Colchicine and antineoplastic therapy for the prevention of restenosis after percutaneous coronary interventions

Colchicine may become a new cornerstone therapy for coronary artery disease: a meta-analysis of randomized controlled trials

PURPOSE

Colchicine is an ancient anti-inflammatory drug. In recent years, an increasing number of studies have shown that colchicine improves the prognosis of patients with coronary artery disease (CAD), while other studies have reported the opposite. The aim of this study was to evaluate the relative efficacy and safety of colchicine in treating CAD.

METHODS

PubMed, EMBASE, the Cochrane Library, and ClinicalTrials.gov were searched from inception to 20 October 2020 for randomized controlled trials (RCTs) comparing colchicine and placebo in patients with CAD. The primary outcomes were the primary composite outcomes of cardiovascular death, myocardial infarction (MI), ischemic stroke, or ischemia-driven coronary revascularization after colchicine administration. The secondary outcomes were cardiovascular death, death from any cause, noncardiac death, MI, ischemic stroke, coronary revascularization, gastrointestinal (GI) symptoms, and the different effects of colchicine in acute and chronic CAD. We assessed the pooled odds ratio (OR) of all-cause and cardiovascular mortality for CAD in fixed-effects models, the pooled risk ratio (RR) of the primary composite outcomes, MI, ischemic stroke, and ischemia-driven coronary revascularization in fixed-effects models and the pooled RR of GI symptoms in random-effects models. The Cochrane risk of bias tool was used to assess the risk of bias in the included RCTs.

FINDINGS

Eleven of the 894 identified studies (n = 12,899 patients) were included (6501 subjects in the colchicine group; 6389 subjects in the control group). The colchicine group had significantly lower pooled RRs of the primary composite outcomes (0.73, 95% confidence interval (CI) 0.64-0.84, P < 0.0001), MI (0.77, 95% CI 0.64-0.92, P = 0.004), ischemic stroke (0.47, 95% CI 0.30-0.76, P = 0.002), and ischemia-driven coronary revascularization (0.77, 95% CI 0.66-0.89, P = 0.0007), while the pooled RR of adverse GI events (2.15 95% CI 1.40-3.31, P = 0.0005) was significantly higher. Colchicine had a lower pooled RR of ischemic stroke (0.28, 95% CI 0.12-0.65, P = 0.003) for patients with acute compared with chronic CAD.

IMPLICATIONS

Colchicine treatment significantly decreased the risk of primary cardiovascular composite outcomes, MI, ischemic stroke, and ischemia-driven coronary revascularization in CAD patients but increased adverse GI events. There was no significant difference in all-cause mortality, cardiovascular mortality, and non-cardiovascular death between the colchicine and control groups. Colchicine performs better in acute CAD patients with ischemic stroke than chronic CAD patients. Colchicine might be a new treatment for patients with CAD.

Inflammation and ischemic heart disease: The next therapeutic target?

Inflammation plays an important role in several stages of the cardiovascular continuum. In recent decades a plethora of studies have provided new data highlighting the role of inflammation in atherogenesis and atherothrombosis in two-way interactions with various cardiovascular risk factors and further influencing these dynamic processes. The concept of targeting residual inflammatory risk among individuals with ischemic heart disease (IHD) is therefore gaining increasing attention. Recently, several landmark randomized controlled trials have assessed different pharmacological approaches that may mitigate this residual risk. The results of some of these studies, such as CANTOS with canakinumab and COLCOT and LoDoCo2 with colchicine, are promising and have provided data to support this concept. Moreover, though several aspects remain to be clarified, these trials have shown the potential of modulating inflammation as a new target to reduce the risk of cardiovascular events in secondary prevention patients. In the present review, we aim to present a pragmatic overview of the complex interplay between inflammation and IHD, and to critically appraise the current evidence on this issue while presenting future perspectives on this topic of pivotal contemporary interest.

Inflammation and ischemic heart disease: The next therapeutic target?

Inflammation plays an important role in several stages of the cardiovascular continuum. In recent decades a plethora of studies have provided new data highlighting the role of inflammation in atherogenesis and atherothrombosis in two-way interactions with various cardiovascular risk factors and further influencing these dynamic processes. The concept of targeting residual inflammatory risk among individuals with ischemic heart disease (IHD) is therefore gaining increasing attention. Recently, several landmark randomized controlled trials have assessed different pharmacological approaches that may mitigate this residual risk. The results of some of these studies, such as CANTOS with canakinumab and COLCOT and LoDoCo2 with colchicine, are promising and have provided data to support this concept. Moreover, though several aspects remain to be clarified, these trials have shown the potential of modulating inflammation as a new target to reduce the risk of cardiovascular events in secondary prevention patients. In the present review, we aim to present a pragmatic overview of the complex interplay between inflammation and IHD, and to critically appraise the current evidence on this issue while presenting future perspectives on this topic of pivotal contemporary interest.

Colchicine in Stable Coronary Artery Disease

PURPOSE

Disease management of stable coronary artery disease consists of controlling hemostasis and lipid regulation. No treatment strategies preventing plaque erosion or rupture are yet available. Cholesterol crystal-induced inflammation leading to plaque destabilization is believed to be an important factor contributing to plaque instability and might well be amenable to treatment with anti-inflammatory drugs. Colchicine has anti-inflammatory properties with the potential to address both the direct and indirect inflammatory mechanisms in the plaque.

METHODS

A literature search was performed in MEDLINE (PubMed), EMBASE, and the Cochrane Central Register of Controlled Trials, as well as in the clinical trial registries, to identify finished and ongoing clinical studies on colchicine in stable coronary artery disease.

FINDINGS

Preclinical findings of colchicine in stable coronary artery disease have shown protective effects on surrogate outcomes, such as myocardial infarction size and postangioplasty restenosis. Retrospective cohort studies in patients with gout report a lower incidence of combined cardiovascular outcomes in those treated with colchicine. Thus far, one prospective, randomized clinical trial has provided evidence on a possible protective effect of colchicine in stable coronary artery disease. Meta-analysis of trials of colchicine in multiple cardiovascular diseases revealed a decrease in myocardial infarction with varying levels of evidence. Currently, 5 major clinical trials involving >10,000 patients are recruiting patients, all focusing on major cardiovascular outcomes.

IMPLICATIONS

The body and quality of evidence regarding the efficacy of colchicine for secondary prevention of stable and acute phases of coronary artery disease will be greatly expanded in the upcoming years, providing less biased and more accurate effect estimates. If colchicine's anti-inflammatory characteristics translate to improved event-free cardiovascular survival, this relatively safe, low-cost, and well-known drug may become the third pillar (next to lipid regulation and platelet inhibition) in the medical management of stable coronary artery disease.

Intramural delivery of rapamycin with alphavbeta3-targeted paramagnetic nanoparticles inhibits stenosis after balloon injury

BACKGROUND

Drug eluting stents prevent vascular restenosis but can delay endothelial healing. A rabbit femoral artery model of stenosis formation after vascular injury was used to study the effect of intramural delivery of alpha(v)beta(3)-integrin-targeted rapamycin nanoparticles on vascular stenosis and endothelial healing responses.

METHODS AND RESULTS

Femoral arteries of 48 atherosclerotic rabbits underwent balloon stretch injury and were locally treated with either (1) alpha(v)beta(3)-targeted rapamycin nanoparticles, (2) alpha(v)beta(3)-targeted nanoparticles without rapamycin, (3) nontargeted rapamycin nanoparticles, or (4) saline. Intramural binding of integrin-targeted paramagnetic nanoparticles was confirmed with MR molecular imaging (1.5 T). MR angiograms were indistinguishable between targeted and control arteries at baseline, but 2 weeks later they showed qualitatively less luminal plaque in the targeted rapamycin treated segments compared with contralateral control vessels. In a first cohort of 19 animals (38 vessel segments), microscopic morphometric analysis of the rapamycin-treated segments revealed a 52% decrease in the neointima/media ratio (P<0.05) compared to control. No differences (P>0.05) were observed among balloon injured vessel segments treated with alpha(v)beta(3)-targeted nanoparticles without rapamycin, nontargeted nanoparticles with rapamycin, or saline. In a second cohort of 29 animals, endothelial healing followed a parallel pattern over 4 weeks in the vessels treated with alpha(v)beta(3)-targeted rapamycin nanoparticles and the 3 control groups.

CONCLUSIONS

Local intramural delivery of alpha(v)beta(3)-targeted rapamycin nanoparticles inhibited stenosis without delaying endothelial healing after balloon injury.

Colchicine Inhibits Intimal Hyperplasia and Leukocyte VEGF Expression in Dogs

BACKGROUND

Restenosis due to intimal hyperplasia following percutaneous transluminal angioplasty limits its long-term efficacy. We evaluated the effect of colchicine on the development of intimal hyperplasia following balloon angioplasty and on the vascular endothelial growth factor (VEGF) expression in leukocytes.

MATERIAL AND METHODS

Adult dogs underwent balloon angioplasty of the right iliofemoral artery. Group 1 served as control, while groups 2 and 3 (six animals per group) received 0.1 and 0.5 mg/kg/d of colchicine p.o., respectively, starting 2 d before angioplasty and continued for 14 d. Before angioplasty and at day 14, blood samples were collected for drug toxicity analysis and the determination of leukocyte expression of VEGF. Animals were euthanized and iliofemoral arteries were perfusion fixed in situ and processed for histological and morphometric analysis.

RESULTS

Balloon angioplasty without colchicine resulted in 446% (P < 0.001), 111% (P = 0.7), and 267% (P < 0.001) increase in intimal and medial thickness and intima/media ratio compared with contralateral uninjured iliofemoral arteries. Low-dose and high-dose colchicine resulted in 32% and 58% reduction in intima/media ratio, respectively (both P < 0.001). VEGF expression in leukocytes of control group was up-regulated (40%), but was down-regulated by 12% and 55%, respectively, in low-dose and high-dose colchicine groups at 2 wk after angioplasty compared with preangioplasty expression. The results of complete blood count and serum transaminases and creatinine were within normal range.

CONCLUSION

This study demonstrates that oral colchicine for 2 wk significantly reduces intimal hyperplasia following balloon angioplasty in dogs through down-regulation of leukocyte VEGF expression and without apparent toxicity.

Extended delivery of the antimitotic agent colchicine from thermoresponsive N-isopropylacrylamide-based copolymer films to human vascular smooth muscle cells

The aim of this study was to establish the capacity of thermoresponsive poly(N-isopropylacrylamide) copolymer films to deliver bioactive concentrations of an antimitotic agent to human vascular smooth muscle cells (HASMC) over an extended period of time. Copolymer films were prepared using a 50:50 (w/w) ratio of N-isopropylacrylamide (NiPAAm) monomer to the more hydrophobic N-tert-butylacrylamide (NtBAAm) and loaded with the antimitotic agent colchicine (0.1 micromol per film) at room temperature. Colchicine release from films was sustained over a 14-day period. At 24 h postloading, the concentration of colchicine in the medium overlying films was 2.12 +/- 0.16 microM; this fell to 0.20 +/- 0.01 microM at 7 days and decreased further to 0.12 +/- 0.01 microM after 14 days. Colchicine released from copolymer films inhibited proliferation when subsequently placed on HASMC: at 0.1 microM, released colchicine reduced proliferation to 18.5 +/- 0.8% of control cells (p < 0.001, n = 9). The antiproliferative effect of released colchicine was comparable to that of native colchicine, as observed in separate experiments. Furthermore, colchicine released from 50:50 polymer films inhibited the proliferation of cells grown in the same environment as the copolymer. Inhibition of cell proliferation was not due to the release of cytotoxic particles from the copolymer because medium incubated with copolymer for 5 days and then applied to HASMC did not alter cell viability. In conclusion, this study demonstrates that 50:50 NiPAAm:NtBAAm copolymers can deliver bioactive concentrations of the antimitotic agent colchicine to human vascular cells over an extended period of time.

Changes in cisplatin delivery due to surface-coated poly (lactic acid)-poly(epsilon-caprolactone) microspheres

Smooth muscle cell proliferation plays a major role in the genesis of restenosis after angioplasty or vascular injury. Local delivery of agents capable of modulating vascular responses, have the potential to prevent restenosis. However, the development of injectable microspheres for sustained drug delivery to the arterial wall is a major challenge. We demonstrated the possibility of entrapping an antiproliferative agent, cisplatin, in a series of surface coated biodegradable microspheres composed of poly(lactic acid)poly(caprolactone) blends, with a mean diameter of 2-10 pm. The microspheres were surface coated with poly ethylene glycol (PEG), chitosan (Chit), or alginate (Alg). A solution of cisplatin and a 50:50 blend of polylactic acid (PLA)-polycaprolactone (PCL) dissolved in acetone-dichloromethane mixture was poured into an aqueous solution of PEG (or polyvinyl alcohol or Chit or Alg) with stirring using a high speed homogenizer, for the formation of microspheres. Cisplatin recovery in microspheres ranged from 25-45% depending on the emulsification system used for the preparations. Scanning electron microscopy revealed that the PLA-PCL microspheres were spherical in shape and had a smooth surface texture. The amount of drug release was much higher initially (20-30%), this was followed by a constant slow-release profile for a 30-day period of study. It has been found that drug release depends on the amount of entrapped drug, on the presence of extra cisplatin in the dispensing phase, and on the polymer coatings. This PEG or Alg-coated PLA/PCL microsphere formulation may have potential for the targeted delivery of antiproliferative agents to treat restenosis.

Carrier proteins determine local pharmacokinetics and arterial distribution of paclitaxel

The growing use of local drug delivery to vascular tissues has increased interest in hydrophobic compounds. The binding of these drugs to serum proteins raises their levels in solution, but hinders their distribution through tissues. Inside the arterial interstitium, viscous and steric forces and binding interactions impede drug motion. As such, this might be the ideal scenario for increasing the amount of drug delivered to, and residence time within, arterial tissues. We quantified carrier-mediated transport for paclitaxel, a model hydrophobic agent with potential use in proliferative vascular diseases, by determining, in the presence or absence of carrier proteins, the maximum concentration of drug in aqueous solution, the diffusivity in free solution, and the diffusivity in arterial tissues. Whereas solubility of paclitaxel was raised 8.1-, 21-, and 57-fold by physiologic levels of alpha(1)-acid glycoproteins, bovine serum albumin, and calf serum over that in protein-free solution, diffusivity of paclitaxel in free solution was reduced by 41, 49, and 74%, respectively. When paclitaxel mixed in these solutions was applied to arteries both in vitro and in vivo, drug was more abundant at the tissue interface, but protein carriers tended to retain drug in the lumen. Once within the tissue, these proteins did not affect the rate at which drug traverses the tissue because this hydrophobic drug interacted with the abundant fixed proteins and binding sites. The protein binding properties of hydrophobic compounds allow for beneficial effects on transvascular transport, deposition, and distribution, and may enable prolonged effect and rationally guide local and systemic strategies for their administration.

Rhenium-188 for inhibition of human aortic smooth muscle cell proliferation

PURPOSE

To evaluate dose-dependent growth-modulating effects of the beta-gamma emitter Rhenium-188 on cultured human aortic smooth muscle cells (haSMC).

METHODS AND MATERIALS

HaSMC were plated in 25 cm(2) flasks. Two days after plating, cells were incubated with the Re-188 (beta E(max) 2.12 MeV, tissue range(max) < 10 mm, T(1/2) 17 h) for five days. The doses administered were 0.2 Gy, 1, 4, 6, 8, 16, and 32 Gy. After five days, the radionuclide was removed. Cell growth, cell cycle distribution, and clonogenic activity were analyzed for the following 25 days.

RESULTS

The 0.2 and 1 Gy groups did not show relevant growth-inhibiting effects compared to the control groups. The 4 to 32 Gy groups presented dose-dependent growth inhibition, with a complete growth arrest of the 16 and 32 Gy groups. Clonogenic activity of the smooth muscle cell was strongly inhibited from doses > or =8 Gy. Flow cytometry showed a lasting dose-dependent G2/M phase block.

CONCLUSION

Smooth muscle cell (SMC) growth can be controlled effectively with Re-188 for at least 25 days after radiation in vitro. As the first four weeks after arterial angioplasty are crucial concerning neointimal formation, Re-188 may be a valuable radionuclide to inhibit restenosis after arterial angioplasty.

Novel beta-emitting poly(ethylene terephthalate) surface modification

Restenosis after percutaneous interventions in coronary and peripheral arteries leads to repeat procedures and surgery in a significant number of patients. We have previously demonstrated that irradiation of an arterial site using an endovascular source (brachytherapy) is highly effective in preventing the restenotic process. To this end, a novel beta radiation delivery system was developed, based on the adsorption of (32)P (o-phosphoric acid) by pH-sensitive chitosan hydrogel on a poly(ethylene terephthalate) (PET) balloon surface. The PET balloon surface was treated with oxygen plasma and coated with chitosan hydrogel. Covalent bonds, ionic bonds, and hydrogen bonds all contribute to the adhesion between chitosan hydrogel and PET. In the aqueous phosphoric acid (PA) solution, the -NH(2) groups of chitosan were protonated by PA and the adsorption of PA occurred at the same time. The effect of PA concentration and temperature on adsorption efficiency and kinetics were studied. More than 70% PA was adsorbed on the sample surface in 0.2 mM PA solution. The surface of samples was also investigated by attenuated total reflection-Fourier transform infrared spectroscopy and scanning electron microscopy. PET surface may be modified to carry high activity beta emitters; such materials may be useful in a therapeutic setting

Preventive effects of the heparin-coated stent on restenosis in the porcine model

The coronary stent reduces acute coronary arterial occlusion and late restenosis during and after coronary intervention. However, stent thrombosis and restenosis are still major limitations in the widespread use of the coronary stent. Local drug delivery using the heparin-coated stent may be a new approach, which reduces the incidence of stent thrombosis and restenosis. In order to evaluate the effects of the heparin-coated stent on stent restenosis, heparin-coated stents were compared with control stents in a porcine coronary stent restenosis model. Stent overdilation injury (stent:artery = 1.3:1.0) was performed with bare Wiktor stents (group I, n = 10) and heparin-coated Wiktor stents (group II, n = 20; HEPAMED, Medtronics) in porcine coronary arteries. Follow-up quantitative coronary angiography (QCA) was performed at 4 weeks after stenting, and histo-pathologic assessments of stented porcine coronary arteries were compared in both groups. On QCA, percent diameter stenosis was significantly higher in group I than in group II (16.3% +/- 6.62% vs. 9.6% +/- 5.06%, P < 0.05). The injury score of stented porcine coronary arteries was the same in both groups (1. 26 +/- 0.23 vs. 1.20 +/- 0.22). The area of pathologic stenosis of the stented arteries was higher in group I than in group II (41.6% +/- 12.5% vs. 27.1% +/- 9.9%, P < 0.005). The neointimal area was higher in group I than in group II (4.58 +/- 1.41 mm(2) vs. 2.57 +/- 1.07 mm(2), P < 0.05). By immunohistochemistry, the proliferating cell nuclear antigen (PCNA) index was higher in group I compared with group II (11.2% +/- 6.75% vs. 6.3% +/- 4.14%, P < 0.05). The heparin-coated stent is effective in the prevention of late coronary stent restenosis in a porcine coronary stent restenosis model. This may be related to the inhibition of neointimal cell proliferation.

Inhibition of intimal thickening after balloon angioplasty in porcine coronary arteries by targeting regulators of the cell cycle

BACKGROUND

Although percutaneous transluminal coronary angioplasty (PTCA) is a highly effective procedure to reduce the severity of stenotic coronary atherosclerotic disease, its long-term success is significantly limited by the high rate of restenosis. Several cellular and molecular mechanisms have been implicated in the development of restenosis post-PTCA, including vascular smooth muscle cell (VSMC) activation, migration, and proliferation. Recently, our group demonstrated that rapamycin, an immunosuppressant agent with antiproliferative properties, inhibits both rat and human VSMC proliferation and migration in vitro. In the present study, we investigated (1) whether rapamycin administration could reduce neointimal thickening in a porcine model of restenosis post-PTCA and (2) the mechanism by which rapamycin inhibits VSMCs in vivo.

METHODS AND RESULTS

PTCA was performed on a porcine model at a balloon/vessel ratio of 1.7+/-0.2. Coronary arteries were analyzed for neointimal formation 4 weeks after PTCA. Intramuscular administration of rapamycin started 3 days before PTCA at a dose of 0.5 mg/kg and continued for 14 days at a dose of 0.25 mg/kg. Cyclin-dependent kinase inhibitor (CDKI) p27(kip1) protein levels and pRb phosphorylation within the vessel wall were determined by immunoblot analysis. PTCA in the control group was associated with the development of significant luminal stenosis 4 weeks after the coronary intervention. Luminal narrowing was a consequence of significant neointimal formation in the injured areas. Rapamycin administration was associated with a significant inhibition in coronary stenosis (63+/-3.4% versus 36+/-4.5%; P<0.001), resulting in a concomitant increase in luminal area (1.74+/-0.1 mm2 versus 3. 3+/-0.4 mm2; P<0.001) after PTCA. Inhibition of proliferation was associated with markedly increased concentrations of the p27(kip1) levels and inhibition of pRb phosphorylation within the vessel wall.

CONCLUSIONS

Rapamycin administration significantly reduced the arterial proliferative response after PTCA in the pig by increasing the level of the CDKI p27(kip1) and inhibition of the pRb phosphorylation within the vessel wall. Therefore, pharmacological interventions that elevate CDKI in the vessel wall and target cyclin-dependent kinase activity may have a therapeutic role in the treatment of restenosis after angioplasty in humans.

Coronary atherosclerosis and interventions: pathological sequences and restenosis

The primary cause of cardiac morbidity and mortality in developed countries is ischemic (coronary) heart disease. The incidence of this disease is virtually all due to atherosclerosis, and ischemic heart disease is also the most prevalent disease in the industrialized world, causing over 40% of all deaths in the United States and Western Europe. In Japan, the incidence of ischemic heart disease due to coronary atherosclerosis is gradually increasing as well. Compared with the classical nomenclature of atherosclerosis; that is, fatty streak, fibrous plaque and complicated lesions, the term Stary's classification has been universally accepted because it reflects the more recently acquired knowledge about the morphological and biochemical details of the processes in coronary atherosclerosis, which have been obtained by new strategies such as angioscopy, intravascular ultrasound and molecular biological methods. The term Stary's classification has been applied for the coronary atherosclerosis of patients with acute coronary syndrome at the National Cardiovascular Center, for the analysis of predisposing atherosclerosis of these patients. The recent findings regarding acute coronary syndrome resulting from a rupture of coronary atherosclerotic plaques indicate that this syndrome is probably the most important mechanism underlying the sudden onset. It has been found that the risk of plaque rupture may depend more on plaque composition than on plaque size. Plaques rich in soft extracellular lipids and macrophages are possibly more vulnerable to plaque rupture. Two of the goals of the present review are to clarify how plaque disruption occurs and to elucidate the relationship between plaque disruption and coronary risk factors in elderly Japanese patients with acute coronary syndrome. Coronary stents have been shown to be efficacious in the treatment of acute and threatened closure complicating percutaneous transluminal coronary angioplasty (PTCA) and have produced encouraging initial results in the prevention of restenosis. In the autopsy study of restenosis after PTCA, it was observed that dense caps of collagen fibers in the adventitia in the vicinity of the disrupted internal elastic laminae were present in all of the remodeling lesions. It is suggested that remodeling, which resulted in adventitial scarring, is one of the major causative factors of restenosis after PTCA. The long-term success of stenting, however, remains limited by the occurrence of late in-stent restenosis, with an incidence of 20-42% depending on the stent design and the patient population studied. Another aim of the present review is to describe the pathological mechanism of restenosis after PTCA and/or stent replacement and, consequently, the vascular remodeling that occurs around adventitial tissue after PTCA and intimal hyperplasia that is chronically irritated by a foreign body granulomatous reaction after stenting. Finally, the results of the investigation of the effect of a tissue factor pathway inhibitor on the prevention of interventional restenosis is described.

Intramural injection of biodegradable microspheres as a local drug-delivery system to inhibit neointimal thickening in a rabbit model of balloon angioplasty

Restenosis remains the major limitation of coronary angioplasty. The objective of this study was to develop microspheres able to be delivered at the angioplasty site for long-term drug release and to test their effects in a model of balloon angioplasty. Polylactic-co-glycolide acid microspheres (5-10 microm in diameter) were prepared by using an oil-in-water emulsion-solvent evaporation method. In vitro experiments with hydrocortisone-loaded microspheres revealed a hydrocortisone release for 4 weeks. We studied the in vivo effect of injection of microspheres into the arterial wall of New Zealand White rabbits by using a perforated balloon. Deep penetration of microspheres in the arterial wall was documented immediately after angioplasty. Intimal hyperplasia was assessed in iliac arteries 4 weeks after angioplasty. The morphometric analysis was performed in four groups of animals; the first group was subjected only to conventional angioplasty (control, n = 10), whereas the other three groups after conventional angioplasty were received perforated balloon angioplasty with saline (n = 10), microspheres (n = 10), or hydrocortisone-loaded microspheres (n = 7). Intramural injection of saline did not induce greater intimal hyperplasia compared with control (0.17 +/- 0.03 vs. 0.18 +/- 0.03 mm2, respectively). Microspheres injection was associated with a trend toward a greater degree of intimal hyperplasia that did not reach statistical significance. Hydrocortisone-loaded microspheres were associated with a significant reduction in intimal hyperplasia compared with unloaded microspheres (0.16 +/- 0.02 vs. 0.26 +/- 0.03 mm2, respectively). The polylactic-co-glycolide acid microspheres are well tolerated, easily injected into the arterial wall, and the increase of intimal hyperplasia is easily inhibited by release of hydrocortisone for 4 weeks after initial injury.

Sustained local drug delivery to the arterial wall via biodegradable microspheres

This study was designed to evaluate the feasibility of applying locally delivered polylactic acid microspheres for drug delivery to the arterial wall. To study drug persistence, rhodamine-loaded microspheres were infused into one carotid artery of 14 rabbits and plain rhodamine solution into the other by using a porous balloon. To study tissue response, plain microspheres and dexamethasone-loaded microspheres were infused into the carotid arteries of another group of rabbits. To study the antiproliferative effects of locally delivered drug, 20 rabbits were subjected to overstretch balloon injury to both carotid arteries and divided into 4 groups: injury alone, plain microspheres, dexamethasone-loaded microspheres, and microspheres containing colchicine and dexamethasone. Fluorescent microspheres persisted in the vessel wall for 4 wk, whereas rhodamine without microspheres disappeared at 72 h. Histopathologic studies in arteries infused with unloaded microspheres showed inflammatory cell infiltrate with polymorphonuclear cells at 1 wk and macrophages and giant cells at 4 wk. Arteries infused with dexamethasone-loaded microspheres did not show any inflammatory cell infiltrate. Local delivery of dexamethasone or dexamethasone plus colchicine did not result in significant change in the intima-to-media ratio or in residual lumen following balloon injury. Polylactic acid microspheres may be used for prolonged delivery of drugs or other bioactive agents locally to the arterial wall. They induce an inflammatory reaction that is suppressable by dexamethasone in the microspheres. Dexamethasone or dexamethasone and colchicine delivered via this system, however, failed to reduce the degree of intimal hyperplasia after overstretch balloon injury to the rabbit carotid arteries.

Tranilast inhibits contraction and Ca2+ movement of porcine coronary arteries

In a recent clinical study, tranilast, an anti-allergic agent, was shown to reduce the rate of coronary restenosis after percutaneous transluminal coronary angioplasty, although the mechanism of this effect is unclear. The present study was undertaken to investigate the effects of tranilast on contraction and Ca2+ movement of the coronary arteries. We characterized the effects of tranilast on isometric force and aequorin-estimated intracellular Ca2+ concentrations ([Ca2+]i) of porcine coronary artery strips. Tranilast concentration-dependently (10-500 microM) inhibited histamine (3 x 10(-5) M)-induced contraction of the coronary arteries. A similar tendency was observed in the response to high K+ (30 mM) stimulation. Histamine caused phasic and tonic increases in [Ca2+]i, and high K+ caused a tonic increase in [Ca2+]i of smooth muscle, both of which were significantly suppressed in the presence of tranilast. These results suggest that tranilast inhibits the contraction of coronary arteries by inhibiting both Ca2+ influx from extracellular environment and Ca2+ release from intracellular Ca2+ stores, which might be related to its preventive effect on restenosis after coronary angioplasty.

Restenosis: is there a pharmacologic fix in the pipeline?

One of the most frustrating aspects of restenosis is that it is the result of advances in medical care (there was no restenosis before the days of balloon angioplasty), yet it seems to be resistant to all that science has to offer. Still we believe there is reason to be optimistic. We are at last beginning to see some promise from clinical trials, and data being generated confirm some of the hypotheses previously generated from animal experiments. Thus the effects seen with the GP IIb/IIIa antibody 7E3 suggest that thrombosis may be as important in its long-term sequelae as it is for acute reocclusion. The jury is still out on whether antiproliferative approaches will be a therapeutic option, but local delivery paradigms using novel formulations delivered by catheter or impregnated in stents may allow the concept to be tested without the risk of systemic toxicity. Plans are also underway for gene therapy trials, although we may have to wait for better vector technology before taking these into the coronary bed. Perhaps we should move away from the "single pill" approach and accept that, like many infections, malignancies, or even heart failure, a multifaceted approach with combination therapy will provide the first glimmer of that brighter tomorrow.

Gene and other biological therapies for vascular diseases

Gene transfer and antisense therapy offer novel approaches to the study and treatment of vascular diseases. The localized nature of vascular diseases like restenosis has made the application of genetic material an attractive therapeutic option. Viral and nonviral vectors have been developed to facilitate the entry of foreign DNA or RNA into cells. Vector improvement and production, demonstration of vector safety and demonstration of therapeutic efficacy are among the main present challenges. Various strategies have already been shown to be successful in preventing restenosis in animal models and include: the transfer of the herpes simplex virus thymidine kinase associated with ganciclovir: transfection of the cell cycle regulatory genes encoding for the active form of retinoblastoma gene product (Rb) or the cyclin-dependent kinase inhibitor p21, and antisense therapy. Therapeutic angiogenesis using gene transfer is a new strategy for the treatment of severe limb ischemia. Transfection of DNA encoding for the vascular endothelial growth factor has resulted in increasing collateral flow in animal models of peripheral ischemia. This approach is currently being investigated in a clinical trial in patients with distal ischemia. Other potential targets for genetic treatment in cardiovascular diseases include thrombosis, extracellular matrix synthesis and lipid metabolism.

Management of peripheral vascular disease: innovative approaches using radiation therapy

Despite the early successes at vascular recanalization with percutaneous transluminal angioplasty, vascular restenosis has emerged as a clinical problem of near epidemic proportions. Numerous pharmacologic and mechanical adjuncts have been tried with little success. Over the last few years, there have major advances in our understanding of the biology of the restenotic process. The process is now recognized as a proliferation disorder, and therapies akin to those used in the treatment of malignant diseases are being explored. Endovascular brachytherapy has shown strong potential in controlling this pathologic proliferative process in the laboratory and in early clinical studies. In this review we discuss some of the basic issues involved in vascular restenosis and the current status of endovascular brachytherapy.

Interleukin-2 receptor-specific fusion toxin inhibits barotrauma-induced arterial atherosclerosis

Immunocytochemical analyses of human plaques and experimental arterial lesions have implicated activated lymphocytes and monocytes in the pathogenesis of atherosclerosis, as demonstrated by the expression of interleukin-2 (IL-2) membrane receptors and major histocompatibility complex class II epitopes. The objective is to determine if targeting these cells with an IL-2 receptor-specific chimeric toxin, DAB486-IL-2, can inhibit experimental post-angioplasty vascular neointimal thickening. Twenty-two atherogenically modeled rabbits were treated in vivo with DAB486-IL-2 (0.1 mg/kg per day i.v.; n = 11) or placebo (n = 11) for 10 days following aortic balloon angioplasty (4 atm x 30 s each x 2 dilatations). In vitro 3H-leucine incorporation studies of mononuclear leukocyte and vascular smooth muscle cell protein synthesis inhibition by DAB486-IL-2 were also performed. Angioplasty sites were examined for evidence of hyperproliferative atherosclerotic narrowing by quantitative angiography and histomorphometry of neointimal cross-sectional area at baseline and 6 weeks after injury. In vitro Concanavalin-A stimulated rabbit mononuclear leukocyte protein synthesis was 50% inhibited by DAB486-IL-2 at a concentration (IC50) of 6 x 10(-11) M. Rabbit vascular smooth muscle cells were approximately 150-fold less sensitive to DAB486-IL-2 (IC50 = 10(-8) M). In vivo studies showed no change in angioplasty site angiographic minimum luminal diameter at 6 weeks in DAB486-IL-2 treated animals (from 2.96 +/- 0.52 to 2.96 +/- 0.48 mm; percent cross-sectional area reduction = 1 +/- 10%; P = N.S.). In control animals, luminal diameter decreased from 2.79 +/- 0.4 to 2.32 +/- 0.52 mm at 6 weeks, and percent cross-sectional area was reduced by 34 +/- 14% (P < 0.01 vs. placebo). Quantitative histomorphometric angioplasty segmental intimal cross-sectional area reduction of treated and placebo vessels also differed significantly (19 +/- 16% vs. 31 +/- 21%; P < 0.05). DAB486-IL-2 caused no adverse effects on animal survival, weight or hepatic transaminase levels. We conclude that post-angioplasty administration of the chimeric toxin DAB486-IL-2 inhibits angiographic narrowing and neointimal thickening in the atherogenic rabbit model. Although this IL-2 receptor-specific molecule was cytotoxic in vitro for activated mononuclear leukocytes and vascular smooth muscle cells, systemic toxicity did not occur in vivo at a dose comparable to that evaluated in clinical trials of this agent. Potential anti-proliferative effects of this chimeric toxin may be mediated by direct local inhibition of leukocyte-mediated inflammation, or through the indirect modification of vascular cell mitogenesis and cytokine release.

Adenovirus-mediated over-expression of the cyclin/cyclin-dependent kinase inhibitor, p21 inhibits vascular smooth muscle cell proliferation and neointima formation in the rat carotid artery model of balloon angioplasty

Vascular smooth muscle cell (VSMC) proliferation after arterial injury is important in the pathogenesis of a number of vascular proliferative disorders, including atherosclerosis and restenosis after balloon angioplasty. Thus, a better understanding of the molecular mechanisms underlying VSMC proliferation in response to arterial injury would have important therapeutic implications for patients with atherosclerotic vascular disease. The p21 protein is a negative regulator of mammalian cell cycle progression that functions both by inhibiting cyclin dependent kinases (CDKs) required for the initiation of S phase, and by binding to and inhibiting the DNA polymerase delta co-factor, proliferating cell nuclear antigen (PCNA). In this report, we show that adenovirus-mediated over-expression of human p21 inhibits growth factor-stimulated VSMC proliferation in vitro by efficiently arresting VSMCs in the G1 phase of the cell cycle. This p21-associated cell cycle arrest is associated both with significant inhibition of the phosphorylation of the retinoblastoma gene product (Rb) and with the formation of complexes between p21 and PCNA in VSMCs. In addition, we demonstrate that localized arterial infection with a p21-encoding adenovirus at the time of balloon angioplasty significantly reduced neointimal hyperplasia in the rat carotid artery model of restenosis. Taken together, these studies demonstrate the important role of p21 in regulating Rb phosphorylation and cell cycle progression in VSMC, and suggest a novel cytostatic gene therapy approach for restenosis and related vascular proliferative disorders.

A prescreening system for potential antiproliferative agents: implications for local treatment strategies of postangioplasty restenosis

BACKGROUND

Recent advances in the understanding of the biology of restenosis indicate that it is predominantly caused by a multifactorial stimulation of smooth muscle cell proliferation. The aim of this study was to investigate the in vitro effect of five potential antiproliferative agents on smooth muscle cells from human atherosclerotic femoral arteries.

METHODS AND RESULTS

Primary stenosing plaque material of 24 patients (aged 63 +/- 14 years) and restenosing plaque material of 7 patients (aged 65 +/- 9 years) was selectively extracted from femoral arteries by the Simpson atherectomy device. Cells were isolated by enzymatic disaggregation and identified as smooth muscle cells by positive reaction with smooth muscle alpha-actin. Dalteparin sodium (0.001-100 anti-Xa units/ml), cyclosporine A (0.005-500 micrograms/ml), colchicine (0.00004-4 pg/ml), etoposide (0.002-200 micrograms/ml), and doxorubicin (0.0005-50 micrograms/ml) were added to the cultures. Six days after seeding, cells were trypsinized and cell number was measured by a cell counter. All five agents tested exhibited a significant inhibition of smooth muscle cell proliferation (P < 0.001). After an incubation time of 48 h, the cytoskeletal components, alpha-actin, vimentin, and microtubules were investigated. At peak concentrations, all five tested agents except dalteparin sodium caused severe damage to the cytoskeleton.

CONCLUSIONS

All five potential antiproliferative agents exhibited a significant inhibition of smooth muscle cell proliferation. The development of new intravascular delivery systems may open the way for local antiproliferative treatment strategies in interventional cardiology.

Experimental therapeutics and clinical studies in (re)stenosis

Restenosis is defined functionally as loss of luminal vessel patency following various methods of interventional cardiology, but ultrastructurally, it represents a wound healing response that involves smooth muscle migration, proliferation and matrix deposition at the site of injury. Currently, despite intensive experimental and clinical studies, there are no therapeutic agents that are able to suppress pharmacologically the clinical restenosis. Ultrastructural pathology and animal modeling have played a pivotal role in defining new experimental therapies and rationales for clinical trials. However, concerns regarding the lack of suitable animal models persist and of the many compounds reported efficacious preclinically, none have demonstrated clinical benefit in preventing restenosis. Animal modeling studies now include the use of true restenosis studies, which may be more clinically relevant and pharmacologically predictive of clinical performance.

Pathobiology of intimal hyperplasia

In the current vascular interventional environment, high restenosis rates have increased awareness of the significance of intimal hyperplasia, a chronic structural lesion that develops after vessel wall injury, and which can lead to luminal stenosis and occlusion. Intimal hyperplasia may be defined as the abnormal migration and proliferation of vascular smooth muscle cells with associated deposition of extracellular connective tissue matrix. The pathology of intimal hyperplasia is reviewed with particular attention to its physiology, pharmacology, cell biology and molecular biology.

Localized intramural drug delivery during balloon angioplasty using hydrogel-coated balloons and pressure-augmented diffusion

OBJECTIVES

This study was designed to assess the feasibility of using hydrogel-coated balloons to deliver biologically active agents to the blood vessel wall.

BACKGROUND

The local intramural delivery of therapeutic agents during balloon angioplasty has been proposed as an adjunctive technique for preventing early intracoronary thrombosis and late restenosis.

METHODS

To assess the efficacy of delivery and depth of penetration in vitro, local delivery of horseradish peroxidase was performed in 40 porcine peripheral arteries, and delivery of fluoresceinated heparin was performed in 20 porcine peripheral arteries and 7 human atheromatous arteries. To determine the persistence of these agents in the vessel wall in vivo, horseradish peroxidase was delivered to 18 porcine peripheral arteries that were harvested at intervals of 45 min to 48 h. Fluoresceinated heparin was delivered to 22 porcine peripheral arteries, 14 with the use of a protective sleeve, harvested at intervals of 30 s to 24 h.

RESULTS

In vitro agent delivery was successful in all specimens. The depth of penetration of horseradish peroxidase was directly related to both balloon pressure (p < 0.04) and duration of inflation (p < 0.01). In vivo peroxidase staining was evident at 45 and 90 min but not thereafter. With the use of a protective sleeve, heparin was present in all arteries harvested at 30 s, with marked dissipation at 1 and 24 h. Without a sleeve, no fluorescein staining was detected in any artery. With both agents, delivery occurred consistently over broad regions of the vessel wall that were free of architectural disruption.

CONCLUSIONS

Hydrogel-coated balloons can deliver biologically active agents to the vessel wall without gross tissue disruption and may provide an atraumatic method for the local delivery of therapeutic agents during balloon angioplasty.

Intracoronary irradiation markedly reduces restenosis after balloon angioplasty in a porcine model

OBJECTIVES

This study examined the effects of intracoronary irradiation on neointimal proliferation after overstretch balloon angioplasty in a normolipemic swine model of restenosis.

BACKGROUND

Restenosis after percutaneous transluminal coronary angioplasty represents, in part, a proliferative response of vascular smooth muscle at the site of injury. We have previously shown that ionizing radiation, delivered by means of an intracoronary source, causes focal medial fibrosis. We therefore hypothesized that intracoronary irradiation delivered at the time of balloon angioplasty might impair the restenosis process.

METHODS

Nineteen juvenile swine underwent coronary angiography; a segment of the coronary artery was chosen as a target for balloon injury. In 10 swine, a ribbon of iridium-192 was positioned at the target segment, and 2,000 cGy was delivered at the vessel wall. Subsequently, overdilation balloon angioplasty was performed at the irradiated segment. In nine control swine, overdilation balloon angioplasty was performed without previous irradiation. Eighteen animals survived and were killed at 30 days. Histopathologic analysis was performed by a pathologist in blinded manner. The area of maximal lumen compromise within the target segment was analyzed by computer-assisted planimetry.

RESULTS

In the control group, mean (+/- SD) neointimal area was 0.84 +/- 0.60 mm2 compared with that in the irradiated group, 0.24 +/- 0.13 mm2 (p = 0.01). In the control group, mean percent area stenosis was 47.6 +/- 20.7%, whereas that in the irradiated group was 17.6 +/- 10.5% (p = 0.001). This represents a 71.4% reduction in neointimal area and a 63.0% reduction in percent area stenosis in the irradiated group. Adjacent coronary segments and surrounding myocardium were unaffected.

CONCLUSIONS

Intracoronary irradiation (2,000 cGy) delivered to a target porcine coronary segment before balloon overdilation markedly reduces neointima formation at 30 days and thus significantly impairs the restenosis process.

Perspectives on invasive cardiology: the 24th Louis F. Bishop Lecture

The fast growing and complex field of invasive cardiology offers a host of opportunities and challenges for the clinician. Scientific and technical advances ranging from molecular biology to microtechnology are changing how physicians make decisions concerning treatment of coronary artery disease, myocardial infarction, unstable angina and electrophysiologic dysfunction. The economic impact and ethical implications presented by these developments contribute to the difficulty of achieving optimal therapeutic solutions for individual patients.

Analysis of atherectomy specimens

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

Southwestern internal medicine conference: restenosis: the Achilles heel of coronary angioplasty

Percutaneous transluminal coronary angioplasty has become the treatment of choice for many patients with symptomatic coronary artery disease. Increased experience with the procedure and improvements in equipment have resulted in high initial success rates; however, a significant number of patients develop restenosis. Insights into the pathophysiologic mechanisms of restenosis have led to the use of various pharmacologic agents and devices to prevent its occurrence. Although many have been successful in decreasing the incidence of restenosis in animal studies, none has yet proven successful in decreasing the incidence of restenosis in humans. Newer approaches and novel therapies are needed to prevent restenosis after percutaneous transluminal coronary angioplasty.

Effects of captopril on platelet cytosolic free Ca2+ concentrations and on suppression of cell proliferation in culture

In order to investigate the feasibility of angiotensin converting enzyme inhibitors (ACEIs) in preventing the development of atherosclerosis and restenosis after coronary angioplasty and to study their mechanisms, we measured the platelet cytosolic free Ca2+ concentration ([Ca2+]i) and observed the effects of captopril on platelet [Ca2+]i in rabbits and also observed the inhibitive action on fibroblast proliferation in culture. The results showed that resting platelet [Ca2+]i,ADP- or thrombin-stimulated platelet elevation amplitude after administration of captopril (12.5 mg, twice daily) for 15 days were significantly reduced in comparison with those before administration. And captopril also significantly inhibited fibroblast proliferation or reduced 3H-thymidine (3H-TdR) incorporation in culture in a dose-dependent manner. These findings suggest that ACEIs are promising drugs to reduce restenosis incidence after coronary angioplasty and to prevent atherosclerosis as well as provide a new explanation for their effects of suppressing cell proliferation.

Pathophysiological mechanisms for restenosis following coronary angioplasty: possible preventive alternatives

Restenosis after successful percutaneous transluminal coronary angioplasty (PTCA) remains an unsolved medical problem. The search for the underlying pathophysiological mechanisms have identified intimal proliferation of smooth muscle cells (SMC) to be the prevailing cause of late restenosis, with endothelial cells (EC) and platelets being important participators in the process. According to the most accepted present theory, SMC would be stimulated to migrate and proliferate shortly after the angioplasty by the release of growth factors from injured EC and accumulated platelets. However, clinical trials of agents interfering with these mechanisms have not significantly diminished the rate of restenosis, which suggest both that our knowledge of the process is incomplete, and that new ways of administering the agents may be required.

Arterial remodelling after percutaneous transluminal balloon angioplasty

Atheromatous coronary artery disease progresses by atheroma accretion, plaque rupture and thrombus formation, with or without spontaneous fibrinolysis. The natural history may be altered by modifying risk factors in an attempt to induce regression, or treated by mechanical means such as balloon angioplasty, directional coronary atherectomy or drills, or flow modulated by the insertion of an aorto coronary bypass graft with or without endarterectomy. Here we discuss the natural history of the atheromatous disease in a series of 355 patients who underwent at least one PTCA procedure and then underwent a second angiographic study to determine the changes in the dilated and nondilated arteries.

The restenosis paradigm revisited: an alternative proposal for cellular mechanisms

Coronary restenosis is a reparative response to arterial injury during angioplasty, and remains a major clinical problem. The reasons for treatment failures likely stem from our incomplete understanding of the cellular mechanisms in restenotic neointimal formation. Restenosis is thought to result from migration and replication of medial smooth muscle cells to form an obstructive neointima, a concept neither observed nor demonstrated in humans. An alternative hypothesis for restenosis is based on observations in the porcine coronary injury model. In this model, there are three cellular stages in neointimal formation: thrombotic (stage I), cellular recruitment (stage II) and proliferative (stage III). The thrombotic stage occurs early and consists of platelets, fibrin and red blood cells accumulating at the vessel injury site. In the recruitment stage, the mural thrombus itself develops an endothelium, followed by a mononuclear leukocytic infiltrate beginning on the lumen side of the vessel. In the proliferative stage, a "cap" of actin-positive cells forms on the lumen surface and progressively thickens. These cells do not arise from media at the injury site. Extracellular matrix secretion and additional recruitment likely add to neointimal volume during this phase. Thrombus assumes a major role in restonosis by providing an absorbable matrix into which smooth muscle cells proliferate. Further studies are needed to validate or modify this hypothesis.

Ineffectiveness of colchicine for the prevention of restenosis after coronary angioplasty

Colchicine, an antimitogenic agent, has shown promise in preventing restenosis after coronary angioplasty in experimental animal models. A prospective trial was conducted involving 197 patients randomized in a 2:1 fashion to treatment with oral colchicine, 0.6 mg twice daily (130 patients), or placebo (67 patients) for 6 months after elective coronary angioplasty. Treatment in all patients began between 12 h before angioplasty and 24 h after angioplasty. Compliance monitoring revealed that 96% of all prescribed pills were ingested. Demographic characteristics were similar in colchicine- and placebo-treated groups. A mean of 2.7 lesions/patient were dilated. Side effects resulted in a 6.9% dropout rate in the colchicine-treated patients. Complete quantitative angiographic follow-up was obtained in 145 patients (74%) with 393 dilated lesions. Quantitative angiographic measurements were obtained in two orthogonal views at baseline before angioplasty and immediately and at 6 months after angioplasty. The quantitative mean lumen diameter stenosis before angioplasty was 67% both in the 152 lesions in the placebo-treated group and in the 241 lesions in the colchicine-treated group; this value was reduced to 24% immediately after angioplasty in the lesions in both treatment groups. At the 6-month angiogram, lesions had restenosed to 47% lumen diameter narrowing in the placebo-treated group compared with 46% in the colchicine-treated group (p = NS). Forty-one percent of colchicine-treated patients developed restenosis in at least one lesion compared with 45% of the placebo-treated group (p = NS). In conclusion, colchicine was ineffective for preventing restenosis after coronary angioplasty.

Experimental models of coronary artery restenosis

The study of potentially effective drug therapies and mechanical devices for the prevention of restenosis after percutaneous coronary revascularization has relied heavily on the use of experimental animal models. To date, greater than 50 experimental studies have been reported and have suggested that at least nine different classes of pharmacologic agents inhibit the intimal proliferative response to arterial injury. However, no pharmacologic intervention has yet been shown to reproducibly reduce the incidence of restenosis after coronary balloon angioplasty in humans. To identify the reasons for the apparent nonspecificity of the animal models and to determine which model should most reliably predict the efficacy of individual therapies in humans, the distinguishing characteristics of the experimental models were compared. Particular attention was paid to the size and morphologic structure of the treated artery, the susceptibility of the species to spontaneous and diet-induced arterial disease, the nature of the stimulus to intimal proliferation and several practical and logistic considerations. Finally, the reported efficacies of specific drug therapies in the respective animal models and in humans were compared. This review suggests that significant interspecies and occasionally intraspecies differences do exist among the respective animal models, particularly in the extent and composition of the neointimal thickening.(ABSTRACT TRUNCATED AT 250 WORDS)