Bertha Chávez

Stereospecificity of the intracellular binding of norethisterone and its A-ring reduced metabolites

The interaction of norethisterone (NET) and four A-ring reduced metabolites of NET with cytosol receptors for progesterone (PR), androgen (AR), and estrogen (ER) was investigated. Cytosol preparations from: uteri of adult estrogen-primed castrated rats, ventral prostates of adult castrated rats and uteri of immature rats were used as the source of PR, AR, and ER respectively. 3H-Labeled ORG-2058, R-1881, and 17 beta-estradiol were used as the radioligands. The results of competitive studies disclosed that: the most efficient competitor for PR binding sites was NET (Ki = 1.1 X 10(-7) M) followed by 5 alpha-dihydro NET (5 alpha-NET), whereas the 3 alpha,5 alpha; 3 beta,5 alpha and 3 alpha,5 beta-tetrahydro NET derivatives were ineffective the most efficient competitor for AR binding sites was 5 alpha-NET (Ki = 1 X 10(-8), immediately followed by NET, while the three tetrahydro NET derivatives were not competitors and remarkable competition for ER binding sites was only exhibited by the 3 beta,5 alpha-tetrahydro NET derivative (Ki = 4.6 X 10(-8) M) and to a lesser extent by its 3 alpha,5 alpha-epimeric alcohol, while NET and 5 alpha-NET were completely ineffective. These findings demonstrate the stereospecificity of the intracellular binding of NET and its reduced metabolites with cytosol steroid putative receptors, and provide biochemical support to the understanding of the variety of hormone-like effects observed after the in vivo administration of NET.

Mutations of the 5α-reductase Type 2 gene in eight Mexican patients from six different pedigrees with 5α-reductase-2 deficiency

BACKGROUND AND OBJECTIVE Male pseudohermaphroditism due to 5α‐reductase deficiency was originally described in 1974. Recently, 5α‐reductase Type 2 gene defects have been found generally to be due to point mutations within the 5 exons of the 5α‐reductase‐2 gene. In this report, we describe the molecular study of patients with 5α‐reductase deficiency.

Mechanism of action of contraceptive synthetic progestins

The antigonadotropic effect of 2 synthetic long-acting progestins medroxyprogesterone acetate (MPA) and norethisterone enanthate (NET-e) was studied. 5 postmenopausal women (PMW) and 3 related castrated individuals with the complete form of testicular feminization syndrome (TFS) were included. Gonadotropin inhibitory potency and pituitary responsiveness was evaluated. Natural progesterone was administered through vaginal medicated devices with an in vivo release rate of progesterone of 4020 +or- 140 mcg/day. MPA and NET-e were intramuscularly administered at the doses of 150 and 200 mcg respectively. In addition in vitro transport and intracellular binding were studied on adult castrated sheep rabbits and rats. Results indicated that sustained vaginal release of natural progesterone in PMW did not induce any significant changes in circulating luteinizing hormone (LH) or follicle stimulating hormone (FSH) levels or modify pituitary response to exogenous gonadotropin-releasing hormones. In contrast with the lack of antigonadotropic activity natural progesterone induced a significant rise on basal body temperature in PMW. Administration of MPA and NET-e resulted in a significant inhibition of serum gonadotropin levels in PMW indicating that both progestins had a mechanism of action at the neuroendocrine level different from that of natural progesterone. Results of tests using NET-e and MPA on castrated TFS patients revealed that while NET-e had potent gonadotropin inhibitory activity and reduced the pituitary LRH responses in 2 TFS patients MPA had neither effect on serum LH and FSH or upon the pituitary response in patients with androgen insensitivity. In binding studies of MPA and NET to sera from humans rats rabbits and sheep it was found that MPA neither binds to testosterone-estradiol binding globulin nor to CBG while NET does. Binding studies of the synthetic progestins to cytosol receptors of rat hypothalamus and pituitaries revealed that in the absence of progesterone receptors both MPA and NET bind to androgen receptors. The progestins interaction with androgen receptors at neuroendocrine levels may explain the gonadotropic inhibitory actions on the ansence of progesterone receptors and may account for their longterm effects on women under contraceptive progestin therapy and subsequent chronic suppression of ovarian function.

The metabolism of 19-nor contraceptive progestins modulates their biological activity at the neuroendocrine level

In this communication, a series of studies from our laboratory dealing with the mechanism of action of 17 alpha-ethinyl derivatives of 19-nor testosterone are reviewed. The administration of norethisterone (NET) to long-term castrated female rats induces the nuclear translocation of pituitary estradiol receptors and is followed by some estrogenic-like effects at the hypothalamic-pituitary unit. It is established that an A-ring reduced metabolite of NET, the 3 beta,5 alpha-tetrahydro NET derivative, is responsible for the observed in vivo estrogenic effects of the parent compound. 3 beta,5 alpha-NET binds to the estrogen receptor and is efficient in inducing the pituitary estrogen-dependent progesterone receptor and in increasing the uterine weight in long-term castrated rats. Furthermore, administration of 3 beta,5 alpha-NET and the 5 alpha-reduced metabolite of NET (5 alpha-NET) are able to inhibit the release of gonadotropins in the castrated animal to a greater extent than NET. Moreover, pretreatment with tamoxifen, an estrogen binding site competitor, results in a significant diminution of the antigonadotropic potency of 3 beta,5 alpha-NET but not of the 5 alpha-NET, which is only inhibited by the administration of cyproterone acetate. These findings underline the importance of the metabolic rate of NET for the expression of its biological effects at the hypothalamic-pituitary unit.

Interaction of medroxyprogesterone acetate with cytosol androgen receptors in the rat hypothalamus and pituitary

The binding of medroxyprogesterone acetate (MPA) with cytosol androgen receptors from rat pituitary and hypothalamus was studied. The pituitary and hypothalamic cytosol androgen receptors from adult castrated female rats were in vitro labeled using 3H natural (testosterone (T) and 5 alpha-dihydrotestosterone (DHT] and [3H]synthetic (methyltrienolone) androgens as radioligands. The [3H]androgen-receptor complexes sedimented with a coefficient of 8S in linear sucrose gradients. When incubated with an excess of radioinert MPA, specific binding was abolished indicating interaction of MPA with androgen receptors. Furthermore specific [3H]MPA-androgen cytosol receptor complexes could be identified in these neuroendocrine tissues when a post-gradient receptor labeling technique was used in the absence or presence of radioinert MPA, DHT, and triamcinolone acetonide. A study of binding kinetics disclosed that the equilibrium dissociation constant and saturation binding capacity for the MPA binder, were similar to those exhibited by DHT binding to androgen receptors in both studied tissues under identical experimental conditions. The overall results were interpreted as demonstrating that MPA interacts with cytosol steroid receptors other than those of progesterone in the rat hypothalamus and anterior pituitary. The data are consistent with MPA binding to androgen receptors.

Phenotypic heterogeneity associated with identical mutations in residue 870 of the androgen receptor.

Background/Aims: Mutations in the androgen receptor (AR) gene result in an X-linked recessive form of male pseudohermaphroditism known as the androgen-insensitivity syndrome (AIS). The alterations most frequently observed are missense or nonsense point mutations in exons 4–8 of the AR gene that affect the steroid-binding domain of the receptor in subjects with various degrees of androgen resistance. Despite the increasing number of AR mutations identified, a reliable genotype-phenotype correlation has not been established and individuals with the same molecular defect may exhibit different phenotypes. Here, we studied a patients with an AIS characterized by bilateral gynecomastia, normal male external genitalia, and normal sperm counts. Methods: Exon-specific polymerase chain reaction, single-stranded conformational polymorphism, and sequencing analysis of the subject’s AR gene were performed in addition to hormone-binding assays in skin fibroblasts from the patient. Results: A point mutation at codon 870 of the AR, changing alanine to valine, was detected. Conclusion: As AR missense mutations changing alanine 870 to valine have been previously described in 3 unrelated patients showing severe AIS phenotypes, we conclude that phenotypic heterogeneity associated to identical mutations in the AR gene is probably due to individual functional differences in AR coregulator molecules.

Expression and localization of endocrine gland-derived vascular endothelial growth factor (EG-VEGF) in human pancreas and pancreatic adenocarcinoma.

Endocrine gland-derived vascular endothelial growth factor (EG-VEGF) was recently identified as the first tissue-specific angiogenic molecule. EG-VEGF (the gene product of PROK-1) appears to be expressed exclusively in steroid-producing organs such as the ovary, testis, adrenals and placenta. Since the human pancreatic cells retain steroidogenic activity, in the present study we ascertained whether this angiogenic factor is expressed in normal pancreas and pancreatic adenocarcinoma. Tissue samples from normal males (n=5), normal females (n=5) and from surgically resected adenocarcinomas (n=2) were processed for RT-PCR and immunohistochemical studies. Results from semi-quantitative analysis by RT-PCR suggest a distinct expression level for EG-VEGF in the different tissue samples. The relative amount of EG-VEGF mRNA in pancreas was more abundant in female adenocarcinoma (0.89) followed by male adenocarcinoma (0.71), than normal female (0.64) and normal male (0.38). The expression of mRNA for EG-VEGF in normal tissue was significantly higher in females than in males. All samples examined showed specific immunostaining for EG-VEGF. In male preparations, the positive labeling was localized predominantly within the pancreatic islets while in female preparations the main staining was detected towards the exocrine portion. Specific immunolabeling was also observed in endothelial cells of pancreatic blood vessels. Our data provide evidence that the human pancreas expresses the EG-VEGF, a highly specific mitogen which regulates proliferation and differentiation of the vascular endothelium. The significance of this finding could be interpreted as either, EG-VEGF is not exclusive of endocrine organs, or the pancreas should be considered as a functional steroidogenic tissue. The extent of the expression of EG-VEGF appears to have a dimorphic pattern in normal and tumoral pancreatic tissue.

Novel compound heterozygous mutations in the SRD5A2 gene from 46,XY infants with ambiguous external genitalia

AbstractDihydrotestosterone is crucial for normal development of external genitalia and prostate in the male embryo. Autosomal recessive mutations in the 5α-reductase type 2 (SRD5A2) gene disrupt the synthesis of dihydrotestosterone in the urogenital tract and give rise to genetic males with undervirilized external genitalia that may be female-like or ambiguous. In this study, three unrelated 46,XY children (0.5, 3, and 8 years old) who presented severe undermasculinization at birth were examined for genetic abnormalities in the SRD5A2 gene. Coding sequence abnormalities were ascertained by exon-specific polymerase chain reaction (PCR), single-stranded conformational polymorphism (SSCP), and sequencing analysis. Functional properties of the mutant alleles were investigated by means of site-directed mutagenesis assays. DNA molecular studies showed that all three patients were compound heterozygotes for SRD5A2 mutations. Patient 1 had a point mutation 547G → A in exon 3 (G183S) and a novel dinucleotidic mutation 634,635CC → TG in exon 4 (P212X). This double change results in premature termination signal (TGA) at codon 212, which predicts the expression of a truncated 211-amino acid protein. Patient 2 was the carrier of mutations G115D in exon 3 and S210F in exon 4. Patient 3 had two substitution mutations in exon 1, including a novel G → C transversion at nucleotide 169 (E57Q) and a G → A transition at nucleotide 254 (G85D). In transitory transfection assays, the recombinant cDNAs harboring mutations E57Q and G85D showed residual 5α-reductase activity, whereas those with mutations G115D, S210F, and P212X were devoided of activity. In contrast, the G183S substitution affected the catalytic activity of the enzyme by decreasing its affinity for testosterone substrate. We describe six different mutations of the SRD5A2 gene detected in three children with genital ambiguity. These genotypes are consistent with the clinical phenotype of steroid 5α-reductase 2 deficiency. Our data suggest that the combined gene variants (E57Q/G85D, G115D/S210F, and G183S/P212X) result in subfunctional or nonfunctional enzymes, causing masculinization defects in these patients. This further underscores that exon 4 of SRD5A2 may be a site prone to inactivating mutations.

Molecular Analysis of the SRD5A2 in 46,XY Subjects With Incomplete Virilization: The P212R Substitution of the Steroid 5α-Reductase 2 May Constitute an Ancestral Founder Mutation in Mexican Patients

Inactivating mutations of the SRD5A2 gene result in steroid 5α-reductase 2 deficiency, an autosomal recessive disorder expressed as a male-limited disorder of sex development. Herein, genomic DNA was isolated from 11 new patients with apparent steroid 5α-reductase 2 deficiency. Coding sequence abnormalities in SRD5A2 were assessed by exon-specific polymerase chain reaction, single-stranded conformation polymorphism, and direct sequencing. Likewise, enzymatic activity of the P212R gene variant of SRD5A2 was assessed. DNA analysis revealed mutations in all patients (G115D, R171S, N193S, E197D, G203S, P212R). Three individuals were compound heterozygotes, 6 were homozygotes, and 2 more were single heterozygotes for SRD5A2 mutations; remarkably, 40% of the mutant alleles (9/22) contained the gene variant P212R. The results described in this study represent, along with our previous reports, the largest number of patients with steroid 5α-reductase 2 deficiency belonging to nonrelated families. Regarding the frequency of the p.P212R mutation in our population and its presence throughout all of our country, it allows us to hypothesize that the presence of this mutation may constitute a founder gene effect.

Inherited impairment of nuclear androgen uptake as a cause of familial androgen insensitivity

Abstract The endocrine and biochemical characteristics of four related 46,XY pseudohermaphrodite patients with the Reifenstein Syndrome are presented. All of them (6 and 9 years old, first generation, and 9 and 12 months old, second generation) exhibited ambiguity of external genitalia and a family pedigree characteristic of an X-linked pattern of inheritance. Serum basal levels of LH, FSH, testosterone (T), androstenedione and 5α-dihydrotestosterone (DHT) were within normal limits. Administration of hCG induced a normal response in terms of serum T in three of the patients, with a concomitant increase in serum DHT. However, an abnormally elevated T : DHT ratio was found in two of these subjects on the day of maximal T response (T : DHT ratio, 24 and 27; normal range, 4–21). Genital skin-derived fibroblasts from all patients were studied for [ 3 H]DHT uptake in a whole-cell monolayer assay. Three of the mutant strains exhibited values of [ 3 H]DHT uptake at 37 ° C within the lower limits of normality (39.4–47.05 fmol/mg protein/h; normal strains, 36–101 fmol/mg protein/h), whereas fibroblasts from the remaining patient presented a slightly decreased uptake (31.66 fmol/mg protein); when studied at 42 ° C, all mutant strains behaved as the normal controls. The existence of a specific 4.6 S cytosol androgen receptor was clearly seen in the two mutant strains when analysed by sucrose gradient centrifugation. Nevertheless, in one of the mutant strains, a significantly low maximal nuclear [ 3 H]DHT uptake was detected (173.6 fmol/mg DNA; control strain, 301.6 fmol/mg DNA). The overall data were interpreted as demonstrating the existence of an impaired uptake of the androgenreceptor complex at the nuclear levels as the cause of the incomplete phenotypic expression of androgen action in this family. In this setting, the presence of low peripheral 5α-reductase activity may be considered as a secondary manifestation of the androgen insensitivity.