Rania Nasrallah

NADPH Oxidases, Reactive Oxygen Species, and the Kidney: Friend and Foe

Reactive oxygen species (ROS) play an important role in normal cellular physiology. They regulate different biologic processes such as cell defense, hormone synthesis and signaling, activation of G protein-coupled receptors, and ion channels and kinases/phosphatases. ROS are also important regulators of transcription factors and gene expression. On the other hand, in pathologic conditions, a surplus of ROS in tissue results in oxidative stress with various injurious consequences such as inflammation and fibrosis. NADPH oxidases are one of the many sources of ROS in biologic systems, and there are seven isoforms (Nox1-5, Duox1, Duox2). Nox4 is the predominant form in the kidney, although Nox2 is also expressed. Nox4 has been implicated in the basal production of ROS in the kidney and in pathologic conditions such as diabetic nephropathy and CKD; upregulation of Nox4 may be important in renal oxidative stress and kidney injury. Although there is growing evidence indicating the involvement of NADPH oxidase in renal pathology, there is a paucity of information on the role of NADPH oxidase in the regulation of normal renal function. Here we provide an update on the role of NADPH oxidases and ROS in renal physiology and pathology.

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 ≥135 ml/min per 1.73 m2), and 12 subjects exhibited normofiltration (GFR <135 ml/min per 1.73 m2). 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 m2) but increased GFR in the normofiltration group (118 ± 5 to 138 ± 5 ml/min per 1.73 m2). 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.

Hyperfiltration and effect of nitric oxide inhibition on renal and endothelial function in humans with uncomplicated type 1 diabetes mellitus

Studies of experimental diabetes mellitus (DM) suggest that increased nitric oxide (NO) bioactivity contributes to renal hyperfiltration. However, the role of NO in mediating hyperfiltration has not been fully elucidated in humans. Our aim was to examine the effect of NO synthase inhibition on renal and peripheral vascular function in normotensive subjects with uncomplicated type 1 DM. Renal function and brachial artery flow-mediated vasodilatation (FMD) were measured before and after an intravenous infusion of the NO synthase inhibitor N(G)-nitro-l-arginine methyl ester (l-NMMA) in 21 healthy control and 37 type 1 DM patients. Measurements in DM participants were made under clamped euglycemic conditions. The effect of l-NMMA on circulating and urinary NO metabolites (NO(x)) and cGMP and on urinary prostanoids was also determined. Baseline characteristics were similar in the two groups. For analysis, the DM patients were divided into those with hyperfiltration (DM-H, n = 18) and normal glomerular filtration rate (GFR) levels (DM-N, n = 19). Baseline urine NO(x) and cGMP were highest in DM-H. l-NMMA led to a decline in GFR in DM-H (152 ± 16 to 140 ± 11 ml·min(-1)·1.73 m(-2)) but not DM-N or healthy control participants. The decline in effective renal plasma flow in response to l-NMMA (806 ± 112 to 539 ± 80 ml·min(-1)·1.73 m(-2)) in DM-H was also exaggerated compared with the other groups (repeated measures ANOVA, P < 0.05), along with declines in urinary NO(x) metabolites and cGMP. Baseline FMD was lowest in DM-H compared with the other groups and did not change in response to l-NMMA. l-NMMA reduced FMD and plasma markers of NO bioactivity in the healthy control and DM-N groups. In patients with uncomplicated type 1 DM, renal hyperfiltration is associated with increased NO bioactivity in the kidney and reduced NO bioactivity in the systemic circulation, suggesting a paradoxical state of high renal and low systemic vascular NO bioactivity.

Renal Hyperfiltration is a Determinant of Endothelial Function Responses to Cyclooxygenase 2 Inhibition in Type 1 Diabetes

OBJECTIVE Our aim was to examine the effect of cyclooxygenase 2 (COX2) inhibition on endothelial function in subjects with type 1 diabetes analyzed on the basis of renal filtration status. RESEARCH DESIGN AND METHODS Flow-mediated dilation (FMD) was determined in type 1 diabetic subjects and hyperfiltration (glomerular filtration rate ≥135 ml/min/1.73 m2, n = 13) or normofiltration (glomerular filtration rate ≥135 ml/min/1.73 m2, n = 11). Studies were performed before and after celecoxib (200 mg daily for 14 days) during euglycemia and hyperglycemia. RESULTS Baseline parameters were similar in the two groups. Pretreatment, FMD was augmented in normofiltering versus hyperfiltering subjects during clamped euglycemia (10.2 ± 5.3% vs. 5.9 ± 2.3%, P = 0.003). COX2 inhibition suppressed FMD in normofiltering (10.2 ± 5.3% to 5.8 ± 3.4%, P = 0.006) versus hyperfiltering subjects (ANOVA interaction, P = 0.003). CONCLUSIONS Systemic hemodynamic function, including the response to COX2 inhibition, is related to filtration status in diabetic subjects and may reflect general endothelial dysfunction.

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.

Renal hemodynamic effect of cyclooxygenase 2 inhibition in young men and women with uncomplicated type 1 diabetes mellitus

In experimental studies, cyclooxygenase 2 (COX2)-derived vasodilatory prostaglandins play a more prominent role in arterial vasoregulation in females. The gender-dependent effect of COX2 modulation in humans with type 1 diabetes mellitus (DM) is unknown. Accordingly, we examined the renal hemodynamic role of prostaglandins by assessing the response to COX2 inhibition in young men and women with type 1 DM. We also used a graded ANG II infusion to determine whether gender-based differences were mediated by effects of COX2 inhibition on the renin angiotensin system (RAS). We hypothesized that COX2 inhibition would be associated with preferential vasoconstriction in women and would augment their response to ANG II. Baseline renal function and the response to an ANG II infusion were assessed during clamped euglycemia, and again after COX2 inhibition (200 mg celecoxib daily for 14 days) in 12 men and 9 women after 1 wk on a controlled protein and sodium diet. COX2 inhibition was associated with increases in filtration fraction (P = 0.045) and renal vascular resistance and a decline in renal blood flow (P = 0.04) in women compared with men. Before COX2 inhibition, women exhibited a decline in glomerular filtration rate in response to ANG II. COX2 inhibition abolished this effect, whereas the response was not altered in men. In summary, COX2 inhibition was associated with hemodynamic effects that differed based on gender. The ANG II response suggests that with uncomplicated type 1 DM, prostaglandins may contribute to RAS-mediated gender differences. Our results are consistent with experimental data suggesting augmented female prostanoid dependence.

Chronic COX inhibition reduces diabetes-induced hyperfiltration, proteinuria, and renal pathological markers in 36-week B6-Ins2(Akita) mice.

Background/Aims: The widespread use of non-steroidal anti-inflammatory drugs (NSAIDs) and the sizeable impact of diabetes on the development of end-stage renal disease substantiate the need to determine their effect on the evolution of diabetic nephropathy (DN). We hypothesized that chronic ibuprofen and NS-398 will differentially affect many aspects of DN in B6-Ins2Akita mice, including glomerular filtration rate (GFR), growth, and fibrosis. Methods: B6-Ins2Akita and wild-type mice were separated into six groups. At 20 weeks of age, NSAIDs (1 mg/kg/day) were added to the drinking water daily. At 36 weeks indicators of renal function and DN were examined. Results:Urinary PGE2, PGEM, TXB2, and 6-keto-PGF1α were increased in diabetics, and reduced by NSAIDs. Regional differences in cyclooxygenases were observed. Diabetics displayed hyperglycemia, albuminuria, and increased kidney/body weights, glomerular diameters, and FITC-inulin clearance. NSAIDs did not affect growth, but albuminuria and FITC-inulin clearance were reduced. Also, p27 and fibronectin were increased in diabetics and attenuated by ibuprofen. Conclusion: NSAIDs reduced diabetic change: GFR, albuminuria, p27, and fibronectin. The effects of ibuprofen are similar if not more beneficial than COX-2 inhibition by NS-398. This study has clinical relevance for diabetics prior to overt nephropathy. Future studies should reveal the effects of NSAIDs in a more severe disease environment.

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.

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.