Attenuation of ketamine-induced impairment in verbal learning and memory in healthy volunteers by the AMPA receptor potentiator PF-04958242.

There is a need to develop treatments for cognitive impairment associated with schizophrenia (CIAS). The significant role played by N-methyl-d-aspartate receptors (NMDARs) in both the pathophysiology of schizophrenia and in neuronal plasticity suggests that facilitation of NMDAR function might ameliorate CIAS. One strategy to correct NMDAR hypofunction is to stimulate α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) as AMPAR and NMDAR functioning are coupled and interdependent. In rats and nonhuman primates (NHP), AMPAR potentiators reduce spatial working memory deficits caused by the nonselective NMDAR antagonist ketamine. The current study assessed whether the AMPAR potentiator PF-04958242 would attenuate ketamine-induced deficits in verbal learning and memory in humans. Healthy male subjects (n=29) participated in two randomized treatment periods of daily placebo or PF-04958242 for 5 days separated by a washout period. On day 5 of each treatment period, subjects underwent a ketamine infusion for 75 min during which the effects of PF-04958242/placebo were assessed on ketamine-induced: (1) impairments in verbal learning and recall measured by the Hopkins Verbal Learning Test; (2) impairments in working memory on a CogState battery; and (3) psychotomimetic effects measured by the Positive and Negative Syndrome Scale and Clinician-Administered Dissociative Symptoms Scale. PF-04958242 significantly reduced ketamine-induced impairments in immediate recall and the 2-Back and spatial working memory tasks (CogState Battery), without significantly attenuating ketamine-induced psychotomimetic effects. There were no pharmacokinetic interactions between PF-04958242 and ketamine. Furthermore, PF-04958242 was well tolerated. 'High-impact' AMPAR potentiators like PF-04958242 may have a role in the treatment of the cognitive symptoms, but not the positive or negative symptoms, associated with schizophrenia. The excellent concordance between the preclinical (rat, NHP) and human studies with PF-04958242, and in silico modeling of AMPAR-NMDAR interactions in the hippocampus, highlights the translational value of this study.

Report of the task force on designing clinical trials in early (predementia) AD.

BACKGROUND: A large number of promising candidate disease-modifying treatments for Alzheimer disease (AD) continue to advance into phase II and phase III testing. However, most completed trials have failed to demonstrate efficacy, and there is growing concern that methodologic difficulties may contribute to these clinical trial failures. The optimal time to intervene with such treatments is probably in the years prior to the onset of dementia, before the neuropathology has progressed to the advanced stage corresponding to clinical dementia. METHOD: An international task force of individuals from academia, industry, nonprofit foundations, and regulatory agencies was convened to discuss optimal trial design in early (predementia) AD. RESULTS: General consensus was reached on key principles involving the scope of the AD diagnosis, the selection of subjects for trials, outcome measures, and analytical methods. CONCLUSION: A consensus has been achieved in support of the testing of candidate treatments in the early (predementia) AD population.

The effect of vasodilators on aspirin-induced antagonism of t-PA thrombolysis.

Although i.v. t-PA has proven successful in reducing neurologic deficits in acute ischemic stroke, the disadvantages of a narrow therapeutic time window and the failure of thrombolysis in more than 50% of patients treated have necessitated an examination of adjuvant therapies to improve the rate of thrombolysis. Experimentally, the combination of aspirin therapy with t-PA has resulted in a paradoxical antagonism of thrombolysis. Reversal of this antagonism with nitric oxide (NO) donors suggested that aspirin may inhibit/ antagonize NO-related mechanisms. Using this rabbit model of thromboembolic stroke, this hypothesis is now expanded to compare two clinically relevant anti-hypertensive agents, atenolol (NO-dependent) and hydralazine (NO-independent), for their ability to improve t-PA-mediated clot lysis following aspirin pre-treatment. Thirty rabbits (10 per group) were pre-treated with aspirin (20mg kg(-1), i.v.) and then randomized to receive either vehicle, atenolol (20 microg kg(-1) h(-1), i.v.) or hydralazine (10 microg kg(-1) min(-1), i.v.) beginning 30 min following autologous clot embolization. All rabbits then received t-PA (6.3 mg kg(-1), i.v.) beginning 1 h after embolization, with completion of the protocol 4 h after embolization. Aspirin therapy reduced regional cerebral blood flow (rCBF) from 82.8m +/- 4.7 to 62.5 +/- 6.6 (n = 30; p = 0.0005). In the aspirin control group only 30% (3 of 10) rabbits demonstrated complete clot lysis, whereas the combined atenolol (60%) and hydralazine (70%) groups experienced a clot lysis rate of 65% (13 of 20 rabbits), similar to clot lysis rates previously observed with t-PA alone. In a separate series of experiments, all agents able to reverse aspirin antagonism of thrombolysis demonstrated an improvement in rCBF, suggesting a common mechanism for this diverse group of agents in reversing aspirin's antagonism of thrombolysis.

The QT interval.

The effects of disease states and therapeutic drugs on the QT interval have been extensively studied in an attempt to understand the relationship between QT and the risk of torsade de pointes and sudden cardiac death. Differences in heart rate correction methods, electrocardiogram lead placement, and other internal (eg, genetic, physiologic) and external (eg, food, time of day) factors have confounded the interpretation of this relationship. A comprehensive review of the epidemiologic literature suggests that the corrected QT interval (QTc) is an important but imprecise marker of cardiovascular disease. The association between QTc prolongation and mortality has been identified in patients with cardiac disease but is unclear in patients without cardiac disease. Drug-related prolongation of QTc can clearly increase the risk of torsade de pointes, but this arrhythmia is rarely associated with a QTc of less than 500 ms. It also appears that noncardiac drugs that are associated with QTc prolongation are not identical in their proarrhythmic capacities and that increased exposure via clinically significant drug interactions is a major contributor to the liability of noncardiac drug-induced arrhythmia. Recognition of the aforementioned variables in conjunction with careful QTc measurements assists in establishing a more precise benefit-risk ratio for a specific drug therapy or for arrhythmia risk associated with various pathophysiologic or genetic states.

16(R)-hydroxyeicosatetraenoic acid, a novel cytochrome P450 product of arachidonic acid, suppresses activation of human polymorphonuclear leukocyte and reduces intracranial pressure in a rabbit model of thromboembolic stroke.

OBJECTIVE: Activated polymorphonuclear leukocytes (PMNs) have been suggested to contribute to the development of increased intracranial pressure (ICP). We recently demonstrated that human PMNs produce a novel cytochrome P450-derived arachidonic acid metabolite, 1 6(R)-hydroxyeicosatetraenoic acid [16(R)-HETE], that modulates their function. It was thus of interest to examine this novel mediator in an acute stroke model. METHODS: 16-HETE was assessed initially in a variety of human PMN and platelet in vitro assays and subsequently in an established rabbit model of thromboembolic stroke. A total of 50 rabbits completed a randomized, blinded, four-arm study, receiving 16(R)-HETE, tissue plasminogen activator, both, or neither. Experiments were completed 7 hours after autologous clot embolization. The primary end point for efficacy was the suppression of increased ICP. RESULTS: In in vitro assays, 16(R)-HETE selectively inhibited human PMN adhesion and aggregation and leukotriene B4 synthesis. In the thromboembolic stroke model, animals that received 16(R)-HETE demonstrated significant suppression of increased ICP (7.7 +/- 1.2 to 13.1 +/- 2.7 mm Hg, baseline versus final 7-h time point, mean +/- standard error), compared with either the vehicle-treated group (7.7 +/- 0.9 to 15.8 +/- 2.6 mm Hg) or the tissue plasminogen activator-treated group (7.6 +/- 0.6 to 13.7 +/- 2.1 mm Hg). The group that received the combination of 16(R)-HETE plus tissue plasminogen activator demonstrated no significant change in ICP for the duration of the protocol (8.6 +/- 0.6 to 11.1 +/- 1.2 mm Hg). CONCLUSION: 16(R)-HETE suppresses the development of increased ICP in a rabbit model of thromboembolic stroke and may serve as a novel therapeutic strategy in ischemic and inflammatory pathophysiological states.

Stroke: antithrombin versus antiplatelet therapy.

The success of thrombolytic therapy for acute stroke has demonstrated that neurologic outcome can be improved with timely treatment. However, the severely restricted use of thrombolytics has reinforced the need to develop alternative and complementary therapies. Antithrombin and antiplatelet agents represent promising therapeutic approaches for stroke management. Antiplatelet therapy has modestly improved outcome in both acute stroke (aspirin) and in secondary stroke prevention (aspirin with or without dipyridamole; adenosine receptor antagonists), although bleeding and other adverse events associated with antithrombin therapy have largely negated their potential benefit. These findings have prompted innovative solutions to the pharmacokinetic and pharmacodynamic challenges that are crucial to advancing these strategies for acute, primary and secondary stroke therapy. Currently, inhibitors of the platelet surface glycoprotein IIb/IIIa (GP IIb/IIIa, fibrinogen) receptor are being examined in clinical trials while antithrombin therapies focus on thrombin antagonists and inhibitors as well as inhibitors of Factor Xa. Further advances in stroke treatment will include combination therapies. Additionally, the successful design of future drug therapies will result from a more complete understanding of the activity of these agents not only on platelet function and the coagulation cascade, but also for their effects on the endothelium and within the brain parenchyma. The sum of these activities will allow for the maintenance of cerebral blood flow, blood-brain barrier integrity and neuronal function.

16(R)-hydroxy-5,8,11,14-eicosatetraenoic acid, a new arachidonate metabolite in human polymorphonuclear leukocytes.

Intact human polymorphonuclear leukocytes (PMNL) incubated with substimulatory amounts of arachidonic acid in the absence of a calcium ionophore formed four metabolites that were isolated by reverse-phase HPLC and characterized structurally by GC/MS. A major metabolite eluting as the most abundant peak of radioactivity lacked UV chromophores above 215 nm, and its formation was sensitive to 2-diethylaminoethyl-2,2-diphenylvalerate hydrochloride (SKF525A) but not 3-amino-1-[m(trifluoromethyl)phenyl]-2-pyrazoline (BW755C), suggesting that it was likely to be a product of cytochrome P450. The GC/MS analysis revealed the presence of two components: 20-hydroxy-5,8,11,14-eicosatetraenoic acid (20-HETE) and 16-hydroxy-5,8,11,14-eicosatetraenoic acid (16-HETE) in an approximate ratio of 4:1. The minor metabolites were identified as 15-HETE and 5-HETE. Although 20-HETE has been observed previously as a product of arachidonic acid metabolism in PMNL, the occurrence of 16-HETE was a novel finding. The stereochemistry of the hydroxyl group in PMNL-derived 16-HETE was established by analysis of 1-pentafluorobenzyl-16-naphthoyl derivatives on a chiral-phase chromatographic column and comparison with authentic synthetic stereoisomers. The PMNL-derived radioactive metabolite co-eluted with the synthetic 16(R)-HETE stereoisomer. Analysis of the total lipid extracts from intact PMNL followed by mild alkaline hydrolysis resulted in detectable amounts of 16-HETE (108+/-26 pg/10(8) cells) and 20-HETE (341+/-69 pg/10(8) cells), which suggested that these HETEs were formed from endogenous arachidonic acid and esterified within PMNL lipids. Thus, in contrast to calcium ionophore-stimulated neutrophils that generate large amounts of 5-lipoxygenase products, the intact PMNL generate 20-HETE and 16(R)-HETE via a cytochrome P450 omega- and omega-4 oxygenase(s).

Aspirin reduces experimental cerebral blood flow in vivo.

Aspirin therapy for stroke prophylaxis in low risk patients has paradoxically demonstrated an increased risk of ischemic stroke in several studies. Moreover, the MAST-Italy trial reported a near doubling of mortality with the addition of aspirin to thrombolytics while experimentally, we have noted that aspirin antagonizes t-PA-mediated clot lysis. The mechanisms responsible for these observations is unclear. Of interest, few studies have examined the effect of aspirin on cerebral blood flow (CBF). The objective of this study was to examine the acute effect of high dose aspirin on CBF in a rabbit model. Mean arterial pressure, arterial blood gases, and core and brain temperature were controlled throughout the protocol. CBF, measured by the technique of hydrogen clearance using Platinum-Iridium flow probes, was measured before and 20 min following aspirin administration (20 mg kg-1 i.v.) in a cohort of 50 rabbits and compared to rabbits receiving vehicle (n = 19). Following aspirin therapy, CBF (cc/100 g-1 min-1) was reduced from 80.8 +/- 27.4 to 65.1 +/- 31.7 (mean +/- SD), a reduction to 80.4 +/- 21.3% of baseline (p < 0.00001, t-test), whereas CBF in the control group remained unchanged (81.0 +/- 25.4 vs. 77.5 +/- 24.0, mean +/- SD). Thus aspirin acutely reduced CBF by approximately 20% in a rabbit model, perhaps related to inhibitory effects on prostacyclin and/or nitric oxide. This result may help explain the possible increase in ischemic stroke seen in low risk patients on aspirin therapy. A reduction in CBF by aspirin may also assist in understanding the antagonism of t-PA-mediated clot lysis by aspirin seen in our rabbit model of thromboembolic stroke, particularly since all agents which share the ability to reverse this antagonism (nitric oxide donors, beta blockers, hydralazine, prostacyclin) also increase CBF by approximately 20%. Future strategies for 'antiplatelet' therapy may benefit from using agents which do not adversely affect CBF.

Complement depletion does not reduce brain injury in a rabbit model of thromboembolic stroke.

The contribution of the complement system to cerebral ischemic and ischemia/reperfusion injury was examined in a rabbit model of thromboembolic stroke by delivery of an autologous clot embolus to the intracranial circulation via the internal carotid artery. A two-by-two factorial design was employed to study the impact of complement depletion via pretreatment with cobra venom factor (CVF, 100 U/kg i.v.) in the setting of permanent (without tissue plasminogen activator; t-PA) and transient (with t-PA) cerebral ischemia. Thirty-two New Zealand white rabbits were assigned to one of four groups (n=8, each group): control without t-PA, control with t-PA, CVF without t-PA and CVF with t-PA. In the complement intact animals, t-PA administration resulted in an approximate 30% reduction in infarct size when compared to the group not receiving t-PA (20.4+/-6.6% of hemisphere area vs. 30.1+/-7.2%; mean+/-SEM). However, infarct sizes in the complement depleted rabbits, with (30.7+/-8.2%) or without (30.2+/-7.9%) t-PA, were no different from the control group receiving no therapy. Similarly, no difference in regional cerebral blood flow or final intracranial pressure values was noted between any of the four groups. Complement activation does not appear to be a primary contributor to brain injury in acute thromboembolic stroke.

Antiplatelet therapy in acute cerebral ischemia.

BACKGROUND: Improved recognition of stroke signs and symptoms has paralleled the development of pharmacological strategies that may be examined to reduce stroke mortality and morbidity. Presently, tissue plasminogen activator is the only therapy that significantly improves outcome in acute stroke, with no agent demonstrating a significant reduction in mortality. SUMMARY OF REVIEW: Antiplatelet agents are a heterogenous class of drugs that have been successfully used for more than 2 decades in secondary stroke prevention. These agents include aspirin, with or without dipyridamole, and more recently, the adenosine antagonists ticlopidine and clopidogrel. However, studies of the use of antiplatelet agents within 48 hours of the ictus have examined only aspirin. Only 1 study, the Multicentre Acute Stroke Trial-Italy (MAST-I), entered patients within 6 hours of the ictus. These data suggest that an improvement in mortality may be related to the speed of administration. No significant adverse events were noted with early antiplatelet monotherapy. However, MAST-I did note a significant increase in early mortality in patients receiving aspirin plus streptokinase, a finding not adequately explained by an increase in the intracranial hemorrhage rate. CONCLUSIONS: The use of antiplatelet therapy in acute stroke, clinical or experimental, has only recently received attention. It is likely that the use of antiplatelet agents for acute stroke therapy will be less restrictive than that currently seen for thrombolytics. Future studies should include an examination of those agents that have previously demonstrated efficacy in secondary stroke prevention, most notably, aspirin. The recognition that all platelet stimuli share a final common pathway that is dependent on the surface glycoprotein IIb/IIIa (fibrinogen) receptor has resulted in the development of various agents which block this receptor and are currently the focus for clinical trials. The role of nitric oxide in stroke therapy will depend on minimizing the hypotensive side effects of this agent. Stroke models are needed to provide preliminary data on the efficacy of antiplatelet therapy, especially as relates to the interaction of antiplatelet agents with thrombolytics.

Preoperative volume expansion improves tolerance to carotid artery cross-clamping during endarterectomy.

OBJECTIVE: The benefit of carotid endarterectomy for carotid artery stenosis relates to both appropriate patient selection and careful surgical technique. Critical to the latter is the ability to afford intraoperative neuroprotection during carotid cross-clamping, although the optimal strategy to assure this protection remains debated. This report describes the impact of adding preoperative colloid volume expansion to a surgical algorithm that includes electroencephalographic (EEG) monitoring and barbiturate-induced burst suppression for EEG lateralization refractory to hypertension. METHODS: The incidence of ischemic EEG change during carotid cross-clamping was observed. The results of an initial series of patients (n = 45) reported before incorporation of volume expansion were compared with the results of the current series (n = 155) of carotid endarterectomies, which included preoperative volume expansion with 6% hetastarch (500 or 1000 cc). RESULTS: With preoperative volume expansion, there was a 40% decrease in the incidence of EEG lateralization during carotid cross-clamping (17.4 versus 28.9%, P < 0.05) and a 63% decrease in the EEG lateralization refractory to induced hypertension (5.8 versus 15.6%, P < 0.05). The combined perioperative stroke and death rate was 1.3%. CONCLUSION: These results support the use of preoperative colloid volume expansion in carotid endarterectomy as a means of increasing the cerebral tolerance to carotid cross-clamping.

Humanized anti-L-selectin monoclonal antibody DREG200 therapy in acute thromboembolic stroke.

Strategies directed against activated neutrophils have reduced ischemia-induced brain injury. However, therapies targeted specially against the neutrophil adhesion protein L-selectin have not yet been examined in stroke. This study therefore examined the effects of a monoclonal antibody directed against L-selectin in a rabbit model of thromboembolic stroke with (n = 16) or without (n = 10) concomitant t-PA therapy. Rabbits received either the humanized monoclonal antibody DREG200 directed against the L-selectin receptor or humanized control monoclonal antibody HuDREG55 which does not bind to rabbit L-selectin in addition to t-PA therapy (n = 8, each group). HuDREG200 (2 mg kg-1 i.v.) was given as a bolus 3 h following clot embolization, followed immediately by a 2 h intravenous infusion of t-PA (6.3 mg kg-1. Without t-PA therapy rabbits received HuDREG200 (2 mgkg-1, i.v.; n = 5) or HuDREG55 (n = 5) 1 h following clot embolization. The group receiving HuDREG200 in addition to t-PA demonstrated a moderate improvement in brain infarct size (8.4 +/- 2.4 vs. 13.5 +/- 3.5, %hemisphere, mean +/- sem), ICP (final reading 10.0 +/- 1.6 vs. 12.4 +/- 3.0 torr) and restoration in regional cerebral blood flow (30.2 +/- 7.8 vs. 21.6 +/- 10.9 cc 100 g-1 min-1) when compared to t-PA therapy alone although statistical significance was not achieved. No efficacy was demonstrated in the group receiving HUDREG200 without concomitant t-PA therapy. The results suggest the addition of a humanized anti-L-selectin monoclonal antibody HuDREG200 in combination with t-PA may further improve outcome in acute thromboembolic stroke, although future studies are necessary to support these findings.

Nitric oxide reverses aspirin antagonism of t-PA thrombolysis in a rabbit model of thromboembolic stroke.

Randomized trials of thrombolytic therapy in stroke have reported an improvement in neurologic outcome; however, the addition of aspirin has resulted in a significant increase in mortality and antagonism of clot lysis in clinical and animal studies, respectively. This finding is in contradistinction to the known synergy in mortality reduction for aspirin and thrombolytics in myocardial infarction. It is hypothesized that aspirin antagonism of clot lysis is related to inhibition of nitric oxide (NO) and may be reversed by providing a source of NO. Twenty rabbits were treated with aspirin (20 mg/kg, i.v.) prior to internal carotid clot embolization. One-half hour following embolization, rabbits were randomized to receive vehicle (n = 5), the NO precursor L-arginine (300 mg/kg, i.v. bolus at 0.5 and 2.5 h postembolus; n = 5), or a nitric oxide donor (nitroprusside, 1 mg/kg/h, i.a., or nitroglycerin, 10 microg/kg/min, i.v., n = 5 each agent). Tissue plasminogen activator (t-PA) (6.3 mg/kg) was administered from 1 to 3 h after embolization. Lysis of the tin-tagged clot was followed with serial X rays and gross examination. No rabbit in the control group experienced complete clot lysis. However, 2 of 5 rabbits in the L-arginine group and 6 of 10 rabbits in the nitric oxide donor (nitroprusside and nitroglycerin) groups noted complete clot lysis (P < 0.05, Fisher exact test). Thus, administration of an NO donor (nitroglycerin or nitroprusside) and, to a lesser extent L-arginine, reversed aspirin's antagonism of t-PA thrombolysis. This study may help explain the discrepant results seen with aspirin and thrombolytics.

Delayed adjuvant therapy with the 21-aminosteroid U74006F and the anion channel blocker L644-711 does not improve outcome following thrombolytic therapy in a rabbit model of thromboembolic stroke.

BACKGROUND: Both the 21-aminosteroid U74006F, a potent inhibitor of lipid peroxidation, and L644-711, an anion channel blocker that inhibits both neutrophil and astrocyte function, have been previously shown to reduce brain injury in pretreatment paradigms of cerebral ischemia. It was therefore of interest to examine the effect of these agents in combination, when given on a delayed basis as adjuvants to thrombolytic therapy in a rabbit model of thromboembolic stroke. METHODS: Animals were mechanically ventilated and arterial blood gases controlled. Core and brain temperature, intracranial pressure, and mean arterial pressure were continuously monitored. Regional cerebral blood flow and hematocrit were measured hourly. Blood samples were taken to measure neutrophil (aggregation and chemiluminescence) and platelet (aggregation) activity. Following delivery of an autologous clot via the carotid artery, all experiments were continued for an 8-hour period. U74006F (3 mg/kg I.V.) and L644,711 (12 mg/kg I.V.) or their vehicle control (n = 8, each group) were given 3.5 hours following autologous clot embolization. Both groups received tissue-type plasminogen activator (t-PA) (6.3 mg/kg I.V.), beginning 4 hours following thromboembolic stroke and continuing over a 2-hour infusion period. Infarct size was determined following staining and image analysis. RESULTS: In the L644,711/U74006F group, neutrophil chemiluminescence was reduced following drug therapy; however, there were no significant differences between groups regarding infarct size (50.3 +/- 8.7 vs. 49.9 +/- 10.6, treatment vs. t-PA control, mean +/- SEM), or in regional cerebral blood flow or intracranial pressure over time. CONCLUSIONS: It is concluded that prolonged (3.5 hours) delay of the initiation of therapy with the anion channel blocker L644,711 and the 21-aminosteroid U74006F fails to further reduce brain injury when given in combination with tissue plasminogen activator in a rabbit model of thromboembolic stroke.

Activation of complement by tissue plasminogen activator, but not acute cerebral ischemia, in a rabbit model of thromboembolic stroke.

Although complement activation is associated with tissue injury during inflammatory and ischemic states, complement activation in states of acute cerebral ischemia before and after administration of tissue plasminogen activator (TPA) has not yet been examined and is the focus of this investigation. Twenty-four New Zealand White rabbits weighing 3 to 3.5 kg were used for this study. Of these, 20 were subjected to intracranial autologous clot embolization via the internal carotid artery. Three hours postembolization, rabbits received an intravenous infusion of TPA (6.3 mg/kg, 20% bolus with the remainder infused over a 2-hour interval; 12 animals) or vehicle (eight animals). All animals were observed for a total of 7 or 8 hours postembolization. These two groups were compared to a cohort undergoing sham operation with subsequent TPA infusion (four animals). Plasma samples to quantify complement component C5 hemolytic activity (C5H5O) were obtained at the following time points: 30 minutes before and after clot embolization; 1 hour before and 1 hour after the initiation of therapy with TPA or vehicle and at the completion of the protocol; 7 to 8 hours after clot embolization. The C5 activation was not detected as the result of acute cerebral ischemia. However, animals receiving TPA with or without concomitant clot embolization exhibited C5 activation as assessed by a reduction in C5 hemolytic function, both 1 hour after initiation of TPA infusion (78.7 +/- 10.3% and 77.5 +/- 9.9% of baseline value, respectively; mean +/- standard error of the mean [SEM]) and at the end of the protocol, 2 hours after the completion of the TPA infusion (72.5 +/- 8.8% and 53.3 +/- 8.1%, respectively; mean +/- SEM, p < 0.05, each group). This study supports the conclusion that TPA, but not acute cerebral ischemia, may activate the complement cascade in this rabbit model of thromboembolic stroke.

Neutrophil activation in acute human central nervous system injury.

The hypothesis that neutrophil activation exacerbates brain injury in acute stroke is currently receiving wide acceptance. However, the temporal relationship of neutrophil activation to the ischemic event in clinical states is not clear. Therefore, this study was undertaken to examine human neutrophil activation by the technique of luminol-dependent chemiluminescence in both acute bland and hemorrhagic stroke. Patients (bland, n = 18; hemorrhagic, n = 16) were entered into this study within six hours of the ictus. These results were compared to other clinical central nervous system insults: subarachnoid hemorrhage (n = 11), spinal trauma (n = 9) and isolated closed head injury (n = 19). All subjects were sampled upon presentation to the emergency room and 0.5, 1, 2, 3, 4 and 5 days following the event. Neutrophil activation, as determined by luminol-dependent chemiluminescence, was evident at day 1 following the ictus in the bland stroke group (p < 0.05), although this trend was not demonstrated for hemorrhagic stroke. Patients suffering a closed head injury demonstrated greater initial neutrophil activation with values being significantly lower than baseline at days 0.5 (p = 0.01) and 1 (p = 0.05). No significant change was demonstrated for the groups with spinal trauma or subarachnoid hemorrhage. These results support a role for neutrophil activation during various central nervous system insults and provide a temporal framework for considering drug therapy directed at transient suppression of neutrophil function.

Peroxynitrite augments fMLP-stimulated chemiluminescence by neutrophils in human whole blood.

The neutrophil respiratory burst was examined by the technique of luminol-dependent chemiluminescence (LDCL) triggered by submaximal concentrations of N-formyl-methionyl-leucyl-phenylalanine (fMLP) in diluted whole blood. We sought to identify the chemical species responsible for LDCL in whole blood, to examine the role of leukotriene B4 (LTB4) and other arachidonic acid metabolites as mediators of the fMLP signaling pathway, and to investigate the effect of peroxynitrite on this response. Both sodium azide and taurine significantly inhibited LDCL (93% inhibition with 100 microM azide, 52% inhibition with 10 mM taurine). More modest inhibition was seen with superoxide dismutase (SOD), catalase, the nitric oxide synthase inhibitor monomethyl-L-arginine (L-NMMA), and with inhibitors of the cyclooxygenase (indomethacin), lipoxygenase (AA-861; no effect), and cytochrome P-450 (SKF 525-A) pathways of arachidonic acid metabolism. The nitric oxide donor SIN-1 (1-100 microM) and peroxynitrite (10-300 microM) also augmented fMLP-induced LDCL. The augmentation seen with peroxynitrite and SIN-1 was attenuated by SOD. Despite the increase in LDCL, peroxynitrite caused a dose-related inhibition of fMLP-stimulated LTB4 release. In summary, our results indicate that (1) LDCL elicited by fMLP in diluted whole blood appears primarily mediated by hypochlorous acid derived from myeloperoxidase; (2) pretreatment with the nitric oxide donor SIN-1 or with peroxynitrite augments LDCL; and (3) LTB4 release does not contribute to fMLP-stimulated LDCL or in the modulation of LDCL by SIN-1 or peroxynitrite.

The effect of oral antiplatelet agents on tissue plasminogen activator-mediated thrombolysis in a rabbit model of thromboembolic stroke.

OBJECTIVE: The success of thrombolytic therapy in acute stroke relies on timely reperfusion. The current study examines the efficacy of antiplatelet agents as adjuvants for thrombolytic therapy. METHODS: Using an established rabbit model of clot embolization and a randomized blinded design, rabbits (n = 8 in each group) were orally pretreated daily for 5 days with adjuvant aspirin (1 mg/kg of body weight or 20 mg/kg), ticlopidine (100 mg/kg), or vehicle (sodium carbonate). On the 6th day, tissue plasminogen activator (6.3 mg/kg administered intravenously over 2 h), was initiated 1 hour after embolization. RESULTS: In all groups, cerebral blood flow (CBF) was reduced to < 10 ml/100 g/min immediately after clot embolization. After the initiation of tissue plasminogen activator (t-PA), there was significant restoration of CBF in the control (t-PA only) and ticlopidine groups (P < 0.05) only. Restoration of CBF generally correlated with brain infarct size (percent hemisphere, mean +/- standard error of the mean), which was 18.0 +/- 7.0 in the t-PA only group versus 11.0 +/- 3.3, 26.5 +/- 5.8, and 21.5 +/- 3.4 in the ticlopidine, low-dose aspirin, and high-dose aspirin groups, respectively (ticlopidine versus aspirin, P < 0.05). Clot lysis was identical in the control and ticlopidine groups, with 6 of 8 animals demonstrating complete clot lysis. Aspirin antagonized clot lysis in a dose-related manner, with low-and high-dose aspirin groups noting clot lysis in four of eight and two of eight animals, respectively. CONCLUSIONS: Pretreatment with ticlopidine significantly reduced brain infarct size when compared with aspirin treatment (P < 0.05). Moreover, whereas ticlopidine treatment did not affect clot lysis or CBF relative to t-PA alone, aspirin therapy resulted in antagonism of clot lysis and was associated with a more modest restoration of blood flow. This study provides a background for a more comprehensive understanding of the balance of thrombogenicity and thrombolysis and may assist in the development of novel therapies to expedite cerebrovascular patency and reduce ischemic and reperfusion-mediated neuronal injury.