In vivo gastric detection of α-synuclein inclusions in Parkinson's disease

A Cortical Pathogenic Theory of Parkinson's Disease

In Parkinson's disease, the progressive neurodegeneration of nigrostriatal dopaminergic neurons in the substantia nigra pars compacta (SNc) is associated with classic motor features, which typically have a focal onset. Since a defined somatotopic arrangement in the SNc has not been recognized, this focal motor onset is unexplained and hardly justified by current pathogenic theories of bottom-up disease progression (Braak's hypothesis, prionopathy). Here we propose that corticostriatal activity may represent a critical somatotopic "stressor" for nigrostriatal terminals, ultimately driving retrograde nigrostriatal degeneration and leading to focal motor onset and progression of Parkinson's disease. As a pathogenic mechanism, corticostriatal activity may promote secretion of striatal extracellular alpha-synuclein, favoring its pathological aggregation at vulnerable dopaminergic synapses. A similar pathogenic process may occur at corticofugal projections to the medulla oblongata and other vulnerable structures, thereby contributing to the bottom-up progression of Lewy pathology. This cortical pathogenesis may co-exist with bottom-up mechanisms, adding an integrative top-down perspective to the quest for the factors that impinge upon the vulnerability of dopaminergic cells in the onset and progression of Parkinson's disease.

Value of in vivo α-synuclein deposits in Parkinson's disease: A systematic review and meta-analysis

Previous studies that have investigated the potential of in vivo abnormal α-synuclein deposits as a pathological biomarker for PD included few participants and reported different diagnostic accuracies. Here, we aimed to confirm the diagnostic value of in vivo α-synuclein deposits in PD through a systematic review and meta-analysis, with special emphasis on determining the tissue most suitable for examination and assessing whether anti-native α-synuclein or anti-phosphorylated α-synuclein antibodies should be used. Databases were searched on December 30, 2018. We finally included 41 case-control studies that examined in vivo tissue samples using anti-native α-synuclein or anti-phosphorylated α-synuclein antibody in PD patients and controls. Using a univariate random-effects model, pooled sensitivity and specificity (95% confidence interval) of anti-native α-synuclein antibody were 0.54 (0.49-0.60) and 0.72 (0.68-0.76) for the gastrointestinal tract and 0.76 (0.60-0.89) and 0.60 (0.43-0.74) for the skin. Pooled sensitivity and specificity (95% confidence interval) of anti-phosphorylated α-synuclein antibody were 0.43 (0.37-0.48) and 0.82 (0.78-0.86) for the gastrointestinal tract, 0.76 (0.69-0.82) and 1.00 (0.98-1.00) for the skin, 0.42 (0.26-0.59) and 0.94 (0.84-0.99) for the minor salivary glands, and 0.66 (0.51-0.79) and 0.96 (0.86-1.00) for the submandibular glands. Although ubiquitous heterogeneity between the included studies should be noted when interpreting our results, our analyses demonstrated the following: (1) in vivo α-synuclein immunoreactivity has the potential as a pathological biomarker for PD; (2) anti-phosphorylated α-synuclein antibody consistently has higher specificity than anti-native α-synuclein antibody; and (3) skin biopsy examination using anti-phosphorylated α-synuclein antibody has the best diagnostic accuracy, although feasibility remains an important issue. © 2019 International Parkinson and Movement Disorder Society.

Acupuncture protects from 6-OHDA-induced neuronal damage by balancing the ratio of DMT1/Fpn1

Objective

Acupuncture is a commonly used method to provide motor-symptomatic relief for patients with Parkinson s disease (PD). Our objective was to evaluate protective effects of acupuncture treatment and potential underlying mechanisms according to the “gut-brain axis” theory.

Methods

We employed a 6-OHDA-induced PD rat model. The effects of acupuncture on disease development were assessed by behavioural tests and immunohistochistry (IHC). ELISA, qPCR and western blot (WB) were employed to measure inflammatory parameters and Fe metabolism in the substantia nigra (SN), striatum, duodenum and blood, respectively.

Results

Our data show that acupuncture can significantly increase the expression of tyrosine hydroxylase (TH), compared with untreated and madopa treated rats (P < 0.01 and P < 0.05, respectively). Furthermore we could observe significantly decreased levels of pro-inflammatory markers in the duodenum and serum (P < 0.05), reduced deposition of Fe in the substantia nigra (P < 0.05) and but no change in transferrin expression after acupuncture treatment. The mRNA ratio of DMT1/Fpn1 in the SN of acupuncture treated rats (1.1) was comparable to that of the sham group (1.0) which differed both significantly from the untreated and madopa treated groups (P < 0.05). Furthermore, after acupuncture expression of α-synuclein was decreased in the duodenum.

Conclusions

Acupuncture can reduce iron accumulation in the SN and protect the loss of dopamine neurons by promoting balanced expression of the iron importer DMT1 and the iron exporter Fpn1. Furthermore CNS iron homeostasis may be affected by reduced systemic and intestinal inflammation.

Skin Fibroblasts as the Object for Clinical Diagnosis of Parkinson's Disease in Persons of Different Ages

We compared the expression of Aβ42 peptide, τ-protein, and α-synuclein in the substantia nigra and skin fibroblasts of elderly and senile patients with Parkinson's disease and subjects without neuropathology. Expression of markers in the studied tissues was assessed by immunohistochemical and immunocytochemical methods. The expression of Aβ42 peptide, τ-protein, and α-synuclein in the substantia nigra of elderly and senile patients with Parkinson's disease was higher by 11-31 times than in subjects without neuropathology. In skin fibroblasts of patients with Parkinson's disease, the expression of Aβ42 peptide and α-synuclein was 3-14 times higher than in subjects without neuropathology, and expression of τ-protein did not significantly differ in the studied groups. Thus, immunocytochemical analysis of the expression Aβ42 peptide and α-synuclein in skin fibroblasts can be a simple method of early diagnosis of Parkinson's disease in elderly persons.

Altered Gut Microbiome and Intestinal Pathology in Parkinson's Disease

Parkinson's disease (PD) is a common neurodegenerative disorder arising from an interplay between genetic and environmental risk factors. Studies have suggested that the pathological hallmarks of intraneuronal α-synuclein aggregations may start from the olfactory bulb and the enteric nervous system of the gut and later propagate to the brain via the olfactory tract and the vagus nerve. This hypothesis correlates well with clinical symptoms, such as constipation, that may develop up to 20 years before the onset of PD motor symptoms. Recent interest in the gut-brain axis has led to vigorous research into the gastrointestinal pathology and gut microbiota changes in patients with PD. In this review, we provide current clinical and pathological evidence of gut involvement in PD by summarizing the changes in gut microbiota composition and gut inflammation associated with its pathogenesis.

Diagnostic utility of gut α-synuclein in Parkinson's disease: A systematic review and meta-analysis

BACKGROUND

The accumulation of misfolded α-synuclein in the brain is associated with Parkinson's disease. However, the association between gut α-synuclein and PD and diagnostic value of α-synuclein in the gut still remain controversial.

METHODS

A literature search from inception to June 2018 was conducted, yielding 21 studies eligible for a systematic review and meta-analysis. We included studies that reported data on gut α-synuclein or phosphorylated α-synuclein in patients with PD and controls. The odds ratio(OR) was pooled using random-effect models, and heterogeneity was reported as I2. Studies were assessed for quality using the Newcastle-Ottawa Scale. Sensitivity and specificity analyses were performed using the summary receiver operating characteristics curve approach.

RESULTS

The database search yielded 395 results, of which 21 studies were deemed relevant. The PD group had a pooled OR of 10.01 (95% CI: 3.15-31.82, I2 = 72%) for gut α-synuclein compared with the control group. Sensitivity and specificity for distinguishing PD from controls were 0.568 and 0.819, respectively, for the colon, and 0.579 and 0.822, respectively, for phosphorylated α-synuclein.

CONCLUSION

Heterogeneity was high in most of the studies. This systematic review and meta-analysis confirmed a high degree of association between gut α-synuclein and PD, which suggested that gut α-synuclein is a potential therapeutic intervention. The measurement of gut α-synuclein alone could lead to the underdiagnosis of PD. Future research combining gut α-synuclein with other biochemical markers could improve the standardization of current assays.

α-synuclein RT-QuIC in cerebrospinal fluid of LRRK2-linked Parkinson's disease

Background

Leucine‐rich kinase 2 (LRRK2)‐linked Parkinson's disease (PD) is clinically indistinguishable from idiopathic PD (IPD). A pleiotropic neuropathology has been recognized but the majority of studies in LRRK2 p.G2019S patients reveal Lewy‐type synucleinopathy as its principal histological substrate. To date no in vivo biomarkers of synucleinopathy have been found in LRRK2 mutation carriers.

Objectives

We used real‐time quaking‐induced conversion (RT‐QuIC) technique to assess the presence of alpha‐synuclein (a‐syn) aggregates in cerebrospinal fluid (CSF) of LRRK2 p.G2019S carriers.

Methods

CSF samples of 51 subjects were analyzed: 15 LRRK2 p.G2019S PD, 10 IPD, 16 LRRK2 p.G2019S nonmanifesting carriers (NMC) and 10 healthy controls. The presence of parkinsonism and prodromal symptoms was assessed in all study subjects.

Results

Forty percent (n = 6) LRRK2‐PD, and 18.8% (n = 3) LRRK2‐NMC had a positive a‐syn RT‐QuIC response. RT‐QuIC detected IPD with 90% sensitivity and 80% specificity. No clinical differences were detected between LRRK2‐PD patients with positive and negative RT‐QuIC. A positive RT‐QuIC result in LRRK2‐NMC occurred in a higher proportion of subjects meeting the Movement Disorder Society research criteria for prodromal PD.

Interpretation

RT‐QuIC detects a‐syn aggregation in CSF in a significant number of patients with LRRK2‐PD, but less frequently than in IPD. A small percentage of LRRK2‐NMC tested also positive. If appropriately validated in long‐term studies with large number of mutation carriers, and hopefully, postmortem or in vivo confirmation of histopathology, RT‐QuIC could contribute to the selection of candidates to receive disease modifying drugs, in particular treatments targeting a‐syn deposition.

Alpha-Synuclein in Peripheral Tissues in Parkinson's Disease

Parkinson's disease (PD) is a common neurodegenerative disorder. To date, the diagnosis of PD relies mainly on clinical manifestations whereas neuropathological confirmation of the brain is only possible with postmortem studies. Neuronal loss in the substantia nigra pars compacta (SNc) associated with Lewy bodies/neurites is the pathological hallmark feature of PD. The major component of Lewy pathology (LP) is misfolded alpha-synuclein (α-SYN). There is evidence that the distribution of LP is not only limited to the brain but extends to peripheral tissues, including gastrointestinal tract, salivary glands, olfactory mucosa, skin, retina, adrenal gland, and heart. Sensitivity and specificity of α-SYN detection in PD vary greatly among studies due to methodological heterogeneity, such as sampling sites and size, tissue preparation, staining techniques, and antibodies used. Of note, α-SYN has also been found in preclinical and prodromal PD. Further in vivo studies focusing on favorable biopsy sites and standard techniques are needed to get better understanding of α-SYN deposits in preclinical, prodromal, and clinical PD.

What is the Evidence That Parkinson's Disease is a Prion Disorder, Which Originates in the Gut?

Parkinson's disease (PD) is a neurodegenerative disorder resulting from degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc). PD is characterized by motor dysfunctions as well as gastrointestinal symptoms and mental impairment. The pathological hallmark of PD is an accumulation of misfolded α-synuclein aggregates within the brain. The etiology of PD and related synucleinopathy is poorly understood, but recently, the hypothesis that α-synuclein pathology spreads in a prion-like fashion originating in the gut has gained much scientific attention. A crucial clue was the appearance of constipation before the onset of motor symptoms, gut dysbiosis and synucleinopathy in PD patients. Another line of evidence, demonstrating accumulation of α-synuclein within the peripheral autonomic nervous system (PANS), including the enteric nervous system (ENS), and the dorsal motor nucleus of the vagus (DMV) support the concept that α-synuclein can spread from the ENS to the brain by the vagus nerve. The decreased risk of PD following truncal vagotomy supports this. The convincing evidence of the prion-like behavior of α-synuclein came from postmortem observations that pathological α-synuclein inclusions appeared in healthy grafted neurons. In this review, we summarize the available data from human subjects' research and animal experiments, which seem to be the most suggestive for explaining the hypotheses.

Relation of Enteric α-Synuclein to Gastrointestinal Dysfunction in Patients With Parkinson's Disease and in Neurologically Intact Subjects

Background/Aims

α-Synucleinopathy in the brain is the neuropathological hallmark of Parkinson’s disease (PD). However, the functional impact of α-synucleinopathy in the enteric nervous system remains unknown. We aim to evaluate the association between gastrointestinal (GI) dysfunction and α-synuclein (αSYN) pathology in the stomach and colon of PD patients and controls, as well as to investigate the association between the αSYN pathology in GI tract and future PD risk.

Methods

A total of 35 PD patients and 52 neurologically intact subjects were enrolled in this study. Endoscopic biopsies were performed, and then immunohistochemical staining for αSYN was performed. All subjects completed the validated Rome III questionnaire for the assessment of GI symptoms. The association between GI symptoms and the αSYN pathology in GI mucosa was evaluated. Incident PD cases were assessed during a median follow-up of 46 months.

Results

The proportion of self-reported constipation and functional constipation through the Rome III questionnaire was significantly higher in PD patients than in controls (P < 0.001 and P = 0.015). However, no significant association was found between the αSYN pathology in the stomach and colon mucosa and constipation, as well as other GI symptoms including dyspepsia symptoms and abdominal discomfort or pain, regardless of the presence or absence of clinical PD (P > 0.05). No incident PD cases were diagnosed during study period.

Conclusions

Our present study suggests that the deposition of αSYN in the mucosal enteric nervous system may not be reflected by functional impairment of the affected segment of the gut.

Peripheral Biomarkers for Early Detection of Alzheimer's and Parkinson's Diseases

Neurological disorders are found to be influencing the peripheral tissues outside CNS. Recent developments in biomarkers for CNS have emerged with various diagnostic and therapeutic shortcomings. The role of central biomarkers including CSF-based and molecular imaging-based probes are still unclear for early diagnosis of major neurological diseases. Current trends show that early detection of neurodegenerative diseases with non-invasive methods is a major focus of researchers, and the development of biomarkers aiming peripheral tissues is in demand. Alzheimer's and Parkinson's diseases are known for the progressive loss in neural structures or functions, including the neural death. Various dysfunctions of metabolic and biochemical pathways are associated with early occurrence of neuro-disorders in peripheral tissues including skin, blood cells, and eyes. This article reviews the peripheral biomarkers explored for early detection of Alzheimer's and Parkinson's diseases including blood cells, skin fibroblast, proteomics, saliva, olfactory, stomach and colon, heart and peripheral nervous system, and others. Graphical Abstract.

Gastrointestinal nervous system α-synuclein as a potential biomarker of Parkinson disease

Lewy bodies (LB) play an essential role in the development, survival, and function maintenance of midbrain dopaminergic (DA) neurons in Parkinson disease (PD). Alpha-synuclein (α-synuclein) is the major component of Lewy bodies and is a potential target for Parkinson's disease (PD) therapies. α-synuclein can be detected in the gastrointestinal (GI) nervous system, but whether there is any association between altered α-synuclein expression in the GI nervous system and the onset of PD is not known. The answer to this question presents the opportunity for a promising biomarker in the pre-clinical diagnosis of PD. As such, this study aimed to measure the α-synuclein level in the GI nervous system of Parkinson's disease patients.The protein levels of α-synuclein in the GI nervous system of 31 PD patients (PD group) and 32 patients without PD or Parkinsonism-plus syndrome (control group) were evaluated via immunohistochemical staining. The χ test was performed to evaluate the differences between the PD group and control group. In addition to the distribution of α-synuclein positive protein, regional distribution of the protein in the stomach was also evaluated across groups.Alpha synuclein overexpression was found in the GI nervous tissue of PD patients. The PD group included 17 positive results and 14 negative results. The control group exhibited 7 positive results and 24 negative results. The χ test showed that χ = 7.255, P = .01. The distribution of these positive cases in the gastrointestinal system, the χ test showed that P = .949. The 21 stomach tissues had 7 α-synuclein positive protein tissues, while the body of stomach (4 α-synuclein positive protein) was higher than in other regions.Aberrant expression of α-synuclein was detected in the GI tissues of PD patients, though the distribution of α-synuclein in the gastrointestinal tract had no specificity. Gastrointestinal mucous biopsy could be regarded as a potential opportunity for the early-stage diagnostic exploration of PD, through the detection of α-synuclein inclusions.

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.

Peripheral and central autonomic nervous system: does the sympathetic or parasympathetic nervous system bear the brunt of the pathology during the course of sporadic PD?

It is a well-established fact that the sympathetic, parasympathetic and enteric nervous systems are affected at early stages in Parkinson's disease (PD). However, it is not yet clarified whether the earliest pathological events preferentially occur in any of these three divisions of the autonomic nervous system (ANS). Significant involvement of the peripheral autonomic nervous system of the heart and gastrointestinal tract has been documented in PD. Accumulating evidence suggests that the PD pathology spreads centripetally from the peripheral to central nervous system through autonomic nerve fibers, implicating the ANS as a major culprit in PD pathogenesis and a potential target for therapy. This study begins with a brief overview of the structures of the central and peripheral autonomic nervous system and then outlines the major clinicopathological manifestations of cardiovascular and gastrointestinal disturbances in PD.

Detection of alpha-synuclein conformational variants from gastro-intestinal biopsy tissue as a potential biomarker for Parkinson's disease

Aims

Gastrointestinal (GI) α‐synuclein (aSyn) detection as a potential biomarker of Parkinson's disease (PD) is challenged by conflicting results of recent studies. To increase sensitivity and specificity, we applied three techniques to detect different conformations of aSyn in GI biopsies obtained from a longitudinal, clinically well‐characterized cohort of PD patients and healthy controls (HC).

Methods

With immunohistochemistry (IHC), we used antibodies reactive for total, phosphorylated and oligomeric aSyn; with aSyn proximity ligation assay (AS‐PLA), we targeted oligomeric aSyn species specifically; and with paraffin‐embedded tissue blot (AS‐PET‐blot) we aimed to detect fibrillary, synaptic aSyn.

Results

A total of 163 tissue blocks were collected from 51 PD patients (113 blocks) and 21 HC (50 blocks). In 31 PD patients, biopsies were taken before the PD diagnosis (Prodromal); while in 20 PD patients biopsies were obtained after diagnosis (Manifest). The majority of tissues blocks were from large intestine (62%), followed by small intestine (21%), stomach (10%) and oesophagus (7%). With IHC, four staining patterns were detected (neuritic, ganglionic, epithelial and cellular), while two distinct staining patterns were detected both with AS‐PLA (cellular and diffuse signal) and with AS‐PET‐blot (aSyn‐localized and pericrypt signal). The level of agreement between different techniques was low and no single technique or staining pattern reliably distinguished PD patients (Prodromal or Manifest) from HC.

Conclusions

Our study suggests that detection of aSyn conformational variants currently considered pathological is not adequate for the diagnosis or prediction of PD. Future studies utilizing novel ultrasensitive amyloid aggregation assays may increase sensitivity and specificity.

Microbes Tickling Your Tummy: the Importance of the Gut-Brain Axis in Parkinson's Disease

Purpose of Review

Patients suffering from Parkinson's disease (PD) are known to experience gastrointestinal dysfunction that might precede the onset of motor symptoms by several years. Evidence suggests an important role of the gut-brain axis in PD pathogenesis. These interactions might be essentially influenced by the gut microbiota. Here, we review recent findings supporting that changes in the gut microbiota composition might be a trigger for inflammation contributing to neurodegeneration in PD.

Recent Findings

Recent research revealed that PD patients exhibit a pro-inflammatory microbiota profile in their intestinal tract that might increase gut permeability, allowing leakage of bacterial products and inflammatory mediators from the intestines. Evidence in literature indicates that alpha-synuclein deposition might start in the enteric nervous system by pro-inflammatory immune activity and then propagates to the CNS. Alternatively, the peripheral inflammatory response could impact the brain through systemic mechanisms.

Summary

A better understanding of the gut-brain interactions and the role of the intestinal microbiota in the regulation of immune responses might bring new insights in PD pathological progression and might lead to novel diagnostics and therapeutic approaches.

REM sleep behavior disorder is related to enteric neuropathology in Parkinson disease

OBJECTIVE

To determine whether REM sleep behavior disorder (RBD) in Parkinson disease (PD) is associated with lesions and dysfunctions of the autonomic nervous system by evaluating enteric phosphorylated α-synuclein histopathology (PASH) and permeability.

METHODS

A total of 45 patients with PD were included in this cross-sectional study. RBD was diagnosed on the basis of a standardized clinical interview and confirmed by polysomnography. For each patient, 5 biopsies were taken at the junction between the sigmoid and descending colon during the course of a rectosigmoidoscopy. For the detection of enteric PASH, 2 colonic biopsies were analyzed by immunohistochemistry with antibodies against phosphorylated α-synuclein and PGP9.5 in 43 patients (2 patients were excluded because only 1 biopsy was available). The paracellular permeability and transcellular permeability were evaluated by measuring sulfonic acid and horseradish peroxidase flux, respectively, in the 3 remaining biopsies mounted in Ussing chambers.

RESULTS

Enteric PASH was more frequent in the subgroup of patients with PD with RBD compared to patients without RBD (18 of 28, 64.3%, vs 2 of 15, 13.3%, respectively, p < 0.01). No differences were observed in intestinal permeability between patients with PD with and without RBD.

CONCLUSIONS

Patients with PD and RBD have a greater frequency of synuclein pathology in the enteric nervous system, suggesting that RBD is associated with widespread synuclein neuropathology.

Alpha-Synuclein to the Rescue: Immune Cell Recruitment by Alpha-Synuclein during Gastrointestinal Infection

Intraneuronal accumulation of misfolded alpha-synuclein in the central and peripheral nervous systems is strongly linked to Parkinson disease (PD) and other related synucleinopathies. In rare inherited forms of PD, point mutations or gene multiplications mediate the formation of alpha-synuclein protein aggregates. However, in most PD cases it is presumed that the combined effects of ageing and environmental factors drive the formation of alpha-synuclein aggregates. Despite advances regarding alpha-synuclein pathobiology, the normal functions of this protein and factors that regulate its expression are not well understood. We discuss a recent study reporting that viral infection induces alpha-synuclein expression in neurons of the gastrointestinal tract. Alpha-synuclein levels increased during norovirus infection in the duodenum of children. In an in vitro paradigm, monomeric and oligomeric alpha-synuclein acted as chemoattractants for neutrophils and monocytes, and promoted the maturation of dendritic cells. This suggests that alpha-synuclein facilitates immune responses to infection. We explore the possibility that intestinal infections, and associated inflammation, place individuals at increased risk of PD by increasing alpha-synuclein levels and promoting the formation of alpha-synuclein aggregates that propagate in a prion-like fashion via the vagal nerve to the brainstem.

Live calcium and mitochondrial imaging in the enteric nervous system of Parkinson patients and controls

Parkinson's disease (PD) is a neurodegenerative disease with motor and non-motor symptoms, including constipation. Therefore, several studies have investigated the gastrointestinal tract, and more specifically the enteric nervous system (ENS), in search of an early biomarker of PD. Besides α-synuclein aggregation, mitochondrial dysfunction and dysregulation of intracellular Ca²⁺ concentration probably contribute to the pathogenesis of PD. Here we assessed neuronal and mitochondrial functioning in primary enteric neurons of PD patients and their healthy partners as controls. Using a unique combination of live microscopy techniques, applied to routine duodenum biopsies, we were able to record neuronal Ca²⁺ responses and mitochondrial membrane potential in these nerve tissues. We found that submucous neurons were not affected in PD patients, which suggests that these neurons are not involved in the pathogenesis or the gastrointestinal symptoms of PD. Our study provides for the first time functional information on live neurons in PD patients.

Serum Growth Differentiation Factor 15 in Parkinson Disease

BACKGROUND

Growth differentiation factor 15 (GDF15) has been shown to be protective for dopaminergic neurons in animal and ex vivo experiments. However, little is known about its effect on the human body.

OBJECTIVE

This study investigated associations between serum GDF15 levels and clinical parameters in patients with Parkinson disease (PD).

METHODS

Idiopathic PD patients (n = 104) and age-matched controls (n = 88) were enrolled. Serum GDF15 levels were measured by human enzyme-linked immunosorbent assay. Univariate and multivariate analyses investigated correlations between GDF15 and clinical characteristics, including disease severity by the Unified PD Rating Scale (UPDRS)-III. The diagnostic value of GDF15 was evaluated by receiver-operating characteristic curve (ROC) analysis.

RESULTS

The serum GDF15 levels of the PD patients were significantly higher than those of the healthy controls. In PD patients, serum GDF15 levels in men were significantly higher than in women. GDF15 levels correlated with age, gender, disease duration, and UPDRS-III score. After adjusting for confounding factors, multiple linear regression analysis showed that the serum GDF15 level (β = 0.015, p = 0.001) was an independent risk factor for UPDRS-III score. In ROC analysis, GDF15 achieved an area under the curve of 0.86 for the identification of PD, with a sensitivity of 71.15% and a specificity of 87.50%.

CONCLUSION

GDF15 may be a potential biomarker for the diagnosis and monitoring of motor severity in PD.

Neuropathology of Nonmotor Symptoms of Parkinson's Disease

Parkinson's disease (PD), a multiorgan neurodegenerative disorder associated with α-synuclein deposits throughout the nervous system and many organs, is clinically characterized by motor and nonmotor features, many of the latter antedating motor dysfunctions by 20 or more years. The causes of the nonmotor manifestations such as olfactory, autonomic, sensory, neuropsychiatric, visuospatial, sleep, and other disorders are unlikely to be related to single lesions. They are mediated by the involvement of both dopaminergic and nondopaminergic systems, and diverse structures outside the nigrostriatal system that is mainly responsible for the motor features of PD. The nonmotor alterations appear in early/prodromal stages of the disease and its further progression, suggesting a topographical and chronological spread of the lesions. This lends further support for the notion that PD is a multiorgan proteinopathy, although the exact relationship between presymptomatic and later developing nonmotor features of PD and neuropathology awaits further elucidation.

A Role for Neuronal Alpha-Synuclein in Gastrointestinal Immunity

BACKGROUND

Alpha-synuclein (αS) is a nerve cell protein associated with Parkinson disease (PD). Accumulation of αS within the enteric nervous system (ENS) and its traffic from the gut to the brain are implicated in the pathogenesis and progression of PD. αS has no known function in humans and the reason for its accumulation within the ENS is unknown. Several recent studies conducted in rodents have linked αS to immune cell activation in the central nervous system. We hypothesized that αS in the ENS might play a role in the innate immune defenses of the human gastrointestinal (GI) tract.

METHODS

We immunostained endoscopic biopsies for αS from children with documented gastric and duodenal inflammation and intestinal allograft recipients who contracted norovirus. To determine whether αS exhibited immune-modulatory activity, we examined whether human αS induced leukocyte migration and dendritic cell maturation.

FINDINGS

We showed that the expression of αS in the enteric neurites of the upper GI tract of pediatric patients positively correlated with the degree of acute and chronic inflammation in the intestinal wall. In intestinal allograft subjects who were closely monitored for infection, expression of αS was induced during norovirus infection. We also demonstrated that both monomeric and oligomeric αS have potent chemoattractant activity, causing the migration of neutrophils and monocytes dependent on the presence of the integrin subunit, CD11b, and that both forms of αS stimulate dendritic cell maturation.

INTERPRETATION

These findings strongly suggest that αS is expressed within the human ENS to direct intestinal inflammation and implicates common GI infections in the pathogenesis of PD.

Non-motor features of Parkinson disease

Many of the motor symptoms of Parkinson disease (PD) can be preceded, sometimes for several years, by non-motor symptoms that include hyposmia, sleep disorders, depression and constipation. These non-motor features appear across the spectrum of patients with PD, including individuals with genetic causes of PD. The neuroanatomical and neuropharmacological bases of non-motor abnormalities in PD remain largely undefined. Here, we discuss recent advances that have helped to establish the presence, severity and effect on the quality of life of non-motor symptoms in PD, and the neuroanatomical and neuropharmacological mechanisms involved. We also discuss the potential for the non-motor features to define a prodrome that may enable the early diagnosis of PD.

Brain-to-stomach transfer of α-synuclein via vagal preganglionic projections

Detection of α-synuclein lesions in peripheral tissues is a feature of human synucleinopathies of likely pathogenetic relevance and bearing important clinical implications. Experiments were carried out to elucidate the relationship between α-synuclein accumulation in the brain and in peripheral organs, and to identify potential pathways involved in long-distance protein transfer. Results of this in vivo study revealed a route-specific transmission of α-synuclein from the rat brain to the stomach. Following targeted midbrain overexpression of human α-synuclein, the exogenous protein was capable of reaching the gastric wall where it was accumulated into preganglionic vagal terminals. This brain-to-stomach connection likely involved intra- and inter-neuronal transfer of non-fibrillar α-synuclein that first reached the medulla oblongata, then gained access into cholinergic neurons of the dorsal motor nucleus of the vagus nerve and finally traveled via efferent fibers of these neurons contained within the vagus nerve. Data also showed a particular propensity of vagal motor neurons and efferents to accrue α-synuclein and deliver it to peripheral tissues; indeed, following its midbrain overexpression, human α-synuclein was detected within gastric nerve endings of visceromotor but not viscerosensory vagal projections. Thus, the dorsal motor nucleus of the vagus nerve represents a key relay center for central-to-peripheral α-synuclein transmission, and efferent vagal fibers may act as unique conduits for protein transfer. The presence of α-synuclein in peripheral tissues could reflect, at least in some synucleinopathy patients, an ongoing pathological process that originates within the brain and, from there, reaches distant organs innervated by motor vagal projections.

Distinct pattern of enteric phospho-alpha-synuclein aggregates and gene expression profiles in patients with Parkinson's disease

Phosphorylated alpha-synuclein (p-α-syn) containing Lewy bodies (LBs) and Lewy neurites (LNs) are neuropathological hallmarks of Parkinson’s disease (PD) in the central nervous system (CNS). Since they have been also demonstrated in the enteric nervous system (ENS) of PD patients, the aim of the study was to analyze enteric p-α-syn positive aggregates and intestinal gene expression. Submucosal rectal biopsies were obtained from patients with PD and controls and processed for dual-label-immunohistochemistry for p-α-syn and PGP 9.5. p-α-syn positive aggregates in nerve fibers and neuronal somata were subjected to a morphometric analysis. mRNA expression of α-syn and dopaminergic, serotonergic, VIP (vaso intestinal peptide) ergic, cholinergic, muscarinergic neurotransmitter systems were investigated using qPCR. Frequency of p-α-syn positive nerve fibers was comparable between PD and controls. Although neuronal p-α-syn positive aggregates were detectable in both groups, total number and area of p-α-syn positive aggregates were increased in PD patients as was the number of small and large sized aggregates. Increased expression of dopamine receptor D1, VIP and serotonin receptor 3A was observed in PD patients, while serotonin receptor 4 and muscarinic receptor 3 (M3R) were downregulated. M3R expression correlated negative with the number of small sized p-α-syn positive aggregates. The findings strengthen the hypothesis that the CNS pathology of increased p-α-syn in PD also applies to the ENS, if elaborated morphometry is applied and give further insights in altered intestinal gene expression in PD. Although the mere presence of p-α-syn positive aggregates in the ENS should not be regarded as a criterion for PD diagnosis, elaborated morphometric analysis of p-α-syn positive aggregates in gastrointestinal biopsies could serve as a suitable tool for in-vivo diagnosis of PD.

Neuropathological Staging of Brain Pathology in Sporadic Parkinson's disease: Separating the Wheat from the Chaff

A relatively small number of especially susceptible nerve cell types within multiple neurotransmitter systems of the human central, peripheral, and enteric nervous systems (CNS, PNS, ENS) become involved in the degenerative process underlying sporadic Parkinson's disease (sPD). The six-stage model we proposed for brain pathology related to sPD (Neurobiol Aging 2003) was a retrospective study of incidental and clinically diagnosed cases performed on unconventionally thick tissue sections (100 μm) from a large number of brain regions.The staging model emphasized what we perceived to be a sequential development of increasing degrees of Lewy pathology in anatomically interconnected regions together with the loss of aminergic projection neurons in, but not limited to, the locus coeruleus and substantia nigra. The same weight was assigned to axonal and somatodendritic Lewy pathology, and the olfactory bulb was included for the first time in a sPD staging system. After years of research, it now appears that the earliest lesions could develop at nonnigral (dopamine agonist nonresponsive) sites, where the surrounding environment is potentially hostile: the olfactory bulb and, possibly, the ENS. The current lack of knowledge regarding the development of Lewy pathology within the peripheral autonomic nervous system, however, means that alternative extra-CNS sites of origin cannot be disregarded as possible candidates. The PD staging system not only caused controversy but contributed a framework for (1) assessing pathology in the spinal cord, ENS, and PNS in relationship to that evolving in the brain, (2) defining prodromal disease and cohorts of at-risk individuals, (3) developing potential prognostic biomarkers for very early disease, (4) testing novel hypotheses and experimental models of α-synuclein propagation and disease progression, and (5) finding causally-oriented therapies that intervene before the substantia nigra becomes involved. The identification of new disease mechanisms at the molecular and cellular levels indicates that physical contacts (transsynaptic) and transneuronal transmission between vulnerable nerve cells are somehow crucial to the pathogenesis of sPD.

The Concept of Prodromal Parkinson's Disease

Parkinson’s disease (PD) is currently clinically defined by a set of cardinal motor features centred on the presence of bradykinesia and at least one additional motor symptom out of tremor, rigidity or postural instability. However, converging evidence from clinical, neuropathological, and imaging research suggests initiation of PD-specific pathology prior to appearance of these classical motor signs. This latent phase of neurodegeneration in PD is of particular relevance in relation to the development of disease-modifying or neuroprotective therapies which would require intervention at the earliest stages of disease. A key challenge in PD research, therefore, is to identify and validate markers for the preclinical and prodromal stages of the illness. Currently, several nonmotor symptoms have been associated with an increased risk to develop PD in otherwise healthy individuals and ongoing research is aimed at validating a variety of candidate PD biomarkers based on imaging, genetic, proteomic, or metabolomic signatures, supplemented by work on tissue markers accessible to minimally invasive biopsies. In fact, the recently defined MDS research criteria for prodromal PD have included combinations of risk and prodromal markers allowing to define target populations of future disease modification trials.

Optimizing Western Blots for the Detection of Endogenous α-Synuclein in the Enteric Nervous System

BACKGROUND

Alpha-synuclein containing inclusions in neurons, the characteristic pathological lesions of Parkinson's disease (PD), are not limited to the central nervous system, but also affect the enteric nervous system (ENS). This suggests that the ENS offer some potential as a surrogate of central nervous system pathology and that it may represent an original source of biomarkers for PD. However, the usefulness of α-synuclein detection in gastrointestinal biopsies as a biomarker for PD is still unclear, as the different immunohistochemical methods employed to date have led to conflicting results.

OBJECTIVE

Our aim is to propose an optimized immunoblotting method for the detection of endogenous α-synuclein in the healthy ENS that may be used to supplement the immunohistochemical analysis.

METHODS

Primary culture of rat ENS and homogenates of human small intestine were analyzed by Western Blot using seven different α-synuclein and phospho-α-synuclein antibodies along with two methods that increase α-synuclein retention on blot membranes, namely incubation of the membranes with paraformaldehyde (PFA) or treatment of samples with the crosslinker dithiobis[succinimidylpropionate] (DSP).

RESULTS

A moderate improvement in the detection of endogenous enteric α-synuclein was observed following membrane fixation with PFA for only two of the seven antibodies we tested. Immunodetection of total and phosphorylated α-synuclein in the ENS was markedly improved when samples were treated with DSP, regardless of the antibody used.

CONCLUSIONS

Our results demonstrate that the detection of α-synuclein in the gut by Western Blot can be optimized by using methods for enhanced membrane retention of the protein along with the appropriate antibody. Such an optimized protocol opens the way to the development of novel biomarkers for PD that will enable a quantification of α-synuclein in gastrointestinal biopsies.

Alpha-Synuclein in Parkinson's Disease: From Pathogenetic Dysfunction to Potential Clinical Application

Parkinson's disease is a neurodegenerative disease/synucleinopathy that develops slowly; however, there is no efficient method of early diagnosis, nor is there a cure. Progressive dopaminergic neuronal cell loss in the substantia nigra pars compacta and widespread aggregation of the α-synuclein protein (encoded by the SNCA gene) in the form of Lewy bodies and Lewy neurites are the neuropathological hallmarks of Parkinson's disease. The SNCA gene has undergone gene duplications, triplications, and point mutations. However, the specific mechanism of α-synuclein in Parkinson's disease remains obscure. Recent research showed that various α-synuclein oligomers, pathological aggregation, and propagation appear to be harmful in certain areas in Parkinson's disease patients. This review summarizes our current knowledge of the pathogenetic dysfunction of α-synuclein associated with Parkinson's disease and highlights current approaches that seek to develop this protein as a possible diagnostic biomarker and therapeutic target.

What a gastrointestinal biopsy can tell us about Parkinson's disease?

BACKGROUND

The intraneuronal inclusions called Lewy bodies and neurites, which represent the characteristic pathological changes in Parkinson's disease, are found in the enteric neurons in the great majority of parkinsonian patients. This observation led to a substantial amount of research over the last few years in order to develop a minimally invasive diagnostic procedure in living patients based on gastrointestinal (GI) biopsies.

PURPOSE

In this review, we will begin by discussing the studies that focused on the detection of Lewy bodies and neurites in GI biopsies, then broaden the discussion to the pathological changes that also occur in the enteric glial cells and intestinal epithelial cells. We conclude by proposing that a GI biopsy could represent a unique window to assess the whole pathological process of the brain in Parkinson's disease.

Quantifying rigidity of Parkinson's disease in relation to laxative treatment: a service evaluation

Aim

To estimate whether laxatives prescribed for constipation in Parkinson's disease (PD) could moderate rigidity. Constipation predates diagnosis of PD by decades. Deposition of misfolded protein may begin in the gut, driven by dysbiosis. Successive antimicrobial exposures are associated with cumulative increase in rigidity, and rigidity has biological gradients on circulating leukocyte‐subset counts.

Methods

Retrospective service evaluation, in a gut/brain axis clinic, yielded an interrupted time series, relating maintenance laxative and other medication to rigidity, in consecutive outpatients identified by inclusion and exclusion criteria. Objective assessment of rigidity was used to bring greater sensitivity to change, validated against subjective gold standard (UPDRS).

Results

There were 1493 measurements of torque required to extend (flexor rigidity) and flex (extensor rigidity) the forearm in 79 PD patients over 374 person‐years. Both were strongly associated with UPDRS (P < 0.001 and P = 0.008, respectively). Before exhibition of laxative, flexor rigidity increased by 6% (95% CI 1, 10) per year, plateauing at −2% (−4, 1) per year after, with no shift at initiation. Change in slope was significant (P = 0.002), and manifest in those naïve to antiparkinsonian medication. The change was replicated for individual laxative classes (bulk, osmotic, enterokinetic). There was no temporal change in extensor rigidity. Limited experience with a quanylate cyclase‐C receptor agonist (17 patients, 6 person‐years) indicated a large and significant step down in flexor and extensor rigidity, of 19% (1, 34) and 16% (6, 24) respectively (P = 0.04 and <0.001).

Conclusions

Maintenance laxative usage was associated with apparent stemming of the temporal increase in rigidity in PD, adding to indicative evidence of a continuing role of gastrointestinal dysbiosis in pathogenesis.

Evaluation of alpha-synuclein immunohistochemical methods for the detection of Lewy-type synucleinopathy in gastrointestinal biopsies

The observation showing that Lewy type synucleinopathy (LTS), the pathological hallmark of Parkinson's disease (PD), is found in the gut of almost all PD subjects led to a substantial amount of research to develop a diagnostic procedure in living patients based on endoscopically obtained gastrointestinal biopsies. However, the existing studies have provided conflicting results regarding the sensitivity and specificity of gastrointestinal biopsies for the detection of LTS. We therefore undertook a multi-center staining and blinded judging of a common set of slides from colonic biopsies to determine the optimal protocol for the detection of LTS. Four different immunohistochemical methods, developed in four separate expert laboratories, were evaluated for their sensitivity and specificity to detect enteric LTS. Test sets of formalin-fixed, paraffin-embedded sections from biopsies of 9 PD subjects and 3 controls were stained with the 4 methods and graded by 4 different observers. Four types of staining morphology (granular staining in the lamina propria, perivascular/vascular wall staining in the submucosa, lacy-granular pattern in the submucosa and epithelial cell nuclear staining) were variably observed in the slides stained by the 4 methods. Positive alpha-synuclein staining was observed by all 5 judges in most of the slides from control cases, regardless of the staining methods that were used. Moreover, none of the tested method or staining pattern had a specificity and sensitivity more than 80 % regarding to PD. Overall, our study suggest that the tested methods are not adequate for the prediction of PD using gastrointestinal biopsies. Future studies are warranted to test new immunostaining methods.

Evaluation of alpha-synuclein immunohistochemical methods for the detection of Lewy-type synucleinopathy in gastrointestinal biopsies

The observation showing that Lewy type synucleinopathy (LTS), the pathological hallmark of Parkinson's disease (PD), is found in the gut of almost all PD subjects led to a substantial amount of research to develop a diagnostic procedure in living patients based on endoscopically obtained gastrointestinal biopsies. However, the existing studies have provided conflicting results regarding the sensitivity and specificity of gastrointestinal biopsies for the detection of LTS. We therefore undertook a multi-center staining and blinded judging of a common set of slides from colonic biopsies to determine the optimal protocol for the detection of LTS. Four different immunohistochemical methods, developed in four separate expert laboratories, were evaluated for their sensitivity and specificity to detect enteric LTS. Test sets of formalin-fixed, paraffin-embedded sections from biopsies of 9 PD subjects and 3 controls were stained with the 4 methods and graded by 4 different observers. Four types of staining morphology (granular staining in the lamina propria, perivascular/vascular wall staining in the submucosa, lacy-granular pattern in the submucosa and epithelial cell nuclear staining) were variably observed in the slides stained by the 4 methods. Positive alpha-synuclein staining was observed by all 5 judges in most of the slides from control cases, regardless of the staining methods that were used. Moreover, none of the tested method or staining pattern had a specificity and sensitivity more than 80 % regarding to PD. Overall, our study suggest that the tested methods are not adequate for the prediction of PD using gastrointestinal biopsies. Future studies are warranted to test new immunostaining methods.

α-Synuclein in Extracellular Vesicles: Functional Implications and Diagnostic Opportunities

Fibrillar inclusions of intraneuronal α-synuclein can be detected in certain brain areas from patients with Parkinson's disease (PD) and other disorders with Lewy body pathology. These insoluble protein aggregates do not themselves appear to have a prominent neurotoxic effect, whereas various α-synuclein oligomers appear harmful. Although it is incompletely known how the prefibrillar species may be pathogenic, they have been detected both within and on the outside of exosomes and other extracellular vesicles (EVs), suggesting that such structures may mediate toxic α-synuclein propagation between neurons. Vesicular transfer of α-synuclein may thereby contribute to the hierarchical spreading of pathology seen in the PD brain. Although the regulation of α-synuclein release via EVs is not understood, data suggest that it may involve other PD-related molecules, such as LRRK2 and ATP13A2. Moreover, new evidence indicates that CNS-derived EVs in plasma have the potential to serve as biomarkers for diagnostic purposes. In a recent study, levels of α-synuclein were found to be increased in L1CAM-positive vesicles isolated from plasma of PD patients compared to healthy controls, and follow-up studies will reveal whether α-synuclein in EVs could be developed as a future disease biomarker. Preferentially, toxic prefibrillar α-synuclein oligomers should then be targeted as a biomarker-as evidence suggests that they reflect the disease process more closely than total α-synuclein content. In such studies, it will be essential to adopt stringent EV isolation protocols in order to avoid contamination from the abundant pool of free plasma α-synuclein in different aggregational states.

Gut Feelings About α-Synuclein in Gastrointestinal Biopsies: Biomarker in the Making?

In recent years, several studies have investigated the potential of immunohistochemical detection of α-synuclein in the gastrointestinal tract to diagnose Parkinson's disease (PD). Although methodological heterogeneity has hindered comparability between studies, it has become increasingly apparent that the high sensitivity and specificity reported in preliminary studies has not been sustained in subsequent large-scale studies. What constitutes pathological α-synuclein in the alimentary canal that could distinguish between PD patients and controls and how this can be reliably detected represent key outstanding questions in the field. In this review, we will comment on and compare the variable technical aspects from previous studies, and by highlighting some advantages and shortcomings we hope to delineate a standardized approach to facilitate the consensus criteria urgently needed in the field. Furthermore, we will describe alternative detection techniques to conventional immunohistochemistry that have recently emerged and may facilitate ease of interpretation and reliability of gastrointestinal α-synuclein detection. Such techniques have the potential to detect the presence of pathological α-synuclein and include the paraffin-embedded tissue blot, the proximity ligation assay, the protein misfolding cyclic amplification technique, and the real-time quaking-induced conversion assay. Finally, we will review 2 nonsynonymous theories that have driven enteric α-synuclein research, namely, (1) that α-synuclein propagates in a prion-like fashion from the peripheral nervous system to the brain via vagal connections and (2) that gastrointestinal α-synuclein deposition may be used as a clinically useful biomarker in PD.

Protective effect of simvastatin on impaired intestine tight junction protein ZO-1 in a mouse model of Parkinson's disease

Recently, several studies showed that gastrointestinal tract may be associated with pathophysiology of Parkinson's disease (PD). Intestine tight junction protein zonula occluden-1 (ZO-1) is an important component of intestinal barrier which can be degraded by matrix metallopeptidase 9 (MMP-9). In our previous study, a significant decline in ZO-1 was observed along with enhanced MMP-9 activity in the duodenum and distal colon of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-intoxicated mice. In this study, the protective effect of simvastatin on ZO-1 was investigated using an MPTP mouse model of PD. Seven days after the end of MPTP application, the expression level of ZO-1 was evaluated by immunohistochemistry. The protein expression levels of ZO-1 and MMP9 were detected by Western blotting. Meanwhile, MMP-9 activity was analyzed by gelatin zymography. MPTP treatment led to a decrease in the expression of ZO-1, which was accompanied by elevated MMP-9 activity. Treatment with simvastatin could partly reverse the MPTP-induced changes in ZO-1 expression and reduce MMP-9 protein and activity. Taken together, these findings suggest that simvastatin administration may partially reverse the impairment of ZO-1 induced by MPTP via inhibiting the activity of MMP9, fortify the impaired intestinal barrier and limit gut-derived toxins that pass across the intestinal barrier.

Biomarkers in Parkinson's disease: Advances and strategies

Parkinson's disease (PD) is a neurodegenerative disorder characterized by progressive motor disturbances and affects more than 1% of the worldwide population. Despite considerable progress in understanding PD pathophysiology, including genetic and biochemical causes, diagnostic approaches lack accuracy and interventions are restricted to symptomatic treatments. PD is a complex syndrome with different clinical subtypes and a wide variability in disorder course. In order to deliver better clinical management of PD patients and discovery of novel therapies, there is an urgent need to find sensitive, specific, and reliable biomarkers. The development of biomarkers will not only help the scientific community to identify populations at risk, but also facilitate clinical diagnosis. Furthermore, these tools could monitor progression, which could ultimately deliver personalized therapeutic strategies. The field of biomarker discovery in PD has attracted significant attention and there have been numerous contributions in recent years. Although none of the parameters have been validated for clinical practice, some candidates hold promise. This review summarizes recent advances in the development of PD biomarkers and discusses new strategies for their utilization.

Colonic bacterial composition in Parkinson's disease

INTRODUCTION

We showed that Parkinson's disease (PD) patients have alpha-synuclein (α-Syn) aggregation in their colon with evidence of colonic inflammation. If PD patients have altered colonic microbiota, dysbiosis might be the mechanism of neuroinflammation that leads to α-Syn misfolding and PD pathology.

METHODS

Sixty-six sigmoid mucosal biopsies and 65 fecal samples were collected from 38 PD patients and 34 healthy controls. Mucosal-associated and feces microbiota compositions were characterized using high-throughput ribosomal RNA gene amplicon sequencing. Data were correlated with clinical measures of PD, and a predictive assessment of microbial community functional potential was used to identify microbial functions.

RESULTS

The mucosal and fecal microbial community of PD patients was significantly different than control subjects, with the fecal samples showing more marked differences than the sigmoid mucosa. At the taxonomic level of genus, putative, "anti-inflammatory" butyrate-producing bacteria from the genera Blautia, Coprococcus, and Roseburia were significantly more abundant in feces of controls than PD patients. Bacteria from the genus Faecalibacterium were significantly more abundant in the mucosa of controls than PD. Putative, "proinflammatory" Proteobacteria of the genus Ralstonia were significantly more abundant in mucosa of PD than controls. Predictive metagenomics indicated that a large number of genes involved in metabolism were significantly lower in the PD fecal microbiome, whereas genes involved in lipopolysaccharide biosynthesis and type III bacterial secretion systems were significantly higher in PD patients.

CONCLUSION

This report provides evidence that proinflammatory dysbiosis is present in PD patients and could trigger inflammation-induced misfolding of α-Syn and development of PD pathology.

Alpha-synuclein immunoreactivity patterns in the enteric nervous system

We aimed to compare immunoreactivity patterns of four different anti-α-syn antibodies in surgical specimens of the gastrointestinal tract of Parkinson disease and control cases. Surgical specimens from stomach, small and large bowel of 6 PD cases and 12 controls were studied. Primary antibodies: anti-α-syn clone KM51, anti-phosphorylated α-syn Ser129, anti-α-syn clone 15G7 and anti-nitrated α-syn505. We found different immunoreactivity patterns: (a) coarse, Lewy-body-like aggregates labelled by the 4 antibodies and detected in 4/6 PD cases and in 1/12 controls; (b) distinct punctate cytoplasmic staining of ganglion cells labelled by anti-phosphorylated-α-syn and detected in 3/6 PD cases and 3/12 controls; (c) fine diffuse, synaptic-type staining of neural structures labelled by anti-α-syn-15G7 and anti-nitrated-α-syn505 and detected in all subjects. We conclude that different specific and non-specific immunoreactivity patterns are detected in surgical specimens of gastrointestinal tract when using different anti-α-syn antibodies, as they recognize different epitopes and states of alpha-synuclein protein. Coarse aggregates in neural structures seem to be the most promising marker for the diagnosis of Lewy-body parkinsonism when evaluating abnormal α-syn in the gastrointestinal tract.

Can we use peripheral tissue biopsies to diagnose Parkinson's disease? A review of the literature

Phosphorylated α-synuclein (phosαSYN) containing inclusions in neurons (Lewy bodies, LB) and nerve terminals (Lewy neurites, LN), the pathological hallmark of Parkinson's disease (PD), are not confined to the central nervous system, but have also been reported in peripheral tissues. However, the usefulness of αSYN/phosαSYN detection in tissues accessible to biopsies as a reliable biomarker for prodromal PD remains unclear. A systematic review of studies using biopsies of skin, olfactory and gastrointestinal (GI) tissues was conducted to evaluate the sensitivity and specificity of both αSYN and phosαSYN staining in PD patients. Data analysis was hampered by the diversity of the methods used, e.g. choice of biopsy sites, tissue processing, staining protocols and evaluation of the findings. Tissue obtained from GI tract/salivary glands (13 post-mortem, 13 in vivo studies) yielded the highest overall sensitivity and specificity compared to skin (three post-mortem, eight in vivo studies) and olfactory mucosa/bulb (six post-mortem studies, one in vivo study). In contrast to phosαSYN, αSYN was more consistently detectable in peripheral tissues of healthy controls. GI tract/salivary glands appear to be the most promising candidate tissue for peripheral biopsy-taking. phosαSYN is considered as the marker of choice to delineate pathological aggregates from normal αSYN regularly found in peripheral neural tissues. However, the sensitivity and specificity of phosαSYN are not yet acceptable for using phosαSYN as a reliable peripheral biomarker for PD in clinical routine. Further refinement regarding the interpretation of the peripheral αSYN/phosαSYN burden and the phenotypical definition of peripheral LB/LN is needed to optimize screening methods for prodromal PD.

Gastrointestinal Biopsies for the Diagnosis of Alpha-Synuclein Pathology in Parkinson's Disease

The diagnosis of Parkinson's disease (PD) relies on clinical features whereas pathological confirmation is only possible with autopsy examination. The neuropathological hallmarks of PD are neuronal loss and the presence of inclusions termed Lewy bodies/neurites in affected regions. A major component of these inclusions is phosphorylated alpha-synuclein (α-SYN) protein. There is evidence that α-SYN pathology is widely distributed outside the central nervous system in patients with PD. The gastrointestinal tract is importantly affected by α-SYN containing inclusions and typically there is a rostrocaudal gradient for the distribution of the pathology. The highest amounts of Lewy bodies/neurites are found at the submandibular gland together with the lower esophagus and the lowest amounts are found in the rectum. Autopsy findings prompted research aimed at achieving in vivo pathological diagnosis of PD by demonstrating the presence of α-SYN pathology in biopsy material of these peripheral accessible tissues. So far, biopsy studies of the gut have demonstrated the presence of α-SYN pathology in the salivary glands, stomach, duodenum, colon, and rectum. Further research is necessary in order to determine which are the most sensitive targets for in vivo α-SYN pathology detection and the safest techniques for these approaches in patients with PD.