Effects of aldehyde dehydrogenase-2 genetic polymorphisms on metabolism of structurally different aldehydes in human liver

Endogenous aldehyde-induced DNA-protein crosslinks are resolved by transcription-coupled repair

DNA-protein crosslinks (DPCs) induced by aldehydes interfere with replication and transcription. Hereditary deficiencies in DPC repair and aldehyde clearance processes cause progeria, including Ruijs-Aalfs syndrome (RJALS) and AMeD syndrome (AMeDS) in humans. Although the elimination of DPC during replication has been well established, how cells overcome DPC lesions in transcription remains elusive. Here we show that endogenous aldehyde-induced DPC roadblocks are efficiently resolved by transcription-coupled repair (TCR). We develop a high-throughput sequencing technique to measure the genome-wide distribution of DPCs (DPC-seq). Using proteomics and DPC-seq, we demonstrate that the conventional TCR complex as well as VCP/p97 and the proteasome are required for the removal of formaldehyde-induced DPCs. TFIIS-dependent cleavage of RNAPII transcripts protects against transcription obstacles. Finally, a mouse model lacking both aldehyde clearance and TCR confirms endogenous DPC accumulation in actively transcribed regions. Collectively, our data provide evidence that transcription-coupled DPC repair (TC-DPCR) as well as aldehyde clearance are crucial for protecting against metabolic genotoxin, thus explaining the molecular pathogenesis of AMeDS and other disorders associated with defects in TCR, such as Cockayne syndrome.

Asian flush gene variant increases mild cognitive impairment risk: a cross-sectional study of the Yoshinogari Brain MRI Checkup Cohort

BACKGROUND

The East Asian-specific genetic diversity, the rs671 variant of aldehyde dehydrogenase 2, causes the "Asian flush" phenomenon following alcohol consumption, resulting in an alcohol avoidance phenotype. The variant is suggested as a risk factor for Alzheimer's disease; however, its association with mild cognitive impairment (MCI), an effective target for secondary prevention of dementia, remains unclear.

METHOD

This cross-sectional study examined 430 individuals aged 60-80 years (251 women) without overt cognitive impairment in Yoshinogari, Japan. The effect of the rs671 variant on MCI, defined by scores <26 or <25 on the Japanese version of the Montreal Cognitive Assessment, was evaluated using multivariate logistic regression.

RESULTS

The models included APOEε4, sex, age, education, history of habitual drinking, Brinkman index, hypertension, diabetes, and subclinical magnetic resonance imaging findings and consistently estimated the risk of the rs671 variant. Subsequently, stratified analyses by history of habitual drinking were performed based on an interactive effect between rs671 and alcohol consumption, and the rs671 variant significantly influenced MCI in participants who did not drink habitually, with odds ratios ranging from 1.9 to 2.1 before and after adjusting for covariates, suggesting an association independent of hippocampal atrophy and small vessel dysfunction. Conversely, no such association with the rs671 variant was observed in participants with a history of habitual alcohol use. Instead, hippocampal atrophy and silent infarcts were associated with MCI.

CONCLUSIONS

This is the first study to demonstrate an association between the rs671 variant and MCI morbidity. The findings highlight the need for race-specific preventive strategies and suggest potential unrecognized mechanisms in dementia development.

Asian flush is a potential protective factor against COVID-19: a web-based retrospective survey in Japan

BACKGROUND

Coronavirus disease 2019 (COVID-19), first reported in December 2019, spread worldwide in a short period, resulting in numerous cases and associated deaths; however, the toll was relatively low in East Asia. A genetic polymorphism unique to East Asians, Aldehyde dehydrogenase 2 rs671, has been reported to confer protection against infections.

METHOD

We retrospectively investigated the association between the surrogate marker of the rs671 variant, the skin flushing phenomenon after alcohol consumption, and the timing of COVID-19 incidence using a web-based survey tool to test any protective effects of rs671 against COVID-19.

RESULTS

A total of 807 valid responses were received from 362 non-flushers and 445 flushers. During the 42 months, from 12/1/2019 to 5/31/2023, 40.6% of non-flushers and 35.7% of flushers experienced COVID-19. Flushers tended to have a later onset (Spearman's partial rank correlation test, p = 0.057, adjusted for sex and age). Similarly, 2.5% of non-flushers and 0.5% of flushers were hospitalized because of COVID-19. Survival analysis estimated lower risks of COVID-19 and associated hospitalization among flushers (p = 0.03 and <0.01, respectively; generalized Wilcoxon test). With the Cox proportional hazards model covering 21 months till 8/31/2021, when approximately half of the Japanese population had received two doses of COVID-19 vaccine, the hazard ratio (95% confidence interval) of COVID-19 incidence was estimated to be 0.21 (0.10-0.46) for flusher versus non-flusher, with adjustment for sex, age, steroid use, and area of residence.

CONCLUSIONS

Our study suggests an association between the flushing phenomenon after drinking and a decreased risk of COVID-19 morbidity and hospitalization, suggesting that the rs671 variant is a protective factor. This study provides valuable information for infection control and helps understand the unique constitutional diversity of East Asians.

Aldehyde Dehydrogenase Genes as Prospective Actionable Targets in Acute Myeloid Leukemia

It has been previously shown that the aldehyde dehydrogenase (ALDH) family member ALDH1A1 has a significant association with acute myeloid leukemia (AML) patient risk group classification and that AML cells lacking ALDH1A1 expression can be readily killed via chemotherapy. In the past, however, a redundancy between the activities of subgroup members of the ALDH family has hampered the search for conclusive evidence to address the role of specific ALDH genes. Here, we describe the bioinformatics evaluation of all nineteen member genes of the ALDH family as prospective actionable targets for the development of methods aimed to improve AML treatment. We implicate ALDH1A1 in the development of recurrent AML, and we show that from the nineteen members of the ALDH family, ALDH1A1 and ALDH2 have the strongest association with AML patient risk group classification. Furthermore, we discover that the sum of the expression values for RNA from the genes, ALDH1A1 and ALDH2, has a stronger association with AML patient risk group classification and survival than either one gene alone does. In conclusion, we identify ALDH1A1 and ALDH2 as prospective actionable targets for the treatment of AML in high-risk patients. Substances that inhibit both enzymatic activities constitute potentially effective pharmaceutics.

Effects of the genetic variants of alcohol-metabolizing enzymes on lipid levels in Asian populations: a systematic review and meta-analysis

CONTEXT

Emerging evidence indicates that variants of alcohol-metabolizing enzymes may influence lipid metabolism.

OBJECTIVE

This study aimed to investigate whether the rs671 and rs1229984 variants affect lipid levels in East Asian individuals.

DATA SOURCES

PubMed, Foreign Medical Journal Service, Embase, Cochrane Library, Scopus, MEDLINE, Web of Science, Web of Knowledge, Wanfang, and Chinese Biomedical Literature databases were searched until December 31, 2021.

DATA EXTRACTION

Meta-analyses of studies that examined the effects of alcohol-metabolizing enzyme variants on lipid levels, as well as the interaction with alcohol intake, were selected. Data extraction was conducted independently by two investigators and confirmed by the third.

DATA ANALYSIS

In total, 86 studies (179 640 individuals) were analyzed. The A allele of rs671 (a functional variant in the ALDH2 gene) was linked to higher levels of low-density lipoprotein cholesterol (LDL-C) and lower levels of triglycerides and high-density lipoprotein cholesterol. In contrast, the A allele of the rs1229984 (a functional variant in the ADH2 gene) was associated only with lower levels of LDL-C. The effects of rs671 and rs1229984 on lipid levels were much stronger in Japanese than in Chinese individuals and in males than in females. Regression analysis indicated that the effects of rs671 on lipid levels were independent of alcohol intake in an integrated East Asian population (ie, Japanese, Chinese, and Korean individuals). Intriguingly, alcohol intake had a statistical influence on lipid levels when the sample analyzed was restricted to Japanese individuals or to males.

CONCLUSIONS

The rs671 and rs1229984 variants of alcohol-metabolizing enzymes have significant effects on lipid levels and may serve as genetic markers for lipid dyslipidemia in East Asian populations. Circulating lipid levels in Japanese individuals and in males were modulated by the interaction between rs671 and alcohol intake.

The Potential Role of Mitochondrial Acetaldehyde Dehydrogenase 2 in Urological Cancers From the Perspective of Ferroptosis and Cellular Senescence

Overproduction of reactive oxygen species (ROS) and superlative lipid peroxidation promote tumorigenesis, and mitochondrial aldehyde dehydrogenase 2 (ALDH2) is associated with the detoxification of ROS-mediated lipid peroxidation-generated reactive aldehydes such as 4-hydroxy-2-nonenal (4-HNE), malondialdehyde, and acrolein due to tobacco smoking. ALDH2 has been demonstrated to be highly associated with the prognosis and chemoradiotherapy sensitivity of many types of cancer, including leukemia, lung cancer, head and neck cancer, esophageal cancer, hepatocellular cancer, pancreatic cancer, and ovarian cancer. In this study, we explored the possible relationship between ALDH2 and urological cancers from the aspects of ferroptosis, epigenetic alterations, proteostasis, mitochondrial dysfunction, and cellular senescence.

Benzaldehyde Attenuates the Fifth Stage Larval Excretory–Secretory Product of Angiostrongylus cantonensis-Induced Injury in Mouse Astrocytes via Regulation of Endoplasmic Reticulum Stress and Oxidative Stress

Excretory–secretory products (ESPs) are the main research targets for investigating the hosts and helminths interaction. Parasitic worms can migrate to parasitic sites and avoid the host immune response by secreting this product. Angiostrongylus cantonensis is an important food-borne zoonotic parasite that causes severe neuropathological damage and symptoms, including eosinophilic meningitis or meningoencephalitis in humans. Benzaldehydes are organic compounds composed of a benzene ring and formyl substituents. This compound has anti-inflammatory and antioxidation properties. Previous studies showed that 3-hydroxybenzaldehyde (3-HBA) and 4-hydroxybenzaldehyde (4-HBA) can reduce apoptosis in A. cantonensis ESP-treated astrocytes. These results on the protective effect underlying benzaldehyde have primarily focused on cell survival. The study was designed to investigate the molecular mechanisms of endoplasmic reticulum stress (ER stress) and oxidative stress in astrocytes in A. cantonensis ESP-treated astrocytes and to evaluate the therapeutic consequent of 3-HBA and 4-HBA. First, we initially established the RNA-seq dataset in each group, including normal, ESPs, ESPs + 3-HBA, and ESPs + 4-HBA. We also found that benzaldehyde (3-HBA and 4-HBA) can stimulate astrocytes to express ER stress-related molecules after ESP treatment. The level of oxidative stress could also be decreased in astrocytes by elevating antioxidant activity and reducing ROS generation. These results suggested that benzaldehyde may be a potential therapeutic compound for human angiostrongyliasis to support brain cell survival by inducing the expression levels of ER stress- and oxidative stress-related pathways.

Formaldehyde toxicity in age-related neurological dementia

The primordial small gaseous molecules, such as: NO, CO, H₂S and formaldehyde (FA) are present in the brains. Whether FA as well as the other molecules participates in brain functions is unclear. Recently, its pathophysiological functions have been investigated. Notably, under physiological conditions, learning activity induces a transient generation of hippocampal FA, which promotes memory formation by enhancing N-methyl-D-aspartate (NMDA)-currents. However, ageing leads to FA accumulation in brain for the dysregulation of FA metabolism; and excessive FA directly impairs memory by inhibiting NMDA-receptor. Especially, in Alzheimer's disease (AD), amyloid-beta (Aβ) accelerates FA accumulation by inactivating alcohol dehydrogenase-5; in turn, FA promotes Aβ oligomerization, fibrillation and tau hyperphosphorylation. Hence, there is a vicious circle encompassing Aβ assembly and FA generation. Even worse, FA induces Aβ deposition in the extracellular space (ECS), which blocks the medicines (dissolved in the interstitial fluid) flowing into the damaged neurons in the deep cortex. However, phototherapy destroys Aβ deposits in the ECS and restores ISF flow. Coenzyme Q10, which scavenges FA, was shown to ameliorate Aβ-induced AD pathological phenotypes, thus suggesting a causative relation between FA toxicity and AD. These findings suggest that the combination of these two methods is a promising strategy for treating AD.

Trigenic ADH5/ALDH2/ADGRV1 mutations in myelodysplasia with Usher syndrome

Trio-next generation sequencing is useful to identify undiagnosed inherited diseases. We have attended a patient with trigenic ADH5/ALDH2/ADGRV1 pathogenic variants, which caused two distinct diseases, myelodysplastic syndrome and Usher syndrome. Whole genome sequencing of peripheral blood from the patient and his parents were applied to identify disease-causing genes. Sanger sequencing was performed to validate the identified ADH5/ALDH2/ADGRV1 variants. Our results identified disease-associated variants in ADGRV1 (disease inheritance autosomal recessive) and in ADH5 (disease inheritance also autosomal recessive) and a variant in ALDH2 (disease inheritance autosomal dominant). Although the variants identified in ADH5 and ALDH2 have been reported, their co-existence in association with disease-causing variation in a third gene has not. They broaden the spectrum of ADGRV1 in Usher syndrome. Findings on next generation sequencing guided rapid and accurate diagnosis, resulting in patient-tailored therapeutic intervention.

•

Trigenic ADH5 / ALDH2 / ADGRV1 ​variants in myelodysplastic syndrome with Usher syndrome were identified.

•

Two novel pathogenic frameshift variants in ​ADGRV1 ​in compound heterozygous state with Usher syndrome type II were described.

•

Findings on next generation sequencing guided rapid and accurate diagnosis, resulting in patient-tailored therapy.

The toxic side of one-carbon metabolism and epigenetics

One-carbon metabolism is a central metabolic hub that provides one-carbon units for essential biosynthetic reactions and for writing epigenetics marks. The leading role in this hub is performed by the one-carbon carrier tetrahydrofolate (THF), which accepts formaldehyde usually from serine generating one-carbon THF intermediates in a set of reactions known as the folate or one-carbon cycle. THF derivatives can feed one-carbon units into purine and thymidine synthesis, and into the methionine cycle that produces the universal methyl-donor S-adenosylmethionine (AdoMet). AdoMet delivers methyl groups for epigenetic methylations and it is metabolized to homocysteine (Hcy), which can enter the transsulfuration pathway for the production of cysteine and lastly glutathione (GSH), the main cellular antioxidant. This vital role of THF comes to an expense. THF and other folate derivatives are susceptible to oxidative breakdown releasing formaldehyde, which can damage DNA -a consequence prevented by the Fanconi Anaemia DNA repair pathway. Epigenetic demethylations catalysed by lysine-specific demethylases (LSD) and Jumonji histone demethylases can also release formaldehyde, constituting a potential threat for genome integrity. In mammals, the toxicity of formaldehyde is limited by a metabolic route centred on the enzyme alcohol dehydrogenase 5 (ADH5/GSNOR), which oxidizes formaldehyde conjugated to GSH, lastly generating formate. Remarkably, this formate can be a significant source of one-carbon units, thus defining a formaldehyde cycle that likely restricts the toxicity of one-carbon metabolism and epigenetic demethylations. This work describes recent advances in one-carbon metabolism and epigenetics, focusing on the steps that involve formaldehyde flux and that might lead to cytotoxicity affecting human health.

Genetically encoded formaldehyde sensors inspired by a protein intra-helical crosslinking reaction

Formaldehyde (FA) has long been considered as a toxin and carcinogen due to its damaging effects to biological macromolecules, but its beneficial roles have been increasingly appreciated lately. Real-time monitoring of this reactive molecule in living systems is highly desired in order to decipher its physiological and/or pathological functions, but a genetically encoded FA sensor is currently lacking. We herein adopt a structure-based study of the underlying mechanism of the FA-responsive transcription factor HxlR from Bacillus subtilis, which shows that HxlR recognizes FA through an intra-helical cysteine-lysine crosslinking reaction at its N-terminal helix α1, leading to conformational change and transcriptional activation. By leveraging this FA-induced intra-helical crosslinking and gain-of-function reorganization, we develop the genetically encoded, reaction-based FA sensor-FAsor, allowing spatial-temporal visualization of FA in mammalian cells and mouse brain tissues.

Digenic mutations in ALDH2 and ADH5 impair formaldehyde clearance and cause a multisystem disorder, AMeD syndrome

Rs671 in the aldehyde dehydrogenase 2 gene (ALDH2) is the cause of Asian alcohol flushing response after drinking. ALDH2 detoxifies endogenous aldehydes, which are the major source of DNA damage repaired by the Fanconi anemia pathway. Here, we show that the rs671 defective allele in combination with mutations in the alcohol dehydrogenase 5 gene, which encodes formaldehyde dehydrogenase (ADH5FDH ), causes a previously unidentified disorder, AMeD (aplastic anemia, mental retardation, and dwarfism) syndrome. Cellular studies revealed that a decrease in the formaldehyde tolerance underlies a loss of differentiation and proliferation capacity of hematopoietic stem cells. Moreover, Adh5-/-Aldh2 E506K/E506K double-deficient mice recapitulated key clinical features of AMeDS, showing short life span, dwarfism, and hematopoietic failure. Collectively, our results suggest that the combined deficiency of formaldehyde clearance mechanisms leads to the complex clinical features due to overload of formaldehyde-induced DNA damage, thereby saturation of DNA repair processes.

3-Hydroxybenzaldehyde and 4-Hydroxybenzaldehyde enhance survival of mouse astrocytes treated with Angiostrongylus cantonensis young adults excretory/secretory products

Background

Methods

Results

Conclusions

Potential Doxorubicin-Mediated Dual-Targeting Chemotherapy in FANC/BRCA-Deficient Tumors via Modulation of Cellular Formaldehyde Concentration

Doxorubicin (DOX) is a widely used classical broad-spectrum anticancer drug. The major mechanism of DOX-mediated anticancer activity at clinically relevant concentrations is believed to be via DNA double-strand breaks due to topoisomerase IIα. However, other mechanisms by which DOX causes cytotoxicity have been proposed, including formaldehyde-dependent virtual interstrand cross-linking (ICL) formation. In this study, a method was established whereby cytotoxicity caused by virtual ICL derived from DOX is turned on and off using a cell culture system. Using this strategy, DOX-mediated cytotoxicity in Fanconi anemia group gene (FANC)/breast cancer susceptibility gene (BRCA)-deficient cells increased up to 70-fold compared to that in cells proficient in DNA repair pathways by increasing intracellular formaldehyde (FA) concentration. This approach also demonstrated that cytotoxicity introduced by DOX-mediated FA-dependent virtual ICL is completely independent of the toxicity induced by topoisomerase II inhibition at the cellular level. The potential of dual-targeting by DOX treatment was verified using an acid-specific FA donor. Overall, anticancer therapy targeting tumors deficient in the FANC/BRCA pathway may be possible by minimizing DOX-induced toxicity in normal cells.

Interaction of Ethanol and Oral ANS-6637, a Selective ALDH2 Inhibitor in Males: A Randomized, Double-Blind, Placebo-Controlled, Single-Ascending Dose Cohort Study

BACKGROUND

ANS-6637, an orally bioavailable selective and reversible aldehyde dehydrogenase-2 (ALDH2) inhibitor, is under development for drug and alcohol use disorders. During the elimination of alcohol, ALDH2 metabolizes acetaldehyde to acetate; inhibiting this enzyme can lead to aversive reactions due to the accumulation of acetaldehyde. Thus, understanding the safety and tolerability of ANS-6637 in combination with alcohol is essential.

TRIAL DESIGN AND METHODS

Forty eight healthy males participated in a randomized, double-blind, placebo-controlled, single-ascending dose cohort study of oral ANS-6637. Eligible participants were randomized to ANS-6637 (n = 36) or placebo (n = 12) in a 3:1 fashion in each of 6 dose cohorts (8 per cohort; ANS-6637 dose levels were 25, 50, 100, 200, 400, and 600 mg). Two hours after receiving study drug, participants drank up to 5 standard drinks, 1 every 30 minutes. Safety assessments, pharmacodynamic measures, and pharmacokinetic blood samples were obtained.

RESULTS

Flushing was the most common adverse event (AE) associated with ANS-6637 (24 of 36 participants) compared with placebo (3 of 12). Statistically significant, but modest, increases in heart rate (HR) occurred (+10.5 bpm after 2 drinks; +16.9 to + 20.5 bpm after 3^rd through 5^th drink). No participant met HR or systolic blood pressure criteria for stopping ethanol administration. There were no clinically significant QTc interval prolongations. Individuals receiving ANS-6637 reported lower ratings of liking, alcohol effects, and feeling drunk.

CONCLUSIONS

A single oral dose of ANS-6637 with up to 5 standards drinks over 2.5 hours was generally well tolerated in healthy males. The most common pharmacological response was flushing and an increase in HR, which are known effects of acetaldehyde accumulation and consistent with inhibition of ALDH2 with oral ANS-6637 in combination with alcohol. The results of this alcohol interaction study support further testing of ANS-6637 in individuals who consume alcohol heavily.

The failure of two major formaldehyde catabolism enzymes (ADH5 and ALDH2) leads to partial synthetic lethality in C57BL/6 mice

Background

Exogenous formaldehyde is classified by the IARC as a Category 1 known human carcinogen. Meanwhile, a significant amount of endogenous formaldehyde is produced in the human body; as such, formaldehyde-derived DNA and protein adducts have been detected in animals and humans in the absence of major exogenous formaldehyde exposure. However, the toxicological effects of endogenous formaldehyde on individuals with normal DNA damage repair functions are not well understood. In this study, we attempted to generate C57BL/6 mice deficient in both Adh5 and Aldh2, which encode two major enzymes that metabolize endogenous formaldehyde, in order to understand the effects of endogenous formaldehyde on mice with normal DNA repair function.

Results

Due to deficiencies in both ADH5 and ALDH2, few mice survived past post-natal day 21. In fact, the survival of pups within the first few days after birth was significantly decreased. Remarkably, two Aldh2 ^-/- /Adh5 ^-/- mice survived for 25 days after birth, and we measured their total body weight and organ weights. The body weight of Aldh2 ^-/- /Adh5 ^-/- mice decreased significantly by almost 37% compared to the Aldh2 ^-/- /Adh5 ^+/- and Aldh2 ^-/- /Adh5 ^+/+ mice of the same litter. In addition, the absolute weight of each organ was also significantly reduced.

Conclusion

Mice deficient in both formaldehyde-metabolizing enzymes ADH5 and ALDH2 were found to develop partial synthetic lethality and mortality shortly after birth. This phenotype may be due to the accumulation of endogenous formaldehyde. No serious phenotype has been reported in people with dysfunctional, dominant-negative ALDH2*2 alleles, but it has been reported that they may be highly susceptible to osteoporosis and neurodegenerative diseases. It is important to further investigate these diseases in individuals with ALDH2*2 alleles, including an association with decreased metabolism, and thus accumulation, of formaldehyde.

Aldehyde dehydrogenase 2 deficiency significantly exacerbates tert-butyl alcohol-induced toxicity in mice

Owing to the use of ethyl tert-butyl ether (ETBE) as a fuel additive, the possible adverse effects of ETBE exposure have become a public concern. Our previous study showed that ETBE-induced toxicity in aldehyde dehydrogenase 2 (Aldh2) gene knockout (KO) mice was caused by its primary metabolite acetaldehyde, which was toxic. However, it is unclear whether tert-butyl alcohol (TBA), another main metabolite of ETBE, plays a role in ETBE-induced toxicity. To investigate this relationship, we analyzed the changes of TBA concentrations in tissues after ETBE exposure, and then evaluated the toxicity after direct TBA treatment in both KO and wild-type (WT) mice. An exposure to 500 ppm ETBE via inhalation resulted in the formation of its three metabolites, TBA, 2-methyl-1,2-propanediol and ethanol, whose concentrations in the liver, brain, fat and testis of male KO mice were significantly higher than the corresponding concentrations observed in male WT mice. Direct treatment to TBA (20 mg/mL of drinking water) caused significant changes in relative organ weights and histopathology, and increased levels of genetic damages in both types of mice. These toxic effects were also seen in KO mice exposed to a lower concentration of TBA (5 mg/mL), which was associated with increased oxidative stress in serum (reduced glutathione and reduced glutathione/oxidized glutathione ratio decreased). Our findings indicate that ALDH2 is involved in the metabolism of ETBE and TBA, and ALDH2 deficiency could greatly increase the sensitivity to TBA-induced toxicity.

Aldehyde oxidase and its role as a drug metabolizing enzyme

Aldehyde oxidase (AO) is a cytosolic enzyme that belongs to the family of structurally related molybdoflavoproteins like xanthine oxidase (XO). The enzyme is characterized by broad substrate specificity and marked species differences. It catalyzes the oxidation of aromatic and aliphatic aldehydes and various heteroaromatic rings as well as reduction of several functional groups. The references to AO and its role in metabolism date back to the 1950s, but the importance of this enzyme in the metabolism of drugs has emerged in the past fifteen years. Several reviews on the role of AO in drug metabolism have been published in the past decade indicative of the growing interest in the enzyme and its influence in drug metabolism. Here, we present a comprehensive monograph of AO as a drug metabolizing enzyme with emphasis on marketed drugs as well as other xenobiotics, as substrates and inhibitors. Although the number of drugs that are primarily metabolized by AO are few, the impact of AO on drug development has been extensive. We also discuss the effect of AO on the systemic exposure and clearance these clinical candidates. The review provides a comprehensive analysis of drug discovery compounds involving AO with the focus on developmental candidates that were reported in the past five years with regards to pharmacokinetics and toxicity. While there is only one known report of AO-mediated clinically relevant drug-drug interaction (DDI), a detailed description of inhibitors and inducers of AO known to date has been presented here and the potential risks associated with DDI. The increasing recognition of the importance of AO has led to significant progress in predicting the site of AO-mediated metabolism using computational methods. Additionally, marked species difference in expression of AO makes it is difficult to predict human clearance with high confidence. The progress made towards developing in vivo, in vitro and in silico approaches for predicting AO metabolism and estimating human clearance of compounds that are metabolized by AO have also been discussed.

Exploring current read-across applications and needs among selected U.S. Federal Agencies

Read-across is a well-established data gap-filling technique applied for regulatory purposes. In US Environmental Protection Agency's New Chemicals Program under TSCA, read-across has been used extensively for decades, however the extent of application and acceptance of read-across among U.S. federal agencies is less clear. In an effort to build read-across capacity, raise awareness of the state of the science, and work towards a harmonization of read-across approaches across U.S. agencies, a new read-across workgroup was established under the Interagency Coordinating Committee on the Validation of Alternative Methods (ICCVAM). This is one of several ad hoc groups ICCVAM has convened to implement the ICCVAM Strategic Roadmap. In this article, we outline the charge and scope of the workgroup and summarize the current applications, tools used, and needs of the agencies represented on the workgroup for read-across. Of the agencies surveyed, the Environmental Protection Agency had the greatest experience in using read-across whereas other agencies indicated that they would benefit from gaining a perspective of the landscape of the tools and available guidance. Two practical case studies are also described to illustrate how the read-across approaches applied by two agencies vary on account of decision context.

Relationship between ALDH2 genotype and in-stent restenosis in Chinese Han patients after percutaneous coronary intervention

BACKGROUND

It is well known that the genotype of ALDH2 is associated with coronary artery disease (CAD), and in-stent restenosis (ISR) is a primary complication of percutaneous coronary intervention (PCI), a primary recommended treatment for CAD. The aim of this study was to identify the relationship between aldehyde dehydrogenase 2 (ALDH2) genotype and in-stent restenosis (ISR).

METHODS

This study recruited 531 patients who were undergoing PCI at two Chinese hospitals from 2015 to 2017 and 183 were diagnosed with ISR after PCI during the one-year follow-up period. We used polymerase chain restriction fragment length polymorphism (PCR-RFLP) and sequencing to determine ALDH2 polymorphisms.

RESULTS

Among all 531 patients (mean age = 59.4 ± 9.8; 65.9% male), 68.7% carried the wild-type genotype, 28.4% were heterozygous for the mutation, and 2.8% were homozygous for the mutation. Multiple logistical regression analyses indicated no correlation between ALDH2 genotype and the occurrence of restenosis after PCI (OR = 1.448, 95% CI: 0.965-2.168, p = 0.073), though a significant association was observed for patients with diabetes (OR = 4.053, 95% CI: 1.668-10.449, p = 0.003).

CONCLUSION

In this study, we found that carrying an ALDH2*2 allele had no notable relationship with ISR one year after PCI but that it did have a significant association with complications in diabetic patients. Further studies with larger sample sizes will be necessary to reveal a consensus.

Inhalation exposure to low levels of ethyl tertiary butyl ether: Its genetic effects were significantly modified by ALDH2 activity

Previous experiments showed that high concentrations of ethyl tertiary butyl ether (ETBE) exposure (500-5,000 ppm) significantly resulted in DNA damages in aldehyde dehydrogenase 2 (Aldh2) knockout (KO) mice. This study was aimed to verify the genotoxic effects in three genetic types, Aldh2 KO, heterogeneous (HT), and wild type (WT), of mice exposed to lower concentrations of ETBE (50-500 ppm) by inhalation. Histopathology assessments in the livers, measurements of genotoxic biomarkers in blood and livers, and urinary 8-hydroxydeoxyguanosion (8-OH-dG) for the oxidative DNA damage of whole body were performed. Significant histopathological changes and DNA strand breaks both in hepatocytes and leukocytes were found in HT and KO male mice exposed to ≥200 ppm ETBE, but not in 50 ppm ETBE. 8-OH-dG levels either in liver or urine were higher in the HT and KO male mice exposed to ≥200 ppm ETBE. The pathological and genetic effects of ETBE were almost at the same extents for HT and KO mice. Thus, 50 ppm could be the no observed adverse effect level for ETBE in HT and KO male mice, which was far lower than the 500 ppm in WT mice. These results suggested that decrease and deficiency of ALDH2 activity would significantly increase the sensitivity to ETBE-induced genotoxicity as well as hepatotoxic effects after exposure even to low concentrations of ETBE. Environ. Mol. Mutagen. 60: 145-153, 2019. © 2018 Wiley Periodicals, Inc.

Environmental Aldehyde Sources and the Health Implications of Exposure

Aldehydes, which are present within the air as well as food and beverage sources, are highly reactive molecules that can be cytotoxic, mutagenic, and carcinogenic. To prevent harm from reactive aldehyde exposure, the enzyme aldehyde dehydrogenase 2 (ALDH2) metabolizes reactive aldehydes to a less toxic form. However, the genetic variant of ALDH2, ALDH2*2, significantly reduces the ability to metabolize reactive aldehydes in humans. Therefore, frequent environmental aldehyde exposure, coupled with inefficient aldehyde metabolism, could potentially lead to an increased health risk for diseases such as cancer or cardiovascular disease.Here, we discuss the environmental sources of reactive aldehydes and the potential health implications particularly for those with an ALDH2*2 genetic variant. We also suggest when considering the ALDH2*2 genetic variant the safety limits of reactive aldehyde exposure may have to be reevaluated. Moreover, the ALDH2*2 genetic variant can also be used as an example for how to implement precision medicine in the field of environmental health sciences.

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

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

Vasodilatory effect of nitroglycerin in Japanese subjects with different aldehyde dehydrogenase 2 (ALDH2) genotypes

The functional genetic polymorphism of aldehyde dehydrogenase 2 (ALDH2) influences the enzymatic activities of its wild type (Glu504 encoded by ALDH2*1) and mutant type (Lys504 encoded by ALDH2*2) proteins. The enzymatic activities of mutant-type ALDH2 are limited compared with those of the wild type. ALDH2 has been suggested as a critical factor for nitroglycerin-mediated vasodilation by some human studies and in vitro studies. Currently, there is no research on direct observations of the vasodilatory effect of nitroglycerin sublingual tablets, which is the generally used dosage form. In the present study, the contribution of ALDH2 to the vasodilatory effect of nitroglycerin sublingual tablets was investigated among three genotype groups (ALDH2*1/*1, ALDH2*1/*2, and ALDH2*2/*2) in Japanese. The results by direct assessments of in vivo nitroglycerin-mediated dilation showed no apparent difference in vasodilation among all genotypes of ALDH2. Furthermore, to analyze the effect of other factors (age and flow-mediated dilation), multiple regression analysis and Pearson's correlation coefficient analysis were carried out. These analyses also indicated that the genotypes of ALDH2 were not related to the degree of vasodilation. These results suggest the existence of other predominant pathway(s) for nitroglycerin biotransformation, at least with regard to clinical nitroglycerin (e.g., a sublingual tablet) in Japanese subjects.

Association between ALDH2 Glu504Lys polymorphism and colorectal cancer risk: a meta-analysis

BACKGROUND

The findings from studies on the relationship between aldehyde dehydrogenases(ALDH) gene Glu504Lys polymorphism and colorectal cancer(CRC) were inconsistent.

OBJECTIVES

The aim of this meta-analysis was to assess ALDH gene Glu504Lys polymorphism and CRC risk.

METHODS

All of the relevant studies were identified from PubMed and Embase database. Statistical analyses were conducted with STATA 12.0 software. Odds ratio (OR) with 95% confidence interval (CI) values were applied to evaluate the strength of the association. Nine studies with 2779 cases and 4533 controls were included.

RESULTS

No significant variation in CRC risk was detected in any of the genetic models overall. To explore the sources of heterogeneity,we performed further sub-group analyses by ethnicity and quality assessment of these studies. In the sub-group analysis by race, significant associations between ALDH gene Glu504Lys polymorphism and CRC risk were found in China(Glu/Lys vs Glu/Glu: OR = 0.70, 95%CI = 0.57-0.85; the dominant model: OR =0.69, 95%CI =0.48-0.98) and Japan(Lys/Lys vs Glu/Glu:OR =0.72, 95%CI =0.55-0.95).

CONCLUSION

This meta-analysis suggests that the ALDH2 Glu504Lys polymorphism may be associated with susceptibility to CRC. Furthermore, large and well-designed studies are needed to confirm these conclusions.

Exome-wide association study identifies genetic polymorphisms of C12orf51, MYL2, and ALDH2 associated with blood lead levels in the general Korean population

BACKGROUND

Lead (Pb) is a ubiquitous toxic metal present in the environment that poses adverse health effects to humans. Inter-individual variation in blood Pb levels is affected by various factors, including genetic makeup. However, limited data are available on the association between genetic variation and blood Pb levels. The purpose of this study was to identify the genetic markers associated with blood Pb levels in the Korean population.

METHODS

The study subjects consisted of 1,483 healthy adults with no history of occupational exposure to Pb. We measured blood Pb levels and calculated probable daily intake of Pb according to dietary data collected using 24-hour recall. We conducted exome-wide association screening using Illumina Human Exome-12v1.2 platform (n = 500) and a replication analysis using VeraCode Goldengate assay (n = 1,483).

RESULTS

Among the 244,770 single nucleotide polymorphisms (SNPs) tested, 12 SNPs associated with blood Pb level were identified, with suggestive significance level (P < 1 × 10^-4). In the Goldengate assay for replication, three SNPs (C12orf51 rs11066280, MYL2 rs12229654, and ALDH2 rs671) were associated with statistically suggestively significant differences in blood Pb levels. When stratified by drinking status, a potential association of C12orf51 rs11066280, MYL2 rs12229654, and ALDH2 rs671 with blood Pb level was observed only in drinkers. A marginally significant gene-environment interaction between ALDH2 rs671 and alcohol consumption was observed in relation to blood Pb levels. The effects of the three suggestively significant SNPs on blood Pb levels was dependent on daily calcium intake amounts.

CONCLUSIONS

This exome-wide association study indicated that C12orf51 rs11066280, MYL2 rs12229654, and ALDH2 rs671 polymorphisms are linked to blood Pb levels in the Korean population. Our results suggest that these three SNPs are involved in the determination of Pb levels in Koreans via the regulation of alcohol drinking behavior, and that their negative effects may be compensated by appropriate calcium intake.

Significant association between decreased ALDH2 activity and increased sensitivity to genotoxic effects in workers occupationally exposed to styrene

ALDH2 is involved in the metabolism of styrene, a widely used industrial material, but no data are available regarding the influence of this enzyme on the metabolic fate as well as toxic effects of this chemical. In this study, we recruited 329 workers occupationally exposed to styrene and 152 unexposed controls. DNA strand breaks, DNA-base oxidation in leukocytes and urinary 8-hydroxydeoxyguanosine (8-OH-dG) were assayed as biomarkers to measure genotoxic effects. Meanwhile, we examined the genetic polymorphisms, including ALDH2, EXPH1, GSTM1, GSTT1 and CYP2E1, and also analyzed the levels of styrene exposure through detecting urinary styrene metabolites and styrene concentration in air. In terms of DNA damage, the three genotoxic biomarkers were significantly increased in exposed workers as compared with controls. And the styrene-exposed workers with inactive ALDH2 *2 allele were subjected to genotoxicity in a higher degree than those with ALDH2 *1/*1 genotype. Also, lower levels of urinary styrene metabolites (MA + PGA) were observed in styrene-exposed workers carrying ALDH2 *2 allele, suggesting slower metabolism of styrene. The polymorphisms of other enzymes showed less effect. These results suggested that styrene metabolism and styrene-induced genotoxicity could be particularly modified by ALDH2 polymorphisms. The important role of ALDH2 indicated that the accumulation of styrene glycoaldehyde, a possible genotoxic intermediate of styrene, could account for the genotoxicity observed, and should be taken as an increased risk of cancer.

Vasculoprotective Effects of 3-Hydroxybenzaldehyde against VSMCs Proliferation and ECs Inflammation

3-hydroxybenzaldehyde (3-HBA) is a precursor compound for phenolic compounds like Protocatechuic aldehyde (PCA). From recent reports, PCA has shown vasculoprotective potency, but the effects of 3-HBA remain unclear. The aim of this study is to investigate the vasculoprotective effects of 3-HBA in endothelial cells, vascular smooth muscle cells and various animal models. We tested effects of 3-HBA in both vitro and vivo. 3-HBA showed that it prevents PDGF-induced vascular smooth muscle cells (VSMCs) migration and proliferation from MTS, BrdU assays and inhibition of AKT phosphorylation. It arrested S and G0/G1 phase of VSMC cell cycle in PI staining and it also showed inhibited expression levels of Rb1 and CD1. In human umbilical vein endothelial cells (HUVECs), 3-HBA inhibited inflammatory markers and signaling molecules (VCAM-1, ICAM-1, p-NF-κB and p-p38). For ex vivo, 3-HBA has shown dramatic effects in suppressing the sprouting from aortic ring of Spargue Dawley (SD) rats. In vivo data supported the vasculoprotective effects of 3-HBA as it inhibited angiogenesis from Matrigel Plug assay in C57BL6 mouse, prevented ADP-induced thrombus generation, increased blood circulation after formation of thrombus, and attenuated neointima formation induced by common carotid artery balloon injury of SD rats. 3-HBA, a novel therapeutic agent, has shown vasculoprotective potency in both in vitro and in vivo.

[Fundamental Properties of Aldehyde Dehydrogenase 2 (ALDH2) and the Importance of the ALDH2 Polymorphism]

Human aldehyde dehydrogenase 2 (ALDH2) is a 56 kDa mitochondrial protein that forms homodimers through hydrogen bonding interactions between the Glu487 and Arg475 residues of two ALDH2 proteins. Two ALDH2 homodimers can interact to form an ALDH2 tetramer. ALDH2 is widely distributed throughout the organs of the body. In addition to its dehydrogenase activity, ALDH2 also exhibits esterase and reductase activities, with the main substrates for these three activities being aldehydes, 4-nitrophenyl acetate and nitroglycerin, respectively. ALDH2 can be readily inhibited by a wide variety of endogenous and exogenous chemicals, but the induction or activation of this enzyme remains unlikely. The polymorphism of ALDH2 to the corresponding ALDH2*2 variant results in a severe deficiency in ALDH2 activity, and this particular polymorphism is prevalent among people of Mongoloid descent. It seems reasonable to expect that people with the ALDH2*2 variant would be more vulnerable to stress and diseases because ALDH2 defends the human body against toxic aldehydes. However, it has been suggested that people with the ALDH2*2 variant are protected by alternative stress-defending systems. The ALDH2*2 variant has been reported to be associated with many different kinds of diseases, although the mechanisms underlying these associations have not yet been elucidated. ALDH2 polymorphism has a significant impact on human health; further studies are therefore required to determine the practical implications of this polymorphism in the fields of preventive and clinical medicine.

ALDH2(E487K) mutation increases protein turnover and promotes murine hepatocarcinogenesis

Mitochondrial aldehyde dehydrogenase 2 (ALDH2) in the liver removes toxic aldehydes including acetaldehyde, an intermediate of ethanol metabolism. Nearly 40% of East Asians inherit an inactive ALDH2*2 variant, which has a lysine-for-glutamate substitution at position 487 (E487K), and show a characteristic alcohol flush reaction after drinking and a higher risk for gastrointestinal cancers. Here we report the characterization of knockin mice in which the ALDH2(E487K) mutation is inserted into the endogenous murine Aldh2 locus. These mutants recapitulate essentially all human phenotypes including impaired clearance of acetaldehyde, increased sensitivity to acute or chronic alcohol-induced toxicity, and reduced ALDH2 expression due to a dominant-negative effect of the mutation. When treated with a chemical carcinogen, these mutants exhibit increased DNA damage response in hepatocytes, pronounced liver injury, and accelerated development of hepatocellular carcinoma (HCC). Importantly, ALDH2 protein levels are also significantly lower in patient HCC than in peritumor or normal liver tissues. Our results reveal that ALDH2 functions as a tumor suppressor by maintaining genomic stability in the liver, and the common human ALDH2 variant would present a significant risk factor for hepatocarcinogenesis. Our study suggests that the ALDH2*2 allele-alcohol interaction may be an even greater human public health hazard than previously appreciated.

Metabolic methanol: molecular pathways and physiological roles

Methanol has been historically considered an exogenous product that leads only to pathological changes in the human body when consumed. However, in normal, healthy individuals, methanol and its short-lived oxidized product, formaldehyde, are naturally occurring compounds whose functions and origins have received limited attention. There are several sources of human physiological methanol. Fruits, vegetables, and alcoholic beverages are likely the main sources of exogenous methanol in the healthy human body. Metabolic methanol may occur as a result of fermentation by gut bacteria and metabolic processes involving S-adenosyl methionine. Regardless of its source, low levels of methanol in the body are maintained by physiological and metabolic clearance mechanisms. Although human blood contains small amounts of methanol and formaldehyde, the content of these molecules increases sharply after receiving even methanol-free ethanol, indicating an endogenous source of the metabolic methanol present at low levels in the blood regulated by a cluster of genes. Recent studies of the pathogenesis of neurological disorders indicate metabolic formaldehyde as a putative causative agent. The detection of increased formaldehyde content in the blood of both neurological patients and the elderly indicates the important role of genetic and biochemical mechanisms of maintaining low levels of methanol and formaldehyde.

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

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.

Acetaldehyde production capacity of salivary microflora in alcoholics during early recovery

This study investigated whether a relationship exists between the acetaldehyde production capacity of salivary microflora (sAPC) in recovering alcoholics, and craving, and/or resumption of drinking within 12 weeks after embarking on an abstinence-based treatment program. Serial sAPC measurements were determined by gas chromatography on spontaneous saliva samples of 30 male alcoholics on days 2, 4, 11, and 18 during a 21-day in-patient treatment program. Craving was measured simultaneously with the Penn Alcohol Craving Scale. Outcome over 12 weeks was assessed by telephone interviews. There was no significant change in sAPC values from day 2 to day 18, while craving scores decreased markedly between day 2 to day 4. Sixteen participants remained abstinent for the full 12 weeks. Statistically significant differences were found between the sAPC values of the group that remained abstinent and the group that resumed drinking within 12 weeks. The highest sAPC value measured on day 2 had a strong predictive value for maintained abstinence at 12 weeks for beer-only drinkers or drinkers consuming less than 320 g of alcohol per week. The study is the first investigation into a potential relationship between the acetaldehyde production capacity of salivary microflora and early resumption of drinking in recovering alcoholics. The findings suggest that such a relationship indeed exists for beer-only drinkers, possibly linked to lower alcohol intake, and that it is unrelated to withdrawal craving. sAPC is proposed as a candidate biomarker with diagnostic and/or prognostic potential.

The ALDH2 rs671 polymorphism affects post-stroke epilepsy susceptibility and plasma 4-HNE levels

Recent studies have demonstrated the protective effect of mitochondrial aldehyde dehydrogenase 2 (ALDH2) in cardiovascular diseases. Increased levels of the potential ALDH2 substrate 4-hydroxynonenal (4-HNE) are involved in myocardial/cerebral ischemia accompanied by a high level of oxidative stress. In this investigation, we first performed a case-control study to explore the potential association of ALDH2 rs671 polymorphism and post-stroke epilepsy (PSE). Then, we performed an in vitro study to determine whether the overexpression of ALDH2 could decrease the level of oxidative stress and the apoptosis ratio induced by 4-HNE. There was a significant difference in the distribution of the allele and genotype frequencies of the rs671 polymorphism between PSE patients and ischemic stroke (IS) patients. Individuals with the rs671 A allele showed significantly higher levels of plasma 4-HNE. The overexpression of ALDH2 partially blocked the increased levels of malondialdehyde (MDA), reactive oxygen species (ROS) and apoptosis ratio induced by 4-HNE and also partially restored the ALDH2 activity in PC12 cells; these effects were reversed in the presence of εV1-2. Our results suggest that the ALDH2 rs671 polymorphism is associated with PSE susceptibility and affects the 4-HNE levels. Targeting ALDH2 might be a useful strategy for the treatment or prevention of PSE.

Targeting aldehyde dehydrogenase 2: new therapeutic opportunities

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.

ALDH2 Glu504Lys polymorphism and susceptibility to coronary artery disease and myocardial infarction in East Asians: a meta-analysis

BACKGROUND AND AIMS

Emerging evidences have shown that the Glu504Lys variant in ALDH2 gene may greatly reduce the ability of ALDH2 to metabolize acetaldehyde, which could increase the risk of coronary artery disease (CAD) and myocardial infarction (MI). However, the reported results are still conflicting. To investigate the association between ALDH2 Glu504Lys polymorphism and the risk of CAD and MI in Asians, we analyzed all available studies in a meta-analysis.

METHODS

A literature search of PubMed, Embase, Web of Science and Chinese BioMedical (CBM) databases was conducted for articles published before March 1, 2013. The principal outcome measure was the crude odds ratios (ORs) with their corresponding confidence intervals (95% CIs) for evaluating the strength of the association.

RESULTS

Meta-analysis showed that carriers of ALDH2 504lys allele were associated with increased risks of both CAD and MI (CAD: OR = 1.28, 95% CI: 1.10-1.48, p = 0.001; MI: OR = 1.58, 95% CI: 1.15-2.19, p = 0.005). Subgroup analysis by country showed significant correlations between mutant genotypes (Glu/Lys + Lys/Lys) and increased risk to MI among Chinese and Korean populations (Chinese: OR = 1.89, 95% CI: 1.16-3.09, p = 0.011; Korean: OR = 1.69, 95%CI: 1.12-2.55, p = 0.013), whereas similar associations were not observed among Japanese populations.

CONCLUSIONS

The current meta-analysis provides strong evidence that ALDH2 Glu504Lys polymorphism may be associated with increased risk of CAD and MI in East Asians, especially among Chinese and Korean populations. However, more detailed and well-designed studies are still warranted to confirm these findings.

Association of a Missense ALDH2 Single Nucleotide Polymorphism (Glu504Lys) With Benign Prostate Hyperplasia in a Korean Population

Purpose

Aldehyde dehydrogenase 2 (ALDH2) is a well-known gene involved in alcohol and aldehyde metabolism. Moreover, recent studies have reported associations between ALDH2 and age-related disorders. Benign prostate hyperplasia (BPH) is an age-related disorder and genetic factors may contribute to its onset. In this study, we investigated the association of a well-studied ALDH2 single nucleotide polymorphism (SNP), rs671, with the onset and clinical features of BPH.

Methods

A total of 222 BPH patients and 214 control subjects were genotyped. The clinical features of the BPH patients (prostate volume, prostate-specific antigen level, and International Prostatic Symptom Score) were analyzed.

Results

The results show that rs671 was only associated with the volume of BPH in genotype and allele frequencies (P<0.05).

Conclusion

We propose that rs671 is an Asian-specific SNP in ALDH2 that may affect the disease progression of BPH in the Korean population.

Urinary biomarkers of smokers' exposure to tobacco smoke constituents in tobacco products assessment: a fit for purpose approach

There are established guidelines for bioanalytical assay validation and qualification of biomarkers. In this review, they were applied to a panel of urinary biomarkers of tobacco smoke exposure as part of a "fit for purpose" approach to the assessment of smoke constituents exposure in groups of tobacco product smokers. Clinical studies have allowed the identification of a group of tobacco exposure biomarkers demonstrating a good doseresponse relationship whilst others such as dihydroxybutyl mercapturic acid and 2-carboxy-1-methylethylmercapturic acid - did not reproducibly discriminate smokers and non-smokers. Furthermore, there are currently no agreed common reference standards to measure absolute concentrations and few inter-laboratory trials have been performed to establish consensus values for interim standards. Thus, we also discuss in this review additional requirements for the generation of robust data on urinary biomarkers, including toxicant metabolism and disposition, method validation and qualification for use in tobacco products comparison studies.

Dominance of the inactive Asian variant over activity and protein contents of mitochondrial aldehyde dehydrogenase 2 in human liver

BACKGROUND

It has been well documented that a variant allele of mitochondrial aldehyde dehydrogenase 2 (ALDH2), ALDH2*2, commonly occurs in East Asians but rarely in other ethnic populations. This unique allelic variation significantly influences drinking behavior and susceptibility to development of alcoholism. Previous structural, functional, and cellular studies indicate that the resulting variant polypeptide subunit K (Lys-487) exerts dominance of null activity and shorter half-life over the tetrameric enzyme molecules in distinct manners. However, the in vivo evidence for the proposed dominance mechanisms remains lacking.

METHODS

To address this question, we investigated 33 surgical liver samples identified to be normal homozygous ALDH2*1/*1 (n = 17), heterozygous ALDH2*1/*2 (n = 13), and variant homozygous ALDH2*2/*2 (n = 3). The ALDH2 activity was determined at a sufficient low acetaldehyde concentration (3 μM) and the isozyme protein amount by immunotitration using purified class-specific antibodies.

RESULTS

The tissue ALDH2 activity in heterozygotes was 17% that of the ALDH2*1/*1 genotype (p < 0.001), whereas the activity of ALDH2*2/*2 was too low to be precisely determined. The protein amounts of tissue ALDH2 in variant homozygotes and heterozygotes were similar but only 30 to 40% that of normal homozygotes (p < 0.01). Linear regression analyses show that ALDH2 activities were significantly correlated with the protein contents in normal homozygotes and heterozygotes, respectively (p < 0.005). The specific activity of ALDH2 per enzyme protein in ALDH2*1/*2 was 38% that of ALDH2*1/*1 (p < 0.001).

CONCLUSIONS

These results are in good agreement with those predicted by the model studies, thus providing in vivo evidence for differential impairments of hepatic acetaldehyde oxidation with alcohol metabolism in individuals carrying ALDH2*1/*2 and ALDH2*2/*2 genotypes.

Formaldehyde in brain: an overlooked player in neurodegeneration?

Formaldehyde is an environmental pollutant that is also generated in substantial amounts in the human body during normal metabolism. This aldehyde is a well-established neurotoxin that affects memory, learning, and behavior. In addition, in several pathological conditions, including Alzheimer's disease, an increase in the expression of formaldehyde-generating enzymes and elevated levels of formaldehyde in brain have been reported. This article gives an overview on the current knowledge on the generation and metabolism of formaldehyde in brain cells as well as on formaldehyde-induced alterations in metabolic processes. Brain cells have the potential to generate and to dispose formaldehyde. In culture, both astrocytes and neurons efficiently oxidize formaldehyde to formate which can be exported or further oxidized. Although moderate concentrations of formaldehyde are not acutely toxic for brain cells, exposure to formaldehyde severely affects their metabolism as demonstrated by the formaldehyde-induced acceleration of glycolytic flux and by the rapid multidrug resistance protein 1-mediated export of glutathione from both astrocytes and neurons. These formaldehyde-induced alterations in the metabolism of brain cells may contribute to the impaired cognitive performance observed after formaldehyde exposure and to the neurodegeneration in diseases that are associated with increased formaldehyde levels in brain.

Accumulated hippocampal formaldehyde induces age-dependent memory decline

Aging is an important factor in memory decline in aged animals and humans and in Alzheimer's disease and is associated with the impairment of hippocampal long-term potentiation (LTP) and down-regulation of NR1/NR2B expression. Gaseous formaldehyde exposure is known to induce animal memory loss and human cognitive decline; however, it is unclear whether the concentrations of endogenous formaldehyde are elevated in the hippocampus and how excess formaldehyde affects LTP and memory formation during the aging process. In the present study, we report that hippocampal formaldehyde accumulated in memory-deteriorating diseases such as age-related dementia. Spatial memory performance was gradually impaired in normal Sprague-Dawley rats by persistent intraperitoneal injection with formaldehyde. Furthermore, excess formaldehyde treatment suppressed the hippocampal LTP formation by blocking N-methyl-D-aspartate (NMDA) receptor. Chronic excess formaldehyde treatment over a period of 30 days markedly decreased the viability of the hippocampus and down-regulated the expression of the NR1 and NR2B subunits of the NMDA receptor. Our results indicate that excess endogenous formaldehyde is a critical factor in memory loss in age-related memory-deteriorating diseases.

Comparative genomics, molecular evolution and computational modeling of ALDH1B1 and ALDH2

Vertebrate ALDH2 genes encode mitochondrial enzymes capable of metabolizing acetaldehyde and other biological aldehydes in the body. Mammalian ALDH1B1, another mitochondrial enzyme sharing 72% identity with ALDH2, is also capable of metabolizing acetaldehyde but has a tissue distribution and pattern of activity distinct from that of ALDH2. Bioinformatic analyses of several vertebrate genomes were undertaken using known ALDH2 and ALDH1B1 amino acid sequences. Phylogenetic analysis of many representative vertebrate species (including fish, amphibians, birds and mammals) indicated the presence of ALDH1B1 in many mammalian species and in frogs (Xenopus tropicalis); no evidence was found for ALDH1B1 in the genomes of birds, reptiles or fish. Predicted vertebrate ALDH2 and ALDH1B1 subunit sequences and structures were highly conserved, including residues previously shown to be involved in catalysis and coenzyme binding for human ALDH2. Studies of ALDH1B1 sequences supported the hypothesis that the ALDH1B1 gene originated in early vertebrates from a retrotransposition of the vertebrate ALDH2 gene. Given the high degree of similarity between ALDH2 and ALDH1B1, it is surprising that individuals with an inactivating mutation in ALDH2 (ALDH2*2) do not exhibit a compensatory increase in ALDH1B1 activity. We hypothesized that the similarity between the two ALDHs would allow for dominant negative heterotetramerization between the inactive ALDH2 mutants and ALDH1B1. Computational-based molecular modeling studies examining predicted protein-protein interactions indicated that heterotetramerization between ALDH2 and ALDH1B1 subunits was highly probable and may partially explain a lack of compensation by ALDH1B1 in ALDH2(∗)2 individuals.

Post-translational modifications of mitochondrial aldehyde dehydrogenase and biomedical implications

Aldehyde dehydrogenases (ALDHs) represent large family members of NAD(P)+-dependent dehydrogenases responsible for the irreversible metabolism of many endogenous and exogenous aldehydes to the corresponding acids. Among 19 ALDH isozymes, mitochondrial ALDH2 is a low Km enzyme responsible for the metabolism of acetaldehyde and lipid peroxides such as malondialdehyde and 4-hydroxynonenal, both of which are highly reactive and toxic. Consequently, inhibition of ALDH2 would lead to elevated levels of acetaldehyde and other reactive lipid peroxides following ethanol intake and/or exposure to toxic chemicals. In addition, many East Asian people with a dominant negative mutation in ALDH2 gene possess a decreased ALDH2 activity with increased risks for various types of cancer, myocardial infarct, alcoholic liver disease, and other pathological conditions. The aim of this review is to briefly describe the multiple post-translational modifications of mitochondrial ALDH2, as an example, after exposure to toxic chemicals or under different disease states and their pathophysiological roles in promoting alcohol/drug-mediated tissue damage. We also briefly mention exciting preclinical translational research opportunities to identify small molecule activators of ALDH2 and its isozymes as potentially therapeutic/preventive agents against various disease states where the expression or activity of ALDH enzymes is altered or inactivated.

Genetic polymorphisms in the formaldehyde dehydrogenase gene and their biological significance

The GSH-dependent formaldehyde dehydrogenase (FDH) is the most important enzyme for the metabolic inactivation of formaldehyde. We studied three polymorphisms of this gene with the intention to elucidate their relevance for inter-individual differences in the protection against the (geno-)toxicity of FA. The first polymorphism (rs11568816) was investigated using real-time PCR and restriction fragment analysis in 150 subjects. However, we did not find the polymorphic sequence in any of the subjects. We studied a second polymorphism (rs17028487), representing a base exchange (c.*114A>G) in exon 9 of the FDH gene. We analyzed 70 subjects with the SNaPshot Primer Extension method and subsequent analysis in a ABI PRISM 3100, but no variant allele was identified. A third polymorphism, rs13832 in exon 9 (c.*493G>T), was studied in a group of 105 subjects by the SNaPshot Primer Extension method. 43 of the subjects were heterozygous for the polymorphism (G/T), 46 homozygous for the T allele, and 16 were homozygous for the G-allele. Real-time RT-PCR measurements of FDH mRNA did not indicate a significant difference in transcript levels between the heterozygous and the homozygous groups. The in vitro comet assay after FA exposure of blood samples obtained from 5 homozygous GG and 3 homozygous TT subjects did not lead to a significant difference between these two groups. Altogether, our study did not identify biologically relevant polymorphisms in transcribed regions of the FDH gene, which may lead to inter-individual differences in the metabolic inactivation of FA.

Aldh2 knockout mice were more sensitive to DNA damage in leukocytes due to ethyl tertiary butyl ether exposure

To clarify the genotoxicity of ethyl tertiary butyl ether (ETBE), a gasoline additive, male and female C57BL/6 mice of Aldh2+/+ and Aldh2-/- genotypes, aged 8 wk, were exposed to 0, 500, 1,750, or 5,000 ppm ETBE for 6 h/day, 5 d per week for 13 wk. DNA damage in leukocytes was measured by the alkaline comet assay and expressed quantitatively as Tail Intensity (TI). For male mice, TI was significantly higher in all three groups exposed to ETBE than in those without exposure within Aldh2-/- mice, whereas within Aldh2+/+ mice, TI increased only in those exposed to 5,000 ppm of ETBE as compared with mice without exposure. For female mice, a significant increase in TI values was observed in the group exposed to 5,000 ppm of ETBE as compared with those without exposure within Aldh2-/- mice; TI in Aldh2-/- mice exposed to 1,750 and 5,000 ppm was significantly higher than in Aldh2+/+ mice without exposure. TI did not significantly increase in any of the groups exposed to ETBE within female Aldh2+/+ mice. Based on the results we suggest that Aldh2-/- mice are more sensitive to DNA damage caused by ETBE than Aldh2+/+ mice and that males seem more susceptible to this effect than females.

Formation of acetaldehyde-derived DNA adducts due to alcohol exposure

Epidemiological studies have identified chronic alcohol consumption as a significant risk factor for cancers of the upper aerodigestive tract, including the oral cavity, pharynx, larynx and esophagus, and for cancer of the liver. Ingested ethanol is mainly oxidized by the enzymes alcohol dehydrogenase (ADH), cytochrome P-450 2E1 (CYP2E1), and catalase to form acetaldehyde, which is subsequently oxidized by aldehyde dehydrogenase 2 (ALDH2) to produce acetate. Polymorphisms of the genes which encode enzymes for ethanol metabolism affect the ethanol/acetaldehyde oxidizing capacity. ADH1B*2 allele (ADH1B, one of the enzyme in ADH family) is commonly observed in Asian population, has much higher enzymatic activity than ADH1B*1 allele. Otherwise, approximately 40% of Japanese have single nucleotide polymorphisms (SNPs) of the ALDH2 gene. The ALDH2 *2 allele encodes a protein with an amino acid change from glutamate to lysine (derived from the ALDH2*1 allele) and devoid of enzymatic activity. Neither the homozygote (ALDH2*2/*2) nor heterozygote (ALDH2*1/*2) is able to metabolize acetaldehyde promptly. Acetaldehyde is a genotoxic compound that reacts with DNA to form primarily a Schiff base N(2)-ethylidene-2'-deoxyguanosine (N(2)-ethylidene-dG) adduct, which may be converted by reducing agents to N(2)-ethyl-2'-deoxyguanosine (N(2)-ethyl-dG) in vivo, and strongly blocked translesion DNA synthesis. Several studies have demonstrated a relationship between ALDH2 genotypes and the development of certain types of cancer. On the other hand, the drinking of alcohol induces the expression of CYP2E1, resulting in an increase in reactive oxygen species (ROS) and oxidative DNA damage. This review covers the combined effects of alcohol and ALDH2 polymorphisms on cancer risk. Studies show that ALDH2*1/*2 heterozygotes who habitually consume alcohol have higher rates of cancer than ALDH2*1/*1 homozygotes. Moreover, they support that chronic alcohol consumption contributes to formation of various DNA adducts. Although some DNA adducts formation is demonstrated to be an initiation step of carcinogenesis, it is still unclear that whether these alcohol-related DNA adducts are true factors or initiators of cancer. Future studies are needed to better characterize and to validate the roles of these DNA adducts in human study.