High Performance Liquid Chromatography-Electrochemistry-Electrospray Ionization Mass Spectrometry (HPLC/EC/ESI-MS) for Detection and Characterization of Roscovitine Oxidation Products

Reactive Metabolites: Generation and Estimation with Electrochemistry Based Analytical Strategy as an Emerging Screening Tool

Background:

Analytical scientists have constantly been in search for more efficient and economical methods for drug simulation studies. Owing to great progress in this field, there are various techniques available nowadays that mimic drug metabolism in the hepatic microenvironment. The conventional in vitro and in vivo studies pose inherent methodological drawbacks due to which alternative analytical approaches are devised for different drug metabolism experiments.

Methods:

Electrochemistry has gained attention due to its benefits over conventional metabolism studies. Because of the protein binding nature of reactive metabolites, it is difficult to identify them directly after formation, although the use of trapping agents aids in their successful identification. Furthermore, various scientific reports confirmed the successful simulation of drug metabolism studies by electrochemical cells. Electrochemical cells coupled with chromatography and mass spectrometry made it easy for direct detection of reactive metabolites. In this review, an insight into the application of electrochemical techniques for metabolism simulation studies has been provided. The sole use of electrochemical cells, as well as their setups on coupling to liquid chromatography and mass spectrometry has been discussed. The importance of metabolism prediction in early drug discovery and development stages along with a brief overview of other conventional methods has also been highlighted.

Conclusion:

To the best of our knowledge, this is the first article to review the electrochemistry based strategy for the analysis of reactive metabolites. The outcome of this ‘first of its kind’ review will significantly help the researchers in the application of electrochemistry based bioanalysis for metabolite detection.

Oxidative metabolism of typical phenolic compounds of Danshen by electrochemistry coupled to quadrupole time-of-flight tandem mass spectrometry

An electrochemistry coupled to online quadrupole time-of-flight tandem mass spectrometry (EC/Q-TOF/MS) was applied to investigate the oxidative transformation and metabolic pathway of five phenolic acids in Danshen sample. Simulation of the phase I oxidative metabolism was carried out in an electrochemical reactor equipped with a glassy carbon working electrode. The phase II reactivity of the generated oxidative products towards biomolecules (such as glutathione) was investigated by ways of covalent adduct formation experiments. The results obtained by EC/MS were compared with well-known in vitro studies by conducting rat liver microsome incubations. Structures of the electrochemically produced metabolites were identified by accurate mass measurement and previously results in vivo metabolites. It was indicated that the electrochemical oxidation was in good accordance with similar products found in vivo experiments. In conclusion, this work confirmed that EC/Q-TOF/MS was a promising analytical tool in the prediction of metabolic transformations of functional foods.

Instrumentation and applications of electrochemistry coupled to mass spectrometry for studying xenobiotic metabolism: A review

The knowledge of metabolic pathways and biotransformation of xenobiotics, artificial substances foreign to the entire biological system, is crucial for elucidation of degradation routes of potentially toxic substances. Nowadays, there are many methods to simulate xenobiotic metabolism in the human body in vitro. In this review, the metabolism of various substances in the human body is described, followed by a summary of methods used for prediction of metabolic pathways and biotransformation. Above all, focus is placed on the coupling of electrochemistry to mass spectrometry, which is still a relatively new technique. This promising tool can mimic both oxidative phase I and conjugative phase II metabolism. Different experimental arrangements, with or without a separation step, and various applications of this technique are illustrated and critically reviewed.

Perspective on electrospray ionization and its relation to electrochemistry

The phenomenon of electrospraying of liquids is presented from the perspective of the electrochemistry involved. Basics of current and liquid flow in the capillary and spray tip are discussed, followed by specifics of charging and discharging of the sprayed liquid surface. Fundamental theories and numerical modeling relating electrospray current to solution and spray parameters are described and then compared with our own experimentally obtained data. The method of mapping potentials and currents inside the electrospray capillary by using an inserted electrically-isolated small wire probe electrode is discussed in detail with illustrations from new and published data. Based on these experimentally obtained results, a new mathematical model is derived. The introduced "nonlinear resistor electrospray capillary model" divides the electrospray capillary into small sections, adds their contributions, and then, by transition to infinitely small section thickness, produces analytical formulas that relate current and potential maps to other properties of the electrospraying liquid: primarily conductivity and current density. The presentation of the model is undertaken from an elementary standpoint, and it offers the possibility to obtain quantitative information regarding operating parameters from typical analytical systems subjected to electrospray. The model stresses simplicity and ease of use; examples applying experimental data are shown and some predictions of the model are also presented. The developed nonlinear resistor electrospray capillary model is intended to provide a new quantitative basis for improving the understanding of electrochemical transformations occurring in the electrospray emitter. A supplemental material section gives full derivation of the model and discusses other consequences.

Mass spectrometric methods for monitoring redox processes in electrochemical cells

Electrochemistry (EC) is a mature scientific discipline aimed to study the movement of electrons in an oxidation-reduction reaction. EC covers techniques that use a measurement of potential, charge, or current to determine the concentration or the chemical reactivity of analytes. The electrical signal is directly converted into chemical information. For in-depth characterization of complex electrochemical reactions involving the formation of diverse intermediates, products and byproducts, EC is usually combined with other analytical techniques, and particularly the hyphenation of EC with mass spectrometry (MS) has found broad applicability. The analysis of gases and volatile intermediates and products formed at electrode surfaces is enabled by differential electrochemical mass spectrometry (DEMS). In DEMS an electrochemical cell is sampled with a membrane interface for electron ionization (EI)-MS. The chemical space amenable to EC/MS (i.e., bioorganic molecules including proteins, peptides, nucleic acids, and drugs) was significantly increased by employing electrospray ionization (ESI)-MS. In the simplest setup, the EC of the ESI process is used to analytical advantage. A limitation of this approach is, however, its inability to precisely control the electrochemical potential at the emitter electrode. Thus, particularly for studying mechanistic aspects of electrochemical processes, the hyphenation of discrete electrochemical cells with ESI-MS was found to be more appropriate. The analytical power of EC/ESI-MS can further be increased by integrating liquid chromatography (LC) as an additional dimension of separation. Chromatographic separation was found to be particularly useful to reduce the complexity of the sample submitted either to the EC cell or to ESI-MS. Thus, both EC/LC/ESI-MS and LC/EC/ESI-MS are common.