Peripheral nervous system involvement in Parkinson's disease: evidence and controversies

Astragaloside depresses compound action potential in sciatic nerve of frogs involved in L-type Ca2+-channel dependent mechanism

The sciatic nerve is the largest sensorimotor nerve within the peripheral nervous system (PNS), possessing the ability to produce endogenous neurotrophins. Compound nerve action potentials (CNAPs) are regarded as a physiological/pathological indicator to identify nerve activity in signal transduction of the PNS. Astragaloside (AST), a small-molecule saponin purified from Astragalus membranaceus, is widely used to treat chronic disease. Nonetheless, the regulatory effects of AST on the sciatic nerve remain unknown. Therefore, the present investigation was undertaken to study the effect of AST on CNAPs of frog sciatic nerves. Here, AST depressed the conduction velocity and amplitude of CNAPs. Importantly, the AST-induced responses could be blocked by a Ca2+-free medium, or by applying all Ca2+ channel antagonists (CdCl2/LaCl3) or L-type Ca2+ channel blockers (nifedipine/diltiazem), but not the T-type and P-type Ca2+ channel antagonist (NiCl2). Altogether, these findings suggested that AST may attenuate the CNAPs of frog sciatic nerves in vitro via the L-type Ca2+-channel dependent mechanisms.

No Evidence of Sensory Neuropathy in a Traditional Mouse Model of Idiopathic Parkinson's Disease

Parkinson's disease (PD) is the second-most common neurodegenerative disorder worldwide and is diagnosed based on motor impairments. Non-motor symptoms are also well-recognised in this disorder, and peripheral neuropathy is a frequent but poorly appreciated non-motor sign. Studying how central and peripheral sensory systems are affected can contribute to the development of targeted therapies and deepen our understanding of the pathophysiology of PD. Although the cause of sporadic PD is unknown, chronic exposure to the pesticide rotenone in humans increases the risk of developing the disease. Here, we aimed to investigate whether peripheral neuropathy is present in a traditional model of PD. Mice receiving intrastriatal rotenone showed greatly reduced dopamine terminals in the striatum and a reduction in tyrosine hydroxylase-positive neurons in the Substantia nigra pars compacta and developed progressive motor impairments in hindlimb stepping and rotarod but no change in spontaneous activity. Interestingly, repeated testing using gold-standard protocols showed no change in gut motility, a well-known non-motor symptom of PD. Importantly, we did not observe any change in heat, cold, or touch sensitivity, again based upon repeated testing with well-validated protocols that were statistically well powered. Therefore, this traditional model fails to replicate PD, and our data again reiterate the importance of the periphery to the disorder.

Parkinson's disease and vitamins: a focus on vitamin B12

Parkinson's disease (PD) has been linked to a vast array of vitamins among which vitamin B12 (Vit B12) is the most relevant and often investigated specially in the context of intrajejunal levodopa infusion therapy. Vit B12 deficiency, itself, has been reported to cause acute parkinsonism. Nevertheless, concrete mechanisms through which B12 deficiency interacts with PD in terms of pathophysiology, clinical manifestation and progression remains unclear. Recent studies have suggested that Vit B12 deficiency along with the induced hyperhomocysteinemia are correlated with specific PD phenotypes characterized with early postural instability and falls and more rapid motor progression, cognitive impairment, visual hallucinations and autonomic dysfunction. Specific clinical features such as polyneuropathy have also been linked to Vit B12 deficiency specifically in context of intrajejunal levodopa therapy. In this review, we explore the link between Vit B12 and PD in terms of physiopathology regarding dysfunctional neural pathways, neuropathological processes as well as reviewing the major clinical traits of Vit B12 deficiency in PD and Levodopa-mediated neuropathy. Finally, we provide an overview of the therapeutic effect of Vit B12 supplementation in PD and posit a practical guideline for Vit B12 testing and supplementation.

Imbalance and gait impairment in Parkinson's disease: discussing postural instability and ataxia

Gait and balance difficulties pose significant clinical challenges in Parkinson's disease (PD). The impairment of physiological mechanisms responsible for maintaining natural orthostatism plays a central role in the pathophysiology of postural instability observed in PD. In addition to the well-known rigidity and abnormalities in muscles and joints, various brain regions involved in the regulation of posture, balance, and gait, such as the basal ganglia, cerebellum, and brainstem regions like the pontine peduncle nucleus, are affected in individuals with PD. The recognition of the cerebellum's role in PD has been increasingly acknowledged. Cortical areas and their connections are associated with freezing of gait, a type of frontal lobe ataxia commonly observed in PD. Furthermore, impairments in the peripheral nervous system, including those caused by levodopatherapy, can contribute to gait impairment and imbalance in PD patients. Consequently, individuals with PD may exhibit frontal ataxia, sensory ataxia, and even cerebellar ataxia as underlying causes of gait disturbances and imbalance, starting from the early stages of the disease. The complex interplay between dysfunctional brain regions, impaired cortical connections, and peripheral nervous system abnormalities contributes to the multifaceted nature of gait and balance difficulties in PD. Understanding the intricate mechanisms is crucial for the development of effective therapeutic approaches targeting these specific deficits in PD.

Mechanisms of Swallowing, Speech and Voice Disorders in Parkinson's Disease: Literature Review with Our First Evidence for the Periperal Nervous System Involvement

The majority of patients with Parkinson's disease (PD) develop swallowing, speech, and voice (SSV) disorders. Importantly, swallowing difficulty or dysphagia and related aspiration are life-threatening conditions for PD patients. Although PD treatments have significant therapeutic effects on limb motor function, their effects on SSV disorders are less impressive. A large gap in our knowledge is that the mechanisms of SSV disorders in PD are poorly understood. PD was long considered to be a central nervous system disorder caused by the death of dopaminergic neurons in the basal ganglia. Aggregates of phosphorylated α-synuclein (PAS) underlie PD pathology. SSV disorders were thought to be caused by the same dopaminergic problem as those causing impaired limb movement; however, there is little evidence to support this. The pharynx, larynx, and tongue play a critical role in performing upper airway (UA) motor tasks and their dysfunction results in disordered SSV. This review aims to provide an overview on the neuromuscular organization patterns, functions of the UA structures, clinical features of SSV disorders, and gaps in knowledge regarding the pathophysiology underlying SSV disorders in PD, and evidence supporting the hypothesis that SSV disorders in PD could be associated, at least in part, with PAS damage to the peripheral nervous system controlling the UA structures. Determining the presence and distribution of PAS lesions in the pharynx, larynx, and tongue will facilitate the identification of peripheral therapeutic targets and set a foundation for the development of new therapies to treat SSV disorders in PD.

Regulatory effect of bacterial melanin on the isoforms of new superoxide-producing associates from rat tissues in rotenone-induced Parkinson's disease

According to recent research, selective neuronal vulnerability in Parkinson's disease (PD) results from several phenotypic traits, including calcium-dependent, feed-forward control of mitochondrial respiration leading to elevated reactive oxygen species and cytosolic calcium concentration, an extensive axonal arbor, and a reactive neurotransmitter. Therefore, antioxidant therapy is a promising direction in the treatment of PD. In vitro studies have indicated the survival-promoting activity of bacterial melanin (BM) on midbrain dopaminergic neuron cultures. It has been established that BM has a number of protective and anti-inflammatory properties, so there is a high probability of a protective effect of BM in the early stages of PD. In this study, PD was induced through the unilateral intracerebral administration of rotenone followed by bacterial melanin. Tissues (brain, lungs, and small intestine) from the observed groups underwent isolation and purification to extract isoforms of new thermostable superoxide (О2-)-producing associates between NADPH-containing lipoprotein (NLP) and NADPH oxidase-Nox (NLP-Nox). The optical absorption spectral characteristics, specific amounts, stationary concentration of the produced О2-, and the content of NADPH in the observed associates were determined. The optical absorption spectra of the NLP-Nox isoforms in the visible and UV regions in the experimental groups did not differ from those of the control group. However, compared with the control group, the specific content of the total fractions of NLP-Nox isoforms associated with PD groups was higher, especially in the small intestine. These findings suggest that the described changes may represent a novel mechanism for rotenone-induced PD. Furthermore, bacterial melanin demonstrated antioxidant properties and regulated membrane formation in the brain, lung, and small intestine. This regulation occurred by inhibiting the release of new membrane-bound formations (NLP-Nox associates) from these membranes while simultaneously regulating the steady-state concentration of the formed О2-.

A systematic review of the potential consequences of abnormal serum levels of vitamin B6 in people living with Parkinson's disease

The prevalences of polyneuropathy and epilepsy are higher in people living with Parkinson's disease (PwPD) when compared to older adults. Vitamin B6 is widely available and affordable. PwPD are at higher risk of having abnormal serum levels of vitamin B6, which are associated with polyneuropathy and epilepsy that are potentially preventable and treatable. Potential contributors to abnormal B6 levels in PwPD include age, dietary habits, vitamin supplement misuse, gastrointestinal dysfunction and complex interactions with levodopa. The literature on the potential consequences of abnormal B6 levels in PwPD is limited by a small number of observational studies focused on polyneuropathy and epilepsy. Abnormal B6 levels have been reported in 60 of 145 PwPD (41.4% relative frequency). Low B6 levels were reported in 52 PwPD and high B6 levels were reported in 8 PwPD. There were 14 PwPD, polyneuropathy and low B6. There were 4 PwPD, polyneuropathy and high B6. There were 4 PwPD, epilepsy and low B6. Vitamin B6 level was low in 44.6% of PwPD receiving levodopa-carbidopa intestinal gel and in 30.1% of PwPD receiving oral levodopa-carbidopa. In almost all studies reporting low B6 in PwPD receiving oral levodopa-carbidopa, the dose of levodopa was ≥1000 mg/day. Rigorous epidemiological studies will clarify the prevalence, natural history and clinical relevance of abnormal serum levels of vitamin B6 in PwPD. These studies should account for diet, vitamin supplement use, gastrointestinal dysfunction, concurrent levels of vitamin B12, folate, homocysteine and methylmalonic acid, formulations and dosages of levodopa and other medications commonly used in PwPD.

The PROB-PD trial: a pilot, randomised, placebo-controlled study protocol to evaluate the feasibility and potential efficacy of probiotics in modulating peripheral immunity in subjects with Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is a common neurodegenerative disease. No disease-modifying treatment is available, and therapy is symptomatic. The histopathologic hallmark is the loss of dopaminergic neurons and accumulation of α-synuclein (α-syn) in surviving neurons, but the underlying pathophysiology is unclear. Inflammatory mechanisms seem to play a prominent role, with an imbalance of immune functions and neurotoxicity caused by reactive oxygen species (ROS). Involvement of peripheral adaptive immunity, with an imbalance in T cell subpopulations and in the expression of transcriptional factors in CD4+ T cells, has also been reported. Although clinical presentation is defined by motor symptoms, patients also report non-motor symptoms, often before the onset of a clinically established disease. Etiopathogenesis of PD is unknown, but an initial aggregation of α-syn in the gut, with subsequent propagation along the vagus nerve to the brain has been hypothesised. Interestingly, in an α-syn overexpressing murine model, the absence of gut microbiota prevented both microglia activation and motor impairment, thus pointing to a fundamental role of microbiota in the development of PD. Magistrelli et al. showed that in peripheral blood mononuclear cells of PD patients, probiotics modulate the in vitro production of cytokines toward an anti-inflammatory profile and reduce the production of ROS.

METHODS

This is a pilot randomised placebo-controlled clinical trial protocol for a 12-week treatment with probiotics. At least 80 patients affected by PD will be recruited and randomly allocated to either the treatment or placebo group in a 1:1 ratio. General inclusion criteria will be the onset of PD 2 to 5 years before the trial and absence of autoimmune comorbidities or immunomodulating therapy. Our primary endpoint is the assessment of changes in extracellular cytokine levels (Interferon (IFN)-γ, tumour necrosis factor (TNF)-α, interleukin (IL)-4, and IL-10) and ROS production. Secondary outcomes include changes in lymphocyte subpopulations and transcriptional factors mRNA levels.

DISCUSSION

This study is designed to highlight the potential beneficial role of probiotics administration on peripheral immunity through the modulation of gut microbiota. Explorative outcomes will be evaluated to assess variations in motor and non-motor symptoms and the possible correlation with probiotics administration.

TRIAL REGISTRATION

ClinicalTrials.gov ID NCT05173701. Registered 08 November 2021.

Current Treatments and New, Tentative Therapies for Parkinson’s Disease

Parkinson’s disease (PD) is a neurodegenerative pathology, the origin of which is associated with the death of neuronal cells involved in the production of dopamine. The prevalence of PD has increased exponentially. The aim of this review was to describe the novel treatments for PD that are currently under investigation and study and the possible therapeutic targets. The pathophysiology of this disease is based on the formation of alpha-synuclein folds that generate Lewy bodies, which are cytotoxic and reduce dopamine levels. Most pharmacological treatments for PD target alpha-synuclein to reduce the symptoms. These include treatments aimed at reducing the accumulation of alpha-synuclein (epigallocatechin), reducing its clearance via immunotherapy, inhibiting LRRK2, and upregulating cerebrosidase (ambroxol). Parkinson’s disease continues to be a pathology of unknown origin that generates a significant social cost for the patients who suffer from it. Although there is still no definitive cure for this disease at present, there are numerous treatments available aimed at reducing the symptomatology of PD in addition to other therapeutic alternatives that are still under investigation. However, the therapeutic approach to this pathology should include a combination of pharmacological and non-pharmacological strategies to maximise outcomes and improve symptomatological control in these patients. It is therefore necessary to delve deeper into the pathophysiology of the disease in order to improve these treatments and therefore the quality of life of the patients.

Serum biomarkers of liver fibrosis identify globus pallidus vulnerability

The CNS manifestation of chronic liver disease can include magnetic resonance (MR) signal hyperintensities in basal ganglia structures. Here, relations between liver (serum-derived fibrosis scores) and brain (regional T1-weighted signal intensities and volumes) integrity were evaluated in a sample of 457 individuals including those with alcohol use disorders (AUD), people living with human immunodeficiency virus (HIV), those comorbid for AUD and HIV, and healthy controls. Liver fibrosis was identified from cutoff scores as follows: aspartate aminotransferase to platelet ratio index (APRI) > 0.7 in 9.4% (n = 43) of the cohort; fibrosis score (FIB4) > 1.5 in 28.0% (n = 128) of the cohort; and non-alcoholic fatty liver disease fibrosis score (NFS) > -1.4 in 30.2% (n = 138) of the cohort. Presence of serum-derived liver fibrosis was associated with high signal intensities selective to basal ganglia (i.e., caudate, putamen, and pallidum) structures. High signal intensities in the pallidum, however, explained a significant portion of the variance in APRI (25.0%) and FIB4 (23.6%) cutoff scores. Further, among the regions evaluated, only the globus pallidus showed a correlation between greater signal intensity and smaller volume (r = -0.44, p <.0001). Finally, higher pallidal signal intensity correlated worse ataxia (eyes open ρ = -0.23, p =.0002; eyes closed ρ = -0.21, p =.0005). This study suggests that clinically relevant serum biomarkers of liver fibrosis such as the APRI may identify individuals vulnerable to globus pallidus pathology and contribute to problems with postural balance.

Probing cellular health at the muscle level-Multi-frequency bioimpedance in Parkinson's disease

Bioimpedance (mfBIA) non-invasively assesses cellular muscle health. Our aim was to explore whether mfBIA captures abnormal cellular muscle health in patients with Parkinson's Disease (PD) and how such changes are modulated with the use of Parkinson's medication. In patients with PD (n = 20) mfBIA measurements were made of biceps brachii, triceps, and extensor carpi radialis longus muscles of the more affected arm whilst at rest, using a mobile mfBIA device (IMPEDIMED, Australia). mfBIA and assessment of motor symptoms were performed in a pragmatic off-medication state, as well as one and 3 h after oral intake of 200 mg levodopa. Age and sex-matched healthy subjects (HC; n = 20) served as controls. PD and HC mfBIA parameters were compared by applying an unpaired two-tailed adjusted t-test and ANOVA with Tukey's correction for multiple comparisons (p ≤ 0.05). The PD group consisted of 13 men (71 ± 17 years) and 7 women (65 ± 7 years). Independent of medication, internal (Ri ) and external resistance (Re ) were found to be significantly higher, and membrane capacitance (Mc) significantly lower, in m.biceps brachii in PD subjects compared to HC. Center frequency (fc) was significantly higher in m.biceps brachii of PD subjects in the "medication-off" state. There was no difference between PD and HC in mfBIA parameters in the measured extensor muscles. The upper limb flexor muscle shows a difference in mfBIA parameters in PD compared to HC. mfBIA may be useful in the diagnosis and assessment of PD patients and is objective, non-invasive, reliable, and easy to use.

Corneal confocal microscopy differentiates patients with Parkinson’s disease with and without autonomic involvement

Autonomic dysregulation in Parkinson’s disease (PD) can precede motor deficits and is associated with reduced quality of life, disease progression, and increased mortality. Objective markers of autonomic involvement in PD are limited. Corneal confocal microscopy (CCM) is a rapid ophthalmic technique that can quantify small nerve damage in a range of peripheral and autonomic neuropathies. Here we investigated whether CCM can be used to assess autonomic symptoms in PD. Based on the scale for outcomes in Parkinson’s disease for autonomic symptoms (SCOPA-AUT), patients with PD were classified into those without autonomic symptoms (AutD-N), with single (AutD-S), and multiple (AutD-M) domain autonomic dysfunction. Corneal nerve fiber pathology was quantified using CCM, and the relationship with autonomic symptoms was explored. The study enrolled 71 PD patients and 30 control subjects. Corneal nerve fiber density (CNFD), corneal nerve branch density (CNBD), corneal nerve fiber length (CNFL), and CNBD/CNFD ratio were lower in PD patients with autonomic symptoms compared to those without autonomic symptoms. Autonomic symptoms correlated positively with CNFD (r = −0.350, p = 0.004), and were not related to Levodopa equivalent daily dose (r = 0.042, p = 0.733) after adjusting for age, disease severity, disease duration or cognitive function. CCM parameters had high sensitivity and specificity in distinguishing patients with PD with and without autonomic symptoms. PD patients with autonomic symptoms have corneal nerve loss, and CCM could serve as an objective ophthalmic imaging technique to identify patients with PD and autonomic symptoms.

Effect of Parkinson’s Disease on Cardio-postural Coupling During Orthostatic Challenge

Cardiac baroreflex and leg muscles activation are two important mechanisms for blood pressure regulation, failure of which could result in syncope and falls. Parkinson’s disease is known to be associated with cardiac baroreflex impairment and skeletal muscle dysfunction contributing to falls. However, the mechanical effect of leg muscles contractions on blood pressure (muscle-pump) and the baroreflex-like responses of leg muscles to blood pressure changes is yet to be comprehensively investigated. In this study, we examined the involvement of the cardiac baroreflex and this hypothesized reflex muscle-pump function (cardio-postural coupling) to maintain blood pressure in Parkinson’s patients and healthy controls during an orthostatic challenge induced via a head-up tilt test. We also studied the mechanical effect of the heart and leg muscles contractions on blood pressure. We recorded electrocardiogram blood pressure and electromyogram from 21 patients with Parkinson’s disease and 18 age-matched healthy controls during supine, head-up tilt at 70°, and standing positions with eyes open. The interaction and bidirectional causalities between the cardiovascular and musculoskeletal signals were studied using wavelet transform coherence and convergent cross mapping techniques, respectively. Parkinson’s patients displayed an impaired cardiac baroreflex and a reduced mechanical effect of the heart on blood pressure during supine, tilt and standing positions. However, the effectiveness of the cardiac baroreflex decreased in both Parkinson’s patients and healthy controls during standing as compared to supine. In addition, Parkinson’s patients demonstrated cardio-postural coupling impairment along with a mechanical muscle pump dysfunction which both could lead to dizziness and falls. Moreover, the cardiac baroreflex had a limited effect on blood pressure during standing while lower limb muscles continued to contract and maintain blood pressure via the muscle-pump mechanism. The study findings highlighted altered bidirectional coupling between heart rate and blood pressure, as well as between muscle activity and blood pressure in Parkinson’s disease. The outcomes of this study could assist in the development of appropriate physical exercise programs to reduce falls in Parkinson’s disease by monitoring the cardiac baroreflex and cardio-postural coupling effect on maintaining blood pressure.

Peripheral neuropathy in Parkinson's disease: prevalence and functional impact on gait and balance

Peripheral neuropathy is a common problem in patients with Parkinson's disease. Peripheral neuropathy's prevalence in Parkinson's disease varies between 4.8-55%, compared with 9% in the general population. It remains unclear whether peripheral neuropathy leads to decreased motor performance in Parkinson's disease, resulting in impaired mobility and increased balance deficits. We aimed to determine the prevalence and type of peripheral neuropathy in Parkinson's disease patients and evaluate its functional impact on gait and balance. A cohort of consecutive Parkinson's disease patients assessed by movement disorders specialists based on the UK Brain Bank criteria underwent clinical, neurophysiological (nerve conduction studies and quantitative sensory testing) and neuropathological (intraepidermal nerve fibre density in skin biopsy punches) evaluation to characterize the peripheral neuropathy type and aetiology using a cross-sectional design. Gait and balance were characterized using wearable health-technology in OFF and ON medication states, and the main parameters were extracted using validated algorithms. A total of 99 Parkinson's disease participants with a mean age of 67.2 (±10) years and mean disease duration of 6.5 (±5) years were assessed. Based on a comprehensive clinical, neurophysiological and neuropathological evaluation, we found that 40.4% of Parkinson's disease patients presented peripheral neuropathy, with a predominance of small fibre neuropathy (70% of the group). In the OFF state, the presence of peripheral neuropathy was significantly associated with shorter stride length (P = 0.029), slower gait speed (P = 0.005) and smaller toe-off angles (P = 0.002) during straight walking; significantly slower speed (P = 0.019) and smaller toe-off angles (P = 0.007) were also observed during circular walking. In the ON state, the above effects remained, albeit moderately reduced. With regard to balance, significant differences between Parkinson's disease patients with and without peripheral neuropathy were observed in the OFF medication state during stance with closed eyes on a foam surface. In the ON states, these differences were no longer observable. We showed that peripheral neuropathy is common in Parkinson's disease and influences gait and balance parameters, as measured with mobile health-technology. Our study supports that peripheral neuropathy recognition and directed treatment should be pursued in order to improve gait in Parkinson's disease patients and minimize balance-related disability, targeting individualized medical care.

Polyneuropathy monitoring in Parkinson's disease patients treated with levodopa/carbidopa intestinal gel

OBJECTIVES

Levodopa-carbidopa-intestinal-gel (LCIG) infusion is an effective treatment for advanced PD with motor fluctuations. Polyneuropathy occurs as a complication in 10-15% of patients. We wanted to assess the frequency of polyneuropathy in Finnish advanced Parkinson's disease (PD) patients with continuous LCIG infusion, and the value of different clinical monitoring parameters during follow-up.

MATERIALS AND METHODS

Patient records of PD patients started on LCIG infusion at Helsinki University Hospital who received nerve conduction studies at baseline and 6 months after treatment initiation were reviewed for epidemiological information, mini mental state examination, baseline and 6 months' UPRDS-III, weight, body mass index, levodopa dose (LD), plasma homocysteine levels, folate, vitamin B6 and B12.

RESULTS

Out of 19 patients (n = 6 on B-vitamin substitution), two (10.5%) developed new-onset polyneuropathy after initiation of LCIG therapy (n = 0 with vitamin substitution). Neuropathy was associated with significant weight loss (BMI reduction > 1.5), but not with other monitoring parameters. Homocysteine rose significantly in patients not substituted with B-vitamin complex, but not in patients with B-vitamin substitution. Homocysteine changes correlated with LD changes in the absence of vitamin B substitution. After oral B-vitamin substitution, both patients' polyneuropathy remained electrophysiologically and clinically stable.

CONCLUSIONS

Rates of polyneuropathy in Finnish PD patients with LCIG treatment are comparable to previous studies. Patients' weight should be included in regular follow up monitoring and can be used for patient self-monitoring. Vitamin B substitution appears to reduce coupling between levodopa dose and homocysteine and may be useful to prevent polyneuropathy related to LCIG.

Roles of α‑synuclein in gastrointestinal microbiome dysbiosis‑related Parkinson's disease progression (Review)

Parkinson's disease (PD) is the second most common neurodegenerative disease amongst the middle-aged and elderly populations. Several studies have confirmed that the microbiota-gut-brain axis (MGBA) serves a key role in the pathogenesis of PD. Changes to the gastrointestinal microbiome (GM) cause misfolding and abnormal aggregation of α-synuclein (α-syn) in the intestine. Abnormal α-syn is not eliminated via physiological mechanisms and is transported into the central nervous system (CNS) via the vagus nerve. The abnormal levels of α-syn aggregate in the substantia nigra pars compacta, not only leading to the formation of eosinophilic Lewis Bodies in the cytoplasm and mitochondrial dysfunction in dopaminergic (DA) neurons, but also leading to the stimulation of an inflammatory response in the microglia. These pathological changes result in an increase in oxidative stress (OS), which triggers nerve cell apoptosis, a characteristic of PD. This increase in OS further oxidizes and intensifies abnormal aggregation of α-syn, eventually forming a positive feedback loop. The present review discusses the abnormal accumulation of α-syn in the intestine caused by the GM changes and the increased levels of α-syn transport to the CNS via the MGBA, resulting in the loss of DA neurons and an increase in the inflammatory response of microglial cells in the brain of patients with PD. In addition, relevant clinical therapeutic strategies for improving the GM and reducing α-syn accumulation to relieve the symptoms and progression of PD are described.

The Impact of SNCA Variations and Its Product Alpha-Synuclein on Non-Motor Features of Parkinson's Disease

Parkinson’s disease (PD) is a common and progressive neurodegenerative disease, caused by the loss of dopaminergic neurons in the substantia nigra pars compacta in the midbrain, which is clinically characterized by a constellation of motor and non-motor manifestations. The latter include hyposmia, constipation, depression, pain and, in later stages, cognitive decline and dysautonomia. The main pathological features of PD are neuronal loss and consequent accumulation of Lewy bodies (LB) in the surviving neurons. Alpha-synuclein (α-syn) is the main component of LB, and α-syn aggregation and accumulation perpetuate neuronal degeneration. Mutations in the α-syn gene (SNCA) were the first genetic cause of PD to be identified. Generally, patients carrying SNCA mutations present early-onset parkinsonism with severe and early non-motor symptoms, including cognitive decline. Several SNCA polymorphisms were also identified, and some of them showed association with non-motor manifestations. The functional role of these polymorphisms is only partially understood. In this review we explore the contribution of SNCA and its product, α-syn, in predisposing to the non-motor manifestations of PD.

Oral subchronic exposure to the mycotoxin ochratoxin A induces key pathological features of Parkinson's disease in mice six months after the end of the treatment

Some epidemiological studies with different levels of evidence have pointed to a higher risk of Parkinson's disease (PD) after exposure to environmental toxicants. A practically unexplored potential etiological factor is a group of naturally-occurring fungal secondary metabolites called mycotoxins. The mycotoxin ochratoxin A (OTA) has been reported to be neurotoxic in mice. To further identify if OTA exposure could have a role in PD pathology, Balb/c mice were orally treated with OTA (0.21, 0.5 mg/kg bw) four weeks and left for six months under normal diet. Effects of OTA on the onset, progression of alpha-synuclein pathology and development of motor deficits were evaluated. Immunohistochemical and biochemical analyses showed that oral subchronic OTA treatment induced loss of striatal dopaminergic innervation and dopaminergic cell dysfunction responsible for motor impairments. Phosphorylated alpha-synuclein levels were increased in gut and brain. LAMP-2A protein was decreased in tissues showing alpha-synuclein pathology. Cell cultures exposed to OTA exhibited decreased LAMP-2A protein, impairment of chaperone-mediated autophagy and decreased alpha-synuclein turnover which was linked to miRNAs deregulation, all reminiscent of PD. These results support the hypothesis that oral exposure to low OTA doses in mice can lead to biochemical and pathological changes reported in PD.

Role of the Peripheral Nervous System in PD Pathology, Diagnosis, and Treatment

Studies on Parkinson disease (PD) have mostly focused on the central nervous system—specifically, on the loss of mesencephalic dopaminergic neurons and associated motor dysfunction. However, the peripheral nervous system (PNS) is gaining prominence in PD research, with increasing clinical attention being paid to non-motor symptoms. Researchers found abnormal deposition of α-synuclein and neuroinflammation in the PNS. Attempts have been made to use these pathological changes during the clinical diagnosis of PD. Animal studies demonstrated that combined transplantation of autologous peripheral nerves and cells with tyrosine hydroxylase activity can reduce dopaminergic neuronal damage, and similar effects were observed in some clinical trials. In this review, we will systematically explain PNS performance in PD pathology and its clinical diagnostic research, describe PNS experimental results [especially Schwann cell (SC) transplantation in the treatment of PD animal models] and the results of clinical trials, and discuss future directions. The mechanism by which SCs produce such a therapeutic effect and the safety of transplantation therapy are briefly described.

A Pilot Study of Changes in the Level of Catecholamines and the Activity of α-2-Macroglobulin in the Tear Fluid of Patients with Parkinson's Disease and Parkinsonian Mice

Development of differential and early (preclinical) diagnostics of Parkinson’s disease (PD) is among the priorities in neuroscience. We searched for changes in the level of catecholamines and α-2-macroglobulin activity in the tear fluid (TF) in PD patients at an early clinical stage. It was shown that TF in patients is characterized by an increased level of noradrenaline mainly on the ipsilateral side of pronounced motor symptoms (72%, p = 0.049), a decreased level of adrenaline on both sides (ipsilateral—53%, p = 0.004; contralateral—42%, p = 0.02), and an increased α-2-macroglobulin activity on both sides (ipsilateral—53%, p = 0.03; contralateral—56%, p = 0.037) compared to controls. These changes are considered as potential biomarkers for differential diagnosis. Similar changes in the TF were found in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice when modeling clinical and preclinical stages of PD. These data show the adequacy of models to the pathogenesis of PD along the selected metabolic pathways, and also suggest that the found TF changes can be considered as potential biomarkers for preclinical diagnosis of PD. In Parkinsonian mice, the level of catecholamines also changes in the lacrimal glands, which makes it possible to consider them as one of the sources of catecholamines in the TF.

The Effect of Parkinson's Disease on Otoacoustic Emissions and Efferent Suppression of Transient Evoked Otoacoustic Emissions

Purpose Several studies have demonstrated increased auditory thresholds in patients with Parkinson's disease (PD) based on subjective tonal audiometry. However, the pathophysiological mechanisms underlying auditory dysfunction in PD remain elusive. The primary aim of this study was to investigate cochlear and olivocochlear function in PD using objective measurements and to assess the effect of dopaminergic medication on auditory function. Method Eighteen patients with PD and 18 gender- and age-matched healthy controls (HCs) were included. Patients with PD participated in medication on and off conditions. Linear mixed models were used to determine the effect of PD on tonal audiometry, transient evoked and distortion product otoacoustic emissions (OAEs), and efferent suppression (ES). Results Tonal audiometry revealed normal auditory thresholds in patients with PD for their age across all frequencies. OAE signal amplitudes demonstrated a significant interaction effect between group (PD vs. HC) and frequency, indicating decreased OAEs at low frequencies and increased OAEs at high frequencies in patients with PD. No significant differences were found between patients with PD and HCs regarding ES. In addition, no significant effect of medication status was found on auditory measurements in patients with PD. Conclusions Altered OAEs support the hypothesis of cochlear alterations in PD. No evidence was found for the involvement of the medial olivocochlear system. Altogether, OAEs may provide an objective early indicator of auditory alterations in PD and should complement subjective tonal audiometry when assessing and monitoring auditory function in PD.

Mechanisms of Neurodegeneration in Various Forms of Parkinsonism-Similarities and Differences

Parkinson’s disease (PD), dementia with Lewy body (DLB), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD) and multiple system atrophy (MSA) belong to a group of neurodegenerative diseases called parkinsonian syndromes. They share several clinical, neuropathological and genetic features. Neurodegenerative diseases are characterized by the progressive dysfunction of specific populations of neurons, determining clinical presentation. Neuronal loss is associated with extra- and intracellular accumulation of misfolded proteins. The parkinsonian diseases affect distinct areas of the brain. PD and MSA belong to a group of synucleinopathies that are characterized by the presence of fibrillary aggregates of α-synuclein protein in the cytoplasm of selected populations of neurons and glial cells. PSP is a tauopathy associated with the pathological aggregation of the microtubule associated tau protein. Although PD is common in the world’s aging population and has been extensively studied, the exact mechanisms of the neurodegeneration are still not fully understood. Growing evidence indicates that parkinsonian disorders to some extent share a genetic background, with two key components identified so far: the microtubule associated tau protein gene (MAPT) and the α-synuclein gene (SNCA). The main pathways of parkinsonian neurodegeneration described in the literature are the protein and mitochondrial pathways. The factors that lead to neurodegeneration are primarily environmental toxins, inflammatory factors, oxidative stress and traumatic brain injury.

Trans-synaptic spreading of alpha-synuclein pathology through sensory afferents leads to sensory nerve degeneration and neuropathic pain

Pain is a common non-motor symptom of Parkinson’s disease (PD), with current limited knowledge of its pathophysiology. Here, we show that peripheral inoculation of mouse alpha-synuclein (α-Syn) pre-formed fibrils, in a transgenic mouse model of PD, elicited retrograde trans-synaptic spreading of α-Syn pathology (pSer129) across sensory neurons and dorsal nerve roots, reaching central pain processing regions, including the spinal dorsal horn and the projections of the anterolateral system in the central nervous system (CNS). Pathological peripheral to CNS propagation of α-Syn aggregates along interconnected neuronal populations within sensory afferents, was concomitant with impaired nociceptive response, reflected by mechanical allodynia, reduced nerve conduction velocities (sensory and motor) and degeneration of small- and medium-sized myelinated fibers. Our findings show a link between the transneuronal propagation of α-Syn pathology with sensory neuron dysfunction and neuropathic impairment, suggesting promising avenues of investigation into the mechanisms underlying pain in PD.

Functional characterization of extrinsic tongue muscles in the Pink1-/- rat model of Parkinson disease

Parkinson disease (PD) is associated with speech and swallowing difficulties likely due to pathology in widespread brain and nervous system regions. In post-mortem studies of PD, pathology has been reported in pharyngeal and laryngeal nerves and muscles. However, it is unknown whether PD is associated with neuromuscular changes in the tongue. Prior work in a rat model of PD (Pink1-/-) showed oromotor and swallowing deficits in the premanifest stage which suggested sensorimotor impairments of these functions. The present study tested the hypothesis that Pink1-/- rats show altered tongue function coinciding with neuromuscular differences within tongue muscles compared to wildtype (WT). Male Pink1-/- and WT rats underwent behavioral tongue function assays at 4 and 6 months of age (n = 7–8 rats per group), which are time points early in the disease. At 6 months, genioglossus (GG) and styloglossus (SG) muscles were analyzed for myosin heavy chain isoforms (MyHC), α-synuclein levels, myofiber size, centrally nucleated myofibers, and neuromuscular junction (NMJ) innervation. Pink1-/- showed greater tongue press force variability, and greater tongue press forces and rates as compared to WT. Additionally, Pink1-/- showed relative increases of MyHC 2a in SG, but typical MyHC profiles in GG. Western blots revealed Pink1-/- had more α-synuclein protein than WT in GG, but not in SG. There were no differences between Pink1-/- and WT in myofiber size, centrally-nucleated myofibers, or NMJ innervation. α-synuclein protein was observed in nerves, NMJ, and vessels in both genotypes. Findings at these early disease stages suggest small changes or no changes in several peripheral biological measures, and intact motor innervation of tongue muscles. Future work should evaluate these measures at later disease stages to determine when robust pathological peripheral change contributes to functional change, and what CNS deficits cause behavioral changes. Understanding how PD affects central and peripheral mechanisms will help determine therapy targets for speech and swallowing disorders.

Gut-Brain Axis: Role of Gut Microbiota on Neurological Disorders and How Probiotics/Prebiotics Beneficially Modulate Microbial and Immune Pathways to Improve Brain Functions

The gut microbiome acts as an integral part of the gastrointestinal tract (GIT) that has the largest and vulnerable surface with desirable features to observe foods, nutrients, and environmental factors, as well as to differentiate commensals, invading pathogens, and others. It is well-known that the gut has a strong connection with the central nervous system (CNS) in the context of health and disease. A healthy gut with diverse microbes is vital for normal brain functions and emotional behaviors. In addition, the CNS controls most aspects of the GI physiology. The molecular interaction between the gut/microbiome and CNS is complex and bidirectional, ensuring the maintenance of gut homeostasis and proper digestion. Besides this, several mechanisms have been proposed, including endocrine, neuronal, toll-like receptor, and metabolites-dependent pathways. Changes in the bidirectional relationship between the GIT and CNS are linked with the pathogenesis of gastrointestinal and neurological disorders; therefore, the microbiota/gut-and-brain axis is an emerging and widely accepted concept. In this review, we summarize the recent findings supporting the role of the gut microbiota and immune system on the maintenance of brain functions and the development of neurological disorders. In addition, we highlight the recent advances in improving of neurological diseases by probiotics/prebiotics/synbiotics and fecal microbiota transplantation via the concept of the gut-brain axis.

Contribution of functional dopamine D2 and D3 receptor variants to motor and non-motor symptoms of early onset Parkinson's disease

In the present study, we focused on investigating the contribution of functional dopamine D2 and D3 receptor variants to motor and/or non-motor symptoms of early onset Parkinson's disease (EOPD). Three functional single nucleotide polymorphisms (SNPs), DRD3 rs6280, DRD2 rs2283265 and DRD2 rs1076560, were genotyped in 128 Turkish EOPD patients and then, statistical analysis was conducted for the potential impacts of SNPs on clinical parameters. All three SNPs were found to be statistically significant in terms of PD-related pain: DRD3 [rs6280; risk allele "T" for pain; p = 0.031; odds ratio (OR)=4.25], DRD2 [rs2283265; risk allele "A" for pain; p = 0.001; OR=8.47] and, DRD2 [rs1076560; risk allele "A" for pain; p = 0.022; OR=4.58]. Additionally, bilateral disease [p = 0.011; OR=5.10] and gender [risk group "female"; p = 0.003; OR=8.53] were also identified as significant univariate risk factors for PD-related pain. Based on logistic regression analysis conducted with the significant univariate risk factors, this the first report to clarify that a female patient with bilateral PD and DRD2 rs2283265 polymorphism has a significant risk for PD-related pain. Our findings might contribute to improve life quality by offering treatment options for pain in PD patients with these clinical and genetic features.

Relationship between circulating CD4+ T lymphocytes and cognitive impairment in patients with Parkinson's disease

INTRODUCTION

Parkinson's disease (PD) is characterized by loss of dopaminergic neurons. Neuroinflammation may represent an important factor in the pathophysiology of PD and recent findings indicate that PD patients present a pro-inflammatory peripheral profile of CD4+ T lymphocytes, which may correlate with motor disability. However, no data are currently available on the relationship between CD4+ T lymphocytes and cognitive function in PD. The aim of our study is to evaluate the relationship between cognitive profile and circulating CD4+ T lymphocyte subsets in PD patients.

METHODS

PD patients underwent blood withdrawal and CD4+ T lymphocyte subpopulations, including CD4+ T naïve and memory cells, Th1, Th2, Th17, Th1/17 and T regulatory (Treg) cells were evaluated by flow cytometry. Cognitive evaluation was performed using Addenbrooke Cognitive Examination (ACE-R).

RESULTS

43 consecutive PD patients (31 males; age [mean ± SD]: 68.9 ± 8.4 years) were enrolled. 14/43 (32.6%) were drug naïve. Based on the ACE-R score, patients were divided in two groups using defined cutoff values. In comparison to patients with normal cognitive profile, patients with cognitive impairment had a higher number of circulating lymphocytes. Moreover, drug naïve patients with a worse cognitive outcome had a lower number of resting Treg and higher number of activated Treg. Furthermore, we found a correlation between pro-inflammatory peripheral immune phenotype and worse cognitive outcome in the ACE-R total and sub-items scores.

CONCLUSIONS

In our cohort of PD patients, cognitive impairment was associated with higher number of circulating lymphocytes, and - at least in drug naïve patients - with dysregulation of the Treg compartment. Further studies are needed to assess whether and to what extent peripheral immunity mechanistically contributes to cognitive decline in PD.

Therapeutic innovation in Parkinson's disease: a 2020 update on disease-modifying approaches

INTRODUCTION

Parkinson's disease (PD) is the second most common neurodegenerative disorder affecting more than 10 million patients worldwide. Despite increasing improvements in disease management, a huge medical need still exists as its relentless progression cannot be delayed by current treatments. Therefore, scientists, clinicians, and pharmaceutical companies are hunting new drugs with 'disease-modifying' properties.

AREAS COVERED

This review concentrates on new therapeutics - excluding cell and gene therapies - under investigation for PD with 'disease-modifying' potential. This is a global, comprehensive picture of the current innovative drug pipeline, where the main preclinical and clinical data available are provided. Drug candidates presented include α-synuclein modulating agents, neuroprotective agents and neuroinflammation modulators, kinase modulators, neurotrophic factors, and drugs acting on emerging targets.

EXPERT OPINION

There is excitement for agents with 'disease-modifying' properties and the authors found more than 130 assets, not including cell and gene therapies under investigation - most of them still in preclinical development - meaning that the science is progressing multiple, diverse new opportunities. Many limitations hamper the successful development of these drug candidates such as the translational accuracy of preclinical models, the current clinical development paradigm as well as the lack of biomarkers to be used in diagnosis and therapy management.

Erythrocytic α-synuclein contained in microvesicles regulates astrocytic glutamate homeostasis: a new perspective on Parkinson's disease pathogenesis

Parkinson's disease is a neurodegenerative disorder characterized by the transmission and accumulation of toxic species of α-synuclein (α-syn). Extracellular vesicles (EVs) are believed to play a vital role in the spread of toxic α-syn species. Recently, peripheral α-syn pathology has been investigated, but little attention has been devoted to erythrocytes, which contain abundant α-syn. In this study, we first demonstrated that erythrocyte-derived EVs isolated from Parkinson's disease patients carried elevated levels of oligomeric α-syn, compared to those from healthy controls. Moreover, human erythrocyte-derived EVs, when injected into peripheral blood in a mouse model of Parkinson's disease, were found to readily cross the blood-brain barrier (BBB). These EVs accumulated in astrocyte endfeet, a component of the BBB, where they impaired glutamate uptake, likely via interaction between excitatory amino acid transporter 2 (EAAT2) and oligomeric α-syn. These data suggest that erythrocyte-derived EVs and the oligomeric α-syn carried in them may play critical roles in the progression or even initiation of Parkinson's disease. Additionally, the mechanisms involved are attributable at least in part to dysfunction of astrocytes induced by these EVs. These observations provide new insight into the understanding of the mechanisms involved in Parkinson's disease.

Biological links between traumatic brain injury and Parkinson's disease

Parkinson's Disease (PD) is a progressive neurodegenerative disorder with no cure. Clinical presentation is characterized by postural instability, resting tremors, and gait problems that result from progressive loss of A9 dopaminergic neurons in the substantia nigra pars compacta. Traumatic brain injury (TBI) has been implicated as a risk factor for several neurodegenerative diseases, but the strongest evidence is linked to development of PD. Mild TBI (mTBI), is the most common and is defined by minimal, if any, loss of consciousness and the absence of significant observable damage to the brain tissue. mTBI is responsible for a 56% higher risk of developing PD in U.S. Veterans and the risk increases with severity of injury. While the mounting evidence from human studies suggests a link between TBI and PD, fundamental questions as to whether TBI nucleates PD pathology or accelerates PD pathology in vulnerable populations remains unanswered. Several promising lines of research point to inflammation, metabolic dysregulation, and protein accumulation as potential mechanisms through which TBI can initiate or accelerate PD. Amyloid precursor protein (APP), alpha synuclein (α-syn), hyper-phosphorylated Tau, and TAR DNA-binding protein 43 (TDP-43), are some of the most frequently reported proteins upregulated following a TBI and are also closely linked to PD. Recently, upregulation of Leucine Rich Repeat Kinase 2 (LRRK2), has been found in the brain of mice following a TBI. Subset of Rab proteins were identified as biological substrates of LRRK2, a protein also extensively linked to late onset PD. Inhibition of LRRK2 was found to be neuroprotective in PD and TBI models. The goal of this review is to survey current literature concerning the mechanistic overlap between TBI and PD with a particular focus on inflammation, metabolic dysregulation, and aforementioned proteins. This review will also cover the application of rodent TBI models to further our understanding of the relationship between TBI and PD.

Associations between Brain Structural Damage and Core Muscle Loss in Patients with Parkinson's Disease

BACKGROUND

Parkinson's disease (PD) is a common neurodegenerative disease associated with progressive gray matter atrophy. In addition to motor function disorder, frailty and decreased muscle mass potentially contribute to increased morbidity risk.

OBJECTIVE

This study aimed to investigate the associations between lean muscle loss and gray matter volume (GMV) in PD patients.

METHODS

Thirty patients with PD and fifteen healthy controls underwent brain and bilateral thigh MRIs. The IDEAL sequence was employed, measuring the regions of interest (ROI) of fat percentage at the 50% point of femur length. Voxel-base morphometry (VBM) was used to assess regional gray matter volume differences between groups. Further correlation analysis was performed to evaluate the changes between gray matter volume and fatty percentage of the bilateral thigh after adjusting for age and gender. Multiple linear regression analysis was applied to evaluate the risk factor of core muscle loss in PD patients.

RESULTS

Compared with controls, patients with PD had significantly higher thigh fat percentage and smaller gray matter volume of several brain locations of the default mode network (DMN), specifically the left superior temporal gyrus, right uncus, and left inferior temporal gyrus, revealing association with higher thigh fat percentage. Further multiple linear regression analysis indicated that higher thigh fat percentage is associated with gender (female), increased disease duration, and smaller gray matter volume of the left superior temporal gyrus and right uncus in PD patients.

CONCLUSIONS

Patients with PD experience core muscle loss in the thigh, associated with default mode network (DMN) degeneration, longer disease duration, and female gender. Identification of risk factors associated with lean muscle mass loss may assist in early prevention of comorbidities such as sarcopenia.

New markers in Parkinson's disease

Parkinson's disease (PD) is a chronic, debilitating neurodegenerative disorder characterized clinically by a variety of progressive motor and nonmotor symptoms. Currently, there is a dearth of diagnostic tools available to predict, diagnose or mitigate disease risk or progression, leading to a challenging dilemma within the healthcare management system. The search for a reliable biomarker for PD that reflects underlying pathology is a high priority in PD research. Currently, there is no reliable single biomarker predictive of risk for motor and cognitive decline, and there have been few longitudinal studies of temporal progression. A combination of multiple biomarkers might facilitate earlier diagnosis and more accurate prognosis in PD. In this review, we focus on the recent developments of serial biomarkers for PD from a variety of clinical, biochemical, genetic and neuroimaging perspectives.

Systematic Audiological Assessment of Auditory Functioning in Patients With Parkinson's Disease

Purpose Alterations in primary auditory functioning have been reported in patients with Parkinson's disease (PD). Despite the current findings, the pathophysiological mechanisms underlying these alterations remain unclear, and the effect of dopaminergic medication on auditory functioning in PD has been explored insufficiently. Therefore, this study aimed to systematically investigate primary auditory functioning in patients with PD by using both subjective and objective audiological measurements. Method In this case-control study, 25 patients with PD and 25 age-, gender-, and education-matched healthy controls underwent an audiological test battery consisting of tonal audiometry, short increment sensitivity index, otoacoustic emissions (OAEs), and speech audiometry. Patients with PD were tested in the on- and off-medication states. Results Increased OAE amplitudes were found when patients with PD were tested without dopaminergic medication. In addition, speech audiometry in silence and multitalker babble noise demonstrated higher phoneme scores for patients with PD in the off-medication condition. The results showed no differences in auditory functioning between patients with PD in the on-medication condition and healthy controls. No effect of disease stage or motor score was evident. Conclusions This study provides evidence for a top-down involvement in auditory processing in PD at both central and peripheral levels. Most important, the increase in OAE amplitude in the off-medication condition in PD is hypothesized to be linked to a dysfunction of the olivocochlear efferent system, which is known to have an inhibitory effect on outer hair cell functioning. Future studies may clarify whether OAEs may facilitate an early diagnosis of PD.

α-Synuclein in blood cells differentiates Parkinson's disease from healthy controls

OBJECTIVE

To determine whether blood cells expressed α-Syn can differentiate Parkinson's disease (PD) from healthy controls (HC).

METHODS

The concentrations of α-Syn were determined in samples of blood cell pellets using a quantitative Lipid-ELISA assay. In addition, the levels of total protein, hemoglobin, iron and H-ferritin were determined. The study includes samples from the Biofind cohort (n = 46 PD and 45 HC) and results were validated with an additional cohort (n = 35 PD and 28 HC).

RESULTS

A composite biomarker consisting of the concentrations of total α-Syn, proteinase-K resistant (PKres ) α-Syn and phospho-Serine 129 α-Syn (PSer 129), is designed based on the analysis of the discovery BioFIND cohort. This composite biomarker differentiates a PD subgroup, presenting motor symptoms without dementia from a HC group, with a convincing accuracy, represented by an AUC = 0.81 (95% CI, 0.71 to 0.92). Closely similar results were obtained for the validation cohort, that is, AUC = 0.81, (95% CI, 0.70 to 0.94).

INTERPRETATION

Our results demonstrate the potential usefulness of blood cells expressed α-Syn as a biomarker for PD.

TAM Receptor Pathways at the Crossroads of Neuroinflammation and Neurodegeneration

Increasing evidence suggests that pathogenic mechanisms underlying neurodegeneration are strongly linked with neuroinflammatory responses. Tyro3, Axl, and Mertk (TAM receptors) constitute a subgroup of the receptor tyrosine kinase family, cell surface receptors which transmit signals from the extracellular space to the cytoplasm and nucleus. TAM receptors and the corresponding ligands, Growth Arrest Specific 6 and Protein S, are expressed in different tissues, including the nervous system, playing complex roles in tissue repair, inflammation and cell survival, proliferation, and migration. In the nervous system, TAM receptor signalling modulates neurogenesis and neuronal migration, synaptic plasticity, microglial activation, phagocytosis, myelination, and peripheral nerve repair, resulting in potential interest in neuroinflammatory and neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and Multiple Sclerosis. In Alzheimer and Parkinson diseases, a role of TAM receptors in neuronal survival and pathological protein aggregate clearance has been suggested, while in Multiple Sclerosis TAM receptors are involved in myelination and demyelination processes. To better clarify roles and pathways involving TAM receptors may have important therapeutic implications, given the fine modulation of multiple molecular processes which could be reached. In this review, we summarise the roles of TAM receptors in the central nervous system, focusing on the regulation of immune responses and microglial activities and analysing in vitro and in vivo studies regarding TAM signalling involvement in neurodegeneration.

Probiotics May Have Beneficial Effects in Parkinson's Disease: In vitro Evidence

Background: Parkinson's disease (PD) is characterized by loss of dopaminergic neurons and intraneuronal accumulation of alpha-synuclein, both in the basal ganglia and in peripheral sites, such as the gut. Peripheral immune activation and reactive oxygen species (ROS) production are important pathogenetic features of PD. In this context, the present study focused on the assessment of in vitro effects of probiotic bacterial strains in PBMCs isolated from PD patients vs. healthy controls.

Methods: 40 PD patients and 40 matched controls have been enrolled. Peripheral blood mononuclear cells (PBMCs) were isolated and co-cultured with a selection of probiotics microorganisms belonging to the lactobacillus and bifidobacterium genus. In vitro release of the major pro- (Tumor Necrosis Factor-alpha and Interleukin-17A and 6) and anti-inflammatory (Interleukin 4 and 10) cytokines by PBMCs, as well as the production of ROS was investigated. Furthermore, we assessed the ability of probiotics to influence membrane integrity, antagonize the growth of potential pathogen bacteria, such as Escherichia coli and Klebsiella pneumoniae and encode tyrosine decarboxylase genes (tdc).

Results: All probiotic strains were able to inhibit inflammatory cytokines and ROS production in both patients and controls. The most striking results were obtained in PD subjects with L. salivarius LS01 and L. acidophilus which significantly reduced pro-inflammatory and increased the anti-inflammatory cytokines (p < 0.05). Furthermore, most strains determined restoration of membrane integrity and inhibition of E. coli and K. pneumoniae. Finally, we also showed that all the strains do not carry tdc gene, which is known to decrease levodopa bioavailability in PD patients under treatment.

Conclusions: Probiotics exert promising in vitro results in decreasing pro-inflammatory cytokines, oxidative stress and potentially pathogenic bacterial overgrowth. In vivo longitudinal data are mandatory to support the use of bacteriotherapy in PD.

Chitosan Nanoparticles Rescue Rotenone-Mediated Cell Death

The aim of the present investigation was to study the anti-oxidant effect of chitosan nanoparticles on a human SH-SY5Y neuroblastoma cell line using a rotenone model to generate reactive oxygen species. Chitosan nanoparticles were synthesized using an ionotropic gelation method. The obtained nanoparticles were characterized using various analytical techniques such as Dynamic Light Scattering, Scanning Electron Microscopy, Transmission Electron Microscopy, Fourier Transmission Infrared spectroscopy and Atomic Force Microscopy. Incubation of SH-SY5Y cells with 50 µM rotenone resulted in 35-50% cell death within 24 h of incubation time. Annexin V/Propidium iodide dual staining verified that the majority of neuronal cell death occurred via the apoptotic pathway. The incubation of cells with chitosan nanoparticles reduced rotenone-initiated cytotoxicity and apoptotic cell death. Given that rotenone insult to cells causes oxidative stress, our results suggest that Chitosan nanoparticles have antioxidant and anti-apoptotic properties. Chitosan can not only serve as a novel therapeutic drug in the near future but also as a carrier for combo-therapy.

Upgraded Methodology for the Development of Early Diagnosis of Parkinson's Disease Based on Searching Blood Markers in Patients and Experimental Models

Numerous attempts to develop an early diagnosis of Parkinson's disease (PD) by searching biomarkers in biological fluids were unsuccessful. The drawback of this methodology is searching markers in patients at the clinical stage without guarantee that they are also characteristic of either preclinical stage or prodromal stage (preclinical-prodromal stage). We attempted to upgrade this methodology by selecting only markers that are found both in patients and in PD animal models. HPLC and RT-PCR were used to estimate the concentration of amino acids, catecholamines/metabolites in plasma and gene expression in lymphocytes in 36 untreated early-stage PD patients and 52 controls, and in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice at modeling the clinical ("symptomatic") stage and preclinical-prodromal ("presymptomatic") stage of PD. It was shown that among 13 blood markers found in patients, 7 markers are characteristic of parkinsonian symptomatic mice and 3 markers of both symptomatic and presymptomatic mice. According to our suggestion, the detection of the same marker in patients and symptomatic animals indicates adequate reproduction of pathogenesis along the corresponding metabolic pathway, whereas the detection of the same marker in presymptomatic animals indicates its specificity for preclinical-prodromal stage. This means that the minority of markers found in patients-decreased concentration of L-3,4-dihydroxyphenylalanine (L-DOPA) and dihydroxyphenylacetic acid (DOPAC) and increased dopamine D3 receptor gene expression-are specific for preclinical-prodromal stage and are suitable for early diagnosis of PD. Thus, we upgraded a current methodology for development of early diagnosis of PD by searching blood markers not only in patients but also in parkinsonian animals.

The enteric nervous system in PD: gateway, bystander victim, or source of solutions

Apart from the characteristic and progressive motor- and movement-related problems, Parkinson's disease (PD) patients also suffer from several non-motor symptoms, including gastrointestinal dysfunction. The fact that the enteric nervous system (ENS) controls motility and that one of the typical PD hallmarks, α-synuclein-positive deposits, has also been found in the intestinal wall have rendered the ENS and the gut a popular subject of study in the context of PD. The possibility that these deposits could serve as an early biomarker is obviously of tremendous medical benefit but also the idea that the gut may possibly be a gateway via which the disease is initiated and progressively makes its way via the peripheral nerves to the central nervous system has increased the interest in the ENS-PD link. Furthermore, the fact that gastrointestinal symptoms are present in PD suggests that the ENS might be affected as well. However, despite a large body of literature on the topic, the actual role or the magnitude of involvement of the ENS in PD remains elusive. The multitudes of experimental approaches and animal models have complicated the interpretation of results and the outcome of different studies does not necessarily align well. In this review, we chose to highlight some elements of interest and some items of confusion, particularly those where research should be focusing. We also list a number of open questions in the field that could serve as a guideline for future, preferably concerted research.

The Length of SNCA Rep1 Microsatellite May Influence Cognitive Evolution in Parkinson's Disease

Background

Alpha-synuclein is a constituent of Lewy bodies and mutations of its gene cause familial Parkinson's disease (PD). A previous study showed that a variant of the alpha-synuclein gene (SNCA), namely the 263 bp allele of Rep1 was associated with faster motor progression in PD. On the contrary, a recent report failed to detect a detrimental effect of Rep1 263 on both motor and cognitive outcomes in PD. Aim of this study was to evaluate the influence of the Rep1 variants on disease progression in PD patients.

Methods

We recruited and genotyped for SNCA Rep1 426 PD patients with age at onset ≥40 years and disease duration ≥4 years. We then analyzed frequency and time of occurrence of wearing-off, dyskinesia, freezing of gait, visual hallucinations, and dementia using a multivariate Cox's proportional hazards regression model.

Results

SNCA Rep1 263 carriers showed significantly increased risk of both dementia (HR = 3.03) and visual hallucinations (HR = 2.69) compared to 263 non-carriers. Risk of motor complications did not differ in the two groups.

Conclusion

SNCA Rep1 263 allele is associated with a worse cognitive outcome in PD.

Sarcopenia in Parkinson Disease: Comparison of Different Criteria and Association With Disease Severity

OBJECTIVES

In Parkinson disease (PD), sarcopenia may represent the common downstream pathway that from motor and nonmotor symptoms leads to the progressive loss of resilience, frailty, and disability. Here we (1) assessed the prevalence of sarcopenia in older adults with PD using 3 different criteria, testing their agreement, and (2) evaluated the association between PD severity and sarcopenia.

DESIGN

Cross-sectional, observation study.

SETTING

Geriatric day hospital.

PARTICIPANTS

Older adults with idiopathic PD.

MEASUREMENTS

Body composition was evaluated through dual energy x-ray absorptiometry. Handgrip strength and walking speed were measured. Sarcopenia was operationalized according to the Foundation for the National Institutes of Health, the European Working Group on Sarcopenia in Older Persons, and the International Working Group. Cohen k statistics was used to test the agreement among criteria.

RESULTS

Among the 210 participants (mean age 73 years; 38% women), the prevalence of sarcopenia was 28.5%-40.7% in men and 17.5%-32.5% in women. The prevalence of severe sarcopenia was 16.8%-20.0% in men and 11.3%-18.8% in women. The agreement among criteria was poor. The highest agreement was obtained between the European Working Group on Sarcopenia in Older Persons (severe sarcopenia) and International Working Group criteria (k = 0.52 in men; k = 0.65 in women; P < .01 for both). Finally, severe sarcopenia was associated with PD severity (odds ratio 2.30; 95% confidence interval 1.15-4.58).

CONCLUSIONS

Sarcopenia is common in PD, with severe sarcopenia being diagnosed in 1 in every 5 patients with PD. We found a significant disagreement among the 3 criteria evaluated, in detecting sarcopenia more than in ruling it out. Finally, sarcopenia is associated with PD severity. Considering its massive prevalence, further studies should address the prognosis of sarcopenia in PD.

Peripheral neuropathy in 30 duodopa patients with vitamins B supplementation

OBJECTIVES

Peripheral neuropathy (PN) is a significant concern and potential cause of withdrawal in patients with Parkinson's disease (PD) treated with Levodopa/Carbidopa Intestinal Gel (LCIG) infusion. Vitamin B deficiency and/or hyperhomocysteinemia levodopa-related are considered possible causative factors. In this study, we evaluated PN incidence in LCIG-PD patients treated since the beginning of infusion with vitamins B supplementation.

MATERIALS & METHODS

In this prospective open-label pilot study, 30 consecutive patients with PD on LCIG infusion were evaluated with clinical, neurophysiological, and biochemical assessments for a mean follow-up of 42.4 months (range 24-72). All evaluations were repeated every 6 months.

RESULTS

At baseline, 21 of 30 presented no signs or symptoms of PN, and 9 of 30 had pre-existing chronic PN. In whole population, a progressive worsening in nerve conduction studies of sural sensory and peroneal motor nerves was observed during the long-term follow-up. 4 of 21 patients, with normal clinical, electrophysiological assessment at baseline, developed distal symmetrical axonal polyneuropathy that remained asymptomatic during the long-term follow-up. Patients with pre-existing PN (9 of 30) showed a mild worsening of electrophysiological features during the period of observation. In none PN was cause of discontinuation of LCIG therapy. No incident cases of acute-subacute PN were documented. No correlation was found with age, sex, Levodopa dosage, duration of levodopa exposure, and homocysteine plasma levels.

CONCLUSION

In this consecutive series of 30 patients with PD on LCIG infusion, with early and continuous vitamins B integration, we observed a low rate (19%) of new onset peripheral polyneuropathy that remained stable after long-term follow-up. Larger studies, controlled, with blinded evaluation, are needed to confirm these findings.

The effectiveness of creatine treatment for Parkinson's disease: an updated meta-analysis of randomized controlled trials

Background

The effectiveness of creatine in treating Parkinson’s disease (PD) has not been conclusively determined. Therefore, we performed a meta-analysis to address this issue.

Methods

The Cochrane Central Register of Controlled Trials, PUBMED, EMBASE, and other databases were searched, and outcomes measured by the Total Unified Parkinson’s Disease Rating Scale (UPDRS) and the Schwab & England Scale were analyzed.

Results

Five randomized controlled trials (RCTs) were selected, and 1339 participants were included in the analysis. There were no significant differences between the control and treatment groups in the total, mental, activities of daily living (ADL), or motor UPDRS scores, but an improvement in Schwab & England Scale scores was observed.

Conclusions

Creatine has no observed benefit in PD patients, although more correlated studies are still needed.

Corneal nerve microstructure in Parkinson's disease

Ocular surface changes and blink abnormalities are well-established in Parkinson's disease. Blink rate may be influenced by corneal sub-basal nerve density, however, this relationship has not yet been investigated in Parkinson's disease. This case-control study examined the ocular surface in patients with moderately severe Parkinson's disease, including confocal microscopy of the cornea. Fifteen patients with moderately severe Parkinson's disease (modified Hoehn and Yahr grade 3 or 4) and fifteen control participants were recruited. Ophthalmic assessment included slit-lamp examination, blink rate assessment, central corneal aesthesiometry and in vivo corneal confocal microscopy. The effect of disease laterality was also investigated. Of the 15 patients with Parkinson's disease, ten were male and the mean age was 65.5±8.6years. The corneal sub-basal nerve plexus density was markedly reduced in patients with Parkinson's disease (7.56±2.4mm/mm²) compared with controls (15.91±2.6mm/mm²) (p<0.0001). Corneal sensitivity did not differ significantly between the patients with Parkinson's disease (0.79±1.2mBAR) and the control group (0.26±0.35mBAR), p=0.12. Sub-basal nerve density was not significantly different between the eye ipsilateral to the side of the body with most-severe motor symptoms, and the contralateral eye. There was a significant positive correlation between ACE-R scores and sub-basal corneal nerve density (R²=0.66, p=0.02). This is the first study to report a significant reduction in corneal sub-basal nerve density in Parkinson's disease and demonstrate an association with cognitive dysfunction. These results provide further evidence to support the involvement of the peripheral nervous system in Parkinson's disease, previously thought to be a central nervous system disorder.