Journal of Human Hypertension (2000) 14, Suppl 2, S23–S31  2000 Macmillan Publishers Ltd All rights reserved 0950-9240/00 $15.00 www.nature.com/jhh Blocking the tissue renin-angiotensin system: the future cornerstone of therapy

T Unger1, M Azizi2 and GG Belz3 1Institute of Pharmacology, Christian Albrechts University, Hospitalstra␤e 4, 24105 Kiel, Germany; 2Centre D’Investigations Cliniques, Hoˆ pital Broussais, 96 Rue Didot – 75674, Paris Cedex 14, France; 3Zentrum fuer Kardiovaskulaere Pharmakologie, ZeKaPha GmbH, Mathildenstra␤e 8, D-55116, Mainz-Wiesbaden, Germany

The development of angiotensin-converting enzyme antagonist, is characterised by its tight binding to and inhibitors and selective angiotensin type 1 (AT1)- slow dissociation from the AT1 receptor, and high antag- receptor antagonists has provided new insights into onistic potency, resulting in long-lasting antagonistic understanding the mechanism of the renin-angiotensin effects. It is anticipated that these pharmacological system (RAS) in the pathophysiology of cardiovascular characteristics may bring additional benefits to patients, disease. There is good evidence from meta-analyses not only for the management of essential hypertension that shows that inhibition of the RAS achieves organ but also for the management of end-organ damage. protection features that go beyond blood pressure con- Journal of Human Hypertension (2000) 14, Suppl 2, S23– trol. Candesartan cilexetil, a new angiotensin II receptor S31

Keywords: renin-angiotensin system; angiotensin-converting enzyme inhibitor; angiotensin type 1 receptor; angiotensin receptor antagonist; candesartan cilexetil

Introduction Blocking the RAS in essential Hypertension is a major risk factor for myocardial hypertension infarction, stroke, and renal and peripheral vascular Angiotensin II, the key effector peptide of the RAS, disease. Epidemiological studies have found a direct exerts a variety of actions in the regulation of arterial linear correlation between the risk of cardiovascular blood pressure and the maintenance of fluid and disease and blood pressure levels. Long-term elev- electrolyte homeostasis. Blood pressure is raised by ations in blood pressure are associated with a direct pressor action, increased sympathetic trans- hypertrophy, hyperplasia and remodelling of the mission, water retention (via direct action on heart, as well as vascular and renal damage. While sodium reabsorption, or indirectly via increased some of these changes are compensatory adaptations aldosterone release) and altered renal haemodynam- to the increased workload associated with raised ics. Angiotensin II also acts centrally to induce thirst blood pressure, structural remodelling of the kidney, and drinking behaviour, to attenuate the barorecep- heart and vasculature may also occur independently tor reflex and to release arginine vasopressin and of blood pressure levels.1 It would appear that the other hormones such as adrenocorticotrophic hor- renin-angiotensin system (RAS) plays a central role mone and oxytocin.5,6 in the acute and chronic development of cardio- Blockade of the RAS using ACE inhibitors or angi- vascular disease. Yet, it is only recently, with the otensin II receptor antagonists (AIIRAs) results in an development of angiotensin-converting enzyme acute hypotensive response in sodium-depleted (ACE) inhibitors and selective angiotensin type 1 animals or humans. In conditions associated with (AT ) receptor antagonists, that the full significance 1 elevated plasma angiotensin II levels, such as of RAS in the acute and chronic development of car- experimental or clinical renovascular hypertension diovascular disease has been realised. There is good and congestive heart failure, these agents bring evidence from meta-analyses that shows that inhi- about a marked depressor response.7 In most acute bition of the RAS achieves organ protection features studies, the magnitude of the depressor response that go beyond blood pressure control.2–4 can be predicted by the pre-treatment plasma levels This paper reviews the possible mechanisms of of renin and consequently of angiotensin II, indicat- ACE inhibition and angiotensin II receptor antagon- ing a causal relationship.7 ism in organ protection and hypothesises on the Although the acute blood pressure-lowering possible clinical benefits that may be achievable effects of RAS inhibition correlate with initial with prolonged angiotensin II receptor blockade. plasma renin activity, the chronic response bears little relation to pre-treatment levels.7 Both ACE inhibitors and AIIRAs can lower blood pressure Correspondence: Professor T Unger, Institute of Pharmacology, levels in hypertensive patients whose plasma renin Christian Albrechts University, Hospitalstra␤e 4, 24105 Kiel, levels are normal or even low, but the magnitude of Germany. Tel: + 49 431 597 3500, Fax: + 49 431 597 3522 the antihypertensive response is often less pro- Blocking tissue renin-angiotensin system T Unger et al S24 nounced in patients with low renin levels. While heart failure and atherosclerosis, the expression and circulating angiotensin levels have an important activity of ACE may be dramatically increased.18,25–27 endocrine function in acute volume and blood Normally absent from vascular smooth muscle, pressure homeostasis, the tissue RAS within the recent immunohistochemical evidence indicates brain, heart, kidney, adrenals and blood vessels acts that ACE can be detected in migrated macrophages as a regulator or amplifier of local function.8 Angiot- and smooth muscle cells of atherosclerotic coronary ensin II, which is released by vascular cells, has both arteries during the progression of atherosclerosis, an autocrine function (causing endothelial dysfunc- and in the early healing processes following percu- tion and smooth muscle hypertrophy) and a parac- taneous transluminal coronary angioplasty rine function (influencing smooth muscle tone).8 It (PTCA).28 has been postulated that abnormal tissue RAS activi- Angiotensin I is not the only substrate for ACE, ties are contributors to the development and mainte- which also degrades bradykinin and a number of nance of essential hypertension.8,9 Both ACE inhibi- other peptides (Figure 1).29 Bradykinin, produced tors and AIIRAs prevent and/or reverse most of the locally within tissues, is thought to have beneficial vasculature changes in experimental and clinical effects promoting vasodilatation, natri/diuresis and hypertension. antiremodelling. In animal experiments, the abilities of ACE inhibitors to potentiate kinins as well as ACE inhibition and end-organ damage inhibit the formation of angiotensin II have both been demonstrated to contribute to organ protection Intervention with ACE inhibitors, introduced 20 in various models of cardiovascular disease.30–32 years ago as antihypertensive agents, has become However, it is still not clear to what degree the one of the most successful therapeutic approaches potentiation of kinins adds to the beneficial effects for reducing left ventricular mass,2 decreasing over- of ACE inhibitors in clinical practice. It seems that all mortality and death from chronic heart failure,10 an increase in bradykinin contributes to the short- improving the outcome for patients with ventricular term effects of ACE inhibition on blood pressure.33 systolic dysfunction and symptomatic heart However, the effect of ACE inhibitors on bradykinin failure,11 reducing post-myocardial infarction mor- does not appear to contribute substantially to the tality,12 retarding the progression of renal insuf- long-term effects of the drug, at least not in patients ficiency in insulin-dependent diabetes mellitus with congestive heart failure.34 (IDDM), improving renal function in IDDM and The local production of angiotensin II augmenting retarding the progression of non-diabetic chronic a tissue-specific response independent of the circu- renal disease.13–15 ACE inhibitors have recently been latory RAS presents a powerful new model for the shown to reduce the rate of death, myocardial pathogenesis of cardiovascular disease. This theory infarction and stroke in a broad range of patients is supported by the recent identification of local with a high cardiovascular risk at baseline.16 In eld- tissue enzymes such as chymase in the heart and erly hypertensive patients, ACE inhibitors have been vasculature which indicate a role of ACE-inde- shown to reduce the incidence of fatal and non-fatal pendent pathways in the production of angiotensin cardiovascular events17 to the same extent as con- at a local tissue level.35 In addition, other proteases ventional therapy with diuretics or ␤-blockers. such as cathepsin G36–38 and elastases39 are thought Research into mechanisms of ACE inhibition in end- to enhance angiotensin II generation locally at sites organ damage has focused on the dual role of the of inflammation and tissue injury. circulating RAS as well as the tissue RAS on end- Although it is still controversial whether active organ damage.8,18 renin is derived directly from the kidney or syn- Angiotensin II is recognised as a growth-promot- thesised locally in the heart or blood vessels,40,41 all ing factor that contributes in an autocrine/paracrine other major components of the RAS have been local- fashion to structural alterations in various organs, ised in the heart and blood vessels. Thus, both circu- most notably the heart, vasculature and kidneys.6,19 lating and tissue angiotensins play important roles It is also involved in cardiac left ventricular in cardiovascular homeostasis. Studies are now hypertrophy and fibrosis, vascular media hyper- underway to determine the relative importance of trophy or neointima formation, structural post- the circulatory versus tissue-specific regulatory infarct remodelling and nephrosclerosis, neointima mechanisms on the production of angiotensin II formation, post-infarction remodelling and under different pathological conditions.18 nephrosclerosis, apart from affecting blood press- ure.5,20,21 The conversion of angiotensin I to the Characterisation of the angiotensin II active octapeptide angiotensin II is catalysed by both circulating ACE as well as a membrane-bound receptors form that is found abundantly in the vascular endo- The effects of angiotensin II receptor ligands are thelium as well as the renal proximal tubules, the mediated predominantly through two pharmaco- myocardium and adrenal glands.22–24 Prolonged logically and physiologically distinct mammalian 1,42–44 inhibition of tissue ACE in the heart vasculature and angiotensin receptors designated AT1 and AT2. kidney may be especially important in pathological The AT1 receptor mediates the classical actions of states. While it is thought that under normal physio- angiotensin II, which include: blood pressure regu- logical conditions the concentrations of ACE remain lation, the drinking response and angiotensin II- constant, under pathological conditions such as left induced cell hypertrophy and hyperplasia29 (Table ventricular hypertrophy, myocardial infarction, 1). In rodents, the AT1 receptor seems to exist in two

Journal of Human Hypertension Blocking tissue renin-angiotensin system T Unger et al S25

Figure 1 The sites of action of ACE inhibition and AT1-receptor blockade in the renin-angiotensin system. (BK) bradykinin, (NO) nitric oxide. Adapted with permission from Willenheimer et al.29

Table 1 Physiological roles of the AT1 receptor in the cardio- typical responses such as vasoconstriction, renal salt vascular system and water retention and changes in glomerular fil- tration rates and renal blood flow. The cascade Vasoconstriction Fluid and sodium retention (aldosterone production) induced by phospholipase D leads to the formation Myocyte and smooth muscle cell hypertrophy of fatty acids such as arachidonic acid, which is a Myocardial and vascular wall fibrosis (collagen synthesis and precursor of leukotrienes and prostaglandins.40 In deposition) addition, angiotensin II-induced cell hypertrophy Fibroblast hyperplasia and hyperplasia are both mediated through the AT Cytotoxic effects in the myocardium 1 Increased endothelin secretion receptor. Protein kinase C as well as elevated intra- Increased vasopressin/antidiuretic hormone release cellular calcium levels have been shown to promote Facilitation of sympathetic-adrenergic activation growth-related inducible transcriptional factors Stimulation of superanoxide formation such as c-fos, c-myc and c-jun involved in the stimu- Increased levels of plasminogen activator inhibitor-1 (PAI-1) 48 lation of mitogenesis. An AT1-receptor-mediated effect also induces platelet-derived growth factor ␣ Adapted with permission from Willenheimer et al.29 ␣ ␤ (PDGF- ) and transforming growth factor 1 (TGF- ␤ 1), which is directly coupled to the expression of isoforms (AT1a and AT1b). While sequence infor- growth factors and smooth muscle cell prolifer- mation seems to indicate that these isoforms also ation.49 Significantly, recent research indicates that exist in humans, only one human gene for the AT1 angiotensin II also mediates proliferative effects receptor has been characterised on chromosome 3. through the Jak/STAT signalling pathway, which AT1a receptors are found mainly in vascular smooth leads to the transcription activation of early growth- muscle suggesting that this subtype plays a role in response genes.50,51 vasoconstriction. The prevalence of the AT1b recep- While much less is known about the functional tor subtype within the anterior pituitary, adrenal properties of the AT2 receptor, it would appear that glands, uterus and several periventricular brain it mediates the effects of angiotensin II on growth areas would seem to indicate that this receptor is control and cell differentiation, as well as neuronal involved in hormonal secretion and central differentiation and apoptosis52–56 (Table 2). The 45 osmotic control. AT2-receptor-mediated effects down-modulate the The binding of angiotensin II to specific actions by the AT1 receptor, resulting in decreased extracellular sites on the AT1 receptor results in the cellular proliferation, modulation of AT1-mediated activation of phospholipases C, D and A2 via the G vasopressin release in certain experimental con- protein (Gq) or inhibition of adenylate cyclase via ditions and a decreased vasoconstrictor response. 42,46,47 the G protein (Gi). Phospholipase C activation When the AT1 receptors are blocked, angiotensin II results in the generation of 1,4,5-triphosphate and appears to have an enhanced depressor response, diacylglycerol, the subsequent activation of protein which is reversed by PD-123177, a selective antag- 42 kinase C and an increase in intracellular calcium. onist at the AT2 receptor. It has been hypothesised The rise in intracellular calcium is associated with that, under certain pathophysiological conditions,

Journal of Human Hypertension Blocking tissue renin-angiotensin system T Unger et al

S26 59,60 Table 2 Physiological roles of the AT2 receptor in the cells. Experiments in utero in the presence of the cardiovascular system AT2-receptor antagonist (PD-123319) and in ‘AT2- receptor knock-out mice’ have demonstrated the Action Cell or tissue modulatory role of the AT2 receptor in the structure and function of blood vessels. Disruption of the AT - Growth inhibition Vascular smooth muscle cells, 2 endothelial cells, receptor gene can result in an increased basal blood cardiomyocytes, cardiac pressure as well as an increased vasoconstriction fibroblasts response to angiotensin II.55 In adults with certain Pro-apoptosis Vascular smooth muscle cells, pathological conditions such as vascular balloon endothelial cells, injury or inflammation induced by cuff placement, cardiomyocytes (neuronal cells, the AT2 receptor is re-expressed (Figure 2). R3T3 fibroblasts) The function of the AT2 receptor was evaluated Differentiation Vascular smooth muscle cells by Yamada et al61 by transfecting either the control (neuronal cells) vector or the AT2-receptor vector to the rat aortic Modulation of cellular matrix Heart vascular smooth muscle cell (which expresses very Decrease in blood pressure Glomerular afferent arteriole low levels of endogenous AT2 receptor). The study Vasodilatation found that under control conditions, angiotensin II Nitric oxide production Kidney, coronary artery significantly increased vascular smooth cell num- microvessels, aorta bers via the AT1 receptor (this response was abol- Improvement in cardiac Heart ished by selective inhibition of the AT1 response). function With the coexpression of the AT2 receptor, angioten- (LVEDV, LVESV, EF) sin II had little or no effect on cell numbers. Treat- Decrease in chronotrophic Heart ment of these cells with the AT2-receptor antagonist effect PD-1233319 unmasked the proliferative response of the AT1 receptor. Consistent with these results, Stoll Adapted with permission from Horiuchi et al,55 Hypertension 33: et al52 also observed an antiproliferative influence of 613–621.  1999 Lippincott, Williams and Wilkins. the AT2 receptor on cultured coronary endothelial cells. By transfecting an AT2-receptor expression the expression of the AT2 receptor may be increased vector into the balloon-injured rat carotid artery, to control the excessive growth mediated via the Nakajima et al59 reported that coexpression of the 55,56 AT1 receptors or other growth factors. AT2 receptor attenuated neointimal formation. Selective AT2-receptor blockade reversed this effect.59 AT1 and AT2 receptors in vascular and cardiac remodelling Experiments evaluating the cellular effects of AT2 receptors in the myocardium are currently incon- 55 Mapping the distribution of the AT1 and AT2 recep- clusive. However, there are several observations tors in normal and diseased heart and blood vessels that point to a role of AT2 receptors in the pathogen- has provided a morphological basis for understand- esis of human cardiac diseases and the subsequent 55 ing the physiological and pathophysiological role of remodelling process. Upregulation of AT1- and these receptors. The AT1 receptor is the predominate AT2-receptor expression have been reported in subtype in human cardiovascular tissue and is human cardiac disease such as cardiac hypertrophy, responsible for acute cardiovascular actions such as myocardial infarction and in mechanical stretch- regulation of vascular tone and extracellular fluid induced hypertrophy of myocytes.57,62 However, in volume. In the great vessels of rat and human heart, failing human hearts, the relative ratio of AT2:AT1 the AT1 receptors are present at high levels in receptor expression is increased due to the down- 63 smooth muscle cells. By contrast, AT2 receptors pre- regulation of the AT1 receptor. Comparisons of dominate in the adventitia of the human renal, arcu- tissue from regions of localised damage with adjac- ate and interlobular arteries and are detectable in the ent normal myocardium in human hearts have media of great vessels and atrial and ventricular shown that endocardial, interstitial, perivascular homogenates of the rat heart,25 but are also present and infarcted regions in the ventricles of patients in the vascular endothelium.52,56 In the human heart, with end-stage ischaemic heart disease or dilated the expression pattern of the AT2 receptor may be cardiomyopathy each exhibited a significantly different from the pattern of expression in the rat greater density of high-affinity AT2-binding sites heart.57 Tsutsumi et al58 found that the proportion of than adjacent non-infarcted myocardium. The AT2 receptors in human left ventricular tissue was regions showing the greatest increase in AT2- approximately 41% of the total angiotensin II bind- binding sites correspond to areas of fibroblast pro- ing sites. While the number of binding sites for angi- liferation and collagen deposition.58,64 These obser- otensin II is confirmed by others, the number of AT2 vations suggest that under pathological conditions, 58 receptors differ between studies. Tsutsumi et al the expression of the AT2 receptor plays some role found that expression of the AT2 receptor was sensi- in cardiac remodelling in humans, possibly being tive to the experimental conditions. increased to control the excessive growth mediated 56 However, it is the relative abundance of the AT2 via the AT1 receptor or other growth factors. receptor in foetal tissue during late gestation that Although the mechanism by which AT2-receptor first alerted scientists to its role in growth inhibition expression is increased is unknown, Ichiki et al65 and differentiation of vascular smooth muscle and Kambayashi et al66 reported the upregulation of

Journal of Human Hypertension Blocking tissue renin-angiotensin system T Unger et al S27

Figure 2 Effect of the AT2 receptor in vasculogenesis and vascular remodelling. The AT2 receptor is abundantly and widely expressed in foetal vasculature and contributes to physiological vascular development. Disruption of the AT2-receptor gene results in an increase in basal blood pressure as walls increased vasoconstriction in response to a vasoactive substance such as angiotensin II. Up-regulation of the AT2 receptor in diseased vessels is induced by injury and inflammation. AT2-receptor disruption results in increased neointimal formation. Adapted with permission from Horiuchi et al,55 Hypertension 33: 613–621.  1999 Lippincott, Williams and Wilkins.

␤ the AT2 gene by interleukin (IL-1 ), insulin and effects of angiotensin II at the AT2 receptor in terms insulin-like growth factor in R3T3 cells and vascular of blood pressure regulation and growth and smooth muscle cells. IL-1␤, an important cytokine remodelling of cardiac and vascular tissue.56 If the mediating inflammation, may be involved in AT2- AT2 receptor contributes to the pathogenesis of car- receptor induction during the process of inflam- diovascular disease and consequent cardiac 57 mation during cardiac remodelling. remodelling in humans, AT1-receptor antagonists may provide some unique cardioprotective bene- fits.55 In experimental animals with heart failure, Role of AT2 receptors in the regulation AT1-receptor antagonists have been shown to have of blood pressure and renal function cardioprotective effects and to improve cardiac Recent studies have demonstrated that stimulation function. Liu and colleagues,68 using a model of of AT2 receptors induces vasodilation and natriur- heart failure in rats induced by myocardial infarc- esis, thus opposing the vasoconstriction and anti- tion, have demonstrated that AT1-receptor blockade natriuretic effects of angiotensin II through the AT1 improved cardiac function and decreased interstitial 67 receptors. The AT2 receptor stimulates a brady- collagen deposition and cardiomyocyte size, and kinin-nitric oxide-cyclic GMP vasodilation cascade that these differences were blocked by the AT2 in blood vessels and in the kidney. It also stimulates antagonist, suggesting that the beneficial effects on the conversion of prostaglandin E2 to prostaglandin the AIIRAs were, in part, due to stimulation of the F2␣.AT1-receptor blockade could therefore be AT2 receptor. Part of this effect may be due to an reinforced by stimulation of AT2 receptors by AT2-mediated stimulation of tissue nitric oxide (NO) increased levels of angiotensin II, due to interrup- and cGMP levels.69 tion of the negative feedback loop on renin Despite the success of ACE inhibitors in the clini- secretion. cal management of cardiovascular disease, mortality remains high in patients with chronic heart failure. This may be due, in part, to the ACE-independent AT1-receptor blockade of RAS pathways for angiotensin II formation.70 In vitro evi- While both ACE inhibitors and AIIRAs are effective dence indicates that a major angiotensin II-forming in the inhibition of the RAS, they differ significantly enzyme in the human heart is chymase, a mast-cell- in their effects on the components of the system. derived chymotrypsin-like serine protease.35 The ACE inhibition results in reduced levels of angioten- highest levels of this enzyme are found in the ven- sin II and elevated levels of renin and possibly of tricles, while ACE levels are highest in the atria. 35 bradykinin, while selective AT1-receptor blockade Urata et al proposed that the different cellular and increases plasma renin and consequently angioten- regional distributions of ACE and heart chymase in sin II by a normal feedback regulatory mechanism the heart as well as the blood vessels implies dis- and has no direct effect on bradykinin metabolism. tinct pharmacological roles of these angiotensin II- As a consequence, selective blockade of angiotensin forming enzymes. Cardiac chymase has a very high II at the AT1 receptor may potentiate the beneficial affinity for angiotensin I but not for bradykinin and

Journal of Human Hypertension Blocking tissue renin-angiotensin system T Unger et al S28 is not blocked by ACE inhibitors. There is little blood pressure, suggesting the tissue protective evidence for the production of angiotensin II by chy- effects of angiotensin AT1 antagonists are not mase in the normal heart.71 However, there is evi- attributable simply to the normalisation of blood dence that cardiac chymase is increased in patho- pressure. In the heart, kidney and vascular tissues physiological states such as heart failure and of SHRSP and the kidney of DOCA-salt hypertensive 35 ␤ following myocardial infarction. Theoretically, rats, mRNA for TGF- 1 and extracellular matrix new therapeutic approaches with selective angioten- components (fibronectin, collagen type I, III and IV sin AT1-receptor antagonists could bring additional and laminin) were increased, and the increase in benefits over ACE inhibition in patients with a fail- gene expression was inhibited by candesartan cilex- ing heart.72,73 However, results of the ELITE II fol- etil.85 Furthermore, there is evidence that angioten- low-up trial, which compared captopril (50 mg three sin AT1-receptor antagonists such as candesartan times daily) and losartan (50 mg daily) in elderly directly inhibit hypertrophy or proliferation of cul- patients with heart failure, failed to demonstrate a tured cardiac myocytes and non-myocytes superiority of AT1-receptor blockade over ACE inhi- (fibroblasts), cultured mesangial cells and cultured bition in terms of cardiovascular benefit, even vascular smooth muscle cells when stimulated by though losartan was better tolerated than capto- angiotensin II.85 pril.74 It is, however, too soon to draw firm con- An in vivo study of spontaneously hypertensive clusions on the use of AT1-receptor antagonists in rats has investigated the effect of candesartan cilexe- heart failure because the losartan dosage used in the til and compared it with that of the vasodilator ELITE II trial was low and the blockade of RAS achi- hydralazine on blood pressure and cardiovascular eved was probably much lower than that achieved structure.86 While the untreated rats became hyper- with higher doses of captopril. Other on-going trials tensive, candesartan cilexetil or hydralazine both (CHARM I,II, III, Val-HeFT, Valiant, OPTIMAAL) blunted the increase in blood pressure. Candesartan will probably give the definite answer. reduced left ventricular weight, left ventricular wall thickness, transverse myocyte diameter, the relative Pharmacological properties of amount of V3 myosin heavy chain and interstitial fibrosis. By contrast, treatment with hydralazine candesartan cilexetil showed a small effect in preventing increased left A variety of AIIRAs have been introduced for the ventricular wall thickness, but did not have a sig- treatment of hypertension. They are all selective for nificant effect on any of the other parameters. the AT1 receptor, but differing pharmacokinetic To further elucidate the effect of angiotensin II, an properties may be important in considering the in vitro study was also carried out by the same wider effects of AIIRAs. Candesartan cilexetil binds authors, in which neonatal rat myocytes were cul- tightly and dissociates slowly from the AT1 receptor tured on deformable silicone dishes. Stretching car- and is an insurmountable antagonist in the presence diomyocytes activated second messengers such as of angiotensin II.75,76 It has recently been shown protein kinase C, Raf-1 kinase and mitogen-activated that, in fact, all AT1-receptor antagonists are com- protein (MAP) kinase – increasing protein synthesis, petitive antagonists, with tight-binding and very enhancing endothelin (ET)-1 release and activating slow dissociation from the receptor.77 This is the Na/K ion exchanger.86 Pre-treatment with cande- especially true for candesartan,78 which has demon- sartan cilexetil diminished the increases in phenyl- strated higher direct angiotensin II antagonistic alanine incorporation, MAP kinase activity and fos activity in vivo than irbesartan, valsartan and losar- gene expression induced by the stretching of cardi- tan.79,80 Thus, the effects of candesartan are likely to omyocytes.86 be long lasting and less easily overcome by The inability of ACE inhibitors to reduce the lev- increased endogeneous angiotensin II. In a model of els of angiotensin II produced by chymase in the mild sodium depletion in normal volunteers, cande- heart also affects local tissue remodelling. Candesar- sartan cilexetil 16 mg achieved a more prolonged tan cilexetil or enalapril were administered to dogs and more potent blockade of the RAS (as defined by twice daily for 5 weeks.87 After the first week of the AUC0–24h plasma active renin levels) than either active drug therapy, the common carotid and fem- losartan 50 mg81 or valsartan (80 mg or 160 mg; oral arteries were unilaterally injured by balloon P Ͻ 0.05).82 These pharmacological characteristics catheterisation. In the common carotid arteries, both may be related to the long duration of action of can- ACE and chymase activities increased, with chym- desartan cilexetil in the clinic.83 In hypertensive ase showing the greater increase; in the femoral patients, the reduction in diastolic and systolic artery, only ACE was increased by the injury. As blood pressure with candesartan cilexetil 16 mg might be predicted from this enzyme distribution, over 0–36 h was significantly greater (P Ͻ 0.05) than candesartan cilexetil significantly suppressed the with losartan 100 mg (Figure 3).84 formation of intimal hyperplasia in both the carotid Candesartan cilexetil has been shown to protect and femoral arteries, while enalapril significantly against end-organ damage in models of stroke-prone suppressed intimal hyperplasia in the femoral but spontaneously hypertensive rats (SHRSP), not the carotid arteries.87 Candesartan cilexetil and DOCA/salt hypertensive rats, Dahl hypertensive rats enalapril reduced blood pressure almost equally, but and five-sixths of nephrectomised rats.85 In the enalapril increased plasma renin activity more SHRSP and DOCA-salt hypertensive rats, candesar- strongly, and significantly decreased vascular and tan markedly reduced the incidence of stroke and plasma ACE activities. These results demonstrate renal injury even at doses that had no effect on that the local production of angiotensin II is

Journal of Human Hypertension Blocking tissue renin-angiotensin system T Unger et al S29

Figure 3 Mean change from baseline at week 8 in diastolic (DBP) and systolic blood pressure (SBP) 0–36 h after dose. Losartan 100 mg (ȦȦ) vs candesartan cilexetil 16 mg (ۙۙ). Reprinted by permission of Elsevier Science from Lacourcie`re et al,84 American Journal of Hypertension 12: 143a.  1999 by American Journal of Hypertension Ltd. involved in the hyperplasia seen in injured intima, 7 Dzau VJ. Significance of the vascular renin-angiotensin and that differences exist in the tissue distribution pathway. Hypertension 1986; 8: 553–559. of the angiotensin II synthetic enzymes, ACE and 8 Naftilan AJ. Role of the tissue renin-angiotensin sys- chymase, which results in a difference in the ability tem in vascular remodelling and smooth muscle cell of ACE inhibitors and AIIRAs to prevent hyperplasia growth. Curr Opin Nephrol Hypertens 1994; 3: 218– 87 227. in different regions of the vascular system. 9 Nicholls MG, Richards AM, Agarwal M. The impor- tance of the renin-angiotensin system in cardiovascu- Conclusions lar disease. J Hum Hypertens 1998; 12: 295–299. 10 Garg R, Yusuf S, for the Collaborative Group on ACE The development of selective AT1-receptor inhibitor trials. Overview of randomized trials of angi- antagonists has provided new insights into the otensin-converting enzyme in patients with heart fail- understanding of the mechanism of the RAS in the ure. J Am Med Assoc 1995; 273: 1450–1456. pathophysiology of cardiovascular disease. Candes- 11 The SOLVD Investigators. Effect of enalapril on mor- artan cilexetil, a new AIIRA, is characterised by its tality and the development of heart failure in asympto- tight binding to and slow dissociation from the AT matic patients with reduced left ventricular ejection 1 fractions. N Engl J Med 1992; 327: 685–691. receptor and its high antagonistic potency, resulting 12 Pfeffer MA et al. Effect of captopril on progressive ven- in long-lasting antagonistic effects. It is anticipated tricular dilatation after anterior myocardial infarction. that these pharmacological characteristics may bring N Engl J Med 1988; 319: 80–86. additional benefits to patients, not only for the man- 13 Lewis EJ, Hunsicker LG, Bain RP, Rhode RD, for the agement of essential hypertension but also for the Collaborative Study Group. The effect of angiotensin- management of end-organ damage. The results of converting-enzyme inhibition on diabetic nephro- on-going clinical studies are awaited with interest pathy. N Engl J Med 1993; 329: 1456–1462. to evaluate whether experience in humans supports 14 Chan JCN et al. Comparison of enalapril and nifedip- the experience in animal models. ine in treating non-insulin dependent diabetes associa- ted with hypertension: one year analysis. BMJ 1992; 305: 981–985. References 15 Giatras I, Lau J, Levey AS, for the Angiotensin-Con- verting Enzyme Inhibition and Progressive Renal Dis- 1 Chung O, Csiko´s T, Unger T. Angiotensin II receptor ease Study Group. Effect of angiotensin-converting pharmacology and AT1 receptor blockers. J Hum Hy- enzyme inhibitors on the progression of non-diabetic pertens 1999; 13 (Suppl 1): S11–S20. renal disease: a meta-analysis of randomized trials. 2 Dahlof B, Pennert K, Hansson L. Reversal of left ven- Ann Intern Med 1997; 127: 337–345. tricular hypertrophy in hypertensive patients: a meta- 16 Yusuf S et al. Effects of an angiotensin-converting- analysis of 109 treatment studies. Am J Hypertens enzyme inhibitor, ramipril, on cardiovascular events 1992; 5: 95–110. in high-risk patients. The Heart Outcomes Prevention 3 Schmieder R, Martus P, Klingbeil A. Reversal of left Evaluation Study Investigators. N Engl J Med 2000; ventricular hypertrophy in essential hypertension. A 342: 145–153. meta-analysis of randomized double-blind studies. 17 Hansson L et al. Randomised trial of old and new anti- JAMA 1996; 275: 1507–1513. hypertensive drugs in elderly patients: cardiovascular 4 Kasiske BL et al. The effects of blood pressure treat- mortality and morbidity. The Swedish Trial in Old ment in the kidneys in diabetes: a meta-regression Patients with Hypertension-2 study. Lancet 1999; 354: analysis. Ann Intern Med 1993; 118: 129–138. 1751–1756. 5 Edling O et al. The renin-angiotensin system (RAS): 18 Atlas SA. The renin-angiotensin system revisited: physiology and pathophysiology. In: Schachter M (ed). classical and non-classical pathways of angiotensin ACE Inhibitors: Current Use and Future Prospects. formation. Mount Sinai J Med 1998; 65: 87–96. Martin Dunitz: London, 1995, pp 3–41. 19 Dzau VJ. Cell biology and genetics of angiotensin in 6 Unger T et al. Angiotensin receptors. J Hum Hypertens cardiovascular disease. J Hypertens 1994; 12 (Suppl 4): 1996; 14 (Suppl 5): S95–S103. S3–S10.

Journal of Human Hypertension Blocking tissue renin-angiotensin system T Unger et al S30 20 Daemen MJ, Lombardi DM, Bosman FT, Schwartz SM. Renin is not synthesized by cardiac and extrarenal vas- Angiotensin II induces smooth muscle cell prolifer- cular tissues. A review of experimental evidence. Cir- ation in the normal and injured rat cell wall. Circ Res culation 1994; 89: 458–470. 1991; 68: 450–456. 42 Chung O, Ku¨ hl H, Stoll M, Unger T. Physiological and 21 Rakugi H et al. Induction of angiotensin converting pharmacological implications of AT1 versus AT2 enzyme in the neointima after vascular injury. Possible receptors. Kidney Int 1998; 54 (Suppl 67): S95–S99. role in re-stenosis. J Clin Invest 1994; 93: 339–346. 43 Stroth U, Unger T. The renin-angiotensin system and 22 Danser AH et al. Metabolism of angiotensin I by differ- its receptors. J Cardiovasc Pharmacol 1999; 33 (Suppl ent tissues in the intact animal. Am J Physiol 1992; 1): S21–S28. 263: H418–H428. 44 Timmermans PBMWM et al. Angiotensin II receptors 23 Admiraal PJ et al. Regional angiotensin II production and angiotensin II receptor antagonists. Pharmacol in essential hypertension and renal artery stenosis. Rev 1993; 45: 205–251. Hypertension 1993; 21: 173–184. 45 Dzau VJ, Sasamura H, Hein L. Heterogeneity of angiot- 24 Pieruzzi F, Abassi ZA, Keiser HR. Expression of renin- ensin synthetic pathways and receptor subtypes: angiotensin system components in the heart, kidneys, physiological and pharmacological implications. J and lungs of rats with experimental heart failure. Cir- Hypertens 1993; 11 (Suppl 3): S13–S18. culation 1995; 92: 3105–3112. 46 Unger T, Culman J, Gohlke P. Angiotensin II receptor 25 Zhuo J et al. Mapping tissue angiotensin-converting blockade and end-organ protection: pharmacological

enzyme and angiotensin AT1 and AT2 and AT4 recep- rationale and evidence. J Hypertens 1998; 16 (Suppl tors. J Hypertens 1998; 16: 2027–2037. 7): S3–S7. 26 Zhu YC et al. Expression of cardiac angiotensin- 47 Csiko´s T, Chung O, Unger T. Receptors and their

converting enzyme after myocardial infarction. Acta classification: focus on angiotensin II and the AT2 Pharmacologica 1999; 20: 97–102. receptor. J Hum Hypertens 1998; 12: 311–318. 27 Falkenhahn M et al. Cellular distribution of angioten- 48 Kawahara Y et al. Angiotensin II induced expression sin-converting enzyme after myocardial infarction. of the c-fos gene through protein kinase C activation Hypertension 1995; 25: 219–226. and calcium ion mobilization in cultured vascular 28 Ohishi M et al. Relative localization of angiotensin- smooth muscle cells. Biochem Biophys Res Commun converting enzyme, chymase and angiotensin II in 1988; 150: 52–59. human coronary atheroslerotic lesions. J Hypertens 49 Stouffer GA, Owens GK. Angiotensin II-induced 1999; 17: 547–553. mitogenesis of spontaneously hypertensive rat-derived

29 Willenheimer R, Dahlo¨f B, Rydberg E, Erhardt L. AT1- cultured smooth muscle cells is dependent on receptor blockers in hypertension and heart failure: autocrine production of transforming growth factor

clinical experience and future directions. Eur Heart J beta1. Circ Res 1992; 70: 820–828. 1999; 20: 997–1008. 50 Pan J et al. Role of angiotensin II in activation of the 30 Erdos EG, Deddish PA, Marcic BM. Potentiation of bra- JAK/STAT signalling pathway induced by acute press- dykinin actions by ACE inhibitors. Trends Endocrinol ure overload in the rat heat. Circ Res 1997; 81: 611– Metab 1999; 10: 223–229. 617. 31 Ito K et al. Contribution of bradykinin to the cardiop- 51 Marrero MB et al. Role of Janus kinase/signal trans- rotective action of angiotensin converting enzyme ducer and activator of transcription and mitogen-acti- inhibition in hypertension and after myocardial infarc- vated protein kinase cascades in angiotensin II- and tion. Jpn J Pharmacol 1997; 75: 311–318. platelet-derived growth factor-induced vascular 32 Linz W et al. Contribution of kinins to the cardio- smooth muscle cell proliferation. J Biol Chem 1997; vascular actions of angiotensin-converting enzyme 272: 24684–24690.

inhibitors. Pharmacol Rev 1995; 47: 25–49. 52 Stoll M et al. Angiotensin AT2 receptor mediates inhi- 33 Gainer JV et al. Effect of bradykinin-receptor blockade bition of cell proliferation in coronary endothelial on the response to angiotensin-converting-enzyme cells. J Clin Invest 1995; 95: 651–657.

inhibitor in normotensive and hypertensive subjects. 53 Meffert S et al. The angiotensin II AT2 receptor N Engl J Med 1998; 339: 1285–1292. inhibits proliferation and promotes differentiation in 34 Davie AP, Dargie HJ, McMurray JJ. Role of bradykinin PC12W cells. Mol Cell Endocrinol 1996; 122: 59–67.

in the vasodilator effects of losartan and enalapril in 54 Gallinat S et al. The angiotensin AT2 receptor down patients with heart failure. Circulation 1999; 100: regulates neurofilament M in PC12W cells. Neurosci 268–273. Lett 1997; 227: 29–32. 35 Urata H, Nishimura H, Ganten D. Chymase-dependent 55 Horiuchi M, Akishita M, Dzau VJ. Recent progress in angiotensin II forming systems in humans. Am J Hyp- angiotensin II type 2 receptor research in the cardio- ertens 1996; 9: 277–284. vascular system. Hypertension 1999; 33: 613–621. 36 Dzau VJ et al. Human neutrophils release serine pro- 56 Unger T. The angiotensin type 2 receptor: variations teases capable of activating pro-renin. Circ Res 1987; on an enigmatic theme. J Hypertens 1999; 17: 1775– 60: 595–601. 1786. 37 Wintroub BU, Klickstein LB, Watt KW. A human neu- 57 Matsubara H. Pathophysiological role of angiotensin II trophil-dependent pathway for generation of angioten- type 2 receptor in cardiovascular and renal diseases. sin II. J Clin Invest 1981; 68: 484–490. Circ Res 1998; 83: 1182–1191. 38 Okunishi H, Miyazaki M, Toda N. Evidence for a puta- 58 Tsutsumi Y et al. Angiotensin II type 2 receptor is tively new angiotensin II-generating enzyme in the upregulated in human heart with interstitial fibrosis vascular wall. J Hypertens 1984; 2: 277–284. and cardiac fibroblasts are the major cell type for its 39 Takada Y et al. Activation of human prorenin by neu- expression. Circ Res 1998; 83: 1035–1046.

trophil elastase. J Clin Endocrinol Metab 1987; 55: 59 Nakajima M et al. The angiotensin II type 2 (AT2) 1225–1230. receptor antagonizes the growth effects of the AT1 40 Danser AH et al. Cardiac renin and angiotensins. receptor: gain-of-function study using gene transfer. Uptake from plasma versus in situ synthesis. Hyper- Proc Natl Acad Sci USA 1995; 92: 10663–10667. tension 1994; 24: 37–48. 60 Yamada H, Horiuchi M, Akishita M, Dzau VJ. Regu- 41 von Lutterotti N, Catanzaro DF, Sealey JE, Laragh JH. lation of vascular development and differentiation by

Journal of Human Hypertension Blocking tissue renin-angiotensin system T Unger et al S31 angiotensin II type 2 receptor. Hypertension 1997; 30: 75 Morsing P, Brandt-Eliasson U, Abrahamsson T. Cande- 470 [abstract]. sartan, an insurmountable antagonist of angiotensin II 61 Yamada T et al. Angiotensin II type 2 receptor mediated contractile effects in isolated vascular prep- mediates vascular smooth muscle cell apoptosis and arations: a comparison with irbesartan, losartan and its antagonizes angiotensin type 1 receptor action: an in active metabolite (EXP 3174). Am J Hypertens 1998; vitro gene transfer study. Life Sci 1998; 63: PL289– 11: 37 [abstract]. PL295. 76 Abrahamsson T et al. Candesartan causes a long-last- 62 Dzau VJ, Horiuchi M. Differential expression of angiot- ing antagonism of the angiotensin II receptor-mediated ensin receptor subtypes in the myocardium: a hypoth- contractile effects in isolated vascular preparations: a esis. Eur Heart J 1996; 17: 978–980. comparison with losartan and its active metabolite

63 Haywood GA et al.AT1 and AT2 receptor gene (EXP 3174). Am J Hypertens 1998; 11: 36 [abstract]. expression in human heart failure. Circulation 1997; 77 Fierens FL, Vanderheyden PM, De Backer JP, Vauque-

95: 1201–1206. lin G. Insurmountable angiotensin AT1-receptor antag- 64 Wharton T et al. Differential distribution of angioten- onists: the role of tight antagonist binding. Eur J Phar-

sin AT2 receptors in the normal and failing human macol 1999; 372: 199–206. heart. J Pharmacol Exp Ther 1998; 284: 323–336. 78 Malerczyk C et al. Angiotensin II antagonism and 65 Ichiki T, Kambayashi Y, Inagami T. Multiple growth plasma radioreceptor-kinetics of candesartan in man. factors modulate mRNA expression of angiotensin II Br J Pharmacol 1998; 45: 567–573. type 2 receptor in R3T3 cells. Circ Res 1995; 77: 79 Belz GG et al. Candesartan cilexetil has the highest

1070–1076. pharmacologic potency of various AT1 antagonists – 66 Kambayashi Y, Bardham S, Inagami T. Peptide growth assessed by the Schild Regression Technique in man. factors markedly decrease the ligand binding of angiot- J Hypertens 1999; 17 (Suppl 3): S66. ensin II type 2 receptor in rat cultured vascular smooth 80 Belz GG et al. Inhibition of angiotensin II pressor msucle cells. Biochem Biophys Res Commun 1993; response and ex vivo angiotensin II radioligand bind- 194: 478–482. ing by candesartan cilexetil and losartan in healthy 67 Carey RM, Wang ZQ, Siragy HM. Role of the angioten- human volunteers. J Hum Hypertens 1997; 11 (Suppl sin type 2 receptor in the regulation of blood pressure 2): S45–S47. and renal function. Hypertension 2000; 35: 155–163. 81 Azizi M, Chatalier G, Guyene TT, Me´nard J. Pharmaco- 68 Liu Y-H et al. Effect of angiotensin-converting enzyme kinetic–pharmacodymanic interactions of candesartan inhibitors and angiotensin II type 1 receptors in rats cilexetil and losartan. J Hypertens 1999; 17: 561–568. with heart failure. J Clin Invest 1998; 101: 527–535. 82 Azizi M, Bernard MC, Me´nard J. Pharmacokinetics–

69 Gohlke P, Pees C, Unger T. AT2-receptor stimulation pharmacodynamic study of renin release during angi- increases aortic cyclic GMP in SHRSP by a kinin- otensin II blockade. J Hypertens 1999; 17 (Suppl 3): dependent mechanism. Hypertension 1998; 31: 349– S195 (P3.147) [abstract]. 355. 83 Inada Y et al. Pharmacologic properties of candesartan 70 Simko F, Simko J. Heart failure and angiotensin con- cilexetil – possible mechanisms of long-acting antihy- verting enzyme inhibition: problems and perspectives. pertensive action. J Hum Hypertens 1999; 13 (Suppl Physiol Res 1999; 48: 1–8. 1): S75–S80. 71 Zisman LS et al. Angiotensin II formation in the intact 84 Lacourciere Y, Asmar R, on behalf of the CHAMP human heart. Predominance of the angiotensin-con- study group. Comparison of the impact of missed verting enzyme pathway. J Clin Invest 1995; 96: doses of candesartan and losartan in ambulatory 1490–1498. hypertensive patients. Am J Hypertens 1999; 12: 72 Sever PS. Key features of candesartan cilexetil and a 143a [abstract].

comparison with other angiotensin II receptor antag- 85 Nishikawa K. Angiotensin AT1 receptor antagonism onists. J Hum Hypertens 1999; 13 (Suppl 1): S3–S10. and protection against cardiovascular end-organ dam- 73 Pitt SR et al, on behalf of the ELITE Study Investi- age. J Hum Hypertens 1998; 5: 301–309. gators. Randomised trial of losartan versus captopril in 86 Yamazaki T, Yazaki Y. Role of tissue angiotensin II in patients over 65 with heart failure. Lancet 1997; 349: myocardial remodelling induced by mechanical stress. 747–752. J Hum Hypertens 1999; 13 (Suppl 1): S43–S48. 74 Pitt B et al. Effect of losartan compared with captopril 87 Miyazaki M, Wada T, Shiota N, Takai S. Effect of an on mortality in patients with symptomatic heart fail- angiotensin II receptor antagonist, candesartan cilexe- ure: randomised trial—the Losartan Heart Failure Sur- til, on canine intima hyperplasia after balloon injury. vival Study ELITE II. Lancet 2000; 355: 1582–1587. J Hum Hypertens 1999; 13 (Suppl 1): S21–S25.

Journal of Human Hypertension