Renal hemodynamic and hormonal responses to the angiotensin II antagonist candesartan

Physiological confounders of renal blood flow measurement

OBJECTIVES

Renal blood flow (RBF) is controlled by a number of physiological factors that can contribute to the variability of its measurement. The purpose of this review is to assess the changes in RBF in response to a wide range of physiological confounders and derive practical recommendations on patient preparation and interpretation of RBF measurements with MRI.

METHODS

A comprehensive search was conducted to include articles reporting on physiological variations of renal perfusion, blood and/or plasma flow in healthy humans.

RESULTS

A total of 24 potential confounders were identified from the literature search and categorized into non-modifiable and modifiable factors. The non-modifiable factors include variables related to the demographics of a population (e.g. age, sex, and race) which cannot be manipulated but should be considered when interpreting RBF values between subjects. The modifiable factors include different activities (e.g. food/fluid intake, exercise training and medication use) that can be standardized in the study design. For each of the modifiable factors, evidence-based recommendations are provided to control for them in an RBF-measurement.

CONCLUSION

Future studies aiming to measure RBF are encouraged to follow a rigorous study design, that takes into account these recommendations for controlling the factors that can influence RBF results.

Physiologically Based Pharmacokinetic Modeling of Fimasartan, Amlodipine, and Hydrochlorothiazide for the Investigation of Drug-Drug Interaction Potentials

PURPOSE

To build a physiologically based pharmacokinetic (PBPK) model for fimasartan, amlodipine, and hydrochlorothiazide, and to investigate the drug-drug interaction (DDI) potentials.

METHODS

The PBPK model of each drug was developed using Simcyp software (Version 15.0), based on the information obtained from literature sources and in vitro studies. The predictive performance of the model was assessed by comparing the predicted PK profiles and parameters with the observed data collected from healthy subjects after multiple oral doses of fimasartan, amlodipine, and hydrochlorothiazide. The DDI potentials after co-administration of three drugs were simulated using the final model.

RESULTS

The predicted-to-observed ratios of all the pharmacokinetic parameters met the acceptance criterion. The PBPK model predicted no significant DDI when fimasartan was co-administered with amlodipine or hydrochlorothiazide, which is consistent with the observed clinical data. In the simulation of DDI at steady-state after co-administration of three drugs, the model predicted that fimasartan exposure would be increased by ~24.5%, while no changes were expected for the exposures of amlodipine and hydrochlorothiazide.

CONCLUSIONS

The developed PBPK model adequately predicted the pharmacokinetics of fimasartan, amlodipine, and hydrochlorothiazide, suggesting that the model can be used to further investigate the DDI potential of each drug.

Regulation, signalling and functions of hormonal peptides in pulmonary vascular remodelling during hypoxia

Hypoxic state affects organism primarily by decreasing the amount of oxygen reaching the cells and tissues. To adjust with changing environment organism undergoes mechanisms which are necessary for acclimatization to hypoxic stress. Pulmonary vascular remodelling is one such mechanism controlled by hormonal peptides present in blood circulation for acclimatization. Activation of peptides regulates constriction and relaxation of blood vessels of pulmonary and systemic circulation. Thus, understanding of vascular tone maintenance and hypoxic pulmonary vasoconstriction like pathophysiological condition during hypoxia is of prime importance. Endothelin-1 (ET-1), atrial natriuretic peptide (ANP), and renin angiotensin system (RAS) function, their receptor functioning and signalling during hypoxia in different body parts point them as disease markers. In vivo and in vitro studies have helped understanding the mechanism of hormonal peptides for better acclimatization to hypoxic stress and interventions for better management of vascular remodelling in different models like cell, rat, and human is discussed in this review.

The DIabetic REtinopathy Candesartan Trials (DIRECT) Programme: baseline characteristics

Renin-angiotensin system blockade has been shown to be superior to other antihypertensive therapy in slowing progression of renal disease in diabetic patients, but questions remain regarding diabetic retinopathy. The primary objective of the DIabetic REtinopathy Candesartan Trials (DIRECT) Programme is to examine primary (incidence) and secondary (progression) prevention of diabetic retinopathy when blocking angiotensin II type 1-receptors with candesartan in normoalbuminuric, normotensive Type 1 diabetic patients, and secondary prevention only in normoalbuminuric, normotensive or treated hypertensive Type 2 diabetic patients. The secondary objectives include examining the effect of candesartan treatment on urinary albumin excretion rate (UAER) in each of the three studies and to examine the incidence of proliferative retinopathy in all three populations combined.

Standardised investigations for patients at enrolment include blood pressure measurement analysis of HbA1C and serum lipids, and a detailed ophthalmological examination. Retinopathy and UAER outcomes are assessed yearly. Retinopathy is graded centrally, based on seven-field stereo photographs using the Early Treatment Diabetic Retinopathy Study (ETDRS) protocol. Randomisation was performed when the results of retinal gradings were available, and treatment with 16 mg candesartan cilexetil or matching placebo was initiated; the dose was increased to 32 mg after one month. Calculations of UAER are based on two timed overnight urine collections.

A sample size re-assessment was carried out when approximately 70% of the patients had been randomised in the DIRECT Programme to ensure the results to be conclusive.

In total, 5,231 patients were randomised in the DIRECT Programme in 30 countries. One thousand, four hundred and twenty one and 1,905 patients are evaluated in the primary and secondary prevention studies in Type 1 diabetes, respectively and 1,905 patients in the secondary prevention study in Type 2 diabetes.

HbA1C showed mean values of 8.1, 8.5 and 8.2% for the Type 1 primary, Type 1 secondary and Type 2 secondary prevention studies, respectively. In the Type 1 secondary prevention study, 49% of the patients had mild nonproliferative retinopathy (level 20) in at least one eye, and 9% had moderate-moderately severe non-proliferative retinopathy (level 43—47). In Type 2 patients, 17% had level 43—47 and the remainder less severe retinopathy.

Modeling of the pharmacokinetic/pharmacodynamic interaction between irbesartan and hydrochlorothiazide in normotensive subjects

PURPOSE

To investigate the pharmacokinetic/pharmacodynamic (PK/PD) interaction between irbesartan (IRB) and hydrochlorothiazide (HCT) in normotensive subjects.

METHODS

A three-way crossover study was used. Serial drug concentrations and drug effects, including systolic and diastolic blood pressure and heart rate were monitored after administration of irbesartan and hydrochlorothiazide alone and in combination. The data were fitted to a PK/PD model and the parameters for irbesartan and hydrochlorothiazide when administered alone and in combination were compared.

RESULTS

The plasma profiles for irbesartan and hydrochlorothiazide followed the two-compartment model after a single dose. The PK parameters of irbesartan were not affected by hydrochlorothiazide; however irbesartan decreased the hydrochlorothiazide AUC by 25% and increased its clearance by 25%. There were no significant changes in heart rate after each drug alone or in combination. Irbesartan plus hydrochlorothiazide had a greater blood pressure lowering effect compared with irbesartan alone, despite the unchanged irbesartan PK. The relationship between irbesartan plasma concentration and its effects plotted in chronological order showed anticlockwise hysteresis. The PD parameter estimates for the effect of irbesartan on systolic blood pressure, when administered with hydrochlorothiazide were significantly different from those when irbesartan was administered alone. This was manifested by a 25% increase in Emax , and a 40% decrease in EC50 , suggesting a synergistic blood pressure lowering effect for the combination. While parameter estimates for the effect of irbesartan on diastolic blood pressure were changed by hydrochlorothiazide, the differences were only significant for EC50 .

CONCLUSION

A limited potential for clinically significant interactions between irbesartan and hydrochlorothiazide at the given doses were observed; therefore, no dosage adjustments were recommended for either drug when used together. (ClinicalTrials.gov Identifier NCT01858610)

Racial differences in renal vascular response to angiotensin blockade with captopril or candesartan

OBJECTIVE

We compared the renal vascular response to captopril and candesartan among nondiabetic, normotensive black and white participants to explore angiotensin-converting enzyme-independent generation of angiotensin II.

METHODS

Thirteen black individuals and 10 white individuals in low-salt balance were given captopril and candesartan on sequential study days, and the renal plasma flow responses to these agents were measured.

RESULTS

Consistent with our prior observations, white individuals demonstrated a strong, significant correlation between responses to these drugs (r = 0.78, P = 0.008) and a significantly greater increase in the renal plasma flow in response to candesartan compared with captopril (104.2 +/- 26.8 versus 52.4 +/- 24.3 ml/min per 1.73 m; P = 0.03). In black participants, however, no correlation between responses to captopril and to candesartan was observed (r = 0.22, P = 0.47) and there was no difference in the renal plasma flow response between the two drugs (90.4 +/- 13.0 versus 80.4 +/- 15.3 ml/min per 1.73 m; P = 0.59). The difference in the response to the two drugs was significantly higher among white participants compared with black participants (P = 0.03).

CONCLUSION

We confirmed the contribution of an angiotensin-converting enzyme-independent pathway for angiotensin II generation in the kidneys of nondiabetic, normotensive white, but not black, individuals.

Effects of the PPAR-gamma agonist rosiglitazone on renal haemodynamics and the renin-angiotensin system in diabetes

BACKGROUND

Thiazolidinediones (TZD) have been reported to improve early stages of diabetic nephropathy independent of glycaemic control. Since blockade of the renin-angiotensin system (RAS) is known to reduce the risk of nephropathy, we hypothesised that the renal effect of TZDs might be related to a favourable effect on the intrarenal RAS. We aimed to determine if the TZD rosiglitazone could reduce RAS activation.

METHODS

We studied adult type 2 diabetic patients and placed them on rosiglitazone for three months. We have previously used the renal haemodynamic response to angiotensin-converting enzyme (ACE) inhibition to demonstrate the state of RAS activation, and thus measured renal plasma flow (RPF) and glomerular filtration rate (GFR) before and after administration of captopril at 0 month and at three months. Plasma renin activity (PRA), active renin, aldosterone and natriuretic peptides were analysed.

RESULTS

The RPF response to ACE inhibition was not altered. There was no change in GFR, PRA, active renin and aldosterone levels. Two patients developed oedema one had an elevated baseline active renin and another had an elevated baseline aldosterone level.

CONCLUSION

The favourable effects of TZDs on diabetic nephropathy is likely not related to an influence on the RAS.

Renin release in response to Renin system blockade: activation of the Renin system in type 1 diabetes mellitus

Activation of the renin-angiotensin system (RAS) in diabetes is thought to contribute to nephropathy. This is suggested by findings of an enhanced renovascular (RPF) response to RAS blockade with angiotensin-converting enzyme inhibitors (ACE-I) and angiotensin receptor blockers (ARBs). An alternative approach to assess RAS activation is the evaluation of renin release following RAS blockade. Forty-four consecutively enrolled Type 1 diabetic patients (28.2+/-1.5 years) and 37 normal subjects (37+/-2.6 years) in high salt balance were given 25 mg of captopril and 16 mg of candesartan p.o. on consecutive days. All subjects were Caucasian. All, except one diabetic patient, had normal renal function. Plasma renin activity (PRA) and renal plasma flow (RPF) were measured for four hours after both drugs, and at eight, and 24 hours after candesartan. As anticipated, both drugs increased PRA. Peak responses (90' after captopril) were 5.6+/-1 ng/mL Ang I/hour in diabetic patients, and 1.7+/-0.9 ng/mL Ang I/hour in normal subjects (p<0.001). Responses to both drugs were correlated in diabetic patients for PRA (r=0.623; p=0.001) and for RPF (r=0.9; p<0.001). When the PRA response to captopril was below the median, the RPF response was limited (22.1+/-17.6 ml/minute/1.73 m2). When it was above the median, the RPF response was also larger (62.2+/-13.9 ml/minute/1.73 m2; p=0.006). Renin response to ACE-I and ARB confirms activation of the RAS in diabetic patients.

Effects of selective angiotensin II and β1-receptor blockade on renal haemodynamics and sodium handling during orthostatic stress in healthy individuals

BACKGROUND

Lower-body negative pressure (LBNP) induces a progressive activation of neurohormonal systems and a renal tubular and haemodynamic response that mimics the renal adaptation observed in congestive heart failure. Both angiotensin II receptor blockers and beta-blockers have been shown to reduce morbidity and mortality in patients with congestive heart failure.

OBJECTIVE

To investigate whether part of the beneficial effects of angiotensin II receptor blockers and beta-blockers in congestive heart failure is mediated through an improvement in renal haemodynamics and sodium excretory capacity.

METHODS AND RESULTS

The study was performed in healthy normotensive individuals exposed to three levels of LBNP and treated with placebo, 200 mg metoprolol once daily, or 16 mg candesartan once daily, for 10 days. Our results show that candesartan increased renal blood flow, and thereby blunted the vasoconstriction induced by LBNP. This effect was not found with metoprolol. More importantly, both metoprolol and candesartan prevented the sodium retention induced by LBNP, but only candesartan promoted sodium excretion during the 2-h recovery period--that is, once LBNP was interrupted.

CONCLUSIONS

These results suggest that blockade of the renin-angiotensin and sympathetic nervous systems in heart failure may be beneficial in part as a result of improved sodium excretion.

ACE and non-ACE pathways in the renal vascular response to RAS interruption in type 1 diabetes mellitus

BACKGROUND

The enormous contribution of renin-angiotensin system (RAS) interruption with ACE (angiotensin-converting enzyme) inhibitors and angiotensin II receptor blockers (ARB) in the treatment of diabetic nephropathy has led to interest in the factors involved in angiotensin II (Ang II) generation. In normal subjects, RAS interruption using an ARB produced a 50% greater renal plasma flow (RPF) rise than with an ACE inhibitor, suggesting a substantial contribution of non-ACE pathways. Moreover, immunohistochemistry studies in kidneys of overtly proteinuric diabetic subjects showed up-regulation of chymase, an alternative Ang II-generating enzyme. Our aim was to determine the degree to which the non-ACE pathways contribute to RAS activation in type 1 diabetes mellitus (DM).

METHODS

Type 1 DM patients (N= 37, 14 M/23 F; age 31 +/- 2 years; DM duration 16 +/- 1.7 years; HbA1c 7.7.0 +/- 0.3%) were studied on a high-salt diet. They received captopril 25 mg po one day and candesartan 16 mg po the next day. RPF and glomerular filtration rate (GFR) were measured before and up to 4 hours after drug administration.

RESULTS

Both captopril and candesartan induced a significant rise in RPF (baseline vs. peak <0.0001 for both), and the rise was concordant for the 2 drugs (r= 0.77, P < 0.001). However, the RPF responses were not significantly different between the 2 drugs (captopril 72 +/- 11 mL/min/1.73 m(2), candesartan 75 +/- 12, P= 0.841).

CONCLUSION

In predominantly normoalbuminuric, normotensive type 1 DM, activation of the intrarenal RAS reflects a mechanism involving primarily the classic ACE pathway.

Ultrasound Evaluation of Valsartan Therapy for Renal Cortical Perfusion

An increase in renal blood flow with a concomitant decrease in filtration fraction at the onset of angiotensin II receptor blocker treatment has been shown to predict a long-term renoprotective effect. However, no studies are available regarding angiotensin receptor blocker-induced changes in renal cortical perfusion observed in the clinical setting. We have recently developed a convenient method of evaluating human renal cortical blood flow with contrast-enhanced harmonic ultrasonography. The goal of this study was to use this method to examine the effect of valsartan, an angiotensin II receptor blocker, on renal cortical perfusion. We performed intermittent second harmonic imaging with venous infusion of a microbubble contrast agent in 7 healthy volunteers. Contrast-enhanced harmonic ultrasonography performed after oral administration of valsartan (80mg) showed a significant increase in microbubble velocity, which correlated well with the increase in total renal blood flow determined by p-aminohippurate clearance (r=0.950, p < 0.001). Although fractional vascular volume was not significantly increased, alterations in renal cortical blood flow calculated by the product of microbubble velocity and fractional volume were also correlated with the change in total renal blood flow (r=0.756, p < 0.05). These results indicate that valsartan increases the renal cortical blood flow in normal kidneys, mainly by increasing blood flow velocity. Contrast-enhanced harmonic ultrasonography is a promising technique for evaluating the precise effect on renal cortical perfusion and optimal dose of valsartan in diseased kidneys.

The DIabetic Retinopathy Candesartan Trials (DIRECT) Programme, rationale and study design

The DIabetic Retinopathy Candesartan Trials (DIRECT) Programme consists of three randomised, double-masked, parallel, placebo-controlled studies to determine the impact of treatment with candesartan on diabetic retinopathy. In Type 1 diabetes, 1,700 patients without retinopathy will be randomised into a primary prevention study, and 1,200 with non-proliferative retinopathy into a secondary prevention study. In Type 2 diabetes, 1,600 patients with non-proliferative retinopathy will be randomised. Patients will be followed for at least three years. Eligible patients must be normotensive (systolic blood pressure [SBP] 130 mmHg and diastolic blood pressure [DBP] 85 mmHg) without antihypertensive medication in Type 1 diabetes, and either normotensive or treated hypertensive (SBP 160 mmHg and SBP 90 mmHg) and not taking angiotensin-converting enzyme inhibitors or AT(1)-receptor blockers in Type 2 diabetes. All patients will be normoalbuminuric, based on two overnight urine collections. The primary endpoint is based upon retinal photographs, graded to the Early Treatment of Diabetic Retinopathy Study scale. A two-step increase on this scale defines incidence, and a three-step increase defines progression of retinopathy. The main secondary endpoint for each study is change in urinary albumin excretion rate. A positive outcome of the DIRECT Programme would be an important step forward in the clinical management of patients with diabetes.

Candesartan cilexetil plus hydrochlorothiazide combination: a review of its use in hypertension

The combination of candesartan cilexetil [an angiotensin II type 1 (AT(1)) receptor antagonist] plus hydrochlorothiazide (a thiazide diuretic), has been used in the treatment of patients with hypertension. The blood pressure (BP) lowering effect of various doses of this combination, administered orally once a day for 4 to 52 weeks, has been demonstrated in clinical trials. These studies showed that combinations of candesartan cilexetil 4 to 16 mg with hydrochlorothiazide 12.5 or 25 mg induced significant reductions reductions in systolic (S) BP and diastolic (D) BP from baseline in patients with mild to severe hypertension. Data from clinical trials indicated that reductions in BP induced by candesartan cilexetil 4 to 32 mg/hydrochlorothiazide 12.5 mg combinations were significantly greater than those observed after monotherapy with either drug. Treatment for 8 weeks with candesartan cilexetil 16 mg/hydrochlorothiazide 12.5 mg or candesartan cilexetil 16 mg induced SBP/DBP reductions of 12.0/7.5 mm Hg and 7.5/5.5mm Hg, respectively (p < 0.05 both comparisons). Moreover, data from a randomised, double-blind, placebo-controlled, dose-finding study in 1038 patients with mild to moderate hypertension showed that the greatest reductions in SBP/DBP were achieved by candesartan cilexetil 16 mg/hydrochlorothiazide 12.5 mg. Significant differences in BP reduction in favour of the combination were observed when hypertensive patients were given candesartan cilexetil 4 or 8 mg/hydrochlorothiazide 12.5 mg or hydrochlorothiazide monotherapy for 8 weeks. Additionally, greater efficacy of the combination compared to monotherapy with either drug was demonstrated by response rates to treatment. Moreover, a fixed combination of candesartan cilexetil 16 mg/hydrochlorothiazide 12.5 mg demonstrated a greater antihypertensive effect than losartan 50 mg/hydrochlorothiazide 12.5 mg in two clinical trials. Candesartan cilexetil 8 mg/hydrochlorothiazide 12.5 mg showed a similar antihypertensive effect compared with that of combined lisinopril 10 mg/hydrochlorothiazide 12.5 mg. Candesartan cilexetil/hydrochlorothiazide combination was well tolerated in patients with hypertension. Combined data from placebo-controlled trials showed that most adverse events were uncommon and not serious. Patients receiving combination therapy exhibited, among other adverse events, headache (3.2 vs 5.5% for candesartan cilexetil/hydrochlorothiazide and placebo, respectively), back pain (3.0 vs 2.4%), dizziness (2.6 vs 1.2%) and respiratory infection (2.5 vs 1.4%). Moreover, 3.3 and 2.7% of patients receiving candesartan cilexetil/hydrochlorothiazide or placebo, respectively, discontinued treatment because of adverse events.

CONCLUSION

The combination of candesartan cilexetil and hydrochlorothiazide (AT(1)-receptor antagonist and thiazide diuretic, respectively) is an effective treatment for patients with hypertension. Data from randomised, double-blind, placebo-controlled clinical trials showed that this combination is significantly more efficacious than either agent alone. Moreover, the combination of these two agents showed an excellent adverse event profile. Current data support the use of this combination as an alternative when monotherapy with either agent is not effective, and there are no compelling or specific indications for other drugs. However, data from large clinical trials, evaluating morbidity and mortality outcomes, are needed to determine the precise role of candesartan cilexetil/hydrochlorothiazide combination in the treatment of patients with hypertension.

Renal vascular responses to captopril and to candesartan in patients with type 1 diabetes mellitus

BACKGROUND

Enhanced renal vasodilator responses to angiotensin-converting enzyme (ACE) inhibition in diabetes mellitus despite a normal or low plasma renin activity level have suggested intrarenal activation of the renin-angiotensin system in this disease. There is, however, a continuing debate as to the mediators of the renal hemodynamic response to ACE inhibition-reduced angiotensin II formation or pathways involving kinins, prostaglandins, and nitric oxide.

METHODS

Twelve patients with type 1 diabetes mellitus of 18 +/- 3.2 (SEM) years of duration (7 females and 5 males, ages 17 to 50, 32 +/- 4.0 years) who were free of sustained microalbuminuria and on a high-salt diet were given the ACE inhibitor captopril (25 mg orally) on one day and the AT1 receptor blocker candesartan (16 mg orally) on another day. Renal plasma flow (RPF) and glomerular filtration rate were measured before and for four hours after administration.

RESULTS

Both drugs caused a significant increase in RPF (captopril 574 +/- 26 to 625 +/- 37 mL/min/1.73 m2, P = 0.008; candesartan 577 +/- 26 to 643 +/- 37, P = 0.004). There was a highly significant correlation between the responses to captopril and to candesartan (r = 0.86, P < 0.001). Seven subjects had an RPF response to captopril that was accentuated (90 +/- 13 mL/min/1.73 m2), while five had a response that was normal (-4 +/- 9). There was no significant change in glomerular filtration rate on either drug.

CONCLUSION

The remarkable rise in RPF in response to captopril and candesartan despite high-salt balance suggests the intrarenal activation of the renin-angiotensin system in diabetes that is not reflected in plasma renin levels. The high correlation between the renal hemodynamic response to captopril and to candesartan indicates that reduced angiotensin II formation is the main mechanism of action of the ACE inhibitor.

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

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