Osteoclasts and transforming growth factor-beta: estrogen-mediated isoform-specific regulation of production.

Estrogen deficiency induced by menopause leads to an increase in bone resorption that is not compensated for by a comparable increase in bone formation, resulting in excessive bone loss. Clinically, estrogen replacement reverses these processes, but the mechanisms by which this takes place are not completely understood. Both osteoclasts and osteoblasts contain functional estrogen receptors and, therefore, may be directly involved in these responses.

Identification of a novel TGF-beta-regulated gene encoding a putative zinc finger protein in human osteoblasts.

The TGF-beta family of growth factors has been extensively studied and found to play major roles in bone physiology and disease. A novel, TGF-beta-inducible early gene (TIEG) in normal human fetal osteoblasts (hFOB) has been identified using differential-display PCR. Using this differentially expressed cDNA fragment of TIEG to screen a hOB cDNA library, a near full-length cDNA for this gene was isolated.

Mechanism of renal calcium conservation with estrogen replacement therapy in women in early postmenopause--a clinical research center study.

To assess the mechanism by which estrogen replacement therapy (ERT) enhances renal calcium conservation in perimenopausal women, we studied 18 normal women in early postmenopause before and after 6 months of ERT (cyclic treatment with transdermal estradiol at 100 micrograms/day and medroxyprogesterone acetate at 10 mg/day for the first 12 days of each cycle). The changes after ERT were: serum ionized calcium and ultrafiltrable calcium, no change; serum intact PTH, 38.2% increase (P < 0.

The worldwide problem of osteoporosis: insights afforded by epidemiology.

Osteoporosis is one of the major problems facing women and older people of both sexes. The morbid event in osteoporosis is fracture. However, the definition of osteoporosis should not require the presence of fractures but only a decrease in bone mass that is associated with an unacceptably high risk of fracture.

Role of parathyroid hormone in mediating nocturnal and age-related increases in bone resorption.

PTH has been postulated to play a role in both nocturnal and age-related increases in bone resorption. We tested this hypothesis directly in 10 young (ages 24-35 yr) and 10 elderly (ages 71-78 yr) normal women by measuring the cross-linked N-telopeptide of type I collagen (NTx), a marker for bone collagen breakdown, in 4-h urine collections before and during suppression of PTH secretion by a 24-h iv infusion of calcium. Serum ionized calcium and PTH levels were also measured every 2 h before and during the infusion.

Estrogen response in the hFOB 1.19 human fetal osteoblastic cell line stably transfected with the human estrogen receptor gene.

The gene coding for the human wild-type estrogen receptor (ER) was stably transfected into the human fetal osteoblastic cell line hFOB 1.19, a clonal cell line which is conditionally immortilized with a temperature sensitive mutant of SV40 large T antigen (tsA58). Five subclones were obtained which express various levels of ER mRNA and protein.

Treatment options for osteoporosis.

The number of women affected by postmenopausal osteoporosis is likely to continue to increase substantially as the population ages. Furthermore, the therapeutic options for such patients are likely to increase. In this brief review, we outline the use of the currently available medications for the management of osteoporosis--namely, estrogen, calcitonin, calcium, and vitamin D.

Role of hyperbilirubinemia in the impairment of osteoblast proliferation associated with cholestatic jaundice.

Because the osteoporosis occurring in chronic cholestatic liver disease (CCLD) is associated with decreased bone formation and is reversible by liver transplantation, substances retained in plasma during cholestasis may impair osteoblast function. This hypothesis was tested using a new bioassay that measures plasma mitogenic activity (PMA) for normal human osteoblast-like (hOB) cells. In 29 jaundiced patients, mean PMA was 56.

The contribution of vitamin D receptor gene alleles to the determination of bone mineral density in normal and osteoporotic women.

Bone mass and its mineral content are under genetic control. The vitamin D receptor (VDR) gene has been shown to be a major locus for genetic effects on bone mineral density (BMD), and polymorphisms in this gene accounted for a large proportion of genetic variance in BMD in an Australian population. In this study, we investigated whether similar associations are present in a North American population.

Zeolite A inhibits osteoclast-mediated bone resorption in vitro.

The effects of Zeolite A on bone resorbing activity of highly purified avian osteoclasts were analyzed. The present study demonstrates that when 100 micrograms/ml of acid-treated Zeolite A is added to the media the number of pits per osteoclast is reduced 3-fold at 24 h after treatment. Secreted cathepsin B enzyme activity was also reduced 3-fold.

Normal human osteoblast-like cells consistently express genes for insulin-like growth factors I and II but transformed human osteoblast cell lines do not.

Insulin-like growth factors I (IGF-I) and II (IGF-II) are anabolic for osteoblastic cells. Although expression of IGF-I and IGF-II mRNA has been demonstrated in rodent osteoblastic cells, little is known about IGF gene expression in human osteoblastic cell models. In this study we characterized IGF-I and -II mRNA expression in (1) normal human osteoblast-like (hOB) cells, (2) a simian virus 40 immortalized hOB (HOBIT) cell line, and (3) human osteosarcoma cell lines SaOS-2, TE-85, MG-63, and U-2.

Alterations in insulin-like growth factor (IGF)-dependent IGF-binding protein-4 proteolysis in transformed osteoblastic cells.

Insulin-like growth factor (IGF)-binding protein-4 (IGFBP-4) is secreted by a variety of osteoblastic cells and appears to be an integral component of bone cell physiology. We have previously reported that normal human osteoblast-like (hOB) cells secrete IGFBP-4 as well as a novel IGFBP-4 protease, which requires IGF for functional activity. In this study we assessed the IGFBP-4/IGFBP-4 protease system in transformed osteoblastic cells by Western ligand blotting and cell-free IGFBP-4 protease assays.

Histomorphometric analysis of iliac crest bone biopsies in placebo-treated versus fluoride-treated subjects.

In a 4-year controlled, prospective trial, histomorphometric analysis was used to compare the tissue-level skeletal effects of fluoride therapy in 43 postmenopausal women (75 mg NaF/day) with those of 35 matching placebo subjects; all subjects received 1500 mg/day elemental calcium supplement. In addition to an initial, baseline biopsy, a second biopsy was obtained after 6, 18, 30 or 48 months. Measurements were made on a third biopsy obtained from 8 subjects following at least 72 months of fluoride therapy.

Transforming growth factor-beta and forskolin increase all classes of insulin-like growth factor-I transcripts in normal human osteoblast-like cells.

In this study, we examined regulation of insulin-like growth factor I (IGF-I) gene expression and transcript splicing in normal human osteoblast-like cells. Previous studies in rat osteoblastic cells have indicated that transforming growth factor-beta (TGF-beta) inhibits IGF-I expression, whereas inducers of intracellular cAMP stimulate IGF-I expression. However, in human osteoblast-like cells both TGF-beta and forskolin increased IGF-I mRNA levels in a time- and dose-dependent manner.

Regulation of c-fos expression and TGF-beta production by gonadal and adrenal androgens in normal human osteoblastic cells.

Although the role of estrogens in bone formation is becoming clarified, the function of androgens in this process remains to be defined. Consequently, we have explored the mechanism of action for both gonadal and adrenal androgens in normal human osteoblastic (hOB) cells, which are responsible for the synthesis and mineralization of bone. Changes in the steady-state mRNA levels for two nuclear proto-oncogenes (c-fos and c-jun) and one cytokine (TGF-beta 1) were quantified in response to short (30 min) and long (24-48 h) treatments of these cells with physiologic concentrations of steroids.

Development and characterization of a conditionally immortalized human fetal osteoblastic cell line.

We report the establishment of a human fetal osteoblast cell line derived from biopsies obtained from a spontaneous miscarriage. Primary cultures isolated from fetal tissue were transfected with a gene coding for a temperature-sensitive mutant (tsA58) of SV40 large T antigen along with a gene coding for neomycin (G418) resistance. Individual neomycin resistant colonies were screened for alkaline phosphatase (AP)-specific staining.

TGF-beta regulation of nuclear proto-oncogenes and TGF-beta gene expression in normal human osteoblast-like cells.

Transforming growth factor-beta (TGF-beta) is present in high levels in bone and plays an important role in osteoblast growth and differentiation. In order to dissect the molecular mechanisms of action of TGF-beta on osteoblasts, the effects of TGF-beta on the steady state mRNA levels of c-fos, c-jun, and jun-B proto-oncogenes on normal human osteoblast-like cells (hOB) and a transformed human osteoblast cell line (MG-63) were measured. Treatment of hOBs with 2 ng/ml of TGF-beta 1 resulted in a rapid increase in c-fos mRNA levels as early as 15 min post-treatment.

Regulation of insulin-like growth factor (IGF)-binding protein-4 availability in normal human osteoblast-like cells: role of endogenous IGFs.

Insulin-like growth factor-binding protein-4 (IGFBP-4) is an important regulator of insulin-like growth factor-I (IGF-I) anabolic activity in bone. Although cultured human osteoblast-like (hOB) cells have been reported to secrete IGFBP-4, we could not detect IGFBP-4 protein in 8 of 27 individual donor-derived hOB-cell conditioned medium (hOB-CM) samples examined by Western ligand blotting. Nonetheless, this subset of hOB cells had normal IGFBP-4 messenger ribonucleic acid expression and protein secretion.

The insulin-like growth factor-binding protein-4 (IGFBP-4)-IGFBP-4 protease system in normal human osteoblast-like cells: regulation by transforming growth factor-beta.

Insulin-like growth factor-binding protein-4 (IGFBP-4) is secreted by normal human osteoblast-like (hOB) cells and acts as a potent inhibitor of IGF action. hOB cells also secrete a protease, which requires IGFs for activation and specifically cleaves IGFBP-4. To study the regulation of this IGFBP-4 protease, hOB cells from 26 different adult donors were cultured in serum-free medium for 24 h in the absence or presence of hormones and other factors known to regulate bone growth.

Influence of age on effects of endogenous 1,25-dihydroxyvitamin D on calcium absorption in normal women.

Recent reports of increases in serum 1,25-dihydroxyvitamin D [1,25(OH2)D] concentration with aging despite no changes or decreases in calcium absorption suggest that elderly women have intestinal resistance to vitamin D action. Thus, in 15 young adult (30 +/- 1 year) and 15 elderly (74 +/- 1 year) women (mean +/- SE), we assessed the responsiveness of intestinal calcium absorption to increases in circulating 1,25(OH)2D induced by 4 days of an experimental diet (150 mg calcium and 1600 mg phosphorus daily). True fractional calcium absorption (FCA) (44Ca mixed with food and 42Ca given intravenously, then their ratio in urine measured by mass spectrometry) was determined.

Pamidronate: an unrecognized problem in gastrointestinal tolerability.

Pamidronate (aminohydroxypropylidine bisphosphonate, APD) is an effective agent for treatment of Paget's disease of bone, and it has also been thought to be effective for treatment of osteoporosis. We desired to study a newer, time-release preparation of pamidronate, and carried out a placebo-controlled, double-masked study of postmenopausal osteoporosis. The original formulation was in a rapidly dissolving gelatin capsule.

Circulating cytokine levels in osteoporotic and normal women.

Interleukin-1 (IL-1) and IL-6 have been postulated to play roles in the pathogenesis of postmenopausal osteoporosis. To test this hypothesis, we measured circulating levels of IL-6, IL-1 alpha, and IL-1 beta in 40 age-matched normal and 40 osteoporotic women with vertebral fractures and increased bone turnover. Since IL-1 activity is modulated by the IL-1 receptor antagonist (IL-1ra), we also measured circulating IL-1ra levels in these women.

Comparison of respondents and nonrespondents in an osteoporosis study.

We attempted to enroll an age-stratified random sample of Rochester, Minnesota women > or = 30 years of age in a population-based prospective study of the determinants of bone loss. Using the resources of the Rochester Epidemiology Project, 541 women were contacted and 305 agreed to participate. Of 236 nonrespondents, 38 were ineligible and 198 refused to participate resulting in a 61% response rate for eligible subjects.