Metabolomic Investigations Into Human Apocrine Sweat Secretions
Total Page:16
File Type:pdf, Size:1020Kb
METABOLOMIC INVESTIGATIONS INTO HUMAN APOCRINE SWEAT SECRETIONS Graham Mullard, BSc (Hons), MSc Thesis submitted to the University of Nottingham for the Degree of Doctor of Philosophy September 2011 Abstract Human axillary odour is formed by the action of Corynebacteria or Stephyloccui bacteria on odourless axilla sections. Several groups have identified axillary odorants, including 3-methyl-2-hexanoic acid (3M2H) and 3-hydroxy-3-methyl-hexenoic acid (HMHA), and how they are pre-formed and bound to amino acid conjugates. However, there is currently a lack of LC-MS methodologies and no reported NMR methods, that are required to further identify the non-volatile constituents, which would provide further information to allow understanding of the underlying physiological biochemistry of malodour. This work has incorporated a three-pronged approach. Firstly, a global strategy, through the use of NMR and LC-MS, provided a complementary unbiased overview of the metabolite composition. Metabolites were identified based on acquired standards, accurate mass and through the use of in-house or online databases. Furthermore, spectra of biological samples are inherently complex, thus, requiring a multivariate data analysis (MVDA) approach to extract the latent chemical information in the data. Secondly, semi-targeted LC-MS/MS methodologies has been used to identify metabolites with a common structural core (i.e. odour precursors) and provide structural information for the reliable identification of known and unknown metabolites. Finally, a targeted LC-MSIMS method provided an increase in specificity and sensitivity to accurately quantify known metabolites of interest (odour precursors). Initially, all methodologies were developed through the use of either an artificial sweat matrix (global strategy) or through the use of synthetic standards (semi-targeted or targeted strategy). The sample complexity was then increased by applying the methodologies to an ASG5 apocrine cell line, in order to provide further knowledge into apocrine cell metabolism and to identify whether there could be any potential male or female differences due to differences in circulating hormones. Changes in the cell metabolism were identified, and both the NMR and LC-MS data could differentiate between control, tamoxifen- and J3-estradiol-treated. However, it is difficult to attribute these changes to specific pathways, as these hormones or the vehicle used (ethanol) are likely to produce a ripple effect across the cell's metabolism. Nonetheless, NMR spectroscopy quantified 25 metabolites with lactate being the most abundant at 19.1 mM, while HILIC-MS could detect a range of lipids, nucleotides, amino acids, fatty acids and vitamins. The methodologies were then applied to human apocrine sweat collected from six volunteers across five days. NMR spectroscopy was able to identify 25 and quantify 19 metabolites, with lactate being the most abundant at 13.2 mM. LC-MS/MS readily identified 12 amino acid conjugates with HMHA being the most abundant. Furthermore, a possible 20 unidentified conjugates were detected (LC-MSIMS semi- targeted methodologies) as well as putatively identifying 473 metabolites (LC-MS global methodologies). MVDA techniques such as principal component analysis (PCA) illustrated that intra-individual variation was greater than inter-individual variation, as well as secretions from both the left and right arm being consistent with one another. Moreover, MVDA illustrated the complementary nature of both NMR and MS, as the data acquired with the two types of instrumentation showed the same trends, even though these trends were based on different subsets of metabolites. The work presented herein, has successfully used a number of analytical technologies to investigate metabolite content of human apocrine sweat. It has been shown that a number of complementary techniques and multivariate analysis can provide a valuable insight into the underlying physiology of malodour. This work was funded by BBSRC and Unilever (Port Sunlight, UK). 11 Acknowledgements I am deeply thankful to my supervisors Dr Clare Daykin and Prof. David Barrett for their encouragement and guidance throughout my time within their lab group. I am also grateful to them for giving me the opportunity to produce this PhD thesis and for always believing in me. I also wish to thank all those who contributed to the project, including Dr Mark Harker and his team at Unilever, for their help during the project and their role in the sample collection. Your help was both inspiring and invaluable during our collaboration. I would also like to thank Dr Catherine Otori and Paul Cooling for their help and technical support. Finally, thanks go to everybody else who has helped me through this project, especially Asa Bluck and Gavin Hackett - just for being there and making me laugh. As well as Amy Wong, Gemma Gaw and Philippine GeiBier for the good atmosphere, friendship, encouragement and many MS and NMR discussions. I would particularly like to thank Rebecca Cooper for her patience and understanding during my time at the University of Nottingham and whilst writing this thesis. Also, I am indebted to my Mum and Dad who have always encouraged and supported me in everything I have done and for that, I am truly grateful. III "It is very obvious that we have many different kinds of smells, all the way from the odour of violets and roses up to asafoetida. But until you can measure their likeness and differences you can have no science of odour. " - ALEXANDER GRAHAM BELL, 1914 IV Table of contents ABSTRACT 1 ACKNOWLEDGEMENTS 111 TABLE OF CONTENTS V ABBREVIATIONS IX INTRODUCTION 1 1.1 MET ABOLOMICS 1 1.2 ApPLICATION OF TECHNIQUES 3 1.3 NMR BACKGROUND AND THEORY 7 1.3.1 ID IH NMR Spectroscopy 9 1.3.2 2D NMR Spectroscopy 10 1.4 MASS SPECTROMETRY 12 1.4.1 Electrospray lonisation 12 1.4.2 Mass Analysers 15 1.4.3 Quadrupole 17 1.4.4 Ion Trap 17 1.4.5 Time-of-Flight 17 1.4.6 Orbital Trap 18 1.4.7 Hybrid Instruments 18 1.5 MULTIVARIATE DATA ANALYSIS 20 1.5.1 Pre-processing of Data 22 1.5.2 Data Pre-treatment Methods 24 1.5.3 Principal Component Analysis 24 1.5.4 Partial Least Squares Regression 25 1.5.5 Principal Component Discriminant Analysis 25 1.6 IDENTIFICATION OF COMPONENTS 26 1.7 SWEAT GLAND BIOLOGY .....................................•................................................................. 28 1.7.1 Sweat Glands 29 1.7.2 Chemical Composition of Eccrine Sweat 32 1.7.3 Axillary Malodour Formation 36 1.7.4 Chemical Nature of Body Malodour 38 1.7.5 Natural Precursors/Apocrine Sweat Composition 43 1.8 AIMS OF THE THESIS 50 2 DEVELOPMENT OF IH NMR SPECTROSCOPY METHODOLOGY FOR THE METABOLOMIC ANALYSIS OF APOCRINE SWEAT 51 2.1 INTRODUCTION 51 2.2 AIMS 54 v 2.3 MATERIALSANDMETHODS 54 2.3.1 Chemicals 54 2.3.2 Sample Preparation 55 2.3.3 IH NMR Spectroscopy 57 2.3.4 Spectral analysis and metabolite quantification 58 2.3.5 Data Pre-Processing 58 2.3.6 Partial Least Squares Regression (PLS) 59 2.4 RESULTSANDDISCUSSION 59 2.4.1 Signal-to-Noise-Ratio 60 2.4.2 Application with Mass Limited Samples 66 2.4.3 The Application of PLS Regression to Determine the Stability of Artificial Sweat Mixture during Storage 70 2.5 CONCLUSION 73 3 DEVELOPMENT OF MASS SPECTROMETRY METHODS FOR THE ANALYSIS OF KEY METABOLITES IN APOCRINE SWEAT 74 3.1 INTRODUCTION 74 3.1.1 Direct Injection Mass Spectrometry (DIMS) 75 3.1.2 Reverse Phase High Performance Liquid Chromatography Mass Spectrometry (RP- HPLC-MS) 75 3.1.3 Hydrophilic Interaction Liquid Chromatography (HILlC) 76 3.1.4 Analytical Strategies for Profiling Apocrine Sweat Metabolites 84 3.1.5 Aims 86 3.2 MATERIALANDMETHODS 86 3.2.1 Chemicals 86 3.2.2 LC-MS Columns 87 3.2.3 Sample Preparation 87 3.2.4 Global Profiling by LC-QTOF-MS 88 3.2.4.1 Preliminary Development Work for LC-QTOF-MS 89 3.2.5 Global Profiling by Direct Injection Mass Spectrometry 90 3.2.6 Targeted Profiling by LC-MS/MS 91 3.2.6.1 Optimisation of compound dependent parameters for MRM Analysis 91 3.2.6.2 Conjugate Profiling using Precursor Ion Scanning 92 3.2.6.3 Chromatographic conditions 93 3.2.7 MSn for Fragmentation Confirmation 93 3.2.8 Data Analysis 93 3.3 RESULTSANDDISCUSSION 94 3.3.1 Direct Injection Mass Spectrometry 94 3.3.2 Global Profiling: HILlC-QTOF 97 3.3.2.1 Column Selection 98 3.3.2.2 Solvent and Buffer Selection 100 VI 3.3.3 Targeted LC-MSIMS 107 3.3.3.1 Optimization of the Dec1ustering Potential and Collision Energy 108 3.3.3.2 LC-MSIMS Analysis of Odour Precursor Standard Compounds 108 3.3.3.3 LC-MSIMS profiling of Odour Precursors using Precursor Ion Survey Scan 113 3.4 CONCLUSIONS 115 4 APPLICATION OF IH NMR SPECTROSCOPY AND LC-MS TO AN IN-VITRO MODEL OF APOCRINE SWEAT PRODUCED FROM ASGS CELL LINES 117 4.1 INTRODUCTION 117 4.l.1 Metabolite Extraction from ASG5 cells 119 4.1.2 Aims 121 4.2 MATERIALANDMEl1IODS 121 4.2.1 Sample Preparation 121 4.2.1.1 Cell Culture 121 4.2.1.2 Cell Extraction 122 4.2.2 IH NMR Spectroscopy 122 4.2.3 2D NMR Spectroscopy 123 4.2.4 HILIC-QTOF-MS 123 4.2.5 Targeted LC-MSIMS 123 4.2.6 Quantification of Artificial Apocrine Sweat Metabolites by INMR Spectroscopy 123 4.2.7 NMR Spectral Data Reduction 123 4.2.8 HILIC-QTOF-MS Data Pre-Processing 124 4.2.9 Multivariate Data Analysis 124 4.2.10 Compound Identification 125 4.3 RESULTSANDDISCUSSION 126 4.3.1 IH NMR Spectra of In-Vitro Model of Apocrine Sweat 126 4.3.2 LC-Mass Spectrometry Analysis of In-Vitro Model of Apocrine Sweat 131 4.3.3 Multivariate Data Analysis 134 4.4 CONCLUSIONS 144 5 METABOLOMIC INVESTIGATIONS OF HUMAN