Stent-mediated methylprednisolone delivery reduces macrophage contents and in-stent neointimal formation

OBJECTIVE: Corticosteroids have a wide range of biological effects. Stent-based methylprednisolone delivery could effectively suppress peri-strut inflammation and neointima induced by a polymer matrix. We tested the safety and efficacy of local stent-mediated methylprednisolone delivery using a biological coating on in-stent neointimal formation in a porcine coronary stent model. METHODS: Stainless steel coronary stents were dip-coated in a biological polymer/ methylprednisolone solution, resulting in total load of 530 mug methylprednisolone per stent. In-vitro drug release was performed. Stainless steel bare stents, polymer-only and methylprednisolone-coated stents (MP) were implanted in coronary arteries of pigs with a stent/artery ratio of 1.2 : 1. Histopathologic evaluation, morphometry and immunohistochemistic staining were analyzed at 4-week follow-up. RESULTS: In-vitro drug release studies showed sustained release up to 10 weeks. In vivo the vascular response of polymer-only-coated stents was comparable with the bare stents. No increased peri-strut inflammation and neointimal hyperplasia were observed. The in-stent neointimal formation of methylprednisolone-coated stents was significantly reduced compared with the bare and polymer-only-coated stents (bare, 1.92+/-0.73; polymer-only, 2.14+/-1.50; MP, 1.01+/-0.47 mm, P=0.019). The macrophage content of methylprednisolone-coated stents (bare, 30.74+/-48.67; polymer-only, 19.55+/-24.60; MP, 1.16+/-3.33/mm, P=0.072) was dramatically decreased. However, there were no significant difference among the three group in terms of the proliferating cells expressed by proliferation cell nuclear antigens. CONCLUSION: Stent-based local methylprednisolone delivery could effectively decrease both vascular macrophage infiltration and in-stent neointimal hyperplasia.     

Serial intravascular ultrasonographic measurements after implantation of biodegradable polymer-coated stents in porcine coronary arteries

BACKGROUND: Biodegradable stent coatings provide a potential for local drug delivery at the time of vascular injury, while possible tissue toxicity is avoided through constant degradation, leaving behind a bare metal stent. DESIGN: Serial three-dimensional (3D) intravascular ultrasonographic results on bare Megaflex stents and biodegradable polymer-coated Megaflex stents (Hyper stents) (Eurocor, Bonn, Germany) were compared 1 and 4 weeks after intracoronary implantation in pigs. METHODS: Under general anaesthesia, the left anterior descending and circumflex coronary arteries of domestic pigs were stented with Megaflex and Hyper stents, using right femoral artery access. Control coronary angiography and intravascular ultrasonography (IVUS) were performed 1 and 4 weeks after stent implantation using left femoral artery access and right carotid artery access. After recording of angiographic and IVUS data, the pigs were allowed to recover. RESULTS: The 1- and 4-week IVUS follow-ups revealed less neointima formation with Hyper stents than with Megaflex stents: 1-week intimal volume, 11.8+/-0.93 compared with 15.02+/-4.18 mm3, P=0.065; intimal area, 0.81+/-0.06 compared with 1.1+/-0.16 mm2, P =0.003; maximal intimal thickness, 0.12+/-0.01 compared with 0.14+/-0.02 mm, P =0.049; 4-week intimal volume, 12.4+/-1.77 compared with 27.32+/-12.79 mm3, P =0.016; intimal area, 0.82+/-0.12 compared with 1.95+/-0.65 mm2, P=0.003; and maximal intimal thickness, 0.13+/-0.04 compared with 0.30+/-0.10 mm, P=0.003. CONCLUSIONS: Implantation of biodegradable polymer-coated (Hyper) stents results in significantly less neointima formation 1 and 4 weeks after intracoronary implantation than with bare Megaflex stents. Taking advantage of the good collateralization of femoral and carotid arteries of pigs, the use of different arterial accesses allows serial angiographic and 3D IVUS measurements on neointimal development without sacrificing the animals.     

Addition of cytochalasin D to a biocompatible oil stent coating inhibits intimal hyperplasia in a porcine coronary model

BACKGROUND: Polymer-based, drug-eluting stents, are currently under extensive investigation in the conquest against in-stent restenosis. Concern remains, however, about potential long-term lack of biocompatibility of the polymers used in these studies. Therefore, this study aimed to evaluate in porcine coronary arteries (1) the in vivo biocompatibility of a new natural, eicosapentaenoic acid oil stent-coating and (2) the efficacy of this coating in preventing in-stent restenosis when cytochalasin D--an inhibitor of actin filament formation, that interferes with cell proliferation and migration--was added. METHODS AND RESULTS: To assess in vivo biocompatibility of the oil coating, 15 bare and 15 oil-coated stents were randomly deployed in coronary arteries of 15 pigs. No difference in tissue response, regarding inflammation or proliferation, was seen between both groups at five days or at four weeks follow-up. To evaluate the efficacy of the coating in preventing in-stent restenosis by adding a potential anti-restenotic drug, stents were dip-coated in 20 mg cytochalasin D/ml oil solution, resulting in 93 +/- 18 microg cytochalasin D/stent load (n = 3). In vitro drug release studies showed sustained release up to four weeks. Next, 11 oil-coated and 11 cytochalasin D-loaded stents were randomly implanted in coronary arteries of 11 pigs. At four weeks, a 39% decrease in neointimal hyperplasia (p < 0.05, ANCOVA, with injury as covariate) was found in cytochalasin D-loaded stents compared to oil-coated stents. CONCLUSIONS: This new natural oil stent-coating shows excellent biocompatibility to vascular tissue. Local cytochalasin D delivery from this stent-platform significantly inhibits neointimal hyperplasia in a porcine coronary model.     

Zotarolimus-eluting stents reduce experimental coronary artery neointimal hyperplasia after 4 weeks.

AIMS: The addition of drug elution to coronary stents plays an integral role in coronary restenosis prevention. The present study was undertaken to determine the mechanism of action and the in vitro and in vivo efficacy of zotarolimus, a new chemical entity designed specifically for elution from phosphorylcholine (PC)-coated stents, for the reduction of neointimal hyperplasia in porcine coronary arteries. METHODS AND RESULTS: In vitro studies of Zotarolimus bound to FKBP-12 potently inhibited smooth muscle cells (SMCs) and endothelial cell (EC) proliferation. Twenty PC-only and 20 stents eluting zotarolimus 10 microg/mm were implanted in the coronary arteries of 20 domestic juvenile swine. After 28 days, zotarolimus stents exhibited less area stenosis (22.4+/-8.6 vs. 35.7+/-13%, P = 0.01), less neointimal area (1.69+/-0.55 vs. 2.78+/-1.07 mm(2), P = 0.01), less neointimal thickness (0.25+/-0.07 vs. 0.38+/-0.13 mm, P = 0.01), and greater lumen area (6.07+/-1.39 vs. 5.02+/-1.3 mm2, P = 0.01). All arteries in both the polymer-only and polymer/drug stent showed near-complete healing and minimal toxicity. Zotarolimus did not affect the extrastent segments nor alter the overall artery size (external elastic lamina cross-sectional area 9.18+/-1.19 vs. 9.06+/-1.28 mm2, P = 0.7). CONCLUSION: Zotarolimus binds to FKBP-12 and in vitro inhibits SMC and EC proliferation. Zotarolimus applied to PC-coated stents reduces neointima in the swine coronary model after 28 days. These results suggest potentially promising human clinical application for coronary stenting with this polymer/drug combination.     

Short- and long-term effects of cytochalasin D, paclitaxel and rapamycin on wall thickening in experimental porcine vein grafts

OBJECTIVES: Neointima formation and wall thickening caused by smooth muscle cell proliferation compromise long-term patency of human aorto-coronary vein-grafts. We investigated short- and long-term effects of anti-proliferative pharmacological agents on experimental pig vein-grafts with similar dimensions and kinetics to human coronary grafts. METHODS AND RESULTS: Saphenous veins were treated for 1 h ex vivo with vehicle or concentrations of cytochalasin D, paclitaxel or rapamycin found to be anti-proliferative in preliminary studies. Vehicle and treated veins were implanted contralaterally, end-to-end into the carotid arteries of pigs. Cytochalasin D 2.5 mug/ml non-significantly reduced neointima formation in 4-week vein-grafts (mean+/-standard error, 2.5+/-0.6 vs. 3.3+/-0.6 mm2, n = 10, p = NS), whilst paclitaxel 10 microM produced significant inhibition (1.7+/-0.2 vs. 3.0+/-0.3 mm2, n = 8, p < 0.01) as did rapamycin 0.1 mg/ml (0.6+/-0.3 vs. 1.7+/-0.5 mm(2), n = 8, p < 0.02). Similar effects were found on total wall cross-sectional area but medial area was unaffected. PCNA staining of 1-week vein grafts confirmed in vivo anti-proliferative effects of paclitaxel (21+/-2 vs. 36+/-3%, n = 5, p < 0.01) and rapamycin (32+/-1 vs. 57+/-6%, n = 6, p < 0.005); neither agent stimulated loss of endothelium at these concentrations. Neointima and total wall area increased significantly between 4- and 12-weeks in all vein-grafts such that there was no longer a significant effect on neointima formation of either paclitaxel (7.5+/-1.3 vs. 8.9+/-1.9 mm2 in control, n = 5, p = NS) or rapamycin (6.0+/-0.9 vs. 7.9+/-1.1 mm2 in control, n = 9, p = NS) or on total wall area in 12-week grafts. CONCLUSIONS: Pre-treatment of saphenous vein with anti-proliferative agents paclitaxel or rapamycin reduced neointima and total wall area after 4 weeks but continued growth abolished differences by 12 weeks. These results may help to understand the failure of clinical studies using anti-proliferative treatments in vein-grafts.     

Does platelet aggregation play a role in the reduction in localized intimal proliferation in normolipidemic pigs with fixed coronary artery stenosis fed dietary fish oil?

In order to investigate the effect of fish oil on intimal proliferation of coronary arteries with a fixed stenosis normolipidemic piglets received a basic diet to which either 9% (w/w) lard (L, n = 8) or 4.5% (w/w) lard and 4.5% (w/w) mackerel oil (ML, n = 8) was added for 4 months. Stenosis was applied by implanting a 4.0 X 2.0 mm (i.d.) Teflon constrictor around the left anterior descending coronary artery (LADCA) (o.d. 2.7 +/- 0.1 mm). During the dietary period ADP-induced platelet aggregation in whole blood was higher in L than in ML. Partial replacement of 20:4 n - 6 by 20:5 n - 3 fatty acids in the platelet membranes of ML may have altered platelet aggregation by changes in eicosanoid synthesis. The plasma cholesterol and triglyceride levels did not change in L, but decreased in ML. At the end of the 4-month dietary period the animals were again anesthetized and regional myocardial perfusion (radioactive labelled microspheres) and systolic segment length shortening (SLS) were measured while the hearts were paced at 160 pulses/min. Perfusion and SLS of non-LADCA nourished segment were similar for L and ML. However, transmural flow to the LADCA perfused myocardium was impaired in both groups, but the deficiency in endocardial perfusion was considerably larger in L than in ML, resulting in a larger loss of SLS in the former. Remote (2-3 cm from the site of the constrictor) luminal encroachment was minimal (less than 2%) in both groups, but at the site of the constrictor there was significant encroachment in both groups which was higher in L (62 +/- 7%) than in ML (11 +/- 4%). It is thought that in these normolipidemic pigs the reduction in platelet aggregation may play a role in the smaller intimal proliferation of the fish oil-fed animals.     

Inflammatory responses in cuff-induced atherosclerosis in rabbits

Cuff-treatment of the rabbit carotid artery produced a diffuse intimal thickening which resembled early lesions of atherosclerosis. A limited amount of focal endothelial damage occurred first (0.5 h), leukocytes infiltrated the subendothelium and extensive endothelial denudation occurred at 24 h. At 3 days, the regenerating endothelium covered the denuded area, and the media was edematous. At 7 days proliferation of intimal cells became visible. Maximum intimal thickening occurred at 3 weeks. Daily injection of dexamethasone (0.01-10 mg/kg i.m.) and ticlopidine (1-100 mg/kg i.m.) dose-dependently attenuated the intimal thickening. Indomethacin had little effect. Inflammatory exudate from zymosan-activated air pouch induced chemotaxis of rat smooth muscle cells (SMC) in vitro. Similar chemotactic activity was observed with leukotriene B4 (LTB4) but not with the other lipoxygenase products tested. The exudate contained reasonable amounts of LTB4, which would account for its chemotactic activity. Dexamethasone inhibited the chemotaxis by the exudate and proliferation of SMC. These results are discussed in relation to the mechanism of atherogenesis. It is concluded that leukocytes play a major role in cuff-induced intimal thickening, and that their products cause endothelial denudation and SMC chemotaxis. Involvement of platelet aggregation in atherogenesis is also suggested.     

Pimecrolimus and dual pimecrolimus-paclitaxel eluting stents decrease neointimal proliferation in a porcine model.

OBJECTIVES AND BACKGROUND: The purpose of this study was to determine the effectiveness and vascular response of a pimecrolimus drug eluting stent and a combination (pimecrolimus + paclitaxel) stent as compared with bare metal controls in the porcine coronary model. METHODS AND RESULTS: In the first phase of the study, cobalt chromium stents were loaded with an erodible polymer and either a slow release or a fast release formulation of pimecrolimus. Thirty stents (metal, n = 10; pimecrolimus slow, n = 10; pimecrolimus fast, n = 10) were implanted in the coronary arteries of 10 pigs. At 30 days, neointimal proliferation and inflammation were both significantly less in the pimecrolimus fast release group as compared with the bare metal controls. Endothelialization was complete and equal in all three groups of stents. In the second phase of the study, stents were loaded with an erodible polymer with alternating reservoirs of paclitaxel and pimecrolimus. Twenty stents (8 control stents and 12 dual stents) were implanted in the coronary arteries of seven pigs. At 30 days, neointimal proliferation was significantly less in the dual drug group as compared with the bare metal controls. Endothelialization was complete in both groups of stents, suggesting complete healing of the arteries. CONCLUSIONS: In a 30-day porcine stent model, pimecrolimus inhibits neointimal proliferation as compared with bare metal stents. Also, the proof of concept of a dual drug eluting stent was established showing both safety and efficacy.     

Stent design related neointimal tissue proliferation in human coronary arteries; an intravascular ultrasound study.

AIMS: Histological restenosis models in animals have indicated that stent design has a significant impact on vessel trauma during stent implantation and on the amount of subsequent neointimal tissue proliferation. The impact of different stent designs on intimal hyperplasia in human atherosclerotic coronary arteries has not been determined. METHODS AND RESULTS: Angiographic and intravascular ultrasound studies were performed at the 6 month follow-up in 131 consecutive native coronary lesions of 131 patients treated with 50 Multi-Link stents, 40 InFlow stents and 41 Palmaz-Schatz stents. Lumen and stent cross-sectional areas (CSA) were measured at 1 mm axial increments. Mean intimal hyperplasia cross-sectional area (stent CSA-lumen CSA) and mean intimal hyperplasia thickness were calculated. Intravascular ultrasound demonstrated different levels of intimal hyperplasia proliferation for the three stents. Mean intimal hyperplasia thickness was 0.16+/-0.08 mm for Multi-Link stents, 0.26+/-0.19 mm for Palmaz-Schatz stents and 0.39+/-0.14 mm for Inflow stents (P<0.001). Multivariate analysis proved that stent type was the only independent predictor of intimal hyperplasia thickness at follow-up (P<0.001). CONCLUSION: Coronary stent design has a significant impact on subsequent intimal hyperplasia after implantation into atherosclerotic human coronary arteries. The corrugated ring design of the Multi-Link stent proved to result in less tissue proliferation at 6-month follow-up than the tubular slotted design of Palmaz-Schatz and InFlow stents.     

Long-term assessment of a novel biodegradable paclitaxel-eluting coronary polylactide stent.

AIM: The aim of this study was to assess technical feasibility, biocompatibility, and impact on coronary stenosis of a new biodegradable paclitaxel-loaded polylactide stent. Due to high rates of in-stent restenosis and permanent nature of metal stent implants, synthetic polymers have been proposed as surrogate materials for stents and local delivery systems for drugs. Paclitaxel was shown to inhibit vascular smooth muscle cell proliferation and migration. METHODS AND RESULTS: A novel biodegradable double-helical stent was manufactured using controlled expansion of saturated polymers (CESP) for the moulding of a bioresorbable poly(D,L)-lactic acid (PDLLA). A modified balloon catheter for stent deployment was developed according to the mechanical stent properties. Twelve paclitaxel-loaded (170 microg) polylactide stents, 12 unloaded polylactide stents, and 12 316L bare metal stents were deployed in porcine coronary arteries of 36 animals. Six pigs of each group were sacrificed after 3 weeks and 3 months, respectively, for every setting. Drug release kinetics as well as histomorphometrical and histopathological analyses were performed. A slow paclitaxel release kinetic for more than 2 months and therapeutic tissue concentrations were demonstrated. Coronary stenosis after implantation of paclitaxel-loaded stents (30+/-5% or 49+/-4%) was significantly inhibited compared to unloaded PDLLA stents (65+/-10%, P=0.021 or 71+/-4%, P=0.004) and metal stents (53+/-6% or 68+/-8%, P=0.029 and P=0.020) after 3 weeks or 3 months. Early complete endothelialisation was shown. Nevertheless, a local inflammatory response to the polylactide as a result of the polymer resorption process was observed. CONCLUSIONS: This novel polylactide stent showed sufficient mechanic stability, and by incorporation of paclitaxel, a significant potential to reduce restenosis development after vascular intervention was seen.     

Experimental efficacy of an everolimus eluting cobalt chromium stent.

INTRODUCTION: Rapamycin and its analogs are now being coated on different stent platforms, using different polymer matrices to prevent restenosis by impairing vascular smooth muscle cell proliferation and neointimal formation. METHODS: We evaluated the feasibility and compared the efficacy of biostable polymeric everolimus and sirolimus (CYPHER, Cordis) eluting stents in a porcine coronary model. Cobalt chromium balloon expandable stents (ML VISION, Guidant) were coated with a polymer containing everolimus (190 mug/cm(2)). Twelve pigs underwent placement of 36 oversized sirolimus (n = 12), everolimus (n = 12), and bare metal (cobalt chromium, n = 12) stents in the coronary arteries. RESULTS: At day 28, vessel injury scores were low (<0.25) and similar between each of the three test groups. The mean neointimal thickness was significantly lower in the everolimus- (0.13 +/- 0.07 mm, P = 0.02) and sirolimus-eluting stents (0.13 +/- 0.08 mm, P = 0.04) versus the bare metal stents (0.20 +/- 0.07 mm). The mean percent area stenosis was similar for the everolimus-eluting stents [(20.8 +/- 6.9)%] and the sirolimus-eluting stents [(20.8 +/- 7.6)%], and each was significantly less than that of bare metal stents [(26.1 +/- 7.8)%, P = 0.05]. CONCLUSION: Stent-based delivery of sirolimus and everolimus delivered via durable polymeric matrices are equally effective in the suppression of neointimal formation at day 28 in the porcine coronary model. Further study is necessary to document dose response and long-term comparative effects of these drug-eluting stents.     

Reduced thrombus formation by hyaluronic acid coating of endovascular devices

Biocompatible stent coatings may alleviate problems of increased (sub)acute thrombosis after stent implantation. Hyaluronic acid (HA), a ubiquitous, nonsulfated glycosaminoglycan, inhibits platelet adhesion and aggregation and prolongs bleeding when administered systemically. However, the effects of immobilized HA for reducing stent platelet deposition in vivo are unknown. We therefore quantified the antithrombotic effects of coating stainless steel stents and tubes with HA using an established baboon thrombosis model under physiologically relevant blood flow conditions. HA-coated and uncoated (control) stents (3.5 mm in diameter, n=32) and stainless steel tubes (4.0 mm in diameter, n=18) were deployed into exteriorized arteriovenous shunts of conscious, nonanticoagulated baboons. Accumulation of (111)In-radiolabeled platelets was quantified by continuous gamma-camera imaging during a 2-hour blood exposure period. HA coating resulted in a significant reduction in platelet deposition in long (4 cm) tubes (0.24+/-0.15 x 10(9) versus 6.12+/-0.49 x 10(9) platelets; P<0.03), short (2 cm) stainless steel tubes (0.18+/-0.06 x 10(9) versus 3.03+/-0.56 x 10(9) platelets; P<0.008), and stents (0.82+/-0.20 x 10(9) versus 1.83+/-0. 23 x 10(9) platelets; P<0.02) compared with uncoated control devices. Thus, HA coating reduces platelet thrombus formation on stainless steel stents and tubes in primate thrombosis models. These results indicate that immobilized HA may represent an attractive strategy for improving the thromboresistance of endovascular devices.     

A 7-day administration of tPA or heparin in the prevention of intimal hyperplasia following vascular injury in atherosclerotic rabbits

The effects on intimal hyperplasia of tissue plasminogen activator (tPA) and heparin following vascular injury were investigated. A common iliac artery in 34 hereditary hypercholesterolemic rabbits was injured by three successive 60-second balloon inflations to a pressure of 6 atm. Thereafter, two groups were continuously infused with tPA for 7 days at rates of 2 mg/kg per 24 hours (tPA-H) or 0.6 mg/kg per 24 hours (tPA-L), and two groups received intraarterial infusions of 750 U/kg (heparin-H) or 150 U/kg (heparin-L) heparin, followed by 625 U/kg or 125 U/kg subcutaneously twice daily for the same period, respectively. Twenty-eight days after injury, the intimal areas of the tPA-H (0.07 +/- 0.13 mm2), tPA-L (0.11 +/- 0.08 mm2), heparin-H (0.17 +/- 0.08 mm2), and heparin-L (0.28 +/- 0.27 mm2) groups were all significantly (P < 0.01) smaller than the controls (0.57 +/- 0.23 mm2), as were the intimal/medial cross-sectional area ratios (0.10 +/- 0.14, 0.21 +/- 0.20, 0.28 +/- 0.10, and 0.50 +/- 0.54 vs 1.13 +/- 0.74, respectively). Thus, attenuation of platelet aggregation by tPA or heparin inhibited medial smooth muscle cell proliferation and intimal hyperplasia in balloon injured arteries.     

A new RXR agonist, HX630, suppresses intimal hyperplasia in a mouse blood flow cessation model

The nuclear receptor retinoid X receptor (RXR) forms heterodimers with other nuclear receptors and exerts anti-inflammatory effects. RXR is implicated in the progression of arteriosclerosis; however, the effects of selective RXR activation on smooth muscle cell (SMC) proliferation are unknown. We synthesized a novel RXR agonist, HX630, and examined its effect on vascular SMC (VSMC) proliferation. Male C57BL/6 mice (n=15) were subjected to ligation of the left carotid artery and fed 5 or 10 mg/kg/day HX630 for 4 weeks. HX630-fed mice showed significantly suppressed intimal hyperplasia progression compared to that in control mice (0.286+/-0.093 vs. 1.022+/-0.134 intima/media ratio, P<0.05).Immunohistochemistry of the carotid artery showed that HX630 suppressed cytokine and adhesion molecule staining in lesions undergoing intimal thickening. Interleukin (IL)-1beta-induced VSMC proliferation was inhibited by HX630 and the expression of IL-6 mRNA and protein in VSMCs was suppressed. The RXR agonist HX630 exerts antiproliferative effects in VSMCs in vivo and in vitro. Thus, the RXR may serve as a therapeutic target for vascular injury and intimal thickening.     

Interaction of angiotensin II type 1 and D5 dopamine receptors in renal proximal tubule cells

Angiotensin II type 1 (AT1) receptor and D1 and D3 dopamine receptors directly interact in renal proximal tubule (RPT) cells from normotensive Wistar-Kyoto rats (WKY). There is indirect evidence for a D5 and AT1 receptor interaction in WKY and spontaneously hypertensive rats (SHR). Therefore, we sought direct evidence of an interaction between AT1 and D5 receptors in RPT cells. D5 and AT1 receptors colocalized in WKY cells. Angiotensin II decreased D5 receptors in WKY cells in a time- and concentration-dependent manner (EC50=2.7x10(-9) M; t(1/2)=4.9 hours), effects that were blocked by an AT1 receptor antagonist (losartan). In SHR, angiotensin II (10(-8) M/24 hours) also decreased D5 receptors (0.96+/-0.08 versus 0.72+/-0.08; n=12) and to the same degree as in WKY cells (1.44+/-0.07 versus 0.92+/-0.08). However, basal D5 receptors were decreased in SHR RPT cells (SHR 0.96+/-0.08; WKY 1.44+/-0.07; n=12 per strain; P<0.05) and renal brush border membranes of SHR compared with WKY (SHR 0.54+/-0.16 versus WKY 1.46+/-0.10; n=5 per strain; P<0.05). Angiotensin II decreased AT1 receptor expression in WKY (1.00+/-0.04 versus 0.72+/-0.08; n=8; P<0.05) but increased it in SHR (0.96+/-0.04 versus 1.32+/-0.08; n=8; P<0.05). AT(1) and D5 receptors also interacted in vivo; renal D5 receptor protein was higher in mice lacking the AT1A receptor (AT1A-/-; 1.61+/-0.31; n=6) than in wild-type littermates used as controls (AT1A+/+; 0.81+/-0.08; n=6; P<0.05), and renal cortical AT1 receptor protein was higher in D5 receptor null mice than in wild-type littermates (1.18+/-0.08 versus 0.84+/-0.07; n=4; P<0.05). We conclude that D5 and AT1 receptors interact with each other. Altered interactions between AT1 and dopamine receptors may play a role in the pathogenesis of hypertension.     

Iliac anastomotic stenting with a biodegradable poly-L-lactide stent: a preliminary study after 1 and 6 weeks.

PURPOSE: To assess the technical feasibility, thrombogenicity, and biocompatibility of a new biodegradable poly-L-lactic acid (PLLA) anastomotic stent. METHODS: A polytetrafluoroethylene bifurcated graft was implanted in 17 pigs through a midline abdominal incision. After transverse graft incision, 17 316L stainless steel stents and 17 PLLA stents were randomly implanted at both iliac anastomotic sites and deployed with a 6-mm balloon under direct vision without angiography. Intended follow-up was 1 week in 6 pigs receiving oral acetylsalicylic acid (ASA) and in 7 pigs receiving ASA/clopidogrel; 4 pigs receiving ASA/clopidogrel were followed for 6 weeks. At the end of the study, the segments containing the stents were surgically explanted and processed for histology to measure the mean luminal diameter, intimal thickness, and the vascular injury and inflammation scores. RESULTS: Initial technical success of stent placement was achieved in all animals without rupture of the suture. Two pigs died (unrelated to the stent) at 3 days after operation (1 in groups A and B). At 1 week, all PLLA stents showed thrombotic occlusion with the use of ASA alone. In contrast, all PLLA stents remained patent with concurrent administration of ASA/clopidogrel. All metal stents were patent regardless of the antiplatelet regimen. The mean luminal diameter of patent PLLA stents (4.13+/-0.17 mm) was comparable to metal stents (4.27+/-0.35 mm, p=0.78) at 1 week, but significantly diminished at 6 weeks (3.21+/-0.44 versus 4.19+/-0.18 mm, p=0.005). Histological analysis showed no signs of excessive recoil. PLLA stents induced a higher inflammation score (1.79+/-0.56) and more intimal hyperplasia (0.34+/-0.11 mm) compared to metal stents [1.27+/-0.44 mm (p<0.001) and 0.18+/-0.04 mm (p=0.006), respectively] at 6 weeks. Vascular injury was comparable between PLLA and metal stents. CONCLUSION: Biodegradable PLLA stents showed higher thrombogenicity and reduced patency compared to metal stents during early follow-up. Although ASA and clopidogrel prevented thrombotic occlusion, the increased inflammatory response and neointima formation remain major concerns of PLLA stents. A solution to this problem might be the incorporation of anti-inflammatory drugs into the PLLA stent.     

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.     

Stent-based tempamine delivery on neointimal formation in a porcine coronary model

BACKGROUND: Tempamine is one of new class of antioxidant agents, the nitroxides, which have shown a wide range of biological effects like suppressing free radical driven reactions to maintain cell functions. The objectives of this study were to evaluate the effect of a biodegradable polymer coated stent loaded with tempamine on in-stent neointimal formation. METHODS: Stainless steel stents were dip coated in biodegradable elastomeric poly (ester-amide) (co-PEA) or in polymer solution mixed with 50% (wt%) and 100% (wt%) tempamine. One group 100% (wt%) tempamine loaded stents were further dip coated in co-PEA polymer to form a top layer. Stainless steel bare, polymer-only, and different doses tempanine coated stents were implanted into porcine coronary arteries with a stent to artery ratio 1.2:1. Histomorphometric analysis was performed at 5 days and 6 weeks respectively. RESULTS: Histomorphometric analysis showed that the bare, polymer-only and tempamine-coated stents elicited a similar tissue response at 5 days. At 6 weeks, the peri-strut inflammation and neointimal hyperplasia of polymer-only stents were comparable to the bare stents. Compared to the bare stents, 50% tempanine coated stents had a trend to decrease the arterial injury (0.62 +/- 0.41 versus 0.34 +/- 0.18, P = 0.075) and neointimal hyperplasia (1.80 +/- 0.77 versus 1.27 +/- 0.39 mm2, P = 0.085). However, 100% tempanine coated showed significantly increased inflammatory response and neointimal formation. CONCLUSION: These co-PEA polymer coatings showed a biocompatible performance. Loaded with 50% tempamine had a trend to decrease neointimal hyperplasia. The 100% tempamine for stent-based delivery may have potential cytotoxic effects to arterial wall. Using a co-PEA polymer topcoat could effectively abolish these side effects.     

The potent platelet inhibitory effects of S-nitrosated albumin coating of artificial surfaces

OBJECTIVES: We studied the antithrombotic effect of coating glass, collagen and metal stent surfaces with bovine serum albumin (BSA) covalently modified to carry S-NO functional groups denoted (pS-NO-BSA). METHODS: Video-enhanced light microscopy was used to visualize canine blood platelet adhesion and aggregation in a parallel plate glass chamber. Platelet adhesion was observed for 60 min on glass, glass coated with BSA, glass coated with pS-NO-BSA, collagen I (CO) surface, CO coated with BSA and CO coated with pS-NO-BSA. We also coated Palmaz-Shatz (P-S) stents with pS-NO-BSA. Coated and uncoated stents were then immersed in porcine platelet-rich plasma for two min and the platelet cyclic GMP level was measured. In six anesthetized pigs, coated and uncoated stents were placed in the carotid arteries and [111In]-labeled platelets were circulated for 2 h. The stented arteries were then removed and placed in a gamma well counter. RESULTS: There was significantly less platelet attachment, adhesion and aggregation on the pS-NO-BSA coated surfaces compared with the BSA coated and uncoated surfaces. The pS-NO-BSA coating increased the platelet cGMP levels to 5.9+/-0.7 pmoles/10(8) platelets compared with 2.7+/-0.9 pmoles/10(8) platelets for control (p < 0.01). The average gamma ray count from [111In]-labeled platelets that attached to the coated stents was 90,000+/-42,000/min and 435,000+/-290,000/min for the uncoated stents (p < 0.01). CONCLUSIONS: The pS-NO-BSA coating of thrombogenic surfaces reduces platelet adhesion and aggregation, possibly by increasing the platelet cGMP. This inhibitory effect appears to be a consequence of the direct antiplatelet actions of NO combined with the antiadhesive properties of albumin.     

Recognition of platelet-associated fibrinogen by polyclonal antibodies: correlation with platelet aggregation.

Progressive decreases in platelet-bound fibrinogen accessibility to antibody and enzymes were recently reported to occur after adenosine diphosphate (ADP)-induced fibrinogen binding. Because previous studies also indicated that platelets that are activated but not aggregated by ADP in the presence of fibrinogen lose their ability to aggregate in a time-dependent manner despite negligible changes in fibrinogen binding, the present study examined the relationship between platelet aggregation and accessibility of platelet-bound fibrinogen to specific polyclonal antibody F(ab')2 fragments over a 60-minute time course. Although 125I-fibrinogen binding remained virtually unchanged, comparison of antifibrinogen antibody F(ab')2 binding and platelet aggregation 5 minutes and 60 minutes after platelet stimulation with ADP or thrombin showed decreases in F(ab')2 binding of 62% +/- 13% and 73% +/- 7% (mean +/- SD, n = 5), respectively, and decreases of 65% +/- 16% and 60% +/- 10% in platelet aggregation. In contrast, platelets stimulated with A23187 or chymotrypsin retained 87% +/- 16% and 76% +/- 12% of their ability to aggregate over the same time course, and lost only 39% +/- 14% and 36% +/- 12% of their ability to bind antifibrinogen antibody F(ab')2 fragments, respectively. Pretreatment of ADP-stimulated platelets with chymotrypsin largely prevented the progressive loss of platelet aggregability and the accompanying decreased recognition of bound fibrinogen by antifibrinogen F(ab')2 fragments. Preincubation of platelets with cytochalasin D (30 micrograms/mL) also inhibited the decrease in platelet aggregation after exposure of ADP-treated platelets to fibrinogen over a 60-minute time course. This was accompanied by only a 25% +/- 18% decrease in antifibrinogen antibody F(ab')2 binding. Present data support the hypothesis that qualitative changes in platelet-bound fibrinogen correlate with loss of the ability of platelets to aggregate, and implicate both the platelet cytoskeleton and chymotrypsin-sensitive surface membrane structures in modulating qualitative changes in bound fibrinogen on the platelet surface.