Protective effects of oligosaccharides in P-selectin-dependent lung injury

Neutrophil Recruitment: From Model Systems to Tissue-Specific Patterns

Neutrophil recruitment is not only vital for host defense, but also relevant in pathological inflammatory reactions, such as sepsis. Model systems have been established to examine different steps of the leukocyte recruitment cascade in vivo and in vitro under inflammatory conditions. Recently, tissue-specific recruitment patterns have come into focus, requiring modification of formerly generalized assumptions. Here, we summarize existing models of neutrophil recruitment and highlight recent discoveries in organ-specific recruitment patterns. New techniques show that previously stated assumptions of integrin activation and tissue invasion may need revision. Similarly, neutrophil recruitment to specific organs can rely on different organ properties, adhesion molecules, and chemokines. To advance our understanding of neutrophil recruitment, organ-specific intravital microscopy methods are needed.

P-Selectin Targeted Dexamethasone-Loaded Lipid Nanoemulsions: A Novel Therapy to Reduce Vascular Inflammation

Inflammation is a common process associated with numerous vascular pathologies. We hypothesized that targeting the inflamed endothelium by coupling a peptide with high affinity for P-selectin to the surface of dexamethasone-loaded lipid nanoemulsions will highly increase their specific binding to activated endothelial cells (EC) and reduce the cell activation. We developed and characterized dexamethasone-loaded lipid nanoemulsions directed towards P-selectin (PLN-Dex) and monitored their anti-inflammatory effects in vitro using cultured EC (EA.hy926 cells) and in vivo using a mouse model of acute inflammation [lipopolysaccharides (LPS) intravenously administered in C57BL/6 mice]. We found that PLN-Dex bound specifically to the surface of activated EC are efficiently internalized by EC and reduced the expression of proinflammatory genes, thus preventing the monocyte adhesion and transmigration to/through activated EC. Given intravenously in mice with acute inflammation, PLN-Dex accumulated at a significant high level in the lungs (compared to nontargeted nanoemulsions) and significantly reduced mRNA expression level of key proinflammatory cytokines such as IL-1β, IL-6, and MCP-1. In conclusion, the newly developed nanoformulation, PLN-Dex, is functional in vitro and in vivo, reducing selectively the endothelium activation and the consequent monocyte infiltration and diminishing significantly the lungs' inflammation, in a mouse model of acute inflammation.

Heparin fails to inhibit the leukocyte recruitment for an extended time following inflammatory stimulus

CONTEXT

Several studies have shown that heparin is able to inhibit leukocyte recruitment during an early acute inflammatory response. However, considering the pharmacokinetic aspects of heparin and the dynamics of inflammation our objective was to determine if heparin is able to retain its antimigratory property during a prolonged inflammatory response.

OBJECTIVE

Compare the effect of heparin on leukocyte recruitment to the peritoneal cavity during early acute inflammatory response and for a longer time post-inflammatory stimulus.

MATERIALS AND METHODS

Wistar rats pre-treated with subcutaneous heparin in doses of 1, 5, and 15 µg/kg were challenged with 2 mL intraperitoneal thioglycollate. After 3 or 8 h, the animals were killed. The cells in the peritoneal cavity were collected and counted. For differential counting, cells from peritoneal lavage and from blood were distended over a glass slide, stained, and counted.

RESULTS

After 3 h, heparin inhibited cell influx to the injury site at all tested dosages. The largest effect was achieved at a 5 µg/kg dose (83% of reduction, p < 0.001). After 8 h, heparin at a 1 µg/kg dose reduced 63% of cellular infiltration (p < 0.001); the group treated with a 15 µg/kg dose presented an pro-inflammatory effect observed by the higher proportions, when compared with the thioglycollate group, of neutrophils on whole blood (60.9%, p < 0.001) and peritoneal fluid (27.3%, p < 0.05), and whole blood monocytes (117.8%, p < 0.01).

CONCLUSION

These findings show that the heparin effect on leukocyte recruitment varies depending on its dosage and the duration of the inflammation.

Expression of human CD46 modulates inflammation associated with GalTKO lung xenograft injury

Evaluation of lungs from GalTKO.hCD46 pigs, genetically modified to lack the galactose-α(1,3)-galactose epitope (GalTKO) and to express human CD46, a complement regulatory protein, has not previously been described. Physiologic, hematologic and biochemical parameters during perfusion with heparinized fresh human blood were measured for 33 GalTKO.hCD46, GalTKO (n = 16), and WT pig lungs (n = 16), and 12 pig lungs perfused with autologous pig blood. Median GalTKO.hCD46 lung survival was 171 min compared to 120 for GalTKO (p = 0.27) and 10 for WT lungs (p < 0.001). Complement activation, platelet activation and histamine elaboration were significantly reduced during the first 2 h of perfusion in GalTKO.hCD46 lungs compared to GalTKO (ΔC3a at 120' 812 ± 230 vs. 1412 ± 1047, p = 0.02; ΔCD62P at 120' 9.8 ± 7.2 vs. 25.4 ± 18.2, p < 0.01; Δhistamine at 60' 97 ± 62 vs. 189 ± 194, p = 0.03). We conclude that, in addition to significant down-modulation of complement activation, hCD46 expression in GalTKO lungs diminished platelet and coagulation cascade activation, neutrophil sequestration and histamine release. Because GalTKO.hCD46 lung failure kinetics correlated directly with platelet and neutrophil sequestration, coagulation cascade activation and a rise in histamine levels within the first hour of perfusion, further progress will likely depend upon improved control of these pathways, by rationally targeted additional modifications to pigs and pharmacologic interventions.

Implications of the E-selectin S128R mutation for drug discovery

The C-type lectin E-selectin mediates the rolling of circulating leukocytes on vascular endothelial cells during the inflammatory process. In numerous studies, the S128R mutation of the E-selectin was associated with cardiovascular and autoimmune diseases. There is evidence that the S128R E-selectin mutation leads to a loss in ligand specificity, thus increasing leukocyte recruitment. Apart from the natural tetrasaccharide ligand sialyl Lewis(x) (sLe(x)), it has previously been proposed that non-fucosylated carbohydrates also bind to S128R E-selectin. To evaluate the therapeutic potential of the antagonism of the E-selectin mutant, ligand specificity was reinvestigated on a molecular basis. We determined the ligand specificity of wild-type and S128R E-selectin in a target-based competitive assay, a glycan array screen and cell-based binding assays under static and flow conditions. Regarding ligand-specificity, the binding properties of S128R E-selectin were identical to those of wt E-selectin, i.e., no mutant-specific binding of 3'-sialyl-N-acetyllactosamine, heparin, fetuin and K562 cells was observed. Additionally, the binding affinities of glycomimetic E-selectin antagonists were identical for wt and S128R E-selectin. Overall, the previous reports on carbohydrate ligand promiscuity of S128R E-selectin could not be confirmed.

Neutrophils in local and systemic antibody-dependent inflammatory and anaphylactic reactions

Neutrophils are notorious for their efficacy in microbial killing. Various mechanisms, such as phagocytosis, production of ROS, cytokines/chemokines and lipid mediators, degranulation of antimicrobials and enzymes, as well as NETosis contribute to this capacity. However, every incidence of neutrophil activation bears a risk to cause damage to the host. Several distinct steps, i.e., adhesion to endothelial cells, transmigration, chemotaxis, cytokine stimulation, and TLR signaling, are thought to control the extent of neutrophil activation. In the absence of a microbial stimulus, other pathways can induce neutrophil activation, among which FcR-induced activation when neutrophils encounter ICs. In these situations (inflammation, autoimmunity, allergy), neutrophils may act as primary or secondary effectors of immune reactions. In the presence of circulating ICs, neutrophils can indeed get stimulated directly in the bloodstream and trigger an immune response. Upon deposition of antibody complexes inside of tissues, neutrophils are first recruited and primed before being highly activated to amplify the ongoing inflammation. This review focuses on the engagement, activation, and responses of neutrophils to antibody ICs, inside of tissues or in the vasculature.

A new generation of carbohydrate-based therapeutics: recombinant mucin-type fusion proteins as versatile inhibitors of protein-carbohydrate interactions

Cell surface carbohydrates are essential for a multitude of biomedically important interactions that take place at the cell surface. Carbohydrate-binding proteins are, therefore, significant targets for the development of carbohydrate-based inhibitors. Due to their multivalent character, monovalent low-molecular-weight sugar homologues or analogues are usually poor inhibitors of these interactions. Recent advances in organic and chemoenzymatic synthesis of carbohydrates will undoubtedly increase the pace by which new multivalent carbohydrate-based drugs are developed. Knowledge gained on the glycosyltransferases that are involved in glycan biosynthesis can be used to engineer host cells for recombinant production of proteins with tailored glycan substitution. In particular, recombinant mucin-type proteins can serve as natural scaffolds for multivalent presentation of therapeutic carbohydrate determinants.

Intravital imaging of phagocyte recruitment

Extravasation of neutrophils and monocytes is a hallmark event in acute and chronic inflammation. Owing to recent improvements in optical imaging techniques, the classical leukocyte extravasation cascade has been refined with intermediate steps being added. Further studies have shown tissue specific leukocyte recruitment patterns, thus allowing for more selective targeting. Here we focus on recent advances in intravital imaging of leukocyte recruitment by means of optical imaging techniques and emphasise the translation thereof into tissue-specific recruitment to the lungs, the liver and large arteries.

Contribution of neutrophils to acute lung injury

Treatment of acute lung injury (ALI) and its most severe form, acute respiratory distress syndrome (ARDS), remain unsolved problems of intensive care medicine. ALI/ARDS are characterized by lung edema due to increased permeability of the alveolar-capillary barrier and subsequent impairment of arterial oxygenation. Lung edema, endothelial and epithelial injury are accompanied by an influx of neutrophils into the interstitium and broncheoalveolar space. Hence, activation and recruitment of neutrophils are regarded to play a key role in progression of ALI/ARDS. Neutrophils are the first cells to be recruited to the site of inflammation and have a potent antimicrobial armour that includes oxidants, proteinases and cationic peptides. Under pathological circumstances, however, unregulated release of these microbicidal compounds into the extracellular space paradoxically can damage host tissues. This review focuses on the mechanisms of neutrophil recruitment into the lung and on the contribution of neutrophils to tissue damage in ALI.

Adhesion molecules: potential therapeutic and diagnostic implications

The role of cell adhesion molecules (CAMs) and extracellular matrix (ECM) proteins in various pathological processes, including angiogenesis, thrombosis, inflammation, apoptosis, cell migration, and proliferation is well documented. These processes can lead to both acute and chronic disease states such as ocular diseases, metastasis, unstable angina, myocardial infarction, stroke, osteoporosis, a wide range of inflammatory diseases, vascular remodeling, and neurodegenerative disorders. A key success in this field was identification of the role of platelet glycoprotein (GP)IIb/IIIa in the prevention and diagnosis of various thromboembolic disorders. The use of soluble adhesion molecules as potential diagnostic markers for acute and chronic leukocyte, platelet, and endothelial cell insult is becoming increasingly common. The development of various therapeutic and diagnostic candidates based on the key role of CAMs, with special emphasis on integrins in various diseases, as well as the structure-function aspects of cell adhesion and signaling of the different CAMs and ECM are highlighted.

The first fifty years in research

It has been an honor for me to write the prefatory article for Volume 4 of the Annual Review of Pathology: Mechanisms of Disease. I decided to describe the first 50 years of my career in research, which started with my entry into medical school. I have tried to outline the numerous scientific mentors who played such an important role in my development as an independent scientific investigator. In general, I have tried to avoid mention in the text of the many, many colleagues who carried out the scientific work, as I would inevitably fail to cite many of them. Rather, I have cited what I think are my most important publications, which identify many of these scientific colleagues. I am now engaged nearly full-time in research and look forward to the next period of research progress.

Expression patterns of adhesion molecules P-selectin, von Willebrand factor and PECAM-1 in lungs: A comparative study in cases of burn shock and hemorrhagic shock

For comparative examination of the pathological findings in burn shock and hemorrhagic shock, histological and immunohistochemical investigations of the lungs were performed. Histological specimens of 30 cases each were examined by means of immunohistological staining with P-selectin, von Willebrand factor (vWF) and PECAM-1. The results showed statistically significant differences between the two groups. There was strong staining for P-selectin (especially in the lumina of the blood vessels) and vWF (especially in the endothelium of medium-sized blood vessels) in the specimens of burn shock fatalities. In cases of rapid death after exposure to fire the strong expression of adhesion molecules, which are mainly responsible for the initial inflammatory reaction of leucocytes and platelets in burn shock, suggests prompt activation of inflammatory cells in the lung tissue. In cases of hemorrhagic shock, this reaction was much less distinct in the early stages. The same is true of the expression of PECAM-1, which was lower in lungs from burn shock fatalities than in those from hemorrhagic shock fatalities. The low expression of PECAM-1 in burn shock is a clue to the migration/diapedesis of leucocytes into the areas of burn damage. In total, the results of the investigation indicate different pathophysiological processes even in the very early stages of burn shock and hemorrhagic shock.

Regulation of lung inflammation in the model of IgG immune-complex injury

Modern techniques of cell and molecular biology have rapidly uncovered the mechanisms underlying inflammatory injury of the lung. This expanding knowledge (which includes an understanding of complement, cell surface receptors, cytokines and chemokines, transcription factors, oxidants, proteinases, and endogenous inhibitors, as well as the role of leukocyte adhesion-promoting molecules) has provided new insights into the inflammatory system in general, as well as in the context of lung injury. In this review, we summarize recent progress in understanding the regulation of lung inflammation by using immunoglobulin G (IgG) immune complex-induced lung injury as a model. These studies have provided information on the role of various inflammatory mediators and their sequence of engagement. Insights into potential interventional approaches for the suppression of inflammatory processes in humans have emerged from those studies.

Emerging therapies for treatment of acute lung injury and acute respiratory distress syndrome

Acute lung injury/acute respiratory distress syndrome (ALI/ARDS) is a life-threatening form of respiratory failure that affects a heterogeneous population of critically ill patients. Although overall mortality appears to be decreasing in recent years due to improvements in supportive care, there are presently no proven, effective pharmacological therapies to treat ARDS and prevent its associated complications. The most common cause of death in ARDS is not hypoxemia or pulmonary failure, but rather multiple organ dysfunction syndrome (MODS), suggesting that improving survival in patients with ARDS may be linked to decreasing the incidence or severity of MODS. The key to developing novel treatments depends, in part, on identifying and understanding the mechanisms by which ARDS leads to MODS, although the heterogeneity and complexity of this disorder certainly poses a challenge to investigators. Novel therapies in development for treatment of ALI/ARDS include exogenous surfactant, therapies aimed at modulating neutrophil activity, such as prostaglandin and complement inhibitors, and treatments targeting earlier resolution of ARDS, such as beta-agonists and granulocyte macrophage colony-stimulating factor. From a clinical perspective, identifying subpopulations of patients most likely to benefit from a particular therapy and recognising the appropriate stage of illness in which to initiate treatment could potentially lead to better outcomes in the short term.

Cell adhesion molecules: potential therapeutic & diagnostic implications

The role of cell adhesion molecules (CAM) and extracellular matrix proteins (ECM) in various pathological processes including angiogenesis, thrombosis, apoptosis, cell migration & proliferation are well documented. These processes can lead to both acute and chronic disease states such as ocular diseases, metastasis, unstable angina, myocardial infarction, stroke, osteoporosis, a wide range of inflammatory diseases, vascular remodeling, and neurodegenerative disorders. A key success in this field is evident from the potential role of the platelet GPIIb/IIIa integrin in the prevention and diagnosis of various thromboembolic disorders. Additionally, the use of soluble adhesion molecules as potential diagnostic markers for acute and chronic leukocyte, platelet, and endothelial cellular insult are increasingly utilized. The development of various therapeutic and diagnostic candidates based on the key role of CAM, with special emphasis on integrins in various diseases as well as the structure-function aspects of cell adhesion and signaling of the different CAM and ECM are highlighted.

Construction of a library of human glycosyltransferases immobilized in the cell wall of Saccharomyces cerevisiae

Fifty-one human glycosyltransferases were expressed in Saccharomyces cerevisiae as immobilized enzymes and were assayed for enzymatic activities. The stem and catalytic regions of sialyl-, fucosyl-, galactosyl-, N-acetylgalactosaminyl-, and N-acetylglucosaminyltransferases were fused with yeast cell wall Pir proteins, which anchor glycosyltransferases at the yeast cell wall glucan. More than 75% of expressed recombinant glycosyltransferases retained their enzymatic activities in the yeast cell wall fraction and will be used as a human glycosyltransferase library. In increasing the enzymatic activities of immobilized glycosyltransferases, several approaches were found to be effective. Additional expression of yeast protein disulfide isomerase increased the expression levels and activities of polypeptide N-acetylgalactosaminyltransferases and other glycosyltransferases. PIR3 and/or PIR4 was more effective than PIR1 as a cell wall anchor when the Pir-glycosyltransferase fusions were expressed under the control of the constitutive glyceraldehyde-3-phosphate dehydrogenase promoter. Oligosaccharides such as Lewis x, Lewis y, and H antigen were successfully synthesized using this immobilized glycosyltransferase library, indicating that the Pir-fused glycosyltransferases are useful for the production of various human oligosaccharides.

The use of levoglucosenone and isolevoglucosenone as templates for the construction of C-linked disaccharides

Because of their functionalities (enone, ketone, and acetal) and their bicyclic structure (steric factors), levoglucosenone (1,6-anhydro-3,4-dideoxy-beta-D-glycero-hex-3-enopyran-2-ulose) and isolevoglucosenone (1,6-anhydro-2,3-dideoxy-beta-D-glycero-hex-3-enopyran-4-ulose) are useful templates for the convergent and combinatorial synthesis of (1-->2), (1-->3), and (1-->4)-linked C-disaccharides in reactions combining them with sugar-derived carbaldehydes. Synthetic methods relying on conjugate nucleophilic additions of these enones, their combination with aluminum reagents and aldehydes (Baylis-Hillman reaction) and modified Takai-Hiyama-Nozaki-Kishi couplings of enol triflates derived from them with sugar-derived aldehydes are reviewed. Highly stereoselective methods have thus been developed. These allow the generation of disaccharide mimetics with a high molecular diversity.

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.

Selectin antagonists : therapeutic potential in asthma and COPD

Asthma and COPD are chronic inflammatory conditions that affect hundreds of millions of patients worldwide. New therapeutics are desperately needed, especially those that target the underlying causes and prevent disease progression. Although asthma and COPD have distinct etiologies, both are associated with reduced airflow caused by excess infiltration of inflammatory cells into healthy lung tissues. As selectin-mediated adhesion of leukocytes to the vascular endothelium is a key early event in the initiation of the inflammatory response, selectin inhibition is thought to be a good target for therapeutic intervention.

Three known selectins are expressed in distinct subsets of cells: P-selectin is presented on the surface of activated platelets and endothelial cells, L-selectin is constitutively expressed on leukocytes, and E-selectin synthesis is upregulated in activated endothelial cells. They mediate cell-cell adhesion in the shear flow of the bloodstream via specialized interactions with clusters of oligosaccharides presented on cell surface glycopeptide ligands. The role of selectin-ligand interactions in the inflammatory response has been demonstrated in various animal models, prompting considerable attention from the pharmaceutical industry.

Drug discovery efforts have yielded many different classes of selectin inhibitors, including soluble protein ligands, antibodies, oligosaccharides and small molecules. Although many selectin inhibitors have shown activity in preclinical models, clinical progress of selectin-directed therapies has been slow. Early approaches employed carbohydrate-based inhibitors to mimic the natural ligand sialyl Lewis X; however, these compounds proved challenging to develop. Cytel’s CY 1503, a complex oligosaccharide, progressed to phase II/III trials for reperfusion injury, but further development was halted when it failed to demonstrate clinical efficacy. Two protein-based selectin inhibitors have reached phase II development. These included Wyeth’s recombinant soluble P-selectin ligand, TSI (PSGL-1), which was discontinued after disappointing results in myocardial infarction trials and Protein Design Labs’ humanized anti-L-selectin monoclonal antibody, which is currently in development for trauma. Bimosiamose, discovered by Encysive Pharmaceutical and presently being developed by Revotar Biopharmaceuticals, is an 863 g/mol molecular weight dimer with minimal carbohydrate content and is, to date, the leading selectin inhibitor in clinical development. This compound has shown promise in a phase Ha ‘proof of concept’ trial in patients with asthma, reducing airway recruitment of eosinophils after intravenous administration. Further clinical development of an inhaled formulation is underway.

Despite a significant need for new therapeutics, selectin inhibitors have not yet been explored for the treatment of COPD. Bimosiamose represents an important proof of principle, and hopefully continued success will spark renewed interest in selectin-directed therapeutics for respiratory diseases.

Monomeric and Multimeric Blockers of Selectins: Comparison of in vitro and in vivo Activity

The potency of the oligosaccharides SiaLe(x), SiaLe(a), HSO(3)Le(x), and HSO(3)Le(a), their conjugates with polyacrylamide (PAA, 40 kD), and other monomeric and polymeric selectin inhibitors has been compared with that of the polysaccharide fucoidan. The following assay systems were used: 1) a 96-well assay based either on the use of recombinant E-, P-, and L-selectins or an analogous assay with natural P-selectin isolated from human platelets; 2) a platelet-based P-selectin cell assay; and 3) a rat model of peritoneal inflammation. IC(50) values for the neoglycoconjugate SiaLe(a)-PAA were 6, 40, and 85 microM for recombinant E-, P-, and L-selectins, respectively; all monomeric inhibitors were about two orders of magnitude weaker. PAA-conjugates, containing as a ligand tyrosine-O-sulfate (sTyr) in addition to one of the sialylated oligosaccharides, were the most potent synthetic blockers in vitro. Compared with fucoidan, the most potent known P- and L-selectin blocker, the bi-ligand glycoconjugate HSO(3)Le(a)-PAA-sTyr displayed similar inhibitory activity in vitro towards L-selectin and about ten times lower activity towards P-selectin. All of the tested synthetic polymers displayed a similar ability to inhibit neutrophil extravasation in the peritonitis model (in vivo) at 10 mg/kg. The data provide evidence that monomeric SiaLe(x) is considerably more effective as a selectin blocker in vivo than in vitro, whereas the opposite is true for fucoidan and the bi-ligand neoglycoconjugate HSO(3)Le(a)-PAA-sTyr.

The synthetic pentasaccharide fondaparinux reduces coagulation, inflammation and neutrophil accumulation in kidney ischemia-reperfusion injury

Ischemia-reperfusion (I/R) injury is associated with activation of coagulation and inflammation. Interestingly, various anticoagulants have been shown to reduce both coagulation and inflammation in animal models of kidney I/R injury. Fondaparinux is a synthetic pentasaccharide that selectively inhibits factor Xa (FXa) in the coagulation cascade. The aim of this study was to investigate the effect of fondaparinux in a lethal murine model of kidney I/R injury. A murine model of kidney I/R was established. In this model, we measured activation of the coagulation cascade and induction of inflammation. Administration of fondaparinux to I/R-injured mice reduced fibrin deposition in the kidney, reduced serum creatinine levels and increased survival from 0 to 44% compared with saline-treated control mice. Fondaparinux also reduced interleukin-6 and macrophage inflammatory protein-2 expression and decreased neutrophil accumulation in the injured kidneys. Finally, we showed that fondaparinux reduced thioglycollate-induced recruitment of neutrophils into the peritoneum and inhibited the binding of U937 cells to P-selectin in vitro. Our data suggest that fondaparinux reduces kidney I/R injury primarily by inhibiting the recruitment of neutrophils.

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.

The design, synthesis and evaluation of high affinity macrocyclic carbohydrate inhibitors

Carbohydrate-protein interactions have been investigated for a model system of a monoclonal antibody, SYA/J6, which binds a trisaccharide epitope of the O-polysaccharide of the Shigella flexneri variant Y lipopolysaccharide. The thermodynamics of binding for the methyl glycoside of the native trisaccharide epitope, Rha-Rha-GlcNAc () to SYA/J6 over a range of temperatures exhibits strong, linear enthalpy-entropy compensation and a negative heat capacity change (DeltaC(p)=-152 cal mol(-1) degree(-1)). At 293 K the free energy of association is the sum of favourable enthalpy and entropy contributions (DeltaH=-3.9 kcal mol(-1) and -TDeltaS=-2.9 kcal mol(-1)). Crystal structures for SYA/J6 Fab detailed the position of the native trisaccharide epitope, Rha-Rha-GlcNAc, and facilitated a strategy to design a tighter binding, low molecular weight ligand. This involved pre-organization of the native trisaccharide in its bound conformation by addition of intramolecular constraints (a beta-alanyl or glycinyl tether). ELISA measurements indicated that the glycinyl tethered trisaccharide was not an optimal candidate for further analysis, while microcalorimetry provided data showing that the beta-alanyl tethered trisaccharide displayed a 15-fold increase in affinity for SYA/J6. Tethering resulted in a favourable entropic contribution to binding, relative to the native trisaccharide (-TDeltaDeltaS=-1.2 kcal mol(-1)). Potential energy and dynamics calculations using the AMBER Plus force fields indicated that trisaccharide adopted a rigid conformation similar to that of the bound conformation of the native trisaccharide epitope. While this strategy resulted in modest free energy gains by minimizing losses due to conformational entropy, thermodynamic data are consistent with significant contributions from solvent reorganization.

P-selectin in arterial thrombosis

P-selectin is a transmembrane protein present in the alpha granules of platelets and the Weibel-Palade bodies of endothelial cells. Following activation, it is rapidly translocated to the cell surface. P-selectin expression in platelets has been shown to be elevated in disorders associated with arterial thrombosis such as coronary artery disease, acute myocardial infarction, stroke, and peripheral artery disease. P-selectin mediates rolling of platelets and leukocytes on activated endothelial cells as well as interactions of platelets with leukocytes. Platelet P-selectin interacts with P-selectin glycoprotein ligand-1 (PSGL-1) on leukocytes to form platelet-leukocyte aggregates. Furthermore, this interaction of P-selectin with PSGL-1 induces the upregulation of tissue factor, several cytokines in leukocytes and the production of procoagulant microparticles, thereby contributing to a prothrombotic state. P-selectin is also involved in platelet-platelet interactions, i. e. platelet aggregation which is a major factor in arterial thrombosis. P-selectin interacts with platelet sulfatides, thereby stabilizing initial platelet aggregates formed by GPIIb/IIIa-fibrinogen bridges. Inhibtion of the P-selectin-sulfatide interaction leads to a reversal of platelet aggregation. Thus, P-selectin plays a significant role in platelet aggregation and platelet- leukocyte interactions, both important mechanisms in the development of arterial thrombosis.

MR molecular imaging of early endothelial activation in focal ischemia

Focal ischemia followed by reperfusion initiates a harmful P- and E-selectin-mediated recruitment of leukocytes in brain microvasculature. In this study, we tested whether a novel magnetic resonance (MR) contrast agent (Gd-DTPA-sLe(x) A), which is designed to bind to activated endothelium could be detected by MR imaging (MRI) in a focal stroke mouse model. MRIs (9.4T) of the brain were acquired 24 hours after transient middle cerebral artery occlusion. T1 maps were acquired repeatedly before and up to 1.5 hours after the intravenous injection of either Gd-DTPA or Gd-DTPA-sLe(x) A. Analysis of images included a pixel-by-pixel subtraction of T1 maps from the precontrast T1 maps and quantification of T1 within the ischemic area. After injection of Gd-DTPA-sLe(x) A, T1 decreased compared with precontrast levels, and an interhemispheric difference between the pre-post contrast T1 developed within the stroke lesion at a mean time of 52 minutes after injection (p < 0.05). Animals injected with Gd-DTPA did not exhibit changes in T1 signal intensity between regions of the ipsilateral and contralateral hemispheres, indicating that the reductions in T1 observed with Gd-DTPA-sLe(x) A were unrelated to blood-brain barrier breakdown. Fluorescent-labeled sLe(x) A administered intravenously was observed to bind to the endothelium of injured but not control brain. The study suggests that the contrast agent Gd-DTPA-sLe(x) A can be used to visualize early endothelial activation after transient focal ischemia in vivo with MRI.

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.

Highly conserved cysteines of mouse core 2 beta1,6-N-acetylglucosaminyltransferase I form a network of disulfide bonds and include a thiol that affects enzyme activity

Core 2 beta1,6-N-acetylglucosaminyltransferase I (C2GnT-I) plays a pivotal role in the biosynthesis of mucin-type O-glycans that serve as ligands in cell adhesion. To elucidate the three-dimensional structure of the enzyme for use in computer-aided design of therapeutically relevant enzyme inhibitors, we investigated the participation of cysteine residues in disulfide linkages in a purified murine recombinant enzyme. The pattern of free and disulfide-bonded Cys residues was determined by liquid chromatography/electrospray ionization tandem mass spectrometry in the absence and presence of dithiothreitol. Of nine highly conserved Cys residues, under both conditions, one (Cys217) is a free thiol, and eight are engaged in disulfide bonds, with pairs formed between Cys59-Cys413, Cys100-Cys172, Cys151-Cys199, and Cys372-Cys381. The only non-conserved residue within the beta1,6-N-acetylglucosaminyltransferase family, Cys235, is also a free thiol in the presence of dithiothreitol; however, in the absence of reductant, Cys235 forms an intermolecular disulfide linkage. Biochemical studies performed with thiolreactive agents demonstrated that at least one free cysteine affects enzyme activity and is proximal to the UDP-GlcNAc binding site. A Cys217 --> Ser mutant enzyme was insensitive to thiol reactants and displayed kinetic properties virtually identical to those of the wild-type enzyme, thereby showing that Cys217, although not required for activity per se, represents the only thiol that causes enzyme inactivation when modified. Based on the pattern of free and disulfide-linked Cys residues, and a method of fold recognition/threading and homology modeling, we have computed a three-dimensional model for this enzyme that was refined using the T4 bacteriophage beta-glucosyltransferase fold.

Recruitment of murine neutrophils in vivo through endogenous sialidase activity

Upon activation with various noncytokine stimuli, polymorphonuclear leukocytes (PMNs) mobilize intracellular sialidase to the plasma membrane, where the sialidase releases sialic acid from the cell surface. This desialylation enhances PMN adherence, spreading, deformability, and motility, functions critical to diapedesis. We now have examined the role of sialidase activity in PMN adhesion to and migration across the endothelium in vivo. A polyclonal antibody prepared against Clostridium perfringens neuraminidase 1) detected surface expression of sialidase on human PMNs stimulated with IL-8 in vitro and on murine PMNs stimulated in vivo, but not on that of unstimulated cells, 2) recognized proteins in human PMN lysates and granule preparations that were not detected by preimmune antibody, 3) inhibited bacterial neuraminidase and human PMN sialidase activities in vitro, and 4) inhibited both pulmonary leukostasis in mice systemically infused with cobra venom factor and intrapulmonary transendothelial migration of PMNs into the bronchoalveolar compartment of mice intranasally challenged with interleukin-8. We conclude that the chemokine interleukin-8, like other PMN agonists, induces the translocation of sialidase to the PMN surface and that surface expression of this sialidase is a prerequisite to PMN recruitment in vivo. The ability of antibodies raised against a prokaryotic neuraminidase to recognize eukaryotic sialidase extends the concept of the neuraminidase superfamily to mammalian enzymes. Inhibition of mobilized endogenous sialidase may provide a novel strategy for limiting the inflammatory response.

Sialyl Lewis X analog attenuates gastric microcirculatory disturbance and gastric mucosal erosion induced by thermal injury in rats

BACKGROUND AND AIM

We hypothesize that selectins, which are adhesion molecules, are involved in the pathogenesis of stress-induced gastropathy. We therefore investigated whether the novel Sialyl Lewis X (SLex) analog, which is a clinically available antagonist of selectins, attenuate gastric mucosal lesions induced by thermal injury.

METHODS

Male Wistar rats were anesthetized and a 30% full-skin thickness dorsal burn was inflicted on each rat. The SLex analog was administrated into the jugular vein 30 min before and 2.5 h after the thermal injury. Saline was administered to the vehicle group. The distribution of E-selectin immunoreactivity on the luminal side of the gastric mucosal microvascular network was observed by immunohistochemical methods. Active oxygen species were measured by the chemiluminescence method. Rolling leukocytes and endothelial damage, investigated by using Monastral Blue B (MBB), of the gastric mucosal microvascular network were observed through an intravital microscope.

RESULTS

A high intensity of E-selectin fluorescence was observed on the luminal surface of the venular endothelial cells 5 h after thermal injury in the vehicle group. However, E-selectin-associated fluorescence was almost negligible in the non-injury group and in the SLex analog group. The SLex analog also attenuated the rolling of leukocytes in the venules, venular deposits of MBB, luminol-dependent chemiluminescence activities, and gastric mucosal lesion formation.

CONCLUSION

It is suggested that the selectin family is involved in gastric microcirculatory disturbance and the pathogenesis of gastric mucosal lesions after thermal injury. A novel preventive therapy using the SLex analog is considered to effectively protect both gastric microcirculation and the gastric mucosa in rats with thermal injury.

Specific inhibition of P-selectin-mediated cell adhesion by phage display-derived peptide antagonists

P-selectin is a leukocyte adhesion receptor expressed on activated vascular endothelium and platelets that mediates leukocyte rolling and attachment. Because P-selectin is critically involved in inflammation, we used phage display libraries to identify P-selectin-specific peptides that might interfere with its proinflammatory function. Isolated phage contained a highly conserved amino acid motif. Synthetic peptides showed calcium-dependent binding to P-selectin, with high selectivity over E-selectin and L-selectin. The peptides completely antagonized adhesion of monocyte-derived HL60 cells to P-selectin and increased their rolling velocities in flow chamber experiments. Peptide truncation and alanine-scanning studies indicated that an EWVDV (single-letter amino acid codes) consensus motif sufficed for effective inhibition. Intriguingly, the apparent avidity of the peptides was increased 200-fold when presented in a tetrameric form (2 microM versus 10 nM), which is consistent with the proposed divalent interaction of P-selectin glycoprotein ligand 1 (PSGL-1) with P-selectin. As the EWVDV peptides inhibit the binding of an established glycoside ligand for P-selectin (sulfated Lewis A), it is conceivable that EWVDV interacts with or in close proximity to the actual carbohydrate recognition domain of P-selectin, without being a direct structural mimic of sialyl Lewis(x). These ligands are among the most potent antagonists of P-selectin yet designed. Their high affinity, selectivity, and accessible synthesis provide a promising entry to the development of new anti-inflammatory therapeutics and might be a powerful tool to provide important information on the binding site of P-selectin.

A selectin inhibitor decreases neutrophil infiltration during acute Mannheimia haemolytica pneumonia

The degree to which the selectin inhibitor TBC1269 reduces neutrophil infiltration in specific microscopic locations of the lung during acute pneumonia of neonates was determined. Neonatal calves were inoculated intrabronchially with Mannheimia (Pasteurella) haemolytica or saline, and lung tissue was collected at 2 and 6 hours postinoculation (PI). One 6-hour group inoculated with M. haemolytica received TBC1269 intravenously before and after inoculation with M. haemolytica. Infiltrates of neutrophils were significantly higher in the alveolar lumen and septae but lower in the bronchial lumen and epithelium at 6 hours PI than at 2 hours PI. Significantly fewer neutrophils (P < 0.05) were present in the alveolar lumen and septae, and the bronchiolar lumen and lamina propria in the lungs of TBC1269-treated calves compared with untreated calves at 6 hours PI. TBC1269 did not alter the infiltration into bronchi and blood vessels or the expression of the selectin-independent adhesion molecule, ICAM-1. This work suggests that during acute pneumonia of neonates 1) neutrophil infiltrates progressively increase in the alveolar lumens and septae but decrease in the bronchial lumen and epithelium with time, 2) TBC1269 reduces neutrophil infiltration into specific regions of alveoli and bronchioles rather than uniformly throughout the lung, and 3) selectin inhibition does not affect the location and intensity of ICAM-1 expression.

Glycosulfopeptides modeled on P-selectin glycoprotein ligand 1 inhibit P-selectin-dependent leukocyte rolling in vivo

Leukocytic inflammation can be limited by inhibiting selectin-dependent leukocyte rolling. In spite of intensive efforts to develop small molecule selectin inhibitors with defined structure-activity profiles, inhibition of P-selectin-dependent leukocyte rolling in vivo by such a compound has yet to be described. We recently reported that glycosulfopeptides (GSP), modeled on the high affinity selectin ligand PSGL-1, inhibit leukocyte binding to P-selectin in vitro. Here, we have used intravital microscopy to investigate whether GSP can inhibit P-selectin-dependent leukocyte rolling in vivo. Surgical preparation of the mouse cremaster muscle for intravital microscopy induced P-selectin-dependent leukocyte rolling. Baseline rolling was recorded for 1 min followed by i.v. injection of GSP. 2-GSP-6 and 4-GSP-6 substantially reversed P-selectin-dependent leukocyte rolling, whereas control GSP, which are not fully glycosylated, did not. Inhibition of leukocyte rolling by 2- and 4-GSP-6 lasted 2-4 min. Clearance studies with 125I-labeled 4-GSP-6 demonstrated rapid reduction in its circulating levels concurrent with accumulation in urine. These data represent the first demonstration that a precisely defined structure based on a natural P-selectin ligand can inhibit P-selectin-dependent leukocyte rolling in vivo.