Sartan-AT1 receptor interactions: in vitro evidence for insurmountable antagonism and inverse agonism

Elucidating nonlinear pharmacokinetics of telmisartan: Integration of target-mediated drug disposition and OATP1B3-mediated hepatic uptake in a physiologically based model

Telmisartan, a selective inhibitor of angiotensin II receptor type 1 (AT1), demonstrates nonlinear pharmacokinetics (PK) when orally administered in ascending doses to healthy volunteers, but the underlying mechanisms remain unclear. This study presents a physiologically based pharmacokinetic model integrated with target-mediated drug disposition (TMDD-PBPK model) to explore the mechanism of its nonlinear PK. We employed the Cluster-Gauss Newton method for top-down analysis, estimating the in vivo Km,OATP1B3 (Michaelis-Menten constant for telmisartan hepatic uptake via Organic Anion Transporting Polypeptide 1B3) to be 2.0-5.7 nM. This range is significantly lower than the reported in vitro value of 810 nM, obtained in 0.3% human serum albumin (HSA) conditions. Further validation was achieved through in vitro assessment in plated human hepatocytes with 4.5% HSA, showing a Km of 4.5 nM. These results underscore the importance of albumin-mediated uptake effect for the hepatic uptake of telmisartan. Our TMDD-PBPK model, developed through a "middle-out" approach, underwent sensitivity analysis to identify key factors in the nonlinear PK of telmisartan. We found that the nonlinearity in the area under the concentration-time curve (AUC) and/or maximum concentration (Cmax) of telmisartan is sensitive to Km,OATP1B3 across all dosages. Additionally, the dissociation constant (Kd) for telmisartan binding to the AT1 receptor, along with its receptor abundance, notably influences PK at lower doses (below 20 mg). In conclusion, the nonlinear PK of telmisartan appears primarily driven by hepatic uptake saturation across all dose ranges and by AT1-receptor binding saturation, notably at lower doses.

Anti-hypertensive effect of a novel angiotensin II receptor neprilysin inhibitor (ARNi) -S086 in DSS rat model

Introduction

Angiotensin receptor-neprilysin inhibitor (ARNi), comprised of an angiotensin receptor blocker (ARB) and a neprilysin inhibitor (NEPi), has established itself as a safe and effective intervention for hypertension. S086 is a novel ARNi cocrystal developed by Salubris for the treatment of heart failure and hypertension.

Methods

Dahl Salt Sensitive (DSS) hypertensive rat model and telemetry system were employed in this study to investigate the anti-hypertensive efficacy of S086 and compare it with the first ARNi-LCZ696.

Results and discussion

The study showed that oral administration of S086 dose-dependently lowered blood pressure (P < 0.001). The middle dosage of S086 (23 mg/kg) exhibited efficacy comparable to LCZ696 (68 mg/kg), while also demonstrating superiority at specific time points (P < 0.05). Notably, water consumption slightly decreased post-treatment compared to the vehicle group. Furthermore, there were significant increases in natriuresis and diuresis observed on the first day of treatment with 23 mg/kg and 68 mg/kg S086 (P < 0.001). However, over the course of treatment, the effects in all treatment groups gradually diminished. This study demonstrates the anti-hypertensive efficacy of S086 in DSS hypertensive rat model, offering promising avenues for the clinical development of S086 as a hypertension treatment.

Effect of Azilsartan on clinical blood pressure reduction compared to other angiotensin receptor blockers: a systematic review and meta-analysis

Background

Hypertension has significantly contributed to morbidity and mortality, necessitating effective management. Angiotensin receptor blockers (ARBs) have emerged as a cornerstone in hypertension treatment. Azilsartan, a relatively recent addition to the ARB family, offers unique characteristics, including prodrug activation. This systematic review and meta-analysis aimed to evaluate Azilsartan's role in reducing clinical blood pressure compared to other ARBs and determine the most effective dosage.

Methods

Following PRISMA guidelines, a comprehensive literature search was conducted in Medline, Web of Science, Cochrane Library, and clinicaltrials.gov. Eligible studies included adult hypertensive patients receiving Azilsartan compared to other ARBs, with clinical systolic blood pressure (SBP) and diastolic blood pressure (DBP) outcomes. Data extraction and quality assessment were performed, and statistical analysis employed comprehensive meta-analysis (CMA) software.

Results

Eleven randomized controlled trials encompassing 18 studies involving 6024 patients were included. Azilsartan demonstrated significant reductions in clinical SBP (mean difference=-2.85 mmHg) and DBP (mean difference=-2.095 mmHg) compared to other ARBs. Higher doses of Azilsartan showed greater efficacy, with 80 mg exhibiting the most substantial reduction in SBP. The analysis emphasized the need for more studies investigating lower Azilsartan doses (10 and 20 mg).

Conclusion

This systematic review and meta-analysis underscore Azilsartan's effectiveness in reducing SBP and DBP. Dose-dependent effects emphasize the importance of optimal dosing when prescribing Azilsartan. These findings provide valuable insights for clinicians in managing hypertension effectively and call for further research, primarily focusing on lower Azilsartan doses and a more diverse patient population.

Angiotensin II-dependent aldosterone production in the adrenal cortex

The adrenal cortex is responsible for production of adrenal steroid hormones and is anatomically divided into three distinct zones: zona glomerulosa secreting mineralocorticoids (mainly aldosterone), zona fasciculata secreting glucocorticoids (cortisol), and zona reticularis producing androgens. Importantly, due to their high lipophilicity, no adrenal steroid hormone (including aldosterone) is stored in vesicles but rather gets synthesized and secreted instantly upon cell stimulation with specific stimuli. Aldosterone is the most potent mineralocorticoid hormone produced from the adrenal cortex in response to either angiotensin II (AngII) or elevated K+ levels in the blood (hyperkalemia). AngII, being a peptide, cannot cross cell membranes and thus, uses two distinct G protein-coupled receptor (GPCR) types, AngII type 1 receptor (AT1R) and AT2R to exert its effects inside cells. In zona glomerulosa cells, AT1R activation by AngII results in aldosterone synthesis and secretion via two main pathways: (a) Gq/11 proteins that activate phospholipase C ultimately raising intracellular free calcium concentration; and (b) βarrestin1 and -2 (also known as Arrestin-2 and -3, respectively) that elicit sustained extracellular signal-regulated kinase (ERK) activation. Both pathways induce upregulation and acute activation of StAR (steroidogenic acute regulatory) protein, the enzyme that catalyzes the rate-limiting step in aldosterone biosynthesis. This chapter describes these two salient pathways underlying AT1R-induced aldosterone production in zona glomerulosa cells. We also highlight some pharmacologically important notions pertaining to the efficacy of the currently available AT1R antagonists, also known as angiotensin receptor blockers (ARBs) or sartans at suppressing both pathways, i.e., their inverse agonism efficacy at G proteins and βarrestins.

Adrenal G Protein-Coupled Receptors and the Failing Heart: A Long-distance, Yet Intimate Affair

ABSTRACT

Systolic heart failure (HF) is a chronic clinical syndrome characterized by the reduction in cardiac function and still remains the disease with the highest mortality worldwide. Despite considerable advances in pharmacological treatment, HF represents a severe clinical and social burden. Chronic human HF is characterized by several important neurohormonal perturbations, emanating from both the autonomic nervous system and the adrenal glands. Circulating catecholamines (norepinephrine and epinephrine) and aldosterone elevations are among the salient alterations that confer significant hormonal burden on the already compromised function of the failing heart. This is why sympatholytic treatments (such as β-blockers) and renin-angiotensin system inhibitors or mineralocorticoid receptor antagonists, which block the effects of angiotensin II (AngII) and aldosterone on the failing heart, are part of the mainstay HF pharmacotherapy presently. The adrenal gland plays an important role in the modulation of cardiac neurohormonal stress because it is the source of almost all aldosterone, of all epinephrine, and of a significant amount of norepinephrine reaching the failing myocardium from the blood circulation. Synthesis and release of these hormones in the adrenals is tightly regulated by adrenal G protein-coupled receptors (GPCRs), such as adrenergic receptors and AngII receptors. In this review, we discuss important aspects of adrenal GPCR signaling and regulation, as they pertain to modulation of cardiac function in the context of chronic HF, by focusing on the 2 best studied adrenal GPCR types in that context, adrenergic receptors and AngII receptors (AT 1 Rs). Particular emphasis is given to findings from the past decade and a half that highlight the emerging roles of the GPCR-kinases and the β-arrestins in the adrenals, 2 protein families that regulate the signaling and functioning of GPCRs in all tissues, including the myocardium and the adrenal gland.

Structural perspectives on the mechanism of signal activation, ligand selectivity and allosteric modulation in angiotensin receptors: IUPHAR Review 34

Functional advances have guided our knowledge of physiological and fatal pathological mechanisms of the hormone angiotensin II (AngII) and its antagonists. Such studies revealed that tissue response to a given dose of the hormone or its antagonist depends on receptors that engage the ligand. Thus, we need to know much more about the structures of receptor-ligand complexes at high resolution. Recently, X-ray structures of both AngII receptors (AT1 and AT2 receptors) bound to peptide and non-peptide ligands have been elucidated, providing new opportunities to examine the dynamic fluxes in the 3D architecture of the receptors, as the basis of ligand selectivity, efficacy, and regulation of the molecular functions of the receptors. Constituent structural motifs cooperatively transform ligand selectivity into specific functions, thus conceptualizing the primacy of the 3D structure over individual motifs of receptors. This review covers the new data elucidating the structural dynamics of AngII receptors and how structural knowledge can be transformative in understanding the mechanisms underlying the physiology of AngII.

Pharmacodynamic model of slow reversible binding and its applications in pharmacokinetic/pharmacodynamic modeling: review and tutorial

Therapeutic responses of most drugs are initiated by the rate and degree of binding to their receptors or targets. The law of mass action describes the rate of drug-receptor complex association (k_on) and dissociation (k_off) where the ratio k_off/k_on is the equilibrium dissociation constant (K_d). Drugs with slow reversible binding (SRB) often demonstrate delayed onset and prolonged pharmacodynamic effects. This report reviews evidence for drugs with SRB features, describes previous pharmacokinetic/pharmacodynamic (PK/PD) modeling efforts of several such drugs, provides a tutorial on the mathematics and properties of SRB models, demonstrates applications of SRB models to additional compounds, and compares PK/PD fittings of SRB with other mechanistic models. We identified and summarized 52 drugs with in vitro-confirmed SRB from a PubMed literature search. Simulations with a SRB model and observed PK/PD profiles showed delayed and prolonged responses and that increasing doses/k_on or decreasing k_off led to greater expected maximum effects and a longer duration of effects. Recession slopes for return of responses to baseline after single doses were nearly linear with an inflection point that approaches a limiting value at larger doses. The SRB model newly captured literature data for the antihypertensive effects of candesartan and antiallergic effects of noberastine. Their PD profiles could also be fitted with indirect response and biophase models with minimal differences. The applicability of SRB models is probably commonplace, but underappreciated, owing to the need for in vitro confirmation of binding kinetics and the similarity of PK/PD profiles to models with other mechanistic determinants.

TMAO Suppresses Megalin Expression and Albumin Uptake in Human Proximal Tubular Cells Via PI3K and ERK Signaling

Trimethylamine-N-oxide (TMAO) is a uremic toxin, which has been associated with chronic kidney disease (CKD). Renal tubular epithelial cells play a central role in the pathophysiology of CKD. Megalin is an albumin-binding surface receptor on tubular epithelial cells, which is indispensable for urine protein reabsorption. To date, no studies have investigated the effect of TMAO on megalin expression and the functional properties of human tubular epithelial cells. The aim of this study was first to identify the functional effect of TMAO on human renal proximal tubular cells and second, to unravel the effects of TMAO on megalin-cubilin receptor expression. We found through global gene expression analysis that TMAO was associated with kidney disease. The microarray analysis also showed that megalin expression was suppressed by TMAO, which was also validated at the gene and protein level. High glucose and TMAO was shown to downregulate megalin expression and albumin uptake similarly. We also found that TMAO suppressed megalin expression via PI3K and ERK signaling. Furthermore, we showed that candesartan, dapagliflozin and enalaprilat counteracted the suppressive effect of TMAO on megalin expression. Our results may further help us unravel the role of TMAO in CKD development and to identify new therapeutic targets to counteract TMAOs effects.

Cardiovascular angiotensin II type 1 receptor biased signaling: Focus on non-Gq-, non-βarrestin-dependent signaling

The physiological and pathophysiological roles of the angiotensin II type 1 (AT₁) receptor, a G protein-coupled receptor ubiquitously expressed throughout the cardiovascular system, have been the focus of intense investigations for decades. The success of angiotensin converting enzyme inhibitors (ACEIs) and of angiotensin receptor blockers (ARBs), which are AT₁R-selective antagonists/inverse agonists, in the treatment of heart disease is a testament to the importance of this receptor for cardiovascular homeostasis. Given the pleiotropic signaling of the cardiovascular AT₁R and, in an effort to develop yet better drugs for heart disease, the concept of biased signaling has been exploited to design and develop biased AT₁R ligands that selectively activate β-arrestin transduction pathways over G_q protein-dependent pathways. However, by focusing solely on G_q or β-arrestins, studies on AT₁R "biased" signaling & agonism tend to largely ignore other non-Gq-, non β-arrestin-dependent signaling modalities the very versatile AT₁R employs in cardiovascular tissues, including two very important types of signal transducers/regulators: other G protein types (e.g., G_i/o, G_12/13) & the Regulator of G protein Signaling (RGS) proteins. In this review, we provide a brief overview of the current state of cardiovascular AT₁R biased signaling field with a special focus on the non-Gq-, non β-arrestin-dependent signaling avenues of this receptor in the cardiovascular system, which usually get left out of the conversation of "biased" AT₁R signal transduction.

The Number of Pills, Rather Than the Type of Renin-Angiotensin System Inhibitor, Predicts Ambulatory Blood Pressure Control in Essential Hypertensives on Triple Therapy: A Real-Life Cross-Sectional Study

Introduction

We evaluated the prevalence and predictors of ambulatory blood pressure (BP) control in patients taking a triple antihypertensive therapy (renin–angiotensin system inhibitor + calcium channel blocker + thiazide/thiazide-like diuretic, in either free or fixed-dose combinations) containing an angiotensin-converting enzyme inhibitor (ACEi) or an angiotensin receptor blocker (ARB).

Methods

We performed an observational cross-sectional study on 520 consecutive patients with essential hypertension taking a stable triple therapy in whom 24-h ambulatory BP was evaluated. Both number of pills and antihypertensive treatment intensity (ATI), as possible pharmacological predictors of ambulatory BP control, were taken into account.

Results

A total of 189 (36.3%) patients were taking triple therapy with ACEi and 331 (63.7%) patients were taking triple therapy with ARB. Mean age was 62.7 ± 12.2 years. Patients on triple therapy with ACEi had a significantly lower ATI and took fewer antihypertensive pills than patients on triple therapy with ARB (22.2% of patients took a single-pill triple fixed-dose combination). Patients taking triple therapy with ACEi had higher prevalence of both 24-h (54.8% vs 44.0%; p = 0.019) and daytime BP control (61.8% vs 49.2%; p = 0.006) than patients taking triple therapy with ARB, even after adjusting for age, sex, body mass index, smoking habit, type 2 diabetes mellitus, estimated glomerular filtration rate, and ATI [OR 1.5 (95% CI 1.1–2.2) and OR 1.6 (95% CI 1.1–2.4), respectively]. However, these independent associations with ambulatory BP control were lost when the number of antihypertensive pills was included in the model.

Conclusion

The higher prevalence of ambulatory BP control found in patients taking a triple therapy with ACEi was affected by the lower number of antihypertensive pills taken, which was also the key predictor of ambulatory BP control in our study. This confirms the importance of fixed-dose combinations in the management of essential hypertension.

Evolution of the drug-target residence time model

IntroductionThe pharmacological action of a drug is linked to its affinity for a specific molecular target as quantified by in vitro equilibrium measurements. However, it is clear that for many highly effective drugs, interactions with their molecular targets do not conform to simple, equilibrium conditions in vivo and this results in a temporal discordance between pharmacokinetics and pharmacodynamics. The drug-target residence time model was developed to provide a theoretical framework with which to understand cases in which very slow dissociation of the drug-target complex in vivo results in durable PD effects even after systemic concentrations of drug have waned.Area coveredIn this article, the author provides a brief description of the drug-target residence time model and focuses on the refinements that have been made to the original model to incorporate the influences of compound rebinding in cells and pharmacokinetic properties of drug molecules.Expert opinionThere is now overwhelming evidence for the utility of the drug-target residence time model as a framework for understanding in vivo drug action. The in vitro measured residence time (τ_R) must be used in concert with equilibrium measures of drug-target affinity (e.g. IC₅₀) and with in vivo measures of pharmacokinetic half-life, to afford the researcher a powerful approach to compound optimization for clinical effect. Despite the significant use and refinement of this model, continued studies are required to better understand the dynamic interplay between residence time, target pathobiology, drug distribution and drug pharmacokinetics.

Adrenal angiotensin II type 1 receptor biased signaling: The case for "biased" inverse agonism for effective aldosterone suppression

Angiotensin II (AngII) uses two distinct G protein-coupled receptor (GPCR) types, AT₁R and AT₂R, to exert a plethora of physiologic effects in the body and to significantly affect cardiovascular homeostasis. Although not much is known about the signaling of the AT₂R, AT₁R signaling is known to be quite pleiotropic, mobilizing a variety of signal transducers inside cells to produce a biological outcome. When the outcome in question is aldosterone production from the adrenal cortex, the main transducers activated specifically by the adrenocortical AT₁R to signal toward that cellular effect are the G_q/11 protein alpha subunits and the β-arrestins (also known as Arrestin-2 and -3). The existence of various downstream pathways the AT₁R signal can travel down on has led to the ever-expanding filed of GPCR pharmacology termed "biased" signaling, which refers to a ligand preferentially activating one signaling pathway over others downstream of the same receptor in the same cell. However, "biased" signaling or "biased" agonism is therapeutically desirable only when the downstream pathways lead to different or opposite cellular outcomes, so the pathway promoting the beneficial effect can be selectively activated over the pathway that leads to detrimental consequences. In the case of the adrenal AT₁R, both G_q/11 proteins and β-arrestins mediate signaling to the same end-result: aldosterone synthesis and secretion. Therefore, both pathways need to remain inactive in the adrenal cortex to fully suppress the production of aldosterone, which is one of the culprit hormones elevated in chronic heart failure, hypertension, and various other cardiovascular diseases. Variations in the effectiveness of the AT₁R antagonists, which constitute the angiotensin receptor blocker (ARB) class of drugs (also known as sartans), at the relative blockade of these two pathways downstream of the adrenal AT₁R opens the door to the flip term "biased" inverse agonism at the AT₁R. ARBs that are unbiased and equipotent inverse agonists for both G proteins and β-arrestins at this receptor, like candesartan and valsartan, are the most preferred agents with the best efficacy at reducing circulating aldosterone, thereby ameliorating heart failure. In the present review, the biased signaling of the adrenal AT₁R, particularly in relation to aldosterone production, is examined and the term "biased" inverse agonism at the AT₁R is introduced and explained, as a means of pharmacological categorization of the various agents within the ARB drug class.

Is the newest angiotensin-receptor blocker azilsartan medoxomil more efficacious in lowering blood pressure than the older ones? A systematic review and network meta-analysis

Angiotensin‐receptor blockers are often considered insufficiently efficacious in reducing blood pressure. However, newer angiotensin‐receptor blockers may be more effective than the older ones. A network meta‐analysis was performed to compare the efficacy of various angiotensin‐receptor blockers in reducing office and ambulatory blood pressure in hypertensive patients. Relevant literature was searched from English and Chinese databases for randomized controlled trials involving angiotensin‐receptor blockers in hypertension. Efficacy variables included systolic and diastolic blood pressure either in the office or on ambulatory blood pressure monitoring. Absolute blood pressure reductions at 6‐12 weeks of treatment and their credible intervals were reported. A total of 34 publications provided adequate data for analysis (n = 14 859). In 28 studies on office systolic blood pressure (n = 12 731), against the common comparator valsartan 80 mg, the differences in systolic blood pressure were in favor of azilsartan medoxomil (20‐80 mg), irbesartan (300 mg), olmesartan (20‐40 mg), telmisartan (80 mg), and valsartan (160‐320 mg), but not candesartan (8‐16 mg), losartan (50‐100 mg), irbesartan (150 mg), olmesartan (10 mg), and telmisartan (40 mg). The ranking plot shows that azilsartan medoxomil 80 mg had a possibility of 99% being the best in the class. Similar results were observed for office diastolic blood pressure and from 13 studies for 24‐hour ambulatory systolic and diastolic blood pressure. In conclusion, angiotensin‐receptor blockers had different blood pressure lowering efficacy. The newest angiotensin‐receptor blocker azilsartan medoxomil at the dose of 80 mg seemed to be most efficacious in reducing both systolic and diastolic blood pressure in the office and on ambulatory measurement.

Perspective: Implications of Ligand-Receptor Binding Kinetics for Therapeutic Targeting of G Protein-Coupled Receptors

The concept of ligand-receptor binding kinetics has been broadly applied in drug development pipelines focusing on G protein-coupled receptors (GPCRs). The ligand residence time (RT) for a receptor describes how long a ligand-receptor complex exists, and is defined as the reciprocal of the dissociation rate constant (k _off). RT has turned out to be a valuable parameter for GPCR researchers focusing on drug development as a good predictor of in vivo efficacy. The positive correlation between RT and in vivo efficacy has been established for several drugs targeting class A GPCRs (e.g., the neurokinin-1 receptor (NK₁R), the β₂ adrenergic receptor (β₂AR), and the muscarinic 3 receptor (M₃R)) and for drugs targeting class B1 (e.g., the glucagon-like peptide 1 receptor (GLP-1R)). Recently, the association rate constant (k _on) has gained similar attention as another parameter affecting in vivo efficacy. In the current perspective, we address the importance of studying ligand-receptor binding kinetics for therapeutic targeting of GPCRs, with an emphasis on how binding kinetics can be altered by subtle molecular changes in the ligands and/or the receptors and how such changes affect treatment outcome. Moreover, we speculate on the impact of binding kinetic parameters for functional selectivity and sustained receptor signaling from endosomal compartments; phenomena that have gained increasing interest in attempts to improve therapeutic targeting of GPCRs.

The place of ARBs in heart failure therapy: is aldosterone suppression the key?

Since the launch of the first orally available angiotensin II (AngII) type 1 receptor (AT₁R) blocker (ARB) losartan (Cozaar) in the late 1990s, the class of ARBs (or ‘sartans’, short for Angiotensin-RecepTor-ANtagonistS) quickly expanded to include candesartan, eprosartan, irbesartan, valsartan, telmisartan, and olmesartan. All ARBs have high affinity for the AT₁ receptor, expressed in various tissues, including smooth muscle cells, heart, kidney, and brain. Since activation of AT₁R, the target of these drugs, leads, among other effects, to vascular smooth muscle cell growth, proliferation and contraction, activation of fibroblasts, cardiac hypertrophy, aldosterone secretion from the adrenal cortex, thirst-fluid intake (hypervolemia), etc., the ARBs are nowadays one of the most useful cardiovascular drug classes used in clinical practice. However, significant differences in their pharmacological and clinical properties exist that may favor use of particular agents over others within the class, and, in fact, two of these drugs, candesartan and valsartan, continuously appear to distinguish themselves from the rest of the ‘pack’ in recent clinical trials. The reason(s) for the potential superiority of these two agents within the ARB class are currently unclear but under intense investigation. The present short review gives an overview of the clinical properties of the ARBs currently approved by the United States Food and Drug Administration, with a particular focus on candesartan and valsartan and the areas where these two drugs seem to have a therapeutic edge. In the second part of our review, we outline recent data from our laboratory (mainly) on the molecular effects of the ARB drugs on aldosterone production and on circulating aldosterone levels, which may underlie (at least in part) the apparent clinical superiority of candesartan (and valsartan) over most other ARBs currently in clinical use.

Angiotensin Analogs with Divergent Bias Stabilize Distinct Receptor Conformations

"Biased" G protein-coupled receptor (GPCR) agonists preferentially activate pathways mediated by G proteins or β-arrestins. Here, we use double electron-electron resonance spectroscopy to probe the changes that ligands induce in the conformational distribution of the angiotensin II type I receptor. Monitoring distances between 10 pairs of nitroxide labels distributed across the intracellular regions enabled mapping of four underlying sets of conformations. Ligands from different functional classes have distinct, characteristic effects on the conformational heterogeneity of the receptor. Compared to angiotensin II, the endogenous agonist, agonists with enhanced Gq coupling more strongly stabilize an "open" conformation with an accessible transducer-binding site. β-arrestin-biased agonists deficient in Gq coupling do not stabilize this open conformation but instead favor two more occluded conformations. These data suggest a structural mechanism for biased ligand action at the angiotensin receptor that can be exploited to rationally design GPCR-targeting drugs with greater specificity of action.

Distinctive Activation Mechanism for Angiotensin Receptor Revealed by a Synthetic Nanobody

The angiotensin II (AngII) type 1 receptor (AT1R) is a critical regulator of cardiovascular and renal function and is an important model for studies of G-protein-coupled receptor (GPCR) signaling. By stabilizing the receptor with a single-domain antibody fragment ("nanobody") discovered using a synthetic yeast-displayed library, we determined the crystal structure of active-state human AT1R bound to an AngII analog with partial agonist activity. The nanobody binds to the receptor's intracellular transducer pocket, stabilizing the large conformational changes characteristic of activated GPCRs. The peptide engages the AT1R through an extensive interface spanning from the receptor core to its extracellular face and N terminus, remodeling the ligand-binding cavity. Remarkably, the mechanism used to propagate conformational changes through the receptor diverges from other GPCRs at several key sites, highlighting the diversity of allosteric mechanisms among GPCRs. Our structure provides insight into how AngII and its analogs stimulate full or biased signaling, respectively.

Cardiovascular risk in type 2 diabetes patients

Cardiovascular diseases remain leading cause of high mortality in diabetes patients. The article is focused on the influence of diabetes on cardiovascular risks. The prevalence presented, as the significance of the main and additional risk factors of cardiovascular diseases in the development of macrovascular complications in diabetes. In the context of influence on cardiovascular risks, modern glucose lowering drugs are considered, the safety and efficacy properties. Advantages of dapagliflozin underscored, the novel oral drug of new generation, with safe and prominent antidiabetic effect and ability to correct the main factors of cardiovascular risk (obesity, hypertension).

Oral vitamin-A-coupled valsartan nanomedicine: High hepatic stellate cell receptors accessibility and prolonged enterohepatic residence

So far, liver fibrosis still has no clinically-approved treatment. The loss of stored vitamin-A (V_A) in hepatic stellate cells (HSCs), the main regulators to hepatic fibrosis, can be applied as a mechanism for their targeting. Valsartan is a good candidate for this approach; it is a marketed oral-therapy with inverse- and partial-agonistic activity to the over-expressed angiotensin-II type1 receptor (AT1R) and depleted nuclear peroxisome proliferator-activated receptor-gamma (PPAR-γ), respectively, in activated HSCs. However, efficacy on AT1R and PPAR-γ necessitates high drug permeability which is lacking in valsartan. In the current study, liposomes were used as nanocarriers for valsartan to improve its permeability and hence efficacy. They were coupled to V_A and characterized for HSCs-targeting. Tracing of orally-administered fluorescently-labeled V_A-coupled liposomes in normal rats and their fluorescence intensity quantification in different organs convincingly demonstrated their intestinal entrapment. On the other hands, their administration to rats with induced fibrosis revealed preferential hepatic, and less intestinal, accumulation which lasted up to six days. This indicated their uptake by intestinal stellate cells that acted as a depot for their release over time. Confocal microscopical examination of immunofluorescently-stained HSCs in liver sections, with considerable formula accumulation, confirmed HSCs-targeting and nuclear uptake. Consequently, V_A-coupled valsartan-loaded liposomes (VLC)-therapy resulted in profound re-expression of hepatic Mas-receptor and PPAR-γ, potent reduction of fibrogenic mediators' level and nearly normal liver function tests. Therefore, VLC epitomizes a promising antifibrotic therapy with exceptional extended action and additional PPAR-γ agonistic activity.

Neuroprotective effects of AT1 receptor antagonists after experimental ischemic stroke: what is important?

The present study conducted in rats defines the requirements for neuroprotective effects of systemically administered AT1 receptor blockers (ARBs) in acute ischaemic stroke. The inhibition of central effects to angiotensin II (ANG II) after intravenous (i.v.) treatment with candesartan (0.3 and 3 mg/kg) or irbesartan and losartan (3 and 30 mg/kg) was employed to study the penetration of these ARBs across the blood-brain barrier. Verapamil and probenecid were used to assess the role of the transporters, P-glycoprotein and the multidrug resistance-related protein 2, in the entry of losartan and irbesartan into the brain. Neuroprotective effects of i.v. treatment with the ARBs were investigated after transient middle cerebral artery occlusion (MCAO) for 90 min. The treatment with the ARBs was initiated 3 h after the onset of MCAO and continued for two consecutive days. Blood pressure was continuously recorded before and during MCAO until 5.5 h after the onset of reperfusion. The higher dose of candesartan completely abolished, and the lower dose of candesartan and higher doses of irbesartan and losartan partially inhibited the drinking response to intracerebroventricular ANG II. Only 0.3 mg/kg candesartan improved the recovery from ischaemic stroke, and 3 mg/kg candesartan did not exert neuroprotective effects due to marked blood pressure reduction during reperfusion. Both doses of irbesartan and losartan had not any effect on the stroke outcome. An effective, long-lasting blockade of brain AT1 receptors after systemic treatment with ARBs without extensive blood pressure reductions is the prerequisite for neuroprotective effects in ischaemic stroke.

Current topics in angiotensin II type 1 receptor research: Focus on inverse agonism, receptor dimerization and biased agonism

Although the octapeptide hormone angiotensin II (Ang II) regulates cardiovascular and renal homeostasis through the Ang II type 1 receptor (AT1R), overstimulation of AT1R causes various human diseases, such as hypertension and cardiac hypertrophy. Therefore, AT1R blockers (ARBs) have been widely used as therapeutic drugs for these diseases. Recent basic research and clinical studies have resulted in the discovery of interesting phenomena associated with AT1R function. For example, ligand-independent activation of AT1R by mechanical stress and agonistic autoantibodies, as well as via receptor mutations, has been shown to decrease the inverse agonistic efficacy of ARBs, though the molecular mechanisms of such phenomena had remained elusive until recently. Furthermore, although AT1R is believed to exist as a monomer, recent studies have demonstrated that AT1R can homodimerize and heterodimerize with other G-protein coupled receptors (GPCR), altering the receptor signaling properties. Therefore, formation of both AT1R homodimers and AT1R-GPCR heterodimer may be involved in the pathogenesis of human disease states, such as atherosclerosis and preeclampsia. Finally, biased AT1R ligands that can preferentially activate the β-arrestin-mediated signaling pathway have been discovered. Such β-arrestin-biased AT1R ligands may be better therapeutic drugs for cardiovascular diseases. New findings on AT1R described herein could provide a conceptual framework for application of ARBs in the treatment of diseases, as well as for novel drug development. Since AT1R is an extensively studied member of the GPCR superfamily encoded in the human genome, this review is relevant for understanding the functions of other members of this superfamily.

Cost-benefit effectiveness of angiotensin-II receptor blockers in patients with uncomplicated hypertension: A comparative analysis

OBJECTIVE

The treatment of hypertensive patients (HTs) requires a long-term commitment of compliance for the patient and resources by the healthcare system. This poses an economic dilemma in countries where universal healthcare is standard. The aim of this study was to evaluate the costs/health benefit and effectiveness of treatment with angiotensin-II receptor blockers (ARBs) in uncomplicated essential hypertension.

DESIGN AND METHODS

The daily and annual economic commitment for treating patients with ARBs was estimated using pharmacy dispensing records and the BP-lowering effects of candesartan, irbesartan, losartan, olmesartan, telmisartan and valsartan was evaluated retrospectively. In 114 HTs (mean age 59.4±13.5year, 57.5% men), the BP-lowering effect of ARBs as in monotherapy and in fixed-dose combination (FDC) with hydrochlorothiazide at the doses commonly used in the market to reach BP control (i.e. BP <140/90mmHg) was analyzed. The BP lowering-effect was evaluated after an average of 6-month follow-up consulting medical professionals. Analysis of variance for repeated measures was provided.

RESULTS

Treatment with candesartan (14.1%) and olmesartan (32,4%) versus other ARBs resulted in a significant decrease in BP as for mono- than for FDC therapy. Our studies suggest that daily (data not shown) and annual costs of olmesartan were higher than candesartan as in mono- (4577.71±1120.55 vs. 894.25±127.75 €) than for FDC therapy (5715.90±459.90 vs. 1580.45±113.15 €).

CONCLUSIONS

Treatment: of BP with candesartan appears to be the most favorable option in terms of cost-effectiveness coupled with favorable health outcomes. These data have some limitations, but open the question if candesartan should be preferred to olmesartan in BP management. Further prospective studies comparing ARBs based on their effect on BP control in uncomplicated HTs are needed for validation.

No substantial gender differences in suspected adverse reactions to ACE inhibitors and ARBs: results from spontaneous reporting system in Campania Region

BACKGROUND

Today, there is a poor knowledge about gender differences in adverse drug reactions (ADRs) to cardiovascular drugs such as angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs). Therefore, the aim of this study was to analyze spontaneous reports of suspected ADRs induced by ACE-inhibitors and ARBs, between January 2001 and June 2015, recorded in a Region of Southern Italy (Campania Region).

METHODS

We performed a descriptive gender-related analysis of regional safety data, obtained from the spontaneous reporting system.

RESULTS

In the considered period, 772 suspected ADRs to ACE inhibitors and ARBs (in monotherapy or in combination) were reported with a slightly higher frequency in men compared with women. In both genders, the most involved category was ARBs in combination, whereas the most prescribed active substance was ramipril. General and administration site conditions, vascular disorders and modification of laboratory parameters were more common in men, while respiratory disorders were most common in women. In 88.2% of cases, not serious ADRs were described more by men than women.

CONCLUSIONS

This analysis suggested no substantial gender differences. Further studies such as randomized population studies or meta-analysis of ACE inhibitors and ARBs randomized studies are needed to clarify whether gender differences exist in the safety profile of these drugs.

Importance of tacit knowledge in incremental innovation

Purpose

The purpose of this paper is to examine the role of tacit knowledge in incremental innovation, which has hitherto been neglected.

Design/methodology/approach

Qualitative case analysis was used to focus on two large Japanese pharmaceutical companies’ development of new antihypertensive drugs. The study uses interview data and documentary research materials to explore the knowledge bases of the companies’ research teams as they refined an existing drug to produce new products – a process of incremental innovation.

Findings

Explicit knowledge (chemical structure of preceding drug) was used in both successful and failed cases of drug discovery. In the two successful cases, the tacit knowledge of key researchers, based on their long-term experience of related research, provided insight into developing compounds with good in vivo efficacy, which led to successful clinical development.

Practical implications

The findings suggest that tacit knowledge may play an important role in incremental innovation processes, and that its influence on product development should be considered in such ways as team and organization structure.

Originality/value

This study addresses a gap in the literature regarding the impact of tacit knowledge on incremental innovation processes. It is often assumed that incremental innovation is based on existing technology. This study suggests that tacit knowledge may play a hitherto largely unrecognized role in incremental product development.

Nifedipine plus candesartan combination increases blood pressure control regardless of race and improves the side effect profile: DISTINCT randomized trial results

OBJECTIVES

DISTINCT (reDefining Intervention with Studies Testing Innovative Nifedipine GITS - Candesartan Therapy) aimed to determine the dose-response and tolerability of nifedipine GITS and/or candesartan cilexetil therapy in participants with hypertension.

METHODS

In this 8-week, multinational, multicentre, randomized, double-blind, placebo-controlled study, adults with mean seated DBP of at least 95 to less than 110 mmHg received combination or monotherapy with nifedipine GITS (N) 20, 30 or 60 mg and candesartan cilexetil (C) 4, 8, 16 or 32 mg, or placebo. The primary endpoint, change in DBP from baseline to Week 8, was analysed using the response surface model (RSM); this analysis was repeated for mean seated SBP.

RESULTS

Overall, 1381 participants (mean baseline SBP/DBP: 156.5/99.6 mmHg) were randomized. Both N and C contributed independently to SBP/DBP reductions [P < 0.0001 (RSM)]. A positive dose-response was observed, with all combinations providing statistically better blood pressure (BP) reductions from baseline versus respective monotherapies (P < 0.05) and N60C32 achieving the greatest reduction [-23.8/-16.5 mmHg; P < 0.01 versus placebo (-5.3/-6.7 mmHg) and component monotherapies]. Even very low-dose (N20 and C4) therapy provided significant BP-lowering, and combination therapy was similarly effective in different racial groups. N/C combination demonstrated a lower incidence of vasodilatory adverse events than N monotherapy (18.3 versus 23.6%), including headache (5.5 versus 11.0%; P = 0.003, chi-square test) and peripheral oedema over time (3.6 versus 5.8%; n.s.).

CONCLUSION

N/C combination was effective in participants with hypertension and showed an improved side effect profile compared with N monotherapy.

On the different experimental manifestations of two-state 'induced-fit' binding of drugs to their cellular targets

'Induced-fit' binding of drugs to a target may lead to high affinity, selectivity and a long residence time, and this mechanism has been proposed to apply to many drugs with high clinical efficacy. It is a multistep process that initially involves the binding of a drug to its target to form a loose RL complex and a subsequent isomerization/conformational change to yield a tighter binding R'L state. Equations with the same mathematical form may also describe the binding of bivalent antibodies and related synthetic drugs. Based on a selected range of 'microscopic' rate constants and variables such as the ligand concentration and incubation time, we have simulated the experimental manifestations that may go along with induced-fit binding. Overall, they validate different experimental procedures that have been used over the years to identify such binding mechanisms. However, they also reveal that each of these manifestations only becomes perceptible at particular combinations of rate constants. The simulations also show that the durable nature of R'L and the propensity of R'L to be formed repeatedly before the ligand dissociates will increase the residence time. This review may help pharmacologists and medicinal chemists obtain preliminary indications for identifying an induced-fit mechanism.

A Four-Point Screening Method for Assessing Molecular Mechanism of Action (MMOA) Identifies Tideglusib as a Time-Dependent Inhibitor of Trypanosoma brucei GSK3β

Background

New therapeutics are needed for neglected tropical diseases including Human African trypanosomiasis (HAT), a progressive and fatal disease caused by the protozoan parasites Trypanosoma brucei gambiense and T. b. rhodesiense. There is a need for simple, efficient, cost effective methods to identify new molecules with unique molecular mechanisms of action (MMOAs). The mechanistic features of a binding mode, such as competition with endogenous substrates and time-dependence can affect the observed inhibitory IC₅₀, and differentiate molecules and their therapeutic usefulness. Simple screening methods to determine time-dependence and competition can be used to differentiate compounds with different MMOAs in order to identify new therapeutic opportunities.

Methodology/Principal Findings

In this work we report a four point screening methodology to evaluate the time-dependence and competition for inhibition of GSK3β protein kinase isolated from T. brucei. Using this method, we identified tideglusib as a time-dependent inhibitor whose mechanism of action is time-dependent, ATP competitive upon initial binding, which transitions to ATP non-competitive with time. The enzyme activity was not recovered following 100-fold dilution of the buffer consistent with an irreversible mechanism of action. This is in contrast to the T. brucei GSK3β inhibitor GW8510, whose inhibition was competitive with ATP, not time-dependent at all measured time points and reversible in dilution experiments. The activity of tideglusib against T. brucei parasites was confirmed by inhibition of parasite proliferation (GI₅₀ of 2.3 μM).

Conclusions/Significance

Altogether this work demonstrates a straightforward method for determining molecular mechanisms of action and its application for mechanistic differentiation of two potent TbGSK3β inhibitors. The four point MMOA method identified tideglusib as a mechanistically differentiated TbGSK3β inhibitor. Tideglusib was shown to inhibit parasite growth in this work, and has been reported to be well tolerated in one year of dosing in human clinical studies. Consequently, further supportive studies on the potential therapeutic usefulness of tideglusib for HAT are justified.

Drug discovery for neglected tropical diseases must use efficient methods due to limited resources. One preferred drug discovery strategy is target-based drug discovery. In this strategy it is assumed that drug action begins with binding of a drug to its target. However, while binding is required, it is not sufficient to describe all the molecular interactions that translate binding to a therapeutically useful response. The contribution of aspects of the molecular mechanism of action (MMOA) such as time-dependence and substrate competition can influence concentration response relationships. To address this, a four point MMOA methodology was developed to evaluate time-dependence and substrate competition. We used this method to evaluate the MMOA for T.brucei GSK3β inhibitors, and observed tideglusib to have a time-dependent, ATP-competitive mechanism that differentiated it from rapidly reversible inhibitors, such as GW8510. Adjusting the enzyme assays to account for these mechanisms showed that GW8510 and tideglusib had similar activities for TbGSK3β. However, this similarity did not translate to cellular activity, where GW-8510 was more active than tideglusib (0.12 μM to 2.3 μM, respectively). These data suggest that factors other than TbGSK3β MMOA differentiate the effect of these molecules against T. brucei.

Radioligand binding to intact cells as a tool for extended drug screening in a representative physiological context

Radioligand binding assays on intact cells offer distinct advantages to those on membrane suspensions. Major pharmacological properties like drug affinity and binding kinetics are more physiologically relevant. Complex mechanisms can be studied with a wider choice of experimental approaches and so provide insights into induced-fit type binding, receptor internalisation and even into pharmacomicrokinetic phenomena like drug rebinding and partitioning into the membrane. Hence, intact cell binding constitutes a valuable addition to the pharmacologist's toolbox.

International Union of Basic and Clinical Pharmacology. XCIX. Angiotensin Receptors: Interpreters of Pathophysiological Angiotensinergic Stimuli [corrected]

The renin angiotensin system (RAS) produced hormone peptides regulate many vital body functions. Dysfunctional signaling by receptors for RAS peptides leads to pathologic states. Nearly half of humanity today would likely benefit from modern drugs targeting these receptors. The receptors for RAS peptides consist of three G-protein-coupled receptors—the angiotensin II type 1 receptor (AT1 receptor), the angiotensin II type 2 receptor (AT2 receptor), the MAS receptor—and a type II trans-membrane zinc protein—the candidate angiotensin IV receptor (AngIV binding site). The prorenin receptor is a relatively new contender for consideration, but is not included here because the role of prorenin receptor as an independent endocrine mediator is presently unclear. The full spectrum of biologic characteristics of these receptors is still evolving, but there is evidence establishing unique roles of each receptor in cardiovascular, hemodynamic, neurologic, renal, and endothelial functions, as well as in cell proliferation, survival, matrix-cell interaction, and inflammation. Therapeutic agents targeted to these receptors are either in active use in clinical intervention of major common diseases or under evaluation for repurposing in many other disorders. Broad-spectrum influence these receptors produce in complex pathophysiological context in our body highlights their role as precise interpreters of distinctive angiotensinergic peptide cues. This review article summarizes findings published in the last 15 years on the structure, pharmacology, signaling, physiology, and disease states related to angiotensin receptors. We also discuss the challenges the pharmacologist presently faces in formally accepting newer members as established angiotensin receptors and emphasize necessary future developments.

On the 'micro'-pharmacodynamic and pharmacokinetic mechanisms that contribute to long-lasting drug action

INTRODUCTION

Optimal drug therapy often requires continuing high levels of target occupancy. Besides the traditional pharmacokinetic (PK) contribution thereto, drug-target interactions that comprise successive 'microscopic' steps as well as the intervention of the cell membrane and other 'micro'-anatomical structures nearby may help attaining this objective.

AREAS COVERED

This article reviews the 'micro'-pharmacodynamic (PD) and PK mechanisms that may increase a drug's residence time. Special focus is on induced-fit- and bivalent ligand binding models as well as on the ability of the plasma membrane surrounding the target to act as a repository for the drug (e.g., microkinetic model), to actively participate in the binding process (e.g., exosite model) and, along with microanatomical elements like synapses and interstitial spaces, to act on the drug's diffusion properties (reduction in dimensionality and drug-rebinding models).

EXPERT OPINION

The PK profile, as well as the target dissociation kinetics of a drug, may fail to account for its long-lasting efficiency in intact tissues and in vivo. This lacuna could potentially be alleviated by incorporating some of the enumerated 'microscopic' mechanisms and, to unveil them, dedicated experiments on sufficiently physiologically relevant biological material like cell monolayers can already be implemented early on in the lead optimization process.

Angiotensin II, oxidative stress and stem cell therapy: a matter of delicacy

Optimization of stem cell therapy after cardiovascular and renal injury depends on many factors, among which is stem cell donor health. The renin-angiotensin system (RAS) plays an important role in cardiovascular and renal homoeostasis and pathophysiology. It is becoming increasingly clear that the RAS affects the therapeutic performance of stem cells. In this issue of Clinical Science, Kankuri et al. dig deeper into the consequences of excessive angiotensin II signalling and reactive oxygen species (ROS) formation in the stem cell donor, applying a model of regenerative medicine after renal injury.

The MCH(1) receptor, an anti-obesity target, is allosterically inhibited by 8-methylquinoline derivatives possessing subnanomolar binding and long residence times

BACKGROUND AND PURPOSE

Melanin-concentrating hormone receptor 1 (MCH1 receptor) antagonists are being considered as anti-obesity agents. The present study reports a new class of MCH1 receptor antagonists with an 8-methylquinoline scaffold. The molecular mechanism of MCH1 receptor blockade by these antagonists was examined.

EXPERIMENTAL APPROACH

The pharmacological properties of the 8-methylquinolines as exemplified by MQ1 were evaluated by use of multiple biophysical and cell-based functional assays.

KEY RESULTS

Multiple signalling pathways for Gαi and Gαq , and β-arrestin were inhibited by MQ1. Furthermore, MQ1 produced an insurmountable antagonism, causing a rightward shift of the curve for concentration-dependent binding of MCH along with a progressive reduction of the maximal response. The dissociation kinetics for MQ1 were determined from washout experiments as well as by affinity selection-MS. In short, MQ1 was shown to be a slowly dissociating reversible MCH1 receptor blocker with a low Koff value.

CONCLUSION AND IMPLICATIONS

This is the first time that a slowly dissociating negative allosteric modulator of the MCH1 receptor has been demonstrated to inhibit the numerous signalling pathways of this receptor. The characteristics of MQ1 are superior and distinct from previously reported MCH1 receptor antagonists, making members of this chemotype attractive as drug candidates.

Agonists for the adenosine A1 receptor with tunable residence time. A Case for nonribose 4-amino-6-aryl-5-cyano-2-thiopyrimidines

We report the synthesis and evaluation of previously unreported 4-amino-6-aryl-5-cyano-2-thiopyrimidines as selective human adenosine A1 receptor (hA1AR) agonists with tunable binding kinetics, this without affecting their nanomolar affinity for the target receptor. They show a very diverse range of kinetic profiles (from 1 min (compound 52) to 1 h (compound 43)), and their structure-affinity relationships (SAR) and structure-kinetics relationships (SKR) were established. When put in perspective with the increasing importance of binding kinetics in drug discovery, these results bring new evidence of the consequences of affinity-only driven selection of drug candidates, that is, the potential elimination of slightly less active compounds that may display preferable binding kinetics.

Comparative assessment of angiotensin II type 1 receptor blockers in the treatment of acute myocardial infarction: surmountable vs. insurmountable antagonist

BACKGROUND

The mechanisms of antagonism vary between the angiotensin II type 1 receptor blockers (ARBs): insurmountable antagonism and surmountable antagonism. Recent retrospective observational studies suggest that ARBs may not have equivalent benefits in various clinical situations. The aim of this study was to compare the effect of two categories of ARBs on the long-term clinical outcomes of patients with acute myocardial infarction (AMI).

METHODS

We analyzed the large-scale, prospective, observational Korea Acute Myocardial Infarction Registry study, which enrolled 2740 AMI patients. They divided by the prescription of surmountable ARBs or insurmountable ARBs at discharge. Primary outcome was major adverse cardiac events (MACEs), defined as a composite of cardiac death, nonfatal MI, and re-percutaneous coronary intervention, coronary artery bypass graft surgery.

RESULTS

In the overall population, the MACEs rate in 1 year was significantly higher in the surmountable ARB group (14.3% vs. 11.2%, p=0.025), which was mainly due to increased cardiac death (3.3% vs. 1.9%, p=0.031). Matching by propensity-score showed consistent results (MACEs rate: 14.9% vs. 11.4%, p=0.037). In subgroup analysis, the insurmountable ARB treatment significantly reduced the incidence of MACEs in patients with left ventricular ejection fraction greater than 40%, with a low killip class, with ST segment elevation MI, and with normal renal function.

CONCLUSIONS

In our study, insurmountable ARBs were more effective on long-term clinical outcomes than surmountable ARBs in patients with AMI.

AT1 receptor blocker potentiates shear-stress induced nitric oxide production via modulation of eNOS phosphorylation of residues Thr(495) and Ser(1177.)

We tested the hypothesis that AT1R blockade modulates the shear stress-induced (SS) synthesis of nitric oxide (NO) in endothelial cells (EC). The AT1R blocker Candesartan in the absence of the ligand angiotensin II (ang II) potentiated SS-induced NO synthesis accompanied by increased p-eNOS(Ser1177) and decreased p-eNOS(Thr495). Candesartan also inhibited SS-induced ERK activation and increased intracellular calcium transient in a time-dependent manner. To confirm the role of ERK to modulate p-eNOS(Thr495) and calcium to modulate p-eNOS(Ser1177), the MEK inhibitor U0126 and the calcium chelator BAPTA-AM were used, respectively. Pre-treatment of EC with U0126 completed abrogated basal and SS-induced ERK activation, inhibited p-eNOS(Thr495) and increased NO production by SS. On the other hand, pre-treatment of EC with BAPTA-AM decreased the effects of SS alone or in combination with Candesartan to induce p-eNOS(Ser1177) and partially inhibited the effects of Candesartan to potentiate NO release by SS. The AT1R blockers Losartan and Telmisartan were also tested but only Telmisartan potentiated NO synthesis and blocked SS-induced AT1R activation. Altogether, we provide evidence that Candesartan and Telmisartan potentiate SS-induced NO production even in the absence of the ligand ang II. This response requires both the inhibition of eNOS phosphorylation at its inhibitory residue Thr(495) as well as the increase of eNOS phosphorylation at its excitatory residue Ser(1177). In addition, the response is associated with inhibition of SS-induced ERK activation as well as increasing intracellular calcium transient. One may speculate that these yet undescribed events may contribute to the benefits of ARBs in cardiovascular diseases.

Novel role of mechanosensitive AT1B receptors in myogenic vasoconstriction

Myogenic vasoconstriction is an inherent property of vascular smooth muscle cells (VSMCs) of resistance arteries harboring ill-defined mechanosensing and mechanotransducing elements. G protein-coupled receptors (GPCRs) are discussed as mechanosensors in VSMCs. In this study, we sought to identify and characterize the role and impact of GPCRs on myogenic vasoconstriction. Thus, we analyzed mRNA expression levels of GPCRs in resistance versus preceding conduit arteries revealing a significant enrichment of several GPCRs in resistance vessels. Selective pharmacological blockade of the highly expressed GPCRs in isolated murine mesenteric arteries ex vivo decreased myogenic vasoconstriction. In particular, candesartan and losartan most prominently suppressed myogenic tone, suggesting that AT1 receptors play a central role in myogenic vasoconstriction. Analyzing angiotensinogen(-/-) mice, a relevant contribution of locally produced angiotensin II to myogenic tone could be excluded. Investigation of AT1A (-/-) and AT1B (-/-) murine mesenteric arteries revealed that AT1B, but not AT1A, receptors are key components of myogenic regulation. This notion was supported by examining fura-2-loaded isolated AT1A (-/-) and AT1B (-/-) VSMCs. Our results indicate that in VSMCs, AT1B receptors are more mechanosensitive than AT1A receptors even at comparable receptor expression levels. Furthermore, we demonstrate that the mechanosensitivity of GPCRs is agonist-independent and positively correlates with receptor expression levels.

Structure-kinetic relationships--an overlooked parameter in hit-to-lead optimization: a case of cyclopentylamines as chemokine receptor 2 antagonists

Preclinical models of inflammatory diseases (e.g., neuropathic pain, rheumatoid arthritis, and multiple sclerosis) have pointed to a critical role of the chemokine receptor 2 (CCR2) and chemokine ligand 2 (CCL2). However, one of the biggest problems of high-affinity inhibitors of CCR2 is their lack of efficacy in clinical trials. We report a new approach for the design of high-affinity and long-residence-time CCR2 antagonists. We developed a new competition association assay for CCR2, which allows us to investigate the relation of the structure of the ligand and its receptor residence time [i.e., structure-kinetic relationship (SKR)] next to a traditional structure-affinity relationship (SAR). By applying combined knowledge of SAR and SKR, we were able to re-evaluate the hit-to-lead process of cyclopentylamines as CCR2 antagonists. Affinity-based optimization yielded compound 1 with good binding (Ki = 6.8 nM) but very short residence time (2.4 min). However, when the optimization was also based on residence time, the hit-to-lead process yielded compound 22a, a new high-affinity CCR2 antagonist (3.6 nM), with a residence time of 135 min.

A systematic comparison of the properties of clinically used angiotensin II type 1 receptor antagonists

Angiotensin II type 1 receptor antagonists (ARBs) have become an important drug class in the treatment of hypertension and heart failure and the protection from diabetic nephropathy. Eight ARBs are clinically available [azilsartan, candesartan, eprosartan, irbesartan, losartan, olmesartan, telmisartan, valsartan]. Azilsartan (in some countries), candesartan, and olmesartan are orally administered as prodrugs, whereas the blocking action of some is mediated through active metabolites. On the basis of their chemical structures, ARBs use different binding pockets in the receptor, which are associated with differences in dissociation times and, in most cases, apparently insurmountable antagonism. The physicochemical differences between ARBs also manifest in different tissue penetration, including passage through the blood-brain barrier. Differences in binding mode and tissue penetration are also associated with differences in pharmacokinetic profile, particularly duration of action. Although generally highly specific for angiotensin II type 1 receptors, some ARBs, particularly telmisartan, are partial agonists at peroxisome proliferator-activated receptor-γ. All of these properties are comprehensively reviewed in this article. Although there is general consensus that a continuous receptor blockade over a 24-hour period is desirable, the clinical relevance of other pharmacological differences between individual ARBs remains to be assessed.

Sympathoinhibitory effects of telmisartan through the reduction of oxidative stress in the rostral ventrolateral medulla of obesity-induced hypertensive rats

OBJECTIVES

Sympathetic nervous system (SNS) activity is critically involved in the development and progression of obesity-induced hypertension. Angiotensin II type 1 receptor (AT1R)-induced oxidative stress in the rostral ventrolateral medulla (RVLM), a vasomotor center in the brainstem, activates the SNS in hypertensive rats. The aim of the present study was to determine whether oral administration of an AT1R blocker (ARB) inhibits SNS activity via antioxidative effects in the RVLM of rats with dietary-induced obesity.

METHODS AND RESULTS

Obesity-prone rats fed a high-fat diet were divided into groups treated with either telmisartan obesity-prone (TLM-OP), or losartan obesity-prone (LOS-OP), or vehicle obesity-prone (VEH-OP). SBP, SNS activity, and oxidative stress in the RVLM were significantly higher in obesity-prone rats than in obesity-resistant rats. Body weight, visceral fat, blood glucose, serum insulin, and plasma adiponectin concentrations were significantly lower in TLM-OP and LOS-OP than in VEH-OP, and plasma adiponectin concentrations were significantly higher in TLM-OP than in LOS-OP. Although SBP was reduced to similar levels both in TLM-OP and LOS-OP, both oxidative stress in the RVLM and SNS activity were significantly lower in TLM-OP than in LOS-OP or VEH-OP.

CONCLUSION

Orally administered telmisartan inhibited SNS activity through antioxidative effects via AT1R blockade in the RVLM of obesity-prone rats. AT1R and oxidative stress in the RVLM might be novel treatment targets for obesity-induced hypertension through sympathoinhibition, and telmisartan might be preferable for obesity-induced hypertension.

Comparative effect of candesartan and amlodipine, and effect of switching from valsartan, losartan, telmisartan and olmesartan to candesartan, on early morning hypertension and heart rate

Early morning hypertension and a high heart rate are risk factors for cardiovascular disease. The DOHSAM study was designed to evaluate the effect of candesartan on early morning blood pressure (BP) and heart rate in hypertensives. We used a prospective, randomized, open-label design. Protocol 1: Patients with early morning BP more than 135/85 mmHg who were not on any antihypertensive drug or on candesartan were given amlodipine 2.5 mg/day (amlodipine group, n = 22) or added candesartan 4 mg/day (candesartan group, n = 36). Candesartan or amlodipine was added when BP did not fall lower than 135/85 mmHg. Protocol 2: Early morning hypertensives who were on other angiotensin receptor blockers (ARBs) (n = 50) such as valsartan, losartan, telmisartan and olmesartan were switched to candesartan. Early morning BP significantly decreased in the candesartan group compared with the amlodipine group 9 and 12 months after treatment. Switching other ARBs except for olmesartan to candesartan significantly decreased early morning systolic and diastolic BP 3, 6, 9 and 12 months after treatment. Heart rate in the office significantly decreased by switching to candesartan 6, 9 and 12 months after treatment. In conclusion, candesartan significantly decreased early morning hypertension more than amlodipine or other ARBs except olmesartan in early morning hypertensives.

Cost-effectiveness of candesartan versus losartan in the primary preventive treatment of hypertension

Background

Although angiotensin receptor blockers have different receptor binding properties, no comparative randomized studies with cardiovascular event endpoints have been performed for this class of drugs. The aim of this study was to assess the long-term cost-effectiveness of candesartan (Atacand^®) versus generic losartan in the primary preventive treatment of hypertension.

Methods

A decision-analytic model was developed to estimate costs and health outcomes over a patient’s lifetime. Data from a clinical registry study were used to estimate event rates for cardiovascular complications, such as myocardial infarction and heart failure. Costs and quality of life data were from published sources. Costs were in Swedish kronor and the outcome was quality-adjusted life-years (QALYs).

Results

Due to reduced rates of cardiovascular complications, candesartan was associated with a QALY gain and lower health care costs compared with generic losartan (0.053 QALYs gained and reduced costs of approximately 4700 Swedish kronor for women; and 0.057 QALYs gained and reduced costs of approximately 4250 Swedish kronor for men). This result was robust in several sensitivity analyses.

Conclusion

When modeling costs and health outcomes based on event rates for cardiovascular complications from a real-world registry study, candesartan appears to bring a QALY gain and a reduction in costs compared with generic losartan in the primary preventive treatment of hypertension in Sweden.

Angiotensin II AT(1) receptor blockers as treatments for inflammatory brain disorders

The effects of brain AngII (angiotensin II) depend on AT(1) receptor (AngII type 1 receptor) stimulation and include regulation of cerebrovascular flow, autonomic and hormonal systems, stress, innate immune response and behaviour. Excessive brain AT(1) receptor activity associates with hypertension and heart failure, brain ischaemia, abnormal stress responses, blood-brain barrier breakdown and inflammation. These are risk factors leading to neuronal injury, the incidence and progression of neurodegerative, mood and traumatic brain disorders, and cognitive decline. In rodents, ARBs (AT(1) receptor blockers) ameliorate stress-induced disorders, anxiety and depression, protect cerebral blood flow during stroke, decrease brain inflammation and amyloid-β neurotoxicity and reduce traumatic brain injury. Direct anti-inflammatory protective effects, demonstrated in cultured microglia, cerebrovascular endothelial cells, neurons and human circulating monocytes, may result not only in AT(1) receptor blockade, but also from PPARγ (peroxisome-proliferator-activated receptor γ) stimulation. Controlled clinical studies indicate that ARBs protect cognition after stroke and during aging, and cohort analyses reveal that these compounds significantly reduce the incidence and progression of Alzheimer's disease. ARBs are commonly used for the therapy of hypertension, diabetes and stroke, but have not been studied in the context of neurodegenerative, mood or traumatic brain disorders, conditions lacking effective therapy. These compounds are well-tolerated pleiotropic neuroprotective agents with additional beneficial cardiovascular and metabolic profiles, and their use in central nervous system disorders offers a novel therapeutic approach of immediate translational value. ARBs should be tested for the prevention and therapy of neurodegenerative disorders, in particular Alzheimer's disease, affective disorders, such as co-morbid cardiovascular disease and depression, and traumatic brain injury.

Differential pharmacology and benefit/risk of azilsartan compared to other sartans

Azilsartan, an angiotensin II type 1 (AT₁) receptor blocker (ARB), was recently approved by regulatory authorities for treatment of hypertension and is the 8th ARB to join the clinical market. This article discusses the medical reasons for introducing a new AT₁ receptor blocker and reviews the experimental and clinical studies that have compared the functional properties of azilsartan to those of other ARBs. The main question addressed is: Does azilsartan have distinguishing features that should motivate choosing it over any of the other sartans for use in clinical practice? Based on studies conducted to date in hypertensive patients without serious comorbidities, azilsartan appears to be characterized by a superior ability to control 24-hour systolic blood pressure (BP) relative to other widely used ARBs including valsartan, olmesartan, and candesartan, and presumably others as well (eg, losartan). Compared to these other ARBs, azilsartan may increase the BP target control and response rate by an absolute value of 8%–10%. Greater antihypertensive effects of azilsartan might be due in part to its unusually potent and persistent ability to inhibit binding of angiotensin II to AT₁ receptors. Preclinical studies have indicated that azilsartan may also have potentially beneficial effects on cellular mechanisms of cardiometabolic disease and insulin sensitizing activity that could involve more than just blockade of AT₁ receptors and/or reduction in BP. However, the clinical relevance of these additional actions is unknown. Given that the general ability of antihypertensive drugs to protect against target organ damage is largely mediated by their ability to decrease BP, the enhanced antihypertensive effects of azilsartan should serve to justify clinical interest in this ARB relative to other molecules in the class that have a lower capacity to reduce BP.