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

Natriuresis During an Acute Intravenous Sodium Chloride Infusion in Conscious Sprague Dawley Rats Is Mediated by a Blood Pressure-Independent α1-Adrenoceptor-Mediated Mechanism

The mechanisms that sense alterations in total body sodium content to facilitate sodium homeostasis in response to an acute sodium challenge that does not increase blood pressure have not been fully elucidated. We hypothesized that the renal sympathetic nerves are critical to mediate natriuresis via α₁- or β-adrenoceptors signal transduction pathways to maintain sodium balance in the face of acute increases in total body sodium content that do not activate the pressure-natriuresis mechanism. To address this hypothesis, we used acute bilateral renal denervation (RDNX), an anteroventral third ventricle (AV3V) lesion and α₁- or β-antagonism during an acute 1M NaCl sodium challenge in conscious male Sprague Dawley rats. An acute 1M NaCl infusion did not alter blood pressure and evoked profound natriuresis and sympathoinhibition. Acute bilateral RDNX attenuated the natriuretic and sympathoinhibitory responses evoked by a 1M NaCl infusion [peak natriuresis (μeq/min) sham 14.5 ± 1.3 vs. acute RDNX: 9.2 ± 1.4, p < 0.05; plasma NE (nmol/L) sham control: 44 ± 4 vs. sham 1M NaCl infusion 11 ± 2, p < 0.05; acute RDNX control: 42 ± 6 vs. acute RDNX 1M NaCl infusion 25 ± 3, p < 0.05]. In contrast, an AV3V lesion did not impact the cardiovascular, renal excretory or sympathoinhibitory responses to an acute 1M NaCl infusion. Acute i.v. α₁-adrenoceptor antagonism with terazosin evoked a significant drop in baseline blood pressure and significantly attenuated the natriuretic response to a 1M NaCl load [peak natriuresis (μeq/min) saline 17.2 ± 1.4 vs. i.v. terazosin 7.8 ± 2.5, p < 0.05]. In contrast, acute β-adrenoceptor antagonism with i.v. propranolol infusion did not impact the cardiovascular or renal excretory responses to an acute 1M NaCl infusion. Critically, the natriuretic response to an acute 1M NaCl infusion was significantly blunted in rats receiving a s.c. infusion of the α₁-adrenoceptor antagonist terazosin at a dose that did not lower baseline blood pressure [peak natriuresis (μeq/min) sc saline: 18 ± 1 vs. sc terazosin 7 ± 2, p < 0.05]. Additionally, a s.c. infusion of the α₁-adrenoceptor antagonist terazosin further attenuated the natriuretic response to a 1M NaCl infusion in acutely RDNX animals. Collectively these data indicate a specific role of a blood pressure-independent renal sympathetic nerve-dependent α₁-adrenoceptor-mediated pathway in the natriuretic and sympathoinhibitory responses evoked by acute increases in total body sodium.

Thromboxane A2 receptor antagonist (ONO-8809) attenuates renal disorders caused by salt overload in stroke-prone spontaneously hypertensive rats

Epidemiological and clinical studies have demonstrated that excessive salt intake causes severe hypertension and exacerbates organ derangement, such as in chronic kidney disease (CKD). In this study, we focused on evaluating the histological and gene expression effects in the kidneys of stroke‐prone spontaneously hypertensive rats (SHRSP) with a high salt intake and the thromboxane A₂/ prostaglandin H₂ receptor (TPR) blocker ONO‐8809. Six‐week‐old SHRSPs were divided into three groups and were fed normal chow containing 0.4% NaCl, 2.0%NaCl or 2.0%NaCl + ONO‐8809 (0.6 mg/kg p.o. daily). Histological analyses with immunohistochemistry and a gene expression assay with a DNA kidney microarray were performed after 8 weeks. The following changes were observed in SHRSPs with the high salt intake. Glomerular sclerotic changes were remarkably observed in the juxtamedullary cortex areas. The ED1, monocyte chemoattractant protein‐1 (MCP‐1), nitrotyrosine and hypoxia inducible factor 1α (HIF‐1α) staining areas were increased in the glomeruli and interstitial portion of the kidneys. The genes Tbxa2r (that encodes TPR), Prcp and Car7 were significantly underexpressed in the kidneys. The plasma 8‐isoprostane level was significantly elevated and was attenuated with the ONO‐8809 treatment. Thromboxane A₂ (TXA₂) and oxidative stress exaggerated renal dysfunction in the salt‐loaded SHRSPs, and ONO‐8809 as a TPR blocker suppressed these changes. Therefore, ONO‐8809 is a candidate drug to prevent CKD in hypertensive patients when CKD is associated with a high salt intake.

Effects of Losartan, Tempol, and Their Combination On Renal Nitric Oxide Synthases in the Animal Model of Chronic Kidney Disease

Down-regulation of nitric oxide synthase (NOS) and NO deficiency in the kidneys have been implicated in the pathogenesis of chronic kidney disease (CKD). In this study we examined the effects of losartan, tempol, and combined treatment on three NOS isoforms expressions, kidney NO content and NOS correlation with renal function and structure in the early stage of adriamycin (ADR)-induced CKD in spontaneously hypertensive rats (SHR). Rats were divided into control group, and four other groups which were treated with ADR and received vehicle, losartan (L, angiotensin II type 1 receptor blocker), tempol (T, redox-cycling nitroxide) or T+L treatment (by gavage) in a six-week study. Reduction of all NOS isoforms expressions were significantly improved by losartan or tempol, and correlated with proteinuria amelioration. Combined treatment induced down-regulation of constitutive NOS isoforms, whilst inducible NOS was up-regulated and followed by increased nitrite content and a significant decline in the glomerular filtration rate. Losartan or tempol prevented ADR-induced neoexpression of vimentin in the glomeruli and tubulointerstital areas, whereas de novo vimentin expression was still observed in the atrophic tubules and in the interstitial fibroblasts and myofibroblasts in combined treatment. It can be concluded that single treatments, contrary to combined, were effective in improving NO bioavailability and slowing down the progression of CKD.

Protective Effect of Tempol on Acute Kidney Injury Through PI3K/Akt/Nrf2 Signaling Pathway

BACKGROUND/AIMS

Tempol is a protective antioxidant against ischemic injury in many animal models. The molecular mechanisms are not well understood. Nuclear factor erythroid 2-related factor (Nrf2) is a master transcription factor during oxidative stress, which is enhanced by activation of protein kinase C (PKC) pathway. Another factor, tubular epithelial apoptosis, is mediated by activation of phosphoinositide 3-kinase (PI3K)/protein kinase B (PKB, Akt) signaling pathway during renal ischemic injury. We tested the hypothesis that tempol activates PKC or PI3K/Akt/Nrf2 pathways to transcribe many genes that coordinate endogenous antioxidant defense.

METHODS

The right renal pedicle was clamped for 45 minutes and the left kidney was removed to study renal ischemia/reperfusion (I/R) injury in C57BL/6 mice. The response was assessed from serum parameters, renal morphology and renal expression of PKC, phosphorylated-PKC (p-PKC), Nrf2, heme oxygenase-1 (HO-1), Akt, phosphorylated-Akt (p-Akt), pro-caspase-3 and cleaved caspase-3 in groups of sham and I/R mice given vehicle, or tempol (50 or 100 mg/kg, intraperitoneal injection).

RESULTS

The serum malondialdehyde (MDA, marker of reactive oxygen species) doubled and the BUN and creatinine increased 5- to 10-fold after I/R injury. Tempol (50 or 100 mg/kg) prevented the increases in MDA but only tempol (50 mg/kg) lessened the increases in BUN and creatinine and moderated the acute tubular necrosis. I/R did not change expression of PKC or p-PKC but reduced renal expression of Nrf2, p-Akt, HO-1 and pro-caspase-3 and increased cleaved caspase-3. Tempol (50 mg/kg) prevented these changes produced by I/R whereas tempol (100 mg/kg) had lesser or inconsistent effects.

CONCLUSION

Tempol (50 mg/kg) prevents lipid peroxidation and attenuates renal damage after I/R injury. The beneficial pathway apparently is not dependent on upregulation or phosphorylation of PKC, at lower tempol doses, does implicate upregulation of Akt with expression of Nrf2 that could account for the increase in the antioxidant gene HO-1 and a reduction in the cleavage of the cellular damage marker pro-caspase-3.

Signaling pathways involved in renal oxidative injury: role of the vasoactive peptides and the renal dopaminergic system

The physiological hydroelectrolytic balance and the redox steady state in the kidney are accomplished by an intricate interaction between signals from extrarenal and intrarenal sources and between antinatriuretic and natriuretic factors. Angiotensin II, atrial natriuretic peptide and intrarenal dopamine play a pivotal role in this interactive network. The balance between endogenous antioxidant agents like the renal dopaminergic system and atrial natriuretic peptide, by one side, and the prooxidant effect of the renin angiotensin system, by the other side, contributes to ensuring the normal function of the kidney. Different pathological scenarios, as nephrotic syndrome and hypertension, where renal sodium excretion is altered, are associated with an impaired interaction between two natriuretic systems as the renal dopaminergic system and atrial natriuretic peptide that may be involved in the pathogenesis of renal diseases. The aim of this review is to update and comment the most recent evidences about the intracellular pathways involved in the relationship between endogenous antioxidant agents like the renal dopaminergic system and atrial natriuretic peptide and the prooxidant effect of the renin angiotensin system in the pathogenesis of renal inflammation.

Role of angiotensin II and oxidative stress on renal aquaporins expression in hypernatremic rats

The aim of this study was to assess whether endogenous Ang II and oxidative stress produced by acute hypertonic sodium overload may regulate the expression of aquaporin-1 (AQP-1) and aquaporin-2 (AQP-2) in the kidney. Groups of anesthetized male Sprague-Dawley rats were infused with isotonic saline solution (control) or with hypertonic saline solution (Na group, 1 M NaCl), either alone or with losartan (10 mg kg(-1)) or tempol (0.5 mg min(-1) kg(-1)) during 2 h. Renal function parameters were measured. Groups of unanesthetized animals were injected intraperitoneally with hypertonic saline solution, with or without free access to water intake, Na+W, and Na-W, respectively. The expression of AQP-1, AQP-2, Ang II, eNOS, and NF-kB were evaluated in the kidney by Western blot and immunohistochemistry. AQP-2 distribution was assessed by immunofluorescence. Na group showed increased natriuresis and diuresis, and Ang II and NF-kB expression, but decreased eNOS expression. Losartan or tempol enhanced further the diuresis, and AQP-2 and eNOS expression, as well as decreased Ang II and NF-kB expression. Confocal immunofluorescence imaging revealed labeling of AQP-2 in the apical plasma membrane with less labeling in the intracellular vesicles than the apical membrane in kidney medullary collecting duct principal cells both in C and Na groups. Importantly, our data also show that losartan and tempol induces a predominantly accumulation of AQP-2 in intracellular vesicles. In unanesthetized rats, Na+W group presented increased diuresis, natriuresis, and AQP-2 expression (112 ± 25 vs 64 ± 16; *p < 0.05). Water deprivation increased plasma sodium and diuresis but decreased AQP-2 (46 ± 22 vs 112 ± 25; §p < 0.05) and eNOS expression in the kidney. This study is a novel demonstration that renal endogenous Ang II-oxidative stress, induced in vivo in hypernatremic rats by an acute sodium overload, regulates AQP-2 expression.

The cooperative roles of inflammation and oxidative stress in the pathogenesis of hypertension

SIGNIFICANCE

Innate and adaptive immunity play fundamental roles in the development of hypertension and its complications. As effectors of the cell-mediated immune response, myeloid cells and T lymphocytes protect the host organism from infection by attacking foreign intruders with bursts of reactive oxygen species (ROS).

RECENT ADVANCES

While these ROS may help to preserve the vascular tone and thereby protect against circulatory collapse in the face of overwhelming infection, aberrant elaboration of ROS triggered by immune cells in the absence of a hemodynamic insult can lead to pathologic increases in blood pressure. Conversely, misdirected oxidative stress in cardiovascular control organs, including the vasculature, the kidney, and the nervous system potentiates inflammatory responses, augmenting blood pressure elevation and inciting target organ damage.

CRITICAL ISSUES

Inflammation and oxidative stress thereby act as cooperative and synergistic partners in the pathogenesis of hypertension.

FUTURE DIRECTIONS

Pharmacologic interventions for hypertensive patients will need to exploit this robust bidirectional relationship between ROS generation and immune activation in cardiovascular control organs to maximize therapeutic benefit, while limiting off-target side effects.

Release from glomerular overload by the addition of low-dose thiazide in patients with angiotensin receptor blocker-resistant hypertension

BACKGROUND/AIMS

This multicenter, prospective, observational study assessed the renoprotective effects of losartan/thiazide combination therapy in terms of lowering the estimated glomerular filtration rate (eGFR).

METHODS

Adult patients with angiotensin receptor blocker (ARB)-resistant essential hypertension (n = 104) were enrolled and switched to combination therapy with losartan (50 mg/day) and hydrochlorothiazide (12.5 mg/day).

RESULTS

eGFR values declined significantly during the first 3 months, and changes in eGFR were assessed according to tertiles of the eGFR decrease ratio at 3 months. Only the high eGFR decrease (1st tertile) group showed significantly greater decreases in baseline eGFR and albumin-to-creatinine ratio (ACR) during the first 3 months. Additionally, the assessment according to tertiles of the baseline eGFR showed a signifcant decrease in eGFR and ACR during the first 3 months in the high baseline eGFR (1st tertile) group, but not in the moderate (2nd tertile) and low baseline eGFR (3rd tertile) groups.

CONCLUSION

The present results revealed that losartan/thiazide combination therapy attenuated glomerular overload, indicating that this therapy may provide glomerular protection in patients with an elevated GFR without causing prolonged damage to renal function.

Oxidative stress contributes to sex differences in blood pressure in adult growth-restricted offspring

Numerous experimental studies suggest that oxidative stress contributes to the pathophysiology of hypertension and, importantly, that oxidative stress plays a more definitive role in mediating hypertension in males than in females. Intrauterine growth restriction induced by reduced uterine perfusion initiated at day 14 of gestation in the rat programs hypertension in adult male growth-restricted offspring; yet, female growth-restricted offspring are normotensive. The mechanisms mediating sex differences in blood pressure in adult growth-restricted offspring are not clear. Thus, this study tested the hypothesis that sex-specific differences in renal oxidative stress contribute to the regulation of blood pressure in adult growth-restricted offspring. A significant increase in blood pressure measured by telemetry in male growth-restricted offspring (P<0.05) was associated with a marked increase in renal markers of oxidative stress (P<0.05). Chronic treatment with the antioxidant Tempol had no effect on blood pressure in male control offspring, but it normalized blood pressure (P<0.05) and renal markers of oxidative stress (P<0.05) in male growth-restricted offspring relative to male control offspring. Renal markers of oxidative stress were not elevated in female growth-restricted offspring; however, renal activity of the antioxidant catalase was significantly elevated relative to female control offspring (P<0.05). Chronic treatment with Tempol did not significantly alter oxidative stress or blood pressure measured by telemetry in female offspring. Thus, these data suggest that sex differences in renal oxidative stress and antioxidant activity are present in adult growth-restricted offspring and that oxidative stress may play a more important role in modulating blood pressure in male but not female growth-restricted offspring.