Human mitochondrial aldehyde dehydrogenase inhibition by diethyldithiocarbamic acid methanethiol mixed disulfide: a derivative of disulfiram

Incorporation of nitric oxide donor into 1,3-dioxyxanthones leads to synergistic anticancer activity

Fifty 1,3-dioxyxanthone nitrates (4a ∼ i-n, n = 1-6) were designed and synthesized based on molecular similarity strategy. Incorporation of nitrate into 1,3-dioxyxanthones with electron-donating groups at 6-8 position brought about synergistic anticancer effect. Among them, compound 4g-4 was confirmed the most active agent against HepG-2 cells growth with an IC₅₀ of 0.33 ± 0.06 μM. It dose-dependently increased intramolecular NO levels. This activity was attenuated by either NO scavenger PTIO or mitochondrial aldehyde dehydrogenase (mtADH) inhibitor PCDA. Apoptosis analysis indicated different contributions of early/late apoptosis and necrosis to cell death for different dose of 4g-4. 4g-4 arrested more cells on S phase. Results from Western Blot implied that 4g-4 regulated p53/MDM2 to promote cancer cell apoptosis. All the evidences support that 4g-4 is a promising anti-cancer agent.

Exploring the structural requirements for inhibition of the ubiquitin E3 ligase breast cancer associated protein 2 (BCA2) as a treatment for breast cancer

The zinc-ejecting aldehyde dehydrogenase (ALDH) inhibitory drug disulfiram (DSF) was found to be a breast cancer-associated protein 2 (BCA2) inhibitor with potent antitumor activity. We herein describe our work in the synthesis and evaluation of new series of zinc-affinic molecules to explore the structural requirements for selective BCA2-inhibitory antitumor activity. An N(C=S)S-S motif was found to be required, based on selective activity in BCA2-expressing breast cancer cell lines and against recombinant BCA2 protein. Notably, the DSF analogs (3a and 3c) and dithio(peroxo)thioate compounds (5d and 5f) were found to have potent activity (submicromolar IC(50)) in BCA2 positive MCF-7 and T47D cells but were inactive (IC(50) > 10 microM) in BCA2 negative MDA-MB-231 breast cancer cells and the normal breast epithelial cell line MCF10A. Testing in the isogenic BCA2 +ve MDA-MB-231/ER cell line restored antitumor activity for compounds that were inactive in the BCA2 -ve MDA-MB-231 cell line. In contrast, structurally related dithiocarbamates and benzisothiazolones (lacking the disulfide bond) were all inactive. Compounds 5d and 5f were additionally found to lack ALDH-inhibitory activity, suggestive of selective E3 ligase-inhibitory activity and worthy of further development.

Metabolism of Homovanillamine to Homovanillic Acid in Guinea Pig Liver Slices

BACKGROUND/AIMS

Homovanillamine is a biogenic amine that it is catalyzed to homovanillyl aldehyde by monoamine oxidase A and B, but the oxidation of its aldehyde to the acid derivative is usually ascribed to aldehyde dehydrogenase and a potential contribution of aldehyde oxidase and xanthine oxidase is usually ignored.

METHODS

The present investigation examines the metabolism of homovanillamine to its acid derivative by concurrent incubation with monoamine oxidase and aldehyde oxidase. In addition, the metabolism of homovanillamine in freshly prepared and cryopreserved liver slices is examined and the relative contribution of aldehyde oxidase, xanthine oxidase and aldehyde dehydrogenase activity by using specific inhibitors of each oxidizing enzyme is compared.

RESULTS

Homovanillamine was rapidly converted mainly to homovanillic acid when incubated with both momoamine oxidase and aldehyde oxidase. Homovanillic acid was also the main metabolite in the incubations of homovanillamine with freshly prepared or cryopreserved liver slices, via the intermediate homovanillyl aldehyde. The acid formation was 70-75 % inhibited by disulfiram (specific inhibitor of aldehyde dehydrogenase), whereas isovanillin (specific inhibitor of aldehyde oxidase) inhibited acid formation to a lesser extent (50-55 %) and allopurinol (specific inhibitor of xanthine oxidase) had almost no effect.

CONCLUSIONS

Homovanillamine is rapidly oxidized to its acid, via homovanillyl aldehyde, by aldehyde dehydrogenase and aldehyde oxidase with little or no contribution from xanthine oxidase.

Modulation of the reactivity of the essential cysteine residue of betaine aldehyde dehydrogenase from Pseudomonas aeruginosa

Betaine aldehyde dehydrogenase (BADH) catalyses the irreversible NAD(P)(+)-dependent oxidation of betaine aldehyde to glycine betaine. In the human opportunistic pathogen Pseudomonas aeruginosa this reaction is an obligatory step in the assimilation of carbon and nitrogen when bacteria are growing in choline or choline precursors. As with every aldehyde dehydrogenase studied so far, BADH possesses an essential cysteine residue involved in the formation of the intermediate thiohemiacetal with the aldehyde substrate. We report here that the chemical modification of this residue is conveniently measured by the loss in enzyme activity, which allowed us to explore its reactivity in a pH range around neutrality. The pH dependence of the observed second-order rate constant of BADH inactivation by methyl methanethiosulphonate (MMTS) suggests that at low pH values the essential cysteine residue exists as thiolate by the formation of an ion pair with a positively charged residue. The estimated macroscopic pK values are 8.6 and 4.0 for the free and ion-pair-forming thiolate respectively. The reactivity towards MMTS of both thiolate forms is notably lower than that of model compounds of similar pK, suggesting a considerable steric inhibition by the structure of the protein. Binding of the dinucleotides rapidly induced a significant and transitory increment of thiolate reactivity, followed by a relatively slow change to an almost unreactive form. Thus it seems that to gain protection against oxidation without compromising catalytic efficiency, BADH from P. aeruginosa has evolved a complex and previously undescribed mechanism, involving several conformational rearrangements of the active site, to suit the reactivity of the essential thiol to the availability of coenzyme and substrate.

S-methyl-N,N-diethylthiocarbamate sulfoxide and S-methyl-N,N-diethylthiocarbamate sulfone, two candidates for the active metabolite of disulfiram

The mechanism of action of disulfiram involves inhibition of hepatic aldehyde dehydrogenase (ALDH). Although disulfiram inhibits ALDH in vitro, it is believed that the drug is too short-lived in vivo to inhibit the enzyme directly. The ultimate inhibitor is thought to be a metabolite of disulfiram. In this study, we examined the effects of S-methyl-N,N-diethylthiocarbamate (MeDTC) sulfoxide and S-methyl-N,N-diethylthiocarbamate sulfone (confirmed and proposed metabolites of disulfiram, respectively) on rat liver mitochondrial low K(m) ALDH. MeDTC sulfoxide and MeDTC sulfone, in 10-min incubations with detergent-solubilized mitochondria, inhibited ALDH activity with an IC50 (mean +/- SD) of 0.93 +/- 0.04 and 0.53 +/- 0.11 microM, respectively, compared with 7.4 +/- 1.0 microM for the parent drug disulfiram. Inhibition by MeDTC sulfone and MeDTC sulfoxide, both at 0.6 microM, was time-dependent, following apparent pseudo-first-order kinetics with a t1/2 of inactivation of 3.5 and 8.8 min, respectively. Dilution of ALDH inhibited by either sulfoxide or sulfone did not restore activity, an indication of irreversible inhibition. Addition of glutathione (50 to 1000 microM) to ALDH before the inhibitors did not alter the inhibition by MeDTC sulfoxide. In contrast, the inhibition by MeDTC sulfone was decreased > 10-fold (IC50 = 6.3 microM) by 50 microM of glutathione and almost completely abolished by 500 microM of glutathione. The cofactor NAD, in a concentration-dependent manner, protected ALDH from inhibition by MeDTC sulfoxide and MeDTC sulfone. In incubations with intact mitochondria, the potency of the two compounds was reversed (IC50 of 9.2 +/- 3.6 and 0.95 +/- 0.30 microM for the MeDTC sulfone and sulfoxide, respectively). Our results suggest that MeDTC sulfone is highly reactive with normal cellular constituents (e.g., glutathione), which may protect ALDH from inhibition, unless this inhibitor is formed very near the target enzyme. In contrast, MeDTC sulfoxide is a better candidate for the ultimate active metabolite of disulfiram, because it is more likely to be sufficiently stable to diffuse from a distant site of formation, such as the endoplasmic reticulum, penetrate the mitochondria, and react with ALDH located in the mitochondrial matrix.

Possible role of liver cytosolic and mitochondrial aldehyde dehydrogenases in acetaldehyde metabolism

To provide a molecular basis for understanding the possible mechanism of action of antidipsotropic agents in laboratory animals, aldehyde dehydrogenase (ALDH) isozymes were purified and characterized from the livers of hamsters and rats and compared with those from humans. The mitochondrial ALDHs from these species exhibit virtually identical kinetic properties in the oxidation and hydrolysis reactions. However, the cytosolic ALDH of human origin differs significantly from those of the rodents. Thus, for human ALDH-1, the Km value for acetaldehyde is 180 +/- 10 micromolar, whereas those for hamster ALDH-1 and rat ALDH-1 are 12 +/- 3 and 15 +/- 3 micromolar, respectively. Km values determined at pH 9.5 are virtually identical to those measured at pH 7.5. In vitro human ALDH-1 is 10 times less sensitive to disulfiram inhibition than are the hamster and rat cytosolic ALDHs. Competition between acetaldehyde and aromatic aldehydes or naphthaldehydes for the binding and catalytic sites of ALDHs shows their topography to be complex with more than one binding site. This also follows from data on substrate inhibition and activation, effects of NAD+ on ALDH-catalyzed hydrolysis of p-nitrophenyl esters, substrate specificity toward aldehydes and p-nitrophenyl esters, and inhibition by disulfiram in relation to oxidation and hydrolysis catalyzed by the ALDHs. The data further suggest that acetaldehyde cannot be considered as a "standard" ALDH substrate for studies aimed at aromatic ALDH substrates, e.g. biogenic aldehydes. Apparently, in human liver, only mitochondrial ALDH oxidizes acetaldehyde at physiological concentrations, whereas in hamster or rat liver, both the mitochondrial and cytosolic isozymes will do so.

Altered methional homoeostasis is associated with decreased apoptosis in BAF3 bcl2 murine lymphoid cells

Methional is a potent inducer of apoptosis in an interleukin 3-dependent murine lymphoid cell line BAF3 b0 when it is added to the culture medium. In these cells transfected with the bcl2 gene, BAF3 bcl2, the apoptotic-inducing activity of methional is dramatically reduced. The addition of disulfiram (an inhibitor of aldehyde dehydrogenase) in order to reduce methional oxidation brought about an increase in apoptosis in BAF3 b0 but not in BAF3 bcl2 cells. In contrast, the addition of quercetin (an inhibitor of aldehyde reductase) in an attempt to diminish methional reduction increased apoptosis in both BAF3 b0 and BAF3 bcl2 cells. The extent of DNA fragmentation in BAF3 bcl2 cells approached that in BAF3 b0 cells in the presence of quercetin and exogenous methional, suggesting a defect in methional biosynthesis in BAF3 bcl2 cells. Direct evidence for this was obtained by measuring labelled methional in cells incubated with the sodium, salt of [U-14C]4-methylthio-2-oxobutanoic acid (MTOB), the precursor of methional. The 80% decrease in labelled methional in BAF3 bcl2 compared with BAF3 b0 cells was accompanied by a concomitant rise in the transamination of [14C]MTOB to [14C]methionine in BAF3 bcl2 cells. Inhibition of the transaminase, however, by a synthetic transition-state-type compound, pyridoxal-L-methionine ethyl ester, induced apoptosis in BAF3 b0 but not in BAF3 bcl2 cells, confirming that the defect in BAF3 bcl2 cells was not in the transaminase itself but rather in the oxidative decarboxylation step MTOB --> methional. In addition, no evidence was obtained for the synthesis of [14C]malondialdehyde from [14C]methional in BAF3 bcl2 cells. As these cells show no deficiency in their content of reactive oxygen species compared with that of BAF3 b0 cells, they may possess some other defect in the beta-hydroxylase enzyme system itself.

In vivo pharmacodynamic studies of the disulfiram metabolite S-methyl N,N-diethylthiolcarbamate sulfoxide: inhibition of liver aldehyde dehydrogenase

S-methyl N,N-diethylthiolcarbamate sulfoxide (DETC-MeSO) is proposed to be the metabolite of disulfiram responsible for the in vivo inhibition of liver low Km aldehyde dehydrogenase (ALDH) in the rat. Studies were conducted in male Sprague-Dawley rats and also in vitro using both rat liver mitochondrial and purified bovine mitochondrial low Km ALDH to investigate further the pharmacodynamic and pharmacokinetic characteristics of DETC-MeSO. Administration of DETC-MeSO to rats produced a rapid and maximal inhibition of liver mitochondrial low Km ALDH within 2 hr, which was still inhibited 30% after 168 hr. After DETC-MeSO treatment, the maximum plasma concentration of DETC-MeSO was reached within 0.5 hr, with DETC-MeSO being undetectable 2 hr after DETC-MeSO dosing. Although a trace amount of DETC-Me was detected in the plasma 0.5 hr after DETC-MeSO administration to rats, this disappeared within 1 hr. When rats were treated with disulfiram, the maximal plasma concentration of DETC-MeSO was found within 2 hr, with only a very small quantity of DETC-MeSO still detectable after 8 hr. Rats also were given the disulfiram metabolites diethyldithiocarbamate (DDTC), diethyldithiocarbamate-methyl ester (DDTC-Me), and S-methyl N,N-diethylthiolcarbamate (DETC-Me), and plasma analyzed for DETC-MeSO 2 hr after the administration of these metabolites. DETC-MeSO was detected in plasma, further illustrating that DETC-MeSO can be found in plasma after the administration of either disulfiram, or the subsequent in vivo metabolites DDTC, DDTC-Me, or DETC-Me.(ABSTRACT TRUNCATED AT 250 WORDS)

Bioactivation of S-methyl N,N-diethylthiolcarbamate to S-methyl N,N-diethylthiolcarbamate sulfoxide. Implications for the role of cytochrome P450

Diethyldithiocarbamate (DDTC), diethyldithiocarbamate methyl ester (DDTC-Me), S-methyl N,N-diethylthiolcarbamate (DETC-Me) and S-methyl N,N-diethylthiolcarbamate sulfoxide (DETC-MeSO) are all metabolites of disulfiram. All inhibit rat liver low Km aldehyde dehydrogenase (ALDH) in vivo, with the order of potency being DETC-MeSO > DETC-Me > DDTC-Me > DDTC. Studies were carried out both in vivo and in vitro to further investigate the role of bioactivation as a requirement for the action of disulfiram as a liver ALDH inhibitor. The cytochrome P450 inhibitor 1-benzylimidazole (NBI) was employed as a pharmacological tool to study the metabolism of DETC-Me to DETC-MeSO. Administration of NBI to rats prior to DETC-Me treatment blocked the inhibition of liver mitochondrial low Km ALDH by DETC-Me. This was accompanied by an increase in plasma DETC-ME and a decrease in plasma DETC-MeSO. Pretreatment of rats with NBI prior to DETC-MeSO administration did not block the inhibition of liver mitochondrial low Km ALDH by DETC-MeSO. In in vitro studies, the inclusion of NBI in an incubation containing rat liver microsomes, mitochondria and an NADPH-generating system blocked the formation of DETC-MeSO and inhibition of liver mitochondrial low Km ALDH by DETC-Me. DETC-MeSO was found to be a potent inhibitor of rat liver mitochondrial low Km ALDH both in vivo and in vitro. The data suggest that the metabolism of DETC-Me to DETC-MeSO is mediated by cytochrome P450, and that inhibition of cytochrome P450 by inhibitors such as NBI block the inhibition of low Km ALDH by DETC-Me.

In vivo effects of disulfiram and cyanamide on canine liver aldehyde dehydrogenase isoenzymes as detected by high-performance (pressure) liquid chromatography

Methods for analysis of aldehyde dehydrogenase isoenzymes using high-performance (pressure) liquid chromatography (HPLC) were used to determine in vivo effects of disulfiram and cyanamide on canine liver aldehyde dehydrogenase (ALDH) isoenzymes. Liver ALDH isoenzymes from control and disulfiram- or cyanamide-treated dogs were separated by ion-exchange HPLC, and enzyme activity was detected using a postcolumn reactor. Two major peaks of ALDH activity (peaks I and II) were detected. Varying the composition of the reaction column reagents resulted in alterations in the elution profiles consistent with the kinetic properties of individual isoenzymes (i.e., ALDH IB in peak I and ALDH IIB in peak II), including estimates of the Km for acetaldehyde and the effects of magnesium ions on ALDH activity. Disulfiram treatment decreased both peaks depending on disulfiram dose and length of treatment, with peak I being more sensitive to inactivation than peak II. Reagents containing MgCl2 (1 mM) decreased peak I and increased peak II compared with EDTA (1 mM) for samples from both control and disulfiram-treated animals. These data are consistent with the assignment of the disulfiram-sensitive isoenzyme (ALDH IB) to peak I and the isoenzyme stimulated by magnesium ions (ALDH IIB) to peak II. In vivo cyanamide treatment produced similar decreases in both peaks to a maximum decrease of approximately 30% of control depending on cyanamide dose. Peak I, however, was more sensitive than peak II to in vitro inactivation by cyanamide, which suggests that cytosolic ALDH in the dog (in contrast to other mammals) is more sensitive to inactivation than mitochondrial ALDH.

Daidzin: a potent, selective inhibitor of human mitochondrial aldehyde dehydrogenase

Human mitochondrial aldehyde dehydrogenase (ALDH-I) is potently, reversibly, and selectively inhibited by an isoflavone isolated from Radix puerariae and identified as daidzin, the 7-glucoside of 4',7-dihydroxyisoflavone. Kinetic analysis with formaldehyde as substrate reveals that daidzin inhibits ALDH-I competitively with respect to formaldehyde with a Ki of 40 nM, and uncompetitively with respect to the coenzyme NAD+. The human cytosolic aldehyde dehydrogenase isozyme (ALDH-II) is nearly 3 orders of magnitude less sensitive to daidzin inhibition. Daidzin does not inhibit human class I, II, or III alcohol dehydrogenases, nor does it have any significant effect on biological systems that are known to be affected by other isoflavones. Among more than 40 structurally related compounds surveyed, 12 inhibit ALDH-I, but only prunetin and 5-hydroxydaidzin (genistin) combine high selectivity and potency, although they are 7- to 15-fold less potent than daidzin. Structure-function relationships have established a basis for the design and synthesis of additional ALDH inhibitors that could both be yet more potent and specific.

Effect of some thiocarbamate compounds on aldehyde dehydrogenase and implications for the disulfiram ethanol reaction

The effects of S-methyl diethyldithiocarbamate, S-methyl diethylmonothiocarbamate and bis(diethylcarbamoyl) disulphide on sheep liver cytoplasmic aldehyde dehydrogenase were investigated in vitro. The first compound has negligible effect. The second one is a weak inhibitor of the esterase activity of the enzyme and a weaker inhibitor of the dehydrogenase activity. A very low concentration of the third compound, however, acts as a potent inactivator of aldehyde dehydrogenase, similar in this respect to disulfiram, although somewhat slower to react. The possible involvement of these compounds in the physiological phenomenon known as the disulfiram ethanol reaction is discussed.

Purification and characterization of aldehyde dehydrogenase from rat liver mitochondrial matrix

Aldehyde dehydrogenase (EC 1.2.1.3) has been purified to homogeneity from Sprague-Dawley rat liver mitochondrial matrix; its specific activity with propionaldehyde (1 mM at pH 9.0) is 1.4 mumol/min/mg. It has a native molecular weight of ca. 260,000 daltons, a subunit weight of 54,000 daltons and separates into two bands on isoelectric focusing (pI, 5.15 and 5.30); its extinction coefficient at 280 nm for 1 mg/ml solution is 1.2 and 280/260 nm ratio is 1.6. The enzyme prefers NAD over NADP as the coenzyme; the Km for NADP (67,000 microM) is three orders of magnitude greater than that for NAD (61 microM); the Km for acetaldehyde is 2 microM and for propionaldehyde is 0.8 microM at pH 7.0. The enzyme is reversibly inhibited by chloral (Ki = 3 microM) but is resistant to disulfiram inhibition. In addition another aldehyde dehydrogenase, first observed in the mitochondrial matrix during isoelectric focusing, has been partially purified. It has a Km for propionaldehyde of 0.7 mM and an isoelectric point of 6.4. Its activity with glutamic-gamma-semialdehyde (Km = 0.13 mM) is ca. 20 times higher than with propionaldehyde identifying the enzyme as glutamic-gamma-semialdehyde dehydrogenase (EC 1.5.1.12).

Use of leukocyte aldehyde dehydrogenase activity to monitor inhibitory effect of disulfiram treatment

Aldehyde dehydrogenase (ALDH; EC 1.2.1.3) activity was determined in leukocytes and erythrocytes from alcoholic patients during different stages of disulfiram (Antabuse) treatment. Assays were performed by incubating intact isolated blood cells in phosphate-buffered saline (pH 7.4, 37 degrees C), using 3,4-dihydroxyphenylacetaldehyde (DOPAL), the biogenic aldehyde derived from dopamine, as substrate. The ALDH activity was assessed from the amount of 3,4-dihydroxyphenylacetic acid (DOPAC) formed, as analysed by high-performance liquid chromatography with electrochemical detection. The leukocyte ALDH, which is similar to the liver "mitochondrial" low-Km ALDH isozyme, was maximally inhibited (about 40-60%) within 2 to 3 days after the initial disulfiram administration (dosage 200 or 400 mg/day orally). The time to reach maximum inhibition (about 95%) of the erythrocyte ALDH, which closely resembles the liver "cytosolic" high-Km isozyme, varied from 3 to more than 6 days. When medication was completed, the leukocyte ALDH activity remained unaltered for the first 2 days, and did not revert to normal levels until about 6 to 7 days after terminating treatment. The erythrocyte ALDH was still inhibited by about 90% 1 week after the last disulfiram administration. These results suggest that the leukocyte ALDH activity might provide an easily accessible marker for monitoring effect and time course of ALDH inhibition during disulfiram treatment.

Inhibition of human erythrocyte and leukocyte aldehyde dehydrogenase activities by diethylthiocarbamic acid methyl ester. An in vivo metabolite of disulfiram

The inhibitory effects of diethylthiocarbamic acid methyl ester (DTC-Me), an in vivo metabolite of disulfiram (Antabuse), on the aldehyde dehydrogenase (ALDH; EC 1.2.1.3) activities in human erythrocytes and leukocytes were studied. ALDH assays were performed by incubating intact isolated blood cells in the presence of different concentrations of DTC-Me, using 3,4-dihydroxy-phenylacetaldehyde, the aldehyde derived from dopamine, as the substrate. DTC-Me was more selective as inhibitor of the leukocyte ALDH activity (which resembles the liver "mitochondrial" low Km ALDH), whereas both disulfiram and diethyldithiocarbamic acid, the reduced monomer of disulfiram, were more selective for the erythrocyte ALDH (which is similar to the "cytosolic" high-Km ALDH). Diethylthiocarbamic acid, the free acid of DTC-Me, was less potent than DTC-Me, and caused similar inactivation of the erythrocyte and leukocyte ALDH activities. The inhibition of ALDH by DTC-Me could not be completely restored by extensive dilution of intact or sonicated blood cell samples, which indicated that ALDH was irreversibly inhibited. Since the inhibition patterns with DTC-Me agrees with the previously reported patterns of inhibition of the high-Km and low-Km isozymes after the administration of disulfiram, the results suggest that DTC-Me might be the active in vivo inhibitory metabolite of disulfiram.

Reaction between sheep liver mitochondrial aldehyde dehydrogenase and various thiol-modifying reagents

Sheep liver mitochondrial aldehyde dehydrogenase reacts with 2,2'-dithiodipyridine and 4,4'-dithiodipyridine in a two-step process: an initial rapid labelling reaction is followed by slow displacement of the thiopyridone moiety. With the 4,4'-isomer the first step results in an activated form of the enzyme, which then loses activity simultaneously with loss of the label (as has been shown to occur with the cytoplasmic enzyme). With 2,2'-dithiodipyridine, however, neither of the two steps of the reaction has any effect on the enzymic activity, showing that the mitochondrial enzyme possesses two cysteine residues that must be more accessible or reactive (to this reagent at least) than the postulated catalytically essential residue. The symmetrical reagent 5,5'-dithiobis-(1-methyltetrazole) activates mitochondrial aldehyde dehydrogenase approximately 4-fold, whereas the smaller related compound methyl l-methyltetrazol-5-yl disulphide is a potent inactivator. These results support the involvement of mixed methyl disulphides in causing unpleasant physiological responses to ethanol after the ingestion of certain antibiotics.

Effects of disulfiram, cyanamide and 1-aminocyclopropanol on the aldehyde dehydrogenase activity in human erythrocytes and leukocytes

The effects of the aldehyde dehydrogenase (ALDH; EC 1.2.1.3) inhibitors disulfiram, cyanamide and 1-aminocyclopropanol (ACP) on the ALDH activities in human erythrocytes and leukocytes were studied. Assays were performed by incubating intact or sonicated blood cells in the presence of different concentrations of the inhibitors, using 3,4-dihydroxyphenylacetaldehyde, the aldehyde derived from dopamine oxidation, as the substrate. The amount of acid metabolite formed was measured using high-performance liquid chromatography with electrochemical detection. The erythrocyte ALDH was extremely sensitive to disulfiram, and only about 0.5 microM was needed to cause a 50% inhibition of the activity. The leukocyte activity was less sensitive, and showed a similar degree of inhibition at an 100-fold higher concentration of disulfiram. Cyanamide and ACP were both potent inactivators of the leukocyte ALDH activity, giving a 50% inhibition at concentrations of 10 and 50 microM, respectively, whereas the erythrocyte activity was much less affected. Diethyldithiocarbamate, the reduced metabolite of disulfiram, and coprine, from which ACP is derived, were much less effective inhibitors of the erythrocyte and leukocyte ALDH activities than were disulfiram and ACP.

Aldehyde dehydrogenase activity in brain and liver of the rainbow trout (Salmo gairdneri Richardson)

Aldehyde dehydrogenase (ALDH) activity was measured in brain and liver of rainbow trout by using 3,4-dihydroxyphenylacetaldehyde (DOPAL, the biogenic aldehyde derived from dopamine) as the substrate. The amount of the corresponding acid produced was quantified by high-performance liquid chromatography with electrochemical detection. Both in brain and liver, the ALDH activity showed a high affinity for the substrate with an apparent Km of 3.7 microM in brain and 2.4 microM in liver. The kinetic experiments with brain ALDH also indicated the presence of an isozyme with a low affinity for DOPAL with a Km around 150 microM. The Vmax of the liver ALDH activity varied between 179 and 536 nmol/min.g, i.e., about 25-75 times higher than that of the low-Km activity in brain. The ALDH activity showed a maximum around pH 8.5, it was stimulated by Mg2+, and disulfiram was found to be a potent inhibitor of the enzyme. The results suggested that the majority of the ALDH activity was located in mitochondria (60-70% with regard to the brain and 70-80% with regard to the liver), while the remaining activity appeared to be cytosolic in both organs. No microsomal ALDH activity could be found.

Effect of disulfiram on the pre-steady-state burst in the reactions of sheep liver cytoplasmic aldehyde dehydrogenase

Stopped-flow spectrophotometric experiments show that modification by disulfiram not only lowers the steady-state rates but also decreases the size of bursts seen in both dehydrogenase and esterase reactions catalysed by sheep liver cytoplasmic aldehyde dehydrogenase. This observation is consistent with the proposal that a catalytically essential group is modified by disulfiram and that this group mediates both dehydrogenase and esterase activities.

The effect of cephalosporin antibiotics on alcohol metabolism: a review

A review is made of the pharmacological, biochemical and chemical aspects of the unpleasant 'Antabuse-like' reaction that may be induced in drinkers of alcohol by pre-treatment with certain beta-lactam antibiotics with a 1-methyltetrazole-5-thiol sidechain (such as moxalactam, cefamandole and cefoperazone). The symptoms are due to abnormally elevated blood acetaldehyde levels consequent upon the inactivation of hepatic aldehyde dehydrogenase. There is very little direct effect of the antibiotics on this enzyme and therefore it is concluded that a reactive metabolite of the antibiotics' essential sidechain is responsible for the reaction. A likely candidate for this active species is either the symmetrical disulphide 5,5'-dithiobis(1-methyltetrazole) formed by oxidation of 1-methyltetrazole-5-thiol, or the related mixed disulphide, methyl 5-(1-methyltetrazolyl) disulphide. The first of these is a potent inactivator of cytoplasmic aldehyde dehydrogenase only, the second affects both cytoplasmic and mitochondrial isoenzymes. 1-Methyltetrazole-5-thiol or derivatives have the potential to be used therapeutically as 'anti-alcohol' compounds in the same way as disulfiram (Antabuse) or calcium cyanamide.

Effects of biogenic aldehydes and aldehyde dehydrogenase inhibitors on rat brain tryptophan hydroxylase activity in vitro

The effect of indole-3-acetaldehyde, 5-hydroxyindole-3-acetaldehyde, disulfiram, diethyldithiocarbamate, coprine, and 1-amino-cyclopropanol on tryptophan hydroxylase activity was studied in vitro using high performance liquid chromatography with electro-chemical detection. With the analytical method developed, 5-hydroxytryptophan, serotonin, and 5-hydroxyindole-3-acetic acid could be measured simultaneously. Indole-3-acetaldehyde (12-1200 microM) was found to cause a 6-33% inhibition of the enzyme. Dependent upon the nature of the sulfhydryl- or reducing-agent (dithiotreitol, glutathione, or ascorbate) present in the incubates, the degree of inhibition by disulfiram varied, probably due to the formation of various mixed disulfides. Also the presence of diethyldithiocarbamate (160-1600 microM) was found to inhibit tryptophan hydroxylase (28-91%), while 5-hydroxyindole-3-acetaldehyde, coprine, or 1-aminocyclopropanol appeared to have no effect on the enzyme activity.

Inactivation of horse liver mitochondrial aldehyde dehydrogenase by disulfiram. Evidence that disulfiram is not an active-site-directed reagent

The inhibition of mitochondrial (pI 5) horse liver aldehyde dehydrogenase by disulfiram (tetraethylthiuram disulphide) was investigated to determine if the drug was an active-site-directed inhibitor. Stoichiometry of inhibition was determined by using an analogue, [35S]tetramethylthiuram disulphide. A 50% loss of the dehydrogenase activity was observed when only one site per tetrameric enzyme was modified, and complete inactivation was not obtained even after seven sites per tetramer were modified. Modification of only two sites accounted for a loss of 75% of the initial catalytic activity. The number of functioning active sites per tetrameric enzyme, as determined by the magnitude of the pre-steady-state burst of NADH formation, did not decrease until approx. 75% of the catalytic activity was lost. These data indicate that disulfiram does not modify the essential nucleophilic amino acid at the active site of the enzyme. The data support an inactivation mechanism involving the formation of a mixed disulphide with a non-essential cysteine residue, resulting in a lowered specific activity of the enzyme.

The effect of 5,5'-dithiobis(1-methyltetrazole) on cytoplasmic aldehyde dehydrogenase and its implications for cephalosporin-alcohol reactions

Cephalosporin antibiotics with a 1-methyltetrazole-5-thio side chain have the ability to cause an unpleasant flushing reaction if they are taken some time before the drinking of alcohol. It is proposed that the explanation for this is that the side chain becomes liberated in vivo and oxidized to 5,5'-dithiobis(1-methyltetrazole) or to a mixed disulfide analogue which then inactivates aldehyde dehydrogenase. Support for this proposal is given by the results below concerning the interaction in vitro between the disulfides and sheep liver cytoplasmic aldehyde dehydrogenase. 5,5'-Dithiobis(1-methyltetrazole) has a rapid and pronounced inactivatory effect, very similar in many ways (though not identical) to that of disulfiram, to which it has a structural similarity. (Disulfiram is widely used therapeutically to deter alcoholics from drinking.) 1-Methyl-5-methylthiotetrazole (which is a simple model of the antibiotics) and the free 1-methyltetrazole-5-thiol have no effect on the enzyme in vitro, but methyl 5-(1-methyltetrazolyl) disulfide is a potent inactivator; this also supports the proposed pathway.

Mitochondrial aldehyde dehydrogenase from human liver. Primary structure, differences in relation to the cytosolic enzyme, and functional correlations

The 500-residue amino acid sequence of the subunit of mitochondrial human liver aldehyde dehydrogenase is reported. It is the first structure determined for this enzyme type from any species, and is based on peptides from treatments with trypsin, CNBr, staphylococcal Glu-specific protease, and hydroxylamine. The chain is not blocked (in contrast to that of the acetylated cytosolic enzyme form), but shows N-terminal processing heterogeneity over the first seven positions. Otherwise, no evidence for subunit microheterogeneities was obtained. The structure displays 68% positional identity with that of the corresponding cytosolic enzyme, and comparisons allow functional interpretations for several segments. A region with segments suggested to participate in coenzyme binding is the most highly conserved long segment of the entire structure (positions 194-274). Cys-302, identified in the cytosolic enzyme in relation to the disulfiram reaction, is also present in the mitochondrial enzyme. A new model of the active site appears possible and involves a hydrophobic cleft. Near-total lack of conservation of the N-terminal segments may reflect a role of the N-terminal region in signaling the transport of the mitochondrial protein chains. Non-conservation of interior regions may reflect the differences between the two enzyme forms in subunit interactions, explaining the lack of heterotetrameric molecules. The presence of some internal repeat structures is also noted as well as apparently general features of differences between cytosolic and mitochondrial enzymes.