Reactive Aldehydes Research Articles

Reactive aldehyde chemistry explains the missing source of hydroxyl radicals

Hydroxyl radicals (OH) determine the tropospheric self-cleansing capacity, thus regulating air quality and climate. However, the state-of-the-art mechanisms still underestimate OH at low nitrogen oxide and high volatile organic compound regimes even considering the latest isoprene chemistry. Here we propose that the reactive aldehyde chemistry, especially the autoxidation of carbonyl organic peroxy radicals (R(CO)O2) derived from higher aldehydes, is a noteworthy OH regeneration mechanism that overwhelms the contribution of the isoprene autoxidation, the latter has been proved to largely contribute to the missing OH source under high isoprene condition. As diagnosed by the quantum chemical calculations, the R(CO)O2 radicals undergo fast H-migration to produce unsaturated hydroperoxyl-carbonyls that generate OH through rapid photolysis. This chemistry could explain almost all unknown OH sources in areas rich in both natural and anthropogenic emissions in the warm seasons, and may increasingly impact the global self-cleansing capacity in a future low nitrogen oxide society under carbon neutrality scenarios.

A translation proofreader of archaeal origin imparts multi-aldehyde stress tolerance to land plants

Aldehydes, being an integral part of carbon metabolism, energy generation, and signalling pathways, are ingrained in plant physiology. Land plants have developed intricate metabolic pathways which involve production of reactive aldehydes and its detoxification to survive harsh terrestrial environments. Here, we show that physiologically produced aldehydes, i.e., formaldehyde and methylglyoxal in addition to acetaldehyde, generate adducts with aminoacyl-tRNAs, a substrate for protein synthesis. Plants are unique in possessing two distinct chiral proofreading systems, D-aminoacyl-tRNA deacylase1 (DTD1) and DTD2, of bacterial and archaeal origins, respectively. Extensive biochemical analysis revealed that only archaeal DTD2 can remove the stable D-aminoacyl adducts on tRNA thereby shielding archaea and plants from these system-generated aldehydes. Using Arabidopsis as a model system, we have shown that the loss of DTD2 gene renders plants susceptible to these toxic aldehydes as they generate stable alkyl modification on D-aminoacyl-tRNAs, which are recycled only by DTD2. Bioinformatic analysis identifies the expansion of aldehyde metabolising repertoire in land plant ancestors which strongly correlates with the recruitment of archaeal DTD2. Finally, we demonstrate that the overexpression of DTD2 offers better protection against aldehydes than in wild type Arabidopsis highlighting its role as a multi-aldehyde detoxifier that can be explored as a transgenic crop development strategy.

Glyoxal in Foods: Formation, Metabolism, Health Hazards, and Its Control Strategies.

Glyoxal is a highly reactive aldehyde widely present in common diet and environment and inevitably generated through various metabolic pathways in vivo. Glyoxal is easily produced in diets high in carbohydrates and fats via the Maillard reaction, carbohydrate autoxidation, and lipid peroxidation, etc. This leads to dietary intake being a major source of exogenous exposure. Exposure to glyoxal has been positively associated with a number of metabolic diseases, such as diabetes mellitus, atherosclerosis, and Alzheimer's disease. It has been demonstrated that polyphenols, probiotics, hydrocolloids, and amino acids can reduce the content of glyoxal in foods via different mechanisms, thus reducing the risk of exogenous exposure to glyoxal and alleviating carbonyl stresses in the human body. This review discussed the formation and metabolism of glyoxal, its health hazards, and the strategies to reduce such health hazards. Future investigation of glyoxal from different perspectives is also discussed.

A comprehensive analysis of the role of native and modified HDL in ER stress in primary macrophages.

Recent findings demonstrate that high density lipoprotein (HDL) function rather than HDL-cholesterol levels themselves may be a better indicator of cardiovascular disease risk. One mechanism by which HDL can become dysfunctional is through oxidative modification by reactive aldehydes. Previous studies from our group demonstrated that HDL modified by reactive aldehydes alters select cardioprotective functions of HDL in macrophages. To identify mechanisms by which dysfunctional HDL contributes to atherosclerosis progression, we designed experiments to test the hypothesis that HDL modified by reactive aldehydes triggers endoplasmic reticulum (ER) stress in primary murine macrophages. Peritoneal macrophages were harvested from wild-type C57BL/6J mice and treated with thapsigargin, oxLDL, and/or HDL for up to 48 hours. Immunoblot analysis and semi-quantitative PCR were used to measure expression of BiP, p-eIF2α, ATF6, and XBP1 to assess activation of the unfolded protein response (UPR). Through an extensive set of comprehensive experiments, and contrary to some published studies, our findings led us to three novel discoveries in primary murine macrophages: (i) oxLDL alone was unable to induce ER stress; (ii) co-incubation with oxLDL or HDL in the presence of thapsigargin had an additive effect in which expression of ER stress markers were significantly increased and prolonged as compared to cells treated with thapsigargin alone; and (iii) HDL, in the presence or absence of reactive aldehydes, was unable blunt the ER stress induced by thapsigargin in the presence or absence of oxLDL. Our systematic approach to assess the role of native and modified HDL in mediating primary macrophage ER stress led to the discovery that lipoproteins on their own require the presence of thapsigargin to synergistically increase expression of ER stress markers. We further demonstrated that HDL, in the presence or absence of reactive aldehydes, was unable to blunt the ER stress induced by thapsigargin in the presence or absence of oxLDL. Together, our findings suggest the need for more detailed investigations to better understand the role of native and modified lipoproteins in mediating ER stress pathways.

Cross aldol OPAL bioconjugation outcompetes intramolecular hemiaminal cyclisation of proline adjacent N-terminal α-oxo aldehydes at acidic pH.

Novel methods to construct small molecule-protein bioconjugates are integral to the development of new biomedicines for a variety of diseases. C-C linked bioconjugates are increasingly desirable in this application due to their in vivo stability and can be accessed through cross aldol bioconjugation of reactive α-oxo aldehyde handles easily introduced at the N-terminus of proteins by periodate oxidation. We previously developed an organocatalyst-mediated protein aldol ligation (OPAL) for chemical modification of these reactive aldehydes, but the efficiency of this method was limited when a proline residue was directly adjacent to the N-terminus due to intramolecular hemiaminal formation. Herein we explore the competition between this cyclisation and the OPAL modification and demonstrate bioconjugation can be favoured through use of acidic pH for both oxidation and OPAL, and optimisation of reaction conditions and organocatalyst. We then showcase the utility of this acidic-OPAL in modification of the cholera toxin B-subunit (CTB), a homo-pentameric protein of biomedical promise.

Histological Visualization of Glyceraldehyde-Derived Glycation with Glucose using Ultrasound Microscopy

Background: Reducing sugars and reactive aldehydes, such as glyceraldehyde (GA), non-enzymatically react with proteins to form advanced glycation end-products (AGEs). GA is produced in the glycolysis pathway, and GA-derived AGEs play an essential role in the pathogenesis of angiopathy associated with hyperglycemia in patients with diabetes. Aims: Several studies have reported on chemical alterations in glycation. However, histological confirmation of these biochemical changes has been relatively rare. This study aimed to visualize glyceraldehyde-induced glycation and evaluate the severity of glycation using attenuation of sound (AOS) values. Given that glycation promotes cross-links between proteins and sugars, the energy loss of sound that passes through them increases. We hypothesized that AOS alteration would reflect the glycation state of the tissues and cells. Methods: Fresh frozen sections or fresh cells were briefly fixed in ethanol and soaked in GA with different glucose concentrations. Thereafter, AOS images were obtained via scanning acoustic microscopy over time, and tissue and cellular glycation induced by GA with glucose was evaluated using AOS values. Results: AOS images were able to visualize GA-induced glycation over time. Compared to GA alone, glucose supplements concentration-dependently accelerated glycation. The arterial smooth muscle, collagen, and intima were apt to accept glycation, whereas the mucosa was unaffected. Conclusion: The comparability and digital nature of AOS images make them suitable for statistical analysis of glycation. Higher glucose concentrations promoted a greater increase in the AOS values of the sections and cells. Moreover, the increase in AOS values varied according to organs and cells, which supports the difference in affected organs among patients with diabetes mellitus. Our findings suggest that a longer hyperglycemic state promotes greater glycation.

Conformational equilibria in acrolein-CO2: the crucial contribution of n → π* interactions unveiled by rotational spectroscopy.

Using gas phase Fourier-transform microwave spectroscopy complemented by theoretical analysis, this study delivers a comprehensive depiction of the physical origin of the 'n → π* interaction' between CO2 and acrolein, one of the most reactive aldehydes. Three distinct isomers of the acrolein-CO2 complex, linked through a C⋯O tetrel bond (or n → π* interaction) and a C-H⋯O hydrogen bond, have been unambiguously identified in the pulsed jet. Relative intensity measurements allowed estimation on the population ratio of the three isomers to be T1/T2/C1 ≈ 25/5/1. Advanced theoretical analyses were employed to elucidate the intricacies of the noncovalent interactions within the examined complex. This study not only sheds light on the molecular underpinnings of n → π* interactions but also paves the way for future exploration in carbon dioxide capture and utilization, leveraging the fundamental principles uncovered in the study of acrolein-carbon dioxide interactions.

High-performance self-bonding bio-composites from wood fibers

Green and low-carbon bio-composites from wood fibers are in great demand in the further due to the global sustainable development. In this work, we successfully manufactured the fully bio-composites with excellent mechanical properties and improved water resistance using the dialdehyde wood fibers as the “glue” and untreated poplar wood fibers with lower particle size. The high reactive aldehyde groups provided internal chemical connection between fiber compositions and uniform size offered tightly connected structure and physical winding, which were synergistically contributed to superior performances of self-bonding bio-composites. The self-adhesive bio-composites owned outstanding flexural strength (105.2 MPa), tensile strength (35.6 MPa), internal bond strength (5.1 MPa), and hardness (0.3 GPa), better than most of the reported non-adhesive biomass materials. An innovative hydrobromic acid destruction method was used to prove the self-assembly mechanism and contributions. Both of the direct characterization and reverse destruction illustrated the covalent and hydrogen bond synergistic self-adhesive contribution of dialdehyde oxidation and homogenization. The self-bonding bio-composites have the potential to be applied to high strength outdoor household materials and structural buildings, which corresponds with the notions of carbon storage, eco-friendly, and degradation.

Mitochondrial aldehyde dehydrogenase-2 coordinates the hydrogen sulfide - AMPK axis to attenuate high glucose-induced pancreatic β-cell dysfunction by glutathione antioxidant system

Progression of β-cell loss in diabetes mellitus is significantly influenced by persistent hyperglycemia. At the cellular level, a number of signaling cascades affect the expression of apoptotic genes, ultimately resulting in β-cell failure; these cascades have not been elucidated. Mitochondrial aldehyde dehydrogenase-2 (ALDH2) plays a central role in the detoxification of reactive aldehydes generated from endogenous and exogenous sources and protects against mitochondrial deterioration in cells. Here we report that under diabetogenic conditions, ALDH2 is strongly inactivated in β-cells through CDK5-dependent glutathione antioxidant imbalance by glucose-6-phosphate dehydrogenase (G6PD) degradation. Intriguingly, CDK5 inhibition strengthens mitochondrial antioxidant defense through ALDH2 activation. Mitochondrial ALDH2 activation selectively preserves β-cells against high-glucose-induced dysfunction by activating AMPK and Hydrogen Sulfide (H2S) signaling. This is associated with the stabilization and enhancement of the activity of G6PD by SIRT2, a cytoplasmic NAD+-dependent deacetylase, and is thereby linked to an elevation in the GSH/GSSG ratio, which leads to the inhibition of mitochondrial dysfunction under high-glucose conditions. Furthermore, treatment with NaHS, an H2S donor, selectively preserves β-cell function by promoting ALDH2 activity, leading to the inhibition of lipid peroxidation by high-glucose concentrations. Collectively, our results provide the first direct evidence that ALDH2 activation enhances H2S-AMPK-G6PD signaling, leading to improved β-cell function and survival under high-glucose conditions via the glutathione redox balance.

Torachrysone-8-O-β-d-glucoside mediates anti-inflammatory effects by blocking aldose reductase-catalyzed metabolism of lipid peroxidation products

Aldose reductase (AR) is an important enzyme involved in the reduction of various aldehyde and carbonyl compounds, including the highly reactive and toxic 4-hydroxynonenal (4-HNE), which has been linked to the progression of various pathologies such as atherosclerosis, hyperglycemia, inflammation, and tumors. AR inhibitors have potential therapeutic benefits for these diseases by reducing lipid peroxidation and mitigating the harmful effects of reactive aldehydes.In this study, we found that torachrysone-8-O-β-d-glucoside (TG), a natural product isolated from Polygonum multiflorum Thunb., functions as an effective inhibitor of AR, exhibiting potent effects in clearing reactive aldehydes and reducing inflammation. TG up-regulated the mRNA levels of several antioxidant factors downstream of NRF2, especially glutathione S-transferase (GST), which is significantly increased, thus detoxifying 4-HNE by facilitating the conjugation of 4-HNE to glutathione, forming glutathione-4-hydroxynonenal (GS-HNE). By employing a combination of molecular docking, cellular thermal shift assay, and enzyme activity experiments, we demonstrated that TG exhibited strong binding affinity with AR and inhibited its activity and blocked the conversion of GS-HNE to glutathionyl-1,4-dihydroxynonene (GS-DHN), thereby preventing the formation of protein adducts and inducing severe cellular damage.This study provides novel insights into the anti-inflammatory mechanisms of AR inhibitors and offers potential avenues for developing therapeutic strategies for AR-related pathologies. Our findings suggest that TG, as an AR inhibitor, may hold promise as a therapeutic agent for treating conditions characterized by excessive lipid peroxidation and inflammation. Further investigations are needed to fully explore the clinical potential of TG and evaluate its efficacy in the treatment and management of these complex diseases.

K6-linked ubiquitylation marks formaldehyde-induced RNA-protein crosslinks for resolution

Reactive aldehydes are produced by normal cellular metabolism or after alcohol consumption, and they accumulate in human tissues if aldehyde clearance mechanisms are impaired. Their toxicity has been attributed to the damage they cause to genomic DNA and the subsequent inhibition of transcription and replication. However, whether interference with other cellular processes contributes to aldehyde toxicity has not been investigated. We demonstrate that formaldehyde induces RNA-protein crosslinks (RPCs) that stall the ribosome and inhibit translation in human cells. RPCs in the messenger RNA (mRNA) are recognized by the translating ribosomes, marked by atypical K6-linked ubiquitylation catalyzed by the RING-in-between-RING (RBR) E3 ligase RNF14, and subsequently resolved by the ubiquitin- and ATP-dependent unfoldase VCP. Our findings uncover an evolutionary conserved formaldehyde-induced stress response pathway that protects cells against RPC accumulation in the cytoplasm, and they suggest that RPCs contribute to the cellular and tissue toxicity of reactive aldehydes.

Repurposing of Strychnine as the Potential Inhibitors of Aldo-keto Reductase Family 1 Members B1 and B10: Computational Modeling and Pharmacokinetic Analysis.

AKR1B1 and AKR1B10 are important members of aldo-keto reductase family which plays a significant role in cancer progression by modulating cellular metabolism. These enzymes are involved in various metabolic processes, including the synthesis and metabolism of hormones, detoxification of reactive aldehydes, and the reduction of various endogenous and exogenous compounds. This study aimed to explore the potential of strychnine as an anticancer agent by targeting AKR1B1 and AKR1B10 via drug repurposing approach. To assess the drug-like properties of strychnine, a physiologically based pharmacokinetic (PKPB) model and High Throughput Pharmacokinetics (HTPK) approach were employed. The obtained results fell within the expected range for drug molecules, confirming its suitability for further investigation. Additionally, density functional theory (DFT) studies were conducted to gain insight into the electronic properties contributing to the drug molecule's reactivity. Building upon the promising DFT results, molecular docking analysis using the AutoDock tool was performed to examine the binding interactions between strychnine and the proposed targets, AKR1B1 and AKR1B10. Findings from the molecular docking studies suggested a higher probability of strychnine acting as an inhibitor of AKR1B1 and AKR1B10 with docking scores of - 30.84 and - 29.36kJ/mol respectively. To validate the stability of the protein-ligand complex, Molecular Dynamic Simulation (MDS) studies were conducted, revealing the formation of a stable complex between the enzymes and strychnine. This comprehensive approach sheds light on the potential effectiveness of strychnine as a treatment for breast, lung, liver, and pancreatic cancers, as well as related malignancies. The novel insights gained from the physiologically based pharmacokinetic modeling, density functional theory, molecular docking, and molecular dynamics simulations collectively support the prospect of strychnine as a promising molecule for anticancer therapy. Further investigations are warranted to validate these findings and explore the therapeutic potential of strychnine in preclinical and clinical settings.

4-Hydroxynonenal impairs miRNA maturation in heart failure via Dicer post-translational modification.

Developing novel therapies to battle the global public health burden of heart failure remains challenging. This study investigates the underlying mechanisms and potential treatment for 4-hydroxynonenal (4-HNE) deleterious effects in heart failure. Biochemical, functional, and histochemical measurements were applied to identify 4-HNE adducts in rat and human failing hearts. In vitro studies were performed to validate 4-HNE targets. 4-HNE, a reactive aldehyde by-product of mitochondrial dysfunction in heart failure, covalently inhibits Dicer, an RNase III endonuclease essential for microRNA (miRNA) biogenesis. 4-HNE inhibition of Dicer impairs miRNA processing. Mechanistically, 4-HNE binds to recombinant human Dicer through an intermolecular interaction that disrupts both activity and stability of Dicer in a concentration- and time-dependent manner. Dithiothreitol neutralization of 4-HNE or replacing 4-HNE-targeted residues in Dicer prevents 4-HNE inhibition of Dicer in vitro. Interestingly, end-stage human failing hearts from three different heart failure aetiologies display defective 4-HNE clearance, decreased Dicer activity, and miRNA biogenesis impairment. Notably, boosting 4-HNE clearance through pharmacological re-activation of mitochondrial aldehyde dehydrogenase 2 (ALDH2) using Alda-1 or its improved orally bioavailable derivative AD-9308 restores Dicer activity. ALDH2 is a major enzyme responsible for 4-HNE removal. Importantly, this response is accompanied by improved miRNA maturation and cardiac function/remodelling in a pre-clinical model of heart failure. 4-HNE inhibition of Dicer directly impairs miRNA biogenesis in heart failure. Strikingly, decreasing cardiac 4-HNE levels through pharmacological ALDH2 activation is sufficient to re-establish Dicer activity and miRNA biogenesis; thereby representing potential treatment for patients with heart failure.

Abstract 15581: Increasing Myocardial Carnosine Levels Reduces Adverse Remodeling During Heart Failure

Background : Lipid peroxidation products, such as acrolein, are highly toxic aldehydes generated during pathological remodeling and associated with heart failure. Until now, no translatable therapy has been tested to remove these toxic products from heart and examine the subsequent effects on failing hearts. The heart contains small histidyl dipeptides, such as carnosine (β-alanine-histidine), which bind lipid peroxidation products. Carnosine is decreased in failing hearts and its levels can be increased by supplementing the precursor, β-alanine. This study investigates the cardioprotective and translational potential of β-alanine supplementation in a transaortic constriction (TAC) model of heart failure. Hypothesis : Increasing myocardial carnosine via β-alanine supplementation will improve cardiac function during heart failure. Approach : Male wild-type C57BL/6J mice were treated either (a) water alone, (b) β-alanine 1 week prior to TAC, or (c) β-alanine (20g/L) in water 4 weeks post TAC. Supplementation of β-alanine was continued for 8 weeks, followed by serial echocardiography, biochemical, and mass spectrometry analysis. Results : Myocardial carnosine increased ~3-4-fold after 1 week of β-alanine feeding compared with water alone (p < 0.05). β-alanine pre-feeding compared with water alone, after 8 weeks of TAC, decreased left ventricular (LV) mass (β-alanine: 174 ± 29 vs water: 241 ± 17 mg, p < 0.05) and LV inner diameter at systole (β-alanine: 2.2 ± 0.6 vs water: 3.5 ± 0.4 mm, p < 0.05) and diastole (β-alanine: 3.5 ± 0.4 vs water: 4.4 ± 0.3 mm, p < 0.05), and increased ejection fraction (β-alanine: 67 ± 14% vs water: 42 ± 9%, p < 0.05) and cardiac output (β-alanine:13.6 ± 2.6 vs water: 10.7 ± 1.0 mL/min, p < 0.05). Post-TAC β-alanine intervention decreased LV mass (β-alanine :177 ± 8 vs water: 214 ± 11 mg, p < 0.05), hypertrophic markers Nppa and Myh7 , and increasingly removed acrolein from heart by conjugation (β-alanine: carnosine-propanal: 12.2 ± 0.4 vs water: 0.7 ± 0.4 pmoles/mg protein, p < 0.0001). Conclusion : Increasing myocardial carnosine via oral supplementation alleviates pathological remodeling, possibly through quenching reactive aldehydes. These findings lay foundation to test the feasibility of β-alanine in heart failure patients.

Polyamine-Derived Aminoaldehydes and Acrolein: Cytotoxicity, Reactivity and Analysis of the Induced Protein Modifications.

Polyamines participate in the processes of cell growth and development. The degradation branch of their metabolism involves amine oxidases. The oxidation of spermine, spermidine and putrescine releases hydrogen peroxide and the corresponding aminoaldehyde. Polyamine-derived aminoaldehydes have been found to be cytotoxic, and they represent the subject of this review. 3-aminopropanal disrupts the lysosomal membrane and triggers apoptosis or necrosis in the damaged cells. It is implicated in the pathogenesis of cerebral ischemia. Furthermore, 3-aminopropanal yields acrolein through the elimination of ammonia. This reactive aldehyde is also generated by the decomposition of aminoaldehydes produced in the reaction of serum amine oxidase with spermidine or spermine. In addition, acrolein is a common environmental pollutant. It causes covalent modifications of proteins, including carbonylation, the production of Michael-type adducts and cross-linking, and it has been associated with inflammation-related diseases. APAL and acrolein are detoxified by aldehyde dehydrogenases and other mechanisms. High-performance liquid chromatography, immunochemistry and mass spectrometry have been largely used to analyze the presence of polyamine-derived aminoaldehydes and protein modifications elicited by their effect. However, the main and still open challenge is to find clues for discovering clear linkages between aldehyde-induced modifications of specific proteins and the development of various diseases.

Simultaneous extraction of crocin and geniposide from gardenia fruits (Gardenia jasminoides Ellis) by probe-type ultrasound-assisted natural deep eutectic solvents and their inhibition effects on low density lipoprotein oxidation

The simultaneous extraction of crocin and geniposide from gardenia fruits (Gardenia jasminoides Ellis) was performed by integrating natural deep eutectic solvents (NADES) and ultrasound-assisted extraction (UAE). Among the eight kinds of NADES screened, choline chloride-1,2-propylene glycol was the most suitable extractant. The probe-type ultrasound-assisted NADES extraction system (pr-UAE-NADES) demonstrated higher extraction efficiency compared with plate-type ultrasound-assisted NADES extraction system (pl-UAE-NADES). Orthogonal experimental design and a modified multi-index synthetic weighted scoring method were adopted to optimize pr-UAE-NADES extraction process. The optimal extraction conditions that had a maximum synthetic weighted score of 29.46 were determined to be 25 °C for extraction temperature, 600 W for ultrasonic power, 20 min for extraction time, and 25% (w/w) for water content in NADES, leading to the maximum yields (7.39 ± 0.20 mg/g and 57.99 ± 0.91 mg/g, respectively) of crocin and geniposide. Thirty-three compounds including iridoids, carotenoids, phenolic acids, flavonoids, and triterpenes in the NADES extract were identified by LC-Q-TOF-MS2 coupled with a feature-based molecular networking workflow. The kinetics evaluation of the conjugated dienes generation on Cu2+-induced low density lipoprotein (LDL) oxidation via the four-parameter logistic regression model showed that crocin increased the lag time of LDL oxidation in a concentration-dependent manner (15 μg/mL, 30 μg/mL, 45 μg/mL) by 12.66%, 35.44%, and 73.42%, respectively. The quantitative determination for fluorescence properties alteration of the apolipoprotein B-100 exhibited that crocin effectively inhibited the fluorescence quenching of tryptophan residues and the modification of lysine residues caused by reactive aldehydes and malondialdehydes. The pr-UAE-NADES showed significant efficiency toward the simultaneous extraction of crocin and geniposide from gardenia fruits. And this study demonstrates the potential utility of gardenia fruits in developing anti-atherogenic functional food.

Recent advances on the role of monoamine oxidases in cardiac pathophysiology

Numerous physiological and pathological roles have been attributed to the formation of mitochondrial reactive oxygen species (ROS). However, the individual contribution of different mitochondrial processes independently of bioenergetics remains elusive and clinical treatments unavailable. A notable exception to this complexity is found in the case of monoamine oxidases (MAOs). Unlike other ROS-producing enzymes, especially within mitochondria, MAOs possess a distinct combination of defined molecular structure, substrate specificity, and clinically accessible inhibitors. Another significant aspect of MAO activity is the simultaneous generation of hydrogen peroxide alongside highly reactive aldehydes and ammonia. These three products synergistically impair mitochondrial function at various levels, ultimately jeopardizing cellular metabolic integrity and viability. This pathological condition arises from exacerbated MAO activity, observed in many cardiovascular diseases, thus justifying the exploration of MAO inhibitors as effective cardioprotective strategy. In this context, we not only summarize the deleterious roles of MAOs in cardiac pathologies and the positive effects resulting from genetic or pharmacological MAO inhibition, but also discuss recent findings that expand our understanding on the role of MAO in gene expression and cardiac development.

Autoreactive B cells against malondialdehyde-induced protein cross-links are present in the joint, lung, and bone marrow of rheumatoid arthritis patients

Autoantibodies to malondialdehyde (MDA) proteins constitute a subset of anti-modified protein autoantibodies in rheumatoid arthritis (RA), which is distinct from citrulline reactivity. Serum anti-MDA IgG levels are commonly elevated in RA and correlate with disease activity, CRP, IL6, and TNF-α. MDA is an oxidation-associated reactive aldehyde that together with acetaldehyde mediates formation of various immunogenic amino acid adducts including linear MDA-lysine, fluorescent malondialdehyde acetaldehyde (MAA)-lysine, and intramolecular cross-linking. We used single-cell cloning, generation of recombinant antibodies (n= 356 from 25 donors), and antigen-screening to investigate the presence of class-switched MDA/MAA+ B cells in RA synovium, bone marrow, and bronchoalveolar lavage. Anti-MDA/MAA+ B cells were found in bone marrow plasma cells of late disease and in the lung of both early disease and risk-individuals and in different B cell subsets (memory, double negative B cells). These were compared with previously identified anti-MDA/MAA from synovial memory and plasma cells. Seven out of eight clones carried somatic hypermutations and all bound MDA/MAA-lysine independently of protein backbone. However, clones with somatic hypermutations targeted MAA cross-linked structures rather than MDA- or MAA-hapten, while the germline-encoded synovial clone instead bound linear MDA-lysine in proteins and peptides. Binding patterns were maintained in germline converted clones. Affinity purification of polyclonal anti-MDA/MAA from patient serum revealed higher proportion of anti-MAA versus anti-MDA compared to healthy controls. In conclusion, IgG anti-MDA/MAA show distinct targeting of different molecular structures. Anti-MAA IgG has been shown to promote bone loss and osteoclastogenesis invivo and may contribute to RA pathogenesis.

Role of NRF2 and reactive aldehydes in acute cellular rejection in liver transplant recipients

ObjectiveTo evaluate the level of oxidative stress and antioxidative response in the transplanted liver and its role in acute cellular rejection (ACR). Particular attention was paid to ACR diagnosis in patients with hepatitis C (HCV), as histopathological features of ACR and viral disease recurrence overlap. MethodsThis retrospective study included 40 liver transplant patients who underwent liver transplantation with two consecutive liver biopsies performed during one hospitalization period: 1.) initial biopsy of the donor liver (before implantation) and 2.) indication biopsy (after suspected ACR). Based on the etiology, patients were divided into two groups: 22 patients with alcoholic liver cirrhosis (EtOH group) and 18 patients with hepatitis C cirrhosis (HCV group). We analyzed the presence of acrolein, HNE (4-hydroxynonenal), and the major antioxidant transcription factor NRF2 (nuclear factor erythroid 2-related factor 2) in both biopsies. ResultsThe presence of acrolein and HNE in both biopsies indicates increased oxidative stress, while the decrease in these aldehydes in the indication biopsies indicates a decrease in oxidative stress over time, reflecting liver graft recovery. The absence of NRF2 in both biopsies reflects significantly reduced antioxidant protection in patients undergoing liver transplantation. ConclusionThe results support the role of oxidative stress in the pathogenesis of ACR. The presence of acrolein and the absence of HNE in the indication biopsy in patients with ACR could contribute to the diagnosis of ACR in clinical practice when functional antibodies are tested in the clinical setting.

Discovery of novel small-molecule aldehyde dehydrogenase 2 activators based on drug repurposing

Aldehyde dehydrogenase 2 (ALDH2) plays an important role in the detoxification of reactive aldehydes under oxidative stress. Because an estimated 50% of East Asians carry a common ALDH2 deficient variant with decreased enzyme activity and are more susceptible to toxic aldehydes, more recent findings have highlighted the therapeutic potential of ALDH2 activators in aldehyde-related diseases such as cardiovascular injury. Drug repurposing has unique advantages in providing new lead compounds with good drug-like properties. Herein, we identified Tadalafil from DrugBank as a novel ALDH2 activator using a combination strategy of docking-based and pharmacophore-based virtual screening based on exploring the activation mechanism. Then a hit-based substructure search was completed and has led to the discovery of 5 hits, among which A1 showed better ALDH2 activation activity than Tadalafil. This study provides a good basis for the further research of ALDH2 activators.