Nonradical oxidants of the phagocyte type induce the activation of plasmatic single chain- urokinase

Singlet Oxygen Enhances Intrinsic Thrombolysis: The Intrinsic Oxidative Clot Lysis Assay (INOXCLA)

Granulocytes are important cells of inflammation and cellular thrombolysis. They produce urokinase (u-PA) and chloramines. In this study, u-PA/chloramine—mediated fibrinolysis is imitated in a microtiter-plate. Seventy-five microliters plasma are incubated with 50 μL 50% Pathromtin SL, 6% BSA, and 38 mM CaCl2 for 30 minutes (37°C). Then, 50 μL 10 mM chloramine-T in PBS are added. After 30 minutes (37°C), 50 μL 0, 100, or 10 IU/mL u-PA in 6% BSA-PBS are added and the turbidity is determined at 405 nm after 0, 3, or 16 hours. Clot lysis was increased more than tenfold by 0.5 to 1 μmoles chloramine (ED50 after 3h = about 0.25 μmoles = 2mM final concentration). The normal range for the present intrinsic oxidative clot lysis assay (INOXCLA) is 100% ± 25% (MV ± SD; 100 relative % of norm; the normal lysis being 60 absolute %; CVs < 10%). Fifty percent lysis of adherent microclots occurred after 0.75 hours, 2 hours, 14 hours, 13 days, or 17 days when using 1000, 100, 10, 1, or 0 IU/mL u-PA reagent. If the u-PA activity is quenched by PAI-2, no clot lysis appears. Chloramines are important physiologic generators of nonradical excited singlet oxygen and enhance u-PA—mediated lysis of plasma clots. Based on the u-PA/chloramines coaction, a new global fibrinolysis assay has been derived.

In vitro Simulation of Therapeutic Plasmatic Fibrinolysis

One type of therapy for thromboembolism is plasmatic thrombolysis. Several plasminogen activators (PA) are clinically available, including urokinase (u-PA), tissue plasminogen activator (t-PA), streptokinase (SK), plasminogen-streptokinase-activator-complex (PSAC), or mutants of t-PA such as reteplase (RP) or tenecteplase (TP). Therapeutic plasmatic fibrinolysis was simulated, using the PA at relevant plasma concentrations, and plasmin (Pli) and PA activities were determined. Normal citrated plasma was supplemented with 31 to 1,000 IU/mL u-PA, 0.31 to 20 μg/mL t-PA, 125 to 4,000 IU/mL SK, 12.5 to 400 U/mL PSAC, 125 to 4,000 U/mL RP, or 0.31 to 10,μg/mL TP. Ten IU/mL urokinase was also incubated with pooled plasma of stroke patients, that was previously oxidized with the singlet oxygen (1O2) donor chloramine T® (CT), to destroy plasmatic PAI-1 and a2-antiplasmin. After 0 to 80 minutes (37°C), 50-μL samples were withdrawn and added to 100 μL 1.5 M arginine, pH 8.7, and oxidized with 50 μL of 20 mM CT. For determination of plasmin activity, 10 μL thereof was incubated with 150 μL 1.5 M arginine, pH 8.7, and 100 μL 20 mM CT preoxidized (15 minutes 37°C) pooled normal citrate buffered EDTA-plasma for 30 minutes (37°C). For determination of [PA+Pli]-activity, arginine was added after this incubation. 25-μL 6 mM Val-Leu-Lys-pNA were added and AA/h at room temperature (RT) was monitored, using a microtiterplate reader. [PA+Pli]-Pli = PA. The PA concentration required to induce 25% [ED25] of the maximally inducible Pli-activity in plasma (= 1 U/mL = 45 mg/L = 0.53 Amol/L active Pli; AA = 363 + 8 mA/h RT) after 10 minutes (37°C) were 320 IU/mL u-PA, 8 μg/mL t-PA, 140 U/mL PSAC, 6,000 IU/mL SK, 720 U/mL RP, and approximately 150 μg/mL TP. The approximate activity half-lives of the PA in plasma were 30 minutes for u-PA, 30 minutes for t-PA, greater than 80 minutes for SK, greater than 80 minutes for PSAC, 50 minutes for RP, and 80 minutes for TP. The present study shows-for the first time-a combined kinetic in vitro simulation of the plasmatic activity of six different PAs. At clinically used concentrations, RP induces the highest plasmatic Pli activity. Due to unselective generation of plasmin in plasma, all PA are of some danger in inducing severe hemorrhagias. Clinical thrombolysis might be improved by usage of more physiologic activators of thrombolysis, such as activators of polymorphonuclear neutrophils.

Singlet oxygen potentiates thrombolysis

Activated polymorphonuclear neutrophils (PMN) participate in physiologic thrombolysis. PMN produce large amounts of urokinase (u-PA) and oxidants of the hypochlorite/chloramine-type that generate nonradical excited singlet oxygen ((1)O(2)). The u-PA/(1)O(2)-mediated thrombolysis was imitated in vitro. One hundred microliters microclots of normal human plasma were oxidized with 25 microL 0 to 5.0 micromoles of chloramine-T in physiol. NaCl in the absence or presence of 100 microL 6% bovine serum albumin or 100 microL normal plasma. Twenty-five microliters 0 to 167 IU/mL (related to 150 microL added supernatant) u-PA or 0 to 2.08 microg/mL t-PA were added. The absorbance at 405 nm was determined after 0 to 27 hours (37 degrees C). The specific clot turbidity was calculated, subtracting the 100% lysis absorbance from the respective measured absorbance. The chloramine-effective dose 50% (ED(50)) after 27 hours was determined in the presence of 2.6 IU/mL u-PA. The plasminogen activator-ED(25) was determined after 2 hours (37 degrees C), and the ET(25); i.e., the time needed to lyse a microclot by 25%, was determined for each respective clot-oxidation. The ED(25) of u-PA depends on the oxidation of the microclots: 1.25 micromoles chloramine/100 microL clot enhances thrombolysis approximately 20-fold; here, 25% of clot lysis is achieved within 50 minutes (using approximately 20 IU/mL u-PA), whereas approximately 5 hours are needed to lyse an unoxidized microclot by 25%. The present global assay technique imitates the u-PA/(1)O(2) aspects of physiologic thrombolysis by PMN.

Monitoring of plasmin and plasminogen activator activity in blood of patients under fibrinolytic treatment by reteplase

There are no reliable data on plasmin or plasminogen activator (PA) activities in blood of patients receiving fibrinolytic treatment. This is due to continuing in vitro action of PA after blood withdrawal. These artefactual changes of PA or plasmin activities have been prevented by arginine stabilization of blood samples of myocardial infarction patients treated with plasminogen activators. Twelve patients with myocardial infarction were treated with reteplase 2 x 10,000,000 units in bolus application; one patient was treated with 100 mg t-PA in continuous infusion. Blood was immediately stabilized with EDTA and arginine. The plasma was analyzed with newly developed assays for plasmin and PA. Maximal plasmin activities in blood were obtained at 40 to 60 minutes reteplase treatment time (0.1-0.6 U/mL = approximately 0.05-0.3 micromol/L plasmin). The 50% clearance rate for plasmatic Pli was greater than 30 minutes. The plasmatic reteplase concentration peaked at approximately 2,000 U/mL after the first bolus infusion and at approximately 1,500-3,500 U/mL after the second bolus infusion. Reteplase was cleared to 50% within less than 30 minutes, also with great inter-individual variation. Arginine stabilization of blood allows reliable determinations of activities of plasmin and PA in blood of patients under fibrinolytic treatment: substantial plasmin activities occur in patients treated by reteplase. Therapeutic thrombolysis might be improved, imitating the physiologic cellular thrombolysis; i.e., polymorphonuclear phagocytes (PMN) that can be activated by singlet oxygen ((1)O(2)). PMN might be superior to PA in selective lysis of pathologic thrombi.

In vitro simulation of therapeutic thrombolysis with microtiter plate clot-lysis assay

Only limited comparable data are available on the clot lysis power of the clinically used plasminogen activators (PA). Here the PA were used at different clinically relevant concentrations, and the lysis of the microclots was determined. A microclot lysis assay was used to study thrombolysis by urokinase, tissue-PA (t-PA), streptokinase, plasminogen-streptokinase activator complex (PSAC), reteplase, or tenecteplase. The clot turbidity served as a tool to determine clot mass: 100 microL fresh microclots were incubated with 25 microL PA in 6% bovine serum albumin (BSA)-phosphate-buffered saline (PBS) and 100 microL BSA-PBS or pooled normal human plasma; that is, the PA were in the liquid supernatant of a plasma clot and were not entrapped in the clot, an assay system comparable to normal physiology. The turbidity was determined after 0 to 5 hours (37 degrees C) by a microtiter plate reader. The lysable clot turbidity (clot mass) was expressed in percent of 100% lysable clot control. The clot lysis activity is 100% minus the clot mass in percent. The effective doses at 50% (ED(50)) of lysis of fresh clots after 4 hours (37 degrees C) with 6% BSA or pooled normal human plasma in the clot-supernatant were urokinase 128 or 180 IU/mL; t-PA 0.3 or 0.2 microg/mL; streptokinase 215 or 1371 IU/mL; PSAC 60 or 91 U/mL; reteplase 664 or 996 U/mL; tenecteplase 0.2 or 0.2 microg/mL. The presence of a plasma thrombus with plasma supernatant increases the activity of t-PA approximately 20-fold and that of tenecteplase approximately 400-fold after 4 hours (37 degrees C), when compared to urokinase; in contrast, the lytic activity induced by reteplase decreases; i.e., the plasmin generated by reteplase is hampered on its lytic action against a thrombus. When comparing the clot lysability of microclots of 29 different donors, the only correlation (r > 0.6) was that between u-PA and t-PA. The lysability of individual clots by PA can be measured with the present routine-suited technique. It is suggested that different thrombolytic agents or concentrations thereof would have a different clinical outcome in different individuals.

Singlet oxygen (1O(2)) disrupts platelet aggregates

INTRODUCTION

Important mediators of activated polymorphonuclear leukocytes (PMN) are the oxidants HOCl and chloramine, which generate the nonradical photon-emitting oxidant singlet oxygen (1O(2)). Since 1O(2) inhibits platelet aggregation, we became interested in a possible oxidant mediated reversibility of platelet aggregation.

METHODS

Chloramine T (CT) is a stable 1O(2) generator that mimics the natural chloramine N-chloro-taurine. Platelet-rich plasma (PRP) was incubated with CT 0-8 min after addition of the aggregation agonist (10 microM adenosine-5'-diphosphate, ADP, or 5 microg/ml collagen) and the aggregation was monitored. Platelet function was also analyzed by the platelet function analyzer, PFA-100. Fifty microliters of 200 micromol/l ADP was added to 400 microl PRP. After 1 min at 37 degrees C, 50 microl of 0 or 30 mmol/l CT was added, and after an incubation for 3 min at 37 degrees C, 50 microl of 25% glutaraldehyde was added. The samples were analyzed in a transmission microscope at x3000 and x7000 magnification.

RESULTS

Chloramines inhibit platelet function in PRP: about 1 mM CT suppresses 50% of the aggregatory capacity of thrombocytes in normal PRP (effective dose 50%, ED(50)=1 mM chloramine), which is identical to the ED(50) for CT in whole blood. The ADP- or collagen-induced platelet aggregation can be reversed by addition of CT: up to 2 min after the addition of ADP as the aggregation inducer, the aggregation is reversible to more than 70% by addition of a 1O(2) release-inducer (3 mM CT). In contrast, addition of CT 8 min after the addition of ADP results only in about 50% reversal of platelet aggregation. The electron microscopic images of platelets before ADP, after incubation for 4 min at 20 micromol/l ADP, after incubation for 1 min at 20 micromol/l ADP, and a further incubation for 3 min at 3 mmol/l CT demonstrate an ADP-dependent formation of platelet aggregates, which are disrupted by 1O(2) into the single platelets; a phenomenon comparable to the decomposition of a puzzle or the continental drift of the major earth plates. The morphology of oxidized and unoxidized platelets is similar.

CONCLUSION

This study demonstrates that 1O(2) inhibits and reverses platelet aggregation. The physiologic signal action and the direct anticoagulant action of 1O(2) might be a new principle for pharmacologic intervention in atherothrombosis.

Singlet oxygen inhibits agonist-induced P-selectin expression and formation of platelet aggregates

Major mediators of activated polymorphonuclear leukocytes (PMN) are the oxidants HOCl and chloramine, which are a source for the nonradical photon-emitting oxidant singlet oxygen (1O2). We were interested in a possible platelet-modulating activity of 1O2. As a stable 1O2 source we chose the mild oxidant chloramine T (CT), which mimics the natural chloramine N-chloro-taurine. Freshly drawn native whole blood from donors (n = 5) was incubated at 0 to 3 mM CT for 1 minute at 37 degrees C. Then saline. 10 microM adenosine diphosphate (ADP), 5 microg/mL collagen, or 6.25 microM thrombin receptor activator peptide (TRAP) were added and the mixtures were allowed to incubate for 3 minutes at 37 degrees C. Aliquots of activated blood were fixed in 1% para-formaldehyde. After removal of the fixative, platelets were labeled with anti-CD61-FITC and anti-CD62P-PE antibodies and analyzed by flow cytometry. An oxidant concentration-dependent decrease in the expression of P-selectin appeared (at 3 mM CT to 39, 23, and 20% of the 100% saline control level for ADP, collagen, and TRAP, respectively). There was also an oxidant concentration-dependent decrease in the formation of platelet aggregates (at 3 mM CT to 8, 12, and 13% of the 100% saline control level for ADP, collagen, and TRAP, respectively; the 50% effective dose was 1.0 to 1.5 mM chloramine). In ADP- and TRAP-stimulated platelets, an oxidant-mediated increase in platelet fragments appeared (at 3 mM CT: three- to fourfold of the initial value). The addition to the blood of 30 mM of the oxyradical scavenger mannitol in contrast to excess methionine did not antagonize these oxidative modulations of platelet activation. The results were confirmed using equimolar concentrations of NaOCI and N-chloro-taurine. This study shows that 1O2 inhibits platelets, decreasing the expression of CD62P and the formation of platelet aggregates. Activated PMN might modulate hemostasis, shifting it into an antithrombotic state. The physiologic signal action and the direct anticoagulant action of 1O2 (released by chloramines such as vancomycin) might be a new principle for pharmacologic intervention in atherothrombosis.

The antithrombotic factor singlet oxygen/light (1O2/h nu)

Activated phagocytes (especially polymorphonuclear granulocytes (PMNs)) by respiratory oxidative/photonic burst (activation of NADPH-oxidase and myeloper-oxidase) generate large amounts of oxidants of the hypochlorite-/chloramine-type, which are physiologic sources for singlet oxygen (1O2), a nonradical-excited (photon (h nu) emitting) oxygen species [Weiss SJ, NEJM 1989;320:365-376]. In vitro experiments show that 1O2 (1) inhibits coagulation by inactivation of thrombocytes, fibrinogen, factor V, factor VIII, and factor X and (2) activates fibrinolysis by inactivation of the main fibrinolysis inhibitors plasminogen activator inhibitor (PAI)-1 and alpha-2-antiplasmin, and by activation of single-chain urokinase by plasmin and oxidized fibrin. Additionally, this work suggests that 1O2/h nu acts antithrombotically, inducing selective thrombolysis in vivo (i.e., thrombolysis induced by 0.1 to 0.5 mmol/l chloramine within 30 to 60 minutes without changes of the plasmatic hemostasis system). 1O2 might activate flowing to (on the endothelium) rolling PMN, increasing their chance to get in contact with fibrin/platelet aggregates deposited on the endothelial layer. Via 1O2 generation, the thrombus-activated phagocytes might call for (acute, physiologic) inflammation/fibrinolysis amplification, resulting in the "moving front" of PMN, which infiltrates and destroys the thrombus. 1O2 seems to (partially) participate in the reactivity of nitric oxide, another prooxidative agent. The inhibition of physiologic amounts of 1O2 by blood cholesterol might be involved in the pathogenesis of atherothrombosis. Consequently, it is suggested that activated PMNs modulate hemostasis, shifting it into an antithrombotic state; this cellular part of fibrinolysis seems to be of greater physiologic importance than the plasmatic one. Impaired PMN function (e.g., as occurring in patients with antineutrophil cytoplasmic antibodies or under cytostatic treatments) often results in serious thrombotic complications. Light is the only signal whose origin can be immediately recognized by a fast moving cell in the (dark) blood stream. The cell signal action of 1O2/h nu (e.g., released by chloramines such as taurine-chloramine or vancomycin, by fiberoptic, by photodynamic therapy, or by so-called redox-cycling drugs such as quinones or tetracyclines) might be a new and physiologic principle for pharmacologic intervention in atherothrombosis.

Reactive oxygen intermediates and ischemia-reperfusion injury release tissue plasminogen activator from isolated rat hearts

Tissue plasminogen activator (t-PA) is a marker of endothelial cell injury or activation. The release of t-PA from isolated rat hearts (Langendorff model) subjected to ischemia-reperfusion or reactive oxygen intermediates (ROI) generated by H2O2 was investigated. H2O2 (200 microM) increased t-PA activity in the coronary effluent to 305 +/- 84% of initial value (mean +/- SEM, p < 0.04 vs controls) at the end of a 10 min intervention. The hydroxyl radical scavenger thiourea (10 mM) only partially inhibited the increase (175 +/- 27%, p < 0.01 compared to controls). 20 min normothermic ischemia increased t-PA activity to 416 +/- 108% (p < 0.005 compared to controls) at the start of reperfusion. In conclusion, cardiac injury by ischemia-reperfusion or ROI increases release of t-PA.