Evaluating Sebum as a Biofluid for Parkinson's Disease Diagnostics using Mass Spectrometry-based Metabolomics

Abstract

Parkinson's disease (PD) is the second most common age related neurodegenerative disorder. Knowledge of disease pathogenesis is rapidly expanding, however, to date there is no definitive clinical diagnostic test. Evidence has arisen that there is a characteristic odour associated with PD sufferers originating from sebum which is a biological matrix secreted on the skin. This has directed the work presented in this thesis, namely: to explore the viability of sebum as a novel biofluid for PD diagnostics and to investigate the potential of mass spectrometry-based metabolomics as a method to identify sebum-based biomarkers. Over 1200 participants were recruited during the course of this study from four cohorts: drug naïve PD, medicated PD, paired control and independent control. Sebum was collected from the upper back of participants via a simple, non-invasive skin swab. Mass spectrometry-based analytical techniques are routinely employed in metabolomics approaches to characterise the metabolome. 498 patient samples were analysed across two complementary analytical techniques to amass maximal information regarding the sebum metabolome. Dynamic Headspace was coupled to Thermal Desorption-Gas Chromatography-Mass Spectrometry (TD-GC-MS) in two studies for the direct analysis of the volatile constituents of sebum. Both studies successfully detected changes within the volatilome of PD patients compared with control subjects and sought to identify candidate biomarker compounds. In a parallel investigation, Liquid Chromatography-Mass Spectrometry (LC-MS) was utilised to detect non-volatile species present in sebum and investigate alterations within metabolic pathways. The results support current understanding of the disease in the elucidation of perturbations to energy metabolism and lipid pathways. A foundational study integrated ion mobility into an LC-MS workflow (LC-IM-MS) to assess the reproducibility of collision cross section measurements. This study was performed with a view to implement IM as an additional separation tool and parameter for metabolite identification in subsequent PD metabolomics studies. This body of work demonstrates how sebum is a highly suitable biological matrix with which to investigate the metabolome after the onset of Parkinson's disease. This novel biofluid is rarely used in disease diagnostics and although further work is required for the standardisation of sampling and analysis protocols, this study proves it's potential. Future studies should aim to increase classification accuracy and heighten identification confidence of candidate biomarker compounds.

Date of Award	1 Aug 2020
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Royston Goodacre (Supervisor) & Perdita Barran (Supervisor)