Cardiac sympathetic innervation and vesicular storage in pure autonomic failure

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.

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.

Pure autonomic failure and the differential diagnosis of autonomic peripheral neuropathies

PURPOSE OF THE REVIEW

Pure autonomic failure (PAF) is a peripheral autonomic neurodegenerative disease caused by alpha-synuclein deposition that is predominantly confined to peripheral autonomic neurons. Patients present with insidious features of autonomic failure that have a chronic course.In this review, we highlight the features of PAF, the differentiating features from other autonomic neuropathies, the diagnostic tests, and the predictors for conversion to a central synucleinopathy.

RECENT FINDINGS

Natural history studies have defined the predictors for and rate of conversion to a central alpha-synucleinopathy. Skin immunohistochemistry techniques and demonstration of length-dependent neuronal loss of both somatic and autonomic small fiber nerves, and intraneural phosphorylated synuclein deposition provide diagnostic biomarkers. In the future, diagnosis maybe supported by measuring cerebrospinal fluid alpha-synuclein oligomers using techniques, such as protein misfolding cyclic amplification assay and real-time quaking-induced conversion.

SUMMARY

PAF is a sporadic peripheral autonomic neurodegenerative disease that belongs to the group of disorders known as alpha-synucleinopathies. Peripheral autonomic manifestations are similar to those seen in other autonomic neuropathies, particularly, diabetic autonomic neuropathy, amyloid polyneuropathy, and autoimmune autonomic neuropathies. Novel diagnostic procedures like skin immunohistochemistry for alpha-synuclein, and protein amplification techniques are being investigated to provide an earlier and more specific diagnosis. A substantial number of PAF patients' phenoconvert to a central alpha-synucleinopathy.

Evidence of Reduced Efferent Renal Sympathetic Innervation After Chemical Renal Denervation in Humans

BACKGROUND

Renal denervation (RDN) is effective at lowering blood pressure. However, it is unknown if ablative procedures elicit sympathetic denervation of the kidneys in humans. The aim of this investigation was to assess sympathetic innervation of the renal cortex following perivascular chemical RDN, which may be particularly effective at ablating perivascular efferent and afferent nerves.

METHODS

Seven hypertensive patients (4F:3M; 50-65 years) completed PET-CT sympathetic neuroimaging of the renal cortex using 11C-methylreboxetine (11C-MRB, norepinephrine transporter ligand) and 6-[18F]-fluorodopamine (18F-FDA; substrate for the cell membrane norepinephrine transporter) before and 8 weeks after chemical RDN (Peregrine System Infusion Catheter, Ablative Solutions; n = 4; 2F:2M) or control renal angiography (n = 3; 2F:1M). Patients completed physiological phenotyping including 24-hour ambulatory blood pressure, hemodynamics, muscle sympathetic nerve activity, and 24-hour urine collection.

RESULTS

RDN decreased 11C-MRB-derived radioactivity by ~30% (Δ  11C-MRB/chamber: -0.95 a.u. confidence interval (CI): -1.36 to -0.54, P = 0.0002), indicative of efferent RDN. In contrast, 18F-FDA-derived radioactivity increased (Δ  18F-FDA/chamber: 2.72 a.u. CI: 0.73-4.71, P = 0.009), consistent with reduced vesicular turnover. Controls showed no change in either marker. Ambulatory systolic pressure decreased in 3 of 4 patients (-9 mm Hg CI: -27 to 9, P = 0.058), and central systolic pressure decreased in all patients (-23 mm Hg CI: -51 to 5, P = 0.095).

CONCLUSIONS

These results are the first to show efferent sympathetic denervation of the renal cortex following RDN in humans. Further studies of mechanisms underlying variable blood pressure lowering in the setting of documented RDN may provide insights into inconsistencies in clinical trial outcomes.

CLINICAL TRIALS REGISTRATION

Trial Number NCT03465917.

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.