Early Upregulation of Matrix Metalloproteinases Following Reperfusion Triggers Neuroinflammatory Mediators in Brain Ischemia in Rat

Contrast-Induced Encephalopathy and the Blood-Brain Barrier

BACKGROUND

Contrast-induced encephalopathy (CIE) is an adverse event associated with diagnostic and therapeutic endovascular procedures. Decades of animal and human research support a mechanistic role for pathological blood-brain barrier dysfunction (BBBd). Here, we describe an institutional case series and review the literature supporting a mechanistic role for BBBd in CIE.

METHODS

A literature review was conducted by searching MEDLINE, Web of Science, Embase, CINAHL and Cochrane databases from inception to January 31, 2022. We searched our institutional neurovascular database for cases of CIE following endovascular treatment of cerebrovascular disease during a 6-month period. Informed consent was obtained in all cases.

RESULTS

Review of the literature revealed risk factors for BBBd and CIE, including microvascular disease, pathological neuroinflammation, severe procedural hypertension, iodinated contrast load and altered cerebral blood flow dynamics. In our institutional series, 6 of 52 (11.5%) of patients undergoing therapeutic neuroendovascular procedures developed CIE during the study period. Four patients were treated for ischemic stroke and two patients for recurrent cerebral aneurysms. Mechanical stenting or thrombectomy were utilized in all cases.

CONCLUSION

In this institutional case series and literature review of animal and human data, we identified numerous shared risk factors for CIE and BBBd, including microvascular disease, increased procedure length, large contrast volumes, severe intraoperative hypertension and use of mechanical devices that may induce iatrogenic endothelial injury.

Blood-Brain Barrier Mechanisms in Stroke and Trauma

The brain microenvironment is tightly regulated. The blood-brain barrier (BBB), which is composed of cerebral endothelial cells, astrocytes, and pericytes, plays an important role in maintaining the brain homeostasis by regulating the transport of both beneficial and detrimental substances between circulating blood and brain parenchyma. After brain injury and disease, BBB tightness becomes dysregulated, thus leading to inflammation and secondary brain damage. In this chapter, we overview the fundamental mechanisms of BBB damage and repair after stroke and traumatic brain injury (TBI). Understanding these mechanisms may lead to therapeutic opportunities for brain injury.

Paradoxical effect of fat diet in matrix metalloproteinases induced mitochondrial dysfunction in diabetic cardiomyopathy

AIMS

Diabetic cardiomyopathy represents the main cause of death among diabetic people. Despite this evidence, the molecular mechanisms triggered by impaired glucose and lipid metabolism inducing heart damage remain unclear. The aim of our study was to investigate the effect of altered metabolism on the early stages of cardiac injury in experimental diabetes.

METHODS

For this purpose, rats were fed a normocaloric diet (NPD) or a high fat diet (HFD) for up to 12 weeks. After the fourth week, streptozocin (35 mg/kg) was administered in a subgroup of both NPD and HFD rats to induce diabetes. Cardiac function was analysed by echocardiography. Matrix metalloproteinases (MMPs) activity and intracellular localization were assessed through zymography and immunofluorescence, whereas apoptotic and oxidative markers by immunohistochemistry and western blot.

RESULTS

Hyperglycaemia or hyperlipidaemia reduced ejection fraction and fractional shortening as compared with control. Unexpectedly, cardiac dysfunction was less marked in diabetic rats fed a hyperlipidaemic diet, suggesting an adaptive response of the myocardium to hyperglycaemia-induced injury. This response was characterized by the inhibition of N-terminal truncated-MMP-2 translocation from endoplasmic reticulum into mitochondria and by superoxide anion overproduction observed in cardiomyocytes under hyperglycaemia.

CONCLUSION

Overall, these findings suggest novel therapeutic targets aimed to counteract mitochondrial dysfunction in the onset of diabetic cardiomyopathy.

Diabetes Mellitus/Poststroke Hyperglycemia: a Detrimental Factor for tPA Thrombolytic Stroke Therapy

Intravenous administration of tissue-type plasminogen activator (IV tPA) therapy has long been considered a mainstay in ischemic stroke management. However, patients respond to IV tPA therapy unequally with some subsets of patients having worsened outcomes after treatment. In particular, diabetes mellitus (DM) is recognized as a clinically important vascular comorbidity that leads to lower recanalization rates and increased risks of hemorrhagic transformation (HT). In this short-review, we summarize the recent advances in understanding of the underlying mechanisms involved in post-IV tPA worsening of outcome in diabetic stroke. Potential pathologic factors that are related to the suboptimal tPA recanalization in diabetic stroke include higher plasma plasminogen activator inhibitor (PAI)-1 level, diabetic atherogenic vascular damage, glycation of the tPA receptor annexin A2, and alterations in fibrin clot density. While factors contributing to the exacerbation of HT in diabetic stroke include hyperglycemia, vascular oxidative stress, and inflammation, tPA neurovascular toxicity and imbalance in extracellular proteolysis are discussed. Besides, impaired collaterals in DM also compromise the efficacy of IV tPA therapy. Additionally, several tPA combination approaches developed from experimental studies that may help to optimize IV tPA therapy are also briefly summarized. In summary, more research efforts are needed to improve the safety and efficacy of IV tPA therapy in ischemic stroke patients with DM/poststroke hyperglycemia.

Connexin Hemichannel Mimetic Peptide Attenuates Cortical Interneuron Loss and Perineuronal Net Disruption Following Cerebral Ischemia in Near-Term Fetal Sheep

Perinatal hypoxia-ischemia is associated with disruption of cortical gamma-aminobutyric acid (GABA)ergic interneurons and their surrounding perineuronal nets, which may contribute to persisting neurological deficits. Blockade of connexin43 hemichannels using a mimetic peptide can alleviate seizures and injury after hypoxia-ischemia. In this study, we tested the hypothesis that connexin43 hemichannel blockade improves the integrity of cortical interneurons and perineuronal nets. Term-equivalent fetal sheep received 30 min of bilateral carotid artery occlusion, recovery for 90 min, followed by a 25-h intracerebroventricular infusion of vehicle or a mimetic peptide that blocks connexin hemichannels or by a sham ischemia + vehicle infusion. Brain tissues were stained for interneuronal markers or perineuronal nets. Cerebral ischemia was associated with loss of cortical interneurons and perineuronal nets. The mimetic peptide infusion reduced loss of glutamic acid decarboxylase-, calretinin-, and parvalbumin-expressing interneurons and perineuronal nets. The interneuron and perineuronal net densities were negatively correlated with total seizure burden after ischemia. These data suggest that the opening of connexin43 hemichannels after perinatal hypoxia-ischemia causes loss of cortical interneurons and perineuronal nets and that this exacerbates seizures. Connexin43 hemichannel blockade may be an effective strategy to attenuate seizures and may improve long-term neurological outcomes after perinatal hypoxia-ischemia.

Matrix Metalloproteinase-9 Relationship With Infarct Growth and Hemorrhagic Transformation in the Era of Thrombectomy

Objective: To assess the relationship between matrix metalloproteinase 9 (MMP-9), a proteolytic enzyme involved in the breakdown of the blood-brain barrier, and infarct growth and hemorrhagic transformation in acute ischemic stroke (AIS) with large vessel occlusion (LVO) in the era of mechanical thrombectomy (MT) using the kinetics of MMP-9 and sequential magnetic resonance imaging (MRI).

Methods: HIBISCUS-STROKE is a cohort study including AIS patients with LVO treated with MT following admission MRI. Patients underwent sequential assessment of MMP-9, follow-up CT at day 1, and MRI at day 6. The CT scan at day 1 classified any hemorrhagic transformation according to the European Co-operative Acute Stroke Study-II (ECASS II) classification. Infarct growth was defined as the difference between final Fluid-Attenuated Inversion Recovery volume and baseline diffusion-weighted imaging volume. Conditional logistic regression analyses were adjusted for main confounding variables including reperfusion status.

Results: One hundred and forty-eight patients represent the study population. A high MMP-9 level at 6 h from admission (H6) (p = 0.02), a high glucose level (p = 0.01), a high temperature (p = 0.04), and lack of reperfusion (p = 0.02) were associated with infarct growth. A high MMP-9 level at H6 (p = 0.03), a high glucose level (p = 0.03) and a long delay from symptom onset to groin puncture (p = 0.01) were associated with hemorrhagic transformation.

Conclusions: In this MT cohort study, MMP-9 level at H6 predicts infarct growth and hemorrhagic transformation.

Bone marrow-derived mesenchymal stem cell transplantation attenuates overexpression of inflammatory mediators in rat brain after cardiopulmonary resuscitation

Emerging evidence suggests that bone marrow-derived mesenchymal stem cell transplantation improves neurological function after cardiac arrest and cardiopulmonary resuscitation; however, the precise mechanisms remain unclear. This study aimed to investigate the effect of bone marrow-derived mesenchymal stem cell treatment on expression profiles of multiple cytokines in the brain after cardiac arrest and cardiopulmonary resuscitation. Cardiac arrest was induced in rats by asphyxia and cardiopulmonary resuscitation was initiated 6 minutes after cardiac arrest. One hour after successful cardiopulmonary resuscitation, rats were injected with either phosphate-buffered saline (control) or 1 × 10⁶ bone marrow-derived mesenchymal stem cells via the tail vein. Serum S100B levels were measured by enzyme-linked immunosorbent assay and neurological deficit scores were evaluated to assess brain damage at 3 days after cardiopulmonary resuscitation. Serum S100B levels were remarkably decreased and neurological deficit scores were obviously improved in the mesenchymal stem cell group compared with the phosphate-buffered saline group. Brains were isolated from the rats and expression levels of 90 proteins were determined using a RayBio Rat Antibody Array, to investigate the cytokine profiles. Brain levels of the inflammatory mediators tumor necrosis factor-α, interferon-γ, macrophage inflammatory protein-1α, macrophage inflammatory protein-2, macrophage inflammatory protein-3α, macrophage-derived chemokine, and matrix metalloproteinase-2 were decreased ≥ 1.5-fold, while levels of the anti-inflammatory factor interleukin-10 were increased ≥ 1.5-fold in the mesenchymal stem cell group compared with the control group. Donor mesenchymal stem cells were detected by immunofluorescence to determine their distribution in the damaged brain, and were primarily observed in the cerebral cortex. These results indicate that bone marrow-derived mesenchymal stem cell transplantation attenuates brain damage induced by cardiac arrest and cardiopulmonary resuscitation, possibly via regulation of inflammatory mediators. This experimental protocol was approved by the Institutional Animal Care and Use Committee of Fujian Medical University, China in January 2016 (approval No. 2016079).

Loss of interneurons and disruption of perineuronal nets in the cerebral cortex following hypoxia-ischaemia in near-term fetal sheep

Hypoxia-ischaemia (HI) in term infants is a common cause of brain injury and neurodevelopmental impairment. Development of gamma-aminobutyric acid (GABA)ergic circuitry in the cerebral cortex is a critical event in perinatal brain development. Perineuronal nets (PNNs) are specialised extracellular matrix structures that surround GABAergic interneurons, and are important for their function. Herein, we hypothesised that HI would reduce survival of cortical interneurons and disrupt PNNs in a near-term fetal sheep model of global cerebral ischaemia. Fetal sheep (0.85 gestation) received sham occlusion (n = 5) or 30 min of reversible cerebral ischaemia (HI group; n = 5), and were recovered for 7 days. Expression of interneurons (glutamate decarboxylase [GAD]⁺; parvalbumin [PV]⁺) and PNNs (Wisteria floribunda agglutinin, WFA) was assessed in the parasagittal cortex by immunohistochemistry. HI was associated with marked loss of both GAD⁺ and PV⁺ cortical interneurons (all layers of the parasagittal cortex and layer 6) and PNNs (layer 6). The expression and integrity of PNNs was also reduced on surviving GAD⁺ interneurons. There was a trend towards a linear correlation of the proportion of GAD⁺ neurons that were WFA⁺ with seizure burden (r² = 0.76, p = 0.0534). Overall, these data indicate that HI may cause deficits in the cortical GABAergic system involving loss of interneurons and disruption of PNNs, which may contribute to the range of adverse neurological outcomes following perinatal brain injury.

Matrix Metalloproteinase 9 in Epilepsy: The Role of Neuroinflammation in Seizure Development

Matrix metalloproteinase 9 is a proteolytic enzyme which is recently one of the more often studied biomarkers. Its possible use as a biomarker of neuronal damage in stroke, heart diseases, tumors, multiple sclerosis, and epilepsy is being widely indicated. In epilepsy, MMP-9 is suggested to play a role in epileptic focus formation and in the stimulation of seizures. The increase of MMP-9 activity in the epileptic focus was observed both in animal models and in clinical studies. MMP-9 contributes to formation of epileptic focus, for example, by remodeling of synapses. Its proteolytic action on the elements of blood-brain barrier and activation of chemotactic processes facilitates accumulation of inflammatory cells and induces seizures. Also modification of glutamatergic transmission by MMP-9 is associated with seizures. In this review we will try to recapitulate the results of previous studies about MMP-9 in terms of its association with epilepsy. We will discuss the mechanisms of its actions and present the results revealed in animal models and clinical studies. We will also provide a comparison of the results of various studies on MMP-9 levels in the context of its possible use as a biomarker of the activity of epilepsy.

Inhibition of Protease-Activated Receptor 1 Does not Affect Dendritic Homeostasis of Cultured Mouse Dentate Granule Cells

Protease-activated receptors (PARs) are widely expressed in the central nervous system (CNS). While a firm link between PAR1-activation and functional synaptic and intrinsic neuronal properties exists, studies on the role of PAR1 in neural structural plasticity are scarce. The physiological function of PAR1 in the brain remains not well understood. We here sought to determine whether prolonged pharmacologic PAR1-inhibition affects dendritic morphologies of hippocampal neurons. To address this question we employed live-cell microscopy of mouse dentate granule cell dendrites in 3-week old entorhino-hippocampal slice cultures prepared from Thy1-GFP mice. A subset of cultures were treated with the PAR1-inhibitor SCH79797 (1 μM; up to 3 weeks). No major effects of PAR1-inhibition on static and dynamic parameters of dentate granule cell dendrites were detected under control conditions. Granule cells of PAR1-deficient slice cultures showed unaltered dendritic morphologies, dendritic spine densities and excitatory synaptic strength. Furthermore, we report that PAR1-inhibition does not prevent dendritic retraction following partial deafferentation in vitro. Consistent with this finding, no major changes in PAR1-mRNA levels were detected in the denervated dentate gyrus (DG). We conclude that neural PAR1 is not involved in regulating the steady-state dynamics or deafferentation-induced adaptive changes of cultured dentate granule cell dendrites. These results indicate that drugs targeting neural PAR1-signals may not affect the stability and structural integrity of neuronal networks in healthy brain regions.

Robust neuroprotective effects of intranasally delivered iNOS siRNA encapsulated in gelatin nanoparticles in the postischemic brain

The therapeutic efficacy of intranasal iNOS siRNA delivery was investigated in the postischemic rat brain after encapsulating on in gelatin nanoparticles (GNPs; diameter 188.0 ± 60.9 nm) cross-linked with 0.0667% glutaraldehyde (GA). Intranasally delivered GNPs were found in extracellular and intracellular compartments of many brain regions, including the olfactory bulb, cerebral cortex, and striatum at 1 hour after infusion and continued to be detected for days. Infarct volumes were markedly suppressed (maximal reduction to 42.1 ± 2.6%) at 2 days after 60 minutes of middle cerebral artery occlusion (MCAO) when iNOS siRNA/GNPs were delivered at 6 hours post-MCAO. In addition, this protective effect was manifested by reductions in neurological and behavioral deficits that were sustained for 2 weeks. Therapeutic potency of iNOS siRNA/GNPs was significantly greater and sustained longer than that of bare siRNA and prolonged and efficient iNOS by iNOS siRNA/GNP is responsible for the robust neuroprotective effect.

Oxidative DNA Damage Mediated by Intranuclear MMP Activity Is Associated with Neuronal Apoptosis in Ischemic Stroke

Evidence of the pathological roles of matrix metalloproteinases (MMPs) in various neurological disorders has made them attractive therapeutic targets. MMPs disrupt the blood-brain barrier and cause neuronal death and neuroinflammation in acute cerebral ischemia and are critical for angiogenesis during recovery. However, some challenges have to be overcome before MMPs can be further validated as drug targets in stroke injury. Identifying in vivo substrates of MMPs should greatly improve our understanding of the mechanisms of ischemic injury and is critical for providing more precise drug targets. Recent works have uncovered nontraditional roles for MMPs in the cytosol and nucleus. These have shed light on intracellular targets and biological actions of MMPs, adding additional layers of complexity for therapeutic MMP inhibition. In this review, we discussed the recent advances made in understanding nuclear location of MMPs, their regulation of intranuclear sorting, and their intranuclear proteolytic activity and substrates. In particular, we highlighted the roles of intranuclear MMPs in oxidative DNA damage, neuronal apoptosis, and neuroinflammation at an early stage of stroke insult. These novel data point to new putative MMP-mediated intranuclear actions in stroke-induced pathological processes and may lead to novel approaches to treatment of stroke and other neurological diseases.

Extracellular proteolysis in structural and functional plasticity of mossy fiber synapses in hippocampus

Brain is continuously altered in response to experience and environmental changes. One of the underlying mechanisms is synaptic plasticity, which is manifested by modification of synapse structure and function. It is becoming clear that regulated extracellular proteolysis plays a pivotal role in the structural and functional remodeling of synapses during brain development, learning and memory formation. Clearly, plasticity mechanisms may substantially differ between projections. Mossy fiber synapses onto CA3 pyramidal cells display several unique functional features, including pronounced short-term facilitation, a presynaptically expressed long-term potentiation (LTP) that is independent of NMDAR activation, and NMDA-dependent metaplasticity. Moreover, structural plasticity at mossy fiber synapses ranges from the reorganization of projection topology after hippocampus-dependent learning, through intrinsically different dynamic properties of synaptic boutons to pre- and postsynaptic structural changes accompanying LTP induction. Although concomitant functional and structural plasticity in this pathway strongly suggests a role of extracellular proteolysis, its impact only starts to be investigated in this projection. In the present report, we review the role of extracellular proteolysis in various aspects of synaptic plasticity in hippocampal mossy fiber synapses. A growing body of evidence demonstrates that among perisynaptic proteases, tissue plasminogen activator (tPA)/plasmin system, β-site amyloid precursor protein-cleaving enzyme 1 (BACE1) and metalloproteinases play a crucial role in shaping plastic changes in this projection. We discuss recent advances and emerging hypotheses on the roles of proteases in mechanisms underlying mossy fiber target specific synaptic plasticity and memory formation.

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

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

Impact of methamphetamine on infection and immunity

The prevalence of methamphetamine (METH) use is estimated at ~35 million people worldwide, with over 10 million users in the United States. METH use elicits a myriad of social consequences and the behavioral impact of the drug is well understood. However, new information has recently emerged detailing the devastating effects of METH on host immunity, increasing the acquisition of diverse pathogens and exacerbating the severity of disease. These outcomes manifest as modifications in protective physical and chemical defenses, pro-inflammatory responses, and the induction of oxidative stress pathways. Through these processes, significant neurotoxicities arise, and, as such, chronic abusers with these conditions are at a higher risk for heightened consequences. METH use also influences the adaptive immune response, permitting the unrestrained development of opportunistic diseases. In this review, we discuss recent literature addressing the impact of METH on infection and immunity, and identify areas ripe for future investigation.

Matrix Metalloproteinase-8 is a Novel Pathogenetic Factor in Focal Cerebral Ischemia

The neutrophil collagenase matrix metalloproteinase-8 (MMP8) is a recently identified member of MMPs that have important roles in various inflammation-related disorders. Previously, we identified MMP8 as a new neuroinflammatory mediator in activated microglia by regulating TNF-α productivity. Here, we present evidence that MMP8 is a critical factor for brain damage in transient focal cerebral ischemia by modulating neuroinflammation likely microglial activation and TNF-α production. Biochemical analyses showed upregulation of MMP8 expression at mRNA and protein levels in transient middle cerebral artery occlusion/reperfusion (M/R)-challenged brains. Furthermore, double immunolabeling showed that MMP8 expression was upregulated in the activated microglia of M/R-challenged brains. Assessment of infarct volume, neurological score, and survival/death of neural cells revealed that administration of an MMP8 inhibitor (M8I) immediately after reperfusion reduced brain damage. Histological analyses showed that microglial activation and TNF-α expression in ischemic conditions was abrogated by exposure to M8I, as demonstrated in our previous study using cultured microglia. These outcomes from a pharmacological approach were reaffirmed by a genetic approach using a lentiviral system. Intracerebroventricular microinjection of MMP8-specific shRNA lentivirus reduced the extent of ischemia-induced brain damage, as assessed by infarct volume, neurological score, microglial activation, and TNF-α expression. These results suggest a novel pathogenetic role of MMP8 and implicate modulation of its activity as a tractable strategy for therapies against cerebral ischemia.

Relationship of gelatinases-tight junction proteins and blood-brain barrier permeability in the early stage of cerebral ischemia and reperfusion

Gelatinases matrix metalloproteinase-2 and matrix metalloproteinase-9 have been shown to mediate claudin-5 and occludin degradation, and play an important regulatory role in blood-brain barrier permeability. This study established a rat model of 1.5-hour middle cerebral artery occlusion with reperfusion. Protein expression levels of claudin-5 and occludin gradually decreased in the early stage of reperfusion, which corresponded to the increase of the gelatinolytic activity of matrix metalloproteinase-2 and matrix metalloproteinase-9. In addition, rats that received treatment with matrix metalloproteinase inhibitor N-[(2R)-2-(hydroxamidocarbonylmethyl)-4-methylpenthanoyl]-L-tryptophan methylamide (GM6001) showed a significant reduction in Evans blue leakage and an inhibition of claudin-5 and occludin protein degradation in striatal tissue. These data indicate that matrix metalloproteinase-2 and matrix metalloproteinase-9-mediated claudin-5 and occludin degradation is an important reason for blood-brain barrier leakage in the early stage of reperfusion. The leakage of the blood-brain barrier was present due to gelatinases-mediated degradation of claudin-5 and occludin proteins. We hypothesized that the timely closure of the structural component of the blood-brain barrier (tight junction proteins) is of importance.

Neuroprotection by the PARP inhibitor PJ34 modulates cerebral and circulating RAGE levels in rats exposed to focal brain ischemia

The receptor for advanced glycation end products (RAGE) has a potential role as a damage-sensing molecule; however, to date, its involvement in the pathophysiology of stroke and its modulation following neuroprotective treatment are not completely understood. We have previously demonstrated that expression of distinct RAGE isoforms, recognized by different antibodies, is differentially modulated in the brain of rats subjected to focal cerebral ischemia. Here, we focus on the full-length membrane-bound RAGE isoform, showing that its expression is significantly elevated in the striatum, whereas it is reduced in the cortex of rats subjected to transient middle cerebral artery occlusion (MCAo). Notably, the reduction of cortical levels of full-length RAGE detected 24 h after reperfusion is abolished by systemic administration of a neuroprotective dose of the poly(ADP-ribose) polymerase (PARP) inhibitor, N-(6-oxo-5,6-dihydrophenanthridin-2-yl)-N,N-dimethylacetamide (PJ34). More interestingly, a significant reduction of plasma soluble RAGE (sRAGE) occurs 24 h after reperfusion and this effect is reverted by a neuroprotective dose of PJ34. Soluble forms of RAGE, generated either by alternative splicing or by proteolysis of the full-length form, effectively bind advanced glycation end products, thereby competing with the cell surface full-length RAGE, thus providing a 'decoy' function that may counteract the adverse effects of receptor signaling in neurons and may possibly exert cytoprotective effects. Thus, our data confirm the important role of RAGE in ischemic cerebral damage and, more interestingly, suggest the potential use of sRAGE as a blood biomarker of stroke severity and of neuroprotective treatment efficacy.

Combination approaches to attenuate hemorrhagic transformation after tPA thrombolytic therapy in patients with poststroke hyperglycemia/diabetes

To date, tissue type plasminogen activator (tPA)-based thrombolytic stroke therapy is the only FDA-approved treatment for achieving vascular reperfusion and clinical benefit, but this agent is given to only about 5% of stroke patients in the USA. This may be related, in part, to the elevated risk of symptomatic intracranial hemorrhage, and consequently limited therapeutic time window. Clinical investigations demonstrate that poststroke hyperglycemia is one of the most important risk factors that cause intracerebral hemorrhage and worsen neurological outcomes. There is a knowledge gap in understanding the underlying molecular mechanisms, and lack of effective therapeutics targeting the severe complication. This short review summarizes clinical observations and experimental investigations in preclinical stroke models of the field. The data strongly suggest that interactions of multiple pathogenic factors including hyperglycemia-mediated vascular oxidative stress and inflammation, ischemic insult, and tPA neurovascular toxicity in concert contribute to the BBB damage-intracerebral hemorrhagic transformation process. Development of combination approaches targeting the multiple pathological cascades may help to attenuate the hemorrhagic complication.

Early reperfusion injury is associated to MMP2 and IL-1β elevation in cortical neurons of rats subjected to middle cerebral artery occlusion

The pathophysiological processes implicated in ischemic brain damage are strongly affected by an inflammatory reaction characterized by activation of immune cells and release of soluble mediators, including cytokines and chemokines. The pro-inflammatory cytokine interleukin (IL)-1β has been implicated in ischemic brain injury, however, to date, the mechanisms involved in the maturation of this cytokine in the ischemic brain have not been completely elucidated. We have previously suggested that matrix metalloproteinases (MMPs) may be implicated in cytokine production under pathological conditions. Here, we demonstrate that significant elevation of IL-1β occurs in the cortex as early as 1h after the beginning of reperfusion in rats subjected to 2-h middle cerebral artery occlusion (MCAo). At this early stage, we observe increased expression of IL-1β in pericallosal astroglial cells and in cortical neurons and this latter signal colocalizes with elevated gelatinolytic activity. By gel zymography, we demonstrate that the increased gelatinolytic signal at 1-h reperfusion is mainly ascribed to MMP2. Thus, MMP2 seems to contribute to early brain elevation of IL-β after transient ischemia and this mechanism may promote damage since pharmacological inhibition of gelatinases by the selective MMP2/MMP9 inhibitor V provides neuroprotection in rats subjected to transient MCAo.

Early inhibition of MMP activity in ischemic rat brain promotes expression of tight junction proteins and angiogenesis during recovery

In cerebral ischemia, matrix metalloproteinases (MMPs) have a dual role by acutely disrupting tight junction proteins (TJPs) in the blood-brain barrier (BBB) and chronically promoting angiogenesis. Since TJP remodeling of the neurovascular unit (NVU) is important in recovery and early inhibition of MMPs is neuroprotective, we hypothesized that short-term MMP inhibition would reduce infarct size and promote angiogenesis after ischemia. Adult spontaneously hypertensive rats had a transient middle cerebral artery occlusion with reperfusion. At the onset of ischemia, they received a single dose of the MMP inhibitor, GM6001. They were studied at multiple times up to 4 weeks with immunohistochemistry, biochemistry, and magnetic resonance imaging (MRI). We observed newly formed vessels in peri-infarct regions at 3 weeks after reperfusion. Dynamic contrast-enhanced MRI showed BBB opening in new vessels. Along with the new vessels, pericytes expressed zonula occludens-1 (ZO-1) and MMP-3, astrocytes expressed ZO-1, occludin, and MMP-2, while endothelial cells expressed claudin-5. The GM6001, which reduced tissue loss at 3 to 4 weeks, significantly increased new vessel formation with expression of TJPs and MMPs. Our results show that pericytes and astrocytes act spatiotemporally, contributing to extraendothelial TJP formation, and that MMPs are involved in BBB restoration during recovery. Early MMP inhibition benefits neurovascular remodeling after stroke.

Carcinoembryonic antigen-related cell adhesion molecule 1 inhibits MMP-9-mediated blood-brain-barrier breakdown in a mouse model for ischemic stroke

RATIONALE

Blood-brain-barrier (BBB) breakdown and cerebral edema result from postischemic inflammation and contribute to mortality and morbidity after ischemic stroke. A functional role for the carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) in the regulation of reperfusion injury has not yet been demonstrated.

OBJECTIVE

We sought to identify and characterize the relevance of CEACAM1-expressing inflammatory cells in BBB breakdown and outcome after ischemic stroke in Ceacam1(-/-) and wild-type mice.

METHODS AND RESULTS

Focal ischemia was induced by temporary occlusion of the middle cerebral artery with a microfilament. Using MRI and Evans blue permeability assays, we observed increased stroke volumes, BBB breakdown and edema formation, reduction of cerebral perfusion, and brain atrophy in Ceacam1(-/-) mice. This translated into poor performance in neurological scoring and high poststroke-associated mortality. Elevated neutrophil influx, hyperproduction, and release of neutrophil-related matrix metalloproteinase-9 in Ceacam1(-/-) mice were confirmed by immune fluorescence, flow cytometry, zymography, and stimulation of neutrophils. Importantly, neutralization of matrix metalloproteinase-9 activity in Ceacam1(-/-) mice was sufficient to alleviate stroke sizes and improve survival to the level of CEACAM1-competent animals. Immune histochemistry of murine and human poststroke autoptic brains congruently identified abundance of CEACAM1(+)matrix metalloproteinase-9(+) neutrophils in the ischemic hemispheres.

CONCLUSIONS

CEACAM1 controls matrix metalloproteinase-9 secretion by neutrophils in postischemic inflammation at the BBB after stroke. We propose CEACAM1 as an important inhibitory regulator of neutrophil-mediated tissue damage and BBB breakdown in focal cerebral ischemia.

DIDS prevents ischemic membrane degradation in cultured hippocampal neurons by inhibiting matrix metalloproteinase release

During stroke, cells in the infarct core exhibit rapid failure of their permeability barriers, which releases ions and inflammatory molecules that are deleterious to nearby tissue (the penumbra). Plasma membrane degradation is key to penumbral spread and is mediated by matrix metalloproteinases (MMPs), which are released via vesicular exocytosis into the extracellular fluid in response to stress. DIDS (4,4′-diisothiocyanatostilbene-2,2′-disulphonic acid) preserves membrane integrity in neurons challenged with an in vitro ischemic penumbral mimic (ischemic solution: IS) and we asked whether this action was mediated via inhibition of MMP activity. In cultured murine hippocampal neurons challenged with IS, intracellular proMMP-2 and -9 expression increased 4–10 fold and extracellular latent and active MMP isoform expression increased 2–22 fold. MMP-mediated extracellular gelatinolytic activity increased ∼20–50 fold, causing detachment of 32.1±4.5% of cells from the matrix and extensive plasma membrane degradation (>60% of cells took up vital dyes and >60% of plasma membranes were fragmented or blebbed). DIDS abolished cellular detachment and membrane degradation in neurons and the pathology-induced extracellular expression of latent and active MMPs. DIDS similarly inhibited extracellular MMP expression and cellular detachment induced by the pro-apoptotic agent staurosporine or the general proteinase agonist 4-aminophenylmercuric acetate (APMA). Conversely, DIDS-treatment did not impair stress-induced intracellular proMMP production, nor the intracellular cleavage of proMMP-2 to the active form, suggesting DIDS interferes with the vesicular extrusion of MMPs rather than directly inhibiting proteinase expression or activation. In support of this hypothesis, an antagonist of the V-type vesicular ATPase also inhibited extracellular MMP expression to a similar degree as DIDS. In addition, in a proteinase-independent model of vesicular exocytosis, DIDS prevented stimulus-evoked release of von Willebrand Factor from human umbilical vein endothelial cells. We conclude that DIDS inhibits MMP exocytosis and through this mechanism preserves neuronal membrane integrity during pathological stress.

Intranuclear matrix metalloproteinases promote DNA damage and apoptosis induced by oxygen-glucose deprivation in neurons

Degradation of the extracellular matrix by elevated matrix metalloproteinase (MMP) activity following ischemia/reperfusion is implicated in blood-brain barrier disruption and neuronal death. In contrast to their characterized extracellular roles, we previously reported that elevated intranuclear MMP-2 and -9 (gelatinase) activity degrades nuclear DNA repair proteins and promotes accumulation of oxidative DNA damage in neurons in rat brain at 3-h reperfusion after ischemic stroke. Here, we report that treatment with a broad-spectrum MMP inhibitor significantly reduced neuronal apoptosis in rat ischemic hemispheres at 48-h reperfusion after a 90-min middle cerebral artery occlusion (MCAO). Since extracellular gelatinases in brain tissue are known to be neurotoxic during acute stroke, the contribution of intranuclear MMP-2 and -9 activities in neurons to neuronal apoptosis has been unclear. To confirm and extend our in vivo observations, oxygen-glucose deprivation (OGD), an in vitro model of ischemia/reperfusion, was employed. Primary cortical neurons were subjected to 2-h OGD with reoxygenation. Increased intranuclear gelatinase activity was detected immediately after reoxygenation onset and was maximal at 24h, while extracellular gelatinase levels remained unchanged. We detected elevated levels of both MMP-2 and -9 in neuronal nuclear extracts and gelatinase activity in neurons co-localized primarily with MMP-2. We found a marked decrease in PARP1, XRCC1, and OGG1, and decreased PARP1 activity. Pretreatment of neurons with selective MMP-2/9 inhibitor II significantly decreased gelatinase activity and downregulation of DNA repair enzymes, decreased accumulation of oxidative DNA damage, and promoted neuronal survival after OGD. Our results confirm the nuclear localization of gelatinases and their nuclear substrates observed in an animal stroke model, further supporting a novel role for intranuclear gelatinase activity in an intrinsic apoptotic pathway in neurons during acute stroke injury.

Chlorogenic acid ameliorates brain damage and edema by inhibiting matrix metalloproteinase-2 and 9 in a rat model of focal cerebral ischemia

Chlorogenic acid (CGA) has been reported to have various beneficial effects on the cardiovascular and central nervous systems. The purpose of the current study was to investigate whether CGA has protective effects against cerebral ischemia and whether these effects are due to modification of brain edema-related vascular factors. In a rat model of transient middle cerebral artery occlusion (MCAo, 2h of occlusion followed by 22 h of reperfusion), we measured infarct volume and performed behavioral test to evaluate the effects of CGA on brain damage and sensory-motor functional deficits. Brain water content and Evans blue extravasation were measured to evaluate brain edema and blood brain barrier (BBB) damage. Lipid peroxidation (LPO) and the expressions and activities of matrix metalloproteinase (MMP)-2 and MMP-9 were measured to investigate the mechanisms of action. Intraperitoneal injection of CGA (3, 10, and 30 mg/kg) at 0 h and 2h after MCAo dose-dependently reduced infarct volume and sensory-motor functional deficits. It also reduced brain water content and Evans blue extravasation. Mechanistically, CGA reduced LPO and MMPs expressions and activities. These results suggest that CGA reduces brain damage, BBB damage and brain edema by radical scavenging activity and the inhibitory effects on MMP-2 and MMP-9.

Nuclear localization of matrix metalloproteinases

Matrix metalloproteinases (MMPs) were originally identified as matrixin proteases that act in the extracellular matrix. Recent works have uncovered nontraditional roles for MMPs in the extracellular space as well as in the cytosol and nucleus. There is strong evidence that subspecialized and compartmentalized matrixins participate in many physiological and pathological cellular processes, in which they can act as both degradative and regulatory proteases. In this review, we discuss the transcriptional and translational control of matrixin expression, their regulation of intracellular sorting, and the structural basis of activation and inhibition. In particular, we highlight the emerging roles of various matrixin forms in diseases. The activity of matrix metalloproteinases is regulated at several levels, including enzyme activation, inhibition, complex formation and compartmentalization. Most MMPs are secreted and have their function in the extracellular environment. MMPs are also found inside cells, both in the nucleus, cytosol and organelles. The role of intracellular located MMPs is still poorly understood, although recent studies have unraveled some of their functions. The localization, activation and activity of MMPs are regulated by their interactions with other proteins, proteoglycan core proteins and / or their glycosaminoglycan chains, as well as other molecules. Complexes formed between MMPs and various molecules may also include interactions with noncatalytic sites. Such exosites are regions involved in substrate processing, localized outside the active site, and are potential binding sites of specific MMP inhibitors. Knowledge about regulation of MMP activity is essential for understanding various physiological processes and pathogenesis of diseases, as well as for the development of new MMP targeting drugs.

Increased cerebral matrix metalloprotease-9 activity is associated with compromised recovery in the diabetic db/db mouse following a stroke

Diabetes is a major risk factor of stroke and is associated with increased frequency of stroke and a poorer prognosis for recovery. In earlier studies we have utilized type 2 diabetic mouse models of stroke and demonstrated that diabetic db/db and ob/ob mice experience larger infarct volumes and impaired recovery associated with greater infiltration of macrophage following hypoxic-ischemic (H/I) insult than their heterozygous non-diabetic db/+ and ob/+ littermates. To obtain a better understanding of the pathogenesis of the impaired recovery, we have investigated the role of matrix metalloproteases and their endogenous inhibitors in the breakdown of the blood-brain barrier (BBB) following H/I. Diabetic db/db mice showed a significant and more rapid increase in matrix metalloprotease (MMP)-9 mRNA, protein and gelatinolytic activity compared with db/+, which resulted in an increased degradation of occludin and collagen IV and subsequently, an increased BBB permeability and greater infiltration of neutrophils into the infarct area. The expression of the MMPs, especially in the db/+ mice, is preceded by an elevated expression of their endogenous tissue inhibitors of metalloproteases (TIMPs) 1, 2, and 3, whereas in the db/db mice, a lower expression of the TIMPs is associated with greater MMP 3 and 9 expression. These results suggest that an imbalance in the MMPs/TIMPs cascade in the diabetic mouse, particularly MMP-9, results in a greater neutrophil invasion, a compromised BBB and consequently a greater insult.

Matrix metalloproteinases as drug targets in ischemia/reperfusion injury

Deficient blood supply (ischemia) is a common consequence of some surgical procedures and certain pathologies. Once blood circulation is re-established (reperfusion), a complex series of events results in recruitment of inflammatory cells, rearrangement of the extracellular matrix and induction of cell death, which lead to organ dysfunction. Although ischemia/reperfusion (I/R) injury is an important cause of death, there is no effective therapy targeting the molecular mechanism of disease progression. Matrix metalloproteinases (MMPs), which are important regulators of many cellular activities, have a central role in disease progression after I/R injury, as suggested by numerous studies using MMP inhibitors or MMP-deficient mice. Here, we review the involvement of MMP activity in the various processes following I/R injury and the therapeutic potential of MMP inhibition.

Metalloproteinase and stroke infarct size: role for anti-inflammatory treatment?

Deregulation of matrix metalloproteinases (MMPs), the largest class of human proteases, has been implicated in brain damage in both animal and human studies. Some MMPs are elevated after stroke (both in plasma and in brain tissue), and their expression is enhanced by t-PA during thrombolysis related to hemorrhagic transformation events. Although the exact cellular source of MMPs remains unknown, brain endothelium, astrocytes, neurons, and inflammatory-activated cells, such as neutrophils, may release MMP-2, MMP-3, MMP-8, MMP-9, MMP-10, and/or MMP-13. Neurovascular perturbations occurring after stroke lead to blood-brain barrier leakage, edema, hemorrhage, leukocyte infiltration, and progressive inflammatory reactions to brain injury over hours or even days after the initial stroke. Synthesized MMP inhibitors and several compounds used for stroke secondary prevention, such as anti-inflammatory drugs, might decrease MMPs and improve the acute treatment of human brain ischemia without compromising the beneficial effects of matrix plasticity during stroke recovery.

The asparaginyl endopeptidase legumain after experimental stroke

Various proteases in the brain contribute to ischemic brain injury. We investigated the involvement of the asparaginyl endopeptidase legumain after experimental stroke. On the basis of gene array studies and in situ hybridizations, we observed an increase of legumain expression in the peri-infarct area of rats after transient occlusion of the middle cerebral artery (MCAO) for 120 mins with a maximum expression at 24 and 48 h. Immunohistochemical analyses revealed the expression of legumain in Iba1(+) microglial cells and glial fibrillary acidic protein-positive astrocytes of the peri-infarct area in mice after MCAO. Post-stroke recovery was also studied in aged legumain-deficient mice (45 to 58 weeks old). Legumain-deficient mice did not show any differences in physiologic parameters compared with respective littermates before, during MCAO (45 mins), and the subsequent recovery period of 8 days. Moreover, legumain deficiency had no effect on mortality, infarct volume, and the neurologic deficit determined by the rotating pole test, a standardized grip strength test, and the pole test. However, a reduced number of invading CD74(+) cells in the ischemic hemisphere indicates an involvement in post-stroke inflammation. We conclude that legumain is not essential for the functional deficit after MCAO but may be involved in mechanisms of immune cell invasion.

Amphetamine toxicities: classical and emerging mechanisms

The drugs of abuse, methamphetamine and MDMA, produce long-term decreases in markers of biogenic amine neurotransmission. These decreases have been traditionally linked to nerve terminals and are evident in a variety of species, including rodents, nonhuman primates, and humans. Recent studies indicate that the damage produced by these drugs may be more widespread than originally believed. Changes indicative of damage to cell bodies of biogenic and nonbiogenic amine-containing neurons in several brain areas and endothelial cells that make up the blood-brain barrier have been reported. The processes that mediate this damage involve not only oxidative stress but also include excitotoxic mechanisms, neuroinflammation, the ubiquitin proteasome system, as well as mitochondrial and neurotrophic factor dysfunction. These mechanisms also underlie the toxicity associated with chronic stress and human immunodeficiency virus (HIV) infection, both of which have been shown to augment the toxicity to methamphetamine. Overall, multiple mechanisms are involved and interact to promote neurotoxicity to methamphetamine and MDMA. Moreover, the high coincidence of substituted amphetamine abuse by humans with HIV and/or chronic stress exposure suggests a potential enhanced vulnerability of these individuals to the neurotoxic actions of the amphetamines.

Brain plasticity after ischemic episode

Brain plasticity describes the potential of the organ for adaptive changes involved in various phenomena in health and disease. A substantial amount of experimental evidence, received in animal and cell models, shows that a cascade of plastic changes at the molecular, cellular, and tissue levels, is initiated in different regions of the postischemic brain. Underlying mechanisms include neurochemical alterations, functional changes in excitatory and inhibitory synapses, axonal and dendritic sprouting, and reorganization of sensory and motor central maps. Multiple lines of evidence indicate numerous points in which the process of postischemic recovery may be influenced with the aim to restore the full capacity of the brain tissue injured by an ischemic episode.

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.

Detection of in vivo matrix metalloproteinase activity using microdialysis sampling and liquid chromatography/mass spectrometry

Matrix metalloproteinases (MMPs) are a family of endoproteases that break down extracellular matrix and whose upregulation contributes to several diseases. A liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was developed to quantify MMP-1 and MMP-9 substrates and their N-terminal peptide products in samples obtained from implanted microdialysis sampling probes. In vitro studies with purified human MMP-1 and MMP-9 were used to optimize the assay and determine the effectiveness of the local delivery of a broad-spectrum MMP inhibitor, GM 6001. Localized delivery of GM 6001 at 10 microM was sufficient to completely inhibit product formation in vitro. In vivo studies in male Sprague-Dawley rats were performed with microdialysis probes implanted into the subcutaneous tissue. Directly after microdialysis probe implantation, infusions of the MMP-1 and MMP-9 substrates (50 microM each) resulted in recovered product concentrations of approximately 2 microM. During a 50 microM GM 6001 coinfusion with the substrates, a 30% and 25% reduction in product formation for the MMP-1 and MMP-9 substrates was obtained, respectively. Blank dialysates were negative for enzymatic activity that could cleave the MMP substrates. This method allowed for the activity of different MMPs surrounding the microdialysis probe to be observed during in vivo sampling.

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.

Berberine reduces the hypoxic-ischemic insult in rat pup brain

Berberine, an isoquinoline alkaloid extracted from medicinal herbs, has been used as antipyretic, antidiarrheal, bactericide and anti-inflammatory agent. In this study, berberine effects on neuronal damage have been examined. The right carotid artery of seven-day-old rat pups was ligated (ischemic insult), then berberine solution (0.2, 0.5, 1 or 2 mg/kg) was injected intra-peritoneally, and 30 minutes later pups were passed through hypoxic condition with breathing in air containing 10% oxygen and 90% nitrogen(hypoxic insult). The day after that the brains of pups were enucleated for pathologic assessment. Pathologic review of the samples obtained from rats treated with different doses of berberine in comparison with samples from pups treated by normal saline showed that there was a significant reduction of brain injury and edema in the rats treated with berberine. Our study also demonstrates that berberine reduces brain ischemic-hypoxic injury dose-dependently. Therefore, beberine may be considered as useful anti-stroke agent.

Post-ischemic brain damage: pathophysiology and role of inflammatory mediators

Neuroinflammatory mediators play a crucial role in the pathophysiology of brain ischemia, exerting either deleterious effects on the progression of tissue damage or beneficial roles during recovery and repair. Within hours after the ischemic insult, increased levels of cytokines and chemokines enhance the expression of adhesion molecules on cerebral endothelial cells, facilitating the adhesion and transendothelial migration of circulating neutrophils and monocytes. These cells may accumulate in the capillaries, further impairing cerebral blood flow, or extravasate into the brain parenchyma. Infiltrating leukocytes, as well as resident brain cells, including neurons and glia, may release pro-inflammatory mediators, such as cytokines, chemokines and oxygen/nitrogen free radicals that contribute to the evolution of tissue damage. Moreover, recent studies have highlighted the involvement of matrix metalloproteinases in the propagation and regulation of neuroinflammatory responses to ischemic brain injury. These enzymes cleave protein components of the extracellular matrix such as collagen, proteoglycan and laminin, but also process a number of cell-surface and soluble proteins, including receptors and cytokines such as interleukin-1beta. The present work reviewed the role of neuroinflammatory mediators in the pathophysiology of ischemic brain damage and their potential exploitation as drug targets for the treatment of cerebral ischemia.

Matrix metalloproteinase-13 is activated and is found in the nucleus of neural cells after cerebral ischemia

Matrix metalloproteinases (MMPs) have been implicated in the pathophysiology of ischemic stroke. In this study, we investigated the time course of gelatinolytic activation in a rat model of permanent ischemia. We observed an activation of MMPs as early as 30 mins after the ischemic insult, mainly in the nuclei of brain cells. Besides, we explored MMP-13 expression in brain samples of the animal model and stroke deceased patients. We observed an upregulation of active MMP-13 in rat brains (P<0.05) after 90 mins of cerebral ischemia. Human infarct/periinfarct samples also showed higher levels of active MMP-13 (P<0.05) compared with contralateral ones. Interestingly, we found that MMP-13 colocalized with 46-diamidino-2-phenyl indole signal by immunohistochemistry in both humans and rats, suggesting an intranuclear localization for MMP-13. Immunohistochemistry also revealed that MMP-13 was mainly produced by neurons, in both species, but also by oligodendrocytes in rats, and by astrocytes in humans. Finally we subjected a rat primary neuronal culture to oxygen and glucose deprivation (OGD) and we reproduced the nuclear translocation of MMP-13 in vitro. Nuclear extracts from cells confirmed upregulation of active MMP-13 after OGD (P<0.05). These results suggest that MMP-13 activation and its nuclear translocation is an early consequence of an ischemic stimulus.

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.