Plasma total and glycosylated corticosteroid-binding globulin levels are associated with insulin secretion.

In humans, steroid hormones circulate in the blood mainly bound to specific steroid transport proteins, namely corticosteroid-binding globulin (CBG) for cortisol and sex hormone-binding globulin (SHBG) for testosterone and estradiol. The binding activities of these proteins are believed to modulate the biodisposal of steroids to target cells. It has been shown in vitro that insulin is a potent inhibitor of both CBG and SHBG secretion by a human hepatoblastoma cell (HepG2) line. To further investigate this potential effect of insulin in vivo, we prospectively studied three groups of lean subjects, obese subjects, and obese subjects with glucose intolerance, all of whom were otherwise healthy. The three groups were comparable in sex and age, and in the two obese groups, body mass index, waist to hip ratio, and blood pressure were similar. Plasma total CBG concentrations (38.2 +/- 5.4 vs. 31.7 +/- 4.05 mg/L; P = 0.016) and glycosylated CBG levels (37.3 +/- 5.2 vs. 31 +/- 3.9 mg/L; P = 0.018) were significantly increased in obese subjects with glucose intolerance. Plasma CBG correlated positively with fasting glucose levels (r = 0.49; P = 0.002), hemoglobin A1c levels (r = 0.35; P = 0.03), and area under the curve of glucose after an oral glucose tolerance test (r = 0.45; P = 0.005) and correlated negatively with the insulin response to i.v. glucose (AIRg; -0.38, P = 0.02) as well as to oral glucose (r = -0.40; P = 0.01) challenge tests. CBG levels did not covariate with insulin sensitivity. Multiple linear regression analysis showed that only AIRg contributed to the variability of the CBG concentration (P = 0.03), explaining 41% of its variance. Morning cortisol levels did not differ between the groups and did not correlate to any of the glucose or insulin metabolism parameters. Because carbohydrate chains influence the biological activity and half-life of glycoproteins, we analyzed the migration profile of CBG by Western blot and the interaction of CBG with lectin, Con A. The results indicated that the CBG mol wt and interaction with Con A did not differ between lean and obese patients. These data favor the hypothesis that the inhibitory effect of insulin on CBG liver secretion might be relevant in vivo and therefore contribute to decrease CBG levels in obese patients with enhanced insulin secretion. In both men and women, SHBG levels correlated negatively with fasting glucose (r = -0.55; P < 0.0001) and hemoglobin A1c (r = -0.38; P = 0.02) and positively with insulin sensitivity (S(I); r = 0.65; P = 0.003 and r = 0.63; P = 0.007 in men and women, respectively), but not with insulin secretion. The disposition index (S(I) x AIRg) was significantly decreased in the obese, glucose-intolerant subjects, suggesting that AIRg was inadequate for their degree of insulin resistance. The disposition index correlated positively with plasma SHBG levels (r = 0.52; P = 0.001) and negatively with plasma CBG levels (r = -0.54; P = 0.001). Our data suggest that CBG is a marker of insulin secretion in a similar way as SHBG is a marker of insulin sensitivity. As high plasma CBG levels have been associated with increased incidence of type 2 diabetes, this important issue merits further investigations.     

Interaction of xenobiotics with estrogen receptors alpha and beta and a putative plasma sex hormone-binding globulin from channel catfish (Ictalurus punctatus)

Estrogens are important regulators of physiological functions. Although environmental contaminants (xenoestrogens) which interfere with estrogen signaling are of increasing concern, there is only limited information about their ability to interact with estrogen-binding proteins (SHBG) or receptors (ER). Recombinant ERalpha and beta were obtained after transient transfection of COS-7 cells with channel catfish ER cDNA. Plasma from adult female channel catfish was the source of SHBG. Tritiated estradiol (3H-E2) was used in standard radioligand-binding assays to characterize the binding properties of channel catfish SHBG (ccfSHBG) and to estimate the inhibition constants for various estrogenic compounds. Binding of 3H-E2 to ccfSHBG was saturable and of high affinity with a Kd (+/-SE) of 1.9+/-0.14 nM and a Bmax of 14.3+/-2.4 pmol/mg protein ( n = 3 assays). Additionally, ccfSHBG displayed binding specificity for androgens and estrogens. Endosulfan, 4-nonylphenol, and 4-octylphenol displaced 3H-E2 binding to ccfSHBG albeit only at very high concentrations, whereas dieldrin and atrazine showed little displacement activity even at the highest concentrations used. The synthetic estrogen ethynylestradiol had higher affinity than E2 for ccfSHBG. This finding differs from results with human and rainbow trout SHBG. The alkylphenolic compounds (4-octylphenol and 4-nonylphenol) displayed some ability to displace 3H-E2 binding from ERalpha and beta at high concentrations, but dieldrin and atrazine had little binding activity for both ER subtypes and endosulfan for ERbeta. The xenobiotics tested generally showed equivalent or greater affinity for ERalpha than ERbeta, whereas natural estrogens had much greater affinity for ERbeta than ERalpha. These observations suggest that results of studies using fish tissue ER extracts must be interpreted with caution, since both ER subtypes may be present, and that the binding of xenoestrogens to SHBG must be taken into account for proper assessment of endocrine disruption caused by environmental contaminants.     

Elevation of serum thyroxine-binding globulin (but not of cortisol-binding globulin and sex hormone-binding globulin) associated with the progression of human immunodeficiency virus infection

PURPOSE: In order to assess the relation of thyroid function tests to human immunodeficiency virus (HIV) infection, we determined the levels of serum thyroid hormones, serum binding proteins [thyroxine-binding globulin (TBG), cortisol-binding globulin (CBG), and sex hormone-binding globulin (SHBG)], and serum tumor necrosis factor (TNF) in HIV-seropositive subjects at different clinical stages. PATIENTS AND METHODS: Thirty-seven HIV-seropositive patients were studied: 7 at stage II, 13 at stage III, and 17 at stage IV (eight ambulatory and nine hospitalized) according to the Centers for Disease Control's criteria. RESULTS: As compared with stage II and stage III patients, stage IV patients had significantly higher mean TBG and total thyroxine (TT4) values, similar and normal total triiodothyronine (TT3) levels, and similar and abnormally low reverse triiodothyronine (rT3) concentrations. However, stage IV hospitalized patients had significantly lower TT3 values than stage IV ambulatory patients. In contrast to TBG, mean levels of CBG and SHBG were comparable in the three groups and within normal limits. For the whole population of HIV patients, there was a highly significant correlation between the CD4 lymphocyte count and TBG (r = -0.529, p less than 0.001) but not with CBG and SHBG levels. Finally, TNF values higher than 10 pg/mL were detected in six of the 17 stage IV patients and in only one of the 13 stage III patients (p = 0.059); elevated TNF levels correlated with a lower CD4 count (p less than 0.01) but not with serum TBG levels. CONCLUSION: The progression of HIV infection is associated with an elevation of serum TNF and TBG, but not of CBG or SHBG. HIV-infected patients have an unexpectedly normal TT3-low rT3 state.     

Molecular basis of estrogen-induced cyclooxygenase type 1 upregulation in endothelial cells

Estrogen upregulates cyclooxygenase-1 (COX-1) expression in endothelial cells. To determine the basis of this process, studies were performed in ovine endothelial cells transfected with the human COX-1 promoter fused to luciferase. Estradiol (E2) caused activation of the COX-1 promoter with maximal stimulation at 10(-8) mol/L E2, and the response was mediated by either ERalpha or ERbeta. Mutagenesis revealed a primary role for a putative Sp1 binding motif at -89 (relative to the ATG codon) and lesser involvement of a consensus Sp1 site at -111. Electrophoretic mobility shift assays yielded a single complex with the site at -89, and supershift analyses implicated AP-2alpha and ERalpha, and not Sp1, in protein-DNA complex formation. In endothelial cells with minimal endogenous ER, the transfection of ERalpha mutants lacking the DNA binding domain or primary nuclear localization signals caused 4-fold greater stimulation of promoter activity with E2 than wild-type ERalpha. In contrast, mutant ERalpha lacking the A-B domains was inactive. Thus, estrogen-mediated upregulation of COX-1 in endothelium is uniquely independent of direct ERalpha-DNA binding and instead entails protein-DNA interaction involving AP-2alpha and ERalpha at a proximal regulatory element. In addition, the process may be initiated by cytoplasmic ERalpha, and critical receptor elements reside within the amino terminus.     

Associations of sex-hormone-binding globulin (SHBG) with non-SHBG-bound levels of testosterone and estradiol in independently living men

Results of in vitro experiments indicate that with increasing concentrations of SHBG, testosterone (T) is preferentially bound to SHBG in comparison with estradiol (E2). In these studies, the ratio of non-SHBG-bound E2 (non-SHBG-E2) to non-SHBG-T increased with increasing levels of SHBG. SHBG has consequently been regarded as an estrogen amplifier. In this cross-sectional study in 399 men aged between 40 and 80 yr we tested whether higher levels of SHBG are associated with a higher estrogen/androgen ratio in vivo. The mean T level of these men was in the eugonadal range [536 +/- 152 ng/dl (18.6 +/- 5.26 nmol/liter), mean +/- sd]. With increasing SHBG levels the non-SHBG-bound fraction of T decreased from 80 to 36% and that of E2 from 89 to 53%. Higher levels of SHBG were associated with higher levels of both total T [regression coefficient (beta) after adjustment for age and body mass index, 286 +/- 15.8; P < 0.001] and total E2 (beta = 4.47 +/- 0.90; P < 0.001). However, SHBG levels were negatively related with levels of non-SHBG-E2 (beta = -1.78 +/- 0.69; P < 0.001), whereas there was a positive association between levels of SHBG and non-SHBG-T (beta = 32.0 +/- 9.78; P = 0.001). Furthermore, we observed a negative relationship between SHBG levels and the E2/T ratio of either total (beta = -0.016 +/- 0.002; P < 0.001) or non-SHBG-bound (beta = -0.011 +/- 0.002; P < 0.001) hormone. Therefore, we conclude that in eugonadal men, higher SHBG levels are associated with lower levels of non-SHBG-E2 but slightly higher levels of non-SHBG-T. This means that SHBG cannot be regarded as an estrogen amplifier in eugonadal men.     

Identification and measurement of sex hormone binding globulin (SHBG) and corticosteroid binding globulin (CBG) in human saliva

Sex hormone binding globulin (SHBG) and corticosteroid binding globulin (CBG) were detected by specific immunoassays in mixed-saliva taken from normal men and women. The immunochemical identity of both proteins was demonstrated by parallelism between dose response curves generated by serial dilutions of saliva and standards in the immunoassays. In addition, the specific removal of both proteins by incubation with steroid affinity-chromatography gels demonstrated the integrity of their steroid binding activity. The mean +/- SD concentrations of SHBG (pmol/l) and CBG (microgram/l) in mixed-saliva taken from normal volunteers were as follows: men (n = 6) 19 +/- 10 and 38 +/- 18; women (n = 6) 63 +/- 60 and 72 +/- 71 and women during late pregnancy (n = 6) 282 +/- 168 and 92 +/- 80, respectively. The data indicate that the concentrations of SHBG and CBG in saliva represent approximately 0.1% of plasma concentrations. It is suggested that these proteins pass from the blood to saliva in a non-specific manner, and may influence the steroid content of saliva under certain physiological circumstances.     

Increase in serum concentrations of thyroxine-binding globulin and of cortisol-binding globulin after the induction of normal thyroid function in previously hyperthyroid patients.

Serum concentrations of thyroxine-binding globulin (TBG) were determined in 36 female patients with hyperthyroidism due to either Graves' disease (n = 33), or autonomous thyroid adenomas (n = 3). After the induction of euthyroidism by antithyroid drugs, serum concentrations of TBG rose from 13.7 +/- 2.4 ng/mL to 17.1 +/- 2.8 ng/mL (p < 0.001) whereas those of sex hormone-binding globulin (SHBG) fell from 142.2 +/- 66.4 nmol/L to 53.6 +/- 21.8 nmol/L (p < 0.001). Serum concentrations of cortisol-binding globulin (CBG) rose to 42.9 +/- 10.3 microg/mL (basal: 36.8 +/- 9.4 microg/mL; p < 0.001) but serum concentrations of total and of free cortisol remained unchanged. Thus, thyroid hormones exert different effects on the production of various carrier proteins in vivo. Whereas they stimulate the production of SHBG, they suppress the level of CBG and of their own carrier protein, TBG.     

Sex hormone-binding globulin secretion by human hepatocarcinoma cells is increased by both estrogens and androgens

The secretion of sex hormone-binding globulin (SHBG) by the human hepatocarcinoma cell line Hep G2 was increased significantly not only by estradiol (E2) but also by testosterone (T), dihydrotestosterone, and the synthetic androgen danazol in the presence, but not the absence, of fetal calf serum. The secretion of SHBG also was stimulated by the antiestrogen tamoxifen, although this required the use of longer incubation periods and higher concentrations than were required for the steroids. The antiandrogen cyproterone acetate and cortisol (5 microM) decreased SHBG secretion. Pregnanediol (5 microM) had no discernible effect. These changes were considered specific as none of the compounds altered either the secretion of total protein by the cells or their total protein content. Cells incubated with a mixture of E2 (0.5 microM) and T (0.5 microM) secreted significantly more SHBG than did cells incubated with E2 (1.0 microM), indicating these steroids exert their effects through different mechanisms. The increases with E2 and T were reduced significantly by tamoxifen and cyproterone acetate, respectively, suggesting receptor mediation of the steroid effects. The E2-related increase was abolished by cycloheximide, indicating that the changes were due to alterations in the synthesis of SHBG rather than to alterations in the release of previously synthesized protein. These findings suggest the T-related decrease in plasma SHBG levels may be due to causes other than a decrease in the hepatic synthesis of the protein. Additionally, they indicate that Hep G2 cells may prove suitable for examining the regulation of the SHBG gene by a variety of compounds.     

Plasma sex hormone-binding globulin rather than corticosteroid-binding globulin is a marker of insulin resistance in obese adult males

Aim:  Plasma levels of corticosteroid-binding globulin (CBG) and sex hormone-binding globulin (SHBG) may be regulated by insulin. The aim of this study was to test the hypothesis that these steroid-binding proteins are markers of insulin resistance and obesity in adult patients with the metabolic syndrome.
Methods:  Fasting blood samples were obtained from 108 male and 88 female overweight adult patients who had varying degrees of dyslipidaemia, adiposity and insulin resistance. We measured plasma levels of SHBG and CBG and investigated their correlation with insulin resistance [homeostasis model assessment (HOMA) % sensitivity] and anthropometric markers of adiposity.
Results:  In male patients, plasma SHBG correlated positively with HOMA (% sensitivity) and negatively with anthropometric measurements, including body mass index, waist circumference (cm) and percentage body fat. There was no correlation with CBG and any other parameter in the male patients. The female patients were treated as two groups, those not using oral contraceptives or hormone replacement therapy (n = 67) and those taking steroid medications (n = 21). Female patients using steroid medications had significantly higher SHBG levels but neither group showed any correlation between SHBG, insulin resistance and adiposity. Correlation studies of CBG with other parameters in the female subgroups did not reach statistical significance.
Conclusions:  We conclude that plasma SHBG is another surrogate marker for insulin resistance in obese males but not in obese females. It also appears that plasma CBG is not a useful marker of insulin resistance in patients with the metabolic syndrome.     

Serum corticosteroid-binding globulin concentration and insulin resistance syndrome: a population study

It has been suggested that a low grade inflammatory state could predispose for developing insulin resistance and contribute to the development of obesity and type 2 diabetes. Corticosteroid-binding globulin (CBG), the main plasma protein transport for cortisol, has been shown to be negatively regulated by insulin and IL-6, at least in vitro, suggesting that insulin resistance and inflammation may both contribute to decreasing CBG levels. In the present study we measured CBG concentrations in a human healthy population and investigated the relationships of CBG with anthropometric and biochemical markers for inflammation and/or insulin resistance. The data showed that the mean serum CBG level was significantly lower in males (n = 151) than in females (n = 113; 32.5 +/- 9.1 vs. 39.2 +/- 13.9 mg/liter; P < 0.0001). In both sexes serum CBG levels were correlated negatively with age (r = -0.12; P = 0.04), body mass index (r = -0.31; P < 0.0001), waist to hip ratio (WHR; r = -0.39; P < 0.0001), systolic (r = -0.15; P < 0.01) and diastolic (r = -0.15; P = 0.01) blood pressures, and HOMA, an index of insulin resistance (r = -0.12; P = 0.04). In addition, the CBG concentration was negatively associated with serum IL-6 concentrations (r = -0.23; P = 0.017) and with the soluble fraction of TNFalpha receptors, soluble TNF receptor 1 (sTNFR1; r = -0.35; P < 0.0001), and sTNFR2 (r = -0.56; P < 0.0001) in women. A stepwise regression analysis using CBG as an independent variable showed that sex (P < 0.00001), body mass index (P = 0.0002), and HOMA (P = 0.0005), but not systolic blood pressure, diastolic blood pressure, IL-6, sTNFR1, or sTNFR2, constituted significant independent factors that explained 21% of the CBG variance (14%, 2%, and 5%, respectively). In a subsample of 120 men and 68 women, fasting serum free cortisol (calculated as the ratio fasting cortisol/CBG) was significantly associated with WHR (r = 0.24; P = 0.001), systolic (r = 0.18; P = 0.01) and diastolic (r = 0.19; P = 0.007) blood pressures, and HOMA value (r = 0.20; P = 0.005), but not with BMI or age. BMI (P < 0.0001), free cortisol (P = 0.003), and CBG (P = 0.009), but not WHR and age, contributed to 20%, 6%, and 8%, respectively, of HOMA variance in women in a multiple regression analysis. In this model only BMI (P < 0.0001) independently contributed to HOMA variance in men. These findings support the hypothesis that the CBG level is an interesting indicator for both insulin resistance and low grade inflammation. Whether the decrease in CBG levels is genetic by nature or directly associated to increased insulin and/or IL-6 merits further investigation. Nevertheless, because CBG has been shown to be expressed by the adipose tissue, decreased CBG could create locally increased cortisol disposal, with no change in circulating cortisol, and facilitate fat accumulation, insulin resistance, and type 2 diabetes.     

Free estradiol, free testosterone, and sex hormone-binding globulin in perimenopausal women

To determine whether menstrual status had an effect on plasma sex hormone-binding globulin (SHBG) capacity and nonprotein-bound estradiol (% free E2) and testosterone (% free T), we measured these as well as plasma FSH, total E2, and T and the MCRs of E2 and T in a group of 78 perimenopausal women. The women were allocated to 4 groups: women with cycles whose plasma FSH level was less than 40 mIU/mL (A; n = 16), women with cycles whose plasma FSH level was greater than 40 mIU/mL (B; n = 19), women who were amenorrheic for less than 1 yr (C; n = 13), and women who were amenorrheic for more than 1 yr (D; n = 30). The mean plasma SHBG values were 51.4 +/- 5.7 (+/- SE), 48.3 +/- 4.3, 45.9 +/- 5.4, and 51.1 +/- 3.7 nM in groups 1-4 respectively, and were not significantly different from one another. The mean % free E2 and % free T values also were not different between the groups. However, the mean total E2 and free E2 (% free E2 X E2/100) concentrations were significantly (P less than 0.05) higher in both groups A and B than in groups C and D. The E2 concentration was also higher in group A than in group B. There were strong correlations between the E2 and free E2 concentrations between the T and free T (% free T X T/100); (P less than 0.0001) concentrations, between SHBG capacity and weight, and between the MCRs of both E2 and T and % free E2 and % free T. In normal women, the menopause is not associated with changes in SHBG or % free steroids. Hence, the measurement of E2 could be used to predict the mass of free E2 in these women.     

Total estradiol, free estradiol, sex hormone-binding globulin, and the fraction of estradiol bound to sex hormone-binding globulin in human follicular fluid

Sex hormone-binding globulin (SHBG), percent free estradiol (E2), the fraction of E2 bound to SHBG, and total E2 were measured in the serum and follicular fluid of 12 women (25 follicles) who had received gonadotropin stimulation in an in vitro fertilization program. The women were classified as high or low responders based on peak serum E2 levels (high responders: peak E2, greater than 1500 pg/ml; low responders: peak E2, less than 1000 pg/ml). During treatment, serum levels of SHBG increased in high responders from 55 +/- 8.8 (+/- SEM) to 96 +/- 16 nM (P less than 0.01), but did not change in low responders. SHBG was more concentrated in follicular fluids from high responders (142 +/- 12.5 nM) than in those from low responders (44.4 +/- 5.8 nM). A positive correlation was found between serum and follicular fluid levels of SHBG (r = 0.873; P less than 0.01). In follicular fluid, total E2 levels, which varied from 100-2650 ng/ml, correlated (r = 0.790; P less than 0.01) closely with SHBG levels. The percent free E2 averaged 5.9% (range, 4-10.6%) in follicular fluid compared to 1.8% (range, 1.5-2.1%) in serum. An inverse correlation (r = -0.661; P less than 0.01) was found between total E2 concentrations and percent free E2 in follicular fluid. The relationship between serum and follicular fluid levels of SHBG suggests that SHBG in follicles arises from the circulation. Although SHBG is present in follicular fluid in amounts similar to those in serum, the large quantities of E2 in preovulatory follicules exceed the binding capacity for SHBG, and the majority of E2 appears to be bound to albumin. Hence, it seems unlikely that SHBG in follicular fluid regulates estrogen action in ovarian target cells.     

Inhibition of sex hormone-binding globulin production in the human hepatoma (Hep G2) cell line by insulin and prolactin

Sex hormone-binding globulin (SHBG) production in humans has been thought to be stimulated by estrogens and thyroid hormone and inhibited by androgens. However, recent data indicate that SHBG production in vitro is stimulated by both androgens and estrogens. This study was designed to determine what other hormonal factors regulate SHBG production. Since hyperinsulinemia and hyperprolactinemia both occur in disease states in which low serum SHBG levels are found, the effects of insulin and PRL were compared to and/or studied in combination with estradiol (E2), T4, and testosterone (T) in a human hepatoma cell line (Hep G2). Hep G2 cells were grown to near confluence in medium including 10% fetal calf serum, and then 72-h experimental incubations were carried out which used only fetal calf serum-free medium. Compared to control incubations, both insulin (10(-8) mol/L) and PRL (10(-8) mol/L) decreased SHBG production from 65.0 +/- 0.6 (+/- SE) to 46.8 +/- 1.1 and 46.8 +/- 1.2 nmol/10(6) cells, respectively (P less than 0.01). Insulin also inhibited both E2 and T4-stimulated SHBG production. T stimulated SHBG production to the same degree as E2. Finally, both E2 and insulin significantly increased cell number, an important consideration when expressing the effect of a hormone on SHBG production in cultured cells. We conclude that insulin and PRL inhibit SHBG production and confirm that T4, T, and E2 stimulate SHBG production in vitro. These findings suggest that insulin and PRL may be important factors in the regulation of SHBG production in vivo.     

Differential interaction of the methoxychlor metabolite 2,2-bis-(p-hydroxyphenyl)-1,1,1-trichloroethane with estrogen receptors alpha and beta

Concern that some chemicals in our environment may affect human health by disrupting normal endocrine function has prompted research on interactions of environmental contaminants with steroid hormone receptors. We compared the activity of 2,2-bis-(p-hydroxyphenyl)-1,1,1-trichloroethane (HPTE), an estrogenic metabolite of the organochlorine pesticide methoxychlor, at estrogen receptor alpha (ERalpha) and estrogen receptor beta (ERbeta). Human hepatoma cells (HepG2) were transiently transfected with either human or rat ERalpha or ERbeta plus an estrogen-responsive, complement 3-luciferase construct containing a complement 3 gene promoter sequence linked to a luciferase reporter gene. After transfection, cells were treated with various concentrations of HPTE in the presence (for detecting antagonism) or absence (for detecting agonism) of 17beta-estradiol. HPTE was a potent ERalpha agonist in HepG2 cells, with EC50 values of approximately 5 x 10(-8) and 10(-8) M for human and rat ERalpha, respectively. In contrast, HPTE had minimal agonist activity with either human or rat ERbeta and almost completely abolished 17beta-estradiol-induced ERbeta-mediated activity. Moreover, HPTE behaved as an ERalpha agonist and an ERbeta antagonist with other estrogen-responsive promoters (ERE-MMTV and vtERE) in HepG2 and HeLa cells. This study demonstrates the complexity involved in determining the mechanism of action of endocrine-active chemicals that may act as agonists or antagonists through one or more hormone receptors.     

A comparison of the short-term effects of oral conjugated equine estrogens versus transdermal estradiol on C-reactive protein, other serum markers of inflammation, and other hepatic proteins in naturally menopausal women

OBJECTIVE: Our objective was to compare the effects of oral vs. transdermal estrogen therapy on C-reactive protein (CRP), IL-6, E- and P-selectin, intercellular adhesion molecule (ICAM)-1 and vascular cell adhesion molecule-1, serum amyloid A, transferrin, prealbumin, IGF-I, SHBG, thyroxine-binding globulin (TBG), and cortisol-binding globulin (CBG) in naturally menopausal women. DESIGN: This was a randomized, open-label crossover clinical trial. A 6-wk withdrawal from prior hormone therapy (baseline) was followed in randomized order by 12-wk oral conjugated equine estrogens (CEEs) (0.625 mg/d) and 12-wk transdermal estradiol (E2) (0.05 mg/d), with oral micronized progesterone (100 mg/d) given continuously during both regimens. RESULTS: A total of 27 women enrolled, and 25 completed both treatment periods. Nine parameters changed significantly during oral CEE (median percent change from baseline; P value): CRP (192%; P <0.001); E-selectin (-16.3%; P = 0.003); P-selectin (-15.3%; P = 0.012); ICAM-1 (-5%; P = 0.015); transferrin (5.3%; P = 0.024); IGF-I (-30.5%; P < 0.001); SHBG (113%; P < 0.001); TBG (38%; P < 0.001); and CBG (20%; P < 0.001). With transdermal E2, only three parameters changed significantly and to a lesser degree: ICAM-1 (-2.1%; P = 0.04); IGF-I (-12.5%; P < 0.001); and SHBG (2.6%; P = 0.042). During oral CEE the intrasubject changes in CRP correlated strongly with the changes in serum amyloid A (r = 0.805; P < 0.001), and were only weakly associated with the changes in SHBG (r = 0.248; nonsignificant), TBG (0.430; P = 0.031), and CBG (r = 0.072; nonsignificant). The log-log relationship between CRP and IL-6 observed at baseline showed a parallel shift during oral CEE, suggesting an amplified hepatic response or a greater sensitivity to IL-6 stimulation. CONCLUSION: Compared with oral CEE, transdermal E2 exerts minimal effects on CRP and the other inflammation and hepatic parameters.     

A prospective longitudinal study of serum testosterone, dehydroepiandrosterone sulfate, and sex hormone-binding globulin levels through the menopause transition

The aims of this study were to describe, in relation to date of final menses, the average androgen levels of women in the years before and after this date, and to determine the extent to which these average levels were dependent on age and body mass index (BMI) and the degree of tracking in residual androgen levels, or the extent to which individuals above (below) the mean for their age or time relative to final menstrual period (FMP) and BMI remain above (below) the mean as time progresses. Serial levels of serum sex hormone-binding globulin (SHBG), testosterone (T), and dehydroepiandrosterone sulfate (DHEAS) were measured annually in 172 women from the Melbourne Women's Midlife Health Project who experienced a natural menopause during 7 yr of follow-up. Fasting blood samples were drawn between days 4-8 if women were still menstruating or after 3 months of amenorrhea. The free androgen index (FAI) was calculated as the ratio ofT to SHBG x 100. Means of the log-transformed androgen levels were analyzed as a double logistic function of time relative to FMP as well as age and BMI, and correlations between repeated androgen levels were measured. Mean SHBG levels decreased by 43% from 4 yr before to 2 yr after the FMP. The time of most change was 2 yr before FMP [95% confidence interval (CI), 0.8-3.2]. SHBG levels were, on the average, 5% lower for each halving of estradiol (E2) levels and 4% lower for each kilogram per m2 of BMI (P < 0.0001). About one third of the decline in SHBG was explained by E2 and BMI. After adjusting for all variables, SHBG showed strong tracking. Mean T levels did not vary with time relative to FMP and were independent of age and BMI. Residual values of T showed weak tracking. The FAI increased by 80% from 4 yr before FMP to 2 yr after FMP, and changed maximally 2.2 yr before FMP (95% CI, 1.2-3.2). The FAI was not related to age or E2, but was, on the average, 4% higher for each kilogram per m2 of BMI (P < 0.0001). Residual values of FAI showed moderate tracking. Mean DHEAS levels were not related to the FMP, but were 1.5% lower for each year of age (P < 0.01) and 3.8% lower for each kilogram per m2 of BMI (P < 0.0001). Residual values of DHEAS showed strong tracking. It is concluded that SHBG and FAI levels change at the time of the menopause, at least partially due to the decline in E2. DHEAS decreases as a function of age, not time relative to FMP, and T remains unchanged during the menopausal years. SHBG and DHEAS show a high degree of stability within an individual over time.     

Regulation of sex hormone-binding globulin production by growth factors

Sex hormone-binding globulin (SHBG) is a glycoprotein whose production has been demonstrated to be regulated by both sex steroids, as well as by thyroid hormone and peptide hormones such as insulin. However, none of these regulatory factors would explain the marked decrease in serum SHBG seen throughout the prepubertal and pubertal time period in both boys and girls. Furthermore, current in vitro data show that both androgens and estrogens can stimulate SHBG production by the human hepatoblastoma cell line Hep G2; yet, in vivo androgens appear to suppress SHBG levels, while estrogens are associated with elevated levels. This study was undertaken to determine possible mechanisms to explain this phenomenon. Hep G2 cell cultures were incubated with insulin-like growth factor I (IGF-I), epidermal growth factor (EGF), transforming growth factor alpha (TGF-alpha), or dehydroepiandrosterone (DHEA). Significant decreases in the level of SHBG in the culture medium relative to control cultures occurred for each of the growth factors (P less than .01), whereas an increase in SHBG levels was observed in the medium of DHEA-treated cells. When cells were coincubated with IGF-I and thyroxine (T4), which alone stimulates SHBG production both in vivo and in vitro, the SHBG response to T4 was blunted. These results suggest that growth factors, as well as insulin, may be important determinants in SHBG production.