Effect of SR 47436, a novel angiotensin II AT1 receptor antagonist, on human vascular smooth muscle cells in vitro

Drug in Adhesive Transdermal Formulation of Valsartan and Nifedipine: Pharmacokinetics and Pharmacodynamics in Rats

Background:

The increasing complications associated with hypertension often require a combination of two or more drugs acting through different routes to counter the elevated blood pressure.

Objective:

The present investigation envisaged at preparing and evaluating a transdermal formulation containing gelled microemulsion drug in adhesive (DIA) patch for simultaneous systemic delivery of valsartan and nifedipine aimed at effective management of hypertension.

Methods:

An optimized microemulsion was prepared by using Captex® 500 (7.34% w/w), Capmul® MCM (4.24% w/w), Acrysol EL 135 (24.43% w/w), Transcutol P® (5% w/w) and water (58.9% w/w). Gelling was contributed by polyvinylpyrrolidone K 90F and polyethyleneimine where the latter also conferred skin adhesion properties to the patch. DIA patches were evaluated for in vitro drug release as well as in vivo pharmacokinetics and pharmacodynamics in rats.

Results:

In vitro permeation of nifedipine or valsartan from the selected DIA patch was 10.67-fold and 1.25-fold higher as compared to their aqueous dispersions. The relative bioavailability of nifedipine was 1.34 and that of valsartan was 2.18 from this DIA patch with respect to the oral administration of their aqueous suspension.

Conclusion:

Transdermal delivery of either drug alone was not effective in reducing methyl prednisolone acetate-induced hypertension, whereas, simultaneous transdermal delivery of both drugs from DIA patch effectively maintained systolic blood pressure at a normal level in these rats for 20 h.

Angiotensin II type 1 receptor antagonists in animal models of vascular, cardiac, metabolic and renal disease

We have reviewed the effects of angiotensin II type 1 receptor antagonists (ARBs) in various animal models of hypertension, atherosclerosis, cardiac function, hypertrophy and fibrosis, glucose and lipid metabolism, and renal function and morphology. Those of azilsartan and telmisartan have been included comprehensively whereas those of other ARBs have been included systematically but without intention of completeness. ARBs as a class lower blood pressure in established hypertension and prevent hypertension development in all applicable animal models except those with a markedly suppressed renin-angiotensin system; blood pressure lowering even persists for a considerable time after discontinuation of treatment. This translates into a reduced mortality, particularly in models exhibiting marked hypertension. The retrieved data on vascular, cardiac and renal function and morphology as well as on glucose and lipid metabolism are discussed to address three main questions: 1. Can ARB effects on blood vessels, heart, kidney and metabolic function be explained by blood pressure lowering alone or are they additionally directly related to blockade of the renin-angiotensin system? 2. Are they shared by other inhibitors of the renin-angiotensin system, e.g. angiotensin converting enzyme inhibitors? 3. Are some effects specific for one or more compounds within the ARB class? Taken together these data profile ARBs as a drug class with unique properties that have beneficial effects far beyond those on blood pressure reduction and, in some cases distinct from those of angiotensin converting enzyme inhibitors. The clinical relevance of angiotensin receptor-independent effects of some ARBs remains to be determined.

A systematic comparison of the properties of clinically used angiotensin II type 1 receptor antagonists

Angiotensin II type 1 receptor antagonists (ARBs) have become an important drug class in the treatment of hypertension and heart failure and the protection from diabetic nephropathy. Eight ARBs are clinically available [azilsartan, candesartan, eprosartan, irbesartan, losartan, olmesartan, telmisartan, valsartan]. Azilsartan (in some countries), candesartan, and olmesartan are orally administered as prodrugs, whereas the blocking action of some is mediated through active metabolites. On the basis of their chemical structures, ARBs use different binding pockets in the receptor, which are associated with differences in dissociation times and, in most cases, apparently insurmountable antagonism. The physicochemical differences between ARBs also manifest in different tissue penetration, including passage through the blood-brain barrier. Differences in binding mode and tissue penetration are also associated with differences in pharmacokinetic profile, particularly duration of action. Although generally highly specific for angiotensin II type 1 receptors, some ARBs, particularly telmisartan, are partial agonists at peroxisome proliferator-activated receptor-γ. All of these properties are comprehensively reviewed in this article. Although there is general consensus that a continuous receptor blockade over a 24-hour period is desirable, the clinical relevance of other pharmacological differences between individual ARBs remains to be assessed.

Long-term use and tolerability of irbesartan for control of hypertension

In this review, we discuss the pharmacological and clinical properties of irbesartan, a noncompetitive angiotensin II receptor type 1 antagonist, successfully used for more than a decade in the treatment of essential hypertension. Irbesartan exerts its antihypertensive effect through an inhibitory effect on the pressure response to angiotensin II. Irbesartan 150-300 mg once daily confers a lasting effect over 24 hours, and its antihypertensive efficacy is further enhanced by the coadministration of hydrochlorothiazide. Additionally and partially beyond its blood pressure-lowering effect, irbesartan reduces left ventricular hypertrophy, favors right atrial remodeling in atrial fibrillation, and increases the likelihood of maintenance of sinus rhythm after cardioversion in atrial fibrillation. In addition, the renoprotective effects of irbesartan are well documented in the early and later stages of renal disease in type 2 diabetics. Furthermore, both the therapeutic effectiveness and the placebo-like side effect profile contribute to a high adherence rate to the drug. Currently, irbesartan in monotherapy or combination therapy with hydrochlorothiazide represent a rationale pharmacologic approach for arterial hypertension and early-stage and late-stage diabetic nephropathy in hypertensive type II diabetics.

Losartan Inhibits Vascular Smooth Muscle Cell Proliferation through Activation of AMP-Activated Protein Kinase

Losartan is a selective angiotensin II (Ang II) type 1 (AT(1)) receptor antagonist which inhibits vascular smooth muscle cells (VSMCs) contraction and proliferation. We hypothesized that losartan may prevent cell proliferation by activating AMP-activated protein kinase (AMPK) in VSMCs. VSMCs were treated with various concentrations of losartan. AMPK activation was measured by Western blot analysis and cell proliferation was measured by MTT assay and flowcytometry. Losartan dose- and time-dependently increased the phosphorylation of AMPK and its downstream target, acetyl-CoA carboxylase (ACC) in VSMCs. Losartan also significantly decreased the Ang II- or 15% FBS-induced VSMC proliferation by inhibiting the expression of cell cycle associated proteins, such as p-Rb, cyclin D, and cyclin E. Compound C, a specific inhibitor of AMPK, or AMPK siRNA blocked the losartan-induced inhibition of cell proliferation and the G(0)/G(1) cell cycle arrest. These data suggest that losartan-induced AMPK activation might attenuate Ang II-induced VSMC proliferation through the inhibition of cell cycle progression.

Vascular benefits of angiotensin receptor blockers

There is convincing evidence that angiotensin II, through activation of the angiotensin II type 1 (AT1) receptor, is involved in the atherosclerotic process. Similarly, angiotensin receptor blockers decrease vascular inflammation, hypertrophy and thrombosis, which are the key components of the progression of atherosclerosis. In addition, in several animal models, angiotensin receptor blockade was able to inhibit atherosclerosis. However, the effects of angiotensin receptor blockers on clinical outcome in cardiovascular patients remains to be established. Contradictory results have been found on the reduction of the risk on myocardial infarctions and in-stent restenosis, although there is solid evidence for cerebroprotective effects of these receptor blockers. These differences may be related to the role of the AT2 receptor. This review discusses the role of angiotensin II and angiotensin receptor blockers in the atherosclerotic process and its translation into clinical practice.

An update on non-peptide angiotensin receptor antagonists and related RAAS modulators

The renin-angiotensin-aldosterone-system (RAAS) is an important regulator of blood pressure and fluid-electrolyte homeostasis. RAAS has been implicated in pathogenesis of hypertension, congestive heart failure, and chronic renal failure. Aliskiren is the first non-peptide orally active renin inhibitor approved by FDA. Angiotensin Converting Enzyme (ACE) Inhibitors are associated with frequent side effects such as cough and angio-oedema. Recently, the role of ACE2 and neutral endopeptidase (NEP) in the formation of an important active metabolite/mediator of RAAS, ang 1-7, has initiated attempts towards development of ACE2 inhibitors and combined ACE/NEP inhibitors. Furukawa and colleagues developed a series of low molecular weight nonpeptide imidazole analogues that possess weak but selective, competitive AT1 receptor blocking property. Till date, many compounds have exhibited promising AT1 blocking activity which cause a more complete RAAS blockade than ACE inhibitors. Many have reached the market for alternative treatment of hypertension, heart failure and diabetic nephropathy in ACE inhibitor intolerant patients and still more are waiting in the queue. But, the hallmark of this area of drug research is marked by a progress in understanding molecular interaction of these blockers at the AT1 receptor and unraveling the enigmatic influence of AT2 receptors on growth/anti-growth, differentiation and the regeneration of neuronal tissue. Different modeling strategies are underway to develop tailor made molecules with the best of properties like Dual Action (Angiotensin And Endothelin) Receptor Antagonists (DARA), ACE/NEP inhibitors, triple inhibitors, AT2 agonists, AT1/TxA2 antagonists, balanced AT1/AT2 antagonists, and nonpeptide renin inhibitors. This abstract gives an overview of these various angiotensin receptor antagonists.

Angiotensin II-induced growth of vascular smooth muscle cells is associated with modulation of cell surface area and platelet-derived growth factor receptor expression

1. Excessive growth of vascular smooth muscle cells (VSMC) can lead to critical problems in the treatment of some vascular diseases. Recent studies suggest a connection between this abnormal growth of VSMC and the octapeptide hormone angiotensin (Ang) II. However, the growth-promotive potential of AngII on VSMC is unclear. 2. Using the novel AngII inhibitor E4177 and an original animal model, we confirmed that AngII does function in abnormal growth of VSMC induced after transplantation of vein grafts in an animal model. 3. Furthermore, using a primary culture of human aortic smooth muscle cells (HASMC), we found that AngII augmented the growth of HASMC in a serum-dependent manner and induced enlargement of the cell surface area in HASMC, both effects being nullified by E4177. The latter effect of AngII was associated with an increase in the expression level of platelet-derived growth factor (PDGF) receptors. In specimens obtained from the animal model, PDGF receptors were highly expressed. 4. These data obtained in vitro and in vivo imply that AngII has the potential to promote growth of VSMC and suggest that this growth promotion may be mediated by enlargement of the cell surface area.

Pharmacology of irbesartan

Despite the introduction of new antihypertensive agents such as angiotensin-converting enzyme inhibitors and calcium channel antagonists, the blood pressure of fewer than 30% of hypertensive patients is controlled with current therapies; compliance and continuation with medication are poor. The renin-angiotensin system is important in the pathophysiology of hypertension, end-organ damage and congestive cardiac failure. Irbesartan is an angiotensin II receptor antagonist that provides dose-dependent, specific, insurmountable blockade of the AT1 receptor both in vivo and in vitro. It is rapidly absorbed after oral administration, has a bioavailability of 60-80% with no food effect, does not require metabolism to a bioactive compound, and is excreted by both biliary and renal routes so that dosage adjustments are unnecessary in patients with renal or hepatic disease. Irbesartan produces dose-dependent blood pressure reductions, with 24 h activity confirmed by ambulatory blood pressure monitoring. Irbesartan is effective in the elderly and non-elderly, men and women and in cases of mild and severe hypertension. The recommended starting dosage is 150 mg once daily (o.d.), which can be increased to 300 mg. Its antihypertensive effect is accentuated by diuretic co-administration. In controlled clinical trials, irbesartan was at least as effective as atenolol, hydrochlorothiazide, amlodipine and enalapril. In a double-blind study, irbesartan 300 mg was more effective than losartan 100 mg, and in a dose-titration study, irbesartan 150-300 mg produced significantly greater blood pressure reductions than losartan 50-100 mg. In pooled data from nine placebo-controlled studies, adverse event and discontinuation rates for irbesartan were similar to those for placebo, and there was no relationship between dose and adverse effects. Preliminary clinical data suggest positive haemodynamic effects in heart failure and renoprotective effects in diabetic nephropathy.

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

Background

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

Methods

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

Results

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

Conclusion

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

Heterogeneity in the acute control of vascular protein synthesis in vivo

In response to both hemodynamic and neurohumoral changes, the cardiovascular system remodels and this process could contribute to end organ damage. The aim of this study was to determine the early in vivo interactions between 3 systems known to contribute to vascular hypertrophic remodeling, in conduit and resistance arteries. Exogenous angiotensin II, norepinephrine and endothelin 1 administration elevated protein synthesis in the aorta and in small mesenteric arteries. In small arteries, the effect of angiotensin II was blocked by angiotensin II type 1, alpha-adrenergic and endothelin receptor antagonists, while only the alpha-adrenergic and endothelin receptor antagonists inhibited the effect of norepinephrine. Moreover, only the endothelin receptor antagonist significantly blunted the effect of exogenous endothelin on protein synthesis. In the aorta, the stimulation of angiotensin II on protein synthesis was also inhibited by the 3 antagonists. However, only the alpha-adrenoceptor antagonist blunted the response to norepinephrine, and the 3 antagonists prevented the endothelin-induced elevation of protein synthesis. The blood pressure effects of the drugs did not correlate with their capacity to stimulate or inhibit vascular protein synthesis. In conclusion, interactions in the control of protein synthesis are heterogeneous along the vascular tree. In small arteries, the interaction is linear with endothelin as the downstream effector. In the aorta, the local sympathetic nervous system appears to control protein synthesis. The heterogeneity in downstream effectors should be considered in studies investigating signaling events related to protein synthesis, which is used as an early marker of hypertrophy.

In vitro and in vivo characterization of the activity of telmisartan: an insurmountable angiotensin II receptor antagonist

In vitro studies have shown that telmisartan is an insurmountable angiotensin II subtype-1 (AT1) receptor antagonist. Herein, the molecular basis of this insurmountable antagonism has been investigated in vitro, and the effect of telmisartan has been compared in vivo with that of irbesartan and candesartan. Association and dissociation kinetics of telmisartan to AT1 receptors have been characterized in vitro on rat vascular smooth muscle cells (RVSMC) expressing solely the AT1 receptor subtype. In a second set of experiments, the antagonistic efficacy of single intravenous doses (0.1, 0.3, and 1 mg/kg) of telmisartan was compared with that of irbesartan (0.3, 1.0, 3.0, and 10.0 mg/kg) and candesartan (0.3 and 1 mg/kg) in conscious, normotensive, male Wistar rats. The results show that the specific binding of [(3)H]telmisartan to the surface of living RVSMC is saturable and increases quickly to reach equilibrium within 1 h. Telmisartan dissociates very slowly from the receptor with a dissociation half-life (t(1/2)) of 75 min, which is comparable with candesartan and almost 5 times slower than angiotensin II (AngII). In vivo, telmisartan blunts the blood pressure response to exogenous AngII dose dependently. The blockade is long lasting and remains significant at 24 h at doses >0.1 mg/kg. Ex vivo assessment of the AT1 receptor blockade using an in vitro AngII receptor binding assay shows similar results. When administered intravenously in rats, telmisartan is 10-fold more potent than irbesartan and comparable to candesartan. Taken together, our in vitro data show that the insurmountable antagonism of telmisartan is due at least in part to its very slow dissociation from AT1 receptors.

Different types of antagonism by losartan and irbesartan on the effects of angiotensin II and its degradation products in rabbit arteries

A previous study by our group has demonstrated that the selective AT1-receptor antagonist losartan behaves as a noncompetitive antagonist in rabbit isolated renal artery (RA). In the present investigation, the influence of losartan and irbesartan on the contractile effects of angiotensin II (AII) and its degradation products angiotensin III (AIII) and angiotensin IV (AIV) was determined in the rabbit isolated RA and femoral artery (FA). The arteries were set up in organ chambers and changes in isometric force were recorded. In both rabbit isolated RA and FA preparations, AII, AIII and AIV elicited significant contractile responses with a similar efficacy. These effects were impaired by the presence of functional endothelium in RA preparations but not in FA preparations. In both preparations studied, the effects of AII, AIII and AIV were influenced neither by the aminopeptidase-A and -M inhibitor amastatin (10 microM), nor by the aminopeptidase-B and -M inhibitor bestatin (10 microM). In endothelium-denuded FA preparations, preincubation with losartan (3-300 nM) antagonized AII-, AIII- and AIV-induced contractions in a competitive manner. However, in endothelium-denuded RA preparations, losartan depressed the maximal contractile responses induced by AII but not those induced by AIII and AIV. In the same preparations, preincubation of another selective AT1-receptor antagonist irbesartan (3-30 nM) concentration-dependently shifted AII and AIII curves to the right in an insurmountable manner. The reduction of the maximal response of AII is more potent when compared to that of AIII (47.7 +/- 1.51% vs. 66.7 +/- 1.88%, percentage of the initial maximal response; P < 0.05; n=5). The selective AT2-receptor antagonist PD123177 (1 microM) did not influence the responses to all three peptides in both RA and FA preparations. These heterogeneous antagonistic effects of the two AT1-receptor antagonists studied with respect to the contractile actions of AII, AIII and AIV suggest the possible existence of multiple, functionally relevant AT1-receptor subtypes in rabbit RA preparations.

Angiotensin II is mitogenic for human lung fibroblasts via activation of the type 1 receptor

The expression of renin-angiotensin system components and the elevation of angiotensin-converting enzyme (ACE) in a number of fibrotic lung diseases suggests angiotensin II (AII) could play a role in the pathogenesis of pulmonary fibrosis. However, the effect of AII on lung fibroblasts has not previously been assessed and the mechanisms by which AII induces cell proliferation in mesenchymal cells are not fully understood. We have examined the ability of AII to stimulate fetal and adult human lung fibroblast proliferation in vitro. In particular, we have assessed the receptor subtypes involved and the possible autocrine role of transforming growth factor beta (TGF-beta) and platelet-derived growth factor (PDGF), two recognized fibroblast mitogens. Angiotensin type 1 (AT1), but not type 2, receptors were identified on fetal and adult human lung fibroblasts by immunocytochemistry. AII (1 microM) increased DNA synthesis (determined by [(3)H]thymidine incorporation) in fetal and adult cells by 211 +/- 18% and 150 +/- 14%, respectively (p < 0.01), and was inhibited by a specific AT1 receptor antagonist, Losartan (74 +/- 14%). A proliferative response to AII was confirmed by direct cell counts. Subsequently, fibroblasts were incubated with neutralizing antibodies to TGF-beta and PDGF. Anti-TGF-beta antibodies inhibited AII-induced DNA synthesis by 73 +/- 13%. However, no effect was seen with anti-PDGF antibodies. In conclusion, we have shown that angiotensin II induces human lung fibroblast proliferation in vitro via activation of the AT1 receptor and involves the autocrine action of TGF-beta.

Irbesartan: an updated review of its use in cardiovascular disorders

Irbesartan interrupts the renin-angiotensin system via selective blockade of the angiotensin II subtype 1 receptor; the latter being responsible for the pressor related effects of angiotensin II. As treatment for mild to moderate hypertension, irbesartan 150 mg/day controlled diastolic BP in 56% of patients according to pooled data from several phase III studies and 77% of patients in a large phase IV study. in comparative trials, irbesartan was significantly more effective than losartan and valsartan as treatment for mild to moderate essential hypertension and as effective as enalapril or atenolol. Results from many studies show an additive antihypertensive effect when hydrochlorothiazide is added to irbesartan monotherapy. The drug also induces statistically significant regression of left ventricular mass in patients with hypertension and left ventricular hypertrophy, and preliminary evidence suggests it has beneficial haemodynamic effects in patients with heart failure. Irbesartan is very well tolerated, exhibiting an adverse event profile similar to that seen with placebo in comparative trials. In conclusion, although the role of irbesartan as a treatment for heart failure is little clearer than it was 2 years ago, the place of the drug in the management of hypertension is now better established. There is evidence to suggest the drug may have a role as initial therapy for hypertension, although formal recommendation in management guidelines will almost certainly not occur until long term morbidity and mortality benefits are established.

Losartan-induced apoptosis as a novel mechanism for the prevention of vascular lesion formation after injury

Smooth muscle cell (SMC) apoptosis is transiently increased at the onset of the regression of aortic hypertrophy in spontaneously hypertensive rats (SHR) treated with the angiotensin II AT(1) antagonist losartan. We postulated that losartan induction of SMC apoptosis contributes to suppression of neointimal hyperplasia after vascular injury. Losartan or placebo treatment was initiated two days before balloon injury in the SHR aorta. Compared with time-matched placebo, losartan decreased neointimal cross-sectional area at Days 5 and 10 after injury by 50% and 64% respectively, without affecting medial mass. At Day 10, losartan significantly decreased SMC number (by 56%) in the neointima, but not in the media. DNA synthesis was significantly inhibited at Day 5 but not at Day 10. Losartan significantly increased aortic DNA fragmentation by 2.6- and 4.1-fold, at Days 5 and 10, respectively. In situ labeling of SMC with terminal deoxynucleotidyltransferase revealed significant 61% and 68% increases in apoptotic SMC at Days 5 and 10 with losartan treatment, predominantly in the neointima. Thus, losartan suppressed neointima formation in part by the induction of SMC apoptosis, which may be dissociated from the inhibition of DNA synthesis. Therefore, losartan-induced SMC apoptosis may be a potential therapeutic approach to control occlusive vascular disorders.

Angiotensin II stimulates collagen synthesis in human vascular smooth muscle cells. Involvement of the AT(1) receptor, transforming growth factor-beta, and tyrosine phosphorylation

Angiotensin II is an established regulator of vascular tone and smooth muscle cell (SMC) growth. However, there are little data about its effect on collagen synthesis by SMCs and none regarding the mechanism of such an effect. We studied the effect of angiotensin II on collagen production by human arterial SMCs, using uptake of [(3)H]proline into collagenase-digestible proteins, and by ribonuclease protection assay for mRNA encoding the proalpha1 chain of type I collagen, the major collagen in arteries. This revealed a dose-dependent increase in relative collagen synthesis rate and a dose-dependent increase in proalpha1(I) collagen mRNA abundance, with the half-maximal effect at 1.7 nmol/L. Angiotensin II-stimulated collagen expression was associated with a 6-fold increase in transforming growth factor-beta (TGF-beta) production and was inhibited by a neutralizing antibody to TGF-beta. Both collagen production and TGF-beta release were inhibited by the AT(1)-specific antagonist, losartan, but not by the AT(2) receptor antagonist, PD123319. To determined if tyrosine phosphorylation was functionally linked to collagen synthesis, we studied the effect of 2 mechanistically distinct inhibitors of tyrosine kinase, genistein, and tyrphostin A25. These inhibitors abrogated angiotensin II-mediated procollagen mRNA expression and angiotensin II-mediated TGF-beta production, whereas the inactive homolog tyrphostin A1 had no effect. We conclude that angiotensin II stimulates collagen production in human arterial SMCs via the AT(1) receptor and an autocrine loop of TGF-beta, induction of which requires tyrosine phosphorylation.

Effects of TH-142177 on angiotensin II-induced proliferation, migration and intracellular signaling in vascular smooth muscle cells and on neointimal thickening after balloon injury

We investigated the effects of TH-142177 (N-n-butyl-N-[2'-(1-H-tetrazole-5-yl) biphenyl-4-yl]-methyl-(N-carboxy methyl-benzylamino)-acetamide), a novel selective antagonist of angiotensin II type 1-receptor (AT1-R) on angiotensin II (AII)-induced proliferation and migration of vascular smooth muscle cells (VSMC), and on neointimal formation in the rat carotid artery after balloon injury, and on the intracellular signaling by the stimulation of AT1-R. High affinity AII receptor sites were detected in rat VSMC by the use of [125I]Sar1,Ile8-AII. TH-142177 and losartan competed with [125I]Sar1,Ile8-AII for the binding sites in VSMC in a monophasic manner, although PD123177, a selective antagonist of angiotensin II type 2-receptor (AT2-R), had little inhibitory effect, demonstrating the predominant existence of AT1-R in rat VSMC. TH-142177 prevented AII-induced DNA synthesis and migration, with a significant inhibition of 74 and 55%, respectively, at the concentration of 100 nM. AII-induced activation of p21ras, mitogen-activated protein kinase (p42MAPK and p44MAPK), and protein kinase C was significantly (50-78%) inhibited by TH-142177 (100 nM), suggesting that the activation of these enzymes is mediated through the stimulation of AT1-R. Balloon-injured left carotid arteries in rats showed extensive neointimal thickening, and TH-142177 (3 mg/kg) brought out a marked decrease in the neointimal thickening after balloon injury. In conclusion, TH-142177 inhibited AII-induced proliferation and migration of rat VSMC and neointimal formation in the carotid artery after balloon injury, and these effects may be related, in part, to the suppression of ras, p42MAPK and p44MAPK, and protein kinase C activities through the blockade of AT1-R. Thus, TH-142177 may have therapeutic potential for the treatment of vascular diseases such as atherosclerosis and restenosis.

Functional involvement of angiotensin AT2 receptor in adrenal catecholamine secretion in vivo

The aim of the present study was to analyse modulations of adrenal catecholamine secretion from the adrenal gland of anesthetized dogs in response to locally administered angiotensin II (AngII) in the presence of either PD 123319 or CGP 42112, both of which are highly specific and selective ligands to angiotensin AT2 receptor. Plasma concentrations of epinephrine and norepinephrine in adrenal venous and aortic blood were quantified by a high performance liquid chromatography coupled with electrochemical detection (HPLC-EC) method. Adrenal venous blood flow was measured by gravimetry. Local administration of AngII (0.05 µg, 0.1 µM) to the left adrenal gland increased adrenal gland catecholamine output more than 30 times that found in nonstimulated states. Administration of either PD 123319 (0.085 µg (0.23 µM) to 8.5 µg (23 µM)) or CGP 42112 (0.005 µg (0.01 µM) to 5 µg (10 µM)) did not affect the basal catecholamine output significantly. The increase in adrenal catecholamine output in response to AngII was inhibited by ~80% following the largest dose of PD 123319. CGP 42112 significantly attenuated the catecholamine response to AngII by ~70%. PD 123319 and CGP 42112 were devoid of any agonist actions with respect to catecholamine output by the adrenal gland in vivo. Furthermore, both PD 123319 and CGP 42112 inhibited the increase in adrenal catecholamine secretion induced by local administration of AngII. The present study suggests that AT2 receptors play a role in mediating catecholamine secretion by the adrenal medulla in response to AngII receptor agonist administration in vivo.Key words: AT1 and AT2 subtypes, PD 123319, CGP 42112, AT2 antagonist, anesthetized dog.

Dose-related beneficial long-term hemodynamic and clinical efficacy of irbesartan in heart failure

OBJECTIVES

The primary purpose of this study was to determine the acute and long-term hemodynamic and clinical effects of irbesartan in patients with heart failure.

BACKGROUND

Inhibition of angiotensin II production by angiotensin-converting enzyme (ACE) inhibitors reduces morbidity and mortality in patients with heart failure. Irbesartan is an orally active antagonist of the angiotensin II AT1 receptor subtype with potential efficacy in heart failure.

METHODS

Two hundred eighteen patients with symptomatic heart failure (New York Heart Association [NYHA] class II-IV) and left ventricular ejection fraction < or = 40% participated in the study. Serial hemodynamic measurements were made over 24 h following randomization to irbesartan 12.5 mg, 37.5 mg, 75 mg, 150 mg or placebo. After the first dose of study medication, patients receiving placebo were reallocated to one of the four irbesartan doses, treatment was continued for 12 weeks and hemodynamic measurements were repeated.

RESULTS

Irbesartan induced significant dose-related decreases in pulmonary capillary wedge pressure (average change -5.9+/-0.9 mm Hg and -5.3+/-0.9 mm Hg for irbesartan 75 mg and 150 mg, respectively) after 12 weeks of therapy without causing reflex tachycardia and without increasing plasma norepinephrine. The neurohormonal effects of irbesartan were highly variable and none of the changes was statistically significant. There was a significant dose-related decrease in the percentage of patients discontinuing study medication because of worsening heart failure. Irbesartan was well tolerated without evidence of dose-related cough or azotemia.

CONCLUSIONS

Irbesartan, at once-daily doses of 75 mg and 150 mg, induced sustained hemodynamic improvement and prevented worsening heart failure.

Increased angiotensin II type 1 receptor expression in hypercholesterolemic atherosclerosis in rabbits

Angiotensin II (Ang II) promotes vascular smooth muscle growth and may be involved in the initiation and progression of atherosclerosis. To examine whether Ang II receptor expression in vascular tissues is altered in atherosclerosis, male New Zealand White rabbits were fed a high-cholesterol diet (1% cholesterol + 4% coconut oil mixed with regular chow; hypercholesterolemic group, n=12) or regular chow (control group, n=8) for 10 weeks. At the end of this period, the serum cholesterol level in the rabbits fed the high-cholesterol diet was higher than that in the control group (3616 +/- 144 versus 30 +/- 1 mg/dL, P<0.001). There was no atherosclerosis in the aortas of the control group, whereas 51 +/- 6% of the aorta was covered with atherosclerosis in the hypercholesterolemic group. Total Ang II receptor expression in the atherosclerotic aortic tissues was increased 5-fold in the hypercholesterolemic rabbits (292 +/- 28 versus 51 +/- 32 fmol/mg tissue, mean +/- SE, P<0.001), and the increased Ang II receptor expression was entirely due to enhanced Ang II type 1 (AT1) receptor expression (289 +/- 38 versus 38 +/- 18 fmol/mg, P<0.001), as Ang II type 2 receptor expression was unaltered (7 +/- 5 versus 3 +/- 2 fmol/mg, P=NS). AT1 receptors were localized primarily in the media and to some extent in the intima of the atherosclerotic aorta, as determined by immunohistochemistry with specific monoclonal and polyclonal AT1 receptor antibodies. Increased synthesis of AT1 receptor mRNA in atherosclerotic tissues was confirmed by reverse transcription-polymerase chain reaction. To evaluate the functional significance of increased AT1 receptor expression, the constrictor response of aortic rings to Ang II was examined and found to be markedly enhanced in atherosclerotic aortic rings (P<0.01 versus control aortic rings). The endothelium-dependent relaxation of aortic rings from hypercholesterolemic rabbits was markedly attenuated (P<0.001). This study shows that hypercholesterolemia in rabbits results in atherosclerosis, loss of endothelium-dependent relaxation, and increased Ang II receptor (entirely AT1 receptor) expression in aortic tissues, which may result in altered vasoreactivity.

Effects of the angiotensin II type-1 receptor antagonist ZD7155 on angiotensin II-mediated regulation of renin secretion and renal renin gene expression, renal vasoconstriction, and blood pressure in rats

Angiotensin II receptors have recently been subclassified as type-1 or type-2 receptors. The in vitro and in vivo effects of blocking the angiotensin II type-1 receptor with ZD7155, an angiotensin II type-1 selective receptor antagonist, have been studied in angiotensin II-mediated increases in cytosolic calcium in rat mesangial cells, in angiotensin II-induced renal and systemic vasoconstriction, and in angiotensin II-mediated regulation of renin secretion and renal renin gene expression. ZD7155 completely blocked the ability of angiotensin II to elicit an increase in free intracellular calcium concentrations in rat mesangial cells. In isolated perfused rat kidneys, ZD7155 completely abolished the angiotensin II-induced vasoconstriction and increased renin secretion to 700% of baseline levels. Furthermore, ZD7155 decreased systolic blood pressure by 16 mm Hg, increased plasma renin activity 3.7-fold, and stimulated renal renin gene expression 4.2-fold in Sprague-Dawley rats in vivo. Our results suggest that ZD7155 is a potent antagonist of the angiotensin II type-1 receptor, which mediates angiotensin II-induced increases of free intracellular calcium concentrations in (e.g., renal mesangial cells), constriction of the renal and systemic vasculature, and inhibition of renin secretion and synthesis.

Pharmacokinetics and pharmacodynamics of irbesartan in patients with hepatic cirrhosis

The effect of hepatic impairment on the clinical pharmacology of the angiotensin II (AII) receptor antagonist irbesartan was assessed by comparing pharmacokinetic and pharmacodynamic parameters in 10 patients with hepatic cirrhosis with a matched group of 10 healthy volunteers. The pharmacokinetics and pharmacodynamics of irbesartan, 300 mg taken orally once daily, were evaluated after single- and multiple-dose (7 consecutive days) administration to normotensive subjects in an open-label, multiple-dose, parallel group study. Pharmacokinetic data obtained after administration of single and multiple doses of irbesartan showed no significant difference between the two groups in time to maximum observed plasma concentration of drug (tmax), half-life (t1/2), area under the plasma concentration-time curve (AUC), apparent oral clearance (Cl(t)/F), renal clearance (Cl(r)), and accumulation index (AI). Steady-state levels of irbesartan were reached within 3 days in both treatment groups. After irbesartan administration on day 1, mean increases from baseline in plasma AII levels and plasma renin activity (PRA) were greater in the group with cirrhosis than in the control group. On day 7, mean increases from baseline in PRA were greater in the control group than in the group with cirrhosis. No discontinuations or serious adverse events occurred during the study. The pharmacokinetics of irbesartan after repeated oral administration were not significantly affected in patients with mild-to-moderate cirrhosis of the liver. No dosage adjustment is necessary in patients with hepatic insufficiency.

The pharmacokinetics of irbesartan in renal failure and maintenance hemodialysis

PURPOSE

An open-label, multiple-dose, parallel-group study was conducted to evaluate the pharmacokinetics of the angiotensin II receptor antagonist irbesartan in subjects with varying degrees of renal function.

METHODS

Forty subjects were divided into four treatment groups on the basis of 24-hour creatinine clearance (CLCR): normal renal function (> 75 ml/min/1.73 m2), mild to moderate renal impairment (30 to 74 ml/min/1.73 m2), severe renal impairment (< 30 ml/min/1.73 m2), and maintenance hemodialysis. Subjects received 100 mg irbesartan daily for 8 days (or 300 mg daily for 9 days for the hemodialysis group). Serial blood and urine samples were collected for 24 hours after the first and last of eight successive daily doses. In addition, arterial and venous blood samples were collected during two hemodialysis sessions from subjects requiring maintenance hemodialysis.

RESULTS

There was no statistically significant linear relationship between CLCR and maximum plasma concentrations, dose-adjusted area under the plasma concentration time curve values on days 1 or 8, or any other pharmacokinetic parameters among the renal function groups studied. There was no indication of drug accumulation with repetitive dosing. In the subjects receiving hemodialysis, arterial-venous concentration differences for irbesartan were negligible, suggesting that this compound is not cleared through hemodialysis. In addition, irbesartan was well tolerated.

CONCLUSION

Based on pharmacokinetic parameters, no starting dose adjustment is necessary in subjects with mild to severe renal impairment, inclusive of hemodialysis. Subjects with volume depletion may have an exaggerated response to an initial dose of irbesartan and, under such circumstances, volume depletion should be corrected or a lower starting dose of irbesartan should be considered.

Irbesartan. A review of its pharmacodynamic and pharmacokinetic properties and therapeutic use in the management of hypertension

Irbesartan inhibits the activity of angiotensin II (AII) via specific, selective noncompetitive antagonism of the AII receptor subtype 1 (AT1) which mediates most of the known physiological activities of AII. In patients with mild to moderate hypertension, once daily administration of irbesartan 150 or 300 mg, with or without adjunctive antihypertensive agents, provides effective 24-hour BP control. Irbesartan reduced BP to a similar extent to enalapril and atenolol and to a significantly greater extent than losartan. The combination of irbesartan and hydrochlorothiazide resulted in additive antihypertensive effects. The drug is effective in the elderly and dosage adjustment is not required in these patients or in those with renal or hepatic failure. Preliminary studies evaluating the efficacy of irbesartan in patients with heart failure have produced encouraging results. Irbesartan is very well tolerated and neither the frequency nor the pattern of adverse events differed from those seen in placebo recipients, although headache was significantly more frequent with the latter. Similarly, the incidence of adverse events did not differ significantly between irbesartan and enalapril in patients who received either drug as monotherapy. Headache, upper-respiratory tract infection and musculoskeletal pain were the most common complaints. Thus, irbesartan is an effective therapy for patients with mild to moderate hypertension and had an adverse event profile similar to that of placebo in clinical trials. On this basis it would appear to be an effective therapeutic option in this indication.

The effects of renin-angiotensin system inhibition on aortic cholesterol content in cholesterol-fed rabbits

To investigate how the renin-angiotensin system (RAS) might be involved in cholesterol-induced atherosclerosis, we studied the effects of a nonsulhydryl angiotensin converting enzyme (ACE) inhibitor, enalapril, and an angiotensin II receptor antagonist, E-4177, in cholesterol fed rabbits. Japanese white rabbits were randomly divided into four groups with the following dietary regimens: group A (n = 8) received a standard diet; group B (n = 8) had a 0.5% cholesterol diet; group C (n = 8) had a 0.5% cholesterol diet plus enalapril (10 mg/kg/day, p.o.); group D (n = 8) received a 0.5% cholesterol diet plus E-4177 (20 mg/kg/day, p.o.) and were fed these diets for 5 weeks. Enalapril or E-4177 had no significant effect on either the total plasma or the high density lipoprotein (HDL) cholesterol concentrations. However, the aortic cholesterol content in groups C and D was equally significantly less than that in group B. The plasma and aortic ACE activities were significantly reduced only in group C compared with those in the other groups. The aortic ACE mRNA and AT1 mRNA levels were assessed by a reverse transcription polymerase chain reaction (RT-PCR). The aortic ACE mRNA level was only significantly less in group C than in any of the other groups. The aortic AT1 mRNA level increased significantly in group B compared with that in group A and was significantly and equally reduced in both groups C and D compared with that in group B. These data indicate that angiotensin II rather than ACE may therefore be related to aortic cholesterol content. It follows therefore that the inhibition of angiotensin II by either ACE inhibitor or angiotensin II (type 1) receptor antagonist may play a role in prevention of atherosclerosis.

Angiotensin-(1-7) inhibits vascular smooth muscle cell growth

Although angiotensin II (Ang II) and the heptapeptide Ang-(1-7) differ by only one amino acid, the two peptides produce different responses in vascular smooth muscle cells. We previously showed that Ang II stimulated phosphoinositide hydrolysis, whereas Ang II and Ang-(1-7) released prostaglandins. We now report that Ang II and Ang-(1-7) differentially modulate rat aortic vascular smooth muscle cell growth. Ang-(1-7) inhibited [3H]thymidine incorporation in response to stimulation by fetal bovine serum, platelet-derived growth factor, or Ang II. The reduction in serum-stimulated thymidine incorporation by Ang-(1-7) depended on the concentration of the heptapeptide over the range of 1 nmol/L to 1 mumol/L, with a maximal inhibition of 60% by 1 mumol/L Ang-(1-7). Ang-(1-7) also inhibited the serum-stimulated increase in cell number to a maximum of 77% by 1 mumol/L Ang-(1-7). The attenuation of serum-stimulated thymidine incorporation by Ang-(1-7) was unaffected by antagonists selective for angiotensin type 1 (AT1) or type 2 (AT2) receptors; however, [Sar1,Ile1]Ang II and [Sar1,Thr2]Ang II were effective antagonists, indicating that growth inhibition by Ang-(1-7) was a result of angiotensin receptor activation. In contrast, Ang II stimulated [3H]thymidine incorporation in cultured vascular smooth muscle cells over the same concentration range, with a maximal stimulation of 314% at 1 mumol/L Ang II. Ang II also increased the total number of cells (to 145% of control), suggesting that enhanced thymidine incorporation was associated with vascular smooth muscle cell proliferation. The AT1 antagonist losartan or L-158,809 but not AT2 antagonists blocked [3H]thymidine incorporation by Ang II. These results suggest that Ang-(1-7) and Ang II exhibit opposite effects on the regulation of vascular smooth muscle cell growth. The inhibition of proliferation by Ang-(1-7) appears to be mediated by a novel angiotensin receptor that is not inhibited by AT1 or AT2 receptor antagonists.

Tranilast antagonizes angiotensin II and inhibits its biological effects in vascular smooth muscle cells

Recent studies have been reported indicating that angiotensin II may potentiate neointimal formation. In the present study, we examined the antagonistic effect of tranilast on angiotensin II. Losartan was used as the reference compound. First, tranilast inhibited the angiotensin II-induced contraction of rabbit aortic strips in a noncompetitive manner (pD'(2) = 3.7), whereas it had little effect on the contraction induced by noradrenaline or endothelin-l. Second, tranilast inhibited the binding of (125)I-labeled angiotensin II to angiotensin AT1 receptors in rat liver membranes with an IC(50) value of 289 mu M. Finally, functional antagonism of tranilast (100 and 300 mu M) was demonstrated by its blockade of angiotensin II (10(-8)M)-induced (45)Ca(2+) -efflux from human vascular smooth muscle cells (VSMC). However, tranilast (30-300 mu M) exerted no influence on PDGF-induced formation of inositol triphosphates which cause an increase in [Ca(2+)]i in human VSMC. The antagonistic activity of tranilast towards angiotensin II may be involved in part in preventing restenosis after percutaneous transluminal coronary angioplasty (PTCA).

Differentiated properties and proliferation of arterial smooth muscle cells in culture

The smooth muscle cell is the sole cell type normally found in the media of mammalian arteries. In the adult, it is a terminally differentiated cell that expresses cytoskeletal marker proteins like smooth muscle alpha-actin and smooth muscle myosin heavy chains, and contracts in response to chemical and mechanical stimuli. However, it is able to revert to a proliferative and secretory active state equivalent to that seen during vasculogenesis in the fetus, and this is a prerequisite for the involvement of the smooth muscle cell in the formation of atherosclerotic and restenotic lesions. A similar transition from a contractile to a synthetic phenotype occurs when smooth muscle cells are established in culture. Accordingly, an in vitro system has been used extensively to study the regulation of differentiated properties and proliferation of these cells. During the first few days after seeding, the cells are reorganized structurally with a loss of myofilaments and formation of a widespread endoplasmic reticulum and a prominent Golgi complex. In parallel, they lose their contractility and instead become competent to divide in response to a large variety of mitogens, including platelet-derived growth factor (PDGF) and basic fibroblast growth factor (bFGF). After entering the cell cycle, they start to produce these and other mitogens on their own, and continue to replicate in the absence of exogenous stimuli for a restricted number of generations. Furthermore, they start to secrete extracellular matrix components such as collagen, elastin, and proteoglycans. The mechanisms that control this change in morphology and function of the smooth muscle cells are still poorly understood. Adhesive proteins such as fibronectin and laminin apparently have an important role in determining the basic phenotypic state of the cells and exert their effects via integrin receptors. The proliferative and secretory activities of the cells are influenced by a multitude of growth factors, cytokines, and other molecules. Although much work remains before an integrated view of this regulatory machinery can be achieved, there is no doubt that the cell culture technique has contributed substantially to our knowledge of smooth muscle differentiation and growth. At the same time, it has been crucial in exploring the role of these cells in vascular disease and developing new therapeutic strategies to cope with major causes of human death and disability.

Angiotensin II-induced responses in vascular smooth muscle cells: inhibition by non-peptide receptor antagonists

The present study investigates the effect of angiotensin II and LR-B/081 (-methyl 2-[[4-butyl-2-methyl-6-oxo-5-[[2'-(1H-tetra-zol-5-yl) [1,1'-biphenyl]-4-yl] methyl]-1(6H)-pyrimidinyl] methyl]-3-thiophenecarboxylate), a novel non-peptide angiotensin II receptor antagonist, on both early and late responses in rat vascular smooth muscle cells. Angiotensin II induced a rapid and transient elevation of inositol trisphosphate intracellular levels, triggered the release of both prostaglandin E2 and prostaglandin I2 (EC50 = 21 +/- 3 and 16 +/- 2 nM, respectively), and, in long-term studies, increased leucine and thymidine incorporation. All angiotensin II effects were antagonized by LR-B/081 and losartan, the reference non-peptide angiotensin AT1-selective receptor antagonist, whereas they were unaffected by PD123177 (1-(4-amino-3-methylphenyl)methyl-5-diphenylacetyl-4,5,6,7-tetr ahy dro-1H- imidazo[4,5-c]pyridine carboxylic acid), a non-peptide angiotensin AT2-selective receptor antagonist. LR-B/081 displayed a much higher potency than losartan in inhibiting angiotensin II-induced prostaglandin E2 (IC50 = 0.15 +/- 0.02 and 39 +/- 9 nM, respectively) and prostaglandin I2 release (IC50 = 0.18 +/- 0.04 and 134 +/- 40 nM, respectively) and was also more potent in blocking the increase in protein synthesis (IC50 = 242 +/- 119 nM and 1221 +/- 687 nM, respectively). Moreover, LR-B/081 and losartan blocked the response to angiotensin III but failed to inhibit the prostaglandin release stimulated by vasopressin or the mitogenic effect of serum. LR-B/081 and losartan were devoid of intrinsic properties in the experimental conditions employed.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of angiotensin II receptor blocker on angiotensin II stimulated DNA synthesis of cultured human aortic smooth muscle cells

To examine the role of the renin-angiotensin system on human vascular smooth muscle cell (VSMC) replication, we studied the effect of DUP 753, an angiotensin II (ANG II) type 1 receptor antagonist, on ANG II stimulated tritiated-thymidine (3H-Tdr) incorporation into cultured human aortic VSMC. ANG II stimulated DNA synthesis of VSMC in a dose-dependent manner as estimated by 3H-Tdr incorporation (control; 2993 +/- 486 cpm, 10(-8)M; 3360 +/- 350 cpm, 10(-7)M; 3474 +/- 516 cpm, 10(-6)M; 4889 +/- 320 cpm, P < 0.01). The effects of ANG II were clearly inhibited by 10(-7) M DUP 753 (ANG II 10(-8) M; 3360 +/- 350 vs 509 +/- 39 cpm, 10(-7) M; 3474 +/- 516 vs 661 +/- 36 cpm, 10(-6) M; 4889 +/- 320 vs 806 +/- 76 cpm, each P < 0.01). This receptor antagonist decreased the basal 3H-Tdr incorporation of VSMC from 2933 +/- 486 to 411 +/- 78 cpm (P < 0.01). Furthermore, DUP 753 decreased 10(-7) M ANG II-stimulated 3H-Tdr incorporation of VSMC in a dose-dependent manner (control; 2627 +/- 256 cpm, 10(-9) M; 2145 +/- 143 cpm, 10(-8) M; 1047 +/- 543 cpm, 10(-7) M; 639 +/- 169 cpm, 10(-6) M; 642 +/- 59 cpm, P < 0.01). These observations suggest that, in human VSMC, ANG II type 1 receptors are important for the regulation of both stimulated and basal cell proliferation. It may therefore be worth while to examine the clinical usefulness of DUP 753 for preventing abnormal VSMC growth.