Changes in platelet membrane glycoproteins and platelet-leukocyte interaction during hemodialysis

Extracellular vesicles: biomarkers and regulators of vascular function during extracorporeal circulation

Extracellular vesicles (EVs) are generated at increased rates from parenchymal and circulating blood cells during exposure of the circulation to abnormal flow conditions and foreign materials associated with extracorporeal circuits (ExCors). This review describes types of EVs produced in different ExCors and extracorporeal life support (ECLS) systems including cardiopulmonary bypass circuits, extracorporeal membrane oxygenation (ECMO), extracorporeal carbon dioxide removal (ECCO₂R), apheresis, dialysis and ventricular assist devices. Roles of EVs not only as biomarkers of adverse events during ExCor/ECLS use, but also as mediators of vascular dysfunction are explored. Manipulation of the number or subtypes of circulating EVs may prove a means of improving vascular function for individuals requiring ExCor/ECLS support. Strategies for therapeutic manipulation of EVs during ExCor/ECLS use are discussed such as accelerating their clearance, preventing their genesis or pharmacologic options to reduce or select which and how many EVs circulate. Strategies to reduce or select for specific types of EVs may prove beneficial in preventing or treating other EV-related diseases such as cancer.

A Clinical Study to Assess the Effect of Heparin in Dialyzer Rinsing Solutions

The solution usually recommended for rinsing the blood side, which is an indispensable step in preparing a dialyzer for hemodialysis (HD), contains saline and heparin. The heparin used for rinsing is said to reduce the thrombogenic properties of the dialysis membrane and, hence, also the need for systemic heparinization during the whole procedure. The aim of our study was to establish whether this postulate also applies to polysulphone steam-sterilized dialyzers. To do so, 16 patients on long-term dialysis were randomized into two groups of eight. One group was subsequently treated with polysulphone low-flux dialyzers (F6HPS), the other with polysulphone high-flux dialyzers (F60S). Both groups were examined, in a crossover manner during HD using a dialyzer previously rinsed with 1000 ml of saline plus 2,000 IU of heparin, and during HD using a dialyzer previously rinsed with 500 ml of saline without heparin. Except for the rinsing, HD conditions were completely identical. Blood obtained before HD, and at 15, 60 and 240 min of HD at the dialyzer inlet, was used to determine the activated partial thromboplastin time (to test heparinization control), the thrombin-antithrombin III complex (ELISA, to evaluate coagulation system activation), platelet factor 4 (ELISA, a substance with antiheparin activity), and platelet count. None of the above parameters showed, at any of the collecting intervals, a statistically significant difference between HD with and without heparin with a reduced volume of rinsing solution, or between HD using low- and high-flux dialyzers. It is concluded that heparin used to rinse polysulphone dialyzers before HD has no effect on blood coagulation or on the need for heparin during the procedure.

State-of-the-Art-Review: Microvesicles in Blood Components: Laboratory and Clinical Aspects

There is ample evidence for the presence of microvesicles (MV) of different sizes and functions in various blood components. A variety of mechanisms have been proposed for the formation of MV. These include mechanical injury, shear stress, cell activation, activation of complements, hypoxia, and the cell aging process. While MV share many biological properties and surface receptors of their parental cells, they demonstrate significant differences in membrane asymmetry of the inner membrane phospholipid, in particular phosphatidylserine (PS). This provides high-affinity binding sites for the components of the prothrombinase complex. To what extent these MV contribute to hemostatic effectiveness, immudomodulation, and some untoward effects of the transfused blood components remains to be fully elucidated. Several methods for qualitative and semiquantitative characterization of MV are now available. Although in most cases it is necessary to separate MV from the intact cells for improved characterization, recent advances in flow cytometry make it possible to accurately differentiate MV in the presence of their parental cells on the basis of light scattering and fluorescent intensity. This review focuses on four main areas of MV in blood components: (1) the proposed mechanisms of platelet vesiculation, (2) factors influencing the formation of MV, (3) laboratory analysis of MV, and (4) the clinical impact of the presence of MV in blood components. Key Words: Microvesicte—Vesicutation—Biood component—Ptatelets—Transfusion.

Elevated levels of procoagulant plasma microvesicles in dialysis patients

Cardiovascular (CV) death remains the largest cause of mortality in dialysis patients, unexplained by traditional risk factors. Endothelial microvesicles (EMVs) are elevated in patients with traditional CV risk factors and acute coronary syndromes while platelet MVs (PMVs) are associated with atherosclerotic disease states. This study compared relative concentrations of circulating MVs from endothelial cells and platelets in two groups of dialysis patients and matched controls and investigated their relative thromboembolic risk. MVs were isolated from the blood of 20 haemodialysis (HD), 17 peritoneal dialysis (PD) patients and 20 matched controls. Relative concentrations of EMVs (CD144(+ ve)) and PMVs (CD42b(+ ve)) were measured by Western blotting and total MV concentrations were measured using nanoparticle-tracking analysis. The ability to support thrombin generation was measured by reconstituting the MVs in normal plasma, using the Continuous Automated Thrombogram assay triggered with 1µM tissue factor. The total concentration of MVs as well as the measured sub-types was higher in both patient groups compared to controls (p<0.05). MVs from HD and PD patients were able to generate more thrombin than the controls, with higher peak thrombin, and endogenous thrombin potential levels (p<0.02). However there were no differences in either the relative quantity or activity of MVs between the two patient groups (p>0.3). Dialysis patients have higher levels of circulating procoagulant MVs than healthy controls. This may represent a novel and potentially modifiable mediator or predictor of occlusive cardiovascular events in these patients.

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.

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.

Clinical outcomes of patients with diabetic nephropathy randomized to clopidogrel plus aspirin versus aspirin alone (a post hoc analysis of the clopidogrel for high atherothrombotic risk and ischemic stabilization, management, and avoidance [CHARISMA] trial)

No prospective randomized trial has specifically examined the long-term outcomes of clopidogrel use in patients with chronic kidney disease. This study aimed to determine the risks and benefits of long-term clopidogrel administration in patients with diabetic nephropathy, the most common form of chronic kidney disease. We performed a post hoc analysis of the CHARISMA trial, which randomly assigned patients without active acute coronary syndrome, but with established atherosclerotic disease (symptomatic) or multiple risk factors for atherosclerotic disease (asymptomatic), to clopidogrel plus aspirin versus placebo plus aspirin. All CHARISMA patients (n = 15,603) were separated into the 3 groups: nondiabetic patients, diabetic patients without nephropathy, and diabetic patients with nephropathy. Within each group, outcomes of patients randomly assigned to clopidogrel were compared with those of patients randomly assigned to placebo. Outcomes in the prespecified CHARISMA subgroups of asymptomatic and symptomatic patients were also compared with respect to study drug assignment and nephropathy status. Patients with nephropathy who received clopidogrel had no difference in bleeding, but experienced significantly increased cardiovascular (CV) and overall mortality compared with those randomly assigned to placebo. There were no differences in bleeding, overall mortality, or CV mortality for nondiabetic or diabetic patients without nephropathy who received clopidogrel versus placebo. In the asymptomatic cohort, patients with nephropathy randomly assigned to clopidogrel had significantly increased overall and CV mortality compared with placebo, whereas asymptomatic patients without nephropathy randomly assigned to clopidogrel had no significant mortality difference compared with placebo. In conclusion, this post hoc analysis suggested that clopidogrel may be harmful in patients with diabetic nephropathy. Additional studies are needed to investigate this possible interaction.

Differential effects of dialysis and ultrafiltrate from individuals with CKD, with or without diabetes, on platelet phosphatidylserine externalization

Individuals with chronic kidney disease (CKD) and/or diabetes mellitus (DM) are at increased risk of cardiovascular events and have elevated externalization of phosphatidylserine (PS; which propagates thrombus formation) in a small subpopulation of platelets. The purpose of this study was to examine the effect of 1) removing uremic toxins by hemodialysis on PS externalization in patients with either CKD or CKD and DM and 2) ultrafiltrate (UF) from these individuals on PS externalization in healthy platelets. PS externalization was quantified by a fluorescence-activated cell sorter using annexin V in platelet-rich plasma. PS externalization was elevated threefold in CKD patients and returned to basal values during 3-h hemodialysis. In contrast, it was elevated fivefold in individuals with CKD and DM and was still threefold above control after 3-h treatment. UF significantly increased PS externalization in a small subpopulation of platelets from healthy controls. The effect of UF from individuals with CKD and DM was significantly greater than that from patients with CKD alone, and the responses were partially inhibited by the protein kinase Cδ (PKCδ) inhibitor rottlerin and the 5-hydroxytryptamine (5-HT)2A/2Creceptor antagonist ritanserin. The data suggest that uremic toxins present in UF mediate PS externalization in a small subpopulation of platelets, at least in part, via the 5-HT2A/2Creceptor and PKCδ and demonstrate that DM further enhances platelet PS externalization in CKD patients undergoing hemodialysis. This may explain, at least in part, the additional increase in vascular damage observed in CKD patients when DM is present.

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.

Increased platelet expression of FcGammaRIIa and its potential impact on platelet reactivity in patients with end stage renal disease

BACKGROUND

Increased platelet reactivity has been implicated in cardiovascular disease - the major cause of death in patients with end stage renal disease (ESRD). FcGammaRIIA is a component of glycoprotein VI and Ib-IX-V that mediate activation of platelets by collagen and von Willebrand factor. To determine whether expression of FcGammaRIIA impacts platelet reactivity we quantified its expression and platelet reactivity in 33 patients with ESRD who were undergoing hemodialysis.

METHODS

Blood samples were obtained from patients immediately before hemodialysis and before administration of heparin. Platelet expression of FcGammaRIIA and the activation of platelets in response to low concentrations of convulxin (1 ng/ml, selected to mimic effects of collagen), thrombin (1 nM), adenosine diphosphate (ADP, 0.2 microM), or platelet activating factor (PAF, 1 nM) were determined with the use of flow cytometry in samples of whole blood anticoagulated with corn trypsin inhibitor (a specific inhibitor of Factor XIIa).

RESULTS

Patients were stratified with respect to the median expression of FcGammaRIIA. Patients with high platelet expression of FcGammaRIIA exhibited 3-fold greater platelet reactivity compared with that in those with low expression in response to convulxin (p < 0.01) and 2-fold greater activation in response to thrombin, ADP, and PAF (p < 0.05 for each). For each agonist, expression of FcGammaRIIA correlated modestly but positively with platelet reactivity. The strongest correlation was with thrombin-induced activation (r = 0.6, p < 0.001).

CONCLUSION

Increased platelet reactivity in response to low concentrations of diverse agonists is associated with high expression of FcGammaRIIA and may contribute to an increased risk of thrombosis in patients with ESRD.

Measurement of platelet activation and adhesion to leukocytes during haemodialysis

In this study we used fluorescent-labelled antibodies to measure the extent of platelet adhesion to polymorphonuclear leukocytes (PMNLs), monocytes and lymphocytes. The activation of platelets, PMNLs and monocytes were also measured during the course of haemodialysis treatment using flow cytometric techniques established in our laboratory. Twenty patients were treated with either a cellulose membrane (TFU) or a polycarbonate filter (Pro 500). Blood samples were taken from the output line of the dialyser 2, 15, 30 and 180 min after commencing dialysis and just before starting treatment. Compared with the pre-dialysis sample, there was a marked increase in platelet-PMNL conjugate formation at 2 min, followed by a decrease in conjugates at 15 and 30 min, and a slight increase at 180 min. During extracorporeal circulation PMNLs become activated as measured by a CD11b upregulation at 15, 30 and 180 min, but not at 2 min. Platelet binding to monocytes was increased above 15 min after starting dialysis, and monocyte activation was slightly increased above basal levels during the same period. The activation state of circulating free platelets, as measured by surface P-selectin exposition, initially decreased slightly, but then returned to basal levels over the 3-h period. Changes in cell counts were also detected: there was a massive decrease in circulating PMNLs and monocytes, and a small decrease in circulating platelets, at 15 and 30 min. These reverted to basal values by the end of the 3-h period. There was no change in the number of circulating lymphocytes or erythrocytes. These results show that flow cytometric studies on whole blood samples may provide important information on the behaviour of circulating blood cells, which could supplement conventional clinical measurements, to give a better insight into changes that occur in the circulation during haemodialysis.

Biphasic effects of hemodialysis on platelet reactivity in patients with end-stage renal disease: a potential contributor to cardiovascular risk

BACKGROUND

Cardiovascular disease is rampant in patients with end-stage renal disease (ESRD), and increased platelet reactivity may contribute. This study is designed to determine effects of hemodialysis in patients with ESRD on platelet reactivity per se.

METHODS

Platelet reactivity was determined by flow cytometry in 36 patients with ESRD undergoing hemodialysis. Blood was obtained from arterial and venous ends of the hemodialysis circuit at the beginning and end of the dialysis session. Platelet reactivity was defined with respect to capacity to bind fibrinogen (activation of glycoprotein IIb-IIIa) and expression of P-selectin in response to adenosine diphosphate (ADP; 0, 0.2, and 1.0 micromol/L). Comparison studies were performed with 55 patients with coronary artery disease (CAD) and 38 healthy subjects.

RESULTS

Platelet reactivity was increased by exposure to the dialysis circuit (capacity to bind fibrinogen: arterial, 28% +/- 13%; venous, 47% +/- 20%; P < 0.001). Despite this effect, surface expression of P-selectin in response to 1 micromol/L of ADP was lower at the end of the dialysis session (arterial blood at its onset, 40% +/- 16%; arterial blood at its conclusion, 24% +/- 15%; P < 0.05). Confocal microscopy showed increased nonspecific association of fibrinogen with platelets after dialysis, suggesting that increased aggregation after dialysis may be secondary to effects of dialysis on fibrinogen binding, rather than on platelet reactivity. Platelet reactivity was increased similarly in patients with ESRD and those with CAD compared with healthy subjects.

CONCLUSION

Although interaction between platelets and the dialysis circuit increases platelet reactivity, continued dialysis decreases platelet reactivity.

Peripheral blood progenitor cell grafts contain high levels of platelet-secreted mediators

BACKGROUND

The cytokine network in peripheral blood progenitor cell (PBPC) grafts may affect hematopoietic reconstitution or the risk of postransplant relapse of malignant disorders through effects on normal progenitor cells or contaminating malignant cells. Whether thrombopoietin (TPO), SCF, and platelet-secreted mediators are parts of this network was investigated.

STUDY DESIGN AND METHODS

Peripheral blood and PBPC plasma samples were collected consecutively from patients with malignant disorders who underwent PBPC harvest. Blood samples were collected immediately before and after apheresis. Patients underwent mobilization by chemotherapy plus G-CSF, except for one patient who received only G-CSF. Plasma levels were also determined for healthy controls.

RESULTS

PBPC grafts had greater levels of platelet-secreted platelet factor 4 (PF4), beta-thromboglobulin, and platelet-derived growth factor isoform AB, as compared with venous levels in patients and controls. Although platelet and PF4 levels in autografts were significantly correlated, the graft:blood ratio was higher for PF4 than for platelets. In both the patients' blood and the autografts, TPO levels were increased from the levels in normal controls. Blood and graft levels of SCF were within the normal range.

CONCLUSION

The cytokine network of PBPC autografts includes increased levels of TPO and several platelet-derived mediators.

Autologous stem cell transplantation as post-remission therapy in adult acute myelogenous leukemia: does platelet contamination of peripheral blood mobilized stem cell grafts influence the risk of leukemia relapse?

Conventional chemotherapy of acute myelogenous leukemia (AML) results in an overall long-term disease-free survival of less than 50%, but for selected subsets of younger patients the prognosis can be improved by allogeneic stem cell transplantation. The use of autologous stem cell transplantation is now investigated as an alternative to allotransplantation due to its lower risk of serious complications. However, autotransplantation is associated with a relatively high risk of post-transplant AML relapse that can be derived from contaminating leukemia cells in the autograft. Peripheral blood mobilized stem cell (PBSC) grafts usually contain a higher number of platelets. The degree of platelet contamination is determined by the peripheral blood platelet count at the time of harvesting, and the platelets become activated and release soluble mediators during the ex vivo handling of PBSC grafts. Many of these platelet-derived mediators can bind to specific receptors expressed by AML blasts, and the platelet contamination may then alter AML blast survival and thereby influence the risk of post-transplant leukemia relapse. Therefore, we conclude that the platelet contamination of autologous stem cell grafts is possibly of clinical importance, but the effect of this nonstandardized parameter is difficult to predict in individual patients because the number of graft-contaminating platelets, the degree of platelet activation, and the effects of platelet-derived mediators on AML blasts differ between patients.

Biocompatibility of a new cell separator studied by flow cytometry: analyses of platelet antigens during apheresis and storage

BACKGROUND

Alterations of platelet antigens are known to occur during cytapheresis and storage. These changes have been shown to be dependent on the biomaterials, techniques, and devices used. In this study, the influence of a new cell separator (AMICUS) and storage container (PL-2410) on platelet glycoproteins was analyzed.

STUDY DESIGN AND METHODS

During plateletpheresis and storage, the levels of platelet glycoproteins and binding of fibrinogen were determined by flow cytometry.

RESULTS

During apheresis, mean channel fluorescence intensity of CD41 a did not change significantly (p = 0.06). A small increase was evident in CD42b mean channel fluorescence intensity, which rose from a baseline level of 178.6 +/- 68.3 to 231.5 +/- 97.9 at the end of the procedure (p<0.05); in CD62p-positive platelets, which increased from 2.0 +/- 0.9 percent to 9.9 +/- 3.9 percent (p<0.05); in CD63-positive platelets, which increased from 1.7 +/- 0.7 percent to 7.9 +/- 2.6 percent (p<0.05); and in the binding of fibrinogen, which increased from 1.9 +/- 0.8 percent positive platelets to 10.5 +/- 2.6 percent (p<0.05). During storage, the mean channel fluorescence intensity of CD41a and CD42b, the percentage of CD62p- and CD63-positive platelets, and the binding of fibrinogen to platelets showed no significant change.

CONCLUSION

These studies show that alterations in platelet antigens and platelet activation occur to a small degree during apheresis and storage. These findings demonstrate generally good biocompatibility of this new cell separator.

Specific activation of platelets by surface-adsorbed plasma proteins

Platelets were isolated from human blood by Percoll density gradient centrifugation in a low Ca2+/high Mg2+ buffer. The buffer reversibly inactivates the cells during separation. The purity of the isolated cells (> 99%) was determined by flow cytometry, their viability was confirmed by fluorescein diacetate hydrolysis, and their morphology was studied with TEM. Plasma proteins were adsorbed onto hydrophobic glass surface, and pure platelets were added and incubated for up to 30 min at 37 degree C. Platelet activation was determined by cell spreading, formation of microparticles and surface exposure of CD62P indicating the release of alpha-granules. Surface-immobilized IgG was shown to cause the release of microparticles and cell lysis, in accordance with data published by others. Surface-immobilized vWF was shown to induce CD62P exposure on the platelet cell surface. The specificity of this response was demonstrated by adsorbing plasma proteins from normal and factor VIII-deficient plasma.

The sepsis-coagulant axis: a review

Activation of coagulation is a normal component of the acute inflammatory response. Inflammatory cytokines initiate coagulation events locally at sites of inflammation by converting endothelium from an antithrombotic surface to a prothrombotic surface; by stimulating tissue factor production, which activates both the extrinsic and intrinsic coagulation systems; and by stimulating production of platelet-activating factors. The fibrinolytic system is initially activated but is subsequently inhibited. This results in a marked imbalance in coagulation and fibrinolysis resulting in a net procoagulant state. When thrombin generation and platelet activation exceed the body's capacity to inactivate or remove these factors, disseminated intravascular coagulation (DIC) results. DIC directly contributes to multiple organ failure and death associated with sepsis. Presently available treatments (i.e., heparin and aspirin) are relatively ineffective in treating DIC; however, newer, more potent drugs may soon be available for clinical use.

The role of flow cytometry in improving biocompatibility in transfusion medicine

In transfusion medicine, blood and blood components, donors and patients are increasingly confronted with biomaterials. The need to understand the response of human blood to contact with these artificial surfaces has led to multiple studies on the biocompatibility of biomaterials. Up to this time, these investigations have predominantly been performed using physical, immunological and biochemical methods. Many of these approaches are useful in investigating the multiple factors involved in blood-biomaterial interactions. However, they always reflect the overall behaviour of whole cellular populations in local or systemic reactions. The application of multiparameter flow cytometry, on the other hand, provides insight into antigenic expression and changes at the single-cell level. Therefore, the technique of flow cytometry represents a new and powerful way of analysing and improving the biocompatibility of these materials in blood-contacting applications in this field.

CD62, thromboxane B2, and beta-thromboglobulin: a comparison between different markers of platelet activation after contact with biomaterials

The authors examined the modifications of some markers of platelet activation after contact with biomaterials. Glycoprotein GMP-140 (CD62) was evaluated by flow cytometry; beta-thromboglobulin (beta-TG) and thromboxane B2 (TXB2) were determined by radioimmunoassay. Polyethylene terephthalate (PET) induced a remarkable platelet adhesion and a significant increase in beta-TG and TXB2, with no increase in CD62 on the nonadherent platelets. Pyrolytic carbon-coated PET (PC) did not induce platelet adhesion after 15 min of contact, but a significant increase in CD62 was detected. After 30 min a significant increase in platelet adhesion as well as the release of beta-TG and TXB2 were noted. The increase was lower than that observed for uncoated PET, and after 30 min of contact with PC the increase no longer was observed.

Alteration of platelet-associated membrane glycoproteins during extracorporeal apheresis of peripheral blood progenitor cells

In extracorporeal circulation, blood is affected by artificial biomaterials and shear forces. We investigated the effects of peripheral blood progenitor cell (PBPC) apheresis on the kinetics and level of platelet membrane antigen expression in 11 breast cancer and 13 testicular cancer patients. After mobilization with rhG-CSF, continuous-flow apheresis was performed. Expression of structural antigens CD41a and CD42b and activation-dependent antigens CD62p, CD63, and fibrinogen was analyzed by flow cytometry at fixed time intervals. Initial changes occurred in all of the antigens within minutes, followed by a progressive increase in the mean channel fluorescence intensities (MCFI) of CD62p from 26 +/- 8 (mean +/- SD) to 73 +/- 29 (p < 0.05), CD63 from 22 +/- 5 to 51 +/- 16 (p < 0.05) and antifibrinogen from 120 +/- 20 to 356 +/- 154 (p < 0.05). In contrast, CD41a and CD42b fluorescence decreased during apheresis (p < 0.05 for both). The more rapid sequestration of P-selectin-expressing platelets known to occur during extracorporeal PBPC apheresis suggests that platelet activation may be associated with the loss of platelets during this procedure. In addition, alteration of platelet surface antigens increases thrombogenic potential and may reduce the in vivo efficacy of the platelet hemostatic potential.

Flow cytometric analysis of platelet membrane antigens during and after continuous-flow plateletpheresis

BACKGROUND

The influence, extent, and duration of changes in platelet antigen expression caused by blood-biomaterial interaction in plateletpheresis were assessed.

STUDY DESIGN AND METHODS

Twenty-two apheresis donors were studied by using two automated continuous-flow apheresis devices. Blood samples were taken before, during, and for 4 days after extracorporeal circulation. The platelet surface expression of glycoproteins CD41a, CD42b, CD62p, and CD63 was analyzed by flow cytometry.

RESULTS

Over the course of plateletpheresis, there was a significant increase in mean channel fluorescence intensity (MCFI) of CD62p, from 25.1 +/- 7.9 (mean +/- SD) to 50.4 +/- 28.9, and of CD63, from 22.3 +/- 6.5 to 33.3 +/- 13.2. There was a significant decrease in CD41a expression as measured by the MCFI, from 1129.8 +/- 125.0 to 1066.6 +/- 102.2, and in CD42b MCFI, from 329.6 +/- 49.4 to 321.4 +/- 52.0. The two apheresis devices showed different platelet activation kinetics, but the overall MCFI of CD62p and CD63 did not significantly diverge after 60 minutes of apheresis. CD62p and CD63 expression as measured by the MCFI returned to preapheresis levels during the follow-up period in 25 and 25 of 44 procedures, respectively, within 24 hours; in 10 and 13 of 44 procedures after 48 hours; in 7 and 3 of 44 procedures after 72 hours; and in 2 and 3 of 44 procedures on Day 5.

CONCLUSION

The varying kinetics of expression, as measured by the MCFI, of platelet antigens CD62p, CD63, CD41a, and CD42b during extracorporeal circulation may be useful for biocompatibility testing. Activated platelets continue to circulate in donors for several days after cytapheresis, which suggests that a sufficient interval between apheresis procedures is necessary to avoid the collection of activated platelets.

Role of hemodialysis in the management of dogs and cats with renal failure

Hemodialysis is a technically sophisticated therapy used to remove accumulated uremia toxins and correct the electrolyte, hydrogen ion, and fluid imbalances associated with renal failure. Hemodialysis is indicated when the morbidity or potential mortality from either acute or chronic renal failure cannot be alleviated by conventional therapies. Additionally, it is useful for the rapid removal of excessive fluid loads associated with congestive heart failure or iatrogenic fluid administration and the elimination of dialyzable poisons like ethylene glycol. The requirements for hemodialysis include repeated access to the vasculature, an artificial kidney, and a dialysis delivery system. Technologic advancements in all these requirements make the delivery of hemodialysis feasible, effective, and safe for both dogs and cats. To date, the limitation of facilities offering dialytic therapy has restricted its use in uremic animals but current improvements in dialysis techniques and the increased sophistication of specialty practice make hemodialysis a realistic adjunct to the conservative management of uremia in veterinary medicine.

Increased neutrophil-platelet adhesion in patients with unstable angina

BACKGROUND

Neutrophil-platelet adhesion may occur as a consequence of platelet activation. The role of this heterotypic adhesion in ischemic disorders is poorly understood thus far.

METHODS AND RESULTS

Systemic venous blood samples were taken from 25 patients with stable angina pectoris and 25 patients with unstable angina pectoris. Neutrophil activation and neutrophil-platelet adhesion were evaluated by two-color flow cytometry. Patients with unstable angina showed a significant increase in neutrophil-platelet adhesion compared with patients with stable angina (mean +/- SEM, 132.1 +/- 20.5 versus 29.8 +/- 4.7 anti-glycoprotein IIb/IIIa mean fluorescence intensity, P = .0001). Systemic neutrophil activation was found in patients with unstable angina compared with those with stable angina assessed by cell surface CD11b expression and shedding of L-selectin (115.6 +/- 10.3 versus 74.0 +/- 6.3 anti-CD11b mean fluorescence intensity, P = .002; 49.8 +/- 6.0 versus 72.1 +/- 4.0 anti-L-selectin mean fluorescence intensity, P = .006). Markers of neutrophil activation were related to the extent of neutrophil-platelet adhesion (CD11b: r = .5, P = .0005; L-selectin: r = .42, P = .012). In vitro studies revealed that binding of purified platelet membranes to control neutrophils caused a dose-dependent increase in CD11b surface expression, a decrease in surface L-selectin, and the release of superoxide anions.

CONCLUSIONS

Thus, this study demonstrates that increased neutrophil-platelet adhesion may contribute to neutrophil activation in unstable angina.

Platelet function and platelet-leukocyte adhesion in symptomatic coronary heart disease. Effects of intravenous magnesium

Spontaneous P-selectin surface expression on platelets and platelet-leukocyte adhesion was increased in patients with symptomatic coronary heart disease (n = 12) compared to normal controls (n = 10) (p < 0.05). ADP-induced P-selectin expression and platelet-leukocyte adhesion was also enhanced in the patient group (p < 0.05). Administration of intravenous Mg2+ significantly reduced both platelet surface expression of P-selectin and platelet-leukocyte adhesion ex vivo (p < 0.02). The effect of extracellular Mg2+ was evaluated in in vitro experiments. Both in whole blood and in isolated neutrophil suspension Mg2+ inhibited platelet adhesion to neutrophils dose dependently with half maximal effects at 4 mM. Moreover, Mg2+ inhibited adhesion of isolated platelet membranes to neutrophils. We conclude that platelet function is altered in symptomatic coronary heart disease and can be modulated by administration of intravenous Mg2+.

Platelet activation and interaction with leucocytes in patients with sepsis or multiple organ failure

This study focuses on the role of platelet membrane glycoproteins and platelet-leucocyte adhesion in patients with sepsis and multiple organ failure (MOF). Specifically, the study raises the following issues: (1) the influence of sepsis and MOF on platelet activation as assessed by surface expression of platelet membrane glycoproteins GPIIb-IIIa and thrombospondin; and (2) the effect of sepsis and MOF on platelet adhesion to circulating leucocytes. In addition, platelet activation and platelet-leucocyte adhesion are evaluated according to clinical outcome. Forty-five patients with suspected sepsis or MOF were evaluated by intensive care scoring systems (APACHE II and Elebute) to assess severity of disease. Flow cytometric techniques were used to examine platelet membrane expression of various adhesion molecules on circulating platelets and the appearance of platelet specific antigen (CD41) on leucocytes as an index of platelet-leucocyte adhesion. The results were compared with severity of disease and according to outcome in patients. Twenty-eight patients of the total study population were septic and 17 were non-septic. Twenty-two of the 28 septic patients suffered from severe MOF (APACHE II > or = 20) whereas in six septic patients MOF was absent. Eleven of the non-septic group suffered from moderate MOF whereas in six, severe MOF was present. In septic patients fibrinogen receptor activity on platelets was significantly above normal values (P < 0.001). When MOF was present, thrombospondin surface expression on circulating platelets also increased significantly (P < 0.05). Concomitantly, platelet-leucocyte adhesion was increased in sepsis (P < 0.05) and decreased in patients with MOF (P < 0.05). Significant lower levels of circulating platelet-leucocyte aggregates occurred in non-survivors (P < 0.05). We conclude that sepsis is associated with increased surface expression of platelet adhesion molecules and an increased occurrence of circulating platelet-leucocyte aggregates. The decrease in circulating platelet-leucocyte peripheral sequestration. An increased platelet-leucocyte adhesion and sequestration might account for development of MOF in the course of sepsis.

Severity of multiple organ failure (MOF) but not of sepsis correlates with irreversible platelet degranulation

Multiple hemostatic changes occur in sepsis and multiple organ failure (MOF). To evaluate the role of platelets in patients with sepsis and MOF, we examined changes in surface glycoproteins on circulating platelets of 14 patients with suspected sepsis and MOF. The severity of sepsis and MOF was assessed by the Elebute and APACHE II scoring systems, respectively. Using flow cytometric techniques and platelet specific monoclonal antibodies, platelet surface expression of fibrinogen receptor on GPIIb-IIIa, of von Willebrand Factor receptor GPIb, and of granule glycoproteins (thrombospondin (TSP), GMP-140, GP53) was measured. Plasma membrane expression of GPIIb-IIIa and GPIb on circulating platelets was not affected by sepsis of MOF. Septic patients, however, showed a significantly elevated fibrinogen receptor activity (LIBS1 expression) (p < 0.05) that correlated with severity of disease (r = 0.597, p = 0.043). No significant change in surface expression of granule glycoproteins (TSP, GMP-140, GP53) was noted in septic patients. In contrast, degranulation of granule glycoproteins was significantly elevated in MOF (p < 0.05) which well with severity of MOF (GMP-140, r = 0.611, p = 0.013; TSP, r = 0.643, p = 0.026). We speculate that platelets in sepsis circulate in a hyperaggregable but still reversible state that results in increased risk of microthrombotic events. In the course of the disease, irreversible platelet degranulation of adhesion molecules occurs that may play an important role in the development of MOF.