¹⁸F-FP-(+)-DTBZ positron emission tomography detection of monoaminergic deficient network in patients with carbon monoxide related parkinsonism

Clinical significance of fractional anisotropy in cerebral white matter regional vulnerability caused by carbon monoxide poisoning: A systematic review and meta-analysis

Carbon monoxide poisoning (COP) can lead to various cerebral white matter (WM) lesions across different disease phases and clinical manifestations, and fractional anisotropy (FA) of diffusion tensor imaging has been widely applied to investigate WM injury in these patients. Here we conduct a systematic review and meta-analysis to investigate the utility of FA in evaluating the regional vulnerability of WM injury caused by COP and explore differences between different disease phases and patient subtypes. We systematically searched PubMed, Medline, Scopus and reference lists of appropriate publications to identify relevant studies. Eight studies with 217 COP patients and 207 healthy controls (HCs) were included. Eight regions of interest were available to investigate regional vulnerability. The results showed the most significant decrease in FA in orbitofrontal subcortical regions. Comparisons of different disease phases revealed lower FA in the centrum semiovale and corpus callosum in the acute phase, while in the chronic phase, only FA in the centrum semiovale remained significantly decreased. Analysis of different patient subtypes showed that the FA values in the splenium of the corpus callosum were significantly decreased in the patients with delayed neurologic sequelae (DNS) but not in the mixed population (with and without DNS). In conclusion, this meta-analysis highlights the frontal-subcortical regional vulnerability in COP. FA changes in the corpus callosum across different disease phases reflect alterations in underlying microstructures. Extended corpus callosum injury involving the splenium could be an imaging biomarker of the occurrence of DNS.

Genetic and Epigenetic Study of Monozygotic Twins Affected by Parkinson’s Disease

Background: Genetic and epigenetic modifiers of age at onset of Parkinson’s disease (PD) are largely unknown. It remains unclear whether DNA methylation (DNAm) age acceleration is linked to age at onset in PD patients of different ethnicities with a similar genetic background. We aim to characterize the clinical, genomic and epigenomic features of three pairs of Chinese monozygotic twins discordant for PD onset by up to 10 years. Methods: We conducted whole genome sequencing, multiplex ligation-dependent probe amplification and genome-wide DNAm array to evaluate the three pairs of Chinese monozygotic twins discordant for age at onset of PD (families A–C). Results: We identified two heterozygous PRKN mutations (exon 2–4 deletion and p.Met1Thr) in PD affected members of one family. Somatic mutation analyses of investigated families did not reveal any variants that could explain the phenotypic discordance in the twin pairs. Of note, our epigenetic study revealed that the twins with earlier-onset had a trend of faster DNAm age acceleration than the later-onset/asymptomatic twins, but without statistical significance. Conclusion: The link between DNAm age acceleration and PD onset in Chinese patients should be interpreted with cautious, and need to be further verified in an extended PD cohort with similar genetic background.

Surface-based morphometry study of brain in patients with carbon monoxide poisoning

PURPOSE

Although cortical volume abnormalities are frequently detected in patients with carbon monoxide poisoning (COP), particularly delayed neurological sequelae (DNS), the associated changes in cortical thickness and shape patterns remain unknown.

MATERIALS & METHODS

Using surface-based morphometry, we investigated the differences in cortical thickness and shape indices between a COP group (n = 44) vs healthy controls (HCs, n = 36), and between the DNS (n = 21) vs non-DNS (n = 23) subgroups. Additionally, the influence of cortical damage on neurological disorders was explored.

RESULTS

The COP group exhibited significant cortical thinning mainly in the bilateral fronto-parietal lobes (P < 0.05, family-wise error corrected). When cortical thinning in the bilateral parietal lobes, bilateral primary motor areas, left primary sensory areas, and bilateral paracentral lobules was explored in the DNS subgroups compared to the non-DNS subgroup (P < 0.05, FWE corrected), no differences in shape indices between the two subgroups were noted. In the COP group, there were significant positive correlations between the Mini-Mental State Examination (MMSE) score and cortical thickness in the right superior frontal gyrus (SFG) and bilateral rostral middle frontal gyrus (rMFG) (P < 0.05, false discovery rate corrected). There was no any significant correlation between cortical thickness and Neuropsychiatric inventory (NPI), UPDRS III scores (P > 0.05, FDR-corrected).

CONCLUSION

Cortical thickness is a more sensitive index than shape for measuring cortical damage in patients with COP exposure, as cortical thinning in the right SFG and bilateral rMFG is related to cognitive impairment.

Early gray matter atrophy and neurological deficits in patients with carbon monoxide poisoning

PURPOSE

To investigate early neurological deficits-related change patterns in gray matter (GM) volume in patients with carbon monoxide poisoning (COP) and GM volume differences between patients with and without delayed neurological sequelae (DNS) and those with and without T2 hyperintense lesions after COP.

METHODS

Forty-one COP patients (24 patients with DNS) and 36 sex- and age-matched healthy controls (HC) were enrolled in this study. The neurological assessments were administered within 24 h after MRI scans. Voxel-based morphometry analysis was used to detect regional GM volume change.

RESULTS

The COP group had statistically significant GM atrophy in the bilateral prefrontal and temporal lobes, anterior cingulate (ACC), thalamus, posterior cerebellum, and right hippocampus compared to the HC group. Atrophy in the left medial orbital superior frontal gyrus (SFG), bilateral ACC, and bilateral thalamus were related to lower Mini-Mental State Examination (MMSE) scores and higher Unified Parkinson's Disease Rating Scale subsection III and neuro-psychiatric inventory scores. Atrophy in the hippocampus and posterior cerebellum were also related to decrease MMSE scores. The DNS subgroup had greater GM atrophy in the limbic system than the non-DNS subgroup. Compared to the subgroup without T2 hyperintense lesions, greater GM atrophy in the limbic system, motor and visual cortex, and default network was observed in the subgroup with T2 hyperintense lesions.

CONCLUSION

GM atrophy in the medial orbital SFG, ACC, thalamus, hippocampus, and posterior cerebellum is associated with early neurological deficits in patients with COP. Greater atrophy occurred in patients with DNS and those with T2 hyperintense lesions.

PET Imaging of VMAT2 with the Novel Radioligand [18F]FE-DTBZ-d4 in Nonhuman Primates: Comparison with [11C]DTBZ and [18F]FE-DTBZ

The vesicular monoamine transporter type 2 (VMAT2) is believed to be responsible for the uptake of monoamines into the vesicles of the synaptic terminals. Two VMAT2 radioligands [¹¹C]DTBZ and [¹⁸F]FP-DTBZ have been used to assess the degree of nigrostriatal deficit in Parkinson’s disease (PD) using positron emission tomography (PET). [¹⁸F]FE-DTBZ-d4, the nondeuterated analogue of [¹⁸F]FE-DTBZ showed similar imaging properties with better stability against defluorination. Therefore, [¹⁸F]FE-DTBZ-d4 draws attention to be investigated as an imaging marker for VMAT2 in the brain. The aim of this study was to investigate the brain kinetics and quantification of [¹⁸F]FE-DTBZ-d4 in nonhuman primates (NHPs), with comparison to [¹¹C]DTBZ and [¹⁸F]FE-DTBZ. Radiolabeling was successfully achieved either by one-step ¹¹C-methylation or by a two-step fluorine-18 nucleophilic substitution reaction. The stability and radiochemical yield were analyzed with high-performance liquid chromatography (HPLC). Three female cynomolgus monkeys were included in the study and underwent a total of 12 positron emission tomography (PET) measurements. Each monkey was examined with each tracer. In addition, two pretreatment and one displacement PET measurements with tetrabenazine (2.0 mg/kg) were performed for [¹⁸F]FE-DTBZ-d4. All PET measurements were conducted using a high-resolution research tomograph (HRRT) system. Radiometabolites were measured in monkey plasma using gradient radio-HPLC. [¹⁸F]FE-DTBZ-d4 (SUV: 4.28 ± 1.01) displayed higher brain uptake compared to both [¹⁸F]FE-DTBZ (SUV: 3.43 ± 0.54) and [¹¹C]DTBZ (SUV: 3.06 ± 0.32) and faster washout. Binding potential (BP_ND) values of [¹⁸F]FE-DTBZ-d4 in different brain regions (putamen: 5.5 ± 1.4; caudate: 4.4 ± 1.1; midbrain: 1.4 ± 0.4) were higher than those of [¹¹C]DTBZ and [¹⁸F]FE-DTBZ. [¹⁸F]FE-DTBZ showed faster radiometabolism in plasma compared to [¹¹C]DTBZ and [¹⁸F]FE-DTBZ-d4. [¹⁸F]FE-DTBZ-d4 is a suitable radioligand for quantification of VMAT2 in the nonhuman primate brain, with better imaging properties than [¹¹C]DTBZ and [¹⁸F]FE-DTBZ. A preliminary comparison suggests that [¹⁸F]FE-DTBZ-d4 has increased stability against defluorination compared to the nondeuterated analogue.

Comparisons of vesicular monoamine transporter type 2 signals in Parkinson's disease and parkinsonism secondary to carbon monoxide poisoning

Parkinson's disease (PD) and carbon monoxide (CO) poisoning demonstrate parkinsonian features related to presynaptic dopaminergic deficits. However, their clinical features and treatment responses are different, indicating other roles of neurotransmitters in symptomatic modulation. In this study, we used ¹⁸F-FP-(+)-DTBZ PET to explore vesicular monoamine transporter type 2 (VMAT2) distributions in 31 patients with PD, 39 patients with CO poisoning and parkinsonian features (n = 39), and 24 age-matched controls. In addition to the disease-specific VMAT2 topographies in PD and CO poisoning, we also constructed feature-specific functional networks. The cardinal features included tremor, rigidity, akinesia, and rapid alternating movements (RAM), and the overall motor severity was scored using Unified Parkinson Disease Rating Scale (UPDRS) and modified Hoehn-Yahr (mH-Y) Scale scores. Our results suggested that a reduction in VMAT2 signals in the caudate, amygdala, and hippocampus were more specific to CO poisoning, while low uptake in the putamen and substantia nigra was more specific to PD. UPDRS and mH-Y scores were related to striatum signals in both groups and hippocampus and raphe in the CO poisoning group. With regards to the cardinal features, the putamen was related to akinesia in both groups. The substantia nigra was related to rigidity in PD, and the caudate and nucleus accumbens were related to akinesia, RAM and rigidity in CO poisoning. Our study enhances the current understanding of different patterns of monoaminergic terminal deficits in patients with CO poisoning and PD.

[11C]dihydrotetrabenazine Positron Emission Tomography in Manganese-Exposed Workers

OBJECTIVE

To understand the neurotoxic effects of manganese (Mn) exposure on monoaminergic function, utilizing [C]dihydrotetrabenazine (DTBZ) positron emission tomography (PET) to measure vesicular monoamine transporter 2 (VMAT2).

METHODS

Basal ganglia and thalamic DTBZ binding potentials (BPND) were calculated on 56 PETs from 41 Mn-exposed workers. Associations between cumulative Mn exposure, regional BPND, and parkinsonism were examined by mixed linear regression.

RESULTS

Thalamic DTBZ BPND was inversely associated with exposure in workers with less than 3 mg Mn/m-yrs, but subsequently remained stable. Pallidal DTBZ binding increased in workers with less than 2 mg Mn/m-yrs of exposure, but decreased thereafter. Thalamic DTBZ binding was inversely associated with parkinsonism (P = 0.003).

CONCLUSION

Mn-dose-dependent associations with thalamic and pallidal DTBZ binding indicate direct effects on monoaminergic VMAT2. Thalamic DTBZ binding was also associated with parkinsonism, suggesting potential as an early biomarker of Mn neurotoxicity.

A Purification Method of 18F-FP-(+)-DTBZ via Solid-Phase Extraction With Combined Cartridges

Background: To optimize [¹⁸F] 9-fluoropropyl-(+)-dihydrotetrabenazine (¹⁸F-FP-(+)-DTBZ) purification via solid-phase extraction (SPE) with combined cartridges to facilitate its widespread clinical application. Methods: A modified SPE purification method, employing Sep-Pak PS-2 and Sep-Pak C18 cartridges, was used for the preparation of ¹⁸F-FP-(+)-DTBZ. This method was compared to the purification method of high-pressure liquid chromatography (HPLC) and SPE with one cartridge, following quality control test and positron emission tomography (PET) imaging in healthy volunteers and patients with parkinsn's disease (PD). Results: A SPE purification method integrating Sep-Pak PS-2 and Sep-Pak C18 cartridges was implemented successfully. The retention time of ¹⁸F-FP-(+)-DTBZ purified by HPLC, SPE with Sep-Pak PS-2, SPE with Sep-Pak C18, and SPE with combined use of Sep-Pak PS-2 and Sep-Pak C18 cartridges was 8.7, 8.8, 8.7, and 8.9 min, respectively. Fewest impurity peak was detected in ¹⁸F-FP-(+)-DTBZ purified by the SPE with combined use of Sep-Pak PS-2 and Sep-Pak C18 cartridges. This modified SPE purification method provided a satisfactory radiochemical yield of 29 ± 1.8% with radiochemical purity >99% and shortened synthesis time to 27 min. The brain uptake of ¹⁸F-FP-(+)-DTBZ purified by the modified SPE was comparable to that purified by HPLC in both healthy volunteers and PD patients. Conclusions: A SPE method integrating Sep-Pak PS-2 and Sep-Pak C18 cartridges for purification of ¹⁸F-FP-(+)-DTBZ may be highly suited to automatic synthesis for routine clinical applications, as it provides excellent radiochemical purity, high yield as well as operational simplicity.

Diffusion kurtosis imaging as a neuroimaging biomarker in patients with carbon monoxide intoxication

Attempting suicide by burning charcoal can lead to carbon monoxide (CO) intoxication and cognitive deficits. Changes in white matter (WM) quantified by diffusion tensor imaging (DTI)-derived parameters have been validated to reflect cognitive test scores. As diffusion kurtosis imaging (DKI) measures biological microstructures using non-Gaussian diffusivity, we assessed the added-information of DKI with neuropsychological test scores as the major outcome measure. A total of 45 patients were enrolled and compared with 30 age-matched controls. The patients were stratified into acute or chronic phase according to the intervals of intoxication and assessments. WM status was assessed using tract-based spatial statistics for DKI and DTI topographies, and the sensitivity/specificity of either model was tested using area under the curve (AUC) analysis. To evaluate their clinical significance, values of DKI- and DTI-derived parameters were extracted from seven regions of interest (ROI) and correlated with neuropsychiatric scores. The kurtosis parameters were lower in the patients than in the controls but none of the parameters provided differentiations between the acute or chronic phase. Kurtosis fractional anisotropy (KFA) had a higher AUC than fractional anisotropy while the other 3 DTI parameters had higher AUC than the corresponding DKI ones. In clinical correlations, KFA value of right posterior WM correlated with visual memory (r = 0.326, p = 0.029), and KFA values of bilateral posterior WM correlated with the digit forward score (right: r = 0.302, p = 0.043; left: r = 0.314, p = 0.036). Although DTI was more sensitive in reflecting disease status, KFA may be more sensitive and specific than fractional anisotropy in cognitive test score predictions.

Deuterated 18F-9-O-hexadeutero-3-fluoropropoxyl-(+)-dihydrotetrabenazine (D6-FP-(+)-DTBZ): A vesicular monoamine transporter 2 (VMAT2) imaging agent

INTRODUCTION

Vesicular monoamine transporters 2 (VMAT2) in the brain serve as transporter for packaging monoamine in vesicles for normal CNS neurotransmission. Several VMAT2 imaging agents, [¹¹C]-(+)-DTBZ, dihydrotetrabenazine and [¹⁸F]FP-(+)-DTBZ (9-O-fluoropropyl-(+)-dihydro tetrabenazine, a.k.a. [¹⁸F]AV-133), are useful for studying the changes in brain function related to monoamine transmission by in vivo imaging. Deuterated analogs have been reported targeting VMAT2 binding sites.

METHODS

A novel deuterated [¹⁸F]9-O-hexaduterofluoropropyl-(+)-dihydrotetrabenazine, [¹⁸F]D6-FP-(+)-DTBZ, [¹⁸F]1, was prepared as a VMAT2 imaging agent. This ¹⁸F agent which targeted VMAT2 was evaluated by in vitro binding, in vivo biodistribution and microPET imaging studies in rodents.

RESULTS

The one step radiolabeling reaction led to the desired [¹⁸F]D6-FP-(+)-DTBZ, [¹⁸F]1, which showed excellent binding affinity to VMAT2 (Ki=0.32±0.07nM) comparable to that of FP-(+)-DTBZ (Ki=0.33±0.02nM) using [¹⁸F]FP-(+)-DTBZ and rat striatum membrane homogenates. In vivo biodistribution in normal rats showed that 1, exhibited excellent brain uptake and comparable high ratio of striatum to cerebellum (target/background) ratio at 1h after injection (ratio of 6.05±0.43 vs 5.66±0.72 for [¹⁸F]FP-(+)-DTBZ vs [¹⁸F]1, respectively). MicroPET imaging studies in rats further confirm that the striatum with high VMAT2 concentration was clearly delineated in normal rat brain after iv injection of [¹⁸F]1. We observed minor changes of metabolism in rat plasma between these two agents; however, the changes showed little effect on regional brain uptake and retention.

CONCLUSIONS

The results reported here lend support for using [¹⁸F]D6-FP-(+)-DTBZ, [¹⁸F]1, as in vivo PET imaging agent for VMAT2 binding in the brain.

Catechol-O-Methyltransferase Val158Met Polymorphism on Striatum Structural Covariance Networks in Alzheimer's Disease

The catechol-O-methyltransferase enzyme metabolizes dopamine in the prefrontal axis, and its genetic polymorphism (rs4680; Val158Met) is a known determinant of dopamine signaling. In this study, we investigated the possible structural covariance networks that may be modulated by this functional polymorphism in patients with Alzheimer’s disease. Structural covariance networks were constructed by 3D T1 magnetic resonance imaging. The patients were divided into two groups: Met-carriers (n = 91) and Val-homozygotes (n = 101). Seed-based analysis was performed focusing on triple-network models and six striatal networks. Neurobehavioral scores served as the major outcome factors. The role of seed or peak cluster volumes, or a covariance strength showing Met-carriers > Val-homozygotes were tested for the effect on dopamine. Clinically, the Met-carriers had higher mental manipulation and hallucination scores than the Val-homozygotes. The volume-score correlations suggested the significance of the putaminal seed in the Met-carriers and caudate seed in the Val-homozygotes. Only the dorsal-rostral and dorsal-caudal putamen interconnected peak clusters showed covariance strength interactions (Met-carriers > Val-homozygotes), and the peak clusters also correlated with the neurobehavioral scores. Although the triple-network model is important for a diagnosis of Alzheimer’s disease, our results validated the role of the dorsal-putaminal-anchored network by the catechol-O-methyltransferase Val158Met polymorphism in predicting the severity of cognitive and behavior in subjects with Alzheimer’s disease.

A Novel Potential Positron Emission Tomography Imaging Agent for Vesicular Monoamine Transporter Type 2

In the early 1990s, 9-(+)-¹¹C-dihydrotetrabenazine (9-(+)-¹¹C-DTBZ) was shown to be a useful positron emission tomography (PET) imaging agent for various neurodegenerative disorders. Here, we described the radiosynthesis and evaluation of the 9-(+)-¹¹C-DTBZ analog, 10-(+)-¹¹C-DTBZ, as a vesicular monoamine transporter 2 (VMAT2) imaging agent and compare it with 9-(+)-¹¹C-DTBZ. 10-(+)-¹¹C-DTBZ was obtained by ¹¹C-MeI methylation with its 10 hydroxy precursor in the presence of 5 M NaOH. It had a slightly better average radiochemical yield of 35.3 ± 3.6% (decay-corrected to end of synthesis (EOS)) than did 9-(+)-¹¹C-DTBZ (30.5 ± 2.3%). MicroPET studies showed that 10-(+)-¹¹C-DTBZ had a striatum-to-cerebellum ratio of 3.74 ± 0.21 at 40 min post-injection, while the ratio of 9-(+)-¹¹C-DTBZ was 2.50 ± 0.33. This indicated that 10-(+)-¹¹C-DTBZ has a higher specific uptake in VMAT2-rich brain regions, and 10-(+)-¹¹C-DTBZ may be a potential VMAT2 radioligand. Our experiment is the first study of 10-(+)-¹¹C-DTBZ to include dynamic brain distribution in rat brains.

Metabolic Covariant Network in Relation to Nigrostriatal Degeneration in Carbon Monoxide Intoxication-Related Parkinsonism

Presence of parkinsonian features after carbon monoxide (CO) intoxication is well known and the severity was found to relate to the pre-synaptic dopaminergic deficits. There is no systemic study to analyse the functional network involved in CO-related Parkinsonism. Forty-five CO-related parkinsonism patients and 25 aged-matched controls completed the 3D T1-weighted imaging and (18)F-fluoro-2-deoxyglucose positron emission tomography (FDG-PET). Voxel-based morphometry (VBM) was performed to assess the structural and functional brain differences between the patients and controls. Spatial covariant networks responsible for distinguishing patients and controls were constructed using independent component analysis. For validation, the pre-synaptic dopaminergic functional network was established by regression model using striatal TRODAT-1 SPECT as the independent variable. The clinical significance of both networks was determined by correlation with the Unified Parkinson's Disease Rating Scale (UPDRS). Compared with controls, the spatial covariant signals of FDG-PET were significantly lower in the medial and lateral frontal, caudate nucleus, dorsomedial prefrontal areas, and temporal-parietal regions while the spatial intensities correlated significantly with UPDRS total scores. The functional network that correlated with striatum pre-synaptic dopaminergic uptakes included the midbrain, thalamus, caudate, lateral frontal cortex, ventral striatum, ventral, or dorsal anterior cingulate cortex. Both networks overlapped considerably and the topographies reflected structural damage pattern. Our study provides evidence that glucose metabolism in CO-parkinsonism patients pertains to an organized covariant pattern in the cortical regions that is spatially coherent with the cortical map of pre-synaptic dopamine deficits. As the fronto-temporal, striatum, and temporal-parietal areas were involved, the unique metabolic covariant network suggests a different pathophysiology in CO-related parkinsonism.