Many different diseases are associated with oxidative stress. One of the main consequences of oxidative stress at the cellular level is lipid peroxidation, from which toxic aldehydes may be ...generated. Below their toxicity thresholds, some aldehydes are involved in signaling processes, while others are intermediaries in the metabolism of lipids, amino acids, neurotransmitters, and carbohydrates. Some aldehydes ubiquitously distributed in the environment, such as acrolein or formaldehyde, are extremely toxic to the cell. On the other hand, aldehyde dehydrogenases (ALDHs) are able to detoxify a wide variety of aldehydes to their corresponding carboxylic acids, thus helping to protect from oxidative stress. ALDHs are located in different subcellular compartments such as cytosol, mitochondria, nucleus, and endoplasmic reticulum. The aim of this review is to analyze, and highlight, the role of different ALDH isoforms in the detoxification of aldehydes generated in processes that involve high levels of oxidative stress. The ALDH physiological relevance becomes evident by the observation that their expression and activity are enhanced in different pathologies that involve oxidative stress such as neurodegenerative disorders, cardiopathies, atherosclerosis, and cancer as well as inflammatory processes. Furthermore, ALDH mutations bring about several disorders in the cell. Thus, understanding the mechanisms by which these enzymes participate in diverse cellular processes may lead to better contend with the damage caused by toxic aldehydes in different pathologies by designing modulators and/or protocols to modify their activity or expression.
Under physiological conditions, cells produce low basal levels of reactive oxygen species (ROS); however, in pathologic conditions ROS production increases dramatically, generating high ...concentrations of toxic unsaturated aldehydes. Aldehyde dehydrogenases (ALDHs) are responsible for detoxification of these aldehydes protecting the cell. Due to the physiological relevance of these enzymes, it is important to design strategies to modulate their activity. It was previously reported that omeprazole activation of ALDH1A1 protected Escherichia coli cells overexpressing this enzyme, from oxidative stress generated by H2O2. In this work, omeprazole cell protection potential was evaluated in eukaryotic cells. AS‐30D cell or hepatocyte suspensions were subjected to a treatment with omeprazole and exposure to light (that is required to activate omeprazole in the active site of ALDH) and then exposed to H2O2. Cells showed viability similar to control cells, total activity of ALDH was preserved, while cell levels of lipid aldehydes and oxidative stress markers were maintained low. Cell protection by omeprazole was avoided by inhibition of ALDHs with disulfiram, revealing the key role of these enzymes in the protection. Additionally, omeprazole also preserved ALDH2 (mitochondrial isoform) activity, diminishing lipid aldehyde levels and oxidative stress in this organelle, protecting mitochondrial respiration and transmembrane potential formation capacity, from the stress generated by H2O2. These results highlight the important role of ALDHs as part of the antioxidant system of the cell, since if the activity of these enzymes decreases under stress conditions, the viability of the cell is compromised.
Treatment of AS‐30D cells and isolated hepatocytes with omeprazole, and exposure to light to activate ALDH, promotes protection from oxidative stress damage by avoiding cell lipid aldehyde accumulation. This protection is not only due to enzyme activation, but also due to the protection of ALDHs from inactivation by lipid aldehydes. The results of this work highlight the role of ALDHs as an important part of the antioxidant system of the cell.
Metformin is an antihyperglycemic drug which is being examined as a repurposed treatment for cardiovascular disease for individuals without diabetes mellitus. Despite evidence that mitochondrial ...respiratory complex I is a target of metformin and inhibition of the enzyme is one of the mechanisms of its therapeutic actions, no systematic studies of the metformin effect on intact mitochondria have been reported. In the presented paper, we described the effect of metformin on respiration and ROS release by intact mitochondria from the liver and brain. By comparing the effect of metformin on mitochondria oxidizing different substrates, we found direct inhibition of respiration and stimulation of ROS release when complex I-based respiration is measured (forward electron transfer). Metformin had no effect on respiration rates but inhibited ROS release when mitochondria oxidize succinate or glycerol 3-phosphate in conditions of reverse electron transfer in complex I. In addition, we found that metformin is a weak effector of the active/deactive (A/D) transition of mitochondrial complex I. At high concentrations, metformin increases the rate of spontaneous deactivation of complex I (A→D transition). The results obtained are consistent with the concept of metformin inhibition of complex I and that it can either stimulate or inhibit mitochondrial ROS production depending on the preferential respiratory substrate. This is relevant during the ischemia/reperfusion process, to counteract the ROS overproduction, which is induced by a high level of reverse electron transfer substrates is generated after an ischemic event.
Aldehyde dehydrogenases (ALDHs) are involved in the detoxification of aldehydes generated as byproducts of lipid peroxidation. In this work, it was determined that, among the three most studied human ...ALDH isoforms, ALDH2 showed the highest catalytic efficiency for oxidation of acrolein, 4-hydroxy-2-nonenal (4-HNE), and malondialdehyde. ALDH1A1 also exhibited significant activity with these substrates, whereas ALDH3A1 only showed activity with 4-HNE. ALDH2 was also the most sensitive isoform to irreversible inactivation by these compounds. Remarkably, ALDH3A1 was insensitive to these aldehydes even at concentrations as high as 20 mM. Formation of adducts of ALDH1A1 and ALDH2 with acrolein increased their K d values for NAD+ by 2- and 3-fold, respectively. NADH exerted a higher protection than propionaldehyde to the inactivation by acrolein, and this protection was additive. These results suggested that both binding sites, those for aldehyde and NAD+ in ALDH2, are targets for the inactivation by lipid peroxidation products. Thus, with the advantage of being relatively inactivation-insensitive, ALDH1A1 and ALDH3A1 may be actively participating in the detoxification of these aldehydes in the cells.
Impairments in mitochondrial energy metabolism have been implicated in human genetic diseases associated with mitochondrial and nuclear DNA mutations, neurodegenerative and cardiovascular disorders, ...diabetes, and aging. Alteration in mitochondrial complex I structure and activity has been shown to play a key role in Parkinson's disease and ischemia/reperfusion tissue injury, but significant difficulty remains in assessing the content of this enzyme complex in a given sample. The present study introduces a new method utilizing native polyacrylamide gel electrophoresis in combination with flavin fluorescence scanning to measure the absolute content of complex I, as well as α-ketoglutarate dehydrogenase complex, in any preparation. We show that complex I content is 19 ± 1 pmol/mg of protein in the brain mitochondria, whereas varies up to 10-fold in different mouse tissues. Together with the measurements of NADH-dependent specific activity, our method also allows accurate determination of complex I catalytic turnover, which was calculated as 104 min−1 for NADH:ubiquinone reductase in mouse brain mitochondrial preparations. α-ketoglutarate dehydrogenase complex content was determined to be 65 ± 5 and 123 ± 9 pmol/mg protein for mouse brain and bovine heart mitochondria, respectively. Our approach can also be extended to cultured cells, and we demonstrated that about 90 × 103 complex I molecules are present in a single human embryonic kidney 293 cell. The ability to determine complex I content should provide a valuable tool to investigate the enzyme status in samples after in vivo treatment in mutant organisms, cells in culture, or human biopsies.
Detoxification of aldehydes by aldehyde dehydrogenases (ALDHs) is crucial to maintain cell function. In cardiovascular diseases, reactive oxygen species generated during ischemia/reperfusion events ...trigger lipoperoxidation, promoting cell accumulation of highly toxic lipid aldehydes compromising cardiac function. In this context, activation of ALDH2, may contribute to preservation of cell integrity by diminishing aldehydes content more efficiently.
The theoretic interaction of piperlonguminine (PPLG) with ALDH2 was evaluated by docking analysis. Recombinant human ALDH2 was used to evaluate the effects of PPLG on the kinetics of the enzyme. The effects of PPLG were further investigated in a myocardial infarction model in rats, evaluating ALDHs activity, antioxidant enzymes, oxidative stress markers and mitochondrial function.
PPLG increased the activity of recombinant human ALDH2 and protected the enzyme from inactivation by lipid aldehydes. Additionally, administration of this drug prevented the damage induced by ischemia/reperfusion in rats, restoring heart rate and blood pressure, which correlated with protection of ALDHs activity in the tissue, a lower content of lipid aldehydes, and the preservation of mitochondrial function.
Activation of ALDH2 by piperlonguminine ameliorates cell damage generated in heart ischemia/reperfusion events, by decreasing lipid aldehydes concentration promoting cardioprotection.
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•Binding of piperlonguminine activates ALDH2 and protects the enzyme from inactivation by lipid aldehydes.•Activation of ALDH2 avoids accumulation of toxic aldehydes protecting the heart.•ALDHs are feasible drug targets for the protection from ischemia-reperfusion events.•Administration of piperlonguminine may reduce the damage during myocardial infarction.
Pathologies associated with tissue ischemia/reperfusion (I/R) in highly metabolizing organs such as the brain and heart are leading causes of death and disability in humans. Molecular mechanisms ...underlying mitochondrial dysfunction during acute injury in I/R are tissue-specific, but their details are not completely understood. A metabolic shift and accumulation of substrates of reverse electron transfer (RET) such as succinate are observed in tissue ischemia, making mitochondrial complex I of the respiratory chain (NADH:ubiquinone oxidoreductase) the most vulnerable enzyme to the following reperfusion. It has been shown that brain complex I is predisposed to losing its flavin mononucleotide (FMN) cofactor when maintained in the reduced state in conditions of RET both in vitro and in vivo. Here we investigated the process of redox-dependent dissociation of FMN from mitochondrial complex I in brain and heart mitochondria. In contrast to the brain enzyme, cardiac complex I does not lose FMN when reduced in RET conditions. We proposed that the different kinetics of FMN loss during RET is due to the presence of brain-specific long 50 kDa isoform of the NDUFV3 subunit of complex I, which is absent in the heart where only the canonical 10 kDa short isoform is found. Our simulation studies suggest that the long NDUFV3 isoform can reach toward the FMN binding pocket and affect the nucleotide affinity to the apoenzyme. For the first time, we demonstrated a potential functional role of tissue-specific isoforms of complex I, providing the distinct molecular mechanism of I/R-induced mitochondrial impairment in cardiac and cerebral tissues. By combining functional studies of intact complex I and molecular structure simulations, we defined the critical difference between the brain and heart enzyme and suggested insights into the redox-dependent inactivation mechanisms of complex I during I/R injury in both tissues.
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•Reverse electron transfer induces loss of complex I FMN in brain but not in heart.•Complex I content is higher in heart than in brain.•Kinetics of complex I FMN-dependent reactions is different in both tissues.•Long isoform of NDUFV3 subunit is present in the brain but not in the heart enzyme.•Molecular simulation predicts interaction of long isoform with FMN-binding site.
Mitochondrial aldehyde dehydrogenase (ALDH2) has been proposed as a key enzyme in cardioprotection during ischemia–reperfusion processes. This proposal led to the search for activators of ALDH2 with ...the aim to develop cardioprotective drugs. Alda‐1 was the first activator of ALDH2 identified and its cardioprotective effect has been extensively proven in vivo; however, the mechanism of activation is not fully understood. A crystallographic study showed that Alda‐1 binds to the entrance of the aldehyde‐binding site; therefore, Alda‐1 should in essence be an inhibitor. In the present study, kinetic experiments were performed to characterize the effect of Alda‐1 on the properties of ALDH2 (kinetic parameters, determination of the rate‐limiting step, reactivity of the catalytic cysteine) and on the kinetic mechanism (type of kinetics, sequence of substrates entering, and products release). The results showed that Alda‐1 dramatically modifies the properties of ALDH2, the Km for NAD+ decreased by 2.4‐fold, and the catalytic efficiency increased 4.4‐fold; however, the Km for the aldehyde increased 8.6‐fold, thus, diminishing the catalytic efficiency. The alterations in these parameters resulted in a complex behavior, where Alda‐1 acts as inhibitor at low concentrations of aldehyde and as an activator at high concentrations. Additionally, the binding of Alda‐1 to ALDH2 made the deacylation less limiting and diminished the pKa of the catalytic cysteine. Finally, NADH inhibition patterns indicated that Alda‐1 induced a change in the sequence of substrates entry and products release, in agreement with the proposal of both substrates entering ALDH2 by the NAD+ entrance site.
Activator of human ALDH2 Alda‐1 protects cell integrity from diverse stress conditions; however, the activation mechanism is not fully understood. Kinetic characterization showed that binding of Alda‐1 to ALDH2 activates the catalytic cysteine reducing its pKa, which induces the switching of order of substrates binding and products release, additionally, Alda‐1 increases the rate of the limiting step of the reaction.
Accumulation of lipid aldehydes plays a key role in the etiology of human diseases where high levels of oxidative stress are generated. In this regard, activation of aldehyde dehydrogenases (ALDHs) ...prevents oxidative tissue damage during ischemia-reperfusion processes. Although omeprazole is used to reduce stomach gastric acid production, in the present work this drug is described as the most potent activator of human ALDH1A1 reported yet.
Docking analysis was performed to predict the interactions of omeprazole with the enzyme. Recombinant human ALDH1A1 was used to assess the effect of omeprazole on the kinetic properties. Temperature treatment and mass spectrometry were conducted to address the nature of binding of the activator to the enzyme. Finally, the effect of omeprazole was evaluated in an in vivo model of oxidative stress, using E. coli cells expressing the human ALDH1A1.
Omeprazole interacted with the aldehyde binding site, increasing 4–6 fold the activity of human ALDH1A1, modified the kinetic properties, altering the order of binding of substrates and release of products, and protected the enzyme from inactivation by lipid aldehydes. Furthermore, omeprazole protected E. coli cells over-expressing ALDH1A1 from the effects of oxidative stress generated by H2O2 exposure, reducing the levels of lipid aldehydes and preserving ALDH activity.
Omeprazole can be repositioned as a potent activator of human ALDH1A1 and may be proposed for its use in therapeutic strategies, to attenuate the damage generated during oxidative stress events occurring in different human pathologies.
•ALDHs detoxify lipid aldehydes implicated in the etiology of different human diseases.•Omeprazole was a potent ALDH1A1 activator, increasing the activity 4–6-fold.•The presence of omeprazole protected ALDH1A1 from inactivation by lipid aldehydes.•Treatment with omeprazole protected bacterial cells from the oxidative stress promoted by H2O2.•Omeprazole may be used in therapeutic strategies to avoid oxidative stress effects.
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