Comparative angiotensin II receptor blockade in healthy volunteers: the importance of dosing.

OBJECTIVES: We have reported previously that 80 mg valsartan and 50 mg losartan provide less receptor blockade than 150 mg irbesartan in normotensive subjects. In this study we investigated the importance of drug dosing in mediating these differences by comparing the AT(1)-receptor blockade induced by 3 doses of valsartan with that obtained with 3 other antagonists at given doses. METHODS: Valsartan (80, 160, and 320 mg), 50 mg losartan, 150 mg irbesartan, and 8 mg candesartan were administered to 24 healthy subjects in a randomized, open-label, 3-period crossover study. All doses were given once daily for 8 days. The angiotensin II receptor blockade was assessed with two techniques, the reactive rise in plasma renin activity and an in vitro radioreceptor binding assay that quantified the displacement of angiotensin II by the blocking agents. Measurements were obtained before and 4 and 24 hours after drug intake on days 1 and 8. RESULTS: At 4 and 24 hours, valsartan induced a dose-dependent "blockade" of AT(1) receptors. Compared with other antagonists, 80 mg valsartan and 50 mg losartan had a comparable profile. The 160-mg and 320-mg doses of valsartan blocked AT(1) receptors at 4 hours by 80%, which was similar to the effect of 150 mg irbesartan. At trough, however, the valsartan-induced blockade was slightly less than that obtained with irbesartan. With use of plasma renin activity as a marker of receptor blockade, on day 8, 160 mg valsartan was equivalent to 150 mg irbesartan and 8 mg candesartan. CONCLUSIONS: These results show that the differences in angiotensin II receptor blockade observed with the various AT(1) antagonists are explained mainly by differences in dosing. When 160-mg or 320-mg doses were investigated, the effects of valsartan hardly differed from those obtained with recommended doses of irbesartan and candesartan.

Ageing-related cardiomyocyte functional decline is sex and angiotensin II dependent.

Clinically, heart failure is an age-dependent pathological phenomenon and displays sex-specific characteristics. The renin-angiotensin system mediates cardiac pathology in heart failure. This study investigated the sexually dimorphic functional effects of ageing combined with angiotensin II (AngII) on cardiac muscle cell function, twitch and Ca(2+)-handling characteristics of isolated cardiomyocytes from young (~13 weeks) and aged (~87 weeks) adult wild type (WT) and AngII-transgenic (TG) mice. We hypothesised that AngII-induced contractile impairment would be exacerbated in aged female cardiomyocytes and linked to Ca(2+)-handling disturbances. AngII-induced cardiomyocyte hypertrophy was evident in young adult mice of both sexes and accentuated by age (aged adult ~21-23 % increases in cell length relative to WT). In female AngII-TG mice, ageing was associated with suppressed cardiomyocyte contractility (% shortening, maximum rate of shortening, maximum rate of relaxation). This was associated with delayed cytosolic Ca(2+) removal during twitch relaxation (Tau ~20 % increase relative to young adult female WT), and myofilament responsiveness to Ca(2+) was maintained. In contrast, aged AngII-TG male cardiomyocytes exhibited peak shortening equivalent to young TG; yet, myofilament Ca(2+) responsiveness was profoundly reduced with ageing. Increased pro-arrhythmogenic spontaneous activity was evident with age and cardiac AngII overexpression in male mice (42-55 % of myocytes) but relatively suppressed in female aged transgenic mice. Female myocytes with elevated AngII appear more susceptible to an age-related contractile deficit, whereas male AngII-TG myocytes preserve contractile function with age but exhibit desensitisation of myofilaments to Ca(2+) and a heightened vulnerability to arrhythmic activity. These findings support the contention that sex-specific therapies are required for the treatment of age-progressive heart failure.

Cardiac Lineage Protein-1 (CLP-1) Regulates Cardiac Remodeling via Transcriptional Modulation of Diverse Hypertrophic and Fibrotic Responses and Angiotensin II-transforming Growth Factor β (TGF-β1) Signaling Axis.

It is well known that the renin-angiotensin system contributes to left ventricular hypertrophy and fibrosis, a major determinant of myocardial stiffness. TGF-β1 and renin-angiotensin system signaling alters the fibroblast phenotype by promoting its differentiation into morphologically distinct pathological myofibroblasts, which potentiates collagen synthesis and fibrosis and causes enhanced extracellular matrix deposition. However, the atrial natriuretic peptide, which is induced during left ventricular hypertrophy, plays an anti-fibrogenic and anti-hypertrophic role by blocking, among others, the TGF-β-induced nuclear localization of Smads. It is not clear how the hypertrophic and fibrotic responses are transcriptionally regulated. CLP-1, the mouse homolog of human hexamethylene bis-acetamide inducible-1 (HEXIM-1), regulates the pTEFb activity via direct association with pTEFb causing inhibition of the Cdk9-mediated serine 2 phosphorylation in the carboxyl-terminal domain of RNA polymerase II. It was recently reported that the serine kinase activity of Cdk9 not only targets RNA polymerase II but also the conserved serine residues of the polylinker region in Smad3, suggesting that CLP-1-mediated changes in pTEFb activity may trigger Cdk9-dependent Smad3 signaling that can modulate collagen expression and fibrosis. In this study, we evaluated the role of CLP-1 in vivo in induction of left ventricular hypertrophy in angiotensinogen-overexpressing transgenic mice harboring CLP-1 heterozygosity. We observed that introduction of CLP-1 haplodeficiency in the transgenic α-myosin heavy chain-angiotensinogen mice causes prominent changes in hypertrophic and fibrotic responses accompanied by augmentation of Smad3/Stat3 signaling. Together, our findings underscore the critical role of CLP-1 in remodeling of the genetic response during hypertrophy and fibrosis.

Effect of angiotensin II and losartan on the phagocytic activity of peritoneal macrophages from Balb/C mice

Angiotensin II (AII), a product of rennin-angiotensin system, exerts an important role on the function of immune system cells. In this study, the effect of AII on the phagocytic activity of mouse peritoneal macrophages was assessed. Mice peritoneal macrophages were cultured for 48 h and the influence of different concentrations of AII (10-14 to 10-7 M) and/or losartan, 10-16 to 10-6 M), an AT1 angiotensin receptor antagonist, on phagocytic activity and superoxide anion production was determined. Dimethylthiazoldiphenyltetrazolium bromide reduction and the nucleic acid content were used to assess the cytotoxicity of losartan. A stimulatory effect on phagocytic activity (P < 0.05) was observed with 10-13 M and 10-12 M AII concentrations. The addition of losartan (up to10-14 M) to the cell cultures blocked (P < 0.001) the phagocytosis indicating the involvement of AT1 receptors. In contrast, superoxide anion production was not affected by AII or losartan. The existence of AT1 and AT2 receptors in peritoneal macrophages was demonstrated by immunofluorescence microscopy. These results support the hypothesis that AII receptors can modulate murine macrophage activity and phagocytosis, and suggest that AII may have a therapeutic role as an immunomodulatory agent in modifying the host resistance to infection.

Comparative vascular and renal tubular effects of angiotensin II receptor blockers combined with a thiazide diuretic in humans.

OBJECTIVE: The goal of this study was to investigate whether angiotensin II receptor blockers (ARBs) induce a comparable blockade of AT1 receptors in the vasculature and in the kidney when the renin-angiotensin system is activated by a thiazide diuretic. METHOD: Thirty individuals participated in this randomized, controlled, single-blind study. The blood pressure and renal hemodynamic and tubular responses to a 1-h infusion of exogenous angiotensin II (Ang II 3 ng/kg per min) were investigated before and 24 h after a 7-day administration of either irbesartan 300 mg alone or in association with 12.5 or 25 mg hydrochlorothiazide (HCTZ). Irbesartan 300/25 mg was also compared with losartan 100 mg, valsartan 160 mg, and olmesartan 20 mg all in association with 25 mg HCTZ. Each participant received two treatments with a 1-week washout period between treatments. RESULTS: The blood pressure response to Ang II was blocked by more than 90% with irbesartan alone or in association with HCTZ and with olmesartan/HCTZ and by nearly 60% with valsartan/HCTZ and losartan/HCTZ (P < 0.05). In the kidney, Ang II reduced renal plasma flow by 36% at baseline (P < 0.001). Irbesartan +/- HCTZ and olmesartan/HCTZ blocked the renal hemodynamic response to Ang II nearly completely, whereas valsartan/HCTZ and losartan/HCTZ only blunted this effect by 34 and 45%, respectively. At the tubular level, Ang II significantly reduced urinary volume (-84%) and urinary sodium excretion (-65%) (P < 0.01). These tubular effects of Ang II were only partially blunted by the administration of ARBs. CONCLUSION: These data demonstrate that ARBs prescribed at their recommended doses do not block renal tubular AT1 receptors as effectively as vascular receptors do. This observation may account for the need of higher doses of ARB for renal protection. Moreover, our results confirm that there are significant differences between ARBs in their capacity to induce a sustained vascular and tubular blockade of Ang II receptors.

Plasma angiotensin-(1-8) octapeptide measurement to assess acute angiotensin-converting enzyme inhibition with captopril administered parenterally to normal subjects.

The blood pressure (BP), heart rate (HR), and humoral effects of single intravenous (i.v.) doses of the angiotensin-converting enzyme (ACE) inhibitor captopril was investigated in five normotensive healthy volunteers. Each subject received at 1-week intervals a bolus dose of either captopril (1, 5, and 25 mg) or its vehicle. The study was conducted in a single-blind fashion, and the order of treatment phases was randomized. The different doses of captopril had no acute effect on BP and HR. They induced a dose-dependent decrease in plasma ACE activity and plasma angiotensin II levels. The angiotensin-(1-8) octapeptide was isolated by solid-phase extraction and high-performance liquid chromatography (HPLC) prior to radioimmunoassay (RIA). All three doses of captopril reduced circulating angiotensin II levels within 15 min of drug administration. Only with the 25-mg dose was the angiotensin II concentration below the detection limit at 15 min and still significantly reduced 90 min after drug administration. Simultaneous and progressive decreases in plasma aldosterone levels were observed both with ACE inhibition and during vehicle injection, but the relative fall was more pronounced after captopril administration. No adverse reaction was noticed. These results demonstrate that captopril given parenterally blocks the renin-angiotensin system in a dose-dependent manner. Only with the dose of 25 mg was the inhibition of plasma-converting enzyme activity and the reduction of plasma angiotensin II sustained for at least 1 1/2 h.

Clinical and hormonal effects of the new angiotensin II receptor antagonist LRB081.

The renin-angiotensin system is a major contributor to the pathophysiology of cardiovascular diseases such as congestive heart failure and hypertension. Antagonizing angiotensin (Ang) II at the receptor site may produce fewer side effects than inhibition of the promiscuous converting enzyme. The present study was designed to assess in healthy human subjects the effect of LRB081, a new orally active AT1-receptor antagonist, on the pressor action of exogenous Ang II. At the same time, plasma hormones and drug levels were monitored. At 1-week intervals and in a double-blind randomized fashion, 8 male volunteers received three doses of LRB081 (10, 40, and 80 mg) and placebo. Blood pressure (BP) was measured at a finger by photoplethysmograph. The peak BP response to intravenous injection of a standard dose of Ang II was determined before and for < or = 24 h after administration of an oral dose of LRB081 or placebo. After drug administration, the blood BP response to Ang II was expressed in percent of the response before drug administration. At the same time, plasma renin activity (PRA), Ang II, aldosterone, catecholamine (radioassays), and drug levels (by high-performance liquid chromatography) were monitored. After LRB081 administration, a dose dependent inhibition of the BP response to Ang II was observed. Maximal inhibition of the systolic BP response was 54 +/- 3 (mean +/- SEM), 63 +/- 2, and 93 +/- 1% with 10, 40, and 80 mg LRB081, respectively. The time to peak was 3 h for 6 subjects and 4 and 6 h for 2 others. Preliminary plasma half-life (t1/2) was calculated at 2 h. With the highest dose, the inhibition remained significant for 24 h (31 +/- 5%, p < 0.05). Maximal BP-blocking effect and maximal plasma drug level coincided, suggesting that the unmetabolized LRB081 is responsible for the antagonistic effect. PRA and Ang II increased dose dependently after LRB081 intake. Aldosterone, epinephrine, and norepinephrine concentrations remained unchanged. No clinically significant adverse reaction was observed during the study. LRB081 is a well-tolerated, orally active, potent, and long-acting Ang II receptor antagonist. Unlike in the case of losartan, no active metabolite of LRB081 has been shown to be responsible for the main effects.

Reactive hyperreninemia is a major determinant of plasma angiotensin II during ACE inhibition.

The new ACE inhibitor trandolapril was administered to normal volunteers at daily doses of 0.5, 2, and 8 mg for 10 days. Twenty-one volunteers, aged 21-30 years, were included in the study. To randomly selected groups of seven subjects, each dose was administered in a single-blind fashion. None of the doses induced a consistent fall in blood pressure. Angiotensin-converting enzyme activity (ACE) was measured in vitro using three different synthetic substrates (i.e., Hip-Gly-Gly, Z-Phe-His-Leu, or angiotensin I). Although the degree of ACE inhibition assessed with the three methods varied widely, all methods clearly indicated dose-dependent ACE inhibition. These in vitro results were confirmed by measuring ACE inhibition in vivo using the ratio of plasma angiotensin II (ANG II) to blood angiotensin I (ANG I). The dose-dependent ACE inhibition was paralleled by a dose-dependent rise in active renin and blood angiotensin I levels, most evident on day 10. In contrast, plasma ANG II levels on day 10 were not different whether the volunteers received 0.5 or 8 mg trandolapril. Thus, whereas increasing doses of this new ACE inhibitor progressively enhanced the blockade of ACE activity, this was not reflected by additional reductions of plasma ANG II levels. The progressive enhancement of ACE inhibition seemed to be offset by the accentuation of the compensatory rise in renin and ANG I, which was still partially converted to ANG II.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased cardiac angiotensin II levels induce right and left ventricular hypertrophy in normotensive mice.

Angiotensin II is a potent arterial vasoconstrictor and induces hypertension. Angiotensin II also exerts a trophic effect on cardiomyocytes in vitro. The goals of the present study were to document an in vivo increase in cardiac angiotensins in the absence of elevated plasma levels or hypertension and to investigate prevention or regression of ventricular hypertrophy by renin-angiotensin system blockade. We demonstrate that high cardiac angiotensin II is directly responsible for right and left ventricular hypertrophy. We used transgenic mice overexpressing angiotensinogen in cardiomyocytes characterized by cardiac hypertrophy without fibrosis and normal blood pressure. Angiotensin-converting enzyme inhibition and angiotensin II type 1 receptor blockade prevent or normalize ventricular hypertrophy. Surprisingly, in control mice, receptor blockade decreases tissue angiotensin II despite increased plasma levels. This suggests that angiotensin II may be protected from metabolization by binding to its receptor. Blocking of the angiotensin II type 1 receptor rather than enhanced stimulation of the angiotensin II type 2 receptor may prevent remodeling and account for the beneficial effects of angiotensin antagonists.

Role of bradykinin in the neonatal renal effects of angiotensin converting enzyme inhibition.

The vascular effects of angiotensin converting enzyme inhibitors are mediated by the inhibition of the dual action of angiotensin converting enzyme (ACE): production of angiotensin II and degradation of bradykinin. The deleterious effect of converting enzyme inhibitors (CEI) on neonatal renal function have been ascribed to the elevated activity of the renin-angiotensin system. In order to clarify the role of bradykinin in the CEI-induced renal dysfunction of the newborn, the effect of perindoprilat was investigated in anesthetized newborn rabbits with intact or inhibited bradykinin B2 receptors. Inulin and PAH clearances were used as indices of GFR and renal plasma flow, respectively. Perindoprilat (20 microg/kg i.v.) caused marked systemic and renal vasodilation, reflected by a fall in blood pressure and renal vascular resistance. GFR decreased, while urine flow rate did not change. Prior inhibition of the B2 receptors by Hoe 140 (300 microg/kg s.c.) did not prevent any of the hemodynamic changes caused by perindoprilat, indicating that bradykinin accumulation does not contribute to the CEI-induced neonatal renal effects. A control group receiving only Hoe 140 revealed that BK maintains postglomerular vasodilation via B2 receptors in basal conditions. Thus, the absence of functional B2 receptors in the newborn was not responsible for the failure of Hoe 140 to prevent the perindoprilat-induced changes. Species- and/or age-related differences in the kinin-metabolism could explain these results, suggesting that in the newborn rabbit other kininases than ACE are mainly responsible for the degradation of bradykinin.

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.

Angiotensin II antagonists DuP 753 and TCV 116.

BACKGROUND: Acute blockade of the renin-angiotensin system with the parenterally active angiotensin II antagonist saralasin has been shown to effectively lower blood pressure in a large fraction of patients with essential hypertension and to improve haemodynamics in some patients with congestive heart failure. It is now possible to chronically antagonize angiotensin II at its receptor using non-peptide angiotensin II inhibitors such as losartan (DuP 753/MK-954) or TCV 116. EFFECT OF NON-PEPTIDE ANGIOTENSIN II ANTAGONISTS: When administered by mouth, DuP 753 and TCV 116 induce dose-dependent inhibition of the pressor response to exogenous angiotensin II. This effect is closely related to circulating levels of the corresponding active metabolites E3174 and CV11974. Preliminary studies performed in hypertensive patients suggest that losartan lowers blood pressure to an equivalent extent to an angiotensin converting enzyme (ACE) inhibitor. CONCLUSIONS: Further investigation is required to show whether these new angiotensin II antagonists compounds compare favourably with ACE inhibitors.

Angiotensin II receptor blockade in normotensive subjects: A direct comparison of three AT1 receptor antagonists.

Use of angiotensin (Ang) II AT1 receptor antagonists for treatment of hypertension is rapidly increasing, yet direct comparisons of the relative efficacy of antagonists to block the renin-angiotensin system in humans are lacking. In this study, the Ang II receptor blockade induced by the recommended starting dose of 3 antagonists was evaluated in normotensive subjects in a double-blind, placebo-controlled, randomized, 4-way crossover study. At 1-week intervals, 12 subjects received a single dose of losartan (50 mg), valsartan (80 mg), irbesartan (150 mg), or placebo. Blockade of the renin-angiotensin system was assessed before and 4, 24, and 30 hours after drug intake by 3 independent methods: inhibition of the blood pressure response to exogenous Ang II, in vitro Ang II receptor assay, and reactive changes in plasma Ang II levels. At 4 hours, losartan blocked 43% of the Ang II-induced systolic blood pressure increase; valsartan, 51%; and irbesartan, 88% (P<0.01 between drugs). The effect of each drug declined with time. At 24 hours, a residual effect was found with all 3 drugs, but at 30 hours, only irbesartan induced a marked, significant blockade versus placebo. Similar results were obtained when Ang II receptor blockade was assessed with an in vitro receptor assay and by the reactive rise in plasma Ang II levels. This study thus demonstrates that the first administration of the recommended starting dose of irbesartan induces a greater and longer lasting Ang II receptor blockade than that of valsartan and losartan in normotensive subjects.

Renal hemodynamic and natriuretic effects of concomitant Angiotensin-converting enzyme and neutral endopeptidase inhibition in men.

This double-blind placebo-controlled study was designed to investigate the acute and sustained hormonal, renal hemodynamic, and tubular effects of concomitant ACE and neutral endopeptidase (NEP) inhibition by omapatrilat, a vasopeptidase inhibitor, in men. Thirty-two normotensive subjects were randomized to receive a placebo, omapatrilat (40 or 80 mg), or the fosinopril/hydrochlorothiazide (FOS/HCTZ; 20 and 12.5 mg, respectively) fixed combination for 1 week. Blood pressure, renal hemodynamics, urinary electrolytes and atrial natriuretic peptide excretion, and several components of the renin-angiotensin system were measured for 6 hours on days 1 and 7 of drug administration. When compared with the placebo and the FOS/HCTZ combination, omapatrilat induced a significant decrease in plasma angiotensin II levels (P<0.001 versus placebo; P<0.05 versus FOS/HCTZ) and an increase in urinary atrial natriuretic peptide excretion (P<0.01). These hormonal effects were associated with a significant fall in blood pressure (P<0.01) and a marked renal vasodilatation, but with no significant changes in glomerular filtration rate. The FOS/HCTZ markedly increased urinary sodium excretion (P<0.001). The acute natriuretic response to FOS/HCTZ was significantly greater than that observed with omapatrilat (P<0.01). Over 1 week, however, the cumulative sodium excretion induced by both doses of omapatrilat (P<0.01 versus placebo) was at least as great as that induced by the dose of FOS/HCTZ (P=NS versus FOS/HCTZ). In conclusion, the results of the present study in normal subjects demonstrate that omapatrilat has favorable renal hemodynamic effects. Omapatrilat combines potent ACE inhibition with a sustained natriuresis, which explains its well-documented potent antihypertensive efficacy.

Angiotensin-converting enzyme inhibition improves vascular function in rheumatoid arthritis.

BACKGROUND: The excess in cardiovascular risk in patients with rheumatoid arthritis provides a strong rationale for early therapeutical interventions. In view of the similarities between atherosclerosis and rheumatoid arthritis and the proven benefit of angiotensin-converting enzyme inhibitors in atherosclerotic vascular disease, it was the aim of the present study to delineate the impact of ramipril on endothelial function as well as on markers of inflammation and oxidative stress in patients with rheumatoid arthritis. METHODS AND RESULTS: Eleven patients with rheumatoid arthritis were included in this randomized, double-blind, crossover study to receive ramipril in an uptitration design (2.5 to 10 mg) for 8 weeks followed by placebo, or vice versa, on top of standard antiinflammatory therapy. Endothelial function assessed by flow-mediated dilation of the brachial artery, markers of inflammation and oxidative stress, and disease activity were investigated at baseline and after each treatment period. Endothelial function assessed by flow-mediated dilation increased from 2.85+/-1.49% to 4.00+/-1.81% (P=0.017) after 8 weeks of therapy with ramipril but did not change with placebo (from 2.85+/-1.49% to 2.84+/-2.47%; P=0.88). Although systolic blood pressure and heart rate remained unaltered, diastolic blood pressure decreased slightly from 78+/-7 to 74+/-6 mm Hg (P=0.03). Tumor necrosis factor-alpha showed a significant inverse correlation with flow-mediated dilation (r=-0.408, P=0.02), and CD40 significantly decreased after ramipril therapy (P=0.049). CONCLUSIONS: Angiotensin-converting enzyme inhibition with 10 mg/d ramipril for 8 weeks on top of current antiinflammatory treatment markedly improved endothelial function in patients with rheumatoid arthritis. This finding suggests that angiotensin-converting enzyme inhibition may provide a novel strategy to prevent cardiovascular events in these patients.