Inhibition of platelet aggregability by losartan in essential hypertension

Pharmacological modulation of fibrinolytic response - In vivo and in vitro studies

Fibrinolysis is an action of converting plasminogen by its activators, like tissue- or urokinase-type plasminogen activators (t-PA, u-PA), to plasmin, which in turn cleaves fibrin, thereby causing clot dissolution and restoration of blood flow. Endothelial cells release t-PA, prostacyclin (PGI2) and nitric oxide (NO), the potent factors playing a crucial role in regulation of the fibrinolytic system. Since blood platelets can release not only prothrombotic, but also antifibrinolytic factors, like plasminogen activator inhibitor type-1 (PAI-1), they are involved in fibrynolysis regulation. Therefore agents enhancing fibrinolysis can be preferred pharmacologicals in many cardiovascular diseases. This review describes mechanisms by which major cardiovascular drugs (renin-angiotensin-aldosterone system inhibitors, statins, adrenergic receptors and calcium channel blockers, aspirin and 1-methylnicotinamide) influence fibrinolysis. The presented data indicate, that the influence of these drugs on endothelium-blood platelets interactions via NO/PGI2 pathway is fundamental for its antithrombotic and profibrinolytic action. We also described new approaches for intravital confocal real-time imaging as a tool useful to investigate mechanisms of thrombus formation and the effects of drugs affecting haemostasis and mechanisms of their action in the circulation.

Antithrombotic effects of losartan in patients with hypertension complicated by atrial fibrillation: 4A (Angiotensin II Antagonist of platelet Aggregation in patients with Atrial fibrillation), a pilot study

Angiotensin receptor blockers (ARBs) are widely used for the treatment of hypertension. It has been reported that the ARB losartan has antiplatelet, anticoagulant and profibrinolytic effects experimentally. These properties could be desirable to treat hypertensive patients with high atherothrombotic and/or thromboembolic risk. To examine the antithrombotic effects of losartan in hypertension, 20 consecutive patients with hypertension complicated by atrial fibrillation (AF) were enrolled in this study. The patients were treated with losartan 50 mg for 8 weeks followed by 100 mg for 4 weeks. Blood samples were obtained from each patient at 0 (pretreatment), 8 and 12 weeks after initiating treatment. Platelet aggregability, plasma levels of tissue factor (TF) and type 1 plasminogen activator inhibitor (PAI-1) activity levels were measured. The area under the curve for small platelet aggregability decreased from 100 to 42.8% at 12 weeks (P<0.0001). TF levels (ng ml(-1)) and PAI-1 activity (IU ml(-1); mean±s.d.) also changed from 14.2±3.6 to 10.9±4.5 at 12 weeks (P=0.0299) and from 11.7±3.6 to 8.5±3.1 at 12 weeks (P=0.0122), respectively. Losartan inhibited platelet activity and coagulation factors in a dose- and time-dependent manner in patients with hypertension complicated by AF, whereas the fibrinolytic capacity was increased. The use of losartan could be advantageous in the treatment of hypertensive patients with high atherothrombotic risk.

The angiotensin-converting enzyme 2/angiotensin-(1-7)/Mas receptor axis: a potential target for treating thrombotic diseases

Despite many therapeutic advances leading to increasingly effective drug treatments, thrombotic events (such as ischaemic stroke, pulmonary embolism, deep venous thrombosis and acute myocardial infarction) still represent a major worldwide cause of morbidity and mortality. Remarkable effort has been made to identify new drug targets. There is growing evidence indicating that the recently described counter-regulator axis of the renin-angiotensin system (RAS), composed of Angiotensin-Converting Enzyme 2 (ACE2), Angiotensin-(1-7) and the Mas receptor, has protective effects against thrombosis. In addition, it could be considered as a promising target for treating or preventing this disease. In this narrative review, we focused on the recent findings of the role of the ACE2/Angiotensin-(1-7)/Mas axis on the haemostatic process and its therapeutic potential.

Platelet activation in essential hypertension: implications for antiplatelet treatment

Essential hypertension is associated with increased risk of arterial thrombotic disease. Among other factors, enhanced platelet activity contributes significantly to this phenomenon. An increased level of circulating monocyte-platelet aggregates (MPAs) represents one of the most robust markers of platelet activation; furthermore, these aggregates are also believed to contribute to the pathophysiology of atherothrombotic disease. Putative mechanisms that contribute to platelet activation in essential hypertension include endothelial dysfunction, neurohumoral (sympathetic and renin-angiotensin systems) overactivity, decreased platelet nitric oxide (NO) biosynthesis, and platelet degranulation secondary to increased shear. Current recommendations are that hypertensive patients receive aspirin therapy only if their calculated cardiovascular risk is high and their blood pressure (BP) is adequately controlled. By contrast, the use of antiplatelet treatment in low-risk hypertensive patients is not established and merits further investigation. Moreover, the place of alternative antiplatelet agents other than aspirin, such as clopidogrel, is unclear at present. Some experimental evidence suggests that clopidogrel may confer an additive protective effect over and above aspirin in hypertensive patients, by virtue of effects on the evolution of the atherosclerotic process. This now needs to be investigated in long-term clinical outcome studies.

Molecule-specific effects of angiotensin II-receptor blockers independent of the renin-angiotensin system

Because all clinically approved angiotensin-receptor blockers (ARBs) have good safety profiles and share the ability to block angiotensin II type 1 (AT1) receptors and reduce blood pressure, it is tempting to assume that all ARBs will yield equivalent degrees of cardiovascular protection. However, such a belief depends on the tacit assumption that with appropriate dosing, all ARBs will also share the same ability to counteract other pathogenetic determinants of cardiovascular disease beyond those involving the renin-angiotensin system. Accumulating evidence from multiple laboratories has shown that this assumption is incorrect and indicates that some ARBs are characterized by an unusual ability to affect potential mechanisms of cardiovascular disease involving more than just the renin-angiotensin system. Ultimately, large-scale clinical trials will be required to better understand the clinical importance of the mechanistic effects of ARBs that involve more than just inhibition of the renin-angiotensin system. Meanwhile, given the many functional differences among ARBs that are not mediated by AT1 receptor blockade, the effects of any particular ARB on cardiovascular outcomes should not be assumed to apply equally to all ARBs let alone to other drugs that inhibit the renin-angiotensin system through different mechanisms.

Antiplatelet Effect of Losartan and Telmisartan in Patients With Ischemic Stroke

Antiplatelet effects of angiotensin II receptor blocker have been suggested, but satisfactory results in clinical settings are lacking. We investigated spontaneous platelet aggregation (SPA) and CD62P levels in patients with hypertension and chronic-stage ischemic stroke. The study comprised 35 patients assigned to losartan (50 mg/day) or telmisartan (40 mg/day) for 4 weeks randomly. SPA was evaluated using laser-scattered light aggregometry and CD62P levels using whole blood flow cytometry before and after treatment. SPA was not significantly reduced after losartan or telmisartan treatment. CD62P was significantly reduced after losartan treatment (P = .016), but no significant differences were noted with telmisartan. These findings suggest that standard doses of losartan display antiplatelet effect as measured by CD62P levels.

Potential mechanisms of stroke benefit favoring losartan in the Losartan Intervention For Endpoint reduction in hypertension (LIFE) study

INTRODUCTION

The Losartan Intervention For Endpoint reduction in hypertension (LIFE) study is the first, and, so far, the only endpoint trial in patients with hypertension and left ventricular hypertrophy (LVH) to show a divergent therapeutic outcome of one treatment modality over another with equivalent blood pressure control. The purpose of this article is to review post hoc sub-analyses of LIFE study data and other clinical studies that offer some insight into possible treatment-related differences contributing to the superior stroke outcome of losartan versus atenolol beyond blood pressure reduction.

METHODS

Relevant randomized clinical trials and review articles were identified through a MEDLINE search of English-language articles published between 1990 and 2006 using the search terms losartan, atenolol, LIFE, hypertension, and LVH. Articles describing major clinical studies, new data, or mechanisms pertinent to the LIFE study were selected for review.

RESULTS

Differences in blood pressure or in the distribution of add-on medications were not evident between study groups in the LIFE study. Thus, the observed outcomes benefits favoring losartan may involve other possible mechanisms, including differential effects of losartan and atenolol on LVH regression, left atrial diameter, atrial fibrillation, brain natriuretic peptide, vascular structure, thrombus formation/platelet aggregation, serum uric acid, albuminuria, new-onset diabetes, and lipid metabolism. Alternative explanations for the LIFE study findings have also been put forward, including the choice of atenolol as an appropriate active comparator and differential effects between treatment groups on central pulse pressure. Additional clinical trials are needed to determine if the beneficial effects of losartan seen in LIFE are shared by other inhibitors of the renin-angiotensin system.

CONCLUSION

Sub-analyses of the LIFE study data suggest that losartan's stroke benefit may arise from a mosaic of mechanisms rather than a single action. Further studies are expected to continue to delineate the mechanisms of differential responses to treatments in LIFE.

Platelet Aggregability in Patients with Hypertension Treated with Angiotensin II Type 1 Receptor Blockers

AIM

Cardiovascular events associated with hypertension often involve thrombosis. Increased platelet activity is one of the risk factors of cardiovascular diseases. Antithrombotic properties of antihypertensive agents are not fully characterized. Angiotensin II type 1 receptor blockers (ARBs) are widely used for the treatment of hypertension. Some ARBs can provoke antiaggregatory effects on platelets in vitro. Whether ARBs can inhibit platelet aggregation was tested in hypertensive patients in vivo.

METHODS

Platelet aggregation was assessed by the highly sensitive particle counting method using laser-light scattering.

RESULTS

Large platelet aggregation induced by adenosine diphosphate (ADP, 3 microM) was 2.6+/-0.4 (x10(7)) (SE) in hypertensive patients treated with losartan (72+/-3 years old, n=10) while it was 3.9+/-0.6 in hypertensive patients treated with candesartan (70+/-5 years old, n=6; p=0.056). Large platelet aggregation induced by thromboxane A2 receptor agonist, U46619 (10 microM), was 2.8+/-0.5 (x10(7)) in hypertensive patients treated with losartan while it was 5.1+/-0.9 in hypertensive patients treated with candesartan (p=0.033). Clinical characteristics including the control of blood pressure did not differ between the two groups (losartan 136+/-5/73+/-3 mmHg vs. candesartan 135+/-4/76+/-5).

CONCLUSION

Thus, losartan may have the possibility to inhibit platelet activation in patients with hypertension independent of blood pressure reduction. Antiaggregatory properties may be independent of angiotensin II type 1 receptor or of antihypertensive actions. The favorable effects of losartan on reduction of adverse cardiovascular events among hypertensive patients may be at least partly mediated by inhibition of platelet activation.

Role of angiotensin II in cardiovascular disease therapeutic implications of more than a century of research

More than a century of research on the reninangiotensin system (RAS) has uncovered the widespread involvement of angiotensin II (Ang II) in the pathophysiology of cardiovascular diseases. A number of outcomes-based mega trials utilising hard clinical endpoints have revealed beneficial effects of angiotensin receptor antagonists (AIIAs/ARBs) in patients with hypertension, heart failure, diabetic nephropathy, and post-myocardial infarction (MI). The results of these studies not only emphasise the importance of Ang II in the pathophysiology of these diseases but have provided the basis for an evidence-based approach for the use of AIIAs in clinical practice. It is hoped that the next 100 years of research into the RAS will uncover hitherto unimaginable therapeutic opportunities.

Review of the molecular pharmacology of Losartan and its possible relevance to stroke prevention in patients with hypertension

BACKGROUND

The Losartan Intervention For End-point reduction in hypertension (LIFE) study found that a losartan-based regimen, compared with an atenolol-based regimen, resulted in a significantly lower risk of stroke in hypertensive patients with left ventricular hypertrophy, despite similar reductions in blood pressure.

OBJECTIVE

The purpose of this review was to examine the molecular and pharmacologic mechanisms that may be associated with the different outcomes observed in the LIFE study.

METHODS

A PubMed/MEDLINE search of English-language articles (1990 to February 2006) with the terms angiotensin II antagonists or AIIAs or angiotensin receptor blockers or losartan or atenolol or beta blocker and terms including, but not limited to, atherosclerosis, left ventricular hypertrophy, carotid artery hypertrophy, fatty streaks, atrial fibrillation, arrhythmias, endothelial function, myocyte hypertrophy, myocardial fibrosis, platelet aggregation, tissue factor, plasminogen activator inhibitor-1, PAI-1, anti-inflammatory, uric acid, or oxidative stress.

RESULTS

Losartan's significant effect on stroke may be related to several possible mechanisms that are independent of blood-pressure reductions. These include improvements in endothelial function and vascular structure; decreases in vascular oxidative stress; reductions in left ventricular hypertrophy, reductions in myocardial fibrosis, or both; and modulation of atherosclerotic disease progression. Although some of these effects may be shared by other angiotensin II receptor antagonists (AIIAs), and perhaps other anti-hypertensive classes (eg, angiotensin-converting enzyme inhibitors), the ability of losartan to lower serum uric acid levels-a proposed independent risk factor for cardiovascular disease-appears to be a molecule-specific effect. Alternative explanations of the results of the LIFE study have also been hypothesized, including inappropriate choice of atenolol as an active comparator and differences in central pulse pressures between study groups.

CONCLUSIONS

This review of the literature suggests that losartan (and perhaps other AIIAs) may possess a number of properties, independent of its antihypertensive effects, that may be associated with decreased vulnerability of the plaque, myocardium, and blood.

Chronic blockade of the angiotensin II receptor has a differential effect on adipose and vascular PAI-1 in OLETF rats

Angiotensinogen (AGT) and plasminogen activator inhibitor-1 (PAI-1) are expressed in both vascular and adipose tissues. Angiotensin II (AG II) has an adipogenic effect and increases PAI-1 expression. To evaluate the chronic effects of AG II type 1 receptor (AT(1)R) antagonism on adipose mass and PAI-1 expression in vascular and adipose tissues, losartan (30mg/kg/day) was administered to Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a model of type 2 diabetes, for 20 weeks. Adipose mass and regional fat distribution in the abdomen did not change after chronic AT(1)R antagonism in OLETF rats. AGT and PAI-1 mRNA expressions in adipose tissue of OLETF rats were significantly increased compared with Long-Evans Tokushima Otsuka (LETO) rats, the normal control. Chronic losartan therapy further increased the level of adipose AGT in OLETF rats, but did not affect the level of adipose PAI-1 mRNA. In contrast, aortic PAI-1 expression in OLETF rats was attenuated by chronic losartan therapy. Our results have two implications. First, adipose tissue may be an important source of AG II in metabolic syndrome even after chronic losartan therapy. Second, chronic AT(1)R antagonism with losartan causes differential effects on vascular and adipose PAI-1 expression.

Vascular and metabolic effects of candesartan: insights from therapeutic interventions

BACKGROUND

Effects of angiotensin II type 1 receptor blockers (ARBs) to improve endothelial dysfunction may be due to mechanisms in addition to the reduction of high blood pressure per se. Endothelial dysfunction is characterized by vascular inflammation that contributes to clinically significant atherosclerosis and by an increased tendency for thrombus formation. Hypertensive patients have impaired endothelial functions that have positive predictive power with respect to future cardiovascular events.

OBJECTIVES

The present review will focus on multiple mechanisms underlying vascular and metabolic effects of ARBs that may synergize to prevent or regress atherosclerosis, onset of diabetes, and coronary heart disease.

CONCLUSIONS

Angiotensin II accelerates the development of atherosclerosis by activating angiotensin II type 1 receptors that then promote superoxide anion generation and oxidative stress, leading to activation of nuclear transcription factor and endothelial dysfunction. Activation of angiotensin II type 1 receptors also stimulates increased expression of plasminogen activator inhibitor type 1 and tissue factor. Endothelial dysfunction associated with the metabolic syndrome and other insulin-resistant states is characterized by impaired insulin-stimulated production of nitric oxide from the endothelium and decreased blood flow to skeletal muscle. Increasing insulin sensitivity therefore improves endothelial function, and this may be an additional mechanism whereby ARBs decrease the incidence of coronary heart disease and the onset of diabetes. Adiponectin serves to link obesity with insulin resistance. In addition, adiponectin has anti-atherogenic properties.

Targeting the renin-angiotensin-aldosterone-system in atrial fibrillation: a shift from electrical to structural therapy?

Despite its increasing incidence and prevalence, treatment options in atrial fibrillation (AF) are far from ideal and often limited. After decades of focus on the electrical aspects of AF with unsatisfactory results, recent research is focusing increasingly on the atrial structural remodelling that underlies the development of AF in different pathological conditions, such as hypertension, heart failure, diabetes mellitus and coronary artery disease. The aim of this review is to provide a comprehensive overview of the role of the renin-angiotensin-aldosterone-system in AF and to highlight the clinical evidence on renin-angiotensin-aldosterone-system blockade as a therapeutic option in AF.

Losartan and simvastatin inhibit platelet activation in hypertensive patients

BACKGROUND

Diabetic patients also show hypercoagulability and platelet hyperaggregability, with increased levels of platelet activation-markers such as P-selectin (CD62P) and platelet-derived microparticles. We investigated the effects of losartan and simvastatin on circulating levels of platelet activation markers, microparticles, soluble selectins, and soluble cell adhesion molecules in hypertensive and hyperlipidemic patients with or without Type 2 diabetes.

METHODS

The subjects included 25 normotensive healthy controls and 41 hypertensive patients. The 41 hypertensive patients were divided into three groups: group A had hypertension and hyperlipidemia (n = 11), group B had hypertension and Type 2 diabetes (n = 14), and group C had hypertension, hyperlipidemia, and diabetes (n = 16). Losartan was administered to all of the patients at a dose of 50 mg/day for 24 weeks. In addition, simvastatin was administered to the hyperlipidemic patients at a dose of 10 mg/day for 24 weeks.

RESULTS

There were significant differences in the levels of CD62P, CD63, PAC-1, platelet microparticles, endothelial microparticles, sE-selectin, and sVCAM-1 between the hypertensive patients and healthy controls. These markers were all significantly increased in hypertensive and hyperlipidemic patients with Type 2 diabetes. In hypertensive patients with diabetes, CD62P, CD63, PAC-1, platelet and endothelial microparticles, and soluble adhesion markers were all decreased by losartan monotherapy. The decrease of each marker in hypertensive and hyperlipidemic patients given combined therapy with losartan plus simvastatin was greater among those with than without Type 2 diabetes. Low-density lipoprotein was decreased significantly by simvastatin and was correlated with CD62P or platelet microparticles in all of the patients.

CONCLUSION

Administration of losartan plus simvastatin to hypertensive and hyperlipidemic patients with Type 2 diabetes may prevent the development of cardiovascular complications caused by activated platelets and microparticles via another mechanism in addition to reduction of the blood pressure or lipid levels.

Addressing the global cardiovascular risk of hypertension, dyslipidemia, and insulin resistance in the southeastern United States

An expanded occurrence of the metabolic syndrome in the U.S. population, especially in the Southeastern United States, has raised awareness of a need to revise our approach to the management of global cardiovascular risk factors while underscoring a need for more aggressive interventions and prevention measures. In defining the components of the metabolic syndrome and the interrelationship among obesity, hypertension, dyslipidemia, and insulin resistance, a basic framework for the medical management of this syndrome has been defined. In Part I of the consensus report prepared by the Workgroup on Medical Guidelines of the Consortium for Southeastern Hypertension Control (COSEHC), we analyze the components of the metabolic syndrome, discuss its pathophysiology, and recommend an approach to the quantitative analysis of the risk factors contributing to excess cardiovascular death in the region.

Is hypertension a prothrombotic state?

Hypertension is complicated by thrombosis-related events (such as myocardial infarction and stroke), and despite the high vascular pressures, these thrombotic occlusive events paradoxically occur more often than hemorrhagic episodes. The predisposition for thrombogenesis is increased in hypertension, which leads to changes in the platelets, endothelium, and matrix metalloproteinases and their inhibitors, as well as the coagulation and fibrinolytic pathways, which help promote the induction and the maintenance of this prothrombotic or hypercoagulable state. Other cardiovascular diseases, such as atrial fibrillation, congestive heart failure, and left ventricular hypertrophy, which may occur as a result of untreated hypertension, can also activate the prothrombotic state. These changes can, to a certain degree, be reversed by the treatment of hypertension, although the effects may be inconsistent. The evidence for antithrombotic therapy is less consistent, but in "high risk" hypertensive patients, antiplatelet therapy is useful.

Chronobiologically explored effects of Telmisartan

Effects of Micardis (Telmisartan), alone or with low-dose aspirin, on blood pressure and other cardiovascular endpoints are examined in 20 patients with MESOR-hypertension in a crossover, double-blind, randomized study consisting of three stages, each lasting 7 days: I-placebo, II-Micardis, and III-Micardis with low-dose aspirin. Treatment was administered each day at a different circadian stage, upon awakening, and 3, 6, 9, 12, 15 and 18 hr after awakening. During each stage, the following variables were measured at 3-hr intervals during waking: systolic and diastolic blood pressure, heart rate, ejection fraction, intrarenal resistive index, acceleration time, and serum creatinine. Each data series was analyzed by single cosinor. Results were summarized by population-mean least squares spectra. At matched treatment times, the MESOR and circadian amplitude of each variable were compared among the three treatments by paired t-tests. A prominent circadian rhythm characterizes all variables. Micardis was associated not only with a lowering of blood pressure, but also with a reduction of the circadian blood pressure amplitude. The ejection fraction was increased, and the resistive index and acceleration time were decreased, the effect being more pronounced when low-dose aspirin was added to Micardis. Any circadian-stage dependent effect of Micardis, with or without low-dose aspirin, will require monitoring over spans longer than a single day for a given treatment administration time.

Emerging drugs in the management of hypertension

Hypertension is a global health problem, affecting developing and developed countries alike. Most patients with hypertension are undiagnosed, and most diagnosed patients are either untreated or inadequately treated. Randomised controlled trial evidence suggests diuretic therapy for hypertension is as effective as newer drugs in reducing cardiovascular events. There is good evidence for the use of specific classes of drugs in hypertensive patients with a variety of associated clinical conditions, but for uncomplicated cases, the current emphasis in hypertension management is on blood pressure lowering rather than drug class. Individual patients vary in their responses to different drug classes, and optimal therapy for the individual is determined by trial and error. Pharmacogenomics may assist in tailoring therapy for individuals in the future. Emerging drugs include newer members of classes already established in clinical practice, for example, angiotensin II receptor antagonists, aldosterone receptor antagonists, calcium antagonists and centrally acting drugs; newer fixed-dose combination therapies; and more novel therapies, for example, endothelin (ET) receptor antagonists, activators of nitric oxide (NO)-sensitive guanylyl cyclase and vasopeptidase inhibitors.

Do angiotensin II antagonists provide benefits beyond blood pressure reduction?

Hypertension is a powerful risk factor for cardiovascular (CV) morbidity and mortality; therefore, blood pressure (BP) lowering plays a central role in reducing the cardiovascular complications of hypertension, including stroke. Recent outcomes studies--Losartan Intervention For Endpoint reduction in hypertension, Reduction of Endpoints in Non-insulin-dependent Diabetes Mellitus with the Angiotensin II Antagonist Losartan, and the Irbesartan Type 2 Diabetic Nephropathy Trial--suggest that some angiotensin II antagonists are associated with CV and renal effects beyond their ability to lower BP in patients with hypertension or diabetic nephropathy and may play a role in the prevention of new-onset type 2 diabetes. Angiotensin II antagonists are associated with a wide variety of vascular, cardiac, and renal effects, as well as molecule-specific effects independent of those induced by the angiotensin-I receptor. These actions may offer a mechanistic explanation for the outcome benefits observed in patients with hypertension or diabetic nephropathy. Angiotensin-converting enzyme inhibitors and calcium-channel blockers may also have effects that are not completely explained by differences in the antihypertensive response to these agents, but the evidence is less robust. Collectively, these findings suggest that management of patients with hypertension, with or without diabetes or renal disease, should no longer be viewed as simply a matter of correcting elevated BP. Antihypertensive agents that possess CV benefits beyond their BP-reducing effects should be used to prevent the development of end-organ damage.

Redefining efficacy of antihypertensive therapies beyond blood pressure reduction--the role of angiotensin II antagonists

Antihypertensive efficacy must be redefined beyond blood pressure (BP) lowering per se to include reducing the cardiovascular complications of hypertension. Treatment decisions should be based on results from large clinical trials with relevant clinical outcomes. Several recent morbidity and mortality trials with angiotensin II receptor antagonists (AIIAs) provide an evidence-based rationale for the use of AIIAs in patients with hypertension. Studies with AIIAs in comparison to conventional antihypertensive agents showed improved morbidity and mortality outcomes in patients with hypertension and left ventricular hypertrophy (losartan) and diabetes mellitus (losartan and irbesartan). Trials with some members of the AIIA class (candesartan and valsartan) have not demonstrated such benefits in comparison to conventional agents, possibly due to differences in BP control during the trials. The results of these AIIA outcome trials have impacted on recently issued clinical guidelines for management of hypertension.

Losartan

Losartan (Cozaar) is an angiotensin AT1 receptor antagonist. It is approved in numerous countries for the treatment of hypertension and has been approved in the UK, the US and several European countries for stroke risk reduction in patients with hypertension and left ventricular hypertrophy (LVH). Losartan is recommended for use alone or with hydrochlorothiazide, but it can also be administered with other antihypertensive medications. In patients with hypertension, losartan effectively lowers blood pressure and also leads to regression of LVH. In the large, well designed LIFE (Losartan Intervention For Endpoint reduction in hypertension) study in patients with hypertension and LVH, losartan was more effective than atenolol in reducing the composite primary endpoint of cardiovascular (CV) mortality, stroke or myocardial infarction (MI). This was mainly due to a significant 25% reduction in the risk of stroke in the losartan group. Losartan recipients also had a significantly lower incidence of new-onset diabetes mellitus compared with atenolol recipients. Similar benefits were observed in several patient subgroups from the LIFE study, but not in the subgroup of Black patients. Losartan is well tolerated and is a cost effective alternative to atenolol in the setting of stroke reduction. Comparative data on clinical outcomes in hypertensive patients for losartan versus other antihypertensive agents would be of interest. Nonetheless, in addition to its established antihypertensive and end organ effects, the LIFE study indicates that, with the possible exception of Black patients, losartan can reduce the risk of stroke in patients with hypertension and LVH.

Is the effect of antihypertensive drugs on platelet aggregability and fibrinolysis clinically relevant?

Hypertension is associated with decreased fibrinolytic potential, mainly expressed as elevated plasma plasminogen activator inhibitor type 1 (PAI-1) levels, and increased platelet aggregability, which may account in part for the increased risk of atherosclerosis and its clinical complications in hypertensive patients. The effects of antihypertensive drugs on this prothrombotic state have been investigated and controversial findings have been reported, possibly because of differences in study designs, patients selected, and methodology used. Scarce and conflicting data exist about the effects of diuretics and beta-adrenoceptor antagonists on the fibrinolytic system, whereas ACE inhibitors have generally been reported to improve the fibrinolytic balance by decreasing plasma PAI-1 levels, calcium channel antagonists have been shown to increase tissue plasminogen activator (tPA) activity, and angiotensin II type 1 (AT(1)) receptor antagonists seem to exert neutral effects. beta-Adrenoceptor antagonists, calcium channel antagonists, and AT(1)-receptor antagonists have been reported to exert anti-aggregatory effects on platelets, while contrasting data exist about the influence of ACE inhibitors. Clinical implications of the changes induced by antihypertensive drugs on the fibrinolytic balance and platelet function are still debated. In particular, the question of whether these changes may translate into different degrees of cardiovascular protection in hypertensive patients remains unanswered. While awaiting more information from clinical trials, the choice of antihypertensive drugs, particularly in high-risk patients, should take into account effects beyond their BP-lowering efficacy. Selected agents should have a favorable, or at least neutral, impact on fibrinolytic function and platelet activity.

The role of angiotensin antagonism in stroke prevention in patients with hypertension: focus on losartan

Optimal management of hypertension has been shown to reduce the risk of stroke. In recent years, newer classes of antihypertensive such as the angiotensin II (Ang II) antagonists have become available. Results from the Losartan Intervention for Endpoint reduction in hypertension (LIFE) study suggest the utility of this particular Ang II antagonist in stroke prevention. Treatment with a losartan-based regimen or an atenolol-based regimen produced similar reductions in blood pressure during almost 5 years of follow up. Losartan, however, reduced the risk of stroke by 25% compared with atenolol (p = 0.001). For a subgroup of patients with isolated systolic hypertension, losartan reduced the risk of stroke by 40% (p = 0.02). As well as blocking the Ang II type 1 receptor, losartan also acts as an antagonist at the thromboxane A2 receptor and has uricosuric effects, which may provide additional mechanisms by which losartan provides protective benefits beyond its antihypertensive action. The relevance of these molecular properties of losartan over other Ang II antagonists is further supported by comparison of the outcomes obtained in clinical trials employing two other Ang II antagonists, valsartan and candesartan.

Upregulation of angiotensin-converting enzyme 2 after myocardial infarction by blockade of angiotensin II receptors

We investigated in Lewis normotensive rats the effect of coronary artery ligation on the expression of cardiac angiotensin-converting enzymes (ACE and ACE 2) and angiotensin II type-1 receptors (AT1a-R) 28 days after myocardial infarction. Losartan, olmesartan, or the vehicle (isotonic saline) was administered via osmotic minipumps for 28 days after coronary artery ligation or sham operation. Coronary artery ligation caused left ventricular dysfunction and cardiac hypertrophy. These changes were associated with increased plasma concentrations of angiotensin I, angiotensin II, angiotensin-(1-7), and serum aldosterone, and reduced AT1a-R mRNA. Cardiac ACE and ACE 2 mRNAs did not change. Both angiotensin II antagonists attenuated cardiac hypertrophy; olmesartan improved ventricular contractility. Blockade of the AT1a-R was accompanied by a further increase in plasma concentrations of the angiotensins and reduced serum aldosterone levels. Both losartan and olmesartan completely reversed the reduction in cardiac AT1a-R mRNA observed after coronary artery ligation while augmenting ACE 2 mRNA by approximately 3-fold. Coadministration of PD123319 did not abate the increase in ACE 2 mRNA induced by losartan. ACE 2 mRNA correlated significantly with angiotensin II, angiotensin-(1-7), and angiotensin I levels. These results provide evidence for an effect of angiotensin II blockade on cardiac ACE 2 mRNA that may be due to direct blockade of AT1a receptors or a modulatory effect of increased angiotensin-(1-7).

Nitric oxide-dependent antiplatelet action of AT1-receptor antagonists in a pulmonary thromboembolism in mice

The aim of this study was to determine whether AT1-receptor antagonists could inhibit platelet activation-dependent pulmonary thromboembolism in mice and to investigate the involvement of nitric oxide in this action. Losartan, its active metabolite EXP3174, and valsartan given intraperitoneally 1 hour before the thrombotic challenge (in doses of 3, 10, or 30 mg/kg) protected mice from death or hind-limb paralysis in response to intravenous injection of a mixture of collagen and epinephrine; losartan was effective in all doses used, whereas EXP3174 and valsartan reduced mortality only in the two higher doses. The protective action of EXP3174 and valsartan was abolished when nitric oxide synthase was inhibited with l-NAME, whereas that of losartan was only partially reduced. Moreover, only losartan protected mice from death caused by intravenous injection of the thromboxane A2 mimetic U46619 and this action was preserved in l-NAME-pretreated animals. Our results demonstrate the ability of AT1-receptor antagonists to inhibit platelet activation in vivo in a nitric oxide-dependent mechanism. Stronger antiplatelet activity of losartan, most likely due to its blockade of thromboxane A2/prostaglandin H2 receptor, could be of potential clinical relevance, particularly in conditions in which synthesis of endogenous nitric oxide is impaired.

AII antagonists in hypertension, heart failure, and diabetic nephropathy: focus on losartan

The goal of antihypertensive therapy is to prevent cardiovascular complications of hypertension, such as heart failure, stroke, end stage renal disease, and death, not just to normalize blood pressure. Recently, several clinical trials investigated the beneficial effects of angiotensin II antagonists (AIIAs) in patients with hypertension, heart failure or diabetic nephropathy utilizing proven clinical outcomes (e.g., all-cause mortality) rather than surrogate outcomes (e.g., blood pressure or proteinuria). The AIIAs may offer therapeutic advantages with respect to particular outcomes in certain types of patients. Evidence is also emerging that losartan may possess beneficial pharmacological properties such as effects on uric acid, platelets, sexual dysfunction, and cognitive function, that may set it apart from other members of the AIIA class. However, further studies are needed to delineate fully these potential pharmacological differences among the AIIAs and their possible clinical relevance. This paper reviews recent AIIA outcomes studies in patients with hypertension, heart failure, or diabetic nephropathy and also examines data suggesting that molecular differences exist within the AIIA class, differences that may assist in explaining the outcomes achieved in these recent trials.

Advances in the treatment of diabetic renal disease: focus on losartan

Diabetic nephropathy is the leading cause of end stage renal disease (ESRD), and given that treating this condition is a considerable economic burden, the prevention of ESRD is a major public health goal. The renin-angiotensin system (RAS) is aberrantly activated in patients with diabetes. Angiotensin II (AII), a downstream effector of the RAS, has haemodynamic and non-haemodynamic effects that contribute to the development and progression of nephropathy. For patients with type 2 diabetes mellitus (T2DM) and hypertension, an AII receptor blocker (AIIRB) is recommended as the first drug that should be used. This review will focus on the rationale for the use of losartan as a treatment for nephropathy associated with T2DM. In animal models of diabetes, losartan reduced proteinuria and conferred renal protection. In RENAAL (Reduction in Endpoints in Non-Insulin-Dependent Diabetes Mellitus with the Angiotensin II Antagonist Losartan), the first major randomised trial that investigated the benefit of losartan in patients with T2DM and nephropathy, losartan significantly reduced the risk of a doubling of serum creatinine and progression to ESRD, significantly lowered the levels of proteinuria and slowed the rate of decline in glomerular filtration rate. This review also discusses other clinical trials of losartan and other AIIRBs in T2DM, and considers alternative mechanisms by which losartan may be exerting its effects. The collective experience in treatment trials highlighted in this review indicate that losartan and other AIIRBs can reduce blood pressure and the progression of proteinuria in diabetic renal disease. However, losartan is thus far the only AIIRB that has been shown to reduce significantly the risk of ESRD and cardiovascular events in patients with T2DM. Its use in hypertensive patients with T2DM and nephropathy may play an important role in reducing the burden of ERSD.

Pleiotropic effects of angiotensin II receptor blocker in hypertensive patients

OBJECTIVES

We investigated the vascular effects of candesartan in hypertensive patients.

BACKGROUND

The renin-angiotensin system may contribute to atherogenesis through the promotion of endothelial dysfunction. The plausible mechanisms are that angiotensin II promotes superoxide anion generation, endothelial dysfunction, inflammation, and impaired fibrinolysis. The effects of candesartan on these conditions have not been clearly observed.

METHODS

We administered placebo or candesartan 16 mg daily during two months to 45 patients with mild-to-moderate hypertension. This was a randomized, double-blind, placebo-controlled, crossover study in design.

RESULTS

Candesartan did not significantly change lipoprotein levels. However, compared with placebo, candesartan significantly reduced plasma levels of malondialdehyde from 1.50 +/- 0.07 to 1.29 +/- 0.09 microM (p = 0.009); improved the percent flow-mediated dilator response to hyperemia from 5.17 +/- 0.24 to 6.22 +/- 0.26% (p < 0.001); and, furthermore, reduced plasma levels of monocyte chemoattractant protein (MCP-1) from 213 +/- 8 to 190 +/- 7 pg/ml (p = 0.003), tumor necrosis factor-alpha from 2.93 to 2.22 pg/ml (p = 0.026), and plasminogen activator inhibitor type 1 from 74 +/- 4 to 53 +/- 4 ng/ml (p < 0.001) but not C-reactive protein (CRP), matrix metalloproteinase protein, and fibrinogen. There were no significant correlations between these changes and reduction of systolic blood pressure (BP) (-0.247 < or = r < or = 0.195) and between these changes and reduction of diastolic BP (-0.262 < or = r < or = 0.197). There were no significant correlations between markers of inflammation and flow-mediated dilation percent or reduction of oxidant stress (-0.119 < or = r < or = 0.127). Furthermore, we observed no significant correlations between CRP and MCP-1 levels (r = -0.162).

CONCLUSIONS

Inhibition of the angiotensin II type 1 (AT1) receptor in hypertensive patients reverses endothelial dysfunction, measured as an improvement in flow-mediated dilation and fibrinolysis and reduction of oxidant stress and inflammatory cytokines, suggesting that AT1 receptor blocker therapy has antiatherogenic effects.

Pharmacological modulation of platelet function in hypertension

Platelets exert a considerable influence on human morbidity and mortality. The rationale for their study in hypertension follows the observation that the major consequences of hypertension are stroke and myocardial infarction. However, the etiology of these consequences in hypertension is, paradoxically, not hemorrhagic (as might be expected from the effects of high blood pressure), but occlusive, with thrombus being the culprit lesion. Mechanisms of platelet activation include high shear force, activation of the renin-angiotensin system, endothelial changes, and the presence of comorbidity, such as atrial fibrillation. The treatment of high blood pressure brings about a reversal of the changes seen in the cell. This could be in part due to the direct effect of the drug on the megakaryocyte and/or the platelets themselves, or it might simply be due to the reduction in blood pressure. Some drugs, such as calcium channel antagonists and angiotensin II receptor blockers, however, might have direct effects on platelet biochemistry other than reducing blood pressure. Finally, antiplatelet drugs are becoming an important part of the management of high-risk hypertensives, which aim to minimize vascular complications.

Arterial hypertension and ischaemic stroke

OBJECTIVES

Arterial hypertension is, besides age, the number one risk factor for ischaemic stroke. Patients with arterial hypertension frequently present with additional coexisting vascular risk factors interacting in a complex way.

MATERIAL AND METHODS

This paper reviews the benefit of antihypertensive treatment, as well as different treatment options of arterial hypertension and their side-effects.

RESULTS

Patients with definite arterial hypertension, but also patients with so-called normal or high-normal blood pressure are at increased risk to develop stroke and other cardiovascular complications. Vascular remodelling of small and large vessels provoked by arterial hypertension is the initial step in the development of atherosclerosis and lipohyalinosis. Vascular remodelling can be improved or even normalized by antihypertensive treatment with angiotensin-converting-enzyme inhibitors and angiotensin-I-receptor antagonists showing the most convincing effects. Angiotensin-converting-enzyme inhibitors and angiotensin-I-receptor antagonists have the lowest rate of side-effects, however, economic restraints hinder their general application. Statins are needed to treat dyslipidaemia. They also lower blood pressure and have a synergistic effect with the above two antihypertensive components in lowering blood pressure. In hypertensive patients, risk of stroke and other cardiovascular complications is determined by the blood pressure level and the presence or absence of target organ damage and the interaction with other risk factors, such as cigarette smoking, dyslipidaemia, and diabetes. These high-risk patients should be treated even more aggressively than usual.

CONCLUSIONS

In the vast majority of patients and healthy individuals, target blood pressure should be as high as or below 120/80 mmHg to minimize the occurrence of stroke and other cardiovascular complications.

Drugs that interrupt the renin-angiotensin system should be among the preferred initial drugs to treat hypertension

The goal of antihypertensive therapy is to provide effective treatment that can be sustained lifelong, while lowering elevated blood pressure and preventing hypertensive end-organ damage and mortality. Angiotensin-converting enzyme (ACE) inhibitors and angiotensin II antagonists (AIIAs) control blood pressure as well as other available classes of antihypertensive drugs. The ACE inhibitors have been demonstrated to reduce the incidence of stroke, reverse left ventricular hypertrophy, and improve congestive heart failure symptomatology and mortality to a similar degree as diuretics and beta-adrenergic blockers. ACE inhibitors reduce postmyocardial infarction recurrence, improve congestive heart failure symptomatology and mortality, and slow the progression of glomerular renal disease. The AIIAs reverse left ventricular hypertrophy. Several of these agents have been shown to improve congestive heart failure symptomology and mortality, to reduce the occurrence of early atherosclerotic vascular disease, and to slow the progression of renal failure in type 2 diabetes mellitus nephropathy. One AIIA has reduced the incidence of end-stage renal disease in non-insulin-dependence diabetes mellitus nephropathy over 3 years. Ideally, antihypertensive therapy should maintain or improve the patients quality of life without creating side effects or adverse laboratory effects. Among the available nine classes of antihypertensive drugs, ACE inhibitors and the AIIAs come close to meeting the description of an ideal drug. AIIAs and ACE inhibitors, two classes of antihypertensive drugs that reduce the activity of the renin-angiotensin II system, should be among the preferred first-step drugs for the treatment of hypertension.

Sexual dysfunction in patients with hypertension: implications for therapy

Sexual dysfunction associated with hypertension or antihypertensive therapies may impact the ability of patients to stay on therapy and lead to deterioration in patients' quality of life. Therefore, it is important for practitioners to become familiar with the wide variation in sexual side effects produced by antihypertensive agents and to discuss the potential occurrence of these side effects with their patients. In many cases, a change in the patient's drug regimen may help patients overcome specific sexual side effects experienced with certain treatments. Practitioners should consider selecting an antihypertensive therapy that is highly effective in lowering blood pressure but preserves patients quality of life. The effect of medications on sexual function remains controversial. Some blinded trials report little difference between placebo and specific medications, whereas other studies indicate that antihypertensive medications increase sexual dysfunction, which has an impact on quality of life. Recent evidence suggests that losartan, an angiotensin II antagonist, is not typically associated with development of sexual dysfunction and may actually positively impact several indices of sexual function (erectile function, sexual satisfaction, and frequency of sexual activity) as well as perceived quality of life. Thus, angiotensin II antagonists may offer a therapeutic option to prevent or correct erectile dysfunction in patients with hypertension. The favorable effects of these agents on sexual function may be related, in part, to their ability to block angiotensin II, which has recently become recognized as an important mediator of detumescence and possibly erectile dysfunction.

[Beyond blood pressure reduction in the treatment of arterial hypertension. Clinical implications of the LIFE study]

To date, blood-pressure lowering has been the main therapeutic objective in patients with arterial hypertension, regardless of the drug used, except for drugs selected for accompanying conditions. The LIFE study, carried out in 9,193 high-risk hypertensive patients (with ECG criteria of left ventricular hypertrophy), has shown that a therapeutic regimen based on losartan combined with a thiazide was accompanied by a significant reduction in the risk of cardiovascular complications in more than 90% of patients compared with atenolol and a thiazide over a mean follow-up period of 4.8 years. The incidence of the primary endpoints (cardiovascular death, stroke, and myocardial infarction) was 11% in the losartan group and 13% in the atenolol group (13% relative risk reduction, p = 0.021). Losartan therapy was associated with more benefits in stroke risk reduction and in the development of new cases of diabetes. In the analysis of the subgroup of 1,195 patients with hypertension and diabetes included in the LIFE study, losartan had a special prognostic benefit. One of the cardiovascular events included as a primary endpoint was observed in 18% of the losartan-treated patients and in 23% of the atenolol-treated patients (24% relative risk reduction, p = 0.031). The LIFE trial showed that losartan produced better cardiovascular protection than atenolol, a similar blood pressure reduction, and was better tolerated. This drug seems to confer extra cardiovascular protection in addition to reducing blood pressure.

Effects of efonidipine on platelet and monocyte activation markers in hypertensive patients with and without type 2 diabetes mellitus

We compared the levels of microparticles, platelet activation markers, soluble cell adhesion molecules, and soluble selectins between hypertensive patients with and without type 2 diabetes and control subjects. Binding of anti-glycoprotein IIb/IIIa and anti-glycoprotein Ib monoclonal antibodies to platelets did not differ significantly between the hypertensive patients and controls, but platelet expression of activation markers (CD62P, CD63, PAC-1, and annexin V) was higher in the hypertensive patients. Platelet-derived microparticle (PDMP) and monocyte-derived microparticle (MDMP) levels were significantly higher in the hypertensive patients than in the controls. Soluble ICAM-1, VCAM-1, P-selectin, and E-selectin levels were also higher in the hypertensive patients, and they were significantly higher in the hypertensive patients with diabetes. After treatment with efonidipine, the levels of PDMPs, CD62P-, CD63-, PAC-1-, and annexin V-positive platelets, sICAM-1, sVCAM-1, sP-selectin, and sE-selectin all decreased significantly. The MDMP levels decreased, and the decrease was significant in the hypertensive patients with diabetes. These findings suggest that administration of efonidipine to hypertension patients with diabetes may prevent the development of cardiovascular complications caused by cell adhesion molecules or activated platelets and monocytes.

The impact of angiotensin II receptor blockade and the DASH diet on markers of endogenous fibrinolysis

Hypertension is associated with impaired fibrinolysis. Both angiotensin receptor blockers (ARB) and the DASH (Dietary Approaches to Stop Hypertension) diet effectively lower blood pressure in hypertensive patients. Some evidence suggests that treatment with ARBs could increase fibrinolysis, however, data is conflicting. The impact of the DASH diet on fibrinolytic parameters is not known. Fifty-five hypertensive participants (35 African-American, 20 white) were randomly assigned to receive 8 weeks of either a control diet or the DASH diet. The diets did not differ in sodium content (approximately 3 g/day). Within each diet, individuals were randomly assigned to receive losartan or placebo for 4 weeks in double-blind, cross-over fashion. Tissue plasminogen activator (t-PA) antigen, t-PA activity, plasminogen activator inhibitor-1 (PAI-1) activity and plasma renin activity (PRA) were measured at the end of a 2-week run-in period on the control diet and after each treatment period. The DASH diet did not affect markers of fibrinolysis. Losartan significantly lowered t-PA antigen levels (-1.8 ng/mL, P = 0.045), but had no effect on t-PA or PAI-1 activities. This effect was more pronounced in whites (-4.1 ng/mL (P = 0.003)) compared with African-Americans (-0.3 ng/mL (P = 0.7), P-interaction = 0.03). Results were not materially affected by adjustment for basline values or changes in blood pressure. This study demonstrates that losartan reduces t-PA antigen levels in white, but not African-American hypertensive individuals. In contrast, the DASH diet had no significant effect on markers of fibrinolysis in whites or African-Americans.

Thromboxane receptor density is increased in human cardiovascular disease with evidence for inhibition at therapeutic concentrations by the AT(1) receptor antagonist losartan

1. The aim of this study was to establish how thromboxane receptors (TP) respond to the increase in levels of plasma thromboxane observed in both cardiac (cardiomyopathy, ischaemic heart disease and pulmonary hypertension) and vascular disease (atherosclerosis of coronary artery disease and accelerated atherosclerosis of saphenous vein grafts). 2. The agonist radioligand [(125)I]-BOP, bound rapidly to TP receptors in normal human cardiovascular tissue, displaying high affinity in left ventricle (K(D) 0.23 +/- 0.06 nM, B(max) 28.4 +/- 5.7 fmol mg(-1) protein) and reversibility with a t(1/2) of 10 min (n = five individuals +/- s.e.mean). 3. In the heart, TP receptor density in the right ventricle of primary pulmonary hypertensive patients were significantly increased (66.6 +/- 6 fmol mg(-1) protein) compared to non-diseased right ventricle (37.9 +/- 4.1 fmol mg(-1) protein, n = six individuals +/- s.e.mean, P<0.05). 4. In diseased vessels, TP receptor densities were significantly increased (3 fold in the intimal layer) in atherosclerotic coronary arteries, saphenous vein grafts with severe intimal thickening (n = 8-12 individuals, P<0.05) and aortic tissue (n=5 - 6 individuals, P<0.05), compared with normal vessels. 5. Losartan, tested at therapeutic doses, competed for [(125)I]-BOP binding to human vascular tissue, suggesting that some of the anti-hypertensive effects of this AT(1) receptor antagonist could also be mediated by blocking human TP receptors. 6. The differential distribution of TP receptors in the human cardiovascular system and the alteration of receptor density, accompanying the increase in endogenous thromboxane levels in cardiovascular disease, suggest that TP receptors represent a significant target for therapeutic interventions and highlights the importance for the development of novel selective antagonist for use in humans.

Hypertension and the kidney

Hypertension and kidney function are intimately related, with each having significant influences on the other. Given the major role played by the kidney in maintenance of extracellular fluid volume and peripheral vascular resistance, the kidney is justifiably a target of investigation to determine its potential role in essential hypertension. Conversely, hypertension is associated with progressive renal failure, and hypertension-associated end-stage renal disease is the second leading cause of end-stage renal disease in the United States. It is therefore important that we continue to investigate the hypertension/renal relationship in an effort to better understand the determinants of essential hypertension and to prevent a major cause of end-stage renal disease.