Androgen receptors in osteoblast-like cell lines

Bone health and prevalent fractures in women with polycystic ovary syndrome: a meta-analysis and endocrine-context pathophysiology review

INTRODUCTION

Bone health in those with Polycystic Ovary Syndrome (PCOS) is complex, but the general consensus is that cortical areal bone mineral density (aBMD) sites will be higher in PCOS than in age- and BMI-similar controls. However, spine aBMD sites may be lower, especially in non-obese PCOS. Whether or not incident fracture risk is increased in PCOS is currently controversial; no meta-analysis has yet assessed prevalent fractures.

AREAS COVERED

We assessed the bone effects of PCOS-related ovarian hormone alterations, e.g. androgen excess, tonically normal/higher estradiol, and lower-than-normal progesterone levels. We also highlighted evidence that common PCOS medications (e.g. combined hormonal contraceptives [CHC], metformin, and spironolactone) have important bone effects. In adolescents, meta-analysis of CHC showed significant negative aBMD changes. Inflammation has negative PCOS bone effects and is linked with CHC use.

EXPERT OPINION

Is fracture risk altered by PCOS? Our meta-analysis showed a 25% increased risk of prevalent fracture in PCOS versus controls; this did not reach statistical significance. Future prospective research needs to collect and evaluate ovulation characteristics, progesterone exposure, and adolescent CHC use, in addition to the complex variables that may influence risks for prevalent or incident fragility fractures and/or for cortical and cancellous aBMD values in PCOS.

Design, synthesis and characterization of a PEGylated stanozolol for potential therapeutic applications

Stanozolol (STZ) is a drug used to treat serious disorders like aplastic anemia and hereditary angioedema. It is also indicated as an adjunct therapy for the treatment of vascular disorders and growth failures. Encouraging results obtained using animal models demonstrated that STZ increases bone formation and mineralization, thus improving both density and biomechanical properties. Like natural androgens, such as TST and 5α-dihydrotestosterone (5α-DHT), STZ binds androgen receptor (AR) to activate AR-mediated signaling. Despite its therapeutic effects, this synthetic anabolic-androgenic steroid (AAS), or 5α-DHT derivative, due to its high lipophilicity, is poor soluble in water. Thus, to increase the water solubility and stability of STZ, as well as its bioavailability and efficacy, an innovative PEGylated STZ (STZ conjugated with (MeO-PEG-NH₂)_10kDa, (MeO-PEG-NH)_10kDa-STZ) was synthesized. As confirmed by chromatography (RP-HPLC) and spectrometry (ATR-FTIR, ¹H NMR, elemental CHNS(O) analysis, MALDI-TOF/TOF) analyses, a very pure, stable and soluble compound was obtained. Acetylcholinesterase (AChE) competitive ELISA demonstrated that the resulting PEGylated STZ competes against biological TST, especially at lower concentrations. Cytotoxicity of increasing concentrations (1, 10, 25 or 50 µM) of STZ and/or (MeO-PEG-NH)_10kDa-STZ was also evaluated for up 80 h by performing the MTT assay on human osteosarcoma Saos-2 cells, which express AR and are responsive to STZ. PEGylation mitigated cytotoxicity of STZ, by increasing the cell viability values, especially at higher drug concentrations. Furthermore, these results suggest that (MeO-PEG-NH)_10kDa-STZ is a promising and reliable drug to be used in clinical conditions in which TST is required.

Androgens and Androgen Receptor Actions on Bone Health and Disease: From Androgen Deficiency to Androgen Therapy

Androgens are not only essential for bone development but for the maintenance of bone mass. Therefore, conditions with androgen deficiency, such as male hypogonadism, androgen-insensitive syndromes, and prostate cancer with androgen deprivation therapy are strongly associated with bone loss and increased fracture risk. Here we summarize the skeletal effects of androgens—androgen receptors (AR) actions based on in vitro and in vivo studies from animals and humans, and discuss bone loss due to androgens/AR deficiency to clarify the molecular basis for the anabolic action of androgens and AR in bone homeostasis and unravel the functions of androgen/AR signaling in healthy and disease states. Moreover, we provide evidence for the skeletal benefits of androgen therapy and elucidate why androgens are more beneficial than male sexual hormones, highlighting their therapeutic potential as osteoanabolic steroids in improving bone fracture repair. Finally, the application of selective androgen receptor modulators may provide new approaches for the treatment of osteoporosis and fractures as well as building stronger bones in diseases dependent on androgens/AR status.

Endocrine Disruptors: A Critical Review of In Vitro and In Vivo Testing Strategies for Assessing Their Toxic Hazard to Humans

Currently, there is much concern that a wide range of both synthetic and naturally occurring environmental chemicals can act as endocrine disruptors (EDs), and can adversely affect humans and wildlife. Many in vivo and in vitro tests have been proposed for screening EDs, and several regulatory agencies, including the US Environmental Protection Agency (EPA), have recommended tier-testing schemes. Unfortunately, most of the proposed toxicity tests have substantial problems, including non-specificity and lack of reproducibility. There is also uncertainty concerning their relevance for generating useful hazard data for risk assessment purposes, in view of the diversity of the possible ED mechanisms of action (for example, receptor binding, steroidogenesis and modulation of the homeostatic processes which regulate endogenous responses to hormones). Moreover, most of the suggested test methods have yet to be validated according to internationally accepted criteria, although the OECD and the US EPA have defined tests for validation, and an interlaboratory “prevalidation” exercise has been initiated by the OECD. All this is compounded by the lack of information regarding human exposure levels to EDs, and a lack of direct evidence for a causal link between exposure and the development of adverse human health effects. In addition, the regulatory testing of EDs has important negative implications for animal welfare, as some of the proposed in vivo tests require large group sizes of animals and stressful procedures. From a detailed analysis of the available published literature, it is concluded that it is impossible to assess the relative values of currently available in vitro and in vivo toxicity tests for EDs, or to recommend any test or test battery. Any plans for the widespread testing of EDs are therefore premature and might be unnecessary, at least for detecting possible human effects. Several recommendations are made for rectifying this unsatisfactory situation, including the postponement of screening programmes pending: a) more information on human exposure; b) further details of the mechanisms of action of EDs; and c) the development of improved tests, followed by their proper scientific validation.

Stanozolol promotes osteogenic gene expression and apposition of bone mineral in vitro

Stanozolol (ST) is a synthetic androgen with high anabolic potential. Although it is known that androgens play a positive role in bone metabolism, ST action on bone cells has not been sufficiently tested to support its clinical use for bone augmentation procedures. Objective: This study aimed to assess the effects of ST on osteogenic activity and gene expression in SaOS-2 cells. Material and Methods: SaOS-2 deposition of mineralizing matrix in response to increasing doses of ST (0-1000 nM) was evaluated through Alizarin Red S and Calcein Green staining techniques at 6, 12 and 24 days. Gene expression of runt-related transcription factor 2 (RUNX2), vitamin D receptor (VDR), osteopontin (SPP1) and osteonectin (ON) was analyzed by RT-PCR. Results: ST significantly influenced SaOS-2 osteogenic activity: stainings showed the presence of rounded calcified nodules, which increased both in number and in size over time and depending on ST dose. RT-PCR highlighted ST modulation of genes related to osteogenic differentiation. Conclusions: This study provided encouraging results, showing ST promoted the osteogenic commitment of SaOS-2 cells. Further studies are required to validate these data in primary osteoblasts and to investigate ST molecular pathway of action.

Recent experimental and clinical findings in the skeleton associated with loss of estrogen hormone or estrogen receptor activity

Studies on rodent models and rare human disorders of estrogen production or response have revealed an increased complexity of the actions of estrogen on bone. ERalpha disruption in human males results in delayed epiphyseal maturation, tall stature, trabecular thinning, marked cortical thinning, genu valgum and significantly reduced cortical vBMD, but trabecular number is preserved and there is normal to increased periosteal expansion. Aromatase deficiency results overall in a similar phenotype, although less is known about skeletal architecture. Importantly, estrogen replacement in these individuals, even if provided late in the third decade, may normalize aBMD. Less certain is whether there is complete recovery of normal skeletal architecture and strength. Rodent models, in general, are consistent with the human phenotype but are confounded by inherent differences between mouse and human physiology and issues regarding the completeness of the different knock-out lines. Both human and rodent studies suggest that residual effects of estrogen through ERbeta, truncated ERalpha forms or nonclassical estrogen receptors might account for different phenotypes in the hERKO man, aromatase deficient subjects and rodents. Importantly, androgen, particularly by preserving trabecular number and augmenting both periosteal and epiphyseal growth, also has significant actions on bone.

Dihydrotestosterone Stimulates Proliferation and Differentiation of Fetal Calvarial Osteoblasts and Dural Cells and Induces Cranial Suture Fusion

BACKGROUND

The higher prevalence of metopic and sagittal suture synostosis in male infants suggests a role for androgens in early craniofacial development. These experiments characterize the influence of androgen stimulation on growth and differentiation of fetal dural and calvarial bone cells and on cranial suture fusion.

METHODS

Primary murine fetal (E18) dural cells and calvarial osteoblasts were isolated and cultured. Cells were treated for 48 hours with 5alpha-dihydrotestosterone (0 to 1000 nM). Cell proliferation was examined by nonradioactive proliferation assay; mRNA expression of alkaline phosphatase, transforming growth factor (TGF)-beta1, and the bone matrix proteins osteopontin, osteocalcin, and type 1 collagen was determined by reverse-transcriptase polymerase chain reaction. In separate experiments, intact fetal calvariae were grown in tissue culture with 10 nM 5alpha-dihydrotestosterone for 7 and 14 days and then examined histologically.

RESULTS

Androgen stimulation at 5 nM increased proliferation of fetal dural cells by 46.0 percent and of fetal calvarial osteoblasts by 20.5 percent. Dural expression of osteopontin, osteocalcin, and type 1 collagen was enhanced by 5alpha-dihydrotestosterone, as was that of TGF-beta1 and alkaline phosphatase. Androgen stimulation increased calvarial osteoblast expression of alkaline phosphatase and TGF-beta1 but induced little change in expression of osteocalcin, osteopontin, and type 1 collagen. In tissue culture, 5alpha-dihydrotestosterone stimulated osteoid formation and fusion of sagittal sutures.

CONCLUSIONS

Androgen stimulation of dural cells and osteoblasts isolated from fetal calvaria promotes cell proliferation and osteoblastic differentiation and can induce cranial suture fusion. These results suggest that sex steroid hormone signaling may stimulate sutural osteogenesis by means of osteodifferentiation of dural cells, thus explaining the male prevalence of nonsyndromic craniosynostosis.

The effect of orchidectomy on thyroid C cells and bone histomorphometry in middle-aged rats

This study was to evaluate the effect of androgen deficiency on thyroid immunoreactive C-cells and bone structure and function in a male orchidectomized middle-aged rat model. Fifteen-month-old male Wistar rats were divided into orchidectomized (Orx) and the sham-operated control (Sham) group. In the Orx group significant decreases (P < 0.05) were found in the volume of C cells (by 14%), their relative volume density (by 13%) and serum calcitonin concentration (by 54%) compared to the controls. Analyses of trabecular microarchitecture of the proximal tibia metaphysis showed that Orx induced marked decreases of cancellous bone area, trabecular thickness and trabecular number (by 52, 20 and 19% respectively; P < 0.05), whereas trabecular separation was increased by 27% (P < 0.05). In Orx rats, serum osteocalcin concentration was increased by 119% (P < 0.05), while serum calcium and phosphorus were 6 and 14% (P < 0.05) lower, respectively, compared to the levels in the Sham. In addition, urine calcium content was considerably higher (by 129%; P < 0.05) in Orx animals. These findings indicate that the androgen deficiency caused by Orx in middle-aged rats modulated the structure of C cells and diminished secretion of calcitonin. Histomorphometrical and biochemical analyses demonstrated a decrease of cancellous bone mass and increased bone turnover.

Periodontal status in men with hypergonadotropic hypogonadism: effects of testosterone deficiency

BACKGROUND

The purpose of this clinical study was to evaluate the possible influence of testosterone hormone on common clinical measurements of periodontal disease in men with hypergonadotropic hypogonadism.

METHODS

Twenty-four hypergonadotropic hypogonadal men (H) and 24 systemically healthy men (S) were divided into two groups as chronic periodontitis and clinically healthy controls after clinical examinations and radiographs. The H group consisted of 12 control (H/C) and 12 chronic periodontitis (H/P) patients, and the S group consisted of 12 control (S/C) and 12 chronic periodontitis (S/P) patients. Plaque index (PI), gingival index (GI), bleeding on probing (BOP), probing depth (PD), and clinical attachment loss (CAL) scores were recorded.

RESULTS

The mean of all clinical parameters (PI, GI, BOP, PD, and CAL) were significantly (P<0.05) higher in periodontitis groups (H/P and S/P) than controls (H/C and S/C). There were no significant differences in the PD and CAL scores between periodontitis groups (S/P and H/P). The mean of GI and BOP scores were statistically higher in the H/P group than the S/P group (P<0.05). There was a negative correlation between GI and free testosterone levels (r=-0.794; P<0.05).

CONCLUSION

According to these results, serum testosterone levels may possibly influence periodontal disease in men, and testosterone may have an inhibitory effect on gingival inflammation.

Estrogen and testosterone use different cellular pathways to inhibit osteoclastogenesis and bone resorption

Using human peripheral blood CD14(+) osteoclast precursors, we show that testosterone directly inhibits osteoclast formation and bone resorption at physiological concentrations. Instead, estrogen has no direct effects, whereas its action seems to be mediated through osteoblasts by producing osteoprotegerin. Both estrogen and testosterone acts through their cognate receptors.

INTRODUCTION

Estrogen (E2) deficiency is associated with both the development of postmenopausal and senile form of osteoporosis in elderly women. Testosterone (Te) deficiency, on the other hand, may cause osteoporosis in men. In both sexes, osteoporosis is associated with disturbed bone turnover, including increased bone resorption caused by enhanced osteoclast formation and increased osteoclast activity. However, the mechanisms by which E2 or Te act on bone are not fully understood, and one of the central questions is whether these hormones act directly on osteoclast precursors or whether their action is mediated through osteoblastic cells.

MATERIALS AND METHODS

We cultured human peripheral blood CD14(+) osteoclast precursors in the presence of RANKL, macrophage-colony stimulating factor (M-CSF), TNF-alpha, and dexamethasone to induce them to differentiate into osteoclasts. To study the possible osteoblast-mediated effects, osteoclast precursors were also co-cultured either with human MG-63 or SaOS-2 osteoblast-derived osteosarcoma cells. These cultures were treated with 10(-8)-10(-12) M of E2 or Te for 7 days.

RESULTS

E2 did not have any direct effect on osteoclast formation, whereas testosterone inhibited osteoclast formation and bone resorption in a dose-dependent manner. In co-cultures, where MG-63 or SaOS-2 cells were present, E2 and Te inhibited osteoclast formation in a dose-dependent manner. At the same time, E2 and Te treatment in MG-63 or SaOS-2 cell-containing cultures stimulated significantly the formation of osteoprotegerin (OPG) compared with untreated cultures measured by ELISA assay from the culture medium. The effects of E2 and Te on osteoclast formation and bone resorption were completely antagonized by an E2 receptor (ER) antagonist, ICI 182,780, and an androgen receptor (AR) antagonist, flutamide, suggesting ER- and AR-mediated mechanisms, respectively, in these cultures.

CONCLUSIONS

Te is likely to have direct and indirect inhibitory effects on human osteoclast formation and bone resorption, whereas the effect of E2 on osteoclast precursors and osteoclasts seems to be mediated by osteoblastic cells. Inhibitory effect of E2 is associated with the stimulated secretion of OPG by osteoblast-derived osteosarcoma cells. Mechanism of action of E2 and Te is mediated by ER and AR, respectively.

Endogenous sex steroids and bone mineral density in healthy men

OBJECTIVE

To evaluate the role of endogenous sex steroids on bone mineral density (BMD) in healthy Turkish men.

METHODS

Serum total testosterone (TT), free testosterone (FT), dehydroepiandrosterone sulfate and estradiol levels were assayed in 174 healthy men of 240 volunteers, aged 22-76 years. Dual-energy X-ray absorptiometry was used to measure the BMD (g/cm(2)) of lumbar spine, femoral neck and non-dominant proximal and distal radius-ulna sites. Linear regressions were conducted using each BMD site as the dependent variable and each sex steroid as the independent variable. Four models were run for each bone site and sex steroid; crude, age-adjusted, adjusted for age and body mass index (BMI), and adjusted for age, BMI and cigarette-smoking.

RESULTS

The mean age and BMI of men enrolled in the study were 47.7 +/- 13.7 years and 26.9 +/- 3.6 kg/m(2). Log of FT was significantly associated with the BMD of distal forearm in all models analyzing the crude and adjusted effects. Dehydroepiandrosterone sulfate effect on BMD of proximal forearm came closer to the level of statistical significance when adjusted with age, BMI and cigarette-smoking. Estradiol and TT levels were not found to be associated with BMD of any sites measured.

CONCLUSION

Among the endogenous sex steroids in men, predominantly FT seems to be one of the determinants of BMD. Therefore a decrease in serum levels of testosterone in aging male or secondary causes may negatively affect BMD.

Androgen replacement in adolescents and young women with hypopituitarism

The aim of this study was to test the hypothesis that young women with androgen deficiency due to hypopituitarism would benefit from androgen replacement in the form of dehydroepiandrosterone (DHEA). Five young women, age 15.2-23.1 years, with panhypopituitarism were studied in a 12-month double blind placebo-controlled crossover trial of DHEA replacement in a dose 50 mg/day (Belmar Pharmacy, Lakewood, CO). All had growth hormone (GH), thyroid stimulating hormone (TSH), adrenocorticotropic hormone (ACTH) and antidiuretic hormone deficiencies. Gonadotropin deficiency was complete in three and partial in two. The patients were evaluated at baseline, 6 months and 12 months. Serum hormone levels, body composition, lumbar bone mineral density (BMD), exercise capacity and tests of psychological function were performed. DHEA replacement restored serum DHEA levels to normal, 359.8+/-337 ng/dl (12.5+/-11.7 nmol/l). The Life Situation Survey showed significantly better life satisfaction on DHEA than placebo (110 vs 102, p = 0.05). Trends for improved maximal oxygen uptake (VO2), and decreased percent body fat did not reach statistical significance. In conclusion, androgen replacement with DHEA should be considered in young women with panhypopituitarism. Further studies over longer periods in larger groups of patients are necessary to better evaluate the effects of DHEA replacement on BMD, muscle strength and body composition.

Immunolocalization of androgen receptor in the developing craniofacial skeleton

Male predominance in metopic and sagittal craniosynostosis and in nonsynostotic plagiocephaly suggests a role for circulating androgens in early craniofacial development. Androgens have been documented to play an important role in postnatal skeletal growth, and the androgen receptor has been recently demonstrated in human and rat osteoblast-like cell lines and in human long bones. The purpose of this study was to describe the expression of androgen receptor in the fetal craniofacial skeleton. The heads of E18 fetal CD-1 male and female mice were fixed in 10% formalin, decalcified, and embedded in paraffin. Four- to 6-mum coronal and sagittal sections were stained with a monoclonal antibody specific to androgen receptor, which was detected by an avidinbiotin conjugate and peroxidase system. The sections were then examined for androgen receptor expression patterns. Strong androgen receptor immunoreactivity was observed in the dura mater of developing fetuses. Androgen receptor expression was also noted in cells lining the osteogenic fronts and in calvarial osteoblasts. Similar androgen receptor expression patterns were found in male and female mice. Androgen receptor is abundantly expressed in fetal dura mater and calvarial bone. This study confirms the presence of androgen receptor in the murine fetal craniofacial skeleton, suggesting a potential role for the anabolic effects of androgens in the developing craniofacial skeleton.

Male Osteoporosis

Osteoporosis is a common condition in men affecting approximately 2 million males in the US. Compared with women, osteoporosis develops later in life and the incidence of osteoporosis-related fractures is lower in men. The morbidity and mortality associated with osteoporotic fractures are much greater in men compared with women, and secondary causes of osteoporosis are more frequently (in approximately 50% of cases) identified in men compared with women with osteoporosis. Excessive alcohol consumption, glucocorticoid excess and hypogonadism are the most commonly identified causes. Primary osteoporosis in men has been linked to changes in sex steroid secretion, the growth hormone-insulin-like growth factor-1 (GH-IGF-1) axis and the vitamin D-parathyroid hormone (PTH) 25-hydroxyvitamin D [25(OH)D]-PTH system. Diagnosing osteoporosis in men is complicated by an ongoing debate on whether to use sex-specific reference values for bone mineral density (BMD) or female reference values. The International Society for Clinical Densitometry recommended using a T score of -2.5 or less of male reference values to diagnose osteoporosis in men who are > or =65 years of age. However, this definition is yet to be validated in terms of fracture incidence and prevalence. Ensuring adequate calcium and vitamin D intake is the cornerstone of any regimen aimed at preventing or treating osteoporosis in men. Bisphosphonates are currently the therapy of choice for treatment of male osteoporosis. A short course of parathyroid hormone (1-34) [teriparatide] may be indicated for men with very low BMD or in those in whom bisphosphonate therapy is unsuccessful. The use of testosterone-replacement therapy for the prevention and treatment of male osteoporosis remains controversial but likely to benefit osteoporotic men with evident hypogonadism.

Androgens Repress the Expression of the Angiogenesis Inhibitor Thrombospondin-1 in Normal and Neoplastic Prostate

In order to understand why the angiogenesis inhibitor thrombospondin-1 (TSP1) is often, although not always, associated with prostatic tumors, we have investigated its relationship with the testosterone and the vasculature on which both normal and tumorigenic prostatic epithelia depend. In vivo, androgen withdrawal led to increased TSP1 production and decreased vascularization in the normal rat prostate which was reversed by androgen replacement. Androgen repression of TSP1 production occurred at the transcriptional level and was dependent on the presence of the first intron of the TSP1 gene. In an experimental model of prostate tumorigenesis, TSP1, when delivered by admixed stromal fibroblasts, markedly delayed LNCaP tumor growth and limited tumor vascularization. However, prolonged exposure to TSP1 resulted in the growth of tumors secreting high levels of vascular endothelial growth factor in the bloodstream of tumor-bearing animals and tumor growth was no longer sensitive to TSP1 inhibitory effects. Clinical evidence also suggested that prostate carcinomas are able to adapt to escape the antiangiogenic effects of TSP1. In human androgen–dependent localized prostate carcinomas, TSP1 expression was inversely correlated with blood vessel density. Androgen deprivation in patients with hormone-responsive tumors led to increased TSP1 expression and vascular regression. In contrast, despite a sustained expression in the tumor bed, TSP1 was no longer associated with decreased vascularization in hormone-refractory prostate tumors. Overall, these results suggest that the high in situ TSP1 exposure triggered by androgen deprivation in patients with prostate cancer could lead to early tumor resistance. Such patients could benefit from a combination of androgen deprivation and antiangiogenic therapy in order to minimize the induction of such tumor escape.

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.

Effect of ovariectomy on dexamethasone- and progesterone-dependent osteoprogenitors in vertebral and femoral rat bone cell populations

We have found previously that the skeleton of adult female rats contains dexamethasone (Dex)- and progesterone (Prog)-dependent osteoprogenitors, and that estrogen treatment in vitro upregulates proliferation and differentiation of the Prog-dependent but not of the Dex-dependent osteoprogenitors (Bone 1997;20:17-25). The purpose of the present study was to determine whether ovariectomy (OVX) would have different effects on these two classes of osteoprogenitors. Six-month-old Sprague-Dawley rats underwent OVX and the lumbar vertebrae and proximal femurs were collected 1.5, 3, and 6 months after OVX. Cells were obtained from outgrowths of explant cultures and grown in alpha-MEM with 10% FBS, 50 microg/ml ascorbic acid, and 5 mM beta-glycerophosphate. Osteoprogenitors were identified by their ability to generate a colony of osteoblastic cells forming bone (bone nodule). We also evaluated the number of colony-forming units-fibroblast (CFU-F) and of alkaline phosphatase (AP)-positive CFU-F. In cell populations obtained from vertebrae of rats ovariectomized for 1.5, 3, and 6 months and their corresponding control rats, both Dex (1-100 nM) and Prog (1-10 microM) dose-dependently stimulated nodule formation. Both Dex- and Prog-induced nodule formation were higher in cell populations from control rats than in those from ovariectomized rats (P < 0.001). Numbers of CFU-F and AP-positive CFU-F were also higher in cell populations from control rats compared with those from ovariectomized rats. Estrogen (10 nM) enhanced Prog-dependent bone nodule formation but decreased Dex-dependent bone nodule formation in populations from both control and ovariectomized rats. In femoral populations, the responses to Dex (10 nM), Prog (3 microM), and estrogen (10 nM) were similar to those of the vertebral populations in both control and ovariectomized rats. Our results demonstrate that ovariectomy in rats results in a dramatic decrease in the number of both Dex- and Prog-dependent osteoprogenitors in cell populations from vertebrae and proximal femurs. In addition, we confirmed our previous observation that estrogen upregulated proliferation and differentiation of Prog-dependent progenitors, but found here that estrogen clearly downregulated proliferation and differentiation of the Dex-dependent progenitors.

Effects of combined androgen blockade on bone metabolism and density in men with locally advanced prostate cancer

OBJECTIVE

To investigate whether combined androgen blockade (CAB) produces any adverse effects on bone metabolism and mineral density in patients with locally advanced prostate cancer.

MATERIALS AND METHODS

The study group consisted of 17 stage T4 prostate cancer patients treated with CAB and had no evidence of bone metastasis on bone scintigraphy. The mean duration of CAB and final total prostate specific antigen (PSA) level at the time of study were found at 28.5 +/- 15.9 (6-58) months and 0.39 +/- 0.5 (0.1-2) ngml, respectively. Twenty age and socioeconomically matched benign prostate hyperplasia (BPH) patients were taken as the control group. Both groups were compared with regard to lumbar bone mineral density (LBD), femur bone mineral density (FBD) and serum parameters of bone metabolism namely calcium (Ca), phosphate (P), magnesium (Mg) and alkaline phosphatase (ALP). Bone mineral density was measured with dual energy x-ray absorptiometry.

RESULTS

The mean FBD, LBD and serum Ca, P, Mg and ALP measurement of the patients treated with CAB were 0.85 +/- 0.1 g/cm2, 1.16 +/- 0.2 g/cm2, 9.1 +/- 0.3 mg/dl, 3.6 +/- 0.6 mg/dl, 1.95 +/- 0.14 mg/dl, 187.5 +/- 61 mg/dl, respectively. No significant difference was found between patients subjected to CAB and the age matched controls in any of the studied parameters namely age, FBD, LBD, Ca, Mg and ALP except serum phosphate. Serum phosphate levels were significantly (p = 0.001) higher in patients treated with CAB suggesting a minor effect of CAB on bone metabolism.

CONCLUSION

No convincing evidence was found about the detrimental effect of CAB on bone mineral density and metabolism in a highly selected group of patients with advanced prostate cancer without bone metastases.

Genetics of osteoporosis: role of steroid hormone receptor gene polymorphisms

Osteoporosis is a common skeletal disease characterized by low bone mass and microarchitectural deterioration of bone tissue with a consequent increase in bone fragility and susceptibility to fracture. In the past years, twin and family study have shown that this disease recognizes a strong genetic component and that genetic factors play an important role in regulating bone mineral density (BMD). While in few isolate conditions osteoporosis can be inherited in a simple Mendelian pattern, due to single gene mutations, in the majority of cases has to be considered a multifactorial polygenic disease in which genetic determinants are modulated by hormonal, environmental and nutritional factors. Given the important role that steroid hormones play in bone cell development and in the maintenance of normal bone architecture, polymorphisms at receptor of the steroid/thyroid hormone receptor superfamily, such as estrogen receptor alpha (ERalpha) and Vitamin D receptor (VDR) have been thoroughly investigated in the last years and appeared to represent important candidate genes. The individual contribution of these genetic polymorphisms to the pathogenesis of osteoporosis remains to be universally confirmed and an important aim in future work will be to define their functional molecular consequences and how these polymorphisms interact with each other and with the environment to cause the osteoporotic phenotype. A further promising application of genetic studies in osteoporosis comes from their pharmacogenomic implications, with the possibility to give a better guidance for therapeutic agents commonly used to treat this invalidating disorder or to identify target molecules for new therapeutic agents.

Osteoporosis in men treated with androgen suppression therapy for prostate cancer

Men with advanced or metastatic prostate cancer commonly receive long-term treatment with luteinizing hormone-releasing hormone (LHRH) agonist therapy. This prolonged treatment causes a hypogonadal state of chronic testosterone deficiency. Similar to estrogen deficiency in postmenopausal women, testosterone deficiency among these men negatively affects bone metabolism through a complex self-regulating, negative feedback system and subsequent reduction in bone formation. If left undetected or untreated, the risk for osteoporosis rises. Osteoporosis increases the likelihood of fracture, especially of the hips. Researchers are studying the effects of LHRH agonist therapy on osteoporosis and other related conditions to determine whether interventions, such as pharmacologic agents (e.g., bisphosphonates), dietary supplements (e.g., calcium, vitamin D), and exercise, can slow or prevent the process and assist healthcare providers in knowing how to counsel patients. Current recommendations are found in the literature on glucocorticoid-induced and menopausal osteoporosis. Nurses need to stay abreast of current knowledge in this area, as it is expanding rapidly.

Effects of transdermal testosterone gel on bone turnover markers and bone mineral density in hypogonadal men

OBJECTIVE

Androgen replacement has been reported to increase bone mineral density (BMD) in hypogonadal men. We studied the effects of 6 months of treatment with a new transdermal testosterone (T) gel preparation on bone turnover markers and BMD.

DESIGN

This was a prospective, randomized, multicentre, parallel clinical trial where 227 hypogonadal men, mean age 51 years (range: 19-68 years) were studied in 16 academic and research institutions in the USA. Subjects were randomized to apply 1% T gel containing 50 or 100 mg T (delivering approximately 5-10 mg T/day) or two T patches (delivering 5 mg T/day) transdermally for 90 days. At day 91, depending on the serum T concentration, the T gel dose was adjusted upward or downward to 75 mg T/day until day 180. No dose adjustment occurred in the T patch group.

MEASUREMENTS

Serum T, free T and oestradiol, bone turnover markers and BMD were measured on days 0, 30, 90 and 180 before and after treatment.

RESULTS

Application of T gel 100 mg/day resulted in serum T concentrations 1.4 and 1.9-fold higher than in the T gel 50 mg/day and the T patch groups, respectively. Proportional increases occurred in serum oestradiol. Urine N-telopeptide/creatinine ratio, a marker for bone resorption, decreased significantly (P = 0.0019) only in the T gel 100 mg/day group. Serum bone osteoblastic activity markers (osteocalcin, procollagen and skeletal alkaline phosphatase) increased significantly during the first 90 days of treatment without intergroup differences but declined to baseline thereafter. BMD increased significantly both in the hip (+1.1 +/- 0.3%) and spine (+2.2 +/- 0.5%) only in the T gel 100 mg/day group (P = 0.0001).

CONCLUSIONS

Transdermal testosterone gel application for 6 months decreased bone resorption markers and increased osteoblastic activity markers for a short period, which resulted in a small but significant increase in BMD. Ongoing long-term studies should answer whether the observed increases in BMD are sustained or continue to be dependent on the dose of testosterone administered.

A common promotor variant in the cytochrome P450c17alpha (CYP17) gene is associated with bioavailability testosterone levels and bone size in men

Cytochrome P450c17alpha (CYP17) encodes an enzyme with 17a-hydroxylase and 17,20-lyase activities, which is essential for the normal production of adrenal and gonadal androgens. Because androgens have powerful effects on bone growth and metabolism, we determined whether a single base pair (bp) substitution (T-->C) in the promoter region (-34 bp) of CYP17 is associated with sex hormone levels, stature, and femoral mass and size in 333 white men aged 51-84 years (mean +/- SD; 66+/-7 years). Femoral neck bone mineral content (BMC), cross-sectional area (CSA), and bone mineral density (BMD) were measured using dual-energy X-ray absorptiometry (DXA). Genotype frequencies did not deviate from Hardy-Weinberg expectations. Serum bioavailable testosterone levels were 20% or 0.5 SDs higher in men with the C/C compared with the T/T genotype, whereas heterozygous men had intermediate hormone levels (p = 0.019). Men with the C/C genotype also were nearly 3 cm taller and had 0.6 SD greater femoral neck CSA than men with the T/T genotype (p < or = 0.01 for both). The association with CSA persisted after adjusting for age, height, and body weight. In contrast, CYP17 genotype was not associated with femoral neck BMC, areal BMD (g/cm2), or estimated volumetric BMD (g/cm3). These results suggest that allelic variation at the CYP17 locus may contribute to the genetic influence on stature and femoral size in men.

Hypogonadism and androgen replacement therapy in elderly men

The decrease in testosterone levels with age is both central (pituitary) and peripheral (testicular) origin. Because serum levels of sex-hormone-binding globulin increase with aging, the decrease in free testosterone is of even greater magnitude. Recent long-term studies of testosterone therapy in hypogonadal elderly men have shown beneficial effects on bone density, body composition, and muscle strength without any substantial adverse effects on lipids and the prostate. Total testosterone level is the test of choice for initial screening of elderly men who present with signs and symptoms of hypogonadism. If the level is below 300 ng/dL, replacement therapy should be initiated. If the level is normal in a symptomatic patient, free or bioavailable testosterone should be determined. The pros and cons of testosterone therapy should be discussed in depth with every patient, and decisions should be made on an individual basis. This review summarizes the trials of testosterone replacement therapy in elderly men and outlines a diagnostic approach to these patients.

Bone mineral density and bone markers in hypogonadotropic and hypergonadotropic hypogonadal men after prolonged testosterone treatment

After prolonged treatment (76.4+/-10 and 70.1+/-12.3 months, respectively) (mean+/-SE) with testosterone enanthate (250 mg i.m. every 3 weeks), bone mineral density (BMD) and bone metabolism were evaluated in 12 patients (aged 29.3+/-1.4 yr) affected by idiopathic hypogonadotropic hypogonadism (IHH), in 8 patients (29.6+/-2.6 yr) affected by Klinefelter's syndrome (KS), and in 10 healthy men (30.6+/-1.7 yr) matched according to age and BMI. Spinal BMD in IHH was significantly lower than in controls (0.804+/-0.04 vs 1.080+/-0.01 g/cm2; p<0.001), while there was no difference in neck BMD (0.850+/-0.01 vs 0.948+/-0.02 g/cm2). Neither spinal (0.978+/-0.05 g/cm2) nor neck (0.892+/-0.03 g/cm2) BMD in KS were significantly different from controls. Six IHH and one KS subjects were osteoporotic, while 6 IHH and 2 KS subjects were osteopenic. A significant inverse correlation was found between spinal BMD and age at the treatment onset in IHH (r=-0.726, p=0.007). In IHH there were significant increases in bone formation (alkaline phosphatase=318.3+/-33.9 vs 205.4+/-20.0 IU/l; osteocalcin=13.44+/-1.44 vs 8.57+/-0.94 ng/ml; p<0.05) and in bone resorption (urinary cross-linked N-telopeptides of type I collagen=149.1+/-32.3 vs 47.07+/-8.4 nmol bone collagen equivalents/mmol creatinine; p<0.05) compared to controls, while such differences were not present in KS. Our results outline the importance of BMD evaluation in all hypogonadal males. Nevertheless, bone loss is a minor characteristic of KS, while it is a distinctive feature of IHH. Therefore, early diagnosis and age-related replacement therapy coupled with a specific treatment for osteoporosis could be useful in preventing future severe bone loss and associated skeletal morbidity.

Hormone replacement therapy and fractures in older adults

Estrogen deficiency in women is associated with accelerated bone loss, and estrogen replacement therapy has been proven to be effective in preventing osteoporosis and fractures in postmenopausal women. The introduction of selective estrogen receptor modulators that have an estrogen-like effect on the skeleton but have a different pattern of effects on other tissues may have an important role in the management of osteoporosis in women in the near future. In men, androgen deficiency has been shown to be associated with osteoporosis. Although androgen replacement in hypogonadal men may decrease bone resorption and increase bone mass, long-term placebo-controlled trials are needed to better define the benefits and risks of such therapy before it can be recommended. Sex hormone deficiency is linked to the development of osteoporosis in both women and men. In women, hormonal replacement by estrogen or the newly developed selective estrogen receptor modulators may prevent the development of osteoporosis and its related fractures. In men, there is early evidence that testosterone replacement therapy may enhance bone mass in hypogonadal men.

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.

Androgens and osteoporosis

Androgen receptors are present in relevant numbers in osteoblasts. Stimulation of androgen receptors in osteoblastic bone marrow stromal cells inhibits the differentiation of osteoclasts in the bone marrow cavity. Androgens not only inhibit osteoclastogenesis but also increase cortical bone formation mainly by stimulating periosteal bone formation. Clinically, androgen action is crucial for the gain of bone mass during puberty and the maintenance of bone mass after puberty. Therefore, androgen replacement is necessary in hypogonadal men. However, the role of androgen replacement in partial androgen deficiency still remains unclear. Thus far, only testosterone has established its role in androgen replacement. However, further clinical and basic research should better define the selective role of androgen versus oestrogen receptor stimulation in male skeletal homeostasis.

Low levels of estradiol are associated with vertebral fractures in older men, but not women: the Rancho Bernardo Study

This longitudinal study included 288 postmenopausal women without estrogen use (median age, 72 yr) and 352 men (median age, 66 yr). All were community-dwelling, ambulatory, and Caucasian. Blood for hormone assays (total and bioavailable estradiol and testosterone, estrone, androstenedione, dihydrotestosterone, dehydroepiandrosterone, and dehydroepiandrosterone sulfate) was obtained in 1984-1987, and vertebral fractures were diagnosed from lateral spine radiographs obtained in 1992-1996. At least one vertebral fracture was found in 21% of women and 8% of men. Among men, age-adjusted hormone levels differed by fracture status only for total (64.1 vs. 75.4 pmol/L, P = 0.012) and bioavailable (43.0 vs. 51.4 pmol/L, P = 0.008) estradiol. There was a graded association between higher concentrations of total and bioavailable estradiol and lower fracture prevalence (trend P<0.01 for both hormones). Men with total testosterone levels compatible with hypogonadism (<7 nmol/L) were not more likely to have vertebral fractures. In women, none of the measured sex hormones was associated with vertebral fractures. There was also no increased prevalence of fractures in women with estradiol levels below the assay sensitivity (<11 pmol/L). These data suggest that estrogen plays a critical role in the skeletal health of older men and confirm other studies showing no association of postmenopausal endogenous estrogen levels with vertebral fractures in older women.

Homologous androgen receptor up-regulation in osteoblastic cells may be associated with enhanced functional androgen responsiveness

Although androgens have myriad effects on the skeleton, the regulation of androgen action in bone is not well understood. Androgen receptors (ARs) are known to play an important role in mediating androgen action. We have examined the effects of androgens and other sex steroids on AR levels in osteoblastic cells in vitro using two clonal human cell lines, SaOS-2 and U-2 OS. AR protein levels were quantitated both by specific androgen binding studies and Western analyses, and AR messenger RNA was measured with RNase protection assays. Potential changes in AR functionality was assessed by reporter assays. Treatment of osteoblastic cells with the nonaromatizable androgen 5alpha-dihydrotestosterone (DHT) increased specific androgen binding 2-to 4-fold. Similar increases in AR protein levels were documented by Western analysis in both cell lines. The androgen-mediated increase in receptor levels was time and dose dependent as well as androgen specific. Steady-state AR messenger RNA levels were also increased by DHT. When AR concentrations in osteoblastic cells were elevated with exogenous receptor, there was an enhancement of DHT responsiveness, measured by increased trans-activation of an androgen-responsive promoter. Thus, androgen exposure increased androgen receptor protein levels and specific androgen binding in osteoblastic cells. Androgen action as measured by androgen-mediated transcriptional activation is enhanced in the presence of elevated AR levels. Consequently, these studies have revealed an additional means by which androgens may modulate skeletal metabolism.

Age-related changes in bone turnover in men

Biochemical markers of bone turnover can be used to study the pathophysiology of osteoporosis. So far there have been few such studies in men. The aims of this study were to determine the effect of aging on bone turnover and to identify which hormones might regulate bone turnover in men. We studied 178 healthy Caucasian men, ages 20-79 years (30 per decade). The data for the effect of age on bone turnover was best fit by a quadratic function (nadirs at age 56, 57, 53, 39, and 58 years for intact propeptide of type I procollagen, osteocalcin, bone alkaline phosphatase, free deoxypyridinoline, and cross-linked N-telopeptides of type I collagen, respectively). For most markers, bone turnover tended to be highest in the third decade, lowest in the fifth and sixth decade, with a small increase in some markers in the eighth decade. Insulin-like growth factor-I (IGF-I), insulin-like growth factor binding protein-3, dehydroepiandrosterone sulfate, testosterone, estradiol, and free androgen index all decreased significantly with age (54, 17, 76, 26, 33, and 57%, respectively), while sex hormone binding globulin and parathyroid hormone increased significantly with age (62% and 43%). IGF-I and sex hormones were positively correlated with bone turnover, and this association was stronger in young men than older men. In conclusion, increased IGF-I and sex hormones may be associated with increased bone turnover in young men, with less influence on bone turnover in older men.

Progesterone- and dexamethasone-dependent osteoprogenitors in bone cell populations derived from rat vertebrae are different and distinct

Previous experiments have demonstrated that bone cell populations derived from explants of lumbar vertebral bone of adult female rats contain osteoprogenitors that require dexamethasone (Dex) or progesterone (Prog) to proliferate and differentiate into fully differentiated bone-forming osteoblasts. We now show that the Prog-dependent population cannot be detected in male rats after sexual maturation, but is present in prepubertal rats of both sexes and can be induced in adult male-derived populations by culturing the explants in medium containing 17beta-estradiol (10(-9)-10(-8) M). This suggested that the Prog- and Dex-dependent osteoprogenitors in adult female-derived populations were probably distinct populations and that the survival of the Prog-dependent osteoprogenitors and/or their ability to proliferate are dependent on the presence of estrogen. We then proceeded to prove this by using replica plating. When one of the paired colonies duplicated was cultured in medium containing Dex (10(-8) M) and the other in medium containing Prog (10(-5) M), 5.0% of duplicates formed bone in Prog only, 11.1% formed bone in Dex only, and 3.4% formed bone in both Prog and Dex. In all cases the size of the bone-forming colonies in Dex-treated cultures was larger than that in Prog-treated cultures, indicating that the effects of Dex on osteoprogenitor proliferation are greater than those of Prog. The results demonstrate the existence of three classes ofosteoprogenitors in adult female rat-derived bone cell populations: a class responding to Dex only, a class responding to Prog only, and a class responding to both Dex and Prog. The results also indicate that the effects of Prog are not mediated by Prog binding to the glucocorticoid receptor and imply that Prog plays an important role in maintaining bone mass through regulating the class of osteoprogenitors responsive to Prog.

Dihydrotestosterone: a rationale for its use as a non-aromatizable androgen replacement therapeutic agent

Testosterone therapy is commonly used to treat male hypogonadism, androgen deficiency of severe illness, androgen deficiency of ageing and microphallus in infancy. The effects of testosterone are mediated directly as testosterone or after conversion to either dihydrotestosterone (DHT) or oestradiol. DHT is a potent androgen and cannot be aromatized to oestrogens, therefore acting as a pure androgen. DHT has been proposed as an androgen replacement therapy, with possible advantages over testosterone in certain circumstances in the ageing population as well as in patients with gynaecomastia and microphallus. A potential advantage of DHT over testosterone as an androgen replacement therapy is the reported and seemingly paradoxically muted effects of DHT on prostate growth. The decreased effect of DHT compared with testosterone on the prostate gland of humans may be due to the decrease in intraprostatic oestradiol levels. The potential beneficial effect of less prostate growth after DHT requires substantiation and, if true, must be balanced against any negative effects that might occur on bone, lipids and sexuality when a pure androgen replaces treatment with an aromatizable androgen.

Therapeutic role of androgens in the treatment of osteoporosis in men

There has been much recent interest in the relationship between androgens and bone mineralization in men. Increases in serum androgens during puberty allow for skeletal maturation and the attainment of peak bone mass, and the persistence of normal testosterone secretion during adulthood is important for the maintenance of bone density. Testosterone deficiency is associated with heightened bone turnover and is a major risk factor for osteoporosis in men. The administration of testosterone to androgen-deficient men leads to an increase in bone mass, particularly in the trabecular bone compartment, and a reduction in levels of surrogate markers of bone turnover, suggesting that androgens have a dampening effect on bone remodelling. In addition, the administration of androgens to eugonadal men with idiopathic osteoporosis, with resulting supraphysiological testosterone concentrations, may lead to increases in bone mineral density. The risk of osteopenia due to androgen deficiency and the benefits of testosterone substitution therapy or supraphysiological administration on bone will be reviewed.

Comparative pharmacokinetics of three doses of percutaneous dihydrotestosterone gel in healthy elderly men--a clinical research center study

Twenty-five men, 60-80 yr old, participated in a pharmacokinetic study to compare three doses (16, 32, and 64 mg/day, n = 8 or 9 in each group) of 5alpha-dihydrotestosterone (DHT) gel (0.7% hydroalcoholic gel with 2.3 g gel delivering 16 mg DHT) applied daily over one upper arm (16 mg); both arms and shoulders (32 mg); and bilateral arms, shoulders, and upper abdomen (64 mg), respectively. Multiple blood samples for the pharmacokinetic profile for DHT and testosterone (T) were drawn over a 24-h period before application, after first application, and after 14 days of daily application of DHT gel. Additional blood samples for DHT, T, and estradiol were obtained 24 h after application on days 3, 5, 7, and 11 and after discontinuation of DHT gel for 3, 5, 7, and 14 days (days 17, 19, 21, and 28 after first instituting treatment). No skin irritation was observed in any of the subjects. Before treatment, mean serum DHT and T levels were not different among the three dose groups. The serum DHT levels increased gradually after gel application on the first day, reaching a plateau between 12-18 h. During the 14 days of daily application of DHT gel, the mean baseline DHT levels reached steady state by day 2 or 3 and were elevated considerably above baseline. Mean serum DHT levels varied between 8-11, 12-17, and 14-24 nmol/L in the 16-, 32-, and 64-mg groups, respectively. The area under curve (AUC) of serum DHT levels over 24 h on day 14 were 6.0-, 6.9-, and 16.1-fold above pretreatment levels for the three doses. Concomitant with the increase in serum DHT levels, the AUC produced by endogenous serum T levels decreased to 75, 56, and 36% of baseline after 14 days of 16, 32, and 64 mg/day DHT gel. Similar patterns of decreases in AUC of serum estradiol levels were found. The calculated mean total androgen levels (T + DHT) rose with DHT gel application in all groups (P < 0.0001) on both days 1 and 14. We conclude that the three doses of DHT gel tested might provide adequate androgen replacement in hypogonadal men at the low, middle, and high physiological androgen (T + DHT) range.

Characterization of aromatase and 17 beta-hydroxysteroid dehydrogenase expression in rat osteoblastic cells

Postmenopausal loss of 17 beta-estradiol (E2) in women is associated with decreased bone mineral density and increased susceptibility to osteoporotic bone fracture. These changes in bone status are assumed to be due to circulating levels of the hormone; therapeutic replacement of E2 can alleviate the bone disease. However, recent reports have shown that human osteoblastic (OB) cells are able to synthesize estrogens locally, via expression of the enzyme aromatase. In this study, we have characterized the expression and activity of aromatase and 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) in rat OB cell lines. Aromatase activity in ROS 17/2.8, ROS 25/1, and UMR 106 cells was similar to that shown in human OB cells, with the highest levels of activity observed in the more differentiated ROS 17/2.8 cells (Vmax = 45 pmol/h/mg of protein). The rat OB cells also showed 17 beta-HSD activity, with the predominant metabolism in all three cell lines being estrone (E1) to E2. As with aromatase, the highest activity was observed in ROS 17/2.8 cells (Vmax = 800 pmol/h/mg of protein). Northern analyses indicated the variable presence of transcripts corresponding to the type 1, 2, 3, and 4 isoforms of 17 beta-HSD. Further analysis of androstenedione metabolism indicated that the net effect of aromatase and 17 beta-HSD activity varied with cell type and culture treatment. All three OB cell lines were able to synthesize E1, E2, and testosterone from androstenedione, although activity varied between OB cell types. Regulatory effects were observed with 1,25-dihydroxyvitamin D3 (positive) and dexamethasone (negative). These data suggest that local synthesis of sex hormones is an important function of OB cells and may play a key role in the modulation of bone turnover independent of circulating hormone concentrations.

Assessment of sex hormones and bone mineral density in relation to occurrence of fracture in men: a prospective population-based study

Patients with fragility fractures have low bone mineral density (BMD)--this statement is supported mainly by data on women. In this study, including only men, the objectives were to determine whether a decline in BMD alone or in combination with data on male sex hormones and skinfold thickness could be of value in predicting forthcoming fractures. We also wanted to find out whether high consumers of alcohol can be identified by measuring BMDs and male sex hormones. A prospective, population-based study was performed in the city of Malmö, Sweden. 242 men were randomly selected; all were of Scandinavian ethnic background, and were aged 50, 60, 70, and 80 years. Forearm BMD, testosterone, sex-hormone-binding globulin (SHBG), and skinfold thickness were analyzed. In addition, alcohol consumption and carbohydrate-deficient transferrin (CDT)--a marker of alcohol abuse--were analyzed. The study group was followed prospectively for 7 years and all fractures sustained were recorded. Prospectively, for a 1 SD decrease in forearm BMD, the Cox proportional hazard model gave a relative risk (RR) of 1.75 with a 95% confidence interval of 1.08-2.83 for a forthcoming fracture and 3.88 (1.30-11.57) for a hip fracture. For a 1 SD change in skinfold thickness, measured on the dorsum of the hand, a RR of 1.69 (0.99-2.87) for a forthcoming fracture was found and the corresponding value for hip fracture was 2.34 (1.10-5.00). Testosterone and SHBG did not enhance fracture prediction. Abusers of alcohol had, retrospectively, significantly more fractures. Individuals with alcohol consumption rates in the highest quartile had significantly higher CDT levels, but we were unable to identify high consumers of alcohol by analyzing BMD or sex hormones. In this study we found that forearm BMD and skinfold thickness could be used in predicting forthcoming fractures in men.

Steroid formation in osteoblast-like cells

For preventing the reduction of bone mass in postmenopausal women, oestrogen replacement is known to be useful and the importance of sex steroids in bone metabolism in both sexes is well established. The presence of steroid-converting-enzyme activities in various osteoblast and osteoblast-like cells has been demonstrated using in vitro culture systems. In the present study, we assessed the expression of messenger ribonucleic acid (mRNA) for aromatase, steroid sulphatase, 5 alpha-reductase, 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) and 3 beta-HSD by reverse transcription-polymerase chain reaction in the human osteoblast-like cell lines, MG 63 and HOS. Oestrogen, androgen and progesterone receptor mRNAs were also measured. Expression of mRNA for these enzymes and receptors was found in both cell lines without induction. From these and previous findings, we conclude that osteoblast-like cells have the capacity to form biologically potent oestrogens and androgens from peripheral circulating steroids. This may indicate an important role of bone in facilitating hormonal action.

The localization of androgen receptors in human bone

Androgens have important effects on the human skeleton, and deficiency has been associated with bone loss in both males and females. The skeletal actions of androgens may be mediated directly via the androgen receptor (AR) or indirectly via the estrogen receptor after aromatization to estrogens. The presence of androgen receptors has been demonstrated in bone cells and chondrocytes in vitro, but their presence in human bone in situ has not been reported. In order to provide further evidence for a direct action of androgens on bone via androgen receptors, we have used specific monoclonal antibodies to investigate the expression of human AR in normal developing and osteophytic bone of both sexes. In the growth plates from the developing bone, androgen receptors were predominantly expressed in hypertrophic chondrocytes and in osteoblasts at sites of bone formation. They were also observed in osteocytes in the bone, and in mononuclear cells and endothelial cells of blood vessels within the bone marrow. In the osteophytes, androgen receptors were widely distributed at sites of endochondral ossification in proliferating, mature, and hypertrophic chondrocytes and at sites of bone remodeling in osteoblasts. They were also expressed in osteocytes and mononuclear cells within the bone marrow. The pattern and number of cells expressing the receptor was similar in both sexes. Our results show for the first time the presence and distribution of androgen receptors in normal developing human and osteophytic bone in situ and further provide evidence for a direct action of androgens on bone and cartilage cells.

Absence of androgen-mediated transcriptional effects in osteoblastic cells despite presence of androgen receptors

Androgen excess and deficiency affect skeletal maturation and bone cell function. Understanding the molecular basis for these androgen effects could improve therapy/prevention of short stature and osteoporosis. Androgens act through binding to androgen receptors (ARs), which modulate gene transcription via interactions with DNA response elements on target genes. Because osteoblasts contain ARs at levels just below certain androgen-sensitive tissues, we sought to define the function of AR in a number of commonly used osteoblastic cell lines. Presence and quantification of AR protein and mRNA were evaluated by ligand binding assay, western blotting, and RNAse protection assay. AR-containing osteoblastic cell lines were exposed to nonaromatizable androgens and effects on gene expression were assessed. We found no evidence for direct effects of androgen on endogenous genes nor was androgen involved in modulation of parathyroid hormone effects on early gene activation. Androgen-sensitive reporter gene constructs were stimulated by androgen only when AR cDNA expression vectors were introduced into cells by cotransfection. We conclude that, in commonly used osteoblastic cell lines, the presence of AR at the levels described here does not guarantee androgen transcriptional activity. The effects of androgen on bone in vivo may involve direct stimulation of osteoblastic cells in a different setting or stage of differentiation. Alternatively, androgen may act on bone cells other than osteoblasts, or through metabolic conversion to estrogens.

Transcriptional up-regulation of the human androgen receptor by androgen in bone cells

Androgen regulation of androgen receptor (AR) expression has been observed in a variety of tissues, generally as inhibition, and is thought to attenuate cellular responses to androgen. AR is expressed in osteoblasts, the bone-forming cell, suggesting direct actions of androgens on bone. Here we characterized the effect of androgen exposure on AR gene expression in human osteoblastic SaOS-2 and U-2 OS cells. Treatment of osteoblastic cells with the nonaromatizable androgen 5alpha-dihydrotestosterone increased AR steady state messenger RNA levels in a time- and dose-dependent fashion. Reporter assays with 2.3 kilobases of the proximal 5'-flanking region of the human AR promoter linked to the chloramphenicol acetyltransferase gene in transfected cultures showed that up-regulation of AR promoter activity by androgen was time and dose dependent. Treatment with other steroid hormones, including progesterone, 17beta-estradiol, and dexamethasone, was without effect. The antiandrogen hydroxyflutamide completely antagonized androgen up-regulation. Thus, in contrast to many other androgen target tissues, androgen exposure increases steady state AR messenger RNA levels in osteoblasts. This regulation occurs at least partially at the level of transcription, is mediated by the 5'-promoter region of the AR gene, and is dependent on functional AR. These results suggest that physiological concentrations of androgens have significant effects on AR expression in skeletal tissue.

Secondary osteoporosis

Secondary osteoporosis is diagnosed when there is a well-established disease-related risk factor for fracture or low bone mass. Secondary osteoporosis is associated with a substantial minority of osteoporotic fractures in women perhaps with a majority of osteoporotic related fractures in men. This chapter does not review all the possible causes of low bone mass and fractures but picks out some of the more important causes of, with an emphasis on the main iatrogenic cause, that is corticosteroid induced osteoporosis. It also highlights some of the possible causes which could be avoidable. Where appropriate the methods of prevention and treatment of secondary osteoporosis are reviewed.

The role of testosterone in cyclosporine-induced osteopenia

Our laboratory has demonstrated that the immunosuppressants Cyclosporin A (CsA) and tacrolimus (FK506), in vivo in the rat, produce a high-turnover osteopenia. CsA is known to decrease serum testosterone (Test) levels both in the rat and in human transplant patients. Less is known of FK506's effect on androgens. CsA-induced hypogonadism may contribute to the aforementioned bone loss because hypogonadism itself is a risk factor for osteoporosis and fracture. The aim of this study was to assess serum androgen levels following CsA and FK506 therapy and to see wether Test replacement therapy, in the form of 28-day controlled release subcutaneous pellet implants, could prevent CsA-induced osteopenia. Two experiments were conducted. In experiment I, four groups of 6-month-old male Sprague-Dawley rats received the following: (A) CsA vehicle and placebo pellet, (B) Test 15 mg pellet and CsA vehicle, (C) CsA 10 mg/kg and placebo pellet, (D) Test 15 mg pellet and CsA 10 mg/kg. In experiment II, two groups of rats received (E) FK506 vehicle and (F) FK506 4 mg/kg. CsA, FK506, and vehicles were given for 28 days by daily oral gavage. The rats were weighted and bled on days 0, 14, and 28. All rats received double fluorescent labeling, and on day 28 the tibiae were removed for histomorphometry. Whole blood was assayed for CsA and FK506 levels. Serum was assayed for total and free Test as well as for osteocalcin (BGP), blood urea nitrogen (BUN), creatinine, and calcium. Whole blood monoclonal CsA levels measured by fluorescent immunoassay were in the therapeutic range, while a drug concentration profile showed good absorption of FK506. Those rats receiving Test and FK506 lost weight, while those receiving CsA remained constant. BUN was only marginally elevated in the CsA-treated groups on day 28 (p < 0.05), while creatinine was unchanged. On day 28, total and free Test was significantly reduced in the CsA-treated rats versus control (p < 0.05), while Test replacement therapy maintained total Test levels above vehicle (p < 0.01) and free Test levels similar to vehicle on day 28. FK506 did not lower total or free Test levels. BGP levels were significantly increased in the CsA (p < 0.01) and FK506 (p < 0.001) groups on day 28. BGP in the groups receiving Test alone and in combination with CsA remained similar to vehicle. Histomorphometry confirmed CsA- and FK506-induced high-turnover osteopenia. The Test alone group marignally increased bone formation. Test replacement failed to prevent the CsA-induced bone loss. In conclusion, immunosuppressive doses of CsA, but not FK506, lowers serum total and free Test. Hypoandrogenemia does not seem to be a major factor in CsA-induced osteopenia because bone loss occurs despite Test replacement.

Immunocytochemical detection of estrogen receptors in bone cells using flow cytometry

A sensitive method for immunocytochemical detection of estrogen receptors using flow cytometry is reported. Using this method, estrogen receptors were detected in several osteoblastic cell lines with established expression of estrogen receptors, and for the first time, estrogen receptors were also demonstrated in murine fibroblasts and in human primary marrow stromal cells. The distribution of estrogen receptors within all cell lines was unimodal. The method enables for studies of estrogen receptors in the cell types which express low to moderate levels of the receptors, for studies of heterogeneity of the receptors' expression and for simultaneous detection of several parameters on a single-cell level.

Steroid sulfatase activity in osteoblast cells

We have demonstrated steroid sulfatase activity in osteoblast cells and characteristics of the enzyme were also investigated. Cell free homogenate of rat osteoblast cell line, UMR106-01 and human osteoblast cell lines, MG-63, HOS were incubated with [3H] dehydroepiandrosterone-sulfate (DHEA-sulfate) or [3H] estrone-sulfate (E1-sulfate). The formation of DHEA or E1 from the corresponding substrate was identified by crystallization to constant specific activity. Michaelis constant (K(m)) for DHEA-sulfate was estimated as 2.1 x 10(-8)M in UMR106-01, 7.4 x 10(-7)M in MG-63, 5.8 x 10(-7)M in HOS and that for E1-sulfate was 4.1 x 10(-7)M, 3.0 x 10(-7)M, 9.8 x 10(-7)M, respectively. The expression of steroid sulfatase messenger ribonucleic acid in human osteoblast cells, HOS and MG-63 was first demonstrated by reverse transcription-polymerase chain reaction. The existence of steroid sulfatase in human and rat osteoblast cells suggests that osteoblast cells have the capacity to convert circulating sulfo-conjugated steroids to more active androgens and estrogens. This may indicate an important role of bone in facilitating hormonal action.

Bone fractures associated with luteinizing hormone-releasing hormone agonists used in the treatment of prostate carcinoma

BACKGROUND

Luteinizing hormone-releasing hormone agonists (LHRH-a) have become an established treatment for certain patients with prostate carcinoma. LHRH-a are known to decrease bone mineral density. The purpose of this study was to determine the risk of bone fracture in men receiving LHRH-a for prostate carcinoma.

METHODS

A retrospective chart review and phone interviews were conducted to determine the incidence of bone fractures occurring in patients receiving LHRH-a for the treatment of prostate carcinoma. Abstracted data included the number of monthly LHRH-a injections, age, clinical stage of disease, sites of metastases, and bone fracture history.

RESULTS

Twenty of the 224 patients (9%) treated with LHRH-a for prostate carcinoma between 1988 and 1995 at 3 teaching hospitals had at least 1 bone fracture during treatment with LHRH-a. The duration of treatment to the time of fracture ranged from 1 to 96 months (mean, 22.2 months). Seven fractures (32%) were osteoporotic in nature (i.e., vertebral compression fractures or hip fractures after a fall from standing), whereas 8 fractures (36%) were associated with a significant traumatic event (i.e., a motor vehicle accident, boxing, etc.) and 5 were of mixed etiology. Two of 22 fractures (9%) were pathologic.

CONCLUSIONS

This study demonstrated a 9% fracture incidence in a cohort of patients receiving LHRH-a for prostate carcinoma for up to 96 months. The incidence of osteoporotic fractures was 5%.