The heart of PD: Lewy body diseases as neurocardiologic disorders

Phenoconversion in pure autonomic failure: a multicentre prospective longitudinal cohort study

We aimed to describe the clinical features of patients with pure autonomic failure (PAF) preceding phenoconversion that could be useful as predictive markers for advancing α-synuclein-associated neurodegeneration of the brain. Patients diagnosed with PAF were evaluated at eight centres (seven US-based and one European) and enrolled in a longitudinal observational cohort study (NCT01799915). Subjects underwent detailed assessments of motor, sleep, olfactory, cognitive and autonomic function and were followed prospectively to determine whether they developed parkinsonism or dementia for up to 10 years. We identified incident cases of Parkinson's disease (PD), dementia with Lewy bodies (DLB) or multiple system atrophy (MSA) and computed hazard ratios for phenoconversion as functions of clinical features. A total of 209 participants with PAF with a median disease duration of 6 years (IQR: 3-10) were enrolled. Of those, 149 provided follow-up information at an office or telemedicine visit. After a mean follow-up duration of 3 years, 48 (33%) participants phenoconverted (42% to PD, 35% to DLB and 23% to MSA). Faster phenoconversion from study enrolment to any diagnosis was associated with urinary and sexual dysfunction [hazard ratio (HR) 5.9, 95% confidence interval (CI): 1.6-22 and HR: 3.6, 95% CI: 1.1-12] followed by subtle motor signs (HR: 2.7, 95% CI: 1.2-6), trouble swallowing (HR 2.5, 95% CI: 1.4-4.5) and changes in speech (HR:2.4, 95% CI:1.1-4.8) at enrolment. Subjects reporting deterioration of handwriting were more likely to phenoconvert to PD (HR: 2.6, 95% CI: 1.1-5.9) and those reporting difficulty handling utensils were more likely to phenoconvert to DLB (HR: 6.8, 95% CI: 1.2-38). Patients with a younger age of PAF onset (HR: 11, 95% CI: 2.6-46), preserved olfaction (HR: 8.7, 95% CI: 1.7-45), anhidrosis (HR: 1.8, 95% CI: 1-3.1, P = 0.042) and severe urinary problems (HR 1.6, 95% CI: 1-2.5, P = 0.033) were more likely to phenoconvert to MSA. The best autonomic predictor of PD was a blunted heart rate increase during the tilt-table test (HR: 6.1, 95% CI: 1.4-26). Patients with PAF have an estimated 12% (95% CI: 9-15%) per year annual risk following study entry of phenoconverting to a manifest CNS synucleinopathy.

Noradrenergic cardiac denervation is associated with gait velocity in Parkinson disease: a dual ligand PET study

PURPOSE

Preliminary data suggest that gait abnormalities in Parkinson disease (PD) may be associated with sympathetic cardiac denervation. No kinematic gait studies were performed to confirm this observation. We aimed to correlate spatiotemporal kinematic gait parameters with cardiac sympathetic denervation as determined by cardiac [11C]HED PET in PD.

METHODS

Retrospective database analysis of 27 PD patients with cardiac sympathetic denervation. All patients underwent spatiotemporal kinematic gait assessment (medication 'off' state), cardiac [11C]HED and dopaminergic brain [11C]DTBZ PET scans. We employed a hierarchical regression approach to examine associations between the extent of cardiac denervation, dopaminergic nigrostriatal neurodegeneration, and three gait parameters - velocity, step length and cadence.

RESULTS

More extensive cardiac denervation was associated with slower velocity (estimate: -1.034, 95% CI [-1.65, -0.42], p = 0.002), shorter step length (estimate: -0.818, 95% CI [-1.43, -0.21], p = 0.011) and lower cadence (estimate: -0.752, 95% CI [-1.28, -0.23], p = 0.007) explaining alone 30% (Adjusted-R²: 0.297), 20% (Adjusted-R²: 0.202) and 23% (Adjusted-R²: 0.227) of the variability, respecivetly. These associations remained independent of striatal dopaminergic impairment and confounding factors such as age, Hoehn and Yahr (HY) stages, peripheral neuropathy, cognition, and autonomic symptoms. In contrast, striatal dopaminergic denervation was significantly associated with step length (estimate: 0.883, 95% CI [0.29, 1.48], p = 0.005), explaining about 24% of the variability but was dependent of HY stage.

CONCLUSIONS

More severe cardiac noradrenergic denervation was associated with lower gait velocity, independent of striatal dopaminergic denervation and HY stage, impacting both step length and cadence. These results suggest independent contributions of the peripheral autonomic system degeneration on gait dynsfunction in PD.

Chronic and acute exposure to rotenone reveals distinct Parkinson's disease-related phenotypes in human iPSC-derived peripheral neurons

Peripheral autonomic nervous system (P-ANS) dysfunction is a critical non-motor phenotype of Parkinson's disease (PD). The majority of PD cases are sporadic and lack identified PD-associated genes involved. Epidemiological and animal model studies suggest an association with pesticides and other environmental toxins. However, the cellular mechanisms underlying toxin induced P-ANS dysfunctions remain unclear. Here, we mapped the global transcriptome changes in human induced pluripotent stem cell (iPSC) derived P-ANS sympathetic neurons during inhibition of the mitochondrial respiratory chain by the PD-related pesticide, rotenone. We revealed distinct transcriptome profiles between acute and chronic exposure to rotenone. In the acute stage, there was a down regulation of specific cation channel genes, known to mediate electrophysiological activity, while in the chronic stage, the human P-ANS neurons exhibited dysregulation of anti-apoptotic and Golgi apparatus-related pathways. Moreover, we identified the sodium voltage-gated channel subunit SCN3A/Nav1.3 as a potential biomarker in human P-ANS neurons associated with PD. Our analysis of the rotenone-altered coding and non-coding transcriptome of human P-ANS neurons may thus provide insight into the pathological signaling events in the sympathetic neurons during PD progression.

Cardiac sympathetic "morbidity" might reflect the neurobiology of early Parkinson's disease

BACKGROUND

An appropriate extracranial biomarker that delineates endophenotypes of Parkinson's disease (PD) at an early stage and reflects the neurodegenerative process is lacking. An evaluation of myocardial sympathetic nerve terminals could be a good candidate. This study aimed to explore subtypes of PD patients that showed cardiac catecholaminergic vesicular defect and their characteristics.

METHODS

This study included 122 early drug-naïve PD patients who were followed for approximately 4-5 years. All patients were examined with 18F-N-(3-fluoropropyl)-2beta-carbon ethoxy-3beta-(4-iodophenyl) nortropane positron-emission tomography and 123I-meta-iodobenzylguanidine myocardial scintigraphy. Cardiac scans were reexamined two or three times. Patients were subgrouped into the sympathetic denervated group at the initial scan, those without evidence of denervated myocardium in the first and subsequent scans, and the converters whose myocardium was initially normal but became impaired in the subsequent scans. Cognition in 99 patients was initially assessed with neuropsychological tests. Any associations between cardiac denervation subtypes and presynaptic dopamine transporter densities were investigated. Cognitive status relevant to cardiac sympathetic denervation status was evaluated.

RESULTS

This study found that cross-sectional comparisons of presynaptic monoamine transporter availability with a predefined order of cardiac denervation groups revealed parallel degeneration. A quadratic correlation between cardiac catecholamine capacity and cognition was observed. This association was interpreted to reflect the early neurobiology of PD.

CONCLUSION

An observed cardiac catecholaminergic gradient was to mirror the central neurobiology of early PD.

Synchronous monitoring of brain-heart electrophysiology using heart rate variability coupled with rapid quantitative electroencephalography in orthostatic hypotension patients with α-synucleinopathies: Rapid prediction of orthostatic hypotension and preliminary exploration of brain stimulation therapy

BACKGROUND

In α-synucleinopathies, the dysfunction of the autonomic nervous system which typically manifests as orthostatic hypotension (OH) often leads to severe consequences and poses therapeutic challenges. This study aims to discover the brain-cardiac electrophysiological changes in OH patients with α-synucleinopathies using the rapid quantitative electroencephalography (qEEG) coupled with heart rate variability (HRV) technique to identify rapid, noninvasive biomarkers for early warning and diagnosis, as well as shed new light on complementary treatment approaches such as brain stimulation targets.

METHODS

In this study, 26 subjects of α-synucleinopathies with OH (α-OH group), 21 subjects of α-synucleinopathies without OH (α-NOH group), and 34 healthy controls (control group) were included from September 2021 to August 2023 (NCT05527067). The heart rate-blood pressure variations in supine and standing positions were monitored, and synchronization parameters of seated resting-state HRV coupled with qEEG were collected. Time-domain and frequency-domain of HRV measures as well as peak frequency and power of the brainwaves were extracted. Differences between these three groups were compared, and correlations between brain-heart parameters were analyzed.

RESULTS

The research results showed that the time-domain parameters such as MxDMn, pNN50, RMSSD, and SDSD of seated resting-state HRV exhibited a significant decrease only in the α-OH group compared to the healthy control group (p < 0.05), while there was no significant difference between the α-NOH group and the healthy control group. Several time-domain and frequency-domain parameters of seated resting-state HRV were found to be correlated with the blood pressure changes within the first 5 min of transitioning from supine to standing position (p < 0.05). Differences were observed in the power of beta1 waves (F4 and Fp2) and beta2 waves (Fp2 and F4) in the seated resting-state qEEG between the α-OH and α-NOH groups (p < 0.05). The peak frequency of theta waves in the Cz region also showed a difference (p < 0.05). The power of beta2 waves in the Fp2 and F4 brain regions correlated with frequency-domain parameters of HRV (p < 0.05). Additionally, abnormal electrical activity in the alpha, theta, and beta1 waves was associated with changes in heart rate and blood pressure within the first 5 min of transitioning from supine to standing position (p < 0.05).

CONCLUSION

Rapid resting-state HRV with certain time-domain parameters below normal levels may serve as a predictive indicator for the occurrence of orthostatic hypotension (OH) in patients with α-synucleinopathies. Additionally, the deterioration of HRV parameters correlates with synchronous abnormal qEEG patterns, which can provide insights into the brain stimulation target areas for OH in α-synucleinopathy patients.

Phosphorylated α-synuclein deposited in Schwann cells interacting with TLR2 mediates cell damage and induces Parkinson's disease autonomic dysfunction

Despite the significant frequency of autonomic dysfunction (AutD) in Parkinson's disease (PD) patients, its pathogenesis and diagnosis are challenging. Here, we aimed to further explore the mechanism of phosphorylated α-synuclein (p-α-syn) deposited in vagus nerve Schwann cells (SCs) causing SCs damage and PD AutD. 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP, 20 mg/kg) was administrated to C57BL/6 mice twice a week for 35 days. Following the final injection, locomotor functions, gastrointestinal symptoms, urine functions, and cardiovascular system functions were evaluated. Meanwhile, we examined p-α-syn deposited in vagus nerve SCs, Toll-like receptor 2 (TLR2) activation, and SCs loss using immunofluorescence, western blot, and Luxol fast blue staining. In vitro, the rat SCs line RSC96 cells were exposed to α-synuclein preformed fibril (α-syn PFF), and cell viability was detected by CCK8. Co-IP was used to identify the interaction between p-α-syn and TLR2. Furthermore, the role of TLR2 in p-α-syn-mediated SCs damage was confirmed by the administration of CU-CPT22, a specific blocker of TLR2. In vivo, apart from dyskinesia, MPTP mice exhibited constipation, urinary dysfunction, and cardiovascular failure, which were associated with the deposition of p-α-syn in vagus nerve SCs, TLR2 activation, and vagus nerve demyelination. In vitro, stimulation of α-syn PFF induced a time-dependent loss of viability, and p-α-syn deposited in RSC96 cells induced a cellular inflammatory response by interacting with TLR2, resulting in cell dysfunction and apoptosis. However, both SCs inflammatory response and cell viability were alleviated after inhibition of TLR2. Furthermore, 1 h fecal pellets and water content, the frequency of 1 h urine, blood pressure, heart rate, and heart rate variability of mice in the MPTP + CU-CPT22 group were also improved. Our results support the perspective that p-α-syn interacts with TLR2 induced SCs damage and is involved in PD AutD, which sheds fresh light on the mechanism of PD AutD and indicates a promising treatment for PD AutD targeting SCs p-α-syn/ TLR2 signaling pathway.

Setting the clinical context to non-motor symptoms reflected by Park-pain, Park-sleep, and Park-autonomic subtypes of Parkinson's disease

Non-motor symptoms (NMS) of Parkinson's disease (PD) are well described in both clinical practice and the literature, enabling their management and enhancing our understanding of PD. NMS can dominate the clinical pictures and NMS subtypes have recently been proposed, initially based on clinical observations, and later confirmed in data driven analyses of large datasets and in biomarker-based studies. In this chapter, we provide an update on what is known about three common subtypes of NMS in PD. The pain (Park-pain), sleep dysfunction (Park-sleep), and autonomic dysfunction (Park-autonomic), providing an overview of their individual classification, clinical manifestation, pathophysiology, diagnosis, and potential treatments.

The Association between Parkinson's Disease and Congestive Heart Failure in Korea: A Nationwide Longitudinal Cohort Study

The purpose of this nationwide longitudinal follow-up study is to investigate the relationship between Parkinson's disease (PD) and congestive heart failure (CHF) patients in Korea. Patient data were collected using the National Health Insurance Service (NHIS) Health Screening (HEALS) cohort. The International Classification of Diseases 10-CM code G-20 distinguished 6475 PD patients who were enrolled in the PD group. After removing 1039 patients who were not hospitalized or attended an outpatient clinic less than twice, the total number of participants was reduced to 5436 individuals. Then, 177 patients diagnosed before 1 January 2004 were removed for relevancy, leaving us with 5259 PD patients. After case-control matching was completed using 1:5 age- and gender-coordinated matching, 26,295 people were chosen as part of the control group. The Cox proportional hazards regression analysis and the Kaplan-Meier technique were used to assess the risk of CHF in patients with Parkinson's disease. After controlling for age and gender, the hazard ratio of CHF in the PD group was 5.607 (95% confidence interval (CI), 4.496-6.993). After that, the hazard ratio of CHF in the PD group was modified against for comorbid medical disorders, resulting in a value of 5.696 (95% CI, 4.566-7.107). In subgroup analysis, CHF incidence rates were significantly increased in the PD group compared to the control group (males and females; aged ≥ 65 and <65; the non-diabetes and diabetes, hypertension and non-hypertension, and dyslipidemia and non-dyslipidemia subgroups). This nationwide longitudinal study shows a higher incidence rate of CHF in PD patients.

Risk of myocardial infarction in Parkinson's disease: A systematic review and meta-analysis

BACKGROUND AND PURPOSE

Previous studies investigating cardiovascular disorders in patients with Parkinson's disease (PD) showed heterogeneous results regarding whether there is a higher or lower risk of myocardial infarction (MI) in these patients compared to the general population. Because of the inconsistency in findings, herein the aim was to perform a systematic review and meta-analysis to investigate the risk of MI in patients with PD.

METHODS

A comprehensive literature search was performed using four databases, PubMed, Web of Science, Scopus and Embase, in June 2022. Peer-reviewed observational studies comprising case-controls, cohort, cross-sectional and longitudinal studies that reported MI in the PD population were included.

RESULTS

After the screening, 20 studies with a total of 80,441 patients with PD and 802,857 controls were included in our qualitative and quantitative synthesis. The pooled estimated odds ratio for MI in PD patients compared to controls was 0.80 (95% confidence interval [CI] 0.56-1.05) which indicates that there is no association. The pooled prevalence of MI was 5% (95% CI 3%-7%) with a range of 1%-20% amongst patients with PD. The men (6%, 95% CI 1%-13%) and women (6%, 95% CI 1%-14%, Q = 29.27, I2 = 98.50%, p < 0.001) had similar MI prevalence.

CONCLUSION

This comprehensive systematic review and meta-analysis provide compelling evidence that PD is associated with a reduced risk of MI. Whilst the exact mechanism underlying this association remains to be fully elucidated, it is clear that certain risk factors for cardiac events appear to be less present in PD patients, which may serve as a protective factor. However, given the reports of increased risk for cerebrovascular events in PD patients, it is possible that the major risk factors for MI and cardiovascular accidents in this population differ. These findings have important implications for clinical management and further research in this area is warranted.

Cardiac 18F-Dopamine Positron Emission Tomography Predicts the Type of Phenoconversion of Pure Autonomic Failure

Background

Pure autonomic failure (PAF) is a rare disease characterized clinically by neurogenic orthostatic hypotension (nOH) and biochemically by peripheral noradrenergic deficiency. Clinically diagnosed PAF can evolve ("phenoconvert") to a central Lewy body disease (LBD, e.g., Parkinson's disease (PD) or dementia with Lewy bodies (DLB)) or to the non-LBD synucleinopathy multiple system atrophy (MSA). We examined whether cardiac 18F-dopamine positron emission tomography (PET) predicts the trajectory of phenoconversion in PAF. Since cardiac 18F-dopamine-derived radioactivity always is decreased in LBDs with nOH and usually is normal in MSA, we hypothesized that PAF patients with low cardiac 18F-dopamine-derived radioactivity may phenoconvert to a central LBD but do not phenoconvert to MSA.

Methods

We reviewed data from all the patients seen at the National Institutes of Health Clinical Center from 1994 to 2023 with a clinical diagnosis of PAF and data about serial 18F-dopamine PET.

Results

Twenty patients met the above criteria. Of 15 with low cardiac 18F-dopamine-derived radioactivity, 6 (40%) phenoconverted to PD or DLB and none to MSA. Of 5 patients with consistently normal 18F-dopamine PET, 4 phenoconverted to MSA, and the other at autopsy had neither a central LBD nor MSA.

Conclusion

In this case series, 40% of patients with nOH and low cardiac 18F-dopamine-derived radioactivity phenoconverted to PD or DLB during follow-up; none phenoconverted to MSA. Cardiac 18F-DA PET therefore can predict the type of phenoconversion in PAF. This capability could refine eligibility criteria for entry into disease-modification trials aiming to prevent evolution of PAF to symptomatic central LBDs.

A 3-year natural history of orthostatic blood pressure dysregulation in early Parkinson's disease

In Parkinson's disease (PD), cardiovascular dysautonomia accumulates with disease progression, but studies are lacking on the natural history behind each subtype except orthostatic hypotension. This study investigated the early natural history of orthostatic blood pressure (BP) subtypes in PD. Two hundred sixty-seven early PD patients were included. Their cardiovascular functions were assessed by head-up tilt-test and ¹²³I-metaiodobenzylguanidine scintigraphy. All patients were classified as having supine hypertension (SH), orthostatic hypertension (OHT), delayed orthostatic hypotension (dOH), or orthostatic hypotension (OH) according to consensus criteria. The patients were assigned to one of three groups: extreme BP dysregulation (BP_extreme), mild BP dysregulation (BP_mild), and no BP dysregulation (BP_none) according to their orthostatic BP subtypes. The autonomic functions of 237 patients were re-assessed after approximately 3 years. Among initially enrolled subjects, 61.8% of the patients showed orthostatic BP dysregulation: 29.6% in the BP_extreme group and 32.2% in the BP_mild group. At follow-up, the BP_extreme group increased in number, while the BP_mild group diminished. Two-thirds of the initial BP_extreme patients maintained their initial subtype at follow-up. In comparison, 40.7% of the initial BP_mild patients progressed to the BP_extreme group, and 32.4% and 14.7% of the initial BP_none group progressed to BP_extreme and BP_mild groups, respectively. Cardiac denervation was most severe in the BP_extreme group, and a linear gradient of impairment was observed across the subtypes. In conclusion, various forms of positional BP dysregulation were observed during the early disease stage. SH and OH increased with disease progression, while OHT and dOH decreased, converting primarily to SH and/or OH.

Heart-rate variability as a new marker for freezing predisposition in Parkinson's disease

INTRODUCTION

Freezing of gait (FoG) is a debilitating symptom of advanced Parkinson's disease (PD) characterized by a sudden, episodic stepping arrest despite the intention to continue walking. The etiology of FoG is still unknown, but accumulating evidence unraveled physiological signatures of the autonomic nervous system (ANS) around FoG episodes. Here we aim to investigate for the first time whether detecting a predisposition for upcoming FoG events from ANS activity measured at rest is possible.

METHODS

We recorded heart-rate for 1-min while standing in 28 persons with PD with FoG (PD + FoG), while OFF, and in 21 elderly controls (EC). Then, PD + FoG participants performed walking trials containing FoG-triggering events (e.g., turns). During these trials, n = 15 did experience FoG (PD + FoG+), while n = 13 did not (PD + FoG-). Most PD participants (n = 20: 10 PD + FoG+ and 10 PD + FoG-) repeated the experiment 2-3 weeks later, while ON, and none experienced FoG. We then analyzed heart-rate variability (HRV), i.e., the fluctuations in time intervals between adjacent heartbeats, mainly generated by brain-heart interactions.

RESULTS

During OFF, HRV was significantly lower in PD + FoG + participants, reflecting imbalanced sympathetic/parasympathetic activity and disrupted self-regulatory capacity. PD + FoG- and EC participants showed comparable (higher) HRV. During ON, HRV did not differ among groups. HRV values did not correlate with age, PD duration, levodopa consumption, nor motor -symptoms severity scores.

CONCLUSIONS

Overall, these results document for the first time a relation between HRV at rest and FoG presence/absence during gait trials, expanding previous evidence regarding the involvement of ANS in FoG.

The noradrenergic subtype of Parkinson disease: from animal models to clinical practice

Many advances in understanding the pathophysiology of Parkinson disease (PD) have been based on research addressing its motor symptoms and phenotypes. Various data-driven clinical phenotyping studies supported by neuropathological and in vivo neuroimaging data suggest the existence of distinct non-motor endophenotypes of PD even at diagnosis, a concept further strengthened by the predominantly non-motor spectrum of symptoms in prodromal PD. Preclinical and clinical studies support early dysfunction of noradrenergic transmission in both the CNS and peripheral nervous system circuits in patients with PD that results in a specific cluster of non-motor symptoms, including rapid eye movement sleep behaviour disorder, pain, anxiety and dysautonomia (particularly orthostatic hypotension and urinary dysfunction). Cluster analyses of large independent cohorts of patients with PD and phenotype-focused studies have confirmed the existence of a noradrenergic subtype of PD, which had been previously postulated but not fully characterized. This Review discusses the translational work that unravelled the clinical and neuropathological processes underpinning the noradrenergic PD subtype. Although some overlap with other PD subtypes is inevitable as the disease progresses, recognition of noradrenergic PD as a distinct early disease subtype represents an important advance towards the delivery of personalized medicine for patients with PD.

Synucleinopathies

The α-synucleinopathies include pure autonomic failure, multiple system atrophy, dementia with Lewy bodies, and Parkinson disease. The past two decades have witnessed significant advances in the diagnostic strategies and symptomatic treatment of motor and nonmotor symptoms of the synucleinopathies. This chapter provides an in-depth review of the pathophysiology, pathology, genetic, epidemiology, and clinical and laboratory autonomic features that distinguish the different synucleinopathies with an emphasis on autonomic failure as a common feature. The treatment of the different synucleinopathies is discussed along with the proposal for multidisciplinary, individualized care models that optimally address the various symptoms. There is an urgent need for clinical scientific studies addressing patients at risk of developing synucleinopathies and the investigation of disease mechanisms, biomarkers, potential disease-modifying therapies, and further advancement of symptomatic treatments for motor and nonmotor symptoms.

Association Between Parkinson's Disease and Coronary Artery Disease: A Systematic Review and Meta-Analysis

BACKGROUND

The relationship between Parkinson's disease (PD) and coronary artery disease (CAD) is unclear.

OBJECTIVE

This study aims to investigate whether PD and CAD are associated through systematic review and meta-analysis of observational studies.

METHODS

Electronic database search of PubMed, EMBASE, and Web of Science for observational studies published from 1 January 2010 to 1 August 2021 was conducted using terms related to PD and CAD. Unadjusted risk ratios (RR) and odds ratios (OR) of included cohort and case-control studies respectively were used to ascertain the association between PD and CAD. Study heterogeneity was evaluated using the I2 test.

RESULTS

Forty-one full-text studies were initially retrieved for eligibility assessment. Five studies that satisfied the inclusion criteria, consisting of three cohort and two case-control studies, were eventually included in this meta-analysis. The five studies enrolled 35,237 PD patients and 650,866 non-PD patients. PD and CAD were found to be significantly associated in cohort studies (RR = 2.23, 95% CI = 1.08-4.59, p = 0.03; Fig. 2), which held after sensitivity analysis (RR = 1.45, 95% CI = 1.31-1.60, p < 0.001; Fig. 3). Case-control studies found a trend towards association of PD and CAD approaching significance (OR = 1.47, 95% CI = 0.84-2.56, p = 0.18; Fig. 2).

CONCLUSION

Overall, this meta-analysis suggests that PD is associated with CAD. The underlying mechanisms, as well as the role of ethnicity and other comorbidities on the relationship between PD and CAD should be further explored.

Modeling the Progression of Cardiac Catecholamine Deficiency in Lewy Body Diseases

Background Lewy body diseases (LBDs) feature deficiency of the sympathetic neurotransmitter norepinephrine in the left ventricular myocardium and sympathetic intra-neuronal deposition of the protein alpha-synuclein (αS). LBDs therefore are autonomic synucleinopathies. Computational modeling has revealed multiple functional abnormalities in residual myocardial sympathetic noradrenergic nerves in LBDs, including decreased norepinephrine synthesis, vesicular storage, and recycling. We report an extended model that enables predictions about the progression of LBDs and effects of genetic predispositions and treatments on that progression. Methods and Results The model combines cardiac sympathetic activation with autotoxicity mediated by the dopamine metabolite 3,4-dihydroxyphenylacetaldehyde. We tested the model by its ability to predict longitudinal empirical data based on cardiac sympathetic neuroimaging, effects of genetic variations related to particular intra-neuronal reactions, treatment by monoamine oxidase inhibition to decrease 3,4-dihydroxyphenylacetaldehyde production, and post-mortem myocardial tissue contents of catecholamines and αS. The new model generated a triphasic decline in myocardial norepinephrine content. This pattern was confirmed by empirical data from serial cardiac ¹⁸F-dopamine positron emission tomographic scanning in patients with LBDs. The model also correctly predicted empirical data about effects of genetic variants and monoamine oxidase inhibition and about myocardial levels of catecholamines and αS. Conclusions The present computational model predicts a triphasic decline in myocardial norepinephrine content as LBDs progress. According to the model, disease-modifying interventions begun at the transition from the first to the second phase delay the onset of symptomatic disease. Computational modeling coupled with biomarkers of preclinical autonomic synucleinopathy may enable early detection and more effective treatment of LBDs.

Pathophysiological significance of increased α-synuclein deposition in sympathetic nerves in Parkinson's disease: a post-mortem observational study

Background

Parkinson’s disease (PD) is characterized by intra-neuronal deposition of the protein α-synuclein (α-syn) and by deficiencies of the catecholamines dopamine and norepinephrine (NE) in the brain and heart. Accumulation of α-syn in sympathetic noradrenergic nerves may provide a useful PD biomarker; however, whether α-syn buildup is pathophysiological has been unclear. If it were, one would expect associations of intra-neuronal α-syn deposition with catecholaminergic denervation and with decreased NE contents in the same samples.

Methods

We assayed immunoreactive α-syn and tyrosine hydroxylase (TH, a marker of catecholaminergic innervation) concurrently with catecholamines in coded post-mortem scalp skin, submandibular gland (SMG), and apical left ventricular myocardial tissue samples from 14 patients with autopsy-proven PD and 12 age-matched control subjects who did not have a neurodegenerative disease.

Results

The PD group had increased α-syn in sympathetic noradrenergically innervated arrector pili muscles (5.7 times control, P < 0.0001), SMG (35 times control, P = 0.0011), and myocardium (11 times control, P = 0.0011). Myocardial TH in the PD group was decreased by 65% compared to the control group (P = 0.0008), whereas the groups did not differ in TH in either arrector pili muscles or SMG. Similarly, myocardial NE was decreased by 92% in the PD group (P < 0.0001), but the groups did not differ in NE in either scalp skin or SMG.

Conclusions

PD entails increased α-syn in skin, SMG, and myocardial tissues. In skin and SMG, augmented α-syn deposition in sympathetic nerves does not seem to be pathogenic. The pathophysiological significance of intra-neuronal α-syn deposition appears to be organ-selective and prominent in the heart.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40035-022-00289-y.

Cardiac Changes in Parkinson's Disease: Lessons from Clinical and Experimental Evidence

Dysautonomia is a common non-motor symptom in Parkinson's disease (PD). Most dysautonomic symptoms appear due to alterations in the peripheral nerves of the autonomic nervous system, including both the sympathetic and parasympathetic nervous systems. The degeneration of sympathetic nerve fibers and neurons leads to cardiovascular dysfunction, which is highly prevalent in PD patients. Cardiac alterations such as orthostatic hypotension, heart rate variability, modifications in cardiogram parameters and baroreflex dysfunction can appear in both the early and late stages of PD, worsening as the disease progresses. In PD patients it is generally found that parasympathetic activity is decreased, while sympathetic activity is increased. This situation gives rise to an imbalance of both tonicities which might, in turn, promote a higher risk of cardiac damage through tachycardia and vasoconstriction. Cardiovascular abnormalities can also appear as a side effect of PD treatment: L-DOPA can decrease blood pressure and aggravate orthostatic hypotension as a result of a negative inotropic effect on the heart. This unwanted side effect limits the therapeutic use of L-DOPA in geriatric patients with PD and can contribute to the number of hospital admissions. Therefore, it is essential to define the cardiac features related to PD for the monitorization of the heart condition in parkinsonian individuals. This information can allow the application of intervention strategies to improve the course of the disease and the proposition of new alternatives for its treatment to eliminate or reverse the motor and non-motor symptoms, especially in geriatric patients.

Different phenoconversion pathways in pure autonomic failure with versus without Lewy bodies

Pure autonomic failure (PAF) is a rare disease in which chronic neurogenic orthostatic hypotension (nOH) dominates the clinical picture. Longitudinal studies have reported that PAF can phenoconvert to a central synucleinopathy with motor or cognitive involvement-i.e., to Parkinson disease (PD), dementia with Lewy bodies (DLB), or multiple system atrophy (MSA). These studies have classified patients clinically as having PAF based on nOH without an identified secondary cause or clinical evidence of motor or cognitive impairment due to central neurodegeneration. This approach lumps together two nOH syndromes that are pathologically and neurochemically distinct. One is characterized by intraneuronal cytoplasmic alpha-synuclein aggregates (i.e., Lewy bodies) and degeneration of postganglionic sympathetic neurons, as in PD and DLB; the other is not, as in MSA. Clinical and postmortem data show that the form of PAF that involves sympathetic intraneuronal synucleinopathy and noradrenergic deficiency can phenoconvert to PD or DLB-but not to MSA. Conversely, PAF without these features leaves open the possibility of premotor MSA.

Parkinson's disease outside the brain: targeting the autonomic nervous system

Patients with Parkinson's disease present with signs and symptoms of dysregulation of the peripheral autonomic nervous system that can even precede motor deficits. This dysregulation might reflect early pathology and therefore could be targeted for the development of prodromal or diagnostic biomarkers. Only a few objective clinical tests assess disease progression and are used to evaluate the entire spectrum of autonomic dysregulation in patients with Parkinson's disease. However, results from epidemiological studies and findings from new animal models suggest that the dysfunctional autonomic nervous system is a probable route by which Parkinson's disease pathology can spread both to and from the CNS. The autonomic innervation of the gut, heart, and skin is affected by α-synuclein pathology in the early stages of the disease and might initiate α-synuclein spread via the autonomic connectome to the CNS. The development of easy-to-use and reliable clinical tests of autonomic nervous system function seems crucial for early diagnosis, and for developing strategies to stop or prevent neurodegeneration in Parkinson's disease.

PINK1 gene mutation by pair truncated sgRNA/Cas9-D10A in cynomolgus monkeys

Mutations of PTEN-induced kinase I (PINK1) cause early-onset Parkinson's disease (PD) with selective neurodegeneration in humans. However, current PINK1 knockout mouse and pig models are unable to recapitulate the typical neurodegenerative phenotypes observed in PD patients. This suggests that generating PINK1 disease models in non-human primates (NHPs) that are close to humans is essential to investigate the unique function of PINK1 in primate brains. Paired single guide RNA (sgRNA)/Cas9-D10A nickases and truncated sgRNA/Cas9, both of which can reduce off-target effects without compromising on-target editing, are two optimized strategies in the CRISPR/Cas9 system for establishing disease animal models. Here, we combined the two strategies and injected Cas9-D10A mRNA and two truncated sgRNAs into one-cell-stage cynomolgus zygotes to target the PINK1 gene. We achieved precise and efficient gene editing of the target site in three newborn cynomolgus monkeys. The frame shift mutations of PINK1 in mutant fibroblasts led to a reduction in mRNA. However, western blotting and immunofluorescence staining confirmed the PINK1 protein levels were comparable to that in wild-type fibroblasts. We further reprogramed mutant fibroblasts into induced pluripotent stem cells (iPSCs), which showed similar ability to differentiate into dopamine (DA) neurons. Taken together, our results showed that co-injection of Cas9-D10A nickase mRNA and sgRNA into one-cell-stage cynomolgus embryos enabled the generation of human disease models in NHPs and target editing by pair truncated sgRNA/Cas9-D10A in PINK1 gene exon 2 did not impact protein expression.

Could Small Heat Shock Protein HSP27 Be a First-Line Target for Preventing Protein Aggregation in Parkinson's Disease?

Small heat shock proteins (HSPs), such as HSP27, are ubiquitously expressed molecular chaperones and are essential for cellular homeostasis. The major functions of HSP27 include chaperoning misfolded or unfolded polypeptides and protecting cells from toxic stress. Dysregulation of stress proteins is associated with many human diseases including neurodegenerative diseases, such as Parkinson's disease (PD). PD is characterized by the presence of aggregates of α-synuclein in the central and peripheral nervous system, which induces the degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc) and in the autonomic nervous system. Autonomic dysfunction is an important non-motor phenotype of PD, which includes cardiovascular dysregulation, among others. Nowadays, the therapies for PD focus on dopamine (DA) replacement. However, certain non-motor symptoms with a great impact on quality of life do not respond to dopaminergic drugs; therefore, the development and testing of new treatments for non-motor symptoms of PD remain a priority. Since small HSP27 was shown to prevent α-synuclein aggregation and cytotoxicity, this protein might constitute a suitable target to prevent or delay the motor and non-motor symptoms of PD. In the first part of our review, we focus on the cardiovascular dysregulation observed in PD patients. In the second part, we present data on the possible role of HSP27 in preventing the accumulation of amyloid fibrils and aggregated forms of α-synuclein. We also include our own studies, highlighting the possible protective cardiac effects induced by L-DOPA treatment through the enhancement of HSP27 levels and activity.

Do indices of baroreflex failure and peripheral noradrenergic deficiency predict the magnitude of orthostatic hypotension in Lewy body diseases?

INTRODUCTION

Patients with neurogenic orthostatic hypotension in the setting of Lewy body diseases (LBnOH) typically have baroreflex failure and peripheral noradrenergic deficiency. Either or both of these abnormalities might determine the magnitude of OH in individual patients. We retrospectively correlated the orthostatic fall in systolic blood pressure (∆BPs) during active standing or 5 min of head-up tilt at 90° from horizontal as a function of several baroreflex and sympathetic noradrenergic indices.

METHODS

Physiological, neurochemical, and sympathetic neuroimaging data from the Valsalva maneuver, head-up tilt table testing, and thoracic ¹⁸F-dopamine positron emission tomographic scanning (¹⁸F-DA PET) were analyzed from 72 patients with LBnOH [44 with Parkinson disease (PD) and nOH, 28 with pure autonomic failure]. Comparison subjects had PD without OH (N = 44) or PD risk factors without parkinsonism or OH (N = 28) or were healthy volunteers (N = 8). Indices of baroreflex function included the Valsalva maneuver-associated baroreflex areas in Phase II (BRA-II) and IV (BRA-IV), the pressure recovery time (PRT), and baroreflex-cardiovagal and adrenergic sensitivities (BRS-V and BRS-A). The fractional orthostatic increment in plasma norepinephrine (Fx∆NE) provided a neurochemical index of baroreflex-sympathoneural function.

RESULTS

As expected, the LBnOH group had baroreflex-sympathoneural and baroreflex-cardiovagal impairment and low cardiac ¹⁸F-DA-derived radioactivity. Among patients, values for ∆BPs correlated with BRA-II, BRA-IV, BRS-V, and Fx∆NE but not with values for PRT, BRS-A, supine plasma NE, or ¹⁸F-DA-derived radioactivity.

CONCLUSION

Across individual patients with LBnOH, quantitative indices of baroreflex dysfunctions and peripheral noradrenergic deficiency are inconsistently associated with the magnitude of OH, even under controlled laboratory conditions.

Baroreflex dysfunction in Parkinson's disease: integration of central and peripheral mechanisms

The incidence of Parkinson's disease (PD) is increasing worldwide. Although the PD hallmark is the motor impairments, nonmotor dysfunctions are now becoming more recognized. Recently, studies have suggested that baroreflex dysfunction is one of the underlying mechanisms of cardiovascular dysregulation observed in patients with PD. However, the large body of literature on baroreflex function in PD is unclear. The baroreflex system plays a major role in the autonomic, and ultimately blood pressure and heart rate, adjustments that accompany acute cardiovascular stressors on a daily basis. Therefore, impaired baroreflex function (i.e., decreased sensitivity or gain) can lead to altered neural cardiovascular responses. Since PD affects parasympathetic and sympathetic branches of the autonomic nervous system and both are orchestrated by the baroreflex system, understanding of this crucial mechanism in PD is necessary. In the present review, we summarize the potential altered central and peripheral mechanisms affecting the feedback-controlled loops that comprise the reflex arc in patients with PD. Major factors including arterial stiffness, reduced number of C1 and activation of non-C1 neurons, presence of central α-synuclein aggregation, cardiac sympathetic denervation, attenuated muscle sympathetic nerve activity, and lower norepinephrine release could compromise baroreflex function in PD. Results from patients with PD and from animal models of PD provide the reader with a clearer picture of baroreflex function in this clinical condition. By doing so, our intent is to stimulate future studies to evaluate several unanswered questions in this research area.

Cardioselective peripheral noradrenergic deficiency in Lewy body synucleinopathies

Objective

Lewy body (LB) synucleinopathies such as Parkinson’s disease (PD) entail profound cardiac norepinephrine deficiency. The status of sympathetic noradrenergic innervation at other extracranial sites has been unclear. Although in vivo neuroimaging studies have indicated a cardioselective noradrenergic lesion, no previous study has surveyed peripheral organs for norepinephrine contents in LB diseases. We reviewed ¹⁸F‐dopamine (¹⁸F‐DA) positron emission tomographic images and postmortem neurochemical data across several body organs of controls and patients with the LB synucleinopathies PD and pure autonomic failure (PAF) and the non‐LB synucleinopathy multiple system atrophy (MSA).

Methods

¹⁸F‐DA–derived radioactivity in the heart, liver, spleen, pancreas, stomach, kidneys, thyroid, and submandibular glands were analyzed from 145 patients with LB synucleinopathies (112 PD, 33 PAF), 74 controls, and 85 MSA patients. In largely separate cohorts, postmortem tissue norepinephrine data were reviewed for heart, liver, spleen, pancreas, kidney, thyroid, submandibular gland, and sympathetic ganglion tissue from 38 PD, 2 PAF, and 5 MSA patients and 35 controls.

Results

Interventricular septal ¹⁸F‐DA–derived radioactivity was decreased in the LB synucleinopathy group compared to the control and MSA groups (P < 0.0001 each). The LB and non‐LB groups did not differ in liver, spleen, pancreas, stomach, or kidney ¹⁸F‐DA–derived radioactivity. The LB synucleinopathy group had markedly decreased apical myocardial norepinephrine, but normal tissue norepinephrine in other organs. The MSA group had normal tissue norepinephrine in all examined organs.

Interpretation

By in vivo sympathetic neuroimaging and postmortem neurochemistry peripheral noradrenergic deficiency in LB synucleinopathies is cardioselective. MSA does not involve peripheral noradrenergic deficiency.

"Sick-but-not-dead": multiple paths to catecholamine deficiency in Lewy body diseases

Profound depletion of the catecholamines dopamine (DA) and norepinephrine in the brain, heart, or both characterizes Lewy body diseases such as Parkinson disease, dementia with Lewy bodies, and pure autonomic failure. Although one might presume that catecholamine deficiency in these disorders results directly and solely from loss of catecholaminergic neurons, there is increasing evidence that functional abnormalities in extant residual neurons contribute to the neurotransmitter deficiencies-the "sick-but-not-dead" phenomenon. This brief review highlights two such functional abnormalities-decreased vesicular sequestration of cytoplasmic catecholamines and decreased catecholamine biosynthesis. Another abnormality, decreased activity of aldehyde dehydrogenase, may have pathogenetic significance and contribute indirectly to the loss of catecholamine stores via interactions between the autotoxic catecholaldehyde 3,4-dihydroxyphenylacetaldehyde and the protein alpha-synuclein, which is a major component of Lewy bodies. Theoretically, chronically repeated stress responses could accelerate these abnormalities, via increased exocytosis and neuronal reuptake, which indirectly shifts tissue catecholamines from vesicular stores into the cytoplasm, and via increased tyrosine hydroxylation, which augments intra-cytoplasmic DA production. The discovery of specific paths mediating the sick-but-not-dead phenomenon offers novel targets for multi-pronged therapeutic approaches.

Comparison of 123I-MIBG scintigraphy and phosphorylated α-synuclein skin deposits in synucleinopathies

INTRODUCTION

Cardiac [123I]metaiodobenzylguanidine scintigraphy (123I-MIBG) is considered a useful test in differentiating multiple system atrophy (MSA) and Lewy body disorders (LBD), including idiopathic Parkinson's disease (IPD), dementia with Lewy bodies (DLB) and pure autonomic failure (PAF). The detection of skin nerve phosphorylated α-synuclein (p-α-syn) deposits could be an alternative marker in vivo. We sought to compare 123I-MIBG scintigraphy and skin biopsy findings in α-synucleinopathies.

METHODS

We studied 54 patients (7 DLB, 21 IPD, 13 PAF, 13 MSA) who underwent 123I-MIBG scintigraphy and skin biopsy to evaluate cardiac innervation and skin p-α-syn deposition, respectively.

RESULTS

Cardiac denervation was observed in 90.5% IPD, 100% DLB and PAF and in none of the MSA patients (P < 0.0001) whereas p-α-syn deposits were detected in all DLB and PAF, in 95.2% of IPD and 69.2% of MSA patients (P = 0.02). However, the analysis of skin structures disclosed a different distribution of the deposits in somatic subepidermal plexus and autonomic fibers among groups, showing that p-α-syn deposits rarely affected the autonomic fibers in MSA as opposed to LBD. Studying the p-α-syn deposition in autonomic nerves, concordance among I123-MIBG scintigraphy and skin biopsy results was observed in 100% of DLB and PAF, 95.2% IPD and 92.3% MSA patients. I123-MIBG scintigraphy and autonomic p-α-syn deposits analysis both showed a sensitivity of 97.5% and a specificity of 100% and 92.3%, respectively, in distinguishing LBD and MSA.

CONCLUSION

Skin biopsy and 123-MIBG scintigraphy can be considered alternative tests for the differential diagnosis of IPD, PAF and DLB versus MSA.

The "Sick-but-not-Dead" Phenomenon Applied to Catecholamine Deficiency in Neurodegenerative Diseases

The catecholamines dopamine and norepinephrine are key central neurotransmitters that participate in many neurobehavioral processes and disease states. Norepinephrine is also the main neurotransmitter mediating regulation of the circulation by the sympathetic nervous system. Several neurodegenerative disorders feature catecholamine deficiency. The most common is Parkinson's disease (PD), in which putamen dopamine content is drastically reduced. PD also entails severely decreased myocardial norepinephrine content, a feature that characterizes two other Lewy body diseases-pure autonomic failure and dementia with Lewy bodies. It is widely presumed that tissue catecholamine depletion in these conditions results directly from loss of catecholaminergic neurons; however, as highlighted in this review, there are also important functional abnormalities in extant residual catecholaminergic neurons. We refer to this as the "sick-but-not-dead" phenomenon. The malfunctions include diminished dopamine biosynthesis via tyrosine hydroxylase (TH) and L-aromatic-amino-acid decarboxylase (LAAAD), inefficient vesicular sequestration of cytoplasmic catecholamines, and attenuated neuronal reuptake via cell membrane catecholamine transporters. A unifying explanation for catecholaminergic neurodegeneration is autotoxicity exerted by 3,4-dihydroxyphenylacetaldehyde (DOPAL), an obligate intermediate in cytoplasmic dopamine metabolism. In PD, putamen DOPAL is built up with respect to dopamine, associated with a vesicular storage defect and decreased aldehyde dehydrogenase activity. Probably via spontaneous oxidation, DOPAL potently oligomerizes and forms quinone-protein adducts with ("quinonizes") α-synuclein (AS), a major constituent in Lewy bodies, and DOPAL-induced AS oligomers impede vesicular storage. DOPAL also quinonizes numerous intracellular proteins and inhibits enzymatic activities of TH and LAAAD. Treatments targeting DOPAL formation and oxidation therefore might rescue sick-but-not-dead catecholaminergic neurons in Lewy body diseases.

Cardiac sympathetic innervation and vesicular storage in pure autonomic failure

Objective

Pure autonomic failure (PAF) is a rare disease characterized by neurogenic orthostatic hypotension (nOH), absence of signs of central neurodegeneration, and profound deficiency of the sympathetic neurotransmitter norepinephrine. Reports have disagreed about mechanisms of the noradrenergic lesion. Neuropathological studies have highlighted denervation, while functional studies have emphasized deficient vesicular sequestration of cytoplasmic catecholamines in extant neurons. We examined both aspects by a combined positron emission tomographic (PET) neuroimaging approach using ¹¹C‐methylreboxetine (¹¹C‐MRB), a selective ligand for the cell membrane norepinephrine transporter, to quantify interventricular septal myocardial noradrenergic innervation and using ¹⁸F‐dopamine (¹⁸F‐DA) to assess intraneuronal vesicular storage in the same subjects.

Methods

Seven comprehensively tested PAF patients and 11 controls underwent ¹¹C‐MRB PET scanning for 45 minutes (dynamic 5X1’, 3X5’, 1X10’, static 15 minutes) and ¹⁸F‐DA scanning for 30 minutes (same dynamic imaging sequence) after 3‐minute infusions of the tracers on separate days.

Results

In the PAF group septal ¹¹C‐MRB‐derived radioactivity in the static frame was decreased by 26.7% from control (p = 0.012). After adjustment for nonspecific binding of ¹¹C‐MRB, the PAF group had a 41.1% mean decrease in myocardial ¹¹C‐MRB‐derived radioactivity (p = 0.015). The PAF patients had five times faster postinfusion loss of ¹⁸F‐DA‐derived radioactivity (70 ± 3% vs. 14 ± 8% by 30 minutes, p < 0.0001). At all time points after infusion of ¹⁸F‐DA and ¹¹C‐MRB mean ¹⁸F/¹¹C ratios in septal myocardium were lower in the PAF than control group.

Interpretation

PAF entails moderately decreased cardiac sympathetic innervation and a substantial vesicular storage defect in residual nerves.

Biofluid Markers for Prodromal Parkinson's Disease: Evidence From a Catecholaminergic Perspective

Parkinson's disease (PD) is the most frequent of all Lewy body diseases, a family of progressive neurodegenerative disorders characterized by intra-neuronal cytoplasmic inclusions of α-synuclein. Its most defining features are bradykinesia, tremor, rigidity and postural instability. By the time PD manifests with motor signs, 70% of dopaminergic midbrain neurons are lost, and the disease is already in the middle or late stage. However, there are various non-motor symptoms occurring up to 20 years before the actual parkinsonism that are closely associated with profound deficiency of myocardial noradrenaline content and peripheral sympathetic denervation, as evidenced by neuroimaging experiments in recent years. Additionally, there is an inherent autotoxicity of catecholamines in the neuronal cells in which they are produced, forming toxic catecholaldehyde intermediates that make α-synuclein prone to aggregation, initiating a cascade of events that ultimately leads to neuronal death. The etiopathogenesis of PD and related synucleinopathies thus may well be a prototypical example of a catecholamine-regulated neurodegeneration, given that the synucleinopathy in PD spreads in synergy with central and peripheral catecholaminergic dysfunction from the earliest phases onward. That is why catecholamines and their metabolites, precursors, or derivatives in cerebrospinal fluid or plasma could be of particular interest as biomarkers for prodromal and de novo PD. Because there is great demand for such markers, this mini-review summarizes all catecholamine-related studies to date, in addition to providing profound neurochemical evidence on a systemic and cellular level to further emphasize this hypothesis and with emphasis on extracellular vesicles as a novel diagnostic and therapeutic incentive.

Altered cardiorespiratory regulation during exercise in patients with Parkinson's disease: A challenging non-motor feature

The incidence of Parkinson’s disease is increasing worldwide. The motor dysfunctions are the hallmark of the disease, but patients also experience non-motor impairments, and over 40% of the patients experience coexistent abnormalities, such as orthostatic hypotension. Exercise training has been suggested as a coping resource to alleviate Parkinson’s disease symptoms and delay disease progression. However, the body of knowledge is showing that the cardiovascular response to exercise in patients with Parkinson’s disease is altered. Adequate cardiovascular and hemodynamic adjustments to exercise are necessary to meet the metabolic demands of working skeletal muscle properly. Therefore, since Parkinson’s disease affects parasympathetic and sympathetic branches of the autonomic nervous system and the latter are crucial in ensuring these adjustments are adequately made, the understanding of these responses during exercise in this population is necessary. Several neural control mechanisms are responsible for the autonomic changes in the cardiovascular and hemodynamic systems seen during exercise. In this sense, the purpose of the present work is to review the current knowledge regarding the cardiovascular responses to dynamic and isometric/resistance exercise as well as the mechanisms by which the body maintains appropriate perfusion pressure to all organs during exercise in patients with Parkinson’s disease. Results from patients with Parkinson’s disease and animal models of Parkinson’s disease provide the reader with a well-rounded knowledge base. Through this, we will highlight what is known and not known about how the neural control of circulation is responding during exercise and the adaptations that occur when individuals exercise regularly.

Characteristic response of striatal astrocytes to dopamine depletion

Astrocytes and astrocyte-related proteins play important roles in maintaining normal brain function, and also regulate pathological processes in brain diseases and injury. However, the role of astrocytes in the dopamine-depleted striatum remains unclear. A rat model of Parkinson’s disease was therefore established by injecting 10 μL 6-hydroxydopamine (2.5 μg/μL) into the right medial forebrain bundle. Immunohistochemical staining was used to detect the immunoreactivity of glial fibrillary acidic protein (GFAP), calcium-binding protein B (S100B), and signal transducer and activator of transcription 3 (STAT3) in the striatum, and to investigate the co-expression of GFAP with S100B and STAT3. Western blot assay was used to measure the protein expression of GFAP, S100B, and STAT3 in the striatum. Results demonstrated that striatal GFAP-immunoreactive cells had an astrocytic appearance under normal conditions, but that dopamine depletion induced a reactive phenotype with obvious morphological changes. The normal striatum also contained S100B and STAT3 expression. S100B-immunoreactive cells were uniform in the striatum, with round bodies and sparse, thin processes. STAT3-immunoreactive cells presented round cell bodies with sparse processes, or were darkly stained with a large cell body. Dopamine deprivation induced by 6-hydroxydopamine significantly enhanced the immunohistochemical positive reaction of S100B and STAT3. Normal striatal astrocytes expressed both S100B and STAT3. Striatal dopamine deprivation increased the number of GFAP/S100B and GFAP/STAT3 double-labeled cells, and increased the protein levels of GFAP, S100B, and STAT3. The present results suggest that morphological changes in astrocytes and changes in expression levels of astrocyte-related proteins are involved in the pathological process of striatal dopamine depletion. The study was approved by Animal Care and Use Committee of Sun Yat-sen University, China (Zhongshan Medical Ethics 2014 No. 23) on September 22, 2014.

Association of innervation-adjusted alpha-synuclein in arrector pili muscles with cardiac noradrenergic deficiency in autonomic synucleinopathies

BACKGROUND

Autonomic synucleinopathies feature deposition of the protein alpha-synuclein (AS) in neurons [e.g., Lewy body neurogenic orthostatic hypotension (nOH)] or glial cells (multiple system atrophy, MSA). AS in skin biopsies might provide biomarkers of these diseases; however, this approach would be complicated or invalidated if there were substantial loss of AS-containing nerves. We report AS content in arrector pili muscles in skin biopsies after adjustment for local innervation in patients with Lewy body nOH or MSA. Cardiac sympathetic neuroimaging by myocardial ¹⁸F-dopamine positron emission tomography (PET) was done to examine pathophysiological correlates of innervation-adjusted AS.

METHODS

Thirty-one patients (19 Lewy body nOH, 12 MSA) underwent thoracic ¹⁸F-dopamine PET and skin biopsies. AS signal intensity analyzed by immunofluorescence microscopy was adjusted for innervation by the ratio of AS to protein gene product (PGP) 9.5, a pan-axonal marker (Harvard lab site), or the ratio of AS to tyrosine hydroxylase (TH), an indicator of catecholaminergic neurons (NIH lab site).

RESULTS

The Lewy body nOH group had higher ratios of AS/PGP 9.5 or log AS/TH than did the MSA group (0.89 ± 0.05 vs. 0.66 ± 0.04, -0.13 ± 0.05 vs. -1.60 ± 0.33; p < 0.00001 each). All 19 Lewy body patients had AS/PGP 9.5 > 0.8 or log AS/TH > 1.2 and had myocardial ¹⁸F-dopamine-derived radioactivity < 6000 nCi-kg/cc-mCi, the lower limit of normal. Two MSA patients (17%) had increased AS/PGP or log AS/TH, and two (17%) had low ¹⁸F-dopamine-derived radioactivity.

CONCLUSIONS

Lewy body forms of nOH are associated with increased innervation-adjusted AS in arrector pili muscles and neuroimaging evidence of myocardial noradrenergic deficiency.

Long-term trends in myocardial sympathetic innervation and function in synucleinopathies

INTRODUCTION

Parkinson disease (PD), pure autonomic failure (PAF), and multiple system atrophy (MSA) are characterized by intra-cerebral deposition of the protein alpha-synuclein and are termed synucleinopathies. Lewy body synucleinopathies involve decreased cardiac sympathetic innervation and functional abnormalities in residual noradrenergic terminals. This observational, retrospective, cohort study describes long-term trends in indices of cardiac sympathetic innervation and function in synucleinopathies.

METHODS

Patients with PD (N = 31), PAF (N = 9), or MSA (N = 9) underwent repeated ¹⁸F-dopamine positron emission tomography (median follow-up 3.5 years). Interventricular septal ¹⁸F-dopamine-derived radioactivity 8 min after tracer injection (8' Radioactivity) was used as an index of sympathetic innervation and the slope of mono-exponential decline of radioactivity between 8 and 25 min (k_8'-25') as an index of intraneuronal vesicular storage. Healthy volunteers (HVs) (N = 33) and individuals at high risk of PD (N = 15) were controls.

RESULTS

Upon initial evaluation the groups with PD and orthostatic hypotension (OH), PAF, or PD and no OH had low mean 8' Radioactivity compared to HVs (p < 0.0001, p = 0.0002, p = 0.006) and had elevated k_8'-25' (p = 0.0007, p = 0.007, p = 0.06). There was no significant difference between MSA and HVs. In PD 8' Radioactivity decreased by a median of 4% per year and did not decrease in MSA. k_8'-25' values did not change during follow-up in any group.

CONCLUSIONS

Neuroimaging evidence of decreased vesicular uptake in cardiac sympathetic nerves is present upon initial evaluation of patients with Lewy body synucleinopathies and may provide a biomarker of catecholaminergic dysfunction early in the disease process.

Computational modeling reveals multiple abnormalities of myocardial noradrenergic function in Lewy body diseases

BACKGROUND

Lewy body diseases, a family of aging-related neurodegenerative disorders, entail loss of the catecholamine dopamine in the nigrostriatal system and equally severe deficiency of the closely related catecholamine norepinephrine in the heart. The myocardial noradrenergic lesion is associated with major non-motor symptoms and decreased survival. Numerous mechanisms determine norepinephrine stores, and which of these are altered in Lewy body diseases has not been examined in an integrated way. We used a computational modeling approach to assess comprehensively pathways of cardiac norepinephrine synthesis, storage, release, reuptake, and metabolism in Lewy body diseases. Application of a novel kinetic model identified a pattern of dysfunctional steps contributing to norepinephrine deficiency. We then tested predictions from the model in a new cohort of Parkinson disease patients.

METHODS

Rate constants were calculated for 17 reactions determining intra-neuronal norepinephrine stores. Model predictions were tested by measuring post-mortem apical ventricular concentrations and concentration ratios of catechols in controls and patients with Parkinson disease.

RESULTS

The model identified low rate constants for three types of processes in the Lewy body group-catecholamine biosynthesis via tyrosine hydroxylase and L-aromatic-amino-acid decarboxylase, vesicular storage of dopamine and norepinephrine, and neuronal norepinephrine reuptake via the cell membrane norepinephrine transporter. Post-mortem catechols and catechol ratios confirmed this triad of model-predicted functional abnormalities.

CONCLUSION

Denervation-independent impairments of neurotransmitter biosynthesis, vesicular sequestration, and norepinephrine recycling contribute to the myocardial norepinephrine deficiency attending Lewy body diseases. A proportion of cardiac sympathetic nerves are "sick but not dead," suggesting targeted disease-modification strategies might retard clinical progression.

TRIAL REGISTRATION

This study was not a clinical trial.

FUNDING

The research reported here was supported by the Division of Intramural Research, NINDS.

Autonomic dysfunction in genetic forms of synucleinopathies

The discovery of genetic links between alpha-synuclein and PD has opened unprecedented opportunities for research into a new group of diseases, now collectively known as synucleinopathies. Autonomic dysfunction, including cardiac sympathetic denervation, has been reported in familial forms of synucleinopathies that have Lewy bodies at the core of their pathogenesis. SNCA mutations and multiplications, LRRK2 disease with Lewy bodies as well as other common, sporadic forms of idiopathic PD, MSA, pure autonomic failure, and dementia with Lewy bodies have all been associated with dysautonomia. By contrast, in familial cases of parkinsonism without Lewy bodies, such as in PARK2, the autonomic profile remains normal throughout the course of the disease. The degeneration of the central and peripheral autonomic systems in genetic as well as sporadic forms of neurodegenerative synucleinopathies correlates with the accumulation of alpha-synuclein immunoreactive-containing inclusions. Given that dysautonomia has a significant impact on the quality of life of sufferers and autonomic symptoms are generally treatable, a prompt diagnostic testing and treatment should be provided. Moreover, new evidence suggests that autonomic dysfunction can be used as an outcome prediction factor in some forms of synucleinopathies or premotor diagnostic markers that could be used in the future to define further research avenues. In this review, we describe the autonomic dysfunction of genetic synucleinopathies in comparison to the dysautonomia of sporadic forms of alpha-synuclein accumulation and provide the reader with an up-to-date overview of the current understanding in this fast-growing field. © 2018 International Parkinson and Movement Disorder Society.

Alpha-Synuclein Deposition Within Sympathetic Noradrenergic Neurons Is Associated With Myocardial Noradrenergic Deficiency in Neurogenic Orthostatic Hypotension

Lewy body diseases involve neurogenic orthostatic hypotension (nOH), cardiac noradrenergic deficiency, and deposition of the protein AS (alpha-synuclein) in sympathetic ganglion tissue. Mechanisms linking these abnormalities are poorly understood. One link may be AS deposition within sympathetic neurons. We validated methodology to quantify AS colocalization with TH (tyrosine hydroxylase), a marker of sympathetic noradrenergic innervation, and assessed associations of AS/TH colocalization with myocardial norepinephrine content and cardiac sympathetic neuroimaging data in nOH. Postmortem sympathetic ganglionic AS/TH colocalization indices and myocardial norepinephrine contents were measured in 4 Lewy body and 3 rare non-Lewy body nOH patients. Sixteen Lewy body and 11 non-Lewy body nOH patients underwent in vivo skin biopsies and thoracic 18F-dopamine positron emission tomographic scanning, with cutaneous colocalization indices expressed versus cardiac 18F-dopamine-derived radioactivity. Ganglionic AS/TH colocalization indices were higher and myocardial norepinephrine lower in Lewy body than non-Lewy body nOH ( P=0.0020, P=0.014). The Lewy body nOH group had higher AS/TH colocalization indices in skin biopsies and lower myocardial 18F-dopamine-derived radioactivity than did the non-Lewy body nOH group ( P<0.0001 each). All Lewy body nOH patients had colocalization indices >1.5 in skin biopsies and 18F-dopamine-derived radioactivity <6000 nCi-kg/cc-mCi, a combination not seen in non-Lewy body nOH patients ( P<0.0001). In Lewy body nOH, AS deposition in sympathetic noradrenergic nerves is related to postmortem neurochemical and in vivo neuroimaging evidence of myocardial noradrenergic deficiency. These associations raise the possibility that intraneuronal AS deposition plays a pathophysiological role in the myocardial sympathetic neurodegeneration attending Lewy body nOH.

Skin nerve α-synuclein deposits in Parkinson's disease and other synucleinopathies: a review

PURPOSE

The in vivo diagnosis of synucleinopathies is an important research aim since clinical diagnostic criteria show low accuracy. The skin innervation, especially the autonomic subdivision, is a useful region to search for abnormal α-syn aggregates in synucleinopathies since the peripheral sympathetic nerves can be the earliest-affected neural region and autonomic symptoms may precede the classical symptoms of these disorders.

METHODS

The major advantages of skin biopsy as an in vivo diagnostic tool for synucleinopathies are that it is an inexpensive and easy-to-perform technique requiring only limited facilities, and that it is repeatable in long-term studies as it causes only minor discomfort to the patient.

RESULTS

This review analyzes current progress in this area of research that may facilitate the standardization of this method, potentially eliminating differences among laboratories in the implementation of the method.

CONCLUSIONS

The most suitable and commonly used technique for identifying in vivo α-syn aggregates in skin nerves is indirect immunofluorescence, although several aspects of this approach need to be standardized, particularly when synucleinopathies without autonomic failure present a patchy distribution of abnormal α-syn aggregates in skin nerves. By contrast, synucleinopathies with autonomic failure may present widespread diffusion of abnormal aggregates in autonomic skin nerves.

Roles of cardiac sympathetic neuroimaging in autonomic medicine

Sympathetic neuroimaging is based on the injection of compounds that either radiolabel sites of the cell membrane norepinephrine transporter (NET) or that are taken up into sympathetic nerves via the NET and radiolabel intra-neuronal catecholamine storage sites. Detection of the radioactivity is by planar or tomographic radionuclide imaging. The heart stands out among body organs in terms of the intensity of radiolabeling of sympathetic nerves, and virtually all of sympathetic neuroimaging focuses on the left ventricular myocardium. The most common cardiac sympathetic neuroimaging method worldwide is ¹²³I-metaiodobenzylguanidine (¹²³I-MIBG) scanning. ¹²³I-MIBG scanning is used routinely in Europe and East Asia in the diagnostic evaluation of neurogenic orthostatic hypotension (nOH), to distinguish Lewy body diseases (e.g., Parkinson disease with orthostatic hypotension (OH), pure autonomic failure) from non-Lewy body diseases (e.g., multiple system atrophy) and to distinguish dementia with Lewy bodies from Alzheimer's disease. In the USA, ¹²³I-MIBG scanning has been approved by the Food and Drug Administration for the evaluation of pheochromocytoma and some forms of heart failure-but not for the above-mentioned differential diagnoses. Positron emission tomographic methods based on imaging agents such as ¹⁸F-dopamine are categorized as research tools, despite more than a quarter century of clinical experience with these modalities. Considering that ¹²³I-MIBG scanning is available at most academic medical centers in the USA, cardiac sympathetic neuroimaging by this methodology merits consideration as an autonomic test, especially in patients with nOH.

Spectrum of abnormalities of sympathetic tyrosine hydroxylase and alpha-synuclein in chronic autonomic failure

OBJECTIVE

Lewy body forms of primary chronic autonomic failure (CAF) such as incidental Lewy body disease (ILBD), Parkinson's disease (PD), and pure autonomic failure evolving into dementia with Lewy bodies (PAF+DLB) feature cardiac sympathetic denervation, whereas multiple system atrophy (MSA) in most cases does not. What links Lewy bodies with cardiac sympathetic denervation in CAF? In familial PD, abnormalities of the alpha-synuclein (AS) gene cause CAF and cardiac sympathetic denervation; and in sporadic PD, brainstem Lewy bodies contain AS co-localized with tyrosine hydroxylase (TH), a marker of catecholaminergic neurons. Cytotoxicity from AS deposition within sympathetic neurons might explain noradrenergic denervation in Lewy body forms of CAF. We used immunofluorescence microscopy (IM) to explore this possibility in sympathetic ganglia obtained at autopsy from CAF patients.

METHODS

Immunoreactive AS and TH were imaged in sympathetic ganglion tissue from 6 control subjects (2 with ILBD), 5 PD patients (1 with concurrent PSP), and 3 patients with CAF (2 PAF + DLB, 1 MSA).

RESULTS

MSA involved normal ganglionic TH and no AS deposition. In ILBD TH was variably decreased, and TH and AS were co-localized in Lewy bodies. In PD TH was substantially decreased, and TH and AS were co-localized in Lewy bodies. In PAF + DLB TH was virtually absent, but AS was present in Lewy bodies. The PD + PSP patient had AS co-localized with tau but not TH.

CONCLUSIONS

Sympathetic denervation and intraneuronal AS deposition are correlated across CAF syndromes, consistent with a pathogenic contribution of synucleinopathy to cardiac noradrenergic deficiency in Lewy body diseases.