Therapeutic strategies for the treatment of stroke

The use of the Chandler loop to examine the interaction potential of NXY-059 on the thrombolytic properties of rtPA on human thrombi in vitro

BACKGROUND AND PURPOSE

Recombinant tissue-type plasminogen activator (rtPA) is the only globally approved treatment for acute ischaemic stroke. Other potential treatments might be administered with rtPA, making it important to discover whether compounds interfere with rtPA-induced lysis. We evaluated methods for examining the effect of the neuroprotectant NXY-059 on the lytic property of rtPA.

EXPERIMENTAL APPROACH

Plasma clot formation and lysis in the presence of rtPA and NXY-059 was measured as the change in plasma turbidity. The effect of NXY-059 on rtPA-induced lysis was similarly assessed on preformed clots. Lysis of the thrombus formed in a Chandler loop measured release of fluorescent-tagged fibrinogen that had been incorporated during thrombus formation. Thrombi were exposed to both rtPA and NXY-059 throughout lysis in the presence of 80% autologous plasma and the release of label during lysis was measured.

KEY RESULTS

Data interpretation is limited in the clot lysis experiments because either the rtPA was present during clot formation or the drug was added to a clot formed in static conditions. In contrast, thrombi were formed in dynamic flow conditions in the Chandler loop and the time course of lysis in plasma was examined. rtPA increased thrombolysis and the antifibrinolytic trans-4-(aminomethyl) cyclohexane carboxylic acid (AMCA) inhibited lysis. Lysis induced by rtPA was unaltered by NXY-059.

CONCLUSIONS AND IMPLICATIONS

The Chandler loop method provides a reliable technique for examining the effect of compounds on rtPA-induced lysis in vitro and demonstrated that NXY-059 does not alter rtPA-induced lysis at clinically relevant concentrations of either drug.

Neuroprotective effects of free radical scavengers in stroke

Acute ischaemic stroke is a leading cause of death in the majority of industrialised countries and also in many developing countries. Free radicals are generated in the brain during ischaemic injury and these radicals are involved in the secondary injury processes. Several free radical scavengers have been developed and some of them have progressed into clinical trials. One of them, edaravone, has been approved by the regulatory authority in Japan for the treatment of stroke patients. Another scavenger, disodium 4-[(tert-butylimino)methyl] benzene-1,3-disulfonate N-oxide (NXY-059; disufenton), has demonstrated efficacy in a phase III clinical trial (SAINT [Stroke Acute Ischaemic NXY-059 Treatment study]-I) involving a large number of stroke patients. Unfortunately, SAINT II did not show efficacy in the treatment of stroke patients. The purpose of this article is to review the current development of antioxidant strategies, update recent findings for NXY-059 in the treatment of stroke patients, and discuss the future development of neuroprotective agents. Although the development of neuroprotective strategies for the treatment of stroke is challenging, progress in molecular and cellular neuroscience will uncover new information about stroke mechanisms, which should result in the realisation of neuroprotective therapy for this disease.

Carnosine is neuroprotective against permanent focal cerebral ischemia in mice

BACKGROUND AND PURPOSE

Carnosine is a naturally occurring dipeptide with multiple neuroprotective properties. In addition, it is well tolerated in high doses with minimal side effects. The purposes of this study were to determine whether carnosine is neuroprotective in permanent focal cerebral ischemia and to determine potential mechanisms of neuroprotection.

METHODS

We investigated the efficacy of carnosine in a mouse model of permanent focal cerebral ischemia. The effects of carnosine were investigated with respect to neuronal damage and infarct formation, endogenous antioxidant status, and matrix metalloproteinase activity.

RESULTS

Carnosine significantly decreased infarct size and neuronal damage when administered at time points both before and after the induction of ischemia. Carnosine also decreased reactive oxygen species levels in the ischemic brain, preserved normal glutathione levels, and decreased matrix metalloproteinase protein levels and activity.

CONCLUSIONS

Carnosine is neuroprotective in focal cerebral ischemia and appears to influence deleterious pathological processes that are activated after the onset of ischemia.

Identification, biological activity, and mechanism of the anti-ischemic quinolone analog

The quinolone analog SQ-4004 has been identified as a potentially excellent anti-ischemic agent, which exhibited highly potent efficacy in reducing infarct volume size in vivo rat MCAO model (32.1% at 0.01mg/kg) and potent cardioprotective effect at myocardial infarction in vivo model (26.6% at 0.01mg/kg) while it exhibited highly reduced anti-bacterial activity. The mechanistic study revealed that the anti-ischemic activity might exert via an anti-apoptotic pathway, which implies its therapeutic uses against the ischemic cell injuries including ischemic stroke and ischemic heart disease.

Neuroprotection: where to now?

Neuroprotection is an attractive potential therapy for acute ischemic stroke and is based on the concept of the ischemic cascade. However, therapeutic use of neuroprotectants in human stroke has proved more difficult than initially realized. The turning point was the finding that an apparently ideal neuroprotectant, NXY-059, was not neuroprotective in human stroke following a number of well-conducted clinical trials. In spite of these difficulties, research in neuroprotection should continue but in a greatly modified form. A number of important issues need to be addressed, ranging from the quality of experimental studies through to the demonstration of compounds reaching the target ischemic penumbra. An incremental approach to neuroprotection research is outlined, including the demonstration of efficacy in human cell cultures and tissues.

Neuroprotection and stroke: time for a compromise

In April 2007, there existed a repertory of 286 trials concerned with acute ischemic stroke on the Stroke Trials Registry (http://www.strokecenter.org/trials/), of which 209 trials were considered as complete (with no evidence of patient benefit unless one considers the much hard fought for and modest results of the tPA studies). Among other questions arising from such failures, one can wonder whether the plethora of pharmacological agents that exhibited neuroprotective properties in pre-clinical studies were selected for clinical trials entirely based upon their experimental efficacy. This mini-review will try to point out some of the weaknesses that could underline the failure of both researchers and clinicians involved in the field of stroke to obtain their ultimate goal--brain protection.

NXY-059 for the treatment of acute ischemic stroke

BACKGROUND

The free-radical-trapping agent NXY-059 showed promise as a neuroprotectant in the Stroke-Acute Ischemic NXY Treatment I (SAINT I) trial, reducing disability when given to patients who had acute ischemic stroke. We sought confirmation of efficacy in a second, larger trial.

METHODS

We enrolled 3306 patients with acute ischemic stroke in a randomized, double-blind trial to receive a 72-hour infusion of intravenous NXY-059 or placebo within 6 hours after the onset of stroke symptoms. Our primary end point was the distribution of disability scores on the modified Rankin scale at 90 days. We examined scores on neurologic and activities-of-daily-living scales as secondary end points. We also tested the hypothesis that NXY-059 would reduce alteplase-related intracranial hemorrhages.

RESULTS

The efficacy analysis was based on 3195 patients. Prognostic factors were well balanced between the treatment groups. Mortality was equal in the two groups, and adverse-event rates were similar. The distribution of scores on the modified Rankin scale did not differ between the group treated with NXY-059 (1588 patients) and the placebo group (1607 patients; P=0.33 by the Cochran-Mantel-Haenszel test; odds ratio for limiting disability, 0.94; 95% confidence interval [CI], 0.83 to 1.06). Analysis of categorized scores on the modified Rankin scale confirmed the lack of benefit: the odds ratio for trichotomization into modified Rankin scale scores of 0 to 1 versus 2 to 3 versus 4 to 6 was 0.92 (95% CI, 0.80 to 1.06). There was no evidence of efficacy for any of the secondary end points. Among patients treated with alteplase, there was no difference between the NXY-059 group and the placebo group in the frequency of symptomatic or asymptomatic hemorrhage.

CONCLUSIONS

NXY-059 is ineffective for the treatment of acute ischemic stroke within 6 hours after the onset of symptoms. (ClinicalTrials.gov number, NCT00061022 [ClinicalTrials.gov].)

A novel approach to screening for new neuroprotective compounds for the treatment of stroke

Despite the significant advances that have been made in understanding the pathophysiology of cerebral ischemia on the cellular and molecular level, only one drug, the thrombolytic tissue plasminogen activator (rt-PA), is approved by the FDA for use in patients with acute ischemic stroke. Therefore, there is a critical need for additional safe and effective treatments for stroke. In order to identify novel compounds that might be effective, we have developed a cell culture-based assay with death being an endpoint as a screening tool. We have performed an initial screening for potential neuroprotective drugs among a group of flavonoids by using the mouse hippocampal cell line, HT22, in combination with chemical ischemia. Further screens were provided by biochemical assays for ATP and glutathione, the major intracellular antioxidant, as well as for long-term induction of antioxidant proteins. Based upon the results of these screens, we tested the best flavonoid, fisetin, in the small clot embolism model of cerebral ischemia in rabbits. Fisetin significantly reduced the behavioral deficits following a stroke, providing proof of principle for this novel approach to identifying new compounds for the treatment of stroke.

Critical role of microvasculature basal lamina in ischemic brain injury

Cerebral vascular system can be divided into two categories: the macrovessels and microvessels. The microvessels consist of arterioles, capillaries and venules. There are three basic components in the microvasculature: endothelial cells, basal lamina and end-feet of astrocytes. The basal lamina is situated between the endothelial cells and the end-feet of astrocytes, and connects these two layers together. Damage to the basal lamina causes the dismantlement of microvascular wall structures, which in turn results in increase of microvascular permeability, hemorrhagic transformation, brain edema and compromise of the microcirculation. The present article reviews microvascular changes during ischemic brain injury, with emphasis on basal lamina damage.

Rodent brain imaging with SPECT/CT

We evaluated methods of imaging rat models of stroke in vivo using a single photon emission computed tomography (SPECT) system dedicated to small animal imaging (X-SPECT, Gamma Medica-Ideas, Northridge, CA). An animal model of ischemic stroke was developed for in vivo SPECT/CT imaging using the middle cerebral artery occlusion (MCAO) technique. The presence of cerebral ischemia was verified in ex vivo studies using triphenyltetrazolium chloride (TTC) staining. In vivo radionuclide imaging of cerebral blood flow was performed in rats following MCAO using dynamic planar imaging of 99mTc-exametazime with parallel hole collimation. This was followed immediately by in vivo radionuclide imaging of cerebral blood flow with 99mTc-exametazime in the same animals using 1-mm pinhole SPECT. Correlated computed tomography imaging was performed to localize radiopharmaceutical uptake. The animals were allowed to recover and ex vivo autoradiography was performed with separate administration of 99mTc-exametazime. Time activity curve of 99mTc-exametazime showed that the radiopharmaceutical uptake could be maintained for over 9 min. The activity would be expected to be relatively stable for a much longer period, although the data were only obtained for 9 min. TTC staining revealed sizable infarcts by visual observation of inexistence of TTC stain in infracted tissues of MCAO rat brains. In vivo SPECT imaging showed cerebral blood flow deficit in the MCAO model, and the in vivo imaging result was confirmed with ex vivo autoradiography. We have demonstrated a capability of imaging regions of cerebral blood flow deficit in MCAO rat brains in vivo using a pinhole SPECT dedicated to small animal imaging.

PPAR-gamma: therapeutic target for ischemic stroke

The peroxisome proliferator activated receptors (PPARs), which belong to the nuclear receptor superfamily, are key regulators of glucose and fat metabolism. The PPAR-gamma isoform is involved in the regulation of cellular glucose uptake, protection against atherosclerosis and control of immune reactions. In addition, the activation of PPAR-gamma effectively attenuates neurodegenerative and inflammatory processes in the brain. Here, we review a novel aspect of beneficial and clinically relevant PPAR-gamma actions: neuroprotection against ischemic injury mediated by intracerebral PPAR-gamma, which is expressed in neurons and microglia. Together with the recent observation that the PPAR-gamma ligand pioglitazone reduces the incidence of stroke in patients with type 2 diabetes, this review supports the concept that activators of PPAR-gamma are effective drugs against ischemic injury.