Effect of Drotrecogin alfa (activated) on platelet receptor expression in vitro

Thrombocytopenia is a common problem in critically ill patients, which is associated with increased mortality. Recently, Drotrecogin alfa (activated) (recombinant human activated protein C (APC)) was shown to reduce mortality in patients with severe sepsis. Only minimal effect of APC on coagulation markers was demonstrated. Nevertheless, low platelet count was identified as a risk factor for bleeding with use of this drug. We conducted this study to evaluate possible influence of APC on in vitro expression of platelet receptors at therapeutic and supra-therapeutic concentrations. Blood samples of volunteers and patients with severe sepsis were adjusted with APC to final concentrations of 0.045 microg mL(-1) APC (APC-45, therapeutic dose) and 0.225 microg mL(-1) APC (APC-225, five-fold therapeutic dose), respectively. The activation of platelets was mediated by two different agonists. APC had no significant influence on platelet activation, with or without stimulation at both concentrations. In group APC-225, CD62P showed a non-significant decrease. This in vitro study demonstrates that therapeutic plasma concentrations of Drotrecogin alfa (activated) have neither influence on expression of platelet activation markers nor on platelet-granulocyte complexes in blood of volunteers and patients with severe sepsis. Thus, a direct drug-platelet interaction seems unlikely.     

Activated protein C action in inflammation

Activated protein C (APC) is a natural anticoagulant that plays an important role in coagulation homeostasis by inactivating the procoagulation factor Va and VIIIa. In addition to its anticoagulation functions, APC also has cytoprotective effects such as anti‐inflammatory, anti‐apoptotic, and endothelial barrier protection. Recently, a recombinant form of human APC (rhAPC or drotrecogin alfa activated; known commercially as ‘Xigris’) was approved by the US Federal Drug Administration for treatment of severe sepsis associated with a high risk of mortality. Sepsis, also known as systemic inflammatory response syndrome (SIRS) resulting from infection, is a serious medical condition in critical care patients. In sepsis, hyperactive and dysregulated inflammatory responses lead to secretion of pro‐ and anti‐inflammatory cytokines, activation and migration of leucocytes, activation of coagulation, inhibition of fibrinolysis, and increased apoptosis. Although initial hypotheses focused on antithrombotic and profibrinolytic functions of APC in sepsis, other agents with more potent anticoagulation functions were not effective in treating severe sepsis. Furthermore, APC therapy is also associated with the risk of severe bleeding in treated patients. Therefore, the cytoprotective effects, rather than the anticoagulant effect of APC are postulated to be responsible for the therapeutic benefit of APC in the treatment of severe sepsis.     

Factor VIII concentrate infusion in patients with haemophilia results in decreased von Willebrand factor and ADAMTS‐13 activity

The effects of coagulation factor concentrate infusion on restoring secondary haemostasis in patients with haemophilia are obvious. It is not known whether coagulation factor concentrate infusion affects primary haemostasis or induces an acute inflammatory response. In this study, the influence of a factor VIII (FVIII) concentrate bolus infusion on platelet activation and responsiveness, endothelial activation, and inflammation in adult patients with severe haemophilia A was assessed. VWF showed a mild, but significant decrease 15 min after FVIII infusion (85.02 IU dL^?1) vs. before infusion (92.04 IU dL^?1; P = 0.017), while ADAMTS‐13 levels also show a mild but significant decrease from 66.1 ng mL^?1 before infusion, to 53.9 ng mL^?1 (P = 0.012) 15 min after and 50.8 ng mL^?1 (P = 0.050) 60 min after infusion. Platelet P‐selectin expression decreased 15 min (33.3 AU) and 60 min (38.7 AU) after infusion compared to before infusion (41.3 AU; P = 0.018 and 0.036). In conclusion, a single infusion of a high dose FVIII concentrate in haemophilia A patients may influence primary haemostasis by decreasing VWF, ADAMTS‐13 and the number of circulating activated platelets. These effects possibly occur as a consequence of binding of the infused FVIII to VWF, influencing its processing. When treating severe haemophilia A patients with coagulation concentrate infusion, one should realize this does not merely correct FVIII levels but also may influence primary haemostasis.     

Septic shock and multiple organ failure after hematopoietic stem cell transplantation: treatment with recombinant human activated protein C

Severe sepsis with multiple organ failure after hematopoietic stem cell transplantation (HSCT) results in extremely high morbidity and mortality. Recent studies have highlighted the importance of sepsis-induced activation of the coagulation system in the pathophysiology of severe sepsis. Activated protein C is an important modulator of coagulation and inflammatory derangements during severe sepsis. Low levels of protein C occur in severe sepsis and are predictive of poor outcome. Recombinant human activated protein C (drotrecogin alfa (activated)) was recently approved by the Food and Drug Administration (FDA) for severe sepsis. The phase III trial that resulted in the approval of this agent, however, enrolled a general sepsis population and excluded patients undergoing HSCT. We report a case of fulminant septic shock and multiple organ failure after HSCT that was treated with drotrecogin alfa (activated) in addition to standard therapy, and recovered. The high mortality rates of patients who develop severe sepsis after HSCT demand that new avenues of treatment be considered for this very high-risk patient population. This case illustrates the potential application of a novel therapeutic approach. Clinical trials are warranted to further investigate the safety and efficacy of drotrecogin alfa (activated) in patients with severe sepsis after HSCT.     

Inverse relationships between coronary blood flow obstruction and platelet reactivity in stable angina pectoris

This study investigates relationships between platelet reactivity and coronary blood flow obstruction in stable angina pectoris. Consented were 36 patients with single-vessel disease. The subjects were divided into two groups. One group (n?=?14) had less severe (<?=?80%) and the second group (n?=?22) had severe coronary flow impairment (90%). Before elective coronary angiography platelet in vitro reactivity in venous whole blood was determined using a flow cytometry technique. A thrombin-receptor activating peptide (TRAP-6) (0.77 and 0.06?g/l) and ADP (8.5 and 1.7?µmol/l) were used to activate platelets. The number of fibrinogen positive cells (%) i.e., activated platelets after stimulation was employed as experimental parameter. Less severe flow obstruction was associated with more reactive platelets. When stimulating with 0.77?g/l TRAP-6 the number of activated platelets was 64?±?15 (SD)%. The corresponding value for the group with severe flow obstruction was 40?±?17(SD)%. The difference is significant (P?<?0.001). 0.06?g/l TRAP-6 yielded similar results (P?<?0.01). Also when using 8.5?µmol/l ADP to challenge platelets less severe flow obstruction was associated with enhanced reactivity (P?<?0.01). 1.7?µmol/l ADP generated comparable results (P?<?0.05). Thus, in stable angina pectoris coronary flow obstruction is inversely related to platelet reactivity.     

The integrin antagonist,cilengitide, is a weak inhibitor of αIIbβ3 mediated platelet activation and inhibits platelet adhesion under flow

The RGD cyclic pentapetide, cilengitide, is a selective inhibitor of αvβ3 and αvβ5 integrins and was developed for antiangiogenic therapy. Since cilengitide interacts with platelet αIIbβ3 and platelets express αv integrins, the effect of cilengitide on platelet pro-coagulative response and adhesion is of interest. Flow-based adhesion assays were performed to evaluate platelet adhesion and rolling on von Willebrand factor (vWf), on fibrinogen and on human umbilical vein endothelial cells (HUVECs). Flow cytometry was used to detect platelet activation (PAC1) and secretion (CD62P) by cilengitide and light transmission aggregometry was used to detect cilengitide-dependent platelet aggregation. Cilengitide inhibited platelet adhesion to fibrinogen at concentrations above 250?µM [which is the C_max in human studies] and adhesion to vWf and HUVECs at higher concentrations under physiologic flow conditions. Platelet aggregation was already impaired at cilengitide concentrations >10?µM. Activation of αIIbβ3 integrin was inhibited by 250?µM cilengitide, whereas platelet secretion was unaffected by cilengitide. No evidence of cilengitide-induced platelet activation was found at all tested concentrations (0.01–1500?µM). At higher concentrations, platelet activation was inhibited, predominantly due to αIIbβ3 inhibition.     

Reduced platelet activation and platelet aggregation in patients with alcoholic liver cirrhosis

Results from previous studies regarding platelet function in liver cirrhosis are discordant. The aim was to investigate platelet activation and platelet aggregation in patients with alcoholic liver cirrhosis. We included 27 patients with alcoholic liver cirrhosis and 22 healthy individuals. A recently established flow cytometric approach was used to measure platelet activation and platelet aggregation independent of sample platelet count. Platelet aggregation was further investigated using light transmission aggregometry (LTA) (for platelet count >100 × 10⁹/L). Platelet agonists were adenosine diphosphate, thrombin receptor-activating peptide, arachidonic acid, collagen, and collagen-related peptide. Patients had lower median platelet count than healthy individuals, 125 × 10⁹/L (interquartile range [IQR] 90?185) versus 240 × 10⁹ (IQR 204?285), p < 0.001. Platelet activation levels in stimulated samples were lower in patients versus healthy individuals, e.g., after collagen-related peptide stimulation, the median percentage of platelets positive for activated glycoprotein IIb/IIIa was 85% (IQR 70–94) in patients versus 97% (IQR 94–99) in healthy individuals, p < 0.001; lower platelet activation capacity being associated with low platelet count and Child–Pugh class B/C cirrhosis. Flow cytometric platelet aggregation was reduced in patients for collagen-related peptide and for adenosine diphosphate, e.g., platelet aggregation (mean ± standard deviation) was 57% ± 4 in patients versus 70% ± 1 in healthy individuals for collagen-related peptide, p = 0.01. Light LTA showed reduced collagen-induced platelet aggregation in some patients compared with healthy individuals. In conclusion, platelet function was reduced in some patients with alcoholic liver cirrhosis and the severity was associated with platelet count and severity of liver cirrhosis.     

The effects of continuous positive airway pressure therapy on mean platelet volume in patients with obstructive sleep apnea

Previous studies have reported increased platelet activation and aggregation in patients with obstructive sleep apnea (OSA). Continuous positive airway pressure (CPAP) treatment has been shown to decrease platelet activation. We aimed to study the effects of nasal CPAP therapy has on MPV values in patients with severe OSA. Thirty-one patients (21 men; mean age 53.8?±?9.2 years) with severe OSA (AHI?>?30 events/hour) constituted the study group. An age, gender and body mass index (BMI) matched control group was composed 25 subjects (14 men; mean age 49.6?±?8.5 years) without OSA (AHI?<?5 events/hour). We measured MPV values in patients with severe OSA and control subjects and we measured MPV values after 6 months of CPAP therapy in severe OS patients. The median (IQR) MPV values were significantly higher in patients with severe OSA than in control group (8.5 [8.3–9.1] vs. 8.3 [7.5–8.8] fL; p?=?0.03). The platelet counts were significantly lower in patients with severe OSA than in control group (217.8?±?45.9 vs. 265.4?±?64.0?×?10⁹/L; p?=?0.002). The six months of CPAP therapy caused significant reductions in median (IQR) MPV values in patients with severe OSA (8.5 [8.3–9.1] to 7.9 [7.4–8.2] fL; p?<?0.001). Six months of CPAP therapy caused significant increase in platelet counts when compared with baseline values (217.8?±?45.9 to 233.7?±?60.6?×?10⁹/L; p?<?0.001). We have found that the MPV values of patients with severe OSA were significantly higher than those of the control subjects and 6 months CPAP therapy caused significant reductions in the MPV values in patients with severe OSA.     

Use of activated protein C has no avail in the early phase of acute pancreatitis

Objectives. Sepsis and acute pancreatitis have similar pathogenetic mechanisms that have been implicated in the progression of multiple organ failure. Drotrecogin alfa, an analogue of endogenous protein C, reduces mortality in clinical sepsis. Our objective was to evaluate the early therapeutic effects of activated protein C (APC) in a rat model of acute necrotizing pancreatitis. Subjects and method. Acute necrotizing pancreatitis was induced by intraductal injection of 5% Na taurocholate. Hourly bolus injections of saline or recombinant human APC (drotrecogin alfa) was commenced via femoral venous catheter four hours after the induction of acute pancreatitis. The experiment was terminated nine hours after pancratitis induction. Animals in group one (n=20) had a sham operation while animals in group two (n=20) received saline and animals in group three (n=20) received drotrecogin alfa boluses after acute pancreatitis induction. Pancreatic tissue for histopathologic scores and myeloperoxidase, glutathione reductase, glutathione peroxidase, and catalase activites were collected, and blood for serum amylase, urea, creatinine, and inleukin-6 measurements was withdrawn. Results. Serum amylase activity was significantly lower in the APC treated group than the untreated group (17,435±432 U/L vs. 27,426±118 U/L, respectively). While the serum interleukin-6 concentration in the APC untreated group was significantly lower than the treated group (970±323 pg/mL vs. 330±368 pg/mL, respectively). Conclusion. In the early phase of acute pancreatitis, drotrecogin alfa treatment did not result in a significant improvement in oxidative and inflammatory parameters or renal functions.     

Extended evaluation of recombinant human activated protein C United States Trial (ENHANCE US): a single-arm, phase 3B, multicenter study of drotrecogin alfa (activated) in severe sepsis

STUDY OBJECTIVE: To gather additional 28-day all-cause mortality and safety data among adult patients with severe sepsis who were treated with drotrecogin alfa (activated). DESIGN: Prospective, single-arm, multicenter clinical trial. SETTING: Eighty-five study sites in the United States and two in Puerto Rico. PARTICIPANTS: Adult patients (273 patients) with a diagnosis of severe sepsis, which was defined as a systemic inflammatory response due to acute infection and one or more sepsis-induced organ dysfunctions present for 相似文献   

Platelets and acute cerebral infarction

Stroke is worldwide a leading cause of death and disability. Its etiology is regarded as heterogeneous. Platelets are implicated in its pathophysiology, but our understanding of their specific role is incomplete. Only sparse and conflicting information exists about platelet reactivity and activity in acute stroke. Some scientists take the view that platelets activate in conjunction with acute cerebral infarctions. Others put forward evidence corroborating the contrary notion. Increased soluble P-selectin as a sign of platelet and/or endothelial activity seems to be a feature of the disease. The latter point of view is opposed by other researchers. Due to these conflicting opinions, this study is devoted to platelet characteristics in acute cerebral infarctions. We studied subjects (n?=?72; age 74?±?10(SD) years; 31 females) having acute stroke. As controls served atrial fibrillation (AF) patients (n?=?58; age 69?±?7(SD) years; 12 females) subject to electrical cardioversion, a flow cytometer was put to use for measuring platelet reactivity and activity. After agonist provocation, both platelet bound P-selectin and fibrinogen were employed as estimates of platelet reactivity. Dilutions of a thrombin-receptor-activating peptide (TRAP-6) (74 and 57?µmol/l) (P-selectin and fibrinogen) and ADP (8.5 and 1.7?µmol/l) (fibrinogen only) were put to use as platelet agonists. Membrane-bound P-selectin without agonist stimulation served as a measure of in vivo platelet activation. Soluble P-selectin, as determined from a commercial ELISA, was used to assess platelet and/or endothelial activity. In acute stroke neither platelet-bound P-selectin nor fibrinogen after stimulation, i.e. reactivity, differed from AF controls. In contrast, lower platelet activity as judged from surface attached and circulating P-selectin without agonist stimulation proved to be a feature of cerebral infarctions. The p-values were p?<?0.001 and p?<?0.01, respectively. It is concluded that acute stroke is not associated with platelet reactivity platelets circulate less activated during the disease. It is evident that the mechanisms reflecting platelet reactivity and activity being investigated in this study play minor roles in stroke pathophysiology. New powerful platelet inhibitory drugs are currently introduced. To avoid major bleeding studies on platelet, behavior in acute stroke are necessary before including these medications in stroke treatment protocols.     

Engineering the proteolytic specificity of activated protein C improves its pharmacological properties

Human activated protein C (APC) is an antithrombotic, antiinflammatory serine protease that plays a central role in vascular homeostasis, and activated recombinant protein C, drotrecogin alfa (activated), has been shown to reduce mortality in patients with severe sepsis. Similar to other serine proteases, functional APC levels are regulated by the serine protease inhibitor family of proteins including alpha(1)-antitrypsin and protein C inhibitor. Using APC-substrate modeling, we designed and produced a number of derivatives with the goal of altering the proteolytic specificity of APC such that the variants exhibited resistance to inactivation by protein C inhibitor and alpha(1)-antitrypsin yet maintained their primary anticoagulant activity. Substitutions at Leu-194 were of particular interest, because they exhibited 4- to 6-fold reductions in the rate of inactivation in human plasma and substantially increased pharmacokinetic profiles compared with wild-type APC. This was achieved with minimal impairment of the anticoagulant/antithrombotic activity of APC. These data demonstrate the ability to selectively modulate substrate specificity and subsequently affect in vivo performance and suggest therapeutic opportunities for the use of protein C derivatives in disease states with elevated serine protease inhibitor levels.     

Anticoagulant factor concentrates in disseminated intravascular coagulation: rationale for use and clinical experience.

Natural inhibitors of coagulation, in other words, antithrombin (AT), the protein C system, and tissue factor pathway inhibitor (TFPI), play an important role in controlling the activation of coagulation during disseminated intravascular coagulation (DIC). Furthermore, they may not only influence coagulation but also attenuate inflammatory responses during sepsis. Low circulating levels of AT and protein C have been associated with poor outcome. Replacement therapy with AT, activated protein C (APC), and TFPI has been shown to attenuate thrombin generation and to reduce mortality in experimental sepsis models. Experience with AT and APC in patients is promising. Data from large phase III trials of AT and APC as treatment of patients with severe sepsis will soon be available. Recombinant TFPI is currently in phase II clinical trials for severe sepsis.     

Platelet and mean platelet volume kinetics in adult patients with sepsis

Abstract

The aims of this study were to evaluate the kinetics of platelet counts and mean platelet volume (MPV) in adults with sepsis and to determine whether the responses are infection-specific. This retrospective cohort study included patients admitted to a tertiary-care teaching hospital with microbiologically proven nosocomial sepsis between January 2006 and January 2011. Platelet counts and MPV measurements were examined daily for 5 days after the onset of sepsis. During the study period, 151 of the 214 sepsis episodes were associated with thrombocytopenia. Gram-positive microorganisms were the most frequently isolated. The decrease in platelet counts was statistically significant for the first 3 days of sepsis in Gram-positive septic patients, for 4 days in Gram-negative septic patients and for all 5 days in fungal septic patients (p?<?0.001). The increase in MPV values was statistically significant for the first 3 days of sepsis in Gram-positive septic patients and for all 5 days in the other groups (p?<?0.001). We conclude that fungal sepsis has a stronger association with thrombocytopenia and increased MPV.     

Increased platelet activation in subjects chronically exposed to cadmium: A pilot study

Cadmium exposure has been reported to be associated with the risk of vascular disorders. Here, we investigated platelet activity in subjects with chronic cadmium exposure. Eighteen and 15 women participated in this study as chronically cadmium-exposed and control non-exposed subjects, respectively. Plasma P-selectin and CD40 ligand (CD40L), soluble markers of platelet activation, were measured. Platelet aggregation in whole blood, P-selectin and activated glycoprotein (aGP) IIb/IIIa expression on platelets and platelet–leukocyte aggregates were determined. The levels of plasma P-selectin and CD40L increased in subjects with chronic cadmium exposure compared with control subjects. Platelet aggregation induced by adenosine diphosphate (ADP) was higher in cadmium-exposed subjects than control subjects. Cadmium-exposed subjects had higher baseline and ADP-induced aGPIIb/IIIa expression on platelets than control subjects. Platelet–neutrophil aggregates also increased in cadmium-exposed subjects. Blood cadmium correlated with ADP-induced aggregation, aGPIIb/IIIa expression and platelet–neutrophil aggregates, while urinary cadmium correlated with soluble P-selectin. However, cadmium only at high concentration (15?µM) could potentiate ADP-induced platelet activation in vitro. In conclusion, our pilot data show that cadmium-exposed subjects have increased baseline platelet activation and reactivity.     

Comparison of cytotoxic and anti-platelet activities of polyphenolic extracts from Arnica montana flowers and Juglans regia husks

Polyphenolic compounds of plant origin are well known to be beneficial to human health: they exert protective effects on haemostasis and have a particular influence on blood platelets. However, the anti-platelet properties of polyphenolic compounds observed so far have not been weighed against their potential cytotoxic action against platelets. The aim of this study was to demonstrate that anti-platelet and cytotoxic effects on blood platelets may interfere and therefore, may often lead to confusion when evaluating the properties of plant extracts or other agents towards blood platelets. The anti-platelet and cytotoxic in vitro effects of plant extracts obtained from the husks of walnuts (J. regia) and flowers of arnica (A. montana) on platelet reactivity and viability were examined. Platelet function was assessed using standard methods (flow cytometry: P-selectin expression, activation of GPIIbIIIa complex, vasodilator-stimulated phosphoprotein, VASP index; turbidimetric and impedance aggregometry) and newly set assays (flow cytometric monitoring of platelet cytotoxicity). The results reveal that none of the studied plant extracts demonstrated cytotoxicity towards blood platelets. The phenolic acid-rich extract of A. montana (7.5 and 15?µg/ml) significantly reduced the ADP-induced aggregation in both whole blood and PRP, and decreased the platelet reactivity index (PRI; VASP phosphorylation) in whole blood, while showing excellent antioxidant capacity. The extract of J. regia husks significantly reduced ADP-induced platelet aggregation in whole blood when applied at 7.5?µg/ml, and only slightly decreased the PRI at 15?µg/ml. Both examined extracts suppressed platelet hyper-reactivity, and such influence did not interfere with cytotoxic effects of the extracts. Thus, its high polyphenol content, excellent antioxidant capacity and distinct anti-platelet properties, in combination with its lack of toxicity, make the extract of A. montana flowers a possible candidate as an anti-platelet agent or a compounding diet supplement.     

Drotrecogin alfa (activated) for the treatment of severe sepsis and septic shock

Coagulopathy and systemic inflammation are almost universal in patients with severe sepsis. Interaction between the two results in an intense inflammatory response and microthrombi formation in the vessels of multiple organs, resulting in organ dysfunction or severe sepsis. Recombinant human activated protein C, also known as drotrecogin alfa (activated), possesses anti-inflammatory, antithrombotic, and profibrinolytic properties. Treatment with drotrecogin alfa (activated) significantly reduces morbidity and mortality in patients with severe sepsis. An increased risk of bleeding during the infusion was the only side effect experienced. Recent data demonstrate that early administration of drotrecogin alfa (activated) is associated with lower mortality rates. Despite concern over its relatively high cost, analysis has demonstrated that recombinant human activated protein C is as cost-effective as other commonly used treatments in the intensive care unit.     

Nephropathy in Type 1 diabetes is associated with increased circulating activated platelets and platelet hyperreactivity

Patients with diabetes mellitus (DM) have increased platelet activation compared to non-diabetic controls. Platelet hyperreactivity has been associated with adverse cardiovascular outcomes in Type 2 DM, and with diabetic nephropathy. We investigated the relationship between platelet activation and nephropathy in Type 1 DM. Patients with Type 1 DM and diabetic nephropathy (n = 35), age- and sex-matched Type 1 DM patients with persistent normoalbuminuria (n = 51), and healthy age- and sex-matched controls (n = 30) were studied. Platelet surface P-selectin, platelet surface activated GPIIb/IIIa, monocyte-platelet aggregates (MPAs) and neutrophil-platelet aggregates (NPAs) were measured by whole blood flow cytometry as markers of platelet activation. Platelet reactivity was assessed in response to exogenously added ADP and thrombin receptor activating peptide (TRAP). Platelet surface P-selectin (basal and in response to 0.5 or 20 µM ADP) was higher in nephropathy patients compared with normoalbuminuric patients (P = 0.027), and non-diabetic controls (P = 0.0057). NPAs were higher in nephropathy patients compared to normoalbuminuric patients (P = 0.0088). MPAs were higher in nephropathy patients compared to non-diabetic controls (P = 0.0075). There were no differences between groups in activated GPIIb/IIIa or in response to TRAP at any end-point. More patients with nephropathy received aspirin (71.4%) compared to normoalbuminuric patients (27.4%) (P < 0.0001). Type 1 diabetic nephropathy, as compared with normoalbuminuria, is associated with circulating activated platelets and platelet hyperreactivity to ADP, despite the confounding variable of more nephropathy patients receiving aspirin. This platelet activation is likely to contribute to the known increased risk of cardiovascular events in patients with diabetic nephropathy.     

Inhibitory effects of staphylococcal enterotoxin type B on human platelet adhesion in vitro

Septic shock was formerly recognized as a consequence of Gram-negative bacteraemia, but at present the incidence of Gram-positive sepsis seems to be more relevant, contributing for more than 50% of cases. Staphylococcal aureus can induce toxic shock in humans through the production of potent toxins termed Staphylococcal enterotoxins, from which Staphylococcal enterotoxin type B (SEB) is one of most studied. Platelets are reported to participate in pathogenesis of severe sepsis, but the exact role of platelets in this event is poorly investigated, particularly that caused by Gram-positive bacteria. Therefore, we have used the model of platelet adhesion to fibrinogen-coated plates to investigate the actions of SEB on human platelets. Ninety-six-well microtiter plates were coated with human fibrinogen (50 µg/mL), and human washed platelet suspension (6 × 10⁶ platelets) was added to each well. Adherent platelets were quantified through measurement of acid phosphatase activity. Staphylococcal enterotoxin B (0.0001–30 µg/mL, incubated for 5 to 60 min) time- and dose-dependently inhibited platelet adhesion. This response was modified neither by the protein synthesis inhibitor puromycin (0.01 and 0.1 mM) nor by the superoxide scavengers superoxide dismutase (SOD, 100 units/mL) and polyethylene glycol-SOD (30 U/mL). The peroxide hydrogen (H₂O₂) scavenger catalase polyethylene glycol (1000 U/mL) significantly attenuated the platelet adhesion inhibition by SEB. The cAMP and cGMP levels were not changed by SEB (0.0001–30 µg/mL, 60 min). Our findings suggest that H₂O₂ at least partly contributes to the inhibitory responses of human platelet adhesion by SEB.     

Upregulation of CD40/CD40L system in rheumatic mitral stenosis with or without atrial fibrillation

Thrombelastography (TEG) analyses the status of blood coagulation including abnormalities associated with low platelet count. The aim of this study was to investigate the changes in TEG parameters in idiopathic thrombocytopenic purpura (ITP) patients. Thirty nine patients with ITP (platelet count?<?100?×?103 µl^?1) were included in the study. Age-matched 17 patients with thrombocytopenia due to chemotherapy were selected as a control group. Platelet count was positively correlated with maximum clot formation (MCF) in INTEM (r?=?0.716, p?<?0.001) and MCF in EXTEM (r?=?0.679, p?<?0.001); negatively correlated with clot formation time (CFT) in INTEM (r?=??0.755, p?<?0.001) and CFT in EXTEM (r?=??0.585, p?<?0.001) in ITP patients. Platelet count was positively correlated with MCF in INTEM (r?=?0.776, p?<?0.001) and MCF in EXTEM (r?=?0.878, p?<?0.001); negatively correlated with CFT in INTEM (r?=??0.627, p?<?0.001) in control group. Receiver operating characteristic curves to describe the critical platelet count and fibrinogen level that affect MCF revealed 31?×?103?µl^?1 and 375 mg?dl^?1 as cut-off values, respectively. In conclusion, ROTEM determines the contribution of fibrinogen and platelets to clot strength in patients with ITP. MCF appears to be the most important TEG parameter in predicting bleeding in ITP patients that makes TEG superior to other hemostatic tests.