Michael B. Gravanis

Endovascular Low-Dose Irradiation Inhibits Neointima Formation After Coronary Artery Balloon Injury in Swine A Possible Role for Radiation Therapy in Restenosis Prevention

BACKGROUND Restenosis after percutaneous transluminal coronary angioplasty remains a major limitation of the long-term success of this procedure. Restenosis is a form of wound healing. Low-dose ionizing radiation has been effective in inhibiting exuberant wound healing responses in a variety of clinical situations. METHODS AND RESULTS Vascular neointimal lesions resembling human restenosis were created in the coronary arteries of normal pigs by overstretch balloon angioplasty injury. To test the effect of low-dose endovascular gamma radiation on lesion formation, a high-activity 192Ir source was introduced into one of the injured arteries in each animal and left in place for a period sufficient to deliver one of three doses: 350, 700, or 1400 cGy. To test potential benefits of delayed irradiation, 700 cGy was given in another group 2 days after injury. Animals were killed 14 days after balloon injury and the coronary vasculature was pressure-perfusion fixed. To test the late effect and safety of endovascular low-dose irradiation, 700 or 1400 cGy was given in miniswine coronary arteries after injury as well as in noninjured carotid arteries; this group was followed up for 6 months. Tissue sections were measured by computer-assisted planimetry. All arteries treated with radiation demonstrated significantly decreased neointima formation compared with control arteries. The ratio of intimal area-to-medial fracture length (IA/FL) was inversely correlated with the different radiation doses: control, 0.59; 350 cGy, 0.38; 700 cGy, 0.42; and 1400 cGy, 0.17 (r = -0.75, P < .0001). Delay of 700-cGy irradiation for 2 days after injury significantly decreased neointima formation compared with the same dose given immediately after injury. Analysis of long-term specimens showed reduction of IA/FL in the arteries irradiated with 700 cGy (0.3, P = .009) and 1400 cGy (0.31, P = .001) compared with control arteries (0.50). There was no excess fibrosis in the media, adventitia, or perivascular space of the coronary arteries or adjacent myocardium in pigs that received radiation compared with control animals. CONCLUSIONS Low-dose intracoronary irradiation delivered to the site of coronary arterial overstretch balloon injury in pigs inhibited subsequent intimal thickening (hyperplasia). A dose-response relationship was demonstrated, and delay of treatment for 48 hours appeared to augment the inhibitory effect. Six months of follow-up without fibrosis or arteriosclerosis demonstrated the durability of the beneficial effect in the treated group. These data suggest that intracoronary irradiation therapy may aid in preventing clinical restenosis.

Coronary intimal proliferation after balloon injury and stenting in swing: An animal model of restenosis

OBJECTIVES This study was designed to compare the proliferative response in coronary arteries after tantalum stent placement or balloon injury in a normolipemic swine model of restenosis. BACKGROUND Restenosis remains a significant complication of percutaneous transluminal coronary angioplasty. Efforts to study restenosis have been hampered by the lack of a suitable animal model. METHODS In an attempt to create lesions resembling those of human restenosis, normolipemic swine underwent injury of either the left anterior descending or the left circumflex coronary artery with either balloon inflation or deployment of a tantalum stent. At 4 weeks, they were killed and the injured vessels processed for histopathologic analysis. Intimal area, lumen area and maximal intimal thickness were measured. The degree of stenosis was expressed as residual lumen area (lumen area/intimal area ratio). RESULTS Vessels injured by either method demonstrated significant intimal smooth muscle proliferation leading to reduction in lumen area. In the 18 stented vessels residual lumen area measured 0.64 +/- 0.18 and maximal intimal thickness measured 0.6 +/- 0.3 mm; in the 15 balloon-injured vessels these values were 0.75 +/- 0.18 and 0.4 +/- 0.3 mm, respectively (p less than 0.05). In addition, most stented vessels had reactive inflammatory infiltrates surrounding the stent wires composed of lymphocytes, histiocytes and many eosinophils. CONCLUSIONS These data indicate that coronary artery injury in swine with either balloon inflation or stenting leads to intimal smooth muscle cell proliferation similar to that seen in human restenosis. The degree of intimal proliferation appears to be greater after stenting than after balloon injury. Intracoronary stenting in swine is associated with a marked inflammatory reaction around the stent wires. These models may be helpful in planning systemic and local antirestenosis strategies.

Intracoronary Radiation Before Stent Implantation Inhibits Neointima Formation in Stented Porcine Coronary Arteries

BACKGROUND Stent implantation has been shown to reduce restenosis by establishing a larger lumen but not by reducing neointima formation. We have previously shown that ionizing radiation reduced neointima formation after balloon injury in a swine model of restenosis. The purpose of this study was to determine whether endovascular irradiation of the coronary artery before stent implantation would affect neointima formation. METHODS AND RESULTS Nine normolipemic pigs underwent coronary angiography, and segments of the left anterior descending and left circumflex arteries were chosen as targets for stenting. A high-activity 192Ir source was used to deliver 14 Gy by random assignment to one of the vessels. After this, 3.5-mm tantalum stents were implanted in both arteries. Three additional pigs were treated with a 90Sr/Y source (a pure beta-emitter) delivering 14 Gy to five segments of coronary vessels that were stented immediately after irradiation. Stent-to-artery ratio was similar in the radiated and the control arteries. Animals received aspirin 325 mg daily and were killed at 28 days. The intimal area was significantly reduced in the irradiated stented arteries compared with control arteries treated with stent only (1.98 mm2 with 192Ir and 2.53 mm2 with 90Sr/Y versus 3.82 mm2 in the control stented arteries, P < .005). CONCLUSIONS Endovascular radiation before coronary stenting reduces neointima formation and may further reduce the restenosis rate after stent implantation.

Probucol decreases neointimal formation in a swine model of coronary artery balloon injury. A possible role for antioxidants in restenosis.

BackgroundRestenosis after percutaneous transluminal coronary angioplasty is the major limitation of the long-term success of this procedure. The process of restenosis is similar to an accelerated form of atherosclerosis. Thus, therapeutic interventions that limit the progression and initiation of atherosclerosis may be beneficial in the treatment of restenosis. One such intervention is the antioxidant drug probucol, which has demonstrated benefit in animal models of atherosclerosis. Methods and ResultsTwenty-six female domestic swine were divided into three study groups (control, n=9; low-dose probucol, n=9; high-dose probucol, n=8) before oversized balloon injury of the left anterior descending and left circumflex coronary arteries. Probucol (1 g/d, low-dose group; 2 g/d, high-dose group) was administered 2 days before balloon injury and was continued until the swine were killed 2 weeks after balloon injury. Morphometric analysis of the injured arteries included the intimal area (square millimeters), maximal intimal thickness (millimeters), and residual lumen (ratio of luminal to intimal plus luminal area). Treatment with high-dose probucol significantly reduced neointimal formation compared with control animals (decreases of 36% in intimal area, P=.007; 20% in maximal intimal thickness, P=NS; and an increase of 15% in residual lumen, P=.02). ConclusionThe major finding of this study is that the antioxidant drug probucol reduces neointimal formation after oversized balloon injury in a swine model of restenosis. This suggests that active oxygen species may play a role in restenosis.

Histopathologic phenomena at the site of percutaneous transluminal coronary angioplasty: The problem of restenosis

Seventeen postangioplasty cases were morphologically studied at postmortem. Four of the eleven, early and intermediate cases (few hours to 1 month from angioplasty to death), revealed intraluminal thrombi, although in only two cases were those thrombi occlusive. Almost all of the nine early cases (eight of nine) exhibited intimal disruptions. Except for two of these cases in which circumferential and/or longitudinal dissections were present, the remainder of the intimal cracks were superficial and of limited extent. Limited dissection between intima and media is not considered a serious or detrimental local event. The early cases showed an aneurysmal dilatation of the plaque-free segment of the arterial wall in eccentric plaques. This finding was interpreted as the result of uneven distribution of the dilating force (circumferential stress) on the aterial wall. Late cases (survival over 1 month) revealed characteristic medial and intimal lesions indicative of the initial dilatation injury. It is hypothesized that intrinsic arterial wall changes (medial disruption) at the plaque-free segment and the resulting altered arterial geometry at the site of dilatation have a significant hemodynamic effect on the vascular conduit and may enhance and sustain the myoproliferative intimal response.

Loss of Extracellular Superoxide Dismutase Leads to Acute Lung Damage in the Presence of Ambient Air A Potential Mechanism Underlying Adult Respiratory Distress Syndrome

The extracellular superoxide dismutase 3 (SOD3) is highly expressed in both blood vessels and lungs. In different models of pulmonary injury, SOD3 is reduced; however, it is unclear whether this contributes to lung injury. To study the role of acute SOD3 reduction in lung injury, the SOD3 gene was deleted in adult mice by using the Cre-Lox technology. Acute reduction of SOD3 led to a fivefold increase in lung superoxide, marked inflammatory cell infiltration, a threefold increase in the arterial-alveolar gradient, respiratory acidosis, histological changes similar to those observed in adult respiratory distress syndrome, and 85% mortality. Treatment with the SOD mimetic MnTBAP and intranasal administration of SOD-containing polyketal microparticles reduced mortality, prevented the histological alterations, and reduced lung superoxide levels. To understand how mice with the SOD3 embryonic deletion survived without lung injury, gene array analysis was performed. These data demonstrated the up-regulation of 37 genes and down-regulation of nine genes, including those involved in cell signaling, inflammation, and gene transcription in SOD3-/- mice compared with either mice with acute SOD3 reduction or wild-type controls. These studies show that SOD3 is essential for survival in the presence of ambient oxygen and that acute loss of this enzyme can lead to severe lung damage. Strategies either to prevent SOD3 inactivation or to augment its levels might prove useful in the treatment of acute lung injury.

Survival and incidence of acute rejection in heart transplant recipients undergoing successful withdrawal from steroid therapy

BACKGROUND Steroid-free immunosuppression is feasible in selected patients after heart transplantation. Survival and incidence of acute rejection are important parameters to evaluate when weighing risks and benefits of steroid withdrawal. METHODS One hundred thirty-seven patients were retrospectively reviewed who underwent heart transplant at Emory University between January 1988 and April 1994 and survived >1 year. Standard immunosuppression (cyclosporine, azathioprine and prednisone) without induction therapy was used. Weaning from steroids was attempted in all patients. Scheduled endomyocardial biopsy was used for long-term surveillance screening. RESULTS Seventy-two patients (52.5%) underwent successful prednisone withdrawal (Group P0) at an average of 13 months after heart transplant, whereas 65 patients (47.5%) did not achieve steroid-free immunosuppression (Group P1). Group P0 had a mean of 1.3 treated rejection episodes (ISHLT Grade > or = 1b) during the first post-transplant year and Group P1 a mean of 2.3 (p <0.0001). In Group P0, 40 patients (55.6%) suffered a subsequent acute rejection with an ISHLT Grade > or = 1b, resulting in treatment. Of these, 15% were ISHLT Grade 1b, 47.5% Grade 2, 35% Grade 3a and 2.5% Grade 3b. The estimated risk of suffering from acute rejection of at least Grade 1b after achieving steroid-free immunosuppression was 50% at 21 months. Estimated survival at 5 years after heart transplant was 92.9% in Group P0 and 72.3% in Group P1 (p <0.01). Cox proportional hazard modeling revealed black recipient race as effect modifier of group status with decreased survival time in both groups. CONCLUSION Steroid-free immunosuppression in white heart transplant recipients is associated with improved survival. A low acute rejection score during the first year predicts successful steroid withdrawal. Black recipient race appears to be negatively associated with survival and deserves further detailed study. Long-term surveillance screening using endomyocardial biopsy is recommended.

Intracoronary radiation decreases the second phase of intimal hyperplasia in a repeat balloon angioplasty model of restenosis

PURPOSE Repeat balloon angioplasty is likely to induce intimal proliferation, which is associated with a higher restenosis rate. This study examined the effect of intracoronary ionizing radiation on restenotic lesions using repeat balloon injury in a normolipemic swine. METHODS AND MATERIALS Eight domestic normolipemic pigs underwent overstretch balloon angioplasty with a 3.5 mm balloon in the LAD and LCX, followed by repeat balloon injury at the same sites 4 weeks after the initial injury. At that time a high activity 192Iridium source was introduced immediately after the angioplasty by random assignment to deliver 14 Gy at 2 mm in eight of the injured coronary arteries (LAD and LCX). One month later the animals were killed and the coronary arteries pressure perfusion fixed. Serial sections were stained with H&E and VVG, then evaluated by histopathologic and morphometric techniques. Maximal intimal thickness (MIT), intimal area (IA), and intimal area corrected for the extent of injury (IA/FL) were measured in the irradiated and control arteries and were compared to control arteries with single injuries from previous studies. RESULTS Repeat balloon injury induced significant additional medial damage, which was associated with marked intimal hyperplasia in a concentric pattern. Intracoronary irradiation significantly decreased the total of neointima area formation (IA 93 + 0.35 mm2 compared to control 1.38 + 0.33 mm2 p < 0.01) and the MIT was also significantly reduced in the irradiated vessels (0.57 + 0.18 mm vs. 0.71 + 0.08 mm, p = 0.05). CONCLUSIONS Intracoronary irradiation immediately after the second balloon dilatation inhibits the intimal hyperplasia due to that injury. However, there was no effect on the existing neointima from the initial injury.

Increased levels of soluble forms of adhesion molecules in Takayasu arteritis

The present series of experiments were designed to determine if soluble forms of vascular cell adhesion molecule-1 and inter cellular adhesion molecule-1 are elevated in the setting of Takayasu arteritis. Plasma levels of these soluble adhesion molecules were measured by enzyme-linked immunosorbent assay in 73 Takayasu arteritis and 36 age-matched normal controls and examined with respect to the age of patients. Soluble vascular cell adhesion molecule-1 levels were significantly higher in Takayasu arteritis (mean 871.4 ng/ml, P<0.01) compared with controls (mean 607.9 ng/ml). No difference was found in soluble inter cellular adhesion molecule-1 levels between these two groups. Comparison of soluble vascular cell adhesion molecule-1 and inter cellular adhesion molecule-1 in these patients subdivided by age into three groups indicated significantly higher levels of these molecules in individuals over 50 years old compared to those under 39 years old (P<0.05). These data suggest that the measurement of soluble vascular cell adhesion molecule-1 may be clinically important in Takayasu arteritis. The correlation of soluble vascular cell adhesion molecule-1 and inter cellular adhesion molecule-1 levels with age may indicate some relationship with progression of this disease.

Stents covered by an autologous arterial graft in porcine coronary arteries: feasibility, vascular injury and effect on neointimal hyperplasia

OBJECTIVE The use of stents has improved results after balloon coronary angioplasty. Several materials have been proposed for covering the metallic surface of the stent to reduce the rate of subacute thrombosis and restenosis. In our institution, an autologous arterial graft was used for covering the external surface of a conventional stent. The angiographic and histological response in a porcine coronary artery model was investigated. METHODS An autologous arterial graft was removed from the femoral artery and carefully prepared. Subsequently, a conventional stent was covered externally by the arterial graft. Twenty-two covered stents and 22 uncovered regular stents were implanted alternatively in the coronary arteries of 22 pigs. One animal died immediately after the procedure, due to thrombus formation in the uncovered stent. Six animals were sacrificed at seven days and the remaining animals were sacrificed at two months. Before the sacrifice, coronary angiography was performed in all animals. RESULTS Thrombosis was detected in two control segments and in one covered stented segment. After seven days, the luminal surface of the covered stents was covered by a new endothelial layer in contrast to partial endothelial cell appearance in the control group. The angiographic parameters were similar between the two groups. Histologically, the covered stents were associated with less vascular injury compared to uncovered stents. In covered stents a trend towards reduction of maximal intimal hyperplasia was detected (covered: 116.6 +/- 47.75 vs uncovered: 150.25 +/- 46.81 microns, p = 0.08); also the thickness of the arterial media was reduced (covered: 21.34 +/- 10.28 vs uncovered: 102.63 +/- 18.71 microns, p = 0.02). The luminal and vessel areas were similar in the two groups. CONCLUSIONS The preparation and implantation of the autologous arterial graft-covered stent is technically safe and feasible. This type of covered stent results in accelerated endothelialization, less vascular injury, thinning of the arterial media and a trend to reduce the intimal hyperplasia in normal coronary arteries.