Does the new angiotensin converting enzyme inhibitor cilazapril prevent restenosis after percutaneous transluminal coronary angioplasty? Results of the MERCATOR study: a multicenter, randomized, double-blind placebo-controlled trial. Multicenter European Research Trial with Cilazapril after Angioplasty to Prevent Transluminal Coronary Obstruction and Restenosis (MERCATOR) Study Group

Halofuginone inhibits neointimal formation of cultured rat aorta in a concentration-dependent fashion in vitro

Halofuginone, an anticoccidial quinoazolinone, can specifically inhibit collagen type alpha1 (I) synthesis and gene expression, and also inhibits cultured smooth muscle cell proliferation. The aim of this study was to investigate the effect of halofuginone on neointimal formation of rat aorta after culture in a concentration-dependent manner in vitro. Thoracic aorta of Wistar rats was removed and manipulated to damage the endothelium under sterile conditions, and culture for 15 days in halofuginone-free or halofuginone-added culture medium (n = 20). Segments of cultured aorta were studied by histologic and immunohistochemical methods. Proliferation of neointimal layers consisting of loose multilayer cellular structure was observed in the halofuginone-free control group after 15 days of rat aorta culture, and neointimal formation was significantly decreased as an increasing concentration of halofuginone was added. As with precultured fresh aorta, no intimal proliferation was observed in the cultured segments of aorta with 500 ng/ml halofuginone added to culture medium. The proliferation of cell nuclear antigen index was significantly higher in the halofuginone-free control group than that in the halofuginone-added groups. The present results suggest that halofuginone can inhibit neointimal formation of rat aorta after culture in a concentration-dependent fashion in vitro.

Dual determination of angiotensin-converting enzyme and angiotensin-II type 1 receptor genotypes as predictors of restenosis after coronary angioplasty

This study sought to assess the potential influence of the angiotensin-converting enzyme (ACE) and angiotensin II type 1 (AT1) receptor gene polymorphisms on restenosis after coronary balloon angioplasty. The authors conclude that screening for genetic suspectibility to restenosis based on genotyping of ACE and AT1 receptor polymorphisms before conventional balloon angioplasty is not clinically useful.

Benazepril on tissue angiotensin-converting enzyme and cellular proliferation in restenosis after experimental angioplasty

We investigated the role of vascular angiotensin-converting enzyme (ACE) activity, cell proliferation, and the effect of different doses of benazepril on intimal hyperplasia after angioplasty in rabbits. Angioplasty was performed in all left iliac arteries in 28 rabbits. Benazepril was administrated to treatment groups in low (1 mg/kg/day) and high (10 mg/kg/day) doses. Two weeks after angioplasty, vascular ACE activity of the angioplasty subgroup was significantly higher than that of the nonangioplasty subgroup (from 0.44 to 1.19 nmol His-Leu/mg/min; p < 0.01). Strong correlation was demonstrated between vascular ACE activity and intimal area (r = 0.708; p < 0.01). Suppression of vascular ACE activity (59% decrease) and inhibition of intimal hyperplasia (43% decrease) was observed in the high-dose subgroup compared with the angioplasty subgroup without drug intervention (p < 0.01). But in the low-dose subgroup, the level of vascular ACE activity decreased moderately (24.4%; p < 0.05), and the intimal area did not alter significantly. Both the low and high dosage of benazepril resulted in a significant decrease in blood pressure (31 and 44 mm Hg, respectively). Striking correlation was displayed between proliferating-cell nuclear antigen (PCNA)-positive cell percentage and intimal area (r = 0.716; p < 0.01). These results indicated that with excessive expression of vascular ACE, intimal cellular proliferation may play a potential role in restenosis after angioplasty. Benazepril could inhibit intimal hyperplasia by suppressing vascular-tissue ACE.

Current perspective on the use of angiotensin-converting enzyme inhibitors in the management of coronary (atherosclerotic) artery disease

OBJECTIVE

To review the pathophysiology of atherosclerosis, the role of the renin-angiotensin system in atherogenesis, and studies supporting the potential beneficial effects of angiotensin-converting enzyme (ACE) inhibitors in reducing cardiovascular events with long-term use.

BACKGROUND

Through its action in converting angiotensin I to angiotensin II and by degrading bradykinin, local tissue ACE exerts many effects that can contribute to the development of atherosclerosis. Therefore, the use of ACE inhibitors can possibly result in antiatherogenic effects. Possible mechanisms for antiatherogenic effects of ACE inhibitors include: (1) reduction of blood pressure; (2) antiproliferative and antimigratory effects on vascular smooth muscle cells, neutrophils, and monocytes; (3) restoration of endothelial function; (4) stabilization of fatty plaque by preventing vasoconstriction; (5) antiplatelet effects; and (6) enhancement of endogenous fibrinolysis.

DATA SOURCES

English-language clinical studies, abstracts, and review articles pertaining to the use of ACE inhibitors and atherosclerosis.

STUDY SELECTION AND DATA EXTRACTION

Relevant human studies examining the role of ACE inhibitors and atherosclerosis.

DATA SYNTHESIS

Studies evaluating the possible beneficial effects of ACE inhibitors in the development of atherosclerosis are reviewed and critiqued. Design of ongoing studies with clinical and surrogate end points are discussed.

CONCLUSIONS

Based on current published studies, recommendations are made regarding the use of ACE inhibitors in atherosclerosis. Therapeutic monitoring parameters for efficacy and adverse effects are also reviewed.

Structural determinants of lumen narrowing after angioplasty in atherosclerotic nonhuman primates

PURPOSE

The relationship between lumen narrowing, intimal hyperplasia, and wall remodeling after angioplasty was explored in a nonhuman primate model of atherosclerosis.

METHODS

Cynomolgus monkeys (n = 37) used in long-term atherosclerosis studies underwent left iliac artery balloon injury. The uninjured right iliac artery served as a reference segment for intraanimal comparisons. One month later iliac arteries were fixed by perfusion (100 mm Hg) and removed for cross-sectional analysis to determine mean values for lumen area (LA), intimal area (IA), internal elastic lamina area (IELA), plaque burden (IA/IELA), and depth of wall injury. Values for each balloon-injured iliac artery were normalized to the contralateral uninjured iliac artery (percent of control), and linear regression analysis was performed comparing LA with IA, with IELA, and with depth of injury. Comparisons were also made between those arteries that remained dilated 1 month after balloon injury (LA > or = 140%; n = 13) and those that renarrowed (LA < or = 100%; n = 14).

RESULTS

For all 37 animals, LA 1 month after balloon injury correlated well with IELA (r = 0.72; p < 0.001) but not with IA (r = 0.10; p = 0.54), suggesting that changes in artery size rather than neointimal mass determined lumen caliber. When comparing arteries that remained dilated (n = 13) with those that renarrowed (n = 14), there were no differences in depth of wall injury (injury depth: 0, no injury; 1, intima; 2, IEL; 3, media; 4, EEL; 2.1 +/- 0.3 vs 1.6 +/- 0.3; p = 0.12), neointimal accumulation (IA, 507% +/- 118% vs. 421% +/- 81% of control; p = 0.55), or plaque burden (IA/IELA, 0.39 +/- 0.04 vs 0.37 +/- 0.06; p = 0.71), respectively. However, wall size defined as IELA was significantly smaller in arteries that renarrowed than in those that remained dilated (IELA, 115% +/- 14% vs 230% +/- 19% of control; p < 0.001).

CONCLUSIONS

Restenosis after angioplasty has been attributed to intimal hyperplasia, equating loss of lumen caliber with neointimal mass. The data presented herein suggest that lumen narrowing after arterial wall injury may have little to do with intimal mass per se, but rather that a change in wall caliber or wall narrowing is the cause of restenosis.

Characterization of chymase from human vascular tissues

A chymostatin-sensitive angiotensin II-generating enzyme was found in human gastroepiploic arteries. The enzyme was purified using heparin affinity and gel filtration columns. The molecular mass of the purified enzyme was 30 kDa, and the optimum pH was between 7.5 and 9.0. Enzyme activity was inhibited by soybean trypsin inhibitor, phenylmethylsulfonyl fluoride and chymostatin, but not by ethylenediaminetetraacetic acid, pepstatin and aprotinin. The enzyme rapidly converted angiotensin I to angiotensin II (K(m), 67 mumol/l; Vmax, 43 pmol/s, kcat, 65/s), but did not hydrolyse angiotensin II, substance P, bradykinin, vasoactive intestinal peptide, luteinizing hormone-releasing hormone, somatostatin and alpha-melanocyte-stimulating hormone. The N-terminal sequence was identical to the sequence for human skin/heart chymase. Thus, the chymostatin-sensitive angiotensin II-generating enzyme in human vascular tissues is identified as chymase.

Renin-angiotensin system: genes to bedside

Atherosclerosis and its vascular sequela are responsible for considerable morbidity and mortality rates. Several risk factors have been implicated in the pathogenesis of atherosclerosis, and the search for other risk factors continues on the medical horizon. Renin-angiotensin system (RAS), a multienzyme, multilocale axis, has been extensively studied as an important mediator of atherosclerosis. Recently, the tissue-based angiotensin system has been suggested as the most significant pathway of RAS. A genetic polymorphism in the human gene for the angiotensin-converting enzyme (ACE), one of the two enzymes of RAS, has been found to have a strong association with higher risk for acute coronary events, sudden cardiac death, vascular restenosis after angioplasty, and idiopathic and hypertrophic cardiomyopathy. Clinical and animal data support angiotensin II to be the final common pathway in the enzyme cascade of RAS and ACE as the key enzyme in the generation of Angiotensin II. ACE gene polymorphism appears to modify expression of cellular and free ACE levels and could represent a genetic marker for cardiovascular disease.

Is there a rationale for combining angiotensin-converting enzyme inhibitors and calcium antagonists in cardiovascular disease?

Coronary artery disease and its sequelae remain the most important cause of morbidity and mortality in Western countries. Because the pathophysiologic characteristics of coronary artery disease are multifactorial, impairment of endothelial function featuring enhanced vasoconstriction, increased platelet vessel wall interaction, adherence of monocytes, migration and proliferation of vascular smooth muscle cells are crucially involved. Endothelial cells release numerous vasoactive substances regulating function of vascular smooth muscle and trafficking blood cells such as nitric oxide (NO), which is a potent vasodilator also inhibiting cellular growth and migration. In addition, NO possesses antiatherogenic and thromboresistant properties by preventing platelet aggregation and cell adhesion. These effects are counterbalanced by endothelial vasoconstrictors such as angiotensin II and endothelin-1. In the blood vessel wall, the local vascular effects of angiotensin-converting enzyme (ACE) inhibitors and calcium antagonists are synergistic. ACE inhibitors diminish the conversion of angiotensin I into angiotensin II and the inactivation of bradykinin. Calcium antagonists counteract angiotensin II and endothelin-1 at the level of vascular smooth muscle by reducing Ca2+ inflow and facilitating the vasodilator effects of NO. In hypertensive animals, long-term combination therapy with verapamil and trandolapril is particularly effective in reversing endothelial dysfunction. Further, ACE inhibitors and calcium antagonists exert beneficial vascular and complementary hemodynamic effects. Whereas ACE inhibitors inhibit the renin-angiotensin system and reduce sympathetic outflow, calcium antagonists dilate large conduit and resistance arteries. Because small vessels appear to be more dependent on extracellular Ca2+ than larger vessels, nifedipine and verapamil effectively inhibit endothelin-induced vasoconstriction in vitro and in vivo in the resistance circulation. Long-term treatment with ACE inhibitors substantially reduces morbidity and mortality rates in patients with left ventricular dysfunction after myocardial infarction; beneficial effects of verapamil in secondary prevention are confined to patients with normal left ventricular ejection fraction. In summary, long-term combination therapy of ACE inhibitors and calcium antagonists might provide beneficial effects in cardiovascular disease because they exert synergistic hemodynamic, antiproliferative, antithrombotic, and antiatherogenic properties.

Effects of pemirolast and tranilast on intimal thickening after arterial injury in the rat

We previously reported that tranilast, an antiallergic agent, reduced intimal thickening after endothelial injury in rats. In this study, to verify whether or not antiallergic agents inhibit intimal thickening, we investigated the effect of pemirolast on intimal thickening after endothelial injury and compared its effect with that of tranilast. Administration of two antiallergic agents, pemirolast (0.1, 1, and 10 mg/kg, p.o.) and tranilast (300 mg/kg, p.o., daily), was begun 2 days before endothelial injury and continued until the animals were killed. Endothelial injury in the rat femoral artery was induced by a photochemical reaction between localized irradiation by green light and intravenously administered rose bengal. To evaluate intimal hyperplasia, we measured the cross-sectional area of the intima 21 days after endothelial damage. Pemirolast at doses of 0.1, 1, and 10 mg/kg reduced the intimal area to 2.10 +/- 0.33, 1.36 +/- 0.19, and 1.35 +/- 0.18 (x0.01 mm2), respectively, and tranilast showed a tendency to reduce the intimal area, which was 1.86 +/- 0.35 x 0.01 mm2, compared with findings for controls (2.83 +/- 0.49 x 0.01 mm2). In rat A10 vascular smooth-muscle cells, we investigated the effects of antiallergic agents on migration by using a modified Boyden chamber assay and on proliferation by using the bromodeoxyuridine-incorporation assay. Two antiallergic agents inhibited in a concentration-dependent manner both migration and proliferation of smooth muscle cells stimulated by platelet-derived growth factor. These results suggest that antiallergic agents directly inhibit migration of smooth-muscle cells to the intima from the media and proliferation in the intima, and that pemirolast has more potent antihyperplastic action than does tranilast. Antiallergic agents may be effective in preventing restenosis after coronary angioplasty.

Activation of cAMP-PKA signaling in vivo inhibits smooth muscle cell proliferation induced by vascular injury

Injury of the arterial wall induces the formation of the neointima. This structure is generated by the growth of mitogenically activated smooth muscle cells of the arterial wall. The molecular mechanism underlying the formation of the neointima involves deregulated cell growth, primarily triggered by the injury of the arterial wall. The activated gene products transmitting the injury-induced mitogenic stimuli have been identified and inhibited by several means: transdominant negative expression vectors, antisense oligodeoxynucleotides, adenovirus-mediated gene transfer, antibodies and inactivating drugs. Results of our study show that local administration of 3',5'-cyclic AMP and phosphodiesterase-inhibitor drugs (aminophylline and amrinone) to rats markedly inhibits neointima formation after balloon injury in vivo and in smooth muscle cells in vitro. The growth inhibitory effect of aminophylline was completely reversed by the inhibition of cAMP-dependent protein kinase A (PKA). These findings indicate an alternative approach to the treatment of diseases associated with injury-induced cell growth of the arterial wall, as stimulation of cAMP signaling is pharmacologically feasible in the clinical setting.

Efficacy of low-molecular-weight heparin delivery with the Dispatch catheter following balloon angioplasty in the rabbit iliac artery

Local drug delivery can be achieved with active injection systems or passive contact of a compound with the arterial wall. The Dispatch catheter allows for passive diffusion of drugs from drug compartments while preserving blood flow through the central conduit. The aim of this study was to investigate whether a reduction in neointima formation can be achieved by local delivery of a limited amount of a highly concentrated solution of the low-molecular-weight heparin Reviparin. In 16 New Zealand white rabbits, successful balloon dilatation was performed in both iliac arteries, followed by local delivery of 4 ml Reviparin (1,000 IU/ml). The arteries were harvested at 7, 28, or 56 d following the procedure. The intimal cell layers increased substantially between 7 and 28 d following balloon dilatation with or without local drug delivery. The medial cell layers showed only a little increase. Proliferation of smooth muscle cells reached an early peak after 7 d, with a significantly higher proliferation index following local delivery. The maximum amount of macrophages in the intima and media was detected after 28 d. The lumen area decreased with time and was 0.6 +/- 0.7 mm2 in the local delivery group at 56 d compared with 0.5 +/- 0.5 mm2 in the control group. In conclusion, local delivery of Reviparin with the Dispatch catheter is safe and feasible. However, the infusion of highly concentrated low-molecular-weight heparin over a short period of time did not result in a reduction of neointima formation and restenosis following balloon dilatation in the rabbit iliac artery.

Elevated vascular angiotensin converting enzyme mediates increased neointima formation after balloon injury in spontaneously hypertensive rats

OBJECTIVE

To measure the effect of hypertension on neointima formation after balloon injury of rat aorta and its association with the local angiotensin converting enzyme (ACE) concentration. Balloon angioplasty of the thoracic aorta using a 2 French Fogarty catheter was performed in spontaneously hypertensive rats (SHR) and normotensive Sprague-Dawley (SD) rats.

RESULTS

The injured aortic wall of SHR had already significantly higher ACE concentrations than did the uninjured aortic wall of normotensive SD rats (media: 729 +/- 37 dpm/mm2 in SHR versus 496 +/- 38 dpm/mm2 in SD rats, P < 0.01; intima: 83 +/- 5 dpm/mm2 versus 68 +/- 6 dpm/mm2 in SD rats, P < 0.01). Fourteen days after injury of the aorta the hypertensive rats had significantly higher neointima: media ratios than did the normotensive rats (0.83 +/- 0.09 versus 068 +/- 0.01, P < 0.01). This was associated with a significant increase in vascular media and neointima ACE concentrations in SHR (media 965 +/- 25 dpm/mm2, neointima 614 +/- 48 dpm/mm2) compared with those in normotensive SD rats after balloon angioplasty (media 669 +/- 23 dpm/mm2, neointima 287 +/- 33 dpm/mm2, P < 0.01). ACE inhibitor treatment with 10 mg/kg body weight lisinopril daily for 14 days by gavage reduced neointima proliferation in hypertensive and normotensive rats (neointima: media ratio: 0.35 +/- 0.02 for SHR, P < 0.01, versus untreated SHR with balloon injury; 0.28 +/- 0.01 for SD, P < 0.01, versus untreated SD rats with balloon injury). This was associated with significant vascular media ACE inhibition (SHR 149 +/- 9 dpm/mm2; SD rats 118 +/- 7 dpm/mm2; P < 0.01 versus untreated controls with balloon injury) and neointima ACE inhibition (SHR 73 +/- 4 dpm/mm2, SD rats 63 +/- 7 dpm/mm2, P < 0.01, versus untreated controls with balloon injury), but also lowered the blood pressure in SHR significantly (to 148 +/- 5 mmHg, P < 0.01, versus untreated SHR with balloon injury). When this drop in blood pressure was prevented by feeding the rats a high-salt diet (SHR with ACE inhibitor plus high salt-diet group blood pressure 193 +/- 3 mmHg, P = 0.57, versus untreated SHR) hypertension per se without the local ACE increase (ACE concentration in SHR with ACE inhibitor high-salt diet rats' media 167 +/- 10 dpm/mm2 and neointima 81 +/- 9 dpm/mm2) had only a mild effect on neointima formation after balloon angioplasty (neointima: media ratio 0.4 +/- 0.01 for SHR with ACE inhibitor plus high-salt diet versus 0.35 +/- 0.02 for SHR with ACE inhibitor plus normal-salt diet P < 0.05). Treatment with 10 mg/kg body weight angiotensin II subtype 1 receptor antagonist losartan potassium daily for 14 days by gavage was associated with a reduction in neointima formation similar to that observed with the ACE inhibitor both for SHR and for SD rats (neointima: media ratio 0.32 +/- 0.04 for SHR with losartan, 0.27 +/- 0.03 for SD rats with losartan; P < 0.01, versus untreated controls with balloon injury) suggesting that ACE inhibitor prevented neointima formation, at least in part by, reducing the local production of angiotensin II.

CONCLUSION

Neointima formation after balloon angioplasty in SHR is increased compared with that in normotensive SD rats. This is due mainly to there being a higher degree of activation of the renin-angiotensin system in the aorta of the SHR before and after balloon injury compared with that in normotensive SD rats measured in terms of the increased vascular ACE concentrations. Blood pressure alone had only a moderate effect on neointima formation.

Effect of cilostazol in preventing restenosis after percutaneous transluminal coronary angioplasty

This study sought to evaluate the effect of cilostazol in preventing restenosis after successful percutaneous transluminal coronary angioplasty (PTCA) in 68 patients: 35 patients received cilostazol immediately after PTCA and 33 patients received aspirin or ticlopidine. Repeat coronary angiography was performed 4 to 6 months after PTCA and the incidence of restenosis was significantly lower (17%) in the cilostazol group than in the non-cilostazol group (40%) (p < 0.05), which indicates that cilostazol has the potential to prevent restenosis after PTCA.

Kinins and the events influenced by an angiotensin-converting enzyme inhibitor during neointima formation in the rat carotid artery

OBJECTIVE

In balloon-injured rat carotid arteries, angiotensin-converting enzyme inhibitors (ACEI) decrease neointima formation, and a kinin receptor antagonist partially reverses this inhibitory effect. We studied which of the events leading to neointima formation are involved in the effects of ACEI and kinins.

METHODS

We administered 5 mg/kg per day ramipril, either alone or combined with the kinin receptor antagonist icatibant (Hoe 140), on the days each wave occurred and studied the effects on neointima formation 14 days after balloon injury. Ramipril alone or combined with icatibant had no effect on neointima formation when administered from 2 days before to 3 or 5 days after balloon injury. In contrast, ramipril inhibited neointima formation when administered from day 7 to day 14. Treatment with icatibant had a small effect, which was sufficient to abolish the effects of ramipril (control 0.11 +/- 0.01 mm2, ramipril 0.08 +/- 0.01 mm2; P < 0.05; ramipril plus icatibant 0.09 +/- 0.01 mm2; NS, ramipril plus icatibant versus control). Thus ramipril was not effective when treatment was stopped after 3 or 5 days, but was mildly effective when treatment was administered during the second week. The effect on migration was studied by counting the number of neointimal cells in rats treated from 2 days before to 4 days after injury. Ramipril decreased the number of cells by 93% compared with controls (control 65.0 +/- 13.5 cells/slice, ramipril 4.7 +/- 2.0 cells/slice; P < 0.001), and this effect was blunted significantly by icatibant (19.5 +/- 5.7 cells/slice; P < 0.009, versus ramipril; P < 0.007, versus controls). The influence of treatment on the rate of proliferation (the 5'-bromo-2'-deoxyuridine index) was studied in the media 3 days, and in the neointima 7 and 10 days after balloon injury. Although proliferation peaked in the neointima after 7 days, there were no differences among the groups at any time. Thus neither ramipril nor icatibant affected the rate of proliferation at the times sampled. Ramipril increased cell density (cells/mm2) in the neointima, and this effect was abolished by cotreatment with icatibant (P < 0.05).

CONCLUSION

The ACEI needs to be present throughout the experimental period to be most effective. ACEI act on neointima formation in part by inhibiting migration; thus, because ramipril was mildly effective when administered from 7 to 10 days after injury, it is likely that vascular smooth muscle cell migration also occurs continuously. Kinins help mediate roughly 30% of the effect of ACEI on migration. In addition, ACEI, through kinins, affect a process that increases the density of the cells in the neointima, perhaps by decreasing extracellular matrix deposition.

Gene therapy and vascular disease: potential applications in vascular surgery

Advances in molecular biology have generated methods that are used to enhance diagnosis and treatment of a variety of human diseases. More recently modification of gene expression in cells by gene transfer has been introduced as a new therapeutic modality. The targeting of vascular cells with this method is appealing not only for anatomical reasons, but also because endovascular techniques provide access to the vasculature and makes site-specific delivery possible. Over the past few years, gene transfer has been widely used to explore the pathophysiology of vascular diseases in experimental models and available data suggests that this method may eventually become a therapeutic alternative for vascular disorders such as restenosis, graft failure, and critical ischaemia. In the following we discuss the methodology of gene transfer, its tentative use in vascular diseases related to vascular surgery, and the problems associated with this new technology.

Validation of a new UNIX-based quantitative coronary angiographic system for the measurement of coronary artery lesions

We describe a method of validation of computerized quantitative coronary arteriography and report the results of a new UNIX-based quantitative coronary arteriography software program developed for rapid on-line (digital) and off-line (digital or cinefilm) analysis. The UNIX operating system is widely available in computer systems using very fast processors and has excellent graphics capabilities. The system is potentially compatible with any cardiac digital x-ray system for on-line analysis and has been designed to incorporate an integrated database, have on-line and immediate recall capabilities, and provide digital access to all data. The accuracy (mean signed differences of the observed minus the true dimensions) and precision (pooled standard deviations of the measurements) of the program were determined x-ray vessel phantoms. Intra- and interobserver variabilities were assessed from in vivo studies during routine clinical coronary arteriography. Precision from the x-ray phantom studies (6-In. field of view) for digital images was 0.066 mm and for digitized cine images was 0.060 mm. Accuracy was 0.076 mm (overestimation) for digital images compared to 0.008 mm for digitized cine images. Diagnostic coronary catheters were also used for calibration; accuracy.varied according to size of catheter and whether or not they were filled with iodinated contrast. Intra- and interobserver variabilities were excellent and indicated that coronary lesion measurements were relatively user-independent. Thus, this easy to use and very fast UNIX based program appears to be robust with optimal accuracy and precision for clinical and research applications.

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.

Deposition of PG-M/versican is a major cause of human coronary restenosis after percutaneous transluminal coronary angioplasty

To clarify the mechanisms of restenosis, restenotic human tissue specimens obtained by directional coronary atherectomy (DCA) in 43 patients were immunohistochemically analysed for cell proliferation and deposition of PG-M/versican, an important extracellular matrix proteoglycan of the vessel wall. The patients were classified into five groups according to the period after percutaneous transluminal coronary angioplasty (PTCA): 0-1 month (N = 6), 1-3 months (N = 12), 3-6 months (N = 11), more than 6 months (N = 6) and de novo lesions (N = 8). The tissue specimens were of 35 restenotic lesions following PTCA and eight primary stenotic lesions with no prior PTCA. Total cell numbers in the atherectomy specimens increased significantly up to 3 months after PTCA. Most cells were alpha-smooth muscle actin (alpha-SMA)-positive. To evaluate cell proliferation, the specimens were immunostained for Ki-67 antigen (clone MIB-1). A significant increase in the positive ratio was observed up to 1 month after PTCA, although the labelling index was less than 1 per cent at every stage. The deposition of PG-M/versican, as analysed by immunohistochemistry, was greatest during the period 1-3 months after primary angioplasty, when restenosis detected by angiography progresses most actively. These results suggest that the peak of cell proliferation in the neointima occurs earlier than angiographic restenosis and that the deposition of PG-M/versican may be a major factor in restenosis following angioplasty.

Angiotensin-converting enzyme inhibitors and coronary artery disease

The renin-angiotensin system and angiotensin converting enzyme (ACE) are increasingly being implicated in the pathogenesis of coronary artery disease and its sequelae. Genetic studies of ACE gene polymorphism hint at an association between the ACE genotype and atherosclerosis. Animal studies have demonstrated the potential beneficial effects of ACE inhibition at a variety of sites, including improvement of endothelial function, inhibition of platelet aggregation, reduction of atherosclerosis, and inhibition of myointimal proliferation. Although these have not all been validated in human studies, the reduction of ischemic events in studies of ACE inhibition in left ventricular dysfunction cannot be explained solely by improved hemodynamics, and it is possible that actions on the endothelium, the atherosclerotic process, and platelets are at least in part responsible. The results of studies in humans looking more directly at the influence of ACE inhibitors on atherosclerosis and ischemic heart disease are awaited.

The renin-angiotensin system and coronary vasomotion

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Cardioprotective effect of angiotensin-converting enzyme inhibitors in patients with coronary artery disease

Clinical and experiments study with angiotensin-converting enzyme (ACE) inhibitors suggest that these agents may improve coronary artery disease by acting at multiple sites in the series of events leading to end-stage heart disease. These agents reduce blood pressure, improve prognosis and symptoms in patients with severe heart failure and in patients after acute myocardial infarction with left ventricular dysfunction. They are useful in the early, acute phase of myocardial infarction. More recently, ACE inhibitors have been shown to reduce in vitro vascular hypertrophy, to attenuate arteriosclerosis, and to maintain endothelium function. Whether these effects occur at clinical levels is still uncertain. The exciting clinical data have led to the proposal that alteration of ACE activity, particularly in tissue, is an important factor in development and progression of CAD. The ACE system is complex, with endocrine, paracrine, and autocrine effects. ACE is present in cardiac and vascular tissue. Therefore, the beneficial effects of ACE inhibitors can be classified as "cardio" and "vasculo" protective. This article summarizes a number of independent and complementary mechanisms pointing to a role of ACE and ACE inhibition in coronary artery disease.

Experimental models of accelerated atherosclerosis syndromes

The processes of angioplasty restenosis, vein graft failure, and transplant atherosclerosis, collectively termed 'syndromes of accelerated atherosclerosis', have been the focus of significant clinical and experimental research. Limitations of clinical studies have forced emphasis onto experimental animal models for the purpose of determining pathophysiology and evaluation of potential therapeutic strategies. However, the apparent failure of many in vivo animal models to predict interventional outcome in humans has raised doubt over their suitability as models of these pathophysiological states. Similar criticism has befallen the use of in vitro techniques for elucidating pathophysiology of the cellular elements. An awareness of the shortcomings of the various experimental models in use would therefore seem prerequisite both to a more critical evaluation of data generated from their use, and to the development of truly effective therapeutic strategies for humans.

Pravastatin reduces restenosis after coronary angioplasty of high grade stenotic lesions: results of SHIPS (SHIga Pravastatin Study)

We conducted a multicenter prospective, randomized, double-blind, placebo-controlled trial to test whether pravastatin, a hydroxymethyl glutaryl coenzyme A reductase inhibitor, can decrease restenosis after percutaneous transluminal coronary angioplasty (PTCA). Pravastatin 10 mg twice daily was begun at least 10 days prior to elective PTCA in patients with total cholesterol less than 280 mg/dl. The end-point was a between-group comparison of the frequency of restenosis defined as a more than 50% loss of the initial gain in diameter stenosis at the PTCA site at 3 months during follow-up by automated quantitative coronary arteriography. Of 207 patients randomly assigned to study groups, 139 patients underwent PTCA; 133 procedures were successful, and 124 patients underwent follow-up angiography at 3 months, and 179 lesions (85 pravastatin, 94 placebo) in 124 patients (62 pravastatin, 62 placebo) were analyzed. The two groups were comparable for baseline characteristics. Total cholesterol decreased by 19.6% in the pravastatin group (p < 0.001) but not in the placebo group. Although the restenosis rate was not different in the two groups (29.4% in pravastatin vs. 39.4% in placebo, p = 0.215) as a whole, it was reduced to about one fifth (8.8%) in the pravastatin group compared with 44.8% in the placebo group (p = 0.0011) when the comparison was restricted to high grade lesions (> or = 75% diameter stenosis, 34 lesions in pravastatin, 29 lesions in placebo). Pravastatin thus reduces restenosis after PTCA of high grade lesions.

Clinical and angiographic comparison of matched patients with successful directional coronary atherectomy or stent implantation for primary coronary artery lesions

OBJECTIVES

This study was designed to compare the long-term clinical and angiographic effects of successful directional atherectomy and stent implantation and to examine whether restenosis is related to the mechanism of lumen improvement as well as the extent of lumen gain.

BACKGROUND

Directional atherectomy and coronary stent implantation have been shown to achieve a more optimal immediate result that may lead to a more favorable long-term angiographic outcome and fewer target vessel revascularizations than does angioplasty. However, it remains to be determined whether one of the devices used in these interventions provides consistently better results than the other.

METHODS

To allow meaningful comparisons a prospectively collected series of 117 patients successfully treated with atherectomy were individually matched with a prospectively collected series of 117 patients successfully treated with stent implantation. Matching for baseline characteristics identified patients with identical lesion location and lesion severity, and immediate and late angiographic and clinical outcome were compared. To evaluate the possibility of a procedure effect on restenosis, patients were further matched for both immediate angiographic outcome and baseline characteristics, providing 150 matched patients for comparison. As confirmatory analysis, multivariate models were constructed to predict late lumen diameter.

RESULTS

Matching resulted in two comparable groups with equivalent baseline clinical and stenosis characteristics (n = 117 pairs). Atherectomy led to a smaller immediate gain than stenting and, because late loss was similar in both groups, stenting resulted in a larger late lumen (1.96 +/- 0.51 vs. 1.66 +/- 0.55 mm, p < 0.0001). When patients were matched for immediate gain and baseline characteristics (n = 75 pairs), lumen loss was more pronounced after atherectomy, and thus the minimal lumen diameter at follow-up differed significantly between the two groups (1.66 +/- 0.53 vs. 1.90 +/- 0.47 mm, p = 0.004). This beneficial angiographic effect of stenting was accompanied by a reduced need for repeat interventions. Multivariate analysis confirmed the independent effect of the interventional device used, whereby less loss and greater lumen diameter at follow-up were predicted for stent implantation than for atherectomy.

CONCLUSIONS

Successful stent implantation provided a more favorable long-term angiographic outcome and lower rates of restenosis and need for target lesion revascularization than did atherectomy. This favorable effect of stenting not only is related to a larger, immediate gain, but also seems to attenuate late lumen loss.

Characterisation of angiotensin II receptor mediated responses and inhibition of intimal hyperplasia in experimental vein grafts by the specific angiotensin II receptor inhibitor, L158,809

OBJECTIVES

This study characterises pharmacologically the angiotensin II receptor in experimental vein grafts and examines the effect of the angiotensin II receptor (type 1) antagonist (L158,809) on the formation of vein graft intimal hyperplasia in vivo, as well as the in vitro physiological response to angiotensin II of vein grafts after chronic oral L158,809 treatment.

MATERIALS

Thirty New Zealand White rabbits had a right carotid interposition bypass graft using the external jugular vein and were killed on the 28th postoperative day.

DESIGN

To characterise the angiotensin II receptors, concentration response curves to angiotensin II were obtained in vitro in the presence or absence of L158,809. To determine the effect of L158,809 on the development of intimal hyperplasia, 10 animals received chronic oral therapy with L158,809 (10 mg/kg/day; begun 5 days before surgery and continued until harvest) and 10 animals received vehicle only as controls. These grafts were harvested either for histology (n = 6 per group) or for in vitro isometric tension studies to angiotensin II.

RESULTS

The monophasic contractile response to angiotensin II in the untreated vein grafts could be inhibited in a concentration dependent manner by L158,809 with first order kinetics. Chronic oral treatment with L158,809 produced a 48% decrease in intimal thickness from 82 +/- 1 micron (mean +/- S.E.M.) in the controls to 43 +/- 7 microns in the treated vein grafts (p = 0.002). There was also a significant decrease (45%) in the medial thickness between the control (76 +/- 6 microns) and L158,809 treated (42 +/- 6 microns) vein grafts (p = 0.007). The responses to angiotensin II were abolished in the vein grafts by chronic L158,809 therapy.

CONCLUSIONS

This study suggests that vein graft angiotensin II responses are mediated through a type 1 receptor and that chronic inhibition with L158,809, significantly reduces intimal hyperplasia and medial hypertrophy in experimental vein grafts and concomitantly abolishes the in vitro responses to angiotensin II. Therefore, angiotensin II acting through AT1 receptors mediates a significant part of the intimal hyperplastic response in vein grafts.

Short- and long-term clinical and quantitative angiographic results with the new, less shortening Wallstent for vessel reconstruction in chronic total occlusion: a quantitative angiographic study

OBJECTIVES

This study was designed to examine whether oversized implantation of the new, less shortening Wallstent provides a more favorable long-term clinical and angiographic outcome in chronic total occlusions than does conventional coronary balloon angioplasty.

BACKGROUND

Restenosis and reocclusion remain major limitations of balloon angioplasty for chronic total occlusions. Enforced mechanical remodeling by implantation of the oversized Wallstent may prevent elastic recoil and improve accommodation of intimal hyperplasia.

METHODS

Lumen dimension was measured by a computer-based quantitative coronary angiography system (CAAS II). These measurements (before and after intervention and at 6-month follow-up) were compared between the groups with Wallstent implantation (20 lesions, 20 patients) and conventional balloon angioplasty (266 lesions, 249 patients) for treatment of chronic total occlusion. Acute gain (minimal lumen diameter after intervention minus that before intervention), late loss (minimal lumen diameter after intervention minus that at follow-up) and net gain (acute gain minus late loss) were examined.

RESULTS

Wallstent deployment was successful in all patients. High pressure intra-Wallstent balloon inflation (mean +/- SD 14 +/- 3 atm) was performed in all lesions. Although vessel size did not differ between the Wallstent and balloon angioplasty groups, acute gain was significantly greater in the Wallstent group (2.96 +/- 0.55 vs. 1.61 +/- 0.34 mm, p < 0.0001). Although late loss was also significantly larger in the Wallstent group (0.81 +/- 0.95 vs. 0.43 +/- 0.68 mm, p < 0.05), net gain was still significantly greater in this group (2.27 +/- 1.00 vs. 1.18 +/- 0.69 mm, p < 0.0001). Angiographic restenosis (> or = 50% diameter stenosis) occurred at 6 months in 29% of lesions in the Wallstent group and in 45% of those in the balloon angioplasty group (p = 0.5150).

CONCLUSIONS

Implantation of the oversized Wallstent, with full coverage of the lesion length, ensures resetting of the vessel size to its original caliber before disease and allows greater accommodation of intimal hyperplasia and chronic vessel recoil. Wallstent implantation provides a more favorable short- and long-term clinical and angiographic outcome than does conventional balloon angioplasty for chronic total occlusions.

Role of endothelial cells in restenosis after coronary angioplasty

Percutaneous transluminal coronary angioplasty (PTCA) is today a procedure of choice in many patients with atherosclerotic coronary artery disease. Despite high rates of initial success, restenosis, occurring in 30 to 40 percent of patients within the first six months, remains the major problem limiting the long-term efficacy of the procedure. Animal models have enhanced our knowledge in the understanding of the mechanisms involved in the restenotic process after experimental angioplasty. In fact, the two known determinants of restenosis are the proliferative and migrative response of underlying smooth muscle cells with production of extracellular matrix and the recently highlighted vascular remodeling. Endothelium, which regenerates from the leading edge of the de-endothelialized area within the weeks following arterial injury, is of particular interest in the modulation of the healing process after the procedure. Endothelial dysfunction, as an imbalance between relaxing and contracting factors, between anti- and pro-coagulant mediators or growth-inhibiting and growth-promoting factors, occurs at sites of regenerating endothelium. Experimental studies, using drugs that enhance endothelium-derived relaxing factors release or drugs that diminish endothelium-derived contracting factors production, have often been shown to be effective in the restenosis prevention. Thus, impairment in endothelial cell function may be considered as one of the major regulatory element in the restenotic process. This review discusses the interactions between endothelial and smooth muscle cells and has for aim to point out the major role of endothelial cells in the development of neointimal thickening and arterial remodeling.

Restenosis--an open file

The main procedural drawback to percutaneous coronary angioplasty is restenosis of the treated site within 6 months. Despite advances in equipment, technique, and adjunctive therapies, restenosis has occurred in approximately one-third to one-half of all patients. The biology of restenosis can be divided into plaque persistence and recoil, thrombus formation and transformation, and cellular proliferation and vascular remodeling. Animal models of restenosis have helped to elucidate these mechanisms of restenosis and provide a means to test pharmacologic and mechanical strategies to reduce stenosis recurrence. While numerous agents have been tested in animal models, until recently none has translated into benefit in large-scale clinical trials. Two therapeutic "hopefuls" which have recently emerged in clinical practice are the potent platelet inhibitors, glycoprotein IIb/IIIa receptor antagonists, and intracoronary metallic stents. The IIb/IIIa receptor antagonists target thrombus formation at the angioplasty site, thereby minimizing abrupt vessel closure acutely and neointimal growth chronically, while intracoronary stents safely produce a large coronary arterial lumen acutely and prevent vessel recoil. Separately, these therapeutic strategies have been shown to reduce clinical restenosis 20-30% at 6-month follow-up. With these encouraging results, the future will certainly provide more pharmacologic and mechanical therapies targeting restenosis. With increased understanding of the restenotic process and continued refinement of effective treatments, it may be possible one day to prevent stenosis recurrence.

Prevention of neointima formation by mibefradil after vascular injury in rats: comparison with ACE inhibition

Cilazapril, an angiotensin-converting enzyme inhibitor, and mibefradil, a selective T-type voltage-operated calcium channel blocker, have been shown to prevent neointima formation after vascular injury. The goal of the present study was to evaluate the mechanism of action of both drugs. For this purpose, the influence of the renin angiotensin system on the effects of mibefradil (30 mg/kg po) and cilazapril (10 mg/kg po) on neointima formation after carotid injury were evaluated in normotensive rats (normal renin angiotensin system) and DOCA hypertensive rats (suppressed renin angiotensin system). In addition, in order to differentiate an effect on cell migration or cell proliferation, both drugs were given either before or after the smooth muscle migration phase. Finally, cilazapril and mibefradil were given in combination. In normotensive rats, mibefradil and cilazapril decreased neointima formation, resulting in neointima/media ratios of 38% (p < 0.05) and 53% (p < 0.01), respectively. However, in DOCA hypertensive rats, mibefradil was active, with a reduction of the neointima/media ratio by 63% (p < 0.001), whereas cilazapril reduced it only slightly (19%) and not significantly. In addition, cilazapril was active only when treatment started before the migration phase (63%, reduction in neointima/media ratio, p < 0.001) but not when started thereafter (13% reduction in neointima/media ratio, n.s.). In contrast, treatment with mibefradil was also active when started after the migration phase (51% reduction in neointima/ media ratio, p < 0.001 when treatment started 1 day before balloon injury and 41%, p < 0.01 when treatment started 5 days after balloon injury). The combination of both drugs was additive (67% reduction in neointima/media ratio, p < 0.001 vs. control). These experiments clearly show that mibefradil and cilazapril have a different mechanism of action after vascular injury. Mibefradil most likely prevents the proliferation of smooth muscle cells. In contrast, cilazapril most likely inhibits the migration of smooth muscle cells. These two different mechanisms of action explain why the effects of both drugs are additive.

Performance standards and edge detection with computerized quantitative coronary arteriography. The Lovastatin Restenosis Trial Group

Quantitative coronary angiography (QCA) has become an important tool for evaluating coronary angiograms. Many methodologic factors, such as the choice of frame to analyze, the selection of the "normal," segment and the method of edge detection used may affect the results of QCA. The sequential steps in performing QCA, including a comparison of visual and automated edge-detection methodologies, were evaluated using 12 precision-drilled phantoms and 20 patient films. Normal diameter, minimal lumen diameter, and diameter stenosis were measured. In the phantom studies, the measurements from both visual and automated systems correlated well with the true measurements of the phantoms and between systems (all r values >0.92). To study the difference between methodologies on QCA results as influenced by the choice of frame and normal segment analyzed, the patient films were analyzed independently in 3 separate rounds of interpretation. In round 1, each system's operator individually chose frames and normal segments for analysis. In round 2, both systems analyzed the same preselected frames, but independently chose normal segments. In round 3, both systems analyzed the same preselected normal segments and frames. The intersystem correlations between visual and automatic systems for rounds 1, 2, and 3 were: normal diameter, r = 0.25, r = 0.37, and r = 0.75, respectively; minimal lumen diameter, r = 0.79, r = 0.86, and r = 0.85, respectively; and diameter stenosis, r = 0.65, r = 0.73, and r = 0.87, respectively. The manual edge-detection and automated edge-detection systems used in this study are reasonably accurate and consistent on phantom studies. In patient studies, the nonautomated processes (choice of frame and normal segment for analysis) produced significant differences in the QCA results, thus illustrating that operator-dependent factors other than edge detection are very important in QCA.

Association between deletion polymorphism of the angiotensin-converting enzyme gene and cerebral atherosclerosis

We investigated deletion polymorphism in the gene for angiotensin-converting enzyme in patients with angiographically verified cerebral atherosclerosis. Genotypes were determined by the polymerase chain reaction with oligonucleotide flanking of the polymorphic region of intron 16 of the angiotensin-converting enzyme gene. Results of angiotensin-converting enzyme genotyping showed 46% of 50 studied patients to be homozygous for the DD allele, whose prevalence was significantly increased as compared with a group of controls without atherosclerotic changes. In this control group, the following genotypes were observed (%): II = 24, ID = 52 and DD = 24. The frequency of the I and D alleles in the group of patients with cerebral atherosclerosis was 0.28 and 0.72, respectively, whereas in the group without atherosclerosis it was 0.50 for both. Furthermore, in the present study, the DD genotype was associated with a high level of serum angiotensin-converting enzyme activity, total and LDL-cholesterol and triacylglycerol. A newly established association between DD genotype and cerebral atherosclerosis, detected even in our small group, supports the view that angiotensin-converting enzyme polymorphism might be indicative of the development of cerebral atherosclerosis.

Local adenoviral-mediated expression of recombinant hirudin reduces neointima formation after arterial injury

Catalytically active thrombin, acting locally, is thought to mediate neointima formation after arterial injury. We constructed an adenovirus vector, AdHV-1.2, containing a complementary DNA for the thrombin inhibitor hirudin. AdHV-1.2 directed the synthesis and secretion of biologically active hirudin from vascular cells in vitro. In vivo gene transfer of hirudin into smooth muscle cells of injured rat carotid arteries resulted in peak secretion of at least 34+/-23 pg hirudin per vessel per 24 hours, and resulted in a significant (P<0.05) 35% reduction in neointima formation. Systemic partial thromboplastin times were not affected by local hirudin expression. These results support the hypothesis that local thrombin activity contributes to neointima formation after arterial injury and suggest that local delivery of a highly specific antithrombin may constitute an effective intervention for arterial proliferative disease.

Regulation of angiotensin AT1 receptor gene expression during cell growth of vascular smooth muscle cells

Cell proliferation influences the expression of numerous tissue-specific genes. The angiotensin AT1 receptor is highly expressed on vascular smooth muscle cells where it mediates cell contraction upon activation with angiotensin II. Since vascular smooth muscle cell de-differentiation leads to differential expression of several genes, we investigated the effects of cell growth on angiotensin AT1 receptor gene expression in vascular smooth muscle cells in culture. Northern hybridization analysis revealed a decrease of angiotensin AT1 receptor mRNA levels to approximately 20% in proliferating cells in comparison to growth-arrested cells. There is a correlative loss of membrane-associated angiotensin AT1 receptor protein in growing cells versus non-growing cells, as assessed by saturation radioligand binding assays. In addition, the BB-isoform of platelet-derived growth factor (PDGF-BB), which induces proliferation of quiescent vascular smooth muscle cells, causes a marked down-regulation of angiotensin AT1 receptor mRNA. These data suggest that proliferation of vascular smooth muscle cells leads to reduced angiotensin AT1 receptor gene expression. The mechanisms underlying this process and its physiological implications remain to be defined.

Restenosis, reocclusion and adverse cardiovascular events after successful balloon angioplasty of occluded versus nonoccluded coronary arteries. Results from the Multicenter American Research Trial With Cilazapril After Angioplasty to Prevent Transluminal Coronary Obstruction and Restenosis (MARCATOR)

OBJECTIVES

This study sought to compare the frequency of restenosis, reocclusion and adverse cardiovascular events after angioplasty of occluded versus nonoccluded coronary arteries.

BACKGROUND

Angioplasty of chronically occluded coronary arteries is believed to be associated with a higher frequency of restenosis and reocclusion than angioplasty of subtotal stenoses. Whether this leads to adverse cardiovascular events is unknown.

METHODS

The Multicenter American Research Trial With Cilazapril After Angioplasty to Prevent Restenosis (MARCATOR) was a placebo-controlled trial with angiographic follow-up to determine the effect of the angiotensin-converting enzyme inhibitor cilazapril on the frequency of restenosis. In this trial, restenosis was defined as 1) angiographic reduction of minimal lumen diameter > or = 0.72 mm between angioplasty and the follow-up visit; and 2) > 50% diameter stenosis on the follow-up angiogram. We identified 139 patients with successful angioplasty of a coronary occlusion (Group 1) and compared the frequency of restenosis, reocclusion and adverse cardiovascular events with that in 1,295 patients with successful angioplasty of a subtotal stenosis (Group 2).

RESULTS

Restenosis occurred in 36 patients with occluded arteries (29%) versus 264 with nonoccluded arteries (23%, p = 0.177) by definition 1 and in 62 patients with occluded arteries (49%) versus 478 with nonoccluded arteries (42%, p = 0.119) by definition 2. Occlusion was present in 24 Group 1 patients (19%) compared with 74 Group 2 patients (7%) (p < 0.001). During the 6 month follow-up period, two Group 1 patients (1.4%) and six Group 2 patients (0.5%) died; no Group 1 patients and 10 Group 2 patients (0.8%) developed severe congestive heart failure; nonfatal myocardial infarction occurred in 4 Group 1 patients (2.9%) and 31 Group 2 patients (2.4%); repeat coronary angioplasty or bypass surgery was performed in 29 Group 1 patients (21%) and 232 Group 2 patients (18%); and angina was present in 18 Group 1 and 163 Group 2 patients (13% for both). Eighty-six Group 1 patients (62%) and 853 Group 2 patients (66%) remained free of these adverse events during the 6-month follow-up period (p = 0.513).

CONCLUSIONS

The frequency of restenosis was slightly but not significantly greater after successful angioplasty of an occluded artery than after angioplasty of a subtotal stenosis. Although reocclusion was more frequent, occurring in 19% of patients, the net clinical benefit of angioplasty in such patients was similar to that in patients with subtotal stenoses over the 6-month follow-up period.

A proliferation analysis of arterial neointimal hyperplasia: lessons for antiproliferative restenosis therapies

Medial smooth muscle cell proliferation is frequently implicated as the major cause of coronary restenosis. Although antiproliferative agents have shown efficacy in animal studies, they are ineffective in human trials. To better understand these discrepancies, we performed a mathematical kinetic analysis of cellular proliferation in the neointimal hyperplasia of rats, pigs, and patients. A model was derived using a differential expression for proliferation, proportional to the number of cells present. Additional terms were included for inhibition of proliferation proportional to neointimal mass and time. The resulting equation was solved in closed form for the number of cells and proliferation rate. These equations were validated in the rat carotid artery injury model from published data. The model was then applied to the porcine coronary injury model, and then to clinical data obtained from angiographic human studies. Peak cellular proliferative activity in patients occurs at 16 days and continues at lower levels for much longer periods of time. Less than 10 generations of cells are sufficient to develop clinically significant restenosis. Conversely, proliferation rates in the two animal models (rats and pigs) are maximal at roughly 2 and 6 days, respectively, also continuing at low levels for extended time periods. Cell proliferation in restenosis is a highly controlled process, with comparatively few cell generations causing enough neointima for arterial obstruction to occur. Substantial cell kinetic differences occur across species. The rat exhibits high proliferation rates and rapid doubling times compared to patients and pigs, and is thus a highly 'proliferative' model. Such differences may be responsible for discrepant animal model and clinical trial results. These data may help determine the timing and strategy of therapy against clinical restenosis.

Nitric oxide in coronary artery disease: roles in atherosclerosis, myocardial reperfusion and heart failure

Nitric oxide (NO), derived from the vascular endothelium or other cells of the cardiovascular system, has an important role in physiological regulation of blood flow and has pathophysiological functions in cardiovascular disease. The mechanisms and enzymes involved in the biosynthesis of NO and biological actions of NO, including vasodilatation, cytotoxicity and inflammation, are briefly reviewed. These reactions involving NO cause pathological disturbances of arterial function, coronary blood flow regulation, and may contribute to cardiac myocyte dysfunction. NO and prostacyclin (PGI2), which is also released from the endothelium, act synergistically to inhibit platelet aggregation and adhesion, and in some arteries these mediators also synergise in terms of vasodilatation. In addition, NO is capable of hyperpolarizing vascular smooth muscle, but activation of the endothelium may cause hyperpolarization and may thus promote vasodilatation by an additional mechanism. After myocardial ischemia and reperfusion, production of NO and superoxide radicals represent important mechanisms of cytotoxicity, causing injury to the coronary endothelium and myocytes and compromising ventricular contractile function. Moreover, upon reperfusion endothelium-dependent vasodilatation is impaired and the coronary arteries constrict, leading to irregular myocardial perfusion. This is a consequence of the accumulation of activated leucocytes that we found to generate endogenous inhibitors of NO. These factors have yet to be fully characterised, but clearly they may have a role in irregularities of myocardial reperfusion and cellular injury. Chronic heart failure is associated both with impairment of endothelium-dependent vasodilatation and with excess production of NO via the inducible NO synthase (iNOS), although it is unclear whether the latter assists or compromises ventricular contractile performance under these conditions. Disturbances in the activity of isoforms of NO synthase in the artery wall also accompany the development of atherosclerosis, providing conditions propitious for vasospasm and thrombosis, and perhaps contributing to cell proliferation. Reversing these NO defects with therapeutic agents including angiotensin converting enzyme (ACE) inhibitors offers promise in protecting against some manifestations of vascular disease.