Aldehyde dehydrogenases (ALDHs) belong to a superfamily of enzymes that play a key role in the metabolism of aldehydes of both endogenous and exogenous derivation. The human ALDH superfamily comprises 19 isozymes that possess important physiological and toxicological functions. The ALDH1A subfamily plays a pivotal role in embryogenesis and development by mediating retinoic acid signaling. ALDH2, as a key enzyme that oxidizes acetaldehyde, is crucial for alcohol metabolism. ALDH1A1 and ALDH3A1 are lens and corneal crystallins, which are essential elements of the cellular defense mechanism against ultraviolet radiation-induced damage in ocular tissues. Many ALDH isozymes are important in oxidizing reactive aldehydes derived from lipid peroxidation and thereby help maintain cellular homeostasis. Increased expression and activity of ALDH isozymes have been reported in various human cancers and are associated with cancer relapse. As a direct consequence of their significant physiological and toxicological roles, inhibitors of the ALDH enzymes have been developed to treat human diseases. This review summarizes known ALDH inhibitors, their mechanisms of action, isozyme selectivity, potency, and clinical uses. The purpose of this review is to 1) establish the current status of pharmacological inhibition of the ALDHs, 2) provide a rationale for the continued development of ALDH isozyme-selective inhibitors, and 3) identify the challenges and potential therapeutic rewards associated with the creation of such agents.

Aldehyde Dehydrogenase Inhibitors: a Comprehensive Review of the Pharmacology, Mechanism of Action, Substrate Specificity, and Clinical Application

Structure of mitochondrial aldehyde dehydrogenase: the genetic component of ethanol aversion.

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)

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

Rare adverse reactions to drugs that are of unknown etiology, or idiosyncratic reactions, can produce severe medical complications or even death in patients. Current hypotheses suggest that metabolic activation of a drug to a reactive intermediate is a necessary, yet insufficient, step in the generation of an idiosyncratic reaction. We review evidence for this hypothesis with drugs that are associated with hepatotoxicity, one of the most common types of idiosyncratic reactions in humans. We identified 21 drugs that have either been withdrawn from the U.S. market due to hepatotoxicity or have a black box warning for hepatotoxicity. Evidence for the formation of reactive metabolites was found for 5 out of 6 drugs that were withdrawn, and 8 out of 15 drugs that have black box warnings. For the other drugs, either evidence was not available or suitable studies have not been carried out. We also review evidence for reactive intermediate formation from a number of additional drugs that have been associated with idiosyncratic hepatotoxicity but do not have black box warnings. Finally, we consider the potential role that high dosages may play in these adverse reactions.

Role of metabolism in drug-induced idiosyncratic hepatotoxicity.

Dithiocarbamates Induce Apoptosis in Thymocytes by Raising the Intracellular Level of Redox-active Copper

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

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

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

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. Rats treated with DETC-MeSO and then challenged with ethanol exhibited an increase in blood acetaldehyde similar to that found from previous studies with disulfiram. In in vitro studies, incubation of rat liver mitochondria with 0.75 μM DETC-MeSO inhibited rat liver mitochondrial low Km ALDH maximally within 2 hr, whereas purified bovine mitochondrial low Km ALDH was inhibited 90% and 99%, respectively, when incubated for 1 hr with 2 and 6 μM DETC-MeSO. These studies with rats and purified bovine ALDH show that DETC-MeSO is a potent inhibitor of mitochondrial low Km ALDH both in vivo and in vitro, providing additional evidence that DETC-MeSO is the metabolite to which disulfiram must be bioactivated for liver ALDH to be inhibited.

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

A method is provided for deterring ethanol ingestion by a human, comprising administering to said human an amount of a compound of the formula (R1)(R2)NC(X)S(O)R3 effective to cause the disulfiram-ethanol reaction in said human, wherein R?1, R2 and R3? are each (C?1?-C4) alkyl groups, e.g., methyl, ethyl, propyl, isopropyl, butyl, i-butyl and t-butyl.

Bruce W. Hart

Papers

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

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

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

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

Thiocarbamate sulfoxide composition for deterring ethanol ingestion