Surgical insights into Parkinson's disease

Old and new challenges in Parkinson's disease therapeutics

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the degeneration of dopaminergic neurons and/or loss od neuronal projections, in several dopaminergic networks. Current treatments for idiopathic PD rely mainly on the use of pharmacologic agents to improve motor symptomatology of PD patients. Nevertheless, so far PD remains an incurable disease. Therefore, it is of utmost importance to establish new therapeutic strategies for PD treatment. Over the last 20 years, several molecular, gene and cell/stem-cell therapeutic approaches have been developed with the aim of counteracting or retarding PD progression. The scope of this review is to provide an overview of PD related therapies and major breakthroughs achieved within this field. In order to do so, this review will start by focusing on PD characterization and current treatment options covering thereafter molecular, gene and cell/stem cell-based therapies that are currently being studied in animal models of PD or have recently been tested in clinical trials. Among stem cell-based therapies, those using MSCs as possible disease modifying agents for PD therapy and, specifically, the MSCs secretome contribution to meet the clinical challenge of counteracting or retarding PD progression, will be more deeply explored.

Mesenchymal stem cells secretome as a modulator of the neurogenic niche: basic insights and therapeutic opportunities

Neural stem cells (NSCs) and mesenchymal stem cells (MSCs) share few characteristics apart from self-renewal and multipotency. In fact, the neurogenic and osteogenic stem cell niches derive from two distinct embryonary structures; while the later originates from the mesoderm, as all the connective tissues do, the first derives from the ectoderm. Therefore, it is highly unlikely that stem cells isolated from one niche could form terminally differentiated cells from the other. Additionally, these two niches are associated to tissues/systems (e.g., bone and central nervous system) that have markedly different needs and display diverse functions within the human body. Nevertheless they do share common features. For instance, the differentiation of both NSCs and MSCs is intimately associated with the bone morphogenetic protein family. Moreover, both NSCs and MSCs secrete a panel of common growth factors, such as nerve growth factor (NGF), glial derived neurotrophic factor (GDNF), and brain derived neurotrophic factor (BDNF), among others. But it is not the features they share but the interaction between them that seem most important, and worth exploring; namely, it has already been shown that there are mutually beneficially effects when these cell types are co-cultured in vitro. In fact the use of MSCs, and their secretome, become a strong candidate to be used as a therapeutic tool for CNS applications, namely by triggering the endogenous proliferation and differentiation of neural progenitors, among other mechanisms. Quite interestingly it was recently revealed that MSCs could be found in the human brain, in the vicinity of capillaries. In the present review we highlight how MSCs and NSCs in the neurogenic niches interact. Furthermore, we propose directions on this field and explore the future therapeutic possibilities that may arise from the combination/interaction of MSCs and NSCs.

Role of radiology in central nervous system stimulation

Central nervous system (CNS) stimulation is becoming increasingly prevalent. Deep brain stimulation (DBS) has been proven to be an invaluable treatment for movement disorders and is also useful in many other neurological conditions refractory to medical treatment, such as chronic pain and epilepsy. Neuroimaging plays an important role in operative planning, target localization and post-operative follow-up. The use of imaging in determining the underlying mechanisms of DBS is increasing, and the dependence on imaging is likely to expand as deep brain targeting becomes more refined. This article will address the expanding role of radiology and highlight issues, including MRI safety concerns, that radiologists may encounter when confronted with a patient with CNS stimulation equipment in situ.

Theoretical and experimental quantification of the role of diffusive chemogradients on neuritogenesis within three-dimensional collagen scaffolds

A critical challenge to regenerating close mimics of native axonal pathways under chronic neurodegenerative disease or injury conditions is the inability to stimulate, sustain and steer neurite outgrowth over a long distance, until they reach their intended targets. Understanding neurite outgrowth necessitates quantitative determination of the role of molecular gradients on growth cone navigation under dynamic physiological conditions. High-fidelity biomimetic platforms are needed to computationally and experimentally acquire and analyze spatiotemporal molecular gradient evolution and the growth cone response across multiple conditions along this gradient pathway. In this study, we utilized a simple microfluidic platform in which diffusive gradients were generated within a 3-D porous scaffold in a defined and reproducible manner. The platform's characteristics (spatiotemporal gradient, steepness, diffusion time, etc.) were precisely quantified at every specified location within the scaffold. Using this platform, we show that the cortical neurite response within 3-D collagen scaffolds, at both the cellular and molecular level, is extremely sensitive to subtle changes in localized concentration and gradient steepness of IGF-1 within that region. This platform could also be used to study other biological processes such as morphogenesis and cancer metastasis, where chemogradients are expected to significantly regulate the outcomes. Results from this study might be of tremendous use in designing biomaterial scaffolds for neural tissue engineering, axonal pathway regeneration under injury or disease, and in formulating targeted drug-delivery strategies.

Neuropathic pain and deep brain stimulation

Deep brain stimulation (DBS) is a neurosurgical intervention the efficacy, safety, and utility of which are established in the treatment of Parkinson's disease. For the treatment of chronic, neuropathic pain refractory to medical therapies, many prospective case series have been reported, but few have published findings from patients treated with current standards of neuroimaging and stimulator technology over the last decade . We summarize the history, science, selection, assessment, surgery, programming, and personal clinical experience of DBS of the ventral posterior thalamus, periventricular/periaqueductal gray matter, and latterly rostral anterior cingulate cortex (Cg24) in 113 patients treated at 2 centers (John Radcliffe, Oxford, UK, and Hospital de São João, Porto, Portugal) over 13 years. Several experienced centers continue DBS for chronic pain, with success in selected patients, in particular those with pain after amputation, brachial plexus injury, stroke, and cephalalgias including anesthesia dolorosa. Other successes include pain after multiple sclerosis and spine injury. Somatotopic coverage during awake surgery is important in our technique, with cingulate DBS under general anesthesia considered for whole or hemibody pain, or after unsuccessful DBS of other targets. Findings discussed from neuroimaging modalities, invasive neurophysiological insights from local field potential recording, and autonomic assessments may translate into improved patient selection and enhanced efficacy, encouraging larger clinical trials.

Deep brain stimulation: indications and evidence

Deep brain stimulation is a minimally invasive targeted neurosurgical intervention that enables structures deep in the brain to be stimulated electrically by an implanted pacemaker. It has become the treatment of choice for Parkinson's disease, refractory to, or complicated by, drug therapy. Its efficacy has been demonstrated robustly by randomized, controlled clinical trials, with multiple novel brain targets having been discovered in the last 20 years. Multifarious clinical indications for deep brain stimulation now exist, including dystonia and tremor in movement disorders; depression, obsessive-compulsive disorder and Tourette's syndrome in psychiatry; epilepsy, cluster headache and chronic pain, including pain from stroke, amputation, trigeminal neuralgia and multiple sclerosis. Current research argues for novel indications, including hypertension and orthostatic hypotension. The development, principles, indications and effectiveness of the technique are reviewed here. While deep brain stimulation is a standard and widely accepted treatment for Parkinson's disease after 20 years of experience, in chronic pain it remains restricted to a handful of experienced, specialist centers willing to publish outcomes despite its use for over 50 years. Reasons are reviewed and novel approaches to appraising clinical evidence in functional neurosurgery are suggested.

RISC in PD: the impact of microRNAs in Parkinson's disease cellular and molecular pathogenesis

Parkinson's disease (PD) is a debilitating neurodegenerative disease characterized primarily by the selective death of dopaminergic (DA) neurons in the substantia nigra pars compacta of the midbrain. Although several genetic forms of PD have been identified, the precise molecular mechanisms underlying DA neuron loss in PD remain elusive. In recent years, microRNAs (miRNAs) have been recognized as potent post-transcriptional regulators of gene expression with fundamental roles in numerous biological processes. Although their role in PD pathogenesis is still a very active area of investigation, several seminal studies have contributed significantly to our understanding of the roles these small non-coding RNAs play in the disease process. Among these are studies which have demonstrated specific miRNAs that target and down-regulate the expression of PD-related genes as well as those demonstrating a reciprocal relationship in which PD-related genes act to regulate miRNA processing machinery. Concurrently, a wealth of knowledge has become available regarding the molecular mechanisms that unify the underlying etiology of genetic and sporadic PD pathogenesis, including dysregulated protein quality control by the ubiquitin-proteasome system and autophagy pathway, activation of programmed cell death, mitochondrial damage and aberrant DA neurodevelopment and maintenance. Following a discussion of the interactions between PD-related genes and miRNAs, this review highlights those studies which have elucidated the roles of these pathways in PD pathogenesis. We highlight the potential of miRNAs to serve a critical regulatory role in the implicated disease pathways, given their capacity to modulate the expression of entire families of related genes. Although few studies have directly linked miRNA regulation of these pathways to PD, a strong foundation for investigation has been laid and this area holds promise to reveal novel therapeutic targets for PD.

Deep brain stimulation for pain

Deep brain stimulation (DBS) is a neurosurgical intervention whose efficacy, safety, and utility have been shown in the treatment of movement disorders. For the treatment of chronic pain refractory to medical therapies, many prospective case series have been reported, but few have published findings from patients treated during the past decade using current standards of neuroimaging and stimulator technology. We summarize the history, science, selection, assessment, surgery, and personal clinical experience of DBS of the ventral posterior thalamus, periventricular/periaqueductal gray matter, and, latterly, the rostral anterior cingulate cortex (Cg24) in 100 patients treated now at two centers (John Radcliffe Hospital, Oxford, UK, and Hospital de São João, Porto, Portugal) over 12 years. Several experienced centers continue DBS for chronic pain with success in selected patients, in particular those with pain after amputation, brachial plexus injury, stroke, and cephalalgias including anesthesia dolorosa. Other successes include pain after multiple sclerosis and spine injury. Somatotopic coverage during awake surgery is important in our technique, with cingulate DBS considered for whole-body pain or after unsuccessful DBS of other targets. Findings discussed from neuroimaging modalities, invasive neurophysiological insights from local field potential recording, and autonomic assessments may translate into improved patient selection and enhanced efficacy, encouraging larger clinical trials.

Twiddler's syndrome in a patient with a deep brain stimulation device for generalized dystonia

Deep brain stimulation (DBS) is the technique of neurostimulation of deep brain structures for the treatment of conditions such as essential tremor, dystonia, Parkinson's disease and chronic pain syndromes. The procedure uses implanted deep brain stimulation electrodes connected to extension leads and an implantable pulse generator (IPG). Hardware failure related to the DBS procedure is not infrequent, and includes electrode migration and disconnection. We describe a patient who received bilateral globus pallidus internus DBS for dystonia with initially good clinical response, but the device eventually failed. Radiographs showed multiple twisting of the extension leads with disconnection from the brain electrodes and a diagnosis of Twiddler's syndrome was made. Twiddler's syndrome was first described in patients with cardiac pacemakers. Patients with mental disability, elderly and obese patients are at increased risk. Twiddler's syndrome should be suspected whenever there is a failure of the DBS device to relieve symptoms previously responsive to stimulation. Surgical correction is usually required.

Advances in the treatment of Parkinson's disease

Parkinson's disease (PD) affects one in every 100 persons above the age of 65 years, making it the second most common neurodegenerative disease after Alzheimer's disease. PD is a disease of the central nervous system that leads to severe difficulties with body motions. The currently available therapies aim to improve the functional capacity of the patient for as long as possible; however they do not modify the progression of the neurodegenerative process. The need for newer and more effective agents is consequently receiving a great deal of attention and consequently being subjected to extensive research. This review concisely compiles the limitations of currently available therapies and the most recent research regarding neuroprotective agents, antioxidants, stem cell research, vaccines and various surgical techniques available and being developed for the management of PD.