Sukru Oguzkan Topcu

Urinary tract obstruction induces transient accumulation of COX-2 derived prostanoids in kidney tissue

Inhibitors of cyclooxygenase (COX)-2 prevent suppression of aquaporin-2 and reduce polyuria in the acute phase after release of bilateral ureteral obstruction (BUO). We hypothesized that BUO leads to COX-2-mediated local accumulation of prostanoids in inner medulla (IM) tissue. To test this, rats were subjected to BUO and treated with selective COX-1 or COX-2 inhibitors. Tissue was examined at 2, 6, 12, and 24 h after BUO. COX-2 protein abundance increased in IM 12 and 24 h after onset of BUO but did not change in cortex. COX-1 did not change at any time points in any region. A full profile of all five primary prostanoids was obtained by mass spectrometric determination of PGE(2), PGF(2alpha), 6-keto-PGF(1alpha), PGD(2), and thromboxane (Tx) B(2) concentrations in kidney cortex/outer medulla and IM fractions. IM concentration of PGE(2), 6-keto-PGF(1alpha), and PGF(2alpha) was increased at 6 h BUO, and PGE(2) and PGF(2alpha) increased further at 12 h BUO. TxB(2) increased after 12 h BUO. 6-keto-PGF(1alpha) remained significantly increased after 24 h BUO. The COX-2 inhibitor parecoxib lowered IM PGE(2,) TxB(2), 6-keto-PGF(1alpha), and PGF(2alpha) below vehicle-treated BUO and sham rats at 6, 12 and, 24 h BUO. The COX-1 inhibitor SC-560 lowered PGE(2), PGF(2alpha), and PGD(2) in IM compared with untreated 12 h BUO, but levels remained significantly above sham. In cortex tissue, PGE(2) and 6-keto-PGF(1alpha) concentrations were elevated at 6 h only. In conclusion, COX-2 activity contributes to the transient increase in prostacyclin metabolite 6-keto-PGF(1alpha) and TxB(2) concentration in the kidney IM, and COX-2 is the predominant isoform that is responsible for accumulation of PGE(2) and PGF(2alpha) with minor, but significant, contributions from COX-1. PGD(2) synthesis is mediated exclusively by COX-1. In BUO, therapeutic interventions aimed at the COX-prostanoid pathway should target primarily COX-2.

Disruption of cyclooxygenase-2 prevents downregulation of cortical AQP2 and AQP3 in response to bilateral ureteral obstruction in the mouse.

Bilateral ureteral obstruction (BUO) in rats is associated with increased cyclooxygenase type 2 (COX-2) expression, and selective COX-2 inhibition prevents downregulation of aquaporins (AQPs) in response to BUO. It was hypothesized that a murine model would display similar changes in renal COX-2 and AQPs upon BUO and that targeted disruption of COX-2 protects against BUO-induced suppression of collecting duct AQPs. COX-2(-/-) and wild-type littermates (C57BL/6) were employed to determine COX-1, -2, AQP2, and AQP3 protein abundances and localization after BUO. In a separate series, sham and BUO wild-type mice were treated with a selective COX-2 inhibitor, parecoxib. The COX-2 protein level increased in wild-type mice in response to BUO and was not detectable in COX-2(-/-). COX-1 protein abundance was increased in sham-operated and BUO mice. Total AQP2 and -3 mRNA and protein levels decreased significantly after BUO in the cortex+outer medulla (C+OM) and inner medulla (IM). The decrease in C+OM AQP2 and -3 levels was attenuated/prevented in COX-2(-/-) mice, whereas there was no change in the IM. In parallel, inhibition of COX-2 by parecoxib rescued C+OM AQP3 and IM AQP2 protein level in wild-type mice subjected to BUO. In summary, 1) In C57BL/6 mice, ureteral obstruction increases renal COX-2 expression in interstitial cells and lowers AQP2/-3 abundance and 2) inhibition of COX-2 activity by targeted disruption or pharmacological blockade attenuates obstruction-induced AQP downregulation. In conclusion, COX-2-derived prostaglandins contribute to downregulation of transcellular water transporters in the collecting duct and likely to postobstruction diureses in the mouse.

Oxygen tension correlates with regional blood flow in obstructed rat kidney.

SUMMARY As renal tissue oxygen tension (PO2) is determined by the balance between oxygen supply and consumption, direct tissue PO2 measurements are essential when evaluating the presence of hypoxia. The present study aimed at evaluating invasively and continuously the renal medullary and cortical tissue PO2 by novel fibre-optic probes in rats subjected to acute unilateral ureteral obstruction (AUUO). In parallel, regional blood flow measurements were obtained by MRI to investigate the relationship between regional blood flow and tissue oxygen tension. The abundance of transport proteins was determined by immunoblotting. In the obstructed kidney, AUUO caused a prompt decrease in medullary tissue PO2 to 60% of baseline level whereas cortical tissue PO2 was unchanged. By contrast, tissue PO2 slightly increased in the non-obstructed kidney. These changes developed during the first 30 min after AUUO and persisted for the 3 h observation period. Medullary blood flow declined 1.5–2 h after induction of AUUO to 61% of baseline level in the obstructed kidney. By contrast, cortical blood flow increased to 108% of baseline level in the non-obstructed kidney. Finally, the abundance of phosphorylated aquaporin 2 decreased significantly in the obstructed kidney medulla, but increased in the obstructed kidney cortex. The Na+/K+-ATPase abundance increased in the obstructed kidney medulla whereas the Na+/K+/2Cl– co-transporter abundance remained unchanged in the obstructed kidney. In conclusion, measurements of regional blood flow reflect tissue PO2 changes during AUUO suggesting that reduced regional blood flow is a predictor of local hypoxia. Furthermore, the abundance of major transport protein is independent of tissue PO2.

Cisplatin decreases renal cyclooxygenase-2 expression and activity in rats

Aim:  Cisplatin (CP) induced acute renal failure (ARF) has previously been associated with decreased urinary prostaglandin E2 (PGE2) excretion and reduced aquaporin 2 (AQP2) expression in kidney collecting duct. In this study we examined the expression of cyclooxygenase (COX)‐1 and ‐2 as well as AQP2 and the Na‐K‐2Cl cotransporter in kidneys from rats with CP induced ARF.

Urinary proteome analysis in congenital bilateral hydronephrosis

Abstract Objective. A proteomics strategy was applied to map protein changes in urine after relief of congenital bilateral hydronephrosis to identify proteins correlated with the pathophysiological processes in congenital obstructive nephropathy as potential urinary biomarkers. Material and methods. Urine samples from 10 infants with bilateral abnormal drainage from the kidneys were collected at the time of relief from obstruction, and after 2 and 4 weeks. Proteomics techniques were used on samples from three patients for identification of protein changes between the three time-points, and enzyme-linked immunosorbent assay (ELISA) was used on samples from all 10 patients for validation of five selected proteins. Results. Mass spectrometry quantified 315 protein hits, out of which 33 proteins showed significantly changed urinary excretion between the time-points. Validation by ELISA showed high urinary excretion of fibrinogen, plasminogen, transthyretin and transferrin at the time of relief from obstruction, followed by a significant reduction. In contrast, Tamm–Horsfall protein exhibited the reverse pattern. Conclusion. Using a mass spectrometry-based proteomics approach, this study identified 33 proteins related to congenital bilateral hydronephrosis, and pinpointed a panel of five proteins consistently linked to this congenital kidney disorder as potential urinary biomarkers.

Regulation of Aquaporins and Sodium Transporter Proteins in the Solitary Kidney in Response to Partial Ureteral Obstruction in Neonatal Rats

Unilateral ureteral obstruction (UUO) impairs function of the obstructed kidney, and the contralateral nonobstructed kidney compensates depending on the degree and duration of UUO. This study aimed to determine the hemodynamic and molecular changes in the solitary kidney in response to partial ureteral obstruction (PUO) where any compensation from the contralateral kidney was eliminated so that all observed changes in the kidney tissue occurred in the kidney with PUO. Newborn rats were subjected to unilateral left nephrectomy (UNX) within the first 48 h of life and a subset of UNX rats was subjected to severe PUO of the right kidney at day 14. Renal blood flow and whole kidney volume were measured with MRI at week 10. The renal protein abundance of aquaporin 1 (AQP1), AQP2 and AQP3 as well as Na,K-ATPase, NaPi-2 (type 2 sodium-phosphate cotransporter) and NHE3 (type 3 sodium-proton exchanger) were examined by immunoblotting and immunocytochemistry. At 10 weeks of age, the protein abundance of AQP2, AQP3, Na,K-ATPase, NaPi-2 and NHE3 were increased in response to PUO. In contrast, AQP1 expression was markedly decreased compared to sham-operated rats. These findings were confirmed by immunohistochemistry. GFR, urine osmolality and urine sodium excretion were reduced and kidney weight increased in response to PUO. In conclusion, the present study demonstrated major changes in the protein abundance of renal AQP1, AQP2 and AQP3 and sodium transporters in the solitary PUO kidney. These changes were paralleled by decreased urinary sodium excretion and a significant reduction in urinary osmolality from the obstructed kidney, suggesting a functional association between the molecular changes and the ability of the obstructed kidney to handle sodium and water in this solitary kidney model.

Hemodynamic and Molecular Changes in the Solitary Kidney in Response to Partial Ureteral Obstruction

Abstract Purpose In conditions with unilateral ureteric obstruction the function of the obstructed kidney is impaired. In addition, the non-obstructed intact kidney suffers during severe unilateral obstruction. The main aim of the present study is to eliminate any compensation in the contralateral kidney so that all observed changes in the kidney tissue occurred in kidneys with a partially obstructed ureter. Material and Methods Newborn rats were subjected to UNX (unilateral left nephrectomy) within the first 48 hr of life and a subset of unilateral nephrectomized rats was subjected to right severe PUO (Partial Ureteral Obstruction) at day 14. Renal blood flow (RBF), Total Kidney Volume (TKV) was measured using MRI at week 10; moreover renal functional and metabolic data were analysed. The renal expression of Na, K-ATPase, Na-Pi2, NHE3 and AQP1, AQP3, AQP2 were examined by immunoblotting and immunocytochemistry. Results PUO resulted in upregulation of type3 Na + /H + exchanger (NHE3) to 157±8%, the NaPi-2 cotransporter to 134±16%, Na, K-ATPase to 139±7%. Furthermore, in the obstructed kidney immunoblotting revealed a significant increase in the expression of AQP2 to 112±3%, AQP3 to 141±6%. In contrast, AQP1 expression markedly decreased to 75±10% of sham level (p Conclusions The contralateral kidney plays a very important compensatory role in regulation of key renal transporters and channels in response to urinary tract obstruction kidney functions.