Publications (4)10.07 Total impact
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ABSTRACT: Expression of proximal tubular organic anion transporters Oat1 and Oat3 is reduced by prostaglandin E2 (PGE2) after renal ischemia and reperfusion (I/R) injury. We hypothesized that impaired expression of Oat1/3 is decisively involved in deterioration of renal function after I/R injury. Therefore, we administered probenecid, which blocks proximal tubular indomethacin uptake, to abolish indomethacin mediated restoration of Oat1/3 regulation and its effect on renal functional and morphological outcome. Ischemic AKI was induced in rats by bilateral clamping of renal arteries for 45 min with 24h follow up. Low-dose indomethacin (1mg/kg) was given i.p. at the end of ischemia. Probenecid (50mg/kg) was administered i.p. 20 min later. Indomethacin restored Oat1/3 expression, PAH net secretion and PGE2 clearance and improved kidney function as measured by GFR, renal perfusion as determined by corrected PAH clearance and morphology, whereas it reduced renal cortical apoptosis and nitric oxide production. Notably, indomethacin did not affect inflammation parameters in the kidneys (e.g. MCP-1, ED1+-cells). On the other hand, probenecid blocked indomethacin induced restoration of Oat1/3 and moreover abrogated all beneficial effects. Our study indicates that the beneficial effect of low-dose indomethacin in iAKI is not due to its anti-inflammatory potency, but to its restoration of Oat1/3 expression and/or general renal function. Inhibition of proximal tubular indomethacin uptake abrogates the beneficial effect of indomethacin by resetting the PGE2 mediated Oat1/3 impairment, thus re-establishing renal damage. This provides evidence for a mechanistic effect of Oat1/3 in a new model of the induction of renal damage following ischemic AKI.
Article: Experimental acute kidney injury.[Show abstract] [Hide abstract]
ABSTRACT: Introduction and Aims: Acute interstitial nephritis (AIN) is a common cause of acute kidney injury (AKI). In severe cases, AIN may progress to chronic kidney disease or end-stage renal disease. We previously reported that WNT10A is a novel angio/stromagenic factor in wound healing and organ fibrosis. In this study, we investigated the role of WNT10A in fibrotic progression of AIN. Methods: Kidney biopsy specimens from 25 AKI patients (all men, ≥60 years) treated in our hospital between 2007 and 2013 were examined for WNT proteins, α-SMA, and fibronectin expression by immunohistochemistry. The relationship between each WNT proteins expression level and estimated glomerular filtration rate (eGFR) was evaluated by the Mann-Whitney U test. COS1 cells (kidney fibroblasts from African green monkey) were transfected with a WNT10A expression plasmid or a siRNA targeting peroxiredoxin 5 (PRDX5). The effects of WNT10A overexpression and PRDX5 knockdown on proliferation and hydrogen peroxide induced cytotoxicity were measured by WST-8 assay. Results: The 10 patients exhibiting WNT10A expression in biopsy tissue had significantly lower eGFR values (median, 11.12 mL/min per 1.73 m2; range, 7.16−28.15 mL/min per 1.73 m2) than the 15 patients exhibiting no detectable WNT10A expression (34.70, 8.37−134.58; p = 0.0033). There was no significant relationship between eGFR and the expression level of any other WNT protein examined (WNT-1, -3, and -4). Overexpression of WNT10A in COS1 cells enhanced proliferation, fibronectin expression, PRDX5 expression, and resistance to hydrogen peroxide, while PRDX5 downregulation sensitized COS1 cells to hydrogen peroxide. Conclusions: WNT10A expression may promote fibrotic progression and kidney dysfunction in AIN. Blockade of WNT10A expression may be a feasible therapeutic strategy against kidney fibrosis.
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ABSTRACT: Availability of L-arginine, the exclusive substrate for nitric oxide synthases, plays an important role in kidney ischemia/reperfusion injury. The endogenous L-arginine derivatives asymmetrical dimethylarginine (ADMA) and symmetrical dimethylarginine (SDMA) block cellular L-arginine uptake competitively, thereby inhibiting the production of nitric oxide. ADMA also blocks nitric oxide synthase activity directly. Here, we investigate the pathomechanistic impact of ADMA/SDMA on ischemic acute kidney injury. Rats were subject to bilateral renal ischemia (60 minutes)/reperfusion (24 hours) injury. Impairment of renal function was determined with inulin clearance (glomerular filtration rate) and para-aminohippurate (PAH) clearance (renal plasma flow). L-arginine, ADMA, and SDMA levels were measured by liquid chromatography-tandem mass spectrometry. L-arginine was extracted from renal tissue and analyzed by enzyme-linked immunosorbent assay, and protein and messenger RNA expressions were determined by Western blot and reverse transcription polymerase chain reaction. Renal function deteriorated severely after ischemia/reperfusion injury, as demonstrated by inulin and PAH clearance. Serum ADMA and SDMA increased, but tissue expression of specific ADMA or SDMA synthesizing and metabolizing enzymes (protein arginine methyltransferases and dimethyl arginine dimethylaminohydrolases) did not alter. Serum L-arginine increased as well, whereas intracellular L-arginine concentration diminished. Renal messenger RNA expression of cationic amino acid transporters, which mediate L-arginine uptake, remained unchanged. In serum, the ratio of L-arginine to ADMA did not alter after ischemia/reperfusion injury, whereas the ratios of L-arginine to SDMA and ADMA to SDMA decreased. A marked increase in serum SDMA, especially when accompanied by a diminished L-arginine-to-SDMA ratio, might reflect competitive inhibition of cellular L-arginine uptake by SDMA. As a consequence, a pathologic renal L-arginine deficiency in ischemic acute kidney injury results.
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ABSTRACT: Renal organic cation transporters are downregulated by nitric oxide (NO) in rat endotoxemia. NO generated by inducible NO synthase (iNOS) is substantially increased in the renal cortex after renal ischemia-reperfusion (I/R) injury. Therefore, we investigated the effects of iNOS-specific NO inhibition on the expression of the organic cation transporters rOct1 and rOct2 (Slc22a1 and Slc22a2, respectively) after I/R injury both in vivo and in vitro. In vivo, N(6)-(1-iminoethyl)-L-lysine (L-NIL) completely inhibited NO generation after I/R injury. Moreover, L-NIL abolished the ischemia-induced downregulation of rOct1 and rOct2 as determined by qPCR and Western blotting. Functional evidence was obtained by measuring the fractional excretion (FE) of the endogenous organic cation serotonin. Concordant with the expression of the rate-limiting organic cation transporter, the FE of serotonin decreased after I/R injury and was totally abolished by L-NIL. In vitro, ischemia downregulated both rOct1 and rOct2, which were also abolished by L-NIL; the same was true for the uptake of the organic cation MPP. We showed that renal I/R injury downregulates rOct1 and rOct2, which is most probably mediated via NO. In principle, this may be an autocrine effect of proximal tubular epithelial cells. We conclude that rOct1, or rOct1 and rOct2 limit the rate of the renal excretion of serotonin.
University of WuerzburgWürzburg, Bavaria, Germany