Renal identification of cyclooxygenase-2 in a subset of thick ascending limb cells

[Current challenges for therapy of comorbid patients: a new look at celecoxib. A review]

The use of non-steroidal anti-inflammatory drugs (NSAIDs) for a wide range of diseases is increasing, in part due to an increasing elderly population. Elderly patients are more vulnerable to adverse drug reactions, including side effects and adverse effects of drug-drug interactions, often occurring in this category of patients due to multimorbidity and polypharmacy. One of the most popular NSAIDs in the world is celecoxib. It is a selective cyclooxygenase (COX)-2 inhibitor with 375 times more COX-2 inhibitory activity than COX-1. As a result, celecoxib has a better gastrointestinal tract safety profile than non-selective NSAIDs. Gastrointestinal tolerance is an essential factor that physicians should consider when selecting NSAIDs for elderly patients. Celecoxib can be used in a wide range of diseases of the musculoskeletal system and rheumatological diseases, for the treatment of acute pain in women with primary dysmenorrhea, etc. It is also increasingly used as part of a multimodal perioperative analgesia regimen. There is strong evidence that COX-2 is actively involved in the pathogenesis of ischemic brain damage, as well as in the development and progression of neurodegenerative diseases, such as Alzheimer's disease. NSAIDs are first-line therapy in the treatment of acute migraine attacks. Celecoxib is well tolerated in patients with risk factors for NSAID-associated nephropathy. It does not decrease the glomerular filtration rate in elderly patients and patients with chronic renal failure. Many meta-analyses and epidemiological studies have not confirmed the increased risk of cardiovascular events reported in previous clinical studies and have not shown an increased risk of cardiovascular events with celecoxib, irrespective of dose. COX-2 activation is one of the key factors contributing to obesity-related inflammation. Specific inhibition of COX-2 by celecoxib increases insulin sensitivity in overweight or obese patients. Combination therapies may be a promising new area of treatment for obesity and diabetes.

Fetal Programming of Renal Dysfunction and High Blood Pressure by Chronodisruption

Adverse prenatal conditions are known to impose significant trade-offs impinging on health and disease balance during adult life. Among several deleterious factors associated with complicated pregnancy, alteration of the gestational photoperiod remains largely unknown. Previously, we reported that prenatal manipulation of the photoperiod has adverse effects on the mother, fetus, and adult offspring; including cardiac hypertrophy. Here, we investigated whether chronic photoperiod shifting (CPS) during gestation may program adult renal function and blood pressure regulation. To this end, pregnant rats were subjected to CPS throughout pregnancy to evaluate the renal effects on the fetus and adult offspring. In the kidney at 18 days of gestation, both clock and clock-controlled gene expression did not display a daily pattern, although there were recurrent weaves of transcriptional activity along the 24 h in the control group. Using DNA microarray, significant differential expression was found for 1,703 transcripts in CPS relative to control fetal kidney (835 up-regulated and 868 down-regulated). Functional genomics assessment revealed alteration of diverse gene networks in the CPS fetal kidney, including regulation of transcription, aldosterone-regulated Na+ reabsorption and connective tissue differentiation. In adult offspring at 90 days of age, circulating proinflammatory cytokines IL-1β and IL-6 were increased under CPS conditions. In these individuals, CPS did not modify kidney clock gene expression but had effects on different genes with specific functions in the nephron. Next, we evaluated several renal markers and the response of blood pressure to 4%NaCl in the diet for 4 weeks (i.e., at 150 days of age). CPS animals displayed elevated systolic blood pressure in basal conditions that remained elevated in response to 4%NaCl, relative to control conditions. At this age, CPS modified the expression of Nhe3, Ncc, Atp1a1, Nr3c1 (glucocorticoid receptor), and Nr3c2 (mineralocorticoid receptor); while Nkcc, Col3A1, and Opn were modified in the CPS 4%+NaCl group. Furthermore, CPS decreased protein expression of Kallikrein and COX-2, both involved in sodium handling. In conclusion, gestational chronodisruption programs kidney dysfunction at different levels, conceivably underlying the prehypertensive phenotype observed in the adult CPS offspring.

Diuretic effects and urinary electrolyte excretion induced by Aspidosperma subincanum Mart. and the involvement of prostaglandins in such effects

ETHNOPHARMACOLOGICAL RELEVANCE

Aspidosperma subincanum Mart. is a medicinal herb known for its diuretic properties and used for the treatment of cardiovascular-related illnesses. Although our earlier study has shown that the ethanol extract of Aspidosperma subincanum (EEAS) induces hypotension and vasodilation, no scientific data have been recorded to evaluate the diuretic effects of this Brazilian medicinal plant. The aim of this study was to evaluate the diuretic activity of EEAS, and possible mechanism of action, using Wistar rats.

MATERIAL AND METHODS

EEAS (60 and 120mg/kg), furosemide (20mg/kg) or saline (control) were orally administered to rats individually held in metabolic cages for urine collection 1, 2, 4, 6, 8, 12 and 24h after treatment. In order to evaluate the involvement of prostaglandins in the diuretic action of EEAS, the animals received piroxicam (5mg/kgi.p.), a nonselective inhibitor of cyclooxygenase, before treatment with EEAS at 120mg/kg. The control groups received only saline (NaCl, 0.9%), or saline and piroxicam. Urinary volume, electrolyte excretion and pH were measured.

RESULTS

Oral administration of EEAS 60 and 120mg/kg significantly increased diuresis and electrolyte excretion of Na(+) and K(+) on a continuous basis throughout the study period. Both EEAS 60 and 120mg/kg caused a relative increase of around 77% and 142%, respectively, in cumulative diuresis compared with the control group. From 4th hour until the end of the experiment, the group treated with EEAS 120mg/kg provided a greater excretion of Na(+) than the furosemide group. The diuretic effects of EEAS were neutralized by piroxicam between 4 and 8h after treatment.

CONCLUSION

The results suggest that EEAS could present compound(s) responsible for diuretic activities, and the mechanism could involve the prostaglandin system.

Effects of meloxicam and phenylbutazone on renal responses to furosemide, dobutamine, and exercise in horses

OBJECTIVE

To compare the effects of 2 NSAIDs (phenylbutazone and meloxicam) on renal function in horses.

ANIMALS

9 Thoroughbred or Standardbred mares (mean ± SD age, 5.22 ± 1.09 years [range, 2 to 12 years]; mean body weight, 470 ± 25 kg [range, 442 to 510 kg]).

PROCEDURES

A randomized blinded placebo-controlled crossover study was conducted to examine the effects of treatment with phenylbutazone, meloxicam, or a placebo (control solution) on renal responses to the administration of furosemide, dobutamine, and exercise (15 minutes at 60% of maximum heart rate). Renal function was assessed by use of bilateral ureteral catheterization for simultaneous determination of creatinine clearance, sodium excretion, and urine flow rate.

RESULTS

Both phenylbutazone and meloxicam attenuated diuresis and natriuresis and reduced glomerular filtration rate, compared with results for the control solution, when horses were treated with furosemide. Mean arterial blood pressure, urine flow rate, and glomerular filtration rate were increased during or after (or both) dobutamine infusion. Both NSAIDs reduced urine flow rate and sodium excretion associated with dobutamine infusion and exercise but had no effect on glomerular filtration rate.

CONCLUSIONS AND CLINICAL RELEVANCE

Responses to meloxicam, a cyclooxygenase (COX)-2 preferential agent, appeared comparable to those detected after phenylbutazone treatment, which suggested that COX-2 was the mediator of prostanoid-induced changes to renal function in horses and indicated that COX-2-preferential agents would be likely to have adverse renal effects similar to those for nonselective COX inhibitors in volume-depleted horses.

PGE(2) EP(3) receptor downregulates COX-2 expression in the medullary thick ascending limb induced by hypertonic NaCl

We tested the hypothesis that inhibition of EP3 receptors enhances cyclooxygenase (COX)-2 expression in the thick ascending limb (TAL) induced by hypertonic stimuli. COX-2 protein expression in the outer medulla increased approximately twofold in mice given free access to 1% NaCl in the drinking water for 3 days. The increase was associated with an approximate threefold elevation in COX-2 mRNA accumulation and an increase in PGE2 production by isolated medullary (m)TAL tubules from 77.3 ± 8.4 to 165.7 ± 10.8 pg/mg protein. Moreover, administration of NS-398 abolished the increase in PGE2 production induced by 1% NaCl. EP3 receptor mRNA levels also increased approximately twofold in the outer medulla of mice that ingested 1% NaCl. The selective EP3 receptor antagonist L-798106 increased COX-2 mRNA by twofold in mTAL tubules, and the elevation in COX-2 protein induced by 1% NaCl increased an additional 50% in mice given L-798106. COX-2 mRNA in primary mTAL cells increased twofold in response to media made hypertonic by the addition of NaCl (400 mosmol/kg H2O). L-798106 increased COX-2 mRNA twofold in isotonic media and fourfold in cells exposed to 400 mosmol/kg H2O. PGE2 production by mTAL cells increased from 79.3 ± 4.6 to 286.7 ± 6.3 pg/mg protein after challenge with 400 mosmol/kg H2O and was inhibited in cells transiently transfected with a lentivirus short hairpin RNA construct targeting exon 5 of COX-2 to silence COX-2. Collectively, the data suggest that local hypertonicity in the mTAL is associated with an increase in COX-2 expression concomitant with elevated EP3 receptor expression, which limits COX-2 activity in this segment of the nephron.

Basic fibroblast growth factor reduces functional and structural damage in chronic kidney disease

Chronic kidney disease (CKD) is characterized by loss of renal function. The pathological processes involved in the progression of this condition are already known, but the molecular mechanisms have not been completely explained. Recent reports have shown the intrinsic capacity of the kidney to undergo repair after acute injury through the reexpression of repairing proteins (Villanueva S, Cespedes C, Vio CP. Am J Physiol Regul Integr Comp Physiol 290: R861-R870, 2006). Stimulation with basic fibroblast growth factor (bFGF) could accelerate this process. However, it is not known whether bFGF can induce this phenomenon in kidney cells affected by CKD. Our aim was to study the evolution of renal damage in animals with CKD treated with bFGF and to relate the amount of repairing proteins with renal damage progression. Male Sprague-Dawley rats were subjected to 5/6 nephrectomy (NPX) and treated with bFGF (30 μg/kg, NPX+bFGF); a control NPX group was treated with saline (NPX+S). Animals were euthanized 35 days after bFGF administration. Functional effects were assessed based on serum creatinine levels; morphological damage was assessed by the presence of macrophages (ED-1), interstitial α-smooth muscle actin (α-SMA), and interstitial collagen through Sirius red staining. The angiogenic factors VEGF and Tie-2 and the epithelial/tubular factors Ncam, bFGF, Pax-2, bone morphogenic protein-7, Noggin, Lim-1, Wnt-4, and Smads were analyzed. Renal stem cells were evaluated by Oct-4. We observed a significant reduction in serum creatinine levels, ED-1, α-SMA, and Sirius red as well as an important induction of Oct-4, angiogenic factors, and repairing proteins in NPX+bFGF animals compared with NPX+S animals. These results open new perspectives toward reducing damage progression in CKD.

Uriniferous tubule: structural and functional organization

The uriniferous tubule is divided into the proximal tubule, the intermediate (thin) tubule, the distal tubule and the collecting duct. The present chapter is based on the chapters by Maunsbach and Christensen on the proximal tubule, and by Kaissling and Kriz on the distal tubule and collecting duct in the 1992 edition of the Handbook of Physiology, Renal Physiology. It describes the fine structure (light and electron microscopy) of the entire mammalian uriniferous tubule, mainly in rats, mice, and rabbits. The structural data are complemented by recent data on the location of the major transport- and transport-regulating proteins, revealed by morphological means(immunohistochemistry, immunofluorescence, and/or mRNA in situ hybridization). The structural differences along the uriniferous tubule strictly coincide with the distribution of the major luminal and basolateral transport proteins and receptors and both together provide the basis for the subdivision of the uriniferous tubule into functional subunits. Data on structural adaptation to defined functional changes in vivo and to genetical alterations of specified proteins involved in transepithelial transport importantly deepen our comprehension of the correlation of structure and function in the kidney, of the role of each segment or cell type in the overall renal function,and our understanding of renal pathophysiology.

Involvement of bradykinin and prostaglandins in the diuretic effects of Achillea millefolium L. (Asteraceae)

ETHNOPHARMACOLOGICAL RELEVANCE

Achillea millefolium L. (Asteraceae), popularly known as "mil-folhas", is well recognized and widely used in Brazilian folk medicine to treat heart and kidney disorders. Among its popularly described effects are diuretic and hypotensive actions.

AIM OF THE STUDY

The diuretic activity of Achillea millefolium L. extracts and its semi-purified fractions, as well as the mechanisms involved, were evaluated in male Wistar rats.

MATERIAL AND METHODS

An aqueous extract (AEAM, 125-500 mg/kg), hydroethanolic extract (HEAM, 30-300 mg/kg), dichloromethane subfractions (DCM-2, 10 and 30 mg/kg), or hydrochlorothiazide (10mg/kg), were orally administered and the animals were kept in metabolic cages for 8h for urine collection. To evaluate the involvement of bradykinin and prostaglandins in the diuretic action of Achillea millefolium, selected groups of rats received HOE-140 (1.5mg/kg, i.p.) or indomethacin (5mg/kg, p.o.), before treatment with a DCM-2 subfraction (30 mg/kg). The urinary volume, conductivity, pH, density and electrolyte excretion were measured.

RESULTS

Similar to hydrochlorothiazide, both HEAM and DCM-2, but not AEAM, increased urinary volume and the excretion of Na(+) and K(+) when compared with the control group (vehicle). The diuretic effect of DCM-2 was abolished by HOE-140 (a bradykinin B2 receptor antagonist), as well as by indomethacin (a cyclooxygenase inhibitor).

CONCLUSION

The present study reveals that extracts obtained from Achillea millefolium are able to effectively increase diuresis when orally administered in rats. This effect depends on both the activation of bradykinin B2 receptors and the activity of cyclooxygenases.

Human mesenchymal stem cells derived from adipose tissue reduce functional and tissue damage in a rat model of chronic renal failure

Therapeutic approaches for CKD (chronic kidney disease) have been able to reduce proteinuria, but not diminish the disease progression. We have demonstrated beneficial effects by injection of BM (bone marrow)-derived MSCs (mesenchymal stem cells) from healthy donors in a rat model with CKD. However, it has recently been reported that BM-MSCs derived from uraemic patients failed to confer functional protection in a similar model. This suggests that autologous BM-MSCs are not suitable for the treatment of CKD. In the present study, we have explored the potential of MSCs derived from adipose tissue (AD-MSCs) as an alternative source of MSCs for the treatment of CKD. We have isolated AD-MSCs and evaluated their effect on the progression of CKD. Adult male SD (Sprague-Dawley) rats subjected to 5/6 NPX (nephrectomy) received a single intravenous infusion of 0.5×10(6) AD-MSCs or MSC culture medium alone. The therapeutic effect was evaluated by plasma creatinine measurement, structural analysis and angiogenic/epitheliogenic protein expression. AD-MSCs were detected in kidney tissues from NPX animals. This group had a significant reduction in plasma creatinine levels and a lower expression of damage markers ED-1 and α-SMA (α-smooth muscle actin) (P<0.05). In addition, treated rats exhibited a higher level of epitheliogenic [Pax-2 and BMP-7 (bone morphogenetic protein 7)] and angiogenic [VEGF (vascular endothelial growth factor)] proteins. The expression of these biomarkers of regeneration was significantly related to the improvement in renal function. Although many aspects of the cell therapy for CKD remain to be investigated, we provide evidence that AD-MSCs, a less invasive and highly available source of MSCs, exert an important therapeutic effect in this pathology.

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.

Tumor necrosis factor-alpha induces renal cyclooxygenase-2 expression in response to hypercalcemia

The effect of tumor necrosis factor-alpha (TNF) on cyclooxygenase-2 (COX-2) expression in the renal outer medulla (OM) was determined in a model of dihydrotachysterol (DHT)-induced hypercalcemia. Increases in serum calcium and water intake were observed during ingestion of a DHT-containing diet in both wild type (WT) and TNF deficient mice (TNF(-/-)). Polyuria and a decrease in body weight were observed in response to DHT treatment in WT and TNF(-/-) mice. A transient elevation in urinary TNF was observed in WT mice treated with DHT. Moreover, increased urinary levels of prostaglandin E(2) (PGE(2)) and a corresponding increase in COX-2 expression in the OM were observed in WT mice fed DHT. Increased COX-2 expression was not observed in TNF(-/-) mice fed DHT, and the characteristics of PGE(2) synthesis were distinct from those in WT mice. This study demonstrates that COX-2 expression in the OM, secondary to hypercalemia, is TNF-dependent.

Tubular control of renin synthesis and secretion

The intratubular composition of fluid at the tubulovascular contact site of the juxtaglomerular apparatus serves as regulatory input for secretion and synthesis of renin. Experimental evidence, mostly from in vitro perfused preparations, indicates an inverse relation between luminal NaCl concentration and renin secretion. The cellular transduction mechanism is initiated by concentration-dependent NaCl uptake through the Na-K-2Cl cotransporter (NKCC2) with activation of NKCC2 causing inhibition and deactivation of NKCC2 causing stimulation of renin release. Changes in NKCC2 activity are coupled to alterations in the generation of paracrine factors that interact with granular cells. Among these factors, generation of PGE2 in a COX-2-dependent fashion appears to play a dominant role in the stimulatory arm of tubular control of renin release. [NaCl] is a determinant of local PG release over an appropriate concentration range, and blockade of COX-2 activity interferes with the NaCl dependency of renin secretion. The complex array of local paracrine controls also includes nNOS-mediated synthesis of nitric oxide, with NO playing the role of a modifier of the intracellular signaling pathway. A role of adenosine may be particularly important when [NaCl] is increased, and at least some of the available evidence is consistent with an important suppressive effect of adenosine at higher salt concentrations.

Prostaglandin E2 EP3 receptor regulates cyclooxygenase-2 expression in the kidney

Cyclooxygenase-2 (COX-2) is constitutively expressed and highly regulated in the thick ascending limb (TAL). As COX-2 inhibitors (Coxibs) increase COX-2 expression, we tested the hypothesis that a negative feedback mechanism involving PGE(2) EP3 receptors regulates COX-2 expression in the TAL. Sprague-Dawley rats were treated with a Coxib [celecoxib (20 mg·kg(-1)·day(-1)) or rofecoxib (10 mg·kg(-1)·day(-1))], with or without sulprostone (20 μg·kg(-1)·day(-1)). Sulprostone was given using two protocols, namely, previous to Coxib treatment (prevention effect; Sulp7-Coxib5 group) and 5 days after initiation of Coxib treatment (regression effect; Coxib10-Sulp5 group). Immunohistochemical and morphometric analysis revealed that the stained area for COX-2-positive TAL cells (μm(2)/field) increased in Coxib-treated rats (Sham: 412 ± 56.3, Coxib: 794 ± 153.3). The Coxib effect was inhibited when sulprostone was used in either the prevention (285 ± 56.9) or regression (345 ± 51.1) protocols. Western blot analysis revealed a 2.1 ± 0.3-fold increase in COX-2 protein expression in the Coxib-treated group, an effect abolished by sulprostone using either the prevention (1.2 ± 0.3-fold) or regression (0.6 ± 0.4-fold vs. control, P < 0.05) protocols. Similarly, the 6.4 ± 0.6-fold increase in COX-2 mRNA abundance induced by Coxibs (P < 0.05) was inhibited by sulprostone; prevention: 0.9 ± 0.3-fold (P < 0.05) and regression: 0.6 ± 0.1 (P < 0.05). Administration of a selective EP3 receptor antagonist, L-798106, also increased the area for COX-2-stained cells, COX-2 mRNA accumulation, and protein expression in the TAL. Collectively, the data suggest that COX-2 levels are regulated by a novel negative feedback loop mediated by PGE(2) acting on its EP3 receptor in the TAL.

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.

Eicosanoids and tumor necrosis factor-alpha in the kidney

The thick ascending limb of Henle's loop (TAL) is capable of metabolizing arachidonic acid (AA) by cytochrome P450 (CYP450) and cyclooxygenase (COX) pathways and has been identified as a nephron segment that contributes to salt-sensitive hypertension. Previous studies demonstrated a prominent role for CYP450-dependent metabolism of AA to products that inhibited ion transport pathways in the TAL. However, COX-2 is constitutively expressed along all segments of the TAL and is increased in response to diverse stimuli. The ability of Tamm-Horsfall glycoprotein, a selective marker of cortical TAL (cTAL) and medullary (mTAL), to bind TNF and localize it to this nephron segment prompted studies to determine the capacity of mTAL cells to produce TNF and determine its effects on mTAL function. The colocalization of calcium-sensing receptor (CaR) and COX-2 in the TAL supports the notion that activation of CaR induces TNF-dependent COX-2 expression and PGE₂ synthesis in mTAL cells. Additional studies showed that TNF produced by mTAL cells inhibits ⁸⁶Rb uptake, an in vitro correlate of natriuresis, in an autocrine- and COX-2-dependent manner. The molecular mechanism for these effects likely includes inhibition of Na⁺-K⁺-2Cl⁻ cotransporter (NKCC2) expression and trafficking.

Convergence of major physiological stimuli for renin release on the Gs-alpha/cyclic adenosine monophosphate signaling pathway

Control of the renin system by physiological mechanisms such as the baroreceptor or the macula densa (MD) is characterized by asymmetry in that the capacity for renin secretion and expression to increase is much larger than the magnitude of the inhibitory response. The large stimulatory reserve of the renin-angiotensin system may be one of the causes for the remarkable salt-conserving power of the mammalian kidney. Physiological stimulation of renin secretion and expression relies on the activation of regulatory pathways that converge on the cyclic adenosine monophosphate/protein kinase A (cAMP/PKA) pathway. Mice with selective Gs-alpha (Gsα) deficiency in juxtaglomerular granular cells show a marked reduction of basal renin secretion, and an almost complete unresponsiveness of renin release to furosemide, hydralazine, or isoproterenol. Cyclooxygenase-2 generating prostaglandin E(2) (PGE(2)) and prostacyclin (PGI(2)) in MD and thick ascending limb cells is one of the main effector systems utilizing Gsα-coupled receptors to stimulate the renin-angiotensin system. In addition, β-adrenergic receptors are critical for the expression of high basal levels of renin and for its release response to lowering blood pressure or MD sodium chloride concentration. Nitric oxide generated by nitric oxide synthases in the MD and in endothelial cells enhances cAMP-dependent signaling by stabilizing cAMP through cyclic guanosine monophosphate-dependent inhibition of phosphodiesterase 3. The stimulation of renin secretion by drugs that inhibit angiotensin II formation or action results from the convergent activation of cAMP probably through indirect augmentation of the activity of PGE(2) and PGI(2) receptors, β-adrenergic receptors, and nitric oxide.

Mesenchymal stem cell injection ameliorates chronic renal failure in a rat model

CKD (chronic kidney disease) has become a public health problem. The therapeutic approaches have been able to reduce proteinuria, but have not been successful in limiting disease progression. In this setting, cell therapies associated with regenerative effects are attracting increasing interest. We evaluated the effect of MSC (mesenchymal stem cells) on the progression of CKD and the expression of molecular biomarkers associated with regenerative effects. Adult male Sprague-Dawley rats subjected to 5/6 NPX (nephrectomy) received a single intravenous infusion of 0.5×106 MSC or culture medium. A sham group subjected to the same injection was used as the control. Rats were killed 5 weeks after MSC infusion. Dye tracking of MSC was followed by immunofluorescence analysis. Kidney function was evaluated using plasma creatinine. Structural damage was evaluated by H&E (haematoxylin and eosin) staining, ED-1 abundance (macrophages) and interstitial α-SMA (α-smooth muscle actin). Repairing processes were evaluated by functional and structural analyses and angiogenic/epitheliogenic protein expression. MSC could be detected in kidney tissues from NPX animals treated with intravenous cell infusion. This group presented a marked reduction in plasma creatinine levels and damage markers ED-1 and α-SMA (P<0.05). In addition, treated rats exhibited a significant induction in epitheliogenic [Pax-2, bFGF (basic fibroblast growth factor) and BMP-7 (bone morphogenetic protein-7)] and angiogenic [VEGF (vascular endothelial growth factor) and Tie-2] proteins. The expression of these biomarkers of regeneration was significantly related to the increase in renal function. Many aspects of the cell therapy in CKD remain to be investigated in more detail: for example, its safety, low cost and the possible need for repeated cell injections over time. Beyond the undeniable importance of these issues, what still needs to be clarified is whether MSC administration has a real effect on the treatment of this pathology. It is precisely to this point that the present study aims to contribute.

Interleukin-6 plays a protective role in development of cisplatin-induced acute renal failure through upregulation of anti-oxidative stress factors

AIMS

Cisplatin, a major chemotherapeutic agent, accumulates in proximal tubules of the kidneys and causes acute renal failure dose-dependently. We previously reported that cisplatin induced more severe renal dysfunction in interleukin-6 (IL-6) knockout (IL-6(-/-)) mice than in wild-type (WT) mice. Expression of a pro-apoptotic protein was significantly increased with cisplatin in IL-6(-/-) mice compared to that in WT mice. IL-6, locally expressed in renal tubular cells after cisplatin administration, prevents the development of renal dysfunction at an early stage. In the present study, we focused on downstream signals of IL-6 and oxidative stress induced by cisplatin in order to evaluate the protective role of IL-6 in the development of acute renal failure.

MAIN METHODS

WT and IL-6(-/-) mice were given either cisplatin (30 mg/kg) or saline intraperitoneally. Blood and kidney samples were collected at 24h and 72 h after cisplatin administration. The changes in expression of 4-hydroxy-2-nonenal protein (4-HNE, oxidative stress marker) and cyclooxygenase-2 (cox-2), activities of superoxide dismutases and caspase-3, and phosphorylation of extracellular signal-regulated kinase (ERK) were examined.

KEY FINDINGS

Cisplatin increased the expression of 4-HNE and cox-2, and phosphorylation of ERK in IL-6(-/-) mice than in WT mice. On the other hand, activity of superoxide dismutase, an anti-oxidative enzyme, was significantly decreased in the kidney obtained from IL-6(-/-) mice after cisplatin administration.

SIGNIFICANCE

Our findings suggest that IL-6 plays a protective role in the development of cisplatin-induced acute renal failure through upregulation of anti-oxidative stress factors.

Physiology of Kidney Renin

The protease renin is the key enzyme of the renin-angiotensin-aldosterone cascade, which is relevant under both physiological and pathophysiological settings. The kidney is the only organ capable of releasing enzymatically active renin. Although the characteristic juxtaglomerular position is the best known site of renin generation, renin-producing cells in the kidney can vary in number and localization. (Pro)renin gene transcription in these cells is controlled by a number of transcription factors, among which CREB is the best characterized. Pro-renin is stored in vesicles, activated to renin, and then released upon demand. The release of renin is under the control of the cAMP (stimulatory) and Ca2+(inhibitory) signaling pathways. Meanwhile, a great number of intrarenally generated or systemically acting factors have been identified that control the renin secretion directly at the level of renin-producing cells, by activating either of the signaling pathways mentioned above. The broad spectrum of biological actions of (pro)renin is mediated by receptors for (pro)renin, angiotensin II and angiotensin-( 1 – 7 ).

E Prostanoid-1 receptor regulates renal medullary alphaENaC in rats infused with angiotensin II

E Prostanoid (EP) receptors play an important role in urinary Na(+) excretion. In the kidney, the epithelial sodium channel (ENaC) is the rate-limiting-step for Na(+) reabsorption. We hypothesized that activation of EP1/EP3 regulates the expression of ENaC in the face of renin-angiotensin-aldosterone-system (RAAS) activation. In primary cultures of inner medullary collecting duct (IMCD) cells, sulprostone (EP1>EP3 agonist, 1 microM) and 17 Phenyl trinor (17 Pt, EP1 agonist, 10 microM) prevented the up-regulation of alphaENaC mRNA induced by aldosterone (10 nM). In Sprague-Dawley rats infused with angiotensin II (0.4 microg/kg/min), alphaENaC expression was up-regulated in renal cortex and medulla coincidently with high plasma aldosterone levels. Sulprostone and/or 17 Pt prevented this effect in renal medulla but not in cortex. Immunocytochemistry demonstrated that IMCD cells express EP1. Our results suggest that specific activation of EP1 receptor during RAAS activation antagonizes the action of aldosterone on alphaENaC expression in the renal medulla.

Inhibition of bFGF-receptor type 2 increases kidney damage and suppresses nephrogenic protein expression after ischemic acute renal failure

Recovery from acute renal failure (ARF) requires the replacement of injured cells by new cells that are able to restore tubule epithelial integrity. We have recently described the expression of nephrogenic proteins [Vimentin, neural cell adhesion molecule, basic fibroblast growth factor (bFGF), Pax-2, bone morphogen protein-7, Noggin, Smad 1-5-8, p-Smad, hypoxia-inducible factor-1alpha, vascular endothelial growth factor], in a time frame similar to that observed in kidney development, after ischemic ARF induced in an ischemia-reperfusion (I/R) model. Furthermore, we show that bFGF, a morphogen involved in mesenchyme/epithelial transition in kidney development, induces a reexpression of morphogenic proteins in an earlier time frame and accelerates the recovery process after renal damage. Herein, we confirm that renal morphogenes are modulated by bFGF and hypothesized that a decrease in bFGF receptor 2 (bFGFR2) levels by the use of antisense oligonucleotides diminishes the expression of morphogenes. Male Sprague-Dawley rats submitted to ischemic injury were injected with 112 microg/kg bFGFR2 antisense oligonucleotide (bFGFR2-ASO) followed by reperfusion. Rats were killed, and the expression of nephrogenic proteins and renal marker damage was analyzed by immunohistochemistry and immunoblot. Animals subjected to I/R treated with bFGFR2-ASO showed a significant reduction in morphogen levels (P < 0.05). In addition, we observed an increase in markers of renal damage: macrophages (ED-1) and interstitial alpha-smooth muscle actin. These results confirm that bFGF participates in the recovery process and that treatment with bFGFR2-ASO induces an altered expression of morphogen proteins.

Sepsis induces an increase in thick ascending limb Cox-2 that is TLR4 dependent

Cyclooxygenase-2 (Cox-2) is an inducible enzyme responsible for the formation of inflammatory prostanoids such as prostaglandins and thromboxane. Its role in the pathophysiology of inflammatory states like sepsis is increasingly recognized. Recently, we demonstrated that sepsis upregulates the endotoxin receptor Toll-like receptor 4 (TLR4) in rat kidney. Because Cox-2 is one of the downstream products of TLR4 activation, we hypothesized that sepsis-induced changes in renal Cox-2 expression are TLR4 dependent. Indeed, we show that in Sprague-Dawley rats, cecal ligation and puncture (a sepsis model) increases Cox-2 expression in cortical and medullary thick ascending loops (cTAL and mTAL, respectively) as well as inner medullary collecting ducts. These are all sites of increased TLR4 expression during sepsis. To determine the actual dependence on TLR4, we measured Cox-2 expression in wild-type and mutant mice which harbor a TLR4 gene deletion (TLR4-/-). In wild-type mice, sepsis increased Cox-2 expression in proximal tubules, cTAL, and mTAL. In contrast, septic TLR4-/- mice showed no significant increase in cTAL or mTAL Cox-2 expression. Furthermore, renin was absent from juxtaglomerular cells of TLR4-/- mice. We conclude that the dependence of sepsis-induced renal Cox-2 expression on TLR4 is tubule specific. The TLR4-dependent Cox-2 expression is mostly restricted to cortical and medullary thick ascending loops of Henle that characteristically express and secrete Tamm-Horsfall protein.

Effects of specific inhibition of cyclooxygenease-2 on kidney in bilateral adrenalectomized rats

In the kidney, prostaglandins represent important physiological modulators of renal hemodynamics and salt and water homeostasis. In this experimental study of bilaterally adrenalectomized (ADX) rats, we aimed to investigate whether the administration of selective (celecoxib) inhibitor of COX-2 would alter the morphological and functional changes in rat kidney tissue. Twenty-one male Sprague-Dawley rats weighing 225-250 g were used. The animals were divided into three groups. Group 1 rats (Sham-control, n = 7) did not receive any treatment. In group 2 rats (ADX/Untreated, n = 7), bilateral ADX was performed via a single dorsal incision. In group 3 (ADX/COX-2) rats, the same operation was performed as described for group 2 and then the COX-2 inhibitor celecoxib was administered by gavage for a period of 7 days. On the 7th day of the study, renal function was assessed by measurements of blood urea nitrogen (BUN) and serum creatinine levels. Biopsies were obtained from the remaining left kidneys before killing the rats. There was no significant difference in the BUN and creatinine values between the groups. In ADX/Untreated group, capillary congestion in glomerule, inflammation, hemorrhage and congestion in intertubular area, and cytoplasmic vacuolation in renal tubules was observed. Mild damage was observed in the ADX/COX-2 group. The number of macrophages was significantly decreased in ADX/COX-2 group when compared to ADX/Untreated group (P < 0.0001). Our study indicates that celecoxib may be an important factor affecting renal morphological changes after the bilaterally ADX.

Extent of renal effect of cyclo-oxygenase-2-selective inhibitors is pharmacokinetic dependent

Non-steroidal anti-inflammatory drugs (NSAIDs) cause renal side-effects. In the present study, we tested the hypothesis that the extent of the renal effects of cyclo-oxygenase (COX)-2-selective NSAIDs is linked to their pharmacokinetics. A single oral dose of rofecoxib (10 mg/kg), celecoxib (40 mg/kg), meloxicam (3 mg/kg) or placebo was administered to rats. Urinary excretion of electrolytes, a marker of renal effects, and plasma and kidney concentrations of NSAIDs were measured. Rofecoxib and celecoxib, but not meloxicam, significantly decreased urinary sodium and potassium excretion. There was a significant correlation between the area under the 24 h plasma concentration-time curve (AUC0-24) of rofecoxib and the change in sodium (r = -0.65; P < 0.02) and potassium (r = -0.82; P < 0.0006) excretion. The AUC0-24 of celecoxib was correlated with sodium (r = -0.80; P < 0.05) but not potassium excretion. The ratios of kidney to plasma drug concentrations were 1.72, 3.16 and 0.17 for rofecoxib, celecoxib and meloxicam, respectively. The renal effect of the COX-2-selective NSAIDs examined, marked by their ability to reduce the excretion of electrolytes, is influenced by systemic exposure to the drugs. The relatively higher distribution into the kidneys of rofecoxib and celecoxib compared with meloxicam suggests involvement of direct drug exposure in the kidneys in the adverse renal effect.

bFGF induces an earlier expression of nephrogenic proteins after ischemic acute renal failure

Recovery from acute renal failure (ARF) requires the replacement of injured cells with new cells that restore tubule epithelial integrity. We described recently the expression of a wide range of nephrogenic proteins in tubular cells after ARF induced by ischemia-reperfusion (I/R) (Villanueva S, Cespedes C, and Vio CP. Am J Physiol Regul Integr Comp Physiol 290: R861-R870, 2006). These markers, namely, Vimentin, neural cell adhesion molecules (Ncam), basic fibroblast growth factor (bFGF), paired homeobox-2 (Pax-2), bone morphogene protein-7 (BMP-7), Noggin, Lim-1, Engrailed, Smad, phospho-Smad, hypoxia-induced factor-1alpha (HIF-1alpha), VEGF, and Tie-2, are expressed in a time frame similar to that observed in normal kidney development. bFGF participates in early kidney development as a morphogen involved in mesenchyme/epithelial transition, and it is reexpressed in the recovery phase of ARF. To test the hypothesis that bFGF can accelerate the regeneration after renal damage, we used recombinant bFGF and studied the expression pattern of the above described morphogens in ARF. Male Sprague-Dawley rats were subjected to 30 min of renal ischemic injury and were injected with bFGF 30 microg/kg followed by reperfusion. Rats were killed and the expression of nephrogenic proteins were analyzed by immunohistochemistry and Western blot analysis. In the animals subjected to I/R treated with bFGF, we observed a 12- to 24-h earlier and more abundant reexpression of the proteins Ncam, bFGF, Pax-2, BMP-7, Noggin, Lim-1, Engrailed, VEGF, and Tie-2 than the I/R untreated rats. In addition, we observed a reduction in renal damage markers ED-1 and alpha-smooth muscle actin. These results indicate that bFGF can participate in the regeneration process and suggest that the treatment with bFGF can induce an earlier regeneration process after ischemic acute renal failure.

Expression of Cyclooxygenase-2 in the Juxtaglomerular Apparatus of Angiotensinogen Gene-Knockout Mice

AIMS

The present study was designed to examine the role of the renin-angiotensin system in the regulation of macula densa cyclooxygenase-2 (COX-2) during altered dietary salt intake.

METHODS

We investigated COX-2 expression in the macula densa of angiotensinogen gene-knockout (Atg-/-) mice. COX-2 expression in the renal cortex was determined by real-time quantitative reverse transcription-polymerase chain reaction and immunohistochemistry.

RESULTS

The renal cortical expression of COX-2 mRNA increased 24.7 times in Atg-/- mice compared with Atg+/+ mice. When Atg-/- mice were fed a high-salt diet (4% NaCl) for 10 days, the levels of COX-2 expression were markedly suppressed. The macula densa COX-2 immunoreactivity was correlated with the mRNA expression. The selective inhibition of neuronal isoform of nitric oxide synthase (N-NOS) activity by 7-nitroindazole significantly reduced the levels of COX-2 mRNA in Atg-/- mice by 54.1%.

CONCLUSION

These results suggest that (1) COX-2 activity in the macula densa can be regulated by salt intake through a mechanism independent of the renin-angiotensin system, and (2) COX-2 expression is functionally linked to renal cortical N-NOS activity in Atg-/- mice.

Cyclooxygenase-2 induction by bradykinin in aortic vascular smooth muscle cells

Vascular smooth muscle cell proliferation and migration play an important role in the pathophysiology of several vascular diseases, including atherosclerosis. Prostaglandins that have been implicated in this process are synthesized by two isoforms of cyclooxygenase (COX), with the expression of the regulated COX-2 isoform increased in atherosclerotic plaques. Bradykinin (BK), a vasoactive peptide increased in inflammation, induces the formation of prostaglandins through specific receptor activation. We hypothesized that BK plays an important role in the regulation of COX-2, contributing to the increase in production of prostaglandins in vascular smooth muscle cells. Herein we examined the signaling pathways that participate in the BK regulation of COX-2 protein levels in primary cultured aortic vascular smooth muscle cells. We observed an increase in COX-2 protein levels induced by BK that was maximal at 24 h. This increase was blocked by a B2 kinin receptor antagonist but not a B1 receptor antagonist, suggesting that the B2 receptor is involved in this pathway. In addition, we conclude that the activation of mitogen-activated protein kinases p42/p44, protein kinase C, and nitric oxide synthase is necessary for the increase in COX-2 levels induced by BK because either of the specific inhibitors for these enzymes blocked the effect of BK. Using a similar approach, we further demonstrated that reactive oxygen species and cAMP were not mediators on this pathway. These results suggest that BK activates several intracellular pathways that act in combination to increase COX-2 protein levels. This study suggests a role for BK on the evolution of the atheromatous plaque by virtue of controlling the levels of COX-2.

Selectivity of cyclooxygenase isoform activity and prostanoid production in normal and diseased Han:SPRD-cy rat kidneys

Renal prostanoids are important regulators of normal renal function and maintenance of renal homeostasis. In diseased kidneys, renal cylooxygenase (COX) expression and prostanoid formation are altered. With the use of the Han:Sprague-Dawley-cy rat, the aim of this study was to determine the relative contribution of renal COX isoforms (protein, gene expression, and activity) on renal prostanoid production [thromboxane B(2) (TXB(2), stable metabolite of TXA(2)), prostaglandin E(2) (PGE(2)), and 6-keto-prostaglandin F(1alpha) (6-keto-PGF(1alpha), stable metabolite of PGI(2))] in normal and diseased kidneys. In diseased kidneys, COX-1-immunoreactive protein and mRNA levels were higher and COX-2 levels were lower compared with normal kidneys. In contrast, COX activities were higher in diseased compared with normal kidneys for both COX-1 [0.05 +/- 0.02 vs. 0.45 +/- 0.11 ng prostanoids x min(-1) x mg protein(-1) (P < 0.001)] and COX-2 [0.64 +/- 0.10 vs. 2.32 +/- 0.22 ng prostanoids x min(-1).mg protein(-1) (P < 0.001)]. As the relative difference in activity was greater for COX-1, the ratio of COX-1/COX-2 was higher in diseased compared with normal kidneys, although the predominant activity was still due to the COX-2 isoform in both genotypes. Endogenous and steady-state in vitro levels of prostanoids were approximately 2-10 times higher in diseased compared with normal kidneys. The differences between normal and diseased kidney prostanoids were in the order of TXB(2) > 6-keto-PGF(1alpha) > PGE(2), as determined by higher renal prostanoid levels and COX activity ratios of TXB(2)/6-keto-PGF(1alpha), TXB(2)/PGE(2), and 6-keto-PGF(1alpha)/PGE(2). This specificity in both the COX isoform type and for the prostanoids produced has implications for normal and diseased kidneys in treatments involving selective inhibition of COX isoforms.

Clinical pharmacology of etoricoxib

Etoricoxib is a highly selective COX-2 inhibitor (coxib) approved in Europe for the treatment of osteoarthritis (OA), rheumatoid arthritis and acute gouty arthritis. Etoricoxib is an effective analgesic drug that has shown some improved efficacy versus traditional NSAIDs and it is the only coxib approved for the treatment of acute gouty arthritis. Moreover, recent studies evidence its efficacy in patients with ankylosing spondylitis. In the Etoricoxib Diclofenac Gastrointestinal Evaluation study performed in patients with OA, etoricoxib significantly reduced the rate of discontinuation by 50% due to gastrointestinal adverse events versus diclofenac. Comparable rates of thrombotic cardiovascular events were detected. Rates of discontinuation due to hypertension-related adverse effects were higher on etoricoxib than diclofenac. Similarly to other selective COX-2 inhibitors, etoricoxib is contraindicated in patients with ischaemic heart disease or stroke and it should be used with caution in patients with risk factors for heart disease. The European Medicines Agency has contraindicated the use of etoricoxib in patients with uncontrolled hypertension. Selective COX-2 inhibitors remain an appropriate choice in patients at low cardiovascular risk, but with increased risk of gastrointestinal complications.

Cyclo-oxygenase-2, endothelium and aortic reactivity during deoxycorticosterone acetate salt-induced hypertension

OBJECTIVE

To test the hypothesis that the enhanced vascular responsiveness to norepinephrine that occurs during deoxycorticosterone acetate (DOCA)-salt induced hypertension is causally related to increased expression of cyclo-oxygenase (COX)-2 and oxidative stress, which diminishes the vasomodulatory influence of endothelium-derived nitric oxide.

METHODS

Four groups of age-matched, male Sprague-Dawley rats were studied: Sham (normotensive); DOCA-salt (hypertensive); DOCA-salt treated with manganese(III) tetra(4-benzoic acid) porphyrin chloride [MnTBAP, an antioxidant; 15 mg/kg intraperitoneally (i.p.) for 21 days]; DOCA-salt treated with {N-[2-(cyclohexyloxy)-4-nitrophenyl]-methane sulfonamide} (NS-398, a COX-2 selective blocker; 5 mg/kg i.p. for 7 days). Contraction and relaxation were measured with FT03 force transducers coupled to a Grass polygraph in aortic rings bathed with physiologic salt solution (37 degrees C) and bubbled with a 5%CO2/95%O2 gas mixture. Aortic sensitivities (pD2 values) to norepinephrine and serum isoprostanes (8-iso-prostaglandin F2alpha, a marker of oxidative stress) were measured for each experimental paradigm.

RESULTS

NS-398 significantly reduced maximal contractions in response to norepinephrine in aortic rings from Sham (44 +/- 3%) and DOCA-salt (96 +/- 2%) group rats. Expression of COX-2 protein increased significantly in vessels from DOCA-salt rats compared with those from Sham group rats. Treatment of DOCA-salt rats with either MnTBAP or NS-398 alleviated hypertension, normalized aortic pD2 values for norepinephrine and restored serum 8-isoprostane concentrations towards those observed in Sham group rats.

CONCLUSIONS

COX-2 expression increases during DOCA-salt hypertension, and mediates production of factors that enhance rat aortic contractility in response to norepinephrine. Our data also suggest a role for increased oxidative stress, which is at least in part dependent on enhanced COX-2 expression, in the mechanism(s) of enhanced aortic contractility in response to norepinephrine during DOCA-salt hypertension.

Effect of nonsteroidal anti-inflammatory drugs with varying extent of COX-2-COX-1 selectivity on urinary sodium and potassium excretion in the rat

Nonsteroidal anti-inflammatory drugs (NSAIDs) have different selectivity to inhibit cyclooxygenase-1 (COX-1) and COX-2. Treatment with NSAIDs has been associated with kidney side effects. We compared the effect of a selected group of NSAIDs with different COX-2--COX-1 selectivities on urinary sodium and potassium excretion in rats. Each treatment with rofecoxib, celecoxib, meloxicam, diclofenac, and flurbiprofen (30, 120, 9, 30, and 125 mg/kg, respectively) and placebo was administered orally once daily for 4 days. Urine was collected 0-8 h after each dose. Urinary sodium and potassium excretion and urine flow rate were compared with placebo. As compared with placebo, rofecoxib, celecoxib, diclofenac, and flurbiprofen significantly reduced excretion rate of sodium (rofecoxib, 0.28 +/- 0.02 vs. 0.41 +/- 0.03; celecoxib, 0.23 +/- 0.03 vs. 0.48 +/- 0.04; diclofenac, 0.09 +/- 0.02 vs. 0.46 +/- 0.03; and flurbiprofen, 0.11 +/- 0.02 vs. 0.47 +/- 0.02 micromol/(min x 100 g)) and potassium (rofecoxib, 0.55 +/- 0.04 vs. 0.68 +/- 0.04; celecoxib, 0.50 +/- 0.06 vs. 0.72 +/- 0.06; diclofenac, 0.26 +/- 0.05 vs. 0.67 +/- 0.04; and flurbiprofen, 0.35 +/- 0.05 vs. 0.62 +/- 0.03 micromol/ (min x 100 g)). Rofecoxib and flurbiprofen significantly reduced urine flow rate. Meloxicam had no significant effect on either sodium and potassium excretion or on the urine flow rate. At the examined dosage level, no relationship was found between reported COX-2--COX-1 selectivity and urinary electrolytes excretion.

Activation of phosphoinositide 3-kinase in response to inflammation and nitric oxide leads to the up-regulation of cyclooxygenase-2 expression and subsequent cell proliferation in mesangial cells

In this study, we showed that nitric oxide (NO) donors induced the mesangial cell proliferation and cyclooxygenase-2 (COX-2) protein expression in murine mesangial cells. An inflammatory condition [lipopolysaccharide (LPS) plus interferon-gamma (IFN-gamma)] could also induce cell proliferation and significantly enhance inducible nitric oxide synthase (iNOS) and COX-2 expression. Phosphoinositide 3-kinase (PI3K) inhibitor, LY294002, inhibited these responses. LPS/IFN-gamma-induced COX-2 expression in mesangial cells could be inhibited by iNOS inhibitor, aminoguanidine. Selective COX-2 inhibitor, NS398, was capable of inhibiting NO donor- or LPS/IFN-gamma-induced mesangial cell proliferation. Both NO donor and LPS/IFN-gamma markedly activated the PI3K activity and the phosphorylation of Akt and nuclear factor (NF)-kappaB DNA binding activity in mesangial cells, which could be inhibited by LY294002 and transfection of dominant-negative vectors of PI3K/p85 and Akt. These results indicate that a PI3K/Akt-dependent pathway involved in the NO-regulated COX-2 expression and cell proliferation in mesangial cells under inflammatory condition.

Ovariectomy enhances renal cortical expression and function of cyclooxygenase-2

BACKGROUND

Cyclooxygenase-2 (COX-2) inhibitors are used as analgesics in postmenopausal women, who develop edema and require a salt-restricted diet. This study was performed to determine the renal expression of COX-2 and on COX-2-dependent regulation of renal blood flow (RBF) in ovariectomized rats.

METHODS

Sprague-Dawley rats were divided into 4 groups: sham-operated rats fed a normal-salt diet (Sh+NS) or a low-salt diet (Sh+LS), and bilaterally ovariectomized rats fed a normal-salt diet (Ox+NS) or a low-salt diet (Ox+LS) (N= 6 in each group). Estrogen replacement therapy was performed on other ovariectomized rats. A renal clearance study was performed in anesthetized animals.

RESULTS

Ovariectomy increased renal cortical COX-2 expression independently of dietary salt intake (Sh+NS <Ox+N; Sh+LS <Ox+LS). Inhibition of COX-2 by NS398 reduced the urinary excretion of 6-keto-prostaglandin F1alpha in all 4 groups, although the reduction was greater in the Ox+LS group than in the Ox+NS and Sh+LS groups, which in turn had a greater reduction than the Sh+NS group. RBF significantly decreased in every group except the Sh+NS group, but no effect on blood pressure, inulin clearance, or urinary sodium excretion was seen. The decrease in RBF was significantly greater in the Ox+LS group than in the Sh+LS and Ox+NS group. The decrease in RBF was dependent on cortical RBF in the Sh+LS and Ox+NS groups, and on both cortical and medullary RBF in the Ox+LS group. Estrogen replacement therapy reversed the ovariectomy-induced changes.

CONCLUSION

Estrogen-dependent COX-2 expression plays an important role in the RBF regulation in female rats.

TNFalpha regulates renal COX-2 in the rat thick ascending limb (TAL)

We have examined cyclooxygenase (COX)-2-dependent mechanisms in preglomerular microvessels and the thick ascending limb (TAL). These renal structures are linchpins in the regulation of the renal circulation and extracellular fluid volume. Cytochrome P450 monooxygenases are the principal oxygenases in the TAL segment; however, COX-2 can be expressed in the TAL, as when challenged by angiotensin II. Glucocorticoids also affect the expression and activity of oxygenases in the TAL. Before adrenalectomy, <2% TAL cells expressed COX-2; after, >30% of TAL cells expressed COX-2. Recruitment of COX-2 is initiated in the renal cortex and proceeds to the medulla associated with: (1) COX-2 mRNA accumulation; (2) increased COX-2 expression; and (3) a two-fold increase in PGE2 production by cortical microsomes. These changes were nullified by dexamethasone. COX-2 mRNA, protein expression and PGE2 synthesis in the TAL are also increased in response to increased extracellular Ca2+. The Ca2+ sensing receptor is G-protein coupled and responds to changes in extracellular Ca2+ concentration by increasing protein kinase C activity to produce expression of COX-2. Thus, multiple signaling pathways contribute to COX-2 expression in TAL cells.

Chronic cyclooxygenase-2 inhibition does not alter blood pressure and kidney function in renovascular hypertensive rats

BACKGROUND

It has been shown that the macula densa participates in the regulation of increased renin expression in two-kidney one-clip (2K1C) renovascular hypertension. Prostaglandins might be one of the mediators of macula densa function, because the cyclooxygenase-2 (COX-2), one of the rate-limiting enzymes of the prostaglandin pathway, is upregulated in 2K1C renovascular hypertensive rats. We tested the effect of chronic COX-2 inhibition on blood pressure, urinary aldosterone excretion and kidney morphology, as well as kidney function.

METHODS

Four groups were established: two groups of 2K1C renovascular hypertensive rats treated with the specific COX-2 inhibitor Celecoxib (cele) (15 mg/kg per day) or placebo immediately after operation, and two sham-operated control groups fed with Celecoxib or placebo.

RESULTS

Long-term COX-2 inhibition in 2K1C renovascular hypertensive rats did not alter blood pressure at any point of time. Urinary aldosterone excretion was elevated by clipping the renal artery (2K1C, 8.1 +/- 1.9, versus controls, 3.6 +/- 0.5 ng/24 h; P = 0.05) but was not influenced by treatment with Celecoxib. Also, Celecoxib treatment did not alter glomerular filtration rate (GFR), serum sodium, serum creatinine, serum urea or proteinuria in 2K1C renovascular hypertensive rats. Interstitial fibrosis of the left clipped kidney was markedly reduced (2K1C, 6.19 +/- 0.83% versus 2K1C + cele 3.00 +/- 0.68% of total area; P = 0.012), whereas the interstitial fibrosis of the non-clipped kidney or the glomerulosclerosis of both kidneys were not affected by Celecoxib treatment.

CONCLUSIONS

Celecoxib reduces the interstitial fibrosis of the clipped kidney. Blood pressure, urinary aldosterone excretion or whole kidney function were not affected in renal hypertensive rats.

Expression of cyclooxygenase-2 in biopsies obtained from human transplanted kidneys undergoing rejection

BACKGROUND

The inducible cyclooxygenase (COX)-2 is a target of immunosuppressive drugs routinely administered to patients after transplantation. This study investigates a potential involvement of COX-2 in transplant rejection. Therefore, we examined the expression of COX-2 in biopsies obtained for diagnostic purposes.

METHODS

COX-2 was detected by immunohistochemistry and in situ hybridization. Congruent staining was obtained by both methods: in specimens of a kidney explanted as the result of vascular rejection, tubular epithelial cells and endothelial cells stained positively for COX-2. Furthermore, in appendiceal specimens obtained at surgery, epithelial cells of the crypts, interstitial cells, and mesothelial cells were positive by both methods, affirming the specificity of the antibody.

RESULTS

Compared with healthy control subjects, intensive staining of COX-2 was observed in most of the 28 biopsies obtained from patients diagnosed with vascular rejection combined with cellular interstitial rejection and tubulitis. Glomeruli and the macula densa area were essentially negative compared with prominent staining in cortical and medullary epithelial cells of the tubuli. Staining was distinct with individual positive cells in the tubular cross sections. Few arteries expressed COX-2 in intimal cells. Less prominent expression of COX-2 was detected in the biopsies of six kidneys obtained from patients diagnosed with acute tubular necrosis.

CONCLUSION

This is the first report to show the up-regulation of COX-2 in human transplanted kidneys, despite ongoing immunosuppressive treatment. It remains to be established whether the up-regulation of COX-2 is part of the rejection process or has to be considered implicated in renal preservative mechanisms.

Key enzymes for renal prostaglandin synthesis: site-specific expression in rodent kidney (rat, mouse)

Prostanoids derived from endogenous cylooxygenase (COX)-mediated arachidonic acid metabolism play important roles in the maintenance of renal blood flow and salt and water homeostasis. The relative importance of COX-1 and COX-2 isoforms is under active investigation. We have performed a comprehensive histochemical analysis by comparing rat and mouse kidneys for cellular and subcellular localization of COX-1 and -2 and microsomal-type PGE synthase (PGES), the rate-limiting biosynthetic enzyme in PGE2 synthesis. A choice of different sera was compared, and the results were confirmed by antigen-retrieval techniques, in situ hybridization, RT-PCR, and the use of COX knockout mice. In the glomerulus, significant COX-1 expression was detected in a subset of mesangial cells. Along the renal tubule, the known COX-2 expression in cTAL and macula densa was paralleled by PGES staining. In the terminal distal convoluted tubule, connecting tubule, and cortical and medullary collecting ducts, a significant COX-1 signal was colocalized with PGES; COX-2 was not found in these sites. Intercalated cells were generally negative. Cortical fibroblasts were COX-1 and PGES positive in mice, whereas in rats only PGES could be reliably detected. Lipid-laden interstitial cells of the inner medulla were COX-1, -2, and PGES positive. Vascular smooth muscle cells were not stained. The present data support prominent functions of renal prostanoids, predominantly PGE2, by defining expression sites of the key enzymes for their biosynthesis in the rat and mouse. Results define the renal cell types involved in prostaglandin autacoid functions within spatially restricted sites such as the juxtaglomerular apparatus, mesangium, distal convolutions and collecting duct, and in compartments of the renal interstitium.

Effects of renal insufficiency and hemodialysis on the pharmacokinetics of rofecoxib

Rofecoxib (VIOXX, Merck & Co., West Point, PA) is a COX-2-selective inhibitor that combines anti-inflammatory and analgesic efficacy with improved gastrointestinal (GI) safety. The present open-label study investigated the pharmacokinetics, safety, and tolerability of a single, oral dose of rofecoxib (50 mg) in patients with end-stage renal failure (creatinine clearance <5 mL/min/1.73 m(2)) requiring hemodialysis. Rofecoxib AUC(0-48 h), AUC(0- infinity), C(max), T(max), and t(1/2) obtained from renal failure patients on hemodialysis were not significantly different from those obtained from healthy subjects. With hemodialysis initiated 48 hours postdose, rofecoxib AUC(0-48 h) adjusted mean ratio (renal failure/healthy subjects) was 0.81, with a corresponding 90% confidence interval (CI; 0.66, 1.00). Hemodialysis per se had no clinically meaningful effect on rofecoxib pharmacokinetics: plasma rofecoxib concentration-time curves were virtually superimposable when hemodialysis was initiated at 4 or 48 hours following rofecoxib dosing, although mean rofecoxib C(max) was 18% lower during the former (325 versus 395 ng/mL; P = 0.014). Overall, rofecoxib was well tolerated in end-stage renal disease patients. In this study, end-stage renal disease and hemodialysis had little effect on rofecoxib pharmacokinetics. Although there are no clinical data to support the use of rofecoxib in patients with severe renal insufficiency (creatinine clearance, 5-30 mL/min/1.73 m(2)), these data suggest that dosage adjustment of rofecoxib is not needed for patients with impaired renal function.

Adverse renal effects of anti-inflammatory agents: evaluation of selective and nonselective cyclooxygenase inhibitors

Conventional nonsteroidal anti-inflammatory drugs (NSAIDs), i.e. nonselective cyclooxygenase COX inhibitors have well-documented nephrotoxicity. Adverse renal effects occur because of inhibition of the synthesis of cyclooxygenase-derived prostaglandins which act to modulate pathologic processes that would normally impair various renal functions. The introduction of the selective COX-2 inhibitors raised hope that this class of drugs would reduce injury in both the gastrointestinal tract and the kidneys. Animal and human data, however, suggest that COX-2 synthesized prostaglandins are important in the modulation of renal physiology during adverse conditions. Hence, it appears that these drugs are equal in causing nephrotoxicity as the nonselective COX inhibitors.

Mesangial cells are able to produce catecholamines in vitro

Mesangial cells (MC) participate in the control of the glomerular function due to their ability to synthesize hormones and induce cell contraction. Since MC can produce various kinds of hormones, the purpose of the present study was to determine if they are able to synthesize catecholamines. For this evaluation, the levels of norepinephrine, epinephrine, dopamine, and biopterin, the enzymatic cofactor of tyrosine hydroxylase (TH), were analyzed by HPLC in the intracellular compartment and in the medium of primary cultured MC. To identify and locate the enzymes responsible for monoamine synthesis, TH, dopa decarboxylase, and dopamine beta-hydroxylase, Western blotting and immunocytochemistry were employed using monoclonal and polyclonal antibodies. Concentrations of NE = 57 +/- 8, EPI = 82 +/- 10, and DA = 52 +/- 9 pg/mg protein (X +/- SEM) were found in the cell homogenate. The culture medium showed concentrations of NE = 25 +/- 3, EPI = 33 +/- 3, and DA = 62 +/- 15 pg/mg protein. Western blotting analysis and immunocytochemistry evidenced the presence of all enzymes. Moreover, biopterin was also detected in the intracellular compartment and in the medium (0.28 +/- 0.03 and 5.70 +/- 2 nmol/mg cell protein, respectively). Overall, the data indicate that MC have the biosynthetic machinery necessary to produce catecholamines, suggesting that they can act as a paracrine/autocrine hormone system, contributing to the regulation of glomerular hemodynamic and renal microcirculation.

Role of nitric oxide and prostaglandin E2 in acute renal hypoperfusion

Although acute renal ischaemia alters the production of various paracrines, there has been little investigation examining the role of intrarenal vasoactive substances. In the present study, we investigated the role of intrarenal nitric oxide and prostaglandins in modulating the acute renal hypoperfusion-induced alterations in renal function. After a 90% clipping of the left renal artery for 60 min, the clip was released, and the renal haemodynamics and sodium excretion were evaluated in both clipped and non-clipped kidneys of anaesthetized dogs. Furthermore, the changes in renal contents of nitrate/nitrite (NOx) and prostaglandin E2 (PGE2) were assessed by using the renal microdialysis technique. The release of the clipping elicited a gradual recovery of renal plasma flow and glomerular filtration rate, and a sustained increase in fractional sodium excretion (FENa) in the clipped kidney. Renal interstitial NOx was reduced in both the cortex (from 8.2 +/- 1.1 to 2.5 +/- 0.3 micromol/L, P < 0.01) and medulla (from 10.1 +/- 0.9 to 3.1 +/- 0.2 micromol/L, P < 0.01), but the levels gradually elevated after declamping. The treatment with nitro-l-arginine methylester only modestly impaired the recovery of renal plasma flow (RPF; at hour 4) and glomerular filtration rate (GFR; at hours 3 and 4 after declamping), without affecting FENa. Conversely, the renal PGE2 levels increased prominently upon the onset of ischaemia (medulla, from 149 +/- 19 to 378 +/- 39 pg/mL, P < 0.01; cortex, from 107 +/- 13 to 302 +/- 34 pg/mL, P < 0.01). Furthermore, the pretreatment with a non-specific cyclo-oxygenase (COX) inhibitor, sulpyrine, and a COX-2-specific inhibitor, NS398, prominently inhibited the increases in FENa induced by the acute renal arterial clipping in a similar manner. In conclusion, in acute renal hypoperfusion, nitric oxide (NO) plays a permissive role in the recovery of the renal haemodynamics. In contrast, sustained increases in renal PGE2 in both clipped and non-clipped kidneys indicate that the COX-2-mediated PGE2 contributes importantly to the failure of the sodium reabsorption in response to acute renal hypoperfusion.

Inhibition of COX-2 prevents hypertension and proteinuria associated with a decrease of 8-iso-PGF2alpha formation in L-NAME-treated rats

BACKGROUND

The inhibition of nitric oxide (NO) exerts injurious effects on the cardiovascular system by several mechanisms, such as the activation of the renin-angiotensin system, oxidative stress, and inflammatory cytokines. We examined whether COX-2, an inducible isoform of cyclooxygenase, is associated with the pathogenesis observed in N(omega)-nitro-L-arginine methyl ester (L-NAME)-induced hypertensive rats.

METHODS

Three groups of 8-week-old male Sprague-Dawley rats were studied (n = 6 in each group): group 1, untreated controls; group 2, treated with L-NAME (1 g/l for 3 weeks, p.o.); and group 3, L-NAME co-treated with COX-2 inhibitor NS-398 (5 mg/kg per day, i.p.). The L-NAME-induced expression of COX-2 mRNA and protein was semi-quantified in the kidneys and the thoracic aorta. Urinary excretion of the prostaglandin 6-keto PGF(1alpha), thromboxane B2 (TXB2), and prostaglandin E2 (PGE2) was measured in the three groups. Moreover, urinary excretion of 8-iso-PGF(2alpha), a potent vasoconstricting arachidonic acid metabolite acting through thromboxane A (TXA) receptor activation, proposed recently as a marker of oxidative stress, was also measured.

RESULTS

L-NAME induced significant increases in systolic blood pressure (P< 0.01), urinary protein (P< 0.05), and renal excretion of 8-iso-PGF(2alpha)(P< 0.01), compared with the control. In L-NAME-treated rats, the levels of COX-2 mRNA and protein were more than 50% higher in the kidneys (P< 0.05), and six-fold higher in the thoracic aorta (P< 0.01) than in control rats. NS-398 significantly ameliorated an increase in systolic blood pressure (P< 0.01) and urinary protein (P< 0.05) induced by L-NAME.

CONCLUSIONS

These data indicate that an increase in COX-2 expression might have a hypertensive effect, partly associated with 8-iso-PGF(2alpha) formation in l-NAME-treated rats.

General inhibition of renocortical cyclooxygenase-2 expression by the renin-angiotensin system

Because across-the-board data indicate that renin and cyclooxygenase-2 (COX-2) expression in the kidney cortex are regulated in parallel and because ANG II can inhibit COX-2 expression, the purpose of our study was to characterize a potential general inhibitory feedback of the renin-angiotensin system on renocortical COX-2 expression in vivo. Rats were fed a high-, normal-, or low-salt diet or were chronically infused with furosemide (60 mg. kg(-1). day(-1)) or the left renal artery was clipped, and the animals were treated in addition to or without the angiotensin-converting enzyme inhibitor ramipril (10 mg. kg(-1). day(-1)). A high-salt diet reduced expression of COX-2, whereas a low-salt diet, furosemide infusion, and renal artery stenosis stimulated COX-2 expression. Additional angiotensin-converting enzyme inhibition led to further increases in renocortical COX-2 expression by 62, 136, 300, 50, and 70% for a high-, normal-, and low-salt diet, furosemide infusion, and renal artery stenosis, respectively. Thus our data suggest a general inhibitory effect of the renin-angiotensin system on renocortical COX-2 expression.

Clinical pharmacology of etoricoxib: a novel selective COX2 inhibitor

The development of COX2 inhibitors with improved biochemical selectivity (such as etoricoxib and valdecoxib) over that of commercially available coxibs has been driven by the potential advantage of safety using higher coxib doses for increased efficacy. Etoricoxib has been approved in the UK as a once-daily medicine for symptomatic relief in the treatment of osteoarthritis (OA), rheumatoid arthritis (RA) and acute gouty arthritis. It is currently approved with additional indications (i.e., for relief of acute pain associated with dental surgery, for primary dysmenorrhoea and for chronic musculo-skeletal pain, including chronic lower-back pain) in Mexico, Brazil and Peru. Etoricoxib has an in vitro COX1/COX2 IC(50) ratio of 344, the highest of any coxib. The administration of therapeutic doses of etoricoxib to healthy subjects does not affect COX1 activity in circulating platelets and gastric biopsies. The profound inhibition of monocyte COX2 activity at 24 h after dosing, as predicted by a pharmacological half-life of approximately 22 h, supports a once-daily dosing regimen of etoricoxib. In randomised, well-controlled clinical trials, etoricoxib has been shown to have a comparable clinical efficacy with traditional NSAIDs. Combined analysis of efficacy trials with etoricoxib versus non-selective NSAIDs has shown that the drug halves both investigator-reported upper gastrointestinal perforation, ulcers and bleeds (PUBs) and confirmed PUBs, and reduces the need for gastroprotective agents and gastrointestinal comedications by approximately 40%. The risk of lower extremity oedema and hypertension adverse experiences with etoricoxib was low and generally similar to comparator NSAIDs in a combined analysis of eight Phase III studies in OA, RA, chronic low-back pain and surveillance endoscopy. Large, randomised clinical trials have been planned to confirm the renal, gastrointestinal and cardiovascular safety of etoricoxib.

Does cyclooxygenase-2 affect blood pressure?

With the development and clinical implementation of the new cyclooxygenase (COX)-2 inhibitors, their safety, including the effects on renal function and blood pressure, is attracting increasing attention. In the kidney, COX-2 is constitutively expressed and is highly regulated in response to alterations in intravascular volume. COX-2 metabolites have been implicated in mediation of renin release, regulation of sodium excretion, and maintenance of renal blood flow. Similar to conventional nonsteroidal anti-inflammatory drugs, inhibition of COX-2 may cause modest elevations in blood pressure in a minority of subjects. COX-2 inhibitors may also exacerbate pre-existing hypertension or interfere with other antihypertensive drugs. Special caution should be taken in patients with volume depletion or decreased organ perfusion.