Role of endothelial cell surface heparin-like polysaccharides

Mechanism of antithrombotic effect of heparin and antithrombin in balloon-injured arteries

The mechanism of the antithrombotic effects of heparin and the synthetic antithrombin agent argatroban was evaluated in a dog model. Thrombus formation following balloon injury was evaluated by angioscopy in the right iliac arteries of 20 dogs to serve as a control. After the evaluation of the growth of thrombus on the control side, heparin (200 U/kg) or argatroban (0.2 mg/kg) was infused intravenously, and the distal site of the contralateral left iliac artery was injured in the same manner. At 30 to 120 min before the final examination, the proximal site of the left iliac artery also was injured. After antithrombotic drug infusion, the percent angioscopic stenosis at the distal site was much lower (P<0.0001) than that of the control site (mean stenosis index: 0.67 in heparin vs. 3.8 in control, and 0.25 in argatroban vs. 4.3 in control); however, thrombus formation was observed at the proximal site. With local delivery of a low dose of either antithrombotic drug (n=10), an antithrombotic effect was maintained until 4 h after the infusion. A very weak fluorescence of FITC-heparin was detected at the injured artery 2 h after infusion. In a shunt experiment involving 5 dogs, carotid arteries were injured and incubated in oxygenated Krebs--Henseleit solution before auto grafting into the femoral artery. At 2 h after the grafting, no thrombus was formed in the grafted vessels incubated for 4 h, but was formed in those incubated for 10 min. These results indicate that the relatively long antithrombotic effect of these drugs may be due to a local drug effect at the injured artery, as well as the recovery of the anti-thrombogenicity of the injured artery.

Platelet factor 4 differentially modulates CD4+CD25+ (regulatory) versus CD4+CD25- (nonregulatory) T cells

Active suppression mediated by CD4(+)CD25(+) T regulatory (Tr) cells plays an important role in the down-regulation of T cell responses to both foreign and self-Ags. Platelet factor 4 (PF4), a platelet-derived CXC chemokine, has been shown to strongly inhibit T cell proliferation as well as IFN-gamma and IL-2 release by isolated T cells. In this report we show that human PF4 stimulates proliferation of the naturally anergic human CD4(+)CD25(+) Tr cells while inhibiting proliferation of CD4(+)CD25(-) T cells. In coculture experiments we found that CD4(+)CD25(+) Tr cells exposed to PF4 lose the ability to inhibit the proliferative response of CD4(+)CD25(-) T cells. Our findings suggest that human PF4, by inducing Tr cell proliferation while impairing Tr cell function, may play a previously unrecognized role in the regulation of human immune responses. Because platelets are the sole source of PF4 in the circulation, these findings may be relevant to the pathogenesis of certain immune-mediated disorders associated with platelet activation, such as heparin-induced thrombocytopenia and autoimmune thrombocytopenic purpura.

Platelet factor 4 neutralizes heparan sulfate-enhanced antithrombin inactivation of factor Xa by preventing interaction(s) of enzyme with polysaccharide

Platelet factor 4 (PF4) is a heparin-binding protein which exhibits anti-heparin activities through the inhibition of antithrombin (AT)-dependent reactions with the serine proteases thrombin and factor Xa. PF4 also neutralizes heparan sulfate (HS), a glycosaminoglycan (GAG) present on the surface of endothelial cells, thereby possibly modulating an anticoagulant response. Previous models of PF4 mechanism did not distinguish whether PF4 causes steric hindrance of AT binding to fXa or of AT binding to the surface of the GAG chain. To shed light on the mechanism of PF4, studies of HS/heparin-catalyzed fXa inactivation by AT were undertaken. The results were consistent with PF4 directly interfering with AT binding to fXa rather than AT binding to the GAG chain, since PF4 did not prevent the heparin-dependent increase in AT intrinsic fluorescence. In fact, PF4 mechanism was competitive with respect to AT and non-competitive with respect to fXa, suggesting inhibition of important regulatory/catalytic interactions of fXa with the polysaccharide. Altogether, the results suggested a model by which PF4 bound to proximal (but distinct) sites to AT, resulting in steric interference of fXa binding to both polysaccharide and AT. It is proposed that PF4 inhibited the sequence of events recapitulated in the template mechanism describing heparin-dependent inhibition of fXa.

The amino acid sequences of the carboxyl termini of human and mouse hepatic lipase influence cell surface association

Human hepatic lipase (hHL) mainly exists cell surface bound, whereas mouse HL (mHL) circulates in the blood stream. Studies have suggested that the carboxyl terminus of HL mediates cell surface binding. We prepared recombinant hHL, mHL, and chimeric proteins (hHLmt and mHLht) in which the carboxyl terminal 70 amino acids of hHL were exchanged with the corresponding sequence from mHL. The hHL, mHL, and hHLmt proteins were catalytically active using triolein and tributyrin as substrates. In transfected cells, the majority of hHLs bound to the cell surface, with only 4% of total extracellular hHL released into heparin-free media, whereas under the same conditions, 61% of total extracellular mHLs were released. Like mHL, hHLmt showed decreased cell surface binding, with 68% of total extracellular hHLmt released. To determine the precise amino acid residues involved in cell surface binding, we prepared a truncated hHL mutant (hHL471) by deleting the carboxyl terminal five residues (KRKIR). The hHL471 also retained hydrolytic activity with triolein and tributyrin, and showed decreased cell surface binding, with 40% of total extracellular protein released into the heparin-free media. These data suggest that the determinants of cell surface binding exist within the carboxyl terminal 70 amino acids of hHL, of which the last five residues play an important role.

Identification of anti-thrombin antibodies in the antiphospholipid syndrome that interfere with the inactivation of thrombin by antithrombin

The combined presence of anti-phospholipid (PL) Ab, including lupus anticoagulants (LAC) and/or anticardiolipin Ab (aCL), and thrombosis is recognized as the antiphospholipid syndrome (APS). LAC are detected as an inhibitory effect on PL-restricted in vitro blood coagulation tests, and are comprised mainly of Ab against beta(2) glycoprotein I and prothrombin (PT). Recently, anti-PT Ab (aPT) were found to be associated with thrombosis by some investigators, although this is not confirmed by others. Considering that aPT are heterogeneous in patients and that PT is converted into thrombin, we hypothesize that certain aPT in patients may bind to thrombin, and that some of such anti-thrombin Ab may interfere with thrombin-antithrombin (AT) interaction and thus reduce the AT inactivation of thrombin. To test this hypothesis, we searched for anti-thrombin Ab in APS patients and then studied those found for their effects on the AT inactivation of thrombin. The results revealed that most, but not all, aPT-positive patient plasma samples contained anti-thrombin Ab. To study the functional significance of these Ab, we identified six patient-derived mAb that bound to both PT and thrombin. Of these mAb, three could reduce the AT inactivation of thrombin, whereas others had minimal effect. These findings indicate that some aPT in patients react with thrombin, and that some of such anti-thrombin Ab could inhibit feedback regulation of thrombin. Because the latter anti-thrombin Ab are likely to promote clotting, it will be important to develop specific assays for such Ab and study their roles in thrombosis in APS patients.

Vascular antithrombin and clinical outcome in heart transplant patients

A procoagulant microvasculature is associated with accelerated development of coronary artery disease (CAD) and failure in heart transplant patients. This study was performed to evaluate how changes in natural anticoagulation within cardiac allografts affect outcome. We prospectively studied 141 consecutive cardiac allograft recipients who underwent transplantation between 1988 and 1997. Serial endomyocardial biopsy specimens (6.5 +/- 0.1 biopsy specimens/patient) obtained during the first 3 months after transplantation were studied immunohistochemically to evaluate vascular antithrombin, and annual coronary angiograms (3.8 +/- 0.2 angiograms/patient) were studied to evaluate CAD. Antithrombin was present in arteries and veins, but not in capillaries, of all donor heart biopsy samples. Allografts that maintained vascular antithrombin had the best prognosis. Allografts with early and persistent loss of vascular antithrombin (n = 21) developed CAD earlier (p < 0.001), developed more severe disease (p < 0.001), showed more disease progression (p < 0.001), and failed more often (p = 0.003) and earlier (p < 0.001) than allografts retaining normal vascular antithrombin (n = 45). However, allografts that lost and recovered vascular antithrombin while developing unusual capillary antithrombin binding (n = 75) had less CAD, developed CAD later, had less severe disease and less disease progression (p < 0.01), and failed less often (p = 0.01) and later (p = 0.03) than allografts with persistent loss of vascular antithrombin. The persistent lack of a thromboresistant microvasculature increases risk of subsequent CAD and graft failure. However, recovery of vascular antithrombin and development of unusual capillary antithrombin binding improves allograft outcome.

Anticoagulant heparan sulfate precursor structures in F9 embryonal carcinoma cells

To understand the mechanisms that control anticoagulant heparan sulfate (HSact) biosynthesis, we previously showed that HSact production in the F9 system is determined by the abundance of 3-O-sulfotransferase-1 as well as the size of the HSact precursor pool. In this study, HSact precursor structures have been studied by characterizing [6-3H]GlcN metabolically labeled F9 HS tagged with 3-O-sulfates in vitro by 3'-phosphoadenosine 5'-phospho-35S and purified 3-O-sulfotransferase-1. This later in vitro labeling allows the regions of HS destined to become the antithrombin (AT)-binding sites to be tagged for subsequent structural studies. It was shown that six 3-O-sulfation sites exist per HSact precursor chain. At least five out of six 3-O-sulfate-tagged oligosaccharides in HSact precursors bind AT, whereas none of 3-O-sulfate-tagged oligosaccharides from HSinact precursors bind AT. When treated with low pH nitrous or heparitinase, 3-O-sulfate-tagged HSact and HSinact precursors exhibit clearly different structural features. 3-O-Sulfate-tagged HSact hexasaccharides were AT affinity purified and sequenced by chemical and enzymatic degradations. The 3-O-sulfate-tagged HSact hexasaccharides exhibited the following structures, DeltaUA-[6-3H]GlcNAc6S-GlcUA-[6-3H]GlcNS3(35)S+/-6S-++ +IdceA2S-[6-3H]Glc NS6S. The underlined 6- and 3-O-sulfates constitute the most critical groups for AT binding in view of the fact that the precursor hexasaccharides possess all the elements for AT binding except for the 3-O-sulfate moiety. The presence of five potential AT-binding precursor hexasaccharides in all HSact precursor chains demonstrates for the first time the processive assembly of specific sequence in HS. The difference in structures around potential 3-O-sulfate acceptor sites in HSact and HSinact precursors suggests that these precursors might be generated by different concerted assembly mechanisms in the same cell. This study permits us to understand better the nature of the HS biosynthetic pathway that leads to the generation of specific saccharide sequences.

Anionic Polysaccharides Inhibit Adhesion of Sickle Erythrocytes to the Vascular Endothelium and Result in Improved Hemodynamic Behavior

The abnormal adherence of sickle red blood cells (SS RBC) to vascular endothelium may play an important role in vasoocclusion in sickle cell anemia. Thrombospondin (TSP), unusually large molecular weight forms of von Willebrand factor, and laminin are known to enhance adhesion of SS RBC. Also, these endothelial proteins bind to sulfated glycolipids and this binding is inhibited by anionic polysaccharides. Reversible sickling may expose normally cryptic membrane sulfatides that could mediate this adhesive interaction. In this study, we have investigated the effect of anionic polysaccharides, in the presence or absence of TSP, on SS RBC adhesion to the endothelium, using cultured human umbilical vein endothelial cells (HUVEC) (for the adhesion assay) and the ex vivo mesocecum of the rat (for hemodynamic evaluation). The baseline adhesion (ie, without added TSP) of SS RBC to HUVEC was most effectively inhibited by high molecular weight dextran sulfate (HDS), whereas low molecular weight dextran sulfate (LDS) and the glycosaminoglycan chondroitin sulfate A (CSA) also had significant inhibitory effects. Heparin was mildly effective whereas other glycosaminoglycans (chondroitin sulfates B and C, heparan sulfate, and fucoidan) were ineffective. Similarly, HDS and CSA resulted in an improved hemodynamic behavior of SS RBC. Soluble TSP caused significant increases in SS RBC adhesion and in the peripheral resistance. Both HDS and CSA prevented TSP-enhanced adhesion and hemodynamic abnormalities. Thus, anionic polysaccharides can inhibit SS RBC-endothelium interaction in the presence or absence of soluble TSP. These agents may interact with RBC membrane component(s) and prevent TSP-mediated adhesion of SS RBC to the endothelium.

Anionic Polysaccharides Inhibit Adhesion of Sickle Erythrocytes to the Vascular Endothelium and Result in Improved Hemodynamic Behavior

The abnormal adherence of sickle red blood cells (SS RBC) to vascular endothelium may play an important role in vasoocclusion in sickle cell anemia. Thrombospondin (TSP), unusually large molecular weight forms of von Willebrand factor, and laminin are known to enhance adhesion of SS RBC. Also, these endothelial proteins bind to sulfated glycolipids and this binding is inhibited by anionic polysaccharides. Reversible sickling may expose normally cryptic membrane sulfatides that could mediate this adhesive interaction. In this study, we have investigated the effect of anionic polysaccharides, in the presence or absence of TSP, on SS RBC adhesion to the endothelium, using cultured human umbilical vein endothelial cells (HUVEC) (for the adhesion assay) and the ex vivo mesocecum of the rat (for hemodynamic evaluation). The baseline adhesion (ie, without added TSP) of SS RBC to HUVEC was most effectively inhibited by high molecular weight dextran sulfate (HDS), whereas low molecular weight dextran sulfate (LDS) and the glycosaminoglycan chondroitin sulfate A (CSA) also had significant inhibitory effects. Heparin was mildly effective whereas other glycosaminoglycans (chondroitin sulfates B and C, heparan sulfate, and fucoidan) were ineffective. Similarly, HDS and CSA resulted in an improved hemodynamic behavior of SS RBC. Soluble TSP caused significant increases in SS RBC adhesion and in the peripheral resistance. Both HDS and CSA prevented TSP-enhanced adhesion and hemodynamic abnormalities. Thus, anionic polysaccharides can inhibit SS RBC-endothelium interaction in the presence or absence of soluble TSP. These agents may interact with RBC membrane component(s) and prevent TSP-mediated adhesion of SS RBC to the endothelium.

Regulation of platelet heparanase during inflammation: role of pH and proteinases

Heparan sulfate is rapidly degraded by an endoglycosidase (heparanase) secreted by activated platelets. Since the cleavage and release of heparan sulfate would profoundly alter the local physiology of the endothelium, platelet heparanase activity should be tightly regulated. Consistent with this hypothesis, platelet heparanase was found to degrade endothelial cell heparan sulfate at pH 6.0 but not at pH 7.4, even though 25% of maximum activity was detected at pH 7.4. Loss of heparanase activity occurred rapidly (t1/2 is approximately equal to 20 min) and reversibly at physiologic pH but did not occur at acidic pH (<7.0). Inactivation of heparanase at pH 7.4 did not affect heparin binding and was reversed by 0.5 M NaCl or by heparan sulfate but not by chondroitin sulfate, suggesting inactive heparanase could be tethered on cell surfaces and the function regulated by heparan sulfate. Heparanase was gradually inactivated by trypsin and urokinase (t1/2 = 5 h) but resisted cleavage by leukocyte cathepsin G, leukocyte elastase, plasmin, and thrombin. These findings are consistent with a model in which platelet heparanase is active at the low pH of inflammation but inactive under physiologic conditions preventing inadvertent cleavage of heparan sulfate and loss of physiologic functions of endothelial cells.

Lipoprotein lipase-enhanced binding of lipoprotein(a) [Lp(a)] to heparan sulfate is improved by apolipoprotein E (apoE) saturation: secretion-capture process of apoE is a possible route for the catabolism of Lp(a)

Recently, it has been recognized that cell-bound heparan sulfate (HS) proteoglycans (HSPG) are able to bind and subsequently initiate degradation of lipoproteins. Two mediators of lipoprotein catabolism, both with HS binding capacity, lipoprotein lipase (LPL) and apolipoprotein E (apoE), are involved in this process. This mechanism is known as the secretion-capture process of apoE. Lipoprotein(a) [Lp(a)] was shown to have a strong binding capacity to cell-associated HSPG. This binding capacity was increased by LPL addition. We investigated the effects of recombinant apoE (r-apoE) enrichment of Lp(a) on the binding to HS. Lp(a), isolated by ultracentrifugation and gel filtration, was incubated with r-apoE and reisolated by ultracentrifugation, resulting in r-apoE-enriched Lp(a). ApoE-enriched Lp(a) and control Lp(a) were coated to microtiter plates. The capacity to bind biotin-conjugated HS (b-HS) in the presence or absence of inactivated bovine LPL was studied. R-apoE-enriched Lp(a) showed increased b-HS binding capacity versus control Lp(a). Addition of LPL resulted in an increased b-HS binding capacity of both control and r-apoE-enriched Lp(a). To investigate whether binding of Lp(a) to endothelial cell HSPG occurred in vivo, 39 volunteers were injected with heparin (50 U/kg) and plasma lipid and Lp(a) levels were determined before and 20 minutes after heparin injection. No significant increase in plasma Lp(a) concentrations was found. The results showed that Lp(a) can be enriched with apoE and that this resulted in increased LPL-enhanced binding to HSPG. From the in vitro studies, it can be concluded that the secretion-capture process of apoE is a possible catabolic route for Lp(a). However, whether this also occurs in vivo remains to be confirmed.

Characterization and hormonal modulation of anticoagulant heparan sulfate proteoglycans synthesized by rat ovarian granulosa cells

Anticoagulant heparan sulfate proteoglycans endow the vascular endothelium with antithrombotic properties, but their role outside the vascular bed is unknown. Granulosa cells form an avascular compartment in the ovarian follicle, in which a heparin-like activity has been described. At ovulation extravascular coagulation occurs around ovulatory follicles, and after expulsion of the oocyte, a fibrin clot forms in the antral cavity. Granulosa cells synthesize two major heparan sulfate proteoglycans, whose anticoagulant nature has not been investigated. The purpose of this study was to characterize anticoagulant heparan sulfate proteoglycans synthesized by rat ovarian granulosa cells. Affinity purified 35S-labeled anticoagulant heparan sulfate glycosaminoglycans represent 6.5% of the total heparan sulfate synthesized, and they contain 13% 3-O-sulfated disaccharides that are markers of the antithrombin-binding site of heparin. The biological activity of granulosa cell heparan sulfate proteoglycans was demonstrated by their ability to bind antithrombin and to accelerate the formation of thrombin-antithrombin complexes. The impact of hormonal stimulation on granulosa cell anticoagulant heparan sulfate proteoglycans was studied using 125I-antithrombin binding assays. Follicle-stimulating hormone induced a redistribution of anticoagulant heparan sulfate proteoglycans from the granulosa cell layer to the culture medium, indicating that their distribution could be modulated according to the stage of follicular development. These results suggest that anticoagulant heparan sulfate might be critically located in the follicle to maintain fluidity around the oocyte until its expulsion at ovulation.

Antithrombin binding by human umbilical vein endothelial cells: effects of exogenous heparin

Human umbilical vein endothelial cells cultured in growth media that did not contain exogenous heparin were found to grow less well while binding significantly more antithrombin (AT) than comparable cells cultured in growth media that did contain exogenous heparin (90 micrograms/ml). The binding of AT to plasma membranes of cultured endothelial cells was measured immunologically by flow cytometry. This binding was eliminated completely by reacting the cells with heparinase III before incubating them with AT, indicating that the most likely heparinase-sensitive process responsible for AT binding to plasma membranes was heparan sulfate proteoglycan. Increased AT binding also was promoted by addition of heparin-binding molecules (protamine, AT, or ECGF) to growth media, and the effects of other glycosaminoglycans and dextran on AT binding were found to be dependent on their sulfation. Thus, one response of endothelial cells to heparin deficiency is up-regulation of the ability to bind AT to plasma membranes.

Human bone marrow heparan sulfate induces leukemia cell differentiation

The proliferation and development of hematopoietic cells occurs in close association with bone marrow stroma. Heparan sulfate is a major component of the stroma. We have isolated a form of heparan sulfate proteoglycan from a human stromal cell line grown in vitro in the presence of [35S]sulfate. This proteoglycan contains a phosphatidylinositol component which likely anchors it to the stromal cell membrane. The glycosaminoglycan chains of this proteoglycan could induce maturation of the HL-60 myeloid leukemia cell line. A less hydrophobic heparan sulfate proteoglycan was also present in the stroma, but could not induce HL-60 maturation. The two heparan sulfates had glycosaminoglycan chains that were similar in size (36 Kd) and charge density. Structural studies suggested only minor but perhaps significant differences in the carbohydrate sequences of the two heparan sulfates. The relationship of these subtle structural differences to the difference observed in differentiation-inducing activity remains to be elucidated.

Enzymatic degradation of glycosaminoglycans

Glycosaminoglycans (GAGs) play an intricate role in the extracellular matrix (ECM), not only as soluble components and polyelectrolytes, but also by specific interactions with growth factors and other transient components of the ECM. Modifications of GAG chains, such as isomerization, sulfation, and acetylation, generate the chemical specificity of GAGs. GAGs can be depolymerized enzymatically either by eliminative cleavage with lyases (EC 4.2.2.-) or by hydrolytic cleavage with hydrolases (EC 3.2.1.-). Often, these enzymes are specific for residues in the polysaccharide chain with certain modifications. As such, the enzymes can serve as tools for studying the physiological effect of residue modifications and as models at the molecular level of protein-GAG recognition. This review examines the structure of the substrates, the properties of enzymatic degradation, and the enzyme substrate-interactions at a molecular level. The primary structure of several GAGs is organized macroscopically by segregation into alternating blocks of specific sulfation patterns and microscopically by formation of oligosaccharide sequences with specific binding functions. Among GAGs, considerable dermatan sulfate, heparin and heparan sulfate show conformational flexibility in solution. They elicit sequence-specific interactions with enzymes that degrade them, as well as with other proteins, however, the effect of conformational flexibility on protein-GAG interactions is not clear. Recent findings have established empirical rules of substrate specificity and elucidated molecular mechanisms of enzyme-substrate interactions for enzymes that degrade GAGs. Here we propose that local formation of polysaccharide secondary structure is determined by the immediate sequence environment within the GAG polymer, and that this secondary structure, in turn, governs the binding and catalytic interactions between proteins and GAGs.

Localized intramural drug delivery during balloon angioplasty using hydrogel-coated balloons and pressure-augmented diffusion

OBJECTIVES

This study was designed to assess the feasibility of using hydrogel-coated balloons to deliver biologically active agents to the blood vessel wall.

BACKGROUND

The local intramural delivery of therapeutic agents during balloon angioplasty has been proposed as an adjunctive technique for preventing early intracoronary thrombosis and late restenosis.

METHODS

To assess the efficacy of delivery and depth of penetration in vitro, local delivery of horseradish peroxidase was performed in 40 porcine peripheral arteries, and delivery of fluoresceinated heparin was performed in 20 porcine peripheral arteries and 7 human atheromatous arteries. To determine the persistence of these agents in the vessel wall in vivo, horseradish peroxidase was delivered to 18 porcine peripheral arteries that were harvested at intervals of 45 min to 48 h. Fluoresceinated heparin was delivered to 22 porcine peripheral arteries, 14 with the use of a protective sleeve, harvested at intervals of 30 s to 24 h.

RESULTS

In vitro agent delivery was successful in all specimens. The depth of penetration of horseradish peroxidase was directly related to both balloon pressure (p < 0.04) and duration of inflation (p < 0.01). In vivo peroxidase staining was evident at 45 and 90 min but not thereafter. With the use of a protective sleeve, heparin was present in all arteries harvested at 30 s, with marked dissipation at 1 and 24 h. Without a sleeve, no fluorescein staining was detected in any artery. With both agents, delivery occurred consistently over broad regions of the vessel wall that were free of architectural disruption.

CONCLUSIONS

Hydrogel-coated balloons can deliver biologically active agents to the vessel wall without gross tissue disruption and may provide an atraumatic method for the local delivery of therapeutic agents during balloon angioplasty.

Mapping the heparin-binding sites on type I collagen monomers and fibrils

The glycosaminoglycan chains of cell surface heparan sulfate proteoglycans are believed to regulate cell adhesion, proliferation, and extracellular matrix assembly, through their interactions with heparin-binding proteins (for review see Ruoslahti, E. 1988. Annu. Rev. Cell Biol. 4:229-255; and Bernfield, M., R. Kokenyesi, M. Kato, M. T. Hinkes, J. Spring, R. L. Gallo, and E. J. Lose. 1992. Annu. Rev. Cell Biol. 8:365-393). Heparin-binding sites on many extracellular matrix proteins have been described; however, the heparin-binding site on type I collagen, a ubiquitous heparin-binding protein of the extracellular matrix, remains undescribed. Here we used heparin, a structural and functional analogue of heparan sulfate, as a probe to study the nature of the heparan sulfate proteoglycan-binding site on type I collagen. We used affinity coelectrophoresis to study the binding of heparin to various forms of type I collagen, and electron microscopy to visualize the site(s) of interaction of heparin with type I collagen monomers and fibrils. Using affinity coelectrophoresis it was found that heparin has similar affinities for both procollagen and collagen fibrils (Kd's approximately 60-80 nM), suggesting that functionally similar heparin-binding sites exist in type I collagen independent of its aggregation state. Complexes of heparin-albumin-gold particles and procollagen were visualized by rotary shadowing and electron microscopy, and a preferred site of heparin binding was observed near the NH2 terminus of procollagen. Native or reconstituted type I collagen fibrils showed one region of significant heparin-gold binding within each 67-nm period, present near the division between the overlap and gap zones, within the "a" bands region. According to an accepted model of collagen fibril structure, our data are consistent with the presence of a single preferred heparin-binding site near the NH2 terminus of the collagen monomer. Correlating these data with known type I collagen sequences, we suggest that the heparin-binding site in type I collagen may consist of a highly basic triple helical domain, including several amino acids known sometimes to function as disaccharide acceptor sites. We propose that the heparin-binding site of type I collagen may play a key role in cell adhesion and migration within connective tissues, or in the cell-directed assembly or restructuring of the collagenous extracellular matrix.

Differential binding of chemokines to glycosaminoglycan subpopulations

BACKGROUND

Specificity in leukocyte trafficking is likely to depend on sequential interactions between various cell-type-specific leukocyte adhesion molecules, such as selectins and integrin ligands, and leukocyte-activating factors. A major class of leukocyte-activating factors, the chemokines, are soluble polypeptides that bind glycosaminoglycans, the polysaccharide components of cell-surface and extracellular-matrix proteoglycans. It has been suggested that cell-surface glycosaminoglycans of the heparin/heparan sulfate class mediate the presentation of chemokines to leukocytes by vascular endothelial cells. We investigated the possibility that specificity exists in the recognition of particular heparin/heparan sulfate structures by chemokines, by studying the binding of four members of the chemokine superfamily to heparin and heparan sulfate.

RESULTS

Using affinity co-electrophoresis we found that interleukin-8 preferentially bound a subfraction of heparin that also showed increased affinity for melanoma growth stimulating activity (also known as MGSA, GRO or GRO alpha). This same subfraction of heparin, however, was not significantly preferentially bound by platelet factor 4 or neutrophil activating factor-2. Subsequent analysis of the three-dimensional structures of these chemokines indicated that their ability to discriminate among heparin subspecies correlates with the presence of paired glutamic acid residues within the putative glycosaminoglycan-binding site of the chemokine. This observation led to predictions about the relative affinities of heparan sulfate for interleukin-8 and platelet factor 4, predictions that were confirmed by further binding assays.

CONCLUSION

Chemokines can bind selectively to subsets of heparin/heparan sulfate glycosaminoglycans, raising the possibility that glycosaminoglycans participate in determining the specificity of leukocyte recruitment in vivo.

Heparin adheres to the damaged arterial wall and inhibits its thrombogenicity

Heparin binds to thrombogenic extracellular matrices as well as to smooth muscle cells of the vascular wall in vitro. The inhibitory effects of heparin on thrombogenicity of the damaged arterial wall were examined in vivo using small mesenteric arteries of rats and a video recording system attached to a microscope. To induce thrombosis, we damaged the vessel wall over a short segment by compression and exposed the media to the blood stream. A platelet-rich thrombus enlarged gradually at the damaged site, occluded the vascular lumen for a short period, and then flowed away. Compression damage induced such thrombus formation several times. Heparin (500 units/ml) was given in three different ways: intravenous and intra-arterial administration (both 300 units/kg) and intraluminal application under stopped-flow conditions (less than 0.01 ml) for 1-2 minutes with subsequent draining out. Intravenous heparin significantly decreased both the total duration and the number of thrombotic occlusions, whereas intra-arterial heparin abolished thrombotic occlusion. Both routes of heparin administration similarly prolonged the blood coagulation time. Intraluminal application of heparin significantly inhibited subsequent thrombus formation after restoring the flow without changes in the blood coagulation time. After an intra-arterial administration or intraluminal application of fluorescein isothiocyanate-bound heparin, strong fluorescence was observed only at the damaged vascular segment. A heparin fraction with low affinity to antithrombin III or chondroitin sulfate A did not inhibit thrombosis. To clarify anticoagulant activity of vascular wall-bound heparin, damaged carotid arterial segments of rats were incubated (inside out) in platelet-poor plasma with thrombin, and fibrin clot formation around the segments with or without heparin binding was measured.(ABSTRACT TRUNCATED AT 250 WORDS)

Heparin-like activity in porcine follicular fluid and rat granulosa cells

Heparin-like activity is present in rat and porcine follicular fluids, as determined by measuring the acceleration of the inactivation of purified human thrombin by antithrombin III. The heparin-like activity is dose-dependent and specific to follicular fluid proteoglycans. Cartilage proteoglycans do not exhibit this activity at any of the concentrations tested. The activity of these macromolecules resides in the polysaccharide unit. Destruction of the protein core of the follicular fluid proteoglycans by alkaline borohydride treatment does not interfere with the "heparin-like" effect, whereas it is completely destroyed by digestion with purified heparinase. Incubation with chondroitinases has no effect. Granulosa cells which are the source of follicular fluid proteoglycans express biologically active heparin-like mucopolysaccharides. These molecules are produced under gonadotropin regulation and are associated with the cell surface material.

Heterogeneous distribution of antithrombin-binding sites in rat brain heparan sulphate proteoglycans

Heparan sulphates with high binding affinity for antithrombin (HA-HS), labelled in vivo with [35S]sulphate, were extracted from rat brains and purified by chromatography on DEAE-cellulose and on antithrombin-agarose. HA-HS proteoglycans (HA-HSPG) were then separated from HA-HS chains on Sepharose CL-6B. The total HA-HSPG product was rechromatographed on antithrombin-agarose. Six HA-HSPG subfractions with differing degrees of affinity for antithrombin were recovered and treated with NaOH to release their chains. Rechromatography of these six 35S-labelled HS chain preparations on antithrombin-agarose showed that their proportions of chains with no affinity for antithrombin (NA-HS chains) ranged from 36 to 71%. There was a reciprocal relationship between the proportion of NA-HS chains in each HA-HSPG subfraction and the degree of affinity for antithrombin of the rest of its chains (assessed relative to 3H-labelled HA-heparin chains with which they were co-chromatographed). Similar characteristics of antithrombin-binding-site distribution apply to HA-heparin proteoglycans from rat skin studied previously [Horner (1987) Biochem. J. 244, 693-698]. The data suggest that the sites at which 3-O-sulphation of some glucosamine N-sulphate residues occurs in the Golgi complex of brain cells (probably endothelial cells) which synthesize HA-HSPGs (as in mast cells, which synthesize HA-heparin PGs) are distributed sparsely but not randomly.

Antiangiogenic effect of heparin and other sulphated glycosaminoglycans in the chick embryo chorioallantoic membrane

The effect of heparin and other sulphated glycosaminoglycans on normal capillary growth was studied in the chick embryo chorioallantoic membrane, with or without hydrocortisone. Contrary to previous reports, heparin was shown to have an antiangiogenic effect in itself, and an additive effect was obtained when it was combined with hydrocortisone. Heparan sulphate also had an antiangiogenic effect in the chorioallantoic membrane, while keratan sulphate, dermatan sulphate or chondroitin sulphate had no such effect. Copper ions, added in small amounts, did not influence the antiangiogenic effect of heparin, and nor did iron, zinc and magnesium ions, and EDTA.

Antiangiogenic effect of sulphated and nonsulphated glycosaminoglycans and polysaccharides in the chick embryo chorioallantoic membrane

The inhibiting effect of sulphated and nonsulphated glycosaminoglycans and polysaccharides on the normal outgrowth of capillaries was tested in the chick embryo chorioallantoic membrane (CAM) with and without the presence of hydrocortisone. An antiangiogenic response to 50 micrograms of heparin and heparan sulphate (without hydrocortisone present) was observed in 38.8% and 23.1% of the CAMs, respectively, while the antiangiogenic response rate for dermatan sulphate, chondroitin sulphate A or C, hyaluronic acid and keratan sulphate was 15.9-0%. All sulphated homopolysaccharides tested were more effective than the naturally occurring glycosaminoglycans. Nonsulphated dextran and (methyl) cellulose had no antiangiogenic effect, while largely desulphated heparin retained such an effect. Hydrocortisone generally improved the antiangiogenic effect, a 100% response was obtained when it was combined with cellulose sulphate or fucoidan (polyfucose sulphate derived from marine algae), but the antiangiogenic effect of the largely desulphated heparin was unaffected by the presence of hydrocortisone. The results show that different polysulphated polysaccharides also have an antiangiogenic effect, without the addition of corticosteroids. The effect was apparently independent of their degree of sulphation, but the glycosidic structure may be of critical importance.

The amino-terminal region of a proteochondroitin core protein, secreted by aortic smooth muscle cells, shares sequence homology with the pre-propeptide region of the biglycan core protein from human bone

Smooth muscle cells, isolated from rat and bovine aortae and grown in vitro, synthesize chondroitin sulfate proteoglycans which are secreted into the growth media. Analysis of metabolically [35S]-labeled macromolecules, employing ion-exchange chromatography, revealed a single peak of radioactivity, upon elution with a linear salt gradient. Treatment of the material with enzymes that specifically degrade chondroitin sulfate demonstrated that chondroitin-4-sulfate was the predominant species isolated from rat smooth muscle cells and that chondroitin-4-sulfate and dermatan sulfate were the predominant species isolated from bovine aortic smooth muscle cells. Treatment of the native proteoglycans with chondroitinase ABC and subsequent SDS-PAGE analysis of the digestion products resulted in the appearance of a band with an apparent molecular weight of 45,000. Electrotransfer of the core protein to Immobilon-P membrane and gas phase sequencing of the amino-terminal region revealed striking homology between the core proteins of the rat and bovine proteochondroitin with the pre-propeptide region of human bone biglycan.