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      Effect of High Glucose on Superoxide in Human Mesangial Cells: Role of Angiotensin II

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          Background/Aims: Reactive oxygen species, and especially superoxide (O<sub>2</sub>·–),have been implicated in diabetic nephropathy. O<sub>2</sub>·– accumulation in cells is dependent on O<sub>2</sub>·– production (by NADH/NADPH oxidase) as well as scavenging by superoxide dismutase (SOD) activity. This study was designed to investigate the effects of high glucose (HG) on O<sub>2</sub>·– accumulation and SOD activity in human mesangial cells (HMC) and to determine if these effects are mediated by angiotensin II (Ang II). Methods: HMC were incubated in media containing 10 m Mglucose (control, C), 30 m M glucose (HG), 10 m M glucose + either 20 m M 2-deoxy- D-glucose (2-DG) or 20 m M mannitol (high mannitol, HM) (osmotic controls), or Ang II (10<sup>–5</sup> M). Ang II action was antagonized by employing 10<sup>–4</sup> M of Ang II receptor antagonists (losartan or irbesartan) or 10<sup>–4</sup> M of NADH/NADPH oxidase inhibitors [diphenyleneiodonium chloride (DPI) or apocynin]. Superoxide and total SOD activity were assayed using chemiluminescence of lucigenin. Results: Incubation of HMC in HG resulted in a 1.6-fold increase in Ang I (p < 0.05) and a 1.4-fold increase in Ang II levels (p < 0.05) in cell lysates. These changes were accompanied by a >2-fold increase in O<sub>2</sub>·– accumulation (p < 0.01), which was inhibited by losartan and irbesartan. Exogenous Ang II increased net O<sub>2</sub>·– accumulation by 2.7-fold (p < 0.01), which was normalized by losartan and irbesartan. DPI and apocynin blocked the HG and Ang II-induced increases in O<sub>2</sub>·– (p < 0.01). HG but not exogenous Ang II inhibited total SOD activity by 30%, which was not affected by losartan. Conclusion: High glucose increases O<sub>2</sub><sup>–</sup>· accumulation in HMC primarily by increasing its production via the Ang II-NADH/NADPH oxidase system.

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          Most cited references 23

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          Regulation of intrarenal angiotensin II in hypertension.

          Intrarenal angiotensin II (Ang II) is regulated by several complex processes involving formation from both systemically delivered and intrarenally formed substrate, as well as receptor-mediated internalization. There is substantial compartmentalization of intrarenal Ang II, with levels in the renal interstitial fluid and in proximal tubule fluid being much greater than can be explained from the circulating levels. In Ang II--dependent hypertension, elevated intrarenal Ang II levels occur even when intrarenal renin expression and content are suppressed. Studies in Ang II--infused rats have demonstrated that augmentation of intrarenal Ang II is due, in part, to uptake of circulating Ang II via an Ang II type 1 (AT(1)) receptor mechanism and also to sustained endogenous production of Ang II. Some of the internalized Ang II accumulates in the light and heavy endosomes and is therefore potentially available for intracellular actions. The enhanced intrarenal Ang II also exerts a positive feedback action to augment intrarenal levels of angiotensinogen (AGT) mRNA and protein, which contribute further to the increased intrarenal Ang II in hypertensive states. In addition, renal AT(1) receptor protein and mRNA levels are maintained, allowing increased Ang II levels to elicit progressive effects. The increased intrarenal Ang II activity and AGT production are associated with increased urinary AGT excretion rates. The urinary AGT excretion rates show a clear relationship to kidney Ang II content, suggesting that urinary AGT may serve as an index of Ang II--dependent hypertension. Collectively, the data support a powerful role for intrarenal Ang II in the pathogenesis of hypertension.
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            Interaction of metabolic and haemodynamic factors in mediating experimental diabetic nephropathy.

            Diabetic nephropathy seems to occur as a result of an interaction of metabolic and haemodynamic factors. Glucose dependent pathways are activated within the diabetic kidney. These include increased oxidative stress, renal polyol formation and accumulation of advanced glycated end-products. Haemodynamic factors are also implicated in the pathogenesis of diabetic nephropathy and include increased systemic and intraglomerular pressure and activation of various vasoactive hormone pathways including the renin-angiotensin system and endothelin. These haemodynamic pathways, independently and with metabolic pathways, activate intracellular second messengers such as protein kinase C and MAP kinase, nuclear transcription factors such as NF-kappaB and various growth factors such as the prosclerotic cytokine, TGF-beta and the angiogenic, permeability enhancing growth factor, VEGF. These pathways ultimately lead to increased renal albumin permeability and extracellular matrix accumulation which results in increasing proteinuria, glomerulosclerosis and tubulointerstitial fibrosis. Therapeutic strategies involved in the management and prevention of diabetic nephropathy include currently available treatments such as intensified glycaemic control and antihypertensive agents, particularly those which interrupt the renin-angiotensin system. More novel strategies to influence vasoactive hormone action or to inhibit various metabolic pathways such as inhibitors of advanced glycation, specific protein kinase C isoforms and aldose reductase are at present under experimental and clinical investigation. It is predicted that multiple therapies will be required to reduce the progression of diabetic nephropathy.
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              Oxidative stress and nitric oxide synthase in rat diabetic nephropathy: effects of ACEI and ARB.

              Angiotensin II (Ang II) can up-regulate nicotinamide adenine dinucleotide phosphate [NAD(P)H] oxidase, whose product superoxide anion (O2-) can interact with nitric oxide (NO) to form peroxynitrite (ONOO-). We tested the hypothesis that Ang II subtype 1 (AT1) receptor activation enhances oxidative stress and nitrotyrosine deposition in the kidneys of rats with diabetes mellitus (DM). After two weeks of streptozotocin-induced DM, rats received either no treatment, an angiotensin-converting enzyme inhibitor (ACEI) or an angiotensin receptor blocker (ARB) for two weeks. At four weeks, renal expression of the p47phox component of NAD(P)H oxidase, endothelial nitric oxide synthase (eNOS), neuronal nitric oxide synthase (nNOS), and nitrotyrosine were evaluated by Western blot and immunohistochemistry and related to plasma lipid peroxidation products (LPO), hydrogen peroxide production in the kidney and 24-hour protein excretion. Immunoreactive expression of p47phox and eNOS were increased in DM with an increase in plasma LPO, renal hydrogen peroxide production and nitrotyrosine deposition. Expression of nNOS was unaltered. Treatment with either ACEI or ARB prevented all these findings and also prevented significant microalbuminuria. The treatments did not affect the elevated blood sugar, nor did DM or its treatment affect the blood pressure or the creatinine clearance. Early proteinuric diabetic nephropathy increases renal expression of the p47phox component of NAD(P)H oxidase and eNOS with increased indices of systemic and renal oxidative/nitrosative stress. An ACEI or an ARB prevents these changes and prevents the development of proteinuria, independent of blood pressure or blood sugar. This finding indicates a pathogenic role for AT1 receptors in the development of oxidative damage in the kidneys during early DM.

                Author and article information

                Nephron Exp Nephrol
                Cardiorenal Medicine
                S. Karger AG
                May 2005
                10 March 2005
                : 100
                : 1
                : 46-53
                aVeterans Affairs Hospital, Hines, Ill. and Loyola University Medical Center, Maywood, Ill.; bHektoen Institute for Medical Research, Chicago, Ill., USA
                84348 Nephron Exp Nephrol 2005;100:46–53
                © 2005 S. Karger AG, Basel

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                Figures: 5, References: 38, Pages: 8
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