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1.  Activation of aldehyde dehydrogenase 2 (ALDH2) confers cardioprotection in protein kinase C epsilon (PKCε) knockout mice 
Acute administration of ethanol can reduce cardiac ischemia/reperfusion injury. Previous studies demonstrated that the acute cytoprotective effect of ethanol on the myocardium is mediated by protein kinase C epsilon (PKCε). We recently identified aldehyde dehydrogenase 2 (ALDH2) as an PKCε substrate, whose activation is necessary and sufficient to confer cardioprotection in vivo. ALDH2 metabolizes cytotoxic reactive aldehydes, such as 4-hydroxy-2-nonenal (4-HNE), which accumulate during cardiac ischemia/reperfusion. Here, we used a combination of PKCε knockout mice and a direct activator of ALDH2, Alda-44, to further investigate the interplay between PKCε and ALDH2 in cardioprotection. We report that ethanol preconditioning requires PKCε, whereas direct activation of ALDH2 reduces infarct size in both wild type and PKCε knockout hearts. Our data suggest that ALDH2 is downstream of PKCε in ethanol preconditioning and that direct activation of ALDH2 can circumvent the requirement of PKCε to induce cytoprotection. We also report that in addition to ALDH2 activation, Alda-44 prevents 4-HNE induced inactivation of ALDH2 by reducing the formation of 4-HNE-ALDH2 protein adducts. Thus, Alda-44 promotes metabolism of cytotoxic reactive aldehydes that accumulate in ischemic myocardium. Taken together, our findings suggest that direct activation of ALDH2 may represent a method of harnessing the cardioprotective effect of ethanol without the side effects associated with alcohol consumption.
doi:10.1016/j.yjmcc.2009.10.030
PMCID: PMC2837767  PMID: 19913552
2.  Isoflurane Preconditioning Confers Cardioprotection by Activation of ALDH2 
PLoS ONE  2013;8(2):e52469.
The volatile anesthetic, isoflurane, protects the heart from ischemia/reperfusion (I/R) injury. Aldehyde dehydrogenase 2 (ALDH2) is thought to be an endogenous mechanism against ischemia-reperfusion injury possibly through detoxification of toxic aldehydes. We investigated whether cardioprotection by isoflurane depends on activation of ALDH2.Anesthetized rats underwent 40 min of coronary artery occlusion followed by 120 min of reperfusion and were randomly assigned to the following groups: untreated controls, isoflurane preconditioning with and without an ALDH2 inhibitor, the direct activator of ALDH2 or a protein kinase C (PKCε) inhibitor. Pretreatment with isoflurane prior to ischemia reduced LDH and CK-MB levels and infarct size, while it increased phosphorylation of ALDH2, which could be blocked by the ALDH2 inhibitor, cyanamide. Isolated neonatal cardiomyocytes were treated with hypoxia followed by reoxygenation. Hypoxia/reoxygenation (H/R) increased cardiomyocyte apoptosis and injury which were attenuated by isoflurane and forced the activation of ALDH2. In contrast, the effect of isoflurane-induced protection was almost abolished by knockdown of ALDH2. Activation of ALDH2 and cardioprotection by isoflurane were substantially blocked by the PKCε inhibitor. Activation of ALDH2 by mitochondrial PKCε plays an important role in the cardioprotection of isoflurane in myocardium I/R injury.
doi:10.1371/journal.pone.0052469
PMCID: PMC3585331  PMID: 23468836
3.  Aldehyde dehydrogenase 2 (ALDH2) rescues myocardial ischaemia/reperfusion injury: role of autophagy paradox and toxic aldehyde 
European Heart Journal  2010;32(8):1025-1038.
Aims
The present study was designed to examine the mechanism involved in mitochondrial aldehyde dehydrogenase (ALDH2)-induced cardioprotection against ischaemia/reperfusion (I/R) injury with a focus on autophagy.
Methods
Wild-type (WT), ALDH2 overexpression, and knockout (KO) mice (n = 4–6 for each index measured) were subjected to I/R, and myocardial function was assessed using echocardiographic, Langendroff, and edge-detection systems. Western blotting was used to evaluate AMP-dependent protein kinase (AMPK), Akt, autophagy, and the AMPK/Akt upstream signalling LKB1 and PTEN.
Results
ALDH2 overexpression and KO significantly attenuated and accentuated, respectively, infarct size, factional shortening, and recovery of post-ischaemic left ventricular function following I/R as well as hypoxia/reoxygenation-induced cardiomyocyte contractile dysfunction. Autophagy was induced during ischaemia and remained elevated during reperfusion. ALDH2 significantly promoted autophagy during ischaemia, which was accompanied by AMPK activation and mammalian target of rapamycin (mTOR) inhibition. On the contrary, ALDH2 overtly inhibited autophagy during reperfusion accompanied by the activation of Akt and mTOR. Inhibition and induction of autophagy mitigated ALDH2-induced protection against cell death in hypoxia and reoxygenation, respectively. In addition, levels of the endogenous toxic aldehyde 4-hydroxy-2-nonenal (4-HNE) were elevated by ischaemia and reperfusion, which was abrogated by ALDH2. Furthermore, ALDH2 ablated 4-HNE-induced cardiomyocyte dysfunction and protein damage, whereas 4-HNE directly decreased pan and phosphorylated LKB1 and PTEN expression.
Conclusion
Our data suggest a myocardial protective effect of ALDH2 against I/R injury possibly through detoxification of toxic aldehyde and a differential regulation of autophagy through AMPK- and Akt-mTOR signalling during ischaemia and reperfusion, respectively.
doi:10.1093/eurheartj/ehq253
PMCID: PMC3076664  PMID: 20705694
ALDH2; Myocardial ischaemia/reperfusion; Akt; AMPK; Autophagy; 4-HNE
4.  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.
doi:10.1038/nsmb.1737
PMCID: PMC2857674  PMID: 20062057
5.  Characterization of the East Asian Variant of Aldehyde Dehydrogenase-2 
The Journal of Biological Chemistry  2009;285(2):943-952.
The East Asian variant of mitochondrial aldehyde dehydrogenase (ALDH2) exhibits significantly reduced dehydrogenase, esterase, and nitroglycerin (GTN) denitrating activities. The small molecule Alda-1 was reported to partly restore low acetaldehyde dehydrogenase activity of this variant. In the present study we compared the wild type enzyme (ALDH2*1) with the Asian variant (ALDH2*2) regarding GTN bioactivation and the effects of Alda-1. Alda-1 increased acetaldehyde oxidation by ALDH2*1 and ALDH2*2 approximately 1.5- and 6-fold, respectively, and stimulated the esterase activities of both enzymes to similar extent as the coenzyme NAD. The effect of NAD was biphasic with pronounced inhibition occurring at ≥5 mm. In the presence of 1 mm NAD, Alda-1 stimulated ALDH2*2-catalyzed ester hydrolysis 73-fold, whereas the NAD-stimulated activity of ALDH2*1 was inhibited because of 20-fold increased inhibitory potency of NAD in the presence of the drug. Although ALDH2*2 exhibited 7-fold lower GTN denitrating activity and GTN affinity than ALDH2*1, the rate of nitric oxide formation was only reduced 2-fold, and soluble guanylate cyclase (sGC) activation was more pronounced than with wild type ALDH2 at saturating GTN. Alda-1 caused slight inhibition of GTN denitration and did not increase GTN-induced sGC activation in the presence of either variant. The present results indicate that Alda-1 stimulates established ALDH2 activities by improving NAD binding but does not improve the GTN binding affinity of the Asian variant. In addition, our data revealed an unexpected discrepancy between GTN reductase activity and sGC activation, suggesting that GTN denitration and bioactivation may reflect independent pathways of ALDH2-catalyzed GTN biotransformation.
doi:10.1074/jbc.M109.014548
PMCID: PMC2801295  PMID: 19906643
Cyclic GMP (cGMP); Enzyme Catalysis; Nitric Oxide; Oxidase; Superoxide Dismutase (SOD); Superoxide Ion; Bioactivation; Nitroglycerin
6.  Effect of overexpression of human aldehyde dehydrogenase 2 in LLC-PK1 cells on glyceryl trinitrate biotransformation and cGMP accumulation 
British Journal of Pharmacology  2013;168(4):978-987.
Background And Purpose
Recent studies suggest a primary role for aldehyde dehydrogenase 2 (ALDH2) in mediating the biotransformation of organic nitrates, such as glyceryl trinitrate (GTN), to the proximal activator of soluble guanylyl cyclase (sGC), resulting in increased cGMP accumulation and vasodilation. Our objective was to assess the role of ALDH2 in organic nitrate action using a cell culture model.
Experimental Approach
Porcine renal epithelial (LLC-PK1) cells possess an intact NO-sGC-cGMP signaling system, and can be used as a biochemical model of organic nitrate action. We used a pcDNA3.1-human ALDH2 expression vector to establish a stably transfected cell line (PK1ALDH2) that overexpressed ALDH2, or small interfering RNA (siRNA) to deplete endogenous ALDH2, and assessed GTN biotransformation and GTN-induced cGMP formation.
Key Results
ALDH2 activity in the stably transfected cells was approximately sevenfold higher than wild-type cells or cells stably transfected with empty vector (PK1vector); and protein expression, as assessed by immunoblot analysis, was markedly increased. In PK1ALDH2, GTN biotransformation was significantly increased as a result of increased glyceryl-1,2-dinitrate formation compared to wild-type or PK1vector. However, the incubation of PK1ALDH2 with 1 or 10 μM GTN did not alter GTN-induced cGMP accumulation compared with wild-type or PK1vector cells. Furthermore, siRNA-mediated depletion of ALDH2 had no effect on GTN-induced cGMP formation.
Conclusions And Implications
In an intact cell system, neither overexpression nor depletion of ALDH2 affects GTN-induced cGMP formation, indicating that ALDH2 does not mediate the mechanism-based biotransformation of GTN to an activator of sGC.
doi:10.1111/j.1476-5381.2012.02220.x
PMCID: PMC3631385  PMID: 22994391
glyceryl trinitrate; NO; aldehyde dehydrogenase; nitrate tolerance; cGMP
7.  Aldehydic load and aldehyde dehydrogenase 2 profile during the progression of post-myocardial infarction cardiomyopathy: benefits of Alda-1 
Background/Objectives
We previously demonstrated that reducing cardiac aldehydic load by aldehyde dehydrogenase 2 (ALDH2), a mitochondrial enzyme responsible for metabolizing the major lipid peroxidation product, protects against acute ischemia/reperfusion injury and chronic heart failure. However, time-dependent changes in ALDH2 profile, aldehydic load and mitochondrial bioenergetics during progression of post-myocardial infarction (post-MI) cardiomyopathy is unknown and should be established to determine the optimal time window for drug treatment.
Methods
Here we characterized cardiac ALDH2 activity and expression, lipid peroxidation, 4-hydroxy-2-nonenal (4-HNE) adduct formation, glutathione pool and mitochondrial energy metabolism and H2O2 release during the 4 weeks after permanent left anterior descending (LAD) coronary artery occlusion in rats.
Results
We observed a sustained disruption of cardiac mitochondrial function during the progression of post-MI cardiomyopathy, characterized by >50% reduced mitochondrial respiratory control ratios and up to 2 fold increase in H2O2 release. Mitochondrial dysfunction was accompanied by accumulation of cardiac and circulating lipid peroxides and 4-HNE protein adducts and down-regulation of electron transport chain complexes I and V. Moreover, increased aldehydic load was associated with a 90% reduction in cardiac ALDH2 activity and increased glutathione pool. Further supporting an ALDH2 mechanism, sustained Alda-1 treatment (starting 24hrs after permanent LAD occlusion surgery) prevented aldehydic overload, mitochondrial dysfunction and improved ventricular function in post-MI cardiomyopathy rats.
Conclusion
Taken together, our findings demonstrate a disrupted mitochondrial metabolism along with an insufficient cardiac ALDH2-mediated aldehyde clearance during the progression of ventricular dysfunction, suggesting a potential therapeutic value of ALDH2 activators during the progression of post-myocardial infarction cardiomyopathy.
doi:10.1016/j.ijcard.2014.10.140
PMCID: PMC4405147  PMID: 25464432
myocardial infarction; 4-hydroxinonenal; oxidative stress; bioenergetics; aldehyde dehydrogenase 2
8.  Mitochondrial Aldehyde Dehydrogenase 2 Plays Protective Roles in Heart Failure After Myocardial Infarction via Suppression of the Cytosolic JNK/p53 Pathway in Mice 
Background
Increasing evidence suggests a critical role for mitochondrial aldehyde dehydrogenase 2 (ALDH2) in protection against cardiac injuries; however, the downstream cytosolic actions of this enzyme are largely undefined.
Methods and Results
Proteomic analysis identified a significant downregulation of mitochondrial ALDH2 in the heart of a rat heart failure model after myocardial infarction. The mechanistic insights underlying ALDH2 action were elucidated using murine models overexpressing ALDH2 or its mutant or with the ablation of the ALDH2 gene (ALDH2 knockout) and neonatal cardiomyocytes undergoing altered expression and activity of ALDH2. Left ventricle dilation and dysfunction and cardiomyocyte death after myocardial infarction were exacerbated in ALDH2‐knockout or ALDH2 mutant‐overexpressing mice but were significantly attenuated in ALDH2‐overexpressing mice. Using an anoxia model of cardiomyocytes with deficiency in ALDH2 activities, we observed prominent cardiomyocyte apoptosis and increased accumulation of the reactive aldehyde 4‐hydroxy‐2‐nonenal (4‐HNE). We subsequently examined the impacts of mitochondrial ALDH2 and 4‐HNE on the relevant cytosolic protective pathways. Our data documented 4‐HNE‐stimulated p53 upregulation via the phosphorylation of JNK, accompanying increased cardiomyocyte apoptosis that was attenuated by inhibition of p53. Importantly, elevation of 4‐HNE also triggered a reduction of the cytosolic HSP70, further corroborating cytosolic action of the 4‐HNE instigated by downregulation of mitochondrial ALDH2.
Conclusions
Downregulation of ALDH2 in the mitochondria induced an elevation of 4‐HNE, leading to cardiomyocyte apoptosis by subsequent inhibition of HSP70, phosphorylation of JNK, and activation of p53. This chain of molecular events took place in both the mitochondria and the cytosol, contributing to the mechanism underlying heart failure.
doi:10.1161/JAHA.113.000779
PMCID: PMC4323818  PMID: 25237043
ALDH2; apoptosis; heart failure; myocardial infarction; p53
9.  Time-dependent and ethanol-induced cardiac protection from ischemia mediated by mitochondrial translocation of εPKC and activation of aldehyde dehydrogenase 2 
The cardioprotective effects of moderate alcohol consumption have been well documented in animal models and in humans. Protection afforded against ischemia and reperfusion injury (I/R) proceeds through an ischemic preconditioning-like mechanism involving the activation of epsilon protein kinase C (εPKC) and is dependent on the time and duration of ethanol treatment. However, the substrates of εPKC and the molecular mechanisms by which the enzyme protects the heart from oxidative damage induced by I/R are not fully described. Using an open-chest model of acute myocardial infarction in vivo, we find that intraperitoneal injection of ethanol (0.5 g/kg) 60 minutes prior to (but not 15 minutes prior to) a 30-minute transient ligation of the left anterior descending coronary artery reduced I/R-mediated injury by 57% (measured as a decrease of creatine phosphokinase release into the blood). Only under cardioprotective conditions, ethanol treatment resulted in the translocation of εPKC to cardiac mitochondria, where the enzyme bound aldehyde dehydrogenase-2 (ALDH2). ALDH2 is an intra-mitochondrial enzyme involved in the detoxification of toxic aldehydes such as 4-hydroxy-2-nonenal (4-HNE) and 4-HNE mediates oxidative damage, at least in part, by covalently modifying and inactivating proteins (by forming 4-HNE adducts). In hearts subjected to I/R after ethanol treatment, the levels of 4-HNE protein adducts were lower and JNK1/2 and ERK1/2 activities were diminished relative to the hearts from rats subjected to I/R in the absence of ethanol. Together, this work provides an insight into the mitochondrial-dependent basis of ethanol-induced and εPKC-mediated protection from cardiac ischemia, in vivo.
doi:10.1016/j.yjmcc.2008.09.713
PMCID: PMC2675554  PMID: 18983847
10.  Aldehyde Dehydrogenase-2 Deficiency Aggravates Cardiac Dysfunction Elicited by Endoplasmic Reticulum Stress Induction 
Molecular Medicine  2012;18(1):785-793.
Mitochondrial aldehyde dehydrogenase-2 (ALDH2) has been characterized as an important mediator of endogenous cytoprotection in the heart. This study was designed to examine the role of ALDH2 knockout (KO) in the regulation of cardiac function after endoplasmic reticulum (ER) stress. Wild-type (WT) and ALDH2 KO mice were subjected to a tunicamycin challenge, and the echocardiographic property was examined. Protein levels of six items—78 kDa glucose-regulated protein (GRP78), phosphorylation of eukaryotic initiation factor 2 subunit α (p-eIF2α), CCAAT/enhancer-binding protein homologous protein (CHOP), phosphorylation of Akt, p47phox nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and 4-hydroxynonenal—were determined by using Western blot analysis. Cytotoxicity and apoptosis were estimated using 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyl-tetrazolium bromide (MTT) assay and caspase-3 activity, respectively. ALDH2 deficiency exacerbated cardiac contractile dysfunction and promoted ER stress after ER stress induction, manifested by the changes of ejection fraction and fractional shortening. In vitro study revealed that tunicamycin significantly upregulated the levels of GRP78, p-eIF2α, CHOP, p47phox NADPH oxidase and 4-hydroxynonenal, which was exacerbated by ALDH2 knockdown and abolished by ALDH2 overexpression, respectively. Overexpression of ALDH2 abrogated tunicamycin-induced dephosphorylation Akt. Inhibition of phosphatidylinositol 3-kinase using LY294002 did not affect ALDH2-conferred protection against ER stress, although LY294002 reversed the antiapoptotic action of ALDH2 associated with p47phox NADPH oxidase. These results suggest a pivotal role of ALDH2 in the regulation of ER stress and ER stress–induced apoptosis. The protective role of ALDH2 against ER stress–induced cell death was probably mediated by Akt via a p47phox NADPH oxidase-dependent manner. These findings indicate the critical role of ALDH2 in the pathogenesis of ER stress in heart disease.
doi:10.2119/molmed.2011.00466
PMCID: PMC3409283  PMID: 22430940
11.  Different effects of ascorbate deprivation and classical vascular nitrate tolerance on aldehyde dehydrogenase-catalysed bioactivation of nitroglycerin 
British Journal of Pharmacology  2009;156(8):1248-1255.
Background and purpose:
Vascular tolerance to nitroglycerin (GTN) may be caused by impaired GTN bioactivation due to inactivation of mitochondrial aldehyde dehydrogenase (ALDH2). As relaxation to GTN is reduced but still sensitive to ALDH2 inhibitors in ascorbate deficiency, we compared the contribution of ALDH2 inactivation to GTN hyposensitivity in ascorbate deficiency and classical in vivo nitrate tolerance.
Experimental approach:
Guinea pigs were fed standard or ascorbate-free diet for 2 weeks. Reversibility was tested by feeding ascorbate-deficient animals standard diet for 1 week. Nitrate tolerance was induced by subcutaneous injection of 50 mg·kg−1 GTN 4 times daily for 3 days. Ascorbate levels were determined in plasma, blood vessels, heart and liver. GTN-induced relaxation was measured as isometric tension of aortic rings; vascular GTN biotransformation was assayed as formation of 1,2-and 1,3-glyceryl dinitrate (GDN).
Key results:
Two weeks of ascorbate deprivation had no effect on relaxation to nitric oxide but reduced the potency of GTN ∼10-fold in a fully reversible manner. GTN-induced relaxation was similarly reduced in nitrate tolerance but not further attenuated by ALDH inhibitors. Nitrate tolerance reduced ascorbate plasma levels without affecting ascorbate in blood vessels, liver and heart. GTN denitration was significantly diminished in nitrate-tolerant and ascorbate-deficient rings. However, while the ∼10-fold preferential 1,2-GDN formation, indicative for active ALDH2, had been retained in ascorbate deficiency, selectivity was largely lost in nitrate tolerance.
Conclusions and implications:
These results indicate that nitrate tolerance is associated with ALDH2 inactivation, whereas ascorbate deficiency possibly results in down-regulation of ALDH2 expression.
doi:10.1111/j.1476-5381.2009.00126.x
PMCID: PMC2697729  PMID: 19254277
ascorbate level; bioactivation; biotransformation; guinea pig; nitrate tolerance; nitric oxide; nitroglycerin; vascular relaxation; mitochondrial aldehyde dehydrogenase; vitamin C
12.  Bioactivation of Nitroglycerin by Purified Mitochondrial and Cytosolic Aldehyde Dehydrogenases* 
The Journal of Biological Chemistry  2008;283(26):17873-17880.
Metabolism of nitroglycerin (GTN) to 1,2-glycerol dinitrate (GDN) and nitrite by mitochondrial aldehyde dehydrogenase (ALDH2) is essentially involved in GTN bioactivation resulting in cyclic GMP-mediated vascular relaxation. The link between nitrite formation and activation of soluble guanylate cyclase (sGC) is still unclear. To test the hypothesis that the ALDH2 reaction is sufficient for GTN bioactivation, we measured GTN-induced formation of cGMP by purified sGC in the presence of purified ALDH2 and used a Clark-type electrode to probe for nitric oxide (NO) formation. In addition, we studied whether GTN bioactivation is a specific feature of ALDH2 or is also catalyzed by the cytosolic isoform (ALDH1). Purified ALDH1 and ALDH2 metabolized GTN to 1,2- and 1,3-GDN with predominant formation of the 1,2-isomer that was inhibited by chloral hydrate (ALDH1 and ALDH2) and daidzin (ALDH2). GTN had no effect on sGC activity in the presence of bovine serum albumin but caused pronounced cGMP accumulation in the presence of ALDH1 or ALDH2. The effects of the ALDH isoforms were dependent on the amount of added protein and, like 1,2-GDN formation, were sensitive to ALDH inhibitors. GTN caused biphasic sGC activation with apparent EC50 values of 42 ± 2.9 and 3.1 ± 0.4 μm in the presence of ALDH1 and ALDH2, respectively. Incubation of ALDH1 or ALDH2 with GTN resulted in sustained, chloral hydrate-sensitive formation of NO. These data may explain the coupling of ALDH2-catalyzed GTN metabolism to sGC activation in vascular smooth muscle.
doi:10.1074/jbc.M801182200
PMCID: PMC2440601  PMID: 18450747
13.  Changes in aldehyde dehydrogenase 2 expression in rat blood vessels during glyceryl trinitrate tolerance development and reversal 
British Journal of Pharmacology  2011;164(2b):632-643.
BACKGROUND AND PURPOSE
Recent studies have suggested an essential role for aldehyde dehydrogenase 2 (ALDH2) in the bioactivation of organic nitrates such as glyceryl trinitrate (GTN). In the present study, we utilized an in vivo GTN tolerance model to further investigate the role of ALDH2 in GTN bioactivation and tolerance.
EXPERIMENTAL APPROACH
We assessed changes in aortic ALDH activity, and in ALDH2 protein expression in various rat blood vessels (aorta, vena cava, femoral artery and femoral vein) during continuous GTN exposure (0.4 mg·h−1 for 6, 12, 24 or 48 h) or after a 1-, 3- or 5-day drug-free period following a 48 h exposure to GTN, in relation to changes in vasodilator responses to GTN and in vascular GTN biotransformation.
KEY RESULTS
A decrease was observed in both ALDH2 protein expression (80% in tolerant veins and 30% in tolerant arteries after 48 h exposure to GTN) and aortic ALDH activity, concomitant with decreased vasodilator responses to GTN and decreased aortic GTN biotransformation. However, after a 24 h drug-free period following 48 h of GTN exposure, vasodilator responses to GTN and aortic GTN biotransformation activity had returned to control values, whereas vascular ALDH2 expression and aortic ALDH activity were still significantly depressed, and remained so for 3–5 days following cessation of GTN exposure.
CONCLUSIONS AND IMPLICATIONS
The dissociation of reduced ALDH activity and ALDH2 expression from the duration of the impaired vasodilator and biotransformation responses to GTN in nitrate-tolerant blood vessels, suggests that factors other than changes in ALDH2-mediated GTN bioactivation contribute to nitrate tolerance.
doi:10.1111/j.1476-5381.2011.01448.x
PMCID: PMC3188919  PMID: 21506955
glyceryl trinitrate; nitric oxide; aldehyde dehydrogenase; nitrate tolerance
14.  Murine hepatic aldehyde dehydrogenase 1a1 is a major contributor to oxidation of aldehydes formed by lipid peroxidation 
Chemico-biological interactions  2011;191(0):278-287.
Reactive lipid aldehydes are implicated in the pathogenesis of various oxidative stress-mediated diseases, including non-alcoholic steatohepatitis, atherosclerosis, Alzheimer’s and cataract. In the present study, we sought to define which hepatic Aldh isoform plays a major role in detoxification of lipid-derived aldehydes, such as acrolein and HNE by enzyme kinetic and gene expression studies. The catalytic efficiencies for metabolism of acrolein by Aldh1a1 was comparable to that of Aldh3a1 (Vmax/Km = 23). However, Aldh1a1 exhibits far higher affinity for acrolein (Km = 23.2 μM) compared to Aldh3a1 (Km = 464 μM). Aldh1a1 displays a 3-fold higher catalytic efficiency for HNE than Aldh3a1 (218 vs 69 ml/min/mg). The endogenous Aldh1a1 gene was highly expressed in mouse liver and a liver-derived cell line (Hepa-1c1c7) compared to Aldh2, Aldh1b1 and Aldh3a1. Aldh1a1 mRNA levels was 34-fold and 73-fold higher than Aldh2 in mouse liver and Hepa-1c1c7 cells respectively. Aldh3a1 gene was absent in mouse liver, but moderately expressed in Hepa-1c1c7 cells compared to Aldh1a1. We demonstrated that knockdown of Aldh1a1 expression by siRNA caused Hepa-1c1c7 cells to be more sensitive to acrolein-induced cell death and resulted in increased accumulation of acrolein-protein adducts and caspase 3 activation. These results indicate that Aldh1a1 plays a major role in cellular defense against oxidative damage induced by reactive lipid aldehydes in mouse liver. We also noted that hepatic Aldh1a1 mRNA levels were significantly increased (≈ 3 fold) in acrolein-fed mice compared to control. In addition, hepatic cytosolic ALDH activity was induced by acrolein when 1 mM NAD+ was used as cofactor, suggesting an Aldh1a1-protective mechanism against acrolein toxicity in mice liver. Thus, mechanisms to induce Aldh1a1 gene expression may provide a useful rationale for therapeutic protection against oxidative stress-induced pathologies.
doi:10.1016/j.cbi.2011.01.013
PMCID: PMC4409133  PMID: 21256123
aldehyde dehydrogenase 1a1; aldehydes; 4-hydroxy-2-nonenal; acrolein; toxicity
15.  The enigma of nitroglycerin bioactivation and nitrate tolerance: news, views and troubles 
British Journal of Pharmacology  2008;155(2):170-184.
Nitroglycerin (glyceryl trinitrate; GTN) is the most prominent representative of the organic nitrates or nitrovasodilators, a class of compounds that have been used clinically since the late nineteenth century for the treatment of coronary artery disease (angina pectoris), congestive heart failure and myocardial infarction. Medline lists more than 15 000 publications on GTN and other organic nitrates, but the mode of action of these drugs is still largely a mystery. In the first part of this article, we give an overview on the molecular mechanisms of GTN biotransformation resulting in vascular cyclic GMP accumulation and vasodilation with focus on the role of mitochondrial aldehyde dehydrogenase (ALDH2) and the link between the ALDH2 reaction and activation of vascular soluble guanylate cyclase (sGC). In particular, we address the identity of the bioactive species that activates sGC and the potential involvement of nitrite as an intermediate, describe our recent findings suggesting that ALDH2 catalyses direct 3-electron reduction of GTN to NO and discuss possible reaction mechanisms. In the second part, we discuss contingent processes leading to markedly reduced sensitivity of blood vessels to GTN, referred to as vascular nitrate tolerance. Again, we focus on ALDH2 and describe the current controversy on the role of ALDH2 inactivation in tolerance development. Finally, we emphasize some of the most intriguing, in our opinion, unresolved puzzles of GTN pharmacology that urgently need to be addressed in future studies.
doi:10.1038/bjp.2008.263
PMCID: PMC2538691  PMID: 18574453
cyclic GMP; endothelial dysfunction; nitric oxide; organic nitrate; soluble guanylate cyclase; smooth muscle; superoxide; thiol; vascular relaxation
16.  Molecular Characterization, Expression Analysis and Role of ALDH3B1 in The Cellular Protection Against Oxidative Stress 
Free radical biology & medicine  2010;49(9):1432-1443.
Aldehyde dehydrogenase (ALDH) enzymes are critical in the detoxification of aldehydes. The human genome contains 19 ALDH genes, mutations in which are the basis of several diseases. The expression, subcellular localization, enzyme kinetics and role of ALDH3B1 against aldehyde- and oxidant-induced cytotoxicity were investigated. ALDH3B1 was purified from Sf9 cells using chromatographic methods and enzyme kinetics were determined spectrophotometrically. ALDH3B1 demonstrated high affinity for hexanal (Km 62 μM), octanal (Km 8 μM), 4-hydroxy-2-nonenal (4HNE) (Km 52 μM) and benzaldehyde (Km 46 μM). Low affinity was seen towards acetaldehyde (Km 23.3 mM), malondialdehyde (Km 152 mM) and the ester p-nitrophenylacetate (Km 3.6 mM). ALDH3B1 mRNA was abundant in testis, lung, kidney and ovary. ALDH3B1 protein was highly expressed in these tissues and the liver. Immunofluorescence microscopy of ALDH3B1-transfected human embryonic kidney (HEK293) cells and subcellular fractionation of mouse kidney and liver revealed a cytosolic protein localization. ALDH3B1-transfected HEK293 cells were significantly protected from the lipid peroxidation-derived aldehydes trans-2-octenal, 4HNE and hexanal, and the oxidants H2O2 and menadione. In addition, ALDH3B1 protein expression was up-regulated by 4HNE in ARPE-19 cells. The results detailed in this study support a pathophysiological role for ALDH3B1 in protecting cells from the damaging effects of oxidative stress.
doi:10.1016/j.freeradbiomed.2010.08.004
PMCID: PMC3457645  PMID: 20699116
aldehyde dehydrogenase 3B1 (ALDH3B1); 4-hydroxy-2-nonenal; lipid peroxidation; mRNA; protein expression; enzyme kinetics; aldehyde toxicity
17.  Number of nitrate groups determines reactivity and potency of organic nitrates: a proof of concept study in ALDH-2−/− mice 
British Journal of Pharmacology  2007;150(4):526-533.
Background and purpose:
Mitochondrial aldehyde dehydrogenase (ALDH-2) has been shown to provide a pathway for bioactivation of organic nitrates and to be prone to desensitization in response to highly potent, but not to less potent, nitrates. We therefore sought to support the hypothesis that bioactivation by ALDH-2 critically depends on the number of nitrate groups within the nitrovasodilator.
Experimental approach:
Nitrates with one (PEMN), two (PEDN; GDN), three (PETriN; glyceryl trinitrate, GTN) and four (pentaerithrityl tetranitrate, PETN) nitrate groups were investigated. Vasodilatory potency was measured in isometric tension studies using isolated aortic segments of wild type (WT) and ALDH-2−/− mice. Activity of the cGMP-dependent kinase-I (reflected by levels of phosphorylated VAsodilator Stimulated Phosphoprotein, P-VASP) was quantified by Western blot analysis, mitochondrial dehydrogenase activity by HPLC. Following incubation of isolated mitochondria with PETN, PETriN-chromophore and PEDN, metabolites were quantified using chemiluminescence nitrogen detection and mass spectrometry.
Key results:
Compared to WT, vasorelaxation in response to PETN, PETriN and GTN was attenuated about 10fold in ALDH-2−/− mice, identical to WT vessels preincubated with inhibitors of ALDH-2. Reduced vasodilator potency correlated with reduced P-VASP formation and diminished biotransformation of the tetranitrate- and trinitrate-compounds. None of these findings were observed for PEDN, GDN and PEMN.
Conclusions and implications:
Our results support the crucial role of ALDH-2 in bioactivating highly reactive nitrates like GTN, PETN and PETriN. ALDH-2-mediated relaxation by organic nitrates therefore depends mainly on the number of nitrate groups. Less potent nitrates like PEDN, GDN and PEMN are apparently biotransformed by other pathways.
doi:10.1038/sj.bjp.0707116
PMCID: PMC2189719  PMID: 17220910
nitric oxide; nitrovasodilators; pentaerithrityl tetranitrate; mitochondrial aldehyde dehydrogenase
18.  Differential effects of organic nitrates on arterial diameter among healthy Japanese participants with different mitochondrial aldehyde dehydrogenase 2 genotypes: randomised crossover trial 
BMJ Open  2011;1(1):e000133.
Objectives
To determine whether polymorphisms at codon 487 (*1, GAA=Glu; *2, AAA=Lys) of mitochondrial aldehyde dehydrogenase 2 (ALDH2) influence nitroglycerine (glyceryl trinitrate (GTN))-induced vasodilation, and whether GTN or isosorbide dinitrate (ISDN) is a more effective antianginal agent in each ALDH2 genotype.
Design
A randomised, open-label, crossover trial with 117 healthy Japanese (20–39 years) whose genotypes were determined (*1/*1, n=47; *1/*2, n=48; *2/*2, n=22) was performed at Kyushu University Hospital, Fukuoka, Japan. Participants were randomly assigned to treatment: sublingual spray of GTN (0.3 mg) or ISDN (1.25 mg). After ≥1 week, measurements were repeated using the other drug. The main outcome measures were the maximal rate of increase in the brachial artery diameter determined by ultrasonography, the time required to attain maximal dilation (Tmax) and the time required to attain 90% maximal dilation (T0.9).
Results
The maximal artery diameter increase in response to GTN or ISDN did not differ among genotypes. However, GTN Tmax was significantly longer for *2/*2 (299.7 s, 269.0–330.4) than *1/*1 (254.7 s, 238.6–273.4; p=0.0190). GTN T0.9 was significantly longer in the *1/*2 (206.1 s, 191.7–219.3) and *2/*2 (231.4 s, 211.8–251.0) genotypes than *1/*1 (174.9 s, 161.5–188.3; p=0.0068, p<0.0001, respectively). In contrast, the time-course of ISDN-induced vasodilation did not differ among genotypes. GTN Tmax and T0.9 among *1 allele carriers (*1/*1 and *1/*2) were significantly shorter than those of ISDN, whereas the time course of GTN and ISDN vasodilation did not differ among participants carrying *2/*2.
Conclusions
The amplitude of GTN-induced vasodilation was not influenced by the ALDH2 genotype, but the response was significantly delayed in *2 allele carriers, especially *2/*2. GTN dilated the artery more quickly than ISDN in *1/*1 and *1/*2, but not in *2/*2.
Trial registration number
UMIN000001492 (UMIN-CTR database).
Article summary
Article focus
There were few reliable human studies on the influence of aldehyde dehydrogenase 2 (ALDH2) polymorphisms at codon 487 on the response to nitroglycerine (GTN). In particular, there was no information about the response to GTN in *2/*2 homozygotes.
It was unclear whether GTN or isosorbide dinitrate (ISDN) is a more effective antianginal agent in each ALDH2 genotype.
We aimed at comparing vasodilation induced by GTN and ISDN in individuals with different ALDH2 genotypes.
Key messages
The maximal rate of increase in arterial diameter after GTN treatment did not differ among ALDH2 genotype groups.
The time required to attain 90% maximal vasodilation was longer in the *1/*2 and *2/*2 groups than in the *1/*1 group.
GTN (0.3 mg) induced vasodilation more rapidly than ISDN (1.25 mg) in the *1/*1 and *1/*2 groups, but there was no difference between GTN and ISDN in the *2/*2 group.
Strengths and limitations of this study
The choice of healthy young individuals as participants may have strengthened the validity of the study; the participants' backgrounds were likely to be more homogeneous by excluding the influence of multiple concomitant factors that could not be controlled when studying patients or older subjects. However, the results could have been different if the study had been performed with patients with angina, because haemodynamic changes in patients might alter the response to nitrates.
Sublingual spray formulations of nitrates were used instead of tablets to minimise the fluctuation in absorption rate. However, this may have made the dosage slightly unreliable.
A randomised crossover design was used, and arterial diameter was determined by a single measurer blinded to genotype. However, the participants and investigators were not blinded to treatment.
Arterial diameter was accurately measured using a semiautomatic ultrasonography system. However, the brachial artery diameter was measured instead of the coronary artery diameter, and moreover, we did not evaluate venous dilation.
doi:10.1136/bmjopen-2011-000133
PMCID: PMC3191425  PMID: 22021773
Clinical pharmacology; therapeutics; hypertension; ischaemic heart disease; heart failure
19.  Central role of mitochondrial aldehyde dehydrogenase and reactive oxygen species in nitroglycerin tolerance and cross-tolerance 
Journal of Clinical Investigation  2004;113(3):482-489.
Recent studies suggest that mitochondrial aldehyde dehydrogenase (ALDH-2) plays a central role in the process of nitroglycerin (glyceryl trinitrate, GTN) biotransformation in vivo and that its inhibition accounts for mechanism-based tolerance in vitro. The extent to which ALDH-2 contributes to GTN tolerance (impaired relaxation to GTN) and cross-tolerance (impaired endothelium-dependent relaxation) in vivo remain to be elucidated. Rats were treated for three days with GTN. Infusions were accompanied by decreases in vascular ALDH-2 activity, GTN biotransformation, and cGMP-dependent kinase (cGK-I) activity. Further, whereas in control vessels, multiple inhibitors and substrates of ALDH-2 reduced both GTN-stimulation of cGKI and GTN-induced vasodilation, these agents had little effect on tolerant vessels. A state of functional tolerance (in the GTN/cGMP pathway) was recapitulated in cultured endothelial cells by knocking down mitochondrial DNA (ρ0 cells). In addition, GTN increased the production of reactive oxygen species (ROS) by mitochondria, and these increases were associated with impaired relaxation to acetylcholine. Finally, antioxidants/reductants decreased mitochondrial ROS production and restored ALDH-2 activity. These observations suggest that nitrate tolerance is mediated, at least in significant part, by inhibition of vascular ALDH-2 and that mitochondrial ROS contribute to this inhibition. Thus, GTN tolerance may be viewed as a metabolic syndrome characterized by mitochondrial dysfunction.
doi:10.1172/JCI200419267
PMCID: PMC324536  PMID: 14755345
20.  Aldehyde dehydrogenase-independent bioactivation of nitroglycerin in porcine and bovine blood vessels 
Biochemical Pharmacology  2015;93(4):440-448.
Graphical abstract
The vascular bioactivation of the antianginal drug nitroglycerin (GTN), yielding 1,2-glycerol dinitrate and nitric oxide or a related activator of soluble guanylate cyclase, is catalyzed by aldehyde dehydrogenase-2 (ALDH2) in rodent and human blood vessels. The essential role of ALDH2 has been confirmed in many studies and is considered as general principle of GTN-induced vasodilation in mammals. However, this view is challenged by an early report showing that diphenyleneiodonium, which we recently characterized as potent ALDH2 inhibitor, has no effect on GTN-induced relaxation of bovine coronary arteries (De La Lande et al., 1996). We investigated this issue and found that inhibition of ALDH2 attenuates GTN-induced coronary vasodilation in isolated perfused rat hearts but has no effect on relaxation to GTN of bovine and porcine coronary arteries. This observation is explained by low levels of ALDH2 protein expression in bovine coronary arteries and several types of porcine blood vessels. ALDH2 mRNA expression and the rates of GTN denitration were similarly low, excluding a significant contribution of ALDH2 to the bioactivation of GTN in these vessels. Attempts to identify the responsible pathway with enzyme inhibitors did not provide conclusive evidence for the involvement of ALDH3A1, cytochrome P450, or GSH-S-transferase. Thus, the present manuscript describes a hitherto unrecognized pathway of GTN bioactivation in bovine and porcine blood vessels. If present in the human vasculature, this pathway might contribute to the therapeutic effects of organic nitrates that are not metabolized by ALDH2.
doi:10.1016/j.bcp.2014.12.021
PMCID: PMC4321882  PMID: 25576686
ALDH, aldehyde dehydrogenase; CB25, 1-{[4-(1,3-benzodioxol-5-ylmethyl)-1-piperazinyl]methyl}-1H-indole-2,3-dione; cGMP, 3′,5′-cyclic guanosine monophosphate; DEA/NO, 2,2-diethyl-1-nitroso-oxyhydrazine; DMSO, dimethyl sulfoxide; DPI, diphenyleneiodonium; DTPA, diethylenetriamine pentaacetic acid; DTT, dithiothreitol; EDTA, ethylene diamine tetraacetic acid; GDN, glycerol dinitrate; GTN, glycerol trinitrate (nitroglycerin); NAD, nicotinamide adenine dinucleotide; l-NNA, NG-nitro-l-arginine; NO, nitric oxide; ODQ, 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one; sGC, soluble guanylate cyclase.; Aldehyde dehydrogenase-2; Denitration; Nitroglycerin; Protein expression; Vascular relaxation
21.  Impaired Cardiac SIRT1 Activity by Carbonyl Stress Contributes to Aging-Related Ischemic Intolerance 
PLoS ONE  2013;8(9):e74050.
Reactive aldehydes can initiate protein oxidative damage which may contribute to heart senescence. Sirtuin 1 (SIRT1) is considered to be a potential interventional target for I/R injury management in the elderly. We hypothesized that aldehyde mediated carbonyl stress increases susceptibility of aged hearts to ischemia/reperfusion (I/R) injury, and elucidate the underlying mechanisms with a focus on SIRT1. Male C57BL/6 young (4-6 mo) and aged (22-24 mo) mice were subjected to myocardial I/R. Cardiac aldehyde dehydrogenase (ALDH2), SIRT1 activity and protein carbonyls were assessed. Our data revealed that aged heart exhibited increased endogenous aldehyde/carbonyl stress due to impaired ALDH2 activity concomitant with blunted SIRT1 activity (P<0.05). Exogenous toxic aldehydes (4-HNE) exposure in isolated cardiomyocyte verified that aldehyde-induced carbonyl modification on SIRT1 impaired SIRT1 activity leading to worse hypoxia/reoxygenation (H/R) injury, which could all be rescued by Alda-1 (ALDH2 activator) (all P<0.05). However, SIRT1 inhibitor blocked the protective effect of Alda-1 on H/R cardiomyocyte. Interestingly, myocardial I/R leads to higher carbonylation but lower activity of SIRT1 in aged hearts than that seen in young hearts (P<0.05). The application of Alda-1 significantly reduced the carbonylation on SIRT1 and markedly improved the tolerance to in vivo I/R injury in aged hearts, but failed to protect Sirt1+/− knockout mice against myocardial I/R injury. This was verified by Alda-1 treatment improved postischemic contractile function recovery in ex vivo perfused aged but not in Sirt1+/− hearts. Thus, aldehyde/carbonyl stress is accelerated in aging heart. These results provide a new insight that impaired cardiac SIRT1 activity by carbonyl stress plays a critical role in the increased susceptibility of aged heart to I/R injury. ALDH2 activation can restore this aging-related myocardial ischemic intolerance.
doi:10.1371/journal.pone.0074050
PMCID: PMC3769351  PMID: 24040162
22.  ALDH2 protects against stroke by clearing 4-HNE 
Cell Research  2013;23(7):915-930.
Aldehyde dehydrogenase 2 (ALDH2) is a mitochondrial enzyme that metabolizes ethanol and toxic aldehydes such as 4-hydroxy-2-nonenal (4-HNE). Using an unbiased proteomic search, we identified ALDH2 deficiency in stroke-prone spontaneously hypertensive rats (SHR-SP) as compared with spontaneously hypertensive rats (SHR). We concluded the causative role of ALDH2 deficiency in neuronal injury as overexpression or activation of ALDH2 conferred neuroprotection by clearing 4-HNE in in vitro studies. Further, ALDH2-knockdown rats revealed the absence of neuroprotective effects of PKCε. Moderate ethanol administration that is known to exert protection against stroke was shown to enhance the detoxification of 4-HNE, and to protect against ischemic cerebral injury through the PKCε-ALDH2 pathway. In SHR-SP, serum 4-HNE level was persistently elevated and correlated inversely with the lifespan. The role of 4-HNE in stroke in humans was also suggested by persistent elevation of its plasma levels for at least 6 months after stroke. Lastly, we observed that 21 of 1 242 subjects followed for 8 years who developed stroke had higher initial plasma 4-HNE levels than those who did not develop stroke. These findings suggest that activation of the ALDH2 pathway may serve as a useful index in the identification of stroke-prone subjects, and the ALDH2 pathway may be a potential target of therapeutic intervention in stroke.
doi:10.1038/cr.2013.69
PMCID: PMC3698638  PMID: 23689279
ALDH2; 4-HNE; stroke; ethanol
23.  A new class of organic nitrates: investigations on bioactivation, tolerance and cross-tolerance phenomena 
British Journal of Pharmacology  2009;158(2):510-520.
Background and purpose:
The chronic use of organic nitrates is limited by serious side effects including oxidative stress, nitrate tolerance and/or endothelial dysfunction. The side effects and potency of nitroglycerine depend on mitochondrial aldehyde dehydrogenase (ALDH-2). We sought to determine whether this concept can be extended to a new class of organic nitrates with amino moieties (aminoalkyl nitrates).
Experimental approach:
Vasodilator potency of the organic nitrates, in vitro tolerance and in vivo tolerance (after continuous infusion for 3 days) were assessed in wild-type and ALDH-2 knockout mice by isometric tension studies. Mitochondrial oxidative stress was analysed by L-012-dependent chemiluminescence and protein tyrosine nitration.
Key results:
Aminoethyl nitrate (AEN) showed an almost similar potency to glyceryl trinitrate (GTN), even though it is only a mononitrate. AEN-dependent vasodilatation was mediated by cGMP and nitric oxide. In contrast to triethanolamine trinitrate (TEAN) and GTN, AEN bioactivation did not depend on ALDH-2 and caused no in vitro tolerance. In vivo treatment with TEAN and GTN, but not with AEN, induced cross-tolerance to acetylcholine (ACh)-dependent and GTN-dependent relaxation. Although all nitrates tested induced tolerance to themselves, only TEAN and GTN significantly increased mitochondrial oxidative stress in vitro and in vivo.
Conclusions and implications:
The present results demonstrate that not all high potency nitrates are bioactivated by ALDH-2 and that high potency of a given nitrate is not necessarily associated with induction of oxidative stress or nitrate tolerance. Obviously, there are distinct pathways for bioactivation of organic nitrates, which for AEN may involve xanthine oxidoreductase rather than P450 enzymes.
doi:10.1111/j.1476-5381.2009.00303.x
PMCID: PMC2757691  PMID: 19563531
organic nitrates; bioactivation; mitochondrial aldehyde dehydrogenase; mitochondrial oxidative stress; vascular function
24.  Neurodegeneration and Motor Dysfunction in Mice Lacking Cytosolic and Mitochondrial Aldehyde Dehydrogenases: Implications for Parkinson's Disease 
PLoS ONE  2012;7(2):e31522.
Previous studies have reported elevated levels of biogenic aldehydes in the brains of patients with Parkinson's disease (PD). In the brain, aldehydes are primarily detoxified by aldehyde dehydrogenases (ALDH). Reduced ALDH1 expression in surviving midbrain dopamine neurons has been reported in brains of patients who died with PD. In addition, impaired complex I activity, which is well documented in PD, reduces the availability of the NAD+ co-factor required by multiple ALDH isoforms to catalyze the removal of biogenic aldehydes. We hypothesized that chronically decreased function of multiple aldehyde dehydrogenases consequent to exposure to environmental toxins and/or reduced ALDH expression, plays an important role in the pathophysiology of PD. To address this hypothesis, we generated mice null for Aldh1a1 and Aldh2, the two isoforms known to be expressed in substantia nigra dopamine neurons. Aldh1a1−/−×Aldh2−/− mice exhibited age-dependent deficits in motor performance assessed by gait analysis and by performance on an accelerating rotarod. Intraperitoneal administration of L-DOPA plus benserazide alleviated the deficits in motor performance. We observed a significant loss of neurons immunoreactive for tyrosine hydroxylase (TH) in the substantia nigra and a reduction of dopamine and metabolites in the striatum of Aldh1a1−/−×Aldh2−/− mice. We also observed significant increases in biogenic aldehydes reported to be neurotoxic, including 4-hydroxynonenal (4-HNE) and the aldehyde intermediate of dopamine metabolism, 3,4-dihydroxyphenylacetaldehyde (DOPAL). These results support the hypothesis that impaired detoxification of biogenic aldehydes may be important in the pathophysiology of PD and suggest that Aldh1a1−/−×Aldh2−/− mice may be a useful animal model of PD.
doi:10.1371/journal.pone.0031522
PMCID: PMC3284575  PMID: 22384032
25.  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.
doi:10.1016/j.jprot.2011.05.013
PMCID: PMC3177986  PMID: 21609791
Aldehyde dehydrogenases; post-translational modifications; cellular defense; drug toxicity; disease states; translational research

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