Human adrenal CYP11B1: localization by in situ-hybridization and functional expression in cell cultures

Adrenal androgens, adrenarche, and zona reticularis: A human affair?

In humans, reticularis cells of the adrenal cortex fuel the production of androgen steroids, constituting the driver of numerous morphological changes during childhood. These steps are considered a precocious stage of sexual maturation and are grouped under the term "adrenarche". This review describes the molecular and enzymatic characteristics of the zona reticularis, along with the possible signals and mechanisms that control its emergence and the associated clinical features. We investigate the differences between species and discuss new studies such as genetic lineage tracing and transcriptomic analysis, highlighting the rodent inner cortex's cellular and molecular heterogeneity. The recent development and characterization of mouse models deficient for Prkar1a presenting with adrenocortical reticularis-like features prompt us to review our vision of the mouse adrenal gland maturation. We expect these new insights will help increase our understanding of the adrenarche process and the pathologies associated with its deregulation.

Antifungal therapy with azoles and the syndrome of acquired mineralocorticoid excess

The syndromes of mineralocorticoid excess describe a heterogeneous group of clinical manifestations leading to endocrine hypertension, typically either through direct activation of mineralocorticoid receptors or indirectly by impaired pre-receptor enzymatic regulation or through disturbed renal sodium homeostasis. The phenotypes of these disorders can be caused by inherited gene variants and somatic mutations or may be acquired upon exposures to exogenous substances. Regarding the latter, the symptoms of an acquired mineralocorticoid excess have been reported during treatment with azole antifungal drugs. The current review describes the occurrence of mineralocorticoid excess particularly during the therapy with posaconazole and itraconazole, addresses the underlying mechanisms as well as inter- and intra-individual differences, and proposes a therapeutic drug monitoring strategy for these two azole antifungals. Moreover, other therapeutically used azole antifungals and ongoing efforts to avoid adverse mineralocorticoid effects of azole compounds are shortly discussed.

Synthesis, biological evaluation, and molecular modeling of 1-benzyl-1H-imidazoles as selective inhibitors of aldosterone synthase (CYP11B2)

Reducing aldosterone action is beneficial in various major diseases such as heart failure. Currently, this is achieved with mineralocorticoid receptor antagonists, however, aldosterone synthase (CYP11B2) inhibitors may offer a promising alternative. In this study, we used three-dimensional modeling of CYP11B2 to model the binding modes of the natural substrate 18-hydroxycorticosterone and the recently published CYP11B2 inhibitor R-fadrozole as a rational guide to design 44 structurally simple and achiral 1-benzyl-1H-imidazoles. Their syntheses, in vitro inhibitor potencies, and in silico docking are described. Some promising CYP11B2 inhibitors were identified, with our novel lead MOERAS115 (4-((5-phenyl-1H-imidazol-1-yl)methyl)benzonitrile) displaying an IC(50) for CYP11B2 of 1.7 nM, and a CYP11B2 (versus CYP11B1) selectivity of 16.5, comparable to R-fadrozole (IC(50) for CYP11B2 6.0 nM, selectivity 19.8). Molecular docking of the inhibitors in the models enabled us to generate posthoc hypotheses on their binding modes, providing a valuable basis for future studies and further design of CYP11B2 inhibitors.

Construction of 3D models of the CYP11B family as a tool to predict ligand binding characteristics

Aldosterone is synthesised by aldosterone synthase (CYP11B2). CYP11B2 has a highly homologous isoform, steroid 11beta-hydroxylase (CYP11B1), which is responsible for the biosynthesis of aldosterone precursors and glucocorticoids. To investigate aldosterone biosynthesis and facilitate the search for selective CYP11B2 inhibitors, we constructed three-dimensional models for CYP11B1 and CYP11B2 for both human and rat. The models were constructed based on the crystal structure of Pseudomonas Putida CYP101 and Oryctolagus Cuniculus CYP2C5. Small steric active site differences between the isoforms were found to be the most important determinants for the regioselective steroid synthesis. A possible explanation for these steric differences for the selective synthesis of aldosterone by CYP11B2 is presented. The activities of the known CYP11B inhibitors metyrapone, R-etomidate, R-fadrazole and S-fadrazole were determined using assays of V79MZ cells that express human CYP11B1 and CYP11B2, respectively. By investigating the inhibitors in the human CYP11B models using molecular docking and molecular dynamics simulations we were able to predict a similar trend in potency for the inhibitors as found in the in vitro assays. Importantly, based on the docking and dynamics simulations it is possible to understand the enantioselectivity of the human enzymes for the inhibitor fadrazole, the R-enantiomer being selective for CYP11B2 and the S-enantiomer being selective for CYP11B1.

The Steroid Hormone Biosynthesis Pathway as a Target for Endocrine-Disrupting Chemicals

Various chemicals found in the human and wildlife environments have the potential to disrupt endocrine functions in exposed organisms. Increasingly, the enzymes involved in the steroid biosynthesis pathway are being recognized as important targets for the actions of various endocrine-disrupting chemicals. Interferences with steroid biosynthesis may result in impaired reproduction, alterations in (sexual) differentiation, growth, and development and the development of certain cancers. Steroid hormone synthesis is controlled by the activity of several highly substrate-selective cytochrome P450 enzymes and a number of steroid dehydrogenases and reductases. Particularly aromatase (CYP19), the enzyme that converts androgens to estrogens, has been the subject of studies into the mechanisms by which chemicals interfere with sex steroid hormone homeostasis and function, often related to (de)feminization and (de)masculinazation processes. Studies in vivo and in vitro have focussed on ovarian and testicular function, with less attention given to other steroidogenic organs, such as the adrenal cortex. This review aims to provide a comprehensive overview of the state of knowledge regarding the mechanisms by which chemicals interfere with the function of steroidogenic enzymes in various tissues and organisms. The endocrine toxicities and mechanisms of action related to steroidogenesis of a number of classes of drugs and environmental contaminants are discussed. In addition, several potential in vitro bioassays are reviewed for their usefulness as screening tools for the detection of chemicals that can interfere with steroidogenesis. Analysis of the currently scattered state of knowledge indicates that still relatively little is known about the underlying mechanisms of interference of chemicals with steroidogenesis and their potential toxicity in steroidogenic tissues, neither in humans nor in wildlife. Considerably more detailed and systematic research in this area of (endocrine) toxicology is required for a better understanding of risks to humans and wildlife.

CYP17- and CYP11B-dependent steroid hydroxylases as drug development targets

Steroid hormone biosynthesis is catalyzed by the action of a series of cytochrome P450 enzymes as well as reductases. Defects in steroid hydroxylating P450s are the cause of several severe defects such as the adrenogenital syndrome (AGS), corticosterone methyl oxidase (CMO) I or II deficiencies, or pseudohermaphroditism. In contrast, overproduction of steroid hormones can be involved in breast or prostate cancer, in hypertension, and heart fibrosis. Besides inhibiting the action of the steroid hormones on the level of steroid hormone receptors by using antihormones, which often is connected with severe side effects, more recently the steroid hydroxylases themselves turned out to be promising new targets for drug development. Since the 3-dimensional structures of steroid hydroxylases are not yet available, computer models of the corresponding CYPs may help to develop new inhibitors of these enzymes. During the past years, the necessary test systems have been developed and new compounds have been synthesized, which displayed selective and specific inhibition of CYP17, CYP11B2, and CYP11B1. With some of these potential new drugs, clinical trials are under way. It can be expected that in the near future some of these compounds will contribute to our arsenal of new and selective drugs.

Deficiência da 11beta-hidroxilase

A hiperplasia congênita da adrenal devido à deficiência da enzima 11beta-hidroxilase é resultado de uma falha na conversão do 11-desoxicortisol em cortisol na última etapa da via sintética dos glicocorticóides. Em geral, esta forma da doença é responsável por cerca de 5% dos casos. A manifestação clínica do excesso de andrógenos em pacientes do sexo feminino inclui graus de ambigüidade genital que podem variar entre uma clitoromegalia até a virilização completa da genitália. Devido ao acúmulo de mineralocorticóides, aproximadamente 50% dos pacientes desenvolvem hipertensão arterial. Mutações no gene CYP11B1, que codifica a enzima 11beta-hidroxilase, são responsáveis pela doença. As características bioquímicas e moleculares da enzima e suas implicações na apresentação clínica da deficiência da 11beta-hidroxilase são abordadas no presente trabalho de revisão.

Modulation of aldosterone and cortisol synthesis on the molecular level

CYP11B1 and the closely related CYP11B2 are involved in the production of adrenal steroid hormones. Although in human their primary structure is 93% identical they are involved in the biosynthesis of functionally diverse products, such as glucocorticoids and mineralocorticoids, respectively. In contrast, bovine CYP11B1 combines both activities in one single enzyme. The CYP11B family belongs to class I cytochromes P450 that have been described in bacteria and mitochondria and receive their electrons from a low molecular weight iron sulphur protein which is reduced by a NADPH-dependent FAD-containing reductase. In this review, we summarise the current knowledge on the modulation of aldosterone and cortisol synthesis by transcriptional regulation, on the molecular level as consequence of mutations found in patients suffering from steroid hormone-related diseases as well as introduced by site-directed mutagenesis and as consequence of protein-protein interaction with both CYP11A1 and the natural redox partner adrenodoxin.

Baboon CYP11B1: the localization and catalytic activity in baboon adrenal tissue

A third gene encoding baboon CYP11B1 was isolated and was shown to catalyze only the metabolism of deoxycorticosterone (DOC) to corticosterone. The investigation into the localization of CYP11B1 in the baboon adrenal tissue, using in situ hybridization, showed that mRNA transcripts were predominantly present in the zona reticularis (ZR) and zona fasciculata (ZF). Signal was also observed in the zona glomerulosa (ZG) and scattered within the medulla. Immunohistochemical studies, using rabbit anti-sheep CYP11B1 IgG, indicated that CYP11B1 was expressed only in the zona fasciculata, zona reticularis and in the medulla. CYP11B1 was not detected in the zona glomerulosa. Subsequent Western Blot investigations into the presence of CYP11B1 in baboon adrenal cortex and medullary homogenates indicated CYP11B1 as a single band in the cortex and as two distinct bands in the medulla. CYP11A was present only in the baboon adrenal cortex. The metabolism of deoxycorticosterone and corticosterone was subsequently investigated in the baboon adrenal cortex and medulla. In cortex homogenates, deoxycorticosterone was converted to corticosterone, and neither 18-hydroxycorticosterone nor aldosterone was detected. In medulla homogenates, however, corticosterone was metabolized to aldosterone, as confirmed by APcI-MS.

The human steroid hydroxylases CYP1B1 and CYP11B2

Major advances have been made during the last decade in our understanding of adrenal steroid hormone biosynthesis. Two key players in these pathways are the human mitochondrial cytochrome P450 enzymes CYP11B1 and CYP11B2, which catalyze the final steps in the biosynthesis of cortisol and aldosterone. Using data from mutations found in patients suffering from steroid hormone-related diseases, from mutagenesis studies and from the construction of three-dimensional models of these enzymes, structural information could be deduced that provide a clue to the stereo- and regiospecific steroid hydroxylation reactions carried out by these enzymes. In this review, we summarize the current knowledge on the physiological function and the biochemistry of these enzymes. Furthermore, the pharmacological and toxicological importance of these steroid hydroxylases, the means for the identification of their potential inhibitors and possible biotechnological applications are discussed.

Primary culture system of adrenocortical cells from dogs to evaluate direct effects of chemicals on steroidogenesis

The present study was conducted to confirm the usefulness of a primary culture system of adrenocortical cells from dogs for detecting the direct effects of the chemicals on adrenal cortex. Corticosteroid levels in the culture supernatant were measured using high-performance liquid chromatography (HPLC) following 24-h incubation with the chemicals. Ketoconazole, miconazole, metyrapone, aminoglutethimide, and 1-(o-chlorophenyl)-1-(p-chlorophenyl)-2,2-dichloroethane (o,p-DDD), which were known to inhibit cortisol production were evaluated in this system. Both viable cells and corticosteroid levels were decreased by o,p-DDD treatment. Other chemicals showed various inhibition patterns of corticosteroid levels as follows without affecting cell viability. Ketoconazole decreased total corticosteroids level by mainly due to the decreases in cortisol and 11-deoxycortisol levels. Miconazole decreased cortisol and 11-deoxycortisol levels, however, slightly increased corticosterone level. Metyrapone decreased cortisol and corticosterone levels as 11-deoxycortisol and 11-deoxycorticosterone levels were increased. Aminoglutethimide decreased total corticosteroids level by mainly decreasing cortisol, corticosterone and 11-deoxycortisol levels. These results suggested that determination of the pattern of corticosteroid levels by HPLC in this system well reflected the mode of their action on steroidogenesis. Thus, we conclude this simple system was useful to determine the direct effects of chemicals on steroidogenesis in the adrenal cortex.

CYP11A1 stimulates the hydroxylase activity of CYP11B1 in mitochondria of recombinant yeast in vivo and in vitro

In mammals, hydrocortisone synthesis from cholesterol is catalyzed by a set of five specialized enzymes, four of them belonging to the superfamily of cytochrome P-450 monooxygenases. A recombinant yeast expression system was recently developed for the CYP11B1 (P45011beta) enzyme, which performs the 11beta hydroxylation of steroids such as 11-deoxycortisol into hydrocortisone, one of the three mitochondrial cytochrome P-450 proteins involved in steroidogenesis in mammals. This heterologous system was used to test the potential interaction between CYP11B1 and CYP11A1 (P450scc), the mitochondrial cytochrome P-450 enzyme responsible for the side chain cleaving of cholesterol. Recombinant CYP11B1 and CYP11A1 were targeted to Saccharomyces cerevisiae mitochondria using the yeast cytochrome oxidase subunit 6 mitochondrial presequence fused to the mature form of the two proteins. In yeast, the presence of CYP11A1 appears to improve 11beta hydroxylase activity of CYP11B1 in vivo and in vitro. Fractionation experiments indicate the presence of the two proteins in the same membrane fractions, i.e. inner membrane and contact sites of mitochondria. Thus, yeast mitochondria provide interesting insights to study some molecular and cellular aspects of mammalian steroid synthesis. In particular, recombinant yeast should permit a better understanding of the mechanism permitting the synthesis of steroids (sex steroids, mineralocorticoids and glucocorticoids) with a minimal set of enzymes at physiological level, thus avoiding disease states.

Regulation of human CYP11B2 and CYP11B1: comparing the role of the common CRE/Ad1 element

In humans, the final steps in corticosteroid production results from the activity of aldosterone synthase in the glomerulosa and 11beta-hydroxylase in the fasciculata. The regional expression of these isozymes is believed to result from transcriptional regulation of the aldosterone synthase (CYP11B2) and 11beta-hydroxylase (CYP11B1) genes. Previous studies suggest that the primary cis-element needed for agonist enhanced transcription of the CYP11B genes shares high sequence similarity to a consensus cAMP Response Element (CRE). Here the role of the CRE/Adl was studied. Reporter constructs prepared with the 5'flanking DNA of hCYP11B2 and hCYP11B1 were transfected into NCI-H295R (H295R) adrenocortical tumor cells. Both hCYP11B2 and hCYP11B1 driven reporter constructs responded in a similar manner to treatment with angiotensin II, potassium, dbcAMP, or forskolin. Mutation of the hCYP11B1 CRE/Adl element decreased basal reporter expression and decreased response to agonist. Mutation of the hCYP11B2 CRE/Adl element caused a loss of basal expression but retained response to agonist suggesting a role for other cis-elements in hormonal regulation of hCYP11B2. In addition, both cis-elements were able to form complexes with in vitro prepared CRE binding (CREB) protein, activating transcription factor (ATF)-1 and ATF-2 in mobility shift assays. However, only the ATF-2 complex migrated similarly to a complex seen using H295R nuclear extract. Taken together these data suggest that the CRE/Adl element plays an important role in the transcriptional regulation of both hCYP11B genes but does not play an important role in the regional distribution of the two isozymes within the adrenal.

Late steps of aldosterone biosynthesis: sheep are not rats

1. The last three steps of aldosterone biosynthesis have been demonstrated to be catalysed by a single enzyme, referred to as CYP11B (or P450(11) beta) in cow, pig, sheep and bullfrog and as CYP11B2 (or P450aldo) in rat, human, mouse and hamster. 2. The related enzyme CYP11B1 (also referred to as P450(11) beta) in rat, human, mouse and hamster does not have aldosterone synthesis activity, but no such enzyme has been reported in the cow, pig or sheep to date. 3. Exclusive aldosterone secretion in the zona glomerulosa (ZG) of the adrenal cortex in species such as rat, human, mouse and hamster could be ascribed to the restricted distribution of CYP11B2 to the same region in the adrenal cortex. 4. In other species, such as cow, pig and sheep, the CYP11B enzyme is expressed throughout the adrenal cortex and, thus, the exclusive aldosterone biosynthesis in the ZG could not be explained simply by the distribution of the enzyme. 5. We have shown in the sheep that potassium loading and acute sodium depletion stimulate the CYP11B transcript levels, which are not further increased by chronic sodium depletion. 6. The predominant CYP11B in the sheep adrenal cortex catalyses the synthesis of aldosterone from deoxycorticosterone (DOC) in vitro, is expressed throughout the adrenal cortex and the corresponding transcript levels are increased by K+ loading or sodium depletion. In short, as far as the last step of aldosterone biosynthesis is concerned, sheep are different from rats. In the rat, the CYP11B2 transcript or protein is elevated by K+ loading or sodium depletion, but not the CYP11B1 transcript or protein. 7. We propose that during severe sodium deficiency there is a switch in the aldosterone pathway to one preferentially involving 18-OH-DOC and not corticosterone.

Structure-activity relationship for inhibition of CYP11B1-dependent glucocorticoid synthesis in Y1 cells by aryl methyl sulfones

The effects of xenobiotics on CYP11B1-dependent corticosterone synthesis (11 beta-hydroxylase) in mouse adrenocortical Y1 cells were studied. 3-Methylsulfonyl-2,2-bis(4-chlorophenyl)-1,1-dichloroethene (MeSO2-DDE) and some methylsulfonyl polychlorinated biphenyls (MeSO2-PCB) inhibited the corticosterone synthesis, whereas PCBs or DDE did not. This indicates a crucial role of the methyl sulfone group for this inhibitory effect. Kinetic analyses of MeSO2-DDE and the two most potent MeSO2-PCBs were conducted using Lineweaver-Burk double-reciprocal plots. The data showed a competitive inhibition of CYP11B1 by the compounds, with apparent inhibitory constants (Ki) of 1.6, 4.6, and 6.7 microM for MeSO2-DDE, 4-MeSO2-2,3,6,4'-tetrachlorobiphenyl, and 4-MeSO2-2,3,6,3',4'-pentachlorobiphenyl, respectively. For comparison, the substrate K(m) was 3.5 microM in the cells, and metyrapone and ketoconazole had apparent Ki-values of 0.8 and 0.04 microM, respectively. In contrast to all previously known inhibitors of CYP11B1, the aryl methyl sulfones are the first examples of CYP11B1 inhibitors not being heterocyclic amines or steroids. The aryl methyl sulfones are widespread environmental pollutants and their inhibition of CYP11B1 constitutes another potential mechanism for endocrine disruption. Their influence on the synthesis of adrenocortical hormones thus merits further interest.

Hypothesis: aldosterone is synthesized by an alternative pathway during severe sodium depletion. 'A new wine in an old bottle'

1. The last three steps of aldosterone biosynthesis, 11 beta-hydroxylation, 18-hydroxylation and 18-oxidation, have been demonstrated to be catalysed by one enzyme, which is the cytochrome P450(11 beta) (CYP11B) in cow, pig, sheep and bullfrog or cytochrome P450aldo (CYP11B2) in rat, human, mouse and hamster. 2. The related enzyme P450(11 beta) (CYP11B1) from rat, human, mouse and hamster adrenals displays 11 beta-hydroxylation and 18-hydroxylation activities, but not 18-oxidation activity in vitro. No such enzyme has been reported in the cow, pig or sheep to date. 3. Data showing the dissociation of aldosterone secretion from plasma angiotensin II (AngII) levels indicate the presence of other factor(s) that regulate aldosterone biosynthesis in response to changes in body sodium status. Thus, we propose the existence of a 'sodium status factor' that regulates aldosterone biosynthesis in addition to AngII, K+, adrenocorticotropic hormone and atrial natriuretic peptide. 4. We propose that during severe sodium deficiency there is a switch in the aldosterone pathway to a pathway using 18-hydroxy-deoxycorticosterone (18-OH-DOC) rather than corticosterone as an intermediate. This switch may be mediated via the putative 'sodium status factor'. 5. Two models of the hypothesis will be discussed in this paper: (i) a 'one-enzyme' model; and (ii) a 'two-enzyme' model. 6. The one-enzyme model proposes that P450aldo (P450(11 beta) as in the case of the cow, sheep and pig) changes its enzymatic activity during severe sodium deficiency (i.e. switching to the alternative aldosterone biosynthesis pathway). 7. The two-enzyme model proposes that, under normal circumstances, P450aldo synthesizes aldosterone from deoxycorticosterone, while during severe sodium deficiency the P450(11 beta) provides the substrate (i.e. 18-OH-DOC) for the P450aldo.

Functional and expression analysis of ovine steroid 11 beta-hydroxylase (cytochrome P450 11 beta)

In this study, the ovine steroid 11 beta-hydroxylase (P450(11 beta) or CYP11B) cDNA previously reported by us (1) was transfected into COS-7 cells. Using 3H-11-deoxycorticosterone (3H-DOC) as the substrate, and paper partition chromatography for separation of steroid products, the expressed enzyme was shown to catalyse the conversion of DOC to corticosterone (B), 18-hydroxy-11-deoxycorticosterone (18-OH-DOC), 18-hydroxy-corticosterone (18-OH-B), and aldosterone (ALDO). These results suggest that the expressed ovine cDNA exhibited 11 beta-hydroxylase, 18-hydroxylase and aldosterone synthesis activities. The enzymatic activity of the enzyme was further analysed by adding unlabelled steroids to compete with 3H-DOC. The conversion of 3H-DOC to 3H-ALDO was inhibited by the addition of excess DOC, B and 18-OH-DOC, indicating that all these steroids were potential substrates of the enzyme. The results also demonstrated that 18-hydroxylation could occur before 11 beta-hydroxylation with this enzyme. However, the addition of excess cold 18-OH-B had no significant effect on the level of 3H-ALDO that was synthesised. This result could imply that 18-OH-B is not an intermediate involved in the conversion of DOC to aldosterone, or, more likely, the enzyme substrate site is not accessible readily. Our results also indicated that DOC was preferred to 18-OH-DOC as a substrate for the enzyme. We have demonstrated by hybridisation histochemistry using specific oligonucleotide probes that the corresponding P450(11 beta) RNA transcript was present in all zones in the sheep adrenal cortex. In summary, we have shown that the enzyme encoded by the predominant P450(11 beta) cDNA isolated from the sheep adrenocortical cDNA library has all the enzymatic activities to biosynthesise ALDO from DOC. The corresponding transcript of this ovine P450(11 beta) cDNA was located throughout the adrenal cortex and thus the inability of the zonae fasciculata-reticularis to secrete ALDO remains to be understood.