Heparan sulphates from porcine intestinal mucosa. Preparation and physicochemical properties

Identification and characterization of a novel heparinase PCHepII from marine bacterium Puteibacter caeruleilacunae

Heparin (HP) and heparan sulfate (HS) are multifunctional polysaccharides widely used in clinical therapy. Heparinases (Hepases) are enzymes that specifically catalyse HP and HS degradation, and they are valuable tools for studying the structure and function of these polysaccharides and for preparing low molecular weight heparins. In this study, by searching the NCBI database, a novel enzyme named PCHepII was discovered in the genome of the marine bacterium Puteibacter caeruleilacuae. Heterologously expressed PCHepII in Escherichia coli (BL21) has high expression levels and good solubility, active in sodium phosphate buffer (pH 7.0) at 20°C. PCHepII exhibits an enzyme activity of 254 mU/mg towards HP and shows weak degradation capacity for HS. More importantly, PCHepII prefers to catalyse the high-sulfated regions of HP and HS rather than the low-sulfated regions. Although PCHepII functions primarily as an endolytic Hepase, it mainly generates disaccharide products during the degradation of HP substrates over time. Investigations reveal that PCHepII exhibits a preference for catalysing the degradation of small substrates, especially HP tetrasaccharides. The catalytic sites of PCHepII include the residues His199, Tyr254, and His403, which play crucial roles in the catalytic process. The study and characterization of PCHepII can potentially benefit research and applications involving HP/HS, making it a promising enzyme.

Abnormally High Content of Free Glucosamine Residues Identified in a Preparation of Commercially Available Porcine Intestinal Heparan Sulfate

Heparan sulfate (HS) polysaccharides are ubiquitous in animal tissues as components of proteoglycans, and they participate in many important biological processes. HS carbohydrate chains are complex and can contain rare structural components such as N-unsubstituted glucosamine (GlcN). Commercially available HS preparations have been invaluable in many types of research activities. In the course of preparing microarrays to include probes derived from HS oligosaccharides, we found an unusually high content of GlcN residue in a recently purchased batch of porcine intestinal mucosal HS. Composition and sequence analysis by mass spectrometry of the oligosaccharides obtained after heparin lyase III digestion of the polysaccharide indicated two and three GlcN in the tetrasaccharide and hexasaccharide fractions, respectively. ¹H NMR of the intact polysaccharide showed that this unusual batch differed strikingly from other HS preparations obtained from bovine kidney and porcine intestine. The very high content of GlcN (30%) and low content of GlcNAc (4.2%) determined by disaccharide composition analysis indicated that N-deacetylation and/or N-desulfation may have taken place. HS is widely used by the scientific community to investigate HS structures and activities. Great care has to be taken in drawing conclusions from investigations of structural features of HS and specificities of HS interaction with proteins when commercial HS is used without further analysis. Pending the availability of a validated commercial HS reference preparation, our data may be useful to members of the scientific community who have used the present preparation in their studies.

Heparan sulphate inhibition of cell proliferation induced by TGFbeta and PDGF

The effect of glycosaminoglycans (GAGs) on the proliferation of smooth muscle cells (SMC) and fibroblasts was assessed by culturing cells with or without GAGs. Porcine heparan sulphate (HS) inhibited proliferation in a dose dependent manner. At 167 mug/ml of HS this reached 88% and 72% inhibition of SMC and fibroblast growth, respectively. Pig and beef mucosal heparins also blocked proliferation, but to a lesser extent. In contrast, beef lung heparin, chondroitin sulphate, and dermatan sulphate failed to block growth factor induced proliferation. Continuous presence of HS was not required, suggesting that the inhibitory effects resulted from a direct effect on the cell rather than an interaction of the GAG with growth factors. The mechanism by which GAGs inhibit proliferation will be addressed in future studies.

IL-12 Is a Heparin-Binding Cytokine

Using an ELISA approach, we demonstrate that recombinant human IL-12 (rhIL-12) binds strongly to an immobilized heparin-BSA complex. This binding is completely displaceable with soluble heparin, IC50∼ 0.1 μg/ml, corresponding to ∼ 10 nM. By interpolation with our previous findings, this indicates an affinity for heparin greater than that of antithrombin III and comparable with that of FGF-2, two high-affinity heparin-binding proteins. Recombinant murine IL-12 also binds strongly to heparin. The binding of rhIL-12 to heparin shows specificity because chondroitin sulfates A and C fail to compete, whereas chondroitin B inhibits weakly. A highly sulfated heparan sulfate is a strong competitor, whereas other heparan sulfates show weak or no activity. Small heparin fragments inhibit binding, although activity decreases with size. An octasaccharide pool derived by cleavage of heparin with nitrous acid is a significantly stronger inhibitor than its heparinase I-derived counterpart, further indicating structural specificity in the interaction between rhIL-12 and heparin. The binding of recombinant p40 to heparin appears indistinguishable from that of the IL-12 heterodimer, implying that the heparin binding site is largely if not solely located in this subunit. These results show for the first time that IL-12 is a heparin-binding cytokine, a property common to the other Th1-response-inducing cytokines, IFN-γ and IL-2. Our findings strongly suggest that IL-12 will tend to be retained close to its sites of secretion in the tissues by binding to heparin-like glycosaminoglycans, thus favoring a paracrine role for IL-12.

Low anticoagulant heparin retains anti-HIV type 1 activity in vitro

Heparin is a potent inhibitor of HIV-1 replication, in addition to being a well-established inhibitor of blood coagulation. The major anticoagulant activity of heparin results from binding to the plasma protein antithrombin (AT). The high-affinity binding site for AT is a specific pentasaccharide sequence that is of low abundance and completely absent from the majority of heparin chains. We have examined the anti-HIV-1 activity of both conventional and low molecular weight heparins fractionated according to affinity for AT. The high- and low-affinity fractions, despite differing markedly in anticoagulant activity, are identical in their ability to bind to the envelope glycoprotein of HIV-1, and in their inhibitory effect on HIV-1 replication in vitro (EC50 1 and 8 micrograms/ml for conventional and low molecular weight fractions, respectively). Our study shows that the anti-HIV activity of heparin is independent of its antithrombin-mediated inhibition of coagulation proteases. Therefore, heparin preparations retaining full anti-HIV-1 activity in vitro but with greatly reduced anticoagulant activity may be readily produced for further clinical investigation in the prophylaxis and therapy of HIV infection.

Modulation of proteoglycan synthesis by bovine vascular smooth muscle cells during cellular proliferation and treatment with heparin

Proliferating cultures of bovine vascular smooth muscle cells synthesized a variety of proteoglycans corresponding closely to those reported previously for monkey smooth muscle cells. These included a chondroitin sulfate proteoglycan (CSPG) (47%), a dermatan sulfate proteoglycan (DSPG) (22%), and a heparan sulfate proteoglycan (HSPG) (6%) which were secreted into the medium. Heparan sulfate proteoglycan (6%) and a second dermatan sulfate proteoglycan (14%) were also present in the cell layer. Confluent cultures synthesized a similar spectrum of proteoglycans although the medium CSPG and DSPG were of smaller hydrodynamic size. The cell layer HSPG was much reduced relative to DSPG in early proliferating cultures. Previous reports have shown that heparin inhibits vascular smooth muscle cell proliferation. Heparin had two effects on proteoglycan synthesis. In control cultures, 35S-Labeled proteoglycan synthesis doubled during the first 12 h after releasing cells from growth arrest, decreasing during the following 12 h during which time cell division occurred. Treatment with heparin delayed the onset of proliferation by 24 h and this was accompanied by a corresponding delay in the increase in 35S-labeled proteoglycan synthesis associated with the early phase of the cell cycle. Secondly, heparin treatment resulted in an increase in the anionic properties of heparan sulfate proteoglycan synthesized by the cells. This was independent of the proliferative state of the cultures. Pentosan polysulfate, semi-synthetic heparin, and a highly sulfated heparan sulfate modulated both cell proliferation and heparan sulfate proteoglycan synthesis in the same way as heparin.

Effect of a heparan sulphate with high affinity for antithrombin III upon inactivation of thrombin and coagulation factor Xa

The kinetics of inhibition of human alpha-thrombin and coagulation Factor Xa by antithrombin III were examined under pseudo-first-order reaction conditions as a function of the concentration of heparan sulphate with high affinity for antithrombin III. The maximum observed second-order rate constant was, for the antithrombin III-thrombin reaction, 1.2 x 10(9) M-1.min-1 compared with 2.4 x 10(9) M-1.min-1 in the presence of high-affinity heparin. However, the maximum rate was catalysed by much higher concentrations of heparan sulphate (1.3 microM) than of heparin (0.025 microM). Differences were also observed in the maximal acceleration of the antithrombin III-Factor Xa interaction: 1.2 x 10(9) M-1.min-1 at 0.2 microM-heparin sulphate compared with 2.2 x 10(9) M-1.min-1 at 0.04 microM-heparin. The differences in properties of heparan sulphate and heparin were analysed by using the random bi-reactant model of heparin action [Griffith (1983) Proc. Natl. Acad. Sci. U.S.A. 80, 5460-5464]. It was observed that the apparent binding affinity for thrombin was higher for heparan sulphate (180 nM) than for heparin (14 nM). The rate constant for transformation of the antithrombin III-Factor Xa complex into irreversible product differed between heparan sulphate (96 min-1) and heparin (429 min-1). These properties of the high-affinity heparan sulphate may be of importance in consideration of a putative role in the control of intravascular haemostasis.

Plasma anticoagulant mechanisms of heparin, heparan sulfate, and dermatan sulfate

The relationship between two anticoagulant actions of glycosaminoglycans (GAGs), namely the catalysis of thrombin inhibition (assessed by thrombin-antithrombin-III and thrombin-heparin-cofactor-II formation) and the inhibition of prothrombin activation, was explored by comparing the effects of heparin, heparan sulfate, and dermatan sulfate on the two reactions in plasma. Heparan sulfate and dermatan sulfate were also resulfated in vitro to yield products with sulfate/carboxylate ratios similar to those of heparin. Their effects on thrombin inhibition and the activation of prothrombin were also determined. The catalytic efficiency of the five GAGs on thrombin inhibition and their inhibitory effects on prothrombin activation decreased in the following order: heparin; resulfated dermatan sulfate; resulfated heparan sulfate; heparan sulfate = dermatan sulfate. These results suggest that the catalytic efficiency of a glycosaminoglycan on thrombin inhibition translates to its inhibitory effect on prothrombin activation, since catalysis of thrombin inhibition results in the inhibition of the thrombin-dependent positive feedback reactions of coagulation which facilitate prothrombinase formation.

Assignment of the 1H-n.m.r. spectra of heparin and heparan sulphate

Resonances from the main repeating unit of heparan, ----4)-beta-D-GlcA-(1----4)-alpha-D-GlcNAc-(1----, have been assigned by using a sample of the capsular polysaccharide of E. coli K5. Comparison of the spectra of heparan sulphate samples before and after O- and/or N-desulphation, with re-N-acetylation or re-N-sulphation, allowed assignment of some of the H-1 doublets in terms of sequence effects. Chemical shifts for H-1 of unsulphated uronic acid residues are influenced by 6-sulphation of the nearest neighbour GlcN on the reducing side; those of GlcN residues vary according to whether they have IdoA or GlcA as the nearest neighbour on the reducing side. The H-1 doublets due to residues in the binding sequence for antithrombin have been assigned by comparison of the spectra of heparins having high and low affinities for immobilised antithrombin.

Increased sulphation improves the anticoagulant activities of heparan sulphate and dermatan sulphate

Heparan sulphate and dermatan sulphate have both antithrombotic and anticoagulant properties. These are, however, significantly weaker than those of a comparable amount of standard pig mucosal heparin. Antithrombotic and anticoagulant effects of glycosaminoglycans depend on their ability to catalyse the inhibition of thrombin and/or to inhibit the activation of prothrombin. Since heparan sulphate and dermatan sulphate are less sulphated than unfractionated heparin, we investigated whether the decreased sulphation contributes to the lower antithrombotic and anticoagulant activities compared with standard heparin. To do this, we compared the anticoagulant activities of heparan sulphate and dermatan sulphate with those of their derivatives resulphated in vitro. The ratio of sulphate to carboxylate in these resulphated heparan sulphate and dermatan sulphate derivatives was approximately twice that of the parent compounds and similar to that of standard heparin. Anticoagulant effects were assessed by determining (a) the catalytic effects of each glycosaminoglycan on the inhibition of thrombin added to plasma, and (b) the ability of each glycosaminoglycan to inhibit the activation of 125I-prothrombin in plasma. The least sulphated glycosaminoglycans were least able to catalyse the inhibition of thrombin added to plasma and to inhibit the activation of prothrombin. Furthermore, increasing the degree of sulphation improved the catalytic effects of glycosaminoglycans on the inhibition of thrombin by heparin cofactor II in plasma. The degree of sulphation therefore appears to be an important functional property that contributes significantly to the anticoagulant effects of the two glycosaminoglycans.

Comparative effect of heparin and heparan sulphate on two abnormal antithrombin III type 3 variants

Two families were found with an antithrombin III that was unresponsive towards heparin (type 3 AT III variants). The abnormal species were purified using affinity chromatography on Sepharose bound anti-AT III antibodies. This yielded active proteins, as judged by their progressive antithrombin activities. In an attempt to explain the thrombotic tendency observed in this abnormality we compared the effect of heparin and heparan sulphate on these abnormal AT III, since, unlike heparin, heparan sulphate is a naturally occurring anticoagulant in the human. In normal plasma the heparan sulphate used in this study had a heparin-like activity of 50 U/mg by anti-F.XA and anti-F.IIa amidolytic assays. Full expression of the heparin cofactor activity in normal plasma could be obtained at a final concentration of 0.024 mg/ml of heparan sulphate (equivalent to 0.007 mg/ml of heparin). At this concentration of heparan sulphate the two abnormal AT III still exhibit a heparin cofactor activity below 10%. This absence of binding of heparan sulphate to abnormal AT III of type 3 could explain why some patients with this abnormality suffer from thrombo-embolic episodes while their AT III acts normally in the absence of heparin.

Molecular distinctions between heparan sulphate and heparin. Analysis of sulphation patterns indicates that heparan sulphate and heparin are separate families of N-sulphated polysaccharides

Heparan sulphate and heparin are chemically related alpha beta-linked glycosaminoglycans composed of alternating sequences of glucosamine and uronic acid. The amino sugars may be N-acetylated or N-sulphated, and the latter substituent is unique to these two polysaccharides. Although there is general agreement that heparan sulphate is usually less sulphated than heparin, reproducible differences in their molecular structure have been difficult to identify. We suggest that this is because most of the analytical data have been obtained with degraded materials that are not necessarily representative of complete polysaccharide chains. In the present study intact heparan sulphates, labelled biosynthetically with [3H]glucosamine and Na2(35)SO4, were isolated from the surface membranes of several types of cells in culture. The polysaccharide structure was analysed by complete HNO2 hydrolysis followed by fractionation of the products by gel filtration and high-voltage electrophoresis. Results showed that in all heparan sulphates there were approximately equal numbers of N-sulpho and N-acetyl substituents, arranged in a similar, predominantly segregated, manner along the polysaccharide chain. O-Sulphate groups were in close proximity to the N-sulphate groups but, unlike the latter, the number of O-sulphate groups could vary considerably in heparan sulphates of different cellular origins ranging from 20 to 75 O-sulphate groups per 100 disaccharide units. Inspection of the published data on heparin showed that the N-sulphate frequency was very high (greater than 80% of the glucosamine residues are N-sulphated) and the concentration of O-sulphate groups exceeded that of the N-sulphate groups. We conclude from these and other observations that heparan sulphate and heparin are separate families of N-sulphated glycosaminoglycans.