MRI study on delayed ancrod therapy of focal cerebral ischaemia in rats

Pre-clinical to Clinical Translational Failures and Current Status of Clinical Trials in Stroke Therapy: A Brief Review

In stroke (cerebral ischemia), despite continuous efforts both at the experimental and clinical level, the only approved pharmacological treatment has been restricted to tissue plasminogen activator (tPA). Stroke is the leading cause of functional disability and mortality throughout worldwide. Its pathophysiology starts with energy pump failure, followed by complex signaling cascade that ultimately ends in neuronal cell death. Ischemic cascade involves excessive glutamate release followed by raised intracellular sodium and calcium influx along with free radicals' generation, activation of inflammatory cytokines, NO synthases, lipases, endonucleases and other apoptotic pathways leading to cell edema and death. At the pre-clinical stage, several agents have been tried and proven as an effective neuroprotectant in animal models of ischemia. However, these agents failed to show convincing results in terms of efficacy and safety when the trials were conducted in humans following stroke. This article highlights the various agents which have been tried in the past but failed to translate into stroke therapy along with key points that are responsible for the lagging of experimental success to translational failure in stroke treatment.

Pharmacological and genetic depletion of fibrinogen protects from kidney fibrosis

Fibrinogen (Fg) has been implicated in the pathogenesis of several fibrotic disorders by acting as a profibrotic ligand for a variety of cellular surface receptors and by modulating the provisional fibrin matrix formed after injury. We demonstrated increased renal Fg expression after unilateral ureteral obstruction and folic acid (FA) nephropathy in mice, respectively. Urinary Fg excretion was also increased in FA nephropathy. Using in vitro and in vivo approaches, our results suggested that IL-6 mediates STAT3 activation in kidney fibrosis and that phosphorylated (p)STAT3 binds to Fgα, Fgβ, and Fgγ promoters in the kidney to regulate their transcription. Genetically modified Fg heterozygous mice (∼75% of normal plasma Fg levels) exhibited only 3% kidney interstitial fibrosis and tubular atrophy after FA nephropathy compared with 24% for wild-type mice. Fibrinogenolysis through Ancrod administration after FA reduced interstitial fibrosis more than threefold compared with vehicle-treated control mice. Mechanistically, we show that Fg acts synergistically with transforming growth factor (TGF)-β1 to induce fibroblast proliferation and activates TGF-β1/pSMAD2 signaling. This study offers increased understanding of Fg expression and molecular interactions with TGF-β1 in the progression to kidney fibrosis and, importantly, indicates that fibrinogenolytics like Ancrod present a treatment opportunity for a yet intractable disease.

Ancrod reduces intracerebral hemorrhage quantified in vivo by magnetic resonance imaging in rats

BACKGROUND AND PURPOSE

Promising results of experimental and clinical stroke studies suggest that ancrod may provide an efficient therapy of brain ischemia. Because ancrod has been shown to produce rapid defibrinogenation, we investigated the effects of this agent in a rat model of intracranial bleeding using noninvasive magnetic resonance imaging (MRI).

METHODS

Intracranial bleeding was induced in anesthetised rats by microinfusion of collagenase into the right striatum. Ancrod was intravenously infused for a period of 30 minutes starting 30 minutes after intrastriatal collagenase infusion. The dosages of ancrod were 0.33 IU . kg(-1) . min(-1) in one group and 1 IU . kg(-1) . min(-1) in another (total dosages were 10 and 30 IU . kg(-1), respectively). Control animals received equal amounts of vehicle solution (0.9% NaCl) only. The volume of intracerebral hemorrhage (ICH) was quantified in vivo by T1-weighted spin-echo MRI in eight consecutive coronal brain planes 24 hours after collagenase infusion.

RESULTS

Plasma fibrinogen was dose-dependently diminished immediately after infusion of ancrod at dosages of 0.33 or 1 IU . kg(-1) . min(-1). Total volume of ICH was significantly (P<.05) reduced by 50% from 48 (35/57) mm(3) in vehicle-treated controls (n=17) to 24 (20/37) mm(3) in rats (n=15) infused with the lower ancrod dosage (median, 25th/75th centiles). Rats (n=15) treated with the higher dosage of ancrod had 34 (27/39) mm(3) volume of ICH, which is 29% lower compared with vehicle-treated controls (P=.05).

CONCLUSIONS

Adverse side effects such as aggravation of intracerebral bleeding did not occur in ancrod-infused rats despite pronounced lowering of the plasma fibrinogen level during ongoing bleeding. In contrast, significant reductions in the volumes of ICH were observed suggesting favorable influence of ancrod in the event of intracranial bleeding in rats.

Extended therapeutic time window after focal cerebral ischemia by non-competitive inhibition of AMPA receptors

In acute stroke, the therapeutic time window is a critical factor which may have contributed to the failure of several phase III clinical trials with so-called neuroprotective agents. Since cerebral glutamate levels are elevated for many hours in progressing stroke, we investigated the novel AMPA glutamate receptor antagonist ZK 187638 in rodent models of stroke using up to 12 h delays in the start of therapy after permanent occlusion of the middle cerebral artery (MCA). In rats, ZK 187638 reduced total infarct volume by 43% and 33% when therapy was started immediately or with a delay of 6 h, respectively, but no effect was observed after a 12 h delay. Dose-dependent decreases of total infarct volume (up to 42%) were measured in mice given the first injection of ZK 187638 6 h after permanent MCA occlusion. In conclusion, the AMPA receptor antagonist ZK 187638 has a therapeutic time window of at least 6 h after permanent focal cerebral ischemia in rodents.

Novel α-Amino-3-hydroxy-5-methyl-4-isoxazole Propionate (AMPA) Receptor Antagonists of 2,3-Benzodiazepine Type: Chemical Synthesis, in Vitro Characterization, and in Vivo Prevention of Acute Neurodegeneration

Under pathophysiological conditions, alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptor activation is considered to play a key role in several disorders of the central nervous system. In the search for AMPA receptor antagonists, the synthesis and pharmacological characterization of a series of novel compounds that are structurally related to GYKI 52466 (1), a well-known selective noncompetitive AMPA receptor antagonist, was performed. In vitro, 2,3-dimethyl-6-phenyl-12H-[1,3]dioxolo[4,5-h]imidazo[1,2-c][2,3]benzodiazepine (ZK 187638, 14a) antagonized the kainate-induced currents in cultured hippocampal neurons with an IC(50) of 3.4 microM in a noncompetitive fashion. When tested in a clinically predictive rat model of acute ischemic stroke, this noncompetitive AMPA receptor antagonist significantly reduced brain infarction, indicating that it is neuroprotective after permanent focal cerebral ischemia.

Reduction of brain injury by antithrombotic agent acutobin after middle cerebral artery ischemia/reperfusion in the hyperglycemic rat

In vivo magnetic resonance imaging (MRI) was used to observe the effect of acutobin, a purified thrombin-like enzyme (TLE), isolated from the snake venom of Deinagkistrodon acutus, on MRI-detected brain lesion volume and tissue perfusion deficit in a hyperglycemic rat right middle cerebral artery occlusion/reperfusion (MCAO/R) model. Acutobin (0.75 U/ml) was intravenously injected with a dosage of 2.5 U/kg body weight 30 min after MCAO (MCAO duration=60 min) and again 24 h after reperfusion. Multislice diffusion weighted imaging (DWI) and single-slice dynamic bolus tracking gradient echo (GE) imaging were sequentially acquired before and after MCAO/R. DWI-detected lesion volume was significantly (p<0.05) reduced by 24-31% from 350+/-45, 369+/-45 and 374+/-36 mm(3) in the saline-treated group to 239+/-17, 282+/-26 and 259+/-32 mm(3) at 3, 4 and 24 h after reperfusion in the acutobin-treated group, respectively. Residual cerebral blood flow (CBF) in the right hemisphere recovered and remained at approximately 80% of normal perfusion over the measurement period in the acutobin-treated group, compared to approximately 40% in the saline-treated group. Mortality at 1 week after MCAO/R in the acutobin-treated group was significantly lower (25% mortality) than the saline control group (85% mortality). Our results indicate that acutobin improves brain tissue perfusion and reduces infarct volume and mortality in the hyperglycemic rat MCAO/R model.

Animal models of stroke: do they have value for discovering neuroprotective agents?

There has been a series of high-profile failures of drugs in clinical trials of acute ischaemic stroke that were designed to meet criteria necessary for drug regulatory approval. This has, again, called into question the value of animal models for identifying effective neuroprotective agents. Here, we review evidence that physiological changes (reperfusion, hyperglycaemia, hypothermia and blood pressure) produce comparable changes in outcome in both animal models and human stroke patients, which indicates that the models should identify clinically effective neuroprotective agents. We suggest that most clinical failures have occurred because compounds were administered differently in animal and clinical studies. We review earlier guidelines on the information that is necessary from preclinical studies before a compound enters clinical trials, and propose modifications to these guidelines.

Stroke trials: what have we learned?

We reviewed the recent, major, therapeutic trials of intravenous thrombolytic therapy and ancrod for ischemic stroke. Randomized, controlled studies of acute ischemic stroke treatment were reviewed. Several post-FDA approval intravenous tPA studies were reviewed to understand the experience of this medication in practice. STAT trial was the major study using ancrod. Of multiple intravenous thrombolytic studies, the NINDS study of intravenous tPA was the only study to demonstrate a significantly higher percentage of patients with complete recovery or minimal deficit at three months. Studies in communities utilizing intravenous tPA for stroke illustrate the need for close adherence to the NINDS study protocol or else the risk of tPA use may exceed the benefits.