Nigrostriatal blood-brain barrier opening in Parkinson's disease

BACKGROUND

The nigrostriatal system is especially vulnerable to neurodegeneration in Parkinson's disease (PD) and the blood-brain barrier (BBB) is a limiting factor for delivery of therapeutic agents to the brain. This pilot study aimed to demonstrate safety, feasibility and tissue penetration (by 18F-Choline-positron emission tomography (PET)) of MR-guided focused ultrasound (MRgFUS) simultaneous BBB opening (BBB-O) in the substantia nigra (SN) and putamen in PD.

METHODS

Three patients underwent MRgFUS for midbrain and putamen BBB-O. Patients were evaluated clinically and underwent brain MRI with gadolinium (baseline, 24 hours, 14 days and 3 months postprocedure). In two patients, BBB-O was repeated after 2-3 weeks, and 18F-Choline-PET was performed immediately after.

RESULTS

The right SN and putamen were simultaneously opened unilaterally in 3 patients once and the left SN in 1 patient in a different session. No severe clinical or neuroimaging adverse events developed in any patient. 18F-Choline-PET uptake was enhanced in the targeted SN and putamen regions.

CONCLUSION

BBB-O of the nigrostriatal system is a feasible and well-tolerated approach in patients with PD. 18F-Choline-PET uptake indicates penetration into the parenchyma after BBB-O, which suggests that the opening is functionally effective. This minimally invasive technique could facilitate delivery of putative neurorestorative molecules to brain regions vulnerable to neurodegeneration.

Gut microbiota produces biofilm-associated amyloids with potential for neurodegeneration

Age-related neurodegenerative diseases involving amyloid aggregation remain one of the biggest challenges of modern medicine. Alterations in the gastrointestinal microbiome play an active role in the aetiology of neurological disorders. Here, we dissect the amyloidogenic properties of biofilm-associated proteins (BAPs) of the gut microbiota and their implications for synucleinopathies. We demonstrate that BAPs are naturally assembled as amyloid-like fibrils in insoluble fractions isolated from the human gut microbiota. We show that BAP genes are part of the accessory genomes, revealing microbiome variability. Remarkably, the abundance of certain BAP genes in the gut microbiome is correlated with Parkinson's disease (PD) incidence. Using cultured dopaminergic neurons and Caenorhabditis elegans models, we report that BAP-derived amyloids induce α-synuclein aggregation. Our results show that the chaperone-mediated autophagy is compromised by BAP amyloids. Indeed, inoculation of BAP fibrils into the brains of wild-type mice promote key pathological features of PD. Therefore, our findings establish the use of BAP amyloids as potential targets and biomarkers of α-synucleinopathies.

Dopaminergic denervation and associated MRI microstructural changes in the nigrostriatal projection in early Parkinson's disease patients

Loss of dopaminergic neurons in the substantia nigra pars compacta (SNc) and a profound reduction of striatal dopamine are two hallmarks of Parkinson's disease (PD). However, it's unclear whether degeneration starts at the neuronal soma or the striatal presynaptic terminals, and how microstructural degeneration is linked to dopaminergic loss is also uncertain. In this study, thirty de novo PD patients and twenty healthy subjects (HS) underwent 6-[18F]-fluoro-L-dopa (FDOPA) PET and MRI studies no later than 12 months from clinical diagnosis. FDOPA uptake rate (Ki), fractional volume of free-water (FW), and iron-sensitive R2* relaxometry were quantified within nigrostriatal regions. Inter-group differences (PD vs HS) were studied using non-parametric statistics and complemented with Cohen's d effect sizes and Bayesian statistics. Correlation analyses were performed exploring biomarker dependencies and their association with bradykinesia scores. PD patients exhibited a significant decline in nigrostriatal dopaminergic activity, being post-commissural putamen (-67%) and posterolateral SNc (-11.7%) the most affected subregions within striatum and SNc respectively. Microstructural alterations (FW) were restricted to the hemisphere corresponding to the most affected side and followed similar spatial gradients as FDOPA Ki (+20% in posterior putamen and +11% in posterolateral SNc). R2* revealed no relevant significant changes. FDOPA and FW were correlated within the posterolateral SNc, and clinical severity was associated with FDOPA Ki loss. The asymmetry between striatal and SNc changes for both dopaminergic depletion and microstructural degeneration biomarkers is consistent with a neurodegenerative process that begins in the striatal terminals before progressing toward the cell bodies in the SNc.

BBB opening with focused ultrasound in nonhuman primates and Parkinson's disease patients: Targeted AAV vector delivery and PET imaging

Intracerebral vector delivery in nonhuman primates has been a major challenge. We report successful blood-brain barrier opening and focal delivery of adeno-associated virus serotype 9 vectors into brain regions involved in Parkinson's disease using low-intensity focus ultrasound in adult macaque monkeys. Openings were well tolerated with generally no associated abnormal magnetic resonance imaging signals. Neuronal green fluorescent protein expression was observed specifically in regions with confirmed blood-brain barrier opening. Similar blood-brain barrier openings were safely demonstrated in three patients with Parkinson's disease. In these patients and in one monkey, blood-brain barrier opening was followed by ¹⁸F-Choline uptake in the putamen and midbrain regions based on positron emission tomography. This indicates focal and cellular binding of molecules that otherwise would not enter the brain parenchyma. The less-invasive nature of this methodology could facilitate focal viral vector delivery for gene therapy and might allow early and repeated interventions to treat neurodegenerative disorders.

Neuroinflammation, immune response and α-synuclein pathology: how animal models are helping us to connect dots

INTRODUCTION

A key pathological event occurring in Parkinson's disease (PD) is the transneuronal spreading of alpha-synuclein (α-syn). Other hallmarks of PD include neurodegeneration, glial activation, and immune cell infiltration in susceptible brain regions. Although preclinical models can mimic most of the key characteristics of PD, it is crucial to know the biological bases of individual differences between them when choosing one over another, to ensure proper interpretation of the results and to positively influence the outcome of the experiments.

AREAS COVERED

This review provides an overview of current preclinical models actively used to study the interplay between α-syn pathology, neuroinflammation and immune response in PD but also to explore new potential preclinical models or emerging therapeutic strategies intended to fulfill the unmet medical needs in this disease. Lastly, this review also considers the current state of the ongoing clinical trials of new drugs designed to target these processes and delay the initiation or progression of the disease.

EXPERT OPINION

Anti-inflammatory and immunomodulatory agents have been demonstrated to be very promising candidates for reducing disease progression; however, more efforts are needed to reduce the enormous gap between these and dopaminergic drugs, which have dominated the therapeutic market for the last sixty years.

Striatal Blood-Brain Barrier Opening in Parkinson's Disease Dementia: A Pilot Exploratory Study

BACKGROUND

Parkinson's disease (PD) exhibits a high prevalence of dementia as disease severity and duration progress. Focused ultrasound (FUS) has been applied for transient blood-brain barrier (BBB) opening of cortical regions in neurodegenerative disorders. The striatum is a primary target for delivery of putative therapeutic agents in PD.

OBJECTIVE

Here, we report a prospective, single-arm, nonrandomized, proof-of-concept, phase I clinical trial (NCT03608553 amended) in PD with dementia to test the safety and feasibility of striatal BBB opening in PD patients.

METHODS

Seven PD patients with cognitive impairment were treated for BBB opening in the posterior putamen. This was performed in two sessions separated by 2 to 4 weeks, where the second session included bilateral putamina opening in 3 patients. Primary outcome measures included safety and feasibility of focal striatal BBB opening. Changes in motor and cognitive functions, magnetic resonance imaging (MRI), ¹⁸ F-fluorodopa (FDOPA), and β-amyloid PET (positron emission tomography) images were determined.

RESULTS

The procedure was feasible and well tolerated, with no serious adverse events. No neurologically relevant change in motor and cognitive (battery of neuropsychological tests) functions was recognized at follow-up. MRI revealed putamen BBB closing shortly after treatment (24 hours to 14 days) and ruled out hemorrhagic and ischemic lesions. There was a discrete but significant reduction in β-amyloid uptake in the targeted region and no change in FDOPA PET.

CONCLUSIONS

These initial results indicate that FUS-mediated striatal BBB opening is feasible and safe and therefore could become an effective tool to facilitate the delivery of putative neurorestorative molecules in PD. © 2022 International Parkinson and Movement Disorder Society.

Neuron types in the primate striatum: stereological analysis of projection neurons and interneurons in control and parkinsonian monkeys

AIMS

The striatum is mainly composed of projection neurons. It also contains interneurons, which modulate and control striatal output. The aim of the present study was to assess the percentages of projection neurons and interneuron populations in the striatum of control monkeys and of parkinsonian monkeys.

METHODS

Unbiased stereology was used to estimate the volume density of every neuron population in the caudate, putamen and ventral striatum of control monkeys and of monkeys treated with MPTP, which results in striatal dopamine depletion. The various neuron population phenotypes were identified by immunohistochemistry. All analyses were performed within the same subjects using similar processing and analysis parameters, thus allowing for reliable data comparisons.

RESULTS

In control monkeys, the projection neurons, which express the Dopamine-and-cAMP-Regulated-Phosphoprotein, 32-KDa (DARPP-32), were the most abundant: ~86% of the total neurons counted. The interneurons accounted for the remaining 14%. Among the interneurons, those expressing Calretinin were the most abundant (Cr+: ~57%; ~8% of the total striatal neurons counted), followed those expressing Parvalbumin (Pv+: ~18 %; 2.6%), Dinucleotide Phosphate-Diaphorase (NADPH+: ~13 %; 1.8%), Choline Acetyltransferase (ChAT+: ~11%; 1.5%) and Tyrosine Hydroxylase (TH+: ~0.5%; 0.1%). No significant changes in volume densities occurred in any population following dopamine depletion, except for the TH+ interneurons, which increased in parkinsonian non-symptomatic monkeys and even more in symptomatic monkeys.

CONCLUSIONS

These data are relevant for translational studies targeting specific neuron populations of the striatum. The fact that dopaminergic denervation does not cause neuron loss in any population has potential pathophysiological implications.

Lack of Parkinsonian Pathology and Neurodegeneration in Mice After Long-Term Injections of a Proteasome Inhibitor in Olfactory Bulb and Amygdala

Proteinaceous inclusions, called Lewy bodies (LBs), are used as a pathological hallmark for Parkinson's disease (PD). Recent studies suggested a prion-like spreading mechanism for α-synucleinopathy where early neuropathological deposits occur, among others, in the olfactory bulb (OB) and amygdala. LBs contain insoluble α-synuclein and many other ubiquitinated proteins, suggesting a role of protein degradation system failure in PD pathogenesis. Therefore, we wanted to study the effects of a proteasomal inhibitor, lactacystin, on the aggregability and transmissibility of α-synuclein in the OB and amygdala. We performed injections of lactacystin in the OB and amygdala of wild-type mice. Motor behavior, markers of neuroinflammation, α-synuclein, and dopaminergic integrity were assessed by immunohistochemistry. Overall, there were no differences in the number of neurons and α-synuclein expression in these regions following injection of lactacystin into either the OB or amygdala. Microglial and astroglial labeling appeared to be correlated with surgery-induced inflammation or local effects of lactacystin. Consistent with the behavior and pathological findings, there was no loss of dopaminergic cell bodies in the substantia nigra and terminals in the striatum. Our data showed that long-term lactacystin injections in extra nigrostriatal regions may not mimic spreading aspects of PD and reinforce the special vulnerability of dopaminergic neurons of the substantia nigra pars compacta (SNc).

Effectiveness of a physiotherapy and nutrition program in patients with coronary artery disease: randomized controlled trial

Funding Acknowledgements

Type of funding sources: None.

Introduction. Dietary and exercise interventions are effective strategies for improving physical and nutritional status of patients with coronary artery disease (CAD). However, few studies have applied a combined exercise protocol based on high intensity interval training (HIIT) and dietary education in patients with CAD with percutaneous coronary intervention (PCI).

Purpose

This study researches the effectiveness of a multidisciplinary program based in HIIT with dietary education (DEHIIT) in comparison with only HIIT, on adherence to Mediterranean diet in CAD patients with PCI.

Methods. A prospective, assessor-blinded, parallel group, randomized trial was developed. The study was developed at a University research lab. Forty-four adults diagnosed with CAD (between 40 and 72 years), were randomized to receive either combined dietary intervention and HIIT (DEHIIT, n = 22) or only HIIT (HIIT, n = 22). The adherence to the Mediterranean diet was assessed with a 14-item tool of adherence to the Mediterranean diet (MEDAS-14) at baseline and after the intervention. DEHIIT performed a 3-month dietary intervention program combined with 24 HIIT sessions at 85-95% of peak heart rate, whilst HIIT performed a 3-month HIIT sessions at 85-95% of peak heart rate. This study did not receive any funding. No conflict of interest is declared.

Results. After three months, regarding to MEDAS-14, DEHIIT increased the fish/seafood consumption significantly (p = 0.001) and decreased the fruit consumption (p = 0.032) and dry fruits (p = 0.006). And, when comparing between groups, DEHIIT obtained significantly more MEDAS-14 score (p = 0.01) and more adherence to dieta mediterránea (p = 0.001). No adverse events were reported.

Conclusions. A combined protocol including dietary intervention and HIIT can bring benefits for CAD patients with PCI on adherence to Mediterranean diet in comparison to only HIIT. Consequently, our combined program could be used as a treatment option in the therapeutic approach for these patients.

Multidisciplinary program based in physiotherapy and nutrition in coronary artery disease patients: randomized controlled trial

Funding Acknowledgements

Type of funding sources: None.

Introduction. The interventions on eating habits and exercise in physiotherapy programs are usually recommended in coronary artery disease (CAD), since they are beneficial to improve physical and nutritional status of patient. Despite this, scarce studies are focused on combined protocols based on high intensity interval training (HIIT) and dietary education in CAD patients with percutaneous coronary intervention (PCI).

Purpose

The main goal of this study was to compare the effectiveness of a multidisciplinary program based in HIIT, with a program based in dietary education and HIIT (DEHIIT), on eating habits in CAD patients with PCI.

Methods. A prospective, randomized controlled trial with blinded outcome assessment was developed. The study was developed at a University research laboratory. 44 participants diagnosed with CAD, aged between 40 and 72 years, were randomly allocated to two treatment groups: HIIT group (HIITG, n = 22) and dietary intervention and HIIT group (DEHIITG, n = 22). The assessment consisted of applying a Food Frequency Questionnaires (FFQ) at baseline and post-intervention. DEHIITG performed a 3-month dietary intervention program combined with 24 HIIT sessions at 85-95% of peak heart rate, whilst HIITG performed a 3-month HIIT sessions at 85-95% of peak heart rate. This study did not receive any funding. No conflict of interest is declared.

Results. At the end of the program, when comparing between groups, statistically significant changes were noted. DEHIITG consumed more olive oil (p = 0.021), chicken or turkey (p = 0.039), stir-fried with vegetables (p = 0.033), vegetables (p = 0.003), fish and seafood (p = 0.039), and quantity of commercial juices (p = 0.042), sweets and snacks (p = 0.033). HIITG showed more improvements than DEHIITG in soups and creams consumption (p = 0.042). No adverse events were reported.

Conclusions. A dietary intervention with HIIT protocol yields better benefits than only HIIT on eating habits in CAD patients with PCI. Thus, our combined program could be considered a suitable treatment option among these patients.

Impact of a program based in eating habits and physiotherapy on anthropometric parameters in patients with coronary artery disease: randomized controlled trial

Funding Acknowledgements

Type of funding sources: None.

Introduction. On the one hand, physical training such as High intensity interval training (HIIT) and on the other, eating habits, it is often prescribed to patients with coronary artery disease (CAD). Nevertheless, the combination of HIIT and eating habits in CAD with percutaneous coronary intervention (PCI) there is no consensus on using a combined protocol of both.

Purpose. The purpose of this study was to evaluate the impact of an HIIT program with eating habits, with a program based in HIIT, on anthropometric parameters in CAD patients with PCI.

Methods. A randomized controlled trial was carried out in a hospital.  44 patients with CAD and PCI were recruited. All participants signed an informed consent. Patients were randomly allocated to a HIIT group (HIIT, n = 22, 81.8% men, 62.05 ± 4.9 years) or to a Dietary education and HIIT (DEHIIT) group (n = 22, 81.8% men, 60.2 ± 5.6 years). HIIT consisted of a 3-month physiotherapy program, twice a week for one hour, at 85-95% peak heart rate. DEHIIT consisted of a multidisciplinary program, including the same HIIT program explained, plus eating habits. Body composition (weight, BMI, % body fat, % visceral fat, muscle mass) and waist circumference, hip circumference and Waste-to-Hip Ratio (WHR) were evaluated at baseline and at week 12.

Results. At the end of the program, DEHIIT significantly decreased all anthropometrics parameters except muscle mass. The following parameters decreased: weight (p ≤ 0.001), BMI (p ≤ 0.001), body fat (p ≤ 0.001), visceral fat (p ≤ 0.001), waist circumference (p ≤ 0.001), hip circumference (p = 0.043) and WHR (p ≤ 0.001). Instead, the muscle mass increased  significantly (p ≤ 0.001). When comparing between groups, DEHIIT did not show significant differences weight (p = 0.575), BMI (p = 0.404), % body fat (p = 0.217), muscle mass (p = 0.508), waist circumference (p = 0.165), hip circumference (p = 0.307), WHR (p = 0.379), except for presenting less visceral fat (p = 0.040) than HIIT.

Conclusions

HIIT programme with eating habits reducing visceral fat in CAD patients with PCI compared to a HIIT-only program.

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

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

Potent neutralization of clinical isolates of SARS-CoV-2 D614 and G614 variants by a monomeric, sub-nanomolar affinity nanobody

Despite unprecedented global efforts to rapidly develop SARS-CoV-2 treatments, in order to reduce the burden placed on health systems, the situation remains critical. Effective diagnosis, treatment, and prophylactic measures are urgently required to meet global demand: recombinant antibodies fulfill these requirements and have marked clinical potential. Here, we describe the fast-tracked development of an alpaca Nanobody specific for the receptor-binding-domain (RBD) of the SARS-CoV-2 Spike protein with potential therapeutic applicability. We present a rapid method for nanobody isolation that includes an optimized immunization regimen coupled with VHH library E. coli surface display, which allows single-step selection of Nanobodies using a simple density gradient centrifugation of the bacterial library. The selected single and monomeric Nanobody, W25, binds to the SARS-CoV-2 S RBD with sub-nanomolar affinity and efficiently competes with ACE-2 receptor binding. Furthermore, W25 potently neutralizes SARS-CoV-2 wild type and the D614G variant with IC50 values in the nanomolar range, demonstrating its potential as antiviral agent.

Glial activation precedes alpha-synuclein pathology in a mouse model of Parkinson's disease

Neuroinflammation is increasingly recognized as an important feature in the pathogenesis of Parkinson's disease (PD). However, it remains unclear whether neuroinflammation contributes to nigral degeneration in PD or is merely a secondary marker of neurodegeneration. We aimed to investigate the temporal relationship between synucleopathy, neuroinflammation and nigrostriatal degeneration in a mouse model of PD. Mice received unilateral intrastriatal injection of alpha-synuclein pre-formed fibrils, alpha-synuclein monomer or vehicle and were sacrificed at 15, 30 and 90 days post-injection. Intrastriatal inoculation of alpha-synuclein fibrils led to significant alpha-synuclein aggregation in the substantia nigra peaking at 30 days after injection while the significant increase in Iba-1 cells, GFAP cells and IL-1β expression peaked earlier at 15 days. At 90 days, the striatal dopaminergic denervation was associated with astroglial activation. Alpha-synuclein monomer did not result in long-term glia activation or increase in inflammatory markers. The spread of alpha-synuclein aggregates into the cortex was not associated with any changes to neuroinflammatory markers. Our results demonstrate that in the substantia nigra glial activation is an early event that precedes alpha-synuclein inclusion formation, suggesting neuroinflammation could play an important early role in the pathogenesis of PD.

Dimensions of household food waste focused on family and consumers

Food waste produced in homes represents the largest fraction of food waste generated along the food chain. Therefore, adequate prevention measures based on the quantitative and qualitative dimensions of the problem need to be put in place to reduce waste. The objective of the review was to identify areas of interest in relation to the food waste in households, considering the family unit as a whole as well as individual family members. Quantifying the problem is an important aspect in order to know its scope and dimension, but prevention also involves knowing the causes in a home. This is a complex issue, which, on a family level, is related to socioeconomic status, educational level, composition and number of members of the household as well as culinary and buying food habits. Individual variables such as age, sex, values, awareness, lifestyle and time spent on food preparation were included to characterize consumers. The focus of the problem is also important because most consumers consider food waste from a social perspective, without being aware of the serious environmental and economic problems. Habits and customs of consumers are considered the leading cause of food waste in homes and knowledge of this issue raises consumer awareness as a preventive tool.

Molecular targets for endogenous glial cell line-derived neurotrophic factor modulation in striatal parvalbumin interneurons

Administration of recombinant glial cell line-derived neurotrophic factor into the putamen has been tested in preclinical and clinical studies to evaluate its neuroprotective effects on the progressive dopaminergic neuronal degeneration that characterizes Parkinson’s disease. However, intracerebral glial cell line-derived neurotrophic factor infusion is a challenging therapeutic strategy, with numerous potential technical and medical limitations. Most of these limitations could be avoided if the production of endogenous glial cell line-derived neurotrophic factor could be increased. Glial cell line-derived neurotrophic factor is naturally produced in the striatum from where it exerts a trophic action on the nigrostriatal dopaminergic pathway. Most of striatal glial cell line-derived neurotrophic factor is synthesized by a subset of GABAergic interneurons characterized by the expression of parvalbumin. We sought to identify molecular targets specific to those neurons and which are putatively associated with glial cell line-derived neurotrophic factor synthesis. To this end, the transcriptomic differences between glial cell line-derived neurotrophic factor-positive parvalbumin neurons in the striatum and parvalbumin neurons located in the nearby cortex, which do not express glial cell line-derived neurotrophic factor, were analysed. Using mouse reporter models, we have defined the genomic signature of striatal parvalbumin interneurons obtained by fluorescence-activated cell sorting followed by microarray comparison. Short-listed genes were validated by additional histological and molecular analyses. These genes code for membrane receptors (Kit, Gpr83, Tacr1, Tacr3, Mc3r), cytosolic proteins (Pde3a, Crabp1, Rarres2, Moxd1) and a transcription factor (Lhx8). We also found the proto-oncogene cKit to be highly specific of parvalbumin interneurons in the non-human primate striatum, thus highlighting a conserved expression between species and suggesting that specific genes identified in mouse parvalbumin neurons could be putative targets in the human brain. Pharmacological stimulation of four G-protein-coupled receptors enriched in the striatal parvalbumin interneurons inhibited Gdnf expression presumably by decreasing cyclic adenosine monophosphate formation. Additional experiments with pharmacological modulators of adenylyl cyclase and protein kinase A indicated that this pathway is a relevant intracellular route to induce Gdnf gene activation. This preclinical study is an important step in the ongoing development of a specific pro-endo-glial cell line-derived neurotrophic factor pharmacological strategy to treat Parkinson’s disease.

Changes in thalamic dopamine innervation in a progressive Parkinson's disease model in monkeys

BACKGROUND

Dopamine loss beyond the mesostriatal system might be relevant in pathogenic mechanisms and some clinical manifestations in PD. The primate thalamus is densely and heterogeneously innervated with dopaminergic axons, most of which express the dopamine transporter, as does the nigrostriatal system. We hypothesized that dopamine depletion may be present in the thalamus of the parkinsonian brain and set out to ascertain possible regional differences.

METHODS

The toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine was administered to adult macaque monkeys using a slow intoxication protocol. The treated macaques were classified into 2 groups according to their motor status: nonsymptomatic and parkinsonian. Dopamine innervation was studied with immunohistochemistry for the dopamine transporter. Topographic maps of the dopamine transporter-immunoreactive axon distribution were generated and the total length and length density of these axons stereologically estimated using a 3-dimensional fractionator.

RESULTS

Parkinsonian macaques exhibited lower dopamine transporter-immunoreactive axon length density than controls in mediodorsal and centromedian-parafascicular nuclei. Dopamine denervation in the mediodorsal nucleus was already noticeable in nonsymptomatic macaques and was even greater in parkinsonian macaques. Reticular nucleus dopamine transporter-immunoreactive axon length density presented an inverse pattern, increasing progressively to the maximum density seen in parkinsonian macaques. No changes were observed in ventral thalamic nuclei. Dopamine transporter-immunoreactive axon maps supported the quantitative findings.

CONCLUSIONS

Changes in the dopamine innervation of various thalamic nuclei are heterogeneous and start in the premotor parkinsonian stage. These changes may be involved in some poorly understood nonmotor manifestations of PD. © 2019 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Serotonergic innervation of the striatum in a nonhuman primate model of Parkinson's disease

Parkinson's disease (PD) is characterized by dopaminergic neurodegeneration in the substantia nigra and dopamine depletion in the striatum. Non-dopaminergic systems are also affected, including the serotonergic system. Enhanced striatal serotonergic innervation is a proposed compensatory mechanism for the dopaminergic deficit. Meanwhile a serotonergic deficit has been suggested as preceding the nigrostriatal dopaminergic pathology in PD. Our aim was to assess the serotonergic innervation of the striatum in a model of progressive experimental parkinsonism in macaques, from pre-symptomatic to symptomatic stages. The neurotoxin 1-methyl-4-phenyl-1,2,3,6 tetrahydropyridine (MPTP) was administered to adult macaque monkeys using a slow intoxication protocol. The intoxicated animals were classified into asymptomatic, recovered, moderate and severe parkinsonian, based on their motor behavior. The serotonergic innervation was studied by immunohistochemistry against serotonin (5-HT). In the striatum, the density of 5-HT-immunoreactive (5-HT+) axons was estimated with stereology. Images of the striatum in the immunostained sections were taken to compare the distribution patterns of the serotonergic innervation between groups. These patterns were apparently similar among the groups. Axonal density estimations showed no differences in striatal 5-HT+ innervation between the intoxicated groups and the control group. Accordingly, this study fails to find significant changes in the striatal serotonergic axonal innervation in MPTP-treated monkeys, coinciding with previous biochemical findings in our model. However, it is possible that alterations in the serotonergic system in PD could be independent of axonal density changes. Consequently, the proposed role for striatal serotonin serving as a compensatory mechanism for dopaminergic denervation merits further study. This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.

Blood-brain barrier opening with focused ultrasound in experimental models of Parkinson's disease

Parkinson's disease has many symptomatic treatments, but there is no neuroprotective therapy currently available. The evolution of this disease is inexorably progressive, and halting or stopping the neurodegenerative process is a major unmet need. Parkinson's disease motor features at onset are typically limited to 1 body segment, that is, focal signs, and the nigrostriatal degeneration is highly asymmetrical and mainly present in the caudal putamen. Thus, clinically and neurobiologically the process is fairly limited early in its evolution. Tentatively, this would allow the possibility of intervening to halt neurodegeneration at the most vulnerable site. The recent use of new technologies such as focused ultrasound provides interesting prospects. In particular, the possibility of transiently opening the blood-brain barrier to facilitate penetrance of putative neuroprotective agents is a highly attractive approach that could be readily applied to Parkinson's disease. However, because there are currently effective treatments available (ie, dopaminergic pharmacological therapy), more experimental evidence is needed to construct a feasible and practical therapeutic approach to be tested early in the evolution of Parkinson's disease patients. In this review, we provide the current evidence for the application of blood-brain barrier opening in experimental models of Parkinson's disease and discuss its potential clinical applicability. © 2019 International Parkinson and Movement Disorder Society.

Systemic Exosomal Delivery of shRNA Minicircles Prevents Parkinsonian Pathology

The development of new therapies to slow down or halt the progression of Parkinson's disease is a health care priority. A key pathological feature is the presence of alpha-synuclein aggregates, and there is increasing evidence that alpha-synuclein propagation plays a central role in disease progression. Consequently, the downregulation of alpha-synuclein is a potential therapeutic target. As a chronic disease, the ideal treatment will be minimally invasive and effective in the long-term. Knockdown of gene expression has clear potential, and siRNAs specific to alpha-synuclein have been designed; however, the efficacy of siRNA treatment is limited by its short-term efficacy. To combat this, we designed shRNA minicircles (shRNA-MCs), with the potential for prolonged effectiveness, and used RVG-exosomes as the vehicle for specific delivery into the brain. We optimized this system using transgenic mice expressing GFP and demonstrated its ability to downregulate GFP protein expression in the brain for up to 6 weeks. RVG-exosomes were used to deliver anti-alpha-synuclein shRNA-MC therapy to the alpha-synuclein preformed-fibril-induced model of parkinsonism. This therapy decreased alpha-synuclein aggregation, reduced the loss of dopaminergic neurons, and improved the clinical symptoms. Our results confirm the therapeutic potential of shRNA-MCs delivered by RVG-exosomes for long-term treatment of neurodegenerative diseases.

Advances in Parkinson's Disease: 200 Years Later

When James Parkinson described the classical symptoms of the disease he could hardly foresee the evolution of our understanding over the next two hundred years. Nowadays, Parkinson’s disease is considered a complex multifactorial disease in which genetic factors, either causative or susceptibility variants, unknown environmental cues, and the potential interaction of both could ultimately trigger the pathology. Noteworthy advances have been made in different fields from the clinical phenotype to the decoding of some potential neuropathological features, among which are the fields of genetics, drug discovery or biomaterials for drug delivery, which, though recent in origin, have evolved swiftly to become the basis of research into the disease today. In this review, we highlight some of the key advances in the field over the past two centuries and discuss the current challenges focusing on exciting new research developments likely to come in the next few years. Also, the importance of pre-motor symptoms and early diagnosis in the search for more effective therapeutic options is discussed.

Compensatory mechanisms in Parkinson's disease: Circuits adaptations and role in disease modification

The motor features of Parkinson's disease (PD) are well known to manifest only when striatal dopaminergic deficit reaches 60-70%. Thus, PD has a long pre-symptomatic and pre-motor evolution during which compensatory mechanisms take place to delay the clinical onset of disabling manifestations. Classic compensatory mechanisms have been attributed to changes and adjustments in the nigro-striatal system, such as increased neuronal activity in the substantia nigra pars compacta and enhanced dopamine synthesis and release in the striatum. However, it is not so clear currently that such changes occur early enough to account for the pre-symptomatic period. Other possible mechanisms relate to changes in basal ganglia and motor cortical circuits including the cerebellum. However, data from early PD patients are difficult to obtain as most studies have been carried out once the diagnosis and treatments have been established. Likewise, putative compensatory mechanisms taking place throughout disease evolution are nearly impossible to distinguish by themselves. Here, we review the evidence for the role of the best known and other possible compensatory mechanisms in PD. We also discuss the possibility that, although beneficial in practical terms, compensation could also play a deleterious role in disease progression.

Early Paradoxical Increase of Dopamine: A Neurochemical Study of Olfactory Bulb in Asymptomatic and Symptomatic MPTP Treated Monkeys

Parkinson's disease (PD) is a neurodegenerative disease with both motor and non-motor manifestations. Hyposmia is one of the early non-motor symptoms, which can precede motor symptoms by several years. The relationship between hyposmia and PD remains elusive. Olfactory bulb (OB) pathology shows an increased number of olfactory dopaminergic cells, protein aggregates and dysfunction of neurotransmitter systems. In this study we examined tissue levels of dopamine (DA) and serotonin (5-hydroxytryptamine, 5-HT) and their metabolites, of noradrenaline (NA) and of the amino acid neurotransmitters aspartate, glutamate, taurine and γ-aminobutyric acid in OBs of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treated Macaca fascicularis in different stages, including monkeys who were always asymptomatic, monkeys who recovered from mild parkinsonian signs, and monkeys with stable moderate or severe parkinsonism. DA was increased compared to controls, while neither NA and 5-HT nor the amino acid neurotransmitters were significantly changed. Furthermore, DA increased before stable motor deficits appear with +51% in asymptomatic and +96% in recovered monkeys. Unchanged DA metabolites suggest a special metabolic profile of the newly formed DA neurons. Significant correlation of homovanillic acid (HVA) with taurine single values within the four MPTP groups and of aspartate with taurine within the asymptomatic and recovered MPTP groups, but not within the controls suggest interactions in the OB between taurine and the DA system and taurine and the excitatory neurotransmitter triggered by MPTP. This first investigation of OB in various stages after MPTP administration suggests that the DA increase seems to be an early phenomenon, not requiring profound nigrostriatal neurodegeneration or PD symptoms.

Identification of neurodegenerative factors using translatome-regulatory network analysis

For degenerative disorders of the CNS, the main obstacle to therapeutic advancement has been the challenge of identifying the key molecular mechanisms underlying neuronal loss. We developed a combinatorial approach including translational profiling and brain regulatory network analysis to search for key determinants of neuronal survival or death. Following the generation of transgenic mice for cell type-specific profiling of midbrain dopaminergic neurons, we established and compared translatome libraries reflecting the molecular signature of these cells at baseline or under degenerative stress. Analysis of these libraries by interrogating a context-specific brain regulatory network led to the identification of a repertoire of intrinsic upstream regulators that drive the dopaminergic stress response. The altered activity of these regulators was not associated with changes in their expression levels. This strategy can be generalized for the identification of molecular determinants involved in the degeneration of other classes of neurons.

Oxidative stress and Parkinson's disease

Parkinson disease (PD) is a chronic, progressive neurological disease that is associated with a loss of dopaminergic neurons in the substantia nigra pars compacta of the brain. The molecular mechanisms underlying the loss of these neurons still remain elusive. Oxidative stress is thought to play an important role in dopaminergic neurotoxicity. Complex I deficiencies of the respiratory chain account for the majority of unfavorable neuronal degeneration in PD. Environmental factors, such as neurotoxins, pesticides, insecticides, dopamine (DA) itself, and genetic mutations in PD-associated proteins contribute to mitochondrial dysfunction which precedes reactive oxygen species formation. In this mini review, we give an update of the classical pathways involving these mechanisms of neurodegeneration, the biochemical and molecular events that mediate or regulate DA neuronal vulnerability, and the role of PD-related gene products in modulating cellular responses to oxidative stress in the course of the neurodegenerative process.

Parkinson's disease: animal models and dopaminergic cell vulnerability

Parkinson's disease (PD) is a neurodegenerative disorder that affects about 1.5% of the global population over 65 years of age. A hallmark feature of PD is the degeneration of the dopamine (DA) neurons in the substantia nigra pars compacta (SNc) and the consequent striatal DA deficiency. Yet, the pathogenesis of PD remains unclear. Despite tremendous growth in recent years in our knowledge of the molecular basis of PD and the molecular pathways of cell death, important questions remain, such as: (1) why are SNc cells especially vulnerable; (2) which mechanisms underlie progressive SNc cell loss; and (3) what do Lewy bodies or α-synuclein reveal about disease progression. Understanding the variable vulnerability of the dopaminergic neurons from the midbrain and the mechanisms whereby pathology becomes widespread are some of the primary objectives of research in PD. Animal models are the best tools to study the pathogenesis of PD. The identification of PD-related genes has led to the development of genetic PD models as an alternative to the classical toxin-based ones, but does the dopaminergic neuronal loss in actual animal models adequately recapitulate that of the human disease? The selection of a particular animal model is very important for the specific goals of the different experiments. In this review, we provide a summary of our current knowledge about the different in vivo models of PD that are used in relation to the vulnerability of the dopaminergic neurons in the midbrain in the pathogenesis of PD.

Is Parkinson's disease a vesicular dopamine storage disorder? Evidence from a study in isolated synaptic vesicles of human and nonhuman primate striatum

The cause of degeneration of nigrostriatal dopamine (DA) neurons in idiopathic Parkinson's disease (PD) is still unknown. Intraneuronally, DA is largely confined to synaptic vesicles where it is protected from metabolic breakdown. In the cytoplasm, however, free DA can give rise to formation of cytotoxic free radicals. Normally, the concentration of cytoplasmic DA is kept at a minimum by continuous pumping activity of the vesicular monoamine transporter (VMAT)2. Defects in handling of cytosolic DA by VMAT2 increase levels of DA-generated oxy radicals ultimately resulting in degeneration of DAergic neurons. Here, we isolated for the first time, DA storage vesicles from the striatum of six autopsied brains of PD patients and four controls and measured several indices of vesicular DA storage mechanisms. We found that (1) vesicular uptake of DA and binding of the VMAT2-selective label [(3)H]dihydrotetrabenazine were profoundly reduced in PD by 87-90% and 71-80%, respectively; (2) after correcting for DA nerve terminal loss, DA uptake per VMAT2 transport site was significantly reduced in PD caudate and putamen by 53 and 55%, respectively; (3) the VMAT2 transport defect appeared specific for PD as it was not present in Macaca fascicularis (7 MPTP and 8 controls) with similar degree of MPTP-induced nigrostriatal neurodegeneration; and (4) DA efflux studies and measurements of acidification in the vesicular preparations suggest that the DA storage impairment was localized at the VMAT2 protein itself. We propose that this VMAT2 defect may be an early abnormality promoting mechanisms leading to nigrostriatal DA neuron death in PD.

Lewy body extracts from Parkinson disease brains trigger α-synuclein pathology and neurodegeneration in mice and monkeys

OBJECTIVE

Mounting evidence suggests that α-synuclein, a major protein component of Lewy bodies (LB), may be responsible for initiating and spreading the pathological process in Parkinson disease (PD). Supporting this concept, intracerebral inoculation of synthetic recombinant α-synuclein fibrils can trigger α-synuclein pathology in mice. However, it remains uncertain whether the pathogenic effects of recombinant synthetic α-synuclein may apply to PD-linked pathological α-synuclein and occur in species closer to humans.

METHODS

Nigral LB-enriched fractions containing pathological α-synuclein were purified from postmortem PD brains by sucrose gradient fractionation and subsequently inoculated into the substantia nigra or striatum of wild-type mice and macaque monkeys. Control animals received non-LB fractions containing soluble α-synuclein derived from the same nigral PD tissue.

RESULTS

In both mice and monkeys, intranigral or intrastriatal inoculations of PD-derived LB extracts resulted in progressive nigrostriatal neurodegeneration starting at striatal dopaminergic terminals. No neurodegeneration was observed in animals receiving non-LB fractions from the same patients. In LB-injected animals, exogenous human α-synuclein was quickly internalized within host neurons and triggered the pathological conversion of endogenous α-synuclein. At the onset of LB-induced degeneration, host pathological α-synuclein diffusely accumulated within nigral neurons and anatomically interconnected regions, both anterogradely and retrogradely. LB-induced pathogenic effects required both human α-synuclein present in LB extracts and host expression of α-synuclein.

INTERPRETATION

α-Synuclein species contained in PD-derived LB are pathogenic and have the capacity to initiate a PD-like pathological process, including intracellular and presynaptic accumulations of pathological α-synuclein in different brain areas and slowly progressive axon-initiated dopaminergic nigrostriatal neurodegeneration.

Sonic hedgehog maintains cellular and neurochemical homeostasis in the adult nigrostriatal circuit

Non cell-autonomous processes are thought to play critical roles in the cellular maintenance of the healthy and diseased brain but mechanistic details remain unclear. We report that the interruption of a non cell-autonomous mode of sonic hedgehog (Shh) signaling originating from dopaminergic neurons causes progressive, adult-onset degeneration of dopaminergic, cholinergic, and fast spiking GABAergic neurons of the mesostriatal circuit, imbalance of cholinergic and dopaminergic neurotransmission, and motor deficits reminiscent of Parkinson's disease. Variable Shh signaling results in graded inhibition of muscarinic autoreceptor- and glial cell line-derived neurotrophic factor (GDNF)-expression in the striatum. Reciprocally, graded signals that emanate from striatal cholinergic neurons and engage the canonical GDNF receptor Ret inhibit Shh expression in dopaminergic neurons. Thus, we discovered a mechanism for neuronal subtype specific and reciprocal communication that is essential for neurochemical and structural homeostasis in the nigrostriatal circuit. These results provide integrative insights into non cell-autonomous processes likely at play in neurodegenerative conditions such as Parkinson's disease.

The nigrostriatal system in the presymptomatic and symptomatic stages in the MPTP monkey model: a PET, histological and biochemical study

Parkinson's disease (PD) is diagnosed when striatal dopamine (DA) loss exceeds a certain threshold and the cardinal motor features become apparent. The presymptomatic compensatory mechanisms underlying the lack of motor manifestations despite progressive striatal depletion are not well understood. Most animal models of PD involve the induction of a severe dopaminergic deficit in an acute manner, which departs from the typical, chronic evolution of PD in humans. We have used 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administered to monkeys via a slow intoxication protocol to produce a more gradual development of nigral lesion. Twelve control and 38 MPTP-intoxicated monkeys were divided into four groups. The latter included monkeys who were always asymptomatic, monkeys who recovered after showing mild parkinsonian signs, and monkeys with stable, moderate and severe parkinsonism. We found a close correlation between cell loss in the substantia nigra pars compacta (SNc) and striatal dopaminergic depletion and the four motor states. There was an overall negative correlation between the degree of parkinsonism (Kurlan scale) and in vivo PET ((18)F-DOPA K(i) and (11)C-DTBZ binding potential), as well as with TH-immunoreactive cell counts in SNc, striatal dopaminergic markers (TH, DAT and VMAT2) and striatal DA concentration. This intoxication protocol permits to establish a critical threshold of SNc cell loss and dopaminergic innervation distinguishing between the asymptomatic and symptomatic parkinsonian stages. Compensatory changes in nigrostriatal dopaminergic activity occurred in the recovered and parkinsonian monkeys when DA depletion was at least 88% of control, and accordingly may be considered too late to explain compensatory mechanisms in the early asymptomatic period. Our findings suggest the need for further exploration of the role of non-striatal mechanisms in PD prior to the development of motor features.

Inter-hemispheric asymmetry of nigrostriatal dopaminergic lesion: a possible compensatory mechanism in Parkinson's disease

The onset of Parkinson’s disease (PD) is characterized by focal motor features in one body part, which are usually correlated with greater dopaminergic depletion in the contralateral posterior putamen. The role of dopamine (DA) hemispheric differences in the onset and progression of motor symptoms of PD, however, remains undefined. Previous studies have demonstrated that unilateral manipulations of one nigrostriatal system affect contralateral DA turnover, indicating a functional and compensatory inter-dependence of the two nigrostriatal systems. In preliminary data obtained by our group from asymmetric PD patients, a higher asymmetry index as measured by 6-[¹⁸F]fluoro-L-dopa (¹⁸ F-DOPA) positron emission tomography (PET) was associated with a higher threshold (i.e., greater dopaminergic loss) for the onset of motor symptoms in the less-affected side. To further elucidate the underlying basis for this, we carried out a complementary study in monkeys using PET to assess and correlate the degree of dopaminergic striatal depletion with motor activity. Control and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-intoxicated monkeys with symmetrical lesions were characterized behaviorally and with ¹⁸F-DOPA PET. In parallel, an acute lesion was inflicted in the nigrostriatal projection unilaterally in one monkey, generating a 30% dopaminergic depletion in the ipsilateral striatum, which was not associated with any noticeable parkinsonian feature or deficit. The monkey remained asymptomatic for several months. Subsequently, this monkey received systemic MPTP, following which motor behavior and PET were repeatedly evaluated during progression of parkinsonian signs. The brains of all monkeys were processed using immunohistochemical methods. Our results suggest that the onset of motor signs is related to and influenced by the dopaminergic status of the less-affected, contralateral striatum. Although this work is still preliminary, the study agrees with our general hypothesis of hemispheric inter-dependence in the compensation of striatal DA deficit in PD.

Progression of dopaminergic depletion in a model of MPTP-induced Parkinsonism in non-human primates. An (18)F-DOPA and (11)C-DTBZ PET study

Dopaminergic depletion in the nigrostriatal system is the neurochemical hallmark of Parkinson's disease (PD). Although numerous efforts have been made to determine the evolution of dopaminergic depletion in PD, "in vivo" data concerning the stages of this process are still scarce. We evaluated 6-[18F]-fluoro-l-DOPA ((18)F-DOPA) and 11C-(+)-alpha-dihydrotetrabenazine ((11)C-DTBZ) using PET in a model of chronically MPTP-induced parkinsonism in non-human primates.

METHODS

Sixty-seven cynomolgus monkeys (Macacafascicularis) were included in the study. Progressive parkinsonism was induced by repeated administration of small doses of MPTP (iv) over several months. Animals were classified as controls, asymptomatic, recovered (having exhibited parkinsonian features transiently) and stable parkinsonian, according to their motor status. Analysis of striatal dopaminergic activity was conducted by regions of interest (ROI) and statistical parametric mapping (SPM) over normalized parametric images.

RESULTS

A progressive loss of striatal uptake was evident among groups for both radiotracers, which correlated significantly with the clinical motor status. Changes occurred earlier, i.e. in the less affected stages, with (11)C-DTBZ. Similar results were achieved by ROI and SPM analysis. Uptake was similar with both radiotracers for the asymptomatic and recovered groups.

CONCLUSIONS

Serial assessment with (18)F-DOPA and (11)C-DTBZ PETs provides an effective approach to evaluate evolution of dopaminergic depletion in monkeys with MPTP-induced parkinsonism. This approach could be useful to perform studies aiming to test the effect of early therapeutic intervention and putative neuroprotective treatments.