Abnormal lymphatic S1P signaling aggravates lymphatic dysfunction and tissue inflammation

BACKGROUND

Lymphedema is a global health problem with no effective drug treatment. Enhanced T cell immunity and abnormal lymphatic endothelial cell (LEC) signaling are promising therapeutic targets for this condition. Sphingosine-1-phosphate (S1P) mediates a key signaling pathway required for normal LEC function, and altered S1P signaling in LECs could lead to lymphatic disease and pathogenic T cell activation. Characterizing this biology is relevant for developing much-needed therapies.

METHODS

Human and mouse lymphedema was studied. Lymphedema was induced in mice by surgically ligating the tail lymphatics. Lymphedematous dermal tissue was assessed for S1P signaling. To verify the role of altered S1P signaling effects in lymphatic cells, LEC-specific S1pr1 -deficient ( S1pr1 LECKO ) mice were generated. Disease progression was quantified by tail-volumetric and -histopathological measurements over time. LECs from mice and humans, with S1P signaling inhibition, were then co-cultured with CD4 T cells, followed by an analysis of CD4 T cell activation and pathway signaling. Finally, animals were treated with a monoclonal antibody specific to P-selectin to assess its efficacy in reducing lymphedema and T cell activation.

RESULTS

Human and experimental lymphedema tissues exhibited decreased LEC S1P signaling through S1PR1. LEC S1pr1 loss-of-function exacerbated lymphatic vascular insufficiency, tail swelling, and increased CD4 T cell infiltration in mouse lymphedema. LECs, isolated from S1pr1 LECKO mice and co-cultured with CD4 T cells, resulted in augmented lymphocyte differentiation. Inhibiting S1PR1 signaling in human dermal LECs (HDLECs) promoted T helper type 1 and 2 (Th1 and Th2) cell differentiation through direct cell contact with lymphocytes. HDLECs with dampened S1P signaling exhibited enhanced P-selectin, an important cell adhesion molecule expressed on activated vascular cells. In vitro , P-selectin blockade reduced the activation and differentiation of Th cells co-cultured with sh S1PR1 -treated HDLECs. P-selectin-directed antibody treatment improved tail swelling and reduced Th1/Th2 immune responses in mouse lymphedema.

CONCLUSION

This study suggests that reduction of the LEC S1P signaling aggravates lymphedema by enhancing LEC adhesion and amplifying pathogenic CD4 T cell responses. P-selectin inhibitors are suggested as a possible treatment for this pervasive condition.

Clinical Perspective

What is New?: Lymphatic-specific S1pr1 deletion exacerbates lymphatic vessel malfunction and Th1/Th2 immune responses during lymphedema pathogenesis. S1pr1 -deficient LECs directly induce Th1/Th2 cell differentiation and decrease anti-inflammatory Treg populations. Peripheral dermal LECs affect CD4 T cell immune responses through direct cell contact.LEC P-selectin, regulated by S1PR1 signaling, affects CD4 T cell activation and differentiation.P-selectin blockade improves lymphedema tail swelling and decreases Th1/Th2 population in the diseased skin.What Are the Clinical Implications?: S1P/S1PR1 signaling in LECs regulates inflammation in lymphedema tissue.S1PR1 expression levels on LECs may be a useful biomarker for assessing predisposition to lymphatic disease, such as at-risk women undergoing mastectomyP-selectin Inhibitors may be effective for certain forms of lymphedema.

A Role for P-selectin and Complement in the Pathological Sequelae of Germinal Matrix Hemorrhage

Background Germinal Matrix Hemorrhage is a devastating disease of pre-term infancy commonly resulting in post-hemorrhagic hydrocephalus, periventricular leukomalacia, and subsequent neurocognitive deficits. We demonstrate vascular expression of the adhesion molecule P-selectin after GMH and investigate a strategy to specifically target complement inhibition to sites of P-selectin expression to mitigate the pathological sequelae of GMH. Methods We prepared two fusion proteins consisting of different anti-P-selectin single chain antibodies (scFv's) linked to the complement inhibitor Crry. One scFv targeting vehicle (2.12scFv) blocked the binding of P-selectin to its PSGL-1 ligand expressed on leukocytes, whereas the other targeting vehicle (2.3scFv) bound P-selectin without blocking ligand binding. Post-natal mice on day 4 (P4) were subjected to collagenase induced-intraventricular hemorrhage and treated with 2.3Psel-Crry, 2.12Psel-Crry, or vehicle. Results Compared to vehicle treatment, 2.3Psel-Crry treatment after induction of GMH resulted in reduced lesion size and mortality, reduced hydrocephalus development, and improved neurological deficit measurements in adolescence. In contrast, 2.12Psel-Crry treatment resulted in worse outcomes compared to vehicle. Improved outcomes with 2.3Psel-Crry were accompanied by decreased P-selectin expression, and decreased complement activation and microgliosis. Microglia from 2.3Psel-Crry treated mice displayed a ramified morphology, similar to naïve mice, whereas microglia in vehicle treated animals displayed a more ameboid morphology that is associated with a more activated status. Consistent with these morphological characteristics, there was increased microglial internalization of complement deposits in vehicle compared to 2.3Psel-Crry treated animals, reminiscent of aberrant C3-dependent microglial phagocytosis that occurs in other (adult) types of brain injury. Also, following systemic injection, 2.3Psel-Crry specifically targeted to the post-GMH brain. Likely accounting for the unexpected finding that 2.12Psel-Crry worsens outcome following GMH was the finding that this construct interfered with coagulation in this hemorrhagic condition, and specifically with heterotypic platelet-leukocyte aggregation, which express P-selectin and PSGL-1, respectively. Conclusion GMH induces expression of P-selectin, the targeting of which with a complement inhibitor protects against pathogenic sequelae of GMH. A dual functioning construct with both P-selectin and complement blocking activity interferes with coagulation and worsens outcomes following GMH, but has potential for treatment of conditions that incorporate pathological thrombotic events, such as ischemic stroke.

Preclinical studies on the use of a P-selectin-blocking monoclonal antibody to halt progression of myelofibrosis in the Gata1low mouse model

The bone marrow (BM) and spleen from patients with myelofibrosis (MF), as well as those from the Gata1low mouse model of the disease contain increased number of abnormal megakaryocytes. These cells express high levels of the adhesion receptor P-selectin on their surface, which triggers a pathologic neutrophil emperipolesis, leading to increased bioavailability of transforming growth factor-β (TGF-β) in the microenvironment and disease progression. With age, Gata1low mice develop a phenotype similar to that of patients with MF, which is the most severe of the Philadelphia-negative myeloproliferative neoplasms. We previously demonstrated that Gata1low mice lacking the P-selectin gene do not develop MF. In the current study, we tested the hypothesis that pharmacologic inhibition of P-selectin may normalize the phenotype of Gata1low mice that have already developed MF. To test this hypothesis, we have investigated the phenotype expressed by aged Gata1low mice treated with the antimouse monoclonal antibody RB40.34, alone and also in combination with ruxolitinib. The results indicated that RB40.34 in combination with ruxolitinib normalizes the phenotype of Gata1low mice with limited toxicity by reducing fibrosis and the content of TGF-β and CXCL1 (two drivers of fibrosis in this model) in the BM and spleen and by restoring hematopoiesis in the BM and the architecture of the spleen. In conclusion, we provide preclinical evidence that treatment with an antibody against P-selectin in combination with ruxolitinib may be more effective than ruxolitinib alone to treat MF in patients.

Experimental Agents for the Treatment of Atherosclerosis: New Directions

Cardiovascular and related metabolic disorders constitute a worldwide health challenge. Atherosclerosis is a chronic inflammatory condition based on both dyslipidemia and inflammation. Therefore, even when dyslipidemia is controlled, the risk of atherosclerosis remains. Among the most efficient inflammatory mediators used as therapeutic tools in cardiovascular disease are the interleukins, which are pro-inflammatory mediators like cytokines. Moreover, a protein kinase inhibitors, p38 mitogen-activated protein kinase (MAPK) inhibitor, and an inhibitor of a leukocyte adhesion molecule, P-Selectin, have also presented therapeutic potential for this disorder. Colchicine, being an inexpensive therapeutic option, has been proved to be suitable for the prevention of atherosclerosis. In this review, we summarize all the studies, from 2010 to 2020, in which treatment approaches based on the agents mentioned above are evaluated in the management of atherosclerosis.

Coagulation Profiles of Pulmonary Arterial Hypertension Patients, Assessed by Non-Conventional Hemostatic Tests and Markers of Platelet Activation and Endothelial Dysfunction

Many pathophysiologic processes of pulmonary arterial hypertension (PAH), namely, excess vasoconstriction, vascular remodeling and in situ thrombosis, involve the coagulation cascade, and more specifically, platelets. The aim of this study was to globally assess coagulation processes in PAH, by using non-conventional hemostatic tests, along with markers of platelet activation and endothelial dysfunction. We studied 44 new PAH patients (22 with idiopathic PAH and 22 with connective tissue disease) and 25 healthy controls. The following tests were performed: platelet function analyzer-100 (PFA-100), light transmission aggregometry (LTA), rotational thromboelastometry (ROTEM), endogenous thrombin potential (ETP), serotonin, thromboxane A2 and p-selectin plasma levels, and von Willebrand antigen (VWF:Ag) and activity (VWF:Ac). Our results showed that PAH patients had diminished platelet aggregation, presence of disaggregation, defective initiation of the clotting process and clot propagation, and diminished thrombin formation capacity. Serotonin, thromboxane A2 and p-selectin levels were increased, and VWF:Ag and VWF:Ac decreased in the same population. The results of this study suggest that the platelets of PAH patients are activated and present functional abnormalities. The procoagulant activity, in general, appears to be impaired probably due to a sustained and prolonged activation of the procoagulant processes. Larger observational studies are warranted to confirm these laboratory findings.

Correlation between P-selectin rs1800807 and rs1800808 Gene polymorphisms and plasma soluble P-selectin concentrations in patients with atrial fibrillation complicated with thromboembolism in Xinjiang, China

This study is to investigate the relationship of P-selectin (Ps) gene rs1800807 and rs1800808 polymorphisms with plasma soluble P-selectin (sPs) in Han, Uygur, and Kazakh people with atrial fibrillation (AF) and thromboembolism (TE) in Xinjiang, China.A total of 778 Han patients (including 131 patients with AF and TE, 229 patients with AF and 418 healthy individuals), 660 Uygur patients (including 118 patients with AF and TE, 232 patients with AF and 310 healthy individuals), and 505 Kazakh patients (including 42 patients with AF and TE, 156 patients with AF and 307 healthy individuals) were enrolled in this study. Polymerase chain reaction-restriction fragment length polymorphism and direct DNA sequence analysis were used to analyze the polymorphisms of rs1800807 and rs1800808 of Ps gene. ELISA was used to determine the plasma sPs level. The association between plasma sPs levels and Ps gene polymorphisms was further analyzed.The sPs concentrations of GG genotype at rs1800807 locus in the Han, Uygur and Kazakh ethnic groups in Xinjiang, China were significantly higher than those of the CC genotype and CG genotype (P < .05). In the rs1800808 locus, plasma sPs concentrations of the heterozygous mutant CT genotypes in Han and Uygur populations were significantly higher than those in the CC and TT genotypes, whereas the plasma sPs concentrations in Kazakh TT genotypes were significantly higher than those in the CC and CT genotypes (P < .05). Among different ethnic groups, there were significant differences in sPs levels of rs1800807 and rs1800808 genotypes (P < .05).Plasma sPs concentrations are associated with Ps genotypes and sPs concentration of the same genotype shows racial differences.

Effect of Acute Altitude Exposure on Serum Markers of Platelet Activation

Background: Platelets are the key factor in primary hemostasis. It has been shown that chronic altitude exposure increases platelets' aggregability. Nevertheless, data about acute effects and the underlying mechanisms are sparse. Methods: Sixteen healthy volunteers were examined in our hospital (519 m alt.) and 30 minutes after arrival in the environmental research station on the Zugspitze Mountain (2656 m alt.). Serum levels of soluble p-selectin were examined to elucidate platelet activation. In addition, serum levels of chromogranin A (CGA) as a measure of adrenergic activation, endothelin 1 (ET-1) representing pulmonary vascular tone and monocyte chemoattractant protein-1 (MCP-1) as a measure of inflammatory response were examined. Results: Acute altitude exposure induced a significant increase of p-selectin (116 ± 4.8 pg/mL vs. 132 ± 6.2 pg/mL; p < 0.01). Whereas MCP-1 was significantly lowered (538 ± 50.6 pg/mL to 470 ± 41.1 pg/mL; p = 0.02) and CGA was not altered significantly (88 ± 47.4 ng/mL vs. 79 ± 44 ng/mL; p = 0.22), ET1 was increased significantly from 0.8 ± 0.07 pg/mL to 1.15 ± 0.09 pg/mL (p < 0.01). Conclusion: Our study could demonstrate relevant platelet activation that was accompanied by a 44% increase of ET-1. This activation might obtain clinical relevance in patients with pre-existing cardiovascular disease as a trigger for acute events.

Circulating Factors and Ultrasono-findings are Linked to Previous Atherosclerotic Burden and Recurrent Risk

Abstract: Background:

In the progression of atherosclerosis, platelet activation and the interaction of platelets with leukocytes play a crucial role in arterial thrombus formation and are associated with the pathophysiology of carotid and cerebrovascular disease (CVD), including ischemic stroke. With aged participants, we evaluated and followed up the change in circulating factor and platelet-leukocyte aggregate levels in participants with or without CVD history. This study investigated whether circulating factor changes and ultrasonographic characteristics link to CVD risk and other relating long-term outcomes.

Materials and Methods:

Two hundred fifteen participants who enrolled in the study were divided into two groups with CVD and without CVD history. We evaluated and analyzed the correlation between ultrasonography-based morphological characteristics and circulating factor-based functional changes in both groups.

Results:

There was no difference in p-selectin level between both groups. However, activated monocyte and platelet-monocyte aggregate levels were higher in patients with previous CVD than without previous CVD. Circulating factor and ultrasonographical characteristics were correlated in the group with CVD, whereas these factors were not correlated in the group without CVD.

Conclusion:

We found that circulating blood factor levels showed a different tendency in participants with and without CVD history. The results depict that atherosclerotic severity might depend on the history of CVD and progression of atherosclerosis. We suggest that the circulating factor levels, atherosclerotic severity, and history of CVD are considered in the observation of pathologic progression to manage the development of CVD risks and CVD relating outcomes.

Positron Emission Tomography and Autoradiography Imaging of P-selectin Activation Using 68Ga-Fucoidan in Photothrombotic Stroke

BACKGROUND

P-selectin is activated early after stroke, followed by a rapid decline. This time course can be used to generate important information on stroke onset. The latter is crucial for therapeutic decision-making of wake-up strokes (i.e. thrombolysis or not). Here, we evaluated the specific p-selectin inhibitor fucoidan labeled with gallium-68 (68Ga-Fucoidan) as an imaging biomarker for assessing p-selectin activation in acute ischemic stroke using Positron Emission Tomography (PET).

METHODS

68Ga-Fucoidan was investigated in rats brain at 2-5 h (n=16), and additionally at 24-26 h (n=9) and 48 h (n=3) after induction of photothrombic stroke or in sham-operated animals (n=6). Correlation of cerebral 68Ga-Fucoidan uptake with p-selectin expression was determined by exposing freshly cut brain cryosections to autoradiography and immunostaining using specific antibodies against p-selectin.

RESULTS

PET scans showed an increased accumulation of 68Ga-Fucoidan in the histologically proven ischemic stroke, as compared to the corresponding contralateral hemisphere in all except one animal. The median ratio between the uptake in the ischemic lesion and the contralateral region was 1.95 (1.45-2.41) at 2-5 h, 1.38 (1.05-1.89) at 24-26 h, and 1.09 (0.81-1.38) at 48 h after stroke, compared to 1.22 (0.99-1.49) for sham-operated animals. In the ex vivo autoradiography, 68Ga-Fucoidan accumulation co-localized with p-selectin as assessed by immunostaining. Control animals and those scanned at 24-26 h and 48 h after stroke exhibited no elevated 68Ga-Fucoidan uptake in either hemisphere.

CONCLUSION

PET imaging using 68Ga-Fucoidan represents a valuable tool for assessing p-selectin activation in vivo discriminating ischemic stroke early after stroke onset.

[Effect of ulinastatin on serum levels of tumor necrosis factor-α, P-selectin, and thrombin-antithrombin complex in young rats with sepsis]

OBJECTIVE

To investigate the effect of ulinastatin (UTI) for early drug intervention on the serum levels of tumor necrosis factor-α (TNF-α), P-selectin, and thrombin-antithrombin complex (TAT) in young rats with sepsis.

METHODS

A total of 120 male rats aged 4 weeks were randomly divided into normal control group, sham-operation group, sepsis group, low-dose UTI group (50 000 U/kg), and high-dose UTI group (200 000 U/kg), with 24 rats in each group. Modified cecal ligation and puncture was performed to establish a rat model of sepsis, and the rats in the low- and high-dose UTI groups were given caudal vein injection of UTI after model establishment. ELISA was used to measure the serum levels of TNF-α, P-selectin, and TAT at 6, 12, and 24 hours after model establishment.

RESULTS

The sepsis group had significant increases in the serum levels of TNF-α, P-selectin, and TAT at 6 hours, and the serum levels of TNF-α and TAT continued to increase by 24 hours (P<0.05); P-selectin reached the peak at 12 hours and decreased slightly at 24 hours (P<0.05). The UTI groups had similar change patterns in the levels of P-selectin and TAT as the sepsis group. The UTI groups had significant increases in the level of TNF-α at 6 hours, but gradually decreased over time. The changes in serum levels of TNF-α, P-selectin, and TAT in the UTI groups were significantly smaller than in the sepsis group (P<0.05). The high-dose UTI group had significantly smaller changes in serum levels of TNF-α, P-selectin, and TAT than the low-dose UTI group (P<0.05).

CONCLUSIONS

Early intervention with UTI can significantly improve coagulation function and inhibit the production of TNF-α, P-selectin, and TAT in young rats with sepsis. High-dose UTI has a significantly greater effect than low-dose UTI.

[Effect of ulinastatin on serum levels of tumor necrosis factor-α, P-selectin, and thrombin-antithrombin complex in young rats with sepsis]

OBJECTIVE

To investigate the effect of ulinastatin (UTI) for early drug intervention on the serum levels of tumor necrosis factor-α (TNF-α), P-selectin, and thrombin-antithrombin complex (TAT) in young rats with sepsis.

METHODS

A total of 120 male rats aged 4 weeks were randomly divided into normal control group, sham-operation group, sepsis group, low-dose UTI group (50 000 U/kg), and high-dose UTI group (200 000 U/kg), with 24 rats in each group. Modified cecal ligation and puncture was performed to establish a rat model of sepsis, and the rats in the low- and high-dose UTI groups were given caudal vein injection of UTI after model establishment. ELISA was used to measure the serum levels of TNF-α, P-selectin, and TAT at 6, 12, and 24 hours after model establishment.

RESULTS

The sepsis group had significant increases in the serum levels of TNF-α, P-selectin, and TAT at 6 hours, and the serum levels of TNF-α and TAT continued to increase by 24 hours (P<0.05); P-selectin reached the peak at 12 hours and decreased slightly at 24 hours (P<0.05). The UTI groups had similar change patterns in the levels of P-selectin and TAT as the sepsis group. The UTI groups had significant increases in the level of TNF-α at 6 hours, but gradually decreased over time. The changes in serum levels of TNF-α, P-selectin, and TAT in the UTI groups were significantly smaller than in the sepsis group (P<0.05). The high-dose UTI group had significantly smaller changes in serum levels of TNF-α, P-selectin, and TAT than the low-dose UTI group (P<0.05).

CONCLUSIONS

Early intervention with UTI can significantly improve coagulation function and inhibit the production of TNF-α, P-selectin, and TAT in young rats with sepsis. High-dose UTI has a significantly greater effect than low-dose UTI.

Soluble vascular cell adhesion molecular-1 is a potential biological indicator of hemophilic arthropathy

Hemophilic arthropathy is the most common chronic complication in patients with hemophilia. The pathogenesis of hemophilic arthropathy involves the inflammatory processes associated with rheumatoid arthritis (RA). Determining the severity and/or progression of joint damage is crucial when evaluating the effect of treatment modalities. Identifying reliable biomarkers in the peripheral blood of patients with hemophilic arthropathy may be beneficial in clinical practice. Circulating soluble vascular cell adhesion molecule-1 (sVCAM-1), E-selectin, and P-selectin levels are elevated in patients with RA. Our study investigated whether these soluble adhesion molecules can be used as biological indicators in the course of joint damage in patients with hemophilia A.Patients with hemophilia A (mild, moderate, and severe) were enrolled. The plasma levels of sVCAM-1, E-selectin, and P-selectin in patients with hemophilia A and control were measured using specific enzyme-linked immunosorbent assay kits. Joint damages were evaluated using Pettersson scores.No statistically significant differences were observed in E-selectin and P-selectin levels between patients and controls. The sVCAM-1 level was significantly higher in patients with hemophilia A than in controls. The differences remained significant in patients with severe hemophilia A but not in patients with mild or moderate hemophilia A. The degree of hemophilic arthropathy was evaluated using Pettersson scores, and a score higher than 5 indicated marked arthropathy. Patients with more than 1 joint with marked arthropathy showed significantly higher sVCAM-1 levels.sVCAM-1 levels in patients with hemophilia A are associated with the severity of hemophilic arthropathy.

Impact of adiposity on cellular adhesion: The Multi-Ethnic Study of atherosclerosis (MESA)

OBJECTIVE

At the cellular level, how excess adiposity promotes atherogenesis is not fully understood. One pathway involves secretion of adipokines that stimulate endothelial dysfunction through increased expression of adhesion molecules. However, the relationship of adiposity to adhesion molecules that promote atherosclerosis is largely unknown.

METHODS

Linear regression models were used to assess the sex-specific associations of soluble cellular adhesion molecules (sP- and sL-selectin, sICAM-1, sVCAM-1, and sHGF) and adiposity in 5,974 adults examined as part of the Multi-Ethnic Study of Atherosclerosis (MESA). Adiposity measures included body mass index (BMI), waist-to-hip-ratio (WHR), and computed tomography measures of subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT).

RESULTS

The mean age was 64 years and 52% were female. In multivariable models adjusting for traditional cardiovascular risk factors, sHGF was positively associated with BMI, WHR, and VAT in both males and females, and sP-selectin with WHR and VAT in males. sVCAM-1 was inversely associated with VAT in females only.

CONCLUSIONS

Our results showed the relation of adiposity to soluble cellular adhesion proteins was similar across adiposity measures and for both sexes. However, the relationship between adiposity and sVCAM-1 and P-selectin may be modified by sex and the measure used to assess adiposity.

Effects of ethyl pyruvate on leukocyte-endothelial interactions in the mesenteric microcirculation during early sepsis treatment

OBJECTIVES

Experimental studies on sepsis have demonstrated that ethyl pyruvate is endowed with antioxidant and anti-inflammatory properties. This study aimed to investigate the effects of ethyl pyruvate on leukocyte-endothelial interactions in the mesenteric microcirculation in a live Escherichia coli-induced sepsis model in rats.

METHODS

Male Wistar rats were administered an intravenous suspension of E. coli bacteria or were subjected to a sham procedure. Three hours after bacterial infusion, the rats were randomized into the following groups: a control group without treatment, a group treated with lactated Ringer's solution (4 mL/kg, i.v.), and a group treated with lactated Ringer's solution (4 mL/kg, i.v.) plus ethyl pyruvate (50 mg/kg). At 24 h after bacterial infusion, leukocyte-endothelial interactions were investigated using intravital microscopy, and the expression of P-selectin and intercellular adhesion molecule-1 was evaluated via immunohistochemistry. White blood cell and platelet counts were also determined at baseline and 3 h and 24 h after E. coli inoculation.

RESULTS

The non-treated and lactated Ringer's solution-treated groups exhibited increases in the numbers of rolling leukocytes (∼2.5-fold increase), adherent cells (∼3.0-fold), and migrated cells (∼3.5-fold) compared with the sham group. In contrast, treatment with Ringer's ethyl pyruvate solution reduced the numbers of rolling, adherent and migrated leukocytes to the levels observed in the sham group. Additionally, the expression of P-selectin and intercellular adhesion molecule-1 was significantly increased on mesenteric microvessels in the non-treated group compared with the sham group (p<0.001). The expression of both adhesion molecules was reduced in the other groups, with ethyl pyruvate being more effective than lactated Ringer's solution. Infusion of bacteria caused significant leukopenia (3 h), followed by leukocytosis with granulocytosis (24 h). There was also an intense and progressive reduction in the number of platelets. However, no differences were observed after treatment with the different solutions.

CONCLUSIONS

The presented data suggest that ethyl pyruvate efficiently reduces the inflammatory response in the mesenteric microcirculation in an experimental model of sepsis induced by live E. coli and is associated, at least in part, with down-regulation of P-selectin and intercellular adhesion molecule-1.

The changes of von willebrand factor/a disintegrin-like and metalloprotease with thrombospondin type I repeats-13 balance in aneurysmal subarachnoid hemorrhage

The aim of this study was to investigate the role of Von Willebrand Factor/thrombospondin type I repeats-13 (VWF/ADAMTS13) balance in aSAH. Fifty eight patients with aSAH at the First Affiliated hospital of Soochow University, Suzhou, China, between January 2012 and January 2014 were eligible for the study. They were divided into delayed cerebral ischemia group (DCI group) and non-delayed cerebral ischemia group (no DCI group), or cerebral vasospasm group (CVS group) and no spasm group (no CVS group), or good outcome group and poor outcome group. The control group consisted of twenty healthy people. All patients underwent CT, DSA, or (and) CTA diagnosed with intracranial subarachnoid hemorrhage which is caused by aneurysm rupture. Venous blood was drawn in tubes at 3 time points: 1 day after SAH (T1), (4±1) days after SAH (T2), and (9±1) days after SAH (T3) to determine plasma concentrations of ADAMTS13, VWF, P-selectin and IL-6 via enzyme-linked immunosorbent assay (ELISA). Transcranial doppler sonography (TCD) was used to measure mean blood flow velocity of the middle cerebral artery (VMCA). Glasgow Outcome Scale (GOS) was measured before discharge. Among 58 patients, 12 (20.7%) had DCI, 40 (68.9%) had TCD evidence of CVS, and 20 (34.5%) had poor outcome. The concentrations of VWF, P-selectin and IL-6 on T1, T2 and T3 after SAH were significantly higher in DCI, CVS and poor outcome groups compared with those of the control group (P < 0.05). The concentrations of VWF, P-selectin and IL-6 were significantly higher in DCI, CVS and poor outcome groups compared with those of the no DCI, no CVS and good outcome groups. The activity of ADAMTS13 was lower in DCI and poor outcome groups compared with those of the no DCI and good outcome groups (P < 0.05). The activity of ADAMTS13 showed no difference in CVS group and no CVS group (P > 0.05). The results of our study suggest that the increased VWF and decreased ADAMTS13 activity were associated with DCI and poor outcome. The balance of VWF/ADAMTS13 could be used to predict the clinical outcome. The deficiency of ADAMTS13 can not only induce DCI but also accelerate inflammatory reaction. Our results reported in this paper may provide new insights into the possible use of ADAMTS13 as a therapeutic agent in aneurysmal subarachnoid hemorrhage.

Six hours of resting platelet concentrates stored at 22-24 ºC for 48 hours in permeable bags preserved pH, swirling and lactate dehydrogenase better and caused less platelet activation

BACKGROUND

During transportation, platelet concentrates (PC) usually undergo a long period without agitation. Whether this interruption improves quality and viability or, contrariwise, has deleterious effects on PC stored for 48 hours (h) is unknown. The aim of this study was to investigate the effects of metabolic resting (6 h of interruption of agitation) vs continue agitation of PC stored for 48 h in the blood bank of Tehran.

MATERIALS AND METHODS

PC were prepared from platelet-rich plasma and stored in permeable bags in a shaker/incubator for 42 h at room temperature (20-24 ºC). Then, simply by stopping the agitator, the PC remained stationary ("resting") without agitation for 6 h (WCA6h), prior to transfusion. In vitro measurements of platelet quality were carried out just after completion of the resting period and the results were compared with those of PC continuously agitated in the same day (designated as the control group, CA6h). The in vitro variables measured were swirling, ristocetin-induced aggregation (GPIb-related function), lactate dehydrogenase (LDH) concentration, platelet factor 4 (PF4) release and P-selectin expression (activation markers).

RESULTS

The mean platelet counts of the control group (CA6h) and rested (WCA6h) PC were not statistically different (P =0.548). Likewise, the mean pH values were not significantly different: WCA6h (7.16 ± 0.08) and CA6h (7.22 ± 0.16) (P =0.300). Although ristocetin-induced aggregation did not differ significantly between CA6h (79.2 ± 4.4) and WCA6h (66.65 ± 28.55) (P =0.186), WCA6h showed significantly less PFA release (P =0.015) and lower P-selectin expression (P =0.006).

CONCLUSIONS

We observed that PC stored under agitation for 42 h at 22-24 ºC in permeable bags and then rested for 6 h had better preserved pH, swirling and LDH and less platelet activation then PC kept under continuous agitation for the whole 48 h storage period.

Sulfochitosan inhibits P-selectin-mediated HL-60 leukocyte adhesion under flow conditions

Excessive trafficking of leukocytes can lead to serious tissue injury. Here, four regioselectively sulfated chitosans were assessed as inhibitors of HL-60 leukocyte binding to P-selectin, by investigating their effect on leukocyte adhesion to CHO cells expressing human P-selectin under static and flow conditions. The results show that the sulfochitosans exhibit inhibitory activity in this general order: heparin > N-sulfated/6-O-sulfated chitosan ≥ 3-O,6-O-sulfated chitosan > 6-O-sulfated chitosan >> N-sulfated chitosan. This suggests that the sulfation of the double site in chitosan is essential for efficient inhibition of P-selectin-mediated HL-60 leukocyte adhesion and that such sulfochitosans may have potential as therapeutic agents against inflammatory disease.

Blockade of p-selectin is sufficient to reduce MHC I antibody-elicited monocyte recruitment in vitro and in vivo

Donor-specific HLA antibodies significantly lower allograft survival, but as yet there are no satisfactory therapies for prevention of antibody-mediated rejection. Intracapillary macrophage infiltration is a hallmark of antibody-mediated rejection, and macrophages are important in both acute and chronic rejection. The purpose of this study was to investigate the Fc-independent effect of HLA I antibodies on endothelial cell activation, leading to monocyte recruitment. We used an in vitro model to assess monocyte binding to endothelial cells in response to HLA I antibodies. We confirmed our results in a mouse model of antibody-mediated rejection, in which B6.RAG1(-/-) recipients of BALB/c cardiac allografts were passively transferred with donor-specific MHC I antibodies. Our findings demonstrate that HLA I antibodies rapidly increase intracellular calcium and endothelial presentation of P-selectin, which supports monocyte binding. In the experimental model, donor-specific MHC I antibodies significantly increased macrophage accumulation in the allograft. Concurrent administration of rPSGL-1-Ig abolished antibody-induced monocyte infiltration in the allograft, but had little effect on antibody-induced endothelial injury. Our data suggest that antagonism of P-selectin may ameliorate accumulation of macrophages in the allograft during antibody-mediated rejection.

Levels of soluble platelet endothelial cell adhesion molecule-1 and P-selectin are decreased in children with autism spectrum disorder

BACKGROUND

Although the etiopathology of autism spectrum disorder (ASD) is not clear, there is increasing evidence that dysfunction in the immune system affects many children with ASD. Findings of immune dysfunction in ASD include increases in inflammatory cytokines, chemokines, and microglial activity in brain tissue and cerebrospinal fluid, as well as abnormal peripheral immune cell function.

METHODS

Adhesion molecules, such as platelet endothelial adhesion molecule-1 (PECAM-1), intercellular adhesion molecule-1 (ICAM-1), vascular adhesion molecule-1 (VCAM-1), P-selectin, and L-selectin, function to facilitate leukocyte transendothelial migration. We assessed concentrations of soluble adhesion molecules, sPECAM-1, sICAM-1, sVCAM-1, sP-selectin, and sL-selectin in the plasma of 49 participants with ASD and 31 typically developing controls of the same age, all of whom were enrolled as part of the Autism Phenome Project. Behavioral assessment, the levels of soluble adhesion molecules, and head circumference were compared in the same subjects.

RESULTS

Levels of sPECAM-1 and sP-selectin were significantly reduced in the ASD group compared to typically developing controls (p < .02). Soluble PECAM-1 levels were negatively associated with repetitive behavior and abnormal brain growth in children with ASD (p = .03).

CONCLUSIONS

Because adhesion molecules modulate the permeability and signaling at the blood-brain barrier as well as leukocyte infiltration into the central nervous system, the current data suggest a role for these molecules in the complex pathophysiology of ASD.

A triple-targeted ultrasound contrast agent provides improved localization to tumor vasculature

OBJECTIVES

Actively targeting ultrasound contrast agents to tumor vasculature improves contrast-enhanced sonography of tumor angiogenesis. This report summarizes an evaluation of multitargeted microbubbles, comparing single-, dual-, and triple-targeted motifs.

METHODS

Microbubbles were avidin-biotin linked to antibodies against mouse α(V)β(3)-integrin, P-selectin, and vascular endothelial growth factor receptor 2. These receptors are constitutively overexpressed in tumor vasculature. Binding comparisons between targeted microbubble groups were evaluated on mouse SVR angiosarcoma endothelial cells. Levels of the targeted receptors were characterized with flow cytometry. Targeted microbubble groups were administered to human MDA-MB-231 breast cancer tumor-bearing mice (n = 3) followed by contrast-enhanced sonography in a microbubble-sensitive harmonic imaging mode implemented on an ultrasound scanner equipped with a linear array transducer (5 MHz transmit and 10 MHz receive) to evaluate differences in microbubble accumulation in the tumor vasculature.

RESULTS

In vitro analysis showed a 50% increase (P < .001) in triple-targeted microbubble binding over dual-targeted microbubble groups in mouse SVR cells. Mice bearing MDA-MB-231 tumors showed a 40% increase in tumor image intensity after dosing with triple-targeted microbubbles compared with single- and dual-targeted microbubbles (P = .006). Histologic staining confirmed the presence of α(V)β(3)-integrin, P-selectin, and vascular endothelial growth factor receptor 2 in the tumors.

CONCLUSIONS

Microbubble accumulation in the tumor vasculature was improved using a triple-targeted microbubble approach.

Effects of Membrane Rheology on Leuko-polymersome Adhesion to Inflammatory Ligands

A strategy for treating inflammatory disease is to create micro-particles with the adhesive properties of leukocytes. The underlying rheology of deformable adhesive microspheres would be an important factor in the adhesive performance of such particles. In this work the effect of particle deformability on the selectin-mediated rolling of polymer vesicles (polymersomes) is evaluated. The rheology of the polymersome membrane was modulated by cross-linking unsaturated side-chains within the hydrophobic core of the membrane. Increased membrane rigidity resulted in decreased rates of particle recruitment rather than decreased average rolling velocities. Reflective interference contrast microscopy of rolling vesicles confirmed that neither flaccid nor rigid vesicles sustained close contacts with the substrate during rolling adhesion. A variable-shear rate parallel-plate flow chamber was employed to evaluate individual vesicles rolling on substrates under different flow conditions. Analysis of the trajectories of single flaccid vesicles revealed several distinct populations of rolling vesicles; however, some of these populations disappear when the vesicle membranes are made rigid. This work shows that membrane mechanics affects the capture, but not the rolling dynamics, of adherent leuko-polymersomes.

Tunable leuko-polymersomes that adhere specifically to inflammatory markers

The polymersome, a fully synthetic cell mimetic, is a tunable platform for drug delivery vehicles to detect and treat disease (theranostics). Here, we design a leuko-polymersome, a polymersome with the adhesive properties of leukocytes, which can effectively bind to inflammatory sites under flow. We hypothesize that optimal leukocyte adhesion can be recreated with ligands that mimic receptors of the two major leukocyte molecular adhesion pathways, the selectins and the integrins. Polymersomes functionalized with sialyl Lewis X and an antibody against ICAM-1 adhere avidly and selectively to surfaces coated with inflammatory adhesion molecules P-selectin and ICAM-1 under flow. We find that maximal adhesion occurs at intermediate densities of both sialyl Lewis X and anti-ICAM-1, owing to synergistic binding effects between the two ligands. Leuko-polymersomes bearing these two receptor mimetics adhere under physiological shear rates to inflamed endothelium in an in vitro flow chamber at a rate 7.5 times higher than those to uninflamed endothelium. This work clearly demonstrates that polymersomes bearing only a single ligand bind less avidly and with lower selectivity, thus suggesting proper mimicry of leukocyte adhesion requires contributions from both pathways. This work establishes a basis for the design of polymersomes for targeted drug delivery in inflammation.

Thrombin upregulates the angiopoietin-Tie2 Axis: endothelial protein C receptor occupancy prevents the thrombin mobilization of angiopoietin 2 and P-selectin from Weibel-Palade bodies

SUMMARY BACKGROUND

Activated protein C (APC) in complex with endothelial protein C receptor (EPCR) can reverse the barrier-disruptive and cytotoxic effects of proinflammatory cytokines by cleaving protease-activated receptor 1 (PAR-1). Recently, it was reported that the PAR-1-dependent vascular barrier-protective effect of APC is mediated through transactivation of the angiopoietin (Ang)-Tie2 signaling pathway. The antagonist of this pathway, Ang2, is stored in Weibel-Palade bodies within endothelial cells.

OBJECTIVES

To determine whether the occupancy of EPCR by its ligand can switch the PAR-1-dependent signaling specificity of thrombin through the Ang-Tie2 axis.

METHODS

We activated endothelial cells with thrombin before and after treating them with the catalytically inactive Ser195-->Ala substitution mutant of protein C. The expression levels of Ang1, Ang2 and Tie2 in response to thrombin were measured by both an enzyme-linked immunosorbent assay and a cell permeability assay in the absence and presence of small interfering RNA and a blocking antibody to Tie2.

RESULTS

Thrombin upregulated the expression of both Ang1 and Tie2 but downregulated the expression of Ang2 when EPCR was occupied by its ligand. The Ang1-Tie2-dependent protective effect of thrombin was initiated through protein C inhibiting the rapid mobilization of Ang2 from Weibel-Palade bodies. Interestingly, the protein C mutant also inhibited the thrombin mobilization of P-selectin.

CONCLUSIONS

These results suggest a physiologic role for the low concentration of thrombin in maintaining the integrity of the EPCR-containing vasculature through the PAR-1-dependent inhibition of Ang2 and P-selectin release from Weibel-Palade bodies.

Basic mechanisms and pathogenesis of venous thrombosis

In 1856 Virchow proposed a triad of causes for venous thrombosis, postulating that stasis, changes in the vessel wall or changes in the blood could lead to thrombosis. We now know that abnormally high levels of some coagulation factors and defects in the natural anticoagulants contribute to thrombotic risk. Among these, factor V Leiden, which renders factor Va resistant to activated protein C, is the most prevalent with approximately 5% of the Caucasian population having this genetic alteration. These genetically controlled variants in coagulation factors work in concert with other risk factors, such as oral contraceptive use, to dramatically increase thrombotic risk. While these abnormalities in the blood coagulation proteins are associated with thrombotic disease propensity, they are less frequent contributors to thrombosis than age or cancer. Cancer increases thrombotic risk by producing tissue factor to initiate coagulation, by shedding procoagulant lipid microparticles or by impairing blood flow. Age is the strongest risk factor for thrombosis. Among possible reasons are fragility of the vessels potentially contributing to stasis, increased coagulation factor levels, impaired function of the venous valves, decreases in the efficacy of natural anticoagulants associated with the vessel wall, increased risk of immobilization and increased risk of severe infection.

P-selectin 1087G/A polymorphism is associated with neuropsychological test performance in older adults with cardiovascular disease

BACKGROUND AND PURPOSE

There is growing evidence that the cell adhesion molecule P-selectin (SELP) contributes to the adverse vascular processes that promote cognitive impairment in individuals with cardiovascular disease. Previous research has shown that SELP genotypes moderate circulating levels of P-selectin and that patients undergoing coronary artery bypass graft with the SELP 1087A allele were less likely to show postoperative cognitive decline and more likely to exhibit lower levels of C-reactive protein than noncarriers. Thus, we expected that carriers of the 1087A allele (n=43) would exhibit better cognitive functioning than persons with 2 1087G alleles (n=77) and that C-reactive protein levels would be important for this relationship.

METHODS

One hundred twenty older adults with diagnosed cardiovascular disease were recruited from outpatient cardiology clinics. Each participant underwent a comprehensive neuropsychological test battery and a blood draw.

RESULTS

Participants with the SELP 1087A allele performed more poorly on tests of attention (Trail Making Test A: t[116]=3.20, P=0.002), executive function (Trail Making Test B: t[116]=2.89, P=0.005), psychomotor speed (Digit-Symbol Coding: t[117]=2.54, P=0.012), and memory (California Verbal Learning Test Discrimination: t[116]=2.05, P=0.04). There were no significant differences between the SELP genotype groups on demographic/medical variables or C-reactive protein levels.

CONCLUSIONS

Contrary to expectations, the present analyses showed that older patients with cardiovascular disease with the SELP 1087A allele performed more poorly on neuropsychological testing. Findings from the present study were counter to previous research with coronary artery bypass graft candidates. Further work using neuroimaging and alternative measures of cardiovascular function is needed to clarify the mechanisms of this association.

Inhibition of VEGF or TGF-{beta} signaling activates endothelium and increases leukocyte rolling

OBJECTIVE

Motivated by the central roles that vascular endothelial growth factor (VEGF) and transforming growth factor (TGF)-beta play in the assembly and maintenance of the vasculature, we examined the impact of systemic VEGF or TGF-beta signal inhibition on endothelial activation as detected by leukocyte-endothelial interactions.

METHODS AND RESULTS

VEGF or TGF-beta inhibition, accomplished using adenovirus expression of soluble Flt1 (Ad-sFlt1) or soluble endoglin (Ad-sEng), resulted in a significant increase in the number of leukocytes rolling along the mesenteric venous endothelium and a significant decrease in rolling velocity in Ad-sEng mice. Neutralization of VEGF or TGF-beta resulted in endothelial surface expression of P-selectin and impaired peripheral vasodilatation. Neither inhibition of VEGF nor TGF-beta was associated with platelet or leukocyte activation, as detected by the activation markers platelet P-selectin and the active integrin alphaIIbbetaIII, or by leukocyte expression of L-selectin. Soluble vascular cell adhesion molecule (VCAM)-1 and E-selectin were increased in sEng-expressing mice, indicating higher levels of these adhesion receptors.

CONCLUSIONS

VEGF or TGF-beta neutralization leads to impaired endothelium-mediated vasodilatation and elevated expression of surface adhesion molecules, resulting in increased leukocyte adhesion. These results indicate an essential role for both VEGF and TGF-beta in maintaining the endothelium in a nonactivated state and have implications for therapeutic approaches that neutralize VEGF or TGF-beta.

Persistent versus transient depressive symptoms in relation to platelet hyperactivation: a longitudinal analysis of dementia caregivers

BACKGROUND

Depressive symptoms and caregiving stress may contribute to cardiovascular disease (CVD) via chronic platelet activation; however, it remains unclear whether this elevated activation constitutes a trait or state marker. The primary objective was to investigate whether persistent depressive symptoms would relate to elevated platelet activation in response to acute psychological stress over a three-year period.

METHODS

Depressive symptoms (Brief Symptom Inventory) were assessed among 99 spousal dementia caregivers (52-88 years). Platelet P-selectin expression was assessed in vivo using flow cytometry at three time-points over the course of an acute stress test: baseline, post-stress, and after 14 min of recovery. Two competing structural analytic models of depressive symptoms and platelet hyperactivity with three yearly assessments were compared.

RESULTS

Although depressive symptoms were generally in the subclinical range, their persistent elevation was associated with heightened platelet reactivity and recovery at all three-years while the change in depressive symptoms from the previous year did not predict platelet activity.

LIMITATIONS

These results focus on caregivers providing consistent home care, while future studies may extend these results by modeling major caregiving stressors.

CONCLUSIONS

Enduring aspects of negative affect, even among those not suffering from clinical depression are related to hemostatic changes, in this case platelet reactivity, which might be one mechanism for previously reported increase in CVD risk among elderly Alzheimer caregivers.

Differential stimulation of monocytic cells results in distinct populations of microparticles

BACKGROUND

Microparticles (MPs), small vesicles shed from stimulated cells, permit cross-talk between cells within a particular environment. Their composition is thought to reflect their cell of origin, and differs according to whether they are produced by stimulation or by apoptosis. Whether MP properties vary according to stimulus is not yet known.

METHODS

We studied the characteristics of MPs produced from monocytic THP-1 cells upon stimulation with lipopolysaccharide or a soluble P-selectin chimera, using proteomics, flow cytometry, western blotting, and electron microscopy.

RESULTS

Utilizing a novel criterion of calcein-AM staining to define MPs, we found that MP populations were similar with respect to size, presence and organization of cytoskeleton, and expression of certain antigens. The MPs shared the same level of procoagulant activity. We found that MPs also have distinct characteristics, depending on stimuli. These include differences in phosphatidylserine expression and expression of proteins from specific subcellular locations such as the mitochondria, and of unique antigens such as leukocyte-associated immunoglobin-like-receptor (LAIR)-1, which was found only upon stimulation with the soluble P-selectin chimera.

CONCLUSION

We found that the properties of MPs depend on the stimulus that produced them. This supports the concept that monocytic MPs differentially modulate thrombosis, inflammation and immune regulation according to stimulus.

Influence of cardiopulmonary bypass on the interaction of recombinant factor VIIa with activated platelets

Recombinant factor VIIa (rFVIIa) interacts preferentially with coated platelets characterized by a high exposure of phosphatidyl serine (PS), FV, FVIII, FIX, and FX binding, and fibrinogen. Cardiopulmonary bypass (CPB) is known to impair platelet function. In this study, the influence of CPB on formation of coated platelets and the interaction of rFVIIa with the platelets were studied. Blood was either exposed to a closed CPB circuit or obtained from patients undergoing CPB-assisted cardiac surgery, and platelets were analyzed by flow cytometry with and without dual agonist stimulation with thrombin and a GPVI collagen receptor agonist known to induce coated platelet formation. Platelets circulated within a closed CPB circuit did not spontaneously form coated platelets. Dual agonists stimulation caused formation of coated platelets at a reduced level compared to pre-CPB level (51 +/- 21% vs. 80 +/- 17% before CPB, p < .001). The rFVIIa interaction with the coated platelets was not impaired after CPB. Platelets isolated from patients undergoing CPB-assisted cardiac surgery also formed coated platelets only after dual agonist stimulation but to the same level as before surgery (76 +/- 8% vs. 83 +/- 14% before surgery, p = .17, n = 10). rFVIIa interaction with the coated platelets was not impaired after surgery. No spontaneous rFVIIa-binding platelets were found. The data indicate that CPB exposure in vivo does not compromise the platelet-dependent effects of rFVIIa either by spontaneous formation of coated platelets, thereby limiting the risk of systemic coagulation, or by impairing rFVIIa interaction with the agonist-induced coated platelets, thereby retaining the hemostatic potential of rFVIIa after CPB.

Cell-surface nucleolin is a signal transducing P-selectin binding protein for human colon carcinoma cells

We have previously shown that P-selectin binding to Colo-320 human colon carcinoma cells induces specific activation of the alpha(5)beta(1) integrin with a concomitant increase of cell adhesion and spreading on fibronectin substrates in a phosphatidylinositol 3-kinase (PI3-K) and p38 MAPK-dependent manner. Here, we identified by affinity chromatography and characterized nucleolin as a P-selectin receptor on Colo-320 cells. Nucleolin mAb D3 significantly decreases the Colo-320 cell adhesion to immobilized P-selectin-IgG-Fc. Moreover, nucleolin becomes clustered at the external side of the plasma membrane of living, intact cells when bound to cross-linked P-selectin-IgG-Fc chimeric protein. We have also found P-selectin binding to Colo-320 cells induces tyrosine phosphorylation specifically of cell-surface nucleolin and formation of a signaling complex containing cell-surface nucleolin, PI3-K and p38 MAPK. Using siRNA approaches, we have found that both P-selectin binding to Colo-320 cells and formation of the P-selectin-mediated p38 MAPK/PI3-K signaling complex require nucleolin expression. These results show that nucleolin (or a nucleolin-like protein) is a signaling receptor for P-selectin on Colo-320 cells and suggest a mechanism for linkage of nucleolin to P-selectin-induced signal transduction pathways that regulate the adhesion and the spreading of Colo-320 on fibronectin substrates.

Fetal wound healing using a genetically modified murine model: the contribution of P-selectin

PURPOSE

During early gestation, fetal wounds heal with paucity of inflammation and absent scar formation. P-selectin is an adhesion molecule that is important for leukocyte recruitment to injury sites. We used a murine fetal wound healing model to study the specific contribution of P-selectin to scarless wound repair.

METHODS

Linear excisional wounds were created on the dorsa of E15.5 and E17.5 gestation fetuses in wild-type and P-selectin (-/-) mice (term = 19 days). Wounds were harvested at various time-points after wounding and analyzed using histology and immunohistochemistry.

RESULTS

The E15.5 wounds in both wild-type and P-selectin (-/-) fetuses healed scarlessly and with minimal inflammation, whereas E17.5 wounds healed with fibrosis and inflammation. However, the scars of the P-selectin (-/-) wounds appeared slightly different than wild-type. There were significantly more inflammatory cells in E17.5 wild-type wounds 6 hours after injury (P < .001), but the difference was no longer significant by 24 hours. Finally, reepithelialization was slower in the E15.5 knockout wounds compared to their wild-type counterparts.

CONCLUSIONS

Absence of P-selectin delays inflammatory cell recruitment and reepithelialization of fetal wounds; however, scar formation still occurs in late gestation wounds. The contribution of specific molecules to fetal wound healing can be elucidated using murine knockout or transgenic models.

Novel Biomarkers Associated with Deep Venous Thrombosis: A Comprehensive Review

Primary and recurrent venous thromboembolic disease (VTE, deep venous thrombosis and pulmonary embolism) remain a significant source of morbidity and mortality in the hospitalized patient. Non-specific subjective complaints and lack of specific objective findings related to acute deep venous thrombosis (DVT) and pulmonary embolism (PE) complicate the diagnosis. There remains no single serum marker available to exclusively confirm the diagnosis of VTE. While D-dimer is highly sensitive and useful for diagnostic exclusion, it lacks the specificity necessary for diagnostic confirmation resulting in the need for a variety of additional studies (i.e.: duplex ultrasound, venography, V/Q scanning, helical thoracic and pelvic CT scans and pulmoary angiography). There is evolving research supporting the utility of various plasma markers as novel "biomarkers" for VTE including selectins, microparticles, interleukin-10 and other cytokines. This review attempts to examine recent literature assessing the utility of P-selectin, microparticles, D-dimer, E-selectin, thrombin, interleukins and fibrin monomers in the diagnosis and guidance of therapy for VTE.

Novel uses for anti-platelet agents as anti-inflammatory drugs

An alteration in the character and function of platelets is manifested in patients with inflammatory diseases, and these alterations have been dissociated from the well-characterized involvement of platelets in thrombosis and haemostasis. Recent evidence reveals platelet activation is sometimes critical in the development of inflammation. The mechanisms by which platelets participate in inflammation are diverse, and offer numerous opportunities for future drug intervention. There is now acceptance that platelets act as innate inflammatory cells in immune responses, with roles as sentinel cells undergoing surveillance, responding to microbial invasion, orchestrating leukocyte recruitment, and migrating through tissue, causing damage and influencing repair processes in chronic disease. Some of these processes are targeted by drugs that are being developed to target platelet participation in atherosclerosis. The actions of platelets therefore influence the pathogenesis of diverse inflammatory diseases in various body compartments, encompassing parasitic and bacterial infection, allergic inflammation (especially asthma and rhinitis), and non-atopic inflammatory conditions, for example, chronic obstructive pulmonary disease (COPD), rheumatoid arthritis (RA), inflammatory bowel disease (IBD) and atherosclerosis. This review will first discuss the evidence for platelet activation in these various inflammatory diseases, and secondly discuss the mechanisms by which this pathogenesis occurs and the various anti-platelet agents which have been developed to combat platelet activation in atherosclerosis and their potential future use for the treatment of other inflammatory diseases.

Specific P-selectin and P-selectin glycoprotein ligand-1 genotypes/haplotypes are associated with risk of incident CHD and ischemic stroke: the Atherosclerosis Risk in Communities (ARIC) study

OBJECTIVE

P-selectin (PSEL) and its ligand, P-selectin glycoprotein ligand-1 (PSGL-1), play key roles in both the inflammatory response and the atherosclerotic process, but there are conflicting results regarding the affect of PSEL and PSGL-1 gene variation on risk for cardiovascular and cerebrovascular disease. We tested the association of four PSEL and two PSGL-1 polymorphisms with incident coronary heart disease (CHD) and ischemic stroke among 13,875 participants in the prospective Atherosclerosis Risk in Communities (ARIC) study. We also tested common haplotypes in the PSEL and PSGL-1 genes to assess associations with incident CHD and ischemic stroke.

METHODS AND RESULTS

Incident ischemic stroke and CHD were identified through annual telephone calls and hospital and death certificate surveillance. Five hundred and twenty-five validated ischemic stroke and 1654 CHD events were identified. Allele frequencies for all PSEL and PSGL-1 polymorphisms were markedly different between whites and African Americans; therefore, all analyses were performed race-specific. Independent analyses showed the PSEL 290NN genotype to be a significant predictor of CHD in whites (HRR 1.30, 95%CI 1.00-1.70, P=0.05). PSGL-1 genotypes carrying the 62I allele were significantly protective for incident CHD (HRR 0.53, 95%CI 0.31-0.92, P=0.02) and ischemic stroke (HRR 0.73, 95%CI 0.55-0.97, P=0.03) in African Americans. Haplotype analyses showed the PSEL NNVP haplotype to be a significant predictor of incident CHD in whites (HRR 2.09, 95%CI 1.23-3.55, P=0.006). No significant haplotype findings were observed in African Americans.

CONCLUSIONS

PSEL S290N, in single polymorphism analysis and in the haplotypic background with T715P, was associated with increased risk of incident CHD in whites. The PSGL-1 M62I polymorphism was associated with decreased risk of both incident CHD and stroke in African Americans. These findings illustrate the complex relationship between genetic variation and disease in different racial groups.

Lung ischemia-reperfusion injury: implications of oxidative stress and platelet-arteriolar wall interactions

Pulmonary ischemia-reperfusion (IR) injury may result from trauma, atherosclerosis, pulmonary embolism, pulmonary thrombosis and surgical procedures such as cardiopulmonary bypass and lung transplantation. IR injury induces oxidative stress characterized by formation of reactive oxygen (ROS) and reactive nitrogen species (RNS). Nitric oxide (NO) overproduction via inducible nitric oxide synthase (iNOS) is an important component in the pathogenesis of IR. Reaction of NO with ROS forms RNS as secondary reactive products, which cause platelet activation and upregulation of adhesion molecules. This mechanism of injury is particularly important during pulmonary IR with increased iNOS activity in the presence of oxidative stress. Platelet-endothelial interactions may play an important role in causing pulmonary arteriolar vasoconstriction and post-ischemic alveolar hypoperfusion. This review discusses the relationship between ROS, RNS, P-selectin, and platelet-arteriolar wall interactions and proposes a hypothesis for their role in microvascular responses during pulmonary IR.

Effects of TRA-418, a novel TP-receptor antagonist, and IP-receptor agonist, on human platelet activation and aggregation

[4-[2-(1,1-Diphenylethylsulfanyl)-ethyl]-3,4-dihydro-2H-benzo[1,4]oxazin-8-yloxy]-acetic acid N-Methyl-d-glucamine salt (TRA-418) has both thromboxane A2 (TP)-receptor antagonist and prostacyclin (IP)-receptor agonist properties. The present study examined the advantageous effects of TRA-418 based on the dual activities, over an agent having either activity alone and also the difference in the effects of TRA-418 and a glycoprotein alphaIIb/beta3 integrin (GPIIb/IIIa) inhibitor. TRA-418 inhibited platelet GPIIb/IIIa activation as well as P-selectin expression induced by adenosine 5'-diphosphate, thrombin receptor agonist peptide 1-6 (Ser-Phe-Leu-Leu-Arg-Asn-NH2), and U-46619 in the presence of epinephrine (U-46619+ epinephrine). TRA-418 also inhibited platelet aggregation induced by those platelet-stimulants in Ca2+ chelating anticoagulant, citrate and in nonchelating anticoagulant, d-phenylalanyl-l-prolyl-l-arginyl-chloromethyl ketone (PPACK). The TP-receptor antagonist SQ-29548 inhibited only U-46619+epinephrine-induced GPIIb/IIIa activation, P-selectin expression, and platelet aggregation. The IP-receptor agonist beraprost sodium inhibited platelet activation. Beraprost also inhibited platelet aggregation induced by platelet stimulants we tested in citrate and in PPACK. The GPIIb/IIIa inhibitor abciximab blocked GPIIb/IIIa activation and platelet aggregation. However, abciximab showed slight inhibitory effects on P-selectin expression. TRA-418 is more advantageous as an antiplatelet agent than TP-receptor antagonists or IP-receptor agonists separately used. TRA-418 showed a different inhibitory profile from abciximab in the effects on P-selectin expression.

Neutrophils and leucocyte adhesion molecules in sickle cell retinopathy

AIMS

The expression of the adhesion molecules ICAM-1, VCAM-1, and P-selectin, and the distribution and number of polymorphonuclear leucocytes (PMNs) were investigated in sickle cell retinopathy (SCR) and compared to the normal retina.

METHODS

Postmortem ocular tissue was obtained from five subjects (16, 21, 28, 40, and 41 years of age) with sickle haemoglobinopathies and from one control subject. Tissue was cryopreserved, and streptavidin peroxidase immunohistochemistry was performed with antibodies against ICAM-1, VCAM-1, and P-selectin. Immunohistochemical reaction product was scored, and PMN numbers were counted in sections stained with non-specific esterase.

RESULTS

Increased ICAM-1, VCAM-1, and P-selectin immunoreactivities were observed in sickle cell subjects compared to the control subject. The highest ICAM and P-selectin immunoreactivity was associated with intraretinal vessels adjacent to the preretinal neovascular formation in subjects with proliferative retinopathy. This was not the case with VCAM-1 immunoreactivity, which was highest in intraretinal vessels adjacent to the sea fan when the sea fan was still "in statu nascendi." Fully formed, "older" sea fans had the highest levels of VCAM-1. The increase in adhesion molecule immunoreactivity was paralleled by an increase in intraretinal PMNs. The number of intraretinal PMNs increased with progression of the disease and the numbers surpassed those in control subjects by threefold. In the sea fan with the greatest VCAM-1 immunoreactivity, there were 20 times more PMNs were observed than in the rest of the retina in the same subject.

CONCLUSION

These data suggest that adhesion molecule mediated leucocyte adhesion might play an important part in the vaso-occlusive phase of sickle cell retinopathy and in autoinfarction of sea fan formations.

Leukocyte rolling is exclusively mediated by P-selectinin colonic venules

1. The objective of the present study was to examine the role of the endothelial selectins (i.e. P- and E-selectin) in leukocyte-endothelium interactions in colonic venules by use of intravital microscopy. 2. Balb/c mice were exposed to dextran sodium sulphate (DSS) in the drinking water for 5 days or treated intraperitoneally (i.p.) with tumour necrosis factor-alpha (TNF-alpha) for 3 h. 3. In DSS-treated mice, mRNA of both P- and E-selectin were expressed and leukocyte rolling and adhesion was increased to 27+/-3 cells min(-1) and 36+/-8 cells mm(-1), respectively. An anti-P-selectin antibody abolished DSS-induced leukocyte rolling, whereas an antibody against E-selectin had no effect. Established leukocyte adhesion was insensitive to inhibition of the selectins. 4. DSS markedly increased production of TNF-alpha in the colon. TNF-alpha increased leukocyte rolling to 22+/-3 cells min(-1) and adhesion to 45+/-4 cells mm(-1). Only inhibition of P-selectin significantly reduced (>94%) leukocyte rolling provoked by TNF-alpha. Leukocyte adhesion was not changed by late anti-P-selectin antibody treatment. In contrast, pretreatment with the anti-P-selectin antibody not only abolished leukocyte rolling but also completely inhibited firm adhesion in response to TNF-alpha. 5. This study demonstrates that P-selectin plays an important role in leukocyte rolling in colonic venules, both in experimental colitis and when stimulated with TNF-alpha. Moreover, P-selectin-dependent leukocyte rolling was found to be a precondition for TNF-alpha-induced firm adhesion. Thus, these findings suggest that P-selectin may be a key target to reduce pathological recruitment of inflammatory cells in the colon.

In vivo evaluation of the early events associated with liver metastasis of circulating cancer cells

The mechanism of metastasis formation remains still largely unknown. Many studies underline the importance and complexity of the initial arrest of the circulating tumour cells in the target organ, a key stage in metastasis occurrence. In our study, we evaluated by visual means the metastasis formation using an in vivo microscopy system in a murine model. Moreover, we investigated the involvement of P-selectin in these processes using immunohistochemistry and P-selectin knockout mice. The present study offers direct evidence of distinct pathways for tumour metastasis formation by a lymphoma cell - EL-4 and a solid tumour cell - C26. Off-line analysis of the images and histological data confirmed that mechanical entrapment of the solid tumour cell, which had a bigger diameter than that of the liver sinusoids, promoted metastasis without any detectable involvement of adhesion molecules. On the other hand, we observed that lymphoma cells, in spite of their smaller diameter as compared to the sinusoids, promoted liver metastasis as well, but with the essential participation in their arrest of P-selectin, indicating an adhesion molecule-mediated pathway.

Platelet CD62 expression and PDGFAB secretion in patients undergoing PTCA and treatment with abciximab

AIMS

To investigate a correlation of the platelet activation marker CD62 and secretion of the growth factor PDGF from platelets in coronary patients under therapy with the GPIIb/IIIa-inhibitor abciximab.

METHODS

Flow cytometric assessment of fibrinogen binding (GPIIb/IIIa-binding site) and CD62 expression, as well as PDGF release of human platelets (immunoassay) and platelet aggregation with 20 microM ADP and 2 microg ml(-1) collagen were evaluated in nine patients with stable coronary artery disease. Patients were undergoing elective balloon angioplasty and were treated with aspirin (100 mg day(-1)), heparin (ACT < 220 s) and abciximab (bolus and infusion over 12 h). Blood samples were obtained before initiation of abciximab therapy (under aspirin and heparin) (I), 3 h after angioplasty under abciximab (II) and 12 h after termination of abciximab infusion (III).

RESULTS

Compared with sample I before abciximab therapy, fibrinogen binding was reduced to 37% (+/- 34 s.d., P < 0.05) (II) and 55% (+/- 40 s.d., P < 0.05) (III). Reduced fibrinogen binding also led to a significant reduction of the aggregation response to ADP (down to 37% +/- 20) and collagen (down to 0%). Mean fluorescence intensity of CD62-expression was 78 units (+/- 20 s.d.) (I), 72 units (+/- 14 s.d.) (II) and 64 units (+/- 12 s.d., P < 0.05) (III). PDGF release from isolated, washed platelets was 99 (+/- 33 s.d.) ng/10(9) platelets at (I), 82 (+/- 31 s.d.) ng/10(9) platelets and 96 (+/- 30 s.d.) ng/10(9) platelets.

CONCLUSIONS

The results indicate that despite a strong reduction of GPIIb/IIIa-binding and platelet aggregation, CD62 as a marker of platelet secretion and the secretion product PDGF were only slightly reduced under abciximab treatment. No direct correlation between CD62 expression and PDGF release could be demonstrated.

P-Selectin glycoprotein ligand 1 (PSGL-1) is a physiological ligand for E-selectin in mediating T helper 1 lymphocyte migration

P-selectin glycoprotein ligand 1 (PSGL-1) is a sialomucin expressed on leukocytes that mediates neutrophil rolling on the vascular endothelium. Here, the role of PSGL-1 in mediating lymphocyte migration was studied using mice lacking PSGL-1. In a contact hypersensitivity model, the infiltration of CD4(+) T lymphocytes into the inflamed skin was reduced in PSGL-1-deficient mice. In vitro-generated T helper (Th)1 cells from PSGL-1-deficient mice did not bind to P-selectin and migrated less efficiently into the inflamed skin than wild-type Th1 cells. To assess the role of PSGL-1 in P- or E-selectin-mediated migration of Th1 cells, the cells were injected into E- or P-selectin-deficient mice. PSGL-1-deficient Th1 cells did not migrate into the inflamed skin of E-selectin-deficient mice, indicating that PSGL-1 on Th1 cells is the sole ligand for P-selectin in vivo. In contrast, PSGL-1-deficient Th1 cells migrated into the inflamed skin of P-selectin-deficient mice, although less efficiently than wild-type Th1 cells. This E-selectin-mediated migration of PSGL-1-deficient or wild-type Th1 cells was not altered by injecting a blocking antibody to L-selectin. These data provide evidence that PSGL-1 on Th1 cells functions as one of the E-selectin ligands in vivo.

Significance of chemokines and activated platelets in patients with diabetes

Levels of platelet-derived microparticles (PMPs), platelet activation markers (P-selectin expressed on, or annexin V binding to, platelets (plt:P-selectin or plt:annexin V, respectively)), chemokines (IL-8, monocyte chemotactic peptide-1 (MCP-1), and regulated on activation normally T-cell expressed and secreted (RANTES)), and soluble P- and E-selectins were compared in peripheral blood from diabetic and control patients in order to develop a better understanding of their potential contribution to diabetic vascular complications. Significant increases were found for PMPs, plt:P-selectin, MCP-1, RANTES and soluble P- and E-selectins in diabetic individuals, whereas IL-8 levels were similar. Furthermore, after ticlopidine treatment, most of these factors receded to baseline levels observed in non-diabetic patients. Our findings indicate that ticlopidine might be able to prevent or reduce vascular complications in diabetic patients.

Direct observation of membrane tethers formed during neutrophil attachment to platelets or P-selectin under physiological flow

Adhesion and subsequent aggregation between neutrophils and platelets is dependent upon the initial binding of P-selectin on activated platelets to P-selectin glycoprotein ligand 1 (PSGL-1) on the microvilli of neutrophils. High speed, high resolution videomicroscopy of flowing neutrophils interacting with spread platelets demonstrated that thin membrane tethers were pulled from neutrophils in 32 +/- 4% of the interactions. After capture by spread platelets, neutrophil membrane tethers (length of 5.9 +/- 4.1 microm, n = 63) were pulled at an average rate of 6-40 microm/s as the wall shear rate was increased from 100-250 s(-1). The average tether lifetime decreased significantly (P < 0.001) from 630 to 133 ms as the shear rate was increased from 100 s(-1) (F(bond) = 86 pN) to 250 s(-1) (F(bond) = 172 pN), which is consistent with P-selectin/PSGL-1 bond dynamics under stress. Tether formation was blocked by antibodies against P-selectin or PSGL-1, but not by anti-CD18 antibodies. During neutrophil rolling on P-selectin at 150 s(-1), thin membrane tethers were also pulled from the neutrophils. The characteristic jerking motion of the neutrophil coexisted with tether growth (8.9 +/- 8.8 microm long), whereas tether breakage (average lifetime of 3.79 +/- 3.32 s) caused an acute jump in the rolling velocity, proving multiple bonding in the cell surface and the tether surface contact area. Extremely long membrane tethers (>40 microm) were sometimes pulled, which detached in a flow-dependent mechanism of microparticle formation. Membrane tethers were also formed when neutrophils were perfused over platelet monolayers. These results are the first visualization of the often hypothesized tethers that shield the P-selectin/PSGL-1 bond from force loading to regulate neutrophil rolling during inflammation and thrombosis.

Correlation of leukocyte adhesiveness, adhesion molecule expression and leukocyte-induced contraction following balloon angioplasty

1. The aim of this study was to examine the changes in leukocyte adhesion and leukocyte-induced contraction in balloon-injured rabbit subclavian artery and to correlate these changes with vessel morphology and expression of adhesion molecules on the injured arteries. 2. Rabbits were anaesthetized and their left subclavian arteries were injured by balloon inflation and withdrawal followed by sacrifice at 2, 24, 48 h or 8 days after injury. The left and right subclavian arteries were removed and leukocytes were isolated from autologous rabbit blood. Leukocyte-induced contraction was measured in 5-HT precontracted artery rings and leukocyte adhesion was measured using (51)Cr-labelled leukocytes. Immunocytochemistry using paraffin-embedded tissue was employed to detect changes in the expression of adhesion molecules on injured arteries. 3. Autologous leukocytes caused a contraction of rabbit subclavian artery rings, which was prevented by L-NAME (10(-3) M). Balloon-induced injury abolished the contractile response to leukocytes, which correlated with loss of carbachol-induced relaxation 4. Balloon injury markedly enhanced the adhesiveness of the subclavian artery for leukocytes, most notably at 24 and 48 h after injury (1.7 and 1.8 fold respectively). Increased leukocyte adhesion at these two time points correlated with an upregulation of E-selectin, P-selectin and VCAM-1 expression on the remaining endothelium of the injured artery. 5. Vessel morphology revealed that balloon inflation had induced an infiltration of inflammatory cells into the vessel wall, the greatest increase being seen at 24 h after injury. 6. It is concluded that an increase in the expression of E-selectin, P-selectin and VCAM-1 following balloon-induced injury leads to enhanced leukocyte adhesion and migration into the injured vessel.

P-Selectin glycoprotein ligand 1 (PSGL-1) is expressed on platelets and can mediate platelet-endothelial interactions in vivo

The platelet plays a pivotal role in maintaining vascular integrity. In a manner similar to leukocytes, platelets interact with selectins expressed on activated endothelium. P-selectin glycoprotein ligand 1 (PSGL-1) is the main P-selectin ligand expressed on leukocytes. Searching for platelet ligand(s), we used a P-selectin-immunoglobulin G (IgG) chimera to affinity purify surface-biotinylated proteins from platelet lysates. P-selectin-bound ligands were eluted with ethylenediaminetetraacetic acid. An approximately 210-kD biotinylated protein was isolated from both human neutrophil and platelet preparations. A band of the same size was also immunopurified from human platelets using a monoclonal anti-human PSGL-1 antibody and could be blotted with P-selectin-IgG. Under reducing conditions, both the predicted PSGL-1 approximately 210-kD dimer and the approximately 120-kD monomer were isolated from platelets. Comparative immunoelectron microscopy and Western blotting experiments suggested that platelet PSGL-1 expression is 25-100-fold lower than that of leukocytes. However, patients with chronic idiopathic thrombocytopenic purpura who harbor predominantly young platelets displayed greater expression, indicating that PSGL-1 expression may be decreased during platelet aging. By flow cytometry, thrombin-activated platelets from normal individuals exhibited greater expression than those unstimulated. An inhibitory anti-PSGL-1 antibody significantly reduced platelet rolling in mesenteric venules, as observed by intravital microscopy. Our results indicate that functional PSGL-1 is expressed on platelets, and suggest an additional mechanism by which selectins and their ligands participate in inflammatory and/or hemostatic responses.

Targeted gene disruption demonstrates that P-selectin glycoprotein ligand 1 (PSGL-1) is required for P-selectin-mediated but not E-selectin-mediated neutrophil rolling and migration

P-selectin glycoprotein ligand 1 (PSGL-1) is a mucin-like selectin counterreceptor that binds to P-selectin, E-selectin, and L-selectin. To determine its physiological role in cell adhesion as a mediator of leukocyte rolling and migration during inflammation, we prepared mice genetically deficient in PSGL-1 by targeted disruption of the PSGL-1 gene. The homozygous PSGL-1-deficient mouse was viable and fertile. The blood neutrophil count was modestly elevated. There was no evidence of spontaneous development of skin ulcerations or infections. Leukocyte infiltration in the chemical peritonitis model was significantly delayed. Leukocyte rolling in vivo, studied by intravital microscopy in postcapillary venules of the cremaster muscle, was markedly decreased 30 min after trauma in the PSGL-1-deficient mouse. In contrast, leukocyte rolling 2 h after tumor necrosis factor alpha stimulation was only modestly reduced, but blocking antibodies to E-selectin infused into the PSGL-1-deficient mouse almost completely eliminated leukocyte rolling. These results indicate that PSGL-1 is required for the early inflammatory responses but not for E-selectin-mediated responses. These kinetics are consistent with a model in which PSGL-1 is the predominant neutrophil P-selectin ligand but is not a required counterreceptor for E-selectin under in vivo physiological conditions.

A complex web of signal-dependent trafficking underlies the triorganellar distribution of P-selectin in neuroendocrine PC12 cells

By analyzing the trafficking of HRP-P-selectin chimeras in which the lumenal domain of P-selectin was replaced with horseradish peroxidase, we determined the sequences needed for targeting to synaptic-like microvesicles (SLMV), dense core granules (DCG), and lysosomes in neuroendocrine PC12 cells. Within the cytoplasmic domain of P-selectin, Tyr777 is needed for the appearance of P-selectin in immature and mature DCG, as well as for targeting to SLMV. The latter destination also requires additional sequences (Leu768 and 786DPSP789) which are responsible for movement through endosomes en route to the SLMV. Leu768 also mediates transfer from early transferrin (Trn)-positive endosomes to the lysosomes; i.e., operates as a lysosomal targeting signal. Furthermore, SLMV targeting of HRP-P-selectin chimeras, but not the endogenous SLMV protein synaptophysin/p38, previously shown to be delivered to SLMV directly from the plasma membrane, is a Brefeldin A-sensitive process. Together, these data are consistent with a model of SLMV biogenesis which involves an endosomal intermediate in PC12 cells. In addition, we have discovered that impairment of SLMV or DCG targeting results in a concomitant increase in lysosomal delivery, illustrating the entwined relationships between routes leading to regulated secretory organelles (RSO) and to lysosomes.

Acquisition of selectin binding and peripheral homing properties by CD4(+) and CD8(+) T cells

Different T cell subsets exhibit distinct capacities to migrate into peripheral sites of inflammation, and this may in part reflect differential expression of homing receptors and chemokine receptors. Using an adoptive transfer approach, we examined the ability of functionally distinct subsets of T cells to home to a peripheral inflammatory site. The data directly demonstrate the inability of naive T cells and the ability of effector cells to home to inflamed peritoneum. Furthermore, interleukin (IL)-12 directs the differentiation of either CD4(+) or CD8(+) T cells into effector populations that expresses functional E- and P-selectin ligand and that are preferentially recruited into the inflamed peritoneum compared with T cells differentiated in the presence of IL-4. Recruitment can be blocked by anti-E- and -P-selectin antibodies. The presence of antigen in the peritoneum promotes local proliferation of recruited T cells, and significantly amplifies the Th1 polarization of the lymphocytic infiltrate. Preferential recruitment of Th1 cells into the peritoneum is also seen when cytokine response gene 2 (CRG-2)/interferon gamma-inducible protein 10 (IP-10) is used as the sole inflammatory stimulus. We have also found that P-selectin binds only to antigen-specific T cells in draining lymph nodes after immunization, implying that both antigen- and cytokine-mediated signals are required for expression of functional selectin-ligand.

Role of P-selectin cytoplasmic domain in granular targeting in vivo and in early inflammatory responses

P-selectin is an adhesion receptor for leukocytes expressed on activated platelets and endothelial cells. The cytoplasmic domain of P-selectin was shown in vitro to contain signals required for both the sorting of this protein into storage granules and its internalization from the plasma membrane. To evaluate in vivo the role of the regulated secretion of P-selectin, we have generated a mouse that expresses P-selectin lacking the cytoplasmic domain (DeltaCT mice). The deletion did not affect the sorting of P-selectin into alpha-granules of platelets but severely compromised the storage of P-selectin in endothelial cells. Unstored P-selectin was proteolytically shed from the plasma membrane, resulting in increased levels of soluble P-selectin in the plasma. The DeltaCT-P-selectin appeared capable of mediating cell adhesion as it supported leukocyte rolling in the mutant mice. However, a secretagogue failed to upregulate leukocyte rolling in the DeltaCT mice, indicating an absence of a releasable storage pool of P-selectin in the endothelium. Furthermore, the neutrophil influx into the inflamed peritoneum was only 30% of the wild-type level 2 h after stimulation. Our results suggest that different sorting mechanisms for P-selectin are used in platelets and endothelial cells and that the storage pool of P-selectin in endothelial cells is functionally important during early stages of inflammation.

The effect of aspirin on thrombin stimulated platelet adhesion receptor expression and the role of neutrophils

AIMS

Aspirin has proven clinical efficacy in limiting the thrombotic complications of atherosclerotic vascular disease but its mechanism of action remains unclear. Recent evidence suggests the anti-platelet action of aspirin may be partly mediated by neutrophil derived nitric oxide (NO). The aim of the study was to determine the effects of aspirin on thrombin-induced platelet expression of the alpha-granule membrane protein, P-selectin, and the platelet surface glycoprotein required for aggregation, GPIIb-IIIa, and to assess whether this was enhanced by the presence of neutrophils.

METHODS

Platelet P-selectin and GPIIb-IIIa receptor expression were assessed by flow cytometric analysis of washed platelets stimulated with thrombin (0.025 iu ml(-1), sub aggregatory concentration) alone or after pre-incubation with aspirin (0.05, 0.1, 0.5, 1.0 mg m1(-1) either in the presence or absence of neutrophils (100 platelets per neutrophil). NO release was determined by assay of nitrite in the supernatants from parallel samples.

RESULTS

In preliminary aggregation studies, aspirin at all concentrations inhibited arachidonic acid but not thrombin-induced platelet aggregation. Similarly, aspirin at all concentrations failed to inhibit thrombin-induced platelet P-selectin or GPIIb-IIIa expression and this was not influenced by the presence of neutrophils. A reduction in P-selectin and GPIIb-IIIa receptor density on non-activated platelets co-incubated with unstimulated neutrophils was associated with NO release from neutrophils, but this was not enhanced by the addition of aspirin.

CONCLUSIONS

These results confirm that thrombin-induced platelet alpha-granule release, with consequent P-selectin expression, and platelet GPIIb-IIIa expression, are not affected by aspirin inhibition of cyclo-oxygenase and suggest that the anti-thrombotic efficacy of aspirin in vivo may partly depend on other mechanisms. This study did not demonstrate an effect of neutrophils or neutrophil derived NO on aspirin inhibition of platelet adhesion receptor expression.