomly divided into five groups: three treatment groups [small dose Wuweizi group (A1), middle dose group (A2) and high dose group (A3)], a blank group (C) and a model group (M). Except group C, liver cirrhosis was induced in all other groups. Groups A1, A2 and A3 were given 1.0, 1.5 and 2.0 mg/200 g Wuweizi, respectively. After treatment, histopathology, liver function [aspartate transaminase (AST), alanine transaminase (ALT) and albumin (ALB)], hepatic fibrosis, stem cell proliferation, and the expression ofCK-18, ALB and α-fetoprotein (AFP) were assessed.

RESULTS: In the treatment groups, there was an improvement in the degree of hepatic fibrosis and the condition of liver cell degeneration and necrosis, as revealed by HE staining and Masson staining, and the liver fibrosis scores were different among each treatment group (P < 0.05). Compared with group M, the liver fibrosis score of group A2 was improved most obviously (P < 0.01). Immunohistochemistry analysis showed that the expression of CK-18, ALB and AFP was different between each treatment group (P < 0.05). By labeling liver tissue stem cells with BrdU, the proliferation and division of stem cells were observed through the method of "regional coexistence". Immunofluorescence analysis revealed that the expression of CK-18, ALB and AFP were different among each treatment group (P < 0.01), with group A2 having the most prominent expression (P < 0.01). Liver function was improved differently in each treatment group (P < 0.05). Compared with group M, AST and ALT were decreased most significantly and ALB increased most obviously in group A2 (P < 0.01).

CONCLUSION: Wuweizi has a protective effect on injured liver cells. Wuweizi could delay the process of liver cirrhosis via mechanisms possibly related to promoting the proliferation of endogenous stem cells.