Angiotensin II-induced modulation of endothelium-dependent relaxation in rabbit mesenteric resistance arteries

Distinct Mechanisms of β-Arrestin-Biased Agonist and Blocker of AT1R in Preventing Aortic Aneurysm and Associated Mortality

BACKGROUND

Aortic aneurysm (AA) is a "silent killer" human disease with no effective treatment. Although the therapeutic potential of various pharmacological agents have been evaluated, there are no reports of β-arrestin-biased AT1R (angiotensin-II type-1 receptor) agonist (TRV027) used to prevent the progression of AA.

METHODS

We tested the hypothesis that TRV027 infusion in AngII (angiotensin II)-induced mouse model of AA prevents AA. High-fat-diet-fed ApoE (apolipoprotein E gene)-null mice were infused with AngII to induce AA and co-infused with TRV027 and a clinically used AT1R blocker Olmesartan to prevent AA. Aortas explanted from different ligand infusion groups were compared with assess different grades of AA or lack of AA.

RESULTS

AngII produced AA in ≈67% male mice with significant mortality associated with AA rupture. We observed ≈13% mortality due to aortic arch dissection without aneurysm in male mice. AngII-induced AA and mortality was prevented by co-infusion of TRV027 or Olmesartan, but through different mechanisms. In TRV027 co-infused mice aortic wall thickness, elastin content, new DNA, and protein synthesis were higher than untreated and Olmesartan co-infused mice. Co-infusion with both TRV027 and Olmesartan prevented endoplasmic reticulum stress, fibrosis, and vasomotor hyper responsiveness.

CONCLUSIONS

TRV027-engaged AT1R prevented AA and associated mortality by distinct molecular mechanisms compared with the AT1R blocker, Olmesartan. Developing novel β-arrestin-biased AT1R ligands may yield promising drugs to combat AA.

ACE (Angiotensin-Converting Enzyme) Inhibition Reverses Vasoconstriction and Impaired Dilation of Pial Collaterals in Chronic Hypertension

Leptomeningeal anastomoses (LMAs) are pial collaterals that perfuse the penumbra and important for stroke outcome. We previously showed LMAs from SHRs (spontaneously hypertensive rats) were vasoconstricted compared with normotensive Wistar rats. Here, we investigated mechanisms by which hypertension causes LMA vasoconstriction. SHRs were treated with the ACE (angiotensin-converting enzyme) inhibitor captopril, an Ang II (angiotensin II)-independent antihypertensive agent hydralazine, or vehicle for 5 weeks in drinking water (n=8/group). A group of Wistar rats (n=8) had regular drinking water served as controls. Blood pressure was measured twice weekly by tail-cuff. LMAs were isolated and studied under pressurized conditions. Vasoreactivity of LMAs, including myogenic responses, reactivity to Rho-kinase inhibitor Y-27632, and nitric oxide were measured. Both captopril and hydralazine lowered blood pressure in SHRs similar to Wistar. However, only captopril normalized LMA increased tone compared with untreated SHRs (15±2% versus 50±3%; P<0.01) that was similar to Wistar (16±2%) but not hydralazine (38±6%; P>0.05). Vasodilatory response of LMAs to Y-27632 was impaired in SHRs compared with Wistar (28±3% versus 81±4%; P<0.01) that was restored by captopril (84±5%; P<0.01) and partially hydralazine (59±4%). LMAs from all groups constricted similarly to NOS (NO synthase) inhibition; however, the vasodilatory response of LMAs to the nitric oxide donor sodium nitroprusside was impaired in SHRs compared with Wistar rats (29±4% versus 80±2%; P<0.01) that was restored by captopril (84±4%; P<0.01), not hydralazine (38±8%; P>0.05). These results suggest that ACE inhibition during chronic hypertension reversed vascular dysfunction and hyperconstriction of LMAs that could improve stroke outcome by increasing collateral perfusion.

Peroxiredoxin6 in Endothelial Signaling

Peroxiredoxins (Prdx) are a ubiquitous family of highly conserved antioxidant enzymes with a cysteine residue that participate in the reduction of peroxides. This family comprises members Prdx1–6, of which Peroxiredoxin 6 (Prdx6) is unique in that it is multifunctional with the ability to neutralize peroxides (peroxidase activity) and to produce reactive oxygen species (ROS) via its phospholipase (PLA₂) activity that drives assembly of NADPH oxidase (NOX2). From the crystal structure, a C47 residue is responsible for peroxidase activity while a catalytic triad (S32, H26, and D140) has been identified as the active site for its PLA₂ activity. This paradox of being an antioxidant as well as an oxidant generator implies that Prdx6 is a regulator of cellular redox equilibrium (graphical abstract). It also indicates that a fine-tuned regulation of Prdx6 expression and activity is crucial to cellular homeostasis. This is specifically important in the endothelium, where ROS production and signaling are critical players in inflammation, injury, and repair, that collectively signal the onset of vascular diseases. Here we review the role of Prdx6 as a regulator of redox signaling, specifically in the endothelium and in mediating various pathologies.

Enhancement of Nitric Oxide Production Is Responsible for Minimal Intimal Hyperplasia of Autogenous Rabbit Arterial Grafts

BACKGROUND

Vascular endothelium induces smooth muscle cell (SMC) relaxation mainly mediated by endothelium-derived nitric oxide (EDNO) and endothelium-derived hyperpolarizing factor (EDHF). It has previously been reported that functions of these endothelium factors have been greatly impaired in vein grafts. The present study was undertaken to determine whether the functions of EDNO and EDHF might be altered in artery graft.Methods and Results:In rabbits, the right carotid artery was excised and implanted in its original position as an autogenous graft ("artery graft") and the non-operated left carotid artery served as the "control artery". Histochemical changes, acetylcholine (ACh)-induced effects on the intracellular concentration of Ca²⁺([Ca²⁺]_i) in endothelial cells, endothelium-dependent SMC hyperpolarization and relaxation, and tissue cGMP content were examined on post-operative day 28. "Artery graft" displayed a minimal amount of intimal hyperplasia. When compared with the "control artery", it exhibited greater ACh-induced, endothelium-dependent relaxation, but the reverse was true when EDNO production was blocked. In the "artery graft" (vs. the "control artery"), basal cGMP content was greater, whereas the [Ca²⁺]_iincrease in endothelial cells and the endothelium-dependent SMC-hyperpolarization induced by ACh were less.

CONCLUSIONS

It is suggested that the [Ca²⁺]_i-independent EDNO production covers the loss of function of endothelium-dependent SMC hyperpolarization and minimizes intimal hyperplasia caused by surgical operation in autogenous carotid artery graft.

Pharmacologic effects of 2-methoxyestradiol on angiotensin type 1 receptor down-regulation in rat liver epithelial and aortic smooth muscle cells

BACKGROUND

Delayed onset of cardiovascular disease (CVD) in female patients is not well understood, but could be due in part to the protective effect of estrogen before menopause. Experimental studies have identified the angiotensin type 1 receptor (AT1R) as a key factor in the progression of CVD.

OBJECTIVE

We examined the effects of the estrogen metabolite 2-methoxyestradiol (2ME2) on AT1R expression.

METHODS

Rat liver cells were exposed to 2ME2 for 24 hours, and angiotensin II (AngII) binding and AT1R mRNA expressions were assessed.

RESULTS

In the presence of 2ME2, cells exhibited significant down-regulation of AngII binding that was both dose and time dependent, independent of estrogen receptors (ERα/ERβ). Down-regulation of AngII binding was AT1R specific, with no change in receptor affinity. Under similar conditions, we observed lower expression of AT1R mRNA, significant inhibition of AngII-mediated increase in intracellular Ca(2+), and increased phosphorylation of ERK1/2. Pretreatment of cells with the MEK inhibitor PD98059 prevented 2ME2-induced ERK1/2 phosphorylation and down-regulation of AT1R expression, which suggests that the observed inhibitory effect is mediated through ERK1/2 signaling intermediates. Similar analyses in stably transfected CHO (Chinese hamster ovary) cell lines with a constitutively active cytomegalovirus promoter showed no change in AT1R expression, which suggests that 2ME2-mediated effects are through transcriptional regulation. The effects of 2ME2 on AT1R down-regulation through ERK1/2 were consistently reproduced in primary rat aortic smooth muscle cells.

CONCLUSIONS

Because AT1R has a critical role in the control of CVD, 2ME2-induced changes in receptor expression may provide beneficial effects to the cardiovascular and other systems.

Renin-angiotensin system activation correlates with microvascular dysfunction in a prospective cohort study of clinical sepsis

Introduction

Microvascular dysregulation characterized by hyporesponsive vessels and heterogeneous bloodflow is implicated in the pathogenesis of organ failure in sepsis. The renin-angiotensin system (RAS) affects the microvasculature, yet the relationships between RAS and organ injury in clinical sepsis remain unclear. We tested our hypothesis that systemic RAS mediators are associated with dysregulation of the microvasculature and with organ failure in clinical severe sepsis.

Methods

We studied 30 subjects with severe sepsis, and 10 healthy control subjects. Plasma was analyzed for plasma renin activity (PRA) and angiotensin II concentration (Ang II). Using near-infrared spectroscopy, we measured the rate of increase in the oxygen saturation of thenar microvascular hemoglobin after five minutes of induced forearm ischemia. In so doing, we assessed bulk microvascular hemoglobin influx to the tissue during reactive hyperemia. We studied all subjects 24 hours after the development of organ failure. We studied a subset of 12 subjects at an additional timepoint, eight hours after recognition of organ failure (early sepsis).

Results

After 24 hours of resuscitation to clinically-defined endpoints of preload and arterial pressure, Ang II and PRA were elevated in septic subjects and the degree of elevation correlated negatively with the rate of microvascular reoxygenation during reactive hyperemia. Early RAS mediators correlated with microvascular dysfunction. Early Ang II also correlated with the extent of organ failure realized during the first day of sepsis.

Conclusions

RAS is activated in clinical severe sepsis. Systemic RAS mediators correlate with measures of microvascular dysregulation and with organ failure.

Characteristic changes in coronary artery at the early hyperglycaemic stage in a rat type 2 diabetes model and the effects of pravastatin

BACKGROUND AND PURPOSE

Diabetes is a risk factor for the development of coronary artery disease but it is not known whether the functions of endothelium-derived nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF) in coronary arteries are altered in the early stage of diabetes. Such alterations and the effects of pravastatin were examined in left anterior descending coronary arteries (LAD) from Otsuka Long-Evans Tokushima Fatty (OLETF) rats (type 2 diabetes model) at the early hyperglycaemic stage [vs. non-diabetic Long-Evans Tokushima Otsuka (LETO) rats].

EXPERIMENTAL APPROACH

Isometric tension, membrane potential and superoxide production were measured, as were protein expression of NAD(P)H oxidase components and endothelial NO synthase (eNOS).

KEY RESULTS

Superoxide production and the protein expressions of both the nicotinamide adenine dinucleotide (phosphate) [NAD(P)H] oxidase components and eNOS were increased in OLETF rats. These changes were normalized by pravastatin administration. Not only acetylcholine (ACh)-induced endothelial NO production but also functions of endothelium-derived NO [from (i) the absolute tension induced by epithio-thromboxane A(2) (STA(2)) or high K(+); (ii) enhancement of the STA(2)-contraction by a nitric oxide synthase (NOS) inhibitor; and (iii) the ACh-induced endothelium-dependent relaxation of high K(+)-induced contraction] or EDHF [from (iv) ACh-induced endothelium-dependent smooth muscle cell hyperpolarization and relaxation in the presence of a NOS inhibitor] were similar between LETO and OLETF rats [whether or not the latter were pravastatin-treated or -untreated].

CONCLUSIONS AND IMPLICATIONS

Under conditions of increased vascular superoxide production, endothelial function is retained in LAD in OLETF rats at the early hyperglycaemic stage, partly due to enhanced endothelial NOS protein expression. Inhibition of superoxide production may contribute to the beneficial vascular effects of pravastatin.

Chronic production of peroxynitrite in the vascular wall impairs vasorelaxation function in SHR/NDmcr-cp rats, an animal model of metabolic syndrome

We have previously reported that peroxynitrite is involved in dysfunction of nitric oxide (NO)-mediated vasorelaxation in SHR/NDmcr-cp rats (SHR-cp), which display typical symptoms of metabolic syndrome. This study investigated whether peroxynitrite is actually generated in the vascular wall with angiotensin II-induced NADPH-oxidase activation, thus contributing to the dysfunction. In isolated mesenteric arteries of male 18-week-old SHR-cp, relaxations in response to acetylcholine and sodium nitroprusside were impaired compared with that in Wistar-Kyoto rats. This impaired relaxation was not restored by treatment with apocynin, an NADPH-oxidase inhibitor. Protein expression of endothelial NO synthase increased while that of soluble guanylyl cyclase (sGC) decreased in the artery. We observed increased production of superoxide anions and peroxynitrite from the artery and their inhibition by apocynin, and also increased contents of nitrotyrosine, a biomarker of peroxynitrite, in mesenteric arteries and angiotensin II in aortas. Long-term (8 weeks) administration of telmisartan, an angiotensin II type 1-receptor antagonist, prevented the impaired vasorelaxation, decreased sGC expression and increased nitrotyrosine content in mesenteric arteries. These findings suggest that in the vascular wall of SHR-cp, peroxynitrite is continually produced by the reaction of NO with NADPH oxidase-derived superoxide via angiotensin II and gradually denatures sGC protein, leading to vasorelaxation dysfunction.

Sarpogrelate hydrochloride reduced intimal hyperplasia in experimental rabbit vein graft

OBJECTIVES

The selective 5-HT(2A) receptor antagonist sarpogrelate has been clinically used for treatment in atherosclerotic diseases. However, it remains unknown whether administration of sarpogrelate inhibits intimal hyperplasia seen in autologous vein grafts. Therefore, we sought to clarify this question using an experimental rabbit vein graft model.

METHODS

Male rabbits were divided into two groups: a control group and a sarpogrelate-treated group. The jugular vein was interposed in the carotid artery in reversed fashion for 4 weeks and intimal hyperplasia of the grafted vein was measured (n = 8, in each group). Acetylcholine (ACh)-induced endothelium-dependent relaxation was tested by precontraction with prostaglandin F(2alpha) (PGF(2alpha), 5 muM) (n = 5, in each). endothelial nitric oxide synthase (eNOS) protein expression and superoxide production of these veins were also assessed.

RESULTS

The suppression of intimal hyperplasia was significantly greater in the sarpogrelate-treated group than in the control group. ACh induced an endothelium-dependent relaxation in the sarpogrelate-treated group (but not in the control group). In endothelium-intact strips from the sarpogrelate-treated group, the nitric oxide (NO) synthase inhibitor nitroarginine enhanced the PGF(2alpha)-induced contraction and blocked the ACh-induced relaxation. Immunoreactive eNOS protein expression was similar between the two groups but superoxide production (estimated from ethidium fluorescence) in endothelial cells was significantly smaller in the sarpogrelate-treated group.

CONCLUSION

The present results indicate that in vivo blockade of 5-HT(2A) receptors leads to an inhibition of intimal hyperplasia in rabbit vein graft. It is suggested that an increased function of endothelium-derived NO through a reduction in endothelial superoxide production may be a possible underlying mechanism for this. These novel findings support the clinical usefulness of sarpogrelate for preventing intimal hyperplasia in vein graft after bypass grafting.

Celiprolol reduces the intimal thickening of autogenous vein grafts via an enhancement of nitric oxide function through an inhibition of superoxide production

BACKGROUND

Beta-adrenoceptor antagonist celiprolol has been widely used as an effective antihypertensive agent. Some studies reported that celiprolol enhances nitric oxide production. The purpose of the present study is to examine the effects of celiprolol on vein graft intimal hyperplasia and endothelium-dependent nitric oxide (NO)-mediated relaxation.

METHODS

Japanese white rabbits were randomized to a control group that was fed regular rabbit chow or to a celiprolol group that was fed regular rabbit chow supplemented with 100 mg/body celiprolol sodium. The reversed jugular vein was implanted into the carotid artery. At 2 and 4 weeks after the operation, vein grafts in both groups were harvested, and intimal hyperplasia of the vein grafts was assessed. At 4 weeks after the operation, harvested vein grafts from both the groups were examined on the endothelium-dependent relaxation by application of Ach and were examined to detect for endothelial NO synthase (eNOS) expression and superoxide anion production.

RESULTS

Celiprolol inhibited intimal hyperplasia of carotid interposition-reversed jugular vein grafts 4 weeks after implantation (Intima/media index of celiprolol group, 0.48 +/- 0.01 vs control group, 1.07 +/- 0.08, P < .05) and suppressed cell proliferation in the neointima 2 weeks after implantation. In addition, celiprolol significantly enhanced endothelium-dependent NO-mediated relaxation in the vein graft with no change in eNOS expression and a reduction in superoxide production.

CONCLUSIONS

These novel findings clearly demonstrate that beta-adrenoceptor antagonist celiprolol can suppress intimal hyperplasia of the vein graft, which may be due to the enhancement of nitric oxide function through an inhibition of superoxide production. These results strongly support the clinical usefulness of celiprolol administration for preventing intimal hyperplasia of the vein graft after bypass grafting.

Murine Pre-Eclampsia Induced by Unspecific Activation of the Immune System Correlates with Alterations in the eNOS and AT1 Receptor Expression in the Kidneys and Placenta

It remains arguable if an animal model can be of use in pre-eclampsia (PE) studies, as it is clearly a human disease not observed spontaneously in other species. The aim of this study was to investigate whether PE-like signs in mice inoculated with activated Th1 cells were accompanied by abnormal expression of molecules related to the regulation of blood pressure, viz. nitric oxide synthase enzymes (eNOS and iNOS) and angiotensin (Ang) II receptors (AT1R and AT2R), in order to analyse the relevance of this model for human disease. In this model, C57/BL6-mated BALB/c females received lymphocytes crosslined with anti-CD3 and cultured with interleukin (IL)-2 and IL-12 to mimic PE pathology. Control mice received PBS. eNOS, iNOS and AT1R but not AT2R expression was augmented in the kidneys of PE-mice compared with control pregnant mice. The expression of eNOS but not of iNOS was augmented at the fetal-maternal interface of PE-mice as compared with the controls. NOSs regulate the synthesis of NO, a blood pressure and parturition mediator. As its expression is increased in PE patients, our data suggest that the Th1 cells-induced signs in this model are due to similar mechanisms as in humans. AT1R and AT2R mediate the effect of Ang II, and particularly the AT1R appears to be involved in the pathogenesis of human PE. The increased AT1R expression in the kidneys of PE-mice reinforces the theory that Th1 cells elicit a pathological situation closely resembling the human PE. All together, our data support the use of this animal model to study mechanisms underlying clinically overt PE.

Reduced Nitric Oxide in Amniotic Fluid of Patients with Chorioamnionitis

OBJECTIVE

Levels of nitric oxide (NO) and cytokines were assessed in amniotic fluid obtained from patients with severe chorioamnionitis (CAM) and appropriate controls.

METHODS

Amniotic fluid was obtained from 12 patients with CAM (17-24 weeks of gestation) and 89 patients undergoing diagnostic amniocentesis (16-18 weeks of gestation). The concentrations of NO, interleukin-6 (IL-6), and leukocyte elastase (LE) in amniotic fluid were then measured and compared.

RESULTS

The concentrations of NO, IL-6, and LE were all higher in CAM cases than in normal pregnant women. Furthermore, an inverse correlation between NO and LE was suggested in the CAM group.

CONCLUSIONS

These results indicate that in severe CAM, the action of NO might be reduced, not only due to blockage of action but also by degradation, despite increased production.

Characteristics of attenuated endothelium-dependent relaxation seen in rabbit intrapulmonary vein following chronic nitroglycerine administration

1 This study was undertaken to determine whether long-term in vivo administration of nitroglycerine (NTG) downregulates the endothelium-dependent relaxation induced by acetylcholine (ACh) in the rabbit intrapulmonary vein and, if so, whether the type 1 angiotensin II receptor (AT(1)R) blocker valsartan normalizes this downregulated relaxation. 2 In strips treated with the cyclooxygenase inhibitor diclofenac, ACh induced a relaxation only when the endothelium was intact. A small part of this ACh-induced relaxation was inhibited by coapplication of two Ca(2+)-activated K(+)-channel blockers (charybdotoxin (CTX)+apamin) and the greater part of the response was inhibited by the nitric-oxide-synthase inhibitor N(omega)-nitro-L-arginine (L-NNA). 3 The endothelium-dependent relaxation induced by ACh, but not the endothelium-independent relaxation induced by the nitric oxide donor NOC-7, was significantly reduced in NTG-treated rabbits (versus those in NTG-nontreated control rabbits). The attenuated relaxation was normalized by coapplication of valsartan with the NTG. 4 In the vascular wall, both the amount of localized angiotensin II and the production of superoxide anion were increased by in vivo NTG treatment. These variables were normalized by coapplication of valsartan with the NTG. 5 It is suggested that long-term in vivo administration of NTG downregulates the ACh-induced endothelium-dependent relaxation, mainly through an inhibition of endothelial nitric oxide production in the rabbit intrapulmonary vein. A possible role for AT(1)R is proposed in the mechanism underlying this effect.

Role of PKC in the attenuation of the cGMP-mediated relaxation of skinned resistance artery smooth muscle seen in glyceryl-trinitrate-tolerant rabbit

We examined whether 10 days' in vivo treatment with glyceryl trinitrate (GTN) might reduce cGMP-induced relaxation in the smooth muscle of rabbit mesenteric resistance arteries and, if so, whether protein kinase C (PKC) plays a role in this downregulation. The relaxation responses to GTN and the nitric oxide donor NOC-7 were significantly reduced in endothelium-denuded strips from GTN-treated rabbits. In beta-escin-skinned smooth muscle, the ability of 8-bromoguanosine 3',5' cyclic monophosphate (8-Br-cGMP, a phosphodiesterase-resistant cGMP analogue) to relax the contraction induced by 0.3 microM Ca2+ was significantly reduced in GTN-treated rabbits. In beta-escin-skinned smooth muscle, an inhibitor of conventional and/or novel PKCs, GF109203X (0.6 microM), inhibited the Ca2+ -induced contraction and enhanced the 8-Br-cGMP-induced relaxation. However, since the relaxing ability of 8-Br-cGMP was found to be unchanged by GF109203X when contractions were amplitude-matched (0.2 microM Ca2+ alone vs 0.3 microm Ca2+ + GF109203X), the increase in the 8-Br-cGMP-response seen with GF109203X was probably due to its inhibitory action on the Ca2+ -induced contraction. Furthermore, although the PKC activator phorbol 12,13-dibutyrate (PDBu, 0.1 microM) decreased the 8-Br-cGMP-induced relaxation of the Ca2+ (0.3 microM) contraction, this was probably due to its enhancement of the Ca2+ -induced contraction since no such effect of PDBu was seen when the Ca2+ -induced contractions were amplitude-matched (0.2 microM Ca2+ + PDBu vs 0.3 microM Ca2+ alone). These results suggest that the relaxing response to cGMP is reduced in the smooth muscle of mesenteric resistance arteries in GTN-treated rabbits but that conventional and/or novel PKCs do not play a major role in maintaining this downregulation. British Journal of Pharmacology (2004) 141, 391-398. doi:10.1038/sj.bjp.0705625