Platelet accumulation induced by bacterial endotoxin in rats

Disseminated Intravascular Coagulation (DIC): Old player creates new perspectives on the polymicrobial sepsis model of CASP

BACKGROUND

Disseminated Intravascular Coagulation (DIC) is a life-threatening complication of sepsis. In surgical ICUs, DIC is frequently caused by abdominal sepsis, and the disarranged coagulation and complications often lead to death. The severity of sepsis is associated with a higher DIC score according to the parameters proposed by the International Society of Hemostasis and Thrombosis (ISTH) in 2001: platelet count, bleeding time (Quick), D-dimer, and fibrinogen. One problem in studying DIC is finding an adequate animal model that reflects the clinical situation of polymicrobial overwhelming infection.

AIMS AND METHODS

We investigated whether a well-established polymicrobial sepsis model of colon ascendens stent peritonitis (CASP) is suited to investigate the complexity of DIC. For this purpose, CASP-operated mice were examined 20 h after the operation with regard to coagulation parameters using cell counts, bleeding times, rotational thromboelastometry (ROTEM), ELISAs for D-dimer and fibrinogen, and platelet accumulation in affected organs via immunohistochemistry to see if the mice develop a coagulation disorder that meets the definition of DIC proposed by the ISTH 2001 consensus conference.

RESULTS

Herein, we showed that the CASP model is an all-encompassing animal model to analyze the complexity of systemic DIC in murine abdominal sepsis. There is highly reproducible thrombocytopenia, a significant prolongation of the bleeding time, and a loss of fibrinogen in plasma. We also observed microvascular thrombosis due to platelet accumulation in the microcirculation of the liver.

CONCLUSION

The CASP model seems superior to other artificial models, e.g., injecting substances, for inducing DIC. CASP is one of the best true-to-life models for analyzing the complexity of disseminated intravascular coagulation in polymicrobial sepsis.

Thrombo-Inflammation: A Focus on NTPDase1/CD39

There is increasing evidence for a link between inflammation and thrombosis. Following tissue injury, vascular endothelium becomes activated, losing its antithrombotic properties whereas inflammatory mediators build up a prothrombotic environment. Platelets are the first elements to be activated following endothelial damage; they participate in physiological haemostasis, but also in inflammatory and thrombotic events occurring in an injured tissue. While physiological haemostasis develops rapidly to prevent excessive blood loss in the endothelium activated by inflammation, hypoxia or by altered blood flow, thrombosis develops slowly. Activated platelets release the content of their granules, including ATP and ADP released from their dense granules. Ectonucleoside triphosphate diphosphohydrolase-1 (NTPDase1)/CD39 dephosphorylates ATP to ADP and to AMP, which in turn, is hydrolysed to adenosine by ecto-5'-nucleotidase (CD73). NTPDase1/CD39 has emerged has an important molecule in the vasculature and on platelet surfaces; it limits thrombotic events and contributes to maintain the antithrombotic properties of endothelium. The aim of the present review is to provide an overview of platelets as cellular elements interfacing haemostasis and inflammation, with a particular focus on the emerging role of NTPDase1/CD39 in controlling both processes.

Radiolabelling and immunohistochemistry reveal platelet recruitment into lungs and platelet migration into airspaces following LPS inhalation in mice

INTRODUCTION

Platelets are under investigation for their role in host defence and inflammatory lung diseases and have been demonstrated to be recruited to the lung. However, the mechanisms and consequences of platelet recruitment into lungs are poorly understood. We have utilised a murine model to investigate the mechanisms of platelet involvement in lung inflammation induced by intranasal administration of LPS.

OBJECTIVES

Our aim was to characterise lung platelet recruitment following LPS inhalation in mice using immunohistochemistry, and non-invasive and invasive radiolabelled platelet tracking techniques.

RESULTS

Intranasal administration of LPS caused an increase in lung platelet staining in lung tissue and elicited the recruitment of radiolabelled platelets into the lung. Prior to these responses in the lung, we observed an earlier decrease in blood platelet counts, temporally associated with platelet recruitment to the liver and spleen. Non-invasive measurements of thoracic radioactivity reflected changes in blood counts rather than extravascular lung platelet recruitment. However, both in situ counting of radiolabelled platelets and immunostaining for platelet surface markers showed LPS-induced increases in extravascular platelets into lung airspaces suggesting that some of the platelets recruited to the lung enter air spaces.

CONCLUSIONS

Intranasal administration of LPS activates the innate immune response which includes a fall in peripheral blood platelet counts with subsequent platelet recruitment to the lung, spleen and liver, measured by immunohistochemistry and radiolabelling techniques.

Platelet Depletion Impairs Host Defense to Pulmonary Infection with Pseudomonas aeruginosa in Mice

Platelets have been implicated in pulmonary inflammatory cell recruitment after exposure to allergic and nonallergic stimuli, but little is known about the role of platelets in response to pulmonary infection with Pseudomonas aeruginosa. In this study, we have investigated the impact of the experimental depletion of circulating platelets on a range of inflammatory and bacterial parameters, and their subsequent impact on mortality in a murine model of pulmonary infection with P. aeruginosa. P. aeruginosa infection in mice induced a mild, but significant, state of peripheral thrombocytopenia in addition to pulmonary platelet accumulation. Increased platelet activation was detected in infected mice through increased levels of the platelet-derived mediators, platelet factor-4 and β-thromboglobulin, in BAL fluid and blood plasma. In mice depleted of circulating platelets, pulmonary neutrophil recruitment was significantly reduced 24 hours after infection, whereas the incidence of systemic dissemination of bacteria was significantly increased compared with non-platelet-depleted control mice. Furthermore, mortality rates were increased in bacterial-infected mice depleted of circulating platelets. This work demonstrates a role for platelets in the host response toward a gram-negative bacterial respiratory infection.

The pathophysiology of thrombocytopenia in chronic liver disease

Thrombocytopenia is the most common hematological abnormality encountered in patients with chronic liver disease (CLD). In addition to being an indicator of advanced disease and poor prognosis, it frequently prevents crucial interventions. Historically, thrombocytopenia has been attributed to hypersplenism, which is the increased pooling of platelets in a spleen enlarged by congestive splenomegaly secondary to portal hypertension. Over the past decade, however, there have been significant advances in the understanding of thrombopoiesis, which, in turn, has led to an improved understanding of thrombocytopenia in cirrhosis. Multiple factors contribute to the development of thrombocytopenia and these can broadly be divided into those that cause decreased production, splenic sequestration, and increased destruction. Depressed thrombopoietin levels in CLD, together with direct bone marrow suppression, result in a reduced rate of platelet production. Thrombopoietin regulates both platelet production and maturation and is impaired in CLD. Bone marrow suppression can be caused by viruses, alcohol, iron overload, and medications. Splenic sequestration results from hypersplenism. The increased rate of platelet destruction in cirrhosis also occurs through a number of pathways: increased shear stress, increased fibrinolysis, bacterial translocation, and infection result in an increased rate of platelet aggregation, while autoimmune disease and raised titers of antiplatelet immunoglobulin result in the immunologic destruction of platelets. An in-depth understanding of the complex pathophysiology of the thrombocytopenia of CLD is crucial when considering treatment strategies. This review outlines the recent advances in our understanding of thrombocytopenia in cirrhosis and CLD.

Accumulation of platelets in the liver may be an important contributory factor to thrombocytopenia and liver fibrosis in chronic hepatitis C

BACKGROUND

Thrombocytopenia is a marked feature of chronic liver disease and cirrhosis. We tried to clarify whether an accumulation of platelets in the liver contributes to thrombocytopenia and liver fibrosis in chronic liver disease.

METHODS

Thirty-eight patients who underwent hepatectomy for hepatocellular carcinoma (HCC) with hepatitis C virus infection were included. The locations of platelets and Kupffer cells and the expression of platelet-derived growth factor (PDGF) receptor-β and smooth muscle actin (SMA) were identified by immunohistochemistry. Perisinusoidal mesenchymal cells that express PDGF receptor-β and SMA were interpreted as transformed hepatic stellate cells (HSCs).

RESULTS

Patients with cirrhosis had a more extensive platelet area in the liver compared to controls (5601 ± 5611 vs. 564 ± 361 μm(2), p = 0.02), although the blood platelet count significantly decreased along with the progression of liver fibrosis. In cirrhotic liver, most platelets were present in the sinusoidal space of the periportal area with inflammation, where HSCs expressing PDGF receptor-β were frequently observed. In addition, the platelet and Kupffer cell areas were significantly smaller in cancerous tissue than those in noncancerous tissues (platelet area: 492 ± 823 vs. 3643 ± 4055 μm(2), p = 0.001; Kupffer cell area: 450 ± 841 vs. 3012 ± 3051 μm(2), p = 0.001).

CONCLUSIONS

The accumulation of platelets in the liver with chronic hepatitis may be involved in thrombocytopenia and liver fibrosis through the activation of HSCs. In addition, our findings also indicate that both platelets and Kupffer cells decrease in HCC tissues.

Viscoelastic and aggregometric point-of-care testing in patients with septic shock - cross-links between inflammation and haemostasis

BACKGROUND

In the pathogenesis of sepsis, inflammation-induced changes in coagulation play a pivotal role.

METHODS

In total, 90 patients (30 patients with septic shock, 30 surgical patients following major abdominal surgery and 30 healthy volunteers) were enrolled. Blood samples from patients with septic shock were collected at the time of sepsis diagnosis as well as 24 h, 4 days, 7 days, 14 days and 28 days later. Samples from surgical patients with a post-surgical inflammatory response were collected three times (before surgery, immediately after surgery and 24 h after surgery) and once from healthy volunteers. Thromboelastometry (ROTEM (®) ), as well as whole blood impedance aggregometry (Multiplate(®) ) were performed. Additionally, plasma concentrations of interleukin-6 and tumour necrosis factor-alpha were measured using enzyme-linked immunosorbent assay kits.

RESULTS

Thromboelastometry lysis index was shown to be a reliable biomarker for septic shock. Furthermore, in septic patients with overt disseminated intravascular coagulation, thromboelastometry revealed signs indicating a hypocoagulable status, whereas patients without overt disseminated intravascular coagulation were found to be hypercoagulable. Platelet aggregation capability, as assessed by whole blood impedance aggregometry, was significantly reduced in septic patients with overt disseminated intravascular coagulation, whereas it was comparable with healthy volunteers and in septic patients without overt disseminated intravascular coagulation.

CONCLUSION

Viscoelastic and aggregometric point-of-care testing was shown to be potentially useful for bedside diagnosis of sepsis. Moreover, viscoelastic and aggregometric point-of-care testing was able to determine the phase of septic coagulopathy (hypercoagulability vs. hypocoagulability) and therefore identified patients at high risk for overt disseminated intravascular coagulation.

Rifaximin improves thrombocytopenia in patients with alcoholic cirrhosis in association with reduction of endotoxaemia

BACKGROUND

Thrombocytopenia is a major haematological disorder of cirrhosis with unclear pathogenesis. Endotoxaemia resulting from intestinal bacterial overgrowth could reduce platelet counts directly or through cytokine release.

AIMS

To correlate endotoxaemia with platelet counts and study the effects of intestinal decontamination with rifaximin on thrombocytopenia in relation to changes in endotoxin and cytokine concentrations in patients with alcoholic cirrhosis.

METHODS

Platelet counts, plasma endotoxin levels and serum interleukin-1 (IL-1), interleukin-6 (IL-6) and tumour necrosis factor-α (TNF-α) levels were measured in 23 thrombocytopenic cirrhotic patients (platelet count<150 000/μl) before and after 4-week treatment with rifaximin 1200 mg/d (n = 13) or no treatment (n = 10) and at baseline in 10 cirrhotic patients without thrombocytopenia; spleen size was measured at baseline in all patients.

RESULTS

Endotoxin and IL-6 levels were significantly higher in patients with thrombocytopenia than in those without thrombocytopenia (2.76 ± 0.69 vs. 0.64 ± 0.09 EU/ml; P < 0.001 and 24.26 ± 3.38 vs. 2.66 ± 0.74 pg/ml; P = 0.001 respectively). Platelet counts were inversely correlated with endotoxin levels (r = -0.589; P = 0.003), Child-Pugh score (r = -0.625; P = 0.001), IL-6 levels (r = -0.464; P = 0.02) and spleen size (r = -0.455; P = 0.02) in patients with thrombocytopenia. Following rifaximin, platelet counts increased significantly (83 100 ± 9700 vs. 99 600 ± 11 200/μl; P = 0.006) in line with significant reductions in endotoxin (1.28 ± 0.41 vs. 2.54 ± 0.86 EU/ml; P = 0.005), IL-1 (3.1 ± 0.5 vs. 4.4 ± 1.2 pg/ml; P = 0.04), IL-6 (12.8 ± 2.5 vs. 21.1 ± 4.2 pg/ml; P = 0.01) and TNF-α (3.6 ± 1.3 vs. 5.8 ± 1.7; P = 0.02) levels. Platelet count changes were correlated with the changes in endotoxin (r = 0.573; P = 0.04), TNF-α (r = 0.554; P = 0.05) and IL-6 (r = 0.495; P = 0.07) levels.

CONCLUSIONS

Rifaximin improves cirrhosis-related thrombocytopenia and this could be related with the reduction of endotoxaemia.

Shiga toxin pathogenesis: kidney complications and renal failure

The kidneys are the major organs affected in diarrhea-associated hemolytic uremic syndrome (D(+)HUS). The pathophysiology of renal disease in D(+)HUS is largely the result of the interaction between bacterial virulence factors such as Shiga toxin and lipopolysaccharide and host cells in the kidney and in the blood circulation. This chapter describes in detail the current knowledge of how these bacterial toxins may lead to kidney disease and renal failure. The toxin receptors expressed by specific blood and resident renal cell types are also discussed as are the actions of the toxins on these cells.

Patients with liver cirrhosis suffer from primary haemostatic defects? Fact or fiction?

Patients with cirrhosis can have abnormalities in laboratory tests reflecting changes in primary haemostasis, including bleeding time, platelet function tests, markers of platelet activation, and platelet count. Such changes have been considered particularly relevant in the bleeding complications that occur in cirrhosis. However, several studies have shown that routine diagnostic tests, such as platelet count, bleeding time, PFA-100, thromboelastography are not clinically useful to stratify bleeding risk in patients with cirrhosis. Moreover, treatments used to increase platelet count or to modulate platelet function could potentially do harm. Consequently the optimal management of bleeding complications is still a matter of discussion. Moreover, in the last two decades there has been an increased recognition that not only bleeding but also thrombosis complicates the clinical course of cirrhosis. Thus, we performed a literature search looking at publications studying both qualitative and quantitative aspects of platelet function to verify which primary haemostasis defects occur in cirrhosis. In addition, we evaluated the contribution of qualitative and quantitative aspects of platelet function to the clinical outcome in cirrhosis and their therapeutic management according to the data available in the literature. From the detailed analysis of the literature, it appears clear that primary haemostasis may not be defective in cirrhosis, and a low platelet count should not necessarily be considered as an automatic index of an increased risk of bleeding. Conversely, caution should be observed in patients with severe thrombocytopenia where its correction is advised if bleeding occurs and before invasive diagnostic and therapeutic procedures.

Scintigraphic evaluation of intrapulmonary shunt in normoxemic cirrhotic patients and effects of terlipressin

AIM

  The magnitude of intrapulmonary shunt (IPS) in cirrhotic patients without hypoxemia remains undefined. We evaluated the severity and clinical correlations of IPS in normoxemic cirrhotics, and possible IPS alterations after terlipressin treatment.

METHODS

  Fifteen patients with alcoholic cirrhosis without hypoxemia were studied at baseline and after the administration of 2 mg of terlipressin. The IPS fraction was evaluated by lung perfusion scan after the i.v. injection of technetium-99m-labeled macroaggregated albumin ((99m) Tc-MAA) and calculation of brain uptake (positive value ≥6%). Cardiac output (CO), pulmonary artery systolic pressure (PASP) and pulmonary vascular resistance (PVR) were evaluated by Doppler echocardiography. Mean arterial pressure (MAP) was measured and the ratio MAP/CO was calculated as an index of systemic vascular resistance (SVR). Portal vein velocity (PVV) and portal venous flow (PVF) were also assessed by Doppler ultrasonography.

RESULTS

  Three patients (20%) had an IPS fraction of more than 6%. A significant inverse correlation with platelet count (P = 0.001) and a direct correlation with Child-Pugh score (P = 0.06), PVV (P = 0.07) and PVF (P = 0.07) were noted. IPS fractions decreased significantly after terlipressin administration (P = 0.00001); the IPS fraction fell below 6% in all three patients with positive baseline values. Terlipressin treatment induced a significant decrease in CO (P = 0.003) and significant increases in MAP (P = 0.0003), SVR (P = 0.0003), SPAP (P = 0.001) and PVR (P = 0.01).

CONCLUSION

  IPS fractions detected by (99m) Tc-MAA lung scan were inversely correlated with platelet count and directly with liver disease severity, and found abnormal in 20% of normoxemic cirrhotic patients. Terlipressin reduced significantly the magnitude of the shunt.

Endotoxaemia in the pathogenesis of cytopenias in liver cirrhosis. Could oral antibiotics raise blood counts?

Cytopenias are frequently observed in patients with cirrhosis and are associated with increased morbidity. In particular, thrombocytopenia can impact routine care of patients with cirrhosis by potentially postponing or interfering with diagnostic and therapeutic procedures including liver biopsy and medically indicated or elective surgery. The pathogenesis of cytopenias in cirrhosis remains largely unknown. Historically, the concept of hypersplenism has long been associated with the cirrhosis-related hematological disorders but was never proven. On the other hand, intestinal bacterial overgrowth and altered gut permeability in cirrhotic patients lead to increased translocation of bacteria and endotoxin into the portal circulation. The impaired phagocytic function of the reticuloendothelial system together with the portosystemic shunting allow endotoxin to reach the systemic circulation and high concentrations of circulating endotoxin are found in cirrhotic patients even with no clinical evidence of infection and correlate with the severity of liver disease. Endotoxin activates monocytes and promotes the release of proinflammatory cytokines. Indeed, serum levels of interleukin-1, interleukin-6, tumor necrosis factor-α, and interferon-γ are elevated in patients with cirrhosis in proportion to the severity of liver disease. Endotoxaemia stimulates the vascular production of nitric oxide (NO) directly or indirectly via the cytokine cascade, and correlates with serum NO metabolite levels in cirrhosis. Several lines of evidence strongly suggest that endotoxaemia may reduce peripheral blood counts either directly or through the release of cytokines and NO. Previous studies in experimental models of cirrhosis and cirrhotic patients have demonstrated that long-term administration of oral antibiotics such as trimethoprim-sulfamethoxazole, norfloxacin, and rifaximin can reduce bacterial translocation and circulating levels of endotoxin, TNF-α, IL-6, and NO. We hypothesize that endotoxaemia plays a pivotal role in the pathogenesis of cytopenias in cirrhosis and that intestinal decontamination could raise peripheral blood counts by the suppression of endotoxaemia and the inhibition of cytokine and NO production.

Platelet aggregation in children with Helicobacter pylori infection

This study was performed to investigate the platelet aggregation alterations in platelet-rich plasma (PRP) samples of children with Helicobacter pylori (H pylori) infection. Platelet aggregation induced by adenosine diphosphate (ADP), collagen, ristocetin, or epinephrine was studied with photometric aggregometry in 30 patients before and after eradication therapy and in a control group including 15 children. The pretreatment mean maximum aggregation values and slope were significantly lower (P < .0001) in the study group at 10 μmol/L concentrations of ADP (ADP-like defect). The maximum aggregation values and slope revealed no significant differences (P > 0.05) between the study group after therapy and the control group. We concluded that H pylori infection may cause dysfunction of platelets in children and can be reversed by H pylori eradication therapy. Further studies should be carried out to determine the mechanisms of platelet dysfunction in children with H pylori infection.

Plasma and platelet serotonin levels in patients with liver cirrhosis

AIM: To analyze the relationship between plasma and platelet serotonin levels and the degree of liver insufficiency.

METHODS: The prospective study included 30 patients with liver cirrhosis and 30 healthy controls. The degree of liver failure was assessed according to the Child-Pugh classification. Platelet and platelet poor plasma serotonin levels were determined.

RESULTS: The mean plasma serotonin level was higher in liver cirrhosis patients than in healthy subjects (215.0 ± 26.1 vs 63.1 ± 18.1 nmol/L; P < 0.0001). The mean platelet serotonin content was not significantly different in patients with liver cirrhosis compared with healthy individuals (4.8 ± 0.6; 4.2 ± 0.3 nmol/platelet; P > 0.05). Plasma serotonin levels were significantly higher in Child-Pugh grade A/B than in grade C patients (246.8 ± 35.0 vs 132.3 ± 30.7 nmol/L; P < 0.05). However, platelet serotonin content was not significantly different between Child-Pugh grade C and grade A/B (4.6 ± 0.7 vs 5.2 ± 0.8 nmol/platelet; P > 0.05).

CONCLUSION: Plasma serotonin levels are significantly higher in patients with cirrhosis than in the controls and represent the degree of liver insufficiency. In addition, platelet poor plasma serotonin estimation is a better marker for liver insufficiency than platelet serotonin content.

Increased platelet aggregation in vivo in the Zucker Diabetic Fatty rat: differences from the streptozotocin diabetic rat

BACKGROUND AND PURPOSE

Diabetes mellitus, especially type 2, is associated with increased arterial thrombosis. Our aims were (i) to characterize and compare platelet aggregation in vivo and in vitro in a type 2 diabetes model; and (ii) to determine whether these results differ from those in a type 1 diabetes model.

EXPERIMENTAL APPROACH

Platelet aggregation to ADP in lean or obese Zucker Diabetic Fatty (ZDF) rats and in streptozotocin (STZ)-treated or control Wistar rats was measured in vitro, using Born aggregometry, and in vivo, by (111)Indium-labelled pulmonary platelet accumulation.

KEY RESULTS

In vivo, ADP responses were higher in obese (type 2 model) than lean ZDF rats. However, in vitro, ADP aggregation did not differ between platelet-rich plasma from ZDF lean or obese rats; nor was any difference seen in ADP responses when platelets from either lean or obese ZDF rats were suspended in plasma from obese or lean ZDF rats, respectively. In vivo, ADP responses were similar in STZ treated (type 1 model) and control rats whereas, in vitro, isolated platelets from STZ diabetic rats were more responsive to ADP aggregation than controls. Platelets from control or STZ-treated rats suspended in plasma from STZ-treated rats exhibited reduced ADP aggregation, compared to when suspended in plasma from control rats.

CONCLUSIONS AND IMPLICATIONS

The platelet aggregation results obtained in vitro do not reflect those in vivo, therefore in vitro aggregation data should be interpreted with caution. Moreover, both in vitro and in vivo, different diabetic models exhibit important differences in platelet responsiveness.

Lipopolysaccharide from enterohemorrhagic Escherichia coli binds to platelets through TLR4 and CD62 and is detected on circulating platelets in patients with hemolytic uremic syndrome

This study presents evidence that human platelets bind lipopolysaccharide (LPS) from enterohemorrhagic Escherichia coli (EHEC) through a complex of toll-like receptor 4 (TLR4) and CD62, leading to their activation. TLR4 colocalized with CD62 on the platelet membrane, and the TLR4 specificity of LPS binding to platelets was confirmed using C57BL/10ScN mice lacking Tlr4. Only platelets from TLR4 wild-type mice bound O157LPS in vitro. After in vivo injection, O157LPS bound to platelets from wild-type mice, which had lower platelet counts than did mice lacking TLR4. Mouse experiments confirmed that O157LPS binding to TLR4 is the primary event leading to platelet activation, as shown by CD40L expression, and that CD62 further contributes to this process. Activation of human platelets by EHEC-LPS was demonstrated by expression of the activated GPIIb/IIIa receptor, CD40L, and fibrinogen binding. In perfusion experiments, platelet activation on endothelial cells was TLR4 and CD62 dependent. O157LPS was detected on platelets from 12 of 14 children with EHEC-associated hemolytic uremic syndrome (HUS) and on platelets from 2 children before the development of HUS but not on platelets of EHEC-infected children in whom HUS did not develop (n = 3). These data suggest that O157LPS on platelets might contribute to platelet consumption in HUS.

Blood platelet and monocyte activations and relation to stages of liver cirrhosis

AIM: Blood platelets (plt) and monocytes are the cells that play a crucial role in the pathogenesis of liver damage and liver cirrhosis (LC). In this paper, the analysis of mutual relationship between platelets and monocytes activation in LC was conducted.

METHODS: Immunofluorescent flow cytometry was used to measure the percentage of activated platelet populations (CD62P, CD63), the percentage of plt-monocyte aggregates (pma) (CD41/CD45), and activated monocytes (CD11b, CD14, CD16) in the blood of 20 volunteers and 40 patients with LC. Platelet activation markers: sP-selectin, platelet factor 4 (PF4), beta-thromboglobulin (βTG) and monocyte chemotactic peptide-1 (MCP-1) were measured and compared in different stages of LC.

RESULTS: Platelet activation with the increase in both βTG serum concentration and elevation of plt population (CD62P and CD63 as well as MIF CD62P and CD63) is elevated as LC develops and thrombocytopenia rises. There is a positive correlation between medial intensity of fluorescence (MIF) CD62P and MIF CD63 in LC. We did not show any relationship between monocyte activation and pma level. SP-selectin concentration correlates positively with plt count and pma, and negatively with stage of plt activation and MIF CD62P and MIF CD63. There was no correlation between MCP-1 concentration and plt, monocyte activation as well as pma level in LC. CD16 monocytes and MIF CD16 populations are significantly higher in the end stage of LC. A positive correlation occurs between the value of CD11b monocyte population and MIF CD14 and MIF CD16 on monocytes in LC.

CONCLUSION: Platelet and monocyte activation plays an important role in LC. Platelet activation stage does not influence monocyte activation and production of plt aggregates with monocytes in LC. With LC development, thrombocytopenia may be the result of plt consumption in platelet-monocyte aggregates.

Platelet function in sepsis

BACKGROUND

Coagulation abnormalities and thrombocytopenia are common in severe sepsis, but sepsis-related alterations in platelet function are ill-defined.

OBJECTIVES

The purpose of this study was to elucidate the effect of sepsis on platelet aggregation, adhesiveness, and growth factor release.

PATIENTS AND METHODS

Agonist-induced platelet aggregation was measured in platelet-rich plasma separated from blood samples collected from 47 critically ill patients with sepsis of recent onset. Expression of platelet adhesion molecules was measured by flow cytometry and the release of vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) was measured by ELISA in the supernatant of platelet aggregation.

RESULTS

Septic patients had consistently decreased platelet aggregation compared with controls, regardless of the platelet count, thrombin generation, or overt disseminated intravascular coagulation (DIC) status. The severity of sepsis correlated to the platelet aggregation defect. Adhesion molecules, receptor expression (CD42a, CD42b, CD36, CD29, PAR-1), and alpha-granule secretion detected by P-selectin expression remained unchanged but the release of growth factors was differentially regulated with increased VEGF and unchanged PDGF after agonist activation even in uncomplicated sepsis.

CONCLUSIONS

Sepsis decreases circulating platelets' hemostatic function, maintains adhesion molecule expression and secretion capability, and modulates growth factor production. These results suggest that sepsis alters the hemostatic function of the platelets and increases VEGF release in a thrombin-independent manner.

Effect of intravenous endotoxin on blood cell profiles of broilers housed in cages and floor litter environments

Commercial broilers are constantly exposed to airborne microorganisms and endotoxin (lipopolysaccharide, LPS). It has been shown that microbial contamination of the air was higher in broiler houses using floor litter than in broiler houses using netting-type floors. The current study evaluated the effect of housing conditions on blood leukocyte profiles and tested the hypothesis that, when compared to broilers reared in clean stainless steel cages (Cage group), broilers raised on floor litter (Floor group) should experience a higher environmental challenge and have a desensitized immune system that may exhibit better tolerance/resistance to subsequent intravenous LPS challenge. Hematological parameters were evaluated prior to and following i.v. administration of 1 mg/kg BW Salmonella typhimurium LPS (dissolved at 1 mg/0.25 mL in PBS) or i.v. injection of 0.25 mL/kg BW PBS alone. The results showed that prior to LPS/PBS injection, broilers in the cage group had higher heterophil and monocyte concentrations, a higher B cell percentage within the lymphocyte population, and a higher heterophil to lymphocyte (H:L) ratio in the blood. The i.v. LPS injection resulted in 25% mortality in the cage group and 42% mortality in the floor group within 8 h post-injection. LPS reduced the concentrations of total white blood cells (WBC) and all differential WBC except eosinophils and increased thrombocyte concentrations within 1 h post-injection in both groups. All of these values returned to their respective pre-injection levels within 48 h post-injection in the surviving birds. The two groups exhibited similar overall hematological changes after LPS injection except that the cage group showed a higher H:L ratio at 8 h post-injection and a lower B-cell percentage within the lymphocyte population at 48 h post-injection when compared with the floor group. We concluded that the immune systems of broilers reared on floor litter were desensitized and exhibited less pronounced leukocyte responses to i.v. LPS when compared with those of broilers reared in clean stainless steel cages. However, such desensitization of the immune system did not help broilers survive subsequent i.v. LPS challenge.

In vivo platelet response to lipopolysaccharide in mice: proposed method for evaluating new antiplatelet drugs

We previously found evidence (based on the use of 5HT as a marker) that i.v. injection of a lipopolysaccharide (LPS) into mice induces a rapid accumulation of platelets in liver and lung. Our previous studies lacked measurement of the platelet count itself, but we have now compared the LPS-induced changes in 5HT levels with the change in platelet count. We also examined the effects on the platelet response of some drugs that act on platelets. In mice, sublethal doses of LPS induced parallel decreases in platelets and 5HT in the blood. The 5HT lost from the blood accounted well for the 5HT accumulated in liver and lung. Soon after this accumulation, the levels of platelets and 5HT in the blood recovered in parallel, and these recoveries corresponded well with the decreases in 5HT occurring in liver and lung. Aspirin and dexamethasone were effective at both reducing pulmonary platelet-accumulation and promoting their return to the circulation. By contrast, oestrogen tended to reduce the return of platelets from lung to circulation. Heparin did not inhibit pulmonary platelet-accumulation but it did decrease their return to the circulation. These results suggest that (i) in response to sublethal doses of LPS, platelets translocate into the liver and lung, then return to the circulation; (ii) this platelet response involves mechanisms that can be modified by drugs; and (iii) the use of this platelet response as a tool for drug evaluation might help identify new drugs with therapeutic potential.

A new model for the continuous monitoring of polymorphonuclear leukocyte trapping in the pulmonary vasculature of the rabbit

INTRODUCTION

Accumulation of polymorphonuclear leukocytes (PMNs) within the pulmonary vasculature contributes to the pathophysiology of a number of diseases, including chronic obstructive pulmonary disease (COPD) and acute respiratory distress syndrome. The techniques available to study this have their limitations.

METHODS

We have developed a minimally invasive technique for the continuous monitoring of 111In-labelled PMNs (111In-PMNs) in the thoracic and groin regions of rabbits. The effects of intravenous injection of the chemoattractants, interleukin (IL)-8, leukotriene (LT) B(4), and lipopolysaccharide (LPS) were studied.

RESULTS

Intravenous injection of LTB(4), IL-8, or LPS caused an accumulation of 111In-PMNs in the lung and a concomitant decrease in counts in the leg and caused no significant change from baseline in counts in the lung or the leg after injection of 111In-labelled red blood cells (RBCs).

CONCLUSION

In conclusion, we have demonstrated a technique that is simple, reproducible, and robust, which can be used to investigate PMN trapping in the lung vasculature in response to well characterised PMN chemoattractants and that may be applied to the preclinical study of new drugs.

Platelet function in sepsis

OBJECTIVE

To evaluate platelet function in sepsis.

DATA SOURCES

The MEDLINE database and bibliographies of selected articles.

DATA SYNTHESIS

The common occurrence of thrombocytopenia in critically ill patients has been recognized for many years and is known to be associated with an increased mortality rate. Platelet function can be divided into four areas: activation, adhesion, aggregation, and secretion. Studies have found that activated platelets secrete key components of the coagulation and inflammatory cascades and are involved in the regulation of vascular tone. However, studies on platelet function in sepsis have been scarce, and their data are often conflicting. In sepsis, aggregation of circulating platelets seems to be reduced, yet platelet receptors are present in normal amounts.

CONCLUSIONS

Platelets play a complex role in sepsis; they are able to modulate not only their own function but also that of cells around them. Further study is needed to better define the precise mechanisms and effects of platelet activation in sepsis and to determine the benefits and risks of inhibiting platelet function.

Neutrophil-platelet interactions and their relevance to bovine respiratory disease

Respiratory disease is a serious and significant health problem for the bovine industry. Classically, the clinical and research focus has been on the putative causative agents and conditions, and their interactions with host inflammatory cells, particularly alveolar macrophages and blood neutrophils. There is, currently, growing acceptance of the concept that blood platelets play a primary role in the inflammatory process. This review explores the implications of such pro-inflammatory activity, especially in the context of neutrophil-platelet interactions, and the species specificity of cellular responses. The relevance of these issues for the treatment and prevention of bovine respiratory disease is also discussed.

Endotoxin and dietary amines may increase plasma 5-hydroxytryptamine in the horse

Uptake of 5-hydroxytryptamine (5-HT) into platelets is an important mechanism by which low plasma concentrations are maintained, and platelet activation may therefore result in significant release of this vasoconstrictor. The present study examined the kinetics of active uptake of radiolabelled [3H]5-HT by washed equine platelets in vitro, and investigated the effects on this process of 4 other naturally occurring monoamines which may be released from the caecum in conditions of carbohydrate overload. The release of [3H]5-HT by platelets was also studied, since platelet accumulation and activation has been associated with acute laminitis. Release of [3H]5-HT was measured in response to platelet activating factor (PAF), unlabelled 5-HT and the indirect activation of platelets by endotoxin in the presence of blood leucocytes. Km value for the uptake of 5-HT by equine platelets was 2.4 +/- 0.6 micromol/l and the Vmax was 8.3 +/- 0.6 pmol [3H]5-HT/10(7) platelets/min. The rate of uptake of 5 micromol/l [3H]5-HT was significantly decreased by the uptake inhibitors fluvoxamine and clomipramine. The 4 other monoamines examined all inhibited the uptake of [3H]5-HT in a noncompetitive manner, decreasing Vmax by between 17 and 82%. Incubation of platelets with LPS (0.1 mg/ml) in the absence of leucocytes did not result in significant release of [3H]5-HT; however, in the presence of leucocytes 3.8 +/- 1.7 pmol [3H]5-HT/10(7) platelets (mean +/- s.e.) were released. This release was significantly inhibited by parthenolide and WEB2086, but not by aspirin. This suggests that PAF from activated leucocytes was responsible for the 5-HT release. These data show that 5-HT uptake by equine platelets is a saturable process operating most efficiently at substrate concentrations in the low micromolar range. The noncompetitive inhibition of 5-HT uptake by other naturally occurring monoamines may result in increased plasma concentrations of 5-HT, as would its release by endotoxin. Such a rise in plasma 5-HT concentrations may contribute to selective vasoconstriction in the equine digital circulation.

Platelet kinetics in dogs treated with a glycoprotein IIb/IIIa peptide antagonist

Platelet glycoprotein IIb/IIIa (GPIIb/IIIa) receptor antagonists have been highly effective inhibitors of platelet aggregation in preclinical studies and in clinical trials. However, decreased platelet counts have been documented in preclinical studies and in some patients receiving GPIIb/IIIa antagonists. We evaluated changes in platelet kinetics and fate in dogs receiving the GPIIb/IIIa receptor antagonist RPR 109891 orally for 4 days. Dogs receiving RPR 109891 had a 22-52% decrease in platelet count with the nadirs at 3-5 days after initiation of treatment. Platelet survival time was reduced by 19%, and platelet half-life was reduced by 63%. Indium-111-labeled platelets were rapidly cleared from the blood within 1 hour after administration of RPR 109891 on treatment days 1 and 2. This clearing was associated with a sharp increase in radioactivity in spleen but not in liver or lung. Platelet clearance was markedly attenuated on treatment days 3 and 4. Platelet counts returned to baseline within 1 week after discontinuation of treatment. These data indicate that RPR 109891 causes rapid and selective sequestration of platelets in the spleen.

Beneficial effects of ACE-inhibition with zofenopril on plaque formation and low-density lipoprotein oxidation in watanabe heritable hyperlipidemic rabbits

The effects of angiotensin-converting enzyme (ACE)-inhibition with zofenopril on the development of atherosclerosis and low-density lipoprotein (LDL) oxidation were determined in Watanabe Heritable Hyperlipidemic (WHHL) rabbits. Rabbits received either placebo (n = 6) or 0.5 mg/kg/day of zofenopril (n = 6). After 6 weeks of treatment, the computer-assisted analysis revealed that zofenopril reduced the aortic and common carotid corrected cumulative lesion area by 34% and 39%, respectively (p < 0.05 vs placebo-treated group). The intimal/medial ratio of the largest fatty streaks was 0.426+/-0.158 in the zofenopril-treated group and 0.875+/-0.238 in the placebo-treated group (p < 0.05). Furthermore, we found in the zofenopril-treated group smaller lesions with an intimal/medial ratio of zofenopril also reduced plasmatic LDL oxidation, as shown by significant reduction of malondialdehyde content (p < 0.01) and relative agarose gel mobility (p < 0.05), as well as by the prolongation of the lag-time (p < 0.05). Compared to zofenopril-treated rabbits, arterial sections of the placebo-group had significant increase in the intimal presence of macrophages-derived foam cells (p < 0.05), ox-LDL (p < 0.01), and native LDL (p < 0.01) detected by immunocytochemistry with RAM-11, MDA2 and NP1533975 monoclonal antibodies, respectively. To investigate the amount of platelet accumulation in the atherosclerotic plaque we also measured platelet-associated radioactivity. Autologous platelets were labeled with 111Indiumoxine and injected intravenously. After 2 hours, WHHL were sacrificed and arterial sections were counted for platelet-associated radioactivity. In the placebo-treated group, platelet radioactivity was 0.52+/-0.12 equivalent of radioactivity per mg of tissue in the common carotid and 0.25+/-0.18 in the abdominal aorta; in contrast, rabbits treated by zofenopril had 0.20+/-0.12 in the common carotid and 0.06+/-0.01 in the abdominal aorta. These data indicate that ACE-inhibition with zofenopril has antiatherosclerotic and antioxidant effects in WHHL-rabbits. Our results also shows that these effects could be linked to a reduced wall-associated platelet deposition at the site of atherosclerotic lesions.

Platelet activation and modulation of the induction of nitric oxide synthase in the conscious rat

Injection of lipopolysaccharide (LPS) (Salmonella W. Typhosa i.v. bolus) into conscious rats, induced a rapid drop of circulating platelets analogous to that induced by ADP. The animals showed a small fall in mean arterial blood pressure (MABP), an increase in heart rate and a significant increase in plasma nitrite and nitrate level. This result is consistent with the stimulation of an inducible NO synthase (i-NOS). The administration of the stable prostacyclin analogue, iloprost plus ADP or LPS, significantly protected against the decrease in free platelet number induced by ADP or LPS. The plasma nitrite and nitrate level stimulated by LPS was significantly reduced by iloprost and also by prostacyclin. These results are consistent with an inhibition of i-NOS by agents that increase the intracellular level of cAMP. The administration of the NO donor S-Nitroso-N-acyl-D-penicillamine (SNAP) plus ADP or LPS, significantly prevented thrombocytopenia induced by ADP and by LPS. SNAP did not decrease the plasma nitrite and nitrate level stimulated by LPS; furthermore it induced a significant increase of heart rate, without affecting MABP, suggesting a direct accelerating effect of NO on the sino-atrial node. The administration of S-nitroso-glutathione (GSNO), a stable nitrosothiol, plus ADP or LPS, significantly prevented thrombocytopenia induced by ADP but not by LPS. GSNO significantly reduced the plasma nitrite and nitrate level stimulated by LPS. These data demonstrate that the L-Arginine: NO pathway in vivo may be modulated by prostanoids and that compounds which increase cAMP, such as iloprost, are able to protect against LPS-induced early thrombocytopenia.

Role of platelet adhesion in homeostasis and immunopathology

Various molecules expressed on the surface of platelets have been shown to mediate the protective or deleterious role of these cells in immuno-inflammatory mechanisms. Increasing evidence points to the involvement of the cell adhesion molecules, gpIIb-IIIa, P-selectin, CD31, LFA-1, and CD36 in the interaction between platelets and endothelial cells as well as other cell types. The possible role of these molecules in the ability of platelets to support endothelium and to protect against tumour necrosis factor mediated cytolysis or parasitic invasion are reviewed. The involvement of platelets as effectors of tissue damage in cerebral malaria, lipopolysaccharide induced pathology, and pulmonary fibrosis is also discussed. This has then been extended to include the intercellular mechanisms underpinning their pathogenic role in metastasis, transplant rejection, stroke, brain hypoxia, and related conditions. A better understanding of the complex regulation and hierarchical organisation of these various platelet adhesion molecules may prove useful in the development of new approaches to the treatment of such diseases.