Metabonomic Studies Comparing Capillary and Conventional HPLC-oa-TOF MS for the Analysis of Urine from Zucker Obese Rats

Untargeted LC/MS-based metabolic phenotyping (metabonomics/metabolomics): The state of the art

Liquid chromatography (LC) hyphenated to mass spectrometry is currently the most widely used means of determining metabolic phenotypes via both untargeted and targeted analysis. At present a range of analytical separations, including reversed-phase, hydrophilic interaction and ion-pair LC are employed to maximise metabolome coverage with ultra (high) performance liquid chromatography (UHPLC) increasingly displacing conventional high performance liquid chromatography because of the need for short analysis times and high peak capacity in such applications. However, it is widely recognized that these methodologies do not entirely solve the problems facing researchers trying to perform comprehensive metabolic phenotyping and in addition to these "routine" approaches there are continuing investigations of alternative separation methods including 2-dimensional/multi column approaches. These involve either new stationary phases or multidimensional combinations of the more conventional materials currently used, as well as application of miniaturization or "new" approaches such as supercritical HP and UHP- chromatographic separations. There is also a considerable amount of interest in the combination of chromatographic and ion mobility separations, with the latter providing both an increase in resolution and the potential to provide additional structural information via the determination of molecular collision cross section data. However, key problems remain to be solved including ensuring quality, comparability across different laboratories and the ever present difficulty of identifying unknowns.

Rugged Large Volume Injection for Sensitive Capillary LC-MS Environmental Monitoring

A rugged and high throughput capillary column (cLC) LC-MS switching platform using large volume injection and on-line automatic filtration and filter back-flush (AFFL) solid phase extraction (SPE) for analysis of environmental water samples with minimal sample preparation is presented. Although narrow columns and on-line sample preparation are used in the platform, high ruggedness is achieved e.g., injection of 100 non-filtrated water samples did not result in a pressure rise/clogging of the SPE/capillary columns (inner diameter 300 μm). In addition, satisfactory retention time stability and chromatographic resolution were also features of the system. The potential of the platform for environmental water samples was demonstrated with various pharmaceutical products, which had detection limits (LOD) in the 0.05–12.5 ng/L range. Between-day and within-day repeatability of selected analytes were <20% RSD.

Improving the Sensitivity, Resolution, and Peak Capacity of Gradient Elution in Capillary Liquid Chromatography with Large-Volume Injections by Using Temperature-Assisted On-Column Solute Focusing

Capillary HPLC (cLC) with gradient elution is the separation method of choice for the fields of proteomics and metabolomics. This is due to the complementary nature of cLC flow rates and electrospray or nanospray ionization mass spectrometry (ESI-MS). The small column diameters result in good mass sensitivity. Good concentration sensitivity is also possible by injection of relatively large volumes of solution and relying on solvent-based solute focusing. However, if the injection volume is too large or solutes are poorly retained during injection, volume overload occurs which leads to altered peak shapes, decreased sensitivity, and lower peak capacity. Solutes that elute early even with the use of a solvent gradient are especially vulnerable to this problem. In this paper, we describe a simple, automated instrumental method, temperature-assisted on-column solute focusing (TASF), that is capable of focusing large volume injections of small molecules and peptides under gradient conditions. By injecting a large sample volume while cooling a short segment of the column inlet at subambient temperatures, solutes are concentrated into narrow bands at the head of the column. Rapidly raising the temperature of this segment of the column leads to separations with less peak broadening in comparison to solvent focusing alone. For large volume injections of both mixtures of small molecules and a bovine serum albumin tryptic digest, TASF improved the peak shape and resolution in chromatograms. TASF showed the most dramatic improvements with shallow gradients, which is particularly useful for biological applications. Results demonstrate the ability of TASF with gradient elution to improve the sensitivity, resolution, and peak capacity of volume overloaded samples beyond gradient compression alone. Additionally, we have developed and validated a double extrapolation method for predicting retention factors at extremes of temperature and mobile phase composition. Using this method, the effects of TASF can be predicted, allowing determination of the usefulness of this technique for a particular application.

Integration of microfluidic LC with HRMS for the analysis of analytes in biofluids: past, present and future

Capillary LC (cLC) coupled to MS has the potential to improve detection limits, address limited sample volumes and allow multiple analyses from one sample. This is particularly attractive in areas where ultrahigh assay sensitivity, low limits of detection and small sample volumes are becoming commonplace. However, implementation of cLC–MS in the bioanalytical–drug metabolism area had been hampered by the lack of commercial instrumentation and the need for experts to operate the system. Recent advances in microfabricated devices such as chip-cube and ion-key technologies offer the potential for true implementation of cLC in the modern laboratory including the benefits of the combination of this type of separation with high-resolution MS.

Liquid Chromatographic Techniques in Metabolomics

In the past decade, LC‐MS‐based metabolomic/metabonomic profiling has become a major analytical focus for biomarker research. Chromatographic resolution is continually improving with the development of more advanced separation platforms based on smaller particle sizes, new types of stationary phase and miniaturized systems allowing the profiling of biological samples for metabolites in ways that were simply not possible before. Chromatographic advances, combined with increased mass resolution instruments that provide sub‐2 ppm mass accuracy and high sensitivity, have greatly facilitated the detection and identification of potential biomarkers. In this chapter, the most common LC(‐MS) methods utilized in metabolic analyses are presented, with emphasis on novel high‐efficiency and high‐throughput analyses and their suitability for metabolic analyses. Guidelines for the selection of the appropriate method for different applications are given, with emphasis on the use of LC‐MS.

Towards an unbiased metabolic profiling of protozoan parasites: optimisation of a Leishmania sampling protocol for HILIC-orbitrap analysis

Comparative metabolomics of Leishmania species requires the simultaneous identification and quantification of a large number of intracellular metabolites. Here, we describe the optimisation of a comprehensive metabolite extraction protocol for Leishmania parasites and the subsequent optimisation of the analytical approach, consisting of hydrophilic interaction liquid chromatography coupled to LTQ-orbitrap mass spectrometry. The final optimised protocol starts with a rapid quenching of parasite cells to 0 °C, followed by a triplicate washing step in phosphate-buffered saline. The intracellular metabolome of 4 × 10(7) parasites is then extracted in cold chloroform/methanol/water 20/60/20 (v/v/v) for 1 h at 4 °C, resulting in both cell disruption and comprehensive metabolite dissolution. Our developed metabolomics platform can detect approximately 20% of the predicted Leishmania metabolome in a single experiment in positive and negative ionisation mode.

Advances in separation science applied to metabonomics

Metabonomics focuses on metabolite profile changes in diverse living systems caused by a biological perturbation. These metabolite signatures can be achieved with techniques such as gas chromatography, high-performance liquid chromatography (ultra-high-performance/pressure liquid chromatography and capHPLC), capillary electrophoresis, and capillary electrochromatography normally hyphenated with MS. In this review we present the latest developments of the abovementioned techniques applied in the field of metabonomics, with applications covering phytochemistry, toxicology and clinical research.

Profiling and biomarker identification in plasma from different Zucker rat strains via high mass accuracy multistage mass spectrometric analysis using liquid chromatography/mass spectrometry with a quadrupole ion trap-time of flight mass spectrometer

High mass accuracy electrospray ionisation multistage tandem mass spectrometry (MS(n)) was applied to metabolite profiling studies on plasma samples derived from two strains of rat (the Zucker (fa/fa) obese strain and the normal wild type). Using a quadrupole ion trap time-of-flight (QIT-TOF) mass spectrometer, metabolite profiling software was applied to locate components of biological significance that could account for the differences between the two strains of rat and a formula prediction software tool was used to help identify individual components. The primary factor discriminating between the two populations was the concentration of endogenous lipids. In the Zucker (fa/fa) obese strain, the dominant ion signals and MS(n) spectra were in agreement with lysoglycerophosphocholine components such as palmitoyllysophosphatidylcholine, 1-oleoylglycerophosphocholine, 1-octadecyl-sn-glycero-3-phosphocholine and 1-stearoylglycerophosphocholine and these were found in relatively higher concentrations compared to the normal wild type. Components were identified using high mass accuracy MS(n) data, formula prediction software and by agreement with published mass spectra through internet databases, rather than using a conventional approach with authentic standards. This application shows that the use of high mass accuracy electrospray ionisation MS(n) together with a software tool can be used effectively to detect and characterise unknown analytes in complex matrices, and represents a promising approach for future profiling studies.

Hydrophilic interaction and reversed-phase ultra-performance liquid chromatography TOF-MS for metabonomic analysis of Zucker rat urine

Hydrophilic interaction chromatography (HILIC) provides a complementary technique to RP methods for the retention of polar analytes for LC-MS-based metabonomic studies. Combining the advantages of both RP and HILIC separations with the efficient and rapid separations obtained using sub-2 mum particles via the recently introduced ultra-performance LC (UPLC) enables increased coverage of the metabolites present in biological samples to be achieved. Here an HILIC-UPLC-MS method was developed to provide metabolite profiles for urine samples obtained from male Zucker rats. The resulting data were compared with results obtained for the same samples by RP-UPLC-MS and demonstrated the complementary nature of the two separations with both methods enabling discrimination between the different sample types. Interestingly sample type differentiation was based on different markers.

LC-MS-based metabonomics analysis

Metabonomics aims at the comprehensive and quantitative analysis of wide arrays of metabolites in biological samples. It has shown particular promise in the areas of toxicology and drug development, functional genomics, systems biology, and clinical diagnosis. Comprehensive metabonomics investigations are primarily a challenge for analytical chemistry. High-performance liquid chromatography-mass spectrometry (HPLC-MS) is an established technology in drug metabolite analysis and is now expanding into endogenous metabolite research. Its main advantages include wide dynamic range, reproducible quantitative analysis, and the ability to analyze biofluids with extreme molecular complexity. The aims of developing HPLC-MS for metabonomics range from understanding basic biochemistry to biomarker discovery and the structural characterization of physiologically important metabolites. In this review, the strategy and application of HPLC-MS-based metabonomics are reviewed.

Analytical strategies in metabonomics

To perform metabonomics investigations, it is necessary to generate comprehensive metabolite profiles for complex samples such as biofluids and tissue/tissue extracts. Analytical technologies that can be used to achieve this aim are constantly evolving, and new developments are changing the way in which such profiles' metabolite profiles can be generated. Here, the utility of various analytical techniques for global metabolite profiling, such as, e.g., 1H NMR, MS, HPLC-MS, and GC-MS, are explored and compared.

A metabonomic study of strain- and age-related differences in the Zucker rat

Ultra-performance liquid chromatography (UPLC) coupled to orthogonal acceleration time-of-flight mass spectrometry (oa-TOFMS) in positive electrospray ionization mode was used to obtain metabolite profiles for urine obtained from three strains of Zucker rat. These were the Zucker lean, the Zucker (fa/fa) obese and the Zucker lean/(fa) cross. Clear age- and strain-related differences were noted with the leptin-deficient (fa/fa) obese animal showing significant differences from both the other Zucker rat strains with respect to metabolite profiles.

OMICS-driven biomarker discovery in nutrition and health

While traditional nutrition research has dealt with providing nutrients to nourish populations, it nowadays focuses on improving health of individuals through diet. Modern nutritional research is aiming at health promotion and disease prevention and on performance improvement. As a consequence of these ambitious objectives, the disciplines "nutrigenetics" and "nutrigenomics" have evolved. Nutrigenetics asks the question how individual genetic disposition, manifesting as single nucleotide polymorphisms, copy-number polymorphisms and epigenetic phenomena, affects susceptibility to diet. Nutrigenomics addresses the inverse relationship, that is how diet influences gene transcription, protein expression and metabolism. A major methodological challenge and first pre-requisite of nutrigenomics is integrating genomics (gene analysis), transcriptomics (gene expression analysis), proteomics (protein expression analysis) and metabonomics (metabolite profiling) to define a "healthy" phenotype. The long-term deliverable of nutrigenomics is personalised nutrition for maintenance of individual health and prevention of disease. Transcriptomics serves to put proteomic and metabolomic markers into a larger biological perspective and is suitable for a first "round of discovery" in regulatory networks. Metabonomics is a diagnostic tool for metabolic classification of individuals. The great asset of this platform is the quantitative, non-invasive analysis of easily accessible human body fluids like urine, blood and saliva. This feature also holds true to some extent for proteomics, with the constraint that proteomics is more complex in terms of absolute number, chemical properties and dynamic range of compounds present. Apart from addressing the most complex "-ome", proteomics represents the only platform that delivers not only markers for disposition and efficacy but also targets of intervention. The Omics disciplines applied in the context of nutrition and health have the potential to deliver biomarkers for health and comfort, reveal early indicators for disease disposition, assist in differentiating dietary responders from non-responders, and, last but not least, discover bioactive, beneficial food components. This paper reviews the state-of-the-art of the three Omics platforms, discusses their implication in nutrigenomics and elaborates on applications in nutrition and health such as digestive health, allergy, diabetes and obesity, nutritional intervention and nutrient bioavailability. Proteomic developments, applications and potential in the field of nutrition have been specifically addressed in another review issued by our group.

The Consortium for Metabonomic Toxicology (COMET): aims, activities and achievements

The utility of metabonomics in the evaluation of xenobiotic toxicity has been comprehensively assessed by the Consortium for Metabonomic Toxicology (COMET), formed between five major pharmaceutical companies and Imperial College London, UK. The main objectives were to assess methodologies, to generate a metabonomic database using (1)H nuclear magnetic resonance (NMR) spectroscopy of rodent urine and blood serum and to build a predictive expert system for target organ toxicity. The analytic and biologic variation that might arise through the use of metabonomics was evaluated and a high degree of robustness demonstrated. With the completion of 147 studies, the chief deliverables of a curated database of rodent biofluid NMR spectra and computer-based expert systems for the prediction of kidney or liver toxicity in rat and mouse based on the spectral data have been generated, and delivered to the sponsoring companies. The project, with its relatively modest resources, has met and exceeded all of its targets and was judged a resounding success by the sponsoring companies who are, in many cases, already enhancing and making use of the data in their in-house studies.