Isotope drug metabolite identification

De Maio, W., Hoffmann, M., Carbonara, M., Moore, R., Mutlib, A., and Talaat, R. E. (2008). Identification of drug metabolites by UPLC-MS with isotope pattern directed mass chromatograms and UPLC with radioactivity flow detection. In Proceedings of the 56th ASMS Conference on Mass Spectrometry and Allied Topics. ASMS, Denver, CO. 

Isotopic cluster analysis can be built into the automated processing method and is used to target potential metabolites with the desired isotope ratios (Kind and Fiehn, 2006). For example, chlorine or bromine or radiolabeled drugs/metabolites can be pinpointed, at low levels, within a complex matrix background to dramatically enhance specificity and increase confidence in metabolite identification (Jindal and Lutz, 1986 Shirley et al., 1997). 

Stable isotope labeling in conjunction with MS has been widely used for the identification of drug metabolites since late 1970s. In addition, stable isotope-labeled drugs... 

Chowdhury, S.K. et al., Detection and characterization of highly polar metabolites by LC-MS Proper selection of LC column and use of stable isotope labeled drug to study metabolism of rabavirin in rats, in Identification and Quantification of Drugs, Metabolites and Metabolizing Enzymes by LC-MS, Chowdhury, S.K. (ed.), Elsevier, Amsterdam, the Netherlands, 277, 2005. 

The use of radiolabeled drugs is not only crucial for the quantification of unknown metabolites but has also long played a critical role in metabolite identification studies. The utility of radiolabeled substrates inelude (1) their use as tracers of drug-related components during sample elean-up, eoneentra-tion, profiling, and isolation from complex biological matrixes and (2) facilitation of LC-MS/MS detection of radiolabeled metabolites based on their HPLC retention times, peak shapes, and in some cases, isotopic ratios. 

The advantage of stable isotope patterns for metabolite identification is the ease of identification of metabolites with the same specific isotope patterns as parent drug in a complex biological sample. For example, chlorine and bromine exhibit unique natural isotopic patterns. Chlorine or bromine-containing compounds will have similar isotopic ratio patterns arising from Cl Cl... 

Bjorge SM. Identification and characterization of drug metabolites using stable isotope techniques. Pharmacochem Libr 1997 26 233-242. 

Mass spectrometric approaches are also very useful for the measurement of stable isotopes in drug metabolism studies. The application of MS to the quantitative measurement of stable isotope has been limited due to the high cost and sophistication of the instruments necessary for stable isotope enrichment studies. Nonetheless, recent improvements in instrument design and performance, as well as computer software for instrument control, data acquisition, and analysis, have increased the sensitivity and reliability of stable isotopic enrichment studies. These new MS instruments, including continuous-flow isotope ratio mass spectrometry (CF-IRMS) and HPLC-chemical reaction interface mass spectrometry (HPLC-CRIMS) are increasingly less expensive, easier to operate, and accessible for mass balance/ metabolite identification studies with stable isotopes. 

E. W. Taylor, W. Jia, M. Bush, and G. D. Dollinger, Accelerating the drug optimization process Identification, structure elucidation, and quantification of in vivo metabolites using stable isotopes with LC/MS" and the chemiluminescent nitrogen detector, Anal Chem. 74 (2002), 3232-3238. 

Taylor, E.W. Jia, W. Bush, M. Dollinger, G.D. Accelerating the Drug Optimization Process Identification, Structure Elucidation, and Quantification of In Vivo Metabolites using stable isotopes with LC/MSn and the chemiluminescent nitrogen detector, AnaZ. Chem. 74(13), 3232-3238 (2002). 

This technique may be used in two distinct ways. The drug may be labeled at a specific site(s) and the mass spectra of metabolites derived from the labeled compound compared with those obtained from the unlabeled drug. Recent examples of this application include reports on the metabolism of oxybutynin,tocainide, and ketamine. Alternatively, a heavy isotope (usually H) is introduced into the metabolite of interest by reaction with a labeled derivatizing reagent. For example, perdeutero-methylation results in a mass difference of 3 daltons between labeled and unlabeled derivatives per methyl group. Structures of metabolites obtained from caffeine and phenytoin have been confirmed by this technique. Tri(deuteromethyl)silylation has been employed in the identification of metabolites of carbamazepine and afloqualone. ... 

The newer MS experiments in a data-dependent acquisition mode provide the MS and MS" data from a single injection. Accurate mass measurements, software-assisted data acquisition, and processing methods have been very useful for metabolite detection and identification. In addition, when MS is combined with other analytical techniques such as derivatization, H/D exchange, and stable isotope labeling have been proven very useful for structural characterization of unusual, uncommon, and difficult metabolites. Further, the flexibility and broad applications of mass spectrometry have allowed for the creation of hybrid instruments and coupling to other powerful analytical techniques, most notably nuclear magnetic resonance (NMR), to further enhance the utility in the field of drug metabolism. 

Hobby K, Gallagher RT, Caldwell P, Wilson ID. A new approach to aid the characterisation and identification of metabolites of a model drug partial isotope enrichment combined with novel formula elucidation software. Rapid Commun Mass Spectrom 2009 23 219-227. 

See also Drug Metabolism Metabolite Isolation and Identification Isotope Studies. Pharmacokinetics Absorption, Distribution, and Elimination Pharmacodynamics. 

See also Drug Metabolism Metabolite Isolation and Identification. Nuclear Magnetic Resonance Spectroscopy Instrumentation. Nuclear Magnetic Resonance Spectroscopy-Applicable Elements Hydrogen Isotopes. Nuclear Magnetic Resonance Spectroscopy Applications Pharmaceutical. Nuclear Magnetic Resonance Spectroscopy Techniques Multidimensional Proton Surface Coil In Vivo Spectroscopy Using Localization Techniques. Polymers Synthetic. 

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