S-methyl-N,N-diethylthiolcarbamate: a disulfiram metabolite and potent rat liver mitochondrial low Km aldehyde dehydrogenase inhibitor

Pharmacoprophylaxis of alcohol dependence: Review and update Part I: Pharmacology

Alcohol dependence is a major problem in India. The pharmacological armamentarium for relapse prevention of alcohol has widened with the addition of new drugs. In this article, we review the pharmacology and efficacy of the four most important such drugs: disulfiram, naltrexone, acamprosate and topiramate. The first part of this two-part review series concerns the comparative pharmacology and the second part concerns the efficacy studies. Overall, all four of these drugs have modest but clinically significant usefulness as pharmacoprophylactic agents for relapse prevention or minimization of alcohol dependence. Combinations might be helpful, especially for naltrexone and acamprosate. The issue of supervision and compliance remains important, especially for such drugs as disulfiram and naltrexone. Topiramate is a promising new agent and requires further study. Disulfiram, while very effective in compliant patients, presents challenges in terms of patient selection and side effects. For patients with hepatic impairment, acamprosate is a good choice.

Segment-specific pattern of sympathetic preganglionic projections in the chicken embryo spinal cord is altered by retinoids

Sympathetic preganglionic neurons exhibit segment-specific projections. Preganglionic neurons located in rostral spinal segments project rostrally within the sympathetic chain, those located in caudal spinal segments project caudally, and those in midthoracic segments project either rostrally or caudally in segmentally graded proportions. Moreover, rostrally and caudally projecting preganglionic neurons are skewed toward the rostral and caudal regions, respectively, of each midthoracic segment. The mechanisms that establish these segment-specific projections are unknown. Here we show that experimental manipulation of retinoid signaling in the chicken embryo alters the segment-specific pattern of sympathetic preganglionic projections and that this effect is mediated by the somitic mesoderm. Application of exogenous retinoic acid to a single rostral thoracic somite decreases the number of rostrally projecting preganglionic neurons at that level. Conversely, disrupting endogenous synthesis of retinoic acid in a single caudal thoracic somite increases the number of rostrally projecting preganglionic neurons at that level. The number of caudally projecting neurons does not change in either case, indicating that the effect is specific for rostrally projecting preganglionic neurons. These results indicate that the sizes of the rostrally and caudally projecting populations may be independently regulated by different factors. Opposing gradients of such factors along the longitudinal axis of the thoracic region of the embryo could be sufficient, in combination, to determine the segment-specific identity of preganglionic projections.

Inhibition of recombinant human mitochondrial aldehyde dehydrogenase by two intermediate metabolites of disulfiram

Disulfiram is used in aversion therapy for alcoholism. S-Methyl-N,N-diethylthiocarbamate (MeDTC) sulfoxide, a potent inhibitor of the target enzyme mitochondrial aldehyde dehydrogenase (ALDH2), is thought to be the principal active metabolite of disulfiram in vivo. We examined the effects on recombinant human ALDH2 of two intermediate metabolites of disulfiram, S-methyl-N,N-diethyldithiocarbamate (MeDDC) sulfoxide and MeDDC sulfine. MeDDC sulfoxide was a potent inhibitor of ALDH2 with an IC50 of 2.2 +/- 0.5 microM (mean +/- SD, N = 4) after preincubation with enzyme for 30 min. MeDDC sulfine was a relatively weak inhibitor of ALDH2 under the same conditions with an IC50 value of 62 +/- 14 microM. The inhibition of ALDH2 by both compounds was irreversible and did not require the cofactor NAD. The latter finding demonstrates that inactivation of ALDH2 is independent of the dehydrogenase activity of the enzyme. GSH blocked almost completely the inhibition by 20 microM of MeDDC sulfoxide and greatly diminished the inhibition by 200 microM of MeDDC sulfine. Inactivation by MeDDC sulfoxide was time dependent. MeDTC sulfoxide was a more potent inhibitor of recombinant human ALDH2 (IC50 = 1.4 +/- 0.3 microM after preincubation for 15 min) than either of the intermediate metabolites, and its inhibition was unaffected by GSH. Our results suggest that these newer intermediate metabolites of disulfiram, especially the more potent MeDTC sulfoxide, have the potential to inhibit the target enzyme ALDH2 in patients receiving disulfiram. However, until the significance of the interactions of the inhibitors with GSH is more fully understood, the contribution of MeDDC sulfine and MeDDC sulfoxide to the pharmacological effects of disulfiram in vivo is uncertain.

Inhibition of aldehyde dehydrogenase by disulfiram and its metabolite methyl diethylthiocarbamoyl-sulfoxide

Disulfiram (DSF) is presently the only available drug used in the aversion therapy of recovering alcoholics. It acts by inhibiting aldehyde dehydrogenase (ALDH), leading to high blood levels of acetaldehyde. The in vitro inhibition of ALDH by DSF and its metabolites was systematically studied by combined enzyme inhibition assay with direct molecular weight determination of the same sample using electrospray ionization-mass spectrometry (ESI-MS). Enzyme activity was measured after incubating yeast ALDH (yALDH) with excess concentrations of DSF, methyl diethyldithiocarbamate (MeDDC) and methyl diethylthiocarbamoyl-sulfoxide (MeDTC-SO) and then subjected to analysis by ESI-MS. Addition of DSF resulted in complete enzyme inhibition; however, ESI-MS analysis demonstrated no discernible shift in molecular weight, indicating that no intermolecular adduct was formed with the protein. Treatment of yALDH with MeDTC-SO also completely abolished yALDH activity with a concomitant increase of + approximately 100 Da in the molecular mass of the enzyme. This indicated formation of a covalent carbamoyl protein adduct. Furthermore, the effects of dithiothreitol (DTT) were examined on samples of inhibited protein in vitro. At pH 7.5, DTT completely reversed inhibition after DSF treatment. yALDH inhibited by MeDTC-SO could not be recovered by DTT at pH 7.5, but at pH 9 the enzymic activity was fully restored and a mass loss of approximately 100 Da was noted. This observations are consistent with mechanisms where inhibition of yALDH by DSF in vitro involves oxidation of the active site, whereas MeDTC-SO forms a covalent adduct with the protein in vitro resulting in cessation of enzyme activity.

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.

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.

Divergence of ethanol and acetaldehyde kinetics and of the disulfiram-alcohol reaction between subjects with and without alcoholic liver disease

Despite standardization, marked interindividual variation in the severity of the disulfiram-alcohol reaction (DAR) has been observed. We studied the DAR in 51 consecutive alcoholics with (n = 16) and without (n = 35) significant alcoholic liver disease. Clinical signs of the DAR were much weaker in the patients with compared with those patients without liver disease. Because acetaldehyde is thought to be the main cause of the DAR, we studied ethanol and acetaldehyde kinetics in 13 patients (6 females, 7 males) with alcoholic liver disease (documented by biopsy, clinical and/or radiological findings, and by quantitative liver function) [galactose elimination capacity (GEC) 4.2 +/- SD 1.0 mg/min/kg; aminopyrine breath test (ABT) 0.14 +/- 0.10% dose x kg/mmol CO2] and 13 age- and sex-matched controls (alcoholics without significant liver disease, GEC 7.1 +/- 0.7; ABT 0.81 +/- 0.35). Clinical signs of acetaldehyde toxicity during the DAR (flush, nausea, tachycardia, and blood pressure drop) were absent in alcoholic liver disease, but clearly evident in controls. Blood ethanol kinetics were similar in both groups, Cmax and area under the concentration-time curve (AUC) being 6.27 +/- 1.82 and 368.9 +/- 72.9 mmol x min/liter in alcoholic liver disease, and 6.62 +/- 1.71 and 377.6 +/- 124.5 in controls, respectively. In contrast, there was a strong (p < 0.001) difference in Cmax and AUC of acetaldehyde, respective values being 33.46 +/- 21.52 and 1463.8 +/- 762.5 mumol x min/liter in alcoholic liver disease, and 110.87 +/- 56.00 and 4162.0 +/- 2424.6 in controls.(ABSTRACT TRUNCATED AT 250 WORDS)

S-methyl N,N-diethylthiocarbamate sulfone, a potential metabolite of disulfiram and potent inhibitor of low Km mitochondrial aldehyde dehydrogenase

Disulfiram inhibits hepatic aldehyde dehydrogenase (ALDH) causing an accumulation of acetaldehyde after ethanol ingestion. It is thought that disulfiram is too short-lived in vivo to directly inhibit ALDH, but instead is biotransformed to reactive metabolites that inhibit the enzyme. S-Methyl N,N-diethylthiocarbamate (MeDTC) sulfoxide has been identified in the blood of animals given disulfiram and is a potent inhibitor of ALDH (Hart and Faiman, Biochem Pharmacol 46: 2285-2290, 1993). MeDTC sulfone is a logical metabolite of MeDTC sulfoxide. Therefore, we investigated the effects of MeDTC sulfone on the activity of rat hepatic low Km mitochondrial ALDH, the major enzyme in the metabolism of acetaldehyde. MeDTC sulfone inhibited the low Km mitochondrial ALDH in vitro with an IC50 of 0.42 +/- 0.04 microM (mean +/- SD, N = 5) compared with disulfiram, which had an IC50 of 7.5 +/- 1.2 microM under the same conditions. The inhibition of ALDH by MeDTC sulfone was time dependent. The decline in ALDH activity followed pseudo first-order kinetics with an apparent half-life of 2.1 min at 0.6 microM MeDTC sulfone. Inhibition of ALDH by MeDTC sulfone was apparently irreversible; dilution of the inhibited enzyme did not restore lost activity. The substrate (acetaldehyde, 80 microM) and cofactor (NAD, 0.5 mM) together completely protected ALDH from inhibition by MeDTC sulfone; substrate alone partially protected the enzyme. Addition of either thiol-containing compound glutathione (GSH) or dithiothreitol (DTT) to MeDTC sulfone before incubation with the enzyme increased the IC50 of MeDTC sulfone by 7- to 14-fold. Neither GSH nor DTT could restore lost ALDH activity after exposure of the enzyme to MeDTC sulfone. Results of these studies indicate that MeDTC sulfone, a potential metabolite of disulfiram, is a potent, irreversible inhibitor of low Km mitochondrial ALDH.

Inhibition of rat liver low Km aldehyde dehydrogenase by thiocarbamate herbicides. Occupational implications

S-Methyl N,N-diethylthiolcarbamate (DETC-Me) is a metabolite formed during the bioactivation of disulfiram. The formation of its corresponding sulfoxide, S-methyl N,N-diethylthiolcarbamate sulfoxide (DETC-MeSO), from DETC-Me is required for low Km mitochondrial aldehyde dehydrogenase (ALDH2, EC 1.2.1.3) inhibition. DETC-Me is similar in structure to thiocarbamate herbicides with the general structure R1R2NC(O)SR3. Representative herbicides studied were n-propyl, n-propylthiocarbamate ethyl ester (EPTC), molinate, vernolate, ethiolate and butylate. All of these thiocarbamate herbicides inhibited rat liver ALDH2 in vivo. The dose of these thiocarbamates that inhibited rat liver ALDH2 by 50% (ID50) when administered 8 hr before determination of ALDH2, was found to be 5.2, 3.1, 1.6, 12, and 174 mg/kg, respectively. These thiocarbamates were ineffective rat liver ALDH2 inhibitors in vitro, unless rat liver microsomes and an NADPH-generating system were added to the incubation. The respective thiocarbamate sulfoxides were formed when the thiocarbamates were incubated with liver microsomes and an NADPH-generating system. The thiocarbamate sulfoxides all inhibited rat liver ALDH2 in vitro. An equimolar dose of molinate and molinate sulfoxide inhibited rat liver ALDH2 in vivo to the same degree. Molinate-treated rats challenged with ethanol exhibited a disulfiram-like ethanol reaction. In conclusion, thiocarbamate herbicides inhibit ALDH2, probably due to the formation of their sulfoxide, and therefore have the potential to produce a disulfiram-like ethanol reaction in an unsuspecting population.

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.

Diethyldithiocarbamate methyl ester sulfoxide, an inhibitor of rat liver mitochondrial low Km aldehyde dehydrogenase and putative metabolite of disulfiram

S-methyl N,N-diethylthiolcarbamate sulfoxide (DETC-MeSO) is a potent inhibitor of rat liver mitochondrial low Km aldehyde dehydrogenase (ALDH2) both in vivo and in vitro, and has been proposed to be the metabolite responsible for ALDH2 inhibition by disulfiram. Diethyldithiocarbamate methyl ester (DDTC-Me), a key intermediate in the metabolism of disulfiram, has been shown to be bioactivated by microsomal monooxygenases to diethyldithiocarbamate methyl ester sulfoxide (DDTC-Me sulfoxide). Studies were conducted to determine if DDTC-Me sulfoxide was also an active metabolite of disulfiram and inhibitor of ALDH2. DDTC-Me sulfoxide inhibited ALDH2 in vitro with an IC50 of 10 microM, and in vivo with an ID50 of 31 mg/kg (170 mumol/kg). Maximal ALDH2 inhibition in vivo was observed 8 hr after the administration of 45.2 mg/kg DDTC-Me sulfoxide, with ALDH2 activity returning to control levels after 48 hr. Although DDTC-Me sulfoxide inhibited ALDH2 in vivo, DDTC-Me sulfoxide was not detected in plasma from rats treated with either disulfiram (75 mg/kg), DDTC-Me (122.25 mg/kg), or DDTC-Me sulfoxide (45.2 mg/kg). However, DDTC-Me and S-methyl N,N-diethylthiolcarbamate (DETC-Me) were detected in plasma from rats treated with DDTC-Me sulfoxide. In rats treated with DDTC-Me sulfoxide and challenged with ethanol, a small increase of approximately microM in blood acetaldhyde and an inconsistent drop in blood pressure was observed. In conclusion, DDTC-Me sulfoxide inhibited ALDH2 in vitro and in vivo, was less potent than DETC- MeSO, and was not detected after disulfiram administration.

S-methyl N,N-diethylthiolcarbamate sulfone, an in vitro and in vivo inhibitor of rat liver mitochondrial low Km aldehyde dehydrogenase

S-Methyl N,N-diethylthiolcarbamate sulfone (DETC-Me sulfone) was investigated for its rat liver mitochondrial low Km aldehyde dehydrogenase (ALDH2) inhibitory properties. DETC-Me sulfone inhibited ALDH2 in vitro (IC50 = 3.8 microM) and in vivo (ID50 = 170 mumol/kg; 31 mg/kg). Maximum inhibition (60%) of ALDH2 was observed 8 hr after DETC-Me sulfone administration. In addition, incubation of S-methyl N,N-diethylthiolcarbamate (DETC-Me) or S-methyl N,N-diethylthiolcarbamate sulfoxide (DETC-Me sulfoxide) with rat liver microsomes and an NADPH-generating system failed to produce DETC-Me sulfone. Furthermore, DETC-Me sulfone could not be detected in plasma from rats treated with either DETC-Me sulfoxide or DETC-Me sulfone. In conclusion, DETC-Me sulfone inhibited ALDH2 in vitro and in vivo. However, there was no evidence suggesting that DETC-Me sulfoxide was metabolized to DETC-Me sulfone.

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)

Role of flavin-dependent monooxygenases and cytochrome P450 enzymes in the sulfoxidation of S-methyl N,N-diethylthiolcarbamate

Disulfiram is bioactivated to S-methyl N,N-diethylthiolcarbamate sulfoxide (DETC-MeSO), the metabolite proposed to be responsible for the action of disulfiram as an aldehyde dehydrogenase inhibitor. This bioactivation process includes a reduction, an S-methylation, and two successive oxidations. Sulfur-containing functional groups are substrates for cytochrome P450 enzymes or flavin-containing monooxygenases (FMO). In the present study, we investigated the contribution of these monooxygenases to the formation of DETC-MeSO from its immediate precursor S-methyl N,N-diethylthiolcarbamate (DETC-Me). Liver microsomes obtained from mature male rats were incubated with DETC-Me. The formation of DETC-MeSO was blocked completely by solubilization of the microsomes with the detergent Emulgen 911, or by the presence of the cytochrome P450 inhibitor 1-benzylimidazole. However, thermal-inactivation of FMO resulted in only a partial loss in DETC-MeSO formation. Liver microsomes from phenobarbital-treated rats showed a 4- to 5-fold increase in the rate of formation of DETC-MeSO, compared with controls. Liver microsomes from pyrazole-treated rats showed a 50% decrease in the sulfoxidation of DETC-Me compared with controls. In a purified reconstituted system, cytochrome P450 2B1 (CYP2B1) catalyzed the formation of DETC-MeSO at a rate of 51 nmol DETC-MeSO formed/min/nmol cytochrome P450. Antibodies to CYP2B1 caused a 60% inhibition of DETC-MeSO formation by liver microsomes from phenobarbital-treated rats. These results suggest that in male rat liver microsomes, cytochrome P450 plays a major role in catalyzing the sulfoxidation of DETC-Me, whereas FMO plays a minor role (< 10%). Also, in liver microsomes from phenobarbital-treated rats, CYP2B1 is the major catalyst for the sulfoxidation of DETC-Me.

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.

Techniques to enhance compliance with disulfiram

Pharmacodynamic benefits of disulfiram in the treatment of alcoholism have yet to be clearly demonstrated. Nevertheless, research does suggest that disulfiram may well have positive effects on drinking if medicational compliance procedures are employed. This paper reviews research on four strategies for enhancing disulfiram compliance: implants, incentives, contracts, and patient information. Generalizations about the strategies are drawn and needs for future research are briefly addressed.

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)

The pharmacology and toxicology of disulfiram and its metabolites

Disulfiram (Antabuse) is one of several aldehyde dehydrogenase (ALDH) inhibitors that raise the plasma level of acetaldehyde following ethanol ingestion. The usually pleasant reaction to ethanol is thereby changed to an unpleasant one, owing to a number of bodily reactions to acetaldehyde. Populations showing genetic polymorphism with a lack of some isozymes of ALDH have exhibited an intolerance to ethanol similar to that seen with disulfiram. A normal isozyme pattern seems to be a prerequisite for the development of alcoholism, which supports the principle of disulfiram treatment. Disulfiram is an irreversible ALDH inhibitor when administered in vivo. Diethylthiomethylcarbamate (Me-DTC) is formed from disulfiram in three metabolic steps. This compound and two further oxidized metabolites appear to be active metabolites of disulfiram. Measurements of plasma Me-DTC or the reduction of leucocyte ALDH 1 activity may be valuable markers for the proper dose titration of disulfiram and the rational use of this drug. Some toxicological points are discussed.

In vitro and in vivo inhibition of rat liver aldehyde dehydrogenase by S-methyl N,N-diethylthiolcarbamate sulfoxide, a new metabolite of disulfiram

In summary, these data provide the first evidence that DETC-MeSO is a natural metabolite of disulfiram, and a potent inhibitor of rat liver mitochondrial low Km ALDH both in vitro and in vivo. It is therefore proposed that, based upon evidence to date, DETC-MeSO appears to be the chemical species to which disulfiram must be bioactivated, and is the metabolite most likely responsible for disulfiram's inhibition of rat liver mitochondrial low Km ALDH in vivo. Characterization of the properties of DETC-MeSO as the metabolite responsible for disulfiram's action as an ALDH inhibitor is presently in the process of being completed.

Disulfiram metabolism as a requirement for the inhibition of rat liver mitochondrial low Km aldehyde dehydrogenase

In humans and animals, disulfiram produces a disulfiram-ethanol reaction after an ethanol challenge, the basis of which is the inhibition of liver aldehyde dehydrogenase (ALDH). Disulfiram and the metabolites diethyldithiocarbamate (DDTC), diethyldithiocarbamate-methyl ester (DDTC-Me), and S-methyl-N,N-diethylthiolcarbamate (DETC-Me) were studied in order to determine the role of bioactivation in disulfiram's action as an inhibitor of rat liver mitochondrial low Km ALDH (RLM low Km ALDH). In in vitro studies, disulfiram and DDTC (0.01 to 2.0 mM) both inhibited RLM low Km ALDH in a concentration-dependent manner. The addition of rat liver microsomes to the mitochondrial incubation did not further increase disulfiram-induced RLM low Km ALDH inhibition. However, DDTC-induced RLM low Km ALDH inhibition was increased further, but only at DDTC concentrations less than 0.05 mM. DDTC-Me and DETC-Me (2.0 mM) similarly exhibited an increased RLM low Km ALDH inhibition after the addition of liver microsomes. In in vivo studies, disulfiram (75 mg/kg), DDTC (114 mg/kg), DDTC-Me (41.2 mg/kg) or DETC-Me (18.6 mg/kg) administered i.p. to female rats inhibited RLM low Km ALDH. Inhibition of drug metabolism by pretreatment of rats with the cytochrome P450 inhibitor N-octylimidazole (NOI) (20 mg/kg, i.p.) prior to either disulfiram, DDTC, DDTC-Me or DETC-Me administration blocked the inhibition of RLM low Km ALDH. The in vitro and in vivo data support the conclusion that bioactivation of disulfiram to a reactive chemical species is required for RLM low Km ALDH inhibition and a disulfiram-ethanol reaction.

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.

Pharmacotherapies for alcoholism: promising agents and clinical issues

The past 10 years have witnessed important advances in research on pharmacotherapy for alcoholism. Promising drugs are discussed under six headings: agents to treat alcohol withdrawal; anticraving agents; agents that make drinking an aversive experience; agents to alleviate concomitant psychiatric problems; agents to treat concurrent drug abuse; and amethystic ("sobering-up") agents. Research on the drug classes is summarized and clinical issues surrounding specific agents and alcoholism pharmacotherapy in general are discussed. Finally, long-range therapeutic implications of recent findings on the actions of alcohol on basic mechanisms of the brain are offered.