Coordinate expression of cyclooxygenase-2 and renin in the rat kidney in renovascular hypertension

Ramatroban for chemoprophylaxis and treatment of COVID-19: David takes on Goliath

INTRODUCTION

In COVID-19 pneumonia, there is a massive increase in fatty acid levels and lipid mediators with a predominance of cyclooxygenase metabolites, notably TxB2 ≫ PGE2 > PGD2 in the lungs, and 11-dehydro-TxB2, a TxA2 metabolite, in the systemic circulation. While TxA2 stimulates thromboxane prostanoid (TP) receptors, 11-dehydro-TxB2 is a full agonist of DP2 (formerly known as the CRTh2) receptors for PGD2. Anecdotal experience of using ramatroban, a dual receptor antagonist of the TxA2/TP and PGD2/DP2 receptors, demonstrated rapid symptomatic relief from acute respiratory distress and hypoxemia while avoiding hospitalization.

AREAS COVERED

Evidence supporting the role of TxA2/TP receptors and PGD2/DP2 receptors in causing rapidly progressive lung injury associated with hypoxemia, a maladaptive immune response and thromboinflammation is discussed. An innovative perspective on the dual antagonism of TxA2/TP and PGD2/DP2 receptor signaling as a therapeutic approach in COVID-19 is presented. This paper examines ramatroban an anti-platelet, immunomodulator, and antifibrotic agent for acute and long-haul COVID-19.

EXPERT OPINION

Ramatroban, a dual blocker of TP and DP2 receptors, has demonstrated efficacy in animal models of respiratory dysfunction, atherosclerosis, thrombosis, and sepsis, as well as preliminary evidence for rapid relief from dyspnea and hypoxemia in COVID-19 pneumonia. Ramatroban merits investigation as a promising antithrombotic and immunomodulatory agent for chemoprophylaxis and treatment.

Modulation of Enzyme-Catalyzed Synthesis of Prostaglandins by Components Contained in Kidney Microsomal Preparations

In the kidney, prostaglandins formed by cyclooxygenase 1 and 2 (COX-1 and COX-2) play an important role in regulating renal blood flow. In the present study, we report our observations regarding a unique modulatory effect of renal microsomal preparation on COX-1/2-mediated formation of major prostaglandin (PG) products in vitro. We found that microsomes prepared from pig and rat kidneys had a dual stimulatory–inhibitory effect on the formation of certain PG products catalyzed by COX-1 and COX-2. At lower concentrations, kidney microsomes stimulated the formation of certain PG products, whereas at higher concentrations, their presence inhibited the formation. Presence of kidney microsomes consistently increased the K_m values of the COX-1/2-mediated reactions, while the V_max might be increased or decreased depending on stimulation or inhibition observed. Experimental evidence was presented to show that a protein component present in the pig kidney microsomes was primarily responsible for the activation of the enzyme-catalyzed arachidonic acid metabolism leading to the formation of certain PG products.

Cyclo-Oxygenase (COX) Inhibitors and Cardiovascular Risk: Are Non-Steroidal Anti-Inflammatory Drugs Really Anti-Inflammatory?

Cyclo-oxygenase (COX) inhibitors are among the most commonly used drugs in the western world for their anti-inflammatory and analgesic effects. However, they are also well-known to increase the risk of coronary events. This area is of renewed significance given alarming new evidence suggesting this effect can occur even with acute usage. This contrasts with the well-established usage of aspirin as a mainstay for cardiovascular prophylaxis, as well as overwhelming evidence that COX inhibition induces vasodilation and is protective for vascular function. Here, we present an updated review of the preclinical and clinical literature regarding the cardiotoxicity of COX inhibitors. While studies to date have focussed on the role of COX in influencing renal and vascular function, we suggest an interaction between prostanoids and T cells may be a novel factor, mediating elevated cardiovascular disease risk with NSAID use.

COX-2-derived PGE2 triggers hyperplastic renin expression and hyperreninemia in aldosterone synthase-deficient mice

Pharmacological inhibition or genetic loss of function defects of the renin angiotensin aldosterone system (RAAS) causes compensatory renin cell hyperplasia and hyperreninemia. The triggers for the compensatory stimulation of renin synthesis and secretion in this situation may be multimodal. Since cyclooxygenase-2 (COX-2) expression in the macula densa is frequently increased in states of a defective RAAS, we have investigated a potential role of COX-2 and its derived prostaglandins for renin expression and secretion in aldosterone synthase-deficient mice (AS^−/−) as a model for a genetic defect of the RAAS. In comparison with wild-type mice (WT), AS^−/− mice had 9-fold and 30-fold increases of renin mRNA and of plasma renin concentrations (PRC), respectively. Renin immunoreactivity in the kidney cortex of AS^−/− mice was 10-fold higher than in WT. Macula densa COX-2 expression was 5-fold increased in AS^−/− kidneys relative to WT kidneys. Treatment of AS^−/− mice with the COX-2 inhibitor SC-236 for 1 week lowered both renal renin mRNA and PRC by 70%. Hyperplastic renin cells in AS^−/− kidneys were found to express the prostaglandin E₂ receptors EP2 and EP4. Global deletion of EP2 receptors did not alter renin mRNA nor PRC values in AS^−/− mice. Renin cell-specific inducible deletion of the EP4 receptor lowered renin mRNA and PRC by 25% in AS^−/− mice. Renin cell-specific inducible deletion of the EP4 receptor in combination with global deletion of the EP2 receptor lowered renin mRNA and PRC by 70–75% in AS^−/− mice. Lineage tracing of renin-expressing cells revealed that deletion of EP2 and EP4 leads to a preferential downregulation of perivascular renin expression. Our findings suggest that increased macula densa COX-2 activity in AS^−/− mice triggers perivascular renin expression and secretion via prostaglandin E₂.

Early co-expression of cyclooxygenase-2 and renin in the rat kidney cortex contributes to the development of N(G)-nitro-L-arginine methyl ester induced hypertension

We investigated the involvement of cyclooxygenase-2 (COX-2) and the renin-angiotensin system in N(G)-nitro-L-arginine methyl ester (L-NAME)-induced hypertension. Male Wistar rats were treated with L-NAME (75.0 mg·(kg body mass)(-1)·day(-1), in their drinking water) for different durations (1-33 days). COX-2 and renin mRNA were measured using real-time PCR in the renal cortex, and prostanoids were assessed in the renal perfusate, whereas angiotensin II (Ang II) and Ang (1-7) were quantified in plasma. In some rats, nitric oxide synthase inhibition was carried out in conjunction with oral administration of captopril (30.0 mg·kg(-1)·day(-1)) or celecoxib (1.0 mg·kg(-1)·day(-1)) for 2 or 19 days. We found a parallel increase in renocortical COX-2 and renin mRNA starting at day 2 of treatment with L-NAME, and both peaked at 19-25 days. In addition, L-NAME increased renal 6-Keto-PGF(1α) (prostacyclin (PGI2) metabolite) and plasma Ang II from day 2, but reduced plasma Ang (1-7) at day 19. Captopril prevented the increase in blood pressure, which was associated with lower plasma Ang II and increased COX-2-derived 6-Keto-PGF(1α) at day 2 and plasma Ang (1-7) at day 19. Celecoxib partially prevented the increase in blood pressure; this effect was associated with a reduction in plasma Ang II. These findings indicate that renal COX-2 expression increased in parallel with renin expression, renal PGI2 synthesis, and plasma Ang II in L-NAME-induced hypertension.

Nonatherosclerotic obstructive vascular diseases of the mesenteric and renal arteries

Nonatherosclerotic vascular diseases of the mesenteric and renal arteries are considered to occur less frequently than those caused by occlusive atherosclerotic disease. However, when present, they pose a significant diagnostic and therapeutic challenge. Such disorders include fibromuscular dysplasia, median arcuate ligament syndrome, the renal nutcracker syndrome, and some forms of acute and chronic mesenteric ischemia (embolic and thrombotic). This is a heterogeneous group of disorders with substantial differences in the pathogenesis and diagnostic approaches to these diseases. We provide an overview of the pathogenesis, clinical presentation, diagnosis, and current management of fibromuscular dysplasia, median arcuate ligament syndrome, and the renal nutcracker syndrome.

Renin inhibition in the treatment of diabetic kidney disease

Inhibition of the RAAS (renin–angiotensin–aldosterone system) plays a pivotal role in the prevention and treatment of diabetic nephropathy and a spectrum of other proteinuric kidney diseases. Despite documented beneficial effects of RAAS inhibitors in diabetic patients with nephropathy, reversal of the progressive course of this disorder or at least long-term stabilization of renal function are often difficult to achieve, and many patients still progress to end-stage renal disease. Incomplete inhibition of the RAAS has been postulated as one of reasons for unsatisfactory therapeutic responses to RAAS inhibition in some patients. Inhibition of renin, a rate-limiting step in the RAAS activation cascade, could overcome at least some of the abovementioned problems associated with the treatment with traditional RAAS inhibitors. The present review focuses on experimental and clinical studies evaluating the two principal approaches to renin inhibition, namely direct renin inhibition with aliskiren and inhibition of the (pro)renin receptor. Moreover, the possibilities of renin inhibition and nephroprotection by interventions primarily aiming at non-RAAS targets, such as vitamin D, urocortins or inhibition of the succinate receptor GPR91 and cyclo-oxygenase-2, are also discussed.

Cyclooxygenase-2 and kidney failure

Cyclooxygenase (COX)-dependent prostaglandins are necessary for normal kidney function. These prostaglandins are associated with inflammation, maintenance of sodium and water homeostasis, control of renin release, renal vasodilation, vasoconstriction attenuation, and prenatal renal development. COX-2 expression is regulated by the renin-angiotensin system, glucocorticoids or mineralcorticoids, and aldosterone, supporting a role for COX-2 in kidney function. Indeed, COX-2 mRNA and protein levels as well as enzyme activity are increased, along with PGE2, during kidney failure. In addition, changes in COX-2 expression are associated with increased blood pressure, urinary volume, sodium and protein and decreased urinary osmolarity. Intrarenal mechanisms such as angiotensin II (Ang II) production, increased sodium delivery, glomerular hypertension, and renal tubular inflammation have been suggested to be responsible for the increase in COX-2 expression. Although, specific COX-2 pharmacological inhibition has been related to the prevention of kidney damage, clinical studies have reported that COX-2 inhibition may cause side effects such as edema or a modest elevation in blood pressure and could possibly interfere with antihypertensive drugs and increase the risk of cardiovascular complications. Thus, administration of COX-2 inhibitors requires caution, especially in the presence of underlying cardiovascular disease.

Effect of celecoxib on the antihypertensive effect of losartan in a rat model of renovascular hypertension

Certain nonsteroidal anti-inflammatory drugs have been reported to elevate blood pressure in some hypertensive patients, who are either untreated or treated with antihypertensive agents. This study was undertaken to determine the effect of a selective cyclooxygenase-2 (COX-2) inhibitor, celecoxib, on the antihypertensive effects of the angiotensin II type 1 receptor (AT1) antagonist, losartan potassium. We studied the effect of oral treatment with losartan (30 mg/kg), celecoxib (3 mg/kg), and their combination on the mean arterial blood pressure (MAP), plasma renin activity (PRA), and plasma prostaglandin E2(PGE2) in male Sprague–Dawley rats with renovascular hypertension (RVH) induced by partial subdiaphragmatic aortic constriction. Treatment was continued for 7 days after aortic coarctation. Aortic coarctation led to significant increases in the MAP, PRA, and plasma PGE2. In RVH rats, losartan treatment caused a significant decrease of MAP with a significant increase in both plasma PGE2and PRA. Celecoxib caused a nonsignificant change in MAP with a significant decrease in the raised levels of plasma PGE2and PRA. Concomitant administration of celecoxib and losartan did not significantly affect the lowering effect of losartan on MAP with a subsequent significant decrease in the plasma PGE2and PRA in RVH rats. Therefore, celecoxib could be used in renin-dependent hypertensive patients who receive losartan, without fear of a rise in their blood pressure.

Regulation of renin release by local and systemic factors

The renin-angiotensin system (RAS) is critically involved in the regulation of the salt and volume status of the body and blood pressure. The activity of the RAS is controlled by the protease renin, which is released from the renal juxtaglomerular epithelioid cells into the circulation. Renin release is regulated in negative feedback-loops by blood pressure, salt intake, and angiotensin II. Moreover, sympathetic nerves and renal autacoids such as prostaglandins and nitric oxide stimulate renin secretion. Despite numerous studies there remained substantial gaps in the understanding of the control of renin release at the organ or cellular level. Some of these gaps have been closed in the last years by means of gene-targeted mice and advanced imaging and electrophysiological methods. In our review, we discuss these recent advances together with the relevant previous literature on the regulation of renin release.

Tetradecylthioacetic acid downregulates cyclooxygenase 2 in the renal cortex of two-kidney, one-clip hypertensive rats

The effect of tetradecylthioacetic acid (TTA) on the cyclooxygenase (COX) system was investigated in two-kidney, one-clip (2K1C) hypertensive rats. The systolic blood pressure (BP) was increased 6 wk after clipping to 183 +/- 4 vs.127 +/- 3 mmHg in TTA-treated 2K1C rats. The COX1 protein expression was not affected either by the 2K1C procedure or by TTA treatment. COX2 expression was upregulated in both kidneys, but to a greater extent in the clipped kidney. COX2 activity was 16 +/- 3% in control and 38 +/- 2% (P < 0.001) in the clipped kidney, and COX2 protein expression was 1.3 +/- 0.04 in control and 1.6 +/- 0.12 in the clipped kidney (P = 0.006). TTA reduced COX2 activity to control levels. Subcutaneously infusion of a COX2 inhibitor did not reduce BP. Peroxisome proliferator-activated receptors (PPARs) were detected in both kidneys, and PPARdelta was upregulated in the nonclipped kidney after TTA treatment. PGE2 in renal cortex was increased in 2K1C (31 +/- 0.3 in the clipped and 28 +/- 0.2 pg/ml nonclipped kidney, P < 0.001 compared with control). TTA lowered the PGE2 to control levels. Renal blood flow (RBF) response to exogenous ANG II injected in the control and nonclipped kidney was exaggerated after indomethacin treatment but unchanged in the nonclipped kidney of the K1C TTA group. Overall, these results indicate that, after 6 wk of treatment, TTA downregulated the COX2 activity, which have potentially important effects on the regulation of renal hemodynamics but does not explain TTAs ability to lower BP.

Renal effects of prostaglandins and cyclooxygenase-2 inhibitors

Prostaglandins (PGs) with best-defined renal functions are PGE₂ and prostacyclin (PGI₂). These vasodilatory PGs increase renal blood flow and glomerular filtration rate under conditions associated with decreased actual or effective circulating volume, resulting in greater tubular flow and secretion of potassium. Under conditions of decreased renal perfusion, the production of renal PGs serves as an important compensatory mechanism. PGI₂ (and possibly PGE₂) increases potassium secretion mainly by stimulating secretion of renin and activating the renin-angiotensin system, which leads to increased secretion of aldosterone. In addition, PGE₂ is involved in the regulation of sodium and water reabsorption and acts as a counterregulatory factor under conditions of increased sodium reabsorption. PGE₂ decreases sodium reabsorption at the thick ascending limb of the loop of Henle probably via inhibition of the Na⁺-K⁺-2Cl^- cotransporter type 2 (NKCC2). Cyclooxygenase inhibitors may enhance urinary concentrating ability in part through effects to upregulate NKCC2 in the thick ascending limb of Henle's loop and aquaporin-2 in the collecting duct. Thus, they may be useful to treat Bartter's syndrome and nephrogenic diabetes insipidus.

The effect of cyclooxygenase-2 inhibition on renal hemodynamic function in humans with type 1 diabetes

OBJECTIVE

Studies in animal models suggest that cyclooxygenase-2 (COX2) plays a role in the regulation of the renal microcirculation in diabetes. Accordingly, we examined the role of COX2 in the control of renal hemodynamic function and in the renal response to hyperglycemia in humans with uncomplicated type 1 diabetes. We hypothesized that COX2 inhibition would alleviate the hyperfiltration state and would abrogate the hyperglycemia-mediated rise in glomerular filtration rate (GFR). RESEARCH DESIGN AND METHODS; Renal function was assessed during clamped euglycemia and hyperglycemia on 2 consecutive days before and then again after 14 days of COX2 inhibition using 200 mg celecoxib once daily by mouth. For analysis, the cohort was then divided into two groups based on the baseline GFR: 9 subjects exhibited hyperfiltration (GFR >or=135 ml/min per 1.73 m(2)), and 12 subjects exhibited normofiltration (GFR <135 ml/min per 1.73 m(2)).

RESULTS

Under euglycemic conditions, COX2 inhibition resulted in a significant decline in GFR in the hyperfiltration group (150 +/- 5 to 139 +/- 5 ml/min per 1.73 m(2)) but increased GFR in the normofiltration group (118 +/- 5 to 138 +/- 5 ml/min per 1.73 m(2)). COX2 inhibition did not blunt the hyperglycemia-associated rise in GFR in the normofiltration group and was instead associated with an augmented rise in GFR.

CONCLUSIONS

In summary, our results support the hypothesis that COX2 is an important determinant of renal hemodynamic function in subjects with type 1 diabetes. The renal response to COX2 inhibition emphasizes that hyperfiltration and normofiltration are distinct physiological states.

Polygonum cuspidatum, compared with baicalin and berberine, inhibits inducible nitric oxide synthase and cyclooxygenase-2 gene expressions in RAW 264.7 macrophages

Polygonum cuspidatum water extract (PCWE) was shown to be a potent inhibitor of lipopolysaccharide (LPS)-induced expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). PCWE was compared to baicalin isolated from Scutellaria baicalensis Georgi and berberine of Coptidis rhizoma and Phellodendri cortex, for their effects on LPS-induced nitric oxide (NO) production and iNOS and COX-2 gene expressions in RAW 264.7 macrophages. Both PCWE and the compounds inhibited LPS-induced NO production in a concentration-dependent manner without a cytotoxicity. The decrease in NO production was in parallel with the inhibition of LPS-induced iNOS gene expression by PCWE and the compounds. In contrast, iNOS enzyme activity was not inhibited by PCWE and two agents. In addition, only PCWE inhibited LPS-induced prostaglandin E2 (PGE2) production and COX-2 gene expression without affecting COX-2 enzyme activity, while baicalin or berberine did not. Furthermore, N-nitro-L-arginine (NLA) and N-nitro-L-arginine methyl ester (L-NAME) pretreatment enhanced LPS-induced iNOS protein expression, which was inhibited by these PCWE and two agents, although LPS-induced COX-2 protein expression was not affected by NLA and L-NAME. PCWE inhibited PGE2 production and COX-2 protein expression in NLA/LPS or L-NAME/LPS-co-treated RAW 264.7 cell, however, baicalin or berberine did not. From the results, it was concluded that co-treatment with NOS inhibitors and PCWE effectively blocks acute production of NO and inhibits expression of iNOS and COX-2 genes.

Effect of the angiotensinogen genotype on experimental hypertension in mice

Polymorphisms of the angiotensinogen (Agt) gene may affect blood pressure. We used a mouse model to test for the role of the Agt genotype in low-renin or high-renin forms of hypertension. Mice bearing one, two, three, or four copies of the Agt gene underwent renal artery clipping to induce high-renin two-kidney, one-clip renovascular hypertension (2K1C), or uninephrectomy, salt loading, and application of deoxycorticosterone-acetate (DOCA) pellets to induce low-renin mineralocorticoid hypertension. Appropriate control animals were also studied. Blood pressure was measured by tail cuff as well as by direct intra-arterial recordings. There was a small effect of the Agt genotype on baseline blood pressure before induction of hypertension. The extent of 2K1C hypertension was not affected by the genotype. In contrast, there was a marked gene-dose effect on DOCA-hypertension (21.2 mmHg over all genotypes). Treatment of DOCA mice with the angiotensin II type 1 receptor antagonist abolished the genotype effect on blood pressure and left ventricular hypertrophy. There was a trend towards less suppression of endogenous aldosterone by DOCA treatment with increasing number of Agt gene copies. We conclude that the Agt genotype exerts a marked effect on blood pressure in a low-renin form of hypertension but no effect in the face of stimulated renin, at least in mice.

Angiotensin II formation in the kidney and nephrosclerosis in Ren-2 hypertensive rats

BACKGROUND

Ren-2 transgenic hypertensive rats develop malignant hypertensive nephrosclerosis despite low to normal plasma angiotensin II and suppressed renal renin. We tested the hypothesis that local angiotensin II formation occurs at sites of renal vascular and interstitial injury in this model.

METHODS

Heterozygous Ren-2 transgenic rats were compared with normotensive Sprague-Dawley-Hannover control rats and Ren-2 transgenic rats treated with a very low dose of an angiotensin II type 1 (AT1) receptor antagonist, 1 mg/kg/day losartan, for 4 weeks. Blood pressure measurements, quantifications of urinary albumin, plasma and tissue angiotensin II as well as immunohistochemical analyses were performed.

RESULTS

Systolic blood pressure was not affected by losartan during the study but intra-arterial recordings revealed a decrease of blood pressure. Losartan reduced albumin excretion, cell proliferation, macrophage influx, collagen I and collagen IV deposition. Plasma angiotensin II was decreased, while kidney tissue angiotensin II content was increased in Ren-2 transgenic rats compared with control rats. In Ren-2 transgenic rats, juxtaglomerular renin and angiotensin II staining were reduced, but there was a marked angiotensin II staining at foci of tubulo-interstitial fibrosis and at proliferative malignant vascular lesions.

CONCLUSION

We conclude that local angiotensin II formation is increased in proliferative or fibrotic kidney lesions in the Ren-2 transgenic rat. Local angiotensin II formation may help to explain why the AT1 receptor antagonist prevents or ameliorates this transgenic model of malignant nephrosclerosis despite low to normal plasma angiotensin II and suppressed renal renin.

An orally active epoxide hydrolase inhibitor lowers blood pressure and provides renal protection in salt-sensitive hypertension

The present study tested the hypothesis that increasing epoxyeicosatrienoic acids by inhibition of soluble epoxide hydrolase (sEH) would lower blood pressure and ameliorate renal damage in salt-sensitive hypertension. Rats were infused with angiotensin and fed a normal-salt diet or an 8% NaCl diet for 14 days. The sEH inhibitor, 12-(3-adamantan-1-yl-ureido)-dodecanoic acid (AUDA), was given orally to angiotensin-infused animals during the 14-day period. Plasma AUDA metabolite levels were measured, and they averaged 10+/-2 ng/mL in normal-salt angiotensin hypertension and 19+/-3 ng/mL in high-salt angiotensin hypertension on day 14 in the animals administered the sEH inhibitor. Mean arterial blood pressure averaged 161+/-4 mm Hg in normal-salt and 172+/-5 mm Hg in the high-salt angiotensin hypertension groups on day 14. EH inhibitor treatment significantly lowered blood pressure to 140+/-5 mm Hg in the normal-salt angiotensin hypertension group and to 151+/-6 mm Hg in the high-salt angiotensin hypertension group on day 14. The lower arterial blood pressures in the AUDA-treated groups were associated with increased urinary epoxide-to-diol ratios. Urinary microalbumin levels were measured, and ED-1 staining was used to determine renal damage and macrophage infiltration in the groups. Two weeks of AUDA treatment decreased urinary microalbumin excretion in the normal-salt and high-salt angiotensin hypertension groups and macrophage number in the high-salt angiotensin hypertension group. These data demonstrate that sEH inhibition lowers blood pressure and ameliorates renal damage in angiotensin-dependent, salt-sensitive hypertension.

Kidney function in mice lacking aldosterone

To explore the effects of decreased amounts or absence of aldosterone, we have disrupted the gene coding for aldosterone synthase (AS) in mice and investigated blood pressure and kidney function in AS+/+, AS+/-, and AS-/- mice. AS+/- mice have normal blood pressures and show no abnormalities in electrolytes or kidney gene expression, but they have significantly higher than normal urine volume and lower urine osmolality. In contrast, the AS-/- mice have low blood pressure, abnormal electrolyte homeostasis (increased plasma concentrations of K+, Ca2+, and Mg2+ and decreased concentrations of HCO3(-) and Cl- but no difference in the plasma Na+ level), and disturbances in water metabolism (higher urine output, decreased urine osmolality, and impaired urine concentrating and diluting ability). Absence of aldosterone in the AS-/- mice induced several compensatory changes: an increased food intake-to-body weight ratio, an elevated plasma concentration of glucocorticoids, and strong activation of the renin-angiotensin system. Parallel with the markedly increased synthesis and release of renin, the AS-/- mice showed increased expression of cyclooxygenase-2 (COX-2) in macula densa. On salt supplementation, plasma electrolyte concentrations and kidney renin and COX-2 levels became similar to those of wild-type mice, but the lower blood pressure of the AS-/- mice was not corrected. Thus absence of aldosterone in AS-/- mice results in impairment of Na+ reabsorption in the distal nephron, decreased blood pressure, and strong renin-angiotensin system activation. Our data show the substantial correction of these abnormalities, except the low blood pressure, by high dietary salt does not depend on aldosterone.

Dominant role of prostaglandin E2 EP4 receptor in furosemide-induced salt-losing tubulopathy: a model for hyperprostaglandin E syndrome/antenatal Bartter syndrome

Increased formation of prostaglandin E2 (PGE2) is a key part of hyperprostaglandin E syndrome/antenatal Bartter syndrome (HPS/aBS), a renal disease characterized by NaCl wasting, water loss, and hyperreninism. Inhibition of PGE2 formation by cyclo-oxygenase inhibitors significantly lowers patient mortality and morbidity. However, the pathogenic role of PGE2 in HPS/aBS awaits clarification. Chronic blockade of the Na-K-2Cl co-transporter NKCC2 by diuretics causes symptoms similar to HPS/aBS and provides a useful animal model. In wild-type (WT) mice and in mice lacking distinct PGE2 receptors (EP1-/-, EP2-/-, EP3-/-, and EP4-/-), the effect of chronic furosemide administration (7 d) on urine output, sodium and potassium excretion, and renin secretion was determined. Furthermore, furosemide-induced diuresis and renin activity were analyzed in mice with defective PGI2 receptors (IP-/-). In all animals studied, furosemide stimulated a rise in diuresis and electrolyte excretion. However, this effect was blunted in EP1-/-, EP3-/-, and EP4-/- mice. Compared with WT mice, no difference was observed in EP2-/- and IP-/- mice. The furosemide-induced increase in plasma renin concentration was significantly decreased in EP4-/- mice and to a lesser degree also in IP-/- mice. Pharmacologic inhibition of EP4 receptors in furosemide-treated WT mice with the specific antagonist ONO-AE3-208 mimicked the changes in renin mRNA expression, plasma renin concentration, diuresis, and sodium excretion seen in EP4-/- mice. The GFR in EP4-/- mice was not changed compared with that in WT mice, which indicated that blunted diuresis and salt loss seen in EP4-/- mice were not a consequence of lower GFR. In summary, these findings demonstrate that the EP4 receptor mediates PGE2-induced renin secretion and that EP1, EP3, and EP4 receptors all contribute to enhanced PGE2-mediated salt and water excretion in the HPS/aBS model.

Effects of sympathetic nerves and angiotensin II on renal sodium and water handling in rats with common bile duct ligature

We tested the hypothesis that angiotensin II is likely to be mandatory for the neurogenic sodium and volume retention in cirrhotic rats with common bile duct ligature (BDL) following an acute volume load. To assess the neural control of volume homeostasis, 21 days after common BDL rats underwent volume expansion (0.9% NaCL; 10% body wt over 30 min) to decrease renal sympathetic nerve activity. Untreated animals, rats with renal denervation or pretreated with a nonhypotensive dose of an angiotensin II type 1 receptor antagonist were studied. The renal renin-angiotensin system was assessed by immunohistochemistry and RT-PCR. Rats with BDL excreted only 71 ± 4% of the administered volume load. In cirrhotic rats pretreated with an angiotensin II AT1inhibitor or after renal denervation, these values ranged significantly higher from 98 to 103% ( P < 0.05 for all comparisons). Renal sympathetic nerve activity decreases by volume expansion were impaired in BDL rats ( P < 0.05) but unaffected by angiotensin II receptor inhibition. In kidneys of BDL animals, renin mRNA was increased, and immunohistochemistry revealed increased staining for peritubular angiotensin II. Renal denervation in BDL animals reduced renin expression within 5 days to control levels. In conclusion, the impaired excretion of an acute volume load in rats with liver cirrhosis is due to effects of an increased renal sympathetic nerve activity that are likely to be dependent on intrarenal angiotensin II and renin. We speculate that similar changes may contribute to long-term volume retention in liver cirrhosis.

Decreased susceptibility to renovascular hypertension in mice lacking the prostaglandin I2 receptor IP

Persistent reduction of renal perfusion pressure induces renovascular hypertension by activating the renin-angiotensin-aldosterone system; however, the sensing mechanism remains elusive. Here we investigated the role of PGI2 in renovascular hypertension in vivo, employing mice lacking the PGI2 receptor (IP-/- mice). In WT mice with a two-kidney, one-clip model of renovascular hypertension, the BP was significantly elevated. The increase in BP in IP-/- mice, however, was significantly lower than that in WT mice. Similarly, the increases in plasma renin activity, renal renin mRNA, and plasma aldosterone in response to renal artery stenosis were all significantly lower in IP-/- mice than in WT mice. All these parameters were measured in mice lacking the four PGE2 receptor subtypes individually, and we found that these mice had similar responses to WT mice. PGI2 is produced by COX-2 and a selective inhibitor of this enzyme, SC-58125, also significantly reduced the increases in plasma renin activity and renin mRNA expression in WT mice with renal artery stenosis, but these effects were absent in IP-/- mice. When the renin-angiotensin-aldosterone system was activated by salt depletion, SC-58125 blunted the response in WT mice but not in IP-/- mice. These results indicate that PGI2 derived from COX-2 plays a critical role in regulating the release of renin and consequently renovascular hypertension in vivo.

Inhibition of lipopolysaccharide-induced expression of inducible nitric oxide synthase by butein in RAW 264.7 cells

Butein has been reported to exert anti-inflammatory effect but the possible mechanism involved is still unclear. Here, we report the inhibitory effect of butein on nitric oxide (NO) production and inducible nitric oxide synthase (iNOS) gene expression. Butein also inhibited the induction of tumor necrosis factor-alpha and cyclooxygenase 2 by LPS. To further investigate the mechanism responsible for the inhibition of iNOS gene expression by butein, we examined the effect of butein on LPS-induced nuclear factor-kappaB (NF-kappaB) activation. The LPS-induced DNA binding activity of NF-kappaB was significantly inhibited by butein, and this effect was mediated through inhibition of the degradation of inhibitory factor-kappaB and phosphorylation of Erk1/2 MAP kinase. Furthermore, increased binding of the osteopontin alphavbeta3 integrin receptor by butein may explain its inhibitory effect on LPS-mediated NO production. Taken together, these results suggest that butein inhibits iNOS gene expression, providing possible mechanisms for its anti-inflammatory action.

The renin-angiotensin system in kidney development: role of COX-2 and adrenal steroids

Recent data from studies in rodents with targeted gene disruption and pharmacological antagonists have shown that the renin-angiotensin-aldosterone system (RAAS) and cyclooxygenase type-2 (COX-2) are necessary for late stages of kidney development. The present review summarizes data on the developmental changes of RAAS and COX-2 and the pathways by which they are activated; their possible interplay and the mechanisms by which they affect kidney development. Intrarenal and circulating renin and angiotensin II (ANG II) are stimulated at birth in most mammals. In rats, renin and ANG II stay significantly elevated in the suckling period while aldosterone stabilizes at an adult level. COX-2 is stimulated in thick ascending limb of Henle's loop in the suckling period at a time when urine concentrating ability is not developed. Data suggest that this induction is mediated by combined low plasma glucocorticoid concentration and by a low NaCl intake. Studies with selective inhibitors of COX-2 and COX-2 null mice show that COX-2 activity stimulates renin secretion from JG-cells during postnatal kidney development and that lack of COX-2 activity leads to pathological change in cortical architecture and eventually to renal failure. In the postnatal period, ANG II initiates and maintains pelvic and ureteric contractions necessary for urine flow. Lack of ANG II in the neonatal period is thought to cause injury by a chronic increase of renal pelvic pressure. Aldosterone is crucial for survival and growth in the neonatal period through its effects on sodium reabsorption and the intrarenal sensitivity to aldosterone is increased in the postnatal period. Final maturation of the kidney occurs through an intimate interplay between a low dietary sodium intake and a non-responsive HPA-axis which stimulates cortical COX-2 activity. COX-2 supports increased activity of the RAAS and may contribute to a low concentrating ability.

Cyclooxygenase-2 and the renal renin-angiotensin system

In the kidney, cyclooxygenase-2 (COX-2) is expressed in the macula densa/cTALH and medullary interstitial cells. The macula densa is involved in regulating afferent arteriolar tone and renin release by sensing alterations in luminal chloride via changes in the rate of Na(+)/K(+)/2Cl(-) cotransport, and administration of non-specific cyclooxygenase inhibitors will blunt increases in renin release mediated by macula densa sensing of decreases in luminal NaCl. High renin states [salt deficiency, angiotensin converting enzyme (ACE) inhibitors or angiotensin receptor blockers, diuretic administration or experimental renovascular hypertension] are associated with increased macula densa/cTALH COX-2 expression. Furthermore, there is evidence that angiotensin II and/or aldosterone may inhibit COX-2 expression. In AT1 receptor knockout mice, COX-2 expression is increased similar to increases with ACE inhibitors or AT1 receptor blockers. Direct administration of angiotensin II inhibits macula densa COX-2 expression. Previous studies demonstrated that alterations in intraluminal chloride concentration are the signal for macula densa regulation of tubuloglomerular feedback and renin secretion, with high chloride stimulating tubuloglomerular feedback and low chloride stimulating renin release. When cultured cTALH or macula densa cells were incubated in media with selective substitution of chloride ions, COX-2 expression and prostaglandin production were significantly increased. A variety of studies have indicated a role for COX-2 in the macula densa mediation of renin release. In isolated perfused glomerular preparations, renin release induced by macula densa perfusion with a low chloride solution was inhibited by a COX-2 inhibitor but not a COX-1 inhibitor. In vivo studies in rats indicated that increased renin release in response to low-salt diet, ACE inhibitor, loop diuretics or aortic coarctation could be inhibited by administration of COX-2-selective inhibitors. In mice with genetic deletion of COX-2, ACE inhibitors or low-salt diet failed to increase renal renin expression, although renin significantly increased in wild type mice. In contrast, in COX-1 null mice there were no significant differences in either the basal or ACE inhibitor-stimulated level of renal renin activity from plasma or renal tissue compared with wild type mice. In summary, there is increasing evidence that COX-2 expression in the macula densa and surrounding cortical thick ascending limb cells is regulated by angiotensin II and is a modulator of renal renin production. These interactions of COX-2 derived prostaglandins and the renin-angiotensin system may underlie physiological and pathophysiological regulation of renal function.

Upregulation of macula densa cyclooxygenase-2 expression is not dependent on glomerular filtration

Although the regulation of cyclooxygenase-2 (COX-2) expression in the kidney cortex has been extensively characterized, the physiological control mechanisms of COX-2 expression at the level of the kidney and at the level of the tubular cells are not well understood. Based on the current hypothesis that tubular salt transport might be a crucial regulator of COX-2 expression, this study aimed to determine the impact of salt delivery to the tubules (glomerular filtration) for the regulation of COX-2 in the kidney cortex in vivo. To this end, glomerular filtration of the right kidney was abrogated by the ligation of the right ureter of male Sprague-Dawley rats. After 1 wk of ligation, the animals were treated with subcutaneous infusions of furosemide (12 mg·kg−1·day−1) or with a low-salt or a high-salt diet (0.02% wt/wt; 8% wt/wt), and COX-2 as well as renin mRNA expression were determined in the ligated and the nonligated contralateral kidney. During ureteral ligation, hydronephrosis developed with a reduction of medullary mass, while the cortex was preserved. Expressions of the Na-K-2Cl cotransporter isoforms A and B were both reduced in the hydronephrotic cortex to 70 and 35% of the corresponding contralateral intact kidney. Despite the abrogation of glomerular filtration, detected by inulin clearance measurements, renocortical COX-2 mRNA abundance was stimulated by furosemide treatment (3.2-fold) or low-salt diet (2.9-fold) to similar degrees compared with the intact contralateral kidney (2.7-fold for both treatments), whereas a high-salt diet did not significantly suppress COX-2 mRNA in the macula densa region of either kidney. Renin mRNA expression was regulated strictly in parallel in both kidneys, a low-salt diet or furosemide treatment stimulating and a high-salt diet suppressing it. We conclude from these findings that salt delivery to the tubules is not an essential requirement for the upregulation of COX-2 by salt deficiency or by loop diuretics in the rat kidney cortex nor is it for chronic stimulation of renin mRNA expression.

Differential regulation of renin and Cox-2 expression in the renal cortex of C57Bl/6 mice

Based on the controversy about the relevance of cyclooxygenase-2 (Cox-2)-derived prostanoids from the macula densa for the control of the renin system, this study aimed to determine the interrelation between Cox-2 and renin expression in the mouse kidney. In control mice renin mRNA was readily detectable whilst renocortical Cox-2 mRNA abundance was at the detection limit of the RNase protection assay and no specific signals for Cox-2 were obtained by in situ hybridization or Western blot analysis. Experimental maneuvers such as low-salt diet, treatment with loop diuretics or angiotensin I converting enzyme inhibitors clearly increased renin mRNA abundance up to sevenfold, but under none of these conditions renocortical Cox-2 mRNA levels were significantly changed. Moreover, the strong stimulation of renin expression by angiotensin I-converting enzyme inhibition was not changed by the cyclooxygenase inhibitor ibuprofen, which in turn clearly lowered tissue prostanoid content. Our data suggest a marked divergence of renin and Cox-2 expression in the kidney cortex of C57Bl/6 mice with no clear evidence for a role of Cox-2-derived prostanoids from the macula densa in the regulation of renin expression.

Doppler ultrasonography in posttransplant renal artery stenosis: a reliable tool for assessing effectiveness of revascularization?

BACKGROUND

Renal artery stenosis is usually treated by angioplasty and stenting, but the effectiveness of graft perfusion is difficult to establish on clinical grounds.

METHODS

We compared changes in Doppler ultrasound parameters such as resistive index and peak systolic velocity with concomitant changes in renal vascular resistances, renal blood velocity, and wall shear stress measured before and 1 month after percutaneous transluminal angioplasty and stenting in 12 renal transplant patients with renal artery stenosis.

RESULTS

After revascularization, peak systolic velocity and resistive index normalized in all patients. Changes in peak systolic velocity (-72%; P<0.001 vs. basal) were positively correlated (P<0.0001; r=0.87) with those in renal blood velocity (-88%; P<0.01 vs. basal) and with those (P<0.0005; r=0.80) in wall shear stress (-97%; P<0.005). Changes in resistive index (+21%; P<0.005) were negatively correlated (P=0.009; r=0.51) with those in renal vascular resistances (-40%; P<0.01). Changes in Doppler parameters (resistive index and peak systolic velocity) reflected those in renal vascular resistances and renal blood velocity with 100% sensitivity and specificity.

CONCLUSIONS

Doppler ultrasound is a reliable, noninvasive, and easily available tool for identifying subjects who may benefit from kidney graft revascularization and to assess the effectiveness of the procedure.

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.

Cyclooxygenase-2 contributes to elevated renin in the early postnatal period in rats

We asked whether cyclooxygenase (COX) activity controls the renin-angiotensin system in the postnatal period. During kidney development, renin peaked at postnatal days 0-1 at the mRNA, tissue protein [renal renin concentration (RRC)], and plasma renin concentration (PRC) levels and was widely expressed along preglomerular vessels. PRC and renin mRNA expression was elevated until weaning in the 4th postnatal week compared with adult rats. Renocortical COX-2 was restricted to Tamm-Horsfall protein-positive cells in the thick ascending limb of Henle's loop, and cortical COX-2 mRNA and protein expression were elevated along with PRC in the 2nd and 3rd postnatal weeks. In contrast, cortical COX-1 expression was constant, but medullary COX-1 expression increased eightfold from the 1st to 4th postnatal week. A COX-2-selective blocker, parecoxib, and a nonselective blocker, indomethacin, given in a period with COX-2 induction from postnatal day 6 to day 12, markedly decreased PRC, but not renin mRNA or RRC. Inhibition of angiotensin AT(1) receptors by candesartan from postnatal day 1 to day 5 increased COX-2 mRNA (2.5-fold), protein, and distribution, renin mRNA (7-fold) and PRC (20- to 70-fold), but had no influence on COX-1 mRNA. Thus, due to very low levels of expression, COX-2 is unlikely to be responsible for the birth peak of renin, but COX-2 activity supports renin secretion later in the suckling period. ANG II negatively feeds back on renocortical COX-2 expression in the 1st postnatal days with high activity of the renin system. We suggest that suckling in the rat is correlated to an enhanced, COX-2-mediated, secretory activity of renin-producing juxtaglomerular cells.

Tyrosine phosphorylation of I-kappa B kinase alpha/beta by protein kinase C-dependent c-Src activation is involved in TNF-alpha-induced cyclooxygenase-2 expression

The signaling pathway involved in TNF-alpha-induced cyclooxygenase-2 (COX-2) expression was further studied in human NCI-H292 epithelial cells. A protein kinase C (PKC) inhibitor (staurosporine), tyrosine kinase inhibitors (genistein and herbimycin A), or a Src kinase inhibitor (PP2) attenuated TNF-alpha- or 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced COX-2 promoter activity. TNF-alpha- or TPA-induced I-kappaB kinase (IKK) activation was also blocked by these inhibitors, which reversed I-kappaBalpha degradation. Activation of c-Src and Lyn kinases, two Src family members, was inhibited by the PKC, tyrosine kinase, or Src kinase inhibitors. The dominant-negative c-Src (KM) mutant inhibited induction of COX-2 promoter activity by TNF-alpha or TPA. Overexpression of the constitutively active PKCalpha (PKCalpha A/E) or wild-type c-Src plasmids induced COX-2 promoter activity, and these effects were inhibited by the dominant-negative c-Src (KM), NF-kappaB-inducing kinase (NIK) (KA), or IKKbeta (KM) mutant. The dominant-negative PKCalpha (K/R) or c-Src (KM) mutant failed to block induction of COX-2 promoter activity caused by wild-type NIK overexpression. In coimmunoprecipitation experiments, IKKalpha/beta was found to be associated with c-Src and to be phosphorylated on its tyrosine residues after TNF-alpha or TPA treatment. Two tyrosine residues, Tyr(188) and Tyr(199), near the activation loop of IKKbeta, were identified to be crucial for NF-kappaB activation. Substitution of these residues with phenylalanines attenuated COX-2 promoter activity and c-Src-dependent phosphorylation of IKKbeta induced by TNF-alpha or TPA. These data suggest that, in addition to activating NIK, TNF-alpha also activates PKC-dependent c-Src. These two pathways cross-link between c-Src and NIK and converge at IKKalpha/beta, and go on to activate NF-kappaB, via serine phosphorylation and degradation of IkappaB-alpha, and, finally, to initiate COX-2 expression.

Interactions between COX-2 and the renin-angiotensin system in the kidney

AIM

In adult mammalian kidney, COX-2 expression is found in a restricted subpopulation of cells. The two sites of renal COX-2 localization detected in all species to date are the macula densa (MD) and associated cortical thick ascending limb cells (cTALH) and medullary interstitial cells. Physiological regulation of COX-2 in these cellular compartments suggests functional roles for eicosanoid products of the enzyme. In the MD region, COX-2 expression increases in high renin states [salt restriction, angiotensin converting enzyme (ACE) inhibition, renovascular hypertension], and selective COX-2 inhibitors significantly decrease plasma renin levels and renal renin activity and mRNA expression. An important role for COX-2-derived prostanoids in regulation of renin expression and secretion has also been determined by using mice with selective genetic deletion of either the COX-1 or COX-2 gene. There is evidence for negative regulation of MD/cTALH COX-2 by angiotensin II and by glucocorticoids and mineralocorticoids, suggesting that in the kidney, cortical COX-2 expression is regulated in part by alterations in activity of the renin-angiotensin system.

Inhibition of cyclooxygenase-2: effects on renin secretion and expression in fetal lambs

The importance of prostaglandins in the regulation of the renin-angiotensin system during development is not known. These experiments were conducted to examine the effects of prostaglandin synthesis inhibitors on basal and isoproterenol-induced plasma renin concentration and renin gene expression in the late-gestation fetal lamb. Eighteen lamb fetuses ranging in gestational age from 129 to 138 days underwent surgical insertion of femoral arterial and venous catheters under general endotracheal anesthesia. After a period of recovery, animals underwent an infusion of isoproterenol after administration of a saline bolus (control experiments); 24-48 h later a second study was performed after administration of NS-398, a cyclooxygenase (COX)-2 inhibitor, or saline for a second control study. Administration of COX-2 inhibitor significantly reduced baseline plasma renin levels and attenuated responses in fetal renin secretion to isoproterenol infusions. Renal cortical cells from animals receiving COX-2 inhibitor had significantly lower levels of renin mRNA compared with animals receiving only saline. Renal cortical cells in culture from animals receiving only saline exhibited increased levels of renin mRNA when treated with isoproterenol, forskolin, or IBMX. Only forskolin increased renin mRNA levels in renal cortical cells in culture from animals receiving COX-2 inhibitor. We conclude that prostaglandins play a stimulatory role in the regulation of the renin-angiotensin system and are necessary for beta-adrenergic stimulation of renin secretion and gene expression in the late-gestation fetal lamb.

Role of macula densa cyclooxygenase-2 in renovascular hypertension

Upregulation of the inducible cyclooxygenase (COX-2) in the macula densa accompanies the activation of the juxtaglomerular apparatus in many high-renin conditions. The functional role of COX-2 in these disease states is poorly understood. We tested whether COX-2 is required to increase renin in renovascular hypertension. Rats with established two-kidney, one-clip (2K1C) hypertension were treated for 2 wk with two different inhibitors of COX-2, NS-398 and rofecoxib, respectively. Hypertension in 2K1C rats was not affected or slightly enhanced by COX-2 inhibition, as measured intra-arterially in conscious animals. The increase in plasma renin activity was also unchanged by both rofecoxib and NS-398. The number of glomeruli with a renin-positive juxtaglomerular apparatus was elevated in clipped kidneys and decreased in contralateral kidneys of 2K1C rats. This pattern was unaltered by COX-2 inhibition. To test the effects of COX-2 blockade on a primarily macula densa-mediated stimulus, we studied salt depletion for comparison. A low-salt diet induced a significant increase in plasma renin activity, which was partially inhibited by treatment with NS-398. We conclude that inhibition of COX-2 in established renovascular hypertension does not affect renin synthesis or release. Thus either COX-2 is not necessary for the macula densa mechanism or the macula densa is not important for maintaining high renin in renovascular hypertension.

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.

COX-2 inhibition potentiates the antiproteinuric effect of enalapril in uninephrectomized SHR

PGE(2) and PGI(2) reduce extracellular matrix deposition and their production is altered after ACE inhibitor (ACEi) treatment. We therefore hypothesized that cyclooxygenase (COX)-2 inhibition would exacerbate renal injury and antagonize the effects of ACEi. To test these hypotheses, WKY and SHR were uninephrectomized (UNX) and treated with either vehicle, enalapril, NS398 or enalapril+NS398. NS398 did not affect systolic blood pressure nor antagonize the antihypertensive effect of enalapril. Urinary protein excretion in UNX WKY was significantly decreased after treatment with either enalapril or NS398. In UNX SHR, enalapril reduced proteinuria, but NS398 alone had no effect. Administration of both drugs, however, further reduced proteinuria. In UNX WKY, treatment with either NS398 alone or both drugs reduced glomerular volume and similar results were observed in SHR. Surprisingly, these results disprove our original hypothesis and suggest that inhibition of COX-2 provides additional renoprotection to that of enalapril alone.

Effects of cyclooxygenase-2 (COX-2) inhibition on plasma and renal renin in diabetes

COX-2-derived prostaglandins (PG) have been suggested to be important modulators of renin release and expression. However, the role of COX-2 in various high-renin states is still being debated. In the present studies we explored the role of COX-2-derived PG on basal and angiotensin converting enzyme inhibitor (ACEI)-stimulated plasma and renal renin concentrations (PRC and RRC, RIA), and mRNA expression (RmRNA, RNAse protection assay) in experimental diabetes (DM). Groups of moderately hyperglycemic (n = 5, approximately 350 mg/dl), streptozotocin-diabetic rats (D) after 3 weeks of DM were treated with a selective COX-2 inhibitor, MF-tricyclic (MF, 5 mg/kg/day for 10 days in food), the combination of MF and the ACEI enalapril (3 mg/kg/day), enalapril alone, or vehicle (MF-free chow), for 10 days. Non-diabetic control rats, fed MF-free chow, were also studied. All groups of diabetic rats demonstrated similar glycemic control. Treatment with ACEI resulted in significant elevations in PRC, RRC and RmRNA as compared to non-ACEI treated groups of diabetic and control rats. A similar rise in these parameters was observed in the rats treated with the combination of ACEI and MF. Furthermore, in diabetic rats treated with MF alone, PRC and RRC were similar to vehicle-treated animals. Diabetic rats demonstrated higher urinary PG as compared to controls. MF-treated rats demonstrated a significant reduction in urinary PG excretion. In summary, selective COX-2 inhibition influenced neither basal renin status nor ACEI-induced renin release and expression in diabetic rats. These findings do not support a significant role for COX-2 in mediating renin status in diabetes.

Cyclosporine A suppresses cyclooxygenase-2 expression in the rat kidney

On the basis of recent evidence that the cyclooxygenase-2 (COX-2) gene promoter contains functional binding sites for the nuclear factor of activated T cells (NFAT) and that COX-2 is expressed in a regulated fashion in the kidney, this study aimed to assess the effect of immunosuppressants on COX-2 expression in the kidney. Therefore, Wistar-Kyoto rats were treated with cyclosporine A (CsA; 15 mg/kg per day) or tacrolimus (5 mg/kg per day) for 7 d each. Both drugs markedly lowered COX-2 expression while COX-1 expression remained unaltered. Furthermore, CsA blunted the increase of renocortical COX-2 expression in response to low salt intake or a combination of low-salt diet with the ACE inhibitor ramipril (10 mg/kg per day), which strongly stimulates renocortical COX-2 expression. At the same time, calcineurin inhibitors moderately enhanced basal as well as stimulated renin secretion and renin gene expression. These findings suggest that inhibition of calcineurin could be a crucial determinant for the regulated expression of COX-2 in the kidney. Inhibition of COX-2 expression may therefore at least in part account for the well-known adverse effects of immunosuppressants in the kidney. Moreover, our data suggest that the stimulation of the renin system by low salt and by ACE inhibitors is not essentially mediated by COX-2 activity.

Anticancer activity of Scutellaria baicalensis and its potential mechanism

OBJECTIVE

Scutellaria baicalensis is a widely used Chinese herbal medicine that historically is used in anti-inflammatory and anticancer therapy. The aim of the study is to determine its ability to inhibit human cancer cells in vitro and to determine whether its anticancer activity is because of the inhibition of prostaglandin E(2) (PGE(2)) production that is derived from arachidonic acid through cyclooxygenase-2 (COX-2) pathway.

METHODS

Cell lines from the most common human cancers, including squamous cell carcinoma (SCC-25, KB), breast cancer (MCF-7), hepatocellular carcinoma (HepG2), prostate carcinoma (PC-3 and LNCaP), and colon cancer (KM-12 and HCT-15) were tested. The cells were treated with various concentrations of Scutellaria baicalensis (0.1-100 mg/mL) for 72 hours. Percentage of viable cells after treatment was assessed using a trypan blue dye exclusion assay and the level of PGE(2) production was determined by enzyme immunoassay (EIA).

RESULTS

Scutellaria baicalensis demonstrated a strong dose-dependent growth inhibition in all cell lines. Inhibition concentration at 50% (IC(50)) for HepG2, MCF-7, PC-3, LNCaP, KM-12, HCT-15, KB and SCC-25 cells was 1.1, 0.9, 0.52, 0.82, 1.1, 1.5, 1.0, and 1.2 mg/mL, respectively. Three cell lines (KB, SCC-25, and HepG2) were assessed for the production of PGE(2) and a high level of extracellular (KB and SCC-25) and intracellular PGE(2) (HepG2) was noted. In the presence of Scutellaria baicalensis extract, there was a significant decrease of PGE(2) in a dose-dependent fashion.

CONCLUSIONS

Scutellaria baicalensis strongly inhibits cell growth in all cancer cell lines tested. However, prostate and breast cancer cells (PC-3, LNCaP, and MCF-7) are slightly more sensitive than other type of cancer cells. It also inhibits PGE(2) production, indicating that suppression of tumor cell growth may be due to its ability to inhibit COX-2 activity. This study supports the notion of using Scutellaria baicalensis as a novel anticancer agent to treat various cancers.

Prostaglandins that increase renin production in response to ACE inhibition are not derived from cyclooxygenase-1

It is well known that nonselective, nonsteroidal anti-inflammatory drugs inhibit renal renin production. Our previous studies indicated that angiotensin-converting enzyme inhibitor (ACEI)-mediated renin increases were absent in rats treated with a cyclooxygenase (COX)-2-selective inhibitor and in COX-2 -/- mice. The current study examined further whether COX-1 is also involved in mediating ACEI-induced renin production. Because renin increases are mediated by cAMP, we also examined whether increased renin is mediated by the prostaglandin E(2) receptor EP(2) subtype, which is coupled to G(s) and increases cAMP. Therefore, we investigated if genetic deletion of COX-1 or EP(2) prevents increased ACEI-induced renin expression. Age- and gender-matched wild-type (+/+) and homozygous null mice (-/-) were administered captopril for 7 days, and plasma and renal renin levels and renal renin mRNA expression were measured. There were no significant differences in the basal level of renal renin activity from plasma or renal tissue in COX-1 +/+ and -/- mice. Captopril administration increased renin equally [plasma renin activity (PRA): +/+ 9.3 +/- 2.2 vs. 50.1 +/- 10.9; -/- 13.7 +/- 1.5 vs. 43.9 +/- 6.6 ng ANG I x ml(-1) x h(-1); renal renin concentration: +/+ 11.8 +/- 1.7 vs. 35.3 +/- 3.9; -/- 13.0 +/- 3.0 vs. 27.8 +/- 2.7 ng ANG I x mg protein(-1) x h(-1); n = 6; P < 0.05 with or without captopril]. ACEI also increased renin mRNA expression (+/+ 2.4 +/- 0.2; -/- 2.1 +/- 0.2 fold control; n = 6-10; P < 0.05). Captopril led to similar increases in EP(2) -/- compared with +/+. The COX-2 inhibitor SC-58236 blocked ACEI-induced elevation in renal renin concentration in EP(2) null mice (+/+ 24.7 +/- 1.7 vs. 9.8 +/- 0.4; -/- 21.1 +/- 3.2 vs. 9.3 +/- 0.4 ng ANG I x mg protein(-1) x h(-1); n = 5) as well as in COX-1 -/- mice (SC-58236-treated PRA: +/+ 7.3 +/- 0.6; -/- 8.0 +/- 0.9 ng ANG I x ml(-1) x h(-1); renal renin: +/+ 9.1 +/- 0.9; -/- 9.6 +/- 0.5 ng ANG I x mg protein(-1) x h(-1); n = 6-7; P < 0.05 compared with no treatment). Immunohistochemical analysis of renin expression confirmed the above results. This study provides definitive evidence that metabolites of COX-2 rather than COX-1 mediate ACEI-induced renin increases. The persistent response in EP(2) nulls suggests involvement of prostaglandin E(2) receptor subtype 4 and/or prostacyclin receptor (IP).

Role of prostanoids in regulation of the renin-angiotensin-aldosterone system by salt intake

We investigated the effect of cyclooxygenase (COX) activity on the regulation of the renin-angiotensin-aldosterone system by salt intake. Therefore, Sprague-Dawley rats were subjected to different salt diets [0.02, 0.6, and 8% NaCl (wt/wt)] and treated with the selective COX-2 inhibitor rofecoxib (10 mg x kg body wt(-1) x day(-1)) or with ketorolac at a dose selective for COX-1 inhibition (2 mg x kg body wt(-1) x day(-1)) for 3, 7, 14, and 21 days. Rofecoxib and ketorolac caused a similar reduction of renocortical PGE2 formation with a low-salt diet. Rofecoxib did not change plasma renin activity or renocortical renin mRNA abundance with any of the diets but clearly lowered plasma aldosterone concentration. In contrast, ketorolac delayed the increase in plasma renin activity and of renin mRNA in response to low salt intake but did not change plasma aldosterone concentration. Prolonged treatment with rofecoxib but not with ketorolac caused an upregulation of COX-2 expression while COX-1 mRNA abundance remained unchanged. These findings suggest that COX-1-derived, but not COX-2-derived, prostanoids are of relevance for the regulation of the renin system by salt intake.

Angiotensin II feedback is a regulator of renocortical renin, COX-2, and nNOS expression

Salt restriction leads to parallel increases of renin, cyclooxygenase-2 (COX-2), and neuronal nitric oxide synthase (nNOS) gene expression in the juxtaglomerular apparatus of rat kidneys. Because the upregulation of these genes is strongly enhanced if salt restriction is combined with inhibition of the renin-angiotensin-aldosterone system, our study aimed to find out whether the juxtaglomerular expressions of renin, COX-2, and nNOS are subject to a common direct negative feedback control by ANG II. For this purpose, male Sprague-Dawley rats were fed a low-salt diet (0.02% wt/wt) with or without additional treatment with the ANG I-converting enzyme (ACE) inhibitor ramipril (10 mg x kg body wt(-1) x day(-1)) for 1 wk, and renocortical renin, COX-2, and nNOS mRNAs were assayed. To narrow down possible indirect effects of the ACE inhibitor that may result from insufficient aldosterone production, the animals received mineralocorticoid substitution with fludrocortisone (6 mg. kg body wt(-1) x day(-1)). Thus mineralocorticoid substitution prevented the fall of systolic blood pressure and of glomerular filtration induced by ramipril in rats on low-salt diet. Although fludrocortisone had no effect on basal renin, COX-2, and nNOS mRNA, it clearly attenuated the threefold increases of both renin and COX-2 mRNA in response to low-salt diet. In rats on low-salt diet, ramipril further increased renin mRNA ninefold, COX-2 mRNA fourfold, and nNOS 2.5-fold in the absence of fludrocortisone. In the presence of fludrocortisone, ramipril increased renin mRNA 10-fold, COX-2 mRNA 2.5-fold, and nNOS mRNA 2.5-fold. These data indicate that mineralocorticoid substitution lowers the overall expression of juxtaglomerular renin and COX-2 during low-salt intake and attenuates a further rise of COX-2 expression by ACE inhibition, but it does not change the stimulatory effect of ACE inhibition on renin and nNOS expression. We conclude that the expression of renin, COX-2, and nNOS in the juxtaglomerular apparatus during low-salt diet is markedly limited by a direct feedback inhibition through ANG II.

Stenosis-dependent role of nitric oxide and prostaglandins in chronic renal ischemia

The role of nitric oxide (NO) and prostaglandins (PG) in modifying renal hemodynamics was examined in clipped and nonclipped kidneys of unilateral renal artery stenosis. Chronic unilateral renal ischemia was established by 4-wk-clipping the left renal artery of canine kidneys, and renal interstitial nitrate+nitrite and PGE(2) contents were evaluated by the microdialysis technique. Unilateral renal artery stenosis caused 45 +/- 1 and 73 +/- 1% decrements in renal plasma flow (RPF) in moderately and severely clipped kidneys and 21 +/- 3% decrements in nonclipped kidneys with severe stenosis. Renal nitrate+nitrite decreased in moderately (-31 +/- 1%) and severely clipped kidneys (-63 +/- 4%). N(omega)-nitro-L-arginine methyl ester reduced RPF (-56 +/- 3%) and glomerular filtration rate (GFR; -54 +/- 3%) in moderately clipped kidneys, whereas this inhibitory effect was abolished in severely clipped kidneys. In contrast, renal PGE(2) contents increased modestly in moderate clipping and were markedly elevated in severely clipped kidneys (from 111 +/- 7 to 377 +/- 22 pg/ml); sulpyrine impaired renal hemodynamics only in severely clipped kidneys. In contralateral nonclipped kidneys, although renal PGE(2) was not increased, sulpyrine reduced RPF (-32 +/- 1%) and GFR (-33 +/- 3%) in severe stenosis. Collectively, NO plays a substantial role in maintaining renal hemodynamics both under basal condition and in moderate renal artery stenosis, whereas the contributory role shifts from NO to PG as renal artery stenosis progresses. Furthermore, because intrarenal angiotensin II is reported to increase in nonclipped kidneys, unilateral severe ischemia may render the nonclipped kidney susceptible to PG inhibition.

Role of renal nerves in stimulation of renin, COX-2, and nNOS in rat renal cortex during salt deficiency

We investigated a possible involvement of the sympathetic nervous system in the parallel increase of renin, cyclooxygenase-2 (COX-2), and neuronal nitric oxide synthase (nNOS) gene expression in the juxtaglomerular apparatus of rat kidneys induced by salt deficiency. Therefore, we determined the effects of renal denervation and the beta-adrenoreceptor antagonist metoprolol (50 mg/kg body wt po, twice a day) on renocortical expression of renin, COX-2, and nNOS in rats fed a low-salt (0.02% wt/wt) diet or treated for 1 wk with ramipril (10 mg/kg body wt) in combination with a low-salt diet. We found that a low-salt diet in combination with ramipril strongly increased renocortical mRNA levels of renin, COX-2, and nNOS 9-, 7-, and 2.5-fold, respectively. Treatment with metoprolol did not change basal expression of the three genes or induction of renin and COX-2 gene expression, while induction of nNOS expression was clearly attenuated. Similarly, unilateral renal denervation attenuated induction of nNOS expression but had no effect on all other parameters. These findings suggest that beta-adrenergic stimulation is not required for stimulation of renin and COX-2 gene expression in the juxtaglomerular apparatus during salt deficiency. However, beta-adrenoreceptor activity or renal nerve activity appears to be required for the full stimulation of nNOS expression by low salt intake or combined with angiotensin-converting enzyme inhibition.

Conjugated polyhydroxybenzene derivatives block tumor necrosis factor-alpha-mediated nuclear factor-kappaB activation and cyclooxygenase-2 gene transcription by targeting IkappaB kinase activity

Because the transcription factor, nuclear factor (NF)-kappaB, plays a key role in cellular inflammatory and immune responses, components of the NF-kappaB-activating signaling pathways are frequently used as targets for anti-inflammatory agents. This study shows that 2-(3',4'-dihydroxyphenyl)-5-hydroxybenzo[b]furan (GF-015) and 2,3-di(3',4'-dihydroxy-transstyryl) pyridine (GF-90), two conjugated polyhydroxybenzene derivatives, inhibited a common step in NF-kappaB activation in human NCI-H292 epithelial cells by preventing tumor necrosis factor (TNF)-alpha- and 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced IkappaB kinase (IKK) complex activation. Both agents inhibited the TNF-alpha- or TPA-induced expression of cyclooxygenase (COX)-2 mRNA and protein, COX-2 promoter activity, and prostaglandin E2 (PGE2) production. Overexpression of wild-type NF-kappaB-inducing kinase, IKKalpha, and IKKbeta led, respectively, to 3.5-, 2.6-, and 2.6-fold increases in COX-2 promoter activity, and these effects were inhibited by both compounds. GF-015 and GF-90 also prevented the TNF-alpha- and TPA-induced activation of IKK and NF-kappaB-specific DNA-protein binding activity. These results suggest that the inhibitory effect of GF-015 and GF-90 on TNF-alpha-induced COX-2 protein expression was caused by suppression of IKK activity and NF-kappaB activation in the COX-2 promoter, resulting in attenuation of COX-2 gene expression and PGE2 production.