Microphysiological System Modeling of Ochratoxin A-Associated Nephrotoxicity
Ochratoxin A (OTA) is one of the most abundant mycotoxin contaminants in food stuffs and possesses carcinogenic, nephrotoxic, teratogenic and immunotoxic properties.  Especially, severe nephrotoxicity is of great concern, as characterized by degeneration of epithelial cells of the proximal tubules and interstitial fibrosis.  However, its mechanism of toxicity, hazard identification as well as genetic risk factors contributing to OTA toxicity in humans has been elusive due to the lack of adequate models that fully recapitulate kidney function in vitro.  The present study attempts to evaluate dose-response relationships, identify the contribution of active transport proteins that govern renal disposition of OTA, and determine the role of metabolism in bioactivation and detoxification of OTA using a 3D human kidney proximal tubule microphysiological system (kidney MPS).  We demonstrated that IC50 values of OTA in kidney MPS culture (0.375 – 1.21 µM) were in good agreement with clinical toxic concentrations of OTA in urine.  Surprisingly, no enhancement of kidney injury biomarkers was evident in the effluents of kidney MPS after OTA exposure despite significant toxicity observed by LIVE/DEAD staining, rather these biomarkers were decreased in OTA concentration-dependent manner.   Furthermore, the effect of 1-aminobenzotriazole (ABT) and 6-(NBD-4-ylthio-) hexanol (NBDHEX), pan-inhibitor of P450 and GST enzymes, respectively, on the OTA-induced toxicity in kidney MPS was examined, which resulted in significant enhancement of OTA-induced toxicity by NBDHEX  (3 µM) treatment whereas ABT (1 mM) treatment decreased OTA-induced toxicity, suggesting the roles of GSTs and P450 enzymes in the detoxification and bioactivation of OTA, respectively.  Additionally, OTA transport studies using kidney MPS in the presence and absence of inhibitor of organic anion transporter(s), probenecid (1 mM), revealed the role of organic anionic membrane transporter(s) in the kidney specific disposition of OTA.  Our findings provide a better understanding of the mechanism of OTA-induced kidney injury which may support changes in risk assessment, regulatory agency policies on allowable exposure levels and determination of genetic factors in high-risk populations against OTA nephrotoxicity. Overall design: Human kidney proximal tubule epithelial cells (PTEC) from two donors were seeded into a total of 34 kidney chips, and effluents of kidney MPS were exposed to 0 to 100 µM OTA  for 72 or 168 hours.