Neutrophil infiltration increases matrix metalloproteinase-9 in the ischemic brain after occlusion/reperfusion of the middle cerebral artery in rats

Extension of the thrombolytic time window with minocycline in experimental stroke

BACKGROUND AND PURPOSE

Thrombolysis with tPA is the only FDA-approved therapy for acute ischemic stroke. But its widespread application remains limited by narrow treatment time windows and the related risks of cerebral hemorrhage. In this study, we ask whether minocycline can prevent tPA-associated cerebral hemorrhage and extend the reperfusion window in an experimental stroke model in rats.

METHODS

Spontaneously hypertensive rats were subjected to embolic focal ischemia using homologous clots and treated with: saline at 1 hour; early tPA at 1 hour, delayed tPA at 6 hours; minocycline at 4 hours; combined minocycline at 4 hours plus tPA at 6 hours. Infarct volumes and hemorrhagic transformation were quantified at 24 hours. Gelatin zymography was used to measure blood levels of circulating matrix metalloproteinase-9 (MMP-9).

RESULTS

Early 1-hour thrombolysis restored perfusion and reduced infarction. Late 6-hour tPA did not decrease infarction but instead worsened hemorrhagic conversion. Combining minocycline with delayed 6-hour tPA decreased plasma MMP-9 levels, reduced infarction, and ameliorated brain hemorrhage. Blood levels of MMP-9 were also significantly correlated with volumes of infarction and hemorrhage.

CONCLUSIONS

Combination therapy with minocycline may extend tPA treatment time windows in ischemic stroke.

White matter injury in young and aged rats after intracerebral hemorrhage

Experimental studies of intracerebral hemorrhage (ICH) have focused on neuron death, with little or no information on axonal and myelin damage outside the hematoma. Because development of effective therapies will require an understanding of white matter injury, we examined white matter injury and its spatial and temporal relationship with microglial/macrophage activation in a collagenase model of rat striatal ICH. The hematoma and parenchyma surrounding the hematoma were assessed in young and aged animals at 6 h, 1, 3 and 28 days after ICH onset. Demyelination occurred inside and at the edge of the hematoma; regions where we have shown substantial neuron death. In contrast, there was axonal damage without demyelination at the edge of the hematoma, and by 3 days this damage had spread to the surrounding parenchyma, a region where we have shown there is no neuron death. Because the axonal damage preceded infiltration of activated microglia into the white matter tracts (seen at 3 days), our results support the hypothesis that these cells respond to, rather than perpetrate the damage. Importantly, axonal damage was worse in aged animals, which provides a plausible explanation for the poorer functional recovery of older animals after ICH, despite a similar loss of grey matter. Our findings support strategies that target white matter injury to reduce neurological impairment after ICH.

Blood-brain barrier tight junction permeability and ischemic stroke

The blood-brain barrier (BBB) is formed by the endothelial cells of cerebral microvessels, providing a dynamic interface between the peripheral circulation and the central nervous system. The tight junctions (TJs) between the endothelial cells serve to restrict blood-borne substances from entering the brain. Under ischemic stroke conditions decreased BBB TJ integrity results in increased paracellular permeability, directly contributing to cerebral vasogenic edema, hemorrhagic transformation, and increased mortality. This loss of TJ integrity occurs in a phasic manner, which is contingent on several interdependent mechanisms (ionic dysregulation, inflammation, oxidative and nitrosative stress, enzymatic activity, and angiogenesis). Understanding the inter-relation of these mechanisms is critical for the development of new therapies. This review focuses on those aspects of ischemic stroke impacting BBB TJ integrity and the principle regulatory pathways, respective to the phases of paracellular permeability.

Diverse roles of matrix metalloproteinases and tissue inhibitors of metalloproteinases in neuroinflammation and cerebral ischemia

Regulation of the extracellular matrix by proteases and protease inhibitors is a fundamental biological process for normal growth, development and repair in the CNS. Matrix metalloproteinases (MMPs) and the tissue inhibitors of metalloproteinases (TIMPs) are the major extracellular-degrading enzymes. Two other enzyme families, a disintegrin and metalloproteinase (ADAM), and the serine proteases, plasminogen/plasminogen activator (P/PA) system, are also involved in extracellular matrix degradation. Normally, the highly integrated action of these enzyme families remodels all of the components of the matrix and performs essential functions at the cell surface involved in signaling, cell survival, and cell death. During the inflammatory response induced in infection, autoimmune reactions and hypoxia/ischemia, abnormal expression and activation of these proteases lead to breakdown of the extracellular matrix, resulting in the opening of the blood-brain barrier (BBB), preventing normal cell signaling, and eventually leading to cell death. There are several key MMPs and ADAMs that have been implicated in neuroinflammation: gelatinases A and B (MMP-2 and -9), stromelysin-1 (MMP-3), membrane-type MMP (MT1-MMP or MMP-14), and tumor necrosis factor-alpha converting enzyme (TACE). In addition, TIMP-3, which is bound to the cell surface, promotes cell death and impedes angiogenesis. Inhibitors of metalloproteinases are available, but balancing the beneficial and detrimental effects of these agents remains a challenge.

Delayed matrix metalloproteinase inhibition reduces intracerebral hemorrhage after embolic stroke in rats

Hemorrhagic transformation (HT) and brain edema are life-threatening complications of recombinant tissue plasminogen activator (rt-PA)-induced reperfusion after ischemic stroke. The risk of HT limits the therapeutic window for reperfusion to 3 h after stroke onset. Pre-treatment with matrix metalloproteinase (MMP) inhibitors reduces HT and cerebral edema in experimental stroke. However, whether a delayed therapeutic intervention would be beneficial is unknown. In this study, 215 male Sprague-Dawley rats were subjected to embolic stroke and 75 rats were included in the final analysis. The animals were treated with the MMP inhibitor p-aminobenzoyl-gly-pro-D-leu-D-ala-hydroxamate before or after 3 or 6 h of ischemia. Animals were monitored for reperfusion and received rt-PA 6 h after ischemia onset. The results at 24 h showed that MMP inhibition 3 h after ischemia significantly decreased the degree of brain edema (17% of hemispheric enlargement in the treated group versus 24% in controls, P=0.018), reduced the risk (OR=0.163; 95% CI: 0.029 to 0.953) and gravity (0.09 versus 0.19 mg of parenchymal hemoglobin, P=0.02) of intracerebral hemorrhage, and improved neurological outcome (20% of the treated animals had a slight deficit; all of the controls had a bad outcome, P<0.05). Delaying MMP inhibition to 6 h after ischemia restricted the beneficial role of the treatment to a reduction in the risk of parenchymal hemorrhage (OR=0.242; 95% CI: 0.060 to 0.989). Our results confirm the involvement of MMPs in HT and support the possibility of extending the therapeutic window for thrombolysis in stroke by administering a broad-spectrum MMP inhibitor after the onset of ischemia.

C3a receptor modulation of granulocyte infiltration after murine focal cerebral ischemia is reperfusion dependent

The complement anaphylatoxin C3a contributes to injury after cerebral ischemia in mice. This study assesses the effect of C3a receptor antagonist (C3aRA) on leukocyte infiltration into the ischemic zone. Transient or permanent middle cerebral artery occlusion (MCAO) was induced in wild-type C57Bl/6 mice. Intraperitoneal C3aRA or vehicle was administered 45 mins before or 1 h after occlusion. Twenty-four hours after occlusion, we harvested brain tissue and purified inflammatory cells using flow cytometry. Soluble intercellular adhesion molecule (ICAM)-1 protein levels were assessed using enzyme-linked immunosorbent assays, and ICAM-1 and C3a receptor (C3aR) expression was confirmed via immunohistochemistry. In the transient MCAO model, animals receiving C3aRA showed smaller strokes, less upregulation of C3aR-positive granulocytes, and less ICAM-1 protein on endothelial cells than vehicle-treated animals; no significant differences in other inflammatory cell populations were observed. C3a receptor antagonist-treated and vehicle-treated animals showed no differences in stroke volume or inflammatory cell populations after permanent MCAO. These data suggest that blocking the binding of C3a to C3aR modulates tissue injury in reperfused stroke by inhibiting the recruitment of neutrophils to the ischemic zone. It further establishes antagonism of the C3a anaphylatoxin as a promising strategy for ameliorating injury after ischemia/reperfusion.

Early release of HMGB-1 from neurons after the onset of brain ischemia

The nuclear protein high-mobility group box 1 (HMGB-1) promotes inflammation in sepsis, but little is known about its role in brain ischemia-induced inflammation. We report that HMGB-1 and its receptors, receptor for advanced glycation end products (RAGE), Toll-like receptor 2 (TLR2), and TLR4, were expressed in normal brain and in cultured neurons, endothelia, and glial cells. During middle cerebral artery occlusion (MCAO), in mice, HMGB-1 immunostaining rapidly disappeared from all cells within the striatal ischemic core from 1 h after onset of occlusion. High-mobility group box 1 translocation from nucleus to cytoplasm was observed within the cortical periinfarct regions 2 h after ischemic reperfusion (2 h MCAO). High-mobility group box 1 predominantly translocated to the cytoplasm or disappeared in cells that colabeled with the neuronal marker NeuN. Furthermore, RAGE was robustly expressed in the periinfarct region after MCAO. Cellular release of HMGB-1 was detected by immunoblotting of cerebrospinal fluid as early as 2 h after ischemic reperfusion (2 h MCAO). High-mobility group box 1 released from neurons, in vitro, after glutamate excitotoxicity, maintained biologic activity and induced glial expression of tumor necrosis factor alpha (TNFalpha). Anti-HMGB-1 antibody suppressed TNFalpha upregulation in astrocytes exposed to conditioned media from glutamate-treated neurons. Moreover, TNFalpha and the cytokine intercellular adhesion molecule-1 increased in cultured glia and endothelial cells, respectively, after adding recombinant HMGB-1. In conclusion, HMGB-1 is released early after ischemic injury from neurons and may contribute to the initial stages of the inflammatory response.

Tissue plasminogen activator (t-PA) promotes neutrophil degranulation and MMP-9 release

Recombinant tissue plasminogen activator (t-PA), the only approved stroke treatment, is used for clot lysis within the occluded brain artery. Unfortunately, matrix metalloproteinase-9 (MMP-9) concentration increases after t-PA treatment and has been related to hemorrhagic transformation after ischemic stroke. Although the exact cellular source of brain MMP-9 remains unknown, invading, inflammatory cells, such as neutrophils, release MMP-9 to cross the blood brain barrier. Therefore, we hypothesize that the most feared side effect of stroke reperfusion therapy, brain hemorrhage, is related to t-PA-induced MMP-9 release by neutrophils. We show by means of ELISA that t-PA treatment promotes MMP-9, MMP-8, and tissue inhibitor metalloproteinase-2 release from human neutrophils ex vivo within 10 and 30 min. Moreover, by zymography and Western blot, we observed that neutrophils are emptied of MMP-9 content after t-PA treatment at those times. Finally, total internal reflection fluorescent imaging allowed us to observe the t-PA effect on neutrophils, showing the promotion of degranulation on these cells in vivo. Our data suggest that neutrophils are good candidates to be the main source of MMP-9 following t-PA stroke treatment and in consequence, partially responsible for thrombolysis-related brain bleedings.

Multiple expression of matrix metalloproteinases in murine neurocysticercosis: Implications for leukocyte migration through multiple central nervous system barriers

During the course of murine neurocysticercosis (NCC), disruption of the unique protective barriers in the central nervous system (CNS) is evidenced by extravasation of leukocytes. This process varies according to the anatomical sites and diverse vascular beds analyzed. To examine mechanisms involved in the observed differences, the expression and activity of eight matrix metalloproteinases (MMPs) were analyzed in a murine model of NCC. The mRNA expression of the MMPs studied was upregulated as a result of infection, and active MMPs were mainly detected in leukocytes migrating into the brain. Polarized expression and gelatinolytic activity of several MMPs were identified in immune cells extravasating pial vessels as early as 1 day post infection. In contrast, leukocytes expressing active MMPs and extravasating parenchymal vessels were not observed until 5 weeks post infection. In ventricular areas, most of the MMP activity was detected in leukocytes traversing the ependyma from leptomeningeal infiltrates. In addition, immune cells continued to express active MMPs after exiting vessels suggesting that enzymatic activity of MMPs is not just required for diapedesis. These results correlate with our previous studies showing differential kinetics in the disruption of the CNS barriers upon infection and help document the important role of MMPs during leukocyte infiltration and inflammation.

MMP-9–Positive Neutrophil Infiltration Is Associated to Blood–Brain Barrier Breakdown and Basal Lamina Type IV Collagen Degradation During Hemorrhagic Transformation After Human Ischemic Stroke

Background and Purpose— An abnormal expression of some matrix metalloproteinases (MMPs) is related with hemorrhagic transformation events after stroke. Our aim was to investigate MMP-2 and MMP-9 in the ischemic brain and its relation with blood–brain barrier breakdown after hemorrhagic transformation in human stroke.

Methods— We assessed 5 cases of fatal ischemic strokes with hemorrhagic complications; brain samples were obtained from infarct, hemorrhagic, and contralateral tissue. MMP-9 and MMP-2 content was analyzed by zymography and immunohistochemistry was performed to localize MMP-9 and to assess collagen IV integrity in the basal lamina. Laser capture microdissection was performed to isolate blood–brain barrier vessels to study these MMPs.

Results— Overall, MMP-9 levels were higher both in hemorrhagic and nonhemorrhagic infarcted tissue compared to contralateral areas ( P <0.0001 and P <0.05). Moreover, levels of the cleaved MMP-9 85kDa-form were significantly elevated in the hemorrhagic compared to nonhemorrhagic and contralateral areas ( P =0.033 and P <0.0001). No changes were found for MMP-2 content. Immunostaining revealed a strong MMP-9–positive neutrophil infiltration surrounding brain microvessels associated with severe basal lamina type IV collagen degradation and blood extravasation. Microdissection confirmed that content of MMP-9 was similarly high in microvessel endothelium from hemorrhagic and infarcted areas compared to contralateral hemisphere vessels ( P <0.05), pointing to neutrophils surrounding dissected microvessels as the main source of MMP-9 in hemorrhagic areas.

Conclusions— Our results show a strong neutrophil infiltration in the infarcted and hemorrhagic areas with local high MMP-9 content closely related to basal lamina collagen IV degradation and blood–brain barrier breakdown. Microvessel and inflammatory MMP-9 response are associated with hemorrhagic complications after stroke.

Matrix metalloproteinase inhibition attenuates brain edema in an in vivo model of surgically-induced brain injury

OBJECTIVE

Neurosurgical procedures can result in brain injury by various means, including direct trauma, hemorrhage, retractor stretch, and electrocautery. This surgically-induced brain injury (SBI) can cause postoperative complications such as brain edema after blood-brain barrier (BBB) disruption. The present study seeks to test a matrix metalloproteinase (MMP) inhibitor for preventing postoperative brain edema and BBB disruption in an in vivo model of surgically-induced brain injury.

METHODS

A rodent model of SBI was used which involves resection of a part of the right frontal lobe. A total of 89 Sprague-Dawley male rats (weight, 300-350 g) were randomly divided into four groups: 1) SBI with vehicle treatment (0.1% dimethyl sulfoxide), 2) SBI with single treatment of MMP inhibitor-1 (an inhibitor of MMP-9 and MMP-2), 3) SBI treated daily (total 3 times) with MMP inhibitor-1, and 4) sham surgical group. Postoperative assessment at different time periods included evaluation of BBB permeability, brain water content (brain edema), neurological scoring, histology, immunohistochemistry, and zymography for MMP enzymatic activity. Temporal magnetic resonance imaging studies were also performed to assess postoperative edema.

RESULTS

The results indicate that SBI caused increased brain water content (ipsilateral frontal lobe) and BBB permeability compared with sham animals. Treatment with MMP inhibitor-1 attenuated MMP-9 and MMP-2 activity and decreased brain water content with preservation of the BBB.

CONCLUSION

Inhibition of MMP-9 and MMP-2 attenuates brain edema and BBB disruption after SBI. The study suggests a potential role for MMP inhibition as preoperative therapy before neurosurgical procedures.

Brain contusions induce a strong local overexpression of MMP-9. Results of a pilot study

BACKGROUND

Brain contusions are inflammatory evolutive lesions that induce intracranial pressure increase and edema, contributing to neurological outcome. Matrix metalloproteinases (MMPs) 2 and 9 can degrade the majority of the extracellular matrix components, and are implicated in blood-brain barrier disruption and edema formation. The aim of this study was to investigate MMP-2 and MMP-9 profiles in human brain contusions using zymography.

METHODS

A prospective study was conducted in 20 traumatic brain injury patients where contusion brain tissue was resected. Brain tissues from lobectomies were used as controls. Brain homogenates were analysed by gelatin zymography and in situ zimography was performed to confirm results, on one control and one brain contusion tissue sample.

FINDINGS

MMP-2 and MMP-9 levels were higher in brain contusions when compared to controls. MMP-9 was high during the first 24 hours and at 48 to 96 hours, whereas MMP-2 was slightly high at 24 to 96 hours. In situ zymography confirmed gelatin zymography results. A relation between outcome and MMP-9 levels was found; MMP-9 levels were higher in patients with worst outcome.

CONCLUSIONS

Our results indicate strong time-dependent gelatinase expression primarily from MMP-9, suggesting that the inflammatory response induced by focal lesions should be considered as a new therapeutic target.

Matrix metalloproteinase inhibition attenuates brain edema after surgical brain injury

BACKGROUND

Neurosurgical operations can result in inevitable brain injury due to the procedure itself. This surgical brain injury (SBI) can cause post-operative complications such as brain edema following blood-brain barrier (BBB) disruption leading to neurological deficits.

METHODS

We tested whether inhibition of matrix metalloproteinases (MMPs) 9 and 2 provided neuroprotection against SBI. A rodent SBI model, which involves a partial frontal lobe resection, was used to evaluate two treatment regimens of MMP inhibitor-1 (inhibitor of MMP-9 and MMP-2); a single dose (5 mg/kg, pretreatment) and daily dose treatment (5 mg/kg x 3, pre- and post-treatment). Postoperative assessment at different time periods included brain water content (brain edema), immunohistochemical analysis, zymography for MMP enzymatic activity, and neurological assessment.

FINDINGS

The results indicate that SBI caused localized edema around the site of surgical resection with concomitant increase in MMP-9 and MMP-2 activity. Both treatment regimens with MMP inhibitor-1 decreased brain edema and attenuated the rise in MMP-9 and MMP-2 activity. An increased expression of MMP-9 was also seen in the neurons and neutrophils in the affected brain tissue at the periphery of surgical resection.

CONCLUSIONS

The study suggests a potential role for MMP inhibition as preoperative therapy before neurosurgical procedures.

Reperfusion activates metalloproteinases that contribute to neurovascular injury

In this study, we examine the effects of reperfusion on the activation of matrix metalloproteinase (MMP) and assess the relationship between MMP activation during reperfusion and neurovascular injury. Ischemia was produced using suture-induced middle cerebral artery occlusion in rats. The MMP activation was examined with in situ and gel zymography. Injury to cerebral endothelial cells and basal lamina was assessed using endothelial barrier antigen (EBA) and collagen IV immunohistochemistry. Injury to neurons and glial cells was assessed using Cresyl violet staining. These were examined at 3 h after reperfusion (8 h after initiation of ischemia) and compared with permanent ischemia at the same time points to assess the effects of reperfusion. A broad-spectrum MMP inhibitor, AHA (p-aminobenzoyl-Gly-Pro-D-Leu-D-Ala-hydroxamate, 50 mg/kg intravenously) was administered 30 min before reperfusion to assess the roles of MMPs in activating gelatinolytic enzymes and in reperfusion-induced injury. We found that reperfusion accelerated and potentiated MMP-9 and MMP-2 activation and injury to EBA and collagen IV immunopositive microvasculature and to neurons and glial cells in ischemic cortex and striatum relative to permanent ischemia. Administering AHA 30 min before reperfusion decreased MMP-9 activation and neurovascular injury in ischemic cerebral cortex.

Neutrophil depletion decreases VEGF-induced focal angiogenesis in the mature mouse brain

To explore the role of neutrophil-derived matrix metalloproteinases (MMPs) during angiogenesis in the brain, we hypothesized that transient neutrophil depletion attenuates the angiogenic response to focal hyperstimulation with vascular endothelial growth factor (VEGF). Brain focal angiogenesis was achieved using an adeno-associated virus delivered VEGF (AAV-VEGF) gene transfer in the mature mouse. Four groups of mice underwent AAV vector injection in the brain parenchyma: (1) AAV-LacZ; (2) AAV-VEGF; (3) AAV-VEGF plus anti-polymorphonuclear (PMN) antibody; and (4) AAV-VEGF plus serum. Animals in groups 3 and 4 underwent 4 days of PMN antibody or serum treatment before transfection; treatment was sustained for an additional 14 days. Anti-PMN treatment decreased circulating neutrophils to 9% of baseline (P<0.001). Microvessels in the AAV-VEGF-group increased 25% compared with the AAV-lacZ-transduced group (256+/-15 versus 208+/-16; P<0.05). Anti-PMN treatment attenuated the increase to 10% compared with control serum treatment (234+/-16 versus 255+/-22; P<0.05). Similarly, compared with control serum treatment, anti-PMN treatment also reduced MMP-9 by 50% (2+/-0.9 versus 4+/-1.4; P<0.05) and MPO expression by 25% (2+/-0.8 versus 3+/-0.9; P<0.05); MMP-9 activity correlated with MPO expression (R(2)=0.8, P<0.05). Our study demonstrated that transient depletion of neutrophils suppressed VEGF-induced angiogenesis, indicating that circulating neutrophils contribute to VEGF-induced focal angiogenesis. In addition, brain MMP-9 activity was attenuated after neutrophil depletion, suggesting that neutrophil is an important source of MMP-9.

Evidence for differential changes of junctional complex proteins in murine neurocysticercosis dependent upon CNS vasculature

The delicate balance required to maintain homeostasis of the central nervous system (CNS) is controlled by the blood-brain barrier (BBB). Upon injury, the BBB is disrupted compromising the CNS. BBB disruption has been represented as a uniform event. However, our group has shown in a murine model of neurocysticercosis (NCC) that BBB disruption varies depending upon the anatomical site/vascular bed analyzed. In this study further understanding of the mechanisms of BBB disruption was explored in blood vessels located in leptomeninges (pial vessels) and brain parenchyma (parenchymal vessels) by examining the expression of junctional complex proteins in murine brain infected with Mesocestoides corti. Both pial and parenchymal vessels from mock infected animals showed significant colocalization of junctional proteins and displayed an organized architecture. Upon infection, the patterned organization was disrupted and in some cases, particular tight junction and adherens junction proteins were undetectable or appeared to be undergoing proteolysis. The extent and timing of these changes differed between both types of vessels (pial vessel disruption within days versus weeks for parenchymal vessels). To approach potential mechanisms, the expression and activity of matrix metalloproteinase-9 (MMP-9) were evaluated by in situ zymography. The results indicated an increase in MMP-9 activity at sites of BBB disruption exhibiting leukocyte infiltration. Moreover, the timing of MMP activity in pial and parenchymal vessels correlated with the timing of permeability disruption. Thus, breakdown of the BBB is a mutable process despite the similar structure of the junctional complex between pial and parenchymal vessels and involvement of MMP activity.

Granulocyte colony-stimulating factor has a negative effect on stroke outcome in a murine model

The administration of CD34-positive cells after stroke has been shown to have a beneficial effect on functional recovery by accelerating angiogenesis and neurogenesis in rodent models. Granulocyte colony-stimulating factor (G-CSF) is known to mobilize CD34-positive cells from bone marrow and has displayed neuroprotective properties after transient ischemic stress. This led us to investigate the effects of G-CSF administration after stroke in mouse. We utilized permanent ligation of the M1 distal portion of the left middle cerebral artery to develop a reproducible focal cerebral ischemia model in CB-17 mice. Animals treated with G-CSF displayed cortical atrophy and impaired behavioral function compared with controls. The negative effect of G-CSF on outcome was associated with G-CSF induction of an exaggerated inflammatory response, based on infiltration of the peri-infarction area with CD11b-positive and F4/80-positive cells. Although clinical trials with G-CSF have been started for the treatment of myocardial and limb ischemia, our results indicate that caution should be exercised in applying these results to cerebral ischemia.

Immunohistochemical changes in vulnerable rat brain regions after reversible global brain ischaemia

Human global ischaemia was simulated in adult rats by inducing 20 min brain ischaemia and 60 min post-ischaemic recirculation. Immunohistochemical expression of MMP-9, TIMP-3, Bax and Bcl-2, and DNA fragmentation (with the TUNEL reaction) were investigated. The morphological data showed different neuronal responses in the hippocampus compared with the cerebral and cerebellar cortices. MMP-9 immunoreactivity was different in the hippocampus, particularly in dentate gyrus and the CA1 region, compared with these cortices. Negative TIMP-3 staining in ischaemic hippocampal neurons may indicate a loss of its inhibitory activity on MMP-9 that could enhance cell death. Bcl-2 down regulation, Bax positivity and TUNEL+ type II cells in the dentate gyrus granular layer could be responsible for induction of apoptotic death in CA1 hippocampal pyramidal cells via loss of fibre input. Results suggest differential behaviours of neural cells after 60 min reperfusion.

Neuroprotection and neuroplasticity – A holistic approach and future perspectives

Modern medicine is facing an increasing number of treatments available for vascular and neurodegenerative brain diseases, but no causal or neuroprotective treatment has yet been established. Almost all neurological conditions are characterized by progressive neuronal disfunction, which, regardless of the pathogenetic mechanism, finally leads to neuronal death. Many agents that proved neuroprotective in experimental studies failed in achieving this goal within clinical studies. This paper briefly reviews the latest etiopathogenetic theories regarding nervous system disorders and the most important endeavors in neuroprotection.

MMPs contribute to TNF-alpha-induced alteration of the blood-cerebrospinal fluid barrier in vitro

The epithelial cells of the choroid plexus separate the central nervous system from the blood forming the blood-cerebrospinal fluid (CSF) barrier. The choroid plexus is the main source of CSF, whose composition is markedly changed during pathological disorders, for example regarding matrix metalloproteases (MMPs) and tissue inhibitors of matrix metalloproteases (TIMPs). In the present study, we analyzed the impact of the proinflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) on the blood-CSF barrier using an in vitro model based on porcine choroid plexus epithelial cells (PCPEC). TNF-alpha evoked distinct inflammatory processes as shown by mRNA upregulation of intercellular adhesion molecule-1 and vascular cell adhesion molecule-1. The cytokine caused a drastic decrease in transepithelial electrical resistance within several hours representing an enhanced permeability of PCPEC monolayers. In addition, the distribution of tight junction proteins was altered. Moreover, MMP activity in PCPEC supernatants was significantly increased by TNF-alpha, presumably due to a diminished expression of TIMP-3 that was similarly observed. MMP-2, -3, and -9 as well as TIMP-1 and -2 were also analyzed and found to be differentially regulated by the cytokine. The TNF-alpha-induced breakdown of the blood-CSF barrier could partially be blocked by the MMP inhibitor GM-6001. Our results show a contribution of MMPs to the inflammatory breakdown of the blood-CSF barrier in vitro. Thus TNF-alpha may mediate the binding of leukocytes to cellular adhesion molecules and the transmigration across the blood-CSF barrier.

Heme oxygenase-1 stabilizes the blood-spinal cord barrier and limits oxidative stress and white matter damage in the acutely injured murine spinal cord

We hypothesized that heme oxygenase (HO)-1, the inducible form of HO, represents an important defense against early oxidative injury in the traumatized spinal cord by stabilizing the blood-spinal cord barrier and limiting the infiltration of leukocytes. To test this hypothesis, we first examined the immunoexpression of HO-1 and compared barrier permeability and leukocyte infiltration in spinal cord-injured HO-1-deficient (+/-) and wild-type (WT, +/+) mice. Heme oxygenase was expressed in both endothelial cells and glia of the injured cord. Barrier disruption to luciferase and infiltration of neutrophils were significantly greater in the HO-1+/- than WT mice at 24 h postinjury (P<or=0.019 and =0.049, respectively). We next examined by Western immunoblots the generation of 4-hydroxynoneal (HNE) and malondialdehyde (MDA), major products of lipid peroxidation, in the injured epicenter. There was a significant increase in 10 kDa HNE- and MDA-modified proteins in the HO-1+/- as compared with WT mice (P=0.037 and 0.043, respectively). Finally, we compared the degradation of myelin basic protein (MBP), an indicator of white matter damage, in the HO-1+/- and WT mice by Western immunoblots. There was significantly greater degradation of MBP in the HO-1+/- compared with WT mice (P=0.049). Together, these findings show that HO-1 modulates oxidative stress and white matter injury in the acutely injured spinal cord. This modulation may be partially attributed to the ability of HO-1 to stabilize the blood-spinal cord barrier and limit neutrophil infiltration.

Neurovascular proteases in brain injury, hemorrhage and remodeling after stroke

Matrix metalloproteinases (MMPs) mediate tissue injury during acute stroke. Clinical data show that elevated MMPs in plasma of stroke patients may correlate with outcomes, suggesting its use as a biomarker. MMP-9 signal has also been detected in clinical stroke brain tissue samples. Because tissue plasminogen activator can upregulate MMPs via lipoprotein receptor signaling, these neurovascular proteolytic events may underlie some of the complications of edema and hemorrhage that plague thrombolytic therapy. However, in contrast to its deleterious actions in acute stroke, MMPs and other neurovascular proteases may play beneficial roles during stroke recovery. MMPs are increased in the subventricular zone weeks after focal stroke, and inhibition of MMPs suppress neurogenic migration from subventricular zone into damaged tissue. In peri-infarct cortex, MMPs may mediate neurovascular remodeling. Delayed inhibition of MMPs decrease markers of remodeling, and these phenomena may be related to reductions in bioavailable growth factors. Acute versus chronic protease profiles within the neurovascular unit are likely to underlie critical responses to stroke, therapy, and recovery.

Transient middle cerebral artery occlusion causes different structural, mechanical, and myogenic alterations in normotensive and hypertensive rats

Transient focal cerebral ischemia in the rat alters vessel properties, and spontaneously hypertensive rats (SHR) show a poorer outcome after ischemia. In the present study we examined the role of hypertension on vessel properties after ischemia-reperfusion. The right middle cerebral artery (MCA) was occluded (90 min) and reperfused (24 h) in SHR (n = 12) and Wistar-Kyoto rats (WKY; n = 11). Sham-operated rats (SHR, n = 10; WKY, n = 10) were used as controls. The structural, mechanical, and myogenic properties of the MCA were assessed by pressure myography. Nuclei distribution and elastin content and organization were analyzed by confocal microscopy. Infarct volume was larger in SHR than in WKY rats. Ischemia-reperfusion induced adventitial hypertrophy associated with an increase in the total number of adventitial cells. In addition, fenestrae area and arterial distensibility increased and myogenic tone decreased in the MCA of WKY rats after ischemia-reperfusion. Hypertension per se induced hypertrophic inward remodeling. Ischemia-reperfusion decreased the cross-sectional area of the MCA in SHR, without significant changes in distensibility, despite an increase in fenestrae area. In addition, MCA myogenic properties were not altered after ischemia-reperfusion in SHR. Our results indicate that in normotensive rats, MCA develops a compensatory mechanism (i.e., enhanced distensibility and decreased myogenic tone) that counteracts the effect of ischemia-reperfusion and ensures correct cerebral irrigation. These compensatory mechanisms are lost in hypertension, thereby explaining, at least in part, the greater infarct volume observed in SHR.

Astrocytic induction of matrix metalloproteinase-9 and edema in brain hemorrhage

We tested the hypothesis that astrocytic matrix metalloproteinase-9 (MMP-9) mediates hemorrhagic brain edema. In a clinical case of hemorrhagic stroke, MMP-9 co-localized with astrocytes and neurons in peri-hematoma areas. In a mouse model where blood was injected into striatum, MMP-9 was colocalized with astrocytes surrounding the hemorrhagic lesion. Because MMP-9 is present in blood as well as brain, we compared four groups of wild type (WT) and MMP-9 knockout (KO) mice: WT blood injected into WT brain, KO blood into KO brain, WT blood into KO brain, and KO blood into WT brain. Gel zymography showed that MMP-9 was elevated in WT hemorrhagic brain tissue but absent from KO hemorrhagic brain tissue. Edematous water content was elevated when WT blood was injected into WT brain. However, edema was ameliorated when MMP-9 was absent in either blood or brain or both. To further assess the mechanisms involved in astrocytic induction of MMP-9, we next examined primary mouse astrocyte cultures. Exposure to hemoglobin rapidly upregulated MMP-9 in conditioned media within 1 to 24 h. Hemoglobin-induced MMP-9 was reduced by the free radical scavenger U83836E. Taken together, these data suggest that although there are large amounts of MMP-9 in blood, hemoglobin-induced oxidative stress can trigger MMP-9 in astrocytes and these parenchymal sources of matrix degradation may also be an important factor in the pathogenesis of hemorrhagic brain edema.

Differential expression of tissue inhibitor of metalloproteinases-3 in cultured astrocytes and neurons regulates the activation of matrix metalloproteinase-2

Matrix metalloproteinases (MMPs) degrade the extracellular matrix and are implicated in the pathogenesis of several neurological diseases. Secreted in proforms, the MMPs require activation. Tissue inhibitors of matrix metalloproteinases (TIMPs) regulate the activity of MMPs. We investigated the expression of MMP-2 and -9, and the role of the TIMP-3 in MMP-2 activation, using cultures of cortical neurons and astrocytes. Under basal conditions, astrocytes and neurons produced low levels of pro-MMP-2, and -9. Stimulation with lipopolysaccharide (LPS) markedly increased pro-MMP-9 production in astrocytes, with only a slight increase in neurons. Pro-MMP-2 were constitutively expressed in both cell types, but with a much higher level in the astrocytes. Real-time RT-PCR showed that the mRNA levels of MMP-2 and -9 paralleled their gelatinolytic activities in the gelatin zymograms. Interestingly, active MMP-2 was observed only in neuronal cultures. TIMP-2 and TIMP-3 are constitutively expressed in astrocytes and neurons. However, astrocytes expressed much higher levels of TIMP-3 mRNA and protein than neurons. Knockdown of TIMP-3 with small interfering RNA (siRNA) significantly increased MMP-2 activation in astrocytes. These results indicate that astrocytes are a more important intrinsic cellular source of MMP-2 and -9 than neurons under normal and neuroinflammatory conditions. TIMP-3 may be the key factor determining the differential activation of MMP-2 in astrocytes and neurons.

Uric acid reduces brain damage and improves the benefits of rt-PA in a rat model of thromboembolic stroke

Uric acid is a natural antioxidant that protects the brain in a model of transient focal ischemia in rats. Here we sought to investigate whether uric acid was protective in a model of thromboembolic brain ischemia in rats, and whether the global benefit of recombinant tissue plasminogen activator (rt-PA) was improved by the combined treatment. Adult male Sprague-Dawley rats underwent either ischemia by thromboembolic middle cerebral artery occlusion (MCAO) or sham operation. Uric acid (16 mg/kg) was injected intravenously (i.v.). 20 mins after MCAO, whereas rt-PA (10 mg/kg) was administered i.v. at 3 h. A group of rats received the combined treatment. Rats underwent two neurologic examinations (30 mins and 24 h after MCAO). At 24 h, infarct volume was measured and brain neutrophil infiltration and protein tyrosine nitration were assessed. Treatment with either uric acid or rt-PA reduced infarct volume versus controls (P<0.05). The protective effect against brain ischemia was greater after cotreatment of uric acid with rt-PA (P<0.001), which added further benefit to rt-PA alone (P<0.05). The neurologic score worsened during the first 24 h in treatment controls, whereas it improved in rats receiving uric acid and/or rt-PA. Uric acid strongly reduced ischemia-induced tyrosine nitration, but it was more effective alone than combined with rt-PA, suggesting that reperfusion enhances nitrotyrosine formation. All treatments reduced postischemic brain neutrophil infiltration. These results show that uric acid administered early after thromboembolic stroke is neuroprotective in the rat brain, as it reduces infarct volume, ameliorates the neurologic function, attenuates the inflammatory response, and extends the benefits of rt-PA.

Endothelium and cardiopulmonary resuscitation

The endothelium is a viable target for injury, repair and cellular modulation. Because of its vast extension and active metabolic status of producing mediators for vasomotor tone, coagulation, and inflammation, it is a key target for therapy during ischemia/reperfusion injury. Cardiopulmonary resuscitation is a model of whole-body ischemia/reperfusion injury. It has become apparent that the endothelium participates in a host of responses elicited by ischemia/reperfusion. This review examines the role of the endothelium during and after ischemia/reperfusion and the participation by its mediators and evidence for endothelial involvement during and after cardiopulmonary resuscitation. The strategic location of the endothelium makes it an excellent signal transduction mechanism for a host of disease processes. In addition to biochemical stimuli, mechanical stimulation of the endothelium elicits production of several mediators, including endothelium-derived nitric oxide, prostaglandins, and antithrombotics and anticoagulants. Whole-body, periodic acceleration is a novel method of stimulating the endothelium via pulsatile shear stress. Periodic acceleration has been shown to be an effective experimental method of cardiopulmonary resuscitation, with evidence of postresuscitation cardioprotective effects. This review indicates that understanding endothelial modulation during and after ischemia/reperfusion will significantly improve therapeutic choices.

Loss of flow induces leukocyte-mediated MMP/TIMP imbalance in dynamic in vitro blood-brain barrier model: role of pro-inflammatory cytokines

There is substantial evidence linking blood-brain barrier (BBB) failure during cerebral ischemia to matrix metalloproteinases (MMP). BBB function may be affected by loss of shear stress under normoxia/normoglycemia, as during cardiopulmonary bypass procedures. The present study used an in vitro flow-perfused BBB model to analyze the individual contributions of flow, cytokine levels, and circulating blood leukocytes on the release/activity of MMP-9, MMP-2, and their endogenous inhibitors, the tissue inhibitors of MMPs (TIMPs), TIMP-1, and TIMP-2. The presence of circulating blood leukocytes under normoxic/normoglycemic flow cessation/reperfusion significantly increased the luminal levels of MMP-9 and activity of MMP-2, accompanied by partial reduction of TIMP-1, complete reduction of TIMP-2 and increased BBB permeability. These changes were not observed during constant flow with circulating blood leukocytes, or after normoxic/normoglycemic or hypoxic/hypoglycemic flow cessation/reperfusion without circulating blood leukocytes. The addition of anti-IL-6 or anti-TNF-α antibody in the lumen before reperfusion suppressed the levels of MMP-9 and activity of MMP-2, had no effect on TIMP-1, and completely restored TIMP-2 and BBB integrity. Injection of TIMP-2 in the lumen before reperfusion prevented the activation of MMP-2 and BBB permeability. These data indicate that blood leukocytes and loss of flow are major factors in the activation of MMP-2, and that cytokine-mediated differential regulation of TIMP-1 and TIMP-2 may contribute significantly to BBB failure.

Inflammation in stroke and focal cerebral ischemia

BACKGROUND

A growing number of recent investigations have established a critical role for leukocytes in propagating tissue damage after ischemia and reperfusion in stroke. Experimental data obtained from animal models of middle cerebral artery occlusion implicate inflammatory cell adhesion molecules, chemokines, and cytokines in the pathogenesis of this ischemic damage.

METHODS

Data from recent animal and human studies were reviewed to demonstrate that inflammatory events occurring at the blood-endothelium interface of the cerebral capillaries underlie the resultant ischemic tissue damage.

RESULTS

After arterial occlusion, the up-regulated expression of cytokines including IL-1, and IL-6 act upon the vascular endothelium to increase the expression of intercellular adhesion molecule-1, P-selectin, and E-selectin, which promote leukocyte adherence and accumulation. Integrins then serve to structurally modify the basal lamina and extracellular matrix. These inflammatory signals then promote leukocyte transmigration across the endothelium and mediate inflammatory cascades leading to further cerebral infarction.

CONCLUSIONS

Inflammatory interactions that occur at the blood-endothelium interface, involving cytokines, adhesion molecules, chemokines and leukocytes, are critical to the pathogenesis of tissue damage in cerebral infarction. Exploring these pathophysiological mechanisms underlying ischemic tissue damage may direct rational drug design in the therapeutic treatment of stroke.

Increased Brain Expression of Matrix Metalloproteinase-9 After Ischemic and Hemorrhagic Human Stroke

Background and Purpose— Abnormal expression of some matrix metalloproteinases (MMP) has shown to play a deleterious role in brain injury in experimental models of cerebral ischemia. We aimed to investigate MMP-2 (gelatinase A) and MMP-9 (gelatinase B) in brain parenchyma in both ischemic and hemorrhagic strokes.

Methods— Postmortem fresh brain tissue from 6 ischemic and 8 hemorrhagic stroke patients was obtained within the first 6 hours after death. Finally, 78 brain tissue samples from different areas (infarct, peri-infarct, perihematoma and contralateral hemisphere) were studied. To quantify gelatinase content we performed gelatin zymograms that were confirmed by Western Blot Analysis, immunohistochemistry to localize MMP source, and in situ zymography to detect gelatinase activity.

Results— Among ischemic cases, gelatin zymography showed increased MMP-9 content in infarct core although peri-infarct tissue presented also higher levels than contralateral hemisphere ( P <0.0001 and P =0.042, respectively). Within infarct core, MMP-9 was mainly located around blood vessels, associated to neutrophil infiltration and activated microglial cells. In peri-infarct areas the major source of MMP-9 were microglial cells. Tissue around intracranial hemorrhage also displayed higher MMP-9 levels than contralateral hemisphere ( P =0.008) in close relationship with glial cells. MMP-2 was constitutively expressed and remained invariable in different brain areas.

Conclusions— Our results demonstrate in situ higher levels of MMP-9 in human brain tissue after ischemic and hemorrhagic stroke, suggesting a contribution of MMP-9 to ischemic brain injury and perihematoma edema.

Why Does Acute Hyperglycemia Worsen the Outcome of Transient Focal Cerebral Ischemia?

Background and Purpose— Hyperglycemia adversely affects the outcome of stroke. Global ischemia data support that the harmful effect of hyperglycemia is mediated by glucose-induced elevated plasma glucocorticoids. Here we sought to evaluate the negative effects of hyperglycemia on transient focal ischemia in the rat, and to test whether these could be prevented by inhibition of either corticosteroid production or neutrophil infiltration.

Methods— Sprague-Dawley rats (n=217) were used. Ischemia was induced by 1 hour middle cerebral artery occlusion (n=196). Acute hyperglycemia was induced by IP injection of dextrose 30 minutes before ischemia. Neutrophil infiltration was blocked by neutropenia with vinblastine. Corticosterone synthesis was inhibited by chemical adrenalectomy with metyrapone. We measured MRI lesion and tissue infarct volumes, evaluated the neurological function, brain myeloperoxidase and matrix metalloproteinase-9 activities, and protein O-glycosylation.

Results— Hyperglycemia significantly enhanced MRI diffusion-weighted imaging alterations, increased cortical, but not subcortical, infarct volume, worsened neurological score, and enhanced brain myeloperoxidase and matrix metalloproteinase-9 activities. Metyrapone did not prevent hyperglycemic brain damage despite successful reduction of plasma corticosterone. Yet, metyrapone tended to reduce cortical infarction and apparent diffusion coefficient lesion volume, indicating some negative contribution of corticosterone. Blocking neutrophil infiltration was also ineffective to prevent the harmful effect of hyperglycemia. A new finding was that O-linked glycosylation of cerebral proteins was increased under hyperglycemia.

Conclusions— In transient middle cerebral artery occlusion, the hyperglycemia-exacerbated brain damage cannot be fully explained by the negative effects of plasma corticosteroids or neutrophil infiltration. The contribution of other intrinsic effects of high glucose, such as brain protein O-glycosylation, deserves further investigation.

Progress in the identification of stroke-related genes: emerging new possibilities to develop concepts in stroke therapy

Stroke is a very complex disease influenced by many risk factors: genetic, environmental and comorbidities, such as hypertension, diabetes mellitus, obesity and having had a previous stroke. Neuroprotective therapies that have been found to be successful in laboratory animals have failed to produce the same benefits in clinical trials. Currently, a re-analysis of the clinical trial failures is underway and new therapeutic approaches using the growing knowledge from neurogenesis and neuroinflammation studies, combined with the information from gene expression studies, are taking place. This review focuses on possible ways to identify therapeutic targets using the new discoveries in neuroinflammation and intrinsic regenerative mechanisms of the brain. Molecular events associated with ischaemia trigger an environment for inflammation. Within the ischaemic region and its penumbra, a battery of chemokines and cytokines are released, which have both detrimental and beneficial effects, depending on the specific timepoint after injury and the current activation status of microglia/macrophages. Preventive therapies and treatments for stroke may be established by identifying the genes that are responsible for the induction of those phenotypic changes of microglia/macrophages that switch them to become players in tissue repair and regeneration processes. To aid in the establishment of new target sources for novel therapeutic agents, animal stroke models should closely mimic stroke in humans. To do so, these models should take into account the various risk factors for stroke. For example, hypertensive animals have a more vulnerable blood-brain barrier that in turn may trigger a greater degree of damage after stroke. Furthermore, in aged animals an accelerated astrocytic and microglial reaction has been observed and the regenerative capacity of aged brains is not as high as young brains. Improvements in animal models may also help to ensure better success rates of potential therapies in clinical studies. Inflammation in the brain is a double-edged sword--characterised by the deleterious effect of nerve cell damage and nerve cell death, as well as the beneficial influence on regeneration. The major challenge to develop successful stroke therapies is to broaden the knowledge regarding the underlying pathologic processes and the intrinsic mechanisms of the brain to drive regenerative and plasticity-related changes. On this basis, new concepts can be created leading to better stroke therapy.

Effect of neutrophil depletion on gelatinase expression, edema formation and hemorrhagic transformation after focal ischemic stroke

Background

While gelatinase (MMP-2 and -9) activity is increased after focal ischemia/reperfusion injury in the brain, the relative contribution of neutrophils to the MMP activity and to the development of hemorrhagic transformation remains unknown.

Results

Anti-PMN treatment caused successful depletion of neutrophils in treated animals. There was no difference in either infarct volume or hemorrhage between control and PMN depleted animals. While there were significant increases in gelatinase (MMP-2 and MMP-9) expression and activity and edema formation associated with ischemia, neutrophil depletion failed to cause any change.

Conclusion

The main finding of this study is that, in the absence of circulating neutrophils, MMP-2 and MMP-9 expression and activity are still up-regulated following focal cerebral ischemia. Additionally, neutrophil depletion had no influence on indicators of ischemic brain damage including edema, hemorrhage, and infarct size. These findings indicate that, at least acutely, neutrophils are not a significant contributor of gelatinase activity associated with acute neurovascular damage after stroke.

Leukocyte-derived matrix metalloproteinase-9 mediates blood-brain barrier breakdown and is proinflammatory after transient focal cerebral ischemia

Results of recent studies reveal vascular and neuroprotective effects of matrix metalloproteinase-9 (MMP-9) inhibition and MMP-9 gene deletion in experimental stroke. However, the cellular source of MMP-9 produced in the ischemic brain and the mechanistic basis of MMP-9-mediated brain injury require elucidation. In the present study, we used MMP-9−/−mice and chimeric knockouts lacking either MMP-9 in leukocytes or in resident brain cells to test the hypothesis that MMP-9 released from leukocytes recruited to the brain during postischemic reperfusion contributes to this injury phenotype. We also tested the hypothesis that MMP-9 promotes leukocyte recruitment to the ischemic brain and thus is proinflammatory. The extent of blood-brain barrier (BBB) breakdown, the neurological deficit, and the volume of infarction resulting from transient focal stroke were abrogated to a similar extent in MMP-9−/−mice and in chimeras lacking leukocytic MMP-9 but not in chimeras with MMP-9-containing leukocytes. Zymography and Western blot analysis from these chimeras confirmed that the elevated MMP-9 expression in the brain at 24 h of reperfusion is derived largely from leukocytes. MMP-9−/−mice exhibited a reduction in leukocyte-endothelial adherence and a reduction in the number of neutrophils plugging capillaries and infiltrating the ischemic brain during reperfusion; microvessel immunopositivity for collagen IV was also preserved in these animals. These latter results document proinflammatory actions of MMP-9 in the ischemic brain. Overall, our findings implicate leukocytes, most likely neutrophils, as a key cellular source of MMP-9, which, in turn, promotes leukocyte recruitment, causes BBB breakdown secondary to microvascular basal lamina proteolysis, and ultimately contributes to neuronal injury after transient focal stroke.

Pharmacological neutropenia prevents endothelial dysfunction but not smooth muscle functions impairment induced by middle cerebral artery occlusion

1. The polymorphonuclear neutrophils (PMN) activation and mobilization observed in acute cerebral infarction contribute to the brain tissue damage, but PMN could also be involved in postischemic functional injury of ischemied blood vessel. 2. This study was undertaken to investigate whether pharmacological neutropenia could modify the postischemic endothelial dysfunction in comparison to smooth muscle whose impairment is likely more related to reperfusion and oxidative stress. 3. A cerebral ischemia-reperfusion by endoluminal occlusion of right middle cerebral artery (MCA) was performed 4 days after intravenous administration of vinblastine or 12 h after RP-3 anti-rat neutrophils monoclonal antibody (mAb RP-3) injection into the peritoneal cavity, on male Wistar rats with 1-h ischemia then followed by 24-h reperfusion period. Brain infarct volume was measured by histomorphometric analysis and vascular endothelial and smooth muscle reactivity of MCA was analysed using Halpern myograph. 4. Neutropenia induced a neuroprotective effect as demonstrated by a significant decrease of brain infarct size. In parallel to neuroprotection, neutropenia prevented postischemic impairment of endothelium-dependent relaxing response to acetylcholine. In contrast, smooth muscle functional alterations were not prevented by neutropenia. Ischemia-reperfusion-induced myogenic tone impairment remained unchanged in vinblastine and mAb RP-3-treated rats. Postischemic Kir2.x-dependent relaxation impairment was not prevented in neutropenic conditions. The fully relaxation of smooth muscle response to sodium nitroprusside was similar in all groups. 5. Our results evidenced the dissociate prevention of pharmacologically induced neutropenia on postischemic vascular endothelial and smooth muscle impairment. The selective endothelial protection by neutropenia is parallel to a neuroprotective effect suggesting a possible relationship between the two phenomena.

Anti-CD11d antibody treatment reduces free radical formation and cell death in the injured spinal cord of rats

Treatment with a monoclonal antibody (mAb) against the CD11d subunit of the leukocyte integrin CD11d/CD18 after spinal cord injury (SCI) decreases intraspinal inflammation and oxidative damage, improving neurological function in rats. In this study we tested whether the anti-CD11d mAb treatment reduces intraspinal free radical formation and cell death after SCI. Using clip-compression SCI in rats, reactive oxygen species (ROS) generated in injured spinal cord were detected using 2',7'-dichlorofluorescin-diacetate and hydroethidine as fluorescent probes. ROS in the injured cord increased significantly after SCI; anti-CD11d mAb treatment significantly reduced this ROS formation. Immunohistochemistry and western blotting were employed to assess the effects of anti-CD11d mAb treatment on spinal cord expression of gp91Phox (a subunit of NADPH oxidase producing superoxide) on formation of 4-hydroxynonenal (HNE, indicating lipid peroxidation) and on expression of caspase-3. We also assessed effects on cell death, determined by cell morphology. The expression of gp91Phox, formation of HNE, and cell death increased after SCI. Anti-CD11d mAb treatment clearly attenuated these responses. In conclusion, anti-CD11d mAb treatment significantly reduces intraspinal free radical formation caused by infiltrating leukocytes after SCI, thereby reducing secondary cell death. These effects likely underlie tissue preservation and improved neurological function that result from the mAb treatment.

Multiple roles for MMPs and TIMPs in cerebral ischemia

Matrix metalloproteinases (MMPs) are matrix-degrading enzymes involved in diverse homeostatic and pathological processes. Several MMPs are expressed within the CNS and serve important normal and pathological functions during development and adulthood. An early and major pathological effect of MMP activity after cerebral ischemia is opening of the blood-brain barrier (BBB). More recent work demonstrates emerging roles for MMPs and their natural inhibitors, tissue inhibitors of metalloproteinases (TIMPs), in the regulation of neuronal cell death. In addition, MMPs and TIMPs are likely to play important roles during the repair phases of cerebral ischemia, particularly during angiogenesis and reestablishment of cerebral blood flow. This review attempts to elucidate how MMPs and TIMPs may provide detrimental or beneficial actions during the injury and repair processes after cerebral ischemia. These processes will have important implications for therapies using MMP inhibitors in stroke.

Reconstituted high-density lipoproteins inhibit the acute pro-oxidant and proinflammatory vascular changes induced by a periarterial collar in normocholesterolemic rabbits

BACKGROUND

HDLs have antiinflammatory and antioxidant properties in vitro. This study investigates these properties in vivo.

METHODS AND RESULTS

Chow-fed, normocholesterolemic New Zealand White rabbits received a daily infusion of (1) saline, (2) reconstituted HDL (rHDL) containing 25 mg apolipoprotein (apo) A-I and 50 mg of either 1-palmitoyl-2-linoleoyl phosphatidylcholine (PLPC) or 1,2-dipalmitoyl phosphatidylcholine (DPPC), (3) 25 mg lipid-free apoA-I, or (4) 50 mg of either PLPC-small unilamellar vesicles (SUVs) or DPPC-SUVs on each of 3 consecutive days. Nonocclusive carotid periarterial collars were implanted after the second dose of treatment. Forty-eight hours after insertion of the collars, the arteries were removed and analyzed for the presence of reactive oxygen species, the infiltration of neutrophils, and the expression of adhesion proteins and chemokines. Insertion of the periarterial collar induced a 4.1-fold increase in presence of vascular wall reactive oxygen species. This effect was completely abolished in the animals infused with rHDL. The periarterial collar was associated with a dense infiltration of the arterial wall by polymorphonuclear leukocytes. This infiltration was inhibited by 73% to 94% in the animals infused with rHDL, by 75% in the animals infused with lipid-free apoA-I, and by 51% to 65% in animals infused with SUVs. There were no significant differences between the effects of PLPC and DPPC in either the rHDL or SUVs. Endothelial expression of vascular cell adhesion molecule-1, intercellular adhesion molecule-1, and monocyte chemoattractant protein-1 was also increased by the collar insertion and inhibited by rHDL, lipid-free apoA-I, and, to a lesser extent, also by the SUVs.

CONCLUSIONS

Infusion of rHDL, apoA-I, and phospholipid-SUVs inhibits the early pro-oxidant and proinflammatory changes induced by a periarterial collar in normocholesterolemic rabbits.

Differential alterations in the expression and activity of matrix metalloproteinases 2 and 9 after transient cerebral ischemia in mice

Abnormal expression and activity of matrix metalloproteinases (MMPs) may contribute to the pathophysiology of cerebral disease such as ischemic injury. In this study, we compared the cellular localization, expression, and activity of MMP-2 and -9 in relation to the evolution of neuronal damage 24 and 72 h after transient global ischemia. In response to ischemia, there was a generalized increase in cellular MMP-2 immunoreactivity at 24-h reperfusion (in neurons, glia and vessels) whereas at 72-h reperfusion the increase in MMP-2 was predominantly in glia. These glial alterations contributed to a significant increase in pro MMP-2 levels in ischemic regions (P < 0.01) as measured by zymography. In contrast, MMP-9 was predominantly upregulated in neurons and this was significantly different to shams at 24- and 72-h reperfusion after ischemia (P < 0.05). Notably, a dramatic increase in proteolytic activity in neurons was observed 24 h after ischemia and this response was absent at 72 h post-ischemia. The present data are supportive of a role for MMPs in contributing to neuronal injury after ischemia.