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Receptor activator of NF-κB(RANK) ligand(RANKL), expressed by cells of the osteoblast lineage binds to RANK, induces signaling and a gene expression cascade that leads to osteoclast differentiation and activation. Recently, osteoblast-derived membrane-type matrix metalloproteinases-1(MT1-MMP) have been implicated in the process of bone resorption by degrading bone matrix. In the present study, we investigated the effects of parathyroid hormone[PTH(1–34)] on RANKL and MT1-MMP production in cultured normal human osteoblast-like cells(hOB). In reverse transcription polymerase chain reaction studies, we observed that PTH(1–34) induced RANKL messenger ribonucleic acid(mRNA) expression. Activity assays demonstrated that PTH(1–34) simultaneously inhibited MT1-MMP protein expression in a dose- and time-dependent manner. The effect of PTH(1–34) on MT1-MMP production was parallel to that on RANKL expression, suggesting a tight inverse relationship between MT1-MMP and RANKL expression. Our findings indicated that the decreased MT1-MMP expression by PTH may be involved in RANKL signaling in osteoblasts and activation of osteoclasts. [ABSTRACT FROM AUTHOR]

OBJECTIVE: To study the effects of progesterone (P) and 18-methyl levonorgestrel (LNG) on the expression of P receptors (PRA and PRB), c-fos, c-jun, and osteocalcin in the human osteosarcoma cell line MG-63 and human normal osteoblasts in order to understand the mechanism of progestin action on the proliferation and differentiation of osteoblasts. METHODS: Cell proliferation was tested by MTT assay. The expression of PR, c-fos, c-jun, and osteocalcin was measured by semi-quantitative RT-PCR, Western immunoblot or immunocytochemistry. RESULTS: Progesterone and LNG (10−10–10−6 M) stimulated cell proliferation in a dose-dependent manner. Progesterone and LNG did not affect the expression of PRA and PRB mRNA and protein, but c-fos and c-jun mRNA and protein were upregulated in a dose-dependent manner. The expression of osteocalcin mRNA was also increased in human osteoblasts in a dose and time-dependent manner with greater effects of LNG than P, while the expression of osteocalcin mRNA in MG-63 cells was not changed by P or LNG. CONCLUSION: Progesterone and LNG promote osteocalcin gene transcription by stimulating the expression of c-fos and c-jun, and result in osteoblast proliferation and differentiation. [ABSTRACT FROM AUTHOR]

Estriol has been showed to prevent bone loss in osteoporotic rats and postmenopausal women, but the mechanisms remain unclear. In the present study, we evaluated the effect of estriol on osteoblastic MG-63 cells in vitro, and compared its action with 17β-estradiol (E2). Cell proliferation was determined by measuring total cell numbers and [3H]thymidine incorporation. Cell function was studied by measuring alkaline phosphatase (ALP) activity and secreted osteocalcin. Our data showed that estriol stimulated MG-63 cells proliferation in a dose-dependent manner, but had no influence on ALP activity in MG-63 cells and osteocalcin production. Compared with estriol treatment, E2 showed a stronger proliferation. Estrogen receptor (ER) α and β expression in MG-63 cells can be detected by Western immunoblot analysis, and the proliferative response to E2 and estriol can be all abrogated by ER antagonist ICI 182,780. In conclusion, estriol stimulates osteoblastic MG-63 cells proliferation, but has no effects on differentiation. The proliferative response to estriol is mediated by the ER. These results suggest that estriol has an effect on osteoblastic proliferation, and this may contribute to its actions on prevention of bone loss. [ABSTRACT FROM AUTHOR]

Recently, membrane-type matrix metalloproteinase-1 (MT1-MMP) was identified, and found that it can activate proMMP-2 on the cell membrane, degrade bone matrix, and participate in bone formation. Since bone is a target tissue of 1α,25-dihydroxyvitamin D3 [1α,25(OH)2D3], in the present study we observed the effects of 1α,25(OH)2D3 on MT1-MMP expression, and proMMP-2 activation in normal human osteoblast-like cells (hOB). Western immunoblots showed 1α,25(OH)2D3 time and dose dependently stimulated MT1-MMP production. By ELISA, we found that the activation of proMMP-2 in cultures of hOB was intensified by 1α,25(OH)2D3. Our studies suggest that 1α,25(OH)2D3 induces MMP-2 activation in part by up-regulating MT1-MMP expression, and since MT1-MMP plays a role in bone metabolism, the induction of MT1-MMP levels by 1α,25(OH)2D3 in hOB cells may contribute to a new mechanism by which 1α,25(OH)2D3 promotes bone formation and stimulates bone resorption. [ABSTRACT FROM AUTHOR]

Objective. Recently our studies have shown that nylestriol in combination with levonorgestrel prevented bone loss, decreased bone turnover rate and increased the maximal loading of bone without obvious side effects in retinoic acid (RA) induced osteoporotic rats. In addition to the animal experiments, we evaluate the effect of Compound Nylestriol Tablet (CNT) on bone mineral density (BMD) in women with postmenopausal osteoporosis. Compound Nylestriol Tablet, which contains 0.5 mg of nylestriol (cyclopentylethinyl estriol) and 0.15 mg of levonorgestrel per tablet, was authorized as a new anti-osteoporotic agent for clinical trial in postmenopausal osteoporosis. Methods. One year's clinical observation was performed in 191 eligible patients who were randomly divided into two groups (A and B). In group A, 119 patients were treated for one year with CNT (one tablet per week) and in group B, 72 patients with placebo. Bone mineral density of lumbar antero-posterior spine (L1-L4), lateral spine, total hip and total forearm positions including radius+ulna at the ultra distal areas, mid areas, and one-third areas, were measured before and after treatment. Biochemical parameters and effects of CNT on uterus, and breast were observed. Results. We found that patients treated with CNT had a significant decrease of bone loss in total forearm, including radius+ulna at the ultra distal, mid, and 1/3 areas compared with control subjects (all P <0.05). An improved BMD tendency could be seen at the lumbar spine. There were no differences in the observed biochemical variables. No side-effects on uterus, or mammary glands were observed. None of the patients had uterine bleeding or vertebral fractures during one year's CNT treatment. Conclusion. These data suggested that CNT is effective, safe and convenient in treating postmenopausal osteoporosis. [ABSTRACT FROM AUTHOR]

Objective. To determine an optimal dosage combination for a nylestriol/levonorgestrel (NYL/LNG) regimen in the treatment of female Sprague-Dawley (SD) rats with retinoic acid (RA)-induced osteoporosis in order to examine the rationale of NYL/LNG use for postmenopausal women. Methods: This study included two sets of experiments; one was designed to confirm the success of the RA-induced osteoporosis model involving 48 SD rats, and the other to determine the optimal dosage combination of NYL/LNG. In the second set of experiments, a total of 160 female SD rats at 7 months of age were randomly divided according to their basal body weights into 16 groups (10 in each). Treatment dosages of NYL and LNG were arrayed in a 2 factor-4 level (2[sup 4]) factorial design, i.e., NYL level I (N1 0.015 mg/kg), level II (N2 0.05 mg/kg), level III (N3 0.15 mg/kg) and level IV (N4 0.5 mg/kg) and LNG level I (L1 0.005 mg/kg), level II (L2 0.015 mg/kg), level III (L3 0.05 mg/kg) and level IV (L4 0.15 mg/kg). For 14 d, 70 mg/kg/d RA was given intragastrically to establish the osteoporofic model and NYL and LNG were then administered in different dosages on alternate days over a 3 wk period. Subsequently, body weight, uterine weight, endometrial status, Bone mineral density (BMD), bone turnover, and morphometry as well as parameters of biomechanics, serum sex hormones and lipids and estrogen receptor-α expression were determined for these rats. Results. Uterine weights at L2, L3, and L4 dosage levels were significantly lower than those at L1 (P < 0.05). Serum estradiol at N4 and progesterone at N2, N3, and N4 had decreased. Bone mineral density at distal tibiae (R5) in L3 and L4, and at proximal femora (R3) in L4 had increased. The peak loading of lumbar vertebrae at N3 was higher than that at N1, N2, and N4 dosage levels and that of femora higher at N3 than that at N1 and N4. Serum alkaline phosphatase (ALP) levels at N3, N4, L2, L3, and L4 dosage levels were lower than those at... [ABSTRACT FROM AUTHOR]