Ochratoxin A Secretion in Primary Cultures of Rabbit Renal Proximal Tubule Cells

Abstract

Abstract. Primary cultures of rabbit renal proximal tubule cells grown under improved culture conditions were used to study the transepithelial transport of the nephrotoxic mycotoxin ochratoxin A. The basal-to-apical transepithelial flux, i.e., secretion, of this fluorescence organic acid was measured in primary cultures of rabbit renal proximal tubule cells. The basal-to-apical flux of ochratoxin A increased with time and reached a steady state after 12 h. On the other hand, the apical-to-basal flux, i.e., reabsorption, of ochratoxin A was minimal over time. The secretory flux of ochratoxin A was as much as eightfold greater than the reabsorptive flux, indicating that net secretion is the primary mechanism for ochratoxin A clearance by the proximal tubule. The kinetic analysis of ochratoxin A flux revealed secretion to be a saturable and very high-affinity process with an apparent K50 of 0.33 ± 0.21 mM. A saturating concentration of the prototypical organic anion substrate para-aminohippurate (PAH) reduced ochratoxin A secretion by approximately 75%. The kinetic analysis of PAH inhibition of ochratoxin A secretion revealed an IC50 of 195 mM, which is similar to the IC50 for PAH inhibition of peritubular ochratoxin A uptake in tubule suspensions and the Km values for peritubular PAH uptake. The organic anions probenecid, octanoate, and α-ketoglutarate reduced ochratoxin A excretion to the same degree as PAH, whereas the amino acid phenylalanine had a minimal effect on ochratoxin A secretion. Thus, collectively, these observations indicate that the secretion of ochratoxin A in primary cultures of rabbit renal proximal tubules is limited to the organic anion secretory pathway. The high affinity measured for the basal-to-apical flux of ochratoxin A suggests that at concentrations typical of naturally occurring exposures, transepithelial secretion by the organic anion transport pathway represents a significant avenue for excretion of this mycotoxin by the renal proximal tubule.

Effect of Ethanol and Red Wine on Ochratoxin A-Induced Experimental Acute Nephrotoxicity

“…In humans it has been associated with so-called Balkan endemic nephropathy and it might be implicated in the onset of urinary tract tumors (8)(9)(10)(11). The proximal tubule of the kidney is a primary target site in OTA-induced nephrotoxicity (12,13): OTA is transported into tubular cells and is eliminated by the classic organic anion transport system (14). The exact mechanism of OTA nephrotoxicity is not completely understood: it may act as a genotoxic carcinogen and/or its nephrotoxicity may be due to an indirect mechanism, such as induction of cytotoxicity or increased cellular proliferation.…”

Molecular Aspects of the Transport and Toxicity of Ochratoxin A

“…The mechanism(s) of OTA entry and accumulation in the renal proximal tubule (PT), which is believed to cause resultant nephrotoxicity, is poorly understood. , All segments of rabbit renal PT show peritubular uptake of OTA, suggesting that several basolateral organic anion transporters (OATs) handle the transport of OTA. , The cloned human organic anion transporters 1 (hOAT1) and 3 (hOAT3) in the secondary and tertiary segments of the mouse PT have also been shown to mediate the transport of OTA. , To date, the binding of OTA to OATs has not been quantified.…”