Urokinase-type plasminogen activator and plasminogen mediate activation of macrophage phagocytosis during liver repair in vivo.

Urokinase-type plasminogen activator (u-PA) and plasminogen play a primary role in liver repair through the accumulation of macrophages and alteration of their phenotype. However, it is still unclear whether u-PA and plasminogen mediate the activation of macrophage phagocytosis during liver repair. Herein, we investigated the morphological changes in macrophages that accumulated at the edge of damaged tissue induced by a photochemical reaction or hepatic ischaemia-reperfusion in mice with u-PA ( u-PA-/- ) or plasminogen ( Plg-/- ) gene deficiency by using transmission electron and fluorescence microscopy. In wild-type mice, the macrophages aligned at the edge of the damaged tissue and extended a large number of long pseudopodia. These macrophages clearly engulfed cellular debris and showed well-developed organelles, including lysosome-like vacuoles, nuclei, and Golgi complexes. In wild-type mice, the distribution of the Golgi complex in these macrophages was biased towards the direction of the damaged tissue, indicating the extension of their pseudopodia in this direction. Conversely, in u-PA-/- and Plg-/- mice, the macrophages located at the edge of the damaged tissue had few pseudopodia and less developed organelles. The Golgi complex was randomly distributed in these macrophages in u-PA-/- mice. Furthermore, interferon γ and IL-4 were expressed at a low level at the border region of the damaged tissue in u-PA-/- mice. Our data provide novel evidence that u-PA and plasminogen are essential for the phagocytosis of cellular debris by macrophages during liver repair. Furthermore, u-PA plays a critical role in the induction of macrophage polarity by affecting the microenvironment at the edge of damaged tissue.

Comparisons of serum sclerostin levels among patients with postmenopausal osteoporosis, primary hyperparathyroidism and osteomalacia.

Wnt-ß-catenin signaling is important for bone formation. Sclerostin inhibits bone formation mainly by suppressing this signal, and several studies suggest that the suppression of sclerostin expression contributes to the bone anabolic action of parathyroid hormone (PTH). We therefore examined serum sclerostin levels using enzyme-linked immunosolvent assay in 18 patients with postmenopausal osteoporosis, 9 postmenopausal women with primary hyperparathyroidism (pHPT) and 7 patients with osteomalacia. Serum levels of sclerostin were significantly lower in the group with pHPT, compared with those with postmenopausal osteoporosis. Moreover, serum sclerostin levels were significantly lower in the group with tumor-induced osteomalacia, but not in the group with osteomalacia without tumor, compared with those with postmenopausal osteoporosis. In patients with pHPT, serum sclerostin levels were significantly and negatively correlated to serum calcium and PTH levels. In patients with postmenopausal osteoporosis, serum levels of sclerostin levels were significantly and positively related to serum calcium and creatinine levels. In conclusion, we showed that serum sclerostin levels are decreased presumably through endogenous PTH elevation in postmenopausal women with pHPT, compared with the patients with postmenopausal osteoporosis.

Menin interacts with ß-catenin in osteoblast differentiation.

Menin promotes the commitment of pluripotent mesenchymal stem cells to the osteoblast lineage by interacting with the BMP-2 signaling molecules Smad1/5, and Runx2. However, the relationship between menin and the Wnt-ß-catenin pathway in bone is unclear. Reduction of menin expression by transfection of a menin antisense construct did not alter the levels of ß-catenin in mouse mesenchymal C2C12 and osteoblastic MC3T3-E1 cells. However, menin co-immunoprecipitated with ß-catenin as well as LEF-1 in C2C12 and MC3T3-E1 cells. Reduction of menin expression by antisense menin transfection antagonized ß-catenin-induced transcriptional activity of the pGL3-OT luciferase reporter construct in C2C12 and MC3T3-E1 cells. Antisense menin transfection antagonized the BMP-2 and ß-catenin-stimulated increases in Runx2 and alkaline phosphatase levels in C2C12 cells. The data show that menin interacts with ß-catenin in mouse mesenchymal and osteoblastic cells, and suggest that the interaction is important for osteoblast differentiation.

Radical scavenging activity of bisbenzylisoquinoline alkaloids and traditional prophylactics against chemotherapy-induced oral mucositis.

BACKGROUND AND OBJECTIVE: Oral mucositis is a major severe toxic side-effect of systemic chemotherapy and irradiation in patients with cancer. Various free radical scavengers have been shown to prevent chemotherapy-induced skin necrosis. The objective of this study was to determine the antioxidant activity of a bisbenzylisoquinoline alkaloidal compound (BIQAC) and a series of chemicals, including allopurinol, used clinically for the treatment of chemotherapy-induced mucositis. METHODS: Allopurinol, melatonin, camostat mesilate, gabexate mesilate, hydroquinone and BIQAC were tested for their radical scavenging activities on four different radical species: 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) cation radical (ABTS(*+)) using standard methods, and superoxide anion radical (O(2) (-)) and hydroxyl radical (OH(*)) using electron spin resonance. RESULTS: Allopurinol had radical scavenging activity against O(2) (-) only. Melatonin had strong radical scavenging activity against ABTS(*+), and weak activity against DPPH radical and OH(*). Camostat mesilate had weak radical scavenging activity against OH(*). Gabexate mesilate had no radical scavenging activity against any of these radicals. Hydroquinone had strong radical scavenging activity against DPPH radical and ABTS(*+), and moderate activity against both O(2) (-) and OH(*). BIQAC had moderate radical scavenging activity against DPPH radical, strong radical scavenging activity against ABTS(*+) and O(2) (-), and weak activity against OH(*). CONCLUSION: The BIQAC had the most braod-spectrum radical scavenging activity, suggesting that it may be effective against chemotherapy-induced mucositis. These findings also suggest that this radical-scavenging activity screening method, against four kinds of radicals, may be useful for the screening of radical scavenging activity of new natural and synthetic chemicals.

Relationship between oral mucositis and high-dose methotrexate therapy in pediatric acute lymphoblastic leukemia.

OBJECTIVE: Oral mucositis is a major toxicity in the high-dose methotrexate (HD-MTX) treatment for children with acute lymphoblastic leukemia (ALL). The first aim of this study was to evaluate the relationship between the MTX serum concentration and occurrence of oral mucositis in pediatric ALL patients. The second aim was to clarify the relationship between MTX exposure and epidermal keratinocyte cell injury using an in vitro study. METHODS: 49 patients were treated according to the Japan Association of Childhood Leukemia Study (JACLS) ALL-HR02 protocol. This protocol involves HD-MTX treatment (3 g/m2 for 24-h i.v. infusion). The MTX serum concentrations were measured by a fluorescence polarization immunoassay. The relationship between oral mucositis and MTX serum concentrations 48 and 72 h after administration was determined. The cell toxicity of MTX for human epidermal keratinocytes was analyzed by using a cell viability assay (WST-1 assay). In addition, pharmacokinetic evaluation for clearance, AUC extrapolated from 48 h to infinity (AUC48h-inf) and elimination half-life (t1/2b) were done using the 1-compartmental models. RESULTS: Oral mucositis occurred in 24 patients (49.0%), in whom 20 patients (83.3% in oral mucositis group) showed WHO severity Grade 1 or 2. Only 4 patients (16.7% in oral mucositis group) showed Grade 3 severity. 22 patients (44.9%) had oral mucositis in the group with a concentration under 10-6 M 48 h after MTX administration. There was no significant deference among the cell viabilities in the concentrations of 10-6 M, 10-5 M and 10-4 M 48 h after the MTX exposure. However, the cell viability obtained 24 h after the MTX exposure was significantly different from the respective cell viability 48, 72 and 96 h after the MTX exposure. In the group with oral mucositis, the clearance decreased significantly (p = 0.042), and the t1/2b (p = 0.025) and AUC48h- yen (p = 0.025) increased significantly compared with the non-symptom group. CONCLUSIONS: It seems that there is no significant relationship between the serum MTX concentration and oral mucositis. This in vitro study has demonstrated that the cell injury was related to the duration of MTX exposure rather than a high MTX concentration.

Bronchogenic glomangiomyoma with local intravenous infiltration.

Most glomus tumours occur in the dermis and subcutaneous tissues. Lung glomus tumours are quite rare. The current authors present the first reported case of a lung-derived glomangiomyoma, the rarest variant of glomus tumour. A 56-yr-old female was admitted with haemoptysis. Chest computed tomography showed an approximately 5-cm-diameter mass in the right lower lobe with mucoid impaction. After a right lower lobectomy, a diagnosis of glomangiomyoma was made. The tumour had grown endobronchially and its maximal diameter was 5.5 cm. Although cytologically benign, glomus tumour cells had visibly infiltrated neighbouring vessels. These results suggest that a bronchogenic glomangiomyoma has a low-grade malignancy potential and warrants close follow-up.

Smad3 differently affects osteoblast differentiation depending upon its differentiation stage.

Smad3, a critical component of the TGF-beta signaling pathways, plays an important role in the regulation of bone formation. However, how Smad3 affects osteoblast at the different differentiation stage remains still unknown. In the present study, we examined the effects of Smad3 on osteoblast phenotype by employing mouse bone marrow ST-2 cells and mouse osteoblastic MC3T3-E1 cells at the different differentiation stage. Smad3 overexpression significantly inhibited bone morphogenetic protein-2 (BMP-2)-induced ALP activity in ST-2 cells, indicating that Smad3 suppresses the commitment of pluripotent mesenchymal cells into osteoblastic cells. Smad3 increased the levels of COLI and ALP mRNA at 7 day cultures in MC3T3-E1 cells, and its effects on COL1 were decreased as the culture periods progress, although its effects on ALP were sustained during 21 day cultures. Smad3 overexpression enhanced the level of Runx2 and OCN mRNA at 14 day and 21 day cultures. Smad3 increased the levels of MGP and NPP-1 mRNA, although the extent of increase in MGP and NPP-1 was reduced and enhanced during the progression of culture period, respectively. Smad3 did not affect the level of ANK mRNA. On the other hand, Smad3 enhanced the level of MEPE mRNA at 14 and 21 day cultures, although Smad3 decreased it at 7 day cultures. In conclusion, Smad3 inhibits the osteoblastic commitment of ST-2 cells, while promotes the early stage of differentiation and maturation of osteoblastic committed MC3T3-E1 cells. Also, Smad3 enhanced the expression of mineralization-related genes at the maturation phase of MC3T3-E1 cells.

Statins modulate the levels of osteoprotegerin/receptor activator of NFkappaB ligand mRNA in mouse bone-cell cultures.

Statins stimulate bone formation partly by inducing osteoblast differentiation, although there is controversy about the effects of statins on bone mineral density and fracture risk. Several studies have revealed that statins suppress bone resorption. However, the mechanism by which statins inhibit bone resorption is still unclear. The present study was performed to clarify the effects of statins on osteoclast formation as well as the levels of osteoprotegerin (OPG) and receptor activator of NFkappaB ligand (RANKL) mRNA in mouse bone-cell cultures by semiquantitative RT-PCR. 10(-8) M 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] significantly stimulated osteoclast formation and 10(-6) M statins (mevastatin and simvastatin) significantly antagonized osteoclast formation stimulated by 1,25(OH)2D3 in mouse bone-cell cultures, including both osteoblasts and osteoclasts. 10(-6) M mevastatin and simvastatin increased the level of OPG mRNA in mouse bone-cell cultures. On the other hand, 10(-6) M mevastatin and simvastatin inhibited the level of RANKL mRNA in these cultures. In conclusion, the present study demonstrates that statins inhibit osteoclast formation in mouse bone-cell cultures. Moreover, statins also increased and decreased the levels of OPG and RANKL mRNA expression in these cultures, respectively. The modulation of OPG/RANKL may be involved in the inhibition of osteoclast formation by statins.

Menin and TGF-beta superfamily member signaling via the Smad pathway in pituitary, parathyroid and osteoblast.

PITUITARY: Menin is a Smad3-interacting protein; inactivation of menin blocks transforming growth factor (TGF)-beta and activin signaling, antagonizing their growth-inhibitory properties in anterior pituitary cells. Menin is also required for the activin-induced inhibition of prolactin expression mediated by the Smads and the transcription factor, Pit-1. The interaction between menin and Smad3 is direct. PARATHYROID: In cultured parathyroid cells from uremic hemodialysis patients, in which the menin signaling pathways are probably still intact, menin inactivation achieved by menin antisense oligonucleotides leads to loss of TGF-beta inhibition of parathyroid cell proliferation and parathyroid hormone (PTH) secretion. Moreover, TGF-beta does not affect the proliferation and PTH production of parathyroid cells from multiple endocrine neoplasia type 1 (MEN1) patients. OSTEOBLAST: Men1-null mouse fetuses that die at day 12 or earlier have cranial/facial hypoplasias implicating menin in bone development. Menin is required for the commitment of multipotential mesenchymal stem cells into the osteoblast lineage. This is achieved by menin interacting physically and functionally with bone morphogenetic protein (BMP)-2 regulated Smads, such as Smad1 and Smad5, and the key osteoblast regulator, Runx2. These interactions are lost as the committed osteoblasts differentiate further at which time menin interacts with Smad3, mediating the negative regulation of Runx2 by TGF-beta. Menin also suppresses osteoblast maturation, partly by inhibiting the differentiation actions of JunD.

Testosterone increases osteoprotegerin mRNA expression in mouse osteoblast cells.

The role that androgens play in the regulation of bone metabolism has been substantiated in animals and humans. We previously demonstrated that testosterone inhibits osteoclast differentiation stimulated by parathyroid hormone through the androgen receptor in mouse bone-cell cultures. However, the details of this mechanism are still unknown. The present study was aimed at examining whether testosterone would affect the mRNA levels of osteoprotegerin (OPG) and receptor activator of Nf kappa B ligand (RANKL) in mouse bone-cell cultures as well as mouse osteoblastic cell-line, MC3T3-E1 cells by employing semi-quantitative RT-PCR. Testosterone increased OPG mRNA expression in both mouse bone-cell cultures and MC3T3-E1 cells. 10-8 M PTH-(1-34) as well as 10-8M 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] inhibited OPG mRNA expression in mouse bone cells. 10-8 M testosterone antagonized OPG mRNA expression inhibited by 10-8 M PTH-(1-34), but failed to affect OPG mRNA expression inhibited by 10-8 M 1,25(OH)2D3. 10-8 M alpha-dehydrotestosterone, a non-aromatizable androgen, increased OPG mRNA expression. On the other hand, testosterone did not affect RANKL mRNA expression in MC3T3-E1 or mouse bone cells. In conclusion, the present study demonstrated that testosterone increased OPG mRNA expression in mouse bone-cell cultures and the osteoblastic cell line. These effects are likely to take place through the androgen receptor.

Complete response of a stage IV mucinous cystadenocarcinoma of the ovary to systemic chemotherapy employing paclitaxel and carboplatin.

BACKGROUND: The survival rate of patients with advanced-stage mucinous cystadenocarcinoma of the ovary is dismal and no best treatment is known. We report a case of complete response of a stage IV mucinous cystadenocarcinoma of the ovary to systemic chemotherapy employing paclitaxel and carboplatin. CASE: A 51-year-old nullipara diagnosed with International Federation of Gynecology and Obstetrics stage IV mucinous cystadenocarcinoma of the ovary underwent cytoreductive surgery followed by systemic chemotherapy employing paclitaxel and carboplatin every 4 weeks for 3 courses. The patient tolerated chemotherapy well, demonstrated a remarkable response showing no evidence of malignancy at a second-look laparotomy. As a consolidation chemotherapy after negative second-look laparotomy, she underwent another three courses of chemotherapy of the same regimen, and is showing no evidence of disease. CONCLUSION: Paclitaxel and carboplatin may be effective in treating mucinous cystadenocarcinoma of the ovary.

Dual action of eicosapentaenoic acid in hepatoma cells: up-regulation of metabolic action of insulin and inhibition of cell proliferation.

Exogenous administration of eicosapentaenoic acid (EPA) improves insulin sensitivity, but its precise mechanism remains unknown. Here we show that EPA stimulates the intracellular insulin signaling pathway in hepatoma cells. Exposure of these cells to EPA caused up-regulation of several insulin-induced activities including tyrosine phosphorylation of insulin receptor substrate-1, insulin receptor substrate-1-associated phosphatidylinositol 3-kinase, and its downstream target Akt kinase activity as well as down-regulation of gluconeogenesis. In contrast, EPA decreased mitogen-activated protein kinase activity and inhibited cell proliferation. These findings raise the possibility that EPA up-regulates metabolic action of insulin and inhibits cell growth in humans.

Hormonal regulation of the human ghrelin receptor gene transcription.

The aim of this study is to clarify the hormonal regulation of the human ghrelin receptor gene expression in GH(3) cells transfected with our previously cloned 5'-flanking region inserted into a luciferase reporter vector. Phorbor 12-tetradecanoate 13-acetate (TPA) with simultaneous addition of Bay K8644 mimicking ghrelin action caused a significant inhibition of the luciferase activity through the ghrelin receptor gene upstream proximal to -669 but not to -608 base pairs (bp). Glucocorticoid caused a weak but significant inhibition of the luciferase activity through the ghrelin receptor gene upstream proximal to -531 but not to -475 bp. Electrophoretic mobility shift assay resulted in binding of oligonucleotides between -669 and -640 bp, and between -520 and -491 bp to GH(3) cell nuclear proteins unlike AP(2) or glucocorticoid receptor. These results suggest that both TPA/Bay K8644 and glucocorticoid downregulate human ghrelin receptor gene expression through the transcriptional mechanism involving some nuclear factors.

Inactivation of menin, a Smad3-interacting protein, blocks transforming growth factor type beta signaling.

Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant disorder characterized by endocrine tumors of parathyroids, pancreatic islets, and anterior pituitary. The MEN1 gene encodes a nuclear protein called menin. In MEN1 carriers inactivating mutations give rise to a truncated product consistent with menin acting as a tumor suppressor gene. However, the role of menin in tumorigenesis and its physiological functions are not known. Here, we show that menin inactivation by antisense RNA antagonizes transforming growth factor type beta-mediated cell growth inhibition. Menin interacts with Smad3, and antisense menin suppresses transforming growth factor type beta-induced and Smad3-induced transcriptional activity by inhibiting Smad3/4-DNA binding at specific transcriptional regulatory sites. These results implicate a mechanism of tumorigenesis by menin inactivation.

Skeletal responsiveness to parathyroid hormone in pseudohypoparathyroidism.

BACKGROUND: Although there have been some case reports suggesting that bone in patients with pseudohypoparathyroidism (PHP) might respond to parathyroid hormone (PTH), no information is available as to whether serum PTH concentration is related to bone metabolic markers or to bone mineral density (BMD) in PHP. OBJECTIVE: To address these relationships, by comparing intact serum PTH, bone metabolic markers and BMD in patients with PHP with those in patients with idiopathic hypoparathyroidism (IHP) and postoperative hypoparathyroidism (OHP). METHODS: Intact serum PTH, bone metabolic markers (osteocalcin, tartrate-resistant acid phosphatase, pyridinoline, deoxypyridinoline) and BMD by dual-energy X-ray absorptiometry or single-photon absorptiometry were measured in patients with PHP Ia (n=2) and PHP Ib (n=8). The results were compared with those in patients with IHP (n=5) and OHP (n=14). RESULTS: All bone metabolic markers measured were present in significantly greater amounts in patients with PHP Ib than in those with IHP+OHP. The Z score (standard deviation of average BMD at each age) of the BMD of femoral neck was significantly lower in patients with PHP Ib than in those with IHP+OHP. The Z scores of BMD of lumbar spine and radius were also lower in patients with PHP Ib than in those with IHP+OHP, but the difference was not significant. Moreover, the intact serum PTH concentrations were significantly and positively related to bone metabolic marker levels in all patients, and the intact serum PTH concentrations were significantly and negatively related to BMD of lumbar spine in PHP patients. CONCLUSIONS: These results suggest that PTH stimulates bone turnover in PHP Ib patients, resulting in a relatively lower BMD in PHP Ib patients than in IHP+OHP patients. The present study indicates that bones of most cases of PHP could respond to PTH.

Testosterone inhibits osteoclast formation stimulated by parathyroid hormone through androgen receptor.

Androgens play an important role in the regulation of bone metabolism in animals and humans. The present study was performed to investigate whether androgens would affect osteoclast formation stimulated by parathyroid hormone (PTH) in mouse bone cell cultures and its mechanism. Testosterone as well as alpha-dihydrotestosterone (DHT) concentration-dependently inhibited osteoclast formation induced by PTH-(1-34). 10(-8) M ICI 182780, an estrogen receptor inhibitor, did not affect PTH-induced osteoclast formation antagonized by 10(-8) M testosterone, although it completely antagonized the effects of 10(-8) M 17beta-estradiol. Moreover, 3 microM 4-androsten-4-ol-3,17-dione, an aromatase inhibitor, did not affect PTH-induced osteoclast formation antagonized by testosterone. Hydroxyflutamide, an androgen receptor antagonist, concentration-dependently antagonized the inhibitory effects of testosterone as well as DHT on PTH-stimulated osteoclast formation. In conclusion, the present study first demonstrated that testosterone inhibited osteoclast formation stimulated by PTH through the androgen receptor, but not through the production of intrinsic estrogen in mouse bone cell cultures.

The V kappa III subgroup light chain proteins in AL amyloidosis & autoimmune diseases.

BACKGROUND & OBJECTIVES: Light chain associated amyloidosis (AL) is characterized by extracellular deposition of immunoglobulin light chain and its fragments. In vitro and in vivo studies have shown that some light chains are nonamyloidogenic and nonnephrotoxic, whereas others are potentially amyloidogenic. Some light chains are prone to be deposited as rheumatoid materials, and also as nodular amorphous aggregates (light chain deposition diseases). These findings suggest that specific sequence element(s) may control the various kinds of light chain associated diseases. In this study we tried to identify such sequence element(s). METHODS: Two Bence Jones proteins (BJPs), NIG93 and NIG2 of subgroup V kappa III, were characterized and compared with other members of the same subgroup whose sequences are available in the data base. RESULTS: Both NIG93 and NIG2 proteins had sequences characteristics of V kappa IIIa as distinguished from V kappa IIIb, subsubgroup proteins. They also contained several novel substitutions, such as Met-37, Leu-40, Val-58, and IIe-85 in NIG93, and Val-2, His-29, Arg-50, and Ile-72 in NIG2. The data accumulated at present indicate that all members of the V kappa IIIa subsubgroup are related to either AL amyloidosis or rheumatoid arthritis, whereas the V kappa IIIb proteins are related to autoimmune diseases. INTERPRETATION & CONCLUSION: These observations indicate that subgroup-specific residues might be critical for light chain pathogenesis, at least for the V kappa III proteins. Point mutations within these proteins may be another structural element controlling their conformation as well as their pathogenic aggregation.

Structure-function study and anti-HIV activity of synthetic peptide analogues derived from viral chemokine vMIP-II.

The viral macrophage inflammatory protein II (vMIP-II) shows a broad spectrum interaction with both CC and CXC chemokine receptors including CCR5 and CXCR4, two principal coreceptors for the cellular entry of human immunodeficiency virus type 1 (HIV-1). Recently, we have shown that a synthetic peptide derived from the N-terminus of vMIP-II, designated as V1, is a potent antagonist of CXCR4 but not CCR5 [Zhou, N., et al. (2000) Biochemistry 39, 3782-3787]. In this study, we synthesized a series of new peptides derived from other regions of vMIP-II and characterized their binding activities with both CXCR4 and CCR5. The results provided further support for the notion that the N-terminus of vMIP-II is the major determinant for CXCR4 recognition and that vMIP-II probably interacts with other chemokine receptors such as CCR5 with different sequence and conformational determinants. To understand the structure-function relationship of V1 peptide, its solution conformation was studied using circular dichroism spectroscopy, which showed a random conformation similar to that of the corresponding N-terminus in native vMIP-II. In addition, we synthesized a series of mutant analogues of V1 containing alanine, glycine, or phenylalanine substitution at various positions. Residues Val-1, Arg-7, and Lys-9 of V1 peptide were found to be critical for receptor interaction, because single alanine replacement at these positions dramatically decreased peptide binding to CXCR4. In contrast, alanine or phenylalanine substitution at Cys-11 led to significant enhancement in peptide affinity for CXCR4. Finally, we showed that V1 peptide inhibits HIV-1 replication in CXCR4(+) T-cell lines. These studies provide new insights into the structure-function relationship of V1 peptide and demonstrate that this peptide may be a lead for the development of therapeutic agents.

Estrogen modulates osteoblast proliferation and function regulated by parathyroid hormone in osteoblastic SaOS-2 cells: role of insulin-like growth factor (IGF)-I and IGF-binding protein-5.

Although there is clinical evidence showing that combined therapy with parathyroid hormone (PTH) and estrogen is additively effective in increasing the bone mass of patients with osteoporosis, the mechanism of the interaction between these hormones remains unclear. The present study was performed to determine whether estrogen would affect osteoblast proliferation and function modulated by PTH in human osteoblastic SaOS-2 cells. Human PTH-(1-34) significantly inhibited [(3)H]thymidine (TdR) incorporation, which was attenuated by 24 h pretreatment with 10(-10) to 10(-7) M 17 beta-estradiol (17 beta-E(2)) in a concentration-dependent manner. PTH significantly stimulated alkaline phosphatase (ALP) activity, collagen synthesis and type-1 procollagen mRNA expression after pretreatment with 17 beta-E(2 )in these cells. Tamoxifen, an anti-estrogen, antagonized these 17 beta-E(2)-induced effects. Pretreatment with insulin-like growth factor-I (IGF-I) mimicked estrogen action, and coincubation of 3 microg/ml anti-IGF-I antibody antagonized the effects of 17 beta-E(2 )as well as those of IGF-I. In the presence of 17 beta-E(2 )pretreatment, PTH strongly stimulated IGF-binding protein (IGFBP)-5 mRNA expression in these cells, and recombinant IGFBP-5 increased type-1 procollagen mRNA expression and ALP activity. In conclusion, estrogen attenuates PTH-induced inhibition of osteoblast proliferation and PTH stimulates osteoblast function in the presence of estrogen pretreatment. IGF-I and/or IGFBP-5 seemed to be involved in the estrogen-induced modulation of PTH action on osteoblast proliferation and function.