Effects of diethyldithiocarbamate and disulfiram on glucose metabolism and glutathione content of human erythrocytes

The repositioned drugs disulfiram/diethyldithiocarbamate combined to benznidazole: Searching for Chagas disease selective therapy, preventing toxicity and drug resistance

Chagas disease (CD) affects at least 6 million people in 21 South American countries besides several thousand in other nations all over the world. It is estimated that at least 14,000 people die every year of CD. Since vaccines are not available, chemotherapy remains of pivotal relevance. About 30% of the treated patients cannot complete the therapy because of severe adverse reactions. Thus, the search for novel drugs is required. Here we tested the benznidazole (BZ) combination with the repositioned drug disulfiram (DSF) and its derivative diethyldithiocarbamate (DETC) upon Trypanosoma cruzi in vitro and in vivo. DETC-BZ combination was synergistic diminishing epimastigote proliferation and enhancing selective indexes up to over 10-fold. DETC was effective upon amastigotes of the BZ- partially resistant Y and the BZ-resistant Colombiana strains. The combination reduced proliferation even using low concentrations (e.g., 2.5 µM). Scanning electron microscopy revealed membrane discontinuities and cell body volume reduction. Transmission electron microscopy revealed remarkable enlargement of endoplasmic reticulum cisternae besides, dilated mitochondria with decreased electron density and disorganized kinetoplast DNA. At advanced stages, the cytoplasm vacuolation apparently impaired compartmentation. The fluorescent probe H2-DCFDA indicates the increased production of reactive oxygen species associated with enhanced lipid peroxidation in parasites incubated with DETC. The biochemical measurement indicates the downmodulation of thiol expression. DETC inhibited superoxide dismutase activity on parasites was more pronounced than in infected mice. In order to approach the DETC effects on intracellular infection, peritoneal macrophages were infected with Colombiana trypomastigotes. DETC addition diminished parasite numbers and the DETC-BZ combination was effective, despite the low concentrations used. In the murine infection, the combination significantly enhanced animal survival, decreasing parasitemia over BZ. Histopathology revealed that low doses of BZ-treated animals presented myocardial amastigote, not observed in combination-treated animals. The picrosirius collagen staining showed reduced myocardial fibrosis. Aminotransferase de aspartate, Aminotransferase de alanine, Creatine kinase, and urea plasma levels demonstrated that the combination was non-toxic. As DSF and DETC can reduce the toxicity of other drugs and resistance phenotypes, such a combination may be safe and effective.

Assessing the effects of Thiram to oxidative stress responses in a freshwater bioindicator cladoceran (Daphnia magna)

Thiram (TMTD) is able to induce antioxidant defense and oxidative stress in different organisms. Moreover, Thiram can act as a prooxidant resulting in the formation of reactive oxygen species (ROS). To our knowledge, this is the first study assessing the oxidative stress induced by Thiram in the cladoceran Daphnia magna. At present, literature focus on the determination of toxicity in vertebrate organisms or cells, however, very few studies were interested to evaluate Thiram's effects in aquatic organisms such as cladoceran. To assess these effects, antioxidant GSH content, CAT and GST enzyme activities, cellular damages and lipid peroxidation indicators (MDA) were evaluated as oxidative stress biomarkers. Our results showed that acute Thiram exposure resulted in significant biochemical responses, demonstrating that Thiram induced oxidative damage. Indeed, following exposure to Thiram, we noticed an intracellular (GSH) depletion, associated with a marked increase of lipid membrane peroxidation as shown by high (MDA) production. Moreover, a dose-dependent induction of antioxidant key enzymes (CAT) and (GST) was found which led to an oxidative stress and finally death of Daphnia magna.

Molecular Mechanisms of Allosteric Inhibition of Brain Glycogen Phosphorylase by Neurotoxic Dithiocarbamate Chemicals

Dithiocarbamates (DTCs) are important industrial chemicals used extensively as pesticides and in a variety of therapeutic applications. However, they have also been associated with neurotoxic effects and in particular with the development of Parkinson-like neuropathy. Although different pathways and enzymes (such as ubiquitin ligases or the proteasome) have been identified as potential targets of DTCs in the brain, the molecular mechanisms underlying their neurotoxicity remain poorly understood. There is increasing evidence that alteration of glycogen metabolism in the brain contributes to neurodegenerative processes. Interestingly, recent studies with N,N-diethyldithiocarbamate suggest that brain glycogen phosphorylase (bGP) and glycogen metabolism could be altered by DTCs. Here, we provide molecular and mechanistic evidence that bGP is a target of DTCs. To examine this system, we first tested thiram, a DTC pesticide known to display neurotoxic effects, observing that it can react rapidly with bGP and readily inhibits its glycogenolytic activity (k_inact = 1.4 × 10⁵ m^-1 s^-1). Using cysteine chemical labeling, mass spectrometry, and site-directed mutagenesis approaches, we show that thiram (and certain of its metabolites) alters the activity of bGP through the formation of an intramolecular disulfide bond (Cys³¹⁸-Cys³²⁶), known to act as a redox switch that precludes the allosteric activation of bGP by AMP. Given the key role of glycogen metabolism in brain functions and neurodegeneration, impairment of the glycogenolytic activity of bGP by DTCs such as thiram may be a new mechanism by which certain DTCs exert their neurotoxic effects.

Effects of pesticide chemicals on the activity of metabolic enzymes: focus on thiocarbamates

INTRODUCTION

Thiocarbamates are chemicals widely used as pesticides. Occupational exposure is associated with acute intoxication. Populations can be exposed through food and water. Moreover, certain thiocarbamates are used clinically. The widespread use of thiocarbamates raises many issues regarding their toxicological and pharmacological impact.

AREAS COVERED

Thiocarbamates and their metabolites can modify biological macromolecules functions, in particular enzymes, through modification of cysteine residues, chelation of metal ions or modulation of the oxidative stress. Loss of enzyme activity can lead to the disruption of metabolic pathways, and explain, at least in part, the effects of these pesticides. Additionally, their reactivity and ability to easily cross biological barrier confer them a great interest for development of clinical applications.

EXPERT OPINION

Many advances in the study of thiocarbamates metabolism and reactivity have led to a better knowledge of biological effects of these compounds. However, more data are needed on the determination of targets and specificity. Only few data concerning the exposure to a cocktail of pesticides/chemicals are available, raising the need to evaluate the toxic side effects of representative pesticides mixtures. Moreover, the dithiocarbamate Disulfiram has shown great potential in therapeutic applications and leads to the development of pharmacological thiocarbamates derivatives, highly specific to their target and easily distributed.

S-(N, N-diethylcarbamoyl)glutathione (carbamathione), a disulfiram metabolite and its effect on nucleus accumbens and prefrontal cortex dopamine, GABA, and glutamate: a microdialysis study

Disulfiram (DSF), used for the treatment of alcohol use disorders (AUDs) for over six decades, most recently has shown promise for treating cocaine dependence. Although DSF's mechanism of action in alcohol abuse is due to the inhibition of liver mitochondrial aldehyde dehydrogenase (ALDH2), its mechanism of action in the treatment of cocaine dependence is unknown. DSF is a pro-drug, forming a number of metabolites each with discrete pharmacological actions. One metabolite formed during DSF bioactivation is S-(N, N-diethylcarbamoyl) glutathione (carbamathione) (carb). We previously showed that carb affects glutamate binding. In the present studies, we employed microdialysis techniques to investigate the effect of carb administration on dopamine (DA), GABA, and glutamate (Glu) in the nucleus accumbens (NAc) and medial prefrontal cortex (mPFC), two brain regions implicated in substance abuse dependence. The effect of DSF on DA, GABA, and Glu in the NAc also was determined. Both studies were carried out in male rats. Carb (20, 50, 200 mg/kg i v) in a dose-dependent manner increased DA, decreased GABA, and had a biphasic effect on Glu, first increasing and then decreasing Glu in both the NAc and mPFC. These changes all occurred concurrently. After carb administration, NAc and mPFC carb, as well as carb in plasma, were rapidly eliminated with a half-life for each approximately 4 min, while the changes in DA, GABA, and GLu in the NAc and mPFC persisted for approximately two hours. The maximal increase in carb (Cmax) in the NAc and mPFC after carb administration was dose-dependent, as was the area under the curve (AUC). DSF (200 mg/kg i p) also increased DA, decreased GABA, and had a biphasic effect on Glu in the NAc similar to that observed in the NAc after carb administration. When the cytochrome P450 inhibitor N-benzylimidazole (NBI) (20 mg/kg i p) was administered before DSF dosing, no carb could be detected in the NAc and plasma and also no changes in NAc DA, GABA, and GLu occurred. Changes in these neurotransmitters occurred only if carb was formed from DSF. When NBI was administered prior to dosing with carb, the increase in DA, decrease in GABA, and biphasic effect on GLu was similar to that seen after dosing with carb only. The i p or i v administration of carb showed similar changes in DA, GABA, and GLu, except the time to reach Cmax for DA as well as the changes in GABA, and GLu after i p administration occurred later. The elimination half-life of carb and the area under the curve (AUC) were similar after both routes of administration. It is concluded that carb must be formed from DSF before any changes in DA, GABA, and GLu in the NAc and mPFC are observed. DSF and carb, when administered to rats, co-release DA, GABA, and GLu. Carb, once formed can cross the blood brain barrier and enter the brain. Although inhibition of liver ALDH2 is the accepted mechanism for DSF's action in treating AUDs, the concurrent changes in DA, GABA, and GLu in the NAc and mPFC after DSF administration suggest that changes in these neurotransmitters as a potential mechanism of action not only for AUDs, but also for cocaine dependence cannot be excluded.

Toxicity of methanol and formaldehyde towards Saccharomyces cerevisiae as assessed by DNA microarray analysis

To assess the toxicity of the C1 compounds methanol and formaldehyde, gene expression profiles of treated baker's yeast were analyzed using DNA microarrays. Among approximately 6,000 open reading frames (ORFs), 314 were repressed and 375 were induced in response to methanol. The gene process category "energy" comprised the greatest number of induced genes while "protein synthesis" comprised the greatest number of repressed genes. Products of genes induced by methanol were mainly integral membrane proteins or were localized to the plasma membrane. A total of 622 and 610 ORFs were induced or repressed by formaldehyde, respectively. More than one-third of the genes found to be strongly repressed by formaldehyde belonged to the "protein synthesis" functional category. Conversely, genes in the subcategory of "nitrogen, sulfur, and selenium metabolism" within "metabolism" and in the category of "cell rescue, defense, and virulence" were up-regulated by exposure to formaldehyde. Our data suggest that membrane structure is a major target of methanol toxicity, while proteins were major targets of formaldehyde toxicity.

Muscular contractions in the zebrafish embryo are necessary to reveal thiuram-induced notochord distortions

Dithiocarbamates form a large group of chemicals that have numerous uses in agriculture and medicine. It has been reported that dithiocarbamates, including thiuram (tetramethylthiuram disulfide), cause wavy distortions of the notochord in zebrafish and other fish embryos. In the present study, we investigated the mechanism underlying the toxicity of thiuram in zebrafish embryos. When embryos were exposed to thiuram (2-1000 nM: 0.48-240 microg/L) from 3 h post fertilization (hpf) (30% epiboly) until 24 hpf (Prim-5), all embryos develop wavy notochords, disorganized somites, and have shortened yolk sac extensions. The thiuram response was specific and did not cause growth retardation or mortality at 24 hpf. The thiuram-dependent responses showed the same concentration dependence with a waterborne EC50 values of approximately 7 nM. Morphometric measurements revealed that thiuram does not affect the rate of notochord lengthening. However, the rate of overall body lengthening was significantly reduced in thiuram-exposed animals. Other dithiocarbamates, such as ziram, caused similar malformations to thiuram. While expression of genes involved in somitogenesis was not affected, the levels of notochord-specific transcripts were altered after the onset of malformations. Distortion of the notochord started precisely at 18 hpf, which is concomitant with onset of spontaneous rhythmic trunk contractions. Abolishment of spontaneous contractions using tricaine, alpha-bungarotoxin, and a paralytic mutant sofa potato, resulted in normal notochord morphology in the presence of thiuram. These results indicate that muscle activity is necessary to reveal the underlying functional deficit and suggest that the developmental target of dithiocarbamates impairs trunk plasticity through an unknown mechanism.

Disulfiram-mediated inhibition of NF-kappaB activity enhances cytotoxicity of 5-fluorouracil in human colorectal cancer cell lines

5-Fluorouracil (5-FU) is the major chemotherapeutic component for colorectal cancer (CRC) and other types of solid tumours. Resistance of cancer cells to 5-FU is considered the major obstacle for successful chemotherapy. NF-kappaB is a transcription factor. Cancer cells with high NF-kappaB nuclear activity demonstrate robust chemo- and radio-resistance. We demonstrated that nuclear NF-kappaB activity in CRC cell lines, DLD-1 and RKO(WT), was significantly induced by 5-FU in a concentration- and time-dependent manner. 5-FU induced IkappaBalpha degradation and promoted both NF-kappaB nuclear translocation and its DNA binding activity. 5-FU treatment did not influence the activities of AP-1, AP-2, Oct-1, SP-1, CRE-B and TFIID. Disulfiram (DS), a clinically used anti-alcoholism drug, strongly inhibited constitutive and 5-FU-induced NF-kappaB activity in a dose-dependent manner. DS inhibited both NF-kappaB nuclear translocation and DNA binding activity but had no effect on 5-FU-induced IkappaBalpha degradation. Used in combination, DS significantly enhanced the apoptotic effect of 5-FU on DLD-1 and RKO(WT) cell lines and synergistically potentiated the cytotoxicity of 5-FU to both cell lines. DS also effectively abolished 5-FU chemoresistance in a 5-FU resistant cell line H630(5-FU) in vitro. As DS has extensive preclinical and clinical experience, translating its anticancer usage from in vitro study to clinical trials is relatively straightforward.

Effects of the pesticide thiuram: genome-wide screening of indicator genes by yeast DNA microarray

Although there have been studies on the toxicity of the pesticide thiuram, the present study is the first one to attempt to integrate a whole genomic response using microarray technology. From the DNA microarray experiment it was found that exposure to thiuram led to alterations of gene expression in yeast cells and that many genes involved in detoxification and stress response were highly induced. The induced genes were classified according to the MIPS yeast database. The induction of genes concerned with folding and proteolysis reflects the protein denaturing and degradation effects of the thiuram treatment The induction of genes involved in redox and defense against reaction oxygen species also suggests that thiuram has other effects, such as oxidative stress. Genes classified for carbohydrate metabolism and energy were also highly induced, and these gene products may play the role of providing the energy for the detoxification mechanism. In addition, in view of the induction of some genes involved in DNA repair, thiuram potentially causes DNA damage. Therefore, as stated in previous reports, thiuram is a potential positive toxic chemical. On the other hand, YKL071W, YCR102C, YLR303W, and YLL057C were selected based on the result of a DNA microarray experiment and used for the promoter activity assay. Thiuram treatment affected the promoter of these genes, indicating that this technique could be used for the selection of biomarker candidates.

Determination of in vivo adducts of disulfiram with mitochondrial aldehyde dehydrogenase

Extensive use for disulfiram (DSF) has been found in the aversion therapy treatment of recovering alcoholics. Although it is known to irreversibly inhibit hepatic aldehyde dehydrogenase (ALDH), the specific mechanism of in vivo inhibition of the enzyme by the drug has not been determined yet. We have demonstrated in this report a novel, but simple and rapid method for structurally characterizing in vivo derived protein-drug adducts by linking on-line sample processing to HPLC-electrospray ionization mass spectrometry (HPLC-MS) and HPLC-tandem mass spectrometry (HPLC-MS/MS). Employing this approach, rats were administered DSF, and their liver mitochondria were isolated and solubilized. Both native and in vivo DSF-treated mitochondrial ALDH (mALDH) were purified in one step with an affinity cartridge. The in vivo DSF-treated mALDH showed 77% inhibition in enzyme activity as compared with that of the control. Subsequently, the control and DSF-inhibited mALDH were both subjected to HPLC-MS analyses. We were able to detect two adducts on DSF-inhibited mALDH, as indicated by the mass increases of approximately 71 and approximately 100 Da. To unequivocally determine the site and structure of these adducts, on-line pepsin digestion-HPLC-MS and HPLC-MS/MS were performed. We observed two new peptides at MH(+) = 973.7 and MH(+) = 1001.8 in the pepsin digestion of DSF-inhibited enzyme. These two peptides were subsequently subjected to HPLC-MS/MS for sequence determination. Both peptides possessed the sequence FNQGQC(301)C(302)C(303), derived from the enzyme active site region, and were modified at Cys(302) by N-ethylcarbamoyl (+71 Da) and N-diethylcarbamoyl (+99 Da) adducts. These findings indicated that N-dealkylation may be an important step in DSF metabolism, and that the inhibition of ALDH occurred by carbamoylation caused by one of the DSF metabolites, most likely S-methyl-N,N-diethylthiocarbamoyl sulfoxide (MeDTC-SO). Finally, there was no evidence of the presence of an intramolecule disulfide bridge modification on the peptide FNQGQCCC.

Overview--in vitro inhibition of aldehyde dehydrogenase by disulfiram and metabolites

Disulfiram (DSF) has found extensive use in the aversion therapy treatment of recovering alcoholics. It is known that DSF or a metabolite irreversibly inhibits aldehyde dehydrogenase (ALDH). However, the actual mechanism of inhibition is still not known. In this work we describe the in vitro interactions of DSF, as well as a principal metabolite S-methyl-N,N-diethylthiocarbamoyl sulfoxide (MeDTC-SO), with both recombinant rat liver mitochondrial monomeric ALDH (rmALDH) and homotetrameric rmALDH. We show that DSF directly inhibits rmALDH (IC(50)=36.4 microM) by inducing the formation of an intramolecular disulfide bond. We also demonstrate by HPLC-MS analysis of a Glu-C digest of DSF-treated rmALDH that the intramolecular disulfide bridge formed involves two of the three cysteines located at the active site of the enzyme. Using a combination of HPLC-MS and HPLC-MS/MS, we further show that the electrophilic metabolite MeDTC-SO also inhibits rmALDH (IC(50)=4.62 microM). We isolate and identify a carbamoylated peptide at Cys(302) with the sequence FNQGQC(301)C(302)C(303). Hence we show that MeDTC-SO exhibits its inhibitory effect by covalently modifying the -SH side-chain of Cys(302), present at the active site rmALDH. Finally we show using SEC-MS that both DSF and MeDTC-SO do not prevent formation of the homotetramer of rmALDH, but inhibit the enzyme by acting directly at the active site of specific monomers of rmALDH.

Role of disulfiram in the in vitro inhibition of rat liver mitochondrial aldehyde dehydrogenase

The alcohol aversion therapy drug disulfiram has been shown to inhibit hepatic aldehyde dehydrogenase (ALDH), one of the key enzymes involved in ethanol metabolism. It is believed by some that disulfiram could be one of the active inhibitors in vivo. However, the actual interaction between disulfiram and ALDH remains ambiguous. We report here that when disulfiram inhibited recombinant rat liver mitochondrial ALDH (rlmALDH) in vitro, no significant molecular mass increase was detected during the first 30 min as determined by on-line HPLC-electrospray ionization mass spectrometry (LC-MS). This indicated that the inhibition in vitro was not caused directly by covalent adduct formation on the enzyme. We subsequently subjected both control and disulfiram-inhibited rlmALDH to Glu-C proteolytic digestion. LC-MS analysis of the Glu-C digestion of disulfiram-inhibited enzyme revealed that one peptide of M(r) = 4821, which contained the putative active site of the enzyme, exhibited a mass decrease of 2 amu as compared with the same peptide found in the Glu-C digestion of the control (M(r) = 4823). We believe that the loss of 2 amu indicated that inhibition of rlmALDH in vitro was due to formation of an intramolecular disulfide bond between two of the three adjacent cysteines in the active site, possibly via a very rapid and unstable mixed disulfide interchange reaction. Further confirmation of the intramolecular disulfide bond formation came from the fact that by adding dithiothreitol (DTT) we were able to recover partial enzyme activity. In addition, the peptide of M(r) = 4821 observed in the Glu-C digestion of the disulfiram-treated ALDH reverted to M(r) = 4823 after treatment with DTT, which indicated that the disulfide bond was reduced. We, thereby, conclude that disulfiram inhibited rlmALDH by forming an intramolecular disulfide, possibly via a fast intermolecular disulfiram interchange reaction.

Induction of cystine transport and other stress proteins by disulfiram: effects on glutathione levels in cultured cells

Disulfiram (Antabuse) (DSF) has been reported to protect rats and other animals from the effects of hyperbaric hyperoxia at 4 to 6 ATA (atmospheres). In contrast, DSF and diethyldithiocarbamate (DDC), its metabolite, accelerate the toxic effects in rats of 100% oxygen at 1 to 2 ATA. We have examined the effects of DSF and DDC on glutathione (GSH) levels in bovine pulmonary artery endothelial cells and Chinese hamster ovary cells. Increases in intracellular GSH occurred 8 to 24 h after addition of DSF to the culture media. These increases in intracellular GSH were associated with increases in the rate of uptake of cystine into the cells. DDC was a less effective inducer of cystine uptake and increased intracellular GSH levels than was DSF. At the concentrations used, neither DDC nor DSF caused significant decreases in intracellular superoxide dismutase levels. Exogenous sulfhydryl compounds including GSH and cysteine partially blocked the induction of cystine transport by DSF or DDC, suggesting that the induction might be mediated through a sulfhydryl reaction between DSF and some cellular components. The increases in GSH in the cultured cells were not significant by 4 h of exposure. In contrast, other stress proteins including heme oxygenase are induced by 2 to 4 h after DSF addition. In previously reported in vivo studies, DSF treatment protected against hyperbaric oxygen damage after as little as 1 to 4 h pre-exposure. This suggests that effects of DSF exposure other than GSH augmentation may be responsible for the protective effects seen in vivo.

Thiram and dimethyldithiocarbamic acid interconversion in Saccharomyces cerevisiae: a possible metabolic pathway under the control of the glutathione redox cycle

A rapid decrease of intracellular glutathione (GSH) was observed when exponentially growing cells of Saccharomyces cerevisiae were treated with sublethal concentrations of either dimethyldithiocarbamic acid or thiram [bis(dimethylthiocarbamoyl) disulfide]. The underlying mechanism of this effect possibly involves the intracellular oxidation of dimethyldithiocarbamate anions to thiram, which in turn oxidizes GSH. Overall, a linear relationship was found between thiram concentrations up to 21 microM and production of oxidized GSH (GSSG). Cytochrome c can serve as the final electron acceptor for dimethyldithiocarbamate reoxidation, and it was demonstrated in vitro that NADPH handles the final electron transfer from GSSG to the fungicide by glutathione reductase. These cycling reactions induce transient alterations in the intracellular redox state of several electron carriers and interfere with the respiration of the yeast. Thiram and dimethyldithiocarbamic acid also inactivate yeast glutathione reductase when the fungicide is present within the cells as the disulfide. Hence, whenever the GSH regeneration rate falls below its oxidation rate, the GSH:GSSG molar ratio drops from 45 to 1. Inhibition of glutathione reductase may be responsible for the saturation kinetics observed in rates of thiram elimination and uptake by the yeast. The data suggest also a leading role for the GSH redox cycle in the control of thiram and dimethyldithiocarbamic acid fungitoxicity. Possible pathways for the handling of thiram and dimethyldithiocarbamic acid by yeast are considered with respect to the physiological status, the GSH content, and the activity of glutathione reductase of the cells.

Effects of disulfiram on positron emission tomography and neuropsychological studies in severe chronic alcoholism

Disulfiram is an aldehyde dehydrogenase inhibitor that is widely used as an adjunctive agent in the treatment of patients with severe chronic alcoholism. Recent positron emission tomography (PET) studies of local cerebral metabolic rates for glucose (ICMRglc) and benzodiazepine receptor binding in alcoholic patients have shown regional cerebral abnormalities; however, some of the patients were studied while receiving disulfiram, which could influence the biochemical processes under investigation. In a retrospective investigation, we examined the influence of disulfiram administration on the results of PET studies of ICMRglc and benzodiazepine receptor binding and neuropsychological tests of cognition and executive function in patients with severe chronic alcoholism. [18F]Fluorodeoxyglucose was used to measure ICMRglc in 48 male patients, including 11 receiving and 37 not receiving disulfiram in therapeutic doses. [11C]Flumazenil was used to measure benzodiazepine receptor binding in 17 male patients, including 3 receiving and 14 not receiving disulfiram. All patients studied with FMZ were also examined with fluorodeoxyglucose. PET studies of ICMRglc revealed significantly decreased global values in the patients receiving disulfiram compared with those not receiving disulfiram. PET studies of benzodiazepine receptor binding revealed decreased flumazenil influx and distribution volume in patients receiving disulfiram. The neuropsychological tests demonstrated no differences between the two groups of subjects. The findings suggest that disulfiram may influence the results of PET studies of glucose metabolism and benzodiazepine receptor binding.

In vitro inhibition of rat and human glutathione S-transferase isoenzymes by disulfiram and diethyldithiocarbamate

The drug disulfiram (DSF, Antabuse) has been used in the therapy of alcohol abuse. It is a potent inhibitor of aldehyde dehydrogenase. Its reduced form, diethyldithiocarbamate (DDTC), and further metabolites show similar activities. DSF and DDTC have also been widely used to inhibit mixed-function oxidases. In this study, the reversible inhibition and time-dependent inactivation of the major rat and human glutathione S-transferase (GST) isoenzymes by DSF and DDTC was investigated. Reversible inhibition, using 1-chloro-2,4-dinitrobenzene as substrate for the GST alpha-, mu-, and pi-class, expressed as I50 (in microM), ranged from 5-18 (human A1-1), 43-57 (rat 4-4) and 66-83 (rat 1-1), for both DSF and DDTC. The I50 for rat GST theta, using 1,2-epoxy-3-(p-nitrophenoxy)-propane as substrate, was 350 microM for DDTC. The other GSTs were significantly less sensitive to inhibition. The major part of reversible inhibition by DSF was shown to be due to DDTC, formed rapidly upon reduction of DSF by the glutathione (GSH) present in the assay to measure GST activity. The oxidized GSH formed upon reduction of DSF might also have made a minor contribution to reversible inhibition. The rat and human pi-class was, by far, the most sensitive class for time-dependent inactivation by DSF, but no such inactivation was observed for any of the GSTs by DDTC. Moderate susceptibility to inactivation by DSF of all the other GSTs was observed, except for human A2-2, which does not possess a cysteine residue. Consistent with the assumption that a thiol residue is involved in this inactivation, a significant part of the activity could be restored by treatment of the inactivated GST with GSH or dithiotreitol.

Metabolism and pharmacokinetics of S-(N,N-diethyldithiocarbamoyl)-N-acetyl-L-cysteine in rats

The metabolism and pharmacokinetics of a mixed disulfide S-(N,N-diethyldithiocarbamoyl)-N-acetyl-L-cysteine (AC-DDTC) were studied in rats. Two metabolites of AC-DDTC following i.v. and p.o. administration were identified in plasma and liver by HPLC and GC, namely N,N-diethyldithiocarbamate (DDTC) and the methyl ester of DDTC (Me-DDTC). AC-DDTC was very unstable in vivo and could not be detected neither in plasma nor in urine. Pharmacokinetic parameters of DDTC following intravenous administration of AC-DDTC (20 mg/kg) were calculated. DDTC has a low affinity to rat tissue and the total body clearance was 9.0 +/- 3.4 ml/min/kg. The mean residence time (MRT) was 111.5 +/- 16.3 min. After oral administration of 20 mg/kg AC-DDTC, maximal plasma concentration (Cmax) was 3.8 +/- 0.2 nmol/ml and the bioavailability was 7.04%. Cmax for DDTC at a dose of 120 mg/kg AC-DDTC was 40.1 +/- 2.2 nmol/ml. MRT was 47.1 +/- 2.8 min at a dose of 20 mg/kg and 110.5 +/- 6.0 min at 120 mg/kg.

Effects of diethyldithiocarbamate on calmodulin in neuroblastoma cells

Diethyldithiocarbamate (DDC) was used to treat the neuroblastoma cell line Neuro-2a. Cell injury caused by DDC affects the calcium-binding protein calmodulin (CaM) and alters copper homeostasis in these cells. Neuro-2a cells were treated with 1 x 10(-5) M DDC for 1 h and were harvested at various time points over a 24-h period. Light microscopy of control cells showed CaM deposited around the cell periphery and along the neuritic processes. Treated cells showed the same distribution until 3 h after treatment. Electron microscopy showed CaM deposited around the cell periphery and within the cytoplasm and nucleus of control cells. Treated cells showed a time-dependent localization of CaM in relation to cellular disorganization. Staining of electrophoretic transfers by ProtoGold showed that CaM was present in all control samples and treated samples through 6 h. Atomic absorption spectrophotometry showed no difference in calcium levels between control and treated samples, but copper levels were significantly elevated. This study indicated that degenerative changes induced by DDC altered calmodulin levels. These changes may have been caused by elevated copper content within the cells and subsequent cell injury.

Deleterious effects of disulfiram on the respiratory electron transport system of liver mitochondria

1. The mechanism of action of disulfiram on the respiratory electron transport system of the liver mitochondria was studied in vitro. 2. Disulfiram inhibited the respiration supported by malate-glutamate as well as succinate. 3. Mitochondrial respiration inhibition was dependent upon alteration of -SH groups. 4. The inhibitory action of disulfiram might be related to the crosslinking of several proteins of the inner mitochondrial membrane. 5. The effects described above could be attributed to disulfiram per se and not to the main metabolite diethyldithiocarbamate.

A review of the pharmacokinetics and pharmacodynamics of disulfiram and its metabolites

After ingestion, disulfiram (DSF) is rapidly converted, probably in the stomach, to its bis (diethyldithiocarbamato) copper complex. Consequently, absorption and distribution via the gastrointestinal mucosa into the blood might involve both the parent drug and its copper complex. In the blood, both compounds are rapidly degraded to form diethyldithiocarbamic acid (DDC), which is unstable and is further degraded to form diethylamine and carbon disulphide. DDC is also a substrate of phase II metabolism, which involves formation of diethyldithiomethylcarbamate (Me-DDC) and the glucuronic acid of DDC. Me-DDC also undergoes oxidative biotransformation to diethylthiomethylcarbamate (Me-DTC), which is further oxidized to its corresponding sulphoxide and sulphone metabolites. Me-DTC may to act as a suicide inhibitor with a preference for the mitochondrial low Km isozyme of aldehyde dehydrogenases (ALDH 1), whereas the two S-oxidized metabolites, especially the sulfone metabolite, are more potent inhibitors not only of ALDH 1, but also of the cytosolic high Km isozyme of ALDH (ALDH 2). The inhibitory reaction between the enzyme and each of the three metabolites is characterized by a covalent adduct formation, probably with the cysteine residue at the active site of the enzymes. The adduct formed is nonreducible at a physiological concentration of glutathione, and inactivation in the presence of this endogenous tripeptide was increased by action in vitro of the sulphoxide and sulphone metabolites. Those findings are all in concordance with the in vivo observations made on DSF. In human volunteers treated with increasing doses of DSF and challenged with ethanol between each of the dosage periods, the mean plasma concentrations of Me-DTC at steady state were proportional to the DSF doses given. There was also a close relationship between increased oxidative metabolic formation of Me-DTC, high oxidative formation of acetaldehyde, and the full complements of a valid disulfiram ethanol reaction (DER). Consequently, Me-DTC in plasma may not only serve as a marker of the oxidative metabolic function of the liver, but also of the therapeutic effectiveness of the treatment in subjects at steady state. Obviously, there is a need for individual dose-titration regimens. In patients with alcohol-related severe hepatocellular damage, the oxidative P 450 catalyzed formation of the Me-DTC and probably also of its sulfoxide and sulphone metabolites is impaired, and thus inactivation of ALDH activity in the liver appears to be delayed or even completely absent. The consequence for the patient may be an insufficient DER.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of disulfiram (DS) on mitochondria from rat hippocampus: metabolic compartmentation of DS neurotoxicity

This experiment was designed to study the acute effects of disulfiram on mitochondrial enzymes in nonsynaptic and synaptic mitochondria from rat hippocampus. Cytochrome c oxidase, monoamine oxidase-B, glycerolphosphate acyltransferase and beta-hydroxybutyrate dehydrogenase were studied. Differences in enzyme activity were seen in controls. Cytochrome c oxidase activity was higher in synaptic mitochondria whereas glycerolphosphate acyltransferase activity was higher in nonsynaptic mitochondria. Mitochondria from disulfiram treated rats, particularly synaptic mitochondria, exhibited lower specific activities of cytochrome c oxidase and monoamine oxidase-B. These alterations were not limited to either the inner or outer mitochondrial membrane. Transmission electron microscopy revealed that mitochondria from disulfiram treated rats were severely altered in isolated preparations as well as in those from whole tissue. This study shows that disulfiram exerts a differential effect on mitochondrial subpopulations.

Role of glutathione reductase system in disulfiram conversion to diethyldithiocarbamate

Experiments were carried out to establish the role of glutathione reductase (GR), if any, in the metabolic conversion of disulfiram (DS) to diethyldithiocarbamate (DDC). It was observed that, under standard assay conditions, whereas DS was incorporated as a substrate instead of oxidised glutathione (GSSG), the enzymes from both human liver extract and yeast sources failed to reduce the parent compound, implying that glutathione reductase perse do not reduce disulfiram. However, the incorporation of disulfiram into an assay system comprising of GSSG, NADPH and reductase resulted in DS reduction to DDC. Further, the observation, that the GR assay system devoid of either GSSG or NADPH was found to lack DS reducing ability, implies that GSH as a reaction product of GR system is responsible for the reduction of DS to DDC. The results of in-vitro experiments indicated that GSH perse could reduce DS to DDC nonenzymatically, with a stoichiometric relationship of 2:1. Thus it is inferred that GR perse do not reduce DS, whereas GSH, as an intermediary metabolite of GR system, brings about non-enzymatic reduction of DS via a sulfhydral group exchange reaction.

Disulfiram may mediate erythrocyte hemolysis induced by diethyldithiocarbamate and 1,4-naphthoquinone-2-sulfonate

The increase in 1,4-naphthoquinone-2-sulfonate (NQS)-induced hemolysis by the superoxide dismutase inhibitor diethyldithiocarbamate (DEDC) was formerly attributed to increased superoxide anion levels in the erythrocyte. Our results show that removal of DEDC after preincubation and prior to the addition of NQS did not produce a significant increase in hemolysis, which suggests that hemolysis is primarily caused by the reaction products of DEDC with NQS and not to the inactivation of superoxide dismutase. Disulfiram, the oxidized product of DEDC, was found to be the main product formed when excess DEDC was reacted with NQS. Oxygen uptake also occurred and hydrogen peroxide was formed. The latter caused the oxidation of DEDC to disulfiram as catalase prevented disulfiram formation. Disulfiram was found to readily hemolyze erythrocytes at low concentrations as well as to crosslink the proteins in the erythrocyte membrane. Furthermore, disulfiram-induced hemolysis was markedly enhanced in glutathione-depleted erythrocytes. Disulfiram was subsequently found to readily oxidize glutathione in red blood cells. When equimolar concentrations of DEDC and NQS were reacted, the major product formed was the diethyldithiocarbamate:1,4-naphthoquinone (DEDC:NQS) conjugate. However, the principal mediator of erythrocyte hemolysis when excess DEDC is reacted with 1,4-naphthoquinone-2-sulfonate is disulfiram, whose mode of action may be to modify membrane protein sulfhydryls.

Comparative aspects of disulfiram and its metabolites in the disulfiram-ethanol reaction in the rat

Diethyldithiocarbamate-methyl ester (DDTC-Me), a metabolite of disulfiram, has been shown recently to produce a disulfiram-ethanol reaction (DER). Studies were carried out to compare the ethanol-sensitizing properties of DDTC-Me with those of disulfiram and diethyldithiocarbamate (DDTC) in the rat. All three drugs inhibited liver mitochondrial low Km aldehyde dehydrogenase (ALDH) in vivo, with maximal ALDH inhibition occurring 8 hr after drug administration. The onset of ALDH inhibition was most rapid after DDTC-Me administration. ALDH was inhibited approximately 50% 0.5 hr after DDTC-Me, whereas ALDH was inhibited only 5 and 10%, respectively, after disulfiram and DDTC. Not until 8 hr after drug treatment was ALDH inhibition the same for disulfiram, DDTC and DDTC-Me. The degree of ALDH inhibition from 8 to 172 hr after dosing was the same for all three drugs. An ethanol (1 g/kg, 20% v/v) challenge administered to rats treated with disulfiram (75 mg/kg), DDTC (114 mg/kg), or DDTC-Me (41.2 mg/kg) for 8 hr produced similar blood acetaldehyde/ethanol concentration-time profiles. In addition, all three agents produced a DER (hypotension, tachycardia). No DER occurred if ethanol was administered more than 24 hr after drug pretreatment. The hypotension associated with the DER correlated with the increased blood acetaldehyde but not blood ethanol. A threshold blood acetaldehyde of 110 microM appeared to be required for hypotension to occur, and this was related to ALDH inhibition of approximately 40%. The tachycardia associated with the DER correlated more with blood ethanol. After DDTC-Me administration, no disulfiram or DDTC could be detected in the plasma. Furthermore, no DDTC-Me was found in the plasma 8 hr after DDTC-Me administration, suggesting that no correlation exists between the DER and plasma concentration of DDTC-Me and most likely disulfiram. These data suggest that the alcohol-sensitizing properties of DDTC-Me are similar to those observed with disulfiram and DDTC. Since DDTC-Me is an active metabolite and more potent than disulfiram and DDTC in producing a DER, disulfiram metabolism is an important consideration in the disulfiram-ethanol reaction.

Serum albumin and the metabolism of disulfiram

The effectiveness of tetraethylthiuram disulfide (DSF) as a drug used in the treatment of alcohol abuse has been limited by the fact that it is degraded rapidly in the tissues and in the serum. Hence, a useful dose-response curve for this drug cannot be determined easily. The degradation in the tissues has been well characterized; however, its fate in the serum is less well understood. Here we kinetically describe the first steps in the degradation of DSF in the serum which results from a covalent interaction of this drug with the free sulfhydryl of serum albumin. DSF and its cleavage product diethyldithiocarbamate (DDC) both absorb significantly in the ultraviolet region. The reduction of DSF with mercaptoethanol to two molecules of DDC resulted in a large change in absorption in this region. The reaction of serum albumin with DSF produced a similar but much slower change in the ultraviolet absorption. As a result of the existence of this slow spectral change, we have been able to directly and continuously monitor the interaction of serum albumin and DSF and have determined that it is an overall first-order process. A model is proposed wherein DSF and serum albumin rapidly form a noncovalent adduct and, subsequently, in a slow unimolecular process, DSF is reduced to one mole of free DDC and one mole of the serum albumin-DDC mixed disulfide. At pH 9 the half-time for this process was 30 to 40 sec, and at pH 7.4 the half-time for this process was 1 to 1.5 min. These results suggest that degradation of DSF by serum albumin is physiologically and clinically important since the drug is maximally active only many hours after administration.

Hydrogen peroxide from cellular metabolism of cystine. A requirement for lysis of murine tumor cells by vernolepin, a glutathione-depleting antineoplastic

The sesquiterpene lactone antineoplastic vernolepin acutely depletes murine tumor cell glutathione (GSH), and lyses the cells by an unknown mechanism that is enhanced synergistically by inhibition of GSH synthesis with buthionine sulfoximine (BSO) (Arrick et al. 1983. J. Clin. Invest. 71:258). We found here that lysis of P815 mastocytoma cells by vernolepin, with or without BSO, required cystine in the culture medium. Addition of catalase markedly suppressed vernolepin-mediated cytolysis in cystine-containing media, suggesting the involvement of hydrogen peroxide in the cytolytic action of vernolepin. Consistent with this, inhibition of tumor cell glutathione disulfide reductase with 1,3-bis(2-chloroethyl)-1-nitrosourea or inhibition of endogenous catalase with aminotriazole synergistically augmented cytolysis by vernolepin. Moreover, H2O2 was released by suspensions of P815 cells in cystine-containing buffer (63 pmol/10(6) cells X h). Omission of cystine reduced the rate of H2O2 accumulation 10-fold. No H2O2 was detected without cells. Cytolysis by vernolepin could be restored in cystine-deficient medium by several other disulfides, themselves noncytolytic, such as disulfiram and oxidized Captopril, as well as by cysteine. In contrast, withholding two other essential amino acids (leucine or tryptophan) or adding cycloheximide did not interfere with cytolysis by vernolepin. These results suggest that cellular uptake of disulfides of physiologic and pharmacologic interest may be followed by their intracellular reduction and autooxidation with generation of H2O2. This previously unrecognized source of intracellular oxidant stress may be an important component of injury to GSH-depleted cells.

Synergistic induction of microsomal heme oxygenase activity in rat liver and kidney by diethyldithiocarbamate and nickel chloride

Microsomal heme oxygenase activity was measured in liver and kidney of rats killed after administration of sodium diethyldithiocarbamate (DDC) and nickel chloride (NiCl2), singly and in combinations (DDC dosages: 0.33 to 1.33 mmol/kg, im, 17 hr before death; NiCl2 dosages: 0.125 and 0.25 mmol/kg, sc, 17 hr before death). Synergistic induction was observed at all dosage combinations. At the highest dosages of DDC and NiCl2, the dual treatments induced heme oxygenase activity 11-fold in liver and 16-fold in kidney; at the same dosages given individually, DDC induction of heme oxygenase activity was 3-fold in liver and 2-fold in kidney, and NiCl2-induction was 1.3-fold in liver and 6-fold in kidney. Synergistic induction of heme oxygenase activity in liver occurred when DDC was injected 6 hr before to 6 hr after NiCl2; synergistic induction in kidney occurred when DDC was injected 6 hr before to 3 hr after NiCl2. Actinomycin D prevented the induction of heme oxygenase activity by DDC or NiCl2, given individually; the effect of actinomycin D on synergistic induction could not be measured, since the rats all died following treatment with DDC, NiCl2, and actinomycin D. Administration of cysteine to rats, po, 18 hr before death, partially suppressed the induction of hepatic heme oxygenase activity by DDC, singly or in combination with NiCl2. Synergistic induction of hepatic heme oxygenase activity also occurred in rats that received dual injections of DDC (1.33 mmol/kg, im) and hemoglobin (0.3 g/kg, iv); the synergism of DDC and hemoglobin, although statistically significant, was small in comparison to the striking synergistic effect of DDC and NiCl2.

Nickel induction of microsomal heme oxygenase activity in rodents

Heme oxygenase activity was measured in tissues of rats killed after administration of NiCl2 or Ni3S2. Induction of renal heme oxygenase activity occurred 6 hr after NiCl2 injection (0.25 mmol/kg, sc), reached a maximum of five to six times the baseline activity at 17 hr, and remained significantly increased at 72 hr. Heme oxygenase activities were also increased in liver, lung, and brain at 17 hr after the NiCl2 injection; heme oxygenase activities in spleen and intestinal mucosa were unchanged. The effects of NiCl2 on heme oxygenase activities in kidney and liver were dose-related from 0.06 to 0.75 mmol/kg, sc. Three Ni chelators were administered (1 mmol/kg, im) prior to injection of NiCl2 (0.25 mmol/kg, sc); d-penicillamine partially prevented Ni induction of renal heme oxygenase activity; triethylenetetramine had no effect; sodium diethyldithiocarbamate enhanced the Ni induction of renal heme oxygenase activity (three times greater than NiCl2 alone). Intrarenal injection of Ni3S2 (10 mg/rat) caused induction of renal heme oxygenase activity at 1 week but not at 2, 3, or 4 weeks; no correlation was observed between induction of renal heme oxygenase activity and erythropoietin-mediated erythrocytosis. Hypoxia (10% O2, 12 hr/day, 7 days) did not affect renal heme oxygenase activity. Induction of renal heme oxygenase activity was observed in mice, hamsters, and guinea pigs killed 17 hr after injection of NiCl2 (0.25 mmol/kg, sc). These studies established (a) the time course, dose-effect, organ selectivity, and species susceptibility relationships for Ni induction of microsomal heme oxygenase activity, (b) the effects of Ni chelators, and (c) the lack of relationship between induction of renal heme oxygenase activity and the erythrocytosis that develops after intrarenal injection of Ni3S2.

Effect of disulfiram and its reduced metabolite, diethyl-dithiocarbamate on aldehyde dehydrogenase of human erythrocytes

Inhibition of human erythrocyte aldehyde dehydrogenase (ALDH) activity was studied using disulfiram and its reduced metabolite, diethyldithiocarbamate (DDC). The enzyme was rapidly inactivated by disulfiram and the inhibition was protected by reduced glutathione (GSH), in a concentration dependent manner when the enzyme premixed with GSH was reacted with disulfiram. Higher reactivity of the thiol group of the enzyme than that of GSH to disulfiram was suggested from the observation that half of the enzyme activity was inhibited when the ratio of disulfiram to GSH was 1:10. Although DDC alone showed no inhibitory effect on the enzyme, inactivation was mediated by a low concentration of heme-containing peroxidases, but not by methemoglobin. Under this condition, the inhibition potential was not protected, even with a high concentration of GSH. The constant reoxidation system of DDC is probably directly related to the enzyme inactivation.

Tetraethylthiuram disulfide (Antabuse) inhibits the human malaria parasite Plasmodium falciparum

Plasmodium falciparum in culture grows optimally at 3% oxygen. Oxygen levels down to 0.5% still support growth, but anaerobic conditions do not. These findings, and the absence of the Krebs cycle in Plasmodium, suggested that in this organism oxygen may not function in electron transport but rather may act through metalloprotein oxygenases. Tetraethylthiuram disulfide (Antabuse, disulfiram) and its reduction product diethyldithiocarbamate inhibit many metalloprotein oxygenases and have a lipid/H2O partition coefficient and high binding constant for metal ions, favoring selective toxicity to the malaria parasite. These compounds exhibited active antimalarial effects in vitro in concentrations down to 0.1 microgram/ml, the lowest level tested. Tetraethylthiuram disulfide at a level as low as 1 microgram/ml inhibited parasite glycolysis with no effect on glycolysis of normal erythrocytes. Erythrocytes pretreated with this drug at 10 microgram/ml did not support growth of the parasite.

Radioactive and nonradioactive methods for the in vivo determination of disulfiram, diethyldithiocarbamate, and diethyldithiocarbamate-methyl ester

Although disulfiram (tetraethylthiuram disulfide; DSF) has been used in the treatment of alcoholism for almost a quarter of a century, little is known about its in vivo metabolism. One reason for this is that few analytical methods are available that can determine DSF and its various metabolites in biologic fluids and tissues. This article describes two simple procedures for the determination of these substances.

Modifications of drug metabolism by disulfiram and diethyldithiocarbamate. II. D-Glucuronic acid pathway

Hepatic enzymes connected with the formation and metabolism of free D-glucuronic acid were affected in rats after treatment with disulfiram or diethyldithiocarbamate (300 mg/kg, intragastrically, per day, 4 X). The activities of UDPglucose dehydrogenase, UDPglucuronic acid pyrophosphatase, UDPglucuronosyltransferase and L-gulonate dehydrogenase were enhanced, while those of glucose-6-phosphate dehydrogenase, beta-glucuronidase and D-glucuronolactone dehydrogenase were inhibited. These changes were more pronounced with disulfiram than diethyldithiocarbamate. Treatment with phenobarbital (80 mg/kg, i.p., per day, 4 X) enhanced UDP glucuronosyl-transferase, but brought about different effects on the other enzymes. Concurrent administration of phenobarbital with disulfiram or diethyldithiocarbamate led to potentiation or antagonism of the primary effects of each compound when given alone. The results suggest that activation of the D-glucuronic acid pathway may proceed in various ways, and that it is not necessarily followed by a simultaneous induction of the microsomal mixed-function oxygenase activity.

Modifications of drug metabolism by disulfiram and diethyldithiocarbamate. I. Mixed-function oxygenase

Disulfiram and diethyldithiocarbamate were administered to rats for 4 days alone (300 mg/kg, daily, per os) or in combination with phenobarbital (80 mg/kg, daily, i.p.), in order to observe the effects of these compounds on the microsomal membrane components and on the mixed-function oxygenase system. Both disulfiram and diethyldithiocarbamate increased the liver to body weight ratio, and the total hepatic protein content. Disulfiram significantly increased also the microsomal protein and phospholipid contents. Diethyldithiocarbamate and disulfiram partially prevented the increase of microsomal protein and phospholipid contents caused by phenobarbital. Disulfiram and diethyldithiocarbamate decreased the amount of cytochrome P-450 and P-420, and the activity of p-nitroanisole O-demethylase. These changes were more pronounced after diethyldithiocarbamate than after disulfiram treatment. On the contrary, the activity of NADPH-cytochrome c reductase was enhanced only by disulfiram. The induction by phenobarbital of cytochrome P-450 and p-nitrosanisole O-demethylase was partially prevented on concomitant treatment with disulfiram and diethyldithiocarbamate. These compounds. however, had an additive effect with phenobarbital in enhancing the microsomal NADPH-cytochrome c reductase activity.

Enzymatic oxidation of diethyldithiocarbamate by xanthine oxidase and its colorimetric assay

Diethyldithiocarbamate is oxidized in vitro by purified cream xanthine oxidase in the presence of nitro blue tetrazolium and phenazine methosulfate. Disulfiram is formed during the enzymatic or nonenzymatic oxidation. When diethyldithiocarbamate is mixed nonenzymatically with nitro blue tetrazolium, the dye is rapidly reduced, but only in the presence of certain organic solvents. This reaction can be used as a convenient colorimetric assay for diethyldithiocarbamate, which gives a stable color over a wide concentration range.

The effect of disulfiram on the aldehyde dehydrogenases of sheep liver

1. The effect of disulfiram on the activity of the cytoplasmic and mitochondrial aldehyde dehydrogenases of sheep liver was studied. 2. Disulfiram causes an immediate inhibition of the enzyme reaction. The effect on the cytoplasmic enzyme is much greater than on the mitochondrial enzyme. 3. In both cases, the initial partial inhibition is followed by a gradual irreversible loss of activity. 4. The pH-rate profile of the inactivation of the mitochondrial enzyme by disulfiram and the pH-dependence of the maximum velocity of the enzyme-catalysed reaction are both consistent with the involvement of a thiol group. 5. Excess of 2-mercaptoethanol or GSH abolishes the effect of disulfiram. However, equimolar amounts of either of these reagents and disulfiram cause an effect greater than does disulfiram alone. It was shown that the mixed disulphide, Et2N-CS-SS-CH2-CH2OH, strongly inhibits aldehyde dehydrogenase. 6. The inhibitory effect of diethyldithiocarbamate in vitro is due mainly to contamination by disulfiram.

Investigations in bitro and in vivo, of the effects of disulfiram (Antabuse) on human lymphocyte chromosomes

Pilinskaya showed that the fungicide ziram induced chrocosome aberrations in the lymphocytes of exposed industrial workers and also in lymphocyte cultures treated in vitro. Ziram is chemically similar to the drug Antabuse (disulfirm) which is used in the treatment of alcoholics. To establish whether disulfirm can also cause chromosome aberrations, we have examined the chrocosomes of lymphocytes from treated and untreated alcoholics and normal controls, and also the chromosomes of lymphocytes treated in vitro. Our results show that disulfirm is 800 times less toxic than ziram and suggest that it is at least 10 000 times less active as an inducer of chromosome aberrations. We found no significant increase in aberrations in vitro or in vivo with disulfiram and conclude taht if it is an inducer of aberrations in lymphoctes then they must be induced with a very low frequency indeed.