Mitochondrial aldehyde dehydrogenase 2 activation and cardioprotection

Advances in Factors Affecting ALDH2 Activity and its Mechanisms

Aldehyde dehydrogenase 2 (ALDH2) is a mitochondrial enzyme primarily involved in the detoxification of alcohol-derived aldehyde and endogenous toxic aldehydes. It exhibits widespread expression across various organs and exerts a broad and significant impact on diverse acute cardiovascular diseases, including acute coronary syndrome, acute aortic dissection, hypoxic pulmonary hypertension, and heart failure. The ALDH2 rs671 variant represents the most prevalent genetic variant in East Asian populations, with carriage rates ranging from 30 to 50% among the Chinese population. Given its widespread presence in the body, the wide range of diseases it affects, and its high rate of variation, it can serve as a crucial tool for the precise prevention and treatment of acute cardiovascular diseases, while offering individualized medication guidance. This review aims to provide a comprehensive overview of the latest advancements in factors affecting ALDH2 activity, encompassing post-transcriptional modifications, modulators of ALDH2, and relevant clinical drugs.

Novel insights into the activating transcription factor 4 in Alzheimer's disease and associated aging-related diseases: Mechanisms and therapeutic implications

Ageing is inherent to all human beings, most mechanistic explanations of ageing results from the combined effects of various physiological and pathological processes. Additionally, aging pivotally contributes to several chronic diseases. Activating transcription factor 4 (ATF4), a member of the ATF/cAMP response element-binding protein family, has recently emerged as a pivotal player owing to its indispensable role in the pathophysiological processes of Alzheimer's disease and aging-related diseases. Moreover, ATF4 is integral to numerous biological processes. Therefore, this article aims to comprehensively review relevant research on the role of ATF4 in the onset and progression of aging-related diseases, elucidating its potential mechanisms and therapeutic approaches. Our objective is to furnish scientific evidence for the early identification of risk factors in aging-related diseases and pave the way for new research directions for their treatment. By elucidating the signaling pathway network of ATF4 in aging-related diseases, we aspire to gain a profound understanding of the molecular and cellular mechanisms, offering novel strategies for addressing aging and developing related therapeutics.

Research Progress on the Correlation between Acetaldehyde Dehydrogenase 2 and Hepatocellular Carcinoma Development

Hepatocellular carcinoma (HCC) is the predominant pathologic type of primary liver cancer. It is a malignant tumor of liver epithelial cells. There are many ways to treat HCC, but the survival rate for HCC patients remains low. Therefore, understanding the underlying mechanisms by which HCC occurs and develops is critical to explore new therapeutic targets. Aldehyde dehydrogenase 2 (ALDH2) is an important player in the redox reaction of ethanol with endogenous aldehyde products released by lipid peroxidation. Increasing evidence suggests that ALDH2 is a crucial regulator of human tumor development, including HCC. Therefore, clarifying the relationship between ALDH2 and HCC is helpful for formulating rational treatment strategies. This review highlights the regulatory roles of ALDH2 in the development of HCC, elucidates the multiple potential mechanisms by which ALDH2 regulates the development of HCC, and summarizes the progress of research on ALDH2 gene polymorphisms and HCC susceptibility. Meanwhile, we envision viable strategies for targeting ALDH2 in the treatment of HCC SIGNIFICANCE STATEMENT: Numerous studies have aimed to explore novel therapeutic targets for HCC, and ALDH2 has been reported to be a critical regulator of HCC progression. This review discusses the functions, molecular mechanisms, and clinical significance of ALDH2 in the development of HCC and examines the prospects of ALDH2-based therapy for HCC.

ALDH7A1 rs12514417 polymorphism may increase ischemic stroke risk in alcohol-exposed individuals

Background:

Epidemiological studies have identified common risk factors for cerebral stroke worldwide. Some of these factors include hypertension, diabetes, smoking, excessive drinking, and dyslipidemia. It is important to note, however, that genetic factors can also contribute to the occurrence of stroke. Here, we evaluated the association of ischemic stroke with rs12514417 polymorphism of the alcohol metabolizing gene, aldehyde dehydrogenase 7A1 (ALDH7A1) and alcohol consumption.

Methods:

Taiwan Biobank (TWB) data collected between 2008 and 2015 were available for 17,985 subjects. The odd ratios for stroke were obtained using logistic regression models.

Results:

Among eligible subjects (n = 17,829), 897 had ischemic stroke and 70 had hemorrhagic stroke. Subjects with ischemic stroke were older (mean ± SE, 58.45 ± 8.19 years vs. 48.33 ± 10.89 years, p < 0.0001) and had a higher body mass index (BMI) than the stroke-free individuals. The risk of ischemic stroke was significantly higher among subjects with the ALDH7A1 rs12514417 TG + GG genotype who also consumed alcohol at least 150 ml/week (odds ratio (OR), 1.79; 95% confidence interval (CI), 1.18–2.72). We found that rs12514417 genotype and alcohol consumption (at least 150 ml/week) showed a significant interaction (p for interaction = 0.0266). Stratification based on alcohol exposure and ALDH7A1 rs12514417 genotypes indicated that ischemic stroke risk was significantly higher among alcohol drinkers with the TG + GG genotype than in those with the TT genotype (OR, 1.64, 95% CI: 1.15–2.33).

Conclusion:

Our study suggests that the combination of ALDH7A1 rs12514417 TG + GG genotype and alcohol exposure of at least 150 ml/week may increase the risk of ischemic stroke in Taiwanese adults.

Role of Oxidative Stress in Cardiac Dysfunction and Subcellular Defects Due to Ischemia-Reperfusion Injury

Ischemia-reperfusion (I/R) injury is well-known to be associated with impaired cardiac function, massive arrhythmias, marked alterations in cardiac metabolism and irreversible ultrastructural changes in the heart. Two major mechanisms namely oxidative stress and intracellular Ca²⁺-overload are considered to explain I/R-induced injury to the heart. However, it is becoming apparent that oxidative stress is the most critical pathogenic factor because it produces myocardial abnormalities directly or indirectly for the occurrence of cardiac damage. Furthermore, I/R injury has been shown to generate oxidative stress by promoting the formation of different reactive oxygen species due to defects in mitochondrial function and depressions in both endogenous antioxidant levels as well as regulatory antioxidative defense systems. It has also been demonstrated to adversely affect a wide variety of metabolic pathways and targets in cardiomyocytes, various resident structures in myocardial interstitium, as well as circulating neutrophils and leukocytes. These I/R-induced alterations in addition to myocardial inflammation may cause cell death, fibrosis, inflammation, Ca²⁺-handling abnormalities, activation of proteases and phospholipases, as well as subcellular remodeling and depletion of energy stores in the heart. Analysis of results from isolated hearts perfused with or without some antioxidant treatments before subjecting to I/R injury has indicated that cardiac dysfunction is associated with the development of oxidative stress, intracellular Ca²⁺-overload and protease activation. In addition, changes in the sarcolemma and sarcoplasmic reticulum Ca²⁺-handling, mitochondrial oxidative phosphorylation as well as myofibrillar Ca²⁺-ATPase activities in I/R hearts were attenuated by pretreatment with antioxidants. The I/R-induced alterations in cardiac function were simulated upon perfusing the hearts with oxyradical generating system or oxidant. These observations support the view that oxidative stress may be intimately involved in inducing intracellular Ca²⁺-overload, protease activation, subcellular remodeling, and cardiac dysfunction as a consequence of I/R injury to the heart.

Aldehyde Dehydrogenase 2 as a Therapeutic Target in Oxidative Stress-Related Diseases: Post-Translational Modifications Deserve More Attention

Aldehyde dehydrogenase 2 (ALDH2) has both dehydrogenase and esterase activity; its dehydrogenase activity is closely related to the metabolism of aldehydes produced under oxidative stress (OS). In this review, we recapitulate the enzyme activity of ALDH2 in combination with its protein structure, summarize and show the main mechanisms of ALDH2 participating in metabolism of aldehydes in vivo as comprehensively as possible; we also integrate the key regulatory mechanisms of ALDH2 participating in a variety of physiological and pathological processes related to OS, including tissue and organ fibrosis, apoptosis, aging, and nerve injury-related diseases. On this basis, the regulatory effects and application prospects of activators, inhibitors, and protein post-translational modifications (PTMs, such as phosphorylation, acetylation, S-nitrosylation, nitration, ubiquitination, and glycosylation) on ALDH2 are discussed and prospected. Herein, we aimed to lay a foundation for further research into the mechanism of ALDH2 in oxidative stress-related disease and provide a basis for better use of the ALDH2 function in research and the clinic.

Radiation-induced cardiovascular disease: an overlooked role for DNA methylation?

Radiotherapy in cancer treatment involves the use of ionizing radiation for cancer cell killing. Although radiotherapy has shown significant improvements on cancer recurrence and mortality, several radiation-induced adverse effects have been documented. Of these adverse effects, radiation-induced cardiovascular disease (CVD) is particularly prominent among patients receiving mediastinal radiotherapy, such as breast cancer and Hodgkin's lymphoma patients. A number of mechanisms of radiation-induced CVD pathogenesis have been proposed such as endothelial inflammatory activation, premature endothelial senescence, increased ROS and mitochondrial dysfunction. However, current research seems to point to a so-far unexamined and potentially novel involvement of epigenetics in radiation-induced CVD pathogenesis. Firstly, epigenetic mechanisms have been implicated in CVD pathophysiology. In addition, several studies have shown that ionizing radiation can cause epigenetic modifications, especially DNA methylation alterations. As a result, this review aims to provide a summary of the current literature linking DNA methylation to radiation-induced CVD and thereby explore DNA methylation as a possible contributor to radiation-induced CVD pathogenesis.

Lipid Oxidation Products on Inflammation-Mediated Hypertension and Atherosclerosis: A Mini Review

Cardiovascular diseases such as hypertension and atherosclerosis are the common causes of mortality in developed and developing countries. Repeated heating of the dietary oil is a common practice to reduce cost during food preparation. When the cooking oil is heated at high temperatures, production of free radicals augments the oxidative degradation of lipids and depletes the natural antioxidant contents of the cooking oil. Chronic intake of foods prepared using reheated oil could impair antioxidant capacity, leading to oxidative stress and inflammation. This review aims to summarize the current evidence of lipid oxidation products on hypertension and atherosclerosis via inflammatory pathway. In particular, toxic lipid oxidation products such as malondialdehyde and 4-hydroxy-2-nonenal are taken into account. Understanding the signaling pathways underlying the pathology associated with the lipid oxidation-derived aldehydes may be useful to develop therapeutic strategies for the prevention of inflammatory-related cardiovascular complications.

The effect of ALDH2 rs671 gene mutation on clustering of cardiovascular risk factors in a big data study of Chinese population: associations differ between the sexes

BACKGROUND

The ALDH2 rs671 genetic polymorphism has been linked with cardiovascular diseases (CVDs), but comprehensive epidemiological studies are lacking. An observational, retrospective big data study was carried out to evaluate the associations between this polymorphism and clustering cardiovascular risk factors (CRFs) in a Chinese population.

METHODS

A total of 13,101 individuals (8431 males and 4670 females) were enrolled. Genetic polymorphism was assessed using gene mutation detection kits, coupled with an automatic fluorescent analyzer. Other data were obtained from the records of the Department of Health Care at Peking Union Medical College Hospital.

RESULTS

Comparing the concentrations of common biochemical analytes, including BMI, SBP, DBP, ALT, AST, γ-GT, TBil, Cr, Glu, TC, TG, and HDL-C among individuals with the GG, GA, and AA genotypes of ALDH2 rs671, we found significant differences in males (all p < 0.001), but not in females. For males, the frequencies of hypertension, diabetes, and obesity were significantly higher for GG than for GA or AA (all p < 0.05). However, there was no significant difference for dyslipidemia, and no significant associations were observed for all frequencies in females. The prevalence of individuals with 1-4 CRFs was significantly higher among GG males than those carrying GA or AA, and fewer GG males had non-CRFs (all p < 0.05).

CONCLUSION

Polymorphisms of ALDH2 rs671 are associated with clustering CRFs, especially hypertension and diabetes in males, but not in females. These associations are likely mediated by alcohol intake, which is also associated with this gene.

Generation and Release of Mitochondrial-Derived Vesicles in Health, Aging and Disease

Mitochondria are intracellular organelles involved in a myriad of activities. To safeguard their vital functions, mitochondrial quality control (MQC) systems are in place to support organelle plasticity as well as physical and functional connections with other cellular compartments. In particular, mitochondrial interactions with the endosomal compartment support the shuttle of ions and metabolites across organelles, while those with lysosomes ensure the recycling of obsolete materials. The extrusion of mitochondrial components via the generation and release of mitochondrial-derived vesicles (MDVs) has recently been described. MDV trafficking is now included among MQC pathways, possibly operating via mitochondrial-lysosomal contacts. Since mitochondrial dysfunction is acknowledged as a hallmark of aging and a major pathogenic factor of multiple age-associated conditions, the analysis of MDVs and, more generally, of extracellular vesicles (EVs) is recognized as a valuable research tool. The dissection of EV trafficking may help unravel new pathophysiological pathways of aging and diseases as well as novel biomarkers to be used in research and clinical settings. Here, we discuss (1) MQC pathways with a focus on mitophagy and MDV generation; (2) changes of MQC pathways during aging and their contribution to inflamm-aging and progeroid conditions; and (3) the relevance of MQC failure to several disorders, including neurodegenerative conditions (i.e., Parkinson's disease, Alzheimer's disease) and cardiovascular disease.

Identification of Candidate Genes and MicroRNAs for Acute Myocardial Infarction by Weighted Gene Coexpression Network Analysis

Background

Identification of potential molecular targets of acute myocardial infarction is crucial to our comprehensive understanding of the disease mechanism. However, studies of gene coexpression analysis via jointing multiple microarray data of acute myocardial infarction still remain restricted.

Methods

Microarray data of acute myocardial infarction (GSE48060, GSE66360, GSE97320, and GSE19339) were downloaded from Gene Expression Omnibus database. Three data sets without heterogeneity (GSE48060, GSE66360, and GSE97320) were subjected to differential expression analysis using MetaDE package. Differentially expressed genes having upper 25% variation across samples were imported in weighted gene coexpression network analysis. Functional and pathway enrichment analyses were conducted for genes in the most significant module using DAVID. The predicted microRNAs to regulate target genes in the most significant module were identified using TargetScan. Moreover, subpathway analyses using iSubpathwayMiner package and GenCLiP 2.0 were performed on hub genes with high connective weight in the most significant module.

Results

A total of 1027 differentially expressed genes and 33 specific modules were screened out between acute myocardial infarction patients and control samples. Ficolin (collagen/fibrinogen domain containing) 1 (FCN1), CD14 molecule (CD14), S100 calcium binding protein A9 (S100A9), and mitochondrial aldehyde dehydrogenase 2 (ALDH2) were identified as critical target molecules; hsa-let-7d, hsa-let-7b, hsa-miR-124-3, and hsa-miR-9-1 were identified as potential regulators of the expression of the key genes in the two biggest modules.

Conclusions

FCN1, CD14, S100A9, ALDH2, hsa-let-7d, hsa-let-7b, hsa-miR-124-3, and hsa-miR-9-1 were identified as potential candidate regulators in acute myocardial infarction. These findings might provide new comprehension into the underlying molecular mechanism of disease.

ALDH2 and Stroke: A Systematic Review of the Evidence

Cerebral stroke is one of the leading causes of mortality and disability worldwide. The prevalence of cerebral stroke is the result of the synergistic effect of genetic susceptibility and numerous vascular risk factors, including hypertension, diabetes, excessive alcohol intake, obesity, and dyslipidemia. Mitochondrial aldehyde dehydrogenase (ALDH2) is a vital enzyme metabolizing various acetaldehyde and toxic aldehydes. The ALDH2 enzymatic activity is severely decreased in the individuals with ALDH2*2 gene mutation, especially in East Asians. Increasing epidemiological surveys have revealed that ALDH2 genetic polymorphism is closely associated with the increasing incidence of cardiovascular risk factors and cerebral stroke. Evidence from experimental studies has also suggested that ALDH2 facilitates the clearance of reactive aldehydes and reduces the size of cerebral infarct. Therefore, targeting ALDH2 may represent a promising avenue for protection against stroke injury. This review will mainly focus on clinical and epidemiological evidence and the underlying molecular mechanisms involved in the protective effect of ALDH2 in stroke-related injury.

Activation of aldehyde dehydrogenase 2 slows down the progression of atherosclerosis via attenuation of ER stress and apoptosis in smooth muscle cells

Aldehyde dehydrogenase 2 (ALDH2) is a key mitochondrial enzyme in the metabolism of aldehydes and may have beneficial cardiovascular effects for conditions such as cardiac hypertrophy, heart failure, myocardial I/R injury, reperfusion, arrhythmia, coronary heart disease and atherosclerosis. In this study we investigated the role of ALDH2 in the progression of atherosclerosis and the underlying mechanisms, with a focus on endoplasmic reticulum (ER) stress. A clinical study was performed in 248 patients with coronary heart disease. The patients were divided into two groups according to their ALDH2 genotype. Baseline clinical characteristics and coronary angiography were recorded, and the coronary artery Gensini score was calculated. Serum levels of 4-hydroxy-2-nonenal (4-HNE) were detected. The clinical study revealed that the mutant ALDH2 genotype was an independent risk factor for coronary heart disease. ALDH2 gene polymorphism is closely associated with atherosclerosis and the severity of coronary artery stenosis. Serum levels of 4-HNE were significantly higher in patients with the mutant ALDH2 genotype than in patients with the wild-type ALDH2 genotype. As an in vitro model of atherosclerosis, rat smooth muscle cells (SMCs) were treated with oxygenized low-density lipoprotein (ox-LDL), which significantly elevated the levels of ER markers glucose-regulated protein78 (GRP78), protein kinase R-like ER kinase (PERK), phosphorylated eukaryotic translation initiation factor α subunit (p-eIF2α), activating transcription factor-4 (ATF-4), CEBP homologous protein (CHOP) and 4-HNE in the cells. All the ox-LDL-induced responses were significantly attenuated in the presence of Alda-1 (an ALDH2 activating agent), and accentuated in the presence of daidzin (an ALDH2 inhibitor). Furthermore, pretreatment with ALDH2 activator Alda-1 significantly decreased ox-LDL-induced apoptosis. Similarly, overexpression of ALDH2 protected SMCs against ox-LDL-induced ER stress as well as ER stress-induced apoptosis. These findings suggest that ALDH2 may slow the progression of atherosclerosis via the attenuation of ER stress and apoptosis in smooth muscle cells.

Baicalin protects H9c2 cardiomyocytes against hypoxia/reoxygenation-induced apoptosis and oxidative stress through activation of mitochondrial aldehyde dehydrogenase 2

Baicalin, a flavonoid glycoside separated from Scutellaria baicalensis, has cardioprotection against ischaemia/reperfusion (I/R) injury. Mitochondrial aldehyde dehydrogenase 2 (ALDH2) is considered as an endogenous protective mechanism against I/R injury depending on its anti-oxidant and anti-apoptotic characteristics. The present study demonstrates whether ALDH2 contributes to the cardioprotection of baicalin against hypoxia/reoxygenation (H/R)-inudced H9c2 cardiomyocytes injury. Our results observed that H/R treatment resulted in a significant decrease in cells viability and obvious increases in caspase-3 activity and apoptosis rate in H9c2 cells, while these alterations were evidently reversed by baicalin pretreatment. Simultaneously, baicalin mitigated H/R-induced the decreases in the levels of ALDH2 mRNA and protein as well as the activity of ALDH2 in H9c2 cells. However, we found that daidzin, an ALDH2 antagonist, remarkably attenuated baicalin-elicited inhibitory action on H/R-induced the downregulation of cells viability and Bcl-2 protein expression, and the upregulations of caspase-3 activity, apoptosis rate, cytochrome c and Bax proteins expressions in H9c2 cells. In addition, baicalin reversed H/R-induced oxidative stress as evidenced by the downregulation of malondialdehyde (MAD) and 4-hydroxy aldehydes (4-HNE) levels, the inhibition of endogenous reactive oxygen species (ROS) generation, and the downregulation of superoxide dismutase (SOD) activity induced by H/R treatment, while these effects were also blocked by daidzin. Furthermore, we found that Alda-1, an ALDH2 agonist, also abolished H/R-induced cytotoxicity, apoptosis, and oxidative stress, indicating that ALDH2 mediated H/R-induced H9c2 cell injury. Overall, these results suggested that baicalin prevents H/R-induced apoptosis and oxidative stress through enhancing ALDH activity and expression in H9c2 cardiomyocytes.

Alda-1 Attenuates Lung Ischemia-Reperfusion Injury by Reducing 4-Hydroxy-2-Nonenal in Alveolar Epithelial Cells

OBJECTIVES

Excessive oxidative stress is a main cause of lung ischemia-reperfusion injury, which often results in respiratory insufficiency after open-heart surgery for a cardiopulmonary bypass. Previous studies demonstrate that the activation of aldehyde dehydrogenase-2 could significantly reduce the oxidative stress mediated by toxic aldehydes and attenuate cardiac and cerebral ischemia-reperfusion injury. However, both the involvement of aldehydes and the protective effect of the aldehyde dehydrogenase-2 agonist, Alda-1, in lung ischemia-reperfusion injury remain unknown.

DESIGN

Prospective laboratory and animal investigation were conducted.

SETTING

State Key Laboratory of Cardiovascular Disease.

SUBJECTS

Primary human pulmonary alveolar epithelial cells, human pulmonary microvascular endothelial cells, and Sprague-Dawley rats.

INTERVENTIONS

A hypoxia/reoxygenation cell-culture model of human pulmonary alveolar epithelial cell, human pulmonary microvascular endothelial cell, and an isolated-perfused lung model were applied to mimic lung ischemia-reperfusion injury. We evaluated the effects of Alda-1 on aldehyde dehydrogenase-2 quantity and activity, on aldehyde levels and pulmonary protection.

MEASUREMENTS AND MAIN RESULTS

We have demonstrated that ischemia-reperfusion-induced pulmonary injury concomitantly induced aldehydes accumulation in human pulmonary alveolar epithelial cells and lung tissues, but not in human pulmonary microvascular endothelial cells. Moreover, Alda-1 pretreatment significantly elevated aldehyde dehydrogenase-2 activity, increased surfactant-associated protein C, and attenuated elevation of 4-hydroxy-2-nonenal, apoptosis, intercellular adhesion molecule-1, inflammatory response, and the permeability of pulmonary alveolar capillary barrier, thus alleviated injury.

CONCLUSIONS

Our study indicates that the accumulation of 4-hydroxy-2-nonenal plays an important role in lung ischemia-reperfusion injury. Alda-1 pretreatment can attenuate lung ischemia-reperfusion injury, possibly through the activation of aldehyde dehydrogenase-2, which in turn removes 4-hydroxy-2-nonenal in human pulmonary alveolar epithelial cells. Alda-1 pretreatment has clinical implications to protect lungs during cardiopulmonary bypass.

Sildenafil reduces signs of oxidative stress in pulmonary arterial hypertension: Evaluation by fatty acid composition, level of hydroxynonenal and heart rate variability

Pulmonary arterial hypertension (PAH) is a rare multifactorial disease with an unfavorable prognosis. Sildenafil therapy can improve functional capacity and pulmonary hemodynamics in PAH patients. Nowadays, it is increasingly recognized that the effects of sildenafil are pleiotropic and may also involve changes of the pro-/antioxidant balance, lipid peroxidation and autonomic control. In present study we aimed to assess the effects of sildenafil on the fatty acids (FAs) status, level of hydroxynonenal (HNE) and heart rate variability (HRV) in PAH patients. Patients with PAH were characterized by an increase in HNE and changes in the FAs composition with elevation of linoleic, oleic, docosahexanoic acids in phospholipids as well as reduced HRV with sympathetic predominance. Sildenafil therapy improved exercise capacity and pulmonary hemodynamics and reduced NT-proBNP level in PAH. Antioxidant and anti-inflammatory effects of sildenafil were noted from the significant lowering of HNE level and reduction of the phopholipid derived oleic, linoleic, docosahexanoic, docosapentanoic FAs. That was also associated with some improvement of HRV on account of the activation of the neurohumoral regulatory component. Incomplete recovery of the functional metabolic disorders in PAH patients may be assumed from the persistent increase in free FAs, reduced HRV with the sympathetic predominance in the spectral structure after treatment comparing to control group. The possibilities to improve PAH treatment efficacy through mild stimulation of free radical reactions and formation of hormetic reaction in the context of improved NO signaling are discussed.

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Sildenafil showed antioxidant and anti-inflammatory effects in pulmonary hypertension.

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Sildenafil reduced hydroxynonenal level and improved fatty acid profile in serum.

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Improvement of heart rate variability and functional capacity was noted after therapy.

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Mild prooxidant activity is suggested as the mechanism to improve sildenafil efficacy.

Role of the MPTP in conditioning the heart - translatability and mechanism

Mitochondria have long been known to be the gatekeepers of cell fate. This is particularly so in the response to acute ischaemia‐reperfusion injury (IRI). Following an acute episode of sustained myocardial ischaemia, the opening of the mitochondrial permeability transition pore (MPTP) in the first few minutes of reperfusion, mediates cell death. Preventing MPTP opening at the onset of reperfusion using either pharmacological inhibitors [such as cyclosporin A (CsA) ] or genetic ablation has been reported to reduce myocardial infarct (MI) size in animal models of acute IRI. Interestingly, the endogenous cardioprotective intervention of ischaemic conditioning, in which the heart is protected against MI by applying cycles of brief ischaemia and reperfusion to either the heart itself or a remote organ or tissue, appears to be mediated through the inhibition of MPTP opening at reperfusion. Small proof‐of‐concept clinical studies have demonstrated the translatability of this therapeutic approach to target MPTP opening using CsA in clinical settings of acute myocardial IRI. However, given that CsA is a not a specific MPTP inhibitor, more novel and specific inhibitors of the MPTP need to be discovered – the molecular identification of the MPTP should facilitate this. In this paper, we review the role of the MPTP as a target for cardioprotection, the potential mechanisms underlying MPTP inhibition in the setting of ischaemic conditioning, and the translatability of MPTP inhibition as a therapeutic approach in the clinical setting.

Linked Articles

This article is part of a themed section on Conditioning the Heart – Pathways to Translation. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue‐8

Aldehyde dehydrogenase-2 activation during cardioplegic arrest enhances the cardioprotection against myocardial ischemia-reperfusion injury

Ischemia/reperfusion damage is common during open-heart surgery. Activation of aldehyde dehydrogenase-2 can significantly reduce ischemia/reperfusion damage. We hypothesized that adding aldehyde dehydrogenase-2 agonist to regular cardioplegia solution would further ameliorate ischemia/reperfusion damage. Alda-1 was used as an aldehyde dehydrogenase-2 agonist. Cardioprotection by histidine-tryptophan-ketoglutarate solution with and without Alda-1 was compared using an ex vivo perfused rat heart model of ischemia/reperfusion. Three groups of ex vivo rat hearts endured different treatments with variant ischemia or an ischemia/reperfusion time course: sham, no ischemia/reperfusion; histidine-tryptophan-ketoglutarate; and histidine-tryptophan-ketoglutarate plus Alda-1. Aldehyde dehydrogenase-2 expressions and activities, oxidative parameters (including 4-hydroxy-2-nonenal-His adducts, malondialdehyde levels, and glutathione/oxidized glutathione ratios), myocardial protein carbonyl levels, coronary effluents creatine kinase isoenzyme MB levels, and heart function parameters were measured and compared. Alda-1 significantly elevated myocardium aldehyde dehydrogenase-2 activity (P < .01). Increased aldehyde dehydrogenase-2 activity in turn attenuated ischemia/reperfusion-induced elevation in cardiac aldehydes, creatine kinase isoenzyme MB leakage, and protein carbonyl formation (P < .01). The Alda-1 group also obtained higher glutathione/oxidized glutathione ratios (P < .01). Aldehyde dehydrogenase-2 activation alleviated ischemia/reperfusion-induced cardiomyocyte contractile function impairment as evidenced by improved maximal velocity of pressure development and decline, left ventricular developed pressure, and heart rate (P < .01). Alda-1 supplementation can significantly improve the cardioprotection effect of cardioplegia solution, possibly through activation of aldehyde dehydrogenase-2, to remove toxic aldehydes. This may aid in the identification of novel cardioplegia solutions.

ALDH2 rs671 Polymorphism and coronary heart disease risk among Asian populations: a meta-analysis and meta-regression

Mitochondrial aldehyde dehydrogenase-2 (ALDH2) is the principal enzyme involved in alcohol metabolism in humans. Emerging evidence has shown that the common rs671 G>A (Glu504Lys) polymorphism in the ALDH2 gene might play a critical role in increasing the susceptibility to coronary heart disease (CHD), including myocardial infarction (MI); however, individually published studies showed inconclusive results. This meta-analysis aimed to derive a more precise estimation of the relationship between the ALDH2 rs671 polymorphism and its influence on the susceptibility to CHD and MI. Nine case-control studies were included with a total of 7358 subjects, including 1961 CHD patients, 1040 MI patients, and 4357 healthy controls. Our meta-analysis results showed that the A variant of the ALDH2 rs671 polymorphism may be associated with increase risks of CHD (odds ratios [OR]=1.36, 95% confidence interval [CI]=1.06-1.75, p=0.017) and MI (OR=1.64, 95% CI=1.22-2.20, p=0.001). Univariate and multivariate meta-regression analyses showed no potential factors explained heterogeneity. No publication bias was detected in this meta-analysis. In conclusion, the current meta-analysis indicates that the A variant of the ALDH2 rs671 polymorphism may increase the risk of both CHD and MI among Asian populations.

Aldehyde dehydrogenase-2 inhibition blocks remote preconditioning in experimental and human models

Mitochondrial aldehyde dehydrogenase-2 (ALDH-2) is involved in preconditioning pathways, but its role in remote ischaemic preconditioning (rIPC) is unknown. We investigated its role in animal and human models of rIPC. (i) In a rabbit model of myocardial infarction, rIPC alone reduced infarct size [69 ± 5.8 % (n = 11) to 40 ± 6.5 % (n = 12), P = 0.019]. However, rIPC protection was lost after pre-treatment with the ALDH-2 inhibitor cyanamide (62 ± 7.6 % controls, n = 10, versus 61 ± 6.9 % rIPC after cyanamide, n = 10, P > 0.05). (ii) In a forearm plethysmography model of endothelial ischaemia-reperfusion injury, 24 individuals of Asian ethnic origin underwent combined rIPC and ischaemia-reperfusion (IR). 11 had wild-type (WT) enzyme and 13 carried the Glu504Lys (ALDH2*2) polymorphism (rendering ALDH-2 functionally inactive). In WT individuals, rIPC protected against impairment of response to acetylcholine (P = 0.9), but rIPC failed to protect carriers of Glu504Lys polymorphism (P = 0.004). (iii) In a second model of endothelial IR injury, 12 individuals participated in a double-blind placebo-controlled crossover study, receiving the ALDH-2 inhibitor disulfiram 600 mg od or placebo for 48 h prior to assessment of flow-mediated dilation (FMD) before and after combined rIPC and IR. With placebo, rIPC was effective with no difference in FMD before and after IR (6.18 ± 1.03 % and 4.76 ± 0.93 % P = 0.1), but disulfiram inhibited rIPC with a reduction in FMD after IR (7.87 ± 1.27 % and 3.05 ± 0.53 %, P = 0.001). This study demonstrates that ALDH-2 is involved in the rIPC pathway in three distinct rabbit and human models. This has potential implications for future clinical studies of remote conditioning.