Role of platelets in restenosis after percutaneous coronary revascularization

High on-aspirin treatment platelet reactivity and restenosis after percutaneous coronary intervention: results of the Intracoronary Stenting and Antithrombotic Regimen-ASpirin and Platelet Inhibition (ISAR-ASPI) Registry

OBJECTIVE

The aim of this study was to assess the association between high on-aspirin treatment platelet reactivity (HAPR) and the subsequent risk of restenosis after percutaneous coronary intervention (PCI) with predominantly drug-eluting stents.

BACKGROUND

The association between HAPR and subsequent risk of restenosis after PCI is unclear.

METHODS

This study included 4839 patients undergoing PCI (02/2007-12/2011) in the setting of the Intracoronary Stenting and Antithrombotic Regimen-ASpirin and Platelet Inhibition (ISAR-ASPI) registry. Platelet function was assessed with impedance aggregometry using the multi-plate analyzer immediately before PCI and after intravenous administration of aspirin (500 mg). The primary outcome was clinical restenosis, defined as target lesion revascularization at 1 year. Secondary outcomes included binary angiographic restenosis and late lumen loss at 6- to 8-month angiography.

RESULTS

The upper quintile cut-off of platelet reactivity measurements (191 AU × min) was used to categorize patients into a group with HAPR (platelet reactivity > 191 AU × min; n = 952) and a group without HAPR (platelet reactivity ≤ 191 AU × min; n = 3887). The primary outcome occurred in 94 patients in the HAPR group and 405 patients without HAPR (cumulative incidence, 9.9% and 10.4%; HR = 0.96, 95% CI 0.77-1.19; P = 0.70). Follow-up angiography was performed in 73.2% of patients. There was no difference in binary restenosis (15.2% vs. 14.9%; P = 0.79) or late lumen loss (0.32 ± 0.57 vs. 0.32 ± 0.59 mm; P = 0.93) between patients with HAPR versus those without HAPR.

CONCLUSIONS

This study did not find an association between HAPR, measured at the time of PCI, and clinical restenosis at 1 year after PCI.

Neointimal Hyperplasia after Carotid Transection and Anastomosis Surgery is Associated with Degradation of Decorin and Platelet Derived Growth Factor Signaling

Objective

Intimal hyperplasia (IH) is the expansion of the vascular intimal region after intervention, which can lead to stenosis and eventual failure of vascular grafts or interventional procedures such as angioplasty or stent placement. Our goals were to investigate the development of IH in a rabbit open surgical model and to evaluate the associated pathophysiologic processes involving decorin and the platelet-derived growth factor-BB/platelet-derived growth factor receptor-β/mitogen-activated protein kinase (PDGF-BB/PDGFR-β/MAPK) pathway.

Methods

We conducted carotid transection and primary anastomosis on five New Zealand white rabbits to induce IH and examined the associated pathophysiologic changes. Tissue was obtained for histological and protein analysis on postoperative day 21 using the contralateral vessel as a control. Intimal medial thickness (IMT) was calculated to measure IH and compared with the unoperated side. Western blot analysis was performed on tissue lysates to determine the expression of decorin core protein, PDGF-BB, PDGFR-β, and phosphorylated-MAPK (ph-MAPK). Immunofluorescence microscopy was used to assess tissue distribution of matrix metalloproteinase-2 (MMP-2) and ph-PDGFR-β.

Results

Bilateral carotid arteries were harvested on postoperative day 21. We compared the IMT in operated with unoperated specimens. IMT was significantly elevated in operated arteries vs unoperated arteries in all five animals (148.6 μm ± 9.09 vs 103.40 μm ± 7.08; 135.2 μm ± 8.30 vs 92.40 μm ± 2.35; 203.1 μm ± 30.23 vs 104.00 μm ± 4.52; 236.2 μm ± 27.22 vs 141.50 μm ± 9.95; 226.9 μm ± 11.12 vs 98.8 μm ± 3.78). Western blot analysis revealed degradation of decorin protein in the operated tissue, including loss of a 50 kDa band and the appearance of a cleaved fragment at 10 kDa. Decorin and MMP-2 were observed, via immunofluorescence microscopy, in the neointima of the operated vessels. Western blot analysis also revealed increased PDGF-BB, PDGFR-β, and ph-MAPK levels in operated tissue. Immunofluorescent staining for ph-PDGFR-β primarily localized to the neointima, indicating increased signaling through PDGF in this region.

Conclusions

Carotid transection and primary reanastomosis in rabbits induced IH that was associated with MMP-2 activation, degradation of decorin, and activation of the PDGF/PDGFR-β/MAPK pathway. The findings in this study should lead to further mechanistic evaluation of these pathways to better understand the potential to modify the intimal hyperplastic response to surgery. (JVS–Vascular Science 2020;2:2-12.)

Clinical Relevance

Intimal hyperplasia remains a significant challenge to the vascular surgeon in open and interventional procedures. Basic science studies have made headway into understanding the process, but this has not translated into many therapeutic options particularly for primary prevention after a procedure. Decorin is gaining popularity as an important mediator of various pathophysiologic processes involving the extracellular matrix. We sought to determine the possible role of decorin in the development of neointimal hyperplasia in an open surgical model. This study provides a replicable model for the development of intimal hyperplasia and potential therapeutic targets going forward.

Comparison of the 9-month intra-stent conditions and 2-year clinical outcomes after Resolute zotarolimus-eluting stent implantation between 3-month and standard dual antiplatelet therapy

BACKGROUND

The use of short-duration dual antiplatelet therapy (DAPT) remains controversial. To investigate efficacy and safety of short-duration DAPT, we performed a detailed comparison of intra-stent conditions by optical coherence tomography (OCT) after second-generation drug-eluting stent implantation with short-term and standard DAPT.

METHODS AND RESULTS

Eighty-two consecutive patients with stable angina pectoris who received Resolute zotarolimus-eluting stents (R-ZESs; Medtronic Cardiovascular, Santa Rosa, CA, USA) were enrolled. Patients were assigned to 3-month (3M group: 41 patients) and standard (standard group: 41 patients) DAPT. In the 3M group, clopidogrel was discontinued 3 months after stent implantation. In the standard group, DAPT was maintained until follow-up OCT. At 9 months, neointimal proliferation was significantly larger in the 3M group, but there were no significant between-group differences in the proportion of uncovered and malapposed strut. The prevalence of abnormal intra-stent tissue (AIT) at 9 months was equivalent between groups. A multiple regression analysis revealed malapposition at 9 months as the strongest independent predictor of AIT at 9 months, and the prevalence of AIT was not associated with DAPT duration. Over 2 years, cardiac events were equal between groups; however, major bleeding was higher tendency in the standard group than in the 3M group.

CONCLUSION

This OCT study indicated that reducing DAPT's duration may provide acceptable arterial healing in patients with implanted R-ZESs.

Influence of dual antiplatelet therapy on mean platelet volume in patients with coronary artery disease undergoing percutaneous coronary intervention

Mean platelet volume (MPV) is a well-established marker of platelet activation, and recent studies have shown that platelet activation is central to the processes in the pathophysiology of coronary artery disease (CAD). The study population consisted of 45 patients with stable CAD who underwent successful percutaneous coronary intervention (PCI) with drug-eluting stents. We selected 45 age- and sex-matched control subjects without cardiovascular diseases who did not require antiplatelet therapy. Hematological test was performed 3 times within 1 month before DAPT (baseline), at 2 weeks after PCI (post PCI) and at 9 months after PCI (follow-up). Compared to control subjects, MPV was significantly larger in patients with CAD (10.0 ± 0.6 vs 10.7 ± 0.8 fl, p < 0.01) although there was no significant difference in white blood cell count, hemoglobin, and platelet count between the 2 groups. In patients with CAD, DAPT did not affect platelet count (19.3 ± 4.8 × 10(4)-18.9 ± 4.6 × 10(4)/μl) or MPV (10.7 ± 0.8-10.5 ± 0.9 fl) during the follow-up period. MPV remained to be higher at follow-up in patients with CAD despite DAPT compared to control subjects (10.1 ± 0.7 vs 10.5 ± 0.9 fl, p < 0.05). Our data suggested that MPV might not be suitable for monitoring the effects of DAPT on platelet activity in patients with CAD undergoing PCI.

A platelet-inspired paradigm for nanomedicine targeted to multiple diseases

Platelets are megakaryocyte-derived anucleated cells found in the blood. They are mainly responsible for rendering hemostasis or clotting to prevent bleeding complications. Decreased platelet numbers or deficiencies in platelet functions can lead to various acute or chronic bleeding conditions and hemorrhage. On the other hand, dysregulated hyperactivity of the clotting process can lead to thrombosis and vascular occlusion. There is significant evidence that beyond hemostasis and thrombosis, platelets play crucial mechanistic roles in other disease scenarios such as inflammation, immune response and cancer metastasis by mediating several cell-cell and cell-matrix interactions, as well as aiding the disease microenvironment via secretion of multiple soluble factors. Therefore, elucidating these mechanistic functions of platelets can provide unique avenues for developing platelet-inspired nanomedicine strategies targeted to these diseases. To this end, the current review provides detailed mechanistic insight into platelets' disease-relevant functions and discusses how these mechanisms can be utilized to engineer targeted nanomedicine systems.

Plasma urokinase antigen and C-reactive protein predict angina recurrence after coronary angioplasty

This study evaluates the predictive value of several biochemical indices of the coagulation-fibrinolysis system, platelet function, and inflammatory state for angina recurrence after successful percutaneous transluminal coronary angioplasty (PTCA). We measured preprocedural and follow-up plasma levels of C-reactive protein (CRP), fibrinogen, and urokinase plasminogen activator antigen (uPA), plasminogen activator inhibitor-1 (PAI-1) activity, tissue plasminogen activator activity, and adenosine diphosphate-induced platelet aggregation in 53 patients with chronic stable angina who underwent successful elective PTCA of single hemodynamically significant lesions in coronary arteries. All patients were followed up for 12 months after PTCA. The Cox proportional hazards model was used to assess the association of variables with angina recurrence rate. At the end of the follow-up, 16 patients had angina recurrence. Among 36 clinical, biochemical, and angiographic variables, the duration of stable angina more than 12 months before PTCA (χ (2) = 5.73; P = 0.02, hazard ratio (HR) 3.7, 95 % confidence interval (CI) 1.26-10.6), high baseline levels of CRP (>7 mg/l) (χ (2) = 8.34; P = 0.004, HR 2.9, 95 % CI 1.4-5.9), uPA antigen baseline (>1 ng/ml) (χ (2) = 17.11; P = 0.0001, HR 11.5, 95 % CI 3.6-36.7) and 48 h after PTCA (χ (2) = 15.73; P = 0.0001, HR 8.8, 95 % CI 3.01-25.96), baseline PAI-1 activity (>18 IU/ml) (χ (2) = 9.37; P = 0.002, HR 7.6, 95 % CI 2.07-27.84) were significant predictors of recurrent angina by univariate analyses. According to stepwise multivariate analyses, only the levels of plasma uPA antigen and serum CRP were shown to be significant independent predictors of angina recurrence (multivariate uPA χ (2) = 8.22, P = 0.004, HR 6.2, 95 % CI 1.78-21.67; CRP χ (2) = 4.09, P = 0.04, HR 1.9, 95 % CI 1.02-3.68). High preprocedural plasma uPA and serum CRP levels are indicative of angina recurrence after successful PTCA, and are valuable for the prognosis of restenosis.

Efficacy and safety of abciximab in diabetic patients who underwent percutaneous coronary intervention with thienopyridines loading: a meta-analysis

BACKGROUND

It has been controversial whether abciximab offered additional benefits for diabetic patients who underwent percutaneous coronary intervention (PCI) with thienopyridines loading.

METHODS

MEDLINE, EMBASE, the Cochrane library clinical trials registry, ISI Science Citation Index, ISI Web of Knowledge and China National Knowledge Infrastructure (CNKI) were searched, supplemented with manual-screening for relevant publications. Quantitative meta-analyses were performed to assess differences between abciximab groups and controls with respect to post-PCI risk of major cardiac events (MACEs), angiographic restenosis and bleeding complications.

RESULTS

9 trials were identified, involving 2,607 diabetic patients receiving PCI for coronary artery diseases. Among those patients who underwent elective PCI or primary PCI, pooling results showed that abciximab did not significantly reduce risks of MACEs (for elective-PCI patients: RR(1-month): 0.93, 95% CI: 0.60-1.44; RR(1-year): 0.95, 95% CI: 0.81-1.11; for primary-PCI patients: RR(1-month): 1.05, 95% CI: 0.70-1.57; RR(1-year): 0.98, 95% CI: 0.80-1.21), nor all-cause mortality, re-infarction and angiographic restenosis in either group. The only beneficial effect by abciximab appeared to be a decrease 1-year TLR (target lesion revascularization) risk in elective-PCI patients (RR1-year: 0.83, 95% CI: 0.70-0.99). Moreover, occurrence of minor bleeding complications increased in elective-PCI patients treated with abciximab (RR: 2.94, 95% CI: 1.68-5.13, P<0.001), whereas major bleedings rate was similar (RR: 0.83, 95% CI: 0.27-2.57).

CONCLUSIONS

Concomitant dosing of abciximab and thienopyridines provides no additional benefit among diabetic patients who underwent PCI; this conclusion, though, needs further confirmation in larger studies.

Platelet response to clopidogrel and restenosis in patients treated predominantly with drug-eluting stents

BACKGROUND

Preclinical studies suggest a relationship between early thrombotic response after vascular injury and later development of restenosis. The aim of this study was to assess the impact of platelet response to clopidogrel on the risk of restenosis after drug-eluting stenting (DES).

METHODS

A total of 1,608 consecutive patients were previously enrolled in a study on the relation between platelet reactivity and outcomes after DES. All patients received a loading dose of 600 mg clopidogrel. Blood samples for the assessment of adenosine diphosphate-induced platelet aggregation with multiple electrode platelet aggregometry were drawn directly before percutaneous coronary intervention. Clopidogrel low response was defined as upper quintile of multiple electrode platelet aggregometry measurements. Accordingly, 323 patients (20%) were considered as low and 1,285 (80%) as normal responders. Primary end point of the present study was target lesion revascularization at 1 year. Secondary end points included binary angiographic restenosis and late lumen loss at 6- to 8-month angiography.

RESULTS

Target lesion revascularization rates were comparable in both groups (10.9% vs 9.5%, hazard rate [HR] 1.2, 95% CI 0.8-1.7, P = .441). Follow-up angiography revealed no difference in binary angiographic restenosis (13.9% vs 15.9%, P = .445) and late lumen loss (0.32 +/- 0.64 vs 0.35 +/- 0.63 mm, P = .477). Low responders had significantly more stent thromboses (2.5% vs 0.5%, HR 5.4, 95% CI 1.9-15.6, P = .002), Q wave myocardial infarctions (2.5% vs 0.6%, HR 4.0, 95% CI 1.5-10.7, P = .005), and ischemic strokes (1.3% vs 0.2%, HR 5.4, 95% CI 1.2-24.0, P = .028) at 1 year.

CONCLUSION

Low platelet responsiveness to clopidogrel, a known predictor of thrombotic complications, does not have a significant impact on restenosis after DES.

In vitro and in vivo platelet targeting by cyclic RGD-modified liposomes

Cell-selective delivery using ligand-decorated nanoparticles is a promising modality for treating cancer and vascular diseases. We are developing liposome nanoparticles surface-modified by RGD peptide ligands having targeting specificity to integrin GPIIb-IIIa. This integrin is upregulated and stimulated into a ligand-binding conformation on the surface activated platelets. Activated-platelet adhesion and aggregation are primary events in atherosclerosois, thrombosis, and restenosis. Hence, platelet-targeted nanoparticles hold the promise of vascular site-selective delivery of drugs and imaging probes. Here, we report in vitro and ex vivo microscopy studies of platelet-targeting by liposomes surface-modified with a cyclic RGD peptide. The peptide-modified liposomes were labeled either with a lipophilic fluorophore or with lipid-tethered Nanogold(R). For in vitro tests, coverslip-adhered activated human platelets were incubated with probe-labeled liposomes, followed by analysis with fluorescence microscopy, phase contrast microscopy, and scanning electron microscopy (SEM). For in vivo tests, the liposomes were introduced within a catheter-injured carotid artery restenosis model in rats and post-euthanasia, the artery was imaged ex vivo by fluorescence microscopy and SEM. All microscopy results showed successful platelet-targeting by the peptide-modified liposomes. The in vitro SEM results also enabled visualization of nanoscopic liposomes attached to activated platelets. The results validate our nanoparticle design for site-selective vascular delivery.

Long-term clopidogrel administration following severe coronary injury reduces proliferation and inflammation via inhibition of nuclear factor-kappaB and activator protein 1 activation in pigs

BACKGROUND

The optimal duration of clopidogrel treatment following percutaneous coronary intervention (PCI) and the patient population that would benefit most are still unknown. In a porcine coronary injury model, we tested two different durations of clopidogrel treatment on severely or moderately injured arteries and examined the arterial response to injury. To understand the molecular mechanism, we also investigated the effects on transcription factors nuclear factor-kappaB (NF-kappaB) and activator protein 1 (AP-1).

MATERIALS AND METHODS

In 24 cross-bred pigs, one coronary artery was only moderately injured by percutaneous transluminal coronary angioplasty (PTCA) and one coronary artery was severely injured by PTCA and subsequent beta-irradiation (Brachy group). Animals received 325 mg aspirin daily for 3 months and 75 mg clopidogrel daily for either 28 days [short-term (ST) clopidogrel group] or 3 months [long-term (LT) clopidogrel group].

RESULTS

After 3 months, the number of proliferating cells per cross-section differed significantly between ST and LT in both injury groups (PTCA(ST) 90.2 +/- 10.3 vs. PTCA(LT )19.2 +/- 4.7, P < 0.05; Brachy(ST) 35.8 +/- 8.4 vs. Brachy(LT) 7.5 +/- 2.0, P < 0.05). Similar results were seen for inflammatory cells (CD3(+) cells): PTCA(ST) 23.5 +/- 3.55 vs. PTCA(LT )4.67 +/- 0.92, P < 0.05; Brachy(ST) 83.17 +/- 11.17 vs. Brachy(LT) 20 +/- 4.82, P < 0.05). Long-term administration also reduced the activity of NF-kappaB and AP-1 by 62-64% and 42-58%, respectively. However, the effects of different durations of clopidogrel administration on artery dimensions were not statistically significant.

CONCLUSIONS

Regarding inflammation and transcription factor activity at the PCI site, long-term clopidogrel administration is superior to short-term administration, especially in severely injured arteries. Transferring our results to the human situation, patients with more severely diseased arteries may benefit from a prolonged clopidogrel medication after PCI.

The application of multiscale modelling to the process of development and prevention of stenosis in a stented coronary artery

The inherent complexity of biomedical systems is well recognized; they are multiscale, multiscience systems, bridging a wide range of temporal and spatial scales. While the importance of multiscale modelling in this context is increasingly recognized, there is little underpinning literature on the methodology and generic description of the process. The COAST (complex autonoma simulation technique) project aims to address this by developing a multiscale, multiscience framework, coined complex autonoma (CxA), based on a hierarchical aggregation of coupled cellular automata (CA) and agent-based models (ABMs). The key tenet of COAST is that a multiscale system can be decomposed into N single-scale CA or ABMs that mutually interact across the scales. Decomposition is facilitated by building a scale separation map on which each single-scale system is represented according to its spatial and temporal characteristics. Processes having well-separated scales are thus easily identified as the components of the multiscale model. This paper focuses on methodology, introduces the concept of the CxA and demonstrates its use in the generation of a multiscale model of the physical and biological processes implicated in a challenging and clinically relevant problem, namely coronary artery in-stent restenosis.

Effect of abciximab on clinical and angiographic restenosis in patients with non-ST-segment elevation acute coronary syndromes

The ISAR-REACT 2 trial was designed to assess the effect of abciximab in patients with acute coronary syndromes undergoing percutaneous coronary intervention after a 600-mg loading dose of clopidogrel. The aim of the present study was to investigate the impact of abciximab on clinical and angiographic restenosis after coronary stenting in patients with acute coronary syndromes. The angiographic substudy included 1,544 patients from the ISAR-REACT 2 trial randomly assigned to abciximab (771 patients) or placebo (773 patients). All patients were scheduled for routine angiographic follow-up at 6 to 8 months after intervention. The primary end point was incidence of angiographic in-segment binary restenosis. The secondary end point was 1-year incidence of target-lesion revascularization. Binary restenosis was observed in 21.9% of patients in the abciximab group and 24.5% of patients in the placebo group (p=0.29). Percentages of in-stent (29+/-22% vs 33+/-24%; p=0.02) and in-segment (35+/-20% vs 38+/-21%; p=0.04) diameter stenoses were significantly lower in the abciximab group than the placebo group. There was a strong trend toward lower 1-year incidence of target-lesion revascularization in patients treated with abciximab than in patients treated with placebo (13.6% vs 16.8%; p=0.08). In conclusion, in patients with non-ST-segment elevation acute coronary syndromes undergoing early percutaneous coronary intervention with stenting after a 600-mg loading dose of clopidogrel, abciximab therapy may have a slight positive impact on the prevention of restenosis.

Effects of Preoperative Abciximab and Eptifibatide on Bleeding Indices in Coronary Artery Bypass Graft Patients

Background:

Glycoprotein (GP) IIb/IIIa antagonists are used routinely for the treatment of acute coronary syndrome and to prevent thromboses during percutaneous coronary interventions. It is not uncommon for patients who initially require a GP IIb/IIIa inhibitor to eventually receive a surgical intervention.

Objective:

To compare the difference in bleeding indices in patients who undergo coronary artery bypass grafting (CABG) after receiving either eptifibatide or abciximab.

Methods:

A retrospective chart review was completed on all adults who received abciximab or eptifibatide within 24 hours prior to undergoing CABG. Patients were excluded if they had received a dose of warfarin within 96 hours prior to the procedure or if they had an incomplete medical record, an off-pump procedure, a known hypercoagulable disorder, or hemophilia. A total of 54 patients were included and preoperative data, including doses of anticoagulant and antiplatelet agents, were recorded. Intraoperative and postoperative data collected for analysis included hemoglobin level, chest tube output, and the amount of blood products transfused for 24 hours postprocedure.

Results:

There was a statistically significant difference between the eptifibatide and abciximab groups in the amount of fresh frozen plasma (mean ± SD, 21 ± 31 vs 187 ± 125 mL, respectively; p < 0.05) and platelets (212 ± 81 vs 433 ± 118 mL, respectively; p < 0.01) transfused during the intraoperative period. However, when the total amount of blood products transfused intraoperatively (769 ± 243 vs 1395 ± 316 mL, respectively; p = 0.47) was evaluated, no significant difference was detected. Likewise, markers for bleeding that were collected during the 24-hour postoperative window (immediate and 24-h postoperative hemoglobin and total 24-h chest tube output) were not significantly different.

Conclusions:

Although there is an increased risk of bleeding when abciximab or eptifibatide is administered prior to CABG, no significant difference in the total amount of blood products used was detected between the 2 agents in this study.

High P-selectin expression and low CD36 occupancy on circulating platelets are strong predictors of restenosis after coronary stenting in patients with coronary artery disease

Recent studies have shown that circulating platelets play an important role in the development of restenosis early after coronary stent implantation. We investigated P-selectin expression and CD36 blockade on platelets by flow cytometry in 48 consecutive patients who underwent coronary stenting. P-selectin expression was significantly higher 1 day after stenting in patients who had restenosis (n = 15) than in those who had no restenosis (n = 28), and the odds ratio for restenosis in patients with high P-selectin levels (MFI > 6.5) was 11.67 (P < 0.001) as compared with patients who had intermediate and low P-selectin levels. CD36 blockade was assessed with the use of two anti-CD36 antibodies, OKM5 and GS95 (our new anti-CD36 antibody), the binding of which indicates total CD36 amount and free CD36 unoccupied by lipid-related ligands, respectively. Binding of OKM5 to platelets was similar before and after stenting in both groups. CD36 blockade on platelets was seen 1 day after stenting in the non-restenosis group, and the odds ratio for restenosis in patients without CD36 blockade [GS95 binding ratio >0.8 as compared with binding before stenting] on day 1 was 28.60 (P < 0.001). P-selectin expression and unoccupied CD36 on platelets shortly after stenting may be strong predictors of post-stent restenosis.

Abciximab and angiographic restenosis after coronary stent placement. Analysis of the angiographic substudy of ISAR-REACT--a double-blind, placebo-controlled, randomized trial evaluating abciximab in patients undergoing elective percutaneous coronary interventions after pretreatment with a high loading dose of clopidogrel

BACKGROUND

ISAR-REACT was a trial designed to evaluate whether the glycoprotein IIb/IIIa inhibitor abciximab is beneficial in patients undergoing elective percutaneous coronary intervention (PCI) with stent placement after pretreatment with a 600 mg loading dose of clopidogrel. Objective for the angiographic substudy was to determine the impact of abciximab on angiographic restenosis after coronary stent placement. Previous analyses have suggested a reduction in the incidence of restenosis after the administration of abciximab.

METHODS

The angiographic substudy comprises 1885 of 2159 patients enrolled in ISAR-REACT: 994 patients were randomly assigned to abciximab and 941 patients to placebo. All patients were scheduled for a routine angiographic follow-up after 6 months (performed in 80% of eligible patients). End points for the angiographic substudy were the rates of angiographic restenosis (> or = 50% diameter stenosis) and target lesion revascularization.

RESULTS

The incidence of angiographic restenosis was 27% in the abciximab group and 29% in the placebo group (relative risk 0.92, 95% CI 0.79-1.06, P = .27). Late angiographic lumen loss was 0.95 +/- 0.68 and 0.99 +/- 0.70 mm, respectively (P = .25). Similar results were obtained in a subgroup analysis focusing on high-risk subsets. The rate of target lesion revascularization procedures was 22% in the abciximab group and 23% in the placebo group (relative risk 0.94, 95% CI 0.79-1.12, P = .52).

CONCLUSIONS

In low- to intermediate-risk patients who undergo elective PCI after pretreatment with a high loading dose of clopidogrel >2 hours before PCI, the additional administration of the glycoprotein IIb/IIIa inhibitor abciximab is not associated with a significant reduction in angiographic restenosis.

Long-term care after percutaneous coronary intervention: focus on the role of antiplatelet therapy

Arterial wall injury caused by percutaneous coronary intervention (PCI) triggers transient platelet activation and mural thrombosis; these effects are superimposed on the preexisting platelet hyperreactivity associated with underlying atherothrombosis. Platelet activation has been implicated in the major complications of PCI: acute and subacute thrombosis and restenosis. Antithrombotic and anticoagulant therapy minimizes thrombotic complications after PCI. Aspirin plus a thienopyridine (ticlopidine or clopidogrel) is more effective than aspirin plus heparin and extended warfarin therapy in preventing periprocedural ischemic events and subsequent stent thrombosis and results in less major and minor bleeding. Dual antiplatelet therapy with aspirin and clopidogrel (the preferred thienopyridine because of its superior hematologic safety) is recommended for at least 4 weeks to prevent subacute stent thrombosis with bare-metal stents and 3 to 6 months to prevent late-stent thrombosis with drug-eluting stents. Coronary atherothrombosis is a diffuse vascular disease, and reduction of the risk of future ischemic events requires strategies that extend beyond the focal treatment of stenotic lesions. Optimal long-term care after PCI requires aggressive systemic pharmacotherapy (antiplatelet agents, statins, beta-blockers, and angiotensin-converting enzyme Inhibitors) in conjunction with therapeutic lifestyle changes (smoking cessation, weight reduction, dietary measures, and exercise). In this context, dual antiplatelet therapy (aspirin plus clopidogrel) is recommended for at least 12 months after PCI for prophylaxis of future atherothrombotic events.

Initial experience with an intravenous P2Y12 platelet receptor antagonist in patients undergoing percutaneous coronary intervention: results from a 2-part, phase II, multicenter, randomized, placebo- and active-controlled trial

BACKGROUND

Platelet-initiated acute thrombosis and coronary embolization are fundamental in the pathophysiology of complications during percutaneous coronary intervention (PCI). Cangrelor (formerly AR-C69931MX) is a novel, rapidly acting, intravenous, specific antagonist of platelet aggregation via binding to the adenosine diphosphate (ADP) P2Y12 receptor subtype. The primary aims of this study were to assess the initial safety and pharmacodynamics of cangrelor in patients undergoing PCI.

METHODS

In part 1, patients undergoing PCI were randomized to an 18- to 24-hour of either placebo, 1-, 2-, or 4-microg/kg per minute cangrelor in addition to aspirin and heparin beginning before PCI. In part 2, patients were randomized to receive either cangrelor (4 microg/kg per minute) or abciximab before PCI. The primary end point was the composite incidence of major and minor bleeding through 7 days. Secondary end points included the occurrence of major adverse coronary events (death, MI, and unplanned repeat coronary intervention) through 30 days plus ex vivo platelet aggregation and bleeding times.

RESULTS

Two hundred patients (3 dosage groups and placebo) were studied in part 1, and 199 additional patients were then randomized in the second part, comparing 1 dose of cangrelor and abciximab. Combined major and minor bleeding occurred in 13% of those receiving cangrelor and in 8% in those randomized to placebo (P = non significant [NS]) during part 1 and in 7% receiving cangrelor compared with 10% randomized to abciximab (P = NS), during part 2. The 30-day composite incidence of adverse cardiac events was similar between those receiving cangrelor and those receiving abciximab during part 2 (7.6% vs 5.3%, respectively, P = NS). Mean inhibition of ex vivo platelet aggregation in response to 3 micromol/L ADP at steady state was 100% for both cangrelor 4 microg/kg per minute and abciximab groups in part 2. After termination of infusion, platelet aggregation returned to baseline response more rapidly with cangrelor compared with abciximab. There was a trend toward longer bleeding time prolongation and lower platelet count with abciximab compared with cangrelor.

CONCLUSIONS

This initial experience with intravenous cangrelor during PCI suggests an acceptable risk of bleeding and adverse cardiac events while achieving rapid, reversible inhibition of platelet aggregation via competitive binding to the ADP P2Y12 platelet receptor with less prolongation of bleeding time then the glycoprotein IIb/IIIa receptor antagonist abciximab.

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.

The role of the platelet in the pathogenesis of atherothrombosis

Platelet adhesion, activation, and aggregation at sites of vascular endothelial disruption caused by atherosclerosis are key events in arterial thrombus formation. Platelet tethering and adhesion to the arterial wall, particularly under high shear forces, are achieved through multiple high-affinity interactions between platelet membrane receptors (integrins) and ligands within the exposed subendothelium, most notably collagen and von Willebrand factor (vWF). Platelet adhesion to collagen occurs both indirectly, via binding of the platelet glycoprotein (GP) Ib-V-IX receptor to circulating vWF, which binds to exposed collagen, and directly, via interaction with the platelet receptors GP VI and GP Ia/IIb. Platelet activation, initiated by exposed collagen and locally generated soluble platelet agonists (primarily thrombin, ADP, and thromboxane A2), provides the stimulus for the release of platelet-derived growth factors, adhesion molecules and coagulation factors, activation of adjacent platelets, and conformational changes in the platelet alpha(IIb)beta3 integrin (GP IIb/IIIa receptor). Platelet aggregation, mediated primarily by interaction between the activated platelet GP IIb/IIIa receptor and its ligands, fibrinogen and vWF, results in the formation of a platelet-rich thrombus. Currently available antiplatelet drugs (aspirin [acetylsalicylic acid], dipyridamole, clopidogrel, ticlopidine, abciximab, eptifibatide, tirofiban) act on specific targets to inhibit platelet activation and aggregation. Elucidation of the multiple mechanisms involved in platelet thrombus formation provides opportunities for selectively inhibiting the pathways most relevant to the pathophysiology of atherothrombosis.

Localized delivery of nitric oxide from hydrogels inhibits neointima formation in a rat carotid balloon injury model

Using novel nitric oxide (NO)-generating polymeric hydrogels that can be rapidly photopolymerized in situ, we can deliver NO locally at the site of vascular injury. Depending on material design, these poly(ethylene glycol) (PEG)-based hydrogels can generate NO for up to 50 d. This study demonstrates the ability of nitric oxide-generating hydrogels (PEG-Cys-NO) to influence key components of the restenosis cascade both in vitro and in vivo. PEG-Cys-NO hydrogels inhibited smooth muscle cell proliferation, increased endothelial cell proliferation, and inhibited platelet adhesion in vitro. Moreover, in vivo, PEG-Cys-NO hydrogels inhibited intimal thickening in a rat carotid balloon injury model. The perivascular application of NO-generating polymers post-injury reduced neointima formation at 14 d by approximately 80% compared to controls (intimal area/medial area (I/M): PEG-Cys-NO=0.20+/-0.17, control=0.84+/-0.19, p<0.00002; intimal thickness: PEG-Cys-NO=12+/-10 microm, control=60+/-18 microm, p<0.00002). Treatment with the PEG-Cys-NO hydrogels caused a significant decrease in the per cent of proliferating cell nuclear antigen positive medial cells (29+/-5%) at 4 d as compared to treatment with the control hydrogels (51+/-1%, p<0.02). Additionally, vessel re-endothelialization at 14 d was slightly enhanced in the presence of the NO-generating hydrogels. These data indicate that localized delivery of NO from these hydrogels can significantly inhibit neointima formation in a rat carotid balloon injury model and suggest that these materials may be useful in preventing restenosis.

Endothelial cells organize fibrin clots into structures that are more resistant to lysis

Acute myocardial infarction is a major cause of death and disability in the United States. Introducing thrombolytic agents into the clot to dissolve occlusive coronary artery thrombi is one method of treatment. However, despite advances in our knowledge of thrombosis and thrombolysis, survival rates following thrombolytic therapy have not improved substantially. This failure highlights the need for further study of the factors mediating clot stabilization. Using laser scanning confocal microscopy of clots formed from fluorescein-labeled fibrinogen, we investigated what effect binding of fibrin to the endothelial surface has on clot structure and resistance to lysis. Fluorescent fibrin clots were produced over human umbilical vein endothelial cells (HUVEC) and the clot structure analyzed. In the presence of HUVEC, fibrin near the endothelial surface was more organized and occurred in tighter bundles compared to fibrin just 50 microm above. The HUVEC influence on fibrin architecture was blocked by inhibitory concentrations of antibodies to alphaV or beta3 integrin subunits. The regions of the clots associated with endothelial cells were more resistant to lysis than the more homogenous regions distal to endothelium. Thus, our data show that binding of fibrin to integrins on endothelial surfaces produces clots that are more resistant to lysis.

Intravascular adenovirus-mediated lipoprotein-associated phospholipase A2 gene transfer reduces neointima formation in balloon-denuded rabbit aorta

Postangioplasty restenosis is a multifactorial process and involves mechanisms such as inflammation and stimulation of the expression of growth factors. Lipoprotein-associated phospholipase A(2) (Lp-PLA(2)) can modify inflammatory responses by hydrolyzing phospholipids with shortened and/or oxidized sn-2 residues. In this study, we tested a hypothesis that adenovirus-mediated Lp-PLA(2) gene transfer can reduce restenosis in rabbits. Aortas of cholesterol-fed NZW rabbits were balloon-denuded and intra-arterial gene transfer was performed using Dispatch catheter with Lp-PLA(2) or LacZ adenoviruses (1.15 x 10(10)pfu). Intima/media ratio (I/M), histology and cell proliferation were analyzed. Two weeks after the gene transfer I/M in the LacZ-transduced control group was 0.45+/-0.05 but Lp-PLA(2) gene transfer reduced I/M to 0.25+/-0.03. At four weeks time point I/M in the Lp-PLA(2) group (0.34+/-0.05) was also lower than in the LacZ group (0.53+/-0.06). Plasma Lp-PLA(2) activity was increased in the Lp-PLA(2) group (48.2+/-4.2) as compared to the LacZ group (33.6+/-3.51) at two weeks time point. Transgene expression was detected in the arterial wall two and four weeks after the procedure. Apoptosis was higher in the control vessels than in the Lp-PLA(2) group at two weeks time point. In conclusion, local adenovirus-mediated Lp-PLA(2) gene transfer resulted in a significant reduction in neointima formation in balloon-denuded rabbit aorta and may be useful for the prevention of restenosis after arterial manipulations.

Ongoing clinical trials of anti-platelet agents in the management of acute ischaemic coronary syndromes

Acute ischaemic coronary syndromes, the clinical sequelae of thrombosis over a fissured atherosclerotic plaque within the coronary circulation, are the leading cause of death and hospitalisation in Western countries. Platelets are fundamental for the initiation and continuation of thrombosis, and currently available anti-platelet agents such as aspirin significantly improve the clinical outcome of patients with these syndromes. Therapeutic success with available therapy is however not universal, and adverse clinical event rates remain high. Several new classes of agents with a variety of anti-platelet actions are currently under development. Those which inhibit the final common pathway of platelet aggregation, the glycoprotein (GP) IIb/IIIa receptor, appear to show the most promise. Much clinical trial evidence already exists supporting the use of GP IIb/IIIa receptor antagonists in the management of acute ischaemic coronary syndromes. Several clinical studies are underway to further refine this knowledge base, and to assess their efficacy in a variety of novel applications.

The effect of long-term clopidogrel use on neointimal formation after percutaneous coronary intervention

OBJECTIVE

The purpose of this study was to evaluate the long term effect of clopidogrel-based antiplatelet therapy on neointimal formation.

METHODS

This study comprised 78 patients with typical stable angina pectoris or documented myocardial ischaemia, and with only one angiographic lesion in one native coronary artery undergoing successful stent implantation without predilatation with C-reactive protein levels < or =5 mg/l at 72 h after the procedure. All patients received dual antiplatelet therapy with 75 mg/day clopidogrel and 300 mg/day aspirin for four weeks. Clopidogrel was switched to isochronous placebo in half of the patients (n=39) at the end of the fourth week. This allocation was maintained for 20 weeks, and at week 24 of the study, coronary angiography and intravascular ultrasound imaging were performed again in all cases in order to evaluate the changes that had occurred in the in-stent neointimal formation; rates of restenosis were also recorded

RESULTS

At the end of the follow-up period, angiographic stenosis diameter and restenosis rates were smaller in the clopidogrel group than in the placebo group (23.3% versus 35.6%, p=0.05 and 5.12% versus 10.25%; p=0.03 respectively); the intravascular ultrasonographic neointimal cross sectional area was also smaller in the clopidogrel group (3.6 +/- 2.7 mm(2) versus 5.2 +/- 2.5 mm(2), p=0.03).

CONCLUSIONS

Long-term clopidogrel administration significantly reduced neointimal formation at the stent site as well as reducing major clinical events in patients who did not develop high-risk systemic inflammatory response after percutaneous coronary intervention.

Volumetric Analysis of In-Stent Intimal Hyperplasia in Diabetic Patients Treated With or Without Abciximab

Background— In diabetic patients in the Evaluation of Platelet IIb/IIIa Inhibitor for Stenting (EPISTENT) trial, abciximab reduced target vessel revascularization by ≈50% compared with placebo. Whether this is a result of a lower restenosis rate caused by inhibition of intimal hyperplasia remains to be defined.

Methods and Results— The purpose of this study was to determine whether abciximab at the time of stent implantation would reduce in-stent intimal hyperplasia measured by intravascular ultrasound at 6-month follow-up in type 2 diabetics. Ninety-six diabetic patients (96 lesions) who underwent elective stent implantation for a de novo lesion in a native coronary artery were randomly assigned to receive abciximab or no abciximab. In-stent intimal hyperplasia volume, expressed as percentage of stent volume, did not differ between groups: 41.3±21.0% for those treated with abciximab versus 40.5±18.3% for those treated without abciximab ( P =0.9). There were also no significant differences in angiographic minimal luminal diameter at follow-up (1.74±0.69 versus 1.66±0.63 mm; P =0.5), late loss (1.03±0.63 versus 1.07±0.58 mm; P =0.7), restenosis rate (17.8% versus 22.9%; P =0.5), or cumulative incidence of major adverse cardiac events at 12 months (19.1% versus 20.4%; P =0.9).

Conclusions— Six-month intravascular ultrasound volumetric analysis showed that abciximab, at the time of coronary stent implantation, was not associated with a reduction of in-stent intimal hyperplasia in diabetic patients.

Effects of 2 different antiplatelet regimens with abciximab or tirofiban on platelet function in patients undergoing coronary stenting

BACKGROUND

We sought to compare the antiplatelet effects of the glycoprotein IIb-IIIa receptor blockers abciximab or tirofiban, combined with an adjuvant therapy with clopidogrel and aspirin.

STUDY DESIGN AND METHODS

Twenty patients undergoing coronary stenting were randomly assigned to receive either abciximab or tirofiban combined with aspirin and clopidogrel. Serial blood samples were taken to assess platelet aggregation, P-selectin expression, thrombin generation, and platelet-induced endothelial cell expression of MCP-1, uPAR, and ICAM-1. Results and conclusions The therapy with aspirin plus clopidogrel attenuated agonist-induced platelet aggregation and P-selectin surface exposure (P <.05 vs aspirin monotherapy). Both tirofiban and abciximab further reduced agonist-induced platelet aggregation (P <.05), and decreased thrombin generation but had no effect on platelet alpha-granule release. None of the antithrombotic strategies significantly affected platelet-induced endothelial cell activation. Since platelet adhesion/degranulation initiates an inflammatory/mitogenic response in the vascular wall, future therapeutic strategies will have to be aimed at the inhibition of platelet release reactions.

Activated platelets trigger an inflammatory response and enhance migration of aortic smooth muscle cells

OBJECTIVE

Exposure of the subendothelium to flowing blood following rupture of atherosclerotic lesions or during balloon angioplasty initiates platelet adhesion to the vascular wall. Because activated platelets release proinflammatory mediators (e.g., interleukin (IL)-1beta) and secrete growth factors, platelet adhesion to the subendothelial matrix might contribute to the recruitment of inflammatory cells and promote migration and proliferation of vascular smooth muscle cells (SMCs).

METHODS AND RESULTS

Here, we demonstrate that incubation of cultured monolayers of aortic SMCs with alpha-thrombin-activated platelets significantly enhances the secretion of monocyte chemoattractant protein-1 (MCP-1) (P<0.05) and promotes SMC migration (P<0.05). Platelet-induced secretion of MCP-1 was abolished by anti-IL-1alpha and beta monoclonal antibodies or the IL-1 receptor antagonist (IL-1RA). In contrast, platelet-mediated SMC migration was attenuated only by anti-platelet-derived growth factor (PDGF)-mAb but not by IL-1RA. Correspondingly, recombinant human interleukin-1 (rhIL-1) beta increased MCP release by SMCs but had no effect on SMC migration. Platelet-mediated MCP secretion by SMCs involved the activation and nuclear translocation of the transcription factor nuclear factor-kappaB (NF-kappaB).

CONCLUSION

Therefore, platelet adhesion to the subendothelium increases the chemotactic and migratory properties of SMC and is likely to contribute substantially to the process of atherosclerosis and vessel (re-)stenosis.

Ramatroban, a thromboxane A2 receptor antagonist, prevents macrophage accumulation and neointimal formation after balloon arterial injury in cholesterol-fed rabbits

Macrophage infiltration appears to play an important role in restenosis after arterial intervention. Monocyte chemoattractant protein-1 (MCP-1) is a major chemotactic factor for macrophages. We have previously shown that ramatroban, a thromboxane A(2) (TXA(2)) receptor antagonist, diminished the expression of MCP-1 in human vascular endothelial cells. The aim of this study was to evaluate whether, after balloon angioplasty of atherosclerotic arteries, ramatroban would reduce MCP-1 expression, macrophage accumulation, and neointimal formation. New Zealand white rabbits were fed a cholesterol-rich diet for 4 weeks, and the abdominal aorta of the rabbits were injured by a 2-French Fogarty catheter. They were randomized to receive 1 or 5 mg/kg daily of ramatroban (n = 7 or n = 8) or saline (n = 6). At 4 weeks after balloon angioplasty, the intimal hyperplasia and the macrophage-positive area in the intima by the ramatroban treatment was significantly reduced. Monocyte chemoattractant protein-1 gene expression in injured aortas of the ramatroban-treated group was significantly less evident than in the vehicle-treated group. Thromboxane A(2) receptor blockade by ramatroban for 4 weeks after balloon angioplasty in the atherosclerotic rabbits prevented macrophage infiltration through MCP-1 downregulation and neointimal formation.

The role of platelet receptors and adhesion molecules in coronary artery disease

Platelets play a significant role in coronary artery disease through interactions with each other and with other cell types. These interactions are mediated by certain receptors on the surface of platelets and other cells which can lead to intra-coronary thrombus formation and occlusion that may result in acute coronary syndromes. The important roles of the currently available anti-platelet therapies have been well established in many clinical outcome trials in cardiovascular patients. An understanding of these different interactions provides the clinician with a background that supports the clinical importance of currently available anti-platelet therapies. Moreover, knowledge of the mechanisms of cellular crosstalk will lead to important advances in the development of better antithrombotic therapies.

Acute procedural complications and in-hospital events after percutaneous coronary interventions: eptifibatide versus abciximab

BACKGROUND

Glycoprotein IIb/IIIa antagonists reduce peri-angioplasty ischemic complications and improve in-hospital outcome in patients undergoing percutaneous coronary interventions (PCI). Prior studies have demonstrated favorable results with both eptifibatide and abciximab. The purpose of this study was to assess whether there are any differences in rates of acute procedural complications and in-hospital events with the use of these two agents.

METHODS

A retrospective review of 359 elective PCIs from June 1998 to August 2000 identified 152 PCIs treated with eptifibatide (bolus 180 microg/kg, infusion 2 microg/kg/min for 12-48 h) and 205 PCIs treated with abciximab (bolus 0.25 mg/kg, infusion 10 microg/min for 12 h). All patients received IIb/IIIa antagonists at the initiation of the intervention.

RESULTS

The clinical demographics, the angiographic morphology, the indications, and the procedural details were similar in both groups. In the eptifibatide group, the maximum ACT was lower (235+/-45 vs. 253+/-40, P<.0001). The incidence of major procedural and in-hospital events was compared. Eptifibatide and abciximab had similar rates of major complications (death or myocardial infarction) (1.4% vs. 2.9%), repeat PTCA (3.4% vs. 1.9%), and major bleeding (3.3% vs. 4.3%).

CONCLUSIONS

Eptifibatide is comparable to abciximab in regards to acute procedural complications and in-hospital events after PCI.

PlA polymorphism of integrin beta 3 differentially modulates cellular migration on extracellular matrix proteins

OBJECTIVE

Cell migration is central to multiple physiological and pathologic processes and involves interactions between integrins on the cell surface and the extracellular matrix. The Leu33Pro (PlA) polymorphism of integrin beta3 has been reported to be associated with a greater rate of restenosis after angioplasty, a process involving endothelial and smooth muscle cell migration. We have addressed the possibility that the Leu33Pro polymorphism could modify the migratory behavior of Chinese hamster ovary (CHO) cells expressing the beta3-containing integrin complexes.

METHODS AND RESULTS

Haptotactic migratory responses of CHO alpha(IIb)beta3 cells to fibronectin and vitronectin were not statistically different between the Leu33 and Pro33 cells. However, CHO cells with the Pro33 (PlA2) polymorphism had an enhanced haptotactic migratory response to fibrinogen and von Willebrand Factor. This enhanced migration (1) could be blocked by the alpha(IIb)beta3-complex-specific neutralizing mAb 10E5, by 7E3, a neutralizing mAb specific for the beta3 integrin, and by the alpha(IIb)beta3-blocking peptide Integrilin; (2) was not observed with a CHO cell line expressing an activating beta3 Cys435 to Ala mutation; and (3) was attributable to increased activity of mitogen-activated protein kinase and cyclooxygenase. CHO cell lines expressing the Pro33 isoform of alpha(v)beta3 had an enhanced haptotactic migratory response to vitronectin and osteopontin but not fibrinogen.

CONCLUSIONS

The Leu33Pro polymorphism alters the migratory behavior of cells on extracellular matrix substrates, and the alpha subunit influences the substrate specificity of this genetic effect.

Administration of glycoprotein IIb-IIIa inhibitors in patients with ST-segment elevation myocardial infarction

Patients with ST-segment elevation acute myocardial infarction require immediate reperfusion therapy. Reperfusion therapy can be provided by either pharmacologic or mechanical means. Pharmacologic reperfusion therapy consists of administering fibrinolytics, whereas mechanical reperfusion consists of performing percutaneous intervention, usually with stent placement. Each approach has been shown to decrease mortality, but each has disadvantages in establishing flow in the infarct-related artery. Regardless of the approach, during an acute myocardial infarction, activation and externalization of glycoprotein (GP) IIb-IIIa receptors occur on the surface of platelets. The GP IIb-IIIa inhibitors block the binding of fibrinogen to these platelet receptors. These inhibitors have been investigated in combination with both reperfusion strategies. The goal of adding GP IIb-IIIa inhibitor therapy to either reperfusion approach is to obtain better early, complete, and sustained reperfusion. Subsequently, this should lead to better clinical outcomes for patients with ST-segment elevation acute myocardial infarction. Although no mortality benefit has been seen with the addition of GP IIb-IIIa inhibitor therapy, ischemic complications have been reduced significantly.

The pharmacodynamics of parenteral glycoprotein IIb/IIIa inhibitors

Glycoprotein (GP) IIb/IIIa antagonists are a unique class of antiplatelet agents introduced for the management of patients undergoing percutaneous coronary intervention (PCI) and those presenting with unstable angina or non-ST segment elevation (NSTE) myocardial infarction (MI), collectively recognized as acute coronary syndromes (ACS). Eptifibatide, abciximab, and tirofiban HCl are three GPIIb/IIIa antagonists approved for use by the Food and Drug Administration. Of the three agents, eptifibatide is approved for use in both PCI and NSTE ACS patient populations, whereas abciximab is indicated for patients undergoing PCI, and tirofiban is approved for patients with NSTE ACS. Dose selection for the initial trials using the three parenteral antagonists was based on in vitro and ex vivo pharmacodynamic assays conducted under different blood collection and platelet function assay conditions. Recent comparative pharmacodynamics studies, which used newly defined and standardized assay conditions, indicate that the platelet aggregation inhibition achieved with these dosing regimens is variable. Therefore, the differences in clinical efficacy as evidenced in the more recent clinical studies (e.g., Enhanced Suppression of the Platelet Receptor GPIIb/IIIa using Integrilin Therapy [ESPRIT], Global Use of Strategies to Open Occluded Coronary Arteries IV Acute Coronary Syndromes [GUSTO-IV ACS], and Do Tirofiban HCl and ReoPro Give Similar Efficacy Outcomes Trial [TARGET]) may be related to the variable antiplatelet effects of the approved dose regimens.

Polyethylene glycol diisocyanate decreases platelet deposition after balloon injury of rabbit femoral arteries

BACKGROUND

Platelet deposition after angioplasty remains problematic and may contribute to intimal hyperplasia and restenosis. We proposed that polyethylene glycol diisocyanate (PEG-DISO), a polymer that rapidly forms covalent linkages with amine residues on proteins, could mask thrombogenic vascular wall proteins from platelets, thereby abrogating acute platelet deposition.

METHODS AND RESULTS

To test this hypothesis, we isolated the femoral arteries of 10 New Zealand White rabbits and injured them with 3 passes of a 2F Fogarty catheter which was inserted through a distal arteriotomy. Immediately after balloon injury, (111)indium-labeled autologous platelets were infused peripherally and the injured femoral arteries were randomly treated for 1 minute with a PEG-DISO solution in one artery and a control solution of the phosphate buffered saline vehicle in the contralateral artery. Following treatment, reflow was initiated. The vessels were harvested after 1 hour and radioactivity was quantified in a gamma counter. Platelet counts were standardized by weight and expressed as platelets/mg (mean +/- SEM). Platelet deposition onto arteries treated with PEG-DISO was (1.2 +/- 0.5) x 10(6) platelets/mg compared to (5.6 +/- 4.2) x 10(6) platelets/mg onto the contralateral control arteries treated with vehicle (P < 0.005). Scanning electron micrographs of the injured vessel segment confirmed qualitatively less platelet deposition on the treated segments than on the control segments.

CONCLUSION

Treatment with PEG-DISO significantly inhibited platelet deposition after vascular injury. These data support the hypothesis that treatment with PEG-DISO masks surface adhesive proteins from platelet receptors in vivo and that the resulting molecular barrier significantly reduces platelet deposition onto the damaged vessel wall for at least one hour. The formation of a molecularly thin barrier to platelet deposition may thus be a novel and effective treatment to abrogate acute intravascular thrombosis and may have value in the treatment of restenosis.

Surface modification of liposomes for selective cell targeting in cardiovascular drug delivery

Cardiovascular disease processes such as atherosclerosis, restenosis, and inflammation are typically localized to discrete regions of the vasculature, affording great opportunity for targeted pharmacological treatment. Liposomes are potentially advantageous targeted drug carriers for such intravascular applications. To facilitate their use as drug delivery vehicles, we have considered three components of liposome design: (i) identification of candidate cell surface receptors for targeting; (ii) identification of ligands that maintain binding specificity and affinity; and (iii) prevention of rapid nonspecific clearance of liposomes into the reticuloendothelial organs. In this report, we describe our work in developing liposomal surface modifications that address both targeting and clearance. An arginine-glycine-aspartic acid (RGD) containing peptide was used as a model ligand to target liposomes to the integrin GPIIb-IIIa on activated platelets. Additionally, oligodextran surfactants incorporated into liposomes provided insight into the effect of vesicle perturbations on liposome clearance, and the importance of molecular geometry in designing oligosaccharide surface modifications. Together these studies demonstrate the feasibility of using peptides to guide liposomes to desired receptors, and illustrate the influence of vesicle stability on liposome interactions in vivo. Furthermore, they underscore the importance of simultaneously considering both targeting specificity and vesicle longevity in the design of effective targeted drug delivery systems.

Platelet inhibition reduces cyclic flow variations and neointimal proliferation in normal and hypercholesterolemic-atherosclerotic canine coronary arteries

BACKGROUND

Platelet-derived growth factors help stimulate the neointimal proliferation of restenosis after coronary interventions. Reducing platelet accumulation at treated sites may attenuate restenosis. We tested this hypothesis by inducing repetitive platelet aggregation at coronary angioplasty sites in dogs and measuring subsequent neointima formation.

METHODS AND RESULTS

Cholesterol-sensitive dogs (n=74) received either 4% cholesterol-enriched diets for >8 months (n=29), creating visible atheromas, or normal canine diets (n=45). A coronary balloon angioplasty cyclic flow variation (CFV) model was used. One group of control dogs (group 1, n=8) had angioplasty with no arterial constriction applied and no drug treatment. Three other groups had arterial constrictors applied to provoke CFVs: group 2 (n=28) received no drug therapy, group 3 (n=18) received oral aspirin alone, and group 4 (n=20) received 3 oral antiplatelet agents: ridogrel, ketanserin, and clopidogrel (R+K+C) to simultaneously inhibit the thromboxane A(2), serotonin, and ADP pathways of platelet aggregation, respectively. Bleeding times were moderately prolonged in the aspirin-treated group (124+/-9 seconds after 3 weeks versus 76+/-6 seconds at baseline, P<0.01) and greatly prolonged on R+K+C (>600 versus 104+/-5 seconds, P<0.001). The frequency and severity of CFVs were inversely related to the degree of platelet inhibition and prolongation of bleeding times, as was sudden death due to acute thrombotic coronary occlusion. Quantitative histology at 8 weeks revealed increased intima-to-media ratio with CFVs: 0.89+/-0.14 in the untreated group 2 versus 0.11+/-0.04 in the control group (P<0.001). Intima-to-media ratio was significantly reduced with antiplatelet treatment (0.27+/-0.05 with aspirin treatment and 0.20+/-0.05 with R+K+C treatment, respectively, P<0.001). Cholesterol feeding did not appear to influence results.

CONCLUSIONS

Repetitive platelet accumulation at coronary angioplasty sites caused enhanced neointimal proliferation by 8 weeks. Oral inhibitors of platelet aggregation attenuated platelet function, prolonged bleeding times, reduced or prevented cyclic flows and abrupt thrombotic occlusions, and thereby inhibited neointimal proliferation. Platelet inhibition should continue to receive attention in efforts to reduce restenosis after coronary interventions.

Initial experience of platelet glycoprotein IIb/IIIa inhibition with abciximab during carotid stenting: a safe and effective adjunctive therapy

BACKGROUND AND PURPOSE

Abciximab has been shown to decrease periprocedural ischemic complications after coronary intervention. However, the adjunctive use of abciximab in carotid stenting has not been adequately studied. We sought to determine the efficacy and safety of abciximab in carotid stenting.

METHODS

Carotid stenting was performed in 151 consecutive patients determined to be at high surgical risk by a vascular surgeon. Of these, 128 consecutive patients received adjuvant therapy with abciximab (0.25 mg/kg bolus before the lesion was crossed with guidewire and 0.125 micro. kg(-1). min(-1) infusion for 12 hours.). A heparin bolus of 50 U/kg was given, and activated clotting time was maintained between 250 to 300 seconds. All patients received aspirin and thienopyridine. Procedural and 30-day outcomes were compared between the control (n=23) and abciximab (n=128) groups.

RESULTS

The 2 groups had similar baseline characteristics. Procedural events were more frequent in the control group (8%; 1 major stroke and 1 neurological death) compared with the abciximab group (1.6%; 1 minor stroke and 1 retinal infarction; P=0.05). On 30-day follow-up, 1 patient presented with delayed intracranial hemorrhage in the abciximab group. There were no other major bleeding complications.

CONCLUSIONS

Adjunctive use of abciximab for carotid stenting is safe with no increase in the risk of intracranial hemorrhage. This adjunctive therapy with potent glycoprotein IIb/IIIa inhibition may help to reduce periprocedural adverse events in patients undergoing carotid stenting.

Fluorescence spectroscopic analysis of circulating platelet activation during coronary angioplasty

BACKGROUND AND OBJECTIVE

Platelet activation during percutaneous transluminal coronary angioplasty (PTCA) initiates thrombus formation and plaque regrowth at sites of arterial injury, limiting procedure efficacy. We have developed a simple assay for circulating platelet activation based on fluorescence analysis of membrane fluidity and intracellular calcium concentration and light scattering analysis of platelet aggregation.

STUDY DESIGN/MATERIALS AND METHODS

Platelet activation state was measured in 45 patients undergoing angioplasty, before and after treatment with platelet inhibitors.

RESULTS

PTCA alone produced a decrease in pyrene dimer formation (P0.0083) and an increase in light scattering at 650 nm (P0.0128). Treatment with ADP and GPIIb/IIIa receptor antagonists reduced PTCA induced changes in pyrene dimer formation. An unexpected decrease in pyrene dimer formation (P0.05) was detected when the GPIIb/IIIa receptor antagonist was given together with an ADP receptor antagonist.

CONCLUSIONS

1) Analysis of membrane fluidity provides a sensitive marker for platelet activation state. 2) Reduced membrane fluidity after combined platelet inhibitor treatments suggests reduced antiplatelet efficacy.

Substantial reduction of platelet adhesion by heparin-coated stents

Although optimized antiplatelet medication has improved the clinical outcome after coronary stenting, vessel occlusion and restenosis still remain a relevant clinical problem. Platelets play a key role in this process. Therefore, the authors compared the platelet adhesion on different stent surface modifications (electropolished without coating or coated with carbon, carbon and additional heparin, silicon carbide, or heparin alone) to investigate their role in reducing platelet adhesion. All stents and additional stainless steel plates were incubated in heparinized whole blood with radiolabeled platelets. After washing the stents and plates four times, radioactivity caused by the adhesion of radiolabeled platelets was measured. The adhesion of radiolabeled platelets, compared to uncoated, electropolished stents, was reduced through silicon carbide coating to 58.6%, by carbon coating with additional heparin to 32.9%, and heparin coating alone to 7.7%. Stent coating with heparin is the most effective among the examined coatings in reducing platelet adhesion in vitro.

Ticlopidine pretreatment before coronary stenting is associated with sustained decrease in adverse cardiac events: data from the Evaluation of Platelet IIb/IIIa Inhibitor for Stenting (EPISTENT) Trial

BACKGROUND

Platelet inhibition at the time of a percutaneous coronary intervention has consistently been shown to decrease the risk of thrombotic adverse events but not restenosis. The role of enhanced antiplatelet protection through pretreatment with the platelet ADP-receptor antagonist ticlopidine in preventing both the early and late complications of coronary stenting has not previously been explored.

METHODS AND RESULTS

In the Evaluation of Platelet IIb/IIIa Inhibitor for Stenting (EPISTENT) trial, approximately 1600 patients were randomized to stenting with either placebo or abciximab in addition to aspirin and heparin. All stented patients also received ticlopidine after the procedure, but 58% of these patients were given ticlopidine before stenting at the discretion of the investigating physician. Among patients randomized to placebo, ticlopidine pretreatment was associated with a significant decrease in the incidence of the composite end point of death, myocardial infarction, or target vessel revascularization (TVR) at 1 year (adjusted hazard ratio, 0.73; 95% CI, 0.54 to 0.98; P:=0.036). Ticlopidine pretreatment did not significantly influence the risk of death or myocardial infarction in patients randomized to abciximab. Controlling for patient characteristics and for the propensity of being on ticlopidine, Cox proportional hazards regression identified ticlopidine pretreatment as an independent predictor of the need for TVR at 1 year (hazard ratio, 0.62; 95% CI, 0.43 to 0.89; P:=0.010) in both placebo-treated and abciximab-treated patients.

CONCLUSIONS

In the EPISTENT trial, among patients randomized to stenting, starting ticlopidine before the percutaneous coronary intervention was associated with a significant decrease in the incidence of the 12-month composite end point for patients not receiving abciximab and the need for TVR among all patients.

Relationship between platelets and neutrophil adhesion and neointimal growth after repeated arterial wall injury induced by angioplasty in pigs

Platelet and neutrophil interactions with injured vascular wall may contribute to restenosis. Their importance was mainly examined following balloon injury of intact arteries. However, dilation of diseased arteries is clinically more relevant and may elicit different responses. We investigated the relationship between platelets and neutrophil adhesion, neointima formation and P-selectin expression on damaged arteries after repeated balloon injury. In an acute single-injury model, 8 pigs were subjected to bilateral carotid angioplasty and sacrificed 1 h later. In a chronic model, 19 pigs were subjected to similar procedures and allowed to recover for 4 weeks; then 18 arteries were redilated at the same previously injured sites (double injury) while the remaining arteries were not redilated and used to investigate the extent and the adhesive properties of the neointima. After single injury, (51)Cr-platelet adhesion (x10(6)/cm(2)) increased significantly from 3.8 +/- 0.6 to 45.9 +/- 6.5 (p < 0.05) on mildly and deeply injured segments, respectively, and were statistically similar after double injury. After single injury, (111)In-neutrophil adhesion (x10(3)/cm(2)) increased from 226.6 +/- 45.5 to 512.5 +/- 70.3 (p < 0.05) on mildly and deeply injured segments, and were significantly higher (p < 0.05) after double injury (mild: 1,289.1 +/- 227.9 and deep: 2,411.8 +/- 333.9). As well, the neo-endothelium expresses P-selectin at 4 weeks and platelet and neutrophil adhesion was directly related to neointimal growth. These results, which indicate ongoing proinflammatory processes 1 month post-angioplasty, suggest that neutrophils may participate in the progression of restenosis.