Soluble CD40 Ligand in Pulmonary Arterial Hypertension

Angiogenic and inflammatory markers of cardiopulmonary changes in children and adolescents with sickle cell disease

Background

Pulmonary hypertension and left ventricular diastolic dysfunction are complications of sickle cell disease. Pulmonary hypertension is associated with hemolysis and hypoxia, but other unidentified factors are likely involved in pathogenesis as well.

Design and Methods

Plasma concentrations of three angiogenic markers (fibroblast growth factor, platelet derived growth factor–BB [PDGF-BB], vascular endothelial growth factor [VEGF]) and seven inflammatory markers implicated in pulmonary hypertension in other settings were determined by Bio-Plex suspension array in 237 children and adolescents with sickle cell disease at steady state and 43 controls. Tricuspid regurgitation velocity (which reflects systolic pulmonary artery pressure), mitral valve E/Edti ratio (which reflects left ventricular diastolic dysfunction), and a hemolytic component derived from four markers of hemolysis and hemoglobin oxygen saturation were also determined.

Results

Plasma concentrations of interleukin-8, interleukin-10 and VEGF were elevated in the patients with sickle cell disease compared to controls (P≤0.003). By logistic regression, greater values for PDGF-BB (P = 0.009), interleukin-6 (P = 0.019) and the hemolytic component (P = 0.026) were independently associated with increased odds of elevated tricuspid regurgitation velocity while higher VEGF concentrations were associated with decreased odds (P = 0.005) among the patients with sickle cell disease. These findings, which are consistent with reports that PDGF-BB stimulates and VEGF inhibits vascular smooth muscle cell proliferation, did not apply to E/Etdi.

Conclusions

Circulating concentrations of angiogenic and pro-Inflammatory markers are altered in sickle cell disease children and adolescents with elevated tricuspid regurgitation velocity, a subgroup that may be at risk for developing worsening pulmonary hypertension. Further studies to understand the molecular changes in these children are indicated.

Prostacyclin inhibits IFN-gamma-stimulated cytokine expression by reduced recruitment of CBP/p300 to STAT1 in a SOCS-1-independent manner

Increasing evidence indicates that pulmonary arterial hypertension is a vascular inflammatory disease. Prostacyclin (PGI(2)) is widely used to treat pulmonary arterial hypertension and is believed to benefit patients largely through vasodilatory effects. PGI(2) is also increasingly believed to have anti-inflammatory effects, including decreasing leukocyte cytokine production, yet few mechanistic details exist to explain how these effects are mediated at the transcriptional level. Because activated monocytes are critical sources of MCP-1 and other cytokines in cardiovascular inflammation, we examined the effects of iloprost on IFN-gamma- and IL-6-stimulated cytokine production in human monocytes. We found that iloprost inhibited IFN-gamma- and IL-6-induced MCP-1, IL-8, RANTES, and TNF-alpha production in monocytes, indicating wide-ranging anti-inflammatory action. We found that activation of STAT1 was critical for IFN-gamma-induced MCP-1 production and demonstrated that iloprost inhibited STAT1 activation by several actions as follows: 1) iloprost inhibited the phosphorylation of STAT1-S727 in the transactivation domain, thereby reducing recruitment of the histone acetylase and coactivator CBP/p300 to STAT1; 2) iloprost selectively inhibited activation of JAK2 but not JAK1, both responsible for activation of STAT1 via phosphorylation of STAT1-Y701, resulting in reduced nuclear recruitment and activation of STAT1; and 3) SOCS-1, which normally terminates IFN-gamma-signaling, was not involved in iloprost-mediated inhibition of STAT1, indicating divergence from the classical pathway for terminating IFN-gamma-signaling. We conclude that PGI(2) exerts anti-inflammatory action by inhibiting STAT1-induced cytokine production, in part by targeting the transactivation domain-induced recruitment of the histone acetylase CBP/p300.

Elevated levels of activin A in clinical and experimental pulmonary hypertension

Activin A, a member of the transforming growth factor (TGF)-β superfamily, is involved in regulation of tissue remodeling and inflammation. Herein, we wanted to explore a role for activin A in pulmonary hypertension (PH). Circulating levels of activin A and its binding protein follistatin were measured in patients with PH ( n = 47) and control subjects ( n = 14). To investigate synthesis and localization of pulmonary activin A, we utilized an experimental model of hypoxia-induced PH. In mouse lungs, we also explored signaling pathways that can be activated by activin A, such as phosphorylation of Smads, which are mediators of TGF-β signaling. Possible pathophysiological mechanisms initiated by activin A were explored by exposing pulmonary arterial smooth muscle cells in culture to this cytokine. Elevated levels of activin A and follistatin were found in patients with PH, and activin A levels were significantly related to mortality. Immunohistochemistry of lung autopsies from PH patients and lungs with experimental PH localized activin A primarily to alveolar macrophages and bronchial epithelial cells. Mice with PH exhibited increased pulmonary levels of mRNA for activin A and follistatin in the lungs, and also elevated pulmonary levels of phosphorylated Smad2. Finally, we found that activin A increased proliferation and induced gene expression of endothelin-1 and plasminogen activator inhibitor-1 in pulmonary artery smooth muscle cells, mediators that could contribute to vascular remodeling. Our findings in both clinical and experimental studies suggest a role for activin A in the development of various types of PH.

Molecular mechanisms of pulmonary hypertension

The pathogenesis of pulmonary arterial hypertension (PAH) is complex, involving multiple modulating genes and environmental factors. Multifactorial impairment of the physiologic balance can lead to vasoconstriction, vascular smooth muscle cell and endothelial cell proliferation/fibrosis, inflammation, remodeling and in-situ thrombosis. These are the likely mechanisms that lead to narrowing of the vessel followed by progressive increase in pulmonary vascular resistance and the clinical manifestations of pulmonary hypertension. Subsequently, major goal of the therapy is to avoid acute pulmonary vasoconstriction, halt the progression of vascular remodeling, and reverse the early vascular remodeling if possible. Recently published data addressing certain molecular mechanisms for pathogenesis of PAH have led to the successful therapeutic interventions. This review will focus on the common and critical molecular pathways including genetic basis of the development of PAH that on the whole may be new targets for therapeutic interventions.

Atherosclerotic plaque stability--what determines the fate of a plaque?

Although the understanding of the underlying pathology of atherosclerosis has improved in recent years, the disease is still the main cause of death globally. Current evidence has implicated the role of inflammation in atherogenesis and plaque destabilization. Thus, inflammatory cytokines may attenuate interstitial collagen synthesis, increase matrix degradation, and promote apoptosis in several atheroma-associated cell types, and all these cellular events may enhance plaque vulnerability. Several cell types found within the lesion (ie, monocyte/macrophages, T cells, mast cells, platelets) contribute to this immune-mediated plaque destabilization, and a better understanding of these processes is a prerequisite for the development of new treatment strategies in these individuals. Such knowledge could also facilitate a better identification of high-risk individuals. In the present study, these issues will be discussed in more detail, particularly focusing on the interactions between matrix degradation, apoptotic, and inflammatory processes in plaque destabilization.

Direct contact of platelets and their released products exert different effects on human dendritic cell maturation

BACKGROUND

Dendritic cells (DCs) are antigen presenting cells capable of inducing innate and adaptive immune responses. According to the stimulus and their maturation state, DCs induce immunogenic or tolerogenic responses. Platelets (PLTs), which are involved in haemostasis and inflammation, can also interact with DCs. In this study, we examined the effect of PLTs on DC maturation in vitro. Human monocyte-derived DCs were co-cultured for 2 days with homologous PLTs either in the same well or in 0.4 mum-pore size filter-separated compartments.

RESULTS

Confocal microscopy showed the attachment of PLTs to DC membranes. The DC receptor involved in this interactions was found to be CD162. In addition, we observed that DCs co-cultured with PLTs in filter-separated compartments acquired a mature phenotype (high CD80, CD86, and intermediate CD83 expression; IL-12(p70) production; efficient stimulation of autologous CD4+ T cell proliferation), while DCs co-cultured with PLTs in the same compartment did not undergo phenotypic maturation, did not secrete IL-12(p70) or IL-1beta, but instead induced moderate Th2-polarized T cell proliferation.

CONCLUSION

These data indicate that (i) PLTs secrete a soluble DC-activating factor that was demonstrated not to be soluble CD40-Ligand (CD154; as could have been expected from in vivo and previous in vitro work) but to be nucleotide, and (ii) that cell-to-cell contact did not induce DC maturation, possibly because nucleotide release by PLTs was prevented by direct contact with DCs. This work demonstrates that PLTs are active elements of the immune system that might play a role in balancing the ability of DCs to polarize T cell responses, therefore making them critical factors in transfusion processes.

Soluble CD40 ligand induces endothelial dysfunction in human and porcine coronary artery endothelial cells

The purpose of this study was to determine the effects and mechanisms of sCD40L on endothelial dysfunction in both human coronary artery endothelial cells (HCAECs) and porcine coronary artery rings. HCAECs treated with sCD40L showed significant reductions of endothelial nitric oxide synthase (eNOS) mRNA and protein levels, eNOS mRNA stability, eNOS enzyme activity, and cellular NO levels, whereas superoxide anion (O(2)(-)) production was significantly increased. sCD40L enhanced eNOS mRNA 3'UTR binding to cytoplasmic molecules and induced a unique expression pattern of 95 microRNAs. sCD40L significantly decreased mitochondrial membrane potential, and catalase and SOD activities, whereas it increased NADPH oxidase (NOX) activity. sCD40L increased phosphorylation of MAPKs p38 and ERK1/2 as well as IkappaBalpha and enhanced NF-kappaB nuclear translocation. In porcine coronary arteries, sCD40L significantly decreased endothelium-dependent vasorelaxation and eNOS mRNA levels, whereas it increased O(2)(-) levels. Antioxidant seleno-l-methionine; chemical inhibitors of p38, ERK1/2, and mitochondrial complex II; as well as dominant negative mutant forms of IkappaBalpha and NOX4 effectively blocked sCD40L-induced eNOS down-regulation in HCAECs. Thus, sCD40L reduces eNOS levels, whereas it increases oxidative stress through the unique molecular mechanisms involving eNOS mRNA stability, 3'UTR-binding molecules, microRNAs, mitochondrial function, ROS-related enzymes, p38, ERK1/2, and NF-kappaB signal pathways in endothelial cells.

Soluble CD40 ligand and atrial fibrillation: Relationship to platelet activation, and endothelial damage/dysfunction

Increased plasma soluble CD40L (sCD40L) is present in many cardiovascular diseases and predicts poor outcome, but levels in atrial fibrillation (AF) are unknown. Although the platelet is frequently cited as the source of sCD40L, this view is not universal. We hypothesised (a) raised sCD40L in non-rheumatic AF, and (b) that sCD40L correlates with platelet, but not endothelial, markers, thus suggesting a platelet origin. Plasma sCD40L, platelet marker soluble P-selectin and endothelial markers von Willebrand factor (vWf) and soluble E-selectin were measured by ELISA in 54 AF patients free of diabetes or major cardiovascular disease, and in 28 age/sex matched controls. Median (inter-quartile range) sCD40L in AF was 0.82 (0-4.8) ng/mL compared to 0.21 (0-5.5 ng/mL) in controls (p=0.0397). vWf and soluble P-selectin (p<0.005), but not soluble E-selectin, were raised in AF, but none of the indices inter-correlated significantly. We find that sCD40L is marginally raised in AF but the stimulus for this is unclear. The lack of clear correlation with relevant plasma markers suggests that the source is unlikely to be the endothelium or platelet alone.

Developmental changes in soluble CD40 ligand

OBJECTIVES

To determine if soluble CD40 ligand (sCD40L; formally CD154) levels vary with age and to identify age-dependent ranges in healthy pediatric and adult populations.

STUDY DESIGN

sCD40L was measured in 25 neonates, 74 children (3 months-15 years of age) and 20 adults using an enzyme-linked immunosorbent assay. For age group comparisons, Mann-Whitney tests were performed. Correlation coefficients assessed relationships between plasma and serum sCD40L.

RESULTS

Plasma sCD40L levels were higher in neonates than in all other age groups, (P <.001). All grouped pediatric plasma levels were significantly higher than in adults (P < .0001). There were no significant differences in plasma sCD40L between pediatric age groups. Serum levels were significantly higher in neonates than in any other age group (P < .0001). Pediatric and adult serum sCD40L levels were not significantly different.

CONCLUSIONS

Plasma sCD40L levels are highest at birth and remain higher than those in adults throughout childhood. Reasons for such developmental changes remain to be investigated. Age-appropriate reference ranges should be used when sCD40L is being evaluated in pediatric disorders.

Pulmonary hypertension in patients with essential thrombocythemia and reactive thrombocytosis

Increased incidence of pulmonary hypertension (PH) has been reported in patients with chronic myeloproliferative disorders. The exact incidence of PH in essential thrombocythemia (ET) is unknown. Most of the reported literature consists of case reports or small studies. We designed this study to asses the incidence of PH in patients with ET and reactive thrombocytosis. Previously or newly diagnosed 46 patients with ET, and 40 patients with reactive thrombocytosis secondary to iron deficiency anemia were found to be eligible for this study. Diagnosis of PH was established via transthoracic echocardiography. PH was found in 22 (47.8%) out of 46 patients with ET. Seven patients with PH were newly diagnosed ET, 5 patients with PH were in low, and the other patients with PH were in intermediate or high risk category. We found statistically significant difference in terms of platelet counts between ET patients with PH and without PH (p = 0.027). None of the patients with reactive thrombocytosis had PH. In conclusion, PH appears to be common in patients with ET. Therefore, all patients with ET should be evaluated for PH. Larger and prospective studies are required to clarify the long-term impact of PH on the survival of these patients. Future studies are also needed to determine whether cytoreductive treatment and aspirin prevent the development of PH, and to determine the effects of cytoreductive treatments and aspirin on the prognosis of PH. The effect of PH on ET prognosis should also be determined in low risk ET patients.

CD40/CD40L system and vascular disease

Several distinct lines of investigation in the context of atherosclerosis dealing with low-grade inflammation, oxidative stress and platelet activation are now emerging, with CD40/CD40L system as the missing link. CD40 ligand is a transmembrane glycoprotein structurally related to tumour necrosis factor-alpha and more than 95% of the circulating CD40L derives from platelets. CD40L appears as a multiplayer of several cell types in the inflammatory network. The peculiarity of CD40L as an inflammatory mediator derived from platelets expands the functional repertoire of platelets from players of haemostasis and thrombosis to powerful amplifiers of inflammation by promoting the release of cytokines and chemokines, cell activation and cell-cell interactions. The multifunctional role of CD40L, as a simultaneous activator of all these systems, further blurs the intricate relationship between such events both in the physiological systems and the pathological derangement occurring in atherothrombosis.

Role of Endothelium-derived CC Chemokine Ligand 2 in Idiopathic Pulmonary Arterial Hypertension

RATIONALE

Inflammatory cytokines may affect pulmonary vascular remodeling in idiopathic pulmonary arterial hypertension (IPAH). CC chemokine ligand 2 (CCL2) is synthesized by vascular cells and can stimulate monocyte/macrophage migration and smooth muscle cell (SMC) proliferation.

OBJECTIVES

To investigate the role of CCL2 in IPAH.

METHODS

CCL2 levels in plasma, monocytes, lungs, and medium from pulmonary endothelial cell (P-EC) or pulmonary artery SMC (PA-SMC) cultures were measured by ELISA and Western blot analysis. CCL2 receptor CCR2 mRNA levels in monocytes, P-ECs, and PA-SMCs were measured by real-time polymerase chain reaction. Effect of CCL2 on PA-SMC proliferation and migration was assessed using [3H]thymidine incorporation and a modified Boyden's chamber. The effect of endothelial cell-derived CCL2 on monocyte migration was measured using a modified Boyden's chamber.

MEASUREMENTS AND MAIN RESULTS

Compared with control subjects, we found the following in patients with IPAH: elevated CCL2 protein levels in plasma and lung tissue, whereas monocyte CCL2 levels were similar between patients and control subjects, and elevated CCL2 release by P-ECs or PA-SMCs. P-ECs released twice as much CCL2 than did PA-SMCs. Monocyte migration was markedly increased in the presence of P-ECs, and the increase was larger with P-ECs from patients with IPAH. CCL2-blocking antibodies reduced P-ECs' chemotactic activity by 60%. Compared with controls, PA-SMCs from patients exhibited stronger migratory and proliferative responses to CCL2, in keeping with the finding that CCR2 was markedly increased in PA-SMCs from patients.

CONCLUSIONS

These results suggest that CCL2 overproduction may be a feature of the abnormal P-EC phenotype in IPAH, contributing to the inflammatory process and to pulmonary vascular remodeling.

Procoagulant membrane microparticles correlate with the severity of pulmonary arterial hypertension

RATIONALE

Procoagulant microparticles constitute valuable hallmarks of cell damage. Microparticles also behave as cellular effectors.

OBJECTIVES

We hypothesized that the extent of the vascular cell damage measured by circulating microparticles could be related to the severity of pulmonary arterial hypertension (PAH).

METHODS

Circulating biomarkers of vascular damage and cell activation were measured in blood samples from 20 patients with PAH. Samples were withdrawn from occluded pulmonary artery and jugular vein. Peripheral venous blood samples were obtained in 23 control subjects. The microparticle procoagulant abilities were quantified by functional prothrombinase and tissue factor assays and their cellular origin was determined.

MEASUREMENTS AND MAIN RESULTS

Soluble vascular cellular adhesion molecule-1 and proinflammatory markers, such as monocyte chemoattractant protein-1 and highly specific C-reactive protein, were elevated in patients with PAH compared with control subjects. Microparticles bearing active tissue factor and CD105 (endoglin) were also elevated in patients with PAH compared with control subjects (29 +/- 13 vs. 16 +/- 6 fmol/L, P < 0.001, and 1.10 +/- 0.46 vs. 0.49 +/- 0.33 nmol/L phosphatidylserine equivalent, P < 0.001, respectively). A further increase in endothelium-derived CD105 microparticles was observed in pulmonary arterial blood compared with venous blood in patients with PAH (1.73 +/- 0.77, P = 0.038). Microparticles bearing active tissue factor were at a higher level in patients in functional class III and IV and who were walking fewer than 380 m with the six-minute-walk test.

CONCLUSIONS

Circulating markers of endothelium damage, proinflammatory markers, and cell stimulation estimated with circulating microparticles appear to be valuable tools in determining the severity of PAH.

Raised LIGHT levels in pulmonary arterial hypertension: potential role in thrombus formation

RATIONALE

Thrombus formation and inflammation are involved in the pathogenesis of pulmonary arterial hypertension (PAH), and LIGHT (Lymphotoxin-like Inducible protein that competes with Glycoprotein D for Herpesvirus entry mediator on T lymphocytes) has been shown to promote vascular inflammation.

OBJECTIVES

We sought to investigate the role of the tumor necrosis factor superfamily ligand LIGHT in the pathogenesis of PAH.

METHODS

We studied 73 patients with severe PAH and 10 control subjects. LIGHT and pro- and antithrombotic markers were assessed by enzyme immunoassays.

MEASUREMENTS AND MAIN RESULTS

(1) Patients with idiopathic PAH (n = 21), patients with PAH related to risk factors or associated conditions (n = 31), and those with chronic thromboembolic PAH (n = 21) all had raised serum levels of LIGHT compared with control subjects (n = 10). (2) LIGHT levels in femoral artery were significantly related to mortality in the patients with PAH. (3) Immunostaining of LIGHT and its receptors was seen in alveolar macrophages, vascular smooth muscle cells, and endothelial cells in lungs from patients with PAH. (4) Thirteen patients received prostacyclin infusion (3 mo), and all showed hemodynamic improvement, accompanied by decreased LIGHT levels. (5) Prostacyclin abolished the release of LIGHT from activated platelets in vitro, suggesting that the decrease in LIGHT during prostacyclin therapy could involve direct effects on platelets. (6) LIGHT increased tissue factor and plasminogen activator inhibitor type 1 and decreased thrombomodulin levels in endothelial cells, inducing a prothrombotic state in these cells.

CONCLUSIONS

Our findings suggest prothrombotic effects of LIGHT in PAH involving endothelium-related mechanisms, potentially contributing to the progression of this disorder.

Homocysteine Modulates the CD40/CD40L System

OBJECTIVES

This study evaluated the impact of hyperhomocysteinemia (HHcy) on the CD40/CD40 ligand (CD40L) dyad in vivo and in vitro.

BACKGROUND

Hyperhomocysteinemia is associated with an increased incidence of atherothrombosis, although the molecular mechanisms of this association are incompletely defined. The CD40L pair triggers inflammatory signals in cells of the vascular wall, representing a major pathogenetic pathway of atherosclerosis.

METHODS

We used a commercially available enzyme-linked immunosorbent assay kit to evaluate circulating levels of soluble (s) CD40L in 24 patients with HHcy and 24 healthy subjects. We also used real-time polymerase chain reaction and flow cytometry to determine expression levels of CD40 and vascular cell adhesion molecule (VCAM)-1 in human umbilical vein endothelial cells (HUVECs) and of CD40L in human platelets.

RESULTS

The sCD40L levels were significantly increased in HHcy patients (median [interquartile range] 8.0 [0.7 to 10.5] ng/ml vs. 2.1 [1.9 to 2.3] ng/ml, p = 0.0001). Positive correlations were noted between log sCD40L and log homocysteine (Hcy) (R = 0.68, p < 0.0001) or log sVCAM-1 (R = 0.41, p < 0.005). Homocysteine significantly stimulated CD40 mRNA expression in HUVECs (p = 0.033). Consistently, 24-h exposure to Hcy increased the percentage of CD40-expressing cells (p = 0.00025). Homocysteine also significantly enhanced CD40L expression in platelets (p = 0.025) to a comparable extent as that of thrombin. Notably, Hcy increased VCAM-1 protein expression induced by CD40L in HUVECs (p = 0.0046).

CONCLUSIONS

The present results uncover a potential molecular target of Hcy, namely the CD40/CD40L dyad. Collectively, they indicate that upregulation of CD40/CD40L signaling may represent a link between HHcy and an increased risk of cardiovascular disease.

Serum monocyte chemotactic protein-1 levels in congenital diaphragmatic hernia

To measure serum monocyte chemotactic protein-1 (MCP-1) in patients with congenital diaphragmatic hernia (CDH) and investigate its relationship to the development of persistent pulmonary hypertension (PPH). Serum MCP-1 was measured in 13 neonates with high risk for CDH at the time of diagnosis and postoperatively, and in five age-matched controls using an ELISA system. The 13 CDH subjects were divided into four groups according to the presence of PPH and outcome. Group I (severe-pre group): subjects with severe PPH who died prior to surgery (n = 5); Group II (mild-pre group): subjects with mild PPH controlled by medications (n = 8); Group IIa (severe-post group): subjects who subsequently developed severe PPH postoperatively and died (n = 3); and Group IIb (mild-post group): subjects who continued to have mild PPH controlled by medications. We also examined nitrofen-induced hypoplastic lungs from five rat fetuses with CDH and five control lung specimens for MCP-1 using immunohistochemistry. Mean serum MCP-1 in Group I was (1038.0 +/- 95.8 pg/ml), which was significantly higher than Group II (444.9 +/- 39.7 pg/ml) (P < 0.0001) and controls (147.3 +/- 11.3 pg/ml) (P < 0.0001). Postoperatively, Group IIa was significantly higher than Group IIb from 24 to 120 h postoperatively (P < 0.001). In Group IIb serum MCP-1 did not rise at all between 24 and 120 h postoperatively. Hypoplastic fetal rat CDH lungs had strong expression of MCP-1 compared with control lungs. Up-regulated expression and high circulating levels of MCP-1 in CDH patients with PPH suggest that MCP-1 may play a role in the development of PPH in CDH.

Platelet-derived LIGHT induces inflammatory responses in endothelial cells and monocytes

Traditionally, platelets are known to play an important role in hemostasis, thrombosis, and wound healing, but increasing evidence suggests that activated platelets also may promote inflammation. Platelet-induced modulation of inflammation seems to involve platelet expression of ligands in the tumor necrosis factor (TNF) superfamily such as CD40 ligand and Fas ligand. The present study demonstrates that LIGHT, another member of the TNF superfamily, is associated with platelets and is released as a soluble ligand on platelet activation. The release of LIGHT involves GP IIb/IIIa-dependent mechanisms and action of metal-dependent proteases as well as intracellular processes such as actin polymerization. We also report that platelet-derived LIGHT is biologically active and can induce an inflammatory response in monocytes and particularly within endothelial cells measured as up-regulation of adhesion molecules and release of chemokines. Moreover, we demonstrate that thrombus material, obtained at the site of plaque rupture in patients with acute myocardial infarction, contains platelet-associated LIGHT, suggesting that LIGHT-mediated inflammation also is operating in vivo within an inflamed and thrombotic vessel wall. The data may suggest a pathogenic role for platelet-derived LIGHT in atherogenesis and plaque destabilization as well as in other inflammatory disorders involving leukocyte infiltration into the vessel wall.

Molecular Biology of Chronic Thromboembolic Pulmonary Hypertension

Recent efforts have seen major advances in elucidating the mechanisms underlying pulmonary arterial hypertension. However, chronic thromboembolic pulmonary hypertension (CTEPH) often has been excluded from these studies. Consequently, whereas the clinical, radiographic, and hemodynamic characteristics of CTEPH have been well described, there remains a deficit in our understanding of the cellular, molecular, and genetic mechanisms underlying CTEPH. Furthermore, although prior venous thromboembolism may act as the inciting event, it is still unclear what predisposes some patients to develop CTEPH. CTEPH has two major pathogenic components. The first is the primary obstruction of central pulmonary arteries by accumulation of thrombotic material. The second is characterized by severe pulmonary vascular remodeling, similar to that seen in idiopathic pulmonary arterial hypertension. Other articles in this series describe the pathological, surgical, and therapeutic aspects of CTEPH. Here, we review the potential molecular and cellular mechanisms that may contribute to the pathogenesis of CTEPH.

Human VIP-alpha: an emerging biologic response modifier to treat primary pulmonary hypertension

Primary pulmonary hypertension (PPH) is a rare life-threatening disorder of unknown etiology manifested by chronic elevation of pulmonary arterial pressure. Given that pulmonary vasoconstriction, endothelial and vascular smooth muscle cell proliferation and in situ thrombosis contribute appreciably to the evolution of PPH, treatment with vasodilators, antiproliferative drugs and anticoagulants, alone or in combination, constitute the pharmacologic standard of care. To this end, long-term administration of oral calcium channel blockers, prostacyclin analogs by various routes and oral endothelin-1 receptor antagonists, alone or in combination, is efficacious in treating patients with PPH. Unfortunately, efficacy is hampered by poor stability, delivery and bioavailability, and by systemic toxicity. Hence, there is an ongoing need to develop and test new drugs to treat patients with PPH. To address this issue, a novel, targeted, long-acting, biocompatible and safe sterically stabilized liposomal and micellar formulation of human vasoactive intestinal peptide (VIP) was developed and tested for human use: the 28-amino acid pleiotropic biologic response modifier, human VIP-alpha. The long-lasting salutary effects of phospholipid-associated VIP on vasomotor tone and arterial pressure were expressed at low concentrations solely in diseased animals and were independent of its route of administration. Thus, the author proposes that human VIP-alpha could be developed as a safe long-acting drug to treat patients with PPH.

Increased Levels of Soluble CD40L in African Tick Bite Fever: Possible Involvement of TLRs in the Pathogenic Interaction betweenRickettsia africae, Endothelial Cells, and Platelets

The pathophysiological hallmark of spotted fever group rickettsioses comprises infection of endothelial cells with subsequent infiltration of inflammatory cells. Based on its ability to promote inflammation and endothelial cell activation, we investigated the role of CD40L in African tick bite fever (ATBF), caused by Rickettsia africae, using different experimental approaches. Several significant findings were revealed. 1) Patients with ATBF (n = 15) had increased serum levels of soluble CD40 ligand (sCD40L), which decreased during follow-up. 2) These enhanced sCD40L levels seem to reflect both direct and indirect (through endothelial cell activation involving CX3CL1-related mechanisms) effects of R. africae on platelets. 3) In combination with sCD40L, R. africae promoted a procoagulant state in endothelial cells by up-regulating tissue factor and down-regulating thrombomodulin expression. 4) Although the R. africae-mediated activation of platelets involved TLR2, the combined procoagulant effects of R. africae and sCD40L on endothelial cells involved TLR4. 5) Doxycycline counteracted the combined procoagulant effects of R. africae and sCD40L on endothelial cells. Our findings suggest an inflammatory interaction between platelets and endothelial cells in ATBF, involving TLR-related mechanisms. This interaction, which includes additive effects between sCD40L and R. africae, may contribute to endothelial inflammation and hypercoagulation in this disorder.

Eisenmenger syndrome: medical prevention and management strategies

The original definition of Eisenmenger syndrome refers to an unrestrictive post-tricuspid valve congenital systemic-to-pulmonary shunt. When the pulmonary arterial systolic pressure becomes equal to the systemic arterial systolic pressure, the direction of the shunt becomes pulmonary-to-systemic. The latter leads to progressive cyanosis, and exercise intolerance is initially proportional to the degree of hypoxaemia. Later, congestive heart failure may occur . The management principle is to avoid any factors that destabilise this delicately balanced physiology. Until recently, this could only be achieved by symptomatic therapy; however, when patients are severely incapacitated, transplantation is needed. At present, new drugs, which are more selective pulmonary vasodilators, are available to interfere with the ongoing disease process to improve functional capacity and delay the decision for transplantation.

Renal and vascular hypertension-induced inflammation: role of angiotensin II

PURPOSE OF REVIEW

We will focus on the recent findings concerning the inflammatory response in vascular and renal tissues caused by hypertension.

RECENT FINDINGS

Angiotensin II is one of the main factors involved in hypertension-induced tissue damage. This peptide regulates the inflammatory process. Angiotensin II activates circulating cells, and participates in their adhesion to the activated endothelium and subsequent transmigration through the synthesis of adhesion molecules, chemokines and cytokines. Among the intracellular signals involved in angiotensin II-induced inflammation, the production of reactive oxygen species and the activation of nuclear factor-kappaB are the best known.

SUMMARY

The pharmacological blockade of angiotensin II actions, by angiotensin-converting enzyme inhibitors or angiotensin receptor antagonists, results in beneficial organ protective effects, in addition to the effects of these agents on blood pressure control, that can be explained by the blockade of the angiotensin II-induced pro-inflammatory response. These data provide a rationale for the use of blockers of the renin-angiotensin system to prevent vascular and renal inflammation in patients with hypertension.

CD40 Ligand Influences Platelet Release of Reactive Oxygen Intermediates

OBJECTIVE

Soluble CD40 ligand (sCD40L) has been recently implicated in the pathogenesis of atherosclerosis. Elevated levels of sCD40L in acute coronary syndrome patients suggests enhanced platelet function; however, the exact mechanism by which this occurs is unknown. In this study, we examined the effect of sCD40L on platelet function and reactive oxygen and nitrogen species (RONS) generation.

METHODS AND RESULTS

Platelet stimulation in the presence of recombinant sCD40L (rsCD40L) led to enhanced generation of RONS as measured by DCFHDA oxidation and confocal microscopy. Incubation with rsCD40L led to enhanced platelet P-selectin expression, aggregation, and platelet-leukocyte conjugation. Platelets isolated from CD40L-deficient mice had decreased agonist-induced NO release as compared with wild-type mice. Incubation of platelets with rsCD40L enhanced stimulation-induced p38 MAP kinase and Akt phosphorylation.

CONCLUSIONS

Soluble CD40L enhances platelet activation, aggregation, and platelet-leukocyte conjugation, as well as increases stimulation-induced platelet release of RONS through activation of Akt and p38 MAP kinase signaling pathways. These data suggest that sCD40L regulates platelet-dependent inflammatory and thrombotic responses that contribute to the pathogenesis of atherothrombosis.