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Microvascular plasticity and neurovascular coupling in the pharmacotherapy of Parkinson's disease

Ohlin, Elisabet LU (2011) In Lund University, Faculty of Medicine Doctoral Dissertation Series 2011:80.
Abstract (Swedish)
Popular Abstract in Swedish

Parkinsons sjukdom är en av våra mest förekommande neurologiska sjukdomar som drabbar den åldrande befolkningen. I åldersgruppen 50-60 år drabbas ca 1 procent av sjukdomen, som karakteriseras av de motoriska symptomen stelhet, långsamma rörelser och skakningar. Symptomen beror på en gradvis förlust av nervceller i en djup del av hjärnan vid namn substantia nigra (den svarta substansen). Här produceras signalsubstansen dopamin, som ser till att vi kan utföra rörelser med lätthet och att inlärda rörelsemönster fungerar. Den mest effektiva behandlingen för sjukdomen består av L-DOPA, ett förstadium till dopamin. L-DOPA omvandlas till dopamin i hjärnan, vilket gör att patienterna återfår sin... (More)
Popular Abstract in Swedish

Parkinsons sjukdom är en av våra mest förekommande neurologiska sjukdomar som drabbar den åldrande befolkningen. I åldersgruppen 50-60 år drabbas ca 1 procent av sjukdomen, som karakteriseras av de motoriska symptomen stelhet, långsamma rörelser och skakningar. Symptomen beror på en gradvis förlust av nervceller i en djup del av hjärnan vid namn substantia nigra (den svarta substansen). Här produceras signalsubstansen dopamin, som ser till att vi kan utföra rörelser med lätthet och att inlärda rörelsemönster fungerar. Den mest effektiva behandlingen för sjukdomen består av L-DOPA, ett förstadium till dopamin. L-DOPA omvandlas till dopamin i hjärnan, vilket gör att patienterna återfår sin naturliga rörlighet. Efter ett antal år drabbas dock de flesta patienter av allvarliga komplikationer i form av ofrivilliga rörelser (överrörlighet) efter varje L-DOPA-dos. Överrörlighet, eller dyskinesier, drabbar inte alla parkinsonpatienter och det är fortfarande inte helt klarlagt varför de uppkommer. Man vet att uppkomsten av dyskinesi påverkas av hur långt sjukdomen fortskridit, d v s hur stor andel av dopamincellerna i hjärnan som dött. Dock tror man att hjärnans ”plastiska potential”, d v s förmåga att förändra sin struktur, kan vara en viktig del i utvecklingen av dyskinesi. För en tid sedan upptäckte vår forskargrupp att det sker förändringar i hjärnans blodkärl till följd av L-DOPA-behandling. Blodförsörjningen till hjärnan är mycket viktig för dess överlevnad och de små blodkärlen (kapillärerna) är ytterst ansvariga för att förse varje del av hjärnan med syre och näring. I den parkinsonmodell på råtta som vi arbetar med har vi tidigare funnit att de små blodkärlen i hjärnan växer efter L-DOPA behandling. Detta minskar i sin tur funktionen av den barriär (blod-hjärnbarriären) som skyddar hjärnan från potentiellt skadliga ämnen som cirkulerar i kroppen.

Denna avhandling syftar till att undersöka effekten på blodkärlen i hjärnan till följd av L-DOPA-behandling, varför de reagerar på behandlingen och vad detta har för konsekvenser. I större delen av avhandlingen har vi använt råttor med en parkinsonliknande skada. I den första delen studerades olika signalvägar som dopamin använder sig av och deras effekt på blodkärlen. Resultaten visade att svaret på blodkärlsnivå är kopplat till en bestämd typ av dopamin receptor (typ-1). Vidare undersöktes en tillväxtfaktor för blodkärl, ”vascular endothelial growth factor” (VEGF), som förutom att stimulera blodkärlstillväxt även ökar genomsläppligheten hos blod-hjärnbarriären. Denna faktor visade sig förekomma i höga nivåer i de dyskinetiska djurens hjärnor. Genom att hämma effekten av VEGF med en medicin, fick råttorna mindre allvarlig dyskinesi under behandlingsperioden. De fynd vi påträffat i råttmodellen undersöktes sedan vidare i material från avlidna patienter från två olika hjärnbanker. I detta material fanns dyskinetiska patienter, de som varit fria från dyskinesi-besvär, samt neurologiskt friska individer. Vi fann liknande förändringar i den mänskliga hjärnan efter långvarig behandling med L-DOPA i dyskinetiska individer, men inte hos de icke-dyskinetiska eller friska. I den sista studien undersökte vi reglering av blodflödet i hjärnan samt dess koppling till den lokala metabolismen (glukosupptaget) i olika delar av hjärnan. Vi kunde bekräfta att ökat blodflöde och metabolism sker i de delar av hjärnan där vi hittat blodkärlsförändringarna i dyskinetiska individer, en mekanism som skulle kunna orsaka blodkärlstillväxten.

Sammanfattningsvis har denna avhandling uppmärksammat och utrönat nya effekter av L-DOPA och dyskinesi, på blodkärl och dess omgivande celler. Dessa beståndsdelar av hjärnan kan i framtiden utgöra nya måltavlor för parkinsonbehandling som syftar till att minska de biverkningar och komplikationer som L-DOPA orsakar. Genom att angripa felaktiga reaktioner på blodkärlsnivå istället för nervcellsnivå, kan man förhoppningsvis komma åt mekanismer som tidigare inte studerats i detta fält. (Less)
Abstract
L-DOPA pharmacotherapy in Parkinson’s disease (PD) is associated with adverse effects occurring after a few years of treatment. Among these, dyskinesia (abnormal involuntary movements) is particularly common and potentially disabling. The causes behind dyskinesia are not completely understood, but intense research has identified a number of neuronal alterations associated with L-DOPA-induced dyskinesia in both PD patients and animal models of PD. In addition to neurons, the brain consists of a dense vascular network and supportive cells. This thesis has focused on non-neuronal aspects contributing to the pathophysiology of dyskinesia. In particular, it has addressed structural and functional changes affecting the microvasculature in the... (More)
L-DOPA pharmacotherapy in Parkinson’s disease (PD) is associated with adverse effects occurring after a few years of treatment. Among these, dyskinesia (abnormal involuntary movements) is particularly common and potentially disabling. The causes behind dyskinesia are not completely understood, but intense research has identified a number of neuronal alterations associated with L-DOPA-induced dyskinesia in both PD patients and animal models of PD. In addition to neurons, the brain consists of a dense vascular network and supportive cells. This thesis has focused on non-neuronal aspects contributing to the pathophysiology of dyskinesia. In particular, it has addressed structural and functional changes affecting the microvasculature in the basal ganglia.



Using rats with unilateral 6-hydroxydopamine (6-OHDA) lesions as an animal model of PD, the first paper of this thesis demonstrates that dyskinesia induced by either direct dopamine D1 agonism or L-DOPA, are indistinguishable at the level of angiogenic activity in the basal ganglia. Endothelial proliferation, nestin upregulation and downregulation of blood-brain barrier indices, were equally present in both D1- or L-DOPA-induced dyskinetic rats. Moreover, concomitant D1 stimulation by L-DOPA and a D2 antagonist, potentiated the angiogenic response without affecting the severity of dyskinesia. The second paper of this thesis shows that indices of angiogenesis and the expression of vascular endothelial growth factor (VEGF) are dose-dependently upregulated in the striatum and the substantia nigra pars reticulata following chronic L-DOPA treatment. Interestingly, VEGF immunoreactivity was mainly expressed in astrocytes in proximity to blood vessels. Induction of VEGF mRNA was seen in rat primary astrocytic cultures following incubation with D1 receptor stimulation. To verify the causal involvement of VEGF in the development of dyskinesia, 6-OHDA-lesioned rats were chronically co-treated with L-DOPA along with an inhibitor of VEGF receptor-signalling (vandetanib). Rats receiving vandetanib co-treatment, but not its vehicle, developed less severe dyskinesia and did not show a significant angiogenic response to L-DOPA. The occurrence of angiogenesis was investigated also on post mortem basal ganglia sections from PD patients. Histological indices of angiogenesis (i.e. the density of CD34- and nestin-immunopositive microvessels) were significantly higher in dyskinetic PD patients compared to non-dyskinetic PD cases and neurologically healthy controls. Striatal tissue samples from a separate set of dyskinetic patients showed a significant upregulation of VEGF mRNA. Prompted by the hypothesis that L-DOPA-induced angiogenesis may be accompanied by changes in regional cerebral blood flow (rCBF) in the affected regions, we carried out an extensive comparison of changes in rCBF and regional cerebral glucose utilization (rCGU) in unilaterally 6-OHDA-lesioned rats both at baseline and following the administration of L-DOPA (third article in the thesis). The results of this study demonstrate robust increases in rCBF at 60 minutes following the administration of L-DOPA (“ON L-DOPA”) in the same basal ganglia nuclei that show angiogenic activity upon chronic L-DOPA treatment. The rCBF response was not always paralleled by an increase in rCGU, pointing to a direct haemodynamic effect of the treatment. By comparing the passage of a tracer molecule across the blood-brain barrier in chronically L-DOPA-treated rats, we could finally show a significantly larger accumulation of the tracer in the striatum and the substantia nigra pars reticulata at 60 minutes (“ON”) compared to 24 hours (“OFF”) following the last peripheral L-DOPA injection.



In conclusion, this thesis provides evidence that dopamine replacement therapy for PD does not only affect neurons, but that important plastic changes occur at the level of the microvasculature in the basal ganglia. These changes are tightly linked to the development of a dyskinetic motor response. On the basis of these findings, it is recommended that future therapeutic initiatives for PD also consider targets that are expressed in the microvasculature and/or neurovascular coupling mechanisms that are specific to the parkinsonian brain. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Professor, MD Kordower, Jeffrey H, Rush University, Chicago, IL, USA
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Parkinson's disease, levodopa, dyskinesia, angiogenesis, cerebral blood flow, blood-brain barrier
in
Lund University, Faculty of Medicine Doctoral Dissertation Series
volume
2011:80
pages
68 pages
publisher
Basal Ganglia Pathophysiology Unit
defense location
Segerfalksalen, Wallenberg Neurocenter, BMC
defense date
2011-09-16 13:00
ISSN
1652-8220
ISBN
978-91-86871-30-7
language
English
LU publication?
yes
id
fc4f4e51-f66f-4cdd-a9e6-7ed983cdefd5 (old id 2113223)
date added to LUP
2011-08-30 08:00:22
date last changed
2016-09-19 08:44:50
@phdthesis{fc4f4e51-f66f-4cdd-a9e6-7ed983cdefd5,
  abstract     = {L-DOPA pharmacotherapy in Parkinson’s disease (PD) is associated with adverse effects occurring after a few years of treatment. Among these, dyskinesia (abnormal involuntary movements) is particularly common and potentially disabling. The causes behind dyskinesia are not completely understood, but intense research has identified a number of neuronal alterations associated with L-DOPA-induced dyskinesia in both PD patients and animal models of PD. In addition to neurons, the brain consists of a dense vascular network and supportive cells. This thesis has focused on non-neuronal aspects contributing to the pathophysiology of dyskinesia. In particular, it has addressed structural and functional changes affecting the microvasculature in the basal ganglia. <br/><br>
<br/><br>
Using rats with unilateral 6-hydroxydopamine (6-OHDA) lesions as an animal model of PD, the first paper of this thesis demonstrates that dyskinesia induced by either direct dopamine D1 agonism or L-DOPA, are indistinguishable at the level of angiogenic activity in the basal ganglia. Endothelial proliferation, nestin upregulation and downregulation of blood-brain barrier indices, were equally present in both D1- or L-DOPA-induced dyskinetic rats. Moreover, concomitant D1 stimulation by L-DOPA and a D2 antagonist, potentiated the angiogenic response without affecting the severity of dyskinesia. The second paper of this thesis shows that indices of angiogenesis and the expression of vascular endothelial growth factor (VEGF) are dose-dependently upregulated in the striatum and the substantia nigra pars reticulata following chronic L-DOPA treatment. Interestingly, VEGF immunoreactivity was mainly expressed in astrocytes in proximity to blood vessels. Induction of VEGF mRNA was seen in rat primary astrocytic cultures following incubation with D1 receptor stimulation. To verify the causal involvement of VEGF in the development of dyskinesia, 6-OHDA-lesioned rats were chronically co-treated with L-DOPA along with an inhibitor of VEGF receptor-signalling (vandetanib). Rats receiving vandetanib co-treatment, but not its vehicle, developed less severe dyskinesia and did not show a significant angiogenic response to L-DOPA. The occurrence of angiogenesis was investigated also on post mortem basal ganglia sections from PD patients. Histological indices of angiogenesis (i.e. the density of CD34- and nestin-immunopositive microvessels) were significantly higher in dyskinetic PD patients compared to non-dyskinetic PD cases and neurologically healthy controls. Striatal tissue samples from a separate set of dyskinetic patients showed a significant upregulation of VEGF mRNA. Prompted by the hypothesis that L-DOPA-induced angiogenesis may be accompanied by changes in regional cerebral blood flow (rCBF) in the affected regions, we carried out an extensive comparison of changes in rCBF and regional cerebral glucose utilization (rCGU) in unilaterally 6-OHDA-lesioned rats both at baseline and following the administration of L-DOPA (third article in the thesis). The results of this study demonstrate robust increases in rCBF at 60 minutes following the administration of L-DOPA (“ON L-DOPA”) in the same basal ganglia nuclei that show angiogenic activity upon chronic L-DOPA treatment. The rCBF response was not always paralleled by an increase in rCGU, pointing to a direct haemodynamic effect of the treatment. By comparing the passage of a tracer molecule across the blood-brain barrier in chronically L-DOPA-treated rats, we could finally show a significantly larger accumulation of the tracer in the striatum and the substantia nigra pars reticulata at 60 minutes (“ON”) compared to 24 hours (“OFF”) following the last peripheral L-DOPA injection. <br/><br>
<br/><br>
In conclusion, this thesis provides evidence that dopamine replacement therapy for PD does not only affect neurons, but that important plastic changes occur at the level of the microvasculature in the basal ganglia. These changes are tightly linked to the development of a dyskinetic motor response. On the basis of these findings, it is recommended that future therapeutic initiatives for PD also consider targets that are expressed in the microvasculature and/or neurovascular coupling mechanisms that are specific to the parkinsonian brain.},
  author       = {Ohlin, Elisabet},
  isbn         = {978-91-86871-30-7},
  issn         = {1652-8220},
  keyword      = {Parkinson's disease,levodopa,dyskinesia,angiogenesis,cerebral blood flow,blood-brain barrier},
  language     = {eng},
  pages        = {68},
  publisher    = {Basal Ganglia Pathophysiology Unit},
  school       = {Lund University},
  series       = {Lund University, Faculty of Medicine Doctoral Dissertation Series},
  title        = {Microvascular plasticity and neurovascular coupling in the pharmacotherapy of Parkinson's disease},
  volume       = {2011:80},
  year         = {2011},
}