Thesis (M. Communication Pathology)--University of Pretoria, 2005. / Summary in English and Afrikaans. Includes bibliographical references.

Soluble amyloid-beta (Aβ) aggregates, including Aβ protofibrils, play a central role in Alzheimer’s disease (AD) and constitute a potential diagnostic biomarker and a therapeutic target. Aβ protofibrils promote synapse dysfunction and neurodegeneration, but the mechanisms behind these effects remain unclear. The aim of this thesis was to increase the knowledge of Aβ protofibrils in AD pathology. When measuring low abundant antigens, such as soluble Aβ aggregates, in plasma and CSF by immunoassays, there is a possibility of interference by heterophilic antibodies (HA). In paper I, we show that HA generate false positive signals, by cross-binding the assay antibodies, when plasma and CSF from AD patients and healthy controls were analyzed for soluble Aβ aggregates, using sandwich ELISAs. Natural anti-Aβ antibodies exist in AD patients and healthy individuals. Circulating Aβ and anti-Aβ antibodies may form immune complexes, masking epitopes on the anti-Aβ antibody, which makes the anti-Aβ antibody concentration difficult to measure. In paper II, the ELISpot technique enabled us to successfully measure B cell production of anti-Aβ antibodies. Our results show that anti-Aβ protofibril antibody production is present in both AD patients and healthy individuals, but is significantly higher in AD patients, indicating that the immune system attempt to eliminate the toxic Aβ species. Insufficient lysosomal degradation is proposed to cause sporadic AD. In paper III, we used a co-culture system of astrocytes, neurons and oligodendrocytes, to clarify the role of astrocytes in Aβ protofibril clearance. Astrocytes are the most prominent glial cell type in the brain, but their role in AD remains elusive. We found that astrocytes effectively engulf, but inefficiently degrade Aβprotofibrils. This result in a high intracellular load of toxic, partly N-terminally truncated Aβ and lysosomal dysfunction. Moreover, we found that secretion of microvesicles, containing N-terminally truncated Aβ, induce neuronal apoptosis. In paper IV, we show that treatment with the protofibril selective antibody mAb158 lead to enhanced Aβ clearance and thereby prevent Aβ neurotoxicity. Taken together, this thesis contributes with important knowledge on the role of Aβ protofibrils in AD pathogenesis and technical aspects that should be considered when measuring Aβ in human tissues.

No description available.

Type II diabetes mellitus (T2D) and Alzheimer's disease (AD) share aetiology and have a high incidence of co-morbidity. Evidence suggests that both diseases are caused by the pathogenic aggregation of an intrinsically disordered native amyloid peptide. Furthermore, T2D and AD share risk factors such as age, obesity and vascular health. Recent studies demonstrate that amylin, an amyloidogenic pancreatic hormone deposited in the pancreas in T2D, is also deposited in the brain in AD. We hypothesised that amylin directly contributes to AD through deposition in the brain and activation of pathogenic signalling cascades. We provide evidence to validate that amylin is deposited in the brain parenchyma and vasculature. Furthermore, we present data demonstrating amylin (IAPP) expression in the brain is significantly elevated in AD; and that amylin treatment increases amyloid-beta (AB) secretion in neuronal culture. Soluble oligomeric species of AB cause AD by initiation of downstream signalling cascades that dysregulate kinase activity, promote tau phosphorylation and result in neuronal death. One such pathway involves AB oligomer activation of the Src-family kinase Fyn, through binding to the cellular prion protein (PrPC) receptor complex. We provide evidence that amylin activates Fyn in neuroblastoma and stem cell derived neurons, this activation is possibly mediated through PrPC. Together the data presented in this thesis demonstrate multiple modes of action whereby amylin may directly propagate or indirectly exacerbate AD-associated processes. Amylin aggregation, deposition, up-regulation and signalling should be considered one of several links between T2D and AD. The pathogenic actions of AB and amylin are mediated by oligomer species. Therefore therapeutics which prevent oligomerisation or oligomer action may be valuable in AD and T2D. One such class of therapeutic are flavonoids. Our collaborators have recently demonstrated the flavonoids rutin and quercetin reduce amylin aggregation and extend lifespan in diabetic animal models. As a result of this we investigated the anti-amyloidogenic and anti-oligomeric properties of the flavonoid quercetin against AB. Quercetin treatment prevented AB oligomerisation, cell binding of pre-formed AB oligomers and also reduced APP processing in cell models. These data suggest quercetin is a multimodal therapeutic with potential utility in AD and T2D and should be explored for further drug development.

Les déficiences en transporteur vésiculaire de l'acétylcholine (VAChT) sont l'un des symptômes précoces de perte neuronale lors de la maladie d'Alzheimer, perte fortement corrélée avec la gravité de la démence associée. Comme le (2R,3R)-5-IBVM est le radioligand de référence du VAChT utilisé en imagerie TEMP, la synthèse par fluoro-de-diazenation a conduit à son analogue fluoré, le 5-FBVM, ainsi qu’à ses énantiomères. Par étude 3D-QSAR, confirmée par évaluation in vitro, chaque énantiomère du 5-FBVM montre une affinité pour le VAChT similaire au 5-IBVM. D'autres travaux ont permis d'améliorer le rendement en 5- FBVM par fluoro-de-triazénation du précurseur triazène, le 5-TVB, en utilisant seulement de l’éthérate de trifluorure de bore qui joue le double rôle d’acide de Lewis et d’agent fluorant, dans le tétrachlorure de carbone, sous irradiation micro-onde. L’optimisation de la fluoro-detriazénation en étudiant différents paramètres expérimentaux compatibles avec un radiomarquage a permis d’obtenir le 5-[18F]FBVM. Ce résultat encourageant devrait conduire à l’obtention du 5-[18F]FBVM. / Deficiencies in vesicular acetylcholine transporter (VAChT) are among the earliest neuronal changes preceding clinical symptoms of Alzheimer's disease, and show a strong correlation with the severity of dementia. As (2R,3R)-5-IBVM is the lead and the only SPECT radioligand for VAChT human imaging, we synthesized by fluoro-de-diazoniation its fluoro analog 5-FBVM with corresponding enantiomers, and confirmed by 3D QSAR and in vitro studies that both enantiomers of 5-FBVM are of the same order affinity as 5-IBVM. Furthermore, we greatly improved 5-FBVM yield via fluoro-de-triazenation of the corresponding triazene precursor 5-TBV using boron trifluoride etherate under non-protic acid conditions in tetrachloromethane under optimized microwave irradiation. By testing different reaction parameters in numerous experimental attempts to find fluoro-de-triazenation conditions which can be transposed to radiofluorination, we may accomplished 5-[18F]FBVM. This encouraging result warrants to optimize 5-[18F]FBVM yield via promising methods obtained in cold chemistry.

No description available.

Bakgrund: Alzheimers sjukdom är en demenssjukdom som främst drabbar äldre men kan även förekomma bland yngre individer. Sjukdomen medför begränsningar så att patienten bland annat får svårigheter att hitta i sin omgivning eller känna igen tidigare bekanta saker. Närstående är därför betydelsefulla i vårdande av den drabbade. Ju mer vårdbehovet ökar, desto mer påverkas närstående socialt, fysiskt och psykiskt då de har ett stort ansvar i vårdande och det påverkar deras hälsa negativt. Det är därför viktig att vårdpersonal erbjuder dem det stöd de behöver i vårdandet. Syfte: Att beskriva närståendes upplevelser av att vårda en familjemedlem som drabbats av Alzheimers sjukdom. Metod: En litteraturöversikt grundad på nio kvalitativa studier som hittades i databaserna: CINAHL, PubMed och Ageline. Studierna söktes fram samt analyserades och gemensamma teman identifierades.  Resultat: Fem huvudteman identifierades: att få diagnos, varierande känslor behov av kunskap och stöd, rollförändringar, och redskap i vårdande. Diskussion: Närståendes upplevelser var både positiva och negativa. Resultatet diskuteras utifrån Roys adaptionsteori med ”individen” i fokus. En bättre förståelse av närståendes upplevelser i vårdande av personer med Alzheimers sjukdom både i samhället och hos vårdpersonal kan underlätta vårdande för familjemedlem och främja hälsa hos närstående. För att förebygga ohälsa och främjar livsvillkor krävs det stöd till både närstående och patienter. Mer forskning samt kontinuerliga utbildningar om närståendes upplevelser i vårdande av en person med Alzheimers sjukdom behövs. / Background: Alzheimer's disease is a dementia that primarily affects elderly but may occur among younger people too. The disease causes severe memory loss so that the patient, among other things, has difficulty finding out in his surroundings or recognizing previously familiar things. The next of kin are therefore important in caring for the sick person. As the need for care increases, the more it affects the next of kin socially, physically and mentally, because they have a major responsibility/role in caring and it can negatively affect their health. It is therefore important that healthcare professionals provide them with the support they need in caregiving. Aim: To describe next of kin’s experiences of caring for a family member affected by Alzheimer's disease. Method: A literature review based on nine qualitative studies found in the databases: CINAHL, PubMed and Ageline. The studies were searched, analyzed, and the common themes identified. Results: Five main themes were identified: to get a diagnosis, the varying feelings, need of knowledge and support, role changes, and tools in caregiving. Discussion: Next of kin’s experiences were both positive and negative. The results are discussed based on Roys adaptation theory with the “individual” in focus. A better understanding of the next of kin’s experience in caring for a person with Alzheimer's disease both in society and healthcare professionals can facilitate care for a family member and promote the health of their next of kin. To prevent ill health and promote good living conditions, support is required for both next of kin and his/her family member. More research as well as good and continuous education about the next of kin’s experiences in caring for a person with Alzheimer’s disease is needed.

This abstract will provide a brief overview of the following literature review. Alzheimer’s disease (AD) is the most common cause of dementia, and is a rapidly growing public health concern, as an increasing number of the world’s population is living well beyond 65 years of age. Alzheimer’s Disease is a progressive neurodegenerative condition, first presenting with mild memory impairment, and advancing over the course of years to profound memory loss, complete immobility, lack of speech and facial recognition. Currently, only palliative treatments are available to delay the progression of the disease, and lessen the severity of the cognitive impairment. However, until a cure is available, researchers and physicians have turned their attention to alternate therapies, one of the most important being exercise. Research efforts have now turned to examining the relationship between the positive physiological responses to exercise, and attenuation of the classic neurodegenerative patterns in patients with AD. The current study examined the effects of aerobic exercise, strength training and resistance-based exercise, and multimodal exercise (containing both of the aforementioned exercise modalities) on the physical and mental/cognitive health of patients with mild cognitive impairment (MCI) and AD. Thus far, exercise therapy has proven to be of great potential value as a supplement to pharmacological treatment, as well as a stand-alone prescription for patients with a milder form of cognitive impairment due to the onset of a neurodegenerative condition. The benefits can be grouped into two categories, cognitive and physiological. The effects on cognitive function range from improved memory to increased independence in activities of daily living, and the physiological effects range from improved clearance of amyloid beta plaques in the brain, to reduction of neuroinflammatory processes. The available research on this subject is extensive, covering a variety of exercise modalities at different intensities, and taking into consideration effects on individuals with MCI, early AD, and advanced AD. The general consensus is that continued, long-term adherence to an appropriate exercise routine can delay cognitive decline, and help patients with neurodegenerative diseases to live independently for a longer period of time. The improvements in cognition, memory, immediate recognition, and other related cognitive functions are mostly attributed to the heightened health of the brain tissue and neural circuitry due to exercise. Exercise (mainly aerobic) enhances cerebral blood flow, improves cardiovascular health, reduces the risk for type 2 diabetes mellitus, and has several other important effects that prevent the formation of pathological biomarkers of AD and promote neurogenesis. Atrophy of regions such as the hippocampus, amygdala, and cerebral cortex can be prevented, and reversed to a certain extent, as a result of long-term exercise therapy. The results of current research could assist physicians and caregivers to provide the appropriate type and intensity of exercise to patients with early, intermediate, and advanced stages of Alzheimer’s disease. Proactive exercise therapy for individuals with a known family history of neurodegenerative disease may help to maintain brain volume, specifically in the hippocampus, and reduce the risk of severe cognitive impairment. Future directions for research include examining the combined effects of pharmacological treatment and exercise therapy, and determining the average amount of time by which exercise delays the progression of early stage cognitive impairment to advanced impairment. Key Terms: aerobic exercise, Alzheimer’s disease, amyloid plaque, hippocampus, mild cognitive impairment, neurodegeneration, neurofibrillary tangle

The study of complex brain networks, where the brain can be viewed as a system with various interacting regions that produce complex behaviors, has grown tremendously over the past decade. With both an increase in longitudinal study designs, as well as an increased interest in the neurological network changes that occur during the progression of a disease, sophisticated methods for dynamic brain network analysis are needed. We first propose a paradigm for longitudinal brain network analysis over patient cohorts where we adapt the Stochastic Actor Oriented Model (SAOM) framework and model a subject's network over time as observations of a continuous time Markov chain. Network dynamics are represented as being driven by various factors, both endogenous (i.e., network effects) and exogenous, where the latter include mechanisms and relationships conjectured in the literature. We outline an application to the resting-state fMRI network setting, where we draw conclusions at the subject level and then perform a meta-analysis on the model output. As an extension of the models, we next propose an approach based on Hidden Markov Models to incorporate and estimate type I and type II error (i.e., of edge status) in our observed networks. Our model consists of two components: 1) the latent model, which assumes that the true networks evolve according to a Markov process as they did in the original SAOM framework; and 2) the measurement model, which describes the conditional distribution of the observed networks given the true networks. An expectation-maximization algorithm is developed for estimation. Lastly, we focus on the study of percolation - the sudden emergence of a giant connected component in a network. This has become an active area of research, with relevance in clinical neuroscience, and it is of interest to distinguish between different percolation regimes in practice. We propose a method for estimating a percolation model from a given sequence of observed networks with single edge transitions. We outline a Hidden Markov Model approach and EM algorithm for the estimation of the birth and death rates for the edges, as well as the type I and type II error rates. / 2018-07-25T00:00:00Z

La maladie d’Alzheimer (MA) constitue la forme la plus commune de démence associée à une perte de mémoire et caractérisée par l’accumulation de plaques extracellulaires contenant des peptides bêta-amyloïdes (Aβ). Des études ont révélé une perte plus importante de synapses que ne peut l’expliquer la mort neuronale, suggérant qu’un déficit synaptique serait présent dès les stades initiaux de la maladie. Bien que le peptide Aβ fût identifié comme un composé des plaques amyloïdes extracellulaires dans les années 1980, des études plus récentes ont mis en évidence la présence intracellulaire de ce peptide. L’accumulation d’Aβ intracellulaire serait un événement antérieur à la formation des plaques séniles dans la pathogenèse de la MA et corrèlerait mieux avec les perturbations de mémoire et d’apprentissage caractéristiques de cette maladie. De plus, des données mettent en évidence la responsabilité des formes oligomériques solubles d’Aβ (Aβo) dans les évènements précoces de la MA. Ce projet vise à mieux comprendre et caractériser l’impact extracellulaire et intracellulaire des peptides Aβo et le lien fonctionnel de leurs effets sur les mécanismes moléculaires impliqués dans les processus mnésiques affectés dans la maladie d’Alzheimer. Dans ce contexte, il nous a paru essentiel d’étudier l’impact extracellulaire et intracellulaire des oligomères d’Aβ sur la transmission synaptique. Ces travaux ont été effectués sur culture primaire de neurones corticaux et sur tranche de cortex de souris par des méthodes d’électrophysiologie via la technique de patch-clamp.Nous avons analysé la fréquence et l’amplitude des courants post-synaptiques excitateurs spontanés (sEPSC) des principaux récepteurs impliqués dans la transmission glutamatergique et dans les mécanismes moléculaires à la base de la mémoire et de l’apprentissage : les récepteurs AMPA et NMDA. Nos données montrent que les peptides Aβo dans le milieu extracellulaire (eAβo) ou dans le milieu intracellulaire (iAβo), affectent spécifiquement les courants associés à l’activation des récepteurs NMDA au niveau postsynaptique sans altérer les courants AMPA. L’application dans le milieu extracellulaire d’Aβo réduit l’amplitude des courants NMDA. Ce phénomène n’est pas lié à la pénétration du peptide Aβo dans les neurones mais à l’activation par l’Aβo de la voie amyloïdogénique induisant une accumulation intrasynaptique d’Aβo responsable de la réduction des courants NMDA.L’ensemble de ces données suggère que l’Aβo perturbe le processing d’APP menant à une production intracellulaire d’Aβo responsable de la réduction de la transmission glutamatergique NMDA-dépendante. Une étape essentielle afin d’améliorer la compréhension des mécanismes moléculaires qui sont à la base des altérations synaptiques glutamatergiques dans la MA est d’approfondir le lien fonctionnel entre les effets extracellulaire et intracellulaire des peptides Aβo. / Alzheimer’s disease (AD) is the most common form of dementia associated with memory loss and characterized by an accumulation of extracellular plaques composed of amyloid-beta peptides (Aβ). Studies have revealed a greater loss of synapses than the neuronal death can explain, suggesting that a synaptic deficit would be present from the early stages of the disease. Although the Aβ peptide has been identified as a component of the extracellular amyloid plaques in the 1980s, recent studies have highlighted the intracellular presence of this peptide. The intracellular accumulation of Aβ precedes the appearance of amyloid plaques in the pathogenesis of AD and seems to be correlated with the memory and learning troubles, characteristic of this disease. Moreover, some data highlight the responsibility of the soluble oligomeric Aβ form (Aβo) in the early events of AD. This project aims to better understand and characterize the extracellular and intracellular impact of Aβo peptides and the functional link of their effects on the molecular mechanisms involved in memory processes affected in AD. In this context, it was essential to study the extracellular and intracellular impact of Aβ oligomers on synaptic transmission. This work was carried out on cultures of primary cortical neurons and mouse cortex slices using electrophysiological methods via the patch-clamp technique.We have recorded the spontaneous excitatory postsynaptic currents (sEPSC) frequency and amplitude from the main receptors implicated in the glutamatergic transmission and in the molecular mechanisms underlying memory and learning processes: AMPA and NMDA receptors. Our data show that external or internal application of Aβo peptides affect specifically the currents associated with NMDA receptors at a postsynaptic level without altering the AMPA currents. The external application of Aβo reduces the NMDA current amplitude. This phenomenon is not due to the penetration of the Aβo peptide into the neurons but rather to the activation of the amyloïdogenic pathway by Aβo inducing an intracellular accumulation of Aβo responsible of the NMDA current reduction.All these data suggest that Aβo perturb the processing of APP leading to an intracellular Aβo production responsible of the glutamatergic NMDA-dependent transmission reduction. An essential step in order to improve our understanding of the molecular mechanisms underlying the altered glutamatergic synaptic alterations found in AD is to deepen the functional link between the extracellular and intracellular effects of the Aβo peptides.