Tomasz Rusak

Peroxynitrite – altered platelet mitochondria—A new link between inflammation and hemostasis

Using porcine blood, we tested the hypothesis that peroxynitrite (ONOO(-)) may affect platelet-fibrin clot formation, clot retraction rate (CRR) and fibrinolysis through the inhibition of platelet energy production. It was found that ONOO(-) reduces CRR and enlarges final clot size in platelet rich plasma (PRP) (IC(50)=100μM) and in whole blood (IC(50)=200μM) dose-dependently. In a reconstituted system (washed platelets+fibrinogen), CRR was inhibited by 5-100nM ONOO(-) (IC(50)=25nM). Concentrations of ONOO(-) reducing CRR in PRP, inhibited platelet oxygen consumption, augmented lactate production and decreased total ATP contents in clots derived from PRP. In washed platelets ONOO(-) (5-20nM) produced a drop of the mitochondrial transmembrane potential (ΔΨ(m)). Blocking of mitochondrial energy production resulted in a reduction of CRR, whereas inhibition of glycolysis failed to affect CRR. ONOO(-), up to 300μM, failed to affect coagulation in platelet free plasma. Fibrinolysis of platelet-fibrin clots was enhanced by ONOO(-) (25-300μM), cytochalasin B and following the reduction of platelet energy production. Fibrinolysis of plasma clots was resistant to ONOO(-) treatment up to a concentration of 500μM. Tromboelastometry (ROTEM) measurements performed in PRP show that inhibition of platelet energy production or treatment with ONOO(-) (100-300μM) diminishes MCF, alpha angle and MCE parameters. Blockage the platelet contractile apparatus by cytochalasin B resulted in reduction of CRR and ROTEM variables (MCF, alpha angle, MCE). We conclude that physiologically relevant ONOO(-) concentrations may inhibit clot retraction, reduce clot stability and accelerate its lysis through the inhibition of platelet mitochondrial energy production.

Vasopressin acts on platelets to generate procoagulant activity.

The aim of our study was to examine whether arginine vasopressin (AVP) is able to evoke in human platelets a procoagulant response due to activation of an Na+/H+ exchanger. It was found that treatment of platelets with AVP (20–100 nmol/l) results in generation of a weak calcium signal, activation of Na+/H+ exchanger, aggregation, and development of a procoagulant response. The AVP-evoked procoagulant response was dose and time dependent, weaker than that produced by collagen or monensin (mimics Na+/H+ exchanger), and less pronounced following the inhibition of Na+/H+ exchanger by 5-(N-ethyl-N-isopropyl) amiloride or genistein. Flow cytometry studies reveal that in-vitro platelet treatment with AVP results in an unimodal left shift in the forward and side scatter of the entire platelet population, indicating morphological changes on the plasma membrane. The shift was dose related, weaker than that evoked by collagen, similar to that produced by monensin and strongly reduced in the presence of 5-(N-ethyl-N-isopropyl) amiloride or genistein. Using flow cytometry, we demonstrated enhanced expression of phosphatidylserine on the AVP-treated platelets. AVP-evoked phosphatidylserine exposure was dose dependent, inhibited by 5-(N-ethyl-N-isopropyl) amiloride or genistein and weaker than that produced by collagen. AVP in a dose-dependent manner produced a rise in platelet volume. The swelling was inhibited by 5-(N-ethyl-N-isopropyl) amiloride, and its kinetics was similar to that observed in the presence of monensin. We conclude that prolonged treatment of platelets with AVP results in a procoagulant response, which may occur as a consequence of Na+ influx mediated by Na+/H+ exchanger.

Platelet-related fibrinolysis resistance in patients suffering from PV. Impact of clot retraction and isovolemic erythrocytapheresis

Using patients with polycythemia vera (PV) as an experimental model, we evaluated the impact of clot retraction (CR) and architecture of the clot on fibrinolysis. We studied the kinetics of clot retraction and the fibrinolysis rate in whole blood from 48 PV patients and 48 healthy controls. Measurements were performed before and after isovolemic eryhrocytapheresis (ECP). CR was measured by optical method. Clot lysis time (CLT) and maximum clot firmness (MCF) were measured by thromboelastometry in recalcified blood supplemented with t-PA and tissue factor. Compared with healthy controls, CR rate in PV patients was higher (0.0219 vs. 0.0138; p<0.001), the clot volume smaller and MCF elevated (64 vs. 58 mm). CR rate correlated with platelet count (r=0.546; p=0.001) but not with erythrocyte concentration (r=0.192; p>0.3). Compared with healthy controls, CLT in PV patients was significantly prolonged (158 min vs. 71 min). Fibrinolysis rate inversely correlated with CR rate (r=-0.566; p<0.001); MCF (r=-0.704; p<0.001) and platelet count (r=-0.461; p<0.001). As judged by confocal microscope, in comparison to healthy controls, clots formed in blood from PV patients demonstrated booth a distinctly higher degree of crosslinking and possessed thinner fibers. Altered CR, MCF and fibrinolysis speeds were not normalized following the ECP procedure. Tirofiban (a blocker of platelet GPIIb/IIIa receptors), unlike aspirin, normalized abnormal CR and fibrinolysis in blood from PV patients. Collectively, our data indicate that in PV patients, abnormal CR may result in formation of thrombi that are more resistant to fibrinolysis. ECP and aspirin failed to normalize platelet-related fibrinolysis resistance.

Peroxynitrite may affect clot retraction in human blood through the inhibition of platelet mitochondrial energy production

Peroxynitrite (ONOO(-)) contributes to hemostasis abnormalities associated with inflammatory states by a poorly understood mechanism. Here we show that ONOO(-) may affect clot retraction (CR), an important step in hemostasis, by reducing contractility of human platelets resulting from the inhibition of mitochondrial energy production. Reduced CR may result in thromboembolic and hemorrhage events. The results show that in human blood, in vitro, physiologically relevant ONOO(-) concentrations reduce clot retraction rate and enlarge final clot size. The stressor was more effective in reconstituted system consisting of washed platelets and fibrinogen, (IC₅₀=25 nM) than in platelet rich plasma (IC₅₀=75 μM) or in whole blood (IC₅₀=120 μM), indicating that its effect depends on the number of targets. Retardation of CR by lower concentrations of ONOO(-) resulted in reduction of platelet energy production due to impairment of mitochondria but not from tyrosine nitration or inhibition of actin polymerization. In washed platelets nanomolar ONOO(-) concentrations produced a drop of the mitochondrial transmembrane potential (ΔΨm) explaining high sensitivity of CR (a large consumer of platelet energy) to stressor. Thromboelastometry measurements showed that ONOO(-) may diminish clot stability and elasticity through the reduction of platelet contractility. Our findings suggest that in humans ONOO(-)- altered platelet mitochondria represent a new link between inflammation and hemostasis.

The involvement of the Na(+)/H(+) exchanger in the formation of microvesicles by porcine platelets.

Activated platelets release microvesicles, which express procoagulant activity. The mechanism by which vesicles are formed is not entirely clear. This study was undertaken to determine whether a link exists between the operation of the plasma membrane Na(+)/H(+) exchanger (NHE) and vesiculation. It was found, that platelets treated with NHE-simulating monensin and the sodium influx-inducing gramicidin (without concomitant H+ efflux) produced vesicles demonstrating procoagulant activity. Alkalinization of platelet cytosol by NH4Cl failed to evoke vesicle release. Collagen and phorbol ester (PMA)-evoked vesiculation was diminished in the presence of 5-(N-ethyl-N-isopropyl amiloride) (EIPA, inhibitor of NHE) or GF 109203X (inhibitor of protein kinase C). Vesicle formation induced by collagen, PMA, and the calcium ionophore A23187 was less pronounced in the absence of external Na+. In comparison with collagen, thrombin was a stronger inducer of vesiculation. Platelets stimulated by thrombin, collagen, and PMA accumulated 22Na+, a phenomenon inhibited in the presence of EIPA. Collagen-evoked vesicle formation started with aggregation but culminated after its completion. The data indicate a significant contribution of the Na(+)/H(+) exchanger in the formation of microvesicles by porcine platelets.

Nitric oxide scavenging by cell-free hemoglobin may be a primary factor determining hypertension in polycythemic patients

Abstract We tested the hypothesis that hypertension associated with polycythemia vera (PV) may be related to hemoglobin released from erythrocytes (cell-free hemoglobin, fHb). We assessed hematocrit, mean arterial pressure (MAP), blood viscosity, and the level of fHb and nitrite/nitrate (NOx) in the plasma of 73 PV patients and 38 healthy controls. The effect of isovolemic erythrocytapheresis (ECP) on the considered parameters was also studied. From the whole group of PV patients a subset of subjects with normal (normotensive patients, n = 16) and elevated MAP (hypertensive patients, n = 57) can be subtracted. It was found that in comparison with healthy controls, PV patients have significantly (p ≤ 0.01) elevated Hct (0.567 vs. 0.422), blood viscosity (5.45 vs. 3.56 cP), MAP (106.8 vs. 93.8 mmHg), plasma fHb (9.7 vs. 2.8 mg/dL), and NOx levels (34.1 vs. 27.5 μM). Compared with normotensive patients, hypertensive PV patients demonstrated a higher rise in fHb (10.2 vs. 8.0) and plasma NOx levels (35.8 vs. 31.0). In PV patients, fHb positively correlates with MAP (r = 0.489), NOx levels (r = 0.461), hematocrit (r = 0.428), and viscosity (r = 0.393). Blood viscosity positively correlated with hematocrit (r = 0.894), but not with other considered parameters. In PV patients MAP poorly correlated with hematocrit, whereas the correlation between MAP and NOx altered from − 0.325 (healthy control) to + 0.268 (PV patients). ECP procedure was associated with a significant (p < 0.01) reduction of hematocrit, fHb, blood viscosity, and MAP. In the normotensive subgroup of PV patients the ECP procedure did not affect MAP. It can be concluded that accelerated scavenging of nitric oxide by fHb rather than high Hct may be a key factor determining the development of hypertension in PV patients.

The Uremic Toxin Indoxyl Sulfate Accelerates Thrombotic Response after Vascular Injury in Animal Models

Chronic kidney disease (CKD) patients are at high risk for thrombotic events. Indoxyl sulfate (IS) is one of the most potent uremic toxins that accumulates during CKD. Even though IS is associated with an increased risk for cardiovascular disease, its impact on thrombotic events still remains not fully understood. The purpose of the study was to evaluate the direct effect of IS on thrombotic process. We examined the impact of acute exposure to IS on thrombus development induced by electric current in Wistar rats, intravital thrombus formation after laser-induced injury in the mice endothelium, coagulation profile, clot formation dynamics, platelet aggregations, and erythrocyte osmotic resistance. IS doses: 10, 30 and 100 mg/kg body weight (b.w.) increased weight of thrombus induced by electric current in dose-dependent manner (p < 0.001). Furthermore, two highest IS doses increased laser-induced thrombus formation observed via confocal system (increase in fluorescence intensity and total thrombus area (p < 0.01)). Only the highest IS dose decreased clotting time (p < 0.01) and increased maximum clot firmness (p < 0.05). IS did not affect blood morphology parameters and erythrocyte osmotic resistance, but augmented collagen-induced aggregation. Obtained data indicate that IS creates prothrombotic state and contributes to more stable thrombus formation. Thus, we concluded that IS may be one of crucial uremic factors promoting thrombotic events in CKD patients.

Evaluation of hemostatic balance in blood from patients with polycythemia vera by means of thromboelastography: The effect of isovolemic erythrocytapheresis

Polycythemia vera (PV) is associated with an increased frequency of thrombotic complications. This study was undertaken to evaluate the hemostatic balance in the blood of PV patients by means of thromboelastography (TEG). The effect of isovolemic erythrocytapheresis (ECP) on the hemostasis of PV patients was also studied. We assessed the coagulation status of 76 PV patients undergoing ECP and 50 of healthy controls. TEG measurements were performed immediately before and after the ECP procedure. Coagulation was triggered by recalcification in freshly collected citrated blood. We recorded clotting time (R), alpha angle, and maximum amplitude (MA) of the clot. The results presented here show that, compared with healthy controls, PV patients demonstrated an increase in alpha angle (p < 0.005) and in MA (p = 0.14). In the subgroup of PV patients with high (>440 × 109 l−1) platelet (PLT) count, differences in MA (p < 0.01) and alpha angle (p < 0.001) were more significant. Following ECP procedure, a significant (p ≤ 0.01) reduction of R time, a rise of alpha angle, and MA were observed, indicating augmentation of a hypercoagulable state. In PV patients, the rise in alpha angle positively correlated (r = 0.549) with platelet count but not with the number of erythrocytes and leukocytes. Following ECP, this correlation was reduced (r = 0.382). Dilution (with saline) of blood from PV patients and of healthy controls, to a degree similar to that used during the ECP procedure, resulted in reduction of R and rise of the alpha angle. In conclusion, TEG measurements show that the majority of PV patients demonstrate abnormal hemostasis in which a major role is played by platelets rather than plasma factors. The hypercoagulable state in PV patients is significantly augmented following the ECP and may be related to the hemodilution intrinsically included in this procedure. TEG may help to assess the thrombotic risk in individual PV patients.

Involvement of hyperglycemia in the development of platelet procoagulant response: the role of aldose reductase and platelet swelling

&NA; Rise in mean platelet volume (MPV) has been demonstrated to be associated with increased platelet reactivity. In diabetes patients, augmented MPV was proposed to contribute to increased risk of thrombotic complications. Therefore, the aim of this study was to investigate whether under hyperglycemic conditions, aldose reductase (AR)-mediated sorbitol formation and associated rise in cell volume, which subsequently results in platelet hyperactivation. Platelets were obtained from 30 healthy volunteers and 13 patients with diabetes. We evaluated changes in platelet size, their reactivity (measured as aggregation and secretion), and sorbitol content evoked by glucose. Measurement of procoagulant activity and thromboelastography were performed to assess how hyperglycemia affects coagulation. We have found that incubation of platelets with glucose (>10 mmol/l) leads to increased MPV, potentiation of collagen-evoked platelet aggregation, secretion, and procoagulant response (measured as platelet-dependent thrombin generation and phosphatidylserine expression). Glucose-treated platelets had higher sorbitol content and demonstrated enhanced tubulin polymerization. All the above-mentioned phenomena were reduced following the blocking of AR or by vincristine (microtubule destabilizing agent). Thromboelastography measurements demonstrated that hyperglycemia is associated with reduction of clotting time (R) and increase in the alpha angle (reflects platelet activation). Addition of sorbinil (AR inhibitor) or vincristine normalized R variable and alpha angle. The hyperglycemic conditions may accelerate platelet-related thrombin generation through the activation of polyol pathway, enhanced tubulin polymerization and associated with it rise in platelet volume.

Asthma is associated with reduced fibrinolytic activity, abnormal clot architecture, and decreased clot retraction rate.

The aim of this study was to assess whether steroid‐naïve asthma modulates hemostasis. We evaluated the clot retraction rate (CRR), fibrinolysis rate (FR), clot density (CD) (by confocal microscopy), plasma levels of plasminogen activator inhibitor (PAI‐1), and factor XIII (FXIII), NO in exhaled breath (FENO), spirometry (FEV1) and eosinophil count (EOS) in 36 patients with allergic, steroid‐naïve asthma and in 34 healthy controls. We observed significantly (P < 0.001) reduced CRR, FR, and FEV1 and increased FENO, EOS, PAI‐1, FXIII, and CD in patients with asthma compared with controls. In patients with asthma, FR negatively correlated with CD, FXIII, PAI‐1, FENO, and EOS and positively with FEV1. FXIII positively correlated with CD. Clot retraction rate negatively correlated with FENO and positively with FEV1 (all P < 0.001). These novel findings suggest that asthma itself is associated with decreased CRR and reduced fibrinolytic potential resulting from alterations in clot architecture and elevated levels of plasma FXIII and PAI‐1.