Phase I and II biotransformation in patients with chronic fatigue

Abstract

This thesis, titled: 'Phase I and II biotransformation in patients with chronic fatigue', forms part of the research and development programme of the Centre for Human Metabolomics at the NWU. There is no consensus definition of fatigue, ranging from idiopathic chronic fatigue (CF) to the more severe chronic fatigue syndrome and myalgic encephalomyelitis (CFS/ME). Against these diverse clinical presentations of fatigue, the working hypothesis formulated for the present study is: 'The wide occurrence of fatigue amongst individuals not suffering from a distinct clinical disorder may be due to an energy deprived state as a consequence of the individual's response to undefined exposure to xenobiotics, and which should be measurable in the metabolite profiles of biofluids from the fatigue cases'. Here we present in a thesis, structured in four parts, the first comprehensive investigation on CF, using a battery of selected indicators for phase I and II biotransformation measured in biofluids from a cohort of 576 female patients, all diagnosed by physicians to suffer from CF. Part I includes two literature reviews. Chapter 1 deals with the mechanism of detoxification of xenobiotics by acyl-CoA synthetases, illustrated for benzoate and aspirin which highlights the complexity of multi-step detoxification. Chapter 2 presents a review on biotransformation and CF to further justify the working hypothesis. This review led to the proposal of a model for the combined influence of genome-based biotransformation and the exposome, leading to CF. A causal relationship is proposed for chronic xenobiotic exposure and the energy demand for the biotransformation responses, which may underlie idiopathic CF. Part II covers the methodological part of the study. Chapter 3 presents detail on selected methods and on patient selection through information gained from our biotransformation test manual. Chapter 4 focus on the analytical aspects with special emphasis on method validation for phase I and II biotransformation analysis. Chapter 5 gives the statistical rationale to enable differentiation between all patients, using the complete set of data. The Chi-square Automatic Interaction Detection (CHAID) decision tree proved to be the preferred method for classification of the patient cohort. Part III presents the results from the study. Chapter 6 is a contribution to improved understanding of the kinetic mechanism involved in human glycine-N-acyltransferase with high-performance liquid chromatography-electrospray ionization tandem mass spectrometry (HPLC-ESI-MS/MS). Chapter 7 represents the culmination of the study, describing the biotransformation profiles from the cohort of patients in response to a hepatic detoxification challenge, identification of a potential biosignature for CF and the classification of all patients

through the CHAID decision tree. Chapter 8 illustrates how untargeted 1H-NMR-metabolomics provided quantitative metabolite information on the detoxification challenge. Part IV is a general discussion leading to a synthesis, proposing that the new insights could contribute to an improved detection and a future treatment strategy on CF. As predicted, no single biomarker account for CF but the use of a biosignature holds promise as a diagnostic tool for a personalized characterization of CF. Part IV is concluded with a few proposals for future research.