Studies on 17beta-hydroxysteroid dehydrogenase in human endometrium and endometrial carcinoma

Intracrine Regulation of Estrogen and Other Sex Steroid Levels in Endometrium and Non-gynecological Tissues; Pathology, Physiology, and Drug Discovery

Our understanding of the intracrine (or local) regulation of estrogen and other steroid synthesis and degradation expanded in the last decades, also thanks to recent technological advances in chromatography mass-spectrometry. Estrogen responsive tissues and organs are not passive receivers of the pool of steroids present in the blood but they can actively modify the intra-tissue steroid concentrations. This allows fine-tuning the exposure of responsive tissues and organs to estrogens and other steroids in order to best respond to the physiological needs of each specific organ. Deviations in such intracrine control can lead to unbalanced steroid hormone exposure and disturbances. Through a systematic bibliographic search on the expression of the intracrine enzymes in various tissues, this review gives an up-to-date view of the intracrine estrogen metabolisms, and to a lesser extent that of progestogens and androgens, in the lower female genital tract, including the physiological control of endometrial functions, receptivity, menopausal status and related pathological conditions. An overview of the intracrine regulation in extra gynecological tissues such as the lungs, gastrointestinal tract, brain, colon and bone is given. Current therapeutic approaches aimed at interfering with these metabolisms and future perspectives are discussed.

Recent advances on the action of estrogens and progestogens in normal and pathological human endometrium

Hormonal control in the development of the normal endometrium is of the utmost importance. It is well established that the two main hormones involved in this process are estradiol and progesterone, which are also implicated in the pathological conditions concerning endometriosis and endometrial carcinoma. There are two types of endometrial carcinoma: type I which represents 80%–90% is hormone-dependent, whereas the remainder is type II and is hormone-independent. The endometrial tissue contains all the enzymatic systems in the formation and transformation of the various hormones, including aromatases, sulfatases, sulfotransferases, hydroxysteroid dehydrogenases, hydroxylases, and glucuronidases. It is interesting to note that increased sulfatase activity is correlated with severity of endometriosis. An increased sulfatase/sulfotransferase ratio represents a poor prognosis in patients with endometrial carcinoma. Treatment with hormone replacement therapy (estrogens+progestogens), as well as with tibolone, is most effective in protecting this tissue by climacteric alterations, owing to the significant decrease of ovarian hormones. In conclusion, enzymatic control can open appealing perspectives to protect this organ from possible pathological alterations.

Induction of estradiol dehydrogenase activity in human uterine endometrium by synthetic steroids

The effects of P and six synthetic steroids (MPA, ENT, CAP, R2323, DL and EEL) on estradiol dehydrogenase (E2DH) activity were studied in normal human uterine endometrium in vitro. The mean value of E2DH activity in the proliferative endometrium was 1.5 +/- 0.2 nmol/mg protein/h and that in the secretory endometrium was 10.2 +/- 1.1 nmol/mg protein/h. There was a 7-fold increase in the secretory phase. E2DH activity in the uterine endometrium was stable during the culture period of up to 72 h. In the proliferative endometrium, P, MPA and ENT (approximately 10(-6)M) induced E2DH activity during a 24-h incubation. CAP and R2323 had no significant effect. EEL and DL had negligible effects. In contrast, E2DH activity in the secretory endometrium was not induced further by the steroids. Therefore, in the proliferative endometrium, the elevation of E2DH activity is attributable to the progestational activity and, in the secretory endometrium, E2DH activity is not increased further by the progestational agents because it has been already activated fully by P.

The relationship between 17 beta-hydroxysteroid dehydrogenase activity and oestrogen concentrations in human breast tumours and in normal breast tissue

The activity of 17 beta-hydroxysteroid dehydrogenase (17 beta HSD) was measured in human breast tumours and in normal breast tissue from premenopausal, perimenopausal and postmenopausal women. Enzyme activity was higher in tumour tissue than in normal tissue from the same breast and under the conditions of the assay the oxidation of oestradiol was higher than the reduction of oestrone. The physiological status of the women in the study did not relate to the activity of the enzyme in either normal or tumour tissue although fibroadenomas had less activity than adenocarcinomas. In postmenopausal women tumour tissue oestrogens were 2-3 fold higher than in normal tissue from the same breast. Furthermore, tumour tissue concentrations of oestradiol tended to be higher than those of oestrone although in normal tissue the two oestrogens were present in similar concentrations. In plasma from the same women oestrone was the predominant oestrogen. There appears to be no direct relationship between 17 beta HSD activity and oestrogen concentrations but the enzyme may play a part in determining the balance between oestrone and oestradiol according to substrate and cofactor availability.

Apparent immunologic nonidentity of human placental and endometrial 17beta-estradiol dehydrogenase

Immunohistochemical techniques were used to search for the presence of 17beta-estradiol dehydrogenase activity in human endometrial and placental tissues, with the use of antibodies raised against highly purified human placental 17beta-estradiol dehydrogenase. Sensitivity and specificity of the antibodies were documented by radioimmunoassay and immunodiffusion on cellulose acetate. Although staining was consistently demonstrated in the syncytiotrophoblast layer of term placentas, in both cytoplasm and nuclei, no immunohistochemical reaction was observed in endometrial samples. These results support the contention that placental 17beta-estradiol dehydrogenase is immunologically dissimilar from the endometrial enzyme.

17 beta-Hydroxysteroid dehydrogenase in monkey endometrium during the menstrual cycle and at the time of implantation

In order to furhter identify physiological similarities between 17 beta-hydroxysteroid dehydrogenase (HSD) in human and monkey endometrium and to evaluate the role of estradiol-17 beta (e2) oxidation to estrone (E1) during periimplantation events, 30 rhesus monkeys were studied at different intervals of the nonfertile menstrual cycle (days 8, 12, 15, 18 and 24). Also, five pregnant monkeys provided endometrial tissue on day 24 of the fertile menstrual cycle, near the expected time of implantation. HSD activity in endometrium was low at midfollicular phase (day 8), increased to maximal levels (8-fold) during the periovulatory span (days 12 and 15), and was intermediate in mid to late luteal phase (days 18 and 24) in non-fertile menstrual cycles. In the absence of ovulation, HSD was low throughout. These enzyme data fit with a pattern of daily peripheral serum levels of E2 and progesterone (P) and suggest that when the normal sequence of P follows elevated estrogens in late follicular phase, HSD activity is markedly enhanced in the early luteal phase. However, HSD activity in endometrium did not increase more in the fertile menstrual cycle, despite further elevations of serum P during rescue of the corpus luteum.

Steroidal control of rat uterine 17 beta-hydroxysteroid dehydrogenase activity

The interconversion of estradiol-17 beta and estrone in the rat uterus is due to the action of 17 beta-hydroxysteroid dehydrogenase. Whole uteri or 800 x g supernatant fractions of the uteri were incubated in the presence of [3H] estradiol-17 beta and NAD at 37 degrees C for 3 h or 1 h, respectively. In the mature rat uterus the oxidation of estradiol-17 beta and estrone was dependent on the stage of the estrous cycle, suggesting hormonal control. The 17 beta-hydroxysteroid dehydrogenase activity was highest at estrus (200 fmol estrone) and lowest at diestrus (80 fmol estrone). An enhancement of activity occurred when adult rats at each stage of the estrous cycle were administered estradiol-17 beta, while progesterone administration at each stage resulted in decreased enzyme activity. The uterine 17 beta-hydroxysteroid dehydrogenase activity of estradiol-17 beta treated ovariectomized rats was time and dose dependent but decreased when progesterone was administered with or without estradiol-17 beta administration. These results suggest that estradiol-17 beta caused an increase in enzyme activity that was inhibitable by progesterone in the rat uterus. The increased 17 beta-hydroxysteroid dehydrogenase activity may reflect a specific response of the rat uterus to estradiol-17 beta.

Estradiol and progesterone receptors in human endometrium: normal and abnormal menstrual cycles and early pregnancy

Estradiol and progesterone receptor sites (empty or filled with endogenous hormone)have been measured in the cytoplasm and nuclei of human endometrium. Receptor changes have been observed throughout the normal menstrual cycle. During the preovulatory phase the cytoplasmic estradiol receptor sites do not change while the nuclear receptor sites more than double. Cytoplasmic estradiol receptor sites decrease very early in the secretory phase, whereas the decrease in nuclear sites occurs later. Cytoplasmic progesterone receptor sites more than double during the preovulatory phase and show a large decrease immediately after ovulation, when the concentration of nuclear receptor is at its highest. Thus the total cellular concentrations of both estradiol and progesterone receptors are lowest in the late secretory phase. It was found that they are positively correlated with the concentration of plasma estradiol only during the proliferative phase. The concentration of cytoplasmic progesterone receptor is negatively correlated with 17 beta-hydroxysteroid oxidoreductase activity during the secretory phase. In anovulatory cycles the concentrations of estradiol and progesterone receptors are high, similar to those of the late proliferative phase. "luteal insufficiency" is characterized by a very low concentration of estradiol receptor. Early pregnancy endometrium (8 to 10 weeks' gestation) is characterized by a large concentration of progesterone receptor, exceeding those of any period of the menstrual cycle.

Endometrial estradiol-17 beta-dehydrogenase activity in women wearing Cu-IUD

In order to determine whether inhibition of the endometrial estradiol-17 beta-dehydrogenase activity by Cu++ could be one of the factors accounting for the enhanced contraceptive efficacy of copper intrauterine devices (Cu-IUD), the activity of the enzyme was measured in endometrial biopsies from women wearing this device. The levels of enzymatic activity found in these specimens were within the range of controls (women without IUD), e.g. 0.1--0.8 and 7--27 nmol E1 formed/mg protein/h in the follicular and luteal phases of the menstrual cycle, respectively. It is concluded that Cu-IUD does not modify significantly either the activity of endometrial-17 beta-dehydrogenase, an enzyme known to regulate the tissular concentration of estradiol, or its response to the inductive effect of progesterone.

17 beta-hydroxysteroid dehydrogenase in monkey endometrium: characterization of enzyme activity, and effects of estradiol alone or in combination with progesterone

17 beta-Hydroxysteroid dehydrogenase (HSD) was studied in endometrium removed surgically from intact female monkeys in the luteal phase of the menstrual cycle. Also castrated monkeys (N=20) implanted with estradiol (E2) and progesterone (P) in silastic capsules were used to investigate the hormonal dependence of this enzyme in endometrium. The activity was characterized by an optimal pH between 9 and 10, a Km for E2 of 14.2 x 10(-6)M, a Vmax of 0.9 x 10(-6)M x min-1 in Tris-HCl buffer 50 mM pH 9. Using these conditions, we found linearity with time and protein concentration. Subcellular fractionation of endometrial homogenate showed a maximal activity in the 105,000 x g ultracentrifugation microsomal pellet and a very low activity in cytosol. HSD activity increased slightly, but distinctly, with E2 capsules alone, and a marked HSD stimulation (10 fold) occurred after P administration in combination with E2. There are strong similarities between this enzyme and the one described in human endometrium.

In vitro conversion of estradiol-17beta into estrone in normal human myometrium and leiomyoma

The specific activity of 17beta-hydroxysteroid dehydrogenase was measured in normal human myometrium, and in leiomyoma specimens obtained from the same tumor-bearing uterus. In all cases the normal tissue showed greater conversion of estradiol-17beta into estrone than the neoplastic tissues. In normal myometrium of fertile women, the specific enzyme activity depended on the phase of the menstrual cycle, the highest values of 17beta-hydroxysteroid dehydrogenase activity being found in the early secretory phase. To determine the intracellular distribution of the 17beta-hydroxysteroid dehydrogenase, purified microsomes, mitochondria, nuclei and cytosol fractions were prepared. The purity of each fraction was monitored by marker enzymes. It was found that the enzyme was mainly located in mitochondria and microsomes. Furthermore it was demonstrated that the microsomal enzyme was bound tightly to the membranes of the endoplasmic reticulum, while the mitochondrial 17beta-hydroxysteroid dehydrogenase was mainly associated with the outer membranes of the organelle. Kinetic parameters (Km-values, coenzyme requirements, temperature and pH-optima) of the cytoplasmic, nuclear, mitochondrial and microsomal enzyme of normal and neoplastic tissue were compared.

Enzymatic modulation of hormonal action at the target tissue

The relevance of metabolism of steroids in target tissues to hormonal action is discussed. Two mechanisms of metabolic regulation at the cellular level are considered: formation of active steroids from steroidal prehormones, and controlled conversion of the active compound to inactive metabolites. Factors regulating the direction in which interconversions between active hormones and inactive metabolites preferentially proceed are mentioned; methods of estimating the preferred direction in vitro and in vivo are described and examples are given. The estradiol-estrone system in human endometrium is used to describe a case in which a hormone (progesterone) induces an enzymatic activity (17 beta-hydroxysteroid dehydrogenase) and lowers the intracellular/extracellular ratio of concentrations of the active hormone (estradiol) by increasing its conversion to an inactive, or less active, metabolite (estrone). That hormone metabolism can effectively determine the level of unbound hormone available for association to receptors is shown with published data on estradiol in human endometrium, using a kinetic analysis in which binding and Michaelis-Menten equations are combined.

Comparison of the in vitro conversion of estradiol-17 beta to estrone of normal and neoplastic human breast tissue

Specific activity of 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) was measured in 48 tissue specimens of human female breast cancer and, in addition, 48 nonmalignant tissue specimens obtained in each case from the same cancer-bearing breast. In all cases the nonmalignant tissue showed greater conversion of estradiol-17 beta into estrone than the neoplastic tissues. In normal human breast tissue of premenopausal women specific enzyme activity depended on the phase of the MENSTRUAL CYCLE: the highest values of 17 beta-HSD activity were found in the early secretory phase. To determine the intracellular distribution of the 17 beta-HSD, purified microsomes, mitochondria, peroxysomes, lysosomes, nuclei and cytosol fractions were prepared. The purity of each fraction was monitored by marker enzymes. It was found that the 17 beta-HSD was mainly located in mitochondria and microsomes. Furthermore it could be demonstrated that the microsomal enzyme was bound tightly to the membranes of the endoplasmic reticulum, while the mitochondrial 17 beta-HSD was mainly associated with the outer membranes of the organelle. Kinetic parameters (Km-values, coenzyme requirements and maximal velocities) of a cytoplasmic, nuclear, mitochondrial and microsomal 17 beta-HSD of normal and neoplastic human mammary tissue were compared. Maximal velocity was highest in enzyme preparations of normal mammary tissue obtained from premenopausal women in the early secretory phase. Km-values wrere nearly identical in normal and neoplastic mammary tissue preparations (approx. 1 X 10(-6) M). NAD was more efficient than NADP as a cofactor. For the conversion of estradiol to estrone the optimum temperature was approximately 40 degrees C and the optimum pH 9.5. For the reduction of estrone the optimum pH was 6.5. Sulphydryl groups were shown to be essential for catalysis.

17 beta-Hydroxysteroid dehydrogenase of the sheep ovary : purification, properties and substrate binding site

Sheep ovarian 17 beta HSDH has been purified about 1000 fold to a specific activity of 0.5 IU/mg protein, using DEAE cellulose chromatography, affinity chromatography on estrone-amino caproate-Sepharose and a second DEAE cellulose chromatography. The molecular weight is 70,000 ; the pH optimum for activity is 9.2 and the energy of activation is 16.5 Kcal/mole. The kinetics of the oxidation of estradiol and many analogues have been studied at various concentrations and in the presence of different amounts of coenzyme. The data are in agreement with a compulsory order mechanism with the binding of NAD+ as the first substrate. Sheep ovarian 17 beta HSDH accepts subtituents in position C3, C11, C13 ; the substrate binding site is open in this region. On the contrary, the binding requirements are strict for the region of C10 since the presence of a C19 methyl group impairs binding and (or) oxidation of the steroid. Sheep ovarian and human placental 17 beta HSDH have close analogies : molecular weight, pH optimum, substrate binding site requirements. Their reaction mechanisms are different : random for the placental 17 beta HSDH, compulsory order for the ovarian 17 beta HSDH : this can be explained by the effect of the coenzyme upon the binding of the substrate : without effect on placental enzyme, the coenzyme fixation enhances the affinity of the ovarian 17 beta HSDH for any substrate.