Functional and biochemical analysis of angiotensin II-forming pathways in the human heart

Effects of ACE inhibition and angiotensin II type 1 receptor blockade on cardiac function and G proteins in rats with chronic heart failure

1. Inhibition of the renin-angiotensin system (RAS) improves symptoms and prognosis in heart failure. The experimental basis for these benefits remains unclear. We examined the effects of inhibition of ACE or blockade of angiotensin II type 1 (AT1) receptor on the haemodynamics, cardiac G-proteins, and collagen synthesis of rats with coronary artery ligation (CAL), a model in which chronic heart failure (CHF) is induced. 2. Rats were orally treated with the ACE inhibitor trandolapril (3 mg kg(-1) day(-1)) or the AT1 receptor blocker L-158809 (1 mg kg(-1) day(-1)) from the 2nd to 8th week after CAL. CAL resulted in decreases in the left ventricular systolic pressure and its positive and negative dP/dt, an increase in the left ventricular end-diastolic pressure, and the rightward shift of the left ventricular pressure-volume curve. Long-term treatment with either drug improved these signs of CHF to a similar degree. 3. Cardiac Gsalpha and Gqalpha protein levels decreased, whereas the level of Gialpha protein increased in the animals with CHF. Long-term treatment with trandolapril or L-158809 attenuated the increase in the level of cardiac Gialpha protein of the animals with CHF without affecting Gsalpha and Gqalpha protein levels. Cardiac collagen content of the failing heart increased, whose increase was blocked by treatment with either drug. 4. Exogenous angiotensin I stimulated collagen synthesis in cultured cardiac fibroblasts, whose stimulation was attenuated by either drug. 5. These results suggest that blockade of the RAS, at either the receptor level or the synthetic enzyme level, may attenuate the cardiac fibrosis that occurs after CAL and thus affect the remodelling of the failing heart.

Angiotensin converting enzyme (ACE) and non-ACE dependent angiotensin II generation in resistance arteries from patients with heart failure and coronary heart disease

OBJECTIVES

We sought to demonstrate non-angiotensin converting enzyme (ACE) dependent angiotensin II (AII) generating pathways in resistance arteries from patients with chronic heart failure (CHF).

BACKGROUND

Non-ACE dependent AII generation occurs in resistance arteries from normal volunteers. Inhibition of non-ACE dependent AII generation may have therapeutic potential in CHF.

METHODS

Resistance arteries were dissected from gluteal biopsies from patients with coronary heart disease (CHD) and preserved left ventricular function and from patients with CHF. Using wire myography, concentration response curves to angiotensin I (AI) and AII were constructed in the presence of 1) vehicle, 2) chymostatin [an inhibitor of chymase], 3) enalaprilat, and 4) the combination of chymostatin and enalaprilat.

RESULTS

In resistance arteries from patients with CHD, the vasoconstrictor response to AI was not inhibited by either inhibitor alone (chymostatin [p > or = 0.05] or enalaprilat [p > or = 0.05]) but was significantly inhibited by the combination (p < 0.001). In arteries from patients with CHF, AI responses were inhibited by enalaprilat (p < 0.05) but not by chymostatin alone (p > 0.05). The combination ofchymostatin and enalaprilat markedly inhibited the response to AI (p < 0.001) to a greater degree than enalaprilat alone (p < or = 0.01).

CONCLUSIONS

Non-ACE dependent AII generating pathways exist in resistance arteries from patients with both CHF and CHD. In resistance arteries from patients with CHD, inhibition of either the ACE or chymase pathway alone has no effect on AII generation, and both pathways must be blocked before the vasoconstrictor action of AI is inhibited. In CHF, blockade of ACE results in marked inhibition of responses to AI, but this is enhanced by coinhibition of chymase. These studies suggest that full suppression of the renin-angiotensin system cannot be achieved by ACE inhibition alone and provide a rationale for developing future therapeutic strategies.

Salt intake and non-ACE pathways for intrarenal angiotensin II generation in man

Angiotensin-converting enzyme (ACE) plays a crucial role in the generation of angiotensin II (Ang II) via conversion from angiotensin I (Ang I). There has been substantial recent interest in non-ACE pathways of Ang II generation in the heart, large arteries, and the kidney. In the case of the human kidney, studied when in balance on a low-salt diet, the renal haemodynamic response to Ang II antagonists substantially exceeds the renal response to ACE inhibitors (ACE-I), suggesting that about 30-40% of Ang II-generation occurs via non-ACE pathways. In this study, we examined the relative contribution of non-ACE pathways, by comparing the response to candesartan and to captopril at the top of the dose-response in normal humans when in balance on a low-salt, as well as a high-salt, diet. As anticipated on a low-salt diet, the increase in renal plasma flow (RPF) in response to candesartan (165+/-14 mL/min/1.73 m2) significantly exceeded the response to captopril (118+/-12 mL/min/1.73 m2; p<0.01). In subjects studied on a high-salt diet, the response to candesartan (97+/-20 mL/min/1.73 m2) also significantly exceeded the response to captopril on the same diet(30+/-15 mL/min/1.73 m2; p<0.01). This remarkable response to candesartan in subjects on a high-salt diet,when compared with the response to captopril,suggests that non-ACE-dependent Ang II generation was influenced less than the classical renal pathway with an increase in salt intake, so that the percentage of Ang II generated via the non-ACE pathway rose to the 60-70% range.

Expression and function of angiotensin converting enzyme, chymase, and angiotensin II in the human radial artery and internal thoracic artery

BACKGROUND

The potential role of the local renin-angiotensin system to differentially affect radial artery and internal thoracic artery graft performance has not been examined.

METHODS

Contractile responses to angiotensin I and II in the radial artery and the internal thoracic artery were examined in vitro. The expression function, and localization of angiotensin receptors, angiotensin converting enzyme, and chymase were studied in radial artery and internal thoracic artery segments.

RESULTS

Angiotensin I and II contractions were significantly greater (p < 0.05) in the radial artery compared to the internal thoracic artery. In both arteries, angiotensin II responses were mediated via the AT1 receptor. Messenger RNA transcripts for angiotensin-converting enzyme and chymase were detected in both arteries. Angiotensin-converting enzyme was localized to luminal and vaso vasorum endothelial cells and smooth muscle cells in both vessels, while chymase was colocalized with mast cells in adventitial and medial layers. An angiotensin converting enzyme or a chymase inhibitor singularly had no effect on angiotensin I contractions, however, when combined, a marked inhibition of the angiotensin I response was observed in both vessels.

CONCLUSIONS

Our results illustrate the complexities which exist within the local renin angiotensin system and suggest that clinical trials which may modulate the system are warranted.

Localization of the mosaic transmembrane serine protease corin to heart myocytes

Corin cDNA encodes an unusual mosaic type II transmembrane serine protease, which possesses, in addition to a trypsin-like serine protease domain, two frizzled domains, eight low-density lipoprotein (LDL) receptor domains, a scavenger receptor domain, as well as an intracellular cytoplasmic domain. In in vitro experiments, recombinant human corin has recently been shown to activate pro-atrial natriuretic peptide (ANP), a cardiac hormone essential for the regulation of blood pressure. Here we report the first characterization of corin protein expression in heart tissue. We generated antibodies to two different peptides derived from unique regions of the corin polypeptide, which detected immunoreactive corin protein of approximately 125-135 kDa in lysates from human heart tissues. Immunostaining of sections of human heart showed corin expression was specifically localized to the cross striations of cardiac myocytes, with a pattern of expression consistent with an integral membrane localization. Corin was not detected in sections of skeletal or smooth muscle. Corin has been suggested to be a candidate gene for the rare congenital heart disease, total anomalous pulmonary venous return (TAPVR) as the corin gene colocalizes to the TAPVR locus on human chromosome 4. However examination of corin protein expression in TAPVR heart tissue did not show evidence of abnormal corin expression. The demonstrated corin protein expression by heart myocytes supports its proposed role as the pro-ANP convertase, and thus a potentially critical mediator of major cardiovascular diseases including hypertension and congestive heart failure.

Combination of non-hypotensive doses of valsartan and enalapril improves survival of spontaneously hypertensive rats with endothelial dysfunction

There is increasing evidence to suggest endothelial dysfunction as a critical factor in vascular diseases. Genetically predisposed spontaneously hypertensive rats (SHR) treated with inhibitors of nitric oxide (NO) synthase, develop a severe hypertensive nephrosclerosis without the necessity for surgical reduction in renal mass, nephrectomy, renal infarction or nephrotoxic drugs. In these animals, endothelial dysfunction is considered a valid model for assessment of the efficacy of cardiovascular therapy. SHR were treated with either the angiotensin-converting enzyme inhibitor enalapril or the angiotensin II (Ang II) AT(1)-receptor antagonist (AIIA) valsartan at sub-hypotensive doses and the effects on survival rates, cardiac and renal changes were monitored. Rats treated with valsartan, alone or in combination with enalapril, showed markedly higher survival rates (67-85%, respectively) than untreated animals (37%) or those treated with enalapril alone (55%). Valsartan at a dose which attenuated blood pressure increase led to even greater survival rates (95%). Despite these improved survival rates, at non-hypotensive doses the drugs had no effect on histological appearance, nor was kidney function improved. Plasma creatinine levels were reduced by valsartan, alone or in combination with enalapril, but proteinuria persisted with all treatments over the 12 weeks of the study. Aldosterone levels were significantly reduced by all treatments. The results suggest a beneficial role for endothelium in hypertension. Reduced renal perfusion pressure probably underlies the beneficial renal effects of high-dose valsartan.

Inhibition of angiotensin converting enzyme cannot prevent increases in angiotensin II production in coronary circulation

OBJECTIVE

To determine whether inhibition of angiotensin converting enzyme (ACE) can prevent angiotensin II production in the coronary circulation induced by percutaneous transluminal coronary angioplasty (PTCA) in patients with myocardial ischaemia.

DESIGN, PATIENTS

41 patients who underwent elective PTCA and six control subjects who received diagnostic coronary angiography were studied. Patients were divided into two groups according to the chronic administration of ACE inhibitors (group A, 15 patients treated with ACE inhibitors; group B, 26 patients without ACE inhibitors). Blood samples were drawn through catheters placed in the aorta and coronary sinus before and 24 hours after PTCA.

RESULTS

Mean levels of ACE activity in the aorta were significantly lower in patients in group A than in group B. However, mean angiotensin II concentrations in the aorta were not significantly different between the two groups. Differences in basal angiotensin II concentrations between the coronary sinus and aorta, which reflected basal angiotensin II production in the coronary circulation, were not significant among group A, group B, and control subjects. The production of angiotensin II in the coronary circulation was significantly increased 24 hours after PTCA in both group A and group B to the same extent. No significant changes were observed in control subjects 24 hours after diagnostic coronary angiography.

CONCLUSIONS

This study revealed that inhibition of ACE activity by ACE inhibitors could not prevent increases in angiotensin II production in the coronary circulation induced by PTCA.

Therapeutic implications of escape from angiotensin-converting enzyme inhibition in patients with chronic heart failure

The level of inhibition of the angiotensin-converting enzyme (ACE) provided by standard doses of ACE inhibitors may only be partial during long-term treatment in patients with severe chronic heart failure (CHF). Partial ACE inhibition with time is often referred to as escape from ACE inhibition and labeled ACE escape. Several lines of evidence suggest that ACE escape occurs in patients with severe CHF. Plasma levels of angiotensin II rise above initial values during long-term ACE inhibition, and the effects of ACE inhibitors on cardiac remodeling and lowering of sympathetic nervous system activity attenuate after 1 year of treatment. Moreover, angiotensin II type I receptor blockade (ARB) produces clinical and hemodynamic benefits in patients with CHF who are already receiving ACE inhibitors. The therapeutic implications of ACE escape include evaluation of higher- than-standard doses of ACE inhibitors and routine addition of ARB to ACE inhibition in patients with severe CHF. Data are reviewed to demonstrate that ACE escape reflects inadequate ACE dosage rather than a decrease in ACE inhibition occurring with time.

Regulation of aldosterone secretion in patients with chronic congestive heart failure by endothelins

We studied acute (day 1) and long-term (day 14) effects of endothelin (ET) receptor blockade with the mixed ET(A/B) antagonist bosentan (1 g twice daily; n = 18) or placebo (n = 12) on plasma angiotensin II and aldosterone in 30 patients with symptomatic chronic heart failure taking angiotensin-converting enzyme inhibitors, diuretics, and digoxin. Hormones were determined before and 3 hours after morning doses of diuretics and digoxin and the double-blind study drug, respectively, on days 1 and 14. On day 1, angiotensin II increased from 16.1+/-17.9 to 27.6+/-5.6 ng/L (p <0.05) with bosentan and similarly with placebo (15.5+/-9.3 and 36.0+/-49.1 ng/L, p = 0.06) after the morning dose of diuretics and digoxin. Aldosterone tended to increase from 322+/-239 to 362+/-254 pmol/L (bosentan) and from 271+/-70 to 297+/-136 pmol/L (placebo). On day 14, before drug intake, angiotensin II was unchanged compared with day 1 in both groups. However, aldosterone was lower than on day 1 with bosentan (213+/-124 vs. 322+/-239 pmol/L, p<0.05) and remained below baseline values 3 hours after drug intake, whereas it was unchanged with placebo. Thus, short-term ET(A/B) receptor antagonism decreases basal aldosterone secretion independently of angiotensin II, suggesting that ET participates in the regulation of aldosterone in patients already treated with angiotensin-converting enzyme inhibitors and diuretics.

Increased brain angiotensin receptor in rats with chronic high-output heart failure

BACKGROUND

The renin-angiotensin system (RAS) plays a key role in the pathophysiology of chronic heart failure (CHF). In rats, we reported that CHF enhances dipsogenic responses to centrally administered angiotensin I, and central inhibition of the angiotensin-converting enzyme (ACE) prevents cardiac hypertrophy in CHF. This suggests that the brain RAS is activated in CHF. To clarify the mechanism of the central RAS activation in CHF, we examined brain ACE and the angiotensin receptor (AT) among rats with CHF.

METHODS AND RESULTS

We created high-output heart failure in 22 male Sprague-Dawley rats by aortocaval shunt. Four weeks after surgery, we examined ACE mRNA by reverse transcriptase polymerase chain reaction (RT-PCR) and AT by binding autoradiography. ACE mRNA levels were not significantly increased in the subfornical organ (SFO), the hypothalamus, or in the lower brainstem of CHF rats (n = 5) compared with sham-operated rats (SHM) (n = 6). Binding densities for type 1 AT (AT1) in the SFO (P < .05), paraventricular hypothalamic nuclei (P < .05), and solitary tract nuclei (P < .05) were higher in rats with CHF (n = 5) than in SHM rats (n = 6). Thus, in rats with CHF, AT1 expression is increased in brain regions that are closely related to water intake, vasopressin release, and hemodynamic regulation.

CONCLUSIONS

The fact that AT1 expression was upregulated in important brain regions related to body fluid control in CHF rats indicates that the brain is a major site of RAS action in CHF rats and, therefore, a possible target site of ACE-inhibitors in the treatment of CHF.

A unifying hypothesis for the renin-angiotensin system and hematopoiesis: sticking the pieces together with the JAK-STAT pathway

JAK-STAT pathway is a recently encountered intracellular signal transduction system. The pathway is utilized by numerous cytokines, growth factors, and hormones for gene expression and a variety of biological activities. Hematopoiesis is regulated by many cytokines and growth factors that support the proliferation and differentiation of progenitor cells in the bone marrow. JAK-STAT pathway arises as the most common signalling cascade of a wide range of cytokines and/or growth factors in propagation of physiological and pathological/neoplastic hematopoiesis. On the other side, renin-angiotensin system (RAS) includes not only the classic circulating endocrine system controlling blood pressure and electrolyte homeostasis, but also tissue-specific RASs with autocrine and/or paracrine functions. Preliminary data suggest the involvement of the RAS components in normal and pathologic hematopoiesis, although the precise mechanism of action has not been elucidated yet. We have hypothesized, in this report, that JAK-STAT pathway serves as a point of crosstalk between the components of the locally present RAS in the bone marrow and hematopoiesis. Demonstration of a local RAS in the bone marrow with clarification of the postreceptor signalling events may play a consequential role not only for further clarification of normal hematopoiesis but also novel therapeutic approaches in pathologic/neoplastic conditions.

Measurement of the renin-angiotensin system in heart failure

Angiotensin II (ANG II), the effector hormone of the renin-angiotensin system (RAS), has been implicated in the pathophysiology and progression of heart failure. Therefore, the measurement of ANG II has become important to characterize the role of this neurohormone in heart failure. However, because ANG II has been difficult to measure, other components of the RAS have been measured to characterize ANG II production. The RAS components (e.g., renin, angiotensin I-converting enzyme [ACE], angiotensin II) have been measured with a variety of techniques. In this review, RAS physiology and the techniques used to measure the RAS components are discussed. In addition, the advantages and disadvantages of the RAS measurement methods are described.

Cloning and characterization of marmoset renin: comparison with human renin

The poor interspecies conservation of the renin-angiotensin system prevents the use of nonprimate in vivo models to test renin inhibitors. Thus the small New-World monkey marmoset is used in many instances as a model. However, large differences between the potencies of renin inhibitors as measured in human and marmoset plasma were observed. To understand this phenomenon, we cloned marmoset renin and angiotensinogen. They were highly homologous to their human counterparts, except for a six-residue deletion in the marmoset renin propeptide. Human and marmoset recombinant renins were found in vitro to display comparable activities, suggesting that the observed differences in plasma apparent affinity of inhibitors could be due to different plasma protein binding of the inhibitors.

The hemodynamic effects of anesthetic induction in vascular surgical patients chronically treated with angiotensin II receptor antagonists

The use of angiotensin II receptor subtype-1 antagonists (ARA), recently introduced as antihypertensive drugs, is becoming more prevalent. We studied the prevalence and severity of hypotension after the induction of general anesthesia in 12 patients treated with ARA until the morning of surgery. The hemodynamic response to induction was compared with that of patients treated with beta-adrenergic blockers (BB) and/or calcium channel blockers (CB) (BB/CB group, n = 45) and angiotensin-converting enzyme inhibitors (ACEI) (ACEI group, n = 27). A standardized anesthesia induction protocol was followed for all patients. Hypotension occurred significantly (p < or = 0.05) more often in ARA-treated patients (12 of 12) compared with BB/CB-treated patients (27 of 45) or with ACEI-treated patients (18 of 27). There was a significantly (P < or = 0.001) increased ephedrine requirement in the ARA group (21+/-3 mg) compared with the BB/CB group (10+/-6 mg) or the ACEI group (7+/-4 mg). Hypotension refractory to repeated ephedrine or phenylephrine administration occurred significantly (P < or = 0.05) more in the ARA group (4 of 12) compared with the BB/CB group (0 of 45) or the ACEI group (1 of 27), but it was treated successfully by using a vasopressin system agonist. Treatment with angiotensin II antagonism until the day of surgery is associated with severe hypotension after the induction of anesthesia, which, in some cases, can only be treated with an agonist of the vasopressin system.

IMPLICATIONS

Hypotensive episodes occur more frequently after anesthetic induction in patients receiving Angiotensin II receptor subtype-1 antagonists under anesthesia than with other hypotensive drugs. They are less responsive to the vasopressors ephedrine and phenylephrine. The use of a vasopressin system agonist was effective in restoring blood pressure when hypotension was refractory to conventional therapy.

Long-term benefits of angiotensin II blockade: is the consensus changing?

The treatment of hypertension and heart failure has evolved in recent years. It may no longer be sufficient to lower blood pressure per se or correct hemodynamics alone in these conditions to achieve optimal long-term outcomes; rather, the effects of drugs on the cellular events and structural alterations that occur in the vasculature, heart, and kidney must be considered. Drugs that target angiotensin II, which include the angiotensin-converting enzyme (ACE) inhibitors and angiotensin II receptor blockers (ARBs), may protect target organs from damage and thereby improve outcomes. Nevertheless, it remains to be demonstrated whether these agents are more effective in reducing cardiovascular morbidity and mortality in hypertensive patients than conventional treatment with diuretics and beta blockers. In certain subgroups of hypertensive patients, including those with heart failure, type 1 diabetes with proteinuria, or after myocardial infarction with systolic dysfunction, there is compelling evidence for use of ACE inhibitors. The results from animal models and initial clinical studies suggest that ARBs are also highly effective in these patients. Several large-scale clinical studies, comparing the effect of ARBs and other drug classes on morbidity and mortality outcomes, have been initiated to better define the long-term benefit of ARBs in the treatment of hypertension and heart failure.

Candesartan in heart failure--assessment of reduction in mortality and morbidity (CHARM): rationale and design. Charm-Programme Investigators

BACKGROUND

Chronic heart failure (CHF) is an increasing burden to health care. Pharmacological treatment with angiotensin-converting enzyme (ACE) inhibitors and beta blockers improve survival and reduce hospitalizations in patients with low left ventricular ejection fraction (LVEF). Despite these therapies, morbidity and mortality remains problematic. Furthermore, 30% to 50% of patients with CHF have a preserved LVEF. It is not known if treatments are of benefit in this group.

DESIGN

Candesartan in Heart Failure-Assessment of Reduction in Mortality and Morbidity (CHARM) is a program designed to investigate the clinical usefulness of the long-acting angiotensin II type 1 receptor blocker, candesartan cilexetil, in a broad spectrum of patients with symptomatic heart failure. Patients with systolic dysfunction, tolerant or intolerant to an ACE-inhibitor, and patients with preserved systolic function are included. Specifically, the CHARM program consists of 3 independent, parallel, placebo-controlled studies in patients with (1) LVEF less than or equal to 40%, ACE-inhibitor treated (n = 2,300); (2) LVEF less than or equal to 40%, ACE-inhibitor intolerant (n = 1,700); (3) LVEF greater than 40%, not treated with ACE inhibitors (n = 2,500). The 3 studies will be combined to evaluate the effect of candesartan cilexetil on all-cause mortality in the broad spectrum of symptomatic heart failure. The primary objective in each trial is to evaluate the effects on the combined endpoint of cardiovascular mortality or CHF hospitalization. Other endpoints include the effects on myocardial infarction, all-cause hospitalization, and resource utilization. CHARM is intended to randomize 6,500 patients with symptomatic heart failure from 26 countries in Europe, the United States, Canada, South Africa, and Australia. The CHARM program started to enroll patients in March 1999. The follow-up period is a minimum of 2 years. The study is expected to end in the third quarter of 2002.

Effect of candesartan cilexetil (TCV-116) in rats with chronic renal failure

BACKGROUND

Inhibition of the renin-angiotensin system by both angiotensin II type 1 receptor antagonists (AT1As) and angiotensin I-converting enzyme inhibitors (ACEIs) shows renoprotective effects in rats with chronic renal failure when treatment is started in the early phase of renal injury. In this study, we examined the renal protective effects of candesartan cilexetil (TCV-116), an AT1A, and enalapril, an ACEI, in the progressive phase of renal injury in 5/6 nephrectomized rats.

METHODS

Candesartan cilexetil (1 mg/kg/day) and enalapril (10 mg/kg/day) were orally administered once a day for 4 weeks (the short-term experiment) or 16 weeks (the long-term experiment) to 5/6 nephrectomized rats beginning 15 weeks after the nephrectomy, that is, after they had already showed marked proteinuria.

RESULTS

In vehicle-treated rats, proteinuria, glomerulosclerosis, and interstitial fibrosis developed. Moreover, enhanced expression of transforming growth factor-beta1 (TGF-beta1) in the injured glomeruli was observed. These adverse changes progressed with time, and in the short-term experiment, both drugs inhibited them. In the long-term experiment, the progressive proteinuria and the elevation of blood pressure were similarly attenuated by both drugs. However, candesartan cilexetil significantly inhibited the progression of glomerulosclerosis, the expression of TGF-beta1, and interstitial fibrosis, whereas enalapril did not.

CONCLUSION

These results indicate that candesartan cilexetil shows potent and long-term preventive effects against the progression of previously developed renal injury.

Human chymase inhibitors based on the 1,2,5-thiadiazolidin-3-one 1,1 dioxide scaffold

A series of compounds that utilize the 1,2,5-thiadiazolidin-3-one 1,1 dioxide scaffold was synthesized and shown to be highly effective inhibitors of recombinant human skin chymase.

Does the addition of losartan improve the beneficial effects of ACE inhibitors in patients with anterior myocardial infarction? A pilot study

OBJECTIVE

To verify the efficacy of the combination of captopril (75 mg day) and losartan (25 mg/day) in early postinfarction phases of reperfused anterior acute myocardial infarction.

DESIGN AND PATIENTS

99 patients, hospitalised for suspected anterior acute myocardial infarction within four hours from the onset of symptoms, were randomised into two groups: group A included 50 patients who received captopril 75 mg/day and placebo; group B included 49 patients who received captopril 75 mg/day within three days of admission plus losartan 12.5 mg, as a first dose, and 25 mg/day successively. An additional 23 patients with anterior acute myocardial infarction received losartan 25 mg alone and acted as controls (group C) to check the effects of losartan on plasma angiotensin II (AII) concentrations. Noradrenaline (norepinephrine) (NA) and AII plasma concentrations were measured on the third and 10th day after admission in 93 patients (35 from group A, 35 from group B, and 23 from group C). 90 days after admission patients underwent echocardiography to determine end systolic volume (ESV) and ejection fraction (EF).

RESULTS

Patients in groups A and B were similar with regard to age, sex, creatine kinase peak, EF, ESV, and risk factors. Group B (captopril plus losartan) patients showed a significant reduction in mean (SD) systolic blood pressure within the group (basal 128 (10) mm Hg; 10 days after admission 105 (9) mm Hg, p < 0.001), and in comparison with group A (captopril) patients (basal 127 (11) mm Hg; 10 days after admission 116 (10) mm Hg, p < 0. 001). Diastolic blood pressure was also lower in group B patients versus group A (66 (11) v 77 (11) mm Hg). Group C (losartan) patients also showed a significant reduction in systolic blood pressure (131 (13) mm Hg down to 121 (12) mm Hg, p < 0.001). Neither NA nor AII plasma concentrations in groups A and B differed significantly in basal samples (NA 673 (138) v 675 (141) pg/ml; AII 12.77 (4.79) v 12.65 (4.71) pg/ml) or 10 days after admission (NA 283 (93) v 277 (98) pg/ml; AII 5.31 (2.25) v 6.09 (3.31) pg/ml). However, patients in group C had higher plasma concentrations of AII (14.79 (5.7) pg/ml on the third day and 7.98 (4.92) pg/ml on the 10th day) than patients in either group A or B (p = 0.006). After 90 days following treatment, group B (captopril plus losartan) patients had a smaller ESV than patients in group A (captopril) and group C (losartan).

CONCLUSION

The data suggest that the combination of captopril plus losartan is feasible in the early treatment of acute myocardial infarction patients, and it appears that this combination has more effect on ESV than captopril alone in the short term.

Practical considerations of the pharmacology of angiotensin receptor blockers

A review of the drug class of angiotensin receptor blockers (ARBs) as well as the ARBs currently available by prescription in the United States is presented. The importance of angiotensin II production by non-angiotensin-converting enzyme (non-ACE) pathways, particularly human chymase, is discussed. Emphasis is placed on the mechanism of action of ARBs and the different binding kinetics of these agents. Although all ARBs, as a group, block the AT1 receptor, they may differ in the pharmacological characteristics of their binding and be classified as either surmountable or insurmountable antagonists. Mechanisms of surmountable and insurmountable antagonism as well as possible benefits of these blocking characteristics are discussed in relation to the various ARBs. The cardiovascular effects of activation of the two main subtypes of angiotensin receptors (AT1 and AT2) are presented. In addition to their treatment of hypertension, ACE inhibitors are recognized as being effective in the management of heart failure, left ventricular hypertrophy, recurrent myocardial infarctions, and renal disease. ARBs are currently indicated only for the treatment of hypertension; however, in vitro and in vivo pharmacological studies as well as preliminary clinical data suggest that ARBs, like ACE inhibitors, may also provide effective protection against end-organ damage in these conditions.

Substituted piperidines--highly potent renin inhibitors due to induced fit adaptation of the active site

The identification, synthesis and activity of a novel class of piperidine renin inhibitors is presented. The most active compounds show activities in the picomolar range and are among the most potent renin inhibitors ever identified.

Bradykinin-dependent cardioprotective effects of losartan against ischemia and reperfusion in rat hearts

It is unclear whether losartan, an angiotensin II type 1 (AT1) receptor antagonist, protects the heart against acute ischemia-reperfusion injury. Therefore we evaluated cardiac protection conferred by pre- and postischemic treatment as well as by exclusive postischemic treatment with losartan. Furthermore, we sought to determine both the extent of this protection and its dependence on bradykinin in comparison with quinaprilat, a cardioprotective angiotensin-converting enzyme inhibitor. Cardiac protection was assessed as recovery of coronary flow, left ventricular developed pressure, phosphocreatine, and adenosine triphosphate (ATP) in isolated perfused rat hearts after 15 min of global ischemia and 30 min of postischemic reperfusion. We found that, in hearts pre- and postischemically treated with losartan (1 microM) or quinaprilat (0.1 microM), these variables all recovered significantly better than those in untreated control hearts. In hearts that were only postischemically treated with losartan, these variables also recovered significantly better than those in control hearts. In contrast, in hearts treated with the combination of the bradykinin B2 receptor antagonist Hoe 140 with quinaprilat or losartan, the recovery of the variables no longer differed from that in control hearts. In conclusion, losartan protects the heart against acute ischemia-reperfusion injury. This protection can be achieved by pre- and postischemic treatment as well as by exclusive postischemic treatment with losartan. Furthermore, the extent of this protection is equivalent to that conferred by quinaprilat and, unexpectedly, dependent on bradykinin.

Special considerations in the therapy of diabetic hypertension

Patients with diabetes mellitus have an increased prevalence of hypertension and associated cardiovascular disease (CVD), including coronary and cerebrovascular disease. The risk of an individual of developing CVD is much greater when both diseases coexist and is further magnified by their frequent association with dyslipidemia, coagulation, platelet, and endothelial abnormalities. Metabolic abnormalities frequently associated with hypertension are insulin resistance, enhanced coagulation, and decreased fibrinolytic activity. Drug treatment of hypertension in diabetic subjects is fraught with potential difficulties, including altered efficacy of medications, possible side effects, worsening of glycemic control, and impairment of lipid metabolism. Because hypertension is a major contributor to morbidity and mortality in diabetes, it should be recognized and treated early and aggressively despite these difficulties. This article reviews the efficacy and side effects of the various classes of antihypertensive agents in patients with diabetes mellitus.

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

OBJECTIVES

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Renin inhibition by substituted piperidines: a novel paradigm for the inhibition of monomeric aspartic proteinases?

BACKGROUND

The aspartic proteinase renin catalyses the first and rate-limiting step in the conversion of angiotensinogen to the hormone angiotensin II, and therefore plays an important physiological role in the regulation of blood pressure. Numerous potent peptidomimetic inhibitors of this important drug target have been developed, but none of these compounds have progressed past clinical phase II trials. Limited oral bioavailability or excessive production costs have prevented these inhibitors from becoming new antihypertensive drugs. We were interested in developing new nonpeptidomimetic renin inhibitors.

RESULTS

High-throughput screening of the Roche compound library identified a simple 3, 4-disubstituted piperidine lead compound. We determined the crystal structures of recombinant human renin complexed with two representatives of this new class. Binding of these substituted piperidine derivatives is accompanied by major induced-fit adaptations around the enzyme's active site.

CONCLUSIONS

The efficient optimisation of the piperidine inhibitors was facilitated by structural analysis of the renin active site in two renin-inhibitor complexes (some of the piperidine derivatives have picomolar affinities for renin). These structural changes provide the basis for a novel paradigm for inhibition of monomeric aspartic proteinases.

Molecular mechanisms of myocardial remodeling

"Remodeling" implies changes that result in rearrangement of normally existing structures. This review focuses only on permanent modifications in relation to clinical dysfunction in cardiac remodeling (CR) secondary to myocardial infarction (MI) and/or arterial hypertension and includes a special section on the senescent heart, since CR is mainly a disease of the elderly. From a biological point of view, CR is determined by 1 ) the general process of adaptation which allows both the myocyte and the collagen network to adapt to new working conditions; 2) ventricular fibrosis, i.e., increased collagen concentration, which is multifactorial and caused by senescence, ischemia, various hormones, and/or inflammatory processes; 3) cell death, a parameter linked to fibrosis, which is usually due to necrosis and apoptosis and occurs in nearly all models of CR. The process of adaptation is associated with various changes in genetic expression, including a general activation that causes hypertrophy, isogenic shifts which result in the appearance of a slow isomyosin, and a new Na+-K+-ATPase with a low affinity for sodium, reactivation of genes encoding for atrial natriuretic factor and the renin-angiotensin system, and a diminished concentration of sarcoplasmic reticulum Ca2+-ATPase, beta-adrenergic receptors, and the potassium channel responsible for transient outward current. From a clinical point of view, fibrosis is for the moment a major marker for cardiac failure and a crucial determinant of myocardial heterogeneity, increasing diastolic stiffness, and the propensity for reentry arrhythmias. In addition, systolic dysfunction is facilitated by slowing of the calcium transient and the downregulation of the entire adrenergic system. Modifications of intracellular calcium movements are the main determinants of the triggered activity and automaticity that cause arrhythmias and alterations in relaxation.

The efficacy and tolerance of one or two daily doses of eprosartan in essential hypertension. The Eprosartan Multinational Study Group

OBJECTIVE

The primary objective of this double-blind, parallel-group, placebo-controlled, multicentre study was to compare the antihypertensive efficacy of one versus two daily doses of eprosartan, a novel nonbiphenyl, nontetrazole angiotensin II receptor antagonist, in 243 patients with mild to moderate hypertension (sitting diastolic blood pressure > or = 95 to < or = 114 mmHg).

PATIENTS AND METHODS

The patients were randomized to titrated doses of eprosartan at 400-800 mg once a day, eprosartan at 200-400 mg twice a day, or placebo, with the incremental dose titrated over a 9-week period. Patients reaching target blood pressure (sitting diastolic blood pressure of < or = 90 mmHg) continued the fixed-dose treatment for 4 weeks. The primary efficacy measure was the mean change in trough sitting diastolic blood pressure from baseline to the study endpoint, determined on an intent-to-treat basis.

RESULTS

By the end of the study, eprosartan had significantly reduced mean trough sitting systolic and diastolic blood pressure relative to baseline and to placebo. The mean +/- SD change from baseline in diastolic pressure was -9 +/- 8.4 mmHg for the single daily dose, -9 +/- 8.5 mmHg for two doses a day and -4 +/- 8.1 mmHg for placebo (P < 0.0001 versus placebo for both eprosartan regimens). Similarly, both eprosartan regimens significantly reduced mean trough standing systolic and diastolic blood pressure. At the end of the study, the response rate in the single daily dose group (46.8%) was significantly higher than in the placebo group (25.6%). There were no significant differences between the treatment groups in the number of patients whose blood pressure responded to treatment; 41.7% of those taking eprosartan once a day and 44.4% of those taking eprosartan twice a day, and who responded to treatment, were maintained on their original starting doses. The total daily dose required to achieve target blood pressure was comparable, whether eprosartan was administered once or twice a day. Both eprosartan regimens were well tolerated and the incidence of adverse events with eprosartan was similar to that of placebo.

CONCLUSIONS

These results demonstrate that there was no significant difference in antihypertensive efficacy or tolerance between eprosartan taken in one or in two daily doses. Both dosing regimens provided significant and clinically meaningful reductions in blood pressure that were superior to placebo. Eprosartan in a single daily dose was shown to be an effective antihypertensive agent. Because of the good adverse-effect profile and the simplicity of a single daily dose, eprosartan has the potential to improve patient compliance.

Angiotensin II induces superoxide anion production by mesangial cells

BACKGROUND

The recognized role of angiotensin II (Ang II) in the pathogenesis of the progression of renal disease cannot be solely attributed to Ang II's hemodynamic effects. Indeed, growth stimulating signals driven by Ang II promote mesangial cell (MC) hypertrophy and extracellular matrix production, prominent features of progressive glomerular injury. Superoxide anion (O2-) avidly interacts with nitric oxide, an endogenous vasodilator that inhibits growth factor stimulated MC growth and matrix production. In addition, O2- acting as an intracellular signal is linked to growth related responses such as activation of mitogen activated protein (MAP) kinases. The studies reported herein were designed to investigate: (a) whether Ang II induces MC O2-production and (b) if increased O2- production elicits growth responses in MC.

METHODS

MC were exposed to Ang II for 24 or 48 hours. In some experiments, in addition to Ang II, MC were exposed to: diphenylenieodonium (DPI), an inhibitor of the flavin containing NADH/NADPH oxidase; losartan (LOS), an Ang II type 1 (AT1) receptor blocker; PD 98059, a MAP kinases inhibitor; the protein kinase C inhibitors Calphostin C or H-7; and the tyrosine kinase inhibitors, herbymycin A or genistein.

RESULTS

Ang II (10(-5) M to 10(-8) M) dose dependently increased MC O2- production up to 125% above control (ED 50 5 x 10(-7) M). LOS as well as DPI, and the PKC inhibitors blocked Ang II stimulated MC O2- production. Ang II dose dependently increased MC 3H-leucine incorporation, and MC protein content, two markers of MC hypertrophy, as well as 3H-thymidine incorporation, a marker of MC hyperplasia. PD98059, a specific inhibitor of MAP kinases prevented Ang II induced MC hypertrophy. Moreover, LOS, DPI, and the PKC inhibitors each independently inhibited MC 3H-leucine incorporation, thereby establishing the specificity of Ang II induced O2- in driving MC hypertrophy.

CONCLUSIONS

The current studies demonstrate a previously unrecognized link between Ang II and MC O2- production that may participate in the pathophysiology of progressive renal disease by concomitantly affecting the hemodynamics of the glomerular microcirculation as well as growth related responses of MC to injury.

Cloning of the gene and cDNA for hamster chymase 2, and expression of chymase 1, chymase 2 and angiotensin-converting enzyme in the terminal stage of cardiomyopathic hearts

Chymase is responsible for the formation of angiotensin II, which plays crucial roles in the pathogenesis of cardiovascular diseases. In the present study we determined the gene organization of a novel hamster chymase (hamster chymase 2) and analysed the expression of chymase 1, chymase 2 and angiotensin-converting enzyme (ACE) in hamster hearts at the terminal stage of cardiomyopathy. The gene encoding hamster chymase 2 is 3.2 kb in length and has five exons and four intervening sequences. The overall organization of this gene is similar to that of several other serine proteases. The deduced amino acid sequence revealed the existence of a preproenzyme composed of a signal peptide with 19 amino acids, a propeptide with two amino acids and a catalytic domain with 226 amino acids. The predicted full sequence of the catalytic domain was revealed to be very similar to the sequences of mouse mast-cell protease 5 (86%), rat mast-cell protease III (85%) and human chymase (70%) and less similar to hamster chymase 1 (56%). The expression of chymase 1 in heart was higher than that of chymase 2. The cardiac chymase-like activity, as well as the mRNA levels of chymase 1 and 2 of BIO 14.6 cardiomyopathic hamsters at the age of 60 weeks were increased 3.4-, 2.8- and 5.1-fold respectively compared with age-matched BIO F1B control hamsters. The cardiac ACE activity and the ACE mRNA level of cardiomyopathic hamsters were also increased 4.1- and 2.4-fold compared with those of age-matched controls. These results suggest that up-regulation of both ACE and chymases participates in the pathophysiology of the terminal stage of cardiomyopathy.

Does blockade of angiotensin II receptors offer clinical benefits over inhibition of angiotensin-converting enzyme?

Angiotensin AT1 receptor antagonists represent a new class of drugs for the treatment of hypertension. They are specific for the renin-angiotensin system, selective for the angiotensin AT1 receptor, and act independently of the angiotensin II synthetic pathway. Blockade of the renin-angiotensin system at the receptor level should therefore be more complete. The high circulating levels of angiotensin II following angiotensin AT1 receptor blockade could be beneficial in stimulating other unblocked angiotensin receptors, especially the AT2 receptor. It has been proposed that the angiotensin AT2 receptor, which is re-expressed or up-regulated during pathological circumstances, counterbalances the effect of the stimulation of the angiotensin AT1 receptor. Through this mechanism, angiotensin AT1 antagonists may be superior to ACE inhibitors in cardiac and vascular remodelling as well as in kidney insufficiency. Long-term trials are required to demonstrate the possible clinical superiority of this new class of antihypertensive agents.

The brain is a possible target for an angiotensin-converting enzyme inhibitor in the treatment of chronic heart failure

BACKGROUND

Although many lines of evidence have shown beneficial effects of angiotensin-converting enzyme (ACE) inhibitors on patients with chronic heart failure (CHF) after myocardial infarction (MI), the target of ACE inhibitors still remains unclear. The objectives of the present study were to evaluate the dipsogenic response to centrally administered angiotensin and to examine the effect of central administration of an ACE inhibitor on cardiac remodeling in rats with CHF after large MI.

METHODS AND RESULTS

The drinking responses to intracerebroventricular (i.c.v.) injections of saline and angiotensin I (100 ng) were measured in 22 male Sprague-Dawley rats with or without CHF at 2-5 weeks after the ligation of the left coronary artery. The dipsogenic responses to i.c.v. angiotensin I were significantly larger in rats with CHF and large MI (infarct size > 30%) than in sham-operated rats. Pretreatment with losartan abolished the significant difference between the two groups. Left ventricular (LV) weights of 32 surviving rats with CHF were measured after the 3-week subcutaneous infusions of vehicle (s.c.-VEH) and captopril (1 mg x kg(-1) x h(-1), s.c.-CAP) or the 3-week i.c.v. infusions of vehicle (i.c.v.-VEH) and captopril (50 microg x kg(-1) x h(-1), i.c.v.-CAP). The LV weights normalized by body weights of s.c.-CAP rats were significantly smaller than those of s.c.-VEH rats (1.73 +/- 0.04 vs 2.08 +/- 0.09 g x kg(-1); P < .01); those of i.c.v.-CAP rats were also significantly smaller than those of i.c.v.-VEH rats (1.84 +/- 0.08 vs 2.1 +/- 0.10 g x kg(-1); P < .05).

CONCLUSIONS

These results suggest that the brain is a possible target for ACE inhibitors in the treatment of CHF after MI.

Inhibitors of the renin angiotensin system: implications for the anaesthesiologist

The major long-term benefits of angiotensin-converting enzyme (ACE) inhibitors have now clearly been demonstrated in patients with arterial hypertension, cardiac insufficiency, coronary artery disease and several renal diseases. Such long-term treatment markedly alters the cardiovascular response to anaesthesia and surgery, whereas preliminary data suggest that short-term renin angiotensin system blockade might provide perioperative organ protection and improved circulatory conditions. Besides the classic view that the conversion of angiotensin I to angiotensin II is mainly due to ACE, alternative pathways have recently been identified, including cathepsin G as well as chymostatin- and aprotinin-sensitive serine proteases that are released from mastocytes and endothelial cells and which are insensitive to the effects of ACE inhibitors. These proteases are thought to contribute to tissue perfusion under hypoxic conditions and to structural remodelling. In clinical practice, ACE inhibitors may be preferred to angiotensin II receptor antagonists since the former, besides reducing angiotensin II synthesis, also lead to an accumulation of kinins (e.g. bradykinin), which have important cardio- and renal protective effects through liberation of prostacyclin and nitric oxide in endothelial cells and through stimulation of guanylate cyclase to form cyclic GMP.

Roles of vascular angiotensin converting enzyme and chymase in two-kidney, one clip hypertensive hamsters

BACKGROUND

A chymase-dependent angiotensin II-forming pathway is present in human vascular tissues; however, the role, if it plays any, of chymase in the pathogenesis of hypertension is not known. When investigating the role of chymase, it is important to recognize marked differences in vascular angiotensin II-forming systems among species. We found recently that hamsters, like humans, possess the dual angiotensin II-forming system.

OBJECTIVE

To analyze the potential involvement of angiotensin converting enzyme and chymase in the pathogenesis of hypertension, and to further characterize the efficiency of angiotensin converting enzyme inhibitors and angiotensin II receptor antagonists for the treatment of hypertension.

METHODS AND RESULTS

The mean arterial pressure in the two-kidney, one clip hamster model had increased significantly 2 weeks after clipping (acute stage), reached a peak after 4 weeks, and was sustained at the high level until 32 weeks after clipping (chronic stage). Plasma renin activity increased markedly during the acute stage, but returned to the normal level during the chronic stage. Vascular angiotensin converting enzyme activity during 4-32 weeks after clipping was significantly higher than that in the control hamsters. By contrast, vascular chymase was not activated throughout the experimental period. Administrations of an angiotensin converting enzyme inhibitor, trandolapril, and an angiotensin II receptor antagonist, CV-11974, equally lowered the mean arterial pressure during the acute and chronic stages.

CONCLUSIONS

Vascular angiotensin converting enzyme plays a predominant role in the maintenance of two-kidney, one clip hypertension in hamsters, which, like humans, possess a dual system of formation of angiotensin II. Vascular chymase was not involved in the pathogenesis of two-kidney, one clip hypertension in the hamster.

Angiotensin II formation from ACE and chymase in human and animal hearts: methods and species considerations

The current study examined the contributions of angiotensin-converting enzyme (ACE) vs. chymase to angiotensin II (ANG II) generation in membrane preparations from left ventricles of humans, dogs, rabbits, and rats and from total heart of mice. ACE and chymase activity were measured in membrane preparations extracted with low or high detergent (LD and HD, respectively) concentrations. We hypothesized that ACE, which is membrane bound in vivo, would be preferentially localized to the HD preparation, whereas chymase, which is localized to the cytoplasm and cardiac interstitium, would be localized to the LD preparation. In human heart, ACE activity was 16-fold higher in the HD than in the LD preparation, whereas chymase activity was 15-fold higher in the LD than in the HD preparation. Total ANG II formation was greater in human heart [15.8 +/- 3.4 (SE) micromol ANG II x g(-1) x min(-1)] than in dog, rat, rabbit, and mouse hearts (3.90 +/- 0.35, 0.41 +/- 0.02, 0.61 +/- 0.07, and 1.16 +/- 0.08 micromol ANG II x g(-1) x min(-1), respectively, P < 0.05, by analysis of variance). ANG II formation from ACE was higher in mouse heart (1.09 +/- 0.05 micromol ANG II x g(-1) x min(-1), p < 0.001) than in rabbit, human, dog, and rat hearts (0.55 +/- 0.06, 0.34 +/- 0.01, 0.32 +/- 0.06, and 0.31 +/- 0.02 micromol ANG II x g(-1) x min(-1), respectively). In contrast, chymase activity was higher in human heart (15.3 +/- 3.4 micromol ANG II x g(-1) x min(-1)) than in dog, rat, rabbit, and mouse hearts (3.59 +/- 0.29, 0.10 +/- 0.01, 0.06 +/- 0.01, and 0.07 +/- 0.01 micromol ANG II x g(-1) x min(-1), respectively). Our results demonstrate important species differences in the pathways of intracardiac ANG II generation. Chymase predominated over ACE activity in human heart, accounting for extremely high total ANG II formation in human heart compared with dog, rat, rabbit, and mouse hearts.