Antagonism of neutrophil adherence in the deteriorating stroke model in rabbits

Enhanced effect of limb remote ischemic postconditioning combined with paeoniflorin on alleviating cerebral ischemic injury via neutrophil NADPH pathway

BACKGROUND

Limb remote ischemic postconditioning (LRIP) and paeoniflorin (PF) both can ameliorate cerebral ischemia reperfusion (I/R) injury. At present, whether LRIP combined with PF can achieve better therapeutic effect is unknown.

PURPOSE

This study explored the alleviating effect and mechanism of LRIP in combination with PF on cerebral I/R injury in rats.

METHODS

Middle cerebral artery occlusion (MCAO) surgery was performed on rats except Sham group. Then PF (2.5 mg/kg, 5 mg/kg, 10 mg/kg) was administrated by intraperitoneal injection 10 min before the start of reperfusion. LRIP was operated on the left femoral artery at 0 h of reperfusion. Behavioral testing was used to assess neurological impairment, while TTC staining was used to examine infarct volume. Protein expression of MyD88, TRAF6, p38-MAPK and phosphorylation of p47phox in neutrophils from rat peripheral blood were tested by Western blot. Rat bone marrow neutrophils were extracted and incubated for 24 h with serum from rats after LRIP combined with PF. p38 MAPK inhibitor group was administrated SB203580 while the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor group was administrated Apocynin. Neutrophils were stimulated by fMLP (10 μM). Reactive oxygen species (ROS) production and protein expression of MyD88, TRAF6, p38 MAPK, and p47phox (ser 304 and ser 345) were detected.

RESULTS

LRIP combined with PF (5 mg/kg) reduced cerebral infarct volume, ameliorated neurological deficit score (NDS), decreased fMLP-stimulated ROS release and downregulated the protein expression of MyD88, TRAF6, p38-MAPK and phosphorylation of p47phox (ser 304 and ser 345) in neutrophils.

CONCLUSION

The protective effect of LRIP combined with PF on cerebral I/R injury was better than either alone. Taken together, we provided solid evidence to demonstrate that the combination of LRIP and PF had potential to alleviate cerebral I/R injury, which was regulated by MyD88-TRAF6-p38 MAPK pathway and neutrophil NADPH oxidase pathway.

Endoplasmic Reticulum Stress is Involved in the Protective Effect of Sivelestat Sodium Hydrate (ONO-5046) in Spinal Cord Ischemia-Reperfusion Injury

BACKGROUND

Postoperative complications of thoracoabdominal aortic aneurysm include paraplegia due to impaired blood flow in the spinal cord. Sivelestat sodium hydrate (ONO-5046), a specific neutrophil elastase inhibitor, can prevent neuropathy after ischemia-reperfusion of the spinal cord; however, the underlying mechanism remains unclear. Here, we examined whether ONO-5046 elicits its protective effects in spinal cord ischemia by affecting endoplasmic reticulum (ER) stress.

METHODS

Forty-five male Japanese white rabbits (weight 2.5-3.0 kg) were assigned to three groups: a sham control group (n = 5), and two other groups (n = 20, respectively; n = 5 each time point) that were subjected to spinal cord ischemia-reperfusion for 15 min and administered saline or ONO-5046 intravenously. From 8 h to 7 d after resumption of blood flow, a neurological evaluation, histological evaluation of the spinal cord, and immunohistochemical evaluation based on the expression of GRP78 and caspase12 were performed.

RESULTS

Rabbits treated with ONO-5046 had fewer functional deficits and more surviving motor neurons after ischemia than did rabbits in the saline and control groups. In rabbits treated with ONO-5046, histological findings of the spinal cord showed a high number of viable motor nerves, whereas induction of GRP78, an ER stress response-related protein, was prolonged. Furthermore, caspase12 expression was activated by excessive ER stress and was downregulated in rabbits treated with ONO-5046, as compared with that in rabbits administered saline.

CONCLUSIONS

ONO-5046 exerts a protective effect on the spinal cord by relieving ER stress during spinal cord ischemia.

Viral mimetic triggers cerebral arteriopathy in juvenile brain via neutrophil elastase and NETosis

Stroke is among the top ten causes of death in children but has received disproportionally little attention. Cerebral arteriopathies account for up to 80% of childhood arterial ischemic stroke (CAIS) cases and are strongly predictive of CAIS recurrence and poorer outcomes. The underlying mechanisms of sensitization of neurovasculature by viral infection are undefined. In the first age-appropriate model for childhood arteriopathy-by administration of viral mimetic TLR3-agonist Polyinosinic:polycytidylic acid (Poly-IC) in juvenile mice-we identified a key role of the TLR3-neutrophil axis in disrupting the structural-functional integrity of the blood-brain barrier (BBB) and distorting the developing neurovascular architecture and vascular networks. First, using an array of in-vivo/post-vivo vascular imaging, genetic, enzymatic and pharmacological approaches, we report marked Poly-IC-mediated extravascular leakage of albumin (66kDa) and of a small molecule DiI (∼934Da) and disrupted tight junctions. Poly-IC also enhanced the neuroinflammatory milieu, promoted neutrophil recruitment, profoundly upregulated neutrophil elastase (NE), and induced neutrophil extracellular trap formation (NETosis). Finally, we show that functional BBB disturbances, NETosis and neuroinflammation are markedly attenuated by pharmacological inhibition of NE (Sivelestat). Altogether, these data reveal NE/NETosis as a novel therapeutic target for viral-induced cerebral arteriopathies in children.

Microglia-leucocyte axis in cerebral ischaemia and inflammation in the developing brain

Development of the Central Nervous System (CNS) is reliant on the proper function of numerous intricately orchestrated mechanisms that mature independently, including constant communication between the CNS and the peripheral immune system. This review summarizes experimental knowledge of how cerebral ischaemia in infants and children alters physiological communication between leucocytes, brain immune cells, microglia and the neurovascular unit (NVU)-the "microglia-leucocyte axis"-and contributes to acute and long-term brain injury. We outline physiological development of CNS barriers in relation to microglial and leucocyte maturation and the plethora of mechanisms by which microglia and peripheral leucocytes communicate during postnatal period, including receptor-mediated and intracellular inflammatory signalling, lipids, soluble factors and extracellular vesicles. We focus on the "microglia-leucocyte axis" in rodent models of most common ischaemic brain diseases in the at-term infants, hypoxic-ischaemic encephalopathy (HIE) and focal arterial stroke and discuss commonalities and distinctions of immune-neurovascular mechanisms in neonatal and childhood stroke compared to stroke in adults. Given that hypoxic and ischaemic brain damage involve Toll-like receptor (TLR) activation, we discuss the modulatory role of viral and bacterial TLR2/3/4-mediated infection in HIE, perinatal and childhood stroke. Furthermore, we provide perspective of the dynamics and contribution of the axis in cerebral ischaemia depending on the CNS maturational stage at the time of insult, and modulation independently and in consort by individual axis components and in a sex dependent ways. Improved understanding on how to modify crosstalk between microglia and leucocytes will aid in developing age-appropriate therapies for infants and children who suffered cerebral ischaemia.

Brothers in arms: platelets and neutrophils in ischemic stroke

PURPOSE OF REVIEW

In this review, we will describe how the combined ability of platelets and neutrophils to interact with each other drives ischemic stroke brain injury.

RECENT FINDINGS

Neutrophils are one of the first cells to respond during ischemic stroke. Although animals stroke models have indicated targeting neutrophils improves outcomes, clinical trials have failed to yield successful strategies. Platelets play a critical role in recruiting neutrophils to sites of injury by acting as a bridge to the injured endothelium. After initial platelet adhesion, neutrophils can rapidly bind platelets through P-selectin and glycoprotein Ibα. In addition, recent data implicated platelet phosphatidylserine as a novel key regulator of platelet-neutrophil interactions in the setting of ischemic stroke. Inhibition of procoagulant platelets decreases circulating platelet-neutrophil aggregates and thereby reduces infarct size. Platelet binding alters neutrophil function, which contributes to the injury associated with ischemic stroke. This includes inducing the release of neutrophil extracellular traps, which are neurotoxic and pro-thrombotic, leading to impaired stroke outcomes.

SUMMARY

Platelet-neutrophil interactions significantly contribute to the pathophysiology of ischemic stroke brain injury. Better understanding the mechanisms behind their formation and the downstream consequences of their interactions will lead to improved therapies for stroke patients.

Myosin1f-mediated neutrophil migration contributes to acute neuroinflammation and brain injury after stroke in mice

Background

During the acute stroke phase, neutrophils from the peripheral blood are first to arrive in the ischemic brain, which then attracts other immune cells that exacerbate neuroinflammation in the ischemic tissue. Myosin1f was reported to specifically mediate neutrophil migration in the peripheral tissues, but whether it plays a critical role in the neuroinflammatory response after ischemic stroke remains unknown. In this study, we aim to test the hypothesis that myosin1f-mediated neutrophil migration is critical in acute neuroinflammation induced by ischemic stroke.

Methods

Myosin1f ^−/− and wild type (WT) mice were subjected to transient middle cerebral artery occlusion (MCAO). To determine which cells determine myosin1f’s transmigration ability, bone marrow transplantation, neutrophil depletion, and adoptive neutrophil transfer were performed. The myosin1f RNA level was assessed in peripheral neutrophils by reverse transcription polymerase chain reaction (RT-PCR) at 1 day and 3 days after stroke. The infiltrating neutrophils were quantified by immunofluorescence staining and FACS at 72 h after reperfusion.

Results

The myosin1f ^−/− mice had significantly smaller infarctions than the myosin1f ^+/+ mice. Bone marrow transplantation from myosin1f ^−/− mice to recipient mice also had smaller infarctions compared to animals receiving bone marrow from myosin1f ^+/+ mice. By performing neutrophil depletion and adoptive transfer, we confirmed that myosin1f acts mainly in circulating neutrophils. RT-PCR showed that myosin1f gene expression was increased in the circulating blood neutrophils at 3 days after ischemia. The confocal immunostaining and FACS results confirmed that fewer neutrophils infiltrated into the ischemic brain in myosin1f ^−/− mice compared to WT mice.

Conclusions

Myosin1f determines neutrophil migration into the ischemic hemisphere, which directly affects stroke outcome.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1465-9) contains supplementary material, which is available to authorized users.

Targeting neutrophils in ischemic stroke: translational insights from experimental studies

Neutrophils have key roles in ischemic brain injury, thrombosis, and atherosclerosis. As such, neutrophils are of great interest as targets to treat and prevent ischemic stroke. After stroke, neutrophils respond rapidly promoting blood-brain barrier disruption, cerebral edema, and brain injury. A surge of neutrophil-derived reactive oxygen species, proteases, and cytokines are released as neutrophils interact with cerebral endothelium. Neutrophils also are linked to the major processes that cause ischemic stroke, thrombosis, and atherosclerosis. Thrombosis is promoted through interactions with platelets, clotting factors, and release of prothrombotic molecules. In atherosclerosis, neutrophils promote plaque formation and rupture by generating oxidized-low density lipoprotein, enhancing monocyte infiltration, and degrading the fibrous cap. In experimental studies targeting neutrophils can improve stroke. However, early human studies have been met with challenges, and suggest that selective targeting of neutrophils may be required. Several properties of neutrophil are beneficial and thus may important to preserve in patients with stroke including antimicrobial, antiinflammatory, and neuroprotective functions.

Ly-6G+CCR2- myeloid cells rather than Ly-6ChighCCR2+ monocytes are required for the control of bacterial infection in the central nervous system

Myeloid cell recruitment is a characteristic feature of bacterial meningitis. However, the cellular mechanisms important for the control of Streptococcus pneumoniae infection remain largely undefined. Previous pharmacological or genetic studies broadly depleted many myeloid cell types within the meninges, which did not allow defining the function of specific myeloid subsets. Herein we show that besides CD11b(+)Ly-6G(+)CCR2(-) granulocytes, also CD11b(+)Ly-6C(high)CCR2(+) but not Ly-6C(low)CCR2(-) monocytes were recruited in high numbers to the brain as early as 12 h after bacterial challenge. Surprisingly, CD11b(+)Ly-6C(high)CCR2(+) inflammatory monocytes modulated local CXCL2 and IL-1beta production within the meninges but did not provide protection against bacterial infection. Consistent with these results, CCR2 deficiency strongly impaired monocyte recruitment to the infected brains but was redundant for disease pathogenesis. In contrast, specific depletion of polymorphonuclear granulocytes caused elevated local bacterial titer within the brains, led to an aggravated clinical course, and enhanced mortality. These findings demonstrate that Ly-6C(high)CCR2(+) inflammatory monocytes play a redundant role for the host defense during bacterial meningitis and that predominantly CD11b(+)Ly-6G(+)CCR2(-) myeloid cells are involved in the restriction of the extracellular bacteria.

ONO-5046 attenuation of delayed motor neuron death and effect on the induction of brain-derived neurotrophic factor, phosphorylated extracellular signal–regulated kinase, and caspase3 after spinal cord ischemia in rabbits

OBJECTIVE

The mechanism of spinal cord injury is believed to be related to the vulnerability of spinal motor neuron cells to ischemia. The aim of this study was to investigate whether ONO-5046, a specific inhibitor of neutrophil elastase that can attenuate tissue or organ injury in various pathologic conditions, could protect against ischemic spinal cord damage.

METHODS

After induction of spinal ischemia, ONO-5046 or vehicle was injected intravenously. Cell damage was analyzed by counting the number of motor neurons. To investigate the mechanism by which ONO-5046 prevents ischemic spinal cord damage, we observed the immunoreactivity of CPP32 (caspase3), brain-derived neurotrophic factor, and phosphorylated extracellular signal-regulated kinase.

RESULTS

ONO-5046 eased the functional deficits and increased the number of motor neurons after ischemia. The induction of caspase3 was significantly reduced by ONO-5046 treatment. Furthermore, the expressions of brain-derived neurotrophic factor and phosphorylated extracellular signal-regulated kinase were prolonged.

CONCLUSION

ONO-5046 may protect motor neurons from ischemic injury by reducing caspase3 and prolonging the expressions of brain-derived neurotrophic factor and phosphorylated extracellular signal-regulated kinase. ONO-5046 may be a strong candidate for use as a therapeutic agent in the treatment of ischemic spinal cord injury.

TLR4 contributes to disease-inducing mechanisms resulting in central nervous system autoimmune disease

Environmental factors strongly influence the development of autoimmune diseases, including multiple sclerosis. Despite this clear association, the mechanisms through which environment mediates its effects on disease are poorly understood. Pertussis toxin (PTX) functions as a surrogate for environmental factors to induce animal models of autoimmunity, such as experimental autoimmune encephalomyelitis. Although very little is known about the molecular mechanisms behind its function in disease development, PTX has been hypothesized to facilitate immune cell entry to the CNS by increasing permeability across the blood-brain barrier. Using intravital microscopy of the murine cerebromicrovasculature, we demonstrate that PTX alone induces the recruitment of leukocytes and of active T cells to the CNS. P-selectin expression was induced by PTX, and leukocyte/endothelial interactions could be blocked with a P-selectin-blocking Ab. P-selectin blockade also prevented PTX-induced increase in permeability across the blood-brain barrier. Therefore, permeability is a secondary result of recruitment, rather than the primary mechanism by which PTX induces disease. Most importantly, we show that PTX induces intracellular signals through TLR4, a receptor intimately associated with innate immune mechanisms. We demonstrate that PTX-induced leukocyte recruitment is dependent on TLR4 and give evidence that the disease-inducing mechanisms initiated by PTX are also at least partly dependent on TLR4. We propose that this innate immune pathway is a novel mechanism through which environment can initiate autoimmune disease of the CNS.

Platelet-activating factor induces cell death in cultured astrocytes and oligodendrocytes: involvement of caspase-3

The biologically active lipid metabolite, platelet-activating factor (PAF), is thought to contribute to inflammatory processes and tissue damage in a variety of central nervous system (CNS) injuries. In previous studies, we found that after contusion spinal cord injury, treatment with a PAF antagonist led to significantly increased white matter tissue sparing as well as decreased mRNA levels for pro-inflammatory cytokines. Some studies suggest that PAF can also have toxic effects on neurons in vitro. Few studies, however, have examined the effects of PAF on glial cells of the CNS. In the present study, the potential for PAF to act as a toxin to cultured astrocytes was examined. Also investigated were the effects of PAF on oligodendrocytes at two different stages of development. Treatment with 0.02-2 microM PAF for 72 h resulted in significant levels of cell death in both cell types (P < 0.05), an effect that was blocked by the PAF receptor antagonists, WEB 2170 and BN 52021. To investigate PAF-induced glial cell death further, we looked for activation of the enzyme, caspase-3, which can be indicative of apoptosis. Immunocytochemistry demonstrated that PAF at all concentrations caused activation of caspase-3 at 24, 48, and 72 h after treatment in both cell types. Caspase-3-dependent cell death was further confirmed using knockout mice (-/-) deficient in the caspase-3 gene. Toxicity was lost when astrocytes (-/-) were exposed to 0.02-2 microM PAF (P < 0.01). Oligodendrocytes (-/-) were not susceptible to toxicity at 2 microM PAF (P < 0.001). The results demonstrate that the pro-inflammatory molecule, PAF, induces cell death in cultured CNS glial cells and that this effect is, in part, dependent on caspase-3 activation.

Pentoxifylline reduces biochemical markers of ischemia-reperfusion induced spinal cord injury in rabbits

STUDY DESIGN

Occlusion of the infrarenal abdominal aorta with administration of pentoxifylline was applied to adult rabbits, followed by removal of aortic clamp and reperfusion. Tissue levels of cytokines, lipid peroxides, and antioxidant enzymes were assayed and compared within groups.

OBJECTIVES

To examine the effect of pentoxifylline (PTX) on cytokine levels, lipid peroxidation, and antioxidant enzymes in a rabbit model of spinal cord ischemia-reperfusion injury induced by aortic occlusion.

SETTING

Isparta, Turkey.

METHODS

Rabbits were randomly allocated into four groups of sham laparotomy (SHAM), sham laparotomy with PTX administration (SHAM+PTX), aortic occlusion and reperfusion (AOR), aortic occlusion and reperfusion with PTX administration (AOR+PTX). An intravenous bolus of 50 mg/kg PTX was given just before aortic cross clamping. An atraumatic microvascular clamp was then placed on the abdominal aorta immediately distal to the left renal artery for 30 min. PTX was infused at a rate of 0.5 mg/kg/min during the aortic occlusion. Animals were subjected to 120 min of reperfusion after removal of the aortic clamp. All animals were sacrificed at the end of reperfusion. The lumbosacral segments of spinal cords were quickly harvested and stored at -78 degrees C for biochemical assays of IL-6, TNF-alpha, MDA, SOD, and CAT levels. Differences among groups were analyzed by one-way analysis of variance followed by a post hoc Tukey's honestly significant difference test.

RESULTS

No differences in mean levels of IL-6, TNF-alpha, MDA, SOD, and CAT were noted between SHAM and SHAM+PTX groups (P>0.05). There was a significant increase in all biochemical parameters in the AOR group (P<0.05). Administration of PTX significantly attenuated the levels of all biochemical parameters in the AOR+PTX group (P<0.05).

CONCLUSION

PTX pretreatment attenuated ischemia-reperfusion induced spinal cord injury in a rabbit model, in terms of biochemical parameters of ischemia and reperfusion.

PAF antagonist treatment reduces pro-inflammatory cytokine mRNA after spinal cord injury

Platelet-activating factor (PAF) is a pro-inflammatory molecule which contributes to secondary damage after spinal cord injury (SCI). To test if PAF contributes to cytokine induction following SCI, female Long-Evans rats were pretreated with the PAF antagonist WEB 2170 prior to receiving a contusion injury at spinal cord level T10 using the NYU impactor. RNase protection assay (RPA) analysis revealed that IL-1alpha mRNA peaked at I h post-injury while IL-1beta and IL-6 mRNA levels were higher and peaked at 6 h.TNF-alpha mRNA was almost undetectable. All mRNA levels approached baseline by 24 h. Treatment with WEB 2170 (1 mg/kg, i.p.) 15 min prior to injury significantly decreased mRNA levels for all three cytokines at 6 h post-injury, but not at I h post-injury. These results demonstrate a role for PAF in proinflammatory cytokine induction after SCI.

CXC chemokine receptor-2 ligands are required for neutrophil-mediated host defense in experimental brain abscesses

We have developed a mouse brain abscess model by using Staphylococcus aureus, one of the main etiologic agents of brain abscesses in humans. Direct damage to the blood-brain barrier was observed from 24 h to 7 days after S. aureus exposure as demonstrated by the accumulation of serum IgG in the brain parenchyma. Evaluation of brain abscesses by immunohistochemistry and flow cytometry revealed a prominent neutrophil infiltrate. To address the importance of neutrophils in the early containment of S. aureus infection in the brain, mice were transiently depleted of neutrophils before implantation of bacteria-laden beads. Neutrophil-depleted animals consistently demonstrated more severe brain abscesses and higher CNS bacterial burdens compared with control animals. S. aureus led to the induction of numerous chemokines in the brain, including macrophage-inflammatory protein (MIP)-1alpha/CCL3, MIP-1beta/CCL4, MIP-2/CXCL1, monocyte chemoattractant protein-1/CCL2, and TCA-3/CCL1, within 6 h after bacterial exposure. These chemokines also were expressed by both primary cultures of neonatal mouse microglia and astrocytes exposed to heat-inactivated S. aureus in vitro. Because neutrophils constitute the majority of the cellular infiltrate in early brain abscess development, subsequent analysis focused on MIP-2 and KC/CXCL1, two neutrophil-attracting CXC chemokines. Both MIP-2 and KC protein levels were significantly elevated in the brain after S. aureus exposure. Neutrophil extravasation into the brain parenchyma was impaired in CXCR2 knockout mice and was associated with increased bacterial burdens. These studies demonstrate the importance of the CXCR2 ligands MIP-2 and KC and neutrophils in the acute host response to S. aureus in the brain.

Pharmacologic neuroprotection in experimental spinal cord ischemia: a systematic review

Various surgical procedures may cause temporary interruption of spinal cord blood supply and may result in irreversible ischemic injury and neurological deficits. The cascade of events that leads to neuronal death following ischemia may be amenable to pharmacological manipulations that aim to increase the tolerable duration of ischemia. Many agents have been evaluated in experimental spinal cord ischemia (SCI). In order to investigate whether an agent is available that justifies clinical evaluation, the literature on pharmacological neuroprotection in experimental SCI was systematically reviewed to assess the neuroprotective efficacy of the various agents. In addition, the strength of the evidence for neuroprotection was investigated by analyzing the methodology. The authors used a systematic review to conduct this evaluation. The included studies were analyzed for neuroprotection and methodology. In order to be able to compare the various agents for neuroprotective efficacy, relative risks and confidence intervals were calculated from the data in the results sections. A total of 103 studies were included. Seventy-nine different agents were tested. Only 14 of the agents tested did not afford protection at all. A large variation was observed in the experimental models to produce SCI. This variation limited comparison of the individual agents. In 48 studies involving 31 single agents, the relative risks and confidence intervals could be calculated. An analysis of the methodology revealed poor temperature management and lack of statistical power in the majority of the 103 studies. The results suggest that numerous agents may protect the spinal cord from transient ischemia. However, poor temperature management and lack of statistical power severely weakened the evidence. Consequently, clinical evaluation of pharmacological neuroprotection in surgical procedures that carry a risk of ischemic spinal cord damage is not justified on the basis of this study.

Antibody to the alpha4 integrin decreases infarct size in transient focal cerebral ischemia in rats

BACKGROUND AND PURPOSE

Inflammation, a process that involves neutrophils, lymphocytes, and monocytes, contributes to cerebral ischemic injury. Blockade of neutrophil adhesion to endothelium improves outcome after experimental stroke. In this study we sought to assess the contribution of lymphocytes and monocytes to ischemic brain injury.

METHODS

Male Lewis rats underwent 3 hours of middle cerebral artery occlusion followed by 45 hours of reperfusion. Two hours after the onset of ischemia, one group of animals received an intraperitoneal injection of antibodies to the alpha(4) integrin (n=16); another group was injected with an isotype control antibody (n=11). Neurological examination, body temperature, and body weight were assessed at different time points after stroke. Animals were killed 48 hours after the onset of ischemia for determination of infarct volume and leukocyte counts.

RESULTS

There were no significant differences in body temperature or weight at any time. Neurological scores (deficits) were significantly less in animals treated with anti-alpha(4) antibodies at 24 (2.0+/-1.2 versus 3. 0+/-0.4; P:=0.006) and 48 (2.0+/-1.2 versus 3.0+/-0.8; P:=0.011) hours after ischemia. Peripheral blood leukocyte counts were significantly higher in anti-alpha(4)-treated animals (6.8+/-2.2 x 10(9) versus 2.9+/-1.9 x 10(9); P:=0.001) and revealed a lymphocyte/monocyte predominance (86.0+/-16.2% versus 71.0+/-15.6%; P:=0.008). Infarct volume was significantly less in animals treated with antibodies to alpha(4) (120.1+/-51.21 versus 173.7+/-42.29 mm(3); P:=0.012).

CONCLUSIONS

These data support a role for lymphocytes and monocytes in cerebral ischemic injury and show that blockade of alpha(4), even when instituted after the onset of ischemia, can improve neurological outcome and decrease infarct volume.

Effect of neutropenia and granulocyte colony stimulating factor-induced neutrophilia on blood-brain barrier permeability and brain edema after traumatic brain injury in rats

OBJECTIVE

Granulocyte colony stimulating factor (GCSF) has been used to increase systemic absolute neutrophil count (ANC) in patients with severe traumatic brain injury to reduce nosocomial infection risk. However, the effect of increasing systemic ANC on the pathogenesis of experimental traumatic brain injury has not been studied. Thus, we evaluated the effect of systemic ANC on blood-brain barrier (BBB) damage and brain edema after traumatic brain injury in rats.

DESIGN

Experimental study.

SETTING

Research laboratory at the University of Pittsburgh, PA.

SUBJECTS

Forty-three adult male Sprague-Dawley rats.

INTERVENTIONS

Protocol I: rats were randomized to receive either vinblastine sulfate to reduce ANC, GCSF to increase ANC, or saline before controlled cortical impact (CCI) of moderate overall severity. Evans blue was used to assess BBB damage at 4-24 hrs after CCI. Protocol II: rats received GCSF or saline before CCI. Brain edema was estimated at 24 hrs using wet - dry) / wet weight method. Protocol III: rats received GCSF or saline before CCI. Brain neutrophil accumulation was estimated at 24 hrs using a myeloperoxidase assay.

MEASUREMENTS AND MAIN RESULTS

Physiologic variables were controlled before CCI was maintained at normal in all animals before traumatic brain injury. No rats were anemic, hypoglycemic, or hypotensive before CCI. Protocol I: compared with control, systemic ANC decreased in vinblastine-treated rats and increased in GCSF-treated rats. BBB damage correlated with systemic ANC. Protocol II: mean systemic ANC before traumatic brain injury increased 15-fold in rats given GCSF vs. control; however no difference in brain edema was observed at 24 hrs after injury between groups. Protocol III: median systemic ANC at the time of CCI was increased ten-fold in rats given GCSF vs. control. No difference in brain myeloperoxidase activity 24 hrs after CCI was observed in rats treated with GCSF vs. control.

CONCLUSIONS

Systemic ANC influences BBB damage after traumatic brain injury produced by CCI. Because BBB damage and brain edema are discordant, mechanisms other than BBB damage likely predominate in the pathogenesis of brain edema after contusion. The implications of increased BBB permeability with the administration of GCSF in our model remains to be determined. Increasing systemic ANC before CCI with GCSF administration does not increase posttraumatic brain neutrophil accumulation or brain edema after CCI in rats. The finding that neutrophil infiltration is not enhanced by systemic neutrophilia suggests that the ability of GCSF-stimulated neutrophils to migrate into injured tissue may be impaired. Further studies are needed to evaluate the effects of GCSF administration on secondary injury and functional outcome in experimental models of traumatic brain injury.

Neutrophils do not mediate blood-brain barrier permeability early after controlled cortical impact in rats

Controlled cortical impact (CCI) produces blood-brain barrier (BBB) permeability and an acute inflammatory response in injured brain, associated with upregulation of cell adhesion molecules and accumulation of neutrophils. Nevertheless, the role of acute inflammation in the pathogenesis of BBB permeability after traumatic brain injury (TBI) is undefined. The purpose of this study was to examine the time course of acute inflammation and BBB permeability after CCI in rats and to determine the effect of neutrophil depletion on BBB permeability early after CCI. In the first protocol, four groups of rats (n = 4-7/group) were subjected to CCI. Expression of endothelial (E)-selectin on cerebrovascular endothelium, accumulation of neutrophils, and BBB permeability were measured in brain at 1, 4, 8, and 24 hours after injury by immunohistochemistry or spectrophotometric quantification of Evans blue. E-selectin upregulation and neutrophil accumulation in injured brain occurred at later times than maximal BBB permeability. In a second protocol, rats made neutropenic with a murine monoclonal IgM antibody (RP-3) specific for rat neutrophils were subjected to CCI, given Evans blue at 3.5 hours, and sacrificed at 4 hours after injury. Neutrophil depletion did not affect BBB permeability at 4 hours after CCI. We conclude that events other than those mediated by neutrophils initiate BBB permeability early after CCI.

CD18-mediated neutrophil recruitment contributes to the pathogenesis of reperfused but not nonreperfused stroke

BACKGROUND AND PURPOSE

Neutrophil (PMN) recruitment mediated by increased expression of intercellular adhesion molecule-1 expression (ICAM-1, CD54) in the cerebral microvasculature contributes to the pathogenesis of tissue injury in stroke. However, studies using blocking antibodies against the common beta2-integrin subunit on the PMN, the counterligand for ICAM-1 (CD18), have demonstrated equivocal efficacy. The current study tested the hypothesis that mice deficient in CD18 would be protected in the setting of reperfused but not nonreperfused stroke.

METHODS

Two groups of mice were studied, those whose PMNs could express CD18 (CD18 +/+) and those mice hypomorphic for the CD-18 gene (CD18 -/-). PMNs obtained from CD18 -/- or CD18 +/+ mice were fluorescently labeled and tested for binding to murine brain endothelial monolayers. Using a murine model of focal cerebral ischemia in which an occluding suture placed in the middle cerebral artery (MCA) is removed after 45 minutes (transient ischemia, reperfused stroke) or left in place (permanent ischemia, nonreperfused stroke), cerebral infarct volumes (% ipsilateral hemisphere by TTC staining), cerebral blood flow (CBF, % contralateral hemisphere by laser-Doppler flowmetry), and survival (%) were examined 24 hours after the initial ischemic event. Adoptive transfer studies used 111In-labeled PMNs (from either CD18 +/+ or CD18 -/- mice) to examine the relative accumulation of PMNs in the ischemic region.

RESULTS

PMNs obtained from CD18 -/- mice exhibit reduced adhesivity (compared with CD18 +/+ PMNs) for both quiescent and cytokine-activated endothelial monolayers. CD18 -/- mice (n=14) subjected to transient focal cerebral ischemia demonstrated a 53% decrease in infarct volumes versus CD18 +/+ mice (n=26, P<0.05), improved penumbral CBF at 24 hours (1.8-fold, P=0.02), and a 3.7-fold decrease in mortality (P=0.02). However, when CD18 -/- mice (n=12) were subjected to permanent focal cerebral ischemia, no differences were noted in infarct volume, mortality, or CBF versus similarly treated CD18 +/+ mice (n=10). There was a greater accumulation of CD18 +/+ PMNs in the ischemic zone of CD18 +/+ animals than CD18 -/- animals subjected to reperfused stroke (82% increase, P=0.02), although there was no difference between groups when subjected to permanent MCA occlusion.

CONCLUSIONS

Deficiency for the CD18 gene confers cerebral protection in a murine model of reperfused stroke, but this benefit does not extend to CD18-deficient animals subjected to permanent MCA occlusion. These data suggest that anti-PMN strategies should be targeted to reperfused stroke and may perhaps be used in conjunction with thrombolytic therapy that establishes reperfusion.

Superoxide anion production during reperfusion is reduced by an antineutrophil antibody after prolonged cerebral ischemia

Neutrophils may be involved in the pathophysiology of reperfusion injury following cerebral ischemia. One potential mechanism of reperfusion injury by neutrophils is through production of the superoxide anion. We hypothesized that, due to progressive endothelial damage during ischemia, neutrophil activation would be more prominent after longer periods of ischemia prior to reperfusion. Thus, neutrophils would contribute more to pathological processes such as superoxide anion formation after longer than after shorter periods of ischemia. A reversible middle cerebral artery occlusion model in rats was employed and superoxide anion concentration was measured with a cytochrome c coated electrode placed on the cortical penumbral region. Occlusion times were varied from 60 min to 2 h, and neutrophils were inhibited with an antiCD18 antibody administered prior to occlusion. Neutrophil accumulation and reduction with antibody treatment was confirmed immunohistochemically. Superoxide anion (O2*-) concentration was detected during the hours following 60 min of occlusion, and increased further with 2 h of occlusion. Treatment with the antiCD18 antibody had no effect on O2*- concentration during reperfusion in the 60-90 min occlusion groups, but O2*- concentration was significantly lower in the antiCD18 antibody treated group than in the control group during reperfusion after 120 min of ischemia. The antibody also reduced cortical neutrophil accumulation in the 120 min ischemia group. These results indicate for the first time that superoxide production by neutrophils becomes more important with longer periods of ischemia, and other quantitatively less important sources of superoxide predominate with shorter periods of ischemia. This phenomenon may explain some of the variation seen between different models of ischemia with different durations of ischemia when targeting reactive oxygen species, and supports an approach to combination therapy to extend the therapeutic window and reduce the deleterious effects of reperfusion.

In vivo rat closed spinal window for spinal microcirculation: observation of pial vessels, leukocyte adhesion, and red blood cell velocity

OBJECTIVES

An in vivo closed spinal window technique in rats was designed for observing the spinal microcirculation, such as the change of vessel diameter, leukocyte adhesion, and red blood cell (RBC) velocity, which has been very rarely examined in vivo in the spinal cord.

METHODS

We made a very precise closed spinal window with a laminectomy at the C5 level using a dental acrylic resin and a cover glass (7 mm in diameter). Through this closed window, the dorsal surface of the rat cervical cord was observed with a video microscope, and the fluorescent images of rhodamine 6G-labeled leukocytes and fluorescein isothiocyanate-labeled RBCs were recorded and analyzed with a silicon-intensified target tube camera (30 frames/s) and an image-intensified high-speed video camera system (1000 frames/s).

RESULTS

During CO2 inhalation, the pial arterioles responded with vasodilation of 12.4+/-10.4% (P<0.01) in 11 arterioles of seven rats. The adhering leukocytes significantly increased in 41 venular segments of seven rats after superfusion of the neutrophil chemoattractant, N-formyl-methionine-leucine-phenylalanine solution for 15 minutes (P<0.001) but not after superfusion of only artificial cerebrospinal fluid for 15 minutes. During these experiments, no adhering leukocyte was seen in the pial arterioles. Fluorescein isothiocyanate-labeled RBCs look like shooting stars in arterioles with silicon-intensified target tube camera processing at 30 frames per second, but individual fluorescein isothiocyanate-labeled RBCs could be recognized frame by frame with the image-intensified high-speed video camera system. In 13 arterioles of four rats, the RBC velocity was 5.3+/-2.0 mm per second.

CONCLUSION

This closed spinal window technique in rats is available and applicable for the study of the spinal microcirculation, such as the pathophysiology of a secondary injury.

Effect of neutrophil depletion in acute cerebritis

Inhibition of the host's neutrophil response has been proposed as one means to reduce tissue damage in acute inflammation. If this approach can be applied in acute central nervous system (CNS) infection, the long-term morbidity, which occurs in CNS infection, might be reduced. Previous studies in models of CNS infection yielded conflicting results whether neutrophil depletion might be protective. To determine whether neutrophil depletion reduces tissue necrosis and cerebrovascular injury in experimental bacterial cerebritis, we depleted circulating neutrophils with an IgM monoclonal antibody, RP3, given after the start of the infection. RP3 treatment successfully depleted circulating neutrophils and reduced the extent of neutrophil influx into the cerebritis region. The extent of tissue necrosis, measured histologically, and the regional increase of blood-brain barrier (BBB) permeability were not inhibited by neutrophil depletion, and in animals treated with RP3 alone, the extent of tissue necrosis and BBB permeability tended to be larger than in S. aureus inoculated controls. We conclude that host neutrophils do not add to the tissue and cerebrovascular damage created by the intracerebral inoculation of a pathogenic bacteria, and the neutrophils serve to diminish local damage in the setting of a cerebritis.

Traumatic spinal cord injury induces nuclear factor-kappaB activation

Inflammatory responses are a major component of secondary injury and play a central role in mediating the pathogenesis of acute and chronic spinal cord injury (SCI). The nuclear factor-kappaB (NF-kappaB) family of transcription factors is required for the transcriptional activation of a variety of genes regulating inflammatory, proliferative, and cell death responses of cells. In this study we examined the temporal and cellular expression of activated NF-kappaB after traumatic SCI. We used a contusion model (N.Y.U. Impactor) to initiate the early biochemical and molecular changes that occur after traumatic injury to reproduce the pathological events associated with acute inflammation after SCI. The activation and cellular distribution of activated NF-kappaB was evaluated by using a monoclonal antibody that selectively recognizes activated p65 in a NF-kappaB dimer. Immunohistochemical and Western blot analyses demonstrated that NF-kappaB activation occurred as early as 0.5 hr postinjury and persisted for at least 72 hr. Using electrophoretic mobility shift assays (EMSA), we demonstrate that NF-kappaB is activated after SCI. In our immunohistochemical, Western, and EMSA experiments there are detectable levels of activated NF-kappaB in our control animals. Using double-staining protocols, we detected activated NF-kappaB in macrophages/microglia, endothelial cells, and neurons within the injured spinal cord. Colocalization of activated NF-kappaB with the NF-kappaB-dependent gene product, inducible nitric oxide synthase (iNOS), suggests functional implications for this transcription factor in the pathogenesis of acute spinal cord injury. Although there is considerable evidence for the involvement of an inflammatory reaction after traumatic SCI, this is the first evidence for the activation of NF-kappaB after trauma. Strategies directed at blocking the initiation of this cascade may prove beneficial as a therapeutic approach for the treatment of acute SCI.

The induction of ICAM-1 in human cerebromicrovascular endothelial cells (HCEC) by ischemia-like conditions promotes enhanced neutrophil/HCEC adhesion

Ischemic brain injury is exacerbated by leukocyte infiltration and formation of vasogenic edema. In this study we demonstrate that intercellular adhesion molecule-1 (ICAM-1) is dramatically (3 to 15-fold) up-regulated in human cerebromicrovascular endothelial cells (HCEC) by a 16 h exposure to the cytokine, IL-1 beta (50-200 u/ml), the phorbol ester, TPA (1-100 nM), or by simulated in vitro ischemia/reperfusion. These treatments also significantly increased the adhesion of allogeneic neutrophils to HCEC monolayers. Both IL-1 beta- and TPA-induced expression of ICAM-1 and increased neutrophil adhesion to HCEC were inhibited by the transcriptional inhibitor, actinomycin D (AcD; 1-10 micrograms/ml), and by an anti-ICAM-1 antibody (ICAM-1 Ab). By contrast, ischemia-induced neutrophil adhesion was only slightly affected by AcD and ICAM-1 Ab alone, but it was abolished by the combination of anti-ICAM-1 and anti-CD18 antibodies. The increase in surface expression of ICAM-1 and neutrophil adhesion by IL-1 beta, TPA and ischemia were significantly reduced by the cyclo-oxygenase (COX) inhibitors, indomethacin (100-300 microM) and dexamethasone (10-50 microM). These results indicate that ICAM-1 expression in HCEC can lead to enhanced neutrophil adhesion and that COX activation in HCEC likely plays a role in the processes by which leukocyte adhesion and recruitment take place in the brain during inflammation and ischemia in vivo.

Cytokines and perinatal brain injury

A rapidly expanding body of data provides support for the hypothesis that pro-inflammatory cytokines including interleukin-1 beta (IL-1 beta), and tumor necrosis factor-alpha (TNF-alpha) are expressed acutely in injured brain and contribute to progressive neuronal damage. Little is known about the pathogenetic role of these cytokines in perinatal brain injury. Recent experimental studies have incorporated two closely related in vivo perinatal rodent brain injury models to evaluate the role(s) of pro-inflammatory cytokines in the progression of neuronal injury: a perinatal stroke model, elicited by unilateral carotid artery ligation and subsequent timed exposure to 8% oxygen in 7-day-old rats, and a model of excitotoxic injury, elicited by stereotactic intra-cerebral injection of the selective excitatory amino acid agonist NMDA. Each of these lesioning methods results in reproducible, quantifiable focal forebrain injury at this developmental stage. Acute brain injury, evoked by cerebral hypoxia-ischemia or excitotoxin lesioning, results in transient marked increases in expression of IL-1 beta, and TNF-alpha mRNA in brain regions susceptible to irreversible injury, and there is evidence that pharmacological antagonism of IL-1 receptors can attenuate injury in both models. Recent studies also suggest that complementary strategies, based on pharmacological antagonism of platelet activating factor and on neutrophil depletion can also limit the extent of irreversible injury. In summary, current data suggest that pro-inflammatory cytokines contribute to the progression of perinatal brain injury, and that these mediators are important targets for neuroprotective interventions in the acute post-injury period.

Endothelial ICAM-1 expression associated with inflammatory cell response in human ischemic stroke

BACKGROUND

After focal brain ischemia, leukocytes adhere to the perturbed endothelium and are believed to aggravate reperfusion injury. Although ischemia-induced upregulation of endothelial adhesion molecules, intercellular adhesion molecule-1 (ICAM-1) and P-selectin, has been observed in experimental animals, the mechanism of cerebral leukocyte infiltration and thus therapeutic possibilities to reduce it in humans are uncertain.

METHODS AND RESULTS

We counted the granulocytes, mononuclear phagocytes, and the percentages of cerebral microvessels expressing ICAM-1 by applying immunohistochemistry on brain sections showing a variable degree of neuronal damage from 11 human subjects who died 15 hours to 18 days after ischemic stroke and from normal control brains. In infarcted regions, granulocytes were detected as early as at 15 hours after injury (11.3 versus 0.5 cells/mm2 in noninfarcted hemisphere); their amount exceeded 200 cells/mm2 by 2.2 days but was back to normal level at 6.3 and 8.5 days. Acute infarctions (0.6 to 8.5 days) harbored significantly more ICAM-1-stained microvessels (up to 97% of microvessels at 1.8 days) than the noninfarcted hemisphere (P < .001), although the noninfarcted hemisphere (1.8 to 6.3 days) also showed higher ICAM-1 expression than controls. In the absence of ICAM-1 upregulation, macrophages (> 200/mm2) were abundant in the core of neuronal damage at 17 and 18 days.

CONCLUSIONS

The striking upregulation of endothelial ICAM-1 expression, functioning in concert with chemotactic factors, may cause granulocyte infiltration during the first 3 days after stroke. This study may support the usage and timing of antibody infusions to block endothelial adhesion molecules in an attempt to reduce leukocyte-induced damage in stroke.

Cerebral protection in homozygous null ICAM-1 mice after middle cerebral artery occlusion. Role of neutrophil adhesion in the pathogenesis of stroke

Acute neutrophil (PMN) recruitment to postischemic cardiac or pulmonary tissue has deleterious effects in the early reperfusion period, but the mechanisms and effects of neutrophil influx in the pathogenesis of evolving stroke remain controversial. To investigate whether PMNs contribute to adverse neurologic sequelae and mortality after stroke, and to study the potential role of the leukocyte adhesion molecule intercellular adhesion molecule-1 (ICAM-1) in the pathogenesis of stroke, we used a murine model of transient focal cerebral ischemia consisting of intraluminal middle cerebral artery occlusion for 45 min followed by 22 h of reperfusion. PMN accumulation, monitored by deposition of 111In-labeled PMNs in postischemic cerebral tissue, was increased 2.5-fold in the ipsilateral (infarcted) hemisphere compared with the contralateral (noninfarcted) hemisphere (P < 0.01). Mice immunodepleted of neutrophils before surgery demonstrated a 3.0-fold reduction in infarct volumes (P < 0.001), based on triphenyltetrazolium chloride staining of serial cerebral sections, improved ipsilateral cortical cerebral blood flow (measured by laser Doppler), and reduced neurological deficit compared with controls. In wild-type mice subjected to 45 min of ischemia followed by 22 h of reperfusion, ICAM-1 mRNA was increased in the ipsilateral hemisphere, with immunohistochemistry localizing increased ICAM-1 expression on cerebral microvascular endothelium. The role of ICAM-1 expression in stroke was investigated in homozygous null ICAM-1 mice (ICAM-1 -/-) in comparison with wild-type controls (ICAM-1 +/+). ICAM-1 -/- mice demonstrated a 3.7-fold reduction in infarct volume (P < 0.005), a 35% increase in survival (P < 0.05), and reduced neurologic deficit compared with ICAM-1 +/+ controls. Cerebral blood flow to the infarcted hemisphere was 3.1-fold greater in ICAM-1 -/- mice compared with ICAM-1 +/+ controls (P < 0.01), suggesting an important role for ICAM-1 in the genesis of postischemic cerebral no-reflow. Because PMN-depleted and ICAM-1-deficient mice are relatively resistant to cerebral ischemia-reperfusion injury, these studies suggest an important role for ICAM-1-mediated PMN adhesion in the pathophysiology of evolving stroke.