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.

Cerebrospinal fluid concentration gradients of catechols in synucleinopathies.

The synucleinopathies Parkinson disease (PD), multiple system atrophy (MSA), and the Lewy body form of pure autonomic failure (PAF) entail intra-cytoplasmic deposition of the protein alpha-synuclein and pathogenic catecholaminergic neurodegeneration. Cerebrospinal fluid (CSF) levels of catecholamines and their metabolites are thought to provide a "neurochemical window" on central catecholaminergic innervation and can identify specific intra-neuronal dysfunctions in synucleinopathies. We asked whether there are CSF concentration gradients for catechols such as 3,4-dihydroxyphenylacetic acid (DOPAC), the main neuronal metabolite of dopamine, and if so whether the gradients influence neurochemical differences among synucleinopathies. In a retrospective cohort study, we reviewed data about concentrations of catechols in the first, sixth, and twelfth 1-mL aliquots from 33 PD, 28 MSA, and 15 PAF patients and 41 controls. There were concentration gradients for DOPAC, dopamine, norepinephrine, and 3,4-dihydroxyphenylglycol (the main neuronal metabolite of norepinephrine) and gradients in the opposite direction for 5-S-cysteinyldopa and 5-S-cysteinyldopamine. In all 3 aliquots, CSF DOPAC was low in PD and MSA compared with controls (p < 0.0001 each) and normal in PAF. Synucleinopathies differ in CSF catechols regardless of concentration gradients. Concentration gradients for 5-S-cysteinyl derivatives in opposite directions from the parent catechols may provide biomarkers of spontaneous oxidation in the CSF space.

Persistent GDNF Expression 45 Months after Putaminal Infusion of AAV2-GDNF in a Patient with Parkinson's Disease.

OBJECTIVE: Gene therapy by convection-enhanced delivery of type 2 adeno-associated virus-glial cell derived neurotrophic factor (AAV2-GDNF) to the bilateral putamina seeks to increase GDNF gene expression and treat Parkinson's disease (PD). METHODS: A 63-year-old man with advanced PD received AAV2-GDNF in a clinical trial. He died from pneumonia after anterior cervical discectomy and fusion 45 months later. An autopsy included brain examination for GDNF transgene expression. Putaminal catecholamine concentrations were compared to in vivo 18F-Fluorodopa (18F-FDOPA) positron emission tomography (PET) scanning results before and 18 months after AAV2-GDNF infusion. RESULTS: Parkinsonian progression stabilized clinically. Postmortem neuropathology confirmed PD. Bilateral putaminal regions previously infused with AAV2-GDNF expressed the GDNF gene. Total putaminal dopamine was 1% of control, confirming the striatal dopaminergic deficiency suggested by baseline 18F-DOPA-PET scanning. Putaminal regions responded as expected to AAV2-GDNF. CONCLUSION: After AAV2-GDNF infusion, infused putaminal regions showed increased GDNF gene expression, tyrosine hydroxylase immunoreactive sprouting, catechol levels, and 18F-FDOPA-PET signal, suggesting the regenerative potential of AAV2-GDNF in PD.

Tilt-evoked, breathing-driven blood pressure oscillations: Independence from baroreflex-sympathoneural function.

PURPOSE: Orthostasis increases the variability of continuously recorded blood pressure (BP). Low-frequency (LF) BP oscillations (Mayer waves) in this setting are related to the vascular-sympathetic baroreflex. Mechanisms of increased high-frequency (HF) BP oscillations at the periodicity of respiration during orthostasis have received less research attention. A previously reported patient with post-neurosurgical orthostatic hypotension (OH) and vascular-sympathetic baroreflex failure had large tilt-evoked, breathing-driven BP oscillations, suggesting that such oscillations can occur independently of vascular-sympathetic baroreflex modulation. In the present study we assessed effects of orthostasis on BP variability in the frequency domain in patient cohorts with or without OH. METHODS: Power spectral analysis of systolic BP variability was conducted on recordings from 73 research participants, 42 with neurogenic OH [13 pure autonomic failure, 14 Parkinson's disease (PD) with OH, 12 parkinsonian multiple system atrophy, and 3 status post-brainstem neurosurgery] and 31 without OH (control group of 16 healthy volunteers and 15 patients with PD lacking OH), before, during, and after 5' of head-up tilt at 90 degrees from horizontal. The data were log transformed for statistical testing. RESULTS: Across all subjects, head-up tilting increased HF power of systolic BP variability (p = 0.001), without a difference between the neurogenic OH and control groups. LF power during orthostasis was higher in the control than in the OH groups (p = 0.009). CONCLUSIONS: The results of this observational cohort study confirm those based on our case report and lead us to propose that even in the setting of vascular-sympathetic baroreflex failure orthostasis increases HF power of BP variability.

A pathophysiological biomarker combination separates Lewy body from non-Lewy body neurogenic orthostatic hypotension ​.

PURPOSE: Neurogenic orthostatic hypotension (nOH) results from deficient reflexive delivery of norepinephrine to cardiovascular receptors in response to decreased cardiac venous return. Lewy body (LB) forms of nOH are characterized by low 18F-dopamine-derived radioactivity (a measure of cardiac noradrenergic deficiency), olfactory dysfunction by the University of Pennsylvania Smell Identification Test (UPSIT), and increased deposition of alpha-synuclein (α-syn) in dermal sympathetic noradrenergic nerves by the α-syn-tyrosine hydroxylase (TH) colocalization index. This observational, cross-sectional study explored whether combinations of these biomarkers specifically identify LB forms of nOH. METHODS: Clinical laboratory data were reviewed from patients referred for evaluation at the National Institutes of Health for chronic autonomic failure between 2011 and 2023. The cutoff value for low myocardial 18F-dopamine-derived radioactivity was 6000 nCi-kg/cc-mCi, for olfactory dysfunction an UPSIT score ≤ 28, and for an increased α-syn-TH colocalization index ≥ 1.57. RESULTS: A total of 44 patients (31 LB, 13 non-LB nOH) had data for all three biomarkers. Compared to the non-LB group, the LB nOH group had low myocardial 18F-dopamine-derived radioactivity, low UPSIT scores, and high α-syn-TH colocalization indexes (p < 0.0001 each). Combining the three biomarkers completely separated the groups. Cluster analysis identified two distinct groups (p < 0.0001) independently of the clinical diagnosis, with one cluster corresponding exactly to LB nOH. CONCLUSION: LB forms of nOH feature cardiac noradrenergic deficiency, olfactory dysfunction, and increased α-syn-TH colocalization in skin biopsies. Combining the data for these variables efficiently separates LB from non-LB nOH. Independently of the clinical diagnosis, this biomarker triad identifies a pathophysiologically distinct cluster of nOH patients.

A phase II study repurposing atomoxetine for neuroprotection in mild cognitive impairment.

The locus coeruleus is the initial site of Alzheimer's disease neuropathology, with hyperphosphorylated Tau appearing in early adulthood followed by neurodegeneration in dementia. Locus coeruleus dysfunction contributes to Alzheimer's pathobiology in experimental models, which can be rescued by increasing norepinephrine transmission. To test norepinephrine augmentation as a potential disease-modifying therapy, we performed a biomarker-driven phase II trial of atomoxetine, a clinically-approved norepinephrine transporter inhibitor, in subjects with mild cognitive impairment due to Alzheimer's disease. The design was a single-centre, 12-month double-blind crossover trial. Thirty-nine participants with mild cognitive impairment and biomarker evidence of Alzheimer's disease were randomized to atomoxetine or placebo treatment. Assessments were collected at baseline, 6- (crossover) and 12-months (completer). Target engagement was assessed by CSF and plasma measures of norepinephrine and metabolites. Prespecified primary outcomes were CSF levels of IL1α and TECK. Secondary/exploratory outcomes included clinical measures, CSF analyses of amyloid-ß42, Tau, and pTau181, mass spectrometry proteomics and immune-based targeted inflammation-related cytokines, as well as brain imaging with MRI and fluorodeoxyglucose-PET. Baseline demographic and clinical measures were similar across trial arms. Dropout rates were 5.1% for atomoxetine and 2.7% for placebo, with no significant differences in adverse events. Atomoxetine robustly increased plasma and CSF norepinephrine levels. IL-1α and TECK were not measurable in most samples. There were no significant treatment effects on cognition and clinical outcomes, as expected given the short trial duration. Atomoxetine was associated with a significant reduction in CSF Tau and pTau181 compared to placebo, but not associated with change in amyloid-ß42. Atomoxetine treatment also significantly altered CSF abundances of protein panels linked to brain pathophysiologies, including synaptic, metabolism and glial immunity, as well as inflammation-related CDCP1, CD244, TWEAK and osteoprotegerin proteins. Treatment was also associated with significantly increased brain-derived neurotrophic factor and reduced triglycerides in plasma. Resting state functional MRI showed significantly increased inter-network connectivity due to atomoxetine between the insula and the hippocampus. Fluorodeoxyglucose-PET showed atomoxetine-associated increased uptake in hippocampus, parahippocampal gyrus, middle temporal pole, inferior temporal gyrus and fusiform gyrus, with carry-over effects 6 months after treatment. In summary, atomoxetine treatment was safe, well tolerated and achieved target engagement in prodromal Alzheimer's disease. Atomoxetine significantly reduced CSF Tau and pTau, normalized CSF protein biomarker panels linked to synaptic function, brain metabolism and glial immunity, and increased brain activity and metabolism in key temporal lobe circuits. Further study of atomoxetine is warranted for repurposing the drug to slow Alzheimer's disease progression.

Baroreflex-sympathoneural dysfunction characterizes at-risk individuals with preclinical central Lewy body diseases.

PURPOSE: In central Lewy body diseases (LBDs) such as Parkinson's disease (PD) and dementia with Lewy bodies (DLB), by the time parkinsonism or cognitive dysfunction becomes manifest, substantial central neurodegeneration has already occurred. Cardiovascular autonomic biomarkers might detect preclinical central LBDs in at-risk individuals, enabling possibly effective disease-modifying treatment. METHODS: In the prospective, longitudinal PDRisk study, 59 participants provided information about family history of PD, olfactory dysfunction, dream enactment behavior, and orthostatic intolerance or hypotension at a protocol-specific website and were screened as outpatients. Thirty-four had three or more confirmed risk factors and were followed until PD was diagnosed or up to 7.5 years. Dependent measures included assessments of baroreflex-sympathoneural function, via the blood pressure recovery time (PRT) after release of the Valsalva maneuver and baroreflex areas; and baroreflex-cardiovagal function, via heart rate variability in the time and frequency domains and Valsalva baroslopes. Data were compared from groups with or without a subsequent diagnosis of a central LBD (LBD+, N = 9; LBD-, N = 25) and PDRisk participants with fewer than three confirmed risk factors (PDRisk-, N = 25). RESULTS: The LBD+ group had larger orthostatic falls in systolic blood pressure than did the LBD- and PDRisk- groups (p < 0.0001 each). The LBD+ group had increased PRTs (p = 0.0114 versus LBD-, p = 0.0094 versus PDRisk-) and baroreflex areas after the Valsalva maneuver (p = 0.0225 versus LBD-, p = 0.0028 versus PDRisk-), whereas the groups did not differ in indices of baroreflex-cardiovagal function. CONCLUSION: Orthostatic hypotension and baroreflex-sympathoneural dysfunction characterize at-risk individuals who go on to be diagnosed with a central LBD during longitudinal follow-up.

Cardiac 18F-dopamine positron emission tomography predicts the type of phenoconversion of pure autonomic failure.

PURPOSE: Pure autonomic failure (PAF) is a rare disease characterized by neurogenic orthostatic hypotension (nOH), no known secondary cause, and lack of a neurodegenerative movement or cognitive disorder. 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). Since cardiac 18F-dopamine-derived radioactivity usually is low in LBDs and usually is normal in MSA, we hypothesized that patients with PAF with low cardiac 18F-dopamine-derived radioactivity would be more likely to phenoconvert to a central LBD than 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 18F-dopamine positron emission tomography (PET). RESULTS: Nineteen patients (15 with low 18F-dopamine-derived radioactivity, 4 with normal radioactivity) met the above criteria and had follow-up data. Nine (47%) phenoconverted to a central synucleinopathy over a mean of 6.6 years (range 1.5-18.8 years). All 6 patients with low cardiac 18F-dopamine-derived radioactivity who phenoconverted during follow-up developed a central LBD, whereas none of 4 patients with consistently normal 18F-dopamine PET phenoconverted to a central LBD (p = 0.0048), 3 evolving to probable MSA and 1 upon autopsy having neither a LBD nor MSA. CONCLUSION: Cardiac 18F-dopamine PET can predict the type of phenoconversion of PAF. This capability could refine eligibility criteria for entry into disease-modification trials aimed at preventing evolution of PAF to symptomatic central LBDs.

Baroreflex-sympathoneural without baroreflex-cardiovagal failure in neurogenic orthostatic hypotension.

We describe a patient with neurogenic orthostatic hypotension (nOH) after brainstem neurosurgery in whom baroreflex-cardiovagal function was normal despite baroreflex-sympathoneural failure. We also cite other conditions entailing differential alterations in the two efferent limbs of the baroreflex. Any condition involving nOH from selective loss of sympathetic noradrenergic innervation, interference with sympathetic pre-ganglionic transmission in the thoracolumbar spinal cord, sympathectomies, or attenuated intra-neuronal synthesis, storage, or release of norepinephrine would be expected to manifest with selective baroreflex-sympathoneural dysfunction. We advise caution in relying on indices of baroreflex-cardiovagal function for diagnosing nOH, since normal values for these indices do not exclude nOH.

Elevated COUP-TFII expression in dopaminergic neurons accelerates the progression of Parkinson's disease through mitochondrial dysfunction.

Parkinson's disease (PD) is a neurodegenerative disorder featuring progressive loss of midbrain dopaminergic (DA) neurons that leads to motor symptoms. The etiology and pathogenesis of PD are not clear. We found that expression of COUP-TFII, an orphan nuclear receptor, in DA neurons is upregulated in PD patients through the analysis of public datasets. We show here that through epigenetic regulation, COUP-TFII contributes to oxidative stress, suggesting that COUP-TFII may play a role in PD pathogenesis. Elevated COUP-TFII expression specifically in DA neurons evokes DA neuronal loss in mice and accelerates the progression of phenotypes in a PD mouse model, MitoPark. Compared to control mice, those with elevated COUP-TFII expression displayed reduced cristae in mitochondria and enhanced cellular electron-dense vacuoles in the substantia nigra pars compacta. Mechanistically, we found that overexpression of COUP-TFII disturbs mitochondrial pathways, resulting in mitochondrial dysfunction. In particular, there is repressed expression of genes encoding cytosolic aldehyde dehydrogenases, which could enhance oxidative stress and interfere with mitochondrial function via 3,4-dihydroxyphenylacetaldehyde (DOPAL) buildup in DA neurons. Importantly, under-expression of COUP-TFII in DA neurons slowed the deterioration in motor functions of MitoPark mice. Taken together, our results suggest that COUP-TFII may be an important contributor to PD development and a potential therapeutic target.

Is 18F-DOPA a valid cardiac sympathetic neuroimaging agent?

PURPOSE: 18F-Dopamine positron emission tomography is a validated method for identifying cardiac noradrenergic deficiency, a characteristic feature of Lewy body forms of neurogenic orthostatic hypotension; however, 18F-dopamine is a research drug. Brain 18F-DOPA positron emission tomography is FDA-approved. Since 18F-DOPA is converted to 18F-dopamine in the heart, 18F-DOPA might be useful for cardiac sympathetic neuroimaging. We compared 18F-DOPA with 18F-dopamine in patients who either had or did not have low 18F-dopamine-derived radioactivity. METHODS: Brain and cardiac 18F-DOPA scanning and cardiac 18F-dopamine scanning were done on separate days in patient groups with neurogenic orthostatic hypotension or Parkinsonism or control subjects across a range of values for 18F-dopamine-derived radioactivity. The lower limit of normal for myocardial 18F-dopamine-derived radioactivity was 6000 Bq-kg/cc-MBq. We also examined inter-relationships among cardiac 18F-DOPA-derived radioactivity, cardiac 18F-dopamine-derived radioactivity, putamen/occipital cortex ratios of 18F-DOPA-derived radioactivity, and Unified Parkinson Disease Rating Scale scores in patients with or without Parkinsonism. For putamen/occipital cortex ratios, the cutoff value was 2.70. RESULTS: Twelve subjects had severely decreased and eight normal cardiac 18F-dopamine-derived radioactivity. Cardiac 18F-DOPA-derived radioactivity did not distinguish the two groups and was unrelated to 18F-dopamine-derived radioactivity. Left ventricular myocardial 18F-DOPA-derived radioactivity was poorly resolved from that in the chamber. Putamen/occipital cortex ratios of 18F-DOPA-derived radioactivity were negatively correlated with Unified Parkinson Disease Rating Scale scores (- 0.67, p = 0.0015). CONCLUSIONS: 18F-DOPA does not seem to be a valid cardiac sympathetic neuroimaging agent, although brain 18F-DOPA scanning provides a biomarker of Parkinsonism.

Sex-Specific Alterations in Dopamine Metabolism in the Brain after Methamphetamine Self-Administration.

Methamphetamine (METH) use disorder affects both sexes, with sex differences occurring in behavioral, structural, and biochemical consequences. The molecular mechanisms underlying these differences are unclear. Herein, we used a rat model to identify potential sex differences in the effects of METH on brain dopaminergic systems. Rats were trained to self-administer METH for 20 days, and a cue-induced drug-seeking test was performed on withdrawal days 3 and 30. Dopamine and its metabolites were measured in the prefrontal cortex (PFC), nucleus accumbens (NAc), dorsal striatum (dSTR), and hippocampus (HIP). Irrespective of conditions, in comparison to females, male rats showed increased 3,4-dihydroxyphenylalanine (DOPA) in the PFC, dSTR, and HIP; increased cys-dopamine in NAc; and increased 3,4-dihydroxyphenylethanol (DOPET) and 3,4-dihydroxyphenylacetic acid (DOPAC) in dSTR. Males also showed METH-associated decreases in DA levels in the HIP but increases in the NAc. Female rats showed METH-associated decreases in DA, DOPAL, and DOPAC levels in the PFC but increases in DOPET and DOPAC levels in the HIP. Both sexes showed METH-associated decreases in NAc DA metabolites. Together, these data document sex differences in METH SA-induced changes in DA metabolism. These observations provide further support for using sex as an essential variable when discussing therapeutic approaches against METH use disorder in humans.

Biochemical Neuroadaptations in the Rat Striatal Dopaminergic System after Prolonged Exposure to Methamphetamine Self-Administration.

Perturbations in striatal dopamine (DA) homeostasis might underlie the behavioral and pathobiological consequences of METH use disorder in humans. To identify potential consequences of long-term METH exposure, we modeled the adverse consequence DSM criterion of substance use disorders by giving footshocks to rats that had escalated their intake of METH during a drug self-administration procedure. Next, DA D1 receptor antagonist, SCH23390 was injected. Thereafter, rats were euthanized to measure several indices of the striatal dopaminergic system. Footshocks split the METH rats into two phenotypes: (i) shock-sensitive that decreased their METH-intake and (ii) shock-resistant that continued their METH intake. SCH23390 caused substantial dose-dependent reduction of METH taking in both groups. Stopping SCH23390 caused re-emergence of compulsive METH taking in shock-resistant rats. Compulsive METH takers also exhibited greater incubation of METH seeking than non-compulsive rats during withdrawal from METH SA. Analyses of DA metabolism revealed non-significant decreases (about 35%) in DA levels in resistant and sensitive rats. However, striatal contents of the deaminated metabolites, DOPAL and DOPAC, were significantly increased in sensitive rats. VMAT2 and DAT protein levels were decreased in both phenotypes. Moreover, protein expression levels of the D1-like DA receptor, D5R, and D2-like DA receptors, D3R and D4R, were significantly decreased in the compulsive METH takers. Our results parallel findings in post-mortem striatal tissues of human METH users who develop Parkinsonism after long-term METH intake and support the use of this model to investigate potential therapeutic interventions for METH use disorder.

Differential abnormalities of cerebrospinal fluid dopaminergic versus noradrenergic indices in synucleinopathies.

The synucleinopathies Parkinson's disease (PD), multiple system atrophy (MSA), and pure autonomic failure (PAF) are characterized by intra-cytoplasmic deposition of the protein alpha-synuclein and by catecholamine depletion. PAF, which manifests with neurogenic orthostatic hypotension (nOH) and no motor signs of central neurodegeneration, can evolve into PD+nOH. The cerebrospinal fluid (CSF) levels of catecholamine metabolites may indicate central catecholamine deficiency in these synucleinopathies, but the literature is inconsistent and incomplete. In this retrospective cohort study we reviewed data about CSF catecholamines, the dopamine metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), and the norepinephrine metabolites 3,4-dihydroxyphenylglycol (DHPG) and 3-methoxy-4-hydroxyphenylglycol (MHPG). The compounds were measured in 36 patients with PD, 37 patients with MSA, and 19 patients with PAF and in 38 controls. Compared to the control group, the PD, MSA, and PAF groups had decreased CSF MHPG (p < .0001 each by Dunnett's post hoc test), DHPG (p = .004; p < .0001; p < .0001) and norepinephrine (p = .017; p = .0003; p = .044). CSF HVA and DOPAC were decreased in PD (p < .0001 each) and MSA (p < .0001 each) but not in PAF. The three synucleinopathies therefore have in common in vivo evidence of central noradrenergic deficiency but differ in the extents of central dopaminergic deficiency-prominent in PD and MSA, less apparent in PAF. Data from putamen 18 F-DOPA and cardiac 18 F-dopamine neuroimaging in the same patients, post-mortem tissue catecholamines in largely separate cohorts, and review of the neuropathology literature fit with these distinctions. The results suggest a 'norepinephrine first' ascending pathogenetic sequence in synucleinopathies, with degeneration of pontine locus ceruleus noradrenergic neurons preceding the loss of midbrain substantia nigra dopaminergic neurons.

Enhanced tyrosine hydroxylase activity induces oxidative stress, causes accumulation of autotoxic catecholamine metabolites, and augments amphetamine effects in vivo.

In Parkinson's disease, dopamine-containing nigrostriatal neurons undergo profound degeneration. Tyrosine hydroxylase (TH) is the rate-limiting enzyme in dopamine biosynthesis. TH increases in vitro formation of reactive oxygen species, and previous animal studies have reported links between cytosolic dopamine build-up and oxidative stress. To examine effects of increased TH activity in catecholaminergic neurons in vivo, we generated TH-over-expressing mice (TH-HI) using a BAC-transgenic approach that results in over-expression of TH with endogenous patterns of expression. The transgenic mice were characterized by western blot, qPCR, and immunohistochemistry. Tissue contents of dopamine, its metabolites, and markers of oxidative stress were evaluated. TH-HI mice had a 3-fold increase in total and phosphorylated TH levels and an increased rate of dopamine synthesis. Coincident with elevated dopamine turnover, TH-HI mice showed increased striatal production of H2 O2 and reduced glutathione levels. In addition, TH-HI mice had elevated striatal levels of the neurotoxic dopamine metabolites 3,4-dihydroxyphenylacetaldehyde and 5-S-cysteinyl-dopamine and were more susceptible than wild-type mice to the effects of amphetamine and methamphetamine. These results demonstrate that increased TH alone is sufficient to produce oxidative stress in vivo, build up autotoxic dopamine metabolites, and augment toxicity.

Differential Susceptibilities of Catecholamines to Metabolism by Monoamine Oxidases.

The endogenous catecholamines dopamine (DA), norepinephrine (NE), and epinephrine (EPI) play key roles in neurobehavioral, cardiovascular, and metabolic processes; various clinical disorders; and effects of numerous drugs. Steps in intracellular catecholamine synthesis and metabolism were delineated long ago, but there remains a knowledge gap. Catecholamines are metabolized by two isoforms of monoamine oxidase (MAO), MAO-A and MAO-B, and although the anatomic localization of MAO-A and MAO-B and substrate specificities of enzyme inhibitors are well characterized, relative susceptibilities of the endogenous catecholamines to enzymatic oxidation by MAO-A and MAO-B have not been studied systematically. MAOs catalyze the conversion of catecholamines to catecholaldehydes-3,4-dihydroxyphenylacetaldehyde (DOPAL) from DA and 3,4-dihydroxyphenylglycolaldehyde (DOPEGAL) from NE and EPI. In this study we exploited the technical ability to assay DOPAL and DOPEGAL simultaneously with the substrate catecholamines to compare DA, NE, and EPI in their metabolism by MAO-A and MAO-B. For both MAO isoforms, DA was the better substrate compared to NE or EPI, which were metabolized equally. Since catecholaminergic neurons express mainly MAO-A, the finding that MAO-A is more efficient than MAO-B in metabolizing endogenous catecholamines reinforces the view that the predominant route of intraneuronal enzymatic oxidation of catecholamines is via MAO-A. The results have implications for clinical neurochemistry, experimental therapeutics, and computational models of catecholaminergic neurodegeneration. For instance, the greater susceptibility of DA than the other catecholamines to both MAO isoforms can help explain relatively high concentrations of the deaminated DA metabolite 3,4-dihydroxyphenylacetic acid than of the NE metabolite 3,4-dihydroxyphenylglycol in human plasma and urine. SIGNIFICANCE STATEMENT: Endogenous catecholamines are metabolized by monoamine oxidase (MAO)-A and -B, yielding the catecholaldehydes 3,4-dihydroxyphenylacetaldehyde (DOPAL) from dopamine (DA) and 3,4-dihydroxyphenylglycolaldehyde (DOPEGAL) from norepinephrine (NE) and epinephrine (EPI). Based on measurements of DOPAL and DOPEGAL production, DA is a better substrate than NE or EPI for both MAO isoforms, and MAO-A is more efficient than MAO-B in metabolizing DA, NE, and EPI. MAO-A is the main route of intraneuronal metabolism of endogenous catecholamines.

α-Synuclein Deposition in Sympathetic Nerve Fibers in Genetic Forms of Parkinson's Disease.

BACKGROUND: Cytoplasmic inclusions of α-synuclein (α-syn) in brainstem neurons are characteristic of idiopathic Parkinson's disease (PD). PD also entails α-syn buildup in sympathetic nerves. Among genetic forms of PD, the relative extents of sympathetic intraneuronal accumulation of α-syn have not been reported. OBJECTIVE: This cross-sectional observational study compared magnitudes of intraneuronal deposition of α-syn in common and rare genetic forms of PD. METHODS: α-Syn deposition was quantified by the α-syn-tyrosine hydroxylase colocalization index in C2 cervical skin biopsies from 65 subjects. These included 30 subjects with pathogenic mutations in SNCA (n = 3), PRKN [biallelic (n = 7) and monoallelic (n = 3)], LRRK2 (n = 7), GBA (n = 7), or PARK7/DJ1 [biallelic (n = 1) and monoallelic (n = 2)]. Twenty-five of the mutation carriers had PD and five did not. Data were also analyzed from 19 patients with idiopathic PD and 16 control participants. RESULTS: α-Syn deposition varied as a function of genotype (F = 16.7, P < 0.0001). It was above the control range in 100% of subjects with SNCA mutations, 100% with LRRK2 mutations, 95% with idiopathic PD, 83% with GBA mutations, and 0% with biallelic PRKN mutations. α-Syn deposition in the biallelic PRKN group was significantly higher than in the control group. In addition, patients with biallelic PRKN mutations had higher α-syn deposition than their unaffected siblings. CONCLUSIONS: Individuals with SNCA, DJ-1, LRRK2, or GBA mutations have substantial intraneuronal α-syn deposition in sympathetic noradrenergic nerves in skin biopsies, whereas those with biallelic PRKN mutations do not. Biallelic PRKN patients may have mildly increased α-syn deposition compared with control subjects. © 2021 International Parkinson and Movement Disorder Society.

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.

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.

The Catecholaldehyde Hypothesis for the Pathogenesis of Catecholaminergic Neurodegeneration: What We Know and What We Do Not Know.

3,4-Dihydroxyphenylacetaldehyde (DOPAL) is the focus of the catecholaldehyde hypothesis for the pathogenesis of Parkinson's disease and other Lewy body diseases. The catecholaldehyde is produced via oxidative deamination catalyzed by monoamine oxidase (MAO) acting on cytoplasmic dopamine. DOPAL is autotoxic, in that it can harm the same cells in which it is produced. Normally, DOPAL is detoxified by aldehyde dehydrogenase (ALDH)-mediated conversion to 3,4-dihydroxyphenylacetic acid (DOPAC), which rapidly exits the neurons. Genetic, environmental, or drug-induced manipulations of ALDH that build up DOPAL promote catecholaminergic neurodegeneration. A concept derived from the catecholaldehyde hypothesis imputes deleterious interactions between DOPAL and the protein alpha-synuclein (αS), a major component of Lewy bodies. DOPAL potently oligomerizes αS, and αS oligomers impede vesicular and mitochondrial functions, shifting the fate of cytoplasmic dopamine toward the MAO-catalyzed formation of DOPAL-destabilizing vicious cycles. Direct and indirect effects of DOPAL and of DOPAL-induced misfolded proteins could "freeze" intraneuronal reactions, plasticity of which is required for neuronal homeostasis. The extent to which DOPAL toxicity is mediated by interactions with αS, and vice versa, is poorly understood. Because of numerous secondary effects such as augmented spontaneous oxidation of dopamine by MAO inhibition, there has been insufficient testing of the catecholaldehyde hypothesis in animal models. The clinical pathophysiological significance of genetics, emotional stress, environmental agents, and interactions with numerous proteins relevant to the catecholaldehyde hypothesis are matters for future research. The imposing complexity of intraneuronal catecholamine metabolism seems to require a computational modeling approach to elucidate clinical pathogenetic mechanisms and devise pathophysiology-based, individualized treatments.