Estradiol entry into endometrial cells in suspension

[7alpha-18F]fluoro-17alpha-methyl-5alpha-dihydrotestosterone: a ligand for androgen receptor-mediated imaging of prostate cancer

We have synthesized a 18F-labeled androgen, [7alpha-18F]fluoro-17alpha-methyl-5alpha-dihydrotestosterone, in a no-carrier-added radiosynthesis by exchange of 18F- (tetrabutylammonium fluoride) with the 7beta-tosyloxy of 17alpha-methyl-5alpha-dihydrotestosterone. The nonradioactive steroid binds with high affinity and specificity to the androgen receptor and binds poorly, if at all, to other steroid receptors and plasma sex hormone binding globulin. The 7alpha-18F-androgen concentrates markedly in the prostate of rats by an androgen receptor-dependent mechanism. It is likely that [7alpha-18F]fluoro-17alpha-methyl-5alpha-dihydrotestosterone will be an excellent positron emission tomography imaging agent for prostate cancer.

Investigation of female survival benefit in metastatic melanoma

Epidemiological studies show female survival benefit in advanced metastatic melanoma. In investigating a possible mechanism for this female survival benefit, we have previously reported that the female steroid 17beta-oestradiol significantly reduces invasion of a human melanoma cell line (A375-SM cells) and ocular melanoma cells through fibronectin. Neither cell type was found to possess oestrogen receptor-alpha. The aim of the current study was to obtain further information on the extent to which progression of cutaneous melanoma might be sex steroid sensitive by (a) examining the relationship between circulating sex steroids, sex hormone binding globulin and disease progression; (b) examining the relationship between sex steroid structure and the ability of steroids to reduce invasion of a melanoma cell line in vitro; and (c) examining the effects of sex steroids on proliferation of these cells in vitro. We report a significant reduction in circulating oestrone with disease progression in male but not female patients. Examining steroids for their ability to inhibit invasion of A375-SM cells through fibronectin in vitro, oestrogenic compounds (17beta-oestradiol and oestrone) were found to inhibit invasion; in this respect, oestrone was approximately 50 times more potent than 17beta-oestradiol; steroids lacking the benzene ring structure did not inhibit invasion, indeed dehydroepiandrosterone (DHEA) which acts as a precursor to androgenic steroids significantly enhanced invasion. Proliferation of A375-SM cells was unaffected by 17beta-oestradiol, oestrone or dihydrotestosterone when cells were cultured on plastic; in contrast, all three steroids induced modest proliferation of cells when grown on fibronectin with dihydrotestosterone the most mitogenic of the three steroids. These data are consistent with sex steroids playing a role in melanoma progression.

Nonlinear binding of sex steroids to albumin and sex hormone binding globulin

We have studied the binding of sex steroids to albumin and sex hormone binding globulin (SHBG) using gel filtration chromatography for the separation of the bound from the free fraction of the steroid. It was found that estradiol binds to the globulin and albumin in a nonlinear manner: a lag period of binding was observed at low concentrations of the proteins, followed by an exponential increase of the bound hormone as the protein concentration increased. The same was observed with dihydrotestosterone (DHT) and albumin but not with globulin. In the presence of a constant concentration of albumin, the increase of SHBG concentrations resulted in a rapid transfer of estradiol from albumin to globulin while the transfer of DHT was moderate. When whole serum was used, the increase of its amount again resulted in the transfer of estradiol from albumin to globulin. Our study showed that a substantial increase of globulin-bound hormone can occur, following small variations of the protein. This offers obvious advantages to the organism, by saving energy, material and time and plays a basic role in estradiol transfer from albumin to the much more biologically active globulin.

In vitro influence of plasma steroid-binding proteins on androgen metabolism in human leukocytes

The purpose of this study was to investigate the influence of plasma steroid-binding proteins on androgen metabolism in intact leukocytes prepared from normal male and female blood samples. Leukocyte preparations were incubated for 24 h at 37 degrees C with either labeled or unlabeled testosterone (T), 5 alpha-dihydrotestosterone (5 alpha-DHT), and androstenedione (A). After extraction, the formed labeled metabolites were first identified by high performance liquid chromatography, then, using unlabeled substrates, metabolite concentrations were measured by specific radioimmunoassays. The conversion ratios of substrate to metabolite were calculated for each preparation using either labeled or unlabeled substrates. In the absence of steroid-binding proteins, the mean conversion ratios of T to A, A to T, T to 5 alpha-DHT, and 5 alpha-DHT to 3 alpha-androstanediol (3 alpha-D) were, in males and females, respectively, 5.6% and 6.1% (n = 11), 5.6% and 5.6% (n = 5), 2.8% and 2.2% (n = 11), 43.1% and 40.0% (n = 5), these sex differences being non-significant. The presence of increasing amounts of plasma, purified albumin or sex hormone binding-globulin (SHBG) in the incubation media reduced metabolite formation dose-dependently. However, a 1000-fold greater concentration of albumin than of SHBG was necessary for 50% inhibition of androgen metabolism by leukocytes, showing SHBG to have the main protective effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Glucocorticoid-recognizing and -effector sites in rat liver plasma membrane. Kinetics of corticosterone uptake by isolated membrane vesicles--II. Comparative influx and efflux

To elucidate the initial step in the interaction between glucocorticoids (GC) and the hepatocyte, we examined at 22 degrees C further kinetic properties of active corticosterone (B) transport mediated by a putative, plasma membrane-inserted carrier for GC (GCC) as previously reported [Alléra and Wildt, J. Steroid Biochem. Molec. Biol. 42 (1992) 737-756]. We used a purified, well-characterized, osmotically active vesicle fraction of plasma membrane (PM), free of ATP, isolated from rat liver and a method developed by us to describe transport processes mathematically: (1) uptake (U) of 7 nM B into the vesicles (influx, I) occurred very rapidly whereby T1/2 = 8.3 s, the time (S) required for half maximum transport; the influx velocity (dU/dS = V) decreased degressively with time following second-order kinetics characterized by an initial transport V (VT0) of 177.7 fmol/mg membrane protein/s. (2) VToI of B-influx rose with temperature biphasically (P less than 0.025): activation energy above and below 15 degrees C (at PM phase transition) amounted to 9.5 and 26.5 kJ/mol. Neither at 45 nor at 60 degrees C did transport take place, revealing the high thermolability of GCC. (3) Efflux (E) of 6.5 nM B, i.e. transport out of the vesicles preincubated with the steroid, showed that influx had resulted in a 19.6-fold intravesicular hormone accumulation, indicating active ("uphill") transport. (4) The efflux velocity (dE/dS = V) exhibited almost the same kinetic quality as that of influx: it decreased following mainly second-order kinetics whereby T1/2 = 8.0 s. However, its whole time-course was much slower and the VT0 of efflux (VToE) was 6.3 lower than VToI. (5) Using physics and thermodynamics, we deduced that the affinity (AF) between B and GCC is proportional to the square of VT0. (6) Thus, because AF approximately (1/6.3)2, AF of the B-GCC interaction after completion of influx was calculated to be 40 times lower (Kd = 708 nM; delta G degrees = -34.9 kJ/mol) than at outset of influx, whereby delta G degrees = -44.0 kJ/mol. Concluding from these and previous findings, we present a new hypothesis on B transport into the hepatocyte: There is no difference (P greater than 0.3) in free enthalpy between transcortin (CBG) and the intracellular GC receptor interacting with B (delta G degrees = -40.1 and -40.4 kJ/mol). The GCC, however, is characterized by its ability to switch from a high- to lower-affinity when interacting with B (and vice versa due to metabolic energy input).(ABSTRACT TRUNCATED AT 400 WORDS)

Glucocorticoid-recognizing and -effector sites in rat liver plasma membrane. Kinetics of corticosterone uptake by isolated membrane vesicles--I. Binding and transport

To gain insight into the mechanisms governing cellular uptake of glucocorticoids, we studied the binding and membrane transport of corticosterone (B) on a highly purified plasma membrane fraction from rat liver that was homogenized using a gentle, isotonic procedure. The fraction was mostly in the form of right-side out and osmotically active vesicles that were free of intracellular glucocorticoid receptors (GCR), transcortin (CBG) and ATP. Our uptake and binding studies carried out at 22 degrees C with [3H]B in physiological concentrations resulted in the following findings: (1) unlabeled B competed with [3H]B for uptake by the membrane vesicles; half-maximal competition of specific uptake was achieved with a 10- to 11-fold molar excess of unlabeled B. (2) [3H]B uptake was a saturable process of unusual kinetics (multiple sigmoidity); modified Scatchard plots revealed three significantly different apparent Kd-values of 1.3, 4.7 and 17.3 nM, corresponding to free B in the blood of non-stressed rats (4-16 nM). (3) Osmotic shrinkage of the vesicles led to a linear decrease in specific uptake, while non-specific uptake was independent of vesicle volume. Passive diffusion of [3H]B took place in leaky, but not in intact, vesicles. Reversible binding to, and mediated transport through, the membrane were interdependent parts of a strongly linked process. B was accumulated inside the vesicle up a concentration gradient by an active transport that followed first-order kinetics (Kt:3.9 nM); for its statistically reliable mathematical formulation and kinetic analysis, a replot was developed that revealed that relative accumulation increased with decreasing external hormone concentration. (4) Comparative binding studies disclosed that the apparent Kd-values (86.5 +/- 7.3 and 77.0 +/- 14.3 nM, respectively) of the [3H]B interactions with CBG and GCR did not differ (P greater than 0.3). These findings permit the conclusion that a plasma membrane-inserted carrier for B, effectively operating at physiological concentrations in the blood, is involved in a functional and regulatory manner in the biological action of glucocorticoids.

The plasma sex steroid binding protein (SBP or SHBG). A critical review of recent developments on the structure, molecular biology and function

Significant developments have taken place within the past five years on the characterization, molecular biology and function of the plasma sex steroid-binding protein, SBP (or sex hormone binding globulin, SHBG). During the span of that time, amino acid sequences of two SBPs have been established, amino acid residues in the steroid-binding site have been identified, the structure of the human SBP gene has been deduced and evidence for the possible existence of a SBP membrane receptor has been presented. This review covers the salient aspects of these and other developments including a critical analysis of the various proposed models and interpretations with regards to the structure, evolution, molecular biology and function of SBP.

Prostate plasma membrane receptor: a hypothesis

Based on 50 years of emerging knowledge about and changing views of prostate biochemistry and physiology and especially on the belief that there is an underlying mechanism of androgen control, the hypothesis is developed and tested that the rates of proliferation, biosynthesis, metabolism, and secretion are modulated through the hormone-sensitive Na, K-ATPase of the plasma membrane. These preliminary experiments, constituting a novel synthesis of technologies from endocrinology, intermediary metabolism, and membrane transport, attempt to explain the extraordinary production and secretion of citrate and how this may be coupled to sustaining prostate cell number and function. Attention is focused on learning where androgen is bound and how it interacts with the Na,K-ATPase. Both the dissimilar properties of epithelial and stromal cells in the separate regions of the acinus and the changing environment of growth factors in which these cells are bathed help account for their unlike reactivities during development and ongoing mature function. Little wonder that one hormone can have so many effects!

Prolactin effect on the permeability of human benign hyperplastic prostate to testosterone

While it has been known for over 30 years that prolactin (Prl) synergizes with androgen in the support and stimulation of prostatic growth and metabolism, the evidence that this is accomplished through increasing access of the steroid to the cellular machinery of the gland has arisen only since about 1970. There is widespread uncertainty as to how the Prl effect takes place: by 1) increasing the free steroid concentration in the blood; 2) facilitating the uptake of protein-bound androgen; 3) increasing, by metabolism or receptor-binding, the concentration gradient that can support passive diffusion of the steroid across the plasma membrane; or 4) modification of the fluidity of the membrane itself to increase the solubility of the steroid in the lipoprotein and, thus, the ease of penetration of the cell. The present study attempted to learn if Prl is an effective stimulus of androgen uptake when the first three options are not operative. Using an equilibrium exchange procedure to track the uptake of [17 alpha-3H]-testosterone ([17 alpha-3H]-T) into minced benign hyperplastic human prostate tissue and the irreversible metabolism of the entering steroid to [17 alpha-3H]-dihydrotestosterone [17 alpha-3H]-DHT, it was found that the rate of production of the 5 alpha-reduced metabolite, during a 1-hr incubation in vitro, was directly proportional to the concentration of ovine Prl over the dose range of 0-160 ng/ml. The clinical significance of Prl mediation of steroid uptake is discussed, and suggestions are made as to how the Prl might alter the permeability of the plasma membrane.