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

Identification of the class-3 aldehyde dehydrogenases present in human MCF-7/0 breast adenocarcinoma cells and normal human breast tissue

Affinity column chromatography was used to semipurify the very small amounts of class-3 aldehyde dehydrogenase (ALDH-3) present in human MCF-7/0 breast adenocarcinoma cells and human normal breast tissue. Characterization of the semipurified enzymes revealed that each was a type-1 ALDH-3 rather than a type-2 ALDH-3 as previously reported. Although clearly a type-1 ALDH-3, the MCF-7/0 enzyme, as well as the type-1 ALDH-3 constitutively present in cultured colon C cells and induced in cultured MCF-7/0 cells by methylcholanthrene, does, however, differ from the prototypical human stomach mucosa type-1 ALDH-3 in one, perhaps pharmacologically important, way, viz. when the ability to catalyse the oxidation of aldophosphamide is normalized by the ability to catalyse the oxidation of benzaldehyde, each of these enzymes, as well as the type-2 ALDH-3 found in MCF-7/OAP cells, exhibits greater ability to catalyse the oxidation of aldophosphamide than does stomach mucosa type-1 ALDH-3; hence, although not type-2 ALDH-3s, they may be slight variants of the prototypical type-1 ALDH-3.

Sensitivity of primary clonogenic blasts from acute lymphoblastic leukemia patients to an activated cyclophosphamide, viz., mafosfamide

Primary cyclophosphamide-naive clonogenic blasts from 32 patients with newly diagnosed acute lymphoblastic leukemia (ALL) were tested for their in vitro sensitivity to an "activated" cyclophosphamide, viz., mafosfamide, using leukemic progenitor cell (LPC) colony assays. Marked interpatient variation in the responses of LPC from newly diagnosed patients to mafosfamide prompted assessment of mafosfamide sensitivity in relation to more frequently measured parameters of newly diagnosed ALL. Only immunophenotype and sex showed a significant association with the intrinsic mafosfamide sensitivity of LPC. LPC from T-lineage ALL patients were more resistant to mafosfamide than LPC from B-lineage ALL patients, as reflected by 1.8-fold and 4.3-fold higher mean SF10 and SF20 (surviving fractions of ALL LPC of 10 and 20 microM mafosfamide, respectively) values. LPC from male patients were more resistant to mafosfamide than LPC from female patients, as reflected by 1.9-fold and 4.8-fold higher mean SF10 and SF20 values. In comparison to T-lineage ALL patients, a significantly greater fraction of B-lineage ALL patients had mafosfamide-sensitive LPC with SF10 values of < 0.25 (61% vs 11%, P = 0.01). Notably, all four cases exhibiting resistance to mafosfamide, i.e., SF20 > or = 0.5, were males with T-lineage ALL. In order to exclude the influence of sex as a confounding factor in the observed immunophenotype-mafosfamide sensitivity association, we also compared the mafosfamide sensitivities of LPC from male patients only. The means of SF10, and SF20 values of LPC from male T-lineage ALL patients were 1.5- and 3.2-fold higher than those of LPC from male B-lineage ALL patients (P < 0.1). Thus, in the male patient subgroup, the immunophenotype-mafosfamide sensitivity association remained significant.

Human liver aldehyde dehydrogenases: new method of purification of the major mitochondrial and cytosolic enzymes and re-evaluation of their kinetic properties

A new purification procedure, based on dye-adsorption and affinity chromatography, has been developed for the isolation of the two major ALDH isozymes from human liver: ALDH-1 (cytosolic, pI 5.2) and ALDH-2 (mitochondrial, pI 4.9). The procedure affords milligram quantities of ALDH-1 and -2 at 850- and 275-fold purifications, respectively, from 50 g of liver in two days. Kinetic parameters for acetaldehyde oxidation were determined with these purified enzymes, because there is a wide discrepancy in the absolute magnitude of these parameters in the biochemical literature. The Michaelis constants for ALDH-1 and -2, determined from initial velocities (for ALDH-1) and single reaction progress curves (for ALDH-2), are 180 +/- 10 microM and 0.20 +/- 0.02 microM, respectively (pH 7.5 and 9.5, saturating NAD+ in both cases). This three orders of magnitude difference in Km values is much greater than that reported previously in all but one study.

Detoxification of cyclophosphamide by human aldehyde dehydrogenase isozymes

In in vitro studies, no turnover of aldophosphamide and mafosfamide was observed with the tumor-specific aldehyde dehydrogenase 3 isozyme (ALDH3) isolated from human stomach mucosa as well as from lung (A549) and pharynx (UMSCC2) carcinoma cell lines. Only the human liver cytosolic ALDH preparation (ALDH1) showed any significant oxidation of aldophosphamide and mafosfamide.

Characteristic properties of retinal oxidase (retinoic acid synthase) from rabbit hepatocytes

Retinal oxidase (retinoic acid synthase) (EC 1.2.3.11) was purified electrophoretically, as a single protein band, from rabbit liver cytosol. The characteristic properties, enzymatic reaction mechanism, substrate specificity and kinetic parameters for retinals and molecular oxygen of the retinal oxidase were investigated. The Km values for all-trans-retinal of the retinal oxidase was the lowest than those for the other retinal derivatives. The retinal oxidase is a metalloflavoenzyme containing 2 FADs as the coenzyme, and 8 irons, 2 molybdenums, 2 disulfide bonds and 8 inorganic sulfurs. Its relative molecular mass was determined to be 270 kDa by gel filtration HPLC on a TSKgel G3000swXL column. Its minimum molecular mass was estimated to be 135 kDa by SDS-PAGE. The optical spectrum of the retinal oxidase showed absorption peaks at 275, 340 and 450 nm, and shoulders at 420 and 473 nm, in the oxidized form. The molecular extinction coefficients of the oxidase at selected wavelengths were determined. Circular dichroism spectra of the retinal oxidase were measured in the ultraviolet and visible regions. These spectra showed positive absorption in the visible region. The amino-acid composition was determined. The activity of the oxidase was not affected by any cofactors, such as NADP+, NAD+, NADPH and NADH, and it did not occur under anaerobic conditions. The oxidase was not inhibited by BOF-4272, a potent inhibitor of xanthine dehydrogenase, or rat anti-xanthine dehydrogenase IgG. Experiments on retinoic acid formation under 18O2 or H2(18)O demonstrated that the oxygen of water was incorporated into retinoic acid by the retinal oxidase, but not molecular oxygen.

Human aldehyde dehydrogenase. cDNA cloning and primary structure of the enzyme that catalyzes dehydrogenation of 4-aminobutyraldehyde

Human liver aldehyde dehydrogenase (E3 isozyme), with wide substrate specificity and low Km for 4-aminobutyraldehyde, was only recently characterized [Kurys, G., Ambroziak, W. & Pietruszko, R. (1989) J. Biol. Chem. 264, 4715-4721] and in this study we report on its primary structure. Polyclonal antibodies, specific for the E3 isozyme and three oligonucleotide probes derived from amino acid sequence of the E3 protein, were used for isolation of the first cDNA clone encoding the human enzyme (1503 bp; coding for 440 amino acid residues). Additional clones were obtained by using the first isolated clone as a probe. The largest clone of 1635 bp coded for 462 amino acid residues; it was longer at the 3'end of the cDNA non-coding region. The identity of the clone was established by DNA sequencing and by comparison with peptide sequences derived from the E3 protein, which constituted approximately 29% of the total primary structure of the E3 isozyme. The start codon was never encountered despite a variety of different approaches (500 amino acid residues were expected on the basis of SDS-gel molecular-mass determination of the E3 isozyme subunit). Despite the great catalytic similarity between the E3 and E1 isozymes [Ambroziak, W. & Pietruszko, R. (1991) J. Biol. Chem. 266, 13011-13018], the primary structure of the E3 isozyme has only approximately 40.6% of positional identity with that of the E1 isozyme. Sequence comparison with GenBank and Protein Identification Resource database sequences indicated no primary structure of aldehyde dehydrogenase more closely resembling the E3 isozyme than that of Escherichia coli betaine aldehyde dehydrogenase (52.7% positional identity), a prokaryotic enzyme specific for betaine aldehyde.

NADPH-dependent enzyme-catalyzed reduction of aldophosphamide, the pivotal metabolite of cyclophosphamide

One of the metabolites found in the urine of mammals given the prodrug cyclophosphamide is alcophosphamide, an alcohol. It is most probably generated from cyclophosphamide via aldophosphamide, an aldehyde which otherwise can directly give rise to phosphoramide mustard; the latter effects the cytotoxic action of cyclophosphamide and other oxazaphosphorines. It has already been demonstrated that horse liver alcohol dehydrogenase catalyzes the reduction of aldophosphamide to alcophosphamide. Herein, we report that aldose reductase and aldehyde reductase purified from human placenta also catalyze this reaction. The Km values for aldose reductase- and aldehyde reductase-catalyzed reduction of aldophosphamide to alcophosphamide were 0.15 and 1.6 mM, respectively. Aldose reductase and aldehyde reductase accounted for 94 and 6%, respectively, of total placental pyridine nucleotide-dependent enzyme-catalyzed aldophosphamide (160 microM) reduction. Aldose reductase-catalyzed reduction of aldophosphamide appeared to be noncompetitively inhibited by sorbinil; the Ki value was 0.4 microM. The in vivo significance of these observations is uncertain but could be of some magnitude since alcophosphamide is known to be only weakly cytotoxic.

Identification and characterization of a novel class 3 aldehyde dehydrogenase overexpressed in a human breast adenocarcinoma cell line exhibiting oxazaphosphorine-specific acquired resistance

Associated with the oxazaphosphorine-specific acquired resistance exhibited by a human breast adenocarcinoma subline growing in monolayer culture, viz. MCF-7/OAP, was the overexpression (> 100-fold as compared with the very small amount expressed in the oxazaphosphorine-sensitive parent line) of a class 3 aldehyde dehydrogenase, viz. ALDH-3, judged to be so because it is a polymorphic enzyme (pI values ca. 6.0) present in the cytosol that is heat labile, is insensitive to inhibition by disulfiram (25 microM), much prefers benzaldehyde to acetaldehyde as a substrate and, at concentrations of 4 mM, prefers NADP to NAD as a cofactor. No other aldehyde dehydrogenases were found in these cells. As compared with those of the prototypical class 3 human ALDH-3, viz. constitutive human stomach mucosa ALDH-3, the physical and catalytic properties of the MCF-7/OAP enzyme differed somewhat with regard to pI values, native M(r), subunit M(r), recognition of the subunit by anti-stomach ALDH-3 IgY, pH stability, cofactor influence on catalytic activity, and the ability to catalyze, albeit poorly, the oxidation of an oxazaphosphorine, viz. aldophosphamide. Hence, the MCF-7/OAP ALDH-3 was judged to be a novel class 3 aldehyde dehydrogenase. Small amounts of a seemingly identical enzyme are also present in normal pre- and post-menopausal breast tissue. None could be detected in human liver, kidney or placenta, suggesting that it may be a tissue-specific enzyme.

Physiology of endocrine skin interrelations

Hormones influence the skin and play a role in normal biologic processes. Keratinocytes can convert and synthesize endocrine hormones. Endocrine dysregulation of the skin and abnormalities of endocrine functions of keratinocytes may produce abnormal changes in the skin. Knowledge of the cutaneous metabolism of thyroid hormones, steroids, peptide hormones, and vitamin A derivatives is being rapidly updated. Skin manifestations of endocrine disorders result from imbalance in feedback loops maintaining endocrine homeostasis. Define molecular mechanisms of hormonal action on target cells underlie functional agonism and antagonism of hormonal signals aimed at governing epidermal turnover. The molecular synergism between vitamin A and other hormones may explain the therapeutic efficiency of combining retinoids with other therapies.

Metabolic polymorphisms

Polymorphisms have been detected in a variety of xenobiotic-metabolizing enzymes at both the phenotypic and genotypic level. In the case of four enzymes, the cytochrome P450 CYP2D6, glutathione S-transferase mu, N-acetyltransferase 2 and serum cholinesterase, the majority of mutations which give rise to a defective phenotype have now been identified. Another group of enzymes show definite polymorphism at the phenotypic level but the exact genetic mechanisms responsible are not yet clear. These enzymes include the cytochromes P450 CYP1A1, CYP1A2 and a CYP2C form which metabolizes mephenytoin, a flavin-linked monooxygenase (fish-odour syndrome), paraoxonase, UDP-glucuronosyltransferase (Gilbert's syndrome) and thiopurine S-methyltransferase. In the case of a further group of enzymes, there is some evidence for polymorphism at either the phenotypic or genotypic level but this has not been unambiguously demonstrated. Examples of this class include the cytochrome P450 enzymes CYP2A6, CYP2E1, CYP2C9 and CYP3A4, xanthine oxidase, an S-oxidase which metabolizes carbocysteine, epoxide hydrolase, two forms of sulphotransferase and several methyltransferases. The nature of all these polymorphisms and possible polymorphisms is discussed in detail, with particular reference to the effects of this variation on drug metabolism and susceptibility to chemically-induced diseases.

Topographic maps and molecular gradients

Topographically organized patterns of connectivity occur throughout the central and peripheral nervous systems. It is commonly supposed that gradients of recognition molecules underlie this form of synaptic specificity. Recent studies have led to new ideas about how such gradients might arise in the retinotectal system, and initiated molecular analyses of position-dependent gene expression in the peripheral motor system.

Sensitivity of aldehyde dehydrogenases in murine tumor and hematopoietic progenitor cells to inhibition by chloral hydrate as determined by the ability of chloral hydrate to potentiate the cytotoxic action of mafosfamide

Several murine aldehyde dehydrogenases, most notably AHD-2, are known to catalyze the detoxification of cyclophosphamide, mafosfamide, and other oxazaphosphorines. Thus, cellular sensitivity to these agents decreases as the relevant aldehyde dehydrogenase activity increases, and vice versa. Chloral hydrate is a sedative/hypnotic agent that is sometimes administered to patients being treated with cyclophosphamide. It is known to inhibit some, but not all, aldehyde dehydrogenases. Murine (CFU-S, CFU-GEMM and CFU-Mk) and human (CFU-Mix, CFU-GM, BFU-E and CFU-Mk) hematopoietic progenitor cells, as well as murine oxazaphosphorine-resistant (L1210/OAP and P388/CLA) tumor cells, are known to contain the relevant aldehyde dehydrogenase activity but the identity of the specific enzyme present in the normal cells is unknown and may be different than that, namely AHD-2, present in neoplastic cells. In that event, the potential exists to inhibit the detoxification of the oxazaphosphorines in tumor cells without inhibiting this event in normal cells; the net effect of such a selective inhibition would be to increase the margin of safety of the oxazaphosphorines. In ex vivo experiments, chloral hydrate markedly potentiated the antitumor activity of mafosfamide against oxazaphosphorine-resistant L1210/OAP and P388/CLA cells. It did not potentiate the cytotoxic action of mafosfamide against any of the murine or human hematopoietic cells tested, even at concentrations which fully restored the sensitivity of the resistant tumor cell lines to this agent. One explanation for these observations is that hematopoietic progenitor, and the resistant tumor, cells express different relevant aldehyde dehydrogenases and that these aldehyde dehydrogenases differ in their sensitivity to inhibition by chloral hydrate. Consistent with this notion were the observations that AHD-2 was exquisitely sensitive to inhibition by chloral hydrate, whereas two other aldehyde dehydrogenases that also catalyze the detoxification of aldophosphamide, namely AHD-12a, b and AHD-13, were relatively unaffected.