Novel mechanisms linking angiotensin II and early atherogenesis

Decreased toll-like receptor 4 and CD11b/CD18 expression on peripheral monocytes of hypertensive patients correlates with a lesser extent of endothelial damage: a preliminary study

BACKGROUND

Low-grade chronic inflammation is recognized to contribute to the physiopathology of arterial hypertension. Therefore, this study aimed to assess the pro-inflammatory phenotype of peripheral monocytes of hypertensive patients by analyzing Toll-like receptor 4 (TLR4) and CD11b/CD18 surface expression. In the second part, the influence of phenotypic alterations of monocytes on the endothelial status reflected by circulating endothelial cells (CECs) was evaluated.

PATIENTS

The study included 60 patients with arterial hypertension, who were divided into two subgroups based on the disease severity according to the applicable criteria. The mild hypertension and resistant hypertension groups included 30 patients each. The control group consisted of 33 normotensive volunteers matched for age and sex.

RESULTS

Both in the entire group of patients and individual subgroups, reduced surface expression of TLR4 and CD11b/CD18 was found compared to normotensive volunteers. A reduced percentage of monocytes with the CD14 + TLR4 + immunophenotype was correlated with a lower MFI level of CD18 and CD11b in the entire group of patients and after division only in the mild hypertension group. Reduced surface expression of TLR4 in hypertensive patients correlated with a lower number of CECs. This relationship was not observed in the resistant hypertension group; instead, an independent effect of reduced CD11b/CD18 expression on the reduction of CEC number was demonstrated.

CONCLUSION

Our preliminary study showed for the first time that hypertension of varying severity is accompanied by phenotypic changes in monocytes, manifested by reduced surface expression of both TLR4 and CD11b/CD18. These phenotypic changes were associated with a reduced degree of endothelial injury. Our study opens a new, unexplored area of research on the protective features of peripheral monocytes in hypertension.

Phosphatidylinositol-4,5-Bisphosphate Binding to Amphiphysin-II Modulates T-Tubule Remodeling: Implications for Heart Failure

BIN1 (amphyphysin-II) is a structural protein involved in T-tubule (TT) formation and phosphatidylinositol-4,5-bisphosphate (PIP2) is responsible for localization of BIN1 to sarcolemma. The goal of this study was to determine if PIP2-mediated targeting of BIN1 to sarcolemma is compromised during the development of heart failure (HF) and is responsible for TT remodeling. Immunohistochemistry showed co-localization of BIN1, Cav1.2, PIP2, and phospholipase-Cβ1 (PLCβ1) in TTs in normal rat and human ventricular myocytes. PIP2 levels were reduced in spontaneously hypertensive rats during HF progression compared to age-matched controls. A PIP Strip assay of two native mouse cardiac-specific isoforms of BIN1 including the longest (cardiac BIN1 #4) and shortest (cardiac BIN1 #1) isoforms as well human skeletal BIN1 showed that all bound PIP2. In addition, overexpression of all three BIN1 isoforms caused tubule formation in HL-1 cells. A triple-lysine motif in a short loop segment between two helices was mutated and replaced by negative charges which abolished tubule formation, suggesting a possible location for PIP2 interaction aside from known consensus binding sites. Pharmacological PIP2 depletion in rat ventricular myocytes caused TT loss and was associated with changes in Ca²⁺ release typically found in myocytes during HF, including a higher variability in release along the cell length and a slowing in rise time, time to peak, and decay time in treated myocytes. These results demonstrate that depletion of PIP2 can lead to TT disruption and suggest that PIP2 interaction with cardiac BIN1 is required for TT maintenance and function.

Targeting inflammation to slow or delay functional decline: where are we?

The role of inflammation in the pathophysiology of chronic age-related diseases is increasingly recognized, and inflammation could represent the common pathway linking diseases and disability. Thus, targeting inflammation could represent a useful strategy at preventing or delaying functional decline. In this paper we review recent evidence suggesting that selected drugs, such as statins, fibrates, angiotensin converting enzyme-inhibitors and angiotensin receptor blockers, and physical exercise may be able to contrast functional decline by blunting inflammation. Results from randomized trials investigating the effects of physical activity programs on inflammation and functional decline is still limited, and further investigations are warranted.

Burden of illness among patients at high risk versus low risk for major cardiovascular events

OBJECTIVE

This study was designed to compare the burden of illness (BOI) in patients at high risk versus low risk of developing a major cardiovascular (CV) event.

METHODS

This retrospective claims data analysis included commercial health plan members identified with a primary diagnosis on a medical claim for cardiovascular disease (CVD) from January 1, 2001 through December 31, 2002. Patients were categorized as: low risk (LR), high risk (HR), or high risk aged≥55 (HR55), based on the ONTARGET clinical trial.

RESULTS

Most patients (85%) were in the LR category (8% in HR55, 7% in HR). A significantly greater proportion of patients in the HR55 group were hospitalized and experienced a greater number of ambulatory visits compared with LR and HR patients. Controlling for covariates, HR55 patients averaged $22,502 in paid healthcare services over 2 years versus $15,645 for HR patients and $11,423 for LR patients (p<0.001). CV-related costs represented about 46% of costs for the HR55 group, versus 41% for the HR group and 31% for the LR group.

LIMITATIONS

Claims data are collected for the purpose of payment and not research and the presence of a diagnosis code is not proof of disease, due to possible coding errors or the use of a rule-out criterion. Also, patients who died in the follow-up were not included in the analyses, resulting in lower BOI estimates. Finally, the results of this study reflect treatment of CVD in managed-care settings, and may not be applicable to a different type of population.

CONCLUSION

This study demonstrates the high BOI associated with CVD, especially for patients within the high-risk group aged≥55 years. Opportunities exist for reducing costs in this population.

Effect of angiotensin receptor blockade on endothelial function: focus on olmesartan medoxomil

Endothelial dysfunction is the common link between cardiovascular disease risk factors and the earliest event in the cascade of incidents that results in target organ damage. Angiotensin II, the terminal pressor effector arm of the renin-angiotensin-aldosterone system, increases blood pressure (BP) by vasoconstriction and sodium and fluid retention, and has a pro-oxidative action that induces endothelial dysfunction and contributes to vascular remodeling. Angiotensin receptor blockers (ARBs) reduce BP and morbidity and mortality in patients with hypertension, ventricular hypertrophy, diabetes mellitus, and renal disease. Olmesartan medoxomil is a long-acting, well-tolerated, effective ARB that prevents or reverses endothelial dysfunction in animal models of atherosclerosis, hypertension, diabetes, nephropathy, and retinopathy. Olmesartan medoxomil, a prodrug of olmesartan approved for the treatment of hypertension, has been shown to ameliorate endothelial dysfunction in patients with hypertension or diabetes. In randomized studies, the drug reduces vascular inflammation and the volume of large atherosclerotic plaques, increases the number of regenerative endothelial progenitor cells in the peripheral circulation, improves endothelium-dependent relaxation, and restores the normal resistance vessel morphology. Importantly, the impact of olmesartan medoxomil on endothelial dysfunction is thought to be independent of BP lowering.

Angiotensin II AT1 blockade reduces the lipopolysaccharide-induced innate immune response in rat spleen

ANG II AT(1) receptor blockade reduces inflammation in hypertension. To determine whether ANG II AT(1) receptor blockers (ARBs) influence the innate immune inflammatory response in normotensive rats, we studied rat plasma and spleen after a 3-day subcutaneous pretreatment with the ARB candesartan followed by a single dose of the bacterial endotoxin LPS (50 microg/kg ip). Peripheral administration of LPS to rodents produced a generalized inflammatory response with increased release of TNF-alpha, IL-1beta, and IL-6 into the circulation. Candesartan pretreatment reduced the LPS-induced release of TNF-alpha, IL-1beta, and IL-6 into the circulation. The red pulp of rat spleen expressed large numbers of AT(1) receptors and the LPS receptors Toll-like receptor 4 and CD14. Candesartan administration significantly blocked AT(1) receptors. The ARB reduced the LPS-induced upregulation of CD14 gene expression; expression of TNF-alpha and IL-6 mRNA and protein; expression of IL-1beta and IkappaB-alpha mRNA; COX-2 mRNA and protein expression and PGE(2) concentration; inducible nitric oxide synthase (iNOS) gene and protein expression and iNOS activity; and Nox2 gene expression and 8-isoprostane levels. In addition, candesartan reduced the CD14 protein expression in saline- and LPS-treated rats. Our results suggest that AT(1) receptors are essential for the development of the full innate immune response to bacterial endotoxin. The ARB decreased the general peripheral inflammatory reaction to LPS and partially decreased the inflammatory response in the spleen. An unrestricted innate immune response to the bacterial endotoxin may have deleterious effects for the organism and may lead to development of chronic inflammatory disease. We postulate that ARBs may have therapeutic effects on inflammatory conditions.

Effect of dual blockade of renin–angiotensin system on TGFβ1 and left ventricular structure and function in hypertensive patients

The effects of 24 weeks losartan and ramipril treatment, both alone and in combination, on left ventricular mass (LVM), circulating transforming growth factor beta1 (TGFbeta1), procollagen type I (PIP) and III (PIIIP), have been evaluated in hypertensive (HT) patients. A total of 57 HT with stage 1 and 2 essential hypertension were included. After 4 weeks run in, a randomized double-blind, three arms, double dummy, independent trial was used. All HT patients were randomly allocated to three treatment arms consisting of losartan (50 mg/daily), ramipril (5 mg/ daily) and combined (losartan 50 mg/daily + ramipril 5 mg/daily) for 24 weeks. TGFbeta1, PIP and PIIIP, LVM, LVM/h(2.7) and other echocardiographic measurements, blood urea nitrogen, creatinine and clearance and potassium were determined after run in and after 24 weeks. All groups were comparable for gender, age, body mass index, blood pressure and LVM. The prevalence of baseline left ventricular hypertrophy (LVH) was not significantly different among three groups. At the end of treatment, a significant (P<0.05) reduction in systolic blood pressure (SBP), diastolic blood pressure (DBP), mean blood pressure (MBP), TGFbeta1, PIP, PIIIP, LVM and LVM/h(2.7) was observed in all groups. The absolute and percent reduction in TGFbeta1 and LVM/h(2.7) were significantly higher in combined than losartan or ramipril groups and also in HT patients with LVH. No significant change in absolute and percent reduction of SBP, DBP and MBP were found. Our data indicate an additional cardioprotective effect of dual blockade of renin-angiotensin in HT patients.

Role of the renin-angiotensin-aldosterone system and proinflammatory mediators in cardiovascular disease

Inflammation is a key mechanism in the initiation, progression, and clinical sequelae of cardiovascular diseases (CVDs), including atherosclerosis, nephropathy, and cardiomyopathy. Angiotensin II, the major effector peptide of the renin-angiotensin-aldosterone system (RAAS), plays a significant role in the advent and perpetuation of these inflammatory diseases, most notably in atherogenesis. Consequently, suppression of the influence of angiotensin II by angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers may reduce or potentially reverse atherosclerosis and other inflammation-associated CVDs. Angiotensin II receptor blockers and angiotensin-converting enzyme inhibitors exert anti-inflammatory actions and prevent or reduce the development of atherosclerosis in animal models. Clinically, RAAS suppression reduces common carotid and femoral artery intima-media thickness, thus indicating moderation of the vascular disease process. These clinical benefits likely involve restraint of the deleterious effects of angiotensin II in addition to, or independent of, lowering blood pressure. Increasing evidence that the detection and monitoring of vascular inflammation are important tools in the management of atherosclerosis also implicates the RAAS in this pathogenic process. Inflammatory molecules such as intercellular adhesion molecule-1, vascular cell adhesion molecule-1, monocyte chemoattractant protein-1, tumor necrosis factor-alpha, and C-reactive protein have potential diagnostic and prognostic values in CVD and are modified by angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers. Monitoring these markers may be crucial for determining which agents, or combinations of agents, will result in the most clinically beneficial outcomes for patients. Large-scale trials are still required to determine the effects of the long-term suppression of inflammation on CVDs through the use of RAAS modulating agents, as well as to determine how closely markers of inflammatory activity may correlate with CVD outcomes.

TGF-β1 regulation of human AT1 receptor mRNA splice variants harboring exon 2

At least four alternatively spliced mRNAs can be synthesized from the human AT(1)R (hAT(1)R) gene that differ only in the inclusion or exclusion of exon 2 and/or 3. RT-PCR experiments demonstrate that splice variants harboring exon 2 accounts for at least 30% of all the hAT(1)R mRNA transcripts expressed in the human tissues investigated. Since exon 2 contains two upstream AUGs or open reading frames (uORFs), we hypothesized that these AUGs would inhibit the translation of the downstream hAT(1)R protein ORF harbored in exon 4. This study demonstrates that the inclusion of exon 2 in hAT(1)R mRNA transcripts dramatically reduces hAT(1)R protein levels (nine-fold) and significantly attenuates Ang II responsiveness ( approximately four-fold). Interestingly, only when both AUGs were mutated in combination were the hAT(1)R density and Ang II signaling levels comparable with those values obtained using mRNA splice variants that did not include exon 2. This observation is consistent with a model where the majority of the ribosomes likely translate uORF#1 and are then unable to reinitiate at the downstream hAT(1)R ORF, in part due to the presence of AUG#2 and to the short intercistronic spacing. Importantly, TGF-beta(1) treatment (4ng/ml for 4h) of fibroblasts up-regulated hAT(1)R mRNA splice variants, which harbored exon 2, six-fold. Since AT(1)R activation is closely associated with cardiovascular disease, the inclusion of exon 2 by alternative splicing represents a novel mechanism to reduce the overall production of the hAT(1)R protein and possibly limit the potential pathological effects of AT(1)R activation.

Effects of oral fixed-dose combinations of telmisartan plus ramipril and losartan plus ramipril in hypertension: A multicenter, prospective, randomized, double-blind, phase iii trial in adult indian patients

BACKGROUND

A new oral fixed-dose combination (FDC) of telmisartan plus ramipril is being introduced in India for the treatment of patients with stage 2 hypertension.

OBJECTIVE

The aim of this study was to compare the effectiveness and tolerability of an oral FDC of telmisartan plus ramipril with those of an oral FDC of losartan plus ramipril in adult Indian patients with stage 2 hypertension.

METHODS

This multicenter, prospective, randomized, double-blind, Phase III study was conducted at 5 centers in India. Indian patients aged 18 to 65 years with uncomplicated stage 2 essential hypertension (systolic/diastolic blood pressure [SBP/DBP], >160/>100 mm Hg) were enrolled. After a 2-week placebo run-in period, patients were randomly assigned to receive telmisartan 40 mg plus ramipril 5 mg (T + R) or losartan 50 mg plus ramipril 5 mg (L + R), PO (tablet) QD (before the morning meal) for 8 weeks. Supine blood pressure (BP) was measured at 0 (baseline) and 8 weeks of treatment. The primary end point was the mean reduction from baseline in BP. Responders were classified as patients who had a DBP <90 mm Hg at the end of 8 weeks of therapy. Tolerability was assessed using spontaneous reports of adverse events (AEs) during the follow-up visits and laboratory analyses performed at week 8.

RESULTS

A total of 289 patients were enrolled (155 men, 134 women; mean age, 50.74 years). Of these, 8 patients in the T + R group and 7 in the L + R group were lost to follow-up and considered withdrawals. At the end of week 8, the mean percentage reduction in SBP was significantly greater in the T + R group compared with that in the L + R group (24.1% vs 19.4%; P < 0.05). The mean percentage reduction in DBP was also significantly greater in the T + R group compared with that in the L + R group (17.3% vs 12.5%; P < 0.05). The response rates in the T + R and L + R groups were statistically similar (79.1% vs 68.7%). The most common AEs in the T + R and L + R groups were cough (9 [6.1%] and 11 [7.8%] patients, respectively) and headache (7 [4.7%] and 8 [5.7%] patients, respectively).

CONCLUSIONS

The results in this study in Indian patients with stage 2 essential hypertension suggest that the FDC of T + R controlled BP more effectively compared with the FDC of L + R over 8 weeks. The response rates were similar between the 2 groups. Both treatments were well tolerated.

Anti-stress and anti-anxiety effects of centrally acting angiotensin II AT1 receptor antagonists

The brain and the peripheral (hormonal) angiotensin II systems are stimulated during stress. Activation of brain angiotensin II AT(1) receptors is required for the stress-induced hormone secretion, including CRH, ACTH, corticoids and vasopressin, and for stimulation of the central sympathetic activity. Long-term peripheral administration of the angiotensin II AT(1) antagonist candesartan blocks not only peripheral but also brain AT(1) receptors, prevents the hormonal and sympathoadrenal response to isolation stress and prevents the formation of stress-induced gastric ulcers. The mechanisms responsible for the prevention of stress-induced ulcers by the AT(1) receptor antagonist include protection from the stress-induced ischemia and inflammation (neutrophil infiltration and increase in ICAM-1 and TNF-alpha) in the gastric mucosa and a partial blockade of the stress-induced sympathoadrenal stimulation, while the protective effect of the glucocorticoid release during stress is maintained. AT(1) receptor antagonism prevents the stress-induced decrease in cortical CRH(1) and benzodiazepine binding and is anxiolytic. Blockade of brain angiotensin II AT(1) receptors offers a novel therapeutic opportunity for the treatment of anxiety and other stress-related disorders.

Irbesartan and Lipoic Acid Improve Endothelial Function and Reduce Markers of Inflammation in the Metabolic Syndrome

Background— The metabolic syndrome is associated with increased angiotensin II activity, induction of a proinflammatory and oxidative state, and endothelial dysfunction. We evaluated the ability of irbesartan, an angiotensin receptor blocker, and lipoic acid, an antioxidant, to affect endothelial function and inflammation in patients with the metabolic syndrome.

Methods and Results— We randomized 58 subjects with the metabolic syndrome in a double-blinded manner to irbesartan 150 mg/d (n=14), lipoic acid 300 mg/d (n=15), both irbesartan and lipoic acid (n=15), or matching placebo (n=14) for 4 weeks. Endothelium-dependent and -independent flow-mediated vasodilation was determined under standard conditions. Plasma levels of interleukin-6, plasminogen activator-1, and 8-isoprostane were measured. After 4 weeks of therapy, endothelium-dependent flow-mediated vasodilation of the brachial artery was increased by 67%, 44%, and 75% in the irbesartan, lipoic acid, and irbesartan plus lipoic acid groups, respectively, compared with the placebo group. Treatment with irbesartan and/or lipoic acid was associated with statistically significant reductions in plasma levels of interleukin-6 and plasminogen activator-1. In addition, treatment with irbesartan or irbesartan plus lipoic acid decreased 8-isoprostane levels. No significant changes in blood pressure were noted in any of the study groups.

Conclusions— Administration of irbesartan and/or lipoic acid to patients with the metabolic syndrome improves endothelial function and reduces proinflammatory markers, factors that are implicated in the pathogenesis of atherosclerosis.

RETRACTED: Transcriptional regulation of the AT1 receptor gene in immortalized human trophoblast cells

Studies investigating the mechanisms that govern the expression of the human angiotensin II (Ang II) type 1 receptor (hAT1R) gene have progressed slowly due to the lack of human cell lines that express the AT1R. Recently, however, an immortalized human trophoblast cell line (HTR-8/SVNeo) was demonstrated to respond to Ang II. Therefore, we utilized this cell line to characterize the AT1R expressed on the cell surface and to investigate the mechanisms by which the hAT1R gene is regulated in these cells. HTR-8/SVNeo cells were shown to express functional high affinity AT1Rs having a Bmax value of 114+/-11 fmol/mg protein and a Kd value of 0.14+/-0.1 nM. Additionally, Ang II-induced IP3 production was mediated via the AT1R. Deletional analysis of the hAT1R promoter localized a major basal regulatory sequence within the -105 to -79 bp region, relative to the transcription start site, in HTR-8/SVNeo cells. Electrophoretic mobility shift assay (EMSA) and Chromatin Immunoprecipitation (ChIP) assay demonstrated that the transcription factors, Sp1 and Sp3, interact with this region of the hAT1R promoter in vitro and in vivo. Taken together, our data demonstrate that HTR-8/SVNeo cells express functional AT1Rs and that basal level expression of this gene is regulated, in part, by Sp1 and Sp3 in this cell line.

Rationale, design, and baseline characteristics of 2 large, simple, randomized trials evaluating telmisartan, ramipril, and their combination in high-risk patients: the Ongoing Telmisartan Alone and in Combination with Ramipril Global Endpoint Trial/Telmisartan Randomized Assessment Study in ACE Intolerant Subjects with Cardiovascular Disease (ONTARGET/TRANSCEND) trials

BACKGROUND

Angiotensin-converting enzyme (ACE) inhibitors reduce mortality, myocardial infarction, stroke, heart failure, need for revascularization, nephropathy, and diabetes and its complications. Although angiotensin-II receptor blockers (ARBs) have been less extensively evaluated, theoretically they may have "protective" effects similar to those of ACE inhibitors, but with better tolerability. Currently, there is uncertainty about the role of ARBs when used alone or in combination with an ACE inhibitor in high-risk populations with controlled hypertension.

OBJECTIVES

Primary objectives of the ONgoing Telmisartan Alone and in Combination with Ramipril Global Endpoint Trial (ONTARGET) are to determine if the combination of the ARB telmisartan and the ACE inhibitor ramipril is more effective than ramipril alone, and if telmisartan is at least as effective as ramipril. The Telmisartan Randomized AssessmeNt Study in aCE iNtolerant subjects with cardiovascular Disease (TRANSCEND) will determine if telmisartan is superior to placebo in patients who are intolerant of ACE inhibitors. The primary outcome for both trials is the composite of cardiovascular death, myocardial infarction, stroke, or hospitalization for heart failure.

METHOD

High-risk patients with coronary, peripheral, or cerebrovascular disease or diabetes with end-organ damage are being recruited and followed for 3.5 to 5.5 years in 2 parallel, randomized, double-blind clinical trials.

PROGRESS

Recruitment from 730 centers in 40 countries for ONTARGET (n = 25,620) was completed in July 2003. For TRANSCEND, 5776 patients (out of a projected total of 6000) have been recruited (by May 10, 2004). Baseline patient characteristics are comparable to the Heart Outcomes Prevention Evaluation (HOPE) trial, the basis of the design of the current study, confirming that patients are at high-risk.

An Open-Label Study Investigating the Efficacy and Safety of 12–96 Weeks of Telmisartan Treatment in Patients with Hypertension

This open-label, multicentre, multinational trial evaluated the efficacy and safety of telmisartan used alone or as add-on therapy in 2121 adults with mild-to-moderate essential hypertension. Patients received telmisartan 40-80 mg once daily for 12 weeks and could participate in the study for up to 96 weeks, or until a marketed supply of telmisartan became available. Mean change from baseline in mean seated trough diastolic blood pressure (DBP) after 12 weeks' treatment, the primary endpoint, was −11.8 mmHg in the intent-to-treat population. The corresponding mean change in mean seated trough systolic blood pressure (SBP) was −20.2 mmHg. Both changes were statistically significant. Mean DBP and SBP reductions were apparent from week 4 and maintained throughout the treatment period. Telmisartan was well tolerated; the most common adverse events were headache (6%) and dizziness (3%), and 10% of adverse events were considered drug-related. In conclusion, telmisartan is an effective and well-tolerated drug when used as monotherapy or add-on treatment in this broad population of patients.

Anti-inflammatory effects of angiotensin II AT1 receptor antagonism prevent stress-induced gastric injury

Stress reduces gastric blood flow and produces acute gastric mucosal lesions. We studied the role of angiotensin II in gastric blood flow and gastric ulceration during stress. Spontaneously hypertensive rats were pretreated for 14 days with the AT1 receptor antagonist candesartan before cold-restraint stress. AT1 receptors were localized in the endothelium of arteries in the gastric mucosa and in all gastric layers. AT1 blockade increased gastric blood flow by 40-50%, prevented gastric ulcer formation by 70-80% after cold-restraint stress, reduced the increase in adrenomedullary epinephrine and tyrosine hydroxylase mRNA without preventing the stress-induced increase in adrenal corticosterone, decreased the stress-induced expression of TNF-alpha and that of the adhesion protein ICAM-1 in arterial endothelium, decreased the neutrophil infiltration in the gastric mucosa, and decreased the gastric content of PGE2. AT1 receptor blockers prevent stress-induced ulcerations by a combination of gastric blood flow protection, decreased sympathoadrenal activation, and anti-inflammatory effects (with reduction in TNF-alpha and ICAM-1 expression leading to reduced neutrophil infiltration) while maintaining the protective glucocorticoid effects and PGE2 release. Angiotensin II has a crucial role, through stimulation of AT1 receptors, in the production and progression of stress-induced gastric injury, and AT1 receptor antagonists could be of therapeutic benefit.

Inflammation and angiotensin II

Angiotensin II (AngII), the major effector peptide of renin-angiotensin system (RAS), is now recognized as a growth factor that regulates cell growth and fibrosis, besides being a physiological mediator restoring circulatory integrity. In the last few years, a large number of experimental studies has further demonstrated that AngII is involved in key events of the inflammatory process. Here, we summarize the wide variety of AngII functions and discuss them in relation with the inflammatory cascade. AngII increases vascular permeability (via the release of prostaglandins and vascular endothelial cell growth factor or rearrangement of cytoskeletal proteins) that initiates the inflammatory process. AngII could contribute to the recruitment of inflammatory cells into the tissue through the regulation of adhesion molecules and chemokines by resident cells. Moreover, AngII could directly activate infiltrating immunocompetent cells, including chemotaxis, differentiation and proliferation. Recent data also suggest that RAS activation could play a certain role even in immunologically-induced inflammation. Transcriptional regulation, predominantly via nuclear factor-kappaB (NF-kappaB) and AP-1 activation, and second mediator systems, such as endothelin-1, the small G protein (Rho) and redox-pathways are shown to be involved in the molecular mechanism by which AngII exerts those functions. Finally, AngII participates in tissue repair and remodeling, through the regulation of cell growth and matrix synthesis. In summary, recent data support the hypothesis that RAS is key mediator of inflammation. Further understanding of the role of the RAS in this process may provide important opportunities for clinical research and treatment of inflammatory diseases.

Alternative splicing: a novel mechanism to fine-tune the expression and function of the human AT1 receptor

Activation of the angiotensin II type 1 (AT(1)) receptor is closely involved in the pathogenesis of cardiovascular diseases; therefore, aberrant regulation of the production of this receptor might play a role in these disorders. Currently, there is strong evidence to suggest that the predominant mechanism regulating the number of AT(1) receptors is the modulation of mRNA stability. Here, we discuss the importance of alternative splicing as an additional post-transcriptional mechanism regulating human AT(1) receptor number and function.

Treatment of hypertension with an angiotensin II-receptor antagonist compared with an angiotensin-converting enzyme inhibitor: a review of clinical studies of telmisartan and enalapril

BACKGROUND

Angiotensin-converting enzyme (ACE) inhibitors and angiotensin II (ATII)-receptor antagonists suppress the effects of ATII and are effective antihypertensive agents. However, the use of ACE inhibitors is sometimes associated with intolerable side effects (eg, cough, angioedema), and patients may develop a compensatory rise in ATII levels. ATII-receptor antagonists have tolerability profiles similar to that of placebo and inhibit the effects of ATII more completely by blocking the AT1 receptor.

OBJECTIVE

This review summarizes clinical studies comparing the efficacy and tolerability of the ATII-receptor antagonist telmisartan with the ACE inhibitor enalapril in patients with hypertension.

METHODS

Randomized, controlled clinical trials comparing telmisartan with enalapril in patients with primary hypertension were identified through a PubMed search of the English-language literature from 1998 through 2001 and from bibliographic data provided by the manufacturer of telmisartan.

RESULTS

In 2 randomized, double-blind, placebo-controlled trials (total number of patients, 647), telmisartan 40 or 80 mg/d was at least as effective as enalapril 20 mg/d for lowering blood pressure (BP) in patients with mild to moderate hypertension. An open-label, titration-to-response study involving 86 patients with severe hypertension found that telmisartan 80 to 160 mg/d was as efficacious as enalapril 20 to 40 mg/d. The antihypertensive effects of telmisartan 20 to 80 mg/d and enalapril 5 to 20 mg/d were comparable in 278 elderly patients (age > or = 65 years) with mild to moderate hypertension enrolled in a 26-week, double-blind, dose-titration study. A double-blind, titration-to-response study in 71 patients with moderate renal impairment and mild to moderate hypertension found equivalent reductions in BP with telmisartan 40 to 80 mg/d and enalapril 10 to 20 mg/d without any clinically relevant decline in renal function. Telmisartan tended to be better tolerated than enalapril in this study, with fewer patients experiencing treatment-related adverse events (8.9% vs 26.9%, respectively).

CONCLUSIONS

Based on the literature included in this review, telmisartan and enalapril produced comparable reductions in BP in a broad range of patients with hypertension. Telmisartan appeared to have a better tolerability profile.

Mechanisms linking angiotensin II and atherogenesis

PURPOSE OF REVIEW

The concept that angiotensin II plays a central role in early atherogenesis, progression to atherosclerotic plaque, and the most serious clinical sequelae of coronary artery disease is the subject of considerable current interest. Results from recent large clinical trials confirm that blunting of the renin-angiotensin system through either angiotensin converting enzyme inhibition or angiotensin II type 1 receptor blockade incurs significant beneficial outcomes in patients with coronary artery disease. The exact mechanisms for these effects are not yet clear, but are suggested by studies demonstrating that suppression of the renin-angiotensin system is associated with muted vascular oxidative stress.

RECENT FINDINGS

As most of the biological effects of the renin-angiotensin system occur through stimulation of the angiotensin II type 1 receptor, the focus of this review is on changes in the vascular wall mediated by this receptor and primarily related to endothelial and vascular smooth muscle cells, monocyte/macrophages and platelets. The interactions between angiotensin II and nitric oxide exert particular demands on the vascular capacity to adapt to dyslipidemia, hypertension, estrogen deficiency and diabetes mellitus that appear to exacerbate atherogenesis. Associated with each of these conditions is angiotensin II-mediated stimulation of macrophages, platelet aggregation, plasminogen activator inhibitor 1, endothelial dysfunction, vascular smooth muscle cell proliferation and migration, apoptosis, leukocyte recruitment, fibrogenesis and thrombosis.

SUMMARY

Inhibition of the actions of angiotensin II serves a dual purpose: indirectly through reduction of mechanical stress on the vascular wall, and directly by diminished stimulation for vascular restructuring and remodeling. Collectively, data from studies published over the last year confirm and extend the notion that angiotensin II is a true cytokine prevalent at all stages of atherogenesis.

The hypertension-lipid connection: insights into the relation between angiotensin II and cholesterol in atherogenesis

Clinical data and experimental studies have established the important role of abnormal lipid metabolism in the causation of atherosclerosis and enthroned the hydroxymethylglutaryl coenzyme reductase inhibitors (statins) as a mainstay in management of patients with coronary heart disease. However, emerging experimental data underline the role of vascular renin-angiotensin systems in mediating the early stages of vascular endothelial dysfunction and inflammation as prerequisites for unleashing the cascade of cellular and molecular events that lead to the deposition of foam cells and their eventual progression to the atherosclerotic plaque. We discuss here the biological effects of statins and angiotensin II in the evolution of atherogenesis, underscoring possible links between statins and angiotensin receptor blockers. From the assessment of the commonality of effects resulting from the nonlipidic actions of statins and angiotensin II on the process of atherogenesis, we develop the argument that dyslipidemia may influence the ability to control blood pressure in hypertensive subjects and hypothesize that the combined use of statins and blockers of the renin-angiotensin system may have an additive effect in the management of hypertensive subjects.