Effects of bone morphogenetic proteins on primary human renal cells and the generation of bone morphogenetic protein-7-expressing cells for application in bioartificial kidneys.

Bioartificial kidneys (BAKs) contain renal cells, and primary human renal proximal tubule cells (HPTCs) have been applied in clinical trials with BAKs. Cell performance within the device is critical. HPTC performance is often compromised under in vitro conditions because of dedifferentiation, transdifferentiation, and tubule formation on substrate surfaces. Herein we tested whether treatments with human recombinant bone morphogenetic protein (BMP)-2 or BMP-7 would improve HPTC performance. We found that both growth factors improved HPTC performance, but more consistent results were obtained with BMP-7. The effects were strongly concentration dependent, and for BMP-7, 25 ng/mL was the optimal concentration, which improved HPTC performance under static and under bioreactor conditions. As an alternative to supplementation with the purified growth factor, we generated HPTCs secreting human recombinant BMP-7. BMP-7 secreted by the cells was bioactive and improved the functional performance of HPTCs, in agreement with our other findings. Together, the results suggested that either supplementation with purified BMP-7 or BMP-7-producing cells could be used to improve cell performance in BAKs. BAKs with BMP-7-producing cells could also be used to deliver the growth factor to kidney patients. Our results suggested that the amount of BMP-7 produced by HPTCs would be sufficient for therapeutic applications.

The performance of primary human renal cells in hollow fiber bioreactors for bioartificial kidneys.

Bioartificial kidneys (BAKs) containing human primary renal proximal tubule cells (HPTCs) have been applied in clinical trials. The results were encouraging, but also showed that more research is required. Animal cells or cell lines are not suitable for clinical applications, but have been mainly used in studies on BAK development as large numbers of such cells could be easily obtained. It is difficult to predict HPTC performance based on data obtained with other cell types. To enable more extensive studies on HPTCs, we have developed a bioreactor containing single hollow fiber membranes that requires relatively small amounts of cells. Special hollow fiber membranes with the skin layer on the outer surface and consisting of polyethersulfone/polyvinylpyrrolidone were developed. The results suggested that such hollow fiber membranes were more suitable for the bioreactor unit of BAKs than membranes with an inner skin layer. An HPTC-compatible double coating was applied to the insides of the hollow fiber membranes, which sustained the formation of functional epithelia under bioreactor conditions. Nevertheless, the state of differentiation of the primary human cells remained a critical issue and should be further addressed. The bioreactor system described here will facilitate further studies on the relevant human cell type.