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Imaging Translocator Protein as a Biomarker of Neuroinflammation in Dementia.

ABSTRACT: Neuroinflammation has long been considered a potential contributor to neurodegenerative disorders that result in dementia. Accumulation of abnormal protein aggregates in Alzheimer's disease, frontotemporal dementia, and dementia with Lewy bodies is associated with the activation of microglia and astrocytes into proinflammatory states, and chronic low-level activation of glial cells likely contributes to the pathological changes observed in these and other neurodegenerative diseases. The 18kDa translocator protein (TSPO) is a key biomarker for measuring inflammation in the brain via positron emission tomography (PET). Increased TSPO density has been observed in brain tissue from patients with neurodegenerative diseases and colocalizes to activated microglia and reactive astrocytes. Several radioligands have been developed to measure TSPO density in vivo with PET, and these have been used in clinical studies of different dementia syndromes. However, TSPO radioligands have limitations, including low specific-to-nonspecific signal and differential affinity to a polymorphism on the TSPO gene, which must be taken into consideration in designing and interpreting human PET studies. Nonetheless, most PET studies have shown that increased TSPO binding is associated with various dementias, suggesting that TSPO has potential as a biomarker to further explore the role of neuroinflammation in dementia pathogenesis and may prove useful in monitoring disease progression.

SUBMITTER: Kreisl WC

PROVIDER: S-EPMC6190574 | biostudies-literature | 2018

REPOSITORIES: biostudies-literature

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Imaging Translocator Protein as a Biomarker of Neuroinflammation in Dementia.

Kreisl William C WC Henter Ioline D ID Innis Robert B RB

Advances in pharmacology (San Diego, Calif.) 20171110

Neuroinflammation has long been considered a potential contributor to neurodegenerative disorders that result in dementia. Accumulation of abnormal protein aggregates in Alzheimer's disease, frontotemporal dementia, and dementia with Lewy bodies is associated with the activation of microglia and astrocytes into proinflammatory states, and chronic low-level activation of glial cells likely contributes to the pathological changes observed in these and other neurodegenerative diseases. The 18kDa tr ...[more]

PMID: 29413519

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Project description:The 18 kDa translocator protein (TSPO) has been proposed as a biomarker for the detection of neuroinflammation. Although various PET probes targeting TSPO have been developed, a highly selective probe for detecting TSPO is still needed because single nucleotide polymorphisms in the human TSPO gene greatly affect the binding affinity of TSPO ligands. Here, we describe the visualization of neuroinflammation with a multimodality imaging system using our recently developed TSPO-targeting radionuclide PET probe [18F]CB251, which is less affected by TSPO polymorphisms. Methods: To test the selectivity of [18F]CB251 for TSPO polymorphisms, 293FT cells expressing polymorphic TSPO were generated by introducing the coding sequences of wild-type (WT) and mutant (Alanine → Threonine at 147th Amino Acid; A147T) forms. Competitive inhibition assay was conducted with [3H]PK11195 and various TSPO ligands using membrane proteins isolated from 293FT cells expressing TSPO WT or mutant-A147T, representing high-affinity binder (HAB) or low-affinity binder (LAB), respectively. IC50 values of each ligand to [3H]PK11195 in HAB or LAB were measured and the ratio of IC50 values of each ligand to [3H]PK11195 in HAB to LAB was calculated, indicating the sensitivity of TSPO polymorphism. Cellular uptake of [18F]CB251 was measured with different TSPO polymorphisms, and phantom studies of [18F]CB251-PET using 293FT cells were performed. To test TSPO-specific cellular uptake of [18F]CB251, TSPO expression was regulated with pCMV-TSPO (or shTSPO)/eGFP vector. Intracranial lipopolysaccharide (LPS) treatment was used to induce regional inflammation in the mouse brain. Gadolinium (Gd)-DOTA MRI was used to monitor the disruption of the blood-brain barrier (BBB) and infiltration by immune cells. Infiltration of peripheral immune cells across the BBB, which exacerbates neuroinflammation to produce higher levels of neurotoxicity, was also monitored with bioluminescence imaging (BLI). Peripheral immune cells isolated from luciferase-expressing transgenic mice were transferred to syngeneic inflamed mice. Neuroinflammation was monitored with [18F]CB251-PET/MR and BLI. To evaluate the effects of anti-inflammatory agents on intracranial inflammation, an inflammatory cytokine inhibitor, 2-cyano-3, 12-dioxooleana-1, 9-dien-28-oic acid methyl ester (CDDO-Me) was administered in intracranial LPS challenged mice. Results: The ratio of IC50 values of [18F]CB251 in HAB to LAB indicated similar binding affinity to WT and mutant TSPO and was less affected by TSPO polymorphisms. [18F]CB251 was specific for TSPO, and its cellular uptake reflected the amount of TSPO. Higher [18F]CB251 uptake was also observed in activated immune cells. Simultaneous [18F]CB251-PET/MRI showed that [18F]CB251 radioactivity was co-registered with the MR signals in the same region of the brain of LPS-injected mice. Luciferase-expressing peripheral immune cells were located at the site of LPS-injected right striatum. Quantitative evaluation of the anti-inflammatory effect of CDDO-Me on neuroinflammation was successfully monitored with TSPO-targeting [18F]CB251-PET/MR and BLI. Conclusion: Our results indicate that [18F]CB251-PET has great potential for detecting neuroinflammation with higher TSPO selectivity regardless of polymorphisms. Our multimodal imaging system, [18F]CB251-PET/MRI, tested for evaluating the efficacy of anti-inflammatory agents in preclinical studies, might be an effective method to assess the severity and therapeutic response of neuroinflammation.

Project description:Parkinson's disease dementia is neuropathologically characterized by aggregates of α-synuclein (Lewy bodies) in limbic and neocortical areas of the brain with additional involvement of Alzheimer's disease-type pathology. Whilst immune activation is well-described in Parkinson's disease (PD), how it links to protein aggregation and its role in PD dementia has not been explored. We hypothesized that neuroinflammatory processes are a critical contributor to the pathology of PDD. To address this hypothesis, we examined 7 brain regions at postmortem from 17 PD patients with no dementia (PDND), 11 patients with PD dementia (PDD), and 14 age and sex-matched neurologically healthy controls. Digital quantification after immunohistochemical staining showed a significant increase in the severity of α-synuclein pathology in the hippocampus, entorhinal and occipitotemporal cortex of PDD compared to PDND cases. In contrast, there was no difference in either tau or amyloid-β pathology between the groups in any of the examined regions. Importantly, we found an increase in activated microglia in the amygdala of demented PD brains compared to controls which correlated significantly with the extent of α-synuclein pathology in this region. Significant infiltration of CD4+ T lymphocytes into the brain parenchyma was commonly observed in PDND and PDD cases compared to controls, in both the substantia nigra and the amygdala. Amongst PDND/PDD cases, CD4+ T cell counts in the amygdala correlated with activated microglia, α-synuclein and tau pathology. Upregulation of the pro-inflammatory cytokine interleukin 1β was also evident in the substantia nigra as well as the frontal cortex in PDND/PDD versus controls with a concomitant upregulation in Toll-like receptor 4 (TLR4) in these regions, as well as the amygdala. The evidence presented in this study show an increased immune response in limbic and cortical brain regions, including increased microglial activation, infiltration of T lymphocytes, upregulation of pro-inflammatory cytokines and TLR gene expression, which has not been previously reported in the postmortem PDD brain.

Project description:BackgroundNeuroinflammation is associated with various chronic neurological diseases, including epilepsy; however, neuroimaging approaches for visualizing neuroinflammation have not been used in the clinical routine yet. In this study, we used the translocator protein positron emission tomography (PET) with [11C] DPA713 to investigate neuroinflammation in the epileptogenic zone in patients with child-onset focal epilepsy.MethodsPatients with intractable focal epilepsy were recruited at the Epilepsy Center of Osaka University; those who were taking any immunosuppressants or steroids were excluded. PET images were acquired for 60 min after intravenous administration of [11C] DPA713. The PET image of [11C] DPA713 was co-registered to individual's magnetic resonance imaging (MRI), and the standardized uptake value ratio (SUVr) in regions of interest, which were created in non-lesions and lesions, was calculated using the cerebellum as a pseudo-reference region. In the case of epilepsy surgery, the correlation between SUVr in lesions and pathological findings was analyzed.ResultsTwenty-seven patients (mean age: 11.3 ± 6.2 years, male/female: 17/10) were included in this study. Of these, 85.1% showed increased uptake of [11C] DPA713 in the focal epileptic lesion. Three patients showed epileptic spasms, suggesting partial seizure onset, and all 18 patients with abnormal lesions on MRI were similarly highlighted by significant uptake of [11C] DPA713. DPA713-positive patients had a broad range of etiologies, including focal cortical dysplasia, tumors, infarction, and hippocampal sclerosis. Five out of nine MRI-negative patients showed abnormal [11C] DPA713 uptake. The SUVr of [11C] DPA713 in lesions was significantly higher than that in non-lesions. In seven patients who underwent epilepsy surgery, increased [11C] DPA713 uptake was associated with microglial activation.ConclusionsThis study indicates that [11C] DPA713 uptake has valuable sensitivity in the identification of epileptic foci in child-onset focal epilepsy, and inflammation is implicated in the pathophysiology in the epileptic foci caused by various etiologies. Further research is required to establish diagnostic tools for identifying focal epileptogenic zones.

Dataset Information

Imaging Translocator Protein as a Biomarker of Neuroinflammation in Dementia.

Publications

Imaging Translocator Protein as a Biomarker of Neuroinflammation in Dementia.

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