Tetsu Kurokawa

Sphingosylphosphorylcholine Is a Novel Messenger for Rho-Kinase–Mediated Ca2+ Sensitization in the Bovine Cerebral Artery: Unimportant Role for Protein Kinase C

Although recent investigations have suggested that a Rho-kinase–mediated Ca2+ sensitization of vascular smooth muscle contraction plays a critical role in the pathogenesis of cerebral and coronary vasospasm, the upstream of this signal transduction has not been elucidated. In addition, the involvement of protein kinase C (PKC) may also be related to cerebral vasospasm. We recently reported that sphingosylphosphorylcholine (SPC), a sphingolipid, induces Rho-kinase–mediated Ca2+ sensitization in pig coronary arteries. The purpose of this present study was to examine the possible mediation of SPC in Ca2+ sensitization of the bovine middle cerebral artery (MCA) and the relation to signal transduction pathways mediated by Rho-kinase and PKC. In intact MCA, SPC induced a concentration-dependent (EC50=3.0 &mgr;mol/L) contraction, without [Ca2+]i elevation. In membrane-permeabilized MCA, SPC induced Ca2+ sensitization even in the absence of added GTP, which is required for activation of G-proteins coupled to membrane receptors. The SPC-induced Ca2+ sensitization was blocked by a Rho-kinase inhibitor (Y-27632) and a dominant-negative Rho-kinase, but not by a pseudosubstrate peptide for conventional PKC, which abolished the Ca2+-independent contraction induced by phorbol ester. In contrast, phorbol ester–induced Ca2+ sensitization was resistant to a Rho-kinase inhibitor and a dominant-negative Rho-kinase. In primary cultured vascular smooth muscle cells, SPC induced the translocation of cytosolic Rho-kinase to the cell membrane. We propose that SPC is a novel messenger for Rho-kinase–mediated Ca2+ sensitization of cerebral arterial smooth muscle and, therefore, may play a pivotal role in the pathogenesis of abnormal contraction of the cerebral artery such as vasospasm. The SPC/Rho-kinase pathway functions independently of the PKC pathway.

Inhibitory Effects of Eicosapentaenoic Acid on Chronic Cerebral Vasospasm after Subarachnoid Hemorrhage: Possible Involvement of a Sphingosylphosphorylcholine-Rho-Kinase Pathway

Background and Purpose: Rho-kinase (ROK)-mediated Ca2+ sensitization of vascular smooth muscle (VSM) contraction plays a pivotal role in cerebral vasospasm (CV). We previously demonstrated that sphingosylphosphorylcholine (SPC) induces Ca2+ sensitization through sequential activation of the Src family protein tyrosine kinases (Src-PTKs) and ROK in vitro, and that Ca2+ sensitization is inhibited by eicosapentaenoic acid (EPA) through the selective inactivation of Src-PTK. In this study, we examined whether SPC induced CV in vivo, and, if it did, whether EPA would inhibit CV, as induced by SPC or in an in vivo model of subarachnoid hemorrhage (SAH). Methods: Changes in the diameter of the canine basilar artery were investigated by angiography after administering SPC into the cisterna magna. Then, Y27632, a specific Rho-kinase inhibitor, or EPA was injected intracisternally and the effects of both agents were investigated. In another experiment using a single-hemorrhage model, Y27632 or EPA was injected on day 7 after SAH and the changes in the diameter of the canine basilar artery were investigated. Results: At cerebrospinal fluid concentrations of 100 and 300 µmol/l, SPC induced severe vasoconstriction (maximum vasoconstriction by SPC (100 µmol/l): 61.8 ± 8.2%), which was markedly reversed by Y27632 (96.3 ± 4.4%) or EPA (92.6 ± 12.8%). SAH caused severe vasospasm on day 7 (67.6 ± 7.8%), which was significantly blocked by Y27632 (95.5 ± 10.6%) or EPA (90.0 ± 4.4%). Conclusions: SPC is a novel mediator of ROK-induced CV in vivo. The inhibition of CV induced by SPC or after SAH by EPA suggests beneficial roles of EPA in the treatment of CV. Our findings are compatible with the notion that the SPC-ROK pathway may be involved in CV.

Does eicosapentaenoic acid (EPA) inhibit cerebral vasospasm in patients after aneurysmal subarachnoid hemorrhage

Background –  Cerebral vasospasm following subarachnoid hemorrhage (SAH) is a significant cause of morbidity and mortality and recent studies indicate that Rho‐kinase plays an important role in the occurrence of such cerebral vasospasm. Eicosapentaenoic acid (EPA), an n‐3 polyunsaturated fatty acid, inhibits sphingosylphosphorylcholine (SPC)‐induced Rho‐kinase activation in vitro, so this study examined whether EPA prevented cerebral vasospasm occurrence after SAH in patients.

Elevated concentrations of sphingosylphosphorylcholine in cerebrospinal fluid after subarachnoid hemorrhage: A possible role as a spasmogen

This study investigates the role of sphingosylphosphorylcholine (SPC) in the mechanisms underlying cerebral vasospasm after subarachnoid hemorrhage (SAH). The levels of SPC were measured in cerebrospinal fluid (CSF) of patients with SAH and also in an experimental canine model. CSF samples were collected from 11 patients with SAH, and from dogs that had received an injection of SPC into the cisterna magna to examine SPC kinetics in the CSF. SPC was assayed using solid-phase extraction and triple quadrupole mass spectrometry. The SPC concentrations in SAH patients on days 3, 8, and 14 after the onset of SAH were significantly higher than those in normal CSF. In the canine model, rapid dilution of SPC in CSF was observed. In combination with data from previous studies, these results suggest that SPC is involved in the development of cerebral vasospasm. Rapid dilution of SPC in CSF suggests that SPC is released into CSF at higher concentrations than those measured in the present study.

Recovered neuronal viability revealed by Iodine-123-iomazenil SPECT following traumatic brain injury.

We evaluated cortical damages following traumatic brain injury (TBI) in the acute phase with [123I] iomazenil (IMZ) single photon emission computed tomography (SPECT). In all, 12 patients with cerebral contusion following TBI were recruited. All patients underwent IMZ SPECT within 1 week after TBI. To investigate the changes in distribution of IMZ in the cortex in the chronic phase, after conventional treatment, patients underwent IMZ SPECT again. A decrease in the accumulation of radioligand for the central benzodiazepine receptor in the cortex corresponding to the contusion revealed with computed tomography (CT) scans and magnetic resonance imaging (MRI) were shown on IMZ SPECT in the acute phase in all patients. In 9 of 12 patients (75%), images of IMZ SPECT obtained in the chronic phase of TBI showed that areas with a decreased distribution of IMZ were remarkably reduced in comparison with those obtained in the acute phase. Both CT scans and MRI showed a normal appearance of the cortex morphologically, where the binding potential of IMZ recovered in the chronic phase. Reduced binding potential of radioligand for the central benzodiazepine receptor is considered to be an irreversible reaction; however, in this study, IMZ accumulation in the cortex following TBI was recovered in the chronic phase in several patients. [123I] iomazenil SPECT may have a potential to disclose a reversible vulnerability of neurons following TBI.

DE Novo ANEURYSM FORMATION ON MIDDLE CEREBRAL ARTERY BRANCHES ADJACENT TO THE ANASTOMOTIC SITE OF SUPERFICIAL TEMPORAL ARTERY-MIDDLE CEREBRAL ARTERY BYPASS SURGERY IN TWO PATIENTS : TECHNICAL CASE REPORT

OBJECTIVE Aneurysm formation is a complication of superficial temporal arterymiddle cerebral artery bypass surgery occurring as pseudoaneurysms caused by technical failure, but also as true aneurysms discovered after long-term follow-up. CLINICAL PRESENTATION A 53-year-old woman presented with a left internal carotid artery cavernous aneurysm manifesting as double vision. Superficial temporal arterymiddle cerebral artery bypass, internal trapping of the internal carotid artery, and embolization were performed. Three years later, angiography disclosed a distal middle cerebral artery aneurysm. A 70-year-old man who had undergone right superficial temporal artery-middle cerebral artery bypass after internal carotid artery occlusion died of subarachnoid hemorrhage from a ruptured anterior spinal artery aneurysm 21 years later. Angiography and postmortem examination revealed de novo aneurysm formation on a middle cerebral artery branch adjoining the anastomotic site. Both patients had hypertension and multiplicity of aneurysms. INTERPRETATION Both cases were de novo true aneurysms caused by hemodynamic stress because of saccular to fusiform shape, location extending to the middle cerebral artery, high perfusion pressure, projection along the hemodynamic stress, and presence of common risk factors. CONCLUSION Bypass surgery is increasingly performed in patients with complicated aneurysms if sacrifice or temporary occlusion of any major vessel is required. Therefore, de novo aneurysm formation may not be rare in patients with risk factors such as hypertension or multiple aneurysms. Extended follow-up examination is required in such patients.

Cerebrovascular moyamoya disease in a 5-year-old girl who underwent interruption of the right common carotid artery in the neonatal period.

The authors report on the case of a girl with cerebrovascular moyamoya disease born with severe respiratory failure caused by a congenital diaphragmatic hernia. Cardiopulmonary management included extracorporeal membrane oxygenation until the diaphragm defect was repaired. The right common carotid artery (CA) was interrupted and cannulated for extracorporeal membrane oxygenation. When she was 5 years of age, the patient experienced ischemic symptoms in her right extremities. Angiography revealed stenosis of the terminal portion of the internal CA (ICA) with the development of moyamoya vessels on the left side of the brain; the right ICA was supplied by extracranial anastomotic arteries. Indirect extracranial-intracranial bypass surgery was performed in the left hemisphere, and the hypoperfusion improved. The same change in the intracranial ICA with the development of moyamoya vessels occurred on her right side when she was 7 years old. Decreased cerebral blood flow occurred twice, and the moyamoya vessels developed to compensate for the cerebral ischemia. However, the occlusion of the extracranial common CA in infancy induced extracranial anastomosis rather than moyamoya vessel proliferation, and collateral circulation was formed at the lesion site. This finding indicates that neoangiogenesis requires both cerebral ischemia and growth factors derived from the lesion.

Operative open intra-aneurysmal thrombectomy for ruptured cerebral aneurysm and peripheral ischemia associated with vasospasm

The endovascular approach has become the standard treatment for ruptured aneurysms during the vasospasm risk period following subarachnoid hemorrhage; however, it may be disadvantageous under certain conditions. We report a patient with a ruptured middle cerebral artery aneurysm with severe vasospasm and thrombosis within the aneurysm immediately after angiography. Emergent operative open thrombectomy of the intra-aneurysmal thrombus restored blood flow to the ischemic penumbra territory demonstrated by single photon emission CT scan and diffusion-weighted MRI.