Transition to fetal calf serum-free culture enhances kidney proximal tubule cell bioenergetics and allows pharmacological applications

Abstract

Proximal tubule in vitro systems are important tools in pre-clinical drug development, providing insights into drug disposition and safety. Cells are often cultured in medium containing fetal calf serum (FCS); however, FCS addition is not physiologically relevant for cells of human origin. Here, in vitro cultures of human kidney proximal tubule cells were transitioned to FCS-free medium. The impact of FCS-free medium on maturation and maintenance for multiple passages of commonly used conditionally immortalized proximal tubule epithelial cells overexpressing the pharmacologically-relevant organic anion transporter 1 (ciPTEC-OAT1) was evaluated. This transport protein is lost upon isolation and in vitro culture of tubule cells, and due to its clinical relevance, an OAT1 expressing cell line was chosen. Supplementation of FCS-free medium with human platelet lysates supported longer-term cell growth. OAT1-mediated fluorescein transport was sensitive to probenecid inhibition under both conditions, although intracellular fluorescein accumulation was reduced in FCS-free cultures. KEGG and GO enrichment analysis of differentially expressed genes revealed that inflammatory response and HIF-1 signaling were downregulated, whereas cell adhesion and ATP-binding cassette transporter genes were upregulated in FCS-free cultures. Interestingly, an increase in bioenergetic profile was observed for ciPTEC-OAT1 cultured in optimized FCS-free medium. Furthermore, in 3D bioengineered kidney tubule cultures, supplementation with an increased concentration of human platelet lysates lead to improved cell viability and fiber coverage. To conclude, we highlighted significant efforts and strategies in transitioning FCS-containing to FCS-free medium for ciPTEC-OAT1 cultures.