New Insights into Dialysis Vascular Access: Molecular Targets in Arteriovenous Fistula and Arteriovenous Graft Failure and Their Potential to Improve Vascular Access Outcomes

Comparison between the 0- and 30-s balloon dilation time in percutaneous transluminal angioplasty for restenosed arteriovenous fistula among hemodialysis patients: a multicenter, prospective, randomized trial (CARP study)

BACKGROUND

This study aims to compare patency rates of the 0- and 30-s (sec) balloon dilation time in hemodialysis (HD) patients with restenosis after percutaneous transluminal angioplasty (PTA).

METHODS

The patients who underwent PTA within 6 months for failed arteriovenous fistula at the forearm were randomly assigned the 0-s or 30-s dilation time group. Effect of dilation time on the 3- and 6-month patency rates after PTA was examined.

RESULTS

Fifty patients were enrolled in this study. The 3-month patency rate in the 30-s dilation group was better than that in the 0-s dilation group (P = 0.0050), while the 6-month patency rates did not show a significant difference between the two groups (P = 0.28). Cox's proportional hazard model revealed that 30-s of inflation time (hazard ratio 0.027; P = 0.0072), diameter of the proximal (hazard ratio 0.32; P = 0.031), and dilation pressure (hazard ratio 0.63; P = 0.014) were associated with better 3-month patency. Dilation pressure between previous and present PTA did not differ in the 0-s (P = 0.15) and 30-s dilation groups (P = 0.16). The 6-month patency rate of the present PTA in the 30-s dilation group was higher than that of the previous PTA (P = 0.015). The visual analog scale did not differ between the two groups (P = 0.51).

CONCLUSION

The presenting data suggest that 30-s dilation potentially results in a better 3-month patency rate than 0-s dilation in HD patients with restenosis after PTA.

The predictive value of systemic immune-inflammation index for vascular access survival in chronic hemodialysis patients

Objective

To examine the prognostic values of systemic immune-inflammation indices of hemodialysis (HD) vascular access failure and develop a prediction model for vascular access failure based on the most pertinent systemic immune-inflammation index.

Study design

A prospective cohort study.

Setting & participants

Patients undergoing autogenous HD vascular access surgeries or arteriovenous graft as a permanent hemodialysis access in a tertiary center in southwest China from January 2020 to June 2022.

Predictors

Systemic immune-inflammation indices, including NLR, dNLR, AAPR, SIRI, SII, PNI, PLR, and LIPI, and clinical variables.

Outcomes

The outcome was defined as survival of the hemodialysis access, with both occluded and stenotic access being considered as instances of access failure.

Analytical approach

Cox proportional hazard regression model.

Results

2690 patients were included in the study population, of whom 658 experienced access failure during the follow-up period. The median duration of survival for HD vascular access was 18 months. The increased systemic immune-inflammation indices, including dNLR, NLR, SII, PNI, SIRI, PLR, and LIPI, are predictive of HD access failure, with SII demonstrating the strongest prognostic value. A simple SII-based prediction model for HD access failure was developed, achieving C-indexes of 0.6314 (95% CI: 0.6249 - 0.6589) and 0.6441 (95% CI: 0.6212 - 0.6670) for predicting 6- and 12-month access survival, respectively.

Conclusions

Systemic immune-inflammation indices are significantly and negatively associated with HD vascular access survival. A simple SII-based prediction model was developed and anticipates further improvement through larger study cohort and validation from diverse centers.

Regulation of vascular remodeling by immune microenvironment after the establishment of autologous arteriovenous fistula in ESRD patients

Autogenous arteriovenous fistula (AVF) is the preferred dialysis access for receiving hemodialysis treatment in end-stage renal disease patients. After AVF is established, vascular remodeling occurs in order to adapt to hemodynamic changes. Uremia toxins, surgical injury, blood flow changes and other factors can induce inflammatory response, immune microenvironment changes, and play an important role in the maintenance of AVF vascular remodeling. This process involves the infiltration of pro-inflammatory and anti-inflammatory immune cells and the secretion of cytokines. Pro-inflammatory and anti-inflammatory immune cells include neutrophil (NEUT), dendritic cell (DC), T lymphocyte, macrophage (Mφ), etc. This article reviews the latest research progress and focuses on the role of immune microenvironment changes in vascular remodeling of AVF, in order to provide a new theoretical basis for the prevention and treatment of AVF failure.

LncRNA-LncDACH1 mediated phenotypic switching of smooth muscle cells during neointimal hyperplasia in male arteriovenous fistulas

Arteriovenous fistulas (AVFs) are the most common vascular access points for hemodialysis (HD), but they have a high incidence of postoperative dysfunction, mainly due to excessive neointimal hyperplasia (NIH). Our previous studies have revealed a highly conserved LncRNA-LncDACH1 as an important regulator of cardiomyocyte and fibroblast proliferation. Herein, we find that LncDACH1 regulates NIH in AVF in male mice with conditional knockout of smooth muscle cell-specific LncDACH1 and in male mice model of AVF with LncDACH1 overexpression by adeno-associated virus. Mechanistically, silence of LncDACH1 activates p-AKT through promoting the expression of heat shock protein 90 (HSP90) and serine/arginine-rich splicing factor protein kinase 1 (SRPK1). Moreover, LncDACH1 is transcriptionally activated by transcription factor KLF9 that binds directly to the promoter region of the LncDACH1 gene. In this work, during AVF NIH, LncDACH1 is downregulated by KLF9 and promotes NIH through the HSP90/ SRPK1/ AKT signaling axis.

Differential expression of serum TM, PAF, and CD62P in patients with autologous arteriovenous fistula and the correlation with vascular access function

BACKGROUND

End-stage renal disease (ESRD) is the final stage of chronic kidney disease (CKD).

AIMS

We aimed to analyze the expression differences of serum thrombomodulin (TM), platelet-activating factor (PAF), and P-selectin (CD62P) in patients with autologous arteriovenous fistula (AVF) and the correlation with vascular access function.

METHODS

The case data were retrospectively analyzed. Moreover, 160 patients with AVF maintenance hemodialysis were selected as the AVF group, and 150 healthy participants were selected as the healthy control group. According to the function of vascular access, patients in the AVF group were divided into Group A (n = 50, after the first establishment of AVF), Group B (n = 64, normal vascular access function after hemodialysis treatment), and Group C (n = 46, vascular access failure). Pearson analysis was conducted to explore the correlation between serum TM, PAF, CD62P content, and vascular pathological examination indicators, to evaluate the value of TM, PAF, and CD62P levels in predicting vascular access failure in patients with AVF.

RESULTS AND DISCUSSION

The serum levels of TM, PAF, and CD62P were positively correlated with the expressions of CD68 and MCP-1, respectively (p < .001). Serum TM was positively correlated with the levels of PAF and CD62P (p < .001), and PAF was positively correlated with the levels of CD62P (p < .001), respectively. Serum levels of TM, PAF and CD62P were risk factors for vascular access failure in AVF patients (p < .05). The area under the curve of serum TM, PAF and CD62P levels in predicting vascular access failure in AVF patients was 0.879.

CONCLUSION

The serum levels of TM, PAF, and CD62P in AVF patients were correlated with the vascular access function of AVF patients, which was very important for maintaining the stability of vascular access function, and had certain value in predicting vascular access failure/disorder in AVF patients, and could be popularized and applied.

Sirolimus-coated balloon angioplasty in maintaining the patency of thrombosed arteriovenous graft: 1-year results of a prospective study

BACKGROUND

A prospective, pilot study was designed to test the feasibility of using sirolimus-coated balloon (SCB) to treat graft vein junction of thrombosed arteriovenous graft (AVG) following successful pharmacomechanical thrombectomy. The present report provides the 1-year results of this study.

METHODS

This is a 1-year follow-up of a single, prospective, single-arm study that was conducted from 2018 to 2019 in 20 patients who presented to a tertiary institution with thrombosed AVG. The recruited patients received SCB angioplasty at the graft-vein junction following successful endovascular thrombectomy of a thrombosed AVG. One year after recruitment, there were three deaths, one AVG revision, and one AVG explantation among the participants recruited. The outcomes of 15 subjects at 1-year following the index procedure obtained from electronic medical records were re-examined.

RESULTS

The 1-year access circuit primary patency rate was 40%, while assisted primary and secondary patency rates were 46.7% and 73.3%, respectively. A total of 16 interventions (4 angioplasties, 12 thrombectomies) were performed in 9 patients over the 12 months. Four AVGs were abandoned. The median number of interventions per patient was 1 (0-3) per year. Using Kaplan-Meier analysis, the mean estimated post-intervention access circuit primary patency was 230 (95% CI: 162-300) days, while access circuit assisted primary patency was 253 (95% CI: 187-320) days, and access circuit secondary patency was 292 (95% CI: 230-356) days. Sub-group analysis did not show a significant difference in the mean estimated primary patency between AVG with de novo and recurrent stenosis (245 days, 95% CI: 151-339 vs 210 days, 95% CI: 113-307; p = 0.29).

CONCLUSIONS

SCB may help sustain the patency of thrombosed AVG following successful thrombectomy.

IN.PACT AV Access Randomized Trial of Drug-Coated Balloons for Dysfunctional Arteriovenous Fistulae: Clinical Outcomes through 36 Months

PURPOSE

To present the 36-month outcomes of the prospective randomized IN.PACT AV Access study of participants with obstructive de novo or restenotic native upper extremity arteriovenous dialysis fistula lesions treated with drug-coated balloon (DCBs) or standard percutaneous transluminal angioplasty (PTA) following successful high-pressure PTA.

MATERIALS AND METHODS

Participants at 29 international sites were randomized 1:1 to receive an IN.PACT AV DCB (n = 170) or undergo PTA (n = 160). The outcomes through 36 months included target lesion primary patency (TLPP) and access circuit primary patency (ACPP) (composites of clinically driven target lesion or access circuit revascularization and/or access circuit thrombosis), number of reinterventions, and serious adverse events involving the access circuit.

RESULTS

TLPP was 52.1% in the DCB group compared with 36.7% in the PTA group through 24 months and 43.1% in the DCB group compared with 28.6% in the PTA group through 36 months (both log-rank P < .001). ACPP was 39.4% in the DCB group compared with 25.3% in the PTA group through 24 months and 26.4% in the DCB group compared with 16.6% in the PTA group through 36 months (both log-rank P < .001). Cumulative incidence of access circuit thrombosis through 36 months was 8.2% in the DCB group compared with 18.3% in the PTA group (log-rank P = .040). Cumulative incidence of mortality through 36 months was 26.6% in the DCB group compared with 30.8% in the PTA group (log-rank P = .71).

CONCLUSIONS

This study demonstrated superior TLPP and ACPP with DCBs compared with PTA, with no difference in mortality through 3 years. Access circuit thrombosis was statistically significantly higher in the PTA group at 3 years.

Hemodynamics in AVF over time: A protective role of vascular remodeling toward flow stabilization

The mechanisms underlying vascular stenosis formation in the arteriovenous fistula (AVF) for hemodialysis (HD) remain mostly unknown. Several computational fluid dynamics (CFD) studies have suggested a potential role for unsteady flow in inducing intimal hyperplasia and AVF stenosis, but the majority of these observations have been limited to a single time point after surgical creation. The aim of the present study was to investigate the relation between hemodynamic conditions and AVF vascular remodeling through a CFD longitudinal study. Non contrast-enhanced MR images and Doppler Ultrasound (US) examinations were acquired at 3 days, 40 days, 6 months, 1 year, and 1.5 years after surgery in a 72-year male referred for native radio-cephalic AVF. Three-dimensional AVF models were generated and high fidelity CFD simulations were performed using pimpleFoam, setting patient-specific boundary conditions derived from US. Morphological and hemodynamic changes over time were then analyzed. Analysis of vessel morphology and hemodynamics during follow-up showed that the AVF had a successful maturation process, characterized by a massive arterial and venous dilatation within the 6 months after surgery, a corresponding increase in blood flow volume and important flow instabilities. Between 6 months and 1 year, a stenosis developed in the juxta-anastomotic vein and caused AVF failure at 1.5 years. The development of stenosis was paralleled by the regularization of blood flow velocity pattern and consequent decrease in the near-wall disturbed flow metrics. These results suggest that development of intimal hyperplasia and vessel stenosis, triggered by unsteady flow, could be the result of vascular inward remodeling toward regularization of turbulent-like flow.

Bioresorbable Mesenchymal Stem Cell-Loaded Electrospun Polymeric Scaffold Inhibits Neointimal Hyperplasia Following Arteriovenous Fistula Formation in a Rat Model of Chronic Kidney Disease

Bioresorbable perivascular scaffolds loaded with antiproliferative agents have been shown to enhance arteriovenous fistula (AVF) maturation by inhibiting neointimal hyperplasia (NIH). These scaffolds, which can mimic the three-dimensional architecture of the vascular extracellular matrix, also have an untapped potential for the local delivery of cell therapies against NIH. Hence, an electrospun perivascular scaffold from polycaprolactone (PCL) to support mesenchymal stem cell (MSC) attachment and gradual elution at the AVF's outflow vein is fabricated. Chronic kidney disease (CKD) in Sprague-Dawley rats is induced by performing 5/6th nephrectomy, then AVFs for scaffold application are created. The following groups of CKD rats are compared: no perivascular scaffold (i.e., control), PCL alone, and PCL+MSC scaffold. PCL and PCL+MSC significantly improve ultrasonographic (i.e., luminal diameter, wall-to-lumen ratio, and flow rate) and histologic (i.e., neointima-to-lumen ratio, neointima-to-media ratio) parameters compared to control, with PCL+MSC demonstrating further improvement in these parameters compared to PCL alone. Moreover, only PCL+MSC significantly reduces 18 F-fluorodeoxyglucose uptake on positron emission tomography. These findings suggest that adding MSCs promotes greater luminal expansion and potentially reduces the inflammatory process underlying NIH. The results demonstrate the utility of mechanical support loaded with MSCs at the outflow vein immediately after AVF formation to support maturation by minimizing NIH.

Effect of far-infrared therapy device on arteriovenous fistula maturation and lifespan in hemodialysis patients: a randomized controlled clinical trial

Introduction

Arteriovenous fistula (AVF) is the first choice of vascular access for hemodialysis treatment, and its surgical maturity rate is not high, and its postoperative complications (mostly stenosis) significantly shorten its life. At present, there are few studies on treatment methods to improve the maturity and survival of AVF. In this study, the effect of far infrared therapy (FIR) on the maturity and longevity of arteriovenous fistula in hemodialysis patients was discussed, and the protective mechanism of AVF induced by FIR therapy was explored, aiming at exploring a new treatment method.

Methods

The hemodialysis patients admitted to the 900th Hospital of the Chinese Joint Logistics Support Force of the People's Liberation Army from January 2021 to April 2023 were randomly divided into control group and intervention group, with 40 cases in each group. Among them, the control group was coated with mucopolysaccharide polysulfonate cream; Intervention group: The patients were treated with mucopolysaccharide polysulfonate cream and far infrared radiation at the same time. After 3 months' intervention, the arteriovenous fistula (vein diameter, mature time of arteriovenous fistula, blood flow controlled by pump during dialysis, blood flow of brachial artery during dialysis and the occurrence of complications of internal fistula (oozing, occlusion and infection) and the pain score (numerical rating scale, NRS) of the two groups were compared, and the curative effects were compared.

Results

There was no significant difference in general data between the two groups (P > 0.05), which indicated that the study was comparable. After 3 months' intervention, the vein diameter, pump-controlled blood flow and brachial artery blood flow in the intervention group were significantly higher than those in the control group (P < 0.05). And the maturity time, NRS score and complication rate of arteriovenous fistula were significantly lower than those of the control group (P < 0.05). The primary patency rate of AVF in the intervention group was higher than that in the control group, and the overall patency rate between the two groups was statistically significant (P < 0.05).

Conclusions

As a promising new treatment method, far infrared therapy can effectively promote the maturity of AVF, increase venous diameter, pump controlled blood flow during dialysis, brachial artery blood flow during dialysis, and prolong the service life of AVF.

Gold Nanoparticles for Monitoring of Mesenchymal Stem-Cell-Loaded Bioresorbable Polymeric Wraps for Arteriovenous Fistula Maturation

Mesenchymal stem cell (MSC)-seeded polymeric perivascular wraps have been shown to enhance arteriovenous fistula (AVF) maturation. However, the wraps' radiolucency makes their placement and integrity difficult to monitor. Through electrospinning, we infused gold nanoparticles (AuNPs) into polycaprolactone (PCL) wraps to improve their radiopacity and tested whether infusion affects the previously reported beneficial effects of the wraps on the AVF's outflow vein. Sprague Dawley rat MSCs were seeded on the surface of the wraps. We then compared the effects of five AVF treatments-no perivascular wrap (i.e., control), PCL wrap, PCL + MSC wrap, PCL-Au wrap, and PCL-Au + MSC wrap-on AVF maturation in a Sprague Dawley rat model of chronic kidney disease (n = 3 per group). Via micro-CT, AuNP-infused wraps demonstrated a significantly higher radiopacity compared to that of the wraps without AuNPs. Wraps with and without AuNPs equally reduced vascular stenoses, as seen via ultrasonography and histomorphometry. In the immunofluorescence analysis, representative MSC-seeded wraps demonstrated reduced neointimal staining for markers of infiltration with smooth muscle cells (α-SMA), inflammatory cells (CD45), and fibroblasts (vimentin) compared to that of the control and wraps without MSCs. In conclusion, AuNP infusion allows in vivo monitoring via micro-CT of MSC-seeded polymeric wraps over time, without compromising the benefits of the wrap for AVF maturation.

Gold Nanoparticles for Monitoring of Mesenchymal Stem Cell-Loaded Bioresorbable Polymeric Wraps for Arteriovenous Fistulas

Background

To address high rates of arteriovenous fistula (AVF) failure, a mesenchymal stem cell (MSC)-seeded polymeric perivascular wrap has been developed to reduce neointimal hyperplasia (NIH) and enhance AVF maturation in a rat model. However, the wrap's radiolucency makes its placement and integrity difficult to monitor.

Purpose

In this study, we infused gold nanoparticles (AuNPs) into the polymeric perivascular wrap to improve its radiopacity and tested the effect of infusion on the previously reported beneficial effects of the polymeric wrap on the AVF outflow vein.

Materials and Methods

We fabricated a polymeric perivascular wrap made of polycaprolactone (PCL) infused with AuNPs via electrospinning. Sprague-Dawley rat mesenchymal stem cells (MSCs) were seeded on the surface of the wraps. We then compared the effect of five AVF treatments-no perivascular wrap (i.e., control), PCL wrap, PCL+MSC wrap, PCL-Au wrap, and PCL-Au+MSC wrap-on AVF maturation in a Sprague-Dawley rat model of chronic kidney disease (n=3 per group). Statistical significance was defined as p<.05, and one-way analysis of variance was performed using GraphPad Prism software.

Results

On micro-CT, AuNP-infused wraps demonstrated significantly higher radiopacity compared to wraps without AuNPs. On ultrasonography, wraps with and without AuNPs equally reduced the wall-to-lumen ratio of the outflow vein, a marker of vascular stenosis. On histomorphometric analysis, wraps with and without AuNPs equally reduced the neointima-to- lumen ratio of the outflow vein, a measure of NIH. On immunofluorescence analysis, representative MSC-seeded wraps demonstrated reduced neointimal staining for markers of smooth muscle cells (α-SMA), inflammatory cells (CD45), and fibroblasts (vimentin) infiltration when compared to control and wraps without MSCs.

Conclusion

Gold nanoparticle infusion allows the in vivo monitoring via micro-CT of a mesenchymal stem cell-seeded polymeric wrap over time without compromising the benefits of the wrap on arteriovenous fistula maturation.

Summary Statement

Gold nanoparticle infusion enables in vivo monitoring via micro-CT of the placement and integrity over time of mesenchymal stem cell-seeded polymeric wrap supporting arteriovenous fistula maturation.

Key Results

Gold nanoparticle (AuNP)-infused perivascular wraps demonstrated higher radiopacity on micro-CT compared with wraps without AuNPs after 8 weeks.AuNP-infused perivascular wraps equally improved the wall-to-lumen ratio of the outflow vein (a marker of vascular stenosis) when compared with wraps without AuNPs, as seen on US.AuNP-infused perivascular wraps equally reduced the neointima-to-lumen ratio of the outflow vein (a measure of neointimal hyperplasia) when compared with wraps without AuNPs, as seen on histomorphometry.

Sex Differences in Arteriovenous Fistula Failure: Insights from Bioinformatics Analysis

(1) Background: Arteriovenous fistulas (AVFs) are the preferred access for hemodialysis. Unfortunately, about 60% of patients, especially female patients, fail to receive normal dialysis within one year after surgery because of AVF failure. However, the underlying mechanisms caused by sex differences in AVF failure remain unclear. (2) Methods: We performed analysis of DEGs and functional analysis with the dataset GSE119296 to reveal the biology underlying AVF failure. Immune responses were calculated using CIBERSORT. A protein-protein interaction network and hub gene were constructed using STRING and stepwise identification of potential drugs was performed online. (3) Results: Functional analysis showed that extracellular matrix reprogramming and PI3K-AKT pathway enrichment were significant in both male and female patients. COL1A1 was the hub gene in male patients, whereas CDK1 was the hub gene in female patients. Immune responses including γδ-T cells and mast cells are activated in female patients while no significant differences were noted in the male group. (4) Conclusions: In this study, we used a series of mature and recognized bioinformatic strategies to determine the following items: (1) Reveal the pathogenesis of AVF failure through HUB genes and signaling pathways between the different sexes. (2) Determine the relationship between sex differences in AVF failure and immune abnormalities. (3) Search for relevant sex-specific drugs targeting AVF failure.

Localized Perivascular Therapeutic Approaches to Inhibit Venous Neointimal Hyperplasia in Arteriovenous Fistula Access for Hemodialysis Use

An arteriovenous fistula (AVF) is the preferred vascular access for chronic hemodialysis, but high failure rates restrict its use. Optimizing patients' perioperative status and the surgical technique, among other methods for preventing primary AVF failure, continue to fall short in lowering failure rates in clinical practice. One of the predominant causes of AVF failure is neointimal hyperplasia (NIH), a process that results from the synergistic effects of inflammation, hypoxia, and hemodynamic shear stress on vascular tissue. Although several systemic therapies have aimed at suppressing NIH, none has shown a clear benefit towards this goal. Localized therapeutic approaches may improve rates of AVF maturation by providing direct structural and functional support to the maturating fistula, as well as by delivering higher doses of pharmacologic agents while avoiding the adverse effects associated with systemic administration of therapeutic agents. Novel materials-such as polymeric scaffolds and nanoparticles-have enabled the development of different perivascular therapies, such as supportive mechanical devices, targeted drug delivery, and cell-based therapeutics. In this review, we summarize various perivascular therapeutic approaches, available data on their effectiveness, and the outlook for localized therapies targeting NIH in the setting of AVF for hemodialysis use. Highlights: Most systemic therapies do not improve AVF patency outcomes; therefore, localized therapeutic approaches may be beneficial. Locally delivered drugs and medical devices may improve AVF patency outcomes by providing biological and mechanical support. Cell-based therapies have shown promise in suppressing NIH by delivering a more extensive array of bioactive substances in response to the biochemical changes in the AVF microenvironment.

Endovascular Management of Thrombosed Dialysis Vascular Circuits

A functional hemodialysis vascular access is the lifeline for patients with end-stage kidney disease and is considered a major determinant of survival and quality of life in this patient population. Hemodialysis therapy can be performed via arteriovenous fistulas, arteriovenous grafts, and central venous catheters (CVCs). Following dialysis vascular access creation, the interplay between several pathologic mechanisms can lead to vascular luminal obstruction due to neointimal hyperplasia with subsequent stenosis, stasis, and eventually access thrombosis. Restoration of the blood flow in the vascular access circuit via thrombectomy is crucial to avoid the use of CVCs and to prolong the life span of the vascular access conduits. The fundamental principles of thrombectomy center around removing the thrombus from the thrombosed access and treating the underlying culprit vascular stenosis. Several endovascular devices have been utilized to perform mechanical thrombectomy and have shown comparable outcomes. Standard angioplasty balloons remain the cornerstone for the treatment of stenotic vascular lesions. The utility of drug-coated balloons in dialysis vascular access remains unsettled due to conflicting results from randomized clinical trials. Stent grafts are used to treat resistant and recurrent stenotic lesions and to control extravasation from a ruptured vessel that is not controlled by conservative measures. Overall, endovascular thrombectomy is the preferred modality of treatment for the thrombosed dialysis vascular conduits.

Nitric oxide releasing nanomatrix gel treatment inhibits venous intimal hyperplasia and improves vascular remodeling in a rodent arteriovenous fistula

Vascular access is the lifeline for hemodialysis patients and the single most important component of the hemodialysis procedure. Arteriovenous fistula (AVF) is the preferred vascular access for hemodialysis patients, but nearly 60% of AVFs created fail to successfully mature due to early intimal hyperplasia development and poor outward remodeling. There are currently no therapies available to prevent AVF maturation failure. First, we showed the important regulatory role of nitric oxide (NO) on AVF development by demonstrating that intimal hyperplasia development was reduced in an overexpressed endothelial nitric oxide synthase (NOS3) mouse AVF model. This supported the rationale for the potential application of NO to the AVF. Thus, we developed a self-assembled NO releasing nanomatrix gel and applied it perivascularly at the arteriovenous anastomosis immediately following rat AVF creation to investigate its therapeutic effect on AVF development. We demonstrated that the NO releasing nanomatrix gel inhibited intimal hyperplasia formation (more than 70% reduction), as well as improved vascular outward remodeling (increased vein diameter) and hemodynamic adaptation (lower wall shear stress approaching the preoperative level and less vorticity). Therefore, direct application of the NO releasing nanomatrix gel to the AVF anastomosis immediately following AVF creation may enhance AVF development, thereby providing long-term and durable vascular access for hemodialysis.

A modified no-touch technique for anastomosis to create a radiocephalic arteriovenous fistula

The application of a no-touch technique to create an autologous radiocephalic arteriovenous fistula might improve the patency rate. In the present report, we have expanded the concept of the no-touch technique by introducing a modified no-touch technique in which we preserve the perivenous vascular tissue, followed by a functional end-to-side anastomosis to create a radiocephalic arteriovenous fistula with early maturation for hemodialysis.

Inhibition of MAD2B alleviates venous neointimal formation by suppressing VSMCs proliferation and migration

The proliferation and migration of vascular smooth muscle cells (VSMCs) are essential events in venous neointimal hyperplasia (VNH), a culprit of arteriovenous fistula (AVF) malfunction. Mitotic arrest-deficient protein 2B (MAD2B) is a critical regulator of cell proliferation and differentiation in many scenarios. To address the role of MAD2B in VSMCs proliferation and migration during VNH, AVFs from patients with end-stage renal disease (ESRD) and chronic kidney disease (CKD) mice were used to evaluate MAD2B expression. In cultured VSMCs treated with platelet-derived growth factor-BB (PDGF-BB), the effect of MAD2B on VSMCs proliferation and migration was detected by cell counting kit-8 (CCK8) assay, immunofluorescence, wound-healing scratch and transwell assays. Besides, we exploited different small interfering RNAs (siRNAs) to explore the potential mechanisms in the issue. Furthermore, rapamycin was applied to reveal whether MAD2B-associated pathways were involved in its inhibitory effect on VSMCs proliferation and migration. Accordingly, we found that MAD2B expression was enhanced in AVFs from patients with ESRD, CKD mice and VSMCs stimulated by PDGF-BB. Meanwhile, inhibition of MAD2B alleviated VSMCs proliferation and migration while the number of ski-related novel gene (SnoN)-positive VSMCs was also increased in vivo and in vitro. Moreover, gene deletion of MAD2B decreased the level of SnoN protein in PDGF-BB-stimulated VSMCs. Furthermore, rapamycin suppressed the increased expressions of MAD2B and SnoN induced by PDGF-BB. Thus, our study demonstrates that inhibition of MAD2B suppresses the proliferation and migration of VSMCs during VNH via reducing SnoN expression. Moreover, rapamycin exerts an inhibitory effect on intimal hyperplasia, possibly via the MAD2B-SnoN axis.

Effect of far infrared therapy on arteriovenous fistula maturation, survival and stenosis in hemodialysis patients, a randomized, controlled clinical trial: the FAITH on fistula trial

BACKGROUND

An arteriovenous fistula (AVF) is the preferred vascular access for hemodialysis treatment. After creation many of the AVFs will never mature or if functioning will need an intervention within 1 year due to an AVF stenosis. Studies investigating possible therapies that improves the AVF maturation and survival are scarce. Far infrared therapy (FIR) has shown promising results. In minor single centre and industry supported trials FIR has shown improved AVF maturation and survival. There is a need of a randomized multicentre controlled trial to examine the effect of FIR on the AVF maturation and survival and to explore the possible AVF protective mechanism induced by the FIR treatment.

METHODS

This investigator initiated, randomized, controlled, open-labeled, multicenter clinical trial will examine the effect of FIR on AVF maturation in patients with a newly created AVF (incident) and AVF patency rate after 1 year of treatment in patients with an existing AVF (prevalent) compared to a control group. The intervention group will receive FIR to the skin above their AVF three times a week for 1 year. The control group will be observed without any treatment. The primary outcome for incident AVFs is the time from surgically creation of the AVF to successful cannulation. The primary outcome for the prevalent AVFs is the difference in number of AVFs without intervention and still functioning in the treatment and control group after 12 months. Furthermore, the acute changes in inflammatory and vasodilating factors during FIR will be explored. Arterial stiffness as a marker of long term AVF patency will also be examined.

DISCUSSION

FIR is a promising new treatment modality that may potentially lead to improved AVF maturation and survival. This randomized controlled open-labelled trial will investigate the effect of FIR and its possible mechanisms.

TRIAL REGISTRATION

Clinicaltrialsgov NCT04011072 (7th of July 2019).

The Role of Oxidative Stress Markers in Predicting Acute Thrombotic Occlusion of Haemodialysis Vascular Access and Progressive Stenotic Dysfunction Demanding Angioplasty

Haemodialysis vascular access (VA) dysfunction is a major cause of morbidity in haemodialysis (HD) patients. Primary venous outflow occlusion and restenosis after percutaneous transluminal angioplasty (PTA) are two major obstacles for the long-term use of dialysis VA. It remains unclear whether oxidative stress markers can be used as predictors for thrombotic occlusion of VA and progressive stenosis dysfunction demanding PTA. All routine HD patients at one teaching hospital participated in this study including ankle-brachial index (ABI) examinations and serum oxidative stress markers. The serum oxidative stress markers (high-sensitivity C-reactive protein (hs-CRP), matrix metalloproteinase-2 (MMP-2), MMP-9, homocysteine, asymmetrical dimethylarginine (ADMA), nitrate oxidase (NO), tumour necrosis factor-α (TNF-α), monocyte chemotactic protein 1 (MCP-1), interleukin-1β (IL-1β), and transforming growth factor-β (TGF-β)) were measured using immunosorbent assays in 159 HD patients (83 men and 76 women; mean age: 65 ± 12 years). The participants met the following criteria: (1) received regular HD treatment for at least 6 months, without clinical evidence of acute or chronic inflammation, recent myocardial infarction, unstable angina or circulatory congestion; and (2) received an arteriovenous fistula (AVF)/arteriovenous graft (AVG: polytetrafluoroethylene, PTFE) as the current VA for more than 6 months, without interventions within the last 6 months. All the participants were followed up clinically for up to 12 months to estimate the amount of primary thrombotic occlusion and VA dysfunction demanding PTA. During the 12-month observation, 24 patients (15.1%) had primary thrombotic occlusion of VAs. Another 24 patients (15.1%) required PTA because of clinical dysfunction of access. Additionally, during the follow-up period, restenosis occurred in 12 patients (50% of 24 patients). The access types of arteriovenous grafts (AVGs) and a diagnosis of peripheral arterial occlusive disease (PAOD) were two strong predictors for acute thrombotic events of VA (hazard ratio (HR): 16.93 vs. 2.35; p < 0.001 vs. 0.047). Comparing dysfunctional with non-dysfunctional VAs, up to 27.7% of patients with high levels of ADMA (>0.6207 μM, N = 65) received required PTA compared with 4.4% of those with low levels (≤0.6207 μM; N = 90; p < 0.001). In multivariate analysis, the plasma baseline levels of ADMA independently conferred nearly 4.55 times the risk of primary stenotic dysfunction of HD VA (HR: 4.55; 95% confidence interval: 1.20 to 17.26; p = 0.026). In conclusion, our findings suggest the role of ADMA in the development of symptomatic VA dysfunction. Additionally, PAOD severity can be used in clinical practice to predict whether acute thrombotic occlusion of VA will easily occur in HD patients.

Hirudin prevents vascular endothelial cell apoptosis and permeability enhancement induced by the serum from rat with chronic renal failure through inhibiting RhoA/ROCK signaling pathway

Endothelial cells injury and activation contribute to arteriovenous fistula (AVF) stenosis. Hirudin (Hiru) can inhibit the activity of thrombin, which was reported to enhance endothelial cell permeability and promote vascular inflammatory responses. RhoA/ROCK signaling pathway is also important in regulating vascular endothelial permeability. This study aimed to investigate the role of Hiru on the viability and permeability of human umbilical vein endothelial cells (HUVECs) following stimulation of serum from rat with chronic renal failure (CRF) and illustrated the effects of Hiru on RhoA/ROCK signaling. Wistar rats were randomly divided into control group and CRF group. Serum from each group was collected to stimulate HUVECs. Proliferation capability was estimated with Cell Count Kit-8 (CCK-8) assay. Transwell assay was performed to determine permeability. Cell apoptosis was examined using Tunel staining. Telomere length and telomerase activity were determined by qPCR. Moreover, the expression of RhoA, ROCK1 and ROCK2 was estimated via western blot. Results showed that the serum from CRF rat significantly inhibited cell viability while enhanced cell permeability and apoptosis. Different concentrations of Hiru prevented the above effects caused by CRF serum. Additionally, Hiru recovered the CRF serum-induced decreased telomere length and telomerase activity. Hiru also inhibited the protein expression of RhoA, ROCK1 and ROCK2, which were activated by CRF serum. Moreover, the ROCK inhibitor, Y27632, exhibited similar effects with Hiru. In conclusion, Hiru-restored HUVECs cell viability, telomere length and telomerase activity, suppressed permeability and apoptosis in the presence of CRF serum might depend on inactivating the RhoA/ROCK signaling.

PDGFRA in vascular adventitial MSCs promotes neointima formation in arteriovenous fistula in chronic kidney disease

Chronic kidney disease (CKD) induces the failure of arteriovenous fistulas (AVFs) and promotes the differentiation of vascular adventitial GLI1-positive mesenchymal stem cells (GMCs). However, the roles of GMCs in forming neointima in AVFs remain unknown. GMCs isolated from CKD mice showed increased potential capacity of differentiation into myofibroblast-like cells. Increased activation of expression of PDGFRA and hedgehog (HH) signaling were detected in adventitial cells of AVFs from patients with end-stage kidney disease and CKD mice. PDGFRA was translocated and accumulated in early endosome when sonic hedgehog was overexpressed. In endosome, PDGFRA-mediated activation of TGFB1/SMAD signaling promoted the differentiation of GMCs into myofibroblasts, extracellular matrix deposition, and vascular fibrosis. These responses resulted in neointima formation and AVF failure. KO of Pdgfra or inhibition of HH signaling in GMCs suppressed the differentiation of GMCs into myofibroblasts. In vivo, specific KO of Pdgfra inhibited GMC activation and vascular fibrosis, resulting in suppression of neointima formation and improvement of AVF patency despite CKD. Our findings could yield strategies for maintaining AVF functions.

Different risk factors are associated with vascular access patency after construction and percutaneous transluminal angioplasty in patients starting hemodialysis

BACKGROUND

The objective of this multicenter, prospective observational study was to determine the factors related to patency rates after construction of vascular access (VA) and the first percutaneous transluminal angioplasty (PTA).

METHODS

The 24-month primary and secondary patency rates after construction of a radiocephalic arteriovenous fistula (RC-AVF) and arteriovenous graft (AVG) were evaluated using the Kaplan-Meier method and log-rank test. The 12-month post-PTA patency rate was also investigated. A Cox proportional hazard model was used to identify clinical parameters associated with the primary patency rate and the post-PTA patency rate.

RESULTS

A total of 611 patients were enrolled in the study. The primary patency rate after VA construction was lower in hemodialysis (HD) patients with an AVG than in those with an AVF. Aging (hazard ratio [HR], 1.02 per 1 year; p < 0.001), female sex (HR, 1.41; p = 0.03), diabetes mellitus (HR, 1.37; p = 0.03), low serum albumin (HR, 0.76 per 1-g/dL decrease; p = 0.02), and use of an erythropoietin-stimulating agent (HR, 1.62; p = 0.02) were risk factors for VA problems. The post-PTA patency rate was associated with aging (HR, 1.02; p < 0.001), diabetes mellitus (HR, 1.49; p = 0.02), polycystic kidney disease (HR, 2.14; p = 0.01), temporary catheter use for initiation of HD (HR, 1.60; p = 0.02), and period from VA construction to use (HR, 0.99; p = 0.04).

CONCLUSION

Although a poor patency rate is commonly associated with advanced age and diabetes, different risk factors affect patency between VA construction and the first PTA.

Heparin-bonded versus standard polytetrafluoroethylene arteriovenous grafts: A Bayesian perspective on a randomized controlled trial for comparative effectiveness

BACKGROUND

Heparin-bonded polytetrafluoroethylene grafts were marketed to improve hemodialysis access outcomes but are twice the cost of standard polytetrafluoroethylene. We launched a randomized trial of heparin-bonded polytetrafluoroethylene versus standard polytetrafluoroethylene for hemodialysis access to compare patency. Since the trial began, additional studies were published with heterogeneous findings. We performed an interim analysis by Bayesian methods using prior probability from meta-analysis of existing literature.

METHODS

NCT01601873 is a randomized, blinded trial of heparin-bonded polytetrafluoroethylene versus standard polytetrafluoroethylene for dialysis access at 5 sites. Planned sample size was 200 with 1-year primary patency as the primary endpoint. At interim analysis (50% of sample size at 1 year), we also performed a meta-analysis for 1-year primary patency with a random effects model to compute summary rate ratio and standard-error estimates. Meta-analysis estimates formed a prior probability for a Bayesian Cox regression model, and trial data were reanalyzed to develop posterior probability of heparin-bonded polytetrafluoroethylene effectiveness at our hypothesized effect size. Futility analysis was conducted using posterior probability estimates.

RESULTS

One hundred and five patients were enrolled at the time of interim analysis. One-year primary patency was 34.9% in the heparin-bonded-polytetrafluoroethylene group vs 32.7% in the standard-polytetrafluoroethylene group (P = .884). Summary rate ratio from the meta-analysis (1,209 patients) was 0.87 favoring heparin-bonded polytetrafluoroethylene (P = .33). Posterior hazard ratio from Cox regression was 0.90 (credible interval 0.70-1.13) favoring heparin-bonded polytetrafluoroethylene, which was not significant. Bayesian posterior probability of the a priori hypothesized 20% better patency with heparin-bonded polytetrafluoroethylene was 24%. Sample size to detect superiority with the small observed effect size would require about 3,800 subjects.

CONCLUSION

Current evidence does not demonstrate sufficiently large benefit of heparin-bonded polytetrafluoroethylene over standard polytetrafluoroethylene for dialysis access to justify higher cost. Given similar 1-year patency rates, a conclusive finding of superiority was judged to be infeasible, and the trial was stopped for futility.

Perspectives in Individualizing Solutions for Dialysis Access

The vascular access is the lifeline for the hemodialysis patient. Previous national vascular access guidelines have emphasized placement of arteriovenous fistulas in most hemodialysis patients. However, the new Kidney Disease Outcomes Quality Initiative guidelines for vascular access, soon to be published, will focus on a patient's end-stage kidney disease "life plan" and take a patient "first" approach. One of the major themes of the new Kidney Disease Outcomes Quality Initiative guidelines is selecting the "right access, for the right patient, at the right time, for the right reason". Given the availability of new advances in biomedical technologies, techniques, and devices in the vascular access field, this shift to a more patient-centered vascular access approach presents unique opportunities to individualize the solutions and care for patients requiring a dialysis vascular access. This review article will address 3 potential areas where there is an unmet need to individualize solutions for dialysis vascular access care: (1) biological approaches to improve vascular access selection and selection of therapies, (2) vascular access care for the post-transplant patient, and (3) vascular access disparities in race, gender, and the elderly patient.

Advances in Endovascular Salvage

Endovascular salvage plays an important role in dialysis access care. Angioplasty using standard high- and ultrahigh-pressure balloon is the mainstay of therapy, while the use of cutting balloons and balloons designed to deliver pharmacologically active agents to the site of recurrent stenosis is demonstrating improved performance for specific targets that have to be further defined. Stents and stent grafts are additional tools for use at access segments predisposed for inward remodeling such as the cephalic arch or basilic swing point. The juxta-anastomotic segment has particular relevance in maturation of autogenous accesses as well as maintenance of access flow volume. Depending on the location of the access in the forearm or upper arm, and which artery is feeding into the access vein, any type of balloon angioplasty and stent or stent graft placement may be used to establish and maintain patency. Successful management of dialysis access options relies on preservation of venous real estate during the chronic kidney disease phase of kidney disease as well as on knowledgeable evaluation of arm veins and the access by physical examination, bed side ultrasound, and angiographic studies.

Lack of PCSK6 Increases Flow-Mediated Outward Arterial Remodeling in Mice

Proprotein convertases (PCSKs) process matrix metalloproteases and cytokines, but their function in the vasculature is largely unknown. Previously, we demonstrated upregulation of PCSK6 in atherosclerotic plaques from symptomatic patients, localization to smooth muscle cells (SMCs) in the fibrous cap and positive correlations with inflammation, extracellular matrix remodeling and cytokines. Here, we hypothesize that PCSK6 could be involved in flow-mediated vascular remodeling and aim to evaluate its role in the physiology of this process using knockout mice. Pcsk6^−/− and wild type mice were randomized into control and increased blood flow groups and induced in the right common carotid artery (CCA) by ligation of the left CCA. The animals underwent repeated ultrasound biomicroscopy (UBM) examinations followed by euthanization with subsequent evaluation using wire myography, transmission electron microscopy or histology. The Pcsk6^−/− mice displayed a flow-mediated increase in lumen circumference over time, assessed with UBM. Wire myography revealed differences in the flow-mediated remodeling response detected as an increase in lumen circumference at optimal stretch with concomitant reduction in active tension. Furthermore, a flow-mediated reduction in expression of SMC contractile markers SMA, MYH11 and LMOD1 was seen in the Pcsk6^−/− media. Absence of PCSK6 increases outward remodeling and reduces medial contractility in response to increased blood flow.

Venous Mechanical Properties After Arteriovenous Fistulae in Mice

BACKGROUND

An arteriovenous fistula (AVF) exposes the outflow vein to arterial magnitudes and frequencies of blood pressure and flow, triggering molecular pathways that result in venous remodeling and AVF maturation. It is unknown, however, how venous remodeling, that is lumen dilation and wall thickening, affects venous mechanical properties. We hypothesized that a fistula is more compliant compared with a vein because of altered contributions of collagen and elastin to the mechanical properties.

METHODS

Ephb4^+/- and littermate wild-type (WT) male mice were treated with sham surgery or needle puncture to create an abdominal aortocaval fistulae. The thoracic inferior vena cava was harvested 3 wk postoperatively for mechanical testing and histological analyses of collagen and elastin.

RESULTS

Mechanical testing of the thoracic inferior vena cava from Ephb4^+/- and WT mice showed increased distensibility and increased compliance of downstream veins after AVF compared with sham. Although Ephb4^+/- veins were thicker than WT veins at the baseline, after AVF, both Ephb4^+/- and WT veins showed similar wall thickness as well as similar collagen and elastin area fractions, but increased collagen undulation compared with sham.

CONCLUSIONS

Fistula-induced remodeling of the outflow vein results in circumferentially increased distensibility and compliance, likely due to post-translational modifications to collagen.

Effect of sex differences in treatment response to angioplasty in a murine arteriovenous fistula model

Failure to mature and venous neointimal hyperplasia formation are the two major causes of hemodialysis arteriovenous fistula (AVF) vascular access failure. Percutaneous transluminal angioplasty (PTA) is the firstline treatment for both of these conditions, but, clinically, women have decreased patency rates compared with men. The hypothesis to be tested in the present study was that female mice after PTA of venous areas of higher intimal thickening have increased gene expression of transforming growth factor-β1 (TGF-β1) and TGF-β receptor 1 (TGFβ-R1) accompanied with histological changes of fibrosis compared with male mice. Seventeen male and eighteen female C57BL/6J mice were used in this study. Chronic kidney disease was induced by partial nephrectomy, and, 28 days later, an AVF was created to connect the left carotid artery to the right jugular vein. Two weeks later, the higher intimal thickening area was treated with PTA, and mice were euthanized 3 days later for gene expression analysis or 14 days later for histopathological analysis. Doppler ultrasound was performed weekly after AVF creation. At day 3, female AVF had significantly higher average gene expression of TGF-β1 and TGFβ-R1 compared with male AVF. At day 14, female outflow veins had a smaller venous diameter, lumen vessel area, decreased wall shear stress, lower average peak systolic velocity, and an increased neointima area-to-media area ratio. Moreover, female outflow veins showed a significant increase in α-smooth muscle actin and fibroblast-specific protein-1. There was a decrease in M1/M2 with an increase in CD68.

Effects of Caveolin-1-ERK1/2 pathway on endothelial cells and smooth muscle cells under shear stress

Hemodynamic forces have an important role in venous intimal hyperplasia, which is the main cause of arteriovenous fistula dysfunction. Endothelial cells (ECs) constantly exposed to the shear stress of blood flow, converted the mechanical stimuli into intracellular signals, and interacted with the underlying vascular smooth muscle cells (VSMCs). Caveolin-1 is one of the important mechanoreceptors on cytomembrane, which is related to vascular abnormalities. Extracellular signal-regulated kinase1/2 (ERK1/2) pathway is involved in the process of VSMCs proliferation and migration. In the present study, we explore the effects of Caveolin-1-ERK1/2 pathway and uremia toxins on the endothelial cells and VSMCs following shear stress application. Different shear stress was simulated with a ECs/VSMCs cocultured parallel-plate flow chamber system. Low shear stress and oscillating shear stress up-regulated the expression of fibroblast growth factor-4, platelet-derived growth factor-BB, vascular endothelial growth factor-A, ERK1/2 phosphorylation in endothelial cells, and proliferation and migration of VSMCs but down-regulated the Caveolin-1 expression in endothelial cells. Uremia toxin induces the proliferation and migration of VSMCs but not in a Caveolin-1-dependent manner in the static environment. Low shear stress-induced proliferation and migration of VSMCs is inhibited by Caveolin-1 overexpression and ERK1/2 suppression. Shear stress-regulated VSMC proliferation and migration is an endothelial cells-dependent process. Low shear stress and oscillating shear stress exert atherosclerotic influences on endothelial cells and VSMCs. Low shear stress modulated proliferation and migration of VSMCs through Caveolin-1-ERK1/2 pathway, which suggested that Caveolin-1 and ERK1/2 can be used as a new therapeutic target for the treatment of arteriovenous fistula dysfunction.

Impact statement

Venous intimal hyperplasia is the leading cause of arteriovenous fistula (AVF) dysfunction. This article reports that shear stress-regulated vascular smooth muscle cells (VSMCs) proliferation and migration is an endothelial cell (EC)-dependent process. Low shear stress (LSS) and oscillating shear stress (OSS) exert atherosclerotic influences on the ECs and VSMCs. LSS-induced proliferation and migration of VSMCs is inhibited by Caveolin-1 overexpression and extracellular signal-regulated kinase1/2 (ERK1/2) suppression, which suggested that Caveolin-1 and ERK1/2 can be used as a new therapeutic target for the treatment of AVF dysfunction.

The Effect of Aspirin on Preventing Vascular Access Dysfunction in Incident Hemodialysis Patients: A Prospective Cohort Study in Korean Clinical Research Centers for End-Stage Renal Disease (CRC for ESRD)

Background: Aspirin is often prescribed empirically to improve the patency of hemodialysis (HD) vascular access. Therefore, this study aimed to investigate the impact of aspirin on the survival of vascular access in incident HD patients with arteriovenous fistula (AVF) or arteriovenous graft (AVG). Methods: A prospective cohort of 881 incident HD patients was enrolled between 2009 and 2014. The primary outcome was defined as the first AVF/AVG intervention or salvage procedure, including percutaneous transluminal angioplasty or surgery for vascular access failure. Cox analyses were performed to determine the association between aspirin usage and the occurrence of the primary outcome. Results: The mean age of the patient group was 57.9 ± 13.4, and 63.8% of the patients were male. Aspirin was prescribed in 241 (27.4%) patients, and the median follow-up duration was 30 months. During follow-up, 180 (20.4%) patients experienced the primary outcome event. Univariate analysis showed that age, gender, presence of diabetes mellitus (DM), preexisting peripheral arterial disease, and the type of vascular access used (AVG versus AVF) were significantly associated with the development of the primary outcome. However, aspirin usage from the baseline was not significantly associated with primary outcome events (hazard ratio (HR): 1.16; 95% confidence interval (CI): 0.84–1.60; p = 0.378). Multivariate analysis showed that gender, the presence of DM, and the type of vascular access were still significantly associated with the occurrence of the primary outcome. Moreover, we did not observe the protective effect of taking aspirin on primary vascular access failure, even in subgroup analyses stratified according to gender, the presence of DM, and the type of vascular access. Conclusion: Physicians should carefully consider when they prescribe aspirin for the prevention of primary vascular access failure in Korean incident HD patients. In addition, larger prospective interventional studies are needed to elucidate the effect of aspirin on vascular access failure.

Intraoperative pneumatic tourniquet use may improve the clinical outcomes of arteriovenous fistula creations

OBJECTIVES

A major pathology affecting the usability of arteriovenous fistulas for hemodialysis is juxta-anastomosis stenosis. Intraoperative pneumatic tourniquet eliminates the use of vascular clamps, reduces vascular trauma, and may then reduce the juxta-anastomosis stenosis. The aim of this study was to compare the outcomes of arteriovenous fistula creations using the tourniquet-assisted approach versus the clamp-assisted approach.

METHODS

This retrospective study analyzed the outcomes of primary arteriovenous fistulas created by the lead author from 2008 to 2017 and met the specified inclusion criteria applied to both groups.

RESULTS

A total of 575 patients were included. Upon comparing the tourniquet group (n = 411) with the clamp group (n = 164): the primary arteriovenous fistula failure rate was significantly lower (2.4% vs 7.3%, p = 0.01); the percentage of arteriovenous fistula used for hemodialysis without initial interventions was significantly higher (71.5% vs 45.1%, p < 0.001) and with initial interventions was conversely lower (26.0% vs 47.6%, p < 0.001); the primary patency rate of the whole fistula conduits was significantly higher (44.2% vs 23.0% at 1 year, p < 0.001) and so was the cumulative patency rate (97.2% vs 92.6% at 1 year, p < 0.001); and the juxta-anastomosis primary patency rate (free of interventions for the juxta-anastomosis region) was higher (71.0% vs 47.8% at 1 year, p < 0.001). Based on multivariate Cox proportional hazards regression analyses, the effect of tourniquet use on the juxta-anastomosis primary patency remained significant (hazard ratio = 2.24, 95% confidence interval = 1.72-2.93, p < 0.001) when other significant factors (fistula location, gender, and diabetes) were considered.

CONCLUSION

Intraoperative pneumatic tourniquet may significantly improve the clinical outcomes of arteriovenous fistula creations by reducing juxta-anastomosis trauma and subsequent stenosis.

Arteriovenous conduits for hemodialysis: how to better modulate the pathophysiological vascular response to optimize vascular access durability

Vascular access is the lifeline for patients on hemodialysis. Arteriovenous fistulas (AVFs) are the preferred vascular access, but AVF maturation failure remains a significant clinical problem. Currently, there are no effective therapies available to prevent or treat AVF maturation failure. AVF maturation failure frequently results from venous stenosis at the AVF anastomosis, which is secondary to poor outward vascular remodeling and excessive venous intimal hyperplasia that narrows the AVF lumen. Arteriovenous grafts (AVGs) are the next preferred vascular access when an AVF creation is not possible. AVG failure is primarily the result of venous stenosis at the vein-graft anastomosis, which originates from intimal hyperplasia development. Although there has been advancement in our knowledge of the pathophysiology of AVF maturation and AVG failure, this has not translated into effective therapies for these two important clinical problems. Further work will be required to dissect out the mechanisms of AVF maturation failure and AVG failure to develop more specific therapies. This review highlights the major recent advancements in AVF and AVG biology, reviews major clinical trials, and discusses new areas for future research.

Retracted: Transforming Growth Factor Beta-1 Promotes Smooth Muscle Cell Proliferation and Migration in an Arteriovenous Fistulae: The Role of Wall Shear Stress

Retraction: Lan Jia, Fang Wei, Lihua Wang, Haiyan Chen, Haibo Yu, Zhe Wang and Aili Jiang "Transforming Growth Factor Beta-1 Promotes Smooth Muscle Cell Proliferation and Migration in an Arteriovenous Fistulae: The Role of Wall Shear Stress" Therapeutic Apheresis and Dialysis (https://onlinelibrary.wiley.com/doi/10.1111/1744-9987.12781). The above article, published online on 06 December 2018 in Wiley Online Library (wileyonlinelibrary.com), has been retracted by agreement between the authors, the journal Editor in Chief, Tadao Akizawa, and John Wiley and Sons Australia Ltd. The retraction has been agreed due to major overlap with a previously published article.

Near-Infrared Fluorescence Imaging of Matrix Metalloproteinase 2 Activity as a Biomarker of Vascular Remodeling in Hemodialysis Access

PURPOSE

To establish the capability of near-infrared fluorescence (NIRF) imaging for the detection of matrix metalloproteinase 2 (MMP-2) activity as a biomarker of vascular remodeling (VR) in arteriovenous fistulae (AVFs) in vivo.

MATERIALS AND METHODS

AVFs were created in the right groins of Wistar rats (n = 10), and sham procedures were performed in the contralateral groins. Fistulography via a left common carotid artery approach confirmed stenosis (> 50%) in a subset of animals (n = 5) 4 weeks after AVF creation. After administration of MMP-2-activated NIRF probe, near-infrared imaging was performed in vivo and ex vivo of both the AVF and the sham-treated vessels to measure radiant efficiency of MMP-2-activated NIRF signal over background. Histologic analyses of AVF and sham-treated vessels were performed to measure VR defined as inward growth of the vessel caused by intimal thickening.

RESULTS

AVFs demonstrated a significantly higher percentage increase in radiant efficiency over background compared with sham vessels (45.5 ± 56% vs 16.1 ± 17.8%; P = .008). VR in AVFs was associated with increased thickness of neointima staining positively for MMP-2 (161.8 ± 45.5 μm vs 73.2 ± 36.7 μm; P = .01). A significant correlation was observed between MMP-2 activity as measured by relative increase in radiant efficiency for AVFs and thickness of neointima staining positively for MMP-2 (P = .039).

CONCLUSIONS

NIRF imaging can detect increased MMP activity in remodeled AVFs compared with contralateral sham vessels. MMP-2-activated NIRF signal correlates with the severity of intimal thickening. These findings suggest NIRF imaging of MMP-2 may be used as a biomarker of the vascular remodeling underlying stenosis.

Toward longitudinal studies of hemodynamically induced vessel wall remodeling

INTRODUCTION:

Autogenous arteriovenous fistula is the preferred vascular access for hemodialysis, but it has high rates of non-maturation and early failure due to vascular stenosis. Convincing evidence supports a key role of local hemodynamics in vascular remodeling, suggesting that unsteady and disturbed flow conditions may be related to stenosis formation in arteriovenous fistula. The purpose of our study was to explore the feasibility of coupling contrast-free magnetic resonance imaging and computational fluid dynamics in longitudinal studies to identify the role of local hemodynamic changes over time in inducing vessel wall remodeling in arteriovenous fistula.

METHODS:

We acquired contrast-free magnetic resonance imaging of arm vasculature at 1 week and 6 weeks after arteriovenous fistula creation in a 72-year-old patient. We then generated three-dimensional models and evaluated lumen cross-sectional area of arteriovenous fistula limbs. We performed high-resolution computational fluid dynamics to evaluate changes in local hemodynamics over time.

RESULTS:

Our contrast-free magnetic resonance imaging protocol provided good quality images in a short scan duration. We observed a homogeneous dilatation in the proximal artery, while there was a more pronounced lumen dilatation in the venous outflow as compared to a limited dilatation in the juxta-anastomotic vein. Furthermore, we observed a slight stabilization of the flow pattern over time, suggesting that vascular outward remodeling accommodates the flow to a more helicoidally phenotype.

CONCLUSION:

Coupling contrast-free magnetic resonance imaging and high-resolution computational fluid dynamics represents a promising approach to shed more light in the mechanisms of vascular remodeling and can be used for prospective clinical investigations aimed at identifying critical hemodynamic factors contributing to arteriovenous fistula failure.

Relaxin receptor deficiency promotes vascular inflammation and impairs outward remodeling in arteriovenous fistulas

The pathophysiology of arteriovenous fistula (AVF) maturation failure is not completely understood but impaired outward remodeling (OR) and intimal hyperplasia are thought to be contributors. This adverse vascular response after AVF surgery results from interplay between vascular smooth muscle cells (VSMCs), the extracellular matrix (ECM), and inflammatory cells. Relaxin (RLN) is a hormone that acts on the vasculature via interaction with RLN/insulin-like peptide family receptor 1 (RXFP1), resulting in vasodilatation, ECM remodeling, and decreased inflammation. In the present study, we evaluated the consequences of RXFP1 knockout ( Rxfp1-/-) on AVF maturation in a murine model of AVF failure. Rxfp1-/- mice showed a 22% decrease in vessel size at the venous outflow tract 14 d after AVF surgery. Furthermore, a 43% increase in elastin content was observed in the lesions of Rxfp1-/- mice and coincided with a 41% reduction in elastase activity. In addition, Rxfp1-/- mice displayed a 6-fold increase in CD45+ leukocytes, along with a 2-fold increase in monocyte chemoattractant protein 1 (MCP1) levels, when compared with wild-type mice. In vitro, VSMCs from Rxfp1-/- mice exhibited a synthetic phenotype, as illustrated by augmentation of collagen, fibronectin, TGF-β, and platelet-derived growth factor mRNA. In addition, VSMCs derived from Rxfp1-/- mice showed a 5-fold increase in cell migration. Finally, RXFP1 and RLN expression levels were increased in human AVFs when compared with unoperated cephalic veins. In conclusion, RXFP1 deficiency hampers elastin degradation and results in induced vascular inflammation after AVF surgery. These processes impair OR in murine AVF, suggesting that the RLN axis could be a potential therapeutic target for promoting AVF maturation.-Bezhaeva, T., de Vries, M. R., Geelhoed, W. J., van der Veer, E. P., Versteeg, S., van Alem, C. M. A., Voorzaat, B. M., Eijkelkamp, N., van der Bogt, K. E., Agoulnik, A. I., van Zonneveld, A.-J., Quax, P. H. A., Rotmans, J. I. Relaxin receptor deficiency promotes vascular inflammation and impairs outward remodeling in arteriovenous fistulas.

The formulation and characterization of 3D printed grafts as vascular access for potential use in hemodialysis

Arteriovenous graft (AVG) failure continues to be a life-threatening problem in haemodialysis. Graft failure can occur if the implanted graft is not well-matched to the vasculature of the patient. Likewise, stenosis often develops at the vein-graft anastomosis, contributing to thrombosis and early graft failure. To address this clinical need, a novel ink formulation comprised of ACMO/TMPTA/TMETA for 3D printing a AVG was developed (ACMO-AVG), in which the printed AVG was biocompatible and did not induce cytotoxicity. The ease of customizing the ACMO-AVG according to different requirements was demonstrated. Furthermore, the AVG displayed similar mechanical properties to the commercially available arteriovenous ePTFE graft (ePTFE-AVG). Unlike ePTFE-AVG, the ACMO-AVG displayed excellent anti-fouling characteristics because no plasma protein adsorption and platelet adhesion were detected on the luminal surfaces after 2 h of incubation. Similarly, exposure to human endothelial cells and human vascular smooth muscle cells did not result in any cell detection on the surfaces of the ACMO-AVG. Thus, the present study demonstrates a newly developed 3D printing ink formulation that can be successfully 3D printed into a clinically applicable vascular access used for haemodialysis.

An arteriovenous graft that was successfully 3D printed with a novel printing ink formulation that displayed excellent mechanical and anti-fouling properties.

Asymmetric Dimethylarginine does not Predict Early Access Events in Hemodialysis Patients with Brachiocephalic Fistula Access

Background

Vascular access for hemodialysis is best provided by an arteriovenous fistula (AVF). AVF fail primarily because of neointimal hyperplasia. Asymmetric dimethlyarginine (ADMA) is a naturally occurring analogue of L-arginine, which is elevated in renal failure and impairs endothelial cell function. ADMA inhibits nitric oxide synthetase, leading to impaired nitric oxide production and contributing to the development of neointimal hyperplasia. ADMA was measured at the time of AVF placement to evaluate associations with access failure.

Methods

ADMA was measured at the time of brachiocephalic access placement. Patients were followed for up to 12 months with end-points of access thrombosis or venous stenosis.

Results

Sixty patients with primary brachiocephalic fistulas were included in the study cohort. The median value for ADMA drawn at the time of AVF creation was 3.1 µmol/L. ADMA was not significantly associated with early thrombosis or venous stenosis events (P>0.05).

Conclusion

Preoperative ADMA levels, as a surrogate for endothelial cell dysfunction and predictor of adverse access event (thrombosis or stenosis), were not associated with subsequent access events Future studies that identify markers of endothelial cell dysfunction are warranted.

Towards the Identification of Hemodynamic Parameters Involved in Arteriovenous Fistula Maturation and Failure: A Review

Native arteriovenous fistulas have a high failure rate mainly due to the lack of maturation and uncontrolled neo-intimal hyperplasia development. Newly established hemodynamics is thought to be central in driving the fistula fate, after surgical creation. To investigate the effects of realistic wall shear stress stimuli on endothelial cells, an in vitro approach is necessary in order to reduce the complexity of the in vivo environment. After a systematic review, realistic WSS waveforms were selected and analysed in terms of magnitude, temporal gradient, presence of reversing phases (oscillatory shear index, OSI) and frequency content (hemodynamics index, HI). The effects induced by these waveforms in cellular cultures were also considered, together with the materials and methods used to cultivate and expose cells to WSS stimuli. The results show a wide heterogeneity of experimental approaches and WSS waveform features that prevent a complete understanding of the mechanisms that regulate mechanotransduction. Furthermore, the hemodynamics derived from the carotid bifurcation is the most investigated (in vitro), while the AVF scenario remains poorly addressed. In conclusion, standardisation of the materials and methods employed, as well as the decomposition of realistic WSS profiles, are required for a better understanding of the hemodynamic effects on AVF outcomes. This standardisation may also lead to a new classification of WSS features according to the risk associated with vascular dysfunction.

Is shear stress the key factor for AVF maturation?

Autologous arteriovenous fistula (AVF) is the preferred choice for providing vascular access to hemodialysis (HD) patients, but it is still affected by high incidence of non-maturation or early failure. After creation, AVF must undergo vascular remodeling, a process characterized by an increase in blood vessel diameter and wall thickness, to allow efficient and adequate HD. A growing body of evidence indicates that AVF maturation is related to the response of endothelial cells (ECs) to changes in wall shear stress (WSS), and in particular, to changes of its peak value. The reasons why important number of AVFs are affected by non-maturation or early failure still remain to be elucidated, but it has been suggested that local hemodynamic conditions with highly disturbed flow patterns may play an important role. In the present contribution, we addressed the role of WSS on AVF maturation, clarifying mechanisms that affect the clinical outcome of AVF creation. We also pointed out the need of non-invasive longitudinal studies, with repeated observations of hemodynamic parameters and structural changes during time, to obtain evidence of a cause-and-effect relationship between the presence of disturbed flow and AVF maturation failure. This understanding may be fundamental in the future to ameliorate clinical outcome of AVF creation, with a great impact on the clinical management of HD patients and their quality of life.