Tissue plasminogen activator worsens experimental autoimmune encephalomyelitis by complementary actions on lymphoid and myeloid cell responses

BACKGROUND

Tissue plasminogen activator (tPA) is a serine protease involved in fibrinolysis. It is released by endothelial cells, but also expressed by neurons and glial cells in the central nervous system (CNS). Interestingly, this enzyme also contributes to pathological processes in the CNS such as neuroinflammation by activating microglia and increasing blood-brain barrier permeability. Nevertheless, its role in the control of adaptive and innate immune response remains poorly understood.

METHODS

tPA effects on myeloid and lymphoid cell response were studied in vivo in the mouse model of multiple sclerosis experimental autoimmune encephalomyelitis and in vitro in splenocytes.

RESULTS

tPA-/- animals exhibited less severe experimental autoimmune encephalomyelitis than their wild-type counterparts. This was accompanied by a reduction in both lymphoid and myeloid cell populations in the spinal cord parenchyma. In parallel, tPA increased T cell activation and proliferation, as well as cytokine production by a protease-dependent mechanism and via plasmin generation. In addition, tPA directly raised the expression of MHC-II and the co-stimulatory molecules CD80 and CD86 at the surface of dendritic cells and macrophages by a direct action dependent of the activation of epidermal growth factor receptor.

CONCLUSIONS

Our study provides new insights into the mechanisms responsible for the harmful functions of tPA in multiple sclerosis and its animal models: tPA promotes the proliferation and activation of both lymphoid and myeloid populations by distinct, though complementary, mechanisms.

tPA Mobilizes Immune Cells That Exacerbate Hemorrhagic Transformation in Stroke

RATIONALE

Hemorrhagic complications represent a major limitation of intravenous thrombolysis using tPA (tissue-type plasminogen activator) in patients with ischemic stroke. The expression of tPA receptors on immune cells raises the question of what effects tPA exerts on these cells and whether these effects contribute to thrombolysis-related hemorrhagic transformation.

OBJECTIVE

We aim to determine the impact of tPA on immune cells and investigate the association between observed immune alteration with hemorrhagic transformation in ischemic stroke patients and in a rat model of embolic stroke.

METHODS AND RESULTS

Paired blood samples were collected before and 1 hour after tPA infusion from 71 patients with ischemic stroke. Control blood samples were collected from 27 ischemic stroke patients without tPA treatment. A rat embolic middle cerebral artery occlusion model was adopted to investigate the underlying mechanisms of hemorrhagic transformation. We report that tPA induces a swift surge of circulating neutrophils and T cells with profoundly altered molecular features in ischemic stroke patients and a rat model of focal embolic stroke. tPA exacerbates endothelial injury, increases adhesion and migration of neutrophils and T cells, which are associated with brain hemorrhage in rats subjected to embolic stroke. Genetic ablation of annexin A2 in neutrophils and T cells diminishes the effect of tPA on these cells. Decoupling the interaction between mobilized neutrophils/T cells and the neurovascular unit, achieved via a S1PR (sphingosine-1-phosphate receptor) 1 modulator RP101075 and a CCL2 (C-C motif chemokine ligand 2) synthesis inhibitor bindarit, which block lymphocyte egress and myeloid cell recruitment, respectively, attenuates hemorrhagic transformation and improves neurological function after tPA thrombolysis.

CONCLUSIONS

Our findings suggest that immune invasion of the neurovascular unit represents a previously unrecognized mechanism underlying tPA-mediated brain hemorrhage, which can be overcome by precise immune modulation during thrombolytic therapy.

YiQiFuMai Lyophilized Injection ameliorates tPA-induced hemorrhagic transformation by inhibiting cytoskeletal rearrangement associated with ROCK1 and NF-κB signaling pathways

ETHNOPHARMACOLOGICAL RELEVANCE

Thrombolytic therapy with tissue plasminogen activator (tPA) after ischemic stroke exacerbates blood-brain barrier (BBB) breakdown and leads to hemorrhagic transformation (HT). YiQiFuMai Lyophilized Injection (YQFM) is a modern preparation derived from Sheng-mai San (a traditional Chinese medicine). YQFM attenuates the BBB dysfunction induced by cerebral ischemia-reperfusion injury. However, whether YQFM can suppress tPA-induced HT remains unknown.

AIM OF THE STUDY

We investigated the therapeutic effect of YQFM on tPA-induced HT and explored the underlying mechanisms in vivo and in vitro to improve the safety of tPA use against stroke.

METHODS

Male C57BL/6J mice were subjected to 45 min of ischemia and 24 h of reperfusion. tPA (10 mg/kg) were infused 2 h after occlusion and YQFM (0.671 g/kg) was injected 2.5 h after occlusion. The in vitro effect of YQFM (100, 200, 400 μg/mL) on tPA (60 μg/mL)-induced dysfunction of the microvascular endothelial barrier in the brain following oxygen-glucose deprivation/reoxygenation (OGD/R) was observed in bEnd.3 cells.

RESULTS

YQFM suppressed tPA-induced high hemoglobin level in the brain, mortality, neurologic severity score, BBB permeability, expression and activation of matrix metalloproteinase (MMP)-9 and MMP-2, and degradation of tight-junction proteins. Furthermore, YQFM significantly blocked tPA-induced brain microvascular endothelial permeability and phosphorylation of Rho-associated kinase (ROCK)1, myosin light chain (MLC), cofilin and p65 in vivo and in vitro.

CONCLUSION

YQFM suppressed tPA-induced HT by inhibiting cytoskeletal rearrangement linked with ROCK-cofilin/MLC pathways and inhibiting the nuclear factor-kappa B pathway to ameliorate BBB damage caused by tPA.

Beneficial actions of prothymosin alpha-mimetic hexapeptide on central post-stroke pain, reduced social activity, learning-deficit and depression following cerebral ischemia in mice

Prothymosin alpha (ProTα)-mimetic hexapeptide (amino acid: NEVDQE, P6Q) inhibits cerebral or retinal ischemia-induced behavioral, electrophysiological and histological damage. P6Q also abolishes cerebral hemorrhage induced by ischemia with tissue plasminogen activator (tPA). In the present study we examined the beneficial effects of P6Q on other post-stroke prognostic psychology-related symptoms, which obstruct the motivation toward physical therapy. Intravenous (i.v.) administration with tPA (10 mg/kg) at 6 h after photochemically induced thrombosis (PIT) in mice resulted in bilateral central post-stroke pain in thermal and mechanical nociception tests and loss of social activity in the nest building test, both of which were significantly blocked by P6Q (30 mg/kg, i.v.) given at 5 h after PIT. P6Q (30 mg/kg, i.v.) also improved the memory-learning deficit in the step-through test and depression-like behavior in the tail suspension test when it was given 1 day after bilateral common carotid arteries occlusion (BCCAO) in mice. Thus, these studies suggest that P6Q could be a promising candidate to prevent negative prognostic psychological symptoms following focal and global ischemia.

The role of connexin43 in hemorrhagic transformation after thrombolysis in vivo and in vitro

Thrombolysis with recombinant tissue plasminogen activator (rtPA) is the most effective drug treatment for acute ischemic stroke within 4.5h after symptom onset. However, the use of rtPA may increase the risk of hemorrhagic transformation (HT), particularly when it is administered after the first 4.5h. However, no effective treatments are available to reduce the HT risk. Disruption of the blood-brain barrier (BBB) is central to the genesis of HT. Connexin43 (Cx43)-mediated gap junction intercellular communication (GJIC) has been demonstrated to regulate the integrity of the BBB in ischemia. We investigated the effect of Cx43 on BBB permeability during rtPA-induced HT. Spontaneously hypertensive rats (SHRs) underwent a 1.5-h middle cerebral artery occlusion and were treated with rtPA at 4.5h. The rats were sacrificed at 24h, and their brains were evaluated for BBB permeability and the expression of tight junction (TJ) proteins and Cx43. We examined whether the effects were Cx43 dependent using multiple Cx43 inhibitors. Phosphorylated Cx43 (p-Cx43) but not total Cx43 protein expression was increased after rtPA treatment. Delayed rtPA administration induced significant HT and BBB disruption. These effects were attenuated by inhibitors that blocked GJIC and Cx43 phosphorylation and expression but not Cx43 redistribution. Additionally, rtPA administration upregulated p-Cx43 expression in hypoxia/reoxygenation (H/R)-exposed brain endothelial cells. These effects were suppressed by the phosphatidylinositol 3'-kinase (PI3K) inhibitor LY294002 and the extracellular signal-regulated kinase 1/2 (ERK1/2) inhibitor U0126. We suggest that rtPA-associated hemorrhage due to an alteration in the integrity of the BBB is highly associated with an increase in p-Cx43 resulting from the activation of the PI3K and ERK pathways.

Molecular requirements for safer generation of thrombolytics by bioengineering the tissue-type plasminogen activator A chain

BACKGROUND

Thrombolysis with tissue-type plasminogen activator (t-PA) is the only treatment approved for acute ischemic stroke. Although t-PA is an efficient clot lysis enzyme, it also causes damage to the neurovascular unit, including hemorrhagic transformations and neurotoxicity.

OBJECTIVES

On the basis of the mechanism of action of t-PA on neurotoxicity, we aimed at studying the molecular requirements to generate safer thrombolytics.

METHODS

We produced original t-PA-related mutants, including a non-cleavable single-chain form with restored zymogenicity (sc*-t-PA) and a t-PA modified in the kringle 2 lysine-binding site (K2*-t-PA). Both sc*-t-PA and K2*-t-PA showed fibrinolytic activities similar to that of wild-type t-PA on both euglobulin-containing and plasma-containing clots. In contrast to wild-type t-PA, the two mutants did not promote N-methyl-d-aspartate receptor-mediated neurotoxicity.

CONCLUSIONS

We designed t-PA mutants with molecular properties that, in contrast to t-PA, do not induce neurotoxicity.

tPA-S481A prevents neurotoxicity of endogenous tPA in traumatic brain injury

Traumatic brain injury (TBI) is associated with loss of autoregulation due to impaired responsiveness to cerebrovascular dilator stimuli, which leads to cerebral hypoperfusion and neuronal impairment or death. Upregulation of tissue plasminogen activator (tPA) post-TBI exacerbates loss of cerebral autoregulation and NMDA-receptor-mediated impairment of cerebral hemodynamics, and enhances excitotoxic neuronal death. However, the relationship between NMDA-receptor activation, loss of autoregulation, and neurological dysfunction is unclear. Here, we evaluated the potential therapeutic efficacy of a catalytically inactive tPA variant, tPA S481A, that acts by competing with wild-type tPA for binding, cleavage, and activation of NMDA receptors. Lateral fluid percussion brain injury was produced in anesthetized piglets. Pial artery reactivity was measured via a closed cranial window, and cerebrospinal fluid (CSF) extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase (MAPK) was quantified by enzyme-linked immunosorbent assay (ELISA). tPA-S481A prevented impairment of cerebral autoregulation and reduced histopathologic changes after TBI by inhibiting upregulation of the ERK isoform of MAPK. Treatment with this tPA variant provides a novel approach for limiting neuronal toxicity caused by untoward NMDA-receptor activation mediated by increased tPA and glutamate following TBI.

Neuroprotective effect of neuroserpin in rat primary cortical cultures after oxygen and glucose deprivation and tPA

Besides its role as a thrombolytic agent, tissue plasminogen activator (tPA) triggers harmful effects in the brain parenchyma after stroke, such as inflammation, excitotoxicity and basal lamina degradation. Neuroserpin, a natural inhibitor of tPA, has shown neuroprotective effects in animal models of brain infarct. However, the molecular mechanisms of neuroserpin-mediated neuroprotection after brain ischemia remain to be well characterized. Then, our aim was to investigate such mechanisms in primary mixed cortical cell cultures after oxygen and glucose deprivation (OGD). Primary rat mixed cortical cultures containing both astrocytes and neurons were subjected to OGD for 150min and subsequently treated with either tPA (5μg/mL), neuroserpin (0.125, 0.25, 0.5 or 1μM), and tPA together with neuroserpin at the mentioned doses. Twenty-four hours after treatment, LDH release, caspase-3 activity, MCP-1, MIP-2, active MMP-9, GRO/KC and COX-2 were measured. Statistical differences were analyzed using Student's t-test or one-way ANOVA as appropriate. Treatment with tPA after OGD increased LDH release, active MMP-9, MCP-1 and MIP-2 (all p≤0.05), but not caspase-3, GRO/KC or COX-2 compared to control. Treatment with neuroserpin after OGD decreased LDH release and active MMP-9 (all p≤0.05). It had no effect on caspase-3 activity, or on MCP-1, MIP-2, GRO/KC or COX-2 expression compared to control. Administration of tPA together with neuroserpin decreased LDH release, active MMP-9 and MIP-2 (all p≤0.05) and showed no effect on MCP-1, GRO/KC or COX-2 compared to control. Our results suggest that neuroprotective activity of neuroserpin involves attenuation on tPA-mediated mechanisms of inflammation and BBB disruption after brain ischemia.

Retinal Toxicity of Commercial Tissue Plasminogen Activator Is Mediated by the Induction of Nitric Oxide in the Mouse Retinal Primary Cells

PURPOSE

Tissue plasminogen activator (tPA) is an efficient thrombolytic agent, but the dose-dependent retinal toxicity of intravitreal injection of commercial tPA (containing L-arginine) has been reported. Here, we sought to investigate the mechanism of tPA-induced cell death in mouse retinal cell cultures and the role of nitric oxide (NO).

METHODS

Primary retinal cell cultures were maintained using glial conditioned medium (GCM) solution. Mouse retinal cell death was observed by using Hoechst-propidium iodide staining. Mouse retinal cell death was also measured by lactate dehydrogenase (LDH) assay. The formation of NO was measured using Griess reagent.

RESULTS

tPA-induced cell death was detected in mouse retinal cell cultures by Hoechst-propidium iodide staining or LDH assay. L-arginine seems to be the major factor in retinal toxicity of commercial tPA (containing L-arginine). The formation of NO was markedly increased in mouse retinal cell cultures treated with tPA (containing L-arginine) or L-arginine. NO inhibitor reduced the cell death induced by commercially available tPA or L-arginine.

CONCLUSIONS

This study suggests that l-arginine from commercial tPA (containing L-arginine) induces the majority of cell death in mouse retinal cell cultures and that its cytotoxicity may depend on the induction of NO.

Antifibrinolytic agents reduce tissue plasminogen activator-mediated neuronal toxicity in vitro

INTRODUCTION

Serine proteases and their inhibitors play an important role in physiological homeostasis including neuronal activity, hemostasis, and wound healing. Tissue plasminogen activator (tPA) is involved in normal neuronal plasticity and memory formation but can also be neurotoxic. We hypothesized that the serine protease inhibitor aprotinin confers neuronal protection by inhibiting tPA activity.

METHODS

Using cultured rat dopaminergic neuroblasts (N27 line), tPA-induced cytotoxicity was quantitated by an MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay and flow cytometry using propidium iodide DNA staining. The anti-apoptotic effects of aprotinin and other protease inhibitors were also evaluated using these systems.

RESULTS

Treatment of cultured neuroblasts with tPA (10-20 microg/ml) caused a dose-dependent decrease in cell viability (71.3+/-2.4 at 10 microg/ml down to 52.7+/-2.5% at 20 microg/m tPA, 24-h treatment), which was potentiated in the absence of serum in the culture medium (59.5+/-6.3% at 10 microg/ml down to 47.9+/-4.7% at 20 microg/ml). Aprotinin was effective in ameliorating cell death when administered 30 min before tPA exposure as shown by increased cell viability (91.8+/-0.6% at tPA at 20 microg/ml), but this protection was significantly reduced when aprotinin was administered after tPA. The efficacy of aprotinin as a neuroprotectant was equivalent or superior to other direct tPA antagonist peptides Glu-Gly-Arg-chlormethylketone (EGRck) and Phe-Pro-Arg-chlormethylketone (FPRck) in this setting.

CONCLUSION

These data suggest that one of the mechanisms of neuroprotection afforded by aprotinin may be inhibition of tPA-mediated neurotoxicity.

Neurotoxic effects of exogenous recombinant tissue-type plasminogen activator on the normal rat brain

Thrombolytic therapy with intravenous and intra-arterial recombinant tissue-type plasminogen activator (rtPA) has been established for the treatment of acute ischemic stroke. However, tPA has also been suggested to have neurotoxic effects. The purpose of this study was to examine direct neurotoxicity of rtPA in vivo. The animals (Wistar rats) were divided to the following three groups: low-dose (15 micromol/L) rtPA group (n = 6); high-dose (30 micromol/L) rtPA group (n = 6); and control (physiological saline) group (n = 6). The rtPA solution was perfused into the cortex via a microdialysis probe. The volume of the lesion was quantified histologically by image analysis of the lesions. Blood-brain barrier (BBB) disruption was evaluated by intravenous injection of Evans blue, and injury to the basal lamina was evaluated by immunohistochemistry using an anti-laminin antibody. In the rtPA-perfused animals, a pale lesion was produced around the probe, and microscopically, neurons showed necrotic changes. The volume of the lesions increased significantly as the concentration of perfused rtPA was increased. Marked extravasation of Evans blue was observed, and laminin immunoreactivity of blood vessels in the rtPA-induced lesions was lost. These results suggest that rtPA promotes acute direct neurotoxicity and participates in disruption of the microvascular basal lamina to cause BBB disruption, thereby increasing edema formation.

Investigation of the safety of tenecteplase to the outer retina

PURPOSE

To investigate the safety of the thrombolytic agent, tenecteplase to the outer retina in pig eyes.

METHODS

Tenecteplase (50 microg) was injected into the subretinal space in one eye while the fellow eye received balanced salt solution. At 24 h, 1 week and 9 weeks the eyes were examined by indirect ophthalmoscopy and photographed. Animals were killed at 9 weeks, eyes enucleated and processed for light and transmission electron microscopy. Three locations within the area of the injection bleb were analysed.

RESULTS

Retinal pigment epithelial defects, which appeared to be iatrogenic and confined to the injection site, were seen in most of the treated and control eyes. There was no significant difference in the degree of retinal damage between the two groups of eyes at the three sites examined (P > 0.05).

CONCLUSION

Fifty micrograms of tenecteplase appears to be a safe dose with no evidence of toxicity to the outer retina and may have a potential role in the treatment of submacular haemorrhage.

Tissue plasminogen activator extravasated through the cerebral vessels: evaluation using a rat thromboembolic stroke model

Neurotoxic effects of endogenous tissue plasminogen activator (tPA) have recently been reported. Employing a rat model of thromboembolic stroke, we evaluated the extent and degree of extravasation of exogenous tPA administered for the purpose of fibrinolysis. In a thromboembolic model using Sprague-Dawley rats, focal cerebral ischemia was induced at the territory of the middle cerebral artery (MCA). Early reperfusion was induced by administering tPA (10 mg/kg) intravenously at 30 minutes after the onset of ischemia. Extravasated tPA was evaluated by immunohistochemistry, and the concentration of tPA in the brain tissue was quantified by enzyme-linked immunosorbent assay methods. The integrity of the blood-brain barrier (BBB) was examined electronmicroscopically. In a thread model of transient ischemia, reperfusion was induced without tPA administration at 30 minutes or 2 hours after the onset of ischemia, and the tPA content of the brain was quantified. In the rats with thromboembolic stroke, extravasation of tPA was observed at the territory of the MCA. Both the endogenous and exogenous tPA contents were 3.5 +/- 1.6 ng/ml of homogenized brain in saline. Electronmicroscopically, mild ischemic changes were observed, although the integrity of the BBB was preserved. In the thread model rats, the endogenous tPA contents of the ischemic hemisphere were 0.9 +/- 0.1 and 1.0 +/- 0.2 ng/ml in the 30-minute and 2-hour ischemia groups, respectively, and were significantly lower than the tPA contents in the thromboembolic stroke rats (p<0.01). The present findings indicate that significant extravasation of exogenous tPA occurs through the cerebral vessels even though early reperfusion is induced.

Tissue plasminogen activator neurovascular toxicity is controlled by activated protein C

Although thrombolytic effects of tissue plasminogen activator (tPA) are beneficial, its neurotoxicity is problematic. Here, we report that tPA potentiates apoptosis in ischemic human brain endothelium and in mouse cortical neurons treated with N-methyl-D-aspartate (NMDA) by shifting the apoptotic pathways from caspase-9 to caspase-8, which directly activates caspase-3 without amplification through the Bid-mediated mitochondrial pathway. In vivo, tPA-induced cerebral ischemic injury in mice was reduced by intracerebroventricular administration of caspase-8 inhibitor, but not by caspase-9 inhibitor, in contrast to controls in which caspase-9 inhibitor, but not caspase-8 inhibitor, was protective. Activated protein C (APC), a serine protease with anticoagulant, anti-inflammatory and antiapoptotic activities, which is neuroprotective during transient ischemia and promotes activation of antiapoptotic mechanisms in brain cells by acting directly on endothelium and neurons, blocked tPA vascular and neuronal toxicities in vitro and in vivo. APC inhibited tPA-induced caspase-8 activation of caspase-3 in endothelium and caspase-3-dependent nuclear translocation of apoptosis-inducing factor in NMDA-treated neurons and reduced tPA-mediated cerebral ischemic injury in mice. Data suggest that tPA shifts the apoptotic signal in stressed brain cells from the intrinsic to the extrinsic pathway which requires caspase-8. APC blocks tPA's neurovascular toxicity and may add substantially to the effectiveness of tPA therapy for stroke.

Comparative effects of microplasmin and tissue-type plasminogen activator (tPA) on cerebral hemorrhage in a middle cerebral artery occlusion model in mice

BACKGROUND

Thrombolytic therapy of ischemic stroke with tissue-type plasminogen activator (tPA) improves clinical outcome which may, however, be partially offset by significant intracerebral bleeding (ICB).

OBJECTS

The comparative effects of microplasmin (microPli) and tPA on ICB were evaluated in a thrombotic middle cerebral artery (MCA) occlusion model in mice.

METHODS

A dose of microPli (5 mg kg(-1)) or tPA (4 mg kg(-1)) which are comparably effective for reduction of brain damage, or a double dose (10 or 8 mg kg(-1), respectively) or the microPli excipient as a control were intravenously administered as a bolus at 30 min or 4 h after MCA occlusion. ICB was measured at 24 h by hemoglobin assay of exsanguinated brain extracts. Bleeding time was measured by tail cutting.

RESULTS

In controls given solvent at 4 h, ICB was on average 8.8 micro L, which was significantly increased with 10 mg kg(-1) microPli and with 4 and 8 mg kg(-1) tPA to 12-13 micro L (P < 0.05 each vs. controls, n = 7-9), whereas 5 mg kg(-1) microPli did not affect bleeding (8.5 micro L P = NS vs. controls, n = 7). When given at 30 min, neither microPli nor tPA altered ICB (6.3-6.8 micro L, mean; n = 7-9). tPA but not microPli increased bleeding time; from 2.4 min in controls to 5.9 min (median, P < 0.05 vs. controls) and 8.7 min (P < 0.01 vs. controls) with 4 and 8 mg kg(-1), respectively, and to 2.3 and 2.9 min with 5 and 10 mg kg(-1) microPli, respectively (n = 10).

CONCLUSIONS

microPli at a dose comparably effective as tPA for brain damage reduction induced significantly less ICB, and less bleeding time prolongation in mice with thrombotic MCA occlusion.

Dose-Finding Based on Efficacy-Toxicity Trade-Offs

We present an adaptive Bayesian method for dose-finding in phase I/II clinical trials based on trade-offs between the probabilities of treatment efficacy and toxicity. The method accommodates either trinary or bivariate binary outcomes, as well as efficacy probabilities that possibly are nonmonotone in dose. Doses are selected for successive patient cohorts based on a set of efficacy-toxicity trade-off contours that partition the two-dimensional outcome probability domain. Priors are established by solving for hyperparameters that optimize the fit of the model to elicited mean outcome probabilities. For trinary outcomes, the new algorithm is compared to the method of Thall and Russell (1998, Biometrics 54, 251-264) by application to a trial of rapid treatment for ischemic stroke. The bivariate binary outcome case is illustrated by a trial of graft-versus-host disease treatment in allogeneic bone marrow transplantation. Computer simulations show that, under a wide rage of dose-outcome scenarios, the new method has high probabilities of making correct decisions and treats most patients at doses with desirable efficacy-toxicity trade-offs.

Retinal toxicity of intravitreal tenecteplase in the rabbit

AIM

To investigate the retinal toxicity of intravitreal injection of a novel fibrinolytic tenecteplase in rabbit eyes.

METHODS

Tenecteplase (25-350 micro g in 0.1 ml BSS) was injected into the vitreous cavity of normal rabbit eyes. Control (fellow) eyes received 0.1 ml of BSS. One day, 1 week, and 2 months post-injection, the eyes were examined by slit lamp biomicroscopy, indirect ophthalmoscopy, and electroretinography, and then harvested for histopathological examination.

RESULTS

No evidence of retinal toxicity was seen with tenecteplase doses up to and including 50 micro g. At a dose of 150 micro g ophthalmoscopy was normal, but histology showed mild retinal damage in the inner nuclear layer and electroretinography showed a temporary reduction in B-wave amplitude. At doses of 200 micro g and above, there was evidence of retinal toxicity on electroretinography, ophthalmoscopy, and histology. Ophthalmoscopic findings included vitreal fibrosis, retinal necrosis and tractional retinal detachment and light microscopy revealed necrosis of retinal pigment epithelium and other retinal layers. Damage was centred around the injection site but was more widespread with the higher doses.

CONCLUSION

A dose of 50 micro g tenecteplase appears safe for intravitreal injection in the rabbit. Tenecteplase could have potential applications in the treatment of submacular haemorrhage and retinal vein occlusion.

Ethanol plus caffeine (caffeinol) for treatment of ischemic stroke: preclinical experience

BACKGROUND AND PURPOSE

Ethanol and caffeine are 2 common psychoactive dietary components. We have recently shown that low-dose ethanol plus caffeine results in a 70% to 80% reduction of infarct volume after reversible common carotid/middle cerebral artery (CCA/MCA) occlusion in rats. The combination (caffeinol) was effective after either oral pretreatment or intravenous administration starting up to 2 hours after stroke onset. Ethanol alone aggravated ischemic damage, while caffeine alone was without effect. Daily caffeinol for 2 weeks before ischemia eliminated the neuroprotection seen with acute treatment (tolerance). The purpose of our present study was to further characterize the properties of caffeinol as a possible treatment for ischemic stroke.

METHODS

The transient CCA/MCA occlusion model was used in all experiments. Five sets of experiments were conducted (1) to test the effectiveness of various doses of ethanol (0.2 to 0.65 g/kg) and caffeine (3 to 10 mg/kg) in the caffeinol mixture; (2) to test whether the neuroprotective dose of caffeinol can improve behavioral dysfunction; (3) to test whether chronic ethanol or caffeine before ischemia will affect efficacy of caffeinol treatment; (4) to test whether the protective effect of caffeinol can be improved by pairing it with 35 degrees C hypothermia; and (5) to test whether caffeinol affects frequency of hemorrhage after administration of recombinant tissue plasminogen activator (rtPA) in ischemic animals.

RESULTS

Doses as low as 0.2 g/kg of ethanol and 6 mg/kg of caffeine in the caffeinol were effective in reducing cortical infarct volume and behavioral dysfunction after transient CCA/MCA occlusion. Daily exposure to ethanol but not caffeine before CCA/MCA occlusion eliminated the therapeutic efficacy of acute caffeinol treatment, similar to the tolerance observed after chronic exposure to caffeinol. The therapeutic effect of caffeinol could be further improved by pairing it with mild intraischemic hypothermia, and caffeinol did not increase hemorrhagic infarction when given in combination with rtPA.

CONCLUSIONS

Low doses of caffeinol, equivalent to no more than 2 to 3 cups of strong coffee and 1 cocktail, are consistently and highly neuroprotective, are well tolerated, can be added to other therapies to increase the effect of each, and do not interfere with or complicate rtPA therapy. Caffeinol is an appropriate candidate for clinical trial in stroke patients, although it may be less effective in patients with regular alcohol intake.

Distinct dose-dependent effects of plasmin and TPA on coagulation and hemorrhage

All thrombolytic agents in current clinical usage are plasminogen activators. Although effective, plasminogen activators uniformly increase the risk of bleeding complications, especially intracranial hemorrhage, and no laboratory test is applicable to avoid such bleeding. We report results of a randomized, blinded, dose-ranging comparison of tissue-type plasminogen activator (TPA) with a direct-acting thrombolytic agent, plasmin, in an animal model of fibrinolytic hemorrhage. This study focuses on the role of plasma coagulation factors in hemostatic competence. Plasmin at 4-fold, 6-fold, and 8-fold the thrombolytic dose (1 mg/kg) induced a dose-dependent effect on coagulation, depleting antiplasmin activity completely, then degrading fibrinogen and factor VIII. However, even with complete consumption of antiplasmin and decreases in fibrinogen and factor VIII to 20% of initial activity, excessive bleeding did not occur. Bleeding occurred only at 8-fold the thrombolytic dose, on complete depletion of fibrinogen and factor VIII, manifest as prolonged primary bleeding, but with minimal effect on stable hemostatic sites. Although TPA had minimal effect on coagulation, hemostasis was disrupted in a dose-dependent manner, even at 25% of the thrombolytic dose (1 mg/kg), manifest as rebleeding from hemostatically stable ear puncture sites. Plasmin degrades plasma fibrinogen and factor VIII in a dose-dependent manner, but it does not disrupt hemostasis until clotting factors are completely depleted, at an 8-fold higher dose than is needed for thrombolysis. Plasmin has a 6-fold margin of safety, in contrast with TPA, which causes hemorrhage at thrombolytic dosages.

The Possible Role of Tissue-Type Plasminogen Activator (tPA) and tPA Blockers in the Pathogenesis and Treatment of Alzheimer's Disease

Alzheimer's disease (AD) is the leading cause of cognitive decline in aged individuals. The pathological hallmarks of AD include the formation of neurofibrillary tangles, along with senile plaques that are mainly composed of the amyloid-beta (Abeta) peptide. Several lines of evidence implicate the tPA/plasmin system in AD. One type of cell death observed in AD is excitotoxic neuronal damage, and the tPA/plasmin system participates in excitotoxic cell death. Recent in vitro experiments report that the addition of aggregated Abeta peptide to primary cortical neurons leads to the up-regulation of tPA mRNA expression. Additionally, plasmin (activated by tPA) attenuates Abeta neurotoxicity by degrading the peptide and rendering it inactive. However, there is no evidence to demonstrate an in vivo contribution of the tPA/plasmin system in AD. We are currently examining the effects of the tPA/plasmin system on the deposition and toxicity of the Abeta peptide with in vivo paradigms of AD. We hope to define the contribution of the tPA/plasmin system in the development of AD pathology.

Smad3-dependent induction of plasminogen activator inhibitor-1 in astrocytes mediates neuroprotective activity of transforming growth factor-beta 1 against NMDA-induced necrosis

The intravenous injection of the serine protease, tissue-type plasminogen activator (t-PA), has shown to benefit stroke patients by promoting early reperfusion. However, it has recently been suggested that t-PA activity, in the cerebral parenchyma, may also potentiate excitotoxic neuronal death. The present study has dealt with the role of the t-PA inhibitor, PAI-1, in the neuroprotective activity of the cytokine TGF-beta1 and focused on the transduction pathway involved in this effect. We demonstrated that PAI-1, produced by astrocytes, mediates the neuroprotective activity of TGF-beta 1 against N-methyl-D-aspartate (NMDA) receptor-mediated excitotoxicity. This t-PA inhibitor, PAI-1, protected neurons against NMDA-induced neuronal death by modulating the NMDA-evoked calcium influx. Finally, we showed that the activation of the Smad3-dependent transduction pathway mediates the TGF-beta-induced up-regulation of PAI-1 and subsequent neuroprotection. Overall, this study underlines the critical role of the t-PA/PAI-1 axis in the regulation of glutamatergic neurotransmission.

Reteplase infusion in the treatment of acute lower extremity occlusions

PURPOSE

Reteplase, a recombinant tissue plasminogen activator, has been used in the treatment of acute coronary occlusion. Experience is accumulating regarding its use in the treatment of peripheral vascular disease. Increased experience with this thrombolytic agent may show that it can be an appropriate alternative agent to currently employed plasminogen activators.

MATERIALS AND METHODS

Over the course of six months, reteplase was used to treat 18 patients with peripheral arterial occlusions, confined to the lower extremities. The agent was infused via "pulse-spray" catheters. Fifteen patients were started on 0.5 U/h. Concurrent heparin therapy was used at 500 U/h in 16 of 18 patients.

RESULTS

The average total dose of reteplase infused was 13.3 units. It ranged from 6.2 to 41.5 units. The average duration of infusion was 26.9 hours with a range of 12-44 hours. Clinical success, defined as restoration of sufficient patency to reestablish limb function and resolution of pain in the symptomatic extremity was 89% (16 out of 18). Hemorrhagic complications occurred in five patients and were major in one patient (5%). No patient experienced intracranial hemorrhage.

CONCLUSION

Increased experience with the use of reteplase in the treatment of acute lower extremity occlusions is accumulating. The safety and efficacy profile in our group appears satisfactory and compares to other studies. However, definite conclusions must await the results of controlled comparisons of different reteplase infusion regimens and controlled comparison to other thrombolytic agents.

Lanoteplase Genetics Institute

Lanoteplase, a modified form of a tissue plasminogen activator (t-PA) lacking fibronectin finger-like and epidermal growth factor domains, was developed by the Genetics Institute for the potential treatment of thromboembolic disorders. Suntory, the Japanese licensee, has filed an NDA in Japan for the treatment of acute myocardial infarction (MI) [301222]. It was also licensed to Bristol-Myers Squibb (BMS) for worldwide development (excluding Japan, China, South Korea and Taiwan) [178225]. BMS conducted phase III trials for acute MI [272490] but discontinued development and returned the license to Genetics Institute during 1999 [359688]. In February 1999, Lehman Brothers predicted the drug had a 60% probability of reaching market, with an estimated first launch date in 2000. The analysts predicted peak sales would occur in 2006, with peak sales of $200 million in the US and US $100 million in the rest of the world at that time [319225].

Retinal toxicity of commercial intravitreal tissue plasminogen activator solution in cat eyes

BACKGROUND

We previously reported retinal toxic reactions in rabbit eyes receiving intravitreal injections of commercial tissue plasminogen activator (tPA) in concentrations greater than or equal to 50 microg/0.1 mL, and recent clinical experience suggests that intravitreal tPA solution may produce toxic effects in human eyes. We therefore investigated the dose-dependent retinal toxicity of intravitreal commercial recombinant tPA solution in cat eyes, which have a vascularized inner retina and vitreous volume similar to that of human eyes.

METHODS

Commercial tPA in L-arginine solution was injected into the mid vitreous cavity of normal cat eyes in doses of 25, 50, 75, and 100 microg/0.1 mL and 200 microg/0.2 mL. Control (fellow) eyes received an equal volume of sterile saline solution. After injection, eyes were evaluated by ophthalmoscopy and electroretinography for 14 days and then enucleated for histopathological evaluation.

RESULTS

Fundus pigmentary alterations were observed in eyes receiving doses greater than or equal to 50 microg/0.1 mL. Changes were centered in the area around the injection site, and the area's size increased in proportion to the dosage. Mean electroretinography B-wave amplitude measured at 14 days was significantly reduced in eyes receiving greater than or equal to 50 microg of tPA in a dose-dependent fashion. Light microscopy of the involved areas showed loss of photoreceptor elements with necrosis and proliferation of the retinal pigment epithelium.

CONCLUSION

Intravitreal injection of commercial tPA solution results in dose-dependent retinal toxicity in cat eyes.

CLINICAL RELEVANCE

Because cat eyes are similar to human eyes regarding retinal vascularity and vitreous volume, intravitreal injections of commercial tPA (with L-arginine vehicle) in concentrations greater than 25 microg/0.1 mL are potentially unsafe in human eyes.

Comparative effects of tissue plasminogen activator, streptokinase, and staphylokinase on cerebral ischemic infarction and pulmonary clot lysis in hamster models

BACKGROUND

The effects of alteplase (rtPA), streptokinase, and staphylokinase (rSak) on focal cerebral ischemia (FCI) and on pulmonary clot lysis (PCL) were studied in hamsters.

METHODS AND RESULTS

++FCI was produced by ligation of the left middle cerebral artery (MCA) and common carotid artery (CCA) and a 10-minute occlusion of the right CCA. FCI was measured after 24 hours by 2,3, 5-triphenyltetrazolium chloride staining. (125)I-fibrin-labeled plasma clots were injected via the jugular vein, and clot lysis was determined from residual radioactivity at 90 minutes. Study drugs were given intravenously over 60 minutes. FCI increased from 1.2 (0. 27 to 2.3) mm(3) (median and 17th to 83rd percentile range, n=24) in controls to 19 to 27 mm(3) with thrombolytic agent, with maximal rates at 0.13+/-0.05 mg/kg rtPA, 0.23+/-0.09 mg/kg streptokinase, and 0.037+/-0.025 mg/kg rSak. PCL increased from 18+/-2% (mean+/-SEM, n=27) in controls to approximately 85% with thrombolytics, with maximal rates at 0.12+/-0.03 mg/kg rtPA, 0.17+/-0.05 mg/kg streptokinase, and 0.018+/-0.002 mg/kg rSak. All agents caused maximal FCI and PCL rates at similar doses without alpha(2)-antiplasmin and fibrinogen depletion. Injection of 6 mg/kg human plasminogen combined with streptokinase caused a "systemic fibrinolytic state" with fibrinogen depletion. Maximal rates of FCI were obtained with 0.097+/-0.077 mg/kg streptokinase (P=0.26 versus streptokinase alone) and of PCL with 0.010+/-0.002 mg/kg (P=0.006 versus streptokinase alone).

CONCLUSIONS

Thrombolytic agents cause similar dose-related extension of FCI after MCA ligation and PCL, irrespective of the agent or systemic plasmin generation.

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.

Early (1 h) administration of tissue plasminogen activator reduces infarct volume without increasing hemorrhagic transformation after focal cerebral embolization in rats

We assessed the incidence of hemorrhagic transformation and infarct volume after early intravenous infusion of recombinant human tissue plasminogen activator (rht-PA) in a newly developed rat cerebral embolic model. Male Wistar rats (n=60) were subjected to middle cerebral artery (MCA) occlusion by a single fibrin rich clot. One hour after embolization, rats were assigned to the following groups: (1) rht-PA treated group (n=20); (2) vehicle treated group (n=20); and (3) saline treated group (n=20). Neurological deficits, lodgement of a clot at the origin of the MCA, infarction volume and microscopic hemorrhage were measured. Animals exhibited moderate to severe neurological deficits 1 h after MCA occlusion in all groups. Administration of rht-PA significantly (P<0.05) reduced the incidence of lodgement of a clot at the origin of the MCA (30%) compared with the saline treated group (100%) and the vehicle treated group (80%). A significant (P<0.05) reduction of percent hemispheric infarct volume was detected between the saline (33.2+/-3.71%) and the rht-PA groups (19.4+/-3.3%). However, no significant difference was found in the total area of microscopic hemorrhage of the rht-PA (0.05+/-0.02 mm2), the vehicle (0.02+/-0.01 mm2), and the saline (0.03+/-0.02 mm2) treated groups. No significant difference of percent hemispheric infarct volume (P=0.08) was observed between the vehicle and the rht-PA treated groups. This study demonstrates that treatment with rht-PA reduced infarct volume without increasing intracerebral hemorrhage in rats with large cerebral infarction when treatment was initiated at 1 h of the onset of embolization.

Effect of a synthetic factor Xa inhibitor, YM-60828, on blood vessel patency in combination with a thrombolytic agent and on blood loss from the operation site in a rat model of arterial thrombosis

We examined the adjunctive effect of a novel factor Xa inhibitor, YM-60828, on vessel patency and blood loss from the operation site after successful thrombolysis with a modified tissue-type plasminogen activator (moPA) in an electrically-induced carotid artery thrombosis model in rats. Five minutes after the induction of occlusive thrombus, a test drug (YM-60828, argatroban, heparin or saline) was administered by i.v. bolus injection followed by continuous infusion. Thrombolysis was induced with moPA by i.v. bolus injection at a dose of 650,000 IU/ kg. YM-60828 at 1 mg/kg i.v. followed by 3 mg/kg/h significantly prevented reocclusion, increased the duration of patency, and improved vessel patency after successful thrombolysis without any significant increase in blood loss from the operation site. Argatroban at 1 mg/kg i.v. followed by 3 mg/kg/h and heparin at 300 U/kg i.v. followed by 150 U/kg/h also significantly improved these parameters, but were accompanied by a significant increase in blood loss. These results suggest that the factor Xa inhibitor YM-60828 may be a potent and useful adjunctive agent with a lower risk of bleeding complications than argatroban and heparin in thrombolytic therapy.

Comparison of enoxaparin, hirulog, and heparin as adjunctive antithrombotic therapy during thrombolysis with rtPA in the stenosed canine coronary artery

A canine model of electrolytic injury-induced coronary artery thrombosis and rtPA-induced thrombolysis was used to evaluate the relative antithrombotic efficacy of enoxaparin (a low molecular weight heparin), conventional therapy (heparin or heparin plus aspirin), and hirulog (a direct thrombin inhibitor), when used as adjunctive therapy during thrombolysis. After 60 min of clot aging, adjunctive therapy was begun at doses which elevated APTT approximately 2-fold over baseline. Fifteen minutes after the start of adjunctive therapy, recombinant tissue plasminogen activator (rtPA) was administered (100 microg/kg i.v. bolus + 20 microg/kg/min for 60 min). Adjunctive therapy continued for 1 h after termination of rtPA and blood flow was monitored for two additional hours. Enoxaparin (1 mg/kg i.v. bolus + 30 microg/kg/min, n = 10 for each treatment group) was the only adjunctive treatment that significantly increased the total minutes of flow (143 +/- 25 min out of a possible 240 min, vs 54 +/- 25 min for vehicle, p <0.05) and decreased thrombus mass (6.0 +/- 1.3 mg vs 11.8 +/- 3.2 mg for vehicle). Although hirulog (2 mg/kg i.v. bolus + 40 microg/kg/min) did not significantly increase the minutes of flow (120 +/- 27 min, p <0.06) or decrease thrombus mass (8.7 +/- 1.7 mg) compared to vehicle, these values were not significantly different than those measured in the enoxaparin group. However, the results with hirulog were achieved at the expense of a significantly greater increase in template bleeding time than that measured during enoxaparin treatment. Minutes of flow for heparin (50 U/kg i.v. bolus + 0.6 U/kg/min) and heparin plus aspirin (5 mg/kg i.v. bolus) were 69 +/- 20 and 60 +/- 23 min, respectively; thrombus masses were 8.2 +/- 1.3 and 7.3 +/- 1.0 mg, respectively. In summary, enoxaparin was more effective than conventional therapy in this model in terms of vessel patency and thrombus mass, and was as effective as hirulog, at least at a dose of hirulog that only modestly impaired hemostasis. Therefore, enoxaparin may prove to be a safe and effective alternative agent for adjunctive therapy during thrombolysis with rtPA.

Reproductive toxicity, mutagenicity and antigenicity of pamiteplase (genetical recombination)

Pamiteplase (genetical recombination), YM866, is a novel recombinant modified human tissue-type plasminogen activator developed by Yamanouchi Pharmaceutical Co. Ltd., Tokyo, Japan. An intended route of administration in the clinical use of this drug is intravenous administration. We conducted an intravenous fertility and general reproduction studies of this drug in male and female rats and teratology study of this drug in rabbits at the dose levels of 0 (vehicle control), 0.1, 0.3 or 1 mg/kg/day. In the rat, no treatment-related abnormalities were observed up to the maximum dose in parental animals and their offspring. In the teratology study in rabbits, prolonged coagulation time at the injection site was observed at 0.3 mg/kg or more. One death and one abortion occurred at 1 mg/kg on days 22 and 23 of pregnancy, respectively. No toxic effects on the litters were observed up to the maximum dose. Results of evaluation of the mutagenicity of YM866 and its ability to induce chromosome aberrations using the L5178Y TK+/- mouse lymphoma assay, human lymphocyte chromosome aberration assay and the micronucleus assay in mice were negative. Evaluation of the immunogenicity of YM866 by repeated intravenous injection in chimpanzees elicited no confirmed antibody titers.

Single and repeated intravenous toxicity studies of pamiteplase (genetical recombination) in rats and monkeys

Single and repeated intravenous toxicity studies of Pamiteplase (genetical recombination) YM866, a novel recombinant human tissue-type plasminogen activator, were conducted. No animal died from toxic effects of YM866 after single administration to F344 rats, squirrel monkeys and cynomolgus monkeys. Male and female F344 rats were given YM866 intravenously for 4 weeks at doses of 0 (vehicle), 0.1, 0.3 and 1 mg/kg/day. An increase in platelet count, slight decreases in hemoglobin and hematocrit, increases in plasma phospholipids, total cholesterol and total protein, and liver weight were observed at 1.0 mg/kg. Histopathology revealed no changes in any organ except for hemorrhage at the injection sites. These changes recovered after 4 weeks of withdrawal. Male and female squirrel monkeys were given YM866 intravenously for 4 weeks at doses of 0 (saline), 0 (vehicle), 0.1, 0.3 and 1 mg/kg/day. Prolongation of coagulation time at the injection site was observed at 0.3 mg/kg or more. Subcutaneous hemorrhage and a transient decrease in locomotor activity were observed at 1 mg/kg. Prolongation of coagulation time at the injection site was considered to be related to the pharmacological action of YM866. The results show that the approximate single lethal dose of YM866 is more than 60 mg/kg in rats, and more than 10 mg/kg in squirrel monkeys and cynomolgus monkeys. The no-toxic-effect level of YM866 after repeated administration for 4 weeks in rats and squirrel monkeys is considered to be 0.3 mg/kg.

Delayed tissue-plasminogen activator therapy in a rabbit model of thromboembolic stroke

This study investigated the efficacy and safety of delayed therapy with tissue-plasminogen activator (t-PA) in a rabbit model of thromboembolic stroke. The t-PA therapy was started 3, 4, or 5 hours after autologous clot embolization. New Zealand rabbits were randomized to receive a 2-hour intravenous infusion of either t-PA (6.3 mg/kg) or a saline solution (0.9% saline) after an autologous clot had embolized the anterior cerebral circulation. Regional cerebral blood flow (rCBF), intracranial pressure (ICP), and infarct size were measured to determine the effects of the delayed administration of the t-PA after intracranial embolization. Additionally, the following physiological parameters were monitored throughout the protocol: mean arterial pressure, hematocrit, arterial blood gases, glucose, and core and brain temperatures. All animals were studied for 4 hours after the administration of the t-PA or control solution; thus, the duration of each experiment was 7, 8, or 9 hours after autologous clot embolization. In control animals, brain infarct size and final ICP values were directly related to the length of time studied after clot embolization; among control animals, the largest infarct size and greatest rise in ICP were seen 9 hours after embolization.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of the bleeding potential of vampire bat salivary plasminogen activator versus tissue plasminogen activator in an experimental rabbit model

BACKGROUND

Vampire bat salivary plasminogen activator (Bat-PA) has significantly greater fibrin specificity than any of the fibrinolytic agents currently in clinical use. This study tests the hypothesis that avoiding fibrinogen depletion may protect against the hemorrhage induced by plasminogen activator treatment.

METHODS AND RESULTS

Bat-PA was compared with tissue-type plasminogen activator (TPA) in a randomized, prospective, and blinded study using a rabbit ear puncture model of fibrinolytic bleeding. The two agents were used at equimolar dosages (42 nmol/kg) that yielded similar thrombolytic efficacies in a rabbit femoral artery thrombosis model. Both Bat-PA and TPA prolong primary bleeding to double the baseline values, from between 2.1 and 2.3 minutes to between 4.8 and 5.2 minutes. Rebleeding from hemostatically stable sites during the 3-hour observation period occurred equally often with Bat-PA and TPA, 31% from preinjection sites and 23% to 25% from postinjection sites. The lag time between the time of plasminogen activator injection and the onset of rebleeding was likewise the same for both agents, most occurring at 41 to 57 minutes. However, a greater number of prolonged primary or rebleeding occurrences continued for longer than 10 minutes (63% versus 36%) or longer than 30 minutes (30% versus 10%) after Bat-PA than TPA injection. Animals treated with TPA showed a dramatic decrease in plasma fibrinogen and factor VIII concentrations, but those in the Bat-PA treatment group showed only a slight decrease from control values.

CONCLUSIONS

The results indicate that fibrinolytic bleeding after plasminogen activator infusion into rabbits did not correlate with the intensity of the plasma proteolytic state. If anything, Bat-PA usage was associated with a higher proportion of more protracted fibrinolytic bleeding episodes, despite the relatively mild lytic state in comparison with that induced by TPA.

Thrombolytic treatment with tissue-type plasminogen activator (t-PA) containing liposomes in rabbits: a comparison with free t-PA

In this study, we aimed at improving the therapeutic index of tissue-type Plasminogen Activator (t-PA) as thrombolytic agent in the treatment of myocardial infarction. Liposome-encapsulated t-PA was tested in a rabbit jugular vein thrombosis model: administration of free t-PA (t-PA) as a bolus injection in the ear vein was compared to a similar administration of liposomal t-PA (t-PA-lip), liposomal t-PA in plasminogen-coated liposomes (Plg-t-PA-lip), a mixture of free t-PA and empty liposomes (t-PA+ empty lip) and a saline-blank (blank) in terms of thrombolytic activity and side effects. Liposomal t-PA (t-PA-lip/Plg-t-PA-lip) showed a significantly better thrombolysis efficiency than equimolar doses of free t-PA (t-PA/ t-PA+ empty lip): about 0.24 mg/kg of liposomal t-PA practically equalled the lysis-activity of a dose of free t-PA of 1.0 mg/kg (t-PA1mg/kg). On the other hand, liposome encapsulation did not affect the systemic activation of alpha 2-antiplasmin and plasminogen by t-PA. We conclude that for this model an improvement in thrombolytic efficacy of t-PA is achieved by liposome encapsulation of t-PA. As t-PA-lip and Plg-t-PA-lip -treatment induced similar results, targeting of liposomal t-PA by coupled glu-Plg remains a topic to be optimized in future studies.

Effect of intravitreal tissue plasminogen activator on experimental subretinal hemorrhage

PURPOSE

To study the effect of intravitreally injected tissue plasminogen activator (tPA) in an experimental model of subretinal hemorrhage.

METHODS

Autologous blood was transsclerally injected into the subretinal space in 34 albino rabbits. One day later tPA was injected into the posterior vitreous in 24 eyes and saline was injected into 10 control eyes. Lysis of the subretinal blood was assessed ophthalmoscopically and retinal function was evaluated electroretinographically.

RESULTS

In all eyes in which tPA was injected intravitreally 1 day after subretinal injection of blood, the formed subretinal clots was not visible within 24 hours of treatment. Liquefied subretinal blood that formed from clot lysis disappeared within 6 days. Conversely, in all saline-injected control animals, the subretinal clots were unchanged at 24 hours and were observed for at least 3 days after injection. As a result of the presence of subretinal blood, scotopic electroretinogram amplitudes were markedly reduced in the tPA and saline-injected groups. In many eyes, blood migrated from the subretinal space into the vitreous, but it was detected later, was less severe, and cleared more rapidly after tPA injection.

CONCLUSION

Intravitreal injection of tPA 1 day after subretinal injection of blood in rabbits facilitated more rapid lysis of the clotted blood, however, retinal damage was not prevented.

Thrombolytic and haemorrhagic effects of bolus doses of tissue-type plasminogen activator and a hybrid plasminogen activator with prolonged plasma half-life (K2tu-PA: CGP 42935)

K2tu-PA is a hybrid plasminogen activator linking the kringle 2 domain of tissue-type plasminogen activator (t-PA) to the catalytic protease domain of single-chain urokinase-type plasminogen activator (scu-PA). K2tu-PA, as t-PA has high affinity for fibrin and is activated by fibrin but has a longer plasma half-life (over 30 min). The aim of this study was to compare the effects of bolus doses of recombinant t-PA (rt-PA) and K2tu-PA, on: 1) lysis of performed thrombi (fibrinolysis), 2) accretion of new fibrin on pre-existing thrombi during fibrinolysis (thrombus growth), 3) thrombolysis as assessed by reduction of thrombus weight and 4) systemic plasma proteolysis and blood loss from a standard wound. A jugular vein thrombosis model and an ear bleeding model were adopted in rabbits. Saline produced 11 +/- 2% fibrinolysis. rt-PA, 0.2 mg/kg, 0.4 mg and 0.8 mg/kg produced 35 +/- 4%, 54 +/- 4% and 78 +/- 6% fibrinolysis, respectively. K2tu-PA, at the same doses, produced 39 +/- 5%, 57 +/- 6% and 83 +/- 6% fibrinolysis, respectively. Thus, no differences in the fibrinolytic activity of rt-PA and K2tu-PA were observed. Injection of saline was followed by an accretion of 56.4 +/- 5.9 micrograms of radioactive new fibrin on the thrombi. The injection of the three increasing doses of rt-PA was followed by an accretion of 54.9 +/- 5.3 micrograms, 49.1 +/- 6.1 micrograms and 47.2 +/- 4.8 micrograms.(ABSTRACT TRUNCATED AT 250 WORDS)

A bleeding model in rabbits demonstrate fresh clot selectivity for a genetically engineered variant of tissue-type plasminogen activator and for streptokinase

The way in which three thrombolytic agents, tissue-type plasminogen activator (t-PA), streptokinase (SK) and a genetically engineered variant of t-PA composed of the second kringle and the protease domain (K2P), cause the dissolution of haemostatic plugs of differing ages was investigated in a novel rabbit model. Standardized incisions were made on the rabbit ear and the wounds were left to heal for 0.5 h or 24 h, before the thrombolytic agents were infused. In the absence of heparin, t-PA showed little discrimination between clots of different ages (36% and 28% lysis of the 0.5 h and 24 h wounds, respectively). In contrast, K2P and SK showed a pronounced fresh clot selectivity since they were significantly more effective in lysing fresh clots than old ones (68% and 4% lysis for K2P and 72% and 36% for SK, respectively). In the presence of heparin the potency of t-PA on fresh clots was considerably increased whilst the effect on old clots was not affected, a fresh clot selectivity for t-PA (64% lysis of fresh clots, 24% lysis of old clots) was thus effected. Heparin did not significantly affect the fresh clot selectivity of K2P or SK, although lysis of old clots was increased (from 4% to 36%) when it was given together with K2P. Furthermore, heparin did not affect the time to onset of bleeding nor was the bleeding time prolonged by its addition. The bleeding time observed for t-PA (20-25 min) was markedly shorter than that found for K2P or SK (40-50 min).(ABSTRACT TRUNCATED AT 250 WORDS)

An animal model of fibrinolytic bleeding based on the rebleed phenomenon: application to a study of vulnerability of hemostatic plugs of different age

The primary bleeding time is prolonged when tested during the infusion of both plasminogen activators and anticoagulants, and such sites frequently exhibit rebleeding after initial hemostatic control. This study describes an animal (rabbit) model which distinguishes fibrinolytic from anticoagulant hemorrhage and further applies the model to the study of hemostatic plugs of increasing age. In this model, rebleeding occurred from hemostatically-stable ear puncture sites induced prior to infusion of streptokinase (SK) or recombinant tissue-plasminogen activator (rt-PA), but not of heparin or hirudin. This distinction was apparent even for lesions induced only 15 minutes prior to the infusion and fibrinolytic bleeding was observed in such lesions induced up to 24 hours earlier. Post-infusion sites bled more quickly than did pre-infusion sites, and there was a gradual decrease in susceptibility of such prior trauma sites for rebleeding, evidenced not only by a lower proportion of sites that rebled, but also by a longer lag time after starting SK or rt-PA before such rebleeding occurred. At the dosages tested, SK showed a trend (not statistically significant) toward more sites that rebled, while rt-PA showed a trend towards a longer duration of rebleeding. Thus, this animal model of rebleeding appears to be unique for fibrinolytic agents and allows for more detailed study of the physiological mechanisms of such bleeding and for a multifaceted comparison of the bleeding potential of plasminogen activators.

K1K2Pu, a recombinant t-PA/u-PA chimera with increased thrombolytic potency, consisting of amino acids 1 to 3 and 87 to 274 of human tissue-type plasminogen activator (t-PA) and amino acids 138 to 411 of human single chain urokinase-type plasminogen activator (scu-PA). Purification in centigram quantities and conditioning for use in man

K1K2Pu, a recombinant t-PA/u-PA chimera with increased thrombolytic potency in animal models of venous and arterial thrombosis, which consists of amino acids 1 to 3 and 87 to 274 of human tissue-type plasminogen activator (t-PA) and amino acids 138 to 411 of human single chain urokinase-type plasminogen activator (scu-PA), was produced and conditioned for use in patients. Chinese hamster ovary cells were transfected with an expression plasmid containing the K1K2Pu cDNA, high producer cell lines were selected and scaled up in 800 cm2 roller bottles, and 350 ml conditioned cell culture medium was harvested 3 to 7 times at 2 to 5 day intervals. Batches of 21 +/- 4 liter (mean +/- SD, n = 28) containing 1.8 +/- 0.6 mg/l of K1K2Pu related antigen were purified by chromatography on Copper chelate-Sepharose and immunoadsorption on an insolubilized murine monoclonal antibody (MA-1C8). Yields were 8.6 +/- 3.4 mg K1K2Pu per batch with a specific activity of 83,000 +/- 44,000 IU/mg. The final material, obtained at a concentration of approximately 0.7 mg/ml, was dialyzed against 0.3 M NaCl, 0.02 M Tris-HCl buffer, pH 7.5, containing 0.01% Tween 80 and 10 KIU/ml aprotinin. It was homogeneous on SDS-PAGE, contained 6.5 +/- 6.9 percent two chain material and the contamination with murine monoclonal antibody was less than 0.1 percent. After filtration of pools of 3 to 5 selected batches on 0.22 microns Millipore filters the material was sterile and virus free by routine screening; it was obtained at a concentration of approximately 0.5 mg/ml with a specific activity of 110,000 +/- 16,000 IU/mg (mean +/- SD, n = 3) and an endotoxin content of 0.5 to 7 units/mg. Bolus injection at a dose of 1 mg/kg in mice did not produce weight loss within 8 days. Thus, this material appears to be suitable for the investigation on a pilot scale of the pharmacokinetic and thrombolytic properties of K1K2Pu in patients with thromboembolic disease.

Evaluation of a commercial recombinant tissue-type plasminogen activator preparation in the subretinal space of the cat

To explore the feasibility of using human recombinant tissue-type plasminogen activator in the management of subretinal hemorrhage, we examined the toxic effects of a commercial preparation of human recombinant tissue-type plasminogen activator in the subretinal space of the holangiotic retina of the cat. Various concentrations of human recombinant tissue-type plasminogen activator and controls were infused into the subretinal space with a glass micropipette (40- to 60-microns tip) to form a retinal bleb. Concentrations from 2.5 mg/L to 200 mg/L were well tolerated without ultrastructural toxic effects, while 1000 mg/L of human recombinant tissue-type plasminogen activator caused severe, irreversible toxic effects to the photoreceptor-retinal pigment epithelium complex. This toxic effect appeared to be due to the carrier vehicle rather than the human recombinant tissue-type plasminogen activator protein itself. Our results demonstrate that commercially prepared human recombinant tissue-type plasminogen activator can be safely used in the subretinal space of the cat with the range necessary for fibrinolysis.

Retinal toxicity of human tissue plasminogen activator in vitrectomized rabbit eyes

The retinal toxicity of human tissue plasminogen activator in normal rabbit eyes has recently been reported. We now report the retinal toxicity of tissue plasminogen activator in three groups of vitrectomized rabbit eyes. Group 1 underwent gas compression of the vitreous followed by tissue plasminogen activator injection in doses of 25, 50, and 100 micrograms (all doses were administered in 100 microL of fluid). Group 2 underwent lensectomy and vitrectomy followed by tissue plasminogen activator injection of 100 micrograms. Group 3 underwent lensectomy, vitrectomy, and complete fluid/gas exchange prior to injections of 12.5 and 25 micrograms of tissue plasminogen activator. Control eyes received 100 microL of balanced salt solution. In group 1, no retinal toxic reactions were observed after administration of 25 or 50 micrograms of tissue plasminogen activator, but all eyes receiving 100 micrograms demonstrated retinal damage on ophthalmoscopy, electroretinography, and light microscopy. In group 2, no retinal toxic reactions were seen after administration of 100 micrograms of tissue plasminogen activator. In group 3, two of 11 eyes receiving 25 micrograms of tissue plasminogen activator demonstrated toxic retinal changes by ophthalmoscopy, electroretinography, and light microscopy. These results suggest that gas compression of the vitreous does not significantly alter the toxic changes seen caused by tissue plasminogen activator. While lensectomy and vitrectomy appears to widen the therapeutic window for tissue plasminogen activator, the margin of safety is reduced with the addition of a large gas bubble.

Resolution of experimental intravitreal fibrin by tissue plasminogen activator

Intravitreal fibrin clots were produced by intravitreal injection of 0.2 ml of autologous plasma in 62 rabbit eyes. The intravitreal injection of 0.25 micrograms or more of tissue plasminogen activator(tPA) resulted in a total clearing of intravitreal fibrin within one day in all treated eyes. This was significantly faster than in the control eyes, in which complete clearing was not seen until 8 days later. This represents the plateau on the dose-response curve in doses ranging from 0.25 to 200 micrograms. With light microscopy and transmission electron microscopy, retinal toxicity was demonstrated in eyes enucleated seven days after injection of 25 micrograms or more of tPA. This study demonstrates that tPA was effective and safe at 12.5 micrograms or less in clearing intravitreal fibrin in an experimental model. These results suggest that low dosages of tPA, probably of 3 micrograms or less, may be useful in the treatment of severe postvitrectomy fibrin formation seen clinically.

The effect of tissue plasminogen activator on retinal bleeding

Tissue plasminogen activator is a potent thrombolytic agent that recently has been used to treat postvitrectomy fibrin formation. However, a recent report noted anterior and posterior segment bleeding following intracameral tissue plasminogen activator injection. In this study, we performed lensectomy and vitrectomy in 20 rabbits. A retinal blood vessel was incised to stimulate intraocular hemorrhage; bleeding was controlled and vitreous hemorrhage aspirated. Postoperatively, one eye received a 0.1-mL injection of tissue plasminogen activator (25 micrograms); the other received balanced salt solution. The eyes receiving tissue plasminogen activator had a 28% incidence of increased anterior chamber blood and a 61% incidence of increased intravitreal blood. There was no evidence of postinjection bleeding in eyes receiving balanced salt solution. Most cases of bleeding occurred within 24 hours of tissue plasminogen activator injection. Administration of tissue plasminogen activator in the setting of segmented blood vessels may lead to intraocular hemorrhage.

Retinal toxicity of recombinant tissue plasminogen activator in the rabbit

We studied the dose-dependent retinal toxicity of the available commercial preparation of human recombinant tissue plasminogen activator in the normal rabbit eye. Tissue plasminogen activator was injected into the midvitreous cavity of albino rabbits in doses (per 100 microL) of 25, 50, 75, and 100 micrograms. Control eyes received 100 microL of balanced salt solution or tissue plasminogen activator vehicle. No evidence of a retinal toxic reaction was seen in eyes receiving 25 micrograms of tissue plasminogen activator. One of four eyes injected with 50 micrograms showed loss of photoreceptor cells by light microscopy. Severe retinal damage was seen by ophthalmoscopy, electroretinography, and light microscopy in three of four eyes receiving 75 micrograms of tissue plasminogen activator and in all eyes treated with 100 micrograms of tissue plasminogen activator or equivalent vehicle. These results suggest that the commercial recombinant tissue plasminogen activator formulation has a narrow margin of safety in nonvitrectomized eyes and that a component of the vehicle is the toxic factor.

Tissue plasminogen activator therapy of rabbit nephrotoxic nephritis

To study the efficacy of tissue plasminogen activator (PA) therapy to prevent deteriorating renal function in experimental proliferative glomerulonephritis we used a model of nephrotoxic nephritis induced in rabbits by injection of antiglomerular basement membrane antiserum. Saline or recombinant tissue plasminogen activator (rt-PA, 1.3 mg/kg body weight) was infused daily for 7 days starting from day 7 after the injection of antiglomerular basement membrane antiserum when the disease had been already triggered. Animals were killed on day 14. Rabbits given saline had abundant deposits of fibrin and crescents in about 67% of glomeruli. rt-PA significantly protected animals from glomerular fibrin deposition and crescent formation with respect to saline-treated animals. Renal function measured as creatinine clearance was dramatically impaired in rabbits given saline. Treatment with rt-PA ameliorated the renal function impairment of nephrotoxic nephritis. rt-PA did not produce a systemic fibrinolytic state as indicated by alpha 2-antiplasmin level measurement. These results suggest that tissue PA may have important implications in preventing renal function deterioration in humans with crescentic glomerulonephritis and fibrin depositions.

Recombinant plasminogen activator inhibitor-1 reverses the bleeding tendency associated with the combined administration of tissue-type plasminogen activator and aspirin in rabbits

The major side effect of thrombolytic therapy is bleeding; however, the pathogenesis of this potential complication is not well understood. Accordingly, we examined the effects of aspirin and recombinant human tissue-type plasminogen activator (rt-PA) on serial template bleeding times and on hemostasis parameters in rabbits. The administration of intravenous aspirin (15 mg/kg) produced a slight prolongation in bleeding times, from 2.1 +/- 0.5 to 2.6 +/- 0.5 min (mean +/- SD, n = 26, P less than 0.01), whereas rt-PA (1 mg/kg per h for 2 h) lengthened the bleeding time from 2.4 +/- 0.3 to 3.2 +/- 0.6 min (n = 5, P = NS). Combination of aspirin with 0.5 mg/kg per h of rt-PA for 2 h prolonged the bleeding time from 2.5 +/- 0.4 to 6.2 +/- 0.9 min (n = 10, P less than 0.01), with an associated fibrinogen decrease of approximately 15%. The combination of aspirin with 1 mg/kg per h of rt-PA for 2 h prolonged the bleeding time from 3.0 +/- 0.3 to 8.3 +/- 1.4 min (n = 8, P less than 0.01) and simultaneously induced a decrease of plasma fibrinogen by approximately 40%. Virtually all animals treated with rt-PA and aspirin manifested a bleeding tendency, as evidenced by spontaneous rebleeding at sites of previously performed template bleeding times or oozing at the femoral venous catheterization site. Intravenous bolus injection of 1 mg/kg of guanidine hydrochloride-reactivated recombinant human plasminogen activator inhibitor-1 (rPAI-1) at the end of the rt-PA infusion resulted in complete reversal, within 5 min, of the prolongation of the bleeding time, and in a disappearance of the bleeding tendency. Nonreactivated rPAI-1 and tranexamic acid were significantly less potent in reversing the bleeding time prolongation. These findings indicate that aspirin and rt-PA given separately do not markedly affect the template bleeding time, but in combination induce a marked prolongation associated with a significant bleeding tendency. This bleeding time prolongation can be rapidly normalized by the administration of reactivated rPAI-1.

Hemorrhagic complications of thrombolytic therapy in experimental stroke

Recent success with thrombolytic therapy for acute myocardial infarction has stimulated interest in its use for stroke. To determine the hemorrhagic potential of thrombolytic therapy in experimental cerebral infarction, we compared a group of tissue plasminogen activator-treated rabbits (n = 4) with 2 groups of streptokinase-treated rabbits (n = 6 in each), as well as with 3 groups of heparin-treated rabbits (n = 5 in each) and untreated controls (n = 12). Focal cerebral infarction was produced in rabbits by occlusion of the right common carotid and middle cerebral arteries coupled with 2 hours of halothane-induced hypotension. Treatment with heparin or thrombolytic agents began 24 hours after occlusion. One additional group was treated with streptokinase 1 hour after occlusion (n = 6) to determine the hemorrhagic potential of thrombolytic agents in evolving infarction. Rabbits were killed 29-33 hours after occlusion, and brain sections were examined using light microscopy. The results demonstrate that microscopic hemorrhage is frequently present in infarcted tissue irrespective of treatment. Gross cerebral hemorrhage did not occur in untreated rabbits or in rabbits treated with streptokinase 1 hour after occlusion. Only rabbits treated with streptokinase, tissue plasminogen activator, or excessive doses of heparin 24 hours after occlusion, at a time when cerebral infarction was well established, exhibited gross hemorrhage in the area of infarction. These data suggest that treatment of ischemic stroke with thrombolytic agents carries an increased risk of cerebral hemorrhage unless the agents are given early after the onset of symptoms.