PET studies in Parkinson's disease motor and cognitive dysfunction

A layered single-side readout depth of interaction time-of-flight-PET detector

We are exploring a scintillator-based PET detector with potential of high sensitivity, depth of interaction (DOI) capability, and timing resolution, with single-side readout. Our design combines two previous concepts: (1) multiple scintillator arrays stacked with relative offset, yielding inherent DOI information, but good timing performance has not been demonstrated with conventional light sharing readout. (2) Single crystal array with one-to-one coupling to the photodetector, showing superior timing performance compared to its light sharing counterparts, but lacks DOI. The combination, where the first layer of a staggered design is coupled one-to-one to a photodetector array, may provide both DOI and timing resolution and this concept is here evaluated through light transport simulations. Results show that: (1) unpolished crystal pixels in the staggered configuration yield better performance across all metrics compared to polished pixels, regardless of readout scheme. (2) One-to-one readout of the first layer allows for accurate DOI extraction using a single threshold. The number of multi pixel photon counter (MPPC) pixels with signal amplitudes exceeding the threshold corresponds to the interaction layer. This approach was not possible with conventional light sharing readout. (3) With a threshold of 2 optical photons, the layered approach with one-to-one coupled first layer improves timing close to the MPPC compared to the conventional one-to-one coupling non-DOI detector, due to effectively reduced crystal thickness. Single detector timing resolution values of 91, 127, 151 and 164 ps were observed per layer in the 4-layer design, to be compared to 148 ps for the single array with one-to-one coupling. (4) For the layered design with light sharing readout, timing improves with increased MPPC pixel size due to higher signal per channel. In conclusion, the combination of straightforward DOI determination, good timing performance, and relatively simple design makes the proposed concept promising for DOI-Time-of-Flight PET detectors.

Altered putamen functional connectivity is associated with anxiety disorder in Parkinson's disease

In this study, we used resting state-functional magnetic resonance imaging (rs-fMRI) to explore altered putamen functional connectivity (FC) in Parkinson's disease patients with anxiety disorder. We divided 65 Parkinson's disease patients into anxiety (PD-A; n=18) and non-anxiety (PD-NA; n=45) groups based on a Hamilton Anxiety Rating Scale cutoff score of 12. The PD-A patients exhibited altered putamen FC with cortical and subcortical regions. The PD-A patients showed enhanced putamen FC with the caudatum, which correlated with increased emotional processing during anxiety. Decreased putamen FC with the orbitofrontal gyrus and cerebellum also correlated with increased anxiety in Parkinson's disease. Our findings demonstrate that anxiety disorder in Parkinson's disease is associated with abnormal putamen FC networks, especially with caudatum, orbitofrontal gyrus and cerebellum.

Cerebral metabolic change in Parkinson's disease patients with anxiety: A FDG-PET study

OBJECT

To detect the cerebral metabolic bases of Parkinson's disease (PD) patients with anxiety.

METHODS

Totally 28 idiopathic PD patients without depression (17-item Hamilton Depression Rating Scale, HAMD score <14) were enrolled in our study. All subjects were classified into PD with anxiety (PD-A) (n=13) and PD without anxiety (PD-NA) (n=15) by cutoff score of 11 according to Hamilton Anxiety Rating Scale (HAMA). Besides, age- and gender- matched healthy controls (HCs) (n=15) were selected. A resting-state F-18 fluorodeoxyglucose positron emission tomography (FDG-PET) scan was applied to estimate cerebral metabolic activity. All statistical analyses were performed using IBM SPSS Statistics V20.0.0 software, while statistical parametric mapping software (SPM) was used to analyze the FDG-PET images.

RESULTS

PD-A showed decreased glucose metabolism in the bilateral orbitofrontal cortex (OFC, BA10 and BA11) when compared with PD-NA. Significant decrease of cerebral glucose metabolism in the bilateral OFC, bilateral supplementary motor area (SMA, BA6), bilateral dorsal anterior cingulate cortex (dACC, BA32), right dorsolateral prefrontal cortex (dlPFC, BA9), right ventrolateral prefrontal cortex (vlPFC, BA44), right putamen and left caudatum was detected in PD-A compared with HCs. There was significant reduced glucose metabolism of the bilateral SMA in PD-NA when compared with HCs (uncorrected p<0.005).

CONCLUSION

The anxiety of PD was associated with the metabolic reductions of PFC and striatal areas. OFC, part of PFC, could be taken as a characteristic feature for anxiety in PD. This metabolic pattern suggested that deficits of prefrontostriatal pathways might affect anxiety mood in PD.

Synthesis and in vitro evaluation of 5-substituted benzovesamicol analogs containing N-substituted amides as potential positron emission tomography tracers for the vesicular acetylcholine transporter

Herein, new ligands for the vesicular acetylcholine transporter (VAChT), based on a benzovesamicol scaffold, are presented. VAChT is acknowledged as a marker for cholinergic neurons and a positron emission tomography tracer for VAChT could serve as a tool for quantitative analysis of cholinergic neuronal density. With an easily accessible triflate precursor, aminocarbonylations were utilized to evaluate the chemical space around the C5 position on the tetrahydronaphthol ring. Synthesized ligands were evaluated for their affinity and selectivity for VAChT. Small, preferably aromatic, N-substituents proved to be more potent than larger substituents. Of the fifteen compounds synthesized, benzyl derivatives (±)-7i and (±)-7l had the highest affinities for VAChT. Compound (±)-7i was chosen to investigate the importance of stereochemistry for binding to VAChT and selectivity toward the σ₁ and σ₂ receptors. Enantiomeric resolution gave (+)-7i and (-)-7i, and the eutomer showed seven times better affinity. Although racemate (±)-7i was initially promising, the affinity of (-)-7i for VAChT was not better than 56.7nM which precludes further preclinical evaluation. However, the nanomolar binding together with the ready synthesis of [¹¹C]-(±)-7i shows that (-)-7i can serve as a scaffold for future optimizations to provide improved ¹¹C-labelled VAChT PET tracers.

Dementia in Parkinson's disease

Dementia can occur in a substantial number of patients with Parkinson's disease with a point prevalence close to 30%. The cognitive profile is characterized by predominant deficits in executive, visuospatial functions, attention and memory. Behavioral symptoms are frequent such as apathy, visual hallucinations and delusions. The most prominent associated pathology is Lewy body-type and biochemical deficit is cholinergic. Placebo-controlled randomized trials with cholinesterase inhibitors demonstrated modest but significant benefits in cognition, behavioral symptoms and global functions.

Abnormal Echogenicity of the Substantia Nigra, Raphe Nuclei, and Third-Ventricle Width as Markers of Cognitive Impairment in Parkinsonian Disorders: A Cross-Sectional Study

Background. Patients with Parkinson's disease (PD) have a high risk of cognitive problems. Objective. This study assesses whether abnormal echogenicity of the substantia nigra (SN) and raphe nuclei (RN) and the diameter of third ventricle are markers of cognitive impairment in patients with PD and other forms of parkinsonism. Methods. 126 outpatients with early signs of parkinsonism underwent transcranial sonography (TCS). The scales for the outcome of Parkinson's disease cognition (SCOPA-COG) were used as cognitive measure. Definite neurological diagnosis was established after two-year follow-up. Results. One-third of the patients with PD and half of those with APS had signs of cognitive impairment. The echogenicity of the SN was not related to cognitive impairment. The diameter of the third ventricle was significantly larger in PD patients with cognitive impairment compared to those without. In patients with APS we found a significantly higher frequency of hypoechogenic RN in patients with cognitive problems. Conclusions. Cognitive impairment is already present in a substantial proportion of patients with PD and APS at first referral. In patients with APS the frequency of hypoechogenic RN points to the direction of other pathophysiology with more emphasis on deficits in the serotonergic neurotransmitter system. The larger diameter of the third ventricle in PD patients with cognitive impairment may reflect Alzheimer like brain atrophy, as has been reported in earlier studies.

Cognitive performances and DAT imaging in early Parkinson's disease with mild cognitive impairment: a preliminary study

OBJECTIVES

Mild cognitive impairment (MCI) is a common feature in Parkinson's disease (PD). We performed an exploratory study to investigate dopaminergic nigrostriatal innervation and its cognitive correlates in early untreated PD patients with MCI as compared to cognitively intact patients.

PATIENTS AND METHODS

A consecutive series of 34-de-novo, drug-naïve patients with PD were enrolled. They underwent [123-I] FP-CIT SPECT and comprehensive neuropsychological battery. MCI was identified in 15 of 34 patients with PD.

RESULTS

The two groups did not show any statistically significant difference in age, sex, disease duration, education, lateralization, and H&Y and Hospital Anxiety and Depression Scale scores. Logistic regression analysis showed that UPDRS-III was weakly associated with MCI (P = 0.034). Partial correlation analysis controlling for UPDRS-III and age suggested that in PD patients with MCI reduced V3″ values in the more affected caudate were correlated with reduced performances in frontal assessment battery, Trail Making Test: part B minus Part A and copy task of the Rey-Osterrieth complex figure test. Reduced V3″ values in the more and less affected putamen were significantly related with reduced performance in frontal assessment battery and in copy task of Rey-Osterrieth complex figure test, respectively. No correlation was found between neuropsychological scores and DAT availability in PD patients without MCI.

CONCLUSIONS

Although preliminary, our results suggest that striatal dopamine depletion may contribute to some cognitive deficit in early never treated PD patients with MCI.

In vitro and ex vivo characterization of (-)-TZ659 as a ligand for imaging the vesicular acetylcholine transporter

The loss of cholinergic neurons and synapses relates to the severity of dementia in several neurodegenerative pathologies; and the vesicular acetylcholine transporter (VAChT) provides a reliable biomarker of cholinergic function. We recently characterized and (11)C-labeled a new VAChT inhibitor, (-)-TZ659. Here we report the in vitro and ex vivo characterization of (-)-TZ659. A stably transfected PC12(A123.7) cell line which expresses human VAChT (hVAChT) was used for the in vitro binding characterization of (-)-[(3)H]TZ659. A saturated binding curve was obtained with Kd=1.97±0.30nM and Bmax=3240±145.9fmol/mg protein. In comparison, a PC12(A123.7) cell line that expresses mutant hVAChT showed decreased binding affinity (Kd=15.94±0.28nM). Competitive binding assays using a panel of other CNS ligands showed no inhibition of (-)-[(3)H]TZ659 binding. On the other hand, binding inhibitions were observed only using VAChT inhibitors (Ki=0.20-31.35nM). An in vitro assay using rat brain homogenates showed that (-)-[(3)H]TZ659 had higher binding in striatum than in cerebellum, with a target: non-target ratio>3.46. Even higher ex vivo striatum-to-cerebellum ratios (9.56±1.11) were observed using filtered homogenates of brain tissue after rats were injected intravenously with (-)-[(11)C]TZ659. Ex vivo autoradiography of (-)-[(11)C]TZ659 confirmed high striatal uptake, with a consistently high striatum-to-cerebellum ratio (2.99±0.44). In conclusion, (-)-TZ659 demonstrated high potency and good specificity for VAChT in vitro and in vivo. These data suggest that (-)-[(11)C]TZ659 may be a promising PET tracer to image VAChT in the brain.

How does the bilingual experience sculpt the brain?

The ability to speak two languages often marvels monolinguals, although bilinguals report no difficulties in achieving this feat. Here, we examine how learning and using two languages affect language acquisition and processing as well as various aspects of cognition. We do so by addressing three main questions. First, how do infants who are exposed to two languages acquire them without apparent difficulty? Second, how does language processing differ between monolingual and bilingual adults? Last, what are the collateral effects of bilingualism on the executive control system across the lifespan? Research in all three areas has not only provided some fascinating insights into bilingualism but also revealed new issues related to brain plasticity and language learning.

Imaging of VMAT2 binding sites in the brain by (18)F-AV-133: the effect of a pseudo-carrier

OBJECTIVES

Recently, 9-[(18)F]fluoropropyl-(+)-dihydrotetrabenazine ((18)F-AV-133) was reported as a new vesicular monoamine transporter (VMAT2) imaging agent for diagnosis of Parkinson's disease (PD). To shorten the preparation of (18)F-AV-133 and to make it more widely available, we evaluated a simple, rapid purification with a solid-phase extraction method (SPE) using an Oasis HLB cartridge instead of high pressure liquid chromatography (HPLC). The SPE method produced doses containing a pseudo-carrier, 9-hydroxypropyl-(+)-dihydrotetrabenazine (AV-149).

METHODS

To test the possible side effects of this pseudo-carrier, comparative dynamic PET scans of the brains of normal monkeys (2 each) and uni-laterally 6-OH-dopamine-lesioned PD monkeys (2 each) were performed using (18)F-AV-133 doses prepared by either SPE (containing pseudo-carrier) or HPLC (containing no pseudo-carrier). Autoradiographs of post mortem monkey brain sections were evaluated to confirm the relative (18)F-AV-133 uptake in the PD monkey brains and the effects of the pseudo-carrier on VMAT2 binding.

RESULTS

The radiochemical purity of the (18)F-AV-133, whether prepared by SPE or by HPLC, was excellent (>99%). PET scans of normal and PD monkey brains showed an expected reduction of VMAT2 in the lesioned areas of the striatum. It was not affected by the presence of the pseudo-carrier, AV-149 (maximally 250 μg/dose). The reduced uptake in the striatum of the lesioned monkey brains was confirmed by autoradiography. Ex vivo inhibition studies of (18)F-AV-133 binding in rat brains, conducted with increasing amounts of AV-149, suggested that at the highest concentration (3.5mg/kg) the VMAT2 binding in the striatum was only moderately blocked (20% reduction).

CONCLUSIONS

The pseudo-carrier, AV-149, did not affect the (18)F-AV-133/PET imaging of VMAT2 binding sites in normal or uni-laterally lesioned monkey brains. The new streamlined SPE purification method will enable (18)F-AV-133 to be widely available for routine clinical application in determining changes in monoamine neurons for patient with movement disorders or other psychiatric illnesses.