We have shown that expression of proximal tubular organic anion transporters OAT1 and OAT3 is diminished by prostaglandin E2 (PGE2) or after renal ischemia and reperfusion (I/R). Indomethacin applied after ischemia (1mg/kg) inhibits I/R induced down regulation of OAT1/3 and improves renal outcome. Indomethacin is taken up into the proximal tubules by OAT1/3 and accumulates. We applied probenecid to block indomethacin uptake into proximal tubules and abolish its effect on OAT1/3 regulation and renal outcome.

iAKI was induced in rats by bilateral clamping of renal arteries for 45 min. Indomethacin (1mg/kg) was given i.p. as soon as reperfusion started. Probenecid (50mg/kg) was applied i.p. 10 min later. The reperfusion period was 24 h.

Indomethacin restored the expression of OAT1/3, PAH net secretion and PGE2 clearance. Additionally, indomethacin improved kidney function as measured by GFR, renal cortical apotosis and PAH clearance. Notably, low-dose indomethacin did not affect inflammation parameters in the kidneys (e.g. MCP-1, ED1+-cells). Probenecid blocked the restoration of OAT1/3 expression induced by indomethacin and moreover abrogated all beneficial effects of indomethacin.

Our study indicates: (i) The beneficial effect of low dose indomethacin is not due to its anti-inflammatory potency, but (ii) due to its effects on regulation of expression of OAT1/3. Probenecid competitively inhibits the uptake of indomethacin into the proximal tubular cells, (iii) thereby restoring PGE2 induced down regulation of OAT1/3 after I/R and as a cause re-establishing renal damage. This is (iv) evidence for a mechanistic effect of OAT1/3 on renal outcome after ischemic acute kidney injury.