Inhibitory effect of heparin on serotonin-induced hyperplasia and hypertrophy of smooth muscle cells

Initial anticoagulation in patients with pulmonary embolism: thrombolysis, unfractionated heparin, LMWH, fondaparinux, or DOACs?

The initial treatment of haemodynamically stable patients with pulmonary embolism (PE) has dramatically changed since the introduction of low molecular weight heparins (LMWHs). With the recent discovery of the direct oral anticoagulant drugs (DOACs), initial treatment of PE will be simplified even further. In several large clinical trials it has been demonstrated that DOACs are not inferior to standard therapy for the initial treatment of PE, and because of their practicability they are becoming the agents of first choice. However, many relative contraindications to DOACs were exclusion criteria in the clinical trials. Therefore, LMWHs will continue to play an important role in initial PE treatment and in some cases there still is a role for unfractionated heparin (UFH). In this review we will give an overview of the biophysical, pharmacokinetic and pharmacodynamic properties of anticoagulants currently available for the initial management of PE. In addition, we will provide a comprehensive overview of the indications for the use of UFH, LMWHs and DOACs in the initial management of PE from a pharmacokinetic/-dynamic point of view.

Cyclin-Dependent Kinase Inhibitor p27 Kip1 , But Not p21 WAF1/Cip1 , Is Required for Inhibition of Hypoxia-Induced Pulmonary Hypertension and Remodeling by Heparin in Mice

Heparin has growth inhibitory effects on pulmonary artery smooth muscle cell (PASMC) in vitro and in vivo. However, the mechanism has not been fully defined. In this study, we investigated the role of cyclin-dependent kinase inhibitors, p21(WAF1/cip1) (p21) and p27Kip1 (p27), in the inhibitory effect of heparin on PASMC proliferation in vitro and on hypoxia-induced pulmonary hypertension in vivo using p21 and p27-null mice. In vitro, loss of the p27 gene negated the inhibitory effect of heparin on PASMC proliferation, but p21 was not critical for this inhibition. In vivo, heparin significantly inhibited the development of hypoxia-induced pulmonary hypertension and remodeling, as evidenced by decreased right ventricular systolic pressure, ratio of right ventricular weight to left ventricle plus septum weight, and percent wall thickness of pulmonary artery, in p21(+/+), p21(-/-), p27(+/+), and p27(+/-), but not in p27(-/-) mice. We also observed that hypoxia decreased p27 expression significantly in mouse lung, which was restored by heparin. Heparin inhibited Ki67 proliferative index in terminal bronchial vessel walls in p27(+/+) and p27(+/-), but not in p27(-/-) mice exposed to hypoxia. Therefore, we conclude that the cyclin-dependent kinase inhibitor p27, but not p21, is required for the inhibition of hypoxic pulmonary vascular remodeling by heparin.

Cardiovascular hypertrophy in one-kidney, one-clip renal hypertension is resistant to heparin

OBJECTIVE

Heparin inhibits vascular hypertrophy in angiotensin-induced hypertension, in addition to its well-known role in inhibiting injury-induced vascular smooth muscle proliferation. We tested whether hypertension and vascular hypertrophy could be reduced by heparin independently from the renin-angiotensin system.

METHODS

Rats were made hypertensive with a one-kidney, one-clip (1K1C) procedure and received heparin from osmotic minipumps (0.3 mg/h per kg i.v.) or saline vehicle for 2 weeks. Blood pressure was measured by the tail-cuff method and vessel cross-sectional area was measured by morphometry in the aorta and mesenteric arteries. Proliferation was assessed with bromodeoxyuridine labelling.

RESULTS

Blood pressure elevation and cardiovascular hypertrophy were evident in 1K1C rats. The media of mesenteric arteries was increased by 25%, and the media : lumen ratio by 35%, in hypertensive rats. DNA synthesis by smooth muscle cells in the mesenteric arteries was increased sevenfold in renal hypertension. Heparin treatment did not influence either the increase in blood pressure, the cardiovascular hypertrophy response or hypertension-mediated proliferation of arterial smooth muscle cells.

CONCLUSIONS

These data suggest that the vascular hypertrophy mechanisms operating in 1K1C renal hypertension are not inhibited by heparin and thus are different from those in angiotensin-mediated hypertension. Identifying such mechanisms in the future will be important for devising appropriate intervention strategies in angiotensin-independent forms of vascular hypertrophy.

Heparin inhibits SMC growth in the presence of human and fetal bovine serum

Heparin (HP) has antiproliferative as well as anticoagulant properties, but not all HP preparations are equally antiproliferative. A recent report found that HP lost its total antiproliferative activity when fetal bovine serum (FBS) was replaced with human serum (HS) in culture media. This observation led to the investigation of our most potent antiproliferative Upjohn HP preparation effects on bovine pulmonary artery smooth muscle cells (PASMC) and systemic SMC growth stimulated in the presence of either FBS or HS. Bovine PASMC, human PASMC, and bovine aortic SMC were treated with 10 microg/ml Upjohn HP in either 15% FBS or 15% HS and the cell number was determined by a Coulter counter. We found that Upjohn HP significantly inhibited bovine PASMC and systemic SMC proliferation in both HS and FBS. The antiproliferative activity of the above HP preparation in HS may lead to an effective treatment of pulmonary vascular and systemic remodeling.

Heparin oligosaccharide sequence and size essential for inhibition of pulmonary artery smooth muscle cell proliferation

Heparin has a wide range of important biological activities including inhibition of pulmonary artery smooth muscle cell proliferation. To determine the minimum size of the heparin glycosaminoglycan chain essential for antiproliferative activity, porcine intestinal mucosal heparin was partially depolymerized with heparinase and fractionated to give oligosaccharides of different sizes. The structure of these oligosaccharides was fully characterized by 1D and 2D 1H NMR spectroscopy. These oligosaccharides were assayed for antiproliferative effects on cultured bovine pulmonary artery smooth muscle cells (PASMCs). The tetrasaccharide (4-mer) exhibited no heparin-like activity. Decasaccharides (10-mers) and dodecasaccharides (12-mers) displayed a reduced level of activity when compared to full-length heparin. Little effect on activity was observed in deca- and dodecasaccharides with one less 2-O-sulfo group. The 14-, 16-, and 18-mers showed comparable growth-inhibition effects on PAMSC as porcine intestinal mucosal heparin. These data suggest that a 14-mer is the minimum size of oligosaccharide that is essential for full heparin-like antiproliferative activity. Since the 14- to 18-mers have no 3-O-sulfo groups in their glucosamine residues, their full activity confirms that these 3-O-sulfonated glucosamine residues, which are required for heparin's anticoagulant activity, are not an essential requirement for antiproliferative activity.

Pulmonary vascular remodeling: a target for therapeutic intervention in pulmonary hypertension

Pulmonary vascular remodelling is an important pathological feature of pulmonary hypertension, leading to increased pulmonary vascular resistance and reduced compliance. It involves thickening of all three layers of the blood vessel wall (due to hypertrophy and/or hyperplasia of the predominant cell type within each layer), as well as extracellular matrix deposition. Neomuscularisation of non-muscular arteries and formation of plexiform and neointimal lesions also occur. Stimuli responsible for remodelling involve transmural pressure, stretch, shear stress, hypoxia, various mediators [angiotensin II, endothelin (ET)-1, 5-hydroxytryptamine, growth factors, and inflammatory cytokines], increased serine elastase activity, and tenascin-C. In addition, there are reductions in the endothelium-derived antimitogenic substances, nitric oxide, and prostacyclin. Intracellular signalling mechanisms involved in pulmonary vascular remodelling include elevations in intracellular Ca2+ and activation of the phosphatidylinositol pathway, protein kinase C, and mitogen-activated protein kinase. In animal models of pulmonary hypertension, various drugs have been shown to attenuate pulmonary vascular remodelling. These include angiotensin-converting enzyme inhibitors, angiotensin receptor antagonists, ET receptor antagonists, ET-converting enzyme inhibitors, nitric oxide, phosphodiesterase 5 inhibitors, prostacyclin, Ca2+ -channel antagonists, heparin, and serine elastase inhibitors. Inhibition of remodelling is generally accompanied by reductions in pulmonary artery pressure. The efficacy of some of the drugs varies, depending on the animal model of the disease. In view of the complexity of the remodelling process and the diverse aetiology of pulmonary hypertension in humans, it is to be anticipated that successful anti-remodelling therapy in the clinic will require a range of different drug options.

Structural determinants of antiproliferative activity of heparin on pulmonary artery smooth muscle cells

In addition to its anticoagulant properties, heparin (HP), a complex polysaccharide covalently linked to a protein core, inhibits proliferation of several cell types including pulmonary artery smooth muscle cells (PASMCs). Commercial lots of HP exhibit varying degrees of antiproliferative activity on PASMCs that may due to structural differences in the lots. Fractionation of a potent antiproliferative HP preparation into high and low molecular weight components does not alter the antiproliferative effect on PASMCs, suggesting that the size of HP is not the major determinant of this biological activity. The protein core of HP obtained by cleaving the carbohydrate-protein linkage has no growth inhibition on PASMCs, demonstrating that the antiproliferative activity resides in the glycosaminoglycan component. Basic sugar residues of glucosamine can be replaced with another basic sugar, i.e., galactosamine, without affecting growth inhibition of PASMCs. N-sulfonate groups on these sugar residues of HP are not essential for growth inhibition. However, O-sulfonate groups on both sugar residues are essential for the antiproliferative activity on PASMCs. In whole HP, in contrast to an earlier finding based on a synthetic pentasaccharide of HP, 3-O-sulfonation is not critical for the antiproliferative activity against PASMCs. The amounts and distribution of sulfonate groups on both sugar residues of the glycosaminoglycan chain are the major determinant of antiproliferative activity.

Differentiation of coronary smooth muscle cells to a cell cycle-arrested hypertrophic growth status by a synthetic non-toxic heparin-mimicking compound

Studies on the mode of action of basic fibroblast growth factor (bFGF) identified an essential role of heparan sulfate and heparin-like molecules in the formation of distinct bFGF-heparan sulfate-bFGF-receptor complexes that are required for bFGF-induced signal transduction. In coronary smooth muscle cells that express 6-8 ng bFGF mg(-1) cell protein, the heparan sulfate chains of membrane-associated proteoheparan sulfate are implicated in bFGF signaling and thus are involved in the regulation of proliferation and differentiation of vascular smooth muscle cells. We studied the mode of action of a synthetic non-sulfated heparin-mimicking compound termed RG-13,577 (poly-4-hydroxyphenoxy acetic acid, Mr approximately 5 kD) and found a dose-dependent antiproliferative effect that was characterized by a block of G(1)/S-phase transition indicated by a marked (80%) reduction of [3H]thymidine incorporation at a concentration of 5 microg ml(-1) RG-13,577. Cell cycle analysis showed a block of cell division in the G(1)-phase. In response to RG-13,577 the cells were converted into a hypertrophic growth status within 72 h as judged from a doubling of the cellular protein content and measurement of cell and nucleus size. The increased cell protein content resulted from a de novo synthesis and was also associated with an increase in the incorporation of [35S]sulfate into cell-associated proteoglycans, including the proteoheparan sulfate coreceptor of bFGF. In contrast, the compound-induced G(1)-phase arrest was associated with an extensive downregulation of the cellular and pericellular bFGF level. The reduced bFGF content was accompanied by downregulation of the bFGF signaling-involved protein kinase C-alpha and MAP kinase, abrogation of MAP kinase phosphorylation and overexpression of protein kinase C-gamma. RG-13,577 failed to elicit apoptotic reactions at a concentration range of 0.5-10 microg ml(-1) and its effect was reversible upon removal of the compound. It appears that RG-13,577 induces a phenotype transformation of coronary SMC into a metabolically active hypertrophic status that could promote repair processes after balloon angioplasty (PTCA) without stimulating cell proliferation. Development of non-toxic polyanionic compounds may provide an effective strategy to inhibit cell proliferation associated with restenosis following balloon angioplasty and coronary artery bypass surgery.

Effect of fully sulfated glycosaminoglycans on pulmonary artery smooth muscle cell proliferation

Fully sulfated heparin and other glycosaminoglycans, namely heparan, chondroitin, and dermatan sulfates, and hyaluronan have been prepared by using sulfur trioxide under mild chemical conditions. All these derivatives were assayed for antiproliferative activity on cultured bovine pulmonary artery smooth muscle cells (BPASMCs). No appreciable difference was found between heparin and fully sulfated heparin. Chondroitin and dermatan sulfates actually stimulated BPASMCs growth but full sulfonation made them strongly antiproliferative. Native hyaluronan was not antiproliferative but became strongly so after sulfonation. Neither acharan sulfate nor N-sulfoacharan sulfate had any antiproliferative activity. This suggests that O-sulfonation of the polysaccharide is critical for antiproliferative activity, whereas N-sulfonation of glucosamine residues is not.

Influence of molecular weight, protein core and charge of native heparin fractions on pulmonary artery smooth muscle cell proliferation

Heparin macromolecules have been shown to inhibit cultured pulmonary artery smooth muscle cell proliferation in vitro and prevent hypoxic vascular remodeling in vivo. In an attempt to understand the structural determinants of heparin's antiproliferative properties, we have fractionated an antiproliferative preparation of commercial heparin into low and high molecular weight fractions. Then the high molecular weight heparin fraction was further fractionated on a DEAE-cellulose column by charge density eluting with 0 - 1 M NaCl linear gradient. The heparin protein peptides were both removed and isolated. These heparin fractions were assayed for antiproliferative effects on cultured bovine pulmonary artery smooth muscle cells. No appreciable differences were found among high and low molecular weight heparin fractions The core peptides showed no antiproliferative activity. However, higher charge density fraction was less antiproliferative.