Doxycycline may reduce the incidence of aneurysms in haemodialysis vascular accesses

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.

ß-Catenin is markedly induced in a murine model of an arteriovenous fistula: the effect of metalloproteinase inhibition

Neointimal hyperplasia contributes to failure of hemodialysis arteriovenous fistulas (AVFs). Increased expression of matrix metalloproteinase (MMP)-9 occurs in AVFs, and MMP-9 is implicated in neointimal hyperplasia and vascular injury. Recent studies demonstrate that MMP-9, by degrading N-cadherin, leads to increased expression of β-catenin and β-catenin-dependent proliferation of smooth muscle cells. The present study examined this pathway in the venous limb of a murine AVF model. Western analyses demonstrate that, in this model, there is diminished expression of N-cadherin accompanied by increased expression of β-catenin, c-Myc, and proliferating cell nuclear antigen (PCNA). By immunohistochemistry, β-catenin and c-Myc localized to proliferating smooth muscle cells in the venous limb of the AVF. Increased expression of β-catenin was accompanied by augmented expression of phosphorylated (p)-glycogen synthase kinase (GSK)-3β, GSK-3β, and integrin-linked kinase. The administration of doxycycline suppressed MMP-9 expression but did not reduce venous histological injury in the AVF, or increase AVF patency assessed 6 wk after its creation. Doxycycline did not influence expression of β-catenin, c-Myc, GSK-3β, or integrin-linked kinase. Thus, in this vascular injury model, the upregulation of β-catenin cannot be readily attributed to MMP-9 upregulation; increased β-catenin expression may reflect either the upregulation of p-GSK-3β, GSK-3β, or integrin-linked kinase. This study provides the first exploration of β-catenin in an AVF, demonstrating substantial upregulation of this mitogenic signaling molecule and uncovering possible mechanisms that may account for such upregulation.

Evolution of shear stress, protein expression, and vessel area in an animal model of arterial dilatation in hemodialysis grafts

PURPOSE

To evaluate the wall shear stress, protein expression of matrix metalloproteinase (MMP)-2 and MMP-9 and tissue inhibitor of matrix metalloproteinase (TIMP)-1 and TIMP-2, and vessel area over time in a porcine model for polytetrafluoroethylene (PTFE) hemodialysis grafts.

MATERIALS AND METHODS

In 21 pigs, subtotal renal infarction was created, and 28 days later, a PTFE graft was placed to connect the carotid artery to the ipsilateral jugular vein. Phase-contrast magnetic resonance imaging was used to measure blood flow and vessel area at 1, 3, 7, and 14 days after graft placement. Wall shear stress was estimated from the law of Poiseuille. Animals were killed at day 3 (n = 7), day 7 (n = 7), and day 14 (n = 7) and expression of MMP-2, MMP-9, TIMP-1, and TIMP-2 were determined at the grafted and control arteries.

RESULTS

The mean wall shear stress of the grafted artery was higher than in the control artery at all time points (P < .05). It peaked by day 3 and decreased by days 7-14 as the vessel area nearly doubled. By days 7-14, there was a significant increase in active MMP-2 followed by a significant increase in pro-MMP-9 and active MMP-9 by day 14 (P < .05, grafted artery vs control). TIMP-1 expression peaked by day 7 and then decreased, whereas TIMP-2 expression was decreased at days 7-14.

CONCLUSIONS

The wall shear stress of the grafted artery peaks by day 3, with increased MMP-2 activity by days 7-14, followed by increase pro-MMP-9 and active MMP-9 by day 14. In addition, the vessel area nearly doubled.

Brachiobasilic versus brachiocephalic arteriovenous fistula: a prospective randomized study

BACKGROUND

The most recent Kidney Disease Outcomes Quality Initiative (KDOQI) guidelines recommend that the order of preference for arteriovenous fistula (AVF) placement is the radial-cephalic primary AVF, followed by the secondary brachiocephalic (BC) and, if either of these is not viable, then brachiobasilic (BB) AVF should be fashioned. However, there is limited prospective data comparing technical and clinical outcomes of these two approaches. The purpose of our study was to compare outcome, patency, and complication rates in these two autogenous upper arm AV accesses.

METHODS

Between December 2003 and and January 2007, patients (61 male, 39 female) who have lost more distal AVFs were enrolled in the study. After preoperative duplex mapping, patients with patent both basilic and cephalic veins greater than 3 mm of diameter were randomized into BCAVF and BBAVF groups, each group consisting of 50 patients. All procedures were performed under local anesthesia as one-stage procedures. Follow-up data were prospectively collected. Kaplan-Meier analysis was used to calculate primary and secondary patency rates. Univariate and multivariate Cox-regression analysis was used to find risks for the occurrence of thrombosis.

RESULTS

Baseline demographics, clinical characteristics, and preoperative history dialysis access were comparable between groups with the exception of the fact that mean caliber of the basilic veins were larger (4.51 +/- 0.93 mm vs 3.90 +/- 0.1 mm; P = .002). The mean duration of operation was significantly shorter in the BC group compared with the BB group (P < .001). There was no significant difference in the thirty day mortality, wound complications, 24 hour thrombosis, postoperative hemorrhage, maturation, and time to maturation between the groups. Mean follow-up was 43.2 +/- 1.8 months. Primary patency at 1 and 3 years of follow-up was 87% and 81% for the BC group and 86% and 73% for the BB group (P = .7) Secondary patency at one and three year follow-up was 87% and 70% for the BC group and 88% and 71% for the BB group, respectively (P = .8). Twenty-eight patients (28%) in the BC (18 patients) and BB (10 patients) group died with a patent fistula during the follow-up period (P = .18). Multivariate analysis revealed that use of dominant arm increased the risk of fistula failure.

CONCLUSION

We conclude that brachiobasilic and brachiocephalic AVF are equally effective alternatives; however, a longer and demanding operation with BB AVF construction should be considered.