Comparative analysis of cellular phenotypes within the neointima from vein segments collected prior to vascular access surgery and stenotic arteriovenous dialysis accesses.

Venous stenosis, secondary to venous neointimal hyperplasia (VNH), at the arteriovenous anastomosis (AV) is a major etiology of vascular access failure in AV fistulas (AVF) and AV grafts (AVG). Recently, our group has reported that severe VNH also occurs prior to vascular access placement. The objective of this study was to perform a comparison of the cellular phenotypes within the neointima from veins collected from subjects at the time of new vascular access creation and stenotic veins from subjects with failed AVGs and AVFs. Vein samples, collected at the time of new access surgery, and stenotic vein segments, collected at access revision, were evaluated for expression of α-smooth muscle actin (SMA), vimentin, and desmin within the neointima, and quantified using semiquantitative scoring. Within the neointima, the majority of cells from vein samples collected at the time of new access surgery were contractile smooth muscle cells, and veins from stenotic AVF and AVG were predominately myofibroblasts. Our results suggest the possibility of different mechanistic pathways in response to vascular injury that occurs prior to vascular access creation vs. after access creation, and that divergent therapeutic approaches may be needed for treating vascular injury in these two settings.

Proliferation patterns in a pig model of AV fistula stenosis: can we translate biology into novel therapies?

Arteriovenous fistula (AVF) stenosis remains an important cause of AVF maturation failure for which there are currently no effective therapies. To understand the mechanisms involved, we have examined the pattern of cellular proliferation at different time points in a pig model of AVF stenosis. Immunohistochemical analysis of cellular proliferation was performed at 2, 7, 28, and 42 days. The distribution of cellular proliferation within the different layers of the vessel wall was also studied. An ANOVA analysis was used to identify differences between the magnitude of cellular proliferation at different time points and within different layers of the vessel wall. Adventitial proliferation occurred at 2 days and declined over time. Intimal and medial proliferation peaked at 7 days and then decreased over time. There was minimal proliferation in all three layers at the 28- and 42-day time points. An important finding was the presence of active myofibroblast proliferation within "neointimal buds" at the 7-day time point. Results suggest that there could be early adventitial activation, followed by a passage of these cells into the medial and intimal layers. These suggest that the application of perivascular antiproliferative (adventitial) therapies at the time of surgery could potentially reduce AVF maturation failure.

Predicting dialysis vascular access blood flow and diameter: too much, too little, or just right.

Arteriovenous fistula (AVF) maturation continues to cause significant morbidity and mortality. Despite the magnitude of the clinical problem, however, there are no effective clinical or biological predictors of AVF success or failure. Caroli et al. describe an innovative technology that may be successful in predicting AVF flow and diameter using standard-of-care preoperative inputs. Pending additional longer-term validation, the use of this technology could help us get the right access into the right patient at the right time.

Preexisting venous calcification prior to dialysis vascular access surgery.

Vascular calcification is present in arterial vessels used for dialysis vascular access creation prior to surgical creation. Calcification in the veins used to create a new vascular access has not previously been documented. The objective of this study was to describe the prevalence of venous calcification in samples collected at the time of vascular access creation. Sixty-seven vein samples were studied. A von Kossa stain was performed to quantify calcification. A semi-quantitative scoring system from 0 to 4+ was used to quantify the percentage positive area for calcification as a fraction of total area (0: 0; 1+: 1-10%; 2+: 11-25%; 3+: 26-50%; 4+: >50% positive). Twenty-two of 67 (33%) samples showed evidence of venous calcification. Histologic examination showed varying degrees of calcification within each cell layer. Among the subset of patients with calcification, 4/22 (18%), 19/22 (86%), 22/22 (100%), and 7/22 (32%) had calcification present within the endothelium, intima, media, and adventitia, respectively. The mean semi-quantitative scores of the 22 samples with calcification were 0.18 ± 0.08, 1.2 ± 0.14, 1.6 ± 0.13, and 0.36 ± 0.12 for the endothelium, intima, media, and adventitia, respectively. Our results demonstrate that vascular calcification is present within veins used to create new dialysis vascular access, and located predominately within the neointimal and medial layers.

Back to the future: how biology and technology could change the role of PTFE grafts in vascular access management.

Although the arteriovenous fistula (AVF) is the preferred mode of dialysis vascular access, AVF maturation failure remains a huge clinical problem, often resulting in a prolonged duration of use of tunneled dialysis catheters. In contrast, polytetrafluoroethylene (PTFE) grafts do not suffer from early failure, but have significant problems with later stenosis and thrombosis. This review will initially summarize the pathology and pathogenesis of PTFE graft dysfunction and will then use this as a basis for describing some novel therapies, which may have the potential to reduce PTFE graft dysfunction. Finally, we will emphasize that the introduction of such therapies could be an important first step toward individualizing overall vascular access care.

Forty-Year Survival of Simultaneous Kidney and Duct-Injected Segmental Pancreas Transplants in a Recipient Maintained on Low-Dose Azathioprine and Prednisone.

Here, we report on the remarkable survival of a simultaneous kidney-pancreas transplant recipient who has received minimal immunosuppression, has had normal kidney function, and has been insulin-free for 40 years since her transplant surgery.

Severe venous neointimal hyperplasia prior to dialysis access surgery.

BACKGROUND: Venous neointimal hyperplasia is the most common cause of arteriovenous (AV) fistula and graft dysfunction following dialysis access surgery. However, the pathogenetic impact of pre-existing venous neointimal hyperplasia at the time of AV access creation on final clinical success is currently unknown in the setting of advanced chronic kidney disease (CKD) and end-stage renal disease (ESRD) patients. The aim of this study was to perform a detailed histological, morphometric, and immunohistochemical analysis of vein specimens in advanced CKD and ESRD patients collected at the time of new vascular access placement. METHODS: Vein samples from 12 patients were collected at the time of AV access creation near the site of AV anastomosis. Histological, immunohistochemistry and morphometric studies were performed on these vein samples. RESULTS: Examination of the tissue specimens obtained at the time of surgery showed neointimal hyperplasia in 10 of 12 specimens, ranging from minimal to very severe. The majority of cells within the neointima were myofibroblasts with a minority of contractile smooth muscle cells present. CONCLUSION: Our work represents a detailed description of the morphometric and cellular phenotypic lesions present in the veins of CKD and ESRD patients, prior to dialysis access placement. These studies (i) suggest the future possibility of a new predictive marker (pre-existing venous neointimal hyperplasia) for AV dialysis access dysfunction and (ii) open the door for the future development of novel local therapies for optimization of the venous substrate on which the dialysis access is created.

Cellular phenotypes in human stenotic lesions from haemodialysis vascular access.

BACKGROUND: Haemodialysis vascular access dysfunction (due to venous stenosis and thrombosis) is a leading cause of hospitalization and morbidity. The aim of the current study was to identify the specific cell types present within stenotic tissue samples from patients with AV fistula and graft failure. METHODS: Discarded tissue segments were collected from the stenotic portions (usually near the graft-vein anastomosis or the AV anastomosis) of 23 dialysis grafts and 20 AV fistulae, and examined for expression of smooth muscle alpha actin, desmin, vimentin and a macrophage marker. RESULTS: The majority of cells within the venous neointima (both grafts and fistulae) were myofibroblasts, with a smaller number of desmin positive smooth muscle cells. The graft neointima had a similar cellular phenotype, albeit without any desmin positive contractile smooth muscle cells. The majority of cells within the PTFE graft material were macrophages. Analysis of sequential sections revealed the presence of fibroblasts within the venous neointima and intragraft region. CONCLUSIONS: Our results demonstrate that contractile smooth muscle cells, myofibroblasts, fibroblasts and macrophages all play a role in the pathogenesis of dialysis access dysfunction (grafts and fistulae). Targeting these specific cell types might result in the development of novel therapeutic paradigms for haemodialysis vascular access dysfunction.

Neointimal hyperplasia in early arteriovenous fistula failure.

BACKGROUND: Hemodialysis vascular access dysfunction currently is a huge clinical problem. Although arteriovenous fistulas (AVFs) are the preferred form of permanent dialysis access, they continue to have significant problems with early AVF failure. Although inadequate dilatation of the venous segment was believed to have a role in early AVF failure, the exact pathogenesis of early AVF failure is unknown despite the magnitude of the clinical problem. STUDY DESIGN: Case series. SETTING & PARTICIPANTS: Hemodialysis patients. OUTCOMES & MEASUREMENTS: Stenotic venous segments from 4 patients with early AVF failure were subjected to a detailed histological, morphometric, and immunohistochemical analysis. RESULTS: All 4 patients had significant luminal stenosis, primarily as a result of eccentric neointimal hyperplasia. This was confirmed through morphometric analysis, which documented intima-media area and thickness ratios that were greater than unity. Cellular phenotyping studies showed that the majority of cells within the region of neointimal hyperplasia were myofibroblasts, with smaller numbers of contractile smooth muscle cells. LIMITATIONS: We described only a limited number of specimens. CONCLUSIONS: We show for the first time that aggressive neointimal hyperplasia is present in venous segment specimens from patients with early AVF failure. Future therapies to address this problem will need to target this pathogenetic pathway.

Body weight alterations under early corticosteroid withdrawal and chronic corticosteroid therapy with modern immunosuppression.

BACKGROUND: Weight gain is a known complication of corticosteroid maintenance therapy. The purpose of the present study was to compare patterns of weight gain under chronic corticosteroid therapy (CCST) with that observed under early (i.e., within 7 days posttransplant) corticosteroid withdrawal (CSWD) in renal-transplant recipients. METHODS: Renal-transplant recipients who underwent early CSWD under four prospective, institutional review board-approved clinical trials were compared with a historic control group of patients receiving maintenance CCST. RESULTS: One hundred sixty-nine patients with early CSWD were compared with 132 patients who received CCST. Mean population weight gain was significantly higher in CCST patients at 3, 6, and 12 months posttransplant. Race influenced weight gain because white CSWD patients demonstrated greater reductions in weight gain compared with African-American patients. Sex also influenced weight gain: women demonstrated a greater benefit from CSWD than did men. Corticosteroid rejection therapy in CSWD patients completely restored weight gain because these patients showed weight gains similar to the CCST group. Finally, pretransplant body mass index (BMI) also influenced weight gain because patients who were overweight (BMI 25-30) or obese (BMI>30) demonstrated a greater reduction in weight gain with CSWD than did patients of normal weight (BMI<25). CONCLUSIONS: Early CSWD minimizes weight gain in renal-transplant recipients. Women, whites, and patients with high pretransplant BMI had greater reductions in weight gain with early CSWD.

The influence of immunomodulatory diets on transplant success and complications.

BACKGROUND: Animal studies have shown that dietary supplementation with arginine and lipids containing the omega-3 and omega-9 fatty acids prolong allograft survival in animals receiving a short course of low-dose cyclosporine. They also reduce cardiovascular complications and infections in humans. METHODS: Adult renal transplant patients receiving standard immunosuppression were stratified according to gender, diabetic state, donor source (LD or CD), and first versus repeat transplant, and randomized to receive or not receive supplemental arginine and canola oil (containing both omega-3 and omega-9 fatty acids) twice daily. Patients were followed for a minimum of 3 years. RESULTS: Seventy-six patients were randomized to the supplement group (S) and 71 patients to the control group (C). Intent-to-treat analysis revealed that S patients had fewer post-30 day first rejection episodes (5.4%) when compared with the C group (23.7%) (P=0.01) and fewer post-30 day episodes of calcineurin inhibitor (CNI) drug toxicity (9.2% vs. 35.3%, P=0.003). S patients developed new onset diabetes mellitus (NODM) less frequently by 3 years (2.3% vs. 14.5%, P=0.04), had fewer cardiac events (5.0% vs. 17.1%, P=0.05), and fewer episodes of sepsis (6.5% vs. 18.7%, P=0.05). CONCLUSIONS: Dietary supplementation with L-arginine and canola oil is a safe, inexpensive, and unique treatment, which is associated with decreased rejection rates and CNI toxicity after the first month in renal transplant patients. Due to reductions in NODM and cardiac events, long-term benefits for patient survival may be particularly important.

Vascular access in hemodialysis: issues, management, and emerging concepts.

This article (1) identifies the types of hemodialysis access, (2) summarizes the clinical standard of care for dialysis access grafts and fistulae, (3) describes the pathology and pathogenesis of venous stenosis in dialysis access grafts and fistulae, (4) tabulates avail-able therapies for hemodialysis vascular access dysfunction and speculates on the rea-sons for the lack of effective therapies, and (5) discusses the development and application of novel therapeutic interventions for this difficult clinical problem. The possibility that dialysis access grafts and fistulae could be the ideal clinical model for testing novel local therapies to block neointimal hyperplasia is discussed.

Natural history of venous morphologic changes in dialysis access stenosis.

PURPOSE: Venous stenosis secondary to neointimal hyperplasia is a major etiology of early arteriovenous fistula (AVF) failure. The natural history of AVF failure is likely influenced by progressive vascular insults to the vein prior to and after AVF creation. The main objectives of this study were to (1) provide a histologic and morphometric description of non-chronic kidney disease (CKD), upper extremity vein specimens and (2) perform a morphometric analysis to study venous histology from non-CKD upper extremity veins, veins collected at the time of new vascular access surgery and veins collected from failed stenotic AVFs. METHODS: Vein samples from 11 non-CKD deceased donors, 29 subjects receiving new vascular access creation and 20 subjects with stenotic failed AVFs were collected for histologic and morphometric analysis. RESULTS: The mean values of average intima/media thickness ± S.E. from veins collected from non-CKD subjects, subjects receiving new vascular access and subjects with stenotic AVFs were 0.16±0.02, 0.43±0.07 and 3.84±0.55, respectively (p<0.0001). Among donor, non-CKD, vein samples, only diabetes (p=0.0007) was associated with increased average intima/media thickness. CONCLUSIONS: Our results demonstrate a progressively increasing venous neointimal hyperplasia development from the non-CKD period through the period of AVF creation and failure. Vascular injuries from complications of progressive CKD prior to access placement and vascular injuries after vascular access placement may play important roles in these progressive vascular changes, and need to be further elucidated.

Pathogenetic role for early focal macrophage infiltration in a pig model of arteriovenous fistula (AVF) stenosis.

PURPOSE: Arteriovenous fistula non-maturation because of a peri-anastomotic venous stenosis is currently a huge clinical problem for which there are no effective therapies. METHODS: In an attempt to further define the cellular pathways involved in this process we have assessed the pattern and intensity of macrophage infiltration at different time points in a pig model of AVF stenosis. RESULTS: Our results demonstrate an early and eccentric pattern of macrophage infiltration at 2d with a rapid disappearance of this infiltrate by 7d. CONCLUSION: We suggest that this early and eccentric macrophage infiltration could play an important role in the pathogenesis of AVF non-maturation.

Balloon-assisted maturation (BAM) of the arteriovenous fistula: the good, the bad, and the ugly.

Arteriovenous fistula (AVF) maturation failure is currently a huge clinical problem. One approach to enhance the AVF maturation rate is an aggressive sequence of balloon angioplasty procedures, often known as balloon-assisted maturation. The goal of the current paper is to explore the pros and cons of this procedure and to try and better identify its impact on AVF maturation.

External beam radiation therapy for PTFE dialysis grafts: a pilot study.

PURPOSE: The aim of this study was to identify the effects of external beam radiation on PTFE dialysis graft dysfunction. METHODS: Seven patients who underwent PTFE dialysis graft angioplasty were randomized to receive either two 8 Gy doses of external beam radiation or no radiation. The primary endpoint was time to graft thrombosis with a secondary endpoint of time to first intervention. RESULTS: There was no statistically significant difference between the two groups in either of the endpoints, although grafts in the radiation group had a shorter time to thrombosis or intervention. CONCLUSIONS: Our results demonstrate technical feasibility for use of external beam radiation in the setting of dialysis vascular access graft dysfunction. Larger randomized studies are required to identify whether there is a clinical benefit from this intervention.

Decreased cumulative access survival in arteriovenous fistulas requiring interventions to promote maturation.

BACKGROUND AND OBJECTIVES: New arteriovenous fistulas (AVF) are frequently unsuitable for hemodialysis because of AVF nonmaturation. Aggressive endovascular or surgical interventions are often undertaken to salvage nonmaturing AVFs. The effect of early interventions to promote AVF maturation on subsequent long-term AVF outcomes is unknown. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: We evaluated 173 hemodialysis patients from two academic centers who received a new AVF. Of these, 96 (56%) required no further intervention, 54 (31%) required one intervention, and 23 (13%) required two or more interventions to achieve suitability for dialysis. We calculated AVF survival and frequency of postmaturation interventions in each group. RESULTS: Cumulative AVF survival (access cannulation to permanent failure) in patients with two or more versus one versus zero interventions before maturation was 68% versus 78% versus 92% at 1 year, 57% versus 71% versus 85% at 2 years, and 42% versus 57% versus 75% at 3 years. Using Cox regression analysis with interventions before maturation, age, sex, race, diabetes, peripheral vascular disease, access site, and obesity in the model, intervention before maturation (two or more) was the only factor associated with cumulative AVF survival. The number of interventions required to maintain patency after maturation was 3.51 ± 2.20 versus 1.37 ± 0.31 versus 0.76 ± 0.10 per year in patients with two or more versus one versus zero interventions before maturation. CONCLUSIONS: Compared with AVF that mature without interventions, AVF that require interventions have decreased cumulative survival and require more interventions to maintain their patency for hemodialysis.