Brain beta 2-microglobulin levels are elevated in the striatum in Parkinson's disease

Virus-induced brain pathology and the neuroinflammation-inflammation continuum: the neurochemists view

Fascinatingly, an abundance of recent studies has subscribed to the importance of cytotoxic immune mechanisms that appear to increase the risk/trigger for many progressive neurodegenerative disorders, including Parkinson's disease (PD), Alzheimer's disease (AD), amyotrophic lateral sclerosis, and multiple sclerosis. Events associated with the neuroinflammatory cascades, such as ageing, immunologic dysfunction, and eventually disruption of the blood-brain barrier and the "cytokine storm", appear to be orchestrated mainly through the activation of microglial cells and communication with the neurons. The inflammatory processes prompt cellular protein dyshomeostasis. Parkinson's and Alzheimer's disease share a common feature marked by characteristic pathological hallmarks of abnormal neuronal protein accumulation. These Lewy bodies contain misfolded α-synuclein aggregates in PD or in the case of AD, they are Aβ deposits and tau-containing neurofibrillary tangles. Subsequently, these abnormal protein aggregates further elicit neurotoxic processes and events which contribute to the onset of neurodegeneration and to its progression including aggravation of neuroinflammation. However, there is a caveat for exclusively linking neuroinflammation with neurodegeneration, since it's highly unlikely that immune dysregulation is the only factor that contributes to the manifestation of many of these neurodegenerative disorders. It is unquestionably a complex interaction with other factors such as genetics, age, and environment. This endorses the "multiple hit hypothesis". Consequently, if the host has a genetic susceptibility coupled to an age-related weakened immune system, this makes them more susceptible to the virus/bacteria-related infection. This may trigger the onset of chronic cytotoxic neuroinflammatory processes leading to protein dyshomeostasis and accumulation, and finally, these events lead to neuronal destruction. Here, we differentiate "neuroinflammation" and "inflammation" with regard to the involvement of the blood-brain barrier, which seems to be intact in the case of neuroinflammation but defect in the case of inflammation. There is a neuroinflammation-inflammation continuum with regard to virus-induced brain affection. Therefore, we propose a staging of this process, which might be further developed by adding blood- and CSF parameters, their stage-dependent composition and stage-dependent severeness grade. If so, this might be suitable to optimise therapeutic strategies to fight brain neuroinflammation in its beginning and avoid inflammation at all.

Are patients with Parkinson's disease at a lower risk of catching the common cold? Propensity score matching

INTRODUCTION

Accumulating evidence indicating that inflammatory responses play crucial roles in Parkinson's disease (PD) development provided a hypothesis that physiological alpha-synuclein may contribute to inflammatory responses against infections during non-advanced stages of PD. Thus, we examined the risk of catching a common cold in patients with PD as compared to other common brain diseases.

METHODS

We extracted PD (non-advanced; without dementia) and control (AD: Alzheimer's disease, migraine, epilepsy, and ischemic stroke) patient data from insurance claim data available between 2010 and 2021. After confirming the clinical PD diagnosis, we investigated factors associated with cold diagnoses and used propensity score matching to identify differences in the incidence of colds between PD and control patients.

RESULTS

Diagnosis of colds in PD patients (n = 726) and controls (AD = 377, migraine = 1019, epilepsy = 3414, ischemic stroke = 6943) was found in 1186 (9.5%) patients, which was independently associated with being female (odds ratio: OR 1.59; 95%CI 1.41-1.79; P < 0.0001), follow-up by neurologists (OR 1.30; 95%CI 1.15-1.48; P < 0.0001), diagnosis of PD (OR 0.30; 95%CI 0.20-0.45; P < 0.0001) and COVID-19 pandemic period (OR 0.58; 95%CI 0.47-0.72; P < 0.0001). After propensity score matching, the incidence of colds was significantly lower in PD (3.4%) versus in controls; AD (9.8%; P < 0.0001), migraine (13.3%; P < 0.0001), epilepsy (11.0%; P < 0.0001), ischemic stroke (8.8%; P < 0.0001).

CONCLUSIONS

Patients with PD were less likely to be diagnosed with colds. However, several confounding factors will need to be examined. Moreover, alpha-synuclein may provide protective resistance to viral infections by activating the immune system due to chronic inflammation in non-advanced PD patients.

Pathogenesis of α-Synuclein in Parkinson's Disease: From a Neuron-Glia Crosstalk Perspective

Parkinson's disease (PD) is a progressive neurodegenerative disorder. The classical behavioral defects of PD patients involve motor symptoms such as bradykinesia, tremor, and rigidity, as well as non-motor symptoms such as anosmia, depression, and cognitive impairment. Pathologically, the progressive loss of dopaminergic (DA) neurons in the substantia nigra (SN) and the accumulation of α-synuclein (α-syn)-composed Lewy bodies (LBs) and Lewy neurites (LNs) are key hallmarks. Glia are more than mere bystanders that simply support neurons, they actively contribute to almost every aspect of neuronal development and function; glial dysregulation has been implicated in a series of neurodegenerative diseases including PD. Importantly, amounting evidence has added glial activation and neuroinflammation as new features of PD onset and progression. Thus, gaining a better understanding of glia, especially neuron-glia crosstalk, will not only provide insight into brain physiology events but also advance our knowledge of PD pathologies. This review addresses the current understanding of α-syn pathogenesis in PD, with a focus on neuron-glia crosstalk. Particularly, the transmission of α-syn between neurons and glia, α-syn-induced glial activation, and feedbacks of glial activation on DA neuron degeneration are thoroughly discussed. In addition, α-syn aggregation, iron deposition, and glial activation in regulating DA neuron ferroptosis in PD are covered. Lastly, we summarize the preclinical and clinical therapies, especially targeting glia, in PD treatments.

β2-microglobulin is overexpressed in buccal cells of elderly and correlated with expression of p16 and inflammatory genes

β2M (Beta 2 microglobulin) is a small protein that is found in all nucleated cells, previous finding showed that its levels increased in the serum of the elderly. Buccal cell samples are none invasive approach for assessing the expression of target genes. There was rationality to assess the expression of β2M in buccal cells of people of a different group of ages. Indeed, the expression of β2M increased significantly with fold change 3.40, 4.80, 6.60^**, 8.20^*** and 12.04^*** for the group of age 18–25 years, 26–35 years, 36–45 years, 46–55 years, and 56–70 years respectively. The same observation was seen with markers of biological aging (p16^INK4a) with fold change 3.19, 3.90, 4.80*, 8.50^*** and 12.40^*** for the group of age 18–25 years, 26–35 years, 36–45 years, 46–55 years, and 56–70 years respectively. As expected, there was an increase in the inflammatory genes (IL-1 β and IL-6) expression in the elderly. Moreover, there was a direct significant correlation (r = 90, p < 0.001) between β2M expression and age (years), and the same direct significant correlation between p16^INK4a expression and age (years) was also seen (r = 90, p < 0.001). In addition, a direct correlation between β2M and p16^INK4a was also seen (r = 0.8.3, p < 0.001), there was also direct correlation between β2M and IL-1 β and IL-6 with (r = 0.5, p < 0.001; r = 0.68, p < 0.001) respectively. This evidence showed that β2M increased in buccal cells of the elderly compared to younger, and thereby buccal cells can be exploited to assess biological aging by measuring β2M levels, however, large sample size and using another assessing method such as β2M protein levels should be performed to confirm the results.

Itaconate alleviates β2-microglobulin-induced cognitive impairment by enhancing the hippocampal amino-β-carboxymuconate-semialdehyde-decarboxylase/picolinic acid pathway

β₂-microglobulin (B₂M) has been established to impair cognitive function. However, no treatment is currently available for B₂M-induced cognitive dysfunction. Itaconate is a tricarboxylic acid (TCA) cycle intermediate that exerts neuroprotective effects in several neurological diseases. The amino-β-carboxymuconate-semialdehyde-decarboxylase (ACMSD)/picolinic acid (PIC) pathway is a crucial neuroprotective branch in the kynurenine pathway (KP). The present study sought to investigate whether Itaconate attenuates B₂M-induced cognitive impairment and examine the mediatory role of the hippocampal ACMSD/PIC pathway. We demonstrated that 4-Octyl Itaconate (OI, an itaconate derivative) significantly alleviated B₂M-induced cognitive dysfunction and hippocampal neurogenesis impairment. OI treatment also increased the expression of ACMSD, elevated the concentration of PIC, and decreased the level of 3-HAA in the hippocampus of B₂M-exposed rats. Furthermore, inhibition of ACMSD by TES-991 significantly abolished the protections of Itaconate against B₂M-induced cognitive impairment and neurogenesis deficits. Exogenous PIC supplementation in hippocampus also improved cognitive performance and hippocampal neurogenesis in B₂M-exposed rats. These findings demonstrated that Itaconate alleviates B₂M-induced cognitive impairment by upregulation of the hippocampal ACMSD/PIC pathway. This is the first study to document Itaconate as a promising therapeutic agent to ameliorate cognitive impairment. Moreover, the mechanistic insights into the ACMSD/PIC pathway improve our understanding of it as a potential therapeutic target for neurological diseases beyond B₂M-associated neurocognitive disorders.

DNA methylation-based surrogates of plasma proteins are associated with Parkinson's disease risk

BACKGROUND

The epigenome may reflect Parkinson's disease (PD) risk, which serves as a point of convergence of genetic and environmental risk factors. Here, we investigate whether blood DNA methylation (DNAm) markers are associated with PD risk.

METHODS

We selected 12 plasma proteins known as predictors of cardiovascular conditions and mortality to evaluate their effects on PD risk in a case-control study. In lieu of protein level measures, however, we assessed the influence of their DNAm surrogates. Primary analysis was restricted to 569 PD patients and 238 controls with DNAm data available. Using univariate logistic regression, we evaluated associations between the DNAm markers and PD.

RESULTS

Of the 12 DNAm surrogates, the most robustly associated were DNAm EFEMP-1 and DNAm CD56, which were associated with PD with and without controlling for blood cell composition. DNAm EFEMP-1 was associated with a decreased risk of PD (OR = 0.83 per SD, 95% CI = 0.70, 0.98) whereas DNAm CD56 was associated with an increased risk of PD (OR = 1.41, 95% CI = 1.11, 1.79).

CONCLUSIONS

Several DNAm markers, selected as part of a panel to track cardiovascular outcomes and mortality, were associated with PD risk. DNAm markers may inform of factors that are affected differentially in early PD patients compared with controls.

The Positive Role and Mechanism of Herbal Medicine in Parkinson's Disease

Parkinson's disease (PD) is a complex neurodegenerative disease, manifested by the progressive functional impairment of the midbrain nigral dopaminergic neurons. Due to the unclear underlying pathogenesis, disease-modifying drugs for PD remain elusive. In Asia, such as in China and India, herbal medicines have been used in the treatment of neurodegenerative disease for thousands of years, which recently attracted considerable attention because of the development of curative drugs for PD. In this review, we first summarized the pathogenic factors of PD including protein aggregation, mitochondrial dysfunction, ion accumulation, neuroinflammation, and oxidative stress, and the related recent advances. Secondly, we summarized 32 Chinese herbal medicines (belonging to 24 genera, such as Acanthopanax, Alpinia, and Astragalus), 22 Chinese traditional herbal formulations, and 3 Indian herbal medicines, of which the ethanol/water extraction or main bioactive compounds have been extensively investigated on PD models both in vitro and in vivo. We elaborately provided pictures of the representative herbs and the structural formula of the bioactive components (such as leutheroside B and astragaloside IV) of the herbal medicines. Also, we specified the potential targets of the bioactive compounds or extractions of herbs in view of the signaling pathways such as PI3K, NF-κB, and AMPK which are implicated in oxidative and inflammatory stress in neurons. We consider that this knowledge of herbal medicines or their bioactive components can be favorable for the development of disease-modifying drugs for PD.

Beta 2 microglobulin correlates with oxidative stress in elderly

Beta 2 microglobulin (Β2M) is expressed in all nucleated cells, it interplays with mediators to regulate and modulate cellular functions. Its role in aging associated disorders has been documented recently. Oxidative stress has been known to play a direct implication on these disorders. Therefore, there is a rationality to explore the function of Β2M in oxidative stress in elderly people. The aim of the study was to assess the Β2M levels in different group of age, and to study the correlation between Β2M and oxidative stress. Actually, the serum levels of Β2M increased significantly in old people comparing to youngers. In addition, there was a positive correlation between Β2M levels and the age of participants (p < 0.001). In addition, there was a positive correlation between Β2M levels and Malondialdehyde (MDA) (p < 0.001), which underscored the possible role of Β2M in oxidative stress. To confirm the previous result, the correlation between total antioxidant capacity (TAC) and Β2M was assessed. There was a negative correlation between them (p < 0.001). These results suggested a possible role of Β2M in oxidative stress status in elderly people; in addition, it suggested the ability of using Β2M as a novel biomarker for oxidative stress. However, further work should be conducted to explore the exact role of Β2M in oxidative stress, and to include large sample size to confirm the results before translating the findings to clinic.

Network-Based Analysis of Cognitive Impairment and Memory Deficits from Transcriptome Data

Aging is an inevitable process that negatively affects all living organisms and their vital functions. The brain is one of the most important organs in living beings and is primarily impacted by aging. The molecular mechanisms of learning, memory and cognition are altered over time, and the impairment in these mechanisms can lead to neurodegenerative diseases. Transcriptomics can be used to study these impairments to acquire more detailed information on the affected molecular mechanisms. Here we analyzed learning- and memory-related transcriptome data by mapping it on the organism-specific protein-protein interactome network. Subnetwork discovery algorithms were applied to discover highly dysregulated subnetworks, which were complemented with co-expression-based interactions. The functional analysis shows that the identified subnetworks are enriched with genes having roles in synaptic plasticity, gliogenesis, neurogenesis and cognition, which are reported to be related to memory and learning. With a detailed analysis, we show that the results from different subnetwork discovery algorithms or from different transcriptomic datasets can be successfully reconciled, leading to a memory-learning network that sheds light on the molecular mechanisms behind aging and memory-related impairments.

Harnessing the immune system for the treatment of Parkinson's disease

Current treatment options for Parkinson's disease (PD) typically aim to replace dopamine, and hence only provide symptomatic relief. However, in the long run, this approach alone loses its efficacy as it is associated with debilitating side effects. Hence there is an unmet clinical need for addressing levodopa resistant symptoms, and an urgency to develop therapies that can halt or prevent the course of PD. The premise that α-syn can transmit from cell-to-cell in a prion like manner has opened up the possibility for the use of immunotherapy in PD. There is evidence for inflammation in PD as is evidenced by microglial activation, as well as the involvement of the peripheral immune system in PD, and peripheral inflammation can exacerbate dopaminergic degeneration as seen in animal models of the disease. However, mechanisms that link the immune system with PD are not clear, and the sequence of immune responses with respect to PD are still unknown. Nevertheless, our present knowledge offers avenues for the development of immune-based therapies for PD. In order to successfully employ such strategies, we must comprehend the state of the peripheral immune system during the course of PD. This review describes the developments in the field of both active and passive immunotherapies in the treatment of PD, and highlights the crucial need for future research for clarifying the role of inflammation and immunity in this debilitating disease.

Allosterism of Nicotinic Acetylcholine Receptors: Therapeutic Potential for Neuroinflammation Underlying Brain Trauma and Degenerative Disorders

Inflammation is a key physiological phenomenon that can be pervasive when dysregulated. Persistent chronic inflammation precedes several pathophysiological conditions forming one of the critical cellular homeostatic checkpoints. With a steady global surge in inflammatory diseases, it is imperative to delineate underlying mechanisms and design suitable drug molecules targeting the cellular partners that mediate and regulate inflammation. Nicotinic acetylcholine receptors have a confirmed role in influencing inflammatory pathways and have been a subject of scientific scrutiny underlying drug development in recent years. Drugs designed to target allosteric sites on the nicotinic acetylcholine receptors present a unique opportunity to unravel the role of the cholinergic system in regulating and restoring inflammatory homeostasis. Such a therapeutic approach holds promise in treating several inflammatory conditions and diseases with inflammation as an underlying pathology. Here, we briefly describe the potential of cholinergic allosterism and some allosteric modulators as a promising therapeutic option for the treatment of neuroinflammation.

[Immunological aspects of Parkinson's disease]

The review summarizes information on immunological disorders in Parkinson's disease (PD). The data on neuroinflammation associated with degeneration of the medial substantia nigra cells are presented. It is pointed out that innate and adaptive immunity cells are involved in the process of neuroinflammation. The authors analyze the cytokine level in the brain, cerebrospinal fluid and peripheral blood as well as the relationship between neuroinflammation and neuron dysfunction and provide information on immunological disorders in people with PD and animal models of PD. Specific features of PD models and data on blood-brain barrier damage and evidence of autoimmune inflammation in PD are presented. Identification of PD preclinical markers, including cytokines, HLA-DR and HLA-DQ antigens, autoantibodies, etc, is discussed. Pre-symptomatic diagnosis of PD, prevention and treatment at the pre-symptomatic stage could lead to interruption or slowdown the neurons death.

Peripheral Immunity, Immunoaging and Neuroinflammation in Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder among elderly population, characterized by the progressive degeneration of dopaminergic neurons in the midbrain. To date, exact cause remains unknown and the mechanism of neurons death uncertain. It is typically considered as a disease of central nervous system (CNS). Nevertheless, numerous evidence has been accumulated in several past years testifying undoubtedly about the principal role of neuroinflammation in progression of PD. Neuroinflammation is mainly associated with presence of activated microglia in brain and elevated levels of cytokine levels in CNS. Nevertheless, active participation of immune system as well has been noted, such as, elevated levels of cytokine levels in blood, the presence of auto antibodies, and the infiltration of T cell in CNS. Moreover, infiltration and reactivation of those T cells could exacerbate neuroinflammation to greater neurotoxic levels. Hence, peripheral inflammation is able to prime microglia into pro-inflammatory phenotype, which can trigger stronger response in CNS further perpetuating the on-going neurodegenerative process. In the present review, the interplay between neuroinflammation and the peripheral immune response in the pathobiology of PD will be discussed. First of all, an overview of regulation of microglial activation and neuroinflammation is summarized and discussed. Afterwards, we try to collectively analyze changes that occurs in peripheral immune system of PD patients, suggesting that these peripheral immune challenges can exacerbate the process of neuroinflammation and hence the symptoms of the disease. In the end, we summarize some of proposed immunotherapies for treatment of PD.

Alpha synuclein in hematopoiesis and immunity

Parkinson's disease (PD) is the second most common neurodegenerative condition and intracellular deposition of Lewy bodies in the substantia nigra (SN), which can cause dopaminergic neuronal death, is the hallmark of this syndrome. α-synuclein (syn) is a small protein expressed mainly in neurons but can also be found in a number of tissues. It can be present as a soluble monomer under normal physiological conditions, but can be toxic in its oligomeric or fibrillary forms. Most of the available literature has focused on the effects of α-syn pathology in the mechanisms leading to PD. However, the normal functions of α-syn still remain to be fully elucidated. Notably, α-syn in the hematopoietic system seems to mediate important functions as indicated by anemia and incomplete cell maturation when this protein is absent. This review will summarize basic genetic and structural findings, and critical information that suggests an essential role of α-syn in the development and activation of the hematopoietic system and immunity.

α-Synuclein in Parkinson's disease: causal or bystander?

Parkinson's disease (PD) comprises a spectrum of disorders with differing subtypes, the vast majority of which share Lewy bodies (LB) as a characteristic pathological hallmark. The process(es) underlying LB generation and its causal trigger molecules are not yet fully understood. α-Synuclein (α-syn) is a major component of LB and SNCA gene missense mutations or duplications/triplications are causal for rare hereditary forms of PD. As typical sporadic PD is associated with LB pathology, a factor of major importance is the study of the α-syn protein and its pathology. α-Syn pathology is, however, also evident in multiple system atrophy (MSA) and Lewy body disease (LBD), making it non-specific for PD. In addition, there is an overlap of these α-synucleinopathies with other protein-misfolding diseases. It has been proven that α-syn, phosphorylated tau protein (pτ), amyloid beta (Aβ) and other proteins show synergistic effects in the underlying pathogenic mechanisms. Multiple cell death mechanisms can induce pathological protein-cascades, but this can also be a reverse process. This holds true for the early phases of the disease process and especially for the progression of PD. In conclusion, while rare SNCA gene mutations are causal for a minority of familial PD patients, in sporadic PD (where common SNCA polymorphisms are the most consistent genetic risk factor across populations worldwide, accounting for 95% of PD patients) α-syn pathology is an important feature. Conversely, with regard to the etiopathogenesis of α-synucleinopathies PD, MSA and LBD, α-syn is rather a bystander contributing to multiple neurodegenerative processes, which overlap in their composition and individual strength. Therapeutic developments aiming to impact on α-syn pathology should take this fact into consideration.

Gene Dysfunction Mediates Immune Response to Dopaminergic Degeneration in Parkinson's Disease

Many publications reported that genetic dysfunction mediates abnormal immune responses in the brain, which is important for the development of neurodegenerative diseases, especially for Parkinson's disease (PD). This immune disorder results in subsequent inflammatory reaction, which stimulates microglia or other immune cells to secrete cytokines and chemokines and disturbs the proportion of peripheral blood lymphocyte subsets contributing to dopaminergic (DA) neuron apoptosis. Furthermore, the abnormal immune related signal pathways caused by genetic variants promote chronic inflammation destroying the blood-brain barrier, which allows infiltration of different molecules and blood cells into the central nervous system (CNS) exerting toxicity on DA neurons. As a result, the inflammatory reaction in the CNS accelerates the progression of Parkinson's disease and promotes α-synuclein aggregation and diffusion among DA neurons in the procession of Parkinson's disease. Thus, for disease evaluation, the genetic mediated abnormal immune response in PD may be assessed based on the multiple immune molecules and inflammatory factors, as well as the ratio of lymphocyte subsets from PD patient's peripheral blood as potential biomarkers.

Inflammation, Infectious Triggers, and Parkinson's Disease

Parkinson's disease is a neurodegenerative disorder characterized by progressive loss of dopaminergic neurons of the substantia nigra pars compacta with a reduction of dopamine concentration in the striatum. The complex interaction between genetic and environmental factors seems to play a role in determining susceptibility to PD and may explain the heterogeneity observed in clinical presentations. The exact etiology is not yet clear, but different possible causes have been identified. Inflammation has been increasingly studied as part of the pathophysiology of neurodegenerative diseases, corroborating the hypothesis that the immune system may be the nexus between environmental and genetic factors, and the abnormal immune function can lead to disease. In this review we report the different aspects of inflammation and immune system in Parkinson's disease, with particular interest in the possible role played by immune dysfunctions in PD, with focus on autoimmunity and processes involving infectious agents as a trigger and alpha-synuclein protein (α-syn).

Autoimmune rheumatic diseases and the risk of Parkinson disease: a nationwide population-based cohort study in Taiwan

BACKGROUNDS

In autoimmune rheumatic diseases (ARDs), the levels of inflammatory mediators are increased and microglia may be activated, resulting in an inflammatory state and the degeneration of dopaminergic neurons. We investigated the association between ARDs and Parkinson disease (PD).

METHODS

We identified ARD patients through the Taiwan National Health Insurance Research Database from 2001 to 2012. From the general population, we randomly selected a comparison cohort that was frequency-matched by age (in 5-year increments), sex and index year. We analysed the risk of PD, stratified by sex, age and comorbidities, by using a Cox regression model.

RESULTS

The risk of PD was 1.37 times greater in ARD patients than in controls after adjustment for age, sex, and comorbidities. ARD subgroups, such as the rheumatoid arthritis and Sjogren syndrome (SS) cohorts, were associated with a significantly higher risk of PD (adjusted hazard ratio [HR], 1.14; 95% confidence interval [CI], 1.03-1.2 and adjusted HR, 1.56; 95% CI, 1.35-1.79, respectively). Furthermore, primary and secondary SS patients had significantly higher risks of PD (adjusted HR, 1.58; 95% CI, 1.32-1.88 and adjusted HR, 1.53, 95% CI, 1.23-1.90, respectively).

CONCLUSIONS

The risk of PD was significantly higher in the ARD patients. Prospective studies are needed to confirm whether ARDs indeed increase the risk of PD.

TNF receptors 1 and 2 exert distinct region-specific effects on striatal and hippocampal grey matter volumes (VBM) in healthy adults

Tumour necrosis factor alpha (TNFα) has been implicated in the pathophysiology of neurodegenerative and neuropsychiatric disease, with research highlighting a role for TNFα in hippocampal and striatal regulation. TNFα signals are primarily transduced by TNF receptors 1 and 2 (TNFR1 and TNFR2), encoded by TNFRSF1A and TNFRSF1B, which exert opposing effects on cell survival (TNFR1, neurodegenerative; TNFR2, neuroprotective). We therefore sought to explore the respective roles of TNFR1 and TNFR2 in the regulation of hippocampal and striatal morphology in an imaging genetics study. Voxel-based morphometry was used to analyse the associations between TNFRSF1A (rs4149576 and rs4149577) and TNFRSF1B (rs1061624) genotypes and grey matter structure. The final samples comprised a total of 505 subjects (mean age = 33.29, SD = 11.55 years; 285 females and 220 males) for morphometric analyses of rs1061624 and rs4149576, and 493 subjects for rs4149577 (mean age = 33.20, SD = 11.56 years; 281 females and 212 males). Analyses of TNFRSF1A single nucleotide polymorphisms (SNPs) rs4149576 and rs4149577 showed highly significant genotypic associations with striatal volume but not the hippocampus. Specifically, for rs4149576, G homozygotes were associated with reduced caudate nucleus volumes relative to A homozygotes and heterozygotes, whereas for rs4149577, reduced caudate volumes were observed in C homozygotes relative to T homozygotes and heterozygotes. Analysis of the TNFRSF1B SNP rs1061624 yielded a significant association with hippocampal but not with striatal volume, whereby G homozygotes were associated with increased volumes relative to A homozygotes and heterozygotes. Our findings indicate a role for TNFR1 in regulating striatal but not hippocampal morphology, as well as a complementary role for TNFR2 in hippocampal but not in striatal morphology.

Prolyl oligopeptidase and dipeptidyl peptidase II/dipeptidyl peptidase IV ratio in the cerebrospinal fluid in Parkinson's disease: historical overview and future prospects

Prolyl oligopeptidase (also named prolyl endopeptidase; PREP) hydrolyzes the Pro-Xaa bonds of biologically active oligopeptides on their carboxyl side. In 1987, we detected PREP activity in human cerebrospinal fluid (CSF) using highly sensitive liquid chromatography-fluorometry with succinyl-Gly-Pro-4-methyl-coumarin amide as a new synthetic substrate, and found a marked decrease in its activity in the cerebrospinal fluid (CSF) from patients with Parkinson's disease (PD) as compared with its level in control patients without neurological diseases. In 2013, Hannula et al. found co-localization of PREP with α-synuclein in the postmortem PD brain. Several recent studies also suggest that the level of PREP in the brain of PD patients may be related to dopamine (DA) cell death via promotion of α-synuclein oligomerization and that inhibitors of PREP may play a neuroprotective role in PD. Although the relationship between another family of prolyl oligopeptidase enzymes, dipeptidyl peptidase II (DPP II) and dipeptidyl peptidase IV (DPP IV), and α-synuclein in the PD brain is not yet clear, we found that the DPP II activity/DPP IV activity ratio in the CSF was significantly increased in PD patients. This review discusses the possibility of PREP as well as the DPP II/DPP IV ratio in the CSF as potential biomarkers of PD.

Chondroitin sulfate proteoglycans in the nervous system: inhibitors to repair

Chondroitin sulfate proteoglycans (CSPGs) are widely expressed in the normal central nervous system, serving as guidance cues during development and modulating synaptic connections in the adult. With injury or disease, an increase in CSPG expression is commonly observed close to lesioned areas. However, these CSPG deposits form a substantial barrier to regeneration and are largely responsible for the inability to repair damage in the brain and spinal cord. This review discusses the role of CSPGs as inhibitors, the role of inflammation in stimulating CSPG expression near site of injury, and therapeutic strategies for overcoming the inhibitory effects of CSPGs and creating an environment conducive to nerve regeneration.

Evidence of inflammatory system involvement in Parkinson's disease

Parkinson's disease (PD) is a chronic neurodegenerative disease underpinned by both genetic and environmental etiologic factors. Recent findings suggest that inflammation may be a pathogenic factor in the onset and progression of both familial and sporadic PD. Understanding the precise role of inflammatory factors in PD will likely lead to understanding of how the disease arises. In vivo evidence for inflammation in PD includes dysregulated molecular mediators such as cytokines, complement system and its receptors, resident microglial activation, peripheral immune cells invasion, and altered composition and phenotype of peripheral immune cells. The growing awareness of these factors has prompted novel approaches to modulate the immune system, although it remains whether these approaches can be used in humans. Influences of ageing and differential exposure to environmental agents suggest potential host-pathogen specific pathophysiologic factors. There is a clear need for research to further unravel the pathophysiologic role of immunity in PD, with the potential of developing new therapeutic targets for this debilitating condition.

Neuroimmunological processes in Parkinson's disease and their relation to α-synuclein: microglia as the referee between neuronal processes and peripheral immunity

The role of neuroinflammation and the adaptive immune system in PD (Parkinson's disease) has been the subject of intense investigation in recent years, both in animal models of parkinsonism and in post-mortem PD brains. However, how these processes relate to and modulate α-syn (α-synuclein) pathology and microglia activation is still poorly understood. Specifically, how the peripheral immune system interacts, regulates and/or is induced by neuroinflammatory processes taking place during PD is still undetermined. We present herein a comprehensive review of the features and impact that neuroinflamation has on neurodegeneration in different animal models of nigral cell death, how this neuroinflammation relates to microglia activation and the way microglia respond to α-syn in vivo. We also discuss a possible role for the peripheral immune system in animal models of parkinsonism, how these findings relate to the state of microglia activation observed in these animal models and how these findings compare with what has been observed in humans with PD. Together, the available data points to the need for development of dual therapeutic strategies that modulate microglia activation to change not only the way microglia interact with the peripheral immune system, but also to modulate the manner in which microglia respond to encounters with α-syn. Lastly, we discuss the immune-modulatory strategies currently under investigation in animal models of parkinsonism and the degree to which one might expect their outcomes to translate faithfully to a clinical setting.

Metal dyshomeostasis and inflammation in Alzheimer's and Parkinson's diseases: possible impact of environmental exposures

A dysregulated metal homeostasis is associated with both Alzheimer's (AD) and Parkinson's (PD) diseases; AD patients have decreased cortex and elevated serum copper levels along with extracellular amyloid-beta plaques containing copper, iron, and zinc. For AD, a putative hepcidin-mediated lowering of cortex copper mechanism is suggested. An age-related mild chronic inflammation and/or elevated intracellular iron can trigger hepcidin production followed by its binding to ferroportin which is the only neuronal iron exporter, thereby subjecting it to lysosomal degradation. Subsequently raised neuronal iron levels can induce translation of the ferroportin assisting and copper binding amyloid precursor protein (APP); constitutive APP transmembrane passage lowers the copper pool which is important for many enzymes. Using in silico gene expression analyses, we here show significantly decreased expression of copper-dependent enzymes in AD brain and metallothioneins were upregulated in both diseases. Although few AD exposure risk factors are known, AD-related tauopathies can result from cyanobacterial microcystin and β-methylamino-L-alanine (BMAA) intake. Several environmental exposures may represent risk factors for PD; for this disease neurodegeneration is likely to involve mitochondrial dysfunction, microglial activation, and neuroinflammation. Administration of metal chelators and anti-inflammatory agents could affect disease outcomes.

The role of innate and adaptive immunity in Parkinson's disease

In recent years, inflammation has become implicated as a major pathogenic factor in the onset and progression of Parkinson's disease. Understanding the precise role for inflammation in PD will likely lead to understanding of how sporadic disease arises. In vivo evidence for inflammation in PD includes microglial activation, increased expression of inflammatory genes in the periphery and in the central nervous system (CNS), infiltration of peripheral immune cells into the CNS, and altered composition and phenotype of peripheral immune cells. These findings are recapitulated in various animal models of PD and are reviewed herein. Furthermore, we examine the potential relevance of PD-linked genetic mutations to altered immune function and the extent to which environmental exposures that recapitulate these phenotypes, which may lead to sporadic PD through similar mechanisms. Given the implications of immune system involvement on disease progression, we conclude by reviewing the evidence supporting the potential efficacy of immunomodulatory therapies in PD prevention or treatment. There is a clear need for additional research to clarify the role of immunity and inflammation in this chronic, neurodegenerative disease.

A comprehensive study on long-term injury to nigral dopaminergic neurons following intracerebroventricular injection of lipopolysaccharide in rats

Parkinson's disease (PD) is characterized by selective and progressive degeneration of dopaminergic neurons in the substantia nigra (SN). Lipopolysaccharide (LPS) can induce chronic inflammation and has been widely used to study the pathogenesis of PD. In this study, a single intracerebroventricular injection of LPS was used to induce neurotoxic effects on dopaminergic neurons in Sprague-Dawley rats. The long-term neurotoxic effects of LPS were evaluated at different time points. Microglia were activated in the hippocampus and striatum at 4 weeks, and in the SN at 24 weeks. Astrocytes were activated in the hippocampus and nigrostriatal system at 2 and 24 weeks. The expression of brain-derived neurotrophic factor in the SN increased at 4 weeks and decreased after 12 weeks, and tyrosine hydroxylase-positive neurons in the SN were shown to have an atrophic appearance, with cell loss evident after 24 weeks. Phospho-α-synuclein expression, a reflection of parkinsonian pathogenesis, increased at 12 weeks, and peaked at 24 weeks. Abnormal motor behavior appeared at 16 weeks and lasted up to 48 weeks. These results indicate that microglia are activated for several months after a single, low dose injection of LPS, which eventually results in progressive and selective damage to dopaminergic neurons in the SN.

Regionally-specific microglial activation in young mice over-expressing human wildtype alpha-synuclein

Parkinson's disease (PD) is characterized by widespread alpha-synuclein pathology and neuronal loss, primarily of the nigrostriatal dopaminergic neurons. Inflammation has been implicated in PD, and alpha-synuclein can initiate microglial activation; however, the kinetics and distribution of inflammatory responses to alpha-synuclein overexpression in vivo are not well understood. We have examined the regional and temporal pattern of microglial activation and pro-inflammatory cytokine production in mice over-expressing wild-type human alpha-synuclein driven by the Thy1-promoter (Thy1-aSyn mice). An increased number of activated microglia, and increased levels of TNF-α mRNA and protein were first detected in the striatum (1 month of age) and later in the substantia nigra (5-6 months), but not the cerebral cortex or cerebellum; in contrast, IL-1β and TGF-β remained unchanged in the striatum and substantia nigra at all ages examined. Microglial activation persisted up to 14 months of age in these regions and only minimal increases were observed in other regions at this later age. Increased concentrations of serum TNF-α were observed at 5-6 months, but not at 1 month of age. The expression of toll-like receptors (TLRs) 1, TLR 4 and TLR 8, which are possible mediators of microglial activation, was increased at 5-6 months in the substantia nigra but not in the cerebral cortex, and TLR 2 was increased in the substantia nigra at 14 months of age. With the exception of a slight increase in the striatum of 14 month old Thy1-aSyn mice, MHCII staining was not detected in the regions and ages examined. Similarly, peripheral CD4 and CD8-postive T cells were increased in the blood but only at 22 months of age, suggesting later involvement of the adaptive immune response. These data indicate that, despite the presence of high levels of alpha-synuclein in other brain regions, alpha-synuclein overexpression caused a selective early inflammatory response in regions containing the axon terminals and cell bodies of the nigrostriatal pathway. Our results suggest that specific factors, possibly involving a regionally and temporally selective increase in TLRs, mediate alpha-synuclein-induced inflammatory responses in the SN, and may play a role in the selective vulnerability of nigrostriatal dopaminergic neurons in PD.

Current understanding of the glial response to disorders of the aging CNS

In this special issue of Frontiers in Pharmacology, we have asked leading experts to comment and review the evidence that inflammatory cells play a leading role in the pathological processes underlying neurodegenerative disorders. We now seek to draw these various observations together into a conclusion, with the hope that this will inform further work in this area and result in the identification of new therapeutic targets that will have a disease modifying effect.

Adjunctive therapy in Parkinson's disease: the role of rasagiline

Parkinson's disease is the second most common neurodegenerative disorder, currently affecting 1.5 million people in the US. In this review, we describe the diagnostic and pathological features of Parkinson's disease, as well as its clinical course. We then review pharmacologic treatments for the disease, with a particular focus on therapies adjunctive to levodopa and specifically the role of rasagiline. We review the four pivotal rasagiline trials, and discuss rasagiline and its use as adjunctive therapy for Parkinson's disease. Finally, we discuss potential side effects, drug interactions, and other practical aspects concerning the use of rasagiline in Parkinson's disease.

The role of the MYD88-dependent pathway in MPTP-induced brain dopaminergic degeneration

Background

Mounting evidence supports a significant role of inflammation in Parkinson's disease (PD) pathophysiology, with several inflammatory pathways being suggested as playing a role in the dopaminergic degeneration seen in humans and animal models of the disease. These include tumor necrosis factor, prostaglandins and oxidative-related stress components. However, the role of innate immunity has not been established in PD.

Methods

Based on the fact that the myeloid differentiation primary response gene (88) (MyD88) is the most common adaptor protein implicated in toll-like receptor (TLR) signaling, critical in the innate immune response, we undertook a study to investigate the potential contribution of this specific pathway to MPTP-induced brain dopaminergic degeneration using MyD88 knock out mice (MyD88-/-), following our observations that the MyD88-dependent pathway was critical for MPTP dopaminergic toxicity in the enteric nervous system. Post-mortem analyses assessing nigrostriatal dopaminergic degeneration and inflammation were performed using HPLC, western blots, autoradiography and immunofluorescence.

Results

Our results demonstrate that MyD88-/- mice are as vulnerable to MPTP-induced dopamine and DOPAC striatal depletion as wild type mice. Furthermore, MyD88-/- mice show similar striatal dopamine transporter and tyrosine hydroxylase loss, as well as dopaminergic cell loss in the substantia nigra pars compacta in response to MPTP. To evaluate the extent of the inflammatory response created by the MPTP regimen utilized, we further performed bioluminescence imaging using TLR2-luc/gfp transgenic mice and microglial density analysis, which revealed a modest brain microglial response following MPTP. This was accompanied by a significant astrocytic reaction in the striatum, which was of similar magnitude both in wild type and MyD88-/- mice.

Conclusions

Our results suggest that subacute MPTP-induced dopaminergic degeneration observed in the central nervous system is MyD88-independent, in contrast to our recent observations that this pathway, in the same cohort of animals, is critical in the loss of dopaminergic neurons in the enteric nervous system.

Tumor necrosis factor-alpha and the roles it plays in homeostatic and degenerative processes within the central nervous system

Tumor Necrosis Factor-alpha (TNF-α) is a prototypic pro-inflammatory cytokine involved in the innate immune response. TNF-α ligation and downstream signaling with one of its cognate receptors, TNF-RI or TNF-RII, modulates fundamental processes in the brain including synapse formation and regulation, neurogenesis, regeneration, and general maintenance of the central nervous system (CNS). During states of chronic neuroinflammation, extensive experimental evidence implicates TNF-α as a key mediator in disease progression, gliosis, demyelination, inflammation, blood-brain-barrier deterioration, and cell death. This review explores the complex roles of TNF-α in the CNS under normal physiologic conditions and during neurodegeneration. We focus our discussion on Multiple Sclerosis, Parkinson's disease, and Alzheimer's disease, relaying the outcomes of preclinical and clinical testing of TNF-α directed therapeutic strategies, and arguing that despite the wealth of functions attributed to this central cytokine, surprisingly little is known about the cell type- and stage-specific roles of TNF-α in these debilitating disorders.

Glia: initiators and progressors of pathology in Parkinson's disease

BACKGROUND

Glia are traditionally known as support cells for neurons, and their role in neurodegeneration has been largely considered secondary to neuronal dysfunction. We review newer concepts on glial function and assess glial changes in Parkinson's disease (PD) at the time of disease initiation when α-synuclein is accumulating in brain tissue but there is limited neuronal loss, and also as the disease progresses and neuronal loss is evident.

RESULTS

Of the two main types of astrocytes, only protoplasmic astrocytes are involved in PD, where they become nonreactive and accumulate α-synuclein. Experimental evidence has shown that astrocytic α-synuclein deposition initiates the noncell autonomous killing of neurons through microglial signaling. As the disease progresses, more protoplasmic astrocytes are affected by the disease with an increasing microglial response. Although there is still controversy on the role microglia play in neurodegeneration, there is evidence that microglia are activated early in PD and possibly assist with the clearance of extracellular α-synuclein at this time. Microglia transform to phagocytes and target neurons as the disease progresses but appear to become dysfunctional with increasing amounts of ingested debris. Only nonmyelinating oligodendroglial cells are affected in PD, and only late in the disease process.

CONCLUSIONS

Glial cells are responsible for the progression of PD and play an important role in initiating the early tissue response. In particular, early dysfunction and α-synuclein accumulation in astrocytes causes recruitment of phagocytic microglia that attack selected neurons in restricted brain regions causing the clinical symptoms of PD.

The endotoxin-induced neuroinflammation model of Parkinson's disease

Parkinson's disease (PD) is a common neurodegenerative disorder characterized by the progressive loss of dopaminergic (DA) neurons in the substantia nigra. Although the exact cause of the dopaminergic neurodegeneration remains elusive, recent postmortem and experimental studies have revealed an essential role for neuroinflammation that is initiated and driven by activated microglial and infiltrated peripheral immune cells and their neurotoxic products (such as proinflammatory cytokines, reactive oxygen species, and nitric oxide) in the pathogenesis of PD. A bacterial endotoxin-based experimental model of PD has been established, representing a purely inflammation-driven animal model for the induction of nigrostriatal dopaminergic neurodegeneration. This model, by itself or together with genetic and toxin-based animal models, provides an important tool to delineate the precise mechanisms of neuroinflammation-mediated dopaminergic neuron loss. Here, we review the characteristics of this model and the contribution of neuroinflammatory processes, induced by the in vivo administration of bacterial endotoxin, to neurodegeneration. Furthermore, we summarize the recent experimental therapeutic strategies targeting endotoxin-induced neuroinflammation to elicit neuroprotection in the nigrostriatal dopaminergic system. The potential of the endotoxin-based PD model in the development of an early-stage specific diagnostic biomarker is also emphasized.

Inflammation and gliosis in neurological diseases--clinical implications

The inflammatory reaction accompany all acute processes in the central nervous system (CNS), (as stroke or traumatic brain injury) and chronic neurodegenerative processes (as Parkinson's or Alzheimer's disease), and through the stage of cleaning of damage tissue, contribute to recovery and regeneration and eventually to restoration of the function. However many studies showed that inflammation in the CNS may be harmful because of an excessive vulnerability of the nervous tissue or impaired regulation. Manipulation of the inflammation is now one of the approaches in the treatment of the various diseases of the CNS.

Diagnostic cerebrospinal fluid biomarkers for Parkinson's disease: a pathogenetically based approach

The inaccuracy of the early diagnosis of Parkinson's disease (PD) has been a major incentive for studies aimed at the identification of biomarkers. Brain-derived cerebrospinal fluid (CSF) proteins are potential biomarkers considering the major role that proteins play in PD pathogenesis. In this review, we discuss the current hypotheses about the pathogenesis of PD and identify the most promising candidate biomarkers among the CSF proteins studied so far. The list of potential markers includes proteins involved in various pathogenetic processes, such as oxidative stress and protein aggregation. This list will undoubtedly grow in the near future by application of CSF proteomics and subsequent validation of identified proteins. Probably a single biomarker will not suffice to reach high sensitivity and specificity, because PD is pathogenetically heterogeneous and shares etiological factors with other neurodegenerative diseases. Furthermore, identified candidate biomarkers will have to be thoroughly validated before they can be implemented as diagnostic aids.

Pharmacological therapy in Parkinson's disease: focus on neuroprotection

Although the number of available therapeutic approaches in Parkinson's disease (PD) is steadily increasing the search for effective neuroprotective agent is continuing. Such research is directed at influencing the key steps in the pathomechanism: the mitochondrial dysfunction, the oxidative stress, the neuroinflammatory processes and the final common apoptotic pathway. Earlier-developed symptomatic therapies were implicated to be neuroprotective, and promising novel disease modifying approaches were brought into the focus of interest. The current review presents a survey of our current knowledge relating to the pathomechanism of PD and discusses the putative neuroprotective therapy.

Microglia acquire distinct activation profiles depending on the degree of alpha-synuclein neuropathology in a rAAV based model of Parkinson's disease

Post-mortem analysis of brains from Parkinson's disease (PD) patients strongly supports microglia activation and adaptive immunity as factors contributing to disease progression. Such responses may be triggered by α-synuclein (α-syn), which is known to be the main constituent of the aggregated proteins found in Lewy bodies in the brains of PD patients. To investigate this we used a recombinant viral vector to express human α-syn in rat midbrain at levels that induced neuronal pathology either in the absence or the presence of dopaminergic cell death, thereby mimicking early or late stages of the disease. Microglia activation was assessed by stereological quantification of Mac1+ cells, as well as the expression patterns of CD68 and MCH II. In our study, when α-syn induced neuronal pathology but not cell death, a fast transient increase in microglia cell numbers resulted in the long-term induction of MHC II+ microglia, denoting antigen-presenting ability. On the other hand, when α-syn induced both neuronal pathology and cell death, there was a delayed increase in microglia cell numbers, which correlated with long-lasting CD68 expression and a morphology reminiscent of peripheral macrophages. In addition T-lymphocyte infiltration, as judged by the presence of CD4+ and CD8+ cells, showed distinct kinetics depending on the degree of neurodegeneration, and was significantly higher when cell death occurred. We have thus for the first time shown that the microglial response differs depending on whether α-syn expression results on cell death or not, suggesting that microglia may play different roles during disease progression. Furthermore, our data suggest that the microglial response is modulated by early events related to α-syn expression in substantia nigra and persists at the long term.

ABCB1: the role in Parkinson's disease and pharmacokinetics of antiparkinsonian drugs

ABCB1/P-glycoprotein (P-gp) is an ATP-dependant transmembrane efflux protein widely expressed in human organs and plays a protective role against endogenous and exogenous substances. It is involved in drug pharmacokinetics affecting drug absorption, disposition and elimination. At the BBB level, due to its luminal localisation, ABCB1 limits drug transport and is important in central detoxification. Inter-individual variability has been described in ABCB1 expression and functionality. Recent work suggests that variability may play a role in the pathogenesis of neurological diseases. Furthermore, ABCB1 expression and/or functionality may modify drug efficacy or increase central adverse events. This paper reviews ABCB1 implication in the pathophysiology of Parkinson's disease and its role in the cerebral distribution of drugs.

Astrocyte-neuron interactions in neurological disorders

Astrocytes have long been considered as just providing trophic support for neurons in the central nervous system, but recently several studies have highlighted their importance in many functions such as neurotransmission, metabolite and electrolyte homeostasis, cell signaling, inflammation, and synapse modulation. Astrocytes are, in fact, part of a bidirectional crosstalk with neurons. Moreover, increasing evidence is stressing the emerging role of astrocyte dysfunction in the pathophysiology of neurological disorders, including neurodegenerative disease, stroke, epilepsy, migraine, and neuroinflammatory diseases.

Meloxicam reduces lipopolysaccharide-induced degeneration of dopaminergic neurons in the rat substantia nigra pars compacta

Inflammation is believed to play an important role in the etiology and pathogenesis of Parkinson's disease (PD). However, experimental and epidemiological evidences from various non-steroidal anti-inflammatory drugs, including cyclooxygenase-2 (COX-2) inhibitors, seem contradictive. Using the intranigral lipopolysaccharide (LPS) rat model, we show that meloxicam, a preferential COX-2 inhibitor, diminishes the activation of OX-42-immunoreactive (ir) microglia and reduces the loss of tyrosine hydroxylase (TH)-ir dopamine (DA) neurons in the substantia nigra pars compacta (SNpc) that is normally induced by exposure to LPS. Double-labelling immunohistochemistry identified that activated microglia rather than intact resting microglia are the main intracellular venues for COX-2 expression. These findings suggest that inhibition of COX-2 activity in activated microglial cells may be potentially neuroprotective for DA neurons in the SNpc.

Neuroinflammation in Parkinson's disease: a target for neuroprotection?

Parkinson's disease is characterised by a slow and progressive degeneration of dopaminergic neurons in the substantia nigra. Despite intensive research, the cause of the neuronal loss in Parkinson's disease is poorly understood. Neuroinflammatory mechanisms might contribute to the cascade of events leading to neuronal degeneration. In this Review, we describe the evidence for neuroinflammatory processes from post-mortem and in vivo studies in Parkinson's disease. We further identify the cellular and molecular events associated with neuroinflammation that are involved in the degeneration of dopaminergic neurons in animal models of the disease. Overall, available data support the importance of non-cell-autonomous pathological mechanisms in Parkinson's disease, which are mostly mediated by activated glial and peripheral immune cells. This cellular response to neurodegeneration triggers deleterious events (eg, oxidative stress and cytokine-receptor-mediated apoptosis), which might eventually lead to dopaminergic cell death and hence disease progression. Finally, we highlight possible therapeutic strategies (including immunomodulatory drugs and therapeutic immunisation) aimed at downregulating these inflammatory processes that might be important to slow the progression of Parkinson's disease.

Circulating interleukin-15 and RANTES chemokine in Parkinson's disease

Interleukin-15 promotes T-cell proliferation, induction of cytolytic effector cells including natural killer (NK) and cytotoxic cells and stimulates B-cell to proliferate and secrete immunoglobulins. RANTES is a C-C beta chemokine with strong chemoattractant activity for T lymphocytes and monocytes.

OBJECTIVES

The objective of our study was to find out whether IL-15 and RANTES are involved in the possible inflammatory reactions of PD.

PATIENTS AND METHODS

We measured by immunoassay serum IL-15 and RANTES levels in 41 patients with PD in comparison with serum levels in 19 healthy subjects age and sex-matched. IL-15 and RANTES levels were correlated with sex, age, disease duration. H-Y stage and the UPDRS III score in all the studied groups and were also correlated with treatment status in PD patients.

RESULTS

The PD group presented with significantly increased RANTES levels as compared to the control group (P = 0.0009). No difference was observed as regards IL-15 levels. A strong and significant correlation between RANTES levels and UPDRS III score was observed in PD patients (R(s) = 0.42, P = 0.007). Untreated patients had significantly higher RANTES levels as compared to the controls.

CONCLUSIONS

Our findings may suggest a recruitment of activated monocytes, macrophages and T lymphocytes to sites of inflammation in the central nervous system of PD patients.

Inflammation as a causative factor in the aetiology of Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder affecting mainly the elderly, although a small proportion of PD patients develop the illness at a much younger age. In the former group, idiopathic PD patients, the causes of the illness have been the subject of longstanding debate with environmental toxins, mitochondrial dysfunction, abnormal protein handling and oxidative stress being suggested. One problem has been that the epidemiology of PD has offered few clues to provide evidence for a single major causative factor. Comparatively recently it has been found that in both patients and experimental models of PD in animals neuroinflammation appears to be a ubiquitous finding. These cases present with all of the classical features of inflammation including phagocyte activation, increased synthesis and release of proinflammatory cytokines and complement activation. Although this process is vital for normal function and protection in both the CNS, as in the periphery, it is postulated that in the aetiology of PD this process may spiral out of control with over activation of microglia, over production of cytokines and other proinflammatory mediators as well as the release of destructive molecules such as reactive oxygen species. Given that dopaminergic neurons in the substantia nigra are relatively vulnerable to 'stress' and the region has a large population of microglia in comparison to other CNS structures, these events may easily trigger neurodegeneration. These factors are examined in this review along with a consideration of the possible use of anti-inflammatory drugs in PD.

Divergent roles for tumor necrosis factor-alpha in the brain

Proinflammatory cytokines and chemokines have been implicated in the pathogenesis of several neurological and neurodegenerative disorders. Prominent among such factors is the pleiotropic cytokine, tumor necrosis factor (TNF)-alpha. Under normal physiological conditions, TNF-alpha orchestrates a diverse array of functions involved in immune surveillance and defense, cellular homeostasis, and protection against certain neurological insults. However, paradoxical effects of this cytokine have been observed. TNF-alpha is elicited in the brain following injury (ischemia, trauma), infection (HIV, meningitis), neurodegeneration (Alzheimer's, Parkinson's), and chemically induced neurotoxicity. The multifarious identity for this cytokine appears to be influenced by several mechanisms. Among the most prominent are the regulation of TNFalpha-induced NF-kappaB activation by adapter proteins such as TRADD and TRAF, and second, the heterogeneity of microglia and their distribution pattern across brain regions. Here, we review the differential role of TNF-alpha in response to brain injury, with emphasis on neurodegeneration, and discuss the possible mechanisms for such diverse and region-specific effects.