Recent development and future application of biodegradable ureteral stents

Ureteral stenting is a common clinical procedure for the treatment of upper urinary tract disorders, including conditions such as urinary tract infections, tumors, stones, and inflammation. Maintaining normal renal function by preventing and treating ureteral obstruction is the primary goal of this procedure. However, the use of ureteral stents is associated with adverse effects, including surface crusting, bacterial adhesion, and lower urinary tract symptoms (LUTS) after implantation. Recognizing the need to reduce the complications associated with permanent ureteral stent placement, there is a growing interest among both physicians and patients in the use of biodegradable ureteral stents (BUS). The evolution of stent materials and the exploration of different stent coatings have given these devices different roles tailored to different clinical needs, including anticolithic, antibacterial, antitumor, antinociceptive, and others. This review examines recent advances in BUS within the last 5 years, providing an in-depth analysis of their characteristics and performance. In addition, we present prospective insights into the future applications of BUS in clinical settings.

Gelatin microgel-coated balloon catheter with enhanced delivery of everolimus for long-term vascular patency

In-stent restenosis (ISR) after percutaneous coronary intervention is a major reason for limited long-term patency due to complex neointimal proliferation caused by vascular injury. Drug-coated balloon (DCB) has been developed to treat various cardiovascular diseases including ISR by providing anti-proliferative drugs into blood vessel tissues. However, a significant proportion of the drug is lost during balloon tracking, resulting in ineffective drug delivery to the target region. In this study, we report an everolimus-coated balloon (ECB) using everolimus-loaded gelatin-hydroxyphenyl propionic acid microgel (GM) with enhanced everolimus delivery to vascular walls for long-term patency. GM with high drug loading (> 97%) was simply prepared by homogenizing enzyme-mediated crosslinked hydrogels. The optimal condition to prepare GM-coated ECB (GM-ECB) was established by changing homogenization time and ethanol solvent concentration (30 ∼ 80%). In vitro sustained everolimus release for 30 d, and cellular efficacy using smooth muscle cells and vascular endothelial cells were evaluated. Additionally, an in vivo drug transfer levels of GM-ECB using rabbit femoral arteries were assessed with reduced drug loss and efficient drug delivery capability. Finally, using ISR-induced porcine models, effective in vivo vascular patency 4 weeks after treatment of ECBs was also confirmed. Thus, this study strongly demonstrates that GM can be used as a potential drug delivery platform for DCB application. STATEMENT OF SIGNIFICANCE: We report an ECB using everolimus-loaded GM prepared by homogenization of enzymatic cross-linked hydrogel. GM showed efficient drug loading (> 97 %) and controllable size. GM-ECB exhibited potential to deliver everolimus in a sustained manner to target area with drug efficacy and viability against SMC and EC. Although GM-ECB had much lower drug content compared to controls, animal study demonstrated enhanced drug transfer and reduced drug loss of GM-ECB due to the protection of encapsulated drugs by GM, and the possible interaction between GM and endothelium. Finally, vascular patency and safety were assessed using ISR-induced porcine models. We suggest an advanced DCB strategy to alleviate rapid drug clearance by bloodstream while improving drug delivery for a long-term vascular patency.

Heterogeneous vascular response after implantation of bare nitinol self-expanding stents in the swine femoropopliteal artery

BACKGROUND

Mechanism of femoropopliteal in-stent restenosis has been underappreciated.

AIM

The aim of this animal study was to elucidate vascular response after femoropopliteal bare nitinol self-expanding stents (SESs) implantation.

METHODS

Misago, Smart Flex, or Innova stent was randomly implanted in 36 swine femoropopliteal arteries. At week 4, quantitative vessel analysis (QVA) was performed on 36 legs, of which 18 underwent histological evaluation after angiography. The remaining 18 legs underwent QVA and histological evaluation at week 13.

RESULTS

Fibrin deposition was excessive at week 4. Internal elastic lamina (IEL) progressively enlarged over time, and vessel injury developed from mild level at week 4 to moderate level at week 13. Vessel inflammatory reaction was mild to moderate at week 4, and was moderate to severe at week 13. Increased fibrin deposition was an early-acting, IEL enlargement and increased vessel inflammation were long-acting, and increased vessel injury and giant cells infiltration were late-acting contributors to neointimal hyperplasia (NIH). Stent type altered time-dependent process of vessel injury, vessel inflammation, eosinophils and giant cells infiltration. Misago had less fibrin deposition and vessel enlargement, and less progressive vessel injury, vessel inflammation, and eosinophils and giant cells infiltration. Net lumen as assessed by percent diameter stenosis or minimum lumen diameter was preserved with Misago, but was not preserved with the other stents.

CONCLUSIONS

In the context of bare nitinol SES platform with less progressive mechanical stress and inflammatory reaction, the advantage of less NIH outweighed the disadvantage of less vessel enlargement, leading to net lumen preservation.

Comparisons of early vascular reactions in biodegradable and durable polymer-based drug-eluting stents in the porcine coronary artery

Current drug-eluting stents have abluminal polymer coating; however, thrombus formation in these compared with that in uniformly coated stents remains controversial. We evaluated thrombus formation and early endothelialization after using abluminal biodegradable polymer-coated sirolimus- (BP-SES), and everolimus-eluting stents (BP-EES) versus a durable polymer-coated everolimus-eluting stent (DP-EES) in an in vivo setting. BP-SES, BP-EES, and DP-EES (n = 6 each) were implanted in coronary arteries of 12 mini-pigs that were then sacrificed after 7 and 10 days. Stents were stained with hematoxylin and eosin, and a combined Verhoeff and Masson trichrome stain. Areas of fibrin deposition were digitally detected and measured with off-line morphometric software. Stents were investigated for re-endothelialization by transmission electron microscopy. At 7 days, histological analysis revealed the lowest area of fibrin deposition in BP-SES (BP-SES vs. BP-EES vs. DP-EES; 0.10 ± 0.06 mm2 vs. 0.15 ± 0.07 mm2 vs. 0.19 ± 0.06 mm2, p = 0.0004). At 10 days, the area of fibrin deposition was significantly greater in DP-EES (0.13 ± 0.04 mm2 vs. 0.14 ± 0.05 mm2 vs. 0.19 ± 0.08 mm2, p = 0.007). Endothelial cells in BP-SES demonstrated a significantly greater number of tight junctions than those in DP-EES according to by transmission electron microscopy for both days (p<0.05). Various parameters, including an inflammatory reaction and neointimal formation, were comparable among the groups at 7 and 10 days. An abluminal biodegradable polymer-coated SES showed the least fibrin deposition and greatest endothelial cell recovery at an early stage following implantation in the coronary arteries of mini-pigs.

Paclitaxel-coated stents to prevent hyperplastic proliferation of ureteral tissue: from in vitro to in vivo

Ureteric stents have become an indispensable tool in the armamentarium of every urologist. However, they carry their own morbidity resulting mostly from infectious or abacterial fouling and biofilm formation, and/or urothelial hyperplastic reaction. All of these may interact and lead to clinical complications. Many different stent designs and coatings have been proposed. In this study, we focused on the effect of paclitaxel-coated stents on hyperplastic proliferation of ureteral tissue, using as example anastomotic strictures after ureteroureterostomy in a rat model. Human urothelial cells (SV-HUC-1) were used to determine paclitaxel dosages in vitro. Polyurethane stents were coated with a paclitaxel containing biodegradable polymer and studied in a ureteroureterostomy rat model. 48 male 9-week-old Sprague-Dawley rats underwent either sham surgery (n = 16) or ureteroureterostomy with sutured anastomosis, and consecutive stenting with either a paclitaxel-coated or an uncoated stent (16 per group), respectively. The animals received daily intraperitoneal injections of 5-bromo-2-deoxyuridine (20 mg/ml, 100 mg/kg body weight) during the first eight postoperative days, and were sacrificed on day 28. Healing of the ureteral anastomosis and proliferation of urothelial cells was examined histologically and immunohistochemically. In vitro, a concentration of 10 ng/mm² paclitaxel can be considered as non-toxic, while still exerting an anti-proliferative effect on urothelial cells. Histologically, typical wound healing processes were seen at the site of the ureteral anastomosis in vivo. Proliferation of urothelial cells was significantly lower in animals with paclitaxel-coated stents compared to those with uncoated stents (LI 41.27 vs. 51.58, p < 0.001). Our results indicate that stenting of ureteral anastomoses with paclitaxel-coated stents can reduce hyperplastic proliferation of ureteral tissue. Paclitaxel-coated stents thus might be able to prevent not only scar-induced postoperative stenosis after reconstructive surgery, but also hyperplastic urothelial reaction in non-anastomotic stent patients as part of their inflammatory response to the foreign material.

Permanent and biodegradable polymer coatings in the absence of antiproliferative drugs in a porcine model of coronary artery stenting

AIMS

The purpose of the present study was to examine the comparative vascular healing response to stents coated with permanent or biodegradable polymer and uncoated stents in a porcine model of coronary artery stenting.

METHODS AND RESULTS

Juvenile pigs were randomly allocated to implantation of stents coated with permanent polymer (PP, methacrylate-based, n=10), biodegradable polymer (BP, poly-lactic acid-based, n=10) or bare metal control stents (n=10), in the absence of antiproliferative drugs. At 28 days, animals were sacrificed and specimens prepared for histopathologic assessment. Endothelialisation was complete in all treatment groups. Vascular injury at 28 days was greater in PP stents as compared with uncoated stents (p=0.05) though not as compared with BP-coated stents (p=ns). PP stents showed increased inflammatory scores compared with BP-coated (p=0.03) and uncoated stents (p=0.02). There was also greater neointimal growth with PP-coated stents compared with uncoated stents (p=0.02).

CONCLUSIONS

In the absence of antiproliferative drugs, stents coated with methacrylate-based PP, but not with poly-lactic acid-based BP, provoked significant vessel wall inflammatory reactions resulting in greater vascular injury and increased neointimal growth compared with uncoated stents. Biodegradable polymer coatings may be considered preferable to facilitate drug elution with minimal vessel wall toxicity.

Very early tissue coverage after drug-eluting stent implantation: an optical coherence tomography study

The aim of this study was to evaluate neointimal coverage in the very early phase after second-generation drug-eluting stent (DES) implantation using optical coherence tomography (OCT). Patients who underwent staged percutaneous coronary intervention within 30 days after DES implantation were enrolled. OCT was performed to observe DES previously implanted. The median time interval from implantation to OCT examination was 21.5 days. A total of 10,625 struts of 54 stents (52 everolimus-eluting stents and 2 zotarolimus-eluting stents) in 42 lesions were analyzed. Strut tissue coverage was observed in 71.1 ± 19.2 % of the struts, malapposed struts in 2.56 ± 3.37 %, strut tissue coverage at the side branch orifice in 10.6 ± 17.2 %, and struts with protrusion in 0.95 ± 3.46 %. Mean tissue thickness on the covered struts was 39.8 ± 14.2 µm. The percentage of stent coverage was significantly lower in the overlapping segments than in the non-overlapping segments (48.4 ± 17.5 % vs. 74.4 ± 20.2 %, P < 0.05). Most of the stent struts were covered by tissue within 30 days after second-generation DES implantation. However, the percentage of strut coverage was lower in the overlapping segments than in the non-overlapping segments, suggesting that very early interruption of dual antiplatelet therapy might result in increased risk of stent thrombosis, even in second-generation DES.

Pathobiology of Ischemic Heart Disease: Past, Present and Future

This review provides a perspective on knowledge of ischemic heart disease (IHD) obtained from the contemporary era of research which began in the 1960s and has continued to the present day. Important discoveries have been made by basic and translational scientists and clinicians. Pathologists have contributed significantly to insights obtained from experimental studies and clinicopathological studies in humans. The review also provides a perspective for future directions in research in IHD aimed at increasing basic knowledge and developing additional therapeutic options for patients with IHD.

Safety and Efficacy of New Sirolimus-eluting Stent Models in a Preclinical Study

INTRODUCTION AND OBJECTIVES

Initial preclinical studies are required during the process of improving polymers, platforms, and drug-eluting systems for new coronary stent designs. Our objective was to analyze the efficacy and safety of new drug-eluting stent models compared with a conventional stent and commercialized drug-eluting stents in an experimental model with healthy porcine coronary arteries.

METHODS

Sixty stents (conventional stent, new sirolimus-eluting stents: drug-eluting stents 1, 2 and 3; Cypher(®) and Xience(®)) were randomly placed in the coronary arteries of 20 Large White domestic pigs. Angiographic and histomorphometric studies were done 28 days later.

RESULTS

The stents were implanted at a stent/artery ratio of 1.34±0.15, with no significant differences between groups. The new stents showed less late loss and angiographic restenosis than conventional stents (P=.006 and P<.001, respectively). Histologically, restenosis and neointimal area were lower with all the new platforms than with the conventional stents (P<.001 for each variable), and no differences were found vs the drug-eluting stents on the market. Safety data showed that endothelialization was lower with drug-eluting stents than with conventional stents, except for drug-eluting stent 3 (P=.084). Likewise, inflammation was lower with drug-eluting stent 3 than with other stents.

CONCLUSIONS

The new drug-eluting stent platforms studied are associated with less restenosis than conventional stents and showed no significant differences in safety or efficacy vs commercialized drug-eluting stents.

Impact of stent strut design in metallic stents and biodegradable scaffolds

Advances in the understanding of healing mechanisms after stent implantation have led to the recognition of stent strut thickness as an essential factor affecting re-endothelialization and overall long term vessel healing response after Percutaneous Coronary Interventions (PCI). Emergence of Drug-eluting stents (DESs) with anti-proliferative coating has contributed to reducing the incidence of restenosis and Target Lesion Revascularization (TVR), while progress and innovations in stent materials have in the meantime facilitated the design of newer platforms with more conformability and thinner struts, producing lesser injury and improving integration into the vessel wall. Recent advances in biodegradable metal and polymer materials now also allow for the design of fully biodegradable platforms, which are aimed at scaffolding the vessel only temporarily to prevent recoil and constrictive remodeling of the vessel during the initial period required, and are then progressively resorbed thereby avoiding the drawback of leaving an unnecessary implant permanently in the vessel. The aim of this article is to review recent evolution in stent material and stent strut design while understanding their impact on PCI outcomes. The article describes the different metallic alloys and biodegradable material properties and how these have impacted the evolution of stent strut thickness and ultimately outcomes in patients.

Resolute zotarolimus-eluting coronary stent system for the treatment of coronary artery disease

Drug eluting stents were an important addition to the interventional options available for patients with coronary artery disease, and they effectively reduced the risk of restenosis observed with bare metal stents. However, the drugs and polymers used in the composition of drug eluting stents were found to delay vascular healing and elicit inflammatory responses, which contributed to late and very late stent thrombosis events. Newer generation drug eluting stents have been engineered with polymers that are more biocompatible and have more favorable drug elution profiles. The Resolute(®) zotarolimus eluting stent (R-ZES) is a new-generation drug eluting stent. The Global RESOLUTE clinical program was designed to evaluate the safety and efficacy of the R-ZES. The studies conducted under this program have established that the R-ZES safely and effectively treats coronary artery stenosis, with low rates of target lesion failure, target vessel revascularization, and stent thrombosis during extended follow-up.

Impact of everolimus versus other rapamycin derivative-eluting stents on clinical outcomes in patients with coronary artery disease: a meta-analysis of 16 randomized trials

BACKGROUND

Everolimus-eluting stent (EES) are considered to have better clinical outcomes than other rapamycin derivative-eluting stents; however, the individual trials may not have sufficient power to prove it. This meta-analysis aimed to compare clinical outcomes of EES against other rapamycin derivative-eluting stents.

METHODS

We searched Medline, the Cochrane Library, and other internet sources, without language or date restrictions for articles comparing clinical outcomes between EES and other rapamycin derivative-eluting stents. Safety endpoints were stent thrombosis (ST), mortality, cardiac death, and myocardial infarction (MI). Efficacy endpoints were major adverse cardiac events (MACE), target lesion revascularization (TLR), and target vessel revascularization (TVR).

RESULTS

We identified 16 randomized controlled trials with 23,481 patients and a weighted mean follow-up of 18 months. Compared with other rapamycin derivative-eluting stents, EES were associated with a significant reduction in definite ST [relative risk (RR): 0.45; 95% confidence interval (CI): 0.30-0.69; p<0.001] and TLR (RR: 0.87; 95% CI: 0.77-0.99; p=0.03). EES also showed a non-significant trend toward reduction in definite/probable ST (RR: 0.75; 95% CI: 0.56-1.01; p=0.06). However, both groups had similar rates of mortality (RR: 0.95; 95% CI: 0.82-1.09; p=0.45), MI (RR: 0.95; 95% CI: 0.82-1.10; p=0.43), and MACE (RR: 0.94; 95% CI: 0.87-1.02; p=0.35). The stratified analysis of the included trials showed that EES was associated with significantly lower rate of definite ST compared with either zotarolimus-eluting stent (p=0.012) or sirolimus-eluting stent (p=0.006), but not biolimus-eluting stent (p=0.16). In longer follow-up (>1 year) stratification, EES was associated with a significant reduction in risk of definite ST (p<0.001).

CONCLUSIONS

EES is associated with a significant reduction in definite ST and TLR for treating patients with coronary artery disease, compared with a pooled group of other rapamycin derivative-eluting stents. Biolimus-eluting stent had similar safety and efficacy for treating patients with coronary artery disease, compared with the EES.

Two-year outcomes after deployment of XIENCE V everolimus-eluting stents in patients undergoing percutaneous coronary intervention of bifurcation lesions: a report from the SPIRIT V single arm study

The aim of this analysis was to analyze outcomes of patients undergoing Xience V EES treatment of bifurcation lesions, a subset in which treatment is particularly challenging. The SPIRIT V Study provided an evaluation of the Xience V everolimus eluting stent (EES) performance in complex patient and lesion population. The SPIRIT V Single Arm Study enrolled 2700 patients with de novo coronary artery lesions suitable to be optimally treated with a maximum of four planned Xience V EES. Lesion evaluation was by visual assessment. The outcomes of the 492 patients undergoing Xience V EES stenting of ≥1 bifurcation lesion were compared to those with no bifurcation lesion treated. Compared to those without bifurcation treatment, patients with bifurcation treatment were more likely to have multi-vessel disease (49% vs 40%), left main treatment (3.1% vs 0.9%), more lesions treated (1.5 vs 1.3), calcification (36.4% vs 27.5%), and ostial (17.1% vs 8.2%) and angulated lesions (29.3% vs 21.1%), all P < 0.001. The 30-day composite rate of death, myocardial infarction (MI), target vessel revascularization (TVR) was 4.3% in patients with bifurcation PCI and 2.2% in those with non-bifurcation PCI (P = 0.017). At 2 years, this composite event rate was 11.3% and 10.0% in these two groups, respectively (P = 0.403). Rates of cardiac death, MI, target lesion revascularization (TLR), TVR, and ARC defined definite or probable stent thrombosis (0.4% vs 0.9%, P = 0.402) were not significantly different between the two groups. Despite greater patient and lesion complexity, treatment of patients with bifurcation lesions using the Xience V EES in the SPIRIT V prospective Single Arm Study was safe and effective, with low overall event rates that were similar to those without bifurcation lesion treatment. © 2013 Wiley Periodicals, Inc.