Olmesartan Improves Endothelin-Induced Hypertension and Oxidative Stress in Rats

Comparative Efficacy of Angiotensin II Type 1 Receptor Blockers Against Ventilator-Induced Diaphragm Dysfunction in Rats

Mechanical ventilation (MV) is a life‐saving intervention for many critically ill patients. Unfortunately, prolonged MV results in the rapid development of inspiratory muscle weakness due to diaphragmatic atrophy and contractile dysfunction (termed ventilator‐induced diaphragm dysfunction (VIDD)). Although VIDD is a major risk factor for problems in weaning patients from MV, a standard therapy to prevent VIDD does not exist. However, emerging evidence suggests that pharmacological blockade of angiotensin II type 1 receptors (AT1Rs) protects against VIDD. Nonetheless, the essential characteristics of AT1R blockers (ARBs) required to protect against VIDD remain unclear. To determine the traits of ARBs that are vital for protection against VIDD, we compared the efficacy of two clinically relevant ARBs, irbesartan and olmesartan; these ARBs differ in molecular structure and effects on AT1Rs. Specifically, olmesartan blocks both angiotensin II (AngII) binding and mechanical activation of AT1Rs, whereas irbesartan prevents only AngII binding to AT1Rs. Using a well‐established preclinical model of prolonged MV, we tested the hypothesis that compared with irbesartan, olmesartan provides greater protection against VIDD. Our results reveal that irbesartan does not protect against VIDD whereas olmesartan defends against both MV‐induced diaphragmatic atrophy and contractile dysfunction. These findings support the hypothesis that olmesartan is superior to irbesartan in protecting against VIDD and are consistent with the concept that blockade of mechanical activation of AT1Rs is a required property of ARBs to shield against VIDD. These important findings provide a foundation for future clinical trials to evaluate ARBs as a therapy to protect against VIDD.

The Protective Effect of L-arginine in Cisplatin-induced Nephrotoxicity in Streptozotocin-induced Diabetic Rats

Background:

Cisplatin (CP) is accompanied with a nephrotoxicity. L-arginine (LA) plays an important role in the regulation of renal function. The present study was designed to investigate the protective role of LA supplementation in CP-induced nephrotoxicity in a diabetic rat's model.

Materials and Methods:

Sixteen adult female and male Wistar rats were used and they received a single dose of streptozotocin (STZ) (60 mg/kg i.p.). Diabetic female and male rats were arranged as groups 1–5 and groups 6–10, respectively. Groups 1 and 6 (LA groups) received LA alone. Groups 2 and 7 (CP groups) received CP alone. Groups 3 and 8 (CP + LA [PT] groups) received LA as prophylaxis and then treated with LA and CP. Groups 4 and 9 (CP + LA [T] groups) were treated with LA and CP simultaneously. Groups 5 and 10 (CP + LA [P] groups) received LA as prophylaxis and then treated with CP.

Results:

The serum creatinine (Cr) level of males in Groups 8 and 9 was significantly increased when compared with LA and CP (P < 0.05), whereas no differences were observed in Cr level in female groups. Blood urea nitrogen/Cr ratio and kidney weight were reduced in all CP-receiving male rats. Such observation was not seen in female rats. Different results related to weight loss were obtained between male and female animals. The kidney tissue damage score in CP + LA (PT) male group was significantly greater than CP group (P < 0.05).

Conclusion:

Our findings indicate that administration of LA in female and male rats has no protective effect on the severity of nephrotoxicity induced by CP in diabetic rats.

Influence of Endothelin 1 Receptor Blockers and a Nitric Oxide Synthase Inhibitor on Reactive Oxygen Species Formation in Rat Lungs

This study was designated to estimate protective role of ETA and ETB receptor antagonist against endothelin 1 (ET-1)-induced oxidative stress in lungs and determine whether these effects are mediated by nitric oxide (NO) synthase. Experiments were performed on Wistar rats divided into the following groups: I – saline (0.9 % NaCl); II – ET-1 (3 μg/kg b.w.), III – BQ123 (1 mg/kg b.w.) + ET-1 (3 μg/kg b.w.), IV – BQ788 (3 mg/kg b.w.) + ET-1 (3 μg/kg b.w.), V – N-nitro-L-arginine methyl ester (L-NAME) (5 mg/kg b.w.) + ET-1 (3 μg/kg b.w.). ETA and ETB receptor antagonists or L-NAME were administered 30 min before ET-1 injection. The levels of the following substances were measured in the lungs homogenates: thiobarbituric acid reactive substances (TBARS), hydrogen peroxide (H2O2), reduced glutathione (GSH) and tumor necrosis factor-alpha (TNF-α). The results showed that ET-1 significantly increased TBARS, H2O2 (respectively: p<0.001, p<0.02) and TNF-α levels (p<0.02) and decreased the GSH level (p<0.01) vs. control group. On the other hand, prior administration of ETA receptor blocker (BQ123) significantly attenuated TBARS (p<0.01), H2O2 (p<0.02), TNF-α (p<0.02) and increased GSH (p<0.02) levels vs. ET-1. However, prior administration of ETB receptor blocker BQ788 did not cause significant changes in the: TBARS, H2O2 and TNF-α (p>0.05) levels, but significantly increased the GSH level and GSH/GSSG ratio (p<0.05). Administration of L-NAME significantly attenuated TBARS (p<0.001), H2O2 (p<0.05), TNF-α (p<0.01) and increased GSH (p<0.05) levels vs. ET-1. In conclusion, we demonstrated that ET-1 induced oxidative stress in the lungs is mediated by ETA receptors. ETA receptor blockage inhibited generation of free radicals and TNF-α and ameliorated antioxidant properties. Moreover, generation of reactive oxygen species is mediated by NOS in the lungs.

Olmesartan, an angiotensin II receptor blocker inhibits the progression of cataract formation in cadmium chloride induced hypertensive albino rats

AIMS

Previously we found that cadmium chloride (CdCl₂) exposure substantially elevates hypertension and potentiates cataract formation. In the present study, we investigated the protective effects of olmesartan, an angiotensin II receptor blocker against cataractogenesis in the CdCl₂-induced hypertensive animal model.

MAIN METHODS

Male Sprague-Dawley albino rats (150-180g) were randomly selected and assigned to four groups (n=6). Among the four groups, one group (normal) received 0.3% carboxymethyl cellulose (10ml/kg/day, p.o.), another group (CdCl₂ control) received CdCl₂ (0.5mg/kg/day, i.p.), and remaining two groups received olmesartan at two doses level (2 and 4mg/kg/day, p.o.) concurrently with CdCl₂ for six consecutive weeks. Blood pressure and cataract formation were examined biweekly, and pathophysiological parameters in serum and eye lenses were evaluated after six weeks of the experimental protocol.

KEY FINDINGS

The olmesartan treatment significantly restored the blood pressure, lenticular opacity, serum and lens antioxidants (catalase, superoxide dismutase, glutathione peroxidase, and glutathione reduced), and malondialdehyde level. Additionally, it significantly restored the proteins, ions (Na⁺, K⁺, and Ca²⁺), and ATPase pumps activity (Na⁺K⁺ ATPase and Ca²⁺ ATPase) in the lens as compared to CdCl₂ control group.

SIGNIFICANCE

The findings demonstrate that olmesartan potentially inhibits the risk of cataract formation in the hypertensive state via restoration of lenticular oxidative stress, ATPase function, and ionic contents in the eye lenses. The results suggest that angiotensin II receptor blockers play an important role to prevent cataract formation in several pathogenic conditions like hypertension, diabetes, and oxidative stress.

End o' the line revisited: moving on from nitric oxide to CGRP

When endothelin-1(ET-1) was discovered it was hailed as the prototypical endothelium-derived contracting factor (EDCF). However, over the years little evidence emerged convincingly demonstrating that the peptide actually contributes to moment-to-moment changes in vascular tone elicited by endothelial cells. This has been attributed to the profound inhibitory effect of nitric oxide (NO) on both the production (by the endothelium) and the action (on vascular smooth muscle) of ET-1. Hence, the peptide is likely to initiate acute changes in vascular diameter only under extreme conditions of endothelial dysfunction when the NO bioavailability is considerably reduced if not absent. The present essay discusses whether or not this concept should be revised, in particular in view of the potent inhibitory effect exerted by calcitonin gene related peptide (CGRP) released from sensorimotor nerves on vasoconstrictor responses to ET-1.

Renoprotective effects of olmesartan medoxomil on diabetic nephropathy in streptozotocin-induced diabetes in rats

Olmesartan medoxomil (OM) is one of the newest members of the angiotensin receptor blocker (ARB) family. The renoprotective effects of the angiotensin II type 1 receptor antagonist OM was investigated in a streptozotocin (STZ)-induced diabetic rat model. In this study, we investigated whether OM was able to ameliorate diabetic nephropathy (DN). Thirty male Sprague Dawley rats were assigned to 3 groups: the non-diabetic (group A, n=10), the untreated STZ-induced DN control (group B, n=10) and the STZ-induced DN treated with OM (group C, n=10). Blood pressure (BP) and glucose, creatinine (Cr), blood urea nitrogen (BUN), superoxide dismutase (SOD), malondialdehyde (MDA) microalbumin and urinary protein concentrations were measured. In STZ diabetic rats, BP, glucose, Cr, BUN, MDA and urinary protein levels were significantly increased compared to the non-diabetic control group. OM significantly improved the biological indices in the DN rats. The renal pathological changes were also observed under a light microscope. Our results suggested that OM exerted renoprotective effects on rats with STZ-induced diabetes.

Addition of ET(A) receptor blockade increases renoprotection provided by renin-angiotensin system blockade in 5/6 nephrectomized Ren-2 transgenic rats

AIMS

There is evidence that in addition to hypertension and hyperactivity of the renin-angiotensin system (RAS), enhanced intrarenal activity of endothelin (ET) system contributes to the pathophysiology and progression of chronic kidney disease (CKD). This prompted us to examine if this progression would be alleviated by addition of type A ET receptor (ETA) blockade to the standard blockade of RAS.

MAIN METHODS

Ren-2 transgenic rats (TGR) after 5/6 renal ablation (5/6 NX) served as a model of CKD. For RAS inhibition a combination of angiotensin-converting enzyme inhibitor (trandolapril, 6 mg/L drinking water) and angiotensin II type 1 receptor blocker (losartan, 100 mg/L drinking water) was used. Alternatively, ETA receptor blocker (atrasentan, 5 mg·kg(-1)·day(-1) in drinking water) was added to the combined RAS blockade. The follow-up period was 44 weeks after 5/6 NX, and the rats' survival rate, systolic blood pressure (SBP), proteinuria and indices of renal glomerular damage were evaluated.

KEY FINDINGS

The survival rate was at first improved, by either therapeutic regime, however, the efficiency of RAS blockade alone considerably decreased 36 weeks after 5/6 NX: final survival rate of 65% was significantly lower than 91% achieved with combined RAS and ETA receptor blockade. SBP was not affected by the addition of ETA blockade while proteinuria and renal glomerular damage were further reduced.

SIGNIFICANCE

Our data show that a combined RAS and ETA receptor blockade exhibits additional beneficial effects on survival rate and the progression of CKD in 5/6 NX TGR, as compared with RAS inhibition alone.

Reduction of Cardiovascular Risk through Angiotensin II Type 1 Receptor Antagonism : Focus on Olmesartan Medoxomil

It is well recognized that angiotensin II is involved in the pathogenesis of hypertension. Less well recognized - until recently, at least - is its involvement in the pathogenesis of atherosclerosis. However, it is now evident that angiotensin II promotes oxidative stress, vascular remodelling, inflammation, and the formation of atherosclerotic lesions. These actions, which are mediated almost exclusively by the angiotensin II type 1 (AT(1)) receptor, can be blocked by administration of angiotensin II type 1 receptor antagonists (angiotensin receptor blockers [ARBs]). Of the seven ARBs currently in clinical use, olmesartan is one of the most effective. The rapid and consistent antihypertensive efficacy of this drug, which allows a high proportion of patients to achieve their target blood pressure (BP), is associated with beneficial effects on oxidative stress, vascular remodelling, inflammation, and atherosclerotic lesion formation. These effects appear to be independent of the BP-lowering activity of olmesartan. In clinical trials, olmesartan has been shown to control microinflammation in hypertensive patients, to reduce oxidative stress in patients with type 2 diabetes mellitus, and to normalize the wall: lumen ratio of small resistance arteries (a measure of vascular remodelling) in patients with hypertension. Moreover, in a 2-year study involving hypertensive patients with carotid atherosclerosis (the MORE [Multicentre Olmesartan atherosclerosis Regression Evaluation] trial), olmesartan reduced the intima-media thickness of the carotid artery and significantly reduced the volume of large atherosclerotic plaques. These data suggest that olmesartan may reduce cardiovascular risk by simultaneously normalizing BP and reversing the proatherogenic effects of angiotensin II.

Endothelin-1 in paraventricular nucleus modulates cardiac sympathetic afferent reflex and sympathetic activity in rats

Background

Cardiac sympathetic afferent reflex (CSAR) is a positive-feedback, sympathoexcitatory reflex. Paraventricular nucleus (PVN) is an important component of the central neurocircuitry of the CSAR. The present study is designed to determine whether endothelin-1 (ET-1) in the PVN modulates the CSAR and sympathetic activity, and whether superoxide anions are involved in modulating the effects of ET-1 in the PVN in rats.

Methodology/Principal Findings

In anaesthetized Sprague–Dawley rats with cervical vagotomy and sinoaortic denervation, renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) were recorded. The CSAR was evaluated by the responses of the RSNA and MAP to epicardial application of capsaicin. Microinjection of ET-1 into the bilateral PVN dose-dependently enhanced the CSAR, increased the baseline RSNA and MAP. The effects of ET-1 were blocked by PVN pretreatment with the ET_A receptor antagonist BQ-123. However, BQ-123 alone had no significant effects on the CSAR, the baseline RSNA and MAP. Bilateral PVN pretreatment with either superoxide anion scavenger tempol or polyethylene glycol-superoxide dismutase (PEG-SOD) inhibited the effects of ET-1 on the CSAR, RSNA and MAP. Microinjection of ET-1 into the PVN increased the superoxide anion level in the PVN, which was abolished by PVN pretreatment with BQ-123. Epicardial application of capsaicin increased superoxide anion level in PVN which was further enhanced by PVN pretreatment with ET-1.

Conclusions

Exogenous activation of ET_A receptors with ET-1 in the PVN enhances the CSAR, increases RSNA and MAP. Superoxide anions in PVN are involved in the effects of ET-1 in the PVN.

Olmesartan attenuates the impairment of endothelial cells induced by oxidized low density lipoprotein through downregulating expression of LOX-1

Oxidized low density lipoprotein (ox-LDL) and its receptor, lectin-Like ox-LDL receptor-1 (LOX-1), play important roles in the development of endothelial injuries. Olmesartan can protect endothelial cells from the impairment caused by various pathological stimulations. In the present study we investigated whether olmesartan decreased the impairment of endothelial cells induced by ox-LDL by exerting its effects on LOX-1 both in vitro and in vivo. Incubation of cultured endothelial cells of neonatal rats with ox-LDL for 24 h or infusion of ox-LDL in mice for 3 weeks led to the remarkable impairment of endothelial cells, including increased lactate dehydrogenase synthesis, phosphorylation of p38 mitogen-activated protein kinases (p38 MAPK) and expression of apoptotic genes such as B-cell leukemia/lymphoma 2 (Bcl-2)-associated X protein (Bax) and caspase-3. Simultaneously, the cell vitality and expression of Bcl-2 gene were greatly reduced. All these effects, however, were significantly suppressed by the treatment with olmesartan. Furthermore, ox-LDL promoted up-regulation of LOX-1 expression either in cultured endothelial cells or in the aortas of mice, which was reversed with the administration of olmesartan. Our data indicated that olmesartan may attenuate the impairment of endothelial cell via down-regulation of the increased LOX-1 expression induced by ox-LDL.

Olmesartan, an AT1 antagonist, attenuates oxidative stress, endoplasmic reticulum stress and cardiac inflammatory mediators in rats with heart failure induced by experimental autoimmune myocarditis

Studies have demonstrated that angiotensin II has been involved in immune and inflammatory responses which might contribute to the pathogenesis of immune-mediated diseases. Recent evidence suggests that oxidative stress may play a role in myocarditis. Here, we investigated whether olmesartan, an AT(1)R antagonist protects against experimental autoimmune myocarditis (EAM) by suppression of oxidative stress, endoplasmic reticulum (ER) stress and inflammatory cytokines. EAM was induced in Lewis rats by immunization with porcine cardiac myosin, were divided into two groups and treated with either olmesartan (10 mg/kg/day) or vehicle for a period of 21 days. Myocardial functional parameters measured by hemodynamic and echocardiographic analyses were significantly improved by the treatment with olmesartan compared with those of vehicle-treated rats. Treatment with olmesartan attenuated the myocardial mRNA expressions of proinflammatory cytokines, [Interleukin (IL)-1β, monocyte chemoattractant protein-1, tumor necrosis factor-α and interferon-γ)] and the protein expression of tumor necrosis factor-α compared with that of vehicle-treated rats. Myocardial protein expressions of AT(1)R, NADPH oxidase subunits (p47phox, p67phox, gp91phox) and the expression of markers of oxidative stress (3-nitrotyrosine and 4-hydroxy-2-nonenal), and the cardiac apoptosis were also significantly decreased by the treatment with olmesartan compared with those of vehicle-treated rats. Furthermore, olmesartan treatment down-regulated the myocardial expressions of glucose regulated protein-78, growth arrest and DNA damage-inducible gene, caspase-12, phospho-p38 mitogen-activated protein kinase (MAPK) and phospho-JNK. These findings suggest that olmesartan protects against EAM in rats, at least in part via suppression of oxidative stress, ER stress and inflammatory cytokines.

Beneficial effects of olmesartan, an angiotensin II receptor type 1 antagonist, in rats with dilated cardiomyopathy

Favorable effects of angiotensin II type 1 receptor blockers on patients with ischemic or idiopathic dilated cardiomyopathy (DCM) have already been suggested by several human trials, but their effects on DCM remain unknown. Hence, we investigated the effect of olmesartan on myocardial remodeling in a rat model in which myosin-induced experimental autoimmune myocarditis (EAM) might develop into DCM. EAM was elicited in Lewis rats by immunization with cardiac myosin, and 28 d after immunization, the surviving Lewis rats were divided into two groups and treated with either olmesartan (10 mg/kg/d) or vehicle. Age-matched normal rats without immunizations were also used. After four weeks of treatment, we investigated the effects of olmesartan on cardiac function, inflammatory cytokines and cardiac remodeling in EAM rats. Myocardial functional parameters measured by hemodynamic and echocardiographic analyses were significantly improved by the treatment with olmesartan compared with those of vehicle-treated rats. Olmesartan significantly reduced cardiac fibrosis as well as hypertrophy and its molecular markers (left ventricular [LV] mRNA expressions of transforming growth factor beta1, collagen-I and -III, and atrial natriuretic peptide) compared with those of vehicle-treated rats. Increased myocardial mRNA expressions of proinflammatory cytokines (interleukin [IL]-6, IL-1β), monocyte chemoattractant protein-1 and matrix metalloproteinases (MMP-2 and -9) were also suppressed by the treatment with olmesartan in rats with DCM. Further, the plasma level of angiotensin II was significantly increased in olmesartan-treated rats. These findings demonstrate that olmesartan treatment significantly improved LV function and ameliorated the progression of cardiac remodeling in rats with DCM after EAM.

Endothelin-1 increases glomerular permeability and inflammation independent of blood pressure in the rat

Endothelin (ET) 1 is a potent vasoactive peptide implicated in the pathogenesis of hypertension and renal disease. The aim of the current study was to test the hypotheses that ET-1 increases albumin permeability of glomeruli isolated from normal rats and that chronic ET-1 infusion will increase glomerular permeability and inflammation independent of blood pressure. Glomerular permeability to albumin was determined from the change in glomerular volume induced by exposing isolated glomeruli to oncotic gradients. Incubation of glomeruli taken from normal rats with ET-1 at a concentration that did not produce direct glomerular contraction (1 nmol/L) significantly increased glomerular permeability to albumin, reaching a maximum after 4 hours. Chronic ET-1 infusion for 2 weeks in Sprague-Dawley rats significantly increased glomerular permeability to albumin and nephrin excretion rate, effects that were attenuated in rats given an ET(A) receptor antagonist (ABT-627, 5 mg/kg per day). Urinary protein and albumin excretion and mean arterial pressure (telemetry) were not changed by ET-1 infusion. Acute incubation of glomeruli isolated from ET-1-infused rats with the selective ET(A) antagonist significantly reduced glomerular permeability to albumin, an effect not observed with acute treatment with a selective ET(B) antagonist. Chronic ET-1 infusion increased glomerular and plasma soluble intercellular adhesion molecule 1 and monocyte chemoattractant protein 1 and elevated the number of macrophages and lymphocytes in renal cortices (ED-1 and CD3-positive staining, respectively). These effects were all attenuated in rats given an ET(A) selective antagonist. These data support the hypothesis that ET-1 directly increases glomerular permeability to albumin and renal inflammation via ET(A) receptor activation independent of changes in arterial pressure.

Circulating and Vascular Bioactive Factors during Hypertension in Pregnancy

Normal pregnancy is associated with significant vascular remodeling in the uterine and systemic circulation in order to meet the metabolic demands of the mother and developing fetus. The pregnancy-associated vascular changes are largely due to alterations in the amount/activity of vascular mediators released from the endothelium, vascular smooth muscle and extracellular matrix. The endothelium releases vasodilator substances such as nitric oxide, prostacyclin and hyperpolarizing factor as well as vasoconstrictor factors such as endothelin, angiotensin II and thromboxane A(2). Vascular smooth muscle contraction is mediated by intracellular free Ca(2+) concentration ([Ca(2+)](i)), and [Ca(2+)](i) sensitization pathways such as protein kinase C, Rho-kinase and mitogen-activated protein kinase. Extracellular matrix and vascular remodeling are regulated by matrix metalloproteases. Hypertension in pregnancy and preeclampsia are major complications and life threatening conditions to both the mother and fetus, precipitated by various genetic, dietary and environmental factors. The initiating mechanism of preeclampsia and hypertension in pregnancy is unclear; however, most studies have implicated inadequate invasion of cytotrophoblasts into the uterine artery, leading to reduction in the uteroplacental perfusion pressure and placental ischemia/hypoxia. This placental hypoxic state is thought to induce the release of several circulating bioactive factors such as growth factor inhibitors, anti-angiogenic proteins, inflammatory cytokines, reactive oxygen species, hypoxia-inducible factors, and vascular receptor antibodies. Increases in the plasma levels and vascular content of these factors during pregnancy could cause an imbalance in the vascular mediators released from the endothelium, smooth muscle and extracellular matrix, and lead to severe vasoconstriction and hypertension. This review will discuss the interactions between the various circulating bioactive factors and the vascular mediators released during hypertension in pregnancy, and provide an insight into the current and future approaches in the management of preeclampsia.

Angiotensin II receptor blocker attenuates PDGF-induced mesangial cell migration in a receptor-independent manner

BACKGROUND

Clinical studies have shown that angiotensin II (Ang II) type 1 (AT1) receptor blockers (ARBs) are able to provide renoprotection independent of their blood pressure lowering effects. ARBs also are reported to suppress oxidative stress, inflammation and certain other cellular responses in a receptor-independent manner. We investigated the effects of an ARB, olmesartan, on the cell migration induced by platelet-derived growth factor (PDGF), a major mitogen involved in the pathogenesis of glomerulonephritis in rat mesangial cells (RMCs).

METHODS

Cell migration was determined by a modified Boyden chamber assay. The intracellular signalling pathway was examined by western blotting. AT1 receptor expression was knocked down by small interfering RNAs. The intracellular reactive oxygen species (ROS) was measured by using a fluorescent probe. The O(2)(.-) scavenging activities were studied by the electron paramagnetic resonance-spin trapping method.

RESULTS

PDGF-induced cell migration was inhibited by olmesartan in AT1 receptor knockdown RMCs. Olmesartan attenuated big mitogen-activated protein (MAP) kinase 1 (BMK1) and Src activation by PDGF in AT1 receptor knockdown RMCs. PDGF-induced BMK1 activation was suppressed by the Src family tyrosine kinase inhibitors, indicating that Src exists upstream of BMK1. The NADPH oxidase inhibitors inhibited not only PDGF-induced BMK1 and Src activation but also RMC migration. The elevation in ROS generation induced by PDGF was decreased by olmesartan. Olmesartan displayed neither directly ROS scavenging activity nor the inhibition of ROS-mediated intracellular signalling in RMCs.

CONCLUSIONS

Olmesartan attenuates ROS generation by PDGF, leading to the subsequent inhibition of Src/ BMK1/migration in an AT1 receptor-independent manner in RMCs.

Renal and vascular glutathione S-transferase mu is not affected by pharmacological intervention to reduce systolic blood pressure

BACKGROUND

Our previous studies demonstrated reduced rat glutathione S-transferase mu type 1 (Gstm1) expression in stroke-prone spontaneously hypertensive rats (SHRSPs), when compared with the normotensive Wistar-Kyoto rat.

METHODS

This study investigated the effects of angiotensin II type 1 receptor blocker (ARB) and a diuretic/vasodilator combination on the expression levels of rat Gstm1 and other Gstm isoforms.

RESULTS

Antihypertensive treatments of young and mature SHRSPs with an ARB and a diuretic/vasodilator combination improved SBP but did not affect the expression levels of Gstm1. Although Gstm1 is a member of a family of highly homologous genes, with the exception of Gstm2, there was no evidence for compensatory increase in expression of other Gstm isoforms. In contrast, we observed reduced expression of several other Gstm isoforms in untreated SHRSPs. Untreated SHRSPs demonstrated increased renal and vascular oxidative stress, both of which were not significantly affected by the antihypertensive treatments. Untreated SHRSPs scored significantly higher when assessed for renal histopathological damage, and this was improved by antihypertensive treatments.

CONCLUSION

These results suggest that reduced Gstm1 expression in SHRSPs is due to strain-dependent genetic abnormalities, playing a causative role in the development of hypertension, probably through oxidative stress pathway. Renal changes occur as a consequence of increased blood pressure and can be improved when treated with antihypertensive drugs. In silico comparative genome analysis combined with expression studies in rat and human vascular tissue revealed that there are possible four human homologues (GSTM1, GSTM2, GSTM4 and GSTM5) for rat Gstm1.

Olmesartan ameliorates progressive glomerular injury in subtotal nephrectomized rats through suppression of superoxide production

Angiotensin type 1 receptor blockers are more effective than other antihypertensive agents in slowing the progression of renal disease. Angiotensin II (Ang II) induces production of NAD(P)H oxidase-dependent superoxide in vascular and mesangial cells, but the direct role of Ang II in glomerular superoxide production remains unknown. Here we examined the effect of Ang II on superoxide production both ex vivo and in vivo. Ang II increased superoxide generation in isolated normal glomeruli in a dose-dependent manner, and co-incubation with olmesartan, an angiotensin type 1 receptor blocker, suppressed such increase. Subtotal nephrectomized rats (Nx, n=8) showed impaired renal function, increased glomerular sclerosis, and significantly high superoxide production in glomeruli. These changes were inhibited in olmesartan-treated (n=8), but not hydralazine-treated (n=8) Nx rats. Oxidative stress and nitrosative stress were observed in Nx glomeruli, as evidenced by increased levels of carbonyl protein and nitrotyrosine formation, respectively. These changes were inhibited by 8-week treatment with olmesartan. The apoptosis observed in Nx glomeruli was also suppressed by olmesartan. Superoxide generation in Nx glomeruli was blocked by an NAD(P)H oxidase inhibitor, diphenylene iodinium. The mRNA expression levels of two NAD(P)H oxidase subunits were increased in Nx, and olmesartan significantly reduced the mRNA expression levels. These results indicate that Ang II directly induced superoxide production through activation of NAD(P)H oxidase, and olmesartan would inhibit superoxide production and oxidative stress independent of its blood pressure-lowering effect. These findings support the notion that superoxide plays a primary role in glomerular injury in chronic kidney disease.

A water-soluble fullerene vesicle alleviates angiotensin II-induced oxidative stress in human umbilical venous endothelial cells

A water-soluble fullerene vesicle based on the Buckminsterfullerene molecule (Ph(5)C(60)K, denoted as PhK) was explored to determine its effects on anti-oxidation of human umbilical endothelial cells (HUVEC) exposed to exogenous and endogenous reactive oxygen species (ROS). Hydrogen peroxide 0.05-0.25 mmol/L remarkably reduced the cellular viability of HUVEC. This reduction in viability was markedly improved when PhK 0.01-1 micromol/L was added simultaneously to the culture medium. The reduction of viability in HUVEC induced by angiotensin II (AII) 10(-9) to 10(-7) mol/L was improved by pretreatment with PhK 0.1 or 10 micromol/L 12 h before AII stimulation. The ROS indicator CM-H(2)DCFDA demonstrated the efficacy of PhK 1 or 10 micromol/L in decreasing AII-induced ROS production to the level induced by the AII receptor blocker RNH-6470 20 micromol/L. The AII-induced peroxynitrite formation, as gauged using hydroxyphenyl fluorescein as a probe, was alleviated significantly by either pretreatment with PhK 0.1 or 1 micromol/L. Electron microscopy revealed intracellular localization of PhK in HUVEC after 12 h incubation. The PhK decreased the AII-induced apoptosis and lipid peroxidation processes as revealed by hexanoyl-lysine adduct formation. These observations show that the PhK water-soluble fullerene vesicle is promising as a compound controlling not only exogenous ROS, but also endogenous AII-mediated pathophysiological conditions.

Receptor-independent intracellular radical scavenging activity of an angiotensin II receptor blocker

OBJECTIVES

Angiotensin II plays a crucial role in the induction of oxidative stress and the pathogenesis of cardiovascular and renal diseases, and the beneficial mechanisms of angiotensin II receptor 1 blockers (ARBs) are multifactorial. We investigated the receptor-independent protective role of an ARB using primary-cultured mesangial cells from angiotensin II receptor 1 knockout or wild-type mice and a highly lipophilic ARB, telmisartan.

METHODS AND RESULTS

Intracellular reactive oxygen species were estimated using a fluorogenic probe, CM-H2DCFDA. Non-angiotensin II-induced reactive oxygen species production was generated by exposing cells to hydrogen peroxide alone or after treatment with telmisartan. Flow cytometry analysis showed that angiotensin II induced an increase in oxidant production in a dose-dependent manner in wild-type cells, but not in knockout cells. In contrast, hydrogen peroxide induced oxidative stress in both wild-type and knockout cells. Interestingly, telmisartan attenuated the oxidative stress induced by hydrogen peroxide in both cells, suggesting that it acted via a receptor-independent antioxidant effect. Intracellular concentrations of telmisartan were confirmed by high-performance liquid chromatography analysis. Expression of plasminogen activator inhibitor 1, which is stimulated by oxidative stress, was also attenuated by telmisartan in a receptor-independent as well as receptor-dependent manner. Telmisartan did not change expression levels of antioxidative enzymes such as catalase or glutathione peroxidase. Furthermore, the amelioration of oxidative stress by telmisartan did not involve the peroxisome proliferator-activated receptor-gamma pathway.

CONCLUSIONS

Telmisartan inhibits intracellular oxidative stress, at least in part, in a receptor-independent manner, possibly owing to its lipophilic and antioxidant structure.

Role of Aldosterone in Oxidative Stress and Renal Injury

Recent clinical studies have indicated the utility of mineralocorticoid receptor (MR) antagonists in cardiovascular and renal injuries. Chronic treatment with aldosterone/salt resulted in severe cardiac and renal injuries in rats. Further studies showed that the aldosterone-induced organ injuries were associated with increases in expression of NADPH oxidase components and reactive oxygen species (ROS) levels. Treatment with a selective MR antagonist, eplerenone, prevented the elevation of ROS levels and ameliorated organ injuries. In vitro studies also showed that MR is highly expressed in cultured vascular smooth muscle cells, glomerular mesangial cells and renal fibroblasts. In these cells, aldosterone-induced cell injuries were associated with increases in NADPH oxidase activity and superoxide generation. Further, the aldosterone-dependent cell injuries were markedly attenuated by treatment with eplerenone. These accumulating data support the notion that the aldosterone/MR is involved in the pathogenesis of cardiovascular and renal injuries through NADPH oxidase-dependent ROS production.

Effect of Olmesartan on Oxidative Stress in Hemodialysis Patients

The effect of olmesartan, an inverse angiotensin II type 1 receptor blocker (ARB), on oxidative stress in hemodialysis (HD) patients is not fully understood, and has not been widely investigated in vitro or in vivo. We determined the amount of oxidized albumin and albumin hydroperoxides formed during incubation in the absence and presence of olmesartan by high-performance liquid chromatography (HPLC) and by a ferrous oxidation xylenol assay in an in vitro study. Six hypertensive HD patients were treated with 40 mg of olmesartan once daily, and blood pressure monitoring (BPM) was performed after 0, 4, and 8 weeks of treatment. The ratio of oxidized to unoxidized albumin was also determined. The oxidized albumin ratios and levels of albumin hydroperoxides were significantly decreased in a concentration-dependent manner in the presence of olmesartan, compared with the absence of olmesartan (p<0.05) in in vitro studies. In HD patients, olmesartan also significantly reduced systolic and diastolic blood pressure after 4 weeks, with a further significant decrease after 8 weeks. The ratio of oxidized to unoxidized albumin was markedly decreased after 4 weeks and these lower levels were maintained at 8 weeks. Olmesartan effectively lowered the extent of oxidation of albumin in both in vitro and in vivo studies, and this effect might confer benefits beyond a reduction in blood pressure.

Interaction between serotonin 2A receptor and endothelin-1 variants in association with hypertension in Japanese

Serotonin has been implicated in the pathogenesis of hypertension because of its ability to induce vasoconstriction via stimulation of serotonin 2 (5-HT2) receptors. Recently, an association between the T102C functional polymorphism of the serotonin 2A (5-HT2A) receptor gene and hypertension in the UK has been reported. Another association study, however, failed to replicate this association in a Chinese population. We therefore investigated the possible association between the 5-HT2A T102C polymorphism and hypertension in two large Japanese populations (n = 2,968 total). We also investigated the possible interaction between the 5-HT2A T102C polymorphism and the G/T (Lys198Asn) polymorphism of the endothelin-1 (ET-1) gene, based on robust biological evidence for the existence of an interaction between the serotonin and endothelin systems. The results showed that there was no significant difference in the frequencies of the alleles and genotypes between the hypertensive and normotensive subjects. However, a significant interaction between the 5-HT2A T102C and ET-1 G/T polymorphisms in their association with hypertension (p = 0.0040) and with diastolic blood pressure (p = 0.0013) was revealed. A marginally significant interaction in the association with systolic blood pressure was also shown (p = 0.045). The associations of the 5-HT2A T102C polymorphism with hypertension and diastolic blood pressure in ET-1 T allele carriers were significant (p = 0.0056 and 0.021, respectively). The association of the 5-HT2A T102C polymorphism with systolic blood pressure in ET-1 T allele carriers was marginally significant (p = 0.054). Thus, the present study suggests that the 5-HT2A T102C and ET-1 G/T polymorphisms are interactively associated with hypertension.

Differences Between Candesartan and Hydralazine in the Protection of Penile Structures in Spontaneously Hypertensive Rats

INTRODUCTION

Previous studies indicate that angiotensin type I receptor antagonists present a beneficial effect on penile structures in hypertensive rats. However, at present there is no substantial information concerning the functional aspect of this class of antihypertensive drugs.

AIM

To determine, by in vitro studies, functional effects of Candesartan in comparison with a traditional vasodilating agent, Hydralazine, on penile structures in a rat model of arterial hypertension.

METHODS

During 4 months, three groups of male spontaneously hypertensive rats (SHR) and one of Wistar-Kyoto (WKY) rats, as control group, were studied: SHR without treatment; SHR with Candesartan cilexetil 7.5 mg/kg/day; SHR with Hydralazine 50 mg/kg/day; and WKY rats without treatment. Cavernous smooth muscle strips were mounted in an organ bath system for in vitro studies. In addition, cavernous smooth muscle and vascular smooth muscle from cavernous arteries, cavernous tissue fibrosis, and collagen type III were also evaluated by immunohistochemistry.

RESULTS

After 4 months, SHR with Candesartan and Hydralazine showed similar reduction in blood pressure compared with untreated SHR. However, in vitro studies revealed that SHR with Candesartan displayed a better relaxation response to acetylcholine than SHR and SHR with Hydralazine (P < 0.01). Immunostaining indicates that only SHR with Candesartan and control WKY rats showed significantly lower values of: (i) cavernous smooth muscle (P < 0.01); (ii) vascular smooth muscle (P < 0.01); and (iii) collagen type III (P < 0.01) when compared with untreated SHR or SHR with Hydralazine. Additionally, SHR with Candesartan presented a higher endothelial nitric oxide synthase expression in sinusoidal endothelium in comparison with SHR, and SHR with Hydralazine (P < 0.01).

CONCLUSION

Candesartan presented equivalent blood pressure control compared with Hydralazine. However, only Candesartan showed a significant better response to acetylcholine, in in vitro studies, with a protective role against structural changes in vessels as well as in cavernous spaces of the erectile tissue.

Medullopressin: a new pressor activity from the renal medulla

The kidney contains blood pressure-lowering substances, such as prostaglandin E2 or prostaglandin A2, and blood pressure-raising substances such as thromboxane A2. Most of the postulated substances, however, have not yet been isolated in a pure state and are of unknown structure. In the present study, we separated a chloroform extract from the medulla of pig kidneys using various chromatography procedures. Each fraction was tested in spontaneously hypertensive Wistar rats. One of these fractions caused a powerful blood pressure increase of 30.1 +/- 7.1 mmHg systolic and 34.7 +/- 6 mmHg diastolic (N=7; p=0.0003), reaching its maximum 55 +/- 27 s after completion of the injection and lasting for 201 +/- 59 s. A long-lasting contractile response in porcine and bovine coronary artery rings was observed. In the mouse aortic rings, the contractile response accounted for 0.38 +/- 0.13 g, ie., 31.9 +/- 10.9% of the maximum potassium response (N=11; p=0.003). Because this activity could not be attributed to any known vasoactive substance, it was considered to arise from a novel underlying active substance in the kidney medulla, which we named medullopressin.

Olmesartan ameliorates insulin sensitivity by modulating tumor necrosis factor-alpha and cyclic AMP in skeletal muscle

We have reported that tumor necrosis factor (TNF)-alpha in skeletal muscle is one of the determinants of insulin resistance and that the renin-angiotensin system may be related to the regulation of TNF-a in skeletal muscle. Recent studies have suggested the involvement of cyclic adenosine monophosphate (cAMP) in the regulation of TNF-a in vascular smooth muscle cells or monocytes. The aim of this study was to determine the relationship between cAMP and TNF-a in skeletal muscle in connection with the renin-angiotensin system. Six-week-old male Sprague-Dawley rats were fed either normal rat chow or fructose-rich chow for 6 weeks. For the last 2 weeks of a 6-week period, the rats were treated with a vehicle or with an angiotensin II type 1 receptor antagonist (olmesartan medoxomil, 0.1 mg/kg/day). TNF-alpha levels in the soleus muscle were significantly higher and cAMP levels in the soleus muscle were significantly lower in fructose-fed rats than in control rats. Olmesartan increased cAMP and reduced TNF-a simultaneously in fructose-fed rats. There was a significant negative correlation between levels of cAMP and TNF-alpha. Moreover, a cAMP analogue reduced TNF-a levels in the soleus muscle. These results indicate that the increase in TNF-alpha via suppression of cAMP may affect the induction of insulin resistance. In addition, the facts that olmesartan increased cAMP and decreased TNF-alpha suggest that a part of the TNF-alpha regulation by angiotensin II might consist of modulation of cAMP through Gi protein activation in skeletal muscle.

Augmentation of Intrarenal Angiotensin II Levels in Uninephrectomized Aldosterone/Salt-Treated Hypertensive Rats; Renoprotective Effects of an Ultrahigh Dose of Olmesartan

Recent studies have suggested that aldosterone plays a role in the pathogenesis of renal injury. In this study, we investigated whether local angiotensin II (Ang II) activity contributes to the progression of renal injury in aldosterone/salt-induced hypertensive rats. Uninephrectomized rats were treated with 1% NaCl in a drinking solution and one of the following combinations for 6 weeks: vehicle (2% ethanol, s.c.; n=9), aldosterone (0.75 mug/h, s.c.; n=8), aldosterone+Ang II type 1 receptor blocker olmesartan (10 mg/kg/day, p.o.; n=8), or aldosterone+olmesartan (100 mg/kg/day, p.o.; n=9). Aldosterone/salt-treated hypertensive rats exhibited severe proteinuria and renal injury characterized by glomerular sclerosis and tubulointerstitial fibrosis. Aldosterone/salt-induced renal injury was associated with augmented expression of angiotensin converting enzyme and Ang II levels in the renal cortex and medullary tissues. Renal cortical and medullary mRNA expression of transforming growth factor-beta (TGF-beta) and connective tissue growth factor (CTGF) as well as the collagen contents were increased in aldosterone/salt-treated hypertensive rats. Treatment with olmesartan (10 or 100 mg/kg/day) had no effect on blood pressure but attenuated proteinuria in a dose-dependent manner. Olmesartan at 10 mg/kg/day tended to decrease renal cortical and medullary Ang II levels, TGF-beta and CTGF expression, and collagen contents; however, these changes were not significant. On the other hand, an ultrahigh dose of olmesartan (100 mg/kg/day) significantly decreased these values and ameliorated renal injury. These data suggest that augmented local Ang II activity contributes, at least partially, to the progression of aldosterone/salt-dependent renal injury.

Pressure Overload-Induced Transient Oxidative Stress Mediates Perivascular Inflammation and Cardiac Fibrosis through Angiotensin II

Oxidative stress is implicated in the pathogenesis of various cardiovascular diseases. We have shown that in Wistar rats with a suprarenal aortic constriction (AC), pressure overload-induced transient perivascular inflammation (monocyte chemoattractant protein-1 [MCP-1] induction and macrophage accumulation) in the early phase is the determinant of reactive myocardial fibrosis and resultant diastolic dysfunction in the late phase. Thus, we investigated the role of reactive oxygen species production in cardiac remodeling in AC rats. Superoxide production and the footprint of lipid peroxidation were assessed using dihydroethidium staining and immunohistostaining against 4-hydroxy-2-nonenal (4-HNE), respectively. In sham rats, dihydroethidium and 4-HNE signals were scarcely found in the heart. At day 3, AC rats showed dihydroethidium signals mainly in the intramyocardial arterial wall, whereas modest 4-HNE staining was observed diffusely in the myocardium. These signals declined to lower levels by day 14 despite sustained hypertension. Chronic administration of a subdepressor dose of an angiotensin II type 1 receptor blocker candesartan reduced the pressure overload-induced dihydroethidium and 4-HNE signals at day 3. Moreover, candesartan decreased MCP-1 induction and macrophage infiltration at day 3 and prevented myocardial fibrosis at day 14, without affecting left ventricle and myocyte hypertrophy. In conclusion, acute pressure overload induced self-limited superoxide production mainly in the vascular wall. The reactive oxygen species production would contribute to the perivascular inflammation and subsequent myocardial fibrosis. Angiotensin II was suggested to have a pressure-independent effect on the reactive oxygen species production.

Olmesartan, a novel AT1 antagonist, suppresses cytotoxic myocardial injury in autoimmune heart failure

Some ANG II receptor type 1 (AT1) antagonists are reported to inhibit proinflammatory cytokine production in vitro and in vivo. However, the effects of the drugs on autoimmune diseases are unknown. We tested the hypothesis that olmesartan, a novel AT1 antagonist, ameliorated experimental autoimmune myocarditis (EAM) in rats attributed to the suppression of inflammatory cytokines as well as to the immunomodulatory action of the heart. We administered olmesartan orally at does of 1, 3, and 10 mg·kg−1·day−1 to rats with EAM for 3 wk. The results showed that olmesartan decreased blood pressure significantly compared with the untreated group and markedly reduced the severity of myocarditis associated with the decrease of myocardial macrophage, CD4+, and CD8+ T-cell expression by comparison of heart wt-to-body wt ratios, pericardial effusion scores, and macroscopic and microscopic scores. Numbers of myocardial interleukin-1β (IL-1β)-positive-staining cells (obtained by immunohistochemistry) and quantities of IL-1β expression (obtained by Western blotting) were significantly lower in rats with EAM given olmesartan treatment compared with rats given vehicle. Cardiac myosin-specific, delayed-type hypersensitivity was significantly lower in olmesartan-treated rats than in control rats. The cytotoxic activities of lymphocytes in rats with EAM treated with olmesartan were reduced compared with untreated control rats. In vitro study showed that both olmesartan and its active metabolite RNH-6270 suppressed IL-1β production in U-937 cells and cultured myocytes. Olmesartan ameliorates acute EAM in rats. The cardioprotection of olmesartan may be due to suppression of inflammatory cytokines as well as to suppressive effects of cytotoxic myocardial injury in addition to hemodynamic modifications.

Temporary angiotensin II blockade at the prediabetic stage attenuates the development of renal injury in type 2 diabetic rats

Whether temporary angiotensin II (AngII) blockade at the prediabetic stage attenuates renal injury in type 2 diabetic OLETF rats later in life was investigated. OLETF rats were treated with an AT(1) receptor antagonist (olmesartan, 0.01% in food), angiotensin-converting enzyme inhibitor (temocapril, 0.01% in food), a combination of the two, or hydralazine (25 mg/kg per d) at the prediabetic stage (4 to 11 wk of age) and then monitored without further treatment until 50 wk of age. At 11 wk of age, blood glucose levels and urinary protein excretion (U(protein)V) were similar between OLETF and control LETO rats. However, OLETF rats showed higher kidney AngII contents and type IV collagen mRNA expression than LETO rats at this age. These decreased with olmesartan, temocapril, and a combination of these but not with hydralazine. At 50 wk of age, diabetic OLETF rats showed higher BP, U(protein)V, and intrarenal AngII levels than LETO rats. Temporary AngII blockade did not affect glucose metabolism or the development of hypertension in OLETF rats but significantly suppressed proteinuria and ameliorated glomerular injury. However, no parameters were affected by temporary hydralazine treatment. The present study demonstrated that intrarenal AngII and type IV collagen expression are already augmented long before diabetes becomes apparent in OLETF rats. Furthermore, temporary AngII blockade at the prediabetic stage attenuates the progression of renal injury in these animals. These data suggest that early AngII blockade could be an effective strategy for preventing the development of type 2 diabetic renal injury later in life.

Caffeic Acid Inhibits Vascular Smooth Muscle Cell Proliferation Induced by Angiotensin II in Stroke-Prone Spontaneously Hypertensive Rats

Epidemiological studies have linked the consumption of phenolic acids with reduced risk of cardiovascular diseases. In the present study, we sought to investigate whether caffeic acid, a phenolic acid which is abundant in normal diet, can antagonize angiotensin II (Ang II)-induced vascular smooth muscle cell (VSMC) proliferation in stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar-Kyoto (WKY) rats, and if so, to elucidate the underlying cell signaling mechanisms. We exposed VSMCs to Ang II and caffeic acid and found that caffeic acid significantly inhibited intracellular superoxide anion generation (decreased from 127 +/- 6.3% to 100.3 +/- 6.6% of the control cells) and the cell proliferation induced by Ang II. Furthermore, caffeic acid significantly abolished the tyrosine phosphorylation of JAK2 (decreased from 7.4 +/- 0.6-fold to 2.4 +/- 0.6-fold at 2 min) and STAT1 (decreased from 1.8 +/- 0.2-fold to 0.5 +/- 0.1-fold at 2 min) and the phosphorylation of ERK1/2 (decreased from 99.2 +/- 10.2-fold to 49.8 +/- 10.9-fold at 2 min) that were induced by Ang II. These effects of caffeic acid were consistent with the inhibition of the proliferation of VSMCs by DPI, an NADPH oxidase inhibitor, and by AG-490, a JAK2 inhibitor. In conclusion, our findings suggest that caffeic acid attenuates the proliferative reaction of VSMCs to Ang II stimulation in both SHRSP and WKY rats by inhibiting the generation of reactive oxygen species and then partially blocking the JAK/STAT signaling cascade and the Ras/Raf-1/ERK1/2 cascade.