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

The Renin Angiotensin System as a Therapeutic Target in Traumatic Brain Injury

Traumatic brain injury (TBI) is a major public health problem, with limited pharmacological options available beyond symptomatic relief. The renin angiotensin system (RAS) is primarily known as a systemic endocrine regulatory system, with major roles controlling blood pressure and fluid homeostasis. Drugs that target the RAS are used to treat hypertension, heart failure and kidney disorders. They have now been used chronically by millions of people and have a favorable safety profile. In addition to the systemic RAS, it is now appreciated that many different organ systems, including the brain, have their own local RAS. The major ligand of the classic RAS, Angiotensin II (Ang II) acts predominantly through the Ang II Type 1 receptor (AT1R), leading to vasoconstriction, inflammation, and heightened oxidative stress. These processes can exacerbate brain injuries. Ang II receptor blockers (ARBs) are AT1R antagonists. They have been shown in several preclinical studies to enhance recovery from TBI in rodents through improvements in molecular, cellular and behavioral correlates of injury. ARBs are now under consideration for clinical trials in TBI. Several different RAS peptides that signal through receptors distinct from the AT1R, are also potential therapeutic targets for TBI. The counter regulatory RAS pathway has actions that oppose those stimulated by AT1R signaling. This alternative pathway has many beneficial effects on cells in the central nervous system, bringing about vasodilation, and having anti-inflammatory and anti-oxidative stress actions. Stimulation of this pathway also has potential therapeutic value for the treatment of TBI. This comprehensive review will provide an overview of the various components of the RAS, with a focus on their direct relevance to TBI pathology. It will explore different therapeutic agents that modulate this system and assess their potential efficacy in treating TBI patients.

Anthracycline-induced cardiotoxicity and renin-angiotensin-aldosterone system-from molecular mechanisms to therapeutic applications

Few millions of new cancer cases are diagnosed worldwide every year. Due to significant progress in understanding cancer biology and developing new therapies, the mortality rates are decreasing with many of patients that can be completely cured. However, vast majority of them require chemotherapy which comes with high medical costs in terms of adverse events, of which cardiotoxicity is one of the most serious and challenging. Anthracyclines (doxorubicin, epirubicin) are a class of cytotoxic agents used in treatment of breast cancer, sarcomas, or hematological malignancies that are associated with high risk of cardiotoxicity that is observed in even up to 30% of patients and can be diagnosed years after the therapy. The mechanism, in which anthracyclines cause cardiotoxicity are not well known, but it is proposed that dysregulation of renin-angiotensin-aldosterone system (RAAS), one of main humoral regulators of cardiovascular system, may play a significant role. There is increasing evidence that drugs targeting this system can be effective in the prevention and treatment of anthracycline-induced cardiotoxicity what has recently found reflection in the recommendation of some scientific societies. In this review, we comprehensively describe possible mechanisms how anthracyclines affect RAAS and lead to cardiotoxicity. Moreover, we critically review available preclinical and clinical data on use of RAAS inhibitors in the primary and secondary prevention and treatment of cardiac adverse events associated with anthracycline-based chemotherapy.

Antioxidant and antiapoptotic effects of sea cucumber and valsartan against doxorubicin-induced cardiotoxicity in rats: The role of low dose gamma irradiation

Doxorubicin (DOX) is a highly effective antineoplastic drug; however, the clinical use of DOX is limited by its dose dependent cardiotoxicity. This study was conducted to evaluate the cardioprotective effect of sea cucumber and valsartan against DOX-induced cardiotoxicity in rats. Also, the role of exposure to low dose γ radiation (LDR) on each of them was investigated, since LDR could suppress various reactive oxygen species-related diseases. Rats received DOX (2.5mg/kg, ip) in six equal injections over a period of 2weeks, sea cucumber (14.4mg/kg, p.o) and valsartan (30mg/kg, p.o) for 8 successive weeks. Exposure to LDR (0.5Gy) was performed one day prior to DOX. Results revealed that DOX administration elevated serum levels of aspartate aminotransferase (AST), lactate dehydrogenase (LDH), creatine kinase (CK-MB) and troponin-I as well as increased cardiac lipid peroxide content and myeloperoxidase (MPO) activity. Additionally, it increased cardiac expressions of iNOS and caspase-3, accompanied by reduction in cardiac total protein and glutathione (GSH) contents. Treatment with sea cucumber or valsartan improved the cardiotoxicity of DOX. Their adjuvant therapy with LDR offers an additional benefit to the cardioprotection of the therapeutic drugs. These results confirmed by histopathological examination. In conclusion, sea cucumber and valsartan alone or combined with LDR attenuated DOX-induced cardiotoxicity via their antioxidant and anti-apoptotic activities and thus might be useful in the treatment of human patients under doxorubicin chemotherapy.

Type-1 angiotensin receptor signaling in central nervous system myeloid cells is pathogenic during fatal alphavirus encephalitis in mice

BACKGROUND

Alphaviruses can cause fatal encephalitis in humans. Natural infections occur via the bite of infected mosquitos, but aerosol transmissibility makes some of these viruses potential bioterrorism agents. Central nervous system (CNS) host responses contribute to alphavirus pathogenesis in experimental models and are logical therapeutic targets. We investigated whether reactive oxygen species (ROS) generated by nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (Nox) activity within the CNS contributes to fatal alphavirus encephalitis in mice.

METHODS

Infected animals were treated systemically with the angiotensin receptor-blocking drug, telmisartan, given its ability to cross the blood-brain barrier, selectively block type-1 angiotensin receptors (AT1R), and inhibit Nox-derived ROS production in vascular smooth muscle and other extraneural tissues. Clinical, virological, biochemical, and histopathological outcomes were followed over time.

RESULTS

The importance of the angiotensin II (Ang II)/AT1R axis in disease pathogenesis was confirmed by demonstrating increased Ang II levels in the CNS following infection, enhanced disease survival when CNS Ang II production was suppressed, increased AT1R expression on microglia and tissue-infiltrating myeloid cells, and enhanced disease survival in AT1R-deficient mice compared to wild-type (WT) controls. Systemic administration of telmisartan protected WT mice from lethal encephalitis caused by two different alphaviruses in a dose-dependent manner without altering virus replication or exerting any anti-inflammatory effects in the CNS. Infection triggered up-regulation of multiple Nox subunits in the CNS, while drug treatment inhibited local Nox activity, ROS production, and oxidative neuronal damage. Telmisartan proved ineffective in Nox-deficient mice, demonstrating that this enzyme is its main target in this experimental setting.

CONCLUSIONS

Nox-derived ROS, likely arising from CNS myeloid cells triggered by AT1R signaling, are pathogenic during fatal alphavirus encephalitis in mice. Systemically administered telmisartan at non-hypotensive doses targets Nox activity in the CNS to exert a neuroprotective effect. Disruption of this pathway may have broader implications for the treatment of related infections as well as for other CNS diseases driven by oxidative injury.

Telmisartan treatment targets inflammatory cytokines to suppress the pathogenesis of acute colitis induced by dextran sulphate sodium

The renin angiotensin system (RAS) is essential for the regulation of cardiovascular and renal functions to maintain the fluid and electrolyte homeostasis. Recent studies have demonstrated a locally expressed RAS in various tissues of mammals, which is having pathophysiological roles in those organ system. Interestingly, local RAS has important role during the inflammatory bowel disease pathogenesis. Further to delineate its role and also to identify the potential effects of telmisartan, an angiotensin receptor blocker, we have used a mouse model of acute colitis induced by dextran sulphate sodium. We have used 0.01 and 5mg/kg body weight doses of telmisartan and administered as enema to facilitate the on-site action and to reduce the systemic adverse effects. Telmisartan high dose treatment significantly reduced the disease activity index score when compared with the colitis control mice. In addition, oxidative stress and endoplasmic reticulum stress markers expression were also significantly reduced when compared with the colitis control mice. Subsequent experiments were carried out to investigate some of the mechanisms underlying its anti-inflammatory effects and identified that the mRNA levels of pro-inflammatory cytokines such as tumour necrosis factor α, interleukin 1β, interleukin 6 and monocyte chemoattractant protein 1 as well as cellular DNA damage were significantly suppressed when compared with the colitis control mice. Similarly the apoptosis marker proteins such as cleaved caspase 3 and 7 levels were down-regulated and anti-apoptotic protein Bcl2 level was significantly upregulated by telmisartan treatment. These results indicate that blockade of RAS by telmisartan can be an effective therapeutic option against acute colitis.

Qian Yang Yu Yin Granule-containing serum inhibits angiotensin II-induced proliferation, reactive oxygen species production, and inflammation in human mesangial cells via an NADPH oxidase 4-dependent pathway

Background

Qian Yang Yu Yin Granule (QYYYG), a traditional Chinese herbal medicine, has been indicated for renal damage in hypertension for decades in China, but little remains known regarding its underlying molecular mechanism. Therefore, we performed the current study in order to investigate the underlying molecular mechanism of QYYYG in the treatment of hypertensive renal damage.

Methods

We hypothesize that QYYYG relieves hypertensive renal injury through an angiotensin II (Ang II)-nicotinamide adenine dinucleotide phosphate (NAPDH)-oxidase (NOX)-reactive oxygen species (ROS) pathway. In this study, we investigated the effects of QYYYG-containing serum (QYGS) in human mesangial cells (HMCs) against Ang II-induced cell proliferation, ROS production, and inflammation through the seropharmacological method.

Results

We found that QYGS could inhibit cell proliferation in Ang II-treated HMCs. In addition, QYGS considerably suppressed production of ROS, decreased mRNA and protein expression of NAPDH-oxidase 4 (NOX4), p22^phox, and activated Ras-related C3 botulinum toxin substrate 1 (GTP-Rac1); as well as counteracted the up-regulation of inflammatory markers including tumor necrosis factor-α (TNF-α), nuclear factor-κB (NF-κB) p65, and interleukin 6 (IL-6). These effects were further confirmed in HMCs transfected with specific small interfering RNA (siRNA) targeting NOX4.

Conclusions

Taken together, these results suggest that a NOX4-dependent pathway plays an important role in regulating the inhibitory effect of QYGS. Our findings provide new insights into the molecular mechanisms of QYYYG and their role in the treatment of hypertensive nephropathy.

Neuroprotective effects of angiotensin receptor blockers

Angiotensin II receptor blockers (ARBs, collectively called sartans) are widely used compounds therapeutically effective in cardiovascular disorders, renal disease, the metabolic syndrome, and diabetes. It has been more recently recognized that ARBs are neuroprotective and have potential therapeutic use in many brain disorders. ARBs ameliorate inflammatory and apoptotic responses to glutamate, interleukin 1β and bacterial endotoxin in cultured neurons, astrocytes, microglial, and endothelial cerebrovascular cells. When administered systemically, ARBs enter the brain, protecting cerebral blood flow, maintaining blood brain barrier function and decreasing cerebral hemorrhage, excessive brain inflammation and neuronal injury in animal models of stroke, traumatic brain injury, Alzheimer's and Parkinson's disease and other brain conditions. Epidemiological analyses reported that ARBs reduced the progression of Alzheimer's disease, and clinical studies suggested amelioration of cognitive loss following stroke and aging. ARBs are pharmacologically heterogeneous; their effects are not only the result of Ang II type 1(AT1) receptor blockade but also of additional mechanisms selective for only some compounds of the class. These include peroxisome proliferator-activated receptor gamma activation and other still poorly defined mechanisms. However, the complete pharmacological spectrum and therapeutic efficacy of individual ARBs have never been systematically compared, and the neuroprotective efficacy of these compounds has not been rigorously determined in controlled clinical studies. The accumulation of pre-clinical evidence should promote further epidemiological and controlled clinical studies. Repurposing ARBs for the treatment of brain disorders, currently without effective therapy, may be of immediate and major translational value.

Protective effect of telmisartan against oxidative damage induced by high glucose in neuronal PC12 cell

Telmisartan is an angiotensin II type 1 receptor blocker and partial agonist of peroxisome proliferator-activated receptor gamma (PPAR-γ). Here, we investigated the protective capacity of telmisartan against high glucose (HG)-elicited oxidative damage in PC12 cells. The activity of lactate dehydrogenase (LDH), NADPH oxidase (NOX), superoxide dismutase (SOD), catalase (CAT) as well as the levels of malondialdehyde (MDA), glutathione (GSH), intracellular reactive oxygen species (ROS), cell viability and DNA fragmentation were measured in HG-treated PC12 cells with and without telmisartan co-treatment. Moreover, the direct antioxidant effect of telmisartan was determined by 2,2-azinobis-(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) assay and protein expression of Bax, Bcl-2, cleaved caspase-3 and NOX subunit p47phox by western blotting. Telmisartan exhibited antioxidant activity in the ABTS assay with the IC50 value of 37.5 μM. Pretreatment of PC12 cells with telmisartan, prior to HG exposure, was associated with a marked diminution in cleaved caspase-3 expression, DNA fragmentation, Bax/Bcl-2 ratio, intracellular ROS and MDA levels. Additionally, the cell viability, GSH level, SOD and CAT activity were notably elevated by telmisartan, whereas the activity and the protein expression of NADPH oxidase subunit p47phox were attenuated. Interestingly, co-treatment with GW9662, a PPAR-γ antagonist, partially inhibited the beneficial effects of telmisartan. These findings suggest that telmisartan has protective effects on HG-induced neurotoxicity in PC12 cells, which may be related to its antioxidant action and inhibition of NADPH oxidase. Furthermore, the results show that PPAR-γ activation is involved in the neuroprotective effects of telmisartan.

A systematic comparison of the properties of clinically used angiotensin II type 1 receptor antagonists

Angiotensin II type 1 receptor antagonists (ARBs) have become an important drug class in the treatment of hypertension and heart failure and the protection from diabetic nephropathy. Eight ARBs are clinically available [azilsartan, candesartan, eprosartan, irbesartan, losartan, olmesartan, telmisartan, valsartan]. Azilsartan (in some countries), candesartan, and olmesartan are orally administered as prodrugs, whereas the blocking action of some is mediated through active metabolites. On the basis of their chemical structures, ARBs use different binding pockets in the receptor, which are associated with differences in dissociation times and, in most cases, apparently insurmountable antagonism. The physicochemical differences between ARBs also manifest in different tissue penetration, including passage through the blood-brain barrier. Differences in binding mode and tissue penetration are also associated with differences in pharmacokinetic profile, particularly duration of action. Although generally highly specific for angiotensin II type 1 receptors, some ARBs, particularly telmisartan, are partial agonists at peroxisome proliferator-activated receptor-γ. All of these properties are comprehensively reviewed in this article. Although there is general consensus that a continuous receptor blockade over a 24-hour period is desirable, the clinical relevance of other pharmacological differences between individual ARBs remains to be assessed.

Telmisartan modulates mitochondrial function in vascular smooth muscle cells

The development of atherosclerosis is associated with disturbances in mitochondrial function that impair effective adenosine triphosphate (ATP) production, increase generation of superoxide and induce subsequent apoptosis in vascular smooth muscle cells (VSMCs). As peroxisome proliferator-activated receptor gamma (PPARγ) has a potentially important role in the regulation of mitochondrial metabolism, we studied effects of the partial PPARγ agonist and angiotensin receptor blocker telmisartan, on mitochondria-related cellular responses in VSMC. In human VSMC, telmisartan increased ATP levels and activation of mitochondrial complex II, succinate dehydrogenase, reduced the release of H2O2 and attenuated H2O2-induced increases in caspase 3/7 activity, a marker of cellular apoptosis. Eprosartan, an angiotensin II receptor blocker that lacks the ability to activate PPARγ, had no effect on these mitochondria-related cellular responses in VSMC. Studies in PPARγ-deficient VSMC revealed that the effects of telmisartan on mitochondrial function were largely independent of PPARγ although the presence of PPARγ modulated effects of telmisartan on H2O2 levels. These findings demonstrate that telmisartan can have significant effects on mitochondrial metabolism in VSMC that are potentially relevant to the pathogenesis of cardiovascular disease and that involve more than just angiotensin receptor blockade and activation of PPARγ.

Angiotensin II receptor blocker improves tumor necrosis factor-α-induced cytotoxicity via antioxidative effect in human glomerular endothelial cells

BACKGROUND/AIMS

Tumor necrosis factor-α (TNF-α) is known to involve the progression of renal dysfunction through its cytotoxicity and proinflammatory effects such as the induction of intercellular adhesion molecule (ICAM)-1 expression in vascular endothelial cells (ECs). Olmesartan, one of the angiotensin II type 1 receptor blockers (ARBs), has been reported to show protective effects on injured ECs by some causal factors of renal disorder other than angiotensin II. However, the effects of olmesartan on TNF-α-induced glomerular EC damage have not been investigated. In the present study, we investigated the effects of RNH-6270, an active metabolite of olmesartan, on TNF-α-induced human glomerular EC (HGEC) damage to clarify the renoprotective mechanisms of ARBs.

METHODS

Cultured HGECs were stimulated by TNF-α, and then cell viability and cytotoxicity were measured by MTT assay and lactate dehydrogenase release assay, respectively. TNF-α-induced oxidative stress was estimated by dihydroethidium assay and lucigenin chemiluminescence assay. ICAM-1 expression and the phosphorylations of mitogen-activated protein kinases were measured using Western blotting assay.

RESULTS

RNH-6270 suppressed cell death and the increase in ICAM-1 expression induced by TNF-α via the inhibition of reactive oxygen species in HGECs.

CONCLUSION

Our findings suggested that olmesartan might have protective effects against TNF-α-induced glomerular EC dysfunction.

Drug discovery for improvement of chronic kidney disease and cardiovascular disease

Chronic kidney disease (CKD) has been increasingly recognized as a major public health problem in the world. Recent studies have showed that CKD is an independent risk factor for the occurrence of cardiovascular disease (CVD). Reactive oxygen species (ROS), generated by reduction-oxidation actions, have been generated by reduction-oxidation actions, recognized as the important chemical mediators that regulate signal transduction in various cells including vascular smooth muscle cells (VSMC) and mesangial cells (MC). It has been showed that increase in ROS generation may relate to a risk for CVD and CKD. In addition, ROS mediate activation of mitogen-activated protein (MAP) kinases, extracellular signal-regulated kinase 1/2, c-Jun N-terminal kinase, p38, and big MAP kinase 1, in various cells leading to change in gene expressions. Control of the oxidative stress and ROS-mediated alterations of signaling molecules including MAP kinases may provide new therapeutic strategy against CKD and CVD. In this review, we summarize mainly our data regarding the pharmacological effects of renin-angiotensin-aldosterone system blockers, bioflavonoids and adiponectin in VSMC and MC. Also we review the data on a possible new class drug against oxidative stress to improve CKD and CVD.

PPARgamma Agonists: Potential as Therapeutics for Neovascular Retinopathies

The angiogenic, neovascular proliferative retinopathies, proliferative diabetic retinopathy (PDR), and age-dependent macular degeneration (AMD) complicated by choroidal neovascularization (CNV), also termed exudative or “wet” AMD, are common causes of blindness. The antidiabetic thiazolidinediones (TZDs), rosiglitazone, and troglitazone are PPARγ agonists with demonstrable antiproliferative, and anti-inflammatory effects, in vivo, were shown to ameliorate PDR and CNV in rodent models, implying the potential efficacy of TZDs for treating proliferative retinopathies in humans. Activation of the angiotensin II type 1 receptor (AT1-R) propagates proinflammatory and proliferative pathogenic determinants underlying PDR and CNV. The antihypertensive dual AT1-R blocker (ARB), telmisartan, recently was shown to activate PPARγ and improve glucose and lipid metabolism and to clinically improve PDR and CNV in rodent models. Therefore, the TZDs and telmisartan, clinically approved antidiabetic and antihypertensive drugs, respectively, may be efficacious for treating and attenuating PDR and CNV humans. Clinical trials are needed to test these possibilities.

Changes in renal vessels following the long-term administration of an angiotensin II receptor blocker in Zucker fatty rats

INTRODUCTION

The nephro-protective effects of angiotensin II receptor blockers (ARBs) are widely known; however, there are few reports of long-term effects focusing on the renal vessels. We studied afferent arteriolar changes induced by the long-term administration of an ARB.

MATERIALS AND METHODS

Thirty-two 6-week-old male Zucker fatty rats (ZFRs) were divided into following four groups (n = 8 in each): ZFR Group and ZFR+High Group fed a standard or high-salt diet, respectively; ZFR+ARB Group and ZFR+High+ARB Group fed a standard or high-salt diet with ARB (Olmesartan, 5 mg/kg/day), respectively. Blood pressure, proteinuria, morphological examinations and glomerular haemodynamics in vivo were studied.

RESULTS

Marked proliferative changes in the afferent arteriolar smooth muscle cells (SMCs) were frequently observed in the two groups given ARBs; in the ZFR+ARB group (77.3±10.3%) compared with the two groups without ARB (1.7%, p < 0.005; 1.2%, p < 0.0005) and 37.4±15.6% in the ZFR+High+ARB group. Proteinuria markedly decreased in the groups treated with ARBs, but the glomerular erythrocyte velocities showed no differences.

CONCLUSIONS

Our findings indicate that long-term ARB administration induced unusual proliferative changes in SMCs of afferent arterioles of ZFRs. These changes could narrow arteriolar lumens and reduce intraglomerular pressure, but they could cause also irreversible damage to the arterioles.

Nuclear-delimited angiotensin receptor-mediated signaling regulates cardiomyocyte gene expression

Angiotensin-II (Ang-II) from extracardiac sources and intracardiac synthesis regulates cardiac homeostasis, with mitogenic and growth-promoting effects largely due to altered gene expression. Here, we assessed the possibility that angiotensin-1 (AT1R) or angiotensin-2 (AT2R) receptors on the nuclear envelope mediate effects on cardiomyocyte gene expression. Immunoblots of nucleus-enriched fractions from isolated cardiomyocytes indicated the presence of AT1R and AT2R proteins that copurified with the nuclear membrane marker nucleoporin-62 and histone-3, but not markers of plasma (calpactin-I), Golgi (GRP-78), or endoplasmic reticulum (GM130) membranes. Confocal microscopy revealed AT1R and AT2R proteins on nuclear membranes. Microinjected Ang-II preferentially bound to nuclear sites of isolated cardiomyocytes. AT1R and AT2R ligands enhanced de novo RNA synthesis in isolated cardiomyocyte nuclei incubated with [alpha-(32)P]UTP (e.g. 36.0 +/- 6.0 cpm/ng of DNA control versus 246.4 +/- 15.4 cpm/ng of DNA Ang-II, 390.1 +/- 15.5 cpm/ng of DNA L-162313 (AT1), 180.9 +/- 7.2 cpm/ng of DNA CGP42112A (AT2), p < 0.001). Ang-II application to cardiomyocyte nuclei enhanced NFkappaB mRNA expression, a response that was suppressed by co-administration of AT1R (valsartan) and/or AT2R (PD123177) blockers. Dose-response experiments with Ang-II applied to purified cardiomyocyte nuclei versus intact cardiomyocytes showed greater increases in NFkappaB mRNA levels at saturating concentrations with approximately 2-fold greater affinity upon nuclear application, suggesting preferential nuclear signaling. AT1R, but not AT2R, stimulation increased [Ca(2+)] in isolated cardiomyocyte nuclei. Inositol 1,4,5-trisphosphate receptor blockade by 2-aminoethoxydiphenyl borate prevented AT1R-mediated Ca(2+) release and attenuated AT1R-mediated transcription initiation responses. We conclude that cardiomyocyte nuclear membranes possess angiotensin receptors that couple to nuclear signaling pathways and regulate transcription. Signaling within the nuclear envelope (e.g. from intracellularly synthesized Ang-II) may play a role in Ang-II-mediated changes in cardiac gene expression, with potentially important mechanistic and therapeutic implications.

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.

Molecule-specific effects of angiotensin II-receptor blockers independent of the renin-angiotensin system

Because all clinically approved angiotensin-receptor blockers (ARBs) have good safety profiles and share the ability to block angiotensin II type 1 (AT1) receptors and reduce blood pressure, it is tempting to assume that all ARBs will yield equivalent degrees of cardiovascular protection. However, such a belief depends on the tacit assumption that with appropriate dosing, all ARBs will also share the same ability to counteract other pathogenetic determinants of cardiovascular disease beyond those involving the renin-angiotensin system. Accumulating evidence from multiple laboratories has shown that this assumption is incorrect and indicates that some ARBs are characterized by an unusual ability to affect potential mechanisms of cardiovascular disease involving more than just the renin-angiotensin system. Ultimately, large-scale clinical trials will be required to better understand the clinical importance of the mechanistic effects of ARBs that involve more than just inhibition of the renin-angiotensin system. Meanwhile, given the many functional differences among ARBs that are not mediated by AT1 receptor blockade, the effects of any particular ARB on cardiovascular outcomes should not be assumed to apply equally to all ARBs let alone to other drugs that inhibit the renin-angiotensin system through different mechanisms.