Identification of the protein-drug adduct formed between aldehyde dehydrogenase and S-methyl-N,N-diethylthiocarbamoyl sulfoxide by on-line proteolytic digestion high performance liquid chromatography electrospray ionization mass spectrometry

Disulfiram: Mechanisms, Applications, and Challenges

Background: Since disulfiram’s discovery in the 1940s and its FDA approval for alcohol use disorder, other indications have been investigated. This review describes potential clinical applications, associated risks, and challenges. Methods: For this narrative review, a PubMed search was conducted for articles addressing in vivo studies of disulfiram with an emphasis on drug repurposing for the treatment of human diseases. The key search terms were “disulfiram” and “Antabuse”. Animal studies and in vitro studies highlighting important mechanisms and safety issues were also included. Results: In total, 196 sources addressing our research focus spanning 1948–2022 were selected for inclusion. In addition to alcohol use disorder, emerging data support a potential role for disulfiram in the treatment of other addictions (e.g., cocaine), infections (e.g., bacteria such as Staphylococcus aureus and Borrelia burgdorferi, viruses, parasites), inflammatory conditions, neurological diseases, and cancers. The side effects range from minor to life-threatening, with lower doses conveying less risk. Caution in human use is needed due to the considerable inter-subject variability in disulfiram pharmacokinetics. Conclusions: While disulfiram has promise as a “repurposed” agent in human disease, its risk profile is of concern. Animal studies and well-controlled clinical trials are needed to assess its safety and efficacy for non-alcohol-related indications.

Active-site inhibitors modulate the dynamic properties of human monoacylglycerol lipase: a hydrogen exchange mass spectrometry study

Human monoacylglycerol lipase (hMGL) regulates endocannabinoid signaling primarily by deactivating the lipid messenger 2-arachidonoylglycerol. Agents that carbamylate hMGLs catalytic Ser(122) constitute a leading class of therapeutically promising hMGL inhibitors. We have applied peptide-level hydrogen/deuterium exchange mass spectrometry to characterize hMGL's conformational responses to two potent carbamylating inhibitors, AM6580 (irreversible) and AM6701 (slowly reversible). A dynamic, solvent-exposed lid domain is characteristic of hMGL's solution conformation. Both hMGL inhibitors restricted backbone enzyme motility in the active-site region and increased substrate binding-pocket solvent exposure. Covalent reaction of AM6580 with hMGL generates a bulkier carbamylated Ser(122) residue as compared to the more discrete Ser(122) modification by AM6701, a difference reflected in AM6580's more pronounced effect upon hMGL conformation. We demonstrate that structurally distinct carbamylating hMGL inhibitors generate particular conformational ensembles characterized by region-specific hMGL dynamics. By demonstrating the distinctive influences of two hMGL inhibitors on enzyme conformation, this study furthers our understanding at the molecular level of the dynamic features of hMGL interaction with small-molecule ligands.

Combination treatment of epilepsy with ketogenic diet and concurrent pharmacological inhibition of cytochrome P450 2E1

While most epileptic patients respond to treatment with existing antiepileptic drugs, there remains a considerable number of patients in whom these drugs do not suffice. Such patients, particularly children, are often treated using the ketogenic diet. This diet imposes a strict limit on carbohydrates; while providing for adequate protein, most of the calories are supplied as triacylglycerol, much of which is metabolized to ketone bodies. Animal experiments have provided evidence that the anticonvulsant effect of the ketogenic diet is mediated by acetone and correlates with blood acetone levels. Acetone can be converted in vivo to glucose via acetol and pyruvate; the initial conversion to acetol is catalyzed by cytochrome P450 2E1 (CYP2E1). When CYP2E1 knockout mice are subjected to starvation to induce ketogenesis, they develop blood acetone levels much higher than those observed in wild-type mice. Similarly, pharmacological inhibition of CYP2E1 significantly increases blood acetone levels in rat and man. Taken together, these observations suggest that pharmacological inhibition of CYP2E1 has the potential to significantly increase the antiepileptic effect of the ketogenic diet. With patients that respond insufficiently to the diet alone, increased acetone levels may improve response. With patients who respond sufficiently to the diet, CYP2E1 inhibitors might allow a relaxation of the fairly severe diet regimen and so improve compliance and quality of life. An existing inhibitor of CYP2E1 is the drug disulfiram. This drug also inhibits the enzyme aldehyde dehydrogenase, which functions in alcohol degradation, and in this capacity has long been used in the treatment of alcohol addiction. Disulfiram inhibits CYP2E1 at conventional therapeutic dosages and increases blood acetone levels in humans and animals. It should therefore be a viable candidate for the proposed drug/diet combination treatment.

Toward an "omic" physiopathology of reactive chemicals: thirty years of mass spectrometric study of the protein adducts with endogenous and xenobiotic compounds

Cancer and degenerative diseases are major causes of morbidity and death, derived from the permanent modification of key biopolymers such as DNA and regulatory proteins by usually smaller, reactive molecules, present in the environment or generated from endogenous and xenobiotic components by the body's own biochemical mechanisms (molecular adducts). In particular, protein adducts with organic electrophiles have been studied for more than 30 [see, e.g., Calleman et al., 1978] years essentially for three purposes: (a) as passive monitors of the mean level of individual exposure to specific chemicals, either endogenously present in the human body or to which the subject is exposed through food or environmental contamination; (b) as quantitative indicators of the mean extent of the individual metabolic processing which converts a non-reactive chemical substance into its toxic products able to damage DNA (en route to cancer induction through genotoxic mechanisms) or key proteins (as in the case of several drugs, pesticides or otherwise biologically active substances); (c) to relate the extent of protein modification to that of biological function impairment (such as enzyme inhibition) finally causing the specific health damage. This review describes the role that contemporary mass spectrometry-based approaches employed in the qualitative and quantitative study of protein-electrophile adducts play in the discovery of the (bio)chemical mechanisms of toxic substances and highlights the future directions of research in this field. A particular emphasis is given to the measurement of often high levels of the protein adducts of several industrial and environmental pollutants in unexposed human populations, a phenomenon which highlights the possibility that a number of small organic molecules are generated in the human organism through minor metabolic processes, the imbalance of which may be the cause of "spontaneous" cases of cancer and of other degenerative diseases of still uncharacterized etiology. With all this in mind, it is foreseen that a holistic description of cellular functions will take advantage of new analytical methods based on time-integrated metabolomic measurements of a new biological compartment, the "adductome," aimed at better understanding integrated organism response to environmental and endogenous stressors.

Development of an automated on-line pepsin digestion-liquid chromatography-tandem mass spectrometry configuration for the rapid analysis of protein adducts of chemical warfare agents

Rapid monitoring and retrospective verification are key issues in protection against and non-proliferation of chemical warfare agents (CWA). Such monitoring and verification are adequately accomplished by the analysis of persistent protein adducts of these agents. Liquid chromatography-mass spectrometry (LC-MS) is the tool of choice in the analysis of such protein adducts, but the overall experimental procedure is quite elaborate. Therefore, an automated on-line pepsin digestion-LC-MS configuration has been developed for the rapid determination of CWA protein adducts. The utility of this configuration is demonstrated by the analysis of specific adducts of sarin and sulfur mustard to human butyryl cholinesterase and human serum albumin, respectively.

Chemical modifications to study mutations that affect the ability of the general base (E268) to function in human liver mitochondrial aldehyde dehydrogenase

The action of a general base is needed in two possible steps during the aldehyde dehydrogenase catalyzed oxidation of an aldehyde to an acid. The base is glutamate at position 268 in the cytosolic and mitochondrial class 1 and 2 enzyme. A chemical modification approach was undertaken to determine if the base were necessary in the initial attack of the nucleophilic cysteine (302) on the aldehyde as well as the attack by water on the acyl intermediate formed after the aldehyde is oxidized. A metabolite of disulfiram, S-methyl-N,N-diethylthiocarbamoyl sulfoxide (MeDTC-SO), was used as the modifying agent. Three recombinantly expressed mutant forms of the human mitochondrial enzyme along with the native one were used. These were the E268Q mutant that was lacking the general base; the E487K Oriental variant of the enzyme and R475Q, a mutant possessing the residue that binds to E487. As expected, the E268Q mutant was inactivated very slowly compared with the native or other mutants that were inactivated more slowly than the native enzyme. The presence of NAD did not increase the rate of inactivation except with the R475Q mutant. It is concluded that it is necessary to activate the cysteine at the active site to make it a good nucleophile as well to activate water during the hydrolysis of the thio-acyl intermediate. Further, it is surmised that the reason some mutants have a lowered specific activity is that in those the general base is not capable of functioning as it does in the native enzyme.

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.

Current literature in mass spectrometry

In order to keep subscribers up-to-date with the latest developments in their field, John Wiley & Sons are providing a current awareness service in each issue of the journal. The bibliography contains newly published material in the field of mass spectrometry. Each bibliography is divided into 11 sections: 1 Books, Reviews & Symposia; 2 Instrumental Techniques & Methods; 3 Gas Phase Ion Chemistry; 4 Biology/Biochemistry: Amino Acids, Peptides & Proteins; Carbohydrates; Lipids; Nucleic Acids; 5 Pharmacology/Toxicology; 6 Natural Products; 7 Analysis of Organic Compounds; 8 Analysis of Inorganics/Organometallics; 9 Surface Analysis; 10 Environmental Analysis; 11 Elemental Analysis. Within each section, articles are listed in alphabetical order with respect to author (3 Weeks journals - Search completed at 28th. June 2000)