Is the glucocorticoid receptor identical in various target organs?

Synthesis and crystal structure of (22R)-6α,9α-difluoro-11β-hydroxy-21-palmitoyloxy-16α,17α-propylmethylenedioxypregn-4-ene-3,20-dione (rofleponide 21-palmitate)

The 21-palmitate of the stereochemically pure glucocorticosteroid rofleponide [(22R)-6α,9α-difluoro-11β,21-dihydroxy-16α,17α-propylmethylenedioxypregn-4-ene-3,20-dione], C41H64O7F2, was synthesised, and its solid-state conformation and absolute configuration were determined at T = 163 ± 2 K using single-crystal X-ray diffraction. The structure has an orthorhombic (P212121, No. 19) unit cell with a = 8.007(2) Å, b = 17.399(5) Å, c = 27.927(6) Å, V c = 3891(2) Å3, containing four molecules [D c = 1.2069(5) g cm−3, F(000) = 1536]. The R configuration for the chiral centre at C(22), created during the synthesis of rofleponide, is deduced using the knowledge of the absolute configuration of the hydrocortisone-related part of the molecule. The long-chained angular 17β-substituent is partially disordered, exhibiting at least two different conformations: it is approximately equatorially connected to the cyclopentane D ring and axially to the dioxolane E ring in the ‘a’ conformer, but has a bisectional attachment to both five-membered rings in the ‘b’ conformer. The O(11)H···O(3) hydrogen bond links the steroid molecules so as to form endless parallel strings. The final structure model, comprising two major disorder sites for each of the eleven most disordered non-hydrogen atoms and also for the hydrogens linked to them, was refined to R = 0.061 for 1332 observations with I > 2σ(I).

The role of glucocorticoid activity in the inheritance of hypertension: studies in the rat

Young (3-week-old) spontaneously hypertensive rats (SHR) had significantly higher basal plasma corticosterone levels than WKY rats and maximum responses to ACTH were also higher. In isolated adrenocortical cells from these rats, corticosterone production was also more responsive to ACTH in SHR. There was no significant difference in aldosterone production. Mononuclear leucocytes from older (10-week-old) SHR had a higher affinity for dexamethasone but a smaller number of binding sites per cell. The SHR therefore has higher circulating glucocorticoid levels and the target cells have a higher apparent affinity for this agonist. However, the target cells also have a smaller binding capacity. The precise resultant effect of these changes on glucocorticoid activity will require additional studies on specific glucocorticoid-dependent variables.

Structural requirements for the binding of dexamethasone to nuclear envelopes and plasma membranes

The specificity of dexamethasone binding sites on nuclear envelopes (NE) and plasma membranes (PM) was determined in competition studies with natural and synthetic steroids. The binding affinities for nuclear envelopes and plasma membranes were then correlated with the three-dimensional structures of the ligands. Three major factors are implicated in the ability of the steroid to bind to the membrane sites: (1) the separation between the terminal oxygen atoms substituted at atoms C3 and C17, or attached to the substituent at C17, is found to be longer than 10 A for the medium and high affinity steroids; (2) the beta-orientation of the oxygen atom in the C17-substituent to the D-ring is favored over alpha-orientation; and (3) bulky substituents and nontypical configurations are not accepted by the binding sites. A nearly linear correlation between the O3...O (substituted at C17) distance and the binding affinity of the tested steroids is observed; explanations for the lack of linear correlation of some steroids are given. A preliminary model for the interaction of steroids with these membrane sites is proposed which requires two hydrogen bonding regions that interact with the 2 oxygen atoms and some steric restriction sites that prevent the binding of steroids with large substituents. The hydrophobicities of the steroids do not correlate with binding affinities to the dexamethasone binding sites; hydrophobicity seems to play a minor role in these steroid-membrane interactions. Comparisons of the specificity of the dexamethasone binding sites on membranes to the specificity of various steroid receptors are also presented.

Characterization of high affinity and low affinity dexamethasone binding sites on male rat liver nuclear envelopes

Steroids must traverse the nuclear envelope before exerting their action at the chromatin. However, few studies have been done to elucidate the mechanism by which steroids traverse this membrane barrier. As first steps towards investigating the mechanism, we have characterized the binding sites for dexamethasone on male rat liver nuclear envelopes. The nuclear envelopes, prepared in the presence of dithiothreitol, were isolated from purified nuclei after treatment with DNase 1 at high pH. Binding of dexamethasone to the nuclear envelopes was measured after 16 h of incubation at 0-4 degrees C. At pH 7.4, only a single high capacity, low affinity binding site for dexamethasone was identified. However, at pH 8.6, two sites were identified; a low capacity, high affinity site and a high capacity, low affinity site. Adrenalectomy of the animal before preparation of the membranes caused loss of the high affinity site and reduction in the number of the lower affinity sites. Acute dexamethasone treatment of adrenalectomized rats resulted in the reappearance of the high affinity site but long term treatment with dexamethasone was required for complete restoration of the high affinity sites and reappearance of any of the low affinity sites. The steroid specificity of these nuclear envelope binding sites was different from that of the cytosolic glucocorticoid receptor, generally showing broader specificity. However, triamcinolone acetonide, which is a potent competitor for binding to the glucocorticoid receptor, did not complete effectively. The binding sites were sensitive to protease treatment and salt extraction studies revealed that the dexamethasone binding sites do not represent proteins non-specifically bound to the nuclear envelope. The affinity and the hormone responsiveness of the high affinity site are similar to those of the nuclear glucocorticoid receptor. Therefore, the nuclear envelope may be a site of action of glucocorticoids.

Differential binding of dexamethasone to ammonium sulfate precipitates of human adipose tissue cytosols

Saturation analysis of the binding of [3H]dexamethasone [( 3H]DEX) to ammonium sulfate precipitates (ASPs) confirmed the presence of a limited-capacity, high-affinity binder in human adipose tissue cytosols. Various non-radioactive steroids competed with [3H]DEX for binding to the ASPs in the following sequence: dexamethasone (DEX) approximately equal to triamcinolone acetonide (TA) greater than progesterone (P) much greater than estradiol (E2). The steroid specificity of the binder precipitated by AS was consistent with the specificities reported for glucocorticoid receptors in a number of systems. In order to investigate possible regional differences, glucocorticoid binding to ASPs derived from adipose tissues removed from two different sites in the same subject was quantitated. ASPs of human omental adipose tissue bound significantly more [3H]DEX than did similar preparations of subcutaneous adipose tissue from the abdominal wall (116 +/- 32 vs. 50 +/- 22 fmol/mg protein; mean +/- SD; p less than 0.02). The findings are consistent with reports from other laboratories suggesting that intra-abdominal fat is more responsive to glucocorticoids than is subcutaneous adipose tissue.

Interaction of rat liver glucocorticoid receptor with lectins: is the glucocorticoid receptor a glycoprotein?

Although glucocorticoid receptors have been extensively studied in a variety of tissues, the precise nature of the receptor protein still remains unknown. To further characterize this protein we assessed the effects of various lectins on [3H]dexamethasone binding to prepurified preparations of rat liver glucocorticoid receptor. Among the lectins tested only Ulex europeus and Lens culinaris induced a concentration-related decrease in [3H]dexamethasone binding. Following Ulex europeus or Lens culinaris exposure Scatchard analysis showed that these lectins led to a 3-fold reduction in receptor affinity without influencing the concentration of binding sites. These results provide new experimental evidence that rat liver glucocorticoid receptor would possess alpha-L-fucosyl and alpha-D-mannopyranoside residues in close proximity to the glucocorticoid receptor binding domain.

Binding of ester and amide epimers of 20 zeta-dihydroprednisolonic acid to cytosol receptors and their acute pharmacological activities in rats

The competitive binding of two new classes of anti-inflammatory steroids, the esters and amides derived from the epimers of 20 zeta-dihydroprednisolonic acid, to cytosol receptors from rat liver and thymus was studied. The relative inhibition of [3H]dexamethasone binding by the steroid derivatives was the same, irrespective of the receptor source, with the following order: dexamethasone greater than prednisolone greater than methyl 17,20 alpha-acetonidodihydroprednisolonate greater than methyl 17,20 beta-acetonidodihydroprednisolonate greater than N-propyl 20 alpha-dihydroprednisolonamide greater than methyl 20 alpha-dihydroprednisolonate greater than methyl 20 beta-dihydroprednisolonate greater than N-propyl 20 beta-dihydroprednisolonamide. The alpha-epimer of the steroids always showed a higher binding affinity than the corresponding beta-epimer. In an acute pharmacological study, prednisolone induced the suppression of plasma corticosterone and an increase in tyrosine aminotransferase activity and glycogen content of rat liver. The esters and amides had no effect on these parameters except in the case of the acetonide derivatives of the steroid acid esters which slightly increased liver glycogen content.

Lymphocyte glucocorticoid receptor binding in depressed patients with hypercortisolemia

Despite elevated levels of serum and urinary cortisol, patients with depressive illness manifest none of the clinical stigmata of glucocorticoid excess. This hypercortisolemia in the absence of clinical effects suggests a state of hormone resistance and could be mediated by alterations in the glucocorticoid receptor. Earlier studies have shown that small doses of glucocorticoids cause a decrease in glucocorticoid receptor binding in normal human lymphocytes. White cells from depressed patients with significant hypercortisolemia would be expected to show a similar change in receptor concentration if peripheral tissues are adequately exposed to and sensitive to the hormone. In this study we compared the binding of [3H]dexamethasone to lymphocytes from normal subjects and depressed patients with hypercortisolemia. Lymphocytes from normal subjects had a mean receptor concentration of 10.2 +/- 0.66 fm/10(6) cells (S.E.M.) and a dissociation constant of 4.8 +/- 0.47 nM. Lymphocytes from depressed patients with abnormal 0800 h serum cortisol after dexamethasone had a mean receptor concentration of 8.8 +/- 0.75 fm/10(6) cells, which was not significantly different from that in lymphocytes from normal subjects or from depressed subjects with normal post-dexamethasone cortisol levels (9.4 +/- 0.95 fm/10(6) cells). Lymphocytes from depressed patients with elevated urinary free cortisol excretion (UFC) also had normal receptor concentration and binding affinity for dexamethasone. The lack of a change in lymphocyte glucocorticoid receptor concentration in the presence of cortisol excess suggests the possibility that hypercortisolemia in depressive illness represents a state of peripheral glucocorticoid resistance.

The interaction of nivazol with the glucocorticoid receptor from rat and rhesus monkey target tissues

Steroid hormone receptor competition techniques were used to evaluate the glucocorticoid receptor binding properties of nivazol and its 11 beta-hydroxy derivative, Win 44577 in rat and monkey target tissues. These agents competitively inhibited the binding of 3H-dexamethasone to the glucocorticoid receptor from the liver and anterior pituitary from both rat and monkey with relative binding affinities of Win 44577 greater than dexamethasone greater than nivazol greater than cortisol in all cases. However, nivazol and Win 44577 had approximately twice the affinity for the anterior pituitary glucocorticoid receptor from both species. Neither compound demonstrated any significant binding to rat estrogen, progestin or androgen receptors. These results are consistent with a glucocorticoid receptor mediated mechanism of action for nivazol and Win 44577; however, the difference in the endocrine profile of nivazol in the rhesus monkey versus the rat does not appear to be due to a species selectivity in the affinity of nivazol for the glucocorticoid receptor from central or peripheral target tissue.

A common 43 K protein induced by glucocorticoids in a variety of cells and tissues

We have investigated the domain of adrenal steroid action in a variety of mammalian cells and tissue by high resolution two-dimensional gel electrophoresis and autoradiography. Following in vivo or in vitro treatment with steroids, minced tissue or cells were pulsed with [35S]methionine, and they newly synthesized polypeptides compared with controls by visual inspection of partial protein maps. We have found a similar protein (Mr approximately 41-44K, pI approximately 6.3-6.5) to be consistently increased by dexamethasone in 3 rat tissues and 9 human, bovine and rat cell lines. The protein was constitutively synthesized in all targets; quantitative measurements on the magnitude of response show a 2-fold induction by dexamethasone in all systems, in vivo and in vitro. Glucocorticoid-specific hormones but not sex steroids increase the rate of synthesis; deoxycorticosterone has agonist or antagonist effects on 43K synthesis in different systems studied. Co-electrophoresis experiments indicated that 43K proteins co-migrate in at least 3 rat cell lines from tissues with diverse functions. The functional significance of this common glucocorticoid-induced protein is unknown; its ubiquity and electrophoretic properties suggest a highly conserved, common indicator of glucocorticoid action in diverse target cells and tissues, rather than a tissue-specific response.

Binding of dexamethasone to rat liver nuclei in vivo and in vitro: evidence for two distinct binding sites

The binding of [3H]dexamethasone (DEX) to rat liver nuclei in vitro and in vivo have been compared. In vitro, purified nuclei displayed a single class of specific glucocorticoid binding sites with a dissociation constant (Kd) of approximately 10(-7) M for [3H]DEX at 4 degrees C. The glucocorticoid agonists prednisolone, cortisol, and corticosterone and the antagonists progesterone and cortexolone competed avidly for this site, but the potent glucocorticoid triamcinolone acetonide (TA) competed poorly in vitro. Nuclei isolated from the livers of intact rats contained 1-2 X 10(4) [3H]DEX binding sites/nucleus. Up to 85% of the binding sites were recovered in the nuclear envelope (NE) fraction when NE were prepared either before or after labeling with [3H]DEX in vitro. After adrenalectomy, the specific [3H]DEX binding capacity of both nuclei and NE decreased to 15-20% of control values, indicating sensitivity of the binding sites to hormonal status of the animals. Efforts to restore the binding capacity by administration of exogenous glucocorticoids, however, were unsuccessful. After labeling of rat liver nuclei in vivo by intraperitoneal injection of [3H]DEX or [3H]TA into living animals, the steroid specificity and subnuclear localization of radiolabel were different. Both [3H]TA (which did not bind in vitro) and [3H]DEX became localized to nuclei in a saturable fashion in vivo. With either of these ligands, approximately 20% of the total nuclear radiolabel was recovered in the NE fraction. These results suggest the presence of two separate and distinct binding sites in rat liver nuclei, one which is localized to the NE and binds [3H]DEX (but not [3H]TA) in vitro, and another which is not localized to the NE but binds [3H]DEX and [3H]TA in vivo.

17 beta-carboxamide steroids: highly effective inhibitors of the phytohaemagglutinin mediated blastogenesis of normal human peripheral lymphocytes

Several novel 17 beta-carboxamide analogues of dexamethasone were synthesized. The common precursor, 9-fluoro-16 alpha-methyl-11 beta,17-dihydroxy-3-oxo-1,4-androstadiene-17 beta-carboxylic acid, did not bind to the glucocorticoid receptors of rat liver and human spleen tumours. In addition, no inhibition of the mitogen-induced blastogenesis of cultured human peripheral lymphocytes was observed. The 17 beta-carboxamide analogues, however, bound with similar affinities to the glucocorticoid receptors of both tissues. They inhibited the mitogen-induced blastogenesis of peripheral lymphocytes, showing the same potency and same order of binding affinity as the natural glucocorticoids.

Ex vivo binding to glucocorticoid receptors in the thymus of the adrenalectomized rat

The interaction of glucocorticoids with thymic cytosol receptors in the adrenalectomized rat was studied by a method based on their capacity to deplete cytosol receptors when administered in vivo. Three h after a single oral administration of reference steroids at various dose levels, thymus cytosol aliquots were incubated with a saturating concentration of [3H]dexamethasone (30 nM) for 24 h at 0-2 degrees C with and without 2000 nM unlabeled dexamethasone. Bound radioactivity was determined by dextran-coated charcoal adsorption. The depletion of cytosol receptors was dose-dependent for each glucocorticoid, with the following ED50 (mg/kg): fluocinolone acetonide 0.032, dexamethasone 0.09, triamcinolone acetonide 0.12, betamethasone 0.24, deflazacort 0.55, triamcinolone 1.6, prednisolone 4.0, hydrocortisone 17.0. A striking correlation (r 0.991) between ex vivo receptor binding and thymolytic effect was observed. When data from in vitro competition studies were compared with those obtained in ex vivo experiments, the latter were correlated more tightly with the biological response.

Molecular action of aldosterone

Aldosterone stimulates the reabsorption of sodium across epithelial cells of various target tissues. The initial events in the molecular action of the mineralocorticoid are the following: (1) Diffusion of the steroid across the cellular (baso-lateral, serosal) plasma membrane into the cytoplasmic compartment. (2) Binding of the steroid to a receptor protein specific for the class of steroid and activation of this steroid-receptor-complex. (3) Translocation of the activated aldosterone-receptor complex to the nucleus and stimulation of RNA synthesis (including the synthesis of messenger RNA and ribosomal RNA). (4) Translation of the steroid-induced messenger RNAs at the ribosomal level into the aldosterone-induced proteins (AIP) within the cytoplasmic compartment. Whereas these induction steps are uniformly accepted, the mechanisms by which the AIPs increase the activity of a rate-limiting step in the sodium transport process are still object of debate. In this paper we discuss the initial events in the mode of action of aldosterone and the biochemical and physiological approaches to the aldosterone-induced proteins with special reference to the "sodium permease", the "energy", and the "sodium pump" theory. Our analysis shows that despite serious efforts by multiple laboratories, the first AIP with an established relationship to the mineralocorticoid actions of aldosterone is yet to be identified.

Influence of 16 alpha, 17 alpha-acetal substitution and steroid nucleus fluorination on the topical to systemic activity ratio of glucocorticoids

The use of topical glucocorticosteroid therapy on large skin areas or in the lung is sometimes restricted by the occurrence of unwanted, general corticoid actions owing to a profound systemic absorption. To decrease this risk potent glucocorticoids with an enhanced ratio between their topical and their systemic glucocorticoid potencies are wanted. Therefore, structure-activity studies were performed in rat models to investigate what influences the type of substitution in the 16 alpha, 17 alpha-acetal group and the introduction of fluorine in the 9 alpha- or the 6 alpha, 9 alpha-positions have on the topical and the systemic activities, respectively. The introduction of an unsymmetrical 16 alpha, 17 alpha-acetal group (named acetal type B) markedly enhanced the topical anti-inflammatory potency compared with that of the conventional 16 alpha, 17 alpha-acetonide group (named acetal type A). Both acetal types had a similar systemic glucocorticoid potency, however, 9 alpha-Fluoro and especially 6 alpha, 9 alpha-difluoro substitution, on the other hand, enhanced the systemic glucocorticoid activity more than they raised the topical anti-inflammatory potency. Optimal topical to systemic activity ratio was obtained with a nonhalogenated corticoid of acetal type B structure. This compound, budesonide, had at least the same high topical anti-inflammatory potency as fluocinolone acetonide but was about 10 times less potent than this reference to induce systemic glucocorticoid actions. Its lower systemic activity is probably due to a more rapid biotransformation in the liver.

Interactions of antiglucocorticoids with glucocorticoid receptors

Six known or potential antiglucocorticoids were used as steroid probes in a competitive binding assay to elucidate the binding specificity of the agonist sites of four different rat glucocorticoid receptors. The object was to determine whether the binding of this class of steroids was particularly sensitive to subtle differences between these sites. Cytosolic extracts of heart, pancreas, kidney and liver were evaluated. The order of competitive potency for the first three preparations was found to be medroxyprogesterone greater than deoxycorticosterone greater than progesterone greater than R-5020 greater than cortexolone greater than 17-hydroxyprogesterone. The order for the glucocorticoid receptor of liver, on the other hand, was R-5020 greater than progesterone greater than deoxycorticosterone greater than medroxyprogesterone greater than cortexolone greater than 17-hydroxyprogesterone. Although this partial reversal of specificity could reflect a difference in the agonist site of the liver receptor, mixing experiments, in which cytosolic extracts of liver were incubated with kidney cytosol extracts, demonstrated that the liver cytosol contained an additional factor that could change the apparent specificity of the kidney glucocorticoid receptor. This factor was stable at 0 degrees C for at least 18 h, heat-labile and non-dialyzable. These results suggest that the liver receptor's specificity may actually be the same as the other three, but appears to be different in this type of assay because of this additional factor. It is similar that their agonist sites are most likely identical.

Differential binding in vitro to glucocorticoid receptors of deflazacort and prednisolone

Deflazacort, a new steroidal anti-inflammatory agent, has remarkable glucocorticoid activity in both animals and humans. Its biologically active form, 21-desacetyl deflazacort, displaces [3H]dexamethasone from its cytosol receptor sites in rat kidney, thymus and liver in vitro. Although less active than prednisolone in its binding to glucocorticoid receptors, deflazacort 'stabilizes' the resulting steroid-receptor complex more effectively than the former in the kidney and thymus but not in the liver. This property might explain the greater activity of deflazacort than of prednisolone in the rat.

Kinetics of the glucocorticoid hormone-receptor interaction. False association constants determined in slowly equilibrating systems

The usual way of in vitro determination of association constants for hormone-receptor complexes is criticized. It is shown that if incubation time is short, relative to the half-life of the hormone-receptor complex, the value of the apparent Ka is proportional to the time of incubation. No sign of lack of equilibrium is apparent from the Scatchard plots. The case of rapidly denaturing receptor molecule is also discussed, with similar conclusions. Although terminology and examples are taken from the field of the glucocorticoid receptor research, all deductions are valid for other systems with similar association (and denaturation or monomolecular transformation) mechanisms and kinetic parameters.

Glucocorticoids and regulation of phosphoenolpyruvate carboxykinase activity in rat brown adipose tissue

Studied were performed to examine the factors that might regulate phosphoenolpyruvate carboxykinase (PEPCK) activity in rat brown adipose tissue (BAT) and to determine the role played by glucocorticoids in regulating this enzyme. Comparison was made to white adipose tissue (WAT) where PEPCK activity is known to be glucocorticoid regulated. PEPCK activity in BAT did not respond to adrenalectomy or dexamethasone, whereas WAT activity was increased and decreased, respectively, by these maneuvers. Three conditions were found in which BAT PEPCK activity was stimulated: 1) fasting, 2) feeding a high-fat/low-carbohydrate diet, and 3) during the neonatal period. In each case glucocorticoid treatment prevented the stimulation in PEPCK activity and restored the enzyme to base-line levels. In conditions 1 and 2, enzyme activity was also stimulated in WAT, but in contradistinction to BAT, glucocorticoid administration reduced activity to low levels significantly below base-line activity. Two conditions were found which suppressed PEPCK activity in BAT: exposure to a cold environment and feeding a high-protein/low-fat diet. WAT PEPCK was unaltered by exposure to cold. Thus, differences in PEPCK regulation between BAT and WAT were demonstrated, and the response to glucocorticoids was unique in BAT.