Distribution of sympathetic tissue plasminogen activator (tPA) to a distant microvasculature

Thrombolysis exacerbates cerebrovascular injury after ischemic stroke via a VEGF-B dependent effect on adipose lipolysis

Cerebrovascular injuries leading to edema and hemorrhage after ischemic stroke are common. The mechanisms underlying these events and how they are connected to known risk factors for poor outcome, like obesity and diabetes, is relatively unknown. Herein we demonstrate that increased adipose tissue lipolysis is a dominating risk factor for the development of a compromised cerebrovasculature in ischemic stroke. Reducing adipose lipolysis by VEGF-B antagonism improved vascular integrity by reducing ectopic cerebrovascular lipid deposition. Thrombolytic therapy in ischemic stroke using tissue plasminogen activator (tPA) leads to increased risk of hemorrhagic complications, substantially limiting the use of thrombolytic therapy. We provide evidence that thrombolysis with tPA promotes adipose tissue lipolysis, leading to a rise in plasma fatty acids and lipid accumulation in the ischemic cerebrovasculature after stroke. VEGF-B blockade improved the efficacy and safety of thrombolysis suggesting the potential use of anti-VEGF-B therapy to extend the therapeutic window for stroke management.

Progress in the Treatment of Central Nervous System Diseases Based on Nanosized Traditional Chinese Medicine

Traditional Chinese Medicine (TCM) is widely used in clinical practice to treat diseases related to central nervous system (CNS) damage. However, the blood-brain barrier (BBB) constitutes a significant impediment to the effective delivery of TCM, thus substantially diminishing its efficacy. Advances in nanotechnology and its applications in TCM (also known as nano-TCM) can deliver active ingredients or components of TCM across the BBB to the targeted brain region. This review provides an overview of the physiological and pathological mechanisms of the BBB and systematically classifies the common TCM used to treat CNS diseases and types of nanocarriers that effectively deliver TCM to the brain. Additionally, drug delivery strategies for nano-TCMs that utilize in vivo physiological properties or in vitro devices to bypass or cross the BBB are discussed. This review further focuses on the application of nano-TCMs in the treatment of various CNS diseases. Finally, this article anticipates a design strategy for nano-TCMs with higher delivery efficiency and probes their application potential in treating a wider range of CNS diseases.

circPSD3 is a promising inhibitor of uPA system to inhibit vascular invasion and metastasis in hepatocellular carcinoma

BACKGROUND

Vascular invasion is a major route for intrahepatic and distant metastasis in hepatocellular carcinoma (HCC) and is a strong negative prognostic factor. Circular RNAs (circRNAs) play important roles in tumorigenesis and metastasis. However, the regulatory functions and underlying mechanisms of circRNAs in the development of vascular invasion in HCC are largely unknown.

METHODS

High throughput sequencing was used to screen dysregulated circRNAs in portal vein tumor thrombosis (PVTT) tissues. The biological functions of candidate circRNAs in the migration, vascular invasion, and metastasis of HCC cells were examined in vitro and in vivo. To explore the underlying mechanisms, RNA sequencing, MS2-tagged RNA affinity purification, mass spectrometry, and RNA immunoprecipitation assays were performed.

RESULTS

circRNA sequencing followed by quantitative real-time PCR (qRT-PCR) revealed that circRNA pleckstrin and Sect. 7 domain containing 3 (circPSD3) was significantly downregulated in PVTT tissues. Decreased circPSD3 expression in HCC tissues was associated with unfavourable characteristics and predicted poor prognosis in HCC. TAR DNA-binding protein 43 (TDP43) inhibited the biogenesis of circPSD3 by interacting with the downstream intron of pre-PSD3. circPSD3 inhibited the intrahepatic vascular invasion and metastasis of HCC cells in vitro and in vivo. Serpin family B member 2 (SERPINB2), an endogenous bona fide inhibitor of the urokinase-type plasminogen activator (uPA) system, is the downstream target of circPSD3. Mechanistically, circPSD3 interacts with histone deacetylase 1 (HDAC1) to sequester it in the cytoplasm, attenuating the inhibitory effect of HDAC1 on the transcription of SERPINB2. In vitro and in vivo studies demonstrated that circPSD3 is a promising inhibitor of the uPA system.

CONCLUSIONS

circPSD3 is an essential regulator of vascular invasion and metastasis in HCC and may serve as a prognostic biomarker and therapeutic target.

Fibrinolysis Shutdown and Hypofibrinolysis Are Not Synonymous Terms: The Clinical Significance of Differentiating Low Fibrinolytic States

Low fibrinolytic activity has been associated with pathologic thrombosis and multiple-organ failure. Low fibrinolytic activity has two commonly associated terms, hypofibrinolysis and fibrinolysis shutdown. Hypofibrinolysis is a chronic state of lack of ability to generate an appropriate fibrinolytic response when anticipated. Fibrinolysis shutdown is the shutdown of fibrinolysis after systemic activation of the fibrinolytic system. There has been interchanging of these terms to describe critically ill patients in multiple settings. This is problematic in understanding the pathophysiology of disease processes related to these conditions. There is also a lack of research on the cellular mediators of these processes. The purpose of this article is to review the on and off mechanisms of fibrinolysis in the context of low fibrinolytic states to define the importance in differentiating hypofibrinolysis from fibrinolysis shutdown. In many clinical scenarios, the etiology of a low fibrinolytic state cannot be determined due to ambiguity if a preceding fibrinolytic activation event occurred. In this scenario, the term "low fibrinolytic activity" or "fibrinolysis resistance" is a more appropriate descriptor, rather than using assumptive of hypofibrinolysis and fibrinolysis shutdown, particularly in the acute setting of infection, injury, and surgery.

SHock-INduced Endotheliopathy (SHINE): A mechanistic justification for viscoelastography-guided resuscitation of traumatic and non-traumatic shock

Irrespective of the reason for hypoperfusion, hypocoagulable and/or hyperfibrinolytic hemostatic aberrancies afflict up to one-quarter of critically ill patients in shock. Intensivists and traumatologists have embraced the concept of SHock-INduced Endotheliopathy (SHINE) as a foundational derangement in progressive shock wherein sympatho-adrenal activation may cause systemic endothelial injury. The pro-thrombotic endothelium lends to micro-thrombosis, enacting a cycle of worsening perfusion and increasing catecholamines, endothelial injury, de-endothelialization, and multiple organ failure. The hypocoagulable/hyperfibrinolytic hemostatic phenotype is thought to be driven by endothelial release of anti-thrombogenic mediators to the bloodstream and perivascular sympathetic nerve release of tissue plasminogen activator directly into the microvasculature. In the shock state, this hemostatic phenotype may be a counterbalancing, yet maladaptive, attempt to restore blood flow against a systemically pro-thrombotic endothelium and increased blood viscosity. We therefore review endothelial physiology with emphasis on glycocalyx function, unique biomarkers, and coagulofibrinolytic mediators, setting the stage for understanding the pathophysiology and hemostatic phenotypes of SHINE in various etiologies of shock. We propose that the hyperfibrinolytic phenotype is exemplified in progressive shock whether related to trauma-induced coagulopathy, sepsis-induced coagulopathy, or post-cardiac arrest syndrome-associated coagulopathy. Regardless of the initial insult, SHINE appears to be a catecholamine-driven entity which early in the disease course may manifest as hyper- or hypocoagulopathic and hyper- or hypofibrinolytic hemostatic imbalance. Moreover, these hemostatic derangements may rapidly evolve along the thrombohemorrhagic spectrum depending on the etiology, timing, and methods of resuscitation. Given the intricate hemochemical makeup and changes during these shock states, macroscopic whole blood tests of coagulative kinetics and clot strength serve as clinically useful and simple means for hemostasis phenotyping. We suggest that viscoelastic hemostatic assays such as thromboelastography (TEG) and rotational thromboelastometry (ROTEM) are currently the most applicable clinical tools for assaying global hemostatic function-including fibrinolysis-to enable dynamic resuscitation with blood products and hemostatic adjuncts for those patients with thrombotic and/or hemorrhagic complications in shock states.

Moscatilin Inhibits Metastatic Behavior of Human Hepatocellular Carcinoma Cells: A Crucial Role of uPA Suppression via Akt/NF-κB-Dependent Pathway

Hepatocellular carcinoma (HCC) frequently shows early invasion into blood vessels as well as intrahepatic metastasis. Innovations of novel small-molecule agents to block HCC invasion and subsequent metastasis are urgently needed. Moscatilin is a bibenzyl derivative extracted from the stems of a traditional Chinese medicine, orchid Dendrobium loddigesii. Although moscatilin has been reported to suppress tumor angiogenesis and growth, the anti-metastatic property of moscatilin has not been elucidated. The present results revealed that moscatilin inhibited metastatic behavior of HCC cells without cytotoxic fashion in highly invasive human HCC cell lines. Furthermore, moscatilin significantly suppressed the activity of urokinase plasminogen activator (uPA), but not matrix metalloproteinase (MMP)-2 and MMP-9. Interestingly, moscatilin-suppressed uPA activity was through down-regulation the protein level of uPA, and did not impair the uPA receptor and uPA inhibitory molecule (PAI-1) expressions. Meanwhile, the mRNA expression of uPA was inhibited via moscatilin in a concentration-dependent manner. In addition, the expression of phosphorylated Akt, rather than ERK1/2, was inhibited by moscatilin treatment. The expression of phosphor-IκBα, and -p65, as well as κB-luciferase activity were also repressed after moscatilin treatment. Transfection of constitutively active Akt (Myr-Akt) obviously restored the moscatilin-inhibited the activation of NF-κB and uPA, and cancer invasion in HCC cells. Taken together, these results suggest that moscatilin impedes HCC invasion and uPA expression through the Akt/NF-κB signaling pathway. Moscatilin might serve as a potential anti-metastatic agent against the disease progression of human HCC.

[The functions of arterial sympathetic innervation: from development to pathology]

Arterial sympathetic innervation (ASI) is a complex biological process requiring a fine axonal guidance by arteries. Its physiological impact has remained unknown for decades but recently started to be better understood and recognized. ASI is a key element of the adaptive response of the cardiovascular system to challenging situations (exposure to cold, exercise…) as ASI controls the diameter of resistance arteries, thus blood supply to organs and systemic arterial blood pressure via arterial tone modulation. Defaults in ASI can lead to diseases, acting as a main cause or as an aggravating factor. Its impact is actively studied in cardiovascular diseases representing major public health issues, like hypertension, but ASI could also play a role in aging and many more pathological processes including cancer.

Multifaceted Role of the Urokinase-Type Plasminogen Activator (uPA) and Its Receptor (uPAR): Diagnostic, Prognostic, and Therapeutic Applications

The plasminogen activator (PA) system is an extracellular proteolytic enzyme system associated with various physiological and pathophysiological processes. A large body of evidence support that among the various components of the PA system, urokinase-type plasminogen activator (uPA), its receptor (uPAR), and plasminogen activator inhibitor-1 and -2 (PAI-1 and PAI-2) play a major role in tumor progression and metastasis. The binding of uPA with uPAR is instrumental for the activation of plasminogen to plasmin, which in turn initiates a series of proteolytic cascade to degrade the components of the extracellular matrix, and thereby, cause tumor cell migration from the primary site of origin to a distant secondary organ. The components of the PA system show altered expression patterns in several common malignancies, which have identified them as ideal diagnostic, prognostic, and therapeutic targets to reduce cancer-associated morbidity and mortality. This review summarizes the various components of the PA system and focuses on the role of uPA-uPAR in different biological processes especially in the context of malignancy. We also discuss the current state of knowledge of uPA-uPAR-targeted diagnostic and therapeutic strategies for various malignancies.

Tissue plasminogen activator (t-PA) and plasminogen activator inhibitor type 1 (PAI-1) in diabetic foot syndrome

PURPOSE

The aim was to evaluate tissue plasminogen activator (tPA) and plasminogen activator inhibitor type 1 (PAI-1) concentration using enzyme linked immunosorbent assay method (ELISA) in diabetic foot syndrome (DFS) as compared to a group of healthy people and patients with diabetes mellitus without symptomatic vascular complications (DM2T).

MATERIAL/METHODS

Venous blood samples were collected from 90 patients with type 2 diabetes mellitus (30 - DM2T; 60 - DFS). Age-matched controls were also included (n=30). tPA and PAI-1 plasma levels were measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

We found a significantly lower concentration of tPA:Ag in patients with DFS in comparison to the DM2T group; tPA concentrations were significantly higher in DM2T as compared to the control group. We observed significantly lower concentration of PAI-1:Ag in DF patients treated for hypertension as compared to patients without hypertension. The tPA:Ag and PAI-1:Ag concentration analysis in DFS depending on age, gender and BMI did not show any significant differences.

CONCLUSIONS

A lower concentration of tPA in patients with DFS may be associated with damage to the endothelial cells, especially in the microvasculature, and the sympathetic nervous system.

Chinese tuina downregulates the elevated levels of tissue plasminogen activator in sciatic nerve injured Sprague-Dawley rats

OBJECTIVE

To elucidate the mechanism of Chinese tuina in treating sciatic nerve crush injury, and to detect the levels of tissue plasminogen activator (tPA) and plasminogen activator inhibitor-1 (PAI-1), which is thought to play an important role in nerve regeneration.

METHODS

Thirty-two adult male Sprague-Dawley rats were subjected to sciatic nerve crush injury and 16 rats (sham-operated group) went through a sham operation. Control group was given no treatment while tuina group received tuina therapy since day 7 post-surgery. Tuina treatment was performed once a day and lasted for 20 days. The sciatic functional index was examined every 5 days during the treatment session. The rats' gastrocnemius muscles were evaluated for changes in mass and immunohistochemistry techniques were performed to detect the levels of tPA and PAI-1.

RESULTS

Tuina therapy improved the motor function of sciatic nerve injured rats (P<0.05), however, it did not increase muscle volume (P<0.05). Tuina downregulated the levels of tPA and PAI-1 (P<0.05).

CONCLUSIONS

The present study implies that tuina treatment could accelerate rehabilitation of peripheral nerve injury.

Involvement of urokinase-type plasminogen activator system in cancer: an overview

Currently, there are several studies supporting the role of urokinase-type plasminogen activator (uPA) system in cancer. The association of uPA to its receptor triggers the conversion of plasminogen into plasmin. This process is regulated by the uPA inhibitors (PAI-1 and PAI-2). Plasmin promotes degradation of basement membrane and extracellular matrix (ECM) components as well as activation of ECM latent matrix metalloproteases. Degradation and remodeling of the surrounding tissues is crucial in the early steps of tumor progression by facilitating expansion of the tumor mass, release of tumor growth factors, activation of cytokines as well as induction of tumor cell proliferation, migration, and invasion. Hence, many tumors showed a correlation between uPA system component levels and tumor aggressiveness and survival. Therefore, this review summarizes the structure of the uPA system, its contribution to cancer progression, and the clinical relevance of uPA family members in cancer diagnosis. In addition, the review evaluates the significance of uPA system in the development of cancer-targeted therapies.

Endothelial cells and astrocytes: a concerto en duo in ischemic pathophysiology

The neurovascular/gliovascular unit has recently gained increased attention in cerebral ischemic research, especially regarding the cellular and molecular changes that occur in astrocytes and endothelial cells. In this paper we summarize the recent knowledge of these changes in association with edema formation, interactions with the basal lamina, and blood-brain barrier dysfunctions. We also review the involvement of astrocytes and endothelial cells with recombinant tissue plasminogen activator, which is the only FDA-approved thrombolytic drug after stroke. However, it has a narrow therapeutic time window and serious clinical side effects. Lastly, we provide alternative therapeutic targets for future ischemia drug developments such as peroxisome proliferator- activated receptors and inhibitors of the c-Jun N-terminal kinase pathway. Targeting the neurovascular unit to protect the blood-brain barrier instead of a classical neuron-centric approach in the development of neuroprotective drugs may result in improved clinical outcomes after stroke.

A potency of plasminogen activation system in long-term prognosis of endometrial cancer: a pilot study

OBJECTIVE

Plasminogen activators released from cancer cells lead to degradation of basement membrane proteins and extracellular matrix, and facilitate cancer cell invasion into surrounding tissues and the blood stream. The aim of this study was to evaluate a complex tissue immunohistochemical expression of the plasminogen activation system--urokinase-type plasminogen activator (uPA) and its receptor (uPAR), tissue-type plasminogen activator (tPA) and plasminogen activator inhibitor (PAI)-1--in endometrial cancer, and to correlate obtained results with disease progression and course.

STUDY DESIGN

The study group was composed of 100 patients classified in three sub-groups according to the FIGO 2010 tumour stratification (G1=70, G2=19, G3=11). Expression of uPA, tPA, uPAR and PAI-1 was examined by means of immunohistochemical staining.

RESULTS

Immunohistochemical expressions of all the studied markers did not differ between G1 and G2 patients. However, G3 subjects were found to have a significantly lower expression of uPA, PAI-1 and tPA. In addition, the patients who survived were found to be PAI-1 negative, while study participants with an unfavourable disease course were PAI-1 positive.

CONCLUSIONS

A significantly higher immunohistochemical expression of PAI-1 was found to correlate with shorter relapse-free and overall survival in patients classified as stages IB and II of endometrial cancer.

Physiological regulation of extracellular matrix collagen and elastin in the arterial wall of rats by noradrenergic tone and angiotensin II

The interactions between the effects of the sympathetic nervous system (SNS) and angiotensin II (ANG II) on vascular extracellular matrix (ECM) synthesis were determined in rats.

The mRNA and protein content of collagen I, collagen III and elastin in the abdominal aorta (AA) and femoral artery (FA) was investigated in Wistar–Kyoto rats treated for 5 weeks with guanethidine, a sympathoplegic, losartan, an ANG II AT1 receptor (AT1R) blocker, or both. The effects of noradrenaline (NE) and ANG II on collagen III and elastin mRNA, and the receptor involved, were tested in cultured vascular smooth muscle cells (VSMCs) in vitro.

Guanethidine increased collagen types I and III and decreased elastin, while losartan had an opposite effect, although without effect on collagen III. The combination of treatments abrogated changes induced by simple treatment with collagen I and elastin, but increased collagen III mRNA in AA and not in FA. NE stimulated collagen III mRNA via β receptors and elastin via α1 and α2 receptors. ANG II stimulated collagen III but inhibited elastin mRNA via AT1R.

Overall, SNS and ANG II exert opposite and antagonistic effects on major components of ECM in the vascular wall. This may be of relevance for the choice of a therapeutic strategy in vascular diseases.

The anti-fibrinolytic SERPIN, plasminogen activator inhibitor 1 (PAI-1), is targeted to and released from catecholamine storage vesicles

Recent studies suggest a crucial role for plasminogen activator inhibitor-1 (PAI-1) in mediating stress-induced hypercoagulability and thrombosis. However, the mechanisms by which PAI-1 is released by stress are not well-delineated. Here, we examined catecholaminergic neurosecretory cells for expression, trafficking, and release of PAI-1. PAI-1 was prominently expressed in PC12 pheochromocytoma cells and bovine adrenomedullary chromaffin cells as detected by Northern blotting, Western blotting, and specific PAI-1 ELISA. Sucrose gradient fractionation studies and immunoelectron microscopy demonstrated localization of PAI-1 to catecholamine storage vesicles. Secretogogue stimulation resulted in corelease of PAI-1 with catecholamines. Parallel increases in plasma PAI-1 and catecholamines were observed in response to acute sympathoadrenal activation by restraint stress in mice in vivo. Reverse fibrin zymography demonstrated free PAI-1 in cellular releasates. Detection of high molecular weight complexes by Western blotting, consistent with PAI-1 complexed with t-PA, as well as bands consistent with cleaved PAI-1, suggested that active PAI-1 was present. Modulation of PAI-1 levels by incubating PC12 cells with anti-PAI-1 IgG caused a marked decrease in nicotine-mediated catecholamine release. In summary, PAI-1 is expressed in chromaffin cells, sorted into the regulated pathway of secretion (into catecholamine storage vesicles), and coreleased, by exocytosis, with catecholamines in response to secretogogues.

The role of plasminogen-plasmin system in cancer

Components of the plasminogen-plasmin system participate in a wide variety of physiologic and pathologic processes, including tumor growth, invasion and metastasis, through their effect on angiogenesis and cell migration. These components are found in most tumors and their expression not only signifies their function but also carries a prognostic value. Their expression is in turn modulated by cytokines and growth factors, many of which are up-regulated in cancer. Though both tPA and uPA are expressed in tumor cells, uPA with its receptor (uPAR) is mostly involved in cellular functions, while tPA with its receptor Annexin II on endothelial surface, regulates intravascular fibrin deposition. Among the inhibitors of fibrinolysis, PAI-1 is a major player in the pathogenesis of many vascular diseases as well as in cancer. Therapeutic interventions, either using plasminogen activators or experimental inhibitor agents against PAI-1, have shown encouraging results in experimental tumors but not been verified clinically.

Modulation of sympathetic activity by tissue plasminogen activator is independent of plasminogen and urokinase

Sympathetic neurons synthesize, transport, and release tissue-type plasminogen activators (t-PAs) and urinary-type plasminogen activators (u-PAs). We reported that t-PA enhances sympathetic neurotransmission and exacerbates reperfusion arrhythmias. We have now assessed the role of u-PA and plasminogen. Neurogenic contractile responses to electrical field stimulation (EFS) were determined in vasa deferentia (VD) from mice lacking t-PA (t-PA(-/-)), plasminogen activator inhibitor-1 (PAI-1(-/-)), plasminogen (plgn(-/-)), u-PA (u-PA(-/-)), and wild-type (WT) controls. Similar levels of t-PA were present in VD and cardiac synaptosomes of WT, PAI-1(-/-), plgn(-/-), and u-PA(-/-) mice, whereas t-PA was undetectable in t-PA(-/-) tissues. EFS responses were potentiated and attenuated in VD from PAI-1(-/-) and t-PA(-/-) mice, respectively, but indistinguishable from WT responses in VD from plgn(-/-) and u-PA(-/-) mice. Moreover, t-PA inhibition with t-PA(stop) decreased EFS response in WT mice, whereas u-PA(stop) did not. VD responses to ATP, norepinephrine, and K(+) in t-PA(-/-), PAI-1(-/-), plgn(-/-), and u-PA(-/-) mice were similar to those in WT, whereas t-PA(stop) did not modify VD responses to norepinephrine in WT, t-PA(-/-), and PAI-1(-/-) mice, indicating a prejunctional site of action for t-PA-induced potentiation of sympathetic neurotransmission. Indeed, K(+)-induced norepinephrine exocytosis from cardiac synaptosomes was potentiated in PAI-1(-/-), attenuated in t-PA(-/-) and not different from WT in u-PA(-/-) and plgn(-/-) mice. Likewise, ATP exocytosis was decreased in t-PA(-/-) and attenuated by t-PA(stop) in WT mice. Thus, t-PA-induced enhancement of sympathetic neurotransmission is a prejunctional event associated with increased transmitter exocytosis and independent of u-PA and plasminogen availability. This novel t-PA action may be a potential therapeutic target in hyperadrenergic states.

Two conserved regions within the tissue-type plasminogen activator gene promoter mediate regulation by brain-derived neurotrophic factor

Tissue-type plasminogen activator (t-PA) has recently been identified as a modulator of neuronal plasticity and can initiate conversion of the pro-form of brain-derived neurotrophic factor (BDNF) into its mature form. BDNF also increases t-PA gene expression implicating t-PA as a downstream effector of BDNF function. Here we demonstrate that BDNF-mediated induction of t-PA mRNA requires an increase in t-PA gene transcription. Reporter constructs harboring 9.5 kb of the human t-PA promoter conferred BDNF-responsiveness in transfected mouse primary cortical neurons. This regulation was recapitulated in HEK 293 cells coexpressing the TrkB neurotrophin receptor. t-PA promoter-deletion analysis revealed the presence of two BDNF-responsive domains, one located between -3.07 and -2.5 kb and the other within the proximal promoter. The upstream region was shown to confer BDNF responsiveness in a TrkB-dependent manner when attached to a heterologous promoter. We also identify homologous regions within the murine and bovine t-PA gene promoters and demonstrate that the equivalent upstream murine sequence functions as a BDNF-responsive enhancer when inserted 5' of the human proximal t-PA promoter. Hence, BDNF-mediated induction of t-PA transcription relies on conserved modular promoter elements including a novel upstream BDNF-responsive domain and the proximal t-PA gene promoter.

The plasminogen activator system modulates sympathetic nerve function

Sympathetic neurons synthesize and release tissue plasminogen activator (t-PA). We investigated whether t-PA modulates sympathetic activity. t-PA inhibition markedly reduced contraction of the guinea pig vas deferens to electrical field stimulation (EFS) and norepinephrine (NE) exocytosis from cardiac synaptosomes. Recombinant t-PA (rt-PA) induced exocytotic and carrier-mediated NE release from cardiac synaptosomes and cultured neuroblastoma cells; this was a plasmin-independent effect but was potentiated by a fibrinogen cleavage product. Notably, hearts from t-PA–null mice released much less NE upon EFS than their wild-type (WT) controls (i.e., a 76.5% decrease; P < 0.01), whereas hearts from plasminogen activator inhibitor-1 (PAI-1)–null mice released much more NE (i.e., a 275% increase; P < 0.05). Furthermore, vasa deferentia from t-PA–null mice were hyporesponsive to EFS (P < 0.0001) but were normalized by the addition of rt-PA. In contrast, vasa from PAI-1–null mice were much more responsive (P < 0.05). Coronary NE overflow from hearts subjected to ischemia/reperfusion was much smaller in t-PA–null than in WT control mice (P < 0.01). Furthermore, reperfusion arrhythmias were significantly reduced (P < 0.05) in t-PA–null hearts. Thus, t-PA enhances NE release from sympathetic nerves and contributes to cardiac arrhythmias in ischemia/reperfusion. Because the risk of arrhythmias and sudden cardiac death is increased in hyperadrenergic conditions, targeting the NE-releasing effect of t-PA may have valuable therapeutic potential.

Cardiac fibrinolytic capacity is markedly increased after brief periods of local myocardial ischemia, but declines following successive periods in anesthetized pigs

BACKGROUND

Fibrinolysis in blood is mainly reflected by the activities of tissue plasminogen activator (tPA) and of plasminogen activator inhibitor-1 (PAI-1). The effect of myocardial ischemia on their activities in the coronary circulation is, however, not established.

OBJECTIVES

With an improved experimental model, we therefore examined the effect of a brief period of myocardial ischemia on their activities. Furthermore, the consequences of repeated periods of ischemia, mimicking the situations in patients with unstable angina, were investigated.

METHODS

In six anesthetized pigs, we occluded the distal left anterior descending coronary artery (LAD) four times for 10 min with 40 min intervals and determined the activities of tPA and PAI-1 in arterial and coronary venous blood. By simultaneously recording LAD flow, we could estimate cardiac release of these factors at baseline conditions and during reperfusion.

RESULTS

Neither net cardiac release of PAI-1 nor alterations in plasma PAI-1 levels were demonstrated during the experiment. However, a significant net release of tPA activity of 10.4 +/- 3.2 IU mL(-1) (P < 0.005) was recorded during baseline conditions. During reperfusion following the first period of ischemia, the cardiac release of tPA activity increased to a peak of 103 +/- 30-fold baseline release, but declined progressively after repeated periods of ischemia. After the fourth period, tPA release did not exceed an estimated baseline accumulation during ischemia and early reperfusion.

CONCLUSIONS

In this porcine model, a substantial local increase in fibrinolytic capacity was observed after brief periods of ischemia, but declined subsequently by repeated periods of ischemia.