An update on cyclooxygenase-2 expression and metabolites in the kidney

The crucial role that hippocampus Cyclooxygenase-2 plays in memory

It is generally accepted that Cyclooxygenase-2 (COX-2) is activated to cause inflammation. However, COX-2 is also constitutively expressed at the postsynaptic dendrites and excitatory terminals of the cortical and spinal cord neurons. Although some evidence suggests that COX-2 release during neuronal signalling may be pivotal for regulating the function of memory, the significance of constitutively expressed COX-2 in neuron is still unclear. This research aims to discover the role of COX-2 in memory beyond neuroinflammation and to determine whether the inhibition of COX-2 can cause cognitive dysfunction by influencing dendritic plasticity and its underlying mechanism. We found COX-2 gene knockout (KO) could significantly impact the learning and memory ability, cause neuronal structure disorder and influence gamma oscillations. These might be mediated by the inhibition of prostaglandin (PG) E2/cAMP pathway and phosphorylated protein kinase A (p-PKA)-phosphorylated cAMP response element binding protein (p-CREB)-brain derived neurotrophic factor (BDNF) axis. It suggested COX-2 might play a critical role in learning, regulating neuronal structure and gamma oscillations in the hippocampus CA1 by regulating COX-2/BDNF signalling pathway.

Assessment of Physicochemical and In Vivo Biological Properties of Polymeric Nanocapsules Based on Chitosan and Poly(N-vinyl pyrrolidone-alt-itaconic anhydride)

Drug delivery is an important field of nanomedicine, and its aim is to deliver specific active substances to a precise site of action in order to produce a desired pharmacological effect. In the present study nanocapsules were obtained by a process of interfacial condensation between chitosan (dissolved in the aqueous phase) and poly(N-vinyl pyrrolidone-alt-itaconic anhydride), a highly reactive copolymer capable of easily opening the anhydride ring under the action of amine groups of chitosan. The formed amide bonds led to the formation of a hydrogel membrane. The morphology of the obtained nanocapsules, their behavior in aqueous solution of physiological pH, and their ability to encapsulate and release a model drug can be modulated by the parameters of the synthesis process, such as the molar ratio between functional groups of polymers and the ratio of the phases in which the polymers are solubilized. Although a priori both polymers are biocompatible, this paper reports the results of a very detailed in vivo study conducted on experimental animals which have received the obtained nanocapsules by three administration routes—intraperitoneal, subcutaneous, and oral. The organs taken from the animals’ kidney, liver, spleen, and lung and analyzed histologically demonstrated the ability of nanocapsules to stimulate the monocytic macrophage system without producing inflammatory changes. Moreover, their in vivo behavior has been shown to depend not only on the route of administration but also on the interaction with the cells of the organs with which they come into contact. The results clearly argue the biocompatibility of nanocapsules and hence the possibility of their safe use in biomedical applications.

Multitarget molecule, PTUPB, to treat diabetic nephropathy in rats

BACKGROUND AND PURPOSE

Diabetic nephropathy is a common complications related to high morbidity and mortality in type 2 diabetes. We investigated the action of the dual modulator, PTUPB, a soluble epoxide hydrolase and cyclooxygenase-2 inhibitor against diabetic nephropathy.

EXPERIMENTAL APPROACH

Sixteen-week-old type 2 diabetic and proteinuric obese ZSF1 rats were treated with vehicle, PTUPB or enalapril for 8 weeks. Measurements were made of epoxyeicosatrienoic acids, thromboxane B2 (TBX2 ) and prostaglandin E2 (PGE2 ) in the kidney of these and lean ZSF1 rats along with their blood pressure.

KEY RESULT

Obese ZSF1 rats were diabetic with fivefold higher fasting blood glucose levels and markedly higher HbA1c levels compared with lean ZSF1 rats. PTUPB nor enalapril reduced fasting blood glucose or HbA1c but alleviated the development of diabetic nephropathy. In PTUPB-treated obese ZSF1 rats, glomerular nephrin expression was preserved. Enalapril also alleviated diabetic nephropathy. Diabetic renal injury in obese ZSF1 rats was accompanied by renal inflammation with six to sevenfold higher urinary MCP-1 (CCR2) level and renal infiltration of CD-68 positive cells. PTUPB and enalapril significantly reduced urinary MCP-1 levels and renal mRNA expression of cytokines. Both PTUPB and enalapril lowered blood pressure. PTUPB but not enalapril decreased hyperlipidaemia and liver injury in obese ZSF1 rats.

CONCLUSION AND IMPLICATIONS

Overall, the dual modulator PTUPB does not treat hyperglycaemia but can effectively alleviate hypertension, diabetic nephropathy, hyperlipidaemia and liver injury in type 2 diabetic rats. Our data further demonstrate that the renal actions of PTUPB are comparable with a current standard diabetic nephropathy treatment.

"I don't get no respect": the role of chloride in acute kidney injury

Acute kidney injury (AKI) is a major public health problem that complicates 10-40% of hospital admissions. Importantly, AKI is independently associated with increased risk of progression to chronic kidney disease, end-stage renal disease, cardiovascular events, and increased risk of in-hospital and long-term mortality. The chloride content of intravenous fluid has garnered much attention over the last decade, as well as its association with excess use and adverse outcomes, including AKI. Numerous studies show that changes in serum chloride concentration, independent of serum sodium and bicarbonate, are associated with increased risk of AKI, morbidity, and mortality. This comprehensive review details the complex renal physiology regarding the role of chloride in regulating renal blood flow, glomerular filtration rate, tubuloglomerular feedback, and tubular injury, as well as the findings of clinical research related to the chloride content of intravenous fluids, changes in serum chloride concentration, and AKI. Chloride is underappreciated in both physiology and pathophysiology. Although the exact mechanism is debated, avoidance of excessive chloride administration is a reasonable treatment option for all patients and especially in those at risk for AKI. Therefore, high-risk patients and those with "incipient" AKI should receive balanced solutions rather than normal saline to minimize the risk of AKI.

Improvement of Cisplatin-induced renal dysfunction by Schisandra chinensis stems via anti-inflammation and anti-apoptosis effects

ETHNOPHARMACOLOGICAL RELEVANCE

Schisandra chinensis (Turcz.) Baill is a frequently used traditional Chinese medicine, and modern pharmacological research has proven that S. chinensis has antioxidant, anti-hepatotoxity, anti-inflammatory, and anti-nephrotoxic effects. Cisplatin is widely used as antineoplastic drug at present, but the clinical application is limited owing to its nephrotoxicity.

AIM OF THE STUDY

To demonstrate the renoprotective activity of the extract of the stems of S. chinensis (SCE) in mice established by cisplatin-triggering acute kidney injury (AKI). The possible molecular mechanism of nephroprotection exhibited by SCE was evaluated for the first time.

MATERIALS AND METHODS

Mice in SCE groups were pre-treated with SCE for 10 consecutive days, and on 7th day 1 h after final administration, following intraperitoneal injection of cisplatin with 20 mg/kg was treated to cisplatin group and SCE groups. On the 10th day, renal function, histopathological change, and oxidative stress markers were investigated.

RESULTS

Renal oxidative stress level characterized by elevated heme oxygenase 1 (HO-1), cytochrome P450 E1 (CYP2E1) and 4-hydroxynonenal (4-HNE) expression was obviously reduced by SCE pre-treatment. In addition, SCE was found to suppress inflammatory response through the reduction of nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2) expression and nuclear factor-kappa B (NF-κB) p65 activation. SCE treatment also inhibited activation of apoptotic pathways through down-regulating Bax, cleaved caspase-3, 8, 9 and up-regulating Bcl-2 expression levels.

CONCLUSION

These findings illustrated that SCE possessed powerful protective effect on AKI caused by cisplatin via amelioration of oxidative stress, inflammation and apoptosis.

Molecular differences in susceptibility of the kidney to sepsis-induced kidney injury

BACKGROUND

Septic acute kidney injury affects 40-50% of all septic patients. Molecular differences between septic patients with and without acute kidney injury (AKI) are only poorly understood. Here, we investigated gene expression changes that differentiated the subjects who developed septic AKI from those who did not and coupled this approach with traditional parameters of renal physiology.

METHODS

In 15 anesthetized, mechanically ventilated and instrumented pigs, progressive sepsis was induced either by peritonitis or by continuous intravenous infusion of Pseudomonas aeruginosa. Animals received standard intensive care including goal-directed hemodynamic management. Analyses were performed on kidneys from sham operated animals, septic pigs without AKI, and pigs with septic AKI. Before, and at 12, 18 and 22 h of progressive sepsis, systemic and renal hemodynamics, cortex microcirculation and plasma IL-6 and TNF-α were measured. At 22 h whole kidney expression of pre-selected genes was analyzed by quantitative Real Time PCR.

RESULTS

Animals with septic AKI had systemic hemodynamic phenotype (normo- or hyperdynamic) comparable with non-AKI subjects, but demonstrated higher plasma levels of cytokines, an increase in renal vascular resistance and early fall in cortical microcirculatory blood flow. The genes whose expression discriminated septic AKI from non-AKI included Toll like receptor 4 (up-regulated 2.7-fold, P = 0.04); Cyclooxygenase-2 (up-regulated 14.6-fold, P = 0.01), Angiotensin II Receptor (up-regulated 8.1-fold, P = 0.01), Caspase 3 (up-regulated 5.1-fold, P = 0.02), Peroxisome Proliferator-Activated Receptor Gamma, Coactivator 1 Alpha (down-regulated 2-fold, P = 0.02).

CONCLUSIONS

In this preliminary experimental study, kidney gene expression was profoundly different in animals that developed septic AKI as opposed to septic animals that did not. The biological functions of the genes differentially expressed support a role of inflammatory overstimulation coupled with metabolic and apoptotic molecular responses in early septic AKI. Cyclooxygenase-2 and angiotensin type 2 receptor-dependent downstream mechanisms appear fruitful targets for future mechanistic research.

COX-2 is involved in vascular oxidative stress and endothelial dysfunction of renal interlobar arteries from obese Zucker rats

Obesity is related to vascular dysfunction through inflammation and oxidative stress and it has been identified as a risk factor for chronic renal disease. In the present study, we assessed the specific relationships among reactive oxygen species (ROS), cyclooxygenase 2 (COX-2), and endothelial dysfunction in renal interlobar arteries from a genetic model of obesity/insulin resistance, the obese Zucker rats (OZR). Relaxations to acetylcholine (ACh) were significantly reduced in renal arteries from OZR compared to their counterpart, the lean Zucker rat (LZR), suggesting endothelial dysfunction. Blockade of COX with indomethacin and with the selective blocker of COX-2 restored the relaxations to ACh in obese rats. Selective blockade of the TXA2/PGH2 (TP) receptor enhanced ACh relaxations only in OZR, while inhibition of the prostacyclin (PGI2) receptor (IP) enhanced basal tone and inhibited ACh vasodilator responses only in LZR. Basal production of superoxide was increased in arteries of OZR and involved NADPH and xanthine oxidase activation and NOS uncoupling. Under conditions of NOS blockade, ACh induced vasoconstriction and increased ROS generation that were augmented in arteries from OZR and blunted by COX-2 inhibition and by the ROS scavenger tempol. Hydrogen peroxide (H2O2) evoked both endothelium- and vascular smooth muscle (VSM)-dependent contractions, as well as ROS generation that was reduced by COX-2 inhibition. In addition, COX-2 expression was enhanced in both VSM and endothelium of renal arteries from OZR. These results suggest that increased COX-2-dependent vasoconstriction contributes to renal endothelial dysfunction through enhanced (ROS) generation in obesity. COX-2 activity is in turn upregulated by ROS.

Renal autoregulation in health and disease

Intrarenal autoregulatory mechanisms maintain renal blood flow (RBF) and glomerular filtration rate (GFR) independent of renal perfusion pressure (RPP) over a defined range (80-180 mmHg). Such autoregulation is mediated largely by the myogenic and the macula densa-tubuloglomerular feedback (MD-TGF) responses that regulate preglomerular vasomotor tone primarily of the afferent arteriole. Differences in response times allow separation of these mechanisms in the time and frequency domains. Mechanotransduction initiating the myogenic response requires a sensing mechanism activated by stretch of vascular smooth muscle cells (VSMCs) and coupled to intracellular signaling pathways eliciting plasma membrane depolarization and a rise in cytosolic free calcium concentration ([Ca(2+)]i). Proposed mechanosensors include epithelial sodium channels (ENaC), integrins, and/or transient receptor potential (TRP) channels. Increased [Ca(2+)]i occurs predominantly by Ca(2+) influx through L-type voltage-operated Ca(2+) channels (VOCC). Increased [Ca(2+)]i activates inositol trisphosphate receptors (IP3R) and ryanodine receptors (RyR) to mobilize Ca(2+) from sarcoplasmic reticular stores. Myogenic vasoconstriction is sustained by increased Ca(2+) sensitivity, mediated by protein kinase C and Rho/Rho-kinase that favors a positive balance between myosin light-chain kinase and phosphatase. Increased RPP activates MD-TGF by transducing a signal of epithelial MD salt reabsorption to adjust afferent arteriolar vasoconstriction. A combination of vascular and tubular mechanisms, novel to the kidney, provides for high autoregulatory efficiency that maintains RBF and GFR, stabilizes sodium excretion, and buffers transmission of RPP to sensitive glomerular capillaries, thereby protecting against hypertensive barotrauma. A unique aspect of the myogenic response in the renal vasculature is modulation of its strength and speed by the MD-TGF and by a connecting tubule glomerular feedback (CT-GF) mechanism. Reactive oxygen species and nitric oxide are modulators of myogenic and MD-TGF mechanisms. Attenuated renal autoregulation contributes to renal damage in many, but not all, models of renal, diabetic, and hypertensive diseases. This review provides a summary of our current knowledge regarding underlying mechanisms enabling renal autoregulation in health and disease and methods used for its study.

Angiotensin II-independent upregulation of cyclooxygenase-2 by activation of the (Pro)renin receptor in rat renal inner medullary cells

During renin-angiotensin system activation, cyclooxygenase-2 (COX-2)-derived prostaglandins attenuate the pressor and antinatriuretic effects of angiotensin II (AngII) in the renal medulla. The (pro)renin receptor (PRR) is abundantly expressed in the collecting ducts (CD) and its expression is augmented by AngII. PRR overexpression upregulates COX-2 via mitogen-activated kinases/extracellular regulated kinases 1/2 in renal tissues; however, it is not clear whether this effect occurs independently or in concert with AngII type 1 receptor (AT1R) activation. We hypothesized that PRR activation stimulates COX-2 expression independently of AT(1)R in primary cultures of rat renal inner medullary cells. The use of different cell-specific immunomarkers (aquaporin-2 for principal cells, anion exchanger type 1 for intercalated type-A cells, and tenascin C for interstitial cells) and costaining for AT(1)R, COX-2, and PRR revealed that PRR and COX-2 were colocalized in intercalated and interstitial cells whereas principal cells did not express PRR or COX-2. In normal rat kidney sections, PRR and COX-2 were colocalized in intercalated and interstitial cells. In rat renal inner medullary cultured cells, treatment with AngII (100 nmol/L) increased COX-2 expression via AT(1)R. In addition, AngII and rat recombinant prorenin (100 nmol/L) treatments increased extracellular regulated kinases 1/2 phosphorylation, independently. Importantly, rat recombinant prorenin upregulated COX-2 expression in the presence of AT(1)R blockade. Inhibition of mitogen-activated kinases/extracellular regulated kinases 1/2 suppressed COX-2 upregulation mediated by either AngII or rat recombinant prorenin. Furthermore, PRR knockdown using PRR-short hairpin RNA blunted the rat recombinant prorenin-mediated upregulation of COX-2. These results indicate that COX-2 expression is upregulated by activation of either PRR or AT(1)R via mitogen-activated kinases/extracellular regulated kinases 1/2 in rat renal inner medullary cells.

Cyclooxygenase (COX) Inhibitors and the Newborn Kidney

This review summarizes our current understanding of the role of cyclo-oxygenase inhibitors (COXI) in influencing the structural development as well as the function of the developing kidney. COXI administered either during pregnancy or after birth can influence kidney development including nephronogenesis, and can decrease renal perfusion and ultrafiltration potentially leading to acute kidney injury in the newborn period. To date, which COX isoform (COX-1 or COX-2) plays a more important role in during fetal development and influences kidney function early in life is not known, though evidence points to a predominant role for COX-2. Clinical implications of the use of COXI in pregnancy and in the newborn infant are also evaluated herein, with specific reference to the potential effects of COXI on nephronogenesis as well as newborn kidney function.

Attenuation of renovascular damage in Zucker diabetic fatty rat by NWT-03, an egg protein hydrolysate with ACE- and DPP4-inhibitory Activity

Background

Dipeptidyl peptidase 4 (DPP4) and angiotensin-converting enzyme (ACE) are important target enzymes in glycemic control and renovascular protection. Here, we studied the effect of NWT-03, an egg protein hydrolysate with DPP4- and ACE-inhibitory activity, on renovascular damage in Zucker diabetic fatty (ZDF) rats. Comparisons were made to rats treated with vildagliptin (VIL), included as a positive control for the effect of DPP4 inhibition.

Methods

ZDF rats received NWT-03 (1 g/kg/day) or VIL (3 mg/kg/day) from 10 to 25 weeks of age. Metabolic and renal functions were assessed; the kidney was removed for histological analysis of glomerulosclerosis and expression of pro-inflammatory/fibrotic markers (RT-PCR and Western blotting); and the aorta was removed for studies of endothelium-dependent relaxation (EDR).

Findings

Hyperinsulinemic ZDF rats typically developed signs of type-2 diabetes and renovascular damage, as evidenced by albuminuria, glomerulosclerosis, and impaired EDR. Neither NWT-03 nor VIL improved metabolic parameters; for VIL, this was despite a 5-fold increase in glucagon-like peptide (GLP)-1 levels. NWT-03 and VIL both reduced renal interleukin (Il)-1β/Il-13 mRNA expression and glomerulosclerosis. However, only NWT-03 additionally decreased renal tumor necrosis factor (TNF)-α mRNA and P22^phox protein expression, reduced albuminuria, and restored aortic EDR. Indomethacin added to the organ bath instantly improved aortic EDR, indicating a role for cyclooxygenase (COX)-derived contractile prostanoids in opposing relaxation in ZDF rats. This indomethacin effect was reduced by NWT-03, but not by VIL, and coincided with decreased renal COX-1/2 protein expression.

Conclusion and Interpretation

Long-term supplementation with the egg protein hydrolysate NWT-03 attenuated renovascular damage in this preclinical rat model of type 2 diabetes. A comparison to the DPP4-inhibitor VIL suggests that the effects of NWT-03 were related to both ACE- and DPP4-inhibitory properties. The development of protein hydrolysates with a multiple-targeting strategy may be of benefit to functional food formulations.

Dopamine, the kidney, and hypertension

There is increasing evidence that the intrarenal dopaminergic system plays an important role in the regulation of blood pressure, and defects in dopamine signaling appear to be involved in the development of hypertension. Recent experimental models have definitively demonstrated that abnormalities in intrarenal dopamine production or receptor signaling can predispose to salt-sensitive hypertension and a dysregulated renin-angiotensin system. In addition, studies in both experimental animal models and in humans with salt-sensitive hypertension implicate abnormalities in dopamine receptor regulation due to receptor desensitization resulting from increased G-protein receptor kinase 4 (GRK4) activity. Functional polymorphisms that predispose to increased basal GRK4 activity both decrease dopamine receptor activity and increase angiotensin II type 1 (AT1) receptor activity and are associated with essential hypertension in a number of different human cohorts.

The complex interplay between cyclooxygenase-2 and angiotensin II in regulating kidney function

PURPOSE OF REVIEW

Cyclooxygenase-2 (COX-2) plays a critical role in modulating deleterious actions of angiotensin II (Ang II) where there is an inappropriate activation of the renin-angiotensin system (RAS). This review discusses the recent developments regarding the complex interactions by which COX-2 modulates the impact of an activated RAS on kidney function and blood pressure.

RECENT FINDINGS

Normal rats with increased COX-2 activity but with different intrarenal Ang II activity because of sodium restriction or chronic treatment with angiotensin-converting enzyme (ACE) inhibitors showed similar renal hemodynamic responses to COX-2-selective inhibition (nimesulide) indicating independence from the intrarenal Ang II activity. COX-2-dependent maintenance of medullary blood flow was consistent and not dependent on dietary salt or ACE inhibition. In contrast, COX-2 influences on sodium excretion were contingent on the prevailing RAS activity. In chronic hypertensive models, COX-2 inhibition elicited similar reductions in kidney function, but COX-2 metabolites contribute to rather than ameliorate the hypertension.

SUMMARY

The maintenance of renal hemodynamics reflects direct and opposing effects of Ang II and COX-2 metabolites. The antagonism in water and electrolyte reabsorption is dependent on the prevailing intrarenal Ang II activity. The recent functional experiments demonstrate a beneficial modulation of Ang II by COX-2 except in the presence of inflammation promoted by hypertension, hyperglycemia, and oxidative stress.

Curcumin and enalapril ameliorate renal failure by antagonizing inflammation in 5/6 nephrectomized rats: role of phospholipase and cyclooxygenase

Previously, we showed that curcumin prevents chronic kidney disease (CKD) development in ⅚ nephrectomized (Nx) rats when given within 1 wk after Nx (Ghosh SS, Massey HD, Krieg R, Fazelbhoy ZA, Ghosh S, Sica DA, Fakhry I, Gehr TW. Am J Physiol Renal Physiol 296: F1146-F1157, 2009). To better mimic the scenario for renal disease in humans, we began curcumin and enalapril therapy when proteinuria was already established. We hypothesized that curcumin, by blocking the inflammatory mediators TNF-α and IL-1β, could also reduce cyclooxygenase (COX) and phospholipase expression in the kidney. Nx animals were divided into untreated Nx, curcumin-treated, and enalapril-treated groups. Curcumin (75 mg/kg) and enalapril (10 mg/kg) were administered for 10 wk. Renal dysfunction in the Nx group, as evidenced by elevated blood urea nitrogen, plasma creatinine, proteinuria, segmental sclerosis, and tubular dilatation, was comparably reduced by curcumin and enalapril, with only enalapril significantly lowering blood pressure. Compared with controls, Nx animals had higher plasma/kidney TNF-α and IL-1β, which were reduced by curcumin and enalapril treatment. Nx animals had significantly elevated kidney levels of cytosolic PLA(2), calcium-independent intracellular PLA(2), COX 1, and COX 2, which were comparably reduced by curcumin and enalapril. Studies in mesangial cells and macrophages were carried out to establish that the in vivo increase in PLA(2) and COX were mediated by TNF-α and IL-1β and that curcumin, by antagonizing the cytokines, could significantly reduce both PLA(2) and COX. We conclude that curcumin ameliorates CKD by blocking inflammatory signals even if it is given at a later stage of the disease.

Eicosanoids, β-cell function, and diabetes

Arachidonic acid (AA) is metabolized by cyclooxygenase (COX), lipoxygenase (LOX), and cytochrome P450 (CYP) enzymes into eicosanoids, which are involved in diverse diseases, including type 1 and type 2 diabetes. During the last 30 years, evidence has been accumulated that suggests important functions for eicosanoids in the control of pancreatic β-cell function and destruction. AA metabolites of the COX pathway, especially prostaglandin E(2) (PGE(2)), appear to be significant factors to β-cell dysfunction and destruction, participating in the pathogenesis of diabetes and its complications. Several elegant studies have contributed to the sorting out of the importance of 12-LOX eicosanoids in cytokine-mediated inflammation in pancreatic β cells. The role of CYP eicosanoids in diabetes is yet to be explored. A recent publication has demonstrated that stabilizing the levels of epoxyeicosatrienoic acids (EETs), CYP eicosanoids, by inhibiting or deleting soluble epoxide hydrolase (sEH) improves β-cell function and reduces β-cell apoptosis in diabetes. In this review we summarize recent findings implicating these eicosanoid pathways in diabetes and its complications. We also discuss the development of animal models with targeted gene deletion and specific enzymatic inhibitors in each pathway to identify potential targets for the treatment of diabetes and its complications.

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.

METHODS

Rats were treated with either CP or saline and followed for 5 days. Kidneys were dissected into three zones and prepared for immunoblotting, quantitative polymerase chain reaction (QPCR) and immunohistochemistry. Renal content and urinary PGE2 excretion was measured.

RESULTS

Cisplatin treatment was associated with polyuria and a significant decreased creatinine clearance. Inner medullary PGE2 content and urinary PGE2 excretion was decreased in CP-treated rats. QPCR and semiquatitative immunoblotting demonstrated that CP treatment reduced COX-2, AQP2 and Na-K-2Cl cotransporter abundance in the different kidney zones, whereas no change in COX-1 was observed. Results were confirmed by immunohistochemistry.

CONCLUSION

Cyclooxygenase-2 expression is decreased in inner medulla and cortex. Consistent with this urinary PGE2 levels were reduced. These data suggest that downregulation of COX-2 is responsible for impaired de novo generation of vasodilatory prostaglandins which may play an important role for the CP induced renal vasoconstriction and development of nephropathy.

Cyclooxygenase 2 inhibition exacerbates AQP2 and pAQP2 downregulation independently of V2 receptor abundance in the postobstructed kidney

Previously we demonstrated that ANG II receptor (AT1R) blockade attenuates V2 receptor (V2R), AQP2, and pS256-AQP2 downregulation in the postobstructed kidney and partially reverses obstruction-induced inhibition of cAMP generation and cyclooxygenase 2 (COX-2) induction. Therefore, we speculated whether the effects of AT1R blockade on V2R and the vasopressin-regulated pathway are attributable to attenuated COX-2 induction. To examine this, rats were subjected to 24-h bilateral ureteral obstruction (BUO) followed by 48-h release and treated with the COX-2 inhibitor parecoxib or saline. Control rats were sham-operated. Parecoxib treatment significantly reduced urine output 24 h after release of BUO whereas urine osmolality and solute-free water reabsorption was comparable between saline- and parecoxib-treated BUO rats. Immunoblotting revealed a significant decrease in AQP2 and pS256-AQP2 abundance to 20 and 23% of sham levels in parecoxib-treated BUO rats compared with 40 and 55% of sham levels in saline-treated BUO rats. Immunohistochemistry confirmed the exacerbated AQP2 and pS256-AQP2 downregulation in parecoxib-treated BUO rats. Finally, parecoxib treatment had no effect on V2R downregulation and the inhibited, vasopressin-stimulated cAMP generation in inner medullary membrane fractions from the postobstructed kidney. In conclusion, COX-2 inhibition exacerbates AQP2 and pS256-AQP2 downregulation 48 h after release of 24-h BUO independently of V2R abundance and vasopressin-stimulated cAMP generation. The results indicate that COX-2 inhibition does not mimic AT1R blockade-mediated effects and that AT1R-mediated AQP2 regulation in the postobstructed kidney collecting duct is independent of COX-2 induction.

Tubuloglomerular feedback is decreased in COX-1 knockout mice after chronic angiotensin II infusion

Prostaglandins (PGs), produced by two isoforms of cyclooxygenase (COX), COX-1 and COX-2, are important modulators of renal hemodynamics. COX-1 and COX-2 are expressed in the kidney often at distinct sites. Thromboxane (TxA(2)), PGE(2), and prostacyclin (PGI(2)) are the major PGs in the renal cortex of mice. Acute infusion of the vasoconstrictor ANG II increases COX-2-dependent PGE(2) and PGI(2). COX-2 is primarily expressed in the macula densa (MD), where several PG synthases are also expressed. We previously showed that MD COX-2 products modulate tubuloglomerular feedback (TGF) in the rat. Genetic deletion of COX-1 enhances COX-2 production of PGs, decreases renal and urinary PGs, and attenuates ANG II-induced hypertension. The present study tested the effects of chronic ANG II infusion on TGF in COX-1 knockout (KO) mice. Basal TGF was similar in COX-1 KO and wild-type (WT) mice. Chronic ANG II infusion increased TGF in WT mice (WT: 9.3 +/- 0.7 vs. WT + ANG II: 12.2 +/- 1.6 mmHg, P < 0.02). However, chronic ANG II decreased TGF in COX-1 KO mice (KO: 11.4 +/- 1.1 vs. KO + ANG II: 8.3 +/- 0.6 mmHg, P < 0.01). Pretreatment with the COX-2 inhibitor SC-58,236 in COX-1 KO mice prevented the ANG II-associated reduction in TGF (11.4 +/- 1.0 vs. 11.5 +/- 0.28 mmHg, not significant). Excretion of 6-keto-PGF(2alpha), the metabolite of PGI(2), was increased by ANG II infusion, whereas excretion of TxB(2), the stable metabolite of TxA(2), was not changed. ANG II infusion increased mean arterial pressure similarly in both WT and KO mice (WT: 93 +/- 2 vs. KO: 92 +/- 3 mmHg), but not in KO mice pretreated with SC-58,236 (85 +/- 2 mmHg). This study shows that COX-1-generated PGs partially mediate ANG II increases in TGF and that COX-2 PGs offset that effect.

An improved terminology and classification of Bartter-like syndromes

This Review outlines a terminology and classification of Bartter-like syndromes that is based on the underlying causes of these inherited salt-losing tubulopathies and is, therefore, more clinically relevant than the classical definition. Three major types of salt-losing tubulopathy can be defined: distal convoluted tubule dysfunction leading to hypokalemia (currently known as Gitelman or Bartter syndrome), the more-severe condition of polyuric loop dysfunction (often referred to as antenatal Bartter or hyperprostaglandin E syndrome), and the most-severe condition of combined loop and distal convoluted tubule dysfunction (antenatal Bartter or hyperprostaglandin E syndrome with sensorineural deafness). These three subtypes can each be further subdivided according to the identity of the defective ion transporter or channel: the sodium-chloride cotransporter NCCT or the chloride channel ClC-Kb in distal convoluted tubule dysfunction; the sodium-potassium-chloride cotransporter NKCC2 or the renal outer medullary potassium channel in loop dysfunction; and the chloride channels ClC-Ka and ClC-Kb or their beta-subunit Barttin in combined distal convoluted tubule and loop dysfunction. This new classification should help clinicians to better understand the pathophysiology of these syndromes and choose the most appropriate treatment for affected patients, while avoiding potentially harmful diagnostic and therapeutic approaches.