Prevention of In vitro neutrophil adhesion to endothelial cells through shedding of L-selectin by C-reactive protein and peptides derived from C-reactive protein.

C-Reactive protein (CRP), the classic acute-phase reactant in humans, diminishes accumulation of neutrophils at inflammatory sites. To evaluate the underlying mechanisms, we have studied whether CRP and peptides derived from CRP could affect the first step of neutrophil extravasation, the L-selectin-mediated interaction of neutrophils with endothelial cells. CRP markedly attenuated attachment of human neutrophils to cultured LPS-activated human coronary artery and pulmonary microvascular endothelial cells with apparent IC50 values of 20 and 22 microg/ml, respectively. At similar concentrations, CRP rapidly downregulated the expression of L-selectin on the neutrophil surface, whereas it failed to affect expression of CD11b and CD45 or to induce granule enzyme release. The loss of L-selectin was due to cleavage and shedding of the molecule from the cell surface, as quantitated by the soluble form of L-selectin in cell-free supernatants. The effects of CRP could be prevented by an anti-CRP antiserum and by KD-IX-73-4, which inhibits shedding of L-selectin. Inhibition of adhesion with CRP was additive with function-blocking anti-E-selectin and anti-CD18 antibodies, but was not additive with anti-L-selectin antibody. Neutrophil attachment and L-selectin expression were also diminished by CRP peptides 174-185 and 201-206, but not peptide 77-82, albeit these peptides showed a weaker inhibitory effect than the parent protein. These studies indicate a specific activation-independent action of CRP and CRP peptides 174-185 and 201-206 on expression of L-selectin, and suggest that by attenuating neutrophil adhesion to the endothelium and consequently neutrophil traffic into tissues, native CRP and peptides 174-185 and 201-206 may be major mechanisms to attenuate or limit the inflammatory response.

Matrix metalloproteinases regulate neutrophil-endothelial cell adhesion through generation of endothelin-1[1-32].

We recently reported that matrix metalloproteinase 2 (MMP-2, gelatinase A) cleaves big endothelin 1 (ET-1), yielding the vasoactive peptide ET-1[1-32]. We tested whether ET-1[1-32] could affect the adhesion of human neutrophils to coronary artery endothelial cells (HCAEC). ET-1[1-32] rapidly down-regulated the expression of L-selectin and up-regulated expression of CD11b/CD18 on the neutrophil surface, with EC50 values of 1-3 nM. These actions of ET-1[1-32] were mediated via ETA receptors and did not require conversion of ET-1[1-32] into ET-1 by neutrophil proteases, as revealed by liquid chromatography and mass spectroscopy. Moreover, ET-1[1-32] evoked release of neutrophil gelatinase B, which cleaved big ET-1 to yield ET-1[1-32], thus revealing a positive feedback loop for ET-1[1-32] generation. Up-regulation of CD11b/CD18 expression and gelatinase release was tightly associated with activation of extracellular signal-regulated kinase (Erk). Stimulation of Erk activity was due to activation of Ras, Raf-1, and MEK (MAPK kinase). ET-1[1-32] also produced slight increases in the expression of ICAM-1 and E-selectin on HCAEC, and markedly enhanced beta2 integrin-dependent adhesion of neutrophils to activated HCAEC. These results are the first indication that gelatinolytic MMPs via cleavage of big ET-1 to yield ET-1[1-32] activate neutrophils and promote leukocyte-endothelial cell adhesion and, consequently, neutrophil trafficking into inflamed tissues.

Peroxynitrite mediates cytokine-induced IL-8 gene expression and production by human leukocytes.

Recent studies indicate that nitric oxide (NO) or related compounds may regulate the production of interleukin (IL)-8, a potent proinflammatory chemokine. Here we report that peroxynitrite (ONOO(-)) formed by a reaction of NO with superoxide mediates IL-8 gene expression and IL-8 production in IL-1beta- and TNF-alpha-stimulated human leukocytes in whole blood. The NO synthase inhibitors aminoguanidine and N(G)-nitro-L-arginine methyl ester blocked nuclear accumulation of activator protein-1 (AP-1) and nuclear factor (NF)-kappaB in both polymorphonuclear (PMN) and mononuclear leukocytes and inhibited IL-8 mRNA expression and IL-8 release by approximately 90% in response to IL-1beta and TNF-alpha. Enhanced ONOO(-) formation was detected in granulocytes, monocytes, and lymphocytes after challenge with IL-1beta or TNF-alpha. The addition of ONOO(-) (0.2-80 microM) to whole blood increased nuclear accumulation of AP-1 and NF-kappaB in PMN and mononuclear leukocytes and augmented IL-8 mRNA expression and IL-8 production in a concentration-dependent fashion. Pyrrolidine dithiocarbamate, an inhibitor of NF-kappaB activation, attenuated approximately 70% of IL-8 release evoked by IL-1beta, TNF-alpha, or ONOO(-). These results indicate that ONOO(-) formation may underlie the action of cytokines towards IL-8 gene expression in human leukocytes.

Endothelin-1 enhances neutrophil adhesion to human coronary artery endothelial cells: role of ET(A) receptors and platelet-activating factor.

1. The potent coronary vasoconstrictor, endothelin-1 (ET-1) may also regulate neutrophil traffic into tissues. The aim of the present study was to characterize the endothelin receptors responsible and to investigate the underlying mechanisms. 2. ET-1 (1 nM - 1 microM) markedly enhanced attachment of human neutrophils to lipopolysaccharide-, and to a lesser extent, to ET-1-activated human coronary artery endothelial cells (HCAEC). This can partially be blocked by monoclonal antibodies against E-selectin, L-selectin or CD18, whereas combination of the three antibodies inhibited adhesion by approximately 83%. Increases in neutrophil adhesion evoked by ET-1 were also blocked by the platelet-activating factor (PAF) antagonists, BN 52021 (50 microM) and WEB 2086 (10 microM). 3. ET-1 downregulated the expression of L-selectin and upregulated expression of CD11b/CD18 and CD45 on the neutrophil surface and induced gelatinase release with EC50 values of approximately 2 nM. These actions of ET-1 were almost completely prevented by the ET(A) receptor antagonist FR 139317 (1 microM) and the ET(A)/ET(B) receptor antagonist bosentan (10 microM), whereas the ET(B) receptor antagonist BQ 788 (1 microM) had no effect. ET-1 slightly increased the expression of E-selectin and ICAM-1 on HCAEC, that was prevented by BQ 788, but not by FR 139317. 4. Receptor binding studies indicated the presence of ET(B) receptors (KD: 40 pM) on phosphoramidon-treated HCAEC and the predominant expression of ET(A) receptors (KD: 38 pM) on neutrophils. 5. These results indicate that promotion by ET-1 of neutrophil adhesion to HCAEC is predominantly mediated through activation of ET(A) receptors on neutrophils and subsequent generation of PAF.

The anti-inflammatory peptides, antiflammins, regulate the expression of adhesion molecules on human leukocytes and prevent neutrophil adhesion to endothelial cells.

Antiflammin-1 and antiflammin-2 are nonapeptides corresponding to the region of highest similarity between glucocorticoid-inducible proteins lipocortin-1 and uteroglobin. We have studied whether antiflammins could affect expression of adhesion molecules on human leukocytes and coronary artery endothelial cells (HCAEC) and binding of neutrophils (PMNs) to HCAEC. Although neither antiflammin-1 nor antiflammin-2 affected expression of adhesion molecules on resting PMNs, monocytes, and lymphocytes in whole blood, they attenuated changes in L-selectin and CD11/CD18 expression evoked by platelet-activating factor or interleukin-8 with IC(50) values of 4-20 micromol/l. The maximum inhibition was similar to those seen with human recombinant lipocortin-1 (100 microgram/ml). Unlike dexamethasone (100 nmol/l), the antiflammins had little effect on LPS-stimulated expression of E-selectin and ICAM-1 on HCAEC. Consistently, culture of HCAEC with dexamethasone, but not with antiflammins, decreased PMN binding to endothelial cells. Preincubation of PMNs with antiflammins markedly decreased their adhesion to LPS-activated HCAEC. Inhibition of adhesion was additive with function blocking anti-E-selectin and anti-L-selectin antibodies, but was not additive with anti-CD18 antibody. These results show that antiflammins inhibit PMN adhesion to HCAEC by attenuating activation-induced up-regulation of CD11/CD18 expression on leukocytes, and suggest that antiflammins may represent a novel therapeutic approach in blocking leukocyte trafficking in host defense and inflammation.

Loss of pentameric symmetry of C-reactive protein is associated with promotion of neutrophil-endothelial cell adhesion.

The classic acute-phase reactant C-reactive protein (CRP) is a cyclic pentameric protein that diminishes neutrophil accumulation in inflamed tissues. When the pentamer is dissociated, CRP subunits undergo conformational rearrangement that results in expression of a distinctive isomer with unique antigenic and physicochemical characteristics (termed modified CRP (mCRP)). Recently, mCRP was detected in the wall of normal human blood vessels. We studied the impact and mechanisms of action of mCRP on expression of adhesion molecules on human neutrophils and their adhesion to human coronary artery endothelial cells. Both CRP and mCRP (0.1-200 microg/ml) down-regulated neutrophil L-selectin expression in a concentration-dependent fashion. Furthermore, mCRP, but not CRP, up-regulated CD11b/CD18 expression and stimulated neutrophil extracellular signal-regulated kinase activity, which was accompanied by activation of p21(ras) oncoprotein, Raf-1, and mitogen-activated protein kinase kinase. These actions of mCRP were sensitive to the mitogen-activated protein kinase kinase inhibitor PD98059. mCRP markedly enhanced attachment of neutrophils to LPS-activated human coronary artery endothelial when added together with neutrophils. This effect of mCRP was attenuated by an anti-CD18 mAb. Thus, loss of pentameric symmetry in CRP is associated with appearance of novel bioactivities in mCRP that enhance neutrophil localization and activation at inflamed or injured vascular sites.

Peroxynitrite induces integrin-dependent adhesion of human neutrophils to endothelial cells via activation of the Raf-1/MEK/Erk pathway.

Accumulating evidence suggests that enhanced peroxynitrite (ONOO-) formation occurs during inflammation. We have studied the impact and the mechanisms of ONOO- action on expression of adhesion molecules on human neutrophils and coronary artery endothelial cells (HCAEC) and binding of neutrophils to HCAEC. Addition of ONOO- (0.1 to 200 5M) to isolated neutrophils resulted in a concentration-dependent down-regulation of L-selectin expression, and up-regulation of CD11b/CD18 expression. ONOO- stimulation of Erk activity was accompanied by activation of Ras, Raf-1 and MEK (mitogen-activated protein kinase kinase), and was sensitive to the MEK inhibitor PD 98059. We have observed a tight association between Erk activation and changes in CD11b/CD18 expression. ONOO- also evoked activation of neutrophil p38 MAPK. Neither ONOO--induced up-regulation of CD11b/CD18 expression nor Erk activation was affected by SB 203580, a selective inhibitor of p38 MAPK. ONOO- by itself had little effect on expression of ICAM-1 and E-selectin on HCAEC, whereas it markedly enhanced attachment of neutrophils to lipopolysaccharide-activated HCAEC only when it was added together with neutrophils. Increases in neutrophil adhesion evoked by ONOO- were blocked by an anti-CD18 monoclonal antibody. These data suggest that ONOO- activates Erk in neutrophils via the Ras/Raf-1/MEK signal transduction pathway, leading to up-regulation of surface expression of CD11b/CD18 and consequently to increased neutrophil adhesion to endothelial cells.

Anti-inflammatory actions of lipoxin A(4) stable analogs are demonstrable in human whole blood: modulation of leukocyte adhesion molecules and inhibition of neutrophil-endothelial interactions.

We have examined in whole blood the actions of 2 lipoxin A(4) (LXA(4)) stable analogs, 15-R/S-methyl-LXA(4) and 16-phenoxy-LXA(4), for their impact on the expression of adhesion molecules on human leukocytes and coronary artery endothelial cells (HCAEC) and on neutrophil adhesion to HCAEC in vitro. Both LXA(4) analogs in nanomolar to micromolar concentrations prevented shedding of L-selectin and downregulated CD11/CD18 expression on resting neutrophils, monocytes, and lymphocytes. Changes in CD11/CD18 expression were blocked by the mitogen-activated protein kinase kinase inhibitor PD98059. The LXA(4) analogs also attenuated changes in L-selectin and CD11/CD18 expression evoked by platelet-activating factor (PAF), interleukin-8, or C-reactive protein-derived peptide 201-206 with IC(50) values of 0.2 to 1.9 micromol/L, whereas they did not affect lipopolysaccharide (LPS)- or tumor necrosis factor-alpha-stimulated expression of E-selectin and intercellular adhesion molecule-1 on HCAEC. These LXA(4) analogs markedly diminished adhesion of neutrophils to LPS-activated HCAEC. Inhibition of adhesion was additive with function blocking anti-E-selectin and anti-L-selectin antibodies, but was not additive with anti-CD18 antibody. Combining LXA(4) analogs with dexamethasone (100 nmol/L) almost completely inhibited PAF-induced changes in adhesion molecule expression on leukocytes and gave additive inhibition of neutrophil adhesion to HCAEC. Culture of HCAEC with dexamethasone, but not with LXA(4) analogs, also decreased neutrophil attachment. Together, these results indicate that LXA(4) stable analogs modulate expression of both L-selectin and CD11/CD18 on resting and immunostimulated leukocytes and inhibit neutrophil adhesion to HCAEC by attenuating CD11/CD18 expression. These actions are additive with those of glucocorticoids and may represent a novel and potent regulatory mechanism by which LXA(4) and aspirin-triggered 15-epi-LXA(4) modulate leukocyte trafficking.