Identification of human liver aldehyde dehydrogenases that catalyze the oxidation of aldophosphamide and retinaldehyde

ALDEFLUOR activity, ALDH isoforms, and their clinical significance in cancers

High aldehyde dehydrogenase (ALDH) activity is a metabolic feature of adult stem cells and various cancer stem cells (CSCs). The ALDEFLUOR system is currently the most commonly used method for evaluating ALDH enzyme activity in viable cells. This system is applied extensively in the isolation of normal stem cells and CSCs from heterogeneous cell populations. For many years, ALDH1A1 has been considered the most important subtype among the 19 ALDH family members in determining ALDEFLUOR activity. However, in recent years, studies of many types of normal and tumour tissues have demonstrated that other ALDH subtypes can also significantly influence ALDEFLUOR activity. In this article, we briefly review the relationships between various members of the ALDH family and ALDEFLUOR activity. The clinical significance of these ALDH isoforms in different cancers and possible directions for future studies are also summarised.

Association between CYP2B6 genetic variability and cyclophosphamide therapy in pediatric patients with neuroblastoma

Cyclophosphamide, an oxazaphosphorine prodrug is frequently used in treatment of neuroblastoma, which is one of the most prevalent solid organ malignancies in infants and young children. Cytochrome P450 2B6 (CYP2B6) is the major catalyst and CYP2C19 is the minor enzyme in bioactivation and inactivation pathways of cyclophosphamide. CYP-mediated metabolism may contribute to the variable pharmacokinetics of cyclophosphamide and its toxic byproducts leading to insufficient response to the therapy and development of clinically significant side effects. The aim of the study was to reveal the contribution of pharmacogenetic variability in CYP2B6 and CYP2C19 to the treatment efficacy and cyclophosphamide-induced side effects in pediatric neuroblastoma patients under cyclophosphamide therapy (N = 50). Cyclophosphamide-induced hematologic toxicities were pivotal in all patients, whereas only moderate hepatorenal toxicity was developed. The patients' CYP2B6 metabolizer phenotypes were associated with the occurrence of lymphopenia, thrombocytopenia, and monocytopenia as well as of liver injury, but not with kidney or urinary bladder (hemorrhagic cystitis) toxicities. Furthermore, the patients' age (< 1.5 years, P = 0.03) and female gender (P ≤ 0.02), but not CYP2B6 or CYP2C19 metabolizer phenotypes appeared as significant prognostic factors in treatment outcomes. Our results may contribute to a better understanding of the impact of CYP2B6 variability on cyclophosphamide-induced side effects.

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.

Differentially expressed genes reflect disease-induced rather than disease-causing changes in the transcriptome

Comparing transcript levels between healthy and diseased individuals allows the identification of differentially expressed genes, which may be causes, consequences or mere correlates of the disease under scrutiny. We propose a method to decompose the observational correlation between gene expression and phenotypes driven by confounders, forward- and reverse causal effects. The bi-directional causal effects between gene expression and complex traits are obtained by Mendelian Randomization integrating summary-level data from GWAS and whole-blood eQTLs. Applying this approach to complex traits reveals that forward effects have negligible contribution. For example, BMI- and triglycerides-gene expression correlation coefficients robustly correlate with trait-to-expression causal effects (rBMI = 0.11, PBMI = 2.0 × 10-51 and rTG = 0.13, PTG = 1.1 × 10-68), but not detectably with expression-to-trait effects. Our results demonstrate that studies comparing the transcriptome of diseased and healthy subjects are more prone to reveal disease-induced gene expression changes rather than disease causing ones.

Molecular mechanisms of ethanol biotransformation: enzymes of oxidative and nonoxidative metabolic pathways in human

Ethanol, as a small-molecule organic compound exhibiting both hydrophilic and lipophilic properties, quickly pass through the biological barriers. Over 95% of absorbed ethanol undergoes biotransformation, the remaining amount is excreted unchanged, mainly with urine and exhaled air.The main route of ethyl alcohol metabolism is its oxidation to acetaldehyde, which is converted into acetic acid with the participation of cytosolic NAD⁺ - dependent alcohol (ADH) and aldehyde (ALDH) dehydrogenases. Oxidative biotransformation pathways of ethanol also include reactions catalyzed by the microsomal ethanol oxidizing system (MEOS), peroxisomal catalase and aldehyde (AOX) and xanthine (XOR) oxidases. The resulting acetic acid can be activated to acetyl-CoA by the acetyl-CoA synthetase (ACS).It is also possible, to a much smaller extent, non-oxidative routes of ethanol biotransformation including its esterification with fatty acids by ethyl fatty acid synthase (FAEES), re-esterification of phospholipids, especially phosphatidylcholines, with phospholipase D (PLD), coupling with sulfuric acid by alcohol sulfotransferase (SULT) and with glucuronic acid using UDP-glucuronyl transferase (UGT, syn. UDPGT).The intestinal microbiome plays a significant role in the ethanol biotransformation and in the initiation and progression of liver diseases stimulated by ethanol and its metabolite - acetaldehyde, or by lipopolysaccharide and ROS.

Relationship between alcohol metabolism and chemotherapy-induced emetic events in breast cancer patients

BACKGROUND

Chemotherapy-induced nausea and vomiting (CINV) can negatively affect quality of life and treatment compliance in breast cancer patients. Habitual alcohol consumption reportedly shows an inverse correlation with CINV, though the underlying mechanism is unknown. Acetaldehyde dehydrogenase 2 (ALDH2), one of the two ALDH isozymes, is reportedly the major factor among several genetic polymorphisms possibly affecting alcohol metabolism. More than 40% of Japanese have ALDH2 mutations, while almost all Westerners have the wild type. We hypothesized that ALDH2 polymorphism status might relate to the metabolism of emetic chemotherapeutic drugs. Relationships among habitual alcohol consumption, ALDH2 polymorphisms, and CINV in Japanese breast cancer patients given adjuvant chemotherapy containing high-emetic drugs were, thus, investigated.

METHODS

We enrolled 81 women, between 20 and 55 years of age, who had been diagnosed with primary breast cancer and received (neo-) adjuvant chemotherapy at our institution. ALDH2 genotypes were analyzed employing the smart amplification process in peripheral blood samples.

RESULTS

The wild type (ALDH2*1/*1), heterozygote (ALDH2*1/*2), and mutant homozygote (ALDH2*2/*2) genotypes were found in 53, 44, and 3% of patients, respectively. Complete response, i.e., no vomiting without rescue anti-emetics, was more frequent in patients who habitually consumed alcohol than in those who did not (p = 0.036). This trend remained only in ALDH2 heterozygotes when patients were categorized according to ALDH2 genotype. Logistic regression analysis revealed alcohol intake to be an independent predictive factor for complete response (p = 0.013).

CONCLUSIONS

Our results revealed habitual alcohol intake to be related to a lower CINV incidence. The impact of alcohol intake on CINV in patients with ALDH2 polymorphisms merits further investigation.

ALDH1A3, a metabolic target for cancer diagnosis and therapy

Metabolism reprogramming has been linked with the initiation, metastasis, and recurrence of cancer. The aldehyde dehydrogenase (ALDH) family is the most important enzyme system for aldehyde metabolism. The human ALDH family is composed of 19 members. ALDH1A3 participates in various physiological processes in human cells by oxidizing all-trans-retinal to retinoic acid. ALDH1A3 expression is regulated by many factors, and it is associated with the development, progression, and prognosis of cancers. In addition, ALDH1A3 influences a diverse range of biological characteristics within cancer stem cells and can act as a marker for these cells. Thus, growing evidence indicates that ALDH1A3 has the potential to be used as a target for cancer diagnosis and therapy.

Posttransplantation cyclophosphamide for prevention of graft-versus-host disease after HLA-matched mobilized blood cell transplantation

The cumulative incidence of National Institutes of Health (NIH)-defined chronic graft-versus-host disease (GVHD) requiring systemic treatment is ∼35% at 1 year after transplantation of granulocyte colony-stimulating factor (G-CSF)-mobilized blood cells from HLA-matched related or unrelated donors. We hypothesized that high-dose cyclophosphamide given after G-CSF-mobilized blood cell transplantation would reduce the cumulative 1-year incidence of chronic GVHD to 15% or less. Forty-three patients with high-risk hematologic malignancies (median age, 43 years) were enrolled between December 2011 and September 2013. Twelve (28%) received grafts from related donors, and 31 (72%) received grafts from unrelated donors. Pretransplant conditioning consisted of fludarabine and targeted busulfan (n = 25) or total body irradiation (≥12 Gy; n = 18). Cyclophosphamide was given at 50 mg/kg per day on days 3 and 4 after transplantation, followed by cyclosporine starting on day 5. The cumulative 1-year incidence of NIH-defined chronic GVHD was 16% (95% confidence interval, 5-28%). The cumulative incidence estimates of grades 2-4 and 3-4 acute GVHD were 77% and 0%, respectively. At 2 years, the cumulative incidence estimates of nonrelapse mortality and recurrent malignancy were 14% and 17%, respectively, and overall survival was projected at 70%. Of the 42 patients followed for ≥1 year, 21 (50%) were relapse-free and alive without systemic immunosuppression at 1 year after transplantation. Thus, myeloablative pretransplant conditioning can be safely combined with high-dose cyclophosphamide after transplantation, and the risk of chronic GVHD associated with HLA-matched mobilized blood cell grafts can be substantially reduced. This trial was registered at www.clinicaltrials.gov as #NCT01427881.

Retinoic Acid Synthesis and Degradation

Retinoic acid (RA) was identified as the biologically active form of vitamin A almost 70 years ago and work on its function and mechanism of action is still of major interest both from a scientific and a clinical perspective. The currently accepted model postulates that RA is produced in two sequential oxidative steps: first, retinol is oxidized reversibly to retinaldehyde, and then retinaldehyde is oxidized irreversibly to RA. Excess RA is inactivated by conversion to hydroxylated derivatives. Much is left to learn, especially about retinoid binding proteins and the trafficking of the hydrophobic retinoid substrates between membrane bound and cytosolic enzymes. Here, background on development of the field and an update on recent advances in our understanding of the enzymatic pathways and mechanisms that control the rate of RA production and degradation are presented with a focus on the many questions that remain unanswered.

Pharmacological inhibition of ALDH1A in mice decreases all-trans retinoic acid concentrations in a tissue specific manner

all-trans retinoic acid (atRA), the active metabolite of vitamin A, is an essential signaling molecule. Specifically the concentrations of atRA are spatiotemporally controlled in target tissues such as the liver and the testes. While the enzymes of the aldehyde dehydrogenase 1A family (ALDH1A) are believed to control the synthesis of atRA, a direct relationship between altered ALDH1A activity and tissue atRA concentrations has never been shown. To test whether inhibition of ALDH1A enzymes decreases atRA concentrations in a tissue specific manner, the potent ALDH1A inhibitor WIN 18,446 was used to inhibit ALDH1A activity in mice. The ALDH1A expression, atRA formation kinetics, ALDH1A inhibition by WIN 18,446 and WIN 18,446 disposition were used to predict the time course and extent of inhibition of atRA formation in the testis and liver. The effect of WIN 18,446 on atRA concentrations in testis, liver and serum were measured following single and multiple doses of WIN 18,446. ALDH1A1 and ALDH1A2 were responsible for the majority of atRA formation in the testis while ALDH1A1 and aldehyde oxidase contributed to atRA formation in the liver. Due to the different complement of enzymes contributing to atRA formation in different tissues and different inhibition of ALDH1A1 and ALDH1A2 by WIN 18,446, WIN 18,446 caused only a 50% decrease in liver atRA but testicular atRA decreased over 90%. Serum atRA concentrations were also reduced. These data demonstrate that inhibition of ALDH1A enzymes will decrease atRA concentrations in a tissue specific manner and selective ALDH1A inhibition could be used to alter atRA concentrations in select target tissues.

Leukocyte homing, fate, and function are controlled by retinoic acid

Although vitamin A was recognized as an "anti-infective vitamin" over 90 years ago, the mechanism of how vitamin A regulates immunity is only beginning to be understood. Early studies which focused on the immune responses in vitamin A-deficient (VAD) animals clearly demonstrated compromised immunity and consequently increased susceptibility to infectious disease. The active form of vitamin A, retinoic acid (RA), has been shown to have a profound impact on the homing and differentiation of leukocytes. Both pharmacological and genetic approaches have been applied to the understanding of how RA regulates the development and differentiation of various immune cell subsets, and how RA influences the development of immunity versus tolerance. These studies clearly show that RA profoundly impacts on cell- and humoral-mediated immunity. In this review, the early findings on the complex relationship between VAD and immunity are discussed as well as vitamin A metabolism and signaling within hematopoietic cells. Particular attention is focused on how RA impacts on T-cell lineage commitment and plasticity in various diseases.

Metabolism of gamma hydroxybutyrate in human hepatoma HepG2 cells by the aldo-keto reductase AKR1A1

Gamma hydroxybutyrate (GHB) is a recreational and date-rape drug, for which the detection following ingestion is hampered by rapid metabolism and its endogenous presence. GHB catabolism occurs mainly by its oxidation to succinic semialdehyde (SSA), which converts to succinate and enters the tricarboxylic acid cycle. A high Km aldehyde reductase has previously been reported to catalyse the NADP-dependent oxidation of GHB at high concentrations. It is assumed that this enzyme is identical to the aldo-keto reductase AKR1A1, but its role in GHB oxidation has not been fully evaluated. In this study, the extent of AKR1A1 in GHB metabolism has been determined in HepG2 cells using RNA-interference technology. The gene encoding AKR1A1 was targeted by siRNA. Results demonstrate a successful knock-down of the AKR1A1 gene with 92% reduction in total mRNA and 93% reduction in protein expression. Demolishing AKR1A1 expression in HepG2 cells leads to significant 82% decrease in NADP-dependent GHB-dehydrogenase activity at high concentration (10mM) of GHB. Moreover, when exposing the cells to 50 μM of GHB for 24h, and measuring intracellular and extracellular GHB levels by GC/MS, a significant two-fold increase was observed on GHB intracellular level in silenced cells. In contrast, measuring SSA-reductase activity in silenced cells indicated that AKR1A1 is not involved in endogenous GHB production. These findings describe a pathway for GHB metabolism in the liver which should be useful in GHB exposure cases, and will enable a better understanding of the enzymes participating in its metabolism at natural and overexposed levels.

Comparison of quantum dot technology with conventional immunohistochemistry in examining aldehyde dehydrogenase 1A1 as a potential biomarker for lymph node metastasis of head and neck cancer

This study explored whether the expression of aldehyde dehydrogenase 1 (ALDH1A1) in the primary tumour correlated with lymph node metastasis (LNM) of squamous cell carcinoma of the head and neck (HNSCC). We used both quantum dot (QD)-based immunohistofluorescence (IHF) and conventional immunohistochemistry (IHC) to quantify ALDH1A1 expression in primary tumour samples taken from 96 HNSCC patients, 50 with disease in the lymph nodes and 46 without. The correlation between the quantified level of ALDH1A1 expression and LNM in HNSCC patients was evaluated with univariate and multivariate analysis. The prognostic value of ALDH1A1 was examined by Kaplan-Meier analysis and Wald test. ALDH1A1 was highly correlated with LNM in HNSCC patients (p<0.0001 by QD-based IHF and 0.039 by IHC). The two methods (QD-based IHF and conventional IHC) for quantification of ALDH1A1 were found to be comparable (R=0.75, p<0.0001), but QD-IHF was more sensitive and objective than IHC. The HNSCC patients with low ALDH1A1 expression had a higher 5-year survival rate than those with high ALDH1A1 level (p=0.025). Our study suggests that ALDH1A1 is a potential biomarker for predicting LNM in HNSCC patients, though it is not an independent prognostic factor for survival of HNSCC patients. Furthermore, QD-IHF has advantages over IHC in quantification of ALDH1A1 expression in HNSCC tissues.

Succinic semialdehyde dehydrogenase: biochemical-molecular-clinical disease mechanisms, redox regulation, and functional significance

Succinic semialdehyde dehydrogenase (SSADH; aldehyde dehydrogenase 5a1, ALDH5A1; E.C. 1.2.1.24; OMIM 610045, 271980) deficiency is a rare heritable disorder that disrupts the metabolism of the inhibitory neurotransmitter 4-aminobutyric acid (GABA). Identified in conjunction with increased urinary excretion of the GABA analog gamma-hydroxybutyric acid (GHB), numerous patients have been identified worldwide and the autosomal-recessive disorder has been modeled in mice. The phenotype is one of nonprogressive neurological dysfunction in which seizures may be prominently displayed. The murine model is a reasonable phenocopy of the human disorder, yet the severity of the seizure disorder in the mouse exceeds that observed in SSADH-deficient patients. Abnormalities in GABAergic and GHBergic neurotransmission, documented in patients and mice, form a component of disease pathophysiology, although numerous other disturbances (metabolite accumulations, myelin abnormalities, oxidant stress, neurosteroid depletion, altered bioenergetics, etc.) are also likely to be involved in developing the disease phenotype. Most recently, the demonstration of a redox control system in the SSADH protein active site has provided new insights into the regulation of SSADH by the cellular oxidation/reduction potential. The current review summarizes some 30 years of research on this protein and disease, addressing pathological mechanisms in human and mouse at the protein, metabolic, molecular, and whole-animal level.

Estrogen receptor alpha regulates retinaldehyde dehydrogenase 1 expression in rat anterior pituitary cells

Retinoic acid (RA) plays a critical role in embryonic development, growth, and reproduction. RA is synthesized from retinoids via oxidation processes, and the oxidation of retinal to RA is catalyzed by the retinaldehyde dehydrogenases (RALDHs). We previously reported that RALDH1 mRNA was expressed in the anterior pituitary glands of adult rats and suppressed by administration of 17beta-estradiol in vivo. However, little is known about the mechanism regulating pituitary RALDH1 expression. In order to characterize the mechanism of estrogen-induced RALDH1 reduction, we examined the effect of 17beta-estradiol on the regulation of pituitary RALDH1 gene expression and protein production both in vivo and in vitro. Using quantitative real-time PCR and immunoblot analysis, we found that levels of RALDH1 gene expression and protein production markedly decreased after 1-week treatment with 17beta-estradiol in male rats. In immunohistochemical analysis, RALDH1-immunoreaction was observed in prolactin cells and folliculo-stellate cells. In 17beta-estradiol-treated rats, RALDH1-immunoreactivity was lower in prolactin cells, but not in folliculo-stellate cells. Treatment of isolated anterior pituitary cells with 17beta-estradiol (10(-14) - 10(-8) M) decreased expression of RALDH1 mRNA in a dose-dependent manner. Estradiol-induced suppression of RALDH1 expression was completely blocked by the estrogen receptor (ER) antagonist ICI 182, 780. The ERalpha-selective agonist propylpyrazole triol (10(-8) M) mimicked the effect of 17beta-estradiol on RALDH1 expression, but the ERbeta-selective agonist diarylpropionitrile (10(-8) M) did not. These results strongly suggest that RALDH1 mRNA expression is suppressed by 17beta-estradiol through ERalpha, and that estrogen regulates the expression of RALDH1 and production of RA in the anterior pituitary gland.

Pharmacogenetics influence treatment efficacy in childhood acute lymphoblastic leukemia

Pharmacogenetics covers the genetic variation affecting pharmacokinetics and pharmacodynamics, and their influence on drug-response phenotypes. The genetic variation includes an estimated 15 million single nucleotide polymorphisms (SNPs) and is a key determinator for the interindividual differences in treatment resistance and toxic side effects. As most childhood acute lymphoblastic leukemia treatment protocols include up to 13 different chemotherapeutic agents, the impact of individual SNPs has been difficult to evaluate. So far focus has mainly been on the widely used glucocorticosteroids, methotrexate, and thiopurines, or on metabolic pathways and transport mechanisms that are common to several drugs, such as the glutathione S-transferases. However, beyond the thiopurine methyltransferase polymorphisms, the candidate-gene approach has not established clear associations between polymorphisms and treatment response. In the future, high-throughput, low-cost, genetic platforms will allow screening of hundreds or thousands of targeted SNPs to give a combined gene-dosage effect (=individual SNP risk profile), which may allow pharmacogenetic-based individualization of treatment.

A point mutation produced a class 3 aldehyde dehydrogenase with increased protective ability against the killing effect of cyclophosphamide

Cyclophosphamides are pro-drugs whose killing agent is produced from an aldehyde that is formed by the action of a P450 oxidation step. The mustard from the aldehyde can destroy bone marrow cells as well as the tumor. Aldehyde dehydrogenase (EC 1.2.1.3) can oxidize the aldehyde and hence inactivate the cytotoxic intermediate but bone marrow has little, if any, of the enzyme. Others have shown that over-expression of the enzyme can afford protection of the marrow. A T186S mutant of the human stomach enzyme (ALDH3) that we developed has increased activity against the aldehyde compared to the native enzyme and HeLa cells transformed with the point mutant are better protected against the killing effect of the drug. It took threefold more drug to kill 90% of the cells transformed with the mutant compared to the native enzyme (15.8 compared to 5.1mM of a precursor of the toxic aldehyde). Analysis of molecular models makes it appear that removing the methyl group of threonine in the T186S mutant allows the bulky aldehyde to bind better. The mutant was found to be a poorer enzyme when small substrates such as benzaldehyde derivatives were investigated. Thus, the enzyme appears to be better only with large substrates such as the one produced by cyclophosphamide.

High and complementary expression patterns of alcohol and aldehyde dehydrogenases in the gastrointestinal tract: implications for Parkinson's disease

Parkinson's disease (PD) is a heterogeneous movement disorder characterized by progressive degeneration of dopamine neurons in substantia nigra. We have previously presented genetic evidence for the possible involvement of alcohol and aldehyde dehydrogenases (ADH; ALDH) by identifying genetic variants in ADH1C and ADH4 that associate with PD. The absence of the corresponding mRNA species in the brain led us to the hypothesis that one cause of PD could be defects in the defense systems against toxic aldehydes in the gastrointestinal tract. We investigated cellular expression of Adh1, Adh3, Adh4 and Aldh1 mRNA along the rodent GI tract. Using oligonucleotide in situ hybridization probes, we were able to resolve the specific distribution patterns of closely related members of the ADH family. In both mice and rats, Adh4 is transcribed in the epithelium of tongue, esophagus and stomach, whereas Adh1 was active from stomach to rectum in mice, and in duodenum, colon and rectum in rats. Adh1 and Adh4 mRNAs were present in the mouse gastric mucosa in nonoverlapping patterns, with Adh1 in the gastric glands and Adh4 in the gastric pits. Aldh1 was found in epithelial cells from tongue to jejunum in rats and from esophagus to colon in mice. Adh3 hybridization revealed low mRNA levels in all tissues investigated. The distribution and known physiological functions of the investigated ADHs and Aldh1 are compatible with a role in a defense system, protecting against alcohols, aldehydes and formaldehydes as well as being involved in retinoid metabolism.

Real-time dose adjustment of cyclophosphamide in a preparative regimen for hematopoietic cell transplant: a Bayesian pharmacokinetic approach

PURPOSE

Dose-related toxicity of cyclophosphamide may be reduced and therapeutic efficacy may be improved by pharmacokinetic sampling and dose adjustment to achieve a target area under the curve (AUC) for two of its metabolites, hydroxycyclophosphamide (HCY) and carboxyethylphosphoramide mustard (CEPM). To facilitate real-time dose adjustment, we developed open-source code within the statistical software R that incorporates individual data into a population pharmacokinetic model.

EXPERIMENTAL DESIGN

Dosage prediction performance was compared to that obtained with nonlinear mixed-effects modeling using NONMEM in 20 cancer patients receiving cyclophosphamide. Bayesian estimation of individual pharmacokinetic parameters was accomplished from limited (i.e., five samples over 0-16 hours) sampling of plasma HCY and CEPM after the initial cyclophosphamide dose. Conditional on individual pharmacokinetics, simulations of the AUC of both HCY and CEPM were provided for a range of second doses (i.e., 0-100 mg/kg cyclophosphamide).

RESULTS

The results compared favorably with NONMEM and returned accurate predictions for AUCs of HCY and CEPM with comparable mean absolute prediction error and root mean square prediction error. With our method, the mean absolute prediction error and root mean square prediction error of AUC CEPM were 11.0% and 12.8% and AUC HCY were 31.7% and 44.8%, respectively.

CONCLUSIONS

We developed dose adjustment software that potentially can be used to adjust cyclophosphamide dosing in a clinical setting, thus expanding the opportunity for pharmacokinetic individualization of cyclophosphamide. The software is simple to use (requiring no programming experience), reads individual patient data directly from an Excel spreadsheet, and runs in less than 5 minutes on a desktop PC.

Involvement of alcohol and aldehyde dehydrogenase activities on hepatic retinoid metabolism and its possible participation in the progression of rat liver regeneration

Liver alcohol dehydrogenase (ADH) activity is decreased towards exogenous substrates after partial hepatectomy (PH), probably due to putative endogenous substrates acting as ADH inhibitors. Hence, retinoids could be suitable candidates as such endogenous substrates. Therefore, cytosolic ADH kinetic analysis using several substrates, liver cytosolic and mitochondrial aldehyde dehydrogenase (ALDH) activities, retinal and retinol content, as well as expression of proteins for ADH and CRBPI (a retinol carrier protein) were determined in liver samples, at two stages of liver regeneration (one- or two-thirds PH). The effect of inhibiting in vivo liver ADH by 4-methylpyrazole (4-MP) was also evaluated after 70%-PH. With 70%-PH, in vitro ADH activity towards exogenous alcohols and aldehydes was diminished, but retinol oxidation was increased and retinal reduction was decreased. These activities that be due to the participation of an ADH type which did not correlate with the amount of immunoreactive ADH protein. Cytosolic and mitochondrial ALDH activities oxidized actively retinal, whereas retinol and CBRP-I expression were reduced in these animals. With 30%-PH, these changes were less evident and sometimes opposite to those found with 70%-PH. In addition, retinol readily inhibited ADH-mediated ethanol oxidation. Interestingly, in vivo 4-MP administration inhibited ADH activity in a dose-dependent manner correlating with a progressive inhibition of liver regeneration. In conclusion, PH-induced inhibition of ADH (mainly type I) seems to be related to ADH-mediated retinoid metabolism during liver proliferation. Thus, results suggest a role of ADH in retinoid metabolism, which is apparently required during rat liver regeneration.

Rapid quantitation of cyclophosphamide metabolites in plasma by liquid chromatography–mass spectrometry

A method is described for the quantification of two metabolites of cyclophosphamide, specifically 4-hydroxycyclophosphamide (HCy), and carboxyethylphosphoramide mustard (CEPM). Plasma HCy is derivatized to the phenylhydrazone which is quantitated by LC-MS monitoring the chloride adduct of the derivative. The LLOQ based on material applied to the system is approximately 20 fmol. Plasma CEPM concentration is determined using LC-MS with a deuterated internal standard. Both assays have 50-fold dynamic range and require less than 4h to complete. The development of this rapid analytical method makes it feasible to adjust the dose of cyclophosphamide based on the pharmacokinetic disposition of HCy and CEPM in hopes of decreasing nonrelapse mortality in cancer patients.

Clinical pharmacokinetics of cyclophosphamide

Cyclophosphamide is an extensively used anticancer and immunosuppressive agent. It is a prodrug undergoing a complicated process of metabolic activation and inactivation. Technical difficulties in the accurate determination of the cyclophosphamide metabolites have long hampered the assessment of the clinical pharmacology of this drug. As these techniques are becoming increasingly available, adequate description of the pharmacokinetics of cyclophosphamide and its metabolites has become possible. There is incomplete understanding on the role of cyclophosphamide metabolites in the efficacy and toxicity of cyclophosphamide therapy. However, relationships between toxicity (cardiotoxicity, veno-occlusive disease) and exposure to cyclophosphamide and its metabolites have been established. Variations in the balance between metabolic activation and inactivation of cyclophosphamide owing to autoinduction, dose escalation, drug-drug interactions and individual differences have been reported, suggesting possibilities for optimisation of cyclophosphamide therapy. Knowledge of the pharmacokinetics of cyclophosphamide, and possibly monitoring the pharmacokinetics of cyclophosphamide in individuals, may be useful for improving its therapeutic index.

Cyclophosphamide disposition in an anephric child

Although limited data are available about cyclophosphamide disposition in patients with renal insufficiency, nothing has been reported in anephric patients. We characterized cyclophosphamide pharmacokinetics in an anephric child with bilateral Wilms tumor, both on (day 1) and off (day 2) hemodialysis. The median cyclophosphamide clearance on and off hemodialysis was 5.34 and 3.82 L/hr*m(2), respectively, demonstrating elimination of cyclophosphamide in this anephric child. The off hemodialysis clearance was similar to that in children with normal renal function. Hydroxycyclophosphamide (HCY) AUC was 20.6 and 8.77 microM*hr on and off hemodialysis. Carboxyethylphosphoramide mustard (CEPM) AUC obtained on hemodialysis (i.e., 194 microM*hr) was similar to that in children with normal renal function, although an elevated CEPM AUC was observed when hemodialysis was not received (i.e., 383 microM*hr). With the recent findings that clinical outcomes are related to CEPM AUC, further data are needed regarding the pharmacokinetics of cyclophosphamide and relevant metabolites in anephric children.

Association of cyclophosphamide pharmacokinetics to polymorphic cytochrome P450 2C19

Cyclophosphamide (CP), a widely used cytostatic, is metabolized by polymorphic drug metabolizing enzymes particularly cytochrome P450 (CYP) enzymes. Its side effects and clinical efficacy exhibit a broad interindividual variability, which might be due to differences in pharmacokinetics. CP-kinetics were determined in 60 patients using a global and a population pharmacokinetic model considering functionally relevant polymorphisms of CYP2B6, CYP2C9, CYP2C19, CYP3A5, and GSTA1. Moreover, metabolic ratios were calculated for selected CP metabolites, analyzed by (31)P-NMR-spectroscopy. Analysis of variance revealed that the CYP2C19*2 genotype influenced significantly pharmacokinetics of CP at doses </=1000 mg/m(2), whereas there was no evidence of an association of other genotypes to CP elimination or clearance. Mean (+/-SD) CP elimination constants k(e) (h(-1)) were 0.109+/-0.025 in 44 CYP2C19*1/*1 subjects, 0.088+/-0.018 in 13 CYP2C19*1/*2, and 0.076+/-0.014 in three inactive CYP2C19*2/*2 carriers (P=0.009). At CP doses higher than 1000 mg/m(2), a significantly increase of elimination was observed (P=0.001), possibly due to CYP induction. Further studies should link these findings with the clinical outcome.

Pharmacokinetics and metabolism of ifosfamide in relation to DNA damage assessed by the COMET assay in children with cancer

The degree of damage to DNA following ifosfamide (IFO) treatment may be linked to the therapeutic efficacy. The pharmacokinetics and metabolism of IFO were studied in 19 paediatric patients, mostly with rhabdomyosarcoma or Ewings sarcoma. Ifosfamide was dosed either as a continuous infusion or as fractionated doses over 2 or 3 days. Samples of peripheral blood lymphocytes were obtained during and up to 96 h after treatment, and again prior to the next cycle of chemotherapy. DNA damage was measured using the alkaline COMET assay, and quantified as the percentage of highly damaged cells per sample. Samples were also taken for the determination of IFO and metabolites. Pharmacokinetics and metabolism of IFO were comparable with previous studies. Elevations in DNA damage could be determined in all patients after IFO administration. The degree of damage increased to a peak at 72 h, but had returned to pretreatment values prior to the next dose of chemotherapy. There was a good correlation between area under the curve of IFO and the cumulative percentage of cells with DNA damage (r²=0.554, P=0.004), but only in those patients receiving fractionated dosing. The latter patients had more DNA damage (mean±s.d., 2736±597) than those patients in whom IFO was administered by continuous infusion (1453±730). The COMET assay can be used to quantify DNA damage following IFO therapy. Fractionated dosing causes a greater degree of DNA damage, which may suggest a greater degree of efficacy, with a good correlation between pharmacokinetic and pharmacodynamic data.

Role of human aldehyde dehydrogenases in endobiotic and xenobiotic metabolism

The human genome contains at least 17 genes that are members of the aldehyde dehydrogenase (ALDH) superfamily. These genes encode NAD(P)(+)-dependent enzymes that oxidize a wide range of aldehydes to their corresponding carboxylic acids. Aldehydes are highly reactive molecules that are intermediates or products involved in a broad spectrum of physiologic, biologic, and pharmacologic processes. Aldehydes are generated during retinoic acid biosynthesis and the metabolism of amino acids, lipids, carbohydrates, and drugs. Mutations in several ALDH genes are the molecular basis of inborn errors of metabolism and contribute to environmentally induced diseases.

Cyclophosphamide metabolism in children with non-Hodgkin's lymphoma

PURPOSE

The purpose of our study was to determine whether variation in cyclophosphamide metabolism influences the incidence of recurrence among children receiving chemotherapy for B-cell non-Hodgkin's lymphoma.

EXPERIMENTAL DESIGN

The pharmacokinetics and metabolism of cyclophosphamide were studied during a single course of treatment in 36 children receiving a uniform chemotherapy regimen for B-cell non-Hodgkin's lymphoma and were analyzed in terms of disease recurrence and hematological toxicity.

RESULTS

At a median follow-up of 43 months (range, 17-98 months), six children had developed recurrent disease, giving an overall disease-free survival of 83%. The median clearance of cyclophosphamide in patients who remain free of B-cell non-Hodgkin's lymphoma was 3.7 liter/h/m(2) (range, 2.3-5.0 liter/h/m(2)), compared with 2.2 (range, 1.5-2.5 liter/h/m(2)) in those with disease recurrence. Likelihood of recurrence was higher in patients with low clearance (<3.5 liter/h/m(2)) of cyclophosphamide (P < 0.01) and positively related to detection of the inactive metabolites carboxyphosphamide and dechloroethylcyclophosphamide in plasma (P = 0.01). There was no correlation between cyclophosphamide metabolism and hematological toxicity.

CONCLUSIONS

Inadequate clearance of cyclophosphamide to active metabolites is associated with increased risk of recurrence of B-cell non-Hodgkin's lymphoma in children. Modified chemotherapy strategies should be considered in patients who exhibit low rates of clearance of the parent drug and/or extensive production of inactive metabolites.

Gene expression profiling of normal human pulmonary fibroblasts following coculture with non-small-cell lung cancer cells reveals alterations related to matrix degradation, angiogenesis, cell growth and survival

Increasing evidence supports a major role for the microenvironment in carcinoma formation and progression. The influence of the stroma is partly mediated by signalling between epithelial tumor cells and neighboring fibroblasts. However, the molecular mechanisms underlying these interactions are largely unknown. To mimic the initial steps of invasive carcinoma in which tumor cells come in contact with normal stromal cells, we used a coculture model of non-small-cell lung cancer tumor cells and normal pulmonary fibroblasts. Using DNA filter arrays, we first analysed the overall modification of gene expression profile after a 24 h period of coculture. Next, we focused our interest on the transcriptome of the purified fibroblastic fraction of coculture using both DNA filter arrays and a laboratory-made DNA microarray. These experiments allowed the identification of a set of modulated genes coding for growth and survival factors, angiogenic factors, proteases and protease inhibitors, transmembrane receptors, kinases and transcription regulators that can potentially affect the regulation of matrix degradation, angiogenesis, invasion, cell growth and survival. This study represents to our knowledge the first attempt to dissect early global gene transcription occurring in a tumor-stroma coculture model and should help to understand better some of the molecular mechanisms involved in heterotypic signalling between epithelial tumor cells and fibroblasts.

Human aldehyde dehydrogenases: potential pathological, pharmacological, and toxicological impact

Aldehyde dehydrogenases catalyze the pyridine nucleotide-dependent oxidation of aldehydes to acids. Seventeen enzymes are currently viewed as belonging to the human aldehyde dehydrogenase superfamily. Summarized herein, insofar as the information is available, are the structural composition, physical properties, tissue distribution, subcellular location, substrate specificity, and cofactor preference of each member of this superfamily. Also summarized are the chromosomal locations and organization of the genes that encode these enzymes and the biological consequences when enzyme activity is lost or substantially diminished. Broadly, aldehyde dehydrogenases can be categorized as critical for normal development and/or physiological homeostasis (1). even when the organism is in a friendly environment or (2). only when the organism finds itself in a hostile environment. The primary, if not sole, evolved raison d'être of first category aldehyde dehydrogenases appears to be to catalyze the biotransformation of a single endobiotic for which they are relatively specific and of which the resultant metabolite is essential to the organism. Most of the human aldehyde dehydrogenases for which the relevant information is available fall into this category. Second category aldehyde dehydrogenases are relatively substrate nonspecific and their evolved raison d'être seems to be to protect the organism from potentially harmful xenobiotics, specifically aldehydes or xenobiotics that give rise to aldehydes, by catalyzing their detoxification. Thus, the lack of a fully functional first category aldehyde dehydrogenase results in a gross pathological phenotype in the absence of any insult, whereas the lack of a functional second category aldehyde dehydrogenase is ordinarily of no consequence with respect to gross phenotype, but is of consequence in that regard when the organism is subjected to a relevant insult.

Oxidation of 4-hydroxy-2-nonenal by succinic semialdehyde dehydrogenase (ALDH5A)

Elevated levels of 4-hydroxy-trans-2-nonenal (HNE) are implicated in the pathogenesis of numerous neurodegenerative disorders. Although well-characterized in the periphery, the mechanisms of detoxification of HNE in the CNS are unclear. HNE is oxidized to a non-toxic metabolite in the rat cerebral cortex by mitochondrial aldehyde dehydrogenases (ALDHs). Two possible ALDH enzymes which might oxidize HNE in CNS mitochondria are ALDH2 and succinic semialdehyde dehydrogenase (SSADH/ALDH5A). It was previously established that hepatic ALDH2 can oxidize HNE. In this work, we tested the hypothesis that SSADH oxidizes HNE. SSADH is critical in the detoxification of the GABA metabolite, succinic semialdehyde (SSA). Recombinant rat SSADH oxidized HNE and other alpha,beta-unsaturated aldehydes. Inhibition and competition studies in rat brain mitochondria showed that SSADH was the predominant oxidizing enzyme for HNE but only contributed a portion of the total oxidizing activity in liver mitochondria. In vivo administration of diethyldithiocarbamate (DEDC) effectively inhibited (86%) ALDH2 activity but not HNE oxidation in liver mitochondria. The data suggest that a relationship between the detoxification of SSA and the neurotoxic aldehyde HNE exists in the CNS. Furthermore, these studies show that multiple hepatic aldehyde dehydrogenases are able to oxidize HNE.

Mouse retinal dehydrogenase 4 (RALDH4), molecular cloning, cellular expression, and activity in 9-cis-retinoic acid biosynthesis in intact cells

This study describes cDNA cloning and characterization of mouse RALDH4. The 2.3-kb cDNA encodes an aldehyde dehydrogenase of 487 amino acid residues, about two-orders of magnitude more active in vitro with 9-cis-retinal than with all-trans-retinal. RALDH4 recognizes as substrate 9-cis-retinal generated in transfected cells by the short-chain dehydrogenases CRAD1, CRAD3, or RDH1, to reconstitute a path of 9-cis-retinoic acid biosynthesis in situ. Northern blot analysis showed expression of RALDH4 mRNA in adult mouse liver and kidney. In situ hybridization revealed expression of RALDH4 in liver on embryo day 14.5, in adult hepatocytes, and kidney cortex. Immunohistochemistry confirmed RALDH4 expression in hepatocytes and showed that hepatocytes also express RALDH1, RALDH2, and RALDH3. Kidney expresses the RALDH4 protein primarily in the proximal and distal convoluted tubules of the cortex but not in the glomeruli or the medulla. Kidney expresses RALDH2 in the proximal convoluted tubules of the cortex but not in the distal convoluted tubules or glomeruli. Kidney expresses RALDH1 and RALDH2 in the medulla. The enzymatic characteristics of RALDH4, its expression in fetal liver, and its unique expression pattern in adult kidney compared with RALDH1, -2, and -3 suggest that it could meet specific needs for 9-cis-retinoic acid biosynthesis.

Differential gene expression in chemically induced mouse lung adenomas

Because of similarities in histopathology and tumor progression stages between mouse and human lung adenocarcinomas, the mouse lung tumor model with lung adenomas as the endpoint has been used extensively to evaluate the efficacy of putative lung cancer chemopreventive agents. In this study, a competitive cDNA library screening (CCLS) was employed to determine changes in the expression of mRNA in chemically induced lung adenomas compared with paired normal lung tissues. A total of 2555 clones having altered expression in tumors were observed following competitive hybridization between normal lung and lung adenomas after primary screening of over 160,000 clones from a mouse lung cDNA library. Among the 755 clones confirmed by dot blot hybridization, 240 clones were underexpressed, whereas 515 clones were overexpressed in tumors. Sixty-five clones with the most frequently altered expression in six individual tumors were confirmed by semiquantitative RT-PCR. When examining the 58 known genes, 39 clones had increased expression and 19 had decreased expression, whereas the 7 novel genes showed overexpression. A high percentage (>60%) of overexpressed or underexpressed genes was observed in at least two or three of the lesions. Reproducibly overexpressed genes included ERK-1, JAK-1, surfactant proteins A, B, and C, NFAT1, alpha-1 protease inhibitor, helix-loop-helix ubiquitous kinase (CHUK), alpha-adaptin, alpha-1 PI2, thioether S-methyltransferase, and CYP2C40. Reproducibly underexpressed genes included paroxanase, ALDH II, CC10, von Ebner salivary gland protein, and alpha- and beta-globin. In addition, CCLS identified several novel genes or genes not previously associated with lung carcinogenesis, including a hypothetical protein (FLJ11240) and a guanine nucleotide exchange factor homologue. This study shows the efficacy of this methodology for identifying genes with altered expression. These genes may prove to be helpful in our understanding of the genetic basis of lung carcinogenesis and in developing biomarkers for lung cancer chemoprevention studies in mice.

4-(N,N-dipropylamino)benzaldehyde inhibits the oxidation of all-trans retinal to all-trans retinoic acid by ALDH1A1, but not the differentiation of HL-60 promyelocytic leukemia cells exposed to all-trans retinal

BACKGROUND

The signal transduction pathways mediated by retinoic acid play a critical role in the regulation of cell growth and differentiation during embryogenesis and hematopoiesis as well as in a variety of tumor cell lines in culture. Following the reports that two members of the superfamily of aldehyde dehydrogenase (ALDH) enzymes, ALDH1A1 and ALDH1A2, were capable of catalyzing the oxidation of all-trans retinal to all-trans retinoic acid with submicromolar Km values, we initiated an investigation of the ability of 4-(N,N-dipropylamino)benzaldehyde (DPAB) to inhibit the oxidation of retinal by purified mouse and human ALDH1A1.

RESULTS

Our results show that DPAB potently inhibits retinal oxidation, with IC50 values of 0.11 and 0.13 microM for purified mouse and human ALDH1A1, respectively. Since the HL-60 human myeloid leukemic cell line has been used extensively to study the retinoic acid induced differentiation of HL-60 cells to granulocytes, and ALDH1A1 activity had previously been reported in HL-60 cells, we investigated the ability of DPAB to block differentiation of HL-60 promyelocytic leukemia cells exposed to retinal in culture. In HL-60 cells coincubated with 1 microM retinal and 50 microM DPAB for 144 hours, cell differentiation was inhibited only 30%. Furthermore, the NAD-dependent oxidation of propanal or retinal was less than 0.05 nmoles NADH formed/min-10(7) cells in spectrophotometric assays using HL-60 cell extracts.

CONCLUSION

Although ALDH1A1 may be the major catalytic activity for retinal oxidation in some retinoid-dependent mouse and Xenopus embryonic tissues and in adult human and mouse hematopoietic stem cells, another catalytic activity appears to synthesize the retinoic acid ligand necessary to stimulate the differentiation of HL-60 cells to end stage granulocytes.

Inhibition of ALDH3A1-catalyzed oxidation by chlorpropamide analogues

In our efforts to identify agents that would specifically inhibit ALDH3A1, we had previously studied extensively the effect of an N(1)-alkyl, an N(1)-methoxy, and several N(1)-hydroxy-substituted ester derivatives of chlorpropamide on the catalytic activities of ALDH3A1s derived from human normal stomach mucosa (nALDH3A1) and human tumor cells (tALDH3A1), and of two recombinant aldehyde dehydrogenases, viz. human rALDH1A1 and rALDH2. The N(1)-methoxy analogue of chlorpropamide, viz. 4-chloro-N-methoxy-N-[(propylamino)carbonyl]benzenesulfonamide (API-2), was found to be a relatively selective and potent inhibitor of tALDH3A1-catalyzed oxidation as compared to its ability to inhibit nALDH3A-catalyzed oxidation, but even more potently inhibited ALDH2-catalyzed oxidation, whereas an ester analogue, viz. (acetyloxy)[(4-chlorophenyl)sulfonyl]carbamic acid 1,1-dimethylethyl ester (NPI-2), selectively inhibited tALDH3A1-catalyzed oxidation as compared to its ability to inhibit nALDH3A1-, ALDH1A1- and ALDH2-catalyzed oxidations, and this inhibition was apparently irreversible. Three additional chlorpropamide analogues, viz. 4-chloro-N,O-bis(ethoxycarbonyl)-N-hydroxybenzenesulfonamide (NPI-4), N,O-bis(carbomethoxy)methanesulfohydroxamic acid (NPI-5), and 2-[(ethoxycarbonyl)oxy]-1,2-benzisothiazol-3(2H)-one 1,1-dioxide (NPI-6), were evaluated in the present investigation. Quantified were NAD-linked oxidation of benzaldehyde catalyzed by nALDH3A1 and tALDH3A1, and NAD-linked oxidation of acetaldehyde catalyzed by rALDH1A1 and rALDH2, all at 37 degrees C and pH 8.1, and in the presence and absence of inhibitor. NPI-4, NPI-5 and NPI-6 were not substrates for the oxidative reactions catalyzed by any of the ALDHs studied. Oxidative reactions catalyzed by the ALDH3A1s, rALDH1A1 and rALDH2 were each inhibited by NPI-4 and NPI-5. NPI-6 was a poor inhibitor of nALDH3A1- and tALDH3A1-catalyzed oxidations, but was a relatively potent inhibitor of rALDH1A1- and rALDH2-catalyzed oxidations. In all cases, inhibition of ALDH-catalyzed oxidation was directly related to the product of inhibitor concentration and preincubation (enzyme+inhibitor) time. As judged by the product values (microM x min) required to effect 50% inhibition (IC(50)): (1) nALDH3A1 and tALDH3A1 were essentially equisensitive to inhibition by NPI-4 and NPI-5, and both enzymes were poorly inhibited by NPI-6; (2) rALDH1A1 was, relative to the ALDH3A1s, slightly more sensitive to inhibition by NPI-4 and NPI-5, and far more sensitive to inhibition by NPI-6; and (3) rALDH1A1 was, relative to rALDH2, essentially equisensitive to inhibition by NPI-5, whereas, it was slightly more sensitive to inhibition by NPI-4 and NPI-6.

Molecular characterization of a mouse short chain dehydrogenase/reductase active with all-trans-retinol in intact cells, mRDH1

Metabolic activation of retinol (vitamin A) via sequential actions of retinol and retinal dehydrogenases produces the active metabolite all-trans-retinoic acid. This work reports cDNA cloning, enzymatic characterization, function in a reconstituted path of all-trans-retinoic acid biosynthesis in cell culture, and mRNA expression patterns in adult tissues and embryos of a mouse retinol dehydrogenase, RDH1. RDH1 represents a new member of the short chain dehydrogenase/reductase superfamily that differs from other mouse RDH in relative activity with all-trans and cis-retinols. RDH1 has a multifunctional catalytic nature, as do other short chain dehydrogenase/reductases. In addition to retinol dehydrogenase activity, RDH1 has strong 3alpha-hydroxy and weak 17beta-hydroxy steroid dehydrogenase activities. RDH1 has widespread and intense mRNA expression in tissues of embryonic and adult mice. The mouse embryo expresses RDH1 as early as 7.0 days post-coitus, and expression is especially intense within the neural tube, gut, and neural crest at embryo day 10.5. Cells cotransfected with RDH1 and any one of three retinal dehydrogenase isozymes synthesize all-trans-retinoic acid from retinol, demonstrating that RDH1contributes to a path of all-trans-retinoic acid biosynthesis in intact cells. These characteristics are consistent with RDH1 functioning in a path of all-trans-retinoic acid biosynthesis starting early during embryogenesis.

Analysis of mouse retinal dehydrogenase type 2 promoter and expression

The mouse RALDH2 gene spans >50 kb, has a structure similar to that of human class 1 aldehyde dehydrogenase genes, and localizes to the central region of chromosome 9 by single-strand polymorphism analysis. Expression of mouse RALDH2 was detected in testis, lung, brain, and heart (Northern blot) and in liver and kidney (RNase protection assays). Expression was not detected by RNase protection assay in testis of vitamin A-deficient rats, and all-trans-retinoic acid dosing did not increase expression in vitamin A-deficient rat testis. A 2.3-kb section of the gene 5' to the transcription start site included neither retinoic acid nor retinoid X response elements, but included TATA and CCAAT motifs and AP, AHR, CREB, ER, Ets, and SREBP sites. The promoter initiated transcription of a luciferase reporter in human embryonic kidney cells (EBNA) and mouse Leydig- (TM3) and Sertoli-derived (TM4) cell lines, but neither all-trans-retinoic acid nor 9-cis-retinoic acid affected reporter transcription. These data suggest that relatively weak RALDH2 expression in vitamin A-deficient testis reflects vastly decreased numbers of germ cells, the major site of expression.

Nicotinamide adenine dinucleotide-dependent retinoic acid formation from retinol in the human gastric mucosa: inhibition by ethanol, acetaldehyde, and H2 blockers

All-trans retinoic acid formation from all-trans retinol (vitamin A) in the human gastric mucosa was studied. When all-trans retinol and the human gastric mucosa were incubated together, all-trans retinoic acid was formed in the presence of nicotinamide adenine dinucleotide (NAD). When the NAD was not added, hardly any formation was observed. The formation of all-trans retinoic acid tended to be attenuated by 10 mM ethanol. Moreover, it was significantly attenuated in a concentration-dependent manner by ethanol at concentrations of 100 mM and above. Acetaldehyde at concentrations of 50 microM and above also significantly attenuated its formation in a concentration-dependent manner. Some H2 blockers, which include ranitidine hydrochloride and cimetidine, significantly attenuated the formation of all-trans retinoic acid, whereas famotidine failed to suppress it. There is an NAD-dependent pathway by which all-trans retinoic acid is produced from all-trans retinol in the human gastric mucosa. Inhibitors of alcohol dehydrogenase, which include ethanol and some H2 blockers, and of aldehyde dehydrogenase, which include acetaldehyde, inhibit its production.

Genetic dissection of retinoid dehydrogenases

Biochemical studies indicate that alcohol dehydrogenase (ADH) metabolizes retinol to retinal, and that aldehyde dehydrogenase (ALDH) metabolizes retinal to retinoic acid, a molecule essential for growth and development. Summarized herein are several genetic studies supporting in vivo functions for ADH and ALDH in retinoic acid synthesis. Gene targeting was used to create knockout mice for either Adh1 or Adh4. Both knockout mice were viable and fertile without obvious defects. However, when wild-type and Adh4 knockout mice were subjected to vitamin A deficiency during gestation, the survival rate at birth was 3.3-fold lower for Adh4 knockout mice. When adult mice were examined for production of retinoic acid following retinol administration, Adh1 knockout mice exhibited 10-fold lower retinoic acid levels in liver compared with wild-type, whereas Adh4 knockout mice differed from wild-type by less than 2-fold. Thus, Adh1 plays a major role in the metabolism of a large dose of retinol to retinoic acid in adults, whereas Adh4 plays a role in maintaining sufficient retinol metabolism for development during retinol deficiency. ALDHs were examined by overexpression studies in frog embryos. Injection of mRNAs for either mouse Raldh1 or Raldh2 stimulated retinoic acid synthesis in frog embryos at the blastula stage when retinoic acid is normally undetectable. Overexpression of human ALDH2, human ALDH3, and mouse Aldh-pb did not stimulate retinoic acid production. In addition, Raldh2 knockout mice exhibit embryonic lethality with defects in retinoid-dependent tissues. Overall, these studies provide genetic evidence that Adh1, Adh4, Raldh1, and Raldh2 encode retinoid dehydrogenases involved in retinoic acid synthesis in vivo.

Inhibition of ALDH3A1-catalyzed oxidation by chlorpropamide analogues

In our efforts to identify agents that would specifically inhibit ALDH3A1, we had previously studied extensively the effect of an N(1)-alkyl, an N(1)-methoxy, and several N(1)-hydroxy-substituted ester derivatives of chlorpropamide on the catalytic activities of ALDH3A1s derived from human normal stomach mucosa (nALDH3A1) and human tumor cells (tALDH3A1), and of two recombinant aldehyde dehydrogenases, viz. human rALDH1A1 and rALDH2. The N(1)-methoxy analogue of chlorpropamide, viz. 4-chloro-N-methoxy-N-[(propylamino)carbonyl]benzenesulfonamide (API-2), was found to be a relatively selective and potent inhibitor of tALDH3A1-catalyzed oxidation as compared to its ability to inhibit nALDH3A-catalyzed oxidation, but even more potently inhibited ALDH2-catalyzed oxidation, whereas an ester analogue, viz. (acetyloxy)[(4-chlorophenyl)sulfonyl]carbamic acid 1,1-dimethylethyl ester (NPI-2), selectively inhibited tALDH3A1-catalyzed oxidation as compared to its ability to inhibit nALDH3A1-, ALDH1A1- and ALDH2-catalyzed oxidations, and this inhibition was apparently irreversible. Three additional chlorpropamide analogues, viz. 4-chloro-N,O-bis(ethoxycarbonyl)-N-hydroxybenzenesulfonamide (NPI-4), N,O-bis(carbomethoxy)methanesulfohydroxamic acid (NPI-5), and 2-[(ethoxycarbonyl)oxy]-1,2-benzisothiazol-3(2H)-one 1,1-dioxide (NPI-6), were evaluated in the present investigation. Quantified were NAD-linked oxidation of benzaldehyde catalyzed by nALDH3A1 and tALDH3A1, and NAD-linked oxidation of acetaldehyde catalyzed by rALDH1A1 and rALDH2, all at 37 degrees C and pH 8.1, and in the presence and absence of inhibitor. NPI-4, NPI-5 and NPI-6 were not substrates for the oxidative reactions catalyzed by any of the ALDHs studied. Oxidative reactions catalyzed by the ALDH3A1s, rALDH1A1 and rALDH2 were each inhibited by NPI-4 and NPI-5. NPI-6 was a poor inhibitor of nALDH3A1- and tALDH3A1-catalyzed oxidations, but was a relatively potent inhibitor of rALDH1A1- and rALDH2-catalyzed oxidations. In all cases, inhibition of ALDH-catalyzed oxidation was directly related to the product of inhibitor concentration and preincubation (enzyme+inhibitor) time. As judged by the product values (microMxmin) required to effect 50% inhibition (IC(50)): (1) nALDH3A1 and tALDH3A1 were essentially equisensitive to inhibition by NPI-4 and NPI-5, and both enzymes were poorly inhibited by NPI-6; (2) rALDH1A1 was, relative to the ALDH3A1s, slightly more sensitive to inhibition by NPI-4 and NPI-5, and far more sensitive to inhibition by NPI-6; and (3) rALDH1A1 was, relative to rALDH2, essentially equisensitive to inhibition by NPI-5, whereas, it was slightly more sensitive to inhibition by NPI-4 and NPI-6.

cDNA cloning and expression of a human aldehyde dehydrogenase (ALDH) active with 9-cis-retinal and identification of a rat ortholog, ALDH12

This report describes the isolation of a heretofore uncharacterized aldehyde dehydrogenase (ALDH) with retinal dehydrogenase activity from rat kidney and the cloning and expression of a cDNA that encodes its human ortholog, the previously unknown ALDH12. The human ALDH12 cDNA predicts a 487-residue protein with the 23 invariant amino acids, four conserved regions, cofactor binding motif (G(209)XGX(3)G), and active site cysteine residue (Cys(287)) that typify members of the ALDH superfamily. ALDH12 seems at least as efficient (V(m)/K(m)) in converting 9-cis-retinal into the retinoid X receptor ligand 9-cis-retinoic acid as two previously identified ALDHs with 9-cis-retinal dehydrogenase activity, rat retinal dehydrogenase (RALDH) 1 and RALDH2. ALDH12, however, has approximately 40-fold higher activity with 9-cis- retinal than with all-trans-retinal, whereas RALDH1 and RALDH2 have equivalent and approximately 4-fold less efficiencies for 9-cis-retinal versus all-trans-retinal, respectively. Therefore, ALDH12 is the first known ALDH to show a preference for 9-cis-retinal relative to all-trans-retinal. Evidence consistent with the possibility that ALDH12 could function in a pathway of 9-cis-retinoic acid biosynthesis in vivo includes biosynthesis of 9-cis-retinoic acid from 9-cis-retinol in cells co-transfected with cDNAs encoding ALDH12 and the 9-cis-retinol/androgen dehydrogenase, cis-retinoid/androgen dehydrogenase type 1. Intense ALDH12 mRNA expression in adult and fetal liver and kidney, two organs that reportedly have relatively high concentrations of 9-cis-retinol, reinforces this notion.

Identification of RALDH-3, a novel retinaldehyde dehydrogenase, expressed in the ventral region of the retina

In the developing retina, a retinoic acid (RA) gradient along the dorso-ventral axis is believed to be a prerequisite for the establishment of dorso-ventral asymmetry. This RA gradient is thought to result from the asymmetrical distribution of RA-generating aldehyde dehydrogenases along the dorso-ventral axis. Here, we identified a novel aldehyde dehydrogenase specifically expressed in the chick ventral retina, using restriction landmark cDNA scanning (RLCS). Since this molecule showed enzymatic activity to produce RA from retinaldehyde, we designated it retinaldehyde dehydrogenase 3 (RALDH-3). Structural similarity suggested that RALDH-3 is the orthologue of human aldehyde dehydrogenase 6. We also isolated RALDH-1 which is expressed in the chick dorsal retina and implicated in RA formation. Raldh-3 was preferentially expressed first in the surface ectoderm overlying the ventral portion of the prospective eye region and then in the ventral retina, earlier than Raldh-1 in chick and mouse embryos. High level expression of Raldh-3 was also observed in the nasal region. In addition, we found that Pax6 mutants are devoid of Raldh-3 expression. These results suggested that Raldh-3 is the key enzyme in the formation of an RA gradient along the dorso-ventral axis during the early eye development, and also in the development of the olfactory system.

Inactivation of aldophosphamide by human aldehyde dehydrogenase isozyme 3

Tumors resistant to chemotherapeutic oxazaphosphorines such as cyclophosphamide often overexpress aldehyde dehydrogenase (ALDH), some isozymes of which catalyze the oxidization of aldophosphamide, an intermediate of cyclophosphamide activation, with formation of inert carboxyphosphamide. Since resistance to oxazaphosphorines can be produced in mammalian cells by transfecting them with the gene for human ALDH isozyme 3 (hALDH3), it seems possible that patients receiving therapy for solid tumors with cyclophosphamide might be protected from myelosuppression by their prior transplantation with autologous bone marrow that has been transduced with a retroviral vector causing overexpression of hALDH3. We investigated whether retroviral introduction of hALDH3 into a human leukemia cell line confers resistance to oxazaphosphorines. This was examined in the polyclonal transduced population, that is, without selecting out high expression clones. hALDH3 activity was 0.016 IU/mg protein in the transduced cells (compared with 2x10(-5) IU/mg in untransduced cells), but there was no detectable resistance to aldophosphamide-generating compounds (mafosfamide or 4-hydroperoxycyclophosphamide). The lack of protection was due, in part, to low catalytic activity of hALDH3 towards aldophosphamide, since, with NAD as cofactor, the catalytic efficiency of homogeneous, recombinant hALDH3 for aldophosphamide oxidation was shown to be about seven times lower than that of recombinant hALDH1. The two polymorphic forms of hALDH3 had identical kinetics with either benzaldehyde or aldophosphamide as substrate. Results of initial velocity measurements were consistent with an ordered sequential mechanism for ALDH1 but not for hALDH3; a kinetic mechanism for the latter is proposed, and the corresponding rate equation is presented.

Families of retinoid dehydrogenases regulating vitamin A function: production of visual pigment and retinoic acid

Vitamin A (retinol) and provitamin A (beta-carotene) are metabolized to specific retinoid derivatives which function in either vision or growth and development. The metabolite 11-cis-retinal functions in light absorption for vision in chordate and nonchordate animals, whereas all-trans-retinoic acid and 9-cis-retinoic acid function as ligands for nuclear retinoic acid receptors that regulate gene expression only in chordate animals. Investigation of retinoid metabolic pathways has resulted in the identification of numerous retinoid dehydrogenases that potentially contribute to metabolism of various retinoid isomers to produce active forms. These enzymes fall into three major families. Dehydrogenases catalyzing the reversible oxidation/reduction of retinol and retinal are members of either the alcohol dehydrogenase (ADH) or short-chain dehydrogenase/reductase (SDR) enzyme families, whereas dehydrogenases catalyzing the oxidation of retinal to retinoic acid are members of the aldehyde dehydrogenase (ALDH) family. Compilation of the known retinoid dehydrogenases indicates the existence of 17 nonorthologous forms: five ADHs, eight SDRs, and four ALDHs, eight of which are conserved in both mouse and human. Genetic studies indicate in vivo roles for two ADHs (ADH1 and ADH4), one SDR (RDH5), and two ALDHs (ALDH1 and RALDH2) all of which are conserved between humans and rodents. For several SDRs (RoDH1, RoDH4, CRAD1, and CRAD2) androgens rather than retinoids are the predominant substrates suggesting a function in androgen metabolism as well as retinoid metabolism.