Inhibition of cellular proliferation after experimental balloon angioplasty by low-molecular-weight heparin

Vascular smooth muscle cell proliferation as a therapeutic target. Part 1: molecular targets and pathways

Cardiovascular diseases are a major cause of human death worldwide. Excessive proliferation of vascular smooth muscle cells contributes to the etiology of such diseases, including atherosclerosis, restenosis, and pulmonary hypertension. The control of vascular cell proliferation is complex and encompasses interactions of many regulatory molecules and signaling pathways. Herein, we recapitulated the importance of signaling cascades relevant for the regulation of vascular cell proliferation. Detailed understanding of the mechanism underlying this process is essential for the identification of new lead compounds (e.g., natural products) for vascular therapies.

Opposing effects of low molecular weight heparins on the release of inflammatory cytokines from peripheral blood mononuclear cells of asthmatics

Background

T-cell-mediated inflammatory cytokines, such as interleukin (IL)-4, IL-5, IL-13 and tumor necrosis factor-alpha (TNF-α), play an important role in the initiation and progression of inflammatory airways diseases. Low-molecular-weight heparins (LMWHs), widely used anticoagulants, possess anti-inflammatory properties making them potential treatment options for inflammatory diseases, including asthma. In the current study, we investigated the modulating effects of two LMWHs (enoxaparin and dalteparin) on the release of cytokines from stimulated peripheral blood mononuclear cells (PBMCs) of asthmatic subjects to identify the specific components responsible for the effects.

Methods

PBMCs from asthmatic subjects (consist of ~75% of T-cells) were isolated from blood taken from ten asthmatic subjects. The PBMCs were pre-treated in the presence or absence of different concentrations of LMWHs, and were then stimulated by phytohaemagglutinin for the release of IL-4, IL-5, IL-13 and TNF-α. LMWHs were completely or selectively desulfated and their anticoagulant effect, as well as the ability to modulate cytokine release, was determined. LMWHs were chromatographically fractionated and each fraction was tested for molecular weight determination along with an assessment of anticoagulant potency and effect on cytokine release.

Results

Enoxaparin inhibited cytokine release by more than 48%, whereas dalteparin increased their release by more than 25%. The observed anti-inflammatory effects of enoxaparin were independent of their anticoagulant activities. Smaller fractions, in particular dp4 (four saccharide units), were responsible for the inhibitory effect of enoxaparin. Whereas, the larger fractions, in particular dp22 (twenty two saccharide units), were associated with the stimulatory effect of dalteparin.

Conclusion

Enoxaparin and dalteparin demonstrated opposing effects on inflammatory markers. These observed effects could be due to the presence of structurally different components in the two LMWHs arising from different methods of depolymerisation. This study provides a platform for further studies investigating the usefulness of enoxaparin in various inflammatory diseases.

The effect of prophylactic dose of a low molecular weight heparin on skin wound healing of rats

PURPOSE: To investigate the effect of prophylactic dose of a low molecular weight heparin, enoxaparin, on skin wound healing of rats. METHODS: Forty rats were used for the study. Rats were randomly assigned to two equal groups. Experimental group received prophylactic dose of enoxaparin. Physiologic saline was administered to the control group. Parameters of wound healing of experimental and control groups were compared. For comparison of the groups in terms of fibrosis, vascularization, inflammation, epithelization, and tensile strength test (Newton). Mann-Whitney-U test was used because variables were categorical data (fibrosis, vascularization, inflammation and epithelization). Differences between groups were analyzed with independent samples t-test (tensile strength). Significance was set at p<0.05. RESULTS: Skin wound of the experimental group presented tensile strength significantly decreased (p<0.001), histopathologic examination revealed a significant (p<0.001) delayed epithelization and decreased in fibrosis, vascularization, inflammation (p<0.001) in the experimental group. CONCLUSION: Enoxaparin delay wound healing by decreased inflammatory cells, fibroblast contents and their products (growth factors), and by promoted hemorrhage.

Delivery of large biopharmaceuticals from cardiovascular stents: a review

This review focuses on new and emerging large-molecule bioactive agents delivered from stent surfaces in drug-eluting stents (DESs) to inhibit vascular restenosis in the context of interventional cardiology. New therapeutic agents representing proteins, nucleic acids (small interfering RNAs and large DNA plasmids), viral delivery vectors, and even engineered cell therapies require specific delivery designs distinct from traditional smaller-molecule approaches on DESs. While small molecules are currently the clinical standard for coronary stenting, extension of the DESs to other lesion types, peripheral vasculature, and nonvasculature therapies will seek to deliver an increasingly sophisticated armada of drug types. This review describes many of the larger-molecule and biopharmaceutical approaches reported recently for stent-based delivery with the challenges associated with formulating and delivering these drug classes compared to the current small-molecule drugs. It also includes perspectives on possible future applications that may improve safety and efficacy and facilitate diversification of the DESs to other clinical applications.

Inhibition of pseudointimal hyperplasia in swine TIPS models: the efficacy of local delivery of paclitaxel using a perforated balloon catheter

The aim of this study was to investigate the efficacy and feasibility of local delivery of paclitaxel to inhibit pseudointimal hyperplasia/intimal hyperplasia in swine transjugular intrahepatic portosystemic shunt (TIPS) models TIPS were created in seven healthy domestic swine (15-20 kg). Before TIPS stent insertion, we performed a short-term infusion of paclitaxel (treatment group: n = 4) and saline (control group: n = 3) into the TIPS tract using a balloon catheter in which two 0.010 inch holes were created on opposite sides of the balloon. Paclitaxel or saline was given to all animals via the hepatic parenchymal and venous outflow tract. The animals were followed for up to two weeks and then killed. Gross and histological evaluations of the shunts were performed, and the maximum pseudointimal/intimal hyperplasia thicknesses were calculated for each animal The average infusion time of paclitaxel or saline was 7.6 min (6-9 min). At gross and histological evaluation, considerable pseudointimal hyperplasia had formed in the control group and statistically significant differences were found upon microscopic evaluation in the maximum pseudointimal hyperplasia thickness between the control (2.41 mm, range 1.7-3.16 mm) and animals receiving paclitaxel (0.63 mm, range 0.42-0.98 mm, p<0.05) Local delivery of paclitaxel at the time of TIPS creation may have been effective in reducing pseudointimal/intimal hyperplasia in swine TIPS models.

Comparative morphometric and immunohistological assessment of the development of restenosis after arterial injury and a cholesterol-rich diet in apolipoprotein E -/-mice and C57BL/6 control mice

OBJECTIVE

Animal models of restenosis have been a cornerstone of testing potential therapies and have improved the understanding of the underlying mechanisms. The aim of this study was to provide an in-depth comparison of the progression of restenotic lesion formation after arterial injury in apolipoprotein E -/- and C57BL/6 control mice.

METHODS

In this study, we investigated the difference in lesion formation of apolipoprotein E -/- and C57BL/6 controls on a high-cholesterol, high-fat diet after arterial injury. One week prior to arterial injury of the left femoral artery, mice were started on a high-cholesterol, high-fat diet. Diets were continued after arterial injury until euthanization. At five consecutive time points (2, 5, 10, 15, and 21 days), the intimal hyperplasia in the injured arteries was analyzed.

RESULTS

In the C57BL/6 control mice, a continuously increasing lesion formation, consisting primarily of alpha-smooth muscle actin-positive cells, was observed. Lesion formation in apolipoprotein E -/- mice was significantly more pronounced, resulting in complete occlusion of the arteries in four out of five vessels after 21 days. Lesions in apolipoprotein E -/- mice consisted predominantly of lipid-loaded foam cells and alpha-smooth muscle actin-positive cells. Further histological evaluation demonstrated cholesterol crystals in the lesions and neovascularizsation in cases of occlusion.

CONCLUSIONS

Thus, apoE -/- mice on a high-cholesterol, high-fat diet provide a more valid model for the characterization of the development of restenotic lesions after mechanical irritation such as angioplasty than C57BL/6 mice.

Low molecular weight heparins: a developmental perspective

Low molecular weight heparins (LMWHs) are now universally accepted as drugs of choice for post-surgical prophylaxis of deep vein thrombosis (DVT). Currently these agents are also being developed for the treatment of thrombosis and various cardiovascular indications. Due to manufacturing differences, each of the LMWHs exhibits a distinct pharmacological and biochemical profile. The specific activity of these agents in the anticoagulant assays ranges from 35 - 45 anti-IIa U/mg, whereas the specific activity in terms of anti-Xa units is designated as 80 - 145 anti-Xa U/mg. These LMWHs are capable of producing product-specific dose- and time-dependent antithrombotic effects in animal models of thrombosis. While the ex vivo effects are initially present at doses that are antithrombotic, these agents have been found to produce sustained antithrombotic effects without any detectable ex vivo anticoagulant actions. In experimental animal models and in various clinical trials, these agents have also been found to release tissue factor pathway inhibitor (TFPI) after both iv. and sc. administration. Repeated administration of LMWHs produces progressively stronger antithrombotic effects; however, the haemorrhagic responses vary and are largely dependent on the product used. The release of TFPI following iv. and sc. administration in a primate model also demonstrates product individuality and the relevance of this inhibitor to the actions of LMWHs. Furthermore, repeated administration, mimicking the post-surgical prophylaxis of DVT, leads to product-based augmentation of the antithrombotic or haemorrhagic effects. Antithrombotic and haemorrhagic studies are discussed, comparing the pharmacological profile of some of the available LMWHs. Product individuality, in terms of relative potency in different assays and the failure of standardisation protocols to provide any guidelines for product substitution and prediction of the clinical effects, is also addressed.

Targeted delivery of heparin and LMWH using a fibrin antibody prevents restenosis

This study investigates a stent-less local delivery system for anti-restenotic agents utilizing antibodies to cross-linked fibrin (XLF). Heparin and low molecular weight heparin (LMWH) were conjugated to an antibody to cross-linked fibrin D-dimer (1D2). Rabbit right carotid arteries were injured with a balloon catheter, then the animals were given a bolus injection of 40 microg/kg 1D2-heparin (26-70 microg/kg heparin) or 1D2-LMWH (29-80 microg/kg LMWH) conjugates or controls of saline (0.5 ml/kg), heparin (150 U/kg), LMWH (2 mg), or 1D2 (40 microg/kg), with or without a heparin bolus and sacrificed after 2 weeks (8 groups, n = 6/group). The injured artery of rabbits given 1D2-heparin or 1D2-LMWH conjugates had reduced neointimal development, with decreased luminal narrowing and positive remodelling compared with animals given control drugs. Animals given 1D2-heparin conjugate (with a heparin bolus) had three to five times more endothelial cells than the rabbits given saline or unconjugated heparin, while rabbits given 1D2-LMWH conjugate had up to 59% fewer neointimal cells than those given unconjugated drugs. There was little difference in extracellular matrix organization or composition. Thus cross-linked fibrin-antibodies can site-deliver anti-restenotic agents to injured areas of the artery wall where they influence wall remodelling and endothelial and neointimal cell number, reducing neointimal formation without systemic complications. Local delivery of anti-restenotic agents should minimise systemic effects, bleeding complications and potentially the cost of treatment due to a single, lower dose.

Induction of heme oxygenase-1 is involved in anti-proliferative effects of paclitaxel on rat vascular smooth muscle cells

In this study, we evaluated the possibility that the anti-proliferative effects of paclitaxel on vascular smooth muscle cells (VSMCs) of the rat might be due to the induction of HO-1 gene expression. Treatment of the cells with paclitaxel resulted in marked time- and dose-dependent inductions of HO-1 mRNA, followed by corresponding increases in HO-1 protein expression and HO enzymatic activities. Furthermore, paclitaxel rapidly activated the JNK, ERK, and p38 mitogen-activated protein kinase pathways. A specific inhibitor of JNK, SP600125, abolished paclitaxel-induced HO-1 mRNA expression, whereas PD98059, a specific inhibitor of ERK, and SB203580, a specific inhibitor of p38, had no significant effect. Finally, the suppression of platelet-derived growth factor induced VSMC proliferation was abolished by the HO inhibitor, ZnPP, as well as by the CO scavenger, hemoglobin. These results demonstrated that paclitaxel induces the expression of HO-1 via the JNK pathway in VSMC and that HO-1 expression might be responsible for the anti-proliferative effect of paclitaxel on VSMC.

The role of enoxaparin in interventional management of patients with acute coronary syndromes

Interventional management strategies involving early angiography and percutaneous coronary intervention (PCI) are increasingly widespread in the management of patients with acute coronary syndromes (ACS). Notwithstanding the benefits of early intervention, there is a significant risk of postprocedural thrombotic complications and a need to optimize antithrombotic regimens for use before and during PCI. It is clear that the current standard therapy with unfractionated heparin (UFH) and aspirin can be improved upon, in terms of both efficacy and safety. The low-molecular-weight heparin(s) (LMWHs) offer pharmacologic and practical advantages over UFH. The LMWH enoxaparin has recently emerged as the anticoagulant of choice for the acute management of ACS. Enoxaparin has also demonstrated sustained benefits over UFH in patients proceeding to PCI, and as a procedural anticoagulant. Combination therapy with enoxaparin and a glycoprotein IIb/IIIa inhibitor may further improve the efficacy and safety of antithrombotic treatment during coronary interventions, as a result of the drugs' complementary mechanisms of action. Early clinical evidence supports the use of enoxaparin in combination with glycoprotein IIb/IIIa inhibitors in high-risk patients with ACS. Ongoing, large-scale, randomized controlled studies will help to clarify the role of enoxaparin in interventional cardiology, either as the primary anticoagulant or as part of a combination regimen, and to define optimal regimens for treatment.

The role of low-molecular-weight heparin in cardiovascular diseases

Unfractionated heparin continues to have important limitations in clinical practice. It has an inconsistent anticoagulant effect, needs frequent monitoring, and is inactivated by several plasma proteins. Low-molecular-weight heparins have a more predictable anticoagulant effect than unfractionated heparin, are easier to administer, and may not require monitoring. The anticoagulation effect of low-molecular-weight heparins is caused by a combination of inhibition of thrombin generation and inhibition of thrombin activity. Low-molecular-weight heparins have now been evaluated for a number of cardiovascular conditions and have been found to be safe and effective. We review and summarize the existing data regarding the use of low-molecular-weight heparins in cardiovascular diseases, including venous thromboembolism, percutaneous coronary interventions, and acute coronary syndromes such as ST-segment elevation myocardial infarction.

Potential use of a low-molecular-weight heparin to prevent restenosis in patients with extensive wall damage following peripheral angioplasty

The long-term outcome of primary successful percutaneous transluminal angioplasty (PTA) for patients with peripheral occlusive arterial disease (POAD) is frequently compromised by the development of restenosis, especially when extensive dissections result from the angioplastic procedure. Unfortunately, prevention of the occlusive process by means of drugs such as antithrombotics, anticoagulants, thrombolytics, corticosteroids, lipid reducers, or cytostatics has not been demonstrated convincingly. The authors sought to clarify whether such patients could benefit from the postsurgical administration of low-molecular-weight heparin. A total of 172 POAD patients with extensive dissections after PTA in the pelvic or upper leg regions were randomized for 7-day post-PTA intravenous treatment with either full heparinization or nadroparin calcium followed by adjunctive oral aspirin for 6 months. The primary outcome measure was the degree of stenosis (normal findings; stenosis < 50%, > 50%, > 80%, occlusion) before and after angioplasty, as well as 3 weeks and 3 and 6 months after dilation; secondary efficacy criteria included changes in the Fontaine stage and in the crurobrachial ratio. No significant treatment-related differences were found at the 3 post-PTA follow-up examinations with regard to the degree of stenosis. This was also the case for the subgroup of patients (n = 62) who had undergone angioplasty in the pelvic region. By contrast, when angioplasty was performed in the superficial femoral artery (n = 110), the degree of restenosis was significantly lower (p<0.01) among patients receiving nadroparin calcium compared to those given heparin at week 3, month 3, and month 6. No intergroup differences emerged for secondary outcome measures in the long term or for safety parameters. These preliminary results indicate that patients with extensive dissections after PTA treatment for POAD in the upper leg region might benefit from a reduction in the rate of restenosis by administration of 7-day weight-adjusted nadroparin calcium.

Factor Xa is a fibroblast mitogen via binding to effector-cell protease receptor-1 and autocrine release of PDGF

The coagulation cascade protease thrombin is a fibroblast mitogen, but the proliferative potential of other coagulation proteases is not known. In this study we show that factor Xa stimulated human fetal lung fibroblast DNA synthesis in a concentration-dependent manner from 1 nM onward with a fourfold increase at 200 nM. The mitogenic effect of factor Xa was confirmed using a colorimetric proliferation assay and direct cell counting. Factor Xa and thrombin had equivalent potencies, and their stimulatory effects followed a similar time course. Comparable results were also obtained with primary human adult fibroblasts derived from lung, kidney, heart, skin, and liver. Factor VIIa also stimulated fibroblast proliferation, but only at concentrations >10 nM, whereas factor IXa had no effect. To begin to address the mechanism by which factor Xa is acting, we show that human fibroblasts express effector-cell protease receptor-1 and that blocking antibodies to this receptor and the catalytic site of factor Xa inhibited its mitogenic effect. Furthermore, factor Xa upregulated platelet-derived growth factor-A (PDGF-A) mRNA expression, whereas PDGF-B could not be detected, and a blocking antibody to PDGF inhibited the mitogenic effect of factor Xa. We conclude that factor Xa acts as a fibroblast mitogen via binding to effector-cell protease receptor-1 and the autocrine release of PDGF.

Endothelial heparan sulfate is necessary but not sufficient for control of vascular smooth muscle cell growth

The state of the endothelial cell (EC) determines the nature of its control of vascular smooth muscle cell (vSMC) biology. Conditioned medium from postconfluent ECs inhibits vSMC proliferation, whereas subconfluent conditioned medium from the same ECs has a stimulatory effect. We and others have identified confluent endothelial cells' production of heparan sulfate proteoglycans (HSPG) as critical to vSMC growth control. The question that arises is whether the stimulation that is observed with subconfluent cells is from (1) aberrant HSPG production, (2) elaboration of noninhibitory species of HSPG, or (3) production of other factors, such as mitogens, which counteract the inhibitory HSPG to stimulate vSMCs. We studied the relative effects of conditioned medium produced by both subconfluent and postconfluent EC cultures on vSMC growth. Conditioned medium was fractionated into nonproteoglycan (non-PG) and proteoglycan (PG) components by anion-exchange chromatography. The PG fractionation profile and the antiproliferative activity of the HSPGs isolated from both subconfluent and postconfluent EC-conditioned media were similar. However, the HSPG fraction alone could not approach the inhibitory potential of unfractionated conditioned medium from postconfluent EC cultures. Non-PG proteins produced by the endothelial cultures had no effect on vSMC growth on their own. Yet, when they were mixed together with HSPG fractions, from either subconfluent or postconfluent EC cultures, the full growth effects were returned. Non-PG protein fractions from postconfluent cultures with HSPG fractions gave maximal inhibition of vSMC growth, whereas non-PG protein fractions from subconfluent EC cultures with HSPG fractions produced the maximal stimulation. Thus, whereas the net stimulatory or inhibitory effect on vSMC growth of EC-conditioned medium is density dependent, this effect does not result from a difference in the antiproliferative heparan sulfate component but rather from non-PG proteins that interact with the heparan sulfates.

The emerging role of low-molecular-weight heparin in cardiovascular medicine

Although unfractionated heparin is widely used in the treatment of acute coronary syndromes, it has several pharmacokinetic, biophysical, and biological limitations. The practical advantages and success of low-molecular-weight heparin administered subcutaneously without laboratory monitoring for the treatment of venous thromboembolism have prompted a number of randomized studies investigating the efficacy and safety of these agents in patients with acute coronary syndromes. This article will review the limitations of unfractionated heparin and the mechanisms by which low-molecular-weight heparin overcomes these limitations, as well as the results of recent trials involving low-molecular-weight heparin in the management of patients with acute coronary syndromes.

Local drug delivery: impact of pressure, substance characteristics, and stenting on drug transfer into the arterial wall

Injection parameters for local drug delivery are frequently determined by studies with marker substances. However, the pharmacologic properties of the actual drug may influence delivery efficiency and lead to different results. Aim of this study was to assess the delivery capacities of two device-drug combinations in order to verify this approach for further in vivo studies. Tritiated (3H) preparations (5 ml) of the hydrophylic low-molecular-weight heparin reviparin and the lipophilic taxane paclitaxel were injected into the left anterior descending artery of freshly explanted porcine hearts with the Infusasleeve II catheter system. A balloon support pressure of 6 atm and infusion pressures of 40, 60, 80, or 100 psi were used. In three additional groups, reviparin was injected following stent implantation and paclitaxel was injected prior to or following stent implantation. Arteries along with surrounding myocardium were harvested. The artery was carefully dissected, and artery and myocardium were separately homogenized, and activity was measured. Of the totally delivered activity, 0.09%+/-0.03% (40 psi) to 0.17%+/-0.13% (100 psi) of reviparin and 2.03%+/-0.67% (60 psi) to 2.68%+/-1.57% (100 psi) of paclitaxel were found in the vessel wall. The results for different injection pressures were not significantly different for either drug. The percentage activity delivered to the vessel wall was substantially larger in the paclitaxel group as compared to reviparin delivery (P < 0.01 at 60, 80, and 100 psi). The mean concentration of reviparin in the artery was 20 to 33 times higher than in the myocardium. For paclitaxel the factors were 110 to 243. Stent implantation prior to or following local delivery did not result in a different delivery efficiency. The results demonstrate that the characteristics of the delivered drug contribute largely to the delivery efficiency. Using identical injection parameters, drug concentrations in the arterial wall were significantly higher for the lipophilic paclitaxel as compared to the hydrophilic reviparin. Stenting of the artery did not influence delivery efficiency.

Low-molecular-weight heparins: pharmacologic profile and product differentiation

The interchangeability of low-molecular-weight heparins (LMWHs) has been the subject of discussion since these products were first introduced for the prophylaxis of deep vein thrombosis. Experimental evidence now exists to show that LMWHs differ from each other in a number of characteristics. Products have been differentiated on the basis of molecular weight and biologic properties, but only limited information derived from the clinical setting is available. Potency has been described on the basis of anti-Factor Xa activity, but at equivalent anti-Xa activities, the anti-Factor IIa activity of different products shows marked variations. At the relatively small doses used for the management of postsurgical deep vein thrombosis, the effect of these interproduct differences may be relatively minor, but as LMWHs are developed for therapeutic use at much higher doses, such differences may become clinically important. Variations in safety and efficacy reported in clinical trials of LMWHs may reflect the known differences in their molecular composition and pharmacologic properties.

Low-molecular-weight heparin (reviparin) reduces the incidence of femoropopliteal in-stent stenosis: preliminary results of an ongoing study

PURPOSE

To examine the efficacy of the low-molecular-weight heparin, reviparin, for prevention of femoropopliteal stent restenosis.

METHODS

Forty-two patients who had implantation of flexible tantalum stents for the treatment of stenosis (n = 24) or occlusion (n = 18) of the femoral (n = 27) or popliteal (n = 15) arteries were included in this study protocol. An intraarterial bolus of 5000 IU heparin was given before percutaneous transluminal angioplasty (PTA), and in the case of stent implantation due to unsuccessful PTA, an additional dose of reviparin (3500 anti-factor Xa IU) was given. Postprocedurally, 10,500 anti-factor Xa IU of reviparin were administered intravenously over 24 hr, followed by 3500 anti-factor Xa IU subcutaneously twice a day for 23 days. Oral aspirin (100 mg/day) was prescribed for the long term. Follow-up criteria (maximum follow-up 37 months) were clinical symptoms, Doppler ankle arm indices, color and duplex sonography, and angiography for suspicion of restenosis.

RESULTS

Early stent thromboses were not observed. Overall primary patency rate (PPR) was 88% +/- 6.0% (1 year) and 74% +/- 10.1% (2 years). Major hemorrhagic complications have not occurred.

CONCLUSION

Reviparin administered in a high dose over a period of 24 days is a safe medication regimen and provides excellent patency rates after stent implantation.

Inhibition of chronic vessel wall intimal hyperplasia following acute anticoagulant treatment: relative effects of heparin and dermatan sulphate

Surface-bound thrombin which contributes to vessel wall hyperplasia, is resistant to inhibition by heparin/antithrombin III (/ATIII) but not to inhibition by dermatan sulphate/heparin cofactor II (/HCII). To determine the effects of heparin and dermatan sulphate on vessel wall hyperplasia after a first or second injury, rabbit carotid arteries first were injured, using a standard procedure (first injury). Half of the first-injury rabbits were given heparin, dermatan sulphate, or saline, 5 minutes before and at 30-minute intervals over 2 hours post-injury, and then allowed to recover. Four weeks later, the first-injury treated animals were killed and their injured carotid arteries were processed histologically. The remaining untreated first-injury rabbits were also allowed to recover. At 4 weeks, those rabbits were re-anesthetized and their first-injury arteries (which were occluded >75%), were isolated, and vessel wall lumen patency was re-established by endarterectomy (second injury). During this second injury, the animals were treated with heparin, dermatan sulphate, or saline as described above. Four weeks after this second injury, these rabbits were killed and their second injury arteries were processed histologically. Intimal hyperplasia determined histologically, was expressed as an x-fold increase in vessel wall cross-sectional area (i.e., [(media+intima area) media area]). Vessel wall lumen occlusion was expressed as [1-(lumen area/internal elastic lamina area) x 100; % occlusion]. Vessel wall area in the saline-treated animals, increased 2.6+/-1.2 and 2.4+/-1.0 fold respectively, means+/-SD, n = 12, within 4 weeks of the first and second injuries. These increases were due to intimal hyperplasia and associated with 75+/-19% and 79+/-21% occlusion of the vessel wall lumen, respectively. Heparin had little effect, whereas dermatan sulphate (1) decreased hyperplasia by 45% after the first injury and by 47% after the second injury, p<0.008 and <0.03, respectively, and (2) decreased vessel wall occlusion 47+/-12% and 33+/-5% after the first and second injury, respectively. We conclude that (1) dermatan sulphate/HCII may be a useful inhibitor of vessel wall hyperplasia following vessel wall injury, and (2) this effect can be achieved by an acute anticoagulant treatment at the time of injury, unlike heparin/ATIII.

Local drug delivery with porous balloons in the rabbit: assessment of vascular injury for an improvement of application parameters

OBJECTIVES

Sufficient intramural drug concentrations with the use of porous balloon catheters can be achieved with additional vascular trauma only. However, effective delivery of a potent drug even in deeper layers of the vessel wall might outweigh these traumatic side effects. Given the porous balloon catheter, the parameters of injection pressure and applied fluid volume will influence the interventional result.

METHODS

We tested a 2.5-mm porous balloon (35 75-micron pores) in the right carotid artery of New Zealand rabbits and used injection pressures of 1, 2, and 5 atm and fluid volumes of 2 and 4 ml of low-molecular-weight heparin solution in combination with the different parameters (n = 5 animals/group). In 50 rabbits, an intimal fibromuscular plaque was induced by using the electrostimulation model. Balloon dilatation and then application of the porous balloon was performed in 30 animals, 10 animals were only electrostimulated, and 10 animals served as a control group with balloon dilatation only. The vessels were excised 7 d after intervention, stained, and analyzed histomorpologically. Anti-Xa assays revealed the extent of systemically escaped drug, and serial cuts allowed for exact determination of vessel wall injuries.

RESULTS

Effective local drug delivery could not be achieved with an injection pressure of less than 2 atm. Specific pressure-driven effects such as jet injuries could be identified. When the pressure was high enough for disruptive drug delivery (> or = 2 atm), fluid volumes of 4 ml led to loose elastic membranes and local thickening within the media.

CONCLUSIONS

Sufficient intramural drug distribution using porous balloon catheters can be achieved with low injection pressures. Different fluid volumes strongly determine the extent of additional vascular injury.

Efficacy of low-molecular-weight heparin delivery with the Dispatch catheter following balloon angioplasty in the rabbit iliac artery

Local drug delivery can be achieved with active injection systems or passive contact of a compound with the arterial wall. The Dispatch catheter allows for passive diffusion of drugs from drug compartments while preserving blood flow through the central conduit. The aim of this study was to investigate whether a reduction in neointima formation can be achieved by local delivery of a limited amount of a highly concentrated solution of the low-molecular-weight heparin Reviparin. In 16 New Zealand white rabbits, successful balloon dilatation was performed in both iliac arteries, followed by local delivery of 4 ml Reviparin (1,000 IU/ml). The arteries were harvested at 7, 28, or 56 d following the procedure. The intimal cell layers increased substantially between 7 and 28 d following balloon dilatation with or without local drug delivery. The medial cell layers showed only a little increase. Proliferation of smooth muscle cells reached an early peak after 7 d, with a significantly higher proliferation index following local delivery. The maximum amount of macrophages in the intima and media was detected after 28 d. The lumen area decreased with time and was 0.6 +/- 0.7 mm2 in the local delivery group at 56 d compared with 0.5 +/- 0.5 mm2 in the control group. In conclusion, local delivery of Reviparin with the Dispatch catheter is safe and feasible. However, the infusion of highly concentrated low-molecular-weight heparin over a short period of time did not result in a reduction of neointima formation and restenosis following balloon dilatation in the rabbit iliac artery.

Low molecular weight heparin (reviparin) in percutaneous transluminal coronary angioplasty. Results of a randomized, double-blind, unfractionated heparin and placebo-controlled, multicenter trial (REDUCE trial). Reduction of Restenosis After PTCA, Early Administration of Reviparin in a Double-Blind Unfractionated Heparin and Placebo-Controlled Evaluation

OBJECTIVES

The specific objective of the REDUCE trial was to evaluate the effect of low molecular weight heparin on the incidence and occurrence of restenosis in patients undergoing percutaneous transluminal coronary angioplasty (PTCA).

BACKGROUND

Unfractionated heparin and its low molecular weight fragments possess antiproliferative effects and have been shown to reduce neointimal smooth muscle cell migration and proliferation in response to vascular injury in experimental studies.

METHODS

The REDUCE trial is an international prospective, randomized, double-blind, multicenter study. Twenty-six centers in Europe and Canada enrolled 625 patients with single-lesion coronary artery obstructions suitable for PTCA. Three hundred six patients received reviparin as a 7,000-U bolus before PTCA, followed by 10,500 U as an infusion over 24 h and then twice-daily 3,500-U subcutaneous application for 28 days. The 306 patients in the control group received a bolus of 10,000 U of unfractionated heparin followed by an infusion of 24,000 U over 24 h. These patients then underwent 28 days of subcutaneous placebo injections. The primary end points were efficacy (defined as a reduction in the incidence of major adverse events [i.e., death, myocardial infarction, need for reintervention or bypass surgery]), absolute loss of minimal lumen diameter and incidence of restenosis during the observation period of 30 weeks after PTCA.

RESULTS

Using the intention to treat analysis for all patients, 102 (33.3%) in the reviparin group and 98 (32%) in the control group have reached a primary clinical end point (relative risk [RR] 1.04, 95% confidence interval [CI] 0.83 to 1.31, p = 0.707). Likewise, no difference in late loss of minimal lumen diameter was evident for both groups. Acute events within 24 h occurred in 12 patients (3.9%) in the reviparin group and 25 (8.2%) in the control group (RR 0.49, 95% CI 0.26 to 0.92, p = 0.027) during or immediately after the initial procedure. In the control group, eight major bleeding complications occurred, and in the reviparin group, seven were observed within 35 days after PTCA.

CONCLUSIONS

Reviparin use during and after coronary angioplasty did not reduce the occurrence of major clinical events or the incidence of angiographic restenosis over 30 weeks.

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.

Effects of a single heparin bolus on neointimal growth after arterial injury in intact rabbits

Heparinization is a routine procedure during angioplasty; however, its consequences on the late vascular response to a severe injury are unclear. The authors' objective was to explore the effect of a single heparin bolus at the time of a severe vascular injury on late intimal proliferation and neointimal thickening. The iliac artery of 57 normolipemic rabbits was overdistended with a balloon catheter. Heparin (250 IU/kg i.v.) was given to 29 rabbits ten minutes before angioplasty, whereas 28 rabbits served as untreated controls. Neointimal thickening was prominent at fourteen days after injury and reached near-maximal values at day 28. The intimal/medial area ratio was reduced by an average 28.3% with heparin (at day 28: 2.19 +/- 0.51 vs 1.57 +/- 0.59, control vs heparin, P = 0.02). Neointimal cells stained positively for HHF-35 antibody, directed against smooth muscle cell antigens. Neointimal proliferation, quantified through the number of cell nuclei peroxidase-stained for PCNA/cyclin antigen, was significantly decreased by 43% and 49% with heparin, respectively, at days 7 and 14 after injury. These data suggest that early exposure even to low doses of heparin accounts for much of its inhibitory effect in vascular response to injury; such an effect might prove important in interpreting results of human trials of interventions against restenosis.

Role of polymers in improving the results of stenting in coronary arteries

This article is a review of recent developments of polymer-related stents mainly employed in the coronary arteries, including polymer-coated stents, biostable stents and biodegradable stents. Polymer paving is covered as well. The problems with the stents currently investigated and the development of new stents are discussed.

Distal coronary hemoperfusion during percutaneous transluminal coronary angioplasty

Distal coronary hemoperfusion during percutaneous transluminal coronary angioplasty (PTCA)-with an autoperfusion balloon or active system-facilitates prolonged balloon inflation. Prolonged inflations may tack up intimal dissections and improve the primary angioplasty result in complex lesions. Additionally, distal perfusion may reduce the likelihood of cardiogenic shock during high-risk PTCA. Autoperfusion balloons are most frequently used to treat acute or threatened closure. There currently is no prospective clinical study showing that stent implantation for this complication is more successful and more cost-effective. The blood flow rates through autoperfusion balloons may not abolish myocardial ischemia, and higher flow rates can often be achieved with pumps. Therefore, during high-risk PTCA, pumps may be preferred to prevent hemodynamic collapse. Clinical application of perfusion pumps is hampered by the risk for mechanical hemolysis during prolonged perfusion and the high velocity of the bloodstream that exits the PTCA catheter, causing distal vessel wall trauma.

Preclinical studies on a low molecular weight heparin

Some major developments in the area of antithrombotic therapy have occurred during the past decade. Of these, the concept of fractionation of heparin has resulted in the development of several products from this agent. The introduction of low molecular weight heparins (LMWHs) has added a new chapter to the prophylactic and therapeutic management of thromboembolic disorders. These agents are now globally accepted as drugs of choice for post-surgical prophylaxis of deep vein thrombosis (DVT). Currently, the LMWHs are being developed for various therapeutic and cardiovascular indications. Reviparin is an optimized LMWH prepared by controlled nitrous acid digestion of porcine mucosal heparin. This drug has been developed using validated procedures and exhibits a relatively narrow molecular weight distribution in contrast to most other commercially available LMWHs. The specific activity in anticoagulant assays is approximately 32 U/mg whereas the specific activity in terms of anti-Xa units is 120 anti-Xa U/mg. Reviparin is capable of producing a dose- and time-dependent antithrombotic effect in animal models of thrombosis. While the ex vivo effects initially occur at dosages that are antithrombotic, this agent has been found to produce sustained antithrombotic effects without any detectable ex vivo anticoagulant actions. This agent has also been found to release tissue factor pathway inhibitor (TFPI) after both intravenous and subcutaneous administration. Repeated administration of reviparin produces progressively stronger antithrombotic effects. The current studies are designed to provide additional data on its molecular profile using new calibration methods and additional results on the pharmacological studies in a dose-dependent manner. In particular, the release of TFPI following i.v. and s.c. administration in a primate model is described. The effect of repeated administration mimicking the post-surgical prophylaxis of DVT is also reported in terms of any increase in the antithrombotic or haemorrhagic effects of this agent. Comparative antithrombotic and pharmacological studies are also reported to compare the pharmacological profiles of reviparin, nadroparin and enoxaparin.

Low molecular weight heparin in prevention of restenosis after PTCA

Late restenosis occurring after successful PTCA continues to represent a major problem limiting the clinical efficacy of the procedure. It has been shown that smooth muscle cell proliferation plays a major role in this accelerated atherosclerotic process. In vitro and in vivo experiments with the low molecular weight heparin reviparin showed a pronounced inhibitory effect by this compound on smooth muscle cell proliferation. To evaluate the safety of reviparin and the incidence of angiographic restenosis in humans, a study of increasing dosages was conducted in 41 patients. Repeat coronary angiography was performed 3 months after angioplasty. Restenosis occurred in 5 of 37 evaluable patients with initially successful PTCA. No major bleeding complication was documented for any patient in this first pilot trial. A randomized, double-blind, multicentre trial is being carried out to define the real impact of this compound in reducing restenosis in patients who undergo successful balloon angioplasty.

Sustained inhibition of intimal thickening. In vitro and in vivo effects of polymeric beta-cyclodextrin sulfate

Intimal thickening after vascular injury may be modulated in part by heparin binding growth factors. We hypothesized that placement of a therapeutic polymer in the periadventitial space capable of tightly binding growth factors might alter the vascular response to injury. We first demonstrated that incubation of rat aortic smooth muscle cells with an insoluble, sulfated polymer of beta-cyclodextrin (P-CDS) was associated with a dose-dependent inhibition of proliferation induced by fetal calf serum, fibroblast growth factor-2 (FGF-2), platelet-derived growth factor BB, or epidermal growth factor. Preincubation studies of P-CDS with FGF-2 revealed a very rapid removal of mitogenic activity. Using radiolabeled FGF-2 (0.25 microg/ml), we observed a very rapid association rate (0.34 +/- 0.07 min-1, n=4) and a very slow dissociation rate (3.3 +/- 0.2 X 10(-7) min-1) at 37 degrees C, suggesting a high affinity interaction. Using both Transwell and linear under-agarose assays, we demonstrated a significant inhibition of random migration (chemokinesis) by P-CDS. Unsulfated polymeric beta-cyclodextrin (P-CD) had little if any of these effects, suggesting that the high negative charge density of P-CDS was important for the effects. Finally, rats undergoing carotid artery balloon injury were randomized to treatment with periadventitial P-CDS or no treatment, and were killed at 4 (n=20), 14 (n=59), and 88 d (n=14). Morphometric analysis demonstrated significant and sustained inhibition of intimal thickening in P-CDS-treated rats at 14 (P < 0.01) and 88 d (P < 0.05) using absolute intimal area or intima/media area ratios. No inhibition was seen in a group of rats treated with P-CD. In P-CDS-treated rats, bromodeoxyuridine labeling studies revealed fewer labeled smooth muscle cells in the intima at 14 d (P=0.01), while staining with Evans blue revealed enhanced late endothelial cell regrowth. Thus, periadventitially applied sulfated beta-cyclodextrin polymer, which can tightly bind heparin binding growth factors, inhibits intimal thickening in vivo in a sustained fashion without using an additional delivery system. These studies suggest that cellular processes mediated by heparin binding growth factors may be modulated by P-CDS.

Kinetics of smooth muscle cell proliferation and intimal thickening in a pig carotid model of balloon injury

Restenosis as a result of neointimal smooth muscle cell accumulation is an important limitation to the effectiveness of balloon angioplasty as a treatment for end-stage atherosclerosis. Quantitative animal models allow the definition of pathophysiological mechanisms and the evaluation of new therapeutic strategies. In this study we quantified the time course of neointima formation by morphometry, and smooth muscle cell (SMC) proliferation by immunocytochemistry for proliferating cell nuclear antigen (PCNA), in the pig carotid artery 0-28 days following balloon injury. This led to two distinct kinds of injury observed also in clinical studies, namely medial dilatation or deep medial tearing with rupture of the internal elastic lamina. Dilatation injury alone led to medial enlargement and neointima formation by 7 days, which did not increase further up to 28 days. Medial enlargement was similar following rupture of the internal elastic lamina; however the sum of neointima formation plus the area of medial repair ('neomedia') increased progressively up to 21 days after balloon injury. Balloon injury increased the PCNA index of smooth muscle cells in the media underlying an intact internal elastic lamina maximally after 3 days. The PCNA index in the neointima and especially in the neomedia was greater and maximal after 7 days. Endothelial regrowth occurred by 21 days in the presence or absence of medial tears. Our results establish a quantitative pig model of balloon injury which will allow the assessment of new therapeutic strategies directed at two clinically relevant types of injury. Medial tearing is associated with an enhanced and localized proliferative response and may therefore be especially important in human restenosis.

A prescreening system for potential antiproliferative agents: implications for local treatment strategies of postangioplasty restenosis

BACKGROUND

Recent advances in the understanding of the biology of restenosis indicate that it is predominantly caused by a multifactorial stimulation of smooth muscle cell proliferation. The aim of this study was to investigate the in vitro effect of five potential antiproliferative agents on smooth muscle cells from human atherosclerotic femoral arteries.

METHODS AND RESULTS

Primary stenosing plaque material of 24 patients (aged 63 +/- 14 years) and restenosing plaque material of 7 patients (aged 65 +/- 9 years) was selectively extracted from femoral arteries by the Simpson atherectomy device. Cells were isolated by enzymatic disaggregation and identified as smooth muscle cells by positive reaction with smooth muscle alpha-actin. Dalteparin sodium (0.001-100 anti-Xa units/ml), cyclosporine A (0.005-500 micrograms/ml), colchicine (0.00004-4 pg/ml), etoposide (0.002-200 micrograms/ml), and doxorubicin (0.0005-50 micrograms/ml) were added to the cultures. Six days after seeding, cells were trypsinized and cell number was measured by a cell counter. All five agents tested exhibited a significant inhibition of smooth muscle cell proliferation (P < 0.001). After an incubation time of 48 h, the cytoskeletal components, alpha-actin, vimentin, and microtubules were investigated. At peak concentrations, all five tested agents except dalteparin sodium caused severe damage to the cytoskeleton.

CONCLUSIONS

All five potential antiproliferative agents exhibited a significant inhibition of smooth muscle cell proliferation. The development of new intravascular delivery systems may open the way for local antiproliferative treatment strategies in interventional cardiology.

Effect of nonanticoagulant heparin (Astenose) on restenosis after balloon angioplasty in the atherosclerotic rabbit

PURPOSE

To determine whether intravenous administration of Astenose, a high-molecular-weight nonanticoagulant heparin, can reduce restenosis following balloon angioplasty in a rabbit model.

MATERIALS AND METHODS

Focal atherosclerosis was induced in 54 rabbits (89 vessel), and angioplasty was performed after animals were randomized into five groups. Group 1 vessels (control) were treated with lactated Ringer solution for 28 days (n = 19); group 2, Astenose at 0.10 mg/kg per hour for 28 days (n = 16); group 3, Astenose at 0.33 mg/kg per hour for 28 days (n = 16); group 4, Astenose at 0.60 mg/kg per hour for 28 days (n = 17); and group 5, Astenose at 0.33 mg/kg per hour for 14 days (n = 21). Arteriograms were obtained to measure minimal luminal diameters before, immediately after, and 28 days after angioplasty, and the rabbits were killed for histologic analysis.

RESULTS

Angiographically demonstrated restenosis was significantly reduced in groups 3 (18.9% +/- 3.7, P = .04) and 4 (20.2% +/- 3.1, P = .04) compared with the control group (32.4% +/- 4.8). Group 5 showed a nonsignificant trend toward reduced restenosis (23.1% +/- 2.9, P = .09), and group 2 showed restenosis similar to that in group 1 (31.0% +/- 2.5, P = .80). However, quantitative histopathologic analysis detected no differences among the groups in absolute plaque area. Medial area was significantly smaller in groups 2 and 5 (P < or = .002) than in group 1, and there was a nonsignificant trend toward reduced medial area in groups 3 and 4 (P = .12).

CONCLUSION

Long-term intravenous Astenose therapy resulted in a modest but statistically significant reduction in angiographically demonstrated restenosis after angioplasty in this atherosclerotic rabbit model.

Experimental therapeutics and clinical studies in (re)stenosis

Restenosis is defined functionally as loss of luminal vessel patency following various methods of interventional cardiology, but ultrastructurally, it represents a wound healing response that involves smooth muscle migration, proliferation and matrix deposition at the site of injury. Currently, despite intensive experimental and clinical studies, there are no therapeutic agents that are able to suppress pharmacologically the clinical restenosis. Ultrastructural pathology and animal modeling have played a pivotal role in defining new experimental therapies and rationales for clinical trials. However, concerns regarding the lack of suitable animal models persist and of the many compounds reported efficacious preclinically, none have demonstrated clinical benefit in preventing restenosis. Animal modeling studies now include the use of true restenosis studies, which may be more clinically relevant and pharmacologically predictive of clinical performance.

Characterization of rat aortic smooth muscle cells resistant to the antiproliferative activity of heparin following long-term heparin treatment

Vascular smooth muscle cells (SMC) do not represent a homogeneous population (Schwartz et al., 1990, Am. J. Pathol. 136: 1417-1428). Cellular clones resistant to the antiproliferative activity of heparin were isolated from rat aortic SMC cultures (Pukac et al., 1990, Cell Regul., 1:435-443; San Antonio et al., 1993, Arterioscler. Thromb., 13:748-757) and from explant of human arterial restenotic lesions (Chan et al., 1993, Lancet, 341:341-342). We have shown in the present study that long-term treatment (growth medium supplemented with 200 micrograms/ml heparin, from the second to the tenth passage) of rat aortic SMC, without cell cloning, resulted in a significant loss of sensitivity to the growth inhibition by heparin and its derivatives. The heparin resistance was stable after growing cells for two passages in heparin-free medium, suggesting the selection of a particular phenotype. We tried to characterize these cells and to determine the causes of the resistance to the growth inhibition by heparin. Heparin-treated SMC (HT-SMC) were smaller than their control culture at the same passage, expressed less alpha-SM actin, and did not overgrow after reaching confluence. As in the heparin-resistant clones (San Antonio et al., 1993, Cell Regul., 1:435-443) expression of alpha-SM actin could be increased in HT-SMC by heparin addition before Western blotting. Heparin resistance was associated with a tenfold decrease in [3H]-heparin binding capacity (Bmax = 1.9 x 10(6) sites per cell) compared to control cultures (Bmax = 1.7 x 10(7) sites per cell), which was irreversible after growing the cells for two additional passages in heparin-free medium. We also investigated protein kinase C (PKC) in HT-SMC in terms of both enzymatic activity and protein expression (evaluated by [3H]-staurosporine and [3H]-phorbol-12,13-dibutyrate binding). We found that HT-SMC had only half the PKC activity and expression as control SMC. Therefore, long-term treatment of rat aortic SMC with heparin allowed the selection of a less differentiated subpopulation of cells, exhibiting low sensitivity to the growth inhibition by heparin, which could be related to the low capacity of binding heparin and to a lower PKC activity and/or expression.

The influence of low molecular weight heparin on neointimal proliferation in cultured human saphenous vein

OBJECTIVES

To investigate the effect of low molecular weight heparin (LMWH) on neointimal proliferation in cultured human saphenous vein, a model of human vein graft intimal hyperplasia.

DESIGN

Dose ranging LMWH concentration study.

SETTING

Culture Laboratory, Department of Surgery.

MATERIALS

Fifteen segments of human long saphenous vein were incubated at 37 degrees C for 14 days in culture medium with 30% foetal calf serum. LMWH was added to one of the paired segments at 1, 10 and 100 micrograms/ml (five veins each dose). 5-bromo-2-deoxyuridine (Brd-U) was used to label proliferating cells.

CHIEF OUTCOME MEASURES

Neointimal thickness (micron and proliferation index (% labelled neointimal cells).

MAIN RESULTS

Neointimal thickness and proliferation index were both significantly reduced by LMWH at 100 micrograms/ml [control vs. LMWH, reduction in thickness 21 microns vs. 7 microns (median difference 12 microns, 95% conf. int. 6-18), reduction in proliferation index 33% to 6% (median difference 19%, 95% C.I. 4-32)].

CONCLUSIONS

High dose LMWH reduces neointimal proliferation in cultured human saphenous vein. The practical clinical application of these results may require the use of non anticoagulant heparin-like molecules and/or local drug delivery systems.

Restenosis after coronary angioplasty

Coronary angioplasty is used to treat coronary disease in many patients. Indications for angioplasty have expanded since it was first performed, mainly as a result of improvement in equipment and techniques. One problem with coronary angioplasty is the phenomenon of renarrowing of the treated coronary lesion, a process called restenosis. The events that constitute restenosis appear to be a universal response to the arterial wall injury of angioplasty. They are currently characterized as follows: platelet adhesion and aggregation on the damaged endothelium and within deep splits into the tunica media; release of platelet-derived growth factors; inflammation of the mechanically injured medial zone; transformation of smooth muscle cells of the tunica media after their activation by several of the growth-promoting substances; migration and proliferation of transformed smooth muscle cells, with secretion of copious amounts of extracellular matrix material; and, finally, termination of the growth process with regrowth of endothelium over the injured area. A decade of research work has helped identify clinical correlates of restenosis after coronary angioplasty procedures. This work is hindered by lack of a uniform angiographic definition of restenosis. In addition, much of the information has come from small studies, with incomplete follow-up and retrospective orientation. Nevertheless, some data are available. Patient-related correlates include male gender, unstable angina, diabetes, and continued smoking after angioplasty. Lesion-related correlates include multilesional and multivessel procedures, higher postangioplasty residual stenosis, proximal vessel location, location in the left anterior descending artery, location in a vein graft, long lesions, and total occlusions. The only consistent procedure-related correlate has been incorrect sizing of the angioplasty balloon to the treated artery. For the purposes of individual patient care, clinical correlates are not helpful. No group of variables has been found to be associated with complete freedom from restenosis, and no group is completely predictive of restenosis. All patients undergoing angioplasty procedures require some follow-up through subsequent months and years. Symptom status and the results of noninvasive studies have been investigated for purposes of follow-up. Symptoms are virtually useless by themselves for predicting restenosis or its absence. When symptom status is combined with exercise thallium 201 scintigraphy performed 4 to 6 months after an angioplasty procedure, the two factors are less than ideal but have a negative predictive value of more than 90%. This means that more than 90% of patients who have neither symptoms nor evidence of ischemia by thallium 201 scintigraphy will not have angiographic restenosis.(ABSTRACT TRUNCATED AT 400 WORDS)

Restenosis after coronary angioplasty

Coronary angioplasty is used to treat coronary atherosclerotic disease in many patients. One problem with coronary angioplasty is the phenomenon of restenosis. Restenosis appears to be a universal response to arterial wall injury. The biological events that underlie restenosis are characterized by: platelet adhesion and aggregation at sites of damaged endothelium, and within dissections into the medial layers, release of platelet derived growth-promoting substances, inflammation of the injured medial zone, transformation, migration, and proliferation of smooth muscle cells of the media following their activation by growth-promoting substances, secretion of copious amounts of extracellular matrix material, and finally, termination of the growth process following regrowth of endothelium over the damaged area. More than a decade of research work has helped identify clinical correlates of restenosis after coronary angioplasty. Patient-related correlates include male gender, unstable angina, diabetes, and continued smoking after angioplasty. Lesion-related correlates include multilesion and multivessel procedures, higher post-angioplasty residual stenosis, proximal vessel location, location in the left anterior descending coronary artery, location in a vein graft, long lesions, and total occlusions. However, for the purposes of individual patient care, clinical correlates are not particularly helpful. No group of variables has predicted complete freedom from restenosis, and conversely no group of variables has reliably indicated its presence. All patients undergoing angioplasty will require some form of follow-up evaluation. Symptom status by itself has not been found to be useful for predicting restenosis. However, when symptom status is combined with exercise thallium-201 scintigraphy, performed 4-6 months after angioplasty, it is less than ideal, but has a negative predictive value of over 90%. This means that over 90% of patients who are asymptomatic and have no evidence of ischemia by thallium-201 scintigraphy, will not have angiographic restenosis. Numerous clinical trials have been performed in order to reduce or prevent restenosis. Almost all have been disappointing, while a few have been encouraging. Studies of antiplatelet agents such as aspirin, dipyridamole (Boehringer Ingelheim Pharmaceuticals Inc., Ridgefield, CT, USA), and Ticlopidine (Syntex, Humgcao, Puerto Rico) have not shown efficacy, yet studies of an inhibitor of platelet-derived growth factor have been provocatively encouraging. No reduction in restenosis rates was found with the anticoagulants Coumadin (Du Pont Pharmaceuticals, Wilmington, DE, USA) and Heparin (Wyeth-Ayerst, Philadelphia, PA, USA). Fish oils (omega fatty acids) have been found in several clinical trials to provide modest, but encouraging, reductions in restenosis, but await further confirmation.(ABSTRACT TRUNCATED AT 400 WORDS)

Characterization of the responses of isolated rings of rabbit left carotid artery. A potential protocol for the assessment of pathologically induced functional changes

Studies on such injury processes as atherosclerosis, angioplasty, and restenosis, have shown an impairment of relaxations mediated by endothelium-derived relaxing factor (EDRF). Increasingly, the rabbit carotid artery is being used as the vessel of choice in such studies, but a definite protocol for the assessment of endothelial dysfunction or denudation has not been developed. Using isolated carotid artery rings, we have obtained reproducible dose-response curves in endothelially intact and denuded vessels from normally fed rabbits to a variety of vasoconstrictors and endothelium-dependent and -independent vasodilators. Endothelium-dependent vasodilators (acetylcholine (1 x 10(-8)-1 x 10(-6) M), carbachol (1 x 10(-8)-5 x 10(-6) M), substance P (0.01-100 nM), and A23187 (1 x 10(-8)-1 x 10(-7) M) relaxed the arteries in a concentration-dependent manner but produced no relaxation in denuded vessels. Endothelium-independent nitric oxide (NO) donors [Sin-1 (1 x 10(-8)-1 x 10(-6) M)] and sodium nitroprusside (1 x 10(-8)-1 x 10(-6) M)) relaxed both intact and denuded vessels to a similar degree (slight augmentation of the relaxation induced in denuded vessels was not significant), demonstrating that denuded vessels did not have an impaired reactivity to NO. Concentration response curves to the vasoconstrictors [5-HT (1 x 10(-7)-1 x 10(-4) M) and KCl (15-60 mM)] were produced in intact vessels and it was shown that similar contraction was produced by 1 x 10(-6) M 5-HT in intact and denuded vessels. This indicated that the vessels retained contractile ability following denudation.(ABSTRACT TRUNCATED AT 250 WORDS)

Infrainguinal vein graft stenosis

Although knowledge of the biological processes involved in the development of intimal hyperplasia has increased markedly in recent years, the precise aetiology of infrainguinal vein graft stenosis remains undetermined. Current therapy is therefore directed at treatment of the established lesion rather than its prevention. There seems little doubt, however, that recent advances in understanding of the vascular biology of normal and pathological saphenous vein will eventually lead to specific targeted therapy that will allow the prevention of vein graft stenosis.

Endovascular stents: preliminary clinical results and future developments

At present, there is an exponential use of new interventional techniques whose proper role and value have not yet been defined. The intracoronary stent is just one example. There is no doubt that stents can be implanted with a high technical success rate associated with highly predictable immediate angiographic results and that they appear to be superior to all other interventional techniques. However, the intrinsic thrombogenicity of all devices currently available for clinical use warrants a vigorous anticoagulation, exposing the patient either to the risk of (sub)acute stent thrombosis or to the risk of hemorrhage and vascular complications. It remains to be determined whether stent implantation will reduce the incidence of restenosis and whether this results in an improved long-term event and symptom-free survival. Experimental studies indicate that the thrombogenic nature of stents may be controlled by coating the struts with endothelial cells or polymers. With respect to restenosis, it is evident that as long as mechanical injury is applied to the vessel wall, the vessel wall will respond with neointimal thickening. The intracoronary stent has the potential to control this tissue response by serving as a carrier for local antiproliferative drug delivery or eventually for genetic manipulation. The intensive research which is now going on in combination with experimental animal data, human postmortem pathologic observations, and angiographic studies is yielding clear insights and future directions to address these issues.

Autoperfusion balloon catheter for complicated coronary angioplasty: a prospective study with retrospective controls

Prolonged angioplasty balloon inflation with an autoperfusion balloon for failed conventional coronary angioplasty, was compared with emergency surgery for this condition. Restenosis was assessed 6 weeks after successful intervention with the autoperfusion balloon. Forty consecutive patients with persistent acute occlusion and/or severe intimal dissection during conventional angioplasty, were treated with the autoperfusion balloon. They were candidates for emergency surgery if it failed. Total inflation time was significantly longer (p < 0.001) with the autoperfusion balloon (27.5; 10-180 min) than with the standard balloon (10; 1-20 min) (median; range). The number of inflations was significantly lower (p < 0.001) with the autoperfusion balloon (2; 1-5 times) than with the standard balloon (5; 2-14 times) (median; range). Two patients died, one before surgery could be performed. The autoperfusion balloon was successful in 26 patients (65%). After 6 weeks, 16 (62%) were asymptomatic without anti-anginal medication, 24 underwent repeat angiography, 10 (42%) had restenosis, 7 (27%) underwent elective bypass surgery. Emergency surgery remained necessary in 13 patients (33%), 9 received arterial grafts. In 31 retrospective controls, who had undergone immediate surgery for the same indication, only venous grafts could be used. Thus, prolonged autoperfusion balloon inflation was successful in 65% of the cases of failed, conventional angioplasty. The angiographic restenosis rate after 6 weeks was 42%. If emergency surgery remained necessary, the autoperfusion balloon facilitated the use of arterial bypass grafts.