Relative potency and structure activity relationships of aldosterone antagonists in healthy man: correlation with animal experience

Spironolactone metabolite concentrations in decompensated heart failure: insights from the ATHENA-HF trial

AIMS

In Aldosterone Targeted Neurohormonal Combined with Natriuresis Therapy in Heart Failure (ATHENA-HF), high-dose spironolactone (100 mg daily) did not improve efficacy endpoints over usual care [placebo or continued low-dose spironolactone (25 mg daily) in patients already receiving spironolactone] in the treatment of acute heart failure (HF). We hypothesized that low concentrations of the long-acting active metabolites of spironolactone [canrenone and 7α-thiomethylspironolactone (7α-TMS)] in the high-dose group could have contributed to these neutral results.

METHODS AND RESULTS

In patients randomized to high-dose spironolactone not previously treated with spironolactone (high-dose-naïve, n = 112), concentrations of canrenone and 7α-TMS increased at 48 and 96 h compared to baseline, and between 48 and 96 h (all P < 0.005), indicating that steady-state concentrations had not been reached by 48 h. In patients previously on low-dose, high-dose spironolactone (high-dose-previous, n = 37), concentrations of canrenone increased at 48 and 96 h compared to baseline (both P < 0.0005), with a marginal increase between 48 and 96 h (P = 0.0507). At 48 h, both high-dose groups had higher concentrations of both metabolites than the low-dose spironolactone group (P < 0.0001). Moreover, concentrations of both metabolites were higher in high-dose-previous vs. high-dose-naïve patients (P < 0.01), indicating that previous spironolactone use was significant, and that steady-state has not been reached in high-dose-naïve patients at 48 h. We found limited and inconsistent evidence of correlation between metabolite concentrations and endpoints.

CONCLUSIONS

Lower-than-anticipated concentrations of spironolactone active metabolites were observed for at least 48 h in the high-dose spironolactone group and may have contributed to the absence of pharmacological effects of spironolactone in the ATHENA-HF trial.

Drug Insight: eplerenone, a mineralocorticoid-receptor antagonist

Increasing recognition of the role of aldosterone in cardiovascular disease has been supported by a significant body of evidence from animal models. This evidence has been translated into clinical practice, and large-scale, randomized, placebo-controlled trials have confirmed the beneficial effects of mineralocorticoid blockade in patients with heart failure. As a consequence, there has been a resurgence in the use of mineralocorticoid-receptor antagonists in clinical practice that has prompted the search for a potent and specific antagonist without the sexual side effects of spironolactone. Eplerenone, a mineralocorticoid-receptor antagonist with minimal binding to the progesterone and androgen receptors, is now licensed for treatment of heart failure in Europe and heart failure and hypertension in the US; it has also been proposed as a treatment for a variety of cardiovascular conditions. This article reviews the current concepts of the actions of aldosterone at a cellular level. Recent findings regarding its role as a cardiovascular hormone, both in animal models and human studies, are discussed. We also describe the development of mineralocorticoid-receptor blockers following the isolation of aldosterone and discuss the subsequent search for a specific mineralocorticoid antagonist. In addition we detail the effects of eplerenone in a number of clinical situations and outline its potential future applications.

Mineralocorticoid receptor mediates glucocorticoid treatment effects in the autoimmune mouse ear

The standard treatment for many hearing disorders is glucocorticoid therapy, although the cochlear mechanisms involved in steroid-responsive hearing loss are poorly understood. Cochlear dysfunction in autoimmune mice has recently been shown to be controlled with the mineralocorticoid aldosterone as effectively as with the glucocorticoid prednisolone. Because aldosterone regulates sodium, potassium, and other electrolyte homeostasis, this implied the restoration of hearing with the mineralocorticoid was due to its impact on cochlear ion transport, particularly in the stria vascularis. This also suggested glucocorticoids may be controlling hearing recovery in part through their binding to the mineralocorticoid receptor in addition to their glucocorticoid receptor-mediated anti-inflammatory and immunosuppressive functions. Therefore, the aim of the present study was to better delineate the role of the mineralocorticoid receptor in steroid control of hearing in the autoimmune mouse. Spironolactone, a mineralocorticoid receptor antagonist, was administered to MRL/MpJ-Fas(lpr) autoimmune mice in combination with either aldosterone or prednisolone to compare their hearing and systemic disease with mice that received either steroid alone. ABR thresholds showed either aldosterone or prednisolone alone preserved hearing in the mice, but spironolactone prevented both steroids from maintaining normal cochlear function. This suggested both steroids are preserving hearing through the mineralocorticoid receptor within the ear to regulate endolymph homeostasis. The spironolactone treatment did not block normal glucocorticoid receptor-mediated immune-suppression functions because mice receiving prednisolone, either with or without spironolactone, maintained normal body weights, hematocrits, and serum immune complexes. Thus, reducing systemic autoimmune disease was not sufficient to control hearing if mineralocorticoid receptor-mediated functions were blocked. It was concluded the inner ear mineralocorticoid receptor is a significant target of glucocorticoids and a factor that should be considered in therapeutic treatments for steroid-responsive hearing loss.

Studies on spirolactone steroid antagonists in ACTH-induced hypertension in sheep

This study investigated the anti-mineralocorticoid potency and haemodynamic effects of a series of mineralocorticoid antagonists of the spirolactone type (RU 28318, spironolactone, K-prorenoate, K-canrenoate and canrenone), for their ability to prevent the development of ACTH-induced hypertension in conscious sheep. In vivo bioassay, using aldosterone dependent changes in parotid salivary [Na+]/[K+] of sodium depleted adrenalectomized sheep, showed spironolactone was the most potent anti-mineralocorticoid tested. Infusions of the antagonists at equal doses alone for 4 days demonstrated that none affected mean arterial pressure, except for K-prorenoate which exhibited slight pressor activity. All the antagonists produced a natriuresis. Some of the steroid antagonists of the spirolactone group blocked the development of ACTH hypertension in sheep, spironolactone being the most effective. This study provides additional evidence for an essential mineralocorticoid component in ACTH-induced hypertension.

The metabolism and biopharmaceutics of spironolactone in man

Spironolactone, a competitive aldosterone antagonist, has been used for almost 30 years in those disorders associated with primary or secondary hyperaldosteronism. This review is confined to its metabolism and biopharmaceutics in man. Spironolactone undergoes extensive metabolism with no unchanged drug appearing in the urine. Its metabolites can be divided into two main categories: those in which the sulfur of the parent molecule is removed and those in which the sulfur is retained. The dethioacetylated metabolite canrenone, belonging to the former category, was long considered to be the major active metabolite of spironolactone. For this reason pharmacokinetic studies have focussed on its kinetic behaviour. However, pharmacodynamic studies indicated that canrenone could only partly explain spironolactone's action. Furthermore, with the advent of modern high-performance liquid chromatographic techniques to measure canrenone concentrations, it was shown that previously employed assay techniques were unspecific and consequently considerably overestimated true canrenone levels. Recently, it was demonstrated that after a single oral dose of spironolactone, 7 alpha-thiomethylspirolactone is the main metabolite and that unchanged spironolactone reaches maximum serum concentrations which are in the same order of magnitude as canrenone. Both spironolactone and 7 alpha-thiomethylspirolactone are known to possess anti-mineralocorticoid activity, and they may be mainly responsible for the activity of spironolactone. It also appears likely that endocrine side effects of spironolactone, such as gynaecomastia, are mediated by these sulfur-containing compounds. The oral absorption of spironolactone is improved by using micronized drug or inclusion complexes of spironolactone with cyclodextrins. Concomitant food intake has also been shown to enhance the bioavailability, by increasing the absorption and decreasing the first-pass effect of spironolactone.