Dual Effect of Ochratoxin A (OTA) on the Renal Expression of Organic Anion Transporters
Oat1 and Oat3 in Rats
Zlender V, Ljubojevic M, Balen D, Breljak D, Brzica H, Fuchs R, Anzai N, Sabolic I
Institute for Medical Research & Occupational Health, Zagreb, Croatia, and Pharmacology &
Toxicology, Kyorin University School of Medicine, Tokyo, Japan
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 μg/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 μg/kg b.w.) increased the expression of Oat1 (~50%) and Oat3 (~300%),
whereas high doses (250-500 μg/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.