Angiotensin blockade for hypertension: a promise fulfilled

Motor sequela of adult and pediatric stroke: Imminent losses and ultimate gains

Stroke is the leading cause of neurological disability in the United States and worldwide. Remarkable advances have been made over the past 20 years in acute vascular treatments to reduce infarct size and improve neurological outcome. Substantially less progress has been made in the understanding and clinical approaches to neurological recovery after stroke. This chapter reviews the epidemiology, bedside examination, localization approaches, and classification of stroke, with an emphasis on motor stroke presentations and management, and promising research approaches to enhancing motor aspects of stroke recovery.

Soluble (Pro)renin Receptor Is Adversely Associated with Indices of Left Ventricular Structure and Function: The African-PREDICT Study

This study aims to compare soluble (pro)renin receptor [s(P)RR] levels between black and white adults and to explore the associations of left ventricular (LV) structure and function with s(P)RR in the total and ethnicity-stratified groups. The study sample included 1172 apparently healthy black (n = 587) and white (n = 585) participants of the African-PREDICT study aged 20−30 years. Echocardiography was performed to determine relative wall thickness (RWT), LV mass index, LV ejection fraction and stroke volume index (SVi). s(P)RR was analyzed from serum samples, while plasma renin activity-surrogate (PRA-S) and eq angiotensin II were determined using the RAS™ Fingerprint. s(P)RR was higher in the white participants compared to the black participants (p < 0.001). In multivariable-adjusted linear regression analyses, we observed a positive association between RWT and s(P)RR (β = 0.141; p = 0.005) and negative associations of LV ejection fraction (β = −0.123; p = 0.016) and SVi (β = −0.144; p = 0.004) with s(P)RR only in white adults. Higher s(P)RR observed in white vs. black participants was associated with higher RWT and poorer LV function only in young white adults but not in their black counterparts. These results suggest that s(P)RR may contribute to LV remodeling and dysfunction in white populations due to its role in volume−pressure regulation and its proinflammatory as well as profibrotic effects.

Impact of Antihypertensive Drug Class on Outcomes in the SPRINT

BACKGROUND

The primary objective of this analysis is to assess if greater exposure to any major antihypertensive drug class was associated with reduced primary composite outcome events in SPRINT (Systolic Blood Pressure Intervention Trial).

METHODS

This is a secondary analysis of the SPRINT trial evaluating whether longitudinal, time varying exposure to any major antihypertensive drug class had any impact on primary outcome events, after adjusting for effects of randomization arm, time varying achieved systolic blood pressure, other drug class exposure, and baseline characteristics.

RESULTS

Nine thousand two hundred fifty-two participants were included. After adjustments, exposure of one year or greater to thiazide-type diuretics or renin-angiotensin system blockers was associated with significantly fewer primary events than exposure of less than one year (hazard ratio, 0.78 [95% CI, 0.64-0.94]). There was no significant difference with longer versus shorter exposure to calcium channel blockers. Greater exposure to beta-blockers was associated with an increase in primary events compared with exposure of <1 year (hazard ratio, 1.35 [95% CI, 1.13-1.62]). Furthermore, thiazide-type diuretics were associated with a reduction in heart failure events and renin-angiotensin system blockers with reduced myocardial infarction. Both were associated with less cardiovascular deaths.

CONCLUSIONS

The SPRINT trial demonstrated a lower target blood pressure led to reductions in adverse cardiovascular events. This analysis suggests greater exposure to thiazide-type diuretics and renin-angiotensin system blockers also contributed to reduced adverse cardiovascular events. Greater exposure to beta-blockers was associated with increased cardiovascular events.

Integration of multi-scale molecular modeling approaches with experiments for the in silico guided design and discovery of novel hERG-Neutral antihypertensive oxazalone and imidazolone derivatives and analysis of their potential restrictive effects on cell proliferation

AT1 antagonists is the most recent drug class of molecules against hypertension and they mediate their actions through blocking detrimental effects of angiotensin II (A-II) when acts on type I (AT1) A-II receptor. The effects of AT1 antagonists are not limited to cardiovascular diseases. AT1 receptor blockers may be used as potential anti-cancer agents - due to the inhibition of cell proliferation stimulated by A-II. Therefore, AT1 receptors and the A-II biosynthesis mechanisms are targets for the development of new synthetic drugs and therapeutic treatment of various cardiovascular and other diseases. In this work, multi-scale molecular modeling approaches were performed and it is found that oxazolone and imidazolone derivatives reveal similar/better interaction energy profiles compared to the FDA approved sartan molecules at the binding site of the AT1 receptor. In silico-guided designed hit molecules were then synthesized and tested for their binding affinities to human AT1 receptor in radioligand binding studies, using [¹²⁵I-Sar¹-Ile⁸] AngII. Among the compounds tested, 19d and 9j molecules bound to receptor in a dose response manner and with relatively high affinities. Next, cytotoxicity and wound healing assays were performed for these hit molecules. Since hit molecule 19d led to deceleration of cell motility in all three cell lines (NIH3T3, A549, and H358) tested in this study, this molecule is investigated in further tests. In two cell lines (HUVEC and MCF-7) tested, 19d induced G2/M cell cycle arrest in a concentration dependent manner. Adherent cells detached from the plates and underwent cell death possibly due to apoptosis at 19d concentrations that induced cell cycle arrest.

Structure-based design of hERG-neutral antihypertensive oxazalone and imidazolone derivatives

Angiotensin II receptor type 1 (AT1) antagonists are the most recent drug class against hypertension. Recently first crystal structure of AT1 receptor is deposited to the protein data bank (PDB ID: 4YAY). In this work, several molecular screening methods such as molecular docking and de novo design studies were performed and it is found that oxazolone and imidazolone derivatives reveal similar/better interaction energy profiles compared to the FDA approved sartan molecules at the binding site of the AT1 receptor. A database consisting of 3500-fragments were used to enumerate de novo designed imidazolone and oxazolone derivatives and hereby more than 50000 novel small molecules were generated. These derivatives were then used in high throughput virtual screening simulations (Glide/HTVS) to find potent hit molecules. In addition, virtual screening of around 18 million small drug-like compounds from ZINC database were screened at the binding pocket of the AT1 receptor via Glide/HTVS method. Filtered structures were then used in more sophisticated molecular docking simulations protocols (i.e., Glide/SP; Glide/XP; Glide/IFD; Glide/QPLD, and GOLD). However, the K⁺ ion channel/drug interactions should also be considered in studies implemented in molecular level against their cardiovascular risks. Thus, selected compounds with high docking scores via all diverse docking algorithms are also screened at the pore domain regions of human ether-a-go-go-related gene (hERG1) K⁺ channel to remove the high affinity hERG1 blocking compounds. High docking scored compounds at the AT1 with low hERG1 affinity is considered for long molecular dynamics (MD) simulations. Post-processing analysis of MD simulations assisted for better understanding of molecular mechanism of studied compounds at the binding cavity of AT1 receptor. Results of this study can be useful for designing of novel and safe AT1 inhibitors.

Obesity and statins are both independent predictors of enhanced coronary arteriolar dilation in patients undergoing heart surgery

Background

A paradoxical inverse relationship between body mass index, morbidity and mortality in patients with ischemic heart disease has been noted; but the underlying mechanisms remain unclear. Given that coronary resistance arteries are the primary regulators of myocardial blood flow, we examined the effects of obesity and medication on dilator function in coronary microvessels.

Methods

Bradykinin-induced coronary dilation was assessed by videomicroscopy in ex vivo coronary arterioles obtained from 64 consecutive patients undergoing heart surgery. Multi-variable linear regression and logistic regression were used to investigate the effects of obesity (BMI ≥ 30 kg/M²) and the influences of medications on vessel responses.

Results

In isolated, pressurized (80 mmHg) coronary arterioles of obese and non-obese patient the active (73±4 vs. 79±13 μm) and passive (111 ± 5.5 vs. 118 ± 5.0 μm) diameters were similar. Bradykinin elicited substantial dilation in coronary arterioles, with a similar magnitude in obese and non-obese patients (to 10^-8 M: 55 ± 5% vs. 46 ± 5%, P = 0.20), but with significantly enhanced sensitivity in obesity (EC50: 8.2x10^-9 M vs. 1.9x10^-8 M, respectively, P = 0.03). When adjusted for other risk factors and medications, obesity and statins were determined to be the only positive predictors of enhanced dilation, as assessed with multiple regression analysis. Moreover, obese patients with or without statin exhibited significantly increased coronary dilation to bradykinin, when compared to non-obese patients without statin therapy.

Conclusions

Obesity and statin therapy are independently associated with an enhanced dilator function of coronary arterioles in patients undergoing heart surgery, which may offer a potential mechanism for the better cardiovascular outcome described earlier as the obesity paradox.

Therapeutic role of toll-like receptor modification in cardiovascular dysfunction

Toll-like receptors (TLR) are key pattern recognition receptors in the innate immune system. The TLR-mediated immune response against pathogens is usually protective however inappropriate TLR activation may lead to excessive tissue damage. It is well recognised that TLRs respond to a variety of endogenous as well as exogenous ligands. By responding to endogenous ligands that are exposed during cellular damage, TLRs have been implicated in a range of pathological conditions associated with cardiovascular dysfunction. Increasing knowledge on the mechanisms involved in TLR signalling has encouraged the exploration of therapeutic pharmacological modulation of TLR activation in conditions such as atherosclerosis, ischaemic heart disease, heart failure and ischaemic reperfusion injury. The aim of this review is to explore the translational potentials of TLR modification in cardiovascular dysfunction, where these agents have been studied.

Acute vascular effects of the angiotensin II receptor antagonist olmesartan in normal subjects: relation to the renin-aldosterone system

The extent to which the clinical effects of angiotensin receptor blockers (ARB) are related to ambient renin system activity remains poorly defined. Therefore, we measured blood pressure (BP), large (C1) and small (C2) arterial compliance, systemic vascular resistance (SVR), plasma renin activity (PRA), and the 24-h urinary excretion of sodium (UNaV) and aldosterone before and 1, 2, 4, and 24 h after administration of single doses of placebo, and 5, 20, and 40 mg of the ARB olmesartan medoxomil to 12 unmedicated normotensive subjects. In the basal state, SVR was inversely related to UNaV (r=-0,3,p=0,04); the greater the UNaV, the more vasodilated the subject. Indices of arterial compliance, both C1 (r=-0,32,p=0,03) and C2 (r=-0,35,p=0,02) were inversely related to the basal PRA. Renin also predicted olmesartan-induced changes in C1 (r=0,43,p=0,004) and C2r=0,33,p=0,04). The greater the basal PRA, the less the arterial compliance, and the more compliance improved after olmesartan. Both systolic (p=0,003) and diastolic (p<0,0001) BP fell significantly on olmesartan compared with placebo (MANOVA with time), and relations were observed between the basal PRA and olmesartan-induced changes in pressure (systolic BP:r=-0,414,p=0,012; diastolic BP:r=-0.561,p<0,0001) — the greater the initial PRA, the more olmesartan lowered BP. Furthermore, the more pressure fell, the more PRA rose reciprocally (r=-0,44,p=0,007). Finally, aldosterone excretion fell (sig=0,05) on each dose of olmesartan compared with placebo. We conclude that 1) the inverse relation of UNaV and SVR illustrates the reciprocal role of volume versus constrictor factors in maintaining normal BP; and 2) PRA is a physiologic determinant of arterial compliance in normal individuals and of the response to the ARB olmesartan. Measurement of PRA may help to predict clinical ARB responses in individual subjects.

An efficient synthesis of a rationally designed 1,5 disubstituted imidazole AT(1) angiotensin II receptor antagonist: reorientation of imidazole pharmacophore groups in losartan reserves high receptor affinity and confirms docking studies

A new 1,5 disubstituted imidazole AT(1) Angiotensin II (AII) receptor antagonist related to losartan with reversion of butyl and hydroxymethyl groups at the 2-, 5-positions of the imidazole ring was synthesized and evaluated for its antagonist activity (V8). In vitro results indicated that the reorientation of butyl and hydroxymethyl groups on the imidazole template of losartan retained high binding affinity to the AT(1) receptor concluding that the spacing of the substituents at the 2,5- positions is of primary importance. The docking studies are confirmed by binding assay results which clearly show a comparable binding score of the designed compound V8 with that of the prototype losartan. An efficient, regioselective and cost effective synthesis renders the new compound as an attractive candidate for advanced toxicological evaluation and a drug against hypertension.

Valsartan preconditioning protects against myocardial ischemia-reperfusion injury through TLR4/NF-kappaB signaling pathway

Toll-like receptor 4 (TLR4) activation has been implicated in the pathogenesis of myocardial ischemia/reperfusion (I/R) injury. The activated TLR4 is capable of activating a variety of proinflammatory mediators, such as tumor necrosis factor-a (TNF-a) and interleukin-6 (IL-6). Valsartan as a kind of Angiotensin II type 1 receptor blockers is gradually used for the treatment of ischemic heart disease depending on its anti-inflammation function. Therefore, we hypothesized that valsartan protects against myocardial I/R injury by suppressing TLR4 activation. We constructed the rat model of myocardial I/R injury. The rats were pretreated with valsartan for 2 weeks, and then subjected to 30 min ischemia and 2 h reperfusion. TLR4 and Nuclear factor kappa-B (NF-kappaB) levels were detected by quantitative real-time PCR and western blot. In order to evaluate myocardial damage, the myocardial infarct size, histopathologic changes, and the release of myocardial enzymes, proinflammation cytokines and Angiotensin II were analyzed by triphenyl tetrazolium chloride (TTC) staining, light microscopy, and enzyme-linked immunosorbent assay (ELISA), respectively. Valsartan preconditioning inhibited TLR4 and NF-kappaB expressions concomitant with an improvement in myocardial injury, such as smaller infarct size, fewer release of myocardial enzymes, and proinflammation mediators. These findings suggest that valsartan plays a pivotal role in the protective effects on myocardial I/R injury. This protection mechanism is possibly due to its anti-inflammation function via TLR4/NF-kappaB signaling pathway.

Blood pressure-lowering efficacy of olmesartan relative to other angiotensin II receptor antagonists: an overview of randomized controlled studies

The aim of the present work was to review published studies investigating the dose-related efficacy on blood pressure (BP) of olmesartan and of other commercially available angiotensin II type I receptor blockers (ARBs). Patient population comprises mild to moderate hypertensive adult patients. We selected studies with comparable design and dose ranges. Dose-effect relationship plots were fitted for diastolic (DBP) and systolic (SBP) BP to the simplified E(max) model. We also examined controlled studies of olmesartan vs. other individual ARBs. Our overview was based on 7280 patients, of which 5769 received an ARB and 1511 received placebo. Except for losartan, the data fitted correctly to the E(max) model, with correlation coefficients ranging from 0.77 to 0.99. BP-lowering efficacy defined as E(max) was superior with olmesartan, (DBP/SBP mmHg: -9.0/-12.4) when compared with candesartan (-6.7/-11.3), irbesartan (-6.5/-11.2) and valsartan (-6.3/-8.9). Head-to-head comparisons of olmesartan to each of the other ARBs used at per-label 'recommended doses', support the finding of a greater BP-lowering effect of olmesartan. This overview suggests that clinically relevant differences in maximal efficacy, as well as in efficacy of per-label recommended doses can be evidenced among individual ARBs. Olmesartan efficacy was consistently at the highest end of the range of efficacy of ARBs studied.

Renin-angiotensin system and cardiovascular risk

The renin-angiotensin system is a major regulatory system of cardiovascular and renal function. Basic research has revealed exciting new aspects, which could lead to novel or modified therapeutic approaches. Renin-angiotensin system blockade exerts potent antiatherosclerotic effects, which are mediated by their antihypertensive, anti-inflammatory, antiproliferative, and oxidative stress lowering properties. Inhibitors of the system-ie, angiotensin converting enzyme inhibitors and angiotensin receptor blockers, are now first-line treatments for hypertensive target organ damage and progressive renal disease. Their effects are greater than expected by their ability to lower blood pressure alone. Angiotensin receptor blockers reduce the frequency of atrial fibrillation and stroke. Renin-angiotensin system blockade delays or avoids the onset of type 2 diabetes and prevents cardiovascular and renal events in diabetic patients. Thus, blockade of this system will remain a cornerstone of our strategies to reduce cardiovascular risk.

Synthesis, binding studies and in vivo biological evaluation of novel non-peptide antihypertensive analogues

AT(1) antagonists (SARTANs) constitute the last generation of drugs for the treatment of hypertension, designed and synthesized to mimic the C-terminal segment of the vasoconstrictive hormone angiotensin II (AngII). They exert their action by blocking the binding of AngII on the AT(1) receptor. Up to date eight AT(1) antagonists have been approved for the regulation of high blood pressure. Although these molecules share common structural features and are designed to act under the same mechanism, they have differences in their pharmacological profiles and antihypertensive efficacy. Thus, there is still a need for novel analogues with better pharmacological and financial profiles. An example of a novel synthetic non peptide AT(1) antagonist which devoids the classical template of SARTANs is MM1. In vivo studies showed that MMK molecules, which fall in the same class of MM1, had a significant antihypertensive (40-80% compared to the drug losartan) activity. However, in vitro affinity studies showed that losartan has considerably higher affinity. The theoretical docking studies showed that MM1 acts on the same site of the receptor as losartan. They exert hydrophobic interactions with amino acid Val108 of the third helix of the AT(1) receptor and other hydrophobic amino acids in spatial vicinity. In addition, losartan favours multiple hydrogen bondings between its tetrazole group with Lys199. These additional interactions may in part explain its higher in vitro binding affinity.

Benefits from angiotensin-converting enzyme inhibitor ‘beyond blood pressure lowering’: beyond blood pressure or beyond the brachial artery?

OBJECTIVE

The substantial benefits of ramipril over conventional therapy in high-risk patients are not always associated with clinically significant differences in brachial arterial pressure, and largely remain unexplained. We undertook this acute study to establish the magnitude of and reason for different acute effects of ramipril and atenolol on arterial pressure.

METHODS

We enrolled 30 patients, who took 10 mg ramipril, 100 mg atenolol, and placebo at intervals of > or = 7 days, in a randomized, double-blind, placebo-controlled trial. After baseline, measurements were taken at 30-60 min intervals for 5 h, and comprised cuff brachial pressure, radial artery tonometry with generation of central aortic pressure, and pulse wave velocity for aorta, upper limb and lower limb arteries.

RESULTS

Both ramipril and atenolol reduced arterial pressure, and the diastolic pressure fall was similar in the aorta and brachial artery, but the systolic pressure fall for ramipril was greater than for atenolol (by 5.2 mmHg, P < 0.0001) in the aorta compared with the brachial artery. The aortic systolic pressure difference with ramipril in comparison with atenolol was accompanied by an absolute difference of 10.7% (P < 0.0001) in the augmentation index, denoting a reduction in peripheral wave reflection by ramipril. The aortic pulse wave velocity fell to a similar degree with ramipril in comparison with atenolol, but fell to a greater degree (1.35 and 0.44 m/s, respectively, P < 0.0001 for both) in muscular arteries of the lower and upper limbs.

CONCLUSION

A greater (average, 5.2 mmHg) decrease in aortic systolic pressure caused by ramipril may explain the greater benefit of ramipril over atenolol. The difference is attributable to decreased stiffness of peripheral arteries and a reduction in wave reflection.

Angiotensin converting enzyme activity in infancy is related to birth weight

AIMS

(a) To measure infant angiotensin converting enzyme (ACE) activity in healthy term infants at birth and during the first three months of life. (b) To determine the relation between serum ACE activity and infant feeding practice during this period. (c) To investigate the relation between serum ACE activity and birth weight and other potential contributing factors including acid-base status at birth, gestation, and maternal ACE genotype.

METHODS

Prospective study of term infants, with clinical and feeding data collected from parents and medical records, and serum ACE measured in the infant at birth and 1 and 3 months of age, and in the mother at the time of birth and one to three months after birth.

RESULTS

At birth and 1 and 3 months of age, infant serum ACE activity was twice that of maternal ACE activity. Infant ACE activity at birth and 1 and 3 months did not significantly differ between breast and formula fed infants. There was a highly significant negative correlation between infant ACE activity at 3 months and birth weight (r = -0.52; p < 0.001). This persisted after the conversion of birth weights to z scores (r = -0.34; p = 0.03). ACE activity at 3 months was also related to placental weight (r = -0.30; p = 0.02) and maternal age (r = -0.30; p = 0.05). The strong correlation between serum ACE activity and birth weight z score persisted after adjustment for maternal age and placental weight (r = -0.34; p = 0.03).

CONCLUSION

As ACE is increasingly identified as a risk factor for cardiovascular disease, serum ACE activity in infancy may contribute to the link between low birth weight and later cardiovascular events.

Novel targets of ANG II regulation in mouse heart identified by serial analysis of gene expression

Although the central role of ANG II in cardiovascular homeostasis is well appreciated, the molecular circuitry of its many actions is not completely understood. With the use of serial analysis of gene expression to assess global transcriptional changes in the heart of mice after continuous 7-day ANG II administration, we identified patterns of gene expression indicative of cardiac remodeling, including coordinate regulation of genes previously described in a context of processes associated with hypertrophy and fibrosis. In addition, we discovered several novel ANG II targets, including characterized genes of known function, recently annotated genes of unknown function, and the putative genes not yet present in current databases. The serial analysis of gene expression approach to assess the role of ANG II presented in this report provides new venues for inquiries into ANG II-mediated cardiac function.

Cardiac transcriptional response to acute and chronic angiotensin II treatments

Exposure of experimental animals to increased angiotensin II (ANG II) induces hypertension associated with cardiac hypertrophy, inflammation, and myocardial necrosis and fibrosis. Some of the most effective antihypertensive treatments are those that antagonize ANG II. We investigated cardiac gene expression in response to acute (24 h) and chronic (14 day) infusion of ANG II in mice; 24-h treatment induces hypertension, and 14-day treatment induces hypertension and extensive cardiac hypertrophy and necrosis. For genes differentially expressed in response to ANG II treatment, we tested for significant regulation of pathways, based on Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Microarray Pathway Profiler (GenMAPP) databases, as well as functional classes based on Gene Ontology (GO) terms. Both acute and chronic ANG II treatments resulted in decreased expression of mitochondrial metabolic genes, notably those for the electron transport chain and Krebs-TCA cycle; chronic ANG II treatment also resulted in decreased expression of genes involved in fatty acid metabolism. In contrast, genes involved in protein translation and ribosomal activity increased expression following both acute and chronic ANG II treatments. Some classes of genes showed differential response between acute and chronic ANG II treatments. Acute treatment increased expression of genes involved in oxidative stress and amino acid metabolism, whereas chronic treatments increased cytoskeletal and extracellular matrix genes, second messenger cascades responsive to ANG II, and amyloidosis genes. Although a functional linkage between Alzheimer disease, hypertension, and high cholesterol has been previously documented in studies of brain tissue, this is the first demonstration of induction of Alzheimer disease pathways by hypertension in heart tissue. This study provides the most comprehensive available survey of gene expression changes in response to acute and chronic ANG II treatment, verifying results from disparate studies, and suggests mechanisms that provide novel insight into the etiology of hypertensive heart disease and possible therapeutic interventions that may help to mitigate its effects.

Ace revisited: a new target for structure-based drug design

Angiotensin-converting enzyme (ACE) is a chloride-dependent metalloenzyme that catalyses the hydrolytic cleavage of dipeptides from the carboxyl terminus of many regulatory oligopeptides. ACE is central to the renin–angiotensin system that regulates blood pressure, fluid homeostasis, and renal and vascular function. It is therefore a major target for cardiovascular therapies.

ACE inhibitors (for example, captopril, enalaprilat and lisinopril) have been on the market for more than 20 years. Side effects of treatment with ACE inhibitors include cough and angioedema.

ACE comprises an N- and a C-domain, each containing an active site with distinct substrates and activation properties. The design of domain-selective inhibitors might produce new drugs with improved safety and efficacy — this endeavour will be facilitated by the recent determination of the three-dimensional structure of ACE.

The C-domain seems to be primarily responsible for the regulation of blood pressure. Data indicate that C-domain-selective inhibitors will have less severe side effects than current-generation inhibitors, which generally target both the N- and C-domains.

In contrast to the C-domain, the N-domain seems to have relatively low affinity for the peptides that control blood pressure. It preferentially hydrolyses at least three other physiologically important peptides, so targeted inhibition of the N-domain might have novel therapeutic applications.

Current-generation angiotensin-converting enzyme (ACE) inhibitors are widely used for cardiovascular diseases, including high blood pressure, heart failure, heart attack and kidney failure, and have combined annual sales in excess of US $6 billion. However, the use of these ACE inhibitors, which were developed in the late 1970s and early 1980s, is hampered by common side effects. Moreover, we now know that ACE actually consists of two parts (called the N- and C-domains) that have different functions. Therefore, the design of specific domain-selective ACE inhibitors is expected to produce next-generation drugs that might be safer and more effective. Here we discuss the structural features of current inhibitors and outline how next-generation ACE inhibitors could be designed by using the three-dimensional molecular structure of human testis ACE. The ACE structure provides a unique opportunity for rational drug design, based on a combination of in silico modelling using existing inhibitors as scaffolds and iterative lead optimization to drive the synthetic chemistry.

Angiotensin II dose-effect curves and Schild regression plots for characterization of different angiotensin II AT1 receptor antagonists in clinical pharmacology

The 'Schild regression' method is based on the principle of assessing the rightward shift of agonist dose-effect curves in the presence of different doses/concentrations of the respective receptor antagonist and presenting their relationship in a double log plot (i.e. the 'Schild plot'). The original method was developed to quantitatively characterize antagonistic drugs in experimental pharmacology. The method was adopted for evaluation of various AT1 antagonists in humans utilizing (human) angiotensin II as the agonist. Angiotensin II (Ang II) in continuous intravenous dose-incremental administration resulted in a clearly dose-dependent increase in blood pressure. All AT1 antagonists tested after oral administration yielded concentration-dependent rightward shifts of those Ang II dose-effect curves that were quantified as dose ratio (DR). DR minus 1 (DR-1) enabled the assessment of antagonist time kinetics in humans and a quantitatively precise determination of the half-life of antagonism in vivo. Schild plots allowed for assessment of apparent Ki doses indicative of a twofold rightward shift of the Ang II effect, thus providing the means for a rational comparison of the pharmacological potency of many of these compounds, where the Ki doses obtained at 24 h after administration were in the range of 'therapeutic' doses. Schild plots of a variety of substances showed linear relations independent of whether the blockade was deemed surmountable or not. It is therefore assumed that this property does not play a role at clinical doses/concentrations. Slopes slightly below 1 in the Schild plots of all tested antagonists point to a second 'counterregulatory' vasodilatory mechanism of action of Ang II which becomes apparent with AT1 blockade in conditions of high doses/concentrations of Ang II. Concentration vs. effect relationships indicate that if assessed at the same degree of direct vascular antagonism, other effects, such as increase in plasma renin activity, may be present to a varying degree with different antagonists. Thus for irbesartan, the potency to stimulate renin release was found to be at least twice that of candesartan. These observations should stimulate further research into the relevance of these dynamic differences between the various compounds. Thus, methodologies relying on fundamental principles of experimental pharmacology can provide the clinical pharmacologist with powerful tools to measure accurately degree of antagonism and time kinetics and to investigate the nature of receptor antagonism in humans.

Losartan and E3174 pharmacokinetics in cytochrome P450 2C9*1/*1, *1/*2, and *1/*3 individuals

STUDY OBJECTIVE

To determine if differences in the pharmacokinetics of losartan and its pharmacologically active E3174 metabolite exist among individuals expressing the cytochrome P450 (CYP) 2C9*1/*1, *1/*2, and *1/*3 genotypes.

DESIGN

Single-dose pharmacokinetic study.

SETTING

University general clinical research center.

SUBJECTS

Fifteen healthy volunteers, five from each genotype: CYP2C9*1/*1, *1/*2, and *1/*3.

INTERVENTION

A single oral dose of losartan 50 mg.

MEASUREMENTS AND MAIN RESULTS

Plasma and urine samples were collected for 24 hours, and losartan and E3174 pharmacokinetic data were compared across the three genotypes. Orthostatic blood pressure was measured over 12 hours after dosing. No significant differences were observed among the three groups in losartan or E3174 area under the plasma concentration-time curve, losartan or E3174 elimination half-life, or losartan oral clearance. A significant association between CYP2C9 genotype and losartan to E3174 formation clearance was observed, such that 50% of the variability was accounted for by the genotype. No significant relationship between that genotype and blood pressure was observed at any time.

CONCLUSION

Differences in the pharmacokinetics of losartan and its active E3174 metabolite were not observed in healthy subjects with the genotype of CYP2C9*1/*2 and *1/*3 compared with those expressing *1/*1. Alterations in losartan dosing in CYP2C9*1/*2 and *1/*3 individuals does not appear necessary.

Treatment with irbesartan counteracts the functional remodeling of ventricular myocytes from hypertensive rats

Changes in electrophysiological (action potential prolongation, decrease in transient outward current I(to), occurrence of the hyperpolarization-activated current I(f)) and contractile properties develop in hypertrophied ventricular myocytes, likely implicated in the increased propensity to arrhythmias. Angiotensin II is a key signal for myocyte hypertrophy; the effect of 8-week treatment with irbesartan, a type 1 angiotensin II receptor (AT(1)) antagonist, on cardiac remodeling was tested. Sixteen-month-old hypertensive rats (SHRs) were treated with irbesartan (20 mg/kg/d) or saline for 8 weeks. At the end of treatment, systolic blood pressure and heart weight to body weight ratio were reduced in irbesartan-treated compared with nontreated SHRs. Electrical and contractile properties were measured in isolated ventricular myocytes, by patch-clamp or video-dimension analysis, respectively. Action potential duration was significantly shorter in irbesartan-treated than in nontreated SHRs (at -60 mV: 119 +/- 24 ms vs 187 +/- 20 ms); correspondingly, maximal I(to) density was larger in irbesartan-treated than in nontreated SHRs (25.4 +/- 2.8 pA/pF vs 18.5 +/- 1.5 pA/pF). Maximal specific conductance of I(f) was lower in irbesartan-treated vs nontreated SHRs (24.8 +/- 3.0 pS/pF vs 35.2 +/- 4.0 pS/pF). Finally, the relaxation rate of shortening in field-stimulated intact myocytes was significantly faster in irbesartan-treated than in nontreated SHRs (7.3 +/- 0.5/s vs 5.7 +/- 0.3/s). Thus, AT(1) blockade with irbesartan, at an oral daily dosage that gave a slight but significant reduction of systolic blood pressure, largely counteracts the development of myocyte hypertrophy and associated functional alterations.

Proportion of treatment effect (PTE) explained by a surrogate marker

In time-varying covariate analysis of clinical survival data, it is often of interest to estimate the proportion of treatment effect (PTE), along with its confidence intervals, explained by a surrogate marker. The conventional procedure for such an analysis fits data into two working models separately to estimate the treatment effects before and after adjustment of the covariate. The construction of confidence intervals for the PTE under the conventional procedure lacks support by standard statistical software such as SAS, and could be very computationally demanding even after the support is available in the future. To overcome this problem, we propose a new procedure to simplify the computation. Under the new procedure, the treatment effects before and after adjustment of the covariate are simultaneously estimated from a single model. More important than saving computational effort, the new procedure can also be effectively applied to multiple-covariate models for the decomposition of overall treatment effect and for the comparison of PTE among several surrogate markers. The new procedure is applied to the motivating data example from the LIFE study, and demonstrates flexibility that the conventional procedure currently lacks.

Risk-benefit assessment of angiotensin II receptor antagonists

Inhibiting the renin-angiotensin-aldosterone system through the use of angiotensin-converting enzyme (ACE) inhibitors has proven very useful in the treatment of hypertension, congestive heart failure (CHF) and progressive renal failure. More recently, agents that directly block the angiotensin II Type 1 (AT(1)) receptor--angiotensin II receptor antagonists (AIIRAs)--have been developed. These agents are thought to have a more specific mechanism of action since they do not affect other hormone systems as do the ACE inhibitors. Whether such specificity results in a different efficacy profile is still being determined. However, these drugs are extremely well-tolerated and very safe. AIIRAs are effective in the reduction of both systolic and diastolic blood pressure and compare favourably to other classes of agents. Recent results indicate that at least one AIIRA has a favourable effect on stroke in hypertensive patients with left ventricular hypertrophy. Additional studies with other members of the class will provide further information on similar outcomes. In CHF patients, ACE inhibitors remain the drug of choice and AIIRAs are best utilised in patients who cannot tolerate an ACE inhibitor or in those receiving an ACE inhibitor who cannot tolerate a beta-blocker and need additional therapy. AIIRAs are effective in slowing the progression of renal failure in patients with Type II diabetes and may be effective in other proteinuric conditions. Whether they are more or less effective than ACE inhibitors is unknown. Overall, AIIRAs represent an important addition to the armamentarium of cardiovascular therapies with an excellent safety record and an emerging profile of utility in multiple cardiovascular conditions.