Identification Of Reactive Metabolites Research Articles

Gas chromatography-tandem mass spectrometry-based detection of half nitrogen mustards in plasma as a new biomarker of nitrogen mustard exposure.

The development and optimization of an analytical method for the detection and identification of reactive metabolite of organochlorine chemical warfare agent nitrogen mustards (NMs), 2-[(2-chloroethyl)(alkyl)amino]ethanol (CEAAE), known as half nitrogen mustard, in blood samples is presented, herein. In this study, half nitrogen mustards in plasma are presented as a new and unambiguous biomarker of NM exposure since the fully hydrolyzed product, i.e., amino alcohols, are common industrial chemicals that can be present as such without getting exposed to NMs. Thus, the detection of half nitrogen mustard as a biomarker holds great significance for verification by the Chemical Weapon Convention (CWC) and will also be helpful in understanding the pharmacokinetics of NM-based chemotherapeutic pro-drugs. To the best of our knowledge, this is the first report on the detection of half nitrogen mustards in any matrice, including plasma. A very simple sample preparation protocol was developed for its extraction from plasma samples. Heptafluorobutyrylation and gas chromatography-tandem mass spectrometry in the positive chemical ionization mode were developed for the detection and identification of halfNMs. The developed method has shown excellent analytical figures of merits such as a wide range of linearity (1.0-50 ng mL-1), low limit of detection (0.3-0.5 ng mL-1), and low limit of quantification (1.0 ng mL-1). The interday and intraday reproducibilities were also less than 15%. The developed method was successfully applied to real-world samples; in vitro human plasma was spiked with ∼1 ng mL-1 of all the NMs and in vivo studies were done with rats intravenously exposed to 1 × LD50 of bis(2-chloroethyl)methylamine (HN2).

Drug metabolism and hypersensitivity reactions to drugs.

The aim of the present review was to discuss recent advances supporting a role of drug metabolism, and particularly of the generation of reactive metabolites, in hypersensitivity reactions to drugs. The development of novel mass-spectrometry procedures has allowed the identification of reactive metabolites from drugs known to be involved in hypersensitivity reactions, including amoxicillin and nonsteroidal antiinflammatory drugs such as aspirin, diclofenac or metamizole. Recent studies demonstrated that reactive metabolites may efficiently bind plasma proteins, thus suggesting that drug metabolites, rather than - or in addition to - parent drugs, may elicit an immune response. As drug metabolic profiles are often determined by variability in the genes coding for drug-metabolizing enzymes, it is conceivable that an altered drug metabolism may predispose to the generation of reactive drug metabolites and hence to hypersensitivity reactions. These findings support the potential for the use of pharmacogenomics tests in hypersensitivity (type B) adverse reactions, in addition to the well known utility of these tests in type A adverse reactions. Growing evidence supports a link between genetically determined drug metabolism, altered metabolic profiles, generation of highly reactive metabolites and haptenization. Additional research is required to developing robust biomarkers for drug-induced hypersensitivity reactions.

Comparison of trapping profiles between d-peptides and glutathione in the identification of reactive metabolites

Qualitative trapping profile of reactive metabolites arising from six structurally different compounds was tested with three different d-peptide isomers (Peptide 1, gly–tyr–pro–cys–pro–his-pro; Peptide 2, gly–tyr–pro–ala–pro–his–pro; Peptide 3, gly–tyr–arg–pro–cys–pro–his–lys–pro) and glutathione (GSH) using mouse and human liver microsomes as the biocatalyst. The test compounds were classified either as clinically “safe” (amlodipine, caffeine, ibuprofen), or clinically as “risky” (clozapine, nimesulide, ticlopidine; i.e., associated with severe clinical toxicity outcomes). Our working hypothesis was as follows: could the use of short different amino acid sequence containing d-peptides in adduct detection confer any add-on value to that obtained with GSH? All “risky” agents’ resulted in the formation of several GSH adducts in the incubation mixture and with at least one peptide adduct with both microsomal preparations. Amlodipine did not form any adducts with any of the trapping agents. No GSH and peptide 2 and 3 adducts were found with caffeine, but with peptide 1 one adduct with human liver microsomes was detected. Ibuprofen produced one Peptide 1-adduct with human and mouse liver microsomes but not with GSH. In conclusion, GSH still remains the gold trapping standard for reactive metabolites. However, targeted d-peptides could provide additional information about protein binding potential of electrophilic agents, but their clinical significance needs to be clarified using a wider spectrum of chemicals together with other safety estimates.

Facile identification of photocleavable reactive metabolites and oxidative stress biomarkers in proteins via mass spectrometry

Described herein is a method which combines bond selective fragmentation by photodissociation with online liquid chromatographic separation and mass spectrometric analysis. Photoexcitation of proteins or peptides with 266-nm light does not normally yield abundant fragmentation; however, incorporation of a suitable carbon-sulfur or carbon-halogen bond that is proximal to a chromophore allows access to direct dissociation pathways, resulting in homolytic cleavage of these bonds. Radicals generated through this process can cause further dissociation of the peptide backbone, which is useful for site specifically identifying the point of modification. Two specific applications of this technique for peptide analysis in model systems are presented: (1) identification of reactive metabolites which covalently modify cysteine residues, and (2) characterization of halogenated tyrosine residues which are biomarkers related to oxidative stress. In both cases, these naturally occurring post translational modifications create photocleavable bonds which can be fragmented by 266-nm light. The selectivity offered by photodissociation allows facile identification of the peptides of interest even in complex mixtures, and subsequent selective radical directed backbone fragmentation pinpoints the site of modification. This combination greatly simplifies data analysis and provides more confident assignments.

Rescue of replication failure by Fanconi anaemia proteins

Chromosomal aberrations are often associated with incomplete genome duplication, for instance at common fragile sites, or as a consequence of chemical alterations in the DNA template that block replication forks. Studies of the cancer-prone disease Fanconi anaemia (FA) have provided important insights into the resolution of replication problems. The repair of interstrand DNA crosslinks induced by chemotherapy drugs is coupled with DNA replication and controlled by FA proteins. We discuss here the recent discovery of new FA-associated proteins and the development of new tractable repair systems that have dramatically improved our understanding of crosslink repair. We focus also on how FA proteins protect against replication failure in the context of fragile sites and on the identification of reactive metabolites that account for the development of Fanconi anaemia symptoms.

Detection and Structural Characterization of Glutathione-Trapped Reactive Metabolites Using Liquid Chromatography−High-Resolution Mass Spectrometry and Mass Defect Filtering

The present study was designed to apply the mass defect filter (MDF) approach to the screening and identification of reactive metabolites using high-resolution mass spectrometry. Glutathione (GSH)-trapped reactive metabolites of acetaminophen, diclofenac, carbamazepine, clozapine, p-cresol, 4-ethylphenol, and 3-methylindole in human liver microsomes (HLM) were analyzed by HPLC coupled with Orbitrap or Fourier transform ion cyclotron resonance mass spectrometry. Through the selective removal of all ions that fall outside of the GSH adduct MDF template windows, the processed full scan MS chromatograms displayed GSH adducts as major components with no or a few interference peaks. The accurate mass LC-MS data sets were also utilized for the elimination of false positive peaks, detection of stable oxidative metabolites with other MDF templates, and determination of metabolite molecular formulas. Compared to the neutral loss scan by a triple quadrupole instrument, the MDF approach was more sensitive and selective in screening for GSH-trapped reactive metabolites in HLM and rat bile and far more effective in detecting GSH adducts that do not afford the neutral loss of 129 Da as a significant fragmentation pathway. The GSH adduct screening capability of the MDF approach, together with the utility of accurate mass MS/MS information in structural elucidation, makes high-resolution LC-MS a useful tool for analyzing reactive metabolites.

Generation and Identification of Reactive Metabolites by Electrochemistry and Immobilized Enzymes Coupled On-Line to Liquid Chromatography/Mass Spectrometry

The detection of reactive metabolites using conventional in vivo and in vitro techniques is hampered because the intermediately formed reactive species are prone to covalent binding to cellular macromolecules. Therefore, the application of improved methods is required. The on-line coupling of an electrochemical reactor and horseradish peroxidase immobilized on magnetic microparticles with liquid chromatography/mass spectrometry (EC/LC/MS or HRP/LC/MS) allows the direct detection of reactive metabolites of the model compounds amodiaquine, amsacrine, and mitoxantrone, which are all known for readily binding to cellular macromolecules after metabolization by cytochrome P450. EC/LC/MS and HRP/LC/MS experiments were compared to rat liver microsome incubations and proved to be valuable complementary methods since reactive quinone, quinone imine, and quinone diimine species could be detected directly and not only after trapping with glutathione. Furthermore, N-dealkylation and N-oxidation of amodiaquine were successfully simulated by electrochemical oxidation reactions, as well as the formation of an aldehyde. Therefore, EC/LC/MS and HRP/LC/MS are promising tools for the identification of both reactive and stable metabolites in drug development.

Dansyl Glutathione as a Trapping Agent for the Quantitative Estimation and Identification of Reactive Metabolites

A sensitive and quantitative method was developed for the estimation of reactive metabolite formation in vitro. The method utilizes reduced glutathione (GSH) labeled with a fluorescence tag as a trapping agent and fluorescent detection for quantitation. The derivatization of GSH was accomplished by reaction of oxidized glutathione (GSSG) with dansyl chloride to form dansylated GSSG. Subsequent reduction of the disulfide bond yielded dansylated GSH (dGSH). Test compounds were incubated with human liver microsomes in the presence of dGSH and NADPH, and the resulting mixtures were analyzed by HPLC coupled with a fluorescence detector and a mass spectrometer for the quantitation and mass determination of the resulting dGSH adducts. The comparative chemical reactivity of dGSH vs GSH was investigated by monitoring the reaction of each with 1-chloro-2,4-dinitrobenzene or R-(+)-pulegone after bioactivation. dGSH was found to be equivalent to GSH in chemical reactivity toward both thiol reactive molecules. dGSH did not serve as a cofactor for glutathione S-transferase (GST)-mediated conjugation of 3,4-dichloronitrobenzene in incubations with either human liver S9 fractions or a recombinant GST, GSTM1-1. Reference compounds were tested in this assay, including seven compounds that have been reported to form GSH adducts along with seven drugs that are among the most prescribed in the current U.S. market and have not been reported to form GSH adducts. dGSH adducts were detected and quantitated in incubations with all seven positive reference compounds; however, there were no dGSH adducts observed with any of the widely prescribed drugs. In comparison with existing methods, this method is sensitive, quantitative, cost effective, and easy to implement.

Idiosyncratic drug reactions: the reactive metabolite syndromes

Idiosyncratic drug reactions are unpredictable reactions that can result in significant morbidity and mortality. Severe reactions are often characterised by fever and internal organ involvement. Despite progress in the identification of reactive metabolites believed to be the cause of idiosyncratic reactions, the basic mechanisms remain elusive. Furthermore, because of the lack of consensus regarding definition of these syndromes, reporting, and therefore epidemiological data, are often unreliable. Research is needed to explore further the pathophysiology of these reactions, so that better diagnostic tests and treatment methods can be developed.