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Steroid-protein interaction: from past to present.

In this review, the association between biologically active compounds and proteins is seen in the light of axioms expressed by Paracelsus and Paul Ehrlich long ago, and the physiological significance of the interactions is pointed out. Of the various types of proteins that form noncovalent complexes with steroid hormones, only the serum proteins will be discussed. Recent results, obtained in several laboratories, on the physicochemical properties of the human corticosteroid-binding globulin (CBG, transcortin) makes this glycoprotein perhaps the best known one among the steroid-binding serum proteins. Influence of pH on stability of the complexes, kinetics of the associations and their significance, as well as thermodynamic parameters of complex formation are being discussed. Characteristics of the binding sites are deduced from specificity studies. Influence of the entrance of hydrophilic or hydrophobic substituents into the steroid molecule illuminates the difference between typically hydrophobic binders such as the progesterone-binding globulin (PBG) of the pregnant guinea-pig and typically hydrophilic binders such as CBG. Complete elucidation of the steroid-binding proteins awaits the determination of the amino acid sequence and the X-ray crystallographic analysis of the steroid-protein complex.

Animals↗

The glucocorticoid properties of the synthetic steroid pregna-1,4-diene-11beta-ol-3,20-dione (deltaHOP) are not entirely correlated with the steroid binding to the glucocorticoid receptor.

The natural steroid 11beta-hydroxyprogesterone is not only a modulator of 11beta-hydroxy-steroid dehydrogenase activity, but also an efficient inducer of tyrosine aminotransferase activity in hepatocytes. In contrast with the low affinity for the mineralocorticoid receptor. 11beta-hydroxyprogesterone binds well to both the glucocorticoid receptor and the carrier protein transcortin. It is accepted that the introduction of a 1:ene double bond into 3-keto 4:ene steroids increases the glucocorticoid potency, so that 3-keto-1,4:diene steroids show improved chemical stability and are more potent glucocorticoids than their respective 4:ene analogs. The steroid pregna-1,4-diene-11beta-ol-3,20-dione (deltaHOP) had previously been described as an anti-inflamatory compound and an inhibitor of macromolecular biosynthesis in thymocytes and lymphocytes. In such studies, deltaHOP also exhibited some particular glucocorticoid properties which made it attractive as a tool for the study of the mechanism of action of glucocorticoids. In the present paper we show that deltaHOP possesses some classical biological actions of glucocorticoids such as deposition of glycogen in rat liver, induction of TAT activity in hepatocytes, and inhibition of the uptake of leucine and thymidine by thymocytes. It also exhibits minimal sodium-retaining properties. Consistent with these biological effects, deltaHOP shows a 70 times lower relative binding affinity for the mineralocortioid receptor than aldosterone, but a reasonable affinity for the glucocorticoid receptor, and is as efficient as dexamethasone in dissociating the 90 kDa heat shock protein from the glucocorticoid receptor heterocomplex. However, the inhibition of the uptake of amino acids and nucleotides observed in the presence of deltaHOP is not efficiently blocked when thymocytes are coincubated in the presence of steroids with known antiglucocorticoid activity. deltaHOP is similarly inefficient in inducing chloramphenicol-acetyl transferase activity in cells transfected with a plasmid that possesses two canonical glucocorticoid-responsive elements. Unlike most glucocorticoids, deltaHOP does not induce the fragmentation of DNA in a regular pattern characteristic of apoptosis and it does not reduce thymus weight. This unusual dissociation of glucocorticoid parameters makes deltaHOP a useful tool to discriminate between mechanisms of action by which steroids can exert their biological effects.

Animals↗

16alpha,17alpha-cycloalkane derivatives of progesterone intensively bind to a rat serum protein.

The interaction of 6alpha-methyl-[1,2-3H]16alpha,17alpha-cyclohexanoprogesterone with rat serum proteins has been studied. Specific binding of this ligand characterized by Kd = 0.36 +/- 0.10 microM and concentration of binding sites (Bmax) of about 1 microM (27.8 +/- 12.5 pmol/mg total protein) was found. According to competitive analysis, the affinity of the studied progestins to a protein that differs from transcortin was to some extent correlated with their hydrophobicity. The dissociation kinetics of 3H-ligand-protein complexes were biphasic, the binding sites forming stable and labile complexes with 3H-ligand being eluted in the same region during ion-exchange chromatography. In overall properties, the serum protein differs from the progesterone receptor and the pregna-D'-pentarane-specific protein from rat uterus. It is suggested that the revealed protein may provide high progestagenic activity of 6alpha-methyl-16alpha,17alpha-cyclohexanoprogesterone by prolonging its retention in the bloodstream.

Animals↗

Prednisolone disposition in obese men.

Obesity is accompanied by altered secretion and disposition of sex and glucocorticoid hormones, including cortisol, and also confounds parameter normalization and drug dosage selection relative to body weight. Prednisolone disposition was assessed in eight obese and four normal male subjects after a dose of 33 mg iv. Steroid concentrations were determined by HPLC. Kinetics were related to ideal body weight (IBW) and total body weight (TBW). Uncorrected steady-state volume of distribution (Vss) of total prednisolone was 20% greater in obese subjects (36.7 and 44.1 l). This effect could be described by the relationship: Vss = 0.54 IBW + 0.09(TBW-IBW), with a distribution coefficient of 0.09 reflecting limited prednisolone uptake by fat. Protein binding parameters and albumin and transcortin concentrations were similar between groups. Uncorrected total and free prednisolone clearances (Cl) were increased in obesity (11.1 and 8.3 l/hr total; 65.4 and 46.5 l/hr free). Free prednisolone Cl correlated strongly (r = 0.80) with degree of obesity expressed as TBW/IBW. In the obese, endogenous cortisol concentrations were initially higher before exogenous steroid dosing, were suppressed at an identical rate, and returned to baseline more slowly than in normal subjects. The apparent hypersensitivity of the adrenal gland offsets the increased Cl of free prednisolone in obesity, indicating that weight-proportional dosage adjustments of this steroid in obesity should reflect TBW.

Adolescent↗

A sensitive direct enzyme immunoassay for cortisol in plasma and saliva.

A sensitive enzyme immunoassay for cortisol in plasma and saliva without extraction has been developed. An antibody was raised in rabbits against cortisol-3-CMO-BSA and compared with anti-cortisol-21-HS-HSA. The enzyme label was a covalently linked cortisol-horseradish peroxidase conjugate. Solvent extraction was avoided by use of heat denaturation of transcortin and dilution of plasma 1:300. This assay had a limit of detection of 3 fmol/tube and satisfied the standard criteria of accuracy and precision. The test requires only a simple photometer. The normal values of cortisol in plasma and saliva before and after ACTH, dexamethasone or metyrapone application were determined. Saliva, being easily collected by a noninvasive, stress-free technique is an alternative to plasma. The cortisol concentrations were significantly increased in plasma and saliva of patients with Cushing's syndrome and decreased in patients with Addison's disease.

Addison Disease↗

Binding of progesterone to specific sites in isolated hepatic cells and purified plasma membrane fraction.

Specific binding for progesterone has been determined in rat hepatocytes and mouse liver purified plasma membranes. The binding is saturable, reversible and temperature dependent. Two types of binding sites have been characterized in hepatocytes. The first is of high affinity and low binding capacity and the other one is of low affinity and high capacity of binding. In plasma membranes one type of specific binding site only exists. These high affinity sites are different from nuclear progesterone receptor, nuclear glucocorticoid receptor, digitalis receptor of Na+, K(+)-ATPase, transcortine and from corticoid binding sites determined previously in plasma membrane. We also have observed that specific progesterone binding to hepatocytes and plasma membrane is independent from the alpha and beta adrenergic receptors and from P-site adenosine receptor.

Animals↗

Glucocorticoid negative feedback and glucocorticoid receptors after hippocampectomy in rats.

In rats with dorsal hippocampectomy, glucocorticoid receptors in the hypothalamus and anterior pituitary, as well as the pituitary transcortin-like compound, are preserved, in spite of a 60% depletion of glucocorticoid receptors in the hippocampus. In the hippocampectomized group, basal levels of serum corticosterone (CORT) were increased, although there was a normal response to ether stress. Inhibition of the response to ether with dexamethasone (DEX) was dose-dependent: whereas 100 micrograms/kg completely suppressed serum CORT, 10 micrograms/kg were ineffective. However, we observed a reduced sensitivity to DEX inhibition with 25 micrograms/kg in hippocampectomized animals. These results indicate that the hippocampus is involved in negative feedback mechanisms, although different doses of DEX are needed for this demonstration. The inhibition of serum CORT due to 100 micrograms/kg DEX suggests that negative feedback at sites other than the hippocampus was still operative, in agreement with normal levels of glucocorticoid receptors in the anterior pituitary and hypothalamus of hippocampectomized rats.

Animals↗

Progesterone "receptors" in the cytoplasm and nucleus of chick oviduct target tissue.

This report demonstrates that the chick oviduct, a specific target organ for progesterone, contains both cytoplasmic and nuclear macromolecules which bind progestins. These binding molecules can be clearly distinguished from transcortin by centrifugation through sucrose gradients of low ionic strength and by agarose gel filtration. The cytoplasmic progesterone-binding molecules also bind 5-alpha-pregnane-3,20-dione, but have significantly lower affinity for cortisol, estrone, or aldosterone. They are absent from blood and nontarget organs such as lung and spleen. The tissue-specific binding components appear to be heat-labile proteins with an average dissociation constant for progesterone of about 8 x 10(-10) M at 2 degrees C. These results are consistent with the identification of the progesterone-binding molecules as the functional hormone receptors. In further support of this concept is the finding that treatment of the chicks with estrogen coordinately induces a 20-fold increase in the number of progesterone-binding molecules and enhances the capacity of progesterone to induce avidin synthesis.A progesterone-"receptor" complex can be detected in both the cytoplasm and nuclei of oviduct tissue after an injection of [(3)H]progesterone to estrogen-treated chicks. By contrast, incubation of oviduct tissue with [(3)H]progesterone in vitro at 2 degrees C for 5 min leads to labeling of the cytoplasmic "receptor" only. Transfer of the "receptor"-steroid complex into the nucleus then appears to occur upon subsequent incubation in vitro at 37 degrees C. This observation suggests that the transfer of bound progesterone across the nuclear membrane may be an energy-requiring enzymatic process.

Aldosterone↗

An antiserum to the rat liver glucocorticoid receptor.

A rabbit immunized with a highly purified preparation of rat liver [3H]triamcinolone-receptor complex developed antibodies to the receptor. Although precipitating reactions were not detected, complexes formed between IgG and the receptor could be detected by Staphylococcus aureus protein A-Sepharose and gel permeation chromatography. IgG was purified and covalently immobilized on Sepharose CL-4B; this affinity matrix adsorbed the ligand-free receptor and both activated and nonactivated forms of the [3H]triamcinolone-receptor complex. Rat liver cytosol proteins adsorbed by control and immune immunoglobulin-Sepharoses were eluted with 0.1 M acetic acid and analyzed by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. A protein with molecular weight 78,000 was the major species eluted from immune immunglobulin-Sepharose, and it was not present in eluates from control columns. Rat transcortin, glucocorticoid binder IB, and an estrogen-binding protein from rat liver were not adsorbed by immune IgG-Sepharose. Mouse and hamster liver glucocorticoid receptors showed only limited adsorption. Thus, the antiserum does not crossreact with other major glucocorticoid-binding proteins and demonstrates species specificity.

Animals↗

Rapid glucocorticoid inhibition of vasoactive intestinal peptide-induced cyclic AMP accumulation and prolactin release in rat pituitary cells in culture.

Vasoactive intestinal peptide (VIP) stimulates both adenosine 3',5'-cyclic monophosphate (cAMP) accumulation and prolactin release in normal rat pituitary cells in culture. cAMP accumulation is significant (P less than 0.01) at VIP concentrations as low as 1 nM and reaches a maximum with 0.1 microM. Addition of dexamethasone as early as 15 min before VIP inhibits VIP stimulation of both cAMP production and PRL secretion. The rapid inhibition is dose-dependent: it appears at doses as low as 0.01 pM and is complete at 1 pM dexamethasone. Increasing concentrations of dexamethasone induce a noncompetitive type of inhibition, as shown by the decrease in Vmax with no change in the apparent Km for VIP. Cycloheximide (1 mM) counteracts the inhibitory effect of dexamethasone on VIP-induced cAMP production, which suggests the involvement of a rapid protein synthesis mechanism. Ru-26988, a specific glucocorticoid devoid of any mineralocorticoid activity and which does not bind to intracellular transcortin-like component, also produces an inhibition of VIP-induced cAMP accumulation. Corticosterone also inhibits VIP-induced cAMP production but at concentrations higher than those of dexamethasone. In contrast, aldosterone, progesterone, estradiol, and testosterone have no effect. These results demonstrate that, in normal rat pituitary cells in culture, glucocorticoids at physiological concentrations rapidly inhibit the cAMP production and prolactin release induced by VIP by acting through specific glucocorticoid receptors.

Animals↗

Antibodies to rabbit progesterone receptor: crossreaction with human receptor.

Progesterone receptor from rabbit uterine cytosol was purified to a specific activity of approximately 2 nmol of bound hormone per mg of protein. A goat was immunized with this preparation and, after two injections of 0.7-0.8 nmol, yielded antireceptor antibodies. The antiserum reacted with both cytosolic and nuclear rabbit progesterone receptor and also with progesterone receptor from other rabbit tissues (vagina and pituitary). A crossreaction was observed with progesterone receptors from other mammalian, especially human, tissues (cytosolic receptor from rat and guinea pig uterus, cytosolic receptor from human breast cancer, and nuclear receptor from human endometrium). On the contrary, there was no interaction with a nonmammalian receptor (chicken oviduct progesterone receptor). The antibodies did not crossreact with other rabbit steroid receptors (uterine estradiol receptor and liver glucocorticoid receptor) or with nonreceptor progesterone-binding proteins (transcortin from plasma and uteroglobin from uterine fluid).

Animals↗

Correlations between the activities of DNA polymerase alpha and the glucocorticoid receptor.

Specific inhibitors and anti-DNA polymerase alpha IgG have been utilized to probe for similarities between cytoplasmic rat hepatic glucocorticoid receptors and DNA polymerase alpha [DNA nucleotidyltransferase (DNA-directed), EC 2.7.7.7]. Rifamycin AF/013, an inhibitor of RNA and DNA polymerase activities, significantly inhibited the binding of activated [6,7-3H]-triamcinolone acetonide (TA) receptor complexes to DNA-cellulose. beta-Lapachone, an inhibitor of DNA polymerase alpha and reverse transcriptase activities, inhibited the specific binding of [6,7-3H]TA when preincubated with unbound receptors. Aphidicolin, another DNA polymerase alpha inhibitor, failed to inhibit any of the glucocorticoid-receptor functions tested. Two specific anti-DNA polymerase alpha IgGs interfered with glucocorticoid receptor functions as measured by their ability to inhibit the binding of [6,7-3H]TA to unbound receptors (85% maximal inhibition) and, to a lesser extent, to inhibit the binding of activated [6,7-3H]TA receptor complexes to DNA-cellulose (50% maximal inhibition). The anti-DNA polymerase alpha IgG and beta-lapachone failed to affect the binding of tritiated estradiol, progesterone, or 5 alpha-dihydrotestosterone to their receptors in appropriate rat target tissues or the binding of [1,2-3H]hydrocortisone to serum transcortin. The most obvious interpretation of these data is that cytoplasmic glucocorticoid receptors and DNA polymerase alpha share antigenic determinants. An alternative interpretation is that the polyclonal anti-DNA polymerase alpha antibody contains IgG molecules raised against calf thymus cytoplasmic activated glucocorticoid-receptor complexes that copurified with DNA polymerase alpha used as the antigen. Taken collectively, however, the antibody and inhibitor data suggest a relationship between DNA polymerase alpha and the glucocorticoid receptor.

Animals↗

Normal serum concentrations of sex hormone binding-globulin in patients with hyperthyroidism due to subacute thyroiditis.

Serum concentrations of sex hormone binding-globulin (SHBG) were determined in patients with hyperthyroidism (n = 94; 12 men, 82 women) due to either Graves' disease (n = 59; 11 men, 48 women), autonomous thyroid adenomas (n = 23; 1 man, 22 women), or subacute thyroiditis (n = 12; all women). Elevated serum concentrations of SHBG were initially seen in 57 of 82 patients (69%) with hyperthyroidism due to either Graves's disease or due to autonomous adenoma. Elevated serum SHBG concentration was more frequent in patients with serum total thyroxine (TT4) concentrations greater than 15.0 microg/dL (32/39 [82%]; including 3 patients with autonomous adenoma) compared to those with serum TT4 concentration between 11.0 and 15.0 microg/dL (21/27 [77%]; including 7 patients with autonomous adenoma), or patients with an isolated elevation of serum total triiodothyronine (TT3) concentration (4/16 [25%]; including 2 patients with autonomous adenoma). Serum SHBG concentration normalized when patients became euthyroid. Only 1 of 12 patients in the hyperthyroid phase of subacute thyroiditis had an elevated serum concentration of SHBG. Serum concentrations of thyroid binding globulin (TBG) and transcortin (CBG) were normal in all but 1 patient. In patients with hyperthyroidism as a result of Graves' disease or autonomous adenoma serum SHBG concentrations were elevated with the greatest elevation found in patients with the highest serum T4 concentrations. The normal concentrations of SHBG in the hyperthyroid phase of subacute thyroiditis most likely reflects the shorter duration of exposure to increased thyroid hormone in this condition.

Adenoma↗

Monitoring prednisone and prednisolone.

Their common clinical use, frequency of adverse effects, serious therapeutic indications, treatment failures, and availability of sensitive assays make corticosteroids such as prednisone and prednisolone candidates for therapeutic drug monitoring. Complicating the interpretation of plasma drug concentrations are the first-pass metabolism of inactive prednisone to active prednisolone and reconversion. Also, the volume of distribution, metabolic clearance, and renal clearance of prednisolone increase with dose. This is due partly to saturable binding of prednisolone to transcortin in plasma, which provides more unbound drug at higher plasma concentrations of steroid. This effect plus the probable uptake of only unbound drug into intracellular receptor sites provides the rationale for measuring free prednisolone in plasma. Drug interactions between prednisolone and anticonvulsants are common. Liver and kidney disease have only limited effects on prednisolone disposition. Changes in clinical efficacy and appearance of side effects have been related to altered prednisolone clearance. Plasma concentrations may be used to determine disease and drug interactions, bioavailability, and patient compliance. The role of pharmacokinetic factors in governing the indirect and variable pharmacodynamic response to corticosteroids at various tissue sites and in disease states currently needs clarification.

Biological Availability↗

Alterations in prednisolone disposition as a result of oral contraceptive use and dose.

The disposition of total and free prednisolone has been studied in eight female subjects who used combined oestrogen-progestogen oral contraceptives and in eight female subjects who did not, each of whom received separate intravenous doses of 0.1 mg/kg (low) and 1.0 mg/kg (high) of prednisolone. Mean free prednisolone clearance was reduced congruent to 30% in oral contraceptive users compared to control subjects (P less than 0.001), the difference being greater for the low dose (39%) than for the high dose (24%). Pre-dose plasma cortisol concentrations were elevated two-fold (P less than 0.001) in oral contraceptive users compared to control subjects. These effects are consistent with a mechanism in which the competitive inhibition of free prednisolone clearance by cortisol contributes to the reduction of free prednisolone clearance by oral contraceptive use. Mean total prednisolone clearance and steady state distribution volume showed an approximate two-fold dose dependent increase consistent with a similar increase in plasma prednisolone free fraction (P less than 0.001). Free prednisolone clearance showed an 18% dose dependent decrease (P less than 0.001) but free steady-state distribution volume did not change with dose. At plasma prednisolone concentrations less than 400 ng/ml, prednisolone free fractions at any prednisolone concentration were greater after the low, than after the high dose. This effect is consistent with the displacement of prednisolone by cortisol from transcortin but not from albumin.

Adolescent↗

Interaction of mixed micelles formed from glycocholic acid and lecithin with the protein binding of various drugs.

Mixed micelles (MM) formed from glycocholic acid and lecithin are suited to solubilize lipophilic drugs for intravenous use. To test for possible drug-drug interactions, the protein binding of a series of agents known to bind to different sites on albumin (diazepam, warfarin, ketoprofen, frusemide, probenecid) and additionally (prazosin, quinidine, propranolol) or exclusively (disopyramide) to alpha 1-acid glycoprotein or to transcortin (prednisolone) was determined in the presence and absence of MM. Concentrations of MM, corresponding to the maximum possible plasma concentration achieved by injecting the highest clinical doses of MM into the systemic circulation, had little or no effect on the unbound fractions of drugs known to bind exclusively to albumin. Only at five times higher MM concentrations were the free fractions substantially increased (by up to 45%). Unbound fractions of drugs bound with high affinity but low capacity to alpha 1-acid glycoprotein were increased between 50-85% even at 'therapeutic' doses of MM. The present study suggests that drugs solubilized by MM should be given by slow injection or infusion to patients already receiving drugs which are highly bound to alpha 1-acid glycoprotein.

Glycocholic Acid↗

A double-blind cross-over 12-month study of L-thyroxine treatment of women with 'subclinical' hypothyroidism.

Twenty women, who had been randomly selected from women with subclinical hypothyroidism identified in a population study were treated with L-thyroxine and placebo in a double-blind cross-over design during 2 x 6 months. Three women did not complete the study, one because she moved to another part of the country, and two because of nervousness and sense of tachycardia. None of these 'drop-outs' had any objective signs of overtreatment; they had normal pulse rate and a serum T3 concentration within the reference interval. During L-thyroxine treatment serum procollagen-III-peptide concentration increased in 13 women out of the 17 women completing the study and at the end of treatment the mean concentration was significantly raised (P less than 0.001). Serum concentrations of procollagen-III-peptide then correlated with those of free thyroxine (P less than 0.01), total thyroxine (P less than 0.05), and reverse triiodothyronine (P less than 0.05). The same comparison revealed little or no effect on the concentrations of serum creatine kinase activity, transcortin or sex-hormone binding globulin. Heart rate-corrected preejection period and symptom score decreased (P less than 0.05). Four women starting with L-thyroxine showed a marked and prolonged (4-6 months) rise in thyrotrophin concentration during the subsequent placebo period, but remained clinically euthyroid. Four women (of 17) improved during therapy as judged by psychometric testing and their own rating. We could not by pretreatment observations identify these four women apart from serum free and total 3,5,3'-triiodothyronine concentrations in the lower part of the health-associated reference interval. Subclinical hypothyroidism is common among middle-aged and old women, and our findings indicate that approximately one woman in four with this 'subclinical' condition will benefit from L-thyroxine treatment.

Aged↗

Orchidectomy or oestrogen treatment in prostatic cancer: effects on serum levels of adrenal androgens and related steroids.

Peripheral serum levels of dehydroepiandrosterone (DHA) and its sulphate (DHAS), 4-androstene-3, 17-dione (A-4), 17 alpha-hydroxyprogesterone (17-OHP), cortisol and albumin were measured in patients with prostatic cancer before treatment and after orchidectomy or during combined oral and intramuscular oestrogen treatment. Orchidectomy caused a pronounced decrease in 17-OHP levels and minor but significant decreases in the levels of A-4 and DHAS. Dehydroepiandrosterone, cortisol and albumin were unaffected by treatment. Oestrogen treatment caused a pronounced decrease in the serum levels of DHA, DHAS, 17-OHP and A-4 and a small but significant decrease in serum albumin. Cortisol levels increased, probably due to elevated transcortin levels. The ratio of DHA to DHAS was unaffected by either orchidectomy or by oestrogen treatment. These results confirm that the testis contributes to circulating DHAS. The mechanism behind the more pronounced decrease in adrenal androgens during oestrogen treatment is not known but, for DHAS, increased metabolic clearance due to the decrease in albumin levels may contribute in this respect. The unchanged values for the ratio of DHA to DHAS indicate that this sex-specific sulphatase/sulphotransferase balance is insensitive to endocrine manipulations in adult men. The results further invalidate the hypothesis that there is a 'compensatory' increase in adrenal androgen output following orchidectomy.

17-alpha-Hydroxyprogesterone↗