About 100,000 people in the United States are in need of a kidney transplant, and 400,000 people are on dialysis. This study aims to discover more about the ability to create a transplantable kidney graft. They decellularized a rat, pig, and human kidney in this study, and recellularized the rat kidney with epithelial and endothelial cells. The grafts made urine in the lab setting. Some grafts were transplanted into the rat, and also produced urine after transplantation.
Dialysis can increase the survival of patients with end-stage renal disease, but a kidney transplant is the only way to cure end stage renal disease. Only 18,000 kidneys are available for transplant each year, leaving 100,000 people waiting on the donor list each year. The wait time is over 3 years for a kidney, and even then, the kidney can be rejected. Other options have been considered for getting those on the waiting list the treatment they need, but are all still in clinical development. This research team has previously made scaffolds from hearts and lungs. A benefit to successfully decellularizing the whole kidney is that the vascularm glomerular, and tubular components are structurally intact.
Perfusion decellularization of cadaveric kidneys
The rat kidney was decellularized with sodium dodecyl sulfate (SDS) until all of the cellular components were removed. The extracellular matrix (ECM) was kept intact since they used a technique called perfusion decellularization, and this is necessary to have proper kidney function. The elastic fibers of the arterioles remained in the parenchyma. Laminin and collagen IV remained as well. In general, what is called the microarchitecture of the kidney remained intact. The SDS and Triton X-100 was able to lower the DNA content of the scaffold to less than 10%. The scaffold was washed with a buffer until there was no more SDS present. The total level of collagen and glycosaminoglycan were similar to that of a normal kidney. They used Krebs-Henseleit solution under normal pressure conditions to see if the decellularized kidney scaffolds would produce any filtered urine. The output of this had high protein, glucose, and electrolytes. This can tell us that some filtration was occurring across the glomerulus and the tubular basement membranes, but there was no active reabsorption. The glomerular diameter, Bowman's space, and glomerular capillary surface area were the same between normal kidneys and the decellularized scaffolds.
Recellularization of acellular kidney scaffolds
The rat kidney scaffold was repopulated with endothelial cells through the renal eatery and epithelial cells through the ureter. The kidney scaffold was repopulated better when the seeding chamber was pressurized to create a pressure gradient across the scaffold. Without the pressure gradient, the cells were not reaching the glomerulus. The ideal pressure to avoid damage was 40 cm H20. After 3 to 5 days in a perfusion bioreactor, the scaffold was then seeded with more cells, but this time the cells were a mixture of all kidney cell types. The scaffold was grown until the cells were all attached, then perfused to give oxygen, nutrients, and stimulate function. They used glucocorticoids and catecholamines to mature the kidney scaffold. All of the cell types seeded in the appropriate anatomical locations. There were some non-site specific cells, but overall, the kidney scaffold was cellularized in a similar fashion to a normal kidney. There were about 70% of the functional glomeruli in the kidney scaffold compared to a normal kidney.
In vitro function of acellular regenerated kidneys
Here, they tested if the regenerated kidneys could properly function. The regenerated kidneys produced steady, but less urine than the normal kidneys. The glomerular filtration was decreased in the regenerated kidney. Vascular resistance was higher in the generated kidney compared to the normal kidney. Albumin retention is morally 89.9%, but was only 46.9% in the regenerated kidneys. Glucose reabsorption is usually 91.7% in normal kidneys, but was 47.4% in the regenerated kidneys. The electrolyte reabsorption for the regenerated kidney was about 50% of the normal kidney’s reabsorption.
Orthotopic transplantation and in vivo function of regenerated kidneys
Since urine was produced in the lab setting, the researchers thought the kidney could be transplanted into a rate and also produce urine. An orthotopic transplant was done, meaning the original kidney was removed and the regenerated kidney was placed in its spot. The kidney graft successfully used the body’s blood supply and began making urine immediately. The urine output was high in glucose and albumin, but low in urea and creatine. The urine output was less, and there was no clot formation or bleeding detected.
A bioengineered kidney using a patient’s own cells could be an alternate treatment for a patient with end stage renal failure. Although there is a lot more research that needs to be done, this study presents three important factors. They were able to 1) generate a 3D kidney scaffold from rat, human, and pig kidneys. 2) they were able to repopulate the scaffolds in a way that was anatomically correct. 3) The kidneys did produce rudimentary urine in the lab setting and in a living organism.
The kidney could be decellularized without altering the microarchitecture of the vessels, glomerulus, and tubules. Recellularizing a more simple organ or tissue like muscle or the lungs is easier than recellularizing a complex organ like the kidney. This is because surface attachment or injection of cells can recellularize the simple tissue or organ. The research team took advantage of the renal artery and ureter to seed the cells deeper inside the organ. More research will need to be done on recellularizing a larger, human sized kidney and where to obtain the cell types for this process. Bioengineered kidneys may eventually become a viable treatment for patients with end stage renal failure.