Aldehyde dehydrogenase 7A1 (ALDH7A1) attenuates reactive aldehyde and oxidative stress induced cytotoxicity

Mammalian aldehyde dehydrogenase 7A1 (ALDH7A1) is homologous to plant ALDH7B1 which protects against various forms of stress such as increased salinity, dehydration and treatment with oxidants or pesticides. Deleterious mutations in human ALDH7A1 are responsible for pyridoxine-dependent and folinic acid-responsive seizures. In previous studies, we have shown that human ALDH7A1 protects against hyperosmotic stress presumably through the generation of betaine, an important cellular osmolyte, formed from betaine aldehyde. Hyperosmotic stress is coupled to an increase in oxidative stress and lipid peroxidation (LPO). In this study, cell viability assays revealed that stable expression of mitochondrial ALDH7A1 in Chinese hamster ovary (CHO) cells provides significant protection against treatment with the LPO-derived aldehydes hexanal and 4-hydroxy-2-nonenal (4HNE) implicating a protective function for the enzyme during oxidative stress. A significant increase in cell survival was also observed in CHO cells expressing either mitochondrial or cytosolic ALDH7A1 treated with increasing concentrations of hydrogen peroxide (H(2)O(2)) or 4HNE, providing further evidence for anti-oxidant activity. In vitro enzyme activity assays indicate that human ALDH7A1 is sensitive to oxidation and that efficiency can be at least partially restored by incubating recombinant protein with the thiol reducing agent β-mercaptoethanol (BME). We also show that after reactivation with BME, recombinant ALDH7A1 is capable of metabolizing the reactive aldehyde 4HNE. In conclusion, ALDH7A1 mechanistically appears to provide cells protection through multiple pathways including the removal of toxic LPO-derived aldehydes in addition to osmolyte generation.     

Selective protection by stably transfected human ALDH3A1 (but not human ALDH1A1) against toxicity of aliphatic aldehydes in V79 cells

Toxic medium chain length alkanals, alkenals, and 4-hydroxyalkenals that are generated during lipid peroxidation are potential substrates for aldehyde dehydrogenase (ALDH) isoforms. We have developed transgenic cell lines to examine the potential for either human ALDH1A1 or ALDH3A1 to protect against damage mediated by these toxic aldehydes. Using crude cytosols from stably transfected cell lines, these aldehydes were confirmed to be excellent substrates for ALDH3A1, but were poorly oxidized by ALDH1A1. Expression of ALDH3A1 by stable transfection in V79 cells conferred a high level of protection against growth inhibition by the medium-chain length aldehyde substrates with highest substrate activity, including hexanal, trans-2-hexenal, trans-2-octenal, trans-2-nonenal, and 4-hydroxy-2-nonenal (HNE). This was reflected in a parallel ability of ALDH3A1 to prevent depletion of glutathione by these aldehydes. Expression of hALDH3 completely blocked the potent induction of apoptosis by HNE in both V79 cells and in a RAW 264.7 murine macrophage cell line, consistent with the observed total prevention of HNE-protein adduct formation. Structure–activity studies indicated that the rank order of potency for the contributions of HNE functional groups to toxicity was aldehyde ≥C2=C3 double bond>>C4-hydroxyl group. Oxidation of the aldehyde moiety of HNE to a carboxyl by ALDH3A1 expressed in stably transfected cell lines drastically reduced its potency for growth inhibition and apoptosis induction. In contrast, ALDH1A1 expression provided only moderate protection against trans-2-nonenal (t2NE), and none against the other six–nine carbon aldehydes. Neither ALDH1A1 nor ALDH3A1 conferred any protection against acrolein, acetaldehyde, or chloroacetaldehyde. A small degree of protection against malondialdehyde was afforded by ALDH1A1, but not ALDH3A1. Paradoxically, cells expressing ALDH3A1 were 1.5-fold more sensitive to benzaldehyde toxicity than control V79 cells. These studies demonstrate that expression of class 3 ALDH, but not class 1 ALDH, can be an important determinant of cellular resistance to toxicity mediated by aldehydes of intermediate chain length that are produced during lipid peroxidation.     

Selective protection by stably transfected human ALDH3A1 (but not human ALDH1A1) against toxicity of aliphatic aldehydes in V79 cells

Toxic medium chain length alkanals, alkenals, and 4-hydroxyalkenals that are generated during lipid peroxidation are potential substrates for aldehyde dehydrogenase (ALDH) isoforms. We have developed transgenic cell lines to examine the potential for either human ALDH1A1 or ALDH3A1 to protect against damage mediated by these toxic aldehydes. Using crude cytosols from stably transfected cell lines, these aldehydes were confirmed to be excellent substrates for ALDH3A1, but were poorly oxidized by ALDH1A1. Expression of ALDH3A1 by stable transfection in V79 cells conferred a high level of protection against growth inhibition by the medium-chain length aldehyde substrates with highest substrate activity, including hexanal, trans-2-hexenal, trans-2-octenal, trans-2-nonenal, and 4-hydroxy-2-nonenal (HNE). This was reflected in a parallel ability of ALDH3A1 to prevent depletion of glutathione by these aldehydes. Expression of hALDH3 completely blocked the potent induction of apoptosis by HNE in both V79 cells and in a RAW 264.7 murine macrophage cell line, consistent with the observed total prevention of HNE-protein adduct formation. Structure-activity studies indicated that the rank order of potency for the contributions of HNE functional groups to toxicity was aldehyde >/=C2=C3 double bond>C4-hydroxyl group. Oxidation of the aldehyde moiety of HNE to a carboxyl by ALDH3A1 expressed in stably transfected cell lines drastically reduced its potency for growth inhibition and apoptosis induction. In contrast, ALDH1A1 expression provided only moderate protection against trans-2-nonenal (t2NE), and none against the other six-nine carbon aldehydes. Neither ALDH1A1 nor ALDH3A1 conferred any protection against acrolein, acetaldehyde, or chloroacetaldehyde. A small degree of protection against malondialdehyde was afforded by ALDH1A1, but not ALDH3A1. Paradoxically, cells expressing ALDH3A1 were 1.5-fold more sensitive to benzaldehyde toxicity than control V79 cells. These studies demonstrate that expression of class 3 ALDH, but not class 1 ALDH, can be an important determinant of cellular resistance to toxicity mediated by aldehydes of intermediate chain length that are produced during lipid peroxidation.     

Expression and initial characterization of human ALDH3B1

Aldehyde dehydrogenases (ALDHs) are critical enzymes in the metabolism of endogenous and exogenous aldehydes. The human genome contains 19 putatively functional ALDH genes; ALDH3B1 belongs to the ALDH3 family. While recent studies have linked the ALDH3B1 locus to schizophrenia, nothing was known, until now, about the properties and significance of the ALDH3B1 protein. The aim of this study was to characterize the ALDH3B1 protein. Human ALDH3B1 was baculovirus-expressed and found to be catalytically active towards medium- and long-chain aliphatic aldehydes and the aromatic aldehyde benzaldehyde. Western blot analyses indicate that ALDH3B1 is highly expressed in kidney and liver and moderately expressed in various brain regions. ALDH3B1-transfected HEK293 cells were significantly protected against cytotoxicity induced by the lipid peroxidation product octanal when compared to vector-transfected cells. This study shows for the first time the functionality, expression and protective role of ALDH3B1 and indicates a potential physiological role of ALDH3B1 against oxidative stress.     

Molecular cloning and baculovirus expression of the rabbit corneal aldehyde dehydrogenase (ALDH1A1) cDNA

Most mammalian species express high concentrations of ALDH3A1 in corneal epithelium with the exception of the rabbit, which expresses high amounts of ALDH1A1 rather than ALDH3A1. Several hypotheses that involve catalytic and/or structural functions have been postulated regarding the role of these corneal ALDHs. The aim of the present study was to characterize the biochemical properties of the rabbit ALDH1A1. We have cloned and sequenced the rabbit ALDH1A1 cDNA, which is 2,073 bp in length (excluding the poly(A+) tail), and has 5' and 3' nontranslated regions of 46 and 536 bp, respectively. This ALDH1A1 cDNA encodes a protein of 496 amino acids (Mr = 54,340) that is: 86-91% identical to mammalian ALDH1A1 proteins, 83-85% identical to phenobarbital-inducible mouse and rat ALDH1A7 proteins, 84% identical to elephant shrew ALDH1A8 proteins (eta-crystallins), 69-73% identical to vertebrate ALDH1A2 and ALDH1A3 proteins, 65% identical to scallop ALDH1A9 protein (omega-crystallin), and 55-57% to cephalopod ALDH1C1 and ALDH1C2 (omega-crystallins). Recombinant rabbit ALDH1A1 protein was expressed using the baculovirus system and purified to homogeneity with affinity chromatography. We found that rabbit ALDH1A1 is catalytically active and efficiently oxidizes hexanal (Km = 3.5 microM), 4-hydroxynonenal (Km = 2.1 microM) and malondialdehyde (Km = 14.0 microM), which are among the major products of lipid peroxidation. Similar kinetic constants were observed with the human recombinant ALDH1A1 protein, which was expressed and purified using similar experimental conditions. These data suggest that ALDH1A1 may contribute to corneal cellular defense against oxidative damage by metabolizing toxic aldehydes produced during UV-induced lipid peroxidation.     

Omeprazole as a potent activator of human cytosolic aldehyde dehydrogenase ALDH1A1

BackgroundAccumulation 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.MethodsDocking 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.ResultsOmeprazole 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.ConclusionOmeprazole 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.     

Mutation of OsALDH7 causes a yellow-colored endosperm associated with accumulation of oryzamutaic acid A in rice

Aldehyde dehydrogenase proteins consist of a superfamily and the family 7 (ALDH7) is a typical group with highly conserved proteins across species. It catalyzes oxidation of α-aminoadipic semialdehyde (AASA) in lysine degradation, participates in protection against hyperosmotic stress, and detoxifies aldehydes in human; however, its function in plants has been much less documented. Here we reported a mutant with yellow-colored endosperm in rice, and showed that the yellow endosperm was caused by mutation of OsALDH7. OsALDH7 is expressed in all tissues detected, with the highest level in mature seeds. We found that oryzamutaic acid A accumulated during late seed development and after a year-long storage in the colored endosperm, whereas it was undetectable in the wild type endosperm. Moreover, lysine degradation was enhanced in yeast over-expressing OsALDH7 and as a result, content of lysine, glutamate and saccharopine was changed, suggesting a role of OsALDH7 in lysine catabolism.     

Mechanisms involved in the protection of UV-induced protein inactivation by the corneal crystallin ALDH3A1

Various lines of evidence have shown that ALDH3A1 (aldehyde dehydrogenase 3A1) plays a critical and multifaceted role in protecting the cornea from UV-induced oxidative stress. ALDH3A1 is a corneal crystallin, which is defined as a protein recruited into the cornea for structural purposes without losing its primary function (i.e. metabolism). Although the primary role of ALDH3A1 in the metabolism of toxic aldehydes has been clearly demonstrated, including the detoxification of aldehydes produced during UV-induced lipid peroxidation, the structural role of ALDH3A1 in the cornea remains elusive. We therefore examined the potential contribution of ALDH3A1 in maintaining the optical integrity of the cornea by suppressing the aggregation and/or inactivation of other proteins through chaperone-like activity and other protective mechanisms. We found that ALDH3A1 underwent a structural transition near physiological temperatures to form a partially unfolded conformation that is suggestive of chaperone activity. Although this structural transition alone did not correlate with any protection, ALDH3A1 substantially reduced the inactivation of glucose-6-phosphate dehydrogenase by 4-hydroxy-2-nonenal and malondialdehyde when co-incubated with NADP(+), reinforcing the importance of the metabolic function of this corneal enzyme in the detoxification of toxic aldehydes. A large excess of ALDH3A1 also protected glucose-6-phosphate dehydrogenase from inactivation because of direct exposure to UVB light, which suggests that ALDH3A1 may shield other proteins from damaging UV rays. Collectively, these data demonstrate that ALDH3A1 can reduce protein inactivation and/or aggregation not only by detoxification of reactive aldehydes but also by directly absorbing UV energy. This study provides for the first time mechanistic evidence supporting the structural role of the corneal crystallin ALDH3A1 as a UV-absorbing constituent of the cornea.     

Identification of aldehyde dehydrogenase 1A1 modulators using virtual screening

The highly similar aldehyde dehydrogenase isozymes (ALDH1A1 and ALDH2) have been implicated in the metabolism of toxic biogenic aldehydes such as 3,4-dihydroxyphenylacetaldehyde (DOPAL) and 4-hydroxy-2E-nonenal. We report the down-regulation of ALDH1A1 mRNA found in substantia nigra tissue of human Parkinson’s disease (PD) samples using the Genome-Wide SpliceArray^? (GWSA^?) technology. Since DOPAL can rapidly inactivate ALDH1A1 in vitro, we set up a DOPAL-induced ALDH1A1 inactivation assay and used this assay to demonstrate that Alda-1, a compound originally identified as an activator of ALDH2, can also activate ALDH1A1. We carried out a virtual screening of 19,943 compounds and the top 21 hits from this screen were tested in the DOPAL inactivation assay with ALDH1A1 which led to identification of an activator as well as two inhibitors among these hits. These findings represent an attractive starting point for developing higher potency activator compounds that may have utility in restoring the metabolism of DOPAL in PD.     

Antioxidant function of corneal ALDH3A1 in cultured stromal fibroblasts

Aldehyde dehydrogenase 3A1 (ALDH3A1) is highly expressed in epithelial cells and stromal keratocytes of mammalian cornea and is believed to play an important role in cellular defense. To explore a potential protective role against oxidative damage, a rabbit corneal fibroblastic cell line (TRK43) was stably transfected with the human ALDH3A1 and subjected to oxidative stress induced by H(2)O(2), mitomycin C (MMC), or etoposide (VP-16). ALDH3A1-transfected cells were more resistant to H(2)O(2,) MMC, and VP-16 compared to the vector-transfected cells. All treatments induced apoptosis only in vector-transfected cells, which was associated with increased levels of 4-hydroxy-2-nonenal (4-HNE)-adducted proteins. Treatment with H(2)O(2) resulted in a rise in reduced glutathione (GSH) levels in all groups but was more pronounced in the ALDH3A1-expressing cells. Treatment with the DNA-damaging agents led to GSH depletion in control groups, although the depletion was significantly less in ALDH3A1-expressing cells. Increased carbonylation of ALDH3A1 but not significant decline in enzymatic activity was observed after all treatments. In conclusion, our results suggest that ALDH3A1 may act to protect corneal cells against cellular oxidative damage by metabolizing toxic lipid peroxidation products (e.g., 4-HNE), maintaining cellular GSH levels and redox balance, and operating as an antioxidant.     

Aldehyde Dehydrogenase 3B1 (ALDH3B1): Immunohistochemical Tissue Distribution and Cellular-specific Localization in Normal and Cancerous Human Tissues

Aldehyde dehydrogenase (ALDH) enzymes are critical in the detoxification of endogenous and exogenous aldehydes. Our previous findings indicate that the ALDH3B1 enzyme is expressed in several mouse tissues and is catalytically active toward aldehydes derived from lipid peroxidation, suggesting a potential role against oxidative stress. The aim of this study was to elucidate by immunohistochemistry the tissue, cellular, and subcellular distribution of ALDH3B1 in normal human tissues and in tumors of human lung, colon, breast, and ovary. Our results indicate that ALDH3B1 is expressed in a tissue-specific manner and in a limited number of cell types, including hepatocytes, proximal convoluted tubule cells, cerebellar astrocytes, bronchiole ciliated cells, testis efferent ductule ciliated cells, and histiocytes. ALDH3B1 expression was upregulated in a high percentage of human tumors (lung > breast = ovarian > colon). Increased ALDH3B1 expression in tumor cells may confer a growth advantage or be the result of an induction mechanism mediated by increased oxidative stress. Subcellular localization of ALDH3B1 was predominantly cytosolic in tissues, with the exception of normal human lung and testis, in which localization appeared membrane-bound or membrane-associated. The specificity of ALDH3B1 distribution may prove to be directly related to the functional role of this enzyme in human tissues. (J Histochem Cytochem 58:765–783, 2010)     

Inhibition of cytosolic class 3 aldehyde dehydrogenase by antisense oligonucleotides in rat hepatoma cells

Aldehyde dehydrogenases (ALDHs) are a superfamily of several isoenzymes widely expressed in bacteria, yeast, plant and animals. Three major classes of ALDHs have been traditionally identified, classes 1, 2 and 3. Both exogenous and endogenous aldehydes, including aldehydes derived from lipid peroxidation, are oxidized by the ALDH superfamily. Several changes in ALDH isoenzyme expression take place in hepatoma cells, in particular cytosolic class 3 ALDH (ALDH3), not expressed in normal hepatocytes, appears and increases with the degree of deviation. It has been demonstrated that cytosolic ALDH3 is important in determining the resistance of tumor cells to antitumor drugs, such as cyclophosphamide. Moreover, hepatoma-associated ALDH3 seems to be important in metabolizing aldehydes derived from lipid peroxidation, and in particular the cytostatic aldehyde 4-hydroxynonenal (4-HNE). We demonstrated previously that restoring endogenous lipid peroxidation in hepatoma cells by enriching them with arachidonic acid causes a decrease of mRNA, protein and enzyme activity of ALDH3 and that this decrease reduces cell growth and/or causes cell death, depending on basal class 3 ALDH activity. To confirm the correlation between inhibition of class 3 ALDH and reduction of cell proliferation, we exposed hepatoma cells to antisense oligonucleotides (ODNs) against ALDH3. In JM2 hepatoma cell line, with high ALDH3 activity, the exposure to antisense ODNs significantly decreases mRNA and enzyme activity (90%). At the same time, cell growth was reduced by about 70%. The results confirm that in hepatoma cells ALDH3 expression is closely related with cell growth, and that its inhibition is important in reducing the proliferation of hepatoma cells overexpressing ALDH3.     

Inhibition of cytosolic class 3 aldehyde dehydrogenase by antisense oligonucleotides in rat hepatoma cells

Aldehyde dehydrogenases (ALDHs) are a superfamily of several isoenzymes widely expressed in bacteria, yeast, plant and animals. Three major classes of ALDHs have been traditionally identified, classes 1, 2 and 3. Both exogenous and endogenous aldehydes, including aldehydes derived from lipid peroxidation, are oxidized by the ALDH superfamily. Several changes in ALDH isoenzyme expression take place in hepatoma cells, in particular cytosolic class 3 ALDH (ALDH3), not expressed in normal hepatocytes, appears and increases with the degree of deviation. It has been demonstrated that cytosolic ALDH3 is important in determining the resistance of tumor cells to antitumor drugs, such as cyclophosphamide. Moreover, hepatoma-associated ALDH3 seems to be important in metabolizing aldehydes derived from lipid peroxidation, and in particular the cytostatic aldehyde 4-hydroxynonenal (4-HNE). We demonstrated previously that restoring endogenous lipid peroxidation in hepatoma cells by enriching them with arachidonic acid causes a decrease of mRNA, protein and enzyme activity of ALDH3 and that this decrease reduces cell growth and/or causes cell death, depending on basal class 3 ALDH activity. To confirm the correlation between inhibition of class 3 ALDH and reduction of cell proliferation, we exposed hepatoma cells to antisense oligonucleotides (ODNs) against ALDH3. In JM2 hepatoma cell line, with high ALDH3 activity, the exposure to antisense ODNs significantly decreases mRNA and enzyme activity (90%). At the same time, cell growth was reduced by about 70%. The results confirm that in hepatoma cells ALDH3 expression is closely related with cell growth, and that its inhibition is important in reducing the proliferation of hepatoma cells overexpressing ALDH3.     

Autophagy in ALDH2-elicited cardioprotection against ischemic heart disease: slayer or savior?

The mitochondrial isoform of aldehyde dehydrogenase (ALDH2) plays a key role in the metabolism of acetaldehyde and other toxic aldehydes. A recent seminal finding has indicated a potential role of ALDH2 activation in the cardioprotection against ischemic injury. Data from our group unveiled a myocardial protective effect of ALDH2 against ischemia/reperfusion (I/R) injury possibly through detoxification of toxic aldehydes: and a differential regulation of autophagy mediated by AMPK-mTOR and Akt-mTOR signaling cascades during ischemia and reperfusion, respectively. These findings suggest not only the therapeutic potential of ALDH2 against I/R injury but also a pivotal role of the AMPK-Akt-mTOR signaling in the paradoxical autophagic regulation of cardiomyocyte survival.     

Detoxification of promutagenic aldehydes derived from methylpyrenes by human aldehyde dehydrogenases ALDH2 and ALDH3A1

Methylated polycyclic aromatic hydrocarbons can be metabolically activated via benzylic hydroxylation and sulpho conjugation to reactive esters, which can induce mutations and tumours. Yet, further oxidation of the alcohol may compete with this toxification. We previously demonstrated that several human alcohol dehydrogenases (ADH1C, 2, 3 and 4) oxidise various benzylic alcohols (derived from alkylated pyrenes) to their aldehydes with high catalytic efficiency. However, all these ADHs also catalysed the reverse reaction, the reduction of the aldehydes to the alcohols, with comparable or higher efficiency. Thus, final detoxification requires elimination of the aldehydes by further biotransformation. We have expressed two human aldehyde dehydrogenases (ALDH2 and 3A1) in bacteria. All pyrene aldehydes studied (1-, 2- and 4-formylpyrene, 1-formyl-6-methylpyrene and 1-formyl-8-methylpyrene) were high-affinity substrates for ALDH2 (K_m = 0.027–0.9 μM) as well as ALDH3A1 (K_m = 0.78–11 μM). Catalytic efficiencies (k_cat/K_m) were higher for ALDH2 than ALDH3A1 by a moderate to a very large margin depending on the substrate. Most important, they were also substantially higher than the catalytic efficiencies of the various ADHs for the reduction the aldehydes to the alcohols. These kinetic properties ensure that ALDHs, and particularly ALDH2, can complete the ADH-mediated detoxification.     

Aldehyde dehydrogenase 1B1 (ALDH1B1) is a potential biomarker for human colon cancer

Aldehyde dehydrogenases (ALDHs) belong to a superfamily of NAD(P)⁺-dependent enzymes, which catalyze the oxidation of endogenous and exogenous aldehydes to their corresponding acids. Increased expression and/or activity of ALDHs, particularly ALDH1A1, have been reported to occur in human cancers. It is proposed that the metabolic function of ALDH1A1 confers the “stemness” properties to normal and cancer stem cells. Nevertheless, the identity of ALDH isozymes that contribute to the enhanced ALDH activity in specific types of human cancers remains to be elucidated. ALDH1B1 is a mitochondrial ALDH that metabolizes a wide range of aldehyde substrates including acetaldehyde and products of lipid peroxidation (LPO). In this study, we immunohistochemically examined the expression profile of ALDH1A1 and ALDH1B1 in human adenocarcinomas of colon (N = 40), lung (N = 30), breast (N = 33) and ovary (N = 33) using an NIH tissue array. The immunohistochemical expression of ALDH1A1 or ALDH1B1 in tumor tissues was scored by their intensity (scale = 1–3) and extensiveness (% of total cancer cells). Herein we report a 5.6-fold higher expression score for ALDH1B1 in cancerous tissues than that for ALDH1A1. Remarkably, 39 out of 40 colonic cancer specimens were positive for ALDH1B1 with a staining intensity of 2.8 ± 0.5. Our study demonstrates that ALDH1B1 is more profoundly expressed in the adenocarcinomas examined in this study relative to ALDH1A1 and that ALDH1B1 is dramatically upregulated in human colonic adenocarcinoma, making it a potential biomarker for human colon cancer.     

Aldehyde dehydrogenase 3A1 protects airway epithelial cells from cigarette smoke-induced DNA damage and cytotoxicity

Aldehyde dehydrogenase 3A1 (ALDH3A1), an ALDH superfamily member, catalyzes the oxidation of reactive aldehydes, highly toxic components of cigarette smoke (CS). Even so, the role of ALDH3A1 in CS-induced cytotoxicity and DNA damage has not been examined. Among all of the ALDH superfamily members, ALDH3A1 mRNA levels showed the greatest induction in response to CS extract (CSE) exposure of primary human bronchial epithelial cells (HBECs). ALDH3A1 protein accumulation was accompanied by increased ALDH enzymatic activity in CSE-exposed immortalized HBECs. The effects of overexpression or suppression of ALDH3A1 on CSE-induced cytotoxicity and DNA damage (γH2AX) were evaluated in cultured immortalized HBECs. Enforced expression of ALDH3A1 attenuated cytotoxicity and downregulated γH2AX. SiRNA-mediated suppression of ALDH3A1 blocked ALDH enzymatic activity and augmented cytotoxicity in CSE-exposed cells. Our results suggest that the availability of ALDH3A1 is important for cell survival against CSE in HBECs.     

Autophagy in ALDH2-elicited cardioprotection against ischemic heart disease: Slayer or savior?

The mitochondrial isoform of aldehyde dehydrogenase (ALDH2) plays a key role in the metabolism of acetaldehyde and other toxic aldehydes. A recent seminal finding has indicated a potential role of ALDH2 activation in the cardioprotection against ischemic injury. Data from our group unveiled a myocardial protective effect of ALDH2 against ischemia/reperfusion (I/R) injury possibly through detoxification of toxic aldehydes

and a differential regulation of autophagy mediated by AMPK-mTOR and Akt-mTOR signaling cascades during ischemia and reperfusion, respectively. These findings suggest not only the therapeutic potential of ALDH2 against I/R injury but also a pivotal role of the AMPK-Akt-mTOR signaling in the paradoxical autophagic regulation of cardiomyocyte survival.     

Human aldehyde dehydrogenase-catalyzed oxidation of ethylene glycol ether aldehydes

Ethylene glycol ethers (EGEs) are primary alcohols commonly used as solvents in numerous household and industrial products. Exposure to EGEs has been correlated with delayed encephalopathy, metabolic acidosis, sub-fertility and spermatotoxicity in humans. In addition, they also cause teratogenesis, carcinogenesis, hemolysis, etc., in various animal models. Metabolism EGEs parallels ethanol metabolism, i.e., EGEs are first converted to 2-alkoxy acetaldehydes (EGE aldehydes) by alcohol dehydrogenases, and then to alkoxyacetic acids by aldehyde dehydrogenases (ALDHs). The acid metabolite of EGEs is considered responsible for toxicities associated with EGEs. The role of human ALDHs in EGE metabolism is not clear; accordingly, we have investigated the ability of five different human ALDHs (ALDH1A1, ALDH2, ALDH3A1, ALDH5A1 and ALDH9A1) to catalyze the oxidation of various EGE aldehydes. The EGE aldehydes used in this study were synthesized via Swern oxidation. All of the human ALDHs were purified from human cDNA clones over-expressing these enzymes in E. coli. The ALDHs tested, so far, differentially catalyze the oxidation of EGE aldehydes to their corresponding acids (K(m) values range from approximately 10 microM to approximately 20.0mM). As judged by V(max)/K(m) ratios, short-chain alkyl-group containing EGE aldehydes are oxidized to their acids more efficiently by ALDH2, whereas aryl- and long-chain alkyl-group containing EGE aldehydes are oxidized to their acid more efficiently by ALDH3A1. Given the product of ALDH-catalyzed reaction is toxic, this process should be considered as a bio-activation (toxification) process.