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

Preparation and characterization of rapamycin-loaded PLGA coating stent

In this study, using polylactic acid-co-glycolic acid (PLGA) with a molecular weight of 95,800 Da as drug carrier, three dose (low, moderate, high) rapamycin-eluting stents and the corresponding coating films were prepared. The pre- and post-expansion morphology of the rapamycin-eluting stent was examined by scanning electron microscopy (SEM), indicating that the coating was very smooth and uniform. The coating had the ability to withstand the compressive and tensile strains imparted without cracking from the stent during expansion process. There were many voids on stent coating surface after released for 18 days in release medium. The thermodynamics data of the stent coating film measured by differential scanning calorimetry (DSC) showed a lack of measurable solubility of rapamycin in the PLGA matrix. The release behavior of rapamycin from stent surface had a two phase release profile with a burst release period of about 2 days, followed by a sustained and slow release phase. The mass loss behavior of PLGA appeared linear throughout most of the degradation period, corresponding to an approximately constant mass loss rate. The platelet adhesion tests showed that the rapamycin-eluting films may have a good blood compatibility compared with control samples. Take into these results account, this novel rapamycin-eluting may be a good candidate to resolve in-stent restenosis.

Neointimal expression of rapamycin receptor FK506-binding protein FKBP12: postinjury animal and human in-stent restenosis tissue characteristics

Despite excellent clinical results for sirolimus (rapamycin)-eluting stents, the exact mechanisms of antirestenotic activity and affected cellular targets are incompletely understood. Therefore, we determined the presence and tem- porospatial expression pattern of FKBP12, the primary intracellular receptor of rapamycin, in rat carotid arteries after balloon injury, as well as in human in-stent restenosis and primary stable coronary atheroma. FKBP12 expression was assessed by immunohistochemistry. Rat carotid arteries revealed maximal expression in 57.7 +/- 4.0% of neointimal cells at day 7. A large proportion of these FKBP12+ cells showed luminally confined co-expression with dendritic cell markers. Despite a considerably thicker neointima at day 28, presence of FKBP12 decreased (8.5 +/- 1.9%, p = 0.02) with a scattered pattern in luminal and deep neointima. Likewise, human in-stent restenosis atherectomy specimens (time after stent implantation 2-12 months) revealed a comparable extent of cellular rapamycin receptor expression (9.3 +/- 1.0%) that significantly differed from that found in primary stable atheroma (1.3 +/- 0.4%, p < 0.001). In conclusion, the rapamycin receptor is predominantly present during early neointima formation, while mature neointimal atheromas show a relatively low expression without confinement to luminal areas. Co-expression of FKBP12 and dendritic cell markers suggests that dendritic cells may be another important target for early and long-term rapamycin effects.

The cell cycle: a critical therapeutic target to prevent vascular proliferative disease

Percutaneous coronary intervention is the preferred revascularization approach for most patients with coronary artery disease. However, this strategy is limited by renarrowing of the vessel by neointimal hyperplasia within the stent lumen (in-stent restenosis). Vascular smooth muscle cell proliferation is a major component in this healing process. This process is mediated by multiple cytokines and growth factors, which share a common pathway in inducing cell proliferation: the cell cycle. The cell cycle is highly regulated by numerous mechanisms ensuring orderly and coordinated cell division. The present review discusses current concepts related to regulation of the cell cycle and new therapeutic options that target aspects of the cell cycle.

A randomized comparison of sirolimus-eluting stent implantation with zotarolimus-eluting stent implantation for the treatment of total coronary occlusions: rationale and design of the PRImary Stenting of Occluded Native coronary arteries III (PRISON III) study

Primary intracoronary drug-eluting stent placement after the successful crossing of total coronary occlusions decreases restenosis rate at long-term follow-up compared with bare-metal stent implantation. The PRISON II trial was the first randomized study to show the safety and efficacy of sirolimus-eluting stents in patients with totally occluded native coronary arteries. The sirolimus-eluting stent is superior to the bare-metal stent in treating patients with total coronary occlusions, with significant reduction in angiographic binary in-stent and in-segment restenosis resulting in significantly reduced need for target lesion and target vessel revascularization. Whether sirolimus-eluting stents are superior to other drug-eluting stents in total coronary occlusions is unknown. In this prospective, randomized trial, sirolimus-eluting stent implantation will be compared with zotarolimus-eluting stent implantation for the treatment of total coronary occlusions. A total of 300 patients will be followed for up to 5 years with angiographic follow-up at 8 months. Quantitative coronary analysis will be performed by an independent core laboratory. The primary end point will be in-segment late luminal loss at 8 months angiographic follow-up.

Sirolimus-eluting coronary stents: a review

The sirolimus-eluting coronary stent received CE Mark approval in Europe in April 2002. In the US, FDA approval followed in April 2003. Since the preliminary results from the First-in-Man feasibility study were presented, several randomized, controlled trials have documented the profound antiproliferative effects of sirolimus, a macrolide antibiotic and potent cytostatic inhibitor of smooth muscle cell proliferation. Subsequently, the body of clinical evidence was increased by the second wave of evidence from trials in more complex lesions (such as in-stent restenosis, small vessels, chronic total occlusions) and "high-risk" patients such as those with diabetes. More recently we have had the opportunity to compare the two commercially available drug-eluting stents following the presentation of data from six head-to-head trials. As a result of numerous single and multi-center, national and international studies in which the safety and efficacy of sirolimus-eluting coronary stents have been subjected to close scrutiny, the global interventional cardiology community now has a wealth of evidence in support of the use of this technology resulting in dramatically improved patient outcomes after percutaneous intervention.

Direct stenting limits sirolimus-eluting stent edge neointimal thickening

OBJECTIVE

The use of sirolimus eluting stent (SES) has strongly limited the incidence of in-stent restenosis that still remains a problem at the stent edge. The aim of this study was to analyze the neointimal thickening after implantation of SES and to assess the influence of the stent implantation procedure on the neointimal thickening in the in-stent segment and at the edge of the stent in an ex-vivo model of stented human artery.

METHODS

Both balloon expandable SES and the corresponding bare metal stent (BMS) were used in a model of human mammary artery culture. Stents were implanted either directly or after predilatation (10 atm, 60 seconds) and analysis of arterial segments were performed at 28 days poststenting. Cell proliferation and neointimal thickening were assessed by immunohistochemistry, western blotting, and histomorphometry, both in the in-stent segment and at the edge of the stent. Neointimal thickening was expressed as the ratio ([neointimal area/neointimal area + media area]).

RESULTS

The in-stent neointimal thickening was dramatically inhibited in the SES group compared with the BMS group whatever the stenting technique was (predilatation: 0.22 +/- 0.05 vs 0.30 +/- 0.10; P < .04; direct stenting 0.16 +/- 0.04 vs 0.30 +/- 0.13; P <.01). This effect of SES was associated with a smallest expression of the small G protein RhoA and an increase of p27kip expression. In the BMS group, predilatation and direct stenting gave similar in-stent neointimal thickening. In contrast, in the SES group, in-stent neointimal thickening was significantly reduced when direct stenting was performed (0.16 +/- 0.04 [direct stenting] vs 0.22 +/- 0.05 [predilatation], P < .03). At the stent edge, a similar neointimal thickening was observed with both type of stent when predilatation was performed on the entire segment of the artery. Direct stenting significantly reduced the neointimal thickness at the stent edge when SES where used (0.06 +/- 0.01 [direct stenting] vs 0.19 +/- 0.06 [predilatation]; P < .001) but not in the BMS group.

CONCLUSION

These results confirm the efficiency of sirolimus released form SES to inhibit RhoA expression and to increase p27kip level in the arterial wall and show the benefit of direct stenting to limit the edge effect with SES.

Effects of tacrolimus or sirolimus on proliferation of vascular smooth muscle and endothelial cells

Local strategies directed against vascular smooth muscle cell (VSMC) proliferation such as drug-eluting stents reduce the occurrence of restenosis. However, these approaches may also inhibit endothelial cell (EC) proliferation and, thus, impair reendothelialization. We compared the effects of tacrolimus on human VSMC and EC proliferation and migration to sirolimus, a compound with similar molecular structure. Thymidine incorporation was determined in growth factor-stimulated VSMC and EC. The drug concentration at which maximal VSMC proliferation was inhibited by 50% (IC50) was about 10-fold higher for tacrolimus (3.8 x 10 M) than for sirolimus (4.1 x 10 M; P = 0.055). It is interesting that the molar IC50 value in EC was around 10-fold higher for tacrolimus (2.3 x 10 M) than for sirolimus (7.1 x 10 M; P < 0.01). The profile of these drugs on VSMC and EC migration was similar to the one found in the proliferation assays. Inhibition of VSMC proliferation by both tacrolimus and sirolimus was associated with upregulation of the cell-cycle inhibitor p27. Thus, tacrolimus is less potent than sirolimus for inhibiting VSMC proliferation or migration. However, tacrolimus exerts markedly less antiproliferative effects on EC compared with sirolimus. In combination with its potent antiinflammatory effects, tacrolimus may represent a promising compound for the use in drug-eluting stents.

Anti-atherosclerotic effects of sirolimus on human vascular smooth muscle cells

Sirolimus is a potent immunosuppressive agent and has an anti-atherosclerotic effect through its anti-proliferative property. The present study was undertaken to investigate the effect of sirolimus on intracellular cholesterol homeostasis in human vascular smooth muscle cells (VSMCs) in the presence of inflammatory cytokine IL-1β. We explored the effect of sirolimus on the lipid accumulation of VSMCs in the presence of IL-1β, using Oil Red O staining and quantitative measurement of intracellular cholesterol. The effect of sirolimus on the gene and protein expression of lipoprotein receptors and ATP binding cassettes (ABCA1 and ABCG1) was examined by real-time PCR and Western blotting, respectively. Furthermore, the effect of sirolimus on cholesterol efflux from VSMCs in the presence or absence of IL-1β was also investigated using [3H] cholesterol efflux. Finally, we examined the effect of sirolimus on the production of inflammatory cytokines in VSMCs using ELISA. Sirolimus reduced intracellular lipid accumulation in VSMCs mediated by IL-1β possibly due to the reduction of expression of low-density lipoprotein (LDL) and very low-density lipoprotein (VLDL) receptors. Sirolimus increased cholesterol efflux from VSMCs and overrode the suppression of cholesterol efflux induced by IL-1β. Sirolimus also increased ABCA1 and ABCG1 genes expression, even in the presence of IL-1β. We further confirmed that sirolimus inhibited mRNA and protein expression of inflammatory cytokines IL-6, tumor necrosis factor-α, IL-8, and monocyte chemoattractant protein-1. Inhibition of lipid uptake together with increasing cholesterol efflux and the inhibition of inflammatory cytokines are all important aspects of the anti-atherosclerotic effects of sirolimus on VSMCs.

Use of sirolimus in solid organ transplantation

Sirolimus is a mammalian target of rapamycin (mTOR) inhibitor that inhibits cell cycle progression and has proven to be a potent immunosuppressive agent for use in solid organ transplant recipients. The drug was initially studied as an adjunct to ciclosporin (cyclosporine) to prevent acute rejection in kidney transplant recipients. Subsequent studies have shown efficacy when combined with a variety of other immunosuppressive agents. The most common adverse effects of sirolimus are hyperlipidaemia and myelosuppression. The drug has unique antiatherogenic and antineoplastic properties, and may promote immunological tolerance and reduce the incidence of chronic allograft nephropathy. Although sirolimus is relatively non-nephrotoxic when administered as monotherapy, it pharmacodynamically enhances the toxicity of calcineurin inhibitors. Ironically, the drug has been used to facilitate calcineurin inhibitor-free protocols designed to preserve renal function after solid organ transplantation. Whether sirolimus can be used safely over the long term with low doses of calcineurin inhibitors requires further study. The use of sirolimus as a corticosteroid-sparing agent also remains to be proven in controlled trials. Postmarketing studies have revealed a number of unforeseen adverse effects including impaired wound healing and possibly proteinuria, oedema, pneumonitis and thrombotic microangiopathy. Overall, sirolimus is a powerful agent when used judiciously with other available immunosuppressants. As is true for all immunosuppressive drugs available for treatment of solid organ transplant recipients, the efficacy of the drug must be balanced against its considerable adverse effects.

Sirolimus inhibits key events of restenosis in vitro/ex vivo: evaluation of the clinical relevance of the data by SI/MPL- and SI/DES-ratios

Background

Sirolimus (SRL, Rapamycin) has been used successfully to inhibit restenosis both in drug eluting stents (DES) and after systemic application. The current study reports on the effects of SRL in various human in vitro/ex vivo models and evaluates the theoretical clinical relevance of the data by SI/MPL- and SI/DES-ratio's.

Methods

Definition of the SI/MPL-ratio: relation between significant inhibitory effects in vitro/ex vivo and the maximal plasma level after systemic administration in vivo (6.4 ng/ml for SRL). Definition of the SI/DES-ratio: relation between significant inhibitory effects in vitro/ex vivo and the drug concentration in DES (7.5 mg/ml in the ISAR drug-eluting stent platform). Part I of the study investigated in cytoflow studies the effect of SRL (0.01–1000 ng/ml) on TNF-α induced expression of intercellular adhesion molecule 1 (ICAM-1) in human coronary endothelial cells (HCAEC) and human coronary smooth muscle cells (HCMSMC). Part II of the study analysed the effect of SRL (0.01–1000 ng/ml) on cell migration of HCMSMC. In part III, IV, and V of the study ex vivo angioplasty (9 bar) was carried out in a human organ culture model (HOC-model). SRL (50 ng/ml) was added for a period of 21 days, after 21 and 56 days cell proliferation, apoptosis, and neointimal hyperplasia was studied.

Results

Expression of ICAM-1 was significantly inhibited both in HCAEC (SRL ≥ 0.01 ng/ml) and HCMSMC (SRL ≥ 10 ng/ml). SRL in concentrations ≥ 0.1 ng/ml significantly inhibited migration of HCMSMC. Cell proliferation and neointimal hyperplasia was inhibited at day 21 and day 56, significance (p < 0.01) was achieved for the inhibitory effect on cell proliferation in the media at day 21. The number of apoptotic cells was always below 1%.

Conclusion

SI/MPL-ratio's ≤ 1 (ICAM-1 expression, cell migration) characterize inhibitory effects of SRL that can be theoretically expected both after systemic and local high dose administration, a SI/MPL-ratio of 7.81 (cell proliferation) represents an effect that was achieved with drug concentrations 7.81-times the MPL. SI/DES-ratio's between 10^-6 and 10^-8 indicate that the described inhibitory effects of SRL have been detected with micro to nano parts of the SRL concentration in the ISAR drug-eluting stent platform. Drug concentrations in DES will be a central issue in the future.

Improved blood compatibility of rapamycin-eluting stent by incorporating curcumin

This paper dealt with improving the blood compatibility of the rapamycin-eluting stent by incorporating curcumin. The rapamycin- and rapamycin/curcumin-loaded PLGA (poly(d,l-lactic acid-co-glycolic acid)) coatings were fabricated onto the surface of the stainless steel stents using an ultrasonic atomization spray method. The structure of the coating films was characterized by Fourier transform infrared spectroscopy (FTIR). The optical microscopy and scanning electron microscopy (SEM) images of the drug-eluting stents indicated that the surface of all drug-eluting stents was very smooth and uniform, and there were not webbings and "bridges" between struts. There were not any cracks and delaminations on stent surface after expanded by the angioplasty balloon. The in vitro platelet adhesion and activation were investigated by static platelet adhesion test and GMP140 (P-selection), respectively. The clotting time was examined by activated partially prothromplastin time (APTT) test. The fibrinogen adsorption on the drug-loaded PLGA films was evaluated by enzyme-linked immunosorbent assay (ELISA). All obtained data showed that incorporating curcumin in rapamycin-loaded PLGA coating can significantly decrease platelet adhesion and activation, prolong APTT clotting time as well as decrease the fibrinogen adsorption. All results indicated that incorporating curcumin in rapamycin-eluting coating obviously improve the blood compatibility of rapamycin-eluting stents. It was suggested that it may be possible to develop a drug-eluting stent which had the characteristics of not only good anti-proliferation but also improved anticoagulation.

Gene therapy and stem cell therapy for cardiovascular diseases today: a model for translational research

Clinical trials looking at ways to promote myocardial regeneration have reported that the administered therapies have either neutral effects or modest benefits of questionable impact. These somewhat disappointing results should emphasize the need for translational research, with bidirectional feedback between the basic research laboratory and the clinical arena. Such a translational pathway is illustrated by the quest to find an effective therapy for restenosis, which culminated in the development of sirolimus. At this point a move away from the bedside and a return to the bench seems necessary to better understand the mechanisms of action of progenitor cells and stimulating factors. Without such basic knowledge research might be prematurely discouraged and the opportunity to fully understand the true potential of cardiovascular regenerative therapy might be missed.

Early restenosis after drug-eluting stent implantation: A putative role for platelet activation

Drug-eluting stents (DES) reduce intimal hyperplasia and restenosis, but they also inhibit stent endothelization, making the vascular surface more thrombogenic. The present report describes two cases of in-stent restenosis after DES deployment at exactly the same sites where subacute stent thrombosis had occurred. Extremely careful follow-up is mandatory after the recognition of intraluminal thrombi inside DES because restenosis may occur at the same site of DES thrombosis.

Sirolimus-eluting biodegradable poly-L-lactide stent for peripheral vascular application: a preliminary study in porcine carotid arteries

BACKGROUND

To assess technical feasibility and biocompatibility of a new Sirolimus (SIR)-eluting biodegradable poly-L-lactide (PLLA) stent for peripheral vascular application.

MATERIAL AND METHODS

In 15 pigs, both common carotid arteries (CCA) were surgically exposed and clamped in the proximal segment. After transverse incision, 12 316L stents, 12 unloaded and 6 SIR-loaded PLLA stents mounted on 6.0 x 40-mm balloon catheters were randomly implanted into the CCA and inflated to 8 bar. Angiographic equipment was not available. Stented CCA were explanted after 1 week (6 pigs; 316L versus PLLA) and 6 weeks (9 pigs; 316L versus PLLA versus SIR-PLLA), and processed for quantitative histomorphometry and estimation of vascular inflammation and injury scores.

RESULTS

No animals were lost during follow-up. All stents were patent on histological analysis without any signs of excessive recoiling or collapse. Unloaded PLLA stents showed decreased residual lumen area and increased neointimal area after 1 week (13.16 +/- 0.34, 1.94 +/- 0.26) and 6 weeks (11.57 +/- 0.30, 2.85 +/- 0.24) as compared with 316L stents (15.26 +/- 0.13, 1.27 +/- 0.41 and 13.99 +/- 0.51, 1.54 +/- 0.59). SIR-eluting stents demonstrated comparable neointimal area (1.75 +/- 0.38) and 50% lower intimal thickness as compared with 316L stents after 6 weeks, but a slightly decreased residual lumen (13.06 +/- 0.32) in the consequence of differences in strut thickness (PLLA, 270 microm; 316L, 155 microm). The vascular inflammation score against PLLA-stents could be reduced by Sirolimus. The vascular injury scores were low and similar in all groups.

CONCLUSIONS

PLLA stents showed sufficient mechanical stability after porcine CCA stenting. By incorporation of Sirolimus, a significant reduction of the inflammatory and neointimal response to the PLLA stent was seen without systemic toxicity or thrombotic complications. These findings need to be assessed with longer follow-up to confirm maintenance of efficacy. The greater strut height of PLLA stents is a major limitation and requires modification.

Novel Bioengineered Small Caliber Vascular Graft With Excellent One-Month Patency

BACKGROUND

A bioengineered microporous polycarbonate-siloxane polyurethane graft has been developed for coronary artery bypass grafting. Biological agents can be impregnated into its absorbable collagen and hyaluronan microstructure and stable macrostructure to promote patency. The objective of this study was to examine the biological performance and biomechanical characteristics of this graft.

METHODS

Heparin-sirolimus (HS) or heparin-sirolimus-vascular endothelial growth factor (HSV) grafts were manufactured for this study. Heparin (40 U) was embedded in the microstructure of the graft for early elution from the graft wall. Heparin (100 U) and sirolimus (450 microg) were incorporated into the macrostructure of the graft for late elution. Vascular endothelial growth factor was also embedded in the microstructure of the graft. Both grafts (3.6 mm internal diameter, 24 mm length) were implanted into the abdominal aortas of rabbits (n = 36) to compare with heparin-alone (H) grafts (n = 9). At 4 hours, 1 day, and 1, 2, and 4 weeks after surgery, the grafts were removed for histologic, immunohistochemical, and biomechanical evaluations.

RESULTS

The patency rate of all grafts was 100% at each time point. None of grafts had stenosis after surgery. Endothelial cells were observed at 4 weeks after surgery in the HS, HSV, and H grafts. Although there was no significant difference of neointima thickness among the HS, HSV, and H grafts (136 +/- 75, 93 +/- 64, and 125 +/- 90 microm; p = 0.08), the H grafts did have more cellular infiltration in the graft than the HS or HSV grafts. There was neocapillary formation inside the graft wall at 4 weeks in all grafts. The graft macrostructure was unchanged based on biomechanical evaluation 4 weeks after surgery.

CONCLUSIONS

A unique drug-eluting graft had excellent patency at 1 month and may encourage luminal endothelialization without excessive intimal hyperplasia. Although vascular endothelial growth factor did not improve intimal formation, cell infiltration, or vascularization, sirolimus might inhibit cell proliferation. Further long-term study would need to evaluate the efficacy of impregnated sirolimus.

Orally Administered Rapamycin Does Not Modify Rat Aortic Vascular Tone

Rapamycin (RP; rapamune, sirolimus) is a potent inhibitor of vascular smooth muscle cell proliferation and migration. RP was demonstrated to reduce vascular neointimal formation in different animal models of vascular smooth muscle cell proliferation, and clinical use of RP-eluting stents promotes significant reductions in in-stent restenosis rates. However, high costs still preclude the widespread use of these devices. Oral administration of RP associated to bare metal stent delivery has been advocated as an effective and considerably less expensive alternative for restenosis prevention. It is noteworthy that the presence of RP-eluting stents has been associated with reduced endothelial-dependent vasodilation and coronary spasm. In addition, RP has been demonstrated to prevent vasculogenesis. This study evaluated the effects of RP on endothelium-dependent vascular tone and demonstrated that in vitro incubation with high concentrations of RP did not modify either contraction or relaxation of aortic rings. Similar results were obtained after in vivo administration of the drug. These findings suggest that function of adult, non-proliferative rat endothelial cells involved in vascular tone control is not affected by orally administered RP.

Mammalian target of rapamycin is activated in human gastric cancer and serves as a target for therapy in an experimental model

The mammalian target of rapamycin (mTOR) has become an interesting target for cancer therapy through its influence on oncogenic signals, which involve phosphatidylinositol-3-kinase and hypoxia-inducible factor-1alpha (HIF-1alpha). Since mTOR is an upstream regulator of HIF-1alpha, a key mediator of gastric cancer growth and angiogenesis, we investigated mTOR activation in human gastric adenocarcinoma specimens and determined whether rapamycin could inhibit gastric cancer growth in mice. Expression of phospho-mTOR was assessed by immunohistochemical analyses of human tissues. For in vitro studies, human gastric cancer cell lines were used to determine S6K1, 4E-BP-1 and HIF-1alpha activation and cancer cell motility upon rapamycin treatment. Effects of rapamycin on tumor growth and angiogenesis in vivo were assessed in both a subcutaneous tumor model and in an experimental model with orthotopically grown tumors. Mice received either rapamycin (0.5 mg/kg/day or 1.5 mg/kg/day) or diluent per intra-peritoneal injections. In addition, antiangiogenic effects were monitored in vivo using a dorsal-skin-fold chamber model. Immunohistochemical analyses showed strong expression of phospho-mTOR in 60% of intestinal- and 64% of diffuse-type human gastric adenocarcinomas. In vitro, rapamycin-treatment effectively blocked S6K1, 4E-BP-1 and HIF-1alpha activation, and significantly impaired tumor cell migration. In vivo, rapamycin-treatment led to significant inhibition of subcutaneous tumor growth, decreased CD31-positive vessel area and reduced tumor cell proliferation. Similar significant results were obtained in an orthotopic model of gastric cancer. In the dorsal-skin-fold chamber model, rapamycin-treatment significantly inhibited tumor vascularization in vivo. In conclusion, mTOR is frequently activated in human gastric cancer and represents a promising new molecular target for therapy.

Sirolimus experience in heart transplantation

INTRODUCTION

Sirolimus is a potent, nonnephrotoxic immunosuppressant with antiproliferative activity in nonimmune cells. Recent data support the conversion in late renal failure secondary to calcineurin inhibitors (CNIs), with limited experience in de novo regimens in patients with predictive factors of postoperative renal impairment.

OBJECTIVE

We evaluated our experience of sirolimus-based immunosuppression administered to 25 heart transplant recipients.

METHODS

A retrospective analysis of 25 heart transplant recipients who received sirolimus included 17 conversions due to late CNI-related chronic renal dysfunction, six patients with a de novo regimen, and two patients who developed posttransplant pulmonary neoplasms. The conversion from CNI to sirolimus was started with 2 mg, with an average time after transplantation of 78 +/- 43 months and a mean baseline serum creatinine level of 2.1 +/- 0.45 mg/dL. The mean clinical follow-up was 17 +/- 9 months postconversion, and included echocardiography and laboratory studies. In the de novo group successive endomyocardial biopsies were performed during the first semester.

RESULTS

Serum creatinine fell from 2.1 +/- 0.45 mg/dL to 1.8 +/- 0.51 mg/dL (P = .012). Mean sirolimus levels were 15 +/- 9 ng/mL (doses 2.2 +/- 0.4 mg). This improvement continued until 3 months (creatinine 1.5 +/- 0.35 P < .01)/sirolimus levels 11.7 +/- 5 ng/mL [1.9 +/- 0.7 mg]), with maintenance at 6 months (1.58 +/- 0.3 mg/dL/14 +/- 4 ng/mL [1.85 +/- 0.7 mg]) and 1-year postconversion (1.53 +/- 0.39 mg/dL; P = .019/10.7 +/- 2.5 ng/mL [1.5 +/- 0.7 mg]). De novo, after a mean follow-up of 13 months (range 3 to 35), sirolimus appeared to increase the incidence of a moderate histological grade of rejection without hemodynamic compromise. Side effects were common (63%), including peripheral edema, skin eruptions, and pericardial effusion. Only one patient discontinued treatment, due to intestinal intolerance. Four patients died during follow-up: two because of lung neoplasms and two because of progressive graft vessel disease.

CONCLUSION

Sirolimus improved late CNI-related chronic renal dysfunction. Kidney function was preserved using a de novo CNI-free immunosuppressive regimen for recent cardiac transplant recipients.

Impact of renal insufficiency on clinical and angiographic outcomes following percutaneous coronary intervention with sirolimus-eluting stents

BACKGROUND

Sirolimus-eluting stents (SES) have been demonstrated to reduce restenosis. However, there have been few studies evaluating the impact of renal insufficiency on the angiographic as well as clinical outcomes after SES implantation.

METHODS

This study was composed of 304 consecutive patients having 361 lesions who underwent percutaneous coronary intervention with SES. The patients were divided into 3 groups according to renal function (group 1 [n = 204]; creatinine clearance (Ccr) > or = 60 ml/min, group 2 [n = 69]; Ccr < 60 ml/min, group 3 [n = 31]; hemodialysis). Clinical and angiographic follow-up were evaluated at 8 months.

RESULTS

Clinical follow-up was obtained in all patients and angiographic follow-up was obtained in 283 patients (93.1%). Patients in group 3 showed a higher incidence of previous coronary artery bypass graft surgery, and there were more female gender, hypertensive, and less hyperlipidemia in this group. Late lumen loss at 8 months was significantly different among the 3 groups (group 1; 0.16 +/- 0.46 mm, group 2; 0.44 +/- 0.62 mm, group 3; 0.81 +/- 0.88 mm, P < 0.0001). Major adverse cardiac events (MACE) were documented in 22 patients (10.8%) in group 1, 13 patients (18.8%) in group 2, and 12 patients (38.7%) in group 3, respectively (P = 0.0002).

CONCLUSION

Neointimal growth following SES implantation is more pronounced in patients with renal insufficiency, especially those undergoing dialysis, compared with patients with normal renal function. Regardless of the beneficial effect of SES, the increased risk of MACE mainly due to high incidence of target vessel revascularization in the subgroup of patients with renal insufficiency should be taken into account.

Determination of sirolimus in rabbit arteries using liquid chromatography separation and tandem mass spectrometric detection

Sirolimus, an effective immunosuppressive agent, is used for drug eluting stents. During stent development, an analytical method for the determination of sirolimus in tissue needs to be established. Normally, tissue samples are homogenized and then analyzed against the calibration standards prepared in a tissue homogenate. This approach provides insufficient control of the homogenization process. In this paper, tissue quality control samples were introduced for the optimization of the homogenization process during method development, but also allowance for the performance evaluation of the entire analytical process. In addition, a new approach using rabbit blood as a homogenization medium was developed to stabilize sirolimus in rabbit tissue homogenates. Calibration standards and quality controls were prepared by spiking different sirolimus working solutions into rabbit blood. Homogenization quality control samples were prepared by injecting other sirolimus working solutions into empty test tubes and pre-cut arteries within pre-defined masses. A high-throughput homogenization procedure was optimized based on the specific chemical properties of sirolimus. The linear dynamic range was between 49.9 pg/mL and 31.9 ng/mL to accommodate the expected artery homogenate concentrations. Additionally, quality controls in rabbit blood were also used in the extraction to support the calibration standards. The accuracy and precision of the quality controls in rabbit blood reflect the extraction performance and the accuracy and precision of the homogenization tissue quality controls reflect the overall performance of the method. The mean bias was between -4.5 and 0.2% for all levels of quality controls in the blood and between 4.8 and 14.9% for all levels of the homogenization tissue quality controls. The CVs of all concentration levels were < or =5.3% for the quality controls in blood and < or =9.2% for the homogenization tissue quality controls. The method was successfully applied to determine the concentration of sirolimus in the rabbit arteries.

From randomized trials to routine clinical practice: an evidence-based approach for the use of drug-eluting stents

The availability of drug-eluting stents has resulted in a paradigm shift in the management of patients with coronary artery disease with a substantial increase in the percentage of patients being revascularized percutaneously rather than surgically. Since its introduction, there has been a tremendous increase in the use of drug-eluting stents with nearly 90% of patients in the US who undergo percutaneous interventions receiving drug-eluting stents. The promising results of several randomized trials that demonstrated a profound reduction in restenosis rates compared with bare-metal stents, underscores the unprecedented enthusiasm among the cardiology community to adopt this new technology swiftly. Data regarding the safety and superiority of drug-eluting stents abound, and it is imperative for the practicing clinician to review and apply them in appropriate clinical settings. In this review, we present general concepts of drug-eluting stents, and attempt to summarize the available data on the approved drug-eluting stents in a variety of patient and lesion subsets. In addition, we share some insights regarding the potential limitations, and issues specific to drug-eluting stents.

Drug-eluting stents for infrainguinal occlusive disease: progress and challenges

High restenosis rate is still the major limitation of peripheral arterial interventions. Within the last years, drug-eluting stents have gained wide acceptance in the coronary arteries, however, these devices are not currently available for arteries outside the coronary vasculature. This article summarizes the special role of the superficial femoral artery in restenosis, with efforts being made to reduce the restenosis rate in this artery, focusing on stents and drug-eluting stents.

The effects of granulocyte-colony stimulating factor in bare stent and sirolimus-eluting stent in pigs following myocardial infarction

OBJECTIVES

The purpose of this study was to compare the effects of granulocyte-colony stimulating factor (G-CSF) on in-stent restenosis (ISR) in bare and sirolimus-eluting stents (SES) in a porcine myocardial infarction model.

BACKGROUND

Using G-CSF to mobilize stem cells has shown promise in infarcted heart. However, G-CSF may aggravate ISR and an aggressive strategy to prevent ISR is needed.

METHODS

Bare stents and SES were implanted in coronary arteries (Group I, bare stents; Group II, bare stents with G-CSF; Group III, SES; Group IV, SES with G-CSF, n=10 in each group) 72 h after experimental myocardial infarction (MI). G-CSF (10 microg/kg/day) was injected for 7 days from 24 h after stent implantation.

RESULTS

In coronary angiographic and histomorphometric analysis, percent area stenosis was significantly increased in Group II compared with that in Group I at 28 days (P<0.05). The ratio of inflammatory cells in the neointima was higher in Group II (P<0.05). No significant differences were observed between Group III and IV. In Group II, phosphorylated signal transducers and activators of transcription (STAT)-3, STAT-3, and vascular endothelial growth factor (VEGF) showed increased neointimal expression. In porcine aortic smooth muscle cells (PASMC), G-CSF increased the growth rate, migration, STAT-3 phosphorylation, and VEGF, which were suppressed by rapamycin and AG490, a STAT-3 inhibitor.

CONCLUSIONS

STAT-3 and VEGF are important in the development of enhanced ISR by G-CSF in bare stents. SES could be a good strategy to prevent the G-CSF-stimulated proliferation and migration of smooth muscle cells, which could be responsible for neointimal hyperplasia.

Iliac Anastomotic Stenting With a Sirolimus-Eluting Biodegradable Poly-L-Lactide Stent: A Preliminary Study After 6 Weeks

PURPOSE

To assess technical feasibility and biocompatibility of a new biodegradable sirolimus-eluting poly-L-lactide (PLLA) vascular anastomotic stent.

METHODS

A polytetrafluoroethylene bifurcated graft was implanted in 9 pigs through a midline abdominal incision. After transverse graft limb incision, 6 unloaded PLLAs, 6 sirolimus-loaded PLLAs, and 6 unloaded stainless steel (316L) stents were randomly implanted at both iliac anastomotic sites. Stents were deployed with a 6-mm balloon under direct vision without the use of angiography. Prior to sacrifice after 6 weeks, contrast-enhanced computed tomography (CT) was performed to determine patency of the target vessels. Stented segments were surgically explanted and processed for histology to measure the mean luminal diameter and intimal thickness and to assign vascular injury and inflammation scores.

RESULTS

No animals were lost during the study period. All stented graft limbs were patent on CT and histology. At the anastomotic sites and iliac arteries, the mean luminal diameter of SIR-PLLA stents (4.11+/-0.15 and 4.08+/-0.13 mm, respectively) were comparable to metal stents (4.23+/-0.35 and 4.21+/-0.26 mm, respectively), but significantly higher compared to unloaded PLLA stents [3.32+/-0.56 mm (p<0.001) and 3.29+/-0.39 mm (p=0.013), respectively]. At the iliac arteries, the mean intimal thickness was significantly lower with SIR-PLLA stents (0.09+/-0.02 mm) compared to unloaded PLLA stents (0.31+/-0.15 mm, p<0.001) and metal stents (0.19+/-0.04 mm, p=0.004). Vascular injury scores demonstrated only mild vascular trauma for all stents (SIR-PLLA: 0.42+/-0.63, PLLA: 0.51+/-0.62, metal: 0.50+/-0.62). Only mild inflammatory reaction was noted around SIR-PLLA stent struts (1.14+/-0.46), which was comparable to metal stents (1.27+/-0.45) but significantly lower than PLLA stents (1.79+/-0.56, p<0.001).

CONCLUSION

SIR-PLLA stents showed comparable luminal diameter compared to metal stents, so incorporating sirolimus could reduce the inflammatory and neointimal response to PLLA stents. These findings need to be assessed with longer follow-up to confirm maintenance of efficacy.

Safety and Pharmacokinetics of Sirolimus-eluting Stents in the Canine Cerebral Vasculature: 180 Day Assessment

OBJECTIVE

We evaluated local and systemic pharmacokinetics and pharmacodynamics of sirolimus-eluting stents (SES) in canine cerebral vessels.

METHODS

SES (1.5 x 8 mm, 79 microg/479 microg sirolimus) and control stents (1.5 x 8 mm stainless steel with or without polymer) were implanted in canine basilar and ventral spinal arteries. Animals were sacrificed for local pharmacokinetic (36 animals at 1, 3, 8, 30, 90, 180 days) and pharmacodynamic (60 animals at 3, 30, 90, 180 days) assessment.

RESULTS

Postrecovery adverse clinical events were not serious, requiring no unscheduled treatment. Histologically, brain and spinal cord sections revealed scattered microinfarcts and minimal gliosis consistent with postprocedure changes in all four stent-treatment groups. All stented vessels at all time points demonstrated good luminal patency with low injury and inflammation scores and no thrombosis of either stented or branch arteries. Endothelialization was complete in all stent groups by 30 days. Intimal smooth muscle cell scores were reduced in both SES groups at 30, 90, and 180 days. Systemic sirolimus levels peaked between 1 and 7 hours postimplant (maximum concentration, 1.2 +/- 1.47, 79 microg; 4.5 +/- 1.23 ng/ml, 479 microg), then declined rapidly to 1 ng/ml or less by 96 hours. Peak local tissue sirolimus levels were 41.5 ng/mg (79 microg) and 65 ng/mg (479 microg).

CONCLUSION

SES in canine cerebral vessels were associated with good luminal patency to 180 days, with complete endothelialization and no evidence of acute thrombosis. This model has shown that SES deployed within the brain do not cause neurotoxicity during a 180-day time course, even when exaggerated doses are used. The findings support the contention that SES are safe to use and maintain patency in cerebral vessels.

Hemodialysis vascular access dysfunction: a cellular and molecular viewpoint

Hemodialysis vascular access dysfunction is a major cause of morbidity and hospitalization in the hemodialysis population. The major cause of hemodialysis vascular access dysfunction is venous stenosis as a result of neointimal hyperplasia. Despite the magnitude of the clinical problem, however, there has been a paucity of novel therapeutic interventions in this field. This is in marked contrast to a recent plethora of targeted interventions for the treatment of arterial neointimal hyperplasia after coronary angioplasty. The reasons for this are two-fold. First there has been a relative lack of cellular and molecular research that focuses on venous neointimal hyperplasia in the specific setting of hemodialysis vascular access. Second, there have been inadequate efforts by the nephrology community to translate the recent advances in molecular and interventional cardiology into therapies for hemodialysis vascular access. This review therefore (1) briefly examines the different forms of hemodialysis vascular access that are available, (2) describes the pathology and pathogenesis of hemodialysis vascular access dysfunction in both polytetrafluoroethylene grafts and native arteriovenous fistulae, (3) reviews recent concepts about the pathogenesis of vascular stenosis that could potentially be applied in the setting of hemodialysis vascular access dysfunction, (4) summarizes novel experimental and clinical therapies that could potentially be used in the setting of hemodialysis vascular access dysfunction, and, finally, (5) offers some broad guidelines for future innovative translational and clinical research in this area that hopefully will reduce the huge clinical morbidity and economic costs that are associated with this condition.

Current development of mTOR inhibitors as anticancer agents

Mammalian target of rapamycin (mTOR) is a kinase that functions as a master switch between catabolic and anabolic metabolism and as such is a target for the design of anticancer agents. The most established mTOR inhibitors--rapamycin and its derivatives--showed long-lasting objective tumour responses in clinical trials, with CCI-779 being a first-in-class mTOR inhibitor that improved the survival of patients with advanced renal cell carcinoma. This heralded the beginning of extensive clinical programmes to further evaluate mTOR inhibitors in several tumour types. Here we review the clinical development of this drug class and look at future prospects for incorporating these agents into multitarget or multimodality strategies against cancer.

Clinical experience and applications of drug-eluting stents in the noncoronary vasculature, bile duct and esophagus

OBJECTIVE

To review the use of drug-eluting stents outside the coronary artery.

FINDINGS

The vast majority of research and clinical data on drug-eluting stents are from their use in coronary artery atherosclerosis; however, these devices can be used outside the coronary circulation in both vascular and nonvascular structures. In noncoronary arteries the principle indication for drug-eluting vascular stents is the same as in the coronary circulation, prevention of restenosis. Human experience has been essentially limited to trials or compassionate use; two small controlled studies and a number of small observational single center reports have been published, and there are trials in progress. To date the data have not been as compelling as in the coronary circulation. The physical characteristics of each vascular bed such as external compressive forces, blood flow rates, wall thickness relative to lumen size, and vessel wall composition differ significantly from the coronary circulation and each presents unique challenges to local drug delivery. Outside the vascular bed, the principle expected use is the prevention of tissue ingrowth after stent insertion in tubular structures such as the trachea, esophagus or bile ducts.

CONCLUSIONS

Considerable further study of drug-eluting stents will be required in each anatomic region to determine the ideal stent/drug combination and clinical appropriateness.

Intramural delivery of Sirolimus prevents vascular remodeling following balloon injury

OBJECTIVE

Several studies have demonstrated that Sirolimus-eluting stents reduce restenosis in patients with coronary artery disease. Here, we tested whether direct delivery of Sirolimus into the vessel wall during balloon angioplasty can modify vascular remodeling over several weeks.

METHODS AND RESULTS

During angioplasty of the rabbit iliac artery we administered an intramural infusion of Sirolimus or its vehicle directly through a balloon catheter into the vessel wall. After 3 weeks neointimal formation was decreased (0.71+/-0.1 vs. 1.4+/-0.12 intima/media ratio), and this process was attributed to the inhibitory properties of Sirolimus on ECM deposition and smooth muscle cell proliferation. Sirolimus also significantly reduced the deposition of elastin, collagen III and fibronectin within the vascular wall. In parallel, proteomic profiles of arterial wall segments were obtained and 485 protein spots were consistently matched between non-dilated and dilated vessels. Differential expression of 12 proteins were observed between the groups and direct sequencing of digested peptides was performed. Local delivery of sirolimus during angioplasty attenuated the expression of structural proteins that included lamin A, vimentin, alpha-1-antitrypsin, and alpha-actin.

CONCLUSIONS

Local administration of Sirolimus during angioplasty prevents smooth muscle cell proliferation associated with vascular remodeling as well as the expression of extracellular matrix and structural proteins. Therefore, local injection of Sirolimus during balloon inflation may be an alternative therapeutic approach for preventing restenosis in small stenotic vessels (i.e., <2.5 mm).

Oral rapamycin after coronary bare-metal stent implantation to prevent restenosis: the Prospective, Randomized Oral Rapamycin in Argentina (ORAR II) Study

OBJECTIVES

The purpose of this study was to assess the role of oral rapamycin in decreased restenosis after bare metal stent implantation.

BACKGROUND

Small observational studies suggest that the administration of oral rapamycin reduces angiographic restenosis after bare metal stent implantation.

METHODS

Between September 2003 and September 2004, 100 patients were randomized to either oral rapamycin (6-mg loading dose given 2.7 h before intervention followed by 3 mg/day for 14 days) plus diltiazem 180 mg/day or no therapy after the implantation of a coronary bare metal stent design. The primary study end point was incidence of angiographic binary restenosis and late loss at nine months. The secondary end points were target lesion revascularization, target vessel revascularization, and incidence of major adverse cardiovascular events at 1 year.

RESULTS

Angiographic follow-up was completed in 87% of patients. In the rapamycin group, the drug was well tolerated (26% minor side effects) and was maintained in 96% of patients. At 9 months, the in-segment binary restenosis was reduced by 72% (11.6% rapamycin vs. 42.8% no-therapy group, p = 0.001) and the in-stent binary restenosis was reduced by 65% (12% rapamycin vs. 34.6% no-therapy group, p = 0.009). The in-segment late loss was also significantly reduced with oral therapy (0.66 vs. 1.13 mm, respectively; 43% reduction, p < 0.001). At 1 year, patients in the oral rapamycin group also showed a significantly lower incidence of target vessel revascularization (8.3% vs. 38%, respectively, p < 0.001), target lesion revascularization (7.6% vs. 37.2%, respectively, p < 0.001), and major adverse cardiovascular events (20% vs. 44%, respectively, p = 0.018).

CONCLUSIONS

This randomized, controlled, and unblinded study showed that the administration of oral rapamycin during 14 days after stent implantation significantly reduces angiographic and clinical parameters of restenosis.

Angiographic pattern of restenosis following implantation of overlapping sirolimus-eluting (Cypher) stents

Sirolimus-eluting stents (Cypher) have been shown to reduce the frequency of neointimal hyperplasia and restenosis compared with bare metal stents. However, the clinical implication of overlapping stents with regard to the pattern of restenosis is unclear. All patients who underwent angiography at our institution from May 2003 to March 2005 who had previously received 2 overlapping Cypher stents in native coronary lesions and had binary restenosis were included in our study. Quantitative coronary analysis was performed to determine the degree and location of the restenotic lesion with respect to the overlapping stented segment. The primary end point was to determine how often restenotic lesions occurred at the overlapped segment versus the nonoverlapped stented segments. During the study, 11 patients fit the inclusion criteria for our study; 91% were men and 55% had diabetes mellitus. The mean total stent length was 33.7 +/- 8.2 mm. The mean length of the overlapped segment was 5.9 +/- 3.8 mm, equating to 19 +/- 16% of the total stented area. The average time to follow-up angiography was 277 +/- 126 days. All 11 lesions exhibited type 1 (focal) restenosis. Of these 11 lesions, 10 had focal restenosis at the overlapped segment (p = 0.01, binomial test). The single case involving in-stent restenosis in the nonoverlapped segment occurred at the proximal stent edge. In conclusion, the pattern of restenosis observed in our study suggests a higher relative incidence of binary restenosis in the overlapped stented segment in patients who receive 2 overlapping Cypher stents.

Synergistic suppression of rat neointimal hyperplasia by rapamycin and imatinib mesylate: implications for the prevention of accelerated arteriosclerosis

BACKGROUND

Accelerated arteriosclerosis remains a major limitation to therapeutic interventions such as angioplasty, stent deployment, and solid organ transplantation. Rapamycin, a powerful new immunosuppressant set to replace calcineurin inhibitors in the transplant setting, and imatinib mesylate, a receptor tyrosine kinase inhibitor, are both angioprotective. Here, we explored the pharmacological and therapeutic interactions of these two agents in a rat model of neointimal hyperplasia.

METHODS

Wistar rats, subjected to balloon catheter-induced aortic injury, received daily drug treatment until postoperative day 14 and were subsequently sacrificed or followed up to day 40 without further treatment. Development of neointimal lesions was assessed histologically and immunohistochemically. Steady-state rapamycin levels in whole blood were determined by HPLC-UV.

RESULTS

Rapamycin and imatinib, administered individually or in combination, produced no signs of overt toxicity. Continuous postoperative therapy with either rapamycin (0.5-1.5 mg/kg/day) or imatinib (2- 50 mg/kg/day) dose-dependently suppressed neointimal hyperplasia on day 14. Combined treatment (0.5 or 1 + 10 mg/kg/day, respectively) showed a trend towards synergistic action on day 14. Withdrawal of medication on day 14 nullified the early therapeutic effect of either agent by day 40. In contrast, early combination therapy (1 + 10 mg/kg/day) achieved long-term suppression of neointimal hyperplasia by approximately 81%. Notably, coadministration of imatinib appeared to reduce exposure to rapamycin, although this finding did not reach statistical significance.

CONCLUSIONS

Short-term combination therapy with rapamycin and imatinib is well tolerated and produces synergistic, sustained suppression of neointimal hyperplasia in rats. Subject to clinical evaluation, this new drug regimen may afford definitive prophylaxis against accelerated arteriosclerosis.

Irinotecan-eluting stents inhibited neointimal proliferation in hypercholesterolemic rabbit aortas

OBJECTIVE

To assess the effect of irinotecan-eluting stents (IS) on neointimal growth in the aortas of hypercholesterolemic rabbits and to determine other local histopathological effects such as necrosis, fibrin, and inflammatory reaction.

METHODS

Phosphorylcholine-coated stents were deployed in the aortas of hypercholesterolemic rabbits. Group 1 (control; n = 8) received unloaded stents, group 2 (n = 7) and group 3 (n = 9) received IS with 0.046 mg and 1.29 mg of irinotecan, respectively. Eight weeks after implantation the rabbits were killed. Neointimal thickness (NT) was assessed by morphometry. Semiquantitative injury score (from 0 to 3+) was used to analyze inflammatory infiltrate, fibrin deposits, and necrosis in the stented segments.

RESULTS

NT was reduced only in high-doses IS (G1, 167.4 +/- 20.8 mu; G2, 170.24 +/- 21.2 mu; G3, 111.56 +/- 12.7 mu; P < 0.05, G3 vs G1 and G2). Necrosis decreased significantly with IS [1.00 +/- 0.10 in G1 to 0.33 +/- 0.07 and 0.02 +/- 0.01 in G2 and G3, respectively] only in the media layer. The inflammatory infiltrate was present in the three layers of aortas from G1, but only decreased significantly in the intimae layer of the high-dose group [1.50 +/- 0.15 in G1 vs 1.00 +/- 0.18 in G3, P < 0.05].

CONCLUSION

Stents loaded with high-dose irinotecan inhibit NT in the aortas of hypercholesterolemic rabbits. This effect was accompanied by decreased inflammatory infiltrate and media necrosis.

Benidipine, a Calcium Channel Blocker, Regulates Proliferation and Phenotype of Vascular Smooth Muscle Cells

Hyperproliferation of phenotypically modified vascular smooth muscle cells (VSMCs) is one of the major factors in the development of atherosclerosis and restenosis. Previously it was demonstrated that benidipine, a dihydropyridine-calcium channel antagonist, reduced neointimal formation in a rat balloon-injury model. In the present study, we examined the effect of benidipine on the phenotypic modulation and proliferation of VSMCs, using primary cultures of rat VSMCs. In the absence of drug treatment, protein levels of the smooth muscle specific markers, such as smooth muscle myosin heavy chain-1 (SM1), calponin 1, and alpha-actin, decreased during culture. However, treatment of VSMCs with benidipine (3 - 10 micromol/L) for 1 week reversed the effect in a concentration-related manner so that high levels of marker proteins were maintained. The expression of calponin mRNAs was reduced markedly during 1-week culture, and treatment with benidipine (3 micromol/L) significantly inhibited the reduction. Treatment with benidipine for 2 days increased the level of p21 protein and partially reduced p70 S6 kinase 1 (p70S6K1) activity. These data suggest that benidipine may arrest the growth of VSMCs, thereby preventing cell dedifferentiation. These additional properties of benidipine suggest that the drug should provide useful therapy for atherosclerosis and restenosis.

Rapamycin-coated expanded polytetrafluoroethylene bypass grafts exhibit decreased anastomotic neointimal hyperplasia in a porcine model

OBJECTIVE

We tested the hypothesis that rapamycin coated onto, and eluted from, expanded polytetrafluoroethylene (ePTFE) grafts would diminish neointimal hyperplasia in a porcine model.

METHODS

Rapamycin (also called sirolimus) was coated onto the luminal surface of 6-mm-internal-diameter thin-walled ePTFE grafts by using an adhesive polymer that allows timed release of the drug. An adhesive polymer that allows timed release of rapamycin from ePTFE was developed with commercially available chemicals and applied on 6-mm ePTFE grafts. Graft integrity was characterized by scanning electron microscopy, and rapamycin levels were quantified by using high-performance liquid chromatography. Twenty-two mongrel pigs were randomized into three groups: untreated ePTFE (n = 6), adhesive-only coated ePTFE (n = 6), or adhesive- and rapamycin-coated ePTFE (n = 10). End-to-side unilateral aortoiliac bypasses were performed by using 6-mm-internal-diameter ePTFE grafts and standardized anastomotic lengths. Unilateral end-to-side aortoiliac ePTFE grafts (6-mm internal diameter) were inserted by using polypropylene sutures, 6-0 proximally and 7-0 distally; all anastomoses were 12 mm long. All animals received aspirin (325 mg orally) daily. All animals were given oral aspirin (325 mg) daily beginning on the day before surgery. At 28 days, the animals were killed, and the grafts were explanted in continuity with the adjacent aortic cuff and the outflow iliac artery. Variables compared between groups included graft patency, distal anastomotic length and cross-sectional narrowing, and intimal thickness at the arterial-graft junction indexed to the adjacent graft thickness. Microscopic analysis was performed with hematoxylin and eosin and Masson trichrome stains on paraffin sections. A pathologist blinded to experimental groups graded sections for collagen deposition, neointima formation, inflammatory cellular infiltrates, medial necrosis, and aneurysmal degeneration.

RESULTS

All animals survived until they were killed without clinical evidence of limb ischemia or graft infection. Preplanned t tests in the context of one-way analysis of variance showed no difference in outcome measures between the untreated ePTFE and adhesive-only coated ePTFE groups; therefore, they were combined in further comparisons with the adhesive- and rapamycin-coated ePTFE group. The Rapamycine eluting expanded polytetrafluoroethylene group had longer anastomoses (85.6% vs 60.6% of the initial anastomotic length maintained; P < .0001) and less cross-sectional narrowing in the outflow graft (16.2% vs 28.5%; P = .0007) when compared with the other two groups by using two-tailed Student t tests. There was no evidence of medial necrosis or aneurysmal degeneration. All patent grafts had complete endothelialization on hematoxylin and eosin sections. Rapamycin was detectable and quantifiable in the arterial wall at 28 days after implantation.

CONCLUSIONS

Rapamycin can be coated onto and eluted from ePTFE by using a nonionic polymer and a simple coating technique. At 4 weeks after implantation, the rapamycin-eluting ePTFE grafts demonstrate gross, pathologic, and morphometric features of diminished neointimal hyperplasia when compared with non-drug-eluting ePTFE. Four weeks after implantation in a porcine model, rapamycin-eluting ePTFE grafts demonstrated gross, pathologic, and morphometric features of diminished neointimal hyperplasia when compared with untreated and adhesive-only coated ePTFE grafts.

CLINICAL RELEVANCE

Rapamycin-eluting ePTFE grafts decrease neointimal hyperplasia in a porcine model. Further studies are needed to evaluate whether patency will be improved. Rapamycin-eluting ePTFE grafts may allow the use of prosthetic grafts in situations in which autologous vein is unavailable and in which neointimal hyperplasia is pronounced, such as in small-diameter (<6-mm) vessels typical of infrapopliteal interventions.

A novel drug-eluting stent spray-coated with multi-layers of collagen and sirolimus

In the study, a novel drug-eluting stent for treating the coronary arterial stenosis was developed. Using a spray-coating method, aqueous bovine type I collagen and sirolimus were coated layer-by-layer alternatively onto the surface of a metallic stent and a topcoat of collagen was used as a barrier to control drug release. To prevent dissolution of the collagen matrices, the spray-coated collagen was further crosslinked by genipin, a naturally occurring crosslinking agent. The results obtained in the atomic force microscopy (AFM) examination suggested that the spray-coated collagen was tightly adhered to the surface of the stent. Additionally, the collagen coating was demonstrated by the scanning electron microscopy (SEM) to be sufficiently flexible to allow balloon expansion of the stent without cracking or peeling from the wire. The resistance against enzymatic degradation and the hemocompatibility of the collagen matrices increased significantly as their degree of crosslinking increased. All the studied sirolimus-loaded stents exhibited a nearly linear sustained-release profile (except at the end stage of release) with no significant burst releases. It was found that a topcoat of collagen on the collagen/sirolimus coated stent did slow down the release of sirolimus to some extent. Additionally, the number of layers of collagen/sirolimus coated significantly affected the duration of sirolimus released. Furthermore, the sustained-release duration of sirolimus was proportional to the actual amount of drug loaded on the stent. The aforementioned results indicated that the drug-eluting stent developed had a tightly adhered collagen coating and can be used as a drug reservoir to sustain release of sirolimus.

Efficacy of drug eluting stents in patients with and without diabetes mellitus: indirect comparison of controlled trials

OBJECTIVE

To examine whether polymer based coronary stents eluting sirolimus or paclitaxel are equally effective in patients with and without diabetes.

METHODS

Systematic review and meta-analysis by indirect comparison of randomised controlled trials comparing stents eluting sirolimus or paclitaxel with conventional bare metal stents. The overall study population and patients with and without diabetes were analysed separately by using the ratio of incidence rate ratios (RIRR).

RESULTS

The analysis was based on 10 trials (six with sirolimus, four with paclitaxel), 4513 patients (1146 patients with diabetes), 5755 years of follow up, and 2464 events. In patients without diabetes sirolimus eluting stents were superior to paclitaxel eluting stents with respect to in-stent (RIRR 0.21, 95% confidence interval (CI) 0.10 to 0.48, p < 0.001) and in-segment restenosis (RIRR 0.47, 95% CI 0.24 to 0.92, p = 0.027), target lesion revascularisation (RIRR 0.54, 95% CI 0.30 to 0.99, p = 0.045), and major adverse cardiac events (RIRR 0.46, 95% CI 0.26 to 0.83, p = 0.010). In patients with diabetes the two drug eluting stents did not differ significantly in any of these end points. Meta-regression analysis showed a significant difference between patients with and without diabetes (tests for interaction for in-stent and in-segment restenosis, p = 0.036 and p = 0.016).

CONCLUSION

Indirect evidence indicates that sirolimus eluting stents are superior to paclitaxel eluting stents in patients without diabetes but not in patients with diabetes.

Delayed renal graft function: the influence of immunosuppression

INTRODUCTION

We evaluated the influence of different immunosuppressive regimens on delayed renal graft function and progression of renal function in the first year after transplantation.

PATIENTS AND METHODS

Patients were divided into four groups according to the immunosuppressive regimen received: (1) rapamycin (Rap) + mycophenolate mofetil (MMF) + methylprednisolone (MP) + daclizumab (Dmab); (n = 44); (2) tacrolimus (Tac) + MMF + MP + Dmab (n = 39); (3) cyclosporine (CsA) + MMF + MP + basiliximab (Bmab); (n = 30); (4) antithymocyte globulin (ATG) + MMF + MP and CsA after ATG withdrawal (n = 40). Data were analyzed using ANOVA and linear regression. Delayed graft function was defined as the need for hemodialysis posttransplantation.

RESULTS

There were no statistically significant differences between the four groups in terms of gender, time on dialysis before transplantation, histocompatibility, donor age, and cold ischemia time. However, age (49.8, 50.4, 49.8, and 43.5 years, P < .05), panel reactive antibodies (22%, 39%, 27%, 34%, P < .05) and time of delayed graft function (12, 7, 3, 6 days, P < .05) were significantly different between the four groups. The time of delayed graft function depended on the immunosuppressive regimen, as well as donor and recipient age (P < .05). The creatinine clearance demonstrated a statistically significant difference between the four groups in the first month after transplantation (45, 46, 61, 53 mL/min, P < .05), though no further difference was observed at the month 12th.

CONCLUSIONS

The type of immunosuppressive therapy seems to substantially influence the time of recovery from delayed renal graft function, even though it does not seem to affect future graft function. Especially Rap, probably due to its potent antiproliferative effects, seems to prolong the length of graft recovery after renal transplantation.

Proprotein convertases furin and PC5: targeting atherosclerosis and restenosis at multiple levels

Several growth factors, chemokines, adhesion molecules, and proteolytic enzymes important for cell-cell/cell-matrix interactions in atherosclerosis and restenosis are initially synthesized as inactive precursor proteins. Activation of proproteins to biologically active molecules is regulated by limited endoproteolytic cleavage at dibasic amino acid residues. This type of activation typically requires the presence of suitable proprotein convertases (PCs). The PC-isozymes furin and PC5 are expressed in human atherosclerotic lesions and have been found to be up-regulated, following vascular injury in animal models in vivo. In vitro, these PCs can regulate vascular smooth muscle cell and macrophage functions and signaling events, through activation of pro-alpha-integrins and/or pro-membrane-type matrix metalloproteinases. Integrins link the cytoskeleton with the extracellular matrix and mediate bidirectional signaling and mechanotransduction, whereas matrix metalloproteinases are the major matrix-degrading enzymes. Both activities are required for cell recruitment to the intima. Furthermore, cleavage of extracellular matrix molecules by matrix metalloproteinases potentially contributes to weakening of the fibrous cap, promoting plaque rupture. Based on these recent in vitro and in vivo data, furin and PC5 are potential contributors to the initiation, progression, and complications of atherosclerosis and restenosis. Targeting these PCs may provide future anti-atherosclerotic therapies.

Rapamycin for treatment of chronic allograft nephropathy in renal transplant patients

Chronic allograft nephropathy (CAN) represents the main cause of renal allograft loss after 1 yr of transplantation. Calcineurin inhibitor (CNI) use is associated with increased graft expression of profibrotic cytokines, whereas rapamycin inhibits fibroblast proliferation. The aim of this randomized, prospective, open-label, single-center study was to evaluate the histologic and clinical effect of rapamycin on biopsy-proven CAN. Eighty-four consecutive patients who had biopsy-proven CAN and received a transplant were randomized to receive either a 40% CNI reduction plus mycophenolate mofetil (group 1; 50 patients) or immediate CNI withdrawal and rapamycin introduction with a loading dose of 0.1 mg/kg per d and a maintaining dose aiming at through levels of 6 to 10 ng/ml (group 2; 34 patients). The follow-up period was 24 mo. At the end of follow-up, 25 patients (group 1, 10 patients; group 2, 15 patients) underwent a second biopsy. CAN lesions were graded according to Banff criteria. alpha-Smooth muscle actin (alpha-SMA) protein expression was evaluated in all biopsies as a marker of fibroblast activation. Graft function and Banff grading were superimposable at randomization. Graft survival was significantly better in group 2 (P = 0.0376, chi2 = 4.323). CAN grading worsened significantly in group 1, whereas it remained stable in group 2. After 24 mo, all group 1 biopsies showed an increase of alpha-SMA expression at the interstitial and vascular levels (P < 0.001); on the contrary, alpha-SMA expression was dramatically reduced in group 2 biopsies (P = 0.005). This study demonstrates that rapamycin introduction/CNI withdrawal improves graft survival and reduces interstitial and vascular alpha-SMA expression, slowing down the progression of allograft injury in patients with CAN.

Vascular injury response in mice is dependent on genetic background

Mouse models are employed to unravel the pathophysiology of vascular restenosis. Although much effort has been spent on how to apply an adequate arterial injury, the influence of the genetic background of mice has not yet received sufficient consideration. The study presented herein was designed to demonstrate the influence of the mouse strain on vascular injury response. Mice of a defined background (50% 129 strain and 50% DBA strain) were backcrossed into either the 129 strain or the DBA strain. Male offspring were subjected to a femoral artery injury model by applying an electric current. Morphometric analysis revealed that backcrossing into the 129 strain resulted in a significant (P < 0.001) 17-fold increase in neointima formation (n = 17 mice) compared with backcrossing into the DBA strain (n = 19). The values of neointima area were 9.18 x 10(3) +/- 2.13 x 10(3) and 0.54 x 10(3) +/- 0.39 x 10(3) microm2, respectively. In conjunction, the vessel wall area was enhanced by 1.8-fold (P < 0.001). In contrast, no significant differences were found for the areas of the lumen and the tunica media. Similarly, a significant increase in neointima formation was also found for mice of pure 129 strain compared with pure DBA strain. The results underline the importance of the genetic background for studies on vascular injury response. Furthermore, because the mouse genome of the various strains is well defined, serial testing of the genetic background of mice will provide candidate genes and/or genetic modifiers controlling vascular injury response.

Rapamycin Attenuates Atherosclerotic Plaque Progression in Apolipoprotein E Knockout Mice

Rapamycin has been shown to reduce neointimal thickening in the setting of balloon angioplasty and chronic graft vessel disease. This study was designed to test the effect of oral rapamycin on atherosclerotic plaque progression and the possible mechanism involved. Apolipoprotein E (apoE) knockout mice were fed either a diet supplemented with cholesterol or with cholesterol and rapamycin. At 4 and 8 weeks, quantitative analyses of plaque area and macrophage numbers were determined. Plasma cholesterol, triglyceride, and whole-blood rapamycin levels were measured. Rapamycin could be detected in the blood of mice (117+/-7 pg/mL). In mice fed with rapamycin, atherosclerotic lesions covered 22% of the aortic arch as compared with 41% in cholesterol-fed mice. The macrophage count was significantly lower in the rapamycin-fed mice as compared with cholesterol-fed mice. Rapamycin, in a dose-dependent manner, inhibited monocyte chemotaxis elicited by stromal cell-derived factor-1. Lesions in the cholesterol-fed mice had complex atherosclerotic plaque with acellular core, cholesterol clefts, and an abundant collection of monocytes/macrophages. Lesions in the rapamycin-fed mice were mainly composed of monocytes/macrophages. Oral rapamycin is effective in slowing the progression of atherosclerosis. Along with its multitude actions, attenuation of monocyte chemotaxis may be one more way by which rapamycin attenuates plaque progression.

Therapeutic potential of target of rapamycin inhibitors

Target of rapamycin (TOR) functions within the cell as a transducer of information from various sources, including growth factors, energy sensors, and hypoxia sensors, as well as components of the cell regulating growth and division. Blocking TOR function mimics amino acid, and to some extent, growth factor deprivation and has a cytostatic effect on proliferating cells in vivo. Inhibition of TOR in vivo, utilising its namesake rapamycin, leads to immunosuppression. This property has been exploited successfully with the use of rapamycin and its derivatives as a therapeutic agent in the prevention of organ rejection after transplantation with relatively mild side effects when compared to other immunosuppressive agents. The cytostatic effect of TOR on vascular smooth muscle cell proliferation has also recently been exploited in the therapeutic application of rapamycin to drug eluting stents for angioplasty. These stents significantly reduce the amount of arterial reblockage that results from proliferating vascular smooth muscle cells. In cancer, the effect of blocking TOR function on tumour growth and disease progression is currently of major interest and is the basis for a number of ongoing clinical trials. However, different cell types and tumours respond differently to TOR inhibition, and TOR is clearly not cytostatic for all types of cancer cells in vitro or in vivo. As the molecular details of how TOR functions and the targets of TOR activity are further elucidated, tumour and tissue specific functions are being identified that implicate TOR in angiogenesis, apoptosis, and the reversal of some forms of cellular transformation. This review will describe our current understanding of TOR function, describe the current strategies for employing TOR inhibitors in clinical and preclinical development, and outline future strategies for appropriate targets of TOR inhibitors in the treatment of disease.