Ronen R. Leker

Growth factors improve neurogenesis and outcome after focal cerebral ischemia

Stem cells have been proposed as a new form of cell-based therapy in a variety of disorders, including acute and degenerative brain diseases. Endogenous neural stem cells (eNSC) reside in the subventricular zone and in the subgranular zone of the hippocampus. eNSC are capable of self-renewal and differentiation into functional glia and neurons. Unfortunately, spontaneous brain regeneration is inefficient for clinically significant improvement following brain injury. However, eNSC responses may be augmented considerably by perturbing the pathways governing cell proliferation, migration and differentiation by application of exogenous growth factors. Importantly, current evidence suggests that such perturbations may lead to better functional outcome after stroke. This article summarizes the progress made in this field.

Leptin Induces Neuroprotection Neurogenesis and Angiogenesis after Stroke

Leptin is a potent AMP kinase (AMPK) inhibitor that is central to cell survival. Hence, we explored the effects of leptin on neurogenesis and angiogenesis after stroke. Neural stem cells (NSC) were grown as neurospheres in culture and treated with vehicle or leptin and neurosphere size and terminal differentiation were then determined. We then explored the effects of leptin on endogenous repair mechanisms in vivo. Sabra mice underwent photothrombotic stroke, were given vehicle or leptin and newborn cells were labeled with Bromo-deoxy-Uridine. Functional outcome was studied with the neurological severity score for 90 days post stroke and the brains were then evaluated with immunohistochemistry. In a subset of animals the brains were also evaluated for changes in the expression of leptin receptor and AMPK. In vitro, leptin led to a 2-fold increase in neurosphere size but did not change the differentiation of newborn cells. Following stroke, exogenous leptin led to a 4-fold increase in the number of NSC in the cortex abutting the lesion. There was a 1.5-fold increase in the number of newborn neurons and glia in leptin treated animals. Leptin also significantly increased the number of blood vessels in the peri-lesioned cortex. Leptin treated mice had increased expression of leptin receptor and increased phosphorylated AMPK concentration. Animals treated with leptin also had significantly better functional states. In conclusion, leptin induces neurogenesis and angiogenesis after stroke and leads to increased leptin receptor and pAMPK concentrations. This may explain at least in part the better functional outcome observed in leptin treated animals after stroke.

State-of-the-art reperfusion strategies for acute ischemic stroke

Timely recanalization of the occluded artery is the only effective treatment for acute ischemic stroke. Intravenous tissue plasminogen activator (i.v. tPA), administered within 3 hours of symptom onset, is the only United States Food and Drug Administration-approved treatment. This short window often precludes effective intervention, and i.v. tPA often fails to recanalize major and mid-sized arteries. Intra-arterial thrombolysis has been used for decades, but its safety and effectiveness in cerebrovascular occlusions is also limited. Recently, new mechanical neuroendovascular devices have shown high recanalization rates with acceptable safety in early studies. Multi-modal reperfusion therapy (MMRT)--including intra-arterial infusion of thrombolytics and/or antiplatelet agents, mechanical clot disruption and retrieval, and balloon angioplasty with stent placement--is the prevailing concept for the management of major acute stroke. Recent results suggest that MMRT results in higher chances for both recanalization of the occluded artery and reperfusion of the ischemic tissue.

Leptin reduces infarct size in association with enhanced expression of CB2, TRPV1, SIRT-1 and leptin receptor.

Brain ischemia is associated with detrimental changes in energy production and utilization. Therefore, we hypothesized that leptin, an adipokynin hormone protecting against severe energy depletion, would reduce infarct volume and improve functional outcome after stroke. Male Sabra mice underwent permanent middle cerebral artery occlusion (PMCAO) by photothrombosis. Following initial dose-response and time-window experiments animals were treated with vehicle or leptin, were examined daily by a neurological severity score (NSS) and were sacrificed 72 hours after stroke. Infarct volume was determined and the expression of key genes involved in neuroprotection and survival including the cannabinoid receptors CB1, CB2 and TRPV1, SIRT-1, leptin receptor and Bcl-2 was quantified in the cortex. A separate group of mice were examined with the neurological severity scale 1, 24 and 48 hours and 1, 2 and 3 weeks after stroke, and were killed 3 weeks post stroke to examine metabolic status in the peri-infarct area. Leptin given at a dose of 1mg/kg intra-peritoneally 30 minutes after PMCAO significantly improved neurological disability and reduced infarct volume. Leptin treatment led to increased expression of CB2 receptor, TRPV1, SIRT-1 and leptin receptor and reduced expression of CB1 receptor. There was also a non-significant increase in Bcl-2 gene expression following leptin administration. These results suggest that leptin may be used for attenuating ischemic injury after stroke via induction of an anti-apoptotic state.

Multimodal reperfusion therapy in patients with acute basilar artery occlusion.

OBJECTIVEMultimodal reperfusion therapy (MMRT) has been advocated for the treatment of acute basilar artery occlusion (ABAO). We aimed to identify prognostic factors in patients with ABAO who underwent MMRT. METHODSClinical and radiological data from consecutive ABAO patients were analyzed. All patients underwent MMRT on an emergency basis. Stroke subtypes were categorized according to TOAST (Trial of ORG 10172 in Acute Stroke Treatment) criteria. Good outcome was defined as a modified Rankin Scale score of 3 or less and poor outcome as a score of 4 or more at 30 days poststroke. RESULTSTwenty-four patients were included (18 men, 6 women) with a mean age of 54.7 years (age range, 26–70 years). Six patients died (25%), and 8 of the surviving 18 patients (44%) achieved a modified Rankin Scale score of 3 or less at 30 days. We could not identify any clinical or radiological variables that were associated with a greater likelihood of good or poor outcome at 30 days other than the presence of good collateral circulation, which was associated with better outcome on univariate analysis. CONCLUSIONMMRT resulted in high survival and good outcome rates. We could not identify prognostic factors in patients with ABAO treated with MMRT other than the presence of collateral flow. Our results imply that patients should not be excluded from treatment based on clinical or radiological parameters, and that all patients with ABAO should be given the chance to benefit from therapy.

Central fever in patients with spontaneous intracerebral hemorrhage: predicting factors and impact on outcome

BackgroundCentral fever (CF) is defined as elevated temperature with no identifiable cause. We aimed to identify risk factors for developing CF among patients with spontaneous intracerebral hemorrhage (ICH) and to evaluate the impact of CF on outcome.MethodsPatients included in our prospective stroke registry between 1/1/09 and 1/10/10 were studied. We identified patients with CF as those with a temperature ≥38.3°C without evidence for infection or drug fever. Patients with CF were compared to those without fever and those with infectious fever. Demographics, risk factors and imaging data as well as outcome parameters were reviewed.ResultsWe identified 95 patients with spontaneous ICH (median age 76, median admission NIHSS 9). CF was identified in 30 patients (32%), infectious etiology was found in 9 patients (9%) and the remaining patients did not develop fever. Baseline variables were similar between the groups except for intra-ventricular extension of the ICH (IVH) and larger ICH volumes that were more common in the CF group (ORu2009=u20094.667, 95% CI 1.658-13.135 and ORu2009=u20091.013/ml, 95% CI 1.004-1.021). Outcome analysis showed higher mortality rates (80% vs. 36%, pu2009<u20090.001) and lower rates of favorable functional outcome defined as a modified Rankin scoreu2009≤u20092 at 90xa0days (0% vs. 53%, pu2009<u20090.001) in the CF group.ConclusionsThe risk of CF is increased in patients with larger ICH and in those with IVH. CF negatively impacts outcome in patients with ICH.

Multi-Modal Reperfusion Therapy for Patients With Acute Anterior Circulation Stroke in Israel

Background and Purpose— We aimed to delineate prognostic variables in Israeli patients with anterior circulation strokes treated with endovascular multi-modal reperfusion therapy (MMRT). Methods— Clinical and radiological data from consecutive tpa-ineligible stroke patients with large anterior circulation infarcts involving either the entire internal carotid artery or the proximal middle cerebral artery territory were analyzed. Stroke subtypes were categorized according to TOAST criteria. Neurological deficits were assessed with the NIH stroke scale (NIHSS), and vessel recanalization was determined using the thrombolysis in myocardial infarction (TIMI) scale at the end of MRRT. Good outcome was defined as a modified Rankin score (mRS) ≤2. Results— Fifty patients were included with a median age of 68. Thirteen patients died and 17 patients achieved an mRS ≤2 at 90 days. Variables associated with survival on multivariate analysis were admission NIHSS <20 (OR 15 95% CI 1 to 230) and postprocedure TIMI score 2 to 3 (OR 35.5 95% CI 2.3 to 603.9). Variables associated with good outcome included admission NIHSS <20 (OR 9.4 95% CI 1.3 to 71.3), day 1 NIHSS <15 (OR 6.4 95% CI 1.1 to 38.4), and postprocedure TIMI 3 (OR 7.4 95% CI 1.1 to 50.3). Conclusions— MMRT resulted in high survival and good outcome rates in these critically ill patients. Lower baseline impairment and vessel recanalization increase the chances for good outcome. Our results suggest that the benefits of MMRT may merit further study and could be generalized to centers outside the United States and Europe.

Delayed leptin administration after stroke induces neurogenesis and angiogenesis

Leptin is a potent AMP kinase (AMPK) inhibitor that induces neuroprotection, neurogenesis, and angiogenesis when administered immediately after stroke. To dissociate these effects, we explored the effects of delayed administration of leptin, at 10 days after stroke onset, on neurogenesis and angiogenesis after stroke. Sabra mice underwent photothrombotic stroke and were treated with vehicle or leptin given either as a single dose or in triple dosing, 10 days later. Newborn cells were labeled with bromodeoxyuridine. Functional outcome was studied with the neurological severity score for 90 days poststroke, and the brains were then evaluated via immunohistochemistry. Final infarct volumes did not differ between the groups. Exogenous leptin led to significant increments in the number of proliferating BrdU+ cells in the subventricular zone and in the cortex abutting the lesion (2.5‐fold and 1.4‐fold, respectively). There were significant increments in the number of newborn neurons and glia (4‐ and 3.4‐fold, respectively) in leptin‐treated animals. Leptin also significantly increased the number of blood vessels in the perilesioned cortex. However, animals treated with leptin failed to demonstrate significantly better functional states. In conclusion, leptin induces neurogenesis and angiogenesis even when given late after stroke but does not lead to better functional outcome in this delayed‐treatment paradigm. These results suggest that the main beneficial effects of leptin after stroke are associated with its early neuroprotective role rather than with its proneurogenic or proangiogenic effects.

Bone marrow-derived nonreactive astrocytes in the mouse brain after permanent middle cerebral artery occlusion

We studied the effect of permanent unilateral middle cerebral artery occlusion (PMCAO) on the generation of bone marrow (BM)-derived astrocytes in female mice previously transplanted with enhanced green fluorescent protein-expressing BM from male donors. In addition to an untreated PMCAO group, one group of mice also received intracerebral infusion of transforming growth factor-alpha, resulting in a decrease in the size of the infarct. Two months after PMCAO, we found a specific type of astrocyte of BM origin in the side of the injury, near the lesion. These astrocytes did not express glial fibrillary acidic protein (GFAP) by conventional fluorescence immunostaining; however, GFAP was easily detectable by tyramide signal amplification. These cells also expressed S100β, confirming their astrocytic character. Unlike the endogenous reactive astrocytes, these BM-derived astrocytes did not proliferate during the first week of ischemia and did not contribute to the glial scar formation. Transforming growth factor-alpha infusion increased the number of BM-derived astrocytes, without affecting their distribution. Interestingly, exclusively by tyramide signal amplification staining, we found that endogenous astrocytes displaying an identical morphology were also present in control mouse and human brains. Our data demonstrate that a subpopulation of nonreactive astrocytes expressing low levels of GFAP can originate from transplanted BM in the ischemic brain. We believe that these cells represent a subpopulation of astrocytes earlier considered to be GFAP negative. The high number of astrocytes with identical morphology and chemical character in control brains suggest that these type of astrocytes may have important functional role in the central nervous system that calls for further studies.

Therapeutic modalities in symptomatic intracranial arterial occlusive disease

Abstract Intracranial atherosclerotic disease (ICAD) is a frequent cause of stroke that is sometimes underdiagnosed. In this review, we survey the literature concerning ICAD and present the prognostic factors and the therapeutic options pertinent to it by comparing medical, surgical and endovascular approaches.