Attenuated Ochratoxin A Transporter Expression in a Mouse Model of Nonalcoholic Steatohepatitis Protects against Proximal Convoluted Tubule Toxicity

Abstract

Ochratoxin A (OTA) is an abundant mycotoxin, yet the toxicological impact of its disposition is not well studied. OTA is an organic anion transporter (OAT) substrate primarily excreted in urine despite a long half-life and extensive protein binding. Altered renal transporter expression during disease, including nonalcoholic steatohepatitis (NASH), may influence response to OTA exposure, but the impact of NASH on OTA toxicokinetics, tissue distribution, and associated nephrotoxicity are unknown. By inducing NASH in fast food-dieted/thioacetamide-exposed mice, we evaluated the effect of NASH on a bolus OTA exposure (12.5 mg/kg p.o.) after 3 days.NASH mice presented with less gross toxicity (44% less bodyweight loss) and kidney and liver weights of NASH mice were 11% and 24%, respectively, higher than healthy mice. Organ and body weight changes coincided with reduced renal proximal tubule cells vacuolation, degeneration and necrosis though no OTA-induced hepatic lesions were found. OTA systemic exposure in NASH mice increased modestly from 5.65 ± 1.10 to 7.95 ± 0.61 mg*h/mL/kg BW, renal excretion increased robustly from 5.55 ± 0.37% to 13.11 ± 3.10%, relative to healthy mice.Total urinary excretion of OTA increased from 24.41 ± 1.74 to 40.07 ± 9.19 μg in NASH mice and kidney-bound OTA decreased ~30%. Renal OAT isoform expression (OAT1-5) in NASH mice decreasd by ~50% with reduced OTA uptake by proximal convoluted cells. These data suggest that NASH-induced OAT transporter reductions attenuate renal secretion and reabsorption of OTA, increasing OTA urinary excretion and reducing renal exposure, thereby reducing nephrotoxicity in NASH.

Representative Rodent Models for Renal Transporter Alterations in Human Nonalcoholic Steatohepatitis

“…A significant decrease in apical transporter OAT4 was also observed in human NASH patients, but the impact of that change is complicated by the absence of a true OAT4 in rodents . However, although not a true ortholog, OAT5 is expressed in rodents (but not humans) and shares some substrate and functional similarities with OAT4 (Jilek et al, 2021b). Therefore, the decrease in OAT5 expression observed in db/db, FFDTH, and ALIOS should be considered for modeling human NASH pharmacokinetics of xenobiotics with substrate specificity to OAT4/5.…”

“…Insoluble membrane protein fractions were isolated and digested from kidney tissue using a method adapted from a published protocol by Jilek et al (Jilek et al, 2021b). Approximately 100 mg of tissue was homogenized in 1 mL of buffer containing 10 mM Tris-HCl (pH 7.4), 10 mM NaCl, 1.5 mM MgCl 2 , 1 mM PMSF, and 1X protease inhibitor per 50mL of water.…”

Special Section on Mechanistic and Translational Research on Transporters in Toxicology–Editorial

“…Human exposure to OTA can occur through food ingestion. In this special section, Dr. Nathan J. Cherrington and his colleagues (Jilek et al, 2022) investigate the alterations in expression of renal transporters during nonalcoholic steatohepatitis (NASH) in mice and their impact on OTA disposition and subsequent nephrotoxicity. Dr. Cherrington is a close collaborator with Dr. Aleksunes.…”