Angiotensin in atherosclerosis

Pressure and stiffness sensing together regulate vascular smooth muscle cell phenotype switching

Vascular smooth muscle cells (VSMCs) play a central role in the progression of atherosclerosis, where they switch from a contractile to a synthetic phenotype. Because of their role as risk factors for atherosclerosis, we sought here to systematically study the impact of matrix stiffness and (hemodynamic) pressure on VSMCs. Thereby, we find that pressure and stiffness individually affect the VSMC phenotype. However, only the combination of hypertensive pressure and matrix compliance, and as such mechanical stimuli that are prevalent during atherosclerosis, leads to a full phenotypic switch including the formation of matrix-degrading podosomes. We further analyze the molecular mechanism in stiffness and pressure sensing and identify a regulation through different but overlapping pathways culminating in the regulation of the actin cytoskeleton through cofilin. Together, our data show how different pathological mechanical signals combined but through distinct pathways accelerate a phenotypic switch that will ultimately contribute to atherosclerotic disease progression.

Indoxyl sulfate impairs valsartan-induced neovascularization

Studies revealed that the use of renin-angiotensin-aldosterone system antagonism is not associated with a statistically significant reduction in the risk of cardiovascular events in patients with chronic kidney disease (CKD) compared with that in the general population. We tested the hypothesis that indoxyl sulfate (IS) can interfere with the protective effect of valsartan-mediated on endothelial function in vitro and neovascularization in mice underwent subtotal nephrectomy. In human aortic endothelial cells, we first demonstrated that IS impaired the valsartan-mediated phosphorylation of eNOS^Thr495, nitric oxide production and tube formation via NADPH oxidase (NOX) and protein kinase C (PKC) phosphorylation, but this effect was suppressed by cotreatment with apocynin and calphostin C. In vivo, IS attenuated valsartan-induced angiogenesis in Matrigel plugs in mice. Moreover, in subtotal nephrectomy mice who underwent hindlimb ischemic surgery, valsartan significantly increased the mobilization of endothelial progenitor cells in circulation as well as the reperfusion of blood flow and density of CD31⁺ capillaries in ischemic limbs. However, IS attenuated the protective effect of valsartan-induced neovascularization and increased the expression of p-PKCα^Ser657 and p-eNOS^Thr497 in ischemic limbs. Cotreatment of apocynin and calphostin C reversed the IS impaired-neovascularization and decreased the expression of p-PKCα^Ser657 and p-eNOS^Thr497 in ischemic limbs. Our study suggests that the NOX/PKC/eNOS signaling pathway plays a pivotal role in the IS-mediated inhibition of valsartan-conferred beneficial effects on endothelial function in vitro and neovascularization in subtotal nephrectomy mice. We proposed a novel causative role for IS in cardiovascular complications in CKD patients.

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The use of renin-angiotensin-aldosterone system antagonism fails to reduce in the risk cardiovascular events in patients with CKD.

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Indoxyl sulfate interferes with the protective effect of angiotensin II receptor blocker-mediated neovascularization in CKD mice.

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Indoxyl sulfate interferes with the beneficial effect of of valsartan on endothelial function by activating the NOX/PKC signaling pathway.

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This article proposed a novel causative role for indoxyl sulfate in cardiovascular complications in CKD patients.

Higher risk of kidney graft failure in the presence of anti-angiotensin II type-1 receptor antibodies

Reports have associated non-HLA antibodies, specifically those against angiotensin II type-1 receptor (AT1R), with antibody-mediated kidney graft rejection. However, association of anti-AT1R with graft failure had not been demonstrated. We tested anti-AT1R and donor-specific HLA antibodies (DSA) in pre- and posttransplant sera from 351 consecutive kidney recipients: 134 with biopsy-proven rejection and/or lesions (abnormal biopsy group [ABG]) and 217 control group (CG) patients. The ABG's rate of anti-AT1R was significantly higher than the CG's (18% vs. 6%, p < 0.001). Moreover, 79% of ABG patients with anti-AT1R lost their grafts (vs. 0%, CG), anti-AT1R levels in 58% of those failed grafts increasing posttransplant. With anti-AT1R detectable before DSA, time to graft failure was 31 months-but 63 months with DSA detectable before anti-AT1R. Patients with both anti-AT1R and DSA had lower graft survival than those with DSA alone (log-rank p = 0.007). Multivariate analysis showed that de novo anti-AT1R was an independent predictor of graft failure in the ABG, alone (HR: 6.6), and in the entire population (HR: 5.4). In conclusion, this study found significant association of anti-AT1R with graft failure. Further study is needed to establish causality between anti-AT1R and graft failure and, thus, the importance of routine anti-AT1R monitoring and therapeutic targeting.

Rationale and design of dal-VESSEL: a study to assess the safety and efficacy of dalcetrapib on endothelial function using brachial artery flow-mediated vasodilatation

OBJECTIVE

Dalcetrapib increases high-density lipoprotein cholesterol (HDL-C) levels through effects on cholesteryl ester transfer protein (CETP). As part of the dalcetrapib dal-HEART clinical trial programme, the efficacy and safety of dalcetrapib is assessed in coronary heart disease (CHD) patients in the dal-VESSEL study (ClinicalTrials.gov identifier: NCT00655538), the design and methods of which are presented here. RESEARCH DESIGN AND STUDY METHOD: Men and women with CHD or CHD risk equivalent, with HDL-C levels <50  mg/dL were recruited for a 36-week, double-blinded, placebo-controlled trial. After a pre-randomisation phase of up to 8 weeks, patients received dalcetrapib 600  mg/day or placebo in addition to their existing treatments. Brachial flow-mediated dilatation (FMD) measured by B-mode ultrasound represents endothelial function and is a validated marker for early atherosclerosis and cardiovascular disease risk.

MAIN OUTCOME MEASURES

The primary efficacy outcome is change from baseline in brachial FMD after 12 weeks. The primary safety endpoint is 24-hour ambulatory blood pressure monitoring (ABPM) assessed at week 4. Secondary endpoints include brachial FMD at 36 weeks, ABPM at 12 and 36 weeks, lipid profile, CETP mass and activity, and markers of inflammation, oxidation, and cardiovascular risk. Clinical endpoints are assessed as a composite endpoint for the dal-HEART Program.

CURRENT STATUS

In 19 European clinical centres, 476 subjects met inclusion criteria and have entered the study. In conclusion, the dal-VESSEL study is the largest multicentre trial with brachial FMD ever performed. The study assesses efficacy and safety of dalcetrapib on endothelial function, blood pressure, lipids, and clinical outcomes in CHD patients with below average HDL-C and will therefore provide vital information regarding its potential role in the preventative treatment of CHD risk.

Cigarette smoke enhances abdominal aortic aneurysm formation in angiotensin II-treated apolipoprotein E-deficient mice

Cigarette smoke, hyperlipidemia, and hypertension with the risk of development and progression of atherosclerosis and associated pathologies such as abdominal aortic aneurysm (AAA) are correlated. We examined the interaction of cigarette mainstream smoke (MS) and angiotensin-II (Ang II)-induced hypertension in the atherosclerotic process using hyperlipidemic apolipoprotein E-knockout (ApoE(-/-)) mice. ApoE(-/-) mice were treated with Ang II for 4 weeks and then further exposed to MS or to fresh air for 4 weeks. AAA formation was observed in all mice treated with Ang II, regardless of smoke exposure; however, smoke exposure increased the incidence of AAA in these mice. Ang II treatment resulted in higher gene expression of matrix metalloproteinases (MMP)-2, -3, -8, -9, and -12 in the abdominal aortas, which was further increased by MS exposure. The proteolytic activity of MMP-2 and MMP-9 was also enhanced in Ang II-treated mice exposed to MS, but only minor changes were seen with either smoke exposure or Ang II treatment alone. This study shows for the first time that both formation and severity of AAA in hypertensive ApoE(-/-) mice are accelerated by exposure to MS and that the proteolytic activity of MMPs is enhanced by the combination of Ang II and MS.

Upregulation of the apelin-APJ pathway promotes neointima formation in the carotid ligation model in mouse

AIMS

To investigate apelin-APJ (angiotensin receptor-like 1) signalling in vascular remodelling, we have examined the pathophysiological response to carotid ligation in apelin knockout mice.

METHODS AND RESULTS

Apelin null animals compared with wild-type mice had significantly decreased neointimal lesion area (1.17 +/- 0.17 vs. 3.33 +/- 1.04 x 10(4) microm(2), P < 0.05) and intima/media ratio (0.81 +/- 0.23 vs. 1.49 +/- 0.44, P < 0.05), averaged over four sites 0.5-2 mm from the ligation. Exogenous apelin infusion rescued the apelin-KO phenotype, promoting neointima formation in the null animals. Apelin null animals showed decreased smooth muscle positive area in the neointima (82.3 +/- 2.4 vs. 63.9 +/- 8.4, P < 0.05), and a smaller percentage BrdU positive cells in the neointima and media (11.06 +/- 1.00 vs. 6.53 +/- 0.86, P < 0.05). Apelin mRNA expression increased initially (5.2-fold, P < 0.01) followed by increased apelin receptor expression (10.1-fold, P < 0.05) in the ligated artery. Cytochemistry studies localized apelin expression to luminal endothelial cells and apelin receptor upregulation to smooth muscle cells (SMC) in the media and neointima. In vitro experiments with cultured rat aortic SMC revealed that apelin stimulation increased migration. In contrast to the increased expression of apelin and apelin receptor in carotid remodelling, expression was not upregulated in the apoE high fat model, and correlated with the known disease-inhibitory effect in this model.

CONCLUSION

These data suggest that increased apelin receptor expression by SMC provides a paracrine pathway in injured vessels that allows endothelial-derived apelin to stimulate their division and migration into the neointima.

Vascular wall ACE is not required for atherogenesis in ApoE(-/-) mice

BACKGROUND

It has been proposed that elements of the renin angiotensin system expressed in the arterial wall are critical for the development of atherosclerosis. Angiotensin converting enzyme (ACE) is highly expressed by the endothelium and is responsible for a critical enzymatic step in the generation of angiotensin II. However, the functional contribution of ACE expression in the vascular wall in atherogenesis is unknown. Therefore, we made use of unique genetic models in which mice without the expression of ACE in the vascular wall were crossed with ApoE(-/-) mice in order to determine the contribution of tissue ACE expression to atherosclerotic lesion formation.

METHODS AND RESULTS

Mice expressing either a soluble form of ACE (ACE 2/2) or mice with somatic ACE expression restricted to the liver and kidney (ACE 3/3) on an ApoE(-/-) background were placed on a standard chow or Western diet for 6 months. Atherosclerotic lesion area in the ACE 2/2 mice was significantly lower than that seen in the ACE 3/3 mice. However, these animals also had significantly lower blood pressure and reduced plasma ACE activity which precluded establishing a specific causal relationship between absent tissue ACE activity and decreased atherosclerotic lesion extent. Therefore, we studied the ACE 3/3 mice which are normotensive and lack vascular ACE expression. In the ACE 3/3 animals, atherosclerotic lesion area was not different from wild type controls despite reduced plasma ACE activity.

CONCLUSIONS

We concluded that under these experimental conditions, expression of ACE in the arterial wall is not required for atherosclerotic lesion formation.

Effect of delapril/manidipine vs olmesartan/ hydrochlorothiazide combination on insulin sensitivity and fibrinogen in obese hypertensive patients

OBJECTIVE

To compare the effect of delapril/manidipine vs olmesartan/hydrochlorothiazide (HCTZ) combination on insulin sensitivity and plasma fibrinogen in obese hypertensive patients.

PATIENTS AND METHODS

After a 4-week placebo period, 88 obese, hypertensive (DBP >95 and <110 mmHg) outpatients were randomized to delapril 30 mg/manidipine 10 mg combination or to olmesartan 20 mg/HCTZ 12.5 mg combination for 24 weeks according to a prospective, randomized, open-label, blinded endpoint, parallel group design. At the end of the placebo period and treatment period, clinical BP, fasting plasma glucose (FPG), plasma insulin, insulin sensitivity (by euglycemic hyperinsulinemic clamp) and plasma fibrinogen were evaluated. Insulin sensitivity was expressed as the amount of glucose infused during the last 30 minutes (glucose infusion rate, GIR) in mg/Kg/min. The total glucose requirement (TGR) to maintain a steady-state blood glucose level in response to a defined increase in plasma insulin concentration was also evaluated.

RESULTS

Both combinations significantly reduced SBP/DBP values (-22.3/16.4 mmHg and -22.6/17.2 mmHg, respectively, all p <0.001 vs placebo). GIR was significantly increased only by delapril/manidipine (+3.01 mg/min/Kg, p=0.038 vs placebo), the difference between treatments being significant (p <0.05). TGR was significantly increased by delapril/manidipine (+9.7 g, p=0.034), while it was unaffected by olmesartan/HCTZ. Plasma insulin as well as fibrinogen were significantly reduced by delapril/manidipine (-17.8 pmol/l, p=0.047 and -67.5 mg/dl, p=0.021, respectively), but not by olmesartan/HCTZ, the difference between the two treatments being statistically significant (p <0.05).

CONCLUSION

In obese hypertensive patients the delapril/manidipine combination but not the olmesartan/HCTZ combination significantly decreased insulin resistance and plasma fibrinogen levels, despite the similar BP lowering efficacy.

NOX1 Deficiency Protects From Aortic Dissection in Response to Angiotensin II

Oxidative stress leads to vascular damage and participates in the pathomechanisms of aortic dissection and aneurysm formation. Here we study aortic dissection in mice deficient in the superoxide-generating reduced nicotinamide-adenine dinucleotide phosphate oxidase NOX1. Seven days of treatment with the hypertensive agent angiotensin II (3 mg/kg per day) led to aortic dissection in 23% of wild-type C57BL/6J mice but in only 4% of NOX1-deficient mice (P=0.05). In contrast, treatment of wild-type C57BL/6J mice with the hypertensive agent norepinephrine (12 mg/kg per day), did not lead to aortic dissection or sudden death, suggesting that hypertension is not sufficient to cause aortic dissection. Interestingly, norepinephrine-dependent blood pressure elevations were conserved in NOX1-deficient mice, demonstrating that, different from angiotensin II, it acts through NOX1-independent hypertensive mechanisms. The resistance of NOX1-deficient mice to angiotensin II-induced aortic dissection suggests a role for NOX1-dependent alterations of the vascular wall. We, therefore, studied gene expression and protease/inhibitor equilibrium. cDNA array analysis demonstrated differential effects of angiotensin II on gene expression in wild-type and NOX1-deficient mice. Tissue inhibitor of metalloproteinase 1 was increased both on the mRNA and the protein level in aortas from NOX1-deficient mice. Thus, our results demonstrate that NOX1 is involved in the mechanisms of angiotensin II-dependent aortic dissection. As one underlying mechanism, we have identified NOX1-dependent suppression of tissue inhibitor of metalloproteinase 1 expression, which could lead to tissue damage through an altered protease/inhibitor balance.

Inflammation and the metabolic syndrome: role of angiotensin II and oxidative stress

Excess body weight, high blood pressure, and insulin resistance together have been denominated the metabolic syndrome. In this review, we analyze the potential role of angiotensin II (Ang II) and reactive oxygen species in mediating inflammation in the metabolic syndrome. Ang II induces pro-inflammatory genes and other pro-inflammatory substances and increases oxidative stress that could damage endothelium, myocardium, and renal tissue. Activation of nuclear factor-kappaB and NAD(P)H oxidase are fundamental steps in these pro-inflammatory mechanisms in which intramitochondrial oxidative stress could play a critical role. This sequence of events might explain why reduction in Ang II synthesis by angiotensin-converting enzyme inhibitors (ACEIs) and Ang II type 1 (AT1) receptor blockers (ARBs) have a protective effect against cardiovascular disease.

In vivo evidence for a role of adipose tissue SR-BI in the nutritional and hormonal regulation of adiposity and cholesterol homeostasis

OBJECTIVES

This study examines the role of insulin and angiotensin II in high-density lipoprotein (HDL) metabolism by focusing on the regulation and function of scavenger receptor type-BI (SR-BI) in adipose tissue.

METHODS AND RESULTS

Insulin or angiotensin II injection in wild-type mice induced a decrease in circulating HDL and it was associated with the translocation of SR-BI from intracellular sites to the plasma membrane of adipose tissue. Refeeding upregulated adipose HDL selective cholesteryl esters uptake and SR-BI proteins through transcriptional and posttranscriptional mechanisms. This occurred along with a decrease in serum HDL and an increase in adipose cholesterol content. Similar results were obtained with transgenic mice overexpressing locally angiotensinogen in adipose tissue. In adipose 3T3-L1 cell line, HDL induced lipogenesis by increasing liver X receptor binding activity. This mechanism was dependent of insulin and angiotensin II.

CONCLUSIONS

Our results raise the possibility that adipose tissue SR-BI translocation might be a link between adipose tissue lipid storage and HDL clearance.

The altered homeostatic theory: A hypothesis proposed to be useful in understanding and preventing ischemic heart disease, hypertension, and diabetes – including reducing the risk of age and atherosclerosis

Evidence will be presented to support the usefulness of the altered homeostatic theory in understanding basic pathogenetic mechanisms of ischemic heart disease (IHD), hypertension, and diabetes, and in improving prevention of these disorders. The theory argues that: IHD, hypertension, and diabetes share the same basic pathogenesis; risk factors favor a sympathetic homeostatic shift; preventative factors favor a parasympathetic homeostatic shift; risk and preventative factors oppose each other through a dynamic risk/prevention balance; and prevention should be based on improving the risk/prevention balance. Prevention based on improving the risk/prevention balance should be more effective, as this method is regarded as reflecting more accurately basic pathogenetic mechanisms. As example, the theory argues that the risk of supposedly nonmodifiable risk factors as age and the risk of relatively nonmodifiable atherosclerosis can be reduced significantly. The possible validity of the altered homeostatic theory was tested by a study based on multiple associations. Findings support a common pathogenesis for IHD, hypertension, and diabetes based on a sympathetic homeostatic shift, and the usefulness of prevention based on improving the risk/prevention balance by using standard pharmaceutical and lifestyle preventative measures. The same set of multiple and diverse risk factors favored IHD, hypertension, and diabetes, and the same set of multiple and diverse pharmaceutical and lifestyle preventative measures prevented these disorders. Also, the same set of preventative agents generally improved cognitive function and bone density, and reduced the incidence of Alzheimer's disease, atrial fibrillation, and cancer. Unexpectedly, evidence was developed that four major attributes of sympathetic activation represent four major risk factors; attributes of sympathetic activation are a tendency toward thrombosis and vasoconstriction, lipidemia, inflammation, and hyperglycemia, and corresponding risk factors are endothelial dysfunction (which expresses thrombosis/vasoconstriction and epitomizes this tendency), dyslipidemia, inflammation, and insulin resistance. These findings, plus other information, provide evidence that dyslipidemia acts mainly as a marker of risk of IHD, rather than being the basic mechanism of this disorder. However, prevention generally is based solely on improvement of dyslipidemia; basing prevention on dyslipidemia relatively underemphasizes the importance of other significant risk factors and, by certifying its validity, discourages alternate pathogenetic approaches. Also, development of myocardial infarction is approached differently. It seems generally accepted that dyslipidemia results rather automatically in infarction through the sequence of atherosclerosis, atherosclerotic complications, and thrombosis. In contrast, distinction is made between development of atherosclerosis and acute induction of infarction--where atherosclerosis is only one of multiple risk factors.

Angiotensin II induces IL-6 expression and the Jak-STAT3 pathway in aortic adventitia of LDL receptor-deficient mice

Angiotensin II (A-II), the major effector peptide of the renin angiotensin system potently accelerates progression of atherosclerosis. To investigate its effects on vascular inflammatory mechanisms, we elucidated vascular cytokine expression during early lesion development in A-II-infused atherosclerosis-prone LDLR-/- mice. Male LDLR-/- mice were placed on a "Western" high-fat diet for 4 weeks, followed by sham or A-II infusion for 7 weeks. Equal blood pressures and elevations in serum lipids were seen in both groups. Mice were sacrificed when significant A-II-induced plaque development was first detectable, aortae were explanted and culture media assayed for secreted cytokines. Nine cytokines were significantly induced with interleukin-6 (IL-6) being the most highly secreted. Local IL-6 production was confirmed by in situ mRNA hybridization and immunostaining, where the most abundant IL-6 was found in the aortic adventitia, with lesser production by the medial and intimal layers. Immunofluorescence colocalization showed IL-6 expression by fibroblasts and activated macrophages. Activation of downstream IL-6 signaling mediated by the Jak-STAT3 pathway was demonstrated by inducible phospho-Tyr705-STAT3 formation in the adventitia and endothelium (of IL-6+/+ mice only). These findings define cytokine profiles in the A-II infusion model and demonstrate that IL-6, produced by activated macrophages and fibroblasts in the adventitia, induces the Jak-STAT3 pathway during early A-II-induced atherosclerosis.

Anti-diabetic effect of blockade of the renin-angiotensin system

Diabetes, which is frequently associated with hypertension, accelerates the development of hypertension-induced cardiovascular disease. Thus, the prevention of diabetes is important in the management of hypertension. Recent clinical megastudies have suggested that the blockade of the renin-angiotensin system (RAS) by angiotensin-converting enzyme (ACE) inhibitors and angiotensin II receptor blockers (ARBs) inhibits new onset of diabetes. Thus, the agents to inhibit the RAS should be beneficial for glucose metabolism. However, the cardiovascular protective effects of ACE inhibitors and ARBs are not always superior to other classes of drugs. Further long-term clinical trials are necessary to clarify the anti-diabetic effect of the RAS-inhibiting agents.

Essential role of PKC-zeta in normal and angiotensin II-accelerated neointimal growth after vascular injury

The contribution of atypical protein kinase C (PKC)-zeta to ANG II-accelerated restenosis after endoluminal vascular injury was investigated by using the rat carotid balloon injury model. Exposure of injured arteries to ANG II resulted in an extensive neointimal thickening (1.9 times) compared with vehicle at day 14. Treatment with PKC-zeta antisense, but not scrambled, oligonucleotides reduced neointimal formation observed in the presence or absence of ANG II. Examination of early events (2 days) after injury showed an increase in cellularity in the perivascular area of the artery wall that was transferred to the adventitia and media after exposure to ANG II, events blocked by PKC-zeta antisense, but not scrambled, oligonucleotides. A positive correlation between medial cellularity at day 2 and extent of neointimal growth at day 14 was established. Immunohistochemical analysis showed that upregulation of inflammatory markers after injury, as well as infiltration of ED1(+) monocytes/macrophages from the perivascular area to the adventitia, was accelerated by ANG II. However, ANG II-stimulated medial increase in cellularity was proliferation independent, and these cells were monocyte chemoattractant protein-1(+)/vimentin(+) but ED1(-)/VCAM(-). PKC-zeta is degraded after injury, and inhibition of its neosynthesis in medial vascular smooth muscle cells or in infiltrating cells with PKC-zeta antisense attenuated medial cellularity and expression of inflammation mediators without reversing smooth muscle cell dedifferentiation. Together, these data indicate that PKC-zeta plays a critical role in normal and ANG II-accelerated neointimal growth through a mechanism involving upregulation of inflammatory mediators, leading to cell infiltration in the media of the vascular wall.

The proinflammatory actions of angiotensin II are dependent on p65 phosphorylation by the IkappaB kinase complex

The vasoactive hormone angiotensin II (Ang II) probably triggers inflammatory cardiovascular diseases by activating transcription factors such as NF-kappaB. We describe here a novel mode of NF-kappaB activation in cultured vascular smooth muscle cells exposed to Ang II. Ang II treatment resulted in an increase in the phosphotransferase activity of the IKK complex, which was mediated through the AT1 receptor subtype. The typical phosphorylation and proteasome-dependent degradation of the NF-kappaB inhibitor IkappaBalpha were not observed. Rather, Ang II treatment of vascular smooth muscle cells led to the phosphorylation of p65 on serine 536, a signal detected in both the cytoplasm and the nuclear compartments. The use of pharmacological inhibitors that inhibit the activation of MEK by Ang II revealed that phosphorylation of p65 on serine 536 did not require the MEK-ERK-RSK signaling pathway. On the other hand, specifically targeting the IKKbeta subunit of the IKK complex by overexpression of a dominant negative version of IKKbeta (IKKbeta K44A) or silencing RNA technology demonstrated that the IKKbeta subunit of the IKK complex was responsible for the detected phosphoserine 536 signal in Ang II-treated cells. Characterization of the signaling pathway leading to activation of the IKK complex by Ang II revealed that neither epidermal growth factor receptor transactivation nor the phosphatidylinositol 3-kinase-AKT signaling cascade were involved. Collectively, our data demonstrate that the proinflammatory activity of Ang II is independent of the classical pathway leading to IkappaBalpha phosphorylation and degradation but clearly depends on the recruitment of an IKK complex signaling cascade leading to phosphorylation of p65 on serine 536.

Decreased blood pressure in NOX1-deficient mice

To understand the role of the superoxide-generating NADPH oxidase NOX1 in the vascular system, we have generated NOX1-deficient mice. NOX1-deficient mice had a moderately decreased basal blood pressure. In response to angiotensin II they showed an almost complete loss of the sustained blood pressure response, while the initial increase was conserved. NOX1-deficient mice showed a marked reduction in aortic media hypertrophy. Angiotensin II-induced smooth muscle cell proliferation was conserved, but there was a marked decrease in extracellular matrix accumulation. Our results establish a role for NOX1 in blood pressure regulation and vascular angiotensin II response.

Antiatherogenic effects of angiotensin receptor antagonism in mild renal dysfunction

Angiotensin II (Ang II) increases atherosclerotic cardiovascular disease. Renal damage that is characterized by activation of Ang II markedly potentiates the risk for atherosclerosis, even in the setting of subtle renal impairment. Therefore, whether antagonism of Ang II actions can modify atherosclerosis in a model of mild renal impairment was examined. Apolipoprotein E-deficient spontaneously hyperlipidemic mice underwent uninephrectomy (UNx) or sham operation (sham) followed by treatment with Ang II receptor antagonist losartan or hydralazine for 12 wk. While UNx did not increase the serum creatinine levels, BP and lipids were higher in UNx mice than in age-matched sham controls with intact kidneys. UNx caused a dramatic increase in the extent and the number of atherosclerotic lesions together with greater macrophage-positive area and more disruption in the elastin component of the extracellular matrix versus sham. Ang II antagonism dramatically decreased the UNx-induced acceleration in atherosclerosis in association with decreased macrophage content, linked to decreased macrophage migration in vitro with losartan but not with hydralazine. Aortae of mice treated with Ang II antagonism had fewer elastin breaks together with less immunostaining for the powerful elastolytic enzyme cathepsin S. None of these benefits was observed in the hydralazine-treated mice despite equivalent reduction in BP. These findings support an important role for endogenous Ang II in accelerated atherosclerosis in renal dysfunction and offer a therapeutic intervention with particular benefit in this setting through mechanisms that include reduced vascular macrophage infiltration and preservation of the elastin component of extracellular matrix.

Role of the renin-angiotensin system in the endocrine pancreas: implications for the development of diabetes

Activation of the renin-angiotensin system has a pivotal role in the pathogenesis of diabetic complications. However, recent evidence suggests that it may also contribute to the development of diabetes itself. In the endocrine pancreas, all the components of an active renin-angiotensin system are present, which modulate a range of activities including local blood flow, hormone release and prostaglandin synthesis. In both types 1 and 2 diabetes, there is an up-regulation of its expression and activity in the endocrine pancreas. Whether these changes have a direct pathogenetic role or reflect a response to local stress or tissue injury remains to be established. Angiotensin-mediated increases in oxidative stress, inflammation and free fatty acids levels potentially contribute to beta-cell dysfunction in diabetes. In addition, activation of the renin-angiotensin system appears to potentiate the action of other pathogenic pathways including glucotoxicity, lipotoxicity and advanced glycation. In experimental models of type 2 diabetes, blockade of the renin-angiotensin system with angiotensin converting enzyme inhibitors or angiotensin receptor antagonists results in the improvement of islet structure and function. Moreover, the incidence of de novo diabetes appears to be significantly reduced by blockade of the renin-angiotensin system in clinical studies. At least two large controlled trials are currently underway to study the role of renin-angiotensin system in the development of diabetes. It is hoped that these studies will demonstrate the true potential of the blockade of the renin-angiotensin system for the prevention of diabetes.

Antihypertensive drugs and incidence of type 2 diabetes: Evidence and implications for clinical practice

The major antihypertensive drug classes appear to exert differing effects on glycemic control and diabetes incidence. Thiazide diuretic and beta-blockers are potentially diabetogenic, whereas calcium channel blockers appear neutral. Inhibitors of the renin-angiotensin system are associated with improvements in glycemic control and may lower diabetes incidence, but it is not clear if this represents a truly preventive effect. Also, it should be noted that previous studies have reported inconsistent results, and the data to date are not definitive. We suggest that inhibitors of the renin-angiotensin system be used as first-line agents in uncomplicated hypertensive patients who are at high risk for developing type 2 diabetes. Thiazides and beta-blockers should not be avoided in patients with compelling indications for these drugs. Many hypertensive patients (particularly those who are obese or have prediabetes) require several agents to achieve target blood pressure levels. Therefore, the choice of initial agent is far less important than ensuring that target blood pressure goals are reached.

Endothelial dysfunction: its role in hypertensive coronary disease

PURPOSE OF REVIEW

Coronary artery disease is the major cause of death worldwide. Hypertension is a major risk factor for developing coronary disease. It is now recognized that endothelial dysfunction is an early marker of coronary artery disease before structural changes to the vessel wall are apparent on angiography or intravascular ultrasound and that it has a prognostic value in predicting cardiovascular events in hypertensive patients. This review addresses recent developments in hypertension-induced endothelial dysfunction.

RECENT FINDINGS

Hyperaldosteronism causes endothelial dysfunction independent of high blood pressure. Exaggerated exercise blood pressure response has been related to endothelial dysfunction. Cyclosporin-A-induced endothelial dysfunction is related to reduced cholesterol content in caveolae. Chronic kidney disease induces changes in caveoli-1 and thus contributes to the reduced nitric oxide bioavailability, and causes oxidative stress independent of the high blood pressure. Asymmetric dimethylarginine plays a role in endothelial dysfunction in hypertensive patients independent of insulin resistance. 20-Hydroxyeicosatetraenoic acid is an independent predictor of hypertension in postmenopausal women. Endothelial dysfunction precedes and predicts the development of hypertension in postmenopausal women. Oral treatment with L-arginine improves endothelial dysfunction in hypertensives and lowers the blood pressure.

SUMMARY

The pathophysiology of endothelial dysfunction in hypertension is multifactorial. Recent findings have contributed to our understanding of mechanisms of endothelial dysfunction and support a role for early intervention to prevent irreversible vascular and organ damage.

Angiotensin II down-regulates the SR-BI HDL receptor in proximal tubular cells

BACKGROUND

The kidney plays an important role in the metabolism of lipoproteins, but renal cells are also a target of lipids under pathophysiological conditions contributing to organ damage and progression of disease. The majority of studies has focused on the interaction of renal cells with low-density lipoproteins. Relatively little is known of potential metabolism of high-density lipoproteins (HDL) on renal cells However, diverse pathophysiological situations, such as the nephrotic syndrome and acute renal injury, may be associated with an activated renin-angiotensin system as well as altered renal handling of HDL. Therefore, the present study sought to gain insight into the expression of the HDL receptor scavenger receptor class B type I (SR-BI) in cultured renal cells and a potential regulation by angiotensin II (ANG II).

METHODS

Different renal cells lines and primary cultures (proximal tubular and mesangial cells) were screened by western blot for the expression of SR-BI. MCT cells, a mouse proximal tubular cell line, were selected for further studies. SR-BI protein and mRNA expression were determined after treatment with various doses of ANG II in the presence or absence of AT(1)- or AT(2)-receptor blocker. Uptake of HDL-associated cholesteryl ester into MCT cells was determined. Finally, rats were infused intraperitoneally with ANG II for 3-7 days, proximal tubules were isolated by differential centrifugation and SR-BI protein expression was assessed. Results. SR-BI protein was expressed in various primary cultures and permanent renal cell lines. ANG II (10(-10)-10(-6) M) treatment for 24 h induced a significant down-regulation of SR-BI protein and mRNA expression in MCT cells. This suppression was attenuated by an AT(1)-receptor antagonist whereas an AT(2)-blocker was without effect. MCT cells revealed a high selective uptake of HDL cholesteryl ester that was significantly higher than that in syngeneic mesangial cells. ANG II for 24 h significantly reduced this selective HDL cholesteryl ester uptake into MCT, but not mesangial cells. Finally, ANG II- infusion into rats for 3 and 7 days induced a significant decrease of SR-BI protein expression in isolated tubules.

CONCLUSIONS

Our data show that ANG II mediates down-regulation of SR-BI expression on proximal tubular cells in vivo and in vitro. However, the effects were small and additional experiments are necessary to confirm these first observations. The attenuated SR-BI expression is functionally relevant and associated with a decrease in cholesteryl ester uptake. ANG II-mediated suppression may contribute to various pathophysiological situations, such as acute tubular injury, the nephrotic syndrome and atherosclerosis.

Pigment epithelium-derived factor (PEDF) blocks angiotensin II signaling in endothelial cells via suppression of NADPH oxidase: a novel anti-oxidative mechanism of PEDF

Angiotensin II (Ang II), the dominant effector of the renin-angiotensin system, regulates numerous inflammatory-proliferative responses in vascular wall cells and is thus involved in atherosclerosis. We have previously shown that pigment epithelium-derived factor (PEDF) inhibits advanced glycation end-product-induced pericyte apoptosis, thereby exerting beneficial effects on diabetic retinopathy. However, a role for PEDF in vascular inflammation and atherosclerosis remains to be elucidated. In this study, we have examined whether PEDF inhibits the Ang-II-induced endothelial cell (EC) activation in vitro and the way that it might achieve this effect. Ang II significantly induced redox-sensitive transcriptional factor NF-kappaB activation and subsequent monocyte chemoattractant protein-1 expression in human umbilical vein ECs (HUVEC), both of which were completely inhibited by PEDF or the anti-oxidant N-acetylcysteine. PEDF or diphenylene iodonium, an inhibitor of NADPH oxidase, inhibited Ang-II-induced intracellular reactive oxygen species (ROS) generation in HUVEC. Furthermore, PEDF inhibited Ang-II-induced up-regulation of mRNA levels of p22phox, Nox4, and gp91phox/Nox2, which are membrane components of NADPH oxidase, and its enzymatic activity in HUVEC. Antisense, but not sense, DNAs against p22phox, Nox4, or gp91phox/Nox2 were found significantly to inhibit Ang-II-induced ROS generation in HUVEC. These results demonstrate that PEDF inhibits Ang-II-induced EC activation by suppressing NADPH-oxidase-mediated ROS generation and that PEDF may play a protective role in the development and progression of atherosclerosis.

Why blockade of the renin–angiotensin system reduces the incidence of new-onset diabetes

Recent trials have suggested that inhibitors of the renin-angiotensin system (RAS), such as angiotensin-converting enzyme (ACE) inhibitors and angiotensin II receptor blockers (ARBs), may reduce the incidence of new-onset diabetes in patients with or without hypertension and at high risk of developing diabetes. In this review, we critically evaluate the evidence from recent clinical trials for such a potential preventive effect of ACE inhibitors and ARBs, including a meta-analysis of these recent trials. The reduced incidence of diabetes in patients at high risk of developing diabetes by ACE inhibitors or ARBs has been explained by haemodynamic effects, such as improved delivery of insulin and glucose to the peripheral skeletal muscle, and non-haemodynamic effects, including direct effects on glucose transport and insulin signalling pathways, all of which decrease insulin resistance. There is now evidence that the pancreas may contain an in situ active RAS, which appears to be upregulated in an animal model of type 2 diabetes. Thus, ACE inhibitors and ARBs may act by attenuating the deleterious effect of angiotensin II on vasoconstriction, fibrosis, inflammation, apoptosis and beta-cell death in the pancreas, thereby protecting a critical beta-cell mass essential for insulin production. New evidence is presented that ACE inhibitors and ARBs may delay or prevent the development of insulin resistance and diabetes, for which novel mechanisms are suggested. The actions of agents that interrupt the RAS on insulin resistance, obesity and diabetes warrant further investigation in other animal models. Prospective clinical studies with the primary endpoint of the prevention of diabetes are now indicated to (i) further explore whether the inhibitors of the RAS are superior compared to other antihypertensive agents such as calcium channel blockers (CCBs) and (ii) to evaluate the potential beneficial effects of combination antihypertensive regimens on the development of diabetes.

Inflammation is a crucial feature of atherosclerosis and a potential target to reduce cardiovascular events

Contrary to popular opinion, atherosclerosis is not a disease unique to modern civilization. In fact, atherosclerotic lesions have been found in the arteries of mummies dating back to 1,500 B.C., and yet our understanding of this complex process is still evolving. A fusion of basic science advances and clinical research findings has radically altered our traditional concepts about the pathogenesis and treatment of the clinical complications of atherosclerosis. Most physicians previously regarded the artery as a being merely a blood conduit that became encrusted with lipid detritus as part of the aging process. Modern-day treatment of atherosclerosis has arisen primarily from an understanding of the epidemiology of the disease rather than its pathophysiology, in that risk factors have traditionally been targeted. Our concepts of atherogenesis have evolved from vague ideas of inevitable degeneration to a much better defined scenario of molecular and cellular events. As we enhance our understanding of its fundamental mechanism, we can begin to approach atherogenesis as a modifiable rather than ineluctable process. Indeed, as we recognize now that inflammation plays a pivotal role in the process of atherosclerosis, it is noteworthy to evaluate the effect of modern therapies on this facet of the disease.