Effects of angiotensin II infusion and inhibition of nitric oxide synthase on the rat aorta

Activation of the Mas receptors by AVE0991 and MrgD receptor using alamandine to limit the deleterious effects of Ang II-induced hypertension

The MrgD receptor agonist, alamandine (ALA) and Mas receptor agonist, AVE0991 have recently been identified as protective components of the renin-angiotensin system. We evaluated the effects of ALA and AVE0991 on cardiovascular function and remodeling in angiotensin (Ang) II-induced hypertension in rats. Sprague Dawley rats were subject to 4-week subcutaneous infusions of Ang II (80 ng/kg/min) or saline after which they were treated with ALA (50 μg/kg), AVE0991 (576 μg/kg), or ALA+AVE0991 during the last 2 weeks. Systolic blood pressure (SBP) and heart rate (HR) values were recorded with tail-cuff plethysmography at 1, 15, and 29 days post-treatment. After euthanization, the heart and thoracic aorta were removed for further analysis and vascular responses. SBP significantly increased in the Ang II group when compared to the control group. Furthermore, Ang II also caused an increase in cardiac and aortic cyclophilin-A (CYP-A), monocyte chemoattractant protein-1 (MCP-1), and cardiomyocyte degeneration but produced a decrease in vascular relaxation. HR, matrix metalloproteinase-2 and -9, NADPH oxidase-4, and lysyl oxidase levels were comparable among groups. ALA, AVE0991, and the drug combination produced antihypertensive effects and alleviated vascular responses. The inflammatory and oxidative stress related to cardiac MCP-1 and CYP-A levels decreased in the Ang II+ALA+AVE0991 group. Vascular but not cardiac angiotensin-converting enzyme-2 levels decreased with Ang II administration but were similar to the Ang II+ALA+AVE0991 group. Our experimental data showed the combination of ALA and AVE0991 was found beneficial in Ang II-induced hypertension in rats by reducing SBP, oxidative stress, inflammation, and improving vascular responses.

Anti-infection mechanism of phosphodiesterase-5 inhibitors and their roles in coronavirus disease 2019 (Review)

Coronavirus disease 2019 (COVID-19) has a variety of impacts on the human body. Severe acute respiratory syndrome coronavirus 2 is the pathogen that causes COVID-19. It invades human tissues through the receptor angiotensin-converting enzyme 2, resulting in an imbalance in the angiotensin II (AngII) level and upregulation of renin-angiotensin system/AngII pathway activity. Furthermore, the binding of AngII to its receptor leads to vasoconstriction, endothelial injury and intravascular thrombosis. In addition, COVID-19 may have adverse effects on male reproductive organs and a marked impact on male reproductive health. Phosphodiesterase-5 inhibitors (PDE5Is) may improve vascular endothelial function, promote testicular and systemic blood circulation and testosterone secretion and enhance epididymal function, as well as sperm maturation and capacitation. PDE5Is may also be of use in the treatment of infectious diseases by enhancing immunity and anti-inflammatory responses and improving vascular endothelial function. Based on the pharmacological mechanism of PDE5Is, they are of unique value in the fight against infectious diseases and may be effective in combination with direct antiviral drugs. The anti-infection mechanisms of PDE5Is and their roles in COVID-19 were reviewed in the present study.

PKR inhibitor imoxin prevents hypertension, endothelial dysfunction and cardiac and vascular remodelling in L-NAME-treated rats

AIMS

Hypertension is one of the leading causes of cardiovascular mortality and morbidity. It is associated with severe cardiac and vascular dysfunction. Double-stranded RNA-dependent protein kinase (PKR), is a known inducer of inflammation and apoptosis. However, no research has been done to elucidate the role of the PKR in an experimental model of hypertension, and related cardiovascular complications.

MAIN METHODS

L-NAME (N^G-Nitro-L-arginine-methyl ester) was used to induce the hypertension. Imoxin treatment was given to Wistar rats for the four weeks along with the L-NAME, to investigate the influence on the hypertension. Changes in physiological parameter were assessed by recording non-invasive blood pressure. Expression of PKR and downstream markers for inflammation, fibrosis, and vascular damage in rat heart and aorta was determined by western blot and immunohistochemistry. Histological examination and fibrosis assessment were done by using assay kits. Vascular reactivity was determined by ex-vivo isometric tension studies on rat aortic rings.

KEY FINDINGS

L-NAME-treated rats showed a significant increase in PKR expression followed by cardiac damage and vascular alterations compared to that of control animals. Results of western blot and immunohistochemistry indicate a significant increase in the inflammatory markers downstream to PKR. Endothelium-dependent vascular relaxation was significantly impaired in L-NAME administered rats. All effects of the L-NAME were attenuated by selective inhibition of PKR by imoxin.

SIGNIFICANCE

Alterations in the heart and vasculature could be mediated in part by activation of the PKR pathway. Hence selective inhibition of PKR has therapeutic potential for combating hypertension and associated cardiovascular complications.

ACE2, Much More Than Just a Receptor for SARS-COV-2

The rapidly evolving pandemic of severe acute respiratory syndrome coronavirus (SARS-CoV-2) infection worldwide cost many lives. The angiotensin converting enzyme-2 (ACE-2) has been identified as the receptor for the SARS-CoV-2 viral entry. As such, it is now receiving renewed attention as a potential target for anti-viral therapeutics. We review the physiological functions of ACE2 in the cardiovascular system and the lungs, and how the activation of ACE2/MAS/G protein coupled receptor contributes in reducing acute injury and inhibiting fibrogenesis of the lungs and protecting the cardiovascular system. In this perspective, we predominantly focus on the impact of SARS-CoV-2 infection on ACE2 and dysregulation of the protective effect of ACE2/MAS/G protein pathway vs. the deleterious effect of Renin/Angiotensin/Aldosterone. We discuss the potential effect of invasion of SARS-CoV-2 on the function of ACE2 and the loss of the protective effect of the ACE2/MAS pathway in alveolar epithelial cells and how this may amplify systemic deleterious effect of renin-angiotensin aldosterone system (RAS) in the host. Furthermore, we speculate the potential of exploiting the modulation of ACE2/MAS pathway as a natural protection of lung injury by modulation of ACE2/MAS axis or by developing targeted drugs to inhibit proteases required for viral entry.

ACE2, Much More Than Just a Receptor for SARS-COV-2

The rapidly evolving pandemic of severe acute respiratory syndrome coronavirus (SARS-CoV-2) infection worldwide cost many lives. The angiotensin converting enzyme-2 (ACE-2) has been identified as the receptor for the SARS-CoV-2 viral entry. As such, it is now receiving renewed attention as a potential target for anti-viral therapeutics. We review the physiological functions of ACE2 in the cardiovascular system and the lungs, and how the activation of ACE2/MAS/G protein coupled receptor contributes in reducing acute injury and inhibiting fibrogenesis of the lungs and protecting the cardiovascular system. In this perspective, we predominantly focus on the impact of SARS-CoV-2 infection on ACE2 and dysregulation of the protective effect of ACE2/MAS/G protein pathway vs. the deleterious effect of Renin/Angiotensin/Aldosterone. We discuss the potential effect of invasion of SARS-CoV-2 on the function of ACE2 and the loss of the protective effect of the ACE2/MAS pathway in alveolar epithelial cells and how this may amplify systemic deleterious effect of renin-angiotensin aldosterone system (RAS) in the host. Furthermore, we speculate the potential of exploiting the modulation of ACE2/MAS pathway as a natural protection of lung injury by modulation of ACE2/MAS axis or by developing targeted drugs to inhibit proteases required for viral entry.

Thioredoxin reverses age-related hypertension by chronically improving vascular redox and restoring eNOS function

The incidence of high blood pressure with advancing age is notably high, and it is an independent prognostic factor for the onset or progression of a variety of cardiovascular disorders. Although age-related hypertension is an established phenomenon, current treatments are only palliative but not curative. Thus, there is a critical need for a curative therapy against age-related hypertension, which could greatly decrease the incidence of cardiovascular disorders. We show that overexpression of human thioredoxin (TRX), a redox protein, in mice prevents age-related hypertension. Further, injection of recombinant human TRX (rhTRX) for three consecutive days reversed hypertension in aged wild-type mice, and this effect lasted for at least 20 days. Arteries of wild-type mice injected with rhTRX or mice with TRX overexpression exhibited decreased arterial stiffness, greater endothelium-dependent relaxation, increased nitric oxide production, and decreased superoxide anion (O₂^•-) generation compared to either saline-injected aged wild-type mice or mice with TRX deficiency. Our study demonstrates a potential translational role of rhTRX in reversing age-related hypertension with long-lasting efficacy.

Damage-associated molecular pattern activated Toll-like receptor 4 signalling modulates blood pressure in L-NAME-induced hypertension

AIMS

Recent publications have shed new light on the role of the adaptive and innate immune system in the pathogenesis of hypertension. However, there are limited data whether receptors of the innate immune system may influence blood pressure. Toll-like receptor 4 (TLR4), a pattern recognition receptor, is a key component of the innate immune system, which is activated by exogenous and endogenous ligands. Hypertension is associated with end-organ damage and thus might lead to the release of damage-associated molecular patterns (DAMPs), which are endogenous activators of TLR4 receptors. The present study aimed to elucidate whether TLR4 signalling is able to modulate vascular contractility in an experimental model of hypertension thus contributing to blood pressure regulation.

METHODS AND RESULTS

NG-nitro-l-arginine methyl ester (l-NAME)-induced hypertension was blunted in TLR4(-/-) when compared with wild-type mice. Treatment with l-NAME was associated with a release of DAMPs, leading to reactive oxygen species production of smooth muscle cells in a TLR4-dependent manner. As oxidative stress leads to an impaired function of the NO-sGC-cyclic GMP (cGMP) pathway, we were able to demonstrate that TLR4(-/-) was protected from sGC inactivation. Consequently, arterial contractility was reduced in TLR4(-/-).

CONCLUSIONS

Cell damage-associated TLR4 signalling might act as a direct mediator of vascular contractility providing a molecular link between inflammation and hypertension.

Effects of taxifolin on the activity of angiotensin-converting enzyme and reactive oxygen and nitrogen species in the aorta of aging rats and rats treated with the nitric oxide synthase inhibitor and dexamethasone

The action of taxifolin on the angiotensin-converting enzyme (ACE) and the formation of reactive oxygen and nitrogen species (ROS/RNS) in the aorta of aging rats and rats treated with nitric oxide synthase inhibitor (N ω-nitro-L-arginine methyl ester (L-NAME)) or dexamethasone have been studied. The ACE activity in aorta sections was determined by measuring the hydrolysis of hippuryl-L-histidyl-L-leucine, and the ROS/RNS production was measured by oxidation of dichlorodihydrofluorescein. It was shown that taxifolin at a dose of 30-100 μg/kg/day decreases the ACE activity in the aorta of aging rats and of rats treated with L-NAME or dexamethasone to the level of the ACE activity in young control rats. Taxifolin (100 μg/kg/day) was found to also reduce the amount of ROS/RNS in the aorta that increased as a result of L-NAME intake. L-NAME treatment increases the contribution of 5-lipoxygenase and NADPH oxidase to ROS/RNS production in the aorta, while taxifolin (100 μg/kg/day) decreases the contribution of these enzymes to the normal level.

Effects of isorhynchophylline on angiotensin II-induced proliferation in rat vascular smooth muscle cells

Proliferation of vascular smooth muscle cells (VSMCs) is a crucial event in cardiovascular diseases. Isorhynchophylline, an alkaloid from a traditional Chinese medicine Gambirplant, has been used to treat cardiovascular diseases. The aim of this study was to investigate the effects of isorhynchophylline on angiotensin II (Ang II)-induced proliferation of rat VSMCs. VSMCs were isolated from rat artery and cultured for 14 days before experimentation. The effect of isorhynchophylline on Ang II-induced proliferation was evaluated by cell number, MTT assay and flow cytometry, and nitric oxide (NO) content and activity of NO synthase (NOS) were measured. The expression of proto-oncogene c-fos, osteopontin (OPN) and proliferating cell nuclear antigen (PCNA) mRNAs was measured by real-time RT-PCR. VSMC cultures were verified by morphology and immunostaining with α-smooth muscle actin. Isorhynchophylline (0.1–10.0 μM) was not toxic to VSMCs, but markedly decreased Ang II (1.0 μm)-enhanced cell number and MTT intensity, and blocked cell transition from G0/G1 to S phase. Furthermore, isorhynchophylline increased the NO content and NOS activity, and suppressed Ang II-induced over-expression of c-fos, OPN and PCNA. Thus, isorhynchophylline was effective against Ang-II induced cell proliferation, an effect that appears to be due, at least in part, to increased NO production, regulation of the cell cycle, and depressed expression of c-fos, OPN and PCNA related to VMSC proliferation.

Nitric oxide, angiotensin II, and hypertension

Although initially adaptive, the changes that accompany hypertension, namely, cell growth, endothelial dysfunction, and extracellular matrix deposition, eventually can become maladaptive and lead to end-organ disease such as heart failure, coronary artery disease, and renal failure. A functional imbalance between angiotensin II (Ang II) and nitric oxide (NO) plays an important pathogenetic role in hypertensive end-organ injury. NO, an endogenous vasodilator, inhibitor of vascular smooth muscle and mesangial cell growth, and natriuretic agent, is synthesized in the endothelium by a constitutive NO synthase. NO antagonizes the effects of Ang II on vascular tone, cell growth, and renal sodium excretion, and also down-regulates the synthesis of angiotensin-converting enzyme (ACE) and Ang II type 1 receptors. On the other hand, Ang II decreases NO bioavailability by promoting oxidative stress. A better understanding of the pathophysiologic mechanisms involved in hypertensive end-organ damage may aid in identifying markers of cardiovascular susceptibility to injury and in developing therapeutic interventions. We propose that those antihypertensive agents that lower blood pressure and concomitantly restore the homeostatic balance of vasoactive agents such as Ang II and NO within the vessel wall would be more effective in preventing or arresting end-organ disease.

Signaling of angiotensin II-induced vascular protein synthesis in conduit and resistance arteries in vivo

Background

From in vitro studies, it has become clear that several signaling cascades are involved in angiotensin II-induced cellular hypertrophy. The aim of the present study was to determine some of the signaling pathways mediating angiotensin II (Ang II)-induced protein synthesis in vivo in large and small arteries.

Methods

Newly synthesized proteins were labeled during 4 hours with tritiated leucine in conscious control animals, or animals infused for 24 hours with angiotensin II (400 ng/kg/min). Hemodynamic parameters were measure simultaneously. Pharmacological agents affecting signaling cascades were injected 5 hours before the end of Ang II infusion.

Results

Angiotensin II nearly doubled the protein synthesis rate in the aorta and small mesenteric arteries, without affecting arterial pressure. The AT₁ receptor antagonist Irbesartan antagonized the actions of Ang II. The Ang II-induced protein synthesis was associated with increased extracellular signal-regulated kinases (ERK)1/2 phosphorylation in aortic, but not in mesenteric vessels. Systemic administration of PD98059, an inhibitor of the ERK-1/2 pathway, produced a significant reduction of protein synthesis rate in the aorta, and only a modest decrease in mesenteric arteries. Rapamycin, which influences protein synthesis by alternative signaling, had a significant effect in both vessel types. Rapamycin and PD98059 did not alter basal protein synthesis and had minimal effects on arterial pressure.

Conclusion

ERK1/2 and rapamycin-sensitive pathways are involved in pressure-independent angiotensin II-induced vascular protein synthesis in vivo. However, their relative contribution may vary depending on the nature of the artery under investigation.

ERK1/2-mediated vasoconstriction normalizes wall stress in small mesenteric arteries during NOS inhibition in vivo

As in essential hypertension, chronic nitric-oxide synthase (NOS) inhibition leads to hypertrophic remodeling in conduit and muscular arteries and inward eutrophic remodeling in small resistance arteries with activation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) in both vessel types. The authors tested the hypothesis that this remodeling heterogeneity could be related to distinct vasoreactivity patterns in small and larger arteries, with a vessel-specific function of ERK1/2 signaling. Using intravital microscopy in rats we have demonstrated that acute NOS inhibition (l-NA injection, 100 mg/kg) produced vasoconstriction of small mesenteric arteries. Consequently, the calculated in vivo wall stress was not significantly modified, despite the local rise in pressure. This could explain the lack of vascular protein synthesis elevation in vivo, an early index of hypertrophy. Inhibition of ERK1/2 activation with PD98059 blunted mesenteric artery contractions. Femoral arteries did not contract and were thus submitted to an enhanced wall stress and underwent hypertrophic remodeling in chronic conditions. In conclusion, the heterogeneous vascular remodeling in the l-NAME model is associated with a heterogeneous vasoconstriction response to acute NOS inhibition. Indeed, in contrast to larger arteries, l-NA-induced vasoconstriction in small arteries normalized wall stress and prevented early signs of hypertrophy. The results also suggest that ERK1/2 is a signaling element in NOS inhibition-induced vasoconstriction of small arteries in vivo.

Role of superoxide anion in regulating pressor and vascular hypertrophic response to angiotensin II

Our purpose was to address the role of NAPDH oxidase-derived superoxide anion in the vascular response to ANG II. Blood pressure, aortic superoxide anion, 3-nitrotyrosine, and medial cross-sectional area were compared in wild-type mice and in mice that overexpress human superoxide dismutase (hSOD). The pressor response to ANG II was significantly less in hSOD mice. Superoxide anion levels were increased twofold in ANG II-treated wild-type mice but not in hSOD mice. 3-Nitrotyrosine increased in aortic endothelium and adventitia in wild-type but not hSOD mice. In contrast, aortic medial cross-sectional area increased 50% with ANG II in hSOD mice, comparable to wild-type mice. The lower pressor response to ANG II in the mice expressing hSOD is consistent with a pressor role of superoxide anion in wild-type mice, most likely because it reacts with nitric oxide. Despite preventing the increase in superoxide anion and 3-nitrotyrosine, the aortic hypertrophic response to ANG II in vivo was unaffected by hSOD.

Angiotensin AT1 receptor antagonist irbesartan decreases lesion size, chemokine expression, and macrophage accumulation in apolipoprotein E-deficient mice

Recent data suggest that angiotensin II AT1 receptor antagonists may be beneficial in the treatment of atherosclerosis. To clarify how AT1 receptor antagonists reduce atherosclerosis, the effect of irbesartan on atherosclerotic lesion development was determined in low-fat, chow-fed apolipoprotein (Apo) E-deficient mice. Irbesartan (50 mg/kg per day) strongly decreased lesion development after a 12-week treatment period (lesion size: irbesartan treated, 20,524 +/- 4,200 microm(2) vs. control, 99,600 +/- 14,500; 79.4% inhibition, p < 0.001). This effect was not due to an effect of irbesartan on lipoprotein levels because irbesartan slightly increased total cholesterol levels and decreased the ratio of Apo A-I relative to Apo B levels. Immunochemical analysis of the atherosclerotic lesions using the mac3 monoclonal antibody showed the presence of macrophages in the lesions of control mice, whereas sections from irbesartan-treated animals only showed occasional labeling in the lesion area. These data suggest that irbesartan inhibits monocyte/macrophage influx into the vessel wall. Therefore, expression levels of monocyte chemoattractant protein-1 (MCP-1), as well as other chemokines involved in macrophage infiltration into the lesion area, were measured in the aortic sinus of control and irbesartan-treated animals. Irbesartan treatment strongly decreased MCP-1 mRNA levels as well as MCP-1 immunostaining in the lesion area. This effect of irbesartan on MCP-1 occurred without an effect on CCR2, the receptor of MCP-1. Expression of macrophage inflammatory protein (MIP)-1alpha, another CC chemokine expressed in atherosclerotic lesions, was also reduced after irbesartan treatment, without effect on CCR3 and CCR5, the receptors of MIP-1alpha. Concomitantly, the expression of the angiogenic chemokines KC and MIP-2, which are functionally related to interleukin-8, were downregulated, whereas their shared receptor CXCR2 was upregulated. These data suggest that inhibition of the inflammatory component of lesion progression plays an important role in the inhibitory effect of AT1 receptor antagonists on atherosclerotic lesion formation.

Chronic inhibition of NO synthesis per se promotes structural intimal remodeling of the rat aorta

OBJECTIVE

We characterized, using histomorphometry and transmission and scanning electron microscopy, the intimal remodeling of the thoracic aorta of normocholesterolemic young rats chronically-treated with N(omega)-nitro-L-arginine methylester (L-NAME) and examined the question whether these changes were caused by the lack of NO per se or by the hypertension which L-NAME administration induces.

METHODS

Male Wistar rats were divided randomly into three sets: control group, standard diet/L-NAME-treated group, and standard diet/L-NAME + captopril-treated group.

RESULTS

The treatment of rats with L-NAME for 4 weeks resulted in increased blood pressure (by 32% at the end of the treatment) as compared with the control value and intimal remodeling comprising a continuous layer of enlarged endothelial cells with irregular nuclear and cytoplasmic contours, lying over a thickened layer of fibrocollagenous support tissue focally expanded with lymphomononuclear cells and mainly diffuse foci of smooth muscle cells. In addition, the NO synthase inhibition caused a marked thickened tunica intima (150% thicker than the control value) and a significantly augmented intima : media ratio (126% higher than the control value). On the other hand, captopril prevented hypertension in rats simultaneously treated with L-NAME as compared with controls, and induced intimal remodeling comprising the same qualitative changes as those observed in L-NAME-treated rats. The tunica intima of l-NAME + captopril-treated rats was moderately thickened (60% increase in comparison with that of controls and 65% thinner as compared with L-NAME-treated rats). In the same way, the mean intima : media ratio of rats concomitantly treated with L-NAME and captopril was moderately increased (45% more) as compared with controls and significantly lower in comparison with rats administered L-NAME alone (36% less).

CONCLUSIONS

Chronic inhibition of NO synthesis per se promotes structural intimal remodeling of the rat aorta, which is potentiated by L-NAME-induced hypertension. Most important, the present findings favor the idea that blockade of NO synthesis by causing intimal remodeling might be a primary cause, as individual biologic phenomenon, in the development of an atherosclerotic plaque.

Cross talk between prostacyclin and nitric oxide under shear in smooth muscle cell: role in monocyte adhesion

We tested the hypothesis that at sites of vascular damage, vessel homeostasis is maintained through the cross talk of shear-induced production of prostacyclin and nitric oxide (NO) in vascular smooth muscle cells (VSMC). Confluent A7r5 cells derived from rat aortic VSMC and mesenteric VSMC were exposed to shear stress at 15 dyn/cm(2) for 90 min with the use of a cone-plate device, and productions of prostacyclin and NO were examined. Shear stress increased cumulative production of prostacyclin by 3- to 3.5-fold and that of NO by 6- to 7.5-fold. Western blot analysis showed that inducible NO synthase protein was expressed after shear stress in both types of VSMC. Inhibition of NO synthase enhanced the shear-induced production of prostacyclin from 40 to 60%. Shear-induced production of NO was suppressed by 70% after treatment with 10(-4) M of indomethacin. A7r5 cells adhesiveness for monocytes was suppressed by 50% after shear stress. This suppression was abolished by pretreatment with 10(-4) M of indomethacin, whereas inhibition of NO synthase only minimally inhibited it. We conclude that there is a cross talk of shear-induced production of prostacyclin and NO in VSMC. At sites of vascular damage, prostacyclin synthesis may prevent monocyte adhesiveness for VSMC through the concomitant enhancement of NO production.

Nitric oxide increases p21(Waf1/Cip1) expression by a cGMP-dependent pathway that includes activation of extracellular signal-regulated kinase and p70(S6k)

Nitric oxide (NO) regulates the expression of p21(Waf1/Cip1) in several cell types. The present study examined the role of both the extracellular signal-regulated kinase (ERK) and p70 S6 kinase (p70(S6k)) in the NO-induced increase in p21 expression that occurred in adventitial fibroblasts during the cell cycle. Both ERK and p70(S6k) were phosphorylated in response to the NO donor S-nitroso-N-acetylpenicillamine (SNAP) and the activation was rapid, transient, and preceded increased p21 expresion under defined conditions where serum was present. Addition of a selective inhibitor of ERK phosphorylation (PD98059) prevented the subsequent phosphorylation of p70(S6k) and the increase in p21 protein. Both cGMP and cAMP activated both ERK and p70(S6k), whereas only selective inhibitors of protein kinase G prevented the activation of the kinases by SNAP. A complex between ERK and p70(S6k) was documented by immunoprecipitation procedures. Rapamycin blocked p70(S6k) phosphorylation induced by NO and also inhibited p53 phosphorylation and p21 expression whereas PD98059 only prevented the NO-induced increase in p21 protein without influencing either p53 activation or p21 mRNA expression. The studies show a unique relationship between NO, ERK, and p70(S6k) and also provide evidence for a novel role of p70(S6k) in the activation of p53.

Chronic hypertension alters the expression of Cx43 in cardiovascular muscle cells

Connexin43 (Cx43), the predominant gap junction protein of muscle cells in vessels and heart, is involved in the control of cell-to-cell communication and is thought to modulate the contractility of the vascular wall and the electrical coupling of cardiac myocytes. We have investigated the effects of arterial hypertension on the expression of Cx43 in aorta and heart in three different models of experimental hypertension. Rats were made hypertensive either by clipping one renal artery (two kidney, one-clip renal (2K,1C) model) by administration of deoxycorticosterone and salt (DOCA-salt model) or by inhibiting nitric oxide synthase with N G-nitro-L-arginine methyl ester (L-NAME model). After 4 weeks, rats of the three models showed a similar increase in intra-arterial mean blood pressure and in the thickness of the walls of both aorta and heart. Analysis of heart mRNA demonstrated no change in Cx43 expression in the three models compared to their respective controls. The same 2K,1C and DOCA-salt hypertensive animals expressed twice more Cx43 in aorta, and the 2K, 1C rats showed an increase in arterial distensibility. In contrast, the aortae of L-NAME hypertensive rats were characterized by a 50% decrease in Cx43 and the carotid arteries did not show increased distensibility. Western blot analysis indicated that Cx43 was more phosphorylated in the aortae of 2K,1C rats than in those of L-NAME or control rats, indicating a differential regulation of aortic Cx43 in different models of hypertension. The data suggest that localized mechanical forces induced by hypertension affect Cx43 expression and that the cell-to-cell communication mediated by Cx43 channels may contribute to regulating the elasticity of the vascular wall.

Cross talk of shear-induced production of prostacyclin and nitric oxide in endothelial cells

We tested the hypothesis that vessel homeostasis is maintained through the cross talk of shear-induced production of prostacyclin and nitric oxide (NO). Confluent human umbilical vein endothelial cells (HUVEC) were exposed to fluid shear stress at 15 dyn/cm(2) using a cone-plate device, and the concentrations of 6-keto-PGF(1alpha) and NO metabolites (nitrate and nitrite) in the medium were measured with radioimmunoassay and the Greiss method, respectively. Compared with static control, shear stress increased cumulative prostacyclin production by twofold after 90 min of exposure. Inhibition of NO synthase enhanced flow-induced prostacyclin production by twofold without affecting the baseline production. Guanylyl cyclase inhibitor enhanced flow-induced prostacyclin production to the same degree. In contrast, a stable agonist of cGMP attenuated the rapid early phase of flow-dependent prostacyclin production. Shear-induced NO metabolite production was unaffected even after indomethacin inhibited prostacyclin production. We conclude that NO shows an inhibitory effect on prostacyclin production under shear stress and that vessel homeostasis may be maintained through an increase in prostacyclin production when NO synthesis is impaired in endothelial cells.

Effects of a novel angiotensin AT(1) receptor antagonist, HR720, on rats with myocardial infarction

Cardiac remodeling after myocardial infarction is associated with impaired ventricular function and heart failure and has important implications for survival. The purpose of the present study was to assess the effects of chronic treatment with a novel angiotensin AT(1) receptor antagonist 2-butyl-4-(methylthio-)-1-[[2'[[[(propylamino)carbonyl]amino]sulfonyl ](1,1'-biphenyl)-4-yl]methyl]-1H-imidazole-5-carboxylate (HR720), on cardiac remodeling and left ventricular dysfunction in a rat model of large myocardial infarction. Rats were subjected to permanent ligation of the left coronary artery and were treated for six weeks with placebo or HR720 (3 mg/kg/day) initiated 24 h after surgery. Sham-operated rats served as normal controls. Mean arterial blood pressure, the maximum rate of rise of the left ventricular systolic pressure (dP/dt(max)), left ventricular end-diastolic pressure, left ventricular inner diameter and circumference, septal thickness, left ventricular collagen content and heart weight were measured at the end of the treatment. HR720 treatment versus placebo attenuated the cardiac hypertrophy (heart weight/body weight: 2.88+/-0.08 mg/g vs. 3.16+/-0.09 mg/g, P<0.05), reduced interstitial collagen content (3. 47+/-0.28% vs. 5.25+/-0.45%, P<0.01), limited infarct size (33.0+/-3. 0% vs. 41.5+/-2.3%, P<0.05), decreased left ventricular end-diastolic pressure (13.7+/-2.2 vs. 21.4+/-1.6 mm Hg, P<0.01) and improved dP/dt(max) (9000+/-430 vs. 6000+/-840 mm Hg/s, P<0.05). The present results demonstrate that chronic treatment with the angiotensin AT(1) receptor antagonist HR720 can limit infarct size, partially prevent cardiac hypertrophic remodeling and improve left ventricular function in rats with myocardial infarction.

Angiotensin converting enzyme inhibition and calcium antagonism attenuate streptozotocin-diabetes-associated mesenteric vascular hypertrophy independently of their hypotensive action

OBJECTIVES

To investigate the relative roles of angiotensin II, bradykinin, and calcium-dependent pathways in the genesis of mesenteric vascular hypertrophy in experimental diabetes.

DESIGN

Streptozotocin-induced diabetic Sprague-Dawley rats were randomly allocated to these treatments for 24 weeks: no treatment; ramipril at a hypotensive dose; ramipril plus the bradykinin type 2 receptor blocker icatibant; icatibant alone; ramipril at a low dose; the angiotensin II type 1 receptor antagonist, valsartan; the dihydropyridine calcium antagonist, lacidipine; and the nondihydropyridine calcium antagonist mibefradil.

METHODS

Systolic blood pressure was serially measured every 4 weeks by tail-cuff plethysmography. We assessed the vascular architecture in sections of mesenteric arteries obtained after in-vivo perfusion, which were stained with an antibody to alpha-smooth muscle actin.

RESULTS

Both blood pressure and the mesenteric arterial wall: lumen ratio were reduced by administration of ramipril, at the high dose, either alone or in combination with icatibant, and also by valsartan. Treatment either with the low dose of ramipril or with the calcium antagonists lacidipine and mibefradil was associated with a decrease in the wall : lumen ratio of the mesenteric arteries without influencing blood pressure.

CONCLUSIONS

These findings demonstrate that blockade both of angiotensin II-dependent and of calcium-dependent pathways attenuates mesenteric vascular hypertrophy in experimental diabetes. Furthermore, the antitrophic effects of these antihypertensive agents may be independent of their hypotensive effects.

Localization of a constitutively active, phagocyte-like NADPH oxidase in rabbit aortic adventitia: enhancement by angiotensin II

Superoxide anion (O2-) plays a key role in the endogenous suppression of endothelium-derived nitric oxide (NO) bioactivity and has been implicated in the development of hypertension. In previous studies, we found that O2- is produced predominantly in the adventitia of isolated rabbit aorta and acts as a barrier to NO. In the present studies, we characterize the enzyme responsible for O2- production in the adventitia and show that this enzyme is a constitutively active NADPH oxidase with similar composition as the phagocyte NADPH oxidase. Constitutive O2--generating activity was localized to aortic adventitial fibroblasts and was enhanced by the potent vasoconstrictor angiotensin II. Immunohistochemistry of aortic sections demonstrated the presence of p22(phox), gp91(phox), p47(phox), and p67(phox) localized exclusively in rabbit aortic adventitia, coincident with the site of staining for O2- production. Furthermore, immunodepletion of p67(phox) from adventitial fibroblast particulates resulted in the loss of NADPH oxidase activity, which could be restored by the addition of recombinant p67(phox). Further study into the regulation of this adventitial source of O2- is important in elucidating the mechanisms regulating the bioactivity of NO and may contribute to our understanding of the pathogenesis of hypertension.

Angiotensin II blockade decreases TGF-beta1 and matrix proteins in cyclosporine nephropathy

Angiotensin II (Ang II) is implicated in fibrosis but the precise mechanism of this effect remains unclear. In a model of chronic cyclosporine (CsA) nephropathy, we previously showed that TGF-beta1 plays a role in CsA-induced tubulointerstitial fibrosis and arteriolopathy by stimulating extracellular matrix (ECM) protein synthesis and inhibiting ECM degradation through increasing the synthesis of plasminogen activator inhibitor (PAI)-1. We hypothesized that Ang II contributes to fibrosis by inducing TGF-beta1. Salt-depleted rats were given placebo, CsA alone, CsA + nilvadipine, CsA + hydralazine/hydrochlorthiazide, CsA + losartan (AT1 receptor antagonist) or CsA + enalapril (Ang converting enzyme inhibitor) and were sacrificed at 7 and 28 days. All treated groups achieved similar blood pressures and glomerular filtration rates. The lesion of chronic CsA nephropathy was ameliorated by concomitant therapy with losartan or enalapril at 28 days, a phenomenon not observed in the other treatment groups. Similarly, Ang II blockade resulted in decreased expression of TGF-beta1 and PAI-1 by Northern and ELISA. Similarly, the expression of ECM proteins directly influenced by TGF-beta decreased with Ang II blockade. These results suggest that CsA-induced fibrosis in this model is independent of renal hemodynamics and is mediated, at least partly, through Ang II induction of TGF-beta1 expression.