Elucidation of puberulic acid–induced nephrotoxicity using stem cell-based kidney organoids

Recent cases of acute kidney injury (AKI) in Japan have been linked to Beni-koji CholesteHelp supplements, with puberulic acid identified as a potential nephrotoxic contaminant. To address the need for a reliable in vitro nephrotoxicity testing platform, we developed a screening model using kidney organoids derived from adult rat kidney stem (KS) cells. The organoids were exposed to known nephrotoxicants, including cisplatin and gentamicin, to validate the system. Puberulic acid toxicity was evaluated in both KS cell-derived organoids and wild-type mice. The organoids recapitulated tubular injury induced by known nephrotoxins and showed significant Kim-1 mRNA upregulation. Puberulic acid-treated organoids and mice exhibited morphological features of acute tubular necrosis (ATN), mitochondrial damage, and reduced cytochrome c oxidase subunit IV (COX-IV) expression. Markers of oxidative stress and apoptosis, such as 8-hydroxy-2'-deoxyguanosine (8-OHdG) and cleaved caspase-3, were also elevated. These findings suggest that puberulic acid induces mitochondrial dysfunction and oxidative stress, leading to tubular cell death. Puberulic acid-induced nephrotoxicity was demonstrated using our kidney organoid model. KS cell-derived kidney organoids may provide a simple, reproducible, and rapid platform for nephrotoxicity assessment, which may complement conventional animal experiments.