Evaluation of the combination of a tissue-type plasminogen activator, SUN9216, and a thromboxane A2 receptor antagonist, vapiprost, in a rat middle cerebral artery thrombosis model

Repair of brain damage size and recovery of neurological dysfunction after ischemic stroke are different between strains in mice: evaluation using a novel ischemic stroke model

In the current study, we established a novel murine ischemic brain damage model using a photochemical reaction to evaluate the recovery of neurological dysfunction and brain repair reactions. In this model, reproducible damage was induced in the frontal lobe of the cortex, which was accompanied by neurological dysfunction. Sequential changes in damage size, microglial accumulation, astrocyte activation, and neurological dysfunction were studied in C57BL/6J and BALB/c mouse strains. Although the initial size of damage was comparable in both strains, the extent of damage was later reduced to a greater extent in C57BL/6J mice than that in BALB/c mice. In addition, C57BL/6J mice showed later edema clearance until day 7, less microglial accumulation, and relatively more astrocyte activation on day 7. Neurologic dysfunction was evaluated by three behavioral tests: the von Frey test, the balance beam test, and the tail suspension test. The behavioral abnormalities evaluated by these tests were remarkable following the induction of damage and recovered by day 21 in both strains. However, the abnormalities were more prominent and the recovery was later in C57BL/6J mice. These findings demonstrate that our novel ischemic stroke model is useful for evaluating brain repair reactions and the recovery of neurological dysfunction in mice with different genetic backgrounds. In addition, we found that both the brain repair reactions and the recovery of neurological dysfunction after comparable ischemic brain damage varied between strains; in that, they both occurred later in C57BL/6J mice.

Different exercises can modulate the differentiation/maturation of neural stem/progenitor cells after photochemically induced focal cerebral infarction

INTRODUCTION

Exercise therapies during rehabilitation significantly promote recovery from various deficits after cerebral infarction, which is mediated by neuronal plasticity with distinct inputs. Although adult neurogenesis can also be modulated by neuronal activity before synaptogenesis, how distinct exercises contribute to the neurological reorganization of the injured cerebral cortex remains unclear. In the present study, we aimed to elucidate the effects of different exercise therapies on motor recovery and neuronal reorganization after photochemically induced focal cerebral infarction.

METHODS

Here, we examined the effects of three different exercises-(a) forced lower-intensity and (b) higher-intensity treadmill exercises, and (c) voluntary exercise with wheel running-on motor recovery and adult neurogenesis in a rat model of focal cerebral infarction. Photochemically induced thrombosis (PIT) was used to generate focal infarction in rats that was mostly confined to their motor cortices.

RESULTS

Beam walking tests showed that recovery after PIT-induced cortical infarction differed in acute and chronic stages and was influenced by the type of exercise. Furthermore, forced low-intensity training had more positive effects on functional recovery than other exercises or control. To evaluate the production of newly generated cells including de novo neurogenesis, we performed lineage analysis with BrdU labeling and immunofluorescence experiments. Lower-intensity treadmill exercise increased the number of BrdU/NeuN colabeled cells, but not total BrdU-retaining or BrdU/Sox2-colabeled cells, in the peri-infarct region of the ipsilateral cortex. In contrast, high-intensity treadmill or voluntary exercises had the opposite effects.

CONCLUSIONS

These results suggest that neuronal maturation can be differently modulated by distinct exercises and that low-intensity treadmill exercise could result in more potent generation of mature neurons. This also suggests the possibility that the generation of neural stem/progenitor cells and differentiation might be modulated by rehabilitation-mediated neural plasticity.

Applications of Liposomal Drug Delivery Systems to Develop Neuroprotective Agents for the Treatment of Ischemic Stroke

Ischemic stroke is one of the leading causes of severe disability and death. In clinical settings, tissue plasminogen activator (t-PA) for thrombolytic therapy is the only globally approved drug for the treatment of ischemic stroke. However, the proportion of patients who receive t-PA therapy is extremely limited due to its narrow therapeutic time window (TTW) and the risk of cerebral hemorrhage. Cerebral ischemia-reperfusion (I/R) injury is also a serious problem for patients' outcomes. Hence, the development of more effective therapies has been desired to prolong the TTW of t-PA and prevent cerebral I/R injury. For delivering drugs into the brain, the blood-brain barrier (BBB) must be overcome since it limits drug penetration into the brain, leading to insufficient therapeutic efficacy. As a distinctive pathology after an ischemic stroke, it was reported that the vascular permeability of the BBB is increased around the ischemic region. We found that nano-sized liposomes can pass through the disrupted BBB and accumulate in the I/R region, and that delivery of neuroprotective agents using a liposomal drug delivery system (DDS) is effective for the treatment of cerebral I/R injury. Moreover, we have recently demonstrated that combination therapy with liposomal drugs and t-PA can suppress the deleterious effects of t-PA and extend its TTW in a rat ischemic stroke model. These findings indicate that applications of nanoparticle DDS technology could be a hopeful approach to drug development for ischemic stroke therapy. In this review, we introduce our findings on ischemic stroke treatment using liposomal DDS and recent advances from other research groups.

Co-administration of liposomal fasudil and tissue plasminogen activator ameliorated ischemic brain damage in occlusion model rats prepared by photochemically induced thrombosis

Delivery of neuroprotectants with liposomes has been shown to be effective for the treatment of ischemic stroke. We have recently revealed that intravenous administration of liposomal fasudil (Fasudil-Lip), a Rho-kinase inhibitor, prior to thrombolysis with tissue plasminogen activator (t-PA) can extend the narrow therapeutic time window (TTW) of t-PA. In the present study, we examined the influence of t-PA treatment on liposomal accumulation into the ischemic region and cerebroprotective effect of combined treatment with Fasudil-Lip and t-PA performed at the same timing after the onset of ischemia in middle cerebral artery occlusion (MCAO) prepared by photochemically induced thrombosis. The t-PA administration into MCAO rats 3 h after occlusion brought about significantly higher accumulation of intravenously injected PEGylated liposomes in wide area of ischemic region. Confocal images showed that extravasation of the liposomes from cerebral vessels into brain parenchyma was markedly facilitated by the t-PA treatment which increased blood flow in cerebral vessels. Importantly, co-administration of Fasudil-Lip and t-PA after 3 h occlusion, beyond the TTW of t-PA in MCAO rats, significantly suppressed brain cell damage compared with t-PA treatment alone. These findings suggest that co-administration of Fasudil-Lip and t-PA should lead to prolong t-PA's TTW and become a useful therapeutic option for ischemic stroke.

Combination therapy with liposomal neuroprotectants and tissue plasminogen activator for treatment of ischemic stroke

For ischemic stroke treatment, extension of the therapeutic time window (TTW) of thrombolytic therapy with tissue plasminogen activator (tPA) and amelioration of secondary ischemia/reperfusion (I/R) injury are most desirable. Our previous studies have indicated that liposomal delivery of neuroprotectants into an ischemic region is effective for stroke treatment. In the present study, for solving the above problems in the clinical setting, the usefulness of combination therapy with tPA and liposomal fasudil (fasudil-Lip) was investigated in ischemic stroke model rats with photochemically induced thrombosis, with clots that were dissolved by tPA. Treatment with tPA 3 h after occlusion markedly increased blood-brain barrier permeability and activated matrix metalloproteinase (MMP)-2 and -9, which are involved in cerebral hemorrhage. However, an intravenous administration of fasudil-Lip before tPA markedly suppressed the increase in permeability and the MMP activation stemming from tPA. The combination treatment showed significantly larger neuroprotective effects, even in the case of delayed tPA administration compared with each treatment alone or the tPA/fasudil-treated group. These findings suggest that treatment with fasudil-Lip before tPA could decrease the risk of tPA-derived cerebral hemorrhage and extend the TTW of tPA and that the combination therapy could be a useful therapeutic option for ischemic stroke.-Fukuta, T., Asai, T., Yanagida, Y., Namba, M., Koide, H., Shimizu, K., Oku, N. Combination therapy with liposomal neuroprotectants and tissue plasminogen activator for treatment of ischemic stroke.

Precise Characterization of the Penumbra Revealed by MRI: A Modified Photothrombotic Stroke Model Study

Aims

To precisely characterize the penumbra by MRI based on a modified photothrombotic stroke mouse model.

Methods

The proximal middle cerebral artery was occluded by a convenient laser system in conjunction with an intravenous injection of Rose Bengal in mice. And the suture MCAO model was performed in seven mice as a comparison of the reproducibility. One hour after occlusion, the penumbra was defined in six random photothrombotic stroke mice by mismatch between perfusion-weighted imaging and the apparent diffusion coefficient map on a home-made workstation. After imaging, three random mice of them were chosen to perform the reperfusion surgery. And the other three mice were sacrificed to stain for several potential penumbra markers, such as c-fos and heart shock protein 90. In the remaining mice, the evolution of the lesions was detected on the apparent diffusion coefficient map, diffusion-weighted imaging and T2-weighted imaging at 1, 3, 6, 12 and 24 hours. After evaluating the neurological deficit scores, the brains were sectioned and stained by triphenyltetrazolium chloride and Nissl.

Results

The mice subjected to photothrombosis showed significant behavioral deficits. One hour after occlusion, the low perfusion areas on the perfusion-weighted imaging interlaced with the hypointense areas on the apparent diffusion coefficient map, demonstrating that the penumbra was located both surrounding and inside the lesions. This phenomenon was subsequently confirmed by the c-fos and heart shock protein 90 staining. The final T2-weighted images of the mice subjected to the reperfusion surgery were also consistent with the penumbra images at one hour. At early stages, the lesions were clearly identified on the apparent diffusion coefficient map; the volumes of the lesions on the diffusion-weighted imaging and T2-weighted imaging did not reach a maximum until 12 hours. The coefficient of variation (CV) of the final lesions in the photothrombotic stroke mice was 21.7% (0.08 of 0.37) on T2-weighted imaging and 27.8% (0.10 of 0.35) on triphenyltetrazolium chloride, representing a high reproducibility (n = 7). While the CV of the lesions in the MCAO stroke mice was only 70% (0.24 of 0.34, n = 4).

Conclusions

This study has provided a precise imaging definition of the penumbra based on a reproducible photothrombotic stroke mouse model.

The use of ¹⁸F-BCPP-EF as a PET probe for complex I activity in the brain

Mitochondria are called "cellular power plants" because they exclusively contain a respiratory electron transfer chain consisting of five components (complexes I-V) to generate most of the ATP required to maintain cellular functions. Mitochondrial complex I (MC-I) is the first and the largest macrocomplex in the pathway for oxidative phosphorylation. We recently synthesized a series of novel PET probes for quantitative imaging of MC-I activity in the living brain. Several in vitro biological evaluations suggested that (18)F-BCPP-EF could be applicable for MC-I assessment in vivo, and the probe has been applied to several animal disease models of stroke, aging, and dementia. The data suggested that (18)F-BCPP-EF could be useful to detect ischemic neuronal damage at the subacute phase, 7 days, after ischemic insult, at which time unexpectedly higher (18)F-FDG uptake was observed in the damaged area than in the contralateral intact area. Our studies with the aged monkeys demonstrated that (18)F-BCPP-EF detected the age-related reduction of MC-I activity in the living monkey brain, and also that the monkeys with higher amyloid-β deposition showed lower MC-I activity. Since PET is a sophisticated medical modality for noninvasive assessment of real-time tissue function by using target-specific radiolabeled probes, the development of novel PET probes for MC-I should be useful for diagnostic, prognostic, and treatment monitoring of diseases related to impaired MC-I function.

Pericytes contribute to the disruption of the cerebral endothelial barrier via increasing VEGF expression: implications for stroke

Disruption of the blood-brain barrier (BBB) integrity occurring during the early onset of stroke is not only a consequence of, but also contributes to the further progression of stroke. Although it has been well documented that brain microvascular endothelial cells and astrocytes play a critical role in the maintenance of BBB integrity, pericytes, sandwiched between endothelial cells and astrocytes, remain poorly studied in the pathogenesis of stroke. Our findings demonstrated that treatment of human brain microvascular pericytes with sodium cyanide (NaCN) and glucose deprivation resulted in increased expression of vascular endothelial growth factor (VEGF) via the activation of tyrosine kinase Src, with downstream activation of mitogen activated protein kinase and PI3K/Akt pathways and subsequent translocation of NF-κB into the nucleus. Conditioned medium from NaCN-treated pericytes led to increased permeability of endothelial cells, and this effect was significantly inhibited by VEGF-neutralizing antibody. The in vivo relevance of these findings was further corroborated in the stroke model of mice wherein the mice, demonstrated disruption of the BBB integrity and concomitant increase in the expression of VEGF in the brain tissue as well as in the isolated microvessel. These findings thus suggest the role of pericyte-derived VEGF in modulating increased permeability of BBB during stroke. Understanding the regulation of VEGF expression could open new avenues for the development of potential therapeutic targets for stroke and other neurological disease.

Novel PET probes 18F-BCPP-EF and 18F-BCPP-BF for mitochondrial complex I: a PET study in comparison with 18F-BMS-747158-02 in rat brain

We developed novel PET probes, 2-tert-butyl-4-chloro-5-{6-[2-(2-(18)F-fluoroethoxy)-ethoxy]-pyridin-3-ylmethoxy}-2H-pyridazin-3-one ((18)F-BCPP-EF) and 2-tert-butyl-4-chloro-5-[6-(4-(18)F-fluorobutoxy)-pyridin-3-ylmethoxy]-2H-pyridazin-3-one ((18)F-BCPP-BF), for quantitative imaging of mitochondrial complex I (MC-I) activity in the brain and preliminarily evaluated their properties in comparison with (18)F-BMS-747158-02 ((18)F-BMS).

METHODS

The affinity of (18)F-BCPP-EF, (18)F-BCPP-BF, and (18)F-BMS to MC-I was analyzed using in vitro binding assays with (3)H-dihydrorotenone and bovine cardiomyocyte submitochondrial particles. (18)F-BCPP-EF, (18)F-BCPP-BF, or (18)F-BMS was intravenously injected into rats, and the uptake (standardized uptake value) in each organ was determined by dissection method. The effects of rotenone, a specific MC-I inhibitor, on the uptake of each probe were assessed by whole-body PET imaging in rats. Ischemic brain model rats were imaged using (18)F-BCPP-EF.

RESULTS

The rank order of affinity to MC-I was (18)F-BCPP-BF > (18)F-BMS > (18)F-BCPP-EF. The uptake of (18)F-BCPP-EF and (18)F-BMS was high in the heart, intermediate in brain, and low in muscle and bone 60 min after the injection. (18)F-BCPP-BF provided increasing bone uptake with time after the injection. The uptake of (18)F-BCPP-EF and (18)F-BMS into the brain and heart was significantly decreased by preadministration of rotenone; however, the reduction degree of (18)F-BCPP-EF was more pronounced than that of (18)F-BMS. Rotenone did not affect (18)F-BCPP-BF uptake in either the brain or the heart. (18)F-BCPP-EF imaged the cortical ischemic neuronal damage without any disturbance by microglial activation even on day 7 when (18)F-FDG showed high uptake in the damaged area.

CONCLUSION

The present study demonstrated that (18)F-BCPP-EF could be a potential PET probe for quantitative imaging of MC-I activity and its ischemic damage in the living brain with PET.

Detection of ischemic neuronal damage with [¹⁸F]BMS-747158-02, a mitochondrial complex-1 positron emission tomography ligand: small animal PET study in rat brain

The acute and subacute ischemic neuronal damage in rat brain caused by photochemically induced thrombosis (PIT) was imaged using [¹⁸F]BMS-747158-02 ([¹⁸F]BMS) for mitochondrial complex-1 (MC-1) and [¹¹C](R)-PK11195 ([¹¹C](R)-PK) for peripheral benzodiazepine receptor [PBR; translocator protein] at preischemic "Normal," 1 (day 1), and 7 days (day 7) after ischemic insult. When [¹⁸F]BMS was intravenously injected into "Normal" rat, it was rapidly taken up into the brain, in which it showed a homogeneous distribution, and the uptake was suppressed by rotenone, a specific MC-1 inhibitor. The specificity of [¹⁸F]BMS binding to MC-1 was also confirmed by living brain slice imaging. At day 1, [¹⁸F]BMS uptake was low in infarct and peri-infarct regions where neuronal damage was detected by 2,3,5-triphenyltetrazolium chloride (TTC) staining. At day 7, the damaged areas determined using [¹⁸F]BMS revealed some discrepancy from those detected by TTC staining, suggesting that TTC stained not only surviving cells but also activated microglial cells in the peri-infarct region. This was also confirmed by [¹¹C](R)-PK imaging and immunohistochemical assessment with Iba1 antibody. In contrast, the uptake pattern of [¹⁸F]BMS was consistent with immunohistochemical assessment with NeuN antibody at both days 1 and 7. These results demonstrated that [¹⁸F]BMS could be a promising positron emission tomography ligand to assess the neuronal damage induced by ischemic insult in both acute and subacute phases.

Multiparametric assessment of acute and subacute ischemic neuronal damage: a small animal positron emission tomography study with rat photochemically induced thrombosis model

We evaluated sequential changes in rat brain function up to 14 days after focal ischemic insult with a small animal positron emission tomography (PET). Unilateral focal ischemic cerebral damage was induced by left middle cerebral artery occlusion with a photochemically induced thrombosis (PIT) method. PET scans were conducted with [(11)C](R)-PK11195 ([(11)C](R)-PK) for peripheral benzodiazepine receptor (PBR), [(11)C]flumazenil ([(11)C]FMZ) for central benzodiazepine receptor (CBR), and [(18)F]fluoro-2-deoxy-D-glucose ([(18)F]FDG) for glucose metabolism at before (as "Normal") and after PIT. At 1 and 3 days after PIT, [(18)F]FDG indicated lower uptake in the infarct area. Interestingly, unexpectedly high-[(18)F]FDG uptake was observed in the peri-infarct area surrounding the infarct area at day 7. The high-[(18)F]FDG uptake region completely overlapped with the high-[(11)C](R)-PK uptake region at day 7, which resulted in the underestimation of neuronal damage. Immunohistochemical data also suggested that the high-[(18)F]FDG uptake peak at day 7 was caused by inflammation including microglial cell activation. In contrast, imaging with [(11)C]FMZ indicated cortical neuronal damage on days 7 and 14 without any disturbance by microglial formation. These results indicated that [(18)F]FDG might not be a suitable ligand for ischemic neuronal damage detection from acute to subacute phases.

A novel inhibitor of plasminogen activator inhibitor-1 provides antithrombotic benefits devoid of bleeding effect in nonhuman primates

Inhibition of plasminogen activator inhibitor (PAI)-1 is useful to treat several disorders including thrombosis. An inhibitor of PAI-1 (TM5275) was newly identified by an extensive study of structure-activity relationship based on a lead compound (TM5007) which was obtained through virtual screening by docking simulations. Its antithrombotic efficacy and adverse effects were tested in vivo in rats and nonhuman primates (cynomolgus monkey). TM5275, administered orally in rats (1 to 10 mg/kg), has an antithrombotic effect equivalent to that of ticlopidine (500 mg/kg) in an arterial venous shunt thrombosis model and to that of clopidogrel (3 mg/kg) in a ferric chloride-treated carotid artery thrombosis model. TM5275 does not modify activated partial thromboplastin time and prothrombin time or platelet activity and does not prolong bleeding time. Combined with tissue plasminogen activator, TM5275 improves the latter's therapeutic efficacy and reduces its adverse effect. Administered to a monkey model of photochemical induced arterial thrombosis, TM5275 (10 mg/kg) has the same antithrombotic effect as clopidogrel (10 mg/kg), without enhanced bleeding. This study documents the antithrombotic benefits of a novel, more powerful, PAI-1 inhibitor in rats and, for the first time, in nonhuman primates. These effects are obtained without adverse effect on bleeding time.

A sartan derivative with a very low angiotensin II receptor affinity ameliorates ischemic cerebral damage

Angiotensin II receptor blockers (ARBs) have a potent ability to inhibit oxidative stress and advanced glycation, in addition to their protective effects originated from blood pressure lowering and angiotensin II type 1 receptor (AT(1))-blockade. To obtain a pharmacological tool to dissect the mechanisms of ARBs' protective benefits in experimental stroke, we synthesized a novel ARB-derivative, R-147176, which is 6,700 times less potent than olmesartan in AT(1)-binding inhibition and therefore has a minimal antihypertensive effect, but retains marked inhibitory effects on oxidative stress and advanced glycation. We evaluated the effect of R-147176 (10-30 mg/kg per day), administered orally or intravenously, on brain infarct volume in transient thread occlusion and photothrombotic models in rats. The antioxidative and antiinflammatory properties were also investigated. R-147176 significantly reduced infarct volume, without influence on blood pressure, in both models. R-147176 significantly reduced the numbers of ED-1-positive cells and of TUNEL-positive cells, and protein carbonyl formation in the damaged brain. This ARB derivative, despite its significantly lower AT1 affinity and virtually no antihypertensive effect, ameliorated ischemic cerebral damage through antioxidative and antiinflammatory properties. These findings suggest potential usefulness of R-147176 as a pharmacological tool to investigate the ARBs' protective effect in experimental stroke and open new therapeutic avenues.

Comparing two methods for assessment of perfusion-diffusion mismatch in a rodent model of ischaemic stroke: a pilot study

This stroke experiment was designed to define the mismatch between perfusion-weighted imaging (PWI) and diffusion-weighted imaging (DWI) in MRI by applying early or instantly acquired PWI. Eight rats were induced with stroke through photothrombotic occlusion of the middle cerebral artery and scanned serially between 1 h and day 3 after induction using DWI and PWI with a 1.5 T MR scanner. The relative lesion volumes (rLV) on MRI and triphenyl tetrazolium chloride-stained specimens were defined as the proportion of lesion volume over brain volume. Discrepancies in the rLV between PWI- and DWI-derived apparent diffusion coefficient (ADC) maps were expressed by subtraction of the ADC from PWI, resulting in three possible patterns: (i) (PWI-ADC > 10% of PWI) denoting a mismatch; (ii) (-(10% of PWI) <or= PWI-ADC <or= 10% of PWI) denoting a match; and (iii) (PWI-ADC < -(10% of PWI)) denoting a reverse mismatch. The differences were compared with the minuend being either early PWI (ePWI) or instant PWI (iPWI) and the subtrahend being instant ADC (iADC). The occurrence and evolution of PWI-ADC patterns were analysed. Over time, PWI-ADC discrepancies evolved from mismatch, through to match, to reversed mismatch. The PWI-ADC mismatch still existed 3 days after MCA occlusion in one to three of the eight cases. The rLVs and mismatch incidences between the ePWI-iADC and iPWI-iADC models were linear correlated. A higher mismatch rate occurred in iPWI-iADC within day 1 and in ePWI-iADC at day 3. Both ePWI and iPWI proved useful to define PWI-ADC patterns within day 1. At day 3, iPWI appeared more adequate.

Novel pyrazolo[1,5-a]pyrimidines as c-Src kinase inhibitors that reduce IKr channel blockade

To improve the in vitro potency of the c-Src inhibitor 1a and to address its hERG liability, a structure-activity study was carried out, focusing on two regions of the lead compound. The blockade of the delayed cardiac current rectifier K(+) (I(Kr)) channel was overcome by replacing the ethylenediamino group with an amino alcohol group at the 7-position. In addition, modifying the substituents at the 5-position and the side chain groups on the amino alcohols at the 7-position enhanced the intracellular c-Src inhibitory activity and increased central nervous system (CNS) penetration. In the present study, 6l exhibited significant in vivo efficacy in a middle cerebral artery (MCA) occlusion model in rats.

A novel inhibitor of advanced glycation and endoplasmic reticulum stress reduces infarct volume in rat focal cerebral ischemia

We have developed a novel, non-toxic inhibitor of advanced glycation and oxidative stress, TM2002, devoid of effect on blood pressure. In transient focal ischemia, TM2002 significantly decreased infarct volume compared with vehicle (79.5+/-18.7 vs. 183.3+/-22.9 mm3, p<0.01). In permanent focal ischemia, TM2002 (2.79, 5.58, and 11.16 mg/kg twice a day) dose-dependently reduced infarct volume (242.1+/-32.3, 201.3+/-15.1, and 171.3+/-15.2 mm3, respectively), and improved neurological deficits. Reduction of infarct volume is demonstrable, provided that TM2002 was administered within 1.5 h after the occlusion. To unravel TM2002's mechanism of action, we examined its in vitro effect on endoplasmic reticulum (ER) stress, using aortic smooth muscle cells isolated from ORP 150(+/-) mice and F9 Herp null mutated cells. Cell death induced by ER stress (tunicamycin or hypoxia) was dose-dependently prevented by TM2002. In vivo immunohistochemical study demonstrated a significant reduction of ORP- and TUNEL-positive apoptotic cells, especially in the penumbra. Inhibition of advanced glycation and oxidative stress was confirmed by a significantly reduced number of cells positive for advanced glycation end products and heme oxygenase-1. TM2002 reduced the levels of protein carbonyl formation in ischemic caudate. The efficacy of TM2002 is equivalent to that of a known neuroprotective agent, NXY-059. In conclusion, TM2002 significantly ameliorates ischemic cerebral damage through reduction of ER stress, advanced glycation, and oxidative stress, independently of blood pressure lowering.

Rodent stroke induced by photochemical occlusion of proximal middle cerebral artery: evolution monitored with MR imaging and histopathology

PURPOSE

To longitudinally investigate stroke in rats after photothrombotic occlusion of proximal middle cerebral artery (MCA) with magnetic resonance imaging (MRI) in correlation with histopathology.

MATERIALS AND METHODS

Forty-two rats were subjected to photochemical MCA occlusion and MRI at 1.5T, and sacrificed in seven groups (n=6 each) at the following time points: 1, 3, 6 and 12h, and at day 1, 3 and 9. T2-weighted (T2WI) and diffusion-weighted imaging (DWI) with apparent diffusion coefficient (ADC) map was performed in all rats. Contrast-enhanced T1-weighted imaging (CE-T1WI) was compared to intravital staining with Evans blue in one group for assessing blood-brain barrier (BBB) integrity. The brain was stained histochemically with triphenyl tetrazolium chloride (TTC) and processed for pathological assessment. The evolutional changes of relative lesion volume, signal intensity (SI), and the BBB integrity on MRI with corresponding histopathology were evaluated.

RESULTS

The ischemic lesion volume reached a maximum around 12h to day 1 as visualized successively by DWI, ADC map and T2WI, implicating the evolving pathology from cytotoxic edema through vasogenic edema to tissue death. The ADC of brain infarction underwent a significant reversion after 12h, reflecting the colliquative necrosis. On CE-T1WI, BBB leakage peaked at 6h and at day 3 with a transitional partial recovery around 24h. The infarct volume on T2WI, DWI and ADC map matched well with that on TTC staining at 12h and at day 1 (p>0.05).

CONCLUSION

The evolution of the present photothrombotic stroke model in rats could be characterized by MRI. The obtained information may help longitudinal studies of cerebral ischemia and anti-stroke agents using the same model.

Therapeutic time window of tacrolimus (FK506) in a nonhuman primate stroke model: Comparison with tissue plasminogen activator

Tacrolimus (FK506), an immunosuppressive drug, has been shown to exert a potent neuroprotective activity when administered immediately after occlusion of the middle cerebral artery (MCA) in a nonhuman primate model of stroke. Here, we assessed the neuroprotective efficacy of tacrolimus with delayed treatment using the same model and compared with that of recombinant tissue plasminogen activator (rt-PA). Ischemic insult was induced by photochemically induced thrombotic occlusion of MCA in cynomolgus monkeys, and tacrolimus (0.2 mg/kg) and/or rt-PA (1.0 mg/kg) was intravenously administered 2 h after MCA occlusion. In another experiment, tacrolimus (0.1 mg/kg) was administered 4 h after MCA occlusion. Neurological deficits were monitored for 28 days after the ischemic insult and cerebral infarct volumes were measured with brain slices. With drug administration 2 h after the ischemic insult, tacrolimus significantly reduced neurological deficits and infarct volumes in the cerebral cortex without affecting the recanalization pattern in the MCA, however, rt-PA did not significantly improve neurological deficits or infarct volumes, even though it increased the recanalization rate of the occluded MCA. Combined treatment with tacrolimus and rt-PA exerted additional protection. Administration of tacrolimus 4 h after the ischemic insult still showed significant amelioration of neurological deficits. These results suggested that tacrolimus had a wider therapeutic time window than rt-PA in the nonhuman primate stroke model.

Discovery of Novel 2-Anilinopyrazolo[1,5-a]pyrimidine Derivatives as c-Src Kinase Inhibitors for the Treatment of Acute Ischemic Stroke

We synthesized a series of novel 2-anilinopyrazolo[1,5-a]pyrimidine derivatives and evaluated their ability to inhibit c-Src kinase; 7-(2-amino-2-methylpropylamino)-5-cyclopropyl-2-(3,5-dimethoxyphenylamino)pyrazolo[1,5-a]pyrimidine-3-carboxamide 7o and 7-(2-amino-2-methylpropylamino)-2-(3,5-dimethoxyphenylamino)-5-methylpyrazolo[1,5-a]pyrimidine-3-carboxamide 7f showed potent inhibitory activity. Compound 7f inhibited c-Src selectively and exhibited satisfactory central nervous system (CNS) penetration. Furthermore, 7f.HCl reduced the infarct volume in vivo in a rat middle cerebral artery (MCA) occlusion model when administrated intraperitoneally.

Synthesis and c-Src inhibitory activity of imidazo[1,5-a]pyrazine derivatives as an agent for treatment of acute ischemic stroke

We synthesized and evaluated a series of C-5 substituted imidazo[1,5-a]pyrazine derivatives to identify potent c-Src inhibitors as potential therapeutic agents for acute ischemic stroke. Among these compounds, compound 14c.HCl demonstrated remarkable central nervous system (CNS) penetration and significant neuroprotective efficacy in vivo in rat models.

Neuroprotective effects of KCL-440, a new poly(ADP-ribose) polymerase inhibitor, in the rat middle cerebral artery occlusion model

It is reported that ischemic brain injury is mediated by the activation of poly(ADP-ribose) polymerase (PARP). In this study, we examined the pharmacological profile of KCL-440, a new PARP inhibitor, and its neuroprotective effects in the rat acute cerebral infarction model induced by photothrombotic middle cerebral artery (MCA) occlusion. In an in vitro study, KCL-440 exhibited potency with regard to inhibition of PARP activity, with an IC50 value of 68 nM. An in vivo pharmacokinetic study showed that the brain concentration of KCL-440 was sufficient to inhibit PARP activity during the intravenous infusion of KCL-440 at the rate of 1 mg/kg/h. KCL-440 at various doses or saline was administered for 24 h immediately after the MCA occlusion. Administration of KCL-440 led to a dose-dependent reduction in the infarct size at 24 h after MCA occlusion. Infarct sizes were 44.8% +/- 3.0% (n = 8), 40.5% +/- 1.1% (n = 8), 38.2% +/- 1.4% (n = 8), 35.1% +/- 2.1% (n = 8), 34.2% +/- 2.3% (n = 7), 32.6% +/- 1.9% (n = 8), and 31.0% +/- 2.1% (n = 5) at doses of 0, 0.01, 0.03, 0.1, 0.3, 1.0, and 3.0 mg/kg/h. When compared to the control group, a statistically significant difference was observed in the doses that were higher than 0.03 mg/kg/h. When the infusion of KCL-440 (1 mg/kg/h, n = 8) was started at 1 h after the MCA occlusion, a significant reduction in infarct size was observed; this was not observed when KCL-440 infusion was started 2 or 3 h after the MCA occlusion. Furthermore, increased poly(ADP-ribose) immunostaining was confirmed at the ischemic border zone 2 h after the MCA occlusion, and it was reduced by KCL-440 treatment. These results suggest that KCL-440 is a possible neuroprotective agent with high blood-brain barrier permeability and high PARP inhibitory activity.

Characterization of a novel thrombotic middle cerebral artery occlusion model in monkeys that exhibits progressive hypoperfusion and robust cortical infarction

In an attempt to establish a thrombotic middle cerebral artery (MCA) occlusion model using cynomolgus monkeys, we measured the blood flow in the main MCA tract and cerebral cortex, brain damage, and neurological deficits, and compared them with those of mechanical MCA occlusion model. Thrombotic occlusion was induced photochemically by green light application on the MCA following rose bengal treatment; mechanical occlusion was induced by MCA clipping for 3h. Patency of the main MCA tract showed two patterns in the thrombotic model: permanent occlusion or cyclical flow reduction (CFR). Regional cerebral blood flow (rCBF) decreased during occlusion followed by post-ischemic hyperperfusion in the clipping model, whereas rCBF reduction expanded time-dependently in the thrombotic occlusion model. Brain infarction and neurological scores in the thrombotic occlusion model were significantly larger than those in the clipping occlusion model. In histological assessment, microthrombi containing myeloperoxidase- and fibrinogen-positive cells were observed in the cortex following the thrombotic but not clipping occlusion. These results collectively suggest that this thrombotic MCA occlusion model, because it shows impairment of cerebral microcirculation, could provide a vital platform for understanding progressive ischemia as well as for evaluating potential therapeutic drugs.

Dynamic susceptibility contrast-enhanced perfusion MR imaging at 1.5 T predicts final infarct size in a rat stroke model

The purpose of the present animal experiment was to determine whether source images from dynamic susceptibility contrast-enhanced perfusion weighted imaging (DSC-PWI) at a 1.5T MR scanner, performed early after photochemically induced thrombosis (PIT) of cerebral middle artery (MCA), is feasible to predict final cerebral infarct size in a rat stroke model. Fifteen rats were subjected to PIT of proximal MCA. T2 weighted imaging (T2WI), diffusion-weighted imaging (DWI), and contrast-enhanced PWI were obtained at 1 h and 24 h after MCA occlusion. The relative lesion size (RLS) was defined as lesion volume/brain volume x 100% and measured for MR images, and compared with the final RLS on the gold standard triphenyl tetrazolium chloride (TTC) staining at 24 h. One hour after MCA occlusion, the RLS with DSC-PWI was 24.9 +/- 6.3%, which was significantly larger than 17.6 +/- 4.8% with DWI (P < 0.01). At 24 h, the final RLS on TTC was 24.3 +/- 4.8%, which was comparable to 25.1 +/- 3.5%, 24.6 +/- 3.6% and 27.9 +/- 6.8% with T2WI, DWI and DSC-PWI respectively (P > 0.05). The fact that at 1 h after MCA occlusion only the displayed perfusion deficit was similar to the final infarct size on TTC (P > 0.05) suggests that early source images from DSC-PWI at 1.5T MR scanner is feasible to noninvasively predict the final infarct size in rat models of stroke.

FK419, a nonpeptide platelet glycoprotein IIb/IIIa antagonist, ameliorates brain infarction associated with thrombotic focal cerebral ischemia in monkeys: comparison with tissue plasminogen activator

The binding of platelet glycoprotein (GP) IIb/IIIa to fibrinogen is the final common pathway in platelet aggregation, a process known to play a key role in the pathogenesis of ischemic brain damage. We compared the effects of FK419, a novel nonpeptide GPIIb/IIIa antagonist, with recombinant tissue plasminogen activator (rt-PA) on middle cerebral artery (MCA) patency and ischemic brain damage in a thrombotic stroke model in squirrel monkeys. FK419 not only inhibited in vitro platelet aggregation (IC50: 88 nmol/L), but also showed disaggregatory activity to aggregated platelet (EC50: 286 nmol/L). FK419 dose-dependently reduced the time to first reperfusion and total occlusion time of MCA blood flow when administered immediately after the termination of photoirradiation. FK419 reduced cerebral infarction and ameliorated neurologic deficits with similar dose-dependency. Although rt-PA reduced the time to first reperfusion, total occlusion time, and cerebral infarction, it did not significantly ameliorate neurologic deficits and induced petechial intracerebral hemorrhages. These results indicate: (1) FK419 restored cerebral blood flow after thrombotic occlusion of MCA, (2) FK419 reduced ischemic brain injury by its thrombolytic actions in a non-human primate stroke model, and (3) FK419 has superior antithrombotic efficacy and is safer than rt-PA.

FK419, a novel nonpeptide GPIIb/IIIa antagonist, restores microvascular patency and improves outcome in the guinea-pig middle cerebral artery thrombotic occlusion model: comparison with tirofiban

The antithrombotic efficacy of FK419, a novel nonpeptide platelet glycoprotein IIb/IIIa antagonist, was compared with tirofiban in guinea-pigs. FK419 and tirofiban similarly inhibited platelet aggregation in vitro (IC50 values: 0.43+/-0.076 and 0.41+/-0.053 micromol/L) and dispersed aggregated platelets (EC50 values: 2.3+/-0.88 and 2.0+/-0.81 micromol/L). FK419 inhibited retention of platelets and neutrophils in a collagen-coated bead column with greater potency than tirofiban (IC50 values of 0.90+/-0.133 and 2.4+/-0.21 micromol/L for platelet retention and 0.32+/-0.078 and 0.57+/-0.180 micromol/L for neutrophil retention). When FK419 or tirofiban were administered after photochemically induced middle cerebral artery (MCA) occlusion in guinea-pigs, they dose-dependently improved MCA patency. FK419 reduced neurological deficits and ischemic brain damage in a dose-dependent fashion, whereas tirofiban did not. Reduced regional cerebral blood flow in the striatum gradually returned to the preoccluded level with FK419 treatment; however, no restoration was observed with tirofiban even though the MCA was recanalized. These results indicate that FK419 ameliorates ischemic brain damage by not only lysing the obstructive thrombus in MCA but also preventing or restoring microcirculation deficits after occlusion/reperfusion, suggesting that FK419 would be an attractive intervention for the treatment of ischemic stroke patients.

Neuroprotective effects of ONO-1924H, an inhibitor of poly ADP-ribose polymerase (PARP), on cytotoxicity of PC12 cells and ischemic cerebral damage

N-[3-(4-Oxo-3,4-dihydro-phthalazin-1-yl)phenyl]-4-(morpholin-4-yl) butanamide methanesulfonate monohydrate (ONO-1924H) is a novel inhibitor of poly ADP-ribose polymerase (PARP). In this study, we examined the effects of ONO-1924H on cytotoxicity induced by hydrogen peroxide in PC12 cells in vitro and cerebral damage and neurological deficits induced by middle cerebral artery (MCA) thrombus occlusion in vivo in rat. In the in vitro cytotoxicity assay, exposure to 0.5 mmol/L hydrogen peroxide induced cell death in differentiated PC12 cells. ONO-1924H, a PARP inhibitor (Ki=0.21 micromol/L), reduced cell death in a concentration-dependent manner that was correlated with inhibition of PARP activation. A 50% reduction in cell death (EC50) was achieved with 2.4 micromol/L ONO-1924H. In the MCA occlusion model, ONO-1924H was injected intravenously at doses of 3, 10 and 30 mg/kg/h for 3 h, and cerebral damage and neurological deficits were estimated 24 h after MCA occlusion. ONO-1924H treatment led to a significant decrease in cerebral damage in the 10 mg/kg/h-treated group (P < 0.05) and the 30 mg/kg/h-treated group (P < 0.01). Further, ONO-1924H at doses of 30 mg/kg/h significantly (P < 0.05) improved neurological deficits. These findings suggest that the novel PARP inhibitor, ONO-1924H, affords effective neuroprotection and is a useful therapeutic candidate for the treatment of ischemic stroke.

Rat cerebral ischemia induced with photochemical occlusion of proximal middle cerebral artery: a stroke model for MR imaging research

A stroke model in rats with photochemically induced thrombosis (PIT) of proximal cerebral middle artery (MCA) is introduced for magnetic resonance imaging (MRI) study. Thirty-seven rats subjected to surgical and optical procedures for inducing the PIT models were scanned using a 1.5-T scanner with T1-weighted imaging (T1WI), T2-weighted imaging (T2WI), diffusion-weighted imaging (DWI), and contrast-enhanced perfusion-weighted imaging (PWI) at 1 h and 24 h after MCA occlusion. The penumbra evolution and PWI-derived parameters including relative cerebral blood volume (rCBV) and relative cerebral blood flow (rCBF) were monitored; and the relative lesion size (RLS) was compared with the final RLS on the gold standard triphenyl tetrazolium chloride (TTC) staining at 24 h. The results showed that the focal cerebral ischemic lesions were detectable in all rats with different MR approaches. The lesion on PWI at 1 h and on all MR images at 24 h was matched well with that seen on TTC staining; the peri-infarct area decreased from 6.2 +/- 7.2% of the brain volume at 1 h to 0.3 +/- 5.6% at 24 h. Compared to that in the contralateral hemisphere, rCBV in ischemic region was 52.6 +/- 21.4 and 40.0 +/- 15.8% (p > 0.05), and rCBF was 64.6 +/- 11.2 and 47.3 +/- 11.1% (p < 0.05) at 1 h and 24 h respectively. The present PIT model in rats has been successfully adopted for MRI research, which might be feasible for certain stroke studies and should be beneficial for the evaluation on effects of potential diagnostic and therapeutic approaches.

Visualization of stroke with clinical MR imagers in rats: a feasibility study

This experiment was conducted in compliance with the guidelines of the International Committee on Thrombosis and Hemostasis and the current institutional regulations for use and care of laboratory animals. The purpose of the present study was to report the feasibility of using clinical magnetic resonance (MR) imaging devices for depiction of stroke in a rat model. Twenty-four rats with photochemically induced thrombosis of the middle cerebral artery were examined at superacute (1 hour, n = 24), acute (12 hours, n = 12), and subacute (24 hours, n = 12) phases with 1.5-T MR imaging weighted for T1, T2, diffusion, and gadopentetate dimeglumine-enhanced perfusion. With reasonable signal-to-noise ratio and imaging times, ischemic lesions were well distinguished on MR images as validated qualitatively and quantitatively with postmortem standard-of-reference techniques, including volume-rendered computed tomography, microangiography, and histochemistry. In the superacute phase, the perfusion defect at perfusion-weighted MR imaging was well matched with microangiographic and pathologic findings (P > .05). There was no difference in lesion size at perfusion-weighted MR imaging between superacute and subacute phases (P > .05). Performance of certain stroke-related research in rats is feasible with clinical MR imagers.

Restoration of middle cerebral artery thrombosis by novel glycoprotein IIb/IIIa antagonist FK419 in guinea pig

We compared the antithrombotic efficacy of FK419 [(S)-2-acetylamino-3-[(R)-[1-[3-(piperidin-4-yl)propionyl]piperidin-3-ylcarbonyl]amino] propionic acid trihydrate], a novel nonpeptide glycoprotein IIb/IIIa antagonist, with recombinant tissue plasminogen activator (rt-PA) and other antithrombotic agents (aspirin, ozagrel, argatroban and heparin). FK419 not only inhibited ADP- and collagen-induced guinea pig platelet aggregation, but also induced disaggregation for ADP-induced aggregated platelets in vitro. In the photochemically induced middle cerebral artery thrombosis model in guinea pigs, FK419 dose-dependently shortened the time to first reperfusion and the total middle cerebral artery occlusion time and reduced ischemic brain damage and ameliorated neurological deficits measured 24 h after middle cerebral artery occlusion. Rt-PA similarly improved the middle cerebral artery patency, brain damage and neurological deficits. Neither aspirin, ozagrel, argatroban nor heparin restored the middle cerebral artery blood flow and improved the brain damage or neurological deficits. These results demonstrated that novel glycoprotein IIb/IIIa antagonist FK419 could disperse thrombus and ameliorated ischemic brain damage, suggesting that FK419 would be an attractive intervention for stroke patients.

Antithrombotic Effects of FK419, a Novel Nonpeptide Platelet GPIIb/IIIa Antagonist, in a Guinea Pig Photochemically Induced Middle Cerebral Artery Thrombosis Model: Comparison with Ozagrel and Argatroban

Platelet activation and subsequent aggregation play a key role in the pathogenesis of ischemic brain damage. Recent studies revealed that enhanced platelet activation is also observed after ischemia, suggesting that secondary thrombus formation might participate in the development of cerebral infarction. The binding of platelet glycoprotein GPIIb/IIIa (integrin alpha(IIb)beta3) to fibrinogen is the final common pathway in platelet aggregation. Therefore, GPIIb/IIIa antagonists might be useful in acute ischemic stroke as well as in the secondary prevention of ischemic stroke. In the present study, we evaluated the effect of three compounds, FK419 ((S)-2-acetylamino-3-[(R)-[1-[3-(piperidin-4-yl) propionyl] piperidin-3-ylcarbonyl] amino] propionic acid trihydrate), a novel nonpeptide GPIIb/IIIa antagonist, ozagrel, a selective thromboxane A(2) synthase inhibitor, and argatroban, a thrombin inhibitor, on middle cerebral artery (MCA) patency and ischemic brain damage using photochemically induced MCA thrombosis model in guinea pigs. FK419, ozagrel, or argatroban was administered 5 min after the termination of photoirradiation. FK419 dose-dependently improved MCA patency by decreasing the total occlusion time, time to continuous reperfusion, and the number of cyclic flow reductions, at doses that inhibited ADP-induced platelet aggregation ex vivo. In contrast, ozagrel only improved total occlusion time, and argatroban showed no improvement in MCA patency. FK419 also reduced ischemic brain damage in a dose-dependent fashion, whereas ozagrel and argatroban did not. Finally, FK419 ameliorated neurological deficits, whereas ozagrel and argatroban did not. These results indicate that FK419, a GPIIb/IIIa antagonist, ameliorates ischemic brain damage by improving MCA patency after occlusion and that FK419 is a promising candidate for the treatment of acute ischemic stroke.

Essential role of endogenous tissue plasminogen activator through matrix metalloproteinase 9 induction and expression on heparin-produced cerebral hemorrhage after cerebral ischemia in mice

Cerebral hemorrhage associated with antithrombotic and thrombolytic therapy in acute stroke continues to present a major clinical problem. Rupture of the cerebral microvasculature involves the degradation and remodeling of extracellular matrix. Here we demonstrated that the delayed administration of heparin 3 hours after photothrombotic middle cerebral artery occlusion (MCAO) caused cerebral hemorrhage in wild-type (WT) mice but not in tissue plasminogen activator (tPA)-deficient knockout (KO) mice. Heparin administration increased tPA activity and its mRNA expression at 6 and 12 hours after MCAO in the ischemic hemispheres of WT mice. The expression of tPA was enhanced in microglial cells in the ischemic border zone. We also observed an exacerbation of matrix metalloproteinase (MMP) 9 expression at the mRNA level and its conversion to an active form after heparin administration in the ischemic hemisphere in WT mice but not in tPA KO mice. The increased MMP 9 expression was localized in microglial cells and endothelial cells. These findings suggest that endogenous tPA, through the enhancement of MMP 9 expression and proteolytic activation, plays an essential role in the pathogenesis of heparin-produced cerebral hemorrhage. Targeting tPA, MMP 9, or both may provide a new approach for preventing cerebral hemorrhage associated with antithrombotic therapy for stroke in humans.

Neuroprotective action of tacrolimus (FK506) in focal and global cerebral ischemia in rodents: dose dependency, therapeutic time window and long-term efficacy

Tacrolimus (FK506), a potent immunosuppressive drug, is effective in attenuating brain infarction after cerebral ischemia. However, there has been no report characterizing the neuroprotective action and therapeutic time window of tacrolimus systematically using different types of stroke models and extended observation periods. Therefore, we evaluated the neuroprotective effect of tacrolimus in three different animal models of cerebral ischemia: transient and permanent focal ischemia in rats and transient global ischemia in gerbils. Tacrolimus at doses higher than 0.1 mg/kg (i.v.) produced a statistically significant reduction in ischemic brain damage following permanent and transient focal ischemia in rats when administered immediately after the onset of ischemia. Tacrolimus (1 mg/kg, i.v.) demonstrated similar neuroprotective activity even after delayed administration (2 h after permanent or 1 h after transient focal ischemia). The neuroprotective effect of tacrolimus was still present 2 weeks after transient focal ischemia and 1 week after permanent focal ischemia. After transient global ischemia in gerbils, tacrolimus (1 mg/kg, i.v.) given immediately after reperfusion also produced long-lasting neuroprotective effects with a protective time-window of 1-2 h. Taken together, the results clearly indicate that tacrolimus exerts potent, long-term neuroprotective effects with a favorable therapeutic time-window, regardless of the model of cerebral ischemia. These results strengthen the notion that tacrolimus might be of clinical value for the treatment of acute stroke.

Recombinant human microplasmin: production and potential therapeutic properties

The effect of recombinant human microplasmin was studied in ischemic stroke models in mice and in an extracorporeal loop thrombosis model in rabbits. Human microplasminogen ( micro Plg), which lacks the five 'kringle' domains of plasminogen was expressed with high yield in Pichia pastoris. It was purified, converted to microplasmin ( micro Pli) and equilibrated with 5 mmol L(-1) citrate, pH 3.1, yielding a stable preparation. In mice with middle cerebral artery (MCA) ligation, an intravenous (i.v.) bolus of 5.0 mg kg(-1) micro Pli reduced infarct size at 24 h from 27 (26-30) to 25 (21-28) mm3 (median and range, n= 16 each, P= 0.0001), whereas 4.0 mg kg(-1) rt-PA and 40 mg kg(-1) micro Plg had no effect. Infarct reduction was observed with administration at 4 h after occlusion. In mice with MCA, infarct size at 24 h was reduced from 20 (14-30) to 9.1 (3.1-25) mm3 with 5.0 mg kg(-1) micro Pli (n = 15 each, P < 0.002) and to 11 (5.2-27) mm3 with 4.0 mg kg(-1) rt-PA (n = 6; P= 0.02). Infarct reduction was still observed at 10 h after occlusion with micro Pli but not with t-PA. In rabbits with radiolabeled clots in an extracorporeal arteriovenous loop, local infusion of 2.5 mg kg(-1) micro Pli over 2 h, induced 51 +/- 15% lysis (mean +/- SD, n= 11) vs. a control value of 23 +/- 5.5%. micro Pli did not prolong template bleeding times, whereas equipotent doses of rt-PA were associated with extensive rebleeding. The potency of micro Pli in both models was similar to that of intact plasmin. These findings indicate that recombinant micro Pli may be useful for treatment of ischemic stroke and arterial thrombosis.

Thrombogenicity of beta 2-glycoprotein I-dependent antiphospholipid antibodies in a photochemically induced thrombosis model in the hamster

We previously showed that beta(2)-glycoprotein I (beta(2)GPI)-dependent lupus anticoagulants (LAs) form bivalent antigen-antibody complexes with high affinity for phospholipids; these complexes are responsible for their in vitro anticoagulant effect. We now studied the role of these bivalent complexes in arterial thrombosis in the hamster. Three monoclonal antibodies (mAbs) raised against human beta(2)GPI were selected on the basis of their cross-reactivity with hamster beta(2)GPI. Two of these, one with LA activity, 5H2, and one with only anticardiolipin properties, 11E8, were infused at 0 to 10 mg/kg prior to photochemically induced vessel damage. 5H2 promoted thrombus formation dose dependently, raising the thrombus size from 6.0 arbitrary units (AU) in controls (n = 9) to 65.0 AU in the high-dose group (10 mg/kg, n = 6, P =.007). The LA(-) mAb 11E8 and mAb 27A8, reactive with human beta(2)GPI exclusively, did not significantly promote thrombus formation. In a second set of experiments, intact mAb 5H2 was compared to its fragments. Intact mAb 5H2 at 3.3 mg/kg and the equimolar dose of F(ab')(2) fragments (2.2 mg/kg) promoted thrombus formation equally well (55.8 AU, n = 8 and 62.5 AU, n = 7, respectively); mAb 5H2-derived Fab' fragments were inactive. Immunohistochemical analysis showed platelet-rich thrombi, with 5H2 or its F(ab')(2) fragments mainly bound to individual platelets. Our results indicate that bivalent immune complex formation plays an important role in the genesis of arterial thrombosis by certain antiphospholipid antibodies. Cellular activation via the Fc portion of these immune complexes, however, is not essential, because F(ab')(2) fragments of 5H2 still promote thrombus formation.

Role of PPAR.GAMMA. in the development of the central nervous system

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a nuclear receptor that plays a central role in adipocyte differentiation and insulin sensitivity. Recently, a diversity of the action of PPARgamma on many other cell types or organs is indicated. We summarize here the possible role of PPARgamma in the development of the murine central nervous system. Expressions of PPARgamma in newborn or adult mouse brain are extremely low, but high in embryo or fetal mouse brain. Furthermore, we investigated the role of PPARgamma in proliferation or differentiation of neural stem cells (NSCs) isolated from murine embryonic brains, because NSCs are considered to be a major source of neurons in developmental brains. Administrations of PPARgamma-specific ligands on the NSCs from wild-type mice resulted in the stimulation of cell growth. On the other hand, administration of PPARgamma-antagonist showed the cell death and apoptosis of NSCs. These results may indicate that PPARgamma plays an important role during the early stage of the development of the central nervous system.

The effect of ozagrel sodium on photochemical thrombosis in rat: therapeutic window and combined therapy with heparin sodium

The therapeutic efficacy of ozagrel sodium (ozagrel), alone and in combination with heparin, and its therapeutic time window were studied in a photochemically induced thrombotic cerebral infarction rat model. Cerebral artery thrombosis was induced by irradiating the brain with green light through intact skull using rose bengal as the photosensitizing dye. One set of animals was treated immediately after thrombosis with (1) vehicle, (2) 10 mg/kg ozagrel in saline, intravenously (i.v.), (3) 150 U/kg unfractioned heparin, subcutaneously (s.c.), or (4) ozagrel, i.v. plus heparin, s.c. Infarct volume was significantly smaller and edema was reduced in the ozagrel-treated groups compared to the vehicle-treated group; heparin did not convey additional benefit. In another set of animals, rats were given either vehicle or 10 mg/kg ozagrel in saline, i.v., 60 min or 120 min after induction of thrombosis. Ozagrel reduced infarct volume, but its effect diminished with delayed administration. The therapeutic window was determined to be less than 60 minutes after induction of thrombosis.

A novel guinea pig model with cyclic flow reductions following thrombotic cerebral ischemia

Cyclic flow reductions (CFRs), a phenomenon indicated with repeating rethrombosis following thrombolysis in clotted vessel has been observed in coronal, carotid and popliteal arteries in various species when they were occluded with vessel damage, suggesting the presence of CFRs in the acute phase of stroke in man. Although much effort has been directed toward rethrombosis or ischemia-reperfusion injuries in acute strokes, a therapy for CFRs in strokes has not been established because of the lack of ideal animal models. We have established a novel guinea pig model with CFRs in the middle cerebral artery (MCA) using a photothrombotic technique, in which the MCA was spontaneously recanalized within 20 min after the first occlusion with subsequent CFRs. We also investigated the effects of antiplatelet agents and the anticoagulant heparin using this model. All tested antiplatelet agents inhibited CFRs, whereas an anticoagulant did not. These results show that this model is unique with respect to its development of MCA cyclic flow reductions, and may be suitable for investigating mechanisms and therapeutic reagents of CFRs in the MCA.

A combined treatment with tacrolimus (FK506) and recombinant tissue plasminogen activator for thrombotic focal cerebral ischemia in rats: increased neuroprotective efficacy and extended therapeutic time window

The authors evaluated the therapeutic efficacy of tacrolimus (FK506), administered alone or in combination with recombinant tissue plasminogen activator (t-PA), on brain infarction following thrombotic middle cerebral artery (MCA) occlusion. Thrombotic occlusion of the MCA was induced by a photochemical reaction between rose bengal and green light in Sprague-Dawley rats, and the volume of ischemic brain damage was determined 24 hours later. Intravenous administration of tacrolimus or t-PA dose-dependently reduced the volume of ischemic brain infarction, whether administered immediately or 1 hour after MCA occlusion. When tacrolimus or t-PA was administered 2 hours after MCA occlusion, each drug showed a tendency to reduce ischemic brain damage. However, combined treatment with both drugs resulted in a significant reduction in ischemic brain damage. On administration 3 hours after MCA occlusion, tacrolimus alone showed no effect, and t-PA tended to worsen ischemic brain damage. However, the combined treatment with both drugs not only ameliorated the worsening trend seen with t-PA alone, but also tended to reduce ischemic brain damage. In conclusion, tacrolimus, used in combination with t-PA, augmented therapeutic efficacy on brain damage associated with focal ischemia and extended the therapeutic time window compared to single-drug treatments.

Effect of TTC-909 in a middle cerebral artery thrombosis model in stroke-prone spontaneously hypertensive rats

We investigated the effect of TTC-909, a preparation of the stable prostaglandin I(2) analogue clinprost (isocarbacyclin methylester; methyl 5-[(1S,5S,6R,7R)-7-hydroxy-6-[(E)-(S)-3-hydroxy-1-octenyl] bicyclo[3.3.0]oct-2-en-3-yl] pentanoate) incorporated into lipid microspheres, on infarct volume 24 h after photochemically induced thrombotic occlusion of the middle cerebral artery in stroke-prone spontaneously hypertensive rats (SHR). Under anesthesia, the photosensitizing dye rose bengal (20 mg/kg) was administered intravenously and photoirradiation with green light (wavelength 540 nm) on the middle cerebral artery above the rhinal fissure was achieved using a xenon lamp for 10 min. Infarct volume 24 h after the photochemically induced thrombotic occlusion of the middle cerebral artery was significantly larger in stroke-prone SHR than in Wistar rats. When TTC-909 in doses of 100, 300 and 900 ng/kg/h was intravenously infused for 3 h, starting immediately after the end of the 10-min photoirradiation, the infarct volume was dose-dependently reduced and was statistically significant at a dose of 900 ng/kg/h (p < 0.05). Ozagrel, a thromboxane A(2) synthetase inhibitor, significantly reduced the infarct volume. The model of photochemically induced thrombotic occlusion of the middle cerebral artery in stroke-prone SHR is very useful, because the cerebral infarction is large enough and reproducible. TTC-909 may be effective for the treatment of acute ischemic stroke.

SM-20220, a Na(+)/H(+) exchanger inhibitor: effects on ischemic brain damage through edema and neutrophil accumulation in a rat middle cerebral artery occlusion model

The Na(+)/H(+) exchanger (NHE) is activated during ischemia-reperfusion in an effort to restore intracellular pH to normal levels. The NHE is recognized to exist as a distinct protein in the plasma membranes of a variety of cells. We investigated the pharmacological effects of a Na(+)/H(+) exchanger inhibitor, SM-20220 (N-(aminoiminomethyl)-1-methyl-1-H-indole-2-carboxamide methanesulfonate), on ischemic brain damage, edema and neutrophil accumulation at 72 h after middle cerebral artery (MCA) occlusion in a rat MCA occlusion model. SM-20220 was intravenously administered as a bolus injection immediately after occlusion, followed by a continuous infusion over 2.5 h. At 72 h after occlusion, the infract area was measured using hematoxylin-eosin staining and, using the same slices, neutrophils in the brain were immuno-stained with anti-myeloperoxidase (n=11). In a separate study, rat behavior was scored and scaled, and brains removed for the determination of water content by the dry-weight method. SM-20220 significantly (P<0.05) attenuated cerebral infarct volume, water content, and the neutrophil accumulation at 72 h after the MCA occlusion, and ameliorated neurological deficits. SM-20220, an NHE inhibitor prevented the progress of cerebral ischemic damage and edema following MCA occlusion in rats though a possible mechanism that may be due to the inhibition of neutrophil accumulation. The NHE in neutrophils may enhance the progress of cerebral damage following cerebral ischemia-reperfusion.

Tissue-type plasminogen activator has paradoxical roles in focal cerebral ischemic injury by thrombotic middle cerebral artery occlusion with mild or severe photochemical damage in mice

The role of endogenous tissue-type plasminogen activator (tPA) in focal cerebral ischemic injury (FCII) after middle cerebral artery occlusion was studied using tPA gene-deficient (KO) mice and their wild-type (WT) littermates. The middle cerebral artery was occluded by thrombi induced by three different intensities of photochemical damage, a method that was newly introduced in mice. In both WT and KO mice, the intensity-dependent increase of FCII size was observed. The FCII size in tPA WT mice was smaller than in KO mice in cases of mild damage, whereas the FCII size was larger in WT mice than in KO mice in cases of severe damage. There was no difference in FCII size between WT and KO mice in cases of moderate damage. The number of microthrombi also increased with damage intensity in both WT and KO mice, but was less in WT mice at all intensities of damage. The results support the validity of the model of thrombotic occlusion by photochemical damage in mice, and suggest that endogenous tPA protects FCII through thrombolytic action on transient occlusion of middle cerebral artery with mild damage, but deteriorates on persistent occlusion with severe damage.

Combining antiplatelet and thrombolytic therapies for stroke

Pharmacological therapy for acute nonhaemorrhagic stroke has become a reality over the last 5 years. Mechanistically, both thrombolytic (tissue plasminogen activator and urokinase) and antiplatelet (aspirin) monotherapy have demonstrated efficacy. However, unintended actions limit the extent of clinical improvement in each circumstance. For example, in addition to excess bleeding, tissue plasminogen activator therapy has been associated with complement activation, neuronal toxicity and laminin degradation, while aspirin may reduce nitric oxide synthase activity and cerebral blood flow. Attention is now directed toward improving the therapeutic index for each class of agents. Generally, while thrombolytic therapy is focused on developing agents with greater fibrin specificity and safety (that is, a reduction in intracranial haemorrhage rate), the development of antiplatelet agents is primarily focused on achieving greater potency. The latter is being investigated by combining agents with different mechanisms (aspirin and dipyridamole, aspirin and clopidogrel) as well as agents designed to block the glycoprotein IIb/IIIa receptor, the final common pathway for platelet aggregation. Thus, combination therapy using both thrombolytic and antiplatelet agents will further attempt to improve the therapeutic index by increasing potency and improving the safety profile. Anecdotal case studies support the merits of this approach and are consistent with the data reported for myocardial ischaemia and interventional strategies. It is anticipated that drug therapy directed at both thrombolytic and antiplatelet targets will ultimately result in a widened therapeutic window that will allow acute stroke therapy to be administrated to a much greater number of patients than is currently possible.

A novel MCA occlusion model of photothrombotic ischemia with cyclic flow reductions: development of cerebral hemorrhage induced by heparin

Intracerebral hemorrhage is the major complication associated with antithrombotic and thrombolytic therapy. Despite efforts directed toward achieving hemorrhagic infarction, an ideal animal model of cerebral hemorrhage has not yet to be established. Using the photothrombotic technique in rabbits, we developed a model of cerebral hemorrhage by inducing cyclic flow reductions in the middle cerebral artery (MCA). Furthermore, the hemorrhage increased 4-fold after infusion of heparin at a dose prolonging activated partial thromboplastin time by about three times that of control animals. The photothrombotic occlusion of the MCA is based on a thrombosis induced by endothelial injury through singlet oxygen produced by Rose Bengal injection and green light irradiation (Acta Neuropathol. 72 (1987) 315; Acta Neuropathol. 72 (1987) 326; J. Pharmacol. Toxicol. Methods. 29 (1993) 165). Using a pulse Doppler flowmeter, spontaneous reperfusion of the MCA after the thrombotic occlusion following cyclic flow reductions was observed within 2 h in the majority of animals. This model is unusual with respect to the development of clinical stroke, because of the MCA cyclic flow reductions. Thus it is different from permanent or ischemia/reperfusion MCA occlusion in rodents and may be suitable for studying hemorrhagic risks associated with the use of antithrombotic agents.

Platelet adhesion and arteriolar dilation in the photothrombosis: observation with the rat closed cranial and spinal windows

The mechanism of cerebral infarction, in which thrombus formation and platelet-endothelium interaction play an important part, have not yet been clearly elucidated in vivo. The aim of this study was to observe rolling and adherent platelets and to analyze adherent leukocytes and vessel diameter change in vivo using a photothrombotic vessel occlusion model.A photothrombosis, which is mediated by free radicals, was induced in male Wistar rats in the presence of a photosensitizing dye (Photofrin II) and exposure to a filtered light. Rhodamine 6G-labeled platelets and leukocytes were visualized with intravital fluorescence videomicroscopy through a closed cranial or spinal window. The vessel diameter, photothrombosis and leukocyte adhesion were analyzed. Rolling and adherent platelets were observed during irradiation through the cerebral and spinal window. Before the platelets were recognized, the irradiated arteriole dilated significantly. After the photochemical occlusion of an arteriole, other arterioles also dilated and the adherent leukocytes increased in the venules. The photothrombosis were almost completely composed of platelets according to electron microscopic analysis. The arteriolar dilation rate and the number of adherent leukocytes in the cerebrum were greater than those in the spinal cord. By combining the photochemical thrombus formation and the fluorescence microscope techniques, we were able for the first time to observe rolling and adherent platelets and microvascular responses during photothrombosis in the cerebral and spinal microvasculature. It is suggested that free radicals, which can lead to platelet aggregation, play an important role as a cerebral vasodilator. This model is useful for cerebral and spinal microcirculatory analysis to investigate the platelet-endothelium interaction, the platelet aggregation and the effect of free radicals on cerebral and spinal microcirculation.

Generation of a constitutively active fragment of PKN in microglia/macrophages after middle cerebral artery occlusion in rats

PKN is a fatty acid- and Rho-activated serine/threonine kinase, which has a catalytic domain highly homologous to that of protein kinase C (PKC). Recent studies have demonstrated that PKN is proteolytically cleaved after apoptotic stimulation and then a constitutively active 55-kDa fragment is generated. However, the role of the 55-kDa fragment are poorly understood. Adult Sprague-Dawley (SD) rats underwent middle cerebral artery occlusion (MCAO), and the temporal and spatial changes in the fragmentation of PKN and of PKC delta were examined by immunoblotting. No proteolytic fragment of PKC delta (about 40 kDa) was detected. The 55-kDa fragment of PKN appeared transiently from 3 days after MCAO at the ipsilateral normal cortex. At the boundary zone of infarction, the 55-kDa fragment was markedly induced from day 5 then peaked on day 21 and persisted until day 28. Analysis of anti-phosphoserine immunoprecipitates with an anti-PKN antibody revealed phosphorylation of the 55-kDa band. Double staining for PKN and Ox42 was used to examine the source of the 55-kDa fragment. PKN immunoreactivity was significantly increased in Ox42-positive cells (microglia/hematogenous macrophages). No DNA laddering and only a few terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL)-positive cells were observed on day 14 in despite of the high level appearance of the 55-kDa band. These results suggest that the constitutively active 55-kDa fragment of PKN does not contribute to apoptosis, but may contribute to a function of microglia/macrophages.

Cerebral hemorrhage due to heparin limits its neuroprotective effects: studies in a rabbit model of photothrombotic middle cerebral artery occlusion

We investigated the efficacy of heparin on cerebral ischemic damage in a rabbit model of middle cerebral artery (MCA) photothrombosis and in the same model, cerebral hemorrhage induced by heparin as its side effect was also investigated. Using a photothrombosis model in rabbits, 38 animals were divided into four groups, heparin low-dose I and II, heparin high-dose and vehicle. In heparin low-dose I (n=10) or II (n=7), heparin was administered for 23.5 or 22 h, respectively, starting 30 or 120 min after the start of photo-irradiation to induce thrombosis. In high-dose (n=7), heparin was administered 30 min after the start of photo-irradiation for 23.5 h. In the vehicle treated group (control), 14 animals were infused continuously with saline for 23.5 h. Heparin at low and high doses prolonged Activated partial thromboplastin time (aPTT) by about 3 and 10 times compared with control group. The results show that cerebral hemorrhage was present in all animals, gross hemorrhage was observed in one animal each of the heparin low-dose I and high-dose groups, and in three animals of the heparin low-dose II group, while no gross hemorrhage was observed in control group. In heparin low-dose I, the size of cerebral infarction was significantly (P<0.01) reduced and neurological deficits were significantly (P<0.01) improved. In contrast, in heparin high-dose, the infarct size significantly increased, especially in the cortex (P<0.0001), and neurological deficits were significantly (P<0.01) worsened. In heparin low-dose II, the size of cerebral hemorrhage significantly (P<0.001) increased compared with the control group. In conclusion, using a photothrombotic model in the rabbit MCA, we have investigated the antithrombotic benefits and hemorrhagic risks associated with heparin. Of unique feature of our model is the fact that in a single animal model, we could evaluate doses of heparin which reduce cerebral infarction and doses which can promote cerebral hemorrhage. This model can be extended to determine both benefits and risks of antithrombotic agents.

Changes in local cerebral blood flow in photochemically induced thrombotic occlusion model in rats

We demonstrated earlier that in a photochemically induced thrombotic occlusion model, a reperfusion-like phenomenon may be involved in the progress of brain damage. Therefore, we now investigated changes in local cerebral blood flow in a photochemical model compared with changes in a thermocoagulated occlusion model, using autoradiography. At 5 min, and 3, 6 and 24 h after middle cerebral artery occlusion, local cerebral blood flow was measured by intravenous injection of 4-iodo[N-methyl-14C]antipyrine (20 mu Ci). In the ischemic core zone, the reduction in blood flow was similar in the two models. However, blood flow in the ischemic border zone in the photochemical model decreased transiently in the third hour after ischemia and then increased again, while the blood flow in a thermocoagulated model continued to decrease. Time courses of brain damage formation in both models were no different up to 24 h. These findings suggest that the transient reduction in cerebral blood flow in the third hour following ischemia may contribute to a reperfusion-like phenomenon in a photochemical model.