Biomedical subjects

E H Lo

Publications and source records attributed to E H Lo.

At least 19 recordsLinked to original sources

PubMed2006

Association between tPA therapy and raised early matrix metalloproteinase-9 in acute stroke.

BACKGROUND: Matrix metalloproteinase-9 (MMP9) is expressed in acute ischemic stroke and up-regulated by tissue plasminogen activator (tPA) in animal models. The authors investigated plasma MMP9 and its endogenous inhibitor, tissue inhibitor of metalloproteinase (TIMP1), in tPA-treated and -untreated stroke patients. METHODS: Nonstroke control subjects and consecutive ischemic stroke patients presenting within 8 hours of onset were enrolled. Blood was sampled within 8 hours and at 24 hours, 2 to 5 days and 4 to 6 weeks. MMP9 and TIMP1 were analyzed by ELISA and gel zymography. RESULTS: Fifty-two cases (26 tPA treated, 26 tPA untreated) and 27 nonstroke control subjects were enrolled. Hyperacute MMP9 was elevated in tPA-treated vs tPA-untreated patients (medians 43 vs 28 ng/mL; p = 0.01). tPA therapy independently predicted hyperacute MMP9 after adjustment for stroke severity, volume, and hemorrhagic transformation (p = 0.01). There was a trend toward lower hyperacute TIMP1 levels in tPA-treated vs tPA-untreated patients (p = 0.06). Hyperacute MMP9 was correlated to poor 3-month modified Rankin Scale outcome (r = 0.58, p = 0.0005). CONCLUSION: Tissue plasminogen activator independently predicted plasma matrix metalloproteinase-9 (MMP9) in the first 8 hours after human ischemic stroke. As MMP9 may be an important mediator of hemorrhagic transformation, alternative thrombolytic agents or therapeutic MMP9 inhibition may increase the safety profile of acute stroke thrombolysis.

Aged↗

PubMed2001

Low density lipoprotein as a targeted carrier for doxorubicin in nude mice bearing human hepatoma HepG2 cells.

Doxorubicin (DOX) was coupled to human low density lipoprotein (LDL) to form a complex (LDL-DOX). When injected into mice, LDL-DOX was more accumulated in liver than free DOX. In contrast, LDL-DOX was less accumulated in heart than free DOX. In in vitro studies on human hepatoma (HepG2) cells, although the cellular uptake of LDL-DOX was higher than that of DOX, the anti-proliferative effect of LDL-DOX on these tumor cells was smaller than that of LDL. However, when LDL-DOX or DOX was administered to nude mice bearing HepG2 cells implanted on the shoulder, the anti-proliferative effects on the tumor cells of both drugs were similar. Histological analyses indicated that organization of myocardial filaments was disrupted and vacuolization was observed in DOX-treated group when compared with control group whereas LDL-DOX-treatment did not exhibit any damage in the host's heart. Enzymatic analyses also demonstrated that plasma lactate dehydrogenase activity, which is a common indicator of heart damage, was elevated in DOX-treated group when compared with control group whereas the activity of this enzyme was unchanged in LDL-DOX-treated group. The results in present study indicate that LDL can be used as a targeted carrier for DOX because LDL-DOX can exhibit similar anti-proliferative effect as DOX on tumor but reduce the DOX-induced cardiotoxicity in the host.

Animals↗

PubMed2001

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.

Animals↗

PubMed2001

Profiles of glutamate and GABA efflux in core versus peripheral zones of focal cerebral ischemia in mice.

Efflux of glutamate during cerebral ischemia is known to contribute to brain cell death via processes of excitotoxicity. However, gamma-aminobutyric acid (GABA) is also released during ischemia, and may be protective. In this study, we used in vivo microdialysis to map the efflux of glutamate and GABA from central core and peripheral zones of focal ischemia in mouse brain. We show that the temporal profiles of glutamate and GABA efflux are significantly different in core versus peripheral zones. Calculation of glutamate/GABA ratios demonstrate that, in the core, there is a significant increase above baseline ratios during the first 30 mm of ischemia, which then rapidly renormalizes. In contrast, no significant changes in glutamate/GABA ratios were seen in the ischemic periphery. These data suggest that imbalances in glutamate versus GABA efflux may be an initial trigger of excitotoxic brain damage in the core but not the peripheral zones of focal cerebral ischemia.

Animals↗

PubMed2001

Effects of matrix metalloproteinase-9 gene knock-out on the proteolysis of blood-brain barrier and white matter components after cerebral ischemia.

Deleterious processes of extracellular proteolysis may contribute to the progression of tissue damage after acute brain injury. We recently showed that matrix metalloproteinase-9 (MMP-9) knock-out mice were protected against ischemic and traumatic brain injury. In this study, we examined the mechanisms involved by focusing on relevant MMP-9 substrates in blood-brain barrier, matrix, and white matter. MMP-9 knock-out and wild-type mice were subjected to transient focal ischemia. MMP-9 levels increased after ischemia in wild-type brain, with expression primarily present in vascular endothelium. Western blots showed that the blood-brain barrier-associated protein and MMP-9 substrate zonae occludens-1 was degraded after ischemia, but this was reduced in knock-out mice. There were no detectable changes in another blood-brain barrier-associated protein, occludin. Correspondingly, blood-brain barrier disruption assessed via Evans Blue leakage was significantly attenuated in MMP-9 knock-out mice compared with wild types. In white matter, ischemic degradation of the MMP-9 substrate myelin basic protein was significantly reduced in knock-out mice compared with wild types, whereas there was no degradation of other myelin proteins that are not MMP substrates (proteolipid protein and DM20). There were no detectable changes in the ubiquitous structural protein actin or the extracellular matrix protein laminin. Finally, 24 hr lesion volumes were significantly reduced in knock-out mice compared with wild types. These data demonstrate that the protective effects of MMP-9 gene knock-out after transient focal ischemia may be mediated by reduced proteolytic degradation of critical blood-brain barrier and white matter components.

Actins↗

PubMed2001

Matrix metalloproteinase 2 gene knockout has no effect on acute brain injury after focal ischemia.

Matrix metalloproteinases (MMPs) may contribute to tissue damage after cerebral ischemia. In this study, wildtype and MMP-2 knockout mice were subjected to permanent and transient (2 h) occlusions of the middle cerebral artery. Gelatin zymography showed that MMP-9 levels were increased in all brains after ischemia. MMP-2 levels did not show a significant increase in wildtype mice, and were not detectable in knockout mice. Laser doppler flowmetry demonstrated equivalent ischemic reductions in perfusion in wildtype and knockout mice. In both permanent and transient occlusion paradigms, there were no statistically significant differences between wildtype and knockout mice in terms of 24 h ischemic lesion volumes. These data suggest that MMP-2 does not contribute to acute tissue damage in this model of focal ischemia.

Animals↗

PubMed2001

Protective effects of pamiteplase, a modified t-PA, in a rat model of embolic stroke.

The effects of alteplase (tissue plasminogen activator, t-PA) and pamiteplase (a modified t-PA with longer half-life and increased potency) were compared in a clinically relevant model of embolic stroke. Rats were treated with pamiteplase (0.5 mg/kg or 1 mg/kg bolus), alteplase (10 mg/kg infusion) or normal saline. Pamiteplase (1 mg/kg) was as effective as alteplase in reducing 24 h brain infarct volumes, neurological deficit scores and residual clot grades. Cerebral blood flow recovery at 30 min after thrombolytic treatment was partial and did not correlate with 24 h infarct volumes or neurological deficits. However, there was good correlation between 24 h residual clot grades and infarct volumes, suggesting a delayed timeframe for pamiteplase- and alteplase-induced reperfusion.

Animals↗

PubMed2001

Drug delivery to damaged brain.

Drug delivery to the brain poses unique challenges. Specialized anatomic and physiological features of the cerebrovasculature and cerebral tissue fluids result in barriers which significantly restrict delivery of a wide range of possible therapeutic agents. In addition to these normal restrictions to brain drug delivery, pathophysiological features and sequelae of acute brain injury will also impact upon the efficiency of drug delivery. This review is focused on acutely damaged brain that occurs after stroke and trauma. Pathophysiological events that may influence drug delivery include blood-brain barrier disruptions, blood flow alterations, edema and increased intracranial pressure, metabolic perturbations, and altered profiles of gene expression and protein synthesis. Careful consideration of these obstacles will provide a framework for further research into the optimization of drug delivery strategies into damaged brain. Without a rigorous assessment of these issues, it may not be possible to translate our mechanistic understanding of acute brain injury into successful clinical therapies.

Animals↗

PubMed2001

Delayed rt-PA treatment in a rat embolic stroke model: diagnosis and prognosis of ischemic injury and hemorrhagic transformation with magnetic resonance imaging.

The authors characterized effects of late recombinant tissue plasminogen activator (rt-PA) administration in a rat embolic stroke model with magnetic resonance imaging (MRI), to assess potential MRI correlates, or predictors, or both, of rt-PA-induced hemorrhage. Diffusion-, perfusion-, and postcontrast T1-weighted MRI were performed between 4 and 9 hours and at 24 hours after embolic stroke in spontaneously hypertensive rats. Treatment with either rt-PA or saline was started 6 hours after stroke. A spectrophotometric hemoglobin assay quantified hemorrhage severity. Before treatment, relative cerebral blood flow index (rCBFi) and apparent diffusion coefficient (ADC) in the ischemic territory were 30% +/- 23% and 60% +/- 5% (of contralateral), respectively, which increased to 45% +/- 39% and 68% +/- 4% 2 hours after rt-PA. After 24 hours, rCBFi and ADC were 27% +/- 27% and 59 +/- 5%. Hemorrhage volume after 24 hours was significantly greater in rt-PA-treated animals than in controls (8.7 +/- 3.7 microL vs. 5.1 +/- 2.4 microL, P < 0.05). Before rt-PA administration, clear postcontrast T1-weighted signal intensity enhancement was evident in areas of subsequent bleeding. These areas had lower rCBFi levels than regions without hemorrhage (23% +/- 22% vs. 36% +/- 29%, P < 0.05). In conclusion, late thrombolytic therapy does not necessarily lead to successful reperfusion. Hemorrhage emerged in areas with relatively low perfusion levels and early blood-brain barrier damage. Magnetic resonance imaging may be useful for quantifying effects of thrombolytic therapy and predicting risks of hemorrhagic transformation.

Animals↗

PubMed2001

Hemorrhagic transformation after fibrinolysis with tissue plasminogen activator: evaluation of role of hypertension with rat thromboembolic stroke model.

BACKGROUND AND PURPOSE: We used a rat model of thromboembolic stroke to evaluate whether hypertension increases the incidence of hemorrhage after fibrinolysis with tissue plasminogen activator (tPA). METHODS: In this model, a microclot suspension was injected into the middle cerebral artery territory to induce focal ischemia. Reperfusion was induced in spontaneously hypertensive rats (SHR) by administering tPA (10 mg/kg) intravenously at 2 hours or 6 hours after the onset of thromboembolic focal ischemia. In untreated control rats, saline was administered at 2 hours after ischemia. RESULTS: Hemorrhagic transformation was observed only in rats that received tPA at 6 hours (6 of 8 rats [75%]). Reduction of mean arterial blood pressure from 122+/-3 to 99+/-2 mm Hg with hydralazine, given to SHR for 1 week before ischemia, significantly decreased the incidence of hemorrhage in 2 of 11 rats (18%). tPA reduced infarct volumes, but cotreatment with hydralazine did not result in further protection. CONCLUSIONS: This study demonstrates that in this rat thromboembolic model of stroke, tPA-induced hemorrhage is dependent on blood pressure and that pharmacological reduction of hypertension during fibrinolysis can reduce the risk of hemorrhagic transformation.

Animals↗

PubMed2000

Effects of matrix metalloproteinase-9 gene knock-out on morphological and motor outcomes after traumatic brain injury.

Matrix metalloproteinases (MMPs) belong to a class of extracellular proteinases responsible for maintaining and remodeling the extracellular matrix. In addition to multiple functions in normal physiology, abnormal MMP expression and activity may also participate in the pathophysiology of cerebral disease. Here, we show that MMP-9 (gelatinase B; EC.3.4.24.35) contributes to the pathophysiology of traumatic brain injury. After controlled cortical impact in mice, MMP-9 was increased in traumatized brain. Total MMP-9 levels at 24 hr were significantly increased as measured by a substrate cleavage assay. Zymograms showed that MMP-9 was elevated as early as 3 hr after traumatic brain injury, reaching a maximum at approximately 24 hr. Increased MMP-9 levels persisted for up to 1 week. Western blot analysis indicated increased profiles of MMP-9 expression that corresponded with the zymographic data. Knock-out mice deficient in MMP-9 gene expression were compared with wild-type littermates in terms of morphological and motor outcomes after trauma. Motor outcomes were measured at 1, 2, and 7 d after traumatic brain injury by the use of a rotarod device. MMP-9 knock-out mice had less motor deficits than wild-type mice. At 7 d, traumatic brain lesion volumes on Nissl-stained histological sections were significantly smaller in MMP-9 knock-out mice. These data demonstrate that MMP-9 contributes to the pathophysiology of traumatic brain injury and suggest that interruption of the MMP proteolytic cascade may be a possible therapeutic approach for preventing the secondary progression of damage after brain trauma.

Analysis of Variance↗

PubMed2000

Hemorrhagic transformation after fibrinolytic therapy with tissue plasminogen activator in a rat thromboembolic model of stroke.

In this study, the effects of early vs. delayed tPA treatment on the development of hemorrhagic transformation was compared in a rat thromboembolic model of stroke. Fibrinolysis was performed by administering tPA intravenously at 2 or 6 h after ischemic onset. Twenty-four hours later, confluent hemorrhagic infarction was observed only in rats treated with tPA at 6 h at the rate of 50%. In this delayed treatment group, significantly increased numbers of polymorphonuclear leukocytes (PMNL) were observed to accumulate inside microvessels within the ischemic core. PMNL accumulation may be related to the induction of hemorrhagic infarction after delayed tPA treatment.

Animals↗

PubMed2000

Impaired neurotransmitter release and elevated threshold for cortical spreading depression in mice with mutations in the alpha1A subunit of P/Q type calcium channels.

The P/Q type voltage-gated Ca2+ channels are involved in membrane excitability and Ca2+-dependent neurotransmitter release within the CNS. Mutations in the CacnalA gene encoding the alpha1A subunit of the P/Q type Ca2+ channel have recently been reported in tottering mice and a more severely affected allele, leaner. Here we show using in vivo cortical microdialysis that evoked increases of extracellular glutamate levels are markedly attenuated in both mutants upon KCl-induced depolarization compared with wild-type mice. Tottering and leaner mice also show a 10-fold resistance to cortical spreading depression induced by cortical electrical stimulation or KCl application to the pial surface. A slower transcortical propagation speed and failure to sustain regenerative spread of the depolarizing wave were more pronounced in leaner neocortex. Both signaling defects appeared unrelated to the developmental history of repeated cortical spike-wave discharges, since neither were observed in the stargazer mouse, a Ca2+ channel gamma2 subunit mutant with a similar seizure phenotype. These data demonstrate two cortical excitability defects revealed by prolonged depolarization in cerebral networks expressing mutant P/Q type Ca2+ channels, and are the first to identify a gene linked to a spreading depression phenotype.

Animals↗

PubMed2000

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.

Amino Acid Chloromethyl Ketones↗

PubMed2000

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.

Animals↗

PubMed2000

Role for matrix metalloproteinase 9 after focal cerebral ischemia: effects of gene knockout and enzyme inhibition with BB-94.

It has been shown recently that matrix metalloproteinases (MMPs) are elevated after cerebral ischemia. In the current study, we investigated the pathophysiologic role for MMP-9 (gelatinase B, EC.3.4.24.35) in a mouse model of permanent focal cerebral ischemia, using a combination of genetic and pharmacologic approaches. Zymography and Western blot analysis demonstrated that MMP-9 protein levels were rapidly up-regulated in brain after ischemic onset. Reverse transcription polymerase chain reaction showed increased transcription of MMP-9. There were no differences in systemic hemodynamic parameters and gross cerebrovascular anatomy between wild type mice and mutant mice with a targeted knockout of the MMP-9 gene. After induction of focal ischemia, similar reductions in cerebral blood flow were obtained. In the MMP-9 knockout mice, ischemic lesion volumes were significantly reduced compared with wild type littermates in male and female mice. In normal wild type mice, the broad spectrum MMP inhibitor BB-94 (batimastat) also significantly reduced ischemic lesion size. However, BB-94 had no detectable protective effect when administered to MMP-9 knockout mice subjected to focal cerebral ischemia. These data demonstrate that MMP-9 plays a deleterious role in the development of brain injury after focal ischemia.

Animals↗

PubMed2000

[New method for evaluating the effects of neuroprotective therapy in the hemodynamic penumbra].

Recently, we established a novel temporal correlation mapping (TCM) technique in combination with high-resolution functional computed tomography (CT) scanning to analyze the temporal changes in bolus transit dynamics of iodinated contrast agents in focal cerebral ischemia. Based on changes in the temporal dynamics of blood flow, we defined a new kind of penumbra and core in focal ischemia: the hemodynamic penumbra and hemodynamic core. We visualized for the first time a larger hemodynamic core and smaller hemodynamic penumbra in endothelial NOS knockout mice than in wild type mice early after focal ischemia by using the TCM analysis technique. In addition, neuroprotective effects of the water-soluble AMPA receptor antagonist YM872 were for the first time observed in the hemodynamic penumbra after focal ischemia. In conclusion, early TCM analysis could be used to directly and quantitatively evaluate the effects of neuroprotective therapy and the evolution of neuronal damage in the hemodynamic penumbra.

Animals↗

PubMed1999

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

Tissue type plasminogen activator (tPA) is clinically used as a form of thrombolytic therapy for acute ischemic stroke. However, recent data suggest that there may be negative effects associated with tPA. Experimental studies show that tPA amplifies excitotoxic neuronal damage and clinical trials show that some stroke patients suffer from hemorrhage after tPA therapy. Since hemoglobin is the major component of blood, we tested the hypothesis that tPA can amplify hemoglobin-induced neurotoxicity. PC12 cells and primary cortical rat neurons were exposed to either hemoglobin alone or hemoglobin plus tPA. Hemoglobin induced dose-dependent cytotoxicity. The addition of tPA significantly increased hemoglobin-induced cell death. These results raise the important possibility that tPA may worsen outcomes after hemorrhage.

Animals↗