Heparin, heparan sulfate, smooth muscle cells, and atherosclerosis

Pharmacology of Heparin and Related Drugs

Heparin has been recognized as a valuable anticoagulant and antithrombotic for several decades and is still widely used in clinical practice for a variety of indications. The anticoagulant activity of heparin is mainly attributable to the action of a specific pentasaccharide sequence that acts in concert with antithrombin, a plasma coagulation factor inhibitor. This observation has led to the development of synthetic heparin mimetics for clinical use. However, it is increasingly recognized that heparin has many other pharmacological properties, including but not limited to antiviral, anti-inflammatory, and antimetastatic actions. Many of these activities are independent of its anticoagulant activity, although the mechanisms of these other activities are currently less well defined. Nonetheless, heparin is being exploited for clinical uses beyond anticoagulation and developed for a wide range of clinical disorders. This article provides a "state of the art" review of our current understanding of the pharmacology of heparin and related drugs and an overview of the status of development of such drugs.

Mechanisms simultaneously regulate smooth muscle proliferation and differentiation

Vascular smooth muscle cell (VSMC) differentiation and proliferation are two important physiological processes during vascular development. The phenotypic alteration from differentiated to proliferative VSMC contributes to the development of several major cardiovascular diseases including atherosclerosis, hypertension, restenosis after angioplasty or bypass, diabetic vascular complications, and transplantation arteriopathy. Since the VSMC phenotype in these pathological conditions resembles that of developing VSMC during embryonic development, understanding of the molecular mechanisms that control VSMC differentiation will provide fundamental insights into the pathological processes of these cardiovascular diseases. Although VSMC differentiation is usually accompanied by an irreversible cell cycle exit, VSMC proliferation and differentiation occur concurrently during embryonic development. The molecular mechanisms simultaneously regulating these two processes, however, remain largely unknown. Our recent study demonstrates that cell division cycle 7, a key regulator of cell cycle, promotes both VSMC differentiation and proliferation through different mechanisms during the initial phase of VSMC differentiation. Conversely, Krüppel-like factor 4 appears to be a repressor for both VSMC differentiation and proliferation. This review attempts to highlight the novel role of cell division cycle 7 in TGF-β-induced VSMC differentiation and proliferation. The role of Krüppel-like factor 4 in suppressing these two processes will also be discussed.

Non-anticoagulant effects of heparin: an overview

Heparin has long been known to possess biological effects that are unrelated to its anticoagulant activity. In particular, much emphasis has been placed upon heparin, or novel agents based upon the heparin template, as potential anti-inflammatory agents. Moreover, heparin has been reported to possess clinical benefit in humans, including in chronic inflammatory diseases and cancer, that are over and above the expected effects on blood coagulation and which in many cases are entirely separable from this role. This chapter aims to provide an overview of the non-anticoagulant effects that have been ascribed to heparin, from those involving the binding and inhibition of specific mediators involved in the inflammatory process to effects in whole system models of disease, with reference to the effects of heparin that have been reported to date in human diseases.

Signaling pathways regulating vascular smooth muscle cell differentiation

Vascular smooth muscle cell (VSMC) differentiation is an essential component of vascular development. These cells perform biosynthetic, proliferative, and contractile roles in the vessel wall. VSMCs are not terminally differentiated and are able to modulate their phenotype in response to changing local environmental cues. There is clear evidence that alterations in the differentiated state of the VSMC play a critical role in the pathogenesis of atherosclerosis and intimal hyperplasia, as well as in a variety of other major human diseases, including hypertension, asthma, atherosclerosis and vascular aneurysms. The focus of this review is to provide an overview of the current state of knowledge of molecular mechanisms involved in controlling phenotypic switching of VSMCs, with particular focus on examination of the signaling pathways that regulate this process.

Regulation of vascular smooth muscle cell differentiation

Vascular smooth muscle cell (VSMC) differentiation is an essential component of vascular development. These cells perform biosynthetic, proliferative, and contractile roles in the vessel wall. VSMCs are not terminally differentiated and are able to modulate their phenotype in response to changing local environmental cues. There is clear evidence that alterations in the differentiated state of the VSMC play a critical role in the pathogenesis of atherosclerosis and intimal hyperplasia, as well as in a variety of other major human diseases, including hypertension, asthma, and vascular aneurysms. The focus of this review is to provide an overview of the current state of knowledge of molecular mechanisms involved in controlling phenotypic switching of SMCs, with particular focus on examination of signaling pathway that regulate this process.

Modulation of smooth muscle cell proliferation and migration: role of smooth muscle cell heterogeneity

Proliferation and migration of smooth muscle cells (SMCs) from the media towards the intima are key events in atherosclerosis and restenosis. During these processes, SMC undergo phenotypic modulations leading to SMC dedifferentiation. The identification and characterization of factors controlling these phenotypic changes are crucial in order to prevent the formation of intimal thickening. One of the questions which presently remains open, is to know whether any SMCs of the media are capable of accumulating into the intima or whether only a predisposed medial SMC subpopulation is involved in this process. The latter hypothesis implies that arterial SMCs are phenotypically heterogenous. In this chapter, we will describe the distinct SMC phenotypes identified in arteries of various species, including humans. Their role in the formation of intimal thickening will be discussed.

Basic fibrobrast growth factor induces the secretion of vascular endothelial growth factor by human aortic smooth muscle cells but not by endothelial cells

BACKGROUND

Endothelial cell dysfunction and smooth muscle cell (SMC) proliferation are major events in atherogenesis. Both cells are a source of growth factors that mediate cellular proliferation and chemotaxis. Inappropriate production of, and/or response to, these growth factors (such as vascular endothelial growth factor, VEGF, and basic fibroblast growth factor (bFGF)) may contribute to atherogenesis and therefore to disease progression.

METHODS

Production of VEGF and its soluble receptor (sFlt-1) by human SMCs and human umbilical endothelial cells (HUVECs) after stimulation with bFGF were examined by ELISA of cell culture media and by Western blotting.

RESULTS

Smooth muscle cells produced significantly more VEGF than HUVECs (P<0.05) after 24 h of culture with bFGF levels > or =0.001 microg mL(-1). bFGF induced dose-dependent production of VEGF by SMCs, where maximum production was present in 1 microg mL(-1) of bFGF. Conversely, the SMCs produced less sFlt-1 than HUVECs (P<0.05). However, bFGF induced dose-dependent phosphorylation of Flt1 and another VEGF receptor, KDR, in HUVECs but not SMCs. There was no VEGF or sFLT-1 after 6 h of culture in any dose of bFGF in either type of cell.

CONCLUSIONS

Differences in the production of VEGF and sFlt-1 by SMCs and HUVECs are consistent with the role of these cells in angiogenesis. Induction of VEGF production and expression by bFGF in these cells indicates that this growth factor may participate in angiogenesis indirectly by the induction of VEGF. The production of sFlt-1 by both cell types is in agreement with the notion that sFlt-1 may be involved in the regulation of VEGF activity. Additionally, the ability of bFGF to induce dose-dependent phosphorylation of KDR in HUVECs highlights the important role of bFGF in VEGF-mediated angiogenic processes.

Suppression of mitogen-activated protein kinase phosphatase-1 (MKP-1) by heparin in vascular smooth muscle cells

Heparin inhibits vascular smooth muscle cell (VSMC) proliferation, but mechanisms remain elusive. Because heparin inhibits signaling through multiple kinase cascades, we investigated the possibility that phosphatases could be involved. Mitogen-activated protein kinase phosphatase-1 (MKP-1) was the predominant MKP detected in VSMC lines. MKP-1 protein was increased by serum stimulation of quiescent cells, and this increase was diminished by heparin (1 microg/mL). Increased MKP-1 expression was dependent on the mitogen-activated protein kinase, Erk. Decreased Erk activity in the presence of heparin preceded, and may account for, decreased MKP-1. The antimitogenic effects of heparin are therefore unlikely to act through a shift in the kinase/phosphatase balance, but rather through direct kinase suppression. However, because MKP-1 is known to cause an increase in activity of kinases upstream of Erk, that may signal through additional pathways, the decrease in MKP-1 activity may paradoxically enhance heparin's antiproliferative effects. VSMC selected to grow in the presence of heparin express decreased levels of MKP-1 that are unresponsive to heparin, and Erk activity becomes unresponsive to heparin in one cell line. We conclude that phosphatase activation is not a direct mechanism of suppression of multiple kinase cascades by heparin.

Arterial smooth muscle cell heterogeneity: implications for atherosclerosis and restenosis development

During atheromatous plaque formation or restenosis after angioplasty, smooth muscle cells (SMCs) migrate from the media toward the intima, where they proliferate and undergo phenotypic changes. The mechanisms that regulate these phenomena and, in particular, the phenotypic modulation of intimal SMCs have been the subject of numerous studies and much debate during recent years. One view is that any SMCs present in the media could undergo phenotypic modulation. Alternatively, the seminal observation of Benditt and Benditt that human atheromatous plaques have the features of a monoclonal or an oligoclonal lesion has led to the hypothesis that a predisposed, medial SMC subpopulation could play a crucial role in the production of intimal thickening. The presence of a distinct SMC population in the arterial wall implies that under normal conditions, SMCs are phenotypically heterogeneous. The concept of SMC heterogeneity is gaining wider acceptance, as shown by the increasing number of publications on this subject. In this review, we discuss the in vitro studies that demonstrate the presence of distinct SMC subpopulations in arteries of various species, including humans. Their specific features and their regulation will be highlighted. Finally, the relevance of an atheroma-prone phenotype to intimal thickening formation will be discussed.

ESDN, a novel neuropilin-like membrane protein cloned from vascular cells with the longest secretory signal sequence among eukaryotes, is up-regulated after vascular injury

A novel cDNA has been isolated from primary culture of human coronary arterial cells by a signal sequence trap method, and designated ESDN (endothelial and smooth muscle cell-derived neuropilin-like molecule). ESDN is a type-I transmembrane protein with the longest cleavable secretory signal sequence among eukaryotes. ESDN contains a CUB domain and a coagulation factor V/VIII homology domain, which reminds us of the structure of neuropilins. ESDN also harbors an LCCL domain, which is shared by Limulus factor C and Coch. Mouse and rat counterparts were also identified revealing >84% amino acid identity with human ESDN. The human ESDN gene was mapped between D3S1552 and D3S1271. Northern blot analysis showed that ESDN mRNA was expressed in various tissues; particularly highly expressed in cultured vascular smooth muscle cells. The ESDN expression was up-regulated in platelet-derived growth factor-BB-stimulated vascular smooth muscle cells in vitro and neointima of the balloon-injured carotid artery in vivo. Overexpression of ESDN in 293T cells suppressed their bromodeoxyuridine uptake. In addition, ESDN protein was strongly expressed in nerve bundles in rodents. Thus, ESDN is considered to play a role in regulation of vascular cell growth and may have a wide variety of functions in other tissues including the nervous system, like neuropilins.

Relationship of glycosaminoglycan and matrix changes to vascular smooth muscle cell phenotype modulation in rabbit arteries after acute injury

PURPOSE

The phenotype of vascular smooth muscle cells (SMCs) is altered in several arterial pathologies, including the neointima formed after acute arterial injury. This study examined the time course of this phenotypic change in relation to changes in the amount and distribution of matrix glycosaminoglycans.

METHODS

The immunochemical staining of heparan sulphates (HS) and chondroitin sulphates (CS) in the extracellular matrix of the arterial wall was examined at early points after balloon catheter injury of the rabbit carotid artery. SMC phenotype was assessed by means of ultrastructural morphometry of the cytoplasmic volume fraction of myofilaments. The proportions of cell and matrix components in the media were analyzed with similar morphometric techniques.

RESULTS

HS and CS were shown in close association with SMCs of the uninjured arterial media as well as being more widespread within the matrix. Within 6 hours after arterial injury, there was loss of the regular pericellular distribution of both HS and CS, which was associated with a significant expansion in the extracellular space. This preceded the change in ultrastructural phenotype of the SMCs. The glycosaminoglycan loss was most exaggerated at 4 days, after which time the HS and CS reappeared around the medial SMCs. SMCs of the recovering media were able to rapidly replace their glycosaminoglycans, whereas SMCs of the developing neointima failed to produce HS as readily as they produced CS.

CONCLUSIONS

These studies indicate that changes in glycosaminoglycans of the extracellular matrix precede changes in SMC phenotype after acute arterial injury. In the recovering arterial media, SMCs replace their matrix glycosaminoglycans rapidly, whereas the newly established neointima fails to produce similar amounts of heparan sulphates.

Basic fibroblast growth factor inhibits cell proliferation in cultured avian inner ear sensory epithelia

Postembryonic production of inner ear hair cells occurs after insult in nonmammalian vertebrates. Recent studies suggest that the fibroblast family of growth factors may play a role in stimulating cell proliferation in mature inner ear sensory epithelium. Effects of acidic fibroblast growth factor (FGF-1) and basic fibroblast growth factor (FGF-2) were tested on progenitor cell division in cultured auditory and vestibular sensory epithelia taken from posthatch chickens. The effects of heparin, a glycosaminoglycan that often potentiates the effects of the FGFs, were also assessed. Tritiated-thymidine autoradiographic techniques and 5-bromo-2;-deoxyuridine (BrdU) immunocytochemistry were used to identify cells synthesizing DNA. The terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine triphosphate (dUTP)-biotin nick-end-label (TUNEL) method was used to identify apoptotic cells. TUNEL and overall counts of sensory epithelial cell density were used to assess possible cytotoxic effects of the growth factors. FGF-2 inhibited DNA synthesis in vestibular and auditory sensory epithelia and was not cytotoxic at the concentrations employed. FGF-1 did not significantly alter sensory epithelial cell proliferation. Heparin by itself inhibited DNA synthesis in the vestibular sensory epithelia and failed to potentiate the effects of FGF-1 or FGF-2. Heparin was not cytotoxic at the concentrations employed. Results presented here suggest that FGF-2 may be involved in inhibiting cell proliferation or stimulating precursor cell differentiation in avian inner ear sensory epithelia.

Heparin sensitive and resistant vascular smooth muscle cells: biology and role in restenosis

Vascular smooth muscle cells (VSMC)s are characterized by their acute growth inhibition by heparin and heparan sulfates; however, recently the isolation of VSMCs which display greatly diminished sensitivity to the antiproliferative action of heparin have been reported. These heparin resistant (HR) VSMCs have been derived through multiple passage of normal rat VSMCs in culture media containing high heparin doses, by transformation of VSMCs with oncogene-containing vectors, or have been isolated from vascular tissues of spontaneously hypertensive rats, healthy humans, or humans with restenosis where their presence is not limited to sites of injury. Initial characterizations of HR VSMCs are reviewed, and here we propose a definition of HR VSMCs. To date the mechanisms underlying heparin insensitivity remain elusive. Further study of HR VSMCs may expand our understanding of cell growth regulation by heparin, establish whether HR VSMCs contribute to the reported failure of heparin to combat restenosis in humans, and identify cellular mechanisms driving certain vascular proliferative diseases.

Nitric oxide degradation of heparin and heparan sulphate

NO is a bioactive free radical produced by NO synthase in various tissues including vascular endothelium. One of the degradation products of NO is HNO2, an agent known to degrade heparin and heparan sulphate. This report documents degradation of heparin by cultured endothelial-cell-derived as well as exogenous NO. An exogenous narrow molecular-mass preparation of heparin was recovered from the medium of cultured endothelial cells using strong-anion exchange. In addition, another narrow molecular-mass preparation of heparin was gassed with exogenous NO under argon. Degradation was evaluated by gel-filtration chromatography. Since HNO2 degrades heparin under acidic conditions, the reaction with NO gas was studied under various pH conditions. The results show that the degradation of exogenous heparin by endothelial cells is inhibited by NO synthase inhibitors. Exogenous NO gas at concentrations as low as 400 p.p.m. degrades heparin and heparan sulphate. Exogenous NO degrades heparin at neutral as well as acidic pH. Endothelial-cell-derived NO, as well as exogenous NO gas, did not degrade hyaluronan, an unrelated glycosaminoglycan that resists HNO2 degradation. Peroxynitrite, a metabolic product of the reaction of NO with superoxide, is an agent that degrades hyaluronan; however, peroxynitrite did not degrade heparin. Thus endothelial-cell-derived NO is capable of degrading heparin and heparan sulphate via HNO2 rather than peroxynitrite. These observations may be relevant to various pathophysiological processes in which extracellular matrix is degraded, such as bone development, apoptosis, tissue damage from inflammatory responses and possible release of growth factors and cytokines.

Inhibition of neointimal proliferation after coronary angioplasty by low-molecular-weight heparin (clivarine) and polyethyleneglycol-hirudin

Proliferation of medial smooth muscle cells (SMC) plays a major role in restenosis after coronary angioplasty and can be inhibited by heparin. Platelets stimulate SMC proliferation, and their aggregation after angioplasty can be reduced by the direct thrombin inhibitor hirudin. In a porcine coronary stent-angioplasty model (16 animals, 4 per group), we studied the effect of 3- and 14-day treatment with a novel long-lasting polyethyleneglycol-conjugated (PEG-hirudin, LU 57291), at a dose of 1 mg/kg intravenously (i.v.) and then subcutaneously once daily as compared with chronic low-molecular-weight heparin (LMWH) clivarine at a dose of 150 IU/kg as an intravenous bolus, followed by 10 IU/kg/h i.v. for 24 h, followed by 75 IU/kg twice daily, as compared with acute unfractionated heparin (100 IU/kg) as a control. Sixteen animals were randomly assigned to the four treatment groups. Four weeks after angioplasty, hearts were perfusion-fixed and six slices per angioplasty segment were analyzed for neointimal thickness and neointimal area (% of total vessel cross-sectional area). Maximal neointimal thickness was 1.10 +/- 0.2 mm in the control group (mean +/- SD, n = 9 arteries) and was significantly lower in both PEG-hirudin (0.62 +/- 0.22 and 0.86 +/- 0.18 mm, 11 and 10 arteries) and in clivarine-treated animals (0.75 +/- 0.33 mm, 11 arteries, p < 0.01). Similarly, neointimal area was smaller in PEG-hirudin groups (20 +/- 12 and 21 +/- 12%) and in the clivarine group (24.8 +/- 13.2%) as compared with the control group (41 +/- 17%, p < 0.02). We conclude that PEG-hirudin and clivarine reduce neointimal proliferation in a coronary stent-angioplasty model. Prolonged PEG-hirudin has no better effect than therapy limited to 3 days.

Cell cycle-dependent regulation of elastin gene in cultured chick vascular smooth-muscle cells

A study was made of the relationship between elastin expression and the proliferative state of chick vascular smooth-muscle cells. Confluent cells of primary culture brought to a quiescent state by the deprivation of serum for 72 h exhibited a 5-, 3.5- and 2-fold increase in elastin synthesis, elastin mRNA level and transcriptional activity of elastin gene respectively over those in the proliferative state. On re-addition of serum in serum-deprived culture, cells started to proliferate, and elastin synthesis, its mRNA level and transcription of the gene decreased to the level of a proliferative state within 24 h, indicating that elastin expression in smooth-muscle cells was controlled by their growth states at least in part at a transcriptional level. A comparable increase in elastin mRNA level was observed when the cell growth was arrested by suspension culture for 72 h. When the cells were synchronized at the G1/S phase with thymidine/hydroxyurea treatment, elastin expression at the G1/S phase was greater than that at the G2/M phase during cell cycling. Elastin mRNA level at the G0 phase brought about by serum-deprivation or suspension culture predominated over that at the G1/S phase during cell cycling. These results indicate that gene expression of elastin and cell cycle are tightly coupled, which is independent of the presence of serum or adhesive state, and that elastin expression could be a biochemical marker for the growth states of smooth-muscle cells.

Effect of a derivatized dextran on human osteoblast growth and phenotype expression

Water soluble derivatized dextran named E9 with a molecular weight of 45,000 g l-1 containing 58% methyl carboxylic acid unit, 19% benzylamide unit, and 26% sulfonate with a specific anticoagulant activity of 0.29 IU mg-1 was studied for its effects on human osteoblast growth and phenotype expression for short-term treatment. At concentrations between 1 ng ml-1 and 1 microgram ml-1 E9 has no effect on DNA synthesis whereas at higher concentrations DNA synthesis is inhibited in a dose related fashion (87% for 400 micrograms ml-1). For concentrations which do not modify osteoblast growth, E9 promotes alkaline phosphatase activity, type I collagen and osteocalcin synthesis with a maximum effect for 0.1-1 microgram ml-1. It has a synergistic effect with hPTH increasing AMPc. Moreover, osteonectin synthesis was enhanced in a dose-dependent manner between 0.1 and 5 micrograms ml-1. These results seem to indicate that E9 is able to stimulate human osteoblast phenotype expression and could be useful in clinical applications.

The heparin-binding domain of heparin-binding EGF-like growth factor can target Pseudomonas exotoxin to kill cells exclusively through heparan sulfate proteoglycans

Heparin-binding EGF-like growth factor (HB-EGF) is a smooth muscle cell mitogen composed of both EGF receptor and heparin-binding domains. To better understand the function of its domains, intact HB-EGF or its heparin-binding (HB) domain (amino acids 1-45) were fused to a mutant Pseudomonas exotoxin with an inactivated cell-binding domain. The resulting chimeric toxins, HB-EGF-PE* and HB-PE*, were tested on tumor cells, proliferating smooth muscle cells and a mutant Chinese hamster ovary cell line deficient in heparan sulfate proteoglycans (HSPGs). Two targets were found for HB-EGF-PE*. Cells were killed mainly through EGF receptors, but the HB domain was responsible for killing via HSPGs. HB-PE* did not bind to the EGF receptor and thus was cytotoxic by interacting exclusively with HSPGs. We conclude that the HB domain of HB-EGF is able to mediate internalization through HSPGs, without requiring the EGF receptor.

Heparin stimulates the proliferation of intestinal epithelial cells in primary culture

Heparin is a sulphated glycosaminoglycan derived from mast cells and has a number of functions including the inhibition of proliferation in several cell types and interactions with a range of heparin-binding growth factors. We report that heparin is a trophic factor in primary cultures of rat small intestinal epithelium. Heparin elicits a dose-dependent increase in epithelial proliferation and inhibits the growth of associated mesenchyme. The trophic effect of this molecule is not reproduced by other glycosaminoglycans including heparan sulphate but is dependent upon extensive molecular sulphation. Highly sulphated polysaccharides that are structurally unrelated to heparin (e.g. dextran sulphate and pentosan polysulphate) also stimulate epithelial proliferation in primary cultures. Heparin may act by the potentiation of mesenchyme-derived heparin-binding growth factors and these data suggest an in vivo role for mast cell-derived heparin in mucosal wound regeneration.

Inhibition of smooth muscle cell proliferation and experimental angioplasty restenosis by beta-cyclodextrin tetradecasulfate

Heparin inhibits smooth muscle cell proliferation in vitro, a property that makes it potentially useful in preventing restenosis after angioplasty. Its utility in this setting is limited by the inability to use high doses (secondary to anticoagulant effects) and the need for subcutaneous administration. We tested the ability of beta-cyclodextrin tetradecasulfate (CDT), a nonanticoagulant synthetic heparin mimic, to inhibit smooth muscle cell proliferation in vitro and tested its efficacy when orally administered for the prevention of angioplasty restenosis in a rabbit atherosclerosis model. Vascular smooth muscle cells were cultured from rabbit aortas by the explant technique. Passaged cells were plated at low density in microtiter plates in the presence or absence of varying concentrations of heparin or CDT in culture medium containing 10% fetal calf serum. Using both 3H-thymidine incorporation and total protein assays, both heparin and CDT caused a similar dose-dependent inhibition of proliferation. We next tested the effect of orally administered CDT in the prevention of restenosis in focal femoral artery arteriosclerotic lesions created in hypercholesterolemic New Zealand White rabbits by air-dessication endothelial injury and subsequent peripheral angioplasty. Animals were followed up for 1 month and were fed normal chow supplemented by tap water with or without CDT. In animals receiving the highest concentration of CDT (2 mg/mL drinking water), the percentage of arterial cross-sectional area with intimal hyperplasia decreased from 50.5 +/- 1.7% (control) to 26.9 +/- 2.2% (p < 0.001), with the intimal/medial ratio being decreased from 1.4 +/- 0.4 to 0.5 +/- 0.2 (p = 0.056).(ABSTRACT TRUNCATED AT 250 WORDS)

A simulated post-angioplasty low molecular weight heparin schedule in a non-human primate model

Due to a variety of pathophysiologic processes the long-term success rate of percutaneous transluminal angioplasty (PTCA) is only 50-70%. Acute restenosis also occurs in 30-40% of patients. Currently, studies are in progress to investigate the influence of low molecular weight heparin (LMWH) prophylaxis on the patency rate after PTCA. Our aim was to determine an optimal schedule to start the LMWH prophylaxis after the routinely performed heparinization. The alterations of the hemostatic parameters during the drug regimen change-over were evaluated. Non-human primates (Macaca mulatta) were divided into 6 treatment groups (n = 3/group). Three groups received heparin i.v. at 15 U/kg to mimic the end phase of therapeutic treatment infusion given 12-24 hrs. after PTCA. Three groups received full heparinization (250 U/kg i.v.) to mimic patients without the above interim phase therapy. Following both regimens, LMWH (Mono-Embolex) (1 mg/kg s.c.) was started at various intervals. The group initially treated with 15 U/kg heparin exhibited a continued anticoagulant effect when LMWH was started 30 min. after the heparin injection. Whereas, when LMWH was started after 2 hrs. the measurable anticoagulant effect was lost during 1 and 3 hrs. after the heparin injection. When LMWH was started 2 or 4 hrs. after the 250 U/kg dose, the anticoagulant response was sustained. Aside from the anti-IIa and the anti-Xa activity, there was no significant difference in other coagulation parameters between these two regimens. The fibrinolytic system was not altered in the therapeutic heparinization group. However, after the initial bolus of 250 mg/kg heparin, the monkeys treated with LMWH exhibited higher t-PA and D-dimer levels. Although our data shows definite differences between the two drug treatment schedules, further studies are warranted before an optimal drug regimen can be suggested for clinical use.

Antiproliferative capacity of synthetic dextrans on smooth muscle cell growth: the model of derivatized dextrans as heparin-like polymers

Proliferation of vascular smooth muscle cells (SMC) is postulated to be a key step in the pathogenesis of atherosclerosis or restenosis after vascular interventions such as angioplasty. Natural glycosaminoglycans, such as heparin and heparan sulfate, are known for their ability to inhibit SMC proliferation in vivo and in vitro. The antiproliferative activity of synthetic derivatized dextrans exhibiting heparin-like anticoagulant and anticomplement capacities have been investigated with rat aorta smooth muscle cells in culture. We report here that some derivatized dextrans grafted with benzylamide sulfonate moieties are potent antiproliferative agents for rat smooth muscle cell (SMC) in vitro. These synthetic polymers inhibit the SMC proliferation as well as heparin. The SMC growth inhibition is dose dependent, reversible and non-toxic. Highly anionic carboxylic dextrans are not capable of inhibiting the SMC growth, excluding a simple charge effect mechanism. Using fluorescent (DTAF) probes, we demonstrated that the synthetic antiproliferative polymers and heparin are internalized into the SMC. No binding or internalization was observed with native dextran devoid of antiproliferative capacity. We conclude that a suitable distribution of functional groups on the dextran backbone can simulate heparin activity in terms of antiproliferative capacity on SMC growth.

Low-molecular-weight heparin reduces neointimal proliferation after coronary stent implantation in hypercholesterolemic minipigs

BACKGROUND

Intracoronary stents have been suggested as a method of reducing the restenosis rate after balloon angioplasty. Proliferation of vascular smooth muscle cells is a major contributing factor to the restenosis process. Heparin and some of its derivatives have been shown to inhibit smooth muscle cell proliferation. We investigated the effect of low-molecular-weight heparin on the proliferative response after implantation of a balloon-expandable tantalum stent in previously deendothelialized coronary artery segments of hypercholesterolemic minipigs.

METHODS AND RESULTS

Minipigs were fed a diet containing 2% cholesterol, starting 1 month before balloon denudation of the endothelium in a coronary artery. One month later, a stent was implanted at this site. Animals were killed after 4 weeks (group 1, n = 6) or 3 months (group 2, n = 6). Animals in group 3 (n = 6), also followed for 4 weeks after stenting, received subcutaneous low-molecular-weight heparin at a dose of 200-300 units/kg anti-factor Xa activity per day in addition to the chronic acetylsalicylic acid (100 mg/day) also administered to groups 1 and 2. Eighteen of 22 animals survived to the end of the study. Angiography revealed patent stents in all surviving animals. In group 1, histological analysis showed extensive neointimal proliferation around stent struts. Maximal neointimal thickness seen in group 1 averaged 0.93 +/- 0.11 mm, was lower after 3 months (0.8 +/- 0.14 mm) in group 2, but was significantly reduced (0.44 +/- 0.18 mm, p less than 0.01) in group 3.

CONCLUSIONS

These data show a significant reduction of the neointimal proliferative response to coronary stent implantation by low-molecular-weight heparin.

Inhibition of phosphatidylinositol 4-phosphate kinase by heparin. A possible mechanism for the antiproliferative effects of heparin

Heparin and related glycosaminoglycans are important modulators of vascular smooth muscle cell growth, and may be involved in pathological processes such as atherosclerosis. Since polyphosphoinositide metabolism is a major mechanism for regulating cellular activities, including proliferation, the effects of glycosaminoglycans and polyanionic compounds on the activities of phosphoinositide kinases were characterized. Heparin and heparan sulphate caused dose-dependent inhibitions of rat brain cytosolic phosphatidylinositol 4-phosphate (PIP) kinase activity, with half-maximal inhibitory concentrations of approx. 0.5 and 5 microM respectively. PIP kinase was also inhibited by several dextran sulphates, but was not sensitive to inhibition by keratin sulphate, chondroitin sulphate or hyaluronic acid. Polynucleotides and acidic polypeptides were only weakly inhibitory. Heparin did not alter either the PIP- or the Mg(2+)-dependence of PIP kinase. Addition of heparin to brain membranes suppressed PIP kinase activity without affecting phosphatidylinositol (PI) kinase activity. Heparin interfered with the ability of a GTP analogue to stimulate PIP kinase activity in these membranes, suggesting that it uncouples the kinase from an activating guanine-nucleotide-binding protein. In cultured A-10 vascular smooth muscle cells, heparin caused dose- and time-dependent inhibition of [3H]thymidine incorporation into DNA. Similar treatments with heparin decreased cellular levels of phosphatidylinositol 4,5-bisphosphate (PIP2) without changing PI and PIP levels. Therefore heparin-mediated inhibition of PIP kinase appears to lead to decreases in PIP2 levels which may attenuate cellular proliferation.

Complex carbohydrates in drug development

Recent advances in carbohydrate chemistry and biochemistry afford the opportunity to develop bioactive complex carbohydrates, per se, as drugs or as lead compounds in drug development. Complex carbohydrates are unique among biopolymers in their inherent potential to generate diverse molecular structures. While proteins vary only in the linear sequence of their monomer constituents, individual monosaccharides can combine at any of several sites on each carbohydrate ring, in linear or branched arrays, and with varied stereochemistry at each linkage bond. This chapter addresses some salient features of mammalian glycoconjugate structure and biosynthesis, and presents examples of the biological activities of complex carbohydrates. The chapter presents selected examples that will provide an accurate introduction to their pharmacological potential. In addition to their independent functions, oligosaccharides can modify the activities of proteins to which they are covalently attached. Many glycoprotein enzymes and hormones require glycosylation for expression and function. The chapter discusses the ancillary role of carbohydrates that is of great importance to the use of engineered glycoproteins as pharmaceuticals.

Proteoglycans in cell regulation

Proteoglycans are a diverse group of proteins carrying one or more glycosaminoglycan side chains linked to the protein as O-glycosides. Our appreciation of these structures has matured from a curiosity about unusual structural glycoproteins, to confer upon them a central role in cell biology. The major classes of glycosaminoglycans are heparan sulfate and heparin, chondroitin and dermatan sulfates, keratan sulfate and hyaluronic acid. The latter is unique in that it does not contain sulfate residues, and appears to be synthesized, at least sometimes, free of a carrier protein. There is now a wealth of information on the ability of these structures to influence the growth and development of cells and tissues. Many direct and specific effects of proteoglycans will undoubtedly be found, and there are likely to be indirect effects of the glycosaminoglycans relating to their polyelectrolyte nature. Convincing arguments that biological activity resides in certain proteoglycan core proteins are also appearing. The following discussion concerns the role of proteoglycans in the regulation and action of autocrine and polypeptide growth factors, direct mitogenic and antimitogenic actions of glycosaminoglycans, the role of these structures in regulating gene expression, and the biological activities of proteoglycan core proteins. The probable role of proteoglycans in normal glomerular cell function, and in progressive renal disease, will be presented as a harbinger of the significant role we can expect them to play in diagnosis and therapy in the near future.

Comparison of the separation of bovine heparin by strong anion exchange and by gel filtration chromatography

Heparin has been fractionated by strong anion exchange chromatography followed by elution of the pools on a gel filtration column. This resulted in the expected inverse relationship in the elution order for the pools run by the two methods. Also chromatography of heparin was performed in the reverse order: gel filtration first, followed by anion exchange of the pools. For this order of separation four of the five gel filtration pools of different molecular weights eluted at a similar LiCl concentration. The specific activities of different pools of heparin were evaluated using a colorimetric microwell kinetics assay using antithrombin and thrombin. For the pools separated by ion exchange first, there was an exponential increase of specific activity with increasing molecular weight for all pools. For the pools isolated by gel filtration first, the specific activities became level after an initial increase in relation to molecular weight. Thus, unique pools of heparin species are being isolated by different modes of chromatography.

Heparin, carboxyl-reduced sulfated heparin, and Trestatin A sulfate. Antiproliferative and anticoagulant activities

Human smooth muscle cells were used to investigate the antiproliferative activities of sulfated carbohydrates. The antiproliferative potencies of coarse heparin fractions prepared by ultrafiltration increased with the mean molecular-weight, whereas the anticoagulant activities of a high-molecular-weight fraction had submaximal values. Furthermore, the dependence of antiproliferative activity on sulfate content is discussed. Carboxyl-reduction of heparin abolished both antiproliferative and anticoagulant activities. Sulfation of this compound yielded CRS-heparin with restored antiproliferative potency but devoid of antithrombin III-mediated anticoagulant activity. Sulfation of the pseudo-nonasaccharide, Trestatin A, yielded a compound having the highest antiproliferative activity, so far observed for a low-molecular-weight compound, and having only weak anticoagulant properties.