Efficient flow cytometric assay for platelet-leukocyte aggregates in whole blood using fluorescence signal triggering

4-Color Flow Cytometric Crossmatch Using Whole Blood Lysis

BACKGROUND

In lymphocyte crossmatch using flow cytometry (flow cytometric crossmatch, FCXM), the conventional tricolor FCXM protocol requires a mononuclear cell isolation step. To develop a new, more streamlined protocol, we introduced whole blood lysis (WBL) and CD45 fluorescence-triggered acquisition using 4-color flow cytometry.

METHODS

A total of 186 donor/recipient pairs for transplantation were classified into donor-specific human leukocyte antigen (HLA) alloantibody-positive (DSA+, n = 78) and DSA-negative (DSA-, n = 108) groups. The latter group was reclassified into blood group ABO-incompatible (ABOi, n = 56) and ABO-compatible (n = 52) subgroups. The WBL FCXM protocol with CD45 V500-C was optimized using a FACSLyric cytometer (BD Biosciences) with 3 lasers. Measurements for T cells or B cells were calculated as a mean fluorescence intensity (MFI) ratio (test divided by control). WBL FCXM was compared with conventional FCXM in each group.

RESULTS

WBL FCXM showed no difference quantitatively compared with conventional FCXM, except for the B cell FCXM in the DSA- group (B cell MFI ratio: 1.06 ± 0.44 and 0.92 ± 0.41, respectively [P = .0001]). There was no ABO antibody interference in the ABOi subgroup. Similar results were observed in the qualitative determinations of FCXM as follows: 1) In the DSA+ group, the sensitivity of B cell WBL FCXM (96.2%) showed no difference compared with that of conventional FCXM (91.0%, P = .2188) and 2) In the DSA- group, the specificity of T cell WBL FCXM (96.3%) showed no difference compared with that of conventional FCXM (98.1%, P = .6250). WBL FCXM reduced the turnaround time by 50 min compared with that by conventional FCXM.

CONCLUSIONS

WBL FCXM demonstrated comparable assay performance to that of conventional FCXM. Because this new FCXM protocol is simple and does not compromise assay sensitivity, it has the potential to replace the conventional method in histocompatibility laboratory settings.

Platelet-leukocyte aggregate formation and inflammation in patients with pulmonary arterial hypertension and CTEPH

Pulmonary hypertension (PH) is defined by increased mean pulmonary artery pressure, and the clinical classification includes five etiologies, of which we investigated subgroup 1, pulmonary arterial hypertension (PAH) and subgroup 4, chronic thrombotic and/or embolic disease (CTEPH). Platelets participate in both innate and adaptive immune responses and could possibly contribute to the suggested systemic inflammation associated with PAH. In this study, we utilized flow cytometry to analyze platelet activation and platelet-monocyte (PMA) and granulocyte (PGA) aggregates in PAH and CTEPH patients and healthy control subjects. The plasma concentration of proinflammatory cytokines was measured by multiplex electrochemiluminescence. Our main finding is that circulating platelets are activated in the circulation and form aggregates with both monocytes and granulocytes in patients with idiopathic PAH (IPAH), associated PAH (APAH) and pulmonary hypertension due to CTEPH. There was a strong correlation between the platelet activation, assessed as P-selectin, and the number of aggregates formed. IL-6, IL-8, IL-10 and TNF-α were increased in all PH subgroups as compared to healthy controls, and PMAs were associated with circulating IL-6, IL-8 and IL-10, whereas PGAs were associated with IL-6. The increased concentrations of platelet-leukocyte aggregates found in PAH/CTEPH patients might thus contribute to the inflammatory state in PH.

In-vivo platelet activation and aggregation during and after acute atherothrombotic myocardial infarction in patients with and without Type-2 diabetes mellitus treated with ticagrelor

INTRODUCTION

Patients with type-2 diabetes are twice as likely to suffer from acute myocardial infarction (AMI) and have a higher incidence of recurrent events than their non-diabetic counterparts. Ticagrelor is a platelet inhibitor known to reduce major adverse cardiovascular events (MACE) in AMI patients. This study measures the level and change in platelet activation and aggregation at the time of and following an AMI in patients with and without diabetes treated with ticagrelor.

MATERIALS/METHODS

P₂Y₁₂ receptor inhibitor naïve patients presenting with AMI were prospectively enrolled. Blood collection occurred before coronary angiography (baseline: T₀), 2, 4, 24, 48 h after baseline, and at a three-month follow-up. Ticagrelor was administered within five minutes of T₀. We assessed platelet activation via measurements of surface P-selectin and platelet activated glycoprotein IIb/IIIa-1 (PAC-1) and assessed platelet aggregation via monocyte, lymphocyte, and granulocyte aggregates. We hypothesize that platelet activation and aggregation will be proportionally impacted to the same degree by ticagrelor, regardless of diabetes status.

RESULTS

Ninety-seven patients were prospectively enrolled (diabetes, N = 33; no diabetes, N = 64). No difference was observed in the expression of P-selectin and PAC-1 at any given point between diabetes and non-diabetes groups (p > 0.05). No difference was observed in the percentage of platelet bound to leukocytes at any measured timepoint between patients with and without diabetes (p > 0.05). Platelet leukocyte aggregation was suppressed during the acute phase compared to quiescence equally among both groups.

DISCUSSION

Ticagrelor demonstrated similar in-vivo effects on platelet activation and aggregation regardless of diabetes status in patients presenting with AMI.

Platelet-Leucocyte Aggregates as Novel Biomarkers in Cardiovascular Diseases

Simple Summary

Cardiovascular diseases are the most common cause of death worldwide. Hence, novel biomarkers are urgently needed to improve diagnosis and treatment. Platelet–leucocyte aggregates are conglomerates of platelets and leucocytes and are widely investigated as biomarkers in cardiovascular diseases. Platelet–leucocytes aggregates are present in health, but increase in patients with cardiovascular risk factors and acute or stable coronary syndromes, making them a potential diagnostic marker. Moreover, platelet–leucocyte aggregates predict outcomes after surgery or percutaneous treatment and could be used to monitor antiplatelet therapy. Emerging data about the participation of platelet–leucocyte aggregates in cardiovascular diseases pathogenesis make them an attractive target for novel therapies. Furthermore, simple detection with conventional flow cytometry provides accurate and reproducible results, although requires specific sample handling. The main task for the future is to determine the standardized protocol to measure blood concentrations of platelet–leucocyte aggregates and subsequently establish their normal range in health and disease.

Abstract

Platelet–leucocyte aggregates (PLA) are a formation of leucocytes and platelets bound by specific receptors. They arise in the condition of sheer stress, thrombosis, immune reaction, vessel injury, and the activation of leukocytes or platelets. PLA participate in cardiovascular diseases (CVD). Increased levels of PLA were revealed in acute and chronic coronary syndromes, carotid stenosis cardiovascular risk factors. Due to accessible, available, replicable, quick, and low-cost quantifying using flow cytometry, PLA constitute an ideal biomarker for clinical practice. PLA are promising in early diagnosing and estimating prognosis in patients with acute or chronic coronary syndromes treated by percutaneous coronary intervention (PCI) and coronary artery bypass grafting (CABG). PLA were also a reliable marker of platelet activity for monitoring antiplatelet therapy. PLA consist also targets potential therapies in CVD. All of the above potential clinical applications require further studies to validate methods of assay and proof clinical benefits.

Activation of metabolite receptor GPR91 promotes platelet aggregation and transcellular biosynthesis of leukotriene C4

BACKGROUND

Succinate is a Krebs cycle intermediate whose formation is enhanced under metabolic stress, and for which a selective sensor GPR91 has been identified on various cell types including platelets. Platelet-derived eicosanoids play pivotal roles in platelet activation/aggregation, which is key to thrombus formation and progression of atherothrombosis.

OBJECTIVES

This study aims to decipher the molecular mechanism(s) and potential involvement of eicosanoids in succinate enhanced platelet activation/aggregation.

METHODS

We used liquid chromatography-mass spectrometry (LC-MS)/MS-based lipid mediator profiling to identify eicosanoids regulated by succinate. We ran light transmittance aggregometry and flow cytometry to assess platelet aggregation, P-selectin expression, and platelet-polymorphonuclear leukocyte (PMN) adherence. Various pharmacological tools were used to assess the contributions of GPR91 signalling and eicosanoids in platelet aggregation.

RESULTS

Succinate and two types of synthetic non-metabolite GPR91 agonists-cis-epoxysuccinate (cES) and Cmpd131-potentiated platelet aggregation, which was partially blocked by a selective GPR91 antagonist XT1. GPR91 activation increased production of 12-hydroxy-eicosatetraenoic acid (12-HETE), thromboxane (TX) A2 , and 12-hydroxy-heptadecatrienoic acid (12-HHT) in human platelets, associated with phosphorylation of cytosolic phospholipase A2 (cPLA2 ), suggesting increased availability of free arachidonic acid. Blocking 12-HETE and TXA2 synthesis, or antagonism of the TXA2 receptor, significantly reduced platelet aggregation enhanced by GPR91 signalling. Moreover, platelet-PMN suspensions challenged with succinate exhibited enhanced transcellular biosynthesis of leukotriene C4 (LTC4 ), a powerful proinflammatory vascular spasmogen.

CONCLUSION

Succinate signals through GPR91 to promote biosynthesis of eicosanoids, which contribute to platelet aggregation/activation and potentially vascular inflammation. Hence, GPR91 may be a suitable target for pharmacological intervention in atherothrombotic conditions.

Analysis of platelet-activating factors in severe sepsis by flow cytometry and its correlation with clinical sepsis scoring system: A pilot study

Background

Sepsis is a major global healthcare concern. Platelets and leucocytes play a key role in sepsis. Whole blood flow cytometry (FCM) is a powerful new technique for the assessment of leucocyte and platelet parameters and their functional state. In the present study, we have used FCM to examine platelet and leucocyte functions and parameters in sepsis patients.

Methods

Prospective, non-interventional cohorts of all adult patients with sepsis and history of intensive care unit stay for more than 24 h at mixed surgical- medical ICU were evaluated. The Simplified Acute Physiology Score-3 (SAPS 3) admission score was obtained, and whole blood FCM analysis of select platelets and leukocyte parameters were performed using a combination of monoclonal antibodies in a predefined panel. We also evaluated the correlation between these parameters and the severity of the illness, based on SAPS 3 admission score.

Results

Total leucocyte count (TLC) was statistically and significantly different between all the study samples, but platelet count was not. SAPS 3 acted as the best discriminant between the study groups. With a cut-off score of 55.5, SAPS 3 score predicted hospital mortality with a sensitivity of 82.8% and a specificity of 83.9%, with an area under receiver operating curves (AUROC) of 0.888 (95% CI = 0.807-0.969, p < 0.000). Parameters for CD62P, platelet-leucocyte aggregates (PLAs) and CD11b showed statistically significant differences between the patients and healthy volunteers. CD62P expression was positively correlated to PLA variables in severe sepsis patients. The median fluorescence intensity was found to be more informative than mean fluorescence intensity. New "62P adhesion index (62P AI)" and "PLA adhesion index" are proposed and is likely to be more informative.

Conclusion

SAPS 3 score was the most robust of the parameters evaluated. Our study suggest the idea that the incorporation of platelet and leucocyte activation parameters, rather than mere static counts, will add the existing prognostic model though we could not conclusively prove the same in this study.

Ozone effects on blood biomarkers of systemic inflammation, oxidative stress, endothelial function, and thrombosis: The Multicenter Ozone Study in oldEr Subjects (MOSES)

The evidence that exposure to ozone air pollution causes acute cardiovascular effects is mixed. We postulated that exposure to ambient levels of ozone would increase blood markers of systemic inflammation, prothrombotic state, oxidative stress, and vascular dysfunction in healthy older subjects, and that absence of the glutathione S-transferase Mu 1 (GSTM1) gene would confer increased susceptibility. This double-blind, randomized, crossover study of 87 healthy volunteers 55-70 years of age was conducted at three sites using a common protocol. Subjects were exposed for 3 h in random order to 0 parts per billion (ppb) (filtered air), 70 ppb, and 120 ppb ozone, alternating 15 min of moderate exercise and rest. Blood was obtained the day before, approximately 4 h after, and approximately 22 h after each exposure. Linear mixed effect and logistic regression models evaluated the impact of exposure to ozone on pre-specified primary and secondary outcomes. The definition of statistical significance was p<0.01. There were no effects of ozone on the three primary markers of systemic inflammation and a prothrombotic state: C-reactive protein, monocyte-platelet conjugates, and microparticle-associated tissue factor activity. However, among the secondary endpoints, endothelin-1, a potent vasoconstrictor, increased from pre- to post-exposure with ozone concentration (120 vs 0 ppb: 0.07 pg/mL, 95% confidence interval [CI] 0.01, 0.14; 70 vs 0 ppb: -0.03 pg/mL, CI -0.09, 0.04; p = 0.008). Nitrotyrosine, a marker of oxidative and nitrosative stress, decreased with increasing ozone concentrations, with marginal significance (120 vs 0 ppb: -41.5, CI -70.1, -12.8; 70 vs 0 ppb: -14.2, CI -42.7, 14.2; p = 0.017). GSTM1 status did not modify the effect of ozone exposure on any of the outcomes. These findings from healthy older adults fail to identify any mechanistic basis for the epidemiologically described cardiovascular effects of exposure to ozone. The findings, however, may not be applicable to adults with cardiovascular disease.

Platelets Activation in Patients Undergoing PTCA and Their Responsiveness After in vitro Stimulation

We evaluated expression of platelet activation markers in blood samples of 15 patients who underwent percutaneous transluminal coronary angioplasty (PTCA) by flow cytometry. Analysis was performed before the beginning of PTCA, during initial coronary angiography and after the end of PTCA or after a stent placement, respectively. We evaluated platelet-derived microparticles, platelet-leukocyte aggregates, platelet aggregates and a membrane expression of CD62P and CD63 molecules. Responsiveness of platelets to the activationin vitrowith thrombin-receptor activating protein – 6 (TRAP-6) was tested simultaneously. Statistically significant differences between patient samples were found only in the expression of the activation markers CD62P (before PTCA 0.22 %, during 0.39 %, after 0.67 %), CD63 (0.26 %/ 0.45 %/ 0.85 %) and platelet-leukocyte aggregates (13.57 %/ 18.39 %/ 23.63 %).In the same group the expression of all constitutive membrane markers was statistically significantly decreased: in patients undergoing PTCA was the expression of CD9:87.98 % (in comparison with control group 94.98 %), CD31: 87.10 % (92.78 %), CD36: 87.37 % (90.98 %), CD41: 88.09 % (95.62 %), CD42a: 88.54 % (94.98 %), CD42a: 88.31 % (94.13 %).

Increased platelet reactivity and platelet-leukocyte aggregation after elective coronary bypass surgery

Inflammatory mechanisms are activated, and thrombotic complications occur during the initial months after coronary artery bypass grafting (CABG). Therefore, changes over time of platelet activation and platelet-leukocyte interactions after CABG are of interest. Whole-blood flow cytometry was performed before, and 4-6 days, one month, and three months after elective CABG in 54 men with stable coronary artery disease treated with acetylsalicylic acid (ASA). Single platelets and platelet-leukocyte aggregates (PLAs) among monocytes (P-Mon), neutrophils (P-Neu), and lymphocytes (P-Lym) were studied without and with stimulation by submaximal concentrations of ADP, thrombin, and the thromboxane analog U46619. White blood cell counts were increased during the initial postoperative course, and platelet counts were increased after one month. Platelet P-selectin expression was significantly enhanced at one month when stimulated by thrombin and U46619 and at three months with ADP and thrombin. All PLAs subtypes were increased at one month without stimulation in vitro. P-Mon and P-Neu stimulated by ADP, thrombin, or U46619 were significantly increased one month after the operation but decreased compared to baseline at three months. Agonist stimulated P-Lyms were increased at one month and remained increased at three months after ADP stimulation. There was significant platelet activation and formation of PLAs unstimulated and after agonist stimulation by ADP, thrombin, and a thromboxane analog after CABG in patients with stable coronary artery disease irrespective of ASA treatment. Changes observed up to three months after CABG support further studies of the clinical implications of protracted increases in platelet activation and platelet-leukocyte interactions.

Phosphatidylserine-mediated platelet clearance by endothelium decreases platelet aggregates and procoagulant activity in sepsis

The mechanisms that eliminate activated platelets in inflammation-induced disseminated intravascular coagulation (DIC) in micro-capillary circulation are poorly understood. This study explored an alternate pathway for platelet disposal mediated by endothelial cells (ECs) through phosphatidylserine (PS) and examined the effect of platelet clearance on procoagulant activity (PCA) in sepsis. Platelets in septic patients demonstrated increased levels of surface activation markers and apoptotic vesicle formation, and also formed aggregates with leukocytes. Activated platelets adhered were and ultimately digested by ECs in vivo and in vitro. Blocking PS on platelets or αvβ3 integrin on ECs attenuated platelet clearance resulting in increased platelet count in a mouse model of sepsis. Furthermore, platelet removal by ECs resulted in a corresponding decrease in platelet-leukocyte complex formation and markedly reduced generation of factor Xa and thrombin on platelets. Pretreatment with lactadherin significantly increased phagocytosis of platelets by approximately 2-fold, diminished PCA by 70%, prolonged coagulation time, and attenuated fibrin formation by 50%. Our results suggest that PS-mediated clearance of activated platelets by the endothelium results in an anti-inflammatory, anticoagulant, and antithrombotic effect that contribute to maintaining platelet homeostasis during acute inflammation. These results suggest a new therapeutic target for impeding the development of DIC.

Meal-induced platelet activation in diabetes mellitus type 1 or type 2 is related to postprandial insulin rather than glucose levels

AIM

Postprandial platelet activation was related to postprandial insulin rather than glucose levels in a previous meal insulin study in type 2 diabetes mellitus (T2DM). We therefore compared postprandial platelet activation in type 1 (T1DM) patients without insulin secretion and T2DM patients with high postprandial insulin levels.

MATERIAL AND METHODS

Patients with T1DM (n=11) and T2DM (n=12) were studied before and 90min after a standardized meal without premeal insulin. Five T1DM patients volunteered for a restudy with their regular premeal insulin. Platelet activation was assessed by flow cytometry, with and without the thromboxane analogue U46619 or ADP, and by whole blood aggregometry (Multiplate®). Effects of insulin (100μU/mL) in vitro were also studied.

RESULTS

Before the meal, glucose, insulin and platelet activation markers other than platelet-leukocyte aggregates (PLAs) were similar in T1DM and T2DM; PLAs were higher in T1DM. Postprandial glucose levels increased more markedly in T1DM (to 22.1±1.4 vs. 11.2±0.6mmol/L) while insulin levels increased only in T2DM (from 24.4±4.4 to 68.8±12.3μU/mL). Platelet P-selectin expression, fibrinogen binding and PLA formation stimulated by U46619 were markedly enhanced (approximately doubled) and whole blood aggregation stimulated by U46619 was increased (p<0.05 for all) after the meal in T2DM patients but not in T1DM patients. The pilot study with premeal insulin in T1DM patients showed postprandial platelet activation when postprandial insulin levels increased. In vitro insulin mildly activated platelets in both groups.

CONCLUSION

Postprandial platelet activation via the thromboxane pathway is related to postprandial hyperinsulinemia and not to postprandial hyperglycaemia in patients with diabetes.

The Marine-Derived Kinase Inhibitor Fascaplysin Exerts Anti-Thrombotic Activity

Background: The marine-derived kinase inhibitor fascaplysin down-regulates the PI3K pathway in cancer cells. Since this pathway also plays an essential role in platelet signaling, we herein investigated the effect of fascaplysin on thrombosis. Methods: Fascaplysin effects on platelet activation, platelet aggregation and platelet-leukocyte aggregates (PLA) formation were analyzed by flow cytometry. Mouse dorsal skinfold chambers were used to determine in vivo the effect of fascaplysin on photochemically induced thrombus formation and tail-vein bleeding time. Results: Pre-treatment of platelets with fascaplysin reduced the activation of glycoprotein (GP)IIb/IIIa after protease-activated receptor-1-activating peptide (PAR-1-AP), adenosine diphosphate (ADP) and phorbol-12-myristate-13-acetate (PMA) stimulation, but did not markedly affect the expression of P-selectin. This was associated with a decreased platelet aggregation. Fascaplysin also decreased PLA formation after PMA but not PAR-1-AP and ADP stimulation. This may be explained by an increased expression of CD11b on leukocytes in PAR-1-AP- and ADP-treated whole blood. In the dorsal skinfold chamber model of photochemically induced thrombus formation, fascaplysin-treated mice revealed a significantly extended complete vessel occlusion time when compared to controls. Furthermore, fascaplysin increased the tail-vein bleeding time. Conclusion: Fascaplysin exerts anti-thrombotic activity, which represents a novel mode of action in the pleiotropic activity spectrum of this compound.

Current status and future prospects for platelet function testing in the diagnosis of inherited bleeding disorders

Platelets play a crucial role in haemostasis by preventing bleeding at the site of vascular injury. Several defects in platelet morphology and function have been identified and described over the years. Although a range of methodologies is available to assess platelet function, a significant proportion of subjects with bleeding symptoms and normal coagulation parameters still appear to have normal results on platelet function testing. This might suggest that the reason for bleeding is multifactorial and is due to a combination of several minor defects in platelet function and/or other parts of the haemostatic system or might indicate that the currently available platelet function tests do not provide optimal diagnostic power. This review will summarize the established platelet function tests used for diagnosing inherited platelet abnormalities in adults and children, and discuss the newly developed methodologies as well as unmet challenges and potential areas for further improvement in this field.

Prefixation of neutrophils for neutrophil antibody testing

OBJECTIVE

The granulocyte immunofluorescence test based on flow cytometry is still the most commonly used method for detecting antineutrophil antibodies. We questioned whether neutrophil prefixation is necessary for this test.

METHODS

Three pretreatment methods using paraformaldehyde were compared: unfixed, short-fixed (3 minutes 40 seconds), and long-fixed (10 minutes) leukocytes. The mean fluorescence intensity (MFI) of a test sample was divided by the average of negative controls, and this MFI ratio of gated neutrophils or lymphocytes was assessed for its discriminatory value based on the pretreatment method used.

RESULTS

In neutrophil antibody positive (Ab+) sera (n = 7), the MFI ratio of unfixed neutrophils (1.97) was higher than that of short- (1.60, P = 0.004) or long- (1.71, P = 0.203) fixed neutrophils. In HLA Ab+ sera (n = 10), the MFI ratio of short-fixed lymphocytes (8.85) was higher than that of unfixed (6.52, P = 0.120) or long-fixed (3.86, P = 0.055) lymphocytes. In antinuclear Ab+ sera (n = 4), the MFI ratio of unfixed neutrophils (2.04) was higher than that of short- (1.23, P = 0.047) or long- (1.14, P = 0.044) fixed neutrophils.

CONCLUSION

The benefit of a prefixation step depends on the diagnostic purpose. Unfixed neutrophils are more sensitive, but the prefixed neutrophils are more specific. For the diagnosis of autoimmune neutropenia of childhood, prefixation can be omitted to enhance sensitivity.

Platelet activation and platelet-monocyte aggregate formation contribute to decreased platelet count during acute simian immunodeficiency virus infection in pig-tailed macaques

Platelets are key participants in innate immune responses to pathogens. As a decrease in circulating platelet count is one of the initial hematologic indicators of human immunodeficiency virus (HIV) infection, we sought to determine whether decline in platelet number during acute infection results from decreased production, increased antibody-mediated destruction, or increased platelet activation in a simian immunodeficiency virus (SIV)/macaque model. During acute SIV infection, circulating platelets were activated with increased surface expression of P-selection, CD40L and major histocompatibility complex class I. Platelet production was maintained and platelet autoantibodies were not detected during acute infection. Concurrent with a decrease in platelet numbers and an increase in circulating monocytes, platelets were found sequestered in platelet-monocyte aggregates, thereby contributing to the decline in platelet counts. Because the majority of circulating CD16(+) monocytes formed complexes with platelets during acute SIV infection, a decreased platelet count may represent platelet participation in the innate immune response to HIV.

Platelet-neutrophil aggregate formation in blood samples from dogs with systemic inflammatory disorders

OBJECTIVE

To evaluate platelet-neutrophil aggregate (PNA) formation and neutrophil shape as indicators of neutrophil activation in dogs with systemic inflammatory diseases and after blood sample incubation with various platelet and neutrophil agonists.

ANIMALS

20 dogs with systemic inflammatory response syndrome (SIRS) and 10 healthy Beagles.

PROCEDURES

Neutrophils were isolated from blood samples directly after blood sample collection and after incubation of blood samples with phorbol myristate acetate, collagen, adenosine diphosphate, epinephrine, or various concentrations of lipopolysaccharide or arachidonic acid. CD61+ neutrophils as an indicator of PNA formation were evaluated, and neutrophil size and granularity were assessed via flow cytometry.

RESULTS

Dogs with SIRS had more PNA formation, larger neutrophil size, and less granularity relative to control dogs, but no differences were evident when these dogs were grouped by whether they had sepsis (n = 6) or disseminated intravascular coagulation (12). A significant increase in PNA formation occurred after neutrophil incubation with all agonists, and incubation with phorbol myristate acetate elicited the strongest response. Neutrophils increased in size and decreased in granularity after incubation with all agonists except epinephrine. Incubation with lipopolysaccharide or arachidonic acid resulted in a dose-dependent effect on PNA formation and neutrophil shape.

CONCLUSIONS AND CLINICAL RELEVANCE

SIRS appeared to increase the degree of PNA formation and neutrophil shape change. Similar changes after neutrophil incubation with platelet agonists suggested that platelet activation has a role in PNA formation. Additional studies are necessary to determine the clinical importance and diagnostic value of PNA formation in dogs with SIRS and sepsis.

Improved accuracy and reproducibility of enumeration of platelet-monocyte complexes through use of doublet-discriminator strategy

BACKGROUND

Platelet-monocyte complex (PMC) formation is a marker of in vivo platelet activation and may be readily measured by flow cytometry. Due to the high frequency of free platelets relative to monocytes and PMCs, false-positive identification through coincidence remains a significant technical problem.To overcome this problem, we evaluated the use of a doublet-discriminator strategy (DDM) to allow faster sample acquisition whilst significantly reducing aberrant coincidence.

METHODS

Fourteen healthy volunteers and 20 patients with coronary artery disease (CAD) gave arterial and/or peripheral venous blood samples (NaCit). Whole blood was labelled in duplicate with anti-CD61 and anti-CD14 using a standard lyse/wash protocol. One of each paired sample was serially diluted before analysis; the second was analyzed at full concentration but using FL1-width to exclude co-incident platelet and monocyte events. Control experiments were performed with ex vivo thrombin activated samples.

RESULTS

With the DDM use PMC frequencies in the peripheral blood of healthy individuals and in CAD patients fell significantly [6.27% ± 1.77 (mean ± sd) to 2.57% ± 0.99 (P = 0.02)] and from 16.04% (± 11.26) to 7.66% (± 5.18) (P < 0.01), respectively. DDM use significantly reduced the percentage of PMCs in the ex vivo thrombin activated samples (P < 0.05).

CONCLUSIONS

Use of DDM effectively reduces the coincidence and enumerates true PMC in the samples of normal individuals and in patients with CAD and in ex vivo thrombin activated samples.

Exaggerated platelet reactivity to physiological agonists in war veterans with posttraumatic stress disorder

An association between traumatic stress and cardiovascular disease (CVD) is supported by various epidemiological studies. Platelet activation and binding of activated platelets to leukocytes contributes to the pathophysiology of CVD. Evidence of hyperactive sympathetic nervous system, altered expression of platelet α(2)-adrenoreceptors (α(2)AR), and altered platelet adenylate cyclase activity in patients with posttraumatic stress disorder (PTSD) suggest that platelet reactivity in PTSD may be altered as well. We tested whether platelet reactivity to increasing doses of adenosine-diphosphate (ADP), epinephrine (EPI), or their combination differs between war veterans with PTSD (n=15) and healthy controls (n=12). For this purpose, citrated whole blood was incubated with increasing concentrations of ADP (0.1, 1, 10 μM), EPI alone (10 nM, 100 nM, 1000 nM), or EPI (10 nM, 100 nM, 1000 nM) in combination with 0.1 μM ADP. A subset of samples was also incubated with 10 μM yohimbine (YOH), α(2)AR antagonist, to distinguish receptor-specific effects. Platelet CD62P expression and formation of platelet-leukocyte aggregates (PLA) [platelet-monocyte (P-Mo), -lymphocyte (P-Ly), and -neutrophil (P-Ne) aggregates] were measured using three-color flow cytometry. Platelet reactivity was higher in war veterans with PTSD when compared to controls, as determined by greater CD62P expression and formation of PLA in response to ADP alone or in combination with EPI. Platelet reactivity also correlated with the severity of PTSD symptoms. Preliminary experiments with YOH indicate that stress-associated EPI elevations may contribute to platelet activation through a α(2)AR-dependent mechanism. The enhanced platelet reactivity observed in our study may be the underlying mechanism contributing to the development of CVD in PTSD patients.

Influence of treatment with ultralow-dose aspirin on platelet aggregation as measured by whole blood impedance aggregometry and platelet P-selectin expression in clinically normal dogs

OBJECTIVE

To evaluate the influence of treatment with ultralow-dose aspirin (ULDAsp) on platelet aggregation, P-selectin (CD62P) expression, and formation of platelet-leukocyte aggregates in clinically normal dogs.

ANIMALS

18 clinically normal dogs.

PROCEDURES

Studies were conducted before and 24 hours after ULDAsp administration (0.5 mg/kg, PO, q 24 h, for 2 days). Whole blood impedance aggregometry for the assessment of platelet function was performed with sodium citrate-anticoagulated blood and aggregation agonists (ADP at 20, 10, and 5 μmol/L; collagen at 10, 5, and 2 μg/mL). Onset, maximum response, and rate of platelet aggregation were recorded. Flow cytometric assays were configured to detect thrombin-induced CD62P expression and platelet-leukocyte aggregates in EDTA-anticoagulated whole blood. Externalized platelet CD62P and constitutive CD61 (GPIIIa) were labeled with antibodies conjugated to phycoerythrin (PE) and fluorescein isothiocyanate (FITC), respectively. Red blood cell-lysed paraformaldehyde-fixed EDTA-anticoagulated whole blood was dual labeled with CD61-FITC and a panleukocyte antibody (CD18-PE) to characterize platelet-leukocyte aggregates.

RESULTS

ULDAsp significantly delayed platelet aggregation onset with ADP at 20 μmol/L by 54% to 104%, attenuated maximum aggregation with various concentrations of ADP and collagen by ≥ 41%, and slowed aggregation rate with the highest ADP and collagen concentrations by ≥ 39%. Depending on the parameter tested, up to 30% of dogs failed to have an ULDAsp effect. Thrombin stimulation significantly increased CD62P expression in platelets and platelet-leukocyte aggregates, but ULDAsp did not alter basal or thrombin-stimulated CD62P expression.

CONCLUSIONS AND CLINICAL RELEVANCE

ULDAsp treatment of clinically normal dogs impaired platelet aggregation in most dogs, but did not influence CD62P platelet membrane expression.

Vascular effects of ultrafine particles in persons with type 2 diabetes

BACKGROUND

Diabetes confers an increased risk for cardiovascular effects of airborne particles.

OBJECTIVE

We hypothesized that inhalation of elemental carbon ultrafine particles (UFP) would activate blood platelets and vascular endothelium in people with type 2 diabetes.

METHODS

In a randomized, double-blind, crossover trial, 19 subjects with type 2 diabetes inhaled filtered air or 50 µg/m³ elemental carbon UFP (count median diameter, 32 nm) by mouthpiece for 2 hr at rest. We repeatedly measured markers of vascular activation, coagulation, and systemic inflammation before and after exposure.

RESULTS

Compared with air, particle exposure increased platelet expression of CD40 ligand (CD40L) and the number of platelet-leukocyte conjugates 3.5 hr after exposure. Soluble CD40L decreased with UFP exposure. Plasma von Willebrand factor increased immediately after exposure. There were no effects of particles on plasma tissue factor, coagulation factors VII or IX, or D-dimer.

CONCLUSIONS

Inhalation of elemental carbon UFP for 2-hr transiently activated platelets, and possibly the vascular endothelium, in people with type 2 diabetes.

Stability validation of paraformaldehyde-fixed samples for the assessment of the platelet PECAM-1, P-selectin, and PAR-1 thrombin receptor by flow cytometry

Sample fixation for storage and/or transportation represents an unsolved challenge for multicenter clinical trials assessing serial changes in platelet activity, or monitoring various antiplatelet regimens. Whole blood flow cytometry represents a major advance in defining platelet function, although special training and expensive equipment is required. We sought to determine how fixation with 2% paraformaldehyde (PFA), and storage of blood samples over 1 week affects the flow cytometry readings for both intact and thrombin-activating four major surface platelet receptors. Whole blood platelet expression of PECAM-1, P-selectin, PAR-1 inactive receptor (SPAN-12), and cleaved (WEDE-15) epitope was assessed immediately after blood draw, after staining with 2% PFA, and at day 1, 3, 5, and 7. The study was performed in 6 volunteers with multiple risk factors for vascular disease, not receiving any antiplatelet agents. Staining with PFA resulted in a slight decrease of fluorescence intensity, especially for PECAM-1, while antigen expression at day 1, 3 and 5 remains consistent, and highly reproducible. At day 7 there was a small but inconsistent trend towards diminished fluorescence intensity. The platelet data were consistent while validated with the isotype-matched irrelevant antibody. These data suggest that there is a 5 day window to perform final flow cytometry readings of whole blood PFA-fixed inactivated platelet samples. In contrast, thrombin activation cause gradual loss of flow cytometry signal, and cannot be recommended for long-term storage. This is critical logistic information for conducting multicenter platelet substudies within the framework of major clinical trials.

The influence of direct thrombin inhibitors on the formation of platelet-leukocyte aggregates and tissue factor expression

INTRODUCTION

High concentrations of platelet-monocyte aggregates (PMAs) have been found in patients with myocardial infarction (MI). Oral direct thrombin inhibitors (DTIs) are under evaluation as long-term antithrombotic treatment. The aim was to evaluate whether DTIs affect the formation of platelet-leukocyte aggregates, TF expression and procoagulant microparticles (MPs).

MATERIAL AND METHODS

DTIs were added to an experimental whole blood model before platelet activation with thrombin or ADP. The concentrations of PMAs, platelet-granulocyte aggregates (PGAs), the amount of platelets bound per leukocyte and MPs were investigated by flow cytometry. TF mRNA and activity were recorded in all settings. TF activity was evaluated in a MI population treated with or without an oral DTI.

RESULTS

In vitro, thrombin and ADP increased the formation of PMAs and PGAs as well as TF mRNA expression. DTIs reduced the amount platelets bound to monocytes (p=0.02) and to granulocytes (p=0.001) upon thrombin stimulation together with a reduction of TF mRNA. In contrast, the ADP-induced formation of PMAs, PGAs and TF mRNA was not affected by the DTIs. Both thrombin and ADP stimulation increased the amount of TF-expressing MPs, which was effectively inhibited by the DTIs (p=0.02-0.002). In the MI population, the DTI reduced the TF activity (p<0.001).

CONCLUSION

DTIs modulate the formation of PMAs, PGAs and the TF production therein. Together with a reduction of procoagulant MPs, these results may contribute to the clinical benefit found of oral DTIs. Targeting different mechanisms in platelet and coagulation activation may be of importance due to the lack of effect of DTIs on ADP-induced platelet-leukocyte aggregates and TF production.

Elevated plasma concentration of NO and cGMP may be responsible for the decreased platelet aggregation and platelet leukocyte conjugation in platelets hypo-responsive to catecholamines

Impaired responsiveness to epinephrine and other catecholamines (CA) were previously reported in platelets of 20 approximately 30% healthy Japanese and Koreans. In the present study, the possible mechanisms of different responsiveness to CA in platelets of CA hypo-responders (CA-HY) and CA good-responders (CA-GR) were investigated. Increased platelet-leukocyte conjugate (PLC) formations were observed with whole blood of CA-GR than with that of CA-HY in both non-stimulated [mean fluorescence intensity (MFI) values: 1.33 +/- 0.26 vs. 1.16 +/- 0.19] and ADP (MFI: 5.54 +/- 3.46 vs. 2.15 +/- 1.13) or TRAP (MFI: 5.11 +/- 2.32 vs. 3.38 +/- 1.47) activated states. The platelets of CA-GR, when stimulated with ADP (10 microM), released approximately twice the amount of ATP than those of CA-HY (0.88 +/- 0.65 and 0.45 +/- 0.36 nmole, respectively). Nitric oxide (NO) and cyclic guanosine monophosphate (cGMP) levels were significantly higher in non-stimulated PRP of CA-HY than in that of CA-GR (70.3 +/- 24.1 microM and 14.1 +/- 4.9 nM vs. 41.1 +/- 15.8 microM and 6.7 +/- 2.4 nM, respectively). The platelet-monocyte conjugation induced with either ADP or TRAP was significantly reduced in CA-GR with the addition of linsidomine, a NO donor, (MFI: 2.78 +/- 0.43 vs. 3.73 +/- 0.90, or 4.28 +/- 0.95 vs. 5.76 +/- 1.33, respectively). Moreover, the degree of platelet aggregation and the ATP secretion induced by epinephrine in CA-GR were significantly retarded with the addition of either linsidomine or 8-Bromo-cGMP (a cGMP analog) with more substantial effects on ATP release than aggregation. The results suggested that elevated NO and/or cGMP plasma levels may be responsible for the lower platelet aggregation and PLC formation observed in CA-HY than that in CA-GR.

The formation of platelet–leukocyte aggregates varies during the menstrual cycle

Platelet-leukocyte aggregates are considered to play a significant role in blood coagulation and inflammatory processes. We hypothesized that hormonal changes during the menstrual cycle affect the formation of heterotypic aggregates and therefore may constitute cycle-dependent variations of the susceptibility for thromboembolic events and inflammatory disease. We therefore measured platelet-leukocyte interaction by the determination of platelet-leukocyte aggregates (PLA), platelet P-Selectin expression, and platelet fibrinogen receptor activation by PAC-1 binding in 20 healthy women during their menstrual cycle by flow cytometry. The number of platelet-granulocyte aggregates (PGA) and platelet-monocyte aggregates (PMA) was higher at ovulation compared to any other time-point of the menstrual cycle (p = 0.005, p = 0.022, respectively). Likewise, P-Selectin expression peaked on day 14 (p = 0.040). The course of PLA formation during the menstrual cycle followed the course of estrogen levels, strongly suggesting direct effects of estrogen on platelet-leukocyte interaction. The susceptibility to form platelet-leukocyte aggregates that are inducible in vitro by a suboptimal concentration of thrombin receptor activating peptide-6 decreased slightly during the transition from day 1 to 14 (p = 0.040). These data indicate that platelet function varies during particular phases of the normal menstrual cycle.

Tissue factor and IL8 production by P-selectin-dependent platelet-monocyte aggregates in whole blood involves phosphorylation of Lyn and is inhibited by IL10

BACKGROUND

P-selectin and CD40L expressed by activated platelets induce tissue factor (TF) and inflammatory cytokines in monocytes, but little is known of the cellular signaling pathways involved. The anti-inflammatory cytokine IL10 reduces atherosclerotic plaque formation.

OBJECTIVES

To evaluate the importance of P-selectin upon platelet-monocyte aggregate (PMA) formation in thrombin receptor activator peptide (TRAP) stimulated whole blood, the P-selectin-P-selectin glycoprotein ligand (PSGL)-1-induced cellular signaling pathway, and the effects of IL10 on these functions.

METHODS

TF, IL8, and monocyte chemotactic protein-1 (MCP-1) production, PMAs and phosphorylation of Lyn were analyzed in whole blood, purified monocytes, and vitamin D(3)-differentiated U-937 cells stimulated with TRAP or P-selectin with or without IL10. Anti-P-selectin or anti-CD40L antibodies (Abs), Src-kinases inhibitors, SU6656 or PP2, were added in some experiments.

RESULTS

TRAP and P-selectin increased TF, IL8, and MCP-1 mRNA in whole blood and purified monocytes. Anti-P-selectin Ab reduced TRAP-induced PMA formation by 80 +/- 2% (P = 0.001) and production of TF (P = 0.04) and IL8 (P = 0.01). IL10 and SU6656 had no effect on PMA formation, although both significantly reduced TF (P = 0.002 and P = 0.02) and IL8 (P = 0.009 and P = 0.001) mRNA upon TRAP and P-selectin stimulation. Induced Lyn phosphorylation in monocytes was diminished by SU6656 (P = 0.02), anti-P-selectin Ab (P = 0.02), and IL10 (P = 0.03) upon TRAP or P-selectin stimulation. These results were confirmed in the vitamin D(3)-differentiated U-937 cells.

CONCLUSIONS

The formation of PMAs in whole blood was P-selectin-dependent in the long term. P-selectin-PSGL-1-induced TF and IL8 expression through Lyn phosphorylation, and part of the inhibitory effect of IL10 depends on reduced phosphorylation.

Cell proliferation, apoptosis and mitochondrial damage in rat B50 neuronal cells after cisplatin treatment

OBJECTIVES

Cisplatin (cisPt) is used as a chemotherapeutic agent for the treatment of a variety of human tumours; more recently, it has been demonstrated that tumour cell exposure to cisPt ultimately results in apoptosis, but the mechanism by which nuclear cisPt/DNA generates the cytoplasmic cascade of events involved has not been clarified. We have investigated the effects of cisPt on proliferation in the neuronal cell line B50, with particular attention being given to understand whether mitochondria are a target of cisPt and their involvement in the apoptotic process.

MATERIALS AND METHODS

Rat neuronal B50 cells were used to investigate the mechanisms of cisPt-induced cytotoxicity; this line has been used as a model system for neurotoxicity in vivo.

RESULTS

Changes in proliferation, induction of apoptosis, activation of caspase-3 and DNA fragmentation were observed in the cells, as well as morphological and biochemical alterations of mithocondria. Activation of caspase-9 confirmed that mitochondria are a target of cisPt.

CONCLUSION

CisPt exerts cytotoxic effects in the neuronal B50 cell line via a caspase-dependent pathway with mitochondria being central relay stations.

Platelet-lymphocyte cross-talk

Platelets and lymphocytes reciprocally regulate mutual functions, i.e., platelet-lymphocyte cross-talk. The heterotypic interactions have emerged as important regulatory mechanisms in the pathophysiological processes of thrombosis, inflammation, immunity, and atherosclerosis. Platelets influence lymphocyte function via direct cell-cell contact and/or soluble mediators. Hence, platelets enhance adhesion and cell migration of T(H), T cytolytic (T(C)), NK, and B cells. Platelets affect other functional aspects of lymphocyte subpopulations in a complex manner. They may attenuate cytokine secretion and immunosuppressive responses of T(H) cells and enhance T(C) cell proliferation and cytotoxicity. Platelets promote isotype shifting and antibody production of B cells but ameliorate cytolytic activity of NK cells. On the other hand, lymphocytes can also regulate platelet aggregation and secretion, as well as the effector cell function of platelets in immune defense. The two cell types collaborate in transcellular phospholipid metabolism, CD40-CD40 ligand-mediated intercellular signaling, and their involvements in atherogenesis. The research perspectives of platelet-lymphocyte cross-talk have also been addressed.

[Experimental Application of Whole Blood Flow Cytometry to HLA Crossmatch for Renal Transplantation.]

BACKGROUND

The lymphocytes separated from whole blood are used in HLA flow cytometry crossmatch (FCXM) for renal transplantation. In this study, the methodology of whole blood flow cytometry was applied to FCXM, omitting lymphocyte separation step.

METHODS

In the 20 cases (including positive 5 cases) of T cell FCXM for renal transplantation, the standard assay using the separated mononuclear cells (MNC) was compared with the two variant assays using whole blood. In the latter assay, the donor whole blood was incubated with the excessive recipient serum. The red cells were lysed (lysed whole blood, LWB). Otherwise, instead of red cell lysis, the signals of T cells among whole blood (WB) were acquired using fluorescence triggering. The sample/negative control mean fluorescence intensity (MFI) ratio was calculated for the interpretation.

RESULTS

The MFI ratio of the 20 cases by MNC, LWB and WB assay were 4.9+/-8.1, 5.4+/-9.7 and 4.8+/-7.8, respectively. Both LWB and WB assay were not significantly different from MNC assay (P= 0.313, 0.831, respectively, paired t-test). The qualitative determinations were concordant in all cases, except for one case which was weakly positive with MFI ratio 2.2 by LWB assay.

CONCLUSIONS

The assays using whole blood were comparable to the standard assay in FCXM for renal transplantation. This study indirectly supports that the variant methods can be used reliably in the case of the MNC preparation erroneously mixed with other blood cells.

Circulating platelet-leukocyte aggregates: a marker of microvascular injury in diabetic patients

Diabetes is associated with multiple disorders including metabolic, cellular and blood disturbances leading to vascular complications. Increased circulating levels of platelet-leukocyte aggregates (PLA) have been described in several thrombotic diseases. In this study, we have evaluated circulating PLA in diabetic patients and we have investigated whether they may be a marker of vascular complications. Using flow cytometry assay, we have quantified PLA percentages in 65 diabetics including 20 patients with type I and 45 with type II diabetes, and 25 healthy subjects. Specific labelling identified platelet-polymorphonuclear aggregates (PPA) and platelet-monocyte aggregates (PMA). We have observed a significant increase of PPA and PMA levels in diabetics (22+/-12% and 45+/-18%, respectively) compared to controls (7+/-4% and 19+/-10%, respectively) (p<0.01). However, both PPA and PMA values were similar in the two diabetes types. Circulating PPA and PMA were significantly enhanced in diabetics with vascular lesions (PPA: 24+/-13%; PMA: 50+/-18%) than in diabetics without vascular lesions (PPA: 18+/-8%; PMA: 38+/-15%) (p<0.05 and p<0.01). Patients with PPA>18% and/or PMA>38% showed a more important vascular injury (OR: 6; 95% CI: 1.6-23). Increased PMA circulating rate is particularly correlated to retinopathic injury (OR: 19; 95% CI: 2.3-154). Our findings established a relationship between increased circulating PLA levels, particularly PMA, and the incidence of microvascular complications in diabetes. They reinforce the concept of pro-inflammatory cells involvement in diabetic retinopathy pathogenesis and their link with thrombotic process.

Impact of coincidence on granulocyte-platelet complex determination by flow cytometry is evaluated by a novel computer simulation model of coincidence

Cell complexes composed of two different cells labeled with different fluorophores can be detected as double positive events in the flow cytometer. Double positivity can originate not only from real complexes but from non-interacting coinciding cells as well. Coincidence has a high impact on the determination of the amount of platelet-granulocyte complexes since platelet concentration is in the orders of magnitude higher than that of the granulocytes. A computer model has been developed to simulate coincidence in the flow cytometer to reveal the contribution of coincidence to the overestimation of the total amount of platelet-granulocyte complexes. Mixtures of non-interacting fluorescent beads as well as EDTA-anticoagulated blood samples were analyzed in the flow cytometer. An excellent fit was found between computer simulated and measured data pairs. Bead mixture in the flow cytometer and simulation of that resulted in 37.3+/-1.3 and 35.7+/-0.6% double positivity, respectively. 30.2+/-4.3% double positivity was measured for EDTA-anticoagulated blood samples while simulation of that resulted in 28.3+/-0.6%. Double positivity attributed to platelet-granulocyte complexes in slightly diluted blood samples might originate in coincidence and not from true complexes.

The effects of chronic tea intake on platelet activation and inflammation: A double-blind placebo controlled trial

BACKGROUND

Tea drinking appears to protect against the development of coronary heart disease (CHD), but the mediating pathways are uncertain. We studied the effects of 6 weeks of black tea or placebo on platelet activation, C-reactive protein (CRP), total antioxidant status, and soluble (s) P-Selectin in a randomized double-blind trial.

METHODS

Healthy non-smoking men aged 18-55 years were randomized to black tea (N=37) or placebo (N=38) following a 4-week washout period during which they drank no tea, coffee or caffeinated beverages, but consumed caffeinated placebo tea. Bloods were drawn after 6 weeks of treatment. Platelet activation was assessed by measuring leukocyte-platelet aggregates using whole blood flow cytometry.

RESULTS

Following treatment, the tea group had fewer monocyte-platelet aggregates (means 5.84 versus 6.60%, P=0.027), neutrophil-platelet aggregates (P=0.017), total leukocyte-platelet aggregates (P=0.027), and lower plasma C-reactive protein (means 0.76 versus 0.97 mg/L, P=0.05) than the placebo group. There were no differences in total antioxidant status or soluble P-Selectin.

CONCLUSIONS

Chronic tea consumption reduces platelet activation and plasma C-reactive protein in healthy men. Effects cannot be attributed to observer bias or lifestyle confounders. These effects of tea may contribute to sustained cardiovascular health.

PDMS content affects in vitro hemocompatibility of synthetic vascular grafts

An unsolved problem when employing small-diameter vascular grafts for aorto-coronary by-pass and peripheral reconstruction is the early thrombotic occlusion. The PEtU-PDMS is a new elastomeric material, composed of poly(ether)urethane and polydimethylsiloxane, synthesized to realize grafts with improved hemocompatibility characteristics. In order to investigate the effect of PDMS content on hemocompatibility, three different percentages of PDMS containing grafts (10, 25 and 40) were evaluated. Grafts realized with Estane 5714-F1 and silicone medical grade tubes were used as references. The hemocompatibility was investigated by an in vitro circuit in which human anticoagulated blood was circulated into grafts by a peristaltic pump modified to obtain a passive flow. For each experiment, 40 cm length graft was closed into a circular loop and put in rotation for 2 h at 37 degrees C. At the end of the experiments different parameters regarding platelet adhesion and activation were evaluated: circulating platelets count, beta-thromboglobulin release, platelet CD62P expression and amount of monocyte-platelet conjugates. PEtU-PDMS grafts with 25 and 40% of PDMS induced the lowest platelet adhesion, plasma level of beta-TG and amount of monocyte-platelet conjugates. No significative variations were observed in CD62P expression. In conclusion, PDMS content significatively affects blood-graft surface interaction, in fact higher PDMS percentage containing grafts showed the best in vitro hemocompatibility.

An increased platelet–leukocytes interaction at the culprit site of coronary artery occlusion in acute myocardial infarction: A pathogenic role for “no-reflow” phenomenon?

BACKGROUND

Distal protection devices have been shown to reduce the incidence of "no flow" phenomenon during primary percutaneous coronary intervention (PCI). So far, it has not been well clarified which mechanism is mainly involved in distal coronary protection.

AIM

To investigate the activation state of leukocytes and platelets locally present within the blood from the site of coronary occlusion.

METHODS

Ten patients with acute myocardial infarction (AMI) underwent primary PCI with an embolization protection device and aspiration catheter (PercuSurge GuardWire) were included. The following functional parameters: a) monocyte and neutrophils surface molecules; b) platelet surface activatory antigens; c) leukocytes-platelet conjugates were studied by flow cytometry in blood obtained from the site of coronary occlusion and from peripheral femoral artery.

RESULTS

The leukocyte-platelet adhesion index was significantly higher in the aspirated blood at the site of coronary occlusion than in the peripheral arterial blood for both monocytes (0.226+/-0.04 vs. 0.084+/-0.01; p=0.004) and neutrophils (1.372+/-0.3 vs. 0.524+/-0.1; p=0.02). Moreover, the volume of coaggregates exhibited a significant increase in coronary blood for both populations (p=0.02 for monocytes and for neutrophils). Interestingly, a significant up-regulation of the adhesive molecule CD18 was observed in coronary blood respect to systemic circulation either in monocytes (p=0.01) than in neutrophils (p=0.003). A significant up-regulation of monocyte (HLA-DR) and neutrophil (CD66b) activatory molecules expression was also observed in the aspirated coronary compared to peripheral artery blood (p=0.02 and p=0.03 for HLA-DR and CD66b, respectively).

CONCLUSIONS

These data indicate an increased leukocyte-platelet functional interaction in AMI at the site of plaque rupture relative to the systemic circulation, which may be one of the pathogenetic mechanisms responsible for myocardial "no-reflow" phenomenon.

Baseline level of platelet-leukocyte aggregates, platelet CD63 expression, and soluble P-selectin concentration in patients with posttraumatic stress disorder: a pilot study

Platelets may have an important role in the development of cardiovascular disease (CVD) as a result of chronic stress. We conducted a pilot study to evaluate the effect of posttraumatic stress disorder (PTSD) on baseline platelet activation. Platelet-leukocyte aggregates (PLA) and CD63 expression were measured by flow cytometry, and soluble (s)P-selectin concentration was determined in sera of 20 Croatian male combat veterans with PTSD and 20 healthy civilians. Groups were matched in sex, age, body mass index (BMI) and traditional CVD risk factors. Our data showed no differences in measured parameters. Other platelet activation markers should be determined and a larger sample size used in future studies.

Spurious counts and spurious results on haematology analysers: a review. Part I: platelets

The widespread use of haematology analysers (HA) has led to a major improvement of cellular haematology, because of quick and accurate results found in most instances. However, in several situations, spurious results are observed. Inadequate blood samples, situations induced by the anticoagulant(s) used, peculiar changes related to the pathology in the patient, and technical considerations about performances of the various HA must be considered. Spurious thrombocytopenia occurs in several circumstances related to the presence of ethylenediamine tetra-acetic acid (EDTA) used as the anticoagulant. Mechanism of EDTA-dependent platelet (PLT) agglutination is related to circulating (auto)antibodies directed against normally hidden epitope(s) in the glycoprotein alpha IIb/beta IIIa complex from PLT membrane exposed only in the presence of EDTA. Other spuriously low PLT counts may be related to EDTA, including PLT rosetting around white blood cells (WBC; satellitism) and PLT-WBC aggregates, but mechanisms responsible for those latter phenomena are less well known. Spurious increase of PLT count may be related to several situations, including fragmented red blood cells, cytoplasmic fragments of nucleated cells, cryoglobulins, bacteria or fungi, and lipids. Flags generated in several of these situations alert the operator on possible abnormal findings and may identify the problem. Analysing only PLT parameters is not sufficient: in many situations the WBC differential scattergram is of crucial help for flagging. Flags generated depend on the software version on the HA used, the performance in detecting the same anomalies may differ according to which analyser is used, even those from the same manufacturer. Operators must be aware of the characteristics of their analyser and be able to recognize and circumvent anomalous results.

Granulocyte– and monocyte–platelet adhesion index in coronary and peripheral blood after extracorporeal circulation and reperfusion

BACKGROUND

Neutrophil-granulocyte and mononuclear-cell functional changes occur during cardiopulmonary bypass and cardiovascular surgery. In particular, leukocyte-platelet interaction, leading to generation of heterotypic coaggregates, represents an amplification mechanism of the local inflammatory response and tissue damage.

METHODS

Samples of 20 patients were drawn from venous coronary sinus before cardioplegic arrest and immediately after reperfusion, as well as from peripheral blood at 5 and 24 h postoperatively. The granulocyte and monocyte surface expression of CD162, CD15s, CD18, and CD11b were quantified by flow cytometry at the different times. Parallel variations of circulating leukocyte-platelet conjugates (percentages) and a derived (cell number-normalized) leukocyte-platelet adhesion index were measured using a combination of antibodies against CD45, CD14, and CD41a. The evaluation of platelet functional state was carried out using antibodies against CD62P (P-selectin) and PAC-1.

RESULTS

Monocyte and granulocyte cell number increased markedly in coronary blood at reperfusion and in peripheral blood postoperatively when compared with measurements done before cardioplegia. A very different course characterized the changes of the leukocyte-platelet adhesion index with respect to the variations of circulating leukocyte-platelet coaggregates (percentages). Leukocyte molecules expression showed no significant variations for CD15s on both the leukocyte subsets, while a significant up-modulation for CD162 was observed on monocytes at 24 h after extracorporeal circulation (P = 0.0002), and for CD11b on granulocytes at 5 h postoperatively (P = 0.033). A loss of CD162 expression was observed in coronary blood at reperfusion (P = 0.0038) on granulocytes, associated to a down-modulation of CD18 (P = 0.0033) and CD11b (P = 0.0184) in peripheral blood at 24 h postoperatively. No significant up-regulation of platelet activatory molecules expression was found at coronary reperfusion, as well as postoperatively in the peripheral blood, when compared with the before-cardioplegia derived data.

CONCLUSIONS

The over time variations of a normalized leukocyte-platelet adhesion index seem to reflect the cumulative leukocyte-platelet functional interaction more accurately than the parallel measurements of cellular conjugates. The absence of platelet activation suggests that the leukocyte membrane modifications play a main role in controlling the formation and stability of heterotypic leukocyte-platelet coaggregates after cardiac surgery with extracorporeal circulation.

Detection of activated platelets in canine blood by use of flow cytometry

OBJECTIVE

To evaluate whether markers of platelet activation, including P-selectin expression, phosphatidylserine exposure, platelet-leukocyte aggregates, and microparticle formation, could be measured in nonstimulated and stimulated canine blood samples and develop a standardized protocol for detection of activated platelet markers in canine blood.

SAMPLE POPULATION

Blood samples from 10 dogs.

PROCEDURE

Platelet activation was determined by flow cytometric measurement of platelets with P-selectin expression, platelet-leukocyte aggregates, platelet microparticles, and platelets with phosphatidylserine exposure. Changes in specific markers of platelet activation in nonstimulated versus stimulated samples were assessed by use of varying concentrations of 2 platelet agonists, platelet-activating factor (PAF) and adenosine diphosphate. Flow cytometry was used to detect platelet CD61 (glycoprotein IIIa), CD62P (P-selectin), and the leukocyte marker CD45. Annexin V was used to identify exposed phosphatidylserine.

RESULTS

A significant difference was detected in the percentages of platelets with P-selectin, plateletleukocyte aggregates, microparticles, and platelets with annexin V exposure (phosphatidylserine) in samples stimulated with 10nM PAF versus the nonstimulated samples, with platelet-leukocyte aggregates having the greatest difference.

CONCLUSIONS AND CLINICAL RELEVANCE

Platelet activation is essential for thrombus formation and hemostasis and may be potentially useful for evaluation of dogs with suspected thromboembolic disease. Prior to development of a thrombotic state, a prothrombotic state may exist in which only a small number of platelets is activated. Identification of a prothrombotic state by use of activated platelets may help direct medical intervention to prevent a thromboembolic episode.

Intravascular neutrophil activation due to carbon monoxide poisoning

RATIONALE

We hypothesized that platelet-neutrophil interactions occur as a result of acute carbon monoxide (CO) poisoning, and subsequent neutrophil activation triggers events that cause neurologic sequelae.

OBJECTIVES

To identify platelet-neutrophil interactions and neutrophil activation in patients and in animal models, and to establish the association between these intravascular events and changes linked to CO-mediated neurologic sequelae in an animal model.

MEASUREMENTS AND MAIN RESULTS

Blood was obtained from 50 consecutive patients. Abnormalities were variable depending on the carboxyhemoglobin level at study admission and duration of CO exposure. Platelet-neutrophil aggregates were detected and plasma myeloperoxidase (MPO) concentration was significantly elevated in those with confirmed CO poisoning. Among patients exposed to CO for over 3 h, flow cytometry scans of neutrophils revealed increased surface expression of CD18 and, in some groups, MPO on the cell surface. Animal models revealed consistent evidence of platelet-neutrophil aggregates, neutrophil activation and surface MPO, and plasma MPO elevation. MPO was deposited along the brain vascular lining and colocalized with nitrotyrosine. CO poisoning caused abnormalities in the charge pattern of myelin basic protein (MBP), changes linked to adaptive immunologic responses responsible for neurologic sequelae in this model. Changes did not occur in thrombocytopenic rats, those receiving tirofiban to inhibit platelet-neutrophil interactions, or those receiving L-nitroarginine methyl ester to inhibit nitric oxide synthesis. Alterations in MBP did not occur in CO-poisoned knockout mice lacking MPO.

CONCLUSIONS

Acute CO poisoning causes intravascular neutrophil activation due to interactions with platelets. MPO liberated by neutrophils mediates perivascular oxidative stress, which is linked to immune-mediated neurologic sequelae.

Venous hypertension induces increased platelet reactivity and accumulation in patients with chronic venous insufficiency

The objective of this study was to determine whether there are changes in platelet activation and rheology in patients with chronic venous insufficiency (CVI) and what their impact is on this disease. Anticoagulated peripheral venous blood collected from 21 patients with CVI and 13 normal control subjects in different bodily positions was incubated either with 0.5 mumol/L adenosine diphosphate (ADP) or without agonist and analyzed by whole blood flow cytometry. Soluble P-selectin was analyzed in obtained sera by enzyme-linked immunosorbent assay. Platelet count was determined by a whole blood analyzer. Circulating platelets were more reactive to stimulation with 0.5 mumol/L ADP in patients with CVI compared with control subjects. There was no statistically significant change in platelet activation without ADP and the level of soluble P-selectin as a function of posture. Under simulated venous hypertension, platelet accumulation was observed in patients with CVI. Patients with CVI had increased platelet reactivity and accumulation during orthostasis, suggesting this might be a contributory factor to CVI pathogenesis.

High glucose levels enhance platelet activation: involvement of multiple mechanisms

Diabetes mellitus (DM) and hyperglycaemia are associated with platelet activation. The present study was designed to investigate how high glucose levels influence platelet function. Fasting human blood was incubated with different concentrations of D-glucose (5, 15 and 30 mmol/l) and other sugars without or with in vitro stimuli. Platelet activation was monitored by whole blood flow cytometry. High glucose levels enhanced adenosine diphosphate (ADP)- and thrombin receptor-activating peptide (TRAP)-induced platelet P-selectin expression, and TRAP-induced platelet fibrinogen binding. Similar effects were seen with 30 mmol/l L-glucose, sucrose and galactose. Hyperglycaemia also increased TRAP-induced platelet-leucocyte aggregation. Protein kinase C (PKC) blockade did not counteract the enhancement of platelet P-selectin expression, but abolished the enhancement of TRAP-induced platelet fibrinogen binding by hyperglycaemia. Superoxide anion scavenging by superoxide dismutase (SOD) attenuated the hyperglycaemic enhancement of platelet P-selectin expression, but did not counteract the enhancement of TRAP-induced platelet fibrinogen binding. Hyperglycaemia did not alter platelet intracellular calcium responses to agonist stimulation. Blockade of cyclo-oxygenase (COX), phosphotidylinositol-3 (PI3) kinase, or nitric oxide synthase, or the addition of insulin did not influence the effect of hyperglycaemia. In conclusion, high glucose levels enhanced platelet reactivity to agonist stimulation through elevated osmolality. This occurred via superoxide anion production, which enhanced platelet P-selectin expression (secretion), and PKC signalling, which enhanced TRAP-induced fibrinogen binding (aggregablity).

Platelet-lymphocyte conjugation differs between lymphocyte subpopulations

BACKGROUND

Platelets can bind to, and thereby influence, lymphocyte function.

OBJECTIVE

The propensities of different lymphocyte subpopulations to form platelet-lymphocyte conjugates/aggregates (P-Lym) was investigated using four-color whole blood flow cytometry.

RESULTS

P-Lym constituted approximately 3% of circulating lymphocytes. Platelet conjugation was most common among large (monocyte-sized) lymphocytes. Platelet activation by ADP slightly increased platelet-T-cell conjugation, mainly to T-cytolytic (Tc) cells, but markedly elevated platelet-natural killer (NK)-cell conjugation. T-cell activation by phytohemagglutinin increased heterotypic conjugation among both T-helper (TH) and Tc cells, whilst NK-cell activation by interleukin-2 affected platelet-NK-cell aggregation little. Neither platelet activation nor lipopolysaccharides-induced B-cell activation enhanced platelet-B-cell aggregation. Activation-dependent heterotypic conjugation was mainly found among large cells, with increased percentages of conjugated cells and more platelets bound per lymphocyte. P-Lym formation initiated by platelet activation was abolished by P-selectin blockade, and tended to be reduced by inhibition of GPIIb/IIIa, CD11b, or CD40L. P-Lym formation initiated by lymphocyte activation was partially inhibited by each of these blocking agents, but more markedly inhibited when the blocking agents were combined.

CONCLUSIONS

Platelets selectively bind to larger and activated lymphocytes. T-lymphocyte activation enhances platelet-T-cell aggregation. Platelet activation enhances platelet-Tc aggregation slightly and platelet-NK-cell aggregation markedly, while cellular activation affects platelet-B-cell aggregation little. P-selectin ligation is essential, but GPIIb/IIIa, CD40L, and CD11b also contribute to the heterotypic conjugation.

Investigation of platelet glycoprotein IIIa polymorphism using flow cytometry in patients with rheumatoid arthritis

OBJECTIVES

Previous work has shown that the human platelet antigen (HPA) 1b polymorphism of platelet glycoprotein IIIa (GPIIIa) is implicated in the development of ischaemic vascular disease. HPA1b positive platelets have a lower threshold for activation and may exert a greater thrombotic tendency than those without the 1b allele. However, platelets heterozygous for the polymorphism are also more sensitive to aspirin than those homozygous for the 1b allele, which have a similar sensitivity to those without the 1b allele. A flow cytometric method has become available to identify this polymorphism. The aim of our study was to evaluate the use of this assay in patients with rheumatoid arthritis (RA) and to determine the incidence of the 1b allele in these patients. We also compared platelet aggregation and platelet/white blood cell interaction in patients with or without this polymorphism.

METHODS

We enrolled 99 patients and measured platelet aggregation in whole blood and platelet-rich plasma (prp), platelet/white blood cell interaction and C-reactive protein (CRP).

RESULTS

Thirty-four of the 99 patients were unsuitable for analysis because their baseline expression of GPIIIa was outwith the normal range, making the results outwith the limits of the flow cytometric method. The incidence of the 1b allele in the patients was 29%, with incidence being higher in females, although this failed to reach statistical significance. The number of circulating platelet aggregates and adenosine diphosphate (ADP)-induced aggregation in prp was significantly higher in those patients with the 1b allele.

CONCLUSIONS

This method may be of use as an initial screening test.

Pathophysiological processes underlying emotional triggering of acute cardiac events

Acute negative emotional states may act as triggers of acute coronary syndrome (ACS), but the biological mechanisms involved are not known. Heightened platelet activation and hemodynamic shear stress provoked by acute stress may contribute. Here we investigated whether patients whose ACS had been preceded by acute anger, stress, or depression would show heightened hemodynamic and platelet activation in response to psychophysiological stress testing. We studied 34 male patients an average of 15 months after they had survived a documented ACS. According to an interview conducted within 5 days of hospital admission, 14 men had experienced acute negative emotion in the 2 h before symptom onset, and 20 men had not experienced any negative emotion. Hemodynamic variables and platelet activation were monitored during performance of challenging color-word interference and public speaking tasks and over a 2-h poststress recovery period. The emotion trigger group showed significantly greater increases in monocyte-platelet, leukocyte-platelet, and neutrophil-platelet aggregate responses to stress than the nontrigger group, after adjusting for age, body mass, smoking status, and medication. Monocyte-platelet aggregates remained elevated for 30 min after stress in the emotion trigger group. The emotion trigger group also showed poststress delayed recovery of systolic pressure and cardiac output compared with the nontrigger group. These results suggest that some patients with coronary artery disease may be particularly susceptible to emotional triggering of ACS because of heightened platelet activation in response to psychological stress, coupled with impaired hemodynamic poststress recovery.

Platelets, coronary heart disease, and stress

Coronary heart disease is the leading cause of death in Western society, and its development is associated with chronic stress and other psychosocial factors. Atherosclerosis, the disorder underlying this disease, is an inflammatory process in which leukocytes interact with structurally intact but dysfunctional endothelium of the arteries. Platelets play a key role in this process by binding to leukocytes and promoting their recruitment to the endothelium. Platelet-leukocyte interactions also stimulate the release of pro-inflammatory and pro-thrombotic factors which promote atherosclerosis. Elevated circulating levels of platelet-leukocyte aggregates have been reported in cardiac patients and in individuals of low socioeconomic status, a factor associated with chronic psychological stress. Increased platelet activation has also been observed in individuals prone to depression or hostility, and in people subject to high levels of work stress. Acute psychological stress increases circulating platelet-leukocyte aggregates in healthy individuals and this effect is prolonged in cardiac patients. Platelet activation may be a mechanism linking psychosocial stress with increased coronary risk, and may also play a role in the emotional triggering of acute coronary syndromes in patients with advanced coronary disease.