Sugar in the crème brûlée: Developing organoid-based bioartificial kidneys transplanted on chicken embryos

Abstract

Chronic kidney disease is a major health problem with over 10% of the world population affected. In the final stage, replacement of the renal function is lifesaving. However, conventional dialysis can only replace the filtering function of the kidney intermittently and leaves the tubular part unattended. Kidney transplants resolve some of these issues, but they are scarce and require lifelong immunosuppressants. An implantable bioartificial kidney (BAK) would deliver a significant improvement to existing renal replacement therapy.

A vascularised connection with the circulation of the recipient is pivotal for functionality of a BAK. The chorioallantoic membrane (CAM) from a chicken embryo is known as a vascularisation model with multiple advantages to conventional test animals. We performed transplantation of static and dynamic chip types on the CAM with the option of growing epithelialised kidney cells on a semipermeable membrane. Tubulus organoids (tubuloids) are one candidate for placement into a functional BAK.

Chicken embryos were incubated ex ovo up to the embryonic day 14. On day 10, the chips were placed on the CAM with a 3D printed stabilising device. On the last day, a fluorescently labeled sugar was administered intravenously to the embryo. In the dynamic chips, dialysate fluid was flushed through at flow rate 1 mL/h during several hours, essentially mimicking membrane dialysis. Fluorescence of the dialysate was determined with a platereader. In the static chips, the interaction between tubuloids and CAM was further investigated with qPCR.

The compound concentration in the dialysate increased over time and reached a stable level after approximately 2 hours. The gradient from blood to dialysate factors to approximately 1000x dilution. Biodistribution experiments confirmed that the chip was exposed to the sugar during at least 30 minutes, before accumulating in the liver. CAM vascular markers were suppressed after xenotransplantation of tubuloids. The tubuloids sustained their molecular identity.

The connection between the dynamic device and the ex ovo CAM acts as a proof-of-principle for in vivo vascularisation of an implantable BAK. We combined focus on implantability with a dynamic fluidic channel to constitute a novel application of the CAM. Further research to in vivo functionalisation of tubuloids is recommended. Outside the nephrology realm, our setup enables a translation into host-derived vascularisation of any epithelial cell type functionalised in a living recipient, with possible applications in personalised therapy evaluation and diagnostics.