Growth factors in pathogenesis of coronary arterial restenosis

Dynamics and Functional Interplay of Nonhistone Lysine Crotonylome and Ubiquitylome in Vascular Smooth Muscle Cell Phenotypic Remodeling

Background

The crotonylation of histones is discovered of late as one of the post-translational modifications (PTMs) that can regulate gene expression. However, the function of crotonylation on nonhistone proteins in vascular smooth muscle cells (VSMCs) is unclear. Here, we aim to find the cellular characteristics of crotonylated nonhistone proteins and the cross talk with ubiquitinated proteins in VSMC phenotypic remodeling using the modified omics and proteomic analysis.

Methods

We performed the modified omics and proteomic analysis of VSMCs before and after the stimulation with platelet-derived growth factor-BB (PDGF-BB). The crotonylated and ubiquitinated pan-antibody was used to enrich proteins and then subjected to a high-throughput mass spectrometry analysis. The enrichment analysis was performed within differentially modified proteins in regard to GO terms, KEGG, and protein domains.

Results

As a result, there were 2,138 crotonylation sites in 534 proteins and 1,359 ubiquitination sites corresponding to 657 proteins. These crotonylated proteins detected after PDGF-BB stimulation might be involved in various vital cellular pathways and carry out important functions in VSMCs. Some of them closely took part in significant physiological processes of VSMC phenotypic remodeling, including glycolysis/gluconeogenesis, vascular smooth muscle contraction, and the PI3K-Akt signaling pathway. Furthermore, the KEGG pathway enrichment analysis showed the involvement of ubiquitinated proteins in the physiological processes of VSMC phenotypic remodeling, including glycolysis/gluconeogenesis, vascular smooth muscle contraction, RAS signaling pathway, or the PI3K-Akt signaling pathway. A cross talk analysis showed that there were 199 sites within the 177 proteins modified by crotonylation and ubiquitination simultaneously. Protein–protein interaction (PPI) network analysis indicated that crotonylated and ubiquitinated proteins play an important role in cellular bioprocess commonly and possibly have a synergistic effect.

Conclusion

In summary, our bioinformatics analysis shows that the crotonylation and ubiquitination of nonhistone proteins play an essential role in VSMC phenotypic transformation induced by PDGF-BB stimulation. The cross talk between crotonylation and ubiquitination in glycolysis is possibly a novel mechanism during VSMC phenotypic remodeling.

The Somatotropic Axis in the Sleep Apnea-Obesity Comorbid Duo

Background: Growth hormone (GH) stimulates the production of insulin-like growth factor 1 (IGF-1) in most tissues and together GH and IGF-1 profoundly impact adipose tissue deposition, glucose metabolism and cardiovascular function. A low serum IGF-I level has been reported as being associated with obstructive sleep apnea (OSA) and might be one of the mechanisms underlying cardio-metabolic risk in OSA patients. Methods: In a multicenter national study, 817 patients consulting for suspicion of OSA (OSA confirmed for 567 patients) underwent serum IGF-1 measurements. We analyzed the association between an IGF-1 level below the median value of the population and variables related to cardio-metabolic risk: body mass index (BMI) and waist circumference, apnea hypopnea index (AHI), cholesterol and triglycerides (expressed as median and divided into quartiles for continuous variables). Results: After adjustment for age and gender, low IGF-1 levels were associated with increased BMI and AHI (Odds ratios (OR) = 2.83; p < 0.0001 and OR = 3.03, p < 0.0001 for Quartile 4 vs. Quartile1, respectively), with elevated cholesterol levels (OR = 1.36, p = 0.0444), and elevated triglyceride levels (OR = 1.36; p = 0.0008). Conclusions: Both adiposity and sleep apnea synergistically predict low levels of IGF-1 and thus could together contribute toward cardio-metabolic risk. Further work are needed to confirm whether IGF-1 levels allow grading severity and predicting response to treatments to aim at a personalized medicine for patients suffering from OSA.

A rapamycin derivative, biolimus, preferentially activates autophagy in vascular smooth muscle cells

Although rapamycin is a well-known conformational inhibitor of mTORC1, it is now widely used for treating arterial restenosis. Various rapamycin analogues (rapalogue) have been made for applying to drug-eluting stents. Here we show that two major rapalogues, everolimus and biolimus, exert a differential effect on the mTORC1-mediated signaling pathways in vascular smooth muscle cells. In balloon-injured carotid arteries, both rapalogues strongly inhibit neointimal hyperplasia. Signaling pathway analyses reveal that everolimus exert cytotoxicity by increasing cellular reactive oxygen species and consequently reduce energy metabolism. By contrast, biolimus confers a preferential induction of autophagy by more strongly activating major autophagy regulator, ULK1, in vascular smooth muscle cells than everolimus does. As a consequence, the implantation of biolimus-eluting stent reduces endothelial loss, which in turn reduces inflammation, in porcine coronary arteries. Thus, this study reveals that a chemical derivatization can cause a change among mTORC1-dependent signaling pathways in vascular smooth muscle cells, thereby enabling to elicit a differential efficacy on arterial restenosis.

Transfer and Expression of the Interferon Gamma Gene in Human Endothelial Cells Inhibits Vascular Smooth Muscle Cell Growth in Vitro

Intimal hyperplasia in blood vessels is primarily caused by the migration and proliferation of vascular smooth muscle cells. Excessive intimal thickening characterizes atherosclerosis as well as bypass graft and angioplasty failures. Endothelial cell-smooth muscle cell interactions and local cytokine production are important regulators of smooth muscle cell growth. Interferon gamma (γ-IFN), a product of T lymphocytes found in atherosclerotic lesions, inhibits smooth muscle cell proliferation in vitro. To determine if local delivery of γ-IFN may be useful in the treatment or prevention of vascular proliferative diseases, we transferred the human γ-IFN gene into endothelial cells isolated from human arteries and microvessels using a retroviral vector. Biologically active γ-IFN was produced and secreted by γ-IFN transduced endothelial cells, but not by control, nontransduced cells, or cells identically transduced with E. coli beta galactosidase (β-gal). To more closely approximate the microenvironment of blood vessels, subconfluent smooth muscle cells were plated in coculture with control, nontransduced endothelial cells, γ-IFN transduced endothelial cells, or β-gal transduced endothelial cells. Smooth muscle cell growth was inhibited 30-70% by coculture with γ-IFN transduced endothelial cells compared to coculture with β-gal transduced or control endothelial cells (p < 0.05). Our results suggest endothelial cells modified to produce γ-IFN may be a useful therapy in proliferative vascular diseases. Copyright © 1997 Elsevier Science Inc.

Blood Pressure Levels at the Time of Percutaneous Coronary Revascularization and Risk of Coronary In-Stent Restenosis

BACKGROUND

High blood pressure (BP) levels expose patients treated with percutaneous coronary interventions (PCI) to very high risk of 10-year cardiovascular morbidity and mortality.

OBJECTIVE

To investigate the role of BP levels at the time of PCI on the risk of in-stent restenosis (ISR).

METHODS

We retrospectively included 796 patients previously treated with PCI, who underwent repeated angiography for recurrent angina or reversible myocardial ischemia. Patients were stratified into either case (n = 354) and control (n = 442) groups in the presence or absence of ISR (defined as in-stent diameter stenosis ≥50%). BP levels were measured at the time of first and second procedures. Normal BP levels were defined for <140/90 mm Hg.

RESULTS

Patients with normal BP showed significantly higher ISR-free survival (Log-rank: 5.937; P = 0.015). Both systolic (HR (95% CI): 0.731 (0.590-0.906)) and systolic/diastolic BP (HR (95% CI): 0.757 (0.611-0.939)) were significantly and independently associated with lower risk of ISR at Cox-regression analysis, adjusted for potential confounding factors, including stent type and concomitant medications. Patients with ISR showed lower rates of normal systolic/diastolic BP values (166 (47%) vs. 254 (57%); P = 0.003) compared to controls. They also received higher stent number (1.40±0.74 vs. 1.24±0.51; P < 0.001) with higher stent length (24.3±15.6 vs. 21.7±13.9 mm; P = 0.012), and lower rate of drug-eluting stents (DESs) (210 (48%) vs. 139 (40%); P = 0.025) compared to controls.

CONCLUSIONS

Normal BP at the time of PCI is associated with nearly 24% risk reduction of ISR as evaluated in a new angiography in patients with coronary artery disease.

Reversion-inducing-cysteine-rich protein with Kazal motif is involved in intimal hyperplasia in carotid arteries: a new insight in the prevention of restenosis after vascular angioplasty

BACKGROUND

Overexpression of matrix metalloproteinase (MMP) has been implicated in the incidence of restenosis after vascular angioplasty. Reversion-inducing cysteine-rich protein with kazal motifs (RECK) is a membrane-anchored glycoprotein that negatively regulates the activity of MMPs, such as MMP-9 and MMP-2, which play a key role in the angiogenesis during tumor growth. This study was designed to investigate the potential association between RECK and restenosis after vascular angioplasty.

METHODS

Balloon-injured rabbit carotid arterial models were established. Arterial morphology was assessed by hematoxylin-eosin staining. The area of intimal hyperplasia was measured using image microscopy and image analyzer. The messenger RNA (mRNA) expression levels of RECK, MMP-9, and MMP-2 were detected using reverse transcription-polymerase chain reaction (RT-PCR) at 7, 14, and 21 days. Vascular smooth muscle cells (VSMCs) were transfected with RECK small interfering RNA (siRNA). VSMC proliferation rate was detected by MTT assay at 24, 48 and 72 hr. The protein expression of RECK, MMP-9, and MMP-2 was determined by Western blot.

RESULTS

MMP-2 and MMP-9 in carotid artery of rats were significantly overexpressed in the injured-artery group, compared with unmanipulated control and contralateral uninjured groups (P < 0.05). With the time of the injury extended, MMP-2 and MMP-9 mRNA levels gradually increased. RECK showed a marked peak of mRNA level at 7 days after injury, compared with unmanipulated control and contralateral uninjured groups (P < 0.001). However, the increasing trend gradually decreased at 14 days after the balloon surgery. RECK mRNA was still detectable at 21 days postoperatively, but the expression level of RECK mRNA in injured and contralateral uninjured groups was significantly lower than that in unmanipulated control group (P < 0.001). The expression level of RECK protein in VSMCs in transfected group was significantly lower compared with that in untransfected group, whereas the expression of MMP-2 and MMP-9 proteins in transfected group was significantly higher compared with that in untransfected group. Over the extension of transfection time, the proliferation of VSMCs in transfected group was increased gradually, compared with negative and blank plasmid controls (P < 0.05).

CONCLUSIONS

RECK, as siRNA-mediated RECK silencing regulation of MMP-9 and MMP-2, plays an important role in intimal hyperplasia, which provides a new target for prevention and treatment of restenosis after vascular angioplasty.

Role of insulin-like growth factor 1 in stent thrombosis under effective dual antiplatelet therapy

Introduction

Accumulating evidence now indicates that insulin-like growth factors (IGF) and their regulatory proteins are growth promoters for arterial cells and mediators of cardiovascular diseases.

Aim

We hypothetised that IGF-1 levels could play a role in the development of stent thrombosis (ST), and aimed to investigate the associations between stent thrombosis under effective dual antiplatelet therapy and IGF-1 levels and other related factors such as disease severity and LV ejection fraction in patients undergoing coronary stent placement.

Material and methods

A total of 128 patients undergoing coronary stent implantation were included in the analysis. Seventy-seven patients experiencing ST in the first year after stent implantation were defined as the ST group. Fifty-one patients without ST at least 1 year after stent implantation were defined as the no-thrombosis (NT) group. The IGF-1 levels, Gensini scores, and other related factors were measured.

Results

The IGF-1 levels were significantly higher in the stent thrombosis group than in the no-thrombosis group (122.22 ±50.61 ng/ml vs. 99.52 ±46.81 ng/ml, respectively, p < 0.039). The left ventricle ejection fraction (LVEF) values were significantly lower (44.13 ±9.25% vs. 55.81 ±8.77%, p < 0.0001) and Gensini scores were significantly higher (63.74 ±26.54 vs. 48.87 ±23.7, p < 0.004) in the ST group than in the NT group, respectively. In the linear regression analysis, IGF-1, Gensini score, LVEF, total cholesterol, and triglycerides were found to be independent risk factors for ST.

Conclusions

This study revealed that the plasma IGF-1 levels, disease severity, were significantly higher and LVEF was lower in patients with ST. High IGF-1 levels may identify patients who are at increased risk for ST. Future trials are necessary to confirm these results.

Location-dependent coronary artery diffusive and convective mass transport properties of a lipophilic drug surrogate measured using nonlinear microscopy

PURPOSE

Arterial wall mass transport properties dictate local distribution of biomolecules or locally delivered dugs. Knowing how these properties vary between coronary artery locations could provide insight into how therapy efficacy is altered between arterial locations.

METHODS

We introduced an indocarbocyanine drug surrogate to the lumens of left anterior descending and right coronary (LADC; RC) arteries from pigs with or without a pressure gradient. Interstitial fluorescent intensity was measured on live samples with multiphoton microscopy. We also measured binding to porcine coronary SMCs in monoculture.

RESULTS

Diffusive transport constants peaked in the middle sections of the LADC and RC arteries by 2.09 and 2.04 times, respectively, compared to the proximal and distal segments. There was no statistical difference between the average diffusivity value between LADC and RC arteries. The convection coefficients had an upward trend down each artery, with the RC being higher than the LADC by 3.89 times.

CONCLUSIONS

This study demonstrates that the convective and diffusive transport of lipophilic molecules changes between the LADC and the RC arteries as well as along their length. These results may have important implications in optimizing drug delivery for the treatment of coronary artery disease.

A proteomic approach to the investigation of early events involved in the activation of vascular smooth muscle cells

Vascular smooth muscle cells (VSMC) are mature cells that maintain great plasticity. This distinctive quality is the basis of the migration and proliferation of VSMC in cardiovascular diseases. We have investigated, via a proteomic approach, the molecular changes that promote VSMC switching from a quiescent to an activated-proliferating phenotype. In particular, we focus on the modulation in tyrosine phosphorylation that occurs in cell activation by serum or by single growth factors, such as insulin-like growth factor 1 (IGF-1) or platelet-derived growth factor (PDGF-BB). A comparison of profiles from two-dimensional polyacrylamide gel electrophoresis analysis of quiescent and activated-proliferating VSMC has revealed a number of differences in protein expression. Several differentially expressed proteins have been identified by mass spectrometry, and their changes during the time course of tyrosine phosphorylation have been documented from time zero up to 48 h after stimulus. The tyrosine-phosphorylation level generally decreases within a few minutes of stimulation, followed by a rapid dramatic recovery of some chaperones and redox enzymes, but no significant recovery for glucose metabolism enzymes. With respect to cytoskeleton components, no remarkable fluctuations have been detected at the earliest time points, except for those relating to alpha-actin, which displays an impressive decrease. A comparison of the early stages of cell stimulation after serum or after single growth factor administration has revealed important differences in the phosphorylation of chaperones, thereby suggesting their crucial role in VSMC activation.

A proteomic approach to the investigation of early events involved in vascular smooth muscle cell activation

Vascular smooth muscle cells (VSMC) are mature cells that maintain great plasticity. This distinctive feature is the basis of the VSMC migration and proliferation involved in cardiovascular diseases. We have used a proteomic approach to the molecular changes that promote the switch of VSMC from having a quiescent to activated-proliferating phenotype. In particular, we have focused on modulations occurring during tyrosine-phosphorylation following cell activation by serum or single growth factors, such as insulin-like growth factor 1 or platelet-derived growth factor. A comparison of two-dimensional polyacrylamide gel profiles from quiescent or activated-proliferating VSMC has allowed us to recognize a number of differences in protein expression. Several differentially expressed proteins have been identified by mass spectrometry, and their time-course changes during tyrosine-phosphorylation have been documented from time zero till 48 h after stimulation. We have documented a general decrease of the tyrosine-phosphorylation level within the first few minutes after stimulation followed by a recovery that is quick and dramatic for some chaperones and redox enzymes but not so significant for enzymes of glucose metabolism. With regard to cytoskeleton components, no remarkable fluctuations have been detected at the earliest time points, except for those relative to alpha-actin, which displays an impressive decrease. A comparison of the early stages of cell stimulation after the administration of serum or single growth factors has brought to light important differences in the phosphorylation of chaperones, thereby suggesting their crucial role in VSMC activation.

In stent restenosis: bane of the stent era

The long term outcome of stent implantation is affected by a process called in stent restenosis (ISR). Multiple contributory factors have been identified, but clear understanding of the overall underlying mechanism remains an enigma. ISR progresses through several different phases and involves numerous cellular and molecular constituents. Platelets and macrophages play a central role via vascular smooth muscle cell migration and proliferation in the intima to produce neointimal hyperplasia, which is pathognomic of ISR. Increased extracellular matrix formation appears to form the bulk of the neointimal hyperplasia tissue. Emerging evidence of the role of inflammatory cytokines and suppressors of cytokine signalling make this an exciting and novel field of antirestenosis research. Activation of Akt pathway triggered by mechanical stretch may also be a contributory factor to ISR formation. Prevention of ISR appears to be a multipronged attack as no therapeutic "magic bullet" exists to block all the processes in one go.

Cells, cytokines and cellular immunity in the pathogenesis of fibroproliferative vasculopathies

Atherosclerosis and restenosis are the result of vascular injury followed by an inflammatory and fibroproliferative response that involves a large number of growth factors, cytokines, and cellular elements. Platelet activation and leukocyte recruitment into the arterial intima play a crucial role, initiating a whole spectrum of reactions leading to vascular smooth muscle cell hyperplasia and intimal migration. The roles of macrophages and lymphocytes and mast cells as mediators of inflammation and immune response is discussed, as are the roles of growth factors and cytokines. New light on the 'old' problems will help us to devise newer and better therapeutic strategies to combat these clinical entities.

Associations of insulin-like growth factors, insulin-like growth factor binding proteins and acid-labile subunit with coronary heart disease

OBJECTIVE

IGFs and their binding proteins (IGFBPs) are produced both systemically and locally by cells of the cardiovascular system. As growth promoters, they may play a role in atherosclerosis.

DESIGN

Case-control, cross-sectional.

PATIENTS

A total of 95 nondiabetic male patients with coronary heart disease (CHD) and 92 probands from the Prospective Cardiovascular Munster (PROCAM) who were below the age of 60 years and matched by age, body mass index (BMI) and smoking habits.

MEASUREMENTS

We analysed the strength and independence of associations of angiographically assessed presence of CHD with BMI, systolic and diastolic blood pressure, total, high-density lipoprotein (HDL) and LDL cholesterol, triglycerides, lipoprotein(a), apolipoproteins A-I and B, total and free IGF-I, IGF-II, IGFBP-1, IGFBP-3, IGFBP-5, acid-labile subunit (ALS), insulin, C-peptide, testosterone, DHEAS and sex hormone binding globulin.

RESULTS

Using multivariate statistical analysis, the presence of CHD had significant positive associations with total IGF-I, IGFBP-5, ALS and IGFBP-3. These associations were independent of each other as well as of traditional risk factors, insulin and sex hormones.

CONCLUSION

These observations may indicate a pathogenetic role of the GH/IGF axis in coronary atherosclerosis.

Role of E2F and ERK1/2 in STI571-mediated smooth muscle cell growth arrest and cyclin A transcriptional repression

Platelet-derived growth factor (PDGF) ligand and receptors (PDGF-R) activate smooth muscle cell (SMC) proliferation, a key event during vascular obstructive disease. The PDGF-R tyrosine kinase inhibitor STI571 attenuates SMC proliferation and experimental neointimal thickening. Here, we investigated the molecular mechanisms underlying STI571-dependent SMC growth arrest. STI571 abrogates PDGF-BB-dependent cyclin D1 and cyclin A protein expression and inhibits transcriptional activation of reporter genes driven by the human cyclin A gene promoter. Repression of cyclin A promoter activity by STI571 requires a functional E2F-binding site, and forced expression of E2F overrides this inhibitory effect. Moreover, STI571 inhibits E2F DNA-binding activity in SMCs. We also found that STI571 abrogates PDGF-BB-dependent activation of extracellular-regulated kinase 1 and 2 (ERK1/2), and forced activation of these factors impaired STI571-dependent inhibition of both cyclin A promoter activity and SMC proliferation. Thus, E2F and ERK1/2 play an important role in STI571-mediated SMC growth arrest and cyclin A transcriptional repression. These findings may have importance in the development of novel therapeutic strategies for the treatment of neointimal hyperplasia.

Assessment of subacute inflammatory and proliferative response to coronary stenting in a porcine model by local gene expression studies and histomorphometry

The aim of the study was to analyse inflammatory and proliferative response early after coronary stenting by angiography, histomorphometry and local gene expression analysis using quantitative rt-PCR. Therefore, eight German domestic pigs underwent stenting of the left coronary artery. Selective coronary angiography was performed after 14 days. Explanted coronary arteries were examined histomorphometrically after methacrylate-embedding. Snap-frozen samples were examined for local gene expression of TGF-beta, TNF-alpha, GM-CSF, VEGF, PDGF and Fas Ligand (FasL) by real-time quantitative rt-PCR normalized to the housekeeping gene GAPDH and compared to unstented coronary arteries. All stented coronaries were patent with only little neointima formation. The median vessel diameter was 2.55 mm (range 2.43-2.68 mm). Histopathology revealed little inflammatory response limited to the tissue surrounding the stent struts; luminal area ranged from 84% to 91%. Compared to unstented control arteries, no significant differences in local gene expression were detected for VEGF, PDGF, TGF-beta, TNF-alpha and GM-CSF. Expression of FasL was upregulated as little as 1.7-fold (p=0.01). We conclude that, in native coronary arteries, no significant upregulation of investigated genes regulating vascular remodelling, inflammation or fibrogenesis was demonstrated 14 days after stenting. Whether upregulation of FasL as a marker gene of apoptosis is transient and biological significant requires further investigation.

Inhibition of aortic allograft vasculopathy by local delivery of platelet-derived growth factor receptor tyrosine-kinase blocker AG-1295

BACKGROUND

Signal transduction through the platelet-derived growth factor (PDGF)/PDGF-receptor (PDGFR) system has been linked to vascular smooth muscle cell migration and proliferation leading to allograft vasculopathy. This study describes the effect of the tyrphostin AG-1295, a specific PDGFR tyrosine-kinase inhibitor, on neointimal formation in this disease.

METHODS AND RESULTS

Rat aortic allografts transplanted from dark agouti (RT1 ) donors to Wistar-Furth (RT1 ) recipients were assessed in a new treatment model for local drug delivery from polymeric carrier matrices precoated with AG-1295. Matrices were wrapped around the graft immediately after transplantation. The recipients received no background immunosuppression. At day 80 posttransplantation, intimal thickness in AG-1295-treated grafts was reduced when compared to controls (11.8+/-9.1% intimal thickness vs. 23.7+/-6.4% intimal thickness; P=0.042). This finding corresponded to inhibition of intimal PDGFR-beta expression in AG-1295-treated grafts at day 20 posttransplantation (P =0.029 vs. allogeneic controls).

CONCLUSIONS

The tyrphostin AG-1295 reduces neointimal formation in aortic allograft vasculopathy by inhibition of PDGFR-beta-triggered tyrosine phosphorylation. Local drug release of specific tyrosine-kinase inhibitors from perivascularly co-implanted polymeric carrier matrices is effective in the prophylaxis of allograft vasculopathy under selected experimental conditions.

Prevention of experimental myointimal hyperplasia by immunomodulation

INTRODUCTION

we have tested the hypothesis that treatment with a mycobacterial preparation that modulates the antibody response, would diminish restenosis in a rat angioplasty model.

MATERIALS/METHODS

male Sprague-Dawley rats were used. All immunisations were given subcutaneously. Group A (control) received normal saline on days 0, 21, and 42. Group B received SRL172 on days 0, 21, and 42. Group C received SRL172 on days 0, 21, and 42, and hsp65/Incomplete Freund's on days 21 and 42. Group D received hsp65/Freund's on days 21 and 42. Right common carotid arteries were balloon-injured on day 63 using a standard technique known to produce MIH and animals were sacrificed on day 77. For each carotid 6 microm cross sections were cut from paraffin blocks. Cross-sectional areas were measured by computerised planimetry.

RESULTS

balloon injury resulted in MIH in all animals. Data represents mean+/-SEM for the percentage of area enclosed within the internal elastic lamina occupied by MIH (% MIH); which for groups A, B, C, and D was 85+/-11, 24+/-3, 27+/-7, and 17+/-3 respectively. All the treatment groups had significantly less MIH when compared to the control group but no statistically significant difference was found between any of the treatment groups.

CONCLUSIONS

this is the first report that immunomodulation with mycobacterial material suitable for use in man, can reduce MIH. Since such modulation has low risk, this raises the prospect of an important new therapeutic modality to combat restenosis.

Activation of mitogenic and antimitogenic pathways in cyclically stretched arterial smooth muscle

Biophysical forces regulate vascular smooth muscle cell (VSMC) physiology and evoke vascular remodeling. Two VSMC autocrine molecules, insulin-like growth factor I (IGF-I) and nitric oxide (NO), are implicated in remodeling attributable to VSMC hyperplasia. We investigated the role of in vitro cyclic stretch on rat VSMC IGF-I, NO, and cellular growth. Cyclic stretch (1 Hz at 120% resting length for 48 h) stimulated VSMC proliferation 2.5-fold vs. unstretched cells and was accompanied by a 1.8-fold increase in VSMC IGF-I secretion. Despite activation of this proliferative pathway, cyclic stretch induced inducible (i) nitric oxide synthase (NOS) expression and a twofold increase in NO secretion, a molecule with documented antiproliferative effects. Cytokine treatment enhanced iNOS expression and NO secretion while inhibiting vascular growth by approximately 50% in static cells. Cytokine treatment of stretched VSMC enhanced NO secretion 2.5-fold while inhibiting growth by approximately 80%. Exogenous IGF-I increased NOS activity 1.5-fold and NO secretion 8.5-fold in static cells. In turn, iNOS inhibition increased IGF-I secretion 1.6-fold and enhanced VSMC growth 1.6-fold in stretched cells. An NO donor (sodium nitroprusside) similarly inhibited VSMC proliferation in static (24%) and stretched (50%) VSMC while also inhibiting IGF-I secretion from stretched cells by approximately 35%. Thus cyclic stretch stimulates mitogenic (IGF-I) and antimitogenic (NO) pathways in VSMC. These two molecules regulate each other's secretory rates, providing tight regulation of VSMC proliferation. These data may have profound implications in understanding vascular growth alterations in vascular injury and hypertension.

The insulin-like growth factor axis: A review of atherosclerosis and restenosis

Insulin-like growth factors I and II (IGF-I and -II) and their regulatory proteins are secreted by cells of the cardiovascular system. They are growth promoters for arterial cells and mediators of cardiovascular disease. IGFs are bound to IGF binding proteins (IGFBPs), which modulate IGF ligand-receptor interaction and consequently to IGF action. IGFBPs are in turn posttranslationally modulated by specific proteases. This dynamic balance (IGFs, IGFBPs, and IGFBP proteases) constitutes the IGF axis and ultimately determines the extent of IGF-dependent cellular effects. Dysregulated actions of this axis influence coronary atherosclerosis through effects on vascular smooth muscle cell growth, migration, and extracellular matrix synthesis in the atherosclerotic plaque. IGF-I promotes macrophage chemotaxis, excess LDL cholesterol uptake, and release of proinflammatory cytokines. Endothelial cells also receive the effects of IGFs stimulating their migration and organization forming capillary networks. Neointimal hyperplasia of restenosis after coronary artery injury is also modulated by the IGF axis. IGFs stimulate vascular smooth muscle cell proliferation and migration to form the neointima and upregulate tropoelastin synthesis after disruption of the elastic layer. Understanding IGF axis regulation establishes a scientific basis for strategies directed to limit or reverse plaque growth and vulnerability in atherosclerosis and in the neointimal hyperplasia of restenosis.

Cyclic stretch regulates autocrine IGF-I in vascular smooth muscle cells: implications in vascular hyperplasia

Vascular smooth muscle cells (VSMC) subjected to acute or chronic stretch display enhanced growth rates in vitro and in vivo. Clinical examples of vascular hyperplasia (e.g., systolic hypertension and postinjury restenosis) suggest that local insulin-like growth factor I (IGF-I) expression is enhanced. Therefore, we investigated the role of in vitro cyclic stretch on rat VSMC IGF-I secretion and cellular growth. In serum-free medium, cyclic stretch (1 Hz at 120% resting length for 48 h) stimulated thymidine incorporation approximately 40% above that seen in nonstretched cells. Graded stretch magnitude (100-125% resting length) yielded graded increases in VSMC growth. Exogenous IGF-I increased growth of serum-starved, nonstretched VSMC in a dose-dependent manner, with maximal growth seen with 10(-7) M. IGF-I secretion from stretched cells was 20- to 30-fold greater than from those cells cultured in a static environment. Stretch-induced increases in growth were completely blocked on addition of anti-IGF-I and partially blocked with platelet-derived growth factor (PDGF) antibodies and with a tyrosine kinase inhibitor (tyrphostin-1). Finally, blockade of stretch-activated cation channels with GdCl3 profoundly inhibited stretch-induced growth. We conclude that stretch increases VSMC IGF-I secretion and that such autocrine IGF-I is required for stretch-induced growth. PDGF and stretch-sensitive cation channels are likely additional components of a complex pathway that regulates stretch-induced VSMC seen in systolic hypertension and postinjury restenosis.

Enhanced secretion of insulin plays a role in the development of atherosclerosis and restenosis of coronary arteries: elective percutaneous transluminal coronary angioplasty in patients with effort angina

OBJECTIVES

We investigated the relation between insulin and coronary atherosclerosis and restenosis of the coronary arteries, by performing elective percutaneous transluminal coronary angioplasty (PTCA).

BACKGROUND

Insulin is known to promote atherosclerosis of the arteries and has been implicated in the development of restenosis after PTCA.

METHODS

Of 210 angina patients who underwent PTCA, newly detected lesions in 35 consecutive nondiabetic subjects without previous intervention on the same main coronary arteries were analyzed after a 75-g oral glucose tolerance test (OGTT) and follow-up coronary angiography. Atherosclerotic lesions were evaluated by pattern, severity and extent. Restenosis was defined as loss of gain, the percentage of loss of the initial gain in the coronary diameter achieved by PTCA > or = 50%.

RESULTS

Patients with restenosis had a significantly higher extent index (a marker of atherosclerosis), insulin area, ratio of insulin area to glucose area, insulinogenic index and minimal lumen diameter after PTCA than those without restenosis (p=0.001, 0.011, 0.002, 0.016 and 0.041, respectively). Simple regression analysis revealed that only the ratio of insulin area to glucose area (a relative marker of enhanced insulin secretion) significantly correlated with the extent index (p=0.035). Extent index, insulin area, the ratio of insulin area to glucose area and insulinogenic index significantly correlated with loss of gain (p=0.001, 0.010, 0.002 and 0.032, respectively). Stepwise multiple regression analyses revealed that extent index and the ratio of insulin area to glucose area significantly correlated with loss of gain.

CONCLUSIONS

Enhanced secretion of insulin during the OGTT might be useful as a predictor of coronary atherosclerosis and of restenosis after elective PTCA in nondiabetic patients with effort angina.

Response of vascular smooth muscle cells to the neuropeptide secretoneurin. A functional role for migration and proliferation in vitro

Mesenchymal cell migration and replication are central biologic events involved in atherosclerosis and lung and hepatic fibrosis. Tissue repair and fibrosis are thought to be regulated by growth regulatory molecules, comprising both stimulators and inhibitors of mesenchymal cell functions, including platelet-derived growth factor (PDGF), transforming growth factor-beta (TGF-beta), fibroblast growth factors, and several neuropeptides such as substance P. Secretoneurin (SN), a novel 33-amino acid neuropeptide derived from secretogranin II (chromogranin C), is widely distributed in the central and peripheral nervous and neuroendocrine systems, including afferent C-fibers, and can be released in the periphery by capsaicin. Recently, we reported that SN triggers the selective migration of human monocytes and fibroblasts in vitro, implicating its involvement in inflammatory responses. We report herein that SN stimulates specific migration (maximal response at 10(-10) M) of cultured arterial smooth muscle cells (SMCs), originating from rat thoracic aorta, and initiates DNA synthesis and SMC growth (BrdU incorporation, MTT test) with a maximum at 10(-8) M SN to a similar extent as observed by PDGF. Both functional activities of SN were inhibited by specific anti-SN immunoglobulins (dilution, 1:1000), and furthermore, a trypsinized SN peptide (10(-8) M) was unable to provoke biologic effects. Our studies suggest that SN functions as a regulatory peptide to modulate SMC migration and proliferation, which in conjunction with other factors could serve to aggravate and accelerate the development of atherosclerotic or restenotic lesions at sites of vascular injury.

Phosphorylation site-specific inhibition of platelet-derived growth factor beta-receptor autophosphorylation by the receptor blocking tyrphostin AG1296

The mechanism of action of AG1296, a potent and specific inhibitor of the platelet-derived growth factor (PDGF) receptor tyrosine kinase [Kovalenko, M., Gazit, A., Böhmer, A., Rorsman, Ch., Rönnstrand, L., Heldin, C.-H., Waltenberger, J., Böhmer, F. D., & Levitzki, A. (1994) Cancer Res. 54, 6106-6114] was investigated. This quinoxalin-type tyrphostin neither interferes with PDGF-BB binding to the PDGF beta-receptor nor has any effect on receptor dimerization. Kinetic analysis of the inhibition was carried out using a synthetic peptide substrate (KY751) corresponding to the sequence around tyrosine 751 autophosphorylation site of the PDGF receptor. It revealed purely competitive inhibition vis-à-vis ATP, mixed competitive inhibition vis-a-vis the peptide substrate for the non-activated receptor, and mixed competitive inhibition vis-à-vis both substrates for the activated receptor. Thus, the type of inhibition apparently changes upon receptor activation, indicating conformational changes at the ATP-binding site. The high degree of selectivity for the tyrphostin AG1296 might result from the complex type of interaction with the active center of the receptor as revealed by the kinetic analysis. Dose-response curves for inhibition of the phosphorylation of individual autophosphorylation sites of the PDGF beta-receptor by AG1296 were different, phosphorylation of tyrosine 857 being the most susceptible to inhibition. Thus, phosphorylation of tyrosine 857 in the PDGF receptor kinase domain seems dispensable for partial kinase activation. The findings are discussed in relation to current models of receptor tyrosine kinase activation.

Lanreotide reduces serum free and total insulin-like growth factor-I after angioplasty

BACKGROUND

Several experiments point to a participating role of insulin-like growth factor-I (IGF-I) in the vascular events leading to restenosis after percutaneous transluminal coronary angioplasty (PTCA).

METHODS AND RESULTS

We measured fasting serum total (extractable) IGF-I in 553 patients in a controlled clinical trial. Half of the patients received continuous subcutaneous infusion of the somatostatin analogue lanreotide from the day before (baseline) and for 4 days after PTCA. We also measured ultrafiltrated serum free IGF-I and IGF-II, total IGF-II, IGF-binding protein-1 (IGFBP-1), IGFBP-3, and insulin in a subgroup of 18 placebo-treated and 20 lanreotide-treated patients. Total IGF-I had decreased by 7% (P < .0001) 1 day after initiation of lanreotide infusion and stayed reduced, whereas no early changes occurred in placebo-treated patients. The same pattern was observed in the subgroup. Free IGF-I decreased significantly from baseline by 22% to 27% (P < .05) in lanreotide-treated patients and increased insignificantly by 10% to 30% (P = .054) in placebo-treated patients. IGFBP-1 increased (P < .05) in both groups postoperatively, but levels in lanreotide-treated patients exceeded (P < .05) those of placebo-treated patients. Lanreotide treatment resulted in minor reductions (P < .05) in free and total IGF-II and IGFBP-3, whereas insulin was unaltered.

CONCLUSIONS

Lanreotide administration acutely decreases circulating total and free IGF-I, the latter relatively more, and increases IGFBP-1. These alterations in the IGF system may participate in the improvement of the long-term outcome after PTCA noted with lanreotide treatment.

Somatostatin, growth hormone, insulin-like growth factor-1, and diabetes: friends or foes?

Major findings with regard to the somatostatin-growth hormone (GH)-insulin-like growth factor (IGF-1) axis and diabetes are summarized. GH hypersecretion and reduced circulating IGF-1 levels are prevalent in insulin-dependent diabetes. Somatostatin improves metabolism in insulin-dependent diabetics. Insulin resistance and poor metabolic regulation, which may partly be due to hypersecretion of GH, are believed to accelerate the development of diabetic angiopathy. Diabetic hypersomatotrophinemia may be due to hepatic resistance to GH and increased hepatic production of IGF-1-binding protein-1 (IGFBP-1), leading to reduced levels of circulating IGF-1 and further stimulation of GH production. Studies in vitro and in diabetics suggest a causal link between diabetic hypersomatotrophinemia and diabetic angiopathy. In vitro evidence for the involvement of IGF-1 in diabetic angiopathy is reviewed. Also reviewed is evidence, from rat and human studies, of the possible involvement of GH and IGF-1 in diabetic nephropathy. The role of somatostatin in late diabetic vascular complications remains to be elucidated.

Prevention of intimal hyperplasia by irradiation. An experimental study in rabbits

PURPOSE

This experimental study was designed to investigate the effect of irradiation in prevention of intimal hyperplasia.

MATERIAL AND METHODS

Twenty rabbits were divided into 4 groups, which were irradiated with 2, 5, 10 and 20 Gy, respectively. The intima of both femoral arteries was injured by air-drying, and irradiation was performed on the unilateral side. The contralateral+ femoral artery served as a control. Angiograms as well as histologic specimens were obtained 1 month later.

RESULTS

Marked intimal hyperplasia was observed in all control sites. There were no significant differences in thickness of intimal hyperplasia between irradiated and control sites in groups irradiated with 2 and 5 Gy. However, in the 10-Gy- and 20-Gy-irradiated groups, intimal hyperplasia of the irradiated site was significantly suppressed. Medial thinning and dilation of the lumen were observed in the 20-Gy-irradiated group.

CONCLUSION

Radiation may prevent intimal hyperplasia. Further investigation of the optimal dose, timing of irradiation, and long-term patency of irradiated vessels may be needed.

A morphological study of the long-term repair process in experimentally stretched but unruptured arteries and veins

As many avulsion amputations are incomplete and the vessels remain intact, the immediate pathology and long-term repair process (to 3 months post-injury) of experimentally stretched but unruptured rabbit femoral arteries and veins were examined. In stretched arteries, circumferential skip lesions involving endothelium, internal elastic lamina (IEL) and media occurred frequently and often up to 3 cm from the point of stretch. Medial smooth muscle cells (SMC) were significantly damaged or lost at lesions. Macrophages and neutrophils were found in lesions 1-4 days post-injury. Between 2-4 days, lesions were covered by endothelium and synthetic state SMC appeared in the media. At 1 week, a thin neointima (which persisted to 3 months) covered many lesions. The media at lesions gradually filled with SMC but generally remained disorganised even at 3 months post-injury. Stretching caused tears in vein walls, particularly close to the point of injury. There was no evidence of venous damage or repair in specimens examined 3 weeks and 3 months post-injury.

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.

Local delivery of an antiproliferative drug with use of hydrogel-coated angioplasty balloons

PURPOSE

To determine the feasibility of using hydrogel-coated angioplasty balloons to deliver drugs that inhibit vascular smooth muscle cell (VSMC) proliferation.

MATERIALS AND METHODS

In initial experiments, the tyrphostin RG-50872 (1 mumol/L) completely inhibited VSMC proliferation induced by platelet-derived growth factor (PDGF) in vitro when RG-50872 treatment preceeded PDGF exposure by 15 minutes. This inhibition was reversible and was not due to cell toxicity. In further experiments, hydrogel-coated and silicone-coated angioplasty balloons (2.5 mm in diameter by 20 mm in length) were coated with either 10 microL of RG-50872 (40 mmol/L in dimethyl sulfoxide [DMSO]) or DMSO vehicle, or were left uncoated. Afterward, each angioplasty balloon was inflated, submerged in 50 mL of culture media, and agitated for 2 minutes to promote drug release. Dilutions of this media were tested for their ability to inhibit VSMC proliferation.

RESULTS

All hydrogel-coated balloons (n = 5) released sufficient RG-50872 to inhibit PDGF-induced VSMC proliferation by 95% or more, whereas none of the silicone-coated balloons (n = 4) did. DMSO-treated and untreated balloons had no effect on proliferation.

CONCLUSION

These findings demonstrate that the hydrogel-coating on angioplasty balloons can take up and release sufficient RG-50872 to significantly inhibit smooth muscle cell proliferation. Further in vivo experiments are needed to determine if hydrogel-coated balloons can deliver sufficient RG-50872 to the arterial wall to affect VSMC proliferation.

Angiopeptin inhibits oncogene induction in rabbit aorta after balloon denudation

BACKGROUND

Angiopeptin, a synthetic cyclic octapeptide analogue of somatostatin, reduces neointimal hyperplasia after balloon denudation of rabbit aorta if administered before injury. The aim of this study was to analyze the effect of angiopeptin pretreatment on the level of expression of the c-fos and c-jun protooncogenes, early markers of smooth muscle cell proliferation, after balloon denudation of rabbit aorta.

METHODS AND RESULTS

For histological analysis of the effect of angiopeptin on neointimal thickening after aortic balloon denudation, rabbits were randomized into three groups: group 1 (controls), twice-daily injections of saline begun 24 hours before balloon denudation (n = 9); group 2, twice-daily injections of angiopeptin 10 micrograms/kg begun 24 hours before balloon denudation (n = 9); and group 3, twice-daily injections of angiopeptin 10 micrograms/kg begun 1 hour after balloon denudation (n = 7). The degree of neointimal thickening 28 days after balloon denudation was significantly less in group 2 than in group 1 (neointimal area: group 1, 0.59 +/- 0.11 mm2; group 2, 0.22 +/- 0.05 mm2; P < .05. Neointima/media: group 1, 0.85 +/- 0.17; group 2, 0.23 +/- 0.05; P < .05). When angiopeptin was started 1 hour after denudation (group 3), however, the neointimal area (0.52 +/- 0.09 mm2) and the neointima/media ratio (0.76 +/- 0.10) were not statistically different from the control group. For analysis of protooncogene induction, rabbits received twice-daily subcutaneous injections of saline (n = 7), angiopeptin 10 micrograms/kg (n = 8), or angiopeptin 100 micrograms/kg (n = 4) begun 24 hours before balloon denudation. The animals were killed 30 minutes after balloon denudation, and total aortic RNA was hybridized with fos and jun probes. Expression of c-fos and c-jun was detected 30 minutes after injury; angiopeptin pretreatment at 20 micrograms.kg-1.d-1 induced a 41% reduction in c-fos expression and a 42% reduction in c-jun expression compared with control animals. The inhibitory effect at the higher dose of angiopeptin was similar.

CONCLUSIONS

Our results show that the inhibitory effect of angiopeptin on neointimal thickening is related to events that occur very early after injury and suggest that the inhibition of smooth muscle cell activation may be responsible, at least in part, for this effect.

Local intramural drug delivery using an infusion balloon following angioplasty in normal and atherosclerotic vessels

Local intramural delivery of various pharmacologic agents following angioplasty has been proposed as a means of reducing restenosis. This study tested whether local intramural delivery of aqueous solutions using an infusion balloon could be accomplished safely in normal vessels and whether such infusion was safe following standard angioplasty in diseased vessels. Infusion of aqueous agents into normal canine arteries had no adverse effect. Infusion of several aqueous agents (< or = 4 cc at 4 atm) into diseased swine iliac arteries following balloon angioplasty did not worsen existing or create new dissections. Histologically, infusion treated vessels did not differ in either model from vessels treated with angioplasty alone. We conclude that local intramural drug infusion does not create new, or worsen existing, dissections produced during standard balloon angioplasty in diseased vessels.

Relation of restenosis after excimer laser angioplasty to fasting insulin levels

Several studies have shown that diabetes mellitus increases the risk of restenosis after coronary intervention, but the role of insulin in restenosis has not been defined. The relation between fasting insulin levels and restenosis was evaluated prospectively at 6-month angiographic follow-up in 70 patients undergoing excimer laser coronary angioplasty of 75 lesions. Restenosis (> 50% diameter narrowing on quantitative angiography) was observed at 37 of 75 treated sites (49%). Although patients with glucose intolerance and noninsulin-dependent diabetes mellitus showed a trend toward increased restenosis (restenosis rate 69%; odds ratio for restenosis 2.7 [95% confidence interval 0.76, 9.82]; p = 0.124), those with increased fasting insulin levels > 15 muU/ml had reduced restenosis (restenosis rate 24%; odds ratio 0.22 [0.07, 0.67]; p = 0.008). Other factors including fasting serum glucose, glycated hemoglobin and lipoprotein fraction were not predictive of restenosis. The relation between insulin levels and restenosis after excimer laser angioplasty may provide insights into the biology of vascular injury and repair after coronary intervention.

Gamma irradiation inhibits neointimal hyperplasia in rats after arterial injury

BACKGROUND AND PURPOSE

Restenosis complicates a significant proportion of endovascular and open vascular procedures such as carotid endarterectomy. In contrast to the primary atheroma, restenosis is characterized by intimal hyperplasia of vascular smooth muscle cells. We hypothesized that gamma radiation would reduce restenosis by limiting intimal hyperplasia after arterial injury.

METHODS

To demonstrate the effect of gamma radiation on smooth muscle hyperplasia in vivo, a standardized bilateral carotid balloon catheter arterial injury was produced in 37 rats. A single dose of 750, 1500, or 2250 cGy (1cGy = 1 rad) gamma radiation was delivered to the right carotid artery at either 1 or 2 days after injury; the shielded contralateral carotid artery served as matched control. At 21 days after injury, vessels were perfusion-fixed in situ, and cross-sectional area of neointima was determined from axial sections using image analysis.

RESULTS

Marked reductions in neointimal cross-sectional area were demonstrated in vessels subjected to 1500- and 2250-cGy radiation at both 1 and 2 days after injury. A less prominent effect was noted for 750 cGy, reaching statistical significance only at 2 days after injury. By two-way ANOVA, radiation dose (P = .0002), timing of radiation delivery (P = .003), and an interaction between timing and dose (P = .0278) were significantly associated with reduction in neointimal cross-sectional area. At 1500 cGy, delivery of radiation 1 day after injury inhibited neointimal hyperplasia more prominently than the same dose 2 days after injury; a dose-response relation was evident at 1 day.

CONCLUSIONS

Radiation may be an important adjunctive therapy for reducing the incidence of restenosis after angioplasty or endarterectomy.

Molecular and cellular concepts in atherosclerosis

Atherosclerosis is a complex disease of uncertain cause. Its pathobiology is believed to represent an abnormal expression of the processes of vascular healing. Etiologic models derive from a 'response to injury' paradigm and can be divided into three separate disease stages: endothelial dysfunction, smooth muscle proliferation and architectural disruption. The initiating event of endothelial dysfunction is unknown, but is believed to be related to low-density lipoproteins and/or their oxidized derivatives. Endothelial injury is signalled to the smooth muscle cells of the media by three routes: direct cell-cell interaction, secretion of soluble growth factors and monocyte-derived cytokines. Monocytes are recruited by the endothelium and invade the subintimal space by a complex interaction of a variety of adhesion proteins and receptors on both cell types. Smooth muscle cell proliferation is initiated by a change in phenotype expression from 'contractile' to 'synthetic' resulting from the binding of fibronectin to specific integrin receptors. Three functionally distinct activities may represent separate subtypes of the 'synthetic phenotype': migration from the media to the intima, increased proliferation and inappropriate extracellular matrix synthesis. The loss of normal regulatory control and anchorage independence of proliferation suggest a relationship to oncogenic transformation. Both migration and proliferation result from the binding of platelet-derived growth factor-like factors to smooth muscle cell receptors, which initiates a cascade of intracellular molecular events leading either to cytoskeletal locomotory restructuring or cell cycle activation. Both pathways also appear to be coregulated by integrin receptors and both depend upon phosphorylation of cell membrane, cytosolic and nuclear regulatory proteins. Clinical expression of atherosclerosis may follow sudden loss of architectural integrity of the intimal plaque by three different mechanisms: plaque fissuring, intraluminal plaque rupture or intramural hemorrhage related to abnormal vessel wall stress and/or biochemistry.

Analysis of atherectomy specimens

Atherectomy specimens may be regarded as biopsy tissue excised from human vascular target lesions. Proceeding from contrary histologic findings that attribute focal hypercellularity to restenosis, and hypocellularity to chronic lesions, further analysis of atherectomy specimens was performed to study ultrastructural characteristics and functional aspects propagated by both lesion types. Transmission electron microscopy examination showed that intimal smooth muscle cells (SMCs) were the predominant cells in both primary and restenotic lesions. SMCs exhibited variable degrees of metabolic activation, typically higher in SMCs of restenotic lesions. This SMC phenotype was equally expressed when tissue samples were placed in a cell culture model. In an attempt to quantify SMC activity, proliferative as well as migratory activities of cultured cells were measured by growth curves and a computer-assisted motion analysis system, respectively. A 2- to 3-fold increase of both activity determinants was observed with SMCs cultivated from restenotic lesions compared with those from primary lesions, irrespective of their coronary or peripheral origin. Drug-induced interference of human SMC metabolic activation and antagonism to their proliferative and migratory activities may be helpful in evaluation of therapeutic concepts to prevent restenosis. The antitubulin colchicine was studied for its effect on the defined determinants. The data in vitro demonstrate that colchicine decreased proliferative and migratory activity of SMCs and caused disorganization of the cytoplasmic ultrastructure. In conclusion, electron microscopy and cell culture studies may help to shed more light on the structures and mechanisms underlying restenosis and plaque growth. Deliberate counteraction of any of the specific early events implicated in these complex pathobiologic processes may eventually become effective means to suppress restenosis and may thus result in a prophylactic as well as therapeutic treatment of the diseased vascular wall.

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.