A Novel Canine Model of Acute Vertebral Artery Occlusion

Timely and Appropriate Administration of Inhaled Argon Provides Better Outcomes for tMCAO Mice: A Controlled, Randomized, and Double-Blind Animal Study

BACKGROUND

Inhaled argon (iAr) has shown promising therapeutic efficacy for acute ischemic stroke and has exhibited impressive advantages over other inert gases as a neuroprotective agent. However, the optimal dose, duration, and time point of iAr for acute ischemic stroke are unknown. Here, we explored variable iAr schedules and evaluated the neuroprotective effects of acute iAr administration on lesion volume, brain edema, and neurological function in a mouse model of cerebral ischemic/reperfusion injury.

METHODS

Adult ICR (Institute of Cancer Research) mice were randomly subjected to sham, moderate (1.5 h), or severe (3 h) transient middle cerebral artery occlusion (tMCAO). One hour after tMCAO, the mice were randomized to variable iAr protocols or air. General and focal deficit scores were assessed during double-blind treatment. Infarct volume, overall recovery, and brain edema were analyzed 24 h after cerebral ischemic/reperfusion injury.

RESULTS

Compared with those in the tMCAO-only group, lesion volume (p < 0.0001) and neurologic outcome (general, p < 0.0001; focal, p < 0.0001) were significantly improved in the group administered iAr 1 h after stroke onset (during ischemia). Short-term argon treatment (1 or 3 h) significantly improved the infarct volume (1 vs. 24 h, p < 0.0001; 3 vs. 24 h, p < 0.0001) compared with argon inhalation for 24 h. The concentration of iAr was confirmed to be a key factor in improving focal neurological outcomes relative to that in the tMCAO group, with higher concentrations of iAr showing better effects. Additionally, even though ischemia research has shown an increase in cerebral damage proportional to the ischemia time, argon administration showed significant neuroprotective effects on infarct volume (p < 0.0001), neurological deficits (general, p < 0.0001; focal, p < 0.0001), weight recovery (p < 0.0001), and edema (p < 0.0001) in general, particularly in moderate stroke.

CONCLUSIONS

Timely iAr administration during ischemia showed optimal neurological outcomes and minimal infarct volumes. Moreover, an appropriate duration of argon administration was important for better neuroprotective efficacy. These findings may provide vital guidance for using argon as a neuroprotective agent and moving to clinical trials in acute ischemic stroke.

Preclinical testing platforms for mechanical thrombectomy in stroke: a review on phantoms, in-vivo animal, and cadaveric models

Preclinical testing platforms have been instrumental in the research and development of thrombectomy devices. However, there is no single model which fully captures the complexity of cerebrovascular anatomy, physiology, and the dynamic artery-clot-device interaction. This article provides a critical review of phantoms, in-vivo animal, and human cadaveric models used for thrombectomy testing and provides insights into the strengths and limitations of each platform. Articles published in the past 10 years that reported thrombectomy testing platforms were identified. Characteristics of each test platform, such as intracranial anatomy, artery tortuosity, vessel friction, flow conditions, device-vessel interaction, and visualization, were captured and benchmarked against human cerebral vessels involved in large-vessel occlusion stroke. Thrombectomy phantoms have been constructed from silicone, direct 3D-printed polymers, and glass. These phantoms represent oversimplified patient-specific cerebrovascular geometry but enable adequate visualization of devices and clots under appropriate flow conditions. They do not realistically mimic the artery-clot interaction. For the animal models, arteries from swine, canines, and rabbits have been reported. These models can reasonably replicate the artery-clot-device interaction and have the unique value of evaluating the safety of thrombectomy devices. However, the vasculature geometries are substantially less complex and flow conditions are different from human cerebral arteries. Cadaveric models are the most accurate vascular representations but with limited access and challenges in reproducibility of testing conditions. Multiple test platforms should be likely used for comprehensive evaluation of thrombectomy devices. Interpretation of the testing results should take into consideration platform-specific limitations.

Endovascular model of ischemic stroke in swine guided by real-time MRI

Modeling stroke in animals is essential for testing efficacy of new treatments; however, previous neuroprotective therapies, based on systemic delivery in rodents failed, exposing the need for model with improved clinical relevance. The purpose of this study was to develop endovascular approach for inducing ischemia in swine. To achieve that goal, we used intra-arterial administration of thrombin mixed with gadolinium and visualized the occlusion with real-time MRI. Placement of the microcatheter proximally to rete allowed trans-catheter perfusion of the ipsilateral hemisphere as visualized by contrast-enhanced perfusion MR scans. Dynamic T2*w MRI facilitated visualization of thrombin + Gd solution transiting through cerebral vasculature and persistent hyperintensities indicated occlusion. Area of trans-catheter perfusion dynamically quantified on representative slice before and after thrombin administration (22.20 ± 6.31 cm² vs. 13.28 ± 4.71 cm² respectively) indicated significantly reduced perfusion. ADC mapping showed evidence of ischemia as early as 27 min and follow-up T2w scans confirmed ischemic lesion (3.14 ± 1.41 cm²). Animals developed contralateral neurological deficits but were ambulatory. Our study has overcome long lasting challenge of inducing endovascular stroke model in pig. We were able to induce stroke using minimally invasive endovascular approach and observe in real-time formation of the thrombus, blockage of cerebral perfusion and eventually stroke lesion.

Canine Model for Selective and Superselective Cerebral Intra-Arterial Therapy Testing

PURPOSE

With advancing endovascular technology and increasing interest in minimally invasive intra-arterial therapies such as stem cell and chemotherapy for cerebral disease, the establishment of a translational model with cerebral circulation accessible to microcatheters is needed. We report our experience catheterizing canine cerebral circulation with microcatheters, present high-resolution angiographic images of the canine vascular anatomy, describe arterial branch flow patterns and provide measurements of canine arterial conduits.

MATERIALS AND METHODS

Angiograms were performed on 10 intact purpose-bred hounds. Angiography, measurements of arterial conduits and catheterization information for intracranial arterial branches were obtained.

RESULTS

Selective and superselective cerebral angiography was successful in all subjects. Relevant arterial mean diameters include the femoral (4.64 mm), aorta (9.38 mm), external carotid (3.65 mm), internal carotid arteries (1.6 mm), vertebrobasilar system and Circle of Willis branches. Catheterization of the Circle of Willis was achieved via the posterior circulation in all subjects tested (n=3) and the use of flow directed microcatheters resulted in reduced arterial tree deformation and improved superselection of intracranial vessels. Catheterization of the intracranial circulation was attempted but not achieved via the internal carotid artery (n=7) due to its tortuosity and subsequent catheter related vasospasm.

CONCLUSION

The canine cerebral vasculature is posterior circulation dominant. Anterior circulation angiography is achievable via the internal carotid artery, but direct cerebral arterial access is best achieved via the posterior circulation using flow-directed microcatheters. It is feasible to deliver intra-arterial therapies to selective vascular territories within the canine cerebral circulation, thus making it a viable animal model for testing novel intra-arterial cerebral treatments.

Large animal ischemic stroke models: replicating human stroke pathophysiology

The high morbidity and mortality rate of ischemic stroke in humans has led to the development of numerous animal models that replicate human stroke to further understand the underlying pathophysiology and to explore potential therapeutic interventions. Although promising therapeutics have been identified using these animal models, with most undergoing significant testing in rodent models, the vast majority of these interventions have failed in human clinical trials. This failure of preclinical translation highlights the critical need for better therapeutic assessment in more clinically relevant ischemic stroke animal models. Large animal models such as non-human primates, sheep, pigs, and dogs are likely more predictive of human responses and outcomes due to brain anatomy and physiology that are more similar to humans-potentially making large animal testing a key step in the stroke therapy translational pipeline. The objective of this review is to highlight key characteristics that potentially make these gyrencephalic, large animal ischemic stroke models more predictive by comparing pathophysiological responses, tissue-level changes, and model limitations.

Development of a Novel Canine Model of Ischemic Stroke: Skull Base Approach with Transient Middle Cerebral Artery Occlusion

OBJECTIVE

Although canine stroke models have several intrinsic advantages, establishing consistent and reproducible territorial stroke in these models has been challenging because of the abundance of collateral circulation. We have described a skull-base surgical approach that yields reproducible stroke volumes.

METHODS

Ten male beagles were studied. In all 10 dogs, a craniectomy was performed to expose the circle of Willis. Cerebral aneurysm clips were temporarily applied to the middle cerebral artery (MCA), anterior cerebral artery (ACA), posterior cerebral artery, and/or ophthalmic artery (OA) for 1 hour, followed by cauterization of the distal MCA pial collateral vessels. Indocyanine green angiography was performed to assess the local blood flow to the intended area of infarction. The dogs' neurologic examination was evaluated, and the stroke burden was quantified using magnetic resonance imaging.

RESULTS

High mortality was observed after 1-hour clip occlusion of the posterior cerebral artery, MCA, ACA, and OA (n = 4). Without coagulation of the MCA collateral vessels, 1-hour occlusion of the MCA and/or ACA and OA yielded inconsistent stroke volumes (n = 2). In contrast, after coagulation of the distal MCA pial collateral vessels, 1-hour occlusion of the MCA, ACA, and OA yielded consistent territorial stroke volumes (n = 4; average stroke volume, 9.13 ± 0.90 cm³; no surgical mortalities), with reproducible neurologic deficits.

CONCLUSION

Consistent stroke volumes can be achieved in male beagles using a skull base surgical approach with temporary occlusion of the MCA, ACA, and OA when combined with cauterization of the distal MCA pial collateral vessels.

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.

Large animal canine endovascular ischemic stroke models: A review

BACKGROUND

Stroke is one of the leading causes of death and long-term disability worldwide. Recent exciting developments in the field with endovascular treatments have shown excellent outcomes in acute ischemic stroke. Prior to translating these treatments to human populations, a large-animal ischemic stroke model is needed. With the advent of new technologies in digital subtraction angiography, less invasive endovascular stroke models have been developed. Canines have gyrencephalic brain similar to human brain and accessible neurovascular anatomy for stroke model creation. Canine stroke model can be widely utilized to understand the disease process of stroke and to develop novel treatment. Less invasive endovascular internal carotid emboli injection and coil embolization methods can be used to simulate transient or permanent middle cerebral artery occlusion. Major restriction includes the extensive collateral circulation of canine cerebral arteries that can limit the stroke size. Transient internal carotid artery occlusion can decrease collateral circulation and increase stroke size to some degree. Additional method of manipulating the extent of collateral circulation needs to be studied. Other types of canine stroke models, including vertebral artery occlusion and basilar artery occlusion, can also be accomplished by endovascular thrombi injection.

CONCLUSIONS

We extensively review the literature on endovascular technique of creating canine ischemic stroke models and their application in finding new therapies for ischemic stroke.