L-Dopa) in Living Brain

Validation of a cornpartmental mode1 of the kinetic behaviour of radiolabelled L-3,4- dihydroxyphenylalanine (L-dopa) in living brain Paul Deep McConnell Brain Imaging Center Department of Neurology and Neurosurgery McGill University, Montreal Submitted: August, 1998 A Thesis submitted to the Faculty of Graduate Studies and Research in partial fulfilment of the requirements of the degree of M.Sc. in Neuroscience 8 Paul Deep, 1998 National Library BibliotMque nationale 1+m of Canada du Canada Acquisitions and Acquisitions et Bibliographie Services services bibliographiques 395 Wellington Street 395. rue Wellington ûltawaON KIAM OltawaON KlAONs Canada Canada Our &I hkmw rirYlsncr The author has granted a non- L'auteur a accordé une Licence non exclusive licence allowing the exclusive permettant à la National Library of Canada to Bibliothèque nationale du Canada de reproduce, loan, distribute or sell reproduire, prêter, distribuer ou copies of this thesis in microform, vendre des copies de cette thèse sous paper or electronic formats. la forme de microfiche/nlm, de reproduction sur papier ou sur format électronique. The author retains ownershp of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantial extracts fiom it Ni la thèse ni des exbaits substantiels may be printed or otheMrise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation. To my beautiful and loving parents, George and Georgette iii TABLE OF CONTENTS ACKNOWLEDGEMENTS v CONTRIBUTION OF AUTHORS vi INTRODUCTION vii ABSTRACT viii RÉsuMÉ ix Chapter 1 - REVIEW OF THE LITERATURE 1. Introduction 2. Dopamine in mammalian brain 2.1. The detection of dopamine in nervous tissue 2.2. The striatum: a component of the basal ganglia 2.3. The nigrostriatal doparninergic pathway 3. The metabolic pathway of dopamine in the striatum 3.1. Rate constants measured in vitro 3.2. Enzymes that regulate the synthesis of striata1 dopamine 32.1. Tyrosine hydroxylase 3.2.2. Dopa decarboxylase 3 -2.3. Catechol-O-methyltransferase 3.3. Blood-brain uptake of L-dopa and dopamine 3.4. Vesicular storage of striatal dopamine 3.5. Metabolisrn of striatal dopamine 4. Parkinson's disease 4.1. A brief history 4.2. Neurochemical basis 4.3. MPTP: a mode1 of Parkinson's disease 4.4. Neuronal circuitry of the basal ganglia 4.5. Pharmacological treatments 4.5.1. Exogenous L-dopa 4.5.2. Adjunct therapeutic agents 5. Radiolabelled analogs of L-dopa 5.1 . Introduction 5.2. 3~-and I4C-labelled L-dopa: beta emitters 5 -3. "C- and '8F-labe11ed L-dopa: positron emitters 5.4. Qualitative validation of radiolabelled L-dopa analogs 5 -4.1. Metabolism 5.4.2. Vesicular storage 6. Visualization of cerebral dopaminergic innervation in vivo 6.1. Quantitative autoradiography 29 6.2. Static autoradiograms with radiolabelled L-dopa 30 6.3. Dynarnic autoradiograms with radiolabelled L-dopa 6.3.1 . Positron emission tomography 3 1 6.3.2. Accumulation of radioactivity in the conscious brain 32 7. Kinetic modelling of radiolabelled L-dopa autoradiographic data 7.1. Introduction 33 7.2. The plasma slope-intercept plot: a linear mode1 34 7.3. The cornpartmental mode1 35 7.4. Physiological constraints 37 8. The presence in brain of radiolabelled O-methyl-L-dopa 8.1. Methods of correction 38 8 2. Radiolabelled analogs of L-m-tyrosine 40 8.3. Advantages and disadvantages of L-[18flfluoro-m-tyrosines 4 1 Chapter II - FIRST ARTICLE 43 On the accuracy of an [18F]FDOPAcompartmental model: evidence for vesicular storage of [18F]fluorodoparninein vivo. Chapter III - SECOND ARTICLE The kinetic behaviour of ['~Idopain living rat brain investigated by compartmental modelling of static autoradiograms. Chapter IV - GENERAL DISCUSSION Chapter V - REFERENCES Chapter VI - APPENDIX #1 Derivations of mathematical terms and equations Chapter VI1 - APPENDIX #2 Publisher reprints of original articles First and foremost, 1 wish to express my sincere gratitude to Dr. Paul Curnming, Assistant Professor in the Department of Neurology and Neurosurgery at McGill University, for accepting me as a graduate student, and supervising my reçearch with cornpetence and patience. 1 had the opportunity to benefit from a stimulating scientific environment that Paul generates by his exceptional enthusiasm for neuroscience. 1 would like to thank my co- supervisors. Dr, Albert Gjedde. Director of the PET Center at the Aarhus University Hospital in Aarhus. Denmark, and Dr. Alan Evans, Director of the McConnell Brain Imaging Center at ;McGill University, for their indispensable advice. 1 would also like to thank al1 the research students, post-doctoral fellows, technicians and administrative assistants in my department whose time and expertise led me through many difficult situations. 1 would like to thank in advance the members of the Thesis cornmittee for contributing their time and effort to the evaluation of this lengthy document- Special appreciation is extended to Dr. Luis Oliva of the Lakeshore General Hospital in Pointe Claire, Quebec. for his last-minute corrections and insights into human pathobiology and wine tasting. This work was made possible by the generous financial support of both the Fonds de Recherche en Santé du Québec, and the Montreal Neurological Institute. CONTRIBUTION OF AUTHORS 1 have chosen the option provided in the "Guidelines Concerning Thesis Preparation" which allows inclusion as chapten of the thesis the text of original papers concerning the thesis research project. The experimental parts of the thesis, Chapter II (Deep et al., 1997~) and Chapter iIi (Deep et al.. 1997b), consist of two original articles that have been recently published. In these two studies, the original experimental work consisted of the development of computer algorithms which were subsequently used for data anal ysis and simulation studies. Some of the data so analyzed in Chapter DI was acquired previously by Cumming et al. ( 199%). Otherwise, 1wrote the manuscripts, performed the calculations and statisticai analyses, derived the equations, and drafted the figures, with supervision from Dr. P. Cumming and Dr. A. Gjedde. Together with my thesis supervisor and my CO-authors,1 have contributed to the design of the experiments, to the formulation of the working hypothesis. and to the interpretation of results. vii INTRODUCTION The subject of the present thesis is the validation of a nonlinear (or compartmental) model of the kinetic behaviour of radiolabelled L-3,4-dihydroxyphenylalanine (L-dopa) in living brain. Several such models describing the cerebral uptake and metabolism of radiolabel led L-dopa analogs. including [)H]dopa and ~-6-[~~F]fluorodo~a,have ken developed in recent years. chromatographic identification of radiolabelled metabolites in brain tissue samples established qualitatively the bio1ogica.i accuracy of the rnodels. However. the work presented in this thesis represents their first quantitative validation. The article in Chapter II (Deep et al.. 1997~)is the first comparison of radiolabelled L-dopa metabolite fractions calculated by a compartmental model with corresponding fractions measured analytically by chromatography in rat brain. The results of this study led to the developrnent of a model describing the vesicular uptake of radiolabelled dopamine in vivo. Rate constants describing the distribution of radiolabelled dopamine between cytosolic and vesicular compartments are now estimated; previous models omitted vesicular storage. Modelling of tissue radioactivities measured from a series of static cerebral autoradiograms in rats had been previously performed folIowing injection of radiolabelled deoxyglucose (Sokoloff et al., 1977), but the article in Chapter III (Deep et al., 1997b) outlines the first attempt at modelling radioactivities derived from radiolabelled L-dopa in rat brain by an analogous autoradiographic technique. Furthemore, in comparing autoradiographic results from right cerebral hemispheres with corresponding analytic results obtained previously based on chromatographic fractionation of radiolabelled L-dopa metabolites in the left cerebral hemispheres of the same rats, we seek to establish the first direct empirical validation of cornpartmental modelling of autoradiographic data for quantitative assays of radiolabelled L-dopa uptdce and metabolism in living brain. A comprehensive general review of the pertinent literature is presented in Chapter 1. The overall conclusions from the results of the different studies of this thesis are discussed in Chapter IV, while a complete set of references is listed alphabetically in Chapter V. An appendix containing the derivations of important equations and mathematical terms appearing in the two original articles is provided in Chapter VI. Finally, the thesis concludes with a second appendix that contains publisher reprints of these articles in Chapter VU. ABSTRACT This research details two experiments that together estabiish the legitimacy of a comprutmental model which describes the cerebral uptake and metabolism of radiolabelled L-dopa in vivo. First, tissue radioactivities calculated with the model were compved with corresponding radioactivities measured previously by chrornatographic fractionation of "F- Iabelled metabolites in striata1 tissue extracts from rats given intravenous injections of L-6- ['XF]fluorodopa. Second. kinetic constants estimated by model fitting to measured radioactivities from combined metabolite pools in a

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