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

Myocardin-Dependent Kv1.5 Channel Expression Prevents Phenotypic Modulation of Human Vessels in Organ Culture

Objective:

We have previously described that changes in the expression of Kv channels associate to phenotypic modulation (PM), so that Kv1.3/Kv1.5 ratio is a landmark of vascular smooth muscle cells phenotype. Moreover, we demonstrated that the Kv1.3 functional expression is relevant for PM in several types of vascular lesions. Here, we explore the efficacy of Kv1.3 inhibition for the prevention of remodeling in human vessels, and the mechanisms linking the switch in Kv1.3 /Kv1.5 ratio to PM.

Approach and Results:

Vascular remodeling was explored using organ culture and primary cultures of vascular smooth muscle cells obtained from human vessels. We studied the effects of Kv1.3 inhibition on serum-induced remodeling, as well as the impact of viral vector-mediated overexpression of Kv channels or myocardin knock-down. Kv1.3 blockade prevented remodeling by inhibiting proliferation, migration, and extracellular matrix secretion. PM activated Kv1.3 via downregulation of Kv1.5. Hence, both Kv1.3 blockers and Kv1.5 overexpression inhibited remodeling in a nonadditive fashion. Finally, myocardin knock-down induced vessel remodeling and Kv1.5 downregulation and myocardin overexpression increased Kv1.5, while Kv1.5 overexpression inhibited PM without changing myocardin expression.

Conclusions:

We demonstrate that Kv1.5 channel gene is a myocardin-regulated, vascular smooth muscle cells contractile marker. Kv1.5 downregulation upon PM leaves Kv1.3 as the dominant Kv1 channel expressed in dedifferentiated cells. We demonstrated that the inhibition of Kv1.3 channel function with selective blockers or by preventing Kv1.5 downregulation can represent an effective, novel strategy for the prevention of intimal hyperplasia and restenosis of the human vessels used for coronary angioplasty procedures.

GPIIb/IIIa inhibitors: From bench to bedside and back to bench again

From the discovery of the platelet glycoprotein (GP) IIb/IIIa and identification of its central role in haemostasis, the integrin GPIIb/IIIa (αIIbβ3, CD41/CD61) was destined to be an anti-thrombotic target. The subsequent successful development of intravenous ligand-mimetic inhibitors occurred during a time of limited understanding of integrin physiology. Although efficient inhibitors of ligand binding, they also mimic ligand function. In the case of GPIIb/IIIa inhibitors, despite strongly inhibiting platelet aggregation, paradoxical fibrinogen binding and platelet activation can occur. The quick progression to development of small-molecule orally available inhibitors meant that this approach inherited many potential flaws, which together with a short half-life resulted in an increase in mortality and a halt to the numerous pharmaceutical development programs. Limited clinical benefits, together with the success of other anti-thrombotic drugs, in particular P2Y12 ADP receptor blockers, have also led to a restrictive use of intravenous GPIIb/ IIIa inhibitors. However, with a greater understanding of this key platelet-specific integrin, GPIIb/IIIa remains a potentially attractive target and future drug developments will be better informed by the lessons learnt from taking the current inhibitors back to the bench. This overview will review the physiology behind the inherent problems of a ligand-based integrin inhibitor design and discuss novel promising approaches for GPIIb/IIIa inhibition.

Integrin αIIbβ3: from discovery to efficacious therapeutic target

From the initial description of platelets in 1882, their propensity to aggregate and to contribute to thrombosis was apparent. Indeed, excessive platelet aggregation is associated with myocardial infarction and other thrombotic diseases whereas Glanzmann thrombasthenia, in which platelet aggregation is reduced, is a bleeding syndrome. Over the last half of the 20th century, many investigators have provided insights into the cellular and molecular basis for platelet aggregation. The major membrane protein on platelets, integrin αIIbβ3, mediates this response by rapidly transiting from its resting to an activated state in which it serves as a receptor for ligands that can bridge platelets together. Monoclonal antibodies, natural products, and small peptides were all shown to inhibit αIIbβ3 dependent platelet aggregation, and these inhibitors became the forerunners of antagonists that proceeded through preclinical testing and into large patient trials to treat acute coronary syndromes, particularly in the context of percutaneous coronary interventions. Three such αIIbβ3 antagonists, abciximab, eptifibatide, and tirofiban, received Food and Drug Administration approval. Over the past 15 years, millions of patients have been treated with these αIIbβ3 antagonists and many lives have been saved by their administration. With the side effect of increased bleeding and the development of new antithrombotic drugs, the use of αIIbβ3 antagonists is waning. Nevertheless, they are still widely used for the prevention of periprocedural thrombosis during percutaneous coronary interventions. This review focuses on the biology of αIIbβ3, the development of its antagonists, and some of the triumphs and shortcomings of αIIbβ3 antagonism.

Protective effect of the CYP2C19 *17 polymorphism with increased activation of clopidogrel on cardiovascular events

BACKGROUND

The prodrug clopidogrel requires activation by cytochrome P-450 (CYP) enzymes for its antiplatelet effect. The genes encoding enzymes for clopidogrel activation are polymorphic, leading to reduced or increased function, depending on the respective genotype. Reduced-function alleles have been associated with an increase in cardiovascular events.

METHODS

We tested the association of the presence of the ABCB1 (C/T) T-allele, CYP2C19*2 (G/A) A-allele, or CYP2C19*17 (C/T) T-allele with the primary end point of the need of clinically-driven target lesion revascularization (TLR) and the secondary end points of major adverse cardiovascular events (MACE; including death, myocardial infarction [MI], and TLR) at 1 year in a high-risk population of 928 patients with acute MI.

RESULTS

Carriers of the CYP2C19*17 T-allele, with increased clopidogrel activation, had a 37% relative reduction in the TLR incidence, the primary end point (14.0% vs 22.3%, P = .002), and a 22% relative reduction of the secondary end point MACE (22.0% vs 28.1%, P = .04) compared with noncarriers, respectively. The association of the T-allele with TLR remained significant in the multivariate analysis (P = .001). The ABCB1 (C/T) and the CYP2C19*2 (G/A) polymorphisms were not associated with the incidence of TLR or MACE.

CONCLUSIONS

Based on the genetic analysis in a high-risk population of acute MI patients with interventional treatment and continuous clopidogrel therapy, our study found a protective effect for carriers of an increased-function CYP2C19*17 T-allele with significantly lower rates of TLR and MACE. T-allele carriers with acute MI and increased clopidogrel activation had significantly reduced clinical event rates.

Antiplatelet therapy in percutaneous coronary intervention: a critical review of the 2007 AHA/ACC/SCAI guidelines and beyond

Antiplatelet therapy is a mainstay in the treatment of patients who have undergone percutaneous coronary intervention (PCI). Although the 2007 PCI treatment guidelines were published by the American College of Cardiology, the American Heart Association, and the Society for Cardiovascular Angiography and Interventions, new clinical evidence has emerged, expanding our understanding of antiplatelet use and potentially affecting the treatment guidelines. For example, clinical trial results prompted a Science Advisory to recommend that dual therapy with aspirin and clopidogrel be used for longer periods-up to 1 year in patients who receive bare metal stents and at least 1 year in patients receiving drug-eluting stents. New trial results have also emerged regarding the use of glycoprotein IIb/IIIa antagonists such as abciximab, eptifibatide, and tirofiban. This article reviews the current recommendations for antiplatelet therapy in PCI patients, recent trial results, newly developed agents, ongoing clinical trials, and the future direction of antiplatelet therapy in patients who undergo PCI.

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.

Platelet Activation in Coronary Artery Disease

BACKGROUND

Platelet activation and aggregation play a key role in coronary artery disease, with antiplatelet therapies leading to improved clinical outcomes. Limited data exist as to whether peripheral venous blood measurements of platelet physical indexes (eg, platelet count, volume, and granularity) and soluble markers of platelet activation (eg, P-selectin [sP-sel] and CD40 ligand [CD40L]) reflect the local (intracardiac) coronary environment. Furthermore, how percutaneous coronary interventions (PCIs) affect levels of peripheral/cardiac platelet indexes is unclear.

METHODS

Blood samples were sequentially acquired from the coronary os, aortic root, coronary sinus, and the femoral vein, and where relevant, pre-PCI and post-PCI. Eighty-seven patients undergoing coronary angiography were recruited (mean [+/-SD] age, 59.8+/-10.8 years; 54 men [62%]), of whom 36 proceeded to PCI. Platelet physical indexes and plasma sP-sel and CD40L levels were measured (by enzyme-linked immunosorbent assay).

RESULTS

At baseline, no intracardiac vs peripheral differences were noted in sP sel levels, while CD40L levels were elevated in the aorta compared to the coronary sinus and femoral venous. The mean platelet count (MPC) was similar at all four sites, but within the coronary sinus blood, mean platelet volume (MPV) was significantly lower and mean platelet granularity (MPG) was higher when compared to arterial levels. Though aortic and femoral levels of sP-sel were raised following PCI, transcardiac gradients of plasma sP-sel levels were unaffected. PCI was associated with lower CD40L, MPC, and MPV levels but with a higher MPG level in all sampling sites.

CONCLUSIONS

sP-sel levels measured peripherally reflect the cardiac environment, unlike CD40L, MPC, MPV, and MPG. PCI leads to further platelet activation (raised sP-sel) despite aggressive antiplatelet therapy.