Age-Related Mitochondrial Impairment and Renal Injury Is Ameliorated by Sulforaphane via Activation of Transcription Factor NRF2.

Age is one of the major risk factors for the development of chronic pathologies, including kidney diseases. Oxidative stress and mitochondrial dysfunction play a pathogenic role in aging kidney disease. Transcription factor NRF2, a master regulator of redox homeostasis, is altered during aging, but the exact implications of altered NRF2 signaling on age-related renal mitochondrial impairment are not yet clear. Herein, we investigated the role of sulforaphane, a well-known NRF2 activator, on age-related mitochondrial and kidney dysfunction. Young (2-4 month) and aged (20-24 month) male Fischer 344 rats were treated with sulforaphane (15 mg/kg body wt/day) in drinking water for four weeks. We observed significant impairment in renal cortical mitochondrial function along with perturbed redox homeostasis, decreased kidney function and marked impairment in NRF2 signaling in aged Fischer 344 rats. Sulforaphane significantly improved mitochondrial function and ameliorated kidney injury by increasing cortical NRF2 expression and activity and decreasing protein expression of KEAP1, an NRF2 repressor. Sulforaphane treatment did not affect the renal NRF2 expression or activity and mitochondrial function in young rats. Taken together, our results provide novel insights into the protective role of the NRF2 pathway in kidneys during aging and highlight the therapeutic potential of sulforaphane in mitigating kidney dysfunction in elders.

Nrf2 inhibition induces oxidative stress, renal inflammation and hypertension in mice.

Oxidative stress and renal inflammation play a pivotal role in the pathogenesis of hypertension. The redox-sensitive transcription factor, nuclear factor E2-related factor 2 (Nrf2) is the master regulator of phase II antioxidant enzymes that protects against oxidative stress and inflammation. This study aimed to investigate the effect of Nrf2 inhibition on oxidative stress-associated hypertension and renal dopamine 1 receptor (D1R) dysfunction in mice. Male C57BL/6 J mice were treated with a pro-oxidant, L-buthionine sulfoximine (BSO) (10 mmol/L in drinking water), and ML385 (10 kg body weight/kg body weight/day, intraperitoneally), a novel Nrf2 inhibitor that blocks Nrf2 regulated downstream target genes expression. Mice treated with BSO exhibited oxidative stress, renal functional impairment, inflammation, and elevated blood pressure. Also, BSO treatment increased the activity of phase II antioxidant enzyme, NAD(P)H: quinone oxidoreductase-1 (NQO-1). BSO and ML385 co-treatment exhibited a robust increase in blood pressure, oxidative stress and intensified the renal function deterioration as indicated by a significant increase in serum creatinine, urinary albumin excretion rate, and albumin to creatinine ratio and decreased glomerular filtration rate (GFR). Also, BSO and ML385 co-treatment downregulated NQO-1 and significantly altered the inflammatory cytokines, IL-1ß and IL-10 levels. A D1R agonist SKF38393 failed to promote urinary sodium excretion indicating functional impairment in renal D1R. ML385 per se did not affect mean arterial pressure, GFR, and renal D1R function. Taken together, we concluded that the Nrf2 inhibition aggravated oxidative stress and inflammation by diminishing phase II antioxidant defense that deteriorates renal function and contributes to the development of hypertension in mice.

Protein disulfide isomerase inhibition impairs Keap1/Nrf2 signaling and mitochondrial function and induces apoptosis in renal proximal tubular cells.

Renal proximal tubular apoptosis plays a critical role in kidney health and disease. However, cellular molecules that trigger renal apoptosis remain elusive. Here, we evaluated the effect of inhibiting protein disulfide isomerase (PDI), a critical thioredoxin chaperone protein, on apoptosis as well as the underlying mechanisms in human renal proximal tubular (HK2) cells. HK2 cells were transfected with PDI-specific siRNA in the absence and presence of an antioxidant, tempol. PDI siRNA transfection resulted in a decrease of ~70% in PDI protein expression and enzyme activity. PDI inhibition increased caspase-3 activity and induced profound cell apoptosis. Mitochondrial function, as assessed by mitochondrial cytochrome c levels, mitochondrial membrane potential, oxygen consumption, and ATP levels, was significantly reduced in PDI-inhibited cells. Also, PDI inhibition caused nuclear factor erythroid 2-related factor 2 (Nrf2; a redox-sensitive transcription factor) cytoplasmic sequestration, decreased superoxide dismutase and glutathione-S-transferase activities, and increased oxidative stress. In PDI-inhibited cells, tempol reduced apoptosis, caspase-3 activity, and oxidative stress and also restored Nrf2 nuclear translocation and mitochondrial function. Silencing Nrf2 in the cells abrogated the beneficial effect of tempol, whereas Kelch-like ECH-associated protein 1 (an Nrf2 regulatory protein) silencing protected cells from PDI inhibitory effects. Collectively, our data indicate that PDI inhibition diminishes Nrf2 nuclear translocation, causing oxidative stress that further triggers mitochondrial dysfunction and renal cell apoptosis. This study suggests an important role for PDI in renal cell apoptosis involving Nrf2 and mitochondrial dysfunction.

Renal Dopamine Oxidation and Inflammation in High Salt Fed Rats.

Background Oxidative stress and high salt intake could be independent or intertwined risk factors in the origin of hypertension. Kidneys are the major organ to regulate sodium homeostasis and blood pressure and the renal dopamine system plays a pivotal role in sodium regulation during sodium replete conditions. Oxidative stress has been implicated in renal dopamine dysfunction and development of hypertension, especially in salt-sensitive animal models. Here we show the nexus between high salt intake and oxidative stress causing renal tubular dopamine oxidation, which leads to mitochondrial and lysosomal dysfunction and subsequently causes renal inflammation and hypertension. Methods and Results Male Sprague Dawley rats were divided into the following groups, vehicle (V)-tap water, high salt (HS)-1% NaCl, L-buthionine-sulfoximine (BSO), a prooxidant, and HS plus BSO without and with antioxidant resveratrol (R) for 6 weeks. Oxidative stress was significantly higher in BSO and HS+BSO-treated rat compared with vehicle; however, blood pressure was markedly higher in the HS+BSO group whereas an increase in blood pressure in the BSO group was modest. HS+BSO-treated rats had significant renal dopamine oxidation, lysosomal and mitochondrial dysfunction, and increased renal inflammation; however, HS alone had no impact on organelle function or inflammation. Resveratrol prevented oxidative stress, dopamine oxidation, organelle dysfunction, inflammation, and hypertension in BSO and HS+BSO rats. Conclusions These data suggest that dopamine oxidation, especially during increased sodium intake and oxidative milieu, leads to lysosomal and mitochondrial dysfunction and renal inflammation with subsequent increase in blood pressure. Resveratrol, while preventing oxidative stress, protects renal function and mitigates hypertension.

Oxidative stress impairs cGMP-dependent protein kinase activation and vasodilator-stimulated phosphoprotein serine-phosphorylation.

Reactive oxygen species induce vascular dysfunction and hypertension by directly interacting with nitric oxide (NO) which leads to NO inactivation. In addition to a decrease in NO bioavailability, there is evidence that oxidative stress can also modulate NO signaling during hypertension. Here, we investigated the effect of oxidative stress on NO signaling molecules cGMP-dependent protein kinase (PKG) and vasodilator-stimulated phosphoprotein (VASP) which are known to mediate vasodilatory actions of NO. Male Sprague Dawley (SD) rats were provided with tap water (control), 30 mM L-buthionine sulfoximine (BSO, a pro-oxidant), 1 mM tempol (T, an antioxidant) and BSO + T for 3 wks. BSO-treated rats exhibited high blood pressure and oxidative stress. Incubation of mesenteric arterial rings with NO donors caused concentration-dependent relaxation in control rats. However, the response to NO donors was significantly lower in BSO-treated rats with a marked decrease in pD2. In control rats, NO donors activated mesenteric PKG, increased VASP phosphorylation and its interaction with transient receptor potential channels 4 (TRPC4) and inhibited store-operated Ca2+ influx. NO failed to activate these signaling molecules in mesenteric arteries from BSO-treated rats. Supplementation of BSO-treated rats with tempol reduced oxidative stress and blood pressure and normalized the NO signaling. These data suggest that oxidative stress can reduce NO-mediated PKG activation and VASP-TRPC4 interaction which leads to failure of NO to reduce Ca2+ influx in smooth muscle cells. The increase in intracellular Ca2+ contributes to sustained vasoconstriction and subsequent hypertension. Antioxidant supplementation decreases oxidative stress, normalizes NO signaling and reduces blood pressure.

Transcriptional regulation of renal dopamine D1 receptor function during oxidative stress.

There exists a strong link between oxidative stress, renal dopaminergic system, and hypertension. It is reported that reactive oxygen species attenuate renal proximal tubular dopamine receptor (D1R) function, which disrupts sodium regulation and leads to hypertension. However, the mechanisms for renal D1R dysfunction are not clear. We investigated the role of redox-sensitive transcription factors AP1 and SP3 in transcriptional suppression of D1R gene and subsequent D1R signaling. Human kidney proximal tubular cells were treated with a pro-oxidant l-buthionine sulfoximine (BSO) with and without an antioxidant tempol. In human kidney cells, BSO caused oxidative stress and reduced D1R mRNA and membrane receptor expression. Incubation of human kidney cells with SKF38393, a D1R agonist, caused a concentration-dependent inhibition of Na/K-ATPase. However, SKF38393 failed to inhibit Na/K-ATPase in BSO-treated cells. BSO increased AP1 and SP3 nuclear expression. Transfection with AP1- or SP3-specific siRNA abolished BSO-induced D1R downregulation. Treatment of rats with BSO for 4 weeks increased oxidative stress and SP3-AP1 expression and reduced D1R numbers in renal proximal tubules. These rats exhibited high blood pressure, and SKF38393 failed to inhibit proximal tubular Na/K-ATPase activity. Control rats were kept on tap water. Tempol per se had no effect on D1R expression or other signaling molecules but prevented BSO-induced oxidative stress, SP3-AP1 upregulation, and D1R dysfunction in both human kidney cells and rats. These data show that oxidative stress via AP1-SP3 activation suppresses D1R transcription and function. Tempol mitigates oxidative stress, blocks AP1-SP3 activation, and prevents D1R dysfunction and hypertension.

Resveratrol restored Nrf2 function, reduced renal inflammation, and mitigated hypertension in spontaneously hypertensive rats.

Compelling evidence supports the role of oxidative stress and renal interstitial inflammation in the pathogenesis of hypertension. Resveratrol is a polyphenolic stilbene, which can lower oxidative stress by activating the transcription factor nuclear factor-E2-related factor-2 (Nrf2), the master regulator of numerous genes encoding antioxidant and phase II-detoxifying enzymes and molecules. Given the role of oxidative stress and inflammation in the pathogenesis of hypertension, we conducted this study to test the hypothesis that long-term administration of resveratrol will attenuate renal inflammation and oxidative stress and, hence, progression of hypertension in the young spontaneously hypertensive rats (SHR). SHR and control [Wistar-Kyoto (WKY)] rats were treated for 9 wk with resveratrol or vehicle in their drinking water. Vehicle-treated SHR exhibited renal inflammatory injury and oxidative stress, as evidenced by glomerulosclerosis, tubulointerstitial injury, infiltration of inflammatory cells, and increased levels of renal 8-isoprostane and protein carbonylation. This was associated with reduced antioxidant capacity and downregulations of Nrf2 and phase II antioxidant enzyme glutathione-S-transferase (GST). Resveratrol treatment mitigated renal inflammation and injury, reduced oxidative stress, normalized antioxidant capacity, restored Nrf2 and GST activity, and attenuated the progression of hypertension in SHR. However, resveratrol had no effect on these parameters in WKY rats. In conclusion, development and progression of hypertension in the SHR are associated with inflammation, oxidative stress, and impaired Nrf2-GST activity in the kidney. Long-term administration of resveratrol restores Nrf2 expression, ameliorates inflammation, and attenuates development of hypertension in SHR. Clinical studies are needed to explore efficacy of resveratrol in human hypertension.

Vascular oxidative stress upregulates angiotensin II type I receptors via mechanisms involving nuclear factor kappa B.

Abstract The association of oxidative stress with hypertension is well known. However, a causal role of oxidative stress in hypertension is unclear. Vascular angiotensin II type 1 receptor (AT1R) upregulation is a prominent contributor to pathogenesis of hypertension. However, the mechanisms causing this upregulation are unknown. Oxidative stress is an important regulator of protein expression via activation of transcription factors such as nuclear factor kappa B (NFκB). The present study was carried out to test the hypothesis that oxidative stress contributes to vascular AT1R upregulation via NFκB in human aortic smooth muscle cells (HASMC) and spontaneously hypertensive rats (SHR). HASMC exposed to oxidative stress exhibited a robust increase in AT1R mRNA in HASMC. Furthermore, oxidative stress failed to upregulate AT1Rs in the presence of either an antioxidant catalase or siRNA against p65 subunit of NFκB. To test the role of oxidative stress and NFκB in hypertension, prehypertensive SHR were treated with NFκB inhibitor pyrrolidine dithiocarbamate from 5 weeks to 11-12 weeks of age. At 11-12 weeks of age, SHR exhibited increased NFκB expression, AT1R upregulation and exaggerated Ang II-induced vasoconstriction as compared to age-matched Wistar Kyoto (WKY) rats. PDTC treatment of SHR lowered NFκB expression, normalized AT1R expression and Ang II-induced vasoconstriction. More importantly, PDTC treatment significantly attenuated hypertension development in SHR. In conclusion, vascular oxidative can upregulate AT1R, via mechanisms involving NFκB, and contribute to the development of hypertension.

Transcription factor Nrf2 protects renal dopamine D1 receptor function during oxidative stress.

The renal dopaminergic system plays a significant role in controlling sodium excretion and blood pressure (BP). Overwhelming evidence shows that oxidative stress downregulates renal dopamine receptors (D1R), and antioxidant supplementation protects D1R function. However, the mechanisms for benefits of antioxidants in protecting D1R function are unknown. We investigated the role of nuclear factor E2-related factor 2 (Nrf2), a redox-sensitive transcription factor, in reducing oxidative stress, protecting renal D1R function and lowering BP in rats. Male Sprague-Dawley rats were treated with L-buthionine-sulfoximine (BSO) and sulforaphane for 4 weeks. Rats treated with BSO exhibited significant increase in oxidative stress and BP. BSO treatment reduced renal D1R expression and abolished SKF38393 (a D1R agonist)-induced Na/K-ATPase and Na/H-exchanger (NHE3) inhibition. Also, in these rats, SKF38393 failed to promote sodium excretion. BSO caused an increase in nuclear factor-κB expression, a modest nuclear translocation of Nrf2 and a moderate activation of phase II antioxidant enzymes. Treatment of rats with sulforaphane alone induced modest activation of Nrf2 and phase II antioxidant enzymes, although having no effect on BP, redox status, or D1R function. However, sulforaphane prevented oxidative stress, protected D1R function, and abrogated hypertension in BSO-treated rats. In these animals, sulforaphane, whereas attenuating nuclear factor-κB activation, caused a robust stimulation of Nrf2 and phase II antioxidant enzyme pathway. In conclusion, oxidative stress via nuclear factor-κB activation downregulated D1R function causing a decrease in sodium excretion, which contributed to an increase in BP. Sulforaphane via activation of Nrf2-phase II antioxidant enzyme pathway mitigated oxidative stress and nuclear factor-κB activation, preserved D1R function, and prevented hypertension.

Astrogliosis in the brain of obese Zucker rat: a model of metabolic syndrome.

Metabolic syndrome (MetS) is a disorder characterized primarily by the development of insulin resistance. Insulin resistance and subsequent hyperinsulinemia, originating from abdominal obesity, increases the risk of cerebrovascular and cardiovascular disease and all-cause mortality. Obesity is probably a risk factor for Alzheimer's disease and vascular dementia and is associated with impaired cognitive function. The obese Zucker rat (OZR) represents a model of type 2 diabetes exhibiting a moderate degree of arterial hypertension and of increased oxidative stress. To clarify the possible relationships between MetS and brain damage, the present study has investigated brain microanatomy in OZRs compared with their littermate controls lean Zucker rats (LZRs). Male OZRs and LZRs of 12 weeks of age were used. Their brain was processed for immunochemical and immunohistochemical analysis of glial fibrillary acidic protein (GFAP). In frontal and parietal cortex of OZRs a significant increase in the number of GFAP immunoreactive astrocytes was observed. Similar findings were found in the hippocampus, where an increased number of GFAP immunoreactive astrocytes were detected in the CA1 and CA3 subfields and dentate gyrus of OZRs compared to the LZRs. These findings indicating the occurrence of brain injury accompanied by astrogliosis in OZRs suggest that these rats, developed as an animal model of type 2 diabetes, may also represent a model for assessing the influence of MetS on brain. The identification of neurodegenerative changes in OZRs may represent the first step for better characterizing neuronal involvement in this model of MetS and possible treatment for countering it.

Novel role of NF-κB-p65 in antioxidant homeostasis in human kidney-2 cells.

Nuclear factor-κB (NF-κB) plays a role in inflammation. However, we recently reported an association between NF-κB and antioxidant enzymes in renal proximal tubules of exercise-trained rats, suggesting its role in antioxidant homeostasis (George L, Lokhandwala MF, Asghar M. Am J Physiol Renal Physiol 297: F1174-F1180, 2009). A direct role of NF-κB in antioxidant homeostasis in renal cells has not been elucidated and warrants investigation. Therefore, we examined whether NF-κB has a direct role in antioxidant homeostasis and redox balance in human kidney-2 cells overexpressing NF-κB-p65 and compared them with the cells overexpressing Nrf-2, a well-known transcription factor involved in antioxidant homeostasis. The ability of NF-κB-p65 to increase antioxidant enzymes, to reduce reactive oxygen species (ROS), and to rescue ROS-induced renal dopamine D1 receptor dysfunction, was studied. The transcription activity of NF-κB-p65 and Nrf-2, measured as luciferase reporter activity, increased in cells overexpressing these nuclear factors. The levels of mRNA and activity of glutathione peroxidase as well as the protein levels of superoxide dismutase-1 and glutamylcystein transferase were increased in cells overexpressing NF-κB-p65 and Nrf-2. Furthermore, the levels of ROS decreased and D1 receptor agonist SKF38393-mediated [(35)S]GTPγS binding (index of D1 receptor function) increased in the presence of hydrogen peroxide in cells overexpressing NF-κB-p65 and Nrf-2. These results suggest a direct role of NF-κB-p65 in antioxidant homeostasis, contributing to redox balance in renal cells.

Altered functioning of both renal dopamine D1 and angiotensin II type 1 receptors causes hypertension in old rats.

Activation of renal dopamine D1 (D1R) and angiotensin II type 1 receptors (AT(1)Rs) influences the activity of proximal tubular sodium transporter Na,K-ATPase and maintains sodium homeostasis and blood pressure. We reported recently that diminished D1R and exaggerated AT(1)R functions are associated with hypertension in old Fischer 344 × Brown Norway F1 (FBN) rats, and oxidative stress plays a central role in this phenomenon. Here we studied the mechanisms of age-associated increase in oxidative stress on diminished D1R and exaggerated AT(1)R functions in the renal proximal tubules of control and antioxidant Tempol-treated adult and old FBN rats. Although D1R numbers and D1R agonist SKF38393-mediated stimulation of [(35)S]-GTPγS binding (index of D1R activation) were lower, G protein-coupled receptor kinase 4 (kinase that uncouples D1R) levels were higher in old FBN rats. Tempol treatment restored D1R numbers and G protein coupling and reduced G protein-coupled receptor kinase 4 levels in old FBN rats. Angiotensin II-mediated stimulation of [(35)S]-GTPγS binding and Na,K-ATPase activity were higher in old FBN rats, which were also restored with Tempol treatment. We also measured renal AT(1)R function in adult and old Fischer 344 (F344) rats, which, despite exhibiting an age-related increase in oxidative stress and diminished renal D1R function, are normotensive. We found that diuretic and natriuretic responses to candesartan (indices of AT(1)R function) were similar in F344 rats, a likely explanation for the absence of age-associated hypertension in these rats. Perhaps, alterations in both D1R (diminished) and AT(1)R (exaggerated) functions are necessary for the development of age-associated hypertension, as seen in old FBN rats.

Defective nitric oxide production impairs angiotensin II-induced Na-K-ATPase regulation in spontaneously hypertensive rats.

Angiotensin (ANG) II via ANG II type 1 receptors (AT1R) activates renal sodium transporters including Na-K-ATPase and regulates sodium homeostasis and blood pressure. It is reported that at a high concentration, ANG II either inhibits or fails to stimulate Na-K-ATPase. However, the mechanisms for these phenomena are not clear. Here, we identified the signaling molecules involved in regulation of renal proximal tubular Na-K-ATPase at high ANG II concentrations. Proximal tubules from spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats were incubated with low concentrations of ANG II (pM), which activated Na-K-ATPase in both the groups; however, the stimulation was more robust in SHR. A high concentration of ANG II (µM) failed to stimulate Na-K-ATPase in WKY rats. However, in SHR ANG II (µM) continued to stimulate Na-K-ATPase, which was sensitive to the AT1R antagonist candesartan. In the presence of N(G)-nitro-l-arginine methyl ester (l-NAME), a nitric oxide (NO) synthase (NOS) inhibitor, ANG II (µM) caused stimulation of Na-K-ATPase in proximal tubules of WKY rats while having no further stimulatory effect in SHR. ANG II (µM), via AT1R, increased proximal tubular NO levels in WKY rats but not in SHR. In SHR, NOS was uncoupled as incubation of proximal tubules with ANG II and l-arginine, a NOS substrate, caused superoxide generation only in SHR and not in WKY rats. The superoxide production in SHR was sensitive to l-NAME. There was exaggerated proximal tubular AT1R-G protein coupling and NAD(P)H oxidase activation in response to ANG II (µM) in proximal tubules of SHR compared with WKY rats. In SHR, inhibition of NADPH oxidase restored NOS coupling and ANG II-induced NO accumulation. In conclusion, at a high concentration ANG II (µM) activates renal NO signaling, which prevents stimulation of Na-K-ATPase in WKY rats. However, in SHR ANG II (µM) overstimulates NADPH oxidase, which impairs the NO system and leads to continued Na-K-ATPase activation.

Dopamine and vascular dynamics control: present status and future perspectives.

The catecholamine dopamine is a precursors in the biosynthesis of norepinephrine and epinephrine as well as a neurotransmitter in the central nervous system. Besides of its well known role of brain neurotransmitter, dopamine exerts specific functions at the periphery, being those at the level of the cardiovascular system and the kidney the most relevant. In fact it plays a role of modulator of blood pressure, sodium balance, and renal and adrenal functions through an independent peripheral dopaminergic system. In vivo administration or in vitro application of dopamine or of dopamine receptor agonists induce vasodilatation in the cerebral, coronary, renal and mesenteric vascular beds and cause hypotension. Moreover, dopamine stimulates cardiac contractility and induces diuresis and natriuresis. Dopamine probably plays a role in the pathogenesis of arterial hypertension by regulating epithelial sodium transport, vascular smooth muscle contractility and production of reactive oxygen species and by interacting with the renin-angiotensin and sympathetic nervous systems. Dopamine exerts its actions via a class of cell surface receptors belonging to the rhodopsin-like family of G-protein coupled receptors. Dopamine receptors are classified into D1-like (D1 and D5) and D2-like (D2, D3 and D4) subtypes based on their structure and pharmacology. Each of the dopamine receptor subtypes can participate in the regulation of blood pressure by specific mechanisms. Some receptors regulate blood pressure by influencing the central and/or autonomic nervous system; others influence epithelial transport and regulate the secretion and receptors of several humeral agents. This paper outlines the biochemistry, anatomical localization and physiology of the different dopamine receptors involved in the regulation of blood pressure, the relationship between dopamine receptor subtypes and hypertension and possibilities of modulating pharmacologically vascular dopamine receptor function.

Potential dopamine-1 receptor stimulation in hypertension management.

The role of dopamine receptors in blood pressure regulation is well established. Genetic ablation of both dopamine D1-like receptor subtypes (D1, D5) and D2-like receptor subtypes (D2, D3, D4) results in a hypertensive phenotype in mice. This review focuses on the dopamine D1-like receptor subtypes D1 and D5 (especially D1 receptors), as they play a major role in regulating sodium homeostasis and blood pressure. Studies mostly describing the role of renal dopamine D1-like receptors are included, as the kidneys play a pivotal role in the maintenance of sodium homeostasis and the long-term regulation of blood pressure. We also attempt to describe the interaction between D1-like receptors and other proteins, especially angiotensin II type 1 and type 2 receptors, which are involved in the maintenance of sodium homeostasis and blood pressure. Finally, we discuss a new concept of renal D1 receptor regulation in hypertension that involves oxidative stress mechanisms.

Resveratrol prevents endothelial nitric oxide synthase uncoupling and attenuates development of hypertension in spontaneously hypertensive rats.

Endothelial dysfunction is a hallmark of hypertension and vascular oxidative stress can contribute to endothelial dysfunction and hypertension development. Resveratrol is an antioxidant polyphenol which improves endothelium dependent relaxation, the mechanisms of which are unknown. Also, the role of resveratrol in hypertension remains to be established. The purpose of this study was to investigate the mechanisms of resveratrol induced improvement of endothelial function and establish its role in hypertension. SHR and WKY rats, 3-4 weeks old, were treated with resveratrol in drinking water for 10 weeks, untreated SHR and WKY rats served as controls. At the end of the treatment, control SHR exhibited increased blood pressure, oxidative stress and attenuated endothelium dependent relaxation in comparison to WKY rats. The impaired endothelium function in SHR was associated with lower nitrite/nitrate levels, elevated nitrotyrosine content and eNOS uncoupling. Resveratrol treatment attenuated hypertension development in SHR as indicated by lower blood pressure in resveratrol treated SHR (SHR-R) compared to control SHR. SHR-R also exhibited reduced H(2)O(2) content and elevated superoxide dismutase activity. Resveratrol treatment normalized endothelium dependent vasorelaxation in SHR. In parallel, resveratrol restored nitrite/nitrate levels and normalized nitrotyrosine content in SHR. SHR exhibited increased l-arginine dependent superoxide production which was blocked by NOS inhibitor l-NNA, suggesting eNOS uncoupling. eNOS uncoupling was prevented by resveratrol treatment. In conclusion, early treatment with resveratrol lowers oxidative stress, preserves endothelial function and attenuates development of hypertension in SHR. More importantly, prevention of eNOS uncoupling and NO scavenging could represent novel mechanisms for resveratrol-mediated antihypertensive effects.

Angiotensin II-mediated biphasic regulation of proximal tubular Na+/H+ exchanger 3 is impaired during oxidative stress.

Angiotensin (ANG) II via AT1 receptors (AT1Rs) maintains sodium homeostasis by regulating renal sodium transporters including Na(+)/H(+) exchanger 3 (NHE3) in a biphasic manner. Low-ANG II concentration stimulates whereas high concentrations inhibit NHE3 activity. Oxidative stress has been shown to upregulate AT1R function that could modulate the ANG II-mediated NHE3 regulation. This study was designed to identify the signaling pathways responsible for ANG II-mediated biphasic regulation of proximal tubular NHE3 and the effect of oxidative stress on this phenomenon. Male Sprague-Dawley rats were chronically treated with a pro-oxidant L-buthionine sulfoximine (BSO) with and without an antioxidant tempol in tap water for 3 wk. BSO-treated rats exhibited oxidative stress and high blood pressure. At low concentration (1 pM) ANG II increased NHE3 activity in proximal tubules from all animals. However, in BSO-treated rats, the stimulation was more robust and was normalized by tempol treatment. ANG II (1 pM)-mediated NHE3 activation was abolished by AT1R blocker, intracellular Ca(2+) chelator, and inhibitors of phospholipase C (PLC) and Ca(2+)-dependent calmodulin (CaM) but it was insensitive to Giα and protein kinase C inhibitors or AT2R antagonist. A high concentration of ANG II (1 µM) inhibited NHE3 activity in control and tempol-treated rats. However, in BSO-treated rats, ANG II (1 µM) continued to induce NHE3 stimulation. Tempol restored the inhibitory effect of ANG II (1 µM) in BSO-treated rats. The inhibitory effect of ANG II (1 µM) involved AT1R-dependent, cGMP-dependent protein kinase (PKG) activation and was independent of AT2 receptor and nitric oxide signaling. We conclude that ANG II stimulates NHE3 via AT1R-PLC-CaM pathway and inhibits NHE3 by AT1R-PKG activation. Oxidative stress impaired ANG II-mediated NHE3 biphasic response in that stimulation was observed at both high- and low-ANG II concentration.

Oxidative stress causes renal angiotensin II type 1 receptor upregulation, Na+/H+ exchanger 3 overstimulation, and hypertension.

Oxidative stress modulates angiotensin (Ang) II type 1 receptor (AT(1)R) expression and function. Ang II activates renal Na(+)/H(+) exchanger 3 (NHE3) to increase sodium reabsorption, but the mechanisms are still elusive. In addition, the upregulation of AT(1)R during oxidative stress could promote sodium retention and lead to an increase in blood pressure. Herein, we investigated the mechanism of Ang II-mediated, AT(1)R-dependent renal NHE3 regulation and effect of oxidative stress on AT(1)R signaling and development of hypertension. Male Sprague-Dawley rats received tap water (control) or 30 mmol/L of l-buthionine-sulfoximine, an oxidant, with and without 1 mmol/L of Tempol, an antioxidant, for 3 weeks. l-Buthionine-sulfoximine-treated rats exhibited oxidative stress and high blood pressure. Incubation of renal proximal tubules with Ang II caused significantly higher NHE3 activation in l-buthionine-sulfoximine-treated rats compared with control. The activation of NHE3 was sensitive to AT(1)R blocker and inhibitors of phospholipase C, tyrosine kinase, janus kinase 2 (Jak2), Ca(2+)-dependent calmodulin (CaM), and Ca(2+) chelator. Also, incubation of proximal tubules with Ang II caused Jak2-dependent CaM phosphorylation, which led to Jak2-CaM complex formation and increased Jak2-CaM interaction with NHE3. The activation of these signaling molecules was exaggerated in l-buthionine-sulfoximine-treated rats, whereas Tempol normalized the AT(1)R signaling. In conclusion, Ang II activates renal proximal tubular NHE3 through novel pathways that involve phospholipase C and an increase in intracellular Ca(2+), Jak2, and CaM. In addition, oxidative stress exaggerates Ang II signaling, which leads to overstimulation of renal NHE3 and contributes to an increase in blood pressure.

Oxidative stress alters renal D1 and AT1 receptor functions and increases blood pressure in old rats.

Aging is associated with an increase in oxidative stress and blood pressure (BP). Renal dopamine D1 (D1R) and angiotensin II AT1 (AT1R) receptors maintain sodium homeostasis and BP. We hypothesized that age-associated increase in oxidative stress causes altered D1R and AT1R functions and high BP in aging. To test this, adult (3 mo) and old (21 mo) Fischer 344 × Brown Norway F1 rats were supplemented without/with antioxidant tempol followed by determining oxidative stress markers (urinary antioxidant capacity, proximal tubular NADPH-gp91phox, and plasma 8-isoprostane), D1R and AT1R functions, and BP. The D1R and AT1R functions were determined by measuring diuretic and natriuretic responses to D1R agonist (SKF-38393; 1 µg·kg(-1)·min(-1) iv) and AT1R antagonist (candesartan; 10 µg/kg iv), respectively. We found that the total urinary antioxidant capacity was lower in old rats, which increased with tempol treatment. In addition, tempol decreased the elevated NADPH-gp91phox and 8-isoprostane levels in old rats. Systolic, diastolic, and mean arterial BPs were higher in old rats and were reduced by tempol. Although SKF-38393 produced diuresis in both adult and old rats, urinary sodium excretion (UNaV) increased only in adult rats. While candesartan increased diuresis and UNaV in adult and old rats, the magnitude of response was greater in old rats. Tempol treatment in old rats reduced candesartan-induced increase in diuresis and UNaV. Our results demonstrate that diminished renal D1R and exaggerated AT1R functions are associated with high BP in old rats. Furthermore, oxidative stress may cause altered renal D1R and AT1R functions and high BP in old rats.