Abstract

BACKGROUND

Multiple studies indicate that primary aldosteronism (PA) is common in patients with resistant hypertension, with an estimated prevalence of approximately 20%. Additional studies suggest that beyond this 20% of patients with classical PA, there is a larger proportion of patients with lesser degrees of hyperaldosteronism which contributes even more broadly to antihypertensive treatment resistance. Given these observations, it is intuitive that use of aldosterone antagonists will provide antihypertensive benefit in patients with resistant hypertension and evidence of aldosterone excess. Intriguingly, however, are clinical findings demonstrating substantive benefit of aldosterone antagonists in patients with resistant hypertension, but without demonstrative evidence of hyperaldosteronism, that is, with seemingly normal or even low aldosterone levels.

CONCLUSION

Spironolactone is clearly established as the most effective fourth agent for treatment of uncontrolled resistant hypertension. Emerging observations suggest a further role of spironolactone for counteracting the effects of diet high in sodium, particularly in obese, hypertensive patients.

Beginning more than 15 years ago, separate studies have demonstrated that primary aldosteronism (PA) is common in patients with resistant hypertension, with a prevalence of approximately 20%.1–4 Beyond this 20% of patients with classical PA, other studies indicated lesser, but even more common degrees of hyperaldosteronism, that, none the less, likely contribute to antihypertensive treatment resistance.5

Coinciding with studies demonstrating that hyperaldosteronism is a common cause of resistant hypertension, there have been an increasing number of studies demonstrating the preferential benefit of aldosterone antagonists for the treatment of resistant hypertension. The early studies, in this regard, were typically small, open-label, uncontrolled assessments of spironolactone used as third- or fourth-line treatment for uncontrolled resistant hypertension.6,7 Subsequent assessments were strengthened and made more compelling in evaluating larger cohorts and in confirming the antihypertensive benefit of spironolactone with use of ambulatory blood pressure (BP) monitoring.8,9 Most recently, the superiority of spironolactone to treat resistant hypertension compared to other classes of agents was clearly demonstrated with the publication of the Pathway-2 results.10 The Pathway-2 findings, combined with preceding study results, clearly establishes spironolactone as the most appropriate fourth agent for treating uncontrolled resistant hypertension. This review attempts to highlight selected studies that critically advanced our understanding of the benefit and provided details in the practical use of aldosterone antagonists for treatment of resistant hypertension. In addition, very recent studies are discussed suggesting a potential role of aldosterone antagonists for treatment of obesity-related hypertension, particularly in the setting of high-dietary sodium ingestion.11

EPLERENONE VS. SPIRONOLACTONE FOR PRIMARY HYPERTENSION

Eplerenone, a selective mineralocorticoid receptor antagonist, with higher affinity for the mineralocorticoid receptor and lower affinity for progesterone and androgen receptors than spironolactone, was extensively tested worldwide in order to gain approval for treatment of generalized hypertension. These studies were informative both in demonstrating benefit of aldosterone blockade for treatment of uncomplicated primary hypertension, but also in comparing the efficacy and tolerability of eplerenone vs. spironolactone in generalized hypertensive cohorts. In this regard, the study of Weinberger et al. was particularly compelling.12 The study was pivotal in leading to the approval of eplerenone for the treatment of mild–moderate hypertension and provided important clinical insight into the use of eplerenone vs. spironolactone.

The Weinberger study was particularly ambitious in having been done as a multicenter, double-blind, placebo-controlled, parallel dose-ranging study conducted at 48 US sites.12 The study was scientifically rigorous in having consisted of a 4-week, single-blind, placebo run-in followed by a randomized, 8-week, double-blind treatment period. The treatment arms included eplerenone 50, 100, or 400mg daily; eplerenone 25, 50, or 200mg twice daily; spironolactone 50mg twice daily; or placebo. Both office and 24-hour ambulatory BP were measured.

A total of 409 subjects completed the study. Eplerenone administered 400mg daily reduced office systolic BP (SBP) and diastolic BP (DBP) compared to baseline by −15.0 and −8.7mm Hg, respectively.12 Eplerenone 200mg twice daily reduced office SBP and DBP to a similar degree (−14.8 and −8.9mm Hg, respectively). Because of concerns of hyperkalemia with this high of a dose, particularly in patients with diabetes, eplerenone was subsequently approved for use up to 100mg daily. At this level, given as single daily dose, office SBP was reduced by −7.9/−4.4mm Hg. When administered as 50mg twice daily, the reduction in office BP was −11.7/−7.8mm Hg, which was statistically greater than the 100mg given as a single daily dose.

Changes in 24-hour ambulatory BP levels demonstrated similar antihypertensive effects in relation to the different doses and dosing schedules of eplerenone. The 400mg dose once daily reduced 24-hour ambulatory SBP and DBP by −13.7/7.7mm Hg, respectively. When administered as 200mg twice daily, the changes in 24-hour SBP and DBP tended to be greater, i.e., −16.1/−9.0mm Hg, respectively. Reductions in ambulatory BP with eplerenone 100mg were considerably less whether administered as a single daily dose or as 50mg twice daily (−9.6/−5.6 and −11.6/−6.6mm Hg, respectively).

Interestingly, spironolactone 50mg twice daily reduced both office and 24-hour ambulatory BP comparable to eplerenone 400mg daily.12 The change in office BP with spironolactone was −16.7/−9.5mm Hg with a corresponding decrease in 24-hour ambulatory BP of −15.8/8.7mm Hg. Although not compared statistically, these observed reductions were clearly numerically superior to the currently recommended maximum dose of eplerenone 100mg daily.

The study of Weinberger et al., even though not done in subjects with resistant hypertension, nonetheless provides important information regarding the dosing of eplerenone when treating resistant hypertension.12 Similarly, it provides important comparative information regarding eplerenone and spironolactone, also relevant to treating resistant hypertension. Firstly, the use of eplerenone at the currently recommended maximum dose of 100mg daily was better if given in divided doses of 50mg. Accordingly, it seems reasonable when using eplerenone to treat resistant hypertension, to use doses of 50mg twice daily to achieve maximum benefit. Secondly, spironolactone 50mg twice daily was much more efficacious in terms of BP reduction than eplerenone at the same dose. Because of its greater mineralocorticoid receptor selectivity, eplerenone does have a lower incidence of adverse effects, particularly breast tenderness, gynecomastia, and sexual dysfunction, compared to use of spironolactone. However, given its antihypertensive advantage it would seem preferable to initiate therapy with spironolactone and titrate as tolerated, but switching to eplerenone if adverse effects necessitate withdrawal of the spironolactone.

HYPERALDOSTERONISM AND RESISTANT HYPERTENSION

Multiple studies suggest that PA is common cause of resistant hypertension. Biochemical assessments of consecutive patients referred to hypertension specialty clinics for uncontrolled resistant hypertension suggest that approximately 20% will fulfill the biochemical criteria for havingPA.1–4 However, beyond that 20% of patients having classical PA, studies further suggest lesser degrees of hyperaldosteronism that are also likely contributing to antihypertensive treatment resistance. For example, Gaddam et al. at the University of Alabama at Birmingham (UAB) found that more than 60% of patients referred to UAB hypertension clinic for resistant hypertension had suppressed plasma renin activity and 35% had an elevated plasma aldosterone/plasma renin activity ratio, both reflecting degrees aldosterone excess even in the absence of 24-hour urinary aldosterone levels sufficient to diagnose true PA.5 Given this evidence of aldosterone excess beyond the minority of patients with demonstrable PA, it would not seem unreasonable to anticipate broad benefit of aldosterone antagonists for treatment of resistant hypertension.

PREFERENTIAL BENEFIT OF SPIRONOLACTONE FOR TREATMENT OF UNCONTROLLED RESISTANT HYPERTENSION

One of the earliest reports of preferential benefit of spironolactone for treatment of resistant hypertension was a French study from Ouzan et al. published in 2002.7 In this study, the authors added spironolactone to the existing regimen of 25 patients uncontrolled with 2 or more antihypertensive medications. The majority of patients were receiving 3 or 4 medications and the BP levels were severe, with office SBP readings for the individual participants ranging from 157 to 230mm Hg and office DBP ranging from 80 to 110mm Hg. Spironolactone was dosed at 1mg/kg of body weight per day. The mean dose used was not reported, but presumably would have been in the 80–100mg range. Change in office BP was reported for each individual participant and as well as the mean change in 24-hour ambulatory BP at 1-month follow-up after adding spironolactone.

All study participants had an improvement in office BP with individual office SBP readings after treatment with spironolactone ranging from 120–150 and diastolic to 80–90mm Hg.7 The mean 24-hour ambulatory SBP decreased significantly from 152±2 to 128±2mm Hg and DBP from 86±2 to 76±2mm Hg. Twenty-three of the 25 subjects had controlled office BP (<140/90mm Hg) at 1-month and all 25 patients by 3-month follow-up. Also by 3-month follow-up, the average number of antihypertensive medications decreased from 3.2±0.2 to 2.1±0.2mm Hg.

This study is important in being perhaps the earliest to demonstrate the add-on benefit of spironolactone to specifically treat resistant hypertension and in having confirmed the benefit with ambulatory BP monitoring.7 The degree of BP reduction was impressive, especially given how severe the office BP readings were prior to adding spironolactone. The finding suggested that spironolactone might provide preferential antihypertensive in reducing BP in patients uncontrolled on multiple other classes of agents.

BROAD BENEFIT OF LOW-DOSE SPIRONOLACTONE

The study of Nishizaka et al. was important in advancing the use of spironolactone for treatment of resistant hypertension by demonstrating antihypertensive benefit with low doses of spironolactone and in having shown broad benefit in a diverse cohort that included both African American and Caucasian subjects with a wide range of aldosterone levels.6 The study was conducted at the UAB as a prospective, open-label evaluation of low doses of spironolactone when added to multidrug regimens of at least 3 or more medications. A total of 76 patients were included in the analysis, of whom, 41 were African American. Study participants were on an average of 4 medications, including, in all subjects, an angiotensin converting enzyme (ACE) inhibitor or angiotensin receptor blocker (ARB), amlodipine, and hydrochlorothiazide. A full biochemical evaluation for aldosterone status was done in all subjects at baseline. Based on that evaluation, 34 of the 76 subjects met the criteria for biochemical PA (24-hour urinary aldosterone ≥12 µg and plasma renin activity <1.0ng/ml/h). Spironolactone was added at 12.5mg/day and titrated to 50mg if the office BP remained uncontrolled at any of the follow-up visits.

Spironolactone treatment resulted in a mean reduction in office SBP and DBP of 25±20 and 12±12mm Hg, respectively.6 The mean dose of spironolactone at study end was approximately 30mg, meaning most subjects had their BP controlled with spironolactone dosed at 25mg daily. There were no racial differences in response to spironolactone in that African American and Caucasian subjects manifested similar degree of benefit with the same mean dose of spironolactone. Interestingly, the antihypertensive benefit of spironolactone was similar in all subjects regardless of aldosterone status. That is, BP reduction was similar regardless of aldosterone levels, although patients diagnosed with PA were more likely to have been titrated to 50mg of spironolactone. This is perhaps one of the most of important clinical implications of this study in demonstrating that the antihypertensive benefit of spironolactone when treating patients with resistant hypertension was not limited to patients with demonstrably high aldosterone levels. Similar antihypertensive benefit was also occurring in patients with seemingly normal or low aldosterone levels, indicating a broad benefit of spironolactone when used to treat patients otherwise failing other classes of antihypertensive agents.

The study of Nishizaka et al. is informative in having shown benefit of spironolactone to treat resistant hypertension with doses as low as 25mg daily. It is also important in having shown benefit regardless of race in that African American and Caucasian patients had similar BP reductions.6 Lastly, the study was important in demonstrating that spironolactone was broadly effective in treating resistant hypertension and that benefit was not limited to patients with the highest aldosterone levels (Figure 1). This observation was mechanistically important in suggesting that relative degrees of hyperaldosteronism likely contribute to antihypertensive treatment resistance beyond the 20% of patients diagnosed with classical PA.

Figure 1.

Spironolactone-induced reduction in SBP (filled bars) and DBP (open bars) at 6-week, 3-month, and 6-month follow-up in subjects with resistant hypertension (upper panel). Spironolactone-induced reduction in SBP and DBP at 6-week, 3-month, and 6-month follow-up in subjects with PA (filled bars) and without PA (non-PA: open bars)(lower panel).6 Abbreviations: DBP, diastolic blood pressure; PA, primary aldosteronism; SBP, systolic blood pressure.

Figure 1.

Spironolactone-induced reduction in SBP (filled bars) and DBP (open bars) at 6-week, 3-month, and 6-month follow-up in subjects with resistant hypertension (upper panel). Spironolactone-induced reduction in SBP and DBP at 6-week, 3-month, and 6-month follow-up in subjects with PA (filled bars) and without PA (non-PA: open bars)(lower panel).6 Abbreviations: DBP, diastolic blood pressure; PA, primary aldosteronism; SBP, systolic blood pressure.

LONG-TERM BENEFIT OF SPIRONOLACTONE

The Anglo-Scandinavian Cardiac Outcomes Trial-Blood Pressure Lowing Arm (ASCOT) was a large, prospective, outcome comparison of an antihypertensive regimen based either on amlodipine or atenolol.13 Per protocol, spironolactone was utilized at the discretion of investigators when study medications failed to control BP. In this setting, over 1,400 ASCOT participants received spironolactone 35–50mg daily as a fourth-line add-on therapy. The median duration of spironolactone treatment was 1.3 years and the median dose was 25mg. The mean starting and final daily doses were 35 and 41mg, respectively.

With the addition of spironolactone, the mean reduction in SBP was 21.9 and DBP was 9.5mm Hg.13 These findings were important in confirming the broad antihypertensive benefit of spironolactone at low doses in a large cohort of patients unselected other than for having uncontrolled resistant hypertension. The study is also important in demonstrating a long-term duration of benefit with use of spironolactone, in this case, exceeding 1 year. With such a large treated cohort, the investigators were able to do multiple subgroup comparisons in an effort to identify predictors of BP response to spironolactone. Broadly, similar BP reductions were observed regardless of age, gender, and having diabetes. The effect of spironolactone was not modified by concomitant use of thiazide diuretics or ACE inhibitors.

Overall, the ASCOT analysis was instrumental in confirming the broad antihypertensive benefit of low-dose spironolactone to substantially reduced BP in patients with uncontrolled resistant hypertension.13 Importantly, the benefit was demonstrated to be persistent. Lastly, benefit was broad based with older vs. younger and men vs. women manifesting similar BP reductions in a sustained fashion.

SPIRONOLACTONE VS. ACE INHIBITOR/ARB COMBINATION

The above-described studies evaluating the antihypertensive benefit of spironolactone to treat resistant hypertension were all done as open-label, uncontrolled assessments, that is, none included an active comparator in terms of BP benefit. A study by Alvarez-Alvarez et al. was one of the first clinical assessments address this deficiency in comparing spironolactone to an active control, in this case, dual blockade of the renin–angiotensin–aldosterone system (RAAS) with combined use of an ACE inhibitor and an ARB.8 The study was done as an open-label, prospective, cross-over evaluation of spironolactone vs. the combination of an ACE inhibitor and an ARB.

The first treatment arm consisted of adding an ACE inhibitor or ARB as needed to the existing antihypertensive regimen to achieve dual RAAS blockade for 12 weeks.8 This followed by a 4-week washout of the added RAAS blocker. Spironolactone was then added to the existing regimen, initially at 25mg and titrating to 50mg, if needed for uncontrolled BP. Treatment with spironolactone was also for 12 weeks. Ambulatory BP monitoring was done prior to and the end of each 12-week treatment period.

A total of 42 subjects completed the protocol. All patient had uncontrolled resistant hypertension with use of an average of 4 medications, such that, in most cases, the tested medications were being added as a fourth or fifth drug.8 Overall, spironolactone was superior to dual RAAS blockade both in reducing office and ambulatory BP. Specifically, combined ACE inhibitor and ARB use reduced office SBP at 12-week follow-up by 12.9±19.2mm Hg, while office DBP was unchanged. In comparison, the addition of spironolactone also at 12-week follow-up, reduced office SBP, and DBP by an extraordinary 32.2±20.6/10.9±11.6mm Hg. Reduction in ambulatory BP levels likewise heavily favored spironolactone. Dual RAAS blockade reduced 24-hour ambulatory SBP and DBP by 7.1±13.4 and 3.4±6.2mm Hg, respectively, while the corresponding values for spironolactone were 20.8±14.6 and 8.8±7.3mm Hg, respectively. In terms of control rates, spironolactone achieved office BP control (<140/90mm Hg) in 53.8% of study participants compared to only 26.6% of the participants during dual RAAS blockade. As measured by ABPM, control was achieved in 20.5% of participants with dual RAAS blockade compared to 56.4% while receiving spironolactone.

This study of Alvarez-Alvarez et al. is informative in being the first to demonstrate that spironolactone is specifically superior to other treatment options, in this case combined use of an ACE inhibitor and ARB use, as a fourth or fifth medication.8 This report is important in that it suggests that spironolactone does have preferential benefit in treating resistant hypertension and that simply adding any other active treatment as a forth of fifth drug will not necessarily achieve the same level of add-on antihypertensive benefit.

RANDOMIZED COMPARISON OF SPIRONOLACTONE WITH PLACEBO

The Addition of Spironolactone in Patients with Resistant Arterial Hypertension (ASPIRANT) trial was a randomized, double-blind, single-center parallel-arm comparison of low-dose spironolactone (25mg daily) with placebo in patients with resistant hypertension.14 The primary endpoints were change in daytime ambulatory BP levels after 8 weeks of treatment. Enrolled patients were on an average of 4.5 antihypertensive medications, including, for most patients, either hydrochlorothiazide or indapamide. The study was terminated early because a substantial reduction in ambulatory SBP with having had 117 patients complete the study. Compared to placebo, spironolactone had significantly reduced daytime ambulatory and nighttime SBP by −5.4 and −8.6mm Hg, respectively. Corresponding differences in daytime and nighttime ambulatory DBP of −1.0 and −3.0mm Hg, respectively, were also in favor of spironolactone, but were not statistically different from placebo.

After analysis of the initial results, study enrollment was resumed, with completion of an additional 33 patients or 150 in total.15 With the larger sample size, the BP reductions in favor of spironolactone were even larger. Compared to placebo, spironolactone significantly reduced daytime and nighttime ambulatory SBP by −9.8 and −13.0mm Hg, respectively. Corresponding reductions in daytime and nighttime ambulatory DBP by −3.2 and −6.4mm Hg, respectively, which were statistically different from placebo.

The APSPIRANT trial is important in confirming, with use of ambulatory monitoring, in a double-blind, randomized design the independent antihypertensive benefit of low-dose spironolactone for treatment of uncontrolled resistant hypertension.14,15 It is also informative in quantifying the degree of antihypertensive benefit with spironolactone in reporting an average reduction in daytime ambulatory BP of approximately −10/−3mm Hg.

DEFINITIVE DEMONSTRATION OF SPIRONOLACTONE AS A FOURTH AGENT COMPARED TO OTHER CLASSES OF AGENTS

While an increasing number of studies were adding to a preponderance of data that spironolactone provided preferential benefit in overcoming antihypertensive treatment resistance, most of the studies lacked the highest level of scientific rigor in being mostly single-center, open-label, and/or uncontrolled assessments of antihypertensive benefit. The very impressive PATHWAY-2 study, sponsored by the British Society of Hypertension, overcame these limitations in conducting a large, multicenter, randomized, double-blind, placebo-controlled cross-over evaluation of spironolactone, doxazosin, and bisoprolol in subjects uncontrolled on a standard 3-drug regimen consisting of a ACE inhibitor or ARB, a calcium channel blocker, and a diuretic.10 Subjects received in random order, placebo, or the 3 active treatment medications for 12 weeks each. The dose amounts were spironolactone 25–50mg, doxazosin 4–8mg, and bisoprolol 5–10mg daily, with all subjects being force titrated to the higher doses, respectively, after the initial 6 weeks of treatment. The primary endpoint was change in home SBP.

At study end, 285 patients received spironolactone, 282 doxazosin, 285 bisoprolol, and 274 received placebo; 230 patients completed all 4 treatment cycles. Spironolactone was by far superior to placebo and the other 2 active treatments.10 Compared to placebo, spironolactone reduced home SBP on average by 8.70mm Hg; by 4.48mm Hg compared to bisoprolol; and by 4.03mm Hg compared to doxazosin. Overall, 56% of patients had their home SBP controlled to <135mm Hg, which was superior to control rates with bisoprolol (44%) and doxazosin (42%).

Interestingly, there was a clear inverse relation between reduction in SBP and plasma renin level, while no relation was observed with bisoprolol or doxazosin. Spironolactone was the best BP-lowering treatment throughout the entire renin distribution, even at the highest levels of renin concentration, but at the lower end of the distribution, the magnitude of spironolactone’s superiority was particularly pronounced, with mean reductions in SBP approaching 20mm Hg compared to placebo. Also informative was the demonstration of a large dose benefit of spironolactone when titrating from 25 to 50 mg. On average, titration of spironolactone resulted in an additional 3.86mm Hg reduction in SBP. In contrast, titration of bisoprolol resulted, on average, of only an additional 1.49mm Hg reduction in SBP, while titration of doxazosin to the higher dose resulted in no additional benefit.

With publication of the Pathway-2 study, spironolactone is clearly established as the most effective fourth agent for treatment of resistant hypertension.10 This benefit was on top of a standardized 3-drug regimen of an ACE inhibitor or ARB, a calcium channel blocker, and a diuretic. Pathway-2 was also important in clearly demonstrating a dose titration benefit of spironolactone up to 50mg daily. Further, the Pathway-2 findings highlight the pronounced benefit of aldosterone antagonists in patients with suppressed renin activity. Such benefit is consistent with aldosterone excess contributing broadly to development of antihypertensive treatment resistance.

USE OF EPLERENONE FOR TREATMENT OF RESISTANT HYPERTENSION

While the benefit of eplerenone to treat mild–moderate hypertension is well established, evaluation of its usefulness to specifically treat resistant hypertension is limited. Calhoun and White conducted a prospective, open-label, 2-center evaluation of eplerenone as add-on therapy for treatment of uncontrolled resistant hypertension.16 Eplerenone was added firstly at 50mg daily and if the BP remained uncontrolled (office BP >140/90mm Hg) after 4-weeks at that dose, it was titrated to 50mg twice daily. The entire active treatment period was for 12 weeks. Endpoints included change in both clinic and ambulatory BP levels.

A total of 52 patients completed the protocol. Patients were receiving at study start an average of 3.7 antihypertensive medications, including in all subjects, an ACE inhibitor or ARB, a calcium channel blocker, and a thiazide diuretic.16 The average final dose of eplerenone was 50mg daily, with 31 of the 52 subjects achieving BP control on the starting dose of 50mg daily. After 12 weeks of treatment, eplerenone reduced the clinic BP by 17.6/7.9mm Hg and 24-hour mean BP by −12.2/−6.0mm Hg. Overall, 63.4% of patients had their clinic BP controlled (<140/90mm Hg) and 39.0% achieved control of their 24-hour ambulatory BP levels (<135/85mm Hg).

Although limited by its open-label design, this study does suggest that eplerenone, like spironolactone, is effective in treating uncontrolled resistant hypertension. Absent a direct comparison, one cannot assume eplerenone is superior or even comparable to spironolactone to treat resistant hypertension. Given the data that is available, i.e., the superiority of spironolactone over eplerenone in mild–moderate hypertension as observed by Weinberger et al., it is likely that spironolactone will likewise be superior to eplerenone when treating resistant hypertension, at least within commonly used dose ranges (i.e., 25–50mg daily for spironolactone and 50–100mg daily for eplerenone).12,16 Accordingly, it seems appropriate, in order to maximize antihypertensive benefit, to firstly use spironolactone as add-on treatment for resistant hypertension, and reserving eplerenone for those patients that cannot tolerate the former, most likely because of breast tenderness, gynecomastia, and/or sexual dysfunction.

VISCERAL OBESITY AS A CAUSE OF HYPERALDOSTERONISM?

Based on an analysis of over 2,000 patients with resistant hypertension, Dudenbostel et al. recently reported that both plasma aldosterone and 24-hour urinary aldosterone is positively correlated with increasing body mass index (BMI) (Figure 2).17 The positive correlation was evident both for men and women, and after correcting for the higher body weight of African American patients, was similarly true of both African American and Caucasian subjects. In contrast, BMI was inversely related to plasma renin activity, suggesting that the increasing aldosterone levels in relation to increasing body weight were independent of renin.

Figure 2.

Mean 24-hour UAldo levels to quartiles of BMI in men vs. women. White columns represent women and black columns represent men.17 Abbreviations: BMI, body mass index; Ualdo, urinary aldosterone

Figure 2.

Mean 24-hour UAldo levels to quartiles of BMI in men vs. women. White columns represent women and black columns represent men.17 Abbreviations: BMI, body mass index; Ualdo, urinary aldosterone

Interestingly, the correlation between aldosterone levels and BMI, while true of both men and women, was more pronounced in the former, such that men had the overall higher aldosterone levels, and compared to women, manifested as steeper increases in aldosterone in relation to increasing BMI.17 While explanation for this gender difference is open to conjecture, the authors suggest that one possible explanation may be that visceral adiposity, which is more characteristic of men, and which is known to be more hormonally active than the peripheral adiposity characteristic of women, may serve as an important source of as of yet unidentified stimulus of aldosterone release. The possibility of such adipocyte-related aldosterone secretagogue is supported by demonstration of release of aldosterone stimulating factors from isolated adipocytes.18,19

The findings of Dudenbostel et al. suggest that the hyperaldosteronism that is prevalent in patients with resistant hypertension may be attributable, at least in part, to increasing obesity, particularly visceral obesity.17 If true, it would implicate excess aldosterone as an important mediator of obesity-related hypertension, and thereby, raising the possibility of preferential role of aldosterone antagonists, not only for the treatment of resistant hypertension, but more broadly for the treatment of obesity-related hypertension.

ADIPOCYTES AS A DIRECT SOURCE OF ALDOSTERONE LEADING TO VASCULAR DYSFUNCTION

Experimental studies indicate, in addition to releasing secretory products that stimulate adrenocortical aldosterone release, adipocytes serve as a direct source of aldosterone in sufficient amount to contribute to perivascular inflammation, endothelial dysfunction, and vascular stiffness.20 Cell culture studies indicate that adipocytes possess aldosterone synthase and that expression of aldosterone synthase and production of aldosterone is increased in mature adipocytes isolated from db/db mice, a model of diabetes-associated obesity. In this same mouse model, aldosterone blockade with use of eplerenone improves arterial endothelial dysfunction.20 These findings suggest that aldosterone released from adipocytes likely contribute to endothelial dysfunction and vascular stiffness, particularly in obese individuals, and thereby contributing to the development of resistant hypertension.

The direct role that adipocyte-derived aldosterone plays in causing vascular stiffness is further supported by clinical studies demonstrating that aldosterone blockade improves vascular function in hypertensive patients. Savoia et al. evaluated the effects of eplerenone vs. atenolol on the stiffness of resistance arteries from human gluteal subcutaneous tissue assessed by pressurized myography.21 In a double-blind evaluation, the authors found that while atenolol use was associated with an increase in arterial wall stiffness, eplerenone significantly reduced wall stiffness to levels comparable to normotensive controls. The improvement in arterial wall stiffness induced by eplerenone was associated with a decreased collagen/elastin ratio, and reduction in circulating inflammatory mediators. In this study, neither atenolol nor eplerenone affected endothelial-dependent relaxation of the small resistance vessels.21 However, other studies clinical have reported improvement in endothelial function of large arteries with spironolactone.22,23 Nishizaka et al., for example, reported significant improvement in brachial artery flow-mediated dilation after 3 months of treatment with spironolactone in patients with resistant hypertension.23 Combined, these experimental and clinical studies provide evidence that adipocyte-related aldosterone release contributes to the development of hypertension, including resistant hypertension, by promoting inflammation, endothelial dysfunction, and vascular stiffening.

SPIRONOLACTONE FOR PREFERENTIAL TREATMENT OF DIETARY SODIUM EXCESS?

Ghazi et al. reported an interesting analysis suggesting that the antihypertensive efficacy of spironolactone is enhanced in patients ingesting a diet high in dietary sodium.11 In this retrospective analysis, the BP response to using spironolactone as add-on therapy for treatment of uncontrolled resistant hypertension was evaluated. Prior to adding spironolactone, all evaluated subjects had undergone, as part of their routine clinical evaluation, analysis of a 24-hour urine collection done during ingestion of each patient’s normal diet. A total of 79 patients were analyzed, of whom, about half were women and half were African American. Importantly, these patients were mostly obese, with 76% have a BMI >30kg/m2.

After the addition of spironolactone 12.5–25mg daily to existing medications, the associated BP reduction was significantly higher in patients ingesting large amounts of sodium based on the 24-hour urinary sodium excretion (>200 meq/day).11 Specifically, the patients on a high-sodium diet manifested a larger reduction in BP with use of spironolactone on the order of about 12mm Hg, and overall, the likelihood of a favorable SBP response (>10mm Hg) was related to increasing sodium ingestion. This positive relation between dietary sodium and spironolactone was true of patients with high or low aldosterone levels, suggesting a preferential natriuretic effect of spironolactone in the setting of dietary sodium ingestion, at least in this cohort of overweight and obese patients.11 If confirmed prospectively, these findings suggest that aldosterone antagonists may be particularly beneficial in counteracting the hypertensive effects of ingesting large amounts of sodium, typical of modern day diets.

CONCLUSION

A series of studies has indicated that PA is a common cause of resistant hypertension.1–4 Related studies further suggest that even more common are lesser degrees hyperaldosteronism that contribute importantly to antihypertensive treatment resistance.5 Given this body of literature, it is not surprising that aldosterone antagonists have now been shown to provide preferential benefit compared to other classes of agents for control of resistant hypertension. With publication of the Pathway-2 results, spironolactone is now firmly established as the most effective fourth agent for treating high BP uncontrolled on triple combinations of an ACE inhibitor or ARB, amlodipine, and a long-acting thiazide diuretic.10 The Pathway-2 results in combination with the earlier studies indicate an effective dose range for spironolactone of 12.5–50mg daily for treating resistant hypertension.

Beyond resistant hypertension, recent findings suggest that aldosterone antagonists may also provide preferential benefit in treating obesity-related hypertension, especially in the setting of high-dietary sodium intake. This hypothesized benefit is based on recent observations relating increasing aldosterone excess to increasing body weight, in both men and women, but particularly in the former.17 In a separate study of mostly obese patients with resistant hypertension, benefit of spironolactone was seemingly enhanced in relation to increasing dietary sodium ingestion as reflected by 24-hour urinary sodium excretion.11 Combined, these recent findings suggest that resistant hypertension, aldosterone excess, and high-dietary sodium intake may be linked to being overweight or obese, such that use of spironolactone, especially in combination with a long-acting thiazide diuretic such as chlorthalidone, may be particularly beneficial in treating obesity-related hypertension.

DISCLOSURE

The authors declared no conflict of interest.

ACKNOWLEDGMENT

This work was supported by NIH grant RO1 HL113004.

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Author notes

Correspondence: Tanja Dudenbostel (tduden@uab.edu).