Background: Hydrophobic bile acids (BA) have long been known to be cytotoxic. Because of this, growing attention has centered on their role in the development of renal injury. So far research has predominantly relied on mouse models to study BA toxicity. This is despite the fact that humans and mice have substantially different BA pool compositions, with hydrophobic BAs being much more predominant in humans than in mice. To address this disparity, this study utilizes Precision-Cut Kidney Slices (PCKS) to conduct a comparative analysis of the impact of Lithocholic acid (LCA), the most hydrophobic BA, on human and mouse kidney tissue.
Methods: Using an Alabama R&D Tissue Slicer (formerly Krumdieck Tissue Slicer), human PCKS (hPCKS) (n=3) were prepared from macroscopically healthy kidney tissue obtained from tumor nephrectomies. Mice PCKS (mPCKS) (n=5) were prepared from kidneys harvested from C57BL/6 mice. Mice were anesthetized with 5% sevoflurane and sacrificed by cervical dislocation. Both hPCKS and mPCKS were cultured for 24H, 48H, and 72H with and without 100 µM LCA. The inflammatory and fibrotic responses in the PCKS were characterized by qPCR of the inflammatory genes IL-6 and IL-1β and the fibrotic genes fibronectin and collagen 1A1. Gene expression levels were compared with two-tailed unpaired T-test. The use of human tissue for the hPCKS was approved by the Central Denmark Region Committees on Biomedical Research Ethics and the Danish Data Protection Agency.
Results: Exposure to LCA for 24H induced a strong inflammatory response in the mPCKS, seen by a large increase in Il6 (p: 0.0034) and in Il1b (p: 0.0088). This was accompanied by an increase in the fibrotic genes Fn(p: 0.0430) and Col1a1 (p: 0.0170). Only the increase in Fn persisted after 48H of exposure (p: 0.0263), and this was likewise no longer evident after 72H of exposure. However, mPCKS exposed to LCA for 48H and 72H exhibited markedly low RNA concentrations, which might indicate low viability. Further viability measures will be done.
hPCKS exhibited no alteration in IL6 and IL1B levels after 24H, 48H, and 72H of LCA exposure. The non-exposed hPCKS exhibited culture-induced fibrosis at 48H and 72H compared to the 24H (p<0.041), a response normally seen in PCKS. This phenomenon was absent in LCA-exposed hPCKS, where FN and COL1A1 levels remained stable throughout all time points.
Conclusion: This study demonstrated that mouse and human kidney tissue differ in their response to LCA. As anticipated, LCA had harmful effects on mPCKS, evidenced by heightened expression of inflammatory and fibrotic genes. Surprisingly the opposite was observed in hPCKS, where LCA protected against culture-induced fibrosis. This species difference in response to BAs emphasizes the importance of incorporating human models in research on the nephrotoxicity of BAs.