Neuroimaging biomarkers associated with clinical dysfunction in Parkinson disease

Parkinson disease (PD) is the second most common neurodegenerative disorder in the world, directly affecting 2-3% of the population over the age of 65. People diagnosed with the disorder can experience motor, autonomic, cognitive, sensory and neuropsychiatric symptoms that can significantly impact quality of life. Uncertainty still exists about the pathophysiological mechanisms that underlie a range of clinical features of the disorder, linked to structural as well as functional brain changes. This thesis thus aimed to uncover neuroimaging biomarkers associated with clinical dysfunction in PD. A 'hubs-and-spokes' neural circuit-based approach can contribute to this aim, by analysing the component elements and also the interconnections of important brain networks. This thesis focusses on structures within basal ganglia-thalamocortical neuronal circuits that are linked to a range functions impacted in the disorder, and that are vulnerable to the consequences of PD pathology. This thesis investigated neuronal 'hubs' by studying the morphology of the caudate nucleus, putamen, thalamus and neocortex. The caudate nucleus, putamen and thalamus are all vital subcortical 'hubs' that play important roles in a number of functional domains that are compromised in PD. The neocortex, on the other hand, has a range of 'hubs' spread across it, regions of the brain that are crucial for neuronal signalling and communication. The interconnections, or 'spokes', between these hubs and other brain regions were investigated using seed-based resting-state functional connectivity analyses. Finally, a morphological analysis was used to investigate possible structural changes to the corpus callosum, the major inter-hemispheric white matter tract of the brain, crucial to effective higher-order brain processes. This thesis demonstrates that the caudate nucleus, putamen, thalamus, corpus callosum and neocortex are all atrophied in PD participants with dementia. PD participants also demonstrated a significant correlation between volumes of the caudate nuclei and general cognitive functioning and speed, while putamina volumes were correlated with general motor function. Cognitively unimpaired PD participants demonstrated minimal morphological alterations compared to control participants, however they demonstrated significant increases in functional connectivity of the caudate nucleus, putamen and thalamus with areas across the frontal lobe, and decreases in functional connectivity with parietal and cerebellar regions. PD participants with mild cognitive impairment and dementia show decreased functional connectivity of the thalamus with paracingulate and posterior cingulate cortices, respectively. This thesis contributes a deeper understanding of the relationship between structures of basal ganglia-thalamocortical neuronal circuits, corpus callosal and neocortical morphology, and the clinical dysfunction associated with PD. This thesis suggests that functional connectivity changes are more common in early stages of the disorder, while morphological alterations are more pronounced in advanced disease stages

Pharmacological and toxicological effects of copper and vanadium using in vitro and in vivo models of Parkinson’s Disease

Parkinson’s disease (PD) pathology is characterised by distinct types of cellular defects: notably, oxidative damage and mitochondria dysfunction, leading to selective loss of dopaminergic neurons in the substantia nigra pars compacta. Exposure to heavy metals and some environmental toxicants have been associated for many years with this disease pathogenesis. Raised iron levels have been consistently observed in the nigrostriatal pathway in PD cases. This thesis focused on the effects of an endogenous heavy metal micronutrient (copper - Cu) and an exogenous environmental heavy metal (vanadium - Vd), and explored the interplay with iron (Fe), focusing for the first time on sub-toxic effects of these metals upon neuronal cell oxidative and ER stress, differentiation, calcium signalling, motor activity, oxidative stress and lifespan in an in vitro (Catecholaminergic a-differentiated (CAD) cells) and in vivo (Drosophila melanogaster) model of PD respectively. Undifferentiated CAD cells were more susceptible to vanadium exposure than differentiated cells and this susceptibility was modulated by iron. Both a natural (Aloysia citrodora) and synthetic iron chelator, Deferoxamine (DFO), significantly and efficiently protected against chronic sub-toxic Vd-induced mitochondrial oxidative stress in contrast, iron chelation exacerbated the oxidative stress elicited by Cu. Low dose Cu had no significant effect upon metabolic rate (in both differentiated and differentiating CAD cells) but significantly protected undifferentiated cells, decreased potassium chloride (KCl)-induced depolarisation and positively enhanced the expression of MAP2 in differentiated cells In vivo exposure of Drosophila melanogaster (DM) to sub-toxic doses of Vd had a range of differential biochemical and behavioural effects upon wild-type (WT) and PD Pink-1B9 drosophila fly models. In pink-1 flies, exposure to chronic low dose of vanadium exacerbated the existing motor deficits, reduced survival, increased the production of reactive oxygen species (ROS), as well as T-SH and a reduction in survival. In WT, it caused an enhancement in motor activity (like L-dopa), in parallel with a reduction in brain RONS generation and increased total thiol levels (T-SH), with a resulting lifespan extension. Both Aloysia citrodora L, and DFO significantly protected against the PD-like phenotypes in both models. The results accrued in this thesis favours the case for iron-chelation therapy as a viable option for the symptomatic treatment of PD

Neuroimaging - Clinical Applications

Modern neuroimaging tools allow unprecedented opportunities for understanding brain neuroanatomy and function in health and disease. Each available technique carries with it a particular balance of strengths and limitations, such that converging evidence based on multiple methods provides the most powerful approach for advancing our knowledge in the fields of clinical and cognitive neuroscience. The scope of this book is not to provide a comprehensive overview of methods and their clinical applications but to provide a "snapshot" of current approaches using well established and newly emerging techniques

Investigating structural plasticity in musicians’ brains using structural magnetic resonance and diffusion tensor imaging techniques

Neuroplasticity is the ability of the brain to change its structure and/or function in response to environmental stimuli. It is implicated in many processes, such as learning, maturation, skill acquisition, and rehabilitation following brain injury. With the advent of neuroimaging techniques, the study of neuroplasticity and its mechanisms have fascinated researchers given the wide scope with which this process is involved. Musicians have long been considered an ideal model to study neuroplasticity in humans. It has been shown that musicians with their early, intensive, and multimodal skilful practice have structural plasticity in different brain regions. The objective of this work was to extend these structural studies through examining different cohorts of musicians, using a multitude of imaging and morphometric techniques, and performing novel examinations of brain regions essential for enabling high level musical performance such as Broca’s area, corpus callosum (CC), and cerebellum. Three age-, gender- and handedness-matched cohorts were examined. The first cohort included 26 orchestral musicians and 26 non-musicians. High resolution T1-weighted structural MR images were acquired to measure gray and white matter volumes and cortical surface area of Broca’s area subparts: pars opercularis/BA44 and pars triangularis/BA45. The second cohort included 12/12/12 professional musicians/amateur musicians/non-musicians. High resolution T1-weighted MR images were acquired to measure cross-sectional areas of four regions of the midsagittal CC: CC1 (rostrum/ genu/anterior body), CC2 (anterior midbody), CC3 (posterior midbody), and CC4 (isthmus and splenium). In the third cohort, 12/12 musicians and non-musicians were examined. High resolution T1-weighted structural MR images were acquired to measure cross-sectional areas of CC1-CC4 regions; and diffusion tensor imaging-based tractography was used to measure average fractional anisotropy (FA), mean diffusivity (MD), tract volume, and number of streamlines of the same regions. In a subset (10/10) of this cohort, high resolution structural scans were used to measure gray and white matter volumes of cerebellar hemispheres; and diffusion tensor imaging-based tractography was used to measure average FA, tract volume, and number of streamlines of superior (SCP) and middle (MCP) cerebellar peduncles. Outcome measures were compared between groups. Compared to controls, musicians possessed greater gray matter volume and cortical surface area of left pars opercularis/BA44 in the first cohort. The volume of left pars opercularis was positively correlated with years of musical performance. Professional musicians possessed greater cross-sectional area of CC1 and CC4 regions compared to amateurs and non-musicians in the second cohort. In the third cohort, musicians possessed greater cross-sectional area, average FA/tract volume/number of streamlines, and lower MD in CC4 region. There was a negative correlation between cross-sectional area of CC4 region and age of starting musical training. There was a positive correlation between average FA values and cross-sectional area of CC4 region in all subjects. In addition, musicians had increased white matter volume of the right cerebellar hemisphere, increased tract volume and number of streamlines of right SCP, and tract volume of right MCP. I hypothesize that these findings represent use-dependent structural plasticity imposed by musical performance. At the microscopic level, these macroanatomical changes may reflect increased synaptogenesis and dendritic growth, generation of new axon collaterals, and formation of new neurons, which would support enhanced functional demands on musicians’ brains

[¹⁸F]fluorination of biorelevant arylboronic acid pinacol ester scaffolds synthesized by convergence techniques

Aim: The development of small molecules through convergent multicomponent reactions (MCR) has been boosted during the last decade due to the ability to synthesize, virtually without any side-products, numerous small drug-like molecules with several degrees of structural diversity.(1) The association of positron emission tomography (PET) labeling techniques in line with the “one-pot” development of biologically active compounds has the potential to become relevant not only for the evaluation and characterization of those MCR products through molecular imaging, but also to increase the library of radiotracers available. Therefore, since the [18F]fluorination of arylboronic acid pinacol ester derivatives tolerates electron-poor and electro-rich arenes and various functional groups,(2) the main goal of this research work was to achieve the 18F-radiolabeling of several different molecules synthesized through MCR. Materials and Methods: [18F]Fluorination of boronic acid pinacol esters was first extensively optimized using a benzaldehyde derivative in relation to the ideal amount of Cu(II) catalyst and precursor to be used, as well as the reaction solvent. Radiochemical conversion (RCC) yields were assessed by TLC-SG. The optimized radiolabeling conditions were subsequently applied to several structurally different MCR scaffolds comprising biologically relevant pharmacophores (e.g. β-lactam, morpholine, tetrazole, oxazole) that were synthesized to specifically contain a boronic acid pinacol ester group. Results: Radiolabeling with fluorine-18 was achieved with volumes (800 μl) and activities (≤ 2 GBq) compatible with most radiochemistry techniques and modules. In summary, an increase in the quantities of precursor or Cu(II) catalyst lead to higher conversion yields. An optimal amount of precursor (0.06 mmol) and Cu(OTf)2(py)4 (0.04 mmol) was defined for further reactions, with DMA being a preferential solvent over DMF. RCC yields from 15% to 76%, depending on the scaffold, were reproducibly achieved. Interestingly, it was noticed that the structure of the scaffolds, beyond the arylboronic acid, exerts some influence in the final RCC, with electron-withdrawing groups in the para position apparently enhancing the radiolabeling yield. Conclusion: The developed method with high RCC and reproducibility has the potential to be applied in line with MCR and also has a possibility to be incorporated in a later stage of this convergent “one-pot” synthesis strategy. Further studies are currently ongoing to apply this radiolabeling concept to fluorine-containing approved drugs whose boronic acid pinacol ester precursors can be synthesized through MCR (e.g. atorvastatin)