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1.  Tryptophan in Alcoholism Treatment I:  Kynurenine Metabolites Inhibit the Rat Liver Mitochondrial Low Km Aldehyde Dehydrogenase Activity, Elevate Blood Acetaldehyde Concentration and Induce Aversion to Alcohol 
Aims: The aims were to provide proofs of mechanism and principle by establishing the ability of kynurenine metabolites to inhibit the liver mitochondrial low Km aldehyde dehydrogenase (ALDH) activity after administration and in vivo, and to induce aversion to alcohol. Methods: Kynurenic acid (KA), 3-hydroxykynurenine (3-HK) and 3-hydroxyanthranilic acid (3-HAA) were administered to normal male Wistar rats and ALDH activity was determined both in vitro in liver homogenates and in vivo (by measuring blood acetaldehyde following ethanol administration). Alcohol consumption was studied in an aversion model in rats and in alcohol-preferring C57 mice. Results: ALDH activity was significantly inhibited by all three metabolites by doses as small as 1 mg/kg body wt. Blood acetaldehyde accumulation after ethanol administration was strongly elevated by KA and 3-HK and to a lesser extent by 3-HAA. All three metabolites induced aversion to alcohol in rats and decreased alcohol preference in mice. Conclusions: The above kynurenine metabolites of tryptophan induce aversion to alcohol by inhibiting ALDH activity. An intellectual property covering the use of 3-HK and 3-HAA and derivatives thereof in the treatment of alcoholism by aversion awaits further development.
PMCID: PMC3196366  PMID: 21896552
2.  Eliciting the Low-Activity Aldehyde Dehydrogenase Asian Phenotype by an Antisense Mechanism Results in an Aversion to Ethanol 
A mutation in the gene encoding for the liver mitochondrial aldehyde dehydrogenase (ALDH2–2), present in some Asian populations, lowers or abolishes the activity of this enzyme and results in elevations in blood acetaldehyde upon ethanol consumption, a phenotype that greatly protects against alcohol abuse and alcoholism. We have determined whether the administration of antisense phosphorothioate oligonucleotides (ASOs) can mimic the low-activity ALDH2–2 Asian phenotype. Rat hepatoma cells incubated for 24 h with an antisense oligonucleotide (ASO-9) showed reductions in ALDH2 mRNA levels of 85% and ALDH2 (half-life of 22 h) activity of 55% equivalent to a >90% inhibition in ALDH2 synthesis. Glutamate dehydrogenase mRNA and activity remained unchanged. Base mismatches in the oligonucleotide rendered ASO-9 virtually inactive, confirming an antisense effect. Administration of ASO-9 (20 mg/kg/day for 4 d) to rats resulted in a 50% reduction in liver ALDH2 mRNA, a 40% inhibition in ALDH2 activity, and a fourfold (P < 0.001) increase in circulating plasma acetaldehyde levels after ethanol (1 g/kg) administration. Administration of ASO-9 to rats by osmotic pumps led to an aversion (−61%, P < 0.02) to ethanol. These studies provide a proof of principle that specific inhibition of gene expression can be used to mimic the protective effects afforded by the ALDH2–2 phenotype.
PMCID: PMC2195938  PMID: 11535626
alcoholism; disulfiram; ALDH2-2; acetaldehyde; treatment
3.  Gene specific modifications unravel ethanol and acetaldehyde actions 
Ethanol is metabolized into acetaldehyde mainly by the action of alcohol dehydrogenase in the liver, while mainly by the action of catalase in the brain. Aldehyde dehydrogenase-2 metabolizes acetaldehyde into acetate in both organs. Gene specific modifications reviewed here show that an increased liver generation of acetaldehyde (by transduction of a gene coding for a high-activity liver alcohol dehydrogenase ADH1*B2) leads to increased blood acetaldehyde levels and aversion to ethanol in animals. Similarly aversive is an increased acetaldehyde level resulting from the inhibition of liver aldehyde dehydrogenase-2 (ALDH2) synthesis (by an antisense coding gene against aldh2 mRNA). The situation is diametrically different when acetaldehyde is generated in the brain. When the brain ventral tegmental area (VTA) is endowed with an increased ability to generate acetaldehyde (by transfection of liver rADH) the reinforcing effects of ethanol are increased, while a highly specific inhibition of catalase synthesis (by transduction of a shRNA anti catalase mRNA) virtually abolishes the reinforcing effects of ethanol as seen by a complete abolition of ethanol intake in rats bred for generations as high ethanol drinkers. Data shows two divergent effects of increases in acetaldehyde generation: aversive in the periphery but reinforcing in the brain.
PMCID: PMC3703538  PMID: 23847486
alcohol dehydrogenase; catalase; aldehyde dehydrogenase; reinforcement; aversion
4.  Declinol, a Complex Containing Kudzu, Bitter Herbs (Gentian, Tangerine Peel) and Bupleurum, Significantly Reduced Alcohol Use Disorders Identification Test (AUDIT) Scores in Moderate to Heavy Drinkers: A Pilot Study 
It is well established that inherited human aldehyde dehydrogenase 2 (ALDH-2) deficiency reduces the risk for alcoholism. Kudzu plants and extracts have been used for 1,000 years in traditional Chinese medicine to treat alcoholism. Kudzu contains daidzin, which inhibits ALDH-2 and suppresses heavy drinking in rodents. Decreased drinking due to ALDH-2 inhibition is attributed to aversive properties of acetaldehyde accumulated during alcohol consumption. However not all of the anti-alcohol properties of diadzin are due to inhibition of ALDH-2. This is in agreement with our earlier work showing significant interaction effects of both pyrozole (ALDH-2 inhibitor) and methyl-pyrozole (non-inhibitor) and ethanol’s depressant effects. Moreover, it has been suggested that selective ALDH 2 inhibitors reduce craving for alcohol by increasing dopamine in the nucleus accumbens (NAc). In addition there is significant evidence related to the role of the genetics of bitter receptors (TAS2R) and its stimulation as an aversive mechanism against alcohol intake. The inclusion of bitters such as Gentian & Tangerine Peel in Declinol provides stimulation of gut TAS2R receptors which is potentially synergistic with the effects of Kudzu. Finally the addition of Radix Bupleuri in the Declinol formula may have some protective benefits not only in terms of ethanol induced liver toxicity but neurochemical actions involving endorphins, dopamine and epinephrine. With this information as a rationale, we report herein that this combination significantly reduced Alcohol Use Disorders Identification Test (AUDIT) scores administered to ten heavy drinkers (M=8, F=2; 43.2 ± 14.6 years) attending a recovery program. Specifically, from the pre-post comparison of the AUD scores, it was found that the score of every participant decreased after the intervention which ranged from 1 to 31. The decrease in the scores was found to be statistically significant with the p-value of 0.00298 (two-sided paired test; p-value = 0.00149 for one-sided test). Albeit this being a small pilot, we are encouraged about these significant results, and caution any interpretation until larger controlled studies are executed.
PMCID: PMC3835486  PMID: 24273684
Declinol; Kudzu; Daidzin; ALDH 2 inhibitors; Dopamine; Gentian and tangerine peel; Radix burpleuri; Alcoholism and reward deficiency
5.  Aldehyde dehydrogenase 2 deficiency ameliorates alcoholic fatty liver but worsens liver inflammation and fibrosis in mice 
Hepatology (Baltimore, Md.)  2014;60(1):146-157.
Aldehyde dehydrogenase 2 (ALDH2) is the major enzyme that metabolizes acetaldehyde produced from alcohol metabolism. Approximately 40~50% of East Asians carry an inactive ALDH2 gene and exhibit acetaldehyde accumulation after alcohol consumption. However, the role of ALDH2 deficiency in the pathogenesis of alcoholic liver injury remains obscure. In the present study, wild-type and ALDH2−/− mice were subjected to ethanol feeding and/or carbon tetrachloride (CCl4) treatment, and liver injury was assessed. Compared with wild-type mice, ethanol-fed ALDH2−/− mice had higher levels of malondialdehyde-acetaldehyde (MAA) adduct and greater hepatic inflammation, with higher hepatic IL-6 expression but surprisingly lower levels of steatosis and serum ALT. Higher IL-6 levels were also detected in ethanol-treated precision-cut-liver-slices from ALDH2−/− mice and in Kupffer cells isolated from ethanol-fed ALDH2−/− mice than those levels in wild-type mice. In vitro incubation with MAA enhanced the LPS-mediated stimulation of IL-6 production in Kupffer cells. In agreement with these findings, hepatic activation of the major IL-6 downstream signaling molecule signal transducer and activator of transcription 3 (STAT3) was higher in ethanol-fed ALDH2−/− mice than in wild-type mice. An additional deletion of hepatic STAT3 increased steatosis and hepatocellular damage in ALDH2−/− mice. Finally, ethanol-fed ALDH2−/− mice were more prone to CCl4-induced liver inflammation and fibrosis than ethanol-fed wild-type mice.
ALDH2−/− mice are resistant to ethanol-induced steatosis but prone to inflammation and fibrosis via MAA-mediated paracrine activation of IL-6 in Kupffer cells. These findings suggest that alcohol, via acetaldehyde and its associated adducts, stimulates hepatic inflammation and fibrosis independent from causing hepatocyte death, and that ALDH2-deficient individuals may be resistant to steatosis and blood ALT elevation, but are prone to liver inflammation and fibrosis following alcohol consumption.
PMCID: PMC4077916  PMID: 24492981
Acetaldehyde; ALDH2; ethanol; fibrosis; inflammation; IL-6; STAT3
6.  Effects of ALDH2 Genotype, PPI Treatment and L-Cysteine on Carcinogenic Acetaldehyde in Gastric Juice and Saliva after Intragastric Alcohol Administration 
PLoS ONE  2015;10(4):e0120397.
Acetaldehyde (ACH) associated with alcoholic beverages is Group 1 carcinogen to humans (IARC/WHO). Aldehyde dehydrogenase (ALDH2), a major ACH eliminating enzyme, is genetically deficient in 30–50% of Eastern Asians. In alcohol drinkers, ALDH2-deficiency is a well-known risk factor for upper aerodigestive tract cancers, i.e., head and neck cancer and esophageal cancer. However, there is only a limited evidence for stomach cancer. In this study we demonstrated for the first time that ALDH2 deficiency results in markedly increased exposure of the gastric mucosa to acetaldehyde after intragastric administration of alcohol. Our finding provides concrete evidence for a causal relationship between acetaldehyde and gastric carcinogenesis. A plausible explanation is the gastric first pass metabolism of ethanol. The gastric mucosa expresses alcohol dehydrogenase (ADH) enzymes catalyzing the oxidation of ethanol to acetaldehyde, especially at the high ethanol concentrations prevailing in the stomach after the consumption of alcoholic beverages. The gastric mucosa also possesses the acetaldehyde-eliminating ALDH2 enzyme. Due to decreased mucosal ALDH2 activity, the elimination of ethanol-derived acetaldehyde is decreased, which results in its accumulation in the gastric juice. We also demonstrate that ALDH2 deficiency, proton pump inhibitor (PPI) treatment, and L-cysteine cause independent changes in gastric juice and salivary acetaldehyde levels, indicating that intragastric acetaldehyde is locally regulated by gastric mucosal ADH and ALDH2 enzymes, and by oral microbes colonizing an achlorhydric stomach. Markedly elevated acetaldehyde levels were also found at low intragastric ethanol concentrations corresponding to the ethanol levels of many foodstuffs, beverages, and dairy products produced by fermentation. A capsule that slowly releases L-cysteine effectively eliminated acetaldehyde from the gastric juice of PPI-treated ALDH2-active and ALDH2-deficient subjects. These results provide entirely novel perspectives for the prevention of gastric cancer, especially in established risk groups.
PMCID: PMC4382225  PMID: 25831092
7.  Impairment of aldehyde dehydrogenase 2 increases accumulation of acetaldehyde-derived DNA damage in the esophagus after ethanol ingestion 
Ethanol and its metabolite, acetaldehyde, are the definite carcinogens for esophageal squamous cell carcinoma (ESCC), and reduced catalytic activity of aldehyde dehydrogenase 2 (ALDH2), which detoxifies acetaldehyde, increases the risk for ESCC. However, it remains unknown whether the ALDH2 genotype influences the level of acetaldehyde-derived DNA damage in the esophagus after ethanol ingestion. In the present study, we administered ethanol orally or intraperitoneally to Aldh2-knockout and control mice, and we quantified the level of acetaldehyde-derived DNA damage, especially N2-ethylidene-2’-deoxyguanosine (N2-ethylidene-dG), in the esophagus. In the model of oral ethanol administration, the esophageal N2-ethylidene-dG level was significantly higher in Aldh2-knockout mice compared with control mice. Similarly, in the model of intraperitoneal ethanol administration, in which the esophagus is not exposed directly to the alcohol solution, the esophageal N2-ethylidene-dG level was also elevated in Aldh2-knockout mice. This result indicates that circulating ethanol-derived acetaldehyde causes esophageal DNA damage, and that the extent of damage is influenced by knockout of Aldh2. Taken together, our findings strongly suggest the importance of acetaldehyde-derived DNA damage which is induced in the esophagus of individuals with ALDH2 gene impairment. This provides a physiological basis for understanding alcohol-related esophageal carcinogenesis.
PMCID: PMC4065408  PMID: 24959382
Carcinogenesis; esophageal squamous cell carcinoma; acetaldehyde; acetaldehyde-derived DNA damage; DNA adduct
8.  Post-translational modifications of mitochondrial aldehyde dehydrogenase and biomedical implications 
Journal of proteomics  2011;74(12):2691-2702.
Aldehyde dehydrogenases (ALDHs) represent large family members of NAD(P)+-dependent dehydrogenases responsible for the irreversible metabolism of many endogenous and exogenous aldehydes to the corresponding acids. Among 19 ALDH isozymes, mitochondrial ALDH2 is a low Km enzyme responsible for the metabolism of acetaldehyde and lipid peroxides such as malondialdehyde and 4-hydroxynonenal, both of which are highly reactive and toxic. Consequently, inhibition of ALDH2 would lead to elevated levels of acetaldehyde and other reactive lipid peroxides following ethanol intake and/or exposure to toxic chemicals. In addition, many East Asian people with a dominant negative mutation in ALDH2 gene possess a decreased ALDH2 activity with increased risks for various types of cancer, myocardial infarct, alcoholic liver disease, and other pathological conditions. The aim of this review is to briefly describe the multiple post-translational modifications of mitochondrial ALDH2, as an example, after exposure to toxic chemicals or under different disease states and their pathophysiological roles in promoting alcohol/drug-mediated tissue damage. We also briefly mention exciting preclinical translational research opportunities to identify small molecule activators of ALDH2 and its isozymes as potentially therapeutic/preventive agents against various disease states where the expression or activity of ALDH enzymes is altered or inactivated.
PMCID: PMC3177986  PMID: 21609791
Aldehyde dehydrogenases; post-translational modifications; cellular defense; drug toxicity; disease states; translational research
9.  Aldehyde Dehydrogenase 2 Knockout Accentuates Ethanol-Induced Cardiac Depression: Role of Protein Phosphatases 
Alcohol consumption leads to myocardial contractile dysfunction possibly due to the toxicity of ethanol and its major metabolite acetaldehyde. This study was designed to examine the influence of mitochondrial aldehyde dehydrogenase-2 (ALDH2) knockout (KO) on acute ethanol exposure-induced cardiomyocyte dysfunction. Wild-type (WT) and ALDH2 KO mice were subjected to acute ethanol (3 g/kg, i.p.) challenge and cardiomyocyte contractile function was assessed 24 hrs later using an IonOptix® edge-detection system. Western blot analysis was performed to evaluate ALDH2, protein phosphatase 2A (PP2A), phosphorylation of Akt and glycogen synthase kinase-3β (GSK-3β). ALDH2 KO accentuated ethanol-induced elevation in cardiac acetaldehyde levels. Ethanol exposure depressed cardiomyocyte contractile function including decreased cell shortening amplitude and maximal velocity of shortening/relengthening as well as prolonged relengthening duration and a greater decline in peak shortening in response to increasing stimulus frequency, the effect of which was significantly exaggerated by ALDH2 KO. ALDH2 KO also unmasked an ethanol-induced prolongation of shortening duration. In addition, short-term in vitro incubation of ethanol-induced cardiomyocyte mechanical defects were exacerbated by the ALDH inhibitor cyanamide. Ethanol treatment dampened phosphorylation of Akt and GSK-3β associated with up-regulated PP2A, which was accentuated by ALDH2 KO. ALDH2 KO aggravated ethanol-induced decrease in mitochondrial membrane potential. These results suggested that ALDH2 deficiency led to worsened ethanol-induced cardiomyocyte function, possibly due to upregulated expression of protein phosphatase, depressed Akt activation and subsequently impaired mitochondrial function. These findings depict a critical role of ALDH2 in the pathogenesis of alcoholic cardiomyopathy.
PMCID: PMC2885537  PMID: 20362583
Ethanol; ALDH2; Cardiomyocyte; Contractile function; Akt; Protein phosphatase
10.  Reduction of Ethanol Consumption in Alcohol-Preferring Rats by Dual Expression Gene Transfer 
Aims: To mimic, in an animal model of alcoholism, the protective phenotype against alcohol consumption observed in humans carrying a fast alcohol dehydrogenase (ADH1B*2) and an inactive aldehyde dehydrogenase (ALDH2*2). Methods: We developed a multiple expression cassette adenoviral vector (AdV-ADH/asALDH2) encoding both a fast rat ADH and an antisense RNA against rat ALDH2. A control adenoviral vector (AdV-C) containing intronic non-coding DNA was also developed. These adenoviral vectors were administered intravenously to rats bred as high alcohol-drinkers (University of Chile bibulous) that were previously rendered alcohol dependent by a 75-day period of voluntary 10% ethanol intake. Results: Animals administered AdV-ADH/asALDH2 showed a 176% increase in liver ADH activity, whereas liver ALDH2 activity was reduced by 24%, and upon the administration of a dose of ethanol (1 g/kg, i.p.), these showed arterial acetaldehyde levels that were 400% higher than those of animals administered AdV-C. Rats that received the AdV-ADH/asALDH2 vector reduced by 60% their voluntary ethanol intake versus controls. Conclusion: This study provides evidence that the simultaneous increase of liver ADH and a reduction of ALDH activity by gene transfer could constitute a potential therapeutic strategy for the treatment of alcoholism.
PMCID: PMC3284687  PMID: 22214999
11.  Disulfiram Attenuates Drug-Primed Reinstatement of Cocaine Seeking via Inhibition of Dopamine β-Hydroxylase 
The anti-alcoholism medication disulfiram (Antabuse) inhibits aldehyde dehydrogenase (ALDH), which results in the accumulation of acetaldehyde upon ethanol ingestion and produces the aversive “Antabuse reaction” that deters alcohol consumption. Disulfiram has also been shown to deter cocaine use, even in the absence of an interaction with alcohol, indicating the existence of an ALDH-independent therapeutic mechanism. We hypothesized that disulfiram’s inhibition of dopamine β-hydroxylase (DBH), the catecholamine biosynthetic enzyme that converts dopamine (DA) to norepinephrine (NE) in noradrenergic neurons, underlies the drug’s ability to treat cocaine dependence. We tested the effects of disulfiram on cocaine and food self-administration behavior and drug-primed reinstatement of cocaine seeking in rats. We then compared the effects of disulfiram with those of the selective DBH inhibitor, nepicastat. Disulfiram, at a dose (100 mg/kg, i.p.) that reduced brain NE by ~40%, did not alter responding for food or cocaine on a fixed ratio 1 (FR1) schedule, whereas it completely blocked cocaine-primed (10 mg/kg, i.p.) reinstatement of drug seeking following extinction. A lower dose of disulfiram (10 mg/kg) that did not reduce NE had no effect on cocaine-primed reinstatement. Nepicastat recapitulated the behavioral effects of disulfiram (100 mg/kg) at a dose (50 mg/kg, i.p.) that produced a similar reduction in brain NE. Food-primed reinstatement of food seeking was not impaired by DBH inhibition. Our results suggest that disulfiram’s efficacy in the treatment of cocaine addiction is associated with the inhibition of DBH and interference with the ability of environmental stimuli to trigger relapse.
PMCID: PMC2956132  PMID: 20736996
dopamine β-hydroxylase; disulfiram; nepicastat; norepinephrine; cocaine; reinstatement
12.  Disulfiram Attenuates Drug-Primed Reinstatement of Cocaine Seeking via Inhibition of Dopamine β-Hydroxylase 
Neuropsychopharmacology  2010;35(12):2440-2449.
The antialcoholism medication disulfiram (Antabuse) inhibits aldehyde dehydrogenase (ALDH), which results in the accumulation of acetaldehyde upon ethanol ingestion and produces the aversive ‘Antabuse reaction' that deters alcohol consumption. Disulfiram has also been shown to deter cocaine use, even in the absence of an interaction with alcohol, indicating the existence of an ALDH-independent therapeutic mechanism. We hypothesized that disulfiram's inhibition of dopamine β-hydroxylase (DBH), the catecholamine biosynthetic enzyme that converts dopamine (DA) to norepinephrine (NE) in noradrenergic neurons, underlies the drug's ability to treat cocaine dependence. We tested the effects of disulfiram on cocaine and food self-administration behavior and drug-primed reinstatement of cocaine seeking in rats. We then compared the effects of disulfiram with those of the selective DBH inhibitor, nepicastat. Disulfiram, at a dose (100 mg/kg, i.p.) that reduced brain NE by ∼40%, did not alter the response for food or cocaine on a fixed ratio 1 schedule, whereas it completely blocked cocaine-primed (10 mg/kg, i.p.) reinstatement of drug seeking following extinction. A lower dose of disulfiram (10 mg/kg) that did not reduce NE had no effect on cocaine-primed reinstatement. Nepicastat recapitulated the behavioral effects of disulfiram (100 mg/kg) at a dose (50 mg/kg, i.p.) that produced a similar reduction in brain NE. Food-primed reinstatement of food seeking was not impaired by DBH inhibition. Our results suggest that disulfiram's efficacy in the treatment of cocaine addiction is associated with the inhibition of DBH and interference with the ability of environmental stimuli to trigger relapse.
PMCID: PMC2956132  PMID: 20736996
dopamine β-hydroxylase; disulfiram; nepicastat; norepinephrine; cocaine; reinstatement; addiction & substance abuse; catecholamines; psychostimulants; animal models; norepinephrine; cocaine; self-administration; rat
13.  Inactivation of cytosolic aldehyde dehydrogenase via-nitrosylation in ethanol-exposed rat liver 
FEBS letters  2007;581(21):3967-3972.
Aldehyde dehydrogenase (ALDH) isozymes are critically important in the metabolism of acetaldehyde, thus preventing its accumulation after ethanol exposure. We previously reported that mitochondrial ALDH2 could be inactivated via -nitrosylation in ethanol-exposed rats. This study was aimed at investigating whether cytosolic ALDH1, with a relatively low- value (11–18 μM) for acetaldehyde, could be also inhibited in ethanol-exposed rats. Chronic or binge ethanol exposure significantly decreased ALDH1 activity, which was restored by addition of dithiothreitol. Immunoblot analysis with the anti--nitroso-Cys antibody showed one immunoreactive band in the immunoprecipiated ALDH1 only from ethanol-exposed rats, but not from pair-fed controls, suggesting -nitrosylation of ALDH1. Therefore inactivation of ALDH1 via -nitrosylation can result in accumulation of acetaldehyde upon ethanol exposure.
PMCID: PMC2693367  PMID: 17673211
Cytosolic aldehyde dehydrogenase (ALDH1); Ethanol; S-nitrosylation; reversible inhibition; acetaldehyde metabolism
14.  Alcohol intake and folate antagonism via CYP2E1 and ALDH1: Effects on oral carcinogenesis 
Medical hypotheses  2011;78(2):197-202.
The interaction of folate and alcohol consumption has been shown to have an antagonistic effect on the risk of oral cancer. Studies have demonstrated that increased intake of folate decreases the risk of oral cancer, while greater alcohol consumption has an opposite effect. However, what is poorly understood is the biological interaction of these two dietary factors in relation to carcinogenesis. We hypothesize that cytochrome P450 2E1 (CYP2E1) and the family of aldehyde dehydrogenase 1 (ALDH1) enzymes may play a causal role in the occurrence of oral cancer. Chronic and high alcohol use has been implicated in the induction of CYP2E1, which oxidizes ethanol to acetaldehyde. Acetaldehyde is a known carcinogen. As the first metabolite of ethanol, it has been shown to interfere with DNA methylation, synthesis and repair, as well as bind to protein and DNA to form stable adducts, which lead to the eventual formation of damaged DNA and cell proliferation. Studies using liver cells have demonstrated that S-adenosyl methionine (SAM), which is a product of folate metabolism, regulates the expression and catalytic activity of CYP2E1. Our first hypothesis is that as increased levels of folate lead to higher concentrations of SAM, SAM antagonizes the expression of CYP2E1, which results in decreased conversion of ethanol into acetaldehyde. Thus, the lower levels of acetaldehyde may lower risk of oral cancer. There are also two enzymes within the ALDH1 family that play an important role both in ethanol metabolism and the folate one-carbon pathway. The first, ALDH1A1, converts acetaldehyde into its non-carcinogenic byproduct, acetate, as part of the second step in the ethanol metabolism pathway. The second, ALDH1L1, also known as FDH, is required for DNA nucleotide biosynthesis, and is upregulated at high concentrations of folate. ALDH1L1 appears to be a chief regulator of cellular metabolism as it is strongly downregulated at certain physiological and pathological conditions, while its upregulation can produce drastic antiproliferative effects. ALDH1 has three known response elements that regulate gene expression (NF-Y, C/EBPβ, and RARα). Our second hypothesis is that folate interacts with one of these response elements to upregulate ALDH1A1 and ALDH1L1 expression in order to decrease acetaldehyde concentrations and promote DNA stability, thereby decreasing cancer susceptibility. Conducting future metabolic and biochemical human studies in order to understand this biological mechanism will serve to support evidence from epidemiologic studies, and ultimately promote the intake of folate to at-risk populations.
PMCID: PMC3250228  PMID: 22100631
15.  Aldehyde dehydrogenase-2 regulates nociception in rodent models of acute inflammatory pain 
Science translational medicine  2014;6(251):251ra118.
Exogenous aldehydes can cause pain in animal models, suggesting that aldehyde dehydrogenase 2 (ALDH2), which metabolizes many aldehydes, may regulate nociception. To test this hypothesis, we generated a knock-in mouse with an inactivating point mutation in ALDH2 (ALDH2*2), which is also present in human ALDH2 of ~540 million East Asians. The ALDH2*1/*2 heterozygotic mice exhibited a larger response to painful stimuli than their wild-type littermates, and this heightened nociception was inhibited by an ALDH2-selective activator (Alda-1). No effect on inflammation per se was observed. Using a rat model, we then showed that nociception tightly correlated with ALDH activity (R2=0.90) and that reduced nociception was associated with less early growth response protein 1 (EGR1) in the spinal cord and less reactive aldehyde accumulation at the insult site (including acetaldehyde and 4-hydroxynonenal). Further, acetaldehyde and formalin-induced nociceptive behavior was greater in the ALDH2*1/*2 mice than wild-type mice. Finally, Alda-1 treatment was also beneficial when given even after the inflammatory agent was administered. Our data in rodent models suggest that the mitochondrial enzyme ALDH2 regulates nociception and could serve as a molecular target for pain control, with ALDH2 activators, such as Alda-1, as potential non-narcotic cardiac-safe analgesics. Furthermore, our results suggest a possible genetic basis for East Asians’ apparent lower pain tolerance.
PMCID: PMC4234033  PMID: 25163478
16.  Aldehyde Dehydrogenase-2 Transgene Ameliorates Chronic Alcohol Ingestion-Induced Apoptosis in Cerebral Cortex 
Toxicology letters  2009;187(3):149-156.
Chronic intake of alcohol results in multiple organ damage including brain. This study was designed to examine the impact of facilitated acetaldehyde breakdown via transgenic overexpression of mitochondrial aldehyde dehydrogenase-2 (ALDH2) on alcohol-induced cerebral cortical injury. ALDH2 transgenic mice were produced using the chicken β-actin promoter. Wild-type FVB and ALDH2 mice were placed on a 4% alcohol or control diet for 12 wks. Protein damage and apoptosis were evaluated with carbonyl formation, caspase and TUNEL assays. Western blot was performed to examine expression (or its activation) of ALDH2, the pro- and anti-apoptotic proteins Caspase-8, Bax, Bcl-2, Omi/HtrA2, apoptosis repressor with caspase recruitment domain (ARC), FLICE-like Inhibitory Protein (FLIP), X-linked inhibitor of apoptosis protein (XIAP), Akt, glycogen synthase kinase-3β (GSK-3β), p38, c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK). Chronic alcohol intake led to elevated apoptosis in the absence of overt protein damage, the effect of which was ablated by the overexpression of ALDH2 transgene. Consistently, ALDH2 transgene significantly attenuated alcohol-induced upregulation of Bax, Omi/HtrA2 and XIAP as well as downregulation of Bcl-2 and ARC without affecting alcohol-induced increase of FLIP in cerebral cortex. Phosphorylation of Akt and GSK-3β was dampened while total/phosphorylated JNK and p38 phosphorylation were elevated following chronic alcohol intake, the effects of which were abrogated by ALDH2 transgene. Expression of total Akt, GSK-3β, p38 and ERK (total or phosphorylated) was not affected by either chronic alcohol intake or ALDH2 transgene. Our results suggested that transgenic overexpression of ALDH2 rescues chronic alcoholism-elicited cerebral injury possibly via a mechanism associated with Akt, GSK-3β, p38 and JNK signaling.
PMCID: PMC2680775  PMID: 19429258
Alcohol; ALDH2 transgene; cerebral cortex; cell injury
17.  Alcohol Intake and Blood Pressure: A Systematic Review Implementing a Mendelian Randomization Approach 
PLoS Medicine  2008;5(3):e52.
Alcohol has been reported to be a common and modifiable risk factor for hypertension. However, observational studies are subject to confounding by other behavioural and sociodemographic factors, while clinical trials are difficult to implement and have limited follow-up time. Mendelian randomization can provide robust evidence on the nature of this association by use of a common polymorphism in aldehyde dehydrogenase 2 (ALDH2) as a surrogate for measuring alcohol consumption. ALDH2 encodes a major enzyme involved in alcohol metabolism. Individuals homozygous for the null variant (*2*2) experience adverse symptoms when drinking alcohol and consequently drink considerably less alcohol than wild-type homozygotes (*1*1) or heterozygotes. We hypothesise that this polymorphism may influence the risk of hypertension by affecting alcohol drinking behaviour.
Methods and Findings
We carried out fixed effect meta-analyses of the ALDH2 genotype with blood pressure (five studies, n = 7,658) and hypertension (three studies, n = 4,219) using studies identified via systematic review. In males, we obtained an overall odds ratio of 2.42 (95% confidence interval [CI] 1.66–3.55, p = 4.8 × 10−6) for hypertension comparing *1*1 with *2*2 homozygotes and an odds ratio of 1.72 (95% CI 1.17–2.52, p = 0.006) comparing heterozygotes (surrogate for moderate drinkers) with *2*2 homozygotes. Systolic blood pressure was 7.44 mmHg (95% CI 5.39–9.49, p = 1.1 × 10−12) greater among *1*1 than among *2*2 homozygotes, and 4.24 mmHg (95% CI 2.18–6.31, p = 0.00005) greater among heterozygotes than among *2*2 homozygotes.
These findings support the hypothesis that alcohol intake has a marked effect on blood pressure and the risk of hypertension.
Using a mendelian randomization approach Sarah Lewis and colleagues find strong support for the hypothesis that alcohol intake has a marked effect on blood pressure and the risk of hypertension.
Editors' Summary
High blood pressure (hypertension) is a common medical condition that affects nearly a third of US and UK adults. Hypertension has no symptoms but can lead to heart attacks or strokes. It is diagnosed by measuring blood pressure—the force that blood moving around the body exerts on the inside of large blood vessels. Blood pressure is highest when the heart is pumping out blood (systolic pressure) and lowest when it is filling up with blood (diastolic pressure). Normal blood pressure is defined as a systolic pressure of less than 130 millimeters of mercury (mmHg) and a diastolic pressure of less than 85 mmHg (a blood pressure of 130/85). A reading of more than 140/90 indicates hypertension. Many factors affect blood pressure, but overweight people and individuals who eat too much salty or fatty foods are at high risk of developing hypertension. Mild hypertension can often be corrected by lifestyle changes, but many people also take antihypertensive drugs to reduce their blood pressure.
Why Was This Study Done?
Another modifiable lifestyle factor thought to affect blood pressure is alcohol intake. Observational studies that ask people about their drinking habits and measure their blood pressure suggest that alcohol intake correlates with blood pressure, but they cannot prove a causal link because of “confounding”—other risk factors associated with alcohol drinking, such as diet, might also affect the study participant's blood pressures. A trial that randomly assigns people to different alcohol intakes could provide this proof of causality, but such a trial is impractical. In this study, therefore, the researchers have used “Mendelian randomization” to investigate whether alcohol intake affects blood pressure. An inactive variant of aldehyde dehydrogenase 2 (ALDH2; the enzyme that removes alcohol from the body) has been identified. People who inherit the variant form of this gene from both parents have an ALDH2 *2*2 genotype (genetic makeup) and become flushed and nauseated after drinking. Consequently, they drink less than people with a *1*2 genotype and much less than those with a *1*1 genotype. Because inheritance of these genetic variants does not affect lifestyle factors other than alcohol intake, an association between ALDH2 genotypes and blood pressure would indicate that alcohol intake has an effect on blood pressure without any confounding.
What Did the Researchers Do and Find?
The researchers identified ten published studies (mainly done in Japan where the ALDH2 gene variant is common) on associations between ALDH2 genotype and blood pressure or hypertension using a detailed search protocol (a “systematic review”). A meta-analysis (a statistical method for combining the results of independent studies) of the studies that had investigated the association between ALDH2 genotype and hypertension showed that men with the *1*1 genotype (highest alcohol intake) and those with the *1*2 genotype (intermediate alcohol intake) were 2.42 and 1.72 times more likely, respectively, to have hypertension than those with the *2*2 genotype (lowest alcohol intake). There was no association between ALDH2 genotype and hypertension among the women in these studies because they drank very little. Systolic and diastolic blood pressures showed a similar relationship to ALDH2 genotype in a second meta-analysis of relevant studies. Finally, the researchers estimated that for men the lifetime effect of drinking 1 g of alcohol a day (one unit of alcohol contains 8 g of alcohol in the UK and 14 g in the US; recommended daily limits in these countries are 3–4 and 1–2 units, respectively) would be an increase in systolic blood pressure of 0.24 mmHg.
What Do These Findings Mean?
These findings support the suggestion that alcohol has a marked effect on blood pressure and hypertension. Consequently, some cases of hypertension could be prevented by encouraging people to reduce their daily alcohol intake. Although the Mendelian randomization approach avoids most of the confounding intrinsic to observational studies, it is possible that a gene near ALDH2 that has no effect on alcohol intake affects blood pressure, since genes are often inherited in blocks. Alternatively, ALDH2 could affect blood pressure independent of alcohol intake. The possibility that ALDH2 could effect blood pressure independently of alcohol is intake made unlikely by the fact that no effect of genotype on blood pressure is seen among women who drink very little. Additional large-scale studies are needed to address these possibilities, to confirm the current finding in more people, and to improve the estimates of the effect that alcohol intake has on blood pressure.
Additional Information.
Please access these Web sites via the online version of this summary at
The MedlinePlus encyclopedia has a page on hypertension (in English and Spanish)
The American Heart Association provides information for patients and health professionals about hypertension
The UK Blood Pressure Association provides information for patients and health professionals on all aspects of hypertension, including information about alcohol affects blood pressure
The Explore@Bristol science center (a UK charity) provides an alcohol unit calculator and information on the effects of alcohol
The International Center for Alcohol Policies provides drinking guidelines for countries around the world
PMCID: PMC2265305  PMID: 18318597
18.  Ethanol Metabolism by HeLa Cells Transduced with Human Alcohol Dehydrogenase Isoenzymes: Control of the Pathway by Acetaldehyde Concentration† 
Human class I alcohol dehydrogenase 2 isoenzymes (encoded by the ADH1B locus) have large differences in kinetic properties; however, individuals inheriting the alleles for the different isoenzymes exhibit only small differences in alcohol elimination rates. This suggests that other cellular factors must regulate the activity of the isoenzymes.
The activity of the isoenzymes expressed from ADH1B*1, ADH1B*2, and ADH1B*3 cDNAs was examined in stably transduced HeLa cell lines, including lines which expressed human low Km aldehyde dehydrogenase (ALDH2). The ability of the cells to metabolize ethanol was compared with that of HeLa cells expressing rat class I ADH (HeLa-rat ADH cells), rat hepatoma (H4IIEC3) cells, and rat hepatocytes.
The isoenzymes had similar protein half-lives in the HeLa cells. Rat hepatocytes, H4IIEC3 cells, and HeLa-rat ADH cells oxidized ethanol much faster than the cells expressing the ADH1B isoenzymes. This was not explained by high cellular NADH levels or endogenous inhibitors; but rather because the activity of the β1 and β2 ADHs were constrained by the accumulation of acetaldehyde, as shown by the increased rate of ethanol oxidation by cell lines expressing β2 ADH plus ALDH2.
The activity of the human β2 ADH isoenzyme is sensitive to inhibition by acetaldehyde, which likely limits its activity in vivo. This study emphasizes the importance of maintaining a low steady–state acetaldehyde concentration in hepatocytes during ethanol metabolism.
PMCID: PMC3059091  PMID: 21166830
ethanol elimination; product inhibition; acetaldehyde; protein half-life; enzyme kinetics
19.  Impaired acetaldehyde metabolism in patients with non-alcoholic liver disorders. 
Gut  1986;27(7):756-764.
In order to determine the specificity of abnormalities of alcohol metabolism in patients with alcoholic liver disease, blood acetaldehyde concentrations after oral ethanol challenge and the activities of alcohol metabolising enzymes in liver biopsy samples have been determined in patients with alcoholic liver disease and a wide variety of non-alcoholic liver disorders. Significant decreases in hepatic cytosolic aldehyde dehydrogenase activity were associated with significant increases in acetaldehyde concentrations after ethanol in both patient groups compared with control subjects. There was a significant correlation between hepatic cytosolic aldehyde dehydrogenase and mean blood acetaldehyde concentration 30-180 min after ethanol ingestion (y = 17.4-0.45x; r = -0.56; p less than 0.01) confirming the importance of this enzyme in controlling blood acetaldehyde concentrations. These findings suggest that disturbances in alcohol metabolism in patients with alcoholic liver disease are the consequence of liver damage rather than a specific abnormality predisposing to alcohol induced liver injury.
PMCID: PMC1433561  PMID: 3732886
20.  mTOR-STAT3-notch signalling contributes to ALDH2-induced protection against cardiac contractile dysfunction and autophagy under alcoholism 
Mitochondrial aldehyde dehydrogenase-2 (ALDH2) has been shown to benefit myopathic changes following alcohol intake, although the precise mechanism is still unclear. This study was designed to evaluate the role of ALDH2 on chronic alcohol intake-induced myocardial geometric and functional damage with a focus on autophagic signalling. Wild-type friendly virus B (FVB) and transgenic mice overexpressing ALDH2 driven by chicken β-actin promoter were fed a 4% alcohol liquid diet for 12 weeks. Cardiac geometry and function were assessed using echocardiographic and IonOptix systems. Western blot analysis was used to evaluate the essential autophagy markers, Akt and AMP-dependent protein kinase (AMPK) as well as their downstream signalling mammalian target of rapamycin (mTOR) and signal transducer and activator of transcription 3 (STAT3). Alcohol intake altered cardiac geometry and function as demonstrated by lessened LV wall and septal thickness, enlarged end systolic and diastolic diameters, decreased fractional shortening and cell shortening, the effects of which were mitigated by ALDH2 transgene. Chronic alcohol intake triggered myocardial autophagy as shown by LC3B II isoform switch, as well as decreased phosphorylation of mTOR, the effects of which were ablated by ALDH2. Chronic alcohol intake suppressed phosphorylation of Akt and AMPK, which was reconciled by ALDH2. Levels of Notch1 and STAT3 phosphorylation were dampened by chronic alcohol intake in FVB but not ALDH2 myocardium. Moreover, the γ-secretase Notch inhibitor N-[N-(3,5-difluorophenacetyl)-1-alany1]-S-phenyglycine t-butyl ester exacerbated ethanol-induced cardiomyocyte contractile dysfunction, apoptosis and autophagy. In summary, these findings suggested that ALDH2 elicits cardioprotection against chronic alcohol intake-induced cardiac geometric and functional anomalies by inhibition of autophagy possibly via restoring the Akt-mTOR-STAT3-Notch signalling cascade.
PMCID: PMC3202644  PMID: 21609394
alcohol; ALDH2; myocardial dysfunction; autophagy; Notch
21.  Drug Interaction Between Ethanol and 3,4-Methylenedioxymethamphetamine (“ecstasy”) 
Toxicology letters  2009;188(2):167-172.
Alcohol and MDMA (ecstasy) are frequently co-abused, but recent findings indicate a harmful drug interaction between these two agents. In our previous study, we showed that MDMA exposure inhibits the activity of the acetaldehyde (ACH) metabolizing enzyme, aldehyde dehydrogenase2 (ALDH2). Based on this finding, we hypothesized that the co-administration of MDMA and ethanol would reduce the metabolism of ACH and result in increased accumulation of ACH. Rats were treated with MDMA or vehicle and then administered a single dose of ethanol. Liver ALDH2 activity decreased by 35% in the MDMA-treated rats compared to control rats. The peak concentration and the area under the concentration versus time curve of plasma ACH was 31% and 59% higher, respectively, in the MDMA-ethanol group compared to the ethanol-only group. In addition, the MDMA-ethanol group had 80% higher plasma transaminase levels than the ethanol-only group, indicating greater hepatocellular damage. Our results not only support a drug interaction between MDMA and ethanol but a novel underlying mechanism for the interaction.
PMCID: PMC3596109  PMID: 19446252
alcohol; ethanol; 3,4-methylenedioxymethamphetamine (MDMA); ecstasy; metabolism; acetaldehyde; aldehyde dehydrogenase; drug interaction; liver toxicity; transaminase
22.  Alda-1 is an agonist and chemical chaperone for the common human aldehyde dehydrogenase 2 variant 
In approximately one billion people, a point mutation inactivates a key detoxifying enzyme, aldehyde dehydrogenase (ALDH2). This mitochondrial enzyme metabolizes toxic biogenic and environmental aldehydes, including the endogenously produced 4-hydroxynonenal (4HNE) and the environmental pollutant, acrolein. ALDH2 also bioactivates nitroglycerin, but it is best known for its role in ethanol metabolism. The accumulation of acetaldehyde following the consumption of even a single alcoholic beverage leads to the Asian Alcohol-induced Flushing Syndrome in ALDH2*2 homozygotes. The ALDH2*2 allele is semi-dominant and heterozygotic individuals exhibit a similar, but not as severe phenotype. We recently identified a small molecule, Alda-1, which activates wild-type ALDH2 and restores near wild-type activity to ALDH2*2. The structures of Alda-1 bound to ALDH2 and ALDH2*2 reveal how Alda-1 activates the wild-type enzyme and how it restores the activity of ALDH2*2 by acting as a structural chaperone.
PMCID: PMC2857674  PMID: 20062057
23.  Effect of alcohol and aldehyde dehydrogenase gene polymorphisms on alcohol-associated hypertension: the Guangzhou Biobank Cohort Study 
Hypertension Research  2013;36(8):741-746.
The effects of alcohol dehydrogenase (ADH) 2 and aldehyde dehydrogenase (ALDH) 2 genotypes on the alcohol–blood pressure association are unclear. We examined the association of ADH2 or ALDH2 genotypes with blood pressure in older Chinese men. Based on the Guangzhou Biobank Cohort Study (GBCS), 4792 men with valid ADH2, ALDH2 genotypes were included, and genotyping of rs1229984 ADH2 and rs671 ALDH2 (AA, AG/GA or GG) was performed using a Sequenom Mass-Array platform. Information on socio-demographics and lifestyle factors, including alcohol use, was obtained from a questionnaire, and blood pressure was measured. Among alcohol drinkers, systolic and diastolic blood pressure (SBP and DBP) and mean arterial pressure (MAP) were highest for men with the GG ADH2 genotype (136.6, 77.9 and 97.5 mm Hg, respectively), followed by those with the (AA/AG ADH2+GG ALDH2) genotype (133.4, 77.6 and 96.2 mm Hg, respectively) and then the (AA/AG ADH2+AA/AG ALDH2) genotype (SBP=132.6, DBP=76.6 and MAP=95.2 mm Hg) (P for trend ranged 0.025–0.035). After adjustment for potential confounders, as well as frequency or amount of alcohol use, men with the GG ADH2 genotype were more likely to have hypertension (odds ratio (OR)=1.62, 95% confidence interval 1.15–2.28) as were men with the (AA/AG ADH2+AA/AG ALDH2) genotype (OR=1.40, 95% confidence interval 1.01–1.96) compared with men with the (AA/AG ADH2+GG ALDH2) genotype). ADH2 or ALDH2 genotypes were unrelated to hypertension among those who never drink alcohol. ADH2 genotype influences blood pressure and risk of hypertension among male alcohol drinkers, suggesting that the hypertensive effect of alcohol is due to ethanol rather than acetaldehyde.
PMCID: PMC3734527  PMID: 23615284
alcohol; aldehyde dehydrogenase gene polymorphisms; blood pressure
24.  Refined Geographic Distribution of the Oriental ALDH2*504Lys (nee 487Lys) Variant 
Annals of human genetics  2009;73(Pt 3):335-345.
Mitochondrial aldehyde dehydrogenase (ALDH2) is one of the most important enzymes in human alcohol metabolism. The oriental ALDH2*504Lys variant functions as a dominant negative greatly reducing activity in heterozygotes and abolishing activity in homozygotes. This allele is associated with serious disorders such as alcohol liver disease, late onset Alzheimer disease, colorectal cancer, and esophageal cancer, and is best known for protection against alcoholism. Many hundreds of papers in various languages have been published on this variant, providing allele frequency data for many different populations. To develop a highly refined global geographic distribution of ALDH2*504Lys, we have collected new data on 4,091 individuals from 86 population samples and assembled published data on a total of 80,691 individuals from 366 population samples. The allele is essentially absent in all parts of the world except East Asia. The ALDH2*504Lys allele has its highest frequency in Southeast China, and occurs in most areas of China, Japan, Korea, Mongolia, and Indochina with frequencies gradually declining radially from Southeast China. As the indigenous populations in South China have much lower frequencies than the southern Han migrants from Central China, we conclude that ALDH2*504Lys was carried by Han Chinese as they spread throughout East Asia. Esophageal cancer, with its highest incidence in East Asia, may be associated with ALDH2*504Lys because of a toxic effect of increased acetaldehyde in the tissue where ingested ethanol has its highest concentration. While the distributions of esophageal cancer and ALDH2*504Lys do not precisely correlate, that does not disprove the hypothesis. In general the study of fine scale geographic distributions of ALDH2*504Lys and diseases may help in understanding the multiple relationships among genes, diseases, environments, and cultures.
PMCID: PMC2846302  PMID: 19456322
East Asia; aldehyde dehydrogenase 2; alcohol associated; allele frequency; esophageal cancer
25.  Possible mechanism of adverse reaction following levodopa plus benserazide treatment. 
1 Rats treated for seven days with seryl-trihydroxybenzylhydrazine (benserazide), and inhibitor of peripheral aromatic L-amino acid decarboxylase (500 mg/kg, daily, i.p.) alone or in combination with L-DOPA methylester (500 mg/kg, daily, i.p.) for seven days showed a moderate but significant decrease of liver aldehyde dehydrogenase (ALDH), without accompanying change in alcohol dehydrogenase (ADH) activity, compared with saline-treated controls. 2 Administration of L-DOPA methylester (500 mg/kg, daily, i.p.) alone for seven days had little effect on liver ADH or ALDH. 3. The combined treatment might be conducive to the in vivo formation of L-DOPA-derived tetrahydroisoquinoline derivatives which might be implicated in L-DOPA produced adverse effects.
PMCID: PMC1667174  PMID: 884390

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