CBFA1 and topoisomerase I mRNA levels decline during cellular aging of human trabecular osteoblasts

In order to understand the reasons for age-related impairment of the function of bone forming osteoblasts, we have examined the steady-state mRNA levels of the transcription factor CBFA1 and topoisomerase I during cellular aging of normal human trabecular osteoblasts, by the use of semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR). There is a progressive and significant reduction of the CBFA1 steady-state mRNA level down to 50% during cellular aging of human osteoblasts. In comparison to the normal cells, human osteosarcoma cell lines SaOS-2 and KHOS/NP, and the SV40-transformed human lung fibroblast cell line MRC5V2 have 20 to 40% higher levels of CBFA1 mRNA. Similar levels of CBFA1 mRNA are detectable in normal human skin fibroblasts, and these cells also exhibit an age-related decline to the same extent. In addition, the expression of topoisomerase I is reduced by 40% in senescent osteoblasts, and the mRNA levels are significantly higher (40-70%) in transformed osteoblasts and fibroblasts. These changes in gene expression may be among the causes of impaired osteoblast functions, resulting in reduced bone formation during aging.

Biochemical markers of bone metabolism reflect osteoclastic and osteoblastic activity in multiple myeloma

In order to evaluate the use of recently developed assays of bone metabolism in multiple myeloma we performed a histomorphometric study of bone biopsies in 16 myeloma patients. Furthermore, we measured the levels of interleukin-6 (IL-6), soluble IL-6 receptor (IL-6sR), IL-1beta, tumour necrosis factor (TNF) alpha, TNFbeta, and transforming growth factor (TGF) beta in marrow plasma aspirated from the biopsy area. MARKERS OF BONE RESORPTION: The N-terminal telopeptide of collagen I (Ntx) in urine showed a strong positive correlation with the dynamic histomorphometric indices of bone resorption (r=0.68-0.72). Slightly weaker correlations were observed between the dynamic indices of bone resorption and the C-terminal telopeptide of collagen I (ICTP) in serum (r= 0.57-0.62) and deoxypyridinoline (Dpyr) in urine (r= 0.54), whereas urinary pyridinoline (Pyr) did not correlate with the histomorphometric findings. MARKERS OF BONE FORMATION: Serum C-terminal propeptide of procollagen I (PICP) and serum bone-specific alkaline phosphatase (bAP) showed significant correlations with the dynamic parameters of bone formation (r=0.57-0.58), whereas serum osteocalcin and serum total AP did not. CYTOKINES: Highly significant correlations were observed between marrow IL-6 and rates of bone resorption and activation frequency (r=0.76-0.82) and with serum ICTP (r=0.63). Minor, but also significant correlations were observed between the resorptive indices and IL-6sR and IL-1beta. The data indicate that measurements of the biochemical markers of bone metabolism may be useful in monitoring myeloma bone disease, and might thus be of use for dose titration of bisphosphonate therapy.

Familial isolated hyperparathyroidism as a variant of multiple endocrine neoplasia type 1 in a large Danish pedigree

We report here our genetic findings of a family in which 14 members were affected with isolated primary hyperparathyroidism. Hyperparathyroidism is the main feature of multiple endocrine neoplasia type 1 (MEN1), making the recently cloned MEN1 gene a prime candidate gene in this family. Significantly positive lod scores were achieved with D11S4946 (3.36) and D11S4940 (3.53), and by combining the results from these two markers, a maximum positive lod score of 4.12 at recombination fraction 0.00 was obtained. Mutation analysis of MEN1 performed by full sequencing identified a missense mutation in exon 4, causing an amino acid change from glutamine to proline at codon 260. This mutation (Q260P) was present in all affected family members, and the inheritance of the mutation was in complete agreement with the disease-associated haplotype. In comparison with the recent functional studies of the menin protein interactions, this mutation is located in a region with little or no binding activity to JunD and activating protein-1 transcription factor. We conclude that some of the familial isolated primary hyperparathyroidism families constitute a milder variant of MEN 1, which is associated with a functionally milder missense mutation.

Hormone replacement therapy prevents osteoclastic hyperactivity: A histomorphometric study in early postmenopausal women

In a randomized, double blind, clinical prospective trial comprising 35 women treated with either hormone replacement therapy (HRT) (cyclic estradiol/norethisterone acetate) or placebo we performed histomorphometric studies on paired bone biopsies obtained before and after 2 years of treatment. Untreated women developed a progressively more negative balance at individual bone multicellular units (BMUs) (i.e., wall thickness-erosion depth) (2.2 +/- 1.7 microm vs. -5.7 +/- 1.4 microm; p < 0.01), while women on HRT displayed preservation of bone balance (2.4 +/- 2.4 microm vs. 2.5 +/- 2.5 microm; NS). No significant differences in wall thickness between the two groups were demonstrable, but the untreated women developed a pronounced increase in erosion depth over 2 years (46.9 +/- 1.8 microm vs. 52.0 +/- 1.9 microm; p < 0.05), while the HRT group revealed no change (47.8 +/- 2.7 microm vs. 44.6 +/- 1.7 microm; NS). Furthermore, the placebo group displayed an increased osteoclastic erosion depth (17.8 +/- 1.6 microm vs. 25.0 +/- 1.7 microm; p < 0.001), compared with unchanged values in the HRT group (20.0 +/- 1.6 microm vs. 16.9 +/- 1.4 microm/day; NS). While the placebo group revealed a slight increase in volume referent resorption rate (35 +/- 8% vs. 38 +/- 8%; NS) the HRT group revealed a pronounced decrease (46 +/- 8% vs. 28 +/- 5%; p < 0.05). No significant changes in marrow star volume (an index of trabecular perforations) were demonstrable in either group. Our results demonstrate that bone remodeling in early postmenopausal women is characterized by progressive osteoclastic hyperactivity, which is reduced by cyclic HRT. This reduction of resorptive activity at the BMU level after HRT seems to precede the reduction in activation frequency demonstrated in previous studies on older postmenopausal women.

Telomere shortening during aging of human osteoblasts in vitro and leukocytes in vivo: lack of excessive telomere loss in osteoporotic patients

We have compared the telomere length, as assessed by Southern analysis, of telomere restriction fragments (TRFs) generated by RsaI/HinfI digestion of genomic DNA in: (i) in vitro cultured human trabecular osteoblasts undergoing cellular aging; and (ii) peripheral blood leukocytes (PBL) obtained from three groups of women: young (aged 20-26 years, n = 15), elderly (aged 48-85 years, n = 15) and osteoporotic (aged 52-81 years, n = 14). The mean TRF length in human osteoblasts undergoing aging in vitro decreased from an average of 9.32 kilobasepairs (kb) in middle-aged cells to an average of 7.80 kb in old cells. The rate of TRF shortening was about 100 bp per population doubling, which is similar to what has been reported for other cell types, such as human fibroblasts. Furthermore, there was a 30% decline in the total amount of telomeric DNA in senescent osteoblasts as compared with young cells. In the case of PBL, TRF length in the DNA extracted from young women was slightly longer (6.76 +/- 0.64 kb) than that from a group of elderly women (6.42 +/- 0.71 kb). A comparison of TRFs in the DNA extracted from the PBL from osteoporotic patients and from age-matched controls did not show any significant differences (6.47 +/- 0.94 versus 6.42 +/- 0.71 kb, respectively). Therefore, using TRF length as a marker for cellular aging in vitro and in vivo, our data comparing TRFs from osteoporotic patients and age-matched controls do not support the notion of the occurrence of a generalized premature cellular aging in osteoporotic patients.

Effects of growth hormone treatment on serum levels of insulin-like growth factors (IGFs) and IGF binding proteins 1-4 in postmenopausal women

BACKGROUND AND OBJECTIVE

Insulin-like growth factor binding proteins (IGFBPs) modulate the actions and bioavailability of insulin-like growth factors (IGFs), however, their regulation in vivo is incompletely understood. In this study we investigated the effects of different doses of growth hormone (GH) on circulating levels of IGFs and IGFBPs.

DESIGN

The study was double-blind and placebo-controlled. Patients were treated with either GH in doses of 0.05, 0.10, or 0.20 lU/kg/day of placebo for one week.

PATIENTS

Forty post-menopausal women aged 52-73 years with low bone mass.

MEASUREMENTS

Serum IGF-I and IGF-II were measured by RIA while IGFBP-1-3 were measured by Western ligand blot (WLB) and compared with determinations by specific immunoassays. IGFBP-4 was measured by WLB alone.

RESULTS

Both IGF-I (P < 0.001) and IGF-II (P < 0.01) increased significantly during GH treatment. Additionally, IGFBP-1 (P < 0.001) and IGFBP-2 (P < 0.001) decreased significantly while IGFBP-3 (P < 0.001) and IGFBP-4 (P < 0.05) increased all in a dose-dependent manner. Stepwise (backwards) multiple regression analyses showed that the changes in IGF-I and IGF-II, and age correlated with the change in serum IGFBP-1. Both GH-dosage, the increase in IGF-II, and body mass index correlated with the decrease in IGFBP-2. Furthermore, the increase in serum IGF-I, IGF-II, and triiodothyronine correlated with the increase in IGFBP-3. Moreover, GH-dosage correlated with the increase in serum IGFBP-4.

CONCLUSION

GH significantly increased serum IGF-I, IGF-II, IGFBP-3, and IGFBP-4 and decreased serum IGFBP-1 and IGFBP-2 in post-menopausal women.

Long-term oral pamidronate treatment inhibits osteoclastic bone resorption and bone turnover without affecting osteoblastic function in multiple myeloma

This study was performed as a cross-sectional substudy to the Danish-Swedish Pamidronate Study, a randomized placebo-controlled multicentre trial in multiple myeloma. The purpose was to evaluate the biological effects of long-term treatment with oral pamidronate 300 mg daily on bone metabolism by using histomorphometry and analysis of cytokines and biochemical markers of bone turnover. Sixteen patients were included after median 27.5 months of protocolized treatment; 10 patients received active treatment and 6 patients placebo. When compared with placebo, pamidronate treatment was associated with: (a) marked decreased osteoclastic resorption rate (0.86+/-0.59 microm/d vs. 5.7+/-5.0 microm/d, p=0.002), and diminished activation frequency (0.20+/-0.18 yr(-1) vs. 0.72+/-0.55 yr(-1), p=0.014); (b) compensatory reduced volume referent bone formation rate (0.17+/-0.21 yr(-1) vs. 0.71+/-0.54 yr(-1), p=0.007), but unaltered mineral appositional rate; (c) neutral (-0.66+/-5.6 mm) vs. negative (-2.15+/-2.2 microm, p=0.013) bone balance per remodelling cycle; (d) higher trabecular bone volume (21.0+/-6.2% vs. 13.0+/-3.7%, p=0.01); (e) suppressed urinary excretion and serum levels of some of the biochemical markers of bone metabolism; and (f) significant reduction of circulating soluble interleukin-6 receptor (IL-6sR) (25.9+/-4.1 ng/ml vs. 32.1+/-6.6 ng/ml, p=0.04), and (g) a uniform tendency of lower serum and marrow plasma levels of IL-6, IL-1beta, and TNFalpha. Thus oral pamidronate was absorbed in biologically active amounts, and reduced overall bone resorption and bone turnover without impairing osteoblastic bone formation. The observation that cytokine and cytokine receptor levels were reduced extends the possible and potential beneficial actions of bisphosphonates in multiple myeloma.

Cloning and identification of genes that associate with mammalian replicative senescence

Cellular senescence and limited proliferative capacity of normal diploid cells has a dominant phenotype over immortality of cancerous cells, suggesting its regulation by the expression of a set of genes. In order to isolate the genes that associate with senescence, we have employed a clonal system of conditional SV40 T antigen rat embryo fibroblast cell lines which undergo senescence upon T antigen inactivation. Construction of cDNA libraries from two conditional cell lines and application of differential screening and subtractive hybridization techniques have resulted in the cloning of eight senescence-induced genes (SGP-2/Apo J, alpha 1-procollagen, osteonectin, fibronectin, SM22, cytochrome C oxidase, GTP-alpha, and a novel gene) and a senescence-repressed gene (FRS-2). Three of these genes encode for extracellular matrix proteins, others are involved in the calcium-dependent signal transduction pathways, while the SGP-2/Apo J gene may have a cellular protective function. RNA analysis has shown that the senescence-associated genes are overexpressed in both normal rat embryonic fibroblasts and human osteoblasts cell cultures undergoing aging in vitro. In comparison, the expression of these genes in a rat fibroblast immortalized cell line (208F cells) was down-regulated after both its partial and its full transformation by ras oncogenes. Thus, cloning of senescence-associated genes opens up new ways to elucidate and/or to modulate aging and cancer.

The effects of IGF-I and IGF-II on proliferation and differentiation of human osteoblasts and interactions with growth hormone

BACKGROUND

We have previously shown that growth hormone (GH) consistently stimulates proliferation of human osteoblasts in vitro. In rat osteoblasts, GH augments the effects of insulin-like growth factor (IGF) I on cell proliferation and differentiation. We therefore investigated the effects of IGF-I and -II alone and in combination with GH on human osteoblasts in vitro.

METHODS

Human osteoblast-like cells (HOB) were established from trabecular explants (n = 18) and human marrow stromal cells (HMS) from marrow aspiration (n = 21). The cell cultures were stimulated with IGF-I or IGF-II (1, 10 or 100 ng mL-1) alone, in combination with hGH (100 ng mL-1) or after prestimulation with hGH.

RESULTS

IGF-I alone, in combination with hGH and after pretreatment with hGH, increased proliferation of HOB and HMS by 49-190% (P < 0.05-0.01). IGF-II alone, in combination with hGH and after pretreatment with hGH increased proliferation of HOB by 57-158% (P < 0.01). In HMS only IGF-II in combination with hGH and after prestimulation with hGH increased proliferation. IGF-I alone and in combination with hGH decreased alkaline phosphatase (AP) in both cell types. IGF-II did not affect AP in HOB, but increased AP in HMS, this effect was abolished by hGH. In HOB, collagen production (PICP) was increased by IGF-II but unaffected by IGF-I. In HMS, PICP was decreased by IGF-I and -II but increased by hGH. Co-stimulation further increased PICP.

CONCLUSION

IGF-I and -II exerted proliferative effects on both HOB and HMS. Co-stimulation with GH exhibited synergism in enhancing the proliferative response. In HMS prestimulation improved the proliferative response significantly. The effects of the IGFs on differentiation are more complex and dependent on cell maturation and of the IGF used.

Estrogen effects on insulin-like growth factor gene expression in a human osteoblastic cell line with high levels of estrogen receptor

Insulin-like growth factors (IGF)-I and IGF-II are produced by osteoblasts and are important paracrine/autocrine regulators of osteoblast proliferation and differentiation. Estrogen has been reported to increase gene expression of IGF-I in rodent osteoblasts. However, because species differences have been demonstrated in expression of various aspects of the IGF system in bone cells, it is not known whether this action also occurs in human osteoblasts. Thus, we assessed the effects of estrogen treatment on IGF-I and IGF-II gene expression in vitro in a recently developed human fetal osteoblast cell line that has high levels of estrogen receptors. As assessed by a quantitative reverse transcriptase-polymerase chain reaction method, treatment of hFOB/ER9 cells with 17beta-estradiol (E2) increased steady state levels of IGF-I mRNA in a time- and dose- dependent fashion with a maximal increase of 319% +/- 33% (P < 0.01) of control occurring after treatment with 10(-7) M E2 for 48 hours. In contrast, E2 did not alter steady state levels of IGF-II mRNA. The pure (type 2) antiestrogens ICI 182,780 (10(-7) M) and ICI 164,384 (10(-6) M) blocked the E2- induced increase in IGF-I mRNA levels. Interestingly, 4-hydroxytamoxifen (10(-7) M), a documented pure antiestrogen in reproductive tissues, also increased IGF-I mRNA to levels similar to those observed in E2-treated cells. Since E2 was shown to mediate its effects on some target genes through a cAMP-dependent pathway, we studied the interaction between E2 and agents that are known to increase intracellular cAMP. Forskolin (10(-8) M) and dibutyryl cAMP (10(-3) M) increased IGF-I mRNA levels sixfold, and cotreatment with E2 did not affect these changes, consistent with a possible mediation of the estrogen effect on IGF-I gene expression by cAMP. We conclude that in human osteoblastic cells, the IGF-I gene is a target for estrogen action, suggesting that IGF-I may mediate part of the effects of estrogen in human bone.

Cellular and molecular effects of growth hormone and estrogen on human bone cells

The aim of the present thesis is to examine some aspects of the biological effects of growth hormone (GH) and estrogen on bone cells in vitro. The first part of the thesis describes characterization of model systems to study normal human osteoblasts and osteoclasts in vitro. Three culture systems for human osteoblasts have been characterized, representing different stages of osteoblasts differentiation/maturation: (1) mature osteoblasts cultured from trabecular bone explants (trabecular osteoblasts), (2) less mature osteoblasts (stromal osteoblasts) cultured from bone marrow and (3) osteoblast precursor cells cultured also from bone marrow. This classification is based on quantitative and qualitative differences in the expression of osteoblast phenotypic markers by these cells. These systems are useful in studying the regulation of hormones and growth factors of different stages of osteoblast differentiation. Further characterization of the osteoblast differentiation pathway is still needed, especially the identification of surface markers that can definitively identify intermediate stages of osteoblast differentiation. Normal human osteoclasts were cultured from bone marrow mononuclear cells and exhibited the main characteristics of osteoclast phenotype: production of tartrate-resistant acid phosphatase, presence of a ruffled border and the ability to resorb mineralized matrix. This model is useful for studying factors regulating osteoclast commitment and differentiation. The second part of the thesis deals with the effects of GH on proliferation and differentiation of trabecular and stromal osteoblasts. Effects of GH on human osteoblasts were dependent on their degree of maturation. GH stimulated cell proliferation in both trabecular and stromal osteoblasts. While it increased the functional activity of trabecular osteoblasts, these effects were absent in stromal osteoblast cultures. Human trabecular osteoblasts produce mainly IGF-II, IGFBP-3 and minute quantities of IGF-I in culture. GH does not seem to regulate the local production of IGF-II or IGFBP-3. However, IGFs and their binding proteins may exert important regulatory effects on the biological effects of GH on human osteoblasts, and this role needs to be studied. Sincer GH exerted profound effects on the biological functions of human osteoblasts in vitro, the hypothesis that either decreased production of GH or decreased sensitivity of bone cells to its action leads to bone loss and osteoporosis was examined. No differences in the basal or GH-stimulated production of IGF-I, IGF-II or IGFBP-3 were found between osteoporotic patients and age-matched normals. Similarly, The response of bone cells to in vivo and in vitro stimulation by GH was similar in the two groups. These studies do not support the hypothesis of the presence of major defects in production of GH or the presence of resistance to its effects in bone cells in patients with osteoporosis. The last part of the thesis deals with the cellular mechanisms mediating estrogen actions on bone cells. Thus, the potential role of estrogen regulation of bone-resorbing cytokines in the pathogenesis of bone loss in postmenopausal women was examined. Estrogen was found to inhibit IL-6 production and gene expression in an immortalized human osteoblastic cell line expressing high levels of estrogen receptors (hFOB/ER9 cell line). To further examine the relationship between estrogen deficiency and early postmenopausal bone loss, levels of IL-6, IL-6sR, IL-1 alpha, IL-1 beta and IL-1ra were measured in bone marrow plasma and bone marrow cultures obtained from 40 postmenopausal women, half of whom were on estrogen replacement therapy. No difference was found between the groups in any of these parameters. This suggests that neither IL-1 nor IL-6 by itself is the major mediator for increased bone loss due to estrogen deficiency in the early postmenopausal period. (ABSTRACT TRUNCATED)

[Apoptosis: molecular aspects]

Many signals and external stimuli regulate the apoptosis activity by interaction with the genome. These stimuli include morphogenetic signals, physiological factors, and environmental influence. The signals mediate their effect on cells with suitable receptors, relevant signalling pathways, and competence to execute the apoptosis cascade. Apoptosis is triggered indirectly by deprivation of survival factors, or directly by intercellular cell death signalling factors, and also by unbalanced intracellular messenger molecules, which are, more or less, involved in regulation of both programmed cell death and survival. Several genes are involved in regulation of cell survival and apoptosis: bcl-2/bax, p53, c-myc and transcription factors such as cdk, c-myc, c-fos and c-jun. Apparently, apoptosis could be triggered by increased or inhibited gene expression as well as biochemical reactions without changed gene expression. The morphological changes during apoptosis reflect a cascade of genetic and biochemical reactions in the cell. In the signal transduction pathway both secondary messenger Ca2+, different kinases, and polyamines are involved. Cysteine proteases cleave cytoskeletal proteins, endonucleases divide DNA into fragments, and transglutaminases cross-link macromolecules. Degradative enzymes such as proteases, endonucleases and transglutaminases are activated during apoptosis, leading to cellular collapse and formation of vesicular apoptotic bodies. Both increased and inhibited apoptosis activity may have pathological consequences. New therapeutic strategies aim to counteract dysregulation of apoptosis in specific tissues by pharmacological intervention. Thus there is a need for identification of molecules and gene products involved in regulation of apoptosis activity and clarification of the conditions where this knowledge may be used.

Demonstration of cellular aging and senescence in serially passaged long-term cultures of human trabecular osteoblasts

The proliferative capacity and cellular and biochemical characteristics of human trabecular bone osteoblasts were analysed throughout their replicative lifespan in vitro. Like several other cell types, human osteoblasts demonstrated a typical Hayflick phenomenon of cellular aging comprising a period of rapid proliferation until cumulative population doubling level (CPDL) 22 to 24, followed by a phase of slow growth and the final cessation of cell division at CPDL 32 to 34. Comparing young cells (less than 20% lifespan completed) and old cells (more than 90% lifespan completed) revealed a progressive increase in population doubling (PD) time, a decrease in attachment frequency, a decrease in the number of S-phase positive cells, a decrease in the rates of DNA, RNA and protein synthesis, an increase in the protein content per cell and an increased proportion of senescence-specific beta-galactosidase positive cells. While osteoblastic production of collagen type I decreased progressively during aging, alkaline phosphatase activity dropped rapidly after the first few passages and then remained constant during the rest of the proliferative lifespan, Significant morphological changes from thin and spindle-shaped early passage young cells to large, flattened and irregularly shaped late passage old cells full of intracellular debris were observed. In comparison, osteoblasts established from an osteoporotic bone sample showed a maximum CPDL of less than 5, had a longer PD time and exhibited abnormal senescent morphology. Thus, we have demonstrated for the first time that human osteoblasts, like several other diploid cell types, have a limited proliferative capacity in vitro and undergo aging and senescence as measured by various cellular and biochemical markers. In addition, preliminary studies show that cells from osteoporotic bone have a severely reduced proliferative capacity. This model of bone cell aging facilitates study of the molecular mechanisms of osteoblast senescence as well as factors related to osteoblast dysfunction in patients with osteoporosis.

European and North American Experience with HRT for the prevention of osteoporosis

Hormone replacement therapy (HRT) has been the method of choice for the prevention of postmenopausal osteoporosis since the early 1990s. Although a number of routes of administration are now available, HRT is still predominantly administered orally. In the United States, HRT formulations traditionally comprise conjugated equine estrogens. In Europe, however, HRT preparations tend to be based on 17 beta-estradiol, a natural human estrogen. Furthermore, distinct patterns of HRT use are apparent based on the age of the woman receiving it. Current recommendations are that early postmenopausal women (in their early 50s) receive sequential combined estrogen/progestogen therapy with continued monthly bleeds, while in women who are at least 1 year postmenopausal, continuous combined HRT, which leads to endometrial atrophy and cessation of monthly bleeding, is preferred. Clinical experience to date clearly demonstrates that long-term HRT unequivocally increases bone mass and reduces the risk of fractures in postmenopausal women, with no significant differences between sequential and continuous combined prescribing regimens. Data demonstrating that antiestrogens such as tamoxifen may preserve bone mass have led to the initiation of large-scale trials to determine the potential clinical utility of such agents for the prevention of osteoporosis in postmenopausal women. Nonhormonal therapeutic approaches are now also available, most notably bisphosphonates and vitamin D analogs. At present, however, traditional HRT remains the regimen of choice for the prevention of postmenopausal osteoporosis, given its additional beneficial effects on acute menopausal symptoms, as well as on the cardiovascular system and brain.

Isolation and characterization of osteoblast precursor cells from human bone marrow

Osteoblasts are derived from precursor cells present in low frequency in the stromal element of bone marrow. Because of the lack of a practical procedure to isolate osteoblast precursors from early cultures of plastic adherent cells from bone marrow, previous studies of marrow stromal cells have been made in confluent cultures of bone marrow when the osteoblast (OB) precursors are already differentiated. Also these studies utilized cultures containing mixed populations of cells including hematopoietic cells. Thus we have employed a negative immunoselection procedure to remove contaminating hematopoietic cells and to isolate nearly homogeneous populations of early human stromal cells derived from the plastic-adherent mononuclear marrow cells cultured in the presence of serum. By reverse transcriptase polymerase chain reaction (RT-PCR) analysis for mRNA, and by immunocytochemical study for protein, we studied the sequential expression in culture of multiple markers of the osteoblast phenotype--alkaline phosphatase, osteopontin, parathyroid hormone receptor, types I and III procollagen, and osteocalcin--as well as lipoprotein lipase (LPL), a marker of the adipocyte phenotype. At an early stage of culture (7-9 days), human OB precursors formed colonies of variable sizes that expressed low levels of mRNA and protein concentrations of OB markers, and their concentration increased on growth to a confluent monolayer (approximately 14 days). LPL mRNA was expressed at high levels in the colony stage, and its level decreased upon confluency, suggesting a loss of potential for commitment to the adipocyte lineage. Interestingly, treatment with dexamethasone at 10(-8) M increased the expression for some of the osteoblast markers and for the LPL gene and was required for the deposition of mineralized matrix and for the formation of adipocytes containing cytoplasmic lipid droplets in confluent cultures. Cloned single early colonies were able to coexpress the osteoblast and adipocyte markers (as assessed by RT-PCR). Thus these immunoselected marrow stromal cells have the characteristics of authentic human osteoblast precursor cells which also are capable of differentiating into adipocytes.

Potential mechanism of estrogen-mediated decrease in bone formation: estrogen increases production of inhibitory insulin-like growth factor-binding protein-4

Using a recently developed human osteoblastic cell line (hFOB/ER9) with high levels (approximately 4,000 per nucleus) of estrogen receptors and the characteristic phenotype of the mature osteoblast, we tested the hypothesis that estrogen decreases bone formation by inhibiting the action of the insulin-like growth factor (IGF) paracrine/autocrine system. IGF-II, the predominant IGF produced by osteoblastic cells, was measurable in hFOB/ER9-conditioned medium (approximately 10 ng/mL) and its level did not change significantly after treatment with 17 beta-estradiol (E2) or anti-estrogens. Treatment with E2 at 0.1-100 nM decreased [3H]thymidine uptake to 53% of control (p < 0.001) in a dose-dependent fashion. The predominant IGF-binding proteins (IGFBPs) produced by hFOB/ER9 and by normal trabecular osteoblasts are IGFBP-3 and IGFBP-4, of which IGFBP-4 is consistently inhibitory of IGF action. Treatment with E2 at 0.01-10 nM for 48 h increased IGFBP-4 mRNA to 346% +/- 90% (mean +/- SE) of control (p < 0.05) and IGFBP-4 protein to 278% +/- 75% of control (p < 0.01) in a dose-dependent fashion but did not alter IGFBP-3 mRNA or protein. E2 treatment also attenuated IGF-dependent, IGFBP-4 specific proteolysis to approximately 50% of control. ICI 182,780, a pure anti-estrogen, completely blocked E2-mediated decreases in cell proliferation and increases in levels of IGFBP-4 mRNA and protein. Treatment of the hFOB/ER9 cells with recombinant human IGFBP-4 (200 ng/mL) decreased cell proliferation to 55% of control (p < 0.01). Thus, E2 acts on osteoblastic cells to increase availability of inhibitory IGFBP-4, by both increasing its production and decreasing its degradation, which may oppose the mitogenic effect of the IGFs on osteoblastic cells. This action may mediate, at least in part, the decreases in bone formation that are observed after estrogen treatment in vivo.

Estrogen inhibits interleukin-6 production and gene expression in a human osteoblastic cell line with high levels of estrogen receptors

Some studies suggest that estrogen acts on bone by decreasing the production of interleukin-6 (IL-6), a cytokine that increases bone resorption, by osteoblasts or bone marrow cells. However, other studies have not confirmed this, possibly because of a low and variable number of estrogen receptors (ER) in the model systems used. Thus, we employed a recently developed human fetal osteoblast cell line with high levels of ER. Treatment (n = 4 experiments) with 0.01 to 10 nM of 17 beta-estradiol had no effect on the constitutive production of IL-6. However, stimulated production, induced by treatment with IL-1 beta plus tumor necrosis factor-alpha (TNF-alpha), was reduced in a dose-dependent manner to 74 +/- 3% (mean +/- SEM) of control (p < 0.01). This response was blocked by cotreatment with the type II antiestrogen ICI 182,780. Treatment with hydrocortisone (1 microM), a known inhibitor of IL-6 production in many cell types, reduced IL-6 production to 17 +/- 1% of control (p < 0.001). As assessed by Northern analysis, treatment (n = 3 experiments) with 0.01-10 nM of 17 beta-estradiol decreased steady-state levels of IL-6 mRNA in a dose-dependent manner. These data support the hypothesis that at least part of the antiresorptive action of estrogen in humans is mediated by decreased production of IL-6 by osteoblastic cells.

Cytokine production in the bone marrow microenvironment: failure to demonstrate estrogen regulation in early postmenopausal women

Recent studies in rodents and in human in vitro systems suggest that the action of estrogen on bone is modulated by various bone-resorbing cytokines produced by osteoblasts, bone marrow cells, or both, but results among studies have been conflicting. Thus, we studied 20 untreated women (controls) and 20 women who had received estrogen replacement therapy since the time of menopause; both groups were 5 +/- 1 yr (mean +/- SE) postmenopausal. From bone marrow aspirates, we obtained marrow plasma to evaluate the production of cytokines by marrow and trabecular bone cells in vivo and marrow mononuclear cells to assess in vitro the constitutive and lipopolysaccharide-stimulated production of cytokines and also to test the in vitro effects of 17 beta-estradiol (10(-8) mol/L). Interleukin-1 alpha (IL-1 alpha), IL-1 beta, IL-6, IL-1 receptor antagonist, and IL-6-soluble receptor were measured by specific enzyme-linked immunosorbent assay. No statistically significant difference between the two groups in the level of any of these cytokines was detected in the bone marrow plasma or the conditioned medium in vitro. Furthermore, in vitro treatment with 17 beta-estradiol did not affect basal or lipopolysaccharide-stimulated cytokine production. Thus, our data suggest that for normal post-menopausal women, mediation of the effects of estrogen by a single cytokine is unlikely. Either multiple cytokines are involved and small changes in these are difficult to detect in clinical investigative studies, or other mechanisms are operative.

Short-term treatment with growth hormone stimulates osteoblastic and osteoclastic activity in osteopenic postmenopausal women: a dose response study

To investigate the potential use of growth hormone (GH) in Activate-Depress-Free-Repeat treatment of postmenopausal osteoporosis, we measured changes in serum levels of biochemical markers of bone turnover, insulin-like growth factor-I (IGF-I), calciotropic hormones, and bone mineral density in 40 postmenopausal women with osteopenia (ages 52-73 years) in response to 7 days of treatment with either placebo or GH (0.05, 0.10, or 0.20 IU/kg/day) administered subcutaneously in the evening. GH treatment increased serum osteocalcin (p < 0.01) and C-terminal type-I procollagen propeptide (p < 0.01) and also serum levels of type-I collagen telopeptide (p < 0.001), fasting urinary hydroxyproline/creatinine (p < 0.05), pyridinoline/creatinine (p < 0.05), and deoxypyridinoline/creatinine (p < 0.01) in a dose-dependent fashion. Even the lowest dose of GH tested induced a significant increase in these parameters; however, the effects were transient lasting only 1-2 weeks. In the highest dose group, however, a somewhat prolonged effect (30 days) on serum osteocalcin was observed. Furthermore, GH increased serum levels of IGF-I, insulin, and tri-iodothyronin. No effect on serum 1,25-dihydroxyvitamin D3 or parathyroid hormone could be demonstrated. Adverse effects were mainly related to fluid retention. They were clearly dose-dependent and rapidly reversible. In conclusion, short-term GH treatment stimulates bone formation and bone resorption in postmenopausal women with osteopenia.

Effect of short-term treatment with recombinant human growth hormone on lipids and lipoproteins in women and men without growth hormone disturbances

The effect of recombinant human growth hormone (rHGH) on cholesterol, high- and low-density lipoprotein (HDL and LDL) cholesterol, triglycerides (TG), apolipoprotein (apo) B, apo A-I, and lipoprotein(a) [Lp(a)] was studied in 40 postmenopausal women treated with 0.05, 0.1, or 0.2 IU/kg/d rHGH or placebo for 7 days. Cholesterol, LDL cholesterol, and HDL cholesterol decreased in a dose-dependent manner (P = .001, P = .001, and P = .003, respectively), whereas apo B decreased insignificantly (P = .15). Apo A-I decreased significantly only among women treated with rHGH at a dose of 0.1 IU/kg/d (P = .03). When all rHGH-treated women were grouped together, Lp(a) increased (P = .001). We also studied 20 young men treated with either 0.2 IU/kg/d rHGH or placebo. As in women, cholesterol and apo B decreased P = .005 and P = .02, respectively), whereas Lp(a) increased (P = .05). There was no detectable effect of rHGH on TG concentrations in men. As in women, there was no significant effect of 0.2 IU/kg/d rHGH on apo A-I concentrations. All lipid and lipoprotein measures reached pretreatment levels during the first week after treatment was stopped, except Lp(a), which remained elevated 2 weeks after rHGH cessation.

Familial isolated primary hyperparathyroidism

Familial primary hyperparathyroidism (PHPT) is usually encountered in the context of multiple endocrine neoplasia (MEN) syndromes. Few families have been reported in the literature where PHPT was the only abnormality. However, in these families no long-term follow-up data were reported and no genetic linkage studies were performed.

OBJECTIVE

We investigated a large family with a familial primary hyperparathyroidism for biochemical and genetic markers of multiple endocrine neoplasia syndromes.

DESIGN

A family screening study.

PATIENTS

Thirty-seven family members participated in this study including 7 patients who had been previously operated upon for PHPT.

MEASUREMENTS

Serum calcium (albumin adjusted), was measured in all family members. Hypercalcaemic subjects and patients who had been operated upon for PHPT were assessed for biochemical markers of MEN syndromes (serum gastrin, prolactin, calcitonin, fasting plasma glucose and 24-hours urinary excretion of adrenaline, noradrenaline and vanillylmandelic acid (VMA)). Genetic linkage analysis was performed using DNA markers linked to chromosome 11q13, the presumed MEN type 1 (MEN-1) locus.

RESULTS

Four new patients with PHPT and two with probable PHPT were discovered. No clinical or biochemical evidence of MEN syndromes could be detected. DNA marker pMS51(D11S97) was informative, maximum two-point lodscore of 2.12 at a recombination fraction of 0.05 confirming linkage to chromosome 11q13.

CONCLUSIONS

Familial PHPT can exist as a separate clinical entity. Isolated familial PHPT is caused by mutation in a gene located in the MEN-1 region on chromosome 11q13, possibly the MEN-1 locus.

Normal osteoclastic and osteoblastic responses to exogenous growth hormone in patients with postmenopausal spinal osteoporosis

The cause of bone loss in patients with osteoporosis is not known, but both increased bone resorption and decreased bone formation have been reported. Theoretically, these effects may result from either increased activity of osteoclasts or decreased activity of osteoblasts, or both. In vivo, growth hormone (GH) administration leads to activation of osteoclasts and osteoblasts as evidenced by increased biochemical markers of bone resorption and bone formation. To test for disturbances in responsiveness of bone cells to exogenous hormonal stimuli in osteoporosis, we compared 15 patients with postmenopausal osteoporosis with 15 healthy age-matched postmenopausal women before and during a 3 day stimulation test with GH (0.2 IU/kg/day). Serum insulin-like growth factor I increased in both groups (p < 0.001). GH treatment increased biochemical markers of bone resorption (serum carboxyl-terminal telopeptide of type I collagen [ICTP] [p < 0.001] and, to a lesser extent, 24 h urinary hydroxyproline/creatinine) in the two groups. Similarly, biochemical markers for bone formation increased in both groups [osteocalcin (p < 0.01) and procollagen type I C-terminal propeptide, PICP (p < 0.001)]. GH treatment reduced alkaline phosphatase (ALP, p < 0.05) and its bone-specific isoenzyme (bone ALP, p < 0.01) in both groups. The maximal response, the area under the curve (AUC) of response curves for IGF-I, bone resorption markers, and bone formation markers were not different between groups. Our data do not support the hypothesis that osteoporotic patients display major disturbances in responsiveness to GH.

Growth hormone stimulates proliferation of normal human bone marrow stromal osteoblast precursor cells in vitro

In this study the effects of growth hormone (GH) in human marrow stromal osteoblast-like [hMS(OB)] cell cultures containing a population of osteoblast precursors, were tested. GH (dose range 0.1-500 ng/ml) stimulated hMS(OB) cell proliferation in a dose-dependent fashion as evidenced by increased 3H-thymidine incorporation into DNA and increased cell number. Maximal stimulation was 173 +/- 35% (P < 0.001, n = 12) and 145 +/- 6% (P < 0.0001, n = 10) of no-treatment controls for 3H-thymidine incorporation and cell number, respectively. GH did not exert major effects on differentiation markers in hMS(OB) cell cultures. 1,25-dihydroxy vitamin D3 (10(-9) M) alone increased cellular production of alkaline phosphatase (AP) and induced expression of osteocalcin. When GH was tested in combination with 1,25(OH)2D3, it tended to inhibit vitamin D-stimulated effects on differentiation markers but these effects were not statistically significant. Our results suggest that GH induces proliferation of less differentiated cells in the osteoblast lineage and this mechanism may in part mediate the in vivo effects of GH on bone formation.

No evidence for reduced spontaneous or growth-hormone-stimulated serum levels of insulin-like growth factor (IGF)-I, IGF-II or IGF binding protein 3 in women with spinal osteoporosis

To test the hypothesis that a dysfunctional growth hormone (GH)-insulin-like growth factor (IGF) axis may play a role in the pathogenesis of osteoporosis, we compared the levels of IGF-I, IGF-II and IGF binding protein 3 (IGFBP-3) in 15 women with spinal osteoporosis (i.e. at least one non-traumatic vertebral fracture) and 15 normal age-matched women. Furthermore, the response to 3 days' treatment with recombinant human GH (r-hGH) (0.2 IU kg-1.day-1) was determined. The basal levels of IGF-I, IGF-II and IGFBP-3 were similar in patients and controls (mean +/- SEM): IGF-I, 16.5 +/- 1.3 versus 16.0 +/- 1.3 nmol/l (NS); IGF-II, 79.9 +/- 3.6 versus 72.5 +/- 4.1 nmol/l (NS); and IGFBP-3, 125.7 +/- 6.5 versus 130.3 +/- 7.8 nmol/l (NS). Stimulation with r-hGH elicited increased levels of IGF-I, IGF-II and IGFBP-3 within both groups (p < 0.001). The maximal values expressed as a percentage of baseline were: IGF-I, 341 +/- 26% versus 369 +/- 22%, IGF-II, 125 +/- 4% versus 119 +/- 5%, IGFBP-3, 141 +/- 5% versus 147 +/- 7% in osteoporotic patients and controls, respectively. No significant differences were observed between patients and controls in either their maximal response or in the area under the response curves. Our results do not support the hypothesis of a dysfunctional GH-IGF axis in women with spinal osteoporosis.

Effects of fluoride on human bone cells in vitro: differences in responsiveness between stromal osteoblast precursors and mature osteoblasts

The cellular effects of sodium fluoride (NaF) on human bone cells in vitro have been variable and dependent on the culture system used. Variability could be attributed to differences in responsiveness to NaF among different populations of cells at various stages of differentiation in the osteoblastic lineage. In this study we compared the effects of NaF in serum-free medium on cultures of more differentiated human osteoblast-like (hOB) cells derived from trabecular bone explants and on osteoblast committed precursors derived from human bone marrow, i.e. human marrow stromal osteoblast-like (hMS(OB)) cells. Sodium fluoride (10(-5) mol/l) increased proliferation of hMS(OB) cells (p < 0.05, N = 10) but was not mitogenic to hOB cells (p > 0.05, N = 10). Alkaline phosphatase (AP) production increased in both hMS(OB) (p < 0.05, N = 9) and hOB cells (p < 0.05, N = 9). No significant effects on procollagen type I propeptide production were obtained in either culture. In the presence of 1,25-dihydroxycholecalciferol (10(-9) mol/l), NaF enhanced alkaline phosphatase (p < 0.05, N = 8), procollagen type I propeptide (p < 0.05, N = 7) and osteocalcin (p < 0.05, N = 7) production by hMS(OB) cells but not by hOB cells. Our results suggest that osteoblast precursors are more sensitive to NaF action than mature osteoblasts and that the in vivo effects of NaF on bone formation may be mediated by stimulating proliferation and differentiation of committed osteoblast precursors in bone marrow.

Human marrow stromal osteoblast-like cells do not show reduced responsiveness to in vitro stimulation with growth hormone in patients with postmenopausal osteoporosis

Decreased osteoblastic activity seems to play an important role in the pathogenesis of postmenopausal osteoporosis. The aim of the present study was to examine the direct effects of human growth hormone (GH) on proliferation and differentiation of osteoblastic cells obtained from patients with postmenopausal osteoporosis and age-matched normals and to compare the cellular responses induced by GH between the two groups. Osteoblast cultures (human marrow stromal osteoblast-like cells) were established from bone marrow aspirates obtained from 9 osteoporotic patients and 12 age-matched normals. Effects on cell proliferation and cell differentiation markers [alkaline phosphatase (AP)], procollagen type I propeptide (PICP), and osteocalcin] were assessed. GH stimulated 3H-thymidine incorporation into DNA in cell cultures of osteoporotic patients to a maximum of 158 +/- 14% of no-treatment controls (n = 9, P < 0.001) and to 203 +/- 52% (n = 9, P < 0.001) in normals. GH increased cell number as measured by methylene blue (MB) assay in cells of osteoporotic patients to 138 +/- 10% (P < 0.05, n = 7) and in normals to 138 +/- 12 (P < 0.05, n = 7). GH alone reduced cellular AP production: 61 +/- 3.8% (P < 0.05, n = 7) versus 65 +/- 16% (P < 0.05, n = 7) and cellular PICP production: 79 +/- 6% (P < 0.05, n = 7) versus 69 +/- 16% (n.s., n = 7), in cell cultures of osteoporotics and normals, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

1,25-dihydroxyvitamin D3 potentiates fluoride-stimulated collagen type I production in cultures of human bone marrow stromal osteoblast-like cells

In this study we tested the effects of sodium fluoride (NaF) in serum-free cultures of human marrow stromal osteoblast-like [hMS(OB)] cells. NaF (10(-5) M) stimulated hMS(OB) cell proliferation up to 220% of control cultures. NaF alone did not increase type I collagen production, but in the presence of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] (10(-9) M), NaF enhanced type I collagen production in a dose-dependent way to 300% of 1,25-(OH)2D3-treated control cultures. The production of alkaline phosphatase (ALP) and osteocalcin (bone gla protein, BGP) was also enhanced in the presence of 1,25-(OH)2D3 to 170 and 200%, respectively, of 1,25-(OH)2D3-treated controls. Our results suggest that 1,25-(OH)2D3 potentiates fluoride-mediated anabolism in hMS(OB) cell cultures and suggest that osteoblast precursors in bone marrow are targets for fluoride action.

Ultrastructural investigations of bone resorptive cells in two types of autosomal dominant osteopetrosis

In order to investigate the ultrastructure of bone resorptive cells in the two types of adult benign human osteopetrosis, iliac crest biopsies were obtained from 11 patients and 10 normal males, who served as a control group. Six patients had the radiological type I (4 women, 2 men, aged 23-58 years, mean = 36.5 years), and 5 type II disease (5 men, aged 20-48 years, mean = 29.8 years). The normal controls (aged 23-48 years, mean 34.1 years) were recruited from the medical staff. The biopsies were immediately divided. From each patients, half was embedded in paraffin for histochemistry and light microscopy, and half in epon for transmission electron microscopy. The osteoclasts were markedly reduced in number and size in Type I disease (0.2 +/- .7 cells vs. 2.9 +/- 1.0 cells per 2.7 mm2 of bone area, p < 0.01) compared to controls, and stained only weakly for tartrate-resistant acid phosphatase (TRAP). At the ultrastructural level, no signs of active bone resorption were identified, whereas numerous mononuclear cells were observed at the bone surfaces. In type II disease, the osteoclasts were large and highly multi-nucleated, with an increased number (8.3 +/- 2.3 cells vs. 2.9 +/- 1.0. cells per 2.7 mm2 of bone area, p < 0.01) compared to controls. In all patients with this type, but never in type I or in the controls, a smooth, TRAP-positive substance was seen between the osteoclasts and the bone surface. Ultrastructurally, this substance was amorphous, with a condensation along the cell membrane.(ABSTRACT TRUNCATED AT 250 WORDS)

Age- and sex-related changes in iliac cortical bone mass and remodeling

Iliac crest bone biopsies were obtained from 64 normal individuals (41 women and 23 men) aged 19-90 (mean 48.2) years. Thirty-four were double-labeled with tetracycline before biopsy. The following variables were measured in all biopsies: biopsy core width (C.Wi), absolute (A.Ct.Wi) and fractional (F.Ct.Wi) cortical width, absolute (A.Cn.Wi) and fractional (F.Cn.Wi) cancellous width, cortical porosity (Ct.Po), osteon diameter (On.Dm), Haversian canal diameter (Ha.Ca.Dm), and wall thickness (W.Th). In the tetracycline-labeled biopsies the typical cortical remodeling cycle was reconstructed and the activation frequency was estimated. A negative cortical bone balance with aging was found in both sexes. In females F.Ct.Wi decreased (p < 0.02) with aging because of marrow expansion (p < 0.05). Furthermore, Ct.Po increased (p < 0.001) because of a decrease in W.Th (p < 0.01) and an increase in H.Ca.Dm (p < 0.001). In males the negative cortical bone balance with aging was exclusively caused by an increase in Ct.Po (p < 0.001) partially explained by an expanding H.Ca.Dm (p < 0.01). The On.Dm increased with aging (p < 0.01), but surprisingly, no fall in W.Th was observed. Reconstruction of the remodeling cycle did not reveal any significant difference between younger women and men. However, the activation frequency rose from 0.5 per year in premenopausal to 1.0 per year in postmenopausal women (p < 0.001), giving rise to a high turnover state, an increase in the remodeling space, and thereby the porosity in the cortical bone immediately after menopause. The present study has shown a reduction in cortical bone mass in elderly people, compared with younger, which may be explained by an age-related remodeling imbalance. This reduction is further increased in women in the postmenopausal state because of a postmenopausal accelerated bone turnover.

Effects of triiodothyronine on DNA synthesis and differentiation markers of normal human osteoblast-like cells in vitro

To study the direct effects of thyroid hormones on human osteoblasts we examined the effects of triiodothyronine (T3) on proliferation and differentiation of human osteoblast-like (hOB) cells in vitro. T3 increased 3H-thymidine incorporation in DNA of hOB cells (p < 0.05, n = 10). Half maximal effects obtained at a T3 concentration of 1-10 nM which lies within the physiological concentration of the hormone. In addition, T3 increased alkaline phosphatase production (p < 0.05, n = 13) and inhibited procollagen type I carboxyterminal propeptide (PICP) production (p < 0.05, n = 13). T3 interaction with 1,25-dihydroxycholecalciferol (1,25-(OH)2D3) was also studied. 1,25-(OH)2D3 (10(-9)M) alone doubled AP production and induced osteocalcin expression by hOB cells. Concurrent addition of T3 and 1,25-(OH)2D3 did not further increase production of AP, PICP or osteocalcin by hOB cells. In conclusion, T3 exerts significant effects on osteoblast proliferation and differentiation, suggesting that human osteoblasts are targets for thyroid hormones.

The von Kossa reaction for calcium deposits: silver lactate staining increases sensitivity and reduces background

The classical von Kossa method has been modified: the high silver nitrate concentration in the original was replaced by 0.05% silver lactate with hydroquinone remaining the reducing agent of choice. The present modification stained calcification nodules with a sensitivity comparable to the original von Kossa reaction, but resulted in a reduced background staining in cultured osteoblasts. The method works well also with plastic- or paraffin-embedded tissue sections.

Growth hormone stimulates proliferation and differentiation of normal human osteoblast-like cells in vitro

In this study we investigated the direct, short-term effects of human growth hormone (hGH) on the biology of normal adult human osteoblast-like (hOB) cells cultured from trabecular bone explants. In Subconfluent cultures, hGH stimulated hOB proliferation in a dose-dependent fashion (P < 0.001, n = 15) with half-maximal effects at a concentration of 10 ng/ml. These mitogenic effects were detectable within 24 hours as shown by bromodeoxyuridine labeling. In confluent cultures containing mainly quiescent cells, hGH increased levels of alkaline phosphatase (P < 0.05, n = 10) and to a lesser degree levels of procollagen type I carboxyterminal propeptide (PICP) (P = 0.07, n = 9). Effects on osteocalcin (bone GLa protein, BGP) levels were highly variable among different cell strains and only 7 of 10 cell strains showed a stimulatory response (P = 0.16). We also studied the effects of hGH on osteoblastic production of insulin-like growth factor I (IGF-I) and IGF-II as well as the production of GH-dependent, insulin-like growth factor binding protein 3 (IGFBP-3). Under basal conditions, human osteoblasts produced IGF-II and IGFBP-3 in the conditioned medium. When stimulated with hGH, minor insignificant increase in both IGF-II and IGFBP-3 (125% and 126% of control, respectively) were detectable. No IGF-I was detectable in the conditioned medium under basal conditions or after stimulation with hGH. In conclusion, the results obtained in this study suggest that GH exerts direct anabolic effects on human osteoblasts.

Growth hormone and insulin-like growth factors as anabolic therapies for osteoporosis

Growth hormone (GH) and insulin-like growth factors (IGFs) play a central role in skeletal growth and bone remodeling. In vitro, both agents display anabolic properties, and patients with acromegaly exhibit increased bone mass. Recent in vivo studies have demonstrated profound activation of bone remodeling that lasted for months after a single 1-week dose of GH or IGF-I. Despite these positive effects, the few clinical studies conducted with GH in osteoporotic patients have shown disappointing results in terms of bone mass changes. Changes in dosing regimens and other adjuvant therapies may, however, lead to more efficient use of these agents.

Growth hormone (GH) and adult bone remodeling: the potential use of GH in treatment of osteoporosis

Decreased osteoblastic activity seems to be of major importance in the pathogenesis of postmenopausal and senile osteoporosis and several lines of evidence suggest that GH may become useful in treatment of osteoporosis. GH stimulates osteoblastic proliferation and differentiation in vitro and increases production of Insulin-like Growth Factor-I and II (IGF-I and IGF-II) which both have profound stimulatory effects on osteoblasts and are important local regulators of bone remodeling. GH affects several other osteotropic hormones in vivo and increases bone turnover while the effect on bone mass is less pronounced and depends on the skeletal compartment. The few published clinical studies on the use of GH in treatment of osteoporosis have been inconclusive and well controlled studies of adequate size are greatly needed. Future research should focus on intermittent use of GH in combination with other hormones stimulating IGF production or antiresorptive agents.

Fetal antigen 2 (FA2) in human fetal osteoblasts, cultured osteoblasts and osteogenic osteosarcoma cells

Immunohistochemical staining techniques used on an 11-week-old fetus showed that fetal antigen 2 (FA2) was present intracellularly in endochondral and perichondral osteoblasts, and the immunoreaction was extended into the adjacent bone matrix. Osteoclasts and chondroblasts were found to be FA2 negative. A granular perinuclear intracytoplasmic FA2 immunoreaction was found in cultured osteoblasts and osteogenic osteosarcoma cells, and immunoelectron-microscopical examination revealed a granular immunoreaction product in the rough endoplasmic reticulum. These findings indicate that FA2 is synthesized by osteoblasts and osteogenic osteosarcoma cells. A reaction of immunological identity was found between FA2 purified from second trimester amniotic fluid and serum-free supernatants of cultured osteogenic osteosarcoma cells. This shows that an antigen recognized by the anti FA2 antibody is secreted by these malignant cells. Thus, FA2 may represent a marker for altered bone metabolism, and have a potential in the classification of osteogenic osteosarcoma/chondrosarcoma.

Inhibition of the morning cortisol peak abolishes the expected morning decrease in serum osteocalcin in normal males: evidence of a controlling effect of serum cortisol on the circadian rhythm in serum osteocalcin

Osteocalcin (OC) in serum varies in a remarkably constant circadian rhythm with zenith at night and nadir in the morning. The factors controlling this rhythm are unknown, but several studies indicate that serum cortisol could be of major importance. We tested this hypothesis in a double-blind, placebo-controlled, cross-over study comprising 10 normal male volunteers (aged 23-31 yr) by measuring the response in serum OC and cortisol rhythms to a single dose of metyrapone (30 mg/kg body weight) administered at midnight. During placebo, serum cortisol consistently peaked early in the morning before 0730 h. Ingestion of metyrapone at 2400 h significantly postponed and flattened this peak (P less than 0.01). On both occasions, serum OC increased towards peak levels around 0300 h (P less than 0.01) with no overall differences in the OC profiles. However, when the serum OC time series were synchronized according to the individual cortisol nadirs, we found a significant (P less than 0.01) decrease in serum OC on the placebo day approximately 4 h after the cortisol nadir, whereas no significant changes (P greater than 0.50) were seen on the metyrapone day. Moreover, the mean serum OC level tended to be higher (P less than 0.10 in the interval 0-12 h, and P = 0.06 in the interval 4-8 h) on the metyrapone day compared with the placebo day. On the placebo day, the mean level of serum cortisol during the interval 0-4 h correlated inversely with the mean level of serum OC in the interval 4-8 h (r = 0.77, P less than 0.05). This relation was not found on the metyrapone day. In conclusion, administration of metyrapone, which reduced and postponed the early morning cortisol peak, abolished the normal morning decrease in serum OC. This strongly supports that changes in endogenous serum cortisol are of major importance for the circadian rhythm in serum OC.

Ultrastructure of human osteoblasts and associated matrix in culture

The ultrastructure, as visualized by transmission electron microscopy, of cells obtained from human bone explants and subsequently cultured is described along with the electron microscopic appearance of the associated intercellular matrix. The cells were characterized as osteoblasts on the basis of immunohistochemical, enzymatic, and functional criteria. Although the osteoblasts could be cultured in standard culture media and always appeared singly, not forming syncytia, the cultures were eventually confluent and formed multilayers. The cells were fusiform or cuboidal with diameters ranging between 10-15 microns. The cytoplasm was characterized by numerous large mitochondria, and especially by a very prominent RER. The intercellular matrix was woven with collagen fibres surrounding large numbers of matrix vesicles. In areas with matrix vesicles, evidence for osteoblast activity, i.e. mineralization related to matrix vesicles, could be observed after incubation with beta-glycerophosphate. In conclusion, we provide evidence that human osteoblasts cultured in vitro synthesize collagen and produce a matrix with vesicles capable of initiating mineralization processes.

Quantification of fetal antigen 2 (FA2) in supernatants of cultured osteoblasts, normal human serum, and serum from patients with chronic renal failure

Fetal antigen 2 (FA2) was found within the cytoplasm of osteoblasts and in osteoid material, in a bone biopsy with morphological changes of renal osteodystrophy. An ELISA technique for FA2 quantification was developed, and the specificity confirmed by comparison with electroimmunoassay. The intra- and interassay coefficient of variations (%) were 8.3 and 9.7 respectively, and the detection limit 0.0004 arbitrary units FA2/1 using second-trimester human amniotic fluid as reference (1 AU FA2/1). FA2 was detected in serum-free supernatants from osteoblast cultures. Following size chromatography, the FA2 distribution (two peaks eluted corresponding to Mw 30 kDa and 100 kDa) in serum from a patient with chronic renal failure complicated with secondary hyperparathyroidism and in human amniotic fluid were identical. Probably due to the detection limit, only one peak fraction (30 kDa) was seen in normal human serum. Significantly greater FA2 concentrations were found in sera (n = 14) from patients with chronic renal failure (median: 11.9 mAU FA2/1; range: 5.2-49.0 mAU FA2/1) compared to normal healthy individuals (n = 23) (median: 4.1 mAU FA2/1; range 2.4-9.4 mAU FA2/1) (P less than 0.00001). A close correlation was found between serum FA2 and alkaline phosphatase (R(s) = 0.761; P = 0.006), c-terminal fraction of PTH (R(s) = 0.872; P = 0.003) and intact PTH(1-84) (R(s) = 0.904; P = 0.011) in the haemodialysis patients. These data indicate that FA2 is synthesized by osteoblasts and may represent a new marker for metabolic bone changes.

Diurnal rhythm in serum osteocalcin: relation with sleep, growth hormone, and PTH(1-84)

We examined the role of sleep, growth hormone (GH), and parathyroid hormone [PTH(1-84)] as regulators of the diurnal rhythm of the osteoblastic bone marker, serum osteocalcin (OC). Nine normal subjects were followed with hourly blood sampling during one 24-hour period with normal sleep pattern, and one 24-hour period with absolute sleep deprivation. We found that the rhythm in serum OC did not exhibit significant changes (P greater than 0.50). Serum OC (mean +/- SE) was 30.9 +/- 2.5 micrograms/liter during sleep (2330-0730 hours) versus 29.9 +/- 4.9 micrograms/liter during sleep deprivation (not significantly different). The serum GH rhythm was significantly different on the two occasions (P less than 0.01). A maximum GH peak (mean +/- SE) of 10.3 +/- 2.4 micrograms/liter occurred at 0136 hours +/- 6 minutes during sleep compared with a maximal peak of 7.6 +/- 1.2 micrograms/liter (P less than 0.01) at 0245 hours +/- 20 minutes (P less than 0.01) during sleep deprivation. During sleep (2330-0730 hours), mean serum GH was 3.61 +/- 0.60 micrograms/liter compared with 2.39 +/- 0.40 micrograms/liter during sleep deprivation (P less than 0.005). Small insignificant changes occurred in serum PTH (1-84) and serum ionized calcium during the two occasions. We conclude that sleep and GH are not acute controlling factors of the diurnal rhythm in serum OC and the role of serum PTH(1-84) remains unsettled.

Acute effect of 1,25-dihydroxyvitamin D3, prednisone, and 1,25-dihydroxyvitamin D3 plus prednisone on serum osteocalcin in normal individuals

Suppression of osteoblastic function plays an important pathogenic role for the development of glucocorticosteroid-induced osteoporosis. Serum osteocalcin (OC) is a sensitive marker of bone formation. The diurnal rhythm in serum OC can be changed by administration of single doses of either 1,25-(OH)2D3 or prednisone. However, the two steroids have opposing effects: 1,25-(OH)2D3 increases and prednisone decreases serum OC. The aim of the present study was to examine whether 1,25-(OH)2D3 can oppose the acute suppressive effect of prednisone on serum OC in normal subjects. We compared the effect of a combined dose of 2 micrograms 1,25-(OH)2D3 and 10 mg prednisone on the diurnal rhythm of serum OC with the effect of 2 micrograms 1,25-(OH)2D3 + placebo in a crossover study. Seven normal subjects aged 23-36 years were investigated twice at an interval of 1 week. Blood samples were collected every 60 minutes from 1900 until 1100 h the following day. Study drugs were given at 2000 h. The data from the present investigation were compared with data obtained from a similar study with placebo and prednisone in the same subjects. After administration of 1,25-(OH)2D3 serum OC followed the placebo curve during the first 8 h, but in contrast to the placebo curve it then continued to increase and remained elevated throughout the observation period (p less than 0.05). Prednisone inhibited and reversed the nocturnal rise in serum OC levels (p less than 0.01). The course of serum OC after administration of 1,25-(OH)2D3 + prednisone almost paralleled the course after placebo. We conclude that 1,25-(OH)2D3 and prednisone have opposing effects on serum OC.

Formation of osteoblast-like cells from human mononuclear bone marrow cultures

Osteoblast-like cells are commonly found in the vicinity of osteoclasts formed in long-term human bone marrow cultures, and they are believed to be derived from osteogenic cell precursors belonging to the stromal cell system. This paper describes a new culture method for human osteoblasts from the adherent cell population of long-term human mononuclear bone marrow cultures. The cells obtained exhibited all the classic characteristics of osteoblasts. They contained high intracellular concentrations of alkaline phosphatase and they secreted the osteoblast-specific marker bone Gla protein. Collagen production was mainly (95-98%) procollagen type I propeptide and only minute quantities of procollagen type III propeptide were detectable by radioimmunoassay in the conditioned medium. After eight weeks the cells formed a mineralized matrix on exposure to beta-glycerophosphate and ascorbic acid. This system provides a model for the study of osteoblast differentiation in vitro and may form the basis for the use of defined media in bone cell cultures due to the presence of high concentrations of osteoblast precursors.

Antacid-induced osteomalacia: a case report with a histomorphometric analysis

The case of a 75-year-old woman with severe osteomalacia secondary to ingestion of large amounts of an aluminum-containing antacid is reported. Biochemical analysis revealed signs of phosphate malabsorption and increased levels of bone markers (S-alkaline phosphatase and U-hydroxyproline). A 99mTc-bone scan revealed multiple areas of increased uptake. The patient was normocalcaemic, with normal serum levels of intact parathyroid hormone and 25-hydroxyvitamin D. Serum 1,25-dihydroxyvitamin D was high normal. A transiliac bone biopsy from the patient showed severe osteomalacia. Symptoms, biochemical parameters, bone scan and bone morphology were all normalized 1 year after stoppage of antacid ingestion and treatment with vitamin D2. calcium phosphate and sodium fluoride because of severe osteopeni. The characteristics of this condition and the role of phosphate depletion and aluminum in the pathogenesis of bone lesions are discussed.

Formation of osteoclasts and osteoblast-like cells in long-term human bone marrow cultures

A culture system for human osteoclasts is described. It is based on incubation of mononuclear marrow cells for three weeks in the presence of 1,25 dihydroxyvitamin D3. The resulting cells exhibited all the classic characteristics of osteoclasts. They formed a true syncytium with up to 25 nuclei per cell. The cells revealed a strong positive reaction for tartrate-resistant acid phosphatase and a ruffled border. When these cells were cultured on 100 microns thick human dentine slices for three weeks, typical resorption pits were formed. In the culture, alkaline phosphatase-positive osteoblast-like cells were formed in the vicinity of osteoclasts. This culture system permits studies of human osteoclasts and their interaction with osteoblast cell precursors in the human bone marrow.