Tissue distribution, ontogeny, and regulation of aldehyde dehydrogenase (Aldh) enzymes mRNA by prototypical microsomal enzyme inducers in mice

Mitochondrial Aldehyde Dehydrogenase 2 (ALDH2) Protects against Binge Alcohol-Mediated Gut and Brain Injury

Mitochondrial aldehyde dehydrogenase-2 (ALDH2) metabolizes acetaldehyde to acetate. People with ALDH2 deficiency and Aldh2-knockout (KO) mice are more susceptible to alcohol-induced tissue damage. However, the underlying mechanisms behind ALDH2-related gut-associated brain damage remain unclear. Age-matched young female Aldh2-KO and C57BL/6J wild-type (WT) mice were gavaged with binge alcohol (4 g/kg/dose, three doses) or dextrose (control) at 12 h intervals. Tissues and sera were collected 1 h after the last ethanol dose and evaluated by histological and biochemical analyses of the gut and hippocampus and their extracts. For the mechanistic study, mouse neuroblast Neuro2A cells were exposed to ethanol with or without an Aldh2 inhibitor (Daidzin). Binge alcohol decreased intestinal tight/adherens junction proteins but increased oxidative stress-mediated post-translational modifications (PTMs) and enterocyte apoptosis, leading to elevated gut leakiness and endotoxemia in Aldh2-KO mice compared to corresponding WT mice. Alcohol-exposed Aldh2-KO mice also showed higher levels of hippocampal brain injury, oxidative stress-related PTMs, and neuronal apoptosis than the WT mice. Additionally, alcohol exposure reduced Neuro2A cell viability with elevated oxidative stress-related PTMs and apoptosis, all of which were exacerbated by Aldh2 inhibition. Our results show for the first time that ALDH2 plays a protective role in binge alcohol-induced brain injury partly through the gut-brain axis, suggesting that ALDH2 is a potential target for attenuating alcohol-induced tissue injury.

Cullin 3 RING E3 ligase inactivation causes NRF2-dependent NADH reductive stress, hepatic lipodystrophy, and systemic insulin resistance

Cullin RING E3 ligases (CRL) have emerged as key regulators of disease-modifying pathways and therapeutic targets. Cullin3 (Cul3)-containing CRL (CRL3) has been implicated in regulating hepatic insulin and oxidative stress signaling. However, CRL3 function in liver pathophysiology is poorly defined. Here, we report that hepatocyte Cul3 knockout results in rapid resolution of steatosis in obese mice. However, the remarkable resistance of hepatocyte Cul3 knockout mice to developing steatosis does not lead to overall metabolic improvement but causes systemic metabolic disturbances. Liver transcriptomics analysis identifies that CRL3 inactivation causes persistent activation of the nuclear factor erythroid 2-related factor 2 (NRF2) antioxidant defense pathway, which also reprograms the lipid transcriptional network to prevent TG storage. Furthermore, global metabolomics reveals that NRF2 activation induces numerous NAD+-consuming aldehyde dehydrogenases to increase the cellular NADH/NAD+ ratio, a redox imbalance termed NADH reductive stress that inhibits the glycolysis-citrate-lipogenesis axis in Cul3 knockout livers. As a result, this NRF2-induced cellular lipid storage defect promotes hepatic ceramide accumulation, elevates circulating fatty acids, and worsens systemic insulin resistance in a vicious cycle. Hepatic lipid accumulation is restored, and liver injury and hyperglycemia are attenuated when NRF2 activation and NADH reductive stress are abolished in hepatocyte Cul3/Nrf2 double-knockout mice. The resistance to hepatic steatosis, hyperglycemia, and NADH reductive stress are observed in hepatocyte Keap1 knockout mice with NRF2 activation. In summary, our study defines a critical role of CRL3 in hepatic metabolic regulation and demonstrates that the CRL3 downstream NRF2 overactivation causes hepatic metabolic maladaptation to obesity and insulin resistance.

A patent review on aldehyde dehydrogenase inhibitors: an overview of small molecule inhibitors from the last decade

INTRODUCTION

Physiological and pathophysiological effects arising from detoxification of aldehydes in humans implicate the enzyme aldehyde dehydrogenase (ALDH) gene family comprising of 19 isoforms. The main function of this enzyme family is to metabolize reactive aldehydes to carboxylic acids. Dysregulation of ALDH activity has been associated with various diseases. Extensive research has since gone into studying ALHD isozymes, their structural biology and developing small-molecule inhibitors. Novel chemical strategies to enhance the selectivity of ALDH inhibitors have now appeared.

AREAS COVERED

A comprehensive review of patent literature related to aldehyde dehydrogenase inhibitors in the last decade and half (2007-2022) is provided.

EXPERT OPINION

Aldehyde dehydrogenase (ALDH) is an important enzyme that metabolizes reactive exogenous and endogenous aldehydes in the body through NAD(P)±dependent oxidation. Hence this family of enzymes possess important physiological as well as toxicological roles in human body. Significant efforts in the field have led to potent inhibitors with approved clinical agents for alcohol use disorder therapy. Further clinical translation of novel compounds targeting ALDH inhibition will validate the promised therapeutic potential in treating many human diseases.The scientific/patent literature has been searched on SciFinder-n, Reaxys, PubMed, Espacenet and Google Patents. The search terms used were 'ALDH inhibitors', 'Aldehyde Dehydrogenase Inhibitors'.

Sex Difference in Cardioprotection against Acute Myocardial Infarction in MAO-B Knockout Mice In Vivo

The cardiomyocyte-specific knockout (KO) of monoamine oxidase (MAO)-B, an enzyme involved in the formation of reactive oxygen species (ROS), reduced myocardial ischemia/reperfusion (I/R) injury in vitro. Because sex hormones have a strong impact on MAO metabolic pathways, we analyzed the myocardial infarct size (IS) following I/R in female and male MAO-B KO mice in vivo. Method and Results: To induce the deletion of MAO-B, MAO-B KO mice (Myh6 Cre+/MAO-Bfl/fl) and wild-type (WT, Cre-negative MAO-Bfl/fl littermates) were fed with tamoxifen for 2 weeks followed by 10 weeks of normal mice chow. Myocardial infarction (assessed by TTC staining and expressed as a percentage of the area at risk as determined by Evans blue staining)) was induced by 45 min coronary occlusion followed by 120 min of reperfusion. Results: The mortality following I/R was higher in male compared to female mice, with the lowest mortality found in MAO-B KO female mice. IS was significantly higher in male WT mice compared to female WT mice. MAO-B KO reduced IS in male mice but had no further impact on IS in female MAO-B KO mice. Interestingly, there was no difference in the plasma estradiol levels among the groups. Conclusion: The cardiomyocyte-specific knockout of MAO-B protects male mice against acute myocardial infarction but had no effect on the infarct size in female mice.

Acetaldehyde dehydrogenase 2 activation attenuates sepsis-induced brain injury through NLRP3 inflammasome regulation

OBJECTIVE

Acetaldehyde dehydrogenase 2 (ALDH2) plays an important part in neuroprotection; however, its effect on sepsis-induced brain injury is nuclear. Our aim is to investigate the potential effect and mechanism of ALDH2 in this condition.

METHODS

We established an animal model using cecal ligation and perforation (CLP). Twenty-four rats were divided into sham group (n = 6), CLP group (n = 6), CLP + Alda-1 group (n = 6) and CLP + Cyanamide (CYA) group (n = 6). Vital signs were monitored, and arterial blood gas analysis, hippocampal histological staining and ALDH2 activity analysis were conducted. Western blot analysis and enzyme-linked immunosorbent assays were also carried out. Lipopolysaccharide (LPS)-treated HT22 cells were employed as an in vitro model of sepsis-induced brain injury, with and without pretreatment with Alda-1 or CYA, to further examine the potential mechanisms. Real-time quantitative polymerase chain reaction and western blot were used to determine the levels of pyrin domain-containing 3 (NLRP3) inflammasome.

RESULTS

We found hippocampal cell injury in the CLP group (p < 0.05), with decreased ALDH2 activity (p < 0.05) and suspected overexpression of NLRP3/caspase-1 axis (p < 0.05). In the group pretreated with Alda-1, there were increased ALDH2 activity (p < 0.05), decreased hippocampal cell damage (p < 0.05), and reduced protein levels of NLRP3, apoptosis-associated speck like protein containing a caspase recruitment domain (ASC), cleaved caspase-1 and Gasdermin D (GSDMD) (p < 0.05). The levels of interleukin 18 (IL-18) and interleukin 1β (IL-1β) were also reduced (p < 0.05). In the group pretreated with CYA, ALDH2 activity was further declined, the cell injury grade increased, and the elevated levels of pyroptosis-related proteins aggravated (p < 0.05). LPS treatment decreased the cell viability and ALDH2 activity of the HT22 cells (p < 0.05), along with increased mRNA levels of the NLRP3 inflammasome, as well as IL-1β and IL-18 (p < 0.05). Western blot further revealed elevated levels of NLRP3, ASC, cleaved caspase-1 and GSDMD (p < 0.05). In the LPS+Alda-1 group, there were increased cell viability (p < 0.05), elevated ALDH2 activity (p < 0.05), and reduced levels of NLRP3 inflammasome and pyroptosis-related proteins (p < 0.05). In the CYA+LPS group, cell viability and ALDH2 activity were further declined (p < 0.05), while levels of NLRP3 /caspase-1 axis were increased (p < 0.05).

CONCLUSIONS

The activation of ALDH2 can attenuate sepsis-induced brain injury, hypothetically through regulation of the NLRP3/caspase-1 signaling pathway. Therefore, ALDH2 could potentially be considered as a new therapeutic target for the treatment of sepsis-induced brain injury.

Nrf2 Modulation in Breast Cancer

Reactive oxygen species (ROS) are identified to control the expression and activity of various essential signaling intermediates involved in cellular proliferation, apoptosis, and differentiation. Indeed, ROS represents a double-edged sword in supporting cell survival and death. Many common pathological processes, including various cancer types and neurodegenerative diseases, are inflammation and oxidative stress triggers, or even initiate them. Keap1-Nrf2 is a master antioxidant pathway in cytoprotective mechanisms through Nrf2 target gene expression. Activation of the Nfr2 pathway benefits cells in the early stages and reduces the level of ROS. In contrast, hyperactivation of Keap1-Nrf2 creates a context that supports the survival of both healthy and cancerous cells, defending them against oxidative stress, chemotherapeutic drugs, and radiotherapy. Considering the dual role of Nrf2 in suppressing or expanding cancer cells, determining its inhibitory/stimulatory position and targeting can represent an impressive role in cancer treatment. This review focused on Nrf2 modulators and their roles in sensitizing breast cancer cells to chemo/radiotherapy agents.

ALDH7A1 rs12514417 polymorphism may increase ischemic stroke risk in alcohol-exposed individuals

Background:

Epidemiological studies have identified common risk factors for cerebral stroke worldwide. Some of these factors include hypertension, diabetes, smoking, excessive drinking, and dyslipidemia. It is important to note, however, that genetic factors can also contribute to the occurrence of stroke. Here, we evaluated the association of ischemic stroke with rs12514417 polymorphism of the alcohol metabolizing gene, aldehyde dehydrogenase 7A1 (ALDH7A1) and alcohol consumption.

Methods:

Taiwan Biobank (TWB) data collected between 2008 and 2015 were available for 17,985 subjects. The odd ratios for stroke were obtained using logistic regression models.

Results:

Among eligible subjects (n = 17,829), 897 had ischemic stroke and 70 had hemorrhagic stroke. Subjects with ischemic stroke were older (mean ± SE, 58.45 ± 8.19 years vs. 48.33 ± 10.89 years, p < 0.0001) and had a higher body mass index (BMI) than the stroke-free individuals. The risk of ischemic stroke was significantly higher among subjects with the ALDH7A1 rs12514417 TG + GG genotype who also consumed alcohol at least 150 ml/week (odds ratio (OR), 1.79; 95% confidence interval (CI), 1.18–2.72). We found that rs12514417 genotype and alcohol consumption (at least 150 ml/week) showed a significant interaction (p for interaction = 0.0266). Stratification based on alcohol exposure and ALDH7A1 rs12514417 genotypes indicated that ischemic stroke risk was significantly higher among alcohol drinkers with the TG + GG genotype than in those with the TT genotype (OR, 1.64, 95% CI: 1.15–2.33).

Conclusion:

Our study suggests that the combination of ALDH7A1 rs12514417 TG + GG genotype and alcohol exposure of at least 150 ml/week may increase the risk of ischemic stroke in Taiwanese adults.

A Major Intestinal Catabolite of Quercetin Glycosides, 3-Hydroxyphenylacetic Acid, Protects the Hepatocytes from the Acetaldehyde-Induced Cytotoxicity through the Enhancement of the Total Aldehyde Dehydrogenase Activity

Aldehyde dehydrogenases (ALDHs) are the major enzyme superfamily for the aldehyde metabolism. Since the ALDH polymorphism leads to the accumulation of acetaldehyde, we considered that the enhancement of the liver ALDH activity by certain food ingredients could help prevent alcohol-induced chronic diseases. Here, we evaluated the modulating effects of 3-hydroxyphenylacetic acid (OPAC), the major metabolite of quercetin glycosides, on the ALDH activity and acetaldehyde-induced cytotoxicity in the cultured cell models. OPAC significantly enhanced the total ALDH activity not only in mouse hepatoma Hepa1c1c7 cells, but also in human hepatoma HepG2 cells. OPAC significantly increased not only the nuclear level of aryl hydrocarbon receptor (AhR), but also the AhR-dependent reporter gene expression, though not the nuclear factor erythroid-2-related factor 2 (Nrf2)-dependent one. The pretreatment of OPAC at the concentration required for the ALDH upregulation completely inhibited the acetaldehyde-induced cytotoxicity. Silencing AhR impaired the resistant effect of OPAC against acetaldehyde. These results strongly suggested that OPAC protects the cells from the acetaldehyde-induced cytotoxicity, mainly through the AhR-dependent and Nrf2-independent enhancement of the total ALDH activity. Our findings suggest that OPAC has a protective potential in hepatocyte models and could offer a new preventive possibility of quercetin glycosides for targeting alcohol-induced chronic diseases.

Gene Expression Profiling of Skeletal Muscles

Next-generation sequencing provides an opportunity for an in-depth biocomputational analysis to identify gene expression patterns between soleus and tibialis anterior, two well-characterized skeletal muscles, and analyze their gene expression profiling. RNA read counts were analyzed for differential gene expression using the R package edgeR. Differentially expressed genes were filtered using a false discovery rate of less than 0.05 c, a fold-change value of more than twenty, and an association with overrepresented pathways based on the Reactome pathway over-representation analysis tool. Most of the differentially expressed genes associated with soleus are coded for components of lipid metabolism and unique contractile elements. Differentially expressed genes associated with tibialis anterior encoded mostly for glucose and glycogen metabolic pathway regulatory enzymes and calcium-sensitive contractile components. These gene expression distinctions partly explain the genetic basis for skeletal muscle specialization, and they may help to explain skeletal muscle susceptibility to disease and drugs and further refine tissue engineering approaches.

Non-cytochrome P450 enzymes involved in the oxidative metabolism of xenobiotics: Focus on the regulation of gene expression and enzyme activity

Oxidative metabolism is one of the major biotransformation reactions that regulates the exposure of xenobiotics and their metabolites in the circulatory system and local tissues and organs, and influences their efficacy and toxicity. Although cytochrome (CY)P450s play critical roles in the oxidative reaction, extensive CYP450-independent oxidative metabolism also occurs in some xenobiotics, such as aldehyde oxidase, xanthine oxidoreductase, flavin-containing monooxygenase, monoamine oxidase, alcohol dehydrogenase, or aldehyde dehydrogenase-dependent oxidative metabolism. Drugs form a large portion of xenobiotics and are the primary target of this review. The common reaction mechanisms and roles of non-CYP450 enzymes in metabolism, factors affecting the expression and activity of non-CYP450 enzymes in terms of inhibition, induction, regulation, and species differences in pharmaceutical research and development have been summarized. These non-CYP450 enzymes are detoxifying enzymes, although sometimes they mediate severe toxicity. Synthetic or natural chemicals serve as inhibitors for these non-CYP450 enzymes. However, pharmacokinetic-based drug interactions through these inhibitors have rarely been reported in vivo. Although multiple mechanisms participate in the basal expression and regulation of non-CYP450 enzymes, only a limited number of inducers upregulate their expression. Therefore, these enzymes are considered non-inducible or less inducible. Overall, this review focuses on the potential xenobiotic factors that contribute to variations in gene expression levels and the activities of non-CYP450 enzymes.

Discovery of benzimidazole derivatives as potent and selective aldehyde dehydrogenase 1A1 (ALDH1A1) inhibitors with glucose consumption improving activity

Aldehyde dehydrogenase 1A1 (ALDH1A1) plays vital physiological and toxicological functions in many areas, such as CNS, inflammation, metabolic disorders, and cancers. Overexpression of ALDH1A1 has been disclosed to play an important role in obesity, diabetes and other diseases, indicating the potential need for the identification and development of small molecule ALDH1A1 inhibitors. Herein, a series of benzimidazole derivatives was designed, synthesized and evaluated. Among them, compounds 21, 27, 29, 61 and 65 exhibited excellent inhibitory activity against ALDH1A1 with IC₅₀ values in the low micromolar range and high selectivity over ALDH1A2, ALDH1A3, ALDH2 and ALDH3A1. Moreover, an in vitro study demonstrated that all five compounds effectively improved glucose consumption in HepG2 cells, of which, 61 and 65 at 10 µM produced nearly equal glucose consumption with positive control Metformin (Met) at 1 mM. Furthermore, 61 and 65 showed desirable metabolic stability in human liver microsomes. All these results suggest that 61 and 65 are suitable for further studies.

Role of NRF2 in Lung Cancer

The gene expression program induced by NRF2 transcription factor plays a critical role in cell defense responses against a broad variety of cellular stresses, most importantly oxidative stress. NRF2 stability is fine-tuned regulated by KEAP1, which drives its degradation in the absence of oxidative stress. In the context of cancer, NRF2 cytoprotective functions were initially linked to anti-oncogenic properties. However, in the last few decades, growing evidence indicates that NRF2 acts as a tumor driver, inducing metastasis and resistance to chemotherapy. Constitutive activation of NRF2 has been found to be frequent in several tumors, including some lung cancer sub-types and it has been associated to the maintenance of a malignant cell phenotype. This apparently contradictory effect of the NRF2/KEAP1 signaling pathway in cancer (cell protection against cancer versus pro-tumoral properties) has generated a great controversy about its functions in this disease. In this review, we will describe the molecular mechanism regulating this signaling pathway in physiological conditions and summarize the most important findings related to the role of NRF2/KEAP1 in lung cancer. The focus will be placed on NRF2 activation mechanisms, the implication of those in lung cancer progression and current therapeutic strategies directed at blocking NRF2 action.

Ontogeny of Hepatic Transporters and Drug-Metabolizing Enzymes in Humans and in Nonclinical Species

The liver represents a major eliminating and detoxifying organ, determining exposure to endogenous compounds, drugs, and other xenobiotics. Drug transporters (DTs) and drug-metabolizing enzymes (DMEs) are key determinants of disposition, efficacy, and toxicity of drugs. Changes in their mRNA and protein expression levels and associated functional activity between the perinatal period until adulthood impact drug disposition. However, high-resolution ontogeny profiles for hepatic DTs and DMEs in nonclinical species and humans are lacking. Meanwhile, increasing use of physiologically based pharmacokinetic (PBPK) models necessitates availability of underlying ontogeny profiles to reliably predict drug exposure in children. In addition, understanding of species similarities and differences in DT/DME ontogeny is crucial for selecting the most appropriate animal species when studying the impact of development on pharmacokinetics. Cross-species ontogeny mapping is also required for adequate translation of drug disposition data in developing nonclinical species to humans. This review presents a quantitative cross-species compilation of the ontogeny of DTs and DMEs relevant to hepatic drug disposition. A comprehensive literature search was conducted on PubMed Central: Tables and graphs (often after digitization) in original manuscripts were used to extract ontogeny data. Data from independent studies were standardized and normalized before being compiled in graphs and tables for further interpretation. New insights gained from these high-resolution ontogeny profiles will be indispensable to understand cross-species differences in maturation of hepatic DTs and DMEs. Integration of these ontogeny data into PBPK models will support improved predictions of pediatric hepatic drug disposition processes. SIGNIFICANCE STATEMENT: Hepatic drug transporters (DTs) and drug-metabolizing enzymes (DMEs) play pivotal roles in hepatic drug disposition. Developmental changes in expression levels and activities of these proteins drive age-dependent pharmacokinetics. This review compiles the currently available ontogeny profiles of DTs and DMEs expressed in livers of humans and nonclinical species, enabling robust interpretation of age-related changes in drug disposition and ultimately optimization of pediatric drug therapy.

Age-related alteration in HNE elimination enzymes

4-hydroxynonenal (HNE, 4-hydroxy-2-nonenal) is a primary α,β-unsaturated aldehyde product of lipid peroxidation. The accumulation of HNE increases with aging and the mechanisms are mainly attributable to increased oxidative stress and decreased capacity of HNE elimination. In this review article, we summarize the studies on age-related change of HNE concentration and alteration of HNE metabolizing enzymes (GCL, GST, ALDHs, aldose reductase, and 20S-proteasome), and discuss potential mechanism of age-related decrease in HNE-elimination capacity by focusing on Nrf2 redox signaling.

Discovery and development of selective aldehyde dehydrogenase 1A1 (ALDH1A1) inhibitors

ALDH1A1, one important member of 19 ALDHs, can metabolize reactive aldehydes to their corresponding carboxylic acid derivatives and play important physiological and toxicological roles in many areas, including CNS, metabolic disorders, and cancers. Overexpression of ALDH1A1 correlates with poor prognosis and tumor aggressiveness, is associated with drug resistance in traditional chemotherapy for cancer treatment and contributes to obesity, diabetes, and inflammation. So, inhibition of ALDH1A1 may offer new therapeutic options for patients with cancer, obesity, diabetes, and inflammation. Up to now, many ALDH1A1 inhibitors with different scaffolds have been identified and developed as useful chemical tools for better understanding of the functions of ALDH1A1 in physiologic and pathophysiologic conditions. In this review, the advances in the discovery and development of selective ALDH1A1 inhibitors are summarized, and opportunities and challenges associated with this field are also discussed.

Tissue distribution, excretion, and metabolism of 2,6-di-tert-butyl-hydroxytoluene in mice

As one typical synthetic phenolic antioxidant, 2,6-di-tert-butyl-hydroxytoluene (BHT) has been widely adopted in food and other human products, and considered as an emerging contaminant due to its toxic effects. Understanding bioaccumulation and metabolism of BHT is crucial to evaluate its environmental fate and toxicity. In this study, the tissue distribution, excretion, and metabolism of BHT in mice were investigated. It was shown that BHT was prone to be accumulated in metabolism-related organs (i.e., liver and kidney) with AUC_{0-120 h} (area under the concentration-time curve from 0 to 120 h) values of 206 h·μg/g in liver and 162 h·μg/g in kidney. For metabolites, 2,6-di-tert-butyl-4-hydroxy-4-methyl-2,5-cyclohexadione (BHT-quinol) was preferentially accumulated in liver, while 3,5-di-tert-butyl-4-hydroxybenzoic acid (BHT-COOH) was the major metabolite in excreta. The major excretion of BHT and metabolites was through feces with a value of 25.1 ± 0.16% of the initial dose compared with urine of 1.27 ± 0.05%. The possible metabolic pathways of BHT were elucidated as the oxidation of the para-methyl, tert-butyl groups, and aromatic ring based on the known and identified unknown metabolites by HPLC-Q-TOF-MS/MS. The preferred accumulation of BHT and metabolites in liver implies their potential hepatotoxicity. Results here also suggested that considering the distribution and excretion of metabolites can better assess BHT's fate and risk in mammals.

Roles of peroxisome proliferator-activated receptor α in the pathogenesis of ethanol-induced liver disease

Alcoholic liver disease (ALD) is a progressively aggravated liver disease with high incidence in alcoholics. Ethanol-induced fat accumulation and the subsequent lipopolysaccharide (LPS)-driven inflammation bring liver from reversible steatosis, to irreversible hepatitis, fibrosis, cirrhosis, and even hepatocellular carcinoma. Peroxisome proliferator-activated receptor α (PPARα) is a member of the nuclear receptor superfamily of ligand-activated transcription factors and plays pivotal roles in the regulation of fatty acid homeostasis as well as the inflammation control in the liver. It has been well documented that PPARα activity and/or expression are downregulated in liver of mice exposed to ethanol, which is thought to be one of the prime contributors to ethanol-induced steatosis, hepatitis and fibrosis. This article summarizes the current evidences from in vitro and animal models for the critical roles of PPARα in the onset and progression of ALD. Importantly, it should be noted that the expression of PPARα in human liver is reported to be similar to that in mice, and PPARα expression is downregulated in the liver of patients with nonalcoholic fatty liver disease (NAFLD), a disease sharing many similarities with ALD. Therefore, clinical trials investigating the expression of PPARα in the liver of ALD patients and the efficacy of strong PPARα agonists for the prevention and treatment of ALD are warranted.

Proteomic analysis of liver proteins of mice exposed to 1,2-dichloropropane

1,2-Dichloropropane (1,2-DCP) is recognized as the causative agent for cholangiocarcinoma among offset color proof-printing workers in Japan. The aim of the present study was to characterize the molecular mechanisms of 1,2-DCP-induced hepatotoxic effects by proteomic analysis. We analyzed quantitatively the differential expression of proteins in the mouse liver and investigated the role of P450 in mediating the effects of 1,2-DCP. Male C57BL/6JJcl mice were exposed to 0, 50, 250, or 1250 ppm 1,2-DCP and treated with either 1-aminobenzotriazole (1-ABT), a nonselective P450 inhibitor, or saline, for 8 h/day for 4 weeks. Two-dimensional difference in gel electrophoresis (2D-DIGE) combined with matrix-assisted laser-desorption ionization time-of-flight mass spectrometry (MALDI-TOF/TOF/MS) was used to detect and identify proteins affected by the treatment. PANTHER overrepresentation test on the identified proteins was conducted. 2D-DIGE detected 61 spots with significantly different intensity between 0 and 250 ppm 1,2-DCP groups. Among them, 25 spots were identified by MALDI-TOF/TOF/MS. Linear regression analysis showed significant trend with 1,2-DCP level in 17 proteins in mice co-treated with 1-ABT. 1-ABT mitigated the differential expression of these proteins. The gene ontology enrichment analysis showed overrepresentation of proteins functionally related to nickel cation binding, carboxylic ester hydrolase activity, and catalytic activity. The results demonstrated that exposure to 1,2-DCP altered the expression of proteins related with catalytic and carboxylic ester hydrolase activities, and that such effect was mediated by P450 enzymatic activity.

Sources of all-trans retinal oxidation independent of the aldehyde dehydrogenase 1A isozymes exist in the postnatal testis†

Despite the essential role of the active metabolite of vitamin A, all-trans retinoic acid (atRA) in spermatogenesis, the enzymes, and cellular populations responsible for its synthesis in the postnatal testis remain largely unknown. The aldehyde dehydrogenase 1A (ALDH1A) family of enzymes residing within Sertoli cells is responsible for the synthesis of atRA, driving the first round of spermatogenesis. Those studies also revealed that the atRA required to drive subsequent rounds of spermatogenesis is possibly derived from the ALDH1A enzymes residing within the meiotic and post-meiotic germ cells. Three ALDH1A isozymes (ALDH1A1, ALDH1A2, and ALDH1A3) are present in the testis. Although, ALDH1A1 is expressed in adult Sertoli cells and is suggested to contribute to the atRA required for the pre-meiotic transitions, ALDH1A2 is proposed to be the essential isomer involved in testicular atRA biosynthesis. In this report, we first examine the requirement for ALDH1A2 via the generation and analysis of a conditional Aldh1a2 germ cell knockout and a tamoxifen-induced Aldh1a2 knockout model. We then utilized the pan-ALDH1A inhibitor (WIN 18446) to test the collective contribution of the ALDH1A enzymes to atRA biosynthesis following the first round of spermatogenesis. Collectively, our data provide the first in vivo evidence demonstrating that animals severely deficient in ALDH1A2 postnatally proceed normally through spermatogenesis. Our studies with a pan-ALDH1A inhibitor (WIN 18446) also suggest that an alternative source of atRA biosynthesis independent of the ALDH1A enzymes becomes available to maintain atRA levels for several spermatogenic cycles following an initial atRA injection.

The Role of Lipoxidation in the Pathogenesis of Diabetic Retinopathy

Lipids can undergo modification as a result of interaction with reactive oxygen species (ROS). For example, lipid peroxidation results in the production of a wide variety of highly reactive aldehyde species which can drive a range of disease-relevant responses in cells and tissues. Such lipid aldehydes react with nucleophilic groups on macromolecules including phospholipids, nucleic acids, and proteins which, in turn, leads to the formation of reversible or irreversible adducts known as advanced lipoxidation end products (ALEs). In the setting of diabetes, lipid peroxidation and ALE formation has been implicated in the pathogenesis of macro- and microvascular complications. As the most common diabetic complication, retinopathy is one of the leading causes of vision loss and blindness worldwide. Herein, we discuss diabetic retinopathy (DR) as a disease entity and review the current knowledge and experimental data supporting a role for lipid peroxidation and ALE formation in the onset and development of this condition. Potential therapeutic approaches to prevent lipid peroxidation and lipoxidation reactions in the diabetic retina are also considered, including the use of antioxidants, lipid aldehyde scavenging agents and pharmacological and gene therapy approaches for boosting endogenous aldehyde detoxification systems. It is concluded that further research in this area could lead to new strategies to halt the progression of DR before irreversible retinal damage and sight-threatening complications occur.

Targeting liver aldehyde dehydrogenase-2 prevents heavy but not moderate alcohol drinking

Aldehyde dehydrogenase 2 (ALDH2), a key enzyme for detoxification the ethanol metabolite acetaldehyde, is recognized as a promising therapeutic target to treat alcohol use disorders (AUDs). Disulfiram, a potent ALDH2 inhibitor, is an approved drug for the treatment of AUD but has clinical limitations due to its side effects. This study aims to elucidate the relative contribution of different organs in acetaldehyde clearance through ALDH2 by using global- (Aldh2 ^-/-) and tissue-specific Aldh2-deficient mice, and to examine whether liver-specific ALDH2 inhibition can prevent alcohol-seeking behavior. Aldh2 ^-/- mice showed markedly higher acetaldehyde concentrations than wild-type (WT) mice after acute ethanol gavage. Acetaldehyde levels in hepatocyte-specific Aldh2 knockout (Aldh2 ^Hep-/-) mice were significantly higher than those in WT mice post gavage, but did not reach the levels observed in Aldh2 ^-/- mice. Energy expenditure and motility were dramatically dampened in Aldh2 ^-/- mice, but moderately decreased in Aldh2 ^Hep-/- mice compared to controls. In the 2-bottle paradigm and the drinking-in-the-dark model, Aldh2 ^-/- mice drank negligible volumes from ethanol-containing bottles, whereas Aldh2 ^Hep-/- mice showed reduced alcohol preference at high but not low alcohol concentrations. Glial cell- or neuron-specific Aldh2 deficiency did not affect voluntary alcohol consumption. Finally, specific liver Aldh2 knockdown via injection of shAldh2 markedly decreased alcohol preference. In conclusion, although the liver is the major organ responsible for acetaldehyde metabolism, a cumulative effect of ALDH2 from other organs likely also contributes to systemic acetaldehyde clearance. Liver-targeted ALDH2 inhibition can decrease heavy drinking without affecting moderate drinking, providing molecular basis for hepatic ALDH2 targeting/editing for the treatment of AUD.

Silencing transcription factor FOXM1 represses proliferation, migration, and invasion while inducing apoptosis of liver cancer stem cells by regulating the expression of ALDH2

OBJECTIVE

This study is performed to explore the role of transcription factor FOXM1 in promoting the self-renewal and proliferation of liver cancer stem cells (LCSCs) by regulating the expression of acetaldehyde dehydrogenase-2 (ALDH2).

METHODS

CD133⁺ CD24⁺ LCSCs were sorted and identified. A series of experiments were carried out to determine the proliferation, colony formation rate, migration, invasion, and apoptosis of LCSCs after interfering with FOXM1. Proliferation-, epithelial-mesenchymal transition (EMT)-, apoptosis-, and stemness-related factors were then detected by western blot analysis. Tumor xenograft in nude mice was used to figure out the role of FOXM1 in tumorigenesis in vivo by regulating ALDH2 expression. Luciferase activity assay was conducted to determine whether FOXM1 could target ALDH2 promoter region and thereby affecting ALDH2 expression.

RESULTS

The sorted CD133⁺ CD24⁺ Huh-7 cells had the characteristic of stem cells. FOXM1 was highly expressed in CD133⁺ CD24⁺ Huh-7 cells. Silencing FOXM1 inhibited the proliferation and colony formation of LCSCs and decreased the expression of proliferating cell nuclear antigen and Ki-67 protein; inhibited the migration, invasion, and EMT of LCSCs while promoting the apoptosis of LCSCs, as well as promoted the expression of Bax and cleaved-caspase-3, and inhibited the expression of Bcl-2. Silencing FOXM1 inhibited the expression of Nanog, Oct4, and Sox2 in LCSCs by decreasing the expression of ALDH2. in vivo experiment, silencing FOXM1 suppressed tumorigenesis of LCSCs by decreasing the expression of ALDH2.

CONCLUSION

Our study provides evidence that silencing FOXM1 inhibits stemness of LCSCs by decreasing the expression of ALDH2, and represses the proliferation, migration, invasion, and tumorigenesis while inducing the apoptosis of LCSCs.

The Basis for Strain-Dependent Rat Aldehyde Dehydrogenase 1A7 (ALDH1A7) Gene Expression

Aldehyde hydrogenases (ALDHs) belong to a large gene family involved in oxidation of both endogenous and exogenous compounds in mammalian tissues. Among ALDHs, the rat ALDH1A7 gene displays a curious strain dependence in phenobarbital (PB)-induced hepatic expression: the responsive RR strains exhibit induction of both ALDH1A7 and CYP2B mRNAs and activities, whereas the nonresponsive rr strains show induction of CYP2B only. Here, we investigated the responsiveness of ALDH1A1, ALDH1A7, CYP2B1, and CYP3A23 genes to prototypical P450 inducers, expression of nuclear receptors CAR and pregnane X receptor, and structure of the ALDH1A7 promoter in both rat strains. ALDH1A7 mRNA, associated protein and activity were strongly induced by PB and modestly induced by pregnenolone 16α-carbonitrile in the RR strain but negligibly in the rr strain, whereas induction of ALDH1A1 and P450 mRNAs was similar between the strains. Reporter gene and chromatin immunoprecipitation assays indicated that the loss of ALDH1A7 inducibility in the rr strain is profoundly linked with a 16-base pair deletion in the proximal promoter and inability of the upstream DNA sequences to recruit constitutive androstane receptor-retinoid X receptor heterodimers. SIGNIFICANCE STATEMENT: Genetic variation in rat ALDH1A7 promoter sequences underlie the large strain-dependent differences in expression and inducibility by phenobarbital of the aldehyde dehydrogenase activity. This finding has implications for the design and interpretation of pharmacological and toxicological studies on the effects and disposition of aldehydes.

Modulating NRF2 in Disease: Timing Is Everything

The transcription factor nuclear factor erythroid 2 (NF-E2)-related factor 2 (NRF2) is a central regulator of redox, metabolic, and protein homeostasis that intersects with many other signaling cascades. Although the understanding of the complex nature of NRF2 signaling continues to grow, there is only one therapeutic targeting NRF2 for clinical use, dimethyl fumarate, used for the treatment of multiple sclerosis. The discovery of new therapies is confounded by the fact that NRF2 levels vary significantly depending on physiological and pathological context. Thus, properly timed and targeted manipulation of the NRF2 pathway is critical in creating effective therapeutic regimens. In this review, we summarize the regulation and downstream targets of NRF2. Furthermore, we discuss the role of NRF2 in cancer, neurodegeneration, and diabetes as well as cardiovascular, kidney, and liver disease, with a special emphasis on NRF2-based therapeutics, including those that have made it into clinical trials.

ALDH1A3 Is the Key Isoform That Contributes to Aldehyde Dehydrogenase Activity and Affects in Vitro Proliferation in Cardiac Atrial Appendage Progenitor Cells

High aldehyde dehydrogenase (ALDH^hi) activity has been reported in normal and cancer stem cells. We and others have shown previously that human ALDH^hi cardiac atrial appendage cells are enriched with stem/progenitor cells. The role of ALDH in these cells is poorly understood but it may come down to the specific ALDH isoform(s) expressed. This study aimed to compare ALDH^hi and ALDH^lo atrial cells and to identify the isoform(s) that contribute to ALDH activity, and their functional role.

Methods and Results: Cells were isolated from atrial appendage specimens from patients with ischemic and/or valvular heart disease undergoing heart surgery. ALDH^hi activity assessed with the Aldefluor reagent coincided with primitive surface marker expression (CD34⁺). Depending on their ALDH activity, RT-PCR analysis of ALDH^hi and ALDH^lo cells demonstrated a differential pattern of pluripotency genes (Oct 4, Nanog) and genes for more established cardiac lineages (Nkx2.5, Tbx5, Mef2c, GATA4). ALDH^hi cells, but not ALDH^lo cells, formed clones and were culture-expanded. When cultured under cardiac differentiation conditions, ALDH^hi cells gave rise to a higher number of cardiomyocytes compared with ALDH^lo cells. Among 19 ALDH isoforms known in human, ALDH1A3 was most highly expressed in ALDH^hi atrial cells. Knocking down ALDH1A3, but not ALDH1A1, ALDH1A2, ALDH2, ALDH4A1, or ALDH8A1 using siRNA decreased ALDH activity and cell proliferation in ALDH^hi cells. Conversely, overexpressing ALDH1A3 with a retroviral vector increased proliferation in ALDH^lo cells.

Conclusions: ALDH1A3 is the key isoform responsible for ALDH activity in ALDH^hi atrial appendage cells, which have a propensity to differentiate into cardiomyocytes. ALDH1A3 affects in vitro proliferation of these cells.

NRF2 and the Hallmarks of Cancer

The transcription factor NRF2 is the master regulator of the cellular antioxidant response. Though recognized originally as a target of chemopreventive compounds that help prevent cancer and other maladies, accumulating evidence has established the NRF2 pathway as a driver of cancer progression, metastasis, and resistance to therapy. Recent studies have identified new functions for NRF2 in the regulation of metabolism and other essential cellular functions, establishing NRF2 as a truly pleiotropic transcription factor. In this review, we explore the roles of NRF2 in the hallmarks of cancer, indicating both tumor suppressive and tumor-promoting effects.

Aldehyde dehydrogenase 2 in the spotlight: The link between mitochondria and neurodegeneration

Growing body of evidence suggests that mitochondrial dysfunctions and resultant oxidative stress are likely responsible for many neurodegenerative diseases, including Alzheimer's disease (AD) and Parkinson's disease (PD). Aldehyde dehydrogenase (ALDH) superfamily plays a crucial role in several biological processes including development and detoxification pathways in the organism. In particular, ALDH2 is crucial in the oxidative metabolism of toxic aldehydes in the brain, such as catecholaminergic metabolites (DOPAL and DOPEGAL) and the principal product of lipid peroxidation process 4-HNE. This review aims to deepen the current knowledge regarding to ALDH2 function and its relation with brain-damaging processes that increase the risk to develop neurodegenerative disorders. We focused on relevant literature of what is currently known at molecular and cellular levels in experimental models of these pathologies. The understanding of ALDH2 contributions could be a potential target in new therapeutic approaches for PD and AD due to its crucial role in mitochondrial normal function maintenance that protects against neurotoxicity.

Pregnane X-receptor promotes stem cell-mediated colon cancer relapse

Colorectal cancer lethality usually results from post-treatment relapse in the majority of stage II-IV patients, due to the enhanced resistance of Cancer Stem Cells (CSCs). Here, we show that the nuclear receptor Pregnane X Receptor (PXR, NR1I2), behaves as a key driver of CSC-mediated tumor recurrence. First, PXR is specifically expressed in CSCs, where it drives the expression of genes involved in self-renewal and chemoresistance. Clinically, high levels of PXR correlate with poor recurrence-free survival in a cohort of >200 stage II/III colorectal cancer patients treated with chemotherapy, for whom finding biomarkers of treatment outcome is an urgent clinical need. shRNA silencing of PXR increased the chemo-sensitivity of human colon CSCs, reduced their self-renewal and tumor-initiating potential, and drastically delayed tumor recurrence in mice following chemotherapy. This study uncovers PXR as a key factor for CSC self-renewal and chemoresistance and targeting PXR thus represents a promising strategy to minimize colorectal cancer relapse by selectively sensitizing CSCs to chemotherapy.

Age-dependent Protein Abundance of Cytosolic Alcohol and Aldehyde Dehydrogenases in Human Liver

Hepatic cytosolic alcohol and aldehyde dehydrogenases (ADHs and ALDHs) catalyze the biotransformation of xenobiotics (e.g., cyclophosphamide and ethanol) and vitamin A. Because age-dependent hepatic abundance of these proteins is unknown, we quantified protein expression of ADHs and ALDH1A1 in a large cohort of pediatric and adult human livers by liquid chromatography coupled with tandem mass spectrometry proteomics. Purified proteins were used as calibrators. Two to three surrogate peptides per protein were quantified in trypsin digests of liver cytosolic samples and calibrator proteins under optimal conditions of reproducibility. Neonatal levels of ADH1A, ADH1B, ADH1C, and ALDH1A1 were 3-, 8-, 146-, and 3-fold lower than the adult levels, respectively. For all proteins, the abundance steeply increased during the first year of life, which mostly reached adult levels during early childhood (age between 1 and 6 years). Only for ADH1A protein abundance in adults (age > 18 year) was ∼40% lower relative to the early childhood group. Abundances of ADHs and ALDH1A1 were not associated with sex in samples with age > 1 year compared with males. Known single nucleotide polymorphisms had no effect on the protein levels of these proteins. Quantification of ADHs and ALDH1A1 protein levels could be useful in predicting disposition and response of substrates of these enzymes in younger children.

ALDH1A3 is epigenetically regulated during melanocyte transformation and is a target for melanoma treatment

Despite the promising targeted and immune-based interventions in melanoma treatment, long-lasting responses are limited. Melanoma cells present an aberrant redox state that leads to the production of toxic aldehydes that must be converted into less reactive molecules. Targeting the detoxification machinery constitutes a novel therapeutic avenue for melanoma. Here, using 56 cell lines representing nine different tumor types, we demonstrate that melanoma cells exhibit a strong correlation between reactive oxygen species amounts and aldehyde dehydrogenase 1 (ALDH1) activity. We found that ALDH1A3 is upregulated by epigenetic mechanisms in melanoma cells compared with normal melanocytes. Furthermore, it is highly expressed in a large percentage of human nevi and melanomas during melanocyte transformation, which is consistent with the data from the TCGA, CCLE and protein atlas databases. Melanoma treatment with the novel irreversible isoform-specific ALDH1 inhibitor [4-dimethylamino-4-methyl-pent-2-ynthioic acid-S methylester] di-methyl-ampal-thio-ester (DIMATE) or depletion of ALDH1A1 and/or ALDH1A3, promoted the accumulation of apoptogenic aldehydes leading to apoptosis and tumor growth inhibition in immunocompetent, immunosuppressed and patient-derived xenograft mouse models. Interestingly, DIMATE also targeted the slow cycling label-retaining tumor cell population containing the tumorigenic and chemoresistant cells. Our findings suggest that aldehyde detoxification is relevant metabolic mechanism in melanoma cells, which can be used as a novel approach for melanoma treatment.

Aldehyde dehydrogenase 2*2 knock-in mice show increased reactive oxygen species production in response to cisplatin treatment

Background

The aldehyde dehydrogenase (ALDH) enzyme family metabolizes and detoxifies both exogenous and endogenous aldehydes. Since chemotherapeutic agents, such as cisplatin, generate cytotoxic aldehydes and oxidative stress, and chemoresistant cancer cells express high levels of ALDH enzymes, we hypothesized that different ALDH expression within cells may show different chemosensitivity. ALDH2 has the lowest Km for acetaldehyde among ALDH isozymes and detoxifies acetaldehydes in addition to other reactive aldehydes, such as 4-hydroxy-nonenal, malondialdehyde and acrolein produced from lipid peroxidation by reactive oxygen species (ROS). Thus, cells with an ALDH2 variant may sensitize them to these ROS-inducing chemotherapy drugs.

Methods

Here, we used wild type C57BL/6 mice and ALDH2*2 knock-in mutant mice and compared the basal level of ROS in different tissues. Then, we treated the mice with cisplatin, isolated cells from organs and fractionated them into lysates containing mitochondrial and cytosolic fractions, treated with cisplatin again in vitro, and compared the level of ROS generated.

Results

We show that overall ROS production increases with cisplatin treatment in cells with ALDH2 mutation. The treatment of cisplatin in the wild type mice did not change the level of ROS compared to PBS treated controls. In contrast, ALDH2*2 knock-in mutant mice showed a significantly increased level of ROS compared to wild type mice in tongue, lung, kidney and brain tissues without any treatment. ALDH2*2 mutant mice showed 20% of the ALDH2 activity in the kidney compared to wild type mice. Treatment of ALDH2*2 mutant mice with cisplatin showed increased ROS levels in the mitochondrial fraction of kidney. In the cytosolic fraction, treatment of mutant mice with cisplatin increased ROS levels in lung and brain compared to PBS treated controls. Furthermore, ALDH2*2 mutant mice treated with cisplatin showed increased cytotoxicity in the kidney cells compared to PBS treated mutant controls.

Conclusions

These data indicate that deficiency in ALDH2 activity may contribute to increased cisplatin sensitivity and cytotoxicity by producing more ROS by the treatment. Based on these data, the amount of cisplatin used in patients may need to be adjusted based on their ALDH2 variant profile.

Effects of long-term ethanol consumption and Aldh1b1 depletion on intestinal tumourigenesis in mice

Ethanol and its metabolite acetaldehyde have been classified as carcinogens for the upper aerodigestive tract, liver, breast, and colorectum. Whereas mechanisms related to oxidative stress and Cyp2e1 induction seem to prevail in the liver, and acetaldehyde has been proposed to play a crucial role in the upper aerodigestive tract, pathological mechanisms in the colorectum have not yet been clarified. Moreover, all evidence for a pro-carcinogenic role of ethanol in colorectal cancer is derived from correlations observed in epidemiological studies or from rodent studies with additional carcinogen application or tumour suppressor gene inactivation. In the current study, wild-type mice and mice with depletion of aldehyde dehydrogenase 1b1 (Aldh1b1), an enzyme which has been proposed to play an important role in acetaldehyde detoxification in the intestines, received ethanol in drinking water for 1 year. Long-term ethanol consumption led to intestinal tumour development in wild-type and Aldh1b1-depleted mice, but no intestinal tumours were observed in water-treated controls. Moreover, a significant increase in DNA damage was detected in the large intestinal epithelium of ethanol-treated mice of both genotypes compared with the respective water-treated groups, along with increased proliferation of the small and large intestinal epithelium. Aldh1b1 depletion led to increased plasma acetaldehyde levels in ethanol-treated mice, to a significant aggravation of ethanol-induced intestinal hyperproliferation, and to more advanced features of intestinal tumours, but it did not affect intestinal tumour incidence. These data indicate that ethanol consumption can initiate intestinal tumourigenesis without any additional carcinogen treatment or tumour suppressor gene inactivation, and we provide evidence for a role of Aldh1b1 in protection of the intestines from ethanol-induced damage, as well as for both carcinogenic and tumour-promoting functions of acetaldehyde, including increased progression of ethanol-induced tumours. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Transcriptomic analysis and plasma metabolomics in Aldh16a1-null mice reveals a potential role of ALDH16A1 in renal function

ALDH16A1 is a novel member of the ALDH superfamily that is enzymatically-inactive and highly expressed in the kidney. Recent studies identified an association between a rare missense single nucleotide variant (SNV) in the ALDH16A1 gene and elevated serum uric acid levels and gout. The present study explores the mechanisms by which ALDH16A1 influences uric acid homeostasis in the kidney. We generated and validated a mouse line with global disruption of the Aldh16a1 gene through gene targeting and performed RNA-seq analyses in the kidney of wild-type (WT) and Aldh16a1 knockout (KO) mice, along with plasma metabolomics. We found that ALDH16A1 is expressed in proximal and distal convoluted tubule cells in the cortex of the kidney and in zone 3 hepatocytes. RNA-seq and gene ontology enrichment analyses showed that cellular lipid and lipid metabolic processes are up-regulated. Three transporters localized in the apical membrane of the proximal convoluted tubule of the kidney known to influence urate/uric acid homeostasis were found to be up-regulated (Abcc4, Slc16a9) or down-regulated (Slc17a3). An initial metabolomics analysis in plasma revealed an altered lipid profile in KO mice that is in agreement with our RNA-seq analysis. This is the first study demonstrating a functional role of ALDH16A1 in the kidney.

RNA Sequencing Reveals Age and Species Differences of Constitutive Androstane Receptor-Targeted Drug-Processing Genes in the Liver

The constitutive androstane receptor (CAR/Nr1i3) is an important xenobiotic-sensing nuclear receptor that is highly expressed in the liver and is well known to have species differences. During development, age-specific activation of CAR may lead to modified pharmacokinetics and toxicokinetics of drugs and environmental chemicals, leading to higher risks for adverse drug reactions in newborns and children. The goal of this study was to systematically investigate the age- and species-specific regulation of various drug-processing genes (DPGs) after neonatal or adult CAR activation in the livers of wild-type, CAR-null, and humanized CAR transgenic mice. At either 5 or 60 days of age, the three genotypes of mice were administered a species-appropriate CAR ligand or vehicle once daily for 4 days (i.p.). The majority of DPGs were differentially regulated by age and/or CAR activation. Thirty-six DPGs were commonly upregulated by CAR activation regardless of age or species of CAR. Although the cumulative mRNAs of uptake transporters were not readily altered by CAR, the cumulative phase I and phase II enzymes as well as efflux transporters were all increased after CAR activation in both species. In general, mouse CAR activation produced comparable or even greater fold increases of many DPGs in newborns than in adults; conversely, humanized CAR activation produced weaker induction in newborns than in adults. Western blotting and enzyme activity assays confirmed the age and species specificities of selected CAR-targeted DPGs. In conclusion, this study systematically compared the effect of age and species of CAR proteins on the regulation of DPGs in the liver and demonstrated that the regulation of xenobiotic biotransformation by CAR is profoundly modified by age and species.

Roles of Retinoic Acid in Germ Cell Differentiation

The modalities of gametogenesis differ markedly between sexes. Female are born with a definitive reserve of oocytes whose size is crucial to ensure fertility. Male fertility, in contrast, relies on a tightly regulated balance between germ cell self-renewal and differentiation, which operates throughout life, according to recurring spatial and temporal patterns. Genetic and pharmacological studies conducted in the mouse and discussed in this review have revealed that all-trans retinoic acid and its nuclear receptors are major players of gametogenesis and are instrumental to fertility in both sexes.

Expression of retinoic acid-metabolizing enzymes, ALDH1A1, ALDH1A2, ALDH1A3, CYP26A1, CYP26B1 and CYP26C1 in canine testis during post-natal development

Mammalian spermatogenesis involves highly regulated temporal and spatial dynamics, carefully controlled by several signalling processes. Retinoic acid (RA) signalling could have a critical role in spermatogenesis by promoting spermatogonia differentiation, adhesion of germ cells to Sertoli cells, and release of mature spermatids. An optimal testicular RA concentration is maintained by retinaldehyde dehydrogenases (ALDHs), which oxidize RA precursors to produce RA, whereas the CYP26 class of enzymes catabolizes (oxidize) RA into inactive metabolites. The objective was to elucidate gene expression of these RA-metabolizing enzymes (ALDH1A1, ALDH1A2, ALDH1A3, CYP26A1, CYP26B1 and CYP26C1) and their protein presence in testes of young, peripubertal and adult dogs. Genes encoding RA-synthesizing isozymes ALDH1A1, ALDH1A2 and ALDH1A3 and RA-catabolizing isomers CYP26A1, CYP26B1 and CYP26C1 were expressed in testis at varying levels during testicular development from birth to adulthood in dogs. Based on detailed analyses of mRNA expression patterns, ALDH1A2 was regarded as a primary RA-synthesizing enzyme and CYP26B1 as a critical RA-hydrolysing enzyme; presumably, these genes have vital roles in maintaining RA homeostasis, which is imperative to spermatogenesis and other testicular functions in post-natal canine testis.

RNA-Seq reveals common and unique PXR- and CAR-target gene signatures in the mouse liver transcriptome

The pregnane X receptor (PXR) and constitutive androstane receptor (CAR) are well-known xenobiotic-sensing nuclear receptors with overlapping functions. However, there lacks a quantitative characterization to distinguish between the PXR and CAR target genes and signaling pathways in the liver. The present study performed a transcriptomic comparison of the PXR- and CAR-targets using RNA-Seq in livers of adult wild-type mice that were treated with the prototypical PXR ligand PCN (200mg/kg, i.p. once daily for 4days in corn oil) or the prototypical CAR ligand TCPOBOP (3mg/kg, i.p., once daily for 4days in corn oil). At the given doses, TCPOBOP differentially regulated many more genes (2125) than PCN (212), and 147 of the same genes were differentially regulated by both chemicals. As expected, the top pathways differentially regulated by both PCN and TCPOBOP were involved in xenobiotic metabolism, and they also up-regulated genes involved in retinoid metabolism, but down-regulated genes involved in inflammation and iron homeostasis. Regarding unique pathways, PXR activation appeared to overlap with the aryl hydrocarbon receptor signaling, whereas CAR activation appeared to overlap with the farnesoid X receptor signaling, acute-phase response, and mitochondrial dysfunction. The mRNAs of differentially regulated drug-processing genes (DPGs) partitioned into three patterns, namely TCPOBOP-induced, PCN-induced, as well as TCPOBOP-suppressed gene clusters. The cumulative mRNAs of the differentially regulated DPGs, phase-I and -II enzymes, as well as efflux transporters were all up-regulated by both PCN and TCPOBOPOP, whereas the cumulative mRNAs of the uptake transporters were down-regulated only by TCPOBOP. The absolute mRNA abundance in control and receptor-activated conditions was examined in each DPG category to predict the contribution of specific DPG genes in the PXR/CAR-mediated pharmacokinetic responses. The preferable differential regulation by TCPOBOP in the entire hepatic transcriptome correlated with a marked change in the expression of many DNA and histone epigenetic modifiers. In conclusion, the present study has revealed known and novel, as well as common and unique targets of PXR and CAR in mouse liver following pharmacological activation using their prototypical ligands. Results from this study will further support the role of these receptors in regulating the homeostasis of xenobiotic and intermediary metabolism in the liver, and aid in distinguishing between PXR and CAR signaling at various physiological and pathophysiological conditions. This article is part of a Special Issue entitled: Xenobiotic nuclear receptors: New Tricks for An Old Dog, edited by Dr. Wen Xie.

RNA Sequencing Quantification of Xenobiotic-Processing Genes in Various Sections of the Intestine in Comparison to the Liver of Male Mice

Previous reports on tissue distribution of xenobiotic-processing genes (XPGs) have limitations, because many non-cytochrome P450 phase I enzymes have not been investigated, and one cannot compare the real mRNA abundance of multiple XPGs using conventional quantification methods. Therefore, this study aimed to quantify and compare the mRNA abundance of all major XPGs in the liver and intestine using RNA sequencing. The mRNA profiles of 304 XPGs, including phase I, phase II enzymes, phase II cosubstrate synthetic enzymes, xenobiotic transporters, as well as xenobiotic-related transcription factors, were systematically examined in the liver and various sections of the intestine in adult male C57BL/6J mice. By two-way hierarchical clustering, over 80% of the XPGs had tissue-divergent expression, which partitioned into liver-predominant, small intestine-predominant, and large intestine-predominant patterns. Among the genes, 54% were expressed highest in the liver, 21% in the duodenum, 4% in the jejunum, 6% in the ileum, and 15% in the large intestine. The highest-expressed XPG in the liver was Mgst1; in the duodenum, Cyp3a11; in the jejunum and ileum, Ces2e; and in the large intestine, Cyp2c55. Interestingly, XPGs in the same family usually exhibited highly different tissue distribution patterns, and many XPGs were almost exclusively expressed in one tissue and minimally expressed in others. In conclusion, the present study is among the first and the most comprehensive investigations of the real mRNA abundance and tissue-divergent expression of all major XPGs in mouse liver and intestine, which aids in understanding the tissue-specific biotransformation and toxicity of drugs and other xenobiotics.

Red meat and colorectal cancer: Nrf2-dependent antioxidant response contributes to the resistance of preneoplastic colon cells to fecal water of hemoglobin- and beef-fed rats

Epidemiological studies have associated red meat intake with risk of colorectal cancer. Experimental studies explain this positive association by the oxidative properties of heme iron released in the colon. This latter is a potent catalyst for lipid peroxidation, resulting in the neoformation of deleterious aldehydes in the fecal water of heme-fed rats. The toxicity of fecal water of heme-fed rats was associated to such lipid peroxidation. This study demonstrated that fecal water of hemoglobin- and beef-fed rats preferentially induced apoptosis in mouse normal colon epithelial cells than in those carrying mutation on Apc (Adenomatous polyposis coli) gene, considered as preneoplastic. Highlighting the importance of lipid peroxidation and neoformation of secondary aldehydes like 4-hydroxy-2-nonenal (HNE), we optimized the depletion of carbonyl compounds in the fecal water which turned out to abolish the differential apoptosis in both cell lines. To explain the resistance of preneoplastic cells towards fecal water toxicity, we focused on Nrf2, known to be activated by aldehydes, including HNE. Fecal water activated Nrf2 in both cell lines, associated with the induction of Nrf2-target genes related to aldehydes detoxification. However, the antioxidant defense appeared to be higher in preneoplastic cells, favoring their survival, as evidenced by Nrf2 inactivation. Taken together, our results suggest that Nrf2-dependent antioxidant response was involved in the resistance of preneoplastic cells upon exposure to fecal water of hemoglobin- and beef-fed rats. This difference could explain the promoting effect of red meat and heme-enriched diet on colorectal cancer, by initiating positive selection of preneoplastic cells.

Global gene expression profiling using heterologous DNA microarrays to analyze alterations in the transcriptome of Mus spretus mice living in a heavily polluted environment

Microarray platforms are a good approach for assessing biological responses to pollution as they enable the simultaneous analyses of changes in the expression of thousands of genes. As an omic and non-targeted methodology, this technique is open to unforeseen responses under particular environmental conditions. In this study, we successfully apply a commercial oligonucleotide microarray containing Mus musculus whole-genome probes to compare and assess the biological effects of living in a heavily polluted settlement, the Domingo Rubio stream (DRS), at the Huelva Estuary (SW Spain), on inhabitant free-living Mus spretus mice. Our microarray results show that mice living in DRS suffer dramatic changes in gene and protein expression compared with reference specimens. DRS mice showed alteration in the oxidative status of hepatocytes, with activation of both the innate and the acquired immune responses and the induction of chronic inflammation, accompanied by metabolic alterations that imply the accumulation of lipids in the liver (hepatic steatosis). The identified deregulated genes may be useful as biomarkers of environmental pollution.

Germ Cell Commitment to Oogenic Versus Spermatogenic Pathway: The Role of Retinoic Acid

The core of the decision to commit to either oogenesis or spermatogenesis lies in the timing of meiotic entry. Primordial germ cells within the fetal ovary become committed to the female pathway prior to birth and enter meiosis during embryonic development. In the fetal testis, however, the germ cells are protected from this signal before birth and instead receive this trigger postnatally. There is a growing body of evidence to indicate that RA is the meiosis-inducing factor in both sexes, with the gender-specific timing of meiotic entry controlled via degradation of this molecule only within the fetal testis. This chapter will review our current understanding of how RA controls germ cell fate in both the embryonic ovary and postnatal testis, highlighting the key studies that have led to the hypothesis that RA can drive the commitment to meiosis in both sexes and discussing the current debate over whether RA truly is the meiosis-inducing factor in the fetal ovary.

Discovery of NCT-501, a Potent and Selective Theophylline-Based Inhibitor of Aldehyde Dehydrogenase 1A1 (ALDH1A1)

Aldehyde dehydrogenases (ALDHs) metabolize reactive aldehydes and possess important physiological and toxicological functions in areas such as CNS, metabolic disorders, and cancers. Increased ALDH (e.g., ALDH1A1) gene expression and catalytic activity are vital biomarkers in a number of malignancies and cancer stem cells, highlighting the need for the identification and development of small molecule ALDH inhibitors. A new series of theophylline-based analogs as potent ALDH1A1 inhibitors is described. The optimization of hits identified from a quantitative high throughput screening (qHTS) campaign led to analogs with improved potency and early ADME properties. This chemotype exhibits highly selective inhibition against ALDH1A1 over ALDH3A1, ALDH1B1, and ALDH2 isozymes as well as other dehydrogenases such as HPGD and HSD17β4. Moreover, the pharmacokinetic evaluation of selected analog 64 (NCT-501) is also highlighted.

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.

Expression of biotransformation and oxidative stress genes in the giant freshwater prawn Macrobrachium rosenbergii exposed to chlordecone

Chlordecone is a persistent organochlorine pesticide widely used between 1972 and 1993 in the French West Indies to control the root borer in banana fields. Chlordecone use resulted in long-term pollution of soils, contamination of waters, of aquatic organisms, and of fields. Chlordecone is known to be neurotoxic, to increase prostate cancer, and to have negative effects on cognitive and motor development during infancy. In Guadeloupe, most of the freshwater species living in contaminated rivers exceed the French legal limit of 20 μg·kg(-1) wet weight. In the present study, we chose a transcriptomic approach to study the cellular effects of chlordecone in the giant freshwater prawn Macrobrachium rosenbergii, an important economical species in Guadeloupe. Quantitative PCR revealed an induction of genes involved in defense mechanism against oxidative stress (catalase and selenium-dependent glutathione peroxidase) in prawns exposed to low environmental concentrations of chlordecone after 12 and 24 h of exposure. In prawns reared in a contaminated farm, transcription of genes involved in the biotransformation process (cytochrome P450 and glutathione-S-transferase (GST)) were induced after 8 days of exposure. Our results provide information on the mechanims of defense induced by chlordecone in aquatic crustacean species. This gene expression study of selected genes should be further strengthened by proteomic analyses and enzymatic activity assays to confirm the response of these biomarkers of stress in crustaceans and to give new insights into the mechanism of toxicity by chlordecone.

Developmental Regulation of Drug-Processing Genes in Livers of Germ-Free Mice

Very little is known about the effect of gut microbiota on the ontogeny of drug-processing genes (DPGs) in liver. In this study, livers were harvested from conventional (CV) and germ-free (GF) male and female mice from 1 to 90 days of age. RNA-Seq in livers of 90-day-old male mice showed that xenobiotic metabolism was the most downregulated pathway within the mRNA transcriptome in absence of intestinal bacteria. In male livers, the mRNAs of 67 critical DPGs partitioned into 4 developmental patterns (real-time-quantitative polymerase chain reaction): Pattern-1 gradually increased to adult levels in livers of CV mice and were downregulated in livers of GF mice, as exemplified by the major drug-metabolizing enzymes cytochrome 3a (Cyp3a) family, which are prototypical pregnane X receptor (PXR)-target genes. Genes in Pattern-2 include Cyp1a2 (aryl hydrocarbon receptor-target gene), Cyp2c family, and Cyp2e1, which were all upregulated mainly at 90 days of age; as well as the peroxisome proliferator-activated receptor α (PPARα)-target genes Cyp4a family and Aldh3a2, which were upregulated not only in 90-days adult age, but also between neonatal and adolescent ages (from 1 to 30 days of age). Genes in Pattern-3 were enriched predominantly in livers of 15-day-old mice, among which the sterol-efflux transporter dimers Abcg5/Abcg8 were downregulated in GF mice. Genes in Pattern-4 were neonatal-enriched, among which the transporter Octn1 mRNA tended to be lower in GF mice at younger ages but higher in adult GF mice as compared with age-matched CV mice. Protein assays confirmed the downregulation of the PXR-target gene Cyp3a protein (Western-blot and liquid chromatography tandem mass spectroscopy), and decreased Cyp3a enzyme activities in male GF livers. Increased microsomal-Cyp4a proteins and nuclear-PPARα were also observed in male GF livers. Interestingly, in contrast to male livers, the mRNAs of Cyp2c or Cyp4a were not readily upregulated in female GF livers approaching adult age, suggesting the maturation of female-specific hormones interferes with the interactions between intestinal microbiota and DPG ontogeny. In conclusion, intestinal microbiota markedly impacts the ontogeny of many hepatic DPGs in a gender-specific manner.

Mono(2-ethylhexyl) phthalate accelerates early folliculogenesis and inhibits steroidogenesis in cultured mouse whole ovaries and antral follicles

Humans are ubiquitously exposed to di(2-ethylhexyl) phthalate (DEHP), which is an environmental toxicant present in common consumer products. DEHP potentially targets the ovary through its metabolite mono(2-ethylhexyl) phthalate (MEHP). However, the direct effects of MEHP on ovarian folliculogenesis and steroidogenesis, two processes essential for reproductive and nonreproductive health, are unknown. The present study tested the hypotheses that MEHP directly accelerates early folliculogenesis via overactivation of phosphatidylinositol 3-kinase (PI3K) signaling, a pathway that regulates primordial follicle quiescence and activation, and inhibits the synthesis of steroid hormones by decreasing steroidogenic enzyme levels. Neonatal ovaries from CD-1 mice were cultured for 6 days with vehicle control, DEHP, or MEHP (0.2-20 μg/ml) to assess the direct effects on folliculogenesis and PI3K signaling. Further, antral follicles from adult CD-1 mice were cultured with vehicle control or MEHP (0.1-10 μg/ml) for 24-96 h to establish the temporal effects of MEHP on steroid hormones and steroidogenic enzymes. In the neonatal ovaries, MEHP, but not DEHP, decreased phosphatase and tensin homolog levels and increased phosphorylated protein kinase B levels, leading to a decrease in the percentage of germ cells and an increase in the percentage of primary follicles. In the antral follicles, MEHP decreased the mRNA levels of 17alpha-hydroxylase-17,20-desmolase, 17beta-hydroxysteroid dehydrogenase, and aromatase leading to a decrease in testosterone, estrone, and estradiol levels. Collectively, MEHP mediates the effect of DEHP on accelerated folliculogenesis via overactivating PI3K signaling and inhibits steroidogenesis by decreasing steroidogenic enzyme levels.

Identification of trans,trans-2,4-decadienal metabolites in mouse and human cells using liquid chromatography-mass spectrometry

trans,trans-2,4-Decadienal (tt-DDE), a lipid peroxidation product of linolieic acid, is the most abundant aldehyde identified in cooking oil fumes and is readily detectable in food products as well as in restaurant emissions. Previously, we have reported the toxicological effects of tt-DDE in vitro and in vivo. However, the metabolic pathways of tt-DDE in vivo remain unclear. In our present study, we combined liquid chromatography-mass spectrometry with triple quadrupole and time-of-flight to identify tt-DDE metabolites in the urine of mice orally administered tt-DDE. We identified two tt-DDE metabolites, 2,4-decadienoic acid and cysteine-conjugated 2,4-decadien-1-ol, in the urine of mice gavaged with tt-DDE and in human hepatoma cell cultures. The structure of 2,4-decadienoic acid was confirmed upon comparison of its tandem mass spectrometry (MS/MS) spectrum and retention time with those of synthetic standards. The moieties of cysteine and alcohol on cysteine-conjugated 2,4-decadien-1-ol were validated by treating cell cultures with stable-isotope-labeled cysteine and 4-methylpyrazole, an alcohol dehydrogenase inhibitor. The MS/MS spectra of a cysteine standard and ionized cysteine detached from cysteine-conjugated 2,4-decadien-1-ol were identical. Two metabolic pathways for the biotransformation of tt-DDE in vivo are proposed: (i) the oxidation of tt-DDE to the corresponding carboxylic acid, 2,4-decadienoic acid, in liver cells and (ii) glutathione (GHS) conjugation, GSH breakdown, and aldehyde reduction, which generate cysteine-conjugated 2,4-decadien-1-ol in both liver and lung cells. In conclusion, this platform can be used to identify tt-DDE metabolites, and cysteine-conjugated 2,4-decadien-1-ol can serve as a biomarker for assessing exposure to tt-DDE.