Structure-function relationships for equine and human aromatases. A comparative study.
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Animals↗
Biomedical subjects
G E Seralini
Publications and source records attributed to G E Seralini.
Inhibition and inactivation of equine aromatase by steroidal and non-steroidal compounds. A comparison with human aromatase inhibition.
In order to approach the detailed structure-function relationships of aromatase, we studied the inhibitory and inactivatory potencies of several steroidal androstenedione analogues (1: 4-hydroxyandrostenedione, 2: 4-acetoxyandrostenedione and 3: 7 alpha-(4'-amino)phenylthio-4-androstene-3, 17-dione) and non-steroidal imidazole derivatives (4: ketoconazole, 5: miconazole and 6: fadrozole) on equine aromatase in placental microsomes, a well established mammalian model. Human placental microsomes and the purified enzyme from equine testis were also used to compare inhibition by 1 and 2. In equine microsomes, all compounds tested exhibited a competitive inhibition, with Ki values of 4.1, 26 and 1.8 nM for 1, 2 and 3, and of 2400, 1.4 and 4 nM for 4, 5, and 6, respectively. The Km for androstenedione, the substrate mainly used in these studies, was 1.8 +/- 0.13 nM. The three non-steroidal derivatives did not inactivate equine aromatase, but 1 and 2 acted as comparable inactivators to a much higher degree than 3. Compound 1 inhibited in a similar manner (89-94%) purified or equine and human microsomal aromatases, whereas 2 inhibited microsomal aromatase more efficiently in the horse than in man (92% and 33% inhibition, respectively). There was only a 40% inhibition with 2 on the purified equine enzyme, which is no more in the natural membrane environment. The comparisons between equine and human microsomal aromatases allow precise functional and structural differences to be observed with these enzymes.
Androstenedione↗
Immunohistochemical localization of cytochrome P450 aromatase in equine gonads.
Estrogens are the major steroids produced by equine gonads. To identify the cells responsible for estrogen synthesis, an antiserum against purified equine testicular cytochrome P450 aromatase was produced in rabbits. The reactivity and specificity of the antiserum were assessed by ELISA, immunoblot analysis, and immunoneutralization studies. Immunofluorescence microscopy demonstrated that in the male gonad, cytochrome P450 aromatase (P450arom) was localized in the interstitial tissue, whereas, under the experimental conditions used, the Sertoli and germ cells did not show any specific staining. In the ovary, the granulosa cells of small follicles exhibited faint immunofluorescent staining for P450arom and the granulosa cells of large, viable more follicles showed a high degree of immunoreactivity. In the corpus luteum, all the luteinized cells showed immunoreactivity. No immunoreactivity was detected in other cells of small and large viable follicles. Immunolocalization of P450arom in the equine testicular Leydig cells and in ovarian granulosa and luteinized cells indicates that these cells have the ability to metabolize androgens to estrogens and possibly to catechol estrogens.
Animals↗
The human corticosteroid binding globulin gene is located on chromosome 14q31-q32.1 near two other serine protease inhibitor genes.
Human corticosteroid binding globulin (CBG) cDNA fragments were radiolabeled and hybridized in situ to metaphase chromosome preparations. The results localized the CBG gene to the q31-q32.1 region of human chromosome 14. This location also contains the genes for two closely related serine protease inhibitors: alpha 1-proteinase inhibitor and alpha 1-antichymotrypsin. It is therefore likely that these genes evolved by duplication events, and it would appear that this region contains a series of functionally related genes.
Chromosome Banding↗
Rabbit corticosteroid-binding globulin: primary structure and biosynthesis during pregnancy.
The cDNA-deduced primary structure of rabbit corticosteroid-binding globulin (CBG) contains 383 amino acids (mol wt, 42,326), including three cysteine residues and four sites for N-glycosylation. It is primarily the product of a 1.68-kilobase hepatic mRNA, but small amounts of CBG mRNA were also found in maternal lung, spleen, and ovary and fetal kidney. In the fetus, hepatic CBG mRNA concentrations increase markedly after day 11 and were 2- to 5-fold higher than those in maternal liver during days 17-23. They then declined to very low levels at term (31 days). By contrast, maternal hepatic CBG mRNA levels did not increase until day 23; reached a peak at about day 27, and then declined to prepregnancy values by 3 days after delivery. In general, fetal and maternal hepatic CBG mRNA concentrations reflect the corresponding serum CBG levels. Our data, therefore, indicate that the marked changes in fetal and maternal plasma CBG levels during pregnancy reflect changes in the biosynthesis of the protein rather than alterations in compartmentalization or clearance.
Amino Acid Sequence↗
Biological half-life and transfer of maternal corticosteroid-binding globulin to amniotic fluid in the rabbit.
Rabbit corticosteroid-binding globulin (CBG) from the serum of pregnant and nonpregnant females differs in terms of charge microheterogeneity, and both forms were, therefore, radiolabeled and injected iv into 23- to 27-day pregnant rabbits (n = 6) to assess their biological half-lives and possible transfer to the fetal compartment. After an initially rapid distribution phase, the serum half-lives of both forms of [125I]CBG were essentially identical (approximately 13 h) and did not vary at different gestational ages. There was also no difference in the transfer of either form of [125I]CBG from maternal to fetal compartments in any of the animals studied. Moreover, [125I]CBG showed no sign of degradation and retained its steroid-binding activity in fetal urine and amniotic fluid. Twenty-two hours after administration of [125I]CBG to rabbits (n = 2) at 23 days gestation, its mean level in fetal urine (7 cpm/microliter) and amniotic fluid (2.5 cpm/microliter) was much higher than that in fetal blood (0.6 cpm/microliter). More importantly, the specific activities of [125I]CBG in fetal urine and amniotic fluid were comparable to that in maternal serum, and approximately 2 orders of magnitude higher than that in fetal serum. Taken together, these results suggest that CBG in fetal urine and amniotic fluid is largely of maternal origin, and that maternal CBG crosses the fetal kidney preferentially.
Amniotic Fluid↗
[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↗
Alphafetoprotein and atretic follicles in the ovary of the pregnant rat.
Previous experiments have been conducted concerning the role of alphafetoprotein in genital system blockade in several cases: during adult rat N2-fluorenylacetamide hepatocarcinogenesis, after alphafetoprotein injections into normal adult female rats, during fetal life, and during postnatal and prepuberal development. In these conditions, alphafetoprotein is present at high plasma levels, and the normal cyclic ovarian function is stopped or nonexistent. The degenerating oocytes observed in the ovaries are often AFP-positive by histo-immunolocalization. Pregnancy corresponds to a physiological state in which alphafetoprotein levels are high while the gonadal activity is not characterized by ovulatory cycles. In order to assess our hypothesis, alpha-fetoprotein was studied in the ovary of pregnant rats from day 18 to 21 of gestation by an immunofluorescent technique, and alpha-fetoprotein was assayed in plasma samples. The results of this work show that, during pregnancy, follicular maturation is blocked at the antral stage, and the follicles contain degenerating oocytes that are AFP-positive in immunofluorescence. In conclusion, we suggest that the alpha-fetoprotein produced by the fetal liver and the yolk sac is disseminated in the amniotic fluid and passes through the placenta, and then reaches the ovarian follicles and the oocytes. The possible role of alphafetoprotein in follicular atresia is discussed.
Animals↗
Ovarian function during aflatoxin B1-induced hepatocarcinogenesis in the rat.
Study of the endocrine status, which is often disturbed during hepatocarcinogenesis, is particularly valuable because gonadal function and hormone production regulate hepatic metabolism of the carcinogen. Sex steroids can even promote carcinogenesis. After aflatoxin B1 induction of liver carcinogenesis in adult female Sprague Dawley rats, livers were examined by histology, fluorescence microscopy of the carcinogen and its metabolites, and alphafetoprotein (AFP) assays. Ovarian activity was assessed, and both progesterone and estradiol levels were determined. Administration of a diet containing 10.32% total protein plus 2 ppm aflatoxin B1 was observed to prevent development of liver tumors during the 300 day study period. This finding is especially interesting for the study of populations suffering from malnutrition and exposed to dietary carcinogens. Under study conditions, aflatoxin B1 did not cause elevation of AFP levels, as occurs with other hepatotoxic substances. This absence of a rise in AFP despite liver alterations explains the surprising lack of ovarian modifications. In other experiments, AFP has been shown to cause genital function blockade which leads to reduced levels of hormonal promoters, for example during N2 fluorenylacetamide carcinogenesis. The endocrine reaction implicated in the development of tumors during carcinogenesis thus appears closely related to the nature of the carcinogen, AFP production, and the composition of the diet.
2-Acetylaminofluorene↗
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↗
[Alpha-fetoprotein and blockade of the sexual cycle].
During chemical hepatocarcinogenesis by N-2 fluorenylacetamide in adult female Rats, vaginal cycle alterations were observed after 30 days of carcinogenic diet, and a blocking at the metestrus stage appeared from the 70th day. This may be explained by the very low serum progesterone level prevailing after the 50th day. An important drop in ovary weight was also noticed; together with the blocking of follicular maturation and ovulation leading to a marked follicular atresia. Simultaneously, alpha-fetoprotein (AFP) seems to interact in the lowering of progesterone level, and AFP was found ten times higher in the serum of treated animals than in controls. AFP was localized in degenerative oocyte cytoplasm by immunofluorescence in the treated animals, but not in the controls. In conclusion, a blocking role of AFP on genital cycles and a relationship between AFP and follicular atresia are suggested.
2-Acetylaminofluorene↗