Motoki Inaji

Imaging of Peripheral Benzodiazepine Receptor Expression as Biomarkers of Detrimental versus Beneficial Glial Responses in Mouse Models of Alzheimer's and Other CNS Pathologies

We demonstrate the significance of peripheral benzodiazepine receptor (PBR) imaging in living mouse models of Alzheimers disease (AD) as biomarkers and functional signatures of glial activation. By radiochemically and immunohistochemically analyzing murine models of the two pathological hallmarks of AD, we found that AD-like Aβ deposition is concurrent with astrocyte-dominant PBR expression, in striking contrast with nonastroglial PBR upregulation in accumulations of AD-like phosphorylated tau. Because tau-induced massive neuronal loss was distinct from the marginal neurodegeneration associated with Aβ plaques in these models, cellular localization of PBR reflected deleterious and beneficial glial reactions to tau versus Aβ pathologies, respectively. This notion was subsequently examined in models of various non-AD neuropathologies, revealing the following reactive glial dynamics underlying differential PBR upregulation: (1) PBR(−) astrogliosis uncoupled with microgliosis or coupled with PBR(+) microgliosis associated with irreversible neuronal insults; and (2) PBR(+) astrogliosis coupled with PBR(− or ±) microgliosis associated with minimal or reversible neuronal toxicity. Intracranial transplantation of microglia also indicated that nontoxic microglia drives astroglial PBR expression. Moreover, levels of glial cell line-derived neurotrophic factor (GDNF) in astrocytes were correlated with astroglial PBR, except for increased GDNF in PBR(-) astrocytes in the model of AD-like tau pathology, thereby suggesting that PBR upregulation in astrocytes is an indicator of neurotrophic support. Together, PBR expressions in astrocytes and microglia reflect beneficial and deleterious glial reactions, respectively, in diverse neurodegenerative disorders including AD, pointing to new applications of PBR imaging for monitoring the impact of gliosis on the pathogenesis and treatment of AD.

Isolation and transplantation of dopaminergic neurons generated from mouse embryonic stem cells

Embryonic stem (ES) cells differentiate into dopamine (DA)-producing neurons when co-cultured with PA6 stromal cells, but the resulting cultures contain a variety of unidentified cells. In order to label live DA neurons in mixed populations, we introduced a GFP reporter under the control of the tyrosine hydroxylase (TH) gene promoter into ES cells. GFP expression was observed in TH-immunoreactive cells that differentiated from the ES cells that carried the TH-GFP reporter gene. DA neurons expressing GFP were sorted from the mixed cell population by fluorescence-activated cell sorting of cells exhibiting GFP fluorescence, and the sorted GFP(+) cells obtained were transplanted into a rat model of Parkinsons disease. Some of these cells survived and innervated the host striatum, resulting in a partial recovery from parkinsonian behavioral defects. This strategy of isolation and transplantation of ES-cell-derived DA neurons should be useful for cellular and molecular studies of DA neurons and for clinical application in the treatment of Parkinsons disease.

Chronological changes of perihematomal edema of human intracerebral hematoma

Recent investigations have indicated the importance of secondary brain damage in the pathophysiology of intracerebral hemorrhage (ICH), which includes ischemic brain damage and edema formation around a hematoma. The purpose of the current study is to investigate chronological changes of perihematomal edema in patients with human ICH and also the correlation between volume of perihematomal edema and neurological status. Fourteen patients with medium-sized putaminal hemorrhage (29.4 +/- 13.2 ml) without hematoma enlargement were included in this study. To investigate chronological changes of perihematomal edema, we performed CT scans prospectively on the day of hemorrhage and repeated them on days 1, 3, 7, 14, and 28. We evaluated the patients neurologically using the NIH stroke scale on the day a CT scan was performed. The volume of perihematomal edema in human ICH increased rapidly three days after hemorrhage and the score on the NIH stroke scale showed a deterioration. The volume of perihematomal edema then increased slowly until day 14 after hemorrhage, and decreased thereafter. Despite progression of perihematomal edema, the score on the NIH stroke scale improved gradually after day 3.

Correlation between quantitative imaging and behavior in unilaterally 6-OHDA-lesioned rats

We evaluated correlation between neurochemical and functional alterations of the nigrostriatal dopaminergic system in rat brains lesioned with 6-hydroxydopamine (6-OHDA), that model hemi-Parkinsons disease (PD), by using three different quantitative in vivo and in vitro methods. Rats unilaterally lesioned with different doses of 6-OHDA underwent two types of in vivo experiments: (1) a rotational behavioral study with methamphetamine (MAP) or apomorphine (APO); and (2) a positron emission tomography (PET) study with [11C]PE2I (radioligand for dopamine transporters) or [11C]raclopride (radioligand for dopamine D2 receptors). An in vitro autoradiographic study with the same radioligands was also conducted. The number of rotations after the MAP or APO injection increased with increased doses of 6-OHDA. The in vitro and in vivo binding of [11C]PE2I dose-dependently decreased in response to the 6-OHDA injections, while that of [11C]raclopride dose-dependently increased. There was a significant negative hyperbolic correlation between the number of rotations after MAP injection and the binding of [11C]PE2I. In contrast, there was a significant positive linear correlation between the number of rotations after APO injections and the binding of [11C]raclopride. These results robustly reveal a molecular pharmacological basis of parkinsonian symptoms in animal models of PD, and indicate the utility and validity of in vivo PET measurements in assessing pre- and post-synaptic dopaminergic functions.

Glial cell-mediated deterioration and repair of the nervous system after traumatic brain injury in a rat model as assessed by positron emission tomography.

Traumatic brain injury (TBI) is one of the most acute degenerative pathologies in the central nervous system, and in vivo indices enabling an assessment of TBI on a mechanistic basis have yet to be established. The aim of this work was to pursue neuroinflammatory changes and their link to functional disruptions of traumatically-damaged neurons in a rat model of TBI by longitudinal positron emission tomographic (PET) assays. TBI was induced in the unilateral frontal cortex of craniotomied rats according to a lateral fluid percussion brain injury protocol. The use of [(18)F]fluoroethyl-DAA1106 as a PET tracer for translocator protein (TSPO) permitted demonstration of the inflammatory response to the injury, peaking at 1 week after impact. This alteration was parallel to metabolic deficits assessed by PET with [(18)F]fluorodeoxyglucose, but the difference in TSPO levels between impacted and non-impacted frontal cortices was more than threefold of the interlateral metabolic difference, indicating superiority of TSPO imaging for sensitive detection of post-traumatic pathologies. Comparative PET, autoradiographic. and immunohistochemical investigations illustrated the primary contribution of hypertrophic microglia and macrophages to acute TSPO signals in the vicinity of the impact. Astrocytes also formed a TSPO-positive glial scar encompassing necrotic inflammation, and were clustered with PET-detectable TSPO signals in the bilateral external and internal capsules at late stages, putatively reacting with diffuse axonal injury. These observations support the applicability of TSPO-PET as an imaging-based preclinical and clinical biomarker assay in TBI, and indicate its potential capability to clarify aggressive and protective roles of glial responses to injury when combined with emerging anti-inflammatory and immunomodulatory treatments.

PET pharmacokinetic analysis to estimate boron concentration in tumor and brain as a guide to plan BNCT for malignant cerebral glioma.

INTRODUCTION To plan the optimal BNCT for patients with malignant cerebral glioma, estimation of the ratio of boron concentration in tumor tissue against that in the surrounding normal brain (T/N ratio of boron) is important. We report a positron emission tomography (PET) imaging method to estimate T/N ratio of tissue boron concentration based on pharmacokinetic analysis of amino acid probes. METHODS Twelve patients with cerebral malignant glioma underwent 60 min dynamic PET scanning of brain after bolus injection of (18)F-borono-phenyl-alanine (FBPA) with timed arterial blood sampling. Using kinetic parameter obtained by this scan, T/N ratio of boron concentration elicited by one-hour constant infusion of BPA, as performed in BNCT, was simulated on Runge-Kutta algorithm. (11)C-methionine (MET) PET scan, which is commonly used in worldwide PET center as brain tumor imaging tool, was also performed on the same day to compare the image characteristics of FBPA and that of MET. RESULT PET glioma images obtained with FBPA and MET are almost identical in all patients by visual inspection. Estimated T/N ratio of tissue boron concentration after one-hour constant infusion of BPA, T/N ratio of FBPA on static condition, and T/N ratio of MET on static condition showed significant linear correlation between each other. CONCLUSION T/N ratio of boron concentration that is obtained by constant infusion of BPA during BNCT can be estimated by FBPA PET scan. This ratio can also be estimated by MET-PET imaging. As MET-PET study is available in many clinical PET center, selection of candidates for BNCT may be possible by MET-PET images. Accurate planning of BNCT may be performed by static images of FBPA PET. Use of PET imaging with amino acid probes may contribute very much to establish an appropriate application of BNCT for patients with malignant glioma.

In vivo PET measurements with [11C]PE2I to evaluate fetal mesencephalic transplantations to unilateral 6-OHDA-lesioned rats.

Positron emission tomography (PET) is a useful tool to assess and visualize neurotransmissions in vivo. In this study, we performed repeated PET scans with [11C]PE2I, a tracer of the dopamine transporter, to evaluate the alteration of the expression of dopamine (DA) transmission component after a fetal mesencephalic transplantation. The fetal mesencephalic cells were transplanted into the striatum of unilateral 6-OHDA-lesioned rats. PET scans with [11C]PE2I were performed to evaluate the DA transporter before and 2 and 4 weeks after the transplantation. Rotation behavior tests, in vitro autoradiography, measurements of DA contents in the striatum by high-performance liquid chromatography (HPLC), and tyrosine hydroxylase (TH) immuno-histological examinations were performed at the same time points and examined for their relationship to changes in the dopamine transporter. The number of ipsilateral rotations induced by methamphetamine injections decreased. DA contents in the striatum measured with HPLC significantly increased. In the PET study, the binding potential of [11C]PE2I increased at 4 weeks. The results of the in vitro autoradiography study corresponded with those of the PET study. The degrees of the change in the binding potentials correlated with those of the numbers of rotations in the behavioral study and the DA contents in the striatum. In the histological examination, TH-positive cells with axons were observed at 2 and 4 weeks after the transplantation. As the dopamine transporter exists only in the axon terminal of DA neurons, these results suggested that PET measurements of [11C]PE2I binding indicated not only survival, but maturity and functioning of the transplanted cells. Repeated PET measurements of DA transporters are a useful tool in assessing the effectiveness of neural transplantations.

Practical clinical use of dynamic susceptibility contrast magnetic resonance imaging for the surgical treatment of moyamoya disease.

BACKGROUND Precise evaluation of hemodynamic stress is important for the treatment of moyamoya disease (MMD). OBJECTIVE To explore whether dynamic susceptibility contrast magnetic resonance imaging could predict the effects and risk of indirect bypass surgery on MMD. METHODS Clinical data of patients with MMD who were evaluated preoperatively and postoperatively with dynamic susceptibility contrast magnetic resonance imaging and digital subtraction angiography were evaluated retrospectively. Indirect bypass surgery was performed on 115 hemispheres of 69 patients (mean age, 15 years; range, 3-54 years). We examined the correlations of ischemic events and revascularization with the mean transit time (MTT) delay to cerebellum. RESULTS The hemispheres that caused the ischemic events (responsible hemisphere) had a significantly longer preoperative MTT delay than the nonresponsible hemispheres (2.66 ± 1.34 vs 1.57 ± 1.09 seconds). The postoperative MTT delay fell significantly in the patients whose symptoms disappeared (preoperative, 2.61 ± 1.35 seconds; postoperative, 1.35 ± 0.96 seconds). Perioperative infarction occurred in 4 hemispheres (3.5%), and the MTT delay was significantly longer in those hemispheres than in the others (3.97 ± 1.20 vs 2.38 ± 1.34 seconds). The MTT delay was significantly longer in patients with higher angiographic stages. Indirect bypass surgery ameliorated the MTT delay to the same degree in adults and children. Digital subtraction angiography revealed that the induced revascularization was far superior in areas with longer MTT delays. CONCLUSION Dynamic susceptibility contrast magnetic resonance imaging proved to be a useful clinical imaging method for patients with MMD. It may be helpful for selecting candidates for MMD intervention and for predicting the effects and risks of surgery. ABBREVIATIONS DSC-MRI, dynamic susceptibility contrast magnetic resonance imagingMMD, moyamoya diseaseMTT, mean transit timeROI, region of interest.

Clinical benefit of 11C methionine PET imaging as a planning modality for radiosurgery of previously irradiated recurrent brain metastases.

Object Stereotactic radiosurgery with gamma knife (GK-SRS) generally improves the focal control of brain metastases. Yet in cases of focal recurrence at a previous radiation site, MRI is often imperfect in differentiating between active tumor and radiation injury. We have examined whether the use of 11C methionine (MET) with PET will facilitate this differentiation and improve the outcome of GK-SRS for focally recurrent brain metastases after prior treatment. Methods Eighty-eight patients underwent GK-SRS for postirradiation recurrent brain metastases. Thirty-four patients received radiation in areas manifesting high MET uptake (PET group) in a dose-planning procedure using MET-PET/MRI fusion images. Fifty-four patients referred from other institutes received radiation based on dose planning information obtained from MRI (MRI group). Results Sex, age, and the ratio of breast cancer differed significantly between the MRI and PET groups. The total irradiation volume was significantly smaller in the PET group, and the minimal irradiation dose was significantly higher. In a multivariable statistical analysis, the use of MET-PET (P = 0.02) was independently associated with prolonged overall survival after treatment, Karnofsky performance status (P = 0.002), the number of lesions (P = 0.03), and patient’s sex (P = 0.02). The median survival time was significantly longer in the PET group (18.1 months) than in the MRI group (8.6 months) (P = 0.01). Conclusion 11C methionine-PET/MRI fusion images for dose planning lengthened survival in patients undergoing GK-SRS for focally recurrent brain metastases.

Noninvasive Evaluation of CBF and Perfusion Delay of Moyamoya Disease Using Arterial Spin-Labeling MRI with Multiple Postlabeling Delays: Comparison with 15 O-Gas PET and DSC-MRI

BACKGROUND AND PURPOSE: Arterial spin-labeling MR imaging with multiple postlabeling delays has a potential to evaluate various hemodynamic parameters. To clarify whether arterial spin-labeling MR imaging can identify CBF and perfusion delay in patients with Moyamoya disease, we compared arterial spin-labeling, DSC, and 15O-gas PET in terms of their ability to identify these parameters. MATERIALS AND METHODS: Eighteen patients with Moyamoya disease (5 men, 13 women; ages, 21–55 years) were retrospectively analyzed. CBF values of pulsed continuous arterial spin-labeling using 2 postlabeling delays (short arterial spin-labeling, 1525 ms; delayed arterial spin-labeling, 2525 ms) were compared with CBF values measured by 15O-gas PET. All plots were divided into 2 groups by the cutoff of time-based parameters (the time of the maximum observed concentration, TTP, MTT, delay of MTT to cerebellum, and disease severity [symptomatic or not]). The ratio of 2 arterial spin-labeling CBFs (delayed arterial spin-labeling CBF to short arterial spin-labeling CBF) was compared with time-based parameters: time of the maximum observed concentration, TTP, and MTT. RESULTS: The short arterial spin-labeling–CBF values were significantly correlated with the PET-CBF values (r = 0.63; P = .01). However, the short arterial spin-labeling–CBF value dropped in the regions with severe perfusion delay. The delayed arterial spin-labeling CBF overestimated PET-CBF regardless of the degree of perfusion delay. Delayed arterial spin-labeling CBF/short arterial spin-labeling CBF was well correlated with the time of the maximum observed concentration, TTP, and MTT (ρ = 0.71, 0.64, and 0.47, respectively). CONCLUSIONS: Arterial spin-labeling using 2 postlabeling delays may detect PET-measured true CBF and perfusion delay in patients with Moyamoya disease. Provided its theoretic basis and limitations are considered, noninvasive arterial spin-labeling could be a useful alternative for evaluating the hemodynamics of Moyamoya disease.