Elazer R. Edelman

Endovascular Stent Design Dictates Experimental Restenosis and Thrombosis

BACKGROUND Vascular interventions that maximize initial lumen diameter provoke extensive neointimal hyperplasia but minimize its effects, causing long-term lumen size to be greater. Nevertheless, interventions such as endovascular stents, which increase lumen size above that achieved with balloon angioplasty, are subject to frequent thrombosis and restenosis. It has been unclear whether the response to stent-induced injury is determined solely by the degree of stent-induced arterial expansion or whether the geometric configuration of the stent or the material left in contact with the vessel wall also contribute. METHODS AND RESULTS We examined the vascular response to steel stents deployed in denuded rabbit iliac arteries for 14 days. In one set of experiments, the effects of sten configuration were examined, holding diameter, mass, surface area, and stent surface material constant. In another set, stent surface material was changed, with mass, configuration, and diameter unaltered. Changing stent configuration to reduce strut-strut intersections by 29% without affecting mass or surface area reduced vascular injury by 42%, thrombosis by 69%, and neointimal hyperplasia by 38%. Monocyte adhesion to stented arteries correlated linearly with vascular trauma and neointimal hyperplasia (r = .96, P < .01 for each). When the stainless steel surface was coated with an inert polymer material, vascular injury and neointimal hyperplasia were unchanged but thrombosis was eliminated. CONCLUSIONS Surface material and geometric configuration of stents may be more important than postplacement diameter in determining neointimal hyperplasia and thrombosis. Alterations in configuration affect vascular injury and neointimal hyperplasia, while surface material plays a greater role in thrombosis. Monocytes may be important modulators of stent-induced intimal thickening. Clinical confirmation of these findings may alter coronary stent deployment techniques and future stent designs.

Stent Thrombogenicity Early in High-Risk Interventional Settings Is Driven by Stent Design and Deployment and Protected by Polymer-Drug Coatings

Background— Stent thrombosis is a lethal complication of endovascular intervention. Concern has been raised about the inherent risk associated with specific stent designs and drug-eluting coatings, yet clinical and animal support is equivocal. Methods and Results— We examined whether drug-eluting coatings are inherently thrombogenic and if the response to these materials was determined to a greater degree by stent design and deployment with custom-built stents. Drug/polymer coatings uniformly reduce rather than increase thrombogenicity relative to matched bare metal counterparts (0.65-fold; P=0.011). Thick-strutted (162 &mgr;m) stents were 1.5-fold more thrombogenic than otherwise identical thin-strutted (81 &mgr;m) devices in ex vivo flow loops (P<0.001), commensurate with 1.6-fold greater thrombus coverage 3 days after implantation in porcine coronary arteries (P=0.004). When bare metal stents were deployed in malapposed or overlapping configurations, thrombogenicity increased compared with apposed, length-matched controls (1.58-fold, P=0.001; and 2.32-fold, P<0.001). The thrombogenicity of polymer-coated stents with thin struts was lowest in all configurations and remained insensitive to incomplete deployment. Computational modeling–based predictions of stent-induced flow derangements correlated with spatial distribution of formed clots. Conclusions— Contrary to popular perception, drug/polymer coatings do not inherently increase acute stent clotting; they reduce thrombosis. However, strut dimensions and positioning relative to the vessel wall are critical factors in modulating stent thrombogenicity. Optimal stent geometries and surfaces, as demonstrated with thin stent struts, help reduce the potential for thrombosis despite complex stent configurations and variability in deployment.

Local perivascular delivery of basic fibroblast growth factor in patients undergoing coronary bypass surgery: results of a phase I randomized, double-blind, placebo-controlled trial.

BACKGROUND Angiogenesis is a promising treatment strategy for patients who are not candidates for standard revascularization, because it promotes the growth of new blood vessels in ischemic myocardium. METHODS AND RESULTS We conducted a randomized, double-blind, placebo-controlled study of basic fibroblast growth factor (bFGF; 10 or 100 microg versus placebo) delivered via sustained-release heparin-alginate microcapsules implanted in ischemic and viable but ungraftable myocardial territories in patients undergoing CABG. Twenty-four patients were randomized to 10 microg of bFGF (n=8), 100 microg of bFGF (n=8), or placebo (n=8), in addition to undergoing CABG. There were 2 operative deaths and 3 Q-wave myocardial infarctions. There were no treatment-related adverse events, and there was no rise in serum bFGF levels. Clinical follow-up was available for all patients (16.0+/-6.8 months). Three control patients had recurrent angina, 2 of whom required repeat revascularization. One patient in the 10-microg bFGF group had angina, whereas all patients in the 100-microg bFGF group remained angina-free. Stress nuclear perfusion imaging at baseline and 3 months after CABG showed a trend toward worsening of the defect size in the placebo group (20.7+/-3.7% to 23.8+/-5.7%, P=0.06), no significant change in the 10-microg bFGF group, and significant improvement in the 100-microg bFGF group (19.2+/-5.0% to 9.1+/-5.9%, P=0.01). Magnetic resonance assessment of the target ischemic zone in a subset of patients showed a trend toward a reduction in the target ischemic area in the 100-microg bFGF group (10.7+/-3.9% to 3. 7+/-6.3%, P=0.06). CONCLUSIONS This study of bFGF in patients undergoing CABG demonstrates the safety and feasibility of this mode of therapy in patients with viable myocardium that cannot be adequately revascularized.

Basic fibroblast growth factor improves myocardial function in chronically ischemic porcine hearts.

The effect of basic fibroblast growth factor (bFGF) administration on regional myocardial function and blood flow in chronically ischemic hearts was studied in 26 pigs instrumented with proximal circumflex coronary artery (LCX) ameroid constrictors. In 13 animals bFGF was administered extraluminally to the proximal left anterior descending (LAD) and LCX arteries with heparin-alginate beads and 13 other animal served as controls. bFGF-treated pigs showed a fourfold reduction in left ventricular infarct size compared to untreated controls (infarct size: 1.2 +/- 0.4% vs. 5.1 +/- 1.3% of LV mass, mean +/- SEM, P < 0.05). Percent fractional shortening (% FS) in the LCX area at rest was reduced compared with the LAD region in both bFGF and control pigs. However, there was better recovery in the LCX area after rapid pacing in bFGF-treated pigs (% FSLCX/% FSLAD, 22.9 +/- 7.3%-->30.5 +/- 8.5%, P < 0.05 vs. prepacing) than in controls (16.0 +/- 7.8%-->14.3 +/- 7.0%, P = NS). Furthermore, LV end-diastolic pressure rise with rapid pacing was less in bFGF-treated than control pigs (pre-pacing; pacing; post-pacing, 10 +/- 1; 17 +/- 3; 11 +/- 1* mmHg vs 10 +/- 1; 24 +/- 4; 15 +/- 1 mmHg, *P < 0.05 vs. control). Coronary blood flow in the LCX territory (normalized for LAD flow) was also better during pacing in bFGF-treated pigs than in controls. Thus, periadventitial administration of bFGF in a gradual coronary occlusion model in pigs results in improvement of coronary flow and reduction in infarct size in the compromised territory as well as in prevention of pacing-induced hemodynamic deterioration.

Analysis of possible triggers of acute myocardial infarction (the MILIS study).

Recent documentation of a circadian variation in acute myocardial infarction (AMI) suggests that AMI is not a random event, but may frequently result from identifiable triggering activities. The possible triggers reported by 849 patients enrolled in the Multicenter Investigation of Limitation of Infarct Size were analyzed. Possible triggers were identified by 48.5% of the population; the most common were emotional upset (18.4%) and moderate physical activity (14.1%). Multiple possible triggers were reported by 13% of the population. Younger patients, men and those without diabetes mellitus were more likely to report a possible trigger than were older patients, women and those with diabetes. The likelihood of reporting a trigger was not affected by infarct size. This study suggests that potentially identifiable triggers may play an important role in AMI. Because potential triggering activities are common in persons with coronary artery disease, yet infrequently result in AMI, further studies are needed to identify (1) the circumstances in which a potential trigger may cause an event, (2) the specific nature of potential triggering activites, (3) the frequency of such activities in individuals who do not develop AMI and (4) the presence or absence of identifiable triggers in various subgroups of patients with infarction.

Neointimal thickening after stent delivery of paclitaxel : change in composition and arrest of growth over six months

OBJECTIVES The purpose of this study was to determine long-term effects of stent-based paclitaxel delivery on amount, rate and composition of neointimal thickening after stent implantation. BACKGROUND Paclitaxel prevents vascular smooth muscle cell proliferation and migration in vitro and in vivo. These actions, coupled with low solubility, make it a viable candidate for modulating vascular responses to injury and prolonged effects after local delivery. We asked whether local delivery of paclitaxel for a period of weeks from a stent coated with a bioerodible polymer could produce a sustained reduction in neointimal hyperplasia for up to six months after stenting. METHODS Stainless steel stents were implanted in the iliac arteries of rabbits after endothelial denudation. Stents were uncoated or coated with a thin layer of poly(lactide-co-sigma-caprolactone) copolymer alone or containing paclitaxel, 200 microg. RESULTS Paclitaxel release in vitro followed first-order kinetics for two months. Tissue responses were examined 7, 28, 56 or 180 days after implantation. Paclitaxel reduced intimal and medial cell proliferation three-fold seven days after stenting and virtually eliminated later intimal thickening. Six months after stenting, long after drug release and polymer degradation were likely complete, neointimal area was two-fold lower in paclitaxel-releasing stents. Tissue responses in paclitaxel-treated vessels included incomplete healing, few smooth muscle cells, late persistence of macrophages and dense fibrin with little collagen. CONCLUSIONS Poly(lactide-co-sigma-caprolactone) copolymer-coated stents permit sustained paclitaxel delivery in a manner that virtually abolishes neointimal hyperplasia for months after stent implantation, long after likely completion of drug delivery and polymer degradation.

Increased Thrombosis After Arterial Injury in Human C-Reactive Protein–Transgenic Mice

Background—C-reactive protein (CRP), an acute-phase reactant long considered merely an innocent bystander in the inflammatory process, is now recognized as a powerful predictor of cardiovascular events. Emerging in vitro evidence suggests that CRP may have direct proinflammatory and prothrombotic effects on monocytes and endothelial cells. To determine whether CRP directly modulates vascular cell function in vivo, we subjected wild-type mice, which do not express CRP, and human CRP–transgenic (CRPtg) mice to 2 models of arterial injury. Methods and Results—Baseline serum CRP levels in CRPtg mice were 18±6 mg/L. CRP levels were undetectable in wild-type mice. Transluminal wire injury led to complete thrombotic occlusion of the femoral artery at 28 days in 75% of CRPtg arteries (6 of 8) compared with 17% (2 of 12) in wild-type mice (P <0.05). In a model of arterial photochemical injury, clot formation time was shortened in CRPtg mice; mean time to occlusion was 33±19 minutes compared with 59±19 minutes in wild-type mice (n=10; P <0.05). Conclusions—Arterial injury in CRPtg mice results in an expedited and higher rate of thrombotic occlusion. This is the first report of a prothrombotic phenotype directly attributable to the presence of human CRP in vivo. Investigation of the inflammatory-thrombotic axis in CRPtg mice may elucidate the prothrombotic actions of CRP in unstable arterial diseases and may pave the way for novel therapeutic interventions for preventing cardiovascular events.

Drug-Eluting Stents in Preclinical Studies: Recommended Evaluation From a Consensus Group

The arrival of drug-eluting stents raises important questions about preclinical evaluation of devices and the optimal means of predicting clinical safety and efficacy. The Interventional, Regulatory, Commercial, and Scientific communities have all asked for assistance in defining criteria for device evaluation. This document is an integrated view of requirements for evaluating drug-eluting stents in preclinical models. The suggested requirements encompass study design, experimental performance, and histopathologic evaluations, emphasizing safety and efficacy at multiple points in time. This is a consensus document assembled by clinical, academic, and industrial investigators engaged in preclinical interventional device evaluation. Suggested requirements might well serve as a standard but do not prescribe a single manner in which all devices should be evaluated. They instead motivate such an evaluation and describe how examinations might be performed. It is understood that methods will change and knowledge will evolve, in particular as corroboration is established with clinical data. The dynamic nature of this document allows for future modifications and additions. A drug-eluting stent presents or releases single or multiple bioactive agents into the blood stream. The drug can deposit in and/or affect blood vessels, cells, plaque, or tissues either adjacent to the stent or at a distance. Systemic drug concentrations may be avoided or desirable. It is assumed that drugs undergoing preclinical evaluation will have sound theoretical and practical reasons for biological success, and that the preclinical studies will help answer the magnitude and safety of effect when presented with or from the stent. It is likely that substantial empirical data already exists documenting the effects of these drugs on isolated cells in culture and even in vivo after systemic administration. Some drugs may already be in clinical use. Drug can be embedded and released from within (“matrix-type”) or surrounded by and released through (“reservoir-type”) polymer materials that coat …

Prediction of the Localization of High-Risk Coronary Atherosclerotic Plaques on the Basis of Low Endothelial Shear Stress An Intravascular Ultrasound and Histopathology Natural History Study

Background— Low endothelial shear stress (ESS) promotes the development of atherosclerosis; however, its role in the progression of atherosclerotic plaques and evolution to inflamed high-risk plaques has not been studied. Our hypothesis was that the lowest values of ESS are responsible for the development of high-risk coronary atherosclerotic plaques associated with excessive expansive remodeling. Methods and Results— Twenty-four swine, treated with streptozotocin to induce diabetes and fed a high-fat diet, were allocated into early (n=12) and late (n=12) atherosclerosis groups. Intima-media thickness was assessed by intravascular ultrasound in the coronary arteries at weeks 4 and 8 in the early group and weeks 23 and 30 in the late group. Plaques started to develop after week 8, leading to marked heterogeneity in plaque severity at week 30. ESS was calculated in plaque-free subsegments of interest (n=142) in the late group at week 23. Coronary arteries (n=31) of this group were harvested at week 30, and the subsegments of interest were identified and analyzed histopathologically. Low ESS was an independent predictor of the development of high-risk plaques, characterized by intense lipid accumulation, inflammation, thin fibrous cap, severe internal elastic lamina degradation, and excessive expansive remodeling. The severity of high-risk plaque characteristics at week 30 was significantly correlated with the magnitude of low ESS at week 23. Conclusions— The magnitude of low ESS determines the complexity and heterogeneity of atherosclerotic lesions and predicts the development of high-risk plaque.

Regulation by Adrenocorticotropic Hormone of the in Vivo Expression of Scavenger Receptor Class B Type I (SR-BI), a High Density Lipoprotein Receptor, in Steroidogenic Cells of the Murine Adrenal Gland

The class B, type I scavenger receptor, SR-BI, binds high density lipoprotein (HDL) and can mediate selective uptake of HDL cholesteryl esters by cultured cells. The high levels of expression of SR-BI in steroidogenic tissues and the importance of selective uptake from HDL as a source of cholesterol for steroidogenesis raised the possibility that SR-BI may participate in cholesterol delivery to steroidogenic tissues in vivo. We have used immunoblotting and immunohistochemical methods to show that SR-BI is specifically expressed in a distinctive pattern on the surfaces of steroid-producing cells in the murine adrenal glands cortex and that its expression in vivo is induced by adrenocorticotropic hormone and suppressed by glucocorticoids. Thus, expression of SR-BI protein is coordinately regulated with adrenal steroidogenesis. These data provide strong support for the hypothesis that SR-BI is a physiologically relevant HDL receptor that provides substrate cholesterol for steroid hormone synthesis.