ALDH2 in alcoholic heart diseases: molecular mechanism and clinical implications

Lipids and Oxidative Stress Associated with Ethanol-Induced Neurological Damage

The excessive intake of alcohol is a serious public health problem, especially given the severe damage provoked by chronic or prenatal exposure to alcohol that affects many physiological processes, such as memory, motor function, and cognitive abilities. This damage is related to the ethanol oxidation in the brain. The metabolism of ethanol to acetaldehyde and then to acetate is associated with the production of reactive oxygen species that accentuate the oxidative state of cells. This metabolism of ethanol can induce the oxidation of the fatty acids in phospholipids, and the bioactive aldehydes produced are known to be associated with neurotoxicity and neurodegeneration. As such, here we will review the role of lipids in the neuronal damage induced by ethanol-related oxidative stress and the role that lipids play in the related compensatory or defense mechanisms.

Mitochondrial aldehyde dehydrogenase protects against doxorubicin cardiotoxicity through a transient receptor potential channel vanilloid 1-mediated mechanism

Cardiotoxicity is one of the major life-threatening effects encountered in cancer chemotherapy with doxorubicin and other anthracyclines. Mitochondrial aldehyde dehydrogenase (ALDH2) may alleviate doxorubicin toxicity although the mechanism remains elusive. This study was designed to evaluate the impact of ALDH2 overexpression on doxorubicin-induced myocardial damage with a focus on mitochondrial injury. Wild-type (WT) and transgenic mice overexpressing ALDH2 driven by chicken β-actin promoter were challenged with doxorubicin (15mg/kg, single i.p. injection, for 6days) and cardiac mechanical function was assessed using the echocardiographic and IonOptix systems. Western blot analysis was used to evaluate intracellular Ca(2+) regulatory and mitochondrial proteins, PKA and its downstream signal eNOS. Doxorubicin challenge altered cardiac geometry and function evidenced by enlarged left ventricular end systolic and diastolic diameters, decreased factional shortening, cell shortening and intracellular Ca(2+) rise, prolonged relengthening and intracellular Ca(2+) decay, the effects of which were attenuated by ALDH2. Doxorubicin challenge compromised mitochondrial integrity and upregulated 4-HNE and UCP-2 levels while downregulating levels of TRPV1, SERCA2a and PGC-1α, the effects of which were alleviated by ALDH2. Doxorubicin-induced cardiac functional defect and apoptosis were reversed by the TRPV1 agonist SA13353 and the ALDH-2 agonist Alda-1 whereas the TRPV1 antagonist capsazepine nullified ALDH2/Alda-1-induced protection. Doxorubicin suppressed phosphorylation of PKA and eNOS, the effect of which was reversed by ALDH2. Moreover, 4-HNE mimicked doxorubicin-induced cardiomyocyte anomalies, the effect of which was ablated by SA13353. Taken together, our results suggested that ALDH2 may rescue against doxorubicin cardiac toxicity possibly through a TRPV1-mediated protection of mitochondrial integrity.

Increased Expression of Aldehyde Dehydrogenase 2 Reduces Renal Cell Apoptosis During Ischemia/Reperfusion Injury After Hypothermic Machine Perfusion

Hypothermic machine perfusion (MP) can reduce graft's injury after kidney transplantation; however, the mechanism has not been elucidated. In the past decade, many studies showed that aldehyde dehydrogenase 2 (ALDH2) is a protease which can inhibit cell apoptosis. Therefore, this study aims to explore whether ALDH2 takes part in reducing organ damage after MP. Eighteen healthy male New Zealand rabbits (12 weeks old, weight 3.0 ± 0.3 kg) were randomly divided into three groups: normal group, MP group, and cold storage (CS) group (n = 6). The left kidney of rabbits underwent warm ischemia for 35 min through clamping the left renal pedicle and then reperfusion for 1 h. Left kidneys were preserved by MP or CS (4°C for 4 h) in vivo followed by the right nephrectomy and 24-h reperfusion, and then the specimens and blood were collected. Finally, concentration of urine creatinine (Cr), blood urea nitrogen (BUN), and 4-HNE were tested. Renal apoptosis was detected by TUNEL staining, and the expression of ALDH2, cleaved-caspase 3, bcl-2/ bax, MAPK in renal tissue was detected by immunohistochemistry or Western blot; 24 h after surgery, the concentration of Cr in MP group was 355 ± 71μmol/L, in CS group was 511 ± 44 μmol/L (P < 0.05), while the BUN was 15.02 ± 2.34 mmol/L in MP group, 22.64 ± 3.58 mmol/L in CS group (P < 0.05). The rate of apoptosis and expression of cleaved caspase-3, p-P38, p-ERK, and p-JNK in MP group was significantly lower than that in CS group (P < 0.05), while expression of ALDH2 and bcl-2/bax in MP group was significantly higher than that in CS group (P < 0.05); expression of cleaved caspase-3 in both MP and CS group significantly increased as compared with that in normal group (P < 0.05). In conclusion, increased expression of ALDH2 can reduce the renal cell apoptosis through inhibiting MAPK pathway during ischemia/reperfusion injury (IRI) after hypothermic MP.

Glu504Lys Single Nucleotide Polymorphism of Aldehyde Dehydrogenase 2 Gene and the Risk of Human Diseases

Aldehyde dehydrogenase (ALDH) 2 is a mitochondrial enzyme that is known for its important role in oxidation and detoxification of ethanol metabolite acetaldehyde. ALDH2 also metabolizes other reactive aldehydes such as 4-hydroxy-2-nonenal and acrolein. The Glu504Lys single nucleotide polymorphism (SNP) of ALDH2 gene, which is found in approximately 40% of the East Asian populations, causes defect in the enzyme activity of ALDH2, leading to alterations in acetaldehyde metabolism and alcohol-induced "flushing" syndrome. Evidence suggests that ALDH2 Glu504Lys SNP is a potential candidate genetic risk factor for a variety of chronic diseases such as cardiovascular disease, cancer, and late-onset Alzheimer's disease. In addition, the association between ALDH2 Glu504Lys SNP and the development of these chronic diseases appears to be affected by the interaction between the SNP and lifestyle factors such as alcohol consumption as well as by the presence of other genetic variations.

Translational Implications of the Alcohol-Metabolizing Enzymes, Including Cytochrome P450-2E1, in Alcoholic and Nonalcoholic Liver Disease

Fat accumulation (hepatic steatosis) in alcoholic and nonalcoholic fatty liver disease is a potentially pathologic condition which can progress to steatohepatitis (inflammation), fibrosis, cirrhosis, and carcinogenesis. Many clinically used drugs or some alternative medicine compounds are also known to cause drug-induced liver injury, which can further lead to fulminant liver failure and acute deaths in extreme cases. During liver disease process, certain cytochromes P450 such as the ethanol-inducible cytochrome P450-2E1 (CYP2E1) and CYP4A isozymes can be induced and/or activated by alcohol and/or high-fat diets and pathophysiological conditions such as fasting, obesity, and diabetes. Activation of these P450 isozymes, involved in the metabolism of ethanol, fatty acids, and various drugs, can produce reactive oxygen/nitrogen species directly and/or indirectly, contributing to oxidative modifications of DNA/RNA, proteins and lipids. In addition, aldehyde dehydrogenases including the mitochondrial low Km aldehyde dehydrogenase-2 (ALDH2), responsible for the metabolism of acetaldehyde and lipid aldehydes, can be inactivated by various hepatotoxic agents. These highly reactive acetaldehyde and lipid peroxides, accumulated due to ALDH2 suppression, can interact with cellular macromolecules DNA/RNA, lipids, and proteins, leading to suppression of their normal function, contributing to DNA mutations, endoplasmic reticulum stress, mitochondrial dysfunction, steatosis, and cell death. In this chapter, we specifically review the roles of the alcohol-metabolizing enzymes including the alcohol dehydrogenase, ALDH2, CYP2E1, and other enzymes in promoting liver disease. We also discuss translational research opportunities with natural and/or synthetic antioxidants, which can prevent or delay the onset of inflammation and liver disease.

Acetaldehyde dehydrogenase 2 (ALDH2) deficiency exacerbates pressure overload-induced cardiac dysfunction by inhibiting Beclin-1 dependent autophagy pathway

Mitochondrial aldehyde dehydrogenase 2 (ALDH2) was demonstrated to play cardioprotective roles in cardiovascular diseases. Nonetheless, little is known about the roles and mechanisms of ALDH2 in pressure overload-induced cardiac damages. In this study, we revealed that ALDH2 deficiency overtly exacerbated transverse aortic constriction (TAC)-induced cardiac dysfunction. Cardiomyocyte enlargement was observed in both WT and ALDH2-/- mice in HE-stained myocardial tissue samples at 8 weeks post TAC surgery. Mitochondrial morphology and structure were also significantly damaged post TAC surgery and the changes were aggravated in ALDH2-/- TAC hearts. ALDH2 deficiency also depressed myocardial autophagy in hearts at 8 weeks post TAC surgery with a potential mechanism of repressing the expression of Beclin-1 and promoting the interaction between Bcl-2 and Beclin-1. These data indicate that ALDH2 deficiency exacerbates the pressure overload induced cardiac dysfunction partly by inhibiting Beclin-1 dependent autophagy pathway. This article is part of a Special Issue entitled: Autophagy and protein quality control in cardiometabolic diseases.

Mitochondrial aldehyde dehydrogenase 2 accentuates aging-induced cardiac remodeling and contractile dysfunction: role of AMPK, Sirt1, and mitochondrial function

Cardiac aging is associated with compromised myocardial function and morphology although the underlying mechanism remains elusive. Aldehyde dehydrogenase 2 (ALDH2), an essential mitochondrial enzyme governing cardiac function, displays polymorphism in humans. This study was designed to examine the role of ALDH2 in aging-induced myocardial anomalies. Myocardial mechanical and intracellular Ca(2+) properties were examined in young (4-5 months) and old (26-28 months) wild-type and ALDH2 transgenic mice. Cardiac histology, mitochondrial integrity, O2(-) generation, apoptosis, and signaling cascades, including AMPK activation and Sirt1 level were evaluated. Myocardial function and intracellular Ca(2+) handling were compromised with advanced aging; the effects were accentuated by ALDH2. Hematoxylin and eosin and Masson trichrome staining revealed cardiac hypertrophy and interstitial fibrosis associated with greater left-ventricular mass and wall thickness in aged mice. ALDH2 accentuated aging-induced cardiac hypertrophy but not fibrosis. Aging promoted O2(-) release, apoptosis, and mitochondrial injury (mitochondrial membrane potential, levels of UCP-2 and PGC-1α), and the effects were also exacerbated by ALDH2. Aging dampened AMPK phosphorylation and Sirt1, the effects of which were exaggerated by ALDH2. Treatment with the ALDH2 activator Alda-1 accentuated aging-induced O2(-) generation and mechanical dysfunction in cardiomyocytes, the effects of which were mitigated by cotreatment with activators of AMPK and Sirt1, AICAR, resveratrol, and SRT1720. Examination of human longevity revealed a positive correlation between life span and ALDH2 gene mutation. Taken together, our data revealed that ALDH2 enzyme may accentuate myocardial remodeling and contractile dysfunction in aging, possibly through AMPK/Sirt1-mediated mitochondrial injury.

A novel protective mechanism for mitochondrial aldehyde dehydrogenase (ALDH2) in type i diabetes-induced cardiac dysfunction: role of AMPK-regulated autophagy

Mitochondrial aldehyde dehydrogenase (ALDH2) is known to offer myocardial protection against stress conditions including ischemia-reperfusion injury, alcoholism and diabetes mellitus although the precise mechanism is unclear. This study was designed to evaluate the effect of ALDH2 on diabetes-induced myocardial injury with a focus on autophagy. Wild-type FVB and ALDH2 transgenic mice were challenged with streptozotozin (STZ, 200mg/kg, i.p.) for 3months to induce experimental diabetic cardiomyopathy. Diabetes triggered cardiac remodeling and contractile dysfunction as evidenced by cardiac hypertrophy, decreased cell shortening and prolonged relengthening duration, the effects of which were mitigated by ALDH2. Lectin staining displayed that diabetes promoted cardiac hypertrophy, the effect of which was alleviated by ALDH2. Western blot analysis revealed dampened autophagy protein markers including LC3B ratio and Atg7 along with upregulated p62 following experimental diabetes, the effect of which was reconciled by ALDH2. Phosphorylation level of AMPK was decreased and its downstream signaling molecule FOXO3a was upregulated in both diabetic cardiac tissue and in H9C2 cells with high glucose exposure. All these effect were partly abolished by ALDH2 overexpression and ALDH2 agonist Alda1. High glucose challenge dampened autophagy in H9C2 cells as evidenced by enhanced p62 levels and decreased levels of Atg7 and LC3B, the effect of which was alleviated by the ALDH2 activator Alda-1. High glucose-induced cell death and apoptosis were reversed by Alda-1. The autophagy inhibitor 3-MA and the AMPK inhibitor compound C mitigated Alda-1-offered beneficial effect whereas the autophagy inducer rapamycin mimicked or exacerbated high glucose-induced cell injury. Moreover, compound C nullified Alda-1-induced protection against STZ-induced changes in autophagy and function. Our results suggested that ALDH2 protects against diabetes-induced myocardial dysfunction possibly through an AMPK -dependent regulation of autophagy. This article is part of a Special Issue entitled: Autophagy and protein quality control in cardiometabolic diseases.

Inhibition of AMPK accentuates prolonged caloric restriction-induced change in cardiac contractile function through disruption of compensatory autophagy

Prolonged caloric restriction often results in alteration in heart geometry and function although the underlying mechanism remains poorly defined. Autophagy, a conserved pathway for bulk degradation of intracellular proteins and organelles, preserves energy and nutrient in the face of caloric insufficiency. This study was designed to examine the role of AMPK in prolonged caloric restriction-induced change in cardiac homeostasis and the underlying mechanism(s) involved with a focus on autophagy. Wild-type (WT) and AMPK kinase dead (KD) mice were caloric restricted (by 40%) for 30 weeks. Echocardiographic, cardiomyocyte contractile and intracellular Ca²⁺ properties, autophagy and autophagy regulatory proteins were evaluated. Caloric restriction compromised echocardiographic indices (decreased ventricular mass, left ventricular diameters, and cardiac output), cardiomyocyte contractile and intracellular Ca²⁺ properties associated with upregulated autophagy (Beclin-1, Atg5 and LC3BII-to-LC3BI ratio), increased autophagy adaptor protein p62, elevated phosphorylation of AMPK and TSC1/2, depressed phosphorylation of mTOR and ULK1. Although AMPK inhibition did not affect cardiac mechanical function, autophagy and autophagy signaling proteins, it significantly accentuated caloric restriction-induced changes in myocardial contractile function and intracellular Ca²⁺ handling. Interestingly, AMPK inhibition reversed caloric restriction-induced changes in autophagy and autophagy signaling. AMPK inhibition led to dampened levels of Beclin-1, Atg 5 and LC3B ratio along with suppressed phosphorylation of AMPK and TSC1/2 as well as elevated phosphorylation of mTOR and ULK1. Taken together, these data suggest an indispensible role for AMPK in the maintenance of cardiac homeostasis under prolonged caloric restriction-induced pathological changes possibly through autophagy regulation. This article is part of a Special Issue entitled: Autophagy and protein quality control in cardiometabolic diseases.

Impairment of aldehyde dehydrogenase-2 by 4-hydroxy-2-nonenal adduct formation and cardiomyocyte hypertrophy in mice fed a high-fat diet and injected with low-dose streptozotocin

Reactive aldehydes such as 4-hydroxy-2-nonenal (4HNE) are generated in the myocardium in cardiac disease. 4HNE and other toxic aldehydes form adducts with proteins, leading to cell damage and organ dysfunction. Aldehyde dehydrogenases (ALDHs) metabolize toxic aldehydes such as 4HNE into nontoxic metabolites. Both ALDH levels and activity are reduced in cardiac disease. We examined whether reduced ALDH2 activity contributes to cardiomyocyte hypertrophy in mice fed a high-fat diet and injected with low-dose streptozotocin (STZ). These mice exhibited most of the characteristics of metabolic syndrome/type-2 diabetes mellitus (DM): increased blood glucose levels depicting hyperglycemia (415.2 ± 18.7 mg/dL vs. 265.2 ± 7.6 mg/dL; P < 0.05), glucose intolerance with normal plasma insulin levels, suggesting insulin resistance and obesity as evident from increased weight (44 ± 3.1 vs. 34.50 ± 1.32 g; P < 0.05) and body fat. Myocardial ALDH2 activity was 60% lower in these mice (0.1 ± 0.012 vs. 0.04 ± 0.015 µmol/min/mg protein; P < 0.05). Myocardial 4HNE levels were also elevated in the hyperglycemic hearts. Co-immunoprecipitation study showed that 4HNE formed adducts on myocardial ALDH2 protein in the mice exhibiting metabolic syndrome/type-2 DM, and they had obvious cardiac hypertrophy compared with controls as evident from increased heart weight (HW), HW to tibial length ratio, left ventricular (LV) mass and cardiomyocyte hypertrophy. Cardiomyocyte hypertrophy was correlated inversely with ALDH2 activity (R (2 )= 0.7; P < 0.05). Finally, cardiac dysfunction was observed in mice with metabolic syndrome/type-2 DM. Therefore, we conclude that reduced ALDH2 activity may contribute to cardiac hypertrophy and dysfunction in mice presenting with some of the characteristics of metabolic syndrome/type-2 DM when on a high-fat diet and low-dose STZ injection.

Alcohol consumption decreases rat hepatic creatine biosynthesis via altered guanidinoacetate methyltransferase activity

BACKGROUND

We have previously shown that decreased S-adenosylmethionine (SAM):S-adenosylhomocysteine (SAH) ratio generated in livers of alcohol-fed rats can impair the activities of many SAM-dependent methyltransferases. One such methyltransferase is guanidinoacetate methyltransferase (GAMT) that catalyzes the last step of creatine synthesis. As GAMT is the major utilizer of SAM, the purpose of the study was to examine the effects of ethanol (EtOH) on liver creatine levels and GAMT activity.

METHODS

Male Wistar rats were pair-fed the Lieber-DeCarli control and EtOH diet for 4 to 5 weeks. At the end of the feeding regimen, the liver, kidney, and blood were removed from these rats for subsequent biochemical analyses.

RESULTS

We observed ~60% decrease in creatine levels in the livers from EtOH-fed rats as compared to controls. The reduction in creatine levels correlated with lower SAM:SAH ratio observed in the livers of the EtOH-fed rats. Further, in vitro experiments with cell-free system and hepatic cells revealed it is indeed elevated SAH and lower SAM:SAH ratio that directly impairs GAMT activity and significantly reduces creatine synthesis. EtOH intake also slightly decreases the hepatocellular uptake of the creatine precursor, guanidinoacetate (GAA), and the GAMT enzyme expression that could additionally contribute to reduced liver creatine synthesis. The consequences of impaired hepatic creatine synthesis by chronic EtOH consumption include (i) increased toxicity due to GAA accumulation in the liver; (ii) reduced protection due to lower creatine levels in the liver, and (iii) reduced circulating and cardiac creatine levels.

CONCLUSIONS

Chronic EtOH consumption affects the hepatic creatine biosynthetic pathway leading to detrimental consequences not only in the liver but could also affect distal organs such as the heart that depend on a steady supply of creatine from the liver.

Targeting aldehyde dehydrogenase 2: new therapeutic opportunities

A family of detoxifying enzymes called aldehyde dehydrogenases (ALDHs) has been a subject of recent interest, as its role in detoxifying aldehydes that accumulate through metabolism and to which we are exposed from the environment has been elucidated. Although the human genome has 19 ALDH genes, one ALDH emerges as a particularly important enzyme in a variety of human pathologies. This ALDH, ALDH2, is located in the mitochondrial matrix with much known about its role in ethanol metabolism. Less known is a new body of research to be discussed in this review, suggesting that ALDH2 dysfunction may contribute to a variety of human diseases including cardiovascular diseases, diabetes, neurodegenerative diseases, stroke, and cancer. Recent studies suggest that ALDH2 dysfunction is also associated with Fanconi anemia, pain, osteoporosis, and the process of aging. Furthermore, an ALDH2 inactivating mutation (termed ALDH2*2) is the most common single point mutation in humans, and epidemiological studies suggest a correlation between this inactivating mutation and increased propensity for common human pathologies. These data together with studies in animal models and the use of new pharmacological tools that activate ALDH2 depict a new picture related to ALDH2 as a critical health-promoting enzyme.

A two-stage association study suggests BRAP as a susceptibility gene for schizophrenia

Schizophrenia (SZ) is a neurodevelopmental disorder in which altered immune function typically plays an important role in mediating the effect of environmental insults and regulation of inflammation. The breast cancer suppressor protein associated protein (BRAP) is suggested to exert vital effects in neurodevelopment by modulating the mitogen-activated protein kinase cascade and inflammation signaling. To explore the possible role of BRAP in SZ, we conducted a two-stage study to examine the association of BRAP polymorphisms with SZ in the Han Chinese population. In stage one, we screened SNPs in BRAP from our GWAS data, which detected three associated SNPs, with rs3782886 being the most significant one (P  =  2.31E-6, OR  =  0.67). In stage two, we validated these three SNPs in an independently collected population including 1957 patients and 1509 controls, supporting the association of rs3782886 with SZ (P  =  1.43E-6, OR  =  0.73). Furthermore, cis-eQTL analysis indicates that rs3782886 genotypes are associated with mRNA levels of aldehyde dehydrogenase 2 family (ALDH2) (P  =  0.0039) and myosin regulatory light chain 2 (MYL2) (P < 1.0E-4). Our data suggest that the BRAP gene may confer vulnerability for SZ in Han Chinese population, adding further evidence for the involvement of developmental and/or neuroinflammatory cascades in the illness.

Aldehyde dehydrogenase 2 ameliorates doxorubicin-induced myocardial dysfunction through detoxification of 4-HNE and suppression of autophagy

Mitochondrial aldehyde dehydrogenase (ALDH2) protects against cardiac injury via reducing production of 4-hydroxynonenal (4-HNE) and ROS. This study was designed to examine the impact of ALDH2 on doxorubicin (DOX)-induced cardiomyopathy and mechanisms involved with a focus on autophagy. 4-HNE and autophagic markers were detected by Western blotting in ventricular tissues from normal donors and patients with idiopathic dilated cardiomyopathy. Cardiac function, 4-HNE and levels of autophagic markers were detected in WT, ALDH2 knockout or ALDH2 transfected mice treated with or without DOX. Autophagy regulatory signaling including PI-3K, AMPK and Akt was examined in DOX-treated cardiomyocytes incubated with or without ALDH2 activator Alda-1. DOX-induced myocardial dysfunction, upregulation of 4-HNE and autophagic proteins were further aggravated in ALDH2 knockout mice while they were ameliorated in ALDH2 transfected mice. DOX downregulated Class I and upregulated Class III PI3-kinase, the effect of which was augmented by ALDH2 deletion. Accumulation of 4-HNE and autophagic protein markers in DOX-induced cardiomyocytes was significantly reduced by Alda-1. DOX depressed phosphorylated Akt but not AMPK, the effect was augmented by ALDH2 knockout. The autophagy inhibitor 3-MA attenuated, whereas autophagy inducer rapamycin mimicked DOX-induced cardiomyocyte contractile defects. In addition, rapamycin effectively mitigated Alda-1-offered protective action against DOX-induced cardiomyocyte dysfunction. Our data further revealed downregulated ALDH2 and upregulated autophagy levels in the hearts from patients with dilated cardiomyopathy. Taken together, our findings suggest that inhibition of 4-HNE and autophagy may be a plausible mechanism underscoring ALDH2-offered protection against DOX-induced cardiac defect. This article is part of a Special Issue entitled "Protein Quality Control, the Ubiquitin Proteasome System, and Autophagy".

Alcoholic Cardiomyopathy: Multigenic Changes Underlie Cardiovascular Dysfunction

Alcoholism is the third leading cause of preventable death in the United States. Aside from promoting cardiomyopathies, chronic alcohol consumption is associated with an increased risk of dementia, the development of liver or pancreas failure, and cancers of the oral cavity and pharynx. Although a J-shaped curve for all cause mortality has been identified for average alcohol consumption, irregular heavy drinking also carries significantly greater risks for cardiovascular disease. Alcohol induced cardiovascular disease has a complex multigenic etiology. There is significant variation in the initial presentation of alcoholic cardiomyopathy with diastolic dysfunction possibly being the first indication. Ethanol exposure generates toxic metabolites, primarily acetaldehyde and ROS, which activate several cell signaling systems to alter cell function across many levels. Sudden cardiac death is a known occurrence of alcoholism that may be linked to an arrhythmogenic effect of alcohol. Microscopic and molecular examination of diseased hearts has demonstrated abnormal alterations to various cellular components, including the mitochondria and myofibrils. These studies have shown not only the direct impact on myocardial contractility but also disrupted metabolism that determines the long-term survival of the myocardium. Significant variations in the response to chronic alcohol consumption may be related to unique genotypes that modify the metabolic response to ethanol. Future studies to further characterize the role of different genotypes will help indentify those genotypes are more susceptible to chronic alcohol consumption.

Regulation and therapeutic strategies of 4-hydroxy-2-nonenal metabolism in heart disease

4-Hydroxy-2-nonenal (4-HNE), a reactive aldehyde, is generated from polyunsaturated fatty acids (PUFAs) in biological membranes. Reactive oxygen species (ROS) generated during oxidative stress react with PUFAs to form aldehydes like 4-HNE, which inactivates proteins and DNA by forming hybrid covalent chemical addition compounds called adducts. The ensuing chain reaction results in cellular dysfunction and tissue damage. It includes a wide spectrum of events ranging from electron transport chain dysfunction to apoptosis. In addition, 4-HNE directly depresses contractile function, enhances ROS formation, modulates cell signaling pathways, and can contribute to many cardiovascular diseases, including atherosclerosis, myocardial ischemia-reperfusion injury, heart failure, and cardiomyopathy. Therefore, targeting 4-HNE could help reverse these pathologies. This review will focus on 4-HNE generation, the role of 4-HNE in cardiovascular diseases, cellular targets (especially mitochondria), processes and mechanisms for 4-HNE-induced toxicity, regulation of 4-HNE metabolism, and finally strategies for developing potential therapies for cardiovascular disease by attenuating 4-HNEinduced toxicity.

Moderate alcohol use and cardiovascular disease from Mendelian randomization

Background

Observational studies show moderate alcohol use negatively associated with ischemic heart disease (IHD) and cardiovascular disease (CVD). However, healthier attributes among moderate users compared to never users may confound the apparent association. A potentially less biased way to examine the association is Mendelian randomization, using alcohol metabolizing genes which influence alcohol use.

Methods

We used instrumental variable analysis with aldehyde dehydrogenase 2 (ALDH2) genotypes (AA/GA/GG) as instrumental variables for alcohol use to examine the association of alcohol use (10 g ethanol/day) with CVD risk factors (blood pressure, lipids and glucose) and morbidity (self-reported IHD and CVD) among men in the Guangzhou Biobank Cohort Study.

Results

ALDH2 genotypes were a credible instrument for alcohol use (F-statistic 74.6). Alcohol was positively associated with HDL-cholesterol (0.05 mmol/L per alcohol unit, 95% confidence interval (CI) 0.02 to 0.08) and diastolic blood pressure (1.15 mmHg, 95% CI 0.23 to 2.07) but not with systolic blood pressure (1.00 mmHg, 95% CI -0.74 to 2.74), LDL-cholesterol (0.03 mmol/L, 95% CI -0.03 to 0.08), log transformed triglycerides (0.03 mmol/L, 95% CI -0.01 to 0.08) or log transformed fasting glucose (0.01 mmol/L, 95% CI -0.006 to 0.03), self-reported CVD (odds ratio (OR) 0.98, 95% CI 0.76 to 1.27) or self-reported IHD (OR 1.10, 95% CI 0.83 to 1.45).

Conclusion

Low to moderate alcohol use among men had the expected effects on most CVD risk factors but not fasting glucose. Larger studies are needed to confirm the null associations with IHD, CVD and fasting glucose.

The combination of mitochondrial low enzyme-activity aldehyde dehydrogenase 2 allele and superoxide dismutase 2 genotypes increases the risk of hypertension in relation to alcohol consumption

A cooperative role of mitochondrial aldehyde dehydrogenase 2 (ALDH2) and superoxide dismutase 2 (SOD2) to maintain the vascular function has recently been demonstrated in nitrate tolerance. The present study examined whether the combination of low enzyme-activity variants of ALDH2 and SOD2 increases the risk of hypertension in relation to alcohol consumption. A total of 444 Japanese participants in a health-screening program were evaluated. The risk of hypertension among the individuals harboring both the ALDH2*2 allele and the SOD2 Val/Val genotype was significantly higher in drinkers than in nondrinkers (adjusted odds ratio, 6.22; 95% confidence interval, 2.26-17.1; P<0.001). Among these individuals, the systolic/diastolic blood pressure also increased by 0.24/0.14 mmHg for each 1g/day increase in alcohol consumption (P<0.001/P=0.003). These associations were observed, but the degree was lower among those with the other genotype combinations (0.11/0.10 mmHg; P=0.012/P=0.001). Information about the genetic predisposition to alcohol-related diseases may thus be useful to promote lifestyle modifications for high-risk individuals.

Nutraceutical strategies for ameliorating the toxic effects of alcohol

Rodent studies reveal that oxidative stress, much of it generated via induction/activation of NADPH oxidase, is a key mediator of a number of the pathogenic effects of chronic ethanol overconsumption. The highly reactive ethanol metabolite acetaldehyde is a key driver of this oxidative stress, and doubtless works in other ways to promote alcohol-induced pathology. Effective antioxidant measure may therefore be useful for mitigating the adverse health consequences of alcohol consumption; spirulina may have particular utility in this regard, as its chief phycochemical phycocyanobilin has recently been shown to function as an inhibitor of certain NADPH oxidase complexes, mimicking the physiological role of its chemical relatives biliverdin/bilirubin in this respect. Moreover, certain nutraceuticals, including taurine, pantethine, and lipoic acid, may have the potential to boost the activity of the mitochondrial isoform of aldehyde dehydrogenase, ALDH-2, accelerating conversion of acetaldehyde to acetate (which arguably has protective health effects). Little noticed clinical studies conducted nearly three decades ago reported that pre-ingestion of either taurine or pantethine could blunt the rise in blood acetaldehyde following ethanol consumption. Other evidence suggests that lipoic acid may function within mitochondria to maintain aldehyde dehydrogenase in a reduced active conformation; the impact of this agent on ethanol metabolism has however received little or no study. Studies evaluating the impact of nutracetical strategies on prevention of hangovers - which likely are mediated by acetaldehyde - may represent a quick, low-cost way to identify nutraceutical regimens that merit further attention for their potential impact on alcohol-induced pathology. Measures which boost or preserve ALDH-2 activity may also have important antioxidant potential, as this enzyme functions physiologically to protect cells from toxic aldehydes generated by oxidant stress.

Mitochondrial aldehyde dehydrogenase obliterates endoplasmic reticulum stress-induced cardiac contractile dysfunction via correction of autophagy

ER stress triggers myocardial contractile dysfunction while effective therapeutic regimen is still lacking. Mitochondrial aldehyde dehydrogenase (ALDH2), an essential mitochondrial enzyme governing mitochondrial and cardiac function, displays distinct beneficial effect on the heart. This study was designed to evaluate the effect of ALDH2 on ER stress-induced cardiac anomalies and the underlying mechanism involved with a special focus on autophagy. WT and ALDH2 transgenic mice were subjected to the ER stress inducer thapsigargin (1mg/kg, i.p., 48h). Echocardiographic, cardiomyocyte contractile and intracellular Ca(2+) properties as well as myocardial histology, autophagy and autophagy regulatory proteins were evaluated. ER stress led to compromised echocardiographic indices (elevated LVESD, reduced fractional shortening and cardiac output), cardiomyocyte contractile and intracellular Ca(2+) properties and cell survival, associated with upregulated autophagy, dampened phosphorylation of Akt and its downstream signal molecules TSC2 and mTOR, the effects of which were alleviated or mitigated by ALDH2. Thapsigargin promoted ER stress proteins Gadd153 and GRP78 without altering cardiomyocyte size and interstitial fibrosis, the effects of which were unaffected by ALDH2. Treatment with thapsigargin in vitro mimicked in vivo ER stress-induced cardiomyocyte contractile anomalies including depressed peak shortening and maximal velocity of shortening/relengthening as well as prolonged relengthening duration, the effect of which was abrogated by the autophagy inhibitor 3-methyladenine and the ALDH2 activator Alda-1. Interestingly, Alda-1-induced beneficial effect against ER stress was obliterated by autophagy inducer rapamycin, Akt inhibitor AktI and mTOR inhibitor RAD001. These data suggest a beneficial role of ALDH2 against ER stress-induced cardiac anomalies possibly through autophagy reduction.

Direct central nervous system effect of alcohol alters synthesis and degradation of skeletal muscle protein

AIMS

Alcohol can directly impair protein synthesis in cultured myocytes as well as in in situ perfused skeletal muscle. However, alcohol in the general circulation diffuses rapidly into the central nervous system (CNS). Therefore, this study determined whether localized elevation of alcohol within the CNS is capable of decreasing muscle protein synthesis.

METHODS

Conscious unstrained male rats received a continuous intracerebroventricular (ICV) infusion of ethanol and skeletal muscle protein synthesis and degradation were assessed.

RESULTS

ICV alcohol decreased protein synthesis in the gastrocnemius after 6 and 24 h, compared with the time-matched controls. The reduction was equivalent for both sarcoplasmic and myofibrillar proteins and was reversible. The inhibitory effect of alcohol was not prevented by the catalase inhibitor 3-amino-1,2,4-triazole and was mimicked by ICV-administered t-butanol. The alcohol-induced decrease in muscle protein synthesis was associated with a concomitant reduction in phosphorylation of 4E-binding protein and ribosomal S6 kinase-1, suggesting impaired mammalian target of rapamycin kinase activity. ICV alcohol also impaired the ability of leucine to stimulate protein synthesis. Conversely, ICV alcohol increased muscle proteasome activity and muscle RING-finger protein-1 mRNA content. Altered muscle protein metabolism was not associated with changes in muscle mRNA content for tumor necrosis factor α, interleukin-6 or insulin-like growth factor (IGF)-I or circulating insulin or IGF-I.

CONCLUSION

Selective elevation of alcohol within the CNS is capable of decreasing protein synthesis and increasing protein degradation in muscle in the absence of alcohol in the general circulation, thus revealing a previously unrecognized central neural mechanism, which may account for part of the inhibitory effect of ingested alcohol on muscle protein homeostasis.

Mitochondria as a source and target of lipid peroxidation products in healthy and diseased heart

The heart is a highly oxidative organ in which cardiomyocyte turnover is virtually absent, making it particularly vulnerable to accumulation of lipid peroxidation products (LPP) formed as a result of oxidative damage. Reactive oxygen and nitrogen species are the most common electrophiles formed during lipid peroxidation and lead to the formation of both stable and unstable LPP. Of the LPP formed, highly reactive aldehydes are a well-recognized causative factor in ageing and age-associated diseases, including cardiovascular disease and diabetes. Recent studies have identified that the mitochondria are both a primary source and target of LPP, with specific emphasis on aldehydes in cardiomyocytes and how these affect the electron transport system and Ca(2+) balance. Numerous studies have found that there are functional consequences in the heart following exposure to specific aldehydes (acrolein, trans-2-hexanal, 4-hydroxynonenal and acetaldehyde). Because these LPP are known to form in heart failure, cardiac ischaemia-reperfusion injury and diabetes, they may have an underappreciated role in the pathophysiology of these disease processes. Lipid peroxidation products are involved in the transcriptional regulation of endogenous anti-oxidant systems. Recent evidence demonstrates that transient increases in LPP may be beneficial in cardioprotection by contributing to mitohormesis (i.e. induction of anti-oxidant systems) in cardiomyocytes. Thus, exploitation of the cardioprotective actions of the LPP may represent a novel therapeutic strategy for future treatment of heart disease.

Inhibition of CYP2E1 attenuates chronic alcohol intake-induced myocardial contractile dysfunction and apoptosis

Alcohol intake is associated with myocardial contractile dysfunction and apoptosis although the precise mechanism is unclear. This study was designed to examine the effect of the cytochrome P450 enzyme CYP2E1 inhibition on ethanol-induced cardiac dysfunction. Adult male mice were fed a 4% ethanol liquid or pair-fed control diet for 6weeks. Following 2weeks of diet feeding, a cohort of mice started to receive the CYP2E1 inhibitor diallyl sulfide (100mg/kg/d, i.p.) for the remaining feeding duration. Cardiac function was assessed using echocardiographic and IonOptix systems. Western blot analysis was used to evaluate CYP2E1, heme oxygenase-1 (HO-1), iNOS, the intracellular Ca(2+) regulatory proteins sarco(endo)plasmic reticulum Ca(2+)-ATPase, Na(+)Ca(2+) exchanger and phospholamban, pro-apoptotic protein cleaved caspase-3, Bax, c-Jun-NH(2)-terminal kinase (JNK) and apoptosis signal-regulating kinase (ASK-1). Ethanol led to elevated levels of CYP2E1, iNOS and phospholamban, decreased levels of HO-1 and Na(+)Ca(2+) exchanger, cardiac contractile and intracellular Ca(2+) defects, cardiac fibrosis, overt O(2)(-) production, and apoptosis accompanied with increased phosphorylation of JNK and ASK-1, the effects were significantly attenuated or ablated by diallyl sulfide. Inhibitors of JNK and ASK-1 but not HO-1 inducer or iNOS inhibitor obliterated ethanol-induced cardiomyocyte contractile dysfunction, substantiating a role for JNK and ASK-1 signaling in ethanol-induced myocardial injury. Taken together, these findings suggest that ethanol metabolism through CYP2E1 may contribute to the pathogenesis of alcoholic cardiomyopathy including myocardial contractile dysfunction, oxidative stress and apoptosis, possibly through activation of JNK and ASK-1 signaling.

Insulin resistance and heart failure: molecular mechanisms

This article addresses the issue of insulin resistance and associated reductions in cardiac insulin metabolic signaling, which is emerging as a major factor in the development of heart failure, and assumes more importance because of an epidemic increase in obesity and the cardiorenal metabolic syndrome in our aging population. The effects of cardiac insulin resistance are exacerbated by metabolic, endocrine, and cytokine alterations associated with systemic insulin resistance. Understanding the molecular mechanisms linking insulin resistance and heart failure may help to design new and more effective mechanism-based drugs to improve myocardial and systemic insulin resistance.

Autophagy is a protective response to ethanol neurotoxicity

Ethanol is a neuroteratogen and neurodegeneration is the most devastating consequence of developmental exposure to ethanol. The mechanisms underlying ethanol-induced neurodegeneration are complex. Ethanol exposure produces reactive oxygen species (ROS) which cause oxidative stress in the brain. We hypothesized that ethanol would activate autophagy to alleviate oxidative stress and neurotoxicity. Our results indicated that ethanol increased the level of the autophagic marker Map1lc3-II (LC3-II) and upregulated LC3 puncta in SH-SY5Y neuroblastoma cells. It also enhanced the levels of LC3-II and BECN1 in the developing brain; meanwhile, ethanol reduced SQSTM1 (p62) levels. Bafilomycin A(1), an inhibitor of autophagosome and lysosome fusion, increased p62 levels in the presence of ethanol. Bafilomycin A(1) and rapamycin potentiated ethanol-increased LC3 lipidation, whereas wortmannin and a BECN1-specific shRNA inhibited ethanol-promoted LC3 lipidation. Ethanol increased mitophagy, which was also modulated by BECN1 shRNA and rapamycin. The evidence suggested that ethanol promoted autophagic flux. Activation of autophagy by rapamycin reduced ethanol-induced ROS generation and ameliorated ethanol-induced neuronal death in vitro and in the developing brain, whereas inhibition of autophagy by wortmannin and BECN1-specific shRNA potentiated ethanol-induced ROS production and exacerbated ethanol neurotoxicity. Furthermore, ethanol inhibited the MTOR pathway and downregulation of MTOR offered neuroprotection. Taken together, the results suggest that autophagy activation is a neuroprotective response to alleviate ethanol toxicity. Ethanol modulation of autophagic activity may be mediated by the MTOR pathway.

DNA damage and neurotoxicity of chronic alcohol abuse

Chronic alcohol abuse results in a variety of pathological effects including damage to the brain. The causes of alcohol-induced brain pathology are presently unclear. Several mechanisms of pathogenicity of chronic alcoholism have been proposed, including accumulation of DNA damage in the absence of repair, resulting in genomic instability and death of neurons. Genomic instability is a unified genetic mechanism leading to a variety of neurodegenerative disorders. Ethanol also likely interacts with various metabolic pathways, including one-carbon metabolism (OCM). OCM is critical for the synthesis of DNA precursors, essential for DNA repair, and as a methyl donor for various methylation events, including DNA methylation. Both DNA repair and DNA methylation are critical for maintaining genomic stability. In this review, we outline the role of DNA damage and DNA repair dysfunction in chronic alcohol-induced neurodegeneration.

Mitochondrial aldehyde dehydrogenase (ALDH2) protects against streptozotocin-induced diabetic cardiomyopathy: role of GSK3β and mitochondrial function

BACKGROUND

Mitochondrial aldehyde dehydrogenase (ALDH2) displays some promise in the protection against cardiovascular diseases although its role in diabetes has not been elucidated.

METHODS

This study was designed to evaluate the impact of ALDH2 on streptozotocin-induced diabetic cardiomyopathy. Friendly virus B(FVB) and ALDH2 transgenic mice were treated with streptozotocin (intraperitoneal injection of 200 mg/kg) to induce diabetes.

RESULTS

Echocardiographic evaluation revealed reduced fractional shortening, increased end-systolic and -diastolic diameter, and decreased wall thickness in streptozotocin-treated FVB mice. Streptozotocin led to a reduced respiratory exchange ratio; myocardial apoptosis and mitochondrial damage; cardiomyocyte contractile and intracellular Ca2+ defects, including depressed peak shortening and maximal velocity of shortening and relengthening; prolonged duration of shortening and relengthening; and dampened intracellular Ca2+ rise and clearance. Western blot analysis revealed disrupted phosphorylation of Akt, glycogen synthase kinase-3β and Foxo3a (but not mammalian target of rapamycin), elevated PTEN phosphorylation and downregulated expression of mitochondrial proteins, peroxisome proliferator-activated receptor γ coactivator 1α and UCP-2. Intriguingly, ALDH2 attenuated or ablated streptozotocin-induced echocardiographic, mitochondrial, apoptotic and myocardial contractile and intracellular Ca2+ anomalies as well as changes in the phosphorylation of Akt, glycogen synthase kinase-3β, Foxo3a and phosphatase and tensin homologue on chromosome ten, despite persistent hyperglycemia and a low respiratory exchange ratio. In vitro data revealed that the ALDH2 activator Alda-1 and glycogen synthase kinase-3β inhibition protected against high glucose-induced mitochondrial and mechanical anomalies, the effect of which was cancelled by mitochondrial uncoupling.

CONCLUSIONS

In summary, our data revealed that ALDH2 acted against diabetes-induced cardiac contractile and intracellular Ca2+ dysregulation, possibly through regulation of apoptosis, glycogen synthase kinase-3β activation and mitochondrial function independent of the global metabolic profile.

Alcohol intake

Alcohol consumption and its association with health or illness states are of great interest from the nutritional genomics point of view. This interest is centered not only on investigating the genetic variants that can modulate the effects of alcoholic beverages on different intermediate and final disease phenotypes (mainly cardiovascular diseases and cancer), but also on finding out how the genome influences the amount of alcohol consumed and consumption habits. This chapter reviews the latest findings on alcohol consumption trends, the methodological limitations in the analysis of alcohol consumption, and the main genes and polymorphisms related to alcohol intake, including the inconsistent results from genome-wide association studies (GWASs). It also reviews the effects of alcohol consumption on cardiovascular diseases and cancer and the studies analyzing the interactions between different genetic polymorphisms and alcohol in phenotypes related to these diseases, discussing the studies' advantages and limitations as well as future research perspectives.

AMP-dependent kinase and autophagic flux are involved in aldehyde dehydrogenase-2-induced protection against cardiac toxicity of ethanol

Mitochondrial aldehyde dehydrogenase-2 (ALDH2) alleviates ethanol toxicity although the precise mechanism is unclear. This study was designed to evaluate the effect of ALDH2 on ethanol-induced myocardial damage with a focus on autophagy. Wild-type FVB and transgenic mice overexpressing ALDH2 were challenged with ethanol (3g/kg/day, ip) for 3days and cardiac mechanical function was assessed using the echocardiographic and IonOptix systems. Western blot analysis was used to evaluate essential autophagy markers, Akt and AMPK, and the downstream signal mTOR. Ethanol challenge altered cardiac geometry and function as evidenced by enlarged ventricular end systolic and diastolic diameters, decreased cell shortening and intracellular Ca(2+) rise, prolonged relengthening and intracellular Ca(2+) decay, as well as reduced SERCA Ca(2+) uptake, which effects were mitigated by ALDH2. Ethanol challenge facilitated myocardial autophagy as evidenced by enhanced expression of Beclin, ATG7, and LC3B II, as well as mTOR dephosphorylation, which was alleviated by ALDH2. Ethanol challenge-induced cardiac defect and apoptosis were reversed by the ALDH2 agonist Alda-1, the autophagy inhibitor 3-MA, and the AMPK inhibitor compound C, whereas the autophagy inducer rapamycin and the AMPK activator AICAR mimicked or exacerbated ethanol-induced cell injury. Ethanol promoted or suppressed phosphorylation of AMPK and Akt, respectively, in FVB but not ALDH2 murine hearts. Moreover, AICAR nullified Alda-1-induced protection against ethanol-triggered autophagic and functional changes. Ethanol increased GFP-LC3 puncta in H9c2 cells, the effect of which was ablated by Alda-1 and 3-MA. Lysosomal inhibition using bafilomycin A1, E64D, and pepstatin A obliterated Alda-1- but not ethanol-induced responses in GFP-LC3 puncta. Our results suggest that ALDH2 protects against ethanol toxicity through altered Akt and AMPK signaling and regulation of autophagic flux.

Cardiac insulin resistance and microRNA modulators

Cardiac insulin resistance is a metabolic and functional disorder that is often associated with obesity and/or the cardiorenal metabolic syndrome (CRS), and this disorder may be accentuated by chronic alcohol consumption. In conditions of over-nutrition, increased insulin (INS) and angiotensin II (Ang II) activate mammalian target for rapamycin (mTOR)/p70 S6 kinase (S6K1) signaling, whereas chronic alcohol consumption inhibits mTOR/S6K1 activation in cardiac tissue. Although excessive activation of mTOR/S6K1 induces cardiac INS resistance via serine phosphorylation of INS receptor substrates (IRS-1/2), it also renders cardioprotection via increased Ang II receptor 2 (AT2R) upregulation and adaptive hypertrophy. In the INS-resistant and hyperinsulinemic Zucker obese (ZO) rat, a rodent model for CRS, activation of mTOR/S6K1signaling in cardiac tissue is regulated by protective feed-back mechanisms involving mTOR↔AT2R signaling loop and profile changes of microRNA that target S6K1. Such regulation may play a role in attenuating progressive heart failure. Conversely, alcohol-mediated inhibition of mTOR/S6K1, down-regulation of INS receptor and growth-inhibitory mir-200 family, and upregulation of mir-212 that promotes fetal gene program may exacerbate CRS-related cardiomyopathy.