Keep warm and get success: The role of postischemic temperature in the mouse middle cerebral artery occlusion model

Bridging the Transient Intraluminal Stroke Preclinical Model to Clinical Practice: From Improved Surgical Procedures to a Workflow of Functional Tests

Acute ischemic stroke (AIS) remains a leading cause of mortality, despite significant advances in therapy (endovascular thrombectomy). Failure in developing novel effective therapies is associated with unsuccessful translation from preclinical studies to clinical practice, associated to inconsistent and highly variable infarct areas and lack of relevant post-stroke functional evaluation in preclinical research. To outreach these limitations, we optimized the intraluminal transient middle cerebral occlusion, a widely used mouse stroke model, in two key parameters, selection of appropriate occlusion filaments and time of occlusion, which show a significant variation in the literature. We demonstrate that commercially available filaments with short coating length (1–2 mm), together with 45-min occlusion, results in a consistent affected brain region, similar to what is observed in most patients with AIS. Importantly, a dedicated post-stroke care protocol, based on clinical practice applied to patients who had stroke, resulted in lower mortality and improved mice welfare. Finally, a battery of tests covering relevant fine motor skills, sensory functions, and learning/memory behaviors revealed a significant effect of tMCAO brain infarction, which is parallel to patient symptomatology as measured by relevant clinical scales (NIH Stroke Scale, NIHSS and modified Rankin Scale, mRS). Thus, in order to enhance translation to clinical practice, future preclinical stroke research must consider the methodology described in this study, which includes improved reproducible surgical procedure, postoperative care, and the battery of functional tests. This will be a major step s closing the gap from bench to bedside, rendering the development of novel effective therapeutic approaches.

Ischemic stroke in PAR1 KO mice: Decreased brain plasmin and thrombin activity along with decreased infarct volume

Background

Ischemic stroke is a common and debilitating disease with limited treatment options. Protease activated receptor 1 (PAR1) is a fundamental cell signaling mediator in the central nervous system (CNS). It can be activated by many proteases including thrombin and plasmin, with various down-stream effects, following brain ischemia.

Methods

A permanent middle cerebral artery occlusion (PMCAo) model was used in PAR1 KO and WT C57BL/6J male mice. Mice were evaluated for neurological deficits (neurological severity score, NSS), infarct volume (Tetrazolium Chloride, TTC), and for plasmin and thrombin activity in brain slices.

Results

Significantly low levels of plasmin and thrombin activities were found in PAR1 KO compared to WT (1.6±0.4 vs. 3.2±0.6 ng/μl, p<0.05 and 17.2±1.0 vs. 21.2±1.0 mu/ml, p<0.01, respectively) along with a decreased infarct volume (178.9±14.3, 134.4±13.3 mm³, p<0.05).

Conclusions

PAR1 KO mice have smaller infarcts, with lower thrombin and plasmin activity levels. These findings may suggest that modulation of PAR1 is a potential target for future pharmacological treatment of ischemic stroke.

Increased brain plasmin levels following experimental ischemic stroke in male mice

Many coagulation factor proteases are increased in the brain during ischemic stroke. One of these proteases is plasmin. In this study we established a novel method for direct quantitative measurement of plasmin activity in male mouse brain slices using a sensitive fluorescent substrate in the presence of specific protease inhibitors. In both the ischemic and contralateral hemispheres, plasmin activity increased 3, 6, and 24 hr following stroke in comparison to healthy mice (F(3, 72) = 39.5, p < 0.0001, repeated measures ANOVA) after the induction of permanent middle cerebral artery occlusion (PMCAo). Plasmin activity was higher in the ischemic hemisphere (F(1,36) = 9.1, p = 0.005) and there was a significant interaction between time and ischemic hemisphere (F(3,36) = 4.4, p = 0.009). Plasmin activity was correlated with infarct volume (R²  = 0.5289, p = 0.0009 by Spearman). The specificity of the assay was verified utilizing tissue-type plasminogen activator (tPA)-deficient mice which, as expected, had significantly lower levels of plasmin 24 hr following ischemia compared to wild-type mice (ischemic (0.6 ± 0.23 and 1.94 ± 0.5, respectively), p = 0.049 and contralateral hemispheres (0.13 ± 0.14 and 0.75 ± 0.10, respectively), p = 0.018 by t test). There is a time-dependent increase in plasmin levels and an association of higher levels of plasmin with larger infarct volumes in an experimental stroke model. This suggests caution in the use of recombinant tPA (rtPA) and that plasmin inhibition in the brain may be a therapeutic target in acute ischemic stroke.

Impact of C57BL/6 substrain on sex-dependent differences in mouse stroke models

We have recently found significant variation in stroke vulnerability among substrains of C57BL/6 mice, observing that commonly used N-lineage substrains exhibit larger infarcts than C57BL/6J and related substrains. Parallel variation was also seen with respect to sex differences in stroke vulnerability, in that C57BL/6 mice of the N-lineage exhibited comparable infarct sizes in males and females, whereas infarcts tended to be smaller in females than in males of J-lineage substrains. This adds to the growing list of recognized phenotypic and genetic differences among C57BL/6 substrains. Although no previous studies have explicitly compared substrains with respect to sex differences in stroke vulnerability, unrecognized background mismatch has occurred in some studies involving control and genetically modified mice. The aims of this review are to: present the evidence for associated substrain- and sex-dependent differences in a mouse permanent occlusion stroke model; examine the extent to which the published literature in other models compares with these recent results; and consider the potential impact of unrecognized heterogeneity in substrain background on the interpretation of studies investigating the impact of genetic modifications on sex differences in stroke outcome. Substrain emerges as a critical variable to be documented in any experimental stroke study in mice.

Induction of Ischemic Stroke and Ischemia-reperfusion in Mice Using the Middle Artery Occlusion Technique and Visualization of Infarct Area

Cerebrovascular disease is highly prevalent in the global population and encompasses several types of conditions, including stroke. To study the impact of stroke on tissue injury and to evaluate the effectiveness of therapeutic interventions, several experimental models in a variety of species were developed. They include complete global cerebral ischemia, incomplete global ischemia, focal cerebral ischemia, and multifocal cerebral ischemia. The model described in this protocol is based on the middle cerebral artery occlusion (MCAO) and is related to the focal ischemia category. This technique produces consistent focal ischemia in a strictly defined region of the hemisphere and is less invasive than other methods. The procedure described is performed on mice, given the availability of several genetic variants and the high number of tests standardized for mice to aid in the behavioral and neurodeficit evaluation.

A review on animal models of stroke: An update

Stroke is one of the major healthcare challenges prevailing across the globe due to its significant rate of mortality and morbidity. Stroke is multifactorial in nature and involves several cellular and molecular signaling cascades that make the pathogenesis complex and treatment difficult. For a deeper understanding of the diverse pathological mechanisms and molecular & cellular cascades during stroke, animal modeling serves as a reliable and an effective tool. This also helps to develop and critically analyse various neuroprotective strategies for the mitigation of this devastating disease. Animal modeling for stroke has been revolutionized with the development of newer and more relevant models or approaches that mimic the clinical setting of stroke to a greater extent. This review analyses experimental models of stroke (ischemic and hemorrhagic) and their reliability in stroke situation. Besides this, the review also stresses upon the use of various preclinical models to understand the pathophysiological mechanisms that operate during stroke and to elucidate new, safe and effective neuroprotective agents to combat this life threatening healthcare concern.

A modification of intraluminal middle cerebral artery occlusion/reperfusion model for ischemic stroke with laser Doppler flowmetry guidance in mice

Stroke is one of the common causes of death and disability in the world. The intraluminal middle cerebral artery occlusion/reperfusion (MCAO/R) model is a "gold standard" in surgical ischemic stroke models. Here, we optimized the procedure of this model by ligating on external carotid artery (ECA) stump and two ligatures prepared on internal carotid artery, which could improve the success and survival rate in mice. The results show that ECA approach was superior to common carotid artery approach. Meanwhile, we found that the exposure of pterygopalatine artery was not an essential step for MCAO/R model in mice.

A novel mouse model of thromboembolic stroke

BACKGROUND

We previously demonstrated that tissue plasminogen activator (tPA) reduces infarct size after mechanical middle cerebral artery occlusion (MCAO) in wild-type (WT) mice and transgenic mice expressing human leukocyte antigen DR2 (DR2-Tg). Clinically, tPA limits ischemic damage by dissolving the clot blocking blood flow through a cerebral artery. To mimic the clinical situation, we developed a new mouse model of thromboembolic stroke, and tested the efficacy of tPA in WT and DR2-Tg mice. New Method Autologous blood is withdrawn into a PE-8 catheter filled with 2 IU α-thrombin. After exposing the catheter briefly to air, the catheter is reintroduced into the external (ECA) and advanced into the internal carotid artery (ICA) to allow for intravascular injection of thrombin at the MCA bifurcation. To validate the model, we tested the effect of tPA on laser-Doppler perfusion (LDP) over the MCA territory and infarct size in WT and DR2-Tg mice.

RESULTS

The procedure results in a consistent drop in LDP, and leads to a highly reproducible ischemic lesion. When administered at 15min after thrombosis, tPA restored LDP and resulted in a significant reduction in infarct size at 24h after thrombosis in both WT and DR2-Tg.

COMPARISON WITH EXISTING METHODS

Our model significantly reduces surgery time, requires a single anesthesia exposure, and produces a consistent and predictable infarction, with low variability and mortality.

CONCLUSION

We validated the efficacy of tPA in restoring blood flow and reducing infarct in a new model of endovascular thromboembolic stroke in the mouse.

Hypothalamic, thalamic and hippocampal lesions in the mouse MCAO model: Potential involvement of deep cerebral arteries?

Intraluminal monofilament occlusion of the middle cerebral artery (MCAO) in mice is the most used rodent model to study the pathophysiology of stroke. However, this model often shows brain damage in regions not supplied by the MCA such as the hypothalamus, hippocampus and thalamus. Several studies have suggested some explanations on these localized infarcts. We aim to provide an alternative explanation which could allow each experimenter to better grasp the MCAO model. We propose that the MCA occlusion by the monofilament also occludes deep and small cerebral arteries arising directly from the internal carotid artery, proximally to the origin of MCA. Then, drawbacks and pitfalls of the MCAO model must be appreciated and the almost systematic risk of inducing lesions in some unwanted territories for neuroanatomical reasons, i.e. vascular connections between deep arteries and hypothalamic, thalamic and hippocampal areas in rodents has to be integrated.

Orosomucoid1: Involved in vascular endothelial growth factor-induced blood-brain barrier leakage after ischemic stroke in mouse

Vascular endothelial growth factor (VEGF) is a promising candidate for the treatment of ischemic stroke. However, accumulating evidence demonstrated that VEGF could exacerbate blood-brain barrier (BBB) disruption after ischemic stroke. This study was designed to investigate the underlying mechanisms. In the present study, a transient (90 min) middle cerebral artery occlusion (MCAO) model was performed to induce ischemic stroke in mice. VEGF was administered intracerebroventricularly 3h after reperfusion. A gene expression microarray was utilized to investigate the differentially expressed genes among the sham, MCAO, and VEGF groups. A total of 3381 mRNAs were significantly altered by cerebral ischemia when compared with the sham group, and 15 of them were changed in the VEGF group when compared with the MCAO group. Among the 15 genes, orosomucoid (Orm) 1 was most sharply changed, and this gene has previously been reported to maintain the permeability of microvessels and integrity of the BBB. Results of the microarray showed that the expression of Orm1 increased after cerebral ischemia, whereas it decreased in response to VEGF, which was confirmed by real-time quantitative PCR, western blotting, immunohistochemistry, and immunofluorescence. The bioinformatics analysis indicated two NF-κB binding sites on the Orm1 promoter, and a super-shift assay verified that NF-κB could bind the Orm1 promoter. Results of the electrophoretic mobility shift assay (EMSA) revealed that VEGF inhibited the DNA-binding activity of NF-κB/p65. Furthermore, the elevated expression and activation of key members in the canonical NF-κB pathway induced by cerebral ischemia were also inhibited by VEGF treatment. In conclusion, this study demonstrated that decreasing the Orm1 expression via inhibition of the NF-κB pathway could be a possible mechanism involved in the aggravation of BBB disruption after stroke by VEGF.

Synergism and rules of the new combination drug Yiqijiedu formulae (YQJD) on ischemic stroke based on amino acids (AAs) metabolism

The use of combination drugs is considered to be a promising strategy to control complex diseases such as ischemic stroke. The detection of metabolites has been used as a versatile tool to reveal the potential mechanism of diverse diseases. In this study, the levels of 12 endogenous AAs were simultaneously determined quantitatively in the MCAO rat brain using RRLC-QQQ method. Seven AAs were chosen as the potential biomarkers, and using PLS-DA analysis, the effects of the new combination drug YQJD, which is composed of ginsenosides, berberine, and jasminoidin, on those 7 AAs were evaluated. Four AAs, glutamic acid, homocysteine, methionine, and tryptophan, which changed significantly in the YQJD-treated groups compared to the vehicle groups (P < 0.05), were identified and designated as the AAs to use to further explore the synergism of YQJD. The result of a PCA showed that the combination of these three drugs exhibits the strongest synergistic effect compared to other combination groups and that ginsenosides might play a pivotal role, especially when combined with jasminoidin. We successfully explored the synergetic mechanism of multi-component and provided a new method for evaluating the integrated effects of combination drugs in the treatment of complex diseases.