JR. Renin-angiotensin-aldosterone system and oxidative stress in cardiovascular insulin resistance. Am J Physiol Heart Circ Physiol 293: H2009 -H2023, 2007. First published June 22, 2007; doi:10.1152/ajpheart.00522.2007.-Hypertension commonly occurs in conjunction with insulin resistance and other components of the cardiometabolic syndrome. Insulin resistance plays a significant role in the relationship between hypertension, Type 2 diabetes mellitus, chronic kidney disease, and cardiovascular disease. There is accumulating evidence that insulin resistance occurs in cardiovascular and renal tissue as well as in classical metabolic tissues (i.e., skeletal muscle, liver, and adipose tissue). Activation of the renin-angiotensin-aldosterone system and subsequent elevations in angiotensin II and aldosterone, as seen in cardiometabolic syndrome, contribute to altered insulin/ IGF-1 signaling pathways and reactive oxygen species formation to induce endothelial dysfunction and cardiovascular disease. This review examines currently understood mechanisms underlying the development of resistance to the metabolic actions of insulin in cardiovascular as well as skeletal muscle tissue.HYPERTENSION is present in ϳ30% of the adult United States population and often occurs in conjunction with insulin resistance and other components of the cardiometabolic syndrome (CMS) (29,115,163,186,190). According to recent data, up to 70 million Americans have insulin resistance, which plays a significant role in the relationship between hypertension, Type 2 diabetes mellitus, chronic kidney disease (CKD), and cardiovascular (CV) disease (CVD) (69). There is accumulating evidence that insulin resistance occurs in CV and renal tissue as well as in classical metabolic tissues (i.e., skeletal muscle, liver, and adipose tissue) (125,186,190). This review focuses on currently accepted mechanisms underlying the development of resistance to the metabolic actions of insulin in CV tissue (see Figs. 1 and 2) as well as skeletal muscle tissues (27,190) (see Fig. 3). Normal Actions of Insulin in CV TissueBoth insulin and IGF-1 receptors exist in CV tissue (186). Upon binding to specific receptors, they activate a number of downstream signaling systems that result in vasorelaxation (125, 188 -191) and myocardial glucose uptake and alteration of cardiac energy homeostasis (125,186,190). Activation of the insulin receptor (IR) and IGF-1 receptor, ligand-activated transmembrane receptors with tyrosine kinase activity, phosphorylates intracellular substrates including IR substrate (IRS) family members and Shc, which, in turn, serve as docking proteins for downstream signaling molecules (27,125). IRS phosphorylation of tyrosine moieties results in the engagement of Src homology 2 (SH2) domain-binding motifs for SH2 domain signaling molecules, including phosphatidyl 3-kinase (PI3K) and Grb-2. When SH2 domains of the p85 regulatory subunit bind to tyrosine-phosphorylated motifs on IRS-1, this activates the preassociated p110 catalytic subunit to generate phosph...

TG(mRen2)27 (Ren2) transgenic rats overexpress the mouse renin gene, manifest hypertension, and exhibit increased tissue ANG II levels and oxidative stress. Evidence indicates that elevated tissue ANG II contributes to oxidative stress, increases in glomerular macromolecular permeability, and consequent albuminuria. Furthermore, angiotensin type 1 receptor (AT1R) blockers reduce albuminuria and slow progression of renal disease. However, it is not known whether improvements in glomerular filtration barrier integrity and albuminuria during treatment are related to reductions in oxidative stress and/or kidney renin-angiotensin system (RAS) activity. To investigate the renal protective effects of AT1R blockade, we treated young (6-7 wk old) male Ren2 rats with valsartan (Ren2-V; 30 mg/kg) for 3 wk and measured urine albumin, kidney malondialdehyde (MDA), RAS component mRNAs, and NADPH oxidase subunits (gp91(phox) and Rac1) compared with age-matched untreated Ren2 and Sprague-Dawley (S-D) rats. Basement membrane thickness, slit pore diameter and number, and foot process base width were measured by transmission electron microscopy (TEM). Results indicate that AT1R blockade lowered systolic blood pressure (30%), albuminuria (91%), and kidney MDA (80%) in Ren2-V compared with untreated Ren2 rats. Increased slit pore number and diameter and reductions in basement membrane thickness and podocyte foot process base width were strongly associated with albuminuria and significantly improved following AT1R blockade. AT1R blockade was also associated with increased angiotensin-converting enzyme-2 and neprilysin expression, demonstrating a beneficial shift in balance of renal RAS. Thus reductions in blood pressure, albuminuria, and tissue oxidative stress with AT1R blockade were associated with improved indexes of glomerular filtration barrier integrity and renal RAS in Ren2 rats.

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Angiotensin II (ANG II) contributes to cardiac remodeling, hypertrophy, and left ventricular dysfunction. ANG II stimulation of the ANG type 1 receptor (AT1R) generates reactive oxygen species via NADPH oxidase, which facilitates this hypertrophy and remodeling. This investigation sought to determine whether cardiac oxidative stress and cellular remodeling could be attenuated by in vivo AT1R blockade (AT1B) (valsartan) or superoxide dismutase/catalase mimetic (tempol) treatment in a rodent model of chronically elevated tissue levels of ANG II, the transgenic (mRen2) 27 rat (Ren2). Ren2 rats overexpress the mouse renin transgene with resultant hypertension, insulin resistance, proteinuria, and cardiovascular damage. Young (6–7 wk old) male Ren2 and age-matched Sprague-Dawley rats were treated with valsartan (30 mg/kg), tempol (1 mmol/l), or placebo for 3 wk. Heart tissue NADPH oxidase (NOX) activity and immunohistochemical analysis of subunits NOX2, Rac1, and p22phox, heart tissue malondialdehyde, and insulin-stimulated protein kinase B (Akt) activation were measured. Structural changes were assessed with cine MRI, transmission electron microscopy, and light microscopy. Increases in septal wall thickness and altered systolic function (cine MRI) were associated with perivascular fibrosis and increased mitochondria in Ren2 on light and transmission electron microscopy ( P < 0.05). AT1B, but not tempol, reduced blood pressure ( P < 0.05); significant improvements were seen with both AT1B and tempol on NOX activity, subunit expression, malondialdehyde, and insulin-mediated activation/phosphorylation of Akt (each P < 0.05). Collectively, these data suggest cardiac oxidative stress-induced structural and functional changes are driven, in part, by AT1R-mediated increases in NADPH oxidase activity.

Abstract-Activation of reduced nicotinamide-adenine dinucleotide phosphate (NADPH) oxidase by angiotensin II is integral to the formation of oxidative stress in the vasculature and the kidney. 3-Hydroxy-3-methylglutaryl-coenzyme A reductase inhibition is associated with reductions of oxidative stress in the vasculature and kidney and associated decreases in albuminuria. Effects of 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibition on oxidative stress in the kidney and filtration barrier integrity are poorly understood. To investigate, we used transgenic TG(mRen2)27 (Ren2) rats, which harbor the mouse renin transgene and renin-angiotensin system activation, and an immortalized murine podocyte cell line. We treated young, male Ren2 and Sprague-Dawley rats with rosuvastatin (20 mg/kg IP) or placebo for 21 days. Compared with controls, we observed increases in systolic blood pressure, albuminuria, renal NADPH oxidase activity, and 3-nitrotryosine staining, with reductions in the rosuvastatin-treated Ren2. Structural changes on light and transmission electron microscopy, consistent with periarteriolar fibrosis and podocyte foot-process effacement, were attenuated with statin treatment. Nephrin expression was diminished in the Ren2 kidney and trended to normalize with statin treatment. Angiotensin II-dependent increases in podocyte NADPH oxidase activity and subunit expression (NOX2, NOX4, Rac, and p22 phox ) and reactive oxygen species generation were decreased after in vitro statin treatment. These data support a role for increased NADPH oxidase activity and subunit expression with resultant reactive oxygen species formation in the kidney and podocyte. Furthermore, statin attenuation of NADPH oxidase activation and reactive oxygen species formation in the kidney/podocyte seems to play roles in the abrogation of oxidative stress-induced filtration barrier injury and consequent albuminuria. Key Words: angiotensin II Ⅲ albuminuria Ⅲ glomerular filtration barrier Ⅲ transgenic Ren2 rat Ⅲ rosuvastatin R enin-angiotensin system (RAS) activation and subsequently elevated angiotensin II (Ang II) exert the pressor, proliferative, profibrotic, and proinflammatory actions. 1-3 Activation of tissue reduced nicotinamide-adenine dinucleotide phosphate (NADPH) oxidase seems to contribute to deleterious actions, such as oxidative stress and endothelial dysfunction manifesting as hypertension, albuminuria, and progressive glomerular dysfunction, that may ultimately lead to chronic kidney disease. 1,4 There is accumulating evidence that tissue-based RAS further modulates cell growth, metabolism, and tissue remodeling. 5,6 Evidence for a local RAS in the glomerulus raises the prospect of NADPH oxidase-induced podocyte and filtration barrier injury. 7,8 Furthermore, in vitro protein exposure, mechanical stretch, and glomerular hypertension enhance tissue Ang II production, which may potentiate the impact of elevated blood pressure on glomerular injury manifesting as albuminuria. 9,10 Previous work related to the pathogenesis...