Paclitaxel-coated expanded polytetrafluoroethylene haemodialysis grafts inhibit neointimal hyperplasia in porcine model of graft stenosis

Multicenter Randomized Controlled Trial of APERTO-Paclitaxel Drug-Eluting Balloon Angioplasty Versus Standard Percutaneous Transluminal Angioplasty in Dysfunctional Hemodialysis Grafts and Native Fistulae

PURPOSE

to assess the safety and efficacy of APERTO-Paclitaxel-coated balloon angioplasty versus standard angioplasty for the treatment of dysfunctional hemodialysis shunts and native arteriovenous fistulae.

METHODS

consecutive patients with dysfunctional dialysis related to underlying efferent vein stenosis were included and randomized 1:1 to either APERTO-paclitaxel drug-coated balloon (study arm) or standard percutaneous transluminal angioplasty (control arm). Primary endpoint is time from treatment until dialysis access dysfunction according to standardized Kidney Disease Outcomes Quality Initiative (KDOQI)-guidelines and assessed by Kaplan-Meier survival curves and tested for significance with log-rank analysis. Secondary endpoints include device, technical, and clinical success of the index angioplasty procedure.

RESULTS

The study included 103 patients (n=51 study-group) with a de novo (n=33) dysfunctional native arteriovenous fistula (n=79) in the forearm (n=60). The majority of included patients were male with a mean age of 69.8 years, presenting with a dysfunctioning autologous arteriovenous fistula in the forearm. Device-related complications did not occur in any of the included patients. Functional hemodialysis access without need for re-intervention at 1 year after index procedure was found in n=10 (19.6%) and n=5 (9.6%) of patients treated with, respectively, paclitaxel drug-coated balloon and percutaneous transluminal angioplasty (p=0.612). A nonsignificant benefit of paclitaxel drug-coated balloon (n=5; 25%) over percutaneous transluminal angioplasty (n=1; 11%) was found (p=0.953) in de novo lesions in autologous fistulas.

CONCLUSION

APERTO-paclitaxel drug-coated balloon is a safe balloon catheter to manage dysfunctional hemodialysis access; however, longer period of adequate hemodialysis circuit functioning after endovascular index stenosis treatment, using APERTO-paclitaxel drug-coated balloon versus percutaneous transluminal angioplasty could not be demonstrated.

CLINICAL IMPACT

APERTO-paclitaxel drug-coated balloon catheter is a safe device to manage dysfunctional hemodialysis access. Compared to conventional angioplasty balloon, the APERTO drug-coated balloon will not result in longer period of adequate hemodialysis circuit functioning. A non-significant benefit of APERTO drug-coated balloon was found in de novo lesions in autologous fistulas.

Histologic evaluation of a catheter coated with paclitaxel PLGA nanoparticles in the internal jugular veins of rats

The aim of this study is to investigate the potential impact of catheterization on intimal hyperplasia and explore the efficacy of Paclitaxel loaded PLGA nanoparticles (PTX-NPs) in preventing stenosis at the site of venous injury. Under general anesthesia, Central Venous Catheters were inserted into the rat's right internal jugular veins (IJV) using the cut-down technique. Twenty bare catheters (C) and twenty PTX-NPs coated catheters (P) were assigned to one of four groups (C2, C4, P2, or P4) based on catheter type and expected survival time. 2 or 4 weeks after surgery, IJVs were completely harvested by formalin fixation and gelatin infusion and slides were stained with H&E (Haematoxylin and Eosin) and Masson's technique. The P2 (Paclitaxel coating, 2 weeks) group showed the most proliferation among the four groups and the P4 (Paclitaxel coating, 4 weeks) showed a tendency to decrease proliferation. Additionally, the lumen size in the P4 group was about 6% smaller than in the P2 group, and there was a lower prevalence of stenotic grade in the P4 group. Our study suggests that PTX-NPs coated catheters may be effective in preventing venous stenosis if the intended usage is prolonged, rather than for a short-term period.

Graphical abstract

Schematic representation of catheter functionalization and coating of PTX-NPs on Catheter.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13534-023-00282-y.

Effect of expanded polytetrafluoroethylene thickness on paclitaxel release and edge stenosis in stent graft

Stent grafts have been widely used to treat lower extremity arterial stenosis or occlusion. However, there are major issues with edge stenosis and loss of patency over time. Paclitaxel-coated stent grafts have been proven to be effective in preventing edge stenosis, but the insufficient amounts of paclitaxel released may limit the effectiveness of drug-eluting stent grafts. In this study, we examined whether paclitaxel-coated expanded polytetrafluoroethylene (ePTFE) stent graft thickness influences paclitaxel release properties and inhibits edge stenosis. Low-, medium-, and high-thickness paclitaxel-coated stent grafts were prepared by varying the thickness of inner and outer ePTFE layers. Surface morphologies of the stent grafts were analyzed using a scanning electron microscope. The stent grafts were then implanted in the iliac arteries of 20 healthy swine. Twelve pigs were used to assess edge stenosis, and digital subtraction angiography was performed at day 30 (n = 4), 90 (n = 4), and 180 (n = 4). Histological evaluation of the treated arteries was also performed. Eight pigs were used for pharmacokinetic analysis, and the treated arteries were obtained at day 1 (n = 2), 30 (n = 2), 90 (n = 2) and 180 (n = 2). Scanning electron microscopy confirmed that the mean pore size of the stent grafts decreased with increasing thickness. The results of angiographic and histological evaluation demonstrated that low-thickness ePTFE-stent grafts resulted in edge stenosis and apparent intimal hyperplasia at 180 days, whereas for medium-thickness ePTFE-stent grafts, no obvious edge stenosis and intimal hyperplasia was noted in the similar time period. The results of pharmacokinetic evaluation showed that at 180 days, the paclitaxel concentration of treated arteries of the medium group was 36 ± 53 ng/g, while concentrations in the low group was not detectable. Stent grafts with increased ePTFE thickness appear to allow for more delayed release of paclitaxel compared to low-thickness ePTFEs.

Drug Coated Balloons for Dysfunctional Haemodialysis Venous Access: A Patient Level Meta-Analysis of Randomised Controlled Trials

OBJECTIVE

To perform an individual patient data level meta-analysis of randomised controlled trials comparing drug coated balloon angioplasty (DCB) against conventional percutaneous transluminal angioplasty (PTA) in the treatment of dysfunctional haemodialysis venous access.

METHODS

A search was conducted from inception to 13 November 2020. Kaplan-Meier curves comparing DCB with PTA by target lesion primary patency (TLPP) and access circuit primary patency (ACPP) were graphically reconstructed to retrieve patient level data. One stage meta-analyses with Cox models with random effects shared frailties were conducted to determine hazard ratios (HRs). Dynamic restricted mean survival times (RMST) were conducted in view of violation of the proportional hazards assumption. Conventional two stage meta-analyses and network meta-analyses under random effects Frequentist models were conducted to determine overall and comparative outcomes of paclitaxel concentrations used. Where outliers were consistently detected through outlier and influence analyses, sensitivity analyses excluding those studies were conducted.

RESULTS

Among 10 RCTs (1 207 patients), HRs across all models favoured DCB (one stage shared frailty HR 0.62, 95% CI 0.53 - 0.73, p < .001; two stage random effects HR 0.60, 95% CI 0.42 - 0.86, p = .018, I² = 65%) for TLPP. Evidence of time varying effects (p = .005) was found. TLPP RMST was + 3.54 months (25.0%) longer in DCB treated patients compared with PTA (p = .001) at three years. TLPP at six months, one year, and two years was 75.3% vs. 58.1%, 51.1% vs. 37.1%, and 31.4% vs. 26.0% for DCB and PTA, respectively. The P-Scores within the Frequentist network meta-analysis suggest that higher concentrations of paclitaxel were associated with better TLPP and ACPP. Among six RCTs (854 patients), the one stage model favoured DCB (shared frailty HR 0.72, 95% CI 0.60 - 0.87, p < .001) for ACPP. Conversely, the two stage random effects model demonstrated no significant difference (HR 0.76, 95% CI 0.35 - 1.67, p = .41, I² = 81%). Sensitivity analysis excluding outliers significantly favoured DCB (HR 0.61, 95% CI 0.41 - 0.91, p = .027, I² = 62%).

CONCLUSION

Overall evidence suggests that DCB is favoured over PTA in TLPP and ACPP.

Challenges and novel therapies for vascular access in haemodialysis

Advances in standards of care have extended the life expectancy of patients with kidney failure. However, options for chronic vascular access for haemodialysis - an essential part of kidney replacement therapy - have remained unchanged for decades. The high morbidity and mortality associated with current vascular access complications highlights an unmet clinical need for novel techniques in vascular access and is driving innovation in vascular access care. The development of devices, biological approaches and novel access techniques has led to new approaches to controlling fistula geometry and manipulating the underlying cellular and molecular pathways of the vascular endothelium, and influencing fistula maturation and formation through the use of external mechanical methods. Innovations in arteriovenous graft materials range from small modifications to the graft lumen to the creation of completely novel bioengineered grafts. Steps have even been taken to create new devices for the treatment of patients with central vein stenosis. However, these emerging therapies face difficult hurdles, and truly creative approaches to vascular access need resources that include well-designed clinical trials, frequent interaction with regulators, interventionalist education and sufficient funding. In addition, the heterogeneity of patients with kidney failure suggests it is unlikely that a 'one-size-fits-all' approach for effective vascular access will be feasible in the current environment.

Treatment of juxta-anastomotic stenoses for failing distal radiocephalic arteriovenous fistulas: Drug-coated balloons versus angioplasty

The aim of our study is to report the results of two types (type A, type B) paclitaxel drug-coated balloon compared with standard percutaneous transluminal angioplasty in the treatment of juxta-anastomotic stenoses of mature but failing distal radiocephalic hemodialysis arteriovenous fistulas. Two groups of 26 and 44 patients treated with two different drug-coated balloon are compared with a control group of 86 treated with standard percutaneous transluminal angioplasty. A color Doppler ultrasound was performed to evaluate stenosis and for treatment planning. We assess primary patency, defined as the absence of dysfunction of the arteriovenous fistulas, patent lesion or residual stenosis < 30% and no need for further reintervention of target lesion. Primary patency and secondary patency are evaluated after 12 months with color Doppler ultrasound for the whole arteriovenous fistulas, defined as absolute (absolute primary patency, absolute secondary patency) and target lesion. Postprocedural technical and clinical success was 100%. After 12 months, absolute primary patency is 81.8% for type A, 84.1% type B, and 54.7% for standard percutaneous transluminal angioplasty; target lesion primary patency is 92% type A, 86.4% type B, and 62.8% standard percutaneous transluminal angioplasty; absolute secondary patency is 95.4% type A, 95.5% type B, and 80.7% standard percutaneous transluminal angioplasty; target lesion secondary patency is 100% type A, 97.7% type B, and 80.7% standard percutaneous transluminal angioplasty. All the patients treated with drug-coated balloon (type A + type B) have an absolute primary patency of 83.3%, a target lesion primary patency of 87.9%, an absolute secondary patency of 95.5%, and a target lesion secondary patency of 98.4%. Our study confirms that the use of drug-coated balloon, indiscriminately among different brands, improves primary patency with statistically significant difference in comparison with standard percutaneous transluminal angioplasty and decreases reintervention of target lesion in juxta-anastomotic stenoses of failing distal arteriovenous fistulas maintaining the radiocephalic fistula as long as possible.

Sheep models for evaluation of novel patch and prosthesis material in vascular surgery: tips and tricks to avoid possible pitfalls

Background

In vascular surgery, novel synthetic prosthesis materials for patch-angioplasties, interpositions, bypasses and shunts are continuously under development and optimization. The characteristics of an ideal vascular prosthesis would display long-term patency, biocompatibility, durability, low porosity, lack of stich hole bleeding, ease of handling, kink resistance, infection resistance and reasonable costs. The aim of this study was to establish and report a reliable sheep model including potential pitfalls where those parameters could be analyzed. Before surgery, sheep were acclimatized for 4–8 weeks, during which parasite infections were treated and blood and serum parameters monitored. Twenty-four sheep underwent surgery, and carotid patch-angioplasties (n = 12), graft interpositions (n = 6) or arteriovenous prosthetic shunts (n = 6) were implanted. Half of the animals in each group were sacrificed after 2 weeks and the other half after 8 weeks. The implants were analyzed for patency, endothelialization, thrombogenicity and biocompatibility by clinical observation, blood flow measurement and pathological and histopathological (H&E, EvG) as well as immunohistochemical (Ki67, CD31) evaluations.

Results

Health monitoring of the sheep revealed a parasitic burden with endoparasites in all animals. Some animals showed thereby infestations in the bile duct causing fibrotic cholangitis with calcifications in the liver. In addition, sarcosporidia were detected in histopathological specimen of the heart in all animals. Parasitic burden correlated with blood counts and serum bilirubin levels. Both were significantly reduced by albendazole treatment within the acclimatization time. Patches, interposition grafts, and straight shunts were successfully implanted bilaterally in all animals. The total average operation time was 136 ± 21 min. Most animals (23/24) showed good patency rates and general condition after implantation. Pathological and histopathological/immunohistochemical analyses were suitable to determine thrombogenicity, endothelialization, cellular/fibroblastic proliferation, biocompatibility, inflammatory cell infiltration, and thickness of neointima in the prosthesis material.

Conclusions

We have developed a suitable experimental protocol with standardized and successful anesthesia- and surgical-procedures for patch-angioplasty, graft interposition, and arteriovenous prosthetic shunts. This sheep model allows testing of new prosthetic materials for biocompatibility, thrombogenicity, and endothelialization.

Inhibiting intimal hyperplasia in prosthetic vascular grafts via immobilized all-trans retinoic acid

Peripheral arterial disease is a leading cause of morbidity and mortality. The most commonly utilized prosthetic material for peripheral bypass grafting is expanded polytetrafluoroethylene (ePTFE) yet it continues to exhibit poor performance from restenosis due to neointimal hyperplasia, especially in femoral distal bypass procedures. Recently, we demonstrated that periadventitial delivery of all-trans retinoic acid (atRA) immobilized throughout porous poly(1,8 octamethylene citrate) (POC) membranes inhibited neointimal formation in a rat arterial injury model. Thus, the objective of this study was to investigate whether atRA immobilized throughout the lumen of ePTFE vascular grafts would inhibit intimal formation following arterial bypass grafting. Utilizing standard ePTFE, two types of atRA-containing ePTFE vascular grafts were fabricated and evaluated: grafts whereby all-trans retinoic acid was directly immobilized on ePTFE (atRA-ePTFE) and grafts where all-trans retinoic acid was immobilized onto ePTFE grafts coated with POC (atRA-POC-ePTFE). All grafts were characterized by SEM, HPLC, and FTIR and physical characteristics were evaluated in vitro. Modification of these grafts, did not significantly alter their physical characteristics or biocompatibility, and resulted in inhibition of intimal formation in a rat aortic bypass model, with atRA-POC-ePTFE inhibiting intimal formation at both the proximal and distal graft sections. In addition, treatment with atRA-POC-ePTFE resulted in increased graft endothelialization and decreased inflammation when compared to the other treatment groups. This work further confirms the biocompatibility and efficacy of locally delivered atRA to inhibit intimal formation in a bypass setting. Thus, atRA-POC-ePTFE grafts have the potential to improve patency rates in small diameter bypass grafts and warrant further investigation.

Inhibitory effect of sustained perivascular delivery of paclitaxel on neointimal hyperplasia in the jugular vein after open cutdown central venous catheter placement in rats

PURPOSE

Inhibitory effect of paclitaxel on neointimal hyperplasia after open cutdown has not been elucidated.

METHODS

For the control group (n = 16), silicone 2.7-Fr catheters were placed via the right external jugular vein with the cutdown method. For the treatment group (n = 16), a mixture of 0.65 mg of paclitaxel and 1 mL of fibrin glue was infiltrated around the exposed vein after cutdown. After scheduled intervals (1, 2, 4, and 8 weeks), the vein segment was harvested and morphometric analysis was performed on cross-sections.

RESULTS

Proliferation of smooth muscle cell (SMC) was strongly suppressed in the treatment group, and the ratio of neointima to vein wall was significantly reduced in the treatment group (8 weeks; 0.63 ± 0.08 vs. 0.2 ± 0.08, P < 0.05). Luminal patency was significantly more preserved in the treatment group, and the luminal area was significantly wider in the paclitaxel-treated group compared to the control group (8 weeks; 1.91 ± 0.43 mm² vs. 5.1 ± 0.43 mm², P < 0.05). Mean SMC counts measured at 1 and 2 weeks after cutdown were significantly lower in the treatment group (2 weeks; 115 ± 22 vs. 62 ± 22). Paclitaxel was undetectable in systemic circulation (<10 ng/mL).

CONCLUSION

Sustained perivascular delivery of paclitaxel with fibrin glue was effective in inhibiting neointimal hyperplasia in rat jugular vein after open cutdown.

Graft Modification Strategies to Improve Patency of Prosthetic Arteriovenous Grafts for Hemodialysis

Prosthetic arteriovenous grafts (AVGs) are indicated for vascular access for long-term hemodialysis in patients in whom creation or maintenance of an arteriovenous fistula (AVF) has failed or is contraindicated. AVGs have an inferior long-term patency as compared to AVFs. To ameliorate patency rates of prosthetic AVGs, different strategies have emerged to improve graft materials. This review aims to describe current strategies and future perspectives on graft modification, by graft geometry, drug coatings and graft surface technology, to improve AVG patency.

Wearable devices for blood purification: principles, miniaturization, and technical challenges

The prevalences of end-stage renal disease (ESRD) and renal replacement therapy (RRT) continue to increase across the world imposing staggering costs on providers. Therefore, strategies to optimize the treatment and improve survival are of fundamental importance. Despite the benefits of daily dialysis, its implementation is difficult and wearable hemodialysis might represent an alternative by which frequent treatments can be delivered to ESRD patients with much less interference in their routines promoting better quality of life. The development of the wearable artificial kidney (WAK) requires incorporation of basic components of a dialysis system into a wearable device that allows mobility, miniaturization, and above all, patient-oriented management. The technical requirements necessary for WAK can be divided into the following broad categories: dialysis membranes, dialysis regeneration, vascular access, patient monitoring systems, and power sources. Pumping systems for blood and other fluids are the most critical components of the entire device.

Inhibitory effects of mesenchymal stem cells in intimal hyperplasia after balloon angioplasty

OBJECTIVE

Intimal hyperplasia is a major cause of restenosis after arterial bypass and balloon angioplasty. Induction of rapid re-endothelialization has been proposed to reduce intimal hyperplasia. The aim of this study was to evaluate the inhibitory effect of mesenchymal stem cells on intimal hyperplasia.

METHODS

Male New Zealand white rabbits were fed 1% cholesterol diets from 1 week before balloon angioplasty to the day of harvest. After dissection of rabbit carotid arteries, balloon angioplasty was performed with a 2F Fogarty embolectomy catheter. The injured carotid artery was coated with a mixture of 7 × 10(6) human umbilical cord mesenchymal stem cells (HUC-MSCs) and fibrin matrix. The carotid arteries were harvested 2, 4, and 8 weeks thereafter, and immunofluorescent staining and quantitative real-time polymerase chain reaction analysis were performed.

RESULTS

The intima/media ratio was significantly reduced in the group treated with HUC-MSCs compared with the nontreated group (Student t-tests, *P < .05). The area of re-endothelialization was significantly higher (Student t-tests, *P < .05) in the group treated with HUC-MSCs than in the nontreated group. Expression of angiogenic genes such as vascular endothelial growth factor, platelet-derived growth factor, kinase insert domain receptor 1, angiopoietin 1, and angio-associated migratory cell protein was increased (analysis of variance, P < .05) in the group treated with HUC-MSCs relative to the nontreated group.

CONCLUSIONS

Our study showed that HUC-MSCs reduce the formation of intimal hyperplasia through rapid re-endothelialization. This result might be applied to development of stem cell-coated stents as well as to development of a stem cell-containing sheet coat for inhibition of intimal hyperplasia after angioplasty or surgery.

Paclitaxel coating on the terminal portion of hemodialysis grafts effectively suppresses neointimal hyperplasia in a porcine model

OBJECTIVE

The local delivery of paclitaxel onto a graft has been reported to prevent neointimal hyperplasia. Because more than half of vascular stenoses occur within 3 cm of the venous anastomosis, this study tested the effectiveness of a paclitaxel coating restricted to both ends of the expanded polytetrafluoroethylene (ePTFE) graft to reduce the amount of drug delivered.

METHODS

Both ends of ePTFE grafts were coated with paclitaxel at a dose of 0.58 μg/mm(2); the total amount of paclitaxel per graft was 0.66 mg. Paclitaxel-coated hemodialysis grafts 15 cm in length were surgically implanted between the common carotid artery and external jugular vein in female Landrace pigs. The animals were sacrificed 6 weeks after graft placement. Cross sections of the anastomosis sites were analyzed histomorphometrically to measure the ratio of neointimal hyperplasia to the graft area (H/G ratio) and the percentage of luminal stenosis. The experimental results were compared between grafts coated with paclitaxel at the ends only (n = 8), grafts coated over the entire length (n = 6), and uncoated control grafts (n = 6).

RESULTS

The mean ± standard error values of the H/G ratios for the arterial anastomosis were 0.82 ± 0.13 (control), 0.41 ± 0.09 (terminal coating), and 0.21 ± 0.04 (whole coating). The values for the venous anastomosis were 0.82 ± 0.12 (control), 0.39 ± 0.11 (terminal coating), and 0.12 ± 0.03 (whole coating). Compared with the uncoated grafts, neointimal hyperplasia was suppressed effectively in the vascular grafts coated terminally with paclitaxel (artery, P = 050; vein, P < .001). However, the suppressive effect was less than that of grafts coated with paclitaxel over the entire length. The percentages of luminal stenosis showed similar tendency to the H/G ratios.

CONCLUSIONS

Despite a reduced amount of the drug, paclitaxel coating applied to both ends of the ePTFE hemodialysis grafts effectively suppressed neointimal hyperplasia at the sites of anastomosis.

Most important chronic complications of arteriovenous fistulas for hemodialysis

The aim of this review was to highlight the most important complications of arteriovenous fistulas (AVFs) for hemodialysis (HD). The quality of vascular access for HD should be suitable for repeated puncture and allow a high blood flow rate for high-efficiency dialysis with minimal complications. The dialysis staff must be well versed in manipulation of the AVF, and there should be a minimal need for corrective interventions. Construction of an AVF creates conditions for increasing the flow of blood through the venous system. Fulfillment of these conditions reduces the risk of turbulence and endothelium injury, which, in turn, minimizes the potential for stenosis. An AVF is closest to the ideal model of vascular access. The most important complications of fistulae for HD are lymphedema, infection, aneurysm, stenosis, congestive heart failure, steal syndrome, ischemic neuropathy and thrombosis. In HD patients, the most common cause of vascular access failure is neointimal hyperplasia. It is important to gain information about early clinical symptoms of AVF dysfunction in order to prevent and adequately treat potential complications.

Biological grafts for hemodialysis access: historical lessons, state-of-the-art and future directions

The vast majority of arteriovenous grafts (AVG) have been constructed using expanded polytetrafluoroethylene (ePTFE). While ePTFE grafts have the advantage of being relatively inexpensive and easy to manufacture, distribute, ship, and store, their primary patency rates are disappointing when compared with the native AVF. Though use of arteriovenous fistulas (AVF) in the United States has increased substantially, approximately 25% of hemodialysis patients continue to use AVG as their vascular access. We present here a comprehensive review of biological grafts and their use in hemodialysis vascular access. In this review, we discuss the use of synthetics and then explore the evolution of biological grafts over the past 20 years, their clinical impact, and future challenges in widespread clinical use in hemodialysis patients. Provided are in depth descriptions of currently used nonbiological arteriovenous grafts and the recent approaches in increasing the patency of synthetic grafts. Recent technological advances using tissue-engineered AVGs have shown promise for patients receiving hemodialysis and their potential to provide an attractive, viable option for vascular access have been discussed.

Microrough cobalt-chromium alloy surfaces for paclitaxel delivery: preparation, characterization, and in vitro drug release studies

Cobalt-chromium (Co-Cr) alloys have extensive biomedical applications including drug-eluting stents (DES). This study investigates the use of eight different microrough Co-Cr alloy surfaces for delivering paclitaxel (PAT) for potential use in DES. The eight different surfaces include four bare microrough and four self-assembled monolayer (SAM) coated microrough surfaces. The bare microrough surfaces were prepared by grit blasting Co-Cr with glass beads (50 and 100 μm in size) and Al(2)O(3) (50 and 110 μm). The SAM coated surfaces were prepared by depositing a -COOH terminated phosphonic acid monolayer on the different microrough surfaces. PAT was then deposited on all the bare and SAM coated microrough surfaces. The surfaces were characterized using scanning electron microscopy (SEM), 3D optical profilometry, and Fourier transform infrared spectroscopy (FTIR). SEM showed the different morphologies of microrough surfaces without and with PAT coating. An optical profiler showed the 3D topography of the different surfaces and the changes in surface roughness and surface area after SAM and PAT deposition. FTIR showed ordered SAMs were formed on glass bead grit blasted surfaces, while the molecules were disordered on Al(2)O(3) grit blasted surfaces. Also, FTIR showed the successful deposition of PAT on these surfaces. The PAT release was investigated for up to two weeks using high performance liquid chromatography. Al(2)O(3) grit blasted bare microrough surfaces showed sustained release profiles, while the glass bead grit blasted surfaces showed burst release profiles. All SAM coated surfaces showed biphasic drug release profiles, which is an initial burst release followed by a slow and sustained release. SAM coated Al(2)O(3) grit blasted surfaces prolonged the sustained release of PAT in a significant amount during the second week of drug elution studies, while this behavior was not observed for any other surfaces used in this study. Thus, this study demonstrates the use of different microrough Co-Cr alloy surfaces for delivering PAT for potential applications in DES and other medical devices.

[Early pathohistological changes in dysfunction of arteriovenous fistula for hemodialysis]

BACKGROUND

In hemodialysis patients the most common cause of vascular access failure is neointimal hyperplasia of vascular smooth muscle cells at the venous anastomosis of arteriovenous fistulas.

CASE REPORT

We presented a 76-year old patient who had developed fistula thrombosis without the presence of known risk factors the eighth day after the initial function. A histopathological finding pointed to a significant rate of neointimal proliferation, as an initial reasons for the fistula stenosis and trombosis.

CONCLUSION

Early pathohistological changes observed in arteriovenous fistula dysfunction are response to hemodynamic changed conditions.

Delivery of paclitaxel from cobalt-chromium alloy surfaces without polymeric carriers

Polymer-based carriers are commonly used to deliver drugs from stents. However, adverse responses to polymer coatings have raised serious concerns. This research is focused on delivering drugs from stents without using polymers or any carriers. Paclitaxel (PAT), an anti-restenotic drug, has strong adhesion towards a variety of material surfaces. In this study, we have utilized such natural adhesion property of PAT to attach these molecules directly to cobalt-chromium (Co-Cr) alloy, an ultra-thin stent strut material. Four different groups of drug coated specimens were prepared by directly adding PAT to Co-Cr alloy surfaces: Group-A (PAT coated, unheated, and ethanol cleaned); Group-B (PAT coated, heat treated, and ethanol cleaned); Group-C (PAT coated, unheated, and not ethanol cleaned); and Group-D (PAT coated, heat treated and not ethanol cleaned). In vitro drug release of these specimens was investigated using high performance liquid chromatography. Groups A and B showed sustained PAT release for up to 56 days. A simple ethanol cleaning procedure after PAT deposition can remove the loosely bound drug crystals from the alloy surfaces and thereby allowing the remaining strongly bound drug molecules to be released at a sustained rate. The heat treatment after PAT coating further improved the stability of PAT on Co-Cr alloy and allowed the drug to be delivered at a much slower rate, especially during the initial 7 days. The specimens which were not cleaned in ethanol, Groups C and D, showed burst release. PAT coated Co-Cr alloy specimens were thoroughly characterized using scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. These techniques were collectively useful in studying the morphology, distribution, and attachment of PAT molecules on Co-Cr alloy surfaces. Thus, this study suggests the potential for delivering paclitaxel from Co-Cr alloy surfaces without using any carriers.

Current advances in research and clinical applications of PLGA-based nanotechnology

Co-polymer poly(lactic-co-glycolic acid) (PLGA) nanotechnology has been developed for many years and has been approved by the US FDA for the use of drug delivery, diagnostics and other applications of clinical and basic science research, including cardiovascular disease, cancer, vaccine and tissue engineering. This article presents the more recent successes of applying PLGA-based nanotechnologies and tools in these medicine-related applications. It focuses on the possible mechanisms, diagnosis and treatment effects of PLGA preparations and devices. This updated information will benefit to both new and established research scientists and clinical physicians who are interested in the development and application of PLGA nanotechnology as new therapeutic and diagnostic strategies for many diseases.

Combining novel technologies with improved logistics to reduce hemodialysis vascular access dysfunction

Hemodialysis (HD) vascular access dysfunction is currently a huge clinical problem for which there are no effective therapies. There are, however, a number of promising technologies that are currently at the experimental or clinical trial stage. We believe that the application of these novel technologies in combination with better clinical protocols for vascular access care could significantly reduce the current problems associated with HD vascular access.

A Novel Technique for Loading of Paclitaxel-PLGA Nanoparticles onto ePTFE Vascular Grafts

The major cause of hemodialysis vascular access dysfunction (HVAD) is the occurrence of stenosis followed by thrombosis at venous anastomosis sites due to the aggressive development of venous neointimal hyperplasia. Local delivery of antiproliferative drugs may be effective in inhibiting hyperplasia without causing systemic side effects. We have previously demonstrated that paclitaxel-coated expanded poly(tetrafluoroethylene) (ePTFE) grafts, by a dipping method, could prevent neointimal hyperplasia and stenosis of arteriovenous (AV) hemodialysis grafts, especially at the graft-venous anastomoses; however, large quntities of initial burst release have remained a problem. To achieve controlled drug release, paclitaxel (Ptx)-loaded poly(lactic-co-glycolic acid) (PLGA) nanoparticles (Ptx-PLGA-NPs) were prepared by the emulsion-solvent evaporation method and then transferred to the luminal surface and inner part of ePTFE vascular grafts through our micro tube pumping and spin penetration techniques. Scanning electron microscope (SEM) images of various stages of Ptx-PLGA-NPs unequivocally showed that micro tube pumping followed by spin penetration effectively transferred Ptx-PLGA-NPs to the inner part, as well as the luminal surface, of an ePTFE graft. In addition, the in vitro release profiles of paclitaxel demonstrated that this new system achieved controlled drug delivery with a reduced initial burst release. These results suggest that loading of Ptx-PLGA-NPs to the luminal surface and the inner part of an ePTFE graft is a promising strategy to ultimately inhibit the development of venous neointimal hyperplasia.

Neointimal hyperplasia associated with synthetic hemodialysis grafts

Stenosis is a major cause of failure of hemodialysis vascular grafts and is primarily caused by neointimal hyperplasia (NH) at the anastomoses. The objective of this article is to provide a scientific review of the biology underlying this disorder and a critical review of the state-of-the-art investigational preventive strategies in order to stimulate further research in this exciting area. The histology of the NH shows myofibroblasts (that are probably derived from adventitial fibroblasts), extracellular matrices, pro-inflammatory cells including foreign-body giant cells, a variety of growth factors and cytokines, and neovasculature. The contributing factors of the pathogenesis of NH include surgical trauma, bioincompatibility of the synthetic graft, and the various mechanical stresses that result from luminal hypertension and compliance mismatch between the vessel wall and graft. These mechanical stimuli are focal in nature and may have a significant influence on the preferential localization of the NH. Novel mechanical graft designs and local drug delivery strategies show promise in animal models in preventing graft NH development. Successful prevention of graft stenosis would provide a superior alternative to the native fistula as hemodialysis vascular access.

Modified prosthetic vascular conduits

Atherosclerosis in the form of peripheral arterial disease results in significant morbidity. Surgical treatment options for peripheral arterial disease include angioplasty, endarterectomy, and bypass grafting. For bypass grafting, vein remains the conduit of choice; however, poor quality and limited availability have led to the use of prosthetic materials. Unfortunately, because of a lack of endothelium and compliance mismatch, neointimal hyperplasia develops aggressively, resulting in high failure rates. To improve graft patency, investigators have developed surgical, chemical, and biological graft modifications. This review describes common prosthetic materials, as well as approaches currently in use and under investigation to modify and improve prosthetic conduits for bypass grafting in an effort to improve graft patency rates.

Pathogenesis and local drug delivery for prevention of vascular access stenosis

A well-functioning vascular access is essential for hemodialysis in end-stage kidney disease patients. Synthetic grafts are more prone to the development of stenosis than native fistulas. Most of the stenosis is caused by neointimal hyperplasia localized at the outflow tract, which is perpetuated by continuous stimuli, such as blood flow disturbance, graft material bioincompatibility, and repeated needle puncture. Hyperplasia formation is also enhanced by the trauma of angioplasty. Recent work suggests that angiogenesis and the migration and proliferation of fibroblasts in the adventitia are important for the pathogenesis of neointimal hyperplasia. Therefore, the perivascular sustained delivery of antiproliferative drugs is a rational approach to inhibit hyperplasia associated with hemodialysis grafts. Because of the chronic nature of the stimuli, strategies that allow for the ready replenishment of the drug depot are preferable and are currently under development.

Coating with paclitaxel improves graft survival in a porcine model of haemodialysis graft stenosis

BACKGROUND

Most commonly resulting from intimal hyperplasia at the venous anastomosis, stenosis leading to thrombosis is a major cause of failure of polytetrafluoroethylene (PTFE) dialysis grafts. We recently reported that coating haemodialysis grafts with paclitaxel could reduce neointimal hyperplasia. This study tested whether paclitaxel-coating could prolong graft survival in a porcine model.

METHODS

PTFE grafts were double-coated with paclitaxel. Bilateral grafts were created between the carotid arteries and the external jugular veins, and we evaluated graft survival by weekly measurements of blood flow for 12 weeks.

RESULTS

We successfully implanted four pairs of paclitaxel-coated grafts and four pairs of control grafts in eight Landrace pigs. One control pig had to be euthanized at 4 weeks after graft placement. The grafts in the other three controls and four paclitaxel pigs survived until harvesting of the grafts. All paclitaxel-coated grafts remained patent for 12 weeks without decrease of blood flow. Median blood flow was 702 ml/min at three weeks and 818 ml/min at 12 weeks after placement. In contrast, the four control grafts lost luminal patency at 5, 6, 6 and 8 weeks, respectively. In Kaplan-Meier analysis, paclitaxel-coated grafts showed better survival than uncoated grafts (P = 0.011).

CONCLUSIONS

Double-coating with paclitaxel improved graft survival. Coated PTFE grafts may be effective for the prevention of graft failure in patients on haemodialysis.

Evaluation of histological techniques for quantifying haemodialysis arteriovenous (AV) graft hyperplasia

BACKGROUND

Assessing treatment efficacies for preventing haemodialysis arteriovenous (AV) graft stenosis requires a reproducible method for quantifying intimal hyperplasia. We identified sources of variability in three histological methods for assessing hyperplasia in a porcine AV graft model.

METHODS

Carotid-jugular synthetic grafts were placed in pigs. After explantation at 3-6 weeks, the tissue was stained with haematoxylin and eosin (H&E), Masson's trichrome or elastic tissue Van Gieson (EVG) stains and examined histologically. Hyperplasia at the anastomosis of 14 grafts was quantified using three different methods, each by four blinded observers. These methods were visual scoring, ratio of intima-to-media surface area (I/M ratio), and ratio of intra-graft hyperplasia to graft surface area (H/G ratio) at the graft-vessel interface.

RESULTS

The EVG stain proved superior in delineation of the elastic lamina yet quantification of the intimal and medial layers was still often difficult. This is illustrated by the greater inter-observer median coefficient of variances (CV) found using the I/M ratio method (intimal area CV=13.7%; medial area CV=32.7%; I/M ratio CV=44.0%) than with the H/G method (intra-graft hyperplasia area CV=7.3%, graft area CV=5.3%; H/G ratio CV=6.9%) or by visual scoring (CV=26.8%). The H/G ratios correlated positively with visual scores (r=0.941; P=0.0007; n=14) and the I/M ratio (r=0.719; P=0.0095; n=14). While hyperplasia was seen in both native vessel and graft lumen, in only one of the 14 anastomoses was the degree of hyperplasia greater in the native vessel than in the graft lumen, suggesting that the degree of hyperplasia occurring within the graft lumen predicted the total hyperplasia around the anastomosis.

CONCLUSIONS

The H/G method for assessing hyperplasia is preferred in a porcine model of AV graft because it is quantitative, less variable and does not require the delineation of the elastic lamina, although it infrequently underestimates the total hyperplasia that occurs.