Natural history of venous morphologic changes in dialysis access stenosis

Zic family member 3 attenuates oxidative stress-induced vascular smooth muscle cell apoptosis in patients with chronic kidney disease

Neointimal hyperplasia is reportedly essential for arteriovenous fistulas (AVF) in patients undergoing hemodialysis. Oxidative stress is vital in the progression of uremic venous intimal hyperplasia. Studies have suggested that zinc ions obstruct vascular calcification in patients with chronic kidney disease (CKD). Recent studies have shown that the zinc finger protein, Zic family member 3 (ZIC3), is crucial for the earliest cardiovascular progenitors. ZIC3 mutations are associated with congenital heart disease. However, the mechanism of action of ZIC3 in vascular intimal hyperplasia in CKD remains unelucidated. Venous specimens were collected during primary AVF surgery and traumatic amputation, and serum samples were collected from patients with CKD and healthy controls. Mouse vascular smooth muscle cells (VSMCs) were treated with hydrogen peroxide (H2O2) to clarify the role of ZIC3 in CKD. ZIC3 expression was reduced in the veins of patients with uremia and the serum of those with CKD. Zic3 and Bcl2 levels were significantly decreased in mouse VSMCs treated with H2O2·H2O2 inhibited mouse VSMC activity, upregulated Bax, and cleaved caspase 3 expression. Following Zic3 overexpression, Bcl2 expression level and cell viability were elevated, whereas Bax and cleaved caspase 3 expression levels were downregulated. In contrast, Zic3 knockdown yielded the opposite results. Therefore, ZIC3 could be a new therapeutic target in venous neointimal hyperplasia of CKD.

Downregulation of the endothelial histone demethylase JMJD3 is associated with neointimal hyperplasia of arteriovenous fistulas in kidney failure

Jumonji domain-containing protein-3 (JMJD3), a histone H3 lysine 27 (H3K27) demethylase, promotes endothelial regeneration, but its function in neointimal hyperplasia (NIH) of arteriovenous fistulas (AVFs) has not been explored. In this study, we examined the contribution of endothelial JMJD3 to NIH of AVFs and the mechanisms underlying JMJD3 expression during kidney failure. We found that endothelial JMJD3 expression was negatively associated with NIH of AVFs in patients with kidney failure. JMJD3 expression in endothelial cells (ECs) was also downregulated in the vasculature of chronic kidney disease (CKD) mice. In addition, specific knockout of endothelial JMJD3 delayed EC regeneration, enhanced endothelial mesenchymal transition, impaired endothelial barrier function as determined by increased Evans blue staining and inflammatory cell infiltration, and accelerated neointima formation in AVFs created by venous end to arterial side anastomosis in CKD mice. Mechanistically, JMJD3 expression was downregulated via binding of transforming growth factor beta 1-mediated Hes family transcription factor Hes1 to its gene promoter. Knockdown of JMJD3 enhanced H3K27 methylation, thereby inhibiting transcriptional activity at promoters of EC markers and reducing migration and proliferation of ECs. Furthermore, knockdown of endothelial JMJD3 decreased endothelial nitric oxide synthase expression and nitric oxide production, leading to the proliferation of vascular smooth muscle cells. In conclusion, we demonstrate that decreased expression of endothelial JMJD3 impairs EC regeneration and function and accelerates neointima formation in AVFs. We propose increasing the expression of endothelial JMJD3 could represent a new strategy for preventing endothelial dysfunction, attenuating NIH, and improving AVF patency in patients with kidney disease.

Vein morphometry in end-stage kidney disease: Teasing out the contribution of age, comorbidities, and vintage to chronic wall remodeling

Background

Chronic kidney disease (CKD) is a highly comorbid condition with significant effects on vascular health and remodeling. Upper extremity veins are important in end-stage kidney disease (ESKD) due to their potential use to create vascular accesses. However, unlike arteries, the contribution of CKD-associated factors to the chronic remodeling of veins has been barely studied.

Methods

We measured morphometric parameters in 315 upper extremity veins, 131 (85% basilic) from stage 5 CKD/ESKD patients and 184 (89% basilic) from non-CKD organ donors. Associations of demographic and clinical characteristics with intimal hyperplasia (IH) and medial fibrosis were evaluated using multivariate regression models.

Results

The study cohort included 33% females, 30% blacks, 32% Hispanics, and 37% whites. Over 60% had hypertension, and 25% had diabetes independent of CKD status. Among kidney disease participants, 26% had stage 5 CKD, while 22 and 52% had ESKD with and without history of a previous arteriovenous fistula/graft (AVF/AVG), respectively. Intimal hyperplasia was associated with older age (β = 0.13 per year, confidence interval [CI] = 0.002-0.26), dialysis vintage > 12 months (β = 0.22, CI = 0.09-0.35), and previous AVF/AVG creation (β = 0.19, CI = 0.06-0.32). Upper quartile values of IH were significantly associated with diabetes (odds ratio [OR] = 2.02, CI = 1.08-3.80), which demonstrated an additive effect with previous AVF/AVG history and longer vintage in exacerbating IH. Medial fibrosis also increased as a function of age (β = 0.17, CI = 0.04-0.30) and among patients with diabetes (β = 0.15, CI = 0.03-0.28). Age was the predominant factor predicting upper quartile values of fibrosis (OR = 1.03 per year, CI = 1.01-1.05) independent of other comorbidities.

Conclusion

Age and diabetes are the most important risk factors for chronic development of venous IH and fibrosis independent of CKD status. Among kidney disease patients, longer dialysis vintage, and history of a previous AVF/AVG are strong predictors of IH.

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

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

Intimal Hyperplasia and Arteriovenous Fistula Failure: Looking Beyond Size Differences

The development of venous intimal hyperplasia (IH) has been historically associated with failure of arteriovenous fistulas (AVF) used for hemodialysis. This long-standing assumption, based on histological observations, has been recently challenged by clinical studies indicating that the size of the intima by itself is not enough to explain stenosis or AVF maturation failure. Irrespective of this lack of association, IH is present in most native veins and fistulas, is prominent in many cases, and suggests a role in the vein that may not be reflected by its dimensions. Therefore, the contribution of IH to AVF dysfunction remains controversial. Using only clinical data and avoiding extrapolations from animal models, we critically discuss the biological significance of IH in vein remodeling, vascular access function, and the response of the venous wall to repeated trauma in hemodialysis patients. We address questions and pose new ones such as: What are the factors that contribute to IH in pre-access veins and AVFs? Do cellular phenotypes and composition of the intima influence AVF function? Are there protective roles of the venous intima? This review explores these possibilities, with hopes of rekindling a critical discussion about venous IH that goes beyond thickness and AVF outcomes.

Outcome of stenting in central venous obstruction of benign etiology

Background: The aim of this study is to evaluate long term outcome in patients treated for benign superior vena cava (SVC) syndrome by endovascular techniques. Patients and methods: Between 2015 and 2018, 62 patients suffering from central venous obstruction of benign etiology underwent balloon angioplasty with stent placement for venous obstruction in our department. Patency was assessed clinically, using duplex ultrasound in all patients or with CT-phlebography in selected cases. Results: Median age was 60 years (23-83), forty-one patients (66%) had central venous devices. Swelling of the arm and face were the main symptoms (71%). During the median follow up of 22 months (9-38), cumulative primary patency was 71% after venous stenting. The cumulative assisted primary and the secondary patency were 85% and 92%, respectively. Conclusions: Recanalization and stenting of central vein obstruction has turned out to be the technique of reference and provides satisfactory mid-term patency rates. After adjusting for the risk factors, presence of AV-fistula remained a significant risk factor for recurrent stenosis or loss of patency after intervention.

Quality indicators of vascular access procedures for hemodialysis

Improved quality of surgical procedures can minimize complications, the morbidity and mortality of patients, and in addition decrease costs. Quality indicators in angioaccess surgery are, however, not clearly defined. The aim of this review article is therefore to find the most important factors affecting quality in vascular access procedures. Even though autogenous arteriovenous fistula has been recognized as the best vascular access for hemodialysis, the high percentage of unsuccessful attempts associated with it raises the question about quality assessment in angioaccess procedures. Unfortunately, quality indicators in vascular access surgery are difficult to define and measure. Among those that can be obtained are: the time between the presentation of patients to a vascular access surgeon and the construction of a fistula, the percentage of autogenous fistulas, the percentage of functional fistulas in prevalent and incident hemodialysis patients, the percentage of creation of a functional fistula in the first attempt, and durability of an access. Organizational improvement and educational programs are also necessary at institutions with inferior quality indicators of vascular access care, as even small increase in quality may mean the survival of an individual patient. Quality indicators in angioaccess surgery can also serve as a helpful tool in choosing the best vascular access surgeon or vascular access center. The choice can consequently reflect on increased survival and quality of life in patients needing hemodialysis.

Abnormalities of vascular histology and collagen fiber configuration in patients with advanced chronic kidney disease

INTRODUCTION:

Several histologic features have been identified in the upper-extremity arteries and veins of patients with advanced chronic kidney disease, which may affect arteriovenous fistula maturation. However, it is unclear whether these chronic kidney disease vascular features are abnormal.

METHODS:

We obtained upper-extremity arterial and venous specimens from 125 advanced chronic kidney disease patients undergoing arteriovenous fistula creation and from 15 control subjects. We quantified medial fibrosis, micro-calcification, and intimal hyperplasia with appropriate histology stains. We characterized medial collagen fiber configuration in second-harmonic-generation microscopy images for the fiber anisotropy index and the dominant fiber direction.

RESULTS:

The advanced chronic kidney disease patients were significantly younger than control subjects (53 ± 14 years vs 76 ± 11 years, p < 0.001). After controlling for age, the chronic kidney disease patients had greater arterial medial fibrosis (69% ± 14% vs 51% ± 10%, p < 0.001) and greater arterial micro-calcification (3.03% ± 5.17% vs 0.01% ± 0.03%, p = 0.02), but less arterial intimal thickness (30 ± 25 µm vs 63 ± 25 µm, p < 0.001), as compared to control subjects. The anisotropy index of medial collagen fibers was lower in both arteries (0.24 ± 0.10 vs 0.44 ± 0.04, p < 0.001) and veins (0.28 ± 0.09 vs 0.53 ± 0.10, p < 0.001) in chronic kidney disease patients, indicating that orientation of the fibers was more disordered. The dominant direction of medial collagen fibers in chronic kidney disease patients was greater in the arteries (49.3° ± 23.6° vs 4.0° ± 2.0°, p < 0.001) and the veins (30.0° ± 19.6° vs 3.9° ± 2.1°, p < 0.001), indicating that the fibers in general were aligned more perpendicular to the lumen.

CONCLUSION:

Advanced chronic kidney disease is associated with several abnormalities in vascular histology and collagen fiber configuration. Future research is needed to investigate whether these abnormalities affect the maturation outcomes of arteriovenous fistulas.

Intracranial Venous Reflux Caused by Occlusion of the Brachiocephalic Vein Mimicking Dural Arteriovenous Fistula

BACKGROUND

High signal intensity of cerebral venous sinuses on magnetic resonance angiography (MRA) indicates high flow of shunt from arterial blood, suggesting dural arteriovenous fistula (dAVF). Herein, we describe the cases of 2 patients with intracranial venous reflux caused by brachiocephalic vein occlusion (BVO) mimicking dAVF on MRA.

CASE DESCRIPTION

Case 1 was a 71-year-old woman who had received arteriovenous graft (AVG) surgery for hemodialysis and presented with headache. MRA depicted high signal intensities in the left jugular vein, inferior petrosal sinus, and ophthalmic vein suggesting intracranial dAVF. However, cerebral angiography revealed intracranial venous reflux through the jugular vein caused by BVO. After balloon angioplasty with stenting for BVO, normal venous drainage was restored and her symptoms resolved. Case 2 was a 62-year-old woman who had received AVG for hemodialysis and was hospitalized due to seizure. MRA revealed high signal intensities of the left transverse-sigmoid sinus and jugular vein, and it was suspected that they were associated with BVO. She did not receive immediate intervention because of her septic condition. The patient ultimately died of fatal intracranial hemorrhage and subarachnoid hemorrhage.

CONCLUSIONS

Central venous occlusion may occur in patients with end-stage renal disease who are receiving AVG for hemodialysis. Intracranial venous reflux resulting from BVO can induce various neurologic disorders including intracranial venous hypertension or hemorrhage. Prompt recognition and implementation of endovascular treatment can be beneficial in cases of symptomatic central venous occlusion.

Dialysis-Related Parameters Influence Remodeling in the Venous Part of the Native Arteriovenous Fistula

BACKGROUND

The aim of this study was to evaluate the association of hemodynamic parameters related to hemodialysis and antropometric parameters of patients with changes in the venous part of the arteriovenous fistula (AVF) at points of needling.

METHODS

Two hundred forty-two hemodialysis (HD) patients (60.3% men), with median age 65 (interquartile range [IQR] 56-75) years, on HD treatment for a median of 49 (IQR 20-88) months with functioning fistula were recruited for the study. The history of vascular access, comorbidity, antropometric (body mass index, body surface area, and body composition), and dialysis-related parameters were analyzed. The cross-sectional area of upper extremity vessels were measured using ultrasound and included 2 points: A (arterial point for blood aspiration) and V (venous point for returning the blood after purification). The difference between A and V (A-V) was calculated.

RESULTS

The median cross-sectional area of A was larger than V (1.04 [IQR 0.58-1.7] vs. 0.74 cm² [IQR: 0.41-1.39], P <0.0001). The median difference between A and V (A-V) was 0.17 cm² and positively correlated with mean blood flow (Qb), effective Kt/V, and time of AVF use. Other analyzed factors had no influence on A-V. In the multivariate analysis, the independent factor increasing the difference (A-V) was mean blood flow measured during HD sessions.

CONCLUSIONS

The needling and utilization of AVF for hemodialysis may affect vein anatomy, namely causing dilatation at the arterial point and narrowing at venous point of AVF. We suggest that blood pump velocity of the dialysis machine may have an impact on these changes, but practical importance of these findings has to be elucidated. The significance of (A-V) factor in the prognosis of fistula complications should be further studied and confirmed in the prospective trials.

New Developments in Our Understanding of Neointimal Hyperplasia

The vascular access remains the lifeline for the hemodialysis patient. The most common etiology of vascular access dysfunction is venous stenosis at the vein-artery anastomosis in arteriovenous fistula and at the vein-graft anastomosis in arteriovenous grafts (AVG). This stenotic lesion is typically characterized on histology as aggressive venous neointimal hyperplasia in both arteriovenous fistula and AVG. In recent years, we have advanced our knowledge and understanding of neointimal hyperplasia in vascular access and begun testing several novel therapies. This article will (1) review recent developments in our understanding of the pathophysiology of neointimal hyperplasia development in AVG and fistula failure, (2) discuss atypical factors leading to neointimal hyperplasia development, (3) highlight key novel therapies that have been evaluated in clinical trials, and (4) discuss future opportunities and challenges to improve our understanding of vascular access dysfunction and translate this knowledge into novel and innovative therapies.

Hemodynamic and biologic determinates of arteriovenous fistula outcomes in renal failure patients

The outcome of patients with end-stage renal disease on hemodialysis depends on a functioning vascular access. Although a variety of access options are available, the arteriovenous fistula remains the best vascular access. Unfortunately the success rate of mature fistula use remains poor. The creation of an arteriovenous fistula is followed by altered hemodynamic and biological changes that may result in neointimal hyperplasia and eventual venous stenosis. This review provides an overview of these changes and the needed research to provide a long lasting vascular access and hence improve outcomes for patients with end-stage renal disease.

Doppler ultrasound and calcification score: improving vascular access surveillance

AIM

Vascular access (VA) dysfunction limits hemodialysis delivery, which increases morbidity and mortality. The most com mon cause of VA failure is thrombosis, due to flow limiting stenosis resulting from neointimal hyperplasia. This occurs not only due to hemodynamic factors but also by systemic ones related to vascular atherosclerosis, inflammation and calcification, which has developed a simple vascular calcification score (SVCS) predictor of vascular calcification and arterial stiffness. The NKF-K/DOQ recommends several diagnostic procedures for VA surveillance. Blood access flow (Qa) has predictive power for the detection of stenosis. Our aim was to evaluate the role of systemic factors, especially SCVS, on Qa.

MATERIAL AND METHODS

Transversal study in 50 patients. Qa value was obtained with Blood Temperature Monitor and Doppler method. Pearson coefficient evaluated correlation between them. Clinical, lab and radiological variables were recorded and non-parametric tests evaluated how both Qa varied with them.

RESULTS

Pearson's corelation between DU-Qa and TD-Qa was 0.851 (p-value <0.001). DU-Qa varied significantly with age (p = 0.012), VA type (p = 0.021), SCVS (p = 0.030), intra-access arterial pressure (p = 0.015) and time on dialysis (p = 0.002). BTM-Qa varied significantly with diabetes status (p = 0.027), age (p = 0.017), first VA status (p = 0.036), intra-access arterial pressure (p = 0.028) and dialysis time (p = 0.001). Nevertheless, gender, hypertensive status and analitical parameters did not change the flow values.

CONCLUSION

Higher SVCS was associated only with lower DU-Qas, giving this method an advantage towards the indirect one. Additionally, a simple method like SVCS may be used to guide new surveillance recommendations accordingly to risk stratification.

CD4(+) lymphocytes improve venous blood flow in experimental arteriovenous fistulae

BACKGROUND

The role of immune cells in arteriovenous fistulae (AVF) maturation is poorly understood and has received, until quite recently, little attention. This study examines the function of T lymphocytes in AVF vascular remodeling.

METHODS

Experimental fistulae were created in athymic rnu nude rats lacking mature T lymphocytes and euthymic control animals by anastomosing the left superior epigastric vein to the nearby femoral artery. Blood flow rates, wall morphology, and histologic changes were assessed in AVF 21 days after creation. The effect of CD4(+) lymphocytes on AVF maturation in athymic animals was analyzed by adoptive transfer of cells after fistula creation.

RESULTS

The absence of T lymphocytes compromised blood flow in experimental fistulae. Histopathologic inspection of AVF from athymic rats revealed that T-cell immunodeficiency negatively affected venous vascular remodeling, as evidenced by a reduced lumen, a thick muscular layer, and a low number of inflammatory cells compared with control animals. Adoptive transfer of CD4(+) lymphocytes from euthymic rats into athymic animals after fistula creation improved blood flow and reduced intima-media thickness.

CONCLUSION

These results point at the protective role of CD4(+) lymphocytes in the remodeling of the AVF vascular wall.

Morphometric and histological parameters in veins of diabetic patients undergoing brachiocephalic fistula placement

Diabetic patients with end-stage renal failure have higher rates of arteriovenous failures when compared with nondiabetics. The aim was to compare differences in indicators of vascular remodeling and endothelial dysfunction in veins of patients with or without diabetes at the time of surgical placement. In this prospective observational trial, vein samples were collected from patients when a brachiocephalic fistula was created. Morphometric measurements and extent of fibrosis were determined using Image J software. Histological analysis, for the presence of myofibroblasts and level of endothelial nitric oxide synthase, was performed by immunohistochemical staining and scored in semi-quantitative manner. Asymmetric dimethylarginine was determined at the time of access placement. Comparison of diabetics and nondiabetics was performed using Wilcoxon rank sum and Fisher's exact tests. Eighteen patients were included; 10 were diabetics. There was a significant difference in the measurement of vein area between groups, with diabetic vein samples having larger luminal area of average 832,001.18 μm(2) (317,582.17-3,695,670.36, P = 0.04). The maximal intimal to medial thickness ratio was higher in diabetic vein samples (0.71 vs. 0.24, P = 0.03) along with statistically significant higher maximal intimal thickness (312.12 vs. 115.14 μm, P = 0.03). There is a significant difference in vascular wall remodeling between diabetics and nondiabetics at the level of the cephalic vein at the time of brachiocephalic placement. The unexpected finding of significantly larger luminal area in diabetic veins could be a major factor positively affecting brachiocephalic outcomes in otherwise impaired remodeling in this patient population.

c-Kit signaling determines neointimal hyperplasia in arteriovenous fistulae

Stenosis of arteriovenous (A-V) fistulae secondary to neointimal hyperplasia (NIH) compromises dialysis delivery, which worsens patients' quality of life and increases medical costs associated with the maintenance of vascular accesses. In the present study, we evaluated the role of the receptor tyrosine kinase c-Kit in A-V fistula neointima formation. Initially, c-Kit was found in the neointima and adventitia of human brachiobasilic fistulae, whereas it was barely detectable in control veins harvested at the time of access creation. Using the rat A-V fistula model to study venous vascular remodeling, we analyzed the spatial and temporal pattern of c-Kit expression in the fistula wall. Interestingly, c-Kit immunoreactivity increased with time after anastomosis, which concurred with the accumulation of cells in the venous intima. In addition, c-Kit expression in A-V fistulae was positively altered by chronic kidney failure conditions. Both blockade of c-Kit with imatinib mesylate (Gleevec) and inhibition of stem cell factor production with a specific short hairpin RNA prevented NIH in the outflow vein of experimental fistulae. In agreement with these data, impaired c-Kit activity compromised the development of NIH in A-V fistulae created in c-KitW/Wv mutant mice. These results suggest that targeting of the c-Kit signaling pathway may be an effective approach to prevent postoperative NIH in A-V fistulae.