Social isolation initiated post-weaning augments ischemic brain injury by promoting pro-inflammatory responses.

Social isolation is associated with poor stroke outcome, but the underlying molecular mechanisms were largely unknown. In male Balb/C mice exposed to transient middle cerebral artery occlusion (MCAo), we examined the effects of social isolation initiated post-weaning on ischemic injury, cytokine/chemokine responses and cell signaling using a broad panel of techniques that involved immunocytochemistry, cytokine/chemokine array and Western blots. Social isolation initiated post-weaning elevated infarct size, brain edema and neuronal injury in the ischemic brain tissue 3 days after MCAo, and increased microglia/ macrophage and leukocyte accumulation. In line with the increased immune cell recruitment, levels of several proinflammatory cytokines (e.g., IL-1α, IL-1ß, IL-13, IL-17, TNF-α, IFN-γ), chemokines (e.g., CCL3, CCL4, CCL12, CXCL2, CXCL9, CXCL12) and adhesion molecules (i.e., ICAM-1) were increased in the ischemic brain tissue of socially isolated compared with paired housing mice, whereas levels of selected cytokines (IL-5, IL-6, IL-16) and colony-stimulating factors (G-CSF, GM-CSF) were reduced. The activity of the transcription factor nuclear factor-ĸB (NF-ĸB), which promotes cell injury via pro-inflammatory responses, was increased by social isolation, whereas that of nuclear factor erythroid related factor-2 (Nrf-2), which mediates anti-oxidative responses under oxidative stress conditions, was reduced. Our study shows that social isolation profoundly alters post-ischemic cell signaling in a way promoting pro-inflammatory responses. Our results highlight the importance of social support in preventing deleterious health effects of social isolation.

The Unconventional Growth Factors Cerebral Dopamine Neurotrophic Factor and Mesencephalic Astrocyte-Derived Neurotrophic Factor Promote Post-ischemic Neurological Recovery, Perilesional Brain Remodeling, and Lesion-Remote Axonal Plasticity.

Considerable efforts are currently made to develop strategies that boost endogenous recovery once a stroke has occurred. Owing to their restorative properties, neurotrophic factors are attractive candidates that capitalize on endogenous response mechanisms. Non-conventional growth factors cerebral dopamine neurotrophic factor (CDNF) and mesencephalic astrocyte-derived neurotrophic factor (MANF) promote neuronal survival and reduce neurological deficits in the acute phase of ischemic stroke in mice. Their effects on endogenous repair and recovery mechanisms in the stroke recovery phase were so far unknown. By intracerebroventricular delivery of CDNF or MANF starting 3 days post-stroke (1 µg/day for 28 days via miniosmotic pumps), we show that delayed CDNF and MANF administration promoted functional neurological recovery assessed by a battery of behavioral tests, increased long-term neuronal survival, reduced delayed brain atrophy, glial scar formation, and, in case of CDNF but not MANF, increased endogenous neurogenesis in the perilesional brain tissue. Besides, CDNF and MANF administration increased long-distance outgrowth of terminal axons emanating from the contralesional pyramidal tract, which crossed the midline to innervate ipsilesional facial nucleus. This plasticity promoting effect was accompanied by downregulation of the axonal growth inhibitor versican and the guidance molecules ephrin B1 and B2 in the previously ischemic hemisphere at 14 dpi, which represents a sensitive time-point for axonal growth. CDNF and MANF reduced the expression of the proinflammatory cytokines IL1ß and TNFα in both hemispheres. The effects of non-conventional growth factors in the ischemic brain should further be examined since they might help to identify targets for restorative stroke therapy.

Phosphorylation of PI3K/Akt at Thr308, but not phosphorylation of MAPK kinase, mediates lithium-induced neuroprotection against cerebral ischemia in mice.

Lithium, in addition to its effect on acute and long-term bipolar disorder, is involved in neuroprotection after ischemic stroke. Yet, its mechanism of action is still poorly understood, which was only limited to its modulatory effect on GSK pathway. Therefore, we initially analyzed the dose-dependent effects of lithium on neurological deficits, infarct volume, brain edema and blood-brain barrier integrity, along with neuronal injury and survival in mice subjected to focal cerebral ischemia. Thereafter, we investigated the involvement of the PI3K/Akt and MEK signal transduction pathways and their components. Our observations revealed that 2 mmol/kg lithium significantly improved post-ischemic brain tissue survival. Although, 2 mmol/kg lithium had no negative effect on brain microcirculation, 5 and 20 mmol/kg lithium reduced brain perfusion. Furthermore, supratherapeutic dose of lithium in 20 mmol/kg lead to animal death. In addition, improvement of brain perfusion with L-arginine, did not change the effect of 5 mmol/kg lithium on brain injury. Additionally, post-stroke blood-brain barrier leakage, hemodynamic impairment and apoptosis have been reversed by lithium treatment. Interestingly, lithium-induced neuroprotection was associated with increased phosphorylation of Akt at Thr308 and suppressed GSK-3ß phosphorylation at Ser9 residue. Lithium upregulated Erk-2 and downregulated JNK-2 phosphorylation. To distinguish whether neuroprotective effects of lithium are modulated by PI3K/Akt or MEK, we sequentially blocked these pathways and demonstrated that the neuroprotective activity of lithium persisted during MEK/ERK inhibition, whereas PI3K/Akt inhibition abolished neuroprotection. Collectively, we demonstrated lithium exerts its post-stroke neuroprotective activity via the PI3K/Akt pathway, specifically via Akt phosphorylation at Thr308, but not via MEK/ERK.

A Co-Doped Fe3O4 Nanozyme Shows Enhanced Reactive Oxygen and Nitrogen Species Scavenging Activity and Ameliorates the Deleterious Effects of Ischemic Stroke.

Acute ischemic stroke has become the major cause of mortality and disability worldwide. Following ischemic stroke, the reperfusion injury is mainly mediated by the burst of reactive oxygen and nitrogen species (RONS). Therefore, blocking the excessive production or removing RONS holds great promise as a potential therapeutic strategy. Herein, we developed a Co-doped Fe3O4 nanozyme that is capable of scavenging H2O2, O2•-, •NO, and ONOO- in vitro and in vivo and provides neuroprotection against ischemic stroke. In vitro experiments showed that pre-incubation with the Co-Fe3O4 nanozyme could prevent neurotoxicity and neuroinflammation induced by H2O2 or lipopolysaccharide, respectively, in HT22 cells. After intravenous administration, the Co-Fe3O4 nanozyme showed no signs of toxicity in peripheral organs of C57BL/6J mice, even after prolonged delivery for 4 weeks. In permanent photothrombotic stroke model and transient middle cerebral artery occlusion stroke model, the Co-Fe3O4 nanozyme specifically accumulated in the infarct rim at 72 h post-stroke and was endocytosed by neurons, astrocytes, microglia, and endothelial cells. Importantly, the Co-Fe3O4 nanozyme delivery reduced the infarct volume in both stroke models. The observation that the Co-Fe3O4 nanozyme was efficacious in two well-characterized ischemic stroke models provides strong evidence that it represents a powerful tool for targeting oxidative and nitrosative stress in the ischemic brain.

Ginkgo biloba and Its Constituent 6-hydroxykynurenic-acid as well as Its Proanthocyanidins Exert Neurorestorative Effects against Cerebral Ischemia.

Neuroprotective effects against cerebral ischemia/reperfusion (I/R) injury by Ginkgo biloba leaves are commonly attributed to the antioxidant activity of its proanthocyanidins. Furthermore, preliminary experiments identified 6-hydroxykynurenic acid (6-HKA) as a major contributor to this effect of extract of G. biloba leaves (EGb) prepared according to the Chinese Pharmacopoeia (ChP). In order to elucidate the specific contribution of both proanthocyanidins and 6-HKA to the overall neurorestorative effects of this extract according to ChP, EGb ChP was separated into pure 6-HKA and a newly developed Ginkgo proanthocyanidin extract (GPE), enriched in proanthocyanidins but not containing 6-HKA. Male Sprague-Dawley rats were divided into the groups: sham: 8; model (placebo): 25; GPE 80 mg/kg: 13; GPE 40 mg/kg: 13; GPE 20 mg/kg: 16; grape seed extract (negative control) 40 mg/kg: 18; nimodipine (positive control) 2 mg/kg: 8. All non-sham animals were subjected to cerebral I/R injury by occluding the middle cerebral artery with a nylon suture that was removed after 2 h of ischemia to establish reperfusion. For comparison, a parallel series of experiments were performed with 6-HKA. In these in vivo experiments, neurological dysfunctions were reduced by both GPE and 6-HKA, and both average infarct size and concentrations of malondialdehyde (MDA) and super oxide dismutase (SOD) were significantly ameliorated as compared to the model group. This data, therefore, demonstrates that the neuroprotective effects of EGb cannot be explained by a purely chemical antioxidative effect alone as has been previously proposed, especially with regards to the proanthocyanidins. A pharmacological neurorestorative effect of EGb on neurons and brain tissue itself seems to be a much more straightforward explanation for the presented observations. This effect is most likely explained by the synergistic action of both its numerous phenolic constituents (GPE) and 6-hydroxykynurenic acid (6-HKA), which could be identified as one major contributor to the observed activity.

Hyperlipidemia attenuates vascular endothelial growth factor-induced angiogenesis, impairs cerebral blood flow, and disturbs stroke recovery via decreased pericyte coverage of brain endothelial cells.

OBJECTIVE: Therapeutic angiogenesis aims at the promotion of vascular growth, usually under conditions of atherosclerosis. It was unknown how hyperlipidemia, a risk factor that is closely associated with atherosclerosis of brain vessels in humans, influences vascular endothelial growth factor-induced angiogenesis and stroke recovery. APPROACH AND RESULTS: Wild-type and apolipoprotein-E (ApoE)(-/-) mice were kept on regular or cholesterol-rich diet for mimicking different severities of hyperlipidemia. Mice were treated intracerebroventricularly with recombinant human vascular endothelial growth factor for 21 days (0.02 µg/d) and subsequently subjected to 90-minute middle cerebral artery occlusion followed by 1 or 24 hours of reperfusion. Histochemical, autoradiographic, and regional bioluminescence techniques were used to evaluate effects of blood lipids on postischemic angiogenesis, histopathologic brain injury, cerebral blood flow, protein synthesis and energy state, and pericyte coverage of brain endothelial cells. Hyperlipidemia dose-dependently attenuated vascular endothelial growth factor-induced capillary formation and pericyte coverage of brain endothelial cells, abolishing the improvement of cerebral blood flow during subsequent stroke, resulting in the loss of the metabolic penumbra and increased brain infarction. The enhanced angiogenesis after vascular endothelial growth factor treatment was accompanied by increased expression of the adhesion protein N-cadherin, which mediates endothelial-pericytic interactions, in ischemic brain microvessels of wild-type mice on regular diet that was blunted in wild-type mice on Western diet and ApoE(-/-) mice on either diet. CONCLUSIONS: The compromised vessel formation and hemodynamics question the concept of therapeutic angiogenesis in ischemic stroke where hyperlipidemia is highly prevalent.