The banking of human leukocyte antigen (HLA)-homozygous-induced pluripotent stem cells (iPSCs) is considered a future clinical strategy for HLA-matched cell transplantation to reduce immunological ...graft rejection. Here we show the efficacy of major histocompatibility complex (MHC)-matched allogeneic neural cell grafting in the brain, which is considered a less immune-responsive tissue, using iPSCs derived from an MHC homozygous cynomolgus macaque. Positron emission tomography imaging reveals neuroinflammation associated with an immune response against MHC-mismatched grafted cells. Immunohistological analyses reveal that MHC-matching reduces the immune response by suppressing the accumulation of microglia (Iba-1+) and lymphocytes (CD45+) into the grafts. Consequently, MHC-matching increases the survival of grafted dopamine neurons (tyrosine hydroxylase: TH+). The effect of an immunosuppressant, Tacrolimus, is also confirmed in the same experimental setting. Our results demonstrate the rationale for MHC-matching in neural cell grafting to the brain and its feasibility in a clinical setting.Major histocompatibility complex (MHC) matching improves graft survival rates after organ transplantation. Here the authors show that in macaques, MHC-matched iPSC-derived neurons provide better engraftment in the brain, with a lower immune response and higher survival of the transplanted neurons.
Background
Most antiepileptic drug therapies are symptomatic and adversely suppress normal brain function by nonspecific inhibition of neuronal activity. In recent times, growing evidence has ...suggested that neuroinflammation triggered by epileptic seizures might be involved in the pathogenesis of epilepsy. Although the potential effectiveness of anti-inflammatory treatment for curing epilepsy has been extensively discussed, the limited quantitative data regarding spatiotemporal characteristics of neuroinflammation after epileptic seizures makes it difficult to be realized. We quantitatively analyzed the spatiotemporal changes in neuroinflammation in the early phase after status epilepticus in rats, using translocator protein (TSPO) positron emission tomography (PET) imaging, which has been widely used for the quantitative evaluation of neuroinflammation in several animal models of CNS disease.
Methods
The second-generation TSPO PET probe,
18
FDPA-714, was used for brain-wide quantitative analysis of neuroinflammation in the brains of rats, when the status epilepticus was induced by subcutaneous injection of kainic acid (KA, 15 mg/kg) into those rats. A series of
18
FDPA-714 PET scans were performed at 1, 3, 7, and 15 days after status epilepticus, and the corresponding histological changes, including activation of microglia and astrocytes, were confirmed by immunohistochemistry.
Results
Apparent accumulation of
18
FDPA-714 was observed in several KA-induced epileptogenic regions, such as the amygdala, piriform cortex, ventral hippocampus, mediodorsal thalamus, and cortical regions 3 days after status epilepticus, and was reversibly displaced by unlabeled PK11195 (1 mg/kg). Consecutive
18
FDPA-714 PET scans revealed that accumulation of
18
FDPA-714 was focused in the KA-induced epileptogenic regions from 3 days after status epilepticus and was further maintained in the amygdala and piriform cortex until 7 days after status epilepticus. Immunohistochemical analysis revealed that activated microglia but not reactive astrocytes were correlated with
18
FDPA-714 accumulation in the KA-induced epileptogenic regions for at least 1 week after status epilepticus.
Conclusions
These results indicate that the early spatiotemporal characteristics of neuroinflammation quantitatively evaluated by
18
FDPA-714 PET imaging provide valuable evidence for developing new anti-inflammatory therapies for epilepsy. The predominant activation of microglia around epileptogenic regions in the early phase after status epilepticus could be a crucial therapeutic target for curing epilepsy.
Cyclooxygenase (COX), a prostanoid-synthesizing enzyme, is considered to be involved in the neuroinflammatory process of neurodegenerative diseases. However, the role of COX in the progression of ...neurodegeneration is not well understood. We hypothesized that in vivo imaging of COX by PET will contribute to elucidation of the function of COX during the neurodegenerative process in Alzheimer's disease (AD). (11)C-labeled ketoprofen methyl ester (racemic (RS)-(11)C-KTP-Me) developed recently by our group is a useful PET probe for in vivo imaging of COX-1 during neuroinflammation. The (S)-enantiomer of ketoprofen is known to be pharmacologically more active than the (R)-enantiomer. We thus synthesized (11)C-labeled (S)-ketoprofen methyl ester ((S)-(11)C-KTP-Me) as an improved PET probe specific for COX-1 and applied it for investigation of the changes in COX-1 during the progression of AD in a mouse model.
The specificity of (S)-(11)C-KTP-Me for COXs was examined in PET studies with rats that had intrastriatal injection of lipopolysaccharide. To determine the details of changes in COX-1 during progression of amyloid-β (Aβ) plaque formation in amyloid precursor protein transgenic (APP-Tg) mice, we performed immunohistochemical studies and ex vivo autoradiography with (S)-(11)C-KTP-Me.
PET studies using hemispheric lipopolysaccharide injection into rats revealed that the sensitivity of (S)-(11)C-KTP-Me in neuroinflammation was much higher than that of (RS)-(11)C-KTP-Me and (R)-(11)C-KTP-Me; these results closely corresponded to the inhibitory activities of each enantiomer against COX-1 estimated by an in vitro assay. In APP-Tg mice, (S)-(11)C-KTP-Me administration resulted in progressive and significant increases in accumulation of radioactivity in the brain from 16 to 24 mo old in accordance with the histopathologic appearance of abundant Aβ plaques and activated microglia, whereas few changes in radioactivity accumulation and few Aβ plaques were seen in age-matched wild-type control mice. High-radioactivity accumulation by (S)-(11)C-KTP-Me was markedly observed in the frontal cortex and hippocampus in which COX-1-expressing activated microglia tightly surrounded and enclosed large and more intensely stained Aβ plaques, indicating neuroinflammation that originated with Aβ.
(S)-(11)C-KTP-Me is a potent PET probe that is highly selective for COX-1. Studies using APP-Tg mice demonstrated that (S)-(11)C-KTP-Me could detect activated microglia that are associated with amyloid plaque progression, suggesting the involvement of COX-1 in the neuroinflammatory process in AD.
Abstract
Aromatase is an estrogen synthetic enzyme that plays important roles in brain functions. To quantify aromatase expression in the brain by positron emission tomography (PET), we had ...previously developed
11
Ccetrozole, which showed high specificity and affinity. To develop more efficient PET tracer(s) for aromatase imaging, we synthesized three analogs of cetrozole. We synthesized meta-cetrozole, nitro-cetrozole, and iso-cetrozole, and prepared the corresponding
11
C-labeled tracers. The inhibitory activities of these three analogs toward aromatase were evaluated using marmoset placenta, and PET imaging of brain aromatase was performed using the
11
C-labeled tracers in monkeys. The most promising analog in the monkey study, iso-cetrozole, was evaluated in the human PET study. The highest to lowest inhibitory activity of the analogs toward aromatase in the microsomal fraction from marmoset placenta was in the following order: iso-cetrozole, nitro-cetrozole, cetrozole, and meta-cetrozole. This order showed good agreement with the order of the binding potential (BP) of each
11
C-labeled analog to aromatase in the rhesus monkey brain. A human PET study using
11
Ciso-analog showed a similar distribution pattern of binding as that of
11
Ccetrozole. The time–activity curves showed that elimination of
11
Ciso-cetrozole from brain tissue was faster than that of
11
C-cetrozole, indicating more rapid metabolism of
11
Ciso-cetrozole.
11
CCetrozole has preferable metabolic stability for brain aromatase imaging in humans, although
11
Ciso-cetrozole might also be useful to measure aromatase level in living human brain because of its high binding potential.
Several limitations of
FFDG have been reported, such as nonspecific uptake of inflammation foci. Moreover,
CMET has been found to accumulate in normal and inflammatory tissues as well as tumors. To ...increase specificity to tumor tissues, PET probes with tumor-specific molecular targets have been actively developed.
FFIMP was found to be highly accumulated in LAT1-positive tumors but not in inflamed tissue. The aim of this study was to explore whether
FFIMP can be used for the early-phase evaluation of radiotherapy accompanied by inflammation, and compare its effectiveness with those of
CMET and
FFDG. Tumor uptake of
FFIMP decreased at day 1 after irradiation, and remained low until day 14. Comparatively, that of
FFDG initially decreased at day 3 but was transiently elevated at day 7 and then decreased again at day 10. Decreased tumor uptake of
CMET was observed at day 10. In line with the uptake of
FFIMP, the ratio of Ki-67 immuno-positive cells in tumor tissues significantly decreased at day 1, 7, and 10 as compared with that in the control. These findings suggest that
FFIMP may be a PET probe involved in the early detection and prediction of radiotherapy efficacy, although further clarification is needed.
Abstract
Positron emission tomography (PET) imaging can assist in the early-phase diagnostic and therapeutic evaluation of tumors. Here, we report the radiosynthesis, small animal PET imaging, and ...biological evaluation of a L-type amino acid transporter 1 (LAT1)-specific PET probe,
18
F-FIMP. This probe demonstrates increased tumor specificity, compared to existing tumor-specific PET probes (
18
F-FET,
11
C-MET, and
18
F-FDG). Evaluation of probes by
in vivo
PET imaging,
18
F-FIMP showed intense accumulation in LAT1-positive tumor tissues, but not in inflamed lesions, whereas intense accumulation of
18
F-FDG was observed in both tumor tissues and in inflamed lesions. Metabolite analysis showed that
18
F-FIMP was stable in liver microsomes, and mice tissues (plasma, urine, liver, pancreas, and tumor). Investigation of the protein incorporation of
18
F-FIMP showed that it was not incorporated into protein. Furthermore, the expected mean absorbed dose of
18
F-FIMP in humans was comparable or slightly higher than that of
18
F-FDG and indicated that
18
F-FIMP may be a safe PET probe for use in humans.
18
F-FIMP may provide improved specificity for tumor diagnosis, compared to
18
F-FDG,
18
F-FET, and
11
C-MET. This probe may be suitable for PET imaging for glioblastoma and the early-phase monitoring of cancer therapy outcomes.
In the first-in-human PET study, we evaluated the biodistribution and tumor accumulation of the novel PET probe, (S)-2-amino-3-3-(2-18F-fluoroethoxy)-4-iodophenyl-2-methylpropanoic acid (18F-FIMP), ...which targets the tumor-related L-type amino acid transporter 1 (LAT1), and compared it with L-methyl-11Cmethionine (11C-MET) and 2-Deoxy-2-18F-fluoro-D-glucose (18F-FDG). 18F-FIMP biodistribution was revealed by whole-body and brain scans in 13 healthy controls. Tumor accumulation of 18F-FIMP was evaluated in 7 patients with a brain tumor, and compared with those of 11C-MET and 18F-FDG. None of the subjects had significant problems due to probe administration, such as adverse effects or abnormal vital signs. 18F-FIMP was rapidly excreted from the kidneys to the urinary bladder. There was no characteristic physiological accumulation in healthy controls. 18F-FIMP PET resulted in extremely clear images in patients with suspected glioblastoma compared with 11C-MET and 18F-FDG. 18F-FIMP could be a useful novel PET probe for LAT1-positive tumor imaging including glioblastoma.
•The biodistribution and tumor accumulation of 18F-FIMP targeting the tumor-related L-type amino acid transporter 1 (LAT1).•18F-FIMP was no characteristic physiological accumulation in healthy controls.•18F-FIMP PET resulted in extremely clear images in patients with suspected glioblastoma compared with 11C-MET and 18F-FDG.
Background
(
S
)-2-amino-3-3-(2-
18
F-fluoroethoxy)-4-iodophenyl-2-methylpropanoic acid (
18
F-FIMP) as a promising PET probe for imaging the tumor-specific L-type amino acid transporter (LAT) 1. Our ...previous study revealed that
18
F-FIMP had a higher affinity for LAT1 than for LAT2 abundantly expressed even in normal cells.
18
F-FIMP showed high accumulation in LAT1-positive tumor tissues and low accumulation in inflamed lesions in tumor-bearing mice. However, the affinity of
18
F-FIMP for other amino acid transporters was not determined yet. Here, we aimed to determine whether
18
F-FIMP has affinity for other tumor-related amino acid transporters, such as sodium- and chloride-dependent neutral and basic amino acid transporter B(0 +) (ATB
0,+
), alanine serine cysteine transporter 2 (ASCT2), and cystine/glutamate transporter (xCT).
Procedures
Cells overexpressing LAT1, ATB
0,+
, ASCT2, or xCT were established by the transfection of expression vectors for LAT1, ATB
0,+
, ASCT2, or xCT. Protein expression levels were determined by western blot and immunofluorescent analyses. Transport function was evaluated by a cell-based uptake assay using
18
F-FIMP and
14
C-labeled amino acids as substrates.
Results
Intense signals were observed only for expression vector-transfected cells on western blot and immunofluorescent analyses. These signals were strongly reduced by gene-specific small interfering ribonucleic acid treatment. The uptake values for each
14
C-labeled substrate were significantly higher in the transfected cells than in the mock-transfected cells and were significantly inhibited by the corresponding specific inhibitors. The
18
F-FIMP uptake values were significantly higher in the LAT1- and ATB
0,+
-overexpressing cells than in the corresponding mock cells, but no such increase was seen in the ASCT2- or xCT-overexpressing cells. These
18
F-FIMP uptake values were significantly decreased by the specific inhibitors for LAT1- and ATB
0,+
.
Conclusions
We demonstrated that
18
F-FIMP has affinity not only for LAT1, but also for ATB
0,+
. Our results may be helpful for understanding the mechanisms of the whole-body distribution and tumor accumulation of
18
F-FIMP.
We previously identified a novel mutation in amyloid precursor protein from a Japanese pedigree of familial Alzheimer's disease, FAD (Osaka). Our previous positron emission tomography (PET) study ...revealed that amyloid β (Aβ) accumulation was negligible in two sister cases of this pedigree, indicating a possibility that this mutation induces dementia without forming senile plaques. To further explore the relationship between Aβ, tau and neurodegeneration, we performed tau and Aβ PET imaging in the proband of FAD (Osaka) and in patients with sporadic Alzheimer's disease (SAD) and healthy controls (HCs). The FAD (Osaka) patient showed higher uptake of tau PET tracer in the frontal, lateral temporal, and parietal cortices, posterior cingulate gyrus and precuneus than the HCs (>2.5 SD) and in the lateral temporal and parietal cortices than the SAD patients (>2 SD). Most noticeably, heavy tau tracer accumulation in the cerebellum was found only in the FAD (Osaka) patient. Scatter plot analysis of the two tracers revealed that FAD (Osaka) exhibits a distinguishing pattern with a heavy tau burden and subtle Aβ accumulation in the cerebral cortex and cerebellum. These observations support our hypothesis that Aβ can induce tau accumulation and neuronal degeneration without forming senile plaques.
A series of symptoms, including fever, widespread pain, fatigue, and even ageusia, have frequently been reported in the context of various infections, such as COVID-19. Although the pathogenic ...mechanisms underlying an infection causing fever and pain have been well established, the mechanisms of fatigue induced by infection in specific brain regions remain unclear.
To elucidate whether and how the peripheral infection cause fatigue via regional neuroinflammation, we performed a brain-wide investigation of neuroinflammation in a peripheral pseudoinfection rat model using
FDPA-714 positron emission tomography (PET) imaging analysis, in which the polyriboinosinic: polyribocytidylic acid (poly I:C) was intraperitoneally injected.
Transient fever lasting for several hours and subsequent suppression of spontaneous activity lasting a few days were induced by poly I:C treatment. Significant increase in plasma interleukin (IL)-1β, IL-6 and tumour necrosis factor (TNF)-α were observed at 2 and 4 h following poly I:C treatment. PET imaging analysis revealed that the brain uptake of
FDPA-714 was significantly increased in several brain regions one day after poly I:C treatment, such as the dorsal raphe (DR), parvicellular part of red nucleus (RPC), A5 and A7 noradrenergic nucleus, compared with the control group. The accumulation of
FDPA-714 in the DR, RPC and A5 was positively correlated with subsequent fatigue-like behavior, and that in the A7 tended to positively correlate with fever.
These findings suggest that peripheral infection may trigger regional neuroinflammation, which may cause specific symptoms such as fatigue. A similar mechanism might be involved in COVID-19.
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