Direct isolation of labeled low density lipoproteins for the determination of cholesteryl ester transfer protein activity

The measurement of the activity of cholesteryl ester transfer protein (CETP), is of high clinical interest and this study reports the use of a direct LDL isolation (d-LDL) technique to determine in one step the amount of radiolabeled cholesteryls esters ([3H]-CE) transferred from exogenous HDL3 to LDL, avoiding the conveniences of the usually used ultracentrifugation or precipitation of apo-B containing lipoproteins in the CETP methodologies. The d-LDL technique providing a specific immunoprecipitation of VLDL, IDL and HDL allowed to directly determine the [3H]-CE transferred on LDL (d-[3H]-CE-LDL). Two methodologies were assayed for the CETP activity using either exogenous or endogenous lipoproteins, and the results with the d-LDL technique were compared with those obtained using the ultracentrifugation (u-[3H]-CE-LDL) considered as the reference method. The intra- and inter-assays were similar in both techniques for the two CETP activity assays. Strong positive correlations were established between values obtained with d-[3H]-CE-LDL and u-[3H]-CE-LDL isolation procedures for CETP activities with exogenous or endogenous lipoproteins (r = 0.972; p = 0.0001 and r = 0.965; p = 0.0001 respectively). In conclusion, the d-LDL technique represents an easy and accurate procedure to measure directly, in normotriglyceridemic plasmas, the amount of [3H]-CE transferred from HDL to LDL by the CETP.

Use of confocal microscopy to localize the SHBG interaction with human breast cancer cell lines--a comparison with serum albumin interaction

This work has allowed a comparison between the interaction of two principal plasma estradiol-binding proteins, serum albumin and Sex Hormone Binding Globulin (SHBG), with human breast cancer cells in culture (MCF-7 and MDA-MB 231), using a protocol which protects the integrity of cell structure. We showed that serum albumin was highly internalized by cells whereas SHBG interacted essentially at the plasma membrane level, and this whatever the contents of the receptor estrogen cells. If, by its high plasma concentration, serum albumin is internalized in a non-specific way and can thus fit into intracellular traffic, SHBG, by its membrane binding, seems to have a specific action toward target cells.

Receptor-mediated and absorptive endocytosis by male germ cells of different mammalian species

The routes for adsorptive and receptor-mediated endocytosis were studied in vivo after microinjection of tracers into the lumen of the seminiferous tubules, and in vitro in isolated germ cells of different mammals. Cationic ferritin was located on the plasma membrane, in vesicles, in tubules, in multivesicular bodies and in lysosome-like granules of mouse spermatocytes. In these cells the number of multivesicular bodies varied during spermatogenesis. Spermatids and to a lesser extent residual bodies also performed adsorptive endocytosis. In the rat and monkey (Macaca fascicularis) diferric transferrin was specifically taken up by germ cells via receptor-mediated endocytosis. The labelling was observed subsequently in membrane pits, vesicles, endosome-like bodies and pale multivesicular bodies. A progressive decrease in the frequency of the labelling of the germ cells by transferrin-gold particles was observed from spermatogonia to spermatocytes and to early spermatids, which could indicate that iron is particularly required by germ cells during the mitotic and meiotic processes. Adsorptive and receptor-mediated endocytosis therefore occurs in all classes of germ cells. These endocytic processes are most probably required for germ cell division, differentiation and metabolism.

The plasma membrane of epididymal epithelial cells has a specific receptor which binds to androgen-binding protein and sex steroid-binding protein

The binding of [3H] delta 6-testosterone photoaffinity-labelled rat androgen-binding protein (rABP) has been studied in an enriched fraction of plasma membranes of epithelial epididymal cells in immature (15 days) and adult rats (40 days). The binding was maximal in less than 30 min and more rapid at 4 degrees C than at 34 degrees C. It was calcium and pH dependent. Scatchard plots of the binding data gave curvilinear plots with two types of binding sites corresponding to a K(ass1) of 18.2 nM-1 and K(ass2) of 1.6 nM-1 (2.2 x 10(11) sites/mg protein and 5.4 x 10(11) sites/mg protein, respectively). In adult rats, only one type of binding site was found, with a K(ass) of 3.7 nM-1 (4.5 x 10(11) sites/mg protein). The number of receptors was 5-fold lower in the cauda than in the caput of the epididymis. The pretreatment of the isolated intact cells with streptozotocin induced a 45% reduction of the binding. Only unlabelled rABP and hSBP (human sex steroid-binding protein) but not other proteins (lactotransferrin, serotransferrin, asialofetuine, fetuine and bovine serum albumin) competed with the labelled ligand to bind plasma membranes. The membrane fraction was solubilized by triton X-100. Its incubation with labelled rABP and hSBP provoked the elution of the tracer as an aggregate into the void volume fraction of superose 6B mini-gel filtration columns. Structural homology between hSBP and rABP could be responsible for the common behaviour of the steroid-carrier molecules for the ABP receptor of rat epididymal epithelial cells.

Endocytosis of human sex steroid-binding protein in monkey germ cells

We investigate in this study the hypothesis of human sex steroid-binding protein hSBP internalization into germ cells in a primate model. Human SBP was purified from late-pregnancy serum and labeled either with colloidal gold particles (18 nm) or with [3H]delta 6-testosterone by photoaffinity treatment. The germ cells were isolated from sexually mature monkey testis or caput epididymis (Macaca fascicularis) by mechanical means and cell suspensions (4 x 10(6) per 100 microliters culture medium) were incubated in presence of hSBP-gold complex (60 ng/100 microliters) or hSBP-[3H]delta 6-testosterone complex (66 ng/100 microliters, 20,000 cpm) for 2, 5, 15, 45, and 60 min. The samples were processed for electron microscopy followed by autoradiographic treatment for the radiolabeled samples. Localization of the label occurred over the whole germ cell lineage whichever tracer was used. Spermatogonia, spermatocytes, spermatids, testicular and epididymal spermatozoa exhibited specific binding sites over the plasma membrane associated with clathrin-like coated pits and vesicles. At 34 degrees C, intracellular localization of the labeled ligand was found within coated vesicles, in early and late endosomes. In addition, in early spermatogenic cells, labeled ligand was detected in the nuclei and/or associated with the nuclear envelope whereas in late spermatids and residual bodies, the labeling was accumulated in multivesicular, prelysosomal structures. Quantitative analysis of the "labeled cells/total cells" ratio exhibited a negative correlation to the maturation steps, epididymal spermatozoa being the least labeled. The cellular distribution is similar with one or the other protein in the same spermatogenic cells. Unlabeled hSBP treatment prior to labeled hSBP reduced significantly the internalization. Lowering the temperature to 4 degrees C prevented endocytosis and enhanced membrane binding. EDTA pretreatment strongly decreased hSBP internalization and modified the early endocytic steps, namely, the pinching off of the coated vesicles. It is concluded that monkey germ cells are able to internalize the human sex steroid-binding protein through specific endocytic organelles. This endocytosis leads to the labeling of the nuclei in the early spermatogenic cells and of the multivesicular bodies in the late germ cells. This strongly suggests that steroid-binding proteins may be required for spermatogenesis in acting at the germ cell lineage level either by themselves or by serving as steroid transmembrane carriers.

Skinfold and body circumferences as measures of body fat patterning in a French female active population: relationships with the metabolic risk profile

Body mass index (BMI), various anthropometric indices of abdominal fat distribution and some metabolic variables (blood lipids, fasting glucose, blood pressure) were measured in 408 French-born women from an occupational population who volunteered for the study. The aim of the study was to determine the best index for describing the relationships between the body fat pattern and the metabolic risk profile. The four age-adjusted circumference ratios (waist/hip, waist/thigh, xiphoid/hip, xiphoid/thigh) showed similar associations with the metabolic variables whereas the three age-adjusted skinfold ratios (epigastric/thigh, mesogastric/thigh, hypogastric/thigh) tended to be more weakly associated with the metabolic variables, particularly with apolipoprotein (Apo) B and fasting glucose. Multiple regression analyses showed that age-adjusted BMI was significantly related to high density lipoprotein (HDL) cholesterol, low density lipoprotein (LDL) cholesterol, Apo A and Apo B, and blood pressure, independently of abdominal fat distribution. After controlling for the effects of BMI, the waist/thigh ratio remained significantly associated to triglyceride, Apo B, fasting glucose, and systolic blood pressure, whereas the waist/hip ratio and the mesogastric/thigh skinfold ratio were significantly related only to triglyceride and systolic blood pressure independently of BMI. With the exception of triglyceride and fasting glucose, the degree of association between the metabolic variables and the abdominal fat distribution tended to be weaker than that observed with the BMI. These results emphasize the importance of the global corpulence in the levels of metabolic variables. However, all indices of abdominal fat distribution were, to varying degrees, independently associated with an unfavorable metabolic profile. Among them, the waist/thigh circumference ratio seems to be a useful indicator of the body fat pattern in women.

Internalization of human sex steroid-binding protein in the monkey epididymis

Human sex steroid-binding protein (hSBP) has been purified from late-pregnancy serum and labelled either by iodination (125I) or by photoaffinity with [3H]delta 6-testosterone. Using a micromanipulator, each labelled protein was separately injected into the lumen of epididymal tubules isolated from the head epididymis of the cynomologus monkey (Macaca fascicularis). Tubules were sampled from 3 to 90 min after the injection and processed for electron microscope autoradiography. Localization of the label occurred over the epididymal epithelium whichever tracer was used. The labelling was not randomly distributed over the different cell types constituting the epithelium, since only the 'principal cells' exhibited a silver grain count significantly greater than the background count. In these cells, labelled protein was found over endocytic organelles (coated structures, endosomes, multivesicular bodies and the trans Golgi network) and nuclei (including the nuclear envelope). Quantitative analysis demonstrated the same pattern of cellular and subcellular distribution for each tracer. Pretreatment with excess unlabelled protein significantly reduced the uptake of radioactivity by the principal cells, demonstrating the specificity of this phenomenon. This is the first study to show direct histological evidence for the internalization of hSBP in the primate epididymis, consistent with earlier immunohistochemical or biochemical localization of this protein. It is concluded that head epididymal cells are able to take up labelled hSBP across their apical membrane. The mechanism of internalization seems to involve endocytosis by the principal cells and leads to labelling of the nuclear compartment. This is strikingly similar to the pattern of uptake of rat androgen-binding protein (rABP) by rat epididymal cells previously demonstrated by our group. To what extent the chemical and structural homology between hSBP and rABP can be held responsible for the common cytophysiological behaviour of these sex steroid-binding proteins remains to be determined.

Hormonal influences on the relationships between body fatness, body fat distribution, lipids, lipoproteins, glucose and blood pressure in French working women

The independent associations between overall obesity, body fat distribution, lipids, lipoproteins, glucose, blood pressure and some hormonal factors (sex hormone-binding globulin (SHBG), corticosteroid binding globulin (CBG) and fasting insulin) were cross-sectionally examined in 205 French working women. After adjustment for age, overall adiposity assessed by body mass index (BMI) was significantly associated with most metabolic parameters, whereas regional adiposity assessed by the waist-hip ratio (WHR) was significantly associated only with triglyceride, systolic and diastolic blood pressure. Blood pressure, glucose but not triglyceride, were also negatively and significantly correlated with SHBG and positively with fasting insulin. Negative independent associations were found between SHBG and both BMI and WHR, whereas CBG was positively associated only with WHR. Fasting insulin was no longer related to WHR after adjustment for BMI. After controlling for the effect of SHBG or insulin, the associations between triglyceride, blood pressure and both BMI and WHR were not substantially modified. After adjustment for BMI and WHR, fasting insulin was independently associated with both HDL cholesterol and diastolic blood pressure. In conclusion, in these French women, hormonal factors under study appeared to have little influence on the relationships between body fatness, body fat distribution, metabolic variables and blood pressure.

Regulation of plasma corticosteroid-binding globulin in adult cynomolgus monkey (Macaca fascicularis) during different reproductive states

The plasma concentration of the corticosteroid-binding globulin (mCBG) has been measured in Macaca fascicularis, during different stages of reproduction and under hormonal treatments. The mCBG level was determined by a specific electroimmunoassay. There was no difference between females in the follicular phase and intact males; mCBG concentrations were respectively (mean +/- SEM) 469 +/- 53 and 443 +/- 25.6 nmol/l. The mCBG levels levels were similar during both the luteal (469 +/- 33.5 nmol/l) and the follicular phase (469 +/- 53 nmol/l). Compared to intact males, the mCBG levels were higher (P less than 0.05) in castrated males (527 +/- 6.6 nmol/l). During gestation, no systematic variations were found and the mCBG levels were not statistically different from the values found during the follicular phase. When estradiol benzoate was administered to castrated animals, the mCBG concentrations increased rapidly. In contrast, the values were reduced slightly by testosterone treatment. The sex-steroid action on the mCBG levels was discussed and compared with the mSBP levels. We question also, the mechanisms involved in the regulation of the mCBG levels during pregnancy.

Immunochemical characterization of corticosteroid-binding globulin in human bronchoalveolar fluid

The corticosteroid-binding globulin (CBG) is a plasma protein which is present both in liver, where it is mainly synthesized, and in cells of different target tissues for glucocorticoids. Using monospecific antibodies raised against human CGB, we could demonstrate the antigenic identity of the protein in human bronchoalveolar fluid. We found that the bronchoalveolar fluid/serum concentration ratio of CBG was similar to that of albumin. Since albumin is not synthesized in pulmonary cells, it was concluded that, in healthy human, CBG enters bronchoalveolar fluid by diffusion through alveolar cells. It is suggested that the expression of the CBG gene in pulmonary cells could occur during the pathological state.

Combined effects of deafferentation and de-efferentation on isthmo-optic neurons during the period of their naturally occurring cell death

We have studied the effects on the chick embryo's isthmo-optic nucleus of de-efferentation alone or in combination with deafferentation. De-efferentation was achieved by pharmacological destruction of the axonal target cells in the retina at E13, or by colchicine-blockade of axoplasmic transport in the intraocular parts of the isthmo-optic axons at E13; deafferentation was by a tectal lesion at E11 or E12. De-efferentation alone causes all the isthmo-optic neurons to die, and mostly by the "endocytic-autophagic" mode of cell death, which is characterized by pronounced endocytosis (of an intravascularly injected label) and by intense, clumped activity of two lysosomal enzymes (acid phosphatase and N-acetyl-beta-glucosaminidase). Deafferentation plus de-efferentation caused there to be less endocytic-autophagic dying cells in the isthmo-optic nucleus than after de-efferentation alone, but all the neurons still died. Our interpretation is that deafferentation switched many of the isthmo-optic neurons to a completely different (nonendocytic, nonautophagic) mode of cell death.

Immunochemical characterization and quantification of the sex steroid-binding protein (SBP) in human amniotic fluid

The sex steroid-binding protein (SBP) is a plasma protein whose concentration in the maternal circulation increases during pregnancy. Using monospecific antibodies raised against human SBP, we could demonstrate the antigenic identity of the protein in human amniotic fluid. In this fluid, we found that the SBP concentration was correlated with the total protein concentration throughout gestation. The concentration gradient of SBP between maternal serum and amniotic fluid was compared to that of other serum proteins, in relation to their relative molecular mass, and it was concluded that SBP enters amniotic fluid in a non-specific manner similar to that of other serum proteins. It is suggested that SBP could act to sequester the sex steroid hormones in amniotic fluid.

Immunohistochemical detection of the sex steroid-binding plasma protein in human mammary carcinoma cells

A sex steroid-binding plasma protein-like antigen has been detected in human mammary carcinoma cells. A monospecific antiserum was used, and this protein was located mainly on the cytoplasmic membranes. These results are in agreement with a recent hypothesis according to which steroid hormones could be carried into cells by specific binding plasma proteins.

[Immunohistochemical study of the human testis and epididymis with a monospecific antiserum against the sex-steroid-binding plasma protein]

Sex-steroid-binding-plasma protein (SBP) is present at a very low concentration in human plasma. The preparation of a monospecific Rabbit antiserum against this protein allowed to demonstrate the tissular localization of antigenic determinants identical to SBP determinants by indirect immunofluorescence in human testis and epididymis.

Immunochemical characterization and quantitation of human sex steroid binding plasma protein

The interest in the measurement of human sex steroid binding plasma protein (h-SBP) is now increasing since it allows the estimation of the free fraction of circulating hormones in plasma. Up to this date, this protein could only be determined by measuring the total binding capacity of serum for dihydrotestosterone (DHT). The purpose of the present work was to purify the protein, to prepare a rabbit monospecific antiserum and to develop an immunoelectrophoretic assay of h-SBP. The immunological assay is specific, accurate and sensitive. A good correlation with the radioligand assay was found. The h-SBP levels obtained by immunoelectrophoretic assay of different serum samples were 5.3 +/- 1.4 (SEM) mg/L in normal men and 13.4 +/- 2.6 (SEM) mg/L in normal women.

Influence of sex hormone binding globulin and serum albumin on the conversion of androstenedione to testosterone by human erythrocytes

The influence of human serum albumin and sex hormone binding globulin (SHBG) on the enzymic conversion of androstenedione to testosterone in human erythrocytes was investigated in vitro. Total plasma and albumin delayed the conversion rate of androstenedione, while SHBG increased it markedly. The effect of SHBG was largely abolished by heating to 60 degrees C for 1 h and by saturating its binding sites by DHT. The effect of both proteins was found to be related to their concentration. It appears that the binding sites of albumin provide a mechanism for retarding androstenedione uptake by the erythrocytes and that the high binding affinity of SHBG for testosterone facilitates the diffusion of this steroid out of the cell and thus, displaces the chemical equilibrium within the cell.