UTILITY OF DRIED BLOOD SPOTS AS MATRICES FOR PHARMACOKINETIC STUDY AND METABOLOMIC PROFILING OF HUMAN DISEASE: THE EPILEPSY EXPERIENCE

Abstract

Drug resistant epilepsy (DRE) is a neurological complication which affects approximately 20 - 40% of epilepsy subjects, causing their overall lower quality of life. Thus, it represents a condition which requires further understanding of its pathogenesis and optimization of its drug treatment for better management of the disease. In this regard, dried blood spot (DBS) appears as an attractive matrix for the study of pathogenesis of a disease as it can be conveniently collected from patients in a large population scale, and DBS can be utilized for selected biomarker profiling or drug quantitation assays. Up to date, there are only few but increasing numbers of studies in recent years on using DBS for metabolomic profiling and clinical monitoring of drug levels. In light of these, I endeavour to explore the application of DBS on epilepsy research in 2 main objectives in this thesis: (1) to investigate the feasibility of applying DBS in profiling epileptogenesis; and (2) to use DBS as matrices for drug monitoring. For the first objective, DRE prevalence study to determine the severity and relevant risk factors was firstly carried out, followed by investigation of the reliability of DBS in metabolomic study. Using finger prick DBS samples, it was observed that the metabolomic profiles of drug responsive epilepsy subjects were distinguishable from those who were drug resistant (Q2 = 0.71). From the metabolite profiles obtained through gas chromatography mass spectrometry (GC-MS), several metabolites were revealed to have different degree of abundance between these 2 groups of subjects. The metabolites were putatively identified as glutamine, aspartic acid, pyruvic acid, caprylic acid, serine, palmitic acid and oxalic acid. For the second objective, clinical validation and population pharmacokinetic modeling using DBS derived concentrations (Cdbs) were conducted to examine their applicability. After the inclusion of individual hematocrit levels and antiepileptic drug (AED) red blood cell:plasma partition ratio, AED concentrations derived using the newly developed DBS assay could accurately predict its plasma concentrations which were measured from plasma immunoassays (within 95% confidence interval of the means of two methods). To further enhance the clinical applicability of Cdbs, clearance of one of the AEDs was estimated through a population approach. Findings from this thesis were to establish the utility of DBS for future larger or population-based clinical research, where sample acquisition can be done by epilepsy subjects at home. As evidenced by the comparable results between DBS and plasma, DBS could be a suitable matrix for both aspects of disease and drug monitoring. Once the relevant biomarkers of epilepsy are established, simultaneous monitoring along with AED concentrations would become feasible. This, in turn, will aid the management of epilepsy subjects by rendering monitoring of disease as well drug levels, just from one dried blood spot.