Effects of tempol on renal angiotensinogen production in Dahl salt-sensitive rats

Potential therapeutic value of melatonin in diabetic nephropathy: improvement beyond anti-oxidative stress

Diabetic nephropathy (DN) is a common complication of diabetes, and it is also the main cause of chronic renal failure. Physiological/pathological changes mediated by high glucose are the main factors causing injury of DN, including the enhancement of polyol pathway, the accumulation of advanced glycation products (AGEs), and the activation of protein kinase C (PKC) and transforming growth factor-β (TGF-β) signals. In addition, the abnormal activation of renin-angiotensin system (RAS) and oxidative stress are also involved. Melatonin is a physiological hormone mainly secreted by the pineal gland which has been proved to be related to diabetes. Studies have shown that exogenous melatonin intervention can reduce blood glucose and alleviate high glucose mediated pathological damage. At the same time, melatonin also has a strong antioxidant effect, and can inhibit the activation of RAS. Therefore, it is of great significance to explore the therapeutic effect and value of melatonin on DN.

Activation of the intestinal tissue renin-angiotensin system by transient sodium loading in salt-sensitive rats

BACKGROUND

The renal tissue renin-angiotensin system is known to be activated by salt loading in salt-sensitive rats; however, the response in other organs remains unclear.

METHOD

Spontaneously hypertensive rats were subjected to normal tap water or transient high-salt-concentration water from 6 to 14 weeks of age and were thereafter given normal tap water. From 18 to 20 weeks of age, rats given water with a high salt concentration were treated with an angiotensin II type 1 receptor blocker, valsartan.

RESULTS

Sustained blood pressure elevation by transient salt loading coincided with a persistent decrease in the fecal sodium content and sustained excess of the circulating volume in spontaneously hypertensive rats. Administration of valsartan sustainably reduced the blood pressure and normalized the fecal sodium levels. Notably, transient salt loading persistently induced the intestinal tissue renin-angiotensin system and enhanced sodium transporter expression exclusively in the small intestine of salt-sensitive rats, suggesting the potential connection of intestinal sodium absorption to salt sensitivity.

CONCLUSION

These results reveal the previously unappreciated contribution of the intestinal tissue renin-angiotensin system to sodium homeostasis and blood pressure regulation in the pathophysiology of salt-sensitive hypertension.

Isocitrate dehydrogenase 2 deficiency aggravates prolonged high-fat diet intake-induced hypertension

The development of hypertension is associated with mitochondrial redox balance disruptions. NADP⁺-dependent isocitrate dehydrogenase 2 (IDH2) plays an important role in the maintenance of mitochondrial redox balance by producing mitochondrial NADPH, which is an essential cofactor in the reduction of glutathione (from GSSG to GSH) to reduced form of glutathione (GSH). We investigated the association of IDH2 between the development of prolonged high-fat diet (HFD)-induced hypertension. Idh2 gene-deleted (Idh2^-/-) male mice and wild-type (Idh2^+/+) littermates were fed either HFD or low-fat diet (LFD). Some mice were administrated with Mito-TEMPO, a mitochondria-specific antioxidant. HFD feeding increased blood pressure (BP) in both Idh2^-/- mice and Idh2^+/+ mice. HFD-induced BP increase was greater in Idh2^-/- than Idh2^+/+ mice. HFD intake decreased IDH2 activity, NADPH levels, and the GSH/(GSH + GSSG) ratio in the renal mitochondria. However, HFD intake increased mitochondrial ROS levels, along with the accompanying oxidative stress and damage. HFD intake increased angiotensin II receptor 1 type 1 mRNA levels in the kidneys and plasma renin and angiotensin II concentrations. These HFD-induced changes were more prominent in Idh2^-/- mice than Idh2^+/+ mice. Mito-TEMPO mitigated the HFD-induced changes in both Idh2^-/- and Idh2^+/+ mice, with greater effects in Idh2^-/- mice than Idh2^+/+ mice. These results indicate that prolonged HFD intake disrupts the IDH2-NADPH-GSH-associated antioxidant system and activates the renin-angiotensin system in the kidney, leading to increased BP, suggesting that IDH2 is a critical enzyme in the development of hypertension and that the IDH2-associated antioxidant system could serve as a potential hypertension treatment target.

NADPH oxidases and oxidase crosstalk in cardiovascular diseases: novel therapeutic targets

Reactive oxygen species (ROS)-dependent production of ROS underlies sustained oxidative stress, which has been implicated in the pathogenesis of cardiovascular diseases such as hypertension, aortic aneurysm, hypercholesterolaemia, atherosclerosis, diabetic vascular complications, cardiac ischaemia-reperfusion injury, myocardial infarction, heart failure and cardiac arrhythmias. Interactions between different oxidases or oxidase systems have been intensively investigated for their roles in inducing sustained oxidative stress. In this Review, we discuss the latest data on the pathobiology of each oxidase component, the complex crosstalk between different oxidase components and the consequences of this crosstalk in mediating cardiovascular disease processes, focusing on the central role of particular NADPH oxidase (NOX) isoforms that are activated in specific cardiovascular diseases. An improved understanding of these mechanisms might facilitate the development of novel therapeutic agents targeting these oxidase systems and their interactions, which could be effective in the prevention and treatment of cardiovascular disorders.

Sex, Oxidative Stress, and Hypertension: Insights From Animal Models

One of the mechanisms responsible for blood pressure (BP) regulation is thought to be oxidative stress. In this review, we highlight preclinical studies that strongly support a role for oxidative stress in development and maintenance of hypertension in male animals, based on depressor responses to antioxidants, particularly tempol and apocynin. In females, oxidative stress seems to be important in the initial development of hypertension. However, whether maintenance of hypertension in females is mediated by oxidative stress is not clear. In clinical studies, pharmacological intervention to reduce BP with antioxidants has conflicting results, mostly negative. This review will discuss the uncertainties regarding blood pressure control and oxidative stress and potential reasons for these outcomes.

The pivotal role of melatonin in ameliorating chronic kidney disease by suppression of the renin-angiotensin system in the kidney

Melatonin is a hormone produced by the pineal gland, predominantly at night, and plays a pivotal role in regulating the circadian rhythm as well as a variety of biological functions, including anti-inflammation, anti-oxidation, inhibition of sympathetic nerve activity, and preservation of endothelial cell function. The intrarenal renin-angiotensin system (RAS) is one of the most important contributors in the pathophysiology of chronic kidney disease (CKD) and hypertension, independent of the circulating RAS, due to sodium reabsorption and inflammation and fibrosis in the kidney. However, the relationship between melatonin secretion and intrarenal RAS activation has remained unknown. It has been recently shown that impaired nighttime melatonin secretion is associated with nighttime urinary angiotensinogen excretion, a surrogate marker of intrarenal RAS activation and renal damage in patients with CKD. Moreover, it has also been indicated that melatonin administered exogenously exercises antioxidant effects that ameliorate intrarenal RAS activation and renal injury in chronic progressive CKD animal models. As a result, the new roles of melatonin in suppressing RAS in the kidney via amelioration of reactive oxygen species have been clarified. Therefore, we review the relationship between melatonin and intrarenal RAS activation and indicate the possibility of a new strategy to suppress CKD, which is a risk factor for cardiovascular and end-stage renal diseases.

Independent regulation of renin-angiotensin-aldosterone system in the kidney

Renin-angiotensin-aldosterone system (RAAS) plays important roles in regulating renal hemodynamics and functions, as well as in the pathophysiology of hypertension and renal disease. In the kidney, angiotensin II (Ang II) production is controlled by independent multiple mechanisms. Ang II is compartmentalized in the renal interstitial fluid with much higher concentrations than those existing in the circulation. Inappropriate activation of the intrarenal RAAS is an important contributor to the pathogenesis of hypertension and renal injury. It has been revealed that intrarenal Ang II levels are predominantly regulated by angiotensinogen and therefore, urinary angiotensinogen could be a biomarker for intrarenal Ang II generation. In addition, recent studies have demonstrated that aldosterone contributes to the progression of renal injury via direct actions on glomerular podocytes, mesangial cells, proximal tubular cells and tubulo-interstitial fibroblasts through the activation of locally expressed mineralocorticoid receptor. Thus, it now appears that intrarenal RAAS is independently regulated and its inappropriate activation contributes to the pathogenesis of the development of hypertension and renal disease. This short review article will focus on the independent regulation of the intrarenal RAAS with an emphasis on the specific role of angiotensinogen.

Blood-borne interleukin-1β acts on the subfornical organ to upregulate the sympathoexcitatory milieu of the hypothalamic paraventricular nucleus

We previously reported that microinjection of the proinflammatory cytokine interleukin-1β (IL-1β) into the subfornical organ (SFO) elicits a pressor response accompanied by increases in inflammation and renin-angiotensin system (RAS) activity in the SFO and hypothalamic paraventricular nucleus (PVN). The present study sought to determine whether blood-borne IL-1β induces similar neurochemical changes in the SFO and PVN and, if so, whether increased inflammation and RAS activity at the SFO level orchestrate the sympathoexcitatory response to circulating IL-1β. In urethane-anesthetized male Sprague-Dawley rats, intravenous injection of IL-1β (500 ng) increased blood pressure, heart rate, renal sympathetic nerve activity, and mRNA for angiotensin-converting enzyme, angiotensin II type 1a receptor, cyclooxygenase-2, tumor necrosis factor-α, and IL-1β, as well as the tumor necrosis factor-α p55 receptor and the IL-1 receptor, in the SFO and PVN. Pretreatment with SFO microinjections of the angiotensin II type 1a receptor blocker losartan (1 µg), the angiotensin-converting enzyme inhibitor captopril (1 µg), or the cyclooxygenase-2 inhibitor NS-398 (2 µg) attenuated expression of these excitatory mediators in the SFO and downstream in the PVN and the IL-1β-induced pressor responses. An SFO lesion minimized the IL-1β-induced expression of inflammatory and RAS components as well as c-Fos, an indicator of neuronal excitation, in the PVN. These studies demonstrate that circulating IL-1β, which increases in cardiovascular disorders such as hypertension and heart failure, acts on the SFO to increase inflammation and RAS activity in the SFO and PVN and that intervening in these neurochemical processes in the SFO can significantly reduce the sympathetic response.

Melatonin ameliorates intrarenal renin-angiotensin system in a 5/6 nephrectomy rat model

BACKGROUND

Activation of the intrarenal renin-angiotensin system (RAS) plays a critical role in the pathophysiology of chronic kidney disease (CKD) and hypertension. It has been reported that reactive oxygen species (ROS) are important components of intrarenal RAS activation. Melatonin is recognized as a powerful antioxidant, and we recently reported that impaired nighttime melatonin secretion correlates negatively with urinary angiotensinogen excretion, the surrogate marker of intrarenal RAS activity in patients with CKD. However, whether melatonin supplementation ameliorates the augmentation of intrarenal RAS in CKD has remained unknown. We aimed to clarify whether exogenous melatonin ameliorates intrarenal RAS activation via the reduction of ROS production.

METHODS

5/6 Nephrectomized (Nx) rats were used as a chronic progressive CKD model and compared with sham-operated control rats. The Nx rats were divided into untreated Nx rats and melatonin-treated Nx rats. The levels of intrarenal RAS, ROS components, and renal injury were evaluated after 4 weeks of treatment.

RESULTS

Compared with the control rats, the untreated Nx rats exhibited significant increases in intrarenal angiotensinogen, angiotensin II (AngII) type 1 receptors, and AngII, accompanied by elevated blood pressure, higher oxidative stress (8-hydroxy-2'-deoxyguanosine), lower antioxidant (superoxide dismutase) activity, and increased markers of interstitial fibrosis (α-smooth muscle actin, Snail, and type I collagen) in the remnant kidneys. Treatment with melatonin significantly reversed these abnormalities.

CONCLUSION

Antioxidant treatment with melatonin was shown to ameliorate intrarenal RAS activation and renal injury in a 5/6 Nx rat model.

Immunohistochemical expression of intrarenal renin angiotensin system components in response to tempol in rats fed a high salt diet

AIM

To determine the effect of tempol in normal rats fed high salt on arterial pressure and the balance between antagonist components of the renal renin-angiotensin system.

METHODS

Sprague-Dawley rats were fed with 8% NaCl high-salt (HS) or 0.4% NaCl (normal-salt, NS) diet for 3 wk, with or without tempol (T) (1 mmol/L, administered in drinking water). Mean arterial pressure (MAP), glomerular filtration rate (GFR), and urinary sodium excretion (UVNa) were measured. We evaluated angiotensin II (Ang II), angiotensin 1-7 (Ang 1-7), angiotensin converting enzyme 2 (ACE2), mas receptor (MasR), angiotensin type 1 receptor (AT1R) and angiotensin type 2 receptor (AT2R) in renal tissues by immunohistochemistry.

RESULTS

The intake of high sodium produced a slight but significant increase in MAP and differentially regulated components of the renal renin-angiotensin system (RAS). This included an increase in Ang II and AT1R, and decrease in ACE-2 staining intensity using immunohistochemistry. Antioxidant supplementation with tempol increased natriuresis and GFR, prevented changes in blood pressure and reversed the imbalance of renal RAS components. This includes a decrease in Ang II and AT1R, as increase in AT2, ACE2, Ang (1-7) and MasR staining intensity using immunohistochemistry. In addition, the natriuretic effects of tempol were observed in NS-T group, which showed an increased staining intensity of AT2, ACE2, Ang (1-7) and MasR.

CONCLUSION

These findings suggest that a high salt diet leads to changes in the homeostasis and balance between opposing components of the renal RAS in hypertension to favour an increase in Ang II. Chronic antioxidant supplementation can modulate the balance between the natriuretic and antinatriuretic components of the renal RAS.

Urine angiotensinogen and salt-sensitivity and potassium-sensitivity of blood pressure

OBJECTIVE

Urinary excretion of angiotensinogen [urine angiotensinogen (UAGT)] has been proposed as a biomarker of intrarenal renin-angiotensin system activity. We investigated the association between UAGT and salt-sensitivity and potassium-sensitivity of blood pressure (BP) among Genetic Epidemiology Network of Salt Sensitivity study participants.

METHODS

The intervention consisted of a 7-day low-sodium diet (51.3  mmol sodium/day), 7-day high-sodium diet (307.8  mmol sodium/day), and 7-day high-sodium diet with potassium supplementation (307.8  mmol sodium/day and 60  mmol potassium/day). Twenty-four-hour UAGT was estimated at baseline and at the end of each intervention for 100 randomly selected participants.

RESULTS

Median UAGT (μg/24  h) and UAGT-to-creatinine ratio (UAGT/Cr, μg/g) were significantly reduced during the low-sodium and potassium-supplementation interventions and increased during the high-sodium intervention (both P = 0.01). Baseline log-transformed UAGT and UAGT/Cr ratio were significantly positively associated with BP at baseline and at the end of each intervention. For example, one standard deviation higher log-UAGT/Cr ratio (1.2  μg/g) was associated with a 5.0-mmHg (95% confidence interval 2.3-7.8) higher SBP at the end of the high-sodium intervention, after adjusting for multiple covariates (P = 0.003). In addition, one standard deviation higher log-UAGT/Cr ratio was associated with a 1.6-mmHg increase in age-adjusted and sex-adjusted SBP from the low-sodium intervention to the high-sodium intervention (95% confidence interval 0.1-3.1, P = 0.04). This association was no longer statistically significant after multivariable adjustment.

CONCLUSION

These data indicate that elevated UAGT are associated with BP sodium sensitivity. Augmentation of intrarenal renin-angiotensin system activity may play an important role in developing salt-sensitive hypertension.

Salt-Sensitive Hypertension: Perspectives on Intrarenal Mechanisms

Salt sensitive hypertension is characterized by increases in blood pressure in response to increases in dietary salt intake and is associated with an enhanced risk of cardiovascular and renal morbidity. Although researchers have sought for decades to understand how salt sensitivity develops in humans, the mechanisms responsible for the increases in blood pressure in response to high salt intake are complex and only partially understood. Until now, scientists have been unable to explain why some individuals are salt sensitive and others are salt resistant. Although a central role for the kidneys in the development of salt sensitivity and hypertension has been generally accepted, it is also recognized that hypertension is of multifactorial origin and a variety of factors can induce, or prevent, blood pressure responsiveness to the manipulation of salt intake. Excess salt intake in susceptible persons may also induce inappropriate central and sympathetic nervous system responses and increase the production of intrarenal angiotensin II, catecholamines and other factors such as oxidative stress and inflammatory cytokines. One key factor is the concomitant inappropriate or paradoxical activation of the intrarenal renin-angiotensin system, by high salt intake. This is reflected by the increases in urinary angiotensinogen during high salt intake in salt sensitive models. A complex interaction between neuroendocrine factors and the kidney may underlie the propensity for some individuals to retain salt and develop salt-dependent hypertension. In this review, we focus mainly on the renal contributions that provide the mechanistic links between chronic salt intake and the development of hypertension.

Urinary Angiotensinogen as a Potential Biomarker of Intrarenal Renin-angiotensin System Activity in Chinese Patients with Chronic Kidney Disease

Urinary angiotensinogen (AGT) mainly derives from the AGT produced in the proximal tubular cells. Evidence exists that supports the correlation between urinary AGT and circulating AGT. Previous studies measured urinary AGT by radioimmunoassay which is not convenient for clinical practice. In this study, we utilized an enzyme-linked immunosorbent assay (ELISA) based method to quantify urinary AGT. We analysed the relationship between urinary AGT and intrarenal angiotensin II (Ang II) activity in patients with chronic kidney disease (CKD). Urinary and plasma renin activity, AGT, Ang II and aldosterone were measured by radioimmunoassay or ELISA in 128 CKD patients. Furthermore, expression levels of intrarenal renin, AGT, Ang II and Ang II receptor were examined by immunohistochemistry staining (IHCS) in 72 CKD patients undergoing renal biopsy. Average urinary AGT was 2.02 ± 0.55 ng/(mg Cr). Hypertension, urinary protein, urinary Ang II and urinary Type IV collagen (Col IV) positively correlated with urinary AGT. Estimated glomerular filtration rate (eGFR), urinary sodium and serum AGT negatively correlated with urinary AGT. Multiple regression analysis indicated that low serum AGT, high urinary protein, urinary Ang II and urinary Col IV correlated significantly with high urinary AGT. Moreover, we observed positive correlation between urinary AGT and positive IHCS area of AGT, Ang II and Ang II Type 1 receptor inrenal tissue. These data suggest that urinary AGT might be a potential biomarker of intrarenal angiotensin II activity in CKD patients.

Circadian rhythm of plasma and urinary angiotensinogen in healthy volunteers and in patients with chronic kidney disease

The urinary angiotensinogen (AGT) excretion rate could be a novel biomarker for the intrarenal activity of the renin-angiotensin system. Little is known about the circadian rhythm of AGT levels in plasma or urine. In this short article, making use of data in plasma and urine of healthy volunteers and patients with chronic kidney diseases, we first report that we were unable to find evidence for a circadian rhythm of AGT under any condition. Next we critically discuss to what degree elevated urinary AGT levels might be considered an independent biomarker that is not simply the non-specific consequence of proteinuria.

Urinary angiotensinogen as a potential biomarker of intrarenal renin-angiotensin system activity in Chinese chronic kidney disease patients

BACKGROUND

Urinary angiotensinogen (AGT) mainly derives from the AGT produced in proximal tubular cells. Evidence exists that supports the correlation between urinary AGT and circulating AGT.

AIM

To investigate the role of urinary AGT as a potential biomarker of intrarenal renin-angiotensin system activity in Chinese chronic kidney disease (CKD) patients.

METHODS

ELISA-based method used to quantify urinary AGT. Analyzed the relationship between urinary AGT and intrarenal angiotensin II (Ang II) activity in 128 CKD patients. ELISA was applied to measure the urinary and plasma renin activity, AGT, Ang II and aldosterone. Furthermore expression levels of intrarenal renin, AGT, Ang II and Ang II receptor were examined by immunohistochemistry staining (IHCS) in 72 CKD patients undergoing renal biopsy.

RESULTS

The logarithmic transformation Log(urinary AGT/UCre) levels showed a normal distribution. Therefore, Log(urinary AGT/UCre) levels were used for the analyses. Average urinary AGT was 2.02 ± 0.55 ng/(mg Cr). Hypertension, urinary protein, urinary Ang II and urinary type IV collagen (Col IV) positively correlated with urinary AGT. Estimated glomerular filtration rate (eGFR), urinary sodium and serum AGT negatively correlated with urinary AGT. Multiple regression analysis indicated that low serum AGT, high urinary protein, urinary Ang II and urinary Col IV correlated significantly with high urinary AGT.

CONCLUSIONS

We observed positive correlation between urinary AGT and positive IHCS area of AGT, Ang II and Ang II type 1 receptor in renal tissue. These data suggest that urinary AGT might be a potential biomarker of intrarenal Ang II activity in CKD patients.

Renal overexpression of atrial natriuretic peptide and hypoxia inducible factor-1α as adaptive response to a high salt diet

In the kidney, a high salt intake favors oxidative stress and hypoxia and causes the development of fibrosis. Both atrial natriuretic peptide (ANP) and hypoxia inducible factor (HIF-1α) exert cytoprotective effects. We tested the hypothesis that renal expression of ANP and HIF-1α is involved in a mechanism responding to the oxidative stress produced in the kidneys of rats chronically fed a high sodium diet. Sprague-Dawley rats were fed with a normal salt (0.4% NaCl) (NS) or a high salt (8% NaCl) (HS) diet for 3 weeks, with or without the administration of tempol (T), an inhibitor of oxidative stress, in the drinking water. We measured the mean arterial pressure (MAP), glomerular filtration rate (GFR), and urinary sodium excretion (UV_Na). We evaluated the expression of ANP, HIF-1α, and transforming growth factor (TGF-β1) in renal tissues by western blot and immunohistochemistry. The animals fed a high salt diet showed increased MAP and UV_Na levels and enhanced renal immunostaining of ANP, HIF-1α, and TGF-β1. The administration of tempol together with the sodium overload increased the natriuresis further and prevented the elevation of blood pressure and the increased expression of ANP, TGF-β1, and HIF-1α compared to their control. These findings suggest that HIF-1α and ANP, synthesized by the kidney, are involved in an adaptive mechanism in response to a sodium overload to prevent or attenuate the deleterious effects of the oxidative stress and the hypoxia on the development of fibrosis.

Cardinal role of the intrarenal renin-angiotensin system in the pathogenesis of diabetic nephropathy

Diabetes mellitus is one of the most prevalent diseases and is associated with increased incidence of structural and functional derangements in the kidneys, eventually leading to end-stage renal disease in a significant fraction of afflicted individuals. The renoprotective effects of renin-angiotensin system (RAS) blockade have been established; however, the mechanistic pathways have not been fully elucidated. In this review article, the cardinal role of an activated RAS in the pathogenesis of diabetic nephropathy (DN) is discussed with a focus on 4 themes: (1) introduction to RAS cascade, (2) intrarenal RAS in diabetes, (3) clinical outcomes of RAS blockade in DN, and (4) potential of urinary angiotensinogen as an early biomarker of intrarenal RAS status in DN. This review article provides a mechanistic rational supporting the hypothesis that an activated intrarenal RAS contributes to the pathogenesis of DN and that urinary angiotensinogen levels provide an index of intrarenal RAS activity.

Oxidative stress/angiotensinogen/renin-angiotensin system axis in patients with diabetic nephropathy

Although recent studies have proven that renin-angiotensin system (RAS) blockades retard the progression of diabetic nephropathy, the detailed mechanisms of their reno-protective effects on the development of diabetic nephropathy remain uncertain. In rodent models, it has been reported that reactive oxygen species (ROS) are important for intrarenal angiotensinogen (AGT) augmentation in the progression of diabetic nephropathy. However, no direct evidence is available to demonstrate that AGT expression is enhanced in the kidneys of patients with diabetes. To examine whether the expression levels of ROS- and RAS-related factors in kidneys are increased with the progression of diabetic nephropathy, biopsied samples from 8 controls and 27 patients with type 2 diabetes were used. After the biopsy, these patients were diagnosed with minor glomerular abnormality or diabetes mellitus by clinical and pathological findings. The intensities of AGT, angiotensin II (Ang II), 4-hydroxy-2-nonenal (4-HNE), and heme oxygenase-1 (HO-1) were examined by fluorescence in situ hybridization and/or immunohistochemistry. Expression levels were greater in patients with diabetes than in control subjects. Moreover, the augmented intrarenal AGT mRNA expression paralleled renal dysfunction in patients with diabetes. These data suggest the importance of the activated oxidative stress/AGT/RAS axis in the pathogenesis of diabetic nephropathy.

Angiotensin II blockade and renal protection

Current national guidelines have recommended the use of renin-angiotensin system inhibitors, including angiotensin II type 1 receptor blockers (ARBs), in preference to other antihypertensive agents for treating hypertensive patients with chronic kidney disease. However, the mechanisms underlying the renoprotective effects of ARBs are multiple and complex. Blood pressure reduction by systemic vasodilation with an ARB contributes to its beneficial effects in treating kidney disease. Furthermore, ARB-induced renal vasodilation results in an increase in renal blood flow, leading to improvement of renal ischemia and hypoxia. ARBs are also effective in reducing urinary albumin excretion through a reduction in intraglomerular pressure and the protection of glomerular endothelium and/or podocyte injuries. In addition to blocking angiotensin II-induced renal cell and tissue injuries, ARBs can decrease intrarenal angiotensin II levels by reducing proximal tubular angiotensinogen and production of collecting duct renin, as well as angiotensin II accumulation in the kidney. In this review, we will briefly summarize our current understanding of the pharmacological effects of an ARB in the kidney. We will also discuss the possible mechanisms responsible for the renoprotective effects of ARBs on type 2 diabetic nephropathy.

ELISA examining urinary angiotensinogen as a potential indicator of intrarenal renin-angiotensin system (RAS) activity: a clinical study of 128 chronic kidney disease patients

In the current study, we measured urinary angiotensinogen (AGT) through enzyme-linked immunoadsordent assay (ELISA) and analyzed its correlation with intrarenal renin-angiotensin system (RAS) activity in 128 chronic kidney disease (CKD) patients. Urinary and plasma renin activity, AGT, angiotensin II (Ang II) and aldosterone levels were also measured by radioimmunoassay (RIA) or ELISA in these participants. Further, the expression level of intrarenal renin, AGT, Ang II and Ang II receptors were examined by immunohistochemistry staining (IHCS) in 72 CKD patients. Their correlations with urinary AGT were also analyzed. We found that the urinary AGT level was positively correlated with hypertension (ρ = 0.28, P < 0.01), urinary protein (r = 0.38, P < 0.01), urinary Ang II (r = 0.29, P < 0.05), urinary type IV collagen (Col IV) (r = 0.56, P < 0.01), and was negatively correlated with estimated glomerular filtration rate (eGFR) (r = -0.28, P < 0.01), urinary sodium (r = -0.22, P < 0.05) and serum AGT (r = -0.27, P < 0.01). Multiple regression analysis indicated low serum AGT (P < 0.01), high urinary protein (P < 0.01), high urinary Ang II (P < 0.05) and high urinary Col IV (P < 0.01) were correlated significantly with high urinary AGT. Urinary AGT level was positively correlated with intrarenal expression level of AGT (ρ = 0.46, P < 0.01), Ang II (ρ = 0.56, P < 0.01) and Ang II type 1 receptor (ρ = 0.32, P < 0.01), as detected by IHCS. Together, these data suggest that urinary AGT might be a potential biomarker of intrarenal RAS and Ang II activities in CKD patients.

Chronic antioxidant therapy lowers blood pressure in adult but not in young Dahl salt hypertensive rats: the role of sympathetic nervous system

AIM

It is well-known that salt hypertension is associated with increased oxidative stress. Since the development of salt hypertension is age-dependent, we were interested whether young and adult salt hypertensive Dahl rats differ in oxidative stress level and/or in the effects of chronic antioxidant therapy on blood pressure (BP) level and on the participation of particular vasoconstrictor/vasodilator systems in BP maintenance.

METHODS

Young (5-week-old) and adult (12-week-old) salt-sensitive (Dahl-S) male rats were fed high-salt diet (5% NaCl) and drank tempol solution (2 mm) for 5 weeks. BP was monitored with radiotelemetry and vasoconstrictor/vasodilator balance was evaluated at the end of experiment. Moreover, NO synthase activity, superoxide production and lipoperoxidation were determined in heart, kidney and aorta in separate subgroups of Dahl rats.

RESULTS

Tempol treatment had quite opposite BP effects in young and adult Dahl-S rats. While it tended to increase BP in young salt hypertensive Dahl-S rats, it significantly lowered BP in the adult ones due to reduced sympathetic vasoconstriction. Importantly, high salt intake substantially reduced NO synthase activity in heart and kidney, and markedly increased superoxide production in kidneys and aorta of adult Dahl-S rats in which BP correlated positively with superoxide production in thoracic aorta and lipoperoxidation in kidneys.

CONCLUSION

Chronic antioxidant therapy lowered BP only in adult salt hypertensive Dahl-S rats in which superoxide levels were increased in both kidneys and aorta. Blood pressure reduction induced by chronic tempol treatment is related to attenuated sympathetic vasoconstriction rather than to augmented NO-dependent vasodilatation.

Divergent localization of angiotensinogen mRNA and protein in proximal tubule segments of normal rat kidney

OBJECTIVES

Angiotensinogen in the kidneys is formed primarily in the proximal tubule cells and is secreted into the tubular fluid. Structurally, proximal tubules can be divided into three segments. The first segment, segment 1 (S1) is mainly confined to the pars convoluta, the second segment, segment 2 (S2) comprises the end of pars convoluta, and the third segment, segment 3 (S3) includes the major part of the pars recta. There are some reports describing angiotensinogen localization in kidneys; however, it remains uncertain which proximal tubule segments express angiotensinogen. To determine the detailed localization of angiotensinogen in the three proximal tubule segments, we established multistaining methods using segment-specific protein markers.

METHODS

Using kidneys from Wistar-Kyoto rats, we performed immunohistochemistry and double or triple staining by fluorescence in-situ hybridization and/or immunofluorescence.

RESULTS

Our results show that angiotensinogen mRNA and protein are expressed in the cortex and outer medulla of the normal rat kidney. Angiotensinogen mRNA was hardly detected in S1, detected weakly in S2 and strongly in S3 segments. In contrast, angiotensinogen protein was detected in S1 at high levels and less in S2 and S3 segments.

CONCLUSION

These data indicate divergence of angiotensinogen mRNA transcription and angiotensinogen protein synthesis and metabolism in different segments of the normal rat proximal tubules.

Important aspects of urine sampling for angiotensinogen measurement: time and preservation conditions in healthy individuals

Intrarenal renin-angiotensin system (RAS) plays an important role for the pathogenesis of renal injuries. Experimental studies have demonstrated that angiotensinogen levels in renal tissues reflect the activity of intrarenal RAS. However, dynamics of urinary angiotensinogen have not been investigated in detail. Therefore, we examined the preservation conditions of the measured values of urinary angiotensinogen concentrations and an ultradian rhythm of urinary angiotensinogen excretion in humans. Urine samples were collected from 24 healthy volunteers. The urinary concentrations of angiotensinogen were measured by using ELISA. Two different urine preservation conditions were examined. One cycle of freeze-and-thaw did not change the measured values of urinary angiotensinogen concentrations. Moreover, to keep urine samples at room temperature for 12 hours did not change the measured values of urinary angiotensinogen concentrations. Thus, preservation conditions do not change the measured values of urinary angiotensinogen concentrations. Regarding an ultradian rhythm, blood pressure and the urinary concentrations of angiotensinogen were measured at 09:00, 13:00, and 16:00. The averaged levels of blood pressure were similar over the time. The average of urinary angiotensinogen/creatinine (Cr) ratios was 8.73 ± 1.15 ng/mg Cr at 09:00, 9.53 ± 1.58 ng/mg Cr at 13:00, and 8.58 ± 1.26 ng/mg Cr at 16:00. The urinary angiotensinogen excretion in healthy volunteers does not have an ultradian change during the daytime (P = 0.482). This may be another indication that the intrarenal RAS is independent of the systemic RAS. We have to pay attention to these findings in handling urine samples for measurements of angiotensinogen.

Cardinal Role of the Intrarenal Renin-Angiotensin System in the Pathogenesis of Diabetic Nephropathy

Diabetes mellitus is one of the most prevalent diseases and is associated with increased incidence of structural and functional derangements in the kidneys, eventually leading to end-stage renal disease in a significant fraction of afflicted individuals. The renoprotective effects of renin-angiotensin system (RAS) blockade have been established; however, the mechanistic pathways have not been fully elucidated. In this review article, the cardinal role of an activated RAS in the pathogenesis of diabetic nephropathy (DN) is discussed with a focus on 4 themes: (1) introduction to RAS cascade, (2) intrarenal RAS in diabetes, (3) clinical outcomes of RAS blockade in DN, and (4) potential of urinary angiotensinogen as an early biomarker of intrarenal RAS status in DN. This review article provides a mechanistic rational supporting the hypothesis that an activated intrarenal RAS contributes to the pathogenesis of DN and that urinary angiotensinogen levels provide an index of intrarenal RAS activity.

Elevated transcriptional co-activator p102 mediates angiotensin II type 1 receptor up-regulation and extracellular matrix overproduction in the high glucose-treated rat glomerular mesangial cells and isolated glomeruli

P102 is a multifunctional transcriptional co-activator. This experiment is designed to investigate the role of p102 in the activation of renin-angiotensin system (RAS) and sequentially extracellular matrix (ECM) over synthesis in diabetic nephropathy. Rat glomerular mesangial cells (MCs) or isolated glomeruli were cultured in normal glucose (NG, 5.5mM) or high glucose (HG, 25 mM) DMEM. The generation of reactive oxygen species was measured by 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA) fluorescent probe assay. The protein levels were analyzed by Western blot and the mRNA levels were evaluated by real-time PCR. HG treatment induced an increase in reactive oxygen species production. Culturing the cells in HG for 48 h, p102 mRNA and protein, angiotensin II type 1 receptor (AT1 receptor) mRNA, transforming growth factor-β1 (TGF-β1) and fibronectin proteins were significantly increased. NADPH oxidase inhibitor DPI blocked the HG-induced p102, TGF-β1 and fibronetcin elevations. Knockdown on p102 expression by siRNA depressed the HG-induced AT1 receptor up-regulation as well as the increases in TGF-β1 and fibronectin. In contrast, AT1 receptor antagonist candesartan did not influence p102 levels under either NG or HG condition, but blocked the HG-induced TGF-β1 and fibronectin increases. The results from isolated glomeruli were consistent with that of MCs, which showed that HG exposure stimulated the expression of p102. These results suggest that the overproduction of reactive oxygen species at the early stage of HG incubation stimulates p102 synthesis, which in turn up-regulates AT1 receptor expression. The activation of RAS stimulates TGF-β1 and fibronectin production, which further results in ECM accumulation.

Augmented intrarenal and urinary angiotensinogen in hypertension and chronic kidney disease

Activated intrarenal renin-angiotensin system plays a cardinal role in the pathogenesis of hypertension and chronic kidney disease. Angiotensinogen is the only known substrate for renin, which is the rate-limiting enzyme of the renin-angiotensin system. Because the levels of angiotensinogen are close to the Michaelis-Menten constant values for renin, angiotensinogen levels as well as renin levels can control the renin-angiotensin system activity, and thus, upregulation of angiotensinogen leads to an increase in the angiotensin II levels and ultimately increases blood pressure. Recent studies using experimental animal models have documented the involvement of angiotensinogen in the intrarenal renin-angiotensin system activation and development of hypertension. Enhanced intrarenal angiotensinogen mRNA and/or protein levels were observed in experimental models of hypertension and chronic kidney disease, supporting the important roles of angiotensinogen in the development and the progression of hypertension and chronic kidney disease. Urinary excretion rates of angiotensinogen provide a specific index of the intrarenal renin-angiotensin system status in angiotensin II-infused rats. Also, a direct quantitative method has been developed recently to measure urinary angiotensinogen using human angiotensinogen enzyme-linked immunosorbent assay. These data prompted us to measure urinary angiotensinogen in patients with hypertension and chronic kidney disease, and investigate correlations with clinical parameters. This short article will focus on the role of the augmented intrarenal angiotensinogen in the pathophysiology of hypertension and chronic kidney disease. In addition, the potential of urinary angiotensinogen as a novel biomarker of the intrarenal renin-angiotensin system status in hypertension and chronic kidney disease will be also discussed.

Asymmetric dimethylarginine and reactive oxygen species: unwelcome twin visitors to the cardiovascular and kidney disease tables

Plasma levels of asymmetric dimethylarginine or markers of reactive oxygen species are increased in subjects with risk factors for cardiovascular disease or chronic kidney disease. We tested the hypothesis that reactive oxygen species generate cellular asymmetric dimethylarginine that together cause endothelial dysfunction that underlies the risk of subsequent disease. Rat preglomerular vascular smooth muscle cells transfected with p22(phox) had increased NADPH oxidase activity, enhanced activity and expression of protein arginine methyltransferase, and reduced activity and protein expression of dimethylarginine dimethylaminotransferase and of cationic amino acid transferase 1 resulting in increased cellular levels of asymmetric dimethylarginine. Rats infused with angiotensin II had oxidative stress. The endothelial function of their mesenteric arterioles was changed from vasodilatation to vasoconstriction, accompanied by increased vascular asymmetric dimethylarginine. All of these changes were prevented by Tempol. In vivo silencing of dimethylarginine dimethylaminotransferase 1 increased plasma levels of asymmetric dimethylarginine, whereas silencing of dimethylarginine dimethylaminotransferase 2 impaired endothelial function. We suggest that initiation factors, such as angiotensin II, expressed in blood vessels or tissues of subjects with cardiovascular and kidney disease risk factors generate reactive oxygen species from NADPH oxidase that enhances cellular asymmetric dimethylarginine in an amplification loop. This leads to adverse changes in vascular and organ functions, as a consequence of reduced tissue levels of NO and increased reactive oxygen species. Thus, we conclude that reactive oxygen species and asymmetric dimethylarginine form a tightly coupled amplification system that translates cardiovascular/kidney risk into overt disease.

Association between circulating specific leukocyte types and incident chronic kidney disease: the Atherosclerosis Risk in Communities (ARIC) study

Progressive renal fibrosis is a characteristic of all the diseases that cause renal failure and is invariably accompanied by a prominent leukocyte infiltration in the kidney. The goal of this study was to determine the association between the circulating specific leukocyte types and incident chronic kidney disease (CKD). In a cohort of 10,056 middle-aged white and African American adults, levels of circulating neutrophils, lymphocytes, and monocytes were measured at baseline; blood pressure (BP) and serum creatinine were measured and estimated glomerular filtration rate (eGFR) was calculated at baseline and 3 and 9 years later; and surveillance for first hospitalization or death with CKD was carried out over a mean follow-up of 7.4 years (maximum, 11.9 years). Increased neutrophil levels and decreased lymphocyte levels were significantly associated with greater CKD incidence after adjustment for covariates. African Americans tended to have similar but stronger patterns of association between circulating leukocytes and CKD incidence than whites, although the differences between race groups were not statistically significant. We also found that eGFR and BP were higher at each visit in African Americans than whites between ages 45 and 65. These findings support a potential role for circulating specific leukocytes in the pathogenesis of kidney dysfunction, especially in African Americans, indicating the leukocyte-related renal mechanism of essential hypertension (HT).

Proteolytic activation of the epithelial sodium channel and therapeutic application of a serine protease inhibitor for the treatment of salt-sensitive hypertension

Proteases are involved in numerous essential biological processes including blood clotting, controlled cell death, and tissue differentiation. Prostasin, a glycosylphosphatidylinositol-anchored serine protease, has been identified as a potential regulator of the epithelial sodium channel (ENaC) function in the kidney, lung, and airways. ENaC is composed of three homologous subunits α, β, and, γ. The dual cleavage of α subunit by furin and γ subunit by prostasin and furin releases inhibitory segments from ENaC, leading to the channel activation. Protease nexin-1, an endogenous prostasin inhibitor, inhibits ENaC activity through the suppression of prostasin activity, strongly suggesting the possibility that a coordinated regulation of serine proteases and serine protease inhibitors plays a key role in the sodium handling in the kidney. Camostat mesilate (CM), a synthetic serine protease inhibitor, reduced prostasin activity and subsequently decreased ENaC current. Oral administration of CM to Dahl salt-sensitive rats resulted in a significant decrease in blood pressure with an elevation of the urinary sodium/potassium ratio. These findings suggest that synthetic serine protease inhibitors such as CM might represent a new class of antihypertensive drugs in patients with salt-sensitive hypertension.

AT1 receptor-mediated augmentation of angiotensinogen, oxidative stress, and inflammation in ANG II-salt hypertension

Augmentation of intrarenal angiotensinogen (AGT) synthesis, secretion, and excretion is associated with the development of hypertension, renal oxidative stress, and tissue injury during ANG II-dependent hypertension. High salt (HS) exacerbates hypertension and kidney injury, but the mechanisms remain unclear. In this study, we determined the consequences of HS intake alone compared with chronic ANG II infusion and combined HS plus ANG II on the stimulation of urinary AGT (uAGT), renal oxidative stress, and renal injury markers. Sprague-Dawley rats were subjected to 1) a normal-salt diet [NS, n = 5]; 2) HS diet [8% NaCl, n = 5]; 3) ANG II infusion in NS rats [ANG II 80 ng/min, n = 5]; 4) ANG II infusion in HS rats [ANG II+HS, n = 5]; and 5) ANG II infusion in HS rats treated with ANG II type 1 receptor blocker (ARB) [ANG II+HS+ARB, n = 5] for 14 days. Rats fed a HS diet alone did not show changes in systolic blood pressure (SBP), proteinuria, cell proliferation, or uAGT excretion although they did exhibit mesangial expansion, collagen deposition, and had increased NADPH oxidase activity accompanied by increased peroxynitrite formation in the kidneys. Compared with ANG II rats, the combination of ANG II infusion and a HS diet led to exacerbation in SBP (175 ± 10 vs. 221 ± 8 mmHg; P < 0.05), proteinuria (46 ± 7 vs. 127 ± 7 mg/day; P < 0.05), and uAGT (1,109 ± 70 vs.. 7,200 ± 614 ng/day; P < 0.05) associated with greater collagen deposition, mesangial expansion, interstitial cell proliferation, and macrophage infiltration. In both ANG II groups, the O(2)(-) levels were increased due to increased NADPH oxidase activity without concomitant increases in peroxynitrite formation. The responses in ANG II rats were prevented or ameliorated by ARB treatment. The results indicate that HS independently stimulates ROS formation, which may synergize with the effect of ANG II to limit peroxynitrite formation, leading to exacerbation of uAGT and greater injury during ANG II salt hypertension.

Urinary angiotensinogen as a biomarker of nephropathy in childhood

While most circulating angiotensinogen (AGT) is synthesized in the liver, the kidneys also produce AGT. Recently, we reported that urinary AGT is mainly originated from AGT. Using newly developed human AGT ELISA, we measured urinary AGT levels in chronic glomerulonephritis (GN) patients and patients with type 1 diabetes in childhood. Urinary AGT level was positively correlated with diastolic blood pressure, urinary albumin, urinary protein levels, and urinary occult blood in chronic GN patients. Furthermore, urinary AGT level was significantly increased in chronic GN patients not treated with renin-angiotensin system (RAS) blockers compared with control subjects. Importantly, patients treated with RAS blockers had a marked attenuation of this increase. Also, urinary AGT level was significantly higher in patients with diabetic nephropathy in the premicroalbuminuric phase than in control subjects. These results suggest that urinary AGT reflects intrarenal RAS status in chronic GN and may be an early marker of diabetic nephropathy.

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.

Angiotensinogen Expression Is Enhanced in the Progression of Glomerular Disease

Intrarenal renin-angiotensin system (RAS) activation plays a critical role in the development and progression of renal injury. In the kidney, all of the RAS components are present and intrarenal angiotensin II (Ang II) is formed by multiple independent mechanisms. Angiotensinogen (AGT) is the only known substrate for renin that is a rate-limiting enzyme of the RAS. Recently, enhanced intrarenal AGT levels have been shown to reflect the intrarenal RAS status in hypertension, chronic glomerular disease and diabetic nephropathy. In this review, we focus on AGT expression of the diseased glomeruli in the progression of glomerular disease. An anti-glomerular basement membrane nephritis rat model developed progressive proteinuria and glomerular crescent formation, accompanied by increased macrophage infiltration and glomerular expression of AGT and Ang II. The addition of Ang II type 1 receptor blocker to CC-chemokine recaptor 2 antagonist markedly attenuated the induction of macrophage infiltration, AGT and Ang II, and reduced glomerular crescent formation. Next, the levels of glomerular AGT expression and marker of reactive oxygen species in Zucker diabetic fatty (ZDF) obese rats were higher than those in ZDF lean rats. Hydrogen peroxide (H(2)O(2)) induced an increase in the AGT expression in primary rat mesangial cells. Furthermore, the H(2)O(2)-induced upregulation of AGT was inhibited by a mitogen-activated protein kinase kinase and a c-Jun N-terminal kinase inhibitor. These data suggest the potential contribution of enhanced AGT expression in glomeruli to the intrarenal RAS activation for the development of glomerular disease.

Urinary Angiotensinogen as a Novel Biomarker of Intrarenal Renin-Angiotensin System in Chronic Kidney Disease

An activated intrarenal reninangiotensin system (RAS) plays a crucial role in the pathogenesis of hypertension and chronic kidney diseases (CKD). Angiotensinogen (AGT) is the only known substrate for renin, which is the rate-limiting enzyme of the RAS. Because the levels of AGT are close to the Michaelis-Menten constant for renin, AGT levels can also control the RAS activity, and upregulation of AGT may lead to elevated angiotensin peptide levels and increases in blood pressure. Recent studies on experimental animal models have documented the involvement of AGT in the intrarenal RAS activation and development of hypertension. Enhanced intrarenal AGT mRNA and/or protein levels occur in experimental models of hypertension and kidney diseases supporting important roles in the development and progression of hypertension and kidney diseases. Urinary excretion rates of AGT provide a specific index of intrarenal RAS status in angiotensin II-infused rats. Also, a direct quantitative method was recently developed to measure urinary AGT using human AGT ELISA. These data prompted us to measure urinary AGT in patients with hypertension and CKD, and investigate correlations with clinical parameters. This brief review will address the potential of urinary AGT as a novel biomarker of the intrarenal RAS status in hypertension and CKD.

Urinary angiotensinogen is correlated with blood pressure in men (Bogalusa Heart Study)

BACKGROUND

The Bogalusa Heart Study is a long-term study on cardiovascular disease and has followed a biracial (black/white) population from childhood. Risk factor data pertaining to many patients have been collected over 35 years, and the time course of hypertension has been documented by repeated examinations and measurements. Considerable sex and racial differences have been found to be related to cardiovascular disease. Urinary angiotensinogen (UAGT) is a novel biomarker for the intrarenal activity of the renin-angiotensin system in hypertension and kidney disease. We aimed to determine the relationship of UAGT with traditional cardiovascular disease risk factors in asymptomatic young adults in this biracial population.

METHOD

We recruited 251 individuals and collected a single random spot urine sample from each one. Because UAGT is significantly increased in diabetic patients and the use of antihypertensive drugs affects UAGT levels, we excluded patients who had diabetes, who were receiving antihypertensive treatment, or both. Consequently, 190 participants were included for this analysis.

RESULTS

UAGT levels did not differ with race or sex, but were significantly correlated with SBP (r = +0.23, P = 0.0015) and DBP (r = +0.24, P = 0.0012). Moreover, high correlations were shown in men, especially in black men (SBP, r = +0.85, P = 0.0005 and DBP, r = +0.72, P = 0.0079). Thus, UAGT is correlated with blood pressure in men, even when they do not show overt proteinuria or albuminuria.

CONCLUSION

The biomarker, UAGT, may facilitate the identification of individuals that are at increased risk for the development of hypertension and early asymptomatic renal disease.

Association between circulating specific leukocyte types and blood pressure: the atherosclerosis risk in communities (ARIC) study

Although total white blood cell (WBC) count has been associated with hypertension, the association between specific WBC types and blood pressure (BP) levels has not been studied. In a cohort of 5746 middle-age African-American and white adults free of clinical cardiovascular disease and cancer and not taking hypertension or anti-inflammatory medications, BP was measured at baseline and 3, 6, and 9 years later. Levels of circulating neutrophils, lymphocytes, and monocytes were measured at baseline. In African-Americans, but much less so in whites, increased neutrophil levels and decreased lymphocyte levels were significantly associated with elevation of BP but did not influence the rate of change of BP over time. The mean BP difference between the highest and lowest quartiles of neutrophils was approximately 8 mm Hg for systolic BP (SBP), 4 mm Hg for mean arterial pressure (MAP), and 5 mm Hg for pulse pressure (PP). The mean BP difference between the lowest and highest quartiles of lymphocytes was approximately 6 mm Hg for SBP, 2 mm Hg for diastolic BP (DBP), 3 mm Hg for MAP, and 4 mm Hg for PP. Increased neutrophils and decreased lymphocytes are significantly correlated with the regulation of BP and the development of hypertension, especially in African-Americans.

Glomerular angiotensinogen is induced in mesangial cells in diabetic rats via reactive oxygen species--ERK/JNK pathways

Whereas intra-renal angiotensinogen is predominantly localized in proximal tubular cells under basal conditions, it has been previously reported that angiotensinogen expression is induced in glomeruli under pathological conditions. However, there is no detailed information regarding the mechanism of the induced glomerular angiotensinogen. We used genetic pairs of Zucker diabetic fatty (ZDF) obese and lean rats to determine glomerular angiotensinogen expression. The levels of glomerular angiotensinogen immunoreactivity in ZDF obese rats were higher than those in ZDF lean rats. Double staining by IHC or IF with angiotensinogen and Thy1.1 antibodies showed that the majority of angiotensinogen in glomeruli was seen in mesangial cells. The levels of glomerular immunoreactivity for 4-HNE and urinary excretion of 8-isoprostane-markers of ROS-in ZDF obese rats were higher than those in ZDF lean rats. To confirm this system, primary rat mesangial cells were treated with hydrogen peroxide (H₂O₂) to clarify the signal transduction pathway for glomerular angiotensinogen expression. H₂O₂ induced an increase in angiotensinogen expression in a dose- and time-dependent manner, and the H₂O₂-induced upregulation of angiotensinogen was suppressed by catalase. Furthermore, the H₂O₂-induced upregulation of angiotensinogen was inhibited by a mitogen-activated protein kinase (MAPK) kinase (MEK) inhibitor and a c-Jun N-terminal kinase (JNK) inhibitor, but not inhibited by a p38 MAPK inhibitor. These data suggest that the majority of angiotensinogen was induced in mesangial cells in glomeruli under pathological conditions such as diabetic nephropathy, and angiotensinogen expression in mesangial cells was mediated by H₂O₂ and the subsequent activation of extracellular-regulated kinase (ERK)/JNK pathways.

Different protective actions of losartan and tempol on the renal inflammatory response to acute sodium overload

The aim of this work was to study the role of local intrarenal angiotensin II (Ang II) and the oxidative stress in the up-regulation of pro-inflammatory cytokines expression observed in rats submitted to an acute sodium overload. Sprague-Dawley rats were infused for 2 h with isotonic saline solution (Control group) and with hypertonic saline solution alone (Na group), plus the AT1 receptor antagonist losartan (10 mg kg(-1) in bolus) (Na-Los group), or plus the superoxide dismutase mimetic tempol (0.5 mg min(-1) kg(-1)) (Na-Temp group). Mean arterial pressure, glomerular filtration rate, and fractional sodium excretion (FE(Na)) were measured. Ang II, NF-kappaB, hypoxia inducible factor-1 alpha (HIF-1 alpha), transforming growth factor beta1 (TGF-beta1), smooth muscle actin (alpha-SMA), endothelial nitric oxide synthase (eNOS), and RANTES renal expression was evaluated by immunohistochemistry. Ang II, NF-kappaB, and TGF-beta1 and RANTES early inflammatory markers were overexpressed in Na group, accompanied by enhanced HIF-1 alpha immunostaining, lower eNOS expression, and unmodified alpha-SMA. Losartan and tempol increased FE(Na) in sodium overload group. Although losartan reduced Ang II and NF-kappaB staining and increased eNOS expression, it did not restore HIF-1 alpha expression and did not prevent inflammation. Conversely, tempol increased eNOS and natriuresis, restored HIF-1 alpha expression, and prevented inflammation. Early inflammatory markers observed in rats with acute sodium overload is associated with the imbalance between HIF-1 alpha and eNOS expression. While both losartan and tempol increased natriuresis and eNOS expression, only tempol was effective in restoring HIF-1 alpha expression and down-regulating TGF-beta1 and RANTES expression. The protective role of tempol, but not of losartan, in the inflammatory response may be associated with its greater antioxidant effects.

Aberrant ENaC activation in Dahl salt-sensitive rats

BACKGROUND

The epithelial sodium channel (ENaC) plays an important role in the regulation of blood pressure by modulating Na reabsorption in the kidney. Dahl salt-sensitive rats on high-salt diet develop severe hypertension, and high-salt diet has been reported to stimulate ENaC mRNA expression in the kidney abnormally in Dahl salt-sensitive rats despite a suppressed plasma aldosterone concentration (PAC).

METHODS

We investigated the effect of high-salt diet on ENaC protein expression in Dahl salt-resistant and Dahl salt-sensitive rats, and examined the effect of amiloride (5 mg/kg per day) and eplerenone (0.125% diet) on blood pressure and renal injury in Dahl salt-sensitive rats.

RESULTS

Dahl salt-sensitive rats developed hypertension and renal damage following 4 weeks of treatment with high-salt diet. Although PAC and kidney aldosterone content were all suppressed by the high-salt diet in Dahl salt-sensitive rats, both beta and gammaENaC mRNA expression and protein abundance were significantly increased. The molecular weight shift of gammaENaC from 85 to 70 kDa, an indication of ENaC activation, was clearly increased in Dahl salt-sensitive rats on high-salt diet compared with the low-salt group or Dahl salt-resistant rats on high-salt diet. Four weeks of treatment with amiloride, but not eplerenone, significantly ameliorated hypertension and kidney injury in Dahl salt-sensitive rats fed high-salt diet, suggesting aberrant aldosterone-independent activation of ENaC.

CONCLUSION

These results suggest that inappropriate expression and activation of ENaC could be one of the underlying mechanisms by which Dahl salt-sensitive rats develop salt-sensitive hypertension and organ damage, and indicate a therapeutic benefit of amiloride in salt-sensitive hypertension where ENaC is excessively activated.

Peroxisome proliferator-activated receptor-alpha activator fenofibrate prevents high-fat diet-induced renal lipotoxicity in spontaneously hypertensive rats

We investigated the effects of a high-fat (HF) diet and peroxisome proliferator-activated receptor (PPAR)-alpha activation on the intrarenal lipotoxicity associated with the renin-angiotensin system (RAS) and oxidative stress using spontaneously hypertensive (SHR) rats. Male SHR and Wistar-Kyoto (WKY) rats at 8 weeks of age were fed either a normal-fat diet or an HF diet without or with fenofibrate treatment for 12 weeks. Severe intrarenal lipid accumulation was noted in the SHR rats fed an HF diet than in WYK rats fed an HF diet (P<0.05). This lipid accumulation was associated with a 70% decrease in renal PPARalpha expression in SHR rats, whereas an HF diet increased the expression of PPARalpha in WKY rats by threefold. An HF diet also activated intrarenal, not systemic, RAS and induced oxidative stress associated with reduced nitric oxide (NO) bioavailability. By contrast, fenofibrate attenuated weight gain, fat mass and insulin resistance. Fenofibrate recovered HF diet-induced decreases in intrarenal PPARalpha expression and fat accumulation, and abolished intrarenal RAS activation and oxidative stress in SHR-HF animals (P<0.01). These activities conferred protection against increased blood pressure (BP), glomerulosclerosis and renal inflammation. Intrarenal free fatty acid and triglyceride concentrations were positively correlated with angiotensin II (gamma=0.63, 0.36) and 24-h urinary 8-hydroxy-deoxyguanosine (gamma=0.36, 0.39), and negatively correlated with PPARalpha contents (gamma=-0.47, -0.44; P<0.05). An HF diet-induced lipotoxicity by depletion of intrarenal PPARalpha aggravated BP and renal inflammation as a result of intrarenal RAS activation and oxidative stress. Therefore, intervention with PPARalpha activators can effectively prevent diet-induced renal lipotoxicity in hypertensive rats.

Role of activated intrarenal reactive oxygen species and renin-angiotensin system in IgA nephropathy model mice

1. Using HIGA (high IgA of ddY) mice as an IgA nephropathy model and BALB/c mice as controls, we demonstrated that reactive oxygen species (ROS) and the renin-angiotensin system (RAS) were activated in kidneys of HIGA mice. However, it was difficult to establish an association between renal damage and changes in ROS and the RAS. Therefore, the present study was performed to determine whether renal injury is associated with changes in ROS and the RAS in HIGA mice. 2. Male HIGA mice were divided into four groups of 10 each: (i) untreated mice (HIGA + null); (ii) mice treated with the angiotensin AT(1) receptor antagonist olmesartan (5 mg/kg per day; HIGA + OLM); (iii) mice treated with the superoxide dismutase mimetic tempol (50 mg/kg per day; HIGA + Tempol); and (iv) mice treated with RAS-independent antihypertensive drugs (30 mg/kg per day hydralazine, 0.6 mg/kg per day reserpine and 12 mg/kg per day hydrochlorothiazide; HIGA + HRH). Mice were treated for 5 weeks. 3. Systolic blood pressure decreased significantly in the HIGA + OLM and HIGA + HRH groups, but not in the HIGA + Tempol group, compared with HIGA + null mice. The expression of two ROS markers (4-hydroxy-2-nonenal and heme oxygenase-1) and angiotensin II as a marker of the RAS decreased significantly in HIGA + OLM and HIGA + Tempol mice, but not in HIGA + HRH mice, compared with HIGA + null mice. As a marker of renal damage, mesangial matrix expansion and the desmin-positive area decreased significantly in the HIGA + OLM and HIGA + Tempol groups, but not in HIGA + HRH group, compared with the HIGA + null group. 4. These data suggest that intrarenal ROS and RAS activation play a pivotal role in the development of IgA nephropathy model mice, from the early phase, independent of blood pressure.

Activated intrarenal reactive oxygen species and renin angiotensin system in IgA nephropathy

Immunoglobulin A (IgA) nephropathy is recognized worldwide as the most common primary glomerulopathy. Although the mechanisms underlying the development of IgA nephropathy are gradually being clarified, their details remain unclear, and a radical cure for this condition has not yet been established. It has been clinically demonstrated that the immunoreactivities of intrarenal heme oxygenase-1 (HO-1) and 4-hydroxy-2-nonenal (4-HNE) markers of reactive oxygen species (ROS) and those of intrarenal angiotensinogen (AGT) and angiotensin II (Ang II) markers of renin angiotensin system (RAS) in IgA nephropathy patients were significantly increased as compared to those of control subjects. In an animal study, high IgA of ddY (HIGA) mice were used as an IgA nephropathy model and compared with BALB/c mice, which served as the control. The levels of markers for ROS (urinary 8-isoprostane and intrarenal 4-HNE), RAS (intrarenal AGT and Ang II), and renal damage in the HIGA mice were significantly increased as compared to those in the BALB/c mice. Moreover, an interventional study using HIGA mice demonstrated that the expressions of 2 lines of intrarenal ROS markers (4-HNE and HO-1), 2 lines of intrarenal RAS markers (AGT and Ang II) and renal damage decreased significantly in HIGA mice receiving treatment with the Ang II receptor blocker olmesartan but not in HIGA mice receiving treatment with RAS-independent antihypertensive drugs (hydralazine, reserpine, and hydrochlorothiazide) when compared with HIGA mice that were not treated. These data suggest that intrarenal ROS and RAS activation plays a pivotal role in the development of IgA nephropathy.

Chemistry and antihypertensive effects of tempol and other nitroxides

Nitroxides can undergo one- or two-electron reduction reactions to hydroxylamines or oxammonium cations, respectively, which themselves are interconvertible, thereby providing redox metabolic actions. 4-Hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (tempol) is the most extensively studied nitroxide. It is a cell membrane-permeable amphilite that dismutates superoxide catalytically, facilitates hydrogen peroxide metabolism by catalase-like actions, and limits formation of toxic hydroxyl radicals produced by Fenton reactions. It is broadly effective in detoxifying these reactive oxygen species in cell and animal studies. When administered intravenously to hypertensive rodent models, tempol caused rapid and reversible dose-dependent reductions in blood pressure in 22 of 26 studies. This was accompanied by vasodilation, increased nitric oxide activity, reduced sympathetic nervous system activity at central and peripheral sites, and enhanced potassium channel conductance in blood vessels and neurons. When administered orally or by infusion over days or weeks to hypertensive rodent models, it reduced blood pressure in 59 of 68 studies. This was accompanied by correction of salt sensitivity and endothelial dysfunction and reduced agonist-evoked oxidative stress and contractility of blood vessels, reduced renal vascular resistance, and increased renal tissue oxygen tension. Thus, tempol is broadly effective in reducing blood pressure, whether given by acute intravenous injection or by prolonged administration, in a wide range of rodent models of hypertension.

Testosterone-dependent hypertension and upregulation of intrarenal angiotensinogen in Dahl salt-sensitive rats

Blood pressure (BP) is more salt sensitive in men than in premenopausal women. In Dahl salt-sensitive rats (DS), high-salt (HS) diet increases BP more in males than females. In contrast to the systemic renin-angiotensin system, which is suppressed in response to HS in male DS, intrarenal angiotensinogen expression is increased, and intrarenal levels of ANG II are not suppressed. In this study, the hypothesis was tested that there is a sexual dimorphism in HS-induced upregulation of intrarenal angiotensinogen mediated by testosterone that also causes increases in BP and renal injury. On a low-salt (LS) diet, male DS had higher levels of intrarenal angiotensinogen mRNA than females. HS diet for 4 wk increased renal cortical angiotensinogen mRNA and protein only in male DS, which was prevented by castration. Ovariectomy of female DS had no effect on intrarenal angiotensinogen expression on either diet. Radiotelemetric BP was similar between males and castrated rats on LS diet. HS diet for 4 wk caused a progressive increase in BP, protein and albumin excretion, and glomerular sclerosis in male DS rats, which were attenuated by castration. Testosterone replacement in castrated DS rats increased BP, renal injury, and upregulation of renal angiotensinogen associated with HS diet. Testosterone contributes to the development of hypertension and renal injury in male DS rats on HS diet possibly through upregulation of the intrarenal renin-angiotensin system.

Activation of reactive oxygen species and the renin-angiotensin system in IgA nephropathy model mice

1. Although IgA nephropathy is the most common form of primary glomerulopathy, the detailed mechanisms underlying its development remain uncertain. 2. In the present study, we used male high IgA strain of ddY (HIGA) mice as the IgA nephropathy model and age-matched male BALB/c mice as the control. Recent studies have demonstrated that reactive oxygen species (ROS)-dependent enhancement of the renin-angiotensin system (RAS) plays a potential role in the development and progression of renal injury. Therefore, in the present study we periodically measured the systolic blood pressure (SBP) of mice over the period 21-25 weeks of age and estimated markers for ROS, RAS and renal damage after mice had been killed at 25 weeks of age. 3. Markers for ROS (urinary 8-isoprostane excretion and renal 4-hydroxy-2-nonenal accumulation), RAS (renal angiotensinogen protein expression, urinary angiotensinogen excretion and renal angiotensin II) and renal damage (desmin-positive area and urinary protein excretion), as well as SBP, were significantly increased in HIGA mice compared with control BALB/c mice. 4. The data suggest that both ROS and the RAS are activated at an early phase in IgA nephropathy model mice.

Role of superoxide and hydrogen peroxide in hypertension induced by an antagonist of adenosine receptors

Treatment of Wistar rats for 7 days with 1,3-dipropyl-8-sulfophenylxanthine (DPSPX), an antagonist of adenosine receptors, induces long-lasting hypertension associated with marked changes in vascular structure and reactivity and renin-angiotensin system activation. This study aimed at evaluating the role of oxidative stress in the development of DPSPX-induced hypertension and also at identifying the relative contribution of superoxide radical (O2.-) vs hydrogen peroxide (H2O2). Vascular and systemic prooxidant/antioxidant status was evaluated in sham (saline, i.p., 7 days) and DPSPX (90 microg/kg/h, i.p., 7 days)-treated rats. Systolic blood pressure was determined by invasive and non-invasive methods. The activity of vascular NADPH oxidase, superoxide dismutase (SOD), catalase and glutathione peroxidase was assayed by fluorometric/spectrophotometric methods. H2O2 levels were measured using an Amplex Red Hydrogen Peroxide kit. Plasma thiobarbituric acid reactive substances and plasma antioxidant capacity were also measured. In addition we tested the effects of antioxidants or inhibitors of reactive oxygen species generation on blood pressure, vascular hyperplasia and oxidative stress parameters. DPSPX-hypertensive rats showed increased activity of vascular NADPH oxidase, SOD, catalase and glutathione peroxidase, as well as increased H2O2 generation. DPSPX-hypertensive rats also had increased plasma lipid peroxidation and decreased plasma antioxidant capacity. Treatment with apocynin (1.5 mmol/l, per os, 14 days), or with polyethylene glycol (PEG)-catalase (10,000 U/kg/day, i.p., 8 days), prevented the DPSPX-induced effects on blood pressure, vascular structure and H2O2 levels. Tempol (3 mmol/l, per os, 14 days) failed to inhibit these changes, unless PEG-catalase was co-administered. It is concluded that O2.- generation with subsequent formation of H2O2 plays a major role in the development of DPSPX-induced hypertension.