Coexpression of CYP11B2 or CYP11B1 with adrenodoxin and adrenodoxin reductase for assessing the potency and selectivity of aldosterone synthase inhibitors

Fluorinated aldosterone synthase (CYP11B2)-inhibitors for differential diagnosis between bilateral and unilateral conditions of primary aldosteronism

The enzyme aldosterone synthase (CYP11B2) is specifically expressed in aldosterone-producing tissue of the adrenal cortex and is overexpressed in aldosterone-producing adenomas (APA). It therefore represents an ideal target for molecular imaging, particularly for the differential diagnosis between bilateral hyperplasia and unilateral APA in primary aldosteronism. However, the presence of the cortisol-producing enzyme 11β-hydroxylase (CYP11B1) in the adrenal cortex remains very challenging owing to its high homology to CYP11B2. Within this study, we efficiently synthesized a variety of disubstituted fluorinated pyridines and pyrazines by Suzuki coupling reactions. These compounds were evaluated for their ability to inhibit CYP11B1 and CYP11B2 in transfected Y1 cells and in NCI-h295 cells. Several compounds were found to exhibit excellent affinity (IC50 < 10 nM) to CYP11B2 as well as strong selectivity (up to 125-fold) over CYP11B1. These findings support the further development of an analogous 18F-labelled PET tracer.

Atractylenolide-I covalently binds to CYP11B2, selectively inhibits aldosterone synthesis, and improves hyperaldosteronism

Hyperaldosteronism is a common disease that is closely related to endocrine hypertension and other cardiovascular diseases. Cytochrome P450 11B2 (CYP11B2), an important enzyme in aldosterone (ALD) synthesis, is a promising target for the treatment of hyperaldosteronism. However, selective inhibitors targeting CYP11B2 are still lacking due to the high similarity with CYP11B1. In this study, atractylenolide-I (AT-I) was found to significantly reduce the production of ALD but had no effect on cortisol synthesis, which is catalyzed by CYP11B1. Chemical biology studies revealed that due to the presence of Ala320, AT-I is selectively bound to the catalytic pocket of CYP11B2, and the C8/C9 double bond of AT-I can be epoxidized, which then undergoes nucleophilic addition with the sulfhydryl group of Cys450 in CYP11B2. The covalent binding of AT-I disrupts the interaction between heme and CYP11B2 and inactivates CYP11B2, leading to the suppression of ALD synthesis; AT-I shows a significant therapeutic effect for improving hyperaldosteronism.

Aldosterone Synthase Structure With Cushing Disease Drug LCI699 Highlights Avenues for Selective CYP11B Drug Design

[Figure: see text].

Aldosterone synthase inhibitors for cardiovascular diseases: A comprehensive review of preclinical, clinical and in silico data

Aldosterone, the main mineralocorticoid hormone, plays a fundamental role in maintaining blood pressure (BP)and volume under hypovolemic conditions. However, in numerous diseases, where it is produced in excess, it plays a detrimental role and contributes to cardiovascular events and ultimately to death in a multitude of patients. The seminal observation that the fungicide-derivative fadrozole blunted steroidogenesis has led to develop several agents to inhibit aldosterone synthase (AS, CYP11B2), the mitochondrial NADH-dependent enzyme that is necessary for aldosterone biosynthesis. Aldosterone synthase inhibitors (ASI) have, thereafter, been conceived and investigated in phase I and phase II studies. We herein reviewed the ASIs available so far considering their chemical structure, the related aldosterone synthase binding and pharmacodynamic properties. We also examined the promising results obtained with ASIs that have already been tested in phase II human studies.

Development of Highly Selective Pyrimidine-Based Aldosterone Synthase (CYP11B2) Inhibitors

Excess aldosterone production and signaling are primary contributors to numerous cardiovascular disorders including primary aldosteronism and resistant hypertension. Recently, inhibition of aldosterone synthesis via the enzyme aldosterone synthase (CYP11B2) has been pursued to ameliorate the negative effects of elevated aldosterone. Herein, we report the development of aldosterone synthase inhibitors using a pyrimidine-based metal binding group leading to the highly selective CYP11B2 inhibitor 22. Superior selectivity combined with robust pharmacokinetics afforded highly selective in vivo aldosterone suppression in a monkey model of adrenal steroidogenesis, demonstrating the potential for selective aldosterone lowering in humans with pyrimidine 22.

Discovery of N-[5-(6-Chloro-3-cyano-1-methyl-1H-indol-2-yl)-pyridin-3-ylmethyl]-ethanesulfonamide, a Cortisol-Sparing CYP11B2 Inhibitor that Lowers Aldosterone in Human Subjects

Human clinical studies conducted with LCI699 established aldosterone synthase (CYP11B2) inhibition as a promising novel mechanism to lower arterial blood pressure. However, LCI699's low CYP11B1/CYP11B2 selectivity resulted in blunting of adrenocorticotropic hormone-stimulated cortisol secretion. This property of LCI699 prompted its development in Cushing's disease, but limited more extensive clinical studies in hypertensive populations, and provided an impetus for the search for cortisol-sparing CYP11B2 inhibitors. This paper summarizes the discovery, pharmacokinetics, and pharmacodynamic data in preclinical species and human subjects of the selective CYP11B2 inhibitor 8.

Development of CYP11B1 and CYP11B2 assays utilizing homogenates of adrenal glands: Utility of monkey as a surrogate for human

Elevated levels of aldosterone are associated with arterial hypertension, congestive heart failure, chronic kidney disease, and obesity. Aldosterone is produced predominantly in the zona glomerulosa of the cortex of the adrenal gland by the enzyme aldosterone synthase (CYP11B2). Treatment of the above indications by decreasing production of aldosterone is thought to be of therapeutic benefit by lessening the deleterious effects of aldosterone mediated through both the mineralocorticoid receptor and also through so called non-genomic pathways. However, inhibition of the highly similar enzyme, CYP11B1, which is responsible for the production of cortisol, must be avoided in the development of clinically useful aldosterone synthase inhibitors due to the resulting impairment of the cortisol-induced stress response. In efforts to assess the interactions of compounds with the CYP11B enzymes, a variety of cell-based inhibitor screening assays for both CYP11B1 and CYP11B2 have been reported. Herein we report details of assays employing both cynomolgus monkey adrenal homogenate (CAH) and human adrenal homogenate (HAH) as sources of CYP11B1 and CYP11B2 enzymes. Utilizing both CAH and HAH, we have characterized the kinetics of the CYP11B1-mediated conversion of 11-deoxycortisol to cortisol and the CYP11B2-mediated oxidation of corticosterone to aldosterone. Inhibition assays for both CYP11B1 and CYP11B2 were subsequently developed. Based on a comparison of human and monkey amino acid sequences, kinetics data, and inhibition values derived from the HAH and CAH assays, evidence is provided in support of using cynomolgus monkey tissue-derived cell homogenates as suitable surrogates for the human enzymes.

Discovery of Triazole CYP11B2 Inhibitors with in Vivo Activity in Rhesus Monkeys

Hit-to-lead efforts resulted in the discovery of compound 19, a potent CYP11B2 inhibitor that displays high selectivity vs related CYPs, good pharmacokinetic properties in rat and rhesus, and lead-like physical properties. In a rhesus pharmacodynamic model, compound 19 displays robust, dose-dependent aldosterone lowering efficacy, with no apparent effect on cortisol levels.

The CYP11B subfamily

The biosynthesis of steroid hormones is dependent on P450-catalyzed reactions. In mammals, cholesterol is the common precursor of all steroid hormones, and its conversion to pregnenolone is the initial and rate-limiting step in hormone biosynthesis in steroidogenic tissues such as gonads and adrenal glands. The production of glucocorticoids and mineralocorticoids takes place in the adrenal gland and the final steps are catalyzed by 2 mitochondrial cytochromes P450, CYP11B1 (11β-hydroxylase or P45011β) and CYP11B2 (aldosterone synthase or P450aldo). The occurrence and development of these 2 enzymes in different species, their contribution to the biosynthesis of steroid hormones as well as their regulation at different levels (gene expression, cellular regulation, regulation on the level of proteins) is the topic of this chapter.

Discovery of Benzimidazole CYP11B2 Inhibitors with in Vivo Activity in Rhesus Monkeys

We report the discovery of a benzimidazole series of CYP11B2 inhibitors. Hit-to-lead and lead optimization studies identified compounds such as 32, which displays potent CYP11B2 inhibition, high selectivity versus related CYP targets, and good pharmacokinetic properties in rat and rhesus. In a rhesus pharmacodynamic model, 32 produces dose-dependent aldosterone lowering efficacy, with no apparent effect on cortisol levels.

Aldosterone synthase inhibition: cardiorenal protection in animal disease models and translation of hormonal effects to human subjects

Background

Aldosterone synthase inhibition provides the potential to attenuate both the mineralocorticoid receptor-dependent and independent actions of aldosterone. In vitro studies with recombinant human enzymes showed LCI699 to be a potent, reversible, competitive inhibitor of aldosterone synthase (K_i = 1.4 ± 0.2 nmol/L in humans) with relative selectivity over 11β-hydroxylase.

Methods

Hormonal effects of orally administered LCI699 were examined in rat and monkey in vivo models of adrenocorticotropic hormone (ACTH) and angiotensin-II-stimulated aldosterone release, and were compared with the mineralocorticoid receptor antagonist eplerenone in a randomized, placebo-controlled study conducted in 99 healthy human subjects. The effects of LCI699 and eplerenone on cardiac and renal sequelae of aldosterone excess were investigated in a double-transgenic rat (dTG rat) model overexpressing human renin and angiotensinogen.

Results

Rat and monkey in vivo models of stimulated aldosterone release predicted human dose– and exposure–response relationships, but overestimated the selectivity of LCI699 in humans. In the dTG rat model, LCI699 dose-dependently blocked increases in aldosterone, prevented development of cardiac and renal functional abnormalities independent of blood pressure changes, and prolonged survival. Eplerenone prolonged survival to a similar extent, but was less effective in preventing cardiac and renal damage. In healthy human subjects, LCI699 0.5 mg selectively reduced plasma and 24 h urinary aldosterone by 49 ± 3% and 39 ± 6% respectively (Day 1, mean ± SEM; P < 0.001 vs placebo), which was associated with natriuresis and an increase in plasma renin activity. Doses of LCI699 greater than 1 mg inhibited basal and ACTH-stimulated cortisol. Eplerenone 100 mg increased plasma and 24 h urinary aldosterone while stimulating natriuresis and increasing renin activity. In contrast to eplerenone, LCI699 increased the aldosterone precursor 11-deoxycorticosterone and urinary potassium excretion.

Conclusions

These results provide new insights into the cardiac and renal effects of inhibiting aldosterone synthase in experimental models and translation of the hormonal effects to humans. Selective inhibition of aldosterone synthase appears to be a promising approach to treat diseases associated with aldosterone excess.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-014-0340-9) contains supplementary material, which is available to authorized users.

Molecular basis of pharmacological therapy in Cushing's disease

Cushing's disease (CD) is a severe endocrine condition caused by an adrenocorticotropin (ACTH)-producing pituitary adenoma that chronically stimulates adrenocortical cortisol production and with potentially serious complications if not or inadequately treated. Active CD may produce a fourfold increase in mortality and is associated with significant morbidities. Moreover, excess mortality risk may persist even after CD treatment. Although predictors of risk in treated CD are not fully understood, the importance of early recognition and adequate treatment is well established. Surgery with resection of a pituitary adenoma is still the first line therapy, being successful in about 60-70 % of patients; however, recurrence within 2-4 years may often occur. When surgery fails, medical treatment can reduce cortisol production and ameliorate clinical manifestations while more definitive therapy becomes effective. Compounds that target hypothalamic-pituitary axis, glucocorticoid synthesis or adrenocortical function are currently used to control the deleterious effects of chronic glucocorticoid excess. In this review we describe and analyze the molecular basis of the drugs targeting the disease at central level, suppressing ACTH secretion, as well as at peripheral level, acting as adrenal inhibitors, or glucocorticoid receptor antagonists. Understanding of the underlying molecular mechanisms in CD and of glucocorticoid biology should promote the development of new targeted and more successful therapies in the future. Indeed, most of the drugs discussed have been tested in limited clinical trials, but there is potential therapeutic benefit in compounds with better specificity for the class of receptors expressed by ACTH-secreting tumors. However, long-term follow-up with management of persistent comorbidities is needed even after successful treatment of CD.

Discovery and in Vivo Evaluation of Potent Dual CYP11B2 (Aldosterone Synthase) and CYP11B1 Inhibitors

Aldosterone is a key signaling component of the renin-angiotensin-aldosterone system and as such has been shown to contribute to cardiovascular pathology such as hypertension and heart failure. Aldosterone synthase (CYP11B2) is responsible for the final three steps of aldosterone synthesis and thus is a viable therapeutic target. A series of imidazole derived inhibitors, including clinical candidate 7n, have been identified through design and structure-activity relationship studies both in vitro and in vivo. Compound 7n was also found to be a potent inhibitor of 11β-hydroxylase (CYP11B1), which is responsible for cortisol production. Inhibition of CYP11B1 is being evaluated in the clinic for potential treatment of hypercortisol diseases such as Cushing's syndrome.

Structural insights into aldosterone synthase substrate specificity and targeted inhibition

Aldosterone is a major mineralocorticoid hormone that plays a key role in the regulation of electrolyte balance and blood pressure. Excess aldosterone levels can arise from dysregulation of the renin-angiotensin-aldosterone system and are implicated in the pathogenesis of hypertension and heart failure. Aldosterone synthase (cytochrome P450 11B2, CYP11B2) is the sole enzyme responsible for the production of aldosterone in humans. Blocking of aldosterone synthesis by mediating aldosterone synthase activity is thus a recently emerging pharmacological therapy for hypertension, yet a lack of structural information has limited this approach. Here, we present the crystal structures of human aldosterone synthase in complex with a substrate deoxycorticosterone and an inhibitor fadrozole. The structures reveal a hydrophobic cavity with specific features associated with corticosteroid recognition. The substrate binding mode, along with biochemical data, explains the high 11β-hydroxylase activity of aldosterone synthase toward both gluco- and mineralocorticoid formation. The low processivity of aldosterone synthase with a high extent of intermediates release might be one of the mechanisms of controlled aldosterone production from deoxycorticosterone. Although the active site pocket is lined by identical residues between CYP11B isoforms, most of the divergent residues that confer additional 18-oxidase activity of aldosterone synthase are located in the I-helix (vicinity of the O(2) activation path) and loops around the H-helix (affecting an egress channel closure required for retaining intermediates in the active site). This intrinsic flexibility is also reflected in isoform-selective inhibitor binding. Fadrozole binds to aldosterone synthase in the R-configuration, using part of the active site cavity pointing toward the egress channel. The structural organization of aldosterone synthase provides critical insights into the molecular mechanism of catalysis and enables rational design of more specific antihypertensive agents.

Aldosterone and cardiovascular disease: the heart of the matter

Aldosterone contributes to the endocrine basis of heart failure, and studies on cardiac aldosterone signaling have reinforced its value as a therapeutic target. Recent focus has shifted to new roles of aldosterone that appear to depend on coexisting pathologic stimuli, cell type, and disease etiology. This review evaluates recent advances in mechanisms underlying aldosterone-induced cardiac disease and highlights the interplay between aldosterone and Ca(2+)/calmodulin dependent protein kinase II, whose hyperactivity during heart failure contributes to disease progression. Increasing evidence implicates aldosterone in diastolic dysfunction, and there is a need to develop more targeted therapeutics such as aldosterone synthase inhibitors and molecularly specific antioxidants. Despite accumulating knowledge, many questions still persist and will likely dictate areas of future research.

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.

A tricistronic human adrenodoxin reductase-adrenodoxin-cytochrome P450 27A1 vector system for substrate hydroxylation in Escherichia coli

Cytochrome P450 (P450) 27A1 catalyzes 27-hydroxylation of cholesterol and 25-hydroxylation of vitamin D(3), serving as an important component for the maintenance of lipid homeostasis. In eukaryotic cells P450 27A1 is a membrane-bound protein located on the inner mitochondrial membrane and requires two auxiliary reduction partners, adrenodoxin (Adx) and NADPH-adrenodoxin reductase (Adr), for catalysis in the bile acid biosynthesis pathway. A strategy was developed for the functional coexpression of P450 27A1 with Adr and Adx in a tricistronic fashion (single RNA, three proteins) in Escherichia coli, mimicking the mitochondrial P450 system. Intact bacterial cells coexpressing the P450 vector (pTC27A1) efficiently hydroxylated cholesterol at the 27 position as well as vitamin D(3) at the 25 position when supplemented with glycerol as a carbon source. Thus, E. coli containing pTC27A1 is able to hydroxylate cholesterol in a self-sufficient fashion and is suitable for further applications of protein interaction, drug discovery, and inhibitor evaluation and for the study of other mitochondrial P450s and oxysterol production in microorganisms without a need for membrane reconstitution, membrane simulation by detergents, or purification of the components.

Aldosterone synthase inhibition with LCI699: a proof-of-concept study in patients with primary aldosteronism

We report the first administration of an orally active aldosterone synthase inhibitor, LCI699, to 14 patients with primary aldosteronism. After a 2-week placebo run-in, patients received oral LCI699 (0.5 mg BID) for 2 weeks, LCI699 (1.0 mg BID) for 2 weeks, and placebo for 1 week. We assessed changes in hormone concentrations, plasma potassium levels, and 24-hour ambulatory systolic blood pressure and safety. The supine plasma aldosterone concentration decreased from 540 pmol/L (95% CI: 394 to 739 pmol/L) to 171 pmol/L (95% CI: 128 to 230 pmol/L) after 0.5 mg of LCI699 (-68%; P<0.0001) and to 133 pmol/L (95% CI: 100 to 177 pmol/L) after 1.0 mg of LCI699 (-75%; P<0.0001). Plasma 11-deoxycorticosterone concentrations increased by 710% after 0.5 mg of LCI699 (P<0.0001) and by 1427% after 1.0 mg of LCI699 (P<0.0001). The plasma potassium concentration increased from 3.27±0.31 to 4.03±0.33 mmol/L (P<0.0001) after only 1 week on 0.5 mg of LCI699. Twenty-four-hour ambulatory systolic blood pressure decreased by -4.1 mm Hg (95% CI: -8.1 to -0.1 mm Hg) after 4 weeks of treatment (P=0.046). Basal plasma cortisol concentrations remained unchanged, whereas plasma adrenocorticotropic hormone concentrations increased by 35% after 0.5 mg of LCI699 (P=0.08) and by 113% after 1.0 mg of LCI699 (P<0.0001), and the plasma cortisol response to an adrenocorticotropic hormone test was blunted. All of the variables except plasma 11-deoxycorticosterone concentration returned to initial levels after the placebo. LCI699 was well tolerated. In conclusion, the administration of LCI699, up to 1.0 mg BID, effectively and safely inhibits aldosterone synthase in patients with primary aldosteronism. This 4-week treatment corrected the hypokalemia and mildly decreased blood pressure. The effects on the glucocorticoid axis were consistent with a latent inhibition of cortisol synthesis.

The discovery of potent inhibitors of aldosterone synthase that exhibit selectivity over 11-beta-hydroxylase

Aldosterone, the final component of the renin-angiotensin-aldosterone system, plays an important role in the pathophysiology of hypertension and congestive heart failure. Aldosterone synthase (CYP11B2) catalyzes the last three steps of aldosterone biosynthesis, and as such appears to be a target for the treatment of these disorders. A sulfonamide-imidazole scaffold has proven to be a potent inhibitor of CYP11B2. Furthermore, this scaffold can achieve high levels of selectivity for CYP11B2 over CYP11B1, a key enzyme in the biosynthesis of cortisol.

Adrenodoxin: the archetype of vertebrate-type [2Fe-2S] cluster ferredoxins

Adrenodoxin is probably the best characterized member of the vertebrate-type [2Fe-2S]-cluster ferredoxins. It has been in the spotlight of scientific interest for many years due to its essential role in mammalian steroid hormone biosynthesis, where it acts as electron mediator between the NADPH-dependent adrenodoxin reductase and several mitochondrial cytochromes P450. In this review we will focus on the present knowledge about protein-protein recognition in the mitochondrial cytochrome P450 system and the modulation of the electron transfer between Adx and its redox partners, AdR and CYP(s). We also intend to point out the potential biotechnological applications of Adx as a versatile electron donor to different cytochromes P450, both in vitro and in vivo. Finally we will address the comparison between the mammalian cytochrome P450-associated adrenodoxin and ferredoxins involved in iron-sulfur-cluster biosynthesis. Despite their different functions, these proteins display an amazing similarity regarding their primary sequence, tertiary structure and biophysical features.

Aldosterone and inflammation

PURPOSE OF REVIEW

Aldosterone causes tissue inflammation leading to fibrosis and remodeling in the heart, vasculature, and kidney. We summarize recent data regarding the mechanism(s) through which aldosterone stimulates inflammation.

RECENT FINDINGS

Studies elucidate the cell-specific effects of mineralocorticoid receptor activation on inflammatory cell infiltration and adhesion, and highlight the role of the macrophage in the development of vascular collagen deposition and hypertension. Activation of nuclear factor-kappaB in vascular smooth muscle cells involves a complex interplay between the angiotensin subtype 1 (AT1) receptor and the mineralocorticoid receptor. Activation of the mineralocorticoid receptor by aldosterone stimulates an inflammatory phenotype in adipocytes and contributes to insulin resistance by increasing oxidative stress.

SUMMARY

Mechanistic studies of aldosterone-induced inflammation provide the rationale for an expanded therapeutic role for mineralocorticoid receptor antagonists and aldosterone synthase inhibitors.

Pharmacodynamic and pharmacokinetic characterization of the aldosterone synthase inhibitor FAD286 in two rodent models of hyperaldosteronism: comparison with the 11beta-hydroxylase inhibitor metyrapone

Aldosterone synthase (CYP11B2) inhibitors (ASIs) represent an attractive therapeutic approach for mitigating the untoward effects of aldosterone. We characterized the pharmacokinetic/pharmacodynamic relationships of a prototypical ASI, (+)-(5R)-4-(5,6,7,8-tetrahydroimidazo[1,5-a]pyridin-5-yl]benzonitrile hydrochloride (CGS020286A, FAD286, FAD) and compared these profiles to those of the 11beta-hydroxylase inhibitor metyrapone (MET) in two rodent models of secondary hyperaldosteronism and corticosteronism. In chronically cannulated Sprague-Dawley rats, angiotensin II (ANG II) (300 ng/kg bolus + 100 ng/kg/min infusion) or adrenocorticotropin (100 ng/kg + 30 ng/kg/min) acutely elevated plasma aldosterone concentration (PAC) from approximately 0.26 nM to a sustained level of approximately 2.5 nM for 9 h. Adrenocorticotropin but not ANG II elicited a sustained increase in plasma corticosterone concentration (PCC) from approximately 300 to approximately 1340 nM. After 1 h of Ang II or adrenocorticotropin infusion, FAD (0.01-100 mg/kg p.o.) or MET (0.1-300 mg/kg p.o.) dose- and drug plasma concentration-dependently reduced the elevated PACs over the ensuing 8 h. FAD was approximately 12 times more dose-potent than MET in reducing PAC but of similar or slightly greater potency on a plasma drug concentration basis. Both agents also decreased PCC in the adrenocorticotropin model at relatively higher doses and with similar dose potencies, whereas FAD was 6-fold weaker based on drug exposures. FAD was approximately 50-fold selective for reducing PAC versus PCC, whereas MET was only approximately 3-fold selective. We conclude that FAD is a potent, orally active, and relatively selective ASI in two rat models of hyperaldosteronism. MET is an order of magnitude less selective than FAD but is, nevertheless, more potent as an ASI than as an 11beta-hydroxylase inhibitor.