Tissue plasminogen activator cerebrovascular thrombolysis in rabbits is dependent on the rate and route of administration

Experimental models of focal and multifocal cerebral ischemia: a review

Rodent and rabbit stroke models have been instrumental in our current understanding of stroke pathophysiology; however, translational failure is a significant problem in preclinical ischemic stroke research today. There are a number of different focal cerebral ischemia models that vary in their utility, pathophysiology of causing disease, and their response to treatments. Unfortunately, despite active preclinical research using these models, treatment options for ischemic stroke have not significantly advanced since the food and drug administration approval of tissue plasminogen activator in 1996. This review aims to summarize current stroke therapies, the preclinical experimental models used to help develop stroke therapies, as well as their advantages and limitations. In addition, this review discusses the potential for naturally occurring canine ischemic stroke models to compliment current preclinical models and to help bridge the translational gap between small mammal models and human clinical trials.

Expression of a novel chimeric truncated t-PA in CHO cells based on in silico experiments

Tissue plasminogen activator (t-PA) is one of the fibrin-specific serine proteases that play a crucial role in the fibrinolytic system. The rapid clearance of the drug from the circulation, caused by its active uptake in the liver, has lead to complicated clinical applications. Different forms of plasminogen activators have been developed to treat thrombotic disease. Deletion of the first three domains of t-PA by gene manipulation techniques has shown a significant increase in its plasma half life. In order to compensate the disadvantage of higher bleeding risk, a novel chimeric truncated form of t-PA with 394 amino acids and more fibrin affinity compared to the truncated form was designed to be expressed in Chinese Hamster Ovarian (CHO) cells. The recombinant chimeric plasminogen activator consists of kringle 2 and serine protease (K2S) domains of t-PA, namely GHRP-SYQ-K2S. The level of expression was found to be 752 IU/ml with 566,917 IU/mg specific activity, based on amidolytic activity. The fibrin binding of this novel chimeric truncated t-PA was 86% of the full length t-PA at a fibrinogen concentration of 0.2 mg/ml. This could be a promising approach with more desirable pharmacodynamic properties compared to existing commercial forms.

Intravenous and local intraarterial tissue-plasminogen activator in a rabbit model of acute thromboembolic stroke: angiographic comparison

The aim of early thrombolytic therapy in acute stroke is to obtain early recanalization of occluded cerebral arteries and prevent or reduce irreversible ischemic brain damage. In this study, Seldinger technique and digital subtraction angiography were used to verify thromboembolic occlusion of the common carotid artery by an autologous 12-hour-old thrombus in 28 rabbits. Thirty minutes after embolization, 2 mg/kg of recombinant tissue-plasminogen activator (rt-PA) was delivered intravenously by way of the femoral vein in group A (n = 8) and through a local intraarterial infusion in group B (n = 8). Twelve control animals received an equivalent volume of saline intravenously (group C, n = 6) or by local intra-arterial infusion (group D, n = 6). A comparison of posttreatment angiographs of the treatment groups and the control groups was used to demonstrate reperfusion induced by thrombolytic therapy. None of the control animals showed any evidence of recanalization. Both intravenously (group A) and intra-arterially (group B) treated animals achieved 100% recanalization, although the average time to recanalization was significantly longer in group A (P = .01; 123.7 vs 82.5 min). These results suggest that local intra-arterial administration of rt-PA within 30 minutes produces more rapid reperfusion compared with the intravenous route. Further studies and additional treatments are needed to widen the therapeutic window and decrease hemorrhagic side effects.

Protocol of a thromboembolic stroke model in the rat: review of the experimental procedure and comparison of models

RATIONALE AND OBJECTIVE

Different models to study the pathophysiology of cerebral ischemia and to evaluate therapeutic strategies exist. Described is the detailed procedure of a thromboembolic stroke model in the rat most closely resembling human embolic stroke and compare the model to other equivalent rodent models.

MATERIALS AND METHODS

An evaluation of a new thromboembolic stroke model was performed on 35 male Wistar rats. After preparation of the carotid artery, a catheter was introduced into the external carotid artery. During injection of autologous, fibrin-rich emboli into the internal carotid artery the common carotid artery was temporarily occluded. Regional cerebral blood flow (rCBF) and lesion size were determined.

RESULTS

Twelve fibrin-rich blood clots of 1.5 mm in length were necessary in order reliably to occlude the origin of the middle cerebral artery. A stable decrease of rCBF and lesion size was confirmed by autoradiography, diffusion, and perfusion MRI, TTC-staining, biochemical imaging, and histology.

CONCLUSION

In this animal model, the situation of human cerebral ischemia is simulated closely. The model is suitable for investigations of the pathophysiology of stroke and facilitates studies on the effects of thrombolytic therapy.

Reducing bleeding complications after thrombolytic therapy for stroke: clinical potential of metalloproteinase inhibitors and spin trap agents

Thrombolysis with alteplase (recombinant tissue plasminogen activator; rtPA) has proven to be beneficial for acute stroke management, despite the narrow window of opportunity for treatment and the increased risk of haemorrhage. Because of the latter, recent studies have attempted to identify compounds that may be given concomitantly with alteplase to reduce the haemorrhage rate Matrix metalloproteinase (MMP) inhibitors have been proposed as potential combination therapy candidates because they prevent MMP-induced production of the cytokine tumour necrosis factor-alpha (TNFalpha), as well as membrane and vessel remodelling following ischaemia. Spin trap agents also have been put forward due to their free radical scavenging capabilities. In the rabbit large clot embolism model, alteplase effectively lysed blood clots, whether or not other drugs were used in combination. However, haemorrhage rate also was increased compared with that in control animals. The alteplase-induced haemorrhage rate was reduced significantly by administration of the MMP inhibitor batimastat (BB-94) or the spin trap agent alpha-phenyl-N-t-butylnitrone (PBN). Other rodent studies have also demonstrated that PBN is effective in decreasing the haemorrhage rate following alteplase administration. Overall, preclinical studies indicate that MMP inhibition or free radical scavenging in combination with alteplase may circumvent the high risk of haemorrhaging with alteplase.

Thrombolytic therapy for stroke: a review with particular reference to elderly patients

Clinical trials in the 1990s of intravenous thrombolysis for ischaemic stroke have involved over 3000 patients. Alteplase given within 3 hours of onset significantly reduces the combined end-point of death and disability. Although alteplase appears safe when given up to 6 hours after onset, individual trials have failed to confirm efficacy beyond 3 hours. Meta-analysis indicates that intravenous alteplase given up to 6 hours after stroke onset significantly reduces death or dependence 3 months after stroke. Two trials of intra-arterial pro-urokinase confirm benefits of treatment up to 6 hours in highly selected patients with angiographically confirmed proximal middle cerebral occlusion. Streptokinase increased the risk of early death significantly in 3 trials, with no overall reduction in eventual death and disability. Patients over 80 years have been excluded from most trials of alteplase, and experience in this age group is minimal. Increased incidence and poorer functional outcome in the elderly mean that thrombolysis may have greater absolute benefit in this group than in the young, but there is also a higher prevalence of absolute or relative potential contraindications to treatment (ranging from increased use of anticoagulant drugs to higher prevalence of atrial fibrillation). Further trials are necessary to address age restrictions and other important issues in the use of alteplase. Thrombolysis is likely to remain feasible for a minority of stroke patients of all ages, and there is a need for other acute treatment options.

Superselective Intra-Arterial Thrombolysis for Acute Cardioembolic Stroke in a Child with Idiopathic Dilated Cardiomyopathy

We describe a case of cardioembolic dominant hemisphere internal carotid artery occlusion in a child with idiopathic dilated cardiomyopathy. The patient was subjected to superselective local intra-arterial thrombolysis using recombinant tissue plasminogen activator (Alteplase; Actilyse®). In presence of good collateral flow local intra-arterial thrombolysis prevented a major dominant hemisphere ischaemic stroke, although post-interventional computed tomographic scans disclosed haemorrhagic conversion in the left corpus striatum. Forty eight months after ischaemic stroke and thrombolysis the patient is ambulatory with a moderate neurologic deficit.

Embolectomy for acute embolic occlusion of the internal carotid artery bifurcation

BACKGROUND

Acute occlusion of the distal intracranial segment of the internal carotid artery (ICA) causes sudden severe hemispheric ischemia. A low rate of recanalization and a high mortality rate for this condition have been noted, even with endovascular treatment.

METHODS

We report the results of emergency embolectomy in six patients with acute embolic occlusion of the internal carotid artery (ICA) bifurcation. All six patients were admitted to our institute within 2 h of the onset of symptoms. Computed tomography (CT) scans on admission revealed no low-density or high-density regions in any patients. The time between onset of symptoms and completion of angiography ranged from 2 to 4 h (2.8 +/- 0.7 h).

RESULTS

Emergency embolectomy was performed for each patient. Recanalization was confirmed angiographically in four of the patients. In the remaining two patients, massive infarction in the territory of the ICA was detected on the CT scans obtained the day of the operation, and postoperative angiography was not performed in these two cases. These two patients died of uncal herniation 6 days after onset. Two of the six patients were able to walk with a cane 2 months after surgery. The remaining two patients were unable to walk or attend to their own bodily needs without assistance. The time elapsed between onset of symptoms to reopening of the occluded vessel was within 6 h in the four surviving patients. The recanalization rate was 66.7% (4/6) for the embolectomy procedure, significantly higher than that (12.5%) of the thrombolytic therapy reported in a previous study.

CONCLUSIONS

In summary, open embolectomy can be performed when the time after onset of symptoms is less than 6 h.

Intravenous thrombolytic therapy in acute stroke

The article reviews the experimental basis of thrombolytic therapy, and summarizes the results of the recent trials of thrombolysis. Five large clinical trails have evaluated intravenous thrombolytic therapy for the treatment of hyperacute (< 6 h) stroke. Three of these studies were negative, one was equivocal, and one was strongly positive. The failure of demonstrate efficacy definitively in four of these trials may be related to a number of methodological factors, including the type and dose of drug administered, the timing of drug administered, and the method of patient selection for treatment. The NINDS recombinant tissue plasminogen activator (rt-PA) study showed that thrombolytic therapy can be of substantial benefit when administered within 3 h of stroke onset using strict patient selection criteria and rt-PA is now FDA approved for treatment of acute stroke. However, the risk of clinically significant bleeding is elevated. To achieve the favorable risk/benefit ratio demonstrated in the NINDS trial, patients must be screened by experienced clinicians for contraindications to thrombolysis and the acute computerized tomography (CT) brain scan must be carefully evaluated for radiographic features that increase the risk of cerebral hemorrhage. Guidelines for the use of rt-PA are provided, as well as insights into future thrombolytic treatment strategies.

Early complete recanalization in internal carotid artery embolism treated with high-dose t-PA: a sequential angiographic study in a novel model of embolism in rats

Complete early recanalization rate of human internal carotid artery embolic occlusion treated with thrombolytic drugs is low. To study factors related with this difficulty to recanalize we have developed a novel model of rat ica embolism using a fragment of human embolus. In 50 male Wistar rats the ica was embolized through the external carotid artery with a fragment of an embolus obtained from a human embolectomy passed through a catheter of 0.8 mm diameter. Recanalization was assessed by sequential angiograms from 15 to 120 min after embolization. Reperfusion was classified according to TIMI grades. Emboli of either 1 (group 1) or 2 mm (group 2) in length were cut. In group 1, four groups of nine animals each were treated, 15 min after embolization, with i.v. t-PA at doses of 1 mg/kg, 10 mg/kg and 20 mg/kg or saline. In group 2 there was one control group of seven animals treated with saline and another of seven animals treated with 10 mg/kg t-PA. Complete recanalization (TIMI grade 3) within the first 30 min was present in two animals treated with 10 and 20 mg/kg. Complete recanalization within the first 60 min was present in 0% of controls and animals treated with 1 mg/kg and in 44% of the 10 and 20 mg/kg groups (P<0.05 in chi-square test). Incomplete recanalization (TIMI grades 0, 1 and 2) occurred in 33%. In group 2 total recanalization occurred in 1/7 controls and in 3/7 animals receiving 10 mg/kg of t-PA. Early (60 min) complete i.v. t-PA induced internal carotid artery embolic recanalization is low with standard doses and increases moderately when high doses are used. Further increases in the dose do not improve recanalization rate, which is not clearly influenced by embolus size. Complete recanalization within 30 min, the period after which infarction develops in the rat, is uncommon in our model.

Improved perfusion with rt-PA and hirulog in a rabbit model of embolic stroke

We conducted a study using diffusion-weighted (DWI) and perfusion-weighted (PWI) magnetic resonance imaging (MRI) to evaluate the efficacy of thrombolysis in an embolic stroke model with recombinant tissue plasminogen activator (rt-PA) and hirulog, a novel direct-acting antithrombin. DWI can identify areas of ischemia minutes from stroke onset, while PWI identifies regions of impaired blood flow. Right internal carotid arteries of 36 rabbits were embolized using aged heterologous thrombi. Baseline DWI and PWI scans were obtained to confirm successful embolization. Four animals with no observable DWI lesion on the initial scan were excluded; therefore, a total of 32 animals were randomized to one of three treatment groups: rt-PA (n = 11), rt-PA plus hirulog (n = 11), or placebo (n = 10). Treatment was begun 1 h after stroke induction. Intravenous doses were as follows: rt-PA, 5 mg/kg over 0.5 h with 20% of the total dose given as a bolus; hirulog, 1 mg/kg bolus followed by 5 mg/kg over 1 h. MRI was performed at 2, 3, and 5 h following embolization. Six hours after embolization, brains were harvested, examined for hemorrhage, then prepared for histologic analysis. The rt-PA decreased fibrinogen levels by 73%, and hirulog prolonged the aPTT to four times the control value. Posttreatment areas of diffusion abnormality and perfusion delay were expressed as a ratio of baseline values. Significantly improved perfusion was seen in the rt-PA plus hirulog group compared with placebo (normalized ratios of the perfusion delay areas were as follows: placebo, 1.58, 0.47-3.59; rt-PA, 1.12, 0.04-3.95; rt-PA and hirulog, 0.40, 0.02-1.08; p < 0.05). Comparison of diffusion abnormality ratios measured at 5 h showed trends favoring reduced lesion size in both groups given rt-PA (normalized ratios of diffusion abnormality areas were as follows: placebo, 3.69, 0.39-15.71; rt-PA, 2.57, 0.74-5.00; rt-PA and hirulog, 1.95, 0.33-6.80; p = 0.32). Significant cerebral hemorrhage was observed in one placebo, two rt-PA, and three rt-PA plus hirulog treated animals. One fatal systemic hemorrhage was observed in each of the rt-PA groups. We conclude that rt-PA plus hirulog improves cerebral perfusion but does not necessarily reduce cerebral injury. DWI and PWI are useful methods for monitoring thrombolysis.

Local thrombolytic therapy for cerebrovascular disease: current Oregon Health Sciences University experience (July 1991 through April 1995)

PURPOSE

This report details experience with local intraarterial or intradural sinus thrombolytic therapy for cerebrovascular thromboembolic occlusions in 40 patients.

PATIENTS AND METHODS

Between July 1991 and April 1995, intracranial local thrombolytic therapy with urokinase was used to treat 40 patients with occlusive vascular disease. Twenty-six patients had acute occlusions of the central retinal artery, middle cerebral artery, basilar artery, or combined internal carotid and middle cerebral arteries. Three patients had embolic complications related to cerebral vascular embolization procedures. Five patients were undergoing intracranial angioplasty procedures for occlusive atheromatous disease. Six patients had dural sinus thrombosis.

RESULTS

Local intraarterial thrombolytic therapy for acute thromboembolic arterial occlusions resulted in excellent restoration of perfusion in 18 patients, partial restoration of flow in four patients, and no effect in five patients. Fourteen of these patients had excellent clinical outcomes, seven made moderate improvements, and six died. In the two patients with central retinal arterial occlusions, no angiographic or clinical response to thrombolytic therapy could be ascertained. There was no angiographic improvement response from thrombolytic therapy in five patients with primary intracranial atheromatous stenosis, and one patient may have had an embolic complication related to this therapy. Three of six patients with dural sinus thrombosis had clearing of the thrombus and an excellent clinical result. The remaining three with extensive dural thrombosis did not have clearing of the thrombus; one patient became blind, and two patients died. Among the 40 patients treated, significant cerebral hemorrhage occurred after therapy in four.

CONCLUSION

Local thrombolytic therapy for thromboembolic occlusive cerebrovascular disease is useful in restoring perfusion of acutely occluded vessels. Further experience is needed to fully identify the most appropriate patients for therapy, dose of thrombolytic agent, timing and length of therapy, and risk factors for hemorrhage.

Temporal profile of ischemic tissue damage, neutrophil response, and vascular plugging following permanent and transient (2H) middle cerebral artery occlusion in the rat

We investigated the temporal profile of ischemic tissue damage, neutrophil response, and vascular occlusion after permanent and transient middle cerebral artery occlusion in the rat. Focal cerebral ischemia was induced by advancing a nylon monofilament to occlude middle cerebral artery (MCA). Two groups of rats were investigated: (1) those with permanent MCA occlusion (n = 29), and (2) and those having the arterial occlusion released after 2 h (n = 34). Experiments were terminated at 6, 12, 24, 48, 72, 96 and 168 h after the onset of ischemia, and brain sections were stained with hematoxylin and eosin for histological evaluation. Initially, the cortical lesion was smaller in rats subjected to transient MCA occlusion than in rats subjected to permanent MCA occlusion (p < 0.02). The surface area of the lesion was identical in both groups at 48 h after the onset of ischemia. Neutrophil infiltration into tissue and the time of peak neutrophil infiltration occurred earlier after transient MCA occlusion than after permanent MCA occlusion (6 h, 48 h in transient; 12 h, 72 h in permanent). Within the lesions, the number of occluded vessels was significantly lower in the transient ischemia group than in the permanent ischemia group during the time interval between 12-48 h (p < 0.01). Our data suggest that the temporal evolution of the lesion, the pattern of neutrophil infiltration and the chronology of microvascular occlusion differs depending on whether the MCA occlusion is transient (2 h) or permanent; however, significant differences in the size of the brain lesion disappeared 48 h after onset of ischemia.