Metabolic Remodeling Induced by Mitochondrial Aldehyde Stress Stimulates Tolerance to Oxidative Stress in the Heart

ALDH2 polymorphism and myocardial infarction: From alcohol metabolism to redox regulation

Acute myocardial infarction (AMI) remains a leading cause of death worldwide. Increased formation of reactive oxygen species (ROS) during the early reperfusion phase is thought to trigger lipid peroxidation and disrupt redox homeostasis, leading to myocardial injury. Whilst the mitochondrial enzyme aldehyde dehydrogenase 2 (ALDH2) is chiefly recognised for its central role in ethanol metabolism, substantial experimental evidence suggests an additional cardioprotective role for ALDH2 independent of alcohol intake, which mitigates myocardial injury by detoxifying breakdown products of lipid peroxidation including the reactive aldehydes, malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE). Epidemiological evidence suggests that an ALDH2 mutant variant with reduced activity that is highly prevalent in the East Asian population increases AMI risk. Additional studies have uncovered a strong association between coronary heart disease and this ALDH2 mutant variant. It appears this enzyme polymorphism (in particular, in ALDH2*2/2 carriers) has the potential to have wide-ranging effects on thiol reactivity, redox tone and therefore numerous redox-related signaling processes, resilience of the heart to cope with lifestyle-related and environmental stressors, and the ability of the whole body to achieve redox balance. In this review, we summarize the journey of ALDH2 from a mitochondrial reductase linked to alcohol metabolism, via pre-clinical studies aimed at stimulating ALDH2 activity to reduce myocardial injury to clinical evidence for its protective role in the heart.

Development of substituted benzimidazoles as inhibitors of human aldehyde dehydrogenase 1A isoenzymes

Aldehyde dehydrogenase 1A (ALDH1A) isoforms may be a useful target for overcoming chemotherapy resistance in high-grade serous ovarian cancer (HGSOC) and other solid tumor cancers. However, as different cancers express different ALDH1A isoforms, isoform selective inhibitors may have a limited therapeutic scope. Furthermore, resistance to an ALDH1A isoform selective inhibitor could arise via induction of expression of other ALDH1A isoforms. As such, we have focused on the development of pan-ALDH1A inhibitors, rather than on ALDH1A isoform selective compounds. Herein, we report the development of a new group of pan-ALDH1A inhibitors to assess whether broad spectrum ALDH1A inhibition is an effective adjunct to chemotherapy in HGSOC. Optimization of the CM10 scaffold, aided by ALDH1A1 crystal structures, led to improved biochemical potencies, improved cellular efficacy as demonstrated by reduction in ALDEFLUOR signal in HGSOC cells, and substantial improvements in liver microsomal stability. Based on this work we identified two compounds 17 and 25 suitable for future in vivo proof of concept experiments.

LncRNA CHKB-DT Downregulation Enhances Dilated Cardiomyopathy Through ALDH2

BACKGROUND

Human cardiac long noncoding RNA (lncRNA) profiles in patients with dilated cardiomyopathy (DCM) were previously analyzed, and the long noncoding RNA CHKB (choline kinase beta) divergent transcript (CHKB-DT) levels were found to be mostly downregulated in the heart. In this study, the function of CHKB-DT in DCM was determined.

METHODS

Long noncoding RNA expression levels in the human heart tissues were measured via quantitative reverse transcription-polymerase chain reaction and in situ hybridization assays. A CHKB-DT heterozygous or homozygous knockout mouse model was generated using the clustered regularly interspaced palindromic repeat (CRISPR)/CRISPR-associated protein 9 system, and the adeno-associated virus with a cardiac-specific promoter was used to deliver the RNA in vivo. Sarcomere shortening was performed to assess the primary cardiomyocyte contractility. The Seahorse XF cell mitochondrial stress test was performed to determine the energy metabolism and ATP production. Furthermore, the underlying mechanisms were explored using quantitative proteomics, ribosome profiling, RNA antisense purification assays, mass spectrometry, RNA pull-down, luciferase assay, RNA-fluorescence in situ hybridization, and Western blotting.

RESULTS

CHKB-DT levels were remarkably decreased in patients with DCM and mice with transverse aortic constriction-induced heart failure. Heterozygous knockout of CHKB-DT in cardiomyocytes caused cardiac dilation and dysfunction and reduced the contractility of primary cardiomyocytes. Moreover, CHKB-DT heterozygous knockout impaired mitochondrial function and decreased ATP production as well as cardiac energy metabolism. Mechanistically, ALDH2 (aldehyde dehydrogenase 2) was a direct target of CHKB-DT. CHKB-DT physically interacted with the mRNA of ALDH2 and fused in sarcoma (FUS) through the GGUG motif. CHKB-DT knockdown aggravated ALDH2 mRNA degradation and 4-HNE (4-hydroxy-2-nonenal) production, whereas overexpression of CHKB-DT reversed these molecular changes. Furthermore, restoring ALDH2 expression in CHKB-DT+/- mice alleviated cardiac dilation and dysfunction.

CONCLUSIONS

CHKB-DT is significantly downregulated in DCM. CHKB-DT acts as an energy metabolism-associated long noncoding RNA and represents a promising therapeutic target against DCM.

Long-Term Alcohol-Activated c-Jun N-terminal Kinase Isoform 2 Preserves Cardiac Function but Drives Ca2+-Triggered Arrhythmias

Long-term alcohol consumption leads to cardiac arrhythmias including atrial fibrillation (AF), the most common alcohol-related arrhythmia. While AF significantly increases morbidity and mortality in patients, it takes years for an alcoholic individual undergoing an adaptive status with normal cardiac function to reach alcoholic cardiomyopathy. The underlying mechanism remains unclear to date. In this study, we assessed the functional role of JNK2 in long-term alcohol-evoked atrial arrhythmogenicity but preserved cardiac function. Wild-type (WT) mice and cardiac-specific JNK2dn mice (with an overexpression of inactive dominant negative (dn) JNK2) were treated with alcohol (2 g/kg daily for 2 months; 2 Mo). Confocal Ca2+ imaging in the intact mouse hearts showed that long-term alcohol prolonged intracellular Ca2+ transient decay, and increased pacing-induced Ca2+ waves, compared to that of sham controls, while cardiac-specific JNK2 inhibition in JNK2dn mice precluded alcohol-evoked Ca2+-triggered activities. Moreover, activated JNK2 enhances diastolic SR Ca2+ leak in 24 h and 48 h alcohol-exposed HL-1 atrial myocytes as well as HEK-RyR2 cells (inducible expression of human RyR2) with the overexpression of tGFP-tagged active JNK2-tGFP or inactive JNK2dn-tGFP. Meanwhile, the SR Ca2+ load and systolic Ca2+ transient amplitude were both increased in ventricular myocytes, along with the preserved cardiac function in 2 Mo alcohol-exposed mice. Moreover, the role of activated JNK2 in SR Ca2+ overload and enhanced transient amplitude was also confirmed in long-term alcohol-exposed HL-1 atrial myocytes. In conclusion, our findings suggest that long-term alcohol-activated JNK2 is a key driver in preserved cardiac function, but at the expense of enhanced cardiac arrhythmogenicity. Modulating JNK2 activity could be a novel anti-arrhythmia therapeutic strategy.

Effect of Exogenous Acute β-Hydroxybutyrate Administration on Different Modalities of Exercise Performance in Healthy Rats

PURPOSE

A ketone body (β-hydroxybutyrate [β-HB]) is used as an energy source in the peripheral tissues. However, the effects of acute β-HB supplementation on different modalities of exercise performance remain unclear. This study aimed to assess the effects of acute β-HB administration on the exercise performance of rats.

METHODS

In study 1, Sprague-Dawley rats were randomly divided into six groups: endurance exercise (EE + PL and EE + KE), resistance exercise (RE + PL and RE + KE), and high-intensity intermittent exercise (HIIE + PL and HIIE + KE) with placebo (PL) or β-HB salt (KE) administration. In study 2, metabolome analysis using capillary electrophoresis mass spectrometry was performed to profile the effects of β-HB salt administration on HIIE-induced metabolic responses in the skeletal and heart muscles.

RESULTS

The maximal carrying capacity (rest for 3 min after each ladder climb, while carrying heavy weights until the rats could not climb) in the RE + KE group was higher than that in the RE + PL group. The maximum number of HIIE sessions (a 20-s swimming session with a 10-s rest between sessions, while bearing a weight equivalent to 16% of body weight) in the HIIE + KE group was higher than that in the HIIE + PL group. However, there was no significant difference in the time to exhaustion at 30 m·min -1 between the EE + PL and the EE + KE groups. Metabolome analysis showed that the overall tricarboxylic acid cycle and creatine phosphate levels in the skeletal muscle were higher in the HIIE + KE group than those in the HIIE + PL group.

CONCLUSIONS

These results indicate that acute β-HB salt administration may accelerate HIIE and RE performance, and the changes in metabolic responses in the skeletal muscle after β-HB salt administration may be involved in the enhancement of HIIE performance.

NET Proteome in Established Type 1 Diabetes Is Enriched in Metabolic Proteins

BACKGROUND AND AIMS

Type 1 diabetes (T1D) is a chronic autoimmune disease characterized by a T-cell-mediated destruction of the pancreatic insulin-producing beta cells. A growing body of evidence suggests that abnormalities in neutrophils and neutrophil extracellular trap (NET) formation (NETosis) are associated with T1D pathophysiology. However, little information is available on whether these changes are primary neutrophil defects or related to the environmental signals encountered during active disease.

METHODS

In the present work, the NET proteome (NETome) of phorbol 12-myristate 13-acetate (PMA)- and ionomycin-stimulated neutrophils from people with established T1D compared to healthy controls (HC) was studied by proteomic analysis.

RESULTS

Levels of NETosis, in addition to plasma levels of pro-inflammatory cytokines and NET markers, were comparable between T1D and HC subjects. However, the T1D NETome was distinct from that of HC in response to both stimuli. Quantitative analysis revealed that the T1D NETome was enriched in proteins belonging to metabolic pathways (i.e., phosphoglycerate kinase, glyceraldehyde-3-phosphate dehydrogenase, and UTP-glucose-1-phosphate uridylyltransferase). Complementary metabolic profiling revealed that the rate of extracellular acidification, an approximate measure for glycolysis, and mitochondrial respiration were similar between T1D and HC neutrophils in response to both stimuli.

CONCLUSION

The NETome of people with established T1D was enriched in metabolic proteins without an apparent alteration in the bio-energetic profile or dysregulated NETosis. This may reflect an adaptation mechanism employed by activated T1D neutrophils to avoid impaired glycolysis and consequently excessive or suboptimal NETosis, pivotal in innate immune defence and the resolution of inflammation.

Caloric restriction increases the resistance of aged heart to myocardial ischemia/reperfusion injury via modulating AMPK-SIRT1-PGC1a energy metabolism pathway

A large number of data suggest that caloric restriction (CR) has a protective effect on myocardial ischemia/reperfusion injury (I/R) in the elderly. However, the mechanism is still unclear. In this study, we created the I/R model in vivo by ligating the mice left coronary artery for 45 min followed by reperfusion. C57BL/6J wild-type mice were randomly divided into a young group fed ad libitum (y-AL), aged fed ad libitum (a-AL) and aged calorie restriction group (a-CR, 70% diet restriction), and fed for 6 weeks. The area of myocardial infarction was measured by Evan's blue-TTC staining, plasma cholesterol content quantified by ELISA, fatty acids and glucose measured by Langendorff working system, as well as protein expression of AMPK/SIRT₁/PGC_1a signaling pathway related factors in myocardial tissue detected by immunoblotting. Our results showed that CR significantly reduced infarct size in elderly mice after I/R injury, promoted glycolysis regardless of I/R injury, and restored myocardial glucose uptake in elderly mice. Compared with a-AL group, CR significantly promoted the expression of p-AMPK, SIRT₁, p-PGC_1a, and SOD₂, but decreased PPARγ expression in aged mice. In conclusion, our results suggest that CR protects elderly mice from I/R injury by altering myocardial substrate energy metabolism via the AMPK/SIRT₁/PGC_1a pathway.

The regulation of cardiac intermediary metabolism by NADPH oxidases

NADPH oxidases (NOXs), enzymes whose primary function is to generate reactive oxygen species, are important regulators of the heart's physiological function and response to pathological insults. The role of NOX-driven redox signalling in pathophysiological myocardial remodelling, including processes such as interstitial fibrosis, contractile dysfunction, cellular hypertrophy, and cell survival, is well recognized. While the NOX2 isoform promotes many detrimental effects, the NOX4 isoform has attracted considerable attention as a driver of adaptive stress responses both during pathology and under physiological states such as exercise. Recent studies have begun to define some of the NOX4-modulated mechanisms that may underlie these adaptive responses. In particular, novel functions of NOX4 in driving cellular metabolic changes have emerged. Alterations in cellular metabolism are a recognized hallmark of the heart's response to physiological and pathological stresses. In this review, we highlight the emerging roles of NOX enzymes as important modulators of cellular intermediary metabolism in the heart, linking stress responses not only to myocardial energetics but also other functions. The novel interplay of NOX-modulated redox signalling pathways and intermediary metabolism in the heart is unravelling a new aspect of the fascinating biology of these enzymes which will inform a better understanding of how they drive adaptive responses. We also discuss the implications of these new findings for therapeutic approaches that target metabolism in cardiac disease.

ALDH2 gene polymorphism is associated with fitness in the elderly Japanese population

PURPOSE

The aldehyde dehydrogenase 2 (ALDH2) rs671 polymorphism, which is exclusive to the Asian population, is related to many diseases. A high reactive oxygen species production in mitochondria, and low muscle strength in athletes and non-athletes, has been observed, as our previous study demonstrated. The purpose of this research was to investigate the influence of ALDH2 rs671 on the loss of muscle strength with aging and replicate our previous study in non-athletes.

METHODS

Healthy Japanese individuals (n = 1804) aged 23-94 years were genotyped using DNA extracted from saliva. Muscle strength was assessed using grip strength and chair stand test (CST). The interaction between age and genotypes was analyzed by two-way analysis of covariance (ANCOVA) adjusted for sex, body mass index (BMI), and exercise habit.

RESULTS

Individuals aged ≧55 with the AA genotype had a lower performance than those with the GG + GA genotype in the grip strength test (28.1 ± 9.1 kg vs. 29.1 ± 8.3 kg, p = 0.021). There was an interaction between age and genotype, where individuals with ≧55 years old AA genotype had a higher loss of strength compared to GG + GA genotypes in the CST (0.025). No interaction in other models and no sex differences were found.

CONCLUSION

This study replicated previous results of the relationship between the AA genotype with lower muscle strength and as a novelty showed that this genotype is associated with a higher age-related loss of strength.

NADPH and Mitochondrial Quality Control as Targets for a Circadian-Based Fasting and Exercise Therapy for the Treatment of Parkinson's Disease

Dysfunctional mitochondrial quality control (MQC) is implicated in the pathogenesis of Parkinson's disease (PD). The improper selection of mitochondria for mitophagy increases reactive oxygen species (ROS) levels and lowers ATP levels. The downstream effects include oxidative damage, failure to maintain proteostasis and ion gradients, and decreased NAD⁺ and NADPH levels, resulting in insufficient energy metabolism and neurotransmitter synthesis. A ketosis-based metabolic therapy that increases the levels of (R)-3-hydroxybutyrate (BHB) may reverse the dysfunctional MQC by partially replacing glucose as an energy source, by stimulating mitophagy, and by decreasing inflammation. Fasting can potentially raise cytoplasmic NADPH levels by increasing the mitochondrial export and cytoplasmic metabolism of ketone body-derived citrate that increases flux through isocitrate dehydrogenase 1 (IDH1). NADPH is an essential cofactor for nitric oxide synthase, and the nitric oxide synthesized can diffuse into the mitochondrial matrix and react with electron transport chain-synthesized superoxide to form peroxynitrite. Excessive superoxide and peroxynitrite production can cause the opening of the mitochondrial permeability transition pore (mPTP) to depolarize the mitochondria and activate PINK1-dependent mitophagy. Both fasting and exercise increase ketogenesis and increase the cellular NAD⁺/NADH ratio, both of which are beneficial for neuronal metabolism. In addition, both fasting and exercise engage the adaptive cellular stress response signaling pathways that protect neurons against the oxidative and proteotoxic stress implicated in PD. Here, we discuss how intermittent fasting from the evening meal through to the next-day lunch together with morning exercise, when circadian NAD⁺/NADH is most oxidized, circadian NADP⁺/NADPH is most reduced, and circadian mitophagy gene expression is high, may slow the progression of PD.

Association of functional variant of aldehyde dehydrogenase 2 with acute myocardial infarction of Chinese patients

BACKGROUND

The variant of ALDH2 was thought to be associated with Acute Myocardial Infarction (AMI) due to the consumption of alcohol. This study focused on how ALDH2 variant acts as an independent risk factor for AMI, regardless of alcohol consumption.

METHODS AND RESULTS

We used the case-control INTERHEART-China study which took place at 25 centres in 17 cities in mainland China. Cases were patients with AMI and matched by age, sex, and site to controls. Information about alcohol consumption and genotype were collected. We divided cases and controls by alcohol consumption: alcohol intake group and no alcohol intake group. Then, calculated the Odd Ratio (OR) value with confidence interval (CI) at 95% level to find the association between ALDH2 variant and AMI. Results were then adjusted by sex, age, BMI, and other common risk factors of AMI. The study involves a total of 2660 controls and 2322 AMI patients. The no drink intake group showed that there was a correlation between the ALDH2 variant and AMI (OR = 1.236, 95% CI = 1.090-1.401, p = 0.00092). After adjustment of different risk factors this association remained (OR = 1.247, 95% CI = 1.099-1.415, p = 0.00062). Similar results were also obtained from the no alcohol intake group (OR = 1.196, 95% CI = 0.993-1.440, p = 0.05963), however, due to the limited sample size, the result was not significant enough statistically.

CONCLUSION

From our results, ALDH2 variant is associated with the risk of AMI even in population that has no alcohol consumption. This suggests that ALDH2 variant may act as an independent risk factor for AMI.

Magnesium Hydride Ameliorates Endotoxin-Induced Acute Respiratory Distress Syndrome by Inhibiting Inflammation, Oxidative Stress, and Cell Apoptosis

Acute respiratory distress syndrome (ARDS) causes uncontrolled pulmonary inflammation, resulting in high morbidity and mortality in severe cases. Given the antioxidative effect of molecular hydrogen, some recent studies suggest the potential use of molecular hydrogen as a biomedicine for the treatment of ARDS. In this study, we aimed to explore the protective effects of magnesium hydride (MgH2) on two types of ARDS models and its underlying mechanism in a lipopolysaccharide (LPS)-induced ARDS model of the A549 cell line. The results showed that LPS successfully induced oxidative stress, inflammatory reaction, apoptosis, and barrier breakdown in alveolar epithelial cells (AEC). MgH2 can exert an anti-inflammatory effect by down-regulating the expressions of inflammatory cytokines (IL-1β, IL-6, and TNF-α). In addition, MgH2 decreased oxidative stress by eliminating intracellular ROS, inhibited apoptosis by regulating the expressions of cytochrome c, Bax, and Bcl-2, and suppressed barrier breakdown by up-regulating the expression of ZO-1 and occludin. Mechanistically, the expressions of p-AKT, p-mTOR, p-P65, NLRP3, and cleaved-caspase-1 were decreased after MgH2 treatment, indicating that AKT/mTOR and NF-κB/NLRP3/IL-1β pathways participated in the protective effects of MgH2. Furthermore, the in vivo study also demonstrated that MgH2-treated mice had a better survival rate and weaker pathological damage. All these findings demonstrated that MgH2 could exert an ARDS-protective effect by regulating the AKT/mTOR and NF-κB/NLRP3/IL-1β pathways to suppress LPS-induced inflammatory reaction, oxidative stress injury, apoptosis, and barrier breakdown, which may provide a potential strategy for the prevention and treatment of ARDS.

The ALDH2 rs671 polymorphism is associated with athletic status and muscle strength in a Japanese population

Aldehyde dehydrogenase 2 (ALDH2) catalyses aldehyde species, including alcohol metabolites, mainly in the liver. We recently observed that ALDH2 is also expressed in skeletal muscle mitochondria; thus, we hypothesize that rs671 polymorphism-promoted functional loss of ALDH2 may induce deleterious effects in human skeletal muscle. We aimed to clarify the association of the ALDH2 rs671 polymorphism with muscle phenotypes and athletic capacity in a large Japanese cohort. A total of 3,055 subjects, comprising 1,714 athletes and 1,341 healthy control subjects (non-athletes), participated in this study. Non-athletes completed a questionnaire regarding their exercise habits, and were subjected to grip strength, 30-s chair stand, and 8-ft walking tests to assess muscle function. The ALDH2 GG, GA, and AA genotypes were detected at a frequency of 56%, 37%, and 7% among athletes, and of 54%, 37%, and 9% among non-athletes, respectively. The minor allele frequency was 25% in athletes and 28% in controls. Notably, ALDH2 genotype frequencies differed significantly between athletes and non-athletes (genotype: p = 0.048, allele: p = 0.021), with the AA genotype occurring at a significantly lower frequency among mixed-event athletes compared to non-athletes (p = 0.010). Furthermore, non-athletes who harboured GG and GA genotypes exhibited better muscle strength than those who carried the AA genotype (after adjustments for age, sex, body mass index, and exercise habits). The AA genotype and A allele of the ALDH2 rs671 polymorphism were associated with a reduced athletic capacity and poorer muscle phenotypes in the analysed Japanese cohort; thus, impaired ALDH2 activity may attenuate muscle function.

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.

A deep learning model for early risk prediction of heart failure with preserved ejection fraction by DNA methylation profiles combined with clinical features

Background

Heart failure with preserved ejection fraction (HFpEF), affected collectively by genetic and environmental factors, is the common subtype of chronic heart failure. Although the available risk assessment methods for HFpEF have achieved some progress, they were based on clinical or genetic features alone. Here, we have developed a deep learning framework, HFmeRisk, using both 5 clinical features and 25 DNA methylation loci to predict the early risk of HFpEF in the Framingham Heart Study Cohort.

Results

The framework incorporates Least Absolute Shrinkage and Selection Operator and Extreme Gradient Boosting-based feature selection, as well as a Factorization-Machine based neural network-based recommender system. Model discrimination and calibration were assessed using the AUC and Hosmer–Lemeshow test. HFmeRisk, including 25 CpGs and 5 clinical features, have achieved the AUC of 0.90 (95% confidence interval 0.88–0.92) and Hosmer–Lemeshow statistic was 6.17 (P = 0.632), which outperformed models with clinical characteristics or DNA methylation levels alone, published chronic heart failure risk prediction models and other benchmark machine learning models. Out of them, the DNA methylation levels of two CpGs were significantly correlated with the paired transcriptome levels (R < −0.3, P < 0.05). Besides, DNA methylation locus in HFmeRisk were associated with intercellular signaling and interaction, amino acid metabolism, transport and activation and the clinical variables were all related with the mechanism of occurrence of HFpEF. Together, these findings give new evidence into the HFmeRisk model.

Conclusion

Our study proposes an early risk assessment framework for HFpEF integrating both clinical and epigenetic features, providing a promising path for clinical decision making.

Strategies for Improving Photodynamic Therapy Through Pharmacological Modulation of the Immediate Early Stress Response

Photodynamic therapy (PDT) is a minimally to noninvasive treatment modality that has emerged as a promising alternative to conventional cancer treatments. PDT induces hyperoxidative stress and disrupts cellular homeostasis in photosensitized cancer cells, resulting in cell death and ultimately removal of the tumor. However, various survival pathways can be activated in sublethally afflicted cancer cells following PDT. The acute stress response is one of the known survival pathways in PDT, which is activated by reactive oxygen species and signals via ASK-1 (directly) or via TNFR (indirectly). The acute stress response can activate various other survival pathways that may entail antioxidant, pro-inflammatory, angiogenic, and proteotoxic stress responses that culminate in the cancer cell's ability to cope with redox stress and oxidative damage. This review provides an overview of the immediate early stress response in the context of PDT, mechanisms of activation by PDT, and molecular intervention strategies aimed at inhibiting survival signaling and improving PDT outcome.

MITOL/MARCH5 determines the susceptibility of cardiomyocytes to doxorubicin-induced ferroptosis by regulating GSH homeostasis

MITOL/MARCH5 is an E3 ubiquitin ligase that plays a crucial role in the control of mitochondrial quality and function. However, the significance of MITOL in cardiomyocytes under physiological and pathological conditions remains unclear. First, to determine the significance of MITOL in unstressed hearts, we assessed the cellular changes with the reduction of MITOL expression by siRNA in neonatal rat primary ventricular cardiomyocytes (NRVMs). MITOL knockdown in NRVMs induced cell death via ferroptosis, a newly defined non-apoptotic programmed cell death, even under no stress conditions. This phenomenon was observed only in NRVMs, not in other cell types. MITOL knockdown markedly reduced mitochondria-localized GPX4, a key enzyme associated with ferroptosis, promoting accumulation of lipid peroxides in mitochondria. In contrast, the activation of GPX4 in MITOL knockdown cells suppressed lipid peroxidation and cell death. MITOL knockdown reduced the glutathione/oxidized glutathione (GSH/GSSG) ratio that regulated GPX4 expression. Indeed, the administration of GSH or N-acetylcysteine improved the expression of GPX4 and viability in MITOL-knockdown NRVMs. MITOL-knockdown increased the expression of the glutathione-degrading enzyme, ChaC glutathione-specific γ-glutamylcyclotransferase 1 (Chac1). The knockdown of Chac1 restored the GSH/GSSG ratio, GPX4 expression, and viability in MITOL-knockdown NRVMs. Further, in cultured cardiomyocytes stressed with DOX, both MITOL and GPX4 were reduced, whereas forced-expression of MITOL suppressed DOX-induced ferroptosis by maintaining GPX4 content. Additionally, MITOL knockdown worsened vulnerability to DOX, which was almost completely rescued by treatment with ferrostatin-1, a ferroptosis inhibitor. In vivo, cardiac-specific depletion of MITOL did not produce obvious abnormality, but enhanced susceptibility to DOX toxicity. Finally, administration of ferrostatin-1 suppressed exacerbation of DOX-induced myocardial damage in MITOL-knockout hearts. The present study demonstrates that MITOL determines the cell fate of cardiomyocytes via the ferroptosis process and plays a key role in regulating vulnerability to DOX treatment. (288/300).

The nexus between redox state and intermediary metabolism

Reactive oxygen species (ROS) are not just a by-product of cellular metabolic processes but act as signalling molecules that regulate both physiological and pathophysiological processes. A close connection exists in cells between redox homeostasis and cellular metabolism. In this review, we describe how intracellular redox state and glycolytic intermediary metabolism are closely coupled. On the one hand, ROS signalling can control glycolytic intermediary metabolism by direct regulation of the activity of key metabolic enzymes and indirect regulation via redox-sensitive transcription factors. On the other hand, metabolic adaptation and reprogramming in response to physiological or pathological stimuli regulate intracellular redox balance, through mechanisms such as the generation of reducing equivalents. We also discuss the impact of these intermediary metabolism-redox circuits in physiological and disease settings across different tissues. A better understanding of the mechanisms regulating these intermediary metabolism-redox circuits will be crucial to the development of novel therapeutic strategies.

Imeglimin prevents heart failure with preserved ejection fraction by recovering the impaired unfolded protein response in mice subjected to cardiometabolic stress

The pathogenesis of heart failure with preserved ejection fraction (HFpEF) in obese diabetic patients has been implicated in metainflammation. Increased expression of inducible nitric oxide synthase (iNOS) and dysfunction of the unfolded protein response (UPR), especially inositol-requiring enzyme 1α-X-box binding protein 1 (IRE1α-Xbp1s) signaling in the heart, have been associated with HFpEF. We investigated the effect of imeglimin, a potential new treatment for type 2 diabetes, on the pathogenesis of HFpEF. We induced obesity, impaired glucose tolerance, and cardiac hypertrophy with fibrosis, fat accumulation, and diastolic dysfunction in wild-type mice with a high-fat diet (HFD) and the nitric oxide synthase (NOS) inhibitor l-NAME for 16 weeks. Treatment with imeglimin starting at 10 weeks not only improved their abnormal systemic glucose metabolism and visceral obesity but also their cardiac abnormalities. We found that imeglimin suppressed the upregulation of iNOS, and restored the expression of Xbp1s and the expression of the E3 ubiquitin ligase STIP1 homology and U-box-containing protein 1 (STUB1), which is responsible for the degradation of Forkhead box protein O1 (FoxO1), a direct transcriptional target of Xbp1s. It also suppressed the excessive transcriptional activity of FoxO1, which is located downstream of Xbp1s and is involved in the form development of HFpEF and cardiac adipogenesis. Imeglimin also restored the expression of Glutathione peroxidase 4 (GPX4), which protects cells against excess lipid peroxidation and governs a novel form of programmed cell death, called ferroptosis.

Acetaldehyde exposure underlies functional defects in monocytes induced by excessive alcohol consumption

Increased intestinal permeability and hepatic macrophage activation by endotoxins are involved in alcohol-induced liver injury pathogenesis. Long-term alcohol exposure conversely induces endotoxin immune tolerance; however, the precise mechanism and reversibility are unclear. Seventy-two alcohol-dependent patients with alcohol dehydrogenase-1B (ADH1B, rs1229984) and aldehyde dehydrogenase-2 (ALDH2, rs671) gene polymorphisms admitted for alcohol abstinence were enrolled. Blood and fecal samples were collected on admission and 4 weeks after alcohol cessation and were sequentially analyzed. Wild-type and ALDH2*2 transgenic mice were used to examine the effect of acetaldehyde exposure on liver immune responses. The productivity of inflammatory cytokines of peripheral CD14⁺ monocytes in response to LPS stimulation was significantly suppressed in alcohol dependent patients on admission relative to that in healthy controls, which was partially restored by alcohol abstinence with little impact on the gut microbiota composition. Notably, immune suppression was associated with ALDH2/ADH1B gene polymorphisms, and patients with a combination of ALDH2*1/*2 and ADH1B*2 genotypes, the most acetaldehyde-exposed group, demonstrated a deeply suppressed phenotype, suggesting a direct role of acetaldehyde. In vitro LPS and malondialdehyde-acetaldehyde adducted protein stimulation induced direct cytotoxicity on monocytes derived from healthy controls, and a second LPS stimulation suppressed the inflammatory cytokines production. Consistently, hepatic macrophages of ethanol-administered ALDH2*2 transgenic mice exhibited suppressed inflammatory cytokines production in response to LPS compared to that in wild-type mice, reinforcing the contribution of acetaldehyde to liver macrophage function. These results collectively provide new perspectives on the systemic influence of excessive alcohol consumption based on alcohol-metabolizing enzyme genetic polymorphisms.

ALDH2 polymorphism rs671 is a predictor of PD-1/PD-L1 inhibitor efficacy against thoracic malignancies

Background

Aldehyde dehydrogenase 2 (ALDH2) plays an important role in the endogenous aldehyde detoxification of various types of cells. ALDH2*2, a variant allele of the ALDH2 polymorphism rs671, leads to decreased enzymatic activity. ALDH2*2 may enhance tumor antigen presentation due to aldehyde-induced DNA damage while suppressing peripheral blood T cell counts and T cell activation.

Methods

On the basis of our hypothesis that rs671 affects the sensitivity of immune checkpoint inhibitors (ICIs), we evaluated the effects of rs671 on patients with thoracic malignancies who started ICI therapy in 2016–2019. The cohort consisted of 105 cases, including 64 cases with adenocarcinoma and 30 cases with squamous cell carcinoma, 49 of whom were ALDH2*2 carriers. The first ICI was PD-1/PD-L1 inhibitor (Nivolumab, Pembrolizumab, or Atezolizumab) in all cases.

Results

The best response to anti-PD-1/PD-L1 therapy (partial response/stable disease/progressive disease) was 36%/50%/14% in the rs671(−) cases; however, the response was relatively poor in the rs671(+) cases (27%/29%/45%, respectively) (p = 0.002). The hazard ratio (95% confidence interval) of disease progression within the observation period of 6 months for the rs671(+) cases was estimated to be 5.0 (2.5–10) after the adjustment for covariates, including sex, Brinkman index, treatment line, tumor tissue programmed death-ligand 1 positivity rate, tumor tissue EGFR mutation. This association was also maintained in a stratified analysis, suggesting that ALDH2*2 is an independent negative predictive factor for the short-term prognosis of anti-PD-1/PD-L1 therapy. Thus, the progression-free survival (PFS) ratio of the rs671(+) cases decreased rapidly after ICI initiation but was eventually higher than that of the rs671(−) cases (restricted mean survival time in 12 months from 2 to 3 years afterward was 1.3 times that of the rs671(−) cases). Moreover, the highest PFS ratio after 2 years among sub-groups was found in the first-line treatment sub-group of rs671(+) group (40%).

Conclusions

Our study suggests that rs671 may be an accurate and cost-effective predictor of PD-1/PD-L1 inhibitor treatment, in which optimal case selection is an important issue.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08329-y.

Oxidative Stress and Pathways of Molecular Hydrogen Effects in Medicine

There are many situations of excessive production of reactive oxygen species (ROS) such as radiation, ischemia/reperfusion (I/R), and inflammation. ROS contribute to and arises from numerous cellular pathologies, diseases, and aging. ROS can cause direct deleterious effects by damaging proteins, lipids, and nucleic acids as well as exert detrimental effects on several cell signaling pathways. However, ROS are important in many cellular functions. The injurious effect of excessive ROS can hypothetically be mitigated by exogenous antioxidants, but clinically this intervention is often not favorable. In contrast, molecular hydrogen provides a variety of advantages for mitigating oxidative stress due to its unique physical and chemical properties. H₂ may be superior to conventional antioxidants, since it can selectively reduce ●OH radicals while preserving important ROS that are otherwise used for normal cellular signaling. Additionally, H₂ exerts many biological effects, including antioxidation, anti-inflammation, anti-apoptosis, and anti-shock. H₂ accomplishes these effects by indirectly regulating signal transduction and gene expression, each of which involves multiple signaling pathways and crosstalk. The Keap1-Nrf2-ARE signaling pathway, which can be activated by H₂, plays a critical role in regulating cellular redox balance, metabolism, and inducing adaptive responses against cellular stress. H₂ also influences the crosstalk among the regulatory mechanisms of autophagy and apoptosis, which involve MAPKs, p53, Nrf2, NF-κB, p38 MAPK, mTOR, etc. The pleiotropic effects of molecular hydrogen on various proteins, molecules and signaling pathways can at least partly explain its almost universal pluripotent therapeutic potential.

Deletion of Superoxide Dismutase 1 Blunted Inflammatory Aortic Remodeling in Hypertensive Mice under Angiotensin II Infusion

Superoxide dismutase (SOD) is an enzyme that catalyzes the dismutation of two superoxide anions (O₂^·−) into hydrogen peroxide (H₂O₂) and oxygen (O₂) and is generally known to protect against oxidative stress. Angiotensin II (AngII) causes vascular hypertrophic remodeling which is associated with H₂O₂ generation. The aim of this study is to investigate the role of cytosolic SOD (SOD1) in AngII-induced vascular hypertrophy. We employed C57/BL6 mice (WT) and SOD1 deficient mice (SOD1^−/−) with the same background. They received a continuous infusion of saline or AngII (3.2 mg/kg/day) for seven days. The blood pressures were equally elevated at 1.5 times with AngII, however, vascular hypertrophy was blunted in SOD1^−/− mice compared to WT mice (WT mice 91.9 ± 1.13 µm versus SOD1^−/− mice 68.4 ± 1.41 µm p < 0.001). The elevation of aortic interleukin 6 (IL-6) and phosphorylation of pro-inflammatory STAT3 due to AngII were also blunted in SOD1^−/− mice’s aortas. In cultured rat vascular smooth muscle cells (VSMCs), reducing expression of SOD1 with siRNA decreased AngII induced IL-6 release as well as phosphorylation of STAT3. Pre-incubation with polyethylene glycol (PEG)-catalase also attenuated phosphorylation of STAT3 due to AngII. These results indicate that SOD1 in VSMCs plays a role in vascular hypertrophy due to increased inflammation caused by AngII, probably via the production of cytosolic H₂O₂.

ALDH2 deficiency induces atrial fibrillation through dysregulated cardiac sodium channel and mitochondrial bioenergetics: A multi-omics analysis

Point mutation in alcohol dehydrogenase 2 (ALDH2), ALDH2*2 results in decreased catalytic enzyme activity and has been found to be associated with different human pathologies. Whether ALDH2*2 would induce cardiac remodeling and increase the attack of atrial fibrillation (AF) remains poorly understood. The present study evaluated the effect of ALDH2*2 mutation on AF susceptibility and unravelled the underlying mechanisms using a multi-omics approach including whole-genome gene expression and proteomics analysis. The in-vivo electrophysiological study showed an increase in the incidence and reduction in the threshold of AF for the mutant mice heterozygous for ALDH2*2 as compared to the wild type littermates. The microarray analysis revealed a reduction in the retinoic acid signals which was accompanied by a downstream reduction in the expression of voltage-gated Na⁺ channels (SCN5A). The treatment of an antagonist for retinoic acid receptor resulted in a decrease in SCN5A transcript levels. The integrated analysis of the transcriptome and proteome data showed a dysregulation of fatty acid β-oxidation, adenosine triphosphate synthesis via electron transport chain, and activated oxidative responses in the mitochondria. Oral administration of Coenzyme Q10, an essential co-factor known to meliorate mitochondrial oxidative stress and preserve bioenergetics, conferred a protection against AF attack in the mutant ALDH2*2 mice. The multi-omics approach showed the unique pathophysiology mechanisms of concurrent dysregulated SCN5A channel and mitochondrial bioenergetics in AF. This inspired the development of a personalized therapeutic agent, Coenzyme Q10, to protect against AF attack in humans characterized by ALDH2*2 genotype.

ALDH2 mutation promotes skeletal muscle atrophy in mice via accumulation of oxidative stress

Muscle atrophy is promoted by various factors including aging, immobilization, unloading and use of drugs such as steroids. However, genetic risk factors for muscle atrophy are less well known. Here, we show that a missense SNP in the ALDH2 gene, rs671 (ALDH2*2), a dominant negative mutation, promotes significant muscle atrophy in the ALDH2*2 mouse model, accompanied by decreased expression of anabolic and catabolic muscle factors and acquisition of a low turnover state. We also demonstrate that expression of LC3, which is require for auto-phagosome formation during autophagy, increases in ALDH2*2 mouse muscles. We show that 4-hydroxynonenal (4HNE), a peroxidated lipid-protein and oxidant, accumulates in ALDH2*2 mouse muscles. We have shown that the rs671 mutation is associated with increased serum levels of acetaldehyde, an alcohol metabolite. We show that expression of the atrogenes Atrogin1 and MuRF1 significantly increased in myogenic cells following acetaldehyde treatment, an outcome significantly inhibited in vitro by Trolox C, an anti-oxidant. Muscle atrophy in ALDH2*2 mice was also significantly rescued by dietary administration of the anti-oxidant vitamin E, which blocked 4HNE accumulation in muscle. Taken together, our data indicate that rs671 is a genetic risk factor for muscle atrophy, but that such atrophy can be rescued by vitamin E treatment.

Antioxidant Activity of Hydrogen Water Mask Pack Composed of Gel-Type Emulsion and Hydrogen Generation Powder

In this study, hydrogen generation powder samples were prepared using zinc carbonate as a precursor, at a temperature varying from 400 to 700 °C in H₂ atmosphere, and were characterized in terms of antioxidant activity. The concentration of dissolved hydrogen obtained by the powder samples was measured using a dissolved hydrogen meter as a function of time. In addition, the antioxidant activity of the samples was evaluated based on the Oyaizu’s method, removal rate of ·OH radicals, and ferric reducing antioxidant power. Finally, the hydrogen mask pack was fabricated using the hydrogen generation powder sample and gel-type emulsion. In the clinical test on the mask pack, the effect of the mask on skin aging was characterized and compared to that of a commercial sample. The skin densities of the participants in the experimental group and the control group increased by 18.41% and 9.93% after 4 weeks, respectively. The improved skin density of the participants who used the hydrogen mask pack in the experimental group, might be attributed to the recovery effect of the hydrogen molecule in the mask pack on the denatured thick skin layer.

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.

A critical assessment of the potential of pharmacological modulation of aldehyde dehydrogenases to treat the diseases of bone loss

Chronic alcoholism (CA) decreases bone mass and increases the risk of hip fracture. Alcohol and its main metabolite, acetaldehyde impairs osteoblastogenesis by increasing oxidative stress. Aldehyde dehydrogenase (ALDH) is the rate-limiting enzyme in clearing acetaldehyde from the body. The clinical relevance of ALDH in skeletal function has been established by the discovery of single nucleotide polymorphism, SNP (rs671) in the ALDH2 gene giving rise to an inactive form of the enzyme (ALDH2*2) that causes increased serum acetaldehyde and osteoporosis in the affected individuals. Subsequent mouse genetics studies have replicated human phenotype in mice and confirmed the non-redundant role of ALDH2 in bone homeostasis. The activity of ALDH2 is amenable to pharmacological modulation. ALDH2 inhibition by disulfiram (DSF) and activation by alda-1 cause reduction and induction of bone formation, respectively. DSF also inhibits peak bone mass accrual in growing rats. On the other hand, DSF showed an anti-osteoclastogenic effect and protected mice from alcohol-induced osteopenia by inhibiting ALDH1a1 in bone marrow monocytes. Besides DSF, there are several classes of ALDH inhibitors with disparate skeletal effects. Alda-1, the ALDH2 activator induced osteoblast differentiation by increasing bone morphogenic protein 2 (BMP2) expression via ALDH2 activation. Alda-1 also restored ovariectomy-induced bone loss. The scope of structure-activity based studies with ALDH2 and the alda-1-like molecule could lead to the discovery of novel osteoanabolic molecules. This review will critically discuss the molecular mechanism of the ethanol and its principal metabolite, acetaldehyde in the context of ALDH2 in bone cells, and skeletal homeostasis.

Astaxanthin improves osteopenia caused by aldehyde-stress resulting from Aldh2 mutation due to impaired osteoblastogenesis

Aldehyde dehydrogenase 2 (ALDH2) plays major roles in aldehyde detoxification and in the catalysis of amino acids. ALDH2∗2, a dominant-negative transgenic expressing aldehyde dehydrogenase 2 (ALDH2) protein, is produced by a single nucleotide polymorphism (rs671) and is involved in the development of osteoporosis and hip fracture with aging. In a previous study, transgenic mice expressing Aldh2∗2(Aldh2∗2 Tg) osteoblastic cells or acetaldehyde -treated MC3T3-E1 showed impaired osteoblastogenesis and caused osteoporosis [1]. In this study, we demonstrated the effects of astaxanthin for differentiation to osteoblasts of MC3T3-E1 by the addition of acetaldehyde and Aldh2∗2 Tg mesenchymal stem cells in bone marrow. Astaxanthin restores the inhibited osteoblastogenesis by acetaldehyde in MC 3T3-E1 and in bone marrow mesenchymal stem cells of Aldh2∗2 Tg mice. Additionally, astaxanthin administration improved femur bone density in Aldh2∗2 Tg mice. Furthermore, astaxanthin improved cell survival and mitochondrial function in acetaldehyde-treated MC 3T3-E1 cells. Our results suggested that astaxanthin had restorative effects on osteoblast formation and provide new insight into the regulation of osteoporosis and suggest a novel strategy to promote bone formation in osteopenic diseases caused by impaired acetaldehyde metabolism.

ALDH2 Activation Inhibited Cardiac Fibroblast-to-Myofibroblast Transformation Via the TGF-β1/Smad Signaling Pathway

Pathological stimulus-triggered differentiation of cardiac fibroblasts plays a major role in the development of myocardial fibrosis. Aldehyde dehydrogenase 2 (ALDH2) was reported to exert a protective role in cardiovascular disease, and whether ALDH2 is involved in cardiac fibroblast differentiation remains unclear. In this study, we used transforming growth factor-β1 (TGF-β1) to induce the differentiation of human cardiac fibroblasts (HCFs) and adopted ALDH2 activator Alda-1 to verify the influence of ALDH2 on HCF differentiation. Results showed that ALDH2 activity was obviously impaired when treating HCFs with TGF-β1. Activation of ALDH2 with Alda-1 inhibited the transformation of HCFs into myofibroblasts, demonstrated by the decreased smooth muscle actin (α-actin) and periostin expression, reduced HCF-derived myofibroblast proliferation, collagen production, and contractility. Moreover, application of Smad2/3 inhibitor alleviated TGF-β1-induced HCF differentiation and improved ALDH2 activity, which was reversed by the application of ALDH2 inhibitor daidzin. Finally, Alda-1-induced HCF alterations alleviated neonatal rat cardiomyocyte hypertrophy, supported by the immunostaining of α-actin. To summarize, activation of ALDH2 enzymatic activity inhibited the differentiation of cardiac fibroblasts via the TGF-β1/Smad signaling pathway, which might be a promising strategy to relieve myocardial fibrosis of various causes.

Proteomic landscape of liver tissue in old male mice that are long-term treated with polysaccharides from Sargassum fusiforme

Sargassum fusiforme is a type of brown algae and well known as a longevity promoting vegetable in Northeastern Asia. The polysaccharides derived from Sargassum fusiforme (SFPs) have been suggested as an antioxidant component for anti-aging function. However, global molecular changes in vivo by SFPs have not been fully elucidated. Here, we present a proteomics study using liver tissues of aged male mice that were fed with SFPs. Of forty-nine protein spots, thirty-eight were up-regulated and eleven were down-regulated, showing significant changes in abundance by two-dimensional gel electrophoresis. These differentially expressed proteins were mainly involved in oxidation-reduction, amino acid metabolism, and energy metabolism. Forty-six proteins were integrated into a unified network, with catalase (Cat) at the center. Intriguingly, most of the proteins were speculated as mitochondrial-located proteins. Our findings suggested that SFPs modulated antioxidant enzymes to scavenge redundant free radicals, thus preventing oxidative damage. In conclusion, our study provides a proteomic view on how SFPs have beneficial effects on the aspects of antioxidant and energy metabolism during the aging process. This study facilitates the understanding of anti-aging molecular mechanisms in polysaccharides derived from Sargassum fusiforme.

Acetaldehyde dehydrogenase 2 deficiency increases mitochondrial reactive oxygen species emission and induces mitochondrial protease Omi/HtrA2 in skeletal muscle

Acetaldehyde dehydrogenase 2 (ALDH2) is an enzyme involved in redox homeostasis as well as the detoxification process in alcohol metabolism. Nearly 8% of the world’s population have an inactivating mutation in the ALDH2 gene. However, the expression patterns and specific functions of ALDH2 in skeletal muscles are still unclear. Herein, we report that ALDH2 is expressed in skeletal muscle and is localized to the mitochondrial fraction. Oxidative muscles had a higher amount of ALDH2 protein than glycolytic muscles. We next comprehensively investigated whether ALDH2 knockout in mice induces mitochondrial adaptations in gastrocnemius muscle (for example, content, enzymatic activity, respiratory function, supercomplex formation, and functional networking). We found that ALDH2 deficiency resulted in partial mitochondrial dysfunction in gastrocnemius muscle because it increased mitochondrial reactive oxygen species (ROS) emission (2′,7′-dichlorofluorescein and MitoSOX oxidation rate during respiration) and the frequency of regional mitochondrial depolarization. Moreover, we determined whether ALDH2 deficiency and the related mitochondrial dysfunction trigger mitochondrial stress and quality control responses in gastrocnemius muscle (for example, mitophagy markers, dynamics, and the unfolded protein response). We found that ALDH2 deficiency upregulated the mitochondrial serine protease Omi/HtrA2 (a marker of the activation of a branch of the mitochondrial unfolded protein response). In summary, ALDH2 deficiency leads to greater mitochondrial ROS production, but homeostasis can be maintained via an appropriate stress response.

ω-3 fish oil fat emulsion preconditioning mitigates myocardial oxidative damage in rats through aldehydes stress

ω-3 fish oil fat emulsions contain a considerable quantity of unsaturated carbon-carbon double bonds, which undergo lipid peroxidation to yield low-dose aldehydes. These aldehydes may stimulate the production of antioxidant enzymes, thereby mitigating myocardial oxidative damage. This study aims to (1) verify the cardioprotective effect of ω-3 fish oil fat emulsion in vivo and in vitro, and (2) determine whether aldehyde stress is a protective mechanism. For modeling purposes, we pretreated rats with 2 ml/kg of a 10% ω-3 fish oil fat emulsion for 5 days in order to generate a sufficient aldehyde stress response to trigger the production of antioxidant enzymes, and we obtained similar response with H9C2 cells that were pretreated with a 0.5% ω-3 fish oil fat emulsion for 24 h. ω-3 fish oil fat emulsion pretreatment in vivo reduced the myocardial infarct size, decreased the incidence of arrhythmias, and promoted the recovery of cardiac function after myocardial ischemia/reperfusion injury. Once the expression of nuclear factor E2-related factor 2 (Nrf2) was silenced in H9C2 cells, aldehydes no longer produced enough antioxidant enzymes to reverse the oxidative damage caused by tert-butyl hydroperoxide (TBHP). Our results demonstrated that ω-3 fish oil fat emulsion enhanced the inhibition of oxidation and production of free radicals, and alleviated myocardial oxidative injury via activation of the Nrf2 signaling pathway.

A New Approach for the Prevention and Treatment of Cardiovascular Disorders. Molecular Hydrogen Significantly Reduces the Effects of Oxidative Stress

Cardiovascular diseases are the most common causes of morbidity and mortality worldwide. Redox dysregulation and a dyshomeostasis of inflammation arise from, and result in, cellular aberrations and pathological conditions, which lead to cardiovascular diseases. Despite years of intensive research, there is still no safe and effective method for their prevention and treatment. Recently, molecular hydrogen has been investigated in preclinical and clinical studies on various diseases associated with oxidative and inflammatory stress such as radiation-induced heart disease, ischemia-reperfusion injury, myocardial and brain infarction, storage of the heart, heart transplantation, etc. Hydrogen is primarily administered via inhalation, drinking hydrogen-rich water, or injection of hydrogen-rich saline. It favorably modulates signal transduction and gene expression resulting in suppression of proinflammatory cytokines, excess ROS production, and in the activation of the Nrf2 antioxidant transcription factor. Although H2 appears to be an important biological molecule with anti-oxidant, anti-inflammatory, and anti-apoptotic effects, the exact mechanisms of action remain elusive. There is no reported clinical toxicity; however, some data suggests that H2 has a mild hormetic-like effect, which likely mediate some of its benefits. The mechanistic data, coupled with the pre-clinical and clinical studies, suggest that H2 may be useful for ROS/inflammation-induced cardiotoxicity and other conditions.

Fos-related antigen-1 transgenic mouse as a model for systemic sclerosis: A potential role of M2 polarization

Objectives:

To investigate the systemic sclerosis–related phenotype in fos-related antigen-1 transgenic mice and its underlying mechanisms.

Methods:

Lung and skin sections of constitutive fos-related antigen-1 transgenic mice and wild-type mice were examined by tissue staining and immunohistochemistry. The tricuspid regurgitation pressure gradient was measured by transthoracic echocardiography with a Doppler technique. To assess the impact of fos-related antigen-1 expression on macrophage function, bone marrow–derived mononuclear cells were derived from mice that expressed fos-related antigen-1 under the control of doxycycline and wild-type littermates. These bone marrow–derived mononuclear cells were induced to differentiate into macrophages with or without doxycycline, and analyzed for gene and protein expression. Finally, lung explants obtained from systemic sclerosis patients and control donors were subjected to immunohistochemistry.

Results:

The lungs of fos-related antigen-1 transgenic mice showed excessive fibrosis of the interstitium and thickening of vessel walls, with narrowing lumen, in an age-dependent manner. The tricuspid regurgitation pressure gradient was significantly elevated in fos-related antigen-1 transgenic versus control mice. Increased dermal thickness and the loss of subdermal adipose tissue were also observed in the fos-related antigen-1 transgenic mice. These changes were preceded by a perivascular infiltration of mononuclear cells, predominantly consisting of alternatively activated or M2 macrophages. Overexpressing fos-related antigen-1 in bone marrow–derived mononuclear cell cultures increased the expression of M2-related genes, such as Il10, Alox15, and Arg1. Finally, fos-related antigen-1-expressing M2 macrophages were increased in the lung tissues of systemic sclerosis patients.

Conclusions:

The fos-related antigen-1 transgenic mouse serves as a genetic model of systemic sclerosis that recapitulates the major vascular and fibrotic manifestations of the lungs and skin in systemic sclerosis patients. M2 polarization mediated by the up-regulation of fos-related antigen-1 may play a critical role in the development of systemic sclerosis.

Effects of Molecular Hydrogen Assessed by an Animal Model and a Randomized Clinical Study on Mild Cognitive Impairment

BACKGROUND

Oxidative stress is one of the causative factors in the pathogenesis of neurodegenerative diseases including mild cognitive impairment (MCI) and dementia. We previously reported that molecular hydrogen (H2) acts as a therapeutic and preventive antioxidant.

OBJECTIVE

We assess the effects of drinking H2-water (water infused with H2) on oxidative stress model mice and subjects with MCI.

METHODS

Transgenic mice expressing a dominant-negative form of aldehyde dehydrogenase 2 were used as a dementia model. The mice with enhanced oxidative stress were allowed to drink H2-water. For a randomized double-blind placebo-controlled clinical study, 73 subjects with MCI drank ~300 mL of H2-water (H2-group) or placebo water (control group) per day, and the Alzheimer's Disease Assessment Scale-cognitive subscale (ADAS-cog) scores were determined after 1 year.

RESULTS

In mice, drinking H2-water decreased oxidative stress markers and suppressed the decline of memory impairment and neurodegeneration. Moreover, the mean lifespan in the H2-water group was longer than that of the control group. In MCI subjects, although there was no significant difference between the H2- and control groups in ADAS-cog score after 1 year, carriers of the apolipoprotein E4 (APOE4) genotype in the H2-group were improved significantly on total ADAS-cog score and word recall task score (one of the sub-scores in the ADAS-cog score).

CONCLUSION

H2-water may have a potential for suppressing dementia in an oxidative stress model and in the APOE4 carriers with MCI.

Molecular hydrogen: potential in mitigating oxidative-stress-induced radiation injury

Uncontrolled production of oxygen and nitrogen radicals results in oxidative and nitrosative stresses that impair cellular functions and have been regarded as causative common denominators of many pathological processes. In this review, we report on the beneficial effects of molecular hydrogen in scavenging radicals in an artificial system of•OH formation. As a proof of principle, we also demonstrate that in rat hearts in vivo, administration of molecular hydrogen led to a significant increase in superoxide dismutase as well as pAKT, a cell survival signaling molecule. Irradiation of the rats caused a significant increase in lipid peroxidation, which was mitigated by pre-treatment of the animals with molecular hydrogen. The nuclear factor erythroid 2-related factor 2 is regarded as an important regulator of oxyradical homeostasis, as well as it supports the functional integrity of cells, particularly under conditions of oxidative stress. We suggest that the beneficial effects of molecular hydrogen may be through the activation of nuclear factor erythroid 2-related factor 2 pathway that promotes innate antioxidants and reduction of apoptosis, as well as inflammation.

Aldehyde Dehydrogenase (ALDH) 2 in Diabetic Heart Diseases

A major pathophysiological mechanism behind the development of diabetic heart diseases is oxidative stress mediated by toxic reactive aldehydes such as 4-hydroxynonenal (4HNE). Aldehyde dehydrogenase (ALDH) 2 is a mitochondrial enzyme that has been found to detoxify these deleterious aldehydes and thereby mitigate cardiac damage. Furthermore, its protective role in cellular signaling reverses aberrations caused by hyperglycemia, thereby protecting cardiac function. This chapter assesses the role of ALDH2 in diabetic heart diseases by examining preclinical studies where ALDH2 activity is perturbed in both decreased and increased directions. In doing so, issues in improving ALDH2 activity in select human populations are elucidated, and further research directions are discussed.

Mitochondrial Aldehyde Dehydrogenase in Myocardial Ischemic and Ischemia-Reperfusion Injury

Myocardial ischemia-reperfusion (IR) injury during acute myocardial infarction or open-heart surgery would promote oxidative stress, leading to the accumulation of reactive aldehydes that cause cardiac damage. It has been well demonstrated that aldehyde dehydrogenase (ALDH)-2 is an important cardioprotective enzyme for its central role in the detoxification of reactive aldehydes. ALDH2 activation by small molecule activators is a promising approach for cardioprotection for myocardial IR injury.

The Bidirectional Effect of Defective ALDH2 Polymorphism and Disease Prevention

Despite the role of aldehyde dehydrogenase 2 (ALDH2) in the detoxification of endogenous aldehydes, the defective polymorphism (rs671), which is highly prevalent among East Asians, does not show a serious phenotype, such as congenital abnormality. However, unfavorable and favorable impacts of the variant allele, ALDH2*2, on various disease risks have been reported. The underlying mechanisms are often complicated due to the compensatory aldehyde detoxification systems. As the phenotypes emerge due to overlapping environmental factors (e.g., alcohol intake and tobacco smoke) or individual vulnerabilities (e.g., aging and apolipoprotein E ε4 allele), polymorphism is therefore considered to be important in the field of preventative medicine. For example, it is important to recognize that ALDH2*2 carriers are at a high risk of alcohol drinking-related cancers; however, their drinking habit has less adverse effects on physiological indices, such as blood pressure, body mass index, levels of lipids, and hepatic deviation enzymes in the blood, than in non-ALDH2*2 carriers. Therefore, opportunities to reconsider their excessive drinking habit before adverse events occur can be missed. To perform effective disease prevention, the effects of ALDH2*2 on various diseases and the biological mechanisms should be clarified.

Carnosine protects cardiac myocytes against lipid peroxidation products

Endogenous histidyl dipeptides such as carnosine (β-alanine-L-histidine) form conjugates with lipid peroxidation products such as 4-hydroxy-trans-2-nonenal (HNE and acrolein), chelate metals, and protect against myocardial ischemic injury. Nevertheless, it is unclear whether these peptides protect against cardiac injury by directly reacting with lipid peroxidation products. Hence, to examine whether changes in the structure of carnosine could affect its aldehyde reactivity and metal chelating ability, we synthesized methylated analogs of carnosine, balenine (β-alanine-N^τ-methylhistidine) and dimethyl balenine (DMB), and measured their aldehyde reactivity and metal chelating properties. We found that methylation of N^τ residue of imidazole ring (balenine) or trimethylation of carnosine backbone at N^τ residue of imidazole ring and terminal amine group dimethyl balenine (DMB) abolishes the ability of these peptides to react with HNE. Incubation of balenine with acrolein resulted in the formation of single product (m/z 297), whereas DMB did not react with acrolein. In comparison with carnosine, balenine exhibited moderate acrolein quenching capacity. The Fe²⁺ chelating ability of balenine was higher than that of carnosine, whereas DMB lacked chelating capacity. Pretreatment of cardiac myocytes with carnosine increased the mean lifetime of myocytes superfused with HNE or acrolein compared with balenine or DMB. Collectively, these results suggest that carnosine protects cardiac myocytes against HNE and acrolein toxicity by directly reacting with these aldehydes. This reaction involves both the amino group of β-alanyl residue and the imidazole residue of L-histidine. Methylation of these sites prevents or abolishes the aldehyde reactivity of carnosine, alters its metal-chelating property, and diminishes its ability to prevent electrophilic injury.

Role of the ISR-ATF4 pathway and its cross talk with Nrf2 in mitochondrial quality control

Recent investigations have clarified the importance of mitochondria in various age-related degenerative diseases, including late-onset Alzheimer’s disease and Parkinson’s disease. Although mitochondrial disturbances can be involved in every step of disease progression, several observations have demonstrated that a subtle mitochondrial functional disturbance is observed preceding the actual appearance of pathophysiological alterations and can be the target of early therapeutic intervention. The signals from damaged mitochondria are transferred to the nucleus, leading to the altered expression of nuclear-encoded genes, which includes mitochondrial proteins (i.e., mitochondrial retrograde signaling). Mitochondrial retrograde signaling improves mitochondrial perturbation (i.e., mitohormesis) and is considered a homeostatic stress response against intrinsic (ex. aging or pathological mutations) and extrinsic (ex. chemicals and pathogens) stimuli. There are several branches of the mitochondrial retrograde signaling, including mitochondrial unfolded protein response (UPR^MT), but recent observations increasingly show the importance of the ISR-ATF4 pathway in mitochondrial retrograde signaling. Furthermore, Nrf2, a master regulator of the oxidative stress response, interacts with ATF4 and cooperatively upregulates a battery of antioxidant and antiapoptotic genes while repressing the ATF4-mediated proapoptotic gene, CHOP. In this review article, we summarized the upstream and downstream mechanisms of ATF4 activation during mitochondrial stresses and disturbances and discuss therapeutic intervention against degenerative diseases by using Nrf2 activators.

[Roles of Sodium-Glucose Cotransporter 1 (SGLT1) in the Induction of Cardiac Remodeling]

　It is well-known that metabolic remodeling occurs in the presence of cardiomyopathy induced by cardiac ischemia and hypertrophy, and diabetes mellitus. It is also known that a novel cardiac glucose transporter, sodium-glucose co-transporter 1 (SGLT1), is expressed in the human heart. However, the role of SGLT1 in the development of cardiac metabolic remodeling is still unclear. Recent studies demonstrated that SGLT1 activation improves ischemia-reperfusion-induced cardiac injury, and increased SGLT1 gene expression is observed in hypertrophic, ischemic, and diabetic cardiomyopathy in human hearts. Moreover, increases in SGLT1 protein expression cause cardiac remodeling such as hypertrophy and increased interstitial fibrosis in mice. We demonstrated that ischemia-reperfusion-induced cardiac injury was potentiated in SGLT1-deficient mice. In contrast, chronic pressure overload induced by transverse aortic constriction (TAC) caused cardiac hypertrophy and reduced left ventricular fractional shortening in C57BL/6J wild-type mice. Moreover, the TAC-induced hypertrophied heart showed increased SGLT1 and AMPKαprotein expressions. These results suggest the different effects of SGLT1 activation on cardiac diseases such as acute ischemia-reperfusion-induced cardiac injury and chronically-induced cardiac hypertrophy. Thus, SGLT1 may be a novel therapeutic target for the treatment of patients with cardiac diseases such as ischemic and hypertrophic cardiomyopathy.

Cardiac-specific overexpression of aldehyde dehydrogenase 2 exacerbates cardiac remodeling in response to pressure overload

Pathological cardiac remodeling during heart failure is associated with higher levels of lipid peroxidation products and lower abundance of several aldehyde detoxification enzymes, including aldehyde dehydrogenase 2 (ALDH2). An emerging idea that could explain these findings concerns the role of electrophilic species in redox signaling, which may be important for adaptive responses to stress or injury. The purpose of this study was to determine whether genetically increasing ALDH2 activity affects pressure overload-induced cardiac dysfunction. Mice subjected to transverse aortic constriction (TAC) for 12 weeks developed myocardial hypertrophy and cardiac dysfunction, which were associated with diminished ALDH2 expression and activity. Cardiac-specific expression of the human ALDH2 gene in mice augmented myocardial ALDH2 activity but did not improve cardiac function in response to pressure overload. After 12 weeks of TAC, ALDH2 transgenic mice had larger hearts than their wild-type littermates and lower capillary density. These findings show that overexpression of ALDH2 augments the hypertrophic response to pressure overload and imply that downregulation of ALDH2 may be an adaptive response to certain forms of cardiac pathology.

Deficiency of aldose reductase exacerbates early pressure overload-induced cardiac dysfunction and autophagy in mice

Pathological cardiac hypertrophy is associated with the accumulation of lipid peroxidation-derived aldehydes such as 4-hydroxy-trans-2-nonenal (HNE) and acrolein in the heart. These aldehydes are metabolized via several pathways, of which aldose reductase (AR) represents a broad-specificity route for their elimination. We tested the hypothesis that by preventing aldehyde removal, AR deficiency accentuates the pathological effects of transverse aortic constriction (TAC). We found that the levels of AR in the heart were increased in mice subjected to TAC for 2 weeks. In comparison with wild-type (WT), AR-null mice showed lower ejection fraction, which was exacerbated 2 weeks after TAC. Levels of atrial natriuretic peptide and myosin heavy chain were higher in AR-null than in WT TAC hearts. Deficiency of AR decreased urinary levels of the acrolein metabolite, 3-hydroxypropylmercapturic acid. Deletion of AR did not affect the levels of the other aldehyde-metabolizing enzyme - aldehyde dehydrogenase 2 in the heart, or its urinary product - (N-Acetyl-S-(2-carboxyethyl)-l-cystiene). AR-null hearts subjected to TAC showed increased accumulation of HNE- and acrolein-modified proteins, as well as increased AMPK phosphorylation and autophagy. Superfusion with HNE led to a greater increase in p62, LC3II formation, and GFP-LC3-II punctae formation in AR-null than WT cardiac myocytes. Pharmacological inactivation of JNK decreased HNE-induced autophagy in AR-null cardiac myocytes. Collectively, these results suggest that during hypertrophy the accumulation of lipid peroxidation derived aldehydes promotes pathological remodeling via excessive autophagy, and that metabolic detoxification of these aldehydes by AR may be essential for maintaining cardiac function during early stages of pressure overload.

Sensing the Stress: A Role for the UPRmt and UPRam in the Quality Control of Mitochondria

Mitochondria exist as compartmentalized units, surrounded by a selectively permeable double membrane. Within is contained the mitochondrial genome and protein synthesis machinery, required for the synthesis of OXPHOS components and ultimately, ATP production. Despite their physical barrier, mitochondria are tightly integrated into the cellular environment. A constant flow of information must be maintained to and from the mitochondria and the nucleus, to ensure mitochondria are amenable to cell metabolic requirements and also to feedback on their functional state. This review highlights the pathways by which mitochondrial stress is signaled to the nucleus, with a particular focus on the mitochondrial unfolded protein response (UPR^mt) and the unfolded protein response activated by the mistargeting of proteins (UPR^am). Although these pathways were originally discovered to alleviate proteotoxic stress from the accumulation of mitochondrial-targeted proteins that are misfolded or unimported, we review recent findings indicating that the UPR^mt can also sense defects in mitochondrial translation. We further discuss the regulation of OXPHOS assembly and speculate on a possible role for mitochondrial stress pathways in sensing OXPHOS biogenesis.

[Importance of an Aldehyde Dehydrogenase 2 Polymorphism in Preventive Medicine]

Unlike genetic alterations in other aldehyde dehydrogenase (ALDH) isozymes, a defective ALDH2 polymorphism (rs671), which is carried by almost half of East Asians, does not show a clear phenotype such as a shortened life span. However, impacts of a defective ALDH2 allele, ALDH2*2, on various disease risks have been reported. As ALDH2 is responsible for the detoxification of endogenous aldehydes, a negative effect of this polymorphism is predicted, but bidirectional effects have been actually observed and the mechanisms underlying such influences are often complex. One reason for this complexity may be the existence of compensatory aldehyde detoxification systems and the secondary effects of these systems. There are many issues to be addressed with regard to the ALDH2 polymorphism in the field of preventive medicine, including the following concerns. First, ALDH2 in the fetal stage plays a role in aldehyde detoxification; therefore, prenatal health effects of environmental aldehyde exposure are of concern for ALDH2*2-carrying fetuses. Second, ALDH2*2 carriers are at high risk of drinking-related cancers. However, their drinking habits result in less worsening of physiological findings, such as energy metabolism index and liver functions, compared with non-ALDH2*2 carriers, and therefore opportunities to detect excessive drinking can be lost. Third, personalized medicine such as personalized prescriptions for ALDH2*2 carriers will be required in the clinical setting, and accumulation of evidence is awaited. Lastly, since the ALDH2 polymorphism is not considered in workers' limits of exposure to aldehydes and their precursors, efforts to lower exposure levels beyond legal standards are required.