The Pathophysiologic Role of the Brain Renin-Angiotensin System in Stroke Protection: Clinical Implications

ACE Inhibitors and Angiotensin Receptor Blockers for the Primary and Secondary Prevention of Cardiovascular Outcomes: Recommendations from the 2024 Egyptian Cardiology Expert Consensus in Collaboration with the CVREP Foundation

INTRODUCTION

The renin-angiotensin-aldosterone system (RAAS) plays a pivotal role in regulating blood pressure (BP), with dysregulation of RAAS resulting in hypertension and potentially heart failure (HF), myocardial infarction (MI), cardio-renal syndrome, and stroke. RAAS inhibitors, such as angiotensin-converting enzyme inhibitors (ACEis) and angiotensin receptor blockers (ARBs), have advantages beyond BP control. However, differences between these two drug classes need to be considered when choosing a therapy for preventing cardiovascular events.

METHODS

A panel of 36 Egyptian cardiologists developed consensus statements on RAAS inhibitors for primary and secondary prevention of cardiovascular outcomes and stroke, using a modified three-step Delphi process.

RESULTS

The consensus statements highlight the importance of effective BP control and the role of RAAS blockade for prevention and management of various cardiovascular diseases. ACEis and ARBs differ in their mode of action and, thus, clinical effects. On the basis of available evidence, the consensus group recommended the following: ACEis should be considered as first choice (in preference to ARBs) to reduce the risk of MI, for primary prevention of HF, and for secondary prevention of stroke. ACEis and ARBs show equivalent efficacy for the primary prevention of stroke. Evidence also favors the preferential use of ACEis in patients with type 2 diabetes, for BP control, for the primary prevention of diabetic kidney disease, and to reduce the risk of major cardiovascular and renal outcomes. Treatment with an ACEi should be started within 24 h of ST segment elevation MI (and continued long term) in patients with HF, left ventricular systolic dysfunction, and/or diabetes. Angiotensin receptor/neprilysin inhibitors (ARNIs) are the first choice for patients with HF and reduced ejection fraction, with ACEis being the second choice in this group. ARBs are indicated as alternatives in patients who cannot tolerate ACEis. ACEis may be associated with cough development, but the incidence tends to be overestimated, and the risk can be reduced by use of a lipophilic ACEi or combining the ACEi with a calcium channel blocker.

CONCLUSION

RAAS blockade is an essential component of hypertension therapy; however, the protective effects provided by ACEis are superior to those of ARBs. Therefore, an ACEi is indicated in almost all cases, unless not tolerated.

Superior stroke prevention with angiotensin receptor blockers compared with other antihypertensive drugs

INTRODUCTION

Stroke is a major cause of death and disability and its incidence is linearly increased with the elevation of blood pressure (BP) and the advancement of age in both men and women, with its incidence being higher in older subjects, the blacks and women.

AREAS COVERED

The annual worldwide incidence of stroke is 7.6 million for subjects ≥ 20 years of age with the average direct and indirect annual costs of stroke care, is expected to be $94.3 billion between 2014 and 2015. With respect to the cause of stroke, this is multifactorial, due to atherosclerotic heart disease, inflammation, atrial fibrillation, and hypertension with the latter being the most important cause. Therefore, control of BP is the major factor for its prevention. In order to get a better perspective on the current management of stroke, a Medline search of the English literature was conducted between 2014 and 2022 and 26 pertinent papers were selected.

EXPERT OPINION

Review of data from the selected papers demonstrated that control of SSBP < 130 mmHg was better in stroke prevention than SBP 130-140 mmHg for primary and secondary strokes. Among the drugs used, angiotensin receptor blockers provided superior stroke prevention compared to angiotensin converting enzyme inhibitors and other antihypertensive drugs.

Neuroprotection in Stroke-Focus on the Renin-Angiotensin System: A Systematic Review

Stroke is the primary cause of disability in the adult population. Hypertension represents the leading risk factor being present in almost half the patients. The renin-angiotensin system is involved in the physiopathology of stroke and has an essential impact on hypertension as a risk factor. This article targeted the role of the renin-angiotensin system in stroke neuroprotection by reviewing the current literature available. The mechanism of action of the renin-angiotensin system was observed through the effects on AT1, AT2, and Mas receptors. The neuroprotective properties ascertained by angiotensin in stroke seem to be independent of the blood pressure reduction mechanism, and include neuroregeneration, angiogenesis, and increased neuronal resistance to hypoxia. The future relationship of stroke and the renin-angiotensin system is full of possibilities, as new agonist molecules emerge as potential candidates to restrict the impairment caused by stroke.

The Protective Effects of Hydrogen Sulfide New Donor Methyl S-(4-Fluorobenzyl)-N-(3,4,5-Trimethoxybenzoyl)-l-Cysteinate on the Ischemic Stroke

In this paper, we report the design, synthesis and biological evaluation of a novel S-allyl-l-cysteine (SAC) and gallic acid conjugate S-(4-fluorobenzyl)-N-(3,4,5-trimethoxybenzoyl)-l-cysteinate (MTC). We evaluate the effects on ischemia-reperfusion-induced PC12 cells, primary neurons in neonatal rats, and cerebral ischemic neuronal damage in rats, and the results showed that MTC increased SOD, CAT, GPx activity and decreased LDH release. PI3K and p-AKT protein levels were significantly increased by activating PI3K/AKT pathway. Mitochondrial pro-apoptotic proteins Bax and Bim levels were reduced while anti-apoptotic protein Bcl-2 levels were increased. The levels of cleaved caspase-9 and cleaved caspase-3 were also reduced in the plasma. The endoplasmic reticulum stress (ERS) was decreased, which in turns the survival rate of nerve cells was increased, so that the ischemic injury of neurons was protected accordingly. MTC activated the MEK-ERK signaling pathway and promoted axonal regeneration in primary neurons of the neonatal rat. The pretreatment of MEK-ERK pathway inhibitor PD98059 and PI3K/AKT pathway inhibitor LY294002 partially attenuated the protective effect of MTC. Using a MCAO rat model indicated that MTC could reduce cerebral ischemia-reperfusion injury and decrease the expression of proinflammatory factors. The neuroprotective effect of MTC may be due to inhibition of the over-activation of the TREK-1 channel and reduction of the current density of the TREK1 channel. These results suggested that MTC has a protective effect on neuronal injury induced by ischemia reperfusion, so it may have the potential to become a new type of neuro-ischemic drug candidate.

Cognitive impact of COVID-19: looking beyond the short term

COVID-19 is primarily a respiratory disease but up to two thirds of hospitalised patients show evidence of central nervous system (CNS) damage, predominantly ischaemic, in some cases haemorrhagic and occasionally encephalitic. It is unclear how much of the ischaemic damage is mediated by direct or inflammatory effects of virus on the CNS vasculature and how much is secondary to extracranial cardiorespiratory disease. Limited data suggest that the causative SARS-CoV-2 virus may enter the CNS via the nasal mucosa and olfactory fibres, or by haematogenous spread, and is capable of infecting endothelial cells, pericytes and probably neurons. Extracranially, SARS-CoV-2 targets endothelial cells and pericytes, causing endothelial cell dysfunction, vascular leakage and immune activation, sometimes leading to disseminated intravascular coagulation. It remains to be confirmed whether endothelial cells and pericytes in the cerebral vasculature are similarly targeted. Several aspects of COVID-19 are likely to impact on cognition. Cerebral white matter is particularly vulnerable to ischaemic damage in COVID-19 and is also critically important for cognitive function. There is accumulating evidence that cerebral hypoperfusion accelerates amyloid-β (Aβ) accumulation and is linked to tau and TDP-43 pathology, and by inducing phosphorylation of α-synuclein at serine-129, ischaemia may also increase the risk of development of Lewy body disease. Current therapies for COVID-19 are understandably focused on supporting respiratory function, preventing thrombosis and reducing immune activation. Since angiotensin-converting enzyme (ACE)-2 is a receptor for SARS-CoV-2, and ACE inhibitors and angiotensin receptor blockers are predicted to increase ACE-2 expression, it was initially feared that their use might exacerbate COVID-19. Recent meta-analyses have instead suggested that these medications are protective. This is perhaps because SARS-CoV-2 entry may deplete ACE-2, tipping the balance towards angiotensin II-ACE-1-mediated classical RAS activation: exacerbating hypoperfusion and promoting inflammation. It may be relevant that APOE ε4 individuals, who seem to be at increased risk of COVID-19, also have lowest ACE-2 activity. COVID-19 is likely to leave an unexpected legacy of long-term neurological complications in a significant number of survivors. Cognitive follow-up of COVID-19 patients will be important, especially in patients who develop cerebrovascular and neurological complications during the acute illness.

YangXue QingNao Wan, a Compound Chinese Medicine, Attenuates Cerebrovascular Hyperpermeability and Neuron Injury in Spontaneously Hypertensive Rat: Effect and Mechanism

Objective

The purpose of the study was to explore the effect of YangXue QingNao Wan (YXQNW), a compound Chinese medicine, on cerebrovascular hyperpermeability, neuronal injury, and related mechanisms in spontaneously hypertensive rat (SHR).

Methods

Fourteen-week-old male SHR were used, with Wistar Kyoto (WKY) rats as control. YXQNW (0.5 g/kg/day), enalapril (EN, 8 mg/kg/day), and nifedipine (NF, 7.1 mg/kg/day) were administrated orally for 4 weeks. To assess the effects of the YXQNW on blood pressure, the systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean blood pressure (MBP) were measured. After administering the drugs for 4 weeks, the cerebral blood flow (CBF), albumin leakage from microvessels in middle cerebral artery (MCA)-dominated area, and the number and morphology of microvessels were assessed in the hippocampus area and cortex. Neuronal damage and apoptosis were assessed by Nissl staining and TUNEL staining. To assess the mechanisms of cerebrovascular hyperpermeability, we performed immunofluorescence and Western blot to assess the expression and integrity of cerebral microvascular tight junction (TJ) and caveolin-1 (Cav-1) in cortex. Energy metabolism and Src-MLC-MLCK pathway in cortex were assessed then for elucidating the underlying mechanism of the observed effect of YXQNW.

Results

Spontaneously hypertensive rat exhibited higher blood pressure, Evans blue (EB) extravasation, albumin leakage, increased brain water content, decreased CBF, perivascular edema, and neuronal apoptosis in the hippocampus and cortex, all of which were attenuated by YXQNW treatment. YXQNW inhibited the downregulation of TJ proteins, mitochondrial Complex I, Complex II, and Complex V, and upregulation of caveolin-1, inhibiting Src/MLCK/MLC signaling in SHR. YXQNW combined with EN + NF revealed a better effect for some outcomes compared with either YXQNW or EN + NF alone.

Conclusion

The overall result shows the potential of YXQNW to attenuate blood–brain barrier (BBB) breakdown in SHR, which involves regulation of energy metabolism and Src/MLCK/MLC signaling. This result provides evidence supporting the application of YXQNW as an adjuvant management for hypertensive patients to prevent hypertensive encephalopathy.

Treatment of Life-Threatening ACE-Inhibitor-Induced Angioedema

Incidence of angioedema associated with angiotensin-converting enzyme inhibitors (ACE-I) has been estimated at 0.1%-2.2% of patients receiving treatment. Despite the potential severity of this disease state, standardized treatment is lacking. Traditional pharmacotherapy options include medications that target inflammatory mediators and the angiotensin pathway. However, because ACE-I-induced angioedema is caused by accumulation of bradykinin, these medications fail to target the underlying pathophysiology. Recently, novel therapies that target the kallikrein-bradykinin pathway have been studied. These include icatibant, ecallantide, C1 esterase inhibitors, and fresh-frozen plasma. Recent randomized controlled trials exhibit contradictory results with the use of icatibant. This is a focused review on traditional and novel treatment strategies for ACE-I-induced angioedema.

Involvement of angiotensin-(1-7) in the neuroprotection of captopril against focal cerebral ischemia

Accumulating evidence suggests that brain angiotensin-converting enzyme (ACE)/angiotensin II/angiotensin II type I receptor axis is activated and thus contributes to the neuronal injury during ischemic stroke. Conversely, inhibition of this axis using centrally active ACE inhibitor captopril was proven neuroprotective in rodents with focal cerebral ischemia. Interestingly, captopril was able to increase angiotensin-(1-7) [Ang-(1-7)] levels in the peripheral organs. As the main component of the alternative renin-angiotensin system axis in the brain, Ang-(1-7) was revealed to protect against focal cerebral ischemia via a MAS1 receptor-dependent manner. Based on this evidence, we hypothesized that Ang-(1-7) might contribute to the neuroprotection of captopril during ischemic stroke. In this study, we evaluated this hypothesis using a rat model of focal cerebral ischemia. We revealed that brain ACE2 activity and Ang-(1-7) levels were significantly elevated following captopril treatment in rats with focal cerebral ischemia. More importantly, we showed that the neuroprotection provided by captopril was partially reversed by A-779, an antagonist for Ang-(1-7) receptor MAS1, indicating that Ang-(1-7) was involved in the neuroprotection of captopril. These findings have uncovered new mechanisms by which captopril protects against focal cerebral ischemia and further suggest that captopril may have practical clinical use for stroke prevention and treatment in addition to its antihypertensive effect.

Renin-angiotensin system as a potential therapeutic target in stroke and retinopathy: experimental and clinical evidence

As our knowledge expands, it is now clear that the renin-angiotensin (Ang) system (RAS) mediates functions other than regulating blood pressure (BP). The RAS plays a central role in the pathophysiology of different neurovascular unit disorders including stroke and retinopathy. Moreover, the beneficial actions of RAS modulation in brain and retina have been documented in experimental research, but not yet exploited clinically. The RAS is a complex system with distinct yet interconnected components. Understanding the different RAS components and their functions under brain and retinal pathological conditions is crucial to reap their benefits. The aim of the present review is to provide an experimental and clinical update on the role of RAS in the pathophysiology and treatment of stroke and retinopathy. Combining the evidence from both these disorders allows a unique opportunity to move both fields forward.

Neuroprotective Effect of Scutellarin on Ischemic Cerebral Injury by Down-Regulating the Expression of Angiotensin-Converting Enzyme and AT1 Receptor

Background and Purpose

Previous studies have demonstrated that angiotensin-converting enzyme (ACE) is involved in brain ischemic injury. In the present study, we investigated whether Scutellarin (Scu) exerts neuroprotective effects by down-regulating the Expression of Angiotensin-Converting Enzyme and AT1 receptor in a rat model of permanent focal cerebral ischemia.

Methods

Adult Sprague–Dawley rats were administrated with different dosages of Scu by oral gavage for 7 days and underwent permanent middle cerebral artery occlusion (pMCAO). Blood pressure was measured 7 days after Scu administration and 24 h after pMCAO surgery by using a noninvasive tail cuff method. Cerebral blood flow (CBF) was determined by Laser Doppler perfusion monitor and the neuronal dysfunction was evaluated by analysis of neurological deficits before being sacrificed at 24 h after pMCAO. Histopathological change, cell apoptosis and infarct area were respectively determined by hematoxylin–eosin staining, terminal deoxynucleotidyl transfer-mediated dUTP nick end labeling (TUNEL) analysis and 2,3,5-triphenyltetrazolium chloride staining. Tissue angiotensin II (Ang II) and ACE activity were detected by enzyme-linked immunosorbent assays. The expression levels of ACE, Ang II type 1 receptor (AT1R), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and interleukin-1β (IL-1β) were measured by Western blot and real-time PCR. ACE inhibitory activity of Scu in vitro was detected by the photometric determination.

Results

Scu treatment dose-dependently decreased neurological deficit score, infarct area, cell apoptosis and morphological changes induced by pMCAO, which were associated with reductions of ACE and AT1R expression and the levels of Ang II, TNF-α, IL-6, and IL-1β in ischemic brains. Scu has a potent ACE inhibiting activity.

Conclusion

Scu protects brain from acute ischemic injury probably through its inhibitory effect on the ACE/Ang II/AT1 axis, CBF preservation and proinflammation inhibition.

Antihypertensive Therapies and Cognitive Function: a Review

Increasing life expectancy has made old age-related health problems like dementia and cognitive decline more prevalent, and these are rapidly becoming important causes of disability and poor quality of life, causing significant add-ons to health-care costs worldwide. Hypertension is the most important modifiable vascular risk factor for the development and progression of both cognitive decline and dementia. In many observational and randomized studies, antihypertensive therapies have been shown to be beneficial in slowing cognitive decline. However, due to observed discrepancies by these studies, there is a lack of consensus on the best antihypertensive strategy for the prevention or slowing of cognitive decline. It is also not clear whether the beneficial effect of antihypertensive therapy is due to the use of a specific class of agents or combination therapy. Thus, we present a comprehensive review of overall antihypertensive therapies and cognition and of the individual antihypertensive therapy classes with their specific protective mechanisms and available clinical evidence behind their effect on cognitive function.

Functional Local Renin-Angiotensin System in Human and Rat Periodontal Tissue

The initiation or progression of periodontitis might involve a local renin-angiotensin system (RAS) in periodontal tissue. The aim of this study was to further characterize the local RAS in human and rat periodontal tissues between healthy and periodontally-affected tissue. Components of the RAS were investigated using in vitro, ex vivo and in vivo experiments involving both human and Wistar rat periodontium. Although not upregulated when challenged with P. gingivalis-lipopolysaccharide, human gingival and periodontal ligament fibroblasts expressed RAS components. Likewise, healthy and inflamed human gingiva expressed RAS components, some of which were shown to be functional, yet no differences in expression were found between healthy and diseased gingiva. However, in inflamed tissue the immunoreactivity was greater for the AT₁R compared to AT₂R in fibroblasts. When compared to healthy tissue, ACE activity was increased in human gingiva from volunteers with gingivitis. Human-gingiva homogenates generated Ang II, Ang 1-9 and Ang 1-7 when incubated with precursors. In gingiva homogenates, Ang II formation from Ang I was nearly abolished only when captopril and chymostatin were combined. Ang 1-7 formation was significantly greater when human gingiva homogenates were incubated with chymostatin alone compared to incubation without any inhibitor, only captopril, or captopril and chymostatin. In rat gingiva, RAS components were also found; their expression was not different between healthy and experimentally induced periodontitis (EP) groups. However, renin inhibition (aliskiren) and an AT₁R antagonist (losartan) significantly blocked EP-alveolar-bone loss in rats. Collectively, these data are consistent with the hypothesis that a local RAS system is not only present but is also functional in both human and rat periodontal tissue. Furthermore, blocking AT₁R and renin can significantly prevent periodontal bone loss induced by EP in rats.

Vascular plasticity in cerebrovascular disorders

Cerebral ischemia remains a major cause of morbidity and mortality with little advancement in subacute treatment options. This review aims to cover and discuss novel insight obtained during the last decade into plastic changes in the vasoconstrictor receptor profiles of cerebral arteries and microvessels that takes place after different types of stroke. Receptors like the endothelin type B, angiotensin type 1, and 5-hydroxytryptamine type 1B/1D receptors are upregulated in the smooth muscle layer of cerebral arteries after different types of ischemic stroke as well as after subarachnoid hemorrhage, yielding rather dramatic changes in the contractility of the vessels. Some of the signal transduction processes mediating this receptor upregulation have been elucidated. In particular the extracellular regulated kinase 1/2 pathway, which is activated early in the process, has proven to be a promising therapeutic target for prevention of vasoconstrictor receptor upregulation after stroke. Together, those findings provide new perspectives on the pathophysiology of ischemic stroke and point toward a novel way of reducing vasoconstriction, neuronal cell death, and thus neurologic deficits after stroke.

Phosphoinositide 3-kinase-gamma expression is upregulated in brain microglia and contributes to ischemia-induced microglial activation in acute experimental stroke

Microglia, the resident microphages of the CNS, are rapidly activated after ischemic stroke. Inhibition of microglial activation may protect the brain by attenuating blood-brain barrier damage and neuronal apoptosis after ischemic stroke. However, the mechanisms by which microglia is activated following cerebral ischemia is not well defined. In this study, we investigated the expression of PI3Kgamma in normal and ischemic brains and found that PI3Kgamma mRNA and protein are constitutively expressed in normal brain microvessels, but significantly upregulated in postischemic brain primarily in activated microglia following cerebral ischemia. In vitro, the expression of PI3Kgamma mRNA and protein was verified in mouse brain endothelial and microglial cell lines. Importantly, absence of PI3Kgamma blocked the early microglia activation (at 4h) and subsequent expansion (at 24-72 h) in PI3Kgamma knockout mice. The results suggest that PI3Kgamma is an ischemia-responsive gene in brain microglia and contributes to ischemia-induced microglial activation and expansion.

Inhibition of the renin-angiotensin-aldosterone system to prevent ischemic and atherothrombotic events

Blood pressure (BP) is a continuous risk factor for ischemic and atherosclerotic events such as stroke and ischemic heart disease, and controlling BP is a well-established component of any cardiovascular or cerebrovascular risk reduction regimen. In most patients, > or =2 medications with different mechanisms of action will be necessary to reach recommended BP goals. The neuroendocrine effects of the renin-angiotensin-aldosterone-system (RAAS) have proven to be excellent therapeutic targets for BP lowering. A number of antiatherosclerotic effects have been attributed to angiotensin-converting enzyme inhibitors and angiotensin receptor blockers in addition to their antihypertensive effects. Because they have complementary actions on the RAAS, combination therapy with these agents has become the focus of recent clinical trials. This review describes the clinical data assessing the efficacy of angiotensin-converting enzyme inhibitors and angiotensin receptor blockers individually and in combination in reducing the risk of stroke and ischemic heart disease.

Candesartan-induced gene expression in five organs of stroke-prone spontaneously hypertensive rats

To test the functional consequences of blocking the local renin-angiotensin system (RAS), we investigated the effects of an angiotensin II type 1 receptor blocker (ARB), candesartan, on the systemic gene expression profile of five important organs (brain, heart, kidney, liver and adipose tissues) in the stroke-prone spontaneously hypertensive rat (SHRSP), an established model of essential hypertension and cardiovascular disorders, and its normotensive control, the Wistar Kyoto (WKY) rat. Rats were treated with candesartan (5 mg/kg/d) for 4 weeks from 12 to 16 weeks of age. DNA microarray technology was used to identify changes in gene expression. Four weeks of treatment with candesartan significantly lowered systolic blood pressure in male rats of both the SHRSP and the WKY strains (p<0.0005). Candesartan differentially modulated the gene expression profile in an organ-specific manner in male SHRSP; of the five organs tested, gene expression was most prominently altered in the hearts of SHRSP. In contrast, candesartan treatment exerted minimal or no significant effects on the gene expression profile of the corresponding organs of male WKY rats. The inter-strain differences in gene expression changes induced by candesartan were considered to be associated with both blood pressure-dependent and independent mechanisms. These results help to delineate the mechanisms that underlie the organ or tissue protection conferred by ARB at the levels of cellular biology and genomics in the context of the local RAS. Further studies are warranted to investigate not only individual genes of interest but also genetic "networks" that involve differential organ- or tissue-specific gene expression induced by the blockade of RAS in essential hypertension. Tokyo, Japan

Current and future status of beta-blockers in the treatment of hypertension

Beta-adrenergic receptor blockers (beta-blockers) are effective and safe antihypertensive drugs, and have been recommended as first-line therapy for hypertension by all Joint National Committees (JNCs) for the prevention, detection, evaluation, and treatment of high blood pressure (BP) from the first to the last (JNC-7) in 2003. However, recently questions have been raised by several investigators regarding the antihypertensive effectiveness and safety of these drugs. The Medline literature on this subject was searched and pertinent studies were retrieved. Other pertinent references from existing publications were retrieved and analyzed up to 2007. Additionally, a historical perspective on the discovery of beta-blockers and their mechanism of action is given. Most of the reviewed short-term and long-term clinical trials demonstrate an effective and safe antihypertensive pattern for the beta-blockers. The weaknesses identified include the adverse effect of older beta-blockers on glucose control and stroke protection, especially in older persons. These adverse effects are attributed to their mechanism of action and BP effectiveness. On the basis of the evidence presented, beta-blockers are effective and safe antihypertensive drugs and should still be recommended as first-line therapy in most uncomplicated hypertensive patients, either alone or in combination with other drugs. There are reservations regarding their administration to diabetic and older hypertensive patients. However, when compelling indications for their use exist, they should not be withheld.

Comparison of angiotensin II type 1 receptor antagonists in the treatment of essential hypertension

Hypertension is a major health problem worldwide, yet remains under-diagnosed and under-treated. Angiotensin II type 1 receptor antagonists (angiotensin receptor blockers [ARBs]) are highly effective at reducing blood pressure (BP), exhibit renoprotective properties and have placebo-like tolerability. However, it is unclear whether there are clinical differences in efficacy and tolerability between the available ARBs. A review of published, randomized, comparative clinical trials suggests that differences in BP-lowering efficacy and 24-hour BP control may exist between ARBs, although it appears that there is no evidence for important differences in tolerability between ARBs. Few studies have assessed attainment rates for important combined systolic BP (SBP)/diastolic BP (DBP) goals recommended in treatment guidelines. Likewise, few studies have directly compared more than two agents or ARB/hydrochlorothiazide fixed-dose combinations, and most ARBs have not been compared across their full recommended dosage ranges. Overall, there is insufficient weight of evidence to allow definitive conclusions to be drawn regarding the comparative efficacy of the available ARBs. However, newer ARBs (e.g. olmesartan medoxomil and telmisartan) appear to be more effective than older ARBs (e.g. losartan and valsartan) in reducing DBP and/or SBP in some trials. In addition, olmesartan medoxomil treatment regimens resulted in high BP control rates in several trials, but head-to-head trials with other ARBs are required to put these control rates into perspective, especially for SBP control with various agents. The purpose of this review is to present published data from ARB efficacy trials for a comparison of various efficacy parameters among the agents within this drug class.