Mustafa Balkaya

Essential role of interleukin-6 in post-stroke angiogenesis

Ambivalent effects of interleukin-6 on the pathogenesis of ischaemic stroke have been reported. However, to date, the long-term actions of interleukin-6 after stroke have not been investigated. Here, we subjected interleukin-6 knockout (IL-6(-/-)) and wild-type control mice to mild brain ischaemia by 30-min filamentous middle cerebral artery occlusion/reperfusion. While ischaemic tissue damage was comparable at early time points, IL-6(-/-) mice showed significantly increased chronic lesion volumes as well as worse long-term functional outcome. In particular, IL-6(-/-) mice displayed an impaired angiogenic response to brain ischaemia with reduced numbers of newly generated endothelial cells and decreased density of perfused microvessels along with lower absolute regional cerebral blood flow and reduced vessel responsivity in ischaemic striatum at 4 weeks. Similarly, the early genomic activation of angiogenesis-related gene networks was strongly reduced and the ischaemia-induced signal transducer and activator of transcription 3 activation observed in wild-type mice was almost absent in IL-6(-/-) mice. In addition, systemic neoangiogenesis was impaired in IL-6(-/-) mice. Transplantation of interleukin-6 competent bone marrow into IL-6(-/-) mice (IL-6(chi)) did not rescue interleukin-6 messenger RNA expression or the early transcriptional activation of angiogenesis after stroke. Accordingly, chronic stroke outcome in IL-6(chi) mice recapitulated the major effects of interleukin-6 deficiency on post-stroke regeneration with significantly enhanced lesion volumes and reduced vessel densities. Additional in vitro experiments yielded complementary evidence, which showed that after stroke resident brain cells serve as the major source of interleukin-6 in a self-amplifying network. Treatment of primary cortical neurons, mixed glial cultures or immortalized brain endothelia with interleukin 6-induced robust interleukin-6 messenger RNA transcription in each case, whereas oxygen-glucose deprivation did not. However, oxygen-glucose deprivation of organotypic brain slices resulted in strong upregulation of interleukin-6 messenger RNA along with increased transcription of key angiogenesis-associated genes. In conclusion, interleukin-6 produced locally by resident brain cells promotes post-stroke angiogenesis and thereby affords long-term histological and functional protection.

Intravenous Rosuvastatin for Acute Stroke Treatment: An Animal Study

Background and Purpose— Statins exert rapid cholesterol-independent vasoprotective effects. Here, we tested whether postevent treatment with intravenously (i.v.) administered rosuvastatin improves acute stroke outcome in mice. Methods— 129/SV wild-type mice were subjected to 1-hour filamentous middle cerebral artery occlusion (MCAo), followed by reperfusion, and were postevent treated with i.v. or intraperitoneal (i.p.) rosuvastatin given up to 6 hours after MCAo (dose range 0.02 to 20 mg kg−1 body weight). Results— Rosuvastatin, when administered i.v., significantly reduced lesion size when given up to 4 hours after MCAo and in doses as low as 0.2 mg kg−1. In contrast, i.p. administration provided protection only when given directly on reperfusion at a dose of 20 mg kg−1 but not at lower doses or later time points. Lesion protection was evident as late as 5 days after brain ischemia and was associated with functional improvements in the pole-test and wire-hanging test (2.0 mg kg−1 dose). Neuroprotection with i.v. rosuvastatin was achieved with peak plasma concentrations <0.5 ng ml−1 (ie, with 0.2 mg kg−1) and was associated with increased levels of phosphorylated Akt kinase and endothelial nitric oxide synthase in the vasculature. Conclusions— Rosuvastatin, given intravenously at pharmacologically relevant concentrations, protects from focal brain ischemia up to 4 hours after an event. In our opinion, the development of an intravenous statin formulation is warranted for acute stroke trials with statins in humans.

Folate Deficiency Induces Neurodegeneration and Brain Dysfunction in Mice Lacking Uracil DNA Glycosylase

Folate deficiency and resultant increased homocysteine levels have been linked experimentally and epidemiologically with neurodegenerative conditions like stroke and dementia. Moreover, folate deficiency has been implicated in the pathogenesis of psychiatric disorders, most notably depression. We hypothesized that the pathogenic mechanisms include uracil misincorporation and, therefore, analyzed the effects of folate deficiency in mice lacking uracil DNA glycosylase (Ung−/−) versus wild-type controls. Folate depletion increased nuclear mutation rates in Ung−/− embryonic fibroblasts, and conferred death of cultured Ung−/− hippocampal neurons. Feeding animals a folate-deficient diet (FD) for 3 months induced degeneration of CA3 pyramidal neurons in Ung−/− but not Ung+/+ mice along with decreased hippocampal expression of brain-derived neurotrophic factor protein and decreased brain levels of antioxidant glutathione. Furthermore, FD induced cognitive deficits and mood alterations such as anxious and despair-like behaviors that were aggravated in Ung−/− mice. Independent of Ung genotype, FD increased plasma homocysteine levels, altered brain monoamine metabolism, and inhibited adult hippocampal neurogenesis. These results indicate that impaired uracil repair is involved in neurodegeneration and neuropsychiatric dysfunction induced by experimental folate deficiency.

Assessing Post-Stroke Behavior in Mouse Models of Focal Ischemia:

Experimental treatment strategies and neuroprotective drugs that showed therapeutic promise in animal models of stroke have failed to produce beneficial effects in human stroke patients. The difficulty in translating preclinical findings to humans represents a major challenge in cerebrovascular research. The reasons behind this translational road block might be explained by a number of factors, including poor quality control in various stages of the research process, the validity of experimental stroke models, and differences in drug administration and pharmacokinetics. Another major difference between animal studies and clinical trials is the choice of end point or outcome measures. Here, we discuss the necessity of poststroke behavioral testing to bridge the gap between clinical and experimental end points. We review established sensory-motor tests for outcome determination after focal ischemia based on the published literature as well as our own personal experience. Selected tests are described in more detail and good laboratory practice standards for behavioral testing are discussed. This review is intended for stroke researchers planning to use behavioral testing in mice.

Anxious and Hyperactive Phenotype Following Brief Ischemic Episodes in Mice

BACKGROUND Poststroke emotional and behavioral abnormalities have an impact on outcome but have scarcely been characterized in animal models. We tested whether brief ischemic episodes induce behavioral changes in mice. METHODS 129/Sv mice were subjected to 30-min occlusion of left or right middle cerebral artery (MCAo) followed by reperfusion or sham operation (n = 9 or 10 per group). Eight to ten weeks later, mice were tested for spontaneous locomotor activity, anxiety in the elevated plus maze, and depressive behavior in the modified Porsolt forced swim test. Outcome was correlated to monoamine and amino acid levels and compared with histologic damage at 10 weeks. RESULTS Ischemia was associated with increased activity (right MCAo) and anxiety (left MCAo), but not poststroke depression. Noradrenaline increased by 30%-45% in the ischemic striatum and correlated with locomotor activity (r = .48); dopamine and homovanillinic acid were decreased compared with sham. The lesion was confined to the striatum, and scattered neuronal death was observed in a number of remote brain regions. CONCLUSION Brief ischemic episodes in the mouse induce an anxious, hyperactive but not depressive phenotype that may relate to left versus right hemispheric lesion location, alterations in brain monoamine levels, and selective neurodegeneration.

Characterization of long-term functional outcome in a murine model of mild brain ischemia.

Evaluation of functional outcome over the course of several weeks after ischemia is a key component in improving the clinical relevance of experimental stroke studies. Using a battery of behavioral tests, we characterized functional outcome in mice over 4 weeks following 30min of proximal middle cerebral artery occlusion (MCAo). We evaluated rotarod, chimney, pole and cylinder tests to assess short term functional deficits in a transient stroke model which induces infarcts mainly in the striatum. The corner test, adhesive removal test, cylinder test, catwalk, paw preference test and novel tests of rotation were evaluated for long-term functional outcome. Rotarod detected deficits within the first week and pole test was reliable up to intermediate time points after MCAo. Corner test, adhesive removal test, catwalk and paw preference test detected deficits for up to 4 weeks, as did the novel corner rotation and bowl tests. Chimney and cylinder test did not prove useful in our model of mild stroke. In summary, we established the pole test and rotarod as useful tools to evaluate sensory motor deficits early after mild stroke, and corner test and adhesive removal test at later time-points. Alternatively, corner rotation may be a suitable test of long-term function. Test batteries may be further complemented by catwalk and paw preference test for clinically relevant deficits. There was no correlation of behavioral outcome with lesion size at 28 days, and determining whether these tests are useful for detecting a potential benefit of neuroprotective or regenerative therapies requires further testing.

Exofocal Dopaminergic Degeneration as Antidepressant Target in Mouse Model of Poststroke Depression

BACKGROUND Although poststroke depression (PSD) is a frequent chronic complication of stroke with high relevance for outcome and survival, underlying pathomechanisms remain inadequately understood. This may be because suitable animal models are largely lacking and existing models are poorly characterized. METHODS Male 129/SV mice were subjected to 30-min middle cerebral artery occlusion (MCAo)/reperfusion and serial magnetic resonance imaging scans. A subset of animals received selective serotonin reuptake inhibitor citalopram starting 7 days after MCAo. Behavioral assessment was performed at 14 weeks. To identify biological correlates of PSD, we quantified corticosterone levels in serum and brain-derived neurotrophic factor levels in brain. The integrity of the mesolimbic dopaminergic system was assessed using tyrosine hydroxylase and dynorphin in situ hybridizations as well as dopamine transporter autoradiography. RESULTS Left, but not right, MCAo, elicited anhedonia and increased anxiety and despair. This depression-like syndrome was associated with alterations in the mesolimbic reward system. MCAo resulted in delayed degeneration of dopaminergic neurons in ipsilateral midbrain, which was accompanied by reduced dopamine concentrations and decreased levels of dopamine transporter density along with increased brain-derived neurotrophic factor protein levels in ischemic striatum and increased dynorphin messenger RNA expression in nucleus accumbens. Chronic antidepressant treatment initiated as late as 7 days after stroke reversed the behavioral phenotype, prevented degeneration of dopaminergic midbrain neurons, and attenuated striatal atrophy at 4 months. CONCLUSIONS Our results highlight the importance of the dopaminergic system for the development of PSD. Prevention of secondary neurodegeneration by antidepressants may provide a novel target for subacute stroke therapy.

Selective ROCK2 inhibition in focal cerebral ischemia

Rho‐associated kinase (ROCK) is a key regulator of numerous processes in multiple cell types relevant in stroke pathophysiology. ROCK inhibitors have improved outcome in experimental models of acute ischemic or hemorrhagic stroke. However, the relevant ROCK isoform (ROCK1 or ROCK2) in acute stroke is not known.

Heart Rate Contributes to the Vascular Effects of Chronic Mental Stress: Effects on Endothelial Function and Ischemic Brain Injury in Mice

Background and Purpose— Vascular effects of mental stress are only partially understood. Therefore, we studied effects of chronic stress and heart rate (HR) on endothelial function and cerebral ischemia. Methods— 129S6/SvEv mice were randomized to the I(f)-channel inhibitor ivabradine (10 mg/kg per day) or vehicle and underwent a chronic stress protocol for 28 days. Results— Stress increased HR from 514±10 bpm to 570±14 bpm, this was prevented by ivabradine (485±7 bpm). Endothelium-dependent relaxation of aortic rings was impaired in mice exposed to stress. HR reduction restored endothelial function to the level of naive controls. Vascular lipid hydroperoxides were increased to 333%±24% and vascular NADPH oxidase activity was upregulated to 223±38% in stressed mice, which was prevented by ivabradine. Stress reduced aortic endothelial nitric oxide synthase mRNA expression to 84%±3% and increased AT1 receptor mRNA to 168%±18%. Both effects were attenuated by HR reduction. In brain tissue, stress resulted in an upregulation of lipid hydroperoxides to 140%±11%, which was attenuated by HR reduction. Ivabradine increased brain capillary density in naive and in stressed mice. Mice exposed to chronic stress before induction of ischemic stroke by transient middle cerebral artery occlusion exhibited increased lesion size (33.7±2.3 mm3 versus 23.9±2.4 mm3). HR reduction led to a marked reduction of the infarct volume to 12.9±3.3 mm3. Conclusions— Chronic stress impairs endothelial function and aggravates ischemic brain injury. HR reduction protects from cerebral ischemia via improvement of endothelial function and reduction of oxidative stress. These results identify heart rate as a mediator of vascular effects induced by chronic stress.

Stress Worsens Endothelial Function and Ischemic Stroke via Glucocorticoids

Background and Purpose— Chronic stress is associated with increased stroke risk. However, the underlying pathophysiological mechanisms are poorly understood. We examined the effects of chronic stress on endothelial function and ischemic brain injury in a mouse model. Methods— 129/SV mice were treated with glucocorticoid receptor antagonist mifepristone (25 mg kg−1/d) or vehicle and exposed to 28 days of chronic stress consisting of exposure to rat, restraint stress, and tail suspension. Heart rate and blood pressure were continuously recorded by telemetry. Endothelial nitric oxide synthase mRNA and protein expression as well as superoxide production and lipid hydroperoxides were quantified. Endothelium-dependent vasorelaxation was measured in aortic rings. Ischemic lesion volume was quantified after 30 minutes filamentous middle cerebral artery occlusion and 72 hours reperfusion. Results— Chronic stress caused a significant increase in heart rate, impaired endothelium-dependent vasorelaxation, increased superoxide production, and reduced aortic and brain endothelial nitric oxide synthase levels. Animals exposed to chronic stress showed major increases in ischemic lesion size. These deleterious effects of stress were completely reversed by treatment with mifepristone. Conclusions— Chronic stress increases stroke vulnerability likely through endothelial dysfunction, which can be reversed by a glucocorticoid receptor antagonist.