Angiotensin II type 1 receptor blockers

Angiotensin receptor blockers as anti-hypertensive treatment for patients with diabetes mellitus: meta-analysis of controlled double-blind randomized trials

AIMS

To assess the evidence for possible reduction of all-cause mortality, cardiovascular morbidity and mortality, and end-stage renal disease in diabetic patients treated with angiotensin II type 1 receptor blockers (ARBs) as an anti-hypertensive treatment.

METHODS

Systematic review and meta-analysis of randomized, double-blind controlled trials of at least 1 year's duration. ARBs were used in the intervention group vs. placebo or standard anti-hypertensive treatment in the control group. The main outcome measures were all-cause mortality, cardiovascular morbidity and mortality, and end-stage renal disease.

RESULTS

Three studies fulfilled the inclusion criteria. Separate analyses were conducted for comparisons of ARBs with groups given placebo and those given standard anti-hypertensive treatment. There was no significant difference in mortality between the ARBs and placebo groups, with an estimated odds ratio (OR) of 0.99 [95% confidence interval (CI) 0.81, 1.20]. There was a non-significant difference in patients treated with ARBs compared with standard anti-hypertensive treatment, with an OR of 0.78 (95% CI 0.45, 1.36). No statistically significant difference in cardiovascular morbidity and mortality between the intervention and placebo groups was found, with an OR of 0.91 (95% CI 0.77, 1.08). When ARBs were compared with standard treatment, the OR was estimated at 0.85 (0.54, 1.33). Data on end-stage renal disease were available for two studies comparing ARBs vs. placebo and showed a statistically significant advantage of ARBs, with an OR of 0.73 (95% CI 0.6, 0.89). As only one study compared end-stage renal disease outcome for ARBs vs. standard treatment, a meta-analysis was not possible. This study reported a considerable benefit of ARBs [OR = 0.73 (0.54, 1.01)] compared with the calcium channel blocker amlodipine.

CONCLUSIONS

ARBs failed to show significant reduction in total mortality and cardiovascular morbidity and mortality in diabetic patients. The only statistical benefit was the reduction of end-stage renal disease compared with placebo. Therefore, at this time ARBs have not proved to be superior to standard anti-hypertensive treatment in diabetic patients.

Tissue renin angiotensin systems

The RAAS is a powerful regulator of vascular tone and intravascular volume and of tissue architecture and a variety of other functions. The recent appreciation of the immunoregulatory role of angiotensin II and its possible involvement in the genesis of atherosclerosis and in plaque rupture all speak to the wide-ranging physiologic and pathophysiologic activities of the peptide. So do its actions in fat cell differentiation and in neuromodulation. The system exists in the circulation, and RAASs, whole or partial, exist in many tissues. These systems are regulated at many levels ranging from the synthesis of renin to the dimerization of angiotensin receptors. Regulation occurs in multiple tissues and, as a result, tissue concentrations of angiotensin II and the concentration of other RAS components and their active metabolites can vary independently of the circulating system in these tissues. An RAS seems also to function within certain cells. Therapeutic interventions involving ACEIs and ARBs seem likely to provide benefit at least in part through the interruption of local systems. It is to be expected that with enhanced understanding of the biology of the multiple RASs, new suggestions for therapeutic interventions will be forthcoming.

Valsartan: a review of its use in patients with heart failure and/or left ventricular systolic dysfunction after myocardial infarction

Valsartan (Diovan) is an oral angiotensin II-receptor antagonist with specificity for the angiotensin II type 1 receptor subtype. It demonstrates antihypertensive activity and slows the progression of chronic heart failure (CHF). Recently it has been evaluated in comparison with an ACE inhibitor regimen in patients with heart failure or left ventricular systolic dysfunction (LVSD) after an acute myocardial infarction (MI), a population known to be at high risk of subsequent death or other major cardiovascular events. In the VALIANT (VALsartan In Acute myocardial iNfarcTion) trial, valsartan was as effective as captopril at reducing mortality and cardiovascular morbidity in patients who developed heart failure and/or LVSD after surviving an MI. It was also generally well tolerated in this population. Treatment with a combination of valsartan plus captopril provided no additional therapeutic benefit over treatment with captopril and was less well tolerated. Valsartan has a potential role as a new treatment for high-risk patients in the post-MI setting.

The constitutively active N111G-AT1 receptor for angiotensin II maintains a high affinity conformation despite being uncoupled from its cognate G protein Gq/11alpha

Asn111, localized in the third transmembrane domain of the AT1 receptor for angiotensin II, plays a critical role in stabilizing the inactive conformation of the receptor. We evaluated the functional and G protein-coupling properties of mutant AT1 receptors in which Asn111 was substituted with smaller (Ala or Gly) or larger residues (Gln or Trp). All four mutants were expressed at high levels in COS-7 cells and, except for N111W-AT1, recognized 125I-Ang II with high affinities comparable to that of the wild-type AT1 receptor. In phospholipase C assays, the four mutants encompassed the entire spectrum of functional states, ranging from constitutive activity (without agonist) for N111A-AT1 and N111G-AT1 to a significant loss of activity (upon maximal stimulation) for N111Q-AT1 and a major loss of activity for N111W-AT1. In Ca2+ mobilization studies, N111W-AT1 produced a weak Ca2+ transient and, unexpectedly, N111G-AT1 also produced a Ca2+ transient that was much weaker than that of the wild-type AT1. The agonist binding affinity of N111W-AT1 was not modified in the presence of GTPgamma S, suggesting that this receptor is not basally coupled to a G protein. GTPgamma S did not modify the high agonist-binding affinity of N111G-AT1 but abolished the coimmunoprecipitation of Gq/11alpha with this constitutively active mutant receptor. These results are a direct demonstration that the N111G-AT1 receptor maintains a high affinity conformation despite being uncoupled from the G protein Gq/11.

Update on therapy for heart failure

The success of angiotensin-converting enzyme (ACE) inhibitors in reducing morbidity and mortality in patients with heart failure has led to investigations of other inhibitors of the renin-angiotensin-aldosterone system. Although ACE inhibitors remain first-line drugs in the treatment of heart failure and left ventricular dysfunction, clinical evidence suggests that a newer class of agents--angiotensin II receptor blockers--may provide additional benefit by blocking the adverse effects of angiotensin II more completely. An improved adverse-effect profile also makes angiotensin II receptor blockers appropriate in patients who cannot tolerate ACE inhibitors. Clinical trials have demonstrated the beneficial effects of angiotensin II receptor blockers on the combined endpoints of morbidity and mortality in patients with heart failure. Aldosterone antagonism with spironolactone has additive benefits in patients receiving an ACE inhibitor. The most recent treatment guidelines for heart failure recommend the use of angiotensin II receptor blockers and spironolactone in selected patients.

Better renoprotective effect of angiotensin II antagonist compared to dihydropyridine calcium channel blocker in childhood

BACKGROUND

The dihydropyridine calcium channel blocker amlodipine and the angiotensin II antagonist irbesartan effectively reduce blood pressure in hypertensive children.

METHODS

Eligible for the open-label, randomized study were nephropathic children between 6.0 and 18 years of age with plasma creatinine <177 micromol/L, overt proteinuria, untreated arterial hypertension (systolic, 5 to 30 mm Hg; and diastolic, 1 to 15 mm Hg;>95th centile) and stable immunosuppressive treatment. The initial dose of amlodipine was 5 mg (body weight, 20 to 40 kg) and 10 mg (body weight,>40 kg), respectively, that of irbesartan, which was 75 mg (body weight, 20 to 40 kg) and 150 mg (body weight,>40 kg), respectively. The dosage was doubled if necessary.

RESULTS

A total of 26 children aged 6.1 to 17 years were allocated to receive either amlodipine (N = 13) or irbesartan (N = 13) for 16 weeks. Severe edema and headache occurred in two patients on amlodipine who withdrew from the study. No adverse experiences were noted in patients given irbesartan. Amlodipine [by 12 (10 to 14)/7 (5 to 10) mm Hg; median and interquartile range, respectively] and irbesartan [by 13 (9 to 16)/9 (7 to 11) mm Hg, respectively] reduced blood pressure (P < 0.01) in a similar fashion. Heart rate, plasma sodium, and creatinine did not change. Irbesartan slightly increased plasma potassium [by 0.1 (0.0 to 0.2) mmol/L; P < 0.05]. Plasma albumin and the urinary albumin/creatinine ratio were similar before and with amlodipine. On the contrary, irbesartan increased plasma albumin [by 4 (3 to 5) g/L; P < 0.03] and decreased the urinary albumin/creatinine ratio [by 242 (68 to 312) mg/mmol; P < 0.03].

CONCLUSION

The study demonstrates that in children the effect of angiotensin II antagonists on proteinuria is better than that of dihydropyridine calcium channel blockers.

Interaction of angiotensin II with the C-terminal 300-320 fragment of the rat angiotensin II receptor AT1a monitored by NMR

Interaction between angiotensin II (Ang II) and the fragment peptide 300-320 (fCT300-320) of the rat angiotensin II receptor AT1a was demonstrated by relaxation measurements, NOE effects, chemical shift variations, and CD measurements. The correlation times modulating dipolar interactions for the bound and free forms of Ang II were estimated by the ratio of the nonselective and single-selective longitudinal relaxation rates. The intermolecular NOEs observed in NOESY spectra between HN protons of 9Lys(fCT) and 6His(ang), 10Phe(fCT) and 8Phe(ang), HN proton of 3Tyr(fCT) and Halpha of 4Tyr(ang), 5Phe(fCT)Hdelta and Halpha of 4Tyr(ang) indicated that Ang II aromatic residues are directly involved in the interaction, as also verified by relaxation data. Some fCT300-320 backbone features were inferred by the CSI method and CD experiments revealing that the presence of Ang II enhances the existential probability of helical conformations in the fCT fragment. Restrained molecular dynamics using the simulated annealing protocol was performed with intermolecular NOEs as constraints, imposing an alpha-helix backbone structure to fCT300-320 fragment. In the built model, one strongly preferred interaction was found that allows intermolecular stacking between aromatic rings and forces the peptide to wrap around the 6Leu side chain of the receptor fragment.

Recent clinical trials with omapatrilat: new developments

Omapatrilat belongs to the vasopeptidase inhibitors, ie, drugs that possess the ability to inhibit simultaneously the membrane-bound zinc metalloproteases, angiotensin-converting enzyme (ACE), and the neutral endopeptidase EC 3.4.24.11 (NEP). Omapatrilat was targeted to treat patients with hypertension and congestive heart failure. The preclinical and early clinical studies conducted with omapatrilat were very promising. Indeed, omapatrilat appeared to be a very potent antihypertensive agent with very favorable effects on cardiac function in heart failure patients. In contrast to these early studies, the large clinical trials were more disappointing. The results of the OCTAVE trial confirmed the antihypertensive efficacy of omapatrilat, but at the price of an angioedema rate more than threefold higher than that of an ACE inhibitor in the overall population (2.17% vs 0.68%), and close to fourfold higher in the black population. In OVERTURE, a large randomized control trial in heart failure, angioedema was also more common with omapatrilat, but the incidence was much lower (0.8% with omapatrilat vs 0.5% with enalapril). However, omapatrilat was not convincingly superior to the ACE inhibitor. Because angioedema is probably a class side effect of vasopeptidase inhibitors, the higher incidence of this potentially life-threatening complication with omapatrilat has likely stopped the development of this new class of agents. The future of vasopeptidase inhibitors will depend on the ability to improve the risk/benefit ratio either by developing agents that produce less angioedema, or by defining more precisely a high-risk population that could take advantage of dual ACE/NEP inhibition.

Role of host angiotensin II type 1 receptor in tumor angiogenesis and growth

Although the renin angiotensin system (RAS) is a major regulator of vascular homeostasis, the role of the RAS in tumor angiogenesis is little understood. Here we show that host angiotensin II (ATII) type 1 (AT1) receptor plays an important role in angiogenesis and growth of tumor cells engrafted in mice. Subcutaneous B16-F1 melanoma-induced angiogenesis as assessed by tissue capillary density and microangiography was prominent in WT mice but was reduced in AT1a receptor-deficient (AT1a-/-) mice. Consequently, tumor growth rate was significantly slower, and the mouse survival rate was greater, in AT1a-/- mice than in WT mice. Tumor growth was also reduced in WT mice treated with TCV-116, a selective blocker of AT1 receptor. Because the beta-galactosidase gene was inserted into the AT1a gene locus in AT1a-/- mice, the site of beta-galactosidase expression represents the AT1a receptor expression in these mutant mice. In tumor-implanted AT1a-/- mice, the major site of the beta-galactosidase expression was macrophages in tissues surrounding tumors. Moreover, the number of infiltrated macrophages was significantly lower in AT1a-/- mice than in WT mice, and double-immunofluorescence staining revealed that these macrophages expressed VEGF protein intensively. Therefore, the host ATII-AT1 receptor pathway supports tumor-associated macrophage infiltration, which results in enhanced tissue VEGF protein levels. The host ATII-AT1 receptor pathway thereby plays important roles in tumor-related angiogenesis and growth in vivo.

No involvement of the AT2-receptor in angiotensin II-enhanced sympathetic transmission in vitro

Angiotensin II (Ang II) enhances sympathetic neurotransmission via AT(1)-receptors located on sympathetic nerve terminals. We recently demonstrated that inhibition of Ang II-mediated facilitation in the pithed rat by irbesartan resulted in a U-shaped dose response curve, which was not observed when PD 123319, at a concentration that selectively blocks the AT(2)-receptor, was co-administered. Hence, the irbesartan-mediated upstroke might be explained by the involvement of the AT(2)-receptor after AT(1) blockade with high-dose irbesartan. In the present study, we further investigated the possible role of the AT(2)-receptor in Ang II-mediated facilitation in vitro. We studied the effect of the AT(2)-receptor antagonist PD 123319 (10 nM) on Ang II-enhanced sympathetic outflow evoked by electrical field stimulation (EFS) in the rat isolated inferior vena cava. Additionally, we investigated the effect of the AT(1)-receptor blocker irbesartan (0.1 nM 1 M) on the sequelae of Ang II-enhanced, EFS-evoked sympathetic nerve traffic in the presence or absence of PD 123319 (10 nM). PD 123319 did not influence Ang II-enhanced sympathetic outflow. Irbesartan dose-dependently attenuate Ang II-augmented transmitter release (pIC50 7.99+0.03), whereas no U-shaped concentration-response relationship for irbesartan was observed. Co-administration of PD 123319 with irbesartan proved unable to influence Ang II-mediated facilitation differently compared with irbesartan alone. The experimental observations indicate that the AT(2)-receptor is not involved in Ang II-mediated enhancement of sympathetic nerve traffic in the present in vitro study.

Pre- and postsynaptic inhibitory potencies of the angiotensin AT1 receptor antagonists eprosartan and candesartan

The aim of the present study was to determine the inhibitory potency of two selective angiotensin AT(1) receptor antagonists, eprosartan and candesartan, at the level of the sympathetic nerve terminal and the vascular smooth muscle. Male New Zealand White rabbits, weighing 2100-2550 g, were used. To study eprosartan and candesartan at the neuronal angiotensin AT(1) receptor, we investigated their influence on the angiotensin II-enhanced, electrical field stimulation-evoked sympathetic transmission in the rabbit isolated thoracic aorta in a noradrenaline spillover model. To study both antagonists at the vascular angiotensin AT(1) receptor, concentration-response curves for angiotensin II were constructed in the presence or absence of the two angiotensin AT(1) receptor antagonists. Angiotensin II (10 nM) caused a significant increase by 107+/-11.1% of the stimulation-evoked sympathetic outflow, which was concentration-dependently inhibited by both eprosartan (pIC(50) 7.91+/-0.12) and candesartan (pIC(50) 10.76+/-0.13). Angiotensin II (1 nM-0.3 microM) caused a concentration-dependent increase in contractile force (E(max) 20.62+/-2.24 mN, pD(2) 8.16+/-0.04). Both eprosartan (pA(2) 8.90+/-0.11, pIC(50) 8.87+/-0.12 (10 nM angiotensin II)) and candesartan (pD(2)' 10.80+/-0.13) counteracted the contractions evoked by cumulative concentrations of angiotensin II. Candesartan proved a more potent antagonist than eprosartan at both the pre- and postjunctional angiotensin AT(1) receptor. For eprosartan, vascular inhibitory concentrations were 10-fold lower than sympatho-inhibitory concentrations, whereas for candesartan, inhibitory concentrations at both sites were similar. The results may be explained by differences between the pre- and postjunctional angiotensin AT(1) receptor subtype.

Pharmacologic therapy for patients with chronic heart failure and reduced systolic function: review of trials and practical considerations

Heart failure (HF) is a complex clinical syndrome resulting from any structural or functional cardiac disorder impairing the ability of the ventricles to fill with or eject blood. The approach to pharmacologic treatment has become a combined preventive and symptomatic management strategy. Ideally, treatment should be initiated in patients at risk, preventing disease progression. In patients who have progressed to symptomatic left ventricular dysfunction, certain therapies have been demonstrated to improve survival, decrease hospitalizations, and reduce symptoms. The mainstay therapies are angiotensin-converting enzyme (ACE) inhibitors and beta-blockers (bisoprolol, carvedilol, and metoprolol XL/CR), with diuretics to control fluid balance. In patients who cannot tolerate ACE inhibitors because of angioedema or severe cough, valsartan can be substituted. Valsartan should not be added in patients already taking an ACE inhibitor and a beta-blocker. Spironolactone is recommended in patients who have New York Heart Association (NYHA) class III to IV symptoms despite maximal therapies with ACE inhibitors, beta-blockers, diuretics, and digoxin. Low-dose digoxin, yielding a serum concentration <1 ng/mL can be added to improve symptoms and, possibly, mortality. The combination of hydralazine and isosorbide dinitrate might be useful in patients (especially in African Americans) who cannot tolerate ACE inhibitors or valsartan because of hypotension or renal dysfunction. Calcium antagonists, with the exception of amlodipine, oral or intravenous inotropes, and vasodilators, should be avoided in HF with reduced systolic function. Amiodarone should be used only if patients have a history of sudden death, or a history of ventricular fibrillation or sustained ventricular tachycardia, and should be used in conjunction with an implantable defibrillator [corrected]. Finally, anticoagulation is recommended only in patients who have concomitant atrial fibrillation or a previous history of cerebral or systemic emboli.

Treatment with irbesartan counteracts the functional remodeling of ventricular myocytes from hypertensive rats

Changes in electrophysiological (action potential prolongation, decrease in transient outward current I(to), occurrence of the hyperpolarization-activated current I(f)) and contractile properties develop in hypertrophied ventricular myocytes, likely implicated in the increased propensity to arrhythmias. Angiotensin II is a key signal for myocyte hypertrophy; the effect of 8-week treatment with irbesartan, a type 1 angiotensin II receptor (AT(1)) antagonist, on cardiac remodeling was tested. Sixteen-month-old hypertensive rats (SHRs) were treated with irbesartan (20 mg/kg/d) or saline for 8 weeks. At the end of treatment, systolic blood pressure and heart weight to body weight ratio were reduced in irbesartan-treated compared with nontreated SHRs. Electrical and contractile properties were measured in isolated ventricular myocytes, by patch-clamp or video-dimension analysis, respectively. Action potential duration was significantly shorter in irbesartan-treated than in nontreated SHRs (at -60 mV: 119 +/- 24 ms vs 187 +/- 20 ms); correspondingly, maximal I(to) density was larger in irbesartan-treated than in nontreated SHRs (25.4 +/- 2.8 pA/pF vs 18.5 +/- 1.5 pA/pF). Maximal specific conductance of I(f) was lower in irbesartan-treated vs nontreated SHRs (24.8 +/- 3.0 pS/pF vs 35.2 +/- 4.0 pS/pF). Finally, the relaxation rate of shortening in field-stimulated intact myocytes was significantly faster in irbesartan-treated than in nontreated SHRs (7.3 +/- 0.5/s vs 5.7 +/- 0.3/s). Thus, AT(1) blockade with irbesartan, at an oral daily dosage that gave a slight but significant reduction of systolic blood pressure, largely counteracts the development of myocyte hypertrophy and associated functional alterations.

Enalaprilat, losartan and LU 135252 in coronary blood flow regulation

BACKGROUND

High plasma levels of angiotensin II are found in several pathologies such as hypertension, heart failure and myocardial infarction. The effect of high concentrations of angiotensin II on coronary circulation is not well defined. The aim of the present study was to assess coronary blood flow regulation during tachycardia in the presence of elevated coronary plasma levels of angiotensin II, and the changes induced by ACE inhibition and blockade of angiotensin II and endothelin-A receptors.

DESIGN

Left anterior coronary artery was catheterized in 38 pigs to infuse the study drugs. Saline was infused for 15 min. Then, the first atrial pacing was performed. The pigs were distributed to: Group 1 (n = 7) angiotensin II; Group 2 (n = 7) enalaprilat + angiotensin II; Group 3 (n = 9) the bradykinin B2 antagonist HOE 140 + enalaprilat + angiotensin II; Group 4 (n = 7) losartan + angiotensin II; and Group 5 (n = 8) endothelin-A receptor antagonist LU 135252 + angiotensin II. After giving these infusions, a second pacing was repeated.

RESULTS

The increase in coronary blood flow induced by pacing with angiotensin II was reduced from 181 +/- 21% to 116 +/- 37% (P = 0.006 vs. saline). Enalaprilat, losartan and LU 135252 restored the capacity of coronary blood flow to increase during pacing (151 +/- 39%, 162 +/- 35% and 161 +/- 16%, respectively; P = NS, vs. saline), while HOE 140 abolished the effect of enalaprilat.

CONCLUSIONS

Moderately elevated coronary concentrations of angiotensin II reduced coronary blood flow during pacing. Enalaprilat, losartan and LU 135252 restored the hyperaemic coronary flow to similar values observed with saline. The beneficial effect of ACE inhibition is mediated through an increase in bradykinin.

Characterization of a fluorescent conjugate of the rabbit angiotensin AT(1) receptor

1. The rabbit AT(1) receptor (AT(1)R) for angiotensin II (A(II)) has been conjugated to the yellow fluorescent protein (YFP) in order to establish the pharmacological profile of such a fusion protein and to facilitate the study of ligand-induced regulation. 2. A(II) bound AT(1)R-YFP (K(D) 8.1 nM in transiently transfected cells) and stimulated HEK 293 cells expressing the fusion protein at concentration ranges similar to the ones that stimulate the contraction of the isolated rabbit aorta. Antagonists found to be insurmountable in the latter assay (candesartan and EXP-3174 being the most extreme cases) were also insurmountable in the phospholipase A(2) assay applied to cells expressing AT(1)R-YFP, whereas losartan appeared to be surmountable in both assays. 3. Cells expressing AT(1)R-YFP exhibited a membrane-associated fluorescence that was partly and reversibly translocated into intracellular structures upon A(II) stimulation (confocal microscopy); the nonpeptide antagonists were not active in this respect, but prevented the effect of the agonist. 4. A(II) treatment increased the quantity of the fusion protein in cells, and phorbol 12-myristate 13-acetate (PMA) treatment even more so (immunoblot, confocal microscopy) but, unlike the agonist, the latter drug did not induce receptor endocytosis. A protein kinase C (PKC) inhibitor prevented the effect of either A(II) or PMA on AT(1)R-YFP abundance. 5. The conjugate AT(1)R-YFP retains the pharmacological properties of the parent rabbit AT(1)R. Agonist-induced downregulation was not documented using this system; to the contrary, we have observed a PKC-mediated increased expression AT(1)R-YFP likely to be the result of a decreased breakdown rate of the fusion protein.

AT1 receptor antagonist therapy preferentially ameliorated right ventricular function and phenotype during the early phase of remodeling post-MI

1. The influence of AII on contractile dysfunction, regulation of the tyrosine kinase-dependent signaling molecule extracellular signal-regulated kinase (ERK), and natriuretic peptide gene expression were examined in the noninfarcted left ventricle (NILV) and right ventricle (RV) during the early phase of remodeling post-myocardial infarct (MI) in the rat. The selective AT(1) receptor antagonist irbesartan was administered <10 h following coronary artery ligation, and rats were killed either at 4-day or 2-week post-MI. 2. At 4 days post-MI, left ventricular systolic pressure (LVSP: sham=125+/-12, MI=91+/-4 mmHg) was decreased, whereas left ventricular end-diastolic pressure (LVEDP: sham=9+/-2, MI=17+/-2 mm Hg), right ventricular systolic (RVSP: sham=26+/-1, MI=34+/-2 mm Hg), and end-diastolic pressures (RVEDP: sham=3+/-0.5, MI=7+/-1 mm Hg) were increased. ERK phosphorylation was significantly elevated in the NILV and RV. 3. Irbesartan (40 mg x kg(-1)/day(-1)) administration did not improve left ventricular function, or suppress increased ERK phosphorylation in the 4-day post-MI rat. By contrast, irbesartan therapy normalized RVSP (MI+irbesartan=25+/-1 mm Hg), RVEDP (MI+irbesartan=3+/-0.3 mm Hg), and reduced ERK1 (MI=3.0+/-0.6, MI+irbesartan=2.0+/-0.3-fold increase), and ERK2 (MI=3.8+/-0.8, MI+irbesartan=2.2+/-0.5-fold increase) phosphorylation. 4. In 2-week post-MI rats, biventricular dysfunction was associated with increased prepro-ANP, and prepro-BNP mRNA expression. Irbesartan therapy normalized RVSP, attenuated RVEDP, and abrogated natriuretic peptide mRNA expression (prepro-ANP; MI=9+/-2, MI+irbesartan=2+/-1-fold increase, prepro-BNP; MI=6+/-2, MI+irbesartan=1+/-1-fold increase), whereas both transcripts remained elevated in the NILV despite the partial attenuation of LVEDP. 5. These data suggest that the therapeutic benefit of irbesartan treatment during the early phase of remodeling post-MI was associated with the preferential amelioration of RV contractile function and phenotype.

Discovery of 4'-[(imidazol-1-yl)methyl]biphenyl-2-sulfonamides as dual endothelin/angiotensin II receptor antagonists

A series of 4'-[(imidazol-1-yl)methyl]biphenylsulfonamides has potent antagonist activity against both angiotensin II AT(1) and endothelin ET(A) receptors. Such dual-acting antagonists could have utility in the treatment of hypertension, heart failure, and other cardiovascular diseases in a broad patient population. Certain compounds in the present series are orally active in a rat model of angiotensin II-mediated hypertension.

Therapeutic role of angiotensin II receptor blockers in the treatment of heart failure

Angiotensin II type 1 receptor blockers (ARBs) are generally as effective as angiotensin-converting enzyme (ACE) inhibitors in patients with hypertension. However, inhibition of angiotensin is not achieved completely through the blocking effects of ACE inhibitors, and the possibility of a non-ACE pathway for generation of angiotensin II has important implications for treating cardiovascular disease. The selective quality of ARBs for the angiotensin II type 1 (AT1) receptor may confer an advantage. In a recently reported trial, the ARB valsartan substantially improved patients' New York Heart Association class, clinical signs and symptoms, and quality of life and provided morbidity and mortality benefits in selected patients. Valsartan was recently approved to treat heart failure in patients who cannot be maintained on an ACE inhibitor. As a class, ARBs are well tolerated and have a good safety profile.

Potential of renin inhibition in cardiovascular disease

Since renin catalyses the first and rate-limiting step of the renin-angiotensin system (RAS) cascade, interruption of the generation of angiotensin II (Ang II) by renin inhibitors at this highly specific initial step of the cascade has long been a therapeutic goal. The early development of renin inhibitors was hampered by problems with bioavailability and high costs of synthesis. However, more recently a potent non-peptidic inhibitor of renin, aliskiren, with acceptable oral bioavailability, has been synthesised. Aliskiren effectively reduces Ang II levels in normal volunteers and has been shown to lower blood pressure (BP) in patients with mild-to-moderate hypertension. Renin inhibitors would be expected to have similar, but not identical effects to those of the established RAS antagonists. Due to the lack of effective alternative enzyme pathways, blockade of Ang II production may be more effective with renin inhibition than with angiotensin-converting enzyme (ACE) inhibition. Furthermore, because renin has high specificity for only one substrate, angiotensinogen, side-effects would be expected to be less frequent. It is currently unclear whether blockade of Ang II type 1 (AT1) receptors, leaving other Ang II receptors (AT2, AT3 and AT4) unblocked, is preferable to the reduction in plasma and tissue Ang II levels achieved with either ACE or renin inhibition. Pharmacological suppression of the RAS, through ACE inhibition, or blockade of AT1, beta-adrenoceptor or mineralocorticoid receptors, has been proven to reduce morbidity and mortality in patients with hypertension, diabetes mellitus, atherosclerosis, heart failure and nephropathy. While, to date, aliskiren has only been shown to reduce BP, it appears likely that orally-active renin inhibitors could prove useful in the management of a wide range of cardiovascular pathologies.

Cardiovascular and renal effects of cyclooxygenase inhibition in transgenic rats harboring mouse renin-2 gene (TGR[mREN2]27)

The present study examined the role of cyclooxygenase-synthetized prostanoids in the pathogenesis of angiotensin-II-induced inflammatory response and vascular injury in transgenic rats harboring mouse renin-2 gene (mREN2 rats). Five- to six-week-old, heterozygous mREN2 rats received the following drug regimens for 8 weeks: (1) controls; (2) cyclooxygenase-2 inhibitor (MF-tricyclic [3-(3,4-difluorophenyl)-4-(4-(methylsulfonyl) phenyl)-2(5H)-furanone], 14 mg kg(-1) p.o.); (3) cyclooxygenase-1/cyclooxygenase-2 inhibitor (sulindac, 14 mg kg(-1) p.o.); (4) angiotensin II receptor antagonist (losartan 40 mg kg(-1) p.o.); (5) MF-tricyclic + losartan; (6) sulindac + losartan. Normotensive Sprague-Dawley rats served as controls. mREN2 rats developed pronounced hypertension, cardiac hypertrophy, and albuminuria as compared to normotensive Sprague-Dawley controls. mREN2 rats showed pronounced perivascular inflammation and morphological damage in the kidneys and the heart. Both MF-tricyclic and sulindac further increased blood pressure and albuminuria in mREN2 rats. Neither MF-tricyclic nor sulindac were able to prevent angiotensin-II-induced perivascular inflammation and morphological changes in the heart or in the kidneys. Myocardial and renal cyclooxygenase-2 mRNA expressions were decreased in mREN2 rats, whereas no difference was found in cyclooxygenase-1 mRNA expressions. Sulindac increased both cyclooxygenase-1 and cyclooxygenase-2 gene expressions, whereas MF-tricyclic increased only cyclooxygenase-2 gene expressions. Losartan normalized blood pressure, cardiac hypertrophy, albuminuria, inflammatory response and morphological changes in mREN2 rats, both in the presence and absence of cyclooxygenase inhibitors. Our findings indicate that cyclooxygenase does not play a central role in the pathogenesis of angiotensin-II-induced inflammatory response and vascular injury in mREN2 rats.

Therapeutic potential of renin inhibitors in the management of cardiovascular disorders

The renin-angiotensin system (RAS) is well recognized for its importance in regulation of BP, electrolyte balance and vascular growth. Pharmacological suppression of the RAS, through ACE inhibition and/or angiotensin receptor blockade, is a proven effective therapeutic approach to the treatment of a range of cardiovascular diseases. Renin is the enzyme that catalyzes the first and rate-limiting step of RAS, the cleavage of angiotensinogen to angiotensin I (A-I). A-I is then further converted by ACE to the biologically active vasoconstrictor, A-II. Interruption of the generation of A-II by renin inhibitors at this highly specific initial step of the cascade would be expected to have similar but not identical effects to those of the already well established RAS antagonists. Due to the lack of effective alternative enzyme pathways, blockade of A-II production may be more effective with renin inhibition than with ACE inhibition, and because of the high specificity of renin for only one substrate, namely angiotensinogen, adverse effects would be expected to be less frequent. It is currently unclear whether blockade of angiotensin II type 1 receptors (AT(1)), leaving other A-II receptors unblocked, is preferable to the reduction in plasma and tissue A-II levels achieved with either ACE or renin inhibition. The development of early peptidic and peptidomimetic renin inhibitors was hampered by problems with oral bioavailability and high costs of synthesis. However recent work has led to the synthesis of a potent non-peptidic inhibitor of renin, aliskiren, which has acceptable oral bioavailability. This renin inhibitor has been shown to effectively reduce A-II levels in normal volunteers and to lower BP in patients with mild to moderate hypertension. It appears likely that aliskiren is the first of a new class of agents that may prove useful in the management of patients with nephropathy, heart failure and atherosclerosis in addition to hypertension.

Acute pancreatitis associated with angiotensin II receptor antagonists

OBJECTIVE

To report a case of acute pancreatitis in a patient receiving a combination formulation of irbesartan and hydrochlorothiazide (HCTZ).

CASE SUMMARY

A 33-year-old white woman developed acute pancreatitis 10 days after starting irbesartan 300 mg and hydrochlorothiazide 12.5 mg for treatment of hypertension. Her symptoms disappeared and serum concentrations of lipase and amylase returned to normal 2 days after irbesartan/HCTZ was discontinued. A search of MEDLINE (1990-September 2002) and the Australian Adverse Drug Reaction Advisory Committee database revealed 1 additional case of pancreatitis associated with irbesartan/HCTZ and 3 cases of pancreatitis associated with losartan.

DISCUSSION

An objective causality assessment indicates that it is probable that pancreatitis was caused by the angiotensin II receptor antagonist irbesartan (and the same is probably true for losartan). It is less likely that the hydrochlorothiazide in irbesartan/HCTZ caused pancreatitis in our patient since the dose was lower than that usually associated with thiazide-induced pancreatitis. Angiotensin II receptors are thought to be important in regulation of pancreatic secretion and microcirculation, but the mechanism of pancreatitis induced by angiotensin II receptor antagonists remains unclear.

CONCLUSIONS

Clinicians should be aware that irbesartan/HCTZ or losartan may cause acute pancreatitis. If abdominal pain develops, the medication should be discontinued and the patient investigated for acute pancreatitis.

Beyond blood pressure: the endothelium and atherosclerosis progression

Endothelial dysfunction and remodeling of the vessel wall of large and small arteries is associated with hypertension and other risk factors for cardiovascular disease. These changes alter vascular function and mechanics, aggravate high blood pressure (BP), and may accelerate the progression of atherosclerosis. Activation of oxidative stress by angiotensin II is a key component of this process. Angiotensin II stimulates nicotinamide adenine dinucleotide phosphate (NADPH)/nicotinamide adenine dinucleotide (NADH) oxidase in endothelium, smooth muscle cells, and the adventitia of blood vessels to generate reactive oxygen species, leading to endothelial dysfunction, growth, and inflammation. Upregulation of endothelin-1, adhesion molecules, nuclear factor-kappaB, and other inflammatory mediators, as well as increased breakdown of nitric oxide and uncoupling of nitric oxide synthase, contribute to the progression of vascular disease and atherogenesis. Clinical studies in which treatment with angiotensin converting enzyme (ACE) inhibitors or angiotensin II receptor blockers (ARBs) was used demonstrated correction of some of the changes in large and small arteries in hypertensive subjects, whereas identical BP lowering with beta-blockers had no effect on endothelial function. In experimental models of atherosclerosis, ARBs, including losartan potassium, valsartan, and olmesartan medoxomil, have demonstrated the ability to prevent the progression of atherosclerosis. This was in part associated with decreased expression of inflammatory mediators and improved endothelial function. Blockade of the renin-angiotensin-aldosterone system with ACE inhibitors or ARBs appears to blunt both the development and progression of vascular disease in both small and large vessels in experimental models and in humans beyond the effect of these agents on BP. This may help to explain the positive results of recently completed trials such as Heart Outcomes Prevention Evaluation (HOPE) and Losartan Intervention for Endpoint Reduction in Hypertension (LIFE).

Vascular and cardiac benefits of angiotensin receptor blockers

Angiotensin II not only is a vasoconstrictor, but it also affects cell growth and apoptosis, inflammation, fibrosis, and coagulation. Blockade of the renin-angiotensin system, either with inhibitors of the generation of angiotensin (angiotensin-converting enzyme [ACE] inhibitors) or with blockers of angiotensin receptors, reduces blood pressure and inhibits other pathophysiological actions. These other effects provide benefits in coronary heart disease, heart failure, diabetic nephropathy, and stroke beyond blood pressure reduction. These benefits were first demonstrated with ACE inhibitors. However, the mechanism of action of angiotensin receptor blockers, which block angiotensin II stimulation at the angiotensin type 1 receptor but not at the type 2 receptor, may have advantages, particularly for endothelial dysfunction and vascular remodeling, as well as cardiac and renal protection. Recent multicenter trials suggest that ACE inhibitors and angiotensin receptor blockers may reduce morbidity and mortality associated with cardiovascular and renal disease beyond blood pressure reduction. Several studies with different angiotensin receptor blockers, including comparisons with ACE inhibitors, are under way, and should provide further guidance for their clinical use.

The role of angiotensin II receptor blockers in preventing the progression of renal disease in patients with type 2 diabetes

Diabetes mellitus is the most common cause of end-stage renal disease in the United States, accounting for about 50% of all new cases. Although we previously established the renoprotective benefits of angiotensin converting enzyme (ACE) inhibitors in patients with coexisting hypertension and type 1 diabetes, evidence of the renoprotective effect of ACE inhibitors in patients with type 2 diabetes is less clear. We conducted the Irbesartan Diabetic Nephropathy Trial (IDNT) to determine whether the angiotensin II receptor blocker (ARB) irbesartan slows the progression of nephropathy in patients with type 2 diabetes independently of its blood pressure (BP)-lowering effect. In this randomized, controlled trial, we found that irbesartan was associated with a 20% reduction in the risk for the primary composite end point (doubling of the baseline serum creatinine concentration, development of end-stage renal disease, or death from any cause) compared with placebo (P =.02) and a 23% reduction compared with amlodipine therapy (P =.006). These results were not explained by differences in the BP that was achieved. In a separate study, losartan was shown to reduce the risk for progression of renal disease in patients with type 2 diabetic nephropathy. Angiotensin II receptor blocker therapy has also been demonstrated to slow the progression to overt nephropathy when initiated early in the course of type 2 diabetic renal disease (ie, in patients with microalbuminuria). Based on these studies, ARBs are clearly effective in protecting against the progression of nephropathy due to type 2 diabetes. This protection is independent of their BP-lowering effect. Preclinical studies with the newest ARB, olmesartan medoxomil, suggest that this agent may provide renoprotective benefits as well.

Angiotensin converting enzyme inhibitors and angiotensin II receptor blockers: evidence for and against the combination in the treatment of hypertension and proteinuria

Several treatment guidelines have made strong recommendations to physicians that treatment of nephropathy and hypertension should be based on the use of a long-acting angiotensin converting enzyme (ACE) inhibitor if tolerated. The recently published clinical trials, based on angiotensin II receptor blockers' effects on diabetic nephropathy and essential hypertension, have also shown significant endpoint reduction. Perhaps the time has come to broaden the recommendations to include the use of a renin-angiotensin-aldosterone system altering drug. But what if the treatment goal cannot be reached, and incessant proteinuria and high blood pressure levels persist despite high dosage treatment of either drug? How should this be handled? The dual blockade principle can possibly provide the solution by obtaining the broadest and most efficient blockade of circulating angiotensin II by using the combination of an ACE inhibitor and an angiotensin II receptor blocker. But large clinical trials are yet to come, and at present large endpoint trials have not been published. This article provides an overview of how far we have come with dual blockade treatment in hypertension and nephropathy.

Strategies to meet lower blood pressure goals with a new standard in angiotensin II receptor blockade

The continued poor rates of blood pressure (BP) control to the recommended target BP of <140/90 mm Hg in patients with hypertension indicate a persistent need for improved antihypertensive therapy. Angiotensin II receptor blockers (ARBs) constitute the newest approved class of antihypertensive agents. As with angiotensin converting enzyme inhibitors, ARBs block the renin-angiotensin-aldosterone system, but do so through a more specific mechanism. Angiotensin converting enzyme inhibitors block the conversion of angiotensin I to angiotensin II, but angiotensin II may be produced by several alternate pathways. Angiotensin II receptor blockers, by contrast, inhibit the binding of angiotensin II to the angiotensin II type 1 (AT1) receptor, independent of the pathway of angiotensin II production. Comparative safety and efficacy trials indicate that ARBs are similar to other antihypertensive drugs in terms of BP-lowering effectiveness and have superior tolerability. Olmesartan medoxomil is the newest and one of the most effective of the ARBs. In controlled trials, it has been shown to provide 24-h BP control with antihypertensive efficacy at least as good as that of the calcium channel blockers amlodipine besylate and felodipine and the beta-blocker atenolol. In a comparative study, olmesartan medoxomil demonstrated significantly greater reductions in diastolic BP than did three other leading ARBs-losartan potassium, irbesartan, and valsartan. With the convenience of placebo-like tolerability and once-daily dosing, combined with excellent antihypertensive efficacy, olmesartan medoxomil may be a useful addition to our management of hypertension.

Contrasting effects of angiotensin type 1 and 2 receptors on nitric oxide release under pressure

This study was designed to test the hypothesis that increased pressure itself could cause endothelial dysfunction and lead to decreased nitric oxide (NO) release, partly through effects on the tissue renin angiotensin system in hypertension. Cultured endothelial cells (ECs) isolated from the aortas of WKY rats were continuously exposed to a pressure of 150 mmHg in a CO2 incubator for 72 h using a pressure system, and the NOx (NO2 and NO3) and angiotensin II (Ang II) concentrations in the supernatant were measured. An Ang II type 1 receptor (AT1R) antagonist (losartan) and an Ang II type 2 receptor (AT2R) antagonist (PD123319) were added to the medium. The expression of AT1R and AT2R mRNAs was also examined. Pressure loading significantly decreased the NO release from ECs. Concomitant administration of losartan restored NO release to the level before the application of pressure (p<0.001). This effect of losartan was blocked by simultaneous administration of PD123319, bradykinin type 2 receptor antagonist, and NO synthase inhibitor (p<0.05). The Ang II concentration was increased by pressure and was further increased by losartan. The gene expression of AT1R was not changed by pressure, but AT2R mRNA was increased almost 2-fold. These results indicate that high pressure itself attenuates NO release from ECs, and that losartan improves NO release by activating the bradykinin system via AT2R stimulation. In addition, the increase of AT2R gene expression in ECs during exposure to pressure may compensate for the reduction of NO.

Sympatholytic properties of several AT1-receptor antagonists in the isolated rabbit thoracic aorta

OBJECTIVE

To evaluate the facilitating effect of angiotensin II on sympathetic neurotransmission to quantitatively compare the sympatho-inhibitory potencies of the selective AT1 -receptor antagonists losartan, irbesartan and telmisartan in the isolated rabbit thoracic aorta.

DESIGN

To investigate the influence of pharmacological compounds on pre-junctional sympathetic transmission, the quantification of sympathetic transmitter release is the most straightforward approach.

METHODS

To investigate the sympatholytic properties of AT1 -blockers, we studied their effects on the enhancement by angiotensin II of electrical field stimulation (EFS)-evoked (2 Hz) sympathetic transmission in a modified spillover model.

RESULTS

Angiotensin II (0.01 nmol/l-0.1 micromol/l) caused a concentration-dependent enhancement of EFS-evoked noradrenaline release (control versus concentrations 0.1 nmol/l-0.1 micromol/l, P<0.05). The maximal augmentation, by almost 100%, was observed at a concentration of 1 nmol/l (FR2/FR1, 2.03 +/- 0.11 versus control, 0.99 +/- 0.03). Higher concentrations (up to 0.1 micromol/l) produced less than maximal facilitation. The AT1 -receptor antagonists losartan (0.1 nmol/l-0.1 micromol/l), telmisartan (0.01-10 nmol/l) and irbesartan (0.1 nmol/l-0.1 micromol/l) concentration dependently attenuated the angiotensin II-mediated (1 nmol/l) enhancement of EFS-evoked sympathetic outflow. The concentrations that reduced the enhancement by 50% (IC50 values, expressed as -log mol/l +/- SEM) were 9.05 +/- 0.16 losartan, 10.28 +/- 0.20 telmisartan and 9.20 +/- 0.23 irbesartan. Accordingly, the order of potency with respect to sympatho-inhibition proved telmisartan> irbesartan = losartan (where > signifies P<0.05).

CONCLUSIONS

The facilitating effect of angiotensin II on the sequelae of neuronal stimulation appears to be mediated by pre-synaptically located AT1 -receptors. Facilitation can be concentration dependently attenuated by AT1 -blockade. The order of potency with respect to sympatho-inhibition is telmisartan irbesartan = losartan. These differences may be explained by differences in affinity for the pre-synaptic AT1 -receptor.

Discovery of N-isoxazolyl biphenylsulfonamides as potent dual angiotensin II and endothelin A receptor antagonists

The ET(A) receptor antagonist (2) (N-(3,4-dimethyl-5-isoxazolyl)-4'-(2-oxazolyl)-[1,1'-biphenyl]-2-sulfonamide, BMS-193884) shares the same biphenyl core as a large number of AT(1) receptor antagonists, including irbesartan (3). Thus, it was hypothesized that merging the structural elements of 2 with those of the biphenyl AT(1) antagonists (e.g., irbesartan) would yield a compound with dual activity for both receptors. This strategy led to the design, synthesis, and discovery of (15) (4'-[(2-butyl-4-oxo-1,3-diazaspiro[4.4]non-1-en-3-yl)methyl]-N-(3,4-dimethyl-5-isoxazolyl)-2'-[(3,3-dimethyl-2-oxo-1-pyrrolidinyl)methyl]-[1,1'-biphenyl]-2-sulfonamide, BMS-248360) as a potent and orally active dual antagonist of both AT(1) and ET(A) receptors. Compound 15 represents a new approach to treating hypertension.

Risk-benefit assessment of angiotensin II receptor antagonists

Inhibiting the renin-angiotensin-aldosterone system through the use of angiotensin-converting enzyme (ACE) inhibitors has proven very useful in the treatment of hypertension, congestive heart failure (CHF) and progressive renal failure. More recently, agents that directly block the angiotensin II Type 1 (AT(1)) receptor--angiotensin II receptor antagonists (AIIRAs)--have been developed. These agents are thought to have a more specific mechanism of action since they do not affect other hormone systems as do the ACE inhibitors. Whether such specificity results in a different efficacy profile is still being determined. However, these drugs are extremely well-tolerated and very safe. AIIRAs are effective in the reduction of both systolic and diastolic blood pressure and compare favourably to other classes of agents. Recent results indicate that at least one AIIRA has a favourable effect on stroke in hypertensive patients with left ventricular hypertrophy. Additional studies with other members of the class will provide further information on similar outcomes. In CHF patients, ACE inhibitors remain the drug of choice and AIIRAs are best utilised in patients who cannot tolerate an ACE inhibitor or in those receiving an ACE inhibitor who cannot tolerate a beta-blocker and need additional therapy. AIIRAs are effective in slowing the progression of renal failure in patients with Type II diabetes and may be effective in other proteinuric conditions. Whether they are more or less effective than ACE inhibitors is unknown. Overall, AIIRAs represent an important addition to the armamentarium of cardiovascular therapies with an excellent safety record and an emerging profile of utility in multiple cardiovascular conditions.

The Losartan Intervention for Endpoint Reduction (LIFE) trial-have angiotensin-receptor blockers come of age?

The Losartan Intervention for Endpoint Reduction trial is one of several end-point trials that are now available with angiotensin-receptor blockers. This trial compared two regimens-losartan-based therapy to atenolol-based therapy-in 9193 hypertensive patients with electrocardiographic evidence of left ventricular hypertrophy. In the instance of each of these therapeutic groups, hydrochlorothiazide add-on therapy was permitted as per protocol. Although blood pressures were comparably reduced in both the losartan and the atenolol-based treatment groups, stroke rate was notably less in the losartan-treatment group. The 1195 patient diabetic cohort in this trial also experienced a substantial reduction in total and cardiovascular mortality favoring losartan. An additional finding in this trial was that new-onset diabetes developed 25% less frequently in the losartan-treated group. The results of this trial are both interesting and relevant to what is an expanding use of angiotensin-receptor blockers in the hypertensive population.

Evidence for the importance of angiotensin II type 1 receptor in ischemia-induced angiogenesis

The role of the renin-angiotensin system (RAS) in angiogenesis is little known. Here, we show that the angiotensin II (ATII) type 1 (AT1) receptor plays an important role in ischemia-induced angiogenesis. Well-developed collateral vessels and angiogenesis were observed in wild-type (WT) mice in response to hindlimb ischemia, whereas these responses were reduced in ATII type 1a receptor knockout (AT1a(-/-)) mice. Ischemia-induced angiogenesis was also impaired in WT mice treated with the AT1 receptor blocker TCV-116. These effects were not due to reduced systemic blood pressure (SBP), because hydralazine treatment preserved angiogenesis in WT mice although it reduced SBP to a level similar to that of AT1a(-/-) mice. Infiltration of inflammatory mononuclear cells (MNCs), including macrophages and T lymphocytes, was suppressed in the ischemic tissues of AT1a(-/-) mice compared with WT mice. Double immunofluorescence staining revealed that infiltrated macrophages and T lymphocytes expressed VEGF, and the expression of VEGF and monocyte chemoattractant protein-1 was also decreased in AT1a(-/-). Finally, the impaired angiogenesis in AT1a(-/-) mice was rescued by intramuscular transplantation of MNCs obtained from WT mice, further indicating the importance of MNC infiltration in ischemia-induced angiogenesis. Thus, the ATII--AT1 receptor pathway promotes early angiogenesis by supporting inflammatory cell infiltration and angiogenic cytokine expression.

Type 2 diabetes: RENAAL and IDNT--the emergence of new treatment options

The Reduction in End Points in NIDDM with the Angiotensin II Antagonist Losartan (RENAAL) study and the Irbesartan Diabetic Nephropathy Trial (IDNT) are two recently reported trials with hard end points, conducted in patients in advanced stages of diabetic nephropathy. Two other studies--the Irbesartan Microalbuminuria Study (IRMA)-2 and the Microalbuminuria Reduction with Valsartan study (MARVAL)--were trials conducted in patients with type 2 diabetes with microalbuminuria, a cardiovascular risk factor associated with early-stage diabetic nephropathy. These trials all had a common theme--that is, does an angiotensin receptor blocker (ARB) interfere with the natural history of diabetic nephropathy in a blood pressure-independent fashion? Without question, the results of these trials legitimatize the use of the ARB class in forestalling the deterioration in renal function, which is almost inevitable in the patient with untreated diabetic nephropathy. These data can now be added to the vast array of evidence supporting angiotensin-converting enzyme (ACE) inhibitor use in patients with nephropathy associated with type 1 diabetes. It now appears a safe conclusion that the patient with diabetic nephropathy should receive therapy with an agent that interrupts the renin-angiotensin system. These studies have not resolved the question as to whether an ACE inhibitor or an ARB is the preferred agent in people with nephropathy from type 1 diabetes, though the optimal doses of these drugs remain to be determined. Head-to-head studies comparing ACE inhibitors to ARBs in diabetic nephropathy are not likely to occur, so it is unlikely that comparable information will be forthcoming with ACE inhibitors. An evidence-based therapeutic approach derived from these trials would argue for ARBs to be the foundation of therapy in the patient with type 2 diabetes and nephropathy.

Inhibition of facilitation of sympathetic neurotransmission and angiotensin II-induced pressor effects in the pithed rat: comparison between valsartan, candesartan, eprosartan and embusartan

BACKGROUND

In the pithed rat model, endogenously generated angiotensin (Ang) II can enhance sympathetic neurotransmission by acting on Ang II type 1 (AT1) receptors that are located on sympathetic nerve terminals.

OBJECTIVE

To compare the inhibitory potency of candesartan, valsartan, eprosartan and embusartan in blocking presynaptically and postsynaptically located AT1 receptors.

DESIGN

To investigate blockade of presynaptic AT1 receptors, we studied the effect of AT1 receptor blockade on the sequelae of electrical stimulation of the thoracolumbar sympathetic outflow (0.25-8 Hz). To investigate the interaction between postsynaptic AT1 blockers and alpha-adrenoceptors, the effects of these compounds on pressor responses to exogenous noradrenaline were determined. To investigate blockade of postsynaptic AT1 receptors, we studied the effect of the AT1 antagonists on dose-response curves elicited by exogenous Ang II.

RESULTS

The stimulation-induced increase in diastolic blood pressure (DBP) and the Ang II-elicited DBP response were dose-dependently reduced by all AT1 receptor blockers. Interestingly, the greatest doses of the AT1 antagonists caused less than maximal reduction in the stimulation-induced increase in DBP, resulting in a U-shaped dose-response relationship. To compare sympathoinhibitory potencies, the doses that, at 2 Hz, reduced the change in DBP by 20 mmHg (ED20 values, expressed as -log mol/kg) were calculated; they were 5.50 +/- 0.12, 5.77 +/- 0.10, 6.32 +/- 0.12 and 5.62 +/- 0.13 for valsartan, candesartan, eprosartan and embusartan, respectively. The order of potency, therefore, was eprosartan> valsartan = candesartan = embusartan (where > signifies P < 0.05). To compare the order of potency for inhibition of the Ang II-induced increase in DBP, we calculated pA2 values (the X intercept in Schild regression). They were 7.20 +/- 0.17, 8.01 +/- 0.01, 7.20 +/- 0.03 and 7.25 +/- 0.16, for valsartan, candesartan, eprosartan and embusartan, respectively. Accordingly, the order of potency for inhibition of the direct pressor effects of Ang II was candesartan> valsartan = eprosartan = embusartan (where > signifies P < 0.05).

CONCLUSION

In the pithed rat, the effects on DBP of stimulation of the thoracolumbar spinal cord are partly dependent on endogenously formed Ang II. These effects can be counteracted by blockade of presynaptically located AT1 receptors. No interaction was found between postsynaptically located AT1 receptors and alpha-adrenoceptors. The order of potency of the agents tested for sympathoinhibition clearly differed from that for inhibition of the direct pressor effects of Ang II. These findings suggest considerable differences in affinity of the various AT1 blockers for pre- and postsynaptic AT1 receptors.

Inhibition of the formation or action of angiotensin II reverses attenuated K+ currents in type 1 and type 2 diabetes

1. Transient and sustained calcium-independent outward K(+) currents (I(t) and I(SS)) as well as action potentials were recorded in cardiac ventricular myocytes isolated from two models of diabetes mellitus. 2. Rats injected (I.V.) with streptozotocin (STZ, 100 mg kg(-1)) 6-10 days before cell isolation developed insulin-dependent (type 1) diabetes. I(t) and I(SS) were attenuated and the action potential prolonged. Incubation of myocytes (6-9 h) with the angiotensin II (ATII) receptor blockers saralasin or valsartan (1 microM) significantly augmented these currents. Inclusion of valsartan (1 g l(-1)) in the drinking water for 5-10 days prior to and following STZ injection partially prevented current attenuation. 3. Incubation of myocytes from STZ-treated rats (6-9 h) with 1 microM quinapril, an angiotensin-converting enzyme (ACE) inhibitor, significantly augmented I(t) and I(SS) and shortened the ventricular action potential. I(t) augmentation was not due to changes in steady-state inactivation or in recovery from inactivation. No acute effects of quinapril were observed. 4. The effects of quinapril and valsartan were abolished by 2 microM cycloheximide. 5. Myocytes were isolated from the db/db mouse, a leptin receptor mutant that develops symptoms of non-insulin-dependent (type 2) diabetes. K+ currents in these cells were also attenuated, and the action potentials prolonged. Incubation of these cells (> 6 h) with valsartan (1 microM) significantly enhanced the transient and sustained outward currents. 6. These results confirm recent suggestions that cardiac myocytes contain a renin-angiotensin system, which is activated in diabetes. It is proposed that chronic release of ATII leads to changes in ionic currents and action potentials, which can be reversed by blocking the formation or action of ATII. This may underlie the proven benefits of ATII receptor blockade or ACE inhibition in diabetes, by providing protection against cardiac arrhythmias.

AT1 receptor is present in glioma cells; its blockage reduces the growth of rat glioma

Malignancy of neoplasms is partly dependent on angiogenesis. Angiotensin II mediates angiogenesis and transcription of growth-related factors through stimulation of the AT1 receptor (AT1R). Losartan, a drug used mostly for treatment of hypertension, binds strongly to this receptor. We found the presence of AT1 receptor on C6 glioma cells and studied the effect of Losartan on the growth and angiogenesis of C6 rat glioma; Losartan in dose of 80 mg/kg induced 79% reduction of tumoural volume with a significant decrease of vascular density, mitotic index and cell proliferation. Our results demonstrate the conspicuous presence of AT1R in malignant glial cells and a favourable therapeutic response in experimental glioma by selective blockage of the AT1 receptor.

Novel angiotensin II inhibitors in cardiovascular medicine

Blockade of the renin-angiotensin-aldosterone cascade is now recognised as a very effective approach to treat hypertensive, heart failure and high cardiovascular risk patients and to retard the development of renal failure. The purpose of this review is to discuss the state of development of currently available drugs blocking the renin-angiotensin system, such as angiotensin converting enzyme (ACE) inhibitors, renin inhibitors and angiotensin II receptor antagonists, with a special emphasis on the results of the most recent trials conducted with AT(2) receptor antagonists in heart failure and Type 2 diabetes. In addition, the future perspectives of drugs with dual mechanisms of action, such as NEP/ACE inhibitors, also named vasopeptidase inhibitors, are presented.

The clinical implication of tissue renin angiotensin systems

The presence, and in many cases the regulated synthesis, of components of the renin-angiotensin system have been demonstrated in multiple tissues, indicating the existence of tissue angiotensin-generating systems. These vary with respect to which renin-angiotensin system components are synthesized locally and which are taken up from plasma. Enzymes unrelated to the classical renin-angiotensin system may also contribute to tissue angiotensin synthesis. However, based on the available data, the prevailing opinion that kidney-derived renin is in all cases the only physiologically relevant renin in tissues must be revised. Also there is evidence indicating a role for tissue angiotensin systems in the pathogenesis of cardiovascular disease and in cardiovascular structural remodeling. The angiotensin-regulated synthesis of aldosterone in cardiac tissue has been described, suggesting the possibility that a renin-angiotensin-aldosterone system exists in the heart. In addition, intracellular (intracrine) sites of angiotensin action have been reported. Some of these findings have implications for therapeutics and, in particular, for the use of angiotensin converting-enzyme inhibitors and angiotensin receptor blockers. Finally, tissue angiotensin systems outside the cardiovascular system also appear to be physiologically relevant.

Therapeutic potential of angiotensin II receptor antagonists

The circulating renin-angiotensin system plays an important role in cardiovascular homeostasis. More importantly, the local tissue renin angiotensin plays a pivotal role in cell growth and remodelling of cardiomyocytes and on the peripheral arterial vasculature. In addition, the renin angiotensin system is related to apoptosis, control of baroreflex and autonomic responses, vascular remodelling and regulation of coagulation, inflammation and oxidation. The cardioprotective and vascular protective effects of the angiotensin receptive blockade appears to be related to selective blockade of the angiotensin II (A-II) Type I (AT(1)) receptors. However, there is now growing evidence showing that some of the effects of AT-II receptor blockers (ARBs) are related to the activation of the kinin pathways. This paper will review some of the recent mechanisms related to the cardiovascular effects of angiotensin and more specifically of ARBs. This paper will present the novel data on the role of ARB in the development of atherosclerosis, vascular remodelling, coagulation balance and autonomic regulation. Finally, the role of ARBs, used alone or in combination with ACE inhibitor in patients with heart failure, will be discussed.

ELITE II and Val-HeFT are different trials: together what do they tell us?

The Losartan Heart Failure Survival Study (ELITE II) and the Valsartan Heart Failure Trial (Val-HeFT) both evaluated the efficacy and tolerability of a selective angiotensin II receptor antagonist on morbidity and mortality in patients with symptomatic heart failure. The trials differed, however, in terms of their primary hypothesis, study design, and treatment regimens, and this must be taken into consideration when comparing and interpreting the data from these studies. The data are in many ways complementary, and add to our understanding of the optimal treatment of symptomatic heart failure. Additional studies are needed, however, to fully define the role of angiotensin II receptor antagonists in the management of this very heterogeneous group of patients.