Tissue type plasminogen activator amplifies hemoglobin-induced neurotoxicity in rat neuronal cultures

Mitochondrial Quality and Quantity Control: Mitophagy Is a Potential Therapeutic Target for Ischemic Stroke

Ischemic stroke is a cerebrovascular disease with high mortality and disability, which seriously affects the health and lives of people around the world. Effective treatment for ischemic stroke has been limited by its complex pathological mechanisms. Increasing evidence has indicated that mitochondrial dysfunction plays an essential role in the occurrence, development, and pathological processes of ischemic stroke. Therefore, strict control of the quality and quantity of mitochondria via mitochondrial fission and fusion as well as mitophagy is beneficial to the survival and normal function maintenance of neurons. Under certain circumstances, excessive mitophagy also could induce cell death. This review discusses the dynamic changes and double-edged roles of mitochondria and related signaling pathways of mitophagy in the pathophysiology of ischemic stroke. Furthermore, we focus on the possibility of modulating mitophagy as a potential therapy for the prevention and prognosis of ischemic stroke. Notably, we reviewed recent advances in the studies of natural compounds, which could modulate mitophagy and exhibit neuroprotective effects, and discussed their potential application in the treatment of ischemic stroke.

Metal ion chelation enhances tissue plasminogen activator (tPA)-induced thrombolysis: an in vitro and in vivo study

Stroke is the third leading cause of death in the United States and the leading cause of adult disability. Despite enormous research efforts including many clinical trials, tissue plasminogen activator (tPA) remains the only FDA-approved treatment for acute ischemic stroke. Unfortunately, only 1-3% of stroke patients in the US receive this therapy because of the narrow time window and severe side effects for using tPA. The most deadly and damaging side effect is the risk of intracranial bleeding or hemorrhage. For that reason, the dose of tPA and its overall administration are under tight control, which may compromise the effect of thrombolysis. Studies have been focused on improving the effectiveness of tPA for higher rate of reperfusion, and the safety for less adverse bleeding episode. We studied how metal ions (zinc & iron) affect tPA-induced thrombolysis in vitro and in vivo, and proposed a method to improve the rate of thrombolysis. The amount of hemoglobin in the blood clot lysis was measured by a spectrophotometer. The tPA-induced thrombolysis was measured in vivo in femoral artery. Our results showed that Zn²⁺, Fe³⁺ and Fe²⁺ inhibited tPA-induced thrombolysis, with Zn²⁺ and Fe²⁺ being the most effective. Metal ion chelating agent EDTA when it was co-applied with tPA significantly enhanced the tPA-induced thrombolysis. The chelation alone did not have noticeable thrombolytic effect. In in vivo study of tPA-induced thrombosis following femoral artery thrombosis, the co-application of tPA and EDTA achieved significant higher rate of reperfusion than that by tPA treatment alone, suggesting that ion chelation facilitates tPA-induced thrombolysis and potentially improves the safety of tPA application by reducing the necessary dose of tPA application. Our results suggest that the co-application of a chelator and tPA improves the efficacy and, potentially, safety of tPA application, by reducing the necessary dose of tPA for thrombolysis.

New insights into targeting mitochondria in ischemic injury

Stroke is the leading cause of adult disability and death worldwide. Mitochondrial dysfunction has been recognized as a marker of neuronal death during ischemic stroke. Maintaining the function of mitochondria is important for improving the survival of neurons and maintaining neuronal function. Damaged mitochondria induce neuronal cell apoptosis by releasing reactive oxygen species (ROS) and pro-apoptotic factors. Mitochondrial fission and fusion processes and mitophagy are of great importance to mitochondrial quality control. This paper reviews the dynamic changes in mitochondria, the roles of mitochondria in different cell types, and related signaling pathways in ischemic stroke. This review describes in detail the role of mitochondria in the process of neuronal injury and protection in cerebral ischemia, and integrates neuroprotective drugs targeting mitochondria in recent years, which may provide a theoretical basis for the progress of treatment of ischemic stroke. The potential of mitochondrial-targeted therapy is also emphasized, which provides valuable insights for clinical research.

NAD replenishment with nicotinamide mononucleotide protects blood-brain barrier integrity and attenuates delayed tissue plasminogen activator-induced haemorrhagic transformation after cerebral ischaemia

BACKGROUND AND PURPOSE

Tissue plasminogen activator (tPA) is the only approved pharmacological therapy for acute brain ischaemia; however, a major limitation of tPA is the haemorrhagic transformation that follows tPA treatment. Here, we determined whether nicotinamide mononucleotide (NMN), a key intermediate of nicotinamide adenine dinucleotide biosynthesis, affects tPA-induced haemorrhagic transformation.

EXPERIMENTAL APPROACH

Middle cerebral artery occlusion (MCAO) was achieved in CD1 mice by introducing a filament to the left MCA for 5 h. When the filament was removed for reperfusion, tPA was infused via the tail vein. A single dose of NMN was injected i.p. (300 mg·kg^-1 ). Mice were killed at 24 h post ischaemia, and their brains were evaluated for brain infarction, oedema, haemoglobin content, apoptosis, neuroinflammation, blood-brain barrier (BBB) permeability, the expression of tight junction proteins (TJPs) and the activity/expression of MMPs.

KEY RESULTS

In the mice infused with tPA at 5 h post ischaemia, there were significant increases in mortality, brain infarction, brain oedema, brain haemoglobin level, neural apoptosis, Iba-1 staining (microglia activation) and myeloperoxidase staining (neutrophil infiltration). All these tPA-induced alterations were significantly prevented by NMN administration. Mechanistically, the delayed tPA treatment increased BBB permeability by down-regulating TJPs, including claudin-1, occludin and zonula occludens-1, and enhancing the activities and protein expression of MMP9 and MMP2. Similarly, NMN administration partly blocked these tPA-induced molecular changes.

CONCLUSIONS AND IMPLICATIONS

Our results demonstrate that NMN ameliorates tPA-induced haemorrhagic transformation in brain ischaemia by maintaining the integrity of the BBB.

Initial multicenter technical experience with the Apollo device for minimally invasive intracerebral hematoma evacuation

BACKGROUND

No conventional surgical intervention has been shown to improve outcomes for patients with spontaneous intracerebral hemorrhage (ICH) compared with medical management.

OBJECTIVE

We report the initial multicenter experience with a novel technique for the minimally invasive evacuation of ICH using the Penumbra Apollo system (Penumbra Inc, Alameda, California).

METHODS

Institutional databases were queried to perform a retrospective analysis of all patients who underwent ICH evacuation with the Apollo system from May 2014 to September 2014 at 4 centers (Medical University of South Carolina, Stony Brook University, University of California at San Diego, and Semmes-Murphy Clinic). Cases were performed either in the neurointerventional suite, operating room, or in a hybrid operating room/angiography suite.

RESULTS

Twenty-nine patients (15 female; mean age, 62 ± 12.6 years) underwent the minimally invasive evacuation of ICH. Six of these parenchymal hemorrhages had an additional intraventricular hemorrhage component. The mean volume of ICH was 45.4 ± 30.8 mL, which decreased to 21.8 ± 23.6 mL after evacuation (mean, 54.1 ± 39.1% reduction; P < .001). Two complications directly attributed to the evacuation attempt were encountered (6.9%). The mortality rate was 13.8% (n = 4).

CONCLUSION

Minimally invasive evacuation of ICH and intraventricular hemorrhage can be achieved with the Apollo system. Future work will be required to determine which subset of patients are most likely to benefit from this promising technology.

Impacts of tissue-type plasminogen activator (tPA) on neuronal survival

Tissue-type plasminogen activator (tPA) a serine protease is constituted of five functional domains through which it interacts with different substrates, binding proteins, and receptors. In the last years, great interest has been given to the clinical relevance of targeting tPA in different diseases of the central nervous system, in particular stroke. Among its reported functions in the central nervous system, tPA displays both neurotrophic and neurotoxic effects. How can the protease mediate such opposite functions remain unclear but several hypotheses have been proposed. These include an influence of the degree of maturity and/or the type of neurons, of the level of tPA, of its origin (endogenous or exogenous) or of its form (single chain tPA versus two chain tPA). In this review, we will provide a synthetic snapshot of our current knowledge regarding the natural history of tPA and discuss how it sustains its pleiotropic functions with focus on excitotoxic/ischemic neuronal death and neuronal survival.

Timing of recanalization and outcome in ischemic-stroke patients treated with recombinant tissue plasminogen activator

BACKGROUND

Intravenous administration of recombinant tissue plasminogen activator (rtPA) is approved treatment for acute ischemic stroke <3 h of symptom onset.

PURPOSE

To determine the impact of the timing and degree of recanalization on clinical outcome after rtPA infusion in patients.

MATERIAL AND METHODS

Seventy-five patients with ischemic stroke in the middle cerebral artery territory treated with intravenous rtPA within 3 h were studied consecutively. Magnetic resonance imaging (MRI), including magnetic resonance angiography (MRA), before, 6 h, and 24 h after thrombolytic therapy was undertaken. Depending on the MRA results acquired 6 h after rtPA infusion, recanalization was graded as: early recanalization (ER), delayed recanalization (DR), and no recanalization (NR). Clinical outcome was assessed using the National Institutes of Health Stroke Scale (NIHSS) and modified Rankin Scale (mRS).

RESULTS

Of patients in the ER, DR and NR groups, 71.4% (15/21), 13.3% (2/15), and 30.7% (12/39), respectively, showed dramatic improvement in NIHSS score 7 days after rtPA administration compared with those scores upon hospital admission. The 6-h and 24-h NIHSS scores and 3-month mRS scores of ER patients were significantly lower than those of the other two groups (P < 0.05). The 24-h, 7-d NHISS and mRS scores of DR patients were significantly higher than NR patients (P = 0.001, 0.002, 0.049, respectively). Three patients in the DR group died during follow-up.

CONCLUSION

These data suggest that DR is associated with clinical deterioration. Patients treated with rtPA thrombolysis should be under close observation for 6-24 h. Corresponding treatment should be considered once DR appears.

Tissue plasminogen activator induced delayed edema in experimental porcine intracranial hemorrhage: reduction with plasminogen activator inhibitor-1 administration

Hematoma puncture and subsequent clot lysis with recombinant tissue plasminogen activator (rtPA) emerged as an alternative therapy for spontaneous intracerebral hemorrhage (ICH) and is associated with delayed edema possibly counteracting the beneficial effects of hematoma volume reduction. We hypothesized that immediate reversal of rtPA activity after clot lysis and hematoma drainage diminishes edema formation. To test this hypothesis, we administered plasminogen activator inhibitor (PAI)-1 after rtPA lysis of experimentally induced ICH. A right frontal ICH was placed through a twist drill burr hole and autologous blood injection. Following creation of the frontal ICH, pigs received no further treatment (n = 5), lysis with rtPA (n = 7), or lysis with rtPA followed by administration of PAI-1 (n = 6). Hematoma and edema volumes were assessed with magnetic resonance imaging on days 0, 4, and 10. The rtPA significantly reduced hematoma volume and contributed to edema on day 10 after experimentally induced ICH. Administration of PAI-1 attenuated the rtPA-induced edema volume on day 10, but the hematoma volume reduction was less pronounced. In conclusion, PAI-1 attenuated delayed cerebral edema after rtPA lysis of experimental ICH but also reduced the lytic activity of rtPA. The combination of rtPA clot lysis with PAI-1 might have the potential to further improve the effect of the lytic therapy of ICH, but additional studies to define the optimum time point for PAI-1 administration are required.

Stachybotrys microspora triprenyl phenol-7, a novel fibrinolytic agent, suppresses superoxide production, matrix metalloproteinase-9 expression, and thereby attenuates ischemia/reperfusion injury in rat brain

Stachybotrys microspora triprenyl phenol-7 (SMTP-7) is a novel fibrinolytic agent with anti-inflammatory effect. Previous study demonstrated that SMTP-7 further ameliorated infarction volume in a mouse embolic stroke model compared with tissue type plasminogen activator (tPA), but the reason SMTP-7 has more beneficial effect than tPA has not yet been determined. In the present study, we investigated whether SMTP-7 has an intrinsic neuroprotective effect against transient focal cerebral ischemia (tFCI). Sprague-Dawley rats were subjected to tFCI by intraluminal middle cerebral artery occlusion for 2h. Following induction of tFCI, rats were randomized into two groups based on the agent administered: SMTP-7 group and vehicle group. We examined cerebral infarction volume 24h after reperfusion, and evaluated superoxide production, the expressions of nitrotyrosine and matrix metalloproteinase-9 (MMP-9), which play major roles in secondary brain injury and hemorrhagic transformation. The findings showed that SMTP-7 significantly suppressed superoxide production, the expression of nitrotyrosine and MMP-9 after tFCI, and consequently attenuated ischemic neuronal damage. These results suggest that SMTP-7 has an intrinsic neuroprotective effect on ischemia/reperfusion injury through the suppression of oxidative stress and MMP-9 activation.

Annexin A2 combined with low-dose tPA improves thrombolytic therapy in a rat model of focal embolic stroke

Recent studies showed that soluble annexin A2 dramatically increases tissue plasminogen activator (tPA)-mediated plasmin generation in vitro, and reduces thrombus formation in vivo. Here, we hypothesize that combining annexin A2 with tPA can significantly enhance thrombolysis efficacy, so that lower doses of tPA can be applied in ischemic stroke to avoid neurotoxic and hemorrhagic complications. In vitro activity assays confirmed tPA-specific amplification of plasmin generation by recombinant annexin A2. In a rat focal embolic stroke model, combination therapy with tPA and recombinant annexin A2 protein at 2 h post-ischemia decreased the effective dose required for tPA by four-fold and reduced brain infarction. Combining annexin A2 with tPA also lengthened the time window for thrombolysis. Compared with tPA (10 mg/kg) alone, the combination of annexin A2 (5 mg/kg) plus low-dose tPA (2.5 mg/kg) significantly enhanced fibrinolysis, attenuated mortality, brain infarction, and hemorrhagic transformation, even when administered at 4 h post-ischemia. Combination with recombinant annexin A2, the effective thrombolytic dose of tPA can be decreased. As a result, brain hemorrhage and infarction are reduced, and the time window for stroke reperfusion prolonged. Our present findings provide a promising new approach for enhancing tPA-based thrombolytic stroke therapy.

G-CSF, rt-PA and combination therapy after experimental thromboembolic stroke

Background

Granulocyte Colony-Stimulating Factor (G-CSF) has remarkable neuroprotective properties. Due to its proven safety profile, G-CSF is currently used in clinical stroke trials. As neuroprotectants are considered to be more effective in the early phase of cerebral ischemia and during reperfusion, G-CSF should to be tested in combination with thrombolysis. Therefore, combination therapy was investigated in an experimental model of thromboembolic stroke.

Methods

Male Wistar rats (n = 72) were subjected to a model of thromboembolic occlusion (TE) of the middle cerebral artery. Different groups (n = 12 each) treated by recombinant tissue-plasminogen activator (rt-PA) or/and G-CSF: group control (control), group early G-CSF (G-CSF 60 min after TE), group rt-PA (rt-PA 60 min after TE), group com (combination rt-PA/G-CSF), group delayed rt-PA (rt-PA after 180 min), group deco (G-CSF after 60 min, rt-PA after 180 min). Animals were investigated by magnetic resonance imaging (MRI) and silver infarct staining (SIS) 24 hours after TE.

Results

Early G-CSF or rt-PA reduced the infarct size compared to all groups (p < 0.05 to p < 0.01) with the exception of group com, (p = n.s.) as measured by T2, DWI, and SIS. Late administration of rt-PA lead to high mortality and larger infarcts compared to all other groups (p < 0.05 to p < 0.01). Pre-treatment by G-CSF (deco) reduced infarct site compared to delayed rt-PA treatment (p < 0.05). G-CSF did not significantly influence PWI when combined with rt-PA. All animals treated by rt-PA showed improved parameters in PWI indicating reperfusion.

Conclusions

G-CSF was neuroprotective when given early after TE. Early combination with rt-PA showed no additional benefit compared to rt-PA or G-CSF alone, but did not lead to side effects. Pretreatment by G-CSF was able to reduce deleterious effects of late rt-PA treatment.

Mechanistic insight into neurotoxicity of tissue plasminogen activator-induced thrombolysis products in a rat intraluminal middle cerebral artery occlusion model

Thrombolytic therapy with recombinant tissue plasminogen activator (rtPA) after ischemic stroke is effective. However, rtPA potentiates neuronal damage, and interactions between rtPA and thrombolysis products (TLP) have been reported to play a role in this. In the present study we investigated the mechanisms underlying rtPA- and TLP-induced neurotoxicity. Adult male Sprague-Dawley rats were subjected to 60-min intraluminal middle cerebral artery (MCA) occlusion, and then treated with rtPA (10 mg/kg), TLP, or saline. To evaluate the effects of a free radical scavenger, treatment with edaravone and TLP was evaluated. To investigate the role of red blood cells (RBCs), RBC-depleted TLP was used. Neurological deficit scores, infarct volume, and immuno-histochemical localization of oxidative end products for lipid and DNA (4-hydroxy-2-nonenal [4-HNE] and 8-hydroxy-deoxyguanosine [8-OHdG]) were evaluated. TLP increased the infarct volume, worsened the neurological deficits, and increased accumulations of 4-HNE and 8-OHdG. Edaravone treatment significantly reduced the lesion volume and improved the neurological score. Both infarct volume and accumulation of oxidative products were significantly suppressed when RBC-depleted TLP was used. In this mechanical model of MCA occlusion, rtPA-induced TLP, especially in the presence of RBCs, contributed to neuronal damage by accelerating free radical injury.

The cytotoxic effect of bromoenol lactone, a calcium-independent phospholipase A2 inhibitor, on rat cortical neurons in culture

This study characterized the phospholipase A(2) (PLA(2)) activity in cerebral cortex of fetal rat brain and investigated effects of chemical inhibition of Ca(2+)-independent PLA(2) (iPLA(2)) on neurite outgrowth and cell development of cortical neurons in vitro. The PLA(2) activity in fetal brain was insensitive to a Ca(2+)-chelator EGTA and was significantly impaired by an iPLA(2) inhibitor, bromoenol lactone (BEL). Following treatment with BEL, cortical neurons showed acute loss of neurites and impaired cell body, which were clearly dose- and time-dependent. Nuclear staining revealed nuclear regression (shrinkage), but not fragmentation, in BEL-treated cells. The cytotoxic effect of BEL was additive with arachidonic acid (AA) and AA alone also induced neurite demise. BEL treatment resulted in increased production of prostaglandin E(2). Overall data suggest that iPLA(2), a primary PLA(2) isoform in cerebral cortex, displays a housekeeping role in development and neurite outgrowth in cortical neurons in vitro probably via maintaining phospholipid membrane remodeling rather than generating free fatty acids and lysophospholipids.

Novel actions of tissue-type plasminogen activator in chronic kidney disease

Tissue-type plasminogen activator (tPA) is traditionally viewed as a simple serine protease whose main function is to convert plasminogen into biologically active plasmin. As a protease, tPA plays a crucial role in regulating blood fibrinolysis, in maintaining the homeostasis of extracellular matrix and in modulating the post-translational activation of growth factors. However, emerging evidence indicates that tPA also functions as a cytokine that transmits its signal across the cell membrane, initiates a diverse array of intracellular signaling, and dictates gene expression in the nuclei. tPA binds to the cell membrane LDL receptor-related protein 1 (LRP-1), triggers its tyrosine phosphorylation. As a cytokine, tPA plays a pivotal role in the pathogenesis of renal interstitial fibrosis through diverse mechanisms. It facilitates tubular epithelial to mesenchymal transition, potentiates myofibroblast activation, and protects renal interstitial fibroblasts/myofibroblasts from apoptosis. Together, growing evidence has implicated tPA as a fibrogenic cytokine that promotes the progression of kidney diseases. These new findings have radically changed our conception of tPA in renal fibrogenesis and represent a paradigm shift towards uncovering its cytokine function.

Tissue-type plasminogen activator as a therapeutic target in stroke

BACKGROUND

Ischemic stroke is a leading cause of morbidity and mortality worldwide and recombinant human tissue-type plasminogen activator (tPA) is the prominent therapeutic among very few therapeutics used in its treatment. Due to complications attributed to the drug, most notably transformation of ischemia to hemorrhage, tPA is only used in a small number of ischemic stroke cases, albeit significantly more often in specialized stroke centers.

OBJECTIVE

What are the mechanisms of tPA action and side effects in ischemic stroke, and can the knowledge about these mechanisms aid in making tPA a more efficacious and safe therapeutic or in developing alternative therapeutics?

METHODS

tPA use and alternative/combination therapies in acute ischemic stroke treatment are summarized. The review focuses on literature concerning tPA neurotoxicity and its implications for further development of tPA as a stroke therapeutic.

RESULTS/CONCLUSION

Exogenously administered recombinant tPA and endogenous tPA have both turned into promising therapeutic targets for the stroke patient.

Enhanced poly(ADP-ribose) polymerase-1 activation contributes to recombinant tissue plasminogen activator-induced aggravation of ischemic brain injury in vivo

Recombinant tissue plasminogen activator (rt-PA) treatment improves functional outcome after acute ischemic stroke, inducing reperfusion by its thrombolytic activity. Conversely, there is evidence that rt-PA can mediate neuronal damage after ischemic brain injury in vivo. In addition to other mechanisms, enhancement of N-methyl-D-aspartate (NMDA) receptor signalling has been proposed to underlie rt-PA-mediated neurotoxicity. However, the role of poly(ADP-ribose) polymerase-1 (PARP-1) activation, which mediates postischemic excitotoxic cell death, in rt-PA-mediated aggravation of ischemic brain injury has not been established and was therefore addressed in this study. After permanent focal cerebral ischemia, intravenous rt-PA application significantly increased early postischemic PARP-1 activation within ischemic hemispheres and infarct volumes compared with control mice without affecting cerebral blood flow. Rt-PA induced increase in PARP-1 activation, and infarct volumes could be blocked by the PARP inhibitor 3-aminobenzamide. Moreover, the rt-PA-induced increase in PARP-1 activation was also prevented by the NMDA antagonist MK-801. In summary, we demonstrate that rt-PA treatment enhances postischemic PARP-1 activation, which contributes to rt-PA induced aggravation of ischemic brain injury in vivo. Furthermore, we provide evidence that NMDA receptor activation is required for rt-PA-mediated effects on postischemic PARP-1 activation.

Addition of intravenous N-methyl-D-aspartate receptor antagonists to local fibrinolytic therapy for the optimal treatment of experimental intracerebral hemorrhages

OBJECT

Fibrinolytic therapy with recombinant tissue plasminogen activator (rtPA) is considered a treatment option in patients with deep-seated intracerebral hemorrhage (ICH). Nevertheless, the results of animal experiments have shown that tPA exerts pleiotropic actions in the brain, including regulation of vasoactivity, amplification of calcium conductance by cleavage of the N-methyl-D-aspartate (NMDA) receptor subunit, and activation of metalloproteinases, which increase excitotoxicity, damage the blood-brain barrier, and worsen edema. The authors investigated whether the noncompetitive NMDA receptor antagonist MK801 can be used as an adjuvant therapy in combination with rtPA to attenuate the unfavorable delayed edema formation and inflammation observed following rtPA therapy in an experimental porcine model of ICH.

METHODS

Twenty pigs were used in this study; MK801 (0.3 mg/kg) was administered to each pig intravenously immediately after hematoma induction and on the 1st and 3rd day after hematoma induction. Ten of the 20 pigs were randomly assigned to fibrinolytic therapy with rtPA (MK801-tPA group), whereas in the remaining 10 control animals (MK801 group) the hematomas were allowed to follow their natural courses of resorption. The extent of edema formation was evaluated using magnetic resonance (MR) imaging volumetry on Days 0, 4, and 10 after hematoma induction and was compared with histopathological changes found at necropsy. The mean edema volumes in these two groups were also compared with that in the group of nine pigs examined in a preceding experimental series, in which the animals' hematomas were only treated with rtPA (tPA group). In the 10 animals in the MK801-tPA group, the mean perihematoma edema volume on MR images had not significantly increased by Day 4 (p < 0.08) or Day 10 (p < 0.35) after hematoma induction. In the 10 animals in the MK801 group, the increase in mean perifocal edema size was significant after 4 days (p < 0.001) and nonsignificant after 10 days (p < 0.09). In the nine animals in the tPA group, the mean edema volume significantly increased by Days 4 (p < 0.002) and 10 (p < 0.03).

CONCLUSIONS

As suggested by the reduction in delayed edema volume and the inflammatory response, MK801 modifies the neurotoxic properties of rtPA but not those of blood degradation products. Possibly, fibrinolytic therapy of ICH is more beneficial if combined with agents such as MK801.

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

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

Serine proteases purified from sera of patients with amyotrophic lateral sclerosis (ALS) induce contrasting cytopathology in murine motoneurones to IgG

Affinity purified IgG from sera of patients with amyotrophic lateral sclerosis (ALS) is claimed to enhance transmitter release, induce apoptotic death of cultured motoneurones, and elicit a distinctive cytopathology with raised Ca(2+) in mouse motoneurones. An alternative hypothesis attributes these events to serine proteases in ALS sera. To test this, motoneurones in BALB/c mice injected intraperitoneally with plasminogen affinity purified from sera of ALS patients and healthy controls were analysed using immunochemical and ultrastructural morphometric methods. The responses were validated in motoneurones of mice injected with commercially purified plasminogen, tissue plasminogen activator (tPA), or plasmin. Motoneurones in non-injected mice had normal morphology and ultrastructure without evidence of electron-dense degeneration. Purified plasminogen from both ALS patients and healthy controls, evoked electron-dense motoneurone degeneration, as did commercially purified plasminogen and tPA. The common cytopathology comprised disruption and distension of Nissl body rough endoplasmic reticulum, cytoplasmic polyribosomal proliferation, and significant Ca(2+) enhancement in mitochondria. By contrast, using affinity purified serum immunoglobulins, ALS-IgG but not IgG from healthy or disease controls, elicited necrosis, with 30% of ALS-IgGs tested evoking electron-dense degeneration in 40% of motoneurones. The primary cytopathology was extensive swelling of Golgi endoplasmic reticulum and mitochondria, with enhancement of Ca(2+) in Golgi endoplasmic reticulum and presynaptic boutons. We conclude that serine proteases purified from sera of ALS patients elicits a distinctive cytopathology and pattern of Ca(2+) enhancement in motoneurones different from that found on passive transfer of affinity purified ALS-IgG.

Memantine reduces hematoma expansion in experimental intracerebral hemorrhage, resulting in functional improvement

Glutamate is accumulated in abundance during the early period of experimental hematoma, and the activation of N-methyl-D-aspartate (NMDA) receptors by glutamate can result in an influx of calcium and neuronal death in cases of intracerebral hemorrhage (ICH). Memantine, which is known to be a moderate-affinity, uncompetitive, NMDA receptor antagonist, was investigated with regard to its ability to block the glutamate overstimulation and tissue plasminogen activator (tPA)/urokinase plasminogen activator (uPA)/matrix metalloproteinase (MMP)-9 modulation in experimental ICH. Intracerebral hemorrhage was induced via the infusion of collagenase into the left basal ganglia of adult rats. Either memantine (20 mg/kg/day) or PBS was intraperitoneally administered 30 min after the induction of ICH, and, at daily intervals afterwards, for either 3 or 14 days. Hemorrhage volume decreased by 47% in the memantine group, as compared with the ICH-only group. In the memantine group, the numbers of TUNEL+, myeloperoxidase (MPO)+, and OX42+ cells decreased in the periphery of the hematoma. Memantine resulted in an upregulation of bcl-2 expression and an inhibition of caspase-3 activation. Memantine also exerted a profound inhibitory effect on the upregulation of tPA/uPA mRNA, and finally decreased the MMP-9 level in the hemorrhagic brain. In modified limb-placing test, the memantine-treated rats exhibited lower scores initially, and recovered more quickly and thoroughly throughout the 35 days of the study. Here, we show that memantine causes a reduction of hematoma expansion, coupled with an inhibitory effect on the tPA/uPA and MMP-9 level. Subsequently, memantine was found to reduce inflammatory infiltration and apoptosis, and was also determined to induce functional recovery after ICH.

Tissue-type plasminogen activator acts as a cytokine that triggers intracellular signal transduction and induces matrix metalloproteinase-9 gene expression

Tissue-type plasminogen activator (tPA), a serine protease well known for generating plasmin, has been demonstrated to induce matrix metalloproteinase-9 (MMP-9) gene expression and protein secretion in renal interstitial fibroblasts. However, exactly how tPA transduces its signal into the nucleus to control gene expression is unknown. This study investigated the mechanism by which tPA induces MMP-9 gene expression. Both wild-type and non-enzymatic mutant tPA were found to induce MMP-9 expression in rat kidney interstitial fibroblasts (NRK-49F), indicating that the actions of tPA are independent of its proteolytic activity. tPA bound to the low density lipoprotein receptor-related protein-1 (LRP-1) in NRK-49F cells, and this binding was competitively abrogated by the LRP-1 antagonist, the receptor-associated protein. In mouse embryonic fibroblasts (PEA-13) lacking LRP-1, tPA failed to induce MMP-9 expression. Furthermore, tPA induced rapid tyrosine phosphorylation on the beta subunit of LRP-1, which was followed by the activation of Mek1 and its downstream Erk-1 and -2. Blockade of Erk-1/2 activation by the Mek1 inhibitor abolished MMP-9 induction by tPA in NRK-49F cells. Conversely, overexpression of constitutively activated Mek1 induced Erk-1/2 phosphorylation and MMP-9 expression. In mouse obstructed kidney, tPA, LRP-1, and MMP-9 were concomitantly induced in the renal interstitium. Collectively, these results suggest that besides its classical proteolytic activity, tPA acts as a cytokine that binds to the cell membrane receptor LRP-1, induces its tyrosine phosphorylation, and triggers intracellular signal transduction, thereby inducing specific gene expression in renal interstitial fibroblasts.

Treatment of intraventricular hemorrhage with intraventricular administration of recombinant tissue plasminogen activator A clinical study of 18 cases

OBJECTIVE

Intraventricular hemorrhage is associated with a very poor outcome. Simple external ventricular drainage alone has not resulted in a decline of mortality. The aim was to study the effect of direct intraventricular administration of recombinant tissue plasminogen activator (rtPA).

PATIENTS AND METHODS

A retrospective series of eighteen adult patients with severe intraventricular hemorrhage, admitted to our university hospital, was studied for the effect of direct intraventricular administration of recombinant tissue plasminogen activator (rtPA). rtPA was administered in a dosage of 2mg. The injection was repeated at 12h intervals until serial CT scans showed a substantial reduction of intraventricular blood.

RESULTS

The total of rtPA doses per patient ranged from 2 to 32mg. Seven out of 18 patients showed good neurological recovery, 4 died. Only one patient had a complication which could be directly attributed to the intraventricular thrombolytic therapy.

CONCLUSION

We conclude that the procedure of intraventricular administration of a thrombolytic agent, i.e. rtPA, seems effective in lysis of the intraventricular hematoma and may, therefore, improve outcome.

Vampire bat salivary plasminogen activator (desmoteplase) inhibits tissue-type plasminogen activator-induced potentiation of excitotoxic injury

BACKGROUND AND PURPOSE

In contrast to tissue-type plasminogen activator (tPA), vampire bat (Desmodus rotundus) salivary plasminogen activator (desmoteplase [DSPA]) does not promote excitotoxic injury when injected directly into the brain. We have compared the excitotoxic effects of intravenously delivered tPA and DSPA and determined whether DSPA can antagonize the neurotoxic and calcium enhancing effects of tPA.

METHODS

The brain striatal region of wild-type c57 Black 6 mice was stereotaxically injected with N-methyl-d-Aspartate (NMDA); 24 hour later, mice received an intravenous injection of tPA or DSPA (10 mg/kg) and lesion size was assessed after 24 hours. Cell death and calcium mobilization studies were performed using cultures of primary murine cortical neurons.

RESULTS

NMDA-mediated injury was increased after intravenous administration of tPA, whereas no additional toxicity was seen after administration of DSPA. Unlike DSPA, tPA enhanced NMDA-induced cell death and the NMDA-mediated increase in intracellular calcium levels in vitro. Moreover, the enhancing effects of tPA were blocked by DSPA.

CONCLUSIONS

Intravenous administration of tPA promotes excitotoxic injury, raising the possibility that leakage of tPA from the vasculature into the parenchyma contributes to brain damage. The lack of such toxicity by DSPA further encourages its use as a thrombolytic agent in the treatment of ischemic stroke.

The neurotoxicity of tissue plasminogen activator?

Tissue plasminogen activator (tPA), a fibrin specific activator for the conversion of plasminogen to plasmin, stimulates thrombolysis and rescues ischemic brain by restoring blood flow. However, emerging data suggests that under some conditions, both tPA and plasmin, which are broad spectrum protease enzymes, are potentially neurotoxic if they reach the extracellular space. Animal models suggest that in severe ischemia with injury to the blood brain barrier (BBB) there is injury attributed to the protease effects of this exogenous tPA. Besides clot lysis per se, tPA may have pleiotropic actions in the brain, including direct vasoactivity, cleaveage of the N-methyl-D-aspartate (NMDA) NR1 subunit, amplification of intracellular Ca++ conductance, and activation of other extracellular proteases from the matrix metalloproteinase (MMP) family, e.g. MMP-9. These effects may increase excitotoxicity, further damage the BBB, and worsen edema and cerebral hemorrhage. If tPA is effective and reverses ischemia promptly, the BBB remains intact and exogenous tPA remains within the vascular space. If tPA is ineffective and ischemia is prolonged, there is the risk that exogenous tPA will injure both the neurovascular unit and the brain. Methods of neuroprotection, which prevent tPA toxicity or additional mechanical means to open cerebral vessels, are now needed.

Can the time window for administration of thrombolytics in stroke be increased?

Level 1 evidence now shows that thrombolysis in cases of acute ischaemic stroke is effective if administered within 3 hours of stroke onset. This benefit has been shown to be time dependent and potentially extends beyond 3 hours, with evidence that potentially viable penumbral tissue may be present in a significant proportion of cases well beyond 3-6 hours and, in isolated cases, perhaps up to 48 hours. This exposes a "stroke recovery gap", the difference observed between the clinical response to thrombolytic therapy in a given population of patients presenting with ischaemic stroke and the potential clinical recovery if all of the penumbra were salvaged under ideal circumstances. The means of bridging this "stroke recovery gap" using thrombolysis must involve extending the therapeutic time window (i.e. the time between stroke onset and administration of thrombolytics). Approaches to do this include the use of: (i) improved patient selection with modern neuroimaging techniques, particularly magnetic resonance imaging using perfusion-weighted image/diffusion-weighted image mismatch; (ii) newer thrombolytic agents; (iii) lower doses of these agents; (iv) varied methods of administration of thrombolytic therapy including combined intravenous and intra-arterial approaches; and (v) adjunctive therapies such as neuroprotectants. Should these means of extending the time window for thrombolysis prove successful, a more widespread use of this form of acute stroke therapy will be possible.

Vampire bat salivary plasminogen activator (desmoteplase): a unique fibrinolytic enzyme that does not promote neurodegeneration

BACKGROUND AND PURPOSE

Tissue-type plasminogen activator (tPA) promotes excitotoxic and ischemic injury within the brain. These findings have implications for the use of tPA in the treatment of acute ischemic stroke. The plasminogen activator from vampire bat (Desmodus rotundus) saliva (D rotundus salivary plasminogen activator [DSPA]; desmoteplase) is an effective plasminogen activator but, in contrast to tPA, is nearly inactive in the absence of a fibrin cofactor. The purpose of this study was to compare the ability of DSPA and tPA to promote kainate- and N-methyl-D-aspartate (NMDA)-induced neurodegeneration in tPA-/- mice and wild-type mice, respectively.

METHODS

tPA-/- mice were infused intracerebrally with either tPA or DSPA. The degree of neuronal survival after hippocampal injection of kainate was assessed histochemically. Wild-type mice were used to assess the extent of neuronal damage after intrastriatal injection of NMDA in the presence of tPA or DSPA. Immunohistochemistry and fibrin zymography were used to evaluate DSPA and tPA antigen or activity.

RESULTS

Infusion of tPA into tPA-/- mice restored sensitivity to kainate-mediated neurotoxicity and activation of microglia. DSPA was incapable of conferring sensitivity to kainate treatment, even when infused at 10-fold higher molar concentration than tPA. The presence of tPA also increased the lesion volume induced by NMDA injection into the striatum of wild-type mice, whereas DSPA had no effect.

CONCLUSIONS

DSPA does not promote kainate- or NMDA-mediated neurotoxicity in vivo. These results provide significant impetus to evaluate DSPA in patients with ischemic stroke.

The polymerized bovine hemoglobin-based oxygen-carrying solution (HBOC-201) is not toxic to neural cells in culture

BACKGROUND

Recent data suggest that a neurotoxic effect of blood or its components may contribute to secondary neural cell dysfunction. This study investigated the effects of HBOC-201 (Hemopure) and purified human hemoglobin (hHgb) on rat fetal neural cell culture.

METHODS

Neural cell cultures were exposed to HBOC-201 and hHgb (0.02, 0.2, 2.0, and 6.5 g/dL) for 24 hours, and then analyzed for proliferation, metabolism, and neurolysis.

RESULTS

Cultures exposed to HBOC-201 maintained levels of proliferation and metabolism similar to controls while demonstrating no cellular lysis. However, cultures exposed to hHgb demonstrated decreased proliferation after exposure to 0.2, 2.0, and 6.5 g/dL hHgb (14,252.14, 3,221.89, and 343.12 vs. 19,509.53; p< 0.05) when compared with controls. In addition, cultures exposed to hHgb demonstrated decreased metabolic activity and increased cell lysis when compared with controls (p < 0.05).

CONCLUSION

Cultures exposed to HBOC-201 displayed sustained metabolic activity and proliferation, and demonstrated no neurolysis, suggesting that HBOC-201 does not display the toxic characteristics of hHgb.

Hemin-induced apoptosis in PC12 and neuroblastoma cells: implications for local neuronal death associated with intracerebral hemorrhage

The exact pathogenesis of neuronal death following bleeding in brain parenchyma is still unknown. Hemoglobin (Hb) toxicity has been postulated to be one of the underlying mechanisms. The purpose of this study was to examine the possible contribution to neurotoxicity of each of the Hb compounds and to characterize the death pathway. Pheochromocytoma (PC12) and neuroblastoma (SH- SY5Y) cell lines were exposed to Hb, globin, hemin, protoporphyrin IX and iron for 1.5- 24 h. We found that Hb and hemin are highly toxic (LD(50) of 8 and 20 &mgr; mol/l, respectively) as compared to globin that was not toxic. In addition, protoporphyrin IX and iron, compounds of hemin, were less toxic than hemin itself (LD(50) of 962 and 2070 &mgr; mol/l respectively). We also demonstrated that non-specific protein digestion with proteinase-K, markedly increased Hb toxicity. Hemin-treated cells caused a typical apoptotic cell death pattern as indicated by DNA fragmentation, caspase activation and reduction in the mitochondrial membrane potential. Treatment with the antioxidant N-acetyl-L-cysteine or iron chelator, deferoxamine, diminished hemin-induced cell death, indicating a role of oxidative stress in this deleterious process. Thus, therapeutic strategies, based on antioxidant, iron chelator and anti-apoptotic agents may be effective in counteracting Hb neurotoxicity.

Oxyhemoglobin produces necrosis, not apoptosis, in astrocytes

OBJECTIVE

Subarachnoid blood, resulting from traumatic brain injury or subarachnoid hemorrhage, has been linked with cell injury and stress gene induction. We investigated whether oxyhemoglobin (OxyHb), a major component in blood clots, exerts a cytotoxic effect on cultured astrocyte cells, and the pattern of cell death.

METHODS

A murine astrocyte cell line was used (passages 28-35). Cell growth studies were performed 24, 48, and 72 h after exposure to OxyHb (1, 10, and 30 microM). Western blot analysis of poly adenosine diphosphate [ADP]-ribose polymerase (PARP) cleavage and TUNEL stain analysis were performed to determine the presence of apoptosis. Cells treated with OxyHb were also evaluated with transmission electron microscopy to determine changes that may have occurred at the ultra-structural level.

RESULTS

OxyHb (10-30 microM), after 72-h incubation, inhibited cell growth. Western blot analysis of PARP and TUNEL staining for the presence of apoptosis were essentially negative in all groups. Ultrastructural analysis revealed an abundance of necrosis and random occurrences of apoptosis in a few cells.

CONCLUSION

Cultured astrocytes exposed to OxyHb causing cell growth inhibition could possibly be a result of cellular cytotoxicity and necrosis.

Hemoglobin-induced cytotoxicity in rat cerebral cortical neurons: caspase activation and oxidative stress

BACKGROUND AND PURPOSE

Apoptotic-like pathways may contribute to brain cell death after intracerebral hemorrhage. In this study, we used a simplified in vitro model of hemoglobin neurotoxicity to map the caspase cascades involved and to document the role of oxidative stress.

METHODS

Primary neuronal cultures were obtained from rat cerebral cortex and exposed to hemoglobin to induce cell death. Cytotoxicity was assessed via measurements of mitochondrial viability (MTT assay) and lactate dehydrogenase (LDH assay). Activation of caspase-3, -8, and -9 was measured by Western blot and enzyme activity assays. Various caspase inhibitors (zVADfmk, zDEVDfmk, zIETDfmk, and zLEHDfmk) were tested for neuroprotective efficacy. The role of oxidative stress was assessed with the use of U83836E as a potent scavenger of free radicals.

RESULTS

Exposure of primary cortical neurons to hemoglobin induced a dose- and time-dependent cytotoxicity. Western blots showed upregulation of cleaved caspase-3. Enzyme assays showed an increase in caspase-9-like and caspase-3-like activity. However, caspase inhibition did not result in neuroprotection. In contrast, the free radical scavenger U83836E significantly reduced hemoglobin-induced neuronal death. Combination treatment with both U83836E and the broad spectrum caspase inhibitor zVADfmk did not yield additional protection.

CONCLUSIONS

Upstream and downstream caspases were upregulated after hemoglobin-induced neurotoxicity in vitro, but only an antioxidant approach with a potent free radical scavenger significantly improved neuronal survival. These data suggest that in addition to the activation of caspase cascades, parallel pathways of oxidative stress may predominate in this model of hemoglobin neurotoxicity.

Extracellular proteolysis in brain injury and inflammation: role for plasminogen activators and matrix metalloproteinases

The role of intracellular proteases (e.g., calpains and caspases) in the pathophysiology of neuronal cell death has been extensively investigated. More recently, accumulating data have suggested that extracellular proteolysis also plays a critical role. The two major systems that modify the extracellular matrix in brain are the plasminogen activator (PA) and matrix metalloproteinase (MMP) axes. This Mini-Review delineates major pathways of PA and MMP action after stroke, brain trauma, and chronic inflammation. Deleterious effects include the disruption of blood-brain barrier integrity, amplification of inflammatory infiltrates, demyelination, and possibly interruption of cell-cell and cell-matrix interactions that may trigger cell death. In contrast, PA-MMP actions may contribute to extracellular proteolysis that mediates parenchymal and angiogenic recovery after brain injury. As the mechanisms of deleterious vs. potentially beneficial PA and MMP actions become better defined, it is hoped that new therapeutic targets will emerge for ameliorating the sequelae of brain injury and inflammation.

Mitogen-activated protein kinase inhibition in traumatic brain injury: in vitro and in vivo effects

The authors provide the first in vitro and in vivo evidence that perturbations in mitogen-activated protein kinase (MAPK) signal-transduction pathways are involved in the pathophysiology of traumatic brain injury. In primary rat cortical cultures, mechanical trauma induced a rapid and selective phosphorylation of the extracellular signal-regulated kinase (ERK) and p38 kinase, whereas there was no detectable change in the c-jun N-terminal kinase (JNK) pathway. Treatment with PD98059, which inhibits MAPK/ERK 1/2, the upstream activator of ERK, significantly increased cell survival in vitro. The p38 kinase and JNK inhibitor SB203580 had no protective effect. Similar results were obtained in vivo using a controlled cortical impact model of traumatic injury in mouse brain. Rapid and selective upregulation occurred in ERK and p38 pathways with no detectable changes in JNK. Confocal immunohistochemistry showed that phospho-ERK colocalized with the neuronal nuclei marker but not the astrocytic marker glial fibrillary acidic protein. Inhibition of the ERK pathway with PD98059 resulted in a significant reduction of cortical lesion volumes 7 days after trauma. The p38 kinase and JNK inhibitor SB203580 had no detectable beneficial effect. These data indicate that critical perturbations in MAPK pathways mediate cerebral damage after acute injury, and further suggest that ERK is a novel therapeutic target in traumatic brain injury.

Inhibition of factor IX(a) is protective in a rat model of thromboembolic stroke

BACKGROUND AND PURPOSE

Although used clinically to prevent stroke, there are few examples of anticoagulant investigations in the treatment of acute thromboembolic stroke in animal models. The treatment of thromboembolic stroke in experimental models has been investigated almost exclusively around the use of tissue plasminogen activator (tPA). In this study, using a rat thromboembolic stroke model, we investigated the use of an inhibitory anti-factor IX(a) monoclonal antibody (SB 249417) for the treatment of thromboembolic stroke and compared its efficacy to that of tPA.

METHODS

Stroke was initiated by delivering 6 clots into the internal carotid artery. After 2, 4, or 6 hours, rats received either intravenous vehicle, 10.0 mg/kg tPA, or 1.0, 2.0, or 3.0 mg/kg SB 249417. At 24 hours after stroke, infarct volumes and neurological deficits were assessed.

RESULTS

Treatment with tPA 2, 4, or 6 hours after stroke reduced infarct volumes by 35% (P=NS), 45%, and 39%, respectively. tPA treatment did not improve neurological deficits at any time point. Treatment with SB 249417 (3.0 mg/kg) 2, 4, or 6 hours after stroke reduced infarct volumes by 44%, 50%, and 13% (P=NS), respectively. Neurological deficits were reduced by 49%, 42%, and 13% (P=NS), respectively. Neither mortality nor hemorrhage was affected by either treatment.

CONCLUSIONS

The data indicate that the inhibition of factor IX(a) within 4 hours of thromboembolic stroke produced a more favorable outcome than tPA. When treatment was initiated 6 hours after stroke, the benefits of factor IX(a) inhibition were lost, whereas tPA continued to suppress lesion development, albeit without a corresponding improvement in functional deficits. This study suggests that cerebral ischemia and the resultant perfusion deficit are exacerbated by the activation of blood coagulation and that anticoagulants like SB 249417 may find utility in the treatment of ischemic stroke.

Plasminogen activator inhibitor-1 induction after experimental intracerebral hemorrhage

Serine proteases, such as thrombin and tissue-type plasminogen activator, play an important role in brain injury after intracerebral hemorrhage and other neurologic disorders. Plasminogen activator inhibitor-1 is one of the serine protease inhibitors, or serpins. The balance between serine proteases and serpins may affect the outcome of intracerebral hemorrhage. The purpose of this study was to determine whether plasminogen activator inhibitor-1 and tissue-type plasminogen activator are upregulated after intracerebral hemorrhage and the role that thrombin plays in that induction. Plasminogen activator inhibitor-1 protein levels were upregulated after intracerebral hemorrhage. Brain plasminogen activator inhibitor-1 content also increased after thrombin infusion in a dose-dependent manner. Hirudin, a specific thrombin inhibitor, blocked the upregulation of plasminogen activator inhibitor-1 after intracerebral hemorrhage. Time courses showed that plasminogen activator inhibitor-1 levels around the hematoma peaked at the first day. Plasminogen activator inhibitor-1-positive cells were detected in the perihematomal area and the ipsilateral basal ganglia after thrombin infusion, but not in the contralateral hemisphere. Plasminogen activator inhibitor-1 messenger RNA levels were increased at 24 hours after intracerebral hemorrhage and after thrombin infusion. However, tissue-type plasminogen activator protein levels were the same in the control, whole-blood, and thrombin-infusion groups. In conclusion, intracerebral hemorrhage and thrombin infusion stimulate plasminogen activator inhibitor-1 but not tissue-type plasminogen activator production in the brain. The upregulation of plasminogen activator inhibitor-1 may be neuroprotective by limiting thrombin or other serine protease-induced toxicity.

Reduced cortical injury and edema in tissue plasminogen activator knockout mice after brain trauma

Tissue plasminogen activator (tPA) may play a deleterious role after brain injury. Here, we compared the response to traumatic brain injury in tPA knockout (KO) and wildtype (WT) mice after controlled cortical impact. At 6 h after trauma, blood-brain barrier permeability was equally increased in all mice. However, by 24 h specific gravity measurements of brain edema were significantly worse in WT mice than in KO mice. At 1 and 2 days post-trauma, mice showed deficits in rotarod performance, but by day 7 all mice recovered motor function and there were no differences between WT and KO mice. At 7 days, cortical lesion volumes were significantly reduced in KO mice compared with WT mice. However, there were no significant differences in CA3 hippocampal neuron survival. These data suggest that tPA amplifies cortical brain damage and edema in this mouse model of traumatic brain injury.

Tissue plasminogen activator protects hippocampal neurons from oxygen-glucose deprivation injury

We have previously shown that tissue plasminogen activator (tPA) participates in the neurotoxicity of microglial conditioned medium (MgCM). Killing of hippocampal neurons by MgCM was prevented by both plasminogen activator inhibitor-1 (PAI-1) and anti-tPA antibody. An N-methyl-D-aspartate (NMDA) receptor blocker protected neurons from MgCM, suggesting that this subtype of glutamate receptor is involved. Whereas glutamate receptor-mediated events are important in cerebral ischemia and tPA has previously been shown to enhance excitotoxicity in hippocampus, we hypothesized that tPA would exaggerate oxygen glucose deprivation (OGD) injury in cultures of hippocampal neurons. Dissociated rat hippocampal cells were grown under conditions designed to optimize neuronal growth while minimizing glial replication. At 7--10 days, cultures were subjected to OGD for 2.5 hr. Recombinant human tPA (1,000 IU) was added immediately after OGD. Viability was assessed 24 hr later. Viable, apoptotic, and necrotic cells were classified and quantified based on staining patterns of acridine orange and ethidium bromide under fluorescence microscopy. tPA alone did not alter neuronal integrity. OGD produced significant neuronal death (viability reduced by 45%, P < 0.001). tPA completely protected OGD-exposed cultures. Potential mechanisms of tPA protection were explored. Whereas tPA antibody abolished the protective effect of tPA, its proteolytic inhibitor PAI-1 did not alter the effect. The effect of tPA was tested in separate free radical and excitatory amino acid insults. It did not protect neurons from hydrogen peroxide (1 microM), S-nitro-acetylpenicillamine (10 microM), glutamate (50 microM), or NMDA (10 microM) damage but significantly attenuated injury caused by 250 microM kainate. We conclude that tPA is capable of protecting hippocampal neurons from OGD by a nonproteolytic action. The mechanism of protection was not defined, although attenuation of AMPA/kainate glutamate receptors may play a role.

Reduction of tissue plasminogen activator-induced hemorrhage and brain injury by free radical spin trapping after embolic focal cerebral ischemia in rats

Thrombolytic stroke therapy with tissue plasminogen activator (tPA) remains complicated by serious risks of cerebral hemorrhage and brain injury. In this study, a novel model of tPA-induced hemorrhage was used in spontaneously hypertensive rats to examine the correlates of hemorrhage, and test methods of reducing hemorrhage and brain injury. Homologous blood clot emboli were used to occlude the middle cerebral artery in spontaneously hypertensive rats, and delayed administration of tPA (6 hours postischemia) resulted in high rates of cerebral hemorrhage 24 hours later. Compared with untreated rats, tPA significantly increased hemorrhage volumes by almost 85%. Concomitantly, infarction and neurological deficits were worsened by tPA. A parallel experiment in normotensive Wistar-Kyoto rats showed markedly reduced rates of hemorrhage, and tPA did not significantly increase hemorrhage volumes. To examine whether tPA-induced hemorrhage was caused by the delayed onset of reperfusion per se, another group of spontaneously hypertensive rats was subjected to focal ischemia using a mechanical method of arterial occlusion. Delayed (6 hours) reperfusion via mechanical means did not induce hemorrhage. However, administration of tPA plus delayed mechanical reperfusion significantly increased hemorrhage volumes. Since reperfusion injury was implicated, a final experiment compared outcomes in spontaneously hypertensive rats treated with tPA plus the free radical spin trap alpha-phenyl tert butyl nitrone (alpha-PBN) versus tPA alone. tPA-induced hemorrhage volumes were reduced by 40% with alpha-PBN, and infarction and neurological deficits were also decreased. These results indicate that (1) blood pressure is an important correlate of tPA-induced hemorrhage, (2) tPA interacts negatively with reperfusion injury to promote hemorrhage, and (3) combination therapies with anti-free radical treatments may reduce the severity of tPA-induced hemorrhage and brain injury after cerebral ischemia.

Evidence for apoptosis after intercerebral hemorrhage in rat striatum

The overall hypothesis that cell death after intracerebral hemorrhage is mediated in part by apoptotic mechanisms was tested. Intracerebral hemorrhage was induced in rats using stereotactic infusions of 0.5 U of collagenase (1-microL volume) into the striatum. After 24 hours, large numbers of TUNEL-positive stained cells with morphologies suggestive of apoptosis were present in the center and periphery of the hemorrhage. Double staining with Nissl and immunocytochemical labeling with antibodies against neuronal nuclei and glial fibrillary acidic protein suggested that these TUNEL-positive cells were mostly neurons and astrocytes. Electrophoresis of hemorrhagic brain extracts showed evidence of DNA laddering into approximately 200-bp fragments. Western blots showed cleavage of the cytosolic caspase substrate gelsolin. The density of TUNEL-positive cells at 24 and 48 hours after hemorrhage was significantly reduced by treatment with the broad-spectrum caspase inhibitor zVADfmk. It was unlikely that apoptotic changes were due to neurotoxicity of injected collagenase because TUNEL-positive cells and DNA laddering were also obtained in an alternative model of hemorrhage where autologous blood was infused into the striatum. Furthermore, equivalent doses of collagenase did not induce cell death in primary neuronal cultures. These results provide initial evidence that apoptotic mechanisms may mediate some of the injury in brain after intracerebral hemorrhage.

Effects of tissue type plasminogen activator in embolic versus mechanical models of focal cerebral ischemia in rats

Tissue type plasminogen activator (tPA) can be effective therapy for embolic stroke by restoring cerebral perfusion. However, a recent experimental study showed that tPA increased infarct size in a mouse model of transient focal ischemia, suggesting a possible adverse effect of tPA on ischemic tissue per se. In this report, the effects of tPA in two rat models of cerebral ischemia were compared. In experiment 1, rats were subjected to focal ischemia via injection of autologous clots into the middle cerebral artery territory. Two hours after clot injection, rats were treated with 10 mg/kg tPA or normal saline. Perfusion-sensitive computed tomography scanning showed that tPA restored cerebral perfusion in this thromboembolic model. Treatment with tPA significantly reduced ischemic lesion volumes measured at 24 hours by >60%. In experiment 2, three groups of rats were subjected to focal ischemia via a mechanical approach in which a silicon-coated filament was used intraluminally to occlude the origin of the middle cerebral artery. In two groups, the filament was withdrawn after 2 hours to allow for reperfusion, and then rats were randomly treated with 10 mg/kg tPA or normal saline. In the third group, rats were not treated and the filament was not withdrawn so that permanent focal ischemia was present. In this experiment, tPA did not significantly alter lesion volumes after 2 hours of transient focal ischemia. In contrast, permanent ischemia significantly increased lesion volumes by 55% compared with transient ischemia. These results indicate that in these rat models of focal cerebral ischemia, tPA did not have detectable negative effects. Other potentially negative effects of tPA may be dependent on choice of animal species and model systems.