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Biomedical subjects

G R Mundy

Publications and source records attributed to G R Mundy.

At least 163 records · Page 9Linked to original sources
PubMed1991

The effects of TGF-beta on bone.

The integrity of the skeleton is maintained by the continued cellular remodelling of bone that occurs throughout life and is characterized by an orderly sequence of events beginning with osteoclastic bone resorption followed by osteoblastic new bone formation to repair the localized defects made by osteoclasts. Bone resorption and formation are closely coupled by mechanisms which, until recently, have been poorly defined in both normal physiological and most pathological conditions, but are probably due to the generation during resorption of local 'coupling' factors. TGF-beta promises to be one of the key factors involved in coupling bone formation to previous bone resorption. This potent osteotropic polypeptide is abundant in the bone matrix, and is produced in response to factors that stimulate osteoclastic bone resorption. It is a very potent stimulator of osteoblastic bone formation, causing chemotaxis, proliferation and differentiation in committed osteoblasts. TGF-beta has complex effects on bone resorption: it inhibits osteoclast formation and osteoclast activity. TGF-beta is released from bone in a biologically inert state that is due to the presence of at least two proteins which appear to regulate TGF-beta activity. Release of active TGF-beta from these latent complexes occurs during bone resorption and is mediated by osteoclasts. Knowledge of the mechanisms responsible for these activation processes may be vital to understanding the role of TGF-beta in bone remodelling.

Animals↗
PubMed1990

Stimulation of tumor necrosis factor release from monocytic cells by the A375 human melanoma via granulocyte-macrophage colony-stimulating factor.

It has long been known that complex interactions occur between tumors and normal host immune cells. The human melanoma cell line A375 has been used previously as an indicator cell for tumor cell cytotoxicity mediated by monocytes. During other studies on this tumor cell line, we noted that the conditioned media harvested from A375 cultures induced both the human monocytoid cell line U937 and human blood monocytes to release the cytokine tumor necrosis factor (TNF). We characterized this tumor factor which induced TNF release by monocytic cells. Purification was performed using ammonium sulfate precipitation, ion exchange (DEAE) chromatography, gel filtration, and reversed-phase high performance liquid chromatography. The factor copurified with granulocyte-macrophage colony-stimulating factor (GM-CSF). The purified material caused the release of TNF by U937 cells and stimulated formation of granulocyte-macrophage colonies in methyl cellulose. TNF release by U937 cells in response to A375-conditioned medium was inhibited by neutralizing antibodies to GM-CSF. The TNF-inducing activity in A375-conditioned medium was completely removed by an anti-GM-CSF affinity column. Western blotting using antibodies to GM-CSF confirmed a single Mr27,000 band in A375-conditioned medium. We found that recombinant human GM-CSF stimulated TNF production by the same cells as the tumor-conditioned medium. These data show that A375 human melanoma cells produce GM-CSF, which in turn causes TNF production by cells in the monocyte lineage. The combination of GM-CSF production by the tumor and TNF production by immune cells may influence not only tumor growth but also some of the paraneoplastic syndromes associated with malignancy such as hypercalcemia, cachexia and leukocytosis.

Colony-Stimulating Factors↗
PubMed1990

Alteration of vitamin D metabolism in Mexican-Americans.

Studies were performed to investigate vitamin D metabolism in Mexican-Americans. Groups of 15 whites and 16 Mexican-Americans ranging in age from 18 to 41 years were evaluated. All of them were within 25% of their ideal body weight. Each of them was admitted to the Clinical Research Center of the University of Texas Health Science Center and placed on a daily diet estimated to contain 400 mg calcium and 900 mg phosphate. It was found that whereas serum vitamin D (1.8 +/- 0.5 versus 7.6 +/- 1.3 ng/ml, P less than 0.001) and serum 25-hydroxyvitamin D (9 +/- 1 versus 17 +/- 2 ng/ml, P less than 0.01) were significantly lower and serum 1,25-dihydroxyvitamin D (37 +/- 2 versus 28 +/- 2 pg/ml, P less than 0.001) was significantly higher in the Mexican-Americans than in the whites, serum calcium (9.1 +/- 0.1 versus 9.2 +/- 0.1 mg/dl), magnesium (1.84 +/- 0.07 versus 1.80 +/- 0.07 mEq/liter), and Gla protein (19 +/- 3 versus 21 +/- 2 ng/ml) were not different in the two groups. Urinary calcium (144 +/- 14 versus 124 +/- 16 mg/day), phosphate (672 +/- 51 versus 683 +/- 44 mg/day), sodium (110 +/- 8 versus 99 +/- 9 mEq/day), potassium (43 +/- 4 versus 49 +/- 3 mEq/day), and magnesium (7.3 +/- 0.7 versus 7.7 +/- 0.5 mEq/day) and creatinine clearance (173 +/- 14 versus 154 +/- 7 liters/day) were not different in the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1990

Characterization of the latent transforming growth factor beta complex in bone.

Transforming growth factor beta (TGF-beta) is a 25 kD multifunctional polypeptide with pronounced effects on the proliferation and differentiation of a variety of cells in vitro. TGF-beta is a potent regulator of the activity of cells with the osteoblast phenotype and of isolated osteoclasts. It is released in increased amounts by bone cultures stimulated to resorb. Organ cultures of neonatal mouse calvaria produce TGF-beta as an inert large-molecular-weight complex that must be dissociated to release biologically active TGF-beta (5-8 ng/ml). We have shown recently that stimulated isolated avian osteoclasts release active TGF-beta from this bone-derived biologically latent form. In this report we have characterized this bone latent form of TGF-beta. Only small amounts of active TGF-beta (less than 0.5 ng/ml) and no free binding protein are detectable in conditioned medium from bone cultures. Active TGF-beta can be detected in acid-treated calvarial conditioned media in which none or only minute amounts could previously be detected. Following incubation at 37 degrees C, this activated TGF-beta gradually loses activity. Cross-linking studies using 125I-labeled TGF-beta show that this loss of activity is due to TGF-beta binding to a protein of approximately 300 kD. The TGF-beta latent complex accumulates in a linear manner and is stable in the presence of serum and the protease trypsin. Increases in temperature and pH extremes dissociate the complex to release active TGF-beta. Decreases in pH result in an exponential increase in TGF-beta activity. Significant activation of the latent TGF-beta was detectable at pH values as high as 4 and 5. Since the osteoclastic microenvironment is acidic during bone resorption, these data suggest that this acidic microenvironment may regulate TGF-beta activity by releasing active TGF-beta from its latent complex.

Animals↗
PubMed1990

Prostaglandin E2 inhibits formation of osteoclastlike cells in long-term human marrow cultures but is not a mediator of the inhibitory effects of transforming growth factor beta.

Prostaglandins are important local regulators of bone cell function and have been shown to have multiple effects on osteoclasts. Using a human bone marrow culture system in which multinucleated cells with osteoclast characteristics form, we have recently shown that TGF-beta is a potent inhibitor of osteoclastlike cell formation and appears to act at several stages of their development. Because it has been suggested that the effects of TGF-beta are mediated via a prostaglandin-dependent mechanism, we determined the effects of prostaglandin E2 (PGE2) on total and osteoclastlike cell formation (detected by reactivity with the 23c6 monoclonal antibody, which identifies osteoclasts) in human marrow cultures and tested whether prostaglandin synthesis was responsible for the inhibitory effects of TGF-beta on multinucleated cell formation. These studies show that PGE2 is a potent inhibitor of both 23c6-positive and negative multinucleate cell formation in human marrow cultures and that the effects of TGF-beta on multinucleated cell formation are not mediated by PGE2.

Bone Marrow Cells↗
PubMed1990

Chemotactic response of osteoblastlike cells to transforming growth factor beta.

Transforming growth factor beta (TGF-beta) has multiple effects on bone cell metabolism in vitro but its exact role in bone remodeling still needs to be defined. Here we demonstrate that TGF-beta is chemotactic for osteoblastlike cells from fetal rat calvariae and osteoblastlike ROS 17/2.8 osteosarcoma cells. Maximal chemotaxis occurred at 5-15 pg/ml of TGF-beta and was observed with TGF-beta 1 and TGF-beta 2 at equivalent concentrations. Conditioned medium from osteoblastlike cells containing latent TGF-beta failed to stimulate chemotactic migration. However, chemotactic activity was observed in conditioned medium that had been transiently acidified. Since acidification is known to activate TGF-beta, these results suggest that only active TGF-beta is capable of inducing a chemotactic response. Preincubation of osteoblastlike cells with TGF-beta in concentrations from 10 pg/ml to 1 ng/ml for 48 h abolished a subsequent chemotactic response of these cells to TGF-beta, indicating that TGF-beta-induced chemotaxis is a transient phenomenon. Since TGF-beta may be released from the bone matrix and/or activated during bone resorption, the chemotactic activity of TGF-beta for osteoblastlike cells may be important for the recruitment of osteoblastlike cells to sites of bone remodeling.

Animals↗
PubMed1990

In vivo effects of human recombinant transforming growth factor beta on bone turnover in normal mice.

Reports of the effects of TGF-beta on bone cells are conflicting and controversial. Different cell culture and organ culture models for both osteoblasts and osteoclasts have given different responses. In some the effects are dependent on prostaglandin synthesis, and in others they are prostaglandin independent. To determine the effects of TGF-beta on osteoblasts and osteoclasts in vivo and the role of prostaglandins in mediating these effects, we injected 2.5-5 micrograms TGF-beta into the subcutaneous tissue overlying the calvariae of normal mice for 2-5 days anc compared the morphologic responses in underlying calvarial bone with those in mice injected caused a marked increase in periosteal thickness (fivefold) and cellularity, morphologic changes in osteoblasts, and new mineralized bone formation. These effects were localized to the site of injection and were partially inhibited by concomitant indomethacin treatment. There was a parallel increase in osteoclast numbers in adjacent marrow spaces, and the osteoclasts formed were unusually large. In contrast, no increase in the numbers of osteoclasts was seen in indomethacin-treat animals. These data show that TGF-beta has powerful effects on local bone cell function in vivo and that these effects may be mediated, in part, by prostaglandin generation.

Animals↗
PubMed1990

Transforming growth factor beta enhances parathyroid hormone stimulation of adenylate cyclase in clonal osteoblast-like cells.

The effects of transforming growth factor beta (TGF beta) on parathyroid hormone (PTH)-responsive adenylate cyclase were examined in clonal rat osteosarcoma cells (UMR-106) with the osteoblast phenotype. Purified TGF beta incubated with UMR-106 cells for 48 hr produced a concentration-dependent increase in PTH stimulation of adenylate cyclase, with maximal increase in PTH response (37%) occurring at 1 ng/ml TGF beta. TGF beta also enhanced receptor-mediated activation of adenylate cyclase by isoproterenol and prostaglandin E2 (PGE2) and nonreceptor-mediated enzyme activation by cholera toxin and forskolin. In cells in which PTH-stimulated adenylate cyclase activity was augmented by treatment with pertussis toxin, the incremental increase in PTH response produced by TGF beta was reduced by 33%. However, TGF beta neither mimicked nor altered the ability of pertussis toxin to catalyze the ADP-ribosylation of a 41,000-Da protein, presumably the alpha subunit of the inhibitory guanine nucleotide-binding regulatory component (Gi) of adenylate cyclase, in cholate-extracted UMR-106 cell membranes. TGF beta also had no effect on the levels of alpha or beta subunits of Gi, as assessed by immunotransfer blotting. In time course studies, brief (less than or equal to 30 min) exposure of cells to TGF beta during early culture was sufficient to increase PTH response but only after exposed cells were subsequently allowed to grow for prolonged periods. TGF beta enhancement of PTH and isoproterenol responses was blocked by prior treatment of cells with cycloheximide but not indomethacin. The results suggest that TGF beta enhances PTH response in osteoblast-like cells by action(s) exerted at nonreceptor components of adenylate cyclase. The effect of TGF beta may involve Gi, although in a manner unrelated to either pertussis toxin-catalyzed ADP-ribosylation of the alpha subunit of Gi or changes in levels of Gi subunits. The regulatory action of TGF beta on adenylate cyclase is likely to be mediated by the rapid generation of cellular signals excluding prostaglandins, followed by a prolonged sequence of events involving protein synthesis. These observations suggest a mechanism by which TGF beta may regulate osteoblast responses to systemic hormones.

Adenylyl Cyclases↗
PubMed1990

Incidence and pathophysiology of hypercalcemia.

Hypercalcemia occurs for various reasons in patients with malignant diseases. Most of these patients show a relative increase in bone resorption over bone formation. Increased renal tubular calcium reabsorption is also important for maintaining hypercalcemia in the majority of patients. Calcium absorption from the gut is usually decreased. In a few patients, fixed impairment of glomerular filtration contributes to hypercalcemia. Because the pathophysiology of hypercalcemia is heterogeneous, it may be considered as three separate syndromes: the humoral hypercalcemia of malignancy caused by systemic mediators; the hypercalcemia associated with localized osteolytic disease; and the hypercalcemia associated with myeloma and related hematologic malignancies. Increased bone resorption is a key feature in each of these syndromes. In malignant disease, bone resorption is enhanced because osteoclast activity is increased by the production of humoral mediators. These mediators are often produced by the tumor cells but are also produced by normal host cells that have been activated by the presence of the tumor. some of these mediators of hypercalcemia are systemic factors, but some act only locally. They include parathyroid hormone-related protein, transforming growth factor alpha, lymphotoxin, tumor necrosis factor, interleukin-1 alpha and 1,25-dihydroxyvitamin D.

Animals↗
PubMed1990

Induction of bone resorbing activity by normal and rheumatoid arthritis T cells.

We studied the role of T cells in the production of osteoclast activating factor (OAF) using anti-CD3 MAb as a specific T cell activator. OAF activity was totally inhibited by anti-IL-1 beta. Peripheral blood mononuclear cells (PBMNC) from normal subjects produced more OAF than did PBMNC from rheumatoid arthritis (RA) patients. Mononuclear cells (MNC) from RA synovial fluid produced less OAF than did RA peripheral blood. We conclude that (i) specific T cell stimulation induces OAF production which may be attributed to interleukin 1 (IL-1) activity, (ii) the inhibition by anti-IL-1 beta of OAF production following anti-CD3 stimulation suggests that the T cell signal is being transmitted to the macrophage, and (iii) RA MNC are deficient in T cell-mediated OAF production.

Antigens, Differentiation, T-Lymphocyte↗
PubMed1990

Osteoinductive factor inhibits formation of human osteoclast-like cells.

Osteoinductive factor (OIF) is a glycoprotein in bone that induces ectopic bone formation. Implantation of OIF plus transforming growth factor beta (TGF-beta) type 1 or 2 into subcutaneous tissues of rats induces formation of bone at the implantation site. Since TGF-beta is also present in bone matrix and inhibits formation of multinucleated cells that express an osteoclast phenotype in long-term human marrow cultures, we tested the effects of OIF on formation of these osteoclast-like cells to determine the effects of OIF on cells in the osteoclast lineage. We found that OIF inhibited total multinucleated cell (MNC) formation in a dose-dependent fashion and preferentially inhibited formation of MNCs that react with monoclonal antibody 23c6 (23c6-positive MNCs), an antibody that identifies osteoclasts. In addition, low concentrations of OIF in combination with low concentrations of TGF-beta acted synergistically to inhibit 23c6-positive MNC formation. The inhibition of 23c6-positive MNC formation by OIF was not mediated by prostaglandin synthesis. These data suggest that regulatory growth factors, such as OIF or TGF-beta, that are stored within the bone matrix and released when bone is resorbed can serve as natural inhibitors of osteoclast activity by inhibiting osteoclast formation.

Alprostadil↗
PubMed1990

Oxygen-derived free radicals stimulate osteoclastic bone resorption in rodent bone in vitro and in vivo.

The mechanisms by which bone resorbing osteoclasts form and are activated by hormones are poorly understood. We show here that the generation of oxygen-derived free radicals in cultured bone is associated with the formation of new osteoclasts and enhanced bone resorption, identical to the effects seen when bones are treated with hormones such as parathyroid hormone (PTH) and interleukin 1 (IL-1). When free oxygen radicals were generated adjacent to bone surfaces in vivo, osteoclasts were also formed. PTH and IL-1-stimulated bone resorption was inhibited by both natural and recombinant superoxide dismutase, an enzyme that depletes tissues of superoxide anions. We used the marker nitroblue tetrazolium (NBT) to identify the cells that were responsible for free radical production in resorbing bones. NBT staining was detected only in osteoclasts in cultures of resorbing bones. NBT staining in osteoclasts was decreased in bones coincubated with calcitonin, an inhibitor of bone resorption. We also found that isolated avian osteoclasts stained positively for NBT. NBT staining in isolated osteoclasts was increased when the cells were incubated with bone particles, to which they attach. We confirmed the formation of superoxide anion in isolated avian osteoclasts using ferricytochrome c reduction as a method of detection. The reduction of ferricytochrome c in isolated osteoclasts was inhibited by superoxide dismutase. Our results suggest that oxygen-derived free radicals, and particularly the superoxide anion, are intermediaries in the formation and activation of osteoclasts.

Animals↗
PubMed1990

Atypical multinucleated cells form in long-term marrow cultures from patients with Paget's disease.

Although Paget's disease is the most flagrant example of a primary osteoclast disorder, little is known of osteoclast biology in this disease. In this report we have studied the formation of cells with the osteoclast phenotype in long-term cultures of marrow mononuclear cells derived from patients with Paget's disease, and compared these with similar cells formed in long-term marrow cultures from normal individuals, and with osteoclasts present in pagetic bone. Osteoclasts formed in pagetic marrow cultures resembled osteoclasts present in pagetic bone, but were distinctly different from osteoclasts formed in normal marrow cultures. Osteoclast formation was 10-20-fold greater in pagetic marrow cultures than in normal cultures. The multinucleated cells formed in cultures of pagetic marrow were much larger in size, were hyperresponsive to 1,25(OH)2 vitamin D, had more nuclei per cell, had increased levels of tartrate-resistant acid phosphatase activity and had ultrastructural features which were not seen in multinucleated cells formed from normal marrow mononuclear cells. These pagetic marrow-derived multinucleated cells formed large resorption lacunae on calcified matrices and cross-reacted with monoclonal antibodies which preferentially bind to osteoclasts. The multinucleated cells formed from marrow obtained from uninvolved sites in Paget's patients also displayed these abnormal features.

Bone Marrow↗
PubMed1990

A noncyclical analog of salmon calcitonin (N alpha-propionyl Di-Ala1,7,des-Leu19 sCT) retains full potency without inducing anorexia in rats.

A new analog of salmon calcitonin (N alpha-propionyl Di-Ala1,7,des-Leu19 sCT; RG-12851; here termed CTR), which lacks the ring structure of native calcitonin, was tested for biological activity in several in vitro and in vivo assay systems. The analog (CTR) and salmon calcitonin (sCT) stimulated kidney cell adenylate cyclase activity and inhibited bone resorption in organ cultures of fetal rat long bones with similar potencies and efficacies. Furthermore, CTR and sCT, at similar doses, induced comparable hypocalcemic responses in mice following sc injection or infusions. However, unlike sCT, CTR did not induce anorexia and weight loss in rats following sc injection. These data suggest that the ring structure of sCT may be important for the anorexigenic effect but is not required for effect on bone resorption or calcium homeostasis. Clinical studies appear warranted as, potentially, CTR might induce fewer side effects than does sCT.

Adenylyl Cyclases↗