Direct identification of the calcium-binding amino acid, gamma-carboxyglutamate, in mineralized tissue

Vitamin K and energy transduction: a base strength amplification mechanism

Energy transfer provides an arrow in the metabolism of living systems. Direct energetic coupling of chemical transformations, such that the free energy generated in one reaction is channeled to another, is the essence of energy transfer, whereas the purpose is the production of high-energy chemical intermediates. Vitamin K provides a particularly instructive example of energy transfer. A key principle at work in the vitamin K system can be termed "base strength amplification." In the base strength amplification sequence, the free energy of oxygenation of vitamin K hydroquinone (vitamin KH2) is used to transform a weak base to a strong base in order to effect proton removal from selected glutamate (Glu) residues in the blood-clotting proteins.

Conformational changes of bovine bone osteonectin induced by interaction with calcium

To clarify calcium-induced conformational changes in bovine bone osteonectin, the protein was labeled with fluorescein isothiocyanate (FITC) in the presence and absence of calcium. By calcium titration using fluorescence spectrometry, it was demonstrated that FITC-osteonectin labeled in the presence of 2 mM CaCl2 showed a much higher affinity for calcium ions than did that labeled in the absence of calcium ions. The midpoint for completion of the increase in the intrinsic fluorescence (K0.5) of the two were 1 x 10(-7) M and 5 x 10(-7) M, respectively. By tryptic digestion and isolation of the fluorescent peptide of both FITC-osteonectins, the site of FITC-labeling was determined to be Lys174. Furthermore, it was found that the efficacy of labeling in this specific binding site was three times higher in the FITC-osteonectin labeled in the presence of 2 mM CaCl2 than in that labeled in the absence of calcium. The results indicate that in the presence of 2 mM CaCl2 the microenvironment around Lys174 of osteonectin was more open to modification than in the absence of calcium.

Indicators of bone formation in weight lifters

Physical activity has been suggested to be one of the determinants of bone turnover and to prevent age-related bone loss. To examine this we measured the serum levels of osteocalcin (bone Gla-protein, BGP), C-terminal procollagen peptide (PICP), serum alkaline phosphatase, bone-specific alkaline phosphatase, and S-calcium as indices of bone formation in 19 actively performing and 15 ex-lifters. All were nationally or internationally ranked male athletes. Their values were compared with those from 38 age- and gender-matched controls. Actively performing weight lifters had 35% higher (P < 0.05) serum concentration of osteocalcin than the controls. The ex-lifters did not differ from the age-matched controls. Also serum calcium was elevated in active lifters (6%) (P < 0.01) but not in ex-lifters. No difference was found for serum-ALP, B-ALP, or PICP in either of the groups. Our study indicates that in addition to an already documented and well-known higher bone mineral density in heavily exercising athletes, they have an indication of higher bone formation as measured by biochemical markers. In athletes who have retired from competitional training, however, the bone formation does not differ from that of more sedentary controls.

Regulation of human bone marrow-derived osteoprogenitor cells by osteogenic growth factors

Human bone marrow contains a distinct cell population that expresses bone proteins and responds to transforming growth factor beta 1 (TGF-beta), but not to hematopoietic growth factors (Long, M. W., J. L. Williams, and K. G. Mann. 1990. J. Clin. Invest. 86:1387-1395). We now report the isolation, characterization, and growth factor responsiveness of these precursors to human osteoblasts and the identification of a human osteoprogenitor cell. Immunological separation of human bone marrow nonadherent low-density (NALD) cells results in a marked enrichment of cells that express osteocalcin, osteonectin, and bone alkaline phosphatase. Flow cytometric analyses show that distinct cell subpopulations exist among these isolated cells. The majority of the bone antigen-positive cells are approximately the size of a lymphocyte, whereas other, less frequent antibody-separated subpopulations consist of osteoblast-like cells and osteoprogenitor cells. In serum-free cultures, TGF-beta stimulates the small, antigen-positive cells to become osteoblast-like, as these cells both increase in size, and express increased levels of osteocalcin and alkaline phosphatase. Antibody-separated cells also contain a separate population of clonal progenitor cells that form colonies of osteoblast-like cells when cultured in serum-free, semi-solid media. Two types of human osteoprogenitor cells are observed: a colony-forming cell (CFC) that generates several hundred bone antigen-positive cells, and a more mature cluster-forming cell that has a lesser proliferative potential and thus generates clusters of 20-50 antigen-positive cells. Osteopoietic colony-forming cells and cluster-forming cells have an obligate but differential requirement for osteogenic growth factors. The CFCs respond to TGF-beta, basic fibroblast growth factor (bFGF), bone morphogenic protein-2 (BMP-2), and 1, 25-dihydroxy vitamin D3 (1,25-OH D3). In contrast to the colony-forming cells, cluster-forming cells are regulated predominantly by 1,25-OH D3 and TGF-beta, but fail to respond to bFGF. We conclude that human bone marrow contains a nonhematogenous, heterogeneous population of bone precursor cells among which exists a population of proliferating osteoprogenitor cells. Further characterization of these bone precursor cell populations should yield important information on their role in osteogenesis in both health and disease.

Exercise and bone mineral density

A decrease in physical activity may lead to an increased loss of bone and an increase in the incidence of osteoporotic fractures. Studies have demonstrated increases in bone formation in animals and increases in bone mineral density in humans. Studies of animals show that bone has enhanced physical and mechanical properties following periods of increased stress. Strains which are high in rate and magnitude, and of abnormal distribution, but not necessarily long in duration, are best for inducing new bone formation, resulting in the strengthening of bone by increased density. Cross-sectional studies show that athletes, especially those who are strength-trained, have greater bone mineral densities than nonathletes, and that strength, muscle mass and maximal oxygen uptake correlate with bone density. Longitudinal training studies indicate that strength training and high impact endurance training increase bone density. Strain induction, the deformation that occurs in bone under loading, may cause a greater level of formation and an inhibition of resorption within the normal remodelling cycle of bone, or it may cause direct activation of osteoblastic bone formation from the quiescent state. Various mechanisms have been proposed for the transformation of mechanical strain into biochemical stimuli to enhance bone formation. These include prostaglandin release, piezoelectric and streaming potentials, increased bone blood flow, microdamage and hormonally mediated mechanisms. These mechanisms may act on their own or in concert, depending on the loading situation and the characteristics of the bone.

Effect of a derivatized dextran on human osteoblast growth and phenotype expression

Water soluble derivatized dextran named E9 with a molecular weight of 45,000 g l-1 containing 58% methyl carboxylic acid unit, 19% benzylamide unit, and 26% sulfonate with a specific anticoagulant activity of 0.29 IU mg-1 was studied for its effects on human osteoblast growth and phenotype expression for short-term treatment. At concentrations between 1 ng ml-1 and 1 microgram ml-1 E9 has no effect on DNA synthesis whereas at higher concentrations DNA synthesis is inhibited in a dose related fashion (87% for 400 micrograms ml-1). For concentrations which do not modify osteoblast growth, E9 promotes alkaline phosphatase activity, type I collagen and osteocalcin synthesis with a maximum effect for 0.1-1 microgram ml-1. It has a synergistic effect with hPTH increasing AMPc. Moreover, osteonectin synthesis was enhanced in a dose-dependent manner between 0.1 and 5 micrograms ml-1. These results seem to indicate that E9 is able to stimulate human osteoblast phenotype expression and could be useful in clinical applications.

Osteocalcin: a non-invasive index of metabolic bone disease in patients treated by CAPD

Serum osteocalcin has been found to correlate with bone formation. However, present literature gives only limited data on osteocalcin and bone histomorphometry in patients undergoing peritoneal dialysis. This study assessed serum osteocalcin, dialysate osteocalcin, peritoneal clearance of osteocalcin (Clp-osteocalcin) and mass transfer of osteocalcin (MTp-osteocalcin), and evaluated relationships between these values and bone histomorphometry. Eighteen patients were treated by continuous ambulatory peritoneal dialysis (CAPD). Bone biopsies, serum and dialysate osteocalcin, serum levels of parathyroid hormone, alkaline phosphatase, aluminum, phosphate, Ca2+ and vitamin D3 metabolites were measured at the start and in 10 of the patients a year later. Serum osteocalcin was found to be elevated. Osteocalcin was detected in the dialysate resulting in significant values of Clp-osteocalcin and MTp-osteocalcin. Serum and dialysate levels of osteocalcin correlated significantly (r = 0.66, P < 0.001) and like MTp-osteocalcin with serum levels of alkaline phosphatase and PTH. Histomorphometry showed that osteitis fibrosa was the predominant bone disease detected. Serum concentration of osteocalcin correlated with osteoid thickness, eroded and osteoclast surfaces, aluminum staining, and some of the bone dynamic parameters. Dialysate osteocalcin, MTp-osteocalcin, PTH and alkaline phosphatase correlated with practically the same histomorphometric parameters as serum osteocalcin. No correlations were seen between Clp-osteocalcin and any histomorphometric parameters. Serum osteocalcin was elevated above the normal range, and significant positive correlations between serum osteocalcin and bone formation parameters were found. Serum osteocalcin correlated with almost the same histomorphometric parameters as PTH. Thus, serum levels of PTH and osteocalcin gave additional information to one another as non-invasive parameters in this group of patients.(ABSTRACT TRUNCATED AT 250 WORDS)

A number of osteocalcin antisera recognize epitopes on proteins other than osteocalcin in cultured skin fibroblasts: implications for the identification of cells of the osteoblastic lineage in vitro

Rabbit antisera to bovine osteocalcin were produced independently in two laboratories and their specificities established by western blot analysis. By immunohistochemistry each of the five polyclonal antisera produced an intense cytoplasmic staining in human bone-derived cells. Staining intensity was strongly attenuated by preabsorption of the antisera with osteocalcin. No staining was observed using nonimmune rabbit serum. However, the choice of skin cells as negative controls for osteocalcin synthesis yielded an unexpected positive staining pattern similar to that seen with the bone-derived cells over a range of antiserum dilutions. This was not caused by the uptake of exogenous osteocalcin from the culture medium because a similar pattern of staining was observed when medium was supplemented with osteocalcin-depleted fetal calf serum. Treatment with 1,25-dihydroxyvitamin D3 induced osteocalcin mRNA expression and osteocalcin secretion in cultures of bone-derived cells but not in skin fibroblasts. The results demonstrate that these polyclonal antisera also recognize epitopes shared with other proteins synthesized in culture by skin fibroblasts. Furthermore, three mouse monoclonal antibodies to distinct regions of the osteocalcin molecule show differential staining of human bone-derived cells, skin cells, and osteosarcoma cells (MG63). These observations indicate that the shared epitope residues in the central region of osteocalcin and are consistent with the specific synthesis of osteocalcin by bone cells alone. The observed nonspecificity of many osteocalcin antisera may compromise immunocytochemical studies of the osteoblast phenotype in studies in vitro when based solely on reactivity with inadequately characterized osteocalcin antisera.

Effect of beta-alanyl-L-histidinato zinc on protein components in osteoblastic MC3T3-El cells: increase in osteocalcin, insulin-like growth factor-I and transforming growth factor-beta

The effect of beta-alanyl-L-histidinato zinc (AHZ) on protein components in osteoblastic MC3T3-E1 cells was investigated. Cells were cultured for 3 days at 37 degrees C in CO2 incubator in plastic dishes containing alpha-modified minimum essential medium supplemented with 10% fetal bovine serum. After the cultures, the medium was exchanged for that containing 0.1% bovine serum albumin plus various concentrations of AHZ or other reagents, and the cells were cultured further 3 or 6 days. The homgenate of cells was analyzed with SDS-polyacrylamide gel electrophoresis (SDS-PAGE). The presence of AHZ (10(-7) to 10(-5) M) caused an appreciable increase of many protein components in cells. Especially, the 67 killo-dalton (kDa) and 44 kDa proteins which are the major components from control cells were clearly increased by the presence of AHZ. Furthermore, the concentrations of osteocalcin, insulin-like growth factor-I and transforming growth factor-beta in the culture medium secreted from osteoblastic cells were markedly increased by the presence of AHZ (10(-6) and 10(-5) M). The effect of AHZ was a greater than that of zinc sulfate (10(-6) and 10(-5) M). The present findings suggest that AHZ can increase many proteins which are involved in the stimulation of bone formation and cell proliferation in osteoblastic cells.

Systemic bone growth factors in light breed mares and their foals

There is a high incidence of bony pathology in race horses. Thus, plasma GH, IGF-1, osteocalcin (OC), calcium (Ca) and inorganic phosphorus (P) concentrations were measured in 12 healthy Selle Français foals and their dams during the first five months after birth. Plasma IGF-1 and OC concentrations were higher in foals than in mares (336 +/- 25 vs 230 +/- 18 ng/ml, P < 0.05; 52.5 +/- 3.2 vs 4.9 +/- 0.1 ng/mg, P < 0.01, respectively). A significant positive linear relationship could be established between these two parameters in foals (IGF-1 = 19 + 0.619 OC; P < 0.05). Another striking evidence was the increase in plasma IGF-1, OC and P concentrations observed during the first week of postnatal life. IGF-1, OC, P and Ca concentrations remained elevated during the experimental period, indicating an intense skeletal growth (confirmed by growth curve) in these animals.

Age- and gender-related changes in the distribution of osteocalcin in the extracellular matrix of normal male and female bone. Possible involvement of osteocalcin in bone remodeling

With increasing age, bone undergoes changes in remodeling that ultimately compromise the structural integrity of the skeleton. The presence of osteocalcin in bone matrix may alter bone remodeling by promoting osteoclast activity. Whether age- and/or gender-related differences exist in the distribution of osteocalcin within individual bone remodeling units is not known. In this study, we determined the immunohistochemical distribution of osteocalcin in the extracellular matrix of iliac crest bone biopsies obtained from normal male and female volunteers, 20-80 yr old. Four different distribution patterns of osteocalcin within individual osteons were arbitrarily defined as types I, II, III, or IV. The frequency of appearance of each osteon type was determined as a percent of the total osteons per histologic section. The proportion of osteons that stained homogeneously throughout the concentric lamellae (type I) decreased in females and males with increasing age. The proportion of osteons that lack osteocalcin in the matrix immediately adjacent to Haversian canals (type III) increased in females and males with age. Osteons staining intensely in the matrix adjacent to Haversian canals (type II) increased in females and was unchanged in aging males. Osteons that contained osteocalcin-positive resting lines (type IV) increased in bone obtained from males with increasing age but were unchanged in females. Sections of bone immunostained for osteopontin (SPP-I), osteonectin, and decorin did not reveal multiple patterns or alterations in staining with gender or increasing age. We suggest that the morphology of individual bone remodeling units is heterogeneous and the particular morphologic pattern of osteocalcin distribution changes with age and gender. These results suggest that differences in the distribution of osteocalcin in bone matrix may be responsible, in part, for the altered remodeling of bone associated with gender and aging.

Coronary arterial calcification as an active process: a new perspective on an old problem

The mechanism and purpose of coronary atherosclerotic calcification remain unknown. However, evidence reviewed here suggests that calcification is not passive precipitation or adsorption, but instead is organized and regulated. Gla containing proteins and other proteins normally associated with bone metabolism appear to play an important role in this process. A variety of studies are currently in progress in our laboratory which we hope will provide a more comprehensive understanding of processes leading to coronary calcification as well as prognostic data useful in clinical cardiologic practice. A clearer understanding of the nature and significance of coronary calcification may well pave the way toward new interventions to protect myocardium and minimize the morbidity and mortality associated with coronary artery disease.

Characterization of immunoreactive forms of human osteocalcin generated in vivo and in vitro

Three monoclonal antibodies recognizing the 5-13, 25-37, and 43-49 sequence of the human osteocalcin were used in competitive and two-site radioimmunoassays (RIA) to characterize specifically various immunoreactive forms of circulating human osteocalcin. The intact molecule accounts for 36% of total in normals (2.6 nM), 46% in patients with osteoporosis (3.1 nM), and 26% in chronic renal failure (6.9 nM). Four fragment were detected in addition to the intact molecule in the serum of healthy adults and patients with metabolic bone disease. N-terminal, mid, and mid C-terminal fragments were present in minute amounts (each accounting for 5-14% of the total circulating osteocalcin immunoreactivity). In contrast, the N-terminal midfragment, probably resulting from the cleavage around amino acids 43-44, represents about 30% (2 nM) of the total osteocalcin immunoreactive level in normals and patients with osteoporosis and up to 50% (13 nM) in patients with chronic renal failure. This large N-terminal midfragment, representing 75-80% of the intact osteocalcin level, is not lower when the plasma assay is performed immediately after sampling (within 20 minutes at 4 degrees C with proteinase inhibitors), indicating that it circulates in vivo. In addition, this fragment was detected in the supernatant of osteoblastic cells, representing about 28% of the intact peptide. Levels of N-terminal midfragment were not changed after treatment of patients with metabolic bone disease (Paget's disease, reflex sympathetic dystrophy, fibrous dysplasia, and osteoporosis) by bisphosphonate, suggesting that it is not released during bone resorption. The osteocalcin level measured with the two-site immunoradiometric assay specific for the intact molecule or with a conventional bovine RIA was rapidly decreased after incubation of serum at room temperature (-20 and -15%, respectively, after 3 h), whereas the total level of intact osteocalcin plus N-terminal midfragment was not changed. Intact osteocalcin loss can be partially avoided by proteinase inhibitors and by incubating serum at 4 degrees C. In conclusion, we characterized multiple immunoreactive forms of osteocalcin that circulate in addition to the intact molecule, none of them being specifically altered in osteoporosis. The N-terminal midfragment circulates in a large amount, probably resulting from cleavage of the intact molecule in the circulation and/or at peripheral sites. These fragments can also be generated in vitro by proteolytic degradation of the intact molecule. To obtain reliable intact osteocalcin values but also reliable levels measured with conventional competitive RIA, careful control of the sampling conditions is warranted.

Localisation of bone-forming cells during fracture healing by osteocalcin immunocytochemistry: an experimental study of the rabbit tibia

An immunocytochemical method was used to localise osteocalcin-producing cells during fracture healing in a rabbit model. In preliminary studies, tibial growth plates from young rabbits were used as a source of new bone formation, in order to determine the optimal tissue preparatory techniques. In the present study, a tibial shaft fracture was created in adult rabbits to study closed fracture healing. An indirect peroxidase method was used to stain paraffin-embedded tissue sections for osteocalcin. Osteocalcin-producing cells were positively identified at the periosteal and endosteal surfaces near the fracture site. Osteocalcin staining was not demonstrated in the surrounding soft tissues. At the interface between newly formed bone trabeculae and the cartilage layer within the callus, chondrocytic cells consistently showed localisation of osteocalcin. Within cartilaginous areas of the callus, some chondrocytes showed positive staining for osteocalcin. These cells were often seen in the proximity of blood vessels. The findings suggest that during fracture healing, under certain conditions, chondrocytes are capable of producing osteocalcin and thus could be considered capable of possible transformation into osteoblasts.

Diagnostic tools and biologic models for studying osteoporosis and oral bone loss: tissue sampling

Study of oral tissues to understand the mechanisms of osteoporosis and oral bone loss includes histologic, biochemical, and molecular assessments of the tissue itself, as well as in vivo analysis of the biology of resident cells. Tissue sampling is limited by the nature of the defect and the use of appropriate controls (contralateral site vs same site, different subjects vs repeated measures of the same sites). Experimental parameters may include histomorphometrics, histochemistry, immunohistochemistry, and in situ hybridization. Molecular and biochemical technology also can be used to study the tissue in vivo. The presence of mineral is a confounding variable. To understand the underlying mechanisms of oral bone loss, cell culture is a powerful tool. The location in the oral cavity, the type of tissue (periosteum/cortical bone/trabecular bone), and the presence of pathology (periodontal disease) affect the biology of the cultured cells. Enzymatic release of cells from their extracellular matrix yields heterogeneous cell populations. Migratory cells from explant cultures are more homogeneous but less differentiated. Fibroblastic and bacterial contamination may be problems. Although cell culture data must be considered in the context of the intact tissue, the potential exists for developing bone cell function tests with diagnostic use in the treatment of bone disease.

Osteopenia and bone-remodeling abnormalities in warfarin-treated lambs

The physiologic role of osteocalcin (OC), a vitamin K-dependent protein specific to bone, remains elusive. It has been shown that rats maintained on chronic treatment with vitamin K1 and its antagonist warfarin exhibit a marked decrease in bone osteocalcin because noncarboxylated osteocalcin does not bind to bone hydroxyapatite. To assess the role of OC in bone remodeling, we applied the warfarin model to growing lambs. We analyzed the bone changes after 3 months of concurrent warfarin and vitamin K1 treatment. Four groups of four lambs were constituted at birth and received daily a saline solution (control group, CT), 4 mg/kd/day of vitamin K1 (vitamin K group), 4 mg/kg/day of vitamin K1 + 75 or 150 mg/kg/day of warfarin (W75 and W150 group, respectively). In warfarin-treated animals, bone osteocalcin levels were decreased, both in the metaphysis (9% compared to controls) and the diaphysis (30% compared to controls) of the metacarpals. The fraction of noncarboxylated osteocalcin measured every month in the serum was significantly higher in warfarin-treated lambs than in controls at each timing point (37.6 +/- 2.6% in W75 and 48.7 +/- 5.2% in W150 versus 14.4 +/- 3.8% in controls at 3 months). Compared to non-warfarin-treated animals (NW), the main histomorphometric parameters measured on the iliac crest after tetracycline double labeling were significantly reduced in the warfarin-treated lambs: 12.2 +/- 5.2 versus 18.6 +/- 4.7% in NW (p < 0.03) for the cancellous bone area, which reflects the trabecular bone density; 14.7 +/- 6.1 versus 21.0 +/- 3.6% in NW (p < 0.03) for the eroded perimeter, and 0.315 +/- 0.064 versus 0.561 +/- 0.23 microns 3/microns 2/day in NW (p < 0.02) for the tetracycline-based bone formation rate. In conclusion, the depletion of osteocalcin in the bone of lambs induced within 3 months a marked osteopenia that resulted from a decrease in resorption and a more pronounced decrease in bone formation. Our data suggest that the presence of osteocalcin, the major gla-containing protein of bone, may be important for the maintenance of a normal bone mass and remodeling of trabecular bone.

Noncollagenous proteins in heterotopic ossification. Immunohistochemical analysis in 15 paraplegies

We used immunohistochemical techniques to investigate the distribution pattern of osteonectin, osteocalcin, bone sialoprotein II and the small proteoglycans decorin and PG 100 during different stages of heterotopic ossification (HO) in pressure sores of paraplegic patients. All these noncollagenous proteins (NCPs) accumulated in fibroblasts and preosteoblasts, predominantly in the activity centers of early osteogenetic areas. Mature types of HO showed a more discrete expression pattern for this protein group, with weaker reactions in the narrow osteoblastic rims. Decorin was detected predominantly in the stroma of HO. Our results indicate that the NCPs are important components during the pathogenesis of HO and that fibroblasts may serve as osteoprogenitor cells.

Endothelin modulates osteopontin and osteocalcin messenger ribonucleic acid expression in rat osteoblastic osteosarcoma cells

Endothelins (ETs) are vasoconstrictive peptides produced mainly by endothelial cells. The ET receptors are expressed in many types of cells including osteoblast-like cells. The purpose of this study was to examine the effects of endothelin on the expression of osteoblastic phenotype-related genes. We found that endothelin-1 (ET-1) enhanced approximately two-fold the mRNA expression of both osteopontin and osteocalcin genes in rat osteoblastic osteosarcoma ROS17/2.8 cells. These effects were dose-dependent, peaking at 10(-7) M. The ET-1 enhancement of the abundance of osteopontin and osteocalcin mRNAs was time-dependent, with a maximal effect at 24 h. ET-1 modulation of the expression of the two phenotype-related gene products of osteoblasts suggests that endothelin is one of the cytokines which modulate osteoblastic functions and that this molecule may play a role in the regulation of bone metabolism.

Distribution of noncollagenous proteins in the matrix of adult human bone: evidence of anatomic and functional heterogeneity

The microanatomic distribution of several noncollagenous proteins (NCPs) in bone matrix was examined by immunohistochemical analysis of glycol-methyl methacrylate-embedded normal adult human bone biopsies. Osteopontin and bone sialoprotein stained throughout the lamellae of both trabecular and cortical bone. Cement lines (cortical and trabecular) and the mineralized matrix immediately adjacent to each Haversian canal were intensely stained. Osteocalcin was detected in cement lines; however, lamellar staining varied depending on the location within the individual unit of bone. In cortical bone, the inner concentric lamellae of osteons were often unstained but the outer lamellae were heavily stained for osteocalcin. Osteonectin was not detected in cement lines and in most specimens revealed a pattern similar to that of osteocalcin with respect to the absence of immunostaining within the inner concentric lamellae. Decorin was prominent in the perilacunar matrix, the canaliculi of osteocytes, and the matrix immediately adjacent to quiescent Haversian canals. Biglycan appeared evenly distributed throughout cortical and trabecular bone matrix. These results suggest that the incorporation of NCPs into matrix may vary depending on the stage of formation of individual bone units. The specific distribution and spatial relationship of these NCPs may be related to the function of each protein during bone resorption and formation. The distinct patterns of NCP localization in bone support the hypothesis that in addition to their structural and mineral-inducing properties, these proteins may influence the events associated with bone remodeling, such as recruitment, attachment, differentiation, and activity of bone cells.

Impairment of bone turnover in elderly women with hip fracture

Hip fracture is one of the most severe consequences of osteoporosis affecting aged women. However, abnormalities of bone turnover responsible for bone loss in this condition have not been clearly defined. To further evaluate the bone metabolic status of women sustaining hip fracture, we have prospectively measured serum osteocalcin as a marker of bone formation and urinary excretion of pyridinoline (Pyr) and deoxypyridinoline (D-pyr) cross-links as markers of bone collagen degradation in 174 independently living women (80 +/- 8 years) within a few hours after a hip fracture. Comparison was made with 77 age-matched controls (80 +/- 5 years) and 17 premenopausal women (39 +/- 3 years). In addition 15 of the patients were followed with daily measurements during the first postoperative week. At the time of admission osteocalcin was 20% lower in the fractured women compared to the elderly controls (7.6 +/- 3.8 vs. 9.5 +/- 4.5 ng/ml, P = 0.001). Pyr and D-pyr were 36% and 40% higher, respectively (P = 0.0001), than in elderly controls and 85% and 76% higher than in premenopausal controls (P = 0.0001). Serum osteocalcin did not correlate with the cortisol level measured at the same time (r = 0.03, ns), nor with serum albumin and creatinine. Serum osteocalcin remained unchanged within 18 hours after fracture, whereafter it progressively decreased until the third postoperative day. No correlation was noted between the excretion of pyridinoline cross-links and the time elapsed from fracture.(ABSTRACT TRUNCATED AT 250 WORDS)

Serum osteocalcin and fracture susceptibility in elderly women

The purpose of this investigation was to evaluate the bone turnover by using bone metabolic markers in relation to previous fracture history and independent of bone mass. Patients and controls were recruited from a population-based study of 193 women, all living in the same city and aged 60, 70, and 80 years. The bone mineral content (BMC) was measured bilaterally in the distal forearm by single-photon absorptiometry (SPA). At the same time, serum samples were obtained for biochemical analysis. Of the 193 women, we identified 26 with at least one major fracture during the past few years. Each of these 26 women with a certified recent previous fracture was individually matched with a woman from the same study group of equal BMC and age but without a fracture history. In the two groups, the serum samples were analyzed for osteocalcin, C-terminal procollagen peptide (P1CP), alkaline phosphatase, bone-specific alkaline phosphatase, calcium, phosphate, and albumin. The serum concentration of osteocalcin was 20% lower in the women with a previous fracture than in the controls (P = 0.03). The other markers of bone formation gave similar values in the two groups. There was a significant correlation between the osteocalcin and P1CP concentrations (P = 0.001). Our findings indicate that the susceptibility to fractures independent of factors such as age and BMC may be related to a decreased bone turnover.

The diagnostic and prognostic value of serum bone Gla protein (osteocalcin) in patients with recurrent breast cancer

Serum bone Gla protein (S-BGP), a marker of bone metabolism, was measured in 60 patients included in a staging programme for recurrent breast cancer. Other diagnostic procedures comprised S-alkaline phosphatase (S-AP), bone scan (B-scan), bilateral iliac crest bone marrow biopsies, and radiological bone survey. The sites of recurrence were bone (61%), bone marrow (46%), soft tissue (52%), lung (13%), pleura (11%), liver (4%), and brain (2%). Radiology and bone biopsy served as key diagnoses as to the presence or absence of bone metastases. The diagnostic efficiency of B-scan and S-AP was greater than that of S-BGP, and the result of BGP measurement was associated with neither extent nor number of bone metastases. However, the BGP values were significantly lower in patients who had visceral metastases, and the median duration of survival after recurrence was 13 months for patients with low S-BGP levels (= < 2.0 nmol l-1), compared to 18 months for patients with medium S-BGP values (2.0-2.9 nmol l-1), and 25 months for patients with high values (> 3.0 nmol l-1) (p = 0.19). Analyses of the simultaneous effect of univariate prognostic factors were performed using the Cox proportional hazards model. S-alkaline phosphatase (S-AP) and S-BGP were the only significant, independent prognostic factors.

Effect of insulin treatment on osteocalcin levels in diabetic children and adolescents

To investigate bone mineral metabolism in insulin-dependent diabetes mellitus, serum osteocalcin, a marker of bone formation, was measured in 31 diabetic children at onset of disease and 15 days after metabolic improvement by insulin therapy. As a control group for osteocalcin levels we studied 31 healthy sex- and age-matched children. Mean values of serum osteocalcin at onset of diabetes were significantly lower than in control group (p < 0.001), but we did not find any difference after 15 days of insulin therapy. Osteocalcin and parathyroid hormone concentrations were significantly greater after 15 days of insulin treatment than at onset of disease (p < 0.001 and p < 0.01, respectively). The osteocalcin levels were negatively correlated both with fructosamine and with glycosylated hemoglobin (p < 0.01 and p < 0.001, respectively), and positively correlated with the degree of metabolic acidosis at onset (p < 0.05). Therefore we postulate that during glycometabolic imbalance there is a decrease in bone turnover that could be one of the etiological factors of diabetic osteopenia.

A major non-collagenous 62 kDa protein from rat bone mineralized matrix is identical to pp63 a phosphorylated glycoprotein from liver

A protein present as a M(r) 62 k monomer and as several differently sized disulfide-bonded oligomers has been isolated from rat bone mineralized matrix. Its overall tissue distribution determined by ELISA immunoassays showed the protein present only in bone, tooth and in serum while aorta, cartilage, intestine, kidney, liver, muscle, skin, spleen and tendon were all negative. Despite that the 62 kDa protein was abundant and selectively found in bone, no positive cDNA clone could be identified in several rat bone libraries. Positive clones were, however, identified in a rat liver expression library. A cDNA clone of 1.3 kb hybridized in a Northern blotting assay to a 1.8 kb mRNA in rat liver. No hybridization signal was detected with RNA from bone, brain, lung, muscle, spleen and kidney. Sequence analysis of the isolated cDNA clone revealed a 50-bp untranslated region followed by an open reading frame of 357 amino acids. The open reading frame can be divided into a 17-amino acid signal peptide followed by the mature protein of 340 amino acids with alanine as its N-terminal amino acid. A short N-terminal amino acid sequence from the isolated 62-kDa bone protein verified the molecular identity of the cDNA clone. The primary structure of the 62-kDa liver protein was identical to a that of a 63-kDa phosphorylated glycoprotein (pp63) from liver.

Characterization of a tumor necrosis factor-responsive element which down-regulates the human osteocalcin gene

Tumor necrosis factor (TNF) down-regulates the production of bone matrix proteins by osteoblasts, thereby inhibiting bone formation. Osteocalcin, the major noncollagenous protein in bone, is inhibited by TNF at the transcriptional level. Mapping studies were undertaken to characterize the TNF-responsive element (TNFRE) in the osteocalcin promoter. Deletion analysis localized the TNFRE to the -522/-511 region, which contains a 9-bp palindromic motif (AGGCTGCCT). Promoter segments containing this sequence down-regulated a heterologous simian virus 40 promoter. Site-specific mutagenesis of the TNFRE eliminated TNF down-regulation. Mobility shift assays demonstrated that a constitutively expressed nuclear factor bound to the TNFRE; this factor was tentatively identified as the p50 homodimer of NF-kappa B. TNF stimulation induced a second TNFRE-binding protein which displaced the constitutive factor. The TNF-induced protein was not inhibitable by the NF-kappa B consensus sequence and was unreactive with anti-NF-kappa B antiserum. DNase footprinting demonstrated that both factors protected the -522/-501 portion of the promoter, consistent with the results of mapping studies and competitive mobility shift assays. It is hypothesized that the generalized catabolic activities of TNF in infectious and malignant diseases may be regulated via this novel element.

Characterization of a tumor necrosis factor-responsive element which down-regulates the human osteocalcin gene

Tumor necrosis factor (TNF) down-regulates the production of bone matrix proteins by osteoblasts, thereby inhibiting bone formation. Osteocalcin, the major noncollagenous protein in bone, is inhibited by TNF at the transcriptional level. Mapping studies were undertaken to characterize the TNF-responsive element (TNFRE) in the osteocalcin promoter. Deletion analysis localized the TNFRE to the -522/-511 region, which contains a 9-bp palindromic motif (AGGCTGCCT). Promoter segments containing this sequence down-regulated a heterologous simian virus 40 promoter. Site-specific mutagenesis of the TNFRE eliminated TNF down-regulation. Mobility shift assays demonstrated that a constitutively expressed nuclear factor bound to the TNFRE; this factor was tentatively identified as the p50 homodimer of NF-kappa B. TNF stimulation induced a second TNFRE-binding protein which displaced the constitutive factor. The TNF-induced protein was not inhibitable by the NF-kappa B consensus sequence and was unreactive with anti-NF-kappa B antiserum. DNase footprinting demonstrated that both factors protected the -522/-501 portion of the promoter, consistent with the results of mapping studies and competitive mobility shift assays. It is hypothesized that the generalized catabolic activities of TNF in infectious and malignant diseases may be regulated via this novel element.

Concentration and hydroxyapatite binding capacity of plasma osteocalcin in chronic alcoholic men: effect of a three-week withdrawal therapy

Plasma concentrations of osteocalcin (OC) were studied in 40 chronic alcoholic men (age range: 21-56 years) before and after 3 weeks of ethanol withdrawal therapy and in 50 non-alcoholic controls selected in respect to age and sex. Plasma OC level in alcoholic subjects was significantly lower than in the controls (3.0 +/- 2.6 micrograms/l and 4.7 +/- 2.8 micrograms/l, respectively). After 21 days of withdrawal therapy, plasma OC level was significantly higher than at the day of admission (5.8 +/- 3.5 micrograms/l, P < 0.001). This level was not statistically different from that of the controls. We also demonstrated that the hydroxyapatite binding capacity of plasma OC before as well as after the withdrawal period was not different from that of the controls. The acetaldehyde adduction of purified bovine OC in vitro did not change any of its immunoactivity and hydroxyapatite binding capacity. The results emphasize the fact that the decrease of plasma osteocalcin in chronic alcoholics is reversible within 3 weeks of alcohol withdrawal and that the circulating protein seems to be similar to that present in controls.

Menatetrenone inhibits bone resorption partly through inhibition of PGE2 synthesis in vitro

We studied the effect of menatetrenone, a vitamin K2 homolog, on bone resorption stimulated by interleukin-1 alpha (IL-1 alpha), prostaglandin E2 (PGE2), parathyroid hormone (PTH), and 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]. Bone-resorbing activity was assessed by measurement of calcium and hydroxyproline in the media and calvariae. IL-1 alpha (0.1-100 U/ml), 1,25-(OH)2D3 (10(-10)-10(-7) M), PGE2 (10(-9)-10(-6) M), and PTH (3 x 10(-8)-3 x 10(-7) M) dose dependently increased the levels of calcium and hydroxyproline in the medium. Indomethacin (10(-6) M) completely inhibited bone resorption induced by IL-1 alpha and partially inhibited bone resorption induced by 1,25-(OH)2D3. However, indomethacin did not affect the action of PGE2 or PTH. Menatetrenone (3 x 10(-6)-3 x 10(-5) M) inhibited the bone resorption induced by IL-1 alpha (2 U/ml), PGE2 (10(-7) M), PTH (3 x 10(-7) M), and 1,25-(OH)2D3 (3 x 10(-10) M) in a dose-dependent manner. Menatetrenone also inhibited the PGE2 production stimulated by IL-1 alpha. These results indicate that menatetrenone may inhibit bone resorption through at least two different mechanisms; one possibly is an inhibitory effect on prostaglandin production.

Effects of 1,25-dihydroxyvitamin D3 and growth hormone therapy on serum osteocalcin levels in children with growth hormone deficiency

In order to investigate the influence on bone metabolism of growth hormone (GH), we evaluated the response to an acute load of 1,25(OH)2D3 (Rocaltrol) (1.5 micrograms/day for 4 days) in 16 growth hormone-deficient prepubertal children (11 boys and 5 girls, aged from 6.2 to 9.6 years) both before and after 1 month of human GH (hGH) therapy (0.1 IU/kg/day, 6 times per week). Before and after the 1,25(OH)2D3 load, serum IGF-I, osteocalcin, Ca, P, alkaline phosphatase (ALP) and urinary excretion of Ca and P were measured. The serum levels of osteocalcin rose significantly after the first 1,25(OH)2D3 load, without an increase in IGF-I values and with a slight non-significant increase in serum Ca and P. Almost superimposable increases of osteocalcin, Ca and P were observed after 1 month of hGH therapy, with a significant increase of IGF-I, but they did not rise further after the second 1,25(OH)2D3 load. On the basis of our results, 1,25(OH)2D3 seems to have a stimulatory action on osteoblastic activity even in the absence of normal levels of GH. However, there is no apparent additional stimulatory activity after administration of hGH. Osteocalcin level behaviour during our study might suggest that GH and 1,25(OH)2D3 have a common and easily saturable stimulatory pathway on osteoblastic function.

Comparison of the anticonflict effect of buspirone and its major metabolite 1-(2-pyrimidinyl)-piperazine (1-PP) in rats

The anxiolytic effects of buspirone and its major metabolite, 1-(2-pyrimidinyl)-piperazine (1-PP) have been investigated with a conflict (shock-induced suppression of drinking) paradigm in rats. Buspirone (10 mg/kg, p.o.) showed an anticonflict activity with a bell-shaped dose-response relationship without any effect on spontaneous water consumption. Higher doses of buspirone reduced the punished response. Diazepam (20 and 40 mg/kg, p.o.) also showed an anticonflict activity in a dose-dependent manner, but animals with diazepam showed an increase in spontaneous water consumption at these doses. On the other hand, 1-PP (6.25-200 mg/kg, p.o.) showed a weak anticonflict activity with a significant effect at 25 mg/kg without any effect on spontaneous water consumption. In the 7-day treatment test, buspirone (5 and 10 mg/kg, p.o.), 1-PP (5 and 25 mg/kg, p.o.) and diazepam (10 and 40 mg/kg, p.o.) did not develop the tolerance to the anticonflict activity. Conversely, the anticonflict activity of diazepam was increased by the repeated treatment. Diazepam (10 mg/kg, p.o.) showed an anticonflict activity without any effect on spontaneous water consumption in this test. These results demonstrated that buspirone clearly exhibited an anticonflict effect similar to that of diazepam in a Vogel-type conflict test, and its real anxiolytic effect may not be always based on 1-PP, the main metabolite of buspirone.

Seasonality of hip fracture and haemorrhagic disease of the newborn

The objective is to examine and compare the seasonalities of fractured neck of femur and haemorrhagic disease of the newborn. The data are from two sources. Admissions for fractured neck of femur in Scotland over five years (1983-87) are examined by age, sex, mortality, operative intervention and source of admission. Data from the United States (1927-36) are examined for infant death rates from suspected haemorrhagic disease of the newborn 3-14 days after birth. The sine curves are examined. The rhythms, while not identical, have similarities. The peaks are in January-February and the troughs in July-August. Amongst hip fractures the peak is one month earlier and the seasonal excess around 20-25 per cent in both conditions. Rickets, haemorrhagic disease of the newborn and fractured neck of femur have comparable seasonal rhythms. Vitamin D regulates the synthesis of the vitamin K dependent bone protein osteocalcin, which is functionally abnormal in postmenopausal women. This may be a significant factor in the seasonal variation of hip fracture.

Gallium nitrate regulates rat osteoblast expression of osteocalcin protein and mRNA levels

Gallium nitrate, a group IIIa metal salt, has been found to be clinically effective for the treatment of accelerated bone resorption in cancer-related hypercalcemia and Paget's disease. Here we report the effects of gallium nitrate on osteocalcin mRNA and protein levels on the rat osteoblast-like cell line ROS 17/2.8. Gallium nitrate reduced both constitutive and vitamin D3-stimulated osteocalcin protein levels in culture medium by one-half and osteocalcin mRNA levels to one-third to one-tenth of control. Gallium nitrate also inhibited vitamin D3 stimulation of osteocalcin and osteopontin mRNA levels but did not affect constitutive osteopontin mRNA levels. Among several different metals examined, gallium was unique in its ability to reduce osteocalcin mRNA levels without decreasing levels of other mRNAs synthesized by ROS 17/2.8 cells. The effects of gallium nitrate on osteocalcin mRNA and protein synthesis mimic those seen when ROS 17/2.8 cells are exposed to transforming growth factor beta 1 (TGF beta 1); however, TGF-beta 1 was not detected in gallium nitrate-treated ROS 17/2.8 cell media. Use of the RNA polymerase II inhibitor 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole demonstrated that gallium nitrate did not alter the stability of osteocalcin mRNA. Transient transfection assays using the rat osteocalcin promoter linked to the bacterial reporter gene chloramphenicol acetyltransferase indicated that gallium nitrate blocked reporter gene expression stimulated by the osteocalcin promoter. This is the first reported effect of gallium nitrate on isolated osteoblast cells.

The hepatic extracellular matrix. I. Components and distribution in normal liver

The unique nature of the hepatic extracellular matrix (ECM) is predicated by the special configuration of the space of Disse. Whereas other epithelial organs have two basement membranes (BM) and a substantial ECM interposed between endothelial and epithelial cells, the liver lobule has no BM and only an attenuated ECM, consisting mostly of fibronectin, some collagen type I, and minor quantities of types III, IV, V, and VI. This configuration, together with the abundant fenestrations and gaps of the sinusoidal endothelial cells, seems ideally suited to facilitate the rapid bidirectional exchange of macromolecules normally taking place between plasma and hepatocytes. During organogenesis, the liver anlage is vascularized by continuous capillaries with BM, but by day 13.5 of development (in the rat) the vessels in the immediate proximity of hepatocytes become fenestrated, lacking specialized junctions and BM, suggesting that the hepatocytes produce signals capable of modulating the endothelial phenotype. In regeneration, hepatocyte proliferation precedes vascular proliferation resulting in the formation of hepatocyte clusters that, temporarily, lack sinusoids. Eventually, vascular proliferation follows and the normal hepatocyte-vascular relationships are restored. During this period laminin synthesis by Ito cells is prominent. As soon as hepatocytes become stable, secretion of the sinusoid phenotype-maintaining factors resumes and laminin synthesis and secretion terminates. The interplay between extracellular matrix and liver cells is essential for normal homeostasis and its modification results in deranged hepatic function.

Measurement of serum osteocalcin with a human-specific two-site immunoradiometric assay

We developed a sensitive and specific two-site radioimmunoassay (IRMA) for human osteocalcin using human osteocalcin as a standard and two monoclonal antibodies raised against human osteocalcin purified from human cortical bone, a solid-phase anti-25-37 region and a tracer anti-5-13 sequence of the molecule. A wide range of osteocalcin levels (up to 300 ng/ml) can be measured with a sensitivity of 0.4 ng/ml. The intra- and interassay coefficients of variation are less than 4 and 6%, respectively. The recovery of human osteocalcin from serum samples ranges from 96 to 103%. IRMA was linear for serial sample dilutions in a wide range of serum osteocalcin levels, even in patients with chronic renal failure on hemodialysis. Depletion of serum in intact osteocalcin demonstrated that IRMA detects, in addition to the intact peptide, a large N-terminal midregion fragment that represents about 50% of total osteocalcin levels in normals and patients with Paget's disease and up to 75% in patients with chronic renal failure. This large fragment, previously unrecognized because it cannot be distinguished from intact osteocalcin with gel filtration chromatography, is not generated in vitro by incubation of the serum up to 26 h. We measured osteocalcin in the serum of 309 healthy adults (180 men and 129 women, age range 20-95 years), 36 patients with Paget's disease, 12 patients with primary hyperparathyroidism, 70 patients with chronic renal failure on hemodialysis, and 10 patients on corticosteroid therapy, simultaneously with human IRMA and with a conventional radioimmunoassay (RIA) based on bovine reagents. A tight correlation (r = 0.889) was observed between the two assays in the normal population, but the values obtained with IRMA were about threefold higher (mean 23.3 +/- 10.5 versus 7.5 +/- 3.4 ng/ml) than those obtained with RIA. Reported as Z scores, that is, number of standard deviations from the predicted normal mean adjusted for sex and age, these two assays (IRMA and RIA) gave concordant results in patients with Paget's disease (4.05 +/- 6.21 versus 2.41 +/- 2.53), primary hyperparathyroidism (4.14 +/- 7.17 versus 2.13 +/- 2.28), chronic renal failure (25.32 +/- 24.49 versus 6.93 +/- 5.48), and glucocorticoid treatment (-1.48 +/- 0.78 versus -1.11 +/- 0.57). However, IRMA was more discriminant from controls for all these metabolic bone diseases because the absolute values of mean Z scores with IRMA were significantly higher than those obtained with the RIA (p < 0.05-0.0001).(ABSTRACT TRUNCATED AT 400 WORDS)

High-resolution immunolocalization of osteopontin and osteocalcin in bone and cartilage during endochondral ossification in the chicken tibia

The ultrastructural distribution of two noncollagenous proteins, osteopontin (OPN) and osteocalcin (OC), originally extracted from bone matrix and proposed to play an important role in bone formation, was examined in the matrices of bone and cartilage from embryonic and postnatal chicken tibial growth plates by high-resolution immunocytochemistry using the colloidal gold technique. In bone, immunolabeling patterns using polyclonal antibodies against chicken OPN and OC were generally similar in that both showed an intense, but regionally variable, labeling of mineralized bone matrix and small mineralization loci dispersed throughout the osteoid and containing prominent condensed organic material. Unmineralized osteoid showed weak-to-moderate labeling. In the mineralized bone matrix proper, labeling was predominantly associated with amorphous, electron-dense patches of organic material among the collagen fibrils. In growth plate cartilage, both proteins first appeared related to calcified cartilage in the hypertrophic zone, although the labeling patterns were somewhat different. For OPN, gold particles were mostly associated with an organic lamina limitans-like density containing condensed, filamentous organic matrix at the periphery of small nodules and large masses of calcified cartilage, with additional moderate labeling throughout the interior of the calcified cartilage. For OC, labeling was observed over filamentous structures throughout the calcified cartilage matrix, with some, but less, labeling at the periphery. In the lowermost zones of the growth plate, the major reaction using both antibodies was found over a layer of dense, amorphous organic material at the periphery of the calcified cartilage at the future bone/calcified cartilage interface, a labeling pattern that persisted following bone deposition at these sites. OPN and to a lesser extent OC were also concentrated in cement (resting, reversal) lines. Throughout the bone and cartilage of the tibia, cells of both the osteoblastic and the osteoclastic lineages were found directly apposed to labeled surfaces and lamina limitans of organic matrix containing OPN and OC. In summary, it is concluded from the immunocytochemical data presented here that the association of OPN and OC with mineralized regions of the extracellular matrices of bone and cartilage and the accumulation of these proteins at tissue surfaces and interfaces are consistent with the hypotheses that they play a role in the extracellular mineralization process per se and/or that they may mediate cell adhesion and dynamics.

Serum osteocalcin in normal and short Chinese children

Serum osteocalcin was measured by radioimmunoassay in 200 normal children and adolescents, and seven growth hormone (GH) deficient and seven non-growth hormone deficient (NGHD) short children. There was a sex- and age-dependent change in the serum osteocalcin concentrations in normal children and adolescents with a pattern similar to the childhood height velocity curves. The serum osteocalcin concentration was in the low normal range in most patients with GH deficiency and NGHD short stature. GH therapy significantly increased the growth velocity in both groups of short children. GH treatment resulted in a significant rise in serum osteocalcin concentrations after 6 and 12 months in NGHD children but a more variable change was observed in GH-deficient children. Although osteocalcin levels may give some biochemical indication of growth, these measurements should be used together with auxological and other biochemical measurements to assess growth reliably.

Usefulness of a novel monoclonal antibody against human osteocalcin in immunohistochemical diagnosis

A novel monoclonal antibody against human osteocalcin, recently established in our laboratory, was shown by immunoblotting and immunohistochemistry to react specifically with human osteoblasts. In the present study, the antibody was applied to the immunohistochemical diagnosis of human bone tumours, especially osteoblastic tumours. The antibody reacted with all 27 osteosarcomas. No positive reaction was found either in chondrosarcoma, giant cell tumours of bone, soft tissue tumours or epithelial tumours. A positive reaction was found preferentially in the cytoplasm of most of the osteosarcoma cells, but not in the extracellular matrix. Since the antibody reacted with formalin-fixed and paraffin-embedded tissues, it will be a useful tool for routine immunohistochemical diagnosis of osteoblastic lesions.

Alterations of the mineralization profile and osteocalcin concentrations in osteoarthritic cortical iliac crest bone

The relation between bone mineralization and osteocalcin content was investigated in iliac crest cortical bone obtained at necropsy in young females and in two groups of elderly women with and without osteoarthritis of the hands evaluated by X-ray. Using density fractionation technique, the bone was separated into fractions of increasing density from 1.72 to 2.30 g/ml. The mineralization profile revealed a significant shift to higher densities in the osteoarthritis cases compared with young adults (P less than 0.005) and age-sex-matched controls (P less than 0.001). The ash, calcium, and phosphorus content of the bone increased with increasing density of the fractions whereas collagen content, measured as hydroxyproline, decreased. The osteocalcin concentration of each fraction was determined in the supernatants obtained after EDTA-extraction in the presence of protease inhibitors. In the young control and osteoarthritis group, the osteocalcin content in the lowest density fractions was higher compared with the older non-osteoarthritic group. Osteocalcin content of the high density fractions, representing highly mineralized osteons, was the same in the three groups studied. These findings support the hypothesis that quality differences in bone may explain the inverse relationship between osteoarthritis and osteoporosis.

Immunohistochemical study of bone GLA protein in primary bone tumors

METHODS

The immunoreactivity of bone GLA protein (BGP) in primary bone tumors, including osteosarcoma, chondrosarcoma, malignant fibrous histiocytoma of bone (MFH), and giant cell tumor of bone (GCT), was investigated with anti-BGP rabbit serum and peroxidase-antiperoxidase complex.

RESULTS

As to intracellular localization, BGP antigenicity was detected in 33 of 35 cases of osteosarcoma and 12 of 25 cases of chondrosarcoma. However, there were no positive findings in all 15 cases of MFH or 20 cases of GCT. In chondrosarcoma, the frequency of positively stained cases increased according to pathologic grading (i.e., 3 of 14 cases of Grade 1, 7 of 9 cases of Grade 2, and 2 of 2 cases of Grade 3). Although the multinucleated cells in MFH or GCT were not immunostained, BGP antigenicity was observed in the multinucleated cells of osteosarcoma (12 of 15 cases). In the matrix of osteosarcoma, BGP immunoreactivity of the tumorous osteoid was observed in 28 of 32 cases. However, in the matrices of chondrosarcoma, MFH, and GCT, BGP immunoreactivity was not observed.

CONCLUSION

These results suggest that the immunohistochemical study of BGP is useful for the differential diagnosis of bone tumors.

Production of new trabecular bone in osteopenic ovariectomized rats by prostaglandin E2

Serum chemistry and bone morphometry of the proximal tibial metaphysis were performed in 3-month-old double fluorescent-labeled, female Sprague-Dawley rats subjected to bilateral ovariectomy or sham surgery for 4 months prior to treatment with 0, 0.3, 1, 3, or 6 mg of prostaglandin E2 (PGE2)/kg/day subcutaneously for 30 days. The 4-month postovariectomized rats possessed an osteopenic proximal tibial metaphysis with 7% trabecular area compared with controls (19%). PGE2 treatment elevated osteocalcin levels and augmented proximal tibial metaphyseal bone area in ovariectomized and sham-operated rats. Osteopenic, ovariectomized rats treated with 6 mg PGE2/kg/day for 30 days restored bone area to levels of age-matched sham-operated rats. Morphometric analyses showed increased woven and lamellar bone area, fluorescent-labeled perimeter (osteoblastic recruitment), mineral apposition rate (osteoblastic activity), bone formation rate (BFR/BV), and longitudinal bone growth. These dramatic bone changes were all significantly increased at the dose-response manner. This study showed that in vivo PGE2 is a powerful activator of bone remodeling, it increases both bone resorption and bone formation, and produces an anabolic effect by shifting bone balance to the positive direction. Furthermore, PGE2-induced augmentation of metaphyseal bone area in ovariectomized rats was at least two times greater than in sham-operated rats.

The osteocalcin propeptide is not secreted in vivo or in vitro

Osteocalcin is initially synthesized as an 11 kD molecule consisting of a 23-residue translocation signal peptide that is cleaved during translation, a 26-residue propeptide that targets the protein for gamma-carboxylation, and the 49-residue mature protein. Although the majority of newly synthesized osteocalcin is deposited into bone matrix, a small amount can be detected in blood, and it is this characteristic that has led to its current clinical use as a specific index of osteoblastic activity. Nothing is known, however, about the fate of the propeptide. If osteocalcin and the propeptide are cosecreted, then the concentration of the propeptide could also be useful as a marker of osteoblastic function and, further, may be superior to osteocalcin because it would be unaffected by binding to bone. To test this hypothesis, we synthesized a peptide corresponding to 21 residues of the osteocalcin propeptide from humans and produced a polyclonal antibody to this peptide. Human sera were screened for the presence of the propeptide, and the human osteosarcoma cell line MG-63 was tested for secretion of the propeptide. We could not detect any osteocalcin propeptide in sera from normal adults or individuals with renal failure or primary hyperparathyroidism or those on long-term coumadin therapy. Likewise there was no propeptide present in media from cells grown in the presence of vitamin K, 1,25-(OH)2D3, warfarin, or warfarin plus 1,25-(OH)2D3. In contrast, the cell extract, characterized by high-performance liquid chromatography, contained mature osteocalcin, free propeptide, and the proosteocalcin precursor when cells were grown in the presence of 1,25-(OH)2D3 alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of warfarin on early rat tooth development

Rat pups were treated from birth to 5 days of age with the vitamin K antagonist warfarin in order to investigate possible functions of the vitamin K-dependent dentin Gla protein (DGP) in tooth development. Warfarin completely eliminated the immunocytochemically detectable DGP which is a prominent feature of dentin in control rat pups, and also caused an increased concentration of DGP in odontoblasts. Warfarin treatment did not affect the ultrastructure of cells or the extracellular matrix in the tooth germs. The width of the predentin layer, which is considered to be correlated with the rate of mineralization, was unchanged. These results are the first to demonstrate that warfarin treatment prevents the accumulation of DGP in dentin, and that the deposition of DGP has no influence on the overall rate of dentin matrix mineralization in tooth germs.

Developmental expression and hormonal regulation of the rat matrix Gla protein (MGP) gene in chondrogenesis and osteogenesis

Matrix Gla protein (MGP), a vitamin K dependent protein, has recently been identified in many tissues. However, it is accumulated only in bone and cartilage suggesting that the expression of MGP may be related to the development and/or maintenance of the phenotypic properties of these tissues. We systematically evaluated MGP mRNA expression as a function of bone and cartilage development and also as regulated by vitamin D during growth and cellular differentiation. Three experimental models of cartilage and bone development were employed: an in vivo model for endochondral bone formation, as well as in primary cells of normal diploid rat chondrocyte and osteoblast cultures. MGP was expressed at the highest level during cartilage formation and calcification in vivo during endochondral bone formation. In chondrocyte cultures, MGP mRNA was present throughout the culture period but increased only after 3 weeks concomitantly with type I collagen mRNA. In osteoblast cultures, MGP mRNA was expressed during the proliferative period and exhibited increased expression during the period of matrix development. In contrast to osteocalcin (bone Gla protein), this increase was not dependent on mineralization but was related to the extent of differentiation associated with and potentially induced by extracellular matrix formation. During the proliferative period, type I collagen mRNA peaked and thereafter declined, while type I collagen protein steadily accumulated in the extracellular matrix. Constant MGP levels were maintained in the mineralization period of osteoblast differentiation in vitro which is consistent with the constant levels found during the osteogenic period of the in vivo system. MGP mRNA levels in both osteoblasts and chondrocytes in culture were significantly elevated by 1,25-(OH)2D3 (10(-8) M, 48 h) throughout the time course of cellular growth and differentiation. Interestingly, when MGP mRNA transcripts from vitamin D treated and untreated chondrocytes and osteoblasts were analyzed by high resolution Northern blot analysis, we observed two distinct species of MGP mRNA in the vitamin D treated chondrocyte cultures while all other cultures examined exhibited only a single MGP mRNA transcript. Primer extension analysis indicated a single transcription start site in both osteoblasts and chondrocytes with or without vitamin D treatment, suggesting that the lower molecular weight MGP message in vitamin D treated chondrocytes may be related to a modification in post-transcriptional processing. In conclusion, these results show that the selective accumulation of MGP in bone and cartilage tissues in vitro may be related to the development and/or maintenance of a collagenous matrix as reflected by increases in MGP mRNA during these periods.(ABSTRACT TRUNCATED AT 400 WORDS)

Normal bone particles are preferentially resorbed in the presence of osteocalcin-deficient bone particles in vivo

In an in vivo model of osteoclastic bone resorption, we previously showed that osteocalcin-deficient bone particles (BPs), derived from warfarin-treated rats, were resorbed 50% as well as normal BPs and that they recruited fewer osteoclastic cells with decreased tartrate-resistant acid phosphatase (TRAP) activity. In order to determine the specificity of the resorption response, we evaluated the fate of implanted mixtures of normal and osteocalcin-deficient BPs. Normal and warfarin-treated donor rats were prelabeled in vivo with oxytetracycline to permit identification of BPs from either source. Normal, osteocalcin-deficient, and 50:50 mixtures of BPs (either labeled or unlabeled) were implanted into normal rats and recovered 12 days later for enzymatic (TRAP) and nondecalcified histomorphometric analyses. The incorporated oxytetracycline had no significant effect on resorption of bone particles. The recovered osteocalcin-deficient BPs were surrounded by fewer osteoclastic cells, were resorbed less, and contained less extractable TRAP activity than normal BPs. In mixed BP implants with normal and osteocalcin-deficient BPs, each type of bone particle elicited the same tissue response as when implanted separately. Remarkably, the different particles evoked dissimilar osteoclastic responses and were resorbed to different extents, even when adjacent within the same implant. These data suggest that osteocalcin may act as a substrate signal for resorption and that osteocalcin in the normal BPs does not influence the cellular response to adjacent osteocalcin-deficient BPs.

Effect of glucocorticoids on bone Gla protein values--BGP as a good marker of osteoporosis

It is important to prevent corticosteroid(CS)-induced osteoporosis, particularly in children. One of the mechanisms is a direct inhibitory effect of CS on osteoblasts. Bone Gla protein (BGP) is produced in osteoblasts, and the serum level of BGP reflects the bone formation rate. The aim of this study is to examine the usefulness of BGP as a marker of CS-induced osteoporosis. In the present study, serum levels of 24 pediatric patients who were given prednisolone (PSL) for long periods were studied in relation to their growth rate. Serum BGP was also determined in 167 healthy children and 16 adults. In healthy children, BGP levels reached a peak at the age of 15 years in boys and 11 years in girls. In patients who were given more than 0.25 mg/kg/day PSL, serum BGP levels were significantly decreased and height growth was remarkably suppressed. In conclusion, the measurement of serum BGP is useful for early detection of CS-induced osteoporosis.

Establishment and characterization of two immortalized cell lines of the osteoblastic lineage

Osteoblastic cells were cloned by culturing rat calvariae cells in agarose in the presence of TGF-beta and EGF. Two bone cell lines were established by immortalizing such an osteoblastic clonal cell population by the introduction of the avian v-mycOK10 gene in the form of a mouse ecotropic retrovirus. Although originating from the same clonal cell population, the two lines exhibited somewhat differing properties. IRC10/30-myc1 expressed alkaline phosphatase (AP), showed PTH- and PGE2-induced cAMP production, synthesized mainly collagen type I and a minor fraction of type III, and produced mRNA for the bone-specific protein osteocalcin. IRC10/30-myc3 did not express AP, showed no PTH responsiveness, and synthesized only about one-third as much collagen as IRC10/30-myc1 (4 versus 12% of total protein synthesis). However, the cell line IRC10/30-myc3 was induced to synthesize cAMP by PGE2 and produced osteocalcin mRNA. When cultured in vivo in diffusion chambers, both lines proved to be osteogenic. Besides bone, both lines also formed cartilage and fibrous tissue. Thus, by immortalizing a clonal cell population of the osteoblastic phenotype, cell lines expressing varying properties can emerge. Furthermore, the expression of alkaline phosphatase and PTH-inducible adenylate cyclase are not prerequisites for a cell to form bone in vivo. Finally, cells expressing the phenotype of differentiated osteoblasts, including osteocalcin synthesis, still have a multipotential differentiation capacity and form bone and cartilage in vivo.

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.