A review of experimental models of focal cerebral ischemia focusing on the middle cerebral artery occlusion model

Abstract

Cerebral ischemic stroke is a leading cause of death and disability, but current pharmacological therapies are limited in their utility and effectiveness. In vitro and in vivo models of ischemic stroke have been developed which allow us to further elucidate the pathophysiological mechanisms of injury and investigate potential drug targets. In vitro models permit mechanistic investigation of the biochemical and molecular mechanisms of injury but are reductionist and do not mimic the complexity of clinical stroke. In vivo models of ischemic stroke directly replicate the reduction in blood flow and the resulting impact on nervous tissue. The most frequently used in vivo model of ischemic stroke is the intraluminal suture middle cerebral artery occlusion (iMCAO) model, which has been fundamental in revealing various aspects of stroke pathology. However, the iMCAO model produces lesion volumes with large standard deviations even though rigid surgical and data collection protocols are followed. There is a need to refine the MCAO model to reduce variability in the standard outcome measure of lesion volume. The typical approach to produce vessel occlusion is to induce an obstruction at the origin of the middle cerebral artery and reperfusion is reliant on the Circle of Willis (CoW). However, in rodents the CoW is anatomically highly variable which could account for variations in lesion volume. Thus, we developed a refined approach whereby reliance on the CoW for reperfusion was removed. This approach improved reperfusion to the ischemic hemisphere, reduced variability in lesion volume by 30%, and reduced group sizes required to determine an effective treatment response by almost 40%. This refinement involves a methodological adaptation of the original surgical approach which we have shared with the scientific community via publication of a visualised methods article and providing hands-on training to other experimental stroke researchers.

Ischemic Stroke, Lessons from the Past towards Effective Preclinical Models

“…Recently, with the introduction of mechanical thrombectomy in the clinic, the MCAO model has gained more significance [ 141 ]. In fact, in 2015, five randomized controlled clinical trials that treated patients with major vessel occlusions either with or without rtPA treatment indicated positive results (significantly reduced disability at 90 days) of mechanical thrombectomy intervention [ 142 ].…”

“…Focal ischemia can also be induced by direct occlusion of the target vessel using a cranial window to clamp, ligate, or cauterize the vessel in situ, causing cortical and striatal lesions ( Table 3 B) [ 141 ]. Similar to the MCAO technique, focal ischemia can be induced either permanently or transiently [ 143 ].…”

“…Since thromboembolism is a cause of stroke in humans, thromboembolic stroke models ( Table 3 C) may have considerable benefits: they may better reflect disease pathology [ 141 ], and offers the chance to evaluate thrombolysis therapy alone or in conjunction with protective drugs [ 144 ]. The reproducibility of thromboembolic stroke models and their usefulness for longitudinal research are negatively impacted by the variability in infarct location and volume; low survival rates; and [ 145 ] potential spontaneous clot formation after embolism disruption and spontaneous reperfusion [ 146 , 147 ].…”

“…Endothelin-1, a peptide with long-lasting action as a vasoconstrictor, is used in endothelin models ( Table 3 D) of ischemia to cause vascular occlusions [ 148 ]. Depending on the concentration of the peptide when applied, the degree and duration of the injury varies [ 141 , 149 ]. The slow lesion development, prolonged cerebral blood flow drop, and eventual progressive reperfusion profile match the progression of a clinical stroke [ 141 , 149 ].…”

Therapeutic Potential and Mechanisms of Novel Simple O-Substituted Isoflavones against Cerebral Ischemia Reperfusion

“…They can induce the pathophysiological phenomena of IR such as energy failure, excitotoxicity, calcium overflow, oxidative stress, endoplasmic reticulum stress, mitochondrial dysfunction, and neuronal apoptosis. In vivo research models, global cerebral ischemia reperfusion, four-vessel occlusion (4-VO), and middle cerebral artery occlusion (MCAO) are often used in gerbils or rodents [ 24 , 25 , 26 , 27 ]. Many natural products have been evaluated for their protective effects on IR using in vitro and in vivo experimental IR models based on the pathological mechanism of IR, and isoflavones are one of them.…”