Aldehyde Dehydrogenase 2 Protein Expression Research Articles

Aldehyde Dehydrogenase 2 (ALDH2): A novel sorafenib target in hepatocellular carcinoma unraveled by the proteome-wide cellular thermal shift assay

Sorafenib is a multikinase inhibitor indicated for first-line treatment of unresectable hepatocellular carcinoma. Despite its widespread use in the clinic, the existing knowledge of sorafenib mode-of-action remains incomplete. To build upon the current understanding, we used the Cellular Thermal Shift Assay (CETSA) coupled to Mass Spectrometry (CETSA-MS) to monitor compound binding to its target proteins in the cellular context on a proteome-wide scale. Among the potential sorafenib targets, we identified aldehyde dehydrogenase 2 (ALDH2), an enzyme that plays a major role in alcohol metabolism. We validated the interaction of sorafenib with ALDH2 by orthogonal methods using pure recombinant protein, proving that this interaction is not mediated by other cellular components. Moreover, we showed that sorafenib inhibits ALDH2 activity, supporting a functional role for this interaction. Finally, we were able to demonstrate that both ALDH2 protein expression and activity were reduced in sorafenib-resistant cells compared to the parental cell line. Overall, our study allowed the identification of ALDH2 as a novel sorafenib target and sheds light on its potential role in both hepatocellular carcinoma and sorafenib resistance condition.

ALDH2 as a potential stem cell-related biomarker in lung adenocarcinoma: Comprehensive multi-omics analysis

Lung adenocarcinoma (LUAD) is the most prevalent lung cancer and one of the leading causes of death. Previous research found a link between LUAD and Aldehyde Dehydrogenase 2 (ALDH2), a member of aldehyde dehydrogenase gene (ALDH) superfamily. In this study, we identified additional useful prognostic markers for early LUAD identification and targeting LUAD therapy by analyzing the expression level, epigenetic mechanism, and signaling activities of ALDH2 in LUAD patients. The obtained results demonstrated that ALDH2 gene and protein expression significantly downregulated in LUAD patient samples. Furthermore, The American Joint Committee on Cancer (AJCC) reported that diminished ALDH2 expression was closely linked to worse overall survival (OS) in different stages of LUAD. Considerably, ALDH2 showed aberrant DNA methylation status in LUAD cancer. ALDH2 was found to be downregulated in the proteomic expression profile of several cell biology signaling pathways, particularly stem cell-related pathways. Finally, the relationship of ALDH2 activity with stem cell-related factors and immune system were reported. In conclusion, the downregulation of ALDH2, abnormal DNA methylation, and the consequent deficit of stemness signaling pathways are relevant prognostic and therapeutic markers in LUAD.

Buyang Huanwu decoction inhibits cardiomyocyte apoptosis after myocardial infarction by enhancing aldehyde dehydrogenase-2 activity and protein expression

ObjectiveTo investigate the potential mechanisms of the protective effects of Buyang Huanwu decoction (BYHWD) on cardiomyocyte apoptosis after myocardial infarction (MI) and to provide the foundation for the clinical application of BYHWD in preventing and treating cardiomyocyte apoptosis-related disorders after MI. MethodsThe MI rat model was established by ligation of the left anterior descending (LAD) coronary artery. After the 20-week treatment with BYHWD, the following parameters were assessed to investigate the protective effects of BYHWD on cardiomyocyte apoptosis after MI, both in vivo and in vitro: mortality rate; heart weight/body weight (HW/BW); transthoracic echocardiography measurements; histopathological analysis; immunohistochemistry (IHC) analysis; TUNEL apoptosis assay; caspase-3 activity assay; aldehyde dehydrogenase-2 (ALDH2) enzymatic activity assay; malondialdehyde (MDA) content analysis; western blot analysis; MTT assay; and Hoechst 33342/PI apoptosis assay. ResultsThe mortality of the MI rats was significantly reduced by BYHWD treatment. Furthermore, BYHWD treatment significantly improved the heart function and significantly reduced the HW/BW ratio. Histopathological analysis showed that BYHWD treatment significantly relieved MI-induced cardiac injury and significantly decreased collagen formation. The TUNEL apoptosis assay showed that treatment with BYHWD reduced the cardiomyocyte apoptosis of MI rats in a dose-dependent manner. Moreover, BYHWD treatment could significantly inhibit oxidative stress-induced neonatal cardiomyocyte apoptosis, which is consistent with the results of animal experiments in vivo. Interestingly, the ALDH2 activity and protein expression was significantly reduced in the MI model group, while the content of toxic aldehydes, including 4-HNE and MDA, was increased. Importantly, BYHWD enhanced the activity of ALDH2 and the expression of ALDH2 protein and attenuated the content of toxic aldehydes in a dose-dependent manner. Furthermore, we found that co-treatment with an ALDH2 inhibitor, disulfiram, partially inhibited the cardiomyocyte protective effects of BYHWD. ConclusionsCollectively, our results suggest that BYHWD exerted anti-apoptotic effects in cardiomyocytes after MI by enhancing the ALDH2 activity and protein expression and decreasing the toxic aldehyde content.

Aldehyde dehydrogenase 2 inhibited oxidized LDL-induced NLRP3 inflammasome priming and activation via attenuating oxidative stress

Oxidized low-density lipoprotein (ox-LDL)-mediated NLRP3 inflammasome activation is crucial in atherosclerosis (AS) initiation and progression. Aldehyde dehydrogenase 2 (ALDH2) has been reported to display protective effects during AS development; however, the underlying mechanisms are largely unknown. Here we investigate the role of ALDH2 in ox-LDL-induced NLRP3 inflammasome priming and activation. We treated RAW264.7 murine macrophages with ox-LDL with or without ALDH2 activator Alda-1 and measured NLRP3 inflammasome priming and activation, ALDH2 protein expression and enzyme activity, IL-1β release, and DNA damage. It was found that ox-LDL impaired ALDH2 activity and induced NLRP3 inflammasome priming and activation. Alda-1 inhibited both of the priming and activation steps of NLRP3 inflammasome as well as subsequent cell pyroptosis and attenuated ROS and 4-HNE levels in ox-LDL-treated macrophages. Taken together, ALDH2 activation inhibits priming and activation of NLRP3 inflammasome via reducing oxidative stress, which suggests that ALDH2 may be a potential target for anti-inflammatory therapies in AS treatment.

ALDH2 Overexpression Alleviates High Glucose-Induced Cardiotoxicity by Inhibiting NLRP3 Inflammasome Activation.

Although the underlying mechanisms of diabetes-induced myocardial injury have not been fully illuminated, the inflammation reaction has been reported intently linked with diabetes. The nucleotide binding oligomerization domain-like receptor protein 3 (NLRP3) inflammasome, the key component of pyroptosis, is involved in inflammation reaction, which may be one of the important mechanisms in diabetes-induced myocardial injury. The purpose of this study was to investigate the changes of NLRP3 inflammasome and pyroptosis in high glucose-induced H9C2 cardiac cell injury and investigate whether overexpression of mitochondrial aldehyde dehydrogenase 2 (ALDH2) can reduce the occurrence of pyroptosis. The H9C2 cardiac cells were exposed to 35 mM glucose for 24 h to induce cytotoxicity. Mitochondrial ALDH2 overexpression cardiac cell line was constructed. The results showed in high glucose condition that ALDH2 overexpression significantly increased H9C2 cardiac cell viability, increased mitochondrial ALDH2 activity and protein expression, and reduced mitochondrial reactive oxygen species (ROS) production, 4-hydroxynonenal (4-HNE), and lactate dehydrogenase (LDH) levels; meanwhile, the pyroptosis key components—NLRP3 inflammasome-related proteins, apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), cysteine-containing aspartate specific protease 1 (Caspase-1), and interleukin-18 (IL-18) protein expressions—were significantly decreased, and IL-18 and interleukin-1β (IL-1β) levels were also decreased. In high glucose-induced cardiac cell injury, ALDH2 overexpression may reduce ROS production, thereby inhibiting the activation of NLRP3 inflammation and cell pyroptosis. ALDH2 gene might play the potential role in the treatment of high glucose-induced H9C2 cardiac cell injury.

[Activation of aldehyde dehydrogenase 2 alleviates H 2O 2-induced injury in cardiomyocytes].

To investigate the changes of aldehyde dehydrogenase 2 (ALDH2) expression in H 2O 2inducedcardiomyocytes oxidative stress injury. Cultured H9C2 cardiomyocytes were exposed to H 2O 2-inducedoxidative stress and the effects of the ALDH2 agonist Alda-1 and ALDH2 inhibitor Daidzin were tested on the stress level ofthe exposed cells. MTT colorimetric assay was used to assess the cell viability after the treatments. The oxidative stress level inthe myocardial cells was detected using DHE fluorescence staining, and the activity and protein level of ALDH2 were detectedwith spectrophotometry and Western blotting. Compared with normal control cells, Alda-1 treatment did notsignificantly affect the cell viability, oxidative stress level, or ALDH2 activity and protein level. H 2O 2 exposure significantlylowered the cell activity and ALDH2 activity and protein expression and increased the oxidative stress level; Alda-1 treatmentobvious antagonized the effects of H 2O 2. Blocking ALDH2 with Daidzin produced similar effects to H 2O 2 exposure on theviability, oxidative stress level, and ALDH2 activity and expression in the myocardial cells. H 2O 2 exposure lowersthe activity and reduces the protein expression of ALDH2 in cardiomyocyte H9C2 cells, and activation of ALDH2 can alleviateH 2O 2-induced oxidative stress in the cells.

Alterations in necroptosis during ALDH2‑mediated protection against high glucose‑induced H9c2 cardiac cell injury.

The aim of the present study was to investigate whether necroptosis occurs in high glucose (HG)-induced H9c2 cardiac cell injury and whether the activation of aldehyde dehydrogenase 2 (ALDH2) can inhibit necroptosis. H9c2 cardiac cells were treated with 35 mM glucose to establish a HG-induced cell injury model. Alda-1 (20 µM), a specific activator of ALDH2 and necrostatin-1 (Nec-1, 100 µM), an inhibitor of necroptosis were used to treat H9c2 cardiac cells under HG conditions. Cell viability was measured using a Cell Counting Kit-8 assay and reactive oxygen species (ROS) generation was measured by the dihydroethidium staining method. ALDH2 activity was measured at 450 nm. The mRNA and protein expression of ALDH2, necroptosis-associated genes, receptor-interacting protein (RIP)1, RIP3 and mixed lineage kinase domain like pseudokinase (MLKL), were analyzed by reverse transcription-quantitative polymerase chain reaction and western blotting. The expression of cleaved caspase-3 protein was also examined by western blotting. The results demonstrated that under HG conditions, cell viability, ALDH2 activity, mRNA and protein expression were decreased. Furthermore, ROS generation, mRNA and protein expression of RIP1, RIP3, MLKL and the protein expression of cleaved caspase-3 were increased. Treatment with Alda-1 or Nec-1 attenuated HG-induced downregulation of ALDH2 activity, mRNA and protein expression. In addition, RIP1, RIP3, MLKL mRNA, and protein expression were downregulated. Furthermore, Alda-1 but not Nec-1 decreased cleaved caspase-3 protein expression. Collectively these data indicated that activation of ALDH2 protected H9c2 cardiac cells against HG-induced injury, partly by inhibiting the occurrence of necroptosis.

Activation of ALDH2 with Low Concentration of Ethanol Attenuates Myocardial Ischemia/Reperfusion Injury in Diabetes Rat Model.

The aim of this paper is to observe the change of mitochondrial aldehyde dehydrogenase 2 (ALDH2) when diabetes mellitus (DM) rat heart was subjected to ischemia/reperfusion (I/R) intervention and analyze its underlying mechanisms. DM rat hearts were subjected to 30 min regional ischemia and 120 min reperfusion in vitro and pretreated with ALDH2 activator ethanol (EtOH); cardiomyocyte in high glucose (HG) condition was pretreated with ALDH2 activator Alda-1. In control I/R group, myocardial tissue structure collapse appeared. Compared with control I/R group, left ventricular parameters, SOD activity, the level of Bcl-2/Bax mRNA, ALDH2 mRNA, and protein expressions were decreased and LDH and MDA contents were increased, meanwhile the aggravation of myocardial structure injury in DM I/R group. When DM I/R rats were pretreated with EtOH, left ventricular parameters, SOD, Bcl-2/Bax, and ALDH2 expression were increased; LDH, MDA, and myocardial structure injury were attenuated. Compared with DM + EtOH I/R group, cyanamide (ALDH2 nonspecific blocker), atractyloside (mitoPTP opener), and wortmannin (PI3K inhibitor) groups all decreased left ventricular parameters, SOD, Bcl-2/Bax, and ALDH2 and increased LDH, MDA, and myocardial injury. When cardiomyocyte was under HG condition, CCK-8 activity and ALDH2 protein expression were decreased. Alda-1 increased CCK-8 and ALDH2. Our findings suggested enhanced ALDH2 expression in diabetic I/R rats played the cardioprotective role, maybe through activating PI3K and inhibiting mitoPTP opening.

Aldehyde dehydrogenase 2 protects human umbilical vein endothelial cells against oxidative damage and increases endothelial nitric oxide production to reverse nitroglycerin tolerance.

Medical nitroglycerin (glyceryl trinitrate, GTN) use is limited principally by tolerance typified by a decrease in nitric oxide (NO) produced by biotransformation. Such tolerance may lead to endothelial dysfunction by inducing oxidative stress. In vivo studies have demonstrated that aldehyde dehydrogenase 2 (ALDH2) plays important roles in GTN biotransformation and tolerance. Thus, modification of ALDH2 expression represents a potentially effective strategy to prevent and reverse GTN tolerance and endothelial dysfunction. In this study, a eukaryotic expression vector containing the ALDH2 gene was introduced into human umbilical vein endothelial cells (HUVECs) by liposome-mediated transfection. An indirect immunofluorescence assay showed that ALDH2 expression increased 24 h after transfection. Moreover, real-time polymerase chain reaction and western blotting revealed significantly higher ALDH2 mRNA and protein expression in the gene-transfected group than in the two control groups. GTN tolerance was induced by treating HUVECs with 10 mM GTN for 16 h + 10 min, which significantly decreased NO levels in control cells, but not in those transfected with ALDH2. Overexpression of ALDH2 increased cell survival against GTN-induced cytotoxicity and conferred protection from oxidative damage resulting from nitrate tolerance, accompanied by decreased production of intracellular reactive oxygen species and reduced expression of heme oxygenase 1. Furthermore, ALDH2 overexpression promoted Akt phosphorylation under GTN tolerance conditions. ALDH2 gene transfection can reverse and prevent tolerance to GTN through its bioactivation and protect against oxidative damage, preventing the development of endothelial dysfunction.

Impaired Regulation of ALDH2 Protein Expression Revealing a Yet Unknown Epigenetic Impact of rs886205 on Specific Methylation of a Negative Regulatory Promoter Region in Alcohol-Dependent Patients

Acetaldehyde, the carcinogenic metabolite of ethanol known to provoke aversive symptoms of alcohol consumption, is predominantly eliminated by aldehyde dehydrogenase 2 (ALDH2). Reduced ALDH2 activity correlates with low alcohol tolerance and low risk for alcohol dependence. The ALDH2 promoter polymorphism rs886205 (A>G) is associated with decreased promoter activity, but a molecular mechanism and allele-dependent ALDH2 protein expression has not been described yet. On the basis of allele-dependent epigenetic effects, we analyzed the rs886205 genotype, methylation rates of cytosine-phosphatidyl-guanine (CpG)-sites within a regulatory promoter region and ALDH2 protein levels in 82 alcohol-dependent patients during a 2-week withdrawal and compared them to 34 matched controls. Patients without the G-allele of rs886205 showed higher methylation of the promoter region than controls and readily adapted epigenetically as well as on protein level during withdrawal, while patients with the G-allele displayed retarded methylation readjustment and no change in ALDH2 protein levels. Our data provide novel insights into an unknown genetic-epigenetic interaction, revealing impaired ALDH2 protein expression in patients with the G-allele of rs886205. Additionally, we checked for an association between rs886205 and protection against alcohol dependence and found a trend association between the G-allele and protection against alcohol dependence that needs replication in a larger Caucasian cohort.

Aldehyde dehydrogenase-independent bioactivation of nitroglycerin in porcine and bovine blood vessels

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.

Aberrant hypermethylation of aldehyde dehydrogenase 2 promoter upstream sequence in rats with experimental myocardial infarction.

Background. Aldehyde dehydrogenase 2 (ALDH2) plays a crucial role in myocardial protection against ischemia. Downregulation of ALDH2 was evidenced after myocardial infarction and the underlying mechanism is not fully understood. DNA methylation can regulate gene transcription in epigenetic level. We thus hypothesized that DNA methylation may affect ALDH2 expression in myocardial infarction (MI). Methods. MI was induced in Sprague-Dawley rats. MI border zone tissues were harvested at 1st week, 2nd week, and 3rd week after MI. Bisulfite sequencing PCR (BSP) was performed to detect the methylation levels of ALDH2 core promoter. Sequenom MassARRAY platform (MassARRAY) was used to examine the methylation levels of ALDH2 promoter upstream sequence. ALDH2 protein and mRNA expression were assayed by Western blot and real-time PCR, respectively. Results. Compared with Sham group, ALDH2 protein and mRNA expression of MI groups was significantly downregulated. Compared with Sham group, DNA methylation level of CpG sites in ALDH2 promoter upstream sequence was significantly higher in MI groups in a time-dependent manner (CpG1, CpG2, and CpG7, P < 0.01). DNA methylation did not affect ALDH2 core promoter sequence during the progress of MI. No significant difference was detected in DNA methylation level of ALDH2 promoter upstream sequence among MI groups. Conclusion. Aberrant hypermethylation of CpG sites in ALDH2 promoter upstream sequence is associated with myocardial ischemia injury and may partly result in ALDH2 downregulation after MI.

Alda-1 reduces cerebral ischemia/reperfusion injury in rat through clearance of reactive aldehydes

Many studies demonstrate that accumulation of reactive aldehydes plays an important role in cellular oxidative injury and aldehyde dehydrogenase 2 (ALDH2)-mediated detoxification of reactive aldehydes is thought as an endogenous protective mechanism against cell injury. This study was performed to explore whether Alda-1, a newly identified ALDH2 activator, was able to protect brain against ischemia/reperfusion injury through clearance of reactive aldehydes. In a rat model of focal cerebral ischemia/reperfusion injury, neurological function, infarct volume, cellular apoptosis, mortality, ALDH2 activity and protein expression, contents of 4-hydroxy-2-nonenal (4-HNE), and malondialdehyde (MDA) were determined. The results showed that ischemia/reperfusion treatment led to increase in neurological deficit score, infarct volume, cellular apoptosis, and mortality accompanied by the elevated levels of reactive aldehydes (4-HNE and MDA). There was no significant change in ALDH2 activity and protein expression. Alda-1 treatment at both dosages (15mg/kg × 2 or 50mg/kg × 2, i.g.) was able to increase the activity of ALDH2 and decrease the accumulation of reactive aldehydes concomitantly with the improvement of brain injury (decrease in infarct volume, cellular apoptosis, and mortality) and neurological function (decrease in neurological deficit score). However, Alda-1 treatment did not affect ALDH2 protein expression. Our results suggest that the protective effect of Alda-1 on cerebral ischemia/reperfusion injury is related to ALDH2 activation and clearance of reactive aldehydes.

ASSA13-03-28 Effect of ALDH2 on Myocardial Ischemia/Reperfusion Injury in Diabetic Rats and Related Mechanism Research

Objective To observe the role of activation of aldehyde dehydrogenase 2 (ALDH2) on myocardial ischemia/reperfusion injury in diabetic rats, and study the relationships of ALDH2, PI3K-Akt and mitochondrial permeability transition pore in myocardial injury. Methods Diabetic rat model was simulated by intraperitoneal injection 55 mg/kg streptozotocin (STZ) and divided into diabetes and ethanol + diabetes groups. After 8 weeks, myocardial ischemia/reperfusion model was mimicked in vitro, and subjected to drug intervention, divided into: diabetic I/R + ethanol +cyanamide (DM +EtOH I/R +CYA); diabetic I/R + ethanol +atractyloside (DM+EtOH I/R+Atr), diabetic I/R + ethanol +wortmannin (DM+EtOH I/R+Wor). The ventricular hemodynamic parameters and lactate dehydrogenase (LDH) content in coronary flow were determined. SOD activity and MDA content were evaluated, the activities of caspase-3 and ALDH2 were evaluated, and the expressions of Bcl-2, Bax and ALDH2 mRNA were detected by RT-PCR; ALDH2 protein expression was evaluated by western blot. Results In contrast to I/R in control rat, left ventricular development pressure (LVDP), maximal rise/fall rate of left ventricular pressure (± dp/dtmax), left ventricular work (RPP), SOD and ALDH2 activities were decreased in diabetic rat, left ventricular end diastolic pressure (LVEDP), LDH release, caspase-3 activity and MDA content were increased, and the expression of Bcl-2/Bax mRNA, ALDH2 mRNA and protein expressions were decreased. Compared with DM I/R group, in DM+EtOH I/R group, LVDP, ± dp/dtmax, RPP, SOD and ALDH2 activities were increased, LVEDP, LDH release, caspase-3 activity and MDA content were increased, and the expression Bcl-2/Bax mRNA, ALDH2 mRNA and protein expressions were increased. Compared with DM+EtOH I/R group, in DM+EtOH+CYA I/R group, DM+EtOH+Atr I/R group and DM+EtOH+ Wor I/R group, LVDP, ±dp/dtmax, RPP, SOD and ALDH2 activities were further decreased, and LVEDP, caspase-3 activity and MDA content were increased, and the expression Bcl-2/Bax mRNA, ALDH2 mRNA and protein expressions were decreased. Conclusions Enhanced mitochondrial ALDH2 expression in diabetic rats can play cardiac protective role, and activation of ALDH2 plays the myocardial protective effect through inhibiting mitoPTP opening and activation of PI3K-Akt signalling pathway.

Tolerance to nitroglycerin through proteasomal down‐regulation of aldehyde dehydrogenase‐2 in a genetic mouse model of ascorbate deficiency

Background and PurposeL-gulonolactone oxidase-deficient (Gulo(-/-)) mice were used to study the effects of ascorbate deficiency on aortic relaxation by nitroglycerin (GTN) with focus on changes in the expression and activity of vascular aldehyde dehydrogenase-2 (ALDH2), which catalyses GTN bioactivation.Experimental ApproachAscorbate deficiency was induced in Gulo(-/-) mice by ascorbate deprivation for 4 weeks. Some of the animals were concomitantly treated with the proteasome inhibitor bortezomib and effects compared with ascorbate-supplemented Gulo(-/-), untreated or nitrate-tolerant wild-type mice. Aortic relaxation of the experimental groups to GTN, ACh and a NO donor was studied. Changes in mRNA and protein expression of vascular ALDH2 were quantified by qPCR and immunoblotting, respectively, and aortic GTN denitration rates determined.Key ResultsLike GTN treatment, ascorbate deprivation induced vascular tolerance to GTN that was associated with markedly decreased rates of GTN denitration. Ascorbate deficiency did not affect ALDH2 mRNA levels, but reduced ALDH2 protein expression and the total amount of ubiquitinated proteins to about 40% of wild-type controls. These effects were largely prevented by ascorbate supplementation or treating Gulo(-/-) mice with the 26S proteasome inhibitor bortezomib.Conclusions and ImplicationsOur data indicate that ascorbate deficiency results in vascular tolerance to GTN via proteasomal degradation of ALDH2. The results support the view that impaired ALDH2-catalysed metabolism of GTN contributes significantly to the development of vascular nitrate tolerance and reveal a hitherto unrecognized protective effect of ascorbate in the vasculature.