Showing papers on "Aldehyde dehydrogenase published in 2014"

Targeting aldehyde dehydrogenase 2: new therapeutic opportunities

Abstract: A family of detoxifying enzymes called aldehyde dehydrogenases (ALDHs) has been a subject of recent interest, as its role in detoxifying aldehydes that accumulate through metabolism and to which we are exposed from the environment has been elucidated. Although the human genome has 19 ALDH genes, one ALDH emerges as a particularly important enzyme in a variety of human pathologies. This ALDH, ALDH2, is located in the mitochondrial matrix with much known about its role in ethanol metabolism. Less known is a new body of research to be discussed in this review, suggesting that ALDH2 dysfunction may contribute to a variety of human diseases including cardiovascular diseases, diabetes, neurodegenerative diseases, stroke, and cancer. Recent studies suggest that ALDH2 dysfunction is also associated with Fanconi anemia, pain, osteoporosis, and the process of aging. Furthermore, an ALDH2 inactivating mutation (termed ALDH2*2) is the most common single point mutation in humans, and epidemiological studies suggest a correlation between this inactivating mutation and increased propensity for common human pathologies. These data together with studies in animal models and the use of new pharmacological tools that activate ALDH2 depict a new picture related to ALDH2 as a critical health-promoting enzyme.

The cancer stem cell marker aldehyde dehydrogenase is required to maintain a drug-tolerant tumor cell subpopulation

Abstract: Selective kinase inhibitors have emerged as an important class of cancer therapeutics, and several such drugs are now routinely used to treat advanced-stage disease. However, their clinical benefit is typically short-lived because of the relatively rapid acquisition of drug resistance following treatment response. Accumulating preclinical and clinical data point to a role for a heterogeneous response to treatment within a subpopulation of tumor cells that are intrinsically drug-resistant, such as cancer stem cells. We have previously described an epigenetically determined reversibly drug-tolerant subpopulation of cancer cells that share some properties with cancer stem cells. Here, we define a requirement for the previously established cancer stem cell marker ALDH (aldehyde dehydrogenase) in the maintenance of this drug-tolerant subpopulation. We find that ALDH protects the drug-tolerant subpopulation from the potentially toxic effects of elevated levels of reactive oxygen species (ROS) in these cells, and pharmacologic disruption of ALDH activity leads to accumulation of ROS to toxic levels, consequent DNA damage, and apoptosis specifically within the drug-tolerant subpopulation. Combining ALDH inhibition with other kinase-directed treatments delayed treatment relapse in vitro and in vivo, revealing a novel combination treatment strategy for cancers that might otherwise rapidly relapse following single-agent therapy.

Essential Role of Aldehyde Dehydrogenase 1A3 for the Maintenance of Non–Small Cell Lung Cancer Stem Cells Is Associated with the STAT3 Pathway

Abstract: Purpose: Lung cancer stem cells (CSC) with elevated aldehyde dehydrogenase (ALDH) activity are self-renewing, clonogenic, and tumorigenic. The purpose of our study is to elucidate the mechanisms by which lung CSCs are regulated. Experimental Design: A genome-wide gene expression analysis was performed to identify genes differentially expressed in the ALDH + versus ALDH − cells. RT-PCR, Western blot analysis, and Aldefluor assay were used to validate identified genes. To explore the function in CSCs, we manipulated their expression followed by colony and tumor formation assays. Results: We identified a subset of genes that were differentially expressed in common in ALDH + cells, among which ALDH1A3 was the most upregulated gene in ALDH + versus ALDH − cells. shRNA-mediated knockdown of ALDH1A3 in non–small cell lung cancer (NSCLC) resulted in a dramatic reduction in ALDH activity, clonogenicity, and tumorigenicity, indicating that ALDH1A3 is required for tumorigenic properties. In contrast, overexpression of ALDH1A3 by itself it was not sufficient to increase tumorigenicity. The ALDH + cells also expressed more activated STAT3 than ALDH − cells. Inhibition of STAT3 or its activator EZH2 genetically or pharmacologically diminished the level of ALDH + cells and clonogenicity. Unexpectedly, ALDH1A3 was highly expressed in female, never smokers, well-differentiated tumors, or adenocarcinoma. ALDH1A3 low expression was associated with poor overall survival. Conclusions: Our data show that ALDH1A3 is the predominant ALDH isozyme responsible for ALDH activity and tumorigenicity in most NSCLCs, and that inhibiting either ALDH1A3 or the STAT3 pathway are potential therapeutic strategies to eliminate the ALDH + subpopulation in NSCLCs. Clin Cancer Res; 20(15); 4154–66. ©2014 AACR .

Aldehyde dehydrogenase variation enhances effect of pesticides associated with Parkinson disease

Abstract: Objective: The objective of this study was to determine whether environmental and genetic alterations of neuronal aldehyde dehydrogenase (ALDH) enzymes were associated with increased Parkinson disease (PD) risk in an epidemiologic study. Methods: A novel ex vivo assay was developed to identify pesticides that can inhibit neuronal ALDH activity. These were investigated for PD associations in a population-based case-control study, the Parkinson9s Environment & Genes (PEG) Study. Common variants in the mitochondrial ALDH2 gene were genotyped to assess effect measure modification (statistical interaction) of the pesticide effects by genetic variation. Results: All of the metal-coordinating dithiocarbamates tested (e.g., maneb, ziram), 2 imidazoles (benomyl, triflumizole), 2 dicarboxymides (captan, folpet), and 1 organochlorine (dieldrin) inhibited ALDH activity, potentially via metabolic byproducts (e.g., carbon disulfide, thiophosgene). Fifteen screened pesticides did not inhibit ALDH. Exposures to ALDH-inhibiting pesticides were associated with 2- to 6-fold increases in PD risk; genetic variation in ALDH2 exacerbated PD risk in subjects exposed to ALDH-inhibiting pesticides. Conclusion: ALDH inhibition appears to be an important mechanism through which environmental toxicants contribute to PD pathogenesis, especially in genetically vulnerable individuals, suggesting several potential interventions to reduce PD occurrence or slow or reverse its progression.

Characterization of the molecular mechanisms underlying increased ischemic damage in the aldehyde dehydrogenase 2 genetic polymorphism using a human induced pluripotent stem cell model system

Abstract: Nearly 8% of the human population carries an inactivating point mutation in the gene that encodes the cardioprotective enzyme aldehyde dehydrogenase 2 (ALDH2). This genetic polymorphism (ALDH2*2) is linked to more severe outcomes from ischemic heart damage and an increased risk of coronary artery disease (CAD), but the underlying molecular bases are unknown. We investigated the ALDH2*2 mechanisms in a human model system of induced pluripotent stem cell–derived cardiomyocytes (iPSC-CMs) generated from individuals carrying the most common heterozygous form of the ALDH2*2 genotype. We showed that the ALDH2*2 mutation gave rise to elevated amounts of reactive oxygen species and toxic aldehydes, thereby inducing cell cycle arrest and activation of apoptotic signaling pathways, especially during ischemic injury. We established that ALDH2 controls cell survival decisions by modulating oxidative stress levels and that this regulatory circuitry was dysfunctional in the loss-of-function ALDH2*2 genotype, causing up-regulation of apoptosis in cardiomyocytes after ischemic insult. These results reveal a new function for the metabolic enzyme ALDH2 in modulation of cell survival decisions. Insight into the molecular mechanisms that mediate ALDH2*2-related increased ischemic damage is important for the development of specific diagnostic methods and improved risk management of CAD and may lead to patient-specific cardiac therapies.

Aldehyde dehydrogenase-2 regulates nociception in rodent models of acute inflammatory pain

Abstract: Exogenous aldehydes can cause pain in animal models, suggesting that aldehyde dehydrogenase-2 (ALDH2), which metabolizes many aldehydes, may regulate nociception. To test this hypothesis, we generated a knock-in mouse with an inactivating point mutation in ALDH2 (ALDH2*2), which is also present in human ALDH2 of ~540 million East Asians. The ALDH2*1/*2 heterozygotic mice exhibited a larger response to painful stimuli than their wild-type littermates, and this heightened nociception was inhibited by an ALDH2-selective activator (Alda-1). No effect on inflammation per se was observed. Using a rat model, we then showed that nociception tightly correlated with ALDH activity (R(2) = 0.90) and that reduced nociception was associated with less early growth response protein 1 (EGR1) in the spinal cord and less reactive aldehyde accumulation at the insult site (including acetaldehyde and 4-hydroxynonenal). Further, acetaldehyde- and formalin-induced nociceptive behavior was greater in the ALDH2*1/*2 mice than in the wild-type mice. Finally, Alda-1 treatment was even beneficial when given after the inflammatory agent was administered. Our data in rodent models suggest that the mitochondrial enzyme ALDH2 regulates nociception and could serve as a molecular target for pain control, with ALDH2 activators, such as Alda-1, as potential non-narcotic, cardiac-safe analgesics. Furthermore, our results suggest a possible genetic basis for East Asians' apparent lower pain tolerance.

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

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

Identification of Biomarker Genes To Predict Biodegradation of 1,4-Dioxane

Abstract: Bacterial multicomponent monooxygenase gene targets in Pseudonocardia dioxanivorans CB1190 were evaluated for their use as biomarkers to identify the potential for 1,4-dioxane biodegradation in pure cultures and environmental samples. Our studies using laboratory pure cultures and industrial activated sludge samples suggest that the presence of genes associated with dioxane monooxygenase, propane monooxygenase, alcohol dehydrogenase, and aldehyde dehydrogenase are promising indicators of 1,4-dioxane biotransformation; however, gene abundance was insufficient to predict actual biodegradation. A time course gene expression analysis of dioxane and propane monooxygenases in Pseudonocardia dioxanivorans CB1190 and mixed communities in wastewater samples revealed important associations with the rates of 1,4-dioxane removal. In addition, transcripts of alcohol dehydrogenase and aldehyde dehydrogenase genes were upregulated during biodegradation, although only the aldehyde dehydrogenase was significantly correlated with 1,4-dioxane concentrations. Expression of the propane monooxygenase demonstrated a time-dependent relationship with 1,4-dioxane biodegradation in P. dioxanivorans CB1190, with increased expression occurring after over 50% of the 1,4-dioxane had been removed. While the fraction of P. dioxanivorans CB1190-like bacteria among the total bacterial population significantly increased with decrease in 1,4-dioxane concentrations in wastewater treatment samples undergoing active biodegradation, the abundance and expression of monooxygenase-based biomarkers were better predictors of 1,4-dioxane degradation than taxonomic 16S rRNA genes. This study illustrates that specific bacterial monooxygenase and dehydrogenase gene targets together can serve as effective biomarkers for 1,4-dioxane biodegradation in the environment.

Selective ALDH3A1 inhibition by benzimidazole analogues increase mafosfamide sensitivity in cancer cells.

Abstract: Aldehyde dehydrogenase enzymes irreversibly oxidize aldehydes generated from metabolism of amino acids, fatty acids, food, smoke, additives, and xenobiotic drugs. Cyclophosphamide is one such xenob...

A gatekeeper helix determines the substrate specificity of Sjögren–Larsson Syndrome enzyme fatty aldehyde dehydrogenase

Abstract: Mutations in the gene coding for membrane-bound fatty aldehyde dehydrogenase (FALDH) lead to toxic accumulation of lipid species and development of the Sjogren-Larsson Syndrome (SLS), a rare disorder characterized by skin defects and mental retardation. Here, we present the crystallographic structure of human FALDH, the first model of a membrane-associated aldehyde dehydrogenase. The dimeric FALDH displays a previously unrecognized element in its C-terminal region, a 'gatekeeper' helix, which extends over the adjacent subunit, controlling the access to the substrate cavity and helping orientate both substrate cavities towards the membrane surface for efficient substrate transit between membranes and catalytic site. Activity assays demonstrate that the gatekeeper helix is important for directing the substrate specificity of FALDH towards long-chain fatty aldehydes. The gatekeeper feature is conserved across membrane-associated aldehyde dehydrogenases. Finally, we provide insight into the previously elusive molecular basis of SLS-causing mutations.

Development of selective inhibitors for human aldehyde dehydrogenase 3A1 (ALDH3A1) for the enhancement of cyclophosphamide cytotoxicity.

Abstract: Aldehyde dehydrogenase 3A1 (ALDH3A1) plays an important role in many cellular oxidative processes, including cancer chemoresistance, by metabolizing activated forms of oxazaphosphorine drugs such as cyclophosphamide (CP) and its analogues, such as mafosfamide (MF), ifosfamide (IFM), and 4-hydroperoxycyclophosphamide (4-HPCP). Compounds that can selectively target ALDH3A1 could permit delineation of its roles in these processes and could restore chemosensitivity in cancer cells that express this isoenzyme. Here we report the detailed kinetic and structural characterization of an ALDH3A1-selective inhibitor, CB29, previously identified in a high-throughput screen. Kinetic and crystallographic studies demonstrate that CB29 binds within the aldehyde substrate-binding site of ALDH3A1. Cellular proliferation of ALDH3A1-expressing lung adenocarcinoma (A549) and glioblastoma (SF767) cell lines, as well as ALDH3A1 non-expressing lung fibroblast (CCD-13Lu) cells, is unaffected by treatment with CB29 and its analogues alone. However, sensitivity toward the anti-proliferative effects of mafosfamide is enhanced by treatment with CB29 and its analogue in the tumor cells. In contrast, the sensitivity of CCD-13Lu cells toward mafosfamide was unaffected by the addition of these same compounds. CB29 is chemically distinct from the previously reported small-molecule inhibitors of ALDH isoenzymes and does not inhibit ALDH1A1, ALDH1A2, ALDH1A3, ALDH1B1, or ALDH2 isoenzymes at concentrations up to 250 μM. Thus, CB29 is a novel small molecule inhibitor of ALDH3A1, which might be useful as a chemical tool to delineate the role of ALDH3A1 in numerous metabolic pathways, including sensitizing ALDH3A1-positive cancer cells to oxazaphosphorines.

Impairment of aldehyde dehydrogenase-2 by 4-hydroxy-2-nonenal adduct formation and cardiomyocyte hypertrophy in mice fed a high-fat diet and injected with low-dose streptozotocin

Abstract: Reactive aldehydes such as 4-hydroxy-2-nonenal (4HNE) are generated in the myocardium in cardiac disease. 4HNE and other toxic aldehydes form adducts with proteins, leading to cell damage and organ dysfunction. Aldehyde dehydrogenases (ALDHs) metabolize toxic aldehydes such as 4HNE into nontoxic metabolites. Both ALDH levels and activity are reduced in cardiac disease. We examined whether reduced ALDH2 activity contributes to cardiomyocyte hypertrophy in mice fed a high-fat diet and injected with low-dose streptozotocin (STZ). These mice exhibited most of the characteristics of metabolic syndrome/type-2 diabetes mellitus (DM): increased blood glucose levels depicting hyperglycemia (415.2 ± 18.7 mg/dL vs. 265.2 ± 7.6 mg/dL; P < 0.05), glucose intolerance with normal plasma insulin levels, suggesting insulin resistance and obesity as evident from increased weight (44 ± 3.1 vs. 34.50 ± 1.32 g; P < 0.05) and body fat. Myocardial ALDH2 activity was 60% lower in these mice (0.1 ± 0.012 vs. 0.04 ± 0.015 µmol/min/mg protein; P < 0.05). Myocardial 4HNE levels were also elevated in the hyperglycemic hearts. Co-immunoprecipitation study showed that 4HNE formed adducts on myocardial ALDH2 protein in the mice exhibiting metabolic syndrome/type-2 DM, and they had obvious cardiac hypertrophy compared with controls as evident from increased heart weight (HW), HW to tibial length ratio, left ventricular (LV) mass and cardiomyocyte hypertrophy. Cardiomyocyte hypertrophy was correlated inversely with ALDH2 activity (R (2 )= 0.7; P < 0.05). Finally, cardiac dysfunction was observed in mice with metabolic syndrome/type-2 DM. Therefore, we conclude that reduced ALDH2 activity may contribute to cardiac hypertrophy and dysfunction in mice presenting with some of the characteristics of metabolic syndrome/type-2 DM when on a high-fat diet and low-dose STZ injection.

Mitochondrial Aldehyde Dehydrogenase Activation by Alda‐1 Inhibits Atherosclerosis and Attenuates Hepatic Steatosis in Apolipoprotein E‐Knockout Mice

Abstract: Background Mitochondrial dysfunction has been shown to play an important role in the development of atherosclerosis and nonalcoholic fatty liver disease (NAFLD). Mitochondrial aldehyde dehydrogenase (ALDH2), an enzyme responsible for the detoxification of reactive aldehydes, is considered to exert protective function in mitochondria. We investigated the influence of Alda‐1, an activator of ALDH2, on atherogenesis and on the liver steatosis in apolipoprotein E knockout (apoE−/−) mice. Methods and Results Alda‐1 caused decrease of atherosclerotic lesions approximately 25% as estimated by “en face” and “cross‐section” methods without influence on plasma lipid profile, atherosclerosis‐related markers of inflammation, and macrophage and smooth muscle content in the plaques. Plaque nitrotyrosine was not changed upon Alda‐1 treatment, and there were no changes in aortic mRNA levels of factors involved in antioxidative defense, regulation of apoptosis, mitogenesis, and autophagy. Hematoxylin/eosin staining showed decrease of steatotic changes in liver of Alda‐1‐treated apoE−/− mice. Alda‐1 attenuated formation of 4‐hydroxy‐2‐nonenal (4‐HNE) protein adducts and decreased triglyceride content in liver tissue. Two‐dimensional electrophoresis coupled with mass spectrometry identified 20 differentially expressed mitochondrial proteins upon Alda‐1 treatment in liver of apoE−/− mice, mostly proteins related to metabolism and oxidative stress. The most up‐regulated were the proteins that participated in beta oxidation of fatty acids. Conclusions Collectively, Alda‐1 inhibited atherosclerosis and attenuated NAFLD in apoE−/− mice. The pattern of changes suggests a beneficial effect of Alda‐1 in NAFLD; however, the exact liver functional consequences of the revealed alterations as well as the mechanism(s) of antiatherosclerotic Alda‐1 action require further investigation.

Acute Ethanol Causes Hepatic Mitochondrial Depolarization in Mice: Role of Ethanol Metabolism

Abstract: Background/Aims An increase of ethanol metabolism and hepatic mitochondrial respiration occurs in vivo after a single binge of alcohol. Here, our aim was to determine how ethanol intake affects hepatic mitochondrial polarization status in vivo in relation to ethanol metabolism and steatosis. Methods Hepatic mitochondrial polarization, permeability transition (MPT), and reduce pyridine nucleotides, and steatosis in mice were monitored by intravital confocal/multiphoton microscopy of the fluorescence of rhodamine 123 (Rh123), calcein, NAD(P)H, and BODIPY493/503, respectively, after gavage with ethanol (1–6 g/kg). Results Mitochondria depolarized in an all-or-nothing fashion in individual hepatocytes as early as 1 h after alcohol. Depolarization was dose- and time-dependent, peaked after 6 to 12 h and maximally affected 94% of hepatocytes. This mitochondrial depolarization was not due to onset of the MPT. After 24 h, mitochondria of most hepatocytes recovered normal polarization and were indistinguishable from untreated after 7 days. Cell death monitored by propidium iodide staining, histology and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) was low throughout. After alcohol, mitochondrial NAD(P)H autofluorescence increased and decreased, respectively, in hepatocytes with polarized and depolarized mitochondria. Ethanol also caused steatosis mainly in hepatocytes with depolarized mitochondria. Depolarization was linked to ethanol metabolism, since deficiency of alcohol dehydrogenase and cytochrome-P450 2E1 (CYP2E1), the major ethanol-metabolizing enzymes, decreased mitochondrial depolarization by ~70% and ~20%, respectively. Activation of aldehyde dehydrogenase decreased depolarization, whereas inhibition of aldehyde dehydrogenase enhanced depolarization. Activation of aldehyde dehydrogenase also markedly decreased steatosis. Conclusions Acute ethanol causes reversible hepatic mitochondrial depolarization in vivo that may contribute to steatosis and increased mitochondrial respiration. Onset of this mitochondrial depolarization is linked, at least in part, to metabolism of ethanol to acetaldehyde.

Characteristics and expression patterns of the aldehyde dehydrogenase (ALDH) gene superfamily of foxtail millet (Setaria italica L.).

Abstract: Recent genomic sequencing of the foxtail millet, an abiotic, stress-tolerant crop, has provided a great opportunity for novel gene discovery and functional analysis of this popularly-grown grass. However, few stress-mediated gene families have been studied. Aldehyde dehydrogenases (ALDHs) comprise a gene superfamily encoding NAD (P) +-dependent enzymes that play the role of “aldehyde scavengers”, which indirectly detoxify cellular ROS and reduce the effect of lipid peroxidation meditated cellular toxicity under various environmental stresses. In the current paper, we identified a total of 20 ALDH genes in the foxtail millet genome using a homology search and a phylogenetic analysis and grouped them into ten distinct families based on their amino acid sequence identity. Furthermore, evolutionary analysis of foxtail millet reveals that both tandem and segmental duplication contributed significantly to the expansion of its ALDH genes. The exon-intron structures of members of the same family in foxtail millet or the orthologous genes in rice display highly diverse distributions of their exonic and intronic regions. Also, synteny analysis shows that the majority of foxtail millet and rice ALDH gene homologs exist in the syntenic blocks between the two, implying that these ALDH genes arose before the divergence of cereals. Semi-quantitative and real-time quantitative PCR data reveals that a few SiALDH genes are expressed in an organ-specific manner and that the expression of a number of foxtail millet ALDH genes, such as, SiALDH7B1, SiALDH12A1 and SiALDH18B2 are up-regulated by osmotic stress, cold, H2O2, and phytohormone abscisic acid (ABA). Furthermore, the transformation of SiALDH2B2, SiALDH10A2, SiALDH5F1, SiALDH22A1, and SiALDH3E2 into Escherichia coli (E.coli) was able to improve their salt tolerance. Taken together, our results show that genome-wide identification characteristics and expression analyses provide unique opportunities for assessing the functional roles of foxtail millet ALDH genes in stress responses.

Benomyl, aldehyde dehydrogenase, DOPAL, and the catecholaldehyde hypothesis for the pathogenesis of Parkinson's disease.

Abstract: The dopamine metabolite 3,4-dihydroxyphenylacetaldehyde (DOPAL) is detoxified mainly by aldehyde dehydrogenase (ALDH). We find that the fungicide benomyl potently and rapidly inhibits ALDH and builds up DOPAL in vivo in mouse striatum and in vitro in PC12 cells and human cultured fibroblasts and glial cells. The in vivo results resemble those noted previously with knockouts of the genes encoding ALDH1A1 and 2, a mouse model of aging-related Parkinson’s disease (PD). Exposure to pesticides that inhibit ALDH may therefore increase PD risk via DOPAL buildup. This study lends support to the “catecholaldehyde hypothesis” that the autotoxic dopamine metabolite DOPAL plays a pathogenic role in PD.

Regulation of ethanol-related behavior and ethanol metabolism by the Corazonin neurons and Corazonin receptor in Drosophila melanogaster.

Abstract: Impaired ethanol metabolism can lead to various alcohol-related health problems. Key enzymes in ethanol metabolism are alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH); however, neuroendocrine pathways that regulate the activities of these enzymes are largely unexplored. Here we identified a neuroendocrine system involving Corazonin (Crz) neuropeptide and its receptor (CrzR) as important physiological regulators of ethanol metabolism in Drosophila. Crz-cell deficient (Crz-CD) flies displayed significantly delayed recovery from ethanol-induced sedation that we refer to as hangover-like phenotype. Newly generated mutant lacking Crz Receptor (CrzR01) and CrzR-knockdown flies showed even more severe hangover-like phenotype, which is causally associated with fast accumulation of acetaldehyde in the CrzR01 mutant following ethanol exposure. Higher levels of acetaldehyde are likely due to 30% reduced ALDH activity in the mutants. Moreover, increased ADH activity was found in the CrzR01 mutant, but not in the Crz-CD flies. Quantitative RT-PCR revealed transcriptional upregulation of Adh gene in the CrzR01. Transgenic inhibition of cyclic AMP-dependent protein kinase (PKA) also results in significantly increased ADH activity and Adh mRNA levels, indicating PKA-dependent transcriptional regulation of Adh by CrzR. Furthermore, inhibition of PKA or cAMP response element binding protein (CREB) in CrzR cells leads to comparable hangover-like phenotype to the CrzR01 mutant. These findings suggest that CrzR-associated signaling pathway is critical for ethanol detoxification via Crz-dependent regulation of ALDH activity and Crz-independent transcriptional regulation of ADH. Our study provides new insights into the neuroendocrine-associated ethanol-related behavior and metabolism.

Structure-based mutational studies of substrate inhibition of betaine aldehyde dehydrogenase BetB from Staphylococcus aureus.

Abstract: Inhibition of enzyme activity by high concentrations of substrate and/or cofactor is a general phenomenon demonstrated in many enzymes, including aldehyde dehydrogenases. Here we show that the uncharacterized protein BetB (SA2613) from Staphylococcus aureus is a highly specific betaine aldehyde dehydrogenase, which exhibits substrate inhibition at concentrations of betaine aldehyde as low as 0.15 mM. In contrast, the aldehyde dehydrogenase YdcW from Escherichia coli, which is also active against betaine aldehyde, shows no inhibition by this substrate. Using the crystal structures of BetB and YdcW, we performed a structure-based mutational analysis of BetB and introduced the YdcW residues into the BetB active site. From a total of 32 mutations, those in five residues located in the substrate binding pocket (Val288, Ser290, His448, Tyr450, and Trp456) greatly reduced the substrate inhibition of BetB, whereas the double mutant protein H448F/Y450L demonstrated a complete loss of substrate inhibition. Substrate inhibition was also reduced by mutations of the semiconserved Gly234 (to Ser, Thr, or Ala) located in the BetB NAD+ binding site, suggesting some cooperativity between the cofactor and substrate binding sites. Substrate docking analysis of the BetB and YdcW active sites revealed that the wild-type BetB can bind betaine aldehyde in both productive and nonproductive conformations, whereas only the productive binding mode can be modeled in the active sites of YdcW and the BetB mutant proteins with reduced substrate inhibition. Thus, our results suggest that the molecular mechanism of substrate inhibition of BetB is associated with the nonproductive binding of betaine aldehyde.

Selective ALDH3A1 Inhibition by Benzimidazole Analogues Increase Mafosfamide Sensitivity in Cancer Cells

Abstract: Aldehyde dehydrogenase enzymes irreversibly oxidize aldehydes generated from metabolism of amino acids, fatty acids, food, smoke, additives, and xenobiotic drugs. Cyclophosphamide is one such xenob...

Impairment of aldehyde dehydrogenase 2 increases accumulation of acetaldehyde-derived DNA damage in the esophagus after ethanol ingestion.

Abstract: Ethanol and its metabolite, acetaldehyde, are the definite carcinogens for esophageal squamous cell carcinoma (ESCC), and reduced catalytic activity of aldehyde dehydrogenase 2 (ALDH2), which detoxifies acetaldehyde, increases the risk for ESCC. However, it remains unknown whether the ALDH2 genotype influences the level of acetaldehyde-derived DNA damage in the esophagus after ethanol ingestion. In the present study, we administered ethanol orally or intraperitoneally to Aldh2-knockout and control mice, and we quantified the level of acetaldehyde-derived DNA damage, especially N(2) -ethylidene-2'-deoxyguanosine (N(2) -ethylidene-dG), in the esophagus. In the model of oral ethanol administration, the esophageal N(2) -ethylidene-dG level was significantly higher in Aldh2-knockout mice compared with control mice. Similarly, in the model of intraperitoneal ethanol administration, in which the esophagus is not exposed directly to the alcohol solution, the esophageal N(2) -ethylidene-dG level was also elevated in Aldh2-knockout mice. This result indicates that circulating ethanol-derived acetaldehyde causes esophageal DNA damage, and that the extent of damage is influenced by knockout of Aldh2. Taken together, our findings strongly suggest the importance of acetaldehyde-derived DNA damage which is induced in the esophagus of individuals with ALDH2 gene impairment. This provides a physiological basis for understanding alcohol-related esophageal carcinogenesis.

Development of selective inhibitors for aldehyde dehydrogenases based on substituted indole-2,3-diones.

Abstract: Aldehyde dehydrogenases (ALDH) participate in multiple metabolic pathways and have been indicated to play a role in several cancerous disease states. Our laboratory is interested in developing novel and selective ALDH inhibitors. We looked to further work recently published by developing a class of isoenzyme-selective inhibitors using similar indole-2,3-diones that exhibit differential inhibition of ALDH1A1, ALDH2, and ALDH3A1. Kinetic and X-ray crystallography data suggest that these inhibitors are competitive against aldehyde binding, forming direct interactions with active-site cysteine residues. The selectivity is precise in that these compounds appear to interact directly with the catalytic nucleophile, Cys243, in ALDH3A1 but not in ALDH2. In ALDH2, the 3-keto group is surrounded by the adjacent Cys301/303. Surprisingly, the orientation of the interaction changes depending on the nature of the substitutions on the basic indole ring structure and correlates well with the observed structure–activity re...

Development of Selective Inhibitors for Aldehyde Dehydrogenases Based on Substituted Indole-2,3-diones

Abstract: Aldehyde dehydrogenases (ALDH) participate in multiple metabolic pathways and have been indicated to play a role in several cancerous disease states. Our laboratory is interested in developing novel and selective ALDH inhibitors. We looked to further work recently published by developing a class of isoenzyme-selective inhibitors using similar indole-2,3-diones that exhibit differential inhibition of ALDH1A1, ALDH2, and ALDH3A1. Kinetic and X-ray crystallography data suggest that these inhibitors are competitive against aldehyde binding, forming direct interactions with active-site cysteine residues. The selectivity is precise in that these compounds appear to interact directly with the catalytic nucleophile, Cys243, in ALDH3A1 but not in ALDH2. In ALDH2, the 3-keto group is surrounded by the adjacent Cys301/303. Surprisingly, the orientation of the interaction changes depending on the nature of the substitutions on the basic indole ring structure and correlates well with the observed structure–activity re...

Oxidizing to death: disulfiram for cancer cell killing.

Abstract: Disulfiram (tetraethylthiuram disulfide) is a highly versatile reagent and has been used for a variety of applications ranging from a vulcanization accelerator to an ointment against endo- and ectoparasites.1 It was noticed more than 70 years ago that rubber-processing workers and patients with scabies exposed to thiuram disulfides experienced strong adverse reactions after drinking alcoholic beverages. This led to identification of the alcohol-deterring quality of disulfiram.1 Since then, disulfiram, also known by its trade name Antabuse, has been approved and used clinically for over 60 years as an alcohol deterrent in the treatment of alcoholism. Clinically, in the absence of alcohol consumption, disulfiram is quite well-tolerated. Orally administered disulfiram is rapidly converted by the gastrointestinal tract or within the blood stream into 2 molecules of its diethyldithiocarbamate salt (Fig. 1). Disulfiram-derived diethyldithiocarbamate can further be metabolized into diethylthiocarbamic acid methyl ester sulfoxide (Fig. 1). This metabolite of disulfiram has been identified as a highly active inhibitor of the catalytic sulfhydryl group of human aldehyde dehydrogenase (ALDH), which metabolizes ethanol-derived noxious acetaldehyde into nontoxic acetate. By the same cysteine-interacting mechanism, disulfiram also inhibits a variety of cancer-promoting proteins, including protein kinase C, P-glycoprotein (P-gp), and DNA methyltransferases (DNMT) (Fig. 1). Figure 1. Metabolism and action of disulfiram. Disulfiram-derived metabolites can inactivate essential sulfhydryl groups either directly by protein carbamoylation or indirectly by complexing with divalent copper or zinc ions to form a redox-active ... Disulfiram metabolites have also been shown to complex with copper or zinc ions, resulting in partial depletion of the intracellular heavy metal ion pool, thereby inhibiting zinc- and copper-dependent enzymes such as superoxide dismutase (protective against oxidative stress), matrix metalloproteinases (promoting cancer cell invasion and metastasis), or dopamine β-monooxygenase (involved in cocaine addiction, for which disulfiram is also under investigation). A strong anti-cancer effect of disulfiram was observed in combination with divalent heavy metal ions, often found enriched in cancer tissues, or orally supplied either as copper or zinc gluconate.2 The redox cycling between Cu(I) and Cu(II) within this complex has been proposed to be responsible for both glutathione oxidation and hydrogen peroxide generation, leading to a combined and perpetual oxidative stress mechanism (Fig. 1). The combination of disulfiram with copper was also shown to have a strong inhibitory effect on the proteasomal protein degradation system.3,4 Since a functional proteasome system is essential for a coordinated expression of cell cycle-regulatory and apoptosis-controlling proteins, its inhibition is particularly fatal for cancer cells, in which proteasome inhibitors induce massive disturbances in protein homeostasis and accumulation of poly-ubiquitinated proteins and cytotoxic protein aggregates.3,4 Another mechanism by which disulfiram may specifically target cancer cells is by its preferential activity against various forms of aldehyde dehydrogenases. The ALDH genes, although primarily known as biotransformation genes, also belong to a small group of genes coding for proteins that, although called “stem cell markers,” are mediators of the range of attributes of what we call stem cells. Cancer stem cells are preferentially resistant to cytotoxic chemotherapies as currently constituted. Selective targeting of ALDH-positive cancer cell sub-populations by disulfiram was shown, as predicted, to preferentially inhibit cancer stem cells.4,5 Disulfiram, and in particular its metabolites, have repeatedly been demonstrated to cause a pro-oxidative environment in cancer cells.2 A recent study performed in our laboratory revealed a pronounced and irreversible induction of apoptosis in ovarian cancer cells by disulfiram in a copper-supported manner, associated with the occurrence of oxidative stress, formation of protein aggregates, and induction of heat shock-response genes.6 Cells protect against cytotoxic oxidative stress by the expression of endogenous antioxidants, which function either as radical scavengers or provide reducing equivalents to re-hydrogenate oxidized disulfide bonds (Fig. 1).2 Two systems provide the main contribution to cellular redox homeostasis: the glutathione and the thioredoxin system. These are both often upregulated in cancer cells to cope with increased intracellular production of oxidants resulting from characteristic metabolic patterns in cancer.7 We reasoned therefore that the combined action of disulfiram with other drugs that interfere with cellular antioxidative defense systems might enhance the anti-tumoral effects of disulfiram.2 Auranofin, an anti-rheumatic drug, is an effective inhibitor of thioredoxin reductase, and it has been proposed that the co-application of auranofin might enhance the anti-cancer efficacy of disulfiram.2 In fact, a proof-of-principle study on ovarian cancer cells revealed that auranofin indeed augmented the cytotoxic effects of disulfiram.6 By preventing thioredoxin-mediated reduction of oxidized proteins (Fig. 1), protein inactivation, misfolding, and aggregation is enhanced. Both auranofin and disulfiram are well-tolerated drugs and indicate that a combined application of repurposed drugs may have promising potential for anti-cancer therapy. In vitro studies, xenograft models, and preliminary data from clinical trials and clinical observations indicate that disulfiram might have promising prospects in cancer therapy that should be further explored by ongoing and future clinical studies.2,8 Therefore, we have several clues which indicate that the repurposed “old drug” disulfiram, particularly when combined with its new partner auranofin, may find a further application as a prospective new medication in cancer.

Mitochondrial aldehyde dehydrogenase, a potential drug target for protection of heart and brain from ischemia/reperfusion injury.

Abstract: Mitochondrial aldehyde dehydrogenase (ALDH2) is an isoenzyme of aldehyde dehydrogenases (ALDH), a group of enzymes that are responsible for clearance of aldehydes in the body. In animal myocardial or cerebral ischemia/ reperfusion (I/R) models, accumulation of toxic aldehydes, such as 4-hydroxy-2-nonenal and malondialdehyde, is thought to be an important mechanism for myocardial and cerebral I/R injury. Among the isoenzymes of ALDH, ALDH2 is believed to play a major role in clearance of toxic aldehydes. Thus, ALDH2 might be a potential drug target for protection of the heart or brain from I/R injury. Indeed, some of the newly identified ALDH2 activators (such as Alda-1) have demonstrated beneficial effects on heart and brain I/R injury. In addition, ALDH activity is present at high levels in some stem or progenitor cells, known as ALDH bright (ALDH(br)) cells, which possess potential value in treating patients with myocardial ischemia. The main purpose of this review is 1) to summarize recent findings regarding the role of ALDH2 in protection of heart or brain from I/R injury, 2) to list the available ALDH2 activators with their potency, selectivity and clinical potentials, and 3) to provide a rationale for ALDH(br) cells in clinical therapeutic value.

Aldehyde dehydrogenase activity enriches for proximal airway basal stem cells and promotes their proliferation.

Abstract: Both basal and submucosal gland (SMG) duct stem cells of the airway epithelium are capable of sphere formation in the in vitro sphere assay, although the efficiency at which this occurs is very low. We sought to improve this efficiency of sphere formation by identifying subpopulations of airway basal stem cells (ABSC) and SMG duct cells based on their aldehyde dehydrogenase (ALDH) activity. ALDHhi ABSCs and SMG duct cells were highly enriched for the population of cells that could make spheres, while the co-culture of ALDHhi differentiated cells with the ALDHhi ABSCs increased their sphere-forming efficiency. Specific ALDH agonists and antagonists were used to show that airway specific ALDH isozymes are important for ABSC proliferation. Pathway analysis of gene expression profiling of ALDHhi and ALDHlo ABSCs revealed a significant upregulation of the arachidonic acid (AA) metabolism pathway in ALDHhi ABSCs. We confirmed the importance of this pathway in the metabolism of proliferating ALDHhi ABSCs using bioenergetics studies as well as agonists and antagonists of the AA pathway. These studies could lead to the development of novel strategies for altering ABSC proliferation in the airway epithelium.