VEGF and TSP1 levels correlate with prognosis in advanced non-small cell lung cancer

PURPOSE: There is a need for biomarkers that may help in selecting the most effective anticancer treatments for each patient. We have investigated the prognostic value of a set of angiogenesis, inflammation and coagulation markers in patients treated for advanced non-small cell lung cancer. PATIENTS AND METHODS: Peripheral blood samples were obtained from 60 patients before first line platinum-based chemotherapy ± bevacizumab, and after the third cycle of treatment. Blood samples from 60 healthy volunteers were also obtained as controls. Angiogenesis, inflammation and coagulation markers vascular endothelial growth factor (VEGF), their soluble receptors 1 (VEGFR1) and 2 (VEGFR2), thrombospondin-1 (TSP-1), interleukin-6 (IL6), sialic acid (SA) and tissue factor (TF) were quantified by ELISA. RESULTS: Except for TSP-1, pre- and post-treatment levels of all markers were higher in patients than in controls (p < 0.05). There was a positive and significant correlation between VEGF and VEGFR2 before treatment. VEGF also correlated with inflammatory markers IL-6 and SA. Moreover, there was a positive and significant correlation between levels of VEGFR1 and TF. Decreased levels of TSP-1 and increased levels of VEGF were associated with shorter survival. Bevacizumab significantly modified angiogenesis parameters and caused a decrease of VEGF and an increase of TSP-1. CONCLUSION: Angiogenesis, inflammation and coagulation markers were increased in NSCLC patients. Increased levels of VEGF and low levels of TSP-1 correlated with a poor prognosis (AU)

VEGF and TSP1 levels correlate with prognosis in advanced non-small cell lung cancer.

PURPOSE: There is a need for biomarkers that may help in selecting the most effective anticancer treatments for each patient. We have investigated the prognostic value of a set of angiogenesis, inflammation and coagulation markers in patients treated for advanced non-small cell lung cancer. PATIENTS AND METHODS: Peripheral blood samples were obtained from 60 patients before first line platinum-based chemotherapy ± bevacizumab, and after the third cycle of treatment. Blood samples from 60 healthy volunteers were also obtained as controls. Angiogenesis, inflammation and coagulation markers vascular endothelial growth factor (VEGF), their soluble receptors 1 (VEGFR1) and 2 (VEGFR2), thrombospondin-1 (TSP-1), interleukin-6 (IL6), sialic acid (SA) and tissue factor (TF) were quantified by ELISA. RESULTS: Except for TSP-1, pre- and post-treatment levels of all markers were higher in patients than in controls (p < 0.05). There was a positive and significant correlation between VEGF and VEGFR2 before treatment. VEGF also correlated with inflammatory markers IL-6 and SA. Moreover, there was a positive and significant correlation between levels of VEGFR1 and TF. Decreased levels of TSP-1 and increased levels of VEGF were associated with shorter survival. Bevacizumab significantly modified angiogenesis parameters and caused a decrease of VEGF and an increase of TSP-1. CONCLUSION: Angiogenesis, inflammation and coagulation markers were increased in NSCLC patients. Increased levels of VEGF and low levels of TSP-1 correlated with a poor prognosis.

Circulating endothelial and endothelial progenitor cells in non-small-cell lung cancer

New treatments have recently been introduced for treating non-small-cell lung cancer. Chemotherapeutic agents, such as pemetrexed, and targeted therapies, such as bevacizumab, erlotinib or gefitinib, have extended treatment options for selected histological subgroups. Antiangiogenic treatments, either associated with conventional chemotherapeutic drugs or given alone as maintenance therapy, constitute an active clinical research field. However, not all lung cancer patients benefit from antiangiogenic compounds. Moreover, tumour response assessment is often difficult when using these drugs, since targeted therapies generally do not cause rapid and measurable tumour shrinkage but, rather, long stabilisations and slight density changes on imaging tests. The finding of clinical or biological factors that might identify patients who will better benefit from these treatments, as well as identifying surrogate markers of tumour response and prognosis, is an issue of great interest. In that sense, different research lines have investigated the epidermal growth factor receptor (EGFR) and the vascular endothelial growth factor receptor (VEGFR) pathways. Circulating endothelial (CECs) and endothelial progenitor cells (CEPCs) are of prognostic value in different types of cancers, and relevant data are published about their potential usefulness as predictors of response to chemotherapy and antiangiogenic treatments. In this review, we discuss the data available on the role of CECs and CEPCs as prognostic factors and as surrogate markers of treatment response in non-small-cell lung cancer (AU)

What is the best biomarker for diagnosis of rejection in heart transplantation?

INTRODUCTION: Acute cellular rejection is a major cause of graft loss in heart transplantation (HT). Endomyocardial biopsy remains the gold standard for its diagnosis, but it is an invasive procedure not without risk. A proinflammatory state exists in rejection that could be assessed by determining plasma levels of inflammatory biomarkers. OBJECTIVE: To analyze the utility of various inflammatory markers, which is most important and what values best classify patients to diagnose rejection. MATERIALS AND METHODS: A prospective study in 123 consecutive cardiac transplant recipients was conducted from January 2002 to December 2006. Fibrinogen protein (Fgp) and function (Fgf), C-reactive protein (CRP), tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), and sialic acid (SA) determinations were performed at one, two, four, six, nine, and 12 months post-HT at the same time as biopsies. Coronary arteriography and intravascular ultrasound were performed on the first and last follow-up visits. Heart-lung transplants, retransplants, pediatric transplants, patients who died in the first month, and patients who refused consent were excluded. Also excluded were determinations that coincided with renal dysfunction, active infection, hemodynamic instability, or a non-evaluable biopsy. The final analysis included 79 patients and 294 determinations. The correlation between the levels of these biomarkers and the presence of rejection in the biopsy (> or = ISHLT grade 3) was studied. RESULTS: We did not find significant differences in the values of any of the markers analyzed on the six follow-up visits. Only CRP showed significant and sustained differences between the two groups (with and without rejection) from the second follow-up visit (month 2). The area under the curve showed significant differences in Fgp (0.614, p = 0.013), Fgf (0.585, p = 0.05), TNF-alpha (0.605, p = 0.02), SA (0.637, p = 0.002) and mainly CRP (0.765, p = 0.0001). CRP levels below 0.87 mg/dL ruled out rejection with a specificity of 90%. CONCLUSIONS: Among the inflammatory markers analyzed, CRP was the most useful parameter for non-invasive screening of acute cellular rejection in the first year post-HT.

Erythrocyte membrane composition in patients with primary hypercholesterolemia.

There are conflicting results regarding the erythrocyte membrane cholesterol and phospholipid content in patients with primary hypercholesterolemia (PHC), due to methodological problems in obtaining haemoglobin-free ghosts. At the same time, the different units used and the fact that the cholesterol and phospholipids are not expressed in relation with integral protein membrane content, produces contradictory results. We have analysed in 33 patients with PHC (12 male, 31 female) aged 43+/-12 years and in 33 healthy normolipaemic volunteers (9 male, 24 female) aged 43+/-13 years plasma lipids, along with, erythrocyte membrane cholesterol, phospholipids and integral proteins. PHC patients showed increased erythrocyte membrane cholesterol: 0.36+/-0.15 mg/mg when compared with controls: 0.29+/-0.75 mg/mg; p=0.018. Phospholipid membrane content, although higher in the cases, did not reach statistical significance (PHC patients: 0.38+/-0.15 mg/mg vs. 0.33+/-0.72 mg/mg; p=0.098). The cholesterol/phospholipids ratio (Chol/Ph) was 0.99+/-0.22 in PHC patients versus 0.92+/-0.28 in controls; p=0.127. Our results suggest that there is a slight increase in erythrocyte membrane cholesterol in patients with PHC. Given the increasing importance of erythrocyte membrane cholesterol in the stability of the atheroma plaque due its possible contribution to the clinical signs of ischaemic heart disease, it seems relevant to determine this parameter in risk populations. Therefore, a simple and reproducible method needs to be standardised which would enable comparisons between laboratories and facilitate further studies aimed to it as a marker of acute coronary syndromes.

Erythrocyte deformability in obesity measured by ektacytometric techniques.

Erythrocyte deformability (ED) has been scarcely evaluated in obese patients without other concomitant cardiovascular risk factors and contradictory results have been published regarding the influence of plasma lipids on the erythrocyte membrane lipid composition and insulin resistance on this rheological parameter. In 67 severe or morbid obese patients without other cardiovascular risk factors (51 women and 11 men, aged 34+/-11 years) and in 67 controls (45 women and 22 men, aged 32+/-10 years), ED has been determined by ektacytometric techniques in a Rheodyn SSD, the elongation index (EI) being measured at 12, 30 and 60 Pa, along with plasma lipids, red blood cell membrane lipids (cholesterol and phospholipids) and insulin resistance indexes in basal conditions and after a three month diet period. No significant differences were obtained in the EI between obese patients and the control group at any of the shear stresses tested (P>0.05). The cholesterol and phospholipid content of the red blood cell membrane did not significantly differ between cases and controls (P>0.05). Obese patients with metabolic syndrome showed lower EI at 30 and 60 Pa than those without metabolic syndrome (P=0.014 and P=0.031 respectively). Weight loss was not accompanied by any changes in these rheological parameters. Obesity itself does not seem to modify ED. However, metabolic syndrome seems to decrease ED, possibly through insulin resistance.

Usefulness of von Willebrand factor in cardiac allograft vasculopathy: preliminary experience.

BACKGROUND: Cardiac allograft vasculopathy (CAV) is a disease that significantly limits the survival of transplant patients intravascular ultrasound (IVUS) is considered the method of choice for its diagnosis. von Willebrand factor (vWf) has been used as a marker of endothelial malfunction. We sought to evaluate the usefulness of vWf as a CAV marker. MATERIALS AND METHODS: We prospectively analyzed 22 cardiac transplant subjects, on whom we performed a first study using coronary angiography and IVUS at 36 +/- 3 days and a second study at 598 +/- 49 days. During the follow-up period, five vWf serum controls were performed per patient. We analyzed the results with the repeated-measures ANOVA test and a ROC curve. RESULTS: CAV was detected in 10 (45.5%) of the 22 patients. Although vWf levels tended to diminish progressively during evolution, this trend was not statistically significant (P = .3). However, differences were appreciated based on the presence versus absence of CAV (298 +/- 139 mg/dL versus 212 +/- 105 mg/dL, P = .02). The ROC curve showed a sensitivity of 40%, a specificity of 83%, and a negative predictive value of 82% with a cutoff point of 300 mg/dL. CONCLUSIONS: Subjects with CAV showed significantly higher vWf serum concentrations, particularly during the preliminary phases of cardiac transplantation decreasing during its evolution. This marker could be useful for early screening of CAV.

Diagnostic usefulness of inflammatory markers in acute cellular rejection after heart transplantation.

BACKGROUND: Acute cellular rejection (ACR) affects early morbidity and mortality after heart transplantation. The diagnostic technique of choice is endomyocardial biopsy. Our aim was to evaluate the diagnostic usefulness of inflammatory markers as a noninvasive method to monitor cellular rejection. MATERIAL AND METHODS: We prospectively analyzed 73 cardiac transplant patients by determining the serum levels of protein fibrinogen (fgpro), functional fibrinogen (fgfun), C-reactive protein (CRP), and sialic acid (SA) coinciding with an endomyocardial biopsy (5.1 revisions/patient). The statistical methods were chi(2), Student's t-test, and ROC curves. RESULTS: Of the 373 controls, significant rejection was detected in 19%. Analysis of the relationship between ACR and the markers showed significantly elevated levels of fgpro (345 +/- 90 versus 307 +/- 74 mg/dL; P = .03), fgfun (361 +/- 101 versus 318 +/- 89 mg/dL; P = .04), and SA (74 +/- 22 versus 66 +/- 15 mg/dL; P = .02), but not CRP (19 +/- 29 versus 10 +/- 21 mg/dL; P = .07). SA displayed a better diagnostic utility (area under the curve 0.7; P < .01), 35% sensitivity, 85% specificity, and 82% negative predictive value for a cutoff point of 80 mg/dL. CONCLUSIONS: Among the inflammatory markers increased in ACR, SA was the most useful noninvasive tool for screening.

La atorvastaina modula a la trombospondina en células endoteliales umbilicales humanas / Atorvastatin modulates thrombospondin in human endothelial cells

El objetivo del presente trabajo es determinar el efecto de la atorvastatina sobre la síntesis y liberación de trombospondina en células endoteliales umbilicales humanas y su regulación por los metabolitos de la vía del mevalonato. Los resultados muestran que la atorvastatina disminuye el contenido celular de trombospondina y su liberación, de forma dependiente de la dosis, en células endoteliales. El mevalonato revierte totalmente el efecto inhibitorio producido por la atorvastatina sobre el contenido y la liberación de la trombospondina celular. El farnesil pirofosfato y el geranilgeranil pirofosfato revierten el efecto inhibitorio producido por la atorvastatina en el contenido celular de trombospondina; sin embargo, ni el farnesil pirofosfato ni el geranilgeranil pirofosfato revierten el efecto inhibitorio producido por la atrovastatina en la liberación de trombospondina. En conclusión, la atorvastatina regula negativamente a la trombospondina, en células endoteliales umbilicales humanas, a través de la inhibición del mevalonato (AU)

The aim of this study was to evaluate the effect of atorvastatin on thrombospondin synthesis and secretion in human umbilical endothelial cells and its regulation by mevalonate or its derivatives. Our results show that atorvastatin decreased endothelial cell thrombospondin content and secretion in a dose-dependent manner. Mevalonate totally reversed the inhibitory effect produced by atorvastatin on the content and secretion of cellular thrombospondin. Farnesyl pyrophosphate and geranylgeranyl pyrophosphate reversed the inhibitory effect produced by atorvastatin on the cellular content of thrombospondin but did not prevent the inhibitory effect of atorvastatin on thrombospondin secretion. In conclusion, atorvastatin down-regulates thrombospondin in human endothelial cells through mevalonate inhibition (AU)

Effects of unfractionated and low molecular weight heparins on plasma levels of hemostatic factors in patients with acute coronary syndromes.

BACKGROUND AND OBJECTIVES: Unfractionated heparin (UFH) and enoxaparin (low molecular weight heparin) constitute fundamental therapies in the treatment of patients with acute coronary syndrome (ACS). Since enoxaparin appears to offer clinical advantages over UFH in managing ACS, markers of thrombin generation, endothelial function and acute phase response could manifest different responses to UFH or enoxaparin. The purpose of the present study was to investigate the effect that treatment with either UFH or enoxaparin has on plasma hemostatic markers in 24 patients with ACS. DESIGN AND METHODS: The patients were randomized to receive 5,000 IU intravenous bolus and continuous infusion of 18 IU/Kg/h UFH (n=11) or 1 mg/kg/12h subcutaneous enoxaparin (n=13). The plasma levels of fibrinogen (Fg), prothrombin fragment 1+2 (F1+2), thrombin antithrombin complex (TAT), von Willebrand factor (vWF), tissue factor (TF) and tissue factor pathway inhibitor (TFPI) were assayed at admission and 6, 12, 24 and 48 hours after heparin treatment. RESULTS: Upon admission, UFH and enoxaparin patients showed a significant increase in all the hemostatic parameters measured with respect to the levels in the control subjects. In comparison with the baseline levels of the UFH- and enoxaparin-treated patients, Fg showed a significant increase at 48 h and TFPI at 6, 12 and 24 hours. However, at 48 hours TFPI levels were not significantly higher than the basal values. There were no significant changes in F1+2, TAT, vWF or TF. INTERPRETATION AND CONCLUSIONS: Markers of thrombin generation, endothelial function and acute-phase reactants manifest a similar response to UFH and enoxaparin. An increase in thrombin generation may be a result of persistently activated inflammatory and endothelial processes, despite UFH and enoxaparin treatment.

Relationship between fibrinogen protein and fibrinogen function in postmyocardial infarction patients.

The present study investigates the association between increases in the concentration and function of plasma fibrinogen in two groups of patients with chronic ischemic heart disease (11 with recurrent ischemic events and 19 free of these episodes) and in 34 healthy controls. The fibrinogen function index (fibrinogen function per unit of fibrinogen protein) (FgFI) was used as a measure of the fibrinogen clotting potential. The prothrombin fragment 1+2 (F1+2) and thrombin-antithrombin (TAT) were used as procoagulant markers. Plasma sialic acid (SA) was also evaluated as an inflammatory marker. No differences were found between FgFI (1.06+/-0.13 vs. 1.02+/-0.13), F1+2 (1.2+/-0.5 vs. 1.1+/-0.4 nmol/l) and TAT (2.5+/-1.3 vs. 2.5+/-0.7 microg/ml) in postinfarction patients without recurrent coronary ischemic events and the control group. However, postinfarction patients who suffered recurrent coronary ischemic events had significantly higher FgFI than patients without these symptoms (1.19+/-0.09 vs. 1.06+/-0.13), P<.01) and than the control group (1.19+/-0.09 vs. 1.02+/-0.13, P<.001). Moreover, the F1+2 (1.4+/-0.5 vs. 1.1+/-0.4 nmol/l, P<.05) and TAT (3.6+/-3.3 vs. 2.5+/-0.7 microg/ml, P<.05) were significantly higher in patients who suffered recurrent coronary ischemic events than in the control group. However, F1+2 and TAT were not different between patients with and without these symptoms. The fibrinogen protein (Fg-protein) concentration and high molecular weight fibrinogen (HMW-Fg) levels were significantly higher in both postinfarction patient groups than in the control group and in postinfarction patients with recurrent coronary ischemic events than in postinfarction patients without these symptoms. The plasma SA levels were significantly increased in postinfarction patients with and without recurrent coronary ischemia as compared with the control group. A positive correlation was found between fibrinogen and SA levels (r=.5, P<.01). In conclusion, our study indicates that the procoagulant factors, among which we include fibrinogen, F1+2 and TAT play a very active role in recurrent ischemic events in postmyocardial infarction patients. High plasma concentrations of both fibrinogen and SA suggests that fibrinogen becomes elevated as a consequence of inflammatory processes. The FgFI as an indicator of clotting potential of fibrinogen appears to be associated with ischemic events in chronic coronary artery disease.

Elevated high molecular weight fibrinogen in plasma is predictive of coronary ischemic events after acute myocardial infarction.

This study investigates the association between the concentration and function of plasma fibrinogen molecules measured at the time of hospital admission in patients with acute myocardial infarction (AMI), with reference to the risk of new coronary ischemic events during a three-day follow-up period of. Before starting fibrinolytic and anticoagulant treatment plasma fibrinogen, high molecular weight fibrinogen (HMW-fibrinogen), fibrin formation rate (FbFR) and phosphorous content in fibrinogen were determined in 90 AMI patients. During a three-day follow-up period 12 patients suffered new ischemic events. The 12 patients with coronary ischemia had higher concentrations of plasma fibrinogen (312+/-23 vs. 270+/-73 mg/dl, p<0.05) and HMW-fibrinogen (246+/-35 vs. 189+/-23 mg/dl, p<0.001) and a higher FbFR (65+/-30 vs. 40+/-25, p<0.001) than patients without these events. No association was found between the phosphorous content in fibrinogen and new coronary ischemic events. We conclude that after myocardial infarction an elevated plasma level of HMW-fibrinogen and a high FbFR value at the time of hospital admission are associated with new coronary ischemic events during a three-day follow-up period.

Increase in thrombin generation after coronary thrombolysis with rt-PA or streptokinase with simultaneous heparin versus heparin alone.

This study compares the extent of inhibition of thrombin generation and activity achieved in patients with acute myocardial infarction receiving fibrinolytic treatment (streptokinase SK, or rt-PA) and concomitant intravenous heparin treatment adjusted to the patients' weight with that achieved with the same heparin regimen but without fibrinolytic therapy. The study involved 90 patients, grouped according to their treatment: SK+heparin; rt-PA+heparin, and heparin without thrombolytic agents. Prothrombin fragment 1+2 (F1+2), thrombin-antithrombin complex (TAT), fibrinopeptide A (FPA) and activated partial thromboplastin time were measured. Patients treated with SK+heparin or rt-PA+heparin and higher F1+2 plasma levels than the patients treated with heparin alone at 12, 48 and 72 h in the case of SK+heparin, and at 12, 24, 48 and 72 h in that of rt-PA+heparin. Compared to baseline, the plasma levels of FPA were decreased in the three treatment groups at 24-48 h. There were no significant changes in TAT and FPA plasma levels among the three treatment groups at the different times. After thrombolytic therapy with both SK and rt-PA, there was an increase in thrombin generation, although high-dose intravenous heparin inhibited the different increases in thrombin associated with the thrombolytic agents to the same extent.

Elevated thrombotic activity after myocardial infarction: A 2-year follow-up study.

This study examines the evolution of the thrombotic activity in patients with myocardial infarction (MI) treated with aspirin (200 mg/day) for 2 years after MI. Plasma samples of 10 patients were collected at 7, 30, 60, 90, 120, 150, 180, 360 and 720 days. In all the samples we measured fibrinogen (Fg), high molecular weight Fg (HMW-Fg), fibrinopeptide A (FPA), prothrombin fragment 1+2 (F1+2), beta-thromboglobulin (beta-TG), von Willebrand factor (vWF), tissue factor (TF) and TF pathway inhibitor (TFPI). The plasma Fg, HMW-Fg, FPA, F1+2, beta-TG and vWF levels were significantly elevated in the patients at the beginning of the study as compared to the normal group. The 95% confidence intervals were Fg 277-333 mg/dl, HMW-Fg 200-244 mg/dl, FPA 5.3-16.5 ng/ml, F1+2 1.4-1.8 nmol/l, beta-TG 110-118 IU/ml and vWF 139-195%. At thirty days Fg and HMW-Fg returned to normal levels, whereas the increase in FPA and F1+2 levels persisted throughout the study. At 120 and 150 days, respectively, beta-TG and vWF returned to normal levels. The increase in thrombin generation and activity pointed to a persistent hypercoagulable state 2 years after MI. Plasma levels of TF and TFPI showed no statistically significant variations with respect to the normal values over the 2-year period studied. In conclusion, these results suggest a persistent generation and activity of thrombin and cellular activation in these patients after MI.

The effect of thrombin on the dynamic exchange between intraplatelet and extraplatelet fibrinogen.

We examined the distribution of platelet fibrinogen and the exchange between intra- and extra-platelet fibrinogen in unstimulated and thrombin-stimulated platelets. In unstimulated platelets 60% of platelet fibrinogen was found in the soluble platelet fraction and 40% in the insoluble one. In platelets activated with thrombin, changes took place in the distribution of intraplatelet fibrinogen but not in the total fibrinogen content. At > or = 0.5 U/ml of thrombin the fibrin(ogen) content of the insoluble and soluble fractions was approximately 80% and 20%, respectively. When we evaluated how extraplatelet fibrinogen affects the content and distribution of intraplatelet fibrinogen, we found that when unlabelled fibrinogen was added to unstimulated and thrombin-stimulated platelets the content and distribution of intraplatelet fibrinogen remained unaltered. However, when 125I-fibrinogen was added, it was incorporated into unstimulated and thrombin-stimulated platelets. In unstimulated platelets, 70% of the incorporated 125I-fibrinogen was in the soluble fraction and 30% in the insoluble. In thrombin-stimulated platelets the distribution of the incorporated 125I-fibrinogen was 62% and 38% in soluble and insoluble fractions respectively. MoAb to GPIIb-IIIa produced 80% and 60% inhibition of 125I-fibrinogen incorporation by unstimulated and thrombin-stimulated platelets. Our data showed dynamic exchange between intraplatelet and extraplatelet fibrinogen both in unstimulated and thrombin-stimulated platelets mediated mainly by GPIIb-IIIa.

Unstimulated and thrombin-stimulated platelets binding to immobilized fibrinogen and fibrin on polystyrene supports.

The binding of unstimulated and thrombin-stimulated platelets was studied with immobilized fibrinogen and fibrin on polystyrene. The amount of fibrinogen bound to the polystyrene support was 2 micrograms/tube, which represents 2.35 micrograms/cm2. Immobilized fibrin was obtained by adding thrombin (5 nM) to immobilized fibrinogen. The number of unstimulated 111In-platelets bound to immobilized fibrinogen and fibrin was similar (3.2 +/- 0.3 x 10(6) and 3.1 +/- 0.4 x 10(6) platelets/micrograms fibrin(ogen), respectively). The platelet binding steadily increased. In the first 2 min, the binding rate was 0.23 x 10(6) platelets/micrograms fibrinogen/min. The binding rate then increased rapidly and saturation was reached at 10 min. The extent of the adhesion of resting platelets to immobilized fibrinogen is about one half that of the same platelets stimulated with thrombin. In thrombin-stimulated 111In-platelets, the binding to immobilized fibrinogen and fibrin is time dependent, and saturation is reached at 5 min. The early rate of thrombin-stimulated platelet binding to fibrinogen is about twice that of binding to fibrin (1.25 and 0.74 x 10(6) platelets/micrograms fibrin(ogen)/min, respectively). In saturation conditions, 1 microgram fibrinogen binds 5.7 +/- 0.6 x 10(6) thrombin-stimulated platelets and 1 microgram fibrin binds 4.6 +/- 0.5 x 10(6) thrombin-stimulated platelets. Our results indicate that the rate of platelet aggregation is faster than fibrin formation, and the rate of fibrinogen-platelet binding is faster than that of fibrin-platelet binding. Therefore, after thrombin stimulation, the binding of platelets to fibrin must be secondary to the binding of platelets to fibrinogen.

Lack of effect of thrombin on fibrin(ogen)-endothelial cell interaction.

In the present study we investigate the fibrin(ogen)-endothelial cell binding and the effect of thrombin on the endothelial cells in relation to fibrin(ogen) binding capacity. Endothelial cell fibrinogen binding was concentration and time-dependent, reaching saturation at 1.4 µM of added ligand. At equilibrium, the number of fibrinogen molecules bound per endothelial cell in the monolayer was 5.8±0.7×10(6). When endothelial cells were activated by different concentrations of thrombin (0-0.1 NIH units ml(-1)), no increase in fibrinogen binding capacity was observed at all the thrombin concentration tested. Whereas disruption of endothelial cell monolayers was observed at thrombin concentrations higher than 0.05 NIH units ml(-1), no increase in the amount of fibrinogen bound was observed. Therefore, resting and thrombin-activated endothelial cells show the same fibrinogen binding capacity.The adhesion of endothelial cells in suspension on immobilized fibrinogen or fibrin was studied to ascertain whether the behavior of fibrin is similar to that of fibrinogen. The extent of endothelial cell attachment to immobilized fibrinogen and fibrin was similar (4275±130 cells cm(-2) for fibrinogen and 4350±235 cells cm(-2) for fibrin) and represent approximately 40% of the added endothelial cells. However, endothelial cell adhesion to immobilized fibrin was significantly faster than endothelial cell adhesion to immobilized fibrinogen. The maximum binding rate was 66±9 and 46±8 cells cm(-2) min(-1) for fibrin and fibrinogen, respectively. Therefore, the fibrinopeptides released by thrombin from fibrinogen induce qualitative changes which enhance the fibrin interaction with the endothelial cells.

Erythrocytes metabolically enhance collagen-induced platelet responsiveness via increased thromboxane production, adenosine diphosphate release, and recruitment.

Erythrocytes promoted platelet reactivity in a plasma medium, as demonstrated in an in vitro system that independently evaluated the biochemistry of platelet activation and recruitment. The prothrombotic erythrocyte effects were metabolically regulated, as evidenced by lack of activity of ATP-depleted or glutaraldehyde-fixed erythrocytes. They occurred in the absence of cell lysis as verified by lactate dehydrogenase assays, and had an absolute requirement for platelet activation. The presence of erythrocytes induced a twofold increase in platelet thromboxane B2 (TXB2) synthesis upon collagen stimulation, indicating that erythrocytes modulated platelet eicosanoid formation. Cell-free releasates from stimulated platelet-erythrocyte suspensions, which exhibited increased recruiting capacity, contained 6.9-fold more ADP and 4.9-fold more ATP than releasates from stimulated platelets alone. Following aspirin ingestion, TXB2 formation was blocked, but erythrocyte promotion of platelet reactivity persisted at those doses of collagen that reinduced platelet activation. Moreover, when platelet mixtures consisted of as little as 10% obtained before aspirin plus 90% obtained post-aspirin ingestion, significant erythrocyte enhancement of platelet reactivity occurred, even at low agonist concentrations. These erythrocyte effects would decrease the therapeutic potential of inhibition of platelet cyclooxygenase by aspirin. The erythrocyte-induced modulation of platelet biochemistry and function emphasizes the importance of cell-cell interactions in stimulus-response coupling.