Progesterone metabolism by guinea pig intrauterine tissues

Are animal models relevant to key aspects of human parturition?

Preterm birth remains the most serious complication of pregnancy and is associated with increased rates of infant death or permanent neurodevelopmental disability. Our understanding of the regulation of parturition remains inadequate. The scientific literature, largely derived from rodent animal models, suggests two major mechanisms regulating the timing of parturition: the withdrawal of the steroid hormone progesterone and a proinflammatory response by the immune system. However, available evidence strongly suggests that parturition in the human has significantly different regulators and mediators from those in most of the animal models. Our objectives are to critically review the data and concepts that have arisen from use of animal models for parturition and to rationalize the use of a new model. Many animal models have contributed to advances in our understanding of the regulation of parturition. However, we suggest that those animals dependent on progesterone withdrawal to initiate parturition clearly have a limitation to their translation to the human. In such models, a linear sequence of events (e.g., luteolysis, progesterone withdrawal, uterine activation, parturition) gives rise to the concept of a "trigger" mechanism. Conversely, we propose that human parturition may arise from the concomitant maturation of several systems in parallel. We have termed this novel concept "modular accumulation of physiological systems" (MAPS). We also emphasize the urgency to determine the precise role of the immune system in the process of parturition in situations other than intrauterine infection. Finally, we accentuate the need to develop a nonprimate animal model whose physiology is more relevant to human parturition. We suggest that the guinea pig displays several key physiological characteristics of gestation that more closely resemble human pregnancy than do currently favored animal models. We conclude that the application of novel concepts and new models are required to advance translational research in parturition.

Dutasteride affects progesterone metabolizing enzyme activity/expression in human breast cell lines resulting in suppression of cell proliferation and detachment

Recent evidence indicates that progesterone metabolites play important roles in regulating breast cancer. Previous studies have shown that breast carcinoma and tumorigenic breast cell lines have higher 5alpha-reductase and lower 3alpha-hydroxysteroid oxidoreductase (3alpha-HSO) and 20alpha-HSO activities and mRNA expression levels than normal tissue and non-tumorigenic cell lines. The 5alpha-reduced progesterone metabolites such as 5alpha-dihydroprogesterone (5alphaP) promote both mitogenic and metastatic activity in breast cell lines in culture, whereas the 4-pregnene metabolites, 4-pregnen-3alpha-ol-20-one (3alphaHP) and 4-pregnen-20alpha-ol-3-one (20alphaHP) have the opposite (anti-cancer-like) effects. The 5alpha-reductase inhibitor dutasteride has been shown to inhibit 5alpha-reduction of testosterone to 5alpha-dihydrotestosterone in prostate tissue, resulting in decreased prostate volume. The aim of this study was to determine if dutasteride is an effective inhibitor of progesterone 5alpha-reduction in human breast cell lines and if such inhibition reduces mammary cell proliferation and detachment. The effect of dutasteride on progesterone metabolizing enzyme activities and mRNA expression were examined in tumorigenic MCF-7 and non-tumorigenic MCF-10A human breast cell lines. Dutasteride (10(-6)M) inhibited progesterone conversion to 5alpha-pregnanes by >95% and increased 4-pregnene production. The results indicated that effects of dutasteride on the progesterone metabolizing enzymes are due to direct inhibition of 5alpha-reductase activity and to altered levels of expression of 5alpha-reductase and HSO mRNAs. Treatment of cells with progesterone without medium change for 72 h resulted in significant conversion to 5alpha-pregnanes and increases in cell proliferation and detachment. The increases in proliferation and detachment were blocked by dutasteride and were reinstated by concomitant treatment with 5alphaP, providing proof-of-principle that the effects were due not to progesterone but to the 5alpha-reduced metabolites. This study provides the first evidence that dutasteride is a potent progesterone 5alpha-reductase inhibitor and that such inhibition may be beneficial in breast cancer.

The role of progesterone metabolites in breast cancer: potential for new diagnostics and therapeutics

Proliferative changes in the normal breast are known to be controlled by female sex steroids. However, only a portion of all breast cancer patients respond to current estrogen based endocrine therapy, and with continued treatment nearly all will become unresponsive and experience relapse. Therefore, ultimately for the majority of breast carcinomas, explanations and treatments based on estrogen are inadequate. Recent observations indicate that 5alpha-pregnane and 4-pregnene progesterone metabolites may serve as regulators of estrogen-responsive as well as unresponsive human breast cancers. The conversion of progesterone to the 5alpha-pregnanes is increased while conversion to the 4-pregnenes is decreased in breast carcinoma tissue, as a result of changes in progesterone metabolizing 5alpha-reductase, 3alpha-hydroxysteroid oxidoreductase (3alpha-HSO) and 20alpha-HSO activities and gene expression. The 5alpha-pregnane, 5alpha-pregnane-3,20-dione (5alphaP) stimulates, whereas the 4-pregnene, 3alpha-hydroxy-4-pregnen-20-one (3alphaHP), inhibits cell proliferation and detachment, by modulation of cytoskeletal and adhesion plaque molecules via the MAP kinase pathway and involving separate and specific plasma membrane-based receptors. The promotion of breast cancer appears to be related to changes in in situ concentrations of cancer-inhibiting and cancer-promoting progesterone metabolites. New diagnostic and therapeutic possibilities for breast cancer are suggested.

Activity and expression of progesterone metabolizing 5alpha-reductase, 20alpha-hydroxysteroid oxidoreductase and 3alpha(beta)-hydroxysteroid oxidoreductases in tumorigenic (MCF-7, MDA-MB-231, T-47D) and nontumorigenic (MCF-10A) human breast cancer cells

BACKGROUND

Recent observations indicate that human tumorous breast tissue metabolizes progesterone differently than nontumorous breast tissue. Specifically, 5alpha-reduced metabolites (5alpha-pregnanes, shown to stimulate cell proliferation and detachment) are produced at a significantly higher rate in tumorous tissue, indicating increased 5alpha-reductase (5alphaR) activity. Conversely, the activities of 3alpha-hydroxysteroid oxidoreductase (3alpha-HSO) and 20alpha-HSO enzymes appeared to be higher in normal tissues. The elevated conversion to 5alpha-pregnanes occurred regardless of estrogen (ER) or progesterone (PR) receptor levels. To gain insight into these differences, the activities and expression of these progesterone converting enzymes were investigated in a nontumorigenic cell line, MCF-10A (ER- and PR-negative), and the three tumorigenic cell lines, MDA-MB-231 (ER- and PR-negative), MCF-7 and T-47D (ER- and PR-positive).

METHODS

For the enzyme activity studies, either whole cells were incubated with [14C]progesterone for 2, 4, 8, and 24 hours, or the microsomal/cytosolic fraction was incubated for 15-60 minutes with [3H]progesterone, and the metabolites were identified and quantified. Semi-quantitative RT-PCR was employed to determine the relative levels of expression of 5alphaR type1 (SRD5A1), 5alphaR type 2 (SRD5A2), 20alpha-HSO (AKR1C1), 3alpha-HSO type 2 (AKR1C3), 3alpha-HSO type 3 (AKR1C2) and 3beta-HSO (HSD3B1/HSD3B2) in the four cell lines using 18S rRNA as an internal control.

RESULTS

The relative 5alpha-reductase activity, when considered as a ratio of 5alpha-pregnanes/4-pregnenes, was 4.21 (+/- 0.49) for MCF-7 cells, 6.24 (+/- 1.14) for MDA-MB-231 cells, 4.62 (+/- 0.43) for T-47D cells and 0.65 (+/- 0.07) for MCF-10A cells, constituting approximately 6.5-fold, 9.6-fold and 7.1 fold higher conversion to 5alpha-pregnanes in the tumorigenic cells, respectively, than in the nontumorigenic MCF-10A cells. Conversely, the 20alpha-HSO and 3alpha-HSO activities were significantly higher (p < 0.001) in MCF-10A cells than in the other three cell types. In the MCF-10A cells, 20alpha-HSO activity was 8-14-fold higher and the 3alpha-HSO activity was 2.5-5.4-fold higher than in the other three cell types. The values of 5alphaR:20alpha-HSO ratios were 16.9-32.6-fold greater and the 5alphaR:3alpha-HSO ratios were 5.2-10.5-fold greater in MCF-7, MDA-MB-231 and T-47D cells than in MCF-10A cells. RT-PCR showed significantly higher expression of 5alphaR1 (p < 0.001), and lower expression of 20alpha-HSO (p < 0.001), 3alpha-HSO2 (p < 0.001), 3alpha-HSO3 (p < 0.001) in MCF-7, MDA-MB-231 and T-47D cells than in MCF-10A cells.

CONCLUSION

The findings provide the first evidence that the 5alphaR activity (leading to the conversion of progesterone to the cancer promoting 5alpha-pregnanes) is significantly higher in the tumorigenic MCF-7, MDA-MB-231 and T-47D breast cell lines than in the nontumorigenic MCF-10A cell line. The higher 5alphaR activity coincides with significantly greater expression of 5alphaR1. On the other hand, the activities of 20alpha-HSO and 3alpha-HSO are higher in the MCF-10A cells than in MCF-7, MDA-MB-231 and T-47D cells; these differences in activity correlate with significantly higher expression of 20alpha-HSO, 3alpha-HSO2 and 3alpha-HSO3 in MCF-10A cells. Changes in progesterone metabolizing enzyme expression (resulting in enzyme activity changes) may be responsible for stimulating breast cancer by increased production of tumor-promoting 5alpha-pregnanes and decreased production of anti-cancer 20alpha--and 3alpha-4-pregnenes.

Synthesis, metabolism and levels of the neuroactive steroid, 3alpha-hydroxy-4-pregnen-20-one (3alphaHP), in rat pituitaries

The neuroactive steroid, 3a-hydroxy-4-pregnen-20-one (3alphaHP), is a metabolite of progesterone and a precursor of 3alpha-hydroxy-5alpha-pregnan-20-one (5alphaP3alpha; allopregnanolone). In addition to analgesic and anxiolytic effects by interaction with the GABA(A) receptor complex, 3alphaHP regulates pituitary FSH secretion by rapid non-genomic interaction with the Ca2+-driven cell signaling mechanisms. Since gonadectomy and adrenalectomy do not result in elimination of 3alphaHP, and since there is the possibility of paracrine and/or autocrine regulation of FSH release, the capacity of pituitary cells to regulate levels (by synthesis, metabolism, and storage) of 3alphaHP was examined. Anterior pituitaries from random cycling female rats were incubated, either as fragments or as cultured cells, for 1, 4 or 8 h with 3H- or 14C-labeled progesterone. The steroid metabolites were identified by thin-layer chromatography, autoradiography, high pressure liquid chromatography (HPLC), derivatization and GC/MS. Pituitary cells actively converted progesterone to 3alphaHP along with 5alphaP3alpha, 5alpha-pregnane-3,20-dione, 20alpha-hydroxy-5alpha-pregnan-3-one, 3beta-hydroxy-5alpha-pregnan-20-one, 5alpha-pregnane-3alpha(beta), 20alpha-diols, 20alpha-hydroxy-4-pregnen-3-one, and 4-pregnene-3alpha(beta), 20alpha-diols. The results indicate the presence of the following steroidogenic enzymes in anterior pituitary cells: 3alpha-hydroxysteroid oxidoreductase (3alpha-HSO), 20alpha-HSO, 3beta-HSO, and 5alpha-reductase. The activities of 5alpha-reductase and 3alpha-HSO were approximately equal and greatly exceeded those of the other enzymes. After 8 h of incubation with 100 ng progesterone per pituitary, about 20% of the progesterone was metabolized and 3.18 ng of 3alphaHP had been formed. The accumulation of 3alphaHP increased approximately linearly with the time of incubation. Metabolism studies using [1,2,6,7-(3)H]3alphaHP showed that pituitary cells convert about 29% and 8% of the 3alphaHP to progesterone and 5alphaP3alpha, respectively, in 2 h. Specific radioimmunoassays determined 11.6 and 7.5 ng of 3alphaHP per pituitary, respectively, in 25- and 40-day-old non-cycling female rats; these concentrations of 3alphaHP were about 2-3-fold greater than those of progesterone in the same pituitaries. In older (80-100 days old) cycling rats, the levels of 3alphaHP were about 9.4 and 18.6 ng/pituitary at 13.00 h and 22.00 h, respectively, on the day of proestrus, while the concomitant circulating levels were 13.7 and 5.4 ng/ml. The results indicate a marked capacity of rat pituitary cells to synthesize the neuroactive and FSH regulating steroid, 3alphaHP, from progesterone, and in turn to metabolize 3alphaHP to the neurosteroid, allopregnanolone, and to progesterone. The studies suggest cyclic biosynthetic and metabolic pathways for 3alphaHP and other steroids in the pituitary. They also indicate that the regulation of FSH secretion by 3alphaHP may be (in part, or in whole) via paracrine or autocrine mechanisms.

The effect of chorion-uterine interaction upon free progesterone metabolism during advanced gestation in the guinea pig

The in vitro fate of [3H]progesterone was studied after incubation with guinea pig tissues at 58/59 days (before pubic symphysis relaxation) and in the final week (post relaxation) of gestation. Buffered steroid was added to the fetal surface of chorion attached to the uterus or to the uterus alone. Neither the amount of recovered progesterone nor its metabolites (6.2% average conversion) differed between the two stages when only uterus was incubated. With chorion present, conversion averaged 28.3% at 58/59 days and 63.4% at the late stage. A 4.6-fold decrease in progesterone concentration, and 3.0-, 2.4- and 3.1-fold increases in the concentrations of 3alpha-hydroxy-5alpha-pregnan-20-one, 3beta-hydroxy-5alpha-pregnan-20-one and 5alpha-pregnane-3,20-dione, respectively, were found in the uterus in the late stage vs 58/59 days. Also, 2.8- and 6.4-fold decreases in progesterone concentration occurred in the myometrium and endometrium, respectively, from 58/59 days to the late stage. In endometrium, the concentrations of the 3alpha- and 3beta-isomers, and 5alpha-pregnane-3,20-dione, increased 2.6-, 2.6- and 5.0-fold, respectively. The above changes were all significant at P < 0.05 or better. Changes in the 3alpha-, 3beta- isomers and dione in the myometrium were not significant. The chorion-uterine interaction and gestation time thus affect the degree of progesterone conversion, and the amounts of metabolites reaching the uterus in the chorion-uterine in vitro system.