Angela J. Funke

Replacement of renal function in uremic animals with a tissue-engineered kidney.

Current renal substitution therapy with hemodialysis or hemofiltration has been the only successful long-term ex vivo organ substitution therapy to date. Although this approach is life sustaining, it is still unacceptably suboptimal with poor clinical outcomes of patients with either chronic end-stage renal disease or acute renal failure. This current therapy utilizes synthetic membranes to substitute for the small solute clearance function of the renal glomerulus but does not replace the transport, metabolic, and endocrinologic functions of the tubular cells. The addition of tubule cell replacement therapy in a tissue-engineered bioartificial kidney comprising both biologic and synthetic components will likely optimize renal replacement to improve clinical outcomes. This report demonstrates that the combination of a synthetic hemofiltration device and a renal tubule cell therapy device containing porcine renal tubule cells in an extracorporeal perfusion circuit successfully replaces filtration, transport, metabolic, and endocrinologic functions of the kidney in acutely uremic dogs.

Tissue engineering of a bioartificial renal tubule

Development of a bioartificial renal tubule with a confluent monolayer of renal epithelial cells supported on a permeable synthetic surface may be the first step to further optimization of renal substitution therapy currently used with hemodialysis or hemofiltration. Madin-Darby canine kidney cells, a permanent renal epithelial cell line, were seeded into the lumen of single hollow fibers. Functional confluence of the cells was demonstrated by the recovery of intraluminally perfused 14C-inulin that averaged >98.9% in the cell lined units vs < 7.4% in the control noncell hollow fibers during identical pressure and flow conditions. The baseline absolute fluid transport rate averaged 1.4 ± 0.4 μl/30 min. To test the dependency of fluid flux with oncotic and osmotic pressure differences across the bioartificial tubule, albumin was added to the extracapillary space, followed by the addition of ouabain, an inhibitor of Na+K+ adenosine triphosphatase, the enzyme responsible for active transport across the renal epithelium. Addition of albumin resulted in a significant increase in volume transport to 4.5 ± 1.0 μl/30 min. Addition of ouabain inhibited transport back to baseline levels of 2.1 ± 0.4 μl/30 min. These results are the first demonstration that renal epithelial cells have been grown successfully as a confluent monolayer along a hollow fiber, and exhibit functional transport capabilities. The next steps in constructing a bioartificial renal tubule successfully are to develop a multi-fiber bioreactor with primary renal proximal tubule cells that maintain not only transport properties but also differentiated metabolic and endocrine functions, including glucose and ammonia production, and the conversion of vitamin D3 to a more active derivative. A renal tubule device may add critical renal functional components not currently substituted for, thereby improving the treatment regimens for patients with acute and chronic renal failure. ASAIO Journal 1998; 44:179–183.

The Bioartificial Renal Tubule Assist Device to Enhance CRRT in Acute Renal Failure

Current therapy for acute tubular necrosis (ATN) continues to have an exceedingly high mortality rate, exceeding 50% even with dialytic or hemofiltrative support. Current renal replacement therapy in ATN only substitutes for filtration function of the kidney but not its cellular metabolic functions. Replacing these metabolic functions may optimize current therapy for this devastating disease process. In this regard, a renal tubule assist device (RAD) has been developed to be placed in an extracorporeal continuous hemoperfusion circuit in series with a hemofilter. The RAD consists of porcine renal proximal tubule cells grown as confluent monolayers of a multifiber bioreactor with a membrane surface area from 0.4 to 1.6 m2. The cells along the inner surface of the hollow fibers are immunoprotected from the patients blood by the hollow fiber membrane. In preliminary experiments in uremic dogs, this device has been shown to tolerate a uremic environment while providing reabsorptive, metabolic, and endocrinologic activity. Pilot human trials of the RAD are anticipated within the next year to improve current renal replacement therapy in ATN.

The role of a bioengineered artificial kidney in renal failure.

Abstract: Renal failure continues to carry substantial burden of morbidity and mortality in both acute and chronic forms, despite advances in transplantation and dialysis. There is evidence to suggest that the kidney has metabolic, endocrine, and immune effects transcending its filtration functions, even beyond secretion of renin and erythropoietin. Our laboratory has developed experience in the tissue culture of renal parenchymal cells, and has now been able to demonstrate the metabolic activity of these cells in an extracorporeal circuit recapitulating glomerulotubular anatomy. We have observed active transport of sodium, glucose, and glutathione. We describe the design and initial preclinical testing of the bioartificial kidney, as well as future directions of our research.

Cell therapy in kidney failure

Current therapy for acute renal failure continues to have an exceedingly high mortality rate, exceeding 50% even with dialytic or hemofiltrative support. Current renal replacement therapy in ARF only substitutes for filtration function of the kidney but not its cellular metabolic functions. Replacing these metabolic functions may optimize current therapy for this devastating disease process. In this regard, a renal tubule assist device (RAD) has been developed to be placed in an extracorporeal continuous hemoperfusion circuit in series with a hemofilter. The RAD consists of porcine renal proximal tubule cells grown as confluent monolayers in a multifiber bioreactor with a membrane surface area from 0.4 to 1.6 m2. The cells along the inner surface of the hollow fibers are immunoprotected from the patients blood by the hollow fiber membrane. In vitro experiments demonstrate that this device possesses differentiated renal transport, metabolic and endocrinologic properties. These properties, in fact, are responsive to normal physiological regulatory parameters. In preliminary experiments in uremic dogs, this device has also been shown to tolerate a uremic environment while providing reabsorptive, metabolic, and endocrinologic activity. Pilot human trials of the RAD are anticipated within the next year to improve current renal replacement therapy in this devastating disease process.