Effects of ochratoxin A in the partially nephrectomized rat

The mycotoxin ochratoxin A deranges pH homeostasis in Madin-Darby canine kidney cells

Ochratoxin A (OTA) is a nephrotoxin which blocks plasma membrane anion conductance in Madin-Darby canine kidney (MDCK) cells. Added to the culture medium, OTA transforms MDCK cells in a manner similar to exposure to alkaline stress. By means of video-imaging and microelectrode techniques, we investigated whether OTA (1 mumol/liter) affects intracellular pH (pHi), Cl- (Cl-i) or cell volume of MDCK cells acutely exposed to normal (pHnorm = 7.4) and alkaline (pHalk = 7.7) conditions. At pHnorm, OTA increased Cl-i by 2.6 +/- 0.4 mmol/liter (n = 14, P < 0.05) but had no effect on pHi. At pHalk, application of OTA increased Cl-i by 8.6 +/- 2.6 mmol/liter (n = 10, P < 0.05) and raised pHi by 0.11 +/- 0.03 (n = 8, P < 0.05). The Cl-/HCO3- exchange inhibitor DNDS (4,4'-dinitro-stilbene-2,2'-disulfonate; 10 mumol/liter) eliminated the OTA-induced changes of pHi and Cl-i. OTA did not affect cell volume under both pHnorm and pHalk conditions. We conclude that the OTA-induced blockade of plasma membrane anion conductance increases Cl-i without changing cell volume. The driving force of plasma membrane Cl-/HCO3- exchange dissipates, leading to a rise of pHi when cells are exposed to an acute alkaline load. Thus, OTA interferes with pHi and Cl-i homeostasis leading to morphological and functional alterations in MDCK cells.

Relevance of a rat model of papillary necrosis and upper urothelial carcinoma in understanding the role of ochratoxin A in Balkan endemic nephropathy and its associated carcinoma

Ochratoxin A is nephrotoxic and has been implicated in the genesis of Balkan endemic nephropathy (BEN), a condition that leads to end-stage renal disease and upper urothelial tumours. This compound induces renal parenchymal carcinoma in male mice only, and is not considered to be a potent carcinogen nor is there experimental evidence of its propensity to cause upper urothelial carcinoma. There is, however, evidence that exposure to more than one mycotoxin may be an important factor in the clinical spectrum of BEN. Analgesic nephropathy is clinically different, but is also associated with an upper urothelial carcinoma. The combination of urothelial initiation and an acute papillary necrosis in rats produces upper urothelial carcinoma. This two-stage experimental model offers the potential to assess the role of ochratoxin A in BEN-associated upper urothelial carcinoma under experimental conditions.

Renal tubular secretion and reabsorption as factors in ochratoxicosis: effects of probenecid on nephrotoxicity

Ochratoxin A (OA) is a food-borne fungal metabolite capable of producing nephrotoxicity. Renal clearance of [3H]OA and the effects of probenecid on clearance were compared in sham-operated and partially nephrectomized (surgical removal of 70% of the total renal mass), impaired renal function rats. Sham-operated and partially nephrectomized rats cleared OA at 0.109 and 0.078 ml/min, respectively. These values were significantly lower than glomerular filtration rate (GFR) determined by inulin clearance, indicating net tubular reabsorption. Clearance of a single dose of OA in both sham-operated and partially nephrectomized rats pretreated with probenecid was significantly diminished and provided evidence for the involvement of secretory processes in the elimination of OA. Probenecid (administered before OA or simultaneously with OA) failed to prevent nephrotoxicity in rats exposed to five daily doses of mycotoxin. On the contrary, enhanced nephrotoxicity was exhibited. Decreases in urine osmolality, Na+ and K+ concentrations, and body weight were prominent and, interestingly, renal levels of parent OA were increased (over OA treatment alone) in the presence of probenecid. These data suggest that renal tubular secretion and reabsorption are important factors in modulating the nephrotoxicity of OA and may facilitate the residual persistence of this mycotoxin in the kidneys (via renal recycling). Renal metabolism may contribute to the detoxification of OA.

Teratogenic effects of Ochratoxin A in rats with impaired renal function

The teratogenic potential of Ochratoxin A (OA), was compared in impaired renal function (IRF) and sham-operated (SO) female rats. Surgical removal of approximately 70% of the total renal tissue was accomplished utilizing unilateral ligation/electrocoagulation procedures. Control animals were sham-operated. All animals were allowed a period of 27 days to recover post surgery. IRF rats exhibited normal mating tendencies and the pregnancy rate was 100%. A single, subcutaneous teratogenic dose of OA (1.75 mg/kg) on gestation day 7 resulted in significantly increased fetal resorptions, decreased fetal body weights and increased fetal malformations in both IRF and SO animals, although the incidence of gross malformations was greater in IRF rats. A subthreshold teratogenic dose (i.e. 1 mg/kg) did not produce any significant increase in embryotoxicity or fetal malformations in IRF animals compared to SO rats.