Hisayasu Saito

Validity of Dual MRI and 18F-FDG PET Imaging in Predicting Vulnerable and Inflamed Carotid Plaque

Background: Vulnerable and inflamed plaques in the carotid artery are at high risk of ischemic stroke, suggesting the importance of diagnostic modalities to detect them in patients with carotid stenosis with high sensitivity and specificity. Although many investigators have reported that magnetic resonance imaging (MRI) is a useful tool to predict the vulnerable components of carotid plaque, its validity is not established. On the other hand, 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) may be an alternative modality to directly identify the inflamed plaque in carotid artery stenosis. Therefore, this study aimed at evaluating the validity of MRI and FDG-PET to predict vulnerable and inflamed carotid plaque. Methods: This prospective study totally included 25 patients who underwent carotid endarterectomy (CEA) for carotid artery stenosis at our institute between January 2009 and January 2012. Prior to CEA, FDG-PET, black-blood T1-weighted imaging (BB-T1WI), and 3-dimensional time-of-flight (TOF) imaging were performed. The specimens were stained with hematoxylin-eosin to assess the different plaque components (lipid, hemorrhage, calcification, and fibrous tissue). In addition, they were stained with primary antibodies against CD68 (activated macrophages) and matrix metalloproteinase (MMP)-9. Results: High FDG uptake was detected in 13 (52.0%) of 25 patients. All of them had lipid-rich plaque. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) to identify the lipid-rich plaques were all 100% for FDG-PET. More importantly, all of the FDG-positive plaques had strong immunoreactivity against both CD68 and MMP-9. There was a significant correlation between the findings on FDG-PET and those on immunohistochemistry against CD68 and MMP-9 (p = 0.006 and 0.004, respectively). On the other hand, 16 (64.0%) of 25 patients had high signal intensity plaque on BB-T1WI. In 7 of these 16 patients, the lesions also showed high signal intensity on TOF imaging. All of them had a large intraplaque hemorrhage. The sensitivity, specificity, PPV, and NPV to identify a large intraplaque hemorrhage were 70, 100, 100, and 83%, respectively, for MRI. Conclusions: These findings suggest that FDG-PET and MRI are complementary to predict high-risk carotid plaque, such as lipid-rich or hemorrhagic plaque. FDG-PET can accurately predict the lipid-rich and inflamed plaque. MRI is valuable to identify unstable plaque with a large intraplaque hemorrhage. The combination of these two modalities may play an important role in predicting carotid plaque at high risk of ischemic stroke.

Bone Marrow Stromal Cells Rescue Ischemic Brain by Trophic Effects and Phenotypic Change Toward Neural Cells

Background. Transplantation of bone marrow stromal cells (BMSCs) may contribute to functional recovery after stroke. This study was designed to clarify their mechanisms, trophic effects of neurotrophic factors, and neural differentiation. Methods. Mouse neurons exposed to glutamate were cocultured with mouse BMSCs. Either neutralizing antibodies against brain-derived neurotrophic factor (BDNF) or nerve growth factor (NGF) or Trk inhibitor K252a was added to explore the mechanism of their protective effects. Fluorescence in situ hybridization (FISH) was used to assess BDNF or NGF mRNA expression in BMSCs. The mice were subjected to permanent focal ischemia, and 7 days later, either BMSCs or the vehicle was stereotactically transplanted into the ipsilateral striatum. The mouse brains were processed for FISH and immunostaining 2 or 4 weeks after transplantation. Results. BMSCs significantly ameliorated glutamate-induced neuronal death. Treatment with anti-BDNF antibody significantly reduced their protective effects. FISH analysis showed that the majority of BMSCs expressed BDNF and NGF mRNA in vitro. BMSC transplantation significantly improved the survival of neurons in peri-infarct areas. FISH analysis revealed that approximately half of BMSCs expressed BDNF and NGF mRNA 2 weeks after transplantation; however, the percentage of BDNF and NGF mRNA-positive cells decreased thereafter. Instead, the percentage of microtubule-associated protein 2–positive BMSCs gradually increased during 4 weeks after transplantation. Conclusions. These findings strongly suggest that BDNF may be a key factor underlying the trophic effects of BMSCs. BMSCs might exhibit the trophic effect in the early stage of cell therapy and the phenotypic change toward neural cells thereafter.

123I-Iomazenil Single Photon Emission Computed Tomography Visualizes Recovery of Neuronal Integrity by Bone Marrow Stromal Cell Therapy in Rat Infarct Brain

Background and Purpose— This study was aimed to assess whether 123I-iomazenil (IMZ) single photon emission computed tomography can serially monitor the effects of bone marrow stromal cell (BMSC) transplantation on neuronal integrity in infarct brain of rats. Methods— The BMSCs were harvested from green fluorescent protein–transgenic rats and were cultured. The rats were subjected to permanent middle cerebral artery occlusion. Their motor function was serially quantified throughout the experiments. The BMSCs or vehicle was stereotactically transplanted into the ipsilateral striatum at 7 days after the insult. Using small-animal single photon emission computed tomography/computed tomography apparatus, the 123I-IMZ uptake was serially measured at 6 and 35 days after the insult. Finally, fluorescence immunohistochemistry was performed to evaluate the distribution of engrafted cells and their phenotypes. Results— The distribution of 123I-IMZ was markedly decreased in the ipsilateral neocortex at 6 days postischemia. The vehicle-transplanted animals did not show a significant change at 35 days postischemia. However, BMSC transplantation significantly improved the distribution of 123I-IMZ in the peri-infarct neocortex as well as motor function. The engrafted BMSCs were densely distributed around cerebral infarct, and some of them expressed neuronal nuclear antigen and &ggr;-aminobutyric acid type-A receptor. Conclusions— The present findings strongly suggest that the BMSCs may enhance functional recovery by improving the neuronal integrity in the peri-infarct area, when directly transplanted into the infarct brain at clinically relevant timing. 123I-IMZ single photon emission computed tomography may be a promising modality to scientifically prove the beneficial effects of BMSC transplantation on the host brain in clinical situation.

Reversible Isolated Accessory Nerve Palsy due to a Large Thrombosed Vertebral Aneurysm

Objective: Isolated accessory nerve palsy due to intracranial disorders is uncommon because intracranial accessory nerve injury usually occurs in case of a skull base tumor or trauma, resulting in one of multiple cranial nerve palsies. We report a very rare case of isolated accessory nerve palsy due to a large thrombosed aneurysm of the intracranial vertebral artery. Full recovery was achieved after surgery. Case Report: A patient complaining of transient numbness in the right side was referred to our hospital. An MRI indicated a large thrombosed aneurysm of the right vertebral artery. The aneurysm severely compressed the medulla oblongata. First, the proximal vertebral artery (VA) was clipped with an aneurysm clip to reduce the pressure inside the aneurysm. However, cerebral angiography revealed a partial recanalization of the right VA. The patient then underwent coil embolization of the right VA just proximal to the aneurysm clip. Subsequently, the right VA was completely obliterated. The patient was discharged without any neurological deficit. Two weeks later, however, she complained of right shoulder pain. Physical and neurological examinations demonstrated atrophy of the right trapezius and sternocleidomastoid muscle, leading to a deepening of the right supraclavicular fossa. The symptoms were considered to result from the right isolated accessory nerve palsy. Follow-up MRI showed that the VA aneurysm gradually decreased in size over a period of several months. At the same time, her symptoms disappeared completely. Conclusion: We should keep in mind that isolated accessory nerve palsy can be caused by a large or giant vertebral aneurysm.

Human Recombinant Peptide Sponge Enables Novel, Less Invasive Cell Therapy for Ischemic Stroke

Bone marrow stromal cell (BMSC) transplantation has the therapeutic potential for ischemic stroke. However, it is unclear which delivery routes would yield both safety and maximal therapeutic benefits. We assessed whether a novel recombinant peptide (RCP) sponge, that resembles human collagen, could act as a less invasive and beneficial scaffold in cell therapy for ischemic stroke. BMSCs from green fluorescent protein-transgenic rats were cultured and Sprague–Dawley rats were subjected to permanent middle cerebral artery occlusion (MCAo). A BMSC-RCP sponge construct was transplanted onto the ipsilateral intact neocortex 7 days after MCAo. A BMSC suspension or vehicle was transplanted into the ipsilateral striatum. Rat motor function was serially evaluated and histological analysis was performed 5 weeks after transplantation. The results showed that BMSCs could proliferate well in the RCP sponge and the BMSC-RCP sponge significantly promoted functional recovery, compared with the vehicle group. Histological analysis revealed that the RCP sponge provoked few inflammatory reactions in the host brain. Moreover, some BMSCs migrated to the peri-infarct area and differentiated into neurons in the BMSC-RCP sponge group. These findings suggest that the RCP sponge may be a promising candidate for animal protein-free scaffolds in cell therapy for ischemic stroke in humans.

Functional Bio-imaging

Cell transplantation therapy has been expected to promote functional recovery in various kinds of central nervous system (CNS) disorders, including cerebral stroke. However, there are several concerns to be resolved before clinical application of cell therapy for CNS disorders. The issues include the development of imaging techniques to monitor the response of the host CNS. It would be essential to establish functional bio-imaging technique serially and noninvasively validating the effects of cell therapy on the host CNS in order to achieve clinical application of cell therapy for cerebral stroke. Nuclear imaging technique is one of the most useful methods to assess the functional change in various kinds of CNS disorders, including cerebral stroke. Very recently, using a small-animal SPECT/CT apparatus, we could serially visualize the effects of BMSC transplantation on the distribution of 123I-IMZ in the infarct brain of the living rodents longitudinally and noninvasively. Furthermore, we serially assessed local glucose metabolism in the rats subjected to permanent MCA occlusion and found that BMSC transplantation significantly enhances the recovery in the peri-infarct area, using small-animal 18F-FDG PET/CT system. The BMSCs may enhance the recovery of local glucose metabolism by improving neuronal integrity in the peri-infarct area, when directly transplanted into the infarct brain. Although there are few studies that indicate the utility of imaging techniques to monitor the response of the host CNS after cell therapy and further investigation is needed, 123I-IMZ SPECT and 18F-FDG PET may be promising modalities to assess the therapeutic benefits of cell therapy for ischemic stroke without subjective bias in clinical situation.