Yoshinori Toshima

A New Model of Cerebral Microthrombosis in Rats and the Neuroprotective Effect of a Rho-Kinase Inhibitor

Background and Purpose The aim of this study was to develop a new model of stroke based on endothelial damage and thrombotic occlusion in a perforating artery, leading to small cerebral infarcts and neurological deficits in rats. Moreover, the neuroprotective efficacy of fasudil, a rho-kinase inhibitor, was investigated in this model. Methods Fifty-six male Sprague-Dawley rats were used in the present study. Rats were anesthetized with sodium pentobarbital, and 100 &mgr;g of sodium laurate was injected into the left internal carotid artery on days 1 and 3. The thrombus induction and consequent of ischemic brain damage were examined by histopathological analyses and neurological deficit scoring in a posture reflex test. To investigate the neuroprotective effects of fasudil, 1 or 10 mg/kg was administered intraperitoneally 5 minutes after the first injection of sodium laurate and once daily thereafter on the following 2 days. Results One hour after the injection of sodium laurate, microscopic examination of phosphotungstic acid hematoxylin–stained sections (n=5) revealed that microthrombi containing fibrin strands obstructed the perforating arteries in the ipsilateral hemisphere. Under a transmission electron microscope (n=6), endothelial cells appeared exfoliated and the vascular lumen was obstructed by a thrombus composed of degranulated platelets, fibrin, leukocytes, and erythrocytes. No evidence of endothelial cell damage or thrombus could be found in the ipsilateral side of the pial artery (middle cerebral artery). Twenty-four hours after the second injection of sodium laurate (day 4), 13 of 15 rats (86.6%) showed mild to severe neurological deficits. Multiple small cerebral infarcts were observed in the hippocampus, cortex, and thalamus. Treatment with fasudil (1 and 10 mg/kg, n=15 each) resulted in a significant improvement in neurological deficits. Fasudil also significantly reduced the area of cerebral infarction. Conclusions We present a new model of stroke in rats, in which the perforating arteries are selectively occluded by microthrombi. This model is useful to investigate the pathophysiology and treatment of small cerebral infarction, which is caused by perforating arterial occlusive diseases such as lacunar infarcts. Fasudil may be beneficial in the treatment of acute ischemic stroke.

Wide therapeutic time window for Rho-kinase inhibition therapy in ischemic brain damage in a rat cerebral thrombosis model

The aim of this study was to investigate the influence of delayed Rho-kinase inhibition with fasudil on second ischemic injury in a rat cerebral thrombosis model. Cerebral ischemia was induced in rats by injecting 150 mug of sodium laurate into the left internal carotid artery on day 1. In the ischemic group, the regional cerebral blood flow (rCBF) was significantly decreased 6.5 h after the injection. Fasudil (3 mg/kg/30 min i.v. infusion) significantly increased rCBF. The viscosity of whole blood was significantly increased 48 h after the injection of sodium laurate. Fasudil (10 mg/kg, i.p.) significantly decreased blood viscosity. To clarify the therapeutic time window of fasudil, rats received their first i.p. administration of fasudil (10 mg/kg) 6 h after an injection of sodium laurate. Administration of fasudil twice daily was continued until day 4. Fasudil prevented the accumulation of neutrophils within the brain as seen from measurements taken on day 3, and improved neuronal functions and reduced the infarction area as seen on day 5. Fasudil and hydroxyfasudil, an active metabolite of fasudil, concentration-dependently inhibited phosphorylation of myosin binding subunit of myosin phosphatase in neutrophils. The present results indicate that inhibition of Rho-kinase activation with fasudil is effective for the treatment of ischemic brain damage with a wide therapeutic time window by improving hemodynamic function and preventing the inflammatory responses. These results suggest that fasudil will be a novel and efficacious approach for the treatment of acute ischemic stroke.

Antianginal effects of hydroxyfasudil, a Rho‐kinase inhibitor, in a canine model of effort angina

The effects of Rho‐kinase inhibitor, fasudil, and of a more specific Rho‐kinase inhibitor, hydroxyfasudil, on pacing‐induced myocardial ischaemia were determined in anaesthetized open‐chest dogs. The dogs were subjected to left anterior descending coronary artery (LAD) stenosis producing a sufficient ischaemia as measured by ST‐segment depression on electrocardiograms only when the hearts were paced 60 beats min−1 above the baseline. After a recovery (nonpacing) period, drugs or saline were infused intravenously over 30 min. The animals were again subjected to 5 min of pacing 25 min after the initiation of the treatment. Hydroxyfasudil (0.1 and 0.3 mg kg−1) and fasudil (0.3 mg kg−1) suppressed the ST‐segment depression. Hydroxyfasudil and fasudil also increased the regional blood flow of the LAD perfused endomyocardium region in the canine model of effort angina. To determine the flow profile for hydroxyfasudil in dogs, blood flow in three vascular beds was measured. Hydroxyfasudil (0.3 mg kg−1 for 30 min) significantly increased coronary blood flow and vertebral blood flow, without significantly changing the femoral blood flow. Hydroxyfasudil had no inotropic or chronotropic effect on the isolated hearts of guinea‐pigs. Hydroxyfasudil (2 mg kg−1 for 20 min) did not affect the PR or QTc interval in anaesthetized dogs. Inhibition of Rho‐kinase appears to protect myocardium subjected to pacing‐induced ischaemia through the increase in the regional myocardial blood flow. Hydroxyfasudil may be categorized as a novel type of anti‐anginal drug, without any inotropic or chronotropic effects.

Demonstration of elevation and localization of Rho-kinase activity in the brain of a rat model of cerebral infarction

Evidence that Rho-kinase is involved in cerebral infarction has accumulated. However, it is uncertain whether Rho-kinase is activated in the brain parenchyma in cerebral infarction. To answer this question, we measured Rho-kinase activity in the brain in a rat cerebral infarction model. Sodium laurate was injected into the left internal carotid artery, inducing cerebral infarction in the ipsilateral hemisphere. At 6 h after injection, increase of activating transcription factor 3 (ATF3) and c-Fos was found in the ipsilateral hemisphere, suggesting that neuronal damage occurs. At 0.5, 3, and 6 h after injection of laurate, Rho-kinase activity in extracts of the cerebral hemispheres was measured by an ELISA method. Rho-kinase activity in extracts of the ipsilateral hemisphere was significantly increased compared with that in extracts of the contralateral hemisphere at 3 and 6 h but not 0.5 h after injection of laurate. Next, localization of Rho-kinase activity was evaluated by immunohistochemical analysis in sections of cortex and hippocampus including infarct area 6 h after injection of laurate. Staining for phosphorylation of myosin-binding subunit (phospho-MBS) and myosin light chain (phospho-MLC), substrates of Rho-kinase, was elevated in neuron and blood vessel, respectively, in ipsilateral cerebral sections, compared with those in contralateral cerebral sections. These findings indicate that Rho-kinase is activated in neuronal and vascular cells in a rat cerebral infarction model, and suggest that Rho-kinase could be an important target in the treatment of cerebral infarction.

Wide therapeutic time window for fasudil neuroprotection against ischemia-induced delayed neuronal death in gerbils.

The neuroprotective potential and therapeutic time window for fasudil, a Rho-kinase inhibitor (RKI), were evaluated for delayed neuronal death in gerbils. A preliminary screening was done on fasudil, ozagrel, and edaravone using a single administration in a delayed neuronal death study. Intraperitoneal (i.p.) administration of edaravone, a free radical scavenger (3, 10 mg/kg) immediately after re-circulation did not reduce neuronal degeneration. We previously reported that ozagrel, a thromboxane A(2) synthetase inhibitor (30 mg/kg) also did not reduce neuronal degeneration, while fasudil (3, 30 mg/kg) significantly protected against the ischemia-induced neuronal loss. To clarify the therapeutic time window of fasudil, which showed a positive effect in a preliminary screening, animals received their first i.p. administration of fasudil (10 mg/kg) 24 or 48 h after ischemia. Administration of fasudil twice daily was continued until day 6. Fasudil significantly protected against the ischemia-induced delayed neuronal death when the treatment was started 24 h after ischemia. In gerbils, hydroxyfasudil, an active metabolite of fasudil, was found following an i.p. administration of fasudil (10 mg/kg), and the value of the area under the plasma level curve of hydroxyfasudil was 7 times higher than that of fasudil. Hydroxyfasudil may contribute to the potency of fasudil. The present findings indicate that the RKI fasudil reduces ischemic neuronal damage with a wide therapeutic time window in gerbil, and may be useful in the treatment of acute ischemic stroke in humans.

Effects of Rho-kinase inhibitor on vasopressin-induced chronic myocardial damage in rats.

The aim of this study was to develop a new model of vasopressin-induced chronic myocardial damage based on sustained ST-segment depression in electrocardiogram (ECG) with progression of myocardial fibrosis in rats. Furthermore, using this model, we examined the prophylactic potential of fasudil, a Rho-kinase inhibitor, against myocardial damage induced by vasopressin. In 10-week old male Donryu rats, intravenous administration of arginine vasopressin (0.5 iu/kg) induced significant ST-segment depression. Two days and one week after the administration of vasopressin, ST-segment depression was -0.19 +/- 0.02 and -0.14 +/- 0.02 mV, respectively. Fasudil (10 and 30 mg/kg, p.o.) significantly attenuated the ST-segment depression induced by vasopressin. One week after the administration of vasopressin, the percent area of myocardial fibrosis in control animals (0.42 +/- 0.11%, p < 0.01) was significantly greater than that in normal animals (0.05 +/- 0.01%). Fasudil (10 and 30 mg/kg) significantly prevented the development of the fibrosis. We present a new model of chronic myocardial damage based on sustained ST-segment depression with progression of myocardial fibrosis in rats, and suggest that this model may be useful to investigate the treatment of chronic angina. Inhibition of Rho-kinase is efficacious in preventing the ECG change and development of fibrosis induced by vasopressin in this model.

Fasudil, a protein kinase inhibitor, prevents the development of endothelial injury and neutrophil infiltration in a two-haemorrhage canine subarachnoid model

We examined the possible prophylactic potential of fasudil, a protein kinase inhibitor, on the development of endothelial injury and neutrophil infiltration after subarachnoid haemorrhage (SAH). Using the two haemorrhage canine model, fasudil (3 mg/kg) was infused intravenously for 30 min twice daily (days 1-7) and related histological changes were observed by light and electron microscopy. On day 7 characteristic features of the basilar arteries included corrugation of the elastic lamina and endothelial disruption; fasudil inhibited this endothelial damage. Marked neutrophil infiltration into the subarachnoid space was not detected until day 3. On day 7 a large number of neutrophils was observed in the subarachnoid space around all the basilar arteries examined; fasudil treatment significantly inhibited neutrophil infiltration. Our findings suggest that: (1) endothelial injury and neutrophils play a major role in the pathogenesis of cerebral vasospasm; and (2) fasudil inhibited both endothelial damage and neutrophil infiltration, and therefore protein kinase pathways may have a role in these pathological events. Copyright 1999 Harcourt Publishers Ltd.

Thromboxane A2 synthetase inhibitor failed to ameliorate the arterial narrowing during the chronic phase of cerebral vasospasm

To determine the pathogenetic mechanism underlying the maintenance of arterial narrowing during the chronic phase of cerebral vasospasm caused by subarachnoid hemorrhage (SAH), we examined the effect of ozagrel, a thromboxane A2 (TXA2) synthetase inhibitor, on chronic vasospasm in a canine two-hemorrhage model in comparison with that of fasudil, an inhibitor of protein kinases. The magnitude of the vasospasm was determined angiographically. On SAH day 7, a vasospasm was observed in every dog. Intraarterial or intravenous administration of ozagrel (3 mg/kg/30 min) did not reverse the vasospasm but tended to increase bleeding. In contrast, intraarterial administration of fasudil (3 mg/kg/30 min) significantly reversed the vasospasm. These findings suggest that: 1) TXA2 does not participate in the maintenance of chronic vasospasm after SAH; and 2) the protein kinases, particularly myosin-light chain kinase and protein kinase C, are involved in the pathogenesis of arterial narrowing during the chronic phase of cerebral vasospasm.