Effectiveness of the selective aldosterone blocker, eplerenone, in patients with resistant hypertension

Mineralocorticoid receptor antagonists: identification of heterocyclic amide replacements in the oxazolidinedione series

Novel potent and selective mineralocorticoid receptor antagonists were identified, utilizing heterocyclic amide replacements in the oxazolidinedione series. Structure-activity relationship (SAR) efforts focused on improving lipophilic ligand efficiency (LLE) while maintaining nuclear hormone receptor selectivity and reasonable pharmacokinetic profiles.

Renal denervation in the management of resistant hypertension: current evidence and perspectives

PURPOSE OF REVIEW

Catheter-based renal denervation has emerged as a novel treatment modality for resistant hypertension. This review summarizes the current evidence on this procedure in treatment of resistant hypertension, limitations of available evidence and questions to be answered.

RECENT FINDINGS

The SYMPLICITY studies showed that renal denervation is feasible in treating resistant hypertension, but failed to provide conclusive evidence on the size and durability of the antihypertensive, renal and sympatholytic effects, as well as the long-term safety. The definition of resistant hypertension was loose in the SYMPLICITY studies and the management of resistant hypertension was suboptimal. Future studies should have a randomized design and enroll truly resistant hypertension patients by excluding secondary hypertension, white-coat hypertension and nonadherent patients. Questions to be addressed by the ongoing and future trials include the long-term efficacy and safety of this procedure, identification of responders and uncovering of the underlying mechanisms.

SUMMARY

Only well-designed, randomized clinical trials addressing the limitations of the SYMPLICITY studies will be able to demonstrate whether renal denervation is an efficacious treatment modality in resistant hypertension and in which patients. For now, renal denervation remains an experimental procedure and should only be offered to truly resistant hypertensive patients in a research context after careful selection.

Size of blood pressure reduction from renal denervation: insights from meta-analysis of antihypertensive drug trials of 4,121 patients with focus on trial design: the CONVERGE report

OBJECTIVE

30 mm Hg drops in office systolic blood pressure are reported in trials of renal denervation, but ambulatory reductions are much smaller. This disparity is assumed to have a physiological basis and also be present with antihypertensive drugs.

DESIGN

We examine this office-ambulatory discrepancy through meta-analysis of drug and denervation trials, categorising by trial design.

PATIENTS (STUDIES)

31 drug trials enrolling 4121 patients and 23 renal denervation trials enrolling 720 patients met the criteria.

RESULTS

In drug trials without randomisation or blinding, pressure reductions are 5.6 mm Hg (95% CI 2.98 to 8.22 mm Hg) larger on office measurements than ambulatory blood pressure monitoring (p<0.0001). By contrast, with randomisation and blinding, office reductions are identical to ambulatory reductions (difference -0.88 mm Hg, 95% CI -3.18 to 1.43, p=0.45). For renal denervation, there are no randomised blinded trial results. In unblinded trials, office pressure drops were 27.6 mm Hg versus pretreatment, and 26.6 mm Hg versus unintervened controls. By contrast, ambulatory pressure drops averaged 15.7 mm Hg across all trials. Among those where the baseline ambulatory pressure was not the deciding factor for enrolment (avoiding regression to the mean), ambulatory drops averaged only 11.9 mm Hg.

CONCLUSIONS

Discrepancies in drug trials between office and ambulatory blood pressure reductions disappear once double-blinded placebo control is implemented. Renal denervation trials may also undergo similar evolution. We predict that as denervation trial designs gradually improve in bias-resistance, office and ambulatory pressure drops will converge. We predict that it is the office drops that will move to match the ambulatory drops, that is, not 30, but nearer 13.

Management of patients with resistant hypertension: current treatment options

Resistant hypertension (RHTN) is an increasingly common clinical problem that is often heterogeneous in etiology, risk factors, and comorbidities. It is defined as uncontrolled blood pressure on optimal doses of three antihypertensive agents, ideally one being a diuretic. The definition also includes controlled hypertension with use of four or more antihypertensive agents. Recent observational studies have advanced the characterization of patients with RHTN. Patients with RHTN have higher rates of cardiovascular events and mortality compared with patients with more easily controlled hypertension. Secondary causes of hypertension, including obstructive sleep apnea, primary aldosteronism, renovascular disease, are common in patients with RHTN and often coexist in the same patient. In addition, RHTN is often complicated by metabolic abnormalities. Patients with RHTN require a thorough evaluation to confirm the diagnosis and optimize treatment, which typically includes a combination of lifestyle adjustments, and pharmacologic and interventional treatment. Combination therapy including a diuretic, a long-acting calcium channel blocker, an angiotensin-converting enzyme inhibitor, a beta blocker, and a mineralocorticoid receptor antagonist where warranted is the classic regimen for patients with treatment-resistant hypertension. Mineralocorticoid receptor antagonists like spironolactone or eplerenone have been shown to be efficacious in patients with RHTN, heart failure, chronic kidney disease, and primary aldosteronism. Novel interventional therapies, including baroreflex activation and renal denervation, have shown that both of these methods may be used to lower blood pressure safely, thereby providing exciting and promising new options to treat RHTN.

Mineralocorticoid receptor antagonists: emerging roles in cardiovascular medicine

Spironolactone was first developed over 50 years ago as a potent mineralocorticoid receptor (MR) antagonist with undesirable side effects; it was followed a decade ago by eplerenone, which is less potent but much more MR-specific. From a marginal role as a potassium-sparing diuretic, spironolactone was shown to be an extraordinarily effective adjunctive agent in the treatment of progressive heart failure, as was eplerenone in subsequent heart failure trials. Neither acts as an aldosterone antagonist in the heart as the cardiac MR are occupied by cortisol, which becomes an aldosterone mimic in conditions of tissue damage. The accepted term "MR antagonist", (as opposed to "aldosterone antagonist" or, worse, "aldosterone blocker"), should be retained, despite the demonstration that they act not to deny agonist access but as inverse agonists. The prevalence of primary aldosteronism is now recognized as accounting for about 10% of hypertension, with recent evidence suggesting that this figure may be considerably higher: in over two thirds of cases of primary aldosteronism therapy including MR antagonists is standard of care. MR antagonists are safe and vasoprotective in uncomplicated essential hypertension, even in diabetics, and at low doses they also specifically lower blood pressure in patients with so-called resistant hypertension. Nowhere are more than 1% of patients with primary aldosteronism ever diagnosed and specifically treated. Given the higher risk profile in patients with primary aldosteronism than that of age, sex, and blood pressure matched essential hypertension, on public health grounds alone the guidelines for first-line treatment of all hypertension should mandate inclusion of a low-dose MR antagonist.

RAAS inhibitors and cardiovascular protection in large scale trials

Hypertension, coronary artery disease and heart failure affect over half of the adult population in most Western societies, and are prime causes of CV morbidity and mortality. With the ever-increasing worldwide prevalence of CV disease due to ageing and the "diabetes" pandemic, guideline groups have recognized the importance of achieving cardioprotection in affected individuals as well as in those at risk for future CV events. The renin-angiotensin-aldosterone system (RAAS) is the most important system controlling blood pressure (BP), cardiovascular and renal function in man. As our understanding of the crucial role of RAAS in the pathogenesis of most, if not all, CV disease has expanded over the past decades, so has the development of drugs targeting its individual components. Angiotensin-converting enzyme inhibitors (ACEi), Ang-II receptor blockers (ARB), and mineralcorticoid receptor antagonists (MRA) have been evaluated in large clinical trials for their potential to mediate cardioprotection, singly or in combination. Direct renin inhibitors are currently under scrutiny, as well as novel dual-acting RAAS-blocking agents. Herein, we review the evidence generated from large-scale clinical trials of cardioprotection achieved through RAAS-blockade.

Effectiveness of the direct renin inhibitor, aliskiren, in patients with resistant hypertension

Currently there is no consensus regarding which add-on therapy to use in resistant hypertension. We have conducted an open observational study of the use of aliskiren in resistant hypertensive patients. Forty-three patients with resistant hypertension were included in the study. The inclusion criteria were as follows: 1) office blood pressure (BP) > 140/90 mmHg despite treatment with at least three or more antihypertensive drugs; 2) no prior therapy with aliskiren; and 3) no renal insufficiency. Follow-up BP was determined at 1 and 3 months. Baseline BP was 153 ± 12/79 ± 12 mmHg. After 3 months, systolic BP (SBP) and diastolic BP (DBP) dropped significantly: 140 ± 19/73 ± 13 mmHg (P < 0.0001). Twenty-one patients (49%) had an office BP < 140/90 mmHg, and these patients were assigned to the good BP control group. Another 22 were placed into the poor BP control group. BP reductions from baseline in the good BP control group (SBP/ DBP: 19 ± 11/8 ± 7 mmHg) were larger than those in the poor BP control group (5 ± 15/3 ± 9 mmHg, P < 0.05). Mean BP (MBP) values at baseline, 1, and 3 months were higher in the poor BP control group. There was no significant difference in pulse pressure at baseline between the 2 groups. In multivariate analysis, only MBP at baseline correlated with lack of BP control. Aliskiren administration to resistant hypertensive patients was effective in reducing BP. The present findings suggest aliskiren may be useful as a fourth-line or fifth-line treatment added to other drugs in the treatment of resistant hypertension.

Determinants of blood pressure reduction by eplerenone in uncontrolled hypertension

BACKGROUND

Add-on therapy with aldosterone receptor antagonists has been reported to lower blood pressure (BP) in patients with uncontrolled hypertension. We assessed potential predictors of this response.

METHODS

In essential hypertensive patients with uncontrolled BP, despite the use of at least two antihypertensives, plasma renin and aldosterone concentrations and the transtubular potassium gradient (TTKG) were measured. Patients were treated with eplerenone 50 mg daily on top of their own medication. The office and ambulatory BP response and biochemical changes were evaluated after 1 week and 3 months of treatment and 6 weeks after discontinuation. Potential predictors for the change in 24-h ambulatory BP were tested in a multivariate regression model.

RESULTS

One hundred and seventeen patients with a mean age of 50.5 ± 6.6 years were included. Office BP decreased from 149/91 to 142/87 mmHg (P < 0.001) and ambulatory BP from 141/87 to 132/83 mmHg after 3 months of treatment (P < 0.001). Six weeks after discontinuation of eplerenone, office and ambulatory BP measurements returned to baseline values. Treatment resulted in a small rise in serum potassium and creatinine, and a small decrease in the TTKG. In a multivariate model, neither renin, aldosterone, or their ratio, nor the TTKG predicted the BP response. Only baseline ambulatory SBP predicted the BP response, whereas the presence of left ventricular hypertrophy was associated with a smaller BP reduction.

CONCLUSION

Add-on therapy with eplerenone effectively lowers BP in patients with difficult-to-treat primary hypertension. This effect is unrelated to circulating renin-angiotensin-aldosterone system activity and renal mineralocorticoid receptor activity as assessed by the TTKG.

Discovery of novel oxazolidinedione derivatives as potent and selective mineralocorticoid receptor antagonists

Novel oxazolidinedione analogs were discovered as potent and selective mineralocorticoid receptor (MR) antagonists. Structure-activity relationship (SAR) studies were focused on improving the potency and microsomal stability. Selected compounds demonstrated excellent MR activity, reasonable nuclear hormone receptor selectivity, and acceptable rat pharmacokinetics.

A critical review of the evidence supporting aldosterone in the etiology and its blockade in the treatment of obesity-associated hypertension

Obesity is epidemic and is associated with increased blood pressure, which often manifests as treatment-resistant hypertension. Mineralocorticoids have been hypothesized to have a pathogenic role in human obesity-associated hypertension. In this review, we critically appraise the existing data regarding aldosterone in the pathophysiology and treatment of obesity-associated hypertension. We begin by reviewing the mechanisms by which obesity may increase mineralocorticoid activity. We then discuss human studies of plasma and urine aldosterone in obesity and with weight loss. From these studies, we conclude that aldosterone is often, but not always, mildly increased in obesity. Further study is needed to define circumstances in which aldosterone is increased in obesity. We discuss clinical studies in which measures of body size or weight were evaluated as potential predictors of response to mineralocorticoid receptor antagonists. In addition, we review three randomized, controlled clinical trials that exemplify a rigorous approach to determining the role of mineralocorticoid activity in a human disease. We propose that a similar clinical trial is warranted in order to definitively clarify the role of inappropriate mineralocorticoid activity in the etiology of human obesity-associated hypertension. Finally, we conclude that additional research is needed into the possible role of non-aldosterone mineralocorticoids in human obesity-associated hypertension.

Aldosterone contributes to elevated left ventricular mass in black boys

BACKGROUND

Left ventricular hypertrophy (LVH) poses a great risk of cardiovascular morbidity and mortality in adults and may pose a serious risk in children. Adult studies have shown that renin-angiotensin-aldosterone system (RAAS) levels directly correlate with left ventricular mass index (LVMI). The purpose of this study is to explore race- and sex-related effects of the RAAS on LVMI in adolescents.

METHODS

Data were collected from a sample of 89 blacks (44 girls, 45 boys) and 102 whites (40 girls, 62 boys) aged 15-19. Data collected included sex, age, body mass index (BMI), LVMI, baseline blood pressure, and levels of aldosterone and angiotensin II.

RESULTS

In black males, increased aldosterone levels correlated with decreased sodium excretion (r= -0.336, p=0.024), increased blood pressure (r=0.358, p=0.016), and increased LVMI (r=0.342, p=0.022). In black females, increased aldosterone levels correlated with increased baseline blood pressure (r=0.356, p=0.018). In white males, increased aldosterone correlated with decreased sodium excretion (r= -0.391, p=0.002). In white females, aldosterone levels correlated with increased baseline blood pressure (r=0.323, p=0.042) and decreased sodium excretion (r= -0.342, p=0.031).

CONCLUSIONS

The results suggest the following model in black males: increased aldosterone leads to increased sodium retention, causing a volume-mediated increase in blood pressure; increased blood pressure results in increased left ventricular mass, and eventually LVH.

How can resistant hypertension be identified and prevented?

Resistant hypertension is highly prevalent, and is the form of arterial hypertension that is most difficult to treat. Many patients diagnosed with this disease do not have resistant hypertension, but rather have mismanaged primary hypertension. In many cases blood pressure can be controlled by directly addressing underlying causes such as primary aldosteronism, obstructive sleep apnoea, or excessive neurogenic stimulation. Clinicians should ensure that appropriate blood-pressure measurements are used to diagnose resistant hypertension, explore a variety of drug combinations, and battle clinical inertia. Patients should comply with medication schedules and dietary modifications. Correction of these factors will greatly diminish the prevalence of 'resistant' hypertension and avoid the consequences of a persistently elevated blood pressure in these patients.

Mechanisms of renal NaCl retention in proteinuric disease

In diseases with proteinuria, for example nephrotic syndrome and pre-eclampsia, there often are suppression of plasma renin-angiotensin-aldosterone system components, expansion of extracellular volume and avid renal sodium retention. Mechanisms of sodium retention in proteinuria are reviewed. In animal models of nephrotic syndrome, the amiloride-sensitive epithelial sodium channel ENaC is activated while more proximal renal Na(+) transporters are down-regulated. With suppressed plasma aldosterone concentration and little change in ENaC abundance in nephrotic syndrome, the alternative modality of proteolytic activation of ENaC has been explored. Proteolysis leads to putative release of an inhibitory peptide from the extracellular domain of the γ ENaC subunit. This leads to full activation of the channel. Plasminogen has been demonstrated in urine from patients with nephrotic syndrome and pre-eclampsia. Urine plasminogen correlates with urine albumin and is activated to plasmin within the urinary space by urokinase-type plasminogen activator. This agrees with aberrant filtration across an injured glomerular barrier independent of the primary disease. Pure plasmin and urine samples containing plasmin activate inward current in single murine collecting duct cells. In this study, it is shown that human lymphocytes may be used to uncover the effect of urine plasmin on amiloride- and aprotinin-sensitive inward currents. Data from hypertensive rat models show that protease inhibitors may attenuate blood pressure. Aberrant filtration of plasminogen and conversion within the urinary space to plasmin may activate γ ENaC proteolytically and contribute to inappropriate NaCl retention and oedema in acute proteinuric conditions and to hypertension in diseases with chronic microalbuminuria/proteinuria.

Study of aldosterone synthase inhibition as an add-on therapy in resistant hypertension

Aldosterone inhibition with mineralcorticoid receptor antagonists (MRAs) is an effective treatment for resistant hypertension. Aldosterone synthase inhibitors (ASIs) are currently being investigated as a new therapeutic strategy to reduce aldosterone secretion from the adrenal gland. In this study, the efficacy and safety of the first-generation ASI LCI699 (0.25 mg twice daily, 1 mg 4 once daily, and 0.5 mg/1 mg twice daily) was compared with placebo and eplerenone (50 mg twice daily), in patients with resistant hypertension. Placebo-adjusted decreases in systolic blood pressure (BP) with LCI699 ranged from 2.6 mm Hg to 4.3 mm Hg at week 8; changes in diastolic BP ranged from +0.3 mm Hg to -1.2 mm Hg. However, reductions were smaller than observed with eplerenone 50 mg twice daily (9.9 mm Hg and 2.9 mm Hg for systolic and diastolic BP, respectively) and not statistically significant vs placebo. LCI699 suppressed plasma aldosterone levels in a dose-related manner with corresponding dose-dependent increases in plasma renin activity and plasma 11-deoxycorticosterone. LCI699 and eplerenone were well tolerated. These data demonstrate that aldosterone synthesis inhibition with LCI699 lowers BP modestly in patients with resistant hypertension. Aldosterone synthesis inhibition might offer an attractive adjunct to aldosterone receptor blockade, although the potential of a combination MRA/ASI has not yet been tested.

Renal denervation: a potential new treatment for severe hypertension

Hypertension is a leading cause of cardiovascular morbidity and mortality. Drug-resistant hypertension remains common despite the availability of several classes of effective antihypertensive agents. Sympathetic hyperactivity has long been recognized as a major contributor to resistant hypertension, but radical sympathectomy was abandoned several decades ago due to its significant side effects. The newly developed, minimally invasive, catheter-based renal sympathetic denervation procedure has been shown in recent trials to produce impressive blood pressure reductions and a favorable safety profile in drug-resistant hypertension. Although the long-term efficacy and safety of renal denervation remains to be determined, emerging data suggest that the benefits of renal denervation may extend beyond blood pressure control.

Hyperaldosteronism as a common cause of resistant hypertension

Resistant hypertension affects an estimated 10-15 million American adults and is increasing in prevalence. The etiology of resistant hypertension is almost always multifactorial, including obesity, older age, high dietary salt, chronic kidney disease, and aldosterone excess. Classical primary aldosteronism and lesser degrees of aldosterone excess, possibly originating from visceral adipocytes, contribute broadly to antihypertensive treatment resistance. Treatment of resistant hypertension is predicated on appropriate lifestyle changes and use of effective combinations of antihypertensive agents from different classes. Blockade of aldosterone with spironolactone has been shown to be particularly effective for treatment of resistant hypertension. The antihypertensive benefit of spironolactone is not limited to patients with demonstrable hyperaldosteronism but instead can be effective in resistant hypertensive patients regardless of aldosterone levels. Chlorthalidone is a potent, long-acting thiazide-like diuretic and should be used preferentially to treat resistant hypertension as it is superior to normally used doses of hydrochlorothiazide.

Aldosterone synthase inhibition in humans

Aldosterone synthase (CYP11B2) inhibition has emerged as a new option for the treatment of hypertension, heart failure and renal disorders, in addition to mineralocorticoid receptor (MR) blockade. The aim is to decrease aldosterone concentrations in both plasma and tissues, thereby decreasing MR-dependent and MR-independent effects in the cardiac, vascular and renal target organs. LCI699 was the first orally active aldosterone-synthase inhibitor to be developed for human use. Its structure is similar to that of FAD286, the dextroenantiomer of the aromatase inhibitor, fadrozole. It dose-dependently decreases plasma and urine aldosterone concentrations by up to 70 or 80% and increases plasma renin activity in healthy male subjects on a low-sodium diet. LCI699 does not decrease basal plasma cortisol concentrations at doses of 0.5-3 mg q.d., but it blocks the cortisol response to adrenocorticotropic hormone (ACTH) at doses ≥ 3 mg q.d. In a proof-of-concept study in patients with primary aldosteronism (PA), LCI699 (0.5-1 mg b.i.d.) induced a dose-dependent and reversible 70-80% decrease in plasma and urinary aldosterone concentration accompanied by a massive dose-dependent accumulation of deoxycorticosterone (>+700%), the aldosterone precursor, in the plasma, thereby confirming the inhibition of the CYP11B2 gene product. This effect was associated with a rapid correction of hypokalaemia, a modest decrease in blood pressure (BP) and a mild increase in plasma renin concentration in patients with PA. LCI699 administration induced biological signs of partial inhibition of the glucocorticoid axis, such as dose-dependent increases in both plasma ACTH and 11-deoxycortisol (the precursor of cortisol) concentrations, consistent with the inhibition of the CYP11B1 gene product. An 8-week placebo-controlled dose-response study on patients with Stage 1 and 2 essential hypertension reported an optimal decrease in BP with a dose of 1 mg LCI699 q.d., which had an antihypertensive effect similar to that of 50 mg b.i.d. eplerenone. A blunted cortisol response to ACTH was observed in 20% of patients, but the clinical and biological safety and tolerability of LCI699 were similar to those of placebo and eplerenone. The discovery of this first orally active aldosterone synthase inhibitor, LCI699, has provided new opportunities to assess the feasibility and the haemodynamic, biological and safety consequences as well as the limitations of this new approach to block the aldosterone pathway in hypertensive patients. However, as the effects of LCI699 on the glucocorticoid axis limit the use of higher doses range because of the loss of selectivity for CYP11B2, this aldosterone synthase inhibitor cannot replace the MR blockade in patients with hypertension, other cardiovascular or renal disorders. The development of second-generation aldosterone synthase inhibitors with a higher selectivity index for CYP11B2 than LCI699 should make it possible to test this approach at much higher doses in these patients, after the necessary toxicology and Phase I studies.

Safety of mineralocorticoid receptor antagonists in patients receiving hemodialysis

OBJECTIVE

To evaluate the literature supporting the safe use of mineralocorticoid antagonists (MRAs) in patients with end-stage renal disease who are receiving hemodialysis.

DATA SOURCES

A review of the literature was performed using MEDLINE (1950 through week 2 of February 2012) using the key words and MeSH terms mineralocorticoid antagonists, aldosterone antagonists, spironolactone, or eplerenone combined with dialysis, renal disease, or kidney disease.

STUDY SELECTION AND DATA EXTRACTION

Studies eligible for inclusion evaluated the impact of MRAs on serum potassium levels in patients with end-stage renal disease receiving hemodialysis. Data related to the patient populations and outcomes of interest were extracted from each publication.

DATA SYNTHESIS

Ten studies were included in this review (spironolactone, 9; eplerenone, 1) and reported on the impact of MRAs on potassium levels in this population. In aggregate, the studies, with spironolactone doses ranging from 25 mg 3 times/week after dialysis to 300 mg/day and eplerenone doses of 25 mg twice daily, have shown little increases in serum potassium, particularly with the lower doses. The overall incidence of severe hyperkalemia was low. The literature base is limited by significant methodologic weaknesses of the studies, including low patient numbers, short follow-up periods, and lack of a blinded control group.

CONCLUSIONS

The current literature suggests that MRAs may be used safely in patients with end-stage renal disease receiving hemodialysis, although additional large controlled trials are needed before definitive treatment recommendations can be made.

Resistant hypertension and aldosterone: an update

Resistant hypertension (RHTN) is defined as a blood pressure remaining above goal despite the concurrent use of 3 antihypertensive medications of different classes, including, ideally a diuretic. RHTN is an important health problem with a prevalence rate expected to increase as populations become older, more obese, and at higher risk of having diabetes and chronic kidney disease, all of which are important risk factors for development of RHTN. The role of aldosterone has gained increasing recognition as a significant contributor to antihypertensive treatment resistance. In prospective studies, the prevalence of primary aldosteronism (PA) has ranged from 14%-21% in patients with RHTN, which is considerably higher than in the general hypertensive population. Furthermore, marked antihypertensive effects are seen when mineralocorticoid antagonists are added to the treatment regimen of patients with RHTN, further supporting aldosterone excess as an important cause of RHTN. A close association exists between hyperaldosteronism, RHTN, and obstructive sleep apnea (OSA) based upon recent studies which indicate that OSA is worsened by aldosterone-mediated fluid retention. This interaction is supported by preliminary data which demonstrates improvement in OSA severity after treatment with spironolactone.

Chronic intrarenal insulin replacement reverses diabetes mellitus-induced natriuresis and diuresis

We showed recently that sustained natriuresis in type 1 diabetic dogs was attributed to the decrease in insulin rather than the hyperglycemia alone. The sodium-retaining action of insulin appeared to require hyperglycemia, and it completely reversed the diabetic natriuresis and diuresis. This study tested whether the sodium-retaining effect was attributed to direct intrarenal actions of insulin. Alloxan-treated dogs (D; n=7) were maintained normoglycemic using 24-h/d IV insulin replacement. After control measurements, IV insulin was decreased to begin a 6-day diabetic period. Blood glucose increased from 84±6 mg/dL to an average of 428 mg/dL on days 5 and 6, sodium excretion increased from 74±8 to 98±7 meq/d over the 6 days, and urine volume increased from 1645±83 to 2198±170 mL/d. Dir dogs (n=7) were subjected to the same diabetic regimen, but, in addition, insulin was infused continuously into the renal artery at 0.3 mU/kg per minute during the 6-day period. This did not affect plasma insulin. Blood glucose increased from 94±10 mg/dL to an average of 380 mg/dL on days 5 and 6, but sodium excretion averaged 76±5 and 69±8 meq/d during control and diabetes mellitus, respectively. The diuresis also was prevented. Glomerular filtration rate increased only in Dir dogs, and there was no change in mean arterial pressure in either group. This intrarenal insulin infusion had no effect on sodium or volume excretion in normal dogs. Intrarenal insulin replacement in diabetic dogs caused a sustained increase in tubular reabsorption that completely reversed diabetic natriuresis. Insulin plus glucose may work to prevent salt wasting in uncontrolled type 2 diabetes mellitus.

The use of plasma aldosterone and urinary sodium to potassium ratio as translatable quantitative biomarkers of mineralocorticoid receptor antagonism

BACKGROUND

Accumulating evidence supports the role of the mineralocorticoid receptor (MR) in the pathogenesis of diabetic nephropathy. These findings have generated renewed interest in novel MR antagonists with improved selectivity against other nuclear hormone receptors and a potentially reduced risk of hyperkalemia. Characterization of novel MR antagonists warrants establishing translatable biomarkers of activity at the MR receptor. We assessed the translatability of urinary sodium to potassium ratio (Na+/K+) and plasma aldosterone as biomarkers of MR antagonism using eplerenone (Inspra®), a commercially available MR antagonist. Further we utilized these biomarkers to demonstrate antagonism of MR by PF-03882845, a novel compound.

METHODS

The effect of eplerenone and PF-03882845 on urinary Na+/K+ and plasma aldosterone were characterized in Sprague-Dawley rats and spontaneously hypertensive rats (SHR). Additionally, the effect of eplerenone on these biomarkers was determined in healthy volunteers. Drug exposure-response data were modeled to evaluate the translatability of these biomarkers from rats to humans.

RESULTS

In Sprague-Dawley rats, eplerenone elicited a rapid effect on urinary Na+/K+ yielding an EC50 that was within 5-fold of the functional in vitro IC50. More importantly, the effect of eplerenone on urinary Na+/K+ in healthy volunteers yielded an EC50 that was within 2-fold of the EC50 generated in Sprague-Dawley rats. Similarly, the potency of PF-03882845 in elevating urinary Na+/K+ in Sprague-Dawley rats was within 3-fold of its in vitro functional potency. The effect of MR antagonism on urinary Na+/K+ was not sustained chronically; thus we studied the effect of the compounds on plasma aldosterone following chronic dosing in SHR. Modeling of drug exposure-response data for both eplerenone and PF-03882845 yielded EC50 values that were within 2-fold of that estimated from modeling of drug exposure with changes in urinary sodium and potassium excretion. Importantly, similar unbound concentrations of eplerenone in humans and SHR rats yielded the same magnitude of elevations in aldosterone, indicating a good translatability from rat to human.

CONCLUSIONS

Urinary Na+/K+ and plasma aldosterone appear to be translatable biomarkers of MR antagonism following administration of single or multiple doses of compound, respectively.

TRIAL REGISTRATION

For clinical study reference EE3-96-02-004, this study was completed in 1996 and falls out scope for disclosure requirements. Clinical study reference A6141115: http://clinicaltrials.gov, http://NIHclinicaltrails.gov; NCTID: NCT00990223.

Prevalence of resistant hypertension in the United States, 2003-2008

The prevalence of resistant hypertension is unknown. Much previous knowledge comes from referral populations or clinical trial participants. Using data from the National Health and Nutrition Examination Survey from 2003 through 2008, nonpregnant adults with hypertension were classified as resistant if their blood pressure was ≥140/90 mm Hg and they reported using antihypertensive medications from 3 different drug classes or drugs from ≥4 antihypertensive drug classes regardless of blood pressure. Among US adults with hypertension, 8.9% (SE: 0.6%) met criteria for resistant hypertension. This represented 12.8% (SE: 0.9%) of the antihypertensive drug-treated population. Of all drug-treated adults whose hypertension was uncontrolled, 72.4% (SE: 1.6%) were taking drugs from <3 classes. Compared with those with controlled hypertension using 1 to 3 medication classes, adults with resistant hypertension were more likely to be older, to be non-Hispanic black, and to have higher body mass index (all P<0.001). They were more likely to have albuminuria, reduced renal function, and self-reported medical histories of coronary heart disease, heart failure, stroke, and diabetes mellitus (P<0.001). Most (85.6% [SE: 2.4%]) individuals with resistant hypertension used a diuretic. Of this group, 64.4% (SE: 3.2%) used the relatively weak thiazide diuretic hydrochlorothiazide. Although not rare, resistant hypertension is currently found in only a modest proportion of the hypertensive population. Among those classified here as resistant, inadequate diuretic therapy may be a modifiable therapeutic target. Cardiovascular diseases, diabetes mellitus, obesity, and renal dysfunction were all common in this population.

Aldosteronism and resistant hypertension

Resistant hypertension (RHTN) is defined as blood pressure (BP) that remains uncontrolled in spite of intake of ≥3 antihypertensive medications, ideally prescribed at optimal doses and one of which is a diuretic. The incidence of primary aldosteronism (PA) in patients with RHTN is estimated in prospective studies to be 14 to 23%, which is higher than in the general hypertensive population. Patients with PA are at an increased cardiovascular risk, as shown by higher rates of stroke, myocardial infarction, and arrhythmias compared to hypertensive individuals without PA. Likewise, RHTN is associated with adverse cardiovascular outcomes, and the contribution of PA to this increased risk is undetermined. Similar to PA, obstructive sleep apnea (OSA) is closely associated with RHTN, and a causal link between PA, OSA, and RHTN remains to be elucidated. The addition of MR antagonists to the antihypertensive regimen in patients with RHTN produces a profound BP-lowering effect, and this effect is seen in patients with or without biochemical evidence of PA, highlighting the role of relative aldosterone excess in driving treatment resistance in this group of patients.

Successful blood pressure control with additive administration of eplerenone, an aldosterone receptor blocker, in a patient with bilateral renovascular hypertension treated with angioplasty

A 29-year-old woman with refractory hypertension who previously suffered from subarchnoid hemorrhage visited our facility. The diagnosis of renovascular hypertension due to fibromuscular dysplasia was made based on a high level of plasma renin activity (PRA) and aldosterone concentration (AC), and computed tomographic image of bilateral renal artery stenosis/obstruction. Angioplasty, which could be performed only to the left renal artery, failed to regain sufficient BP control. The addition of eplerenone, an aldosterone receptor blocker, to the conventional antihypertensive drugs successfully and safely lowered BP and preserved the renal function despite the persistence of high PRA and AC values.