Antioxidative effect of p38 mitogen-activated protein kinase inhibitor in the kidney of hypertensive rat

Eucommia ulmoides (Tochu) and its extract geniposidic acid reduced blood pressure and improved renal hemodynamics

INTRODUCTION

Eucommia ulmoides leaves are used as Tochu tea, which has a blood pressure lowering effect of unknown mechanism.

PURPOSE AND METHODS

The effects of Tochu tea and its component, geniposidic acid, on blood pressure and renal hemodynamics were investigated in Dahl salt-sensitive (DS) rats received 1% saline solution from 4 weeks of age. At 9 weeks of age, 1% saline alone (DSHS), Tochu tea extract added 1% saline (DSHS+T), or geniposidic acid added 1% saline (DSHS+G) was administered for another 4 weeks. DS rats fed with tap water were used as controls (DSLS). At 13 weeks, the blood pressure, the renal plasma flow (RPF) and the renal NADPH oxidase, endothelial nitric oxide synthase (eNOS) were examined.

RESULTS

Blood pressure in DSHS rats was significantly increased in comparison to DSLS (144 vs. 196 mmHg, p < 0.01), and was significantly reduced in DSHS+T (158 mmHg) and DSHS+G (162 mmHg) rats. RPF in DSHS+T rats was significantly higher than in DSHS rats (p < 0.05). The expression of NADPH oxidase in DSHS rats was enhanced in comparison to DSLS rats; however, it was suppressed in DSHS+T and DSHS+G rats, and the NO production by eNOS was increased; thus, RPF was improved. The urinary Na excretion in DSHS rats was higher than that in DSLS rats; however it was further increased in DSHS+T rats without changes in the tubular Na transporters.

CONCLUSION

Tochu tea and geniposidic acid suppressed NADPH oxidase, increased eNOS, and improved blood pressure and renal hemodynamics.

(-)-Epicatechin and the colonic metabolite 2,3-dihydroxybenzoic acid protect against high glucose and lipopolysaccharide-induced inflammation in renal proximal tubular cells through NOX-4/p38 signalling

Chronic hyperglycaemia and inflammation are present in diabetes and both processes have been related to the pathogenesis of diabetic kidney disease. Epicatechin (EC) and main colonic phenolic acids derived from flavonoid intake, such as 2,3-dihydroxybenzoic acid (DHBA), 3,4-dihydroxyphenylacetic acid (DHPAA) and 3-hydroxyphenylpropionic acid (HPPA), have been suggested to exert beneficial effects in diabetes. This study was aimed at investigating whether the mentioned compounds could prevent inflammation in renal proximal tubular NRK-52E cells induced by high glucose and lipopolysaccharide (LPS). Pre-treatment of cells with EC and DHBA (5 μM) reverted the enhanced levels of pro-inflammatory cytokines, such as tumour necrosis factor-α (TNF-α), interleukin-6 (IL-6) and monocyte chemoattractant protein 1 (MCP-1), activated by high glucose and LPS. Additionally, EC and DHBA pre-incubation reduced the increased values of adhesion molecules, namely, intercellular cell adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1), as well as those of mitogen-activated protein kinases (MAPKs) [extracellular signal-regulated kinase (ERK), -c-jun N-terminal kinase (JNK) and -p38 protein kinase (p38)] activated by the high glucose and LPS challenge. Thus, in EC and DHBA pre-treated cells ICAM-1, p-ERK and p-JNK were returned to control values, and VCAM-1 and p-p38 levels were reduced by ∼20 and 25%, respectively, when compared to high glucose plus LPS-stimulated cells. Likewise, pre-treatment with EC and DHBA protected against high glucose plus LPS-triggered oxidative stress by preventing increased ROS and NADPH oxidase 4 (NOX-4) levels (∼25 and 45% reduction, respectively). By using specific inhibitors of p38 and NOX-4, the participation of both proteins in EC- and DHBA-mediated protection against inflammation and associated oxidative stress was shown. Taken together, EC and DHBA exert beneficial effects in renal proximal tubular cells, as they contribute to preventing the inflammatory-induced milieu and the accompanying redox imbalance, playing NOX-4/p38 a crucial role.

Natriuretic peptide receptor guanylyl cyclase-A pathway counteracts glomerular injury evoked by aldosterone through p38 mitogen-activated protein kinase inhibition

Guanylyl cyclase-A (GC-A) signaling, a natriuretic peptide receptor, exerts renoprotective effects by stimulating natriuresis and reducing blood pressure. Previously we demonstrated massive albuminuria with hypertension in uninephrectomized, aldosterone-infused, and high salt-fed (ALDO) systemic GC-A KO mice with enhanced phosphorylation of p38 mitogen-activated protein kinase (MAPK) in podocytes. In the present study, we examined the interaction between p38 MAPK and GC-A signaling. The administration of FR167653, p38 MAPK inhibitor, reduced systolic blood pressure (SBP), urinary albumin excretion, segmental sclerosis, podocyte injury, and apoptosis. To further investigate the local action of natriuretic peptide and p38 MAPK in podocytes, we generated podocyte-specific (pod) GC-A conditional KO (cKO) mice. ALDO pod GC-A cKO mice demonstrated increased urinary albumin excretion with marked mesangial expansion, podocyte injury and apoptosis, but without blood pressure elevation. FR167653 also suppressed urinary albumin excretion without reducing SBP. Finally, we revealed that atrial natriuretic peptide increased phosphorylation of MAPK phosphatase-1 (MKP-1) concomitant with inhibited phosphorylation of p38 MAPK in response to MAPK kinase 3 activation, thereby resulting in decreased mRNA expression of the apoptosis-related gene, Bax, and Bax/Bcl2 ratio in cultured podocytes. These results indicate that natriuretic peptide exerts a renoprotective effect via inhibiting phosphorylation of p38 MAPK in podocytes.

Diabetes and Kidney Disease: Role of Oxidative Stress

Intrarenal oxidative stress plays a critical role in the initiation and progression of diabetic kidney disease (DKD). Enhanced oxidative stress results from overproduction of reactive oxygen species (ROS) in the context of concomitant, insufficient antioxidant pathways. Renal ROS production in diabetes is predominantly mediated by various NADPH oxidases (NOXs), but a defective antioxidant system as well as mitochondrial dysfunction may also contribute. Recent Advances: Effective agents targeting the source of ROS generation hold the promise to rescue the kidney from oxidative damage and prevent subsequent progression of DKD. Critical Issues and Future Directions: In the present review, we summarize and critically analyze molecular and cellular mechanisms that have been demonstrated to be involved in NOX-induced renal injury in diabetes, with particular focus on the role of increased glomerular injury, the development of albuminuria, and tubulointerstitial fibrosis, as well as mitochondrial dysfunction. Furthermore, novel agents targeting NOX isoforms are discussed. Antioxid. Redox Signal. 25, 657-684.

Rodent animal models: from mild to advanced stages of diabetic nephropathy

Diabetic nephropathy (DN) is a secondary complication of both type 1 and type 2 diabetes, resulting from uncontrolled high blood sugar. 30-40% of diabetic patients develop DN associated with a poor life expectancy and end-stage renal disease, causing serious socioeconomic problems. Although an exact pathogenesis of DN is still unknown, several factors such as hyperglycemia, hyperlipidemia, hypertension and proteinuria may contribute to the progression of renal damage in diabetic nephropathy. DN is confirmed by measuring blood urea nitrogen, serum creatinine, creatinine clearance and proteinuria. Clinical studies show that intensive control of hyperglycemia and blood pressure could successfully reduce proteinuria, which is the main sign of glomerular lesions in DN, and improve the renal prognosis in patients with DN. Diabetic rodent models have traditionally been used for doing research on pathogenesis and developing novel therapeutic strategies, but have limitations for translational research. Diabetes in animal models such as rodents are induced either spontaneously or by using chemical, surgical, genetic, or other techniques and depicts many clinical features or related phenotypes of the disease. This review discusses the merits and demerits of the models, which are used for many reasons in the research of diabetes and diabetic complications.

Enhanced p22phox expression impairs vascular function through p38 and ERK1/2 MAP kinase-dependent mechanisms in type 2 diabetic mice

Type 2 diabetes is associated with vascular complication. We hypothesized that increased nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunit p22(phox) expression impairs vascular endothelium-dependent relaxation (EDR) in type 2 diabetes. Type 2 diabetic (db(-)/db(-)) and control (db(-)/db(+)) mice were treated with reactive oxygen species (ROS) scavenger, polyethylene glycol superoxide dismutase (1,000 U/kg daily ip), or small interfering RNA p22(phox) (p22(phox)-lentivirus-small interfering RNA, 100 μg iv, 2 times/wk) for 1 mo. EDR was impaired in microvascular bed (coronary arteriole and femoral and mesenteric resistance arteries) from diabetic mice compared with control. Interestingly, ROS scavenger and p22(phox) downregulation did not affect blood glucose level or body weight but significantly improved EDR. Mitogen-activated protein kinases (ERK1/2 and p38) phosphorylation and NADPH oxidase activity were increased in arteries from diabetic mice and were reduced after ROS scavenger or p22(phox) downregulation in db(-)/db(-) mice. The present study showed that enhanced p22(phox) expression causes vascular dysfunction through ERK1/2 and p38-mitogen-activated protein kinase-dependent mechanisms in male type 2 diabetic mice. Therefore, p22(phox) could be an important target to improve vascular function in diabetes.

Silencing of HIF prolyl-hydroxylase 2 gene in the renal medulla attenuates salt-sensitive hypertension in Dahl S rats

BACKGROUND

In response to high salt intake, transcription factor hypoxia-inducible factor (HIF) 1α activates many antihypertensive genes, such as heme oxygenase 1 (HO-1) 1 and cyclooxygenase 2 (COX-2) in the renal medulla, which is an important molecular adaptation to promote extra sodium excretion. We recently showed that high salt inhibited the expression of HIF prolyl-hydroxylase 2 (PHD2), an enzyme that promotes the degradation of HIF-1α, thereby upregulating HIF-1α, and that high salt-induced inhibition in PHD2 and subsequent activation of HIF-1α in the renal medulla was blunted in Dahl salt-sensitive hypertensive rats. This study tested the hypothesis that silencing the PHD2 gene to increase HIF-1α levels in the renal medulla attenuates salt-sensitive hypertension in Dahl S rats.

METHODS

PHD2 short hairpin RNA (shRNA) plasmids were transfected into the renal medulla in uninephrectomized Dahl S rats. Renal function and blood pressure were then measured.

RESULTS

PHD2 shRNA reduced PHD2 levels by >60% and significantly increased HIF-1α protein levels and the expression of HIF-1α target genes HO-1 and COX-2 by >3-fold in the renal medulla. Functionally, pressure natriuresis was remarkably enhanced, urinary sodium excretion was doubled after acute intravenous sodium loading, and chronic high salt-induced sodium retention was remarkably decreased, and as a result, salt-sensitive hypertension was significantly attenuated in PHD2 shRNA rats compared with control rats.

CONCLUSIONS

Impaired PHD2 response to high salt intake in the renal medulla may represent a novel mechanism for hypertension in Dahl S rats, and inhibition of PHD2 in the renal medulla could be a therapeutic approach for salt-sensitive hypertension.

Age-dependent salt hypertension in Dahl rats: fifty years of research

Fifty years ago, Lewis K. Dahl has presented a new model of salt hypertension - salt-sensitive and salt-resistant Dahl rats. Twenty years later, John P. Rapp has published the first and so far the only comprehensive review on this rat model covering numerous aspects of pathophysiology and genetics of salt hypertension. When we summarized 25 years of our own research on Dahl/Rapp rats, we have realized the need to outline principal abnormalities of this model, to show their interactions at different levels of the organism and to highlight the ontogenetic aspects of salt hypertension development. Our attention was focused on some cellular aspects (cell membrane function, ion transport, cell calcium handling), intra- and extrarenal factors affecting renal function and/or renal injury, local and systemic effects of renin-angiotensin-aldosterone system, endothelial and smooth muscle changes responsible for abnormal vascular contraction or relaxation, altered balance between various vasoconstrictor and vasodilator systems in blood pressure maintenance as well as on the central nervous and peripheral mechanisms involved in the regulation of circulatory homeostasis. We also searched for the age-dependent impact of environmental and pharmacological interventions, which modify the development of high blood pressure and/or organ damage, if they influence the salt-sensitive organism in particular critical periods of development (developmental windows). Thus, severe self-sustaining salt hypertension in young Dahl rats is characterized by pronounced dysbalance between augmented sympathetic hyperactivity and relative nitric oxide deficiency, attenuated baroreflex as well as by a major increase of residual blood pressure indicating profound remodeling of resistance vessels. Salt hypertension development in young but not in adult Dahl rats can be attenuated by preventive increase of potassium or calcium intake. On the contrary, moderate salt hypertension in adult Dahl rats is attenuated by superoxide scavenging or endothelin-A receptor blockade which do not affect salt hypertension development in young animals.

Altered MAPK signaling in progressive deterioration of endothelial function in diabetic mice

We aimed to investigate specific roles of mitogen-activated protein kinases (MAPK) in the deterioration of endothelial function during the progression of diabetes and the potential therapeutic effects of MAPK inhibitors and agonists in the amelioration of endothelial function. Protein expression and phosphorylation of p38, c-Jun NH(2)-terminal kinase (JNK), and extracellular signal-regulated kinase (Erk) were assessed in mesenteric arteries of 3- (3M) and 9-month-old (9M) male diabetic and control mice. The expression of p38, JNK, and Erk was comparable in all groups of mice, but the phosphorylation of p38 and JNK was increased in 3M and further increased in 9M diabetic mice, whereas the phosphorylation of Erk was substantially reduced in 9M diabetic mice. NADPH oxidase-dependent superoxide production was significantly increased in vessels of two ages of diabetic mice. Inhibition of either p38 with SB203580 or JNK with SP600125 reduced superoxide production and improved shear stress-induced dilation (SSID) in 3M, but not in 9M, diabetic mice. Treating the vessels of 9M diabetic mice with resveratrol increased Erk phosphorylation and shear stress-induced endothelial nitric oxide synthase (eNOS) phosphorylation and activity, but resveratrol alone did not improve SSID. Administration of resveratrol and SB203580 or resveratrol and SP600125 together significantly improved SSID in vessels of 9M diabetic mice. The improved response was prevented by U0126, an Erk inhibitor. Thus, p38/JNK-dependent increase in oxidative stress diminished nitric oxide-mediated dilation in vessels of 3M diabetic mice. Oxidative stress and impaired Erk-dependent activation of eNOS exacerbates endothelial dysfunction in the advanced stage of diabetes.

Restraint of spreading-dependent activation of polymorphonuclear leukocyte NADPH oxidase in an acidified environment

Elucidation of the mechanisms by which environmental pH affects or regulates the functions of polymorphonuclear leukocytes (PMNs) is important because severe acidification of the microenvironment often prevails at sites of inflammation where they act in host defense. In the present study, we investigated the effect of an acidic environment on spreading-dependent activation of O2- -producing NADPH oxidase in PMNs. We found that PMNs underwent spreading spontaneously over type I collagen and plastic surfaces at both neutral and acidic pH, although spreading over fibrinogen surfaces, for which cellular stimulation with H2O2 is required, was inhibited by acidic pH. At acidic pH, however, PMNs were unable to undergo spreading-dependent production of O2-. Pharmacological experiments showed that p38 mitogen-activated protein kinase (MAPK) was involved in the signaling pathways mediating the spreading-dependent activation of NADPH oxidase, and that its spreading-dependent phosphorylation of Thr-180 and Tyr-182, a hallmark of activation, was impaired at acidic pH. Furthermore, the inhibition by acidic pH of O2- production as well as p38 MAPK phosphorylation subsequent to spreading induction was reversible; environmental neutralization and acidification after induction of spreading at acidic and neutral pH, respectively, up- and down-regulated the two phenomena. Acidic pH did not affect the O2- production activity of NADPH oxidase pre-activated by phorbol 12-myristate 13-acetate (PMA). These results suggest that, in PMNs, the p38 MAPK-mediated signaling pathway functions as a pH-sensing regulator of spreading-dependent NADPH oxidase activation.

Overexpression of HIF-1α transgene in the renal medulla attenuated salt sensitive hypertension in Dahl S rats

Hypoxia inducible factor (HIF)-1α-mediated gene activation in the renal medulla in response to high salt intake plays an important role in the control of salt sensitivity of blood pressure. High salt-induced activation of HIF-1α in the renal medulla is blunted in Dahl S rats. The present study determined whether the impairment of the renal medullary HIF-1α pathway was responsible for salt sensitive hypertension in Dahl S rats. Renal medullary HIF-1α levels were induced by either transfection of HIF-1α expression plasmid or chronic infusion of CoCl₂ into the renal medulla, which was accompanied by increased expressions of anti-hypertensive genes, cyclooxygenase-2 and heme oxygenase-1. Overexpression of HIF-1α transgenes in the renal medulla enhanced the pressure natriuresis, promoted the sodium excretion and reduced sodium retention after salt overload. As a result, hypertension induced by 2-week high salt was significantly attenuated in rats treated with HIF-1α plasmid or CoCl₂. These results suggest that an abnormal HIF-1α in the renal medulla may represent a novel mechanism mediating salt-sensitive hypertension in Dahl S rats and that induction of HIF-1α levels in the renal medulla could be a therapeutic approach for the treatment of salt-sensitive hypertension.

Cardioprotective effect of a combination of Rho-kinase inhibitor and p38 MAPK inhibitor on cardiovascular remodeling and oxidative stress in Dahl rats

AIM

Rho-kinase plays a critical role in various cellular functions. p38 mitogen-activated protein kinase (p38 MAPK) plays a central role in the inflammatory cytokine response to immune challenge. We evaluated the effects of a combination of fasudil, a Rho-kinase inhibitor, and FR167653, a p38 MAPK inhibitor, on cardiovascular remodeling, inflammation, and oxidative stress in Dahl salt-sensitive hypertensive (DS) rats.

METHODS

DS and Dahl salt-resistant (DR) rats were fed a high-salt diet at 6 weeks of age. Vehicle, fasudil (100 mg/kg per day), FR167653 (2 mg/kg per day), and a combination of fasudil and FR167653 were administered to 6-week-old DS rats for 5 weeks.

RESULTS

At the age of 11 weeks, in the left ventricle, DS rats were characterized by increased myocardial fibrosis, phosphorylation of p38 MAPK, and myosin phosphatase targeting subunit (MYPT-1), and NAD(P)H oxidase p22(phox), p47(phox), gp91(phox), tumor necrosis factor-α and interleukin-1β expression compared with DR rats. Fasudil improved cardiovascular remodeling, inflammation, NAD(P)H oxidase subunits, and phosphorylation of p38 MAPK and MYPT-1. FR167653 also similarly ameliorated these indices but not MYPT-1 phosphorylation. Compared with either agent alone, a combination of fasudil and FR167653 was more effective for the improvement of myocardial damage, inflammation and oxidative stress.

CONCLUSION

These findings suggest that the Rho-kinase and p38 MAPK pathways may play a pivotal role in ventricular hypertrophy; thus, we obtained the first evidence that a combination of Rho-kinase inhibitor and p38 MAPK inhibitor may provide a potential therapeutic target in hypertension with cardiovascular remodeling.

Relationship between urinary angiotensinogen and salt sensitivity of blood pressure in patients with IgA nephropathy

We demonstrated previously that the blood pressure of patients with IgA nephropathy becomes salt sensitive as renal damage progresses. We also showed that increased urinary angiotensinogen levels in such patients closely correlate with augmented renal tissue angiotensinogen gene expression and angiotensin II levels. Here, we investigated the relationship between urinary angiotensinogen and salt sensitivity of blood pressure in patients with IgA nephropathy. Forty-one patients with IgA nephropathy consumed an ordinary salt diet (12 g/d of NaCl) for 1 week and a low-salt diet (5 g/d of NaCl) for 1 week in random order. The salt-sensitivity index was calculated as the reciprocal of the slope of the pressure-natriuresis curve drawn by linking 2 data points obtained during consumption of each diet. The urinary angiotensinogen:creatinine ratio was significantly higher in patients who consumed the ordinary salt diet compared with the low-salt diet (17.5 μg/g [range: 7.3 to 35.6 μg/g] versus 7.9 μg/g [range: 3.1 to 14.2 μg/g] of creatinine, respectively; P<0.001). The sodium sensitivity index in our patients positively correlated with the glomerulosclerosis score (r=0.43; P=0.008) and changes in logarithmic urinary angiotensinogen:creatinine ratio (r=0.37; P=0.017) but not with changes in urinary protein excretion (r=0.18; P=0.49). In contrast, changes in sodium intake did not alter the urinary angiotensinogen:creatinine ratio in patients with Ménière disease and normal renal function (n=9). These data suggest that the inappropriate augmentation of intrarenal angiotensinogen induced by salt and associated renal damage contribute to the development of salt-sensitive hypertension in patients with IgA nephropathy.

Blockade of AT1 receptors protects the blood-brain barrier and improves cognition in Dahl salt-sensitive hypertensive rats

BACKGROUND

The present study tested the hypothesis that inappropriate activation of the brain renin-angiotensin system (RAS) contributes to the pathogenesis of blood-brain barrier (BBB) disruption and cognitive impairment during development of salt-dependent hypertension. Effects of an angiotensin II (AngII) type-1 receptor blocker (ARB), at a dose that did not reduce blood pressure, were also examined.

METHODS

Dahl salt-sensitive (DSS) rats at 6 weeks of age were assigned to three groups: low-salt diet (DSS/L; 0.3% NaCl), high-salt diet (DSS/H; 8% NaCl), and high-salt diet treated with ARB, olmesartan at 1 mg/kg.

RESULTS

DSS/H rats exhibited hypertension, leakage from brain microvessels in the hippocampus, and impaired cognitive functions, which were associated with increased brain AngII levels, as well as decreased mRNA levels of tight junctions (TJs) and collagen-IV in the hippocampus. In DSS/H rats, olmesartan treatment, at a dose that did not alter blood pressure, restored the cognitive decline, and ameliorated leakage from brain microvessels. Olmesartan also decreased brain AngII levels and restored mRNA expression of TJs and collagen-IV in DSS/H rats.

CONCLUSIONS

These results suggest that during development of salt-dependent hypertension, activation of the brain RAS contributes to BBB disruption and cognitive impairment. Treatment with an ARB could elicit neuroprotective effects in cognitive disorders by preventing BBB permeability, which is independent of blood pressure changes.

The contribution of reactive oxygen species and p38 mitogen-activated protein kinase to myofilament oxidation and progression of heart failure in rabbits

BACKGROUND AND PURPOSE

The formation of reactive oxygen species (ROS) is increased in heart failure (HF). However, the causal and mechanistic relationship of ROS formation with contractile dysfunction is not clear in detail. Therefore, ROS formation, myofibrillar protein oxidation and p38 MAP kinase activation were related to contractile function in failing rabbit hearts.

EXPERIMENTAL APPROACH AND KEY RESULTS

Three weeks of rapid left ventricular (LV) pacing reduced LV shortening fraction (SF, echocardiography) from 32 +/- 1% to 13 +/- 1%. ROS formation, as assessed by dihydroethidine staining, increased by 36 +/- 8% and was associated with increased tropomyosin oxidation, as reflected by dimer formation (dimer to monomer ratio increased 2.28 +/- 0.66-fold in HF vs. sham, P < 0.05). Apoptosis (TdT-mediated dUTP nick end labelling staining) increased more than 12-fold after 3 weeks of pacing when a significant increase in the phosphorylation of p38 MAP kinase and HSP27 was detected (Western blotting). Vitamins C and E abolished the increases in ROS formation and tropomyosin oxidation along with an improvement of LVSF (19 +/- 1%, P < 0.05 vs. untreated HF) and prevention of apoptosis, but without modifying p38 MAP kinase activation. Inhibition of p38 MAP kinase by SB281832 counteracted ROS formation, tropomyosin oxidation and contractile failure, without affecting apoptosis.

CONCLUSIONS AND IMPLICATIONS

Thus, p38 MAP kinase activation appears to be upstream rather than downstream of ROS, which impacts on LV function through myofibrillar oxidation. p38 MAP kinase inhibition is a potential target to prevent or treat HF.

Hypoxia-inducible factor prolyl-hydroxylase 2 senses high-salt intake to increase hypoxia inducible factor 1alpha levels in the renal medulla

High salt induces the expression of transcription factor hypoxia-inducible factor (HIF) 1alpha and its target genes in the renal medulla, which is an important renal adaptive mechanism to high-salt intake. HIF prolyl-hydroxylase domain-containing proteins (PHDs) have been identified as major enzymes to promote the degradation of HIF-1alpha. PHD2 is the predominant isoform of PHDs in the kidney and is primarily expressed in the renal medulla. The present study tested the hypothesis that PHD2 responds to high salt and mediates high-salt-induced increase in HIF-1alpha levels in the renal medulla. In normotensive rats, high-salt intake (4% NaCl, 10 days) significantly inhibited PHD2 expressions and enzyme activities in the renal medulla. Renal medullary overexpression of the PHD2 transgene significantly decreased HIF-1alpha levels. PHD2 transgene also blocked high-salt-induced activation of HIF-1alpha target genes heme oxygenase 1 and NO synthase 2 in the renal medulla. In Dahl salt-sensitive hypertensive rats, however, high-salt intake did not inhibit the expression and activities of PHD2 in the renal medulla. Correspondingly, renal medullary HIF-1alpha levels were not upregulated by high-salt intake in these rats. After transfection of PHD2 small hairpin RNA, HIF-1alpha and its target genes were significantly upregulated by high-salt intake in Dahl salt-sensitive rats. Overexpression of PHD2 transgene in the renal medulla impaired renal sodium excretion after salt loading. These data suggest that high-salt intake inhibits PHD2 in the renal medulla, thereby upregulating the HIF-1alpha expression. The lack of PHD-mediated response to high salt may represent a pathogenic mechanism producing salt-sensitive hypertension.

Tumor necrosis factor-alpha induces renal vasoconstriction as well as natriuresis in mice

Tumor necrosis factor-α (TNF-α) has been implicated in the pathogenesis of hypertension and renal injury. However, the direct effects of TNF-α on renal hemodynamic and excretory function are not yet clearly defined. We examined the renal responses to infusion of TNF-α (0.33 ng·g⁻¹·min⁻¹) in anesthetized mice. Renal blood flow (RBF) and glomerular filtration rate (GFR) were determined by PAH and inulin clearance. The urine was collected from a cannula inserted into the bladder. Following the 60-min control clearance period, TNF-α infusion was initiated and 15 min were given for stabilization followed by another 60-min clearance period. TNF-α alone (n = 7) caused decreases in RBF (7.9 ± 0.3 to 6.4 ± 0.3 ml·min⁻¹·g⁻¹) and GFR (1.04 ± 0.06 to 0.62 ± 0.08 ml·min⁻¹·g⁻¹) as well as increases in absolute (0.8 ± 0.3 to 1.4 ± 0.3 μmol·min⁻¹·g⁻¹) and fractional excretion of sodium (0.5 ± 0.2 to 1.5 ± 0.4%) without affecting arterial pressure. TNF-α also increased 8-isoprostane excretion (8.10 ± 1.09 to 11.13 ± 1.34 pg·min⁻¹·g⁻¹). Pretreatment with TNF-α blocker etanercept (5 mg/kg sc; 24 and 3 h before TNF-α infusion; n = 6) abolished these responses. However, TNF-α induced an increase in RBF and caused attenuation of the GFR reduction in mice pretreated with superoxide (O₂⁻) scavenger tempol (2 μg·g⁻¹·min⁻¹; n = 6). Pretreatment with nitric oxide (NO) synthase inhibitor nitro-l-arginine methyl ester (0.1 μg·g⁻¹·min⁻¹; n = 6) resulted in further enhancement in vasoconstriction while natriuresis remained unaffected in response to TNF-α. These data suggest that TNF-α induces renal vasoconstriction and hypofiltration via enhancing the activity of O₂⁻ and thus reducing the activity of NO. The natriuretic response to TNF-α is related to its direct effects on tubular sodium reabsorption.

FR167653 inhibits fibronectin expression and apoptosis in diabetic glomeruli and in high-glucose-stimulated mesangial cells

Previous in vitro studies suggest that the p38 MAPK pathway may be involved in the pathogenesis of diabetic nephropathy, but the consequences of the inhibition of the p38 MAPK pathway have not been well elucidated in diabetic (DM) glomeruli. This study was undertaken to investigate the effect of p38 MAPK inhibitor, FR167653, on fibronectin expression and apoptosis in DM glomeruli and in high-glucose-stimulated mesangial cells (MC). In vivo, 32 Sprague-Dawley rats were injected with diluent (control, N = 16) or streptozotocin intraperitoneally (DM, N = 16). Eight rats from each group were treated with FR167653 for 3 mo. In vitro, rat MC were exposed to medium containing 5.6 mM glucose or 30 mM glucose [high glucose (HG)] with or without 10−6 M FR167653 for 24 h. Fibronectin mRNA and protein expression were determined by real-time PCR and Western blot, respectively. Western blot for apoptosis-related molecules, terminal deoxynucleotidyl transferase dUTP-mediated nick-end labeling assay, and Hoechst 33342 staining were performed to determine apoptosis. FR167653 ameliorated the increases in fibronectin-to-GAPDH mRNA ratio and protein expression in DM glomeruli by 89 and 79% and in HG-stimulated MC by 70 and 91%, respectively ( P < 0.05). Under diabetic conditions, Bcl-2 protein expression was decreased, whereas cleaved caspase-3 protein expression was increased ( P < 0.05), and these changes were inhibited by FR167653 treatment. Apoptotic cells were also significantly increased in DM glomeruli and in HG-stimulated MC ( P < 0.05), and FR167653 ameliorated these increases in apoptotic cells, both in vivo and in vitro. In conclusion, these findings suggest that the inhibition of the p38 MAPK pathway has a beneficial effect on the development of diabetic nephropathy by inhibiting the increase in fibronectin expression and apoptosis.

Helicobacter pylori-induced inhibition of vascular endothelial cell functions: a role for VacA-dependent nitric oxide reduction

Epidemiological and clinical studies provide compelling support for a causal relationship between Helicobacter pylori infection and endothelial dysfunction, leading to vascular diseases. However, clear biochemical evidence for this association is limited. In the present study, we have conducted a comprehensive investigation of endothelial injury in bovine aortic endothelial cells (BAECs) induced by H. pylori-conditioned medium (HPCM) prepared from H. pylori 60190 [vacuolating cytotoxin A (Vac(+))]. BAECs were treated with either unconditioned media, HPCM (0-25% vol/vol), or Escherichia coli-conditioned media for 24 h, and cell functions were monitored. Vac(+) HPCM significantly decreased BAEC proliferation, tube formation, and migration (by up to 44%, 65%, and 28%, respectively). Posttreatment, we also observed sporadic zonnula occludens-1 immunolocalization along the cell-cell border, and increased BAEC permeability to FD40 Dextran, indicating barrier reduction. These effects were blocked by 5-nitro-2-(3-phenylpropylamino)benzoic acid (VacA inhibitor) and were not observed with conditioned media prepared from either VacA-deleted H. pylori or E. coli. The cellular mechanism mediating these events was also considered. Vac(+) HPCM (but not Vac(-)) reduced nitric oxide (NO) by >50%, whereas S-nitroso-N-acetylpenicillamine, an NO donor, recovered all Vac(+) HPCM-dependent effects on cell functions. We further demonstrated that laminar shear stress, an endothelial NO synthase/NO stimulus in vivo, could also recover the Vac(+) HPCM-induced decreases in BAEC functions. This study shows, for the first time, a significant proatherogenic effect of H. pylori-secreted factors on a range of vascular endothelial dysfunction markers. Specifically, the VacA-dependent reduction in endothelial NO is indicated in these events. The atheroprotective impact of laminar shear stress in this context is also evident.

Pharmacological modulation of epithelial mesenchymal transition caused by angiotensin II. Role of ROCK and MAPK pathways

PURPOSE

Tubulointerstitial fibrosis is a final common pathway to end-stage chronic kidney diseases, which are characterized by elevated renal angiotensin II (AngII) production. This peptide participates in kidney damage inducing fibrosis and epithelial mesenchymal transition (EMT). Our aim was to describe potential therapeutic targets in AngII-induced EMT, investigating the blockade of different intracellular pathways.

METHODS

Studies were done in human tubular epithelial cells (HK2 cell line), evaluating changes in phenotype and EMT markers (Western blot and immunofluorescence).

RESULTS

Treatment of HK2 cells with AngII for 3 days caused transdifferentiation into myofibroblast-like cells. The blockade of MAPKs cascade, using specific inhibitors of p38 (SB203580), extracellular signal-regulated kinase1/2 (ERK; PD98059) and Jun N-terminal kinase (JNK) (SP600125), diminished AngII-induced EMT. The blockade of RhoA/ROCK pathway, by transfection of a RhoA dominant-negative vector or by ROCK inhibition with Y-27632 or fasudil, inhibited EMT caused by AngII. Connective tissue growth factor (CTGF) is a downstream mediator of AngII-induced EMT. MAPKs and ROCK inhibitors blocked CTGF overexpression induced by AngII. HMG-CoA reductase inhibitors, although blocked AngII-mediated kinases activation, only partially diminished EMT and did not regulate CTGF.

CONCLUSIONS

These data suggest a potential therapeutic use of kinase inhibitors in renal fibrosis.

Salt-sensitive hypertension induced by decoy of transcription factor hypoxia-inducible factor-1alpha in the renal medulla

Hypoxia inducible factor (HIF)-1alpha, a transcription factor, is abundantly expressed in the renal medulla and regulates many oxygen-sensitive genes such as nitric oxide synthase, cyclooxygenase-2, and heme oxygenase-1. Given the important roles of these genes in the control of arterial pressure, the present study was to test the hypothesis that HIF-1alpha-mediated gene activation serves as an antihypertensive pathway by regulating renal medullary function and sodium excretion. HIF-1alpha decoy oligodeoxynucleotides (ODNs) or scrambled ODNs were transfected into the renal medulla in uninephrectomized Sprague-Dawley rats. Two weeks after ODN transfection, the HIF-1alpha binding activities were significantly inhibited by 45%, and high salt-induced increases of nitric oxide synthase-2 and heme oxygenase-1 transcriptions were also inhibited by 70% and 61% in the renal medulla from decoy rats. The natriuretic responses and increases of renal medullary blood flow responding to the elevations of renal perfusion pressure were significantly blunted by 50% and 37% in decoy rats. Intravenously acute sodium loading increased medullary blood flow and urinary sodium excretion, which was remarkably attenuated in decoy rats. In decoy rats, high salt intake caused a greater positive sodium balance. Consequently, arterial pressure was remarkably increased (from 118+/-1.9 to 154+/-6.3 mm Hg) in decoy rats but not in control rats when the rats were challenged with a high salt diet. There was no blood pressure change in decoy rats that were maintained in normal salt diet. In conclusion, HIF-1alpha-mediated gene activation importantly participates in the regulation of renal medullary function and long-term arterial blood pressure.

Effects of p38 mitogen-activated protein kinase inhibition on blood pressure, renal hemodynamics, and renal vascular reactivity in normal and diabetic rats

p38 mitogen-activated protein kinase (p38) has been implicated in mediating vascular smooth muscle and mesangial cell contraction in response to several vasoactive factors, including angiotensin II. Early stages of diabetic nephropathy are associated with renal hemodynamic changes that are, at least in part, attributable to the dysbalance of vasoactive factors that control afferent and efferent arteriolar tone resulting in increased glomerular capillary pressure. Vascular and renal p38 have been found to be activated in diabetes. Therefore, p38 may be involved in the control of systemic and renal hemodynamics in diabetes. To address this issue, mean arterial blood pressure (MAP), glomerular filtration rate (GFR, inulin clearance), renal plasma flow (RPF, PAH clearance), metabolic parameters, and plasma renin concentrations (PRC) were determined in streptozotocin-diabetic rats (DM), and in age-matched non-diabetic controls (C), administered with the p38 inhibitor SB 239063 (SB, 50 mg/bwt, p.o.) or with vehicle. Furthermore, renal vascular responses to p38 inhibition (SB 202190, 25 microM) before and after stimulation with the endothelium-dependent vasodilator acetylcholine (ACh) were studied in vitro in tertiary branches of the renal artery from separate groups of DM and C rats, using a fixed support and a force transducer in a myograph system. SB treatment was associated with marked reductions in MAP and GFR in both C and DM rats, whereas RPF remained unchanged, as compared with vehicle-treated animals. Observed differences in MAP and renal hemodynamics were not associated with changes in urinary sodium excretion or PRC. Incubation of KCl-contracted renal arteries from both C and DM rats with the p38 inhibitor resulted in progressive and significant vasorelaxation. Also, vessels from control and diabetic rats treated with the p38 inhibitor exhibited enhancement of ACh-induced vasorelaxation. These data indicate the role of p38 in the control of systemic and renal hemodynamics both in normal and in diabetic rats. The observed effects of p38 inhibition could be mediated at least in part by enhancement of endothelium-dependent vasodilation.

Suppressing renal NADPH oxidase to treat diabetic nephropathy

Renal nicotinamide adenine dinucleotide phosphate reduced form (NADPH) oxidase is an important source of oxidative stress and its expression is enhanced in the glomerulus and distal tubules of diabetic nephropathy. High glucose-induced protein kinase C signalling or renal angiotensin II signalling increases the membrane translocation of cytosolic component p47phox. NADPH oxidase-derived reactive oxygen species (ROS) in the podocytes damage the glomerular basement membrane and the slit diaphragm causing proteinuria, and mesangial and glomerular endothelial NADPH oxidase increase TGF-beta and cause collagen and fibronectin accumulation. Tubular NADPH oxidase stimulated by angiotensin II or aldosterone contributes to sodium retention and to tubulointerstitial damage. Thus, inhibition of the renal renin-angiotensin II-aldosterone system with angiotensin-converting enzyme inhibitor, angiotensin II type 1 receptor blocker or selective aldosterone inhibitor indirectly suppresses NADPH oxidase reducing renal ROS, proteinuria and glomerulosclerosis. Statins are also effective in blocking the membrane translocation of Rac, especially in diabetes with hypercholesterolemia where ROS is produced by the intrinsic NADPH oxidase and by the activated macrophages. A medical herb, picrorhiza, inhibits the membrane translocation of p47phox, is a specific inhibitor of NADPH oxidase and, more so than superoxide dismutase mimetics, may be a promising strategy for the treatment of diabetic nephropathy.

Cardioprotective effect of angiotensin II type 1 receptor antagonist associated with bradykinin-endothelial nitric oxide synthase and oxidative stress in Dahl salt-sensitive hypertensive rats

OBJECTIVES

The interactions between eNOS or oxidative stress and bradykinin under long-term treatment of angiotensin II type 1 receptor antagonists (ATRA) remain unknown. To elucidate the molecular mechanisms of the cardioprotective effect of ATRA, we evaluated whether valsartan affects the bradykinin-eNOS and nicotinamide adenine dinucleotide (NAD(P)H) oxidase pathway.

METHODS

After 5 weeks of feeding an 8% NaCl diet to 6-week-old Dahl salt-sensitive hypertensive (DS) rats, a distinct stage of concentric left ventricular hypertrophy (LVH) was noted. Six-week-old DS rats were treated with one of the following drug combinations for 5 weeks until the onset of LVH: vehicle; bradykinin B2 receptor antagonist FR172,357 alone; high-dose hydralazine; low-dose hydralazine; high-dose valsartan; low-dose valsartan; high and low-dose valsartan plus FR172,357. Age-matched Dahl salt-resistant rats fed the same diet served as controls.

RESULTS

eNOS expression and activity, which was decreased in hypertrophy, was increased by high or low-dose valsartan, but not by high and low-dose valsartan plus FR172,357 or FR172,357 alone or high and low-dose hydralazine. The increased expression of NAD(P)H oxidase p22phox, p47phox, p67phox, and gp91phox in DS rats was suppressed by high or low-dose valsartan, but not by high or low-dose valsartan plus FR172,357 or FR172,357 alone or high and low-dose hydralazine. Valsartan effectively inhibited vascular lesion formation and suppressed the expression of transforming growth factor-beta1, connective tissue growth factor, and type I collagen, but not valsartan plus FR172,357 or FR172,357 alone or high and low-dose hydralazine.

CONCLUSION

These findings suggest that valsartan may have cardioprotective effects in this model, partly associated with the bradykinin-eNOS and oxidative stress pathway.

Female protection in progressive renal disease is associated with estradiol attenuation of superoxide production

BACKGROUND

Several types of renal disease progress at a faster rate in men compared with women, but the reasons for this sex difference are not well understood. Chronic renal disease is associated with elevated levels of toxic reactive oxygen species (ROS). Superoxide, the major ROS in the kidney, is generated by nicotinamide adenine dinucleotide phosphate (NADPH) oxidase.

OBJECTIVE

To determine if female protection from renal disease progression is consistent with 17beta-estradiol (E2) attenuation of superoxide production, this study was conducted to assess superoxide production in the renal cortex of male and female control and renal wrap (RW) rats, as well as in ovariectomized rats treated with vehicle or E2.

METHODS

Sprague-Dawley rats were divided into 2 sham operation male (Sham-M) and female (Sham-F) control groups, and 4 RW hypertensive groups: RW-M; RW-F; RW ovariectomized females treated with vehicle (RW-OVX); and RW ovariectomized females treated with E2, supplied as a 0.24 mg/60-day release pellet (RW-OVX+E2). All groups were maintained on a high-sodium (4% NaCl) diet for 6 weeks.

RESULTS

Mean (SEM) markers of renal injury and oxidative stress, including urinary protein (mg/24 h: RW-M, 298 [31] vs RW-F, 169 [22]; P < 0.001), microalbuminuria (RW/Sham arbitrary units [AU]/24 h: M, 8.78 [0.58] vs F, 4.31 [1.0]; P < 0.005), and malondialdehyde (nmol/24 h: RW-M, 167 [23] vs RW-F, 117 [8.5]; P < 0.05) levels, as well as mean glomerular volume (microm3 x 10(6): RW-M, 2.25 [0.16] vs RW-F, 1.25 [0.04]; P < 0.001) and the glomerulosclerotic index (AU: RW-M, 2.64 [0.19] vs RW-F, 1.10 [0.09]; P < 0.001) were greater in both control and RW males compared with females in the same treatment groups. Though RW surgery increased mean arterial pressure in both male and female rats, no sex difference was observed. Under these conditions, mean (SEM) renal cortical NADPH oxidase activity was 1.3-fold higher in RW males compared with RW females (relative light units [RLU]/180 sec: RW-M, 4080 [240] vs RW-F, 3200 [260]; P < 0.05). Ovariectomy increased NADPH oxidase activity by 1.4-fold (RLU/180 sec: RW-OVX, 4520 [184]; P < 0.01) under conditions in which the mean glomerular volume and glomerulosclerotic index were both increased by 1.5-fold, whereas E2 replacement (RLU/180 sec: RW-OVX+E2, 2745 [440]) prevented these effects. Furthermore, the effects on NADPH oxidase activity were mirrored by changes in the protein abundance of NADPH oxidase subunit p22P(phox).

CONCLUSION

These results suggest that E2 protects the female kidney in part by attenuating injury-induced increases in renal superoxide production.

NADPH oxidases in the kidney

NADPH oxidases have a distinct cellular localization in the kidney. Reactive oxygen species (ROS) are produced in the kidney by fibroblasts, endothelial cells (EC), vascular smooth muscle cells (VSMC), mesangial cells (MCs), tubular cells, and podocyte cells. All components of the phagocytic NADPH oxidase, as well as the Nox-1 and -4, are expressed in the kidney, with a prominent expression in renal vessels, glomeruli, and podocytes, and cells of the thick ascending limb of the loop of Henle (TAL), macula densa, distal tubules, collecting ducts, and cortical interstitial fibroblasts. NADPH oxidase activity is upregulated by prolonged infusion of angiotensin II (Ang II) or a high salt diet. Since these are major factors underlying the development of hypertension, renal NADPH oxidase may have an important pathophysiological role. Indeed, recent studies with small interference RNAs (siRNAs) targeted to p22( phox ) implicate p22( phox ) in Ang II-induced activation of renal NADPH oxidase and the development of oxidative stress and hypertension, while studies with apocynin implicate activation of p47( phox ) in the development of nephropathy in a rat model of type 1 diabetes mellitus (DM). Experimental studies of the distribution, signaling, and function of NADPH oxidases in the kidney are described.

Critical role of bradykinin-eNOS and oxidative stress-LOX-1 pathway in cardiovascular remodeling under chronic angiotensin-converting enzyme inhibition

To elucidate the molecular mechanisms of the cardioprotective effect of angiotensin-converting enzyme (ACE) inhibitors, we evaluated whether the effect of quinapril involved in bradykinin-endothelial nitric oxide synthase (eNOS) and oxidative stress-lectin-like oxidized LDL receptor-1 (LOX-1) pathway. Dahl salt-sensitive hypertensive (DS) rats were fed a diet containing 8% NaCl and treated with one of the following drug combinations for 5 weeks, from 6 weeks of age to left ventricular hypertrophy stage (11 weeks): vehicle; quinapril; quinapril plus the bradykinin B2 receptor antagonist FR172357; the NAD(P)H oxidase inhibitor apocynin; or quinapril plus apocynin. eNOS expression, which was decreased in hypertrophy stage, was significantly increased by quinapril and/or apocynin, but not by quinapril plus FR172357. Upregulated expression of NAD(P)H oxidase p22phox, p47phox, gp91phox and LOX-1 was significantly decreased by quinapril to a similar degree as after treatment with apocynin, but not by quinapril plus FR172357. Quinapril and/or apocynin treatment effectively ameliorated left ventricular weight and vascular changes such as increase in medial thickness and perivascular fibrosis and suppressed expression of transforming growth factor-beta1, type I collagen and fibronectin mRNA, but not that of quinapril plus FR172357. These results suggest that the ACE inhibitor quinapril may have cardioprotective effects in this model of hypertension mediated at least in part through effects on the bradykinin-eNOS and oxidative stress-LOX-1 pathway.

Contribution of reactive oxygen species to the pathogenesis of left ventricular failure in Dahl salt-sensitive hypertensive rats: effects of angiotensin II blockade

OBJECTIVE

We investigated the contribution of reduced nicotinamide-adenine dinucleotide phosphate (NADPH) oxidase-dependent reactive oxygen species (ROS) generation to the pathogenesis of diastolic heart failure (DHF) in Dahl salt-sensitive (DS) hypertensive rats, with the aim of testing our hypothesis that the cardioprotective effects of angiotensin II (Ang II) blockade are provided by the suppression of this pathway.

METHODS

DS rats were maintained on high (H: 8.0% NaCl) or low (L: 0.3% NaCl) salt diets from age 7 to 17 weeks. DS/H rats were also treated with candesartan cilexetil (10 mg/kg per day, orally) or a superoxide dismutase mimetic, tempol (3 mmol/l in drinking water) from age 7 to 17 weeks.

RESULTS

DS/H rats represented hypertension, left ventricular (LV) relaxation abnormality and myocardial stiffening with preserved systolic heart function. As compared with DS/L rats, DS/H rats showed higher levels of transforming growth factor-beta (TGF-beta), connective tissue growth factor (CTGF), p22phox and gp91phox mRNA expression, NADPH oxidase activity and thiobarbituric acid-reactive substance (TBARS) contents in LV tissues. Gene expression of uncoupling protein-2 (UCP-2), an inner mitochondrial membrane proton transporter, was also 2.8 +/- 0.5-fold higher. In DS/H rats, treatment with candesartan did not alter blood pressure, but resulted in a marked improvement of the hemodynamic deterioration; these therapeutic effects were accompanied by decreases in myocardial NADPH oxidase activity, TBARS contents and the expression of TGF-beta, CTGF, p22phox, gp91phox and UCP-2. Similar therapeutic effects were provided by treatment with tempol in DS/H rats.

CONCLUSIONS

Our data suggest that NADPH oxidase-mediated ROS production contributes to the pathogenesis of DHF in DS hypertensive rats, and that the cardioprotective effects of AngII blockade are, at least partially, mediated through the suppression of this pathway.

Activation of tubular epithelial cells in diabetic nephropathy and the role of the peroxisome proliferator-activated receptor-gamma agonist

The effects of advanced glycation end products (AGE) in the form of glycated albumin (GA) on the proinflammatory phenotype of cultured renal proximal tubular epithelial cells (PTEC) and the therapeutic potential of the peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonist were studied. Human PTEC were exposed to medium alone or supplemented with albumin or GA with or without previous addition of rosiglitazone (0.1 to 0.5 microM). Exposure to GA (up to 0.5 mg/ml) but not the equivalent dose of neat albumin significantly upregulated both mRNA and protein expression of IL-8 and soluble intercellular adhesion molecule-1 (sICAM-1) in a dose- and time-dependent manner. Using immunohistochemistry, ICAM-1 signals were detected in the tubular epithelia and peritubular capillaries in association with AGE deposition and leukocyte infiltration, whereas IL-8 staining was localized in the tubular epithelia of human diabetic kidney biopsies. Also in a dose-dependent manner, GA (0.5 mg/ml) but not albumin caused nuclear translocation of NF-kappaB and activation of mitogen-activated protein kinase (MAPK) p44/p42 and signal transducer and activator of transcription (STAT-1). Inhibition of these pathways with pyrrolidine dithiocarbamate, PD 98059, and fludarabine, respectively, attenuated GA-induced IL-8 secretion. Rosiglitazone dose-dependently attenuated GA-induced IL-8 and ICAM-1 signals in PTEC and completely abolished GA-induced STAT-1 signals but had no effect on NF-kappaB and MAPK activation. These findings suggest that AGE stimulate renal tubular expression of adhesion molecule and chemokine that together may account for the transmigration of inflammatory cells into the interstitial space during diabetic tubulopathy. Such proinflammatory phenotype may be partially modified by PPAR-gamma ligation through STAT-1 inhibition independent of NF-kappaB transcriptional activity and MAPK signaling.

Targeting reactive oxygen species in hypertension

PURPOSE OF REVIEW

Hypertension is a major risk factor for vascular diseases such as stroke, myocardial infarction, and renal microvascular disease. The mechanism by which vascular disease develops is complex, and growing evidence suggests that an increase in reactive oxygen species during hypertension is a major contributing factor. NADPH oxidase, the primary source of reactive oxygen species in the cardiovascular system, is a strong candidate for the development of therapeutic agents to ameliorate hypertension and end-organ damage.

RECENT FINDINGS

Various scavengers and inhibitors of reactive oxygen species have been proposed for use in animal as well as human studies. While many of these agents are effective at lowering tissue reactive oxygen species levels, their specificity is a serious concern. Our laboratory has developed cell-permeant peptidic inhibitors targeting key interactions among the different NAD(P)H oxidase homologues. One of these inhibitors targeting nox2 and p47-phox interaction has proven useful in attenuating target neoplasia and hypertrophy.

SUMMARY

Strategies aimed at specifically inhibiting NAD(P)H oxidase have proven effective in attenuating cardiovascular oxidative stress. The development of new inhibitors targeting novel oxidase homologues appears to hold significant promise for clarifying the physiologic role of these homologues as well as for the development of new antioxidant therapies.

Angiotensin II compartmentalization within the kidney: effects of salt diet and blood pressure alterations

PURPOSE OF REVIEW

All components of the renin-angiotensin-aldosterone system are present within the kidney. Renin, renin receptor, angiotensinogen and angiotensin AT1 and AT2 receptor and aldosterone synthase messenger RNA and protein are present in close proximity to the renal vasculature and tubules. The interaction between the different components of the renin-angiotensin-aldosterone system determines the level of activity of this system and in turn may influence the regulation of blood pressure and renal sodium handling.

RECENT FINDINGS

Angiotensin through the stimulation of its subtype AT2 receptor regulates sodium excretion, renin synthesis and secretion. Aldosterone synthase mRNA and protein are expressed in glomeruli, renal vasculature and tubules, and are regulated by angiotensin AT1 receptor, diabetes and salt. Although aldosterone is known to influence renal tubular channels with the subsequent enhancement of sodium reabsorption, it is not clear if the renally produced aldosterone also influences renal sodium handling or blood pressure regulation. In addition, angiotensin II influences kidney function and structure through the stimulation of renal inflammation. New data suggest that the renal AT1 receptor plays an important role in the determination of blood pressure levels, and this effect is unique and non-redundant in the actions of extrarenal AT1 receptors.

SUMMARY

The finding of new functions and components of the renin-angiotensin-aldosterone system clearly adds new knowledge to our understanding of how angiotensin II influences the kidney and blood pressure.

The interrelation of the angiotensin and endothelin systems on the modulation of NAD(P)H oxidaseThis paper is one of a selection of papers published in this Special issue, entitled Young Investigator's Forum

The NAD(P)H oxidase is an enzyme assembled at the cellular membrane able to produce superoxide anion from NADH or NAD(P)H (nicotinamide adenine dinucleotide phosphate). It is one of the main sources of superoxide anion in cardiovascular tissues and its role in a variety of cardiovascular disorders such as atherosclerosis, cardiac hypertrophy, and endothelial dysfunction was recently proposed. Although, many factors and receptors were shown to lead to the activation of the enzyme, particulary the type 1 angiotensin receptor, the pathways involved are still widely unknown. Despite the identification of factors such as c-Src and protein kinase C implicated in the acute activation of NAD(P)H oxidase, the signalling involved in the sustained activation of the enzyme is probably far more complex than was previously envisioned. In this review, we describe the role of endothelin-1 in NAD(P)H oxidase signalling after a sustained stimulation by angiotensin II. Since most pathologies caused by an NAD(P)H oxidase overactivation develop over a relatively long period of time, it is necessary to better understand the long-term signalling of the enzyme for the development or use of more specific therapeutic tools.

Antioxidant and nitric oxide-sparing actions of dihydropyridines and ACE inhibitors differ in human endothelial cells

The effects of dihydropyridine Ca2+ channel blockers (DHP) and ACE inhibitors on superoxide formation and nitric oxide (NO) bioavailability were compared in human EA.Hy926 endothelial cells (EC). EC were stimulated 4 h with angiotensin II (Ang II, 10 nM) +/- study drugs. Specific superoxide formation was measured by lucigenin-enhanced chemiluminescence, reduction of cytochrome c and rhodamine-123 fluorescence. Free NO release was determined with an amperometric NO sensor. NADPH oxidase subunits expression was examined with Western Blot. In untreated EC the intracellular superoxide is -64.3 +/- 6.0% decreased compared to Ang II stimulated EC. Elevated extracellular superoxide formation was on a -43.0 +/- 1.7% lower level in untreated EC. The DHP Ca2+-channel agonist BayK8644 and ACE inhibitors captopril and ramiprilat led extracellular superoxide concentration to control level. Enalaprilat blocked extracellular superoxide, the DHP amlodipine and nisoldipine prevented intracellular increases only (n = 8-9, p < 0.05). Icatibant (HOE 140), a kinin-B2 receptor antagonist, attenuated antioxidant actions of all tested agents except of nisoldipine. Ang II-induced superoxide was elevated by the phorbolester PMA and blocked by the protein kinase C (PKC) inhibitor chelerythrine. Suppression of substance P-evoked NO release by Ang II (>70%, n = 6) was reversed by the PKC inhibitor chelerythrine, the DHP amlodipine and nisoldipine and the ACE inhibitor ramiprilat. Further, Ang II reduces Nox-4 expression by 34.5 +/- 4.9. Nox-2 expression was not regulated. DHP and ACE inhibitors exert different antioxidant effects in human EC stimulated with Ang II, but both improve NO bioavailability via bradykinin and modulation of redox-regulating enzymes.