Inducible nitric oxide synthase in neutrophils and endothelium contributes to ischemic brain injury in mice

Diet-induced vitamin D deficiency has no effect on acute post-stroke outcomes in young male mice

Recent observational studies have reported that patients with low circulating levels of vitamin D experience larger infarct volumes and worse functional outcomes after ischemic stroke compared to those with sufficient levels. However, it is unknown whether a causal relationship exists between low vitamin D levels and poor stroke outcome. This study aimed to assess the effect of vitamin D deficiency on acute outcomes post-stroke. Male C57Bl6 mice (six week old) were assigned to either a control or vitamin D deficient diet for four weeks prior to stroke. Stroke was induced by 1 h middle cerebral artery occlusion (MCAO) with reperfusion. At 24 h, we assessed functional outcomes, infarct volume, quantified immune cells in the brain by immunofluorescence and examined susceptibility to lung infection. ELISAs showed that the plasma level of hydroxyvitamin D₃ was 85% lower in mice fed the vitamin D-deficient diet compared with the control group. Despite this, vitamin D deficiency had no impact on functional outcomes or infarct volume after stroke. Further, there were no differences in the numbers of infiltrating immune cells or bacterial load within the lungs. These data suggest that diet-induced vitamin D deficiency has no effect on acute post-stroke outcomes.

Neuroinflammatory mechanisms of blood-brain barrier damage in ischemic stroke

As part of the neurovascular unit, the blood-brain barrier (BBB) is a unique, dynamic regulatory boundary that limits and regulates the exchange of molecules, ions, and cells between the blood and the central nervous system. Disruption of the BBB plays an important role in the development of neurological dysfunction in ischemic stroke. Blood-borne substances and cells have restricted access to the brain due to the presence of tight junctions between the endothelial cells of the BBB. Following stroke, there is loss of BBB tight junction integrity, leading to increased paracellular permeability, which results in vasogenic edema, hemorrhagic transformation, and increased mortality. Thus, understanding principal mediators and molecular mechanisms involved in BBB disruption is critical for the development of novel therapeutics to treat ischemic stroke. This review discusses the current knowledge of how neuroinflammation contributes to BBB damage in ischemic stroke. Specifically, we provide an updated overview of the role of cytokines, chemokines, oxidative and nitrosative stress, adhesion molecules, matrix metalloproteinases, and vascular endothelial growth factor as well as the role of different cell types in the regulation of BBB permeability in ischemic stroke.

MicroRNA-122 Mimic Improves Stroke Outcomes and Indirectly Inhibits NOS2 After Middle Cerebral Artery Occlusion in Rats

Aim: Our previous study demonstrated miR-122 mimic decreased NOS2 expression in blood leucocytes and improved stroke outcomes when given immediately after middle cerebral artery occlusion (MCAO) in rats. Since NOS2 is associated with neuro-inflammation in stroke and decreasing NOS2 expression alone in leucocytes is insufficient to improve stroke outcomes, we hypothesized that miR-122 mimic may also decrease NOS2 expression in brain microvascular endothelial cells (BMVECs) even at extended time windows.

Methods: We administered PEG-liposome wrapped miR-122 mimic (2.4 mg/kg, i.v.) 0 or 6 h after MCAO, and assessed stroke volume and NOS2 expression in BMVECs 24 h following MCAO in rats. Luciferase reporter assays were used to determine if miR-122 binds to 3′ untranslated regions (3′UTR) of NOS2.

Results: The data showed that miR-122 mimic decreased infarct volumes and decreased MCAO-induced NOS2 over-expression in BMVECs. However, miR-122 did not bind to 3′UTR of NOS2 in the luciferase assays.

Conclusion: The data show the 6-h period of therapeutic efficacy of miR-122 mimic which could relate to indirect knockdown of NOS2 in both BMVECs and leucocytes.

Tangeretin protects human brain microvascular endothelial cells against oxygen-glucose deprivation-induced injury

Tangeretin, a citrus flavonoid extracted from the peel of citrus fruits, was reported to possess antiasthmatic, antioxidant, anti-inflammatory, and neuroprotective properties. However, the effect of tangeretin on human brain microvascular endothelial cells (HBMECs) has not been examined. This study was designed to investigate the protective effects of tangeretin on oxygen-glucose deprivation (OGD)-induced injury of HBMECs, and explore the underlying mechanisms. Our results showed that tangeretin improved HBMECs viability in response to OGD. In addition, tangeretin was able to increase the activity of superoxide dismutase and decrease the levels of reactive oxygen species and malondialdehyde (MDA), as well as ameliorate cell apoptosis in OGD-stimulated HBMECs. Mechanistic studies showed that tangeretin prevented the activation of JNK signaling pathway in OGD-stimulated HBMECs. Taken together, our current study demonstrated that tangeretin could ameliorate OGD-induced HBMECs injury through the JNK signaling pathway. Thus, tangeretin might be used as a therapeutic strategy for ischemia-reperfusion brain injury and related diseases.

Pitavastatin ameliorates myocardial damage by preventing inflammation and collagen deposition via reduced free radical generation in isoproterenol-induced cardiomyopathy

Pitavastatin inhibits 3 hydroxy 3 methyl glutaryl coenzyme A (HMGCoA) reductase enzyme, preventing cholesterol synthesis along with elevating high density apolipoprotein A1 (Apo-A1). The present study was designed to evaluate cardioprotective potential of pitavastatin at 1 mg/kg/day and 3 mg/kg/day dose for 14 days in low dose isoproterenol (ISO) (5 mg/kg/day for 7 consecutive days) induced myocardial damage. ISO administration induced significant reduction in endogenous antioxidant enzymes like reduced glutathione (GSH), superoxide dismutase (SOD), catalase (CAT) and raised thiobarbituric acid reactive substances (TBARS) indicating activated lipid peroxidation. Along with this, a significant increase in level of cardiac injury biomarkers vie, creatine kinase (CK-MB), lactate dehydrogenase (LDH), aspartate amino transferase (AST), tumor necrosis factor (TNF-α) and transforming growth factor (TGF-β) as well as brain natriuretic peptide (BNP). Histological examination also revealed marked myocardial tissue damage in ISO treated rats. However, pretreatment with pitavastatin (3 mg/kg/day) significantly maintained nearly normal levels of cardiac biomarkers and oxidant antioxidant status as well as lipid peroxidation in ISO induced MI rats. Cardiac histological assessment and infarct size assessment also showed marked reduction in myocardial architecture alteration including infarct size as well as collagen deposition by pitavastatin that strongly supported biochemical findings. These observations strongly corroborate that pitavastatin prevents myocardial damages via up regulation of endogenous oxidants along with its hypocholesterolemic activity.

Gastroprotective effect of oral kefir on indomethacin-induced acute gastric lesions in mice: Impact on oxidative stress

AIMS

This study investigated the gastroprotective effects and the systemic oxidative status of oral kefir pretreatment in albino mice submitted to acute gastric ulcer induced by indomethacin.

MAIN METHODS

Male Swiss mice were divided into three groups (n = 7): Vehicle (0.3 mL of whole milk/100 g body weight, pH adjusted to 5.0), Kefir (0.3 mL of kefir/100 g body weight) and Proton Pump Inhibitor (PPI, 30 mg/kg of lansoprazole), via gavage for 14 days. Animals were fasted for 16 h and treated orally with indomethacin (40 mg/kg). After 6 h the animals were euthanized, the blood samples were obtained and used for the determination of ROS production, oxidation of macromolecules and apoptosis. The stomachs were removed, opened by the greater curvature, and a macroscopic analysis of the gastric lesions was performed.

KEY FINDINGS

Our findings demonstrated that the symbiotic kefir significantly alleviated blood oxidative stress by reducing superoxide anion, hydrogen peroxide and hydroxyl/peroxynitrite radicals, thereby leading to reduced oxidative damage to macromolecules due to a decreased oxidative stress status in induced gastric lesions. These anti-oxidative properties might contribute favorably to the ulcer attenuation in the kefir group.

SIGNIFICANCE

Taken together, these findings support a significant role played by the antioxidant actions of kefir in counteracting the gastric damage induced by this cyclooxygenase inhibitor. It is also worthy to mention that, kefir also exerted the gastroprotective property partly by inhibiting oxidative systemic damage. Based on these considerations, it was implied that kefir might be a contributor for the ROS-scavenging effect.

Endogenous Protection from Ischemic Brain Injury by Preconditioned Monocytes

Exposure to low-dose lipopolysaccharide (LPS) before cerebral ischemia is neuroprotective in stroke models, a phenomenon termed preconditioning (PC). Although it is well established that LPS-PC induces central and peripheral immune responses, the cellular mechanisms modulating ischemic injury remain unclear. Here, we investigated the role of immune cells in the brain protection afforded by PC and tested whether monocytes may be reprogrammed by ex vivo LPS exposure, thus modulating inflammatory injury after cerebral ischemia in male mice. We found that systemic injection of low-dose LPS induces a Ly6C^hi monocyte response that protects the brain after transient middle cerebral artery occlusion (MCAO) in mice. Remarkably, adoptive transfer of monocytes isolated from preconditioned mice into naive mice 7 h after transient MCAO reduced brain injury. Gene expression and functional studies showed that IL-10, inducible nitric oxide synthase, and CCR2 in monocytes are essential for neuroprotection. This protective activity was elicited even if mouse or human monocytes were exposed ex vivo to LPS and then injected into male mice after stroke. Cell-tracking studies showed that protective monocytes are mobilized from the spleen and reach the brain and meninges, where they suppress postischemic inflammation and neutrophil influx into the brain parenchyma. Our findings unveil a previously unrecognized subpopulation of splenic monocytes capable of protecting the brain with an extended therapeutic window and provide the rationale for cell therapies based on the delivery of autologous or allogeneic protective monocytes in patients after ischemic stroke.SIGNIFICANCE STATEMENT Inflammation is a key component of the pathophysiology of the brain in stroke, a leading cause of death and disability with limited therapeutic options. Here, we investigate endogenous mechanisms of protection against cerebral ischemia. Using lipopolysaccharide (LPS) preconditioning (PC) as an approach to induce ischemic tolerance in mice, we found generation of neuroprotective monocytes within the spleen, from which they traffic to the brain and meninges, suppressing postischemic inflammation. Importantly, systemic LPS-PC can be mimicked by adoptive transfer of in vitro-preconditioned mouse or human monocytes at translational relevant time points after stroke. This model of neuroprotection may facilitate clinical efforts to increase the efficacy of BM mononuclear cell treatments in acute neurological diseases such as cerebral ischemia.

Role of Nitric Oxide and Hydrogen Sulfide in Ischemic Stroke and the Emergent Epigenetic Underpinnings

Nitric oxide (NO) and hydrogen sulfide (H₂S) are the key gasotransmitters with an imperious role in the maintenance of cerebrovascular homeostasis. A decline in their levels contributes to endothelial dysfunction that portends ischemic stroke (IS) or cerebral ischemia/reperfusion (CI/R). Nevertheless, their exorbitant production during CI/R is associated with exacerbation of cerebrovascular injury in the post-stroke epoch. NO-producing nitric oxide synthases are implicated in IS pathology and their activity is regulated, inter alia, by various post-translational modifications and chromatin-based mechanisms. These account for heterogeneous alterations in NO production in a disease setting like IS. Interestingly, NO per se has been posited as an endogenous epigenetic modulator. Further, there is compelling evidence for an ingenious crosstalk between NO and H₂S in effecting the canonical (direct) and non-canonical (off-target collateral) functions. In this regard, NO-mediated S-nitrosylation and H₂S-mediated S-sulfhydration of specific reactive thiols in an expanding array of target proteins are the principal modalities mediating the all-pervasive influence of NO and H₂S on cell fate in an ischemic brain. An integrated stress response subsuming unfolded protein response and autophagy to cellular stressors like endoplasmic reticulum stress, in part, is entrenched in such signaling modalities that substantiate the role of NO and H₂S in priming the cells for stress response. The precis presented here provides a comprehension on the multifarious actions of NO and H₂S and their epigenetic underpinnings, their crosstalk in maintenance of cerebrovascular homeostasis, and their "Janus bifrons" effect in IS milieu together with plausible therapeutic implications.

The modular architecture and neurochemical patterns in the cerebellar cortex

The review deals with topical issues of the neuronal arrangement underlying basic cerebellar functions. The cerebellum and its auxiliary structures contain several hundreds of modules (so called "microzones"). Each module receives the corticopetal input specific for the lobule it belongs to and forms the topographic projection. The precision of the major input-output signal flow in the cerebellar cortex is provided by a pronounced stratification of its synaptic zones of a various origin and regular topography of its afferent connections, interneurons, and efferent neurons. There is a nice match between the anatomical and functional coordinates of the modules, whose spatial boundaries are determined by the spread of afferent excitation and local interneuron connections. The dynamic characteristics of the modules are analyzed by the example of the formation of the nitrergic neuron ensembles and cerebellar projections of corticopetal fibers. The authors discuss the cerebellar blood flow and its relation to the activity of NO/GABAergic Lugaro cells and other interneurons in the cerebellar cortex. A generalized scheme of intra- and intermodular communication is proposed.

Paradigm Shift to Neuroimmunomodulation for Translational Neuroprotection in Stroke

The treatment of acute ischemic stroke is still an unresolved clinical problem since the only approved therapeutic intervention relies on early blood flow restoration through pharmacological thrombolysis, mechanical thrombus removal, or a combination of both strategies. Due to their numerous complications and to the narrow time-window for the intervention, only a minority of stroke patients can actually benefit from revascularization procedures, highlighting the urgent need of identifying novel strategies to prevent the progression of an irreversible damage in the ischemic penumbra. During the past three decades, the attempts to target the pathways implicated in the ischemic cascade (e.g., excitotoxicity, calcium channels overactivation, reactive oxygen species (ROS) production) have failed in the clinical setting. Based on a better understanding of the pathobiological mechanisms and on a critical reappraisal of most failed trials, numerous findings from animal studies have demonstrated that targeting the immune system may represent a promising approach to achieve neuroprotection in stroke. In particular, given the dualistic role of distinct components of both the innate and adaptive arms of the immune system, a strategic intervention should be aimed at establishing the right equilibrium between inflammatory and reparative mechanisms, taking into consideration their spatio-temporal recruitment after the ischemic insult. Thus, the application of immunomodulatory drugs and their ability to ameliorate outcomes deserve validation in patients with acute ischemic stroke.

Effectiveness of arginase inhibitors against experimentally induced stroke

Stroke is a lethal disease, but it disables more than it kills. Stroke is the second leading cause of death and the most frequent cause of permanent disability in adults worldwide, with 90% of survivors having residual deficits. The pathophysiology of stroke is complex and involves a strong inflammatory response associated with oxidative stress and activation of several proteolytic enzymes. The current study was designed to investigate the effect of arginase inhibitors (L-citruline and L-ornithine) against ischemic stroke induced in rats by middle cerebral artery occlusion (MCAO). MCAO resulted in alteration in rat behavior, brain infarct, and edema associated with disruption of the blood-brain barrier (BBB). This was mediated through overexpression of arginase I and II, inducible NOS (iNOS), malondialdehyde (MDA), advanced glycation end products (AGEs), TNF-α, and IL-1β and downregulation of endothelial nitric oxide synthase (eNOS). Treatment with L-citruline and L-ornithine and the standard neuroprotective drug cerebrolysin ameliorated all the deleterious effects of stroke. These results indicate the possible use of arginase inhibitors in the treatment of stroke after suitable clinical trials are done.

Peripheral immune cells infiltrate into sites of secondary neurodegeneration after ischemic stroke

Experimental stroke leads to microglia activation and progressive neuronal loss at sites of secondary neurodegeneration (SND). These lesions are remote from, but synaptically connected to, primary infarction sites. Previous studies have demonstrated that immune cells are present in sites of infarction in the first hours and days after stroke, and are associated with increased neurodegeneration in peri-infarct regions. However, it is not known whether immune cells are also present in more distal sites where SND occurs. Our study aimed to investigate whether immune cells are present in sites of SND and, if so, how these cell populations compare to those in the peri-infarct zone. Cells were isolated from the thalamus, the main site of SND, and remaining brain tissue 14days post-stroke. Analysis was performed using flow cytometry to quantify microglia, myeloid cell and lymphocyte numbers. We identified a substantial infiltration of immune cells in the ipsilateral (stroked) compared to the contralateral (control) thalamus, with a significant increase in the percentage of CD4⁺ and CD8⁺ T cells. This result was further quantified using immunofluorescent labelling of fixed tissue. In the remaining ipsilateral hemisphere tissue, there were significant increases in the frequency of CD4⁺ and CD8⁺ T lymphocytes, B lymphocytes, Ly6G⁺ neutrophils and both Ly6G^-Ly6C^LO and Ly6G^-Ly6C^HI monocytes. Our results indicate that infiltrating immune cells persist in ischemic tissue after the acute ischemic phase, and are increased in sites of SND. Importantly, immune cells have been shown to play pivotal roles in both damage and repair processes after stroke. Our findings indicate that immune cells may also be involved in the pathogenesis of SND and further clinical studies are warranted to characterise the nature of inflammatory cell infiltrates in human disease.

Madecassoside protects BV2 microglial cells from oxygen-glucose deprivation/reperfusion-induced injury via inhibition of the toll-like receptor 4 signaling pathway

In a previous study, the authors reported that madecassoside (MA) exerted a potent neuroprotective effect against cerebral ischemia-reperfusion (I/R) injury in rats, mediated by anti-oxidative, anti-inflammatory, and anti-apoptotic mechanisms. However, the cellular and molecular bases for its neuroprotective effects have not been fully elucidated. In this study, an in vitro ischemic model of oxygen-glucose deprivation followed by reperfusion (OGD/R) was used to investigate the role of the toll-like receptor 4 (TLR4)/myeloid differentiation factor 88 (MyD88)/nuclear factor-kappa B (NF-κB) pathway in the neuroprotective and anti-inflammatory effects of MA. BV2 microglia viability after OGD/R, treated with or without MA, was measured using the MTT assay. Messenger RNA and protein expression of pro-inflammatory cytokines (tumor necrosis factor α [TNF-α], interleukin-1β [IL-1β], interleukin-6 [IL-6]) were measured using real-time polymerase chain reaction (RT-PCR) and ELISA after OGD/R or lipopolysaccharide treatment. Expression of TLR4/MyD88 and NF-κB p65 were measured using RT-PCR, Western blotting, and immunofluorescence analysis. MA significantly rescued OGD/R-induced cytotoxicity in BV2 microglia. Meanwhile, MA suppressed the secretion of pro-inflammatory mediators, including TNF-α, IL-1β, and IL-6, induced by OGD/R or lipopolysaccharide in BV2 microglia. The mechanism of its neuroprotection and anti-inflammation from OGD/R may involve the inhibition of activation of TLR4 and MyD88 in BV2 microglia, and the blockage of NF-κB p65 nuclear translocation. MA exhibited a significant neuroprotective effect against I/R injury in both in vivo and in vitro experiments by attenuating microglia-mediated neuroinflammation via inhibition of the TLR4/MyD88/NF-κB signaling pathway.

Neutrophil polarization by IL-27 as a therapeutic target for intracerebral hemorrhage

Shortly after intracerebral hemorrhage, neutrophils infiltrate the intracerebral hemorrhage-injured brain. Once within the brain, neutrophils degranulate, releasing destructive molecules that may exacerbate brain damage. However, neutrophils also release beneficial molecules, including iron-scavenging lactoferrin that may limit hematoma/iron-mediated brain injury after intracerebral hemorrhage. Here, we show that the immunoregulatory cytokine interleukin-27 is upregulated centrally and peripherally after intracerebral hemorrhage. Data from rodent models indicate that interleukin-27 modifies neutrophil maturation in the bone marrow, suppressing their production of pro-inflammatory/cytotoxic products while increasing their production of beneficial iron-scavenging molecules, including lactoferrin. Finally, interleukin-27 or lactoferrin administration results in reduced edema, enhanced hematoma clearance, and improved neurological outcomes in an animal model of intracerebral hemorrhage. These results suggest that interleukin-27/lactoferrin-mediated modulations of neutrophil function may represent a therapeutically viable concept for the modification of neutrophils toward a “beneficial” phenotype for the treatment of intracerebral hemorrhage.

Neutrophils are important modulators of tissue damage after intracerebral hemorrhage (ICH), but how this function is regulated is not clear. Here, the authors show interleukin-27 promotes the tissue-protecting functions of neutrophils via, at least partly, the induction of lactoferrin to present a potential therapy for ICH.

Felodipine inhibits ox-LDL-induced reactive oxygen species production and inflammation in human umbilical vein endothelial cells

Oxidative stress and inflammation are involved in the pathogenesis of atherosclerosis. Calcium channel blockers (CCBs) inhibit the development of atherosclerosis, although the underlying molecular basis has not been completely elucidated. The present study was designed to investigate the effects of felodipine, a CCB, on inflammation and oxidative stress in human umbilical vein endothelial cells (HUVECs) and to examine the underlying mechanisms of action. Oxidized low‑density lipoprotein (ox‑LDL) was used to induce an inflammatory response in HUVECs. The effects of felodipine were investigated by measuring the content of nitric oxide (NO) and reactive oxygen species (ROS), the mRNA and protein levels of intercellular adhesion molecule 1 (ICAM‑1) and vascular cell adhesion protein 1 (VCAM‑1), and the mRNA levels of endothelial NO synthase (eNOS) and inducible NO synthase (iNOS), in addition to the adhesion ability of U937 cells to HUVECs. ROS and NO levels were significantly increased in HUVECs following 24‑h treatment with 25 mg/l ox‑LDL (P<0.01). The increase in ROS was reversed by treatment with felodipine. In addition, NO levels were increased following treatment with 1 µmol/l felodipine (P<0.05). The mRNA expression of ICAM‑1, VCAM‑1, eNOS and iNOS was increased (P<0.05). Administration of 0.1 µM felodipine significantly decreased the expression of ICAM‑1, VCAM‑1, and iNOS (P<0.05). The number of U937 cells adhered to ox‑LDL‑treated HUVECs was significantly increased compared with control, which was reversed by felodipine (0.1 µM). In conclusion, felodipine was demonstrated to inhibit oxidative stress and inflammatory responses, suggesting that it may be used to treat atherosclerosis.

Comparative effects of EtOH consumption and thiamine deficiency on cognitive impairment, oxidative damage, and β-amyloid peptide overproduction in the brain

The effects of chronic EtOH consumption, associated or not with thiamine deficiency (TD), on cognitive impairment, oxidative damage, and β-amyloid (Aβ) peptide accumulation in the brain were investigated in male C57BL/6 mice. We established an alcoholic mouse model by feeding an EtOH liquid diet, a TD mouse model by feeding a thiamine-depleted liquid diet, and an EtOH treatment associated with TD mouse model by feeding a thiamine-depleted EtOH liquid diet for 7 weeks. The learning and memory functions of the mice were detected through the Y-maze test. Biochemical parameters were measured using corresponding commercial kits. The Aβ expression in the hippocampus was observed by immunohistochemical staining. Several results were obtained. First, EtOH significantly reduced cognitive function by significantly decreasing the Glu content in the hippocampus; increasing the AChE activity in the cortex; and reducing the thiamine level, and superoxide dismutase (SOD), glutathione peroxidase (GPx), and choline acetyltransferase (ChAT) activities in both the hippocampus and cortex. The treatment also increased the levels of malondialdehyde (MDA), protein carbonyl, 8-hydroxydeoxyguanosine (8-OHdG), and nitric oxide (NO) and the activities of total nitric oxide synthase (tNOS), inducible nitric oxide synthase (iNOS), and monoamine oxidase B (MAO-B). Furthermore, EtOH enhanced the expression levels of Aβ_1-42 and Aβ_1-40 in the hippocampus. Second, TD induced the same dysfunctions caused by EtOH in the biochemical parameters, except for learning ability, 8-OHdG content, and GPx, tNOS, and AChE activities in the cortex. Third, the modification of MDA, protein carbonyl and NO levels, and GPx, iNOS, ChAT, and MAO-B activities in the brain induced by chronic EtOH treatment associated with TD was greater than that induced by EtOH or TD alone. The synergistic effects of EtOH and TD on Aβ_1-40 and Glu release, as well as on SOD activity, depended on their actions on the hippocampus or cortex. These findings suggest that chronic EtOH consumption can induce TD, cognitive impairment, Aβ accumulation, oxidative stress injury, and neurotransmitter metabolic abnormalities. Furthermore, the association of chronic EtOH consumption with TD causes dramatic brain dysfunctions with a severe effect on the brain.

A Combination of Three Repurposed Drugs Administered at Reperfusion as a Promising Therapy for Postischemic Brain Injury

Cerebral ischemia leads to multifaceted injury to the brain. A polytherapeutic drug that can be administered immediately after reperfusion may increase protection to the brain by simultaneously targeting multiple deleterious cascades. This study evaluated efficacy of the combination of three clinically approved drugs: lamotrigine, minocycline, and lovastatin, using two mouse models: global and focal cerebral ischemia induced by transient occlusion of the common carotid arteries or the middle cerebral artery, respectively. In vitro, the combination drug, but not single drug, protected neurons against oxygen-glucose deprivation (OGD)-induced cell death. The combination drug simultaneously targeted cell apoptosis and DNA damage induced by ischemia. Besides acting on neurons, the combination drug suppressed inflammatory processes in microglia and brain endothelial cells induced by ischemia. In a transient global ischemia model, the combination drug, but not single drug, suppressed microglial activation and inflammatory cytokine production, and reduced neuronal damage. In a transient focal ischemia model, the combination drug, but not single drug, attenuated brain infarction, suppressed infiltration of peripheral neutrophils, and reduced neurological deficits following ischemic stroke. In summary, the combination drug confers a broad-spectrum protection against ischemia/reperfusion (I/R) injury and could be a promising approach for early neuroprotection after out-of-hospital cardiac arrest or ischemic stroke.

Endothelial nitric oxide synthase inhibition triggers inflammatory responses in the brain of male rats exposed to ischemia-reperfusion injury

Nitric oxide (NO) derived from endothelial NO synthase (eNOS) plays a role in preserving and maintaining the brain's microcirculation, inhibiting platelet aggregation, leukocyte adhesion, and migration. Inhibition of eNOS activity results in exacerbation of neuronal injury after ischemia by triggering diverse cellular mechanisms, including inflammatory responses. To examine the relative contribution of eNOS in stroke-induced neuroinflammation, we analyzed the effects of systemic treatment with l-N-(1-iminoethyl)ornithine (L-NIO), a relatively selective eNOS inhibitor, on the expression of MiR-155-5p, a key mediator of innate immunity regulation and endothelial dysfunction, in the cortex of male rats subjected to transient middle cerebral artery occlusion (tMCAo) followed by 24 hr of reperfusion. Inducible NO synthase (iNOS) and interleukin-10 (IL-10) mRNA expression were evaluated by real-time polymerase chain reaction in cortical homogenates and in resident and infiltrating immune cells isolated from ischemic cortex. These latter cells were also analyzed for their expression of CD40, a marker of M1 polarization of microglia/macrophages.tMCAo produced a significant elevation of miR155-5p and iNOS expression in the ischemic cortex as compared with sham surgery. eNOS inhibition by L-NIO treatment further elevated the cortical expression of these inflammatory mediators, while not affecting IL-10 mRNA levels. Interestingly, modulation of iNOS occurred in resident and infiltrating immune cells of the ischemic hemisphere. Accordingly, L-NIO induced a significant increase in the percentage of CD40⁺ events in CD68⁺ microglia/macrophages of the ischemic cortex as compared with vehicle-injected animals. These findings demonstrate that inflammatory responses may underlie the detrimental effects due to pharmacological inhibition of eNOS in cerebral ischemia.

Microglia: Housekeeper of the Central Nervous System

Microglia, of myeloid origin, play fundamental roles in the control of immune responses and the maintenance of central nervous system homeostasis. These cells, just like peripheral macrophages, may be activated into M1 pro-inflammatory or M2 anti-inflammatory phenotypes by appropriate stimuli. Microglia do not respond in isolation, but form part of complex networks of cells influencing each other. This review addresses the complex interaction of microglia with each cell type in the brain: neurons, astrocytes, cerebrovascular endothelial cells, and oligodendrocytes. We also highlight the participation of microglia in the maintenance of homeostasis in the brain, and their roles in the development and progression of age-related neurodegenerative disorders.

Mechanism of salutary effects of melatonin-mediated liver protection after trauma-hemorrhage: p38 MAPK-dependent iNOS/HIF-1α pathway

Although melatonin attenuates the increases in inflammatory mediators and reduces organ injury during trauma-hemorrhage, the mechanisms remain unclear. This study explored whether melatonin prevents liver injury after trauma-hemorrhage through the p38 mitogen-activated protein kinase (MAPK)-dependent, inducible nitrite oxide (iNOS)/hypoxia-inducible factor (HIF)-1α pathway. After a 5-cm midline laparotomy, male rats underwent hemorrhagic shock (mean blood pressure ~40 mmHg for 90 min) followed by fluid resuscitation. At the onset of resuscitation, rats were treated with vehicle, melatonin (2 mg/kg), melatonin plus p38 MAPK inhibitor SB203580 (2 mg/kg), or melatonin plus the melatonin receptor antagonist luzindole (2.5 mg/kg). At 2 h after trauma-hemorrhage, histopathology score of liver injury, liver tissue myeloperoxidase activity, malondialdehyde, adenosine triphosphate, serum alanine aminotransferase, and asparate aminotransferase levels were significantly increased compared with sham-operated control. Trauma-hemorrhage resulted in a significant decrease in the p38 MAPK activation compared with that in the sham-treated animals. Administration of melatonin after trauma-hemorrhage normalized liver p38 MAPK phosphorylation and iNOS and HIF-1α expression and attenuated cleaved caspase 3 and receptor interacting protein kinase-1 levels. Coadministration of SB203580 or luzindole abolished the melatonin-mediated attenuation of the trauma-hemorrhage-induced increase of iNOS/HIF-1α protein expression and liver injury markers. Taken together, our results suggest that melatonin prevents trauma-hemorrhage-induced liver injury in rats, at least in part, through melatonin receptor-related, p38 MAPK-dependent iNOS/HIF-1α pathway.NEW & NOTEWORTHY Trauma-hemorrhage resulted in a significant decrease in liver p38 MAPK activation and increase in nitrite oxide synthase (iNOS) and hypoxia-inducible factor (HIF)-1α expression. Administration of melatonin after trauma-hemorrhage normalized liver p38 MAPK phosphorylation and iNOS and HIF-1α expression, which was abolished by coadministration of SB203580 or luzindole. Melatonin prevents trauma-hemorrhage-induced liver injury in rats via the melatonin receptor-related, p38 MAPK-dependent iNOS/HIF-1α pathway.

Role of Transporters in Central Nervous System Drug Delivery and Blood-Brain Barrier Protection: Relevance to Treatment of Stroke

Ischemic stroke is a leading cause of morbidity and mortality in the United States. The only approved pharmacologic treatment for ischemic stroke is thrombolysis via recombinant tissue plasminogen activator (r-tPA). A short therapeutic window and serious adverse events (ie, hemorrhage, excitotoxicity) greatly limit r-tPA therapy, which indicates an essential need to develop novel stroke treatment paradigms. Transporters expressed at the blood-brain barrier (BBB) provide a significant opportunity to advance stroke therapy via central nervous system delivery of drugs that have neuroprotective properties. Examples of such transporters include organic anion–transporting polypeptides (Oatps) and organic cation transporters (Octs). In addition, multidrug resistance proteins (Mrps) are transporter targets in brain microvascular endothelial cells that can be exploited to preserve BBB integrity in the setting of stroke. Here, we review current knowledge on stroke pharmacotherapy and demonstrate how endogenous BBB transporters can be targeted for improvement of ischemic stroke treatment.

Thrombosis, Neuroinflammation, and Poststroke Infection: The Multifaceted Role of Neutrophils in Stroke

Immune cells can significantly predict and affect the clinical outcome of stroke. In particular, the neutrophil-to-lymphocyte ratio was shown to predict hemorrhagic transformation and the clinical outcome of stroke; however, the immunological mechanisms underlying these effects are poorly understood. Neutrophils are the first cells to invade injured tissue following focal brain ischemia. In these conditions, their proinflammatory properties enhance tissue damage and may promote ischemic incidences by inducing thrombus formation. Therefore, they constitute a potential target for therapeutic approaches and prevention of stroke. Indeed, in animal models of focal brain ischemia, neutrophils have been targeted with successful results. However, even in brain lesions, neutrophils also exert beneficial effects, because they are involved in triggering immunological removal of cell debris. Furthermore, intact neutrophil function is essential for maintaining immunological defense against bacterial infections. Several studies have demonstrated that stroke-derived neutrophils displayed impaired bacterial defense capacity. Because infections are known to impair the clinical course of stroke, therapeutic interventions that target neutrophils should preserve or even restore their function outside the central nervous system (CNS). This complex situation requires well-tailored therapeutic approaches that can effectively tackle immune cell invasion in the brain but avoid increasing poststroke infections.

Postischemic Inflammation in Acute Stroke

Cerebral ischemia is caused by arterial occlusion due to a thrombus or an embolus. Such occlusion induces multiple and concomitant pathophysiological processes that involve bioenergetic failure, acidosis, loss of cell homeostasis, excitotoxicity, and disruption of the blood-brain barrier. All of these mechanisms contribute to neuronal death, mainly via apoptosis or necrosis. The immune system is involved in this process in the early phases after brain injury, which contributes to potential enlargement of the infarct size and involves the penumbra area. Whereas inflammation and the immune system both exert deleterious effects, they also contribute to brain protection by stimulating a preconditioning status and to the concomitant repair of the injured parenchyma. This review describes the main phases of the inflammatory process occurring after arterial cerebral occlusion, with an emphasis on the role of single mediators.

Spatio-temporal profile, phenotypic diversity, and fate of recruited monocytes into the post-ischemic brain

Background

A key feature of the inflammatory response after cerebral ischemia is the brain infiltration of blood monocytes. There are two main monocyte subsets in the mouse blood: CCR2⁺Ly6C^hi “inflammatory” monocytes involved in acute inflammation, and CX3CR1⁺Ly6C^lo “patrolling” monocytes, which may play a role in repair processes. We hypothesized that CCR2⁺Ly6C^hi inflammatory monocytes are recruited in the early phase after ischemia and transdifferentiate into CX3CR1⁺Ly6C^lo “repair” macrophages in the brain.

Methods

CX3CR1^GFP/+CCR2^RFP/+ bone marrow (BM) chimeric mice underwent transient middle cerebral artery occlusion (MCAo). Mice were sacrificed from 1 to 28 days later to phenotype and map subsets of infiltrating monocytes/macrophages (Mo/MΦ) in the brain over time. Flow cytometry analysis 3 and 14 days after MCAo in CCR2^−/− mice, which exhibit deficient monocyte recruitment after inflammation, and NR4A1^−/− BM chimeric mice, which lack circulating CX3CR1⁺Ly6C^lo monocytes, was also performed.

Results

Brain mapping of CX3CR1^GFP/+ and CCR2^RFP/+ cells 3 days after MCAo showed absence of CX3CR1^GFP/+ Mo/MΦ but accumulation of CCR2^RFP/+ Mo/MΦ throughout the ischemic territory. On the other hand, CX3CR1⁺ cells accumulated 14 days after MCAo at the border of the infarct core where CCR2^RFP/+ accrued. Whereas the amoeboid morphology of CCR2^RFP/+ Mo/MΦ remained unchanged over time, CX3CR1^GFP/+ cells exhibited three distinct phenotypes: amoeboid cells with retracted processes, ramified cells, and perivascular elongated cells. CX3CR1^GFP/+ cells were positive for the Mo/MΦ marker Iba1 and phenotypically distinct from endothelial cells, smooth muscle cells, pericytes, neurons, astrocytes, or oligodendrocytes. Because accumulation of CX3CR1⁺Ly6C^lo Mo/MΦ was absent in the brains of CCR2 deficient mice, which exhibit deficiency in CCR2⁺Ly6C^hi Mo/MΦ recruitment, but not in NR4A1^−/− chimeric mice, which lack of circulating CX3CR1⁺Ly6C^lo monocytes, our data suggest a local transition of CCR2⁺Ly6C^hi Mo/MΦ into CX3CR1⁺Ly6C^lo Mo/MΦ phenotype.

Conclusions

CX3CR1⁺Ly6C^lo arise in the brain parenchyma from CCR2⁺Ly6C^hi Mo/MΦ rather than being de novo recruited from the blood. These findings provide new insights into the trafficking and phenotypic diversity of monocyte subtypes in the post-ischemic brain.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0750-0) contains supplementary material, which is available to authorized users.

Inflammation after Ischemic Stroke: The Role of Leukocytes and Glial Cells

The immune response after stroke is known to play a major role in ischemic brain pathobiology. The inflammatory signals released by immune mediators activated by brain injury sets off a complex series of biochemical and molecular events which have been increasingly recognized as a key contributor to neuronal cell death. The primary immune mediators involved are glial cells and infiltrating leukocytes, including neutrophils, monocytes and lymphocyte. After ischemic stroke, activation of glial cells and subsequent release of pro- and anti-inflammatory signals are important for modulating both neuronal cell damage and wound healing. Infiltrated leukocytes release inflammatory mediators into the site of the lesion, thereby exacerbating brain injury. This review describes how the roles of glial cells and circulating leukocytes are a double-edged sword for neuroinflammation by focusing on their detrimental and protective effects in ischemic stroke. Here, we will focus on underlying characterize of glial cells and leukocytes under inflammation after ischemic stroke.

Inflammation and Stroke: An Overview

The immune response to acute cerebral ischemia is a major factor in stroke pathobiology and outcome. While the immune response starts locally in occluded and hypoperfused vessels and the ischemic brain parenchyma, inflammatory mediators generated in situ propagate through the organism as a whole. This "spillover" leads to a systemic inflammatory response first, followed by immunosuppression aimed at dampening the potentially harmful proinflammatory milieu. In this overview we will outline the inflammatory cascade from its starting point in the vasculature of the ischemic brain to the systemic immune response elicited by brain ischemia. Potential immunomodulatory therapeutic approaches, including preconditioning and immune cell therapy will also be discussed.

Platelet Supernatant Suppresses LPS-Induced Nitric Oxide Production from Macrophages Accompanied by Inhibition of NF-κB Signaling and Increased Arginase-1 Expression

We previously reported that mouse bone marrow-derived macrophages (BMDMs) that had been co-cultured with platelets exhibited lower susceptibility to bacterial lipopolysaccharide (LPS) and produced lower levels of nitric oxide (NO) and inflammatory cytokines including TNF-α and IL-6. The suppression of macrophage responses was mediated, at least in part, by platelet supernatant. In the present study, we assessed phenotypic changes of BMDMs induced by incubation with the supernatant from thrombin-activated platelets (PLT-sup) and found that BMDMs cultured with PLT-sup (PLT-BMDMs) expressed a lower level of inducible NO synthase (iNOS) and a higher level of arginase-1, both of which are involved in the L-arginine metabolism, upon stimulation with LPS or zymosan. We also examined possible modulation of the NF-κB signaling pathway and observed suppression of IκBα phosphorylation and a decrease of NF-κB p65 expression in LPS-stimulated PLT-BMDMs. These results suggest that PLT-sup suppresses inflammatory responses of BMDMs via negative regulation of NF-κB signaling leading to lowered expression of iNOS and enhanced L-arginine catabolism by arginase-1.

Recurrent mild cerebral ischemia: enhanced brain injury following acute compared to subacute recurrence in the rat

BACKGROUND

In the current study, a transient cerebral ischemia producing selective cell death was designated a mild ischemic insult. A comparable insult in humans is a transient ischemic attack (TIA) that is associated with functional recovery but can have imaging evidence of minor ischemic damage including cerebral atrophy. A TIA also predicts a high risk for early recurrence of a stroke or TIA and thus multiple ischemic insults are not uncommon. Not well understood is what the effect of differing recovery times between mild ischemic insults has on their pathophysiology. We investigated whether cumulative brain damage would differ if recurrence of a mild ischemic insult occurred at 1 or 3 days after a first insult.

RESULTS

A transient episode of middle cerebral artery occlusion via microclip was produced to elicit mild ischemic changes-predominantly scattered necrosis. This was followed 1 or 3 days later by a repeat of the same insult. Brain damage assessed histologically 7 days later was substantially greater in the 1 day recurrent group than the 3 days recurrent group, with areas of damage consisting predominantly of regions of incomplete infarction and pannecrosis in the 1 day group but predominantly regions of selective necrosis and smaller areas of incomplete infarction in the 3 days group (P < 0.05). Enhanced injury was reflected by greater number of cells staining for macrophages/microglia with ED1 and greater alterations in GFAP staining of reactive astrocytes in the 1 day than 3 days recurrent groups. The differential susceptibility to injury did not correspond to higher levels of injurious factors present at the time of the second insult such as BBB disruption or increased cytokines (tumor necrosis factor). Microglial activation, with potential for some beneficial effects, appeared greater at 3 days than 1 day. Also blood analysis demonstrated changes that included an acute increase in granulocytes and decrease in platelets at 1 day compared to 3 days post transient ischemia.

CONCLUSIONS

Dynamic changes in multiple inflammatory responses likely contribute to the time dependence of the extent of damage produced by recurrent mild ischemic insults. The time of mild stroke recurrence is crucial with early recurrence producing greater damage than subacute recurrence and this supports urgency for determining and implementing optimal stroke management directly after a TIA.

Mitochondrial dysfunction and cell death in neurodegenerative diseases through nitroxidative stress

Mitochondria are important for providing cellular energy ATP through the oxidative phosphorylation pathway. They are also critical in regulating many cellular functions including the fatty acid oxidation, the metabolism of glutamate and urea, the anti-oxidant defense, and the apoptosis pathway. Mitochondria are an important source of reactive oxygen species leaked from the electron transport chain while they are susceptible to oxidative damage, leading to mitochondrial dysfunction and tissue injury. In fact, impaired mitochondrial function is commonly observed in many types of neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, Huntington's disease, alcoholic dementia, brain ischemia-reperfusion related injury, and others, although many of these neurological disorders have unique etiological factors. Mitochondrial dysfunction under many pathological conditions is likely to be promoted by increased nitroxidative stress, which can stimulate post-translational modifications (PTMs) of mitochondrial proteins and/or oxidative damage to mitochondrial DNA and lipids. Furthermore, recent studies have demonstrated that various antioxidants, including naturally occurring flavonoids and polyphenols as well as synthetic compounds, can block the formation of reactive oxygen and/or nitrogen species, and thus ultimately prevent the PTMs of many proteins with improved disease conditions. Therefore, the present review is aimed to describe the recent research developments in the molecular mechanisms for mitochondrial dysfunction and tissue injury in neurodegenerative diseases and discuss translational research opportunities.

Accessible Method for the Development of Novel Sterol Analogues with Dipeptide-like Side Chains That Act as Neuroinflammation Inhibitors

A number of novel sterol derivatives with dipeptide-like side chains were synthesized using an Ugi four-component condensation method and assayed to test their anti-inflammatory effects in activated microglial cells. Compound 18b ((3S,10R,13S)-N-((R)-1-(tert-butylamino)-1-oxo-3-phenylpropan-2-yl)-3-hydroxy-N,10,13-trimethyl-2,3,4,7,8,9,10,11,12,13,14,15-dodecahydro-1H-cyclopenta[a]phenanthrene-17-carboxamide) was identified as the most potent anti-inflammatory agent in the series of compounds analyzed. Compound 18b markedly inhibited the expression of proinflammatory factors, including inducible nitric oxide synthase, interleukin (IL)-6, IL-1β, tumor necrosis factor-α, and cyclooxygenase-2 in lipopolysaccharide-stimulated microglial cells. Further studies showed that compound 18b significantly suppressed the transcriptional activity of AP-1 and NF-κB in activated microglial cells, which was likely mediated by the inhibition of the p38 MAPK and JNK signal transduction pathways. In addition, compound 18b displayed neuroprotective effects in a microglial-conditioned medium/neuron coculture and an experimental focal ischemic mouse model.

Endothelial CD36 Contributes to Postischemic Brain Injury by Promoting Neutrophil Activation via CSF3

The scavenger receptor CD36 is a critical factor initiating ischemic brain injury, but the cell type(s) expressing CD36 and responsible for its harmful effects remain unknown. Using bone marrow (BM) chimeras subjected to transient middle cerebral artery occlusion, we found that CD36(-/-) mice transplanted with wild-type (WT) BM (WT→CD36(-/-)) have smaller infarcts (-67%), comparable with those of mice lacking CD36 both in brain and hematogenous cells (CD36(-/-) →CD36(-/-); - 72%). Conversely, WT mice receiving CD36(-/-) BM (CD36(-/-) →WT) have infarcts similar to WT→WT mice, suggesting that CD36 in the host brain (i.e., in microglia and endothelial cells), and not in hematogenous cells is involved in the damage. As anticipated, postischemic neutrophil infiltration in CD36(-/-) →CD36(-/-) mice was attenuated. Surprisingly, however, in WT→CD36(-/-) mice, in which infarcts were small, neutrophil infiltration was large and similar to that of CD36(-/-) →WT mice, in which infarcts were not reduced. Postischemic neutrophil free radical production was attenuated in WT→CD36(-/-) mice compared with CD36(-/-) →WT mice, whereas expression of the neutrophil activator colony-stimulating factor 3 (CSF3) was suppressed in CD36(-/-) cerebral endothelial cells, but not microglia. In CD36(-/-) cerebral endothelial cultures exposed to extracts from stroke brains, the upregulation of CSF3, but not neutrophil attractant chemokines, was suppressed. Intracerebroventricular administration of CSF3, 24 h after stroke, reconstituted neutrophil radical production and increased infarct volume in WT→CD36(-/-) mice. The findings identify endothelial cells as a key player in the deleterious effects of CD36 in stroke, and unveil a novel role of endothelial CD36 in enabling neutrophil neurotoxicity through CSF3.

SIGNIFICANCE STATEMENT

Ischemic stroke is a leading cause of death and disability worldwide with limited therapeutic options. The inflammatory response initiated by cerebral ischemia-reperfusion contributes to ischemic brain injury and is a potential therapeutic target. Here we report that CD36, an innate immunity receptor involved in the initiation of postischemic inflammation, is a previously unrecognized regulator of neutrophil cytotoxicity. The effect is mediated by endothelial CD36 via upregulation of the neutrophil activator CSF3 in cerebral endothelial cells. Therefore, approaches to modulate cerebral endothelial CD36 signaling or to neutralize CSF3 may provide novel therapeutic opportunities to ameliorate postischemic inflammatory injury.

Reactive astrocytes undergo M1 microglia/macrohpages-induced necroptosis in spinal cord injury

Background

A unique feature of the pathological change after spinal cord injury (SCI) is the progressive enlargement of lesion area, which usually results in cavity formation and is accompanied by reactive astrogliosis and chronic inflammation. Reactive astrocytes line the spinal cavity, walling off the lesion core from the normal spinal tissue, and are thought to play multiple important roles in SCI. The contribution of cell death, particularly the apoptosis of neurons and oligodendrocytes during the process of cavitation has been extensively studied. However, how reactive astrocytes are eliminated following SCI remains largely unclear.

Results

By immunohistochemistry, in vivo propidium iodide (PI)-labeling and electron microscopic examination, here we reported that in mice, reactive astrocytes died by receptor-interacting protein 3 and mixed lineage kinase domain-like protein (RIP3/MLKL) mediated necroptosis, rather than apoptosis or autophagy. Inhibiting receptor-interacting protein 1 (RIP1) or depleting RIP3 not only significantly attenuated astrocyte death but also rescued the neurotrophic function of astrocytes. The astrocytic expression of necroptotic markers followed the polarization of M1 microglia/macrophages after SCI. Depleting M1 microglia/macrophages or transplantation of M1 macrophages could significantly reduce or increase the necroptosis of astrocytes. Further, the inflammatory responsive genes Toll-like receptor 4 (TLR4) and myeloid differentiation primary response gene 88 (MyD88) are induced in necroptotic astrocytes. In vitro antagonizing MyD88 in astrocytes could significantly alleviate the M1 microglia/macrophages-induced cell death. Finally, our data showed that in human, necroptotic markers and TLR4/MyD88 were co-expressed in astrocytes of injured, but not normal spinal cord.

Conclusion

Taken together, these results reveal that after SCI, reactive astrocytes undergo M1 microglia/macrophages-induced necroptosis, partially through TLR/MyD88 signaling, and suggest that inhibiting astrocytic necroptosis may be beneficial for preventing secondary SCI.

Electronic supplementary material

The online version of this article (doi:10.1186/s13024-016-0081-8) contains supplementary material, which is available to authorized users.

Overproduction of nitric oxide intensifies brain infarction and cerebrovascular damage through reduction of claudin-5 and ZO-1 expression in striatum of ischemic brain

Nitric oxide (NO) overproduction has been demonstrated from different NO-synthase overexpression or hyperactivity after brain ischemia. Here, we examined the effects of inhibition of NO overproduction on brain infarction, cerebrovascular damage and expression of claudin-5 and zonula occludens-1 (ZO-1) in striatum of ischemic brain. The experiment was performed in three groups of rats; sham, control ischemia and ischemic treatment. Brain ischemia was induced by 60min of middle cerebral artery occlusion (MCAO) followed by 24h of reperfusion. Treated rats received L-NAME 30min before induction of ischemia (1mg/kg, i.p.). Infarct volume and histopathological changes of ischemic striatum were assessed by TTC and LFB staining methods, respectively. Ultimately, quantitative RT-PCR was used for assessment of claudins-5 and ZO-1 expression. MCAO in the control group induced infarction (135±25mm³) at large areas of striatum in accompany with neuronal damages, whereas L-NAME significantly reduced infarction (87±16mm³) and neuronal injuries. The mRNA of ZO-1 and claudin-5 decreased in ischemic striatum, whereas inhibition of NO overproduction by L-NAME attenuated this reduction for these genes. Our findings indicated that NO overproduction after brain ischemia plays a crucial role in neuronal damage especially at striatal regions. Hence, inhibition of excessive NO production may save striatal cerebrovascular integrity of ischemic brain.

Novel Stroke Therapeutics: Unraveling Stroke Pathophysiology and Its Impact on Clinical Treatments

Stroke remains a leading cause of death and disability in the world. Over the past few decades our understanding of the pathophysiology of stroke has increased, but greater insight is required to advance the field of stroke recovery. Clinical treatments have improved in the acute time window, but long-term therapeutics remain limited. Complex neural circuits damaged by ischemia make restoration of function after stroke difficult. New therapeutic approaches, including cell transplantation or stimulation, focus on reestablishing these circuits through multiple mechanisms to improve circuit plasticity and remodeling. Other research targets intact networks to compensate for damaged regions. This review highlights several important mechanisms of stroke injury and describes emerging therapies aimed at improving clinical outcomes.

Blocking a vicious cycle nNOS/peroxynitrite/AMPK by S-nitrosoglutathione: implication for stroke therapy

BACKGROUND

Stroke immediately sets into motion sustained excitotoxicity and calcium dysregulation, causing aberrant activity in neuronal nitric oxide synthase (nNOS) and an imbalance in the levels of nitric oxide (NO). Drugs targeting nNOS-originated toxicity may therefore reduce stroke-induced damage. Recently, we observed that a redox-modulating agent of the NO metabolome, S-nitrosoglutathione (GSNO), confers neurovascular protection by reducing the levels of peroxynitrite, a product of aberrant NOS activity. We therefore investigated whether GSNO-mediated neuroprotection and improved neurological functions depend on blocking nNOS/peroxynitrite-associated injurious mechanisms using a rat model of cerebral ischemia reperfusion (IR).

RESULTS

IR increased the activity of nNOS, the levels of neuronal peroxynitrite and phosphorylation at Ser(1412) of nNOS. GSNO treatment of IR animals decreased IR-activated nNOS activity and neuronal peroxynitrite levels by reducing nNOS phosphorylation at Ser(1412). The Ser(1412) phosphorylation is associated with increased nNOS activity. Supporting the notion that nNOS activity and peroxynitrite are deleterious following IR, inhibition of nNOS by its inhibitor 7-nitroindazole or reducing peroxynitrite by its scavenger FeTPPS decreased IR injury. GSNO also decreased the activation of AMP Kinase (AMPK) and its upstream kinase LKB1, both of which were activated in IR brain. AMPK has been implicated in nNOS activation via Ser(1412) phosphorylation. To determine whether AMPK activation is deleterious in the acute phase of IR, we treated animals after IR with AICAR (an AMPK activator) and compound c (an AMPK inhibitor). While AICAR potentiated, compound c reduced the IR injury.

CONCLUSIONS

Taken together, these results indicate an injurious nNOS/peroxynitrite/AMPK cycle following stroke, and GSNO treatment of IR inhibits this vicious cycle, resulting in neuroprotection and improved neurological function. GSNO is a natural component of the human body, and its exogenous administration to humans is not associated with any known side effects. Currently, the FDA-approved thrombolytic therapy suffers from a lack of neuronal protective activity. Because GSNO provides neuroprotection by ameliorating stroke's initial and causative injuries, it is a candidate of translational value for stroke therapy.

Preferential Recruitment of Neutrophils into the Cerebellum and Brainstem Contributes to the Atypical Experimental Autoimmune Encephalomyelitis Phenotype

The JAK/STAT pathway is critical for development, regulation, and termination of immune responses, and dysregulation of the JAK/STAT pathway, that is, hyperactivation, has pathological implications in autoimmune and neuroinflammatory diseases. Suppressor of cytokine signaling 3 (SOCS3) regulates STAT3 activation in response to cytokines that play important roles in the pathogenesis of neuroinflammatory diseases, including IL-6 and IL-23. We previously demonstrated that myeloid lineage-specific deletion of SOCS3 resulted in a severe, nonresolving atypical form of experimental autoimmune encephalomyelitis (EAE), characterized by lesions, inflammatory infiltrates, elevated STAT activation, and elevated cytokine and chemokine expression in the cerebellum. Clinically, these mice exhibit ataxia and tremors. In this study, we provide a detailed analysis of this model, demonstrating that the atypical EAE observed in LysMCre-SOCS3(fl/fl) mice is characterized by extensive neutrophil infiltration into the cerebellum and brainstem, increased inducible NO synthase levels in the cerebellum and brainstem, and prominent axonal damage. Importantly, infiltrating SOCS3-deficient neutrophils produce high levels of CXCL2, CCL2, CXCL10, NO, TNF-α, and IL-1β. Kinetic studies demonstrate that neutrophil infiltration into the cerebellum and brainstem of LysMCre-SOCS3(fl/fl) mice closely correlates with atypical EAE clinical symptoms. Ab-mediated depletion of neutrophils converts the atypical phenotype to the classical EAE phenotype and, in some cases, a mixed atypical/classical phenotype. Blocking CXCR2 signaling ameliorates atypical EAE development by reducing neutrophil infiltration into the cerebellum/brainstem. Thus, neutrophils lacking SOCS3 display elevated STAT3 activation and expression of proinflammatory mediators and play a critical role in the development of atypical EAE.

iNOS Activity Modulates Inflammation, Angiogenesis, and Tissue Fibrosis in Polyether-Polyurethane Synthetic Implants

There is considerable interest in implantation techniques and scaffolds for tissue engineering and, for safety and biocompatibility reasons, inflammation, angiogenesis, and fibrosis need to be determined. The contribution of inducible nitric oxide synthase (iNOS) in the regulation of the foreign body reaction induced by subcutaneous implantation of a synthetic matrix was never investigated. Here, we examined the role of iNOS in angiogenesis, inflammation, and collagen deposition induced by polyether-polyurethane synthetic implants, using mice with targeted disruption of the iNOS gene (iNOS^−/−) and wild-type (WT) mice. The hemoglobin content and number of vessels were decreased in the implants of iNOS^−/− mice compared to WT mice 14 days after implantation. VEGF levels were also reduced in the implants of iNOS^−/− mice. In contrast, the iNOS^−/− implants exhibited an increased neutrophil and macrophage infiltration. However, no alterations were observed in levels of CXCL1 and CCL2, chemokines related to neutrophil and macrophage migration, respectively. Furthermore, the implants of iNOS^−/− mice showed boosted collagen deposition. These data suggest that iNOS activity controls inflammation, angiogenesis, and fibrogenesis in polyether-polyurethane synthetic implants and that lack of iNOS expression increases foreign body reaction to implants in mice.

Complexity of the cell-cell interactions in the innate immune response after cerebral ischemia

In response to brain ischemia a cascade of signals leads to the activation of the brain innate immune system and to the recruitment of blood borne derived cells to the ischemic tissue. These processes have been increasingly shown to play a role on stroke pathogenesis. Here, we discuss the key features of resident microglia and different leukocyte subsets implicated in cerebral ischemia with special emphasis of neutrophils, monocytes and microglia. We focus on how leukocytes are recruited to injured brain through a complex interplay between endothelial cells, platelets and leukocytes and describe different strategies used to inhibit their recruitment. Finally, we discuss the possible existence of different leukocyte subsets in the ischemic tissue and the repercussion of different myeloid phenotypes on stroke outcome. The knowledge of the nature of these heterogeneous cell-cell interactions may open new lines of investigation on new therapies to promote protective immune responses and tissue repair after cerebral ischemia or to block harmful responses. This article is part of a Special Issue entitled SI: Cell Interactions In Stroke.

The Role of Reactive Oxygen Species (ROS) in the Formation of Extracellular Traps (ETs) in Humans

Extracellular traps (ETs) are reticulate structures of extracellular DNA associated with antimicrobial molecules. Their formation by phagocytes (mainly by neutrophils: NETs) has been identified as an essential element of vertebrate innate immune defense. However, as ETs are also toxic to host cells and potent triggers of autoimmunity, their role between pathogen defense and human pathogenesis is ambiguous, and they contribute to a variety of acute and chronic inflammatory diseases. Since the discovery of ET formation (ETosis) a decade ago, evidence has accumulated that most reaction cascades leading to ET release involve ROS. An important new facet was added when it became apparent that ETosis might be directly linked to, or be a variant of, the autophagy cell death pathway. The present review analyzes the evidence to date on the interplay between ROS, autophagy and ETosis, and highlights and discusses several further aspects of the ROS-ET relationship that are incompletely understood. These aspects include the role of NADPH oxidase-derived ROS, the molecular requirements of NADPH oxidase-dependent ETosis, the roles of NADPH oxidase subtypes, extracellular ROS and of ROS from sources other than NADPH oxidase, and the present evidence for ROS-independent ETosis. We conclude that ROS interact with ETosis in a multidimensional manner, with influence on whether ETosis shows beneficial or detrimental effects.

Rational modulation of the innate immune system for neuroprotection in ischemic stroke

The innate immune system plays a dualistic role in the evolution of ischemic brain damage and has also been implicated in ischemic tolerance produced by different conditioning stimuli. Early after ischemia, perivascular astrocytes release cytokines and activate metalloproteases (MMPs) that contribute to blood–brain barrier (BBB) disruption and vasogenic oedema; whereas at later stages, they provide extracellular glutamate uptake, BBB regeneration and neurotrophic factors release. Similarly, early activation of microglia contributes to ischemic brain injury via the production of inflammatory cytokines, including tumor necrosis factor (TNF) and interleukin (IL)-1, reactive oxygen and nitrogen species and proteases. Nevertheless, microglia also contributes to the resolution of inflammation, by releasing IL-10 and tumor growth factor (TGF)-β, and to the late reparative processes by phagocytic activity and growth factors production. Indeed, after ischemia, microglia/macrophages differentiate toward several phenotypes: the M1 pro-inflammatory phenotype is classically activated via toll-like receptors or interferon-γ, whereas M2 phenotypes are alternatively activated by regulatory mediators, such as ILs 4, 10, 13, or TGF-β. Thus, immune cells exert a dualistic role on the evolution of ischemic brain damage, since the classic phenotypes promote injury, whereas alternatively activated M2 macrophages or N2 neutrophils prompt tissue remodeling and repair. Moreover, a subdued activation of the immune system has been involved in ischemic tolerance, since different preconditioning stimuli act via modulation of inflammatory mediators, including toll-like receptors and cytokine signaling pathways. This further underscores that the immuno-modulatory approach for the treatment of ischemic stroke should be aimed at blocking the detrimental effects, while promoting the beneficial responses of the immune reaction.

Autoregulation of inducible nitric oxide synthase expression by RNA interference provides neuroprotection in neonatal rats

We have shown that autoregulation of gene expression by RNA interference is achievable in cell cultures. To determine whether this novel concept could be used to produce neuroprotection under in vivo condition, postnatal day (PND) 3 rats received intracerebroventricular injection of lentivirus that carried or did not carry code for short hairpin RNA (shRNA) of inducible nitric oxide synthase (iNOS). The expression of this shRNA was controlled by an iNOS promoter (piNOS-shRNA) or cytomegalovirus promoter (pCMV-shRNA). The rats were subjected to brain hypoxia-ischemia at PND7. Ischemic brain tissues had increased iNOS expression. This increase was attenuated by virus carrying piNOS-shRNA. Virus carrying pCMV-shRNA reduced iNOS to a level that was lower than control. Brain tissue loss and functional impairment after the hypoxia-ischemia were attenuated by the virus carrying piNOS-shRNA but not by pCMV-shRNA. Our results provide proof-of-concept evidence that autoregulation of iNOS expression by RNA interference induces neuroprotection in vivo and that appropriate regulation of gene expression is important.

The role of microglia and myeloid immune cells in acute cerebral ischemia

The immune response to acute cerebral ischemia is a major contributor to stroke pathobiology. The inflammatory response is characterized by the participation of brain resident cells and peripheral leukocytes. Microglia in the brain and monocytes/neutrophils in the periphery have a prominent role in initiating, sustaining and resolving post-ischemic inflammation. In this review we aim to summarize recent literature concerning the origins, fate and role of microglia, monocytes and neutrophils in models of cerebral ischemia and to discuss their relevance for human stroke.