Liposome-coated metal stents: an in vitro evaluation of controlled-release modality in the ureter

Drug-delivering devices in the urinary tract: A systematic review

Objective

: To systematically review the use of drug-eluting stents (DES) and drug-coated balloons (DCB) in urology.

Materials and Methods

The systematic review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. PubMed, Scopus, Web of science and Cochrane Library online databases were searched in February 2019. Experimental and clinical studies, which included the placement of a DES or dilatation with DCB for investigating their potential use in the urinary tract for the management of ureteric or urethral pathologies, were included. The primary endpoint was to evaluate the current use of DES and DCB in urology.

Results

A total of 29 articles were included in the systematic review. A total of 10 studies tested DES or DCB containing anti-proliferative agents (paclitaxel, zotarolimus, sirolimus, halofugione). Antibiotic agent-containing DES were tested in nine studies (triclosan, quinolones, teicoplanin, nitrofurantoin, silver sulfadiazine). A total of eight studies investigated the release of anti-inflammatory agents by DES (ketorolac, indomethacin, EW-7197). Another group studied heparin-eluting stents.

Conclusion

Despite the inconclusive outcomes of the three randomised controlled trials, drug-coated/eluting devices constitute a promising field in urology for the prevention of complications associated with conventional stents including pain and encrustation. Pre-clinical in vitro and in vivo studies have shown their ability to mitigate inflammation, inhibit re-stenosis and improve pain as indicated by declined use of anti-inflammatory drugs.

Abbreviations: DES: drug-eluting stents; DCB: drug-coated balloons; DCS: drug-coated stents; HF: halofungione; MCP-1: monocyte chemoattractant protein 1; PRISMA, Preferred Reporting Items for Systematic Reviews and Meta-Analyses; PTCA: percutaneous transluminal coronary angioplasty; RANTES: regulated on activation, normal T-cell expressed and secreted; RCT: randomised controlled trial; USSQ, Ureteric Stent Symptoms Questionaire.

Nitric Oxide Releasing Coronary Stent: A New Approach Using Layer-by-Layer Coating and Liposomal Encapsulation

The sustained or controlled release of nitric oxide (NO) can be the most promising approach for the suppression or prevention of restenosis and thrombosis caused by stent implantation. The aim of this study is to investigate the feasibility in the potential use of layer-by-layer (LBL) coating with a NO donor-containing liposomes to control the release rate of NO from a metallic stent. Microscopic observation and surface characterizations of LBL-modified stents demonstrate successful LBL coating with liposomes on a stent. Release profiles of NO show that the release rate is sustained up to 5 d. In vitro cell study demonstrates that NO release significantly enhances endothelial cell proliferation, whereas it markedly inhibits smooth muscle cell proliferation. Finally, in vivo study conducted with a porcine coronary injury model proves the therapeutic efficacy of the NO-releasing stents coated by liposomal LBL technique, supported by improved results in luminal healing, inflammation, and neointimal thickening except thrombo-resistant effect. As a result, all these results demonstrate that highly optimized release rate and therapeutic dose of NO can be achieved by LBL coating and liposomal encapsulation, followed by significantly efficacious outcome in vivo.

From drug delivery systems to drug release, dissolution, IVIVC, BCS, BDDCS, bioequivalence and biowaivers

This is a summary report of the conference on drug absorption and bioequivalence issues held in Titania Hotel in Athens (Greece) from the 28(th) to the 30(th) of May 2009. The conference included presentations which were mainly divided into three sections. The first section focused on modern drug delivery systems such as polymer nanotechnology, cell immobilization techniques to deliver drugs into the brain, nanosized liposomes used in drug eluting stents, encapsulation of drug implants in biocompatible polymers, and application of differential scanning calorimetry as a tool to study liposomal stability. The importance of drug release and dissolution were also discussed by placing special emphasis on camptothecins and oral prolonged release formulations. The complexity of the luminal environment and the value of dissolution in lyophilized products were also highlighted. The second session of the conference included presentations on the Biopharmaceutics Classification Scheme (BCS), the Biopharmaceutics Drug Disposition Classification System (BDDCS), and the role of transporters in the classification of drugs. The current status of biowaivers and a modern view on non-linear in vitro-in vivo (IVIVC) correlations were also addressed. Finally, this section ended with a special topic on biorelevant dissolution media and methods. The third day of the conference was dedicated to bioequivalence. Emphasis was placed on high within-subject variability and its impact on study design. Two unresolved issues of bioequivalence were also discussed: the use of generic antiepileptic drugs and the role of metabolites in bioequivalence assessment. Finally, the conference closed with a presentation of the current regulatory status of WHO and EMEA.

Liposome Coated Stents: A Method to Deliver Drugs to the Site of Action and Improve Stent Blood-Compatibility

A method to correct stent related complications non-invasively, is the local delivery of therapeutic agents. Different drugs have been delivered on stents, after being either dispersed or encapsulated in polymeric materials, and placed on stents to form drug-eluting-stents (DE-stents). Investigation of possibility to cover polymer - coated metallic stents, with liposomal drugs, for preparation of novel DE-liposome-coated-stents, has been initiated few years ago. In this context our research has been focused on answering the following questions: (i) Can liposomes be applied as coatings on polymer covered stents? (ii) Can drug release from liposome coated-stents be controlled? And: (iii) how is haemo-compatibility of stents affected? The results of the experiments carried out demonstrate that liposomal formulations of drugs can be used as coating systems of polymer covered stents for achieving sustained release of drugs at the site of interest. By modifying liposome characteristics, different amounts of drugs may be placed on the stents and their release rates can be adjusted for maximum therapeutic benefit. Finally, haemocompatibility of stents is highly improved (mainly in terms of cell adhesion and activation of coagulation system), when stents are coated with heparin-encapsulating -DRV liposomes.

Dexamethasone incorporating liposomes: effect of lipid composition on drug trapping efficiency and vesicle stability

Effect of lipid composition on encapsulation and stability of dexamethasone (DXM) incorporating multilamellar vesicles (MLV) is studied. MLVs composed of phosphatidylcholine (PC) or distearoyl-glycero-PC (DSPC), with or without cholesterol (Chol), are prepared and the release of DXM during vesicle incubation in buffer or plasma proteins is evaluated. Incorporation of DXM is slightly higher in DSPC liposomes compared with PC, whereas the drug is displaced from liposomes, as the Chol content of liposome membranes increases. Plain lipid and Chol-containing liposomes lose similar fractions of vesicle-incorporated DXM during incubation in buffer or serum, whereas DXM release kinetics are similar (for each liposome type studied), implying that drug release is due mainly to dilution of liposome dispersions that leads to repartitioning of DXM.

Long-term results of permanent metallic stent implantation in the treatment of benign upper urinary tract occlusion

AIM

The management of complicated benign upper urinary tract occlusion is extremely challenging, especially in patients unable to undergo an open operative procedure. We report the long-term results of a permanent metallic stent for benign upper urinary tract occlusion.

METHODS

From October 1995 to December 1998, 13 patients (8 men and 5 women, with a mean age of 43 years) with benign upper tract occlusion have been treated by metallic stent implantation. All patients had a nephrostomy tube to relieve the obstruction and the average time of the nephrostomy tube stay was 27 months, ranging from 3 to 131 months. The average length of occlusion was 2.7 cm, ranging from 1 to 3.6 cm. Ultrasonography, urography, diuresis renography and urine culture were performed every 3 months after stent insertion. Ureteroscopy was done when needed.

RESULTS

The mean follow-up was 92 months (12-132 months). Ureteral patency was achieved in six patients and assisted patency with a Double-J stent was achieved in three patients. In two patients the kidney had to be removed because of progressive malfunction and in two patients the metal stent had to be extracted with the Holmium: YAG laser, burning it down due to the uncontrollable pyonephrosis. In three patients the ipsilateral flank pain recurred. One of these patients experienced urine leakage due to the initial nephrostomy tract: a ureteroscopy revealed a complete hyperplastic urothelial response. Proximal stone formations were found in 2 patients and all were removed by percutaneous nephrolithotomy (PCNL). No stent migration or fragmentation was observed.

CONCLUSION

The implantation of metal stent is a safe and effective treatment for benign upper urinary tract occlusion, and has satisfying long-term outcome in selected cases. A further investigation is needed for its impact on the urodynamics of upper urinary tract.

Second Prize: Double-Blind Randomized Controlled Trial Assessing the Safety and Efficacy of Intravesical Agents for Ureteral Stent Symptoms after Extracorporeal Shockwave Lithotripsy

BACKGROUND AND PURPOSE

Ureteral stents are a significant source of pain and discomfort for many urologic patients. A novel approach to addressing this problem is the intravesical instillation of a selected pharmacologic agent after stent insertion. The purpose of this study was to assess the safety and efficacy of intravesical instillation of various agents in reducing ureteral stent-associated discomfort in patients requiring a stent after extracorporeal shockwave lithotripsy (SWL).

PATIENTS AND METHODS

In this double-blind prospective trial, 42 patients were randomized to receive intravesical instillation of one of three agents (oxybutynin, alkalinized lidocaine, or ketorolac) or a control solution (0.9% sodium chloride) immediately after stent insertion at time of SWL. The four groups of patients were demographically similar. Preoperative, intraoperative, and postoperative data were collected prospectively and analyzed statistically. The primary outcome measure was reduction in ureteral stent symptoms, and the secondary outcome measure was the safety of intravesical instillation of each agent through assessment of drug-related adverse events.

RESULTS

There were no intraoperative or postoperative complications, nor were there any serious side effects attributable to any of the intravesically instilled agents. There was a statistically significant decrease in stent-related discomfort at the 1-hour time point in the group of patients who received intravesical ketorolac compared with the control group.

CONCLUSIONS

Intravesical instillation represents a novel approach to the problem of ureteral stent-related discomfort. From our results, ketorolac appears to be the most effective intravesical agent in reducing stent-related patient discomfort, and we have established that intravesical instillation of ketorolac is safe in humans.

URINARY TRACT BIOMATERIALS

PURPOSE

As a result of endourological advances, biomaterials have become increasingly used within the urinary tract. This review article provides an update on the current status of urinary tract biomaterials, discussing issues of biocompatibility, biomaterials available for use, clinical applications and biomaterial related complications. Perspectives on future materials for use in the urinary tract are also provided.

MATERIALS AND METHODS

We performed a comprehensive search of the peer reviewed literature on all aspects of biomaterials in the urinary tract using PubMed and MEDLINE. All pertinent articles were reviewed in detail.

RESULTS

Any potential biomaterial must undergo rigorous physical and biocompatibility testing prior to its commercialization and use in humans. There are currently many different bulk materials and coatings available for the manufacturing of biomaterials, although the ideal material has yet to be discovered. For use in the urinary tract, biomaterials may be formed into devices, including ureteral and urethral stents, urethral catheters and percutaneous nephrostomy tubes. Despite significant advances in basic science research involving biocompatibility issues and biofilm formation, infection and encrustation remain associated with the use of biomaterials in the urinary tract and, therefore, limit their long-term indwelling time.

CONCLUSIONS

Prosthetic devices formed from biomaterials will continue to be an essential tool in the practicing urologist's armamentarium. Ongoing research is essential to optimize biocompatibility and decrease biomaterial related complications such as infection and encrustation within the urinary tract. Future advances include biodegradables, novel coatings and tissue engineering.

Advances in ureteral stent design

BACKGROUND AND PURPOSE

Ureteral stents are widely used in patients with urologic disorders. This review critically evaluates the recent literature, providing an update on advances in the development and design of stents.

METHODS

A thorough MEDLINE and PubMed literature search on ureteral stents was performed, and all pertinent articles were reviewed in detail. This review was formulated on the basis of these articles, encompassing both basic science and clinical aspects of advances in ureteral stent design.

RESULTS

The advances in development and design have been directed primarily toward decreasing stent-related morbidity such as discomfort, bladder irritability, infection, encrustation, and the need for an additional cystoscopic procedure to remove the stent. In recent years, there have been many significant advances in the design of ureteral stents, including tapered distal ends, and construction, such as magnetic, biodegradable, and tissue-engineered materials.

CONCLUSIONS

There are many different bulk materials and coatings available for the manufacturing of ureteral stents, many of which are new. However, the ideal biomaterial has yet to be discovered. With ongoing research in this area, further advances in ureteral stent design will continue to improve outcomes for patients who require stents. Future advances are likely to include drug-coated stents, drug-eluting stents, and localized stenting techniques such as endoluminal gel paving.

Ureteropelvic junction obstruction: an innovative approach combining metallic stenting and virtual endoscopy

PURPOSE

We report our experience with auto-expandable metallic stents for treating ureteropelvic junction obstruction.

MATERIALS AND METHODS

We treated 4 patients with a mean age of 45 years who had ureteropelvic junction obstruction with placement of a self-expandable intraureteral metallic stent (Wallstent, Schneider, Zurich, Switzerland). All patients presented with recurrent ureteropelvic junction obstruction after open pyeloplasty. Excretory urography and 3-dimensional reconstruction computerized tomography were performed 1 and 6 months after stent insertion. Virtual endoscopy images were obtained at followup due to the need to define ureteral patency.

RESULTS

Mean followup was 16 months (range 9 to 24). Wallstent placement was successful and immediate patency was achieved in all cases. During followup 3 patients required no further intervention and the stented ureteropelvic junction remained patent. In the remaining patient stricture recurred 2 months after initial stent insertion due to the ingrowth of scar tissue through the prosthesis. Additional intervention was deemed necessary after placing a longer 6 cm., completely coaxial overlapping metal stent. Virtual endoscopy and excretory urography findings concurred. Virtual endoscopy allows visualization of the stented ureteropelvic junction lumen cephalad and caudal to the prosthesis. It also enables easy navigation within the stent at different angles of view.

CONCLUSIONS

The concept of applying metallic stents for ureteropelvic junction obstruction and adjacent adynamic ureteral segments combined with virtual endoscopy is strengthened by the results of this study.

Dexamethasone incorporating liposomes: an in vitro study of their applicability as a slow releasing delivery system of dexamethasone from covered metallic stents

AIM

To investigate the possibility of covering PET-covered commercially available metallic stents, with liposomal dexamethasone that will act as a slow releasing drug-depot at the site of interest.

METHODS

Large multilamellar (MLV), sonicated (SUV) and dried reconstituted (DRV) liposomes entrapping dexamethasone were prepared by thin film hydration, sonication and the DRV method, respectively, and applied on stents using a simple evaporation technique. Drug encapsulation and retention in liposomes were measured by HPLC. The presence of liposomes on the stent surface was confirmed by scanning electron microscopy, while the release of dexamethasone and lipid from the liposome-covered stent was evaluated under different conditions (flow rate, presence of plasma proteins), in an in vitro assembly that was developed to simulate in vivo conditions.

RESULTS

The release of dexamethasone from liposome-covered stents ranged from 25% to 50% after 48 h of incubation in buffer, depending on the type of liposome. The release was highest from stents covered with DRV liposomes. When increasing the flow rate from 2 to 6 ml/min a slight increase in release of drug was observed, while a higher release was measured when stents were incubated in plasma proteins. Liposome size does not affect liposome placement on stents.

CONCLUSION

The basic characteristics that should be considered when preparing liposomes to cover stents should be their drug loading capacity and their stability under the conditions prevailing at the site of interest. By preparing the appropriate formulation, it is possible that liposomal drugs may be used to cover stents and serve as drug releasing depots at the site of interest. Further in vitro and in vivo studies are needed in order to exploit the possible applications of this methodology.

Coated v noncoated ureteral metal stents: an experimental model

PURPOSE

The purpose of the present study was to compare the standard metal stents with internally and externally coated metal stents in the pig model.

MATERIALS AND METHODS

In nine female pigs weighing between 25 and 30 kg, the metal stents were randomly placed in either the right or left ureter, for a total of 18 stented ureters. Six ureters were stented with a Wallstent (Schneider, Zurich, Switzerland), six with a Passager stent (Boston Scientific, Natick, MA, USA), and six with a Corvita endoluminal graft (CEG) (Boston Scientific, Natick, MA, USA). Patency was examined by nephrostotomography 24 hours and 21 days after the initial procedure.

RESULTS

Free flow of urine through the stents into the bladder was revealed in all ureters with the exemption of four cases where a Passager stent migrated into the bladder, jeopardizing ureteral patency. The Wallstent generated mild inflammation with metaplasia of the urothelium; the CEG a more pronounced inflammatory response in the adjacent ureter; and the Passager stent severe inflammatory reaction with necrosis of the urothelium. The sections of the Wallstents revealed the presence of a mild polypoid reaction adherent to the internal surface of the devices. The coated stents showed no tissue ingrowth through the lining material into the ureteral lumen, and thus, the urothelium was compressed beneath the prostheses.

CONCLUSIONS

Our experimental results suggest that the standard Wallstent generates less inflammation of the surrounding tissues than coated stents. The coated stents have the advantage of minimal tissue ingrowth but have a tendency to migrate toward the bladder.