Efficient transgene expression from naked DNA delivered into an arterio-venous fistula model for kidney dialysis

Periadventitial β-aminopropionitrile-loaded nanofibers reduce fibrosis and improve arteriovenous fistula remodeling in rats

Background

Arteriovenous fistula (AVF) postoperative stenosis is a persistent healthcare problem for hemodialysis patients. We have previously demonstrated that fibrotic remodeling contributes to AVF non-maturation and lysyl oxidase (LOX) is upregulated in failed AVFs compared to matured. Herein, we developed a nanofiber scaffold for the periadventitial delivery of β-aminopropionitrile (BAPN) to determine whether unidirectional periadventitial LOX inhibition is a suitable strategy to promote adaptive AVF remodeling in a rat model of AVF remodeling.

Methods

Bilayer poly (lactic acid) ([PLA)-]- poly (lactic-co-glycolic acid) ([PLGA)] scaffolds were fabricated with using a two-step electrospinning process to confer directionality. BAPN-loaded and vehicle control scaffolds were wrapped around the venous limb of a rat femoral-epigastric AVF during surgery. AVF patency and lumen diameter were followed monitored using Doppler ultrasound surveillance and flow was measured before euthanasia. AVFs were harvested after 21 days for histomorphometry and immunohistochemistry. AVF compliance was measured using pressure myography. RNA from AVF veins was sequenced to analyze changes in gene expression due to LOX inhibition.

Results

Bilayer periadventitial nanofiber scaffolds extended BAPN release compared to the monolayer design (p < 0.005) and only released BAPN in one direction. Periadventitial LOX inhibition led to significant increases in AVF dilation and flow after 21 days. Histologically, BAPN trended toward increased lumen and significantly reduced fibrosis compared to control scaffolds (p < 0.01). Periadventitial BAPN reduced downregulated markers associated with myofibroblast differentiation including SMA, FSP-1, LOX, and TGF-β while increasing the contractile marker MYH11. RNA sequencing revealed differential expression of matrisome genes.

Conclusion

Periadventitial BAPN treatment reduces fibrosis and promotes AVF compliance. Interestingly, the inhibition of LOX leads to increased accumulation of contractile VSMC while reducing myofibroblast-like cells. Periadventitial LOX inhibition alters the matrisome to improve AVF vascular remodeling.

Pathological analysis of vascularization of the arterialized veins in failed arteriovenous fistulas among uremic patients

PURPOSE

To assess venous wall vascularization and its correlation with neointimal hyperplasia (NIH) in failed arteriovenous fistulas (AVFs).

METHODS

A total of 43 uremic patients who received a first AVF creation and 39 patients who received reconstruction of failed fistulas were enrolled in the study. A 5-10 mm vein segment adjacent to future fistula creation or reconstruction site was surgically removed and assessed using histopathological analyses and stained by immunohistochemistry to quantify vasa vasorum density (VVD).

RESULTS

Both the intimal thickness (70.68 [28.81-99.54] vs. 4.53 [2.69-7.30] μm, P < 0.001) and the intimal thickness/medial thickness ratio (2.20 [0.77-4.36] vs. 0.15 [0.10-0.30], P < 0.001) were higher in failed AVFs than in pre-access veins. CD31 and factor VIII marked VVDs both in the intima (6.31 [1.62-12.53] vs. 0.0 [0.0-0.0], P < 0.001; 7.82 [3.33-11.61] vs. 0.0 [0.0-0.0], P < 0.001) and media (10.0 [7.59-12.95] vs. 3.71 [2.44-4.87], P < 0.001; 8.33 [5.55-13.0] vs. 3.57 [2.53-4.82], P < 0.001), and the intimal VVD/medial VVD ratio (0.67 [0.19-1.08] vs. 0.0 [0.0-0.0], P < 0.001; 0.71 [0.39-1.14] vs. 0.0 [0.0-0.0], P < 0.001) were significantly higher in failed AVFs than in pre-access veins. There was also a positive relationship between the intimal VVD/medial VVD ratio and the intimal thickness/medial thickness ratio (P < 0.001). In addition, compared to pre-access veins, vascular endothelial cell growth factor-A (VEGF-A) expression was higher in failed AVFs.

CONCLUSIONS

Vascularization of the vessel wall was noticeably more developed in the arterialized veins, especially among the NIH regions in failed AVFs.

Inhibition of Lysyl Oxidase with β-aminopropionitrile Improves Venous Adaptation after Arteriovenous Fistula Creation

BACKGROUND

The arteriovenous fistula (AVF) is the preferred hemodialysis access for end-stage renal disease (ESRD) patients. Yet, establishment of a functional AVF presents a challenge, even for the most experienced surgeons, since postoperative stenosis frequently occludes the AVF. Stenosis results from the loss of compliance in fibrotic areas of the fistula which turns intimal hyperplasia into an occlusive feature. Fibrotic remodeling depends on deposition and crosslinking of collagen by lysyl oxidase (LOX), an enzyme that catalyzes the deamination of lysine and hydroxylysine residues, facilitating intra/intermolecular covalent bonds. We postulate that pharmacological inhibition of lysyl oxidase (LOX) increases postoperative venous compliance and prevents stenosis in a rat AVF model.

METHODS

LOX gene expression and vascular localization were assayed in rat AVFs and human pre-access veins, respectively. Collagen crosslinking was measured in humans AVFs that matured or failed, and in rat AVFs treated with β-aminopropionitrile (BAPN), an irreversible LOX inhibitor. BAPN was either injected systemically or delivered locally around rat AVFs using nanofiber scaffolds. The major endpoints were AVF blood flow, wall fibrosis, collagen crosslinking, and vascular distensibility.

RESULTS

Non-maturation of human AVFs was associated with higher LOX deposition in pre-access veins (N=20, P=0.029), and increased trivalent crosslinks (N=18, P=0.027) in human AVF tissues. Systemic and local inhibition of LOX increased AVF distensibility, while reducing wall fibrosis and collagen crosslinking in rat fistulas.

CONCLUSIONS

Our results demonstrate that BAPN-mediated inhibition of LOX significantly improves vascular remodeling in experimental fistulas.

Assessment of micro-mechanical variations in experimental arteriovenous fistulae using atomic force microscopy

PURPOSE

This study presents a method to quantify micro-stiffness variations in experimental arteriovenous fistulae (AVF).

METHODS

AVF created by anastomosing the superficial epigastric vein to the femoral artery in Sprague-Dawley rats were allowed to remodel for 21 days before being harvested and preserved in culture medium. A custom atomic force microscope was used to measure microvascular stiffness (Young's modulus) in three areas of the AVF: the inflow artery, the juxta-anastomotic area, and the outflow vein. Morphometric measurements and collagen and elastin contents were also determined.

RESULTS

Atomic force microscopy indentation revealed an increased stiffness in the juxta-anastomotic area of the AVF compared to the outflow vein and inflow artery. The juxta-anastomotic area was also significantly stiffer than the contralateral vein. The lack of elasticity (higher Young's modulus) of the juxta-anastomotic region was associated with a thicker vascular wall that was rich in collagen but poor in elastin.

CONCLUSIONS

This study demonstrates for the first time the feasibility of using atomic force microscopy to measure local stiffness variations in experimental AVF. This technique could be instrumental in advancing our understanding of how micro-spatial organization of the AVF wall determines the overall biomechanical performance of this type of vascular access.

Intraluminal Drug Delivery to the Mouse Arteriovenous Fistula Endothelium

Delivery of therapeutic agents to enhance arteriovenous fistula (AVF) maturation can be administered either via intraluminal or external routes. The simple murine AVF model was combined with intraluminal administration of drug solution to the venous endothelium at the same time as fistula creation. Technical aspects of this model are discussed. Under general anesthesia, an abdominal incision is made and the aorta and inferior vena cava (IVC) are exposed. The infra-renal aorta and IVC are dissected for clamping. After proximal and distal clamping, the puncture site is exposed and a 25 G needle is used to puncture both walls of the aorta and into the IVC. Immediately after the puncture, a reporter gene-expressing viral vector was infused in the IVC via the same needle, followed by 15 min of incubation. The intraluminal administration method enabled more robust viral gene delivery to the venous endothelium compared to administration by the external route. This novel method of delivery will facilitate studies that explore the role of the endothelium in AVF maturation and enable intraluminal drug delivery at the time of surgical operation.

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.

Novel therapies for hemodialysis vascular access dysfunction: myth or reality?

Hemodialysis vascular access dysfunction is a major source of morbidity for patients with ESRD. Development of effective approaches to prevent and treat vascular access failure requires an understanding of the underlying mechanisms, suitable models for preclinical testing, systems for targeted delivery of interventions to maximize efficacy and minimize toxicity, and rigorous clinical trials that use appropriate outcome measures. This article reviews the substantial progress and ongoing challenges in developing novel treatments for arteriovenous vascular access failure and focuses on localized rather than systemic interventions.