Role of prostaglandin E receptor EP1 subtype in the development of renal injury in genetically hypertensive rats

EP1 receptor antagonism mitigates early and late stage renal fibrosis

AIM

Renal fibrosis is a major driver of chronic kidney disease, yet current treatment strategies are ineffective in attenuating fibrogenesis. The cyclooxygenase/prostaglandin system plays a key role in renal injury and holds great promise as a therapeutic target. Here, we used a translational approach to evaluate the role of the PGE₂ -EP₁ receptor in the pathogenesis of renal fibrosis in several models of kidney injury, including human (fibrotic) kidney slices.

METHODS

The anti-fibrotic efficacy of a selective EP₁ receptor antagonist (SC-19220) was studied in mice subjected to unilateral ureteral obstruction (UUO), healthy and fibrotic human precision-cut kidney slices (PCKS), Madin-Darby Canine Kidney (MDCK) cells and primary human renal fibroblasts (HRFs). Fibrosis was evaluated on gene and protein level using qPCR, western blot and immunostaining.

RESULTS

EP₁ receptor inhibition diminished fibrosis in UUO mice, illustrated by a decreased protein expression of fibronectin (FN) and α-smooth muscle actin (αSMA) and a reduction in collagen deposition. Moreover, treatment of healthy human PCKS with SC-19220 reduced TGF-β-induced fibrosis as shown by decreased expression of collagen 1A1, FN and αSMA as well as reduced collagen deposition. Similar observations were made using fibrotic human PCKS. In addition, SC-19220 reduced TGF-β-induced FN expression in MDCK cells and HRFs.

CONCLUSION

This study highlights the EP₁ receptor as a promising target for preventing both the onset and late stage of renal fibrosis. Moreover, we provide strong evidence that the effect of SC-19220 may translate to clinical care since its effects were observed in UUO mice, cells and human kidney slices.

Involvement of Fatty Acids and Their Metabolites in the Development of Inflammation in Atherosclerosis

Despite all the advances of modern medicine, atherosclerosis continues to be one of the most important medical and social problems. Atherosclerosis is the cause of several cardiovascular diseases, which are associated with high rates of disability and mortality. The development of atherosclerosis is associated with the accumulation of lipids in the arterial intima and the disruption of mechanisms that maintain the balance between the development and resolution of inflammation. Fatty acids are involved in many mechanisms of inflammation development and maintenance. Endothelial cells demonstrate multiple cross-linkages between lipid metabolism and innate immunity. In addition, these processes are linked to hemodynamics and the function of other cells in the vascular wall, highlighting the central role of the endothelium in vascular biology.

Agonism of Prostaglandin E2 Receptor 4 Ameliorates Tubulointerstitial Injury in Nephrotoxic Serum Nephritis in Mice

Selectively targeting the E-type prostanoid receptor 4 (EP4) might be a new therapeutic option in the treatment of glomerulonephritis (GN), since the EP4 receptor is expressed on different immune cells, resident kidney cells, and endothelial cells, which are all involved in the pathogenesis of immune-complex GN. This study aimed to evaluate the therapeutic potential and to understand the mode of action of EP4 agonist in immune-complex GN using the murine model of nephrotoxic serum nephritis (NTS). In vivo, NTS mice were treated two times daily with two different doses of an EP4 agonist ONO AE1-329 or vehicle for 14 days total. The effect of PGE2 and EP4 agonism and antagonism was tested on murine distal convoluted tubular epithelial cells (DCT) in vitro. In vivo, the higher dose of the EP4 agonist led to an improved NTS phenotype, including a reduced tubular injury score and reduced neutrophil gelatinase-associated lipocalin (NGAL) and blood urea nitrogen (BUN) levels. EP4 agonist treatment caused decreased CD4+ T cell infiltration into the kidney and increased proliferative capacity of tubular cells. Injection of the EP4 agonist resulted in dose-dependent vasodilation and hypotensive episodes. The low-dose EP4 agonist treatment resulted in less pronounced episodes of hypotension. In vitro, EP4 agonism resulted in cAMP production and increased distal convoluted tubular (DCT) proliferation. Taken together, EP4 agonism improved the NTS phenotype by various mechanisms, including reduced blood pressure, decreased CD4+ T cell infiltration, and a direct effect on tubular cells leading to increased proliferation probably by increasing cAMP levels.

Inhibition of Endothelin system during the postnatal nephrogenic period in the rat. Its relationship with hypertension and renal disease in adulthood

The aim of this work was to study the effect of a high sodium (HS) diet on blood pressure and renal function in male adult rats that have been treated with a dual Endothelin receptor antagonist (ERA) during their early postnatal period (day 1 to 20 of life). Male Sprague-Dawley rats were divided in four groups: C_NS: control rats with normosodic diet; ERA_NS: ERA-treated rats with normosodic diet; C_HS: control rats with high sodium diet; ERA_HS: ERA-treated rats with HS diet. Systolic blood pressure (SBP) was recorded before and after the diet and 24-hour metabolic cage studies were performed. AQP2 and α-ENac expressions were measured by western blot and real time PCR in the renal medulla. Vasopressin (AVP) pathway was evaluated by measuring V2 receptor and adenylyl cyclase 6 (AC6) expression and cAMP production in the renal medulla. Pre-pro ET-1mRNA was also evaluated in the renal medulla. Only rats that had been treated with an ERA during their postnatal period increased their SBP after consumption of a HS diet, showing an impaired capacity to excrete sodium and water, i.e. developing salt sensitivity. This salt sensitivity would be mediated by an increase in renomedullary expression and activity of AQP2 and α-ENaC as a consequence of increased AC6 expression and cAMP production and/or a decreased ET-1 production in the renal medulla. The knowledge of the molecular mechanisms underlying the perinatal programming of salt sensitive hypertension will allow the development of reprogramming strategies in order to avoid this pathology.

Prostaglandin E2 receptor EP1 (PGE2/EP1) deletion promotes glomerular podocyte and endothelial cell injury in hypertensive TTRhRen mice

Prostaglandin E2 receptor EP1 (PGE₂/EP₁) promotes diabetic renal injury, and EP₁ receptor deletion improves hyperfiltration, albuminuria, and fibrosis. The role of EP₁ receptors in hypertensive kidney disease (HKD) remains controversial. We examined the contribution of EP₁ receptors to HKD. EP₁ null (EP₁^-/-) mice were bred with hypertensive TTRhRen mice (Htn) to evaluate kidney function and injury at 24 weeks. EP₁ deletion had no effect on elevation of systolic blood pressure in Htn mice (HtnEP₁^-/-) but resulted in pronounced albuminuria and reduced FITC-inulin clearance, compared with Htn or wild-type (WT) mice. Ultrastructural injury to podocytes and glomerular endothelium was prominent in HtnEP₁^-/- mice; including widened subendothelial space, subendothelial lucent zones and focal lifting of endothelium from basement membrane, with focal subendothelial cell debris. Cortex COX2 mRNA was increased by EP₁ deletion. Glomerular EP₃ mRNA was reduced by EP₁ deletion, and EP₄ by Htn and EP₁ deletion. In WT mice, PGE₂ increased chloride reabsorption via EP₁ in isolated perfused thick ascending limb (TAL), but PGE₂ or EP₁ deletion did not affect vasopressin-mediated chloride reabsorption. In WT and Htn mouse inner medullary collecting duct (IMCD), PGE₂ inhibited vasopressin-water transport, but not in EP₁^-/- or HtnEP₁^-/- mice. Overall, EP₁ mediated TAL and IMCD transport in response to PGE₂ is unaltered in Htn, and EP₁ is protective in HKD.

Effect of levosimendan, an inodilator, on streptozotocin-induced diabetic nephropathy in rats

This study examined the effect of levosimendan on streptozotocin-induced early diabetic nephropathy. Rats were distributed into four groups and treated for six weeks. The first and third group received either vehicle or levosimendan (1 mg/kg/day) for the last three weeks, respectively. The second and fourth groups were rendered diabetic by a single intraperitoneal injection of streptozotocin (60 mg/kg) and were treated as the first and third groups, respectively. In the untreated diabetic group, there was a significant decrease in body weight, polyuria and hyperglycemia as well as, increased urinary albumin/creatinine ratio (UACR) and N-acetyl-β-D-glucosaminidase (NAG)/creatinine ratio (UNCR) with no change in creatinine clearance. In addition, diabetes was associated with increased oxidative stress as evidenced by reduced plasma total antioxidant capacity (TAC) and catalase activity and increased plasma malondialdhyde (MDA) and the inflammatory marker, tumor necrosis factor-alpha, (TNF-α). Kidneys from streptozotocin-treated rats showed focal clear renal tubular cells affecting proximal convoluted tubules and mild interstitial fibrosis at the cortico-medullary junction. Levosimendan significantly attenuated the streptozotocin-induced physiological and biochemical changes and there was less clear renal tubular cells. This study shows that levosimendan ameliorated some of the changes seen in streptozotocin-induced early diabetic nephropathy in rats. This could be partly due to its antioxidative and anti-inflammatory effects.

Dietary oleuropein and its new acyl-derivate attenuate murine lupus nephritis through HO-1/Nrf2 activation and suppressing JAK/STAT, NF-κB, MAPK and NLRP3 inflammasome signaling pathways

Systemic lupus erythemathosus (SLE) is a chronic inflammatory and autoimmune disease which can affect multiple organ systems, without an effective and safe treatment. Olive leaf extracts are of special interest for their therapeutic effects. Oleuropein (OL) is the most abundant constituents of olive leaf extract and possesses many beneficial properties. In this study, we evaluated the effects of dietary OL and its new derivate, peracetylated oleuropein (Per-OL), in a pristane-induced SLE model. Mice received an injection of pristane or saline solution and were fed with experimental diets: enriched with OL and Per-OL. The levels of proinflammatory cytokines and markers were evaluated by enzyme-linked immunosorbent assay. The protein expressions of inducible nitric oxide synthase, microsomal prostaglandin E synthase 1, heme oxygenase (HO-1), nuclear factor E2-related factor 2 (Nrf2), mitogen-activated protein kinases (MAPKs), Janus kinase/signal transducer and activator of transcription (JAK/STAT), nuclear transcription factor-kappa B (NF-κB) and inflammasome nucleotide-binding domain, leucine-rich repeats-containing family, pyrin domain-containing-3 (NLRP3) pathways activation were determined in kidneys by Western blot. OL and Per-OL significantly reduced renal damage and decreased serum matrix metalloproteinase 3 and prostaglandine E₂ kidneys levels. Our findings indicate that Nrf2 and HO-1 antioxidant protein expressions were up-regulated in mice fed with OL and Per-OL diets, whereas the activation of JAK/STAT, MAPK, NF-κB and NLRP3 inflammasome pathways was significantly ameliorated. These results suggest that OL and Per-OL supplementation might provide a new alternative approach as a preventive/palliative treatment of nephritis in SLE management.

Maternal Protein Restriction Alters the Renal Ptger1 DNA Methylation State in SHRSP Offspring

We previously reported that maternal protein restriction (LP) during pregnancy increases salt sensitivity in offspring using the Stroke-Prone Spontaneously Hypertensive Rat (SHRSP). In the present study, we focus on DNA methylation profiles of prostaglandin E receptor 1 gene (ptger1), which is known to be associated with hypertension. We evaluated the ptger1 DNA methylation status via bisulfite sequencing, and analyzed the expression of ptger1-related genes. The results of these analyses showed that, compared to controls, the LP-S offspring exhibited both marked ptger1 hypermethylation, and significantly increased ptger1 expression. Moreover, they also exhibited significantly decreased expression of the downstream gene epithelial Na⁺ channel alpha (enacα). Interestingly, LP offspring that were provided with a standard water drinking supply (W) also exhibited increased ptger1 methylation and expression. Together, these results suggest that maternal protein restriction during pregnancy modulates the renal ptger1 DNA methylation state in SHRSP offspring, and thereby likely mediates ptger1 and enacα gene expression to induce salt sensitivity.

Common Impact of Chronic Kidney Disease and Brain Microhemorrhages on Cerebral Aβ Pathology in SHRSP

While chronic kidney disease seems to be an independent risk factor for cognitive decline, its impact on cerebral amyloid-β (Aβ) depositions, one hallmark of Alzheimer's Disease (AD) pathology, has not been investigated. Utilizing 80 male nontransgenic spontaneously hypertensive stroke prone rats (SHRSP) at various ages (12 to 44 weeks), tubulointerstitial renal damage, prevalence of cerebral microhemorrhages and Aβ accumulations were quantified. Using age-adjusted general linear models we investigated the main and interaction effects of renal damage and cerebral microhemorrhages on cerebral Aβ load. In addition, using post mortem human brain tissue of 16 stroke patients we examined the co-localization of perivascular Aβ deposits and small vessel wall damage. Statistical models revealed an age-independent main effect of tubulointerstitial kidney damage on brain Aβ accumulations, which was reinforced by the consecutive presence of cerebral microhemorrhages. Moreover, cerebral microhemorrhages independently predicted brain Aβ burden in SHRSP. In up to 69% of all human cases perivascular Aβ deposits were detected in the direct vicinity of small vessel wall damage. Our results support the associations between vascular pathology and Aβ deposition, and demonstrate a relationship between chronic kidney disease and cerebral Aβ pathology. Hence, our data suggest that prevention of chronic renal damage may reduce cerebral Aβ pathology.

The Role of Endothelin System in Renal Structure and Function during the Postnatal Development of the Rat Kidney

Renal development in rodents, unlike in humans, continues during early postnatal period. We aimed to evaluate whether the pharmacological inhibition of Endothelin system during this period affects renal development, both at structural and functional level in male and female rats. Newborn rats were treated orally from postnatal day 1 to 20 with vehicle or bosentan (Actelion, 20 mg/kg/day), a dual endothelin receptor antagonist (ERA). The animals were divided in 4 groups: control males, control females, ERA males and ERA females. At day 21, we evaluated renal function, determined the glomerular number by a maceration method and by morphometric analysis and evaluated possible structural renal alterations by three methods: 〈alpha〉-Smooth muscle actin (α-SMA) immunohistochemistry, Masson's trichrome and Sirius red staining. The pharmacological inhibition of Endothelin system with a dual ERA during the early postnatal period of the rat did not leads to renal damage in the kidneys of male and female rats. However, ERA administration decreased the number of glomeruli, the juxtamedullary filtration surface area and the glomerular filtration rate and increased the proteinuria. These effects could predispose to hypertension or renal diseases in the adulthood. On the other hand, these effects were more pronounced in male rats, suggesting that there are sex differences that could be greater later in life. These results provide evidence that Endothelin has an important role in rat renal postnatal development. However these results do not imply that the same could happen in humans, since human renal development is complete at birth.

Dietary extra virgin olive oil attenuates kidney injury in pristane-induced SLE model via activation of HO-1/Nrf-2 antioxidant pathway and suppression of JAK/STAT, NF-κB and MAPK activation

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by a widespread organ involvement. Recent studies have suggested that extra virgin olive oil (EVOO) might possess preventive effects on this immunoinflammation-related disease. However, its role in SLE remained unknown. In this work, we evaluated the effects of EVOO diet in a pristane-induced SLE model in mice. Three-month-old mice received an injection of pristane or saline solution and were fed with different experimental diets: sunflower oil diet or EVOO diet. After 24weeks, mice were sacrificed, spleens were collected and kidneys were removed for immunoinflammatory detections. The kidney expression of microsomal prostaglandin E synthase 1, heme oxygenase 1 (HO-1), nuclear factor E2-related factor 2 (Nrf-2), mitogen-activated protein kinases (MAPKs), Janus kinase/signal transducer and activator of transcription (JAK/STAT) and nuclear transcription factor-kappa B (NF-κB) pathways were studied by western blotting. In addition to macroscopic and histological analyses, serum matrix metalloproteinase 3 (MMP-3) levels and proinflammatory cytokines production in splenocytes were evaluated by enzyme-linked immunoassay. We have demonstrated that EVOO diet significantly reduced renal damage and decreased MMP-3 serum and PGE2 kidney levels as well as the proinflammatory cytokines production in splenocytes. Our data indicate that Nrf-2 and HO-1 protein expressions were up-regulated in those mice fed with EVOO and the activation of JAK/STAT, MAPK and NF-κB pathways were drastically ameliorated. These results support the interest of EVOO as a beneficial functional food exerting a preventive/palliative role in the management of SLE.

PGE2, Kidney Disease, and Cardiovascular Risk: Beyond Hypertension and Diabetes

An important measure of cardiovascular health is obtained by evaluating the global cardiovascular risk, which comprises a number of factors, including hypertension and type 2 diabetes, the leading causes of illness and death in the world, as well as the metabolic syndrome. Altered immunity, inflammation, and oxidative stress underlie many of the changes associated with cardiovascular disease, diabetes, and the metabolic syndrome, and recent efforts have begun to elucidate the contribution of PGE2 in these events. This review summarizes the role of PGE2 in kidney disease outcomes that accelerate cardiovascular disease, highlights the role of cyclooxygenase-2/microsomal PGE synthase 1/PGE2 signaling in hypertension and diabetes, and outlines the contribution of PGE2 to other aspects of the metabolic syndrome, particularly abdominal adiposity, dyslipidemia, and atherogenesis. A clearer understanding of the role of PGE2 could lead to new avenues to improve therapeutic options and disease management strategies.

Cytochrome P450 1B1 contributes to increased blood pressure and cardiovascular and renal dysfunction in spontaneously hypertensive rats

PURPOSE

We investigated the contribution of cytochrome P450 (CYP) 1B1 to hypertension and its pathogenesis by examining the effect of its selective inhibitor, 2,4,3',5'-tetramethoxystilbene (TMS), in spontaneously hypertensive rats (SHR).

METHODS

Blood pressure (BP) was measured bi-weekly. Starting at 8 weeks, TMS (600 μg/kg, i.p.) or its vehicle was injected daily. At 14 weeks, samples were collected for measurement.

RESULTS

TMS reversed increased BP in SHR (207 ± 7 vs. 129 ± 2 mmHg) without altering BP in Wistar-Kyoto rats. Increased CYP1B1 activity in SHR was inhibited by TMS (RLU: aorta, 5.4 ± 0.7 vs. 3.7 ± 0.7; heart, 6.0 ± 0.8 vs. 3.4 ± 0.4; kidney, 411 ± 45 vs. 246 ± 10). Increased vascular reactivity, cardiovascular hypertrophy, endothelial and renal dysfunction, cardiac and renal fibrosis in SHR were minimized by TMS. Increased production of reactive oxygen species and NADPH oxidase activity in SHR, were diminished by TMS. In SHR, TMS reduced increased plasma levels of nitrite/nitrate (46.4 ± 5.0 vs. 28.1 ± 4.1 μM), hydrogen-peroxide (36.0 ± 3.7 vs. 14.1 ± 3.8 μM), and thiobarbituric acid reactive substances (6.9 ± 1.0 vs. 3.4 ± 1.5 μM). Increased plasma levels of pro-inflammatory cytokines and catecholamines, and cardiac activity of extracellular signal-regulated kinase, p38 mitogen-activated protein kinase, c-Src tyrosine kinase, and protein kinase B in SHR were also inhibited by TMS.

CONCLUSIONS

These data suggests that increased oxidative stress generated by CYP1B1 contributes to hypertension, increased cytokine production and sympathetic activity, and associated pathophysiological changes in SHR. CYP1B1 could be a novel target for developing drugs to treat hypertension and its pathogenesis.

Antagonism of the prostaglandin E2 EP1 receptor in MDCK cells increases growth through activation of Akt and the epidermal growth factor receptor

The actions of prostaglandin E2 (PGE2) in the kidney are mediated by G protein-coupled E-prostanoid (EP) receptors, which affect renal growth and function. This report examines the role of EP receptors in mediating the effects of PGE2 on Madin-Darby canine kidney (MDCK) cell growth. The results indicate that activation of Gs-coupled EP2 and EP4 by PGE2 results in increased growth, while EP1 activation is growth inhibitory. Indeed, two EP1 antagonists (ONO-8711 and SC51089) stimulate, rather than inhibit, MDCK cell growth, an effect that is lost following an EP1 knockdown. Similar observations were made with M1 collecting duct and rabbit kidney proximal tubule cells. ONO-8711 even stimulates growth in the absence of exogenous PGE2, an effect that is prevented by ibuprofen (indicating a dependence upon endogenous PGE2). The involvement of Akt was indicated by the observation that 1) ONO-8711 and SC51089 increase Akt phosphorylation, and 2) MK2206, an Akt inhibitor, prevents the increased growth caused by ONO-8711. The involvement of the EGF receptor (EGFR) was indicated by 1) the increased phosphorylation of the EGFR caused by SC51089 and 2) the loss of the growth-stimulatory effect of ONO-8711 and SC51089 caused by the EGFR kinase inhibitor AG1478. The growth-stimulatory effect of ONO-8711 was lost following an EGFR knockdown, and transduction of MDCK cells with a dominant negative EGFR. These results support the hypothesis that 1) signaling via the EP1 receptor involves Akt as well as the EGFR, and 2), EP1 receptor pharmacology may be employed to prevent the aberrant growth associated with a number of renal diseases.

Chronic kidney disease: targeting prostaglandin E2 receptors

Chronic kidney disease is a leading cause of morbidity and mortality in the world. A better understanding of disease mechanisms has been gained in recent years, but the current management strategies are ineffective at preventing disease progression. A widespread focus of research is placed on elucidating the specific processes implicated to find more effective therapeutic options. PGE2, acting on its four EP receptors, regulates many renal disease processes; thus EP receptors could prove to be important targets for kidney disease intervention strategies. This review summarizes the major pathogenic mechanisms contributing to initiation and progression of chronic kidney disease, emphasizing the role of hyperglycemia, hypertension, inflammation, and oxidative stress. We have long recognized the multifaceted role of PGs in both the initiation and progression of chronic kidney disease, yet studies are only now seriously contemplating specific EP receptors as targets for therapy. Given the plethora of renal complications attributed to PG involvement in the kidney, this review highlights these pathogenic events and emphasizes the PGE2 receptor targets as options available to complement current therapeutic strategies.

PTGER1 deletion attenuates renal injury in diabetic mouse models

We hypothesized that the EP1 receptor promotes renal damage in diabetic nephropathy. We rendered EP1 (PTGER1, official symbol) knockout mice (EP1(-/-)) diabetic using the streptozotocin and OVE26 models. Albuminuria, mesangial matrix expansion, and glomerular hypertrophy were each blunted in EP1(-/-) streptozotocin and OVE26 cohorts compared with wild-type counterparts. Although diabetes-associated podocyte depletion was unaffected by EP1 deletion, EP1 antagonism with ONO-8711 in cultured podocytes decreased angiotensin II-mediated superoxide generation, suggesting that EP1-associated injury of remaining podocytes in vivo could contribute to filtration barrier dysfunction. Accordingly, EP1 deletion in OVE26 mice prevented nephrin mRNA expression down-regulation and ameliorated glomerular basement membrane thickening and foot process effacement. Moreover, EP1 deletion reduced diabetes-induced expression of fibrotic markers fibronectin and α-actin, whereas EP1 antagonism decreased fibronectin in cultured proximal tubule cells. Similarly, proximal tubule megalin expression was reduced by diabetes but was preserved in EP1(-/-) mice. Finally, the diabetes-associated increase in angiotensin II-mediated constriction of isolated mesenteric arteries was blunted in OVE26EP1(-/-) mice, demonstrating a role for EP1 receptors in the diabetic vasculature. These data suggest that EP1 activation contributes to diabetic nephropathy progression at several locations, including podocytes, proximal tubule, and the vasculature. The EP1 receptor facilitates the actions of angiotensin II, thereby suggesting that targeting of both the renin-angiotensin system and the EP1 receptor could be beneficial in diabetic nephropathy.

Distinct roles of central and peripheral prostaglandin E2 and EP subtypes in blood pressure regulation

Prostaglandin E(2) (PGE(2)) is a major prostanoid with a wide variety of biological activities. PGE(2) can influence blood pressure (BP) both positively and negatively. In particular, centrally administered PGE(2) induces hypertension whereas systemic administration of PGE(2) produces a hypotensive effect. These physiologically opposing effects are generated by the existence of multiple EP receptors, namely EP(1-4), which are G protein-coupled receptors with distinct signaling properties. This review highlights the distinct roles of PGE(2) in BP regulation and the involvement of specific EP receptor subtypes.

EP1 disruption attenuates end-organ damage in a mouse model of hypertension

Prostaglandin E(2) is a major prostanoid found in the kidney and vasculature contributing to the regulation of blood pressure. The prostaglandin E(2) receptor EP1 has been shown to contribute to hypertension by mediating angiotensin II-dependent vasoconstriction, although its precise role is incompletely characterized. Disruption of the EP1 receptor in C57BL/6J mice reduced the incidence of mortality during severe hypertension induced by uninephrectomy, deoxycorticosterone acetate, and angiotensin II. Mortality was dependent on all components of the model. Death was a result of aortic aneurysm rupture or occurred after development of anasarca, each of which was reduced in EP1-/- mice. Mean arterial pressure was increased in treated EP1+/+ and EP1-/- mice; however, this elevation was significantly lower in EP1-/- mice. Blood pressure reduction via administration of hydralazine phenocopied EP1-/- mice. Thus, reduction in blood pressure by disruption of EP1 reduced incidence of mortality and decreased organ damage, suggesting that EP1 receptor blockade may be a viable target for antihypertensive therapy.

Angiotensin II-dependent hypertension requires cyclooxygenase 1-derived prostaglandin E2 and EP1 receptor signaling in the subfornical organ of the brain

Cyclooxygenase (COX)-derived prostanoids have long been implicated in blood pressure (BP) regulation. Recently prostaglandin E(2) (PGE(2)) and its receptor EP(1) (EP(1)R) have emerged as key players in angiotensin II (Ang II)-dependent hypertension (HTN) and related end-organ damage. However, the enzymatic source of PGE(2,) that is, COX-1 or COX-2, and its site(s) of action are not known. The subfornical organ (SFO) is a key forebrain region that mediates systemic Ang II-dependent HTN via reactive oxygen species (ROS). We tested the hypothesis that cross-talk between PGE(2)/EP(1)R and ROS signaling in the SFO is required for Ang II HTN. Radiotelemetric assessment of blood pressure revealed that HTN induced by infusion of systemic "slow-pressor" doses of Ang II was abolished in mice with null mutations in EP(1)R or COX-1 but not COX-2. Slow-pressor Ang II-evoked HTN and ROS formation in the SFO were prevented when the EP(1)R antagonist SC-51089 was infused directly into brains of wild-type mice, and Ang-II-induced ROS production was blunted in cells dissociated from SFO of EP(1)R(-/-) and COX-1(-/-) but not COX-2(-/-) mice. In addition, slow-pressor Ang II infusion caused a ≈3-fold increase in PGE(2) levels in the SFO but not in other brain regions. Finally, genetic reconstitution of EP(1)R selectively in the SFO of EP(1)R-null mice was sufficient to rescue slow-pressor Ang II-elicited HTN and ROS formation in the SFO of this model. Thus, COX 1-derived PGE(2) signaling through EP(1)R in the SFO is required for the ROS-mediated HTN induced by systemic infusion of Ang II and suggests that EP(1)R in the SFO may provide a novel target for antihypertensive therapy.

Prostaglandin E2 modulation of blood pressure homeostasis: studies in rodent models

Hypertension is a well established risk factor for cardiovascular diseases such as stroke and is the leading cause of chronic kidney failure. Although a number of pharmacologic agents are available for the treatment of hypertension including agents that affect the renin-angiotensin-aldosterone system (RAAS), unmet needs in the treatment of hypertension suggest that identification of novel pharmacological targets would be an important healthcare goal. One potential target is prostaglandin E(2) (PGE(2)), a potent lipid mediator with a diverse and sometimes opposing range of biological effects. PGE(2) signals through four subtypes of G-protein coupled receptors designated EP1 through EP4. PGE(2) functions primarily as a vasodepressor; under certain conditions PGE(2) administration mediates vasopressor activity. This review focuses on the current understanding of the roles of PGE(2) receptors in vascular reactivity, hypertension and end-organ damage.

International Union of Basic and Clinical Pharmacology. LXXXIII: classification of prostanoid receptors, updating 15 years of progress

It is now more than 15 years since the molecular structures of the major prostanoid receptors were elucidated. Since then, substantial progress has been achieved with respect to distribution and function, signal transduction mechanisms, and the design of agonists and antagonists (http://www.iuphar-db.org/DATABASE/FamilyIntroductionForward?familyId=58). This review systematically details these advances. More recent developments in prostanoid receptor research are included. The DP(2) receptor, also termed CRTH2, has little structural resemblance to DP(1) and other receptors described in the original prostanoid receptor classification. DP(2) receptors are more closely related to chemoattractant receptors. Prostanoid receptors have also been found to heterodimerize with other prostanoid receptor subtypes and nonprostanoids. This may extend signal transduction pathways and create new ligand recognition sites: prostacyclin/thromboxane A(2) heterodimeric receptors for 8-epi-prostaglandin E(2), wild-type/alternative (alt4) heterodimers for the prostaglandin FP receptor for bimatoprost and the prostamides. It is anticipated that the 15 years of research progress described herein will lead to novel therapeutic entities.

Modulating P-glycoprotein regulation: future perspectives for pharmacoresistant epilepsies?

Enhanced brain efflux of antiepileptic drugs by the blood-brain barrier transporter P-glycoprotein is discussed as one mechanism contributing to pharmacoresistance of epilepsies. P-glycoprotein overexpression has been proven to occur as a consequence of seizure activity. Therefore, blocking respective signaling events should help to improve brain penetration and efficacy of P-glycoprotein substrates. A series of recent studies revealed key signaling factors involved in seizure-associated transcriptional activation of P-glycoprotein. These data suggested several interesting targets, including the N-methyl-d-aspartate (NMDA) receptor, the inflammatory enzyme cyclooxygenase-2, and the prostaglandin E2 EP1 receptor. These targets have been further evaluated in rodent models, demonstrating that targeting these factors can control P-glycoprotein expression, improve antiepileptic drug brain penetration, and help to overcome pharmacoresistance. In general, the approach offers particular advantages over transporter inhibition as it preserves basal transporter function. In this review the different strategies for blocking P-glycoprotein upregulation, including their therapeutic promise and drawbacks are discussed. Moreover, pros and cons of the approach are compared to those of alternative strategies to overcome transporter-associated resistance. Regarding future perspectives of the novel approach, there is an obvious need to more clearly define the clinical relevance of transporter overexpression. In this context current efforts are discussed, including the development of imaging tools that allow an evaluation of P-glycoprotein function in individual patients.

Cyclooxygenase 1-derived prostaglandin E2 and EP1 receptors are required for the cerebrovascular dysfunction induced by angiotensin II

Prostaglandin E(2) (PGE(2)) EP1 receptors (EP1Rs) may contribute to hypertension and related end-organ damage. Because of the key role of angiotensin II (Ang II) in hypertension, we investigated the role of EP1R in the cerebrovascular alterations induced by Ang II. Mice were equipped with a cranial window, and cerebral blood flow was monitored by laser-Doppler flowmetry. The attenuation in cerebral blood flow responses to whisker stimulation (-46+/-4%) and the endothelium-dependent vasodilator acetylcholine (-40+/-4%) induced by acute administration of Ang II (250 ng/kg per minute; IV for 30 to 40 minutes) were not observed after cyclooxygenase 1 or EP1R inhibition or in cyclooxygenase 1 or EP1-null mice. In contrast, cyclooxygenase 2 inhibition or genetic inactivation did not prevent the attenuation. Ang II-induced oxidative stress was not observed after cyclooxygenase 1 or EP1R inhibition or in EP1R-null mice. Prostaglandin E(2) reinstated the Ang II-induced cerebrovascular dysfunction and oxidative stress after cyclooxygenase 1 inhibition. Brain prostaglandin E(2) levels were not increased by Ang II but were attenuated by cyclooxygenase 1 and not cyclooxygenase 2 inhibition. The cerebrovascular dysfunction induced by 14-day administration of "slow-pressor" doses of Ang II (600 ng/kg per minute) was attenuated by neocortical application of SC51089. Cyclooxygenase 1 immunoreactivity was observed in microglia and EP1R in endothelial cells. We conclude that the cerebrovascular dysfunction induced by Ang II requires activation of EP1R by constitutive production of prostaglandin E(2) derived from cyclooxygenase 1. The findings provide the first evidence that EP1Rs are involved in the deleterious cerebrovascular effects of Ang II and suggest new therapeutic approaches to counteract them.

Targeting regulation of ABC efflux transporters in brain diseases: a novel therapeutic approach

Blood-brain barrier efflux transporters limit the brain penetration and efficacy of various central nervous system drugs. In several CNS diseases, therapy- or pathophysiology-associated transcriptional activation of efflux transporters further strengthens the barrier function. Targeting the regulatory pathways that drive efflux transporter expression in different diseases represents an intriguing approach for prevention of these events thereby promoting delivery to the brain and enhancing or restoring drug efficacy. In particular, the approach holds the promise to preserve basal transporter expression and activity, which is of specific relevance in view of the protective function of efflux transport. The elucidation of the signaling cascades involved in transporter regulation is a major presupposition for the development of preventive strategies. Orphan nuclear receptors as well as the Wnt/beta-catenin signaling pathway have been implicated in drug-induced changes in transporter expression. Targeting these xenobiotic sensors is therefore discussed as a means to optimize brain delivery and therapeutic outcome. Relevant progress has also been made with the identification of key signaling events that drive P-glycoprotein expression in response to pathophysiological mechanisms. In the epileptic brain, complex signaling events involving cyclooxygenase-2 activity trigger P-glycoprotein expression in response to glutamate release and activation of endothelial NMDA receptors. Moreover, reactive oxygen species and inflammatory cytokines have been identified as regulatory factors which might affect P-glycoprotein in several CNS diseases. Recent data substantiated several interesting targets in the respective signaling cascades thereby rendering a basis for the ongoing development of innovative approaches to optimize central nervous system drug brain penetration and efficacy.

Influence of conjugated linoleic acids on functional properties of vascular cells

Conjugated linoleic acids (CLA) are biologically highly active lipid compounds that inhibit the development of atherosclerotic plaques in experimental animals. The underlying mechanisms of action, however, are only poorly understood. Since cell-culture experiments are appropriate to provide a detailed view into the mechanisms of action of a compound, the present review summarises results fromin vitrostudies dealing with the effects of CLA isomers and CLA mixtures on functional properties of cells of the vascular wall, such as endothelial cells, smooth muscle cells and monocyte-derived macrophages, which are amongst the major cells contributing to atherosclerotic lesion development. Based on these studies, it can be concluded that CLA exert several beneficial actions in cells of the vascular wall through the activation of nuclear PPAR. These actions of CLA, which may, at least partially, explain the inhibition of atherogenesis by dietary CLA, include modulation of vasoactive mediator release from endothelial cells, inhibition of inflammatory and fibrotic processes in activated smooth muscle cells, abrogation of inflammatory responses in activated macrophages, and reduction of cholesterol accumulation in macrophage-derived foam cells.

Targeting prostaglandin E2 EP1 receptors prevents seizure-associated P-glycoprotein up-regulation

Up-regulation of the blood-brain barrier efflux transporter P-glycoprotein in central nervous system disorders results in restricted brain access and limited efficacy of therapeutic drugs. In epilepsies, seizure activity strongly triggers expression of P-glycoprotein. Here, we identified the prostaglandin E2 receptor, EP1, as a key factor in the signaling pathway that mediates seizure-induced up-regulation of P-glycoprotein at the blood-brain barrier. In the rat pilocarpine model, status epilepticus significantly increased P-glycoprotein expression by 92 to 197% in the hippocampal hilus and granule cell layer as well as the piriform cortex. The EP1 receptor antagonist 8-chlorodibenz[b,f][1,4]oxazepine-10(11H)-carboxylic acid, 2-[1-oxo-3-(4-pyridinyl)propyl]hydrazide hydrochloride (SC-51089) abolished seizure-induced P-glycoprotein up-regulation and retained its expression at the control level. The control of P-glycoprotein expression despite prolonged seizure activity suggests that EP1 receptor antagonism will also improve antiepileptic drug efficacy. Preliminary evidence for this concept has been obtained using a massive kindling paradigm during which animals received a subchronic SC-51089 treatment. After withdrawal of the EP1 receptor antagonist, a low dose of the P-glycoprotein substrate phenobarbital resulted in an anticonvulsant effect in this pretreated group, whereas the same dosage of phenobarbital did not exert a significant effect in the respective control group. In conclusion, our data demonstrate that EP1 is a key signaling factor in the regulatory pathway that drives P-glycoprotein up-regulation during seizures. These findings suggest new intriguing possibilities to prevent and interrupt P-glycoprotein overexpression in epilepsy. Future studies are necessary to further evaluate the appropriateness of the strategy to enhance the efficacy of antiepileptic drugs.

Activation of prostaglandin E2 EP1 receptor increases arteriolar tone and blood pressure in mice with type 2 diabetes

AIMS

Type 2 diabetes mellitus is frequently associated with hypertension, but the underlying mechanisms are not completely understood. We tested the hypothesis that activation of type 1 prostaglandin E(2) (PGE(2)) receptor (EP1) increases skeletal muscle arteriolar tone and blood pressure in mice with type 2 diabetes.

METHODS AND RESULTS

In 12-week-old, male db/db mice (with homozygote mutation in leptin receptor), systolic blood pressure was significantly elevated, compared with control heterozygotes. Isolated, pressurized gracilis muscle arterioles ( approximately 90 microm) of db/db mice exhibited an enhanced pressure- and angiotensin II (0.1-10 nM)-induced tone, which was reduced by the selective EP1 receptor antagonist, AH6809 (10 microM), to the level observed in arterioles of control mice. Exogenous application of PGE(2) (10 pM-100 nM) or the selective agonist of the EP1 receptor, 17-phenyl-trinor-PGE(2) (10 pM-100 nM), elicited arteriolar constrictions that were significantly enhanced in db/db mice (max: 31 +/- 4 and 29 +/- 5%), compared with controls (max: 20 +/- 2 and 14 +/- 3%, respectively). In the aorta of db/db mice, an increased protein expression of EP1, but not EP4, receptor was also detected by western immunoblotting. Moreover, we found that oral administration of the EP1 receptor antagonist, AH6809 (10 mg/kg/day, for 4 days), significantly reduced the systolic blood pressure in db/db, but not in control mice.

CONCLUSION

Activation of EP1 receptors increases arteriolar tone, which could contribute to the development of hypertension in the db/db mice.

Chemistry and antihypertensive effects of tempol and other nitroxides

Nitroxides can undergo one- or two-electron reduction reactions to hydroxylamines or oxammonium cations, respectively, which themselves are interconvertible, thereby providing redox metabolic actions. 4-Hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (tempol) is the most extensively studied nitroxide. It is a cell membrane-permeable amphilite that dismutates superoxide catalytically, facilitates hydrogen peroxide metabolism by catalase-like actions, and limits formation of toxic hydroxyl radicals produced by Fenton reactions. It is broadly effective in detoxifying these reactive oxygen species in cell and animal studies. When administered intravenously to hypertensive rodent models, tempol caused rapid and reversible dose-dependent reductions in blood pressure in 22 of 26 studies. This was accompanied by vasodilation, increased nitric oxide activity, reduced sympathetic nervous system activity at central and peripheral sites, and enhanced potassium channel conductance in blood vessels and neurons. When administered orally or by infusion over days or weeks to hypertensive rodent models, it reduced blood pressure in 59 of 68 studies. This was accompanied by correction of salt sensitivity and endothelial dysfunction and reduced agonist-evoked oxidative stress and contractility of blood vessels, reduced renal vascular resistance, and increased renal tissue oxygen tension. Thus, tempol is broadly effective in reducing blood pressure, whether given by acute intravenous injection or by prolonged administration, in a wide range of rodent models of hypertension.

PGE(2) induces COX-2 expression in podocytes via the EP(4) receptor through a PKA-independent mechanism

Cyclooxygenase-2 (COX-2)-dependent prostaglandin E(2) (PGE(2)) synthesis correlates with the onset of proteinuria and increased glomerular capillary pressure (P(gc)) glomerular disease models. We previously showed that an in vitro surrogate for P(gc) (cyclical mechanical stretch) upregulates the expression of both COX-2 and the PGE(2) responsive E-Prostanoid receptor, EP(4) in cultured mouse podocytes. In the present study we further delineate the signaling pathways regulating podocyte COX-2 induction. Time course experiments carried out in conditionally-immortalized mouse podocytes revealed that PGE(2) transiently increased phosphorylated p38 MAPK levels at 10 min, and induced COX-2 protein expression at 4 h. siRNA-mediated knockdown of EP(4) receptor expression, unlike treatment with the EP(1) receptor antagonist SC 19220, completely abrogated PGE(2)-induced p38 phosphorylation and COX-2 upregulation suggesting the involvement of the EP(4) receptor subtype. PGE(2)-induced COX-2 induction was abrogated by inhibition of either p38 MAPK or AMP activated protein kinase (AMPK), and was mimicked by AICAR, a selective AMPK activator, and by the cAMP-elevating agents, forskolin (FSK) and IBMX. Surprisingly, neither PGE(2) nor FSK/IBMX-dependent p38 activation and COX-2 expression were blocked by PKA inhibitors or mimicked by 8-cPT-cAMP a selective EPAC activator, but were instead abrogated by Compound C, suggesting the involvement of AMPK. These results indicate that in addition to mechanical stretch, PGE(2) initiates a positive feedback loop in podocytes that drives p38 MAPK activity and COX-2 expression through a cAMP/AMPK-dependent, but PKA-independent signaling cascade. This PGE(2)-induced signaling network activated by increased P(gc) could be detrimental to podocyte health and glomerular filtration barrier integrity.

Conjugated linoleic acid isomers inhibit platelet-derived growth factor-induced NF-kappaB transactivation and collagen formation in human vascular smooth muscle cells

BACKGROUND

Atherosclerosis is characterized by extensive thickening of the arterial intima partially resulting from deposition of collagen by vascular smooth muscle cells (SMCs). Polyunsaturated fatty acids stimulate collagen formation through NF-kappaB activation.

AIM OF THE STUDY

The present study aimed to explore the effect of conjugated linoleic acids (CLAs) which are known to inhibit NF-kappaB activation on collagen formation by SMCs.

METHODS

Vascular SMCs were cultured with 50 micromol/l of CLA isomers (c9t11-CLA, t10c12-CLA) or linoleic acid (LA) and analysed for collagen formation and NF-kappaB p50 transactivation.

RESULTS

Treatment with CLA isomers but not LA significantly reduced PDGF-stimulated [(3)H] proline incorporation into cell layer protein of SMCs without altering cell proliferation. Simultaneous treatment with the PPARgamma inhibitor T0070907 abrogated this effect. Treatment of SMCs with c9t11-CLA and t10c12-CLA significantly reduced PDGF-induced NF-kappaB p50 activation.

CONCLUSIONS

CLA isomers inhibit PDGF-stimulated collagen production by vascular SMCs, which is considered to be a hallmark of atherosclerosis, in a PPARgamma-dependent manner. Whether inhibition of the NF-kappaB-pathway is of significance for the reduction of collagen formation by CLA isomers needs further investigation.

Upregulation of cortical COX-2 in salt-sensitive hypertension: role of angiotensin II and reactive oxygen species

Salt-sensitive (SS) hypertension is a vascular diathesis characterized by reduced cardiovascular and renal nitric oxide bioavailability and local upregulation of ANG II. We have demonstrated that rats infused with ANG II manifest increased cortical cyclooxygenase (COX)-2 expression and activity via NADPH oxidase-derived reactive oxygen species (ROS). In the present studies we used Dahl salt-sensitive (DS) rats to test the hypothesis that hypertensive SS rats have increased cortical COX-2 upregulation, which is mediated by ANG II and ROS. DS rats were placed on either a normal-salt diet (0.5% NaCl) or a high-salt diet (4% NaCl) for 6 wk and treated with either the ANG II type 1 (AT1) receptor blocker candesartan (Can, 10 mg·kg−1·day−1) or the SOD mimetic tempol (1 mmol/l). Hypertensive SS rats had a twofold increase in the cortical expression of COX-2 as assessed by Western blot. These changes in COX-2 expression were accompanied by a 10-fold increase in COX-2 mRNA expression and a 2-fold increase in the urinary excretion of PGE2. Treatment with either the AT1receptor blocker Can or the SOD mimetic tempol did not reduce blood pressure but resulted in significant reductions in the cortical expression of COX-2 and the urinary excretion of PGE2. In conclusion, we have demonstrated that local activation of the renin-angiotensin system, via increased ROS generation, mediates COX-2 upregulation in hypertensive SS rats. These studies unveil novel mechanistic pathways that may play a role in the pathogenesis of hypertensive renal injury.

Effects of EP1 receptor on cerebral blood flow in the middle cerebral artery occlusion model of stroke in mice

The lipid mediator prostaglandin E2 (PGE2) exhibits diverse biologic activity in a variety of tissues. Four PGE2 receptor subtypes (EP1-4) are involved in various physiologic and pathophysiologic conditions, but differ in tissue distribution, ligand-binding affinity, and coupling to intracellular signaling pathways. To characterize the role of the EP1 receptor, physiologic parameters (mean arterial blood pressure, pH, blood gases PaO2 and PaCO2, and body temperature), cerebral blood flow (CBF), and neuronal cell death were studied in a middle cerebral artery occlusion model of ischemic stroke in wild-type (WT) and EP1 knockout (EP1-/-) mice. The right middle cerebral artery was occluded for 60 min, and absolute CBF was measured by [14C] iodoantipyrine autoradiography. The effect of EP1 receptor on oxidative stress in neuronal cultures was investigated. Although no differences were observed in the physiologic parameters, CBF was significantly (P < 0.01) higher in EP1-/- mice than in WT mice, suggesting a role for this receptor in physiologic and pathophysiologic control of vascular tone. Similarly, neuronal cultures derived from EP1-/- mice were more resistant (90.6 +/- 5.8% viability) to tert-butyl hydroperoxide-induced oxidative stress than neurons from WT mice (39.6 +/- 17.2% viability). The EP1 receptor antagonist SC-51089 and calcium channel blocker verapamil each attenuated the neuronal cell death induced by PGE2. Thus, the prostanoid EP1 receptor plays a significant role in regulating CBF and neuronal cell death. These findings suggest that pharmacologic modulation of the EP1 receptor might be a means to improve CBF and neuronal survival during ischemic stroke.

Prostaglandins in the kidney: developments since Y2K

There are five major PGs (prostaglandins/prostanoids) produced from arachidonic acid via the COX (cyclo-oxygenase) pathway: PGE(2), PGI(2) (prostacyclin), PGD(2), PGF(2alpha) and TXA(2) (thromboxane A(2)). They exert many biological effects through specific G-protein-coupled membrane receptors, namely EP (PGE(2) receptor), IP (PGI(2) receptor), DP (PGD(2) receptor), FP (PGF(2alpha) receptor) and TP (TXA(2) receptor) respectively. PGs are implicated in physiological and pathological processes in all major organ systems, including cardiovascular function, gastrointestinal responses, reproductive processes, renal effects etc. This review highlights recent insights into the role of each prostanoid in regulating various aspects of renal function, including haemodynamics, renin secretion, growth responses, tubular transport processes and cell fate. A thorough review of the literature since Y2K (year 2000) is provided, with a general overview of PGs and their synthesis enzymes, and then specific considerations of each PG/prostanoid receptor system in the kidney.

Urine concentrating defect in prostaglandin EP1-deficient mice

We investigated the role of the prostaglandin E2(PGE2) EP1receptor in modulating urine concentration as it is expressed along the renal collecting duct where arginine-vasopressin (AVP) exerts its anti-diuretic activity, and in the paraventricular and supraoptic nuclei of the hypothalamus where AVP is synthesized. The urine osmolality of EP1-null mice (EP1−/−) failed to match levels achieved by wild-type (WT) counterparts upon water deprivation (WD) for 24 h. This difference was reflected by higher plasma osmolality in WD EP1−/−mice. Along the collecting duct, the induction and subapical to plasma membrane translocation of the aquaporin-2 water channel in WD EP1−/−mice appeared equivalent to that of WD WT mice as determined by quantitative RT-PCR and immunohistochemistry. However, medullary interstitial osmolalities dropped significantly in EP1−/−mice following WD. Furthermore, urinary AVP levels of WD EP1−/−mice were significantly lower than those of WD WT mice. This deficit could be traced back to a blunted induction of hypothalamic AVP mRNA expression in WD EP1−/−mice as determined by quantitative RT-PCR. Administration of the AVP mimetic [deamino-Cys1,d-Arg8]-vasopressin restored a significant proportion of the urine concentrating ability of WD EP1−/−mice. When mice were water loaded to suppress endogenous AVP production, urine osmolalities increased equally for WT and EP1−/−mice. These data suggest that PGE2modulates urine concentration by acting at EP1receptors, not in the collecting duct, but within the hypothalamus to promote AVP synthesis in response to acute WD.

Arachidonic Acid Metabolism as a Potential Mediator of Cardiac Fibrosis Associated with Inflammation

An increase in left ventricular collagen (cardiac fibrosis) is a detrimental process that adversely affects heart function. Strong evidence implicates the infiltration of inflammatory cells as a critical part of the process resulting in cardiac fibrosis. Inflammatory cells are capable of releasing arachidonic acid, which may be further metabolized by cyclooxygenase, lipoxygenase, and cytochrome P450 monooxygenase enzymes to biologically active products, including PGs, leukotrienes, epoxyeicosatrienoic acids, and hydroxyeicosatetraenoic acids. Some of these products have profibrotic properties and may represent a pathway by which inflammatory cells initiate and mediate the development of cardiac fibrosis. In this study, we critically review the current literature on the potential link between this pathway and cardiac fibrosis.

Endothelin A receptor blockade reduces diabetic renal injury via an anti-inflammatory mechanism

Endothelin (ET) receptor blockade delays the progression of diabetic nephropathy; however, the mechanism of this protection is unknown. Therefore, the aim of this study was to test the hypothesis that ET(A) receptor blockade attenuates superoxide production and inflammation in the kidney of diabetic rats. Diabetes was induced by streptozotocin (diabetic rats with partial insulin replacement to maintain modest hyperglycemia [HG]), and sham rats received vehicle treatments. Some rats also received the ETA antagonist ABT-627 (sham+ABT and HG+ABT; 5 mg/kg per d; n = 8 to 10/group). During the 10-wk study, urinary microalbumin was increased in HG rats, and this effect was prevented by ET(A) receptor blockade. Indices of oxidative stress, urinary excretion of thiobarbituric acid reactive substances, 8-hydroxy--deoxyguanosine, and H2O2 and plasma thiobarbituric acid reactive substances were significantly greater in HG rats than in sham rats. These effects were not prevented by ABT-627. In addition, renal cortical expression of 8-hydroxy--deoxyguanosine and NADPH oxidase subunits was not different between HG and HG+ABT rats. ETA receptor blockade attenuated increases in macrophage infiltration and urinary excretion of TGF-beta and prostaglandin E2 metabolites in HG rats. Although ABT-627 did not alleviate oxidative stress in HG rats, inflammation and production of inflammatory mediators were reduced in association with prevention of microalbuminuria. These observations indicate that ETA receptor activation mediates renal inflammation and TGF-beta production in diabetes and are consistent with the postulate that ETA blockade slows progression of diabetic nephropathy via an anti-inflammatory mechanism.

Increased severity of renal impairment in nephritic mice lacking the EP1 receptor

In experimental glomerulonephritis, inhibition of renal prostaglandin (PG) synthesis by nonsteroidal-anti-inflammatory drugs (NSAIDs) moderates proteinuria, yet can induce harmful effects on renal blood flow and Na+–K+–water balance thereby implicating 1 or more prostanoid receptor subtypes. We investigated the role of the PGE2 EP1 receptor in nephritis since it is expressed in the glomerulus, collecting duct and vasculature in which its activity might contribute to adaptive or maladaptive responses. Accordingly, a mouse model of accelerated antiglomerular basement membrane (anti-GBM) nephrotoxic serum (NTS) nephritis was induced in mice with targeted-deletion of the EP1 receptor (EP1−/−). Proteinuria was similar between wild-type (wt) and EP1−/− NTS groups, thus negating a role for this subtype in modulating the glomerular permeability barrier in this model of anti-GBM NTS. However, overall renal damage was more acute in NTS EP1−/− mice, as evidenced by the degree of glomerular mesangial matrix expansion and the frequency of tubular dilatations. These changes in renal pathology were accompanied by stronger impairment of renal function in NTS EP1−/− mice, such that levels of serum creatinine, urea, Na+, and K+ were each significantly higher than those observed in NTS wt mice. Lastly, compared with wt mice, induction of NTS more severely reduced urine osmolality and body mass in EP1−/− mice. Taken together, the increased renal impairment seen in NTS EP1−/− mice suggests that the EP1 subtype plays a compensatory role in the context of acute nephritis.

Eicosanoids and renal vascular function in diseases

Arachidonic acid metabolites are vital for the proper control of renal haemodynamics and, when not properly controlled, can contribute to renal vascular injury and end-stage renal disease. Three major enzymatic pathways, COX (cyclo-oxygenase), CYP450 (cytochrome P450) and LOX (lipoxygenase), are responsible for the metabolism of arachidonic acid metabolites to bioactive eicosanoids. These eicosanoids can dilate or constrict the renal vasculature and maintain vascular resistance in the face of changing vasoactive hormones. Renal vascular generation of eicosanoids is altered in pathophysiological conditions such as hypertension, diabetes, metabolic syndrome and acute renal failure. Experimental evidence supports the concept that altered eicosanoid metabolism contributes to renal haemodynamic alterations and the development and progression of nephropathy. The possible beneficial renal vascular actions of enzymatic inhibitors, eicosanoid analogues and receptor antagonists have been examined in hypertension, diabetes and metabolic syndrome. This review highlights the roles of renal vascular eicosanoids in the pathogenesis of nephropathy and therapeutic targets for renal disease related to hypertension, diabetes, metabolic syndrome and acute renal failure.

Disruption of COX-2 modulates gene expression and the cardiac injury response to doxorubicin

To determine the role of cyclooxygenase (COX)-2 in anthracycline-induced cardiac toxicity, we administered doxorubicin (Dox) to mice with genetic disruption of COX-2 (COX-2-/-). After treatment with Dox, COX-2-/- mice had increased cardiac dysfunction and cardiac cell apoptosis compared with Dox-treated wild-type mice. The expression of the death-associated protein kinase-related apoptosis-inducing protein kinase-2 was also increased in Dox-treated COX-2-/- animals. The altered gene expression, cardiac injury, and dysfunction after Dox treatment in COX-2-/- mice was attenuated by a stable prostacyclin analog, iloprost. Wild-type mice treated with Dox developed cardiac fibrosis that was absent in COX-2-/- mice and unaffected by iloprost. These results suggest that genetic disruption of COX-2 increases the cardiac dysfunction after treatment with Dox by an increase in cardiac cell apoptosis. This Dox-induced cardiotoxicity in COX-2-/- mice was attenuated by a prostacyclin analog, suggesting a protective role for prostaglandins in this setting.

Does Colchicine Have an Antifibrotic Effect on Development of Interstitial Fibrosis in Renal Allografts of Recipients With Familial Mediterranean Fever?

Colchicine, which has been reported to inhibit fibrosis, has been successfully used to treat fibrotic disorders, such as liver cirrhosis, scleroderma, and idiopathic pulmonary fibrosis. We hypothesized that besides its ability to prevent amyloid deposition, colchicine may prevent the development of interstitial fibrosis (IF) in amyloidosis patients who had undergone renal transplantation. We evaluated the influence of colchicine therapy on the development of IF in 25 patients with systemic amyloidosis secondary to familial Mediterranean fever (group 1). Twenty-five nonamyloidotic patients who did not receive colchicine therapy served as controls (group 2). The incidences of recurrence and development of IF in the first, second, and third years after transplantation were evaluated from follow-up allograft biopsies. Only four patients showed amyloid recurrence in their renal allografts. IF developed in 44% (11/25) of group 1 patients and 80% (20/25) of group 2 patients during the 36 months posttransplantation (P < .01). Development of IF in the first, second, and third years posttransplantation was significantly greater among group 2 recipients than group 1 recipients (P < .01). The overall 1-, 2-, and 3-year graft survival rates for group 1 recipients were 96%, 92%, and 80%, and those for group 2 recipients were 96%, 88%, and 60%, respectively. Our results support the thesis that colchicine therapy may help prevent the development of interstitial fibrosis in renal allografts.

Prostaglandin E2 EP1 receptors: downstream effectors of COX-2 neurotoxicity

Cyclooxygenase-2 (COX-2), a rate-limiting enzyme for prostanoid synthesis, has been implicated in the neurotoxicity resulting from hypoxia-ischemia, and its inhibition has therapeutic potential for ischemic stroke. However, COX-2 inhibitors increase the risk of cardiovascular complications. We therefore sought to identify the downstream effectors of COX-2 neurotoxicity, and found that prostaglandin E(2) EP1 receptors are essential for the neurotoxicity mediated by COX-2-derived prostaglandin E(2). EP1 receptors disrupt Ca(2+) homeostasis by impairing Na(+)-Ca(2+) exchange, a key mechanism by which neurons cope with excess Ca(2+) accumulation after an excitotoxic insult. Thus, EP1 receptors contribute to neurotoxicity by augmenting the Ca(2+) dysregulation underlying excitotoxic neuronal death. Pharmacological inhibition or gene inactivation of EP1 receptors ameliorates brain injury induced by excitotoxicity, oxygen glucose deprivation and middle cerebral artery (MCA) occlusion. An EP1 receptor inhibitor reduces brain injury when administered 6 hours after MCA occlusion, suggesting that EP1 receptor inhibition may be a viable therapeutic option in ischemic stroke.

Prostaglandin EP1 receptor contributes to excitotoxicity and focal ischemic brain damage

The clinical side effects associated with the inhibition of cyclooxygenase enzymes under pathologic conditions have recently raised concerns. A better understanding of neuroinflammatory mechanisms and neuronal survival requires knowledge of cyclooxygenase downstream pathways, especially PGE2 and its G-protein-coupled receptors. In this study, we postulate that EP1 receptor is one of the mechanisms that propagate neurotoxicity and could be a therapeutic target in brain injury. This hypothesis was tested by pretreating C57BL/6 wildtype mice with the EP1 receptor selective agonist ONO-DI-004 and the selective antagonist ONO-8713, followed by striatal unilateral NMDA injection. Results revealed that ONO-DI-004 increased NMDA-induced lesion volume up to 128.7 +/- 12.0%, while ONO-8713 significantly decreased lesion volume to 71.3 +/- 10.9%, as compared to the NMDA-control group. Neurotoxic EP1 receptor properties were also studied using C57BL/6 EP1 receptor knockout (EP1-/-) mice, which revealed a significant decrease to 74.5 +/- 8.2%, as compared to wildtype controls. The protective effect of the antagonist ONO-8713 was also tested in the EP1-/- mice, revealing no additional protection in these mice. Together, these results support the selectivity of ONO-8713 toward EP1 receptor and suggest the neurotoxic role of EP1 receptor. Furthermore, the EP1 receptor role in ischemic brain damage was investigated using a model of middle cerebral artery occlusion (MCAO) and reperfusion. The infarct volume was significantly reduced to 56.9 +/- 11.5% in EP1-/- mice, as compared to wildtype controls. This is the first study that demonstrates that EP1 receptor aggravates neurotoxicity and that modulation of this receptor can determine the outcomes in both excitotoxic and focal ischemic neuronal damage.

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.

Prevention and reversal of renal injury by leptin in a new mouse model of diabetic nephropathy

Diabetic nephropathy is the leading cause of end-stage renal disease, for which effective therapy to prevent the progression at advanced stages remains to be established. There is also a long debate whether diabetic glomerular injury is reversible or not. Lipoatrophic diabetes, a syndrome caused by paucity of adipose tissue, is characterized by severe insulin resistance, dyslipidemia, and fatty liver. Here, we show that a genetic model of lipoatrophic diabetes (A-ZIP/F-1 mice) manifests a typical renal injury observed in human diabetic nephropathy that is associated with glomerular hypertrophy, diffuse and pronounced mesangial widening, accumulation of extracellular matrix proteins, podocyte damage, and overt proteinuria. By crossing A-ZIP/F-1 mice with transgenic mice overexpressing an adipocyte-derived hormone leptin, we also reveal that leptin completely prevents the development of hyperglycemia and nephropathy in A-ZIP/F-1 mice. Furthermore, continuous leptin administration to A-ZIP/F-1 mice by minipump beginning at 40 weeks of age significantly alleviates the glomerular injury and proteinuria. These findings demonstrate the therapeutic usefulness of leptin at least for a certain type of diabetic nephropathy. The model presented here will serve as a novel tool to analyze the molecular mechanism underlying not only the progression but also the regression of diabetic nephropathy.

Vasoconstriction induced by activation of EP1 and EP3 receptors in human lung: effects of ONO-AE-248, ONO-DI-004, ONO-8711 or ONO-8713

This study investigated the effects and selectivity of ONO-AE-248, ONO-DI-004, ONO-8711 and ONO-8713 on EP1 and EP3 receptors in human pulmonary vessels. The prostanoid receptors involved in the vasoconstriction of human pulmonary arteries (HPA) are TP and EP3 whereas in pulmonary veins (HPV), this response is associated with TP and EP1. The experiments were performed in presence of BAY u3405 (TP antagonist). ONO-DI-004 (EP1 agonist) and ONO-AE-248 (EP3 agonist), exhibited little or no activity in HPV whereas contractions were induced in HPA with ONO-AE-248. In HPV, the contractions produced with sulprostone (EP1,3 agonist) were blocked in a non competitive manner by both EP1 antagonists (ONO-8711, 30 microM; ONO-8713, 10 microM). The involvement of EP1 mediated contraction in HPV was also observed during the vasorelaxations induced with PGE1 and 5-cis-carba-PGI2. In pre-contracted HPV treated with AH6809 (30 microM; EP1 antagonist) the PGE1 vasorelaxations were potentiated, while unchanged in HPA. These results demonstrate the selectivity of ONO-AE-248 for the EP3 receptor in HPA, ONO-DI-004 was ineffective on the EP1 receptor present in HPV while ONO-8713 was the more potent EP1 antagonist used in this tissue.