Vasogenic edema due to tight junction disruption by matrix metalloproteinases in cerebral ischemia

Oxidative stress and blood-brain barrier dysfunction under particular consideration of matrix metalloproteinases

A cell's "redox" (oxidation and reduction) state is determined by the sum of all redox processes yielding reactive oxygen species (ROS), reactive nitrogen species (RNS), and other reactive intermediates. Low amounts of ROS/RNS are generated by different mechanisms in every cell and are important regulatory mediators in many signaling processes (redox signaling). When the physiological balance between the generation and elimination of ROS/RNS is disrupted, oxidative/nitrosative stress with persistent oxidative damage of the organism occurs. Oxidative stress has been suggested to act as initiator and/or mediator of many human diseases. The cerebral vasculature is particularly susceptible to oxidative stress, which is critical since cerebral endothelial cells play a major role in the creation and maintenance of the blood-brain barrier (BBB). This article will only contain a focused introduction on the biochemical background of redox signaling, since this has been reported already in a series of excellent recent reviews. The goal of this work is to increase the understanding of basic mechanisms underlying ROS/RNS-induced BBB disruption, with a focus on the role of matrix metalloproteinases, which, after all, appear to be a key mediator in the initiation and progression of BBB damage elicited by oxidative stress.

Matrix metalloproteinase-2 and -9 secreted by leukemic cells increase the permeability of blood-brain barrier by disrupting tight junction proteins

Central nervous system (CNS) involvement remains an important cause of morbidity and mortality in acute leukemia, the mechanisms of leukemic cell infiltration into the CNS have not yet been elucidated. The blood-brain barrier (BBB) makes CNS become a refugee to leukemic cells and serves as a resource of cells that seed extraneural sites. How can the leukemic cells disrupt this barrier and invasive the CNS, even if many of the currently available chemotherapies can not cross the BBB? Tight junction in endothelial cells occupies a central role in the function of the BBB. Except the well known role of degrading extracellular matrix in metastasis of cancer cells, here we show matrix metalloproteinase (MMP)-2 and -9, secreted by leukemic cells, mediate the BBB opening by disrupting tight junction proteins in the CNS leukemia. We demonstrated that leukemic cells impaired tight junction proteins ZO-1, claudin-5 and occludin resulting in increased permeability of the BBB. However, these alterations reduced when MMP-2 and -9 activities were inhibited by RNA interference strategy or by MMP inhibitor GM6001 in an in vitro BBB model. We also found that the disruption of the BBB in company with the down-regulation of ZO-1, claudin-5 and occludin and the up-regulation of MMP-2 and -9 in mouse brain tissues with leukemic cell infiltration by confocal imaging and the assay of in situ gelatin zymography. Besides, GM6001 protected all mice against CNS leukemia. Our findings suggest that the degradation of tight junction proteins ZO-1, claudin-5 and occludin by MMP-2 and -9 secreted by leukemic cells constitutes an important mechanism in the BBB breakdown which contributes to the invasion of leukemic cells to the CNS in acute leukemia.

Neutrophil transmigration, focal adhesion kinase and endothelial barrier function

Neutrophil activation is an essential component of innate immune defense against infection and injury. In response to inflammatory stimulation, circulating neutrophils undergo a series of dynamic and metabolic changes characterized by β2-intergrin mediated adhesion to microvascular endothelium and subsequent transendothelial migration. During this process, neutrophils release granular contents containing digestive enzymes and produce cytotoxic agents such as reactive oxygen species and cytokines. These products target endothelial barriers inducing phosphorylation-triggered junction dissociation, actin stress fiber formation, and actomyosin contraction, manifest as paracellular hyperpermeability. Endothelial cell-matrix focal adhesions play an integral role in this process by providing structural support for endothelial conformational changes that facilitate neutrophil transmigration, as well as by recruiting intracellular molecules that constitute the hyperpermeability signaling cascades. As a central connector of the complex signaling network, focal adhesion kinase (FAK) is activated following neutrophil adhesion, and further mediates the reorganization of endothelial integrin-matrix attachments in a pattern coordinating with cytoskeleton contraction and junction opening. In this review, we present recent experimental evidence supporting the importance of FAK in neutrophil-dependent regulation of endothelial permeability. The discussion focuses on the mechanisms by which neutrophils activate FAK and its downstream effects on endothelial barriers.

Impairment of tight junctions and glucose transport in endothelial cells of human cerebral cavernous malformations

Cerebral cavernous malformations (CCMs) often cause hemorrhages that can result in severe clinical manifestations, including hemiparesis and seizures. The underlying mechanisms of the aggressive behavior of CCMs are undetermined to date, but alterations of vascular matrix components may be involved. We compared the localization of the tight junction proteins (TJPs) in 12 CCM specimens and the expression of glucose transporter 1 (GLUT-1), which is sensitive to alterations in TJP levels, in 5 CCM specimens with those in 5 control temporal lobectomy specimens without CCM by immunofluorescence microscopy. The TJPs occludin, claudin-5, and zonula occludens ZO-1 were downregulated at intercellular contact sites and partly redistributed within the surrounding tissue in the CCM samples; there was also a marked reduction of GLUT-1 immunoreactivity compared with that in control specimens. Corresponding analysis using quantitative real-time reverse transcription polymerase chain reaction on 8 CCM and 8 control specimens revealed significant downregulation of mRNA expression of occludin, claudin-5, ZO-1, and GLUT-1. The altered expression and localization of the TJPs at interendothelial contact sites accompanied by a reduction of GLUT-1 expression in dilated CCM microvessels likely affect vascular matrix stability and may contribute to hemorrhages of CCMs.

Application of medical gases in the field of neurobiology

Medical gases are pharmaceutical molecules which offer solutions to a wide array of medical needs. This can range from use in burn and stroke victims to hypoxia therapy in children. More specifically however, gases such as oxygen, helium, xenon, and hydrogen have recently come under increased exploration for their potential theraputic use with various brain disease states including hypoxia-ischemia, cerebral hemorrhages, and traumatic brain injuries. As a result, this article will review the various advances in medical gas research and discuss the potential therapeutic applications and mechanisms with regards to the field of neurobiology.

Natural haemozoin modulates matrix metalloproteinases and induces morphological changes in human microvascular endothelium

Severe malaria, including cerebral malaria (CM), is characterized by the sequestration of parasitized erythrocytes in the microvessels after cytoadherence to endothelial cells. Products of parasite origin, such as haemozoin (HZ), contribute to the pathogenesis of severe malaria by interfering with host inflammatory response. In human monocytes, HZ enhanced the levels of matrix metalloproteinase-9 (MMP-9), a protease involved in neuroinflammation. Here the effects of HZ on the regulation of MMPs by the human microvascular endothelial cell line HMEC-1 were investigated. Cells treated with natural (n)HZ appeared elongated instead of polygonal, and formed microtubule-like vessels on synthetic basement membrane. nHZ enhanced total gelatinolytic activity by inducing proMMP-9 and MMP-9 without affecting basal MMP-2. The level of the endogenous tissue inhibitor of MMP-9 (TIMP-1) was not altered by nHZ, while TIMP-2, the MMP-2 inhibitor, was enhanced. Additionally, nHZ induced MMP-1 and MMP-3, two enzymes sequentially involved in collagenolysis and proMMP-9 proteolytic activation. Lipid-free HZ did not reproduce nHZ effects. Present data suggest that the lipid moiety of HZ alters the MMP/TIMP balances and promotes the proteolytic activation of proMMP-9 in HMEC-1, thereby enhancing total gelatinolytic activity, cell activation and inflammation. These findings might help understanding the mechanisms of blood brain barrier damage during CM.

Methods to assess pericyte-endothelial cell interactions in a coculture model

The blood-brain barrier (BBB) comprises the microvascular endothelial cells, pericytes, and astrocytes, which are connected by the extracellular matrix (ECM). Current BBB models focus solely on the microvascular endothelial cells which constitute a physical barrier by formation of tight junctions (TJs), while the impact of pericytes on barrier regulation is poorly understood. We established a coculture model from primary porcine brain capillary endothelial cells (PBCECs) and pericytes (PBCPs) to approach the in vivo situation. This model allows the examination of pericyte impact on pharmacological, transport, migration, and metabolic activity of the BBB. In vivo the interaction between pericytes and endothelial cells is partly controlled by the ECM which is remodeled by matrix metalloproteinases (MMPs). Both endothelial cells and pericytes secrete MMPs which are important not only for ECM remodeling but also for TJ cleavage. In this chapter, current methods to study the interactions of these cell types by ECM signaling as well as MMP secretion are described.

Matrix Metalloproteinase-9 and Haemozoin: Wedding Rings for Human Host and Plasmodium falciparum Parasite in Complicated Malaria

It is generally accepted that the combination of both Plasmodium falciparum parasite and human host factors is involved in the pathogenesis of complicated severe malaria, including cerebral malaria (CM). Among parasite products, the malarial pigment haemozoin (HZ) has been shown to impair the functions of mononuclear and endothelial cells. Different CM models were associated with enhanced levels of matrix metalloproteinases (MMPs), a family of proteolytic enzymes able to disrupt subendothelial basement membrane and tight junctions and shed, activate, or inactivate cytokines, chemokines, and other MMPs through cleavage from their precursors. Among MMPs, a good candidate for targeted therapy might be MMP-9, whose mRNA and protein expression enhancement as well as direct proenzyme activation by HZ have been recently investigated in a series of studies by our group and others. In the present paper the role of HZ and MMP-9 in complicated malaria, as well as their interactions, will be discussed.

Doxycycline, a matrix metalloprotease inhibitor, reduces vascular remodeling and damage after cerebral ischemia in stroke-prone spontaneously hypertensive rats

Matrix metalloproteases (MMPs) are a family of zinc peptidases involved in extracellular matrix turnover. There is evidence that increased MMP activity is involved in remodeling of resistance vessels in chronic hypertension. Thus we hypothesized that inhibition of MMP activity with doxycycline (DOX) would attenuate vascular remodeling. Six-week-old male stroke-prone spontaneously hypertensive rats (SHRSP) were treated with DOX (50 mg·kg(-1)·day(-1) in the drinking water) for 6 wk. Untreated SHRSP were controls. Blood pressure was measured by telemetry during the last week. Middle cerebral artery (MCA) and mesenteric resistance artery (MRA) passive structures were assessed by pressure myography. MMP-2 expression in aortas was measured by Western blot. All results are means ± SE. DOX caused a small increase in mean arterial pressure (SHRSP, 154 ± 1; SHRSP + DOX, 159 ± 3 mmHg; P < 0.001). Active MMP-2 expression was reduced in aorta from SHRSP + DOX (0.21 ± 0.06 vs. 0.49 ± 0.13 arbitrary units; P < 0.05). In the MCA, at 80 mmHg, DOX treatment increased the lumen (273.2 ± 4.7 vs. 238.3 ± 6.3 μm; P < 0.05) and the outer diameter (321 ± 5.3 vs. 290 ± 7.6 μm; P < 0.05) and reduced the wall-to-lumen ratio (0.09 ± 0.002 vs. 0.11 ± 0.003; P < 0.05). Damage after transient cerebral ischemia (transient MCA occlusion) was reduced in SHRSP + DOX (20.7 ± 4 vs. 45.5 ± 5% of hemisphere infarcted; P < 0.05). In the MRA, at 90 mmHg DOX, reduced wall thickness (29 ± 1 vs. 22 ± 1 μm; P < 0.001) and wall-to-lumen ratio (0.08 ± 0.004 vs. 0.11 ± 0.008; P < 0.05) without changing lumen diameter. These results suggest that MMPs are involved in hypertensive vascular remodeling in both the peripheral and cerebral vasculature and that DOX reduced brain damage after cerebral ischemia.

Review: molecular pathogenesis of blood-brain barrier breakdown in acute brain injury

Historically, the blood-brain barrier (BBB) was considered to be at the level of cerebral endothelium. Currently, the interaction of endothelium with other components of the vessel wall and with neurones and glial cells is considered to constitute a functional unit, termed the neurovascular unit that maintains cerebral homeostasis in steady states and brain injury. The emphasis of this review is on cerebral endothelium, the best-studied component of the neurovascular unit, and its permeability mechanisms in health and acute brain injury. Major advances have been made in unravelling the molecular structure of caveolae and tight junctions, both of which are components of the structural barrier to the entry of plasma proteins into brain. Time course studies suggest that caveolar changes precede junctional changes in acute brain injury. Additional factors modulating BBB permeability in acute brain injury are matrix metalloproteinases-2 and 9 and angiogenic factors, the most notable being vascular endothelial growth factor-A and angiopoietins (Ang) 1 and 2. Vascular endothelial growth factor-A and Ang2 have emerged as potent inducers of BBB breakdown while Ang1 is a potent anti-leakage factor. These factors have the potential to modulate permeability in acute brain injury and this is an area of ongoing research. Overall, a combination of haemodynamic, structural and molecular alterations affecting brain endothelium results in BBB breakdown in acute brain injury.

How do immune cells overcome the blood-brain barrier in multiple sclerosis?

The presence of the blood-brain barrier (BBB) restricts the movement of soluble mediators and leukocytes from the periphery to the central nervous system (CNS). Leukocyte entry into the CNS is nonetheless an early event in multiple sclerosis (MS), an inflammatory disorder of the CNS. Whether BBB dysfunction precedes immune cell infiltration or is the consequence of perivascular leukocyte accumulation remains enigmatic, but leukocyte migration modifies BBB permeability. Immune cells of MS subjects express inflammatory cytokines, reactive oxygen species (ROS) and enzymes that can facilitate their migration to the CNS by influencing BBB function, either directly or indirectly. In this review, we describe how immune cells from the peripheral blood overcome the BBB and promote CNS inflammation in MS through BBB disruption.

Role of matrix metalloproteinases and therapeutic benefits of their inhibition in spinal cord injury

This review will focus on matrix metalloproteinases (MMPs) and their inhibitors in the context of spinal cord injury (SCI). MMPs have a specific cellular and temporal pattern of expression in the injured spinal cord. Here we consider their diverse functions in the acutely injured cord and during wound healing. Excessive activity of MMPs, and in particular gelatinase B (MMP-9), in the acutely injured cord contributes to disruption of the blood-spinal cord barrier, and the influx of leukocytes into the injured cord, as well as apoptosis. MMP-9 and MMP-2 regulate inflammation and neuropathic pain after peripheral nerve injury and may contribute to SCI-induced pain. Early pharmacologic inhibition of MMPs or the gelatinases (MMP-2 and MMP-9) results in an improvement in long-term neurological recovery and is associated with reduced glial scarring and neuropathic pain. During wound healing, gelatinase A (MMP-2) plays a critical role in limiting the formation of an inhibitory glial scar, and mice that are genetically deficient in this protease showed impaired recovery. Together, these findings illustrate complex, temporally distinct roles of MMPs in SCIs. As early gelatinase activity is detrimental, there is an emerging interest in developing gelatinase-targeted therapeutics that would be specifically tailored to the acute injured spinal cord. Thus, we focus this review on the development of selective gelatinase inhibitors.

Caspase-3 contributes to ZO-1 and Cl-5 tight-junction disruption in rapid anoxic neurovascular unit damage

Background

Tight-junction (TJ) protein degradation is a decisive step in hypoxic blood-brain barrier (BBB) breakdown in stroke. In this study we elucidated the impact of acute cerebral ischemia on TJ protein arrangement and the role of the apoptotic effector protease caspase-3 in this context.

Methodology/Principal Findings

We used an in vitro model of the neurovascular unit and the guinea pig whole brain preparation to analyze with immunohistochemical methods the BBB properties and neurovascular integrity. In both methodological approaches we observed rapid TJ protein disruptions after 30 min of oxygen and glucose deprivation or middle cerebral artery occlusion, which were accompanied by strong caspase-3 activation in brain endothelial cells (BEC). Surprisingly only few DNA-fragmentations were detected with TUNEL stainings in BEC. Z-DEVD-fmk, an irreversible caspase-3 inhibitor, partly blocked TJ disruptions and was protective on trans-endothelial electrical resistance.

Conclusions/Significance

Our data provide evidence that caspase-3 is rapidly activated during acute cerebral ischemia predominantly without triggering DNA-fragmentation in BEC. Further we detected fast TJ protein disruptions which could be partly blocked by caspase-3 inhibition with Z-DEVD-fmk. We suggest that the basis for clinically relevant BBB breakdown in form of TJ disruptions is initiated within minutes during ischemia and that caspase-3 contributes to this process.

Neurological complications of acute ischaemic stroke

Complications after ischaemic stroke, including both neurological and medical complications, are a major cause of morbidity and mortality. Neurological complications, such as brain oedema or haemorrhagic transformation, occur earlier than do medical complications and can affect outcomes with potential serious short-term and long-term consequences. Some of these complications could be prevented or, when this is not possible, early detection and proper management could be effective in reducing the adverse effects. However, there is little evidence-based data to guide the management of these neurological complications. There is a clear need for improved surveillance and specific interventions for the prevention, early diagnosis, and proper management of neurological complications during the acute phase of stroke to reduce stroke morbidity and mortality.

Assessment of permeability in barrier type of endothelium in brain using tracers: Evans blue, sodium fluorescein, and horseradish peroxidase

Blood-brain barrier (BBB) constituted primarily by the capillary endothelial cells functions to maintain a constant environment for the brain, by preventing or slowing down the passage of a variety of blood-borne substances, such as serum proteins, chemical compounds, ions, and hormones from the circulation into the brain parenchyma. Various diseases such as brain tumors, epilepsy, and sepsis disturb the BBB integrity leading to enhanced permeability of brain microvessels. In animal models, a variety of experimental insults targeted to the BBB integrity have been shown to increase BBB permeability causing enhanced passage of molecules into the brain paranchyma by transcellular and/or paracellular pathways. This alteration can be demonstrated by intravascular infusion of exogenous tracers and subsequent detection of extravasated molecules in the brain tissue. A number of exogenous BBB tracers are available, and they can be used for functional and structural analysis of BBB permeability. In this chapter, we aimed to highlight the basic knowledge on the use of three most commonly performed tracers, namely Evans blue dye, sodium fluorescein, and horseradish peroxidase. The experimental methodologies that we use in our laboratory for the detection of these tracers by macroscopy, spectrophotometry, spectrophotofluorometry, and electron microscopy are also discussed. While tracing studies at the morphological level are mainly aimed at the identification and characterization of the tracers both in the barrier related cells and brain parenchyma, spectrophotometric and spectrophotofluorometric assays enable quantification of BBB permeability. The results of our studies that we performed using the mentioned tracers indicate that barrier type of endothelial cells in brain play an important role in paracellular and/or transcytoplasmic trafficking of macromolecules across BBB under various experimental settings, which may provide new insights in both designing approaches for the management of diseases with BBB breakdown and developing novel trans-BBB drug delivery strategies.

Morphology and properties of brain endothelial cells

The molecular advances in various aspects of brain endothelial cell function in steady states are considerable and difficult to summarize in one chapter. Therefore, this chapter focuses on endothelial permeability mechanisms in steady states and disease namely vasogenic edema. The morphology and properties of caveolae and tight junctions that are involved in endothelial permeability to macromolecules are reviewed. Endothelial transport functions are briefly reviewed. Diseases with alterations of endothelial permeability are mentioned and details are provided of the molecular alterations in caveolae and tight junctions in vasogenic edema. Other factors involved in increased endothelial permeability such as the matrix metalloproteinases are briefly discussed. Of the modulators of endothelial permeability, angioneurins such as the vascular endothelial growth factors and angiopoietins are discussed. The chapter concludes with a brief discussion on delivery of therapeutic substances across endothelium.

Matrix metalloproteinases and neurotrauma: evolving roles in injury and reparative processes

Matrix metalloproteinases (MMPs) are involved in a wide range of proteolytic events in fetal development and normal tissue remodeling as well as wound healing and inflammation. In the CNS, they have been implicated in a variety of neurodegenerative diseases ranging from multiple sclerosis to Alzheimer disease and are integral to stroke-related cell damage. Although studies implicate increased activity of MMPs in pathogenesis in the CNS, there is also a growing literature to support their participation in events that support recovery processes. Here the authors provide a brief overview of MMPs and their regulation, address their complex roles following traumatic injuries to the adult and developing CNS, and consider their time- and context-dependent signatures that influence both injury and reparative processes.

Suppression of hypoxia-inducible factor-1alpha and its downstream genes reduces acute hyperglycemia-enhanced hemorrhagic transformation in a rat model of cerebral ischemia

We evaluated a role of hypoxia-inducible factor-1alpha (HIF-1alpha) and its downstream genes in acute hyperglycemia-induced hemorrhagic transformation in a rat model of focal cerebral ischemia. Male Sprague-Dawley rats weighing 280-300 g (n = 105) were divided into sham, 90 min middle cerebral artery occlusion (MCAO), MCAO plus HIF-1alpha inhibitors, 2-methoxyestradiol (2ME2) or 3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole (YC-1), groups. Rats received an injection of 50% dextrose (6 ml/kg intraperitoneally) at 15 min before MCAO. HIF-1alpha inhibitors were administered at the onset of reperfusion. The animals were examined for neurological deficits and sacrificed at 6, 12, 24, and 72 hr following MCAO. The cerebral tissues were collected for histology, zymography, and Western blot analysis. The expression of HIF-1alpha was increased in ischemic brain tissues after MCAO and reduced by HIF-1alpha inhibitors. In addition, 2ME2 reduced the expression of vascular endothelial growth factor (VEGF) and the elevation of active matrix metalloproteinase-2 and -9 (MMP-2/MMP-9) in the ipsilateral hemisphere. Both 2ME2 and YC-1 reduced infarct volume and ameliorated neurological deficits. However, only 2ME2 attenuated hemorrhagic transformation in the ischemic territory. In conclusion, the inhibition of HIF-1alpha and its downstream genes attenuates hemorrhagic conversion of cerebral infarction and ameliorates neurological deficits after focal cerebral ischemia.

Progesterone and allopregnanolone attenuate blood-brain barrier dysfunction following permanent focal ischemia by regulating the expression of matrix metalloproteinases

Blood-brain barrier (BBB) breakdown after stroke is linked to the up-regulation of metalloproteinases (MMPs) and inflammation. This study examines the effects of progesterone (PROG) and its neuroactive metabolite allopregnanolone (ALLO) on BBB integrity following permanent middle cerebral artery occlusion (pMCAO). Rats underwent pMCAO by electro-coagulation and received intraperitoneal injections of PROG (8 mg/kg), ALLO (8 mg/kg) or vehicle at 1 h post-occlusion and then subcutaneous injections (8 mg/kg) at 6, 24, and 48 h. MMP activation and expression were analyzed by Western blot, immunohistochemistry and gelatin zymography 72 h post-pMCAO. Occludin1, claudin5, tumor necrosis factor-alpha (TNF-α) and Interleukin-6 (IL-6) were analyzed at 72 h post-pMCAO with Western blots. BBB permeability was measured by Evans blue extravasation and infarct size was evaluated by cresyl violet at 72 h after pMCAO. Ischemic injury significantly (p<0.05) increased the expression of MMP-9, MMP-2, TNF-α and IL-6, and reduced the levels of occludin1 and claudin5. These changes were followed by increased infarct size (% contralateral hemisphere) and Evans blue extravasation into the brain indicating compromise of the BBB. PROG and ALLO attenuated BBB disruption and infarct size following pMCAO by reducing MMPs and the inflammatory response and by preventing the degradation of occludin1 and claudin5. We conclude that PROG and ALLO can help to protect BBB disruption following pMCAO.

Mechanisms of cerebral edema in traumatic brain injury: therapeutic developments

PURPOSE OF REVIEW

Although a number of factors contribute to the high mortality and morbidity associated with traumatic brain injury (TBI), the development of cerebral edema with brain swelling remains the most significant predictor of outcome. The present review summarizes the most recent advances in the understanding of mechanisms associated with development of posttraumatic cerebral edema, and highlights areas of therapeutic promise.

RECENT FINDINGS

Despite the predominance of cytotoxic (or cellular) edema in the first week after traumatic brain injury, brain swelling can only occur with addition of water to the cranial vault from the vasculature. As such, regulation of blood-brain barrier permeability has become a focus of recent research seeking to manage brain edema. Aquaporins, matrix metalloproteinases and vasoactive inflammatory agents have emerged as potential mediators of cerebral edema following traumatic brain injury. In particular, kinins (bradykinins) and tachykinins (substance P) seem to play an active physiological role in modulating blood-brain barrier permeability after trauma. Substance P neurokinin-1 receptor antagonists show particular promise as novel therapeutic agents.

SUMMARY

Attenuating blood-brain barrier permeability has become a promising approach to managing brain edema and associated swelling given that increases in cranial water content can only be derived from the vasculature. Inflammation, both classical and neurogenic, offers a number of attractive targets.

The role of hypoxia-inducible factor-1α, aquaporin-4, and matrix metalloproteinase-9 in blood-brain barrier disruption and brain edema after traumatic brain injury

OBJECT

The present study investigated the role of hypoxia-inducible factor-1α (HIF-1α), aquaporin-4 (AQP-4), and matrix metalloproteinase-9 (MMP-9) in blood-brain barrier (BBB) permeability alterations and brain edema formation in a rodent traumatic brain injury (TBI) model.

METHODS

The brains of adult male Sprague-Dawley rats (400-425 g) were injured using the Marmarou closed-head force impact model. Anti-AQP-4 antibody, minocycline (an inhibitor of MMP-9), or 2-methoxyestradiol (2ME2, an inhibitor of HIF-1α), was administered intravenously 30 minutes after injury. The rats were killed 24 hours after injury and their brains were examined for protein expression, BBB permeability, and brain edema. Expression of HIF-1α, AQP-4, and MMP-9 as well as expression of the vascular basal lamina protein (laminin) and tight junction proteins (zona occludens-1 and occludin) was determined by Western blotting. Blood-brain barrier disruption was assessed by FITC-dextran extravasation, and brain edema was measured by the brain water content.

RESULTS

Significant (p < 0.05) edema and BBB extravasations were observed following TBI induction. Compared with sham-operated controls, the injured animals were found to have significantly (p < 0.05) enhanced expression of HIF-1α, AQP-4, and MMP-9, in addition to reduced amounts (p < 0.05) of laminin and tight junction proteins. Edema was significantly (p < 0.01) decreased after inhibition of AQP-4, MMP-9, or HIF-1α. While BBB permeability was significantly (p < 0.01) ameliorated after inhibition of either HIF-1α or MMP-9, it was not affected following inhibition of AQP-4. Inhibition of MMP reversed the loss of laminin (p < 0.01). Finally, while inhibition of HIF-1α significantly (p < 0.05) suppressed the expression of AQP-4 and MMP-9, such inhibition significantly (p < 0.05) increased the expression of laminin and tight junction proteins.

CONCLUSIONS

The data support the notion that HIF-1α plays a role in brain edema formation and BBB disruption via a molecular pathway cascade involving AQP-4 and MMP-9. Pharmacological blockade of this pathway in patients with TBI may provide a novel therapeutic strategy.

Endothelial dysfunction and claudin 5 regulation during acrolein-induced lung injury

An integral membrane protein, Claudin 5 (CLDN5), is a critical component of endothelial tight junctions that control pericellular permeability. Breaching of endothelial barriers is a key event in the development of pulmonary edema during acute lung injury (ALI). A major irritant in smoke, acrolein can induce ALI possibly by altering CLDN5 expression. This study sought to determine the cell signaling mechanism controlling endothelial CLDN5 expression during ALI. To assess susceptibility, 12 mouse strains were exposed to acrolein (10 ppm, 24 h), and survival monitored. Histology, lavage protein, and CLDN5 transcripts were measured in the lung of the most sensitive and resistant strains. CLDN5 transcripts and phosphorylation status of forkhead box O1 (FOXO1) and catenin (cadherin-associated protein) beta 1 (CTNNB1) proteins were determined in control and acrolein-treated human endothelial cells. Mean survival time (MST) varied more than 2-fold among strains with the susceptible (BALB/cByJ) and resistant (129X1/SvJ) strains (MST, 17.3 ± 1.9 h vs. 41.4 ± 5.1 h, respectively). Histological analysis revealed earlier perivascular enlargement in the BALB/cByJ than in 129X1/SvJ mouse lung. Lung CLDN5 transcript and protein increased more in the resistant strain than in the susceptible strain. In human endothelial cells, 30 nM acrolein increased CLDN5 transcripts and increased p-FOXO1 protein levels. The phosphatidylinositol 3-kinase inhibitor LY294002 diminished the acrolein-induced increased CLDN5 transcript. Acrolein (300 nM) decreased CLDN5 transcripts, which were accompanied by increased FOXO1 and CTNNB1. The phosphorylation status of these transcription factors was consistent with the observed CLDN5 alteration. Preservation of endothelial CLDN5 may be a novel clinical approach for ALI therapy.

Looking at the blood-brain barrier: molecular anatomy and possible investigation approaches

The blood-brain barrier (BBB) is a dynamic and complex interface between blood and the central nervous system that strictly controls the exchanges between the blood and brain compartments, therefore playing a key role in brain homeostasis and providing protection against many toxic compounds and pathogens. In this review, the unique properties of brain microvascular endothelial cells and intercellular junctions are examined. The specific interactions between endothelial cells and basement membrane as well as neighboring perivascular pericytes, glial cells and neurons, which altogether constitute the neurovascular unit and play an essential role in both health and function of the central nervous system, are also explored. Some relevant pathways across the endothelium, as well as mechanisms involved in the regulation of BBB permeability, and the emerging role of the BBB as a signaling interface are addressed as well. Furthermore, we summarize some of the experimental approaches that can be used to monitor BBB properties and function in a variety of conditions and have allowed recent advances in BBB knowledge. Elucidation of the molecular anatomy and dynamics of the BBB is an essential step for the development of new strategies directed to maintain or restore BBB integrity and barrier function and ultimately preserve the delicate interstitial brain environment.

Hydrogen gas reduced acute hyperglycemia-enhanced hemorrhagic transformation in a focal ischemia rat model

Hyperglycemia is one of the major factors for hemorrhagic transformation after ischemic stroke. In this study, we tested the effect of hydrogen gas on hemorrhagic transformation in a rat focal cerebral ischemia model. Sprague-Dawley rats (n=72) were divided into the following groups: sham; sham treated with hydrogen gas (H(2)); Middle Cerebral Artery Occlusion (MCAO); and MCAO treated with H(2) (MCAO+H(2)). All rats received an injection of 50% dextrose (6 ml/kg i.p.) and underwent MCAO 15 min later. Following a 90 min ischemic period, hydrogen was inhaled for 2 h during reperfusion. We measured the level of blood glucose at 0 h, 0.5 h, 4 h, and 6 h after dextrose injection. Infarct and hemorrhagic volumes, neurologic score, oxidative stress (evaluated by measuring the level of 8 Hydroxyguanosine (8OHG), 4-Hydroxy-2-Nonenal (HNE) and nitrotyrosine), and matrix metalloproteinase (MMP)-2/MMP-9 activity were measured at 24 h after ischemia. We found that hydrogen inhalation for 2 h reduced infarct and hemorrhagic volumes and improved neurological functions. This effect of hydrogen was accompanied by a reduction of the expression of 8OHG, HNE, and nitrotyrosine and the activity of MMP-9. Furthermore, a reduction of the blood glucose level from 500+/-32.51 to 366+/-68.22 mg/dl at 4 h after dextrose injection was observed in hydrogen treated animals. However, the treatment had no significant effect on the expression of ZO-1, occludin, collagen IV or aquaporin4 (AQP4). In conclusion, hydrogen gas reduced brain infarction, hemorrhagic transformation, and improved neurological function in rats. The potential mechanisms of decreased oxidative stress and glucose levels after hydrogen treatment warrant further investigation.

Prolyl hydroxylase domain inhibitors: a route to HIF activation and neuroprotection

Abstract Ischemic stroke is a major cause of death worldwide, and current therapeutic options are very limited. Preconditioning with an ischemic or hypoxic insult is beneficial in experimental models of ischemic stroke. Ischemia/hypoxia results in activation of numerous transcription factors, including hypoxia inducible factor (HIF), which is a master regulator of oxygen homeostasis. HIF activation induces a diverse range of target genes, encompassing a wide variety of cellular processes; including angiogenesis, energy metabolism, cell survival, radical production/scavenging, iron metabolism, stem cell homing, and differentiation. Inhibition of HIF prolyl hydroxylase domain (PHD) enzymes results in activation of HIF and is likely to mimic, at least in part, the effects of hypoxia preconditioning. A caveat is that not all consequences of HIF activation will be beneficial and some could even be deleterious. Nevertheless, PHD inhibitors may be therapeutically useful in the treatment of stroke. Prototype PHD inhibitors have shown promising results in preclinical models.

Molecular insights and therapeutic targets for blood-brain barrier disruption in ischemic stroke: critical role of matrix metalloproteinases and tissue-type plasminogen activator

Blood-brain barrier (BBB) disruption, mediated through matrix metalloproteinases (MMPs) and other mechanisms, is a critical event during ischemic stroke. Tissue plasminogen activator (tPA) is the only FDA-approved thrombolytic therapy for acute ischemic stroke, but the efficacy and safety of its therapeutic application are limited by narrow treatment time windows and side effects. Thus, there is a pressing need to develop combinational therapy that could offset tPA side effects and improve efficacy in clinical practice. Recent experimental studies indicate that tPA has previously unidentified functions in the brain beyond its well-established thrombolytic activity, which might contribute to tPA-related side effects through MMPs (mainly MMP-9) and several signaling pathways involved in LDL receptor-related protein (LRP), activated protein C (APC) and protease-activated receptor 1 (PAR-1), platelet-derived growth factor C (PDGF-C), and N-methyl-d-aspartate (NMDA) receptor. Therapeutic targeting of MMPs and/or tPA-related signaling pathways might offer promising new approaches to combination therapies for ischemic stroke. This review provides an overview of the relationship between structural components and function of the BBB/neurovascular unit with respect to ischemic stroke. We discuss how MMPs and tPA contribute to BBB disruption during ischemic stroke and highlight recent findings of molecular signaling pathways involved in neurotoxicity of tPA therapy.

MMP-9 levels in elderly patients with cognitive dysfunction after carotid surgery

Approximately 25% of elderly patients scheduled for carotid endarterectomy (CEA) develop post-operative cognitive dysfunction (CD). We tested the hypothesis that the plasma levels of matrix metalloproteinase 9 (MMP-9) are predictive of moderate to severe CD after CEA. A total of 73 patients were prospectively enrolled in this Institutional Review Board-approved study. Plasma samples were obtained at baseline and day 1 post-surgery. We measured the plasma concentrations of both MMP-9 and its inhibitor, tissue inhibitor of metalloproteinases 1 (TIMP-1). We estimated the MMP-9 activity by calculating the MMP-9:TIMP-1 ratio. The cognitive performance day 1 post-surgery was quantified with z-scores, using a control group who were undergoing spinal surgery. The criteria used to define CD was performance of >or=1.5 standard deviations worse than the control group; approximately 19% of eligible patients developed CD. Compared to patients without CD, this group had both higher total (81.66+/-12.25 ng/mL versus [vs.] 43.18+/-4.44 ng/mL, p=0.005) and activity (0.88+/-0.24 ng/mL vs. 0.54+/-0.06 ng/mL, p=0.003) MMP-9 levels at baseline. All of the results were adjusted for age, diabetes and neurovascular symptoms.

Blood-brain barrier disruption in humans is independently associated with increased matrix metalloproteinase-9

BACKGROUND AND PURPOSE

Matrix metalloproteinases (MMP) may play a role in blood-brain barrier (BBB) disruption after ischemic stroke. We hypothesized that plasma concentrations of MMP-9 are associated with a marker of BBB disruption in patients evaluated for acute stroke.

METHODS

Patients underwent MRI on presentation and approximately 24 hours later. The MRI marker, termed hyperintense acute reperfusion injury marker (HARM), is gadolinium enhancement of cerebrospinal fluid on fluid-attenuated inversion recovery MRI. Plasma MMP-9 and tissue inhibitor of matrix metalloproteinase-1 were measured by enzyme-linked immunosorbent assay. Logistic regression models tested for predictors of HARM on 24-hour follow-up scans separately for MMP-9 and the ratio of MMP-9 to TIMP-1.

RESULTS

For the 41 patients enrolled, diagnoses were: acute ischemic cerebrovascular syndrome, 33 (80.6%); intracerebral hemorrhage, 6 (14.6%); stroke mimic, 1 (2.4%); and no stroke, 1 (2.4%). HARM was present in 17 (41.5%) patients. In model 1, HARM was associated with baseline plasma MMP-9 concentration (odds ratio [OR], 1.01; 95% confidence interval [CI], 1.001-1.019; P=0.033). In model 2, HARM was associated with the ratio of MMP-9 to tissue inhibitor of matrix metalloproteinase-1 (OR, 4.94; 95% CI, 1.27-19.14; P=0.021).

CONCLUSIONS

Baseline MMP-9 was a significant predictor of HARM at 24-hour follow-up, supporting the hypothesis that MMP-9 is associated with BBB disruption. If the association between MMP-9 and BBB disruption is confirmed in future studies, HARM may be a useful imaging marker to evaluate MMP-9 inhibition in ischemic stroke and other populations with BBB disruption.

Reversal of West Nile virus-induced blood-brain barrier disruption and tight junction proteins degradation by matrix metalloproteinases inhibitor

Though compromised blood-brain barrier (BBB) is a pathological hallmark of WNV-associated neurological sequelae, underlying mechanisms are unclear. We characterized the expression of matrix metalloproteinases (MMP) in WNV-infected human brain microvascular endothelial cells (HBMVE) and human brain cortical astrocytes (HBCA), components of BBB and their role in BBB disruption. Expression of multiple MMPs was significantly induced in WNV-infected HBCA cells. Naïve HBMVE cells incubated with the supernatant from WNV-infected HBCA cells demonstrated loss of tight junction proteins, which were rescued in the presence of MMP inhibitor, GM6001. Further, supernatant from WNV-infected HBCA cells compromised the in vitro BBB model integrity. Our data suggest astrocytes as one of the sources of MMP in the brain, which mediates BBB disruption allowing unrestricted entry of immune cells into the brain, thereby contributing to WNV neuropathogenesis. Because of the unavailability of WNV antivirals and vaccines, use of MMP inhibitors as an adjunct therapy to ameliorate WNV disease progression is warranted.

Increased intranuclear matrix metalloproteinase activity in neurons interferes with oxidative DNA repair in focal cerebral ischemia

Increased matrix metalloproteinase (MMP) activity is implicated in proteolysis of extracellular matrix in ischemic stroke. We recently observed intranuclear MMP activity in ischemic brain neurons at early reperfusion, suggesting a possible role in nuclear matrix proteolysis. Nuclear proteins, poly-ADP-ribose polymerase-1 (PARP-1) and X-ray cross-complementary factor 1 (XRCC1), as well as DNA repair enzymes, are important in DNA fragmentation and cell apoptosis. We hypothesized that intranuclear MMP activity facilitates oxidative injury in neurons during early ischemic insult by cleaving PARP-1 and XRCC1, interfering with DNA repair. We induced a 90-min middle cerebral artery occlusion in rats. Increase activity of MMP-2 and -9, detected in the ischemic neuronal nuclei at 3 h, was associated with DNA fragmentation at 24 and 48 h reperfusion. The intranuclear MMPs cleaved PARP-1. Treatment of the rats with a broad-spectrum MMP inhibitor, BB1101, significantly attenuated ischemia-induced PARP-1 cleavage, increasing its activity. Degradation of XRCC1 caused by ischemic insult in rat brain was also significantly attenuated by BB1101. We found elevation of oxidized DNA, apurinic/apyrimidinic sites, and 8-hydroxy-2'-deoxyguanosine, in ischemic brain cells at 3 h reperfusion. BB1101 markedly attenuated the early increase of oxidized DNA. Using tissue from stroke patients, we found increased intranuclear MMP expression. Our data suggest that intranuclear MMP activity cleaves PARP-1 and XRCC1, interfering with oxidative DNA repair. This novel role for MMPs could contribute to neuronal apoptosis in ischemic injuries.

The blood-brain barrier in neurodegenerative disease: a rhetorical perspective

Recent studies suggest that the function of the blood-brain barrier (BBB) is not static under normal physiologic conditions and is likely altered in neurodegenerative disease. Prevailing thinking about CNS function, and neurodegenerative disease in particular, is neurocentric excluding the impact of factors outside the CNS. This review challenges this perspective and discusses recent reports suggesting the involvement of peripheral factors including toxins and elements of adaptive immunity that may not only play a role in pathogenesis, but also progression of neurodegenerative diseases. Central to this view is neuroinflammation. Several studies indicate that the neuroinflammatory changes that accompany neurodegeneration affect the BBB or its function by altering transport systems, enhancing immune cell entry, or influencing the BBB's role as a signaling interface. Such changes impair the BBB's normal homeostatic function and affect neural activity. Moreover, recent studies reveal that alterations in BBB and its transporters affect the entry of drugs used to treat neurodegenerative diseases. Incorporating BBB compromise and dysfunction into our view of neurodegenerative disease leads to the inclusion of peripheral mediators in its pathogenesis and progression. In addition, this changing view of the BBB raises interesting new therapeutic possibilities for drug delivery as well as treatment strategies designed to reinstate normal barrier function.

eNOS gene deletion restores blood-brain barrier integrity and attenuates neurodegeneration in the thiamine-deficient mouse brain

Wernicke's encephalopathy is a cerebral disorder caused by thiamine (vitamin B(1)) deficiency (TD). Neuropathologic consequences of TD include region-selective neuronal cell loss and blood-brain barrier (BBB) breakdown. Early increased expression of the endothelial isoform of nitric oxide synthase (eNOS) occurs selectively in vulnerable brain regions in TD. We hypothesize that region-selective eNOS induction in TD leads to altered expression of tight junction proteins and BBB breakdown. In order to address this issue, TD was induced in C57BL/6 wild-type (WT) and eNOS(-/-) mice by feeding a thiamine-deficient diet and treatment with the thiamine antagonist pyrithiamine. Pair-fed control mice were fed the same diet with additional thiamine. In medial thalamus of TD-WT mice (vulnerable area), increased heme oxygenase-1 and S-nitrosocysteine immunostaining was observed in vessel walls, compared to pair-fed control-WT mice. Concomitant increases in IgG extravasation, decreases in expression of the tight junction proteins occludin, zona occludens-1 and zona occludens-2, and up-regulation of matrix metalloproteinase-9 in endothelial cells were observed in the medial thalamus of TD-WT mice. eNOS gene deletion restored these BBB alterations, suggesting that eNOS-derived nitric oxide is a major factor leading to cerebrovascular alterations in TD. However, eNOS gene deletion only partially attenuated TD-related neuronal cell loss, suggesting the presence of mechanisms additional to BBB disruption in the pathogenesis of these changes.

Structure and function of the blood-brain barrier

Neural signalling within the central nervous system (CNS) requires a highly controlled microenvironment. Cells at three key interfaces form barriers between the blood and the CNS: the blood-brain barrier (BBB), blood-CSF barrier and the arachnoid barrier. The BBB at the level of brain microvessel endothelium is the major site of blood-CNS exchange. The structure and function of the BBB is summarised, the physical barrier formed by the endothelial tight junctions, and the transport barrier resulting from membrane transporters and vesicular mechanisms. The roles of associated cells are outlined, especially the endfeet of astrocytic glial cells, and pericytes and microglia. The embryonic development of the BBB, and changes in pathology are described. The BBB is subject to short and long-term regulation, which may be disturbed in pathology. Any programme for drug discovery or delivery, to target or avoid the CNS, needs to consider the special features of the BBB.

Pathology and new players in the pathogenesis of brain edema

Brain edema continues to be a major cause of mortality after diverse types of brain pathologies such as major cerebral infarcts, hemorrhages, trauma, infections and tumors. The classification of edema into vasogenic, cytotoxic, hydrocephalic and osmotic has stood the test of time although it is recognized that in most clinical situations there is a combination of different types of edema during the course of the disease. Basic information about the types of edema is provided for better understanding of the expression pattern of some of the newer molecules implicated in the pathogenesis of brain edema. These molecules include the aquaporins, matrix metalloproteinases and growth factors such as vascular endothelial growth factors A and B and the angiopoietins. The potential of these agents in the treatment of edema is discussed. Since many molecules are involved in the pathogenesis of brain edema, effective treatment cannot be achieved by a single agent but will require the administration of a "magic bullet" containing a variety of agents released at different times during the course of edema in order to be successful.

Minocycline effects on cerebral edema: relations with inflammatory and oxidative stress markers following traumatic brain injury in mice

One of the severe complications following traumatic brain injury (TBI) is cerebral edema and its effective treatment is of great interest to prevent further brain damage. This study investigated the effects of minocycline, known for its anti-inflammatory properties, on cerebral edema and its respective inflammatory markers by comparing different dose regimens, on oxidative stress and on neurological dysfunction following TBI. The weight drop model was used to induce TBI in mice. The brain water content was measured to evaluate cerebral edema. Inflammatory markers were detected by ELISA (IL-1beta), zymography and Western blot (MMP-9). The oxidative stress marker (glutathione levels) and neurological function were measured by Griffith technique and string test, respectively. Minocycline was administered i.p. once (5 min), twice (5 min and 3 h) or triple (5 min, 3 h and 9 h) following TBI. The first dose of minocycline only varied (45 or 90 mg/kg), whereas the following doses were all at 45 mg/kg. The single and double administrations of minocycline reduced the increase of inflammatory markers at 6 h post-TBI. Minocycline also reduced cerebral edema at this time point, only after double administration and at the high dose regimen, although with no effect on the TBI-induced oxidized glutathione increase. The anti-edematous effect of minocycline persisted up to 24 h, upon a triple administration, and accompanied by a neurological recovery. In conclusion, we reported an anti-edematous effect of minocycline after TBI in mice according to a specific treatment regimen. These findings emphasize that the beneficial effects of minocycline depend on the treatment regimen following a brain injury.

Doxycycline treatment decreases morbidity and mortality of murine neurocysticercosis: evidence for reduction of apoptosis and matrix metalloproteinase activity

Murine neurocysticercosis is a parasitic infection transmitted through the direct ingestion of Taenia solium eggs, which differentially disrupts the barriers that protect the microenvironment of the central nervous system. Among the host factors that are involved in this response, matrix metalloproteinases (MMPs) have been recently described as important players. Doxycycline is a commonly prescribed antimicrobial drug that acts as an anti-inflammatory agent with broad inhibitory properties against MMPs. In this study, we examined the effects of doxycycline treatment in a murine model of neurocysticercosis. Animals treated with doxycycline exhibited reduced morbidity and mortality throughout the course of infection. Although similar levels of leukocyte infiltration were observed with both treatment regimens, doxycycline appeared to provide improved conditions for host survival, as reduced levels of apoptosis were detected among infiltrates as well as in neurons. As an established MMP blocker, doxycycline reduced the degradation of junctional complex proteins in parenchymal vessels. In addition, doxycycline treatment was associated with an overall reduction in the expression and activity of MMPs, particularly in areas of leukocyte infiltration. These results indicate that a broad-range inhibitor of MMPs promotes host survival and suggest the potential of doxycycline as a therapeutic agent for the control of inflammatory responses associated with neurocysticercosis.

Tobacco smoke: a critical etiological factor for vascular impairment at the blood-brain barrier

Active and passive tobacco smoke are associated with the dysfunction of endothelial physiology and vascular impairment. Studies correlating the effects of smoking and the brain microvasculature at the blood-brain barrier (BBB) level have been largely limited to few selective compounds that are present in the tobacco smoke (TS) yet the pathophysiology of smoking has not been unveiled. For this purpose, we characterized the physiological response of isolated human brain microvascular endothelial cells (HBMEC) and monocytes to the exposure of whole soluble TS extract. With the use of a well established humanized flow-based in vitro blood-brain barrier model (DIV-BBB) we have also investigated the BBB physiological response to TS under both normal and impaired hemodynamic conditions simulating ischemia. Our results showed that TS selectively decreased endothelial viability only at very high concentrations while not significantly affecting that of astrocytes and monocytes. At lower concentrations, despite the absence of cytotoxicity, TS induced a strong vascular pro-inflammatory response. This included the upregulation of endothelial pro-inflammatory genes, a significant increase of the levels of pro-inflammatory cytokines, activated matrix metalloproteinase, and the differentiation of monocytes into macrophages. When flow-cessation/reperfusion was paired with TS exposure, the inflammatory response and the loss of BBB viability were significantly increased in comparison to sham-smoke condition. In conclusion, TS is a strong vascular inflammatory primer that can facilitate the loss of BBB function and viability in pathological settings involving a local transient loss of cerebral blood flow such as during ischemic insults.

Effects of novel semiselective matrix metalloproteinase inhibitors on ex vivo cardiac structure-function

The purpose of this study was to evaluate the ability of novel semiselective matrix metalloproteinase inhibitors (MMPI) to protect myocardial structure-function in the setting of ischemia-reperfusion injury. For this purpose, an isolated rat model of myocardial stunning and infarction was used. Isolated hearts were subjected to 20-30 minutes of global no-flow ischemia and 30-minute reperfusion. Myocardial performance was assessed as the product of the heart rate and left ventricular developed pressure (rate-pressure product, RPP). Coronary flow rates, ventricular weights, indicators of muscle (troponin I), and fibrillar collagen damage (collagen opalation) were measured. Four MMPI were tested: 2 non-hydroxamate, semiselective inhibitors (PY-2 and 1,2-HOPO-2) and 2 broad-spectrum inhibitors (PD166793 and CGS27023A). The non-hydroxamate, semiselective inhibitors were shown to be nontoxic in cocultures of cardiac cells. Results indicate that semiselective inhibitors (in particular 1,2-HOPO-2) yield improved cardiac performance (approximately 23% higher RPP vs. controls) and coronary flow rates (approximately 22%), reducing muscle (approximately 25%) and fibrillar collagen damage (approximately 60%). Evidence suggests the involvement of matrix metalloproteinase-2 in these actions. Interestingly, broad-spectrum inhibitors only show modest improvement (approximately 8% higher RPP vs. controls) without affecting the other measured parameters. In conclusion, semiselective MMPI can act as cardioprotectors in isolated perfused rat hearts. Protection is observed in all structural components of the myocardium translating into improved contractile function. Based on these findings, non-hydroxamate, semiselective MMPI warrant further studies as to their ability to protect ischemic myocardium in the in vivo setting.

Occludin oligomeric assemblies at tight junctions of the blood-brain barrier are altered by hypoxia and reoxygenation stress

Hypoxic (low oxygen) and reperfusion (post-hypoxic reoxygenation) phases of stroke promote an increase in microvascular permeability at tight junctions (TJs) of the blood-brain barrier (BBB) that may lead to cerebral edema. To investigate the effect of hypoxia (Hx) and reoxygenation on oligomeric assemblies of the transmembrane TJ protein occludin, rats were subjected to either normoxia (Nx, 21% O(2), 60 min), Hx (6% O(2), 60 min), or hypoxia/reoxygenation (H/R, 6% O(2), 60 min followed by 21% O(2), 10 min). After treatment, cerebral microvessels were isolated, fractionated by detergent-free density gradient centrifugation, and occludin oligomeric assemblies associated with plasma membrane lipid rafts were solubilized by perfluoro-octanoic acid (PFO) exclusively as high molecular weight protein complexes. Analysis by non-reducing and reducing sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis/western blot of PFO-solubilized occludin revealed that occludin oligomeric assemblies co-localizing with 'TJ-associated' raft domains contained a high molecular weight 'structural core' that was resistant to disassembly by either SDS or a hydrophilic reducing agent ex vivo, and by Hx and H/R conditions in vivo. However, exposure of PFO-solubilized occludin oligomeric assemblies to SDS ex vivo revealed the non-covalent association of a significant amount of dimeric and monomeric occludin isoforms to the disulfide-bonded inner core, and dispersal of these non-covalently attached occludin subunits to lipid rafts of higher density in vivo was differentially promoted by Hx and H/R. Our data suggest a model of isoform interaction within occludin oligomeric assemblies at the BBB that enables occludin to simultaneously perform a structural role in inhibiting paracellular diffusion, and a signaling role involving interactions of dimeric and monomeric occludin isoforms with a variety of regulatory molecules within different plasma membrane lipid raft domains.

Neuroinflammation and MMPs: potential therapeutic targets in neonatal hypoxic-ischemic injury

Exposure to hypoxic-ischemic insults during the neonatal or perinatal developmental periods produces various forms of pathology. Injuries that occur in response to these events often manifest as severe cognitive and/or motor disturbances over time. Due to difficulties regarding the early diagnosis and treatment of hypoxic-ischemic injury, there is a growing need for effective therapies that can be delivered at delayed time points. Much of the research into mechanisms of neural injury has focused on molecular targets associated with excitotoxicity and free oxygen radicals. Despite repeated success in animal models, these compounds have failed to show efficacy in clinical trials. Increasing evidence indicates that hypoxic-ischemic injury in the neonate is progressive, and the resulting neuropathies are linked to the activation of neuroinflammatory processes that occur in response to the initial wave of cell death. Understanding this latter response, therefore, will be critical in the development of novel therapies to block the progression of the injury. In this review, we summarize emerging concepts from rodent models concerning the regulation of various cytokines, chemokines, and matrix metalloproteinases in response to ischemia, and the various ways in which the delayed neuroinflammatory response may contribute to the progressive nature of neonatal hypoxic-ischemic injury in rat. Finally, we discuss data that supports the potential to target these neuroinflammatory signals at clinically relevant time points.

Decompressive surgery for severe brain edema

Decompressive surgery has since long been a promising therapeutic approach for patients with acute severe brain injury at risk to develop severe brain edema. The underlying rationale of removing part of the cranium is to create space for the expanding brain to prevent secondary damage to vital brain tissue. However, until recently, randomized controlled trials that demonstrate the efficacy of decompressive surgery or benefit for outcome were missing. This has changed since the results of 3 randomized trials on hemicraniectomy in malignant infarction of the middle cerebral artery have been published in 2007. In this article, the current evidence for decompressive surgery in the treatment of cerebral ischemia, intracranial hemorrhage, traumatic brain injury, inflammatory diseases, or severe metabolic derangements is reviewed. Although there is increasing evidence for the efficacy of decompressive surgery in reducing intracranial pressure and even mortality, a critical point remains the definition of good or acceptable outcome.

Inhibition of gelatinase activity reduces neural injury in an ex vivo model of hypoxia-ischemia

Perinatal hypoxia-ischemia (H-I) often manifests as cognitive and/or motor disturbances that appear early in development. Growing evidence indicates that neuroinflammation may exacerbate H-I injury. Resident microglia release proinflammatory cytokines and proteases in response to ischemia. Matrix metalloproteinases (MMPs), in particular, activate cytokines and degrade basement membrane proteins. These actions ultimately permit entry of peripheral leukocytes into the CNS neuropil, enhancing neuroinflammation and cell death. Currently, the relative contributions of resident and peripheral immune cells to ischemic brain injury are unclear. The present study employed an ex vivo model of H-I through oxygen glucose deprivation (OGD) to identify the cellular localization of MMP-9 in organotypic hippocampal slices from rat, and to determine whether inhibiting gelatin-degrading MMPs affords neuroprotection in the absence of peripheral immune cells. Immunohistochemistry revealed ubiquitous neuronal MMP-9 expression in both normoxic and hypoxic slices. Increased MMP-9 expression was detected in CD11b-positive microglia after 48 h exposure to OGD relative to normoxic controls. Consistent with these data, in situ zymography showed increased gelatinolytic activity after OGD. Gelatin-cleaved fluorescence localized to astrocytic processes and somata of various cellular morphologies. Treatment with either the MMP inhibitor AG3340 (prinomastat) or minocycline dampened OGD-induced gelatinolytic activity and neural injury, as measured by Fluoro-Jade staining, relative to vehicle controls. These results show that resident microglia, in the absence of peripheral immune cells, were sufficient to enhance neural injury after OGD in the organotypic hippocampal slice. Additionally, these effects were associated with upregulation or secretion of MMP-9, and were blocked after treatment with either the gelatinase-selective compound AG3340 or the anti-inflammatory compound minocycline. These data, coupled with the effectiveness of these compounds previously shown in vivo, support the selective targeting of gelatin-degrading MMPs and activated microglia as potential therapeutic approaches to combat neonatal H-I injury.