Elucidation of Puberulic Acid–Induced Nephrotoxicity Using Stem Cell-based Kidney Organoids
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Background and hypothesis
Recent cases of acute kidney injury (AKI) in Japan have been linked to the Beni-koji CholesteHelp supplement. Renal biopsies from affected patients revealed tubular damage, and puberulic acid was subsequently identified as a potential nephrotoxic contaminant. Recognizing the urgent need for a reliable in vitro nephrotoxicity testing platform, we hypothesized that a kidney organoid-based system could replicate nephrotoxic injury and help identify novel nephrotoxicants. In this study, we developed a screening model using kidney organoids derived from adult rat kidney stem (KS) cells and applied it to evaluate the toxicity of puberulic acid.
Methods
Kidney organoids were generated from KS cells and exposed to established nephrotoxicants, including cisplatin and gentamicin, to validate the model. The nephrotoxicity of puberulic acid was evaluated using both KS cell-derived organoids and wild-type mice. Nephrotoxicity was assessed by morphological changes, Kim-1 mRNA expression, transmission electron microscopy (TEM), and analysis of markers related to mitochondrial injury, oxidative stress, and apoptosis.
Results
The kidney organoids reproduced morphological features of injury induced by known nephrotoxins and showed significant upregulation of Kim-1 mRNA. Puberulic acid-treated organoids displayed ultrastructural features consistent with acute tubular necrosis (ATN) and increased Kim-1 expression. In vivo, puberulic acid-exposed mice exhibited impaired renal function and histological findings consistent with ATN. Both in vitro and in vivo models revealed mitochondrial structural abnormalities and reduced expression of cytochrome c oxidase subunit IV (COX-IV). Additionally, oxidative stress and apoptotic markers, including 8-hydroxy-2’-deoxyguanosine (8-OHdG) and cleaved caspase-3, were significantly elevated, suggesting that puberulic acid induces mitochondrial dysfunction and oxidative stress, leading to tubular cell death.
Conclusion
Puberulic acid-induced nephrotoxicity was demonstrated using our kidney organoid model. KS cell-derived kidney organoids provide a simple, reproducible, and rapid platform for nephrotoxicity assessment, which contribute to a reduction of animal use in toxicology research.
