Xenobiotics metabolite identification

Ramanathan, R., Chowdhury, S. K, and Alton, K. B. (2005). Oxidative metabolites of drugs and xenobiotics LC-MS methods to identify and characterize in biological matrices. In Identification and Quantification of Drugs, Metabolites and Metabolizing... 

Few detailed studies of xenobiotic metabolism vivo have been carried out In Invertebrates, and these few have concentrated on Identification of phase 1 metabolites. It Is presumed that invertebrates, like Insects, use glucose rather than glucuronic acid (36). 

Improved methods and instrumentation for metabolite isolation and identification, such as capillary GC, GC/MS, HPLC, high field NMR, FAB/MS, CI/MS, FT-IR and HPLC/MS have made the identification of new or unusual metabolites more practical. As these advanced techniques are employed to study xenobiotic metabolism in more diverse species of plants, additional classes of xenobiotics will no doubt be discovered. 

Dramatic improvements in instrumentation and methods used for the identification of xenobiotic conjugates (and other metabolites), notably proton nuclear magnetic resonance and mass spectroscopy, have significantly influenced the strategies for the isolation of conjugates. The recently developed soft ionization techniques make it possible to obtain useful mass spectral information for a wide variety of intact underivatized xenobiotic conjugates. The state of... 

The use of NMR in the identification of xenobiotic conjugates is quite limited. Many recent publications that include NMR in structural characterizations used high field instruments (200 NHz or higher). Thus, the use of NMR in metabolite characterization may increase with increased availability of high field instruments... 

This class of lipid conjugates Is the most nonpolar yet Identified, a characteristic which Is often useful In pursuing the Identification of unknown metabolites. The first cholesterol ester of a xenobiotic was reported In 1976 for a saturated methoprene metabolite which contributed 15% of the total C-resldue In the liver of a chicken given a single oral dose of methoprene at 64 mg/kg (17). The tai-cyc lop ropy 1 fatty acids derived from cycloprate also form esters of cholesterol. Three such esters contributed 5% of the total residual radiocarbon In rat carcasses four days after a single oral dose of cycloprate at 21 mg/kg ( ). 

Proper sample preparation and analysis are essential in all studies of xenobiotic metabolism. With known standards of the free metabolites and often with just a radioactive unknown, it is customary to test their stability under conditions of analysis. The same caution is not always possible with conjugates, but much can be done to improve the validity of conjugate identification. Not only will greater caution in sample handling improve the chances of correctly identifying conjugates, it will also reduce the endless hours of time spent by metabolism chemists in inventing bizarre pathways to justify the formation of metabolites which never existed in the first place. 

To date, HPLC-NMR spectroscopy has been applied to the profiling and identification of the metabolites of a number of drugs and xenobiotics present in biofluids such as plasma, urine and in bile samples from rat and... 

The identification of xenobiotics at the concentrations existing in environmental contaminants and of metabolites formed during laboratory experiments in biodegradation and transformation has been completely revolutionized by the availability of modern... 

This book is divided into three parts. The first section contains introductory chapters on MS and MSI. Chapter I provides an overview of MSI and focuses on current and future trends in the field. The success of a particular MSI experiment depends on the specific MS approach used. Therefore, the second chapter describes the basic principles of mass spectrometry relevant to MSI and includes cross-references to other chapters of this volume for easier navigation. The third chapter reviews the application of MSI to the study of elemental distributions. Following these introductory chapters, there are multiple protocols that describe qualitative and quantitative measurements of endogenous metabolites and xenobiotics as well as their identification and localization. The last section includes protocols for a variety of MSI approaches developed to study peptide and protein distributions. The experimental protocols presented herein encompass most MSI approaches and technologies for samples from a wide range of biological models including plants, invertebrates, and vertebrates. 

Mechanisms that regulate the bioavailability of flavanols have been further elarified in the last several years. The general pathways of metabolism—glueuronidation, sulfation, and methylation—have been identified, and the importanee of the small intestine and the liver in metabolism has been reeognized. Future identification of the isoforms of the enzymes involved in flavanol metabolism will be a key to predicting interactions with drugs and xenobiotics as well as understanding the interindividual variability in levels of flavanol metabolites. 

Martinoia E, Klein M, Sanchez-Femandez R, et al. (2000) Vacuolar uptake of secondary metabolites and xenobiotics. In DG Robinson, JC Rogers, eds. Vacuolar compartments, Vol 5. Sheffield Academic Press, Sheffield, pp 221-253 Masuda S, Terada T, Yonezawa A, et al. (2006) Identification and functional characterization of a new human kidney-specific HVorganic cation antiporter, kidney-specific Multidnig and Toxin Extrusion 2. J Am Soc Nephrol 17 2127-2135... 

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