Reinventing the Penumbra - the Emerging Clockwork of a Multi-modal Mechanistic Paradigm

Early localization of tissue at risk for delayed cerebral ischemia after aneurysmal subarachnoid hemorrhage: blood distribution on initial imaging vs early CT perfusion

OBJECTIVE

Delayed cerebral ischemia (DCI) is a potentially reversible adverse event after aneurysmal subarachnoid hemorrhage (aSAH), when early detected and treated. Computer tomography perfusion (CTP) is used to identify the tissue at risk for DCI. In this study, the predictive power of early CTP was compared with that of blood distribution on initial CT for localization of tissue at risk for DCI.

METHODS

A consecutive patient cohort with aSAH treated between 2012 and 2020 was retrospectively analyzed. Blood distribution on CT was semi-quantitatively assessed with the Hijdra-score. The vessel territory with the most surrounding blood and the one with perfusion deficits on CTP performed on day 3 after ictus were considered to be at risk for DCI, respectively.

RESULTS

A total of 324 patients were included. Delayed infarction occurred in 17% (56/324) of patients. Early perfusion deficits were detected in 82% (46/56) of patients, 85% (39/46) of them developed infarction within the predicted vessel territory at risk. In 46% (25/56) a vessel territory at risk was reliably determined by the blood distribution. For the prediction of DCI, blood amount/distribution was inferior to CTP. Concerning the identification of "tissue at risk" for DCI, a combination of both methods resulted in an increase of sensitivity to 64%, positive predictive value to 58%, and negative predictive value to 92%.

CONCLUSIONS

Regarding the DCI-prediction, early CTP was superior to blood amount/distribution, while a consideration of subarachnoid blood distribution may help identify the vessel territories at risk for DCI in patients without early perfusion deficits.

Acute Ischemic Stroke in the Clinic and the Laboratory: Targets for Translational Research

Ischemic stroke research has enabled significant advancements in diagnosis, treatment, and management of this debilitating disease, yet challenges remain standing in the way of better patient prognoses. In this narrative review, a fictional case illustrates challenges and uncertainties that medical professionals still face - penumbra identification, lack of neuroprotective agents, side-effects of tissue plasminogen activator, dearth of molecular biomarkers, incomplete microvascular reperfusion or no-reflow, post-recanalization hyperperfusion, blood pressure management and procedural anesthetic effects. The current state of the field is broadly reviewed per topic, with the aim to introduce a broad audience (scientist and clinician alike) to recent successes in translational stroke research and pending scientific queries that are tractable for preclinical assessment. Opportunities for co-operation between clinical and experimental stroke experts are highlighted to increase the size and frequency of strides the field makes to improve our understanding of this disease and ways of treating it.

Depth-Specific Hypoxic Responses to Spreading Depolarizations in Gyrencephalic Swine Cortex Unveiled by Photoacoustic Imaging

Spreading depolarizations (SDs) are a marker of brain injury and have a causative effect on ischemic lesion progression. The hemodynamic responses elicited by SDs are contingent upon the metabolic integrity of the affected tissue, with vasoconstrictive reactions leading to pronounced hypoxia often indicating poor outcomes. The stratification of hemodynamic responses within different cortical layers remains poorly characterized. This pilot study sought to elucidate the depth-specific hemodynamic changes in response to SDs within the gray matter of the gyrencephalic swine brain. Employing a potassium chloride-induced SD model, we utilized multispectral photoacoustic imaging (PAI) to estimate regional cerebral oxygen saturation (rcSO2%) changes consequent to potassium chloride-induced SDs. Regions of interest were demarcated at three cortical depths covering up to 4 mm. Electrocorticography (ECoG) strips were placed to validate the presence of SDs. Through PAI, we detected 12 distinct rcSO2% responses, which corresponded with SDs detected in ECoG. Notably, a higher frequency of hypoxic responses was observed in the deeper cortical layers compared to superficial layers, where hyperoxic and mixed responses predominated (p < 0.001). This data provides novel insights into the differential oxygenation patterns across cortical layers in response to SDs, underlining the complexity of cerebral hemodynamics post-injury.

Generation of two human induced pluripotent stem cell lines with BAX and BAK1 double knock-out using CRISPR/Cas9

Bcl-2-associated X protein (BAX) and Blc-2 homologous antagonist killer 1 (BAK) are two pro-apoptotic members of BCL2 family. Here, two BAX/BAK double knock-out human induced pluripotent stem cell lines (iPSC) we generated using CRISPR-Cas9 to generate apoptosis incompetent cell lines. The resulting cell lines were karyotypically normal, had typical morphology and expressed typical markers for the undifferentiated state.

Stroke in the Time of Circadian Medicine

Time-of-day significantly influences the severity and incidence of stroke. Evidence has emerged not only for circadian governance over stroke risk factors, but also for important determinants of clinical outcome. In this review, we provide a comprehensive overview of the interplay between chronobiology and cerebrovascular disease. We discuss circadian regulation of pathophysiological mechanisms underlying stroke onset or tolerance as well as in vascular dementia. This includes cell death mechanisms, metabolism, mitochondrial function, and inflammation/immunity. Furthermore, we present clinical evidence supporting the link between disrupted circadian rhythms and increased susceptibility to stroke and dementia. We propose that circadian regulation of biochemical and physiological pathways in the brain increase susceptibility to damage after stroke in sleep and attenuate treatment effectiveness during the active phase. This review underscores the importance of considering circadian biology for understanding the pathology and treatment choice for stroke and vascular dementia and speculates that considering a patient's chronotype may be an important factor in developing precision treatment following stroke.

An Assessment of Physical and N6-Cyclohexyladenosine-Induced Hypothermia in Rodent Distal Focal Ischemic Stroke

Therapeutic hypothermia (TH) mitigates damage in ischemic stroke models. However, safer and easier TH methods (e.g., pharmacological) are needed to circumvent physical cooling complications. This study evaluated systemic and pharmacologically induced TH using the adenosine A1 receptor agonist, N6-cyclohexyladenosine (CHA), with control groups in male Sprague-Dawley rats. CHA was administered intraperitoneally 10 minutes following a 2-hour intraluminal middle cerebral artery occlusion. We used a 1.5 mg/kg induction dose, followed by three 1.0 mg/kg doses every 6 hours for a total of 4 doses, causing 20-24 hours of hypothermia. Animals assigned to physical hypothermia and CHA-hypothermia had similar induction rates and nadir temperatures, but forced cooling lasted ∼6 hours longer compared with CHA-treated animals. The divergence is likely attributable to individual differences in CHA metabolism, which led to varied durations at nadir, whereas physical hypothermia was better regulated. Physical hypothermia significantly reduced infarction (primary endpoint) on day 7 (mean reduction of 36.8 mm3 or 39% reduction; p = 0.021 vs. normothermic animals; Cohen's d = 0.75), whereas CHA-induced hypothermia did not (p = 0.33). Similarly, physical cooling improved neurological function (physical hypothermia median = 0, physical normothermia median = 2; p = 0.008) and CHA-induced cooling did not (p > 0.99). Our findings demonstrate that forced cooling was neuroprotective compared with controls, but prolonged CHA-induced cooling was not neuroprotective.

Rectangular method: a modified technique for sampling the ischemic border zone in a rat model of transient middle cerebral artery occlusion

To date, there have been three common methods for sampling the cerebral ischemic border zone in a rat model of transient middle cerebral artery occlusion (tMCAO): the "two o'clock method", the "diagonal method", and the "parallel line method". However, these methods have their own advantages and limitations. Here, we propose a modified technique (the "rectangular method") for sampling the ischemic border zone. A rat tMCAO model was prepared under the support of a compact small animal anesthesia machine. Cerebral blood flow was monitored by high-resolution laser Doppler to control the quality of modeling, and 2,3,5-triphenyl tetrazolium chloride (TTC) staining was used for cerebral infarction location assessment. Superoxide dismutase 2 (SOD2), cysteinyl aspartate specific proteinase (caspase)-3, caspase-9, and heat shock protein 70 (HSP70) were used to verify the reliability and reproducibility of the rectangular method. The expression of biomarkers (SOD2, caspase-3, caspase-9, and HSP70) in the traditional (two o'clock method after TTC staining) and modified (rectangular method) groups were increased. There were no significant differences between the groups. The rectangular method proposed herein is based on a modification of the diagonal method and parallel line method, which could provide a directly observable infarct borderline and a sufficient sampling area for subsequent experimental operations regardless of the cerebral infarct location. The assessed biomarkers (SOD2, caspase-3, caspase-9, and HSP70) demonstrated the reliability and reproducibility of the rectangular method, which may facilitate inter-laboratory comparisons.

Ischemic stroke-related gene expression profiles across species: a meta-analysis

Stroke patients are often left with permanent disabilities with no regenerative treatment options. Unbiased RNA sequencing studies decoding the transcriptional signature of stroked tissue hold promise to identify new potential targets and pathways directed to improve treatment for stroke patients. Here, gene expression profiles of stroked tissue across different time points, species, and stroke models were compared using NCBI GEO database. In total, 34 datasets from mice, rats, humans, and primates were included, exploring gene expression differences in healthy and stroked brain tissue. Distinct changes in gene expression and pathway enrichment revealed the heterogenicity of the stroke pathology in stroke-related pathways e.g., inflammatory responses, vascular repair, remodelling and cell proliferation and adhesion but also in diverse general, stroke-unrelated pathways that have to be carefully considered when evaluating new promising therapeutic targets.

Perfusion Status in Lacunar Stroke: A Pathophysiological Issue

The pathophysiology of lacunar infarction is an evolving and debated field, where relevant information comes from histopathology, old anatomical studies and animal models. Only in the last years, have neuroimaging techniques allowed a sufficient resolution to directly or indirectly assess the dynamic evolution of small vessel occlusion and to formulate hypotheses about the tissue status and the mechanisms of damage. The core-penumbra concept was extensively explored in large vessel occlusions (LVOs) both from the experimental and clinical point of view. Then, the perfusion thresholds on one side and the neuroimaging techniques studying the perfusion of brain tissue were focused and optimized for LVOs. The presence of a perfusion deficit in the territory of a single small perforating artery was negated for years until the recent proposal of the existence of a perfusion defect in a subgroup of lacunar infarcts by using magnetic resonance imaging (MRI). This last finding opens pathophysiological hypotheses and triggers a neurovascular multidisciplinary reasoning about how to image this perfusion deficit in the acute phase in particular. The aim of this review is to summarize the pathophysiological issues and the application of the core-penumbra hypothesis to lacunar stroke.

[Oxidative stress in the pathogenesis of stroke and its correction]

We reviewed the role of oxidative stress (OS) in the pathogenesis of ischemic (IS) and hemorrhagic stroke (HS). OS plays a major role in programmed cell death, increased permeability of the blood-brain barrier, astroglial and microglial activation, and local inflammatory response. We also reviewed the current state of neuro- and cytoprotection studies and their translation in clinical practice. With respect to experimental and clinical data the efficacy of long term administration of multimodal cytoprotective drug with antioxidant effect - ethylmethylhydroxypyridine succinate (Mexidol) is discussed during the acute and early recovery period after stroke.