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G Vallette

Publications and source records attributed to G Vallette.

At least 37 records · Page 2Linked to original sources
PubMed1993

Interaction of unsaturated fatty acids with rat liver glucocorticoid receptors: studies to localize the site of interaction.

Polyunsaturated fatty acids have been shown to decrease the binding of [3H]dexamethasone to rat liver glucocorticoid receptors by mixed non-competitive inhibition, suggesting that these fatty acids interact at a site on the receptor different from the hormone binding site. The present study was undertaken to localize the site of interaction of polyunsaturated fatty acids on the receptor by comparing the differential effects of docosahexaenoic acid (a 22-carbon polyunsaturated fatty acid of the series n-3) on antagonist (RU486) and agonist binding, by covalent cross-linking of the hsp 90 and other proteins to the receptor to attempt to mask the site of interaction, by limited trypsinization to cleave the site and by using antibodies against specific epitopes to prevent fatty acid access by steric hindrance. Binding [3H]RU486 was not inhibited by docosahexaenoic acid at a concentration (60 mumol/l) that increases the dissociation constant of [3H]dexamethasone eightfold. Covalent stabilization of the hetero-oligomeric glucocorticoid receptor structure did not keep the fatty acid from inhibiting [3H]dexamethasone binding. The binding to the receptor of monoclonal and polyclonal antibodies against different domains of the receptor did not sterically hinder the fatty acid interaction with the receptor. After limited trypsinization of the receptor, the fatty acid still increased the dissociation rate constant of [3H]dexamethasone binding, indicating that the site of interaction of polyunsaturated fatty acids is on a fragment of the receptor containing the hormone-binding domain and some sequences C-terminal of the DNA-binding domain.

Animals↗
PubMed1992

Modulation of glucocorticoid binding to rat liver cytosol receptor by lipid-soluble extracts from the serum of AIDS patients.

The total liposoluble extract of sera from AIDS patients, IVC1 and IVD stages, containing cortisol and free fatty acids (FFA) inhibited [3H]dexamethasone binding to a lesser extent than did the same quantity of total liposoluble extract of sera from healthy men. FFA isolated from extracts of AIDS sera by Sephadex LH20 chromatography had less effect on [3H]dexamethasone binding to rat liver glucocorticoid receptor than those extracted from sera of healthy men. These results suggest the presence in sera of AIDS patients of a liposoluble substance which could be limiting the inhibitory effect of FFA on [3H]dexamethasone binding to glucocorticoid receptor by inducing a conformational change in glucocorticoid receptor that could alter the biological action of glucocorticoids. The pathological consequence could be the apparent contradiction of high cortisolemia and clinical symptoms of adrenal insufficiency that have been observed in AIDS patients.

Acquired Immunodeficiency Syndrome↗
PubMed1991

Phytoestrogens: new ligands for rat and human alpha-fetoprotein.

The binding of the lignans, enterolactone, enterodiol, nordihydroguaiaretic acid (NDGA), and the isoflavonic phytoestrogen equol, to human and rat alpha-fetoprotein (AFP) was studied. They had differential inhibitory effects (NDGA greater than equol greater than enterolactone greater than enterodiol) on the binding of estrone and estradiol to rat AFP and the binding of unsaturated fatty acid to both rat and human AFP. Inhibition was dose-dependent. The apparent dissociation constants (Kd) for phytoestrogens binding to AFP were: Kd NDGA = 5 +/- 1.2.10(-7) M, Kd equol = 6.7 +/- 0.8.10(-6) M, Kd enterolactone = 1.7 +/- 0.4.10(-5) M and Kd enterodiol = 2.2 +/- 0.6.10(-5) M. The Kd for estrone binding to rat AFP was increased by increasing concentrations of equol, but the number of esterone binding sites remained unchanged. This, plus the results of double-reciprocal plots, suggests that they compete for the same site(s). NDGA also competitively inhibited estrone binding at low NDGA concentrations (increased Kd), but high concentrations induced conformational changes in rat AFP, as both Kd and the number of binding sites (n) were altered. Both rat and human AFPs underwent changes in electrophoretic behaviour and loss of immunoreactivity with increasing NDGA, suggesting that NDGA binding induces conformational changes in the AFPs. However, equol did not alter the electrophoretic or immunological properties of either rat or human AFP, providing further evidence for qualitative differences in the effects of these diphenols. These findings indicate that phytoestrogens could play a role in AFP-dependent normal and pathological growth and development.

4-Butyrolactone↗
PubMed1991

Modulatory effects of unsaturated fatty acids on the binding of glucocorticoids to rat liver glucocorticoid receptors.

Binding of the synthetic glucocorticoid dexamethasone to the rat liver cytosol glucocorticoid receptor was inhibited by physiological concentrations of nonesterified fatty acids as a function of increasing dose, degree of unsaturation, and chain length of the fatty acid. Polyunsaturated fatty acids were the most potent inhibitors. Scatchard analysis and Line-weaver-Burk plots of the binding data revealed that both the association constants and number of binding sites decreased and that polyunsaturated fatty acids inhibition was of a mixed non-competitive type. The dissociation rate constant of [3H]dexamethasone from glucocorticoid receptors was increased by up to 10 times in the presence of docosahexaenoic acid, whereas a competitive inhibitor like the glucocorticoid antagonist RU 38486 had no effect. Moreover, sucrose density gradient analysis showed that docosahexaenoic acid inhibited the binding of [3H] dexamethasone to both the 8.8S and 4S forms. The results strongly suggest that unsaturated fatty acids are interacting at a site on the receptor different from the hormone binding site and the heat shock protein and that by binding to a second site unsaturated fatty acids greatly change the conformation of the hormone binding site to reduce its affinity for the hormone, either partially or completely depending on the concentration and the class of the fatty acid.

Animals↗
PubMed1989

Conformational changes in rodent and human alpha-fetoprotein: influence of fatty acids.

Binding, spectral and immunological studies were performed to demonstrate the conformational changes in rodent and human alpha-fetoprotein (AFP) induced by a free fatty acid environment. Scatchard analysis of estradiol (E2) binding to purified rat AFP indicated that unsaturated fatty acids changed the number of binding E2 sites and the apparent E2 equilibrium dissociation constant which varied non-linearly with docosahexaenoic acid concentration. UV spectral analysis of rodent and human AFPs showed that the absorbance minimum of AFP incubated with unsaturated fatty acid (L-AFP) was red-shifted, broadened and less pronounced than that of purified native AFP (N-AFP). Immunochemical studies with specific polyclonal antibodies to purified rodent and human AFPs (N-AFP antibodies) showed that these proteins lost immunoreactivity after incubation with unsaturated fatty acid. N-AFP antibodies recognized fewer epitopes on L-AFP than on N-AFP, whatever the species. Specific anti-rat L-AFP antibodies were used to demonstrate specific epitopes on rat L-AFP. Rat L-AFP antibodies did not recognize rat N-AFP. Saturated fatty acids were without effect on the binding, spectral and immunological properties of rodent and human AFPs. RIA or ELISA values for human AFP from fetal serum, hepatoma serum, and cord serum, were reduced 80, 50 and 5%, respectively, by unsaturated fatty acids. This decrease correlated with the relative percentage of polyunsaturated fatty acid in each biological fluid. Such results indicate that an unsaturated fatty acid environment induces conformational changes in AFP which may modulate the endocrine and immune functions of this protein.

Animals↗
PubMed1988

Dynamic pattern of estradiol binding to uterine receptors of the rat. Inhibition and stimulation by unsaturated fatty acids.

The binding of estradiol to uterine cytosoluble receptors from 24-day-old rats was reduced or potentiated by unsaturated fatty acids (NEFAs), depending on the concentrations of estradiol and unsaturated NEFAs. At estradiol concentrations of up to 1.5 x 10(-8) M, unsaturated NEFAs inhibited estradiol binding to the 8 S cytosol receptor. This inhibition was dose-dependent (10-70%, p less than 0.001) and a function of NEFA unsaturation. Scatchard analysis indicated that unsaturated NEFAs caused a large decrease in receptor affinity for estradiol. Polyunsaturated NEFAs had no apparent effect on estradiol binding at estradiol concentrations of 2-4 x 10(-8) M. At high estradiol concentrations (above 4 x 10(-8) M), estradiol binding was increased 130-250% (p less than 0.01) by polyunsaturated NEFAs. This increased binding was particularly associated with proteins sedimenting at 12.5 S and the 8 S binding was, in fact, reduced. Metabolic studies showed that the reduced binding in the presence of unsaturated fatty acids was correlated with a decrease in reversibly bound estradiol at low estradiol concentrations. The increase in estradiol binding at high estradiol concentrations is the result of a reduction in reversibly bound estradiol and an increase in nonorganic solvent-extractable (water-soluble) estradiol. The amounts of these water-soluble estradiol derivatives depended on both estradiol and unsaturated NEFA concentrations. 70% of the water-soluble estradiol derivatives were trichloroacetic acid-precipitable, suggesting a covalent protein-steroid link. Thus, changes in the hydrophobic fatty acid environment of the uterine cytosol estrogen receptor could modify estrogen-receptor function by altering binding site conformation and/or by inducing changes in estradiol metabolism.

Animals↗
PubMed1986

Potentiation of estradiol binding to human tissue proteins by unsaturated nonesterified fatty acids.

Nonesterified fatty acids (NEFAs) have been recently shown in the rat to be involved in steroid hormone expression, having effects on plasma transport and intracellular activity. This study examines the influence of saturated and unsaturated NEFAs on estradiol (E2) binding to cytosol from human uterus, breast, and melanoma. Binding was analyzed after separation with dextran-coated charcoal or hydroxylapatite and by sucrose density gradient centrifugation. Unsaturated NEFAs induced a 2- to 10-fold increase (P less than 0.001) in E2 binding to cytosol from normal, fibromatous, and neoplastic uteri, while saturated NEFAs had a slight inhibitory effect (P less than 0.05). Similar effects were seen with cytosol from metastatic melanoma lymph nodes and neoplastic breast tissues. By contrast, unsaturated NEFAs did not increase E2 binding to serum from these patients. Density gradient centrifugation indicated that the increased binding was associated with the proteins present in the 2- to 4 S region. Analysis of E2 metabolites in the presence of unsaturated NEFAs showed the formation of water-soluble derivatives. Seventy percent of these E2 derivatives were trichloracetic acid precipitable, suggesting a covalent link between the steroid and a protein. The existence of such water-soluble metabolites could be erroneously interpreted as a true binding to soluble cytoplasmic receptors.

Breast↗
PubMed1986

[Effect of alpha-fetoprotein on isolated mouse oocytes].

Data are presented which indicate a possible action of alpha-fetoprotein (AFP) on female germinal cells. The in vitro maturation of mature mice oocytes was significantly inhibited when mouse AFP replaced albumin in the culture medium. In addition, the degenerative aspect of oocytes cultured with AFP seemed to indicate that this meïotic inhibition was caused by a premature degeneration of oocytes rather than by a blockage at a specific stage of maturation. Thus AFP, perhaps through its ligands, may play a role in the reduction of germinal cells during fetal and immediate post-natal life rather than in the arrest of meïosis at the diplotene stage.

Animals↗
PubMed1986

Effects of alphafetoprotein on isolated mouse oocytes.

The supposition of an effect of alphafetoprotein (AFP) on female germinal cells is put forward. The spontaneous in vitro maturation of adult mouse oocytes is significantly inhibited when mouse AFP replaces albumin in culture medium. Furthermore, the very unusual degenerative appearance of the cells subjected to AFP seems to indicate that this meiotic inhibition is linked to a premature degeneration of the oocytes rather than to a blockage of the cells at an earlier stage of maturation. Accordingly AFP, perhaps through its ligands, may play a role in reducing the number of gonocytes during fetal and immediate post-natal life rather than in stopping oocyte meiosis at the diplotene stage.

Animals↗
PubMed1984

Age-dependent responses of the serum non-esterified fatty acids to adrenalectomy and ovariectomy in developing rats.

We report detailed gas chromatography analyses of the non-esterified fatty acids in the sera of female rats during post-natal maturation. A marked age-dependent decrease of concentration is demonstrated for all classes of compounds. Total levels fall from about 0.8 mM at birth to about 0.25 mM, 60 days later. The decrease is most pronounced for the polyunsaturated acids, which represent 27 +/- 9% of total fatty acids at birth and 13 +/- 3% 60 days later. The effects of ovariectomy and adrenalectomy on the free fatty acid levels as a function of age are strikingly different before and after maturation. When ovariectomy is performed at 5, 9 and 15 days, the fatty acid levels respond by a significant (30-40%) decrease; when adrenalectomy is carried out at the same ages, a dramatic 3-5-fold increase of all classes of fatty acids is observed. By contrast, in older animals, both responses have virtually disappeared. Possible mechanisms underlying the age-dependent patterns and behaviour of the serum free fatty acids are briefly discussed.

Adrenalectomy↗
PubMed1984

[Non-esterified fatty acids and alpha 1-fetoprotein are the modulators of uterine binding of estrogens during development in the rat].

We studied the effects of different classes of non-esterified fatty acids (NEFA) on the binding of natural and synthetic estrogens by uterine cytosolic receptors. The role of alpha 1-fetoprotein (AFP) in this process was also studied. Saturated fatty acids, irrespective of their concentration, slightly increased (120%) E2 binding to the 4S and 8S uterine cytosolic receptors. The effect of unsaturated fatty acids was dependent on their concentration: at 0.5 X 10(-4) M unsaturated NEFA potentiated the E2 binding to the receptor. At a higher concentration (2.0 X 10(-4) M), the NEFAs were highly inhibitory. This inhibition was dependent on the degree of unsaturation of the fatty acids. Tritiated arachidonic acid interacted directly with the 4S and 8S cytosol receptor. Furthermore, we demonstrated a double competition between murine AFP and the 8S receptor for estrogens and unsaturated NEFA. The effect of these hydrophobic ligand exchanges between transport proteins and receptors on the modulation of the action of estrogen is discussed.

Animals↗
PubMed1983

[Inhibition of the uterine binding of estrogens by unsaturated fatty acids in immature female rats].

We demonstrate that the interactions between the uterine cytosol proteins of 24 day old Rats and estradiol-17 beta (E2) are significantly influenced by physiological concentrations of non esterified fatty acids (2. 10(-4)M). We show that the specific binding of the hormone to the 8S uterine receptor, is markedly inhibited (50-80%) by the unsaturated fatty acids. The observed inhibition is a function both of acid dose and acid unsaturation degree. The polyunsaturated arachidonic and docosahexaenoic acids are the strongest inhibitors, whereas the saturated palmitic and stearic acids do not displace the E2 from the 8S receptor.

Animals↗
PubMed1983

The role of nonesterified fatty acids and of alpha 1-fetoprotein in estrogen-dependent endocrine systems.

We discuss the various experimental findings to date that indicate that AFP may be considered as a positive or negative modulator of estrogenic action. Moreover, we show that this protein, even when nonestrogenophilic, is able to bind other hydrophobic ligands, in particular nonesterified fatty acids. These fatty acids inhibit the binding of estrogens to murine AFP as well as to the cytosolic estrogen receptors. Thus, the AFPs of all species--whether or not estrogenophilic--might play an endocrinologic role through the intermediary of the unsaturated fatty acids to which they associate with high affinity.

Animals↗
PubMed1982

Developmental patterns of levels of corticosterone and of corticosterone binding in the serum of female rats: effects of ovariectomy and adrenalectomy.

Corticosterone concentrations and corticosterone binding in the serum were studied in immature female rats, using radioimmunoassay and batchwise gel equilibrium techniques. A parallel developmental pattern was found for corticosterone levels and its serum binding with a neonatal drop, followed by low levels until 12 days of age and a rise between 12 and 28 days of age. Effects of adrenalectomy, of ovariectomy, of the combined operation and of sham-operations, performed at various ages, were also studied. Adrenalectomy performed at 5 days of age did not decrease serum corticosterone concentrations within a 6-day period whereas it did in older rats. Complete disappearance of corticosterone from the blood occurred only in adult rats after combined adrenalectomy/ovariectomy. Ovariectomy and sham-operations in the younger age groups (5-15 days) caused a gradual increase in corticosterone concentration with maximal values 6 days after operation or later. The response of corticosterone secretion to these operations became more moderate and quicker, i.e. more adult-like, at 28 days of age, the age where corticosterone concentrations in intact rats also seemed to reach a plateau at an adult-like level. Corticosterone binding changed only marginally after ovariectomy or sham-operations until 28 days of age, when an increase was induced by these operations. After adrenalectomy or combined adrenalectomy/ovariectomy, however, marked increases in serum binding of corticosterone were always seen. In summary: though a parallel developmental pattern of serum corticosterone levels and corticosterone binding was seen in the maturing rat, interference with the normal condition causes divergent responses in these two parameters. Moreover, the responses vary with maturational age.

Adrenalectomy↗
PubMed1981

Mouse alpha 1-fetoprotein and albumin. A comparison of their binding properties with estrogen and fatty acid ligands.

The binding of estradiol-17 beta (E2), diethylstilbestrol (DES), and polyene fatty acids, in particular arachidonate (C20:4), to alpha 1-fetoprotein (alpha-FP) and albumin purified from mouse embryo sera was studied using equilibrium dialysis and electrophoretic techniques. E2, arachidonate, and DES all bind to alpha-FP, but with decreasing strength. E2 is a high affinity, low capacity ligand (Ka approximately 0.8 X 10(8) M-1 and approximately 0.3 sites/mol of alpha-FP at 25 degrees C); arachidonate is a weaker ligand disposing of more sites (Ka approximately 0.3 X 10(7) M-1 and 4-5 sites/mol of alpha-FP); the binding of DES is of comparatively low affinity and capacity (Ka approximately 0.2 X 10(7) M-1 and n approximately 0.7/mol of alpha-FP). In spite of different structures and equilibrium parameters, E2, DES, and arachidonate are able to compete with each other for binding to the fetoprotein. The C22:4 and C22:6 fatty acids are also efficient concentration-dependent inhibitors of E2 or DES binding. Albumin binds the fatty acids and DES, but equilibrium parameters are different from those of alpha-FP. In particular, arachidonate is a better ligand for albumin, where it interacts with at least two classes of apparent sites (Ka1 approximately 0.3 X 10(8) M-1 and n1 approximately 1; Ka2 approximately 0.2 X 10(7) M-1 and n2 approximately 30). In contrast to alpha-FP, albumin virtually does not bind E2. Also, no competition could be demonstrated between DES and fatty acid ligands for binding to albumin. None of the studied interactions, with either albumin or alpha-FP, was modified even by high doses of bilirubin. The possible functions of the various binding activities present in fetal sera in the process of growth are discussed.

Animals↗