Steroid formation in osteoblast-like cells

Insulin Resistance and Bone Metabolism Markers in Women with Polycystic Ovary Syndrome: A Cross-Sectional Study on Females from the Islamic University Medical Center

Background and Objectives: polycystic ovarian syndrome (PCOS) prevails in females in the 18–40-year-old age group and varies from 5–20% depending on the demographic and diagnostic standards. It is unknown how long passes between the onset of a specific symptom and the appearance of the disease. The three most significant characteristics of PCOS include irregular menstruation, a polycystic ovarian shape found by pelvic ultrasound, and hyperandrogenism, which could possibly delay menarche. This study’s objective was to assess insulin resistance and bone bio-markers’ metabolism-involved characteristics of females with PCOS. Materials and Methods: We present a cross-sectional study carried out on 100 female patients suffering from PCOS and 100 healthy female subjects as a control living in Saudi Arabia in the Al-Madinah Al-Munawara Region between May 2021 and March 2022. The age of the studied groups ranges from 20–40 years, and patients were categorized into three groups; group I (control, n = 100), group IIa (overweight or obese females with PCOS, n = 70), and group IIb (non-obese females with PCOS, n = 30). The diagnosis of PCOS was carried out as per Rotterdam criteria as recommended for adolescent and adult subjects. All the groups were subjected to physical examination, and anthropometric measures, biochemical parameters, endocrine activity, and clinical parameters were determined. The data obtained were computerized and analyzed statistically using the SPSS program for range, mean, and standard deviation. ANOVA test with post hoc Tukey test was applied to assess the pattern and variation among the test and control groups. Results: In the present study, age, waist circumstances, systolic blood pressure, and diastolic blood pressure were reported enhanced in the PCOS over the control group. Additionally, anthropometric measures were reported slightly upregulated in group IIa over group IIb (p < 0.001). Biochemical parameters including glucose, insulin incidence, and lipids were reported higher in the PCOS over the control group, where group IIa showed slightly increased values compared to group IIb (p < 0.001). On the contrary, PTH, Ca+2, and 25(OH)D levels were reported lower in the PCOS over the control group. However, in the control groups, a slight variation was reported as higher in group IIa compared to group II. In the study, PTH and 25(OH)D were found associated with bone metabolism; a lower level of PTH and 25 (OH) D is linked with a decline in bone density. Conclusions: Lower serum levels of PINP and osteocalcin along with the 25(OH)D were associated with the PCOS compared to the control group, imposing a higher risk of the syndrome. On the contrary, an elevated level of NTx in groups IIa and IIb over the control group was associated with insulin resistance and bone metabolism.

Osteoblasts Generate Testosterone From DHEA and Activate Androgen Signaling in Prostate Cancer Cells

Bone metastasis is a complication of prostate cancer in up to 90% of men afflicted with advanced disease. Therapies that reduce androgen exposure remain at the forefront of treatment. However, most prostate cancers transition to a state whereby reducing testicular androgen action becomes ineffective. A common mechanism of this transition is intratumoral production of testosterone (T) using the adrenal androgen precursor dehydroepiandrosterone (DHEA) through enzymatic conversion by 3β- and 17β-hydroxysteroid dehydrogenases (3βHSD and 17βHSD). Given the ability of prostate cancer to form blastic metastases in bone, we hypothesized that osteoblasts might be a source of androgen synthesis. RNA expression analyses of murine osteoblasts and human bone confirmed that at least one 3βHSD and 17βHSD enzyme isoform was expressed, suggesting that osteoblasts are capable of generating androgens from adrenal DHEA. Murine osteoblasts were treated with 100 nM and 1 μM DHEA or vehicle control. Conditioned media from these osteoblasts were assayed for intermediate and active androgens by liquid chromatography-tandem mass spectrometry. As DHEA was consumed, the androgen intermediates androstenediol and androstenedione were generated and subsequently converted to T. Conditioned media of DHEA-treated osteoblasts increased androgen receptor (AR) signaling, prostate-specific antigen (PSA) production, and cell numbers of the androgen-sensitive prostate cancer cell lines C4-2B and LNCaP. DHEA did not induce AR signaling in osteoblasts despite AR expression in this cell type. We describe an unreported function of osteoblasts as a source of T that is especially relevant during androgen-responsive metastatic prostate cancer invasion into bone. © 2021 American Society for Bone and Mineral Research (ASBMR). This article has been contributed to by US Government employees and their work is in the public domain in the USA.

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.

Bone markers in polycystic ovary syndrome: A multicentre study

OBJECTIVE

Hyperandrogenism, hyperinsulinaemia and obesity, known characteristics of polycystic ovary syndrome (PCOS), may influence bone mineral density and biochemical markers of bone turnover (BTMs) can provide a noninvasive assessment of bone turnover. To this end, the serum concentrations of BTMs and 25-hydroxyvitamin D (25OHD) were analysed in women with PCOS, and their possible associations with metabolic parameters of PCOS were determined.

SUBJECTS AND METHODS

Bone formation markers procollagen type I amino-terminal propeptide (PINP) and osteocalcin (OC), and bone resorption marker carboxy-terminal cross-linking telopeptide of type I collagen (CTX), along with 25OHD, were measured in 298 women with PCOS and 194 healthy controls.

RESULTS

Serum levels of PINP (47.0 ± 20.2 vs 58.1 ± 28.6 μg/L, P < .001) and OC (18.2 ± 7.5 vs 20.6 ± 9.8 μg/L, P < .001) were decreased in women with PCOS compared with controls, whereas no significant differences were found in CTX and 25OHD levels. Age-stratified analyses suggested that PINP (50.5 ± 21.7 vs 68.2 ± 26.6 μg/L, P < .001) and OC levels (20.4 ± 7.6 vs 25.5 ± 9.6 μg/L, P < .001) were decreased only in the younger age group (≤30 years) women with PCOS compared with controls. The formation markers and resorption marker decreased with age in both study groups.

CONCLUSIONS

Bone formation markers were decreased in younger women with PCOS when compared with healthy women, which may affect bone mass in these women.

Steroid sulfatase mediated growth Sof human MG-63 pre-osteoblastic cells

Estrogen plays an important role in maintaining bone density. Postmenopausal women have low plasma estrogen, but have high levels of conjugated steroids, particularly estrone sulfate (E1S) and dehydroepiandrosterone sulfate (DHEAS). Conversion of these precursors to active estrogens may help maintain bone density in postmenopausal women. The enzyme steroid sulfatase (STS) converts sulfated steroids into active forms in peripheral tissues. STS occurs in bone, but little is known about its role in bone function. In this study, we investigated STS activity and expression in the human MG-63 pre-osteoblastic cell line. We also tested whether sulfated steroids can stimulate growth of these cells. MG-63 cells and microsomes both possessed STS activity, which was blocked by the STS inhibitors EMATE and 667 Coumate. Further evidence for STS in these cells was provided by RT-PCR, using STS specific primers, which resulted in cDNA products of the predicted size. We then tested for growth of MG-63 cells in the presence of estradiol-17β, E1S and DHEAS. All three steroids stimulated MG-63 cell growth in a steroid-free basal medium. We also tested whether the cell growth induced by sulfated steroids could be blocked using a STS inhibitor (667 Coumate) or using an estrogen receptor blocker (ICI 182,780). Both compounds inhibited E1S-induced cell growth, indicating that E1S stimulates MG-63 cell growth through a mechanism involving both STS and the estrogen receptor. Finally, we demonstrated using RT-PCR that MG-63 cells contain mRNA for both estrogen receptor alpha and estrogen receptor beta. Our data reveal that STS is present in human pre-osteoblastic bone cells and that it can influence bone cell growth by converting inactive sulfated steroids to estrogenic forms that act via estrogen receptor alpha or beta.

Expression of hormonal receptors in osteosarcomas of the jaw bones: clinico-pathological analysis of 21 cases

Background: Sexual hormones have an important role in many hormone-dependant tumors like breast and prostate carcinomas, and also a relationship has been found with bone metabolism and bone tumors. Some studies have demonstrated that the expression of hormonal receptors (HR) in osteosarcomas (OS) of long bones is associated with gender, histological grade, histological type, and possibly may be connection with pathogenesis and evolution. However, to our knowledge there are no studies of HR in osteosarcomas of craniofacial bones (OS-CF). Objectives: To assess the expression of hormonal receptors in OS-CF. Material and Methods: Twenty one cases of OS-CF were included in this study. Clinical outcome was obtained from clinical charts. Histological sections were reviewed, and immunohistochemistry studies for estrogen, progesterone and androgen receptors were performed. Results: A striking female predominance was found (2:1), with a median age of 35 years. The predominant type of OS was osteoblastic (52.4%), and histological grade was high in 86%. Follow-up was obtained in 13 cases and ranged from 6 to 118 months (median 29 months). There were 8 patients (61.5%) dead or alive with progressive disease in the last follow up. Negative expression of HR was found in 19/21 cases; one showed weak nuclear expression for estrogen receptor, and another for androgen receptor. Progesterone receptor was negative in all cases. Conclusions: OS-CF mostly affected females, most of them were of the osteoblastic type and of high grade. Hormonal expression was practically negative in osteosarcoma of craniofacial bones.

Key words:Osteosarcoma, jaws, estrogen, progesterone, androgen receptors.

Overexpression of steroid receptor coactivator-3 in bone cancers: an in vivo immunohistochemical study with tissue microarray

Bone tissue is steroid-responsive and profoundly regulated by steroids and/or their receptors. Bone cancers (either primary or metastatic) belong to the most dangerous tumors. Previous studies have demonstrated overexpression of steroid receptor coactivator-3 (SRC-3) in many cancers, such as breast cancer, prostate cancer, thyroid cancer, functioning in the regulation of cancer cell proliferation, invasion, and metastasis. However, so far, the expression and function of SRC-3 in bone cancers have not yet been clarified. In this study, nickel-intensified immunohistochemistry was conducted using a commercial tissue microarray (with 94 cases of bone cancer tissue and 10 normal bone tissues), and the 4-scoring system was employed to evaluate the expression levels of SRC-3 immunoreactivity. The results showed that in normal bone tissue, levels of SRC-3 are almost negative (score=0), the total positivity (score=1-3) of SRC-3 immunoreactivities in bone cancers was 74.47%. There were no significant differences in gender, status (malignant or benign) or (mean) age (p>0.05). The percentage of positivity was 77.78% in osteogenic tumors, 58.82% in cartilage tumors, 70% in giant cell tumors, 100% in hematopoietic tumors, 77.78% in miscellaneous lesions, and 75% in miscellaneous tumors. Age related differences of SRC-3 immunoreactivities were detected in cartilage tumors and giant cell tumors (p<0.05). The above results clearly demonstrated a high frequency of overexpression of SRC-3 immunoreactivities in different bone cancers, indicating its potential roles in the prognosis and treatment of these cancers.

Characterization of steroid sulfatase in the MC3T3-E1 mouse pre-osteoblastic cell line

Regulation of bone density is partly dependent upon steroid hormones, with estrogens playing an important role. Inactive conjugated estrogens may serve as precursors to active estrogens, especially in post-menopausal women, via steroid sulfatase, which converts conjugated estrogens into unconjugated estrogens. The purpose of this study was to characterize steroid sulfatase in the MC3T3-E1 mouse pre-osteoblastic cell line. Enzyme conversion assays were performed on whole MC3T3-E1 cells in culture and on microsomes prepared by differential centrifugation. (3)H-E(1)S and (3)H-DHEAS were used as tracers, and radioinert E(1)S and DHEAS were used as substrate. Whole cells and microsomes exhibited steroid sulfatase activity, which was blocked by the specific inhibitor estrone-3-O-sulfamate (EMATE). The K(m) of steroid sulfatase in microsomes averaged 83 μM when using E(1)S as substrate and 64 μM when using DHEAS. Western blotting of MC3T3-E1 microsomes for steroid sulfatase was performed, after SDS-PAGE, using an antibody generated against a peptide based on a conserved region of steroid sulfatase. Western blotting revealed three bands of cross-reactivity, ranging from 50 to 79 kDa. Reverse transcriptase polymerase chain reaction (RT-PCR), using specific primers, resulted in a single cDNA band of the expected size (100 bp) and sequence, indicating the presence of steroid sulfatase mRNA. Growth assays revealed that the MC3T3-E1 cells were stimulated by estradiol-17β, and also by estrone sulfate and DHEAS, revealing that the cells can use steroid sulfatase to produce active estrogens. Furthermore, growth of these cells in the presence of estradiol, estrone and estrone sulfate was inhibited by the estrogen receptor blocker ICI 182,780, indicating that stimulation of cell growth is mediated by the estrogen receptor. In our studies, four lines of evidence (enzyme activity, immunoassay, RT-PCR and growth assays) demonstrated the presence of steroid sulfatase in mouse MC3T3-E1 bone cells. The existence of steroid sulfatase in these pre-osteoblastic cells, along with the ability of sulfated steroids to promote their growth, suggest the possibility that this enzyme is involved in regulation of bone density in mice.

Steroid hormone metabolizing enzymes in benign and malignant human bone tumors

IMPORTANCE IN THE FIELD: Primary bone tumors are considered as (sex steroid) hormone-dependent tumors. Osteosarcoma, osteoblastoma and bone cysts are preferentially found in males, while giant cell tumors are more common in females. Indeed, bone tumor development and progression are influenced by sex steroid hormones derived from in situ synthesis in bone cells.

AREAS COVERED IN THIS REVIEW

This review describes intracrine mechanisms for local formation of the biologically most active estrogen, 17beta-estradiol (E2), from circulating steroid precursors through the 'aromatase' (aromatization of androgens) and the 'sulfatase' (conversion of inactive estrone-sulfate) pathway.

WHAT THE READER WILL GAIN

The reader gains knowledge on both pathways and the enzymes, which contribute to the in situ availability of active hormones, namely 3beta-hydroxysteroid dehydrogenases, 17beta-hydroxysteroid dehydrogenases, aromatase, steroid sulfatases and sulfotransferases. An overview is given and the expression and function of these enzymes in bone tumors are discussed.

TAKE HOME MESSAGE

Knowledge on pathways for the in situ formation of E2 in bone cells may allow the identification of potential targets for i) novel endocrine therapeutic options in primary bone tumors and ii) future preventive interventions.

Estrogen sulfotransferase (SULT1E1) expression in benign and malignant human bone tumors

BACKGROUND AND OBJECTIVES

17beta-estradiol regulates growth and differentiation in normal and malignant bone. E2 is inactivated to 17beta-estradiol-sulfate through estrogen sulfotransferase (SULT1E1).

RESULTS

In an explorative study, SULT1E1 mRNA expression was assessed in a broad range of samples from benign, primary and secondary malignant bone tumors. We detected SULT1E1 mRNA in 31/50 tumor samples (10/19 malignant, 6/13 benign tumors; 15/18 metastases). Significantly more SULT1E1-positive samples were found in metastases than in primary bone tumors (P = 0.019). Yet, there was no difference between malignant and benign primary tumors (P = 0.718). SULT1E1 mRNA levels were not related to patients' age, gender, tumor location, stage, grading, and chemotherapy pretreatment. Relative SULT1E1 mRNA levels did not correlate with that of estrogen-receptor alpha (ERalpha) as assessed by quantitative TaqMan PCR (10 malignant, 8 benign tissue samples). In the latter, ERalpha mRNA, but not SULT1E1 mRNA levels were significantly lower than in the malignant samples (P = 0.006 and P = 0.71, respectively). Also, pronounced expression of SULT1E1 mRNA but not of ERalpha mRNA was observed in osteosarcoma (MG-63, HOS) and Ewing's sarcoma (TC-71) cells, while human osteoblasts and BMSC contained ERalpha but not SULT1E1 mRNA.

CONCLUSION

Frequent expression of SULT1E1 mRNA in various human bone tumors suggests that sulfonation might be important to control E2 levels and activity.

Molecular biology of the 3beta-hydroxysteroid dehydrogenase/delta5-delta4 isomerase gene family

The 3beta-hydroxysteroid dehydrogenase/Delta(5)-Delta(4) isomerase (3beta-HSD) isoenzymes are responsible for the oxidation and isomerization of Delta(5)-3beta-hydroxysteroid precursors into Delta(4)-ketosteroids, thus catalyzing an essential step in the formation of all classes of active steroid hormones. In humans, expression of the type I isoenzyme accounts for the 3beta-HSD activity found in placenta and peripheral tissues, whereas the type II 3beta-HSD isoenzyme is predominantly expressed in the adrenal gland, ovary, and testis, and its deficiency is responsible for a rare form of congenital adrenal hyperplasia. Phylogeny analyses of the 3beta-HSD gene family strongly suggest that the need for different 3beta-HSD genes occurred very late in mammals, with subsequent evolution in a similar manner in other lineages. Therefore, to a large extent, the 3beta-HSD gene family should have evolved to facilitate differential patterns of tissue- and cell-specific expression and regulation involving multiple signal transduction pathways, which are activated by several growth factors, steroids, and cytokines. Recent studies indicate that HSD3B2 gene regulation involves the orphan nuclear receptors steroidogenic factor-1 and dosage-sensitive sex reversal adrenal hypoplasia congenita critical region on the X chromosome gene 1 (DAX-1). Other findings suggest a potential regulatory role for STAT5 and STAT6 in transcriptional activation of HSD3B2 promoter. It was shown that epidermal growth factor (EGF) requires intact STAT5; on the other hand IL-4 induces HSD3B1 gene expression, along with IL-13, through STAT 6 activation. However, evidence suggests that multiple signal transduction pathways are involved in IL-4 mediated HSD3B1 gene expression. Indeed, a better understanding of the transcriptional factors responsible for the fine control of 3beta-HSD gene expression may provide insight into mechanisms involved in the functional cooperation between STATs and nuclear receptors as well as their potential interaction with other signaling transduction pathways such as GATA proteins. Finally, the elucidation of the molecular basis of 3beta-HSD deficiency has highlighted the fact that mutations in the HSD3B2 gene can result in a wide spectrum of molecular repercussions, which are associated with the different phenotypic manifestations of classical 3beta-HSD deficiency and also provide valuable information concerning the structure-function relationships of the 3beta-HSD superfamily. Furthermore, several recent studies using type I and type II purified enzymes have elegantly further characterized structure-function relationships responsible for kinetic differences and coenzyme specificity.

Genomic and non-genomic actions of sex steroids in the growth plate

Sex steroids, and particularly estrogens, are important regulators of bone growth and bone mass accrual. For a long time, it was thought that these effects were mainly caused by their modulatory effects on the somatotrophic axis. Data gathered in the past years have challenged this view and it is now widely accepted that many of the effects of sex steroids on growth and bone mass accrual are caused by direct effects on target cells in the growth plate and bone. This review summarizes and discusses some of our latest findings on the expression of sex steroid receptors in the growth plate, the source of the ligands activating these receptors, and their putatitive mechanism of action predominantly focusing on observations in the rat.

Androgens and bone

Loss of estrogens or androgens increases the rate of bone remodeling by removing restraining effects on osteoblastogenesis and osteoclastogenesis, and also causes a focal imbalance between resorption and formation by prolonging the lifespan of osteoclasts and shortening the lifespan of osteoblasts. Conversely, androgens, as well as estrogens, maintain cancellous bone mass and integrity, regardless of age or sex. Although androgens, via the androgen receptor (AR), and estrogens, via the estrogen receptors (ERs), can exert these effects, their relative contribution remains uncertain. Recent studies suggest that androgen action on cancellous bone depends on (local) aromatization of androgens into estrogens. However, at least in rodents, androgen action on cancellous bone can be directly mediated via AR activation, even in the absence of ERs. Androgens also increase cortical bone size via stimulation of both longitudinal and radial growth. First, androgens, like estrogens, have a biphasic effect on endochondral bone formation: at the start of puberty, sex steroids stimulate endochondral bone formation, whereas they induce epiphyseal closure at the end of puberty. Androgen action on the growth plate is, however, clearly mediated via aromatization in estrogens and interaction with ERalpha. Androgens increase radial growth, whereas estrogens decrease periosteal bone formation. This effect of androgens may be important because bone strength in males seems to be determined by relatively higher periosteal bone formation and, therefore, greater bone dimensions, relative to muscle mass at older age. Experiments in mice again suggest that both the AR and ERalpha pathways are involved in androgen action on radial bone growth. ERbeta may mediate growth-limiting effects of estrogens in the female but does not seem to be involved in the regulation of bone size in males. In conclusion, androgens may protect men against osteoporosis via maintenance of cancellous bone mass and expansion of cortical bone. Such androgen action on bone is mediated by the AR and ERalpha.

Systemic and local regulation of the growth plate

The growth plate is the final target organ for longitudinal growth and results from chondrocyte proliferation and differentiation. During the first year of life, longitudinal growth rates are high, followed by a decade of modest longitudinal growth. The age at onset of puberty and the growth rate during the pubertal growth spurt (which occurs under the influence of estrogens and GH) contribute to sex difference in final height between boys and girls. At the end of puberty, growth plates fuse, thereby ceasing longitudinal growth. It has been recognized that receptors for many hormones such as estrogen, GH, and glucocorticoids are present in or on growth plate chondrocytes, suggesting that these hormones may influence processes in the growth plate directly. Moreover, many growth factors, i.e., IGF-I, Indian hedgehog, PTHrP, fibroblast growth factors, bone morphogenetic proteins, and vascular endothelial growth factor, are now considered as crucial regulators of chondrocyte proliferation and differentiation. In this review, we present an update on the present perception of growth plate function and the regulation of chondrocyte proliferation and differentiation by systemic and local regulators of which most are now related to human growth disorders.

Sex steroid metabolism in the tibial growth plate of the rat

To assess whether growth plate-specific production of sex steroids is possible, we have surveyed the presence of several key-enzymes involved in androgen and estrogen metabolism in the tibial growth plate of female and male rats during development. Using in situ hybridization, mRNAs of aromatase p450, type I and II 17beta-hydroxysteroid dehydrogenase (HSD), steroid sulfatase (STS), and 5alpha-reductase were detected in proliferating and hypertrophic chondrocytes of the growth plate. The former three were strongly up-regulated around sexual maturation (7 wk), whereas the latter two were expressed at a relatively constant level during development. These data were supported by measuring aromatase, type I 17beta-HSD, and STS enzyme activities in chondrocytes collected from tibial growth plates at 1 and 7 wk of age. Of the enzymes studied, there were minor differences between the sexes in aromatase and 5alpha-reductase expression only. In conclusion, our findings clearly indicate the presence of various enzymes involved in sex steroid metabolism in the tibial growth plate, especially in sexually maturing rats, a timepoint at which sex steroids have major effects on longitudinal growth. Our data suggest that intracrinology in the rat growth plate can occur and may be a major source of local sex steroid delivery.

Polycystic ovary syndrome, androgen excess, and the impact on bone

Polycystic ovary syndrome (PCOS) is a unique, natural model for the study of the influence of androgen excess on bone mass among women. Both thin and obese women develop PCOS, a presentation that allows for the evaluation of the effects of life-long obesity, alterations in body composition (central adiposity), and related metabolic abnormalities (hyperandrogenemia, hyperinsulinemia) on the skeleton. The relatively high prevalence of PCOS and its manifestation early in life render this disorder of particular importance in assessing the influence of androgens and androgen-estrogen balance on the attainment of maximal bone mass and subsequent development of osteoporosis later in life.

Sex steroids and bone

Sex steroids are essential for skeletal development and the maintenance of bone health throughout adult life, and estrogen deficiency at menopause is a major pathogenetic factor in the development of osteoporosis in postmenopausal women. The mechanisms by which the skeletal effects of sex steroids are mediated remain incompletely understood, but in recent years there have been considerable advances in our knowledge of how estrogens and, to a lesser extent androgens, influence bone modeling and remodeling in health and disease. New insights into estrogen receptor structure and function, recent discoveries about the development and activity of osteoclasts, and lessons learned from human and animal genetic mutations have all contributed to increased understanding of the skeletal effects of estrogen, both in males and females. Studies of untreated and treated osteoporosis in postmenopausal women have also contributed to this knowledge and have provided unequivocal evidence for the potential of high-dose estrogen therapy to have anabolic skeletal effects. The development of selective estrogen receptor modulators has provided a new approach to the prevention of osteoporosis and other major diseases of menopause and has implications for the therapeutic use of other steroid hormones, including androgens. Further elucidation of the mechanisms by which sex steroids affect bone thus has the potential to improve the clinical management not only of osteoporosis, both in men and women, but also of a number of other diseases related to sex hormone status.

Mechanical strain stimulates osteoblast proliferation through the estrogen receptor in males as well as females

Mechanical strain, testosterone, and estrogen all stimulate proliferation of primary cultures of male rat long bone (LOB)-derived osteoblast-like cells as determined by [3H]thymidine incorporation. The maximum proliferative effect of a single period of mechanical strain (3400 microepsilon, 1 Hz, and 600 cycles) is additional to that of testosterone (10(-8) M) or estrogen (10(-8) M). The cells' proliferative response to strain is abolished both by concentrations of tamoxifen that cause proliferation (10(-8) M) and by those that have no effect (10(-6) M). Strain-related proliferation also is reduced by the estrogen antagonist ICI 182,780 (10(-8) M) but is unaffected by the androgen receptor antagonist hydroxyflutamide (10(-7) M). Tamoxifen, ICI 182,780, and the aromatase inhibitor 4-dihydroandrostenedione, at concentrations that have no effect on basal proliferation, significantly reduce the proliferative effect of the aromatizable androgen testosterone but not that of the nonaromatizable androgen 5alpha-dihydrotestosterone. Hydroxyflutamide, at a concentration that has no effect on basal proliferation (10(-7) M), eliminates the proliferative effect of 5alpha-dihydro-testosterone but had no significant effect on that caused by testosterone. Proliferation associated with strain is blocked by neutralizing antibody to insulin-like growth factor II (IGF-II) but not by antibody to IGF-I. Proliferation associated with testosterone is blocked by neutralizing antibody to IGF-I but is unaffected by antibody to IGF-II. These data suggest that in rat osteoblast-like cells from males, as from females, strain-related proliferation is mediated through the estrogen receptor (ER) in a manner that does not compete with estrogen but that can be blocked by ER modulators. Proliferation associated with testosterone appears to follow its aromatization to estrogen and is mediated through the ER, whereas proliferation associated with 5alpha-dihydrotestosterone is mediated by the androgen receptor. Strain-related proliferation in males, as in females, is mediated by IGF-II, whereas proliferation associated with estrogen and testosterone is mediated by IGF-I.

Estradiol-17beta sulfotransferase activity in canine osteosarcoma D17 cells

Estrogen sulfatase and sulfotransferase (EST) activities are present in breast cancer tissues but there are no reports on EST in cancerous bone cells. We incubated [(3)H]estradiol-17beta with cells from a canine osteosarcoma D17 line for periods up to 24 h. Radioactive steroids were recovered from the media and separated into unconjugated and conjugated fractions using Sep-Pak C18 cartridges. The conjugate fraction was solvolyzed and the resulting free steroids were obtained from a second C18 cartridge. Little metabolism was apparent in 4 h of incubation, but by 24 h as much as one half of the radioactivity was seen in the conjugate fraction. Most of the conjugates were recovered as sulfates in all three experiments. HPLC profiles showed a limited metabolism of estradiol to other compounds except for estrone, which was clearly present in both free and sulfate fractions. These results suggest that EST may have a role in the local metabolism of estrogens in bone.

Effect of interleukin-1beta on aromatase activity and cell proliferation in human osteoblast-like cells (HOS)

Osteoblast cells have a capacity to produce estrogen from androgen. It is known that inflammatory cytokines in bone increase during estrogen deficiency. In the present study, the effect of interleukin-1beta (IL-1beta) on aromatase (Arom) activity in human osteoblast-like cells (HOS) was investigated. We also investigated the effect of IL-1beta and estradiol (E2) on cell proliferation in HOS. [(3)H] water method was employed to measure Arom activity. Expression of Arom mRNA was determined by the reverse-transcription polymerase chain reaction (RT-PCR) method. The PCR products were confirmed by Southern blot analysis. Cell proliferation was measured by an ELISA-bromo deoxyuridine (BrdU) kit. Addition of IL-1beta increased Arom activity in a dose-dependent manner and addition of IL-1beta (10 ng/ml) resulted in 40% greater activity than control. Addition of 500 ng/ml of human recombinant IL-1 receptor antagonist neutralized the increased Arom activity to control level. Stimulation of Arom mRNA expression by IL-1beta was also found. IL-1beta and E2 stimulate osteoblastic cell proliferation significantly. These findings suggest for the first time that IL-1beta stimulates Arom activity through the IL-1 receptor and also cell proliferation in osteoblast-like cells. It is also demonstrated that this stimulatory effect may be through the IL-1 receptor. Cell proliferation stimulated by IL-1beta was reduced by the addition of the Arom inhibitor fadrozole-HCL (CGS-16949A). These results imply that IL-1beta has a stimulatory effect on estrogen formation and sequentially cell proliferation in bone, and this mechanism may play an important role in osteoblastic function especially in postmenopausal women.