PET Molecular Imaging of Phosphodiesterase 10A: An Early Biomarker of Huntington's Disease Progression.

BACKGROUND: Changes in phosphodiesterase 10A enzyme levels may be a suitable biomarker of disease progression in Huntington's disease. OBJECTIVES: To evaluate phosphodiesterase 10A PET imaging as a biomarker of HD progression using the radioligand, [18 F]MNI-659. METHODS: The cross-sectional study (NCT02061722) included 45 Huntington's disease gene-expansion carriers stratified into four disease stages (early and late premanifest and Huntington's disease stages 1 and 2) and 45 age- and sex-matched healthy controls. The primary analysis compared striatal and pallidal phosphodiesterase 10A availability between Huntington's disease gene-expansion carriers and healthy controls as assessed by [18 F]MNI-659 binding. We assessed changes in phosphodiesterase 10A expression using several PET methodologies and compared with previously proposed measures of Huntington's disease progression (PET imaging of D2/3 receptors and anatomical volume loss on MRI). The longitudinal follow-up study (NCT02956148) continued evaluation of phosphodiesterase 10A availability in 35 Huntington's disease gene-expansion carriers at a mean of 18 months from baseline of the cross-sectional study. RESULTS: Primary analyses revealed that phosphodiesterase 10A availability in caudate, putamen, and globus pallidus was significantly lower in Huntington's disease gene-expansion carriers versus healthy controls across all stages. Striatal and pallidal phosphodiesterase 10A availability progressively declined in the premanifest stages and appeared to plateau between stages 1 and 2. The percentage decline of phosphodiesterase 10A availability measured cross-sectionally between Huntington's disease gene-expansion carriers and healthy controls was greater than that demonstrated by D2/3 receptor availability or volumetric changes. Annualized rates of phosphodiesterase 10A change showed a statistically significant decline between the cross-sectional study and follow-up. CONCLUSIONS: [18 F]MNI-659 PET imaging is a biologically plausible biomarker of Huntington's disease progression that is more sensitive than the dopamine-receptor and volumetric methods currently used. © 2020 International Parkinson and Movement Disorder Society.

Patterns of age related changes for phosphodiesterase type-10A in comparison with dopamine D2/3 receptors and sub-cortical volumes in the human basal ganglia: A PET study with 18F-MNI-659 and 11C-raclopride with correction for partial volume effect.

Phosphodiesterase 10A enzyme (PDE10A) is an important striatal target that has been shown to be affected in patients with neurodegenerative disorders, particularly Huntington´s disease (HD). PDE10A is expressed on striatal neurones in basal ganglia where other known molecular targets are enriched such as dopamine D2/3 receptors (D2/3 R). The aim of this study was to examine the availability of PDE10A enzyme in relation with age and gender and to compare those changes with those related to D2/3 R and volumes in different regions of the basal ganglia. As a secondary objective we examined the relative distribution of D2/3 R and PDE10A enzyme in the striatum and globus pallidus. Forty control subjects (20F/20M; age: 44±11y, age range 27-69) from an ongoing positron emission tomography (PET) study in HD gene expansion carriers were included. Subjects were examined with PET using the high-resolution research tomograph (HRRT) and with 3T magnetic resonance imaging (MRI). The PDE10A radioligand 18F-MNI-659 and D2/3 R radioligand 11C-raclopride were used. The outcome measure was the binding potential (BPND) estimated with the two-tissue compartment model (18F-MNI-659) and the simplified reference tissue model (11C-raclopride) using the cerebellum as reference region. The PET data were corrected for partial volume effects. In the striatum, PDE10A availability showed a significant age-related decline that was larger compared to the age-related decline of D2/3 R availability and to the age-related decline of volumes measured with MRI. In the globus pallidus, a less pronounced decline of PDE10A availability was observed, whereas D2/3 R availability and volumes seemed to be rather stable with aging. The distribution of the PDE10A enzyme was different from the distribution of D2/3 R, with higher availability in the globus pallidus. These results indicate that aging is associated with a considerable physiological reduction of the availability of PDE10A enzyme in the striatum. Moreover as result of the analysis, in the striatum for both the molecular targets, we observed a gender effect with higher BPND the female group.

Time- and frequency-domain parameters of heart rate variability and sympathetic skin response in Parkinson's disease.

The autonomic nervous system (ANS) is regularly affected in Parkinson's disease (PD). Information on autonomic dysfunction can be derived from e.g. altered heart rate variability (HRV) and sympathetic skin response (SSR). Such parameters can be quantified easily and measured repeatedly which might be helpful for evaluating disease progression and therapeutic outcome. In this 2-center study, HRV and SSR of 45 PD patients and 26 controls were recorded. HRV was measured during supine metronomic breathing and analyzed in time- and frequency-domains. SSR was evoked by repetitive auditory stimulation. Various ANS parameters were compared (1) between patients and healthy controls, (2) to clinical scales (Unified Parkinson's disease rating scale, Mini-Mental State Examination, Becks Depression Inventory), and (3) to disease duration. Root mean square of successive differences (RMSSD) and low frequency/high frequency (LF/HF) ratio differed significantly between PD and controls. Both, HRV and SSR parameters showed low or no association with clinical scores. Time-domain parameters tended to be affected already at early PD stages but did not consistently change with longer disease duration. In contrast, frequency-domain parameters were not altered in early PD phases but tended to be lower (LF, LF/HF ratio), respectively higher (HF) with increasing disease duration. This report confirms previous results of altered ANS parameters in PD. In addition, it suggests that (1) these ANS parameters are not relevantly associated with motor, behavioral, and cognitive changes in PD, (2) time-domain parameters are useful for the assessment of early PD, and (3) frequency-domain parameters are more closely associated with disease duration.

Prerequisites to launch neuroprotective trials in Parkinson's disease: an industry perspective.

Realizing that 60% to 80% of dopaminergic nigrostriatal neurons are nonfunctional at the time of clinical diagnosis, there is an emerging consensus that disease-modifying treatments should be initiated in the earliest stages of Parkinson's disease (PD). To date, clinical trial designs and metrics in PD have been focused on motor symptoms as the core feature of the clinical disease. To identify earlier or "pre-motor" populations in PD, new markers have been proposed. We address the prerequisites needed to use these pre-motor markers in clinical trials for the selection of subjects, definition of populations, and monitoring of disease progression. This may require the development of new diagnostic criteria potentially based on non-motor clinical signs, imaging techniques, or biological features, all requiring discussion in a regulatory framework. Questions addressed include: Which steps must be taken to gain a broad consensus in the field from academic opinion leaders, patient advocacy groups, regulatory bodies, and industry? How do we prevent the selection of subgroups, which may not be representative of the full disease spectrum? Is there a way forward in personalized medicine? How do we balance risk and benefit in an at-risk population? While many tools are available, a concerted effort is required to develop integrated data sets, as well as to achieve the necessary standardization for multicenter clinical trials. To this end, public-private consortia (including academic centers, patient advocacy groups, and industry) will be of crucial importance to prospectively investigate and define the best tools and treatment paradigms.

Pardoprunox in early Parkinson's disease: results from 2 large, randomized double-blind trials.

This report presents the results of 2 randomized trials-Rembrandt and Vermeer-on the efficacy and safety of pardoprunox in patients with early Parkinson's disease. Patients with Parkinson's disease with a Unified Parkinson's Disease Rating Scale-Motor score ≥ 10 and modified Hoehn and Yahr stage ≤ 3 were randomized to pardoprunox (fixed doses of 6 mg/day [n = 115] or 12 mg/day [n = 118] or a flexible-dose range of 12-42 mg/day [n = 116]) or placebo (n = 119) in Rembrandt and pardoprunox 12-42 mg/day (n = 108), pramipexole 1.5-4.5 mg/day (n = 116), or placebo (n = 110) in Vermeer. Pardoprunox showed a significant benefit over placebo in the primary efficacy variable, least-square mean change from baseline in Unified Parkinson's Disease Rating Scale-Motor score: Rembrandt-fixed doses of 6 and 12 mg/day, -6.0 and -4.7 points, respectively; flexible-dose 12-42 mg/day, -5.5 points; placebo, -2.9 points; Vermeer-flexible-dose 12-42 mg/day, -4.9 points; placebo, -2.5 points; pramipexole, -5.7 points. No minimum effective dose was established. Secondary efficacy parameters supported the results of the primary efficacy variable. Pardoprunox tolerability was dose related: flexible-dose 12-42 mg/day showed the highest dropout rate due to treatment-emergent adverse events (Rembrandt, 56.0%; Vermeer, 46.3%) and overall incidence of treatment-emergent adverse events (Rembrandt, 97.4%; Vermeer, 92.6%), primarily due to nausea, somnolence, and dizziness. Because pardoprunox showed similar efficacy across all dose groups, these observations suggest that the 12-42 mg/day dose range was higher than therapeutically required. Furthermore, the early onset of treatment-emergent adverse events and dropouts observed for pardoprunox suggest that titration was too rapid. Pardoprunox significantly improved motor symptoms in patients with early Parkinson's disease, but further investigation into the dose and titration schedule is required to improve tolerability.

Temporal stability of the Unified Dyskinesia Rating Scale.

BACKGROUND: The objective of this study was to establish temporal stability characteristics for objective components of the Unified Dyskinesia Rating Scale (UDysRS). The UDysRS has strong internal consistency and a reliable factor structure, but the important issue of temporal stability has not been established. METHODS: Using intraclass correlation coefficient (ICC) analyses, we examined UDysRS temporal stability for the objective scale components (Part III and IV) over an 8-hour observation period. We assessed ICCs for the single centralized rater, the on-site raters, and the agreement between the single centralized rater and the on-site raters. Kappa statistic assessed agreement between the single centralized and on-site raters for clinical state (ON vs OFF). RESULTS: For both the single centralized rater and the on-site raters, there was high temporal stability of the UDysRS Part III, Part IV, and Total Objective UDysRS in both ON and OFF states, with ICCs ranging from 0.822 (P < .0005) to 0.513 (P < .013). The agreement between the 2 rating techniques (centralized vs on-site) was significant for ON and OFF ratings of Part III, Part IV, and Total Objective UDysRS, ranging from 0.821 (P < .0005) to 0.703 (P < .0005). CONCLUSIONS: The UDysRS is highly stable for ON and OFF. Our data suggest that a single UDysRS evaluation for ON and for OFF states is highly representative of that state regardless of time. Likewise, if appropriate protocols need to assess dyskinesia in a field or community setting, the UDysRS can be filmed without an on-site rater and rated centrally with retained validity.

Double-blind study of pardoprunox, a new partial dopamine agonist, in early Parkinson's disease.

This study examined the efficacy and safety of the partial dopamine agonist, pardoprunox (SLV308), in the treatment of patients with early Parkinson's disease (PD). Patients were randomized to receive pardoprunox (n = 69) or placebo (n = 70). Pardoprunox was titrated to each patient's optimal dose (9-45 mg/d) over 2 to 6 weeks and then maintained at this dose for a further 3 weeks. Concomitant anti-Parkinson treatment was not permitted. In the primary analysis, Unified PD Rating Scale (UPDRS)-Motor score was improved in pardoprunox-treated patients (overall mean dose 23.8 mg/d; -7.3 points), as compared with placebo (-3.0 points; P = 0.0001), from baseline to end point. At end point, there were more responders (> or = 30% reduction in UPDRS-Motor score) in the pardoprunox group (50.7%) than in the placebo group (15.7%; P < 0.0001). In other secondary analyses, UPDRS-activities of daily living (ADL) and -ADL+Motor scores were also significantly more improved in the pardoprunox group. Nausea was reported by 32 of 68 (47.1%) pardoprunox-treated patients (vs. 3/70, 4.3%, placebo-treated patients), with dizziness, somnolence, headache, and asthenia also reported by > or = 10 patients. In this exploratory proof-of-concept study, pardoprunox significantly improved motor function in patients with early PD. The efficacy and safety profile of pardoprunox justifies its further investigation in PD.

Comparison of Huntington's Disease in Europe and North America.

BACKGROUND: In a rare disorder such as Huntington's disease (HD), a global network of clinical trial sites with access to patients speeds up recruitment into clinical trials. The objective was to test the hypothesis that demographics, HTT genotype, clinical spectrum, and progression are similar in HD participants of two large observational HD studies, the European Huntington's Disease Network's European REGISTRY study and the North American COHORT study. METHODS: REGISTRY cross-sectional data were available from a total of 7,384 participants (1,125 [15.2%] premanifest and 6,259 [84.8%] manifest HD). COHORT cross-sectional data from 1,499 participants at 44 study sites were available (175 pre-HD [11.7%], 1,324 manifest HD [88.3%]). Participants were assessed clinically using the Unified Huntington's Disease Rating Scale (UHDRS). Longitudinal data were available for total motor score and cognitive performance in more than 50% of REGISTRY participants and more than 70% of COHORT participants. RESULTS: Demographics, HTT genotypes, phenotype, and progression were similar in the two studies. Patients in Europe were prescribed antidyskinetics more frequently, and antidepressants less frequently, than in North America. In either study, participants on antidyskinetic medication had higher UHDRS total motor scores, worse function assessment scores, and worse cognitive scores than those taking antidepressants or no medication. In contrast, motor, function assessment, and cognitive scores were broadly similar in participants taking antidepressants or no medication. The differences in cognitive performances between languages were small. CONCLUSIONS: Our data suggest that HD patients, and the way they are assessed, are similar across two continents with different cultures and languages.

Revisiting the Logan plot to account for non-negligible blood volume in brain tissue.

BACKGROUND: Reference tissue-based quantification of brain PET data does not typically include correction for signal originating from blood vessels, which is known to result in biased outcome measures. The bias extent depends on the amount of radioactivity in the blood vessels. In this study, we seek to revisit the well-established Logan plot and derive alternative formulations that provide estimation of distribution volume ratios (DVRs) that are corrected for the signal originating from the vasculature. RESULTS: New expressions for the Logan plot based on arterial input function and reference tissue were derived, which included explicit terms for whole blood radioactivity. The new methods were evaluated using PET data acquired using [11C]raclopride and [18F]MNI-659. The two-tissue compartment model (2TCM), with which signal originating from blood can be explicitly modeled, was used as a gold standard. DVR values obtained for [11C]raclopride using the either blood-based or reference tissue-based Logan plot were systematically underestimated compared to 2TCM, and for [18F]MNI-659, a proportionality bias was observed, i.e., the bias varied across regions. The biases disappeared when optimal blood-signal correction was used for respective tracer, although for the case of [18F]MNI-659 a small but systematic overestimation of DVR was still observed. CONCLUSIONS: The new method appears to remove the bias introduced due to absence of correction for blood volume in regular graphical analysis and can be considered in clinical studies. Further studies are however required to derive a generic mapping between plasma and whole-blood radioactivity levels.