Roflumilast inhibits leukocyte-platelet interactions and prevents the prothrombotic functions of polymorphonuclear leukocytes and monocytes

ESSENTIALS: Thrombosis is a major comorbidity in patients with chronic obstructive pulmonary disease (COPD). Roflumilast is a selective phosphodiesterase type-4 (PDE4) inhibitor approved for treatment of severe COPD. PDE4 blockade by roflumilast inhibits prothrombotic functions of neutrophils and monocytes. PDE4 inhibitors may reduce thrombotic risk in COPD as well as in other vascular diseases.

BACKGROUND

Roflumilast, an oral selective phosphodiesterase type 4 inhibitor, is approved for the treatment of severe chronic obstructive pulmonary disease (COPD). A recent meta-analysis of trials on COPD revealed that treatment with roflumilast was associated with a significant reduction in the rate of major cardiovascular events. The mechanisms of this effect remain unknown.

OBJECTIVES

We tested the hypothesis that roflumilast N-oxide (RNO), the active metabolite of roflumilast, curbs the molecular mechanisms required for leukocyte-platelet (PLT) interactions and prevents the prothrombotic functions of polymorphonuclear leukocytes (PMNs) and monocytes (MNs).

METHODS

Using well-characterized in vitro models, we analysed the effects of RNO on: (i) PMN adhesiveness; (ii) the release of neutrophil extracellular traps (NETs); and (iii) tissue factor expression in MNs. Key biochemical events underlying the inhibitory effects of RNO were defined.

RESULTS AND CONCLUSIONS

In PMNs, RNO prevented phosphoinositide 3-kinase (PI3K)-dependent phosphorylation of Akt on Ser473, and Src family kinase (SFK)-mediated Pyk2 phosphorylation on Tyr579-580, while inducing protein kinase A-mediated phosphorylation of C-terminal Src kinase, the major negative regulator of SFKs. Modulation of these signaling pathways by RNO resulted in a significant impairment of PMN adhesion to activated PLTs or human umbilical vein endothelial cells, mainly mediated by inhibition of the adhesive function of Mac-1. Moreover RNO curbed SFK/PI3K-mediated NET release by PMNs adherent on fibrinogen-coated surfaces. In MNs interacting with activated PLTs, RNO curbed PI3K-mediated expression of tissue factor. The efficacy of RNO was significantly potentiated by formoterol, a long acting β-adrenergic receptor agonist. This study reveals novel antithrombotic activities by which roflumilast may exert protective effects against cardiovascular comorbodities in COPD.

Persistent platelet activation in patients with type 2 diabetes treated with low doses of aspirin

BACKGROUND

The percentage of diabetic patients who do not benefit from the protective effect of aspirin is larger than in other populations at cardiovascular risk.

OBJECTIVE

We compared the ability of aspirin to suppress TxA2 and platelet activation in vivo, in type-2 diabetics vs. high-risk non-diabetic patients.

METHODS

Urinary 11-dehydro-TXB2, plasma sCD40 L, and sP-selectin were measured, together with indices of low-grade inflammation, glycemic control, and lipid profile, in 82 patients with type-2 diabetes and 39 without diabetes, treated with low doses of aspirin.

RESULTS

Urinary 11-dehydro-TxB2, plasma sCD40L and sP-selectin were significantly higher in diabetics than in controls: [38.9 (27.8-63.3) vs. 28.5 (22.5-43.9) ng mmol(-1) of creatinine, P = 0.02], [1.06 (0.42-3.06) vs. 0.35 (0.22-0.95) ng mL(-1); P = 0.0001], [37.0 (16.8-85.6) vs. 20.0 (11.2-35.6) ng mL(-1), P = 0.0001], respectively. The proportion of individuals with diabetes increased across quartiles of 11-dehydro-TxB2, sCD40L, and sP-selectin, with the highest quartiles of 11-dehydro-TxB2, sCD40L and sP-selectin, including 66%, 93.3%, and 93.3% of individuals with diabetes. Markers of platelet activation positively correlated with indices of glycemic control but not with markers of low-grade inflammation.

CONCLUSIONS

Platelet dysfunction associated with insufficient glycemic control, may mediate persistent platelet activation under aspirin treatment.

Platelet/polymorphonuclear leukocyte interaction: P-selectin triggers protein-tyrosine phosphorylation-dependent CD11b/CD18 adhesion: role of PSGL-1 as a signaling molecule

Polymorphonuclear leukocyte (PMN) adhesion to activated platelets is important for the recruitment of PMN at sites of vascular damage and thrombus formation. We have recently shown that binding of activated platelets to PMN in mixed cell suspensions under shear involves P-selectin and the activated beta2-integrin CD11b/CD18. Integrin activation required signaling mechanisms that were sensitive to tyrosine kinase inhibitors.1 Here we show that mixing activated, paraformaldehyde (PFA)-fixed platelets with PMNs under shear conditions leads to rapid and fully reversible tyrosine phosphorylation of a prominent protein of 110 kD (P approximately 110). Phosphorylation was both Ca2+ and Mg2+ dependent and was blocked by antibodies against P-selectin or CD11b/CD18, suggesting that both adhesion molecules need to engage with their respective ligands to trigger phosphorylation of P approximately 110. The inhibition of P approximately 110 phosphorylation by tyrosine kinase inhibitors correlates with the inhibition of platelet/PMN aggregation. Similar effects were observed when platelets were substituted by P-selectin-transfected Chinese hamster ovary (CHO-P) cells or when PMN were stimulated with P-selectin-IgG fusion protein. CHO-P/PMN mixed-cell aggregation and P-selectin-IgG-triggered PMN/PMN aggregation as well as P approximately 110 phosphorylation were all blocked by antibodies against P-selectin or CD18. In each case PMN adhesion was sensitive to the tyrosine kinase inhibitor genistein. The antibody PL-1 against P-selectin glycoprotein ligand-1 (PSGL-1) blocked platelet/PMN aggregation, indicating that PSGL-1 was the major tethering ligand for P-selectin in this experimental system. Moreover, engagement of PSGL-1 with a nonadhesion blocking antibody triggered beta2-integrin-dependent genistein-sensitive aggregation as well as tyrosine phosphorylation in PMN. This study shows that binding of P-selectin to PSGL-1 triggers tyrosine kinase-dependent mechanisms that lead to CD11b/CD18 activation in PMN. The availability of the beta2-integrin to engage with its ligands on the neighboring cells is necessary for the tyrosine phosphorylation of P approximately 110.

Polymorphonuclear leukocytes induce PDGF release from IL-1beta-treated endothelial cells: role of adhesion molecules and serine proteases

Polymorphonuclear leukocytes (PMNs) and endothelial cells interact at sites of vascular injury during inflammatory response and during the development of atherosclerotic lesions. Such close proximity leads to the modulation of several of the biological functions of the 2 cell types. Because we have shown previously that PMNs enhance release of growth factors from resting endothelial cells, we decided to evaluate whether coincubation of PMNs with interleukin-1beta (IL-1beta)-stimulated human umbilical vein endothelial cells (HUVEC) could further modulate mitogen release from HUVEC. We found that PMN-HUVEC coincubation resulted in a 10-fold increase in mitogen release, compared with HUVEC alone (14+/-6 versus 1.3+/-0.1). When PMNs were incubated with IL-1beta-treated HUVEC, a further increase in mitogen release (up to 35-fold) was observed. The mitogenic activity was immunologically related to platelet-derived growth factor (PDGF) because the activity was abolished by an anti-PDGF antibody. PDGF-AB antigen, detected in low concentrations in conditioned medium from HUVEC alone, was increased 4-fold when IL-1beta or PMNs were incubated with HUVEC and dramatically upregulated (up to 40-fold) when PMNs were cocultured with IL-1beta-treated HUVEC. The presence of the protease inhibitor eglin C abolished mitogenic activity generation, suggesting a role for PMN-derived elastase and cathepsin G. Indeed, purified elastase and cathepsin G mimicked PMN-induced mitogen release from HUVEC. Because PMNs firmly adhered to IL-1beta-treated HUVEC, we investigated the role of cell-cell adhesion in mitogen release. Adhesion and PDGF release were inhibited by approximately 60% in the presence of anti-CD11a/CD18 and anti-intercellular adhesion molecule-1 monoclonal antibodies. This study suggests a new role for PMNs and their interaction with endothelium in pathological conditions in which intimal hyperplasia is a common feature.

Polymorphonuclear leukocytes enhance release of growth factors by cultured endothelial cells

Porcine aortic endothelial cells (PAECs) in culture constitutively secrete polypeptide (endothelium-derived) growth factors (EDGFs) into the surrounding medium. Incubation of PAECs with human peripheral blood polymorphonuclear leukocytes (PMNs) caused a significant increase in EDGF release as assessed by [3H]thymidine incorporation into BALB/c 3T3 mouse fibroblasts and cell proliferation assay. The effect was time dependent and correlated with the number of PMNs, reaching a maximum with a 1:1 PAEC to PMN ratio. Generation of mitogenic activity was prevented by cycloheximide, indicating a requirement for de novo protein synthesis. Antibody-mediated inhibition assays suggested that mitogenic activity was due to platelet-derived growth factor and basic fibroblast growth factor. When supernatant from N-formyl-methionyl-leucyl-phenylalanine-stimulated PMNs was substituted for PMNs during incubation with PAECs, powerful mitogenic activity was generated, indicating the involvement of soluble mediators. A role for free oxygen radicals was ruled out by experiments in which superoxide dismutase and catalase did not prevent the increase in mitogenic activity. By contrast, serine protease inhibitors such as soybean trypsin inhibitor, alpha 1-antitrypsin, and eglin C reduced the PMN-stimulating activity by 70%, 80%, and 100%, respectively. The possible involvement of cathepsin G and elastase was investigated. Cathepsin G and elastase, when substituted for PMNs, increased the release of EDGFs in a dose-dependent fashion, mimicking the effect of PMNs. These findings suggest a new role for leukocyte-vessel wall interactions in the proliferative feature of atherosclerosis.

The Italian National Research Council project on homocystinuria

The Italian National Research Council (CNR) has launched a special project aiming at gathering competences on rare diseases, their pathogenesis and their possible pharmacological management. The subproject on homocystinuria has three main objectives: to establish the prevalence and incidence of the disease in the Italian population, to develop sensitive assays of sulfated amino acids which allow discrimination of heterozygotes from normal subjects and to better define the complex interactions between homocystinuria and vascular complications.