Effects of clopidogrel with or without aspirin on the generation of extracellular vesicles in the microcirculation and in venous blood: A randomized placebo controlled trial

BACKGROUND

Dual-antiplatelet therapy (DAPT) is a standard strategy in acute coronary heart disease; however, it confers a considerable bleeding risk. Single-antiplatelet therapy (SAPT) inhibits haemostatic system activation ex vivo to a similar extent as DAPT. Extracellular vesicles (EV) are procoagulant and contribute to haemostatic system activation. We aimed to investigate the effect of DAPT compared with SAPT on EV.

METHODS

In a randomized, double-blind, placebo-controlled trial, 44 healthy volunteers received DAPT (clopidogrel + aspirin) or SAPT (clopidogrel + placebo) for 7 days. Blood was obtained from a standardized microvascular injury and through venipuncture at baseline (BL) and at 2 h, 24 h, and 8 days after treatment initiation. The number, origin, and surface expression of EV were assessed using flow cytometry. Data are given as median (quartiles). Non-parametric tests were used to evaluate the short-term (BL vs 2 h) and long-term differences (2 h to 8 days), as well as the differences between treatment groups.

RESULTS

There was no difference either in the short-term effects on the number (×10³ mL^-1) of EV in microvascular blood between DAPT [BL: 1433 (653; 3184) vs 2 h: 862 (545; 2026), p = 0.39] and SAPT [(BL: 614 (552; 1402) vs 2 h: 1079 (781; 1538), p = 0.75)] or in the long-term effects. DAPT and SAPT did not exhibit differential short-term effects on the number and proportion (36% and 27% vs 55% and 36%) of platelet-derived EV. DAPT and SAPT resulted in a significant short-term increase in phosphatidylserine expression in microvascular blood. The effects of DAPT and SAPT on EV in venous blood were similar to those in microvascular blood.

CONCLUSION

DAPT and SAPT have comparable effects on the amount, origin, and surface characteristics of EV.

Effects of P2Y12 receptor inhibition with or without aspirin on hemostatic system activation: a randomized trial in healthy subjects

ESSENTIALS: In acute coronary syndromes, dual antiplatelet therapy inhibits platelets but confers a bleeding risk. Healthy male volunteers received clopidogrel or ticagrelor plus aspirin or clopidogrel or ticagrelor alone. The decrease in β-thromboglobulin in shed blood was comparable after single and dual antiplatelet therapy. We hypothesize that patients with acute coronary syndromes may not require dual antiplatelet therapy.

BACKGROUND

Dual antiplatelet therapy with a P2Y12 inhibitor and aspirin is standard in acute coronary syndromes. Dual antiplatelet therapy causes more bleeding than single antiplatelet therapy with a P2Y12 inhibitor.

OBJECTIVES

To compare the effects of dual and single antiplatelet therapies on hemostatic system activation.

PATIENTS/METHODS

In a randomized, parallel-group, double-blind, placebo-controlled study, 44 healthy volunteers received clopidogrel (600 mg, then 150 mg d(-1) ) and aspirin (100 mg d(-1) ) or placebo for 7 days; An additional 44 volunteers received single-dose ticagrelor (180 mg) and aspirin (300 mg) or placebo. β-Thromboglobulin (β-TG [IU L(-1) ]) and prothrombin fragment 1.2 (f1.2 [nmol L(-1) ]) were measured in blood obtained from bleeding time incisions. Data are given as geometric mean ratio (GMR [95% confidence interval]) to describe the differences in the first 2 h and as mean differences (Δ [95% confidence interval]) in area under the curve (AUC) to discriminate differences in effects over the total observation time.

RESULTS

Clopidogrel plus aspirin and clopidogrel plus placebo reduced β-TG by a GMR of 0.51 (0.42-0.63) and 0.54 (0.46-0.64) at 2 h. Ticagrelor plus aspirin and ticagrelor plus placebo decreased β-TG by a GMR of 0.38 (0.26-0.57) and 0.47 (0.31-0.72). Ticagrelor plus aspirin and ticagrelor plus placebo reduced f1.2 by a GMR of 0.58 (0.45-0.75) and 0.55 (0.38-0.80); clopidogrel did not. Over 24 h, no difference in β-TG occurred between clopidogrel plus aspirin and clopidogrel plus placebo (ΔAUC = -2.9 [-9.9 to 4.1]) or between ticagrelor plus aspirin and ticagrelor plus placebo (ΔAUC = -3.5 [-11.8 to 4.7]). No difference in f1.2 occurred between clopidogrel plus aspirin and clopidogrel plus placebo (ΔAUC = -4.2 [-10.2 to 1.8]) or between ticagrelor plus aspirin and ticagrelor plus placebo (ΔAUC = -3.6 [-10.9 to 3.7]).

CONCLUSIONS

P2Y12 inhibitor monotherapy and dual antiplatelet therapy inhibit hemostatic system activation to a comparable extent.

Thrombin generation in haemophilia A patients with factor VIII inhibitors after infusion of recombinant factor VIIa

BACKGROUND

Development of factor VIII inhibitors is a serious complication in haemophilia A patients. Recombinant factor VIIa (rVIIa) is clinically effective, but its effects on haemostatic system need still to be fully elucidated.

MATERIAL AND METHODS

In an open controlled study, we measured thrombin generation (peak thrombin) in venous blood and prothrombin fragment F1 + 2 (F1 + 2) and D-dimer in venous and in shed blood in five haemophilia A patients with inhibitors before and after rVIIa infusion. A total of five healthy individuals who did not receive rVIIa served as controls.

RESULTS

At baseline, patients had lower mean (min-max) peak thrombin levels than controls [0.12 (0.0-0.6) vs. 186.9 (116.0-254.4) nM, P = 0.001]. After infusion, peak thrombin levels increased in average to 40.7 (28.3-51.6) nM, which translates into 80.2% (95% CI 65.4-88.6%) lower levels compared to that of controls. Mean (min-max) F1 + 2 levels in venous blood did not differ significantly between patients and controls [160.7 (89.8-331.3) vs. 160.8 (104.4-242.3) pmol L(-1)], but increased in average (min-max) by 39.4% (14.1-58.5%) after infusion. In blood emerging from incisions made to determine the bleeding (shed blood), F1 + 2 levels were lower in patients than controls [1383.3 (906.4-2044.6) vs. 2981.7 (1610.0-4539.6) pmol L(-1); P = 0.04], but were not affected by rVIIa; D-dimer levels were significantly higher in haemophiliacs than in controls and remained unchanged after infusion.

CONCLUSIONS

Haemophilia A patients with factor VIII inhibitors have low thrombin generation. After rVIIa, the extent of coagulation activation as measured by levels of F1 + 2 is increased, but thrombin generation is restored to only 20%. Peak thrombin levels could reflect the effects of rVIIa on coagulation mechanisms, and their relevance with regard to the clinical coagulation defect of haemophilia A patients with factor VIII inhibitors might be evaluated.

Chemotherapy-induced thrombin generation via procoagulant endothelial microparticles is independent of tissue factor activity

BACKGROUND

Cisplatin-based chemotherapy predisposes cancer patients to thromboembolic events.

OBJECTIVES

To investigate whether endothelial damage, via formation of procoagulant endothelial microparticles (EMPs), contributes to cisplatin-related hypercoagulability.

METHODS

Cell viability and caspase-3/7 activities were assessed in two endothelial cell (EC) lines [human umbilical vein ECs (HUVECs) and human pulmonary microvascular ECs (HMVEC-Ls)] after exposure to cisplatin (1, 2.5, 5, 10 and 20 microm) for up to 120 h. Counts and procoagulant activity of EMPs were measured by flow cytometry and a thrombin generation assay, respectively. Tissue factor (TF) antigen and TF-dependent procoagulant activity of EMP were determined by enzyme-linked immunosorbent assay and a novel functional assay.

RESULTS

By inducing apoptosis, cisplatin dose- and time-dependently decreased the viability of confluent HUVECs and HMVEC-Ls. Progression of EC death was accompanied by an increased release of EMPs (relative increase at 20 microm cisplatin for 48 h vs. control: HUVECs 6.5-fold, P < 0.001; HMVEC-Ls 18.4-fold, P < 0.001). EMPs were highly procoagulant (relative increase at 20 microm cisplatin for 48 h vs. control: HUVECs 2.5-fold, P < 0.001; HMVEC-Ls 5.9-fold, P < 0.001). EMP-driven thrombin generation, however, was not dependent on TF: TF expression and TF procoagulant activity levels on microparticles were only marginal and EMP-associated thrombin generation remained unchanged when the extrinsic pathway was blocked by omission of factor VIIa and/or incubation with an anti-human TF antibody. In contrast, blocking of phospholipids by annexin V markedly diminished EMP-associated procoagulant activity.

CONCLUSIONS

In vitro, cisplatin induced the release of EMPs that showed TF-independent procoagulant activity.

Kinetics of CFU-Mk after automated plateletpheresis

BACKGROUND AND OBJECTIVES

Platelet count, thrombopoetin (TPO) level and the compartment of megakaryocyte progenitor cells (CFU-Mk) are major determinants in the regulation of thrombopoiesis. The aim of this study was to investigate the potential changes in the compartment of CFU-Mk and their correlation with serum TPO levels and platelet count after plateletpheresis.

MATERIALS AND METHODS

Twelve healthy individuals were randomly assigned to undergo single-donor plateletpheresis. A collagen-based in vitro culture system was used to determine the number of peripheral blood (PB) CFU-Mk before and after donation and on days 1, 4 and 7 thereafter. TPO levels were measured by a specific enzyme-linked immunosorbent assay and whole blood counts were performed using an automated cell counter.

RESULTS

The pre-apheresis platelet count (mean +/- SEM: 276 +/- 13 x 10(9)/l) decreased after plateletpheresis to a nadir of 194 +/- 8 x 10(9)/l (P < 0.001), showed a gradual increase on days 1 and 4, and reached pre-apheresis values by day 7 (280 +/- 11). The serum TPO levels were found to be significantly increased on days 1 and 7 as compared to baseline levels (baseline value 103.3 +/- 18.5 pg/ml versus day-1 value 135.8 +/- 25.8 pg/ml and day-7 value 132 +/- 30.19 pg/ml; P < 0.03 and P < 0.03, respectively). The numbers of CFU-Mk in PB were significantly elevated on day 4 only (125 +/- 21 colonies/ml of PB versus pre-apheresis values of 68 +/- 18 colonies/ml of PB, P < 0.005).

CONCLUSIONS

These findings suggest that platelet loss during plateletpheresis affects thrombopoiesis at the progenitor cell level, probably through alterations in TPO plasma concentrations.

Culture requirements for induction of dendritic cell differentiation in acute myeloid leukemia

Peripheral blood mononuclear cells (PBMCs) from 15 newly diagnosed acute myeloid leukemia (AML) patients were cultured in fetal calf serum-free media supplemented with either granulocyte/macrophage-colony stimulating factor (GM-CSF), interleukin (IL)-4 and tumor necrosis factor alpha (TNFalpha), or GM-CSF, stem cell factor (SCF), TNFalpha and transforming growth factor beta (TGFbeta) in order to generate leukemia-derived dendritic cells (DCs). Cultured cells were analyzed by flow cytometry with respect to DC-associated surface molecules (CD1a, CD83, CD40, CD80, CD86, HLA-DR) when they showed significant DC morphology in culture (14 cases). After cultivation, neo-expression or upregulation of CD1a antigen was found in 8 samples, CD83 in 2, CD40 in 14, CD80 in 7, and CD86 in 9. Twelve of 14 AMLs, in which DC morphology could be induced upon cultivation, showed upregulation of at least 2 DC-associated molecules. For induction of DC differentiation. GM-CSF, IL-4 plus TNFalpha was superior in 11 cases, and better results were obtained with GM-CSF, SCF, TNFalpha plus TGFbeta in 3 cases. In 7 of 14 samples tested, a marked increase of the T-cell stimulatory capacity could be demonstrated in the allogeneic mixed lymphocyte reaction. The leukemic origin of in vitro-generated DCs was demonstrated by fluorescence in situ hybridization in a patient with translocation t(15;17). Our results suggest that the use of different culture conditions may extend the number of AML patients in which a differentiation towards the DC lineage can be induced in vitro.

1,25-Dihydroxyvitamin D(3) inhibits dendritic cell differentiation and maturation in vitro

OBJECTIVE

Because of its potent immunosuppressive properties in vitro as well as in vivo, we studied the effect of 1,25-dihydroxyvitamin D(3) (calcitriol) on differentiation, maturation, and function of dendritic cells (DC).

MATERIALS AND METHODS

Monocyte-derived DCs were generated with GM-CSF plus IL-4, and maturation was induced by a 2-day exposure to TNFalpha. DCs were derived from CD34(+) progenitors using SCF plus GM-CSF plus TNFalpha. For differentiation studies, cells were exposed to calcitriol at concentrations of 10(-)(9)- 10(-7) M at days 0, 6, and 8, respectively. The obtained cell populations were evaluated by morphology, phenotype, and function.

RESULTS

When added at day 0, calcitriol blocked DC differentiation from monocytes and inhibited the generation of CD1a(+) cells from progenitor cells while increasing CD14(+) cells. Exposure of immature DCs to calcitriol at day 6 resulted in a loss of the DC-characteristic surface molecule CD1a, downregulation of the costimulatory molecules CD40 and CD80, and MHC class II expression, whereas the monocyte/macrophage marker CD14 was clearly reinduced. In addition, calcitriol hindered TNFalpha-induced DC maturation, which is usually accompanied with induction of CD83 expression and upregulation of costimulatory molecules. In contrast, the mature CD83(+) DCs remained CD1a(+)CD14(-) when exposed to calcitriol. The capacity of cytokine-treated cells to stimulate allogeneic and autologous T cells and to take up soluble antigen was inhibited by calcitriol.

CONCLUSION

The potent suppression of DC differentiation, the reversal of DC phenotype, and function in immature DCs, as well as the inhibition of DC maturation by calcitriol, may explain some of its immunosuppressive properties.

Interleukin-10 inhibits burst-forming unit-erythroid growth by suppression of endogenous granulocyte-macrophage colony-stimulating factor production from T cells

Numerous cytokines released from accessory cells have been shown to exert either stimulatory or inhibitory growth signals on burst-forming unit-erythroid (BFU-E) growth. Because of its cytokine synthesis-inhibiting effects on T cells and monocytes, interleukin-10 (IL-10) may be a potential candidate for indirectly affecting erythropoiesis. We investigated the effects of IL-10 on BFU-E growth from normal human peripheral blood mononuclear cells (PBMC) using a clonogenic progenitor cell assay. The addition of recombinant human IL-10 to cultures containing recombinant human erythropoietin suppressed BFU-E growth in a dose-dependent manner (by 55.2%, range 47.3-63.3%, p < 0.01, at 10 ng/mL). In contrast, no inhibitory effect of IL-10 was seen when cultivating highly enriched CD34+ cells. BFU-E growth from PBMC also was markedly suppressed in the presence of a neutralizing anti-granulocyte-macrophage colony-stimulating factor (GM-CSF) antibody (by 48.7%, range 32.9-61.2% inhibition,p < 0.01), but not by neutralizing antibodies against granulocyte colony-stimulating factor and interleukin-3. This suggests a stimulatory role of endogenously released GM-CSF on BFU-E formation. Also, the addition of exogenous GM-CSF completely restored IL-10-induced suppression of BFU-E growth. To determine the cellular source of GM-CSF production, we analyzed GM-CSF levels in suspension cultures containing PBMC that were either depleted of monocytes or T cells. Monocyte-depleted PBMC showed spontaneous production of increasing amounts of GM-CSF on days 3, 5, and 7, respectively, which could be suppressed by IL-10, whereas GM-CSF levels did not increase in cultures containing T-cell-depleted PBMC. Our data indicate that IL-10 inhibits the growth of erythroid progenitor cells in vitro, most likely by suppression of endogenous GM-CSF production from T cells.

Interleukin-10 inhibits erythropoietin-independent growth of erythroid bursts in patients with polycythemia vera

In polycythemia vera (PV) erythroid colonies that grow in vitro in the absence of exogenous erythropoietin (EPO) arise from the abnormal clone that is responsible for overproduction of red blood cells. Although the mechanism of autonomous formation of burst-forming units-erythroid (BFU-E) is not fully understood, a spontaneous release of growth regulatory molecules by PV cells and/or by accessory cells is likely to be involved. Because of its cytokine synthesis inhibiting action, interleukin-10 (IL-10) could be a potentially useful molecule to modulate abnormal erythropoiesis in PV. We studied the effect of recombinant human IL-10 on the EPO-independent growth of erythroid bursts derived from peripheral blood mononuclear cells (PBMNCs) of patients with PV. IL-10 showed a profound, dose-dependent, and specific inhibitory effect on autonomous BFU-E formation. Ten nanograms per milliliter of IL-10 significantly suppressed spontaneous growth of erythroid colonies in methylcellulose in five of five PV patients tested with a mean inhibition by 81% (range, 72-94). To elucidate the possible mechanism of the inhibitory action of IL-10 we further studied the effect of anticytokine antibodies on autonomous BFU-E growth and the ability of exogenous cytokines to restore IL-10-induced suppression of erythroid colony growth. Among a panel of growth regulatory factors tested (granulocyte-macrophage colony-stimulating factor [GM-CSF], IL-3, granulocyte colony-stimulating factor, stem cell factor, and insulin-like growth factor-1) GM-CSF was the only molecule for which both an inhibition of spontaneous BFU-E formation by its respective antibody as well as a significant restimulation of erythroid colonies in IL-10-treated cultures by exogenous addition was found. Moreover, inhibition of GM-CSF production by IL-10 was shown in PV PBMNCs at the mRNA level. Our data indicate that autonomous BFU-E growth in PV can be profoundly inhibited by IL-10 and that this inhibitory effect seems to be at least in part secondary to suppression of endogenous GM-CSF production.

Interleukin-10 inhibits spontaneous colony-forming unit-granulocyte-macrophage growth from human peripheral blood mononuclear cells by suppression of endogenous granulocyte-macrophage colony-stimulating factor release

Spontaneous growth of myeloid colonies (colony-forming unit-granulocyte-macrophage [CFU-GM]) can be observed in methylcellulose cultures containing peripheral blood mononuclear cells (PB-MNCs) and is supposedly caused by the release of colony-stimulating factors (CSF) by accessory cells. Because of its cytokine synthesis-inhibiting effects on T lymphocytes and monocytes, interleukin-10 (IL-10) may be a potential candidate for indirect modulation of hematopoiesis. We studied the effect of recombinant human IL-10 (rhIL-10) on spontaneous growth of myeloid colonies derived from human PB-MNCs. A total of 10 ng/mL of IL-10 almost completely inhibited spontaneous CFU-GM proliferation (by 95.1%; P < .001, n = 7) in unseparated PB-MNCs. This effect was dose-dependent and specific, because a neutralizing anti-IL-10 antibody was able to prevent IL-10-induced suppression of CFU-GM growth. Spontaneous CFU-GM growth, which required the presence of both monocytes (CD14+ cells) and T lymphocytes (CD3+ cells), was also greatly suppressed by a neutralizing anti-granulocyte-macrophage CSF (GM-CSF) antibody but was only slightly or not at all inhibited by antibodies against G-CSF or IL-3. Moreover, IL-10-suppressed colony growth could be completely restored by the addition of exogenous GM-CSF. Using semiquantitative polymerase chain reaction, we were able to show that GM-CSF transcripts that spontaneously increased in PB-MNCs within 48 hours of culture were markedly reduced by the addition of IL-10. Inhibiton of GM-CSF production in PB-MNCs by IL-10 was also confirmed at the protein level by measuring GM-CSF levels in suspension cultures. Our findings suggest that autonomous CFU-GM growth, resulting from an interaction of monocytes and T lymphocytes, is mainly caused by endogenous GM-CSF release and can be profoundly suppressed by the addition of exogenous IL-10. Considering the strong inhibitory action of IL-10 on GM-CSF production and spontaneous cell growth in vitro, this cytokine may be useful in myeloid malignancies in which autocrine and/or paracrine mechanisms involving GM-CSF are likely to play a pathogenetic role.

Interleukin 10 inhibits growth and granulocyte/macrophage colony-stimulating factor production in chronic myelomonocytic leukemia cells

Autonomous release of hematopoietic growth factors may play a crucial role in the pathogenesis of certain hematological malignancies. Because of its cytokine synthesis-inhibiting action, interleukin 10 (IL-10) could be a potentially useful molecule to affect leukemic cell growth in such disorders. Chronic myelomonocytic leukemia (CMML) cells spontaneously form myeloid colonies (colony-forming units-granulocyte/macrophage) in methylcellulose, suggesting an autocrine growth factor-mediated mechanism. We studied the effect of recombinant human IL-10 (rhIL-10) on the in vitro growth of mononuclear cells obtained from peripheral blood or bone marrow of patients with CMML. IL-10 specifically binding to leukemic cells had a profound and dose-dependent inhibitory effect on autonomous in vitro growth of CMML cells. IL-10 significantly inhibited the spontaneous growth of myeloid colonies in methylcellulose in 10/11 patients, and autonomous CMML cell growth in suspension in 5/5 patients tested. Spontaneous colony growth from CMML cells was also markedly reduced by addition of antigranulocyte/macrophage colony-stimulating factor (GM-CSF) antibodies, but not by addition of antibodies against G-CSF, IL-3, or IL-6, IL-10-induced suppression of CMML cell growth was reversed by the addition of exogenous GM-CSF and correlated with a substantial decrease in GM-CSF production by leukemic cells, both at the mRNA and protein levels. Our data indicate that IL-10 profoundly inhibits the autonomous growth of CMML cells in vitro most likely through suppression of endogenous GM-CSF release. This observation suggests therapeutic evaluation of rhIL-10 in patients with CMML.