Relationship of vascular thrombosis and inflammatory leukocyte infiltration to neointimal growth following porcine coronary artery stent placement

Peri-Interventional Triple Therapy with Dabigatran Modifies Vasomotion after Bare-Metal Stent Implantation in a Pig Coronary Artery Model

(1) Background: Coronary artery stenting leads to local inflammation, disturbs vasomotion, and slows endothelialization, increasing vascular thrombus risk. We used a pig stenting coronary artery model to assess how peri-interventional triple therapy with dabigatran ameliorates these effects. (2) Methods: In a total of 28 pigs bare-metal stents were implanted. Four days before the percutaneous coronary intervention (PCI), we started 16 of the animals on dabigatran, maintained through 4 days after the procedure. As controls, the remaining 12 pigs received no therapy. In both groups, dual antiplatelet therapy (DAPT) (clopidogrel, 75 mg plus aspirin, 100 mg) was administered until animals were euthanized. Just after the PCI and on day 3 after the procedure, we performed optical coherence tomography (OCT) in eight animals in the dabigatran group and four controls and euthanized them. We followed the eight remaining animals in each group with OCT and angiography for one month before euthanizing them and performed in vitro myometry and histology on harvested coronary arteries from all animals. (3) Results: The dabigatran group showed a significantly increased vasoconstriction at 3 days after PCI (10.97 ± 3.85 mN vs. 7.32 ± 5.41 mN, p = 0.03), but we found no differences between endothelium-dependent and -independent vasodilatation. We also found no group differences in OCT, quantitative angiography, or histomorphometry findings. (4) Conclusions: Starting a short course of dabigatran just before PCI and continuing for a 3-day window along with usual post-PCI DAPT is associated with enhanced vasoconstriction after bare-metal stent implantation without reducing neointimal formation at one month.

Peri-interventional Triple Therapy With Dabigatran Improves Vasomotion and Promotes Endothelialization in Porcine Coronary Stenting Model

Objective: We evaluated the short and long-term effect of peri-interventional dabigatran therapy on vasomotion, endothelialization, and neointimal formation in a porcine coronary artery stenting model.

Background: Stenting of coronary arteries induces local inflammation, impairs vasomotion and delays endothelialization.

Methods: Twenty-eight animals underwent percutaneous coronary intervention (PCI) with drug eluting stents. Sixteen pigs started dabigatran therapy 4 days prior to PCI and continued for 4 days post-stenting, while 12 animals served as controls. Post-stenting dual antiplatelet therapy (75 mg clopidogrel and 100 mg aspirin) was continued in both groups until termination. Immediately post-stenting and at day 3 optical coherence tomography (OCT) was performed in all animals, followed by euthanasia of 8 dabigatran and 4 control animals. The remaining pigs (8 of each group) were followed up for 1 month, with control angiography and OCT. Tissue burden (degree of peri-strut structure—thrombus and/or fibrin) was evaluated. After euthanasia coronary arteries were harvested for in-vitro myometry and histology.

Results: Thrombin generation was lower (p < 0.001) and tissue burden (0.83 ± 0.98 vs. 3.0 ± 2.45; p = 0.031) was significantly decreased in dabigatran treated animals. After 3 days post-PCI endothelium-dependent vasodilation was significantly improved (77 ± 40% vs. 41 ± 31%, p = 0.02) in dabigatran animals. Neither quantitative angiography nor histomorphometry showed differences between the groups. Endothelialization was faster in the dabigatran group as compared with controls (p = 0.045).

Conclusion: Short-term peri-interventional triple therapy with dabigatran, aspirin, and clopidogrel led to an enhanced endothelium dependent vasodilation and faster endothelialization. However, neointimal formation 1-month after stent implantation was comparable between groups.

Histological and Mechanical Behavior of INC 01 and 02 Bare Metal Stents Against a Commercial Stent: A Preclinical Study in a Porcine Model

BACKGROUND

PCI is an expensive procedure in our population and it implies a huge cost for the institutions and National Health Service.

AIM OF THE STUDY

The main objective was to evaluate the technical and biological success of two stents designed in Mexico.

METHODS

Ten York pigs, 4-6 months of age, underwent implantation of the bare metal INC-01 (10 stents) and INC-02 (6 stents) coronary stent in addition to a conventional commercial stent (10 stents). Technical success was evaluated immediately with angiography and Intravascular Ultrasound IVUS, continued by a mean follow-up of 4 month and a final angiographic, IVUS and histological evaluation.

RESULTS

Initial technical success, angiography and IVUS between the three stents were not significant. One stent presented restenosis in follow-up (commercial stent), but all other stents presented excellent clinical outcome, satisfactory angiographic and IVUS results. Inflammation, proliferation and endothelialization between the stents had no major differences in histological analysis in a mean of 4 months follow-up.

CONCLUSIONS

In this pig model, the INC 01 and INC 02 stents showed the same delivering technical success, angiographic and IVUS features, biological and histological response compared to commercial last generation stents.

Preclinical randomised safety, efficacy and physiologic study of the silicon dioxide inert-coated Axetis and bare metal stent: short-, mid- and long-term outcome

AIMS

To evaluate the short-, mid- and long-term safety, efficacy and vascular physiology of Axetis silicon dioxide (SiO2, abrading the micropores) inert-coated stent implantation in a randomised preclinical setting.

METHODS AND RESULTS

Coronary arteries of domestic pigs were randomised to receive either Axetis or BMS (same design) stents with one-, three- and six-month follow-up (FUP), controlled by coronary angiography, optical coherence tomography (OCT), intravascular ultrasound (IVUS) and histology (n=32). The time-dependent vasomotor reaction of coronary arteries to stenting was measured using modified myography (n=12). Complete endothelialisation of the Axetis stent was confirmed by OCT, IVUS and histology at one-month FUP. Histopathology revealed continuous healing of the vessel wall with a gradual reduction of inflammation and fibrin score during the six-month FUP in both stent types. Significantly smaller neointimal area and %area stenosis were measured in Axetis stents compared with BMS at each FUP time point. Vascular reactivity measurements showed significantly better endothelium-dependent vasodilation of stented arteries with Axetis implantation.

CONCLUSIONS

Implantation of the Axetis SiO2-coated stent resulted in a significantly better safety, efficacy and vessel physiology profile compared with BMS of the same design with a continuous decrease in vessel inflammation during the six-month FUP.

A novel mouse model of in situ stenting

AIMS

Animal models of stenting are mostly limited to larger animals or involve substantial abdominal surgery in rodents. We aimed to develop a simple, direct model of murine stenting.

METHODS AND RESULTS

We designed a miniature, self-expanding, nitinol wire coil stent that was pre-loaded into a metal stent sheath. This was advanced into the abdominal aorta of the mouse, via femoral access, and the stent deployed. In-stent restenosis was investigated at 1, 3, 7, and 28 days post-stenting. The model was validated by investigation of neointima formation in mice deficient in signalling via the interleukin-1 receptor (IL-1R1), compared with other injury models. Ninety-two per cent of mice undergoing the procedure were successfully stented. All stented vessels were patent. Inflammatory cells were seen in the adventitia and around the stent strut up to 3 days post-stenting. At 3 days, an early neointima was present, building to a mature neointima at 28 days. In mice lacking IL-1R1, the neointima was 64% smaller than that in wild-type controls at the 28-day timepoint, in agreement with other models.

CONCLUSION

This is the first description of a successful model of murine in situ stenting, using a stent specifically tailored for use in small thin-walled arteries. The procedure can be undertaken by a single operator without the need for an advanced level of microsurgical skill and is reliable and reproducible. The utility of this model is demonstrated by a reduction in in-stent restenosis in IL-1R1-deficient mice.

Frequency and consequences of early in-stent lesions after carotid artery stent placement

PURPOSE

To examine the prevalence of in-stent lesions 1 month after carotid artery stent placement with multidetector computed tomography (CT) angiography and to evaluate their possible causes and their consequences during 1-year follow-up.

MATERIALS AND METHODS

Sixty-nine patients with symptomatic carotid artery stenosis underwent multidetector CT angiography of the carotid arteries 1 month after carotid artery stent placement. Patients were followed-up until 1 year after stent placement, when duplex ultrasonography (US) was performed. In-stent lesions were defined as hypo- or hyperattenuating lesions at the stent wall found with multidetector CT. Significant restenosis (70%) at 1 year was defined as a peak systolic velocity of more than 300 cm/sec at duplex US. The Fisher exact test was used to assess the relationship between early in-stent lesions and ischemic events and restenosis.

RESULTS

At 1 month, 14 of the 69 patients (20%) were found to have in-stent lesions. In one patient, the stent was occluded. The other 13 in-stent lesions did not result in significant lumen reduction. In the year following stent placement, no difference in ischemic events was found between patients with (14%) and those without (13%) early in-stent lesions (P = .99). There was no difference in the occurrence of restenosis at 1 year (7% vs 4%, P = .59).

CONCLUSIONS

At 1 month after carotid artery stent placement, in-stent lesions are found in about one-fifth of patients. These lesions do not appear to be related to recurrent ischemic events or to restenosis at 1 year.

Increased In-Stent Stenosis in ApoE Knockout Mice

OBJECTIVE

We aimed to develop and validate a model of angioplasty and stenting in mice that would allow investigation of the response to stent injury using genetically modified mouse strains.

METHODS AND RESULTS

Aortic segments from either C57BL/6 wild-type or atherosclerotic ApoE-KO mice underwent balloon angioplasty alone or balloon angioplasty and stenting with a 1.25x2.5 mm stainless steel stent. Vessels were carotid-interposition grafted into genetically identical littermate recipients and harvested at 1, 7, 14, or 28 days. In wild-type mice, stenting generated an inflammatory vascular injury response between days 1 to 7, leading to the development of neointimal hyperplasia by day 14, which further increased in area by day 28 leading to the development of in-stent stenosis. Uninjured vessels and vessels injured by balloon angioplasty alone developed minimal neointimal hyperplasia. In stented ApoE-KO mice, neointimal area at 28 days was 30% greater compared with wild-type mice.

CONCLUSIONS

By reproducing important features of human stenting in atherosclerotic mice, we provide the potential to investigate molecular pathways and evaluate novel therapeutic targets for stent injury and restenosis.

Angioscopic evaluation of neointima coverage: sirolimus drug-eluting stent versus bare metal stent

BACKGROUND

The process of neointima formation after bare metal stent (BMS) implantation has been previously elucidated by angioscopic observations; however, that after drug-eluting stent (DES) implantation has not been clarified. Therefore, we compared the angioscopic appearance of neointima over DESs with that over BMSs 6 months after implantation.

METHODS AND RESULTS

Patients who received an implantation of a BMS (n = 13) or a sirolimus DES (n = 24) were included in this study. Angiographic and angioscopic examinations were performed at 6 months. The color of the stented lesion (white or yellow), coverage of stent by neointima (not covered, covered by a thin layer, or buried under neointima), and thrombus at the stented lesion (presence or absence) were angioscopically evaluated. Of the 24 lesions in which a DES was implanted, 11 (46%) had a part where the stent strut had no coverage, 21 (88%) had a part where it was covered by a thin layer, and 11 (46%) had a part where it was buried under neointima. Of the 13 lesions in which a BMS was implanted, 1 (8%) lesion had a part where the stent strut had no coverage, 4 (31%) lesions had a part where it was covered by a thin layer, and 13 (100%) lesions had a part where it was buried under neointima. The prevalence of a stent buried under neointima (46% vs 100%, P = .001) was lower and that of thrombus (42% vs 8%, P = .03) was higher in DES-implanted lesions as compared with BMS-implanted lesions. The prevalence of thrombus (64% vs 17%, P = .005) was higher in the yellow area than in the white area when a DES was implanted.

CONCLUSION

Sirolimus DESs, as compared with BMSs, were poorly covered by neointima and were accompanied by thrombus especially when there was a yellow plaque under the stents. Thus, the thrombogenic potential in DES-implanted lesions may be sustained by the inhibition of neointima formation over thrombogenic plaques.

The Role of Coagulation and Inflammation After Angioplasty in Patients with Peripheral Arterial Disease

PURPOSE

Restenosis remains a frequent complication after angioplasty in peripheral arterial disease. Inflammation plays a critical role in the vascular response to injury. Effective medical treatment to improve patency after angioplasty is still elusive. The aims of this prospective clinical study were to investigate changes in blood coagulation and inflammatory markers after angioplasty and their significance for restenosis.

METHODS

Thirty-four patients with peripheral arterial disease underwent angioplasty of the iliac and superficial femoral arteries. Ten patients undergoing diagnostic angiography were included in the study as controls. Plasma levels of tissue factor, prothrombin fragment 1 + 2, D-dimer, P-selectin, C-reactive protein (CRP), and fibrinogen were analyzed before and after angioplasty. Patients were followed up with angiography after 6 months to assess restenosis.

RESULTS

CRP was elevated the day after angioplasty (6.6 mg/l, p = 0.0001) and tended to peak after 1 week (11 mg/l, p = 0.09). There was a significant increase of D-dimer and P-selectin 1-4 hr after angioplasty (0.4 mg/l, p = 0.001 and 68 ng/ml, p = 0.05, respectively). None of the biochemical markers was a statistically significant predictor of restenosis.

CONCLUSION

We have observed a much more prolonged inflammatory response than previously noted, but only minor changes in coagulation activity after angioplasty. The biochemical markers, before and after angioplasty, were not related to restenosis. Further studies are needed to delineate the molecular mechanisms behind these observations and their involvement in thrombosis and restenosis. If these pathways are further defined, improved treatment strategies, including antithrombotic treatments and statins, could be tailored to modulate postprocedural inflammation.

99mTc-interleukin-2 scintigraphy for the in vivo imaging of vulnerable atherosclerotic plaques

PURPOSE

Several histopathological studies have demonstrated that vulnerable plaques are enriched in inflammatory cells. The aims of this study were: (1a) to test the ability of 99mTc-labelled interleukin-2 (99mTc-IL2) to bind to IL2R-positive (IL2R+) cells in carotid plaques and (1b) to correlate the plaque uptake of 99mTc-IL2, measured in vivo, with the number of IL2R+ cells within the plaque, measured ex vivo by histology (transversal study, TS), and (2) to evaluate changes in 99mTc-IL2 uptake in plaques, before and after treatment with a statin or a hypocholesterolaemic diet (longitudinal study, LS).

METHODS

Ultrasound scan was performed for plaque characterisation and localisation. Fourteen patients (16 plaques) eligible for endoarterectomy were recruited for the TS and underwent 99mTc-IL2 scintigraphy before surgery. Nine patients (13 plaques) were recruited for the LS; these patients received atorvastatin or a standard hypocholesterolaemic diet and 99mTc-IL2 scintigraphy was performed before and after 3 months of treatment.

RESULTS

The degree of 99mTc-IL2 uptake was expressed as the plaque/background (T/B) ratio. In patients from TS, T/B ratios correlated with the percentage of IL2R+ cells at histology (r = 0.707; p = 0.002) and the number of IL2R+ cells at flow cytometry (r = 0.711; p = 0.006). No correlations were observed between ultrasound scores and either scintigraphic or histological findings. In patients from the LS, the mean 99mTc-IL2 uptake decreased in statin-treated patients (1.75+/-0.50 vs 2.16+/-0.44; p = 0.012), while it was unchanged in the patients on the hypocholesterolaemic diet (2.33+/-0.45 vs 2.34+/-0.5).

CONCLUSION

99mTc-IL2 accumulates in vulnerable carotid plaques; this accumulation is correlated with the amount of IL2R+ cells and is influenced by lipid-lowering treatment with a statin.

Rat Abdominal Aorta Stenting: A New and Reliable Small Animal Model for In-Stent Restenosis

BACKGROUND

A high throughput animal model may enhance pathophysiological studies to mechanisms of in-stent restenosis (ISR). More and appropriate antibodies and transgenic and knockout strains are available in rats. Consequently, a model for ISR in the rat would be convenient for pathobiological studies. Here we present the full characteristics of a rat ISR model suitable for high throughput stent research.

METHODS

The abdominal aorta of rats was separated from surrounding tissue and a BeStenttrade mark 2 or a Cyphertrade mark sirolimus-eluting stent was locally inserted. After 1, 3, 7, 28 and 56 days, the aortas were harvested, fixed, embedded and cut. Morphometric analysis was performed and inflammation scored.

RESULTS

The neointimal area increased to a maximum after 28 days (0.55 +/- 0.08 mm(2)). Subsequently, the neointimal area slightly decreased. The injury score and the neointimal area were linearly correlated (r = 0.85, p < 0.01). Thrombus formation was present after 1 day. Leukocyte adherence was evident after 1 day, maximal after 3 days (93 +/- 21 cells/section) and decreased thereafter. The inflammation score increased after 3 days to a maximum after 7 days (1.37 +/- 0.06) and declined thereafter. After 28 days the Cypher sirolimus-eluting stent decreased the stenosis in comparison to the BeStent 2 (10.2 +/- 0.85 vs. 18.0 +/- 2.0%, respectively, p < 0.01).

CONCLUSIONS

Stent deployment in the rat abdominal aorta results in thrombus formation, inflammation and neointimal formation. Moreover, there is a linear correlation between the injury score and the neointimal area. These responses resemble ISR events as seen in other animal models. Moreover, a known anti-restenotic stent also reduces neointimal formation in this model. Rat abdominal aorta stenting is a promising animal model for ISR, it is suitable for testing commercially manufactured stents and studying the pathophysiology of ISR.

Color of culprit lesion at 6 months after plain old balloon angioplasty versus stenting in patients with acute myocardial infarction

BACKGROUND

Although the healing process of disrupted yellow plaques at myocardial infarction (MI) culprit lesions has been reported, the effect of stenting on this process has not been clarified. Stenting has been reported to deteriorate the endothelial function after percutaneous coronary intervention (PCI). Therefore, we compared the angioscopic morphology of culprit lesions at 6 months after plain old balloon angioplasty (POBA) and stenting to clarify the effect of stenting on the healing of disrupted culprit plaques of acute MI.

METHODS

Patients with acute MI who had yellow culprit plaque, successful reperfusion therapy with POBA (n = 21) or stenting (n = 22), and a successful 6-month follow-up angioscopic examination were included in this study. Oral ticlopidine (200 mg/day) was administered for 3 to 6 months after stenting.

RESULTS

At 6 months after reperfusion therapy, the color of the culprit lesion became white in significantly more patients treated with stenting than treated with POBA (50% vs 14%; P = .01). However, the prevalence of thrombus appeared to be higher in patients treated with stenting than in patients treated with POBA (27% vs 5%; P = .04). Although there was some difference in the patients' characteristics in the groups, logistic regression analysis revealed no significant influence of those factors on the color of or on the prevalence of thrombus at the culprit lesion.

CONCLUSIONS

Coronary stenting in patients with acute MI leads to the disappearance of yellow color at a significantly higher rate than POBA; however, whether it stabilizes the plaque requires further investigation.

Stent-induced restenosis in the swine coronary artery is inhibited by a platelet-derived growth factor receptor tyrosine kinase inhibitor, TKI963

Activities of vascular smooth muscle cells (SMCs) such as proliferation, migration, and matrix production contribute to restenosis following clinical interventions of angioplasty and stent placement. Because activation of platelet-derived growth factor (PDGF)-receptor tyrosine kinase (PDGFr-TK) influences these processes and promotes restenosis, TKI963, an inhibitor of the PDGFr-TK was discovered, and its efficacy was evaluated in blocking stent-induced restenosis as analyzed by intravascular ultrasound (IVUS). TKI963, a low-molecular-weight compound, inhibited the cell-free PDGFbetar-TK with a K(i) value of 56 +/- 14 nM. TKI963 also inhibited PDGF-dependent events in human aortic SMCs (e.g., in situ PDGFr autophosphorylation, mitogenesis, chemotaxis, and collagen production with median inhibitory concentration values of approximately 300 nM) without affecting the activity of a series of membrane receptor tyrosine kinases and intracellular serine/threonine kinases. In vivo, stent-induced restenosis in the swine coronary artery was reduced by oral administration of TKI963 (1.25, 2.5, and 5 mg/kg BID, for 28 days). Late lumen cross-sectional area (CSA) loss, plaque CSA growth, and plaque volume in the stent determined by IVUS were dose-relatedly decreased (33-62% at 1.25 mg/kg BID to 66-92% at 5 mg/kg BID, depending on the parameter) compared with controls. TKI963 treatment of </=1 week following stent placement had no effect on the prevention of restenosis. TKI963, a selective, orally bioavailable inhibitor of the PDGFr-TK, dose-relatedly reduced stent-induced restenosis and did so by inhibiting PDGF-dependent activities that occur as late events following stent placement.

Inflammation and restenosis: implications for therapy

Restenosis is the process of luminal narrowing in an atherosclerotic artery after an intra-arterial intervention such as balloon angioplasty and stenting. It is believed that this process is mainly characterized by migration and proliferation of smooth muscle cells and extracellular matrix accumulation. However, there is now increasing evidence for a role of inflammation in the development of restenosis. The underlying molecular mechanisms of restenosis are, in fact, most probably regulated by inflammatory mediators, such as cytokines. Understanding the molecular mechanisms in restenosis is crucial for the development of a suitable therapy for this disease. Recently, the use of immunosuppressives in drug-eluting stents has provided very promising results in the treatment of restenosis. In this review, we will describe the molecular mechanisms involved in restenosis with a focus on the role of inflammation and the use of immunosuppressive therapy.

Preserved endothelial vasomotion and fibrinolytic function in patients with acute stent thrombosis or in-stent restenosis

INTRODUCTION

Acute stent thrombosis and in-stent restenosis are serious complications of percutaneous coronary intervention (PCI) and may be associated with vascular or platelet abnormalities. We aimed to assess endothelium-dependent vasomotion, endogenous fibrinolysis and platelet function in patients with acute stent thrombosis or in-stent restenosis.

MATERIALS AND METHODS

Thirty-six subjects were enrolled into four groups: acute stent thrombosis, in-stent restenosis, uncomplicated PCI with stent implantation and healthy matched controls. Forearm blood flow was measured using bilateral venous occlusion plethysmography during intra-brachial acetylcholine, substance P and sodium nitroprusside infusion. Venous blood samples were withdrawn for estimation of plasma fibrinolytic variables and platelet aggregometry.

RESULTS

Acetylcholine, substance P and sodium nitroprusside caused dose-dependent increases in blood flow (P < 0.001) and substance P caused a dose-dependent increase in tissue-type plasminogen activator (t-PA) release (P < 0.001) in all groups. Thrombin, collagen, adenosine diphosphate (ADP) and the thromboxane A2 analogue, U46619, caused dose-dependent platelet aggregation (P < 0.001) in all groups. There were no significant between group differences in these responses except that, in keeping with aspirin therapy, collagen-induced platelet aggregation was impaired in patient groups compared with healthy controls (P < 0.01). Post-hoc analysis demonstrated a significant impairment of acute t-PA release in current smokers compared to non-smokers (P < 0.05).

CONCLUSIONS

Despite previous reports suggesting impaired vascular function, endothelium-dependent vasomotion, endogenous fibrinolysis and platelet aggregation do not appear to play a major role in the pathogenesis of acute stent thrombosis or in-stent restenosis.

Relationship between residual atheroma burden and neointimal growth in patients undergoing stenting: analysis of the atherectomy before MULTI-LINK improves lumen gain and clinical outcomes trial intravascular ultrasound substudy

OBJECTIVES

The objective of this study was to examine the relationship between quantitative volumetric and cross-sectional measures of residual atheroma burden and neointimal growth after coronary stenting.

BACKGROUND

Previous intravascular ultrasound (IVUS) studies have demonstrated a correlation between residual atheroma burden and neointimal growth after coronary stenting. However, postmortem studies contradict this finding.

METHODS

The study population included 34 patients who underwent IVUS six to eight months after stent placement, including 26 patients who underwent IVUS immediately after stent placement and at six to eight months follow-up. Using manual planimetry, the lumen cross-sectional area (LA), stent cross-sectional area (SA) and external elastic membrane cross-sectional area (EEM) were measured at 1-mm intervals after the procedure and at follow-up. Percent neointimal area (NA) and atheroma area (AA) were calculated as: percent neointimal area = ([SA - LA]/SA) x 100; percent AA = ([EEM - SA]/EEM) x 100 in the entire cross section and in individual quadrants. Postinterventional atheroma volume and neointimal volume at follow-up were calculated using Simpsons's rule.

RESULTS

In pooled analyses using all cross sections and cross-sectional quadrants, there was a weak correlation between percent AA and NA (r = 0.11 and 0.12, respectively). Analysis in individual patients demonstrated no significant relationship between total or quadrant measurements of percent AA and NA (p = 0.47 and 0.4, respectively). No relationship between atheroma volume postintervention and neointimal volume at follow-up was observed (r = 0.1, p = 0.62).

CONCLUSIONS

This study failed to demonstrate a clinically significant relationship between quantitative volumetric and cross-sectional measures of residual atheroma burden and subsequent neointimal growth.

Synthesis of highly potent and selective hetaryl ureas as integrin alpha(V)beta3-receptor antagonists

Solid-phase synthesis and SAR of integrin alpha(V)beta3-receptor antagonists containing a urea moiety as non-basic guanidine mimetic are described. The most potent compounds exhibited IC(50) values towards alpha(V)beta3 in the nanomolar range and high selectivity versus related integrins like alpha(IIb)beta3. For selected examples efficacy in functional cellular assays is demonstrated.

Validation of a technique to measure leukocyte adhesion to arterial segments: effects of drug treatments

Adhesion and transmigration of leukocytes into arterial walls occurs after vascular injury and may play a role in the development of atherosclerosis and restenosis. This protocol presents a simple, rapid method for quantifying leukocyte adhesion to artery segments ex vivo. The procedure involves isolating leukocytes from rabbit whole blood and labelling with the gamma-emitting isotope 51Cr. Labelled leukocytes are added to open rings of subclavian artery taken from the same rabbit. After gamma counting, percentage leukocyte adhesion can be calculated with reference to a sample containing a quantity of labelled leukocytes equivalent to that which was added to the artery. Leukocyte adhesion was increased by L-NAME, thrombin and increasing incubation time and decreased by low temperatures. In addition, leukocyte adhesion was found to be increased following a vascular stretch injury performed in vitro. This protocol offers a number of advantages: the rapidity of the leukocyte isolation and labelling; the small quantity of leukocytes required; the ability to use autologous leukocytes; the applicability to whole arteries and arteries injured in vitro or in vivo, allowing the effects of vascular injury on leukocyte adhesion to be studied.

Inflammation as a key event in the development of neointima following vascular balloon injury

1. The present review discusses the current evidence to implicate leucocytes as key players in the development of neointima in arteries that have been subjected to balloon angioplasty injury. 2. There is substantial clinical evidence that leucocytes are activated after angioplasty, as determined by increased plasma levels of both leucocyte granulation products and soluble leucocyte and endothelial cell adhesion molecules. 3. Experimental evidence to implicate leucocytes in neointimal formation comes from studies that demonstrate leucocyte accumulation occurs within the vascular wall soon after injury and that induction of leukopenia prevents neointimal formation. 4. The evidence implicating specific adhesion molecules and cytokines in the key events leading to neointimal formation is discussed.

There is no effect on remodeling of vascular wall 4 weeks after local delivery of antithrombin in a porcine model of coronary overstretching

BACKGROUND

Antithrombin III is an effective endogenous inhibitor of thrombin with antiproliferative and anti-inflammatory capabilities. Systematic administration of direct thrombin inhibitors as well as of antithrombin has proven effective at reducing formation of neointima after injury to vessel wall in various animal models. Local delivery of antithrombin attenuates deposition of platelets after balloon injury to porcine coronary vessels.

OBJECTIVE

To test our hypothesis that local delivery of antithrombin affects remodeling of vessel wall after balloon injury to the left anterior descending artery (LAD) in pigs.

METHODS

With a balloon:vessel diameter ratio of 1.5 deep vessel-wall injury was performed with conventional balloon angioplasty in the LAD in 16 pigs. After balloon injury the pigs were administered locally two doses of 2.5 ml antithrombin (250 U) or, as a control, two doses of 2.5 ml albumin (10 mg). All pigs were administered 200 U/kg bodyweight heparin before catheterization. The animals were then kept in stalls and fed normal grain. After approximately 4 weeks the animals were killed and lesions were assessed by computer-assisted image analysis. The areas of each vessel-wall layer and the percentage area stenosis were calculated. As a measure of injury, the length of rupture of the lamina elastica interna was measured.

RESULTS

The injury was found to be equally profound in pigs of these groups. There was no significant difference between the groups concerning the areas of vessel-wall layers. The percentage area stenosis was similar for pigs in these two groups (36.5 +/- 14.9% for pigs in the antithrombin group versus 35.4 +/- 16.2% for pigs in the control group, NS).

CONCLUSIONS

Local delivery of 250 U antithrombin to the LAD in pigs did not affect remodeling of the vessel wall 4 weeks after balloon injury.

EGF-genistein inhibits neointimal hyperplasia after vascular injury in an experimental restenosis model

A murine model of vascular injury-induced neointimal hyperplasia was developed by using a photoactive dye, rose bengal. Photoactivation of rose bengal induced vascular injury to the femoral arteries of C57B1/6 mice and resulted in an occlusive neointimal hyperplasia after 4 weeks. The cellular elements of the hyperplastic neointima were found to be alpha-actin-positive vascular smooth muscle cells expressing epidermal growth factor (EGF) receptor at high levels. EGF-Gen, an EGF-R-specific inhibitor with potent anticancer activity, suppressed the formation of hyperplastic neointima. Morphometric analysis of serial tissue sections at 4 weeks after vascular injury showed that in 75% of the EGF-Gen-treated mice, the maximal stenosis index was only 0.44 +/- 0.13, whereas in 75% of phosphate-buffered saline (PBS)-treated mice, the maximal stenosis index was 1.20 +/- 0.25. The mean neointima/media ratios for areas of maximum neointimal hyperplasia were 0.59 +/- 0.16 (n = 24) for the EGF-Gen-treated group, 0.99 +/- 16 (n = 45) for the PBS group (EGF-Gen vs. PBS, p = 0.0017), and 1.03 +/- 18 (n = 8) for group treated with unconjugated genistein (EGF-Gen vs. Gen, p = 0.0088). EGF-Gen treatment of mice with vascular injury to the left femoral artery was not associated with any clinical signs of toxicity or histopathologic lesions in any of the organs, including the uninjured right femoral artery. EGF-Gen also inhibited VSMC migration in vitro, without affecting VSMC proliferation and viability, suggesting that EGF-Gen is blocking neointima formation by inhibiting cellular migration to vascular injury sites. In conclusion, EGF-Gen may be useful as a nontoxic prophylactic agent for prevention of restenosis in clinical settings.

Modulation of protein expression and activity by radiation: relevance to intracoronary radiation for the prevention of restenosis

Restenosis is a common complication of percutaneous transluminal coronary angioplasty. Recent studies have demonstrated a striking reduction in the neointimal hyperplasia characteristic of restenosis following intracoronary radiation (IR), but the mechanisms by which radiation reduces neointima formation following balloon overstretch injury are not elucidated fully. In addition to direct antimitotic effects mediated via oxygen free radicals, ionizing radiation can induce the expression of numerous genes and thereby mediate indirect effects. Additionally, IR prevents restenosis at the cost of decreased healing and increased thrombosis, and we suggest that these adverse reactions can be modulated by adjunct pharmacology or gene-based strategies. This review discusses several genes and proteins modulated by radiation in the context of arterial injury, and their possible therapeutic relevance.

Acute platelet inhibition with abciximab does not reduce in-stent restenosis (ERASER study). The ERASER Investigators

BACKGROUND

Although stents reduce restenosis compared with balloon angioplasty, their long-term efficacy is limited by neointimal hyperplasia. Platelet and alpha(v)beta(3) integrin receptor inhibition limits neointimal proliferation in animal models of arterial injury.

METHODS AND RESULTS

We tested whether the dual beta(3) integrin blocking agent abciximab, administered for 12 or 24 hours at the same intravenous dose as that shown to reduce adverse clinical events (death, infarction, and revascularization) after angioplasty, would reduce restenotic tissue volume, as measured by intravascular ultrasound at 6 months. Two hundred twenty-five patients were randomly allocated to placebo or abciximab before coronary intervention. Of the 215 patients who received stents and study drug, 191 (88.8%) returned for late (>/=4 months) coronary evaluation. Tissue volume, expressed as a percentage of stent volume, did not differ: 25+/-15%, 27+/-15%, and 29+/-14% for the patients in the placebo and the 12- and 24-hour abciximab groups, respectively. Lack of abciximab benefit was confirmed by quantitative coronary angiography (dichotomous restenosis: 11.6%, 18. 9%, and 19.4%; loss index: 0.33, 0.52, and 0.47, respectively, P=NS).

CONCLUSIONS

Potent platelet inhibition with abciximab, as administered in this study, does not reduce in-stent restenosis. The interrelationship between stents, platelets, and neointimal proliferation requires further study.

Effects of a positron-emitting vanadium-48 nitinol stent on experimental restenosis in porcine coronary arteries: an injury-response study

BACKGROUND

The major limitation of coronary stenting is restenosis due to exaggerated neointimal thickening. We evaluated a positron-emitting V48 nitinol stent in a porcine coronary model of restenosis.

METHODS AND RESULTS

Pigs (n = 16) received a control nonradioactive and a V48 stent (1.5 or 10.6 muCi) randomized to the left anterior descending artery (LAD) and right coronary artery (RCA). Histology, morphometric variables, and strut injury scores were evaluated after 32 days. Peristrut fibrinoid deposits were greater in the high-dose group (p < 0.0001). Control stent area stenosis (AS) and mean neointimal thickness (NIT) correlated with injury (r = 0.81 and 0.79, respectively). Higher-dose stents reduced AS by 20% (0.57 +/- 0.13 vs. 0.71 +/- 0.16; p = 0.029) and mean NIT by 35% (0.44 +/- 0.16 vs. 0.71 +/- 0.24mm; p = 0.001) compared with controls. Lower-dose 1.5-muCi stents did not differ from controls. NIT over individual struts was reduced in the high-dose group compared with controls by 0.18 mm for grade 1 injury, 0.31 mm for grade 2, and 0.38 mm for grade 3 (p < 0.02 for all comparisons).

CONCLUSIONS

1.5-muCi V48 nitinol stents did not influence vessel histology or restenotic parameters in pig coronary arteries. In contrast, 10.6-muCi stents created a distinctive histological picture consisting of increased fibrinoid deposits on the neointimal-facing side of the struts without cellular organization. Higher dose radioactive stents significantly reduced AS and mean NIT. The reduction in neointimal thickening was greatest when the depth of strut penetration into the vascular wall was most severe.

Materials and biomaterials for interventional radiology

Devices used in interventional radiology have significantly developed in the past few years. In order to understand the trends of this development, we analyzed how new interventional devices are progressively incorporating materials having original physical properties, and how developers are today progressively turning towards biomaterials, with respect to the new regulatory environment, and the requirements of biocompatibility.

[Morphometric study of the wall of the caudal vena cava after the implantation of a filter in the sheep]

The long stabilizers of the VT-LGM filter rest on large areas of the vascular wall. The morphometric study of the layers of the vascular wall, after implantation of filter in 15 ewes, divided into 3 groups of follow-up (2, 4 or 8 weeks) of 5 animals, was made at 3 levels opposite the filter and 1 level outside of it. Changes are seen for all the layers. Filter produces intimal hyperplasia. Stabilizers are quickly isolated from the blood flow. The thickness of the intimal hyperplasia grows for 4 weeks. It is more important at the base of the filter than at its head. There is also hyperplasia of the media with no change according to the follow-up or the level opposite the filter. The adventitia becomes thinner without variation of time or level of the filter. Smooth muscle cells of the adventitia become less frequent and smaller. Their density in front of the stabilizers, is the smallest by 4 week follow-up and remains the same along the stabilizer. The full thickness of the wall is bigger opposite the stabilizers than between them. The filter produces changes that are limited in time and in space. The most important changes are seen at 4 weeks after insertion and opposite the stabilizers.

Coronary artery aneurysmal fistula: a late complication of stent deployment

An unusual case of a coronary artery fistula with the right atrium is described. Four months following the placement of a stent in a high grade, complex lesion of the proximal right coronary artery, restenosis, and contrast spill with rapid clearance into the right atrial space was evident on coronary angiogram. The calculated shunt fraction was trivial and hemodynamically insignificant.