Role of nitric oxide in restenosis after experimental balloon angioplasty in the hypercholesterolemic rabbit: effects on neointimal hyperplasia and vascular remodeling

PDGF regulates guanylate cyclase expression and cGMP signaling in vascular smooth muscle

The nitric oxide-cGMP (NO-cGMP) pathway is of outstanding importance for vascular homeostasis and has multiple beneficial effects in vascular disease. Neointimal hyperplasia after vascular injury is caused by increased proliferation and migration of vascular smooth muscle cells (VSMCs). However, the role of NO-cGMP signaling in human VSMCs in this process is still not fully understood. Here, we investigate the interaction between platelet derived growth factor (PDGF)-signaling, one of the major contributors to neointimal hyperplasia, and the cGMP pathway in vascular smooth muscle, focusing on NO-sensitive soluble guanylyl cyclase (sGC). We show that PDGF reduces sGC expression by activating PI3K and Rac1, which in turn alters Notch ligand signaling. These data are corroborated by gene expression analysis in human atheromas, as well as immunohistological analysis of diseased and injured arteries. Collectively, our data identify the crosstalk between PDGF and NO/sGC signaling pathway in human VSMCs as a potential target to tackle neointimal hyperplasia.

PDGF reduces expression of nitric oxide-sensitive soluble guanylyl cyclase (NO-sGC) through PI3K-P-Rex1-Rac1 signaling in vascular smooth muscle cells. These insights provide possible avenues to prevent dysregulation of NO/cGMP signaling in vascular disease.

Nanomatrix Coated Stent Enhances Endothelialization but Reduces Platelet, Smooth Muscle Cell, and Monocyte Adhesion under Physiologic Conditions

Cardiovascular disease is presently the number one cause of death worldwide. Current stents used to treat cardiovascular disease have a litany of unacceptable shortcomings: adverse clinical events including restenosis, neointimal hyperplasia, thrombosis, inflammation, and poor re-endothelialization. We have developed a biocompatible, multifunctional, peptide amphiphile-based nanomatrix coating for stents. In this study, we evaluated the ability of the nanomatrix coated stent to simultaneously address the issues facing current stents under physiological flow conditions in vitro. We found that the nanomatrix coated stent could increase endothelial cell migration, adhesion, and proliferation (potential for re-endothelialization), discourage smooth muscle cell migration and adhesion (potential to reduce neointimal hyperplasia and restenosis), and decrease both platelet activation and adhesion (potential to prevent thrombosis) as well as monocyte adhesion (potential to attenuate inflammatory responses) under physiological flow conditions in vitro. These promising results demonstrate the potential clinical utility of this nanomatrix stent coating, and highlight the importance of biocompatibility, multifunctionality, and bioactivity in cardiovascular device design.

Iliac artery myointimal hyperplasia in rabbits submitted to angioplasty and treated with Moringa oleifera

OBJECTIVE

to assess post-angioplasty myointimal hyperplasia in iliac artery of rabbits treated with extract of Moringa oleifera leaves.

METHODS

we conducted a randomized trial in laboratory animals for five weeks of follow-up, developed in the Vivarium of Pharmaceutical Technology Laboratory of the Universidade Federal da Paraíba. We used rabbits from the New Zealand breed, subjected to a hypercholesterolemic diet and angioplasty of the external iliac artery, randomized into two groups: M200 Group (n=10) - rabbits treated with 200mg/kg/day of Moringa oleifera leaves extract orally; SF group (n=10) - rabbits treated with 0.9% saline orally. After five weeks, the animals were euthanized and the iliac arteries prepared for histology. Histological sections were analyzed by digital morphometry. Statistical analysis was performed using the Student's t test. The significance level was 0.05.

RESULTS

there was no significant difference in myointimal hyperplasia between M200 and SF groups when comparing the iliac arteries submitted to angioplasty.

CONCLUSION

there was no difference of myointimal hyperplasia between groups treated with saline and Moringa oleifera after angioplasty.

Nitric oxide prevents aortic neointimal hyperplasia by controlling macrophage polarization

OBJECTIVE

Nitric oxide synthase 3 (NOS3) prevents neointima hyperplasia by still unknown mechanisms. To demonstrate the significance of endothelial nitric oxide in the polarization of infiltrated macrophages through the expression of matrix metalloproteinase (MMP)-13 in neointima formation.

APPROACH AND RESULTS

After aortic endothelial denudation, NOS3 null mice show elevated neointima formation, detecting increased mobilization of LSK (lineage-negative [Lin]-stem-cell antigen 1 [SCA1]+KIT+) progenitor cells, and high ratios of M1 (proinflammatory) to M2 (resolving) macrophages, accompanied by high expression of interleukin-5, interleukin-6, MCP-1 (monocyte chemoattractant protein), VEGF (vascular endothelial growth factor), GM-CSF (granulocyte-macrophage colony stimulating factor), interleukin-1β, and interferon-γ. In conditional c-Myc knockout mice, in which M2 polarization is defective, denuded aortas showed extensive wall thickening as well. Conditioned medium from NOS3-deficient endothelium induced extensive repolarization of M2 macrophages to an M1 phenotype, and vascular smooth muscle cells proliferated and migrated faster in conditioned medium from M1 macrophages. Among the different proteins participating in cell migration, MMP-13 was preferentially expressed by M1 macrophages. M1-mediated vascular smooth muscle cell migration was inhibited when macrophages were isolated from MMP-13-deficient mice, whereas exogenous administration of MMP-13 to vascular smooth muscle cell fully restored migration. Excess vessel wall thickening in mice lacking NOS3 was partially reversed by simultaneous deletion of MMP-13, indicating that NOS3 prevents neointimal hyperplasia by preventing MMP-13 activity. An excess of M1-polarized macrophages that coexpress MMP-13 was also detected in human carotid samples from endarterectomized patients.

CONCLUSIONS

These findings indicate that at least M1 macrophage-mediated expression of MMP-13 in NOS3 null mice induces neointima formation after vascular injury, suggesting that MMP-13 may represent a new promising target in vascular disease.

Genetic causation of neointimal hyperplasia in hemodialysis vascular access dysfunction

The major cause of hemodialysis vascular access failure is venous stenosis resulting from neointimal hyperplasia. Genetic factors have been shown to be associated with cardiovascular disease and peripheral vascular disease (PVD) in the general population. Genetic factors may also play an important role in vascular access stenosis and development of neointimal hyperplasia by affecting pathways that lead to inflammation, endothelial function, oxidative stress, and vascular smooth muscle proliferation. This review will discuss the role of genetics in understanding neointimal hyperplasia development in hemodialysis vascular access dysfunction and other disease processes with similar neointimal hyperplasia development such as coronary artery disease and PVD.

Oral administration of glycine in the prevention of restenosis after coronary angioplasty. A double blind placebo controlled randomized feasibility trial evaluating safety and efficacy of glycine in the prevention of restenosis after angioplasty

OBJECTIVES

Evaluation of safety, feasibility, and efficacy of oral administered glycine in prevention of angiographic restenosis six months after percutaneous coronary intervention (PCI).

BACKGROUND

The amino acid glycine modulates immunological response and enhances the production of endothelial derived nitric oxide (EDNO) factor. This factor has been shown to possess anti-atherosclerotic properties, actions of which are thought to reduce neo-intimal hyperplasia. Furthermore, glycine significantly elevates arginine serum levels. This amino acid has been extensively studied for its effects on the endothelium, nitric oxide (NO) metabolism and effects on several biochemical pathways interfering with the process of restenosis after PCI.

METHODS

A prospective double blind placebo controlled randomized study evaluated safety and feasibility of chronic oral administration of glycine. In addition, the efficacy was determined by evaluation of six months angiographic restenosis rates.

RESULTS

214 patients scheduled for elective PCI were randomized to receive glycine or placebo. At follow-up, there was no significant difference in side effects and in major adverse cardiac events (MACE) between both groups. Six-month angiograms revealed similar restenosis rates for the glycine group (17.5%) and for the placebo group (20.2%) (P = 0.82).

CONCLUSION

Chronic oral administration of glycine was safe and feasible and had similar side effects compared to placebo. However, chronic oral administration of glycine did not lead to a significant reduction in restenosis rates at six months after elective PCI.

Anti-atherogenic effect of statins: role of nitric oxide, peroxynitrite and haem oxygenase-1

BACKGROUND AND PURPOSE

The pleiotropic effects of HMG-CoA inhibitors (statins), which include anti-inflammation, antioxidation and immunomodulation, are not yet fully understood. The present study was designed to elucidate the role of nitric oxide (NO), peroxynitrite (ONOO(-)) and haem oxygenase-1 (HO-1) in the anti-atherogenic effect of statins.

EXPERIMENTAL APPROACH

Normal and atherosclerotic New Zealand rabbits were treated with atorvastatin or simvastatin in the presence or absence of inhibitors and promoters of endothelial nitric oxide synthase (eNOS) and HO-1. NO and ONOO(-) released from isolated aortae by calcium ionophore were measured with nanosensors placed 6 +/- 2 nm from aortic endothelium. Expression of eNOS and HO-1 protein, HO activity, plasma malondialdehyde (MDA) and vessel wall thickness were also measured.

KEY RESULTS

Hypercholesterolaemia decreased eNOS expression by 31 +/- 3%, decreased NO (230 +/- 16 vs. 433 +/- 17 nmol x L(-1) control) and increased cytotoxic ONOO(-) (299 +/- 15 vs. 187 +/- 11 nmol x L(-1) control). The concentration ratio of [NO]/[ONOO(-)] decreased from 2.3 +/- 0.1 (normal) to 0.7 +/- 0.1 indicating an increase of nitroxidative stress in atherosclerotic endothelium. Expression of HO-1 protein increased by 20 +/- 8% in atherosclerosis and further increased (about 30%) after treatment with statins. Statins partially restored the [NO]/[ONOO(-)] balance (1.5 +/- 0.1 for atorvastatin and 1.4 +/- 0.1 simvastatin), decreased MDA and wall thickening. Promoters of eNOS and HO-1 (L-arginine and haemin) ameliorated the [NO]/[ONOO(-)] ratio while their inhibitors (L-NAME or tin-protoporphyrin) showed no improvement in these ratio.

CONCLUSIONS AND IMPLICATIONS

Atherosclerosis induced an endothelial [NO]/[ONOO(-)] balance indicative of endothelial dysfunction. Statins showed anti-atherosclerotic effects mediated by HO-1/eNOS, restoring the [NO]/[ONOO(-)] imbalance and reducing lipid peroxidation.

Plasma ADMA predicts restenosis of arteriovenous fistula

Plasma levels of asymmetrical dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide production, correlate with endothelial dysfunction and the development of cardiovascular events in patients with uremia. It is not known whether endothelial dysfunction contributes to the dysfunction of arteriovenous fistulas (AVFs) in hemodialysis patients. Here, we studied the predictive value of baseline plasma ADMA for symptomatic restenosis of an AVF after percutaneous transluminal angioplasty in dialysis patients. We obtained baseline plasma ADMA levels before percutaneous transluminal angioplasty in 100 consecutive patients with dysfunctional AVFs. Patients were followed up clinically for up to 6 mo after angioplasty for recurrent dysfunction. During the 6 mo after angioplasty, 46 patients experienced recurrent dysfunction of their AVF; of these, follow-up fistulography showed restenosis at the same location in 41, new stenosis at different locations in two, and no significant stenosis in three patients. Up to 60% of the patients with high levels of ADMA (>0.910 microM) had target lesion restenosis compared with 25% of those with low levels (<0.910 microM; P < 0.001). In multivariate analysis, plasma ADMA independently nearly tripled the risk for recurrent symptomatic stenosis of an AVF after percutaneous transluminal angioplasty (hazard ratio 2.65; 95% confidence interval 1.33 to 5.28). These results suggest a role for ADMA in the progression of symptomatic restenoses of AVFs after percutaneous transluminal angioplasty and call for preventive strategies that target ADMA and/or endothelial dysfunction to decrease the risk for AVF restenosis.

The prevention of endothelial dysfunction through endothelial cell apoptosis inhibition in a hypercholesterolemic rabbit model: the effect of L-arginine supplementation

BACKGROUND

The impact of L-arginine on atherogenesis and its ability to prevent endothelial dysfunction have been studied extensively during the past years. L-arginine is a substance for nitric oxide synthesis which involves in apoptosis. Hypercholesterolemia promotes endothelial dysfunction, and it is hypothesized that L-arginine prevents endothelial dysfunction through endothelial cells apoptosis inhibition. To test this hypothesis, thirty rabbits were assigned into two groups. The control group received 1% cholesterol diet for 4 weeks, and the L-arginine group received same diets plus 3% L-arginine in drinking water.

RESULTS

No significant differences were observed in cholesterol level between two groups, but the nitrite concentration in L-arginine group was significantly higher than other group (control group: 11.8 +/- 1; L-arginine group: 14.7 +/- 0.5 micromol/l); (p < 0.05). The aorta score of fatty streak in control group was 0.875 +/- 0.35, but no fatty streak lesion was detected in L-arginine group (p < 0.05). The number of intimal apoptotic cells/500 cells of aorta in two groups of experiment were statistically different (control group: 39.3 +/- 7.6; L-arginine group: 21.5 +/- 5.3) (p < 0.05).

CONCLUSION

The inhibition of endothelial cells apoptosis by L-arginine restores endothelial function in a model of hypercholesterolemia.

Regulation of eNOS-derived superoxide by endogenous methylarginines

The endogenous methylarginines, asymmetric dimethylarginine (ADMA) and N (G)-monomethyl- l-arginine (L-NMMA) regulate nitric oxide (NO) production from endothelial NO synthase (eNOS). Under conditions of tetrahydrobiopterin (BH 4) depletion eNOS also generates (*)O 2 (-); however, the effects of methylarginines on eNOS-derived (*)O 2 (-) generation are poorly understood. Therefore, using electron paramagnetic resonance spin trapping techniques we measured the dose-dependent effects of ADMA and L-NMMA on (*)O 2 (-) production from eNOS under conditions of BH 4 depletion. In the absence of BH 4, ADMA dose-dependently increased NOS-derived (*)O 2 (-) generation, with a maximal increase of 151% at 100 microM ADMA. L-NMMA also dose-dependently increased NOS-derived (*)O 2 (-), but to a lesser extent, demonstrating a 102% increase at 100 microM L-NMMA. Moreover, the native substrate l-arginine also increased eNOS-derived (*)O 2 (-), exhibiting a similar degree of enhancement as that observed with ADMA. Measurements of NADPH consumption from eNOS demonstrated that binding of either l-arginine or methylarginines increased the rate of NADPH oxidation. Spectrophotometric studies suggest, just as for l-arginine and L-NMMA, the binding of ADMA shifts the eNOS heme to the high-spin state, indicative of a more positive heme redox potential, enabling enhanced electron transfer from the reductase to the oxygenase site. These results demonstrate that the methylarginines can profoundly shift the balance of NO and (*)O 2 (-) generation from eNOS. These observations have important implications with regard to the therapeutic use of l-arginine and the methylarginine-NOS inhibitors in the treatment of disease.

Endothelial dysfunction and restenosis following percutaneous coronary intervention

BACKGROUND

Restenosis remains an important limitation of PCI. Although local factors such as small vessel diameter and systemic factors such as diabetes explain some of its incidence, it nevertheless also occurs in low-risk patients. We hypothesize that endothelial dysfunction may be an independent risk factor in some of these cases.

METHODS

20 patients who had previously undergone PCI were studied at cardiac catheterization (10 with restenotic lesions were matched to 10 without restenosis). Infusion of multiple concentrations of acetylcholine (ACh) and nitroglycerine (GTN) were made via a 3F infusion catheter into the target artery. Following infusion, changes in diameter of segments proximal and distal to the PCI site were measured.

RESULTS

There was a significant impairment in endothelium-dependent dilatation at the maximal dose of acetylcholine in those with restenosis compared to those without restenosis, both proximal and distal to the stented area (proximal; 11.5+/-7.0% versus -20.9+/-9.0% p<0.001, distal; 12.0+/-3.1% versus -17.8+/-8.1% p<0.001), but there was no difference in the response to GTN. There was a significant correlation between the endothelium-dependent dilatation response and the percent restenosis (r=-0.65, p=0.003).

CONCLUSIONS

Coronary endothelium-dependent dilatation is reduced in subjects with restenosis in arterial segments separate from the stented lesion. This supports a hypothesis that endothelial dysfunction contributes to the development of restenosis, following percutaneous coronary intervention.

Mechanisms of disease: L-arginine in coronary atherosclerosis--a clinical perspective

L-arginine is the substrate of endothelial nitric oxide synthase and the main precursor of nitric oxide in the vascular endothelium, thus its effects are mediated largely by increases in nitric oxide production. L-arginine has antioxidant and antiapoptotic properties, increases smooth muscle relaxation, inhibits the expression of adhesion molecules and chemotactic peptides, decreases endothelin-1 expression, and inhibits platelet aggregation. This amino acid also improves endothelial function in patients with coronary artery disease and dilates human epicardial atheromatous coronary arteries. Despite the positive results from small case-control studies, it is still unclear whether chronic administration of L-arginine has any effect on clinical outcome in patients with coronary artery disease. In addition, other indirect strategies, such as the inhibition of arginase, could prove more effective at improving intracellular L-arginine bioavailability than exogenous L-arginine administration. The potential clinical usefulness of L-arginine, therefore, needs further evaluation in large, prospective clinical trials. Here, we present a critique of the existing literature about the role of L-arginine in the prevention of atherosclerosis.

Therapeutic effects of nitric oxide-aspirin hybrid drugs

This review examines the therapeutic potential and mechanisms of action of drugs known as nitric oxide (NO)-aspirins. Drugs of this class have an NO-releasing moiety joined by ester linkage to the aspirin molecule. NO-aspirins have the capability to release NO in addition to retaining the cyclooxygenase-inhibitory action of aspirin. The protective nature of NO led to the development of NO-aspirins in the hope that they might avoid the gastric side effects associated with aspirin. However, it has become apparent that the drug-derived NO instills potential for a wide range of added beneficial effects over the parent compound. In this review, the authors focus on the analgesic, anti-inflammatory, cardiovascular and chemopreventative actions of compounds of this emerging drug class.

Apoptosis bcl-2 and nitrotyrosine expression in an angioplasty-restenosis rabbit: an experimental model

Apoptosis has been suggested to have an important role in the pathogenesis of restenosis in addition to cell migration and proliferation. The aim of the present study was to investigate in an experimental in vivo model the occurrence of apoptosis postangioplasty and its relation to bcl-2 and peroxynitrite detection. Eighteen hypercholesterolemic rabbits underwent transluminal angioplasty of the right iliac artery. The rabbits were sacrificed on the 1st, 2nd, 3rd, 7th, 15th, and 28th day postangioplasty (3 animals per time point) and both the angioplasted and non-injured arteries were studied. Apoptosis was assessed by the terminal uridine nick-end labeling method (TUNEL). Bcl-2 and peroxynitrite were detected by immunochemistry using anti-bcl-2 and anti-nitrotyrosine antibodies. In the angioplasted arteries the number of apoptotic cells was <or=1% of the total cell population in both media and neointima at any of the postangioplasty time points examined. Bcl-2 and nitrotyrosines were detected at all time points in the angioplasted arteries (vs. non-injured, P<0.001), showed similar localization and had the same peaks of expression both in the media (7th day: Bcl-2 66% and nitrotyrosines 74%) and neointima (15th day: Bcl-2 67% and nitrotyrosines 61%). In this experimental model we observed low apoptotic rates while bcl-2 and peroxynitrite products were detected. We can hypothesize that the detection of nitrotyrosines is related with reduced levels of nitric oxide resulting in increased expression of the bcl-2, preventing thus cell death due to either apoptosis or necrosis. Further studies are needed in order to elucidate their role in the restenosis process.

Evidence for the pathophysiological role of endogenous methylarginines in regulation of endothelial NO production and vascular function

In endothelium, NO is derived from endothelial NO synthase (eNOS)-mediated L-arginine oxidation. Endogenous guanidinomethylated arginines (MAs), including asymmetric dimethylarginine (ADMA) and NG-methyl-L-arginine (L-NMMA), are released in cells upon protein degradation and are competitive inhibitors of eNOS. However, it is unknown whether intracellular MA concentrations reach levels sufficient to regulate endothelial NO production. Therefore, the dose-dependent effects of ADMA and L-NMMA on eNOS function were determined. Kinetic studies demonstrated that the Km for L-arginine is 3.14 microM with a Vmax of 0.14 micromol mg-1 min-1, whereas Ki values of 0.9 microM and 1.1 microM were determined for ADMA and L-NMMA, respectively. EPR studies of NO production from purified eNOS demonstrated that, with a physiological 100 microM level of L-arginine, MA levels of >10 microM were required for significant eNOS inhibition. Dose-dependent inhibition of NO formation in endothelial cells was observed with extracellular MA concentrations as low 5 microm. Similar effects were observed in isolated vessels where 5 microm ADMA inhibited vascular relaxation to acetylcholine. MA uptake studies demonstrated that ADMA and L-NMMA accumulate in endothelial cells with intracellular levels greatly exceeding extracellular concentrations. L-arginine/MA ratios were correlated with cellular NO production. Although normal physiological levels of MAs do not significantly inhibit NOS, a 3- to 9-fold increase, as reported under disease conditions, would exert prominent inhibition. Using a balloon model of vascular injury, approximately 4-fold increases in cellular MAs were observed, and these caused prominent impairment of vascular relaxation. Thus, MAs are critical mediators of vascular dysfunction following vascular injury.

Reciprocal changes in endothelium-derived hyperpolarizing factor- and nitric oxide-system in the mesenteric artery of adult female rats following ovariectomy

1. To explore the effects of estrogen on arterial functions, we examined endothelium-derived hyperpolarizing factor (EDHF)- and NO-mediated responses in isolated mesenteric arteries of female rats, 4 weeks after sham-operation (CON), ovariectomy (OVX) and OVX plus chronic estrogen treatment (OVX+E(2)). Tissue levels of connexins-40, 43 (major components of gap junction), inducible NOS (iNOS), endothelial NOS (eNOS) and eNOS regulator proteins such as calmodulin, heat shock protein 90 (hsp90) and caveolin-1 were also examined using Western blot. 2. In OVX, acetylcholine (ACh)-induced EDHF-mediated relaxation and membrane hyperpolarization of arterial smooth muscles were reduced, whereas ACh-induced NO-mediated relaxation was enhanced, leading to no change in ACh-induced relaxation. 3. In OVX, connexin-40 and 43 were decreased. Tissue levels of eNOS and its positive regulators (calmodulin and hsp90) were unchanged, but that of its negative regulator, caveolin-1, was decreased. The levels of iNOS in mesenteric artery and aorta and plasma levels of NO metabolites and cholesterol were elevated. 4. In OVX, contraction of the artery by phenylephrine was reduced, but augmented by nonspecific inhibitor of NOS to the comparable level as that in CON group. The contraction in OVX group unlike that in CON group was augmented by specific iNOS inhibitor, and the difference between contractions in the presence of nonspecific and specific inhibitor as an index of eNOS activity was increased. 5. In OVX+E(2), all these changes were recovered. 6. In all groups, EDHF-mediated relaxation was suppressed by 18beta-glycyrrhetinic acid, an inhibitor of gap junction. 7. These results indicate that estrogen deficiency does not change the diameter of mesenteric artery: it reduces EDHF-mediated relaxation by decreasing gap junction, whereas it augments NO-mediated relaxation via an increase in NO release. Increased NO result from increased activity of eNOS subsequent to a decrease in caveolin-1 and from induction of iNOS. However, excessive NO generation with elevated plasma cholesterol would raise a risk for atherosclerosis.

Pharmacological treatment for prevention of restenosis

Coronary artery disease (CAD) is the leading cause of mortality and morbidity among adults in the Western world. Coronary artery bypass grafting and percutaneous coronary interventions (PCI) have gained widespread acceptance for the treatment of symptomatic CAD. There has been an explosive growth worldwide in the utilisation of PCI, such as balloon angioplasty and stenting, which now accounts for over 50% of coronary revascularisation. Despite the popularity of PCI, the problem of recurrent narrowing of the dilated artery (restenosis) continues to vex investigators. In recent years, significant advances have occurred in the understanding of restenosis. Two processes seem to contribute to restenosis: remodelling (vessel size changes) and intimal hyperplasia (vascular smooth muscle cell [VSMC] proliferation and extracellular matrix [ECM] deposition). Despite considerable efforts, pharmacological approaches to decrease restenosis have been largely unsuccessful and the only currently applied modality to reduce the restenosis rate is stenting. However, stenting only prevents remodelling and does not inhibit intimal hyperplasia. Several potential targets for inhibiting restenosis are currently under investigation including platelet activation, the coagulation cascade, VSMC proliferation and migration, and ECM synthesis. In addition, new approaches for local drug therapy, such as drug eluting stents, are currently being evaluated in preclinical and clinical studies. In this article, we critically review the current status of drugs that are being evaluated for restenosis at various stages of development (in vitro, preclinical animal models and human trials).

Local drug delivery in restenosis injury: thermoresponsive co-polymers as potential drug delivery systems

The success of percutaneous transluminal coronary angioplasty in treatment of acute coronary syndromes has been compromised by the incidence of restenosis. The physical insult of balloon insertion can damage or remove the endothelial monolayer, thereby generating a prothrombotic surface. The resulting inappropriate response to injury can also lead to penetration of inflammatory cells, conversion of the underlying media to a synthetic phenotype, deposition of extracellular matrix, constrictive remodeling, and neointimal hyperplasia. While stent implantation at the time of balloon insertion has offset some of these events, inflammatory responses to the implanted biomaterial (stent) and intimal hyperplasia are still prominent features of the procedure, leading in 20-30% of cases to in-stent restenosis within a year. Systemic delivery of drugs designed to offset in-stent restenosis injury has been largely unsuccessful, which has led to the development of strategies for coating stents with drugs for local delivery. Drug-eluting stents constitute an innovative means of further reducing the incidence of restenosis injury and clinical trials have shown encouraging results. This review focuses on properties of a class of environment-sensitive hydrogels, the N-isopropylacrylamide-based thermoresponsive co-polymers, on their potential roles as stent coatings, on their demonstrated ability to incorporate and release drugs that modify vascular endothelial and smooth muscle cell functions, and on issues that still await clarification, prior to their adoption in a clinical setting.

Human free apolipoprotein A-I and artificial pre-beta-high-density lipoprotein inhibit eNOS activity and NO release

Little is known about the effects of human free apolipoprotein A-I (Free-Apo A-I) and pre-beta-high density lipoprotein (pre-beta-HDL) on the endothelium function. In this study, we have investigated the effects of Free-Apo A-I and artificial pre-beta-HDL on endothelial NO synthase (eNOS) activity and on NO production by endothelial cells. Free-Apo A-I drastically inhibited NO production in human umbilical cord vein endothelial cells (HUVECs) and eNOS activity in bovine aortic endothelial cells (BAECs). Pre-beta-HDL and serum from human apolipoprotein A-I transgenic rabbits inhibited eNOS activity in BAECs but HDL3 did not. Free-Apo A-I displaced eNOS from BAEC plasma membrane towards intracellular pools without affecting eNOS activity and eNOS mass in BAEC crude homogenates. Free-Apo A-I and HDL3 did not decrease either caveolin bound to BAEC plasma membrane or caveola cholesterol content. As previously described, we showed that HDL3 directly induced endothelium-dependent relaxation of rings from rat aorta. We observed that pre-beta-HDL significantly decreased endothelium-dependent relaxation of rat aortic rings ex vivo.

L-arginine supplementation does not inhibit neointimal formation after coronary stenting in human beings: an intravascular ultrasound study

BACKGROUND

In-stent restenosis results from neointimal tissue proliferation. L-arginine supplementation improves endothelial function and reduces neointimal formation after arterial injury in animals. The aim of the study was to assess the influence of L-arginine administration on neointimal proliferation after coronary stenting in human beings.

METHODS

We performed a prospective, randomized, double-blinded, placebo-controlled study in 60 men without diabetes. L-arginine/placebo was administered intravenously 12 hours before percutaneous coronary intervention (200 mg/kg for 240 minutes), during the procedure (200 mg/kg for 240 minutes), and intracoronarily immediately before stent implantation (500 mg for 10 minutes), and it was followed by oral treatment for next 2 weeks (6.0 g/d). By quantitative coronary angiography, late lumen loss, and intravascular ultrasound, neointimal volume and percent neointimal volume were calculated after 7 months of follow-up to assess neointimal formation.

RESULTS

There were no differences in baseline clinical or angiographic characteristics between the two groups. Intravenous infusion of L-arginine increased plasma L-arginine concentrations 6-fold compared with placebo (661 +/- 264 vs 107 +/- 71 mmol/L, P <.001). During the 2-week period of oral treatment with L-arginine there was a sustained, significant increase of plasma L-arginine level (150 +/- 50 vs 100 +/- 17, P <.001, 135 +/- 42 vs 89 +/- 27, P <.001, respectively, on days 7 and 14 in the L-arginine group vs placebo). However, at 7-month follow-up, there was no difference in neointimal formation measured both by quantitative coronary angiography and intravascular ultrasound between the study groups.

CONCLUSIONS

Chronic systemic L-arginine administration has no effect on neointimal formation after coronary stenting in human beings.

The Glu298Asp polymorphism in endothelial nitric oxide synthase gene is associated with coronary in-stent restenosis

BACKGROUND

Reduced or impaired synthesis of nitric oxide promotes the proliferation of vascular smooth muscle cells, and thus may induce the neointimal formation leading to coronary in-stent restenosis. Recent reports have suggested that the Glu298Asp polymorphism in exon 7 of the endothelial nitric oxide synthase gene is associated with coronary spasm and acute myocardial infarction. In this study, we have examined the implication of this polymorphism with regard to coronary restenosis after Palmaz-Schatz stent deployment.

METHODS

Eighty-nine lesions in 85 consecutive patients were treated with Palmaz-Schatz stents, and were prospectively followed up for 6 months. The lesions were classified into a restenosis group (% diameter stenosis=50%) and a non-restenosis group. Assessment was made using an automated quantitative angiographic system. We performed polymerase chain reaction-restriction fragment length polymorphism analysis to detect the missense Glu298Asp variant in exon 7 of the endothelial nitric oxide synthase gene.

RESULTS

Coronary risk factors and angiographic findings of stenotic lesions did not differ between the groups. Univariate analyses showed that the missense Glu298Asp variant was the only statistically significant predictor of restenosis (odds ratio, 4.27; P=0.025). In addition, multiple logistic regression analysis revealed the missense Glu298Asp variant as the only independent predictor for in-stent restenosis (odds ratio, 3.90; P=0.036).

CONCLUSIONS

The missense Glu298Asp variant may be an independent risk factor for in-stent restenosis.

Potential cardioprotective actions of no-releasing aspirin

The use of low doses of aspirin on a daily basis has increased greatly in the past 20 years, based on observations that it can significantly reduce the risk of heart attacks and strokes. However, aspirin can also cause severe damage to the stomach. A modified version of aspirin that releases nitric oxide has been developed that seems to offer important advantages over its 103-year-old parent--namely, improved protection for the heart without the unwanted effects on the stomach.

Vascular effects of dietary L-arginine supplementation

The vascular endothelium is acknowledged to play an important role in vascular physiology. Attention has focused on endothelial production of nitric oxide as a key element in many of the processes associated with the development of atherosclerosis. L-arginine is the substrate for the enzyme nitric oxide synthase (NOS), which is responsible for the endothelial production of nitric oxide. Therefore, many investigators have been interested in whether dietary L-arginine supplementation can augment nitric oxide production and thereby improve vascular health. The effects of oral L-arginine on vascular health and disease have been examined both in human beings and in various animal models. In this review, we summarize the results of studies of oral L-arginine supplementation on atherosclerotic lesion formation, as well as markers of endothelial function (e.g. macrophage function, platelet aggregation and adhesion, and in vitro vascular ring studies). Although results of oral L-arginine supplementation in hypercholesterolemic animals have generally shown beneficial effects, the data in humans are varied, possibly because of small sample sizes and brief periods of study. Long-term randomized clinical trials are needed to more definitively address whether oral L-arginine supplementation could be advantageous for vascular health.

Maintaining the endothelium: preventive strategies for vessel integrity

The endothelium is a diaphanous membrane, only one cell layer thick, that lines all of our blood vessels. Despite its apparent fragility, it exerts profound control over vascular tone, structure, and intersection with circulating blood elements. One of the factors that the endothelium synthesizes is nitric oxide, which is the most potent endogenous vasodilator known. In addition to its blood flow regulating effects, nitric oxide also inhibits key processes in atherosclerosis, including monocyte adherence, platelet aggregation, and proliferation of vascular smooth muscle cells. Nitric oxide synthesis is impaired, and its degradation is accelerated, in many of the conditions associated with atherosclerosis, including hypercholesterolemia. Restoration of nitric oxide synthesis and activity in these disorders can improve blood flow, relieve symptoms, and perhaps reduce the progression of atherosclerosis.(c) 2001 by CHF, Inc.

Efficacy and age-related effects of nitric oxide-releasing aspirin on experimental restenosis

Restenosis after percutaneous transluminal coronary angioplasty is caused by neointimal hyperplasia, which involves impairment of nitric oxide (NO)-dependent pathways, and may be further exacerbated by a concomitant aging process. We compared the effects of NO-releasing-aspirin (NCX-4016) and aspirin (ASA) on experimental restenosis in both adult and elderly rats. Moreover, to ascertain the efficacy of NCX-4016 during vascular aging, we fully characterized the release of bioactive NO by the drug. Sprague-Dawley rats aged 6 and 24 months were treated with NO releasing-aspirin (55 mg/kg) or ASA (30 mg/kg) for 7 days before and 21 days after standard carotid balloon injury. Histological examination and immunohistochemical double-staining were used to evaluate restenosis. Plasma nitrite and nitrate and S-nitrosothiols were determined by a chemiluminescence-based assay. Electron spin resonance was used for determining nitrosylhemoglobin. Treatment of aged rats with NCX-4016 was associated with increased bioactive NO, compared with ASA. NO aspirin, but not ASA, reduced experimental restenosis in old rats, an effect associated with reduced vascular smooth muscle cell proliferation. NCX-4016, but not ASA, was well tolerated and virtually devoid of gastric damage in either adult or old rats. Thus, impairment of NO-dependent mechanisms may be involved in the development of restenosis in old rats. We suggest that an NCX-4016 derivative could be an effective drug in reducing restenosis, especially in the presence of aging and/or gastrointestinal damage.

Minimal duration of oral matrix metalloproteinase inhibition to prevent constrictive arterial remodeling after balloon dilation in the pig

PURPOSE

To determine the minimal duration of oral matrix metalloproteinase (MMP) inhibition to prevent constrictive remodeling after balloon dilation.

MATERIALS AND METHODS

In 37 nonatherosclerotic pigs, balloon dilation was performed in 145 peripheral arteries. Pigs were treated with an MMP inhibitor for 2, 7, 14, 28, or 42 days, or they served as controls and were killed 42 days after intervention. Arteries were visualized with angiography and intravascular ultrasonography.

RESULTS

A 69% reduction in late vessel area (VA) loss was achieved after 14 days of treatment: 1.27 mm(2) +/- 0.55 (standard error of the mean [SEM]) versus 4.04 mm(2) +/- 0.93 (SEM) in the control group (P =.1). A consistent inhibition of late VA loss was observed in the 28-day (0.89 mm(2) +/- 0.83 [SEM], P =.03) and 42-day (0.74 mm(2) +/- 0.66 [SEM], P =.02) groups treated with the MMP inhibitor. After 14 and 28 days of treatment, late lumen area loss was 65% and 55% of control values, and it decreased to 41% (P =.04) after 42 days of treatment.

CONCLUSION

MMP inhibition for 14-28 days is sufficient to inhibit constrictive remodeling after balloon dilation. This implies that an essential MMP-dependent initiator of constrictive remodeling was mainly active in the first 2 weeks after intervention.

Mutated p21/WAF/CIP transgene overexpression reduces smooth muscle cell proliferation, macrophage deposition, oxidation-sensitive mechanisms, and restenosis in hypercholesterolemic apolipoprotein E knockout mice

We have investigated whether by introducing a mutated p21 cyclin-dependent kinase inhibitor through a standard type 5 adenovirus (Ad), it would be possible to interfere with restenosis in hypercholesterolemic apolipoprotein E knockout mice. Restenosis is a clinically relevant, undesired effect of percutaneous transluminal coronary angioplasty (PTCA). A critical event underlying restenosis is smooth muscle cell (SMC) proliferation leading to neointimal formation and vessel reocclusion. Recent data demonstrated that it is possible to reduce restenosis by introducing various genes blocking the cell cycle through Ad vectors. Nonetheless, most experiments were conducted in the healthy carotid artery of rat, which is far from the condition of human disease. Therefore, we investigated whether antiproliferative or proapoptotic genes affect restenosis in a model of atherosclerosis closer to clinical settings. Ad-mutated(m)-p21WAF/CIP1 transgene overexpression induces a significant reduction of restenosis in hypercholesterolemic apolipoprotein E knockout mice subjected to injury of common carotid artery. This was associated with reduced SMC density and proliferation, macrophage deposition, and oxidation-sensitive mechanisms. Treatment with p21/WAF also enhanced TUNEL positivity of arterial cells. We show that in an experimental model of atherosclerosis, braking the cell proliferation through increased vascular apoptosis and reduced oxidation-sensitive signal transduction and macrophage accumulation can significantly ameliorate the deleterious effects of vascular injuries similar to those that occur during PTCA and related procedures.

Atherogenesis and the arginine hypothesis

In patients who have elevated levels of plasma ADMA, a relative deficiency of L-arginine has been found to contribute to the pathophysiology of athersclerosis, causing vasoconstriction, and accelerating atherogenesis. This finding--that there is a relative deficiency of L-arginine in atherosclerotic disease--is a breakthrough that will open new avenues of therapy.

Differential remodeling after balloon overstretch injury and either beta- or gamma-intracoronary radiation of porcine coronary arteries

BACKGROUND

Restenosis is a consequence of both neointimal hyperplasia and vessel remodeling. Prior studies have shown that intracoronary radiation (IR) prevents neointima accumulation, but its contribution to vessel remodeling is unknown. The purpose of this study was to evaluate the effect of IR on differential vascular remodeling after balloon angioplasty in porcine coronary arteries.

METHODS

A total of 20 juvenile swine (30 coronary arteries) were subjected to overstretch balloon injury (BI) followed by IR with either beta- or gamma-radiation ((90)Y or (192)Ir). After 2 weeks following treatment, serial tissue sections were perfusion fixed and stained by hematoxylin and eosin (H&E), Verhoeff von Giesson (VVG), or Masson Trichrome. Adventitial area (AA), lumen area (LA), vessel area (VA), intimal area (IA), and IA corrected for medial fracture length (IA/FL) were quantified by digital image analysis. The vessel circumference was divided into two regions containing (1) the undisrupted region (UReg) with the undisrupted arc of media and internal elastic lamina (IEL) and (2) the disrupted region (DReg) with the disrupted arc between the medial tears. Quantitative regional analysis was performed by (1) measuring the IEL to define the UReg, (2) calculating the area of the UReg with the perimeter value derived from measurement of the IEL, and (3) calculating the DReg as follows: LA+IA-UReg. Immunohistochemical smooth muscle cell alpha-actin and Masson Trichrome were quantified by digital image analysis.

RESULTS

The IA/FL was significantly smaller following treatment with (90)Y or (192)Ir vs. control (P<.01). A smaller AA was obtained following IR with both beta- and gamma-sources vs. control (P<.01). The UReg calculation was smaller in the irradiated arteries as compared to control (beta: 2.3+/-0.4 mm(2), gamma: 2.1+/-0.5 mm(2), P<.01 vs. control; control: 3.6+/-0.7 mm(2)). In contrast, the DReg was increased following IR, as demonstrated by the FL and the calculated area of the injured segment (control: 2.7+/-0.5 mm(2); beta: 5.5+/-1.1 mm(2), gamma: 5.5+/-1.1 mm(2), P<.01 vs. control). Adventitial alpha-actin positive cell density (CD) was decreased after IR; however, the collagen density was similar. In contrast, the neointimal collagen density in the injured segment was significantly decreased following IR.

CONCLUSION

We consider that the global arterial remodeling after IR is a heterogeneous process that includes the absence of retraction in an UReg and a positive remodeling in the DReg as shown in the porcine coronary model. These changes in adventitia and neointima appear to contribute to differential vascular remodeling caused by IR in injured vessels.

Effects of nitric oxide-releasing aspirin versus aspirin on restenosis in hypercholesterolemic mice

Restenosis is due to neointimal hyperplasia, which occurs in the coronary artery after percutaneous transluminal coronary angioplasty (PTCA). During restenosis, an impairment of nitric oxide (NO)-dependent pathways may occur. Concomitant hypercholesterolemia may exacerbate restenosis in patients undergoing PTCA. Here, we show that a NO-releasing aspirin derivative (NCX-4016) reduces the degree of restenosis after balloon angioplasty in low-density lipoprotein receptor-deficient mice and this effect is associated with reduced vascular smooth muscle cell (VSMC) proliferation and macrophage deposition at the site of injury. Drugs were administered following both therapeutic or preventive protocols. We demonstrate that NCX-4016 is effective both in prevention and treatment of restenosis in the presence of hypercholesterolemia. These data indicate that impairment of NO-dependent mechanisms may be involved in the development of restenosis in hypercholesterolemic mice. Although experimental models of restenosis may not reflect restenosis in humans in all details, we suggest that a NO-releasing aspirin derivative could be an effective drug in reducing restenosis following PTCA, especially in the presence of hypercholesterolemia and/or gastrointestinal damage.

Endothelial NO synthase overexpression inhibits lesion formation in mouse model of vascular remodeling

NO produced by endothelial NO synthase (eNOS) plays important roles in the regulation of vascular tone and structure. The purpose of this study was to clarify the role of eNOS-derived NO on vascular remodeling by use of eNOS-transgenic (eNOS-Tg) mice. The common carotid artery was ligated just proximal to the carotid bifurcation. Four weeks later, the proximal carotid artery of the ligation site was histologically examined. In this vascular remodeling model, the endothelium remains uninjured, but neointimal and medial thickening occurs in combination with a reduction in vascular diameter at the proximal portion of the ligation. At 4 weeks after ligation, the respective neointimal and medial areas in wild-type mice were 17 200+/-1100 and 24 300+/-1500 microm(2), whereas both were reduced to 8000+/-1900 (P:<0.01) and 18 400+/-700 microm(2) (P:<0.01) in eNOS-Tg mice (n=8). Total vascular area was not different between the 2 genotypes. N:(G)-Nitro-L-arginine methyl ester treatment increased neointimal and medial areas to the same extent in both genotypes. Leukocyte infiltration was observed in the luminal side of the vessel, but the number of infiltrating cells was significantly attenuated in eNOS-Tg mice compared with wild-type mice. This reduction of leukocyte infiltration in eNOS-Tg mice was associated with reduced expressions of intracellular adhesion molecule-1 and vascular cellular adhesion molecule-1 on the endothelium. In conclusion, chronic eNOS overexpression in the endothelium reduced leukocyte infiltration and inhibited neointimal formation and medial thickening. Our data provide the evidence for the regulatory role of NO from the endothelium on vascular structure integrity.

Nitric oxide and postangioplasty restenosis: pathological correlates and therapeutic potential

Balloon angioplasty revolutionized interventional cardiology as a nonsurgical procedure to clear a diseased artery of atherosclerotic blockage. Despite its procedural reliability, angioplasty's long-term outcome can be compromised by restenosis, the recurrence of arterial blockage in response to balloon-induced vascular trauma. Restenosis constitutes an important unmet medical need whose pathogenesis has yet to be understood fully and remains to be solved therapeutically. The radical biomediator, nitric oxide (NO), is a natural modulator of several processes contributing to postangioplasty restenosis. An arterial NO deficiency has been implicated in the establishment and progression of restenosis. Efforts to address the restenosis problem have included trials evaluating a wide range of NO-based interventions for their potential to inhibit balloon-induced arterial occlusion. All types of NO-based interventions yet investigated benefit at least one aspect of balloon injury to a naive vessel in a laboratory animal without inducing significant side effects. The extent to which this positive, albeit largely descriptive, body of experimental data can be translated into the clinic remains to be determined. Further insight into the pathogenesis of restenosis and the molecular mechanisms by which NO regulates vascular homeostasis would help bridge this gap. At present, NO supplementation represents a unique and potentially powerful approach to help control restenosis, either alone or as a pharmaceutical adjunct to a vascular device.

Does ADMA cause endothelial dysfunction?

Asymmetric dimethylarginine (ADMA) is an endogenous and competitive inhibitor of nitric oxide synthase. Plasma levels of this inhibitor are elevated in patients with atherosclerosis and in those with risk factors for atherosclerosis. In these patients, plasma ADMA levels are correlated with the severity of endothelial dysfunction and atherosclerosis. By inhibiting the production of nitric oxide, ADMA may impair blood flow, accelerate atherogenesis, and interfere with angiogenesis. ADMA may be a novel risk factor for vascular disease.

Endothelial cell delivery for cardiovascular therapy

Obstructive atherosclerotic vascular disease stands as one of the greatest public health threats in the world. While a number of therapies have been developed to combat vascular disease, endothelial cell delivery has emerged as a distinct therapeutic modality. In this article, we will review the anatomy of the normal blood vessel and the biology of the intact endothelium, focusing upon its centrality in vascular biology and control over the components of the vascular response to injury so as to understand better the motivation for a cell-based form of therapy. Our discussion of cell delivery for cardiovascular therapy will be divided into surgical and interventional approaches. We will briefly recount the development of artificial grafts for surgical vascular bypass before turning our attention towards endothelial cell seeded vascular grafts, in which endothelial cells effectively provide local delivery of endogenous endothelial secretory products to maintain prosthetic integrity after surgical implantation. New techniques in tissue and genetic engineering of vascular grafts and whole blood vessels will be presented. Methods for percutaneous interventions will be examined as well. We will evaluate results of endoluminal endothelial cell seeding for treatment of restenosis and gene therapy approaches to enhance endogenous re-endothelialization. Finally, we will examine some innovations in endothelial cell delivery that may lead to the development of endothelial cell implants as a novel therapy for controlling proliferative vascular arteriopathy.

Pathophysiology of atherosclerosis: development, regression, restenosis

There is now a very large number of patients with coronary artery disease who have also undergone percutaneous interventions such as coronary angioplasty. Atherosclerosis and restenosis are two distinct pathologic processes with different underlying pathophysiologic mechanisms, different natural histories, different clinical presentations, and treatment strategies. Management strategies to target both processes are currently poorly applied in clinical practice. The development of integrated management strategies to target atherosclerosis, as well as restenosis in the postprocedural period remains a priority.

The mechanisms of coronary restenosis: insights from experimental models

Since its introduction into clinical practice, more than 20 years ago, percutaneous transluminal coronary angioplasty (PTCA) has proven to be an effective, minimally invasive alternative to coronary artery bypass grafting (CABG). During this time there have been great improvements in the design of balloon catheters, operative procedures and adjuvant drug therapy, and this has resulted in low rates of primary failure and short-term complications. However, the potential benefits of angioplasty are diminished by the high rate of recurrent disease. Up to 40% of patients undergoing angioplasty develop clinically significant restenosis within a year of the procedure. Although the deployment of endovascular stents at the time of angioplasty improves the short-term outcome, 'in-stent' stenosis remains an enduring problem. In order to gain an insight into the mechanisms of restenosis, several experimental models of angioplasty have been developed. These have been used together with the tools provided by recent advances in molecular biology and catheter design to investigate restenosis in detail. It is now possible to deliver highly specific molecular antagonists, such as antisense gene sequences, to the site of injury. The knowledge provided by these studies may ultimately lead to novel forms of intervention. The present review is a synopsis of our current understanding of the pathological mechanisms of restenosis.

Pentoxifylline inhibits neointimal formation and stimulates constrictive vascular remodeling after arterial injury

Pentoxifylline (PTX) is a phosphodiesterase inhibitor used in the treatment of peripheral vascular disease, and this agent can suppress inflammatory vascular damage. Inflammation has been implicated in vascular lesion formation, and we examined the effects of PTX in a model of arterial injury. Sprague-Dawley rats were treated with intraperitoneal PTX (75 mg/kg/day) or saline starting 3 days before carotid balloon injury, and killed 24 h or 14 days later. Carotid arteries were analyzed by cross-sectional morphometry, immunostaining for proliferating cell nuclear antigen (PCNA) and subjected to terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling (TUNEL). Moreover, the effects of PTX on vascular smooth-muscle cell (VSMC) migration and production of collagen types I, IV, and VI were examined in vitro. At 14 days after balloon injury, PTX reduced the neointimal area (0.074+/-0.001 vs. 0.172+/-0.003 mm2; p<0.001), media area (0.143+/-0.001 vs. 0.176+/-0.001 mm2; p<0.01), intima/media ratio (0.50+/-0.02 vs. 0.99+/-0.12; p<0.001), and total vessel area (0.601+/-0.010 vs. 0.744+/-0.011 mm2; p<0.01). The lumen area, PCNA expression, and TUNEL were similar in the two treatment groups, whereas the neointimal cell density was increased by PTX (3,476+/-504 cells/mm2 vs. 2,215+/-232 cells/mm2; p<0.05). In vitro, PTX inhibited VSMC production of collagen type I in a concentration-dependent manner and did not influence VSMC migration. We conclude that PTX inhibits neointimal formation and induces constrictive vascular remodeling in the rat model of balloon injury by mechanisms involving decreased VSMC collagen type I production.