Apical-out Tubuloids for Accurate Kidney Toxicity Studies

In kidney organoids, typically only the basal membrane is exposed, limiting toxicity assessments of apically transported drugs. Although the reversion of basal-out organoids has successfully created apical-out organoids of the intestine and airway, this method has not yet been applied to kidney organoids. Here, a technique to reverse tubuloid polarity is reported, enabling the apical surface to evert and face the medium by dissolving extracellular matrix proteins in the culture system. The resulting apical-out tubuloids maintain high viability, exhibit proper morphological characteristics, and express cell adhesion proteins and biomarkers appropriately. Further analyses, including RNA sequencing and scanning electron microscopy, confirm the presence of primary cilia on the outer surface, along with albumin receptors and Na⁺/K⁺-ATPase on the outer and inner surfaces, respectively, and apical proteins such as zonula occludens-1 on the lateral membrane, verifying the apical-out orientation. These apical-out tubuloids demonstrate selective albumin internalization, greater sensitivity to apically transported colistin, and reduced sensitivity to basally transported tenofovir, effectively mimicking drug transport mechanisms. This approach for generating apical-out tubuloids is a valuable tool for assessing drug efficacy and toxicity in physiologically relevant, tissue-like microenvironments, significantly advancing the field of nephrotoxicity research.