Roles of Plasminogen Activator Inhibitor-1 in Heterotopic Ossification Induced by Achilles Tenotomy in Thermal Injured Mice.

Heterotopic ossification (HO) is the process by which ectopic bone forms at an extraskeletal site. Inflammatory conditions induce plasminogen activator inhibitor 1 (PAI-1), an inhibitor of fibrinolysis, which regulates osteogenesis. In the present study, we investigated the roles of PAI-1 in the pathophysiology of HO induced by trauma/burn treatment using PAI-1-deficient mice. PAI-1 deficiency significantly promoted HO and increased the number of alkaline phosphatase (ALP)-positive cells in Achilles tendons after trauma/burn treatment. The mRNA levels of inflammation markers were elevated in Achilles tendons of both wild-type and PAI-1-deficient mice after trauma/burn treatment and PAI-1 mRNA levels were elevated in Achilles tendons of wild-type mice. PAI-1 deficiency significantly up-regulated the expression of Runx2, Osterix, and type 1 collagen in Achilles tendons 9 weeks after trauma/burn treatment in mice. In in vitro experiments, PAI-1 deficiency significantly increased ALP activity and mineralization in mouse osteoblasts. Moreover, PAI-1 deficiency significantly increased ALP activity and up-regulated osteocalcin expression during osteoblastic differentiation from mouse adipose-tissue-derived stem cells, but suppressed the chondrogenic differentiation of these cells. In conclusion, the present study showed that PAI-1 deficiency promoted HO in Achilles tendons after trauma/burn treatment partly by enhancing osteoblast differentiation and ALP activity in mice. Endogenous PAI-1 may play protective roles against HO after injury and inflammation.

Compartmentalized Actions of the Plasminogen Activator Inhibitors, PAI-1 and Nsp, in Ischemic Stroke.

Tissue plasminogen activator (tPA) is a multifunctional protease. In blood tPA is best understood for its role in fibrinolysis, whereas in the brain tPA is reported to regulate blood-brain barrier (BBB) function and to promote neurodegeneration. Thrombolytic tPA is used for the treatment of ischemic stroke. However, its use is associated with an increased risk of hemorrhagic transformation. In blood the primary regulator of tPA activity is plasminogen activator inhibitor 1 (PAI-1), whereas in the brain, its primary inhibitor is thought to be neuroserpin (Nsp). In this study, we compare the effects of PAI-1 and Nsp deficiency in a mouse model of ischemic stroke and show that tPA has both beneficial and harmful effects that are differentially regulated by PAI-1 and Nsp. Following ischemic stroke Nsp deficiency in mice leads to larger strokes, increased BBB permeability, and increased spontaneous intracerebral hemorrhage. In contrast, PAI-1 deficiency results in smaller infarcts and increased cerebral blood flow recovery. Mechanistically, our data suggests that these differences are largely due to the compartmentalized action of PAI-1 and Nsp, with Nsp deficiency enhancing tPA activity in the CNS which increases BBB permeability and worsens stroke outcomes, while PAI-1 deficiency enhances fibrinolysis and improves recovery. Finally, we show that treatment with a combination therapy that enhances endogenous fibrinolysis by inhibiting PAI-1 with MDI-2268 and reduces BBB permeability by inhibiting tPA-mediated PDGFRα signaling with imatinib significantly reduces infarct size compared to vehicle-treated mice and to mice with either treatment alone.

Role of Macrophages and Plasminogen Activator Inhibitor-1 in Delayed Bone Repair Induced by Glucocorticoids in Mice.

Glucocorticoids delay fracture healing and induce osteoporosis. However, the mechanisms by which glucocorticoids delay bone repair have yet to be clarified. Plasminogen activator inhibitor-1 (PAI-1) is the principal inhibitor of plasminogen activators and an adipocytokine that regulates metabolism. We herein investigated the roles of macrophages in glucocorticoid-induced delays in bone repair after femoral bone injury using PAI-1-deficient female mice intraperitoneally administered with dexamethasone (Dex). Dex significantly decreased the number of F4/80-positive macrophages at the damaged site two days after femoral bone injury. It also attenuated bone injury-induced decreases in the number of hematopoietic stem cells in bone marrow in wild-type and PAI-1-deficient mice. PAI-1 deficiency significantly weakened Dex-induced decreases in macrophage number and macrophage colony-stimulating factor (M-CSF) mRNA levels at the damaged site two days after bone injury. It also significantly ameliorated the Dex-induced inhibition of macrophage phagocytosis at the damaged site. In conclusion, we herein demonstrated that Dex decreased the number of macrophages at the damaged site during early bone repair after femoral bone injury partly through PAI-1 and M-CSF in mice.

The utility of thromboelastography and tranexamic acid in plasminogen activator inhibitor deficiency during pregnancy: a rare case report.

: Complete plasminogen activator inhibitor-1 (PAI-1) deficiency is a very rare genetic disorder that is associated with an increased risk of bleeding diathesis. Patients with PAI-1 deficiency are also known to be at increased risk for massive postpartum hemorrhage. We discuss one such rare case of PAI-1 deficiency in a young pregnant patient at 22 weeks of gestation with history of prolonged bleeding. Tranexamic acid was administered for menorrhagia and resumed later for labor and continued into the postpartum period since antifibrinolytics have been the mainstay in the management of PAI-1 deficiency. The patient delivered a healthy infant at 39 weeks. As PAI-1 deficiency causes increased fibrinolysis, the patient's coagulation panel was monitored by performing serial thromboelastograms to monitor for any increase in fibrinolysis. We believe that thromboelastograms might be a useful tool in the monitoring and management of fibrinolytic conditions such as PAI-1 deficiency.

Thrombin and plasmin generation in patients with plasminogen or plasminogen activator inhibitor type 1 deficiency.

INTRODUCTION: Deficiencies of plasminogen and plasminogen activator inhibitor type 1 (PAI-1) are rare disorders of fibrinolysis. Current laboratory assays for analysis of activity of plasminogen and PAI-1 do not provide an accurate correlation with clinical phenotype. METHODS: The Nijmegen Hemostasis Assay (NHA) was used to simultaneously measure thrombin and plasmin generation in 5 patients with plasminogen deficiency (PLGD) and 10 patients with complete PAI-1 deficiency. Parameters analysed included: lag time ratio, thrombin peak time ratio, thrombin peak height, thrombin potential (AUC), fibrin lysis time, plasmin peak height and plasmin potential. Parameters were expressed as a percentage compared to a reference value of 53 healthy normal controls. RESULTS: Patients with PLGD demonstrated a short lag time and thrombin peak time, with normal thrombin peak height but an increased AUC. Plasmin generation was able to be detected in only one (23% plasminogen activity) of the five PLGD patients. All ten PAI-1 deficient patients demonstrated a short lag and thrombin peak time, low thrombin peak height with normal AUC. Plasmin generation revealed an increased plasmin peak and plasmin potential; interestingly, there was a large variation between individual patients despite all patients having the same homozygous defect. CONCLUSION: Patients with either PLGD or PAI-1 deficiency show distinct abnormalities in plasmin and thrombin generation in the NHA. The differences observed in the propagation phase of thrombin generation may be explained by plasmin generation. These results suggest that disorders of fibrinolysis also influence coagulation and a global assay measuring both activities may better correlate with clinical outcome.

Inherited disorders of the fibrinolytic pathway.

Deficiencies or excessive activation of the fibrinolytic system can result in severe, lifelong bleeding disorders. The most severe clinical phenotype is caused by α2-Antiplasmin (α2-AP) deficiency which results in excess fibrinolysis due to the inability to inhibit plasmin. Another bleeding disorder due to a defect in the fibrinolytic pathway results from Plasminogen activator inhibitor-1 (PAI-1) deficiency causing enhanced fibrinolysis due to the decreased inhibition of plasminogen activators resulting in increased conversion of plasminogen to plasmin. Both these disorders are rare and have an autosomal recessive pattern of inheritance. They can remain undetected as routine coagulation and platelet function tests are normal. A unique gain-of-function defect in fibrinolysis causes the Quebec platelet disorder (QPD) which is characterized by profibrinolytic platelets containing increased urokinase-type plasminogen activator (uPA) in the α-granules. A high index of suspicion based on clinical phenotype along with the availability of specialized hemostasis testing is required for timely and accurate diagnosis. Antifibrinolytic agents, such as tranexamic acid or ε-aminocaproic acid, are the mainstays of treatment which inhibit fibrinolysis by preventing the binding of plasminogen to fibrin and thereby stabilizing the fibrin clot. The purpose of this review is to summarize the pathogenesis, clinical phenotype, approaches to diagnosis and treatment for these three major disorders of fibrinolysis.

Non-Antithrombin-Mediated Heparin Resistance During Cardiac Surgery: Two Case Reports.

It is well known that antithrombin (AT) deficiency results in decreased heparin sensitivity, also known as "heparin resistance." However, non-AT-mediated causes of heparin resistance are generally poorly characterized and less prevalent in the literature. We present 2 case reports of non-AT-mediated heparin resistance during cardiac surgery due to paraproteinemia and hyperfibrinogenemia. These cases highlight the challenges posed by unusual conditions in achieving adequate anticoagulation for cardiopulmonary bypass (CPB). The pros and cons of the treatment selections for these cases are discussed, and the potential complications of large doses of unfractionated heparin are considered.

Plasminogen activator inhibitor-1 deficiency suppresses osteoblastic differentiation of mesenchymal stem cells in mice.

Plasminogen activator inhibitor-1 (PAI-1) is known as an inhibitor of fibrinolytic system. Previous studies suggest that PAI-1 is involved in the pathogenesis of osteoporosis induced by ovariectomy, diabetes, and glucocorticoid excess in mice. However, the roles of PAI-1 in early-stage osteogenic differentiation have remained unknown. In the current study, we investigated the roles of PAI-1 in osteoblastic differentiation of mesenchymal stem cells (MSCs) using wild-type (WT) and PAI-1-deficient (PAI-1 KO) mice. PAI-1 mRNA levels were increased with time during osteoblastic differentiation of MSCs or mesenchymal ST-2 cells. However, the increased PAI-1 levels declined at the mineralization phase in the experiment using MC3T3-E1 cells. PAI-1 deficiency significantly blunted the expression of osteogenic gene, such as osterix and alkaline phosphatase enhanced by bone morphogenetic protein (BMP)-2 in bone marrow-derived MSCs (BM-MSCs), adipose-tissue-derived MSCs (AD-MSCs), and bone marrow stromal cells of mice. Moreover, a reduction in endogenous PAI-1 levels by small interfering RNA significantly suppressed the expression of osteogenic gene in ST-2 cells. Plasmin did not affect osteoblastic differentiation of AD-MSCs induced by BMP-2 with or without PAI-1 deficiency. PAI-1 deficiency and a reduction in endogenous PAI-1 levels did not affect the phosphorylations of receptor-specific Smads by BMP-2 and transforming growth factor-ß in AD-MSCs and ST-2 cells, respectively. In conclusion, we first showed that PAI-1 is crucial for the differentiation of MSCs into osteoblasts in mice.

Plasminogen Activator Inhibitor-1 Promotes Neutrophil Infiltration and Tissue Injury on Ischemia-Reperfusion.

OBJECTIVE: Ischemia-reperfusion (I/R) injury significantly contributes to organ dysfunction and failure after myocardial infarction, stroke, and transplantation. In addition to its established role in the fibrinolytic system, plasminogen activator inhibitor-1 has recently been implicated in the pathogenesis of I/R injury. The underlying mechanisms remain largely obscure. APPROACH AND RESULTS: Using different in vivo microscopy techniques as well as ex vivo analyses and in vitro assays, we identified that plasminogen activator inhibitor-1 rapidly accumulates on microvascular endothelial cells on I/R enabling this protease inhibitor to exhibit previously unrecognized functional properties by inducing an increase in the affinity of ß2 integrins in intravascularly rolling neutrophils. These events are mediated through low-density lipoprotein receptor-related protein-1 and mitogen-activated protein kinase-dependent signaling pathways that initiate intravascular adherence of these immune cells to the microvascular endothelium. Subsequent to this process, extravasating neutrophils disrupt endothelial junctions and promote the postischemic microvascular leakage. Conversely, deficiency of plasminogen activator inhibitor-1 effectively reversed leukocyte infiltration, microvascular dysfunction, and tissue injury on experimental I/R without exhibiting side effects on microvascular hemostasis. CONCLUSIONS: Our experimental data provide novel insights into the nonfibrinolytic properties of the fibrinolytic system and emphasize plasminogen activator inhibitor-1 as a promising target for the prevention and treatment of I/R injury.

Role of plasminogen activator inhibitor-1 in glucocorticoid-induced muscle change in mice.

We recently revealed that plasminogen activator inhibitor-1 (PAI-1), a serine protease inhibitor, is involved in diabetes, osteoporosis and muscle wasting induced by glucocorticoid (GC) treatment in mice. In the present study, we investigated the detailed mechanisms by which GC induces muscle wasting through PAI-1 in vivo and in vitro. PAI-1 deficiency suppressed the mRNA levels of atrogin1 and muscle RING-Finger Protein 1 (MuRF1), ubiquitin ligases leading to muscle degradation, elevated by GC treatment in the gastrocnemius muscle of mice. In vitro study revealed that active PAI-1 treatment augmented the increase in atrogin1 mRNA levels enhanced by dexamethasone (Dex) in mouse myoblastic C2C12 cells. Moreover, a reduction in endogenous PAI-1 level by siRNA suppressed the mRNA levels of atrogin1 and MuRF1 enhanced by Dex in C2C12 cells. In contrast, a reduction in endogenous PAI-1 levels and active PAI-1 did not affect the phosphorylations of Akt and p70S6 kinase nor myogenic differentiation with or without Dex in C2C12 cells. In addition, PAI-1 deficiency blunted IGF-1 mRNA levels decreased by GC treatment in the gastrocnemius muscle of mice, although neither active PAI-1 nor a reduction in endogenous PAI-1 levels affected the levels of IGF-1 mRNA in C2C12 cells in the presence of Dex. In conclusion, our data suggest that paracrine PAI-1 is involved in GC-induced muscle wasting through the enhancement of muscle degradation in mice.

Conditional Plasminogen Activator Inhibitor Type 1 Deletion in the Endothelial Compartment Has No Beneficial Effect on Radiation-Induced Whole-Lung Damage in Mice.

PURPOSE: To investigate whether the endothelial pool of plasminogen activator inhibitor type 1 (PAI-1) plays a role in the development of radiation-induced lung damage, as previously demonstrated in the intestine. METHODS AND MATERIALS: Human lung microvascular endothelial cells were exposed to 10 Gy irradiation so as to study their ability to acquire an "activated" phenotype. Mice in which the Cre-Lox strategy was used to produce PAI-1 deletion specifically in the endothelial compartment were exposed to 17 Gy whole-thorax irradiation and followed up for 2, 13, and 23 weeks after irradiation. RESULTS: Human lung microvascular endothelial cells had an activated phenotype after radiation exposure, overexpressed PAI-1, and underwent endothelial-to-mesenchymal transition. In mice, knockout of PAI-1 in the endothelium had no beneficial effect on radiation-induced lung damage and showed a tendency to worsen acute lesions. CONCLUSIONS: As opposed to the intestine, the endothelial pool of PAI-1 does not play a determinant role in the development of radiation-induced lung damage. The therapeutic value of PAI-1 inhibition in lung radiation injury may be associated with other types of cells.

Serpine 1 induces alveolar type II cell senescence through activating p53-p21-Rb pathway in fibrotic lung disease.

Senescence of alveolar type 2 (ATII) cells, progenitors of the alveolar epithelium, is implicated in the pathogeneses of idiopathic pulmonary fibrosis (IPF), an aging-related progressive fatal lung disorder with unknown etiology. The mechanism underlying ATII cell senescence in fibrotic lung diseases, however, remains poorly understood. In this study, we report that ATII cells in IPF lungs express higher levels of serpine 1, also known as plasminogen activator inhibitor 1 (PAI-1), and cell senescence markers p21 and p16, compared to ATII cells in control lungs. Silencing PAI-1 or inhibition of PAI-1 activity in cultured rat ATII (L2) cells leads to decreases in p53 serine 18 phosphorylation (p53S18P ), p53 and p21 protein expressions; an increase in retinoblastoma protein phosphorylation (ppRb); and a reduction in the sensitivity to bleomycin- and doxorubicin-induced senescence. Silencing p53, on the other hand, abrogates PAI-1 protein-stimulated p21 expression and cell senescence. In vivo studies, using ATII cell-specific PAI-1 conditional knockout mouse model generated recently in this laboratory, further support the role of PAI-1 in the activation of p53-p21-Rb cell cycle repression pathway, ATII cell senescence, and lung fibrosis induced by bleomycin. This study reveals a novel function of PAI-1 in regulation of cell cycle and suggests that elevation of PAI-1 contributes importantly to ATII cell senescence in fibrotic lung diseases.

Plasminogen Activator Inhibitor Type I Controls Cardiomyocyte Transforming Growth Factor-ß and Cardiac Fibrosis.

BACKGROUND: Fibrosis is the pathological consequence of stress-induced tissue remodeling and matrix accumulation. Increased levels of plasminogen activator inhibitor type I (PAI-1) have been shown to promote fibrosis in multiple organ systems. Paradoxically, homozygous genetic deficiency of PAI-1 is associated with spontaneous age-dependent, cardiac-selective fibrosis in mice. We have identified a novel PAI-1-dependent mechanism that regulates cardiomyocyte-derived fibrogenic signals and cardiac transcriptional pathways during injury. METHODS: Cardiac fibrosis in subjects with homozygous mutation in SERPINE-1 was evaluated with late gadolinium-enhanced cardiac magnetic resonance imaging. A murine cardiac injury model was performed by subcutaneous infusion of either saline or Angiotensin II by osmotic minipumps. We evaluated blood pressure, cardiac function (by echocardiography), fibrosis (with Masson Trichrome staining), and apoptosis (with TUNEL staining), and we performed transcriptome analysis (with RNA sequencing). We further evaluated fibrotic signaling in isolated murine primary ventricular myocytes. RESULTS: Cardiac fibrosis was detected in 2 otherwise healthy humans with complete PAI-1 deficiency because of a homozygous frameshift mutation in SERPINE-1. In addition to its suppressive role during spontaneous cardiac fibrosis in multiple species, we hypothesized that PAI-1 also regulates fibrosis during cardiac injury. Treatment of young PAI-1-/- mice with Angiotensin II induced extensive hypertrophy and fibrotic cardiomyopathy, with increased cardiac apoptosis and both reactive and replacement fibrosis. Although Angiotensin II-induced hypertension was blunted in PAI-1-/- mice, cardiac hypertrophy was accelerated. Furthermore, ventricular myocytes were found to be an important source of cardiac transforming growth factor-ß (TGF-ß) and PAI-1 regulated TGF-ß synthesis by cardiomyocytes in vitro as well as in vivo during cardiac injury. Transcriptome analysis of ventricular RNA after Angiotensin II treatment confirmed that PAI-1 deficiency significantly enhanced multiple TGF-ß signaling elements and transcriptional targets, including genes for extracellular matrix components, mediators of extracellular matrix remodeling, matricellular proteins, and cardiac integrins compared with wild-type mice. CONCLUSIONS: PAI-1 is an essential repressor of cardiac fibrosis in mammals. We define a novel cardiomyocyte-specific regulatory mechanism for TGF-ß production by PAI-1, which explains the paradoxical effect of PAI-1 deficiency in promoting cardiac-selective fibrosis. Thus, PAI-1 is a molecular switch that controls the cardiac TGF-ß axis and its early transcriptional effects that lead to myocardial fibrosis.

Plasminogen Activator Inhibitor-1 Is Critical in Alcohol-Enhanced Acute Lung Injury in Mice.

Chronic alcohol exposure is a clinically important risk factor for the development of acute respiratory distress syndrome, the most severe form of acute lung injury (ALI). However, the mechanisms by which alcohol sensitizes the lung to development of this disease are poorly understood. We determined the role of the antifibrinolytic protein plasminogen activator inhibitor-1 (PAI-1) in alcohol enhancement of experimental endotoxin-induced ALI. Wild-type, PAI-1-/-, and integrin ß3-/- mice were fed ethanol-containing Lieber-DeCarli liquid or a control diet for 6 weeks, followed by systemic LPS challenge. LPS administration triggered coagulation cascade activation as evidenced by increased plasma thrombin-antithrombin levels and pulmonary fibrin deposition. Ethanol-exposed animals showed enhanced PAI-1 expression and pulmonary fibrin deposition with coincident exaggeration of pulmonary inflammatory edematous injury. PAI-1 deficiency markedly reduced pulmonary fibrin deposition and greatly reduced inflammation and injury without impacting upstream coagulation. Interestingly, pulmonary platelet accumulation was effectively abolished by PAI-1 deficiency in ethanol/LPS-challenged mice. Moreover, mice lacking integrin αIIBß3, the primary platelet receptor for fibrinogen, displayed a dramatic reduction in early inflammatory changes after ethanol/LPS challenge. These results indicate that the mechanism whereby alcohol exaggerates LPS-induced lung injury requires PAI-1-mediated pulmonary fibrin accumulation, and suggest a novel mechanism whereby alcohol contributes to inflammatory ALI by enhancing fibrinogen-platelet engagement.

The Role of Plasminogen Activator Inhibitor Type-1 in Fibrosis.

Extracellular matrix (ECM) deposition during wound healing is a physiological response to an insult. Wound healing becomes deregulated in the setting of chronic injury or long-standing metabolic disease, leading to the accumulation of ECM components and fibrosis. Matrix protein turnover is determined by the rate of synthesis as well as the rate of proteolytic degradation and clearance by matrix metalloproteinases (MMPs). The persistent activation of interstitial myofibroblasts, coupled with defects in matrix proteolysis, ultimately disrupts tissue architecture and leads to biochemical and mechanical organ dysfunction with eventual organ failure. Plasminogen activator inhibitor type-1 (PAI-1) regulates tissue homeostasis and wound healing by inhibiting plasmin-mediated MMP activation. Multiple reports using models of liver, lung, and kidney fibrosis suggest that PAI-1 deficiency or inhibition of PAI-1 activity attenuates fibrosis. The disinhibition of plasmin-mediated MMP activation leads to collagen degradation and its diminished accumulation, resulting in the reduction of fibrotic matrix deposition in these organs. Paradoxically, homozygous deficiency of PAI-1 promotes age-dependent spontaneous cardiac fibrosis, suggesting a protective role for PAI-1 in the heart. It remains unclear whether PAI-1-deficient cardiac fibroblasts have increased proliferative, migratory, or differentiation capabilities, that allow them to overcome increased plasmin and MMP activity and matrix clearance. In this review, we examine the specific roles of PAI-1 in fibrosis of different organs including the lung, liver, kidney, and cardiovascular system.

Pharmacological Targeting of Plasminogen Activator Inhibitor-1 Decreases Vascular Smooth Muscle Cell Migration and Neointima Formation.

OBJECTIVE: Plasminogen activator inhibitor-1 (PAI-1), a serine protease inhibitor that promotes and inhibits cell migration, plays a complex and important role in adverse vascular remodeling. Little is known about the effects of pharmacological PAI-1 inhibitors, an emerging drug class, on migration of vascular smooth muscle cells (SMCs) and endothelial cells (ECs), crucial mediators of vascular remodeling. We investigated the effects of PAI-039 (tiplaxtinin), a specific PAI-1 inhibitor, on SMC and EC migration in vitro and vascular remodeling in vivo. APPROACH AND RESULTS: PAI-039 inhibited SMC migration through collagen gels, including those supplemented with vitronectin and other extracellular matrix proteins, but did not inhibit migration of PAI-1-deficient SMCs, suggesting that its antimigratory effects were PAI-1-specific and physiologically relevant. However, PAI-039 did not inhibit EC migration. PAI-039 inhibited phosphorylation and nuclear translocation of signal transducers and activators of transcription-1 in SMCs, but had no discernable effect on signal transducer and activator of transcription-1 signaling in ECs. Expression of low-density lipoprotein receptor-related protein 1, a motogenic PAI-1 receptor that activates Janus kinase/signal transducers and activators of transcription-1 signaling, was markedly lower in ECs than in SMCs. Notably, PAI-039 significantly inhibited intimal hyperplasia and inflammation in murine models of adverse vascular remodeling, but did not adversely affect re-endothelialization after endothelium-denuding mechanical vascular injury. CONCLUSIONS: PAI-039 inhibits SMC migration and intimal hyperplasia, while having no inhibitory effect on ECs, which seems to be because of differences in PAI-1-dependent low-density lipoprotein receptor-related protein 1/Janus kinase/signal transducer and activator of transcription-1 signaling between SMCs and ECs. These findings suggest that PAI-1 may be an important therapeutic target in obstructive vascular diseases characterized by neointimal hyperplasia.

Plasminogen activator inhibitor type 1 in platelets induces thrombogenicity by increasing thrombolysis resistance under shear stress in an in-vitro flow chamber model.

INTRODUCTION: Despite the proven benefits of thrombolytic therapy with tissue plasminogen activator (t-PA) for peripheral thromboembolism, perfusion failure frequently occurs, particularly in arterial circulation. We evaluated how the modification of fibrinolytic activity affects thrombus formation under flow and static conditions. MATERIALS AND METHODS: t-PA-treated human whole-blood samples (n=6) were perfused over a microchip coated with collagen and tissue thromboplastin at different shear rates, and thrombus formation was quantified by measuring flow pressure changes. For comparison, rotational thromboelastometry (ROTEM) was used to evaluate fibrinolytic activity under static conditions. RESULTS: At a shear rate of 240s-1, t-PA (200-800IU/ml) concentration-dependently delayed capillary occlusion, whereas at 600s-1, capillary occlusion was significantly faster and t-PA had limited effects, even at a supra-pharmacological concentration (800IU/ml). In contrast, 200IU/ml t-PA efficiently prevented clot formation in the ROTEM assay. The combined treatment of blood with a specific PAI-1 inhibitor (PAI-039) moderately enhanced the efficacy of t-PA, but only under flow conditions. In addition, 1:1-diluted blood samples of PAI-1-deficient (-/-) mice showed a significant delay of capillary occlusion at 240s-1, compared with those from wild-type mice (1.55 fold; P<0.001). This delayed occlusion was reproduced in samples containing platelets from PAI-1-/- and plasma from wild type, but was not observed by the opposite combination of blood components. CONCLUSIONS: The present results suggest that the anti-thrombotic efficacy of t-PA is sensitive to arterial shear flow, and that PAI-1 secreted from activated platelets plays an essential role in thrombolytic resistance.

High-fat Diet Enhances and Plasminogen Activator Inhibitor-1 Deficiency Attenuates Bone Loss in Mice with Lewis Lung Carcinoma.

This study determined the effects of a high-fat diet and plasminogen activator inhibitor-1 deficiency (Pai1(-/-)) on the bone structure in male C57BL/6 mice bearing Lewis lung carcinoma (LLC) in lungs. Significant reduction in bone volume fraction (BV/TV), trabecular number (Tb.N) and bone mineral density (BMD) in femurs and vertebrae were found in LLC-bearing mice compared to non-tumor-bearing mice. In LLC-bearing mice, the high-fat diet compared to the AIN93G control diet significantly reduced BV/TV, Tb.N and BMD in femurs and BV/TV in vertebrae. The high-fat diet significantly reduced BMD in vertebrae in wild-type mice but not in Pai1(-/-) mice. Compared to wild-type mice, PAI1 deficiency significantly increased BV/TV and Tb.N in femurs. The plasma concentration of osteocalcin was significantly lower and that of tartrate-resistant acid phosphatase 5b (TRAP5b) was significantly higher in LLC-bearing mice. The high-fat diet significantly reduced plasma osteocalcin and increased TRAP5b. Deficiency in PAI1 prevented the high-fat diet-induced increases in plasma TRAP5b. These findings demonstrate that a high-fat diet enhances, whereas PAI1 deficiency, attenuates metastasis-associated bone loss, indicating that a high-fat diet and PAI1 contribute to metastasis-associated bone deterioration.