In vitro oxidative damage to tissue-type plasminogen activator: a selective modification of the biological functions

Post-Translational Oxidative Modifications of Hemostasis Proteins: Structure, Function, and Regulation

Reactive oxygen species (ROS) are constantly generated in a living organism. An imbalance between the amount of generated reactive species in the body and their destruction leads to the development of oxidative stress. Proteins are extremely vulnerable targets for ROS molecules, which can cause oxidative modifications of amino acid residues, thus altering structure and function of intra- and extracellular proteins. The current review considers the effect of oxidation on the structural rearrangements and functional activity of hemostasis proteins: coagulation system proteins such as fibrinogen, prothrombin/thrombin, factor VII/VIIa; anticoagulant proteins - thrombomodulin and protein C; proteins of the fibrinolytic system such as plasminogen, tissue plasminogen activator and plasminogen activator inhibitor-1. Structure and function of the proteins, oxidative modifications, and their detrimental consequences resulting from the induced oxidation or oxidative stress in vivo are described. Possible effects of oxidative modifications of proteins in vitro and in vivo leading to disruption of the coagulation and fibrinolysis processes are summarized and systematized, and the possibility of a compensatory mechanism in maintaining hemostasis under oxidative stress is analyzed.

Antioxidant role of methionine-containing intra- and extracellular proteins

Significant evidence suggests that reversible oxidation of methionine residues provides a mechanism capable of scavenging reactive species, thus creating a cycle with catalytic efficiency to counteract or mitigate deleterious effects of ROS on other functionally important amino acid residues. Because of the absence of MSRs in the blood plasma, oxidation of methionines in extracellular proteins is effectively irreversible and, therefore, the ability of methionines to serve as interceptors of oxidant molecules without impairment of the structure and function of plasma proteins is still debatable. This review presents data on the oxidative modification of both intracellular and extracellular proteins that differ drastically in their spatial structures and functions indicating that the proteins contain antioxidant methionines/the oxidation of which does not affect (or has a minor effect) on their functional properties. The functional consequences of methionine oxidation in proteins have been mainly identified from studies in vitro and, to a very limited extent, in vivo. Hence, much of the functioning of plasma proteins constantly subjected to oxidative stress remains unclear and requires further research to understand the evolutionary role of methionine oxidation in proteins for the maintenance of homeostasis and risk factors affecting the development of ROS-related pathologies. Data presented in this review contribute to increased evidence of antioxidant role of surface-exposed methionines and can be useful for understanding a possible mechanism that supports or impairs structure-function relationships of proteins subjected to oxidative stress.

Improved cultivation of Chinese hamster ovary cells in bioreactor with reciprocal mixing

We have constructed a new bioreactor with reciprocal mixing that is better suited for the cultivation of delicate animal cells. In-silico simulation (computational fluid dynamics) suggested both maximum and average shear stresses in the bioreactor with reciprocal mixing to be remarkably lower than in a conventional bioreactor with rotary mixing. Although we could not find any difference in growth speed and cell density between the bioreactors with reciprocal and rotary mixing, we did find cell viability in the reciprocal-mixing bioreactor to be retained longer than in the rotary-paddle bioreactor. This implied that cell culture in a bioreactor with reciprocal mixing could be prolonged for the production of target proteins. Leakage of lactate dehydrogenase activity into the culture medium was suppressed much more in the reciprocal-mixing bioreactor than in the rotary-paddle one. Production of human tissue plasminogen activator in the former system was also observed to be much higher than in the latter. Therefore, a bioreactor with reciprocal mixing was concluded to be better suited for the cultivation of animal cells and efficient production of proteins, such as antibody drugs and various growth factors.

E8002 Inhibits Peripheral Nerve Adhesion by Enhancing Fibrinolysis of l-Ascorbic Acid in a Rat Sciatic Nerve Model

Perineural adhesions leading to neuropathy are one of the most undesirable consequences of peripheral nerve surgery. However, there are currently no widely used compounds with anti-adhesive effects in the field of peripheral nerve surgery. E8002 is a novel, anti-adhesive, multi-layer membrane that contains L-ascorbic acid (AA). Here, we investigated the effect and mechanism of E8002 in a rat sciatic nerve adhesion model. A total of 21 rats were used. Six weeks after surgery, macroscopic adhesion scores were significantly lower in the E8002 group (adhesion procedure followed by nerve wrapping with E8002) compared to the E8002 AA(−) group (adhesion procedure followed by nerve wrapping with the E8002 membrane excluding AA) and adhesion group (adhesion procedure but no treatment). Correspondingly, a microscopic examination revealed prominent scar tissue in the E8002 AA(−) and adhesion groups. Furthermore, an in vitro study using human blood samples showed that AA enhanced tissue-type, plasminogen activator-mediated fibrinolysis. Altogether, these results suggest that E8002 may exert an anti-adhesive action via AA and the regulation of fibrinolysis.

The myeloperoxidase product, hypochlorous acid, reduces thrombus formation under flow and attenuates clot retraction and fibrinolysis in human blood

Hypochlorite (HOCl), a strong oxidant and antimicrobial agent, has been proposed to be associated with hemostatic abnormalities during inflammatory response. However, its complex impact on hemostasis is not completely understood. In this report we studied the effect of clinically relevant (micromolar) HOCl concentrations on thrombus formation under flow, kinetics of platelet-fibrin clot formation, its architecture, retraction, and lysis. We found that HOCl (up to 500 µM) did not affect kinetics of coagulation measured in whole blood. HOCl (500-1000 µM) markedly diminished thrombus formation under flow. Clot retraction rate was reduced by HOCl dose-dependently (50-500 µM). HOCl (125-500 µM) inhibited fibrinolysis in whole blood and in platelet-depleted plasma, dose-dependently. Activity of plasmin was reduced by HOCl at concentrations started from 500 µM. HOCl (up to 500 µM) did not reduce plasminogen binding to fibrin under flow. HOCl (125-500 µM) modulated architecture of fibrin- and platelet-fibrin clots towards structures made of thin and densely packed fibers. Exposure of pure fibrinogen to HOCl (10-1000 µM) resulted in formation of dityrosine and was associated with altered fibrin structure derived from such modified fibrinogen. HOCl-altered fibrin net structure was not related with modulation of platelet procoagulant response, thrombin generation, and factor XIII activity. We conclude that, in human blood, clinically relevant HOCl concentrations may inhibit thrombus formation under flow, clot retraction and fibrinolysis. Fibrinolysis and clot retraction seem to be the most sensitive to HOCl-evoked inhibition. HOCl-modified fibrinogen and altered clot structure associated with it are likely to be primary sources of attenuated fibrinolysis.

Effects of Genetically Determined Iron Status on Risk of Venous Thromboembolism and Carotid Atherosclerotic Disease: A Mendelian Randomization Study

Background Systemic iron status has been implicated in atherosclerosis and thrombosis. The aim of this study was to investigate the effect of genetically determined iron status on carotid intima-media thickness, carotid plaque, and venous thromboembolism using Mendelian randomization. Methods and Results Genetic instrumental variables for iron status were selected from a genome-wide meta-analysis of 48 972 subjects. Genetic association estimates for carotid intima-media thickness and carotid plaque were obtained using data from 71 128 and 48 434 participants, respectively, and estimates for venous thromboembolism were obtained using data from a study incorporating 7507 cases and 52 632 controls. Conventional 2-sample summary data Mendelian randomization was performed for the main analysis. Higher genetically determined iron status was associated with increased risk of venous thromboembolism. Odds ratios per SD increase in biomarker levels were 1.37 (95% CI 1.14-1.66) for serum iron, 1.25 (1.09-1.43) for transferrin saturation, 1.92 (1.28-2.88) for ferritin, and 0.76 (0.63-0.92) for serum transferrin (with higher transferrin levels representing lower iron status). In contrast, higher iron status was associated with lower risk of carotid plaque. Corresponding odds ratios were 0.85 (0.73-0.99) for serum iron and 0.89 (0.80-1.00) for transferrin saturation, with concordant trends for serum transferrin and ferritin that did not reach statistical significance. There was no Mendelian randomization evidence of an effect of iron status on carotid intima-media thickness. Conclusions These findings support previous work to suggest that higher genetically determined iron status is protective against some forms of atherosclerotic disease but increases the risk of thrombosis related to stasis of blood.

Plasma hepcidin is associated with future risk of venous thromboembolism

Red cell distribution width (RDW) is associated with venous thromboembolism (VTE), but the underlying mechanism(s) is unclear. Iron deficiency is associated with high RDW, and studies suggest an association between iron deficiency and VTE. To assess whether iron deficiency is a risk factor for VTE that explains the association between RDW and VTE, we conducted a nested case-control study of 390 patients with VTE and 802 age- and sex-matched controls selected from the population-based cohort of the Tromsø Study. Physical measurements and blood samples were collected from 1994 to 1995. Logistic regression models were used to calculate odds ratios (ORs) with 95% confidence intervals (CIs) for VTE by RDW, hepcidin, and ferritin light chain (FtL). RDW was inversely associated with hepcidin, FtL, and hemoglobin. The risk of VTE increased linearly across categories of higher plasma hepcidin levels. Participants with hepcidin in the highest quartile had an OR for VTE of 1.32 (95% CI, 1.00-2.42), and those in the >90% percentile had an OR for VTE of 1.66 (95% CI, 1.14-2.42) compared with the reference group (quartiles 2 and 3). The risk estimates remained similar after adjustment for C-reactive protein. The risk of VTE increased by categories of higher RDW and was strengthened after inclusion of hepcidin and FtL in the multivariable model. Our findings reject the hypothesis that iron deficiency explains the association between RDW and VTE and suggest, in contrast, that high body iron levels might increase the risk of VTE.

Uric acid enhances alteplase-mediated thrombolysis as an antioxidant

Uric acid (UA) therapy may prevent early ischemic worsening after acute stroke in thrombolysis patients. The aim of this study was to examine the influence of UA on the thrombolytic efficacy of alteplase in human blood samples by measuring thrombolysis under flow conditions using a newly developed microchip-based flow-chamber assay. Human blood samples from healthy volunteers were exposed to UA, alteplase, or a combination of UA and alteplase. Whole blood and platelet-rich plasma were perfused over a collagen- and thromboplastin-coated microchip, and capillary occlusion was monitored with a video microscope and flow-pressure sensor. The area under the curve (extent of thrombogenesis or thrombolysis) at 30 minutes was 92% lower in the UA-alteplase-treated group compared with the alteplase-treated group. D-dimers were measured to evaluate these effects in human platelet-poor plasma samples. Although hydrogen peroxide significantly decreased the elevation of D-dimers by alteplase, UA significantly inhibited the effect of hydrogen peroxide. Meanwhile, rat models of thromboembolic cerebral ischemia were treated with either alteplase or UA-alteplase combination therapy. Compared with alteplase alone, the combination therapy reduced the infarct volume and inhibited haemorrhagic transformation. UA enhances alteplase-mediated thrombolysis, potentially by preventing oxidative stress, which inhibits fibrinolysis by alteplase in thrombi.

Erythrocytes, leukocytes and platelets as a source of oxidative stress in chronic vascular diseases: Detoxifying mechanisms and potential therapeutic options

Oxidative stress is involved in the chronic pathological vascular remodelling of both abdominal aortic aneurysm and occlusive atherosclerosis. Red blood cells (RBCs), leukocytes and platelets present in both, aneurysmal intraluminal thrombus and intraplaque haemorraghes, could be involved in the redox imbalance inside diseased arterial tissues. RBCs haemolysis may release the pro-oxidant haemoglobin (Hb), which transfers heme to tissue and low-density lipoproteins. Heme-iron potentiates molecular, cell and tissue toxicity mediated by leukocytes and other sources of reactive oxygen species (ROS). Polymorphonuclear neutrophils release myeloperoxidase and, along with activated platelets, produce superoxide mediated by NADPH oxidase, causing oxidative damage. In response to this pro-oxidant milieu, several anti-oxidant molecules of plasma or cell origin can prevent ROS production. Free Hb binds to haptoglobin (Hp) and once Hp-Hb complex is endocytosed by CD163, liberated heme is converted into less toxic compounds by heme oxygenase-1. Iron homeostasis is mainly regulated by transferrin, which transports ferric ions to other cells. Transferrin-bound iron is internalised via endocytosis mediated by transferrin receptor. Once inside the cell, iron is mainly stored by ferritin. Other non hemo-iron related antioxidant enzymes (e.g. superoxide dismutase, catalase, thioredoxin and peroxiredoxin) are also involved in redox modulation in vascular remodelling. Oxidative stress is a main determinant of chronic pathological remodelling of the arterial wall, partially linked to the presence of RBCs, leukocytes, platelets and oxidised fibrin within tissue and to the imbalance between pro-/anti-oxidant molecules. Understanding the complex mechanisms underlying redox imbalance could help to define novel potential targets to decrease atherothrombotic risk.

Edaravone, a Synthetic Free Radical Scavenger, Enhances Alteplase-Mediated Thrombolysis

The combination of alteplase, a recombinant tissue plasminogen activator, and edaravone, an antioxidant, reportedly enhances recanalization after acute ischemic stroke. We examined the influence of edaravone on the thrombolytic efficacy of alteplase by measuring thrombolysis using a newly developed microchip-based flow-chamber assay. Rat models of embolic cerebral ischemia were treated with either alteplase or alteplase-edaravone combination therapy. The combination therapy significantly reduced the infarct volume and improved neurological deficits. Human blood samples from healthy volunteers were exposed to edaravone, alteplase, or a combination of alteplase and edaravone or hydrogen peroxide. Whole blood was perfused over a collagen- and thromboplastin-coated microchip; capillary occlusion was monitored with a video microscope and flow-pressure sensor. The area under the curve (extent of thrombogenesis or thrombolysis) at 30 minutes was 69.9% lower in the edaravone-alteplase- than alteplase-treated group. The thrombolytic effect of alteplase was significantly attenuated in the presence of hydrogen peroxide, suggesting that oxidative stress might hinder thrombolysis. D-dimers were measured to evaluate these effects in human platelet-poor plasma samples. Although hydrogen peroxide significantly decreased the elevation of D-dimers by alteplase, edaravone significantly inhibited the decrease. Edaravone enhances alteplase-mediated thrombolysis, likely by preventing oxidative stress, which inhibits fibrinolysis by alteplase in thrombi.

Neutrophil Activation Promotes Fibrinogen Oxidation and Thrombus Formation in Behçet Disease

Background—

Behçet disease (BD) is a systemic vasculitis with a broad range of organ involvement, characterized by a multisystemic, immune-inflammatory disorder involving vessels of all sizes and often complicated by thrombosis. Systemic redox imbalance and circulating neutrophil hyperactivation have been observed in BD patients and are thought to be responsible for impaired coagulation. We here focused on the pathogenetic mechanisms potentially linking immune cell activation and thrombosis, and specifically examined whether neutrophil activation can affect fibrinogen modifications and consequently elicit thrombosis.

Methods and Results—

Blood samples were collected from 98 consecutive BD patients attending our dedicated Center and from 70 age- and sex-matched healthy controls; in all patients fibrinogen function and structure, fibrin susceptibility to plasmin-lysis, plasma redox status, leukocyte oxidative stress markers, and possible reactive oxygen species sources were examined. Thrombin-catalyzed fibrin formation and fibrin susceptibility to plasmin-induced lysis were significantly impaired in BD patients ( P <0.001). These findings were associated with increased plasma oxidative stress markers ( P <0.001) and with a marked carbonylation of fibrinogen ( P <0.001), whose secondary structure appeared deeply modified. Neutrophils displayed an enhanced NADPH oxidase activity and increased reactive oxygen species production ( P <0.001), which significantly correlated with fibrinogen carbonylation level ( r 2 =0.33, P <0.0001), residual β-band intensity ( r 2 =0.07, P <0.01), and fibrinogen clotting ability ( r 2 =0.073, P <0.01)

Conclusions—

In BD patients, altered fibrinogen structure and impaired fibrinogen function are associated with neutrophil activation and enhanced reactive oxygen species production whose primary source is represented by neutrophil NADPH oxidase.

Diagnostic morphology: biophysical indicators for iron-driven inflammatory diseases

Most non-communicable diseases involve inflammatory changes in one or more vascular systems, and there is considerable evidence that unliganded iron plays major roles in this. Most studies concentrate on biochemical changes, but there are important biophysical correlates. Here we summarize recent microscopy-based observations to the effect that iron can have major effects on erythrocyte morphology, on erythrocyte deformability and on both fibrinogen polymerization and the consequent structure of the fibrin clots formed, each of which contributes significantly and negatively to such diseases. We highlight in particular type 2 diabetes mellitus, ischemic thrombotic stroke, systemic lupus erythematosus, hereditary hemochromatosis and Alzheimer's disease, while recognizing that many other diseases have co-morbidities (and similar causes). Inflammatory biomarkers such as ferritin and fibrinogen are themselves inflammatory, creating a positive feedback that exacerbates disease progression. The biophysical correlates we describe may provide novel, inexpensive and useful biomarkers of the therapeutic benefits of successful treatments.

Fibrin clot structure and function: a role in the pathophysiology of arterial and venous thromboembolic diseases

The formation of fibrin clots that are relatively resistant to lysis represents the final step in blood coagulation. We discuss the genetic and environmental regulators of fibrin structure in relation to thrombotic disease. In addition, we discuss the implications of fibrin structure for treatment of thrombosis. Fibrin clots composed of compact, highly branched networks with thin fibers are resistant to lysis. Altered fibrin structure has consistently been reported in patients with several diseases complicated by thromboembolic events, including patients with acute or prior myocardial infarction, ischemic stroke, and venous thromboembolism. Relatives of patients with myocardial infarction or venous thromboembolism display similar fibrin abnormalities. Low-dose aspirin, statins, lowering of homocysteine, better diabetes control, smoking cessation, and suppression of inflammatory response increase clot permeability and susceptibility to lysis. Growing evidence indicates that abnormal fibrin properties represent a novel risk factor for arterial and venous thrombotic events, particularly of unknown etiology in young and middle-aged patients.

Tissue plasminogen activator and plasminogen activator inhibitor-1 levels in patients with acute paraquat intoxication

To investigate the effects of reactive oxygen species (ROS) on tissue plasminogen activator (tPA) and plasminogen activator inhibitor-1 (PAI-1) plasma levels, and their possible implications on clinical outcome, we measured tPA and PAI-1 levels in 101 patients with acute paraquat (PQ) intoxication. The control group consisted of patients who ingested non-PQ pesticides during the same period. tPA and PAI-1 levels were higher in the PQ group than in the controls. PQ levels were significantly correlated with ingested amount, timelag to hospital, tPA level, and hospitalization duration. tPA levels were correlated with PAI-1, fibrin degradation product (FDP), and D-dimer. D-dimer levels were lower in the PQ group than in the controls. Univariate analysis indicated the following significant determinants of death: age, ingested amount, PQ level, timelag to hospital, serum creatinine, lipase, pH, pCO(2), HCO(3) (-), WBC, FDP, PAI-1, and tPA. However, multivariate analysis indicated that only PQ level was significant independent factor predicting death. In conclusion, tPA and PAI-1 levels were higher, while D-dimer levels were lower in the PQ group than in the controls, implying that ROS stimulate tPA and PAI-1, but PAI-1 activity overrides tPA activity in this setting. Decreased fibrinolytic activity appears to be one of the clinical characteristics of acute PQ intoxication.

Acute cigarette smoke exposure reduces clot lysis--association between altered fibrin architecture and the response to t-PA

BACKGROUND

Enhanced thrombolysis is a proposed mechanism for reduced mortality in cigarette smokers with STEMI ("smoker's paradox"). The mechanisms remain unclear but studies suggest fibrin architecture (FA) may affect thrombolysis. Our group has previously shown that acute cigarette smoke exposure (CSE) alters FA. This study was done to evaluate the association between FA, thrombolysis and CSE.

METHODS AND RESULTS

Otherwise healthy smokers (n=22) were studied before and after smoking two cigarettes. Non-smokers (n=22) served as controls. Two ex-vivo models were used to evaluate clot lysis of venous blood and these data were compared to FA as determined by SEM. In the first model, clot lysis in a glass tube at 60minutes after addition of t-PA was measured. The second model quantified lysis utilizing thromboelastography. With the latter, after a clot reached maximum strength, t-PA was added and clot lysis at 60min was noted. SEM studies were performed on platelet poor plasma mixed with thrombin and FA was examined at 20K. Clot lysis was similar in both groups except that post-smoking, TEG showed a significantly lower lysis compared to pre- and non-smoking clots. SEM analysis showed significantly thinner fibers and denser clots post-smoking.

CONCLUSIONS

Venous clots from smokers failed to show an enhanced lysis when exposed to t-PA. In fact, acute CSE was associated with changes in FA and increased resistance to thrombolysis. These findings in part may explain enhanced thrombogenicity but suggest that mechanisms other than enhanced fibrinolysis are likely to be responsible for "smoker's paradox."

Oxidative stress after thrombolysis-induced reperfusion in human stroke

BACKGROUND AND PURPOSE

Animal models of transient ischemia suggest that oxygen-derived free radicals produced on reperfusion of ischemic brain could constitute the main cause of reperfusion injury. We aimed to determine the presence and role of lipid peroxidation and protein oxidation-related molecules after tissue plasminogen activator-induced recanalization in human stroke.

METHODS

A total of 160 patients with strokes involving the middle cerebral artery and treated with tissue plasminogen activator and 60 healthy controls were included. Blood samples, transcranial Doppler recordings, and National Institutes of Health Stroke Scale scores were obtained at baseline (pretreatment), 1 hour and 2 hours after tissue plasminogen activator bolus, and 12 hours and 24 hours after stroke onset. The main lipid peroxidation end-product malondialdehyde, advanced oxidation protein products, and plasma concentrations of myeloperoxidase were assessed.

RESULTS

At baseline, all oxidative stress biomarkers were higher than in control subjects (P<0.01 for all comparisons). Malondialdehyde remained high compared with controls during the study period, whereas myeloperoxidase concentrations were significantly raised at baseline, 1 hour after tissue plasminogen activator administration, and 12 hours after stroke onset. Malondialdehyde concentrations correlated with stroke severity and were associated with outcome and with hemorrhagic complications. Regarding recanalization, among those patients with middle cerebral artery recanalization by the end of tissue plasminogen activator infusion (44%) or anytime thereafter, no peaking of any of the studied molecules could be identified.

CONCLUSIONS

Our study showed that systemic oxidative damage to lipids and proteins had already occurred at baseline in stroke. In contrast to animal studies, a relationship between free radical-mediated oxidative damage to lipids or proteins and reperfusion injury after arterial recanalization could not be established.

Effect of oxidative stress on the expression of t-PA, u-PA, u-PAR, and PAI-1 in endothelial cells

In this study we examined the effects of exogenous nitric oxide (sodium nitroprusside, SNP) and hydrogen peroxide (H2O2) on the expression level of tissue-type plasminogen activator (t-PA), urokinase-type plasminogen activator (u-PA), urokinase-type plasminogen activator receptor (u-PAR), and plasminogen activator inhibitor type 1 (PAI-1) in human umbilical vein endothelial cells (HUVEC). The expression of selected genes involved in fibrynolysis under the influence of oxidative stress was analyzed at the levels of mRNA, protein, and promoter activity. The results of the conducted studies revealed that oxidative stress in endothelial cells causes a significant increase in PAI-1 and u-PAR expression and a moderate increase in t-PA and u-PA expression at all of the investigated levels. We attempted to elucidate the molecular signaling mechanisms by which SNP and H2O2 regulate expression of the respective fibrinolytic factors. Therefore, we tested the protein levels of AP-1, NF-κB, and HIF-1 and their DNA-binding activity in endothelial cells subjected to oxidative stress. We found strong correlation between AP-1, NF-κB, and HIF-1 in the contribution of regulation of selected genes. In addition, we also found that the inhibition of PAI-1 synthesis by antisense oligonucleotide to PAI-1 mRNA results in markedly increased u-PAR expression and that NF-κB and AP-1 are involved in this regulation.

Acute and chronic effects of vitamin C on endothelial fibrinolytic function in overweight and obese adult humans

We determined the effects of acute intra-arterial vitamin C administration and chronic oral vitamin C supplementation on the capacity of the endothelium to release t-PA in overweight and obese adults. Net endothelial t-PA release was determined in vivo in response to intrabrachial infusions of bradykinin and sodium nitroprusside in 33 sedentary adults: 10 normal-weight (BMI: 23.4 +/- 0.5 kg m(-2); 7M/3F); and 23 overweight/obese (BMI: 31.2 +/- 0.8 kg m(-2); 15M/8F). In 10 normal weight and eight overweight/obese adults the dose-response curves to bradykinin and sodium nitroprusside were repeated with a coinfusion of the antioxidant vitamin C (24 mg min(-1)). Seventeen of the 23 overweight/obese adults completed a 3 month chronic oral vitamin C (500 mg day(-1)) supplementation intervention. Intra-arterial administration of vitamin C significantly potentiated t-PA release in overweight/obese adults. Net release of t-PA was approximately 95% higher (P < 0.01) after (from -0.9 +/- 1.1 to 94.6 +/- 16.2 ng (100 ml tissue)(-1) min(-1)) compared with before (from -0.8 +/- 0.8 to 49.9 +/- 7.7 ng (100 ml tissue)(-1) min(-1)) vitamin C administration. Daily vitamin C supplementation significantly increased t-PA release in overweight/obese adults (from 0.2 +/- 0.9 to 48.2 +/- 6.5 ng (100 ml tissue)(-1) min(-1)) before supplementation versus (0.3 +/- 0.5 to 66.3 +/- 8.7 ng (100 ml tissue)(-1) min(-1)) after supplementation. These results indicate that the antioxidant vitamin C favourably affects the capacity of the endothelium to release t-PA in overweight/obese adults. Daily vitamin C supplementation represents an effective lifestyle intervention strategy for improving endothelial fibrinolytic regulation in this at-risk population.

Stability of alteplase in presence of cavitation

Several experimental studies have demonstrated that ultrasound (US) can accelerate enzymatic fibrinolysis and this effect is further enhanced in the presence of ultrasound contrast agents (UCA). Although UCA have been shown to be safe when administered to ischemic stroke patients, safety information of these agents in the thrombolysis setting is limited. Therefore, in this study we investigated potential adverse effects of acoustic cavitation generated by UCA on alteplase (t-PA), the drug used for treatment of ischemic stroke patients. A volume of 0.9 mL of alteplase was dispensed into a custom-made polyester sample tube. For treatments in the presence or absence of cavitation either 0.1 mL Optison or phosphate buffer saline was combined with alteplase. Three independent samples of each treatment group were exposed to ultrasound of 2 MHz frequency at three different peak negative acoustic pressures of 0.5, 1.7, and 3.5 MPa for a duration of 60 min. All treatments were carried out in a cavitation detection system which was used to insonify the samples and record acoustic emissions generated within the sample. After ultrasound exposure, the treated samples and three untreated drug samples were tested for their enzymatic activity using a chromogenic substrate. The insonified samples containing Optison demonstrated cavitational activity proportional to acoustic pressure. No significant cavitation activity was observed in the absence of Optison. Enzymatic activity of alteplase in both insonified groups was comparable to that in the control group. These tests demonstrated that exposure of alteplase to 60 min of 2 MHz ultrasound at acoustic pressures ranging from 0.5 MPa to 3.5 MPa, in the presence or absence of Optison had no adverse effects on the stability of this therapeutic compound.

Intraperitoneal Administration of Methylene Blue Attenuates Oxidative Stress, Increases Peritoneal Fibrinolysis, and Inhibits Intraabdominal Adhesion Formation

BACKGROUND

Mounting evidence indicates that postoperative oxidative stress may be linked to decreased fibrinolytic activity and, subsequently, the development of intraabdominal adhesions. The goal of this study was to determine if methylene blue, a highly redox active dye that has been shown to inhibit adhesion formation (1) acts as an antioxidant in the postoperative peritoneum, and (2) subsequently affects fibrinolytic activity.

MATERIALS AND METHODS

Intraabdominal adhesions were surgically induced in rats receiving methylene blue (30 mg/kg) or vehicle (sterile water) intraperitoneally at surgery. At 24 h and 7 d following surgery, adhesion formation, oxidative stress, and peritoneal fibrinolytic activity were assessed.

RESULTS

Methylene blue did not affect adhesion formation at 24 h, but did induce a >50% regression in adhesions after 7 d (P < 0.05). Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and myeloperoxidase (MPO) activities, and 8-isoprostane and thiobarbituric acid-reactive substances were all significantly increased in peritoneal tissue samples (P < 0.05) by 24 h following surgery. Methylene blue inhibited NADPH oxidase by 98% and MPO activity by 78% in the 24 h tissue samples, and blunted the corresponding surgery-induced increases in tissue lipid and protein oxidation. Furthermore, methylene blue significantly increased (P < 0.05) fibrinolytic activity in peritoneal fluid at 24 h.

CONCLUSIONS

Methylene blue acts as an antioxidant in this experimental system and may reduce intraabdominal adhesion formation by enhancing peritoneal fibrinolytic activity following surgery.

Reduced clot permeability and susceptibility to lysis in patients with acute coronary syndrome: effects of inflammation and oxidative stress

BACKGROUND

Stable angina is associated with unfavorable fibrin structure/function. It is not known how acute coronary syndromes (ACS) affect fibrin architecture.

OBJECTIVE

We investigated fibrin clot properties and their determinants in ACS patients.

PATIENTS AND METHODS

Clot permeability, turbidity and fibrinolysis were assessed in 40 patients with ACS versus 40 controls with stable angina matched for age, sex, and risk factors.

RESULTS

Patients with ACS had lower clot permeability (p=0.001), faster fibrin polymerization (p=0.008), and prolonged fibrinolysis time (p<0.0001) than controls. C-reactive protein (CRP) and 8-epi-prostaglandin F(2alpha), a marker of oxidative stress, were the only independent predictors of clot permeability (R(2)=-0.74; p<0.0001 and R(2)=-0.65; p<0.0001, respectively) and fibrinolysis time in ACS patients (R(2)=0.60; p<0.0001 and R(2)=0.59; p=0.0002, respectively). In angina patients, fibrinogen and CRP predicted permeability (R(2)=-0.71; p<0.0001 and R(2)=-0.62; p<0.0001), and D-dimer predicted lysis time (R(2)=0.54; p=0.0005). In regression analysis models incorporating all patients, the only independent predictor of all clot variables was being an ACS patient (R(2) 0.51 to 0.85; p<0.001).

CONCLUSIONS

This first study of clot properties in patients during an ACS demonstrated that compared with stable angina patients, their clots are composed of dense networks that are more resistant to lysis and these features are correlated with raised CRP and oxidative stress.

Endothelial t-PA release is impaired in overweight and obese adults but can be improved with regular aerobic exercise

Endothelial release of tissue-type plasminogen activator (t-PA) regulates fibrinolysis and is considered to be a primary endogenous defense mechanism against thrombosis. Adiposity is associated with an increased risk of atherothrombotic events. We determined the influence of overweight and obesity on the capacity of the vascular endothelium to release t-PA and the effects of regular aerobic exercise on endothelial t-PA release in previously sedentary overweight and obese adults. First, we studied 66 sedentary adults: 28 normal-weight (BMI < 25 kg/m2); 22 overweight (BMI > or = 25 and < 30 kg/m2); and 16 obese (BMI > or = 30 kg/m2). Net endothelial t-PA release was determined in vivo in response to intrabrachial infusions of bradykinin (BK) and sodium nitroprusside. Second, we studied 17 overweight and obese adults who completed a 3-mo aerobic exercise intervention. Net release of t-PA in response to BK was approximately 45% lower (P < 0.01) in overweight (from 0.1 +/- 0.4 to 41.7 +/- 4.9 ng x 100 ml tissue(-1) x min(-1)) and obese (-0.1 +/- 0.6 to 47.7 +/- 5.2 ng x 100 ml tissue(-1) x min(-1)) compared with normal-weight (0.1 +/- 0.8 to 77.5 +/- 6.7 ng x 100 ml tissue(-1) x min(-1)) adults. There was no difference in t-PA release between the overweight and obese groups. Exercise training significantly increased t-PA release capacity in overweight and obese adults (from -0.3 +/- 0.5 to 37.1 +/- 4.9 ng x 100 ml tissue(-1) x min(-1) before training vs. 1.0 +/- 0.9 to 65.4 +/- 6.3 ng x 100 ml tissue(-1) x min(-1) after training) to levels comparable with those of their normal-weight peers. These results indicate that overweight and obesity are associated with profound endothelial fibrinolytic dysfunction. Importantly, however, regular aerobic exercise can increase the capacity of the endothelium to release t-PA in this at-risk population.

Peroxynitrite inactivates tissue plasminogen activator

Tissue plasminogen activator (tPA) has a prominent role in physiological fibrinolysis in vivo. Thrombosis has been associated with clinical scenarios (e.g., atherosclerotic disease) known to involve local decreases in tPA activity with concomitant formation of reactive nitrogen species such as peroxynitrite (OONO(-)), a molecule formed from nitric oxide and superoxide. We hypothesized that exposure of tPA to OONO(-) would result in a decrease in tPA activity. OONO(-) was generated with 3-morpholinosydnonimine (SIN-1), a molecule that produces both nitric oxide and superoxide. Recombinant tPA was incubated at 37 degrees C for 60 min with 0 microM SIN-1; 100 microM SIN-1; 100 microM SIN-1 and 4000 U/mL recombinant human superoxide dismutase; or 4000 U/mL recombinant human superoxide dismutase (n = 8 separate reactions per condition). Changes in tPA activity were assessed by addition of tPA samples to tissue factor-exposed human plasma and measuring clot fibrinolysis with a thrombelastograph. Exposure to SIN-1 resulted in a decrease in tPA-mediated fibrinolysis (<1% activity of tPA not exposed to SIN-1) that was significantly (P < 0.001) different from the other three conditions. There were no significant differences between the other conditions. We conclude that tPA is inhibited by OONO(-), and that OONO(-) may have a role in clinical thrombotic scenarios.

IMPLICATIONS

Tissue plasminogen activator (tPA) has a prominent role in fibrinolysis in vivo. Thrombosis has been associated with clinical scenarios involving decreases in tPA activity with concomitant formation of the oxidant peroxynitrite. We determined that peroxynitrite decreased tPA activity via thrombelastography. Peroxynitrite-mediated tPA inactivation may have a role in thrombotic states.

Reversible inactivation of AT(2) angiotensin II receptor from cysteine-disulfide bond exchange

Dithiothreitol (DTT) treatment of angiotensin II (Ang II) type 2 (AT(2)) receptor potentiates ligand binding, but the underlying mechanism is not known. Two disulfide bonds proposed in the extracellular domain were examined in this report. Based on the analysis of ligand affinity of cysteine (Cys, C) to alanine (Ala, A) substitution mutants, we provide evidence that Cys(35)-Cys(290) and Cys(117)-Cys(195) disulfide bonds are formed in the wild-type AT(2) receptor. Disruption of the highly conserved Cys(117)-Cys(195) disulfide bond linking the second and third extracellular segments leads to inactivation of the receptor. The Cys(35)-Cys(290) bond is highly sensitive to DTT. Its breakage results in an increased binding affinity for both Ang II and the AT(2) receptor-specific antagonist PD123319. Surprisingly, in the single Cys mutants, C35A and C290A, a labile population of receptors is produced which can be re-folded to high-affinity state by DTT treatment. These results suggest that the free -SH group of Cys(35) or Cys(290) competes with the disulfide bond formation between Cys(117) and Cys(195). This Cys-disulfide bond exchange results in production of the inactive population of the mutant receptors through formation of a non-native disulfide bond.