Sheathless Capillary Electrophoresis-Mass Spectrometry for Metabolic Profiling of Biological Samples

Understanding the Significance of Sample Preparation in Studies of the Nanoparticle Metabolite Corona

The adsorption of metabolites to the surface of nanomaterials is a growing area of interest in the field of bionanointeractions. Like its more-established protein counterpart, it is thought that the metabolite corona has a key role in the uptake, distribution, and toxicity of nanomaterials in organisms. Previous research has demonstrated that nanomaterials obtain a unique metabolite fingerprint when exposed to biological matrices; however, there have been some concerns raised over the reproducibility of bionanointeraction research due to challenges in dispersion of nanomaterials and their stability. As such, this work investigates a much-overlooked aspect of this field, i.e., sample preparation, which is vital to the accurate, reproducible, and informative analysis of the metabolite corona. The impact of elution buffer pH, volume, and ionic strength on the metabolite corona composition acquired by uncapped and polyvinylpyrrolidone (PVP)-capped TiO₂ from mixtures of cationic and anionic metabolites was studied. We demonstrate the temporal evolution of the TiO₂ metabolite corona and the recovery of the metabolite corona, which resulted from a complex biological matrix, in this case human plasma. This work also demonstrates that it is vital to optimize sample preparation for each nanomaterial being investigated, as the metabolite recovery from Fe₃O₄ and Dispex-capped TiO₂ nanomaterials is significantly reduced compared to the aforementioned uncapped and PVP-capped TiO₂ nanomaterials. These are important findings for future bionanointeraction studies, which is a rapidly emerging area of research in nanoscience.

Sheathless Capillary Electrophoresis-Mass Spectrometry for the Profiling of Charged Metabolites in Biological Samples

Capillary electrophoresis (CE) is well suited for the profiling of highly polar and charged metabolites as compounds are separated on the basis of their charge-to-size ratio. The protocol presented here is based on using a recently developed sheathless interfacing design, i.e., a porous tip interface, for coupling CE to electrospray ionization mass spectrometry (MS). It is demonstrated that sheathless CE-MS employing a bare fused-silica capillary at low-pH separation conditions can be used for the profiling of both cationic and anionic metabolites by only switching the MS detection and electrophoretic separation voltage polarity. The proposed sheathless CE-MS protocol allows efficient and sensitive profiles to be obtained for a broad array of charged metabolites, including amino acids, organic acids, nucleotides, and sugar phosphates, in various biological samples, such as urine and extracts of the glioblastoma cell line.

Capillary Electrophoresis-Mass Spectrometry for Metabolic Profiling of Biomass-Limited Samples

Capillary electrophoresis-mass spectrometry (CE-MS) is a strong separation technique for the highly efficient and selective analysis of polar and charged metabolites in biological samples. The CE approach is especially suited for the analysis of limited sample amounts due to its nanoliter injections from only a few microliters of material in the sample injection vial. In this protocol, a CE-MS strategy is outlined for the profiling of cationic metabolites in biomass-limited samples using a small amount of human hepatocellular carcinoma (HepG2) cells as a model system. By employing a sheathless interfacing design for coupling CE to MS, it is shown that information-rich profiles for cationic metabolites can be obtained when working with a starting amount of 10,000 HepG2 cells and even lower. Overall, the proposed CE-MS-based analytical workflow may be considered a useful tool for biomass-limited metabolomics studies.

CE-MS for metabolomics: Developments and applications in the period 2016-2018

In the field of metabolomics, CE-MS is now recognized as a strong analytical technique for the analysis of (highly) polar and charged metabolites in a wide range of biological samples. Over the past few years, significant attention has been paid to the design and improvement of CE-MS approaches for (large-scale) metabolic profiling studies and for establishing protocols in order to further expand the role of CE-MS in metabolomics. In this paper, which is a follow-up of a previous review paper covering the years 2014-2016 (Electrophoresis 2017, 38, 190-202), main advances in CE-MS approaches for metabolomics studies are outlined covering the literature from July 2016 to June 2018. Aspects like developments in interfacing designs and data analysis tools for improving the performance of CE-MS for metabolomics are discussed. Representative examples highlight the utility of CE-MS in the fields of biomedical, clinical, microbial, and plant metabolomics. A complete overview of recent CE-MS-based metabolomics studies is given in a table, which provides information on sample type and pretreatment, capillary coatings and MS detection mode. Finally, some general conclusions and perspectives are given.