Transforming growth factor beta1 genotype polymorphisms determine AV fistula patency in hemodialysis patients

Sustained tenascin-C expression drives neointimal hyperplasia and promotes aortocaval fistula failure

End-stage kidney disease (ESKD) impacts over 740,000 individuals in the United States, with many patients relying on arteriovenous fistulae (AVF) for hemodialysis due to superior patency and reduced infections. However, AVF patency is reduced by thrombosis and neointimal hyperplasia, yielding a 1-yr patency of only 40%-50%. We hypothesized that tenascin-C (TNC), a regulator of inflammation and immune responses after injury, also regulates venous remodeling during AVF maturation. AVF were created in wild-type (WT) and Tnc knockout (Tnc-/-) mice, and proteomic analyses were conducted to identify protein changes between sham and AVF WT tissue. Immunofluorescence and Western blot assays compared venous tissue from WT and Tnc-/- mice. In vitro studies using human umbilical vein endothelial cells and human umbilical vein smooth muscle cells examined TNC-siRNA effects on thrombomodulin (THBD) and NF-κB. Macrophages from WT and Tnc-/- mice were assessed for anti-inflammatory phenotype polarization and tissue factor expression. TNC expression was spatially and temporally regulated in WT mice with AVF, and TNC colocalized with matrix remodeling but not with THBD expression; TNC expression was downregulated in patent AVF but sustained in occluded AVF, both in WT mice and human AVF specimens. Tnc-/- mice had reduced AVF patency, less wall thickening, and increased thrombosis, with increased THBD expression. In vitro, TNC-siRNA increased THBD and reduced NF-κB activation. Macrophages from Tnc-/- mice showed increased anti-inflammatory macrophage polarization and tissue factor expression, facilitating thrombosis. Sustained TNC expression drives neointimal hyperplasia and AVF failure by promoting a prothrombotic, inflammatory microenvironment. Targeting TNC pathways may enhance AVF patency and improve dialysis outcomes.NEW & NOTEWORTHY This study identifies Tenascin-C (TNC) as a key regulator of arteriovenous fistula (AVF) patency. TNC is spatially and temporally regulated, driving neointimal hyperplasia and thrombosis by promoting a prothrombotic, inflammatory microenvironment. In Tnc-/- mice, reduced TNC expression increased thrombomodulin and anti-inflammatory macrophage polarization but impaired wall thickening and AVF patency. These findings link sustained TNC expression to AVF failure and suggest that targeting TNC pathways could enhance AVF outcomes in patients requiring hemodialysis.

Role of platelet factor 4 in arteriovenous fistula maturation failure: What do we know so far?

The rate of arteriovenous fistula (AVF) maturation failure remains unacceptably high despite continuous efforts on technique improvement and careful pre-surgery planning. In fact, half of all newly created AVFs are unable to be used for hemodialysis (HD) without a salvage procedure. While vascular stenosis in the venous limb of the access is the culprit, the underlying factors leading to vascular narrowing and AVF maturation failure are yet to be determined. We have recently demonstrated that AVF non-maturation is associated with post-operative medial fibrosis and fibrotic stenosis, and post-operative intimal hyperplasia (IH) exacerbates the situation. Multiple pathological processes and signaling pathways are underlying the stenotic remodeling of the AVF. Our group has recently indicated that a pro-inflammatory cytokine platelet factor 4 (PF4/CXCL4) is upregulated in veins that fail to mature after AVF creation. Platelet factor 4 is a fibrosis marker and can be detected in vascular stenosis tissue, suggesting that it may contribute to AVF maturation failure through stimulation of fibrosis and development of fibrotic stenosis. Here, we present an overview of the how PF4-mediated fibrosis determines AVF maturation failure.

Increased expression of the P2Y12 receptor is involved in the failure of autogenous arteriovenous fistula caused by stenosis

OBJECTIVE

This study investigated the role of the P2Y12 receptor in autogenous arteriovenous fistula (AVF) failure resulting from stenosis.

METHODS

Stenotic venous tissues and blood samples were obtained from patients with end-stage renal disease (ESRD) together with AVF stenosis, while venous tissues and blood samples were collected from patients with ESRD undergoing initial AVF surgery as controls. Immunohistochemistry and/or immunofluorescence techniques were utilized to assess the expression of P2Y12, transforming growth factor-β1 (TGF-β1), monocyte chemotactic protein 1 (MCP-1), and CD68 in the venous tissues. The expression levels of P2Y12, TGFβ1, and MCP-1 were quantified using quantitative reverse transcription-polymerase chain reaction and western blot analyses. Double and triple immunofluorescence staining was performed to precisely localize the cellular localization of P2Y12 expression.

RESULTS

Expression levels of P2Y12, TGFβ1, MCP-1, and CD68 were significantly higher in stenotic AVF venous tissues than in the control group tissues. Double and triple immunofluorescence staining of stenotic AVF venous tissues indicated that P2Y12 was predominantly expressed in α-SMA-positive vascular smooth muscle cells (VSMCs) and, to a lesser extent, in CD68-positive macrophages, with limited expression in CD31-positive endothelial cells. Moreover, a subset of macrophage-like VSMCs expressing P2Y12 were observed in both stenotic AVF venous tissues and control venous tissues. Additionally, a higher number of P2Y12+/TGF-β1+ double-positive cells were identified in stenotic AVF venous tissues than in the control group tissues.

CONCLUSION

Increased expression of P2Y12 in stenotic AVF venous tissues of patients with ESRD suggests its potential involvement in the pathogenesis of venous stenosis within AVFs.

Building a Scaffold for Arteriovenous Fistula Maturation: Unravelling the Role of the Extracellular Matrix

Vascular access is the lifeline for patients receiving haemodialysis as kidney replacement therapy. As a surgically created arteriovenous fistula (AVF) provides a high-flow conduit suitable for cannulation, it remains the vascular access of choice. In order to use an AVF successfully, the luminal diameter and the vessel wall of the venous outflow tract have to increase. This process is referred to as AVF maturation. AVF non-maturation is an important limitation of AVFs that contributes to their poor primary patency rates. To date, there is no clear overview of the overall role of the extracellular matrix (ECM) in AVF maturation. The ECM is essential for vascular functioning, as it provides structural and mechanical strength and communicates with vascular cells to regulate their differentiation and proliferation. Thus, the ECM is involved in multiple processes that regulate AVF maturation, and it is essential to study its anatomy and vascular response to AVF surgery to define therapeutic targets to improve AVF maturation. In this review, we discuss the composition of both the arterial and venous ECM and its incorporation in the three vessel layers: the tunica intima, media, and adventitia. Furthermore, we examine the effect of chronic kidney failure on the vasculature, the timing of ECM remodelling post-AVF surgery, and current ECM interventions to improve AVF maturation. Lastly, the suitability of ECM interventions as a therapeutic target for AVF maturation will be discussed.

Oxidative stress: An essential factor in the process of arteriovenous fistula failure

For more than half a century, arteriovenous fistula (AVFs) has been recognized as a lifeline for patients requiring hemodialysis (HD). With its higher long-term patency rate and lower probability of complications, AVF is strongly recommended by guidelines in different areas as the first choice for vascular access for HD patients, and its proportion of application is gradually increasing. Despite technological improvements and advances in the standards of postoperative care, many deficiencies are still encountered in the use of AVF related to its high incidence of failure due to unsuccessful maturation to adequately support HD and the development of neointimal hyperplasia (NIH), which narrows the AVF lumen. AVF failure is linked to the activation and migration of vascular cells and the remodeling of the extracellular matrix, where complex interactions between cytokines, adhesion molecules, and inflammatory mediators lead to poor adaptive remodeling. Oxidative stress also plays a vital role in AVF failure, and a growing amount of data suggest a link between AVF failure and oxidative stress. In this review, we summarize the present understanding of the pathophysiology of AVF failure. Furthermore, we focus on the relation between oxidative stress and AVF dysfunction. Finally, we discuss potential therapies for addressing AVF failure based on targeting oxidative stress.

Endothelial Cell TGF-β (Transforming Growth Factor-Beta) Signaling Regulates Venous Adaptive Remodeling to Improve Arteriovenous Fistula Patency

BACKGROUND

Arteriovenous fistulae (AVF) are the gold standard for vascular access for hemodialysis. Although the vein must thicken and dilate for successful hemodialysis, excessive wall thickness leads to stenosis causing AVF failure. Since TGF-β (transforming growth factor-beta) regulates ECM (extracellular matrix) deposition and smooth muscle cell (SMC) proliferation-critical components of wall thickness-we hypothesized that disruption of TGF-β signaling prevents excessive wall thickening during venous remodeling.

METHODS

A mouse aortocaval fistula model was used. SB431542-an inhibitor of TGF-β receptor I-was encapsulated in nanoparticles and applied to the AVF adventitia in C57BL/6J mice. Alternatively, AVFs were created in mice with conditional disruption of TGF-β receptors in either SMCs or endothelial cells. Doppler ultrasound was performed serially to confirm patency and to measure vessel diameters. AVFs were harvested at predetermined time points for histological and immunofluorescence analyses.

RESULTS

Inhibition of TGF-β signaling with SB431542-containing nanoparticles significantly reduced p-Smad2-positive cells in the AVF wall during the early maturation phase (days 7-21) and was associated with decreased AVF wall thickness that showed both decreased collagen density and decreased SMC proliferation. SMC-specific TGF-β signaling disruption decreased collagen density but not SMC proliferation or wall thickness. Endothelial cell-specific TGF-β signaling disruption decreased both collagen density and SMC proliferation in the AVF wall and was associated with reduced wall thickness, increased outward remodeling, and improved AVF patency.

CONCLUSIONS

Endothelial cell-targeted TGF-β inhibition may be a translational strategy to improve AVF patency.

Hydraulic expansion facilitates remodeling of arteriovenous fistulas without increasing venous intimal hyperplasia in rabbits

Background

An arteriovenous fistula (AVF) is considered essential for chronic hemodialysis.

Objective

To determine the effects of hydraulic expansion on the intimal hyperplasia of an AVF.

Methods

We divided 12 healthy male New Zealand white rabbits into a control group (vein without special handling and direct anastomosis with an artery, n = 6) and a hydraulic expansion group (vein dilated by hydraulic pressure before anastomosis, n = 6). Histopathomorphology was examined with hematoxylin and eosin staining and immunohistochemistry. Analysis of covariance (ANCOVA) was used to compare the data between the groups.

Results

Immediately and 1 day after surgery, the diameter of the fistula vein in rabbits in the hydraulic expansion group was significantly larger than it was in the control group (P = 0.02 and 0.03 respectively), but not on subsequent days. After hydraulic expansion and before construction of the fistula, the wall of vein was noticeably thinner on macroscopic observation, and the anterior and posterior walls were indistinguishable. At 3 weeks after surgery in the hydraulic expansion group, cells in the vein wall were disordered, there were fewer elastic fibers, tissues from the endothelium to tunica externa were less dense, and there was less extracellular matrix than in the control group. Expression of connective tissue growth factor in the hydraulic expansion group was significantly less than that in the control group (P = 0.01). No differences were found in intimal thickness or immunohistochemistry scores for transforming growth factor-β1 between the groups.

Conclusion

Hydraulic expansion did not increase intimal hyperplasia of an AVF, but facilitates remodeling of AVFs in rabbits.

Is fetuin-A a biomarker of dialysis access dysfunction?

BACKGROUND

The arteriovenous (AV) access function of hemodialysis (HD) patients can be impaired by afferent artery stiffness due to preexisting microcalcification and by venous stenosis secondary to neointimal hyperplasia in whose development participates an upregulated local inflammatory process. Fetuin-A is a circulating potent inhibitor of vascular calcification and plays an important anti-inflammatory role. The aims of this prospective study were to investigate the relationship between baseline serum fetuin-A levels and: blood flow (Q_A) values at baseline, AV access failure (thrombosis or intervention for stenosis) during follow-up and primary unassisted AV access patency.

METHODS

We measured baseline serum fetuin-A levels and Q_A values of the AV access in 64 HD patients under routine Q_A surveillance for stenosis. Patients were classified into tertiles according to their baseline fetuin-A levels (g/L): <0.5 (tertile-1), 0.5-1.20 (tertile-2), and >1.20 (tertile-3).

RESULTS

Fetuin-A was positively correlated with Q_A (Spearman coefficient = 0.311, p = 0.012). Fourteen patients (21.9%) underwent AV access failure and they had lower fetuin-A (0.59 ± 0.32 g/L) and lower Q_A (739.4 ± 438.8 mL/min) values at baseline compared with the remaining patients (1.05 ± 0.65 g/L and 1273.0 ± 596.3 mL/min, respectively) (p = 0.027 and p < 0.001, respectively). The AV access failure rate was highest (34.8%) in tertile-1 (lowest fetuin-A level). Unadjusted Cox regression analysis showed a decrease in the risk of AV access patency loss by increasing fetuin-A concentration (hazard ratio 0.395 (95% confidence interval: 1.42-1.69), p = 0.044) but it was not confirmed in the adjusted model, although the hazard ratio was low (0.523). Kaplan-Meier analysis showed that patients in tertile-3 (highest fetuin-A concentration) had the highest primary unassisted AV access patency (λ² = 4.68, p = 0.030, log-rank test).

CONCLUSION

If our results are confirmed in further studies, fetuin-A could be used as a circulating biomarker to identify HD patients at greater risk for AV access dysfunction, who would benefit from much closer dialysis access surveillance.

Sex Differences in Inflammation During Venous Remodeling of Arteriovenous Fistulae

Vascular disorders frequently have differing clinical presentations among women and men. Sex differences exist in vascular access for hemodialysis; women have reduced rates of arteriovenous fistula (AVF) maturation as well as fistula utilization compared with men. Inflammation is increasingly implicated in both clinical studies and animal models as a potent mechanism driving AVF maturation, especially in vessel dilation and wall thickening, that allows venous remodeling to the fistula environment to support hemodialysis. Sex differences have long been recognized in arterial remodeling and diseases, with men having increased cardiovascular events compared with pre-menopausal women. Many of these arterial diseases are driven by inflammation that is similar to the inflammation during AVF maturation. Improved understanding of sex differences in inflammation during vascular remodeling may suggest sex-specific vascular therapies to improve AVF success.

Distinct subsets of T cells and macrophages impact venous remodeling during arteriovenous fistula maturation

Patients with end-stage renal failure depend on hemodialysis indefinitely without renal transplantation, requiring a long-term patent vascular access. While the arteriovenous fistula (AVF) remains the preferred vascular access for hemodialysis because of its longer patency and fewer complications compared with other vascular accesses, the primary patency of AVF is only 50-60%, presenting a clinical need for improvement. AVF mature by developing a thickened vascular wall and increased diameter to adapt to arterial blood pressure and flow volume. Inflammation plays a critical role during vascular remodeling and fistula maturation; increased shear stress triggers infiltration of T-cells and macrophages that initiate inflammation, with involvement of several different subsets of T-cells and macrophages. We review the literature describing distinct roles of the various subsets of T-cells and macrophages during vascular remodeling. Immunosuppression with sirolimus or prednisolone reduces neointimal hyperplasia during AVF maturation, suggesting novel approaches to enhance vascular remodeling. However, M2 macrophages and CD4+ T-cells play essential roles during AVF maturation, suggesting that total immunosuppression may suppress adaptive vascular remodeling. Therefore it is likely that regulation of inflammation during fistula maturation will require a balanced approach to coordinate the various inflammatory cell subsets. Advances in immunosuppressive drug development and delivery systems may allow for more targeted regulation of inflammation to improve vascular remodeling and enhance AVF maturation.

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.

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.

Molecular Targets for Improving Arteriovenous Fistula Maturation and Patency

The increasing prevalence of chronic and end-stage renal disease creates an increased need for reliable vascular access, and although arteriovenous fistulae (AVF) are the preferred mode of hemodialysis access, 60% fail to mature and only 50% remain patent at one year. Fistulae mature by diameter expansion and wall thickening; this outward remodeling of the venous wall in the fistula environment relies on a delicate balance of extracellular matrix (ECM) remodeling, inflammation, growth factor secretion, and cell adhesion molecule upregulation in the venous wall. AVF failure occurs via two distinct mechanisms with early failure secondary to lack of outward remodeling, that is insufficient diameter expansion or wall thickening, whereas late failure occurs with excessive wall thickening due to neointimal hyperplasia (NIH) and insufficient diameter expansion in a previously functional fistula. In recent years, the molecular basis of AVF maturation and failure are becoming understood in order to develop potential therapeutic targets to aide maturation and prevent access loss. Erythropoietin-producing hepatocellular carcinoma (Eph) receptors, along with their ligands, ephrins, determine vascular identity and are critical for vascular remodeling in the embryo. Manipulation of Eph receptor signaling in adults, as well as downstream pathways, is a potential treatment strategy to improve the rates of AVF maturation and patency. This review examines our current understanding of molecular changes occurring following fistula creation, factors predictive of fistula success, and potential areas of intervention to decrease AVF failure.

C-reactive protein as a prognostic risk factor for loss of arteriovenous fistula patency in hemodialyzed patients

BACKGROUND

Inflammation is a cardiovascular risk factor in hemodialysis patients, but its influence on vascular access patency is still debatable. Our prospective study investigated this issue.

METHODS

A total of 258 patients receiving an arteriovenous fistula (AVF) between 2006 and 2016 at the Municipal Hospital Arad were included. Demographic, clinical, and laboratory characteristics were collected at the time of creation of the AVF. The primary study end point was AVF patency loss, defined as an event occurring at least 2 months after AVF formation and requiring surgical revision or replacement of the fistula. The patients were followed up for a median time of 26 months.

RESULTS

In our group, the mean age was 59.7 ± 13.2 years (median, 62 years), and 60.1% were male. During follow-up, 134 patients (51.9%) maintained AVF patency, whereas 124 (48.1%) lost AVF patency within a mean time of 23.3 ± 28.1 months (median, 10.5 months). We found that age (hazard ratio [HR], 1.015; P = .035) and C-reactive protein (CRP) level (HR, 1.17; P < .0001) were associated with a higher risk of loss of AVF patency. The protective factors for AVF patency were autosomal dominant polycystic kidney disease (HR, 0.336; P = .009), pre-emptive AVF (HR, 0.648; P = .031), and higher level of triglycerides (HR, 0.998; P = .035). In the multivariate adjusted Cox model, CRP level remained an independent predictor for loss of AVF patency (HR, 1.17; 95% confidence interval, 1.1-1.3; P < .0001).

CONCLUSIONS

In our study, CRP level was an independent predictor of AVF patency loss, whereas better AVF survival was independently associated with autosomal dominant polycystic kidney disease and pre-emptive AVF. As a simple noninvasive marker of chronic inflammation, CRP level may be a useful tool to predict AVF outcomes. Further research is needed to assess the protective effects of inflammation reduction on AVF survival.

Opportunities and Challenges for Genetic Studies of End-Stage Renal Disease in Canada

Purpose of review:

Genetic testing can improve diagnostic precision in some patients with end-stage renal disease (ESRD) providing the potential for targeted therapy and improved patient outcomes. We sought to describe the genetic architecture of ESRD and Canadian data sources available for further genetic investigation into ESRD.

Sources of information:

We performed PubMed searches of English, peer-reviewed articles using keywords “chronic kidney disease,” “ESRD,” “genetics,” “sequencing,” and “administrative databases,” and searched for nephrology-related Mendelian diseases on the Online Mendelian Inheritance in Man database.

Methods:

In this narrative review, we discuss our evolving understanding of the genetic architecture of kidney disease and ESRD, the risks and benefits of using genetic data to help diagnose and manage patients with ESRD, existing public Canadian biobanks and databases, and a vision for future genetic studies of ESRD in Canada.

Key findings:

ESRD has a polygenic architecture including rare Mendelian mutations and common small effect genetic polymorphism contributors. Genetic testing will improve diagnostic accuracy and contribute to a precision medicine approach in nephrology. However, the risk and benefits of genetic testing needs to be considered from an individual and societal perspective, and further research is required. Merging existing health data, linking biobanks and administrative databases, and forming Canadian collaborations hold great potential for genetic research into ESRD. Large sample sizes are necessary to perform the suitably powered investigations required to bring this vision to reality.

Limitations:

This is a narrative review of the literature discussing future directions and opportunities. It reflects the views and academic biases of the authors.

Implications:

National collaborations will be required to obtain sample sizes required for impactful, robust research. Merging established datasets may be one approach to obtain adequate samples. Patient education and engagement will improve the value of knowledge gained.

Association of vitamin D receptor gene TaqI, FokI and ApaI variants with arteriovenous fistula failure in hemodialysis patients

PURPOSE

We investigated the influence of the vitamin D receptor gene TaqI (rs731236), ApaI (rs7975232), and FokI (rs2228570) polymorphisms in arteriovenous fistula failure in hemodialysis patients.

METHODS

This study was carried out with 54 patients who experienced two or more fistula failures in the late period after arteriovenous fistula operation and 58 control patients with no history of arteriovenous fistula failure in 3 years or longer. The polymerase chain reaction-restriction fragment length polymorphism method was used to determine the vitamin D receptor TaqI, FokI, and ApaI polymorphisms.

RESULTS

For vitamin D receptor gene TaqI and Fok1 polymorphisms, no significant association was found between the two groups ( p > 0.05). However, a statistically significant association was determined for ApaI polymorphism between the two groups ( p = 0.02). In patients, ApaI AA, AC, and CC genotype frequencies were found as 21 (38.9%), 32 (59.3%), and 1 (1.8%), respectively. However, genotype frequencies of AA, AC, and CC in the control group were 29 (50%), 22 (37.9%), and 7 (12.1%), respectively. In all three polymorphisms, no significant difference was found between the two groups in terms of allele frequencies ( p > 0.05).

CONCLUSION

Vitamin D receptor ApaI AC genotype may be a possible cardiovascular risk factor for the development of arteriovenous fistula failure.

The association of genotype polymorphisms with vascular access patency in hemodialysis patients

Some hemodialysis patients suffer from repeat dysfunction of dialysis vascular access and need procedures of angioplasty, thrombectomy, and even temporary catheter use. Why these patients are vulnerable to vascular access dysfunction and how to improve its patency are imperative to be discovered. Traditional risk factors for vascular access function had been widely investigated but could not fully explain this question. Several genotype polymorphisms were demonstrated to increase the incidence of cardiovascular disease and might also be linked to higher risk of vascular access dysfunction. As the major causes of arteriovenous access thrombosis are hypercoagulable status and arteriovenous access stenosis, the investigated genes mainly focus on the mediators of the coagulation cascade, inflammatory process, and endothelial dysfunction. The reported polymorphisms of genes significantly associated with arteriovenous access dysfunction included genes encoding methylene tetrahydrofolate reductase, coagulation factors, heme oxygenase-1, matrix metalloproteinase, transforming growth factor-β1, tumor necrosis factor-α, vascular endothelial growth factor-A, renin-angiotensin-aldosterone system, and protein methyl transferase. However, further prospective study is indispensable to elucidate the association between the genotype polymorphisms and the outcome of vascular access. More and more therapeutic options that focus on genotype polymorphisms may generate a great benefit to the patency of vascular access of uremic patients.

Fibrotic Venous Remodeling and Nonmaturation of Arteriovenous Fistulas

The frequency of primary failure in arteriovenous fistulas (AVFs) remains unacceptably high. This lack of improvement is due in part to a poor understanding of the pathobiology underlying AVF nonmaturation. This observational study quantified the progression of three vascular features, medial fibrosis, intimal hyperplasia (IH), and collagen fiber organization, during early AVF remodeling and evaluated the associations thereof with AVF nonmaturation. We obtained venous samples from patients undergoing two-stage upper-arm AVF surgeries at a single center, including intraoperative veins at the first-stage access creation surgery and AVFs at the second-stage transposition procedure. Paired venous samples from both stages were used to evaluate change in these vascular features after anastomosis. Anatomic nonmaturation (AVF diameter never ≥6 mm) occurred in 39 of 161 (24%) patients. Neither preexisting fibrosis nor IH predicted AVF outcomes. Postoperative medial fibrosis associated with nonmaturation (odds ratio [OR], 1.55; 95% confidence interval [95% CI], 1.05 to 2.30; P=0.03, per 10% absolute increase in fibrosis), whereas postoperative IH only associated with failure in those individuals with medial fibrosis over the population's median value (OR, 2.63; 95% CI, 1.07 to 6.46; P=0.04, per increase of 1 in the intima/media ratio). Analysis of postoperative medial collagen organization revealed that circumferential alignment of fibers around the lumen associated with AVF nonmaturation (OR, 1.38; 95% CI, 1.03 to 1.84; P=0.03, per 10° increase in angle). This study demonstrates that excessive fibrotic remodeling of the vein after AVF creation is an important risk factor for nonmaturation and that high medial fibrosis determines the stenotic potential of IH.

Preoperative management of arteriovenous fistula (AVF) for hemodialysis

Native arteriovenous fistula (AVF) is the favorite access for hemodialysis (HD). The National Kidney Foundation's Kidney Disease Outcomes Quality Initiative (KDOQI) recommends its creation in most patients with renal failure. Unfortunately, intensive efforts to promote native AVF in patients with marginal vessels have increased the rate of primary fistula failure. A non-functioning fistula prompts the use of central venous catheter (CVC) that, unlike AVF, has been associated with an increased risk of morbidity and mortality among patients receiving HD. We believe that successful and timely AVF placement relies on the development of a multidisciplinary integrated preoperative program divided into five stages: (i) management of patients with advanced chronic kidney disease (CKD), (ii) management of preoperative risk factors for AVF failure, (iii) planning of native AVF, (iv) assessment of patient eligibility and (v) preoperative vascular mapping. Focusing specifically on native AVF, we review scientific evidence regarding preoperative management of this vascular access in order to favor construction of long-term functioning fistula minimizing development of severe complications.

The molecular mechanisms of hemodialysis vascular access failure

The arteriovenous fistula has been used for more than 50 years to provide vascular access for patients undergoing hemodialysis. More than 1.5 million patients worldwide have end stage renal disease and this population will continue to grow. The arteriovenous fistula is the preferred vascular access for patients, but its patency rate at 1 year is only 60%. The majority of arteriovenous fistulas fail because of intimal hyperplasia. In recent years, there have been many studies investigating the molecular mechanisms responsible for intimal hyperplasia and subsequent thrombosis. These studies have identified common pathways including inflammation, uremia, hypoxia, sheer stress, and increased thrombogenicity. These cellular mechanisms lead to increased proliferation, migration, and eventually stenosis. These pathways work synergistically through shared molecular messengers. In this review, we will examine the literature concerning the molecular basis of hemodialysis vascular access malfunction.

Future research directions to improve fistula maturation and reduce access failure

With the increasing prevalence of end-stage renal disease, there is a growing need for hemodialysis. Arteriovenous fistulae (AVF) are the preferred type of vascular access for hemodialysis, but maturation and failure continue to present significant barriers to successful fistula use. AVF maturation integrates outward remodeling with vessel wall thickening in response to drastic hemodynamic changes in the setting of uremia, systemic inflammation, oxidative stress, and pre-existent vascular pathology. AVF can fail due to both failure to mature adequately to support hemodialysis and development of neointimal hyperplasia that narrows the AVF lumen, typically near the fistula anastomosis. Failure due to neointimal hyperplasia involves vascular cell activation and migration and extracellular matrix remodeling with complex interactions of growth factors, adhesion molecules, inflammatory mediators, and chemokines, all of which result in maladaptive remodeling. Different strategies have been proposed to prevent and treat AVF failure based on current understanding of the modes and pathology of access failure; these approaches range from appropriate patient selection and use of alternative surgical strategies for fistula creation, to the use of novel interventional techniques or drugs to treat failing fistulae. Effective treatments to prevent or treat AVF failure require a multidisciplinary approach involving nephrologists, vascular surgeons, and interventional radiologists, careful patient selection, and the use of tailored systemic or localized interventions to improve patient-specific outcomes. This review provides contemporary information on the underlying mechanisms of AVF maturation and failure and discusses the broad spectrum of options that can be tailored for specific therapy.

A novel factor for primary arteriovenous fistula failure: hyperinsulinism

INTRODUCTION

Dysfunction of vascular access is an important reason of morbidity for dialysis patients and it is a major factor affecting the economical burden of hemodialysis. The preferred type of vascular access is creation of an arteriovenous fistula (AVF). However, the problem of fistula maturation rate is still a challenge. Herein, we tried to search the role of hyperinsulinism and insulin resistance as a new predictor of primary AVF failure (pAVFF) that may be a cause of intimal damage.

METHODS

We included 119 patients (73 male and 46 female) with a diagnosis of end-stage renal disease (ESRD) who had undergone an AVF operation by a vascular surgeon. The AVF was examined for presence of thrill on the first postoperative day. A successful cannulation with two fistula needles with a blood flow of 250 mL/min for at least one complete dialysis session, after 4 weeks of AVF surgery was defined as functioning access. Insulin resistance in our patients was determined by the standard homeostasis model assessment (homa-IR). A logistic-regression analysis was performed to investigate the independent factors related with pAVFF.

FINDINGS

Detection of pAVFF occurred in 27 (22.7%) patients. The presence of thrill, amount of daily proteinuria, insulin levels, homa-IR, and serum albumin levels were found to be significantly different between patients with fistula failure and those without pAVFF. The logistic-regression analysis of preoperative factors revealed the following OR (odds ratio) and 95% CI values: homa-IR 1.205 (1.063-1.366) (p = 0.004), serum albumin 0.398 (0.178-0.892) (p = 0.025), and the amount of daily proteinuria 1.307 (1.012-1.688) (p = 0.041). Even after addition of the presence of postoperative thrill on AVF, which was a postoperative strong clinical factor to the analysis, mean homa-IR and mean serum albumin continued to be independent predictors of pAVFF.

DISCUSSION

Insulin resistance or hyperinsulinism may be a significant cause of pAVFF, which emphasizes the role of endothelium in fistula dysfunction.

An update of the effect of far infrared therapy on arteriovenous access in end-stage renal disease patients

The life qualities of end-stage renal disease (ESRD) patients rely largely on adequate dialysis, and a well-functioning vascular access is indispensable for high quality hemodialysis. Despite the advancement of surgical skills and the optimal maintenance of arteriovenous fistula (AVF), malfunction of AVF is still frequently encountered and has great impact on the life of ESRD patients. Several medical, mechanical and genetic prognostic factors are documented to affect the patency of AVF and arteriovenous graft (AVG). Heme oxygenase-1 (HO-1) is one of the genetic factors reported to play a role in cardiovascular disease and the patency of vascular access. Far infrared (FIR), a novel therapeutic modality, can not only conduct heat energy to AVF but also stimulate the non-thermal reactions mediated by HO-1. The use of FIR therapy significantly enhances the primary patency rate and maturation of AVF with fewer unfavorable adverse effects, and also achieves higher post-angioplasty patency rate for AVG. The only limitation in proving the effectiveness of FIR therapy in enhancing patency of AVF is that all the studies were conducted in Chinese people in Taiwan and thus, there is a lack of evidence and experience in people of other ethnicities.

The Biology of Hemodialysis Vascular Access Failure

Arteriovenous fistulas (AVFs) are essential for patients and clinicians faced with end-stage renal disease (ESRD). While this method of vascular access for hemodialysis is preferred to others due to its reduced rate of infection and complications, they are plagued by intimal hyperplasia. The pathogenesis of intimal hyperplasia and subsequent thrombosis is brought on by uremia, hypoxia, and shear stress. These forces upregulate inflammatory and proliferative cytokines acting on leukocytes, fibroblasts, smooth muscle cells, and platelets. This activation begins initially with the progression of uremia, which induces platelet dysfunction and primes the body for an inflammatory response. The vasculature subsequently undergoes changes in oxygenation and shear stress during AVF creation. This propagates a strong inflammatory response in the vessel leading to cellular proliferation. This combined response is then further subjected to the stressors of cannulation and dialysis, eventually leading to stenosis and thrombosis. This review aims to help interventional radiologists understand the biological changes and pathogenesis of access failure.

Genotype polymorphisms of genes regulating nitric oxide synthesis determine long-term arteriovenous fistula patency in male hemodialysis patients

OBJECTIVES

Nitric oxide (NO) is a pivotal vasoactive substance modulating arteriovenous fistula (AVF) patency for hemodialysis (HD). Since genetic background could be the predicting factor of AVF malfunction, we aimed to investigate whether the NO-related genotype polymorphisms determine AVF survival rates.

METHODS

This is a retrospective, observational, multi-center study involving eight HD units in Taiwan, enrolled 580 patients initiating maintenance HD via AVFs. Genotype polymorphisms of NO-biosynthesis regulating enzymes (DDAH-1, DDAH-2, eNOS and PRMT1) were compared between HD patients with (n = 161) and without (n = 419) history of AVF malfunction. Subgroup analyses by gender were performed to evaluate the genetic effect in difference sexes.

RESULTS

In overall population, statistically significant associations were not found between AVF malfunction and the genetic polymorphisms. In the male subgroup (n = 313), a single nucleotide polymorphism (SNP) of PRMT1, rs10415880 (IVS9-193 A/G), showed a significant association with AVF malfunction. Male patients with AA/AG genotype had inferior AVF outcomes compared to GG genotype, regarding primary patency (70.6% vs. 40.9%, p = 0.001), assisted primary patency (81.0% vs. 58.4%, p < 0.001) and secondary patency (83.7% vs. 63.3%, p < 0.001) at a 5-year observation period. From multivariate Cox regression model, the AA/AG genotypes of PRMT1 were an independent risk factor for AVF malfunction in men (HR: 4.539, 95% CI 2.015-10.223; p < 0.001). However, such associations were not found in women.

CONCLUSIONS

rs10415880, the SNP of PRMT1 could be a novel genetic marker associated with AVF malfunction risk in male HD patients. Those with AA and AG genotypes of rs10415880 may predict a poorer long-term patency of AVF.

Hyperphosphatemia is associated with patency loss of arteriovenous fistula after 1 year of hemodialysis

BACKGROUND

The patency of arteriovenous access is important for stable and effective hemodialysis, and long-term technical survival is best achieved with a native arteriovenous fistula (AVF). However, maintaining AVF patency remains a challenge. This study was designed to determine the independent prognostic factors for AVF patency according to hemodialysis duration.

METHODS

The primary study end point was unassisted patency of the AVF, which was defined as the time from the first fistula surgery to the first AVF failure. AVF failure was defined as an event that required percutaneous intervention or surgery to revise or replace the fistula, which occurred at least 2 months after fistula formation.

RESULTS

We enrolled 478 patients with a mean age of 55.5±14.0 years, and mean duration of dialysis was 2.5±2.1 years. There were 109 cases (22.8%) of AVF failure. The factors related to AVF patency differed according to hemodialysis duration. Using a Cox-adjusted model, we observed a significant correlation between the incidence of AVF failure and diabetes within the initial 12 months of hemodialysis. Uncontrolled hyperphosphatemia (mean serum phosphorus>5.5 mg/dL during hemodialysis) was associated with patency loss of AVF after 1 year of hemodialysis.

CONCLUSION

Various factors were associated with the development of patency loss of AVF as hemodialysis duration differed, and a preventive role of hyperphosphatemia control in AVF survival needs further clinical study.

Vein graft adaptation and fistula maturation in the arterial environment

Veins are exposed to the arterial environment during two common surgical procedures, creation of vein grafts and arteriovenous fistulae (AVF). In both cases, veins adapt to the arterial environment that is characterized by different hemodynamic conditions and increased oxygen tension compared with the venous environment. Successful venous adaptation to the arterial environment is critical for long-term success of the vein graft or AVF and, in both cases, is generally characterized by venous dilation and wall thickening. However, AVF are exposed to a high flow, high shear stress, low-pressure arterial environment and adapt mainly via outward dilation with less intimal thickening. Vein grafts are exposed to a moderate flow, moderate shear stress, high-pressure arterial environment and adapt mainly via increased wall thickening with less outward dilation. We review the data that describe these differences, as well as the underlying molecular mechanisms that mediate these processes. Despite extensive research, there are few differences in the molecular pathways that regulate cell proliferation and migration or matrix synthesis, secretion, or degradation currently identified between vein graft adaptation and AVF maturation that account for the different types of venous adaptation to arterial environments.

Arteriovenous access failure: more than just intimal hyperplasia?

Haemodialysis vascular access patency is severely compromised by fistula non-maturation and access stenosis. Intimal hyperplasia (IH) is considered the culprit lesion in failed fistulas, resulting in luminal narrowing and stenosis. This review focuses on the biology and pathophysiology of fistula failure and highlights not only the classically associated IH but also some relatively neglected but potentially important contributors such as inadequate outward remodelling. In addition, the complex process and fragile balance of successful fistula maturation might be partially hindered by pre-existent chronic kidney disease-mediated vasculopathy. Further unravelling the (patho)physiology of outward remodelling and IH could contribute to novel therapies and enhance fistula patency.

Association of factor V gene polymorphism with arteriovenous graft failure

BACKGROUND

Dialysis grafts fail due to recurrent stenosis and thrombosis. Vasoactive and prothrombotic substances affecting intimal hyperplasia or thrombosis may modify graft outcomes.

STUDY DESIGN

Genetic polymorphisms association study of patients enrolled in a multicenter randomized clinical trial.

SETTING & PARTICIPANTS

354 Dialysis Access Consortium (DAC) Study patients receiving a new graft with DNA samples obtained. Participants were randomly assigned to treatment with aspirin plus dipyridamole versus placebo.

PREDICTOR

DNA sequence polymorphisms for the following candidate genes and their interaction with the study intervention: methylenetetrahydrofolate reductase (MTHFR), heme oxygenase 1 (HO-1), factor V (F5), transforming growth factor β1 (TGFβ1), klotho, nitric oxide synthase (NOS), and angiotensin-converting enzyme (ACE).

OUTCOME

Graft failure (>50% stenosis, angioplasty, thrombosis, surgical intervention, or permanent loss of function).

RESULTS

During a median patient follow-up of 34.3 months, 304 grafts failed. After adjusting for clinical factors (patient age, sex, access location, diabetes, cardiovascular disease, baseline aspirin use, body mass index, timing of graft placement, and study treatment) and genetic ancestral background, single-nucleotide polymorphism rs6019 of the factor V gene was associated significantly with graft failure in a dominant model (HR of 1.70 [95% CI, 1.32-2.19; P < 0.001] for G/C and G/G genotypes vs C/C genotypes). There was no significant association between graft failure and polymorphisms of MTHFR, HO-1, TGFβ1, klotho, NOS, or ACE.

LIMITATIONS

Small sample size.

CONCLUSION

The rs6019 genotype of Factor V is associated with increased risk of graft failure. Anticoagulation may reduce graft failure in patients with the G/C or G/G genotypes.

Genetic causation of neointimal hyperplasia in hemodialysis vascular access dysfunction

The major cause of hemodialysis vascular access failure is venous stenosis resulting from neointimal hyperplasia. Genetic factors have been shown to be associated with cardiovascular disease and peripheral vascular disease (PVD) in the general population. Genetic factors may also play an important role in vascular access stenosis and development of neointimal hyperplasia by affecting pathways that lead to inflammation, endothelial function, oxidative stress, and vascular smooth muscle proliferation. This review will discuss the role of genetics in understanding neointimal hyperplasia development in hemodialysis vascular access dysfunction and other disease processes with similar neointimal hyperplasia development such as coronary artery disease and PVD.

Increased plasma chymase concentration and mast cell chymase expression in venous neointimal lesions of patients with CKD and ESRD

The underlying inflammatory component of chronic kidney disease may predispose blood vessels to intimal hyperplasia (IH), which is the primary cause of dialysis access failure. We hypothesize that vascular pathology and markers of IH formation are antecedent to arteriovenous (AV) fistula creation. Blood, cephalic, and basilic vein segments were collected from predialysis chronic kidney disease (CKD) patients with no previous AV access and patients with end-stage renal disease (ESRD). Immunohistochemistry was performed with antibodies against mast cell chymase, transforming growth factor-beta (TGF-β) and interleukin-6 (IL-6), which cause IH. Plasma chymase was measured by ELISA. IH was present in 91% of CKD and 75% of ESRD vein segments. Chymase was abundant in vessels with IH, with the greatest expression in intima and medial layers, and virtually absent in the controls. Chymase colocalized with TGF-β1 and IL-6. Plasma chymase concentration was elevated up to 33-fold in patients with CKD versus controls and was associated with increased chymase in vessels with IH. We show that chymase expression in vessels with IH corresponds with plasma chymase concentrations. As chymase inhibition attenuates IH in animal models, and we find chymase is highly expressed in IH lesions of patients with CKD and ESRD, we speculate that chymase inhibition could have therapeutic value in humans.

"Venopathy" at work: recasting neointimal hyperplasia in a new light

Hemodialysis vascular access is a unique form of vascular anastomosis. Although it is created in a unique disease state, it has much to offer in terms of insights into venous endothelial and anastomotic biology. The development of neointimal hyperplasia (NH) has been identified as a pathologic entity, decreasing the lifespan and effectiveness of hemodialysis vascular access. Subtle hints and new data suggest a contrary idea-that NH, to some extent an expected response, if controlled properly, may play a beneficial role in the promotion of maturation to a functional access. This review attempts to recast our understanding of NH and redefine research goals for an evolving discipline that focuses on a life-sustaining connection between an artery and vein.

Functional polymorphisms in matrix metalloproteinases-1, -3, -9 are associated with arteriovenous fistula patency in hemodialysis patients

BACKGROUND AND OBJECTIVES

Matrix metalloproteinases (MMPs) are risk factors for cardiovascular diseases. This study evaluated the association of genotype polymorphisms of MMPs and tissue inhibitors of metalloproteinases (TIMPs) in hemodialysis (HD) patients with arteriovenous fistula (AVF) failure.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Genotype polymorphism of MMP-1, MMP-2, MMP-3, and MMP-9 and TIMP-1 and TIMP-2 and clinical and laboratory parameters were compared between Chinese HD patients with (n = 170) and without (n = 426) AVF failure.

RESULTS

Significant associations were found between AVF failure and the following factors (hazard ratio): longer HD duration (1.007 per month), lower pump flow (0.991 per ml/min), higher dynamic venous pressure (1.016 per mmHg), location of AVF on right side (1.630 versus left side) and upper arm (2.385 versus forearm), history of cardiovascular disease (1.656 versus absence of history), 1G/1G genotype of MMP-1 -1607 1G >2G SNP (2.315 versus 1G/2G + 2G/2G genotypes), 6A/6A genotype of MMP-3 -1612 5A >6A SNP (1.712 versus 5A/6A + 5A/5A), and C/C genotype of MMP-9 -1562 C>T SNP (1.650 versus C/T+T/T). The positive predictive rates for AVF failure were 63.0% and 6.7% for patients with the highest-risk (1G1G/6A6A/CC) and lowest-risk (2G2G or 2G1G/5A5A or 6A6A/TT or TC) composite MMP-1/MMP-3/MMP-9 genotype, respectively. The unassisted patency of AVF at 5 years decreased significantly from 93.3% to 38.4% for the composite MMP-1/MMP-3/MMP-9 genotypes (lowest versus highest risk, P < 0.001).

CONCLUSIONS

Specific genotypes of MMP-1, MMP-3 and MMP-9 with lower transcriptional activity are associated with higher frequencies of AVF failure, which may result from more accumulation of extracellular matrix, leading to AVF stenosis.

Prognostic factors influencing the patency of hemodialysis vascular access: literature review and novel therapeutic modality by far infrared therapy

In Taiwan, more than 85% of patients with end-stage renal disease undergo maintenance hemodialysis (HD). The native arteriovenous fistula (AVF) accounts for a prevalence of more than 80% of the vascular access in our patients. Some mechanical factors may affect the patency of hemodialysis vascular access, such as surgical skill, puncture technique and shear stress on the vascular endothelium. Several medical factors have also been identified to be associated with vascular access prognosis in HD patients, including stasis, hypercoagulability, endothelial cell injury, medications, red cell mass and genotype polymorphisms of transforming growth factor-beta1 and methylene tetrahydrofolate reductase. According to our previous study, AVF failure was associated with a longer dinucleotide (GT)n repeat (n > or = 30) in the promoter of the heme oxygenase-1 (HO-1) gene. Our recent study also demonstrated that far-infrared therapy, a noninvasive and convenient therapeutic modality, can improve access flow, inflammatory status and survival of the AVF in HD patients through both its thermal and non-thermal (endothelial-improving, anti-inflammatory, antiproliferative, antioxidative) effects by upregulating NF-E2-related factor-2-dependent HO-1 expression, leading to the inhibition of expression of E-selectin, vascular cell adhesion molecule-1, and intercellular adhesion molecule-1.

Plasma ADMA predicts restenosis of arteriovenous fistula

Plasma levels of asymmetrical dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide production, correlate with endothelial dysfunction and the development of cardiovascular events in patients with uremia. It is not known whether endothelial dysfunction contributes to the dysfunction of arteriovenous fistulas (AVFs) in hemodialysis patients. Here, we studied the predictive value of baseline plasma ADMA for symptomatic restenosis of an AVF after percutaneous transluminal angioplasty in dialysis patients. We obtained baseline plasma ADMA levels before percutaneous transluminal angioplasty in 100 consecutive patients with dysfunctional AVFs. Patients were followed up clinically for up to 6 mo after angioplasty for recurrent dysfunction. During the 6 mo after angioplasty, 46 patients experienced recurrent dysfunction of their AVF; of these, follow-up fistulography showed restenosis at the same location in 41, new stenosis at different locations in two, and no significant stenosis in three patients. Up to 60% of the patients with high levels of ADMA (>0.910 microM) had target lesion restenosis compared with 25% of those with low levels (<0.910 microM; P < 0.001). In multivariate analysis, plasma ADMA independently nearly tripled the risk for recurrent symptomatic stenosis of an AVF after percutaneous transluminal angioplasty (hazard ratio 2.65; 95% confidence interval 1.33 to 5.28). These results suggest a role for ADMA in the progression of symptomatic restenoses of AVFs after percutaneous transluminal angioplasty and call for preventive strategies that target ADMA and/or endothelial dysfunction to decrease the risk for AVF restenosis.

Interleukin-10 and tumor necrosis factor-alpha polymorphisms in vascular access failure in patients on hemodialysis: preliminary data in Korea

Neointimal hyperplasia causes vascular stenosis and subsequent thrombosis, which result in vascular access failure in patients undergoing hemodialysis. Interleukin-10 (IL-10) and tumour necrosis factor-alpha(TNF-alpha) are involved in this inflammatory process. The aim of this study was to investigate the relationship between vascular access failure and various inflammatory markers including the genetic polymorphisms of IL-10 and TNF-alpha. Seventy-five patients on hemodialysis with an arteriovenous fistula in place or an artificial graft (18 with vascular access failure and 82 without failure) and 98 healthy individuals were genotyped for IL-10 and TNF-alpha single nucleotide polymorphisms. Clinical and laboratory data including serum IL-10 and TNF-alpha levels were compared. Stimulated IL-10 levels, from in vitro incubation of blood with lipopolysaccharide, were also obtained and compared. Female gender, hypoproteinemia, and hypertriglyceridemia were associated with vascular access failure. The basal TNF-alpha level was significantly higher in patients with access failure. The distribution of IL-10 and TNF-alpha genotype did not differ among patients with or without access failure. This study could not demonstrate a relationship between genetic polymorphisms and vascular access failure. However, an altered immune response and inflammation might contribute to vascular access failure.

A mathematical model of venous neointimal hyperplasia formation

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 and grafts. The release of growth factors due to surgical injury, oxidative stress and turbulent flow has been suggested as a possible mechanism for neointimal hyperplasia.

RESULTS

In this work, we construct a mathematical model which analyzes the role that growth factors might play in the stenosis at the venous anastomosis. The model consists of a system of partial differential equations describing the influence of oxidative stress and turbulent flow on growth factors, the interaction among growth factors, smooth muscle cells, and extracellular matrix, and the subsequent effect on the stenosis at the venous anastomosis, which, in turn, affects the level of oxidative stress and degree of turbulent flow. Computer simulations suggest that our model can be used to predict access stenosis as a function of the initial concentration of the growth factors inside the intimal-luminal space.

CONCLUSION

The proposed model describes the formation of venous neointimal hyperplasia, based on pathogenic mechanisms. The results suggest that interventions aimed at specific growth factors may be successful in prolonging the life of the vascular access, while reducing the costs of vascular access maintenance. The model may also provide indication of when invasive access surveillance to repair stenosis should be undertaken.

Far infrared therapy inhibits vascular endothelial inflammation via the induction of heme oxygenase-1

OBJECTIVE

Survival of arteriovenous fistulas (AVFs) in hemodialysis patients is associated with both far infrared (FIR) therapy and length polymorphisms of the heme oxygenase-1 (HO-1) promoter. In this study, we evaluated whether there is an interaction between FIR radiation and HO-1 in regulating vascular inflammation.

METHODS AND RESULTS

Treatment of cultured human umbilical vein endothelial cells (ECs) with FIR radiation stimulated HO-1 protein, mRNA, and promoter activity. HO-1 induction was dependent on the activation of the antioxidant responsive element/NF-E2-related factor-2 complex, and was likely a consequence of heat stress. FIR radiation also inhibited tumor necrosis factor (TNF)-alpha-mediated expression of E-selectin, vascular cell adhesion molecule-1, intercellular cell adhesion molecule-1, monocyte chemoattractant protein-1, interleukin-8, and the cytokine-mediated adhesion of monocytes to ECs. The antiinflammatory action of FIR was mimicked by bilirubin, and was reversed by the HO inhibitor, tin protoporphyrin-IX, or by the selective knockdown of HO-1. Finally, the antiinflammatory effect of FIR was also observed in patients undergoing hemodialysis.

CONCLUSIONS

These results demonstrate that FIR therapy exerts a potent antiinflammatory effect via the induction of HO-1. The ability of FIR therapy to inhibit inflammation may play a critical role in preserving blood flow and patency of AVFs in hemodialysis patients.

Neoangiogenesis and the presence of progenitor cells in the venous limb of an arteriovenous fistula in the rat

Venous injury and attendant venous stenosis are major contributors to the failure of hemodialysis vascular accesses. This report describes the presence of neoangiogenesis in the intima and adventitia of the venous limb of an arteriovenous (AV) fistula in the rat, the latter induced by creating an aortocaval fistula. Immunohistochemistry of the venous limb demonstrated the presence of c-Kit-positive cells lining new microvessels with lumen formation and that these c-Kit-positive cells exhibited either a smooth muscle phenotype as reflected by concomitant expression of calponin, or an endothelial phenotype as reflected by expression of endothelial nitric oxide synthase (eNOS). Western analysis confirmed upregulation of eNOS in the venous limb of the AV fistula. Measurement of systemic concentrations of angiogenic cytokines, namely, monocyte chemotactic protein-1, stromal cell-derived factor-1 (SDF-1), cytokine-induced neutrophil chemoattractant, and VEGF, failed to reveal an increase in these cytokines either at 3 or 10 wk after creation of the AV fistula. The angiogenic cytokines VEGF and SDF-1 were not upregulated in the venous limb of the AV fistula either at 2 or 16 wk. We conclude that in this model of an AV fistula in the rat, neoangiogenesis occurs and is constituted, at least in part, by bone marrow-derived cells, the latter differentiating to exhibit either an endothelial or smooth muscle phenotype. In view of these findings, we suggest that this model may offer an experimental approach by which to explore the evolution and significance of neoangiogenesis in the formation and pathobiology of vascular plaques, and the mechanisms that promote dysfunction of hemodialysis AV fistulas.

Over-expression of IGF-related peptides in stenoses of native arteriovenous fistulas in hemodialysis patients

INTRODUCTION

Insulin-like growth factors (IGFs) are known to play an important role in atherogenesis. The aim of our study was to assess the local expression of IGF-related peptides in stenosed hemodialysis fistulas and compare these with their respective serum levels.

METHODS

We investigated 15 stenosed vein segments of primary arteriovenous fistulas, 29 non-stenosed control vein segments from uremic patients and 15 non-stenosed control saphenous vein segments. Immunohistochemistry was performed for IGF-I, insulin, IGF-binding proteins (IGFBPs)-1, -2, -3 and -4, the acid labile subunit (ALS) and type 1 IGF-receptor (IGF-R). Serum levels were measured by specific radioimmunoassays.

RESULTS

Compared to both control groups, a significantly higher expression of the following IGF-related peptides was seen in the stenotic (neo)intima: IGF-I, IGFBP-1, -2, -3, -4 and IGF-R; in the stenotic media: IGF-I and IGFBP-3 and in the endothelium of stenotic fistulas: IGF-I (all p<0.05). Staining against ALS and insulin was negative in all vessels. Serum IGF-I levels did not differ. Serum levels of IGFBP-1, -2, -3 and -4 were significantly higher in patients with renal disease (all p<0.05). There were no correlations between local and systemic IGF-related peptide levels. There were correlations of neointimal expression of IGF-I, IGFBP-1, -2, -3, -4 and IGF-R with both hypercellularity and the presence of inflammatory cells (p<0.05).

CONCLUSION

In the stenotic arteriovenous fistula of hemodialysis patients, expression of the peptides IGF-I, IGFBP-1, -2, -3, -4 and IGF-R was significantly increased and showed a positive correlation with neointimal inflammation and hypercellularity (all p<0.05). IGF-related peptides are most likely synthesized locally and might be involved in the initiation and/or progression of neointimal thickening of primary arteriovenous fistulas.

Comparison of Survival of Upper Arm Arteriovenous Fistulas and Grafts after Failed Forearm Fistula

Although arteriovenous fistulas are considered superior to grafts, it is unknown whether that is true in the subset of patients with a previous failed fistula. For investigation of this question, a prospective vascular access database was queried retrospectively to compare the outcomes of 59 fistulas and 51 grafts that were placed in the upper arm after primary failure of an initial forearm fistula. Primary access failure was higher for subsequent fistulas than for subsequent grafts (44 versus 20%; P = 0.006). Fistulas required more interventions than grafts before their successful use (0.42 versus 0.16 per patient; P = 0.04). The time to catheter-free dialysis was longer for fistulas than for grafts (131 versus 34 d; P < 0.0001) and was associated with more episodes of bacteremia before permanent access use (1.3 versus 0.4 per patient; P = 0.003). Cumulative survival (from placement to permanent failure) was higher for fistulas than for grafts when primary failures were excluded (hazard ratio 0.51; 95% confidence interval 0.27 to 0.94; P = 0.03), but similar when primary failures were included (hazard ratio 0.99; 95% confidence interval 0.61 to 1.62; P = 0.97). Fistulas required fewer interventions to maintain long-term patency for dialysis after maturation (0.73 versus 2.38 per year; P < 0.001). In conclusion, as compared with grafts, subsequent upper arm fistulas are associated with a higher primary failure rate, more interventions to achieve maturation, longer catheter dependence, and more frequent catheter-related bacteremia. However, once the access is usable for dialysis, fistulas have superior cumulative patency than do grafts and require fewer interventions to maintain patency.

Local Activation of Interleukin 6 Signaling Is Associated With Arteriovenous Fistula Stenosis in Hemodialysis Patients

BACKGROUND

Vascular access failure is the main cause of morbidity in hemodialysis patients. Stenosis of the arteriovenous fistula (AVF) is similar histologically to atherosclerosis. Recent studies showed that interleukin 6 (IL-6) has a key role in the pathogenesis of atherosclerosis by binding 2 specific receptors, gp80 and gp130. When activated, gp130 interacts with a tyrosine kinase, Janus kinase (JAK2), which then activates a transcription factor, signal transducers and activators of transcription (STAT3), directly turning on several proinflammatory genes. The aim of this study is to evaluate gp130 expression and JAK2/STAT3 activation within stenotic AVFs.

METHODS

44 patients undergoing surgery for AVF creation were enrolled; 10 of them had AVF failure with histologically proven AVF stenosis (wall-lumen ratio > 1). A venous fragment of the AVFs was collected during creation and revision of the vascular access. gp130 and gp80 expression, as well as JAK/STAT activation, were evaluated by means of confocal microscopy. Peripheral-blood mononuclear cells were isolated at the time of AVF creation and revision.

RESULTS

gp130 protein expression, barely detectable in native AVFs, was strikingly increased within the venous branch of stenotic AVFs. The signaling subunit of the IL-6 receptor broadly colocalized with gp80, the IL-6-binding subunit. gp130-expressing cells were mainly CD34(+), suggesting that this receptor is expressed primarily by neovasculature endothelial cells. At the same time, a significant increase in phosphorylation of JAK2/STAT3 was observed in endothelial cells of stenotic AVFs. Interestingly, peripheral-blood mononuclear cells isolated at the time of AVF failure presented strikingly greater IL-6 expression compared with dialysis age-matched controls.

CONCLUSION

IL-6 receptor activation may have a role in the pathogenesis of AVF failure in hemodialysis patients and may represent a potential therapeutic target in this setting.

Gene polymorphism association studies in dialysis: vascular access

Complications of the vascular access site for hemodialysis are a major cause of morbidity, suboptimal dialysis, and hospitalization. Vascular access for dialysis that is achieved by central venous catheters is associated with complications such as infection and thrombosis. Arteriovenous fistulas and grafts are also at risk for infectious complications. Further, proliferation of the venous wall with secondary thrombosis is a common pathophysiological process that leads to vascular access dysfunction. Genetic polymorphisms that contribute to vascular access failure are found among factors of the coagulation cascade, and host mediators that induce endothelial dysfunction as well as vessel wall proliferation. The two most common mutations of coagulation factors seem to influence the risk of central venous catheter and fistula thrombosis. Indeed, both the single nucleotide polymorphism of the factor V gene at amino acid position 506 (factor V Leiden mutation) and the prothrombin 20210 polymorphism have been associated with thrombotic complications of the vascular access. Among the endothelium-directed factors, a polymorphism of the methylene tetrahydrofolate reductase gene coding for an enzyme that degrades the endothelium toxic product homocysteine, has been associated with fistula failure. While the angiotensin converting enzyme polymorphism does not seem to be associated with vascular access complications, polymorphisms of the profibrogenic cytokine transforming growth factor-beta1 are associated with the prognosis of native arteriovenous fistulae. The role of pro- and anti-inflammatory cytokine gene polymorphisms as prognostic factors for vascular access is yet to be clearly defined.

Vascular access thrombosis prophylaxis

Vascular access thrombosis in the hemodialysis patient leads to significant cost and morbidity. Fistula patency supersedes graft patency, therefore obtaining a mature functioning fistula in patients approaching end-stage renal disease (ESRD) by early patient education and referral needs to be practiced. Current methods to maintain vascular access patency rely on early detection and radiologic or surgical prevention of thrombosis. Study of thrombosis biology has elucidated other potential targets for the prophylaxis of vascular access thrombosis. The goal of this review is to examine the current available methods for vascular access thrombosis prophylaxis.

The risk of dialysis access thrombosis is related to the transforming growth factor-beta1 production haplotype and is modified by polymorphisms in the plasminogen activator inhibitor-type 1 gene

Transforming growth factor-beta1 (TGF-beta1) and plasminogen activator inhibitor-type 1 (PAI-1) might play a role in the development of fibrosis and stenosis of hemodialysis vascular accesses. We studied polymorphisms in the TGFbeta1 (869T>C; 915G>C), and PAI-1 (4G/5G) genes in 416 hemodialysis patients (107 access thrombosis cases, 309 controls), to determine if they are related to vascular access thrombosis. Three TGF-beta1 production haplotypes (low, intermediate, and high) were defined according to the combination of polymorphisms found. The adjusted odds ratio (OR) and 95% confidence interval (CI) for access thrombosis in low TGF-beta1 producers was 7.31 (2.15-24.88; P = .001). The interaction between low TGF-beta1 production haplotype and the 4G/4G PAI-1 genotype was strongly associated with access thrombosis (adjusted OR 19.3; 95% CI 2.82-132.40; P = .003). Mean access thrombosis-free survival times in years (95% CI) were 14.65 (12.05-17.25), 11.96 (8.67-15.25), and 4.94 (3.06-6.83) in high, intermediate, and low TGF-beta1 producers, respectively (P = .044). Analysis of the synergy index and the case-only cross-product supported the presence of an interaction. We concluded that low TGF-beta1 production haplotype is a risk factor for hemodialysis access thrombosis and that in the presence of the 4G/4G PAI-1 genotype there is an additional increase in risk.

Length polymorphism in heme oxygenase-1 is associated with arteriovenous fistula patency in hemodialysis patients

Heme oxygenase-1 (HO-1) is a rate-limiting enzyme in heme degradation, producing carbon monoxide (CO), which carries potent antiproliferative and anti-inflammatory effects in the vascular walls. Transcription of the HO-1 gene is regulated by the length polymorphism of dinucleotide guanosine thymine repeat (GT)(n) in the promoter region, which was measured in this study to determine its association with arteriovenous fistula (AVF) failure in Chinese hemodialysis (HD) patients in Taiwan. L allele means (GT)(n)>or=30 and S allele means (GT)n<30. Therefore, there are two L alleles for L/L genotype, one L and one S allele for L/S genotype, and two S alleles for S/S genotype. Among the 603 HD patients who were enrolled in this study, 178 patients had history of AVF failure, while 425 patients did not. Significant associations were found between AVF failure and the following factors (hazard ratio): longer HD duration (1.004 month), lower pump flow (0.993 ml/min), higher dynamic venous pressure (1.010 mmHg), location of AVF on the right side (1.587 vs left side) and upper arm (2.242 vs forearm), and L/L and L/S genotypes of HO-1 (2.040 vs S/S genotype). The proportion of AVF failure increased from 20.3% in S/S genotype and 31.0% in L/S genotype to 35.4% in L/L genotype (P=0.011). Relative incidences were 1/87.6 (1 episode per 87.6 patient-months), 1/129, and 1/224.9 for HD patients with L/L, L/S, and S/S genotypes, respectively (P<0.002). The unassisted patency of AVF at 5 years decreased significantly from 83.8% (124/148) to 75.1% (223/297) and 69% (109/158) in S/S, L/S, and L/L genotypes, respectively (P<0.0001). In comparison with HD patients with S/S genotype, those with L/L genotype had a higher prevalence of coronary artery disease (29.1 vs 14.2%; P=0.005). A longer length polymorphism with (GT)(n) >or=30 in the HO-1 gene was associated with a higher frequency of access failure and a poorer patency of AVF in HD patients. The longer GT repeat in the HO-1 promoter might inhibit gene transcription, and consequently offset the CO-mediated protective effect against vascular injury.