The influence of antiadhesion therapies on leukocyte subset accumulation in central nervous system ischemia in rats

Cellular and Molecular Mechanisms of R/S-Roscovitine and CDKs Related Inhibition under Both Focal and Global Cerebral Ischemia: A Focus on Neurovascular Unit and Immune Cells

Ischemic stroke is the second leading cause of death worldwide. Following ischemic stroke, Neurovascular Unit (NVU) inflammation and peripheral leucocytes infiltration are major contributors to the extension of brain lesions. For a long time restricted to neurons, the 10 past years have shown the emergence of an increasing number of studies focusing on the role of Cyclin-Dependent Kinases (CDKs) on the other cells of NVU, as well as on the leucocytes. The most widely used CDKs inhibitor, (R)-roscovitine, and its (S) isomer both decreased brain lesions in models of global and focal cerebral ischemia. We previously showed that (S)-roscovitine acted, at least, by modulating NVU response to ischemia. Interestingly, roscovitine was shown to decrease leucocytes-mediated inflammation in several inflammatory models. Specific inhibition of roscovitine majors target CDK 1, 2, 5, 7, and 9 showed that these CDKs played key roles in inflammatory processes of NVU cells and leucocytes after brain lesions, including ischemic stroke. The data summarized here support the investigation of roscovitine as a potential therapeutic agent for the treatment of ischemic stroke, and provide an overview of CDK 1, 2, 5, 7, and 9 functions in brain cells and leucocytes during cerebral ischemia.

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.

Neutrophil-To-Lymphocyte Ratio Predicts 3-Month Outcome of Acute Ischemic Stroke

Increasing evidences have demonstrated that inflammation is involved in the mechanisms of acute ischemic stroke (AIS). As an important and easy-to-measure inflammatory marker, neutrophil-to-lymphocyte ratio (NLR) shows a high association with mortality in patients with stroke in recent studies. In this study, we evaluated the prognostic role of NLR in patients with AIS. One hundred forty-three patients with AIS were enrolled. Clinical data were collected and the NLR was calculated from the admission blood work. The patients were followed up for 3 months after stroke onset. The occurrence of death and the major disability at 3 months after onset were end points in this study. Modified Rankin Scale score ≥3 was considered as poor outcome. In this study, 75 patients (52%) had poor outcome. We used binary logistic regression model to evaluate risk factor for poor outcome of AIS and found that the NLR was independently associated with the poor outcome of 3 months (P < 0.001). The optimal cutoff value for NLR as a predictor for 3-month outcome was 2.995. Therefore, in our study, high NLRs inversely predicted 3-month outcome in patients with AIS.

Inflammatory responses in brain ischemia

Brain infarction causes tissue death by ischemia due to occlusion of the cerebral vessels and recent work has shown that post stroke inflammation contributes significantly to the development of ischemic pathology. Because secondary damage by brain inflammation may have a longer therapeutic time window compared to the rescue of primary damage following arterial occlusion, controlling inflammation would be an obvious therapeutic target. A substantial amount of experimentall progress in this area has been made in recent years. However, it is difficult to elucidate the precise mechanisms of the inflammatory responses following ischemic stroke because inflammation is a complex series of interactions between inflammatory cells and molecules, all of which could be either detrimental or beneficial. We review recent advances in neuroinflammation and the modulation of inflammatory signaling pathways in brain ischemia. Potential targets for treatment of ischemic stroke will also be covered. The roles of the immune system and brain damage versus repair will help to clarify how immune modulation may treat stroke.

Antimicrobial peptides and complement in neonatal hypoxia-ischemia induced brain damage

Hypoxic-ischemic encephalopathy (HIE) is a clinical condition in the neonate, resulting from oxygen deprivation around the time of birth. HIE affects 1-5/1000 live births worldwide and is associated with the development of neurological deficits, including cerebral palsy, epilepsy, and cognitive disabilities. Even though the brain is considered as an immune-privileged site, it has innate and adaptive immune response and can produce complement (C) components and antimicrobial peptides (AMPs). Dysregulation of cerebral expression of AMPs and C can exacerbate or ameliorate the inflammatory response within the brain. Brain ischemia triggers a prolonged inflammatory response affecting the progression of injury and secondary energy failure and involves both innate and adaptive immune systems, including immune-competent and non-competent cells. Following injury to the central nervous system (CNS), including neonatal hypoxia-ischemia (HI), resident microglia, and astroglia are the main cells providing immune defense to the brain in a stimulus-dependent manner. They can express and secrete pro-inflammatory cytokines and therefore trigger prolonged inflammation, resulting in neurodegeneration. Microglial cells express and release a wide range of inflammation-associated molecules including several components of the complement system. Complement activation following neonatal HI injury has been reported to contribute to neurodegeneration. Astrocytes can significantly affect the immune response of the CNS under pathological conditions through production and release of pro-inflammatory cytokines and immunomodulatory AMPs. Astrocytes express β-defensins, which can chemoattract and promote maturation of dendritic cells (DC), and can also limit inflammation by controlling the viability of these same DC. This review will focus on the balance of complement components and AMPs within the CNS following neonatal HI injury and the effect of that balance on the subsequent brain damage.

Role of blood cells in ischaemia-reperfusion induced endothelial barrier failure

Ischaemia and reperfusion (I/R) elicits an acute inflammatory response that is characterized by the recruitment of inflammatory cells, oxidative stress, and endothelial barrier failure. Over the past three decades, much progress has been made in our understanding of the mechanisms that underlie the inflammatory response and microvascular dysfunction associated with I/R. This review is focused on the role of leucocytes (neutrophils and T-lymphocytes) and platelets, and their activation products, as mediators of I/R-induced endothelial barrier failure. The contributions of cytokines, chemokines, and oxidative stress to I/R-induced barrier dysfunction are also discussed. It concludes with an analysis of how risk factors for cardiovascular disease, i.e. hypertension, diabetes, hypercholesterolaemia, and obesity, influence the vascular permeability response to I/R. Areas of uncertainty and controversy in this field of investigation are also identified.

Role of transcription factors in mediating post-ischemic cerebral inflammation and brain damage

Inflammation is a known precipitator of neuronal death after cerebral ischemia. The mechanisms that promote or curtail the start and spread of inflammation in brain are still being debated. By virtue of their capability to modulate gene expression, several transcription factors induced in the ischemic brain can modulate the post-ischemic inflammation. While the induction of transcription factors such as IRF1, NF-kappaB, ATF-2, STAT3, Egr1 and C/EBPbeta is thought to promote post-ischemic inflammation, activation of transcription factors such as HIF-1, CREB, c-fos, PPARalpha, PPARgamma and p53 is thought to prevent post-ischemic inflammation and neuronal damage. Of these, PPARgamma which is a ligand-activated transcription factor was recently shown to prevent inflammatory gene expression in several animal models CNS disorders. This review article discusses some of the molecular mechanisms of PPARgamma induction by its agonists following focal cerebral ischemia.

The inflammatory response in stroke

Recent works in the area of stroke and brain ischemia has demonstrated the significance of the inflammatory response accompanying necrotic brain injury. Acutely, this response appears to contribute to ischemic pathology, and anti-inflammatory strategies have become popular. This chapter will discuss the current knowledge of the contribution of systemic and local inflammation in experimental stroke. It will review the role of specific cell types including leukocytes, endothelium, glia, microglia, the extracellular matrix and neurons. Intracellular inflammatory signaling pathways such as nuclear factor kappa beta and mitogen-activated protein kinases, and mediators produced by inflammatory cells such as cytokines, chemokines, reactive oxygen species and arachidonic acid metabolites will be reviewed as well as the potential for therapy in stroke and hypoxic-ischemic injury.

Inflammation in adult and neonatal stroke

This chapter will discuss the current knowledge of the contribution of systemic and local inflammation in acute and sub-chronic stages of experimental stroke in both the adult and neonate. It will review the role of specific cell types and interactions among blood cells, endothelium, glia, microglia, the extracellular matrix and neurons - cumulatively called "neurovascular unit" - in stroke induction and evolution. Intracellular inflammatory signaling pathways such as nuclear factor kappa beta and mitogen-activated protein kinases, and mediators produced by inflammatory cells such as cytokines, chemokines, reactive oxygen species and arachidonic acid metabolites, as well as the modifying role of age on these mechanisms, will be reviewed as well as the potential for therapy in stroke and hypoxic-ischemic injury.

Reduced cerebral injury in CRH-R1 deficient mice after focal ischemia: a potential link to microglia and atrocytes that express CRH-R1

Corticotropin releasing hormone (CRH) and its family of related peptides are involved in regulating physiologic responses to multiple stressors, including stroke. Although CRH has been implicated in the exacerbation of injury after stroke, the mechanism remains unclear. After ischemia, both excitotoxic damage and inflammation contribute to the pathology of stroke. CRH is known to potentiate excitotoxic damage in the brain and has been shown to modulate inflammatory responses in the periphery. Here the present authors examine the relative contribution of the two known CRH receptors, CRH-R1 and CRH-R2, to ischemic injury using CRH receptor knockout mice. These results implicate CRH-R1 as the primary mediator of ischemic injury in this mouse model of stroke. In addition, the authors examine a potential role for CRH in inflammatory injury after stroke by identifying functional CRH receptors on astrocytes and microglia, which are cells that are known to be involved in brain inflammation. By single cell PCR, the authors show that microglia and astrocytes express mRNA for both CRH-R1 and CRH-R2. However, CRH-R1 is the primary mediator of cAMP accumulation in response to CRH peptides in these cells. The authors suggest that astrocytes and microglia are cellular targets of CRH, which could serve as a link between CRH and inflammatory responses in ischemic injury via CRH-R1.

Fractalkine and fractalkine receptors in human neurons and glial cells

Fractalkine has been identified as a novel chemokine that exhibits cell adhesion and chemoattractive properties in the central nervous system (CNS), and the fractalkine receptors, CX3CR1, are also expressed in the CNS. In the present study, the expression of fractalkine and fractalkine receptors was investigated in enriched populations of human CNS neurons, astrocytes, and microglia. In addition, the regulatory role played by protein kinase C (PKC) in fractalkine secretion in neurons was determined in A1 human hybrid neuronal cell line produced between a human cerebral neuron and a human neuroblastoma cell. Human neurons and astrocytes expressed fractalkine mRNA as determined by the revserse transcriptase-polymerase chain reaction (RT-PCR) analysis, while human microglia preparation did not express the fractalkine message. Human neurons and microglia expressed CX3CR1 mRNA, but astrocytes did not. These results suggest that fractalkine secreted by CNS neurons and astrocytes produce biological effects in neurons and microglia. Although phorbol ester did not change the expression of fractalkine mRNA level in A1 hybrid neurons, it did upregulate fractalkine secretion over unstimulated controls. This upregulation of fractalkine production was suppressed by the treatment with Ro32-0432, a PKC inhibitor. These results indicate that intracellular signals transduced by PKC play an important role in the regulation of soluble fractalkine at the post-transcriptional level in human neurons. As for the biological function of fractalkine, extracellularly applied fractalkine increased the number of bromodeoxyuridine-labeled microglia 3-fold over the untreated controls, indicating fractalkine induces proliferation of human microglia. These observations suggest that fractalkine released by injured neurons could induce proliferation, activation and/or migration of microglia at the injured brain sites.

The use of flow cytometry to evaluate temporal changes in inflammatory cells following focal cerebral ischemia in mice

Recent studies indicate that inflammation following cerebral ischemia contributes to neuronal damage. The local activation of resident cells and efficient recruitment of leukocytes into the central nervous system are critical steps in this inflammatory process. Here we describe studies using flow cytometry to examine the temporal pattern of inflammatory cell activation and infiltration following transient middle cerebral artery occlusion (MCAO) in mice. We found an increase in activated microglia/macrophages as early as 18 h post occlusion, which peaked at 48 h and remained abundant at 96 h post occlusion. Neutrophils were significantly increased by 48 h and remained elevated at 96 h post occlusion. T lymphocytes were increased relatively late (72 and 96 h) post occlusion. The flow cytometry data correlate well both quantitatively and qualitatively with immunohistochemistry analysis performed on the same mice. The present study demonstrates the power of flow cytometry in analyzing the inflammatory process following cerebral ischemia and offers temporal information on the cellular changes in mice following transient MCAO.

Temporal modulation of cytokine expression following focal cerebral ischemia in mice

There is increasing evidence that the inflammatory response plays an important role in CNS ischemia. The murine model of focal ischemia, however, remains incompletely characterized. In this study we examined expression of several cytokines and the vascular adhesion molecule E-selectin, in order to characterize the molecular events following stroke in the C57BL/6J mouse. Using a multi-probe RNAse protection assay (RPA), mRNA for 19 cytokines was analyzed following permanent and transient occlusion of the middle cerebral artery in mice. In addition, samples from the same mice were analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR) to evaluate E-selectin mRNA expression levels. Several cytokine mRNAs showed a similar expression pattern in both permanent and transient CNS ischemia while others showed a temporal expression pattern that was dependent on the type of stroke. For both models, mRNA levels of TNFalpha rose early (4 h) followed by IL-6 (10-18 h) and a comparatively late increase (96 h) in TGFbeta1. IL-1alpha, IL-1beta and IL-1ra levels showed a model dependent shift in temporal expression. Reperfusion appeared to delay the induction of these cytokines. Temporal changes in cytokine mRNA expression in the mouse CNS occur following ischemic damage. Our findings demonstrate the utility and power of multi-probe RPA for evaluation of changes in cytokine mRNA levels. Moreover, this study is, to our knowledge the first to show temporal changes in cytokine mRNA in mouse cerebral ischemia, forming a basis for further exploration of the roles of these cytokines in modulating ischemic neuronal damage in this model.

Expression of membrane-bound and soluble cell adhesion molecules by human brain microvessel endothelial cells

Expression of membrane-bound (mb) and soluble (s) forms of vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1) induced by tumor necrosis factor-alpha (TNF-alpha) has been measured by enzyme-linked immunosorbent assay in cultured human brain microvessel endothelial cells. Both the mb and the s forms of VCAM-1 and ICAM-1 were upregulated by TNF-alpha; however, the stimulation of the s forms was delayed in time. When piracetam, a neuroprotective drug, was added to the tissue culture medium simultaneously with TNF-alpha, the expression of mbVCAM-1 and ICAM-1 was lowered. Differential upregulation of mb and s forms of adhesion molecules and a novel effect of piracetam have been demonstrated in human brain microvessel endothelial cell cultures.

Localization of fractalkine and CX3CR1 mRNAs in rat brain: does fractalkine play a role in signaling from neuron to microglia?

Localization of the mRNAs for fractalkine, a CX3C chemokine, and for its receptor CX3CR1 was investigated in the rat brain. In situ hybridization study revealed that fractalkine mRNA was dominantly expressed in neuronal cells particularly in the olfactory bulb, cerebral cortex, hippocampus, caudate putamen and nucleus accumbens. In vitro study using enriched neuronal or glial culture supported the dominant expression of fractalkine mRNA in neurons. On the other hand, CX3CR1 mRNA was dominantly expressed in glial cells throughout the whole brain. The in vitro study suggested the cells expressing CX3CR1 mRNA are microglia, not astrocytes or neurons. Fractalkine appears to function as a signal molecule from neuron to microglia.

The immunosuppressant drug FK506 ameliorates secondary mitochondrial dysfunction following transient focal cerebral ischemia in the rat

Recirculation following 2 h of focal ischemia due to transient middle cerebral artery (MCA) occlusion has previously been found to be accompanied by an initial, partial recovery of the cellular bioenergetic state and of mitochondrial respiratory functions, with secondary deterioration during the first 2-4 h of reflow. Both the free radical spin trap alpha-phenyl-N-tert-butyl nitrone (PBN) and the immunosuppressant drug FK506 ameliorate the damage incurred by the 2-h period of focal ischemia, even when given 1-3 h after the start of the recirculation. The primary objective of this study was to find out if FK506, like PBN, prevents the secondary deterioration of mitochondrial function, as this can be studied in vitro. Since this proved to be the case, we addressed the question of whether the secondary mitochondrial dysfunction and bioenergetic failure were related to a secondary compromise of microcirculation and cellular oxygen delivery. Six groups of male Wistar rats were studied for measurement of mitochondrial respiratory activity (total, n = 36). One group was used as control (n = 6). In the other groups of animals, MCA occlusion of 2 h duration was induced by an intraluminal filament technique, Neocortical focal and perifocal ("penumbra") tissues were sampled after 2 h of ischemia (n = 6) and after 1 h (n = 6), 2 h (n = 6 with vehicle), and 4 h (n = 6 with vehicle; n = 6 with FK506) of recirculation. The vehicle or 1.0 mg.kg-1 of FK506 was injected intravenously after 1 h of recirculation. Homogenates were prepared, and stimulated (+ADP), nonstimulated (-ADP), and uncoupled respiratory rates were measured polarographically. The uncoupling agent used was carbonyl cyanide m-chlorophenylhydrazone. Local CBF and tissue oxygen tension were evaluated by laser-Doppler flowmetry and PO2 microelectrodes, respectively, throughout the whole periods of 2 h of ischemia and 4 h of recirculation, using a remote MCA occlusion technique. After 2 h of ischemia, the penumbra showed a moderate decrease and the focus a marked decrease in ADP-stimulated and uncoupled respiratory rates, with a marked fall in the respiratory control ratio, defined as ADP-stimulated divided by nonstimulated respiration. Recirculation (1 h) brought about partial recovery, but continued reflow (2 and 4 h) was associated with a secondary deterioration of respiratory functions. The secondary deterioration was prevented by FK506. The results thus confirm previous findings showing that secondary mitochondrial dysfunction occurs following transient focal cerebral ischemia and demonstrate that FK506, like PBN, improves the in vitro performance of mitochondria in focal and penumbral areas. Following MCA occlusion, local CBF in a penumbral area and tissue PO2 in a focal area decreased to about 30 and 5% of control, respectively. However, recirculation brought about rapid recovery of blood flow and oxygen delivery. During the whole 4-h period of recirculation, local CBF and tissue PO2 were maintained close to 100% and at about 160% of the preischemic level, respectively. The results make it highly unlikely that the secondary bioenergetic failure during recirculation is due to a compromised microcirculation. It follows that oxygen delivery is not rate-limiting for recovery events. Very likely, FK506 (and PBN) acts at the cellular level to improve mitochondrial energy functions.

Doxycycline treatment reduces ischemic brain damage in transient middle cerebral artery occlusion in the rat

Agents that inhibit leukocyte adhesion including intercellular adhesion molecule-1 antibodies (anti-ICAM-1) have shown beneficial effects in experimental central nervous system (CNS) ischemia. Doxycycline inhibits leukocyte function in vitro by binding divalent cations and reduces spinal cord reperfusion injury. The authors used a clinically relevant model of focal CNS reperfusion injury to test whether treatment with doxycycline would reduce cerebral ischemic damage and improve functional outcome. Reversible middle cerebral artery occlusion was produced in adult Sprague-Dawley rats by advancing a filament into the internal carotid artery for 2 h. Animals received either i.p. doxycycline (10 mg/kg) (N = 13) or saline (N = 11) 30 min before ischemia, followed by 10 mg/kg every 8 h x 6. Both functional assessment (5 point neurologic scale) and infarct volume was evaluated at 48 h. Functional efficacy: doxycycline 0.5 +/- 0.2 (mean +/- SE) vs control 1.3 +/- 0.3 (p = 0.03). Infarct volume: doxycycline 56 +/- 18 mm3 vs control 158 +/- 44 mm3 (p = 0.03); This protective effect supports the role of doxycycline in reducing CNS reperfusion injury.