The serum steroid transport proteins: biochemistry and clinical significance

Exercise Is Medicine, But Does It Interfere With Medicine?

Exercise frequently is prescribed therapeutically, either on its own or combined with drugs. A drug's absorption, distribution, metabolism, and excretion can be affected by the user's anatomy and physiology, which are both changed by the myriad of complex adaptations to acute and chronic exercise. This article reviews the research that suggests exercise may influence a drug's plasma concentration, and thus its efficacy and safety.

Fetal origin of endocrine dysfunction in the adult: the phthalate model

Di-(2-ethylhexyl) phthalate (DEHP) is a plasticizer with endocrine disrupting properties that is found ubiquitously in the environment as well as in human amniotic fluid, umbilical cord blood, human milk, semen, and saliva. It is used in the industry to add flexibility to polyvinyl chloride-derived plastics and its wide spread use and presence has resulted in constant human exposure through fetal development and postnatal life. Epidemiological studies have suggested an association between phthalate exposures and human reproductive effects in infant and adult populations. The effects of fetal exposure to phthalates on the male reproductive system were unequivocally shown on animal models, principally rodents, in which short term deleterious reproductive effects are well established. By contrast, information on the long term effects of DEHP in utero exposure on gonadal function are scarce, while its potential effects on other organs are just starting to emerge. The present review focuses on these novel findings, which suggest that DEHP exerts more complex and broader disruptive effects on the endocrine system and metabolism than previously thought. This article is part of a Special Issue entitled "CSR 2013".

Effect of hydroxylpropyl-beta-cyclodextrin on Solubility of Carvedilol

The present study was undertaken to examine the effect of pH and concentration of hydroxypropyl-β-cyclodextrin on the solubility of carvedilol as it shows pH-dependent solubility. The equilibrium solubility of carvedilol in a series of solutions of varying pH (from 1.2 to 11) was determined and compared with the equilibrium solubility of carvedilol in the presence of 20% hydroxypropyl-β-cyclodextrin at same pH values. It was observed that solubility of protonated form is more than neutral molecule. Hydroxypropyl-β-cyclodextrin resulted in increased solubility at all the pH. But inclusion in the cavity of hydroxypropyl-β-cyclodextrin might depend upon charge state of the molecule. So it can be concluded that solubility of carvedilol, can be increased either by the addition of hydroxypropyl-β-cyclodextrin or by adding pH lowering agents. But both these methods if are to be used together, pH should be selected carefully.

Inclusion complexes of ketosteroids with beta-cyclodextrin

Inclusion complexes of several steroid derivatives with beta-cyclodextrin (7) were studied in dimethylsulfoxide solution. The investigated molecules were ketosteroids with different functional groups on the skeleton: 3beta-acetoxypregn-5-en-20-one (1), 3beta-acetoxypregna-5,16-dien-20-one (2), 3beta-acetoxyandrost-5-en-17-one (3), 3beta-hydroxyandrost-5-en-17-one (4), 5alpha-androstane-3,17-dione (5) and 17beta-hydroxyandrost-4-en-3-one (6). Complex formation was monitored by two-dimensional ROESY experiments through the detection of intermolecular dipolar interactions. In case of inclusion complex formation, the steroid molecule penetrates the cavity of the cyclodextrin and dipole-dipole interactions (ROEs) can be detected between the glucose H-3 and H-5 protons inside the cyclodextrin cavity and the steroid skeletal protons. Intermolecular interactions were detected in all six cases. However, ROESY experiments provided data indicating only partial immersion (A and B ring of the steroid skeleton) in case of 1, 2 and 6. On the contrary, compounds 3 and 5, showing the most correlation rich spectra, seem to fully immerse in the beta-cyclodextrin cavity.

Water-soluble conductive polymer homogeneous immunoassay (SOPHIA). A novel immunoassay capable of automation

Conductive polymers are extensively conjugated macromolecules able to conduct electricity in their doped state and having a UV-visible spectrum which undergoes important chromatic modifications when subjected to pH changes or to oxido-reductive processes. This article describes a novel homogeneous immunoassay in which a water-soluble conductive polymer is used as the label. When antigen-antibody binding occurs, the local pH near the complex is modified. Such a pH change is in turn able to induce modifications in the absorbance at a characteristic wavelength of a conductive polymer covalently linked to either the antigen or the antibody. Consequently, the extent of tracer binding can be directly monitored by photometry during incubation. We present examples which validate the concept and exemplify its applicability in quantitative competitive immunoassays for human C-reactive protein and human serum albumin, as performed in a Cobas-Mira automated analyzer.

Structure, function, and regulation of androgen-binding protein/sex hormone-binding globulin

Despite over 20 years of research, the functions of ABP and SHBG remain elusive. The major reason for this lack of knowledge has been the unavailability of natural mutants with clinical defects for study. There is strong evidence that these binding proteins do act to modulate the gene regulatory actions of nuclear sex steroid receptors by controlling the availability of androgens and estrogens. In plasma, SHBG controls the metabolic clearance rate of sex steroids. In addition there is strong evidence that they have a much broader function. The identification of plasma membrane receptors in target tissues and the finding of homologous domains in several developmental proteins support other functions. Moreover, other experiments suggest the proteins may actually be hormones or growth factors. These findings are not compatible with a model that has the proteins only regulating free steroid hormone levels. Obviously, much more experimentation will be necessary to reveal the functions of ABP and SHBG. The recent discoveries have offered several clues to their functions and open new routes for study. These experiments, coupled with newly developed techniques, such as gene knockout by homologous recombination, make one optimistic that the functions of these unique proteins will be deciphered in the near future.

Pathophysiology of sex hormone binding globulin (SHBG): relation to insulin

In humans, the plasma level of sex hormone binding globulin (SHBG) is regulated by several hormones. We have now accumulated evidence that SHBG is also intimately related to nutritional state. However, we do not yet know what specific signal, if any, may be the regulator of SHBG. There is a strong and negative correlation between fasting insulin level and SHBG in obese as in hyperandrogenic women. Under such circumstances, a high fasting insulin level, normal glycemia and a low SHBG level suggest insulin resistance in terms of glucose disposal but not in terms of SHBG inhibition. This is a rather complex situation. It is too early to judge the importance of IGF-I in the regulation of SHBG. But it may turn out that IGF-I is the main regulator of SHBG and that, by interaction with the IGF-I receptors, insulin carries on its inhibitory activity on SHBG.

A comparison between the composition of maternal peripheral plasma and plasma collected from the retroplacental compartment at caesarean section. A study on protein and steroid hormones and binding proteins

In the pregnant uterus unique immunological conditions must prevail. Since compounds of possible fetoplacental origin may modulate the local maternal immunological response, higher concentrations of such compounds in the vicinity of the conceptus might be expected. We have measured the concentrations of several compounds in peripheral and retroplacental plasma, mainly by immunological methods, from women delivered by caesarean section in pregnancy week 38-40. Significantly higher (P less than 0.001) retroplacental concentrations were found for human placental lactogen, prolactin, alpha-fetoprotein, tissue polypeptide antigen, non-conjugated estriol and progesterone. Peripheral plasma levels were significantly higher for cortisol (P less than 0.01), transcortin (P less than 0.001) and sex-hormone binding globulin (P less than 0.002). No difference was found for albumin, alpha 2-macroglobulin, estradiol, placental alkaline phosphatase and human chorionic gonadotrophin. Significant correlations between retroplacental and maternal peripheral plasma levels were found for progesterone, cortisol, estradiol, estriol, transcortin, sex-hormone binding globulin, prolactin, human placental lactogen, human chorionic gonadotrophin, placental alkaline phosphatase, albumin and alpha 2-macroglobulin. There were also significant correlations between estradiol and sex-hormone binding globulin as well as transcortin in peripheral maternal plasma.

Elevation of serum sex hormone-binding globulin in females with fulminant hepatitis B virus infection

Amongst adults exposed to the hepatitis B virus (HBV), the infection pursues a fulminant course more frequently in females, while conversely a chronic carrier state is more frequent in males. Because of these differences in sex ratio, we investigated the relationship between the outcome of HBV infection and serum concentrations of sex hormone-binding globulin (SHBG), a circulating glycoprotein that exerts an important influence on the balance of free sex hormones. SHBG levels were significantly elevated in females with fulminant HBV infection compared to females with either uncomplicated acute or chronic HBV infection (P less than .05 and P less than .001, respectively). That this was not a nonspecific effect of fulminant hepatitis was confirmed by the significantly higher levels in this group than in age-matched females with fulminant hepatitis unrelated to HBV (P less than .05). In contrast, four of 15 female HBsAg carriers had SHBG values in the male range, and these included three of four patients who had acquired HBV as adults. SHBG levels were normal in all male groups. These results suggested that for adults the hormonal environment may be important in determining the course of HBV infection.

Sex steroid-binding protein in nonendocrine diseases

In humans, sex steroid-binding protein (SBP) is a protein from the liver which binds with high affinity sex steroid hormones. The plasma concentration of SBP is regulated in part by hormonal factors. It has been shown that estrogens and/or thyroid hormones increase the production of SBP by hepatoma cell lines. It is therefore assumed that the increase in SBP levels in patients given oral estrogens or thyroid hormones is the consequence of a direct stimulation of the liver production of SBP by these hormones. The effects of androgen, progestagen and glucocorticoid hormones are unclear or still a matter of controversy. Moreover, the regulation of the metabolic clearance rate of SBP and the influence of nonhormonal factors on the production of SBP are still speculative. Changes in SBP have been described in a few nonendocrine diseases. A slight hormonal dysfunction may be either the primary or the sole cause of the changes in SBP occurring in these diseases. As an example, elevated SBP levels have been reported in men with liver cirrhosis together with testicular hypofunction and increased estrogen levels. It is therefore difficult to demonstrate that the increase in SBP is due to the liver dysfunction rather than to the endocrinological side effects of cirrhosis. The aim of this review is to present some aspects of the nonhormonal regulation of SBP. There is accumulating evidence in the literature for a relation between SBP levels and body weight and fat distribution, energy balance, diet and physical activity, and lipid metabolism. Therefore, it is tempting to propose that SBP is an index which reflects the status of endocrine, metabolic and nutritional functions. Measurement of SBP may be considered of interest in the light of previous epidemiological studies and the preventive approach to diseases such as hormone dependent tumors, cardiovascular diseases and osteoporosis.

Dimerization of SHBG by gelatin and dithiothreitol. Implications for the measurement of SHBG binding capacity in human serum

In individual serum samples, the sex hormone-binding globulin (SHBG) binding capacity for dihydrotestosterone (DHT) was systematically found to be decreased by 30-60% when either gelatin or dithiothreitol (DTT) was present in the assay buffer. The presence of gelatin in the buffer prevented DTT from further decreasing the SHBG binding capacity of serum samples, suggesting a similar mechanism of action on SHBG for both of these substances. This observation led us to compare the molecular forms of SHBG by high performance liquid chromatography on a TSK G 3000 SW column, in the presence or absence of DTT. When undiluted serum previously incubated with [3H]DHT was chromatographed, only monomeric SHBG could be detected, independently of the presence or absence of DTT in the elution buffer. When the serum was diluted, incubated and chromatographed with buffer devoid of DTT, a dimeric SHBG peak was progressively observed, as a function of the sample dilution. Furthermore, for a given serum dilution, the relative size of the dimeric SHBG peak was also dependent on the steroid concentration present in the sample. By contrast, when serum was diluted, incubated and chromatographed with DTT-supplemented buffer, only the SHBG dimer peak could be detected. These results suggest that in serum, in vitro at least, SHBG is present in its monomeric form. Serum dilution with buffer devoid of DTT or gelatin induces the progressive dimerization of the protein, resulting in a progressive decrease of its apparent binding capacity. This could explain the great discrepancies of SHBG levels as reported in the literature. Because serum dilution with buffer supplemented with DTT or gelatin induces the complete dimerization of SHBG, independently of the sample dilution, we suggest that these substances be routinely used for the measurement of SHBG binding capacity. The SHBG binding capacity obtained in these latter conditions reflects however half the binding capacity of undiluted serum.

Purification and binding site characterization of the circulating trophoblastic androgen-binding protein

The trophoblastic androgen-binding protein (t-ABP) was purified 150-fold with a recovery of 51% from serum of patients with hydatidiform mole using various chromatographic techniques, successively affinity on concanavalin A, ion exchange on QAE-Sephadex A 50, gel filtration on Sephadex G 200 and chromatofocusing. The chromatofocusing step eliminated any trace of contaminating sex-hormone binding globulin. Competitive binding experiments using the purified material, [3H]dihydrotestosterone and various steroid derivatives allowed an attempt at characterizing the steroid-binding site of the protein. This latter possess respectively hydrophilic domains facing position 2 and 17 of the steroid molecule, a hydrophilic and proton donor sequence facing position 3 of the steroid molecule, hydrophobic regions facing positions 6, 11 and 16 of the steroid molecule and electron donor domains facing positions 1 and 6 of the steroid molecule. These characteristics are compared with those of the sex hormone-binding globulin (SHBG), rat epididymis androgen-binding protein (RABP) and rat prostate cytoplasmic androgen receptor (CAR) binding sites, respectively. The results of this specificity study indicate that the t-ABP behaves very similarly to CAR, although major differences are likely to exist between the binding sites of both proteins, particularly in the protein domains facing C-1 and C-2 of the steroid.