Sialyl Lewisx-containing oligosaccharide attenuates myocardial reperfusion injury in cats

Selectins in Biology and Human Disease: Opportunity in E-selectin Antagonism

Selectins are cell adhesion proteins discovered in the 1980s. As C-type lectins, selectins contain an essential calcium ion in the ligand-binding pocket and recognize the isomeric tetrasaccharides sialyl Lewisx (sLex) and sialyl Lewisa (sLea). Three selectins, E-selectin, P-selectin, and L-selectin, play distinct, complementary roles in inflammation, hematopoiesis, and tumor biology. They have been implicated in the pathology of diverse inflammatory disorders, and several selectin antagonists have been tested clinically. E-selectin plays a unique role in leukocyte activation, making it an attractive target for intervention, for example, in sickle cell disease (SCD). This review summarizes selectin biology and pathology, structure and ligand binding, and selectin antagonists that have reached clinical testing with an emphasis on E-selectin.

Targeting fibrosis in the failing heart with nanoparticles

Heart failure (HF) is a clinical syndrome characterized by typical symptoms and signs caused by a structural and/or functional cardiac abnormality, resulting in a reduced cardiac output and/or elevated intracardiac pressures at rest or during stress. Due to increasing incidence, prevalence and, most importantly mortality, HF is a healthcare burden worldwide, despite the improvement of treatment options and effectiveness. Acute and chronic cardiac injuries trigger the activation of neurohormonal, inflammatory, and mechanical pathways ultimately leading to fibrosis, which plays a key role in the development of cardiac dysfunction and HF. The use of nanoparticles for targeted drug delivery would greatly improve therapeutic options to identify, prevent and treat cardiac fibrosis. In this review we will highlight the mechanisms of cardiac fibrosis development to depict the pathophysiological features for passive and active targeting of acute and chronic cardiac fibrosis with nanoparticles. Then we will discuss how cardiomyocytes, immune and inflammatory cells, fibroblasts and extracellular matrix can be targeted with nanoparticles to prevent or restore cardiac dysfunction and to improve the molecular imaging of cardiac fibrosis.

The clinical impact of glycobiology: targeting selectins, Siglecs and mammalian glycans

Carbohydrates - namely glycans - decorate every cell in the human body and most secreted proteins. Advances in genomics, glycoproteomics and tools from chemical biology have made glycobiology more tractable and understandable. Dysregulated glycosylation plays a major role in disease processes from immune evasion to cognition, sparking research that aims to target glycans for therapeutic benefit. The field is now poised for a boom in drug development. As a harbinger of this activity, glycobiology has already produced several drugs that have improved human health or are currently being translated to the clinic. Focusing on three areas - selectins, Siglecs and glycan-targeted antibodies - this Review aims to tell the stories behind therapies inspired by glycans and to outline how the lessons learned from these approaches are paving the way for future glycobiology-focused therapeutics.

Selectins and Immune Cells in Acute Myocardial Infarction and Post-infarction Ventricular Remodeling: Pathophysiology and Novel Treatments

The glycosciences aim to understand the impact of extracellular and intracellular carbohydrate structures on biological function. These glycans primarily fall into three major groups: lipid-linked carbohydrates that are referred to as glycosphingolipids or simply glycolipids; relatively short carbohydrate chains that are often O- or N-linked to proteins yielding common glycoproteins; and extended linear polymeric carbohydrate structures that are referred to as glycosaminoglycans (GAGs). Whereas, the impact of such carbohydrate structures has been extensively examined in cancer biology, their role in acute and chronic heart disease is less studied. In this context, a growing body of evidence indicates that glycans play an important role in immune mediated cell recruitment to damaged heart tissue to initiate wound healing and repair after injury. This is particularly important following ischemia and reperfusion that occurs in the heart in the setting of acute myocardial infarction. Here, immune system-mediated repair of the damaged myocardium plays a critical role in determining post-infarction ventricular remodeling, cardiac function, and patient outcome. Further, alterations in immune cell activity can promote the development of heart failure. The present review summarizes our current understanding of the phases of immune-mediated repair following myocardial infarction. It discusses what is known regarding glycans in mediating the recruitment of circulating immune cells during the early inflammatory stage of post-infarction repair, with focus on the selectin family of adhesion molecules. It offers future directions for research aimed at utilizing our knowledge of mechanisms underlying immune cell recruitment to either modulate leukocyte recruitment to the injured tissue or enhance the targeted delivery of biologic therapeutics such as stem cells in an attempt to promote repair of the damaged heart.

Adhesion receptors as therapeutic targets for circulating tumor cells

Metastasis contributes to >90% of cancer-associated mortality. Though primary tumors can be removed by surgical resection or chemo/radiotherapy, metastatic disease is a great challenge to treatment due to its systemic nature. As metastatic “seeds,” circulating tumor cells (CTCs) are believed to be responsible for dissemination from a primary tumor to anatomically distant organs. Despite the possibility of physical trapping of CTCs in microvessels, recent advances have provided insights into the involvement of a variety of adhesion molecules on CTCs. Such adhesion molecules facilitate direct interaction with the endothelium in specific tissues or indirectly through leukocytes. Importantly, significant progress has been made in understanding how these receptors confer enhanced invasion and survival advantage during hematogenous circulation of CTCs through recruitment of macrophages, neutrophils, platelets, and other cells. This review highlights the identification of novel adhesion molecules and how blocking their function can compromise successful seeding and colonization of CTCs in new microenvironment. Encouraged by existing diagnostic tools to identify and isolate CTCs, strategic targeting of these adhesion molecules to deliver conventional chemotherapeutics or novel apoptotic signals is discussed for the neutralization of CTCs in the circulation.

Anti-inflammatory actions of aprotinin provide dose-dependent cardioprotection from reperfusion injury

BACKGROUND AND PURPOSE

Myocardial injury following ischaemia and reperfusion has been attributed to activation and transmigration of polymorphonuclear leukocytes (PMNs) with release of mediators including oxygen-derived radicals and proteases causing damage.

EXPERIMENTAL APPROACH

We studied the serine protease inhibitor aprotinin in an in vivo rabbit model of 1 h of myocardial ischaemia followed by 3 h of reperfusion (MI+R). Aprotinin (10,000 Ukg(-1)) or its vehicle were injected 5 min prior to the start of reperfusion.

KEY RESULTS

Myocardial injury was significantly reduced with aprotinin treatment as indicated by a reduced necrotic area (11+/-2.7% necrosis as percentage of area at risk after aprotinin; 24+/-3.1% after vehicle; P<0.05) and plasma creatine kinase activity (12.2+/-1.5 and 17.3+/-2.3 IU g(-1) protein in aprotinin and vehicle groups, respectively, P<0.05). PMN infiltration (assessed by myeloperoxidase activity) was significantly decreased in aprotinin-treated animals compared to vehicle (P<0.01). Histological analysis also revealed a substantial increase in PMN infiltration following MI+R and this was significantly reduced by aprotinin therapy (44+/-15 vs 102+/-2 PMN mm2 in aprotinin vs vehicle-treated animals, P<0.05). In parallel in vitro experiments, aprotinin inhibited neutrophil-endothelium interaction by reducing PMN adhesion on isolated, activated aortic endothelium. Finally, immunohistochemical analysis illustrated aprotinin significantly reduced myocardial apoptosis following MI+R.

CONCLUSIONS AND IMPLICATIONS

Inhibition of serine proteases by aprotinin inhibits an inflammatory cascade initiated by MI+R. The cardioprotective effect appears to be at least partly due to reduced PMN adhesion and infiltration with subsequently reduced myocardial necrosis and apoptosis.

Hemodynamic improvement following levosimendan treatment in patients with acute myocardial infarction and cardiogenic shock*

OBJECTIVES

Levosimendan, a novel inodilator, has been shown to improve hemodynamic function in patients with acute exacerbation of congestive heart failure. We wanted to determine the hemodynamic effects of levosimendan following ineffective conventional therapy (with catecholamines) in patients with cardiogenic shock following myocardial infarction.

DESIGN

Observational hemodynamic study.

SETTING

Tertiary care center university hospital.

PATIENTS

Fifty-six patients with cardiogenic shock secondary to myocardial infarction were treated with percutaneous revascularization (intra-aortic balloon pump where appropriate) and commenced on conventional inotropic therapy.

INTERVENTIONS

Patients with persisting cardiogenic shock 24 hrs after revascularization were additionally treated with levosimendan (rapid bolus of 12 microg/kg for 10 mins, then 0.05-0.2 mug/kg/min for 24 hrs) (n = 25).

MEASUREMENTS AND MAIN RESULTS

With conventional catecholamine therapy (norepinephrine and dobutamine), we observed only marginal improvement in mean arterial pressure or cardiac index. In contrast, the addition of levosimendan produced a significant increase in cardiac index (2.1 +/- 0.56 to 3.0 +/- 1.11 L/min/m2, p < .01) and cardiac power index (0.32 +/- 0.08 to 0.44 +/- 0.18 W, p < .01), whereas systemic vascular resistance decreased significantly (1208 +/- 333 to 858 +/- 299 dyne.sec.cm(-5), p < .01). There was no significant change in blood pressure during levosimendan treatment. Hemodynamic improvement was sustained after levosimendan infusion was stopped.

CONCLUSIONS

Levosimendan infusion in cardiogenic shock following acute myocardial infarction improved cardiovascular hemodynamics without leading to hypotension.

Leukocyte and endothelial adhesion molecules in ischaemia/reperfusion injuries

Tissue ischaemia and/or reperfusion cause some of the injury seen in several clinical disorders and are responsible for considerable mortality and morbidity in humans. Part of the injury occurring after reperfusion of ischaemic tissue is the result of interactions between leukocytes adhering to vascular endothelium. Blocking the function of the leukocyte adhesion beta 2 integrin complex (CD11/CD18) leads to improved outcome following ischaemia and reperfusion. Functional blockade of either P-selectin or L-selectin prevents leukocyte rolling. Blocking leukocyte adherence at one of several levels may provide improved outcome in a variety of diseases associated with ischaemia and reperfusion.

Kinetic Analysis of Heparin and Glucan Sulfates Binding to P-Selectin and Its Impact on the General Understanding of Selectin Inhibition

P-Selectin, expressed on activated endothelial cells and platelets, is a high kinetic adhesion receptor involved in leukocyte rolling of the inflammatory response, or in tumor cell binding in the course of metastasis. Thus, P-selectin inhibition is a promising therapeutic target. The anti-inflammatory and anti-metastatic activities of heparin have partly been related to the inhibition of P-selectin binding. Here we apply a quartz crystal microbalance (QCM) biosensor to determine the kinetic constants of heparin and other sulfated polysaccharides binding to immobilized P-selectin. Binding kinetics of the derivatives were correlated with their inhibitory capacity in a P-selectin cell rolling assay. Three commercial heparins differ in cell rolling inhibition and display slightly different affinities (KD 1.21 x 10(-6) M to 5.86 x 10(-7) M). Inhibitory capacity appears to be mainly driven by a slow off-rate from the receptor (2.27 x 10(-3) s-1 to 1.23 x 10(-3) s-1). To correlate the impact of binding kinetics on inhibitory capacity structurally, we analyzed six semisynthetic glucan sulfates. They display different degrees of sulfation (DS), which has a strong influence on inhibitory activity. Kinetic data illustrate that the inhibitory capacity correlates excellently with the off-rate of these polysaccharides (R = 0.99), while the association (on-rate) affects activity to a lesser extent. In general, the consideration of binding kinetics sheds new light on the mechanism of selectin inhibition. A much slower dissociation of the inhibitors from the receptor than the physiological ligands is key for inhibitory capacity. Structurally, highly charged compounds with a slow off-rate, such as heparin or glucan sulfates, appear as potent candidates for P-selectin inhibition.

Neutrophil adherence to activated saphenous vein and mammary endothelium after graft preparation

BACKGROUND

Interaction of circulating leukocytes and vascular endothelium plays an important role in vasoconstriction, endothelial dysfunction, and vascular injury. Dilation procedures of grafts before coronary artery bypass graft surgery might lead to vascular injury and subsequent bypass graft disease.

METHODS

We analyzed in vitro the adherence of fluorescence-labeled polymorphonuclear neutrophils (PMNs) to endothelium of human saphenous vein grafts or internal mammary artery grafts after stimulation with thrombin (0.5 to 2 U/mL) or dilating procedures. Furthermore, we investigated endothelial function of prepared grafts.

RESULTS

Thrombin stimulation resulted in a dose-dependent increase of PMN adherence to the endothelium of saphenous vein and internal mammary artery, which was attenuated by the selectin-blocking carbohydrate fucoidin or anti-P-selectin monoclonal antibody. Mechanical dilation of saphenous vein or internal mammary artery led to a marked increase in PMN adherence (65 +/- 5 versus 5 +/- 3 PMN/mm2; p < 0.01), which was significantly attenuated by fucoidin or anti-P-selectin monoclonal antibodies. Treatment of internal mammary artery with the vasodilator papaverine led to a marked increase of PMN adherence (59 +/- 8 versus 12 +/- 4 PMN/mm2; p < 0.01) when papaverine was administered directly into the vessel. However, external treatment with papaverine did not affect PMN adhesion. Endothelial dysfunction was observed in dilated venous grafts and in arterial grafts internally treated with papaverine; in contrast, external treatment did not affect endothelial function.

CONCLUSIONS

This study showed that mechanical or pharmacologic dilation of venous or arterial coronary grafts, usually performed before anastomosis of aortocoronary bypass grafts, led to increased selectin-mediated PMN adhesion on vascular endothelium and subsequent endothelial dysfunction.

High level expression of monomeric and dimeric human α1,3-fucosyltransferase V

alpha3/4-Fucosyltransferases play a crucial role in inflammatory processes and tumor metastasis. While several human fucosyltransferases (FucTs) with different acceptor substrate specificities have been identified, the design of specific inhibitors for therapeutic approaches is hampered by the lack of structural information. In this study, we evaluated the expression of different constructs of human fucosyltransferase V to generate the large amounts required for structural studies. The truncated constructs lacking the transmembrane region and the cytosolic N-terminus, were expressed in baculovirus-infected Trichoplusia ni (Tn) insect cells and in two non-lytic expression systems, stably transfected human HEK 293 and T. ni cells. Since secretion of some glycosyltransferases is controlled by formation of dimeric molecules via disulfide bonds, one of the fucosyltransferase V constructs contained the N-terminal cysteine residue 64 for dimerization, whereas this residue was replaced in the other construct by serine. In both human and insect cells dimerization did not prove to be essential for efficient expression and secretion. On the basis of enzymatic activity, the yield of secreted fucosyltransferase V was approximately 10-fold higher in stably transfected insect cells than in HEK 293 cells. In particular the monomeric form of the enzyme provides a valuable tool for structural analyses to elucidate the fine specifity of fucosyltransferase V-mediated fucosylation of Lewis type glycans.

L-selectin: adhesion, signalling and its importance in pathologic posttraumatic endotoxemia and non-septic inflammation

The leucocyte expressed surface-bound L-selectin belongs to the selectin family of adhesion molecules. It exhibits adhesive as well as signalling functions. Mainly, it is of importance in lymphocyte homing and in the extravasation of leucocytes into the surrounding tissue during inflammation. Acting in the initial step of the cell adhesion cascade, L-selectin is responsible for the rolling of leucocytes on endothelial layers. Therefore, L-selectin is thought to be an adequate target for pharmacological interventions. Beneath the discussion of the molecules' general features like molecule structure and its regulation, the review focuses firstly on L-selectin in the context of posttraumatic inflammatory disorders, and secondly on the importance of L-selectin specific signalling events.

A comparison of two progestins on myocardial ischemia???reperfusion injury in ovariectomized monkeys receiving estrogen therapy

OBJECTIVE

It has been reported that the progestin medroxyprogesterone acetate (MPA), but not norethindrone acetate (NETA), inhibits the beneficial vascular effects of post-menopausal estrogen therapy, but their effects on the myocardium are unclear. The goal of this study is to compare the effects of these two progestins on post-ischemic myocardial damage.

METHODS

Ovariectomized monkeys were fed an atherogenic diet for 18 months while receiving, or not receiving (control, n=15), the monkey equivalent to a woman's dose of 5 mug ethinyl estradiol with either 1 mg NETA daily (n=15) or 2.5 mg MPA daily (n=15). The left anterior descending coronary artery was occluded for 1 h and then released to allow myocardial reperfusion for 4 h. Infarct size was quantified using the histochemical stain triphenyl-tetrazolium chloride. Regional myocardial blood flow was measured by 15 mum neutron-activated microspheres, blood pressure and heart rates with a pneumatic cuff, stroke volume by echocardiography, coronary output by thermodilution and neutrophil accumulation in the myocardium using myeloperoxidase (MPO) activity.

RESULTS

The infarct size (area of necrosis/area at risk) was similar between the control group (21+/-3%) and the MPA group (29+/-3%) (P<0.05) but significantly less in the NETA group (3+/-2%) than other groups (P<0.05). The hemodynamic myocardial function and regional myocardial blood values were similar among groups before, during and 4 h after reperfusion (all P-values >0.05). Similarly, there were no treatment effects on MPO activity (P>0.05).

CONCLUSIONS

NETA, but not MPA, diminished ischemia-reperfusion injury in estrogen-treated post-menopausal females. The mechanism(s) of this difference remains unclear.

Affinity and kinetics of sialyl Lewis-X and core-2 based oligosaccharides binding to L- and P-selectin

Soluble oligosaccharide mimetics of natural selectin ligands act as competitive inhibitors of leukocyte adhesion in models of inflammation. We quantified the binding of simple oligosaccharides based on sialyl Lewis-X (sLe(X)) and complex molecules with the core-2 structure to L- and P-selectin, under both static and fluid flow conditions. Isolated human neutrophils were employed to mimic the physiological valency of selectins and selectin ligands. Surface plasmon resonance studies quantified binding kinetics. We observed the following: (i) The functional group at the anomeric position of carbohydrates plays an important role during selectin recognition, since sLe(X) and sialyl Lewis-a (sLe(a)) were approximately 5-7-fold poorer inhibitors of L-selectin mediated cell adhesion compared to their methyl glycosides. (ii) Despite their homology to physiological glycans, the putative carbohydrate epitopes of GlyCAM-1 and PSGL-1 bound selectins with low affinity comparable to that of sLe(X)-selectin interactions. Thus, besides the carbohydrate portion, the protein core of GlyCAM-1 or the presentation of carbohydrates in clusters on this glycoprotein may contribute to selectin recognition. (iii) A compound Galbeta1,4(Fucalpha1,3)GlcNAcbeta1,6(GalNAcbeta1,3)GalNAcalpha-OMe was identified which blocked L- and P-selectin binding at 30-100-fold lower doses than sLe(X). (iv) Surface plasmon resonance experiments determined that an sLe(X) analogue (TBC1269) competitively inhibited, via steric/allosteric mechanisms, the binding of two anti-P-selectin function blocking antibodies that recognized different epitopes of P-selectin. (v) TBC1269 bound P-selectin via both calcium-dependent and -independent mechanisms, with K(D) of approximately 111.4 microM. The measured on- and off-rates were high (k(off) > 3 s(-)(1), k(on) > 27,000 M(-)(1) s(-)(1)). Similar binding kinetics are expected for sLe(X)-selectin interactions. Taken together, our study provides new insight into the kinetics and mechanisms of carbohydrate interaction with selectins.

Co-expression of two mammalian glycosyltransferases in the yeast cell wall allows synthesis of sLex

Interactions between selectins and their oligosaccharide-decorated counter-receptors play an important role in the initiation of leukocyte extravasation in inflammation. L-selectin ligands are O-glycosylated with sulphated sialyl Lewis X epitopes (sulpho-sLex). Synthetic sLex oligosaccharides have been shown to inhibit adhesion of lymphocytes to endothelium at sites of inflammation. Thus, they could be used to prevent undesirable inflammatory reactions such as rejection of organ transplants. In vitro synthesis of sLex glycans is dependent on the availability of recombinant glycosyltransferases. Here we expressed the catalytic domain of human alpha-1,3-fucosyltransferase VII in the yeasts Saccharomyces cerevisiae and Pichia pastoris. To promote proper folding and secretion competence of this catalytic domain in yeast, it was fused to the Hsp150 delta carrier, which is an N-terminal fragment of a secretory glycoprotein of S. cerevisiae. In both yeasts, the catalytic domain acquired an active conformation and the fusion protein was externalised, but remained mostly attached to the cell wall in a non-covalent fashion. Incubation of intact S. cerevisiae or P. pastoris cells with GDP-[14C]fucose and sialyl-alpha-2,3-N-acetyllactosamine resulted in synthesis of radioactive sLex, which diffused to the medium. Finally, we constructed an S. cerevisiae strain co-expressing the catalytic domains of alpha-2,3-sialyltransferase and alpha-1,3-fucosyltransferase VII, which were targeted to the cell wall. When these cells were provided with N-acetyllactosamine, CMP-sialic acid and GDP-[14C]fucose, radioactive sLex was produced to the medium. These data imply that yeast cells can provide a self-perpetuating source of fucosyltransferase activity immobilized in the cell wall, useful for the in vitro synthesis of sLex.

Blockade of cell adhesion by a small molecule selectin antagonist attenuates myocardial ischemia/reperfusion injury

Reperfusion injury is related closely to inflammatory reactions such as the activation and accumulation of neutrophils. We investigated the efficacy of a novel small molecule selectin antagonist (bimosiamose) in a rat model of transient left coronary artery occlusion (30 min) and reperfusion (24 h). Treatment with bimosiamose (25 mg/kg, intravenously at reperfusion) showed a significant reduction in infarction area/area at risk of approximately 41% compared to vehicle control (P=0.01) and preserved the left ventricular function. The accumulation of polymorphonuclear neutrophils at the site of area at risk was decreased significantly, accompanied by 78% reduction of the myeloperoxidase activity. Parallel-plate flow chamber analysis revealed that bimosiamose showed a significant inhibition in rolling (62%, P<0.001) and adhesion (38%, P<0.05) of HL-60 cells to activated human umbilical vein endothelial cells compared with vehicle control. This study demonstrates for the first time that bimosiamose, a novel small molecule selectin antagonist, attenuates significantly ischemia/reperfusion injury.

[Cardiogenic shock: pathophysiology, clinics, therapeutical options and perspectives]

Documented mortality from myocardial infarction (MI) has significantly decreased from around 30% in the 1960s to 6-7% currently, following the introduction of intensive care treatment, thrombolysis, effective antithrombotic therapy and coronary angioplasty. However, the approximate mortality of 70-80% of patients with cardiogenic shock following acute MI has hardly improved despite the introduction of modern treatment strategies. The major cause of in-hospital MI mortality remains myocardial failure with consecutive cardiogenic shock and multi-organ failure. Prompt coronary revascularisation by "facilitated" or "adjunctive" percutaneous coronary intervention (PCI), is currently considered the best method to reduce the high mortality in these patients. Facilitated PCI includes administration of glycoproteine receptor antagonists, mechanical circulation support strategies, such as, intraaortic balloon counterpulsation and potentially prehospital thrombolysis.

Synthesis and Physicochemical Characterization of Gd−DTPA−B(sLex)A, a New MRI Contrast Agent Targeted to Inflammation

A new magnetic resonance imaging (MRI) contrast agent designed to mimic sialyl Lewis X (sLeX) and to target inflammation has been synthesized and characterized. The evolution of its proton longitudinal relaxivity as a function of the magnetic field (NMRD) and temperature has been studied. The exchange rate of the water coordinated to the metal has been assessed by oxygen-17 relaxometry. The transmetalation by zinc(II) ions and the noncovalent binding to human serum albumin have been evaluated. The results show no limitation by the residence time of the coordinated water molecule above room temperature, a higher stability of the complex versus transmetalation by zinc(II) ions than a parent complex, the clinically used Gd-DTPA-BMA, and negligible interaction with human serum albumin.

Inhibition of P-selectin-mediated cell adhesion by a sulfated derivative of sialic acid

P-selectin, a carbohydrate-binding cell adhesion molecule expressed on activated endothelial cells and platelets, plays a key role in the recruitment of leukocytes to inflammatory and hemorrhagic sites. It simultaneously recognizes a sialic acid-containing carbohydrate chain and the sulfated tyrosine residues of a specific counter-receptor expressed on the leukocyte surface. We examined the inhibitory effects of a synthetic sulfated derivative of sialic acid (NMSO3) on P-selectin-mediated cell adhesion and found the following: (1) P-selectin/IgG chimera bound to immobilized NMSO3. (2) The binding of P-selectin/IgG chimera to purified P-selectin glycoprotein ligand-1 was inhibited by soluble NMSO3. (3) The adhesion of HL60 cells to P-selectin-expressing CHO cells was inhibited by NMSO3. (4) NMSO3 inhibited P-selectin-induced tumor necrosis factor-alpha production in monocytes and activated platelet-induced generation of reactive oxygen species in neutrophils. In conclusion, NMSO3 acts as a specific inhibitor for P-selectin-mediated cell adhesion and for adhesion-dependent leukocyte activation.

Heparin's anti-inflammatory effects require glucosamine 6-O-sulfation and are mediated by blockade of L- and P-selectins

Heparin has been used clinically as an anticoagulant and antithrombotic agent for over 60 years. Here we show that the potent anti-inflammatory property of heparin results primarily from blockade of P-selectin and L-selectin. Unfractionated heparin and chemically modified analogs were tested as inhibitors of selectin binding to immobilized sialyl Lewis(X) and of cell adhesion to immobilized selectins or thrombin-activated endothelial cells. Compared with unfractionated heparin, the modified heparinoids had inhibitory activity in this general order: over-O-sulfated heparin > heparin > 2-O,3-O-desulfated > or = N-desulfated/N-acetylated heparin > or = carboxyl-reduced heparin > or= N-,2-O,3-O-desulfated heparin >> 6-O-desulfated heparin. The heparinoids also showed similar differences in their ability to inhibit thioglycollate-induced peritonitis and oxazolone-induced delayed-type hypersensitivity. Mice deficient in P- or L-selectins showed impaired inflammation, which could be further reduced by heparin. However, heparin had no additional effect in mice deficient in both P- and L-selectins. We conclude that (a) heparin's anti-inflammatory effects are mainly mediated by blocking P- and L-selectin-initiated cell adhesion; (b) the sulfate groups at C6 on the glucosamine residues play a critical role in selectin inhibition; and (c) some non-anticoagulant forms of heparin retain anti-inflammatory activity. Such analogs may prove useful as therapeutically effective inhibitors of inflammation.

Heparin's anti-inflammatory effects require glucosamine 6-O-sulfation and are mediated by blockade of L- and P-selectins

Heparin has been used clinically as an anticoagulant and antithrombotic agent for over 60 years. Here we show that the potent anti-inflammatory property of heparin results primarily from blockade of P-selectin and L-selectin. Unfractionated heparin and chemically modified analogs were tested as inhibitors of selectin binding to immobilized sialyl Lewis(X) and of cell adhesion to immobilized selectins or thrombin-activated endothelial cells. Compared with unfractionated heparin, the modified heparinoids had inhibitory activity in this general order: over-O-sulfated heparin > heparin > 2-O,3-O-desulfated > or = N-desulfated/N-acetylated heparin > or = carboxyl-reduced heparin > or= N-,2-O,3-O-desulfated heparin >> 6-O-desulfated heparin. The heparinoids also showed similar differences in their ability to inhibit thioglycollate-induced peritonitis and oxazolone-induced delayed-type hypersensitivity. Mice deficient in P- or L-selectins showed impaired inflammation, which could be further reduced by heparin. However, heparin had no additional effect in mice deficient in both P- and L-selectins. We conclude that (a) heparin's anti-inflammatory effects are mainly mediated by blocking P- and L-selectin-initiated cell adhesion; (b) the sulfate groups at C6 on the glucosamine residues play a critical role in selectin inhibition; and (c) some non-anticoagulant forms of heparin retain anti-inflammatory activity. Such analogs may prove useful as therapeutically effective inhibitors of inflammation.

Cell adhesion molecules, leukocyte trafficking, and strategies to reduce leukocyte infiltration

Leukocyte-endothelial cell interactions are mediated by various cell adhesion molecules. These interactions are important for leukocyte extravasation and trafficking in all domestic animal species. An initial slowing of leukocytes on the vascular endothelium is mediated by selectins. This event is followed by (1) activation of beta2 integrins after leukocyte exposure to cytokines and pro-inflammatory mediators, (2) adherence of leukocyte beta2 integrins to vascular endothelial ligands (eg, intercellular adhesion molecule-1 [ICAM-1]), (3) extravasation of leukocytes into tissues through tight junctions of endothelial cells mediated by platelet and endothelial cell adhesion molecule-1 (PECAM-1), and (4) perivascular migration through the extracellular matrix via beta1 integrins. Inhibiting excessive leukocyte egress and subsequent free radical-mediated damage caused by leukocyte components may attenuate or eliminate tissue damage. Several methods have been used to modify leukocyte infiltration in various animal models. These methods include nonspecific inhibition of pro-inflammatory mediators and adhesion molecules by nonsteroidal anti-inflammatory drugs (NSAIDs) and glucocorticoids, inhibition of cytokines and cytokine receptors, and inhibition of specific types of cell adhesion molecules, with inhibitors such as peptides and antibodies to beta2 integrins, and inhibitors of selectins, ICAMs, and vascular cell adhesion molecule-1 (VCAM-1). By understanding the cellular and molecular events in leukocyte-endothelial cell interactions, therapeutic strategies are being developed in several animal models and diseases in domestic animal species. Such therapies may have clinical benefit in the future to overcome tissue damage induced by excessive leukocyte infiltration.

Staphylococcus aureus alpha toxin mediates polymorphonuclear leukocyte-induced vasocontraction and endothelial dysfunction

The effect of Staphylococcus aureus alpha toxin (alpha-toxin) on selectin-mediated neutrophil adhesion was investigated in polymorphonuclear leukocyte- (PMN) induced vasocontraction and endothelial dysfunction. Adherence of human PMNs to rat aortic endothelium increased significantly following stimulation of the endothelium with alpha-toxin (0.1, 0.5, and 1 microg/mL). This effect could be significantly attenuated by monoclonal antibodies directed against P-selectin or fucoidin, a carbohydrate known to block selectins. Unstimulated human PMNs (10(6)cells/mL) were added to organ chambers containing rat aortic rings stimulated with alpha-toxin (0.5 microg/mL). PMNs elicited a significant vasocontraction in alpha-toxin-stimulated, but not in control aortic, rings (142+/-12 mg versus 12+/-4 mg, P < 0.05). This PMN-induced vasocontraction was virtually blunted by pretreatment with MAb directed against P-selectin or fucoidin (P < 0.05). Endothelial function as assessed by endothelium-dependent vasorelaxation to acetylcholine was substantially inhibited after induction of PMN-induced vasocontraction in alpha-toxin-stimulated aortic rings. This endothelial dysfunction was reduced by P-selectin MAb or fucoidin. In contrast, endothelium-independent relaxation to sodium nitrite was not altered by PMN incubation, indicating that vascular smooth muscle function was unaffected. Thus, PMN-endothelial interaction following S. aureus a-toxin activation of the vascular endothelium is at least, in part, mediated by selectins. As a consequence, PMN-induced vasocontraction and endothelial dysfunction occur. Such mechanisms may be involved in microcirculation abnormalities encountered in sepsis or septic shock due to S. aureus infection.

Novel small molecule inhibitor of C1s exerts cardioprotective effects in ischemia-reperfusion injury in rabbits

Myocardial ischemia-reperfusion injury can be related to complement activation with generation of chemotactic agents, adhesion molecule expression, release of cytokines and oxygen-derived free radicals, and subsequent neutrophil accumulation. In the present study the cardioprotective effects of a novel highly selective small molecule C1s inhibitor (C1s-INH-248, Knoll) were examined in a rabbit model of myocardial ischemia (I) and reperfusion (R; i.e., 60 min I + 180 min R). In in vitro tests (enzyme activity and SRBC lysis) C1s-INH-248 demonstrated profound inhibitory potency. In vivo C1s-INH-248 (1 mg/kg body weight) administered 5 min before reperfusion significantly attenuated myocardial injury (31.9 +/- 2.5 vs 8.9 +/- 1.6% necrosis/area at risk; p < 0.01). The cardioprotective effect was dose dependent. The reduction of myocardial injury was also observed as diminished plasma creatine kinase activity in C1s-INH-248-treated animals (70.7 +/- 6.8 vs 45.1 +/- 3.9 U/g protein after 3 h of reperfusion, p < 0.05). Further, cardiac myeloperoxidase activity (i.e., a marker of PMN accumulation) in the ischemic and necrotic area was significantly reduced following C1s-INH-248 treatment (1.31 +/- 0.23 vs 0.4 +/- 0.05 U/100 mg tissue in necrotic area, p < 0.01). Thus, blocking the classical complement pathway with a highly specific and potent synthetic inhibitor of the activated C1 complex appears to be an effective mean to preserve ischemic myocardium from injury following reperfusion.

Complement and its implications in cardiac ischemia/reperfusion: strategies to inhibit complement

Although reperfusion of the ischemic myocardium is an absolute necessity to salvage tissue from eventual death, it is also associated with pathologic changes that represent either an acceleration of processes initiated during ischemia or new pathophysiological changes that were initiated after reperfusion. This so-called "reperfusion injury" is accompanied by a marked inflammatory reaction, which contributes to tissue injury. In addition to the well known role of oxygen free radicals and white blood cells, activation of the complement system probably represents one of the major contributors of the inflammatory reaction upon reperfusion. The complement may be activated through three different pathways: the classical, the alternative, and the lectin pathway. During reperfusion, complement may be activated by exposure to intracellular components such as mitochondrial membranes or intermediate filaments. Two elements of the activated complement contribute directly or indirectly to damages: anaphylatoxins (C3a and C5a) and the membrane attack complex (MAC). C5a, the most potent chemotactic anaphylatoxin, may attract neutrophils to the site of inflammation, leading to superoxide production, while MAC is deposited over endothelial cells and smooth vessel cells, leading to cell injury. Experimental evidence suggests that tissue salvage may be achieved by inhibition of the complement pathway. As the complement is composed of a cascade of proteins, it provides numerous sites for pharmacological interventions during acute myocardial infarction. Although various strategies aimed at modulating the complement system have been tested, the ideal approach probably consists of maintaining the activity of C3 (a central protein of the complement cascade) and inhibiting the later events implicated in ischemia/reperfusion and also in targeting inhibition in a tissue-specific manner.

The potential of monoclonal antibodies to reduce reperfusion injury in myocardial infarction

Reperfusion injury is mediated, in part, by the accumulation of platelets and leucocytes in the microvasculature after reflow. These components of the blood pool form aggregates that can obstruct flow in small vessels. In addition, mediators released from leucocytes and platelets further damage the reperfused myocardium. A strategy to limit reperfusion injury exploits the important role of membrane-bound adhesion molecules that attach platelets and leucocytes to themselves and to the vascular endothelium. Monoclonal antibodies against specific adhesion receptors effectively eliminate the function of the receptor. The most widely investigated receptors are P-selectin, present on platelets and the endothelium, CD11/CD18, present on leucocytes, and the fibrinogen receptor on platelets. Numerous animal studies have strongly supported the use of these monoclonal antibodies to block adhesion receptors as adjunctive reperfusion therapy. However, recent human trials have yielded disappointing results.

Inhibition of coronary thrombosis and local inflammation by a noncarbohydrate selectin inhibitor

We tested the hypothesis that selectin inhibition with blocking antibodies or a small-molecular-weight inhibitor of L-, P-, and E-selectin, methoxybenzoylpropionic acid (MBPA), prevents thrombus formation in a canine coronary Folts' model. Cyclic flow variations (CFVs) were induced by crush injury and constriction of the left anterior descending coronary artery in dogs. Systemic infusion of antibodies to P- and L-selectin abolished CFVs, respectively, in 50% and 17% of treated dogs [P = not significant (NS)]. The combination of P- and L-selectin antibodies suppressed CFVs in 60% of treated dogs (P = NS). In contrast, systemic selectin blockade by intravenous infusion or local adventitial application of MBPA markedly reduced CFVs and, in addition, reduced myocardial myeloperoxidase (MPO) activity. We conclude that inhibition of L-, P-, and E-selectin binding by a small-molecular-weight, noncarbohydrate compound markedly reduces arterial thrombosis, whereas systemic administration of antibodies to L- and P-selectin fail to reproduce this antithrombotic effect. These results underscore the role of selectins in the pathogenesis of arterial thrombosis under high shear stress and suggest that inhibition of P- and L- selectin may not suffice to prevent thrombus formation in this model. The role of E-selectin in thrombus formation in this model awaits further testing.

Leukocyte and endothelial cell adhesion molecules in a chronic murine model of myocardial reperfusion injury

Expression of endothelial and leukocyte cell adhesion molecules is a principal determinant of polymorphonuclear neutrophil (PMN) recruitment during inflammation. It has been demonstrated that pharmacological inhibition of these molecules can attenuate PMN influx and subsequent tissue injury. We determined the temporal expression of alpha-granule membrane protein-40 (P-selectin), endothelial leukocyte adhesion molecule 1 (E-selectin), and intercellular cell adhesion molecule 1 (ICAM-1) after coronary artery occlusion and up to 3 days of reperfusion. The expression of all of these cell adhesion molecules peaked around 24 h of reperfusion. We determined the extent to which these molecules contribute to PMN infiltration by utilizing mice deficient (-/-) in P-selectin, E-selectin, ICAM-1, and CD18. Each group underwent 30 min of in vivo, regional, left anterior descending (LAD) coronary artery ischemia and 24 h of reperfusion. PMN accumulation in the ischemic-reperfused (I/R) zone was assessed using histological techniques. Deficiencies of P-selectin, E-selectin, ICAM-1, or CD18 resulted in significant (P < 0.05) attenuation of PMN infiltration into the I/R myocardium (MI/R). In addition, P-selectin, E-selectin, ICAM-1, and CD18 -/- mice exhibited significantly (P < 0.05) smaller areas of necrosis after MI/R compared with wild-type mice. These data demonstrate that MI/R induces coronary vascular expression of P-selectin, E-selectin, and ICAM-1 in mice. Furthermore, genetic deficiency of P-selectin, E-selectin, ICAM-1, or CD18 attenuates PMN sequestration and myocardial injury after in vivo MI/R. We conclude that P-selectin, E-selectin, ICAM-1, and CD18 are involved in the pathogenesis of MI/R injury in mice.

Protective effects of selectin ligands/inhibitor (SKK-60060) against retinal ischemia-reperfusion injury

A newly developed selSep;71(3)28 to block P- and L-selectins in vitro. We examined its inhibition of leukocyte-endothelial interactions in vivo against retinal ischemia-reperfusion injury and protective effects on ischemia-induced retinal damage. Retinal ischemia was induced by temporary ligation of the optic sheath for 60 min in anesthetized pigmented rats. SKK-60060 was administered 5 min before reperfusion and 4, 12, 24 and 48 hr thereafter, and leukocyte dynamics in the retinal microcirculation were evaluated using acridine orange digital fluorography. After 7 days of reperfusion, ischemia-induced retinal damage was also assessed histologically.SKK-60060 treatment suppressed leukocyte rolling during the reperfusion period; their numbers in the SKK-60060-treated rats were reduced by 67.0% (P < 0. 01) and 53.2% (P < 0.01) at 12 and 24 hr, respectively. The subsequent leukocyte accumulation was also inhibited in SKK-60060-treated rats; accumulated leukocytes in the SKK-60060-treated rats were reduced by 72.8% (P < 0.01) and 53.4% (P < 0.01) at 12 and 24 hr, respectively. Retinal venous vasodilation in SKK-60060-treated rats were significantly suppressed at each time point (P < 0.05). Histological examination demonstrated protective effects of SKK-60060 on ischemia-induced retinal damage, which were more substantial in the inner retina (P < 0.01).SKK-60060 significantly inhibits the leukocyte rolling along the major retinal veins and their accumulation during the reperfusion period. These results suggest therapeutic potential of SKK-60060 for ischemia-reperfusion injury.

Sialyl LewisX oligosaccharide preserves myocardial and endothelial function during cardioplegic ischemia

BACKGROUND

Neutrophil adhesion to endothelium contributes to myocardial reperfusion injury after cardiac operation. Initial neutrophil-endothelial interactions involve selectins, which bind Sialyl-LewisX on neutrophils. Blockade of selectin-mediated neutrophil-endothelial interactions with CY-1503, a synthetic analogue of Sialyl-LewisX, might reduce reperfusion injury after myocardial ischemia.

METHODS

The efficacy of CY-1503 to attenuate global myocardial reperfusion injury was assessed in isolated blood-perfused neonatal lamb hearts that had 2 hours of cold cardioplegic ischemia. CY-1503 (40 mg/L) or saline vehicle was added to blood perfusate before ischemia. Contractile function (developed pressure, dP/dt) and coronary vascular endothelial function (acetylcholine response) were assessed at base line and during reperfusion. Myocardial neutrophil accumulation was assessed by myeloperoxidase quantification.

RESULTS

Compared to controls, treatment with CY-1503 improved recovery of all indices of contractile function, preserved coronary vascular endothelial function, and reduced myocardial neutrophil accumulation.

CONCLUSIONS

In isolated neonatal lamb hearts that underwent hypothermic cardioplegic ischemia, CY-1503 administration reduced myocardial neutrophil accumulation and preserved endothelial and contractile function. Selectin blockade of leukocyte-endothelial interactions might attenuate reperfusion injury and enhance myocardial protection during cardiac surgical procedures.

Pharmacology of selectin inhibitors in ischemia/reperfusion states

Recently, the selectin family of glycoprotein adhesion molecules (P-selectin, E-selectin, and L-selectin) has been implicated in the pathogenesis of a number of inflammatory disease states. The selectins modulate the early adhesive interactions between circulating neutrophils and the endothelium. Both P-selectin and E-selectin can be expressed on the surface of endothelial cells following stimulation by a number of inflammatory mediators. In contrast, L-selectin is constitutively expressed on the surface of neutrophils at very high levels. In addition, neutrophils also express ligands for the endothelial selectins, including the carbohydrate sialyl Lewis(x) and the high-affinity ligand P-selectin glycoprotein ligand 1, which facilitate neutrophil-endothelial interactions. Selectins have been extensively investigated in ischemia/reperfusion injury states. The study of selectin involvement in ischemia/reperfusion injury has been facilitated by the development of highly specific selectin antagonists, including monoclonal antibodies, carbohydrates, small molecule inhibitors, and soluble forms of P-selectin glycoprotein ligand 1. This article reviews the results of current studies of selectin antagonists in experimental models of ischemia/reperfusion injury.

Sialyl lewis oligosaccharide preserves cardiopulmonary and endothelial function after hypothermic circulatory arrest in lambs

OBJECTIVE

Neutrophil adhesion to endothelium contributes to cardiopulmonary dysfunction after cardiac surgical procedures. Initial neutrophil-endothelial interactions involve selectins, which bind carbohydrate ligands, such as sialyl-Lewis(X). Blockade of selectin-mediated neutrophil interactions with CY1503, a synthetic oligosaccharide analog of sialyl-Lewis(X), could limit neutrophil-mediated injury after cardiopulmonary bypass.

METHODS

The efficacy of CY1503 treatment was tested in a lamb model of cardiopulmonary bypass with hypothermic circulatory arrest. Neonatal lambs received CY1503 (n = 6, CPB-CY1503) or saline solution vehicle (n = 7, CPB-saline) into the pump prime before bypass and as a continuous infusion throughout reperfusion. Five lambs served as control animals for in vitro microvessel studies. Indexes of myocardial function (preload recruitable stroke work index, and rate of pressure rise) and pulmonary function (compliance, airway resistance, and arterial PO (2)) were measured before bypass and during reperfusion. The effect of CY1503 on endothelium-dependent vascular reactivity was assessed by means of in vitro pulmonary and coronary microvessel studies.

RESULTS

Myocardial function was depressed after circulatory arrest, but CY1503 preserved function near baseline (36% +/- 25% vs 99% +/- 19% of baseline at 3 hours of reperfusion). CY1503-treated animals also demonstrated improved pulmonary function during reperfusion. In vitro microvessel analysis of vascular reactivity revealed endothelial dysfunction after circulatory arrest compared with control lambs. CY1503-treated lambs (CPB-CY1503) had intact endothelial function, as demonstrated by normal vasodilatory responses to endothelium-dependent vasodilators.

CONCLUSIONS

CY1503 preserves cardiopulmonary and endothelial function after cardiopulmonary bypass and hypothermic circulatory arrest in neonatal lambs. This suggests a role for selectin-mediated, neutrophil-endothelial interactions in the inflammatory response after cardiac operations.

Cytomegalovirus induces sialyl Lewis(x) and Lewis(x) on human endothelial cells

BACKGROUND

Cytomegalovirus (CMV) is the primary viral cause of complications in transplant recipients. We sought to understand the mechanisms of its dissemination and induction of vascular disease, which may lead to transplant complications. Sialyl Lewis(x) (sLe(x)) and Lewis(x) (Le(x)) are known for their roles in mediating cell adhesion and as tumor-associated carbohydrate antigens. Herein we explore whether CMV induces surface expression of these important molecules in endothelial cells (EC).

METHODS

Flow cytometry was used to detect surface expression of sLe(x) and Le(x) on CMV-infected human umbilical vein endothelial cells (HUVEC), with or without ultraviolet inactivation of the virus. To elucidate mechanisms of CMV-mediated induction, mRNA coding for predominant HUVEC sialyltransferases (ST) and fucosyltransferases (FT), key enzymes in sLe(x) and Le(x) synthesis, was analyzed by Northern blot. Dual immunohistochemical staining for sLe(x) and Le(x) expression of human colon and placental tissue was performed to investigate in vivo relevance.

RESULTS

sLe(x) expression on CMV-infected HUVEC was strongly up-regulated by 8 days after inoculation. Le(x) expression was detectable earlier and increased steadily over time. In contrast, ultraviolet-inactivated CMV did not induce expression of these molecules. Northern blot assays demonstrated higher levels of important EC glycosyltransferases ST-IV, FT-III, and FT-IV in CMV-infected EC. Finally, high levels of sLe(x) and Le(x) were expressed in CMV-infected EC in vivo.

CONCLUSIONS

Given the known biologic functions of sLe(x) and Le(x), we suggest that CMV induction of these molecules may have widespread consequences ranging from CMV dissemination to induction of CMV-associated vascular disease, including thrombosis.

The effects of delayed treatment with sialyl Lewis X against lipopolysaccharide-induced acute lung injury in rabbits

The therapeutic effects of a selectin inhibitor against lipopolysaccharide-induced acute lung injury were studied in rabbits by using sialyl Lewis X-oligosaccharide. Lipopolysaccharide-induced acute lung injury, as characterized by an impairment of pulmonary gas exchange, clinically resembles that of the acute respiratory distress syndrome. Delayed treatments with sialyl Lewis X-oligosaccharide (55 mg kg(-1) i.v. bolus injection 0.5, 1 or 2 h after lipopolysaccharide administration+36 mg kg(-1) h(-1) i.v. infusion for 5.5, 5 or 4 h, respectively) prevented the lipopolysaccharide-induced impairments in pulmonary gas exchange, as well as the accumulation of polymorphonuclear leukocytes in the lung tissue. In contrast, this agent had no significant effects on lipopolysaccharide-induced systemic hypotension, the decrease in the number of circulating white blood cells and platelets or the decline in blood pH. This is the first demonstration that sialyl Lewis X-oligosaccharide is effective against the impairments in pulmonary gas exchange even if administered 0.5, 1 or 2 h following the lipopolysaccharide injection.

Pathobiology and Clinical Impact of Reperfusion Injury

Reperfusion injury refers to cellular death or dysfunction caused by restoration of blood flow to previously alchemic tissue. This should be differentiated from the normal reparative processes that follow an ischemic insult. Four types of reperfusion injury have been described in the literature: (1) lethal reperfusion injury, (2) nonlethal reperfusion injury, (myocardial stunning), (3) reperfusion arrhythmias, and (4) vascular injury (including the "no-reflow" phenomenon). There is continued debate whether reperfusion itself is capable of killing viable myocytes, which otherwise would have survived the ischemic insult. However, there is firm evidence for the existence of myocardial stunning following various ischemic syndromes, including reperfusion therapy for acute myocardial infarction, unstable angina pectoris, vasospastic angina, effort-induced ischemia, coronary artery bypass surgery, and cardiac transplantation. Reperfusion arrhythmia is more common after short ischemic episodes than after long ischemic periods. Thus, while reperfusion arrhythmias in the setting of acute myocardial infarction are relatively rare, reperfusion arrhythmias may be an important cause of sudden death. The "no-reflow" phenomenon has been described following reperfusion in patients with acute myocardial infarction. Three major components have been proposed as mediators of reperfusion injury: (1) oxygen free radicals, (2) the complement system, and (3) neutrophils. Numerous experimental studies have shown short-term benefit by blocking various stages of the postischemic inflammatory response. Oxygen free radicals scavengers, complement inhibition, leukocyte depletion, and the use of antibodies against various adhesion molecules have shown a reduction of infarct size in many ischemic/reperfusion experimental models. However, many of these agents failed to show a benefit in the clinical setting. Moreover, the long-term benefit of such intervention is still unknown.

Cholesterol feeding exacerbates myocardial injury in Zucker diabetic fatty rats

We measured infarct size after coronary occlusion (30 min) and reperfusion (24 h) in genetic non-insulin-dependent Zucker diabetic fatty (ZDF) rats with and without 4-wk cholesterol feeding. Infarct size was similar in ZDF rats and lean control rats but was significantly larger in cholesterol-fed diabetic rats than in cholesterol-fed lean rats (P < 0.05). Plasma levels of glucose, insulin, and triglycerides were significantly higher in diabetic rats and were not influenced by cholesterol feeding. The increase in total plasma cholesterol induced by cholesterol feeding was significantly greater in diabetic rats than in lean rats (P < 0.05). A significant positive correlation was found between total plasma cholesterol and infarct size (P < 0.05). Myeloperoxidase activity, as an index of neutrophil accumulation, was significantly higher and expression of P-selectin was more marked in the ischemic myocardium of cholesterol-fed diabetic rats than of cholesterol-fed lean rats. Acetylcholine-induced endothelium-dependent relaxation (EDR) of aortic rings was markedly impaired in cholesterol-fed diabetic rats. Thus cholesterol feeding significantly exacerbated myocardial injury produced by coronary occlusion-reperfusion in non-insulin-dependent diabetic rats, possibly because of enhanced expression of P-selectin and impairment of EDR in the coronary bed.

Pathobiology and Clinical Impact of Reperfusion Injury

Reperfusion injury refers to cellular death or dysfunction caused by restoration of blood flow to previously ischemic tissue. This should be differentiated from the normal reparative processes that follow an ischemic insult. Four types of reperfusion injury have been described in the literature: (1) lethal reperfusion injury, (2) nonlethal reperfusion injury (myocardial stunning), (3) reperfusion arrhythmias, and (4) vascular injury (including the "no-reflow" phenomenon). There is continued debate whether reperfusion itself is capable of killing viable myocytes, which otherwise would have survived the ischemic insult. However, there is firm evidence for the existence of myocardial stunning following various ischemic syndromes, including reperfusion therapy for acute myocardial infarction, unstable angina pectoris, vasospastic angina, effort-induced ischemia, coronary artery bypass surgery, and cardiac transplantation. Reperfusion arrhythmia is more common after short ischemic episodes than after long ischemic periods. Thus, while reperfusion arrhythmias in the setting of acute myocardial infarction are relatively rare, reperfusion arrhythmias may be an important cause of sudden death. The "no-reflow" phenomenon has been described following reperfusion in patients with acute myocardial infarction. Three major components have been proposed as mediators of reperfusion injury: (1) oxygen free radicals, (2) the complement system, and (3) neutrophils. Numerous experimental studies have shown short-term benefit by blocking various stages of the postischemic inflammatory response. Oxygen free radicals scavangers, complement inhibition, leukocyte depletion, and the use of antibodies against various adhesion molecules have shown a reduction of infarct size in many ischemic/reperfusion experimental models. However, many of these agents failed to show a benefit in the clinical setting. Moreover, the long-term benefit of such intervention is still unknown.

Attenuation of renal ischemia-reperfusion injury with selectin inhibition in a rabbit model

BACKGROUND

The selectin glycoproteins are involved in the pathogenesis of renal ischemia-reperfusion injury. We investigated the ability of glycyrrhizin, a known selectin inhibitor, to attenuate renal ischemia-reperfusion injury.

METHODS

Eighteen New Zealand white rabbits underwent midline laparotomy with renal artery cross-clamping. After 30 minutes of reperfusion, group 1 (control, n = 10) animals received a saline infusion, while group 2 (GLY, n = 8) animals received a glycyrrhizin infusion. Renal function was compared between the two groups after 72 hours of reperfusion. A t test was utilized, with alpha set at P<0.05.

RESULTS

Group 1 and group 2 animals had similar baseline renal function. However, after 72 hours of reperfusion, group 1 animals had a significantly higher mean blood urea nitrogen creatinine ratio than group 2 animals (P<0.01), indicating preserved renal function in rabbits treated with glycyrrhizin.

CONCLUSIONS

Selectin blockade using glycyrrhizin attenuates renal ischemia-reperfusion injury when given 30 minutes after the onset of reperfusion in a rabbit model.

Reduction of myocardial infarct size with sCR1sLe(x), an alternatively glycosylated form of human soluble complement receptor type 1 (sCR1), possessing sialyl Lewis x

1 This study investigated the effects of soluble complement receptor type 1 (sCR1) or sCR1sLex, agents which function as a complement inhibitor or as a combined complement inhibitor and selectin adhesion molecule antagonist, respectively, on the infarct size and cardiac troponin T (cTnT) release caused by regional myocardial ischaemia and reperfusion in the rat. 2 Eighty-two, male Wistar rats were subjected to 30 min occlusion of the left anterior descending coronary artery (LAD) followed by 2 h of reperfusion. Haemodynamic parameters were continuously recorded and at the end of the experiments infarct size (with p-nitro-blue tetrazolium) and cTnT release were determined. 3 Infusion of sCR1 (1, 5 or 15 mg kg-1, each n=7) or sCR1sLe(x) (1, 5 or 15 mg kg-1, n=7, 13 or 13, respectively) 5 min prior to LAD-reperfusion caused a reduction in infarct size from 59+/-2% (PBS - control, n=12) to 46+/-6%, 25+/-9% and 37+/-6% or 42+/-6%, 35+/-6% and 35+/-4%, respectively. 4 Infusion of sCR1 (15 mg kg-1, n=5) or sCR1sLe(x) (15 mg kg-1, n=5) also reduces the myocardial TnT release from 80+/-20 ng ml-1 (control) to 13+/-7 or 4+/-1 ng ml-1, respectively. 5 Thus, sCR1 or sCRsLe(x) significantly reduce infarct size and cardiac TnT release caused by 30 min of regional myocardial ischaemia and 2 h of reperfusion in the rat. The mechanisms of the cardioprotective effects of sCR1 or sCR1sLe(x) are not entirely clear, but may be due complement inhibition and/or prevention of the adhesion and activation of neutrophils.

Endothelial L-selectin ligands are likely to recruit lymphocytes into rejecting human heart transplants

L-selectin-dependent lymphocyte extravasation is a hallmark of acute heart allograft rejection in rats. On screening over 600 endomyocardial biopsies (EMBs), taken at different time points after heart transplantation in man, we identified 91 samples with histological signs of acute rejection. Rejection and nonrejection EMBs were analyzed for the presence of properly glycosylated, ie, sulfated sialyl Lewis-x (sLex) decorated L-selectin ligands. Two anti-sLex (2F3 and HECA-452) and one anti-6- or 6'-sulfated and/or 6, 6'-bisulfation (MECA-79) monoclonal antibodies were used. Nonrejecting heart endothelium did not express, or expressed only weakly, sulfated and or sLex decorations of L-selectin ligands. On the contrary, these epitopes were readily detectable on endothelium of capillaries and venules at the onset and during acute rejection episodes. The more intense the sulfated sLex expression was, the more severe the rejection episode was in histological grading. The endothelial expression of L-selectin ligands decreased to background levels as the rejection resolved. Our data demonstrate a complete correlation between the level of expression of the sulfated sLex-decorated ligands on the one hand and the histological severity of acute heart allograft rejection on the other hand. These data suggest that functionally active endothelial L-selectin ligands are instrumental in lymphocyte extravasation into the human heart allografts at the onset and during acute rejection episodes.

Protective effect of anti-P-selectin monoclonal antibody in lipopolysaccharide-induced lung hemorrhage

Excessive leukocyte accumulation is involved in the pathogenesis of the sepsis-induced acute lung injury. Selectins are essential to the interaction between leukocytes and endothelial cells. In this report, we investigated the role of selectins in the severe lung injury induced by lipopolysaccharide (LPS). Significant lung hemorrhage was observed 24 h after the intravenous administration of LPS (1 mg/kg). First, we evaluated the effect of sialyl Lewis X-oligosaccharide (SLeX-OS), a derivative of sialyl Lewis X which is one of the ligands for E-, P- and L-selectins. The treatment with SLeX-OS (26.5 mg/kg iv bolus + 19.8 mg/kg iv infusion) resulted in a decrease of lung hemorrhage by 49.5% (P<0.05 versus the control group). Second, we tested the effect of anti-P-selectin monoclonal antibody (MAb), PB 1.3, to investigate the role of P-selectin. The bolus administration of PB1.3 at a dose of 5 mg/kg attenuated the lung hemorrhage by 74.6% (P<0.05 versus the control group). In addition, we also detected an increase of soluble P-selectin in plasma 24 h after the injection of LPS. These results suggest that P-selectin has a substantial role in the pathogenesis of the lung injury induced by LPS.

Complete enzymic synthesis of the mucin-type sialyl Lewis x epitope, involved in the interaction between PSGL-1 and P-selectin

Sialyl Lewis x (sLe(x)) is an established selectin ligand occurring on N- and O-linked glycans. Using a completely enzymic approach starting from p-nitrophenyl N-acetyl-alpha-D-galactosaminide (GalNAc(alpha1-pNp as core substrate, the sLe(x)-oligosaccharide Neu5Ac(alpha2-3)Gal(beta1-4)[Fuc(alpha1-3)]GlcNAc(beta1-6)[Gal(bet a1-3)]GalNAc(alpha1-pNp, representing the O-linked form, was synthesized in an overall yield of 32%. In a first step, Gal(beta1-3)GalNAc(alpha1-pNp was prepared in a yield of 52% using UDP-Gal and an enriched preparation of beta3-galactosyltransferase (EC 2.4.1.122) from rat liver. UDP-GlcNAc and a recombinant affinity-purified preparation of core 2 beta6-N-acetylglucosaminyltransferase (EC 2.4.1.102) fused to Protein A were used to branch the core 1 structure, affording GlcNAc(beta1-6)[Gal(beta1-3)]GalNAc(alpha1-pNp in a yield of >85%. The core 2 structure was galactosylated using UDP-Gal and purified human milk beta4-galactosyltransferase 1 (EC 2.4.1.38) (yield of >85%), then sialylated using CMP-Neu5Ac and purified recombinant alpha3-sialyltransferase 3 (EC 2.4.99.X) (yield of 87%), and finally fucosylated using GDP-Fuc and recombinant human alpha3-fucosyltransferase 6 (EC 2.4.1.152) produced in Pichia pastoris (yield of 100%). Overall 1.5 micromol of product was prepared. MALDI TOF mass spectra, and 1D and 2D TOCSY and ROESY 1H NMR analysis confirmed the obtained structure.