Selectin on activated platelets enhances neutrophil endothelial adherence in myocardial reperfusion injury

A fresh look at coronary microembolization

Mechanical stress from haemodynamic perturbations or interventional manipulation of epicardial coronary atherosclerotic plaques with inflammatory destabilization can release particulate debris, thrombotic material and soluble substances into the coronary circulation. The physical material obstructs the coronary microcirculation, whereas the soluble substances induce endothelial dysfunction and facilitate vasoconstriction. Coronary microvascular obstruction and dysfunction result in patchy microinfarcts accompanied by an inflammatory reaction, both of which contribute to progressive myocardial contractile dysfunction. In clinical studies, the benefit of protection devices to retrieve atherothrombotic debris during percutaneous coronary interventions has been modest, and the treatment of microembolization has mostly relied on antiplatelet and vasodilator agents. The past 25 years have witnessed a relative proportional increase in non-ST-segment elevation myocardial infarction in the presentation of acute coronary syndromes. An associated increase in the incidence of plaque erosion rather than rupture has also been recognized as a key mechanism in the past decade. We propose that coronary microembolization is a decisive link between plaque erosion at the culprit lesion and the manifestation of non-ST-segment elevation myocardial infarction. In this Review, we characterize the features and mechanisms of coronary microembolization and discuss the clinical trials of drugs and devices for prevention and treatment.

Reducing Cardiac Injury during ST-Elevation Myocardial Infarction: A Reasoned Approach to a Multitarget Therapeutic Strategy

The significant reduction in ‘ischemic time’ through capillary diffusion of primary percutaneous intervention (pPCI) has rendered myocardial-ischemia reperfusion injury (MIRI) prevention a major issue in order to improve the prognosis of ST elevation myocardial infarction (STEMI) patients. In fact, while the ischemic damage increases with the severity and the duration of blood flow reduction, reperfusion injury reaches its maximum with a moderate amount of ischemic injury. MIRI leads to the development of post-STEMI left ventricular remodeling (post-STEMI LVR), thereby increasing the risk of arrhythmias and heart failure. Single pharmacological and mechanical interventions have shown some benefits, but have not satisfactorily reduced mortality. Therefore, a multitarget therapeutic strategy is needed, but no univocal indications have come from the clinical trials performed so far. On the basis of the results of the consistent clinical studies analyzed in this review, we try to design a randomized clinical trial aimed at evaluating the effects of a reasoned multitarget therapeutic strategy on the prevention of post-STEMI LVR. In fact, we believe that the correct timing of pharmacological and mechanical intervention application, according to their specific ability to interfere with survival pathways, may significantly reduce the incidence of post-STEMI LVR and thus improve patient prognosis.

The Coronary Circulation as a Target of Cardioprotection

The atherosclerotic coronary vasculature is not only the culprit but also a victim of myocardial ischemia/reperfusion injury. Manifestations of such injury are increased vascular permeability and edema, endothelial dysfunction and impaired vasomotion, microembolization of atherothrombotic debris, stasis with intravascular cell aggregates, and finally, in its most severe form, capillary destruction with hemorrhage. In animal experiments, local and remote ischemic pre- and postconditioning not only reduce infarct size but also these manifestations of coronary vascular injury, as do drugs which recruit signal transduction steps of conditioning. Clinically, no-reflow is frequently seen after interventional reperfusion, and it carries an adverse prognosis. The translation of cardioprotective interventions to clinical practice has been difficult to date. Only 4 drugs (brain natriuretic peptide, exenatide, metoprolol, and esmolol) stand unchallenged to date in reducing infarct size in patients with reperfused acute myocardial infarction; unfortunately, for these drugs, no information on their impact on the ischemic/reperfused coronary circulation is available.

Myocardial interstitial levels of serotonin and its major metabolite 5-hydroxyindole acetic acid during ischemia-reperfusion

The aim of this study was to examine the accumulation of serotonin (5-HT) and degradation of 5-HT taken up into cells in the ischemic region during myocardial ischemia-reperfusion. Using microdialysis technique in anesthetized rats, we monitored myocardial interstitial levels of 5-HT and its metabolite produced by monoamine oxidase (MAO), 5-hydroxyindole acetic acid (5-HIAA), during 30-min coronary occlusion followed by 45-min reperfusion, and investigated the effects of local administration of the MAO inhibitor pargyline and the 5-HT uptake inhibitor fluoxetine. In the vehicle group, the dialysate 5-HT concentration increased from 1.3 ± 0.2 nM at baseline to 29.6 ± 2.8 nM at 22.5-30 min of occlusion, but the dialysate 5-HIAA concentration did not change from baseline (9.9 ± 1.1 nM). Upon reperfusion, the dialysate 5-HT concentration increased further to a peak (34.2 ± 4.2 nM) at 0-7.5 min and then declined. The dialysate 5-HIAA concentration increased to 31.9 ± 5.2 nM at 7.5-15 min of reperfusion and maintained this high level until 45 min. Pargyline markedly suppressed the increase in dialysate 5-HIAA concentration after reperfusion and increased the averaged dialysate 5-HT concentration during the reperfusion period. Fluoxetine suppressed the increase in dialysate 5-HT concentration during occlusion but did not change dialysate 5-HT or 5-HIAA concentration after reperfusion. During ischemia, 5-HT secreted from ischemic tissues accumulates but 5-HT degradation by MAO is suppressed. After reperfusion, degradation of 5-HT taken up into cells is enhanced and contributes to the clearance of accumulated 5-HT. This degradation following cellular uptake is dependent on MAO activity but not the fluoxetine-sensitive uptake transporter.

NEW & NOTEWORTHY

By monitoring myocardial interstitial levels of 5-HT and its metabolite, 5-hydroxyindole acetic acid, we investigated 5-HT kinetics during myocardial ischemia-reperfusion. 5-HT accumulates but 5-HT degradation is suppressed during ischemia. After reperfusion, 5-HT degradation is enhanced and this degradation is dependent on monoamine oxidase activity but not fluoxetine-sensitive uptake transporter.

Contribution of serotonin uptake and degradation to myocardial interstitial serotonin levels during ischaemia-reperfusion in rabbits

AIM

Although deleterious effects of serotonin (5-HT) have been demonstrated during myocardial ischaemia-reperfusion, little information is available on myocardial interstitial 5-HT kinetics. This study evaluated the contribution of 5-HT reuptake and degradation to myocardial interstitial 5-HT levels during ischaemia-reperfusion.

METHODS

Using microdialysis technique in anaesthetized rabbits, we monitored myocardial interstitial 5-HT levels in the ischaemic region during ischaemia (30 min) followed by reperfusion (60 min) and investigated the effects of local infusion of fluoxetine, a 5-HT uptake inhibitor, and/or pargyline, a monoamine oxidase inhibitor.

RESULTS

In vehicle control, dialysate 5-HT concentration increased gradually from 16 ± 3 at baseline to 85 ± 18 nM during 20-30 min of ischaemia. Dialysate 5-HT concentration further increased to 236 ± 47 nM at 0-10 min of reperfusion and then began to decline. Averaged 5-HT concentration was 61 ± 11 during ischaemia and 113 ± 13 nM during reperfusion. Fluoxetine elevated dialysate 5-HT level at baseline and at 10-30 min of reperfusion; it increased averaged dialysate 5-HT concentration by approx. 304% during reperfusion compared to control. Pargyline elevated averaged dialysate 5-HT concentration during ischaemia by approx. 243% and that during reperfusion by approx. 250% compared to control. The changes in dialysate 5-HT concentration by fluoxetine + pargyline were similar to those of fluoxetine alone.

CONCLUSION

The 5-HT reuptake function plays an important role in the clearance of myocardial interstitial 5-HT during reperfusion. When 5-HT reuptake function is intact, degradation of 5-HT by monoamine oxidase contributes to reduce myocardial interstitial 5-HT level throughout ischaemia-reperfusion.

P-selectin-mediated platelet-neutrophil aggregate formation activates neutrophils in mouse and human sickle cell disease

OBJECTIVE

To determine the role of platelets in stimulating mouse and human neutrophil activation and pulmonary injury in sickle cell disease (SCD).

METHODS AND RESULTS

Both platelet and neutrophil activation occur in SCD, but the interdependence of these events is unknown. Platelet activation and binding to leukocytes were measured in mice and patients with SCD and in controls. Relative to controls, blood obtained from mice or patients with SCD contained significantly elevated platelet-neutrophil aggregates (PNAs). Both platelets and neutrophils found in sickle PNAs were activated. Multispectral imaging (ImageStream) and conventional flow cytometry revealed a subpopulation of activated neutrophils with multiple adhered platelets that expressed significantly more CD11b and exhibited greater oxidative activity than single neutrophils. On average, wild-type and sickle PNAs contained 1.1 and 2.6 platelets per neutrophil, respectively. Hypoxia/reoxygenation induced a further increase in PNAs in mice with SCD and additional activation of both platelets and neutrophils. The pretreatment of mice with SCD with clopidogrel or P-selectin antibody reduced the formation of PNAs and neutrophil activation and decreased lung vascular permeability.

CONCLUSIONS

Our findings suggest that platelet binding activates neutrophils and contributes to a chronic inflammatory state and pulmonary dysfunction in SCD. The inhibition of platelet activation may be useful to decrease tissue injury in SCD, particularly during the early stages of vaso-occlusive crises.

Donor heart preservation in an empty beating state under mild hypothermia

BACKGROUND

Cardiac surgery during an empty beating heart state has proven to be beneficial in myocardial protection. Based on this, we hypothesized that maintaining this state for donor heart preservation would have the same efficacy and a prolonged preservation period.

METHODS

Part 1: 12 pigs were divided into two groups (n = 6 per group). Donor hearts were preserved in group A by perfusion with leukocyte-depleted blood in the beating state, and in group B, in the traditional hypothermic static state with University of Wisconsin solution. After 8 hours, myocardial samples were obtained to detect myocardial edema, adenosine triphosphate, and ultrastructure. Part 2: 12 donor-recipient swine pairs were randomly allocated to either beating heart preservation with perfusion (group C) or traditional static preservation (group D). Donor hearts were stored for 8 hours after isolation, followed by implantation into recipient animals. Implanted hearts recovered for 120 minutes in an empty and beating state followed by 30 minutes in a working state, after which cardiac function was measured.

RESULTS

After preservation, myocardial adenosine triphosphate levels in group A were significantly higher than in group B. However, myocardial water content was not significantly different between these two groups. The damage of myocardial ultrastructure in group A was slight compared with that of group B. The experimental transplant group C showed excellent heart function after implantation when compared with group D.

CONCLUSIONS

Our study reveals greater effects of donor heart preservation in a beating state rather than simply with hypothermic storage in University of Wisconsin solution.

Effect of osmotic shock and urea on phosphatidylserine scrambling in thrombocyte cell membranes

Blood passing the renal medulla enters a strongly hypertonic environment challenging functional properties and survival of blood cells. In erythrocytes, exposure to hyperosmotic shock stimulates Ca(2+) entry and ceramide formation with subsequent cell membrane scrambling, an effect partially reversed by high concentrations of Cl(-) or urea. Cell membrane scrambling with phosphatidylserine exposure is part of the procoagulant phenotype of platelets. Coagulation in the hypertonic renal medulla would jeopardize blood flow in the vasa recta. The present study thus explored whether hypertonic environment and urea modify phosphatidylserine exposure of human platelets. FACS analysis was employed to estimate cytosolic Ca(2+) activity with Fluo3 fluorescence, ceramide formation, P-selectin, and glycoprotein IIb/IIIa activation with fluorescent antibodies and phosphatidylserine exposure with annexin V-binding. The spontaneous platelet aggregation was measured by impedance aggregometry. Hyperosmotic shock (addition of 500 mM sucrose or 250 mM NaCl) significantly enhanced cytosolic Ca(2+) activity, ceramide formation, phosphatidylserine exposure, platelet degranulation, and aggregability. Addition of 500 mM urea to isotonic saline did not significantly modify cytosolic Ca(2+) activity, ceramide abundance, or annexin V-binding but significantly blunted the respective effects of hypertonic shock following addition of 500 mM sucrose. In isotonic solutions, both ceramide (20 microM) and Ca(2+) ionophore ionomycin (0.5 microM) increased annexin V-binding, effects again significantly blunted by 500 mM urea. Moreover, oxidative stress by addition of 0.5 mM peroxynitrite increased cytosolic Ca(2+) activity and triggered annexin V-binding, effects again blunted in the presence of 500 mM urea. The observations reveal that hyperosmotic shock and oxidative stress trigger a procoagulant platelet phenotype, an effect blunted by the presence of high urea concentrations.

Targeted delivery of antibody conjugated liposomal drug carriers to rat myocardial infarction

Immunoliposome (IL) targeting to areas of inflammation after an acute myocardial infarction (MI) could provide the means by which pro-angiogenic compounds can be selectively targeted to the infarcted region. The adhesion of model drug carriers and ILs coated with an antibody to P-selectin was quantified in a rat model of MI following left coronary artery ligation. Anti-P-selectin coated model drug carriers showed a 140% and 180% increase in adhesion in the border zone of the MI 1 and 4 h post-MI, respectively. Radiolabeled anti-P-selectin ILs injected immediately post-MI and allowed to circulate 24 h showed an 83% increase in targeting to infarcted myocardium when compared to adjacent non-infarcted myocardium. Radiolabeled anti-P-selectin ILs injected 4 h post-MI and allowed to circulate for 24 h showed a 92% increase in accumulation in infarcted myocardium when compared to adjacent non-infarcted myocardium. Targeting to upregulated adhesion molecules on the endothelium provides a promising strategy for selectively delivering compounds to the infarct region of the myocardium using our liposomal-based drug delivery vehicle.

[Platelet activation and hypercholesterolemia in the pathogenesis of deep vein thrombosis]

Currently it is accepted that deep vein thrombosis is a multifactorial event in which the presence of activated platelets and also plasmatic lipids seems to play a pivotal role that it is not well established in the scientific bibliography. Due to the non consensus state about these topics between the different groups working in these aspects, the topic involving deep vein thrombosis-platelets-lipids, and also their interactions, still is an interesting area of investigation, in which it is necessary to carry out studies with the aim of establishing risk factors, initial diagnostic methods and clinical assays to probe the efficacy of new therapies.

Isoflurane Prevents Platelets from Enhancing Neutrophil-Induced Coronary Endothelial Dysfunction

We evaluated whether platelets can enhance polymorphonuclear neutrophil-induced coronary endothelial dysfunction, and, after observing this, whether isoflurane can prevent the effect. Neutrophils, coronary artery segments, and platelets were obtained from 25 healthy dogs. Coronary artery rings were exposed to neutrophils activated with platelet-activating factor (1.0 microM), and after washing and preconstriction with U46619, were evaluated for concentration-related responses to acetylcholine, an endothelium-dependent vasorelaxing drug. Superoxide production by activated neutrophils was measured spectrophotometrically. Adherence of the activated neutrophils to the endothelium of coronary segments was assessed by direct counting of neutrophils labeled with fluorescent dye. Measurements were performed in absence and presence of isoflurane (1 minimum alveolar concentration) both with and without platelets. The presence of platelets enhanced the neutrophil-induced rightward shift in the concentration-vasorelaxation response curve to acetylcholine (the concentration of acetylcholine required to elicit 50% of maximal relaxation (-log M) was increased from 6.78 +/- 0.7 to 5.26 +/- 0.6), and it increased superoxide oxide production from 45.0 +/- 4.2 to 54.3 +/- 4.2 nM O2-/5 x 10(6) neutrophils and adherence of activated neutrophils from 204 +/- 10 to 268 +/- 5 neutrophils/mm2. Isoflurane abolished these effects of platelets. In conclusion, platelets enhanced the ability of neutrophils to cause coronary endothelial dysfunction. This effect was prevented by isoflurane. This may be attributable to an inhibitory action on superoxide production by the neutrophils leading to reduced expression of endothelial adhesion molecules and, in turn, reduced neutrophil adherence.

Ligand-specific glucocorticoid receptor activation in human platelets

Few studies have addressed the effects of classical anti-inflammatory glucocorticoids on platelet function. Here, we report for the first time that human platelets contain the glucocorticoid receptor (GR) as identified by a combination of biochemical and functional techniques. Ligand-binding studies revealed the presence of a high- and low-affinity binding site for [3H]-dexamethasone in platelets. The 2 GR ligands prednisolone and dexamethasone competed for [3H]-dexamethasone binding, as did the mineralocorticoid aldosterone. However, while prednisolone (1-10 microM) reduced adenosine diphosphate (ADP, 4 microM) and thromboxane A2 receptor agonist U46619 induced platelet aggregation (up to 75%), dexamethasone had no effect. The inhibition produced by prednisolone was reversed by preincubation with the GR antagonist mifepristone (10 microM; RU486), suggesting the functional importance of the ligand-receptor complex. In addition, prednisolone caused a marked (approximately 50%) reduction in thromboxane B2 levels, whereas dexamethasone was without effect. The apparently anomalous binding data were clarified by the fact that washed platelets (1) contained mineralocorticoid receptor and that (2) it was associated with GR. Taken together, our data suggest that platelet GR forms a heterodimeric complex with the mineralocorticoid receptor that is susceptible to differential activation by specific receptor ligands.

Changes in P-selectin expression on cardiac microvessels in blood-perfused rat hearts subjected to ischemia-reperfusion

BACKGROUND

During cardiac surgery involving cardiopulmonary bypass, activation of polymorphonuclear cells is believed to contribute to ischemia-reperfusion injury and subsequent myocardial impairment of function. The early tethering of polymorphonuclear cells to blood vessel walls depends upon recognition of the adhesion molecule P-selectin on endothelium. The purpose of this study was to define the kinetic changes in expression of P-selectin on myocardial vessels in a model of global ischemia-reperfusion injury.

METHODS

In a novel recirculating blood-based perfusion system, rat hearts were subjected to 30 minutes of aerobic perfusion, 60 minutes of global ischemia, and 60 minutes of reperfusion, or to 120 minutes of continuous aerobic blood perfusion (with or without leukocyte/platelet depletion). Heart function (left ventricular developed pressure), heart rate, and perfusion pressure were monitored throughout. Hearts were sampled at defined periods for microvascular expression of P-selectin, identified by immunohistochemistry.

RESULTS

In control (nonperfused) hearts and in hearts subjected to perfusion and ischemia, few cardiac vessels (8% to 16%) expressed P-selectin. After 15 minutes of reperfusion, P-selectin was present on the majority of vessels (77%; p < 0.05) but expression decreased subsequently throughout the remaining duration of reperfusion. Interestingly, upregulation of P-selectin also occurred when hearts were subjected to continuous perfusion alone (no ischemia), but this upregulation was less rapid. Depletion of leukocytes/platelets from the blood perfusate did not modify P-selectin expression.

CONCLUSIONS

The augmented expression of P-selectin on myocardial vessels during reperfusion of ischemic hearts probably reflects changes induced during global ischemia and by the duration of perfusion through the nonbiological tubing of the circuit. That is likely to mimic the effects initiated during cardiopulmonary bypass.

Effect of atorvastatin upon platelet activation in hypercholesterolemia, evaluated by flow cytometry

Hyperlipidemia is a well established risk factor for cardiovascular disease and atherothrombotic events, in which platelet activation also plays a significant role. However, very few studies have addressed platelet activation in hypercholesterolemia, the potential effect of lipid lowering drugs upon platelet hyperfunction, and the question of whether changes in the latter are correlated to normalization of plasma lipids. This study used whole blood flow cytometry to assess in vivo and in vitro platelet activation in a group of 33 patients with hypercholesterolemia, and also the ex vivo effect of atorvastatin (20 mg/day) upon such activation. A control group of 40 normolipidemic volunteers matched in terms of age, sex and added risk factors to the patient group was used. The results showed that hypercholesterolemic patients had in vivo a significantly greater percentage of GPIIb/IIIa- and phosphatidylserine-positive platelets compared with the control group (4.62+/-3.51% and 2.58+/-1.19% versus 2.73+/-1.08% and 1.54+/-0.68%, respectively). In vitro response of CD62 expression to thrombin was also greater in the patients than in the controls (92.51+/-6.00% versus 89.63+/-10.72%, p<0.05). Atorvastatin therapy normalized platelet hyperfunction in the patients studied and reduced GPIIb/IIIa response to ADP (from 82.65+/-6.43% to 75.84+/-4.89%, p<0.01). A significant correlation can be seen between such normalization and the decrease in plasma levels of total and LDL cholesterol.

alphaB-crystallin is phosphorylated during myocardial infarction: involvement of platelet-derived growth factor-BB

alphaB-crystallin is the most abundant low-molecular-weight heat shock protein in heart and recent studies have demonstrated that it plays a cardioprotective role during myocardial infarction both in vivo and in vitro. On the other hand, platelet-derived growth factor (PDGF), a potent serum mitogen, has been reported to improve cardiac function after myocardial infarction. In the present study, using a mouse myocardial infarction model, we investigated whether alphaB-crystallin is phosphorylated during myocardial infarction and the implication of PDGF-BB. Phosphorylation of alphaB-crystallin at Ser-59 was time dependently induced and plasma PDGF-BB levels were concomitantly increased. Moreover, PDGF-BB-stimulated phosphorylation of alphaB-crystallin was suppressed by SB203580, a specific inhibitor of p38 mitogen-activated protein (MAP) kinase, in primary cultured cardiac myocytes. Our results indicate that PDGF-BB induces phosphorylation of alphaB-crystallin via p38 MAP kinase during myocardial infarction.

Platelet-neutrophil conjugate formation is increased in diabetic women with cardiovascular disease

Background

More than seventeen million Americans are afflicted with diabetes and these people have four times the rate of coronary heart disease (CHD) as non-diabetics. Furthermore, diabetic women have a 3.8 fold greater risk for CHD compared to diabetic men. Little is known why diabetic women are at an increased risk for CHD. It is possible that diabetic women with cardiovascular disease (CVD) have a greater inflammatory response resulting in an increased platelet neutrophil conjugate formation than diabetic men with CVD or non-diabetic women with CVD. This study tested the hypothesis that platelet-neutrophil conjugates, which are associated with several cardiovascular diseases, are increased in diabetic women with CVD compared to diabetic men with CVD and non-diabetic women with CVD.

Methods

Platelet-neutrophil conjugates were quantified by flow cytometry. The primary method is through direct binding of the neutrophil PSGL-1 receptor with P-selectin expressed on the platelet.

Results

In this study, we found when the blood was stimulated with PAF (platelet activating factor), diabetic women without CVD demonstrated an increase in platelet-neutrophil conjugates compared to diabetic women with CVD and non-diabetic women with CVD (% conjugates: 63.3 ± 5.2 vs 46.8 ± 4.3 vs 48.6 ± 3.4, p < 0.05). The stimulation ratio was significantly increased in diabetic and non-diabetic women with CVD in comparison to diabetic men with CVD (ratio: 3.3 ± 0.4 vs 3.3 ± 0.3 vs 2.1 ± 0.3, p < 0.05).

Conclusion

These results suggest that platelets and neutrophils in diabetic women have a greater potential for activation compared to diabetic men and may contribute to thrombosis/inflammation and the greater severity of coronary heart disease observed in diabetic women as compared to diabetic men.

Flow cytometric analysis of platelet activation in hypertensive patients. Effect of doxazosin

The percentage of spontaneously activated platelets and the platelet response to several agonists were studied in 26 hypertensive patients. The percentage of platelets expressing glycoprotein (GP) IIb/IIIa in its active conformation (GPIIb/IIIa*), P-selectin and phosphatidylserine (PS) was measured by flow cytometry at baseline and 1 and 2 months after treatment with doxazosin (4 mg/day). The response to ADP and Ca2+ ionophore was also evaluated. The results were compared with those of a control group of 71 normotensive volunteers. Spontaneous platelet activation was higher in patients than in controls (P-selectin-positive results in 4.4+/-2.0% patients vs. 2.7+/-1.7 controls, p<0.05; phosphatidylserine-positive results in 0.7+/-0.4% vs. 0.5+/-0.3%, respectively, p<0.05), and higher in response to ionophore action (phosphatidylserine-positive results 51.8+/-11.1% vs. 43.4+/-11.7%, p<0.01). Platelet activation in patients decreased after 2 months of doxazosin administration compared to baseline (P-selectin-positive results 2.7+/-1.4% vs. 4.4+/-2.0%, p<0.05; phosphatidylserine-positive results 0.3+/-0.2% vs. 0.7+/-0.4%, p<0.05). No significant differences were noted in GPIIb/IIIa*. The clinical significance of normalization of platelet activity by doxazosin remains to be established.

Platelet-activating factor promotes mucosal apoptosis via FasL-mediating caspase-9 active pathway in rat small intestine after ischemia-reperfusion

Platelet activating factor (PAF) is a proinflammatory lipid mediator for inflammatory response. It is unclear whether PAF is involved in the very complex process of ischemia-reperfusion (I/R) induced mucosal apoptosis in small intestine. Intestinal I/R was induced in rats intestine by 60 min occlusion of the superior mesenteric artery, followed by a 60 min reperfusion. I/R induced mucosal apoptosis and PAF activity but inhibited PAF-acetylhydrolase activity. Increases in interleukin-6 (IL-6) and decreases in IL-10 were observed. Western blot analysis showed that I/R induced expressions of platelet endothelial cell adhesion molecule-1 (PECAM-1) and Fas and Fas ligand (FasL) proteins, cleaved Bid, and enhanced the release of cytochrome c from mitochondria to activate caspase-9. Pretreatment of PAF antagonist BN-52021 attenuated these changes, except the increase in Fas. The results showed that I/R-inhibited mucosal PAF-acetylhydrolase activity resulted in an increase of activated PAF. The activated PAF increased the mucosal IL-6 and PECAM-1, enhanced the expression of FasL but not Fas, and led to the cleavage of Bid and the release of cytochrome c from mitochondria to activate caspase-9. This finding suggests that PAF promotes mucosal apoptosis after I/R in the rat small intestine partly through FasL mediating caspase-9 active pathway.

Time-dependent platelet-vessel wall interactions induced by intestinal ischemia-reperfusion

Platelets roll and adhere in venules exposed to ischemia-reperfusion (I/R). This platelet-endothelial adhesion may influence leukocyte trafficking because platelet depletion decreases I/R-induced leukocyte emigration. The objectives of this study were 1) to assess the time course of platelet adhesion in the small bowel after I/R and 2) to determine the roles of endothelial and/or platelet P-selectin and P-selectin glycoprotein ligand-1 (PSGL-1) in this adhesion. The adhesion of fluorescently labeled platelets was monitored by intravital microscopy in postcapillary venules exposed to 45 min of ischemia and up to 8 h of reperfusion. Peak platelet adhesion was observed at 4 h of reperfusion. To assess the contributions of platelet and endothelial cell P-selectin, platelets from P-selectin-deficient and wild-type mice were infused into wild-type and P-selectin-deficient mice, respectively. Platelets deficient in P-selectin exhibited low levels of adhesion comparable to that in sham-treated animals. In the absence of endothelial P-selectin, platelet adhesion was reduced by 65%. Treatment with a blocking antibody against PSGL-1 reduced adhesion by 57%. These results indicate that I/R induces a time-dependent platelet-endothelial adhesion response in postcapillary venules via a mechanism that involves PSGL-1 and both platelet and endothelial P-selectin, with platelet P-selectin playing a greater role.

Oxidative stress and neutrophil activation—the two keystones of ischemia/reperfusion injury

The widespread introduction of fibrinolytics and recently also PTCA in the treatment of myocardial infarction has changed the picture of modern cardiology. But this therapy also raises new problems and challenges. One of them is the occurrence of extensive tissue injury caused by reperfusion. Reinstitution of oxygen to the ischemic tissues initiates various processes leading to generation of reactive oxygen species (ROSs). Acting on the plasma membrane ROS damage its organization and release various proinflammatory agents. Different proteins, including receptors, ionic channels, transporters or components of transduction pathways are substrates of oxidation by ROSs. Their changed structure results in altered functioning and disruption of vital cellular processes. Another key factor of reperfusion injury is activation and infiltration of infarcted area by polymorphonuclear leukocytes (PMNs). Multiple studies identified consecutive stages of PMN activation and substances being involved in it. Main interest lies in cellular adhesion molecules, particularly selectins and beta2 integrins, as their antagonists were repeatedly found to diminish neutrophil activation and infarct size. Nevertheless new publications strike at the foundations of the established order and confront the relation between neutrophil infiltration and infarct size. PMNs are linked by close ties to other cells involved in inflammatory response. Seemingly also in cardiac ischemia-reperfusion injury, the activity of neutrophils is modulated by lymphocytes and macrophages. The article describes mutual interactions between different factors involved in the reperfusion injury that may enable preparing new treatments, hopefully as effective and successful as reperfusion therapy.

Platelet-erythrocyte interactions enhance alpha(IIb)beta(3) integrin receptor activation and P-selectin expression during platelet recruitment: down-regulation by aspirin ex vivo

Activated platelets release biologically active compounds, which then recruit additional platelets into an evolving thrombus. We studied activation of alpha(IIb)beta(3) and exposure of P-selectin on platelets recruited by releasates obtained from collagen-treated platelets and evaluated modifications in prothrombotic effects of releasates induced by platelet-erythrocyte interactions and aspirin treatment. Releasates from collagen-stimulated platelets induced alpha(IIb)beta(3) activation and P-selectin exposure (monitored by flow cytometry using fluorescein isothiocyanate-PAC-1 and phycoerythrin-CD62 antibodies). These responses were markedly amplified by releasates from combined platelet-erythrocyte suspensions. This finding demonstrates a novel mechanism(s) by which erythrocytes intensify platelet aggregability and mediate increased platelet recruitment. Because P-selectin and alpha(IIb)beta(3) are potential sites for platelet-leukocyte interactions, erythrocytes may also modulate leukocyte recruitment. Following aspirin ingestion both the recruiting capacity of platelet releasates and erythrocyte-induced amplification of platelet recruitment were down-regulated. These events represent an additional antithrombotic property of aspirin. We also examined the possibility that arachidonic acid, or eicosanoids derived therefrom, can induce a prothrombotic activity of erythrocytes. The TXA(2)-analog U46 619 and free arachidonate, but not PGI(2) or 12-HETE, induced increases in cytosolic Ca(++) and promoted phosphatidylserine (PS) exposure on a subpopulation of erythrocytes. PS exposure and increases in erythrocyte [Ca(++)](i) are associated with enhanced procoagulant activity, increased endothelial adhesion, and reduced erythrocyte deformability. Our findings, therefore, suggest that TXA(2) and arachidonic acid, derived from activated platelets, induce a prothrombotic phenotype on erythrocytes in proximity. We conclude that by these mechanisms, erythrocytes can actively contribute to platelet-driven thrombogenesis and microvascular occlusion.

Effectiveness of a unique dihydropyridine (BAYTG 1000) for prevention of laminitis in horses

OBJECTIVE

To determine whether a unique dihydropyridine (BAYTG 1000) would be beneficial in preventing laminitis in horses.

ANIMALS

16 clinically normal adult horses.

PROCEDURE

8 pairs of horses were used in a controlled double-blind study, using sex- and age-matched horses randomly assigned to treatment or control groups. Horses were subjected to carbohydrate overload to induce laminitis. Treated horses were administered BAY TG 1000 (30 mg/kg, PO, q 24 h) for 3 days. Hoof wall surface temperature (HWST) and lameness were recorded at 4-hour intervals. The HWST was adjusted on the basis of time of onset of lameness and evaluated, using a repeated-measures ANOVA. Lameness 8 hours after onset and clinical status 72 hours after onset of lameness were evaluated, using Mann-Whitney procedures.

RESULTS

Analysis revealed that BAYTG 1000 did not decrease the incidence of lameness but significantly ameliorated prodromal hypothermia, lessened the severity of lameness 8 hours after onset of lameness, and improved the clinical status of horses 72 hours after onset of lameness.

CONCLUSION AND CLINICAL RELEVANCE

Results support the conclusion that BAYTG 1000 was protective when used in prevention of laminitis. The drug decreased severity and improved clinical status (recovery) of induced lameness, which was interpreted to mean that the drug's actions were on mechanisms important but secondary to primary causal mechanisms of laminitis. Therefore, drugs that enhance digital perfusion via alteration of rheologic activity may have potential use in the prevention and management of laminitis in horses.

Side-effects of a systemic injection of linear polyethylenimine-DNA complexes

BACKGROUND

Systemic administration of linear polyethylenimine-DNA complexes (L-PEI/DNA) results in transient expression of the transgene in the lung. This study analyzes the side-effects associated with L-PEI-mediated transfection.

METHODS

Mice weighing from 16 to 25 g received increasing amounts of L-PEI/DNA intravenously. Gene expression was evaluated using luciferase as a reporter gene. Toxicity was evaluated by monitoring the appearance of shock after injection, the survival of the animals, and the microscopic damage in the tissues. Adherence of blood cells and endothelium activation were observed after CD11-b and von Willebrand immunostaining. Anti-aggregant treatments were used in order to prevent the formation of thrombi.

RESULTS

Increasing the quantity of L-PEI/DNA resulted in a marked augmentation of the luciferase activity in the lung, but was associated with liver necrosis and death. Lethality was reached at lower doses in older mice, suggesting an age influence. Transfection was associated with activation of the lung endothelium and increased adhesion of small aggregates containing platelets and CD11-b-positive cells, without the appearance of large thrombi and of lung injury. Anti-aggregant treatments (aspirin, EDTA, heparin or clopidogrel) decreased the L-PEI-mediated transfection, supporting the hypothesis that platelets participate in the blocking of DNA complexes in the lung capillaries.

CONCLUSION

This study demonstrates that L-PEI/DNA activates the lung endothelium and forms small aggregates, a side-effect linked to the transfection efficiency.

Platelets modulate ischemia/reperfusion-induced leukocyte recruitment in the mesenteric circulation

P-selectin-dependent leukocyte-endothelial cell adhesion has been implicated in the pathogenesis of ischemia/reperfusion (I/R) injury in several vascular beds, including the gut. Because platelet-endothelial (P/E) cell adhesion also occurs in postischemic venules, the possibility exists that the expression of P-selectin on the surface of platelets that are adherent to venular endothelial cells may mediate the leukocyte recruitment elicited by I/R. P-selectin expression [dual radiolabeled monoclonal antibody (MAb) technique] and neutrophil accumulation [myeloperoxidase (MPO) activity] were measured in the postischemic small intestine of untreated rats and rats treated with either antiplatelet serum (APS) or MAbs directed against either P-selectin, GPIIb/IIIa, or fibrinogen. The increases in P-selectin expression and tissue MPO normally elicited by I/R were significantly attenuated in the different treatment groups, suggesting that I/R-induced neutrophil recruitment is a platelet-dependent, P-selectin-mediated process. Intravital microscopy was then employed to examine this process relative to leukocyte-endothelial cell adhesion in postischemic rat mesenteric venules. The recruitment of adherent and emigrated leukocytes after I/R was attenuated by pretreatment with a MAb against, either P-selectin, GPIIb/IIIa, or fibrinogen, as well as an Arg-Gly-Asp peptide. Whereas thrombocytopenia greatly blunted leukocyte emigration, it did not alter the leukocyte adherence response to I/R. These findings suggest that platelet-associated P-selectin contributes to the accumulation of leukocytes in postischemic tissue via a mechanism that alters transendothelial leukocyte migration.

Platelet, but not endothelial, P-selectin is critical for neutrophil-mediated acute postischemic renal failure

In a neutrophil-dependent model of acute postischemic renal failure (APRF), eliminating or blocking P-selectin reduces postischemic neutrophil infiltration and preserves kidney function. This study was designed to identify the role of platelet vs. endothelial P-selectin in APRF. Using wild-type (wt) and P-selectin-deficient (P-/-) mice, we generated chimeric mice by bone marrow transplantation. Chimeric mice exclusively expressed either platelet (Plt-P) or endothelial P-selectin (EC-P). APRF was induced by bilateral renal ischemia in situ (32 min), followed by reperfusion; 48 h after reperfusion, EC-P had significantly lower creatinine concentrations (twofold over sham) than Plt-P (eightfold over sham). Compared with wt, protection from renal failure in EC-P was similar to that observed in P-/-. Plt-P and EC-P demonstrated similar overall postischemic neutrophil infiltration as measured by renal myeloperoxidase activity. However, Plt-P showed massive neutrophil infiltration into outer and inner medulla, similar to that in wt. EC-P had only patchy, more diffuse neutrophil influx. Our study identifies platelet P-selectin as crucial for postischemic neutrophil recruitment into outer and inner medulla, which is detrimental to the development of APRF. This suggests that novel therapeutic strategies for postischemic organ failure could be aimed at neutrophil-platelet interactions.

P-selectin participates in cardiopulmonary bypass-induced inflammatory response in association with nitric oxide and peroxynitrite production

OBJECTIVES

P-selectin participates in the development of inflammatory disorders. Cardiopulmonary bypass is thought to induce inflammatory response and increase nitric oxide production. To evaluate the role of P-selectin in bypass-induced inflammatory response and its association with nitric oxide production, we examined the effect of P-selectin monoclonal antibody in a rat model of cardiopulmonary bypass.

METHODS

Twenty adult Sprague-Dawley rats undergoing cardiopulmonary bypass for 60 minutes were divided into 2 groups. A 3-mg/kg dose of anti-rat specific P-selectin monoclonal antibody (ARP2-4; Sumitomo Pharmaceuticals, Osaka, Japan) was administered into the priming solution before bypass in group P (n = 10) and a 3-mg/kg dose of PNB1.6 (nonblocking monoclonal antibody) was added in group C for control (n = 10).

RESULTS

At the termination of bypass and 3 hours after the termination of bypass, plasma levels of interleukins 6 and 8, nitrate/nitrite, the percentage ratio of nitrotyrosine to tyrosine (an indicator of peroxynitrite formation), and the respiratory index were significantly higher than before bypass in both groups, and they were significantly lower in group P than in group C. Plasma P-selectin level in group C and exhaled nitric oxide concentration in both groups at termination of bypass were significantly lower than those before bypass, and they were significantly higher 3 hours after termination of bypass than before bypass in both groups. Plasma P-selectin level and exhaled nitric oxide concentration in group P were significantly higher than those in group C at the end of bypass, but they were significantly lower 3 hours after the termination of bypass.

CONCLUSIONS

These results demonstrate that P-selectin may participate in the augmentation of bypass-induced inflammatory response in association with nitric oxide and peroxynitrite production.