Periadventitial biomaterials to improve arteriovenous fistula and graft outcomes

The changing face of dialyzer membranes and dialyzers

The key goals for dialysis treatments are to prevent the progressive accumulation of waste products of metabolism and volume overload. Traditionally uremic solutes have been classified according to molecular weight and termed small, middle sized, and large solutes. Solute clearance during dialysis sessions will potentially be by diffusion, convection and adsorption. Dialyzer membranes act as a semi-permeable membrane restricting solute removal predominantly by size. Small molecules move faster than large molecules, so small solutes are readily removed by diffusion. Increasing the size of the pores in the membrane will potentially allow middle and larger sized solutes to pass through the dialyzer membrane, although in practice there is a limit to increasing pore sizes to prevent the loss of albumin and other important proteins. Differences in membrane surface and charge will influence protein absorption. The removal of fluid during dialysis depends in part on the hydraulic permeability of the membrane. Combining higher hydraulic permeability and larger sized pores increases convective clearance with solutes moving across the membrane with the water movement. Depending upon dialyzer design, higher hydrostatic pressure as blood enters the dialyzer leads to a variable amount of internal diafiltration, so improving the clearance of middle sized solutes. Although the dialyzer membrane plays a key role in solute clearance, the design of the casing and header also play a role in directing the countercurrent blood and dialysate flows to maximize the surface area available for diffusive and convective clearances.

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.