engleski

Dual effect of ochratoxin A (OTA) on the expression of organic anion transporters Oat1 and Oat3 in rats

OTA is an environmental mycotoxin that can impair human and animal health. In the kidney, OTA primarily targets epithelial cells in the proximal tubule (PT). PT is the major site of organic anion (OA) secretion via basolateral transporters Oat1 (Slc22a6) and Oat3 (Slc22a8). Earlier studies have shown that OTA inhibits the renal secretion of OA p-aminohyppurate (PAH), possibly by targeting the expression of Oat1 and Oat3, but this possibility has not been verified. To see if OTA affects the expression of these two Oats, we treated adult male Wistar rats with various doses of OTA (0, 50, 125, 250 & 500 μ g/kg b.w., p.o.) every 2nd day for 10 days, and determined: a) the expression of Oat1 and Oat3 proteins by Western blotting (WB) of total cell membranes isolated from the kidney and by immunocytochemistry (IC) in tissue cryosections, and b) the tissue expression of Oat1 and Oat2 mRNA by end-point PCR. The WB study of protein expression revealed a dual, dose-dependent effect of OTA ; low doses (50-125 μ g/kg b.w.) increased the expression of Oat1 (~50%) and Oat3 (~300%), whereas high doses (250-500 μ g/kg b.w.) decreased the expression of Oat1 (~70%) but not Oat3 in respect to control. The IC data on staining intensity of both transporters in the PT completely matched the WB data. At the mRNA level the expression of Oat1 was unaffected by low OTA doses and downregulated by high OTA doses, whereas the expression of Oat3 was unaffected by any OTA dose. The mRNA expression of housekeeping gene GAPDH remained unchanged in all OTA-treated animals. We conclude that: a) low doses of OTA upregulate the expression of Oat1 and Oat3 proteins in the rat kidney, while high doses downregulate only the expression of Oat1, b) upregulation of Oat1 and Oat3 proteins is mRNA-unrelated, and seems to be post-transcriptional, c) previously observed inhibition of the renal PAH secretion in rodents may be related to the loss of Oat1 protein ; and d) at lower OAT doses, upregulated Oat1 and Oat3 proteins may enhance OTA uptake and accelerate the development of nephrotoxicity.

Mycotoxins; Nephrotoxicity; Kidney; Organic anions

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