PubMed Health⌕ Search

Biomedical subjects

V Shen

Publications and source records attributed to V Shen.

At least 73 records · Page 4Linked to original sources
PubMed1991

Response of the parathyroid gland to infusion of human parathyroid hormone-(1-34) [PTH-(1-34)]: demonstration of suppression of endogenous secretion using immunoradiometric intact PTH-(1-84) assay.

Alterations in the sensitivity of the parathyroid gland to both stimulative and suppressive stimuli may be partially responsible for skeletal changes that occur with age, estrogen deficiency, osteoporosis, and estrogen treatment of osteoporosis. We sought to define the changes in intact PTH-(1-84) secretion in normal premenopausal and postmenopausal, osteoporotic and estrogen-treated osteoporotic women during the infusion of human (h) PTH-(1-34). hPTH-(1-34) was infused at 0.55 U/kg.h for 24 h, with serum sampling every 4 h. Serum was analyzed for calcium (ionized and total), hPTH-(1-34), and PTH-(1-84). Basal chemistries were no different among groups, except for serum phosphorus, which was highest in osteoporotic women (1.31 vs. 1.07 mmol/L in premenopausal; P less than 0.02), and hPTH-(1-34), which was slightly higher in normal postmenopausal women (19.31 vs. 13.24 ng/L in estrogen treated; P less than 0.02). No differences in PTH-(1-84) were found among groups. hPTH-(1-34) rose similarly in all patient groups, while the calcemic response was somewhat more sluggish in estrogen-treated women, although statistically significant differences were not found. PTH-(1-84) declined rapidly in all patient groups, although estrogen-treated women had a smaller maximal decrease in PTH-(1-84), and the slope of the decremental change in PTH-(1-84) was lower in estrogen-treated women than in osteoporotic or normal postmenopausal women. Untreated osteoporotic women had less suppression of PTH-(1-84) than normal postmenopausal women at every calcium level. Estrogen treatment decreases the calcemic effects of infused hPTH-(1-34) and at the same time reduces calcium-induced suppression of parathyroid secretion. It is possible that such changes in the set-point of the gland contribute to the alterations in bone turnover that result in osteoporosis and the mechanisms by which estrogen prevents bone loss.

Calcium↗
PubMed1990

Absence of isochromosome 12p in a pineal region malignant germ cell tumor.

We report the first cytogenetic investigation of a rare pineal region mixed germ cell tumor. The mean modal number was 78. Multiple numerical and structural abnormalities were noted. Chromosomes 21 and 1q were consistently overrepresented, and chromosome 13 was underrepresented. A translocation involving chromosome 11 occurred in all metaphases examined. The Y chromosome was lost, and three copies of the X chromosome were present. No isochromosome 12p was identified, but four copies of chromosome 12 were present.

Adolescent↗
PubMed1990

Characterization and hormonal modulation of IL-1 binding in neonatal mouse osteoblastlike cells.

Considerable evidence indicates that interleukin-1 (IL-1) is a potent regulator of bone cell activity. Consequently, we studied its binding to neonatal mouse osteoblastlike cells. Purified, labeled recombinant IL-1 alpha bound specifically to neonatal mouse osteoblastlike cells with a dissociation constant of 30-200 pM at 22 degrees C. There were 3000-15,000 receptors per cell. IL-1 bound to cell surfaces at 4 degrees C was rapidly internalized when the temperature was raised to 37 degrees C. Receptor specificity was confirmed by demonstrating that, among a series of 11 polypeptides, only IL-1 inhibited 125I-IL-1 binding. Treatment of surface-bound 125I-IL-1 alpha with a bivalent water-soluble cross-linker identified a membrane peptide of Mr 70,000 cross-linked to IL-1. The apparent IL-1 receptor was solubilized from a plasma membrane-enriched fraction using 3-[(3-cholamidopropyldimethylammonio]-1-propanesulfonate (CHAP). The resulting material exhibited specific IL-1 binding. Preincubation of cells with IL-1, retinoic acid, transforming growth factor beta (TGF-beta), or phorbol ester caused a reduction in apparent receptor numbers per cell, while preincubation with epidermal growth factor (EGF), dexamethasone, or parathyroid hormone (PTH) increased receptor numbers per cell. Preincubation with insulin, vitamin D, prostaglandin E2 (PGE2), interferon-gamma (IFN-gamma), and 17 beta-estradiol had no effect. These results suggest that specific, high-affinity IL-1 receptors are present on osteoblastlike cells and that the receptor number can be modified by various osteotropic agents. Regulation of bone cell IL-1 receptors may contribute to the control of bone remodeling.

Animals↗
PubMed1990

Cyclic AMP-dependent and calcium-dependent signals in parathyroid hormone function.

Previous work demonstrated that parathyroid hormone (PTH) activates the Ca2+/protein kinase C (PKC) system in addition to cAMP production. Therefore, the authors explored the role of cAMP-dependent and Ca2(+)-dependent signals in the regulation of osteoblastic growth and bone resorption. In exponentially growing UMR 106-01 osteogenic sarcoma cells, PTH (10(-7) M) inhibited [3H] thymidine incorporation by 80%. This effect was reproduced by maximal doses of both dibutyryl-cAMP (dbcAMP) and forskolin. The Ca2+ ionophore ionomycin (10(-7) M) had no effect, whereas phorbol 12-myristate 13-acetate (PMA) was slightly mitogenic. The antimitogenic action of dbcAMP was dose-dependent, with ED0.5 at about 3 X 10(-5) M. Ionomycin enhanced this dbcAMP effect at submaximal doses of the cAMP analog. PMA used in combination with both dbcAMP and ionomycin induced further depression of cell proliferation, indicating synergism with cAMP. Both dbcAMP (10(-4) M) and ionomycin (10(-7) M) stimulated 45Ca release from fetal rat limb bones after five days in culture, although the Ca2+ ionophore was less potent. 1-Oleoyl 2-acetyl-glycerol (2 X 10(-6) M) was ineffective alone, and slightly inhibited the 45Ca release produced by the other second messenger analogs in all combinations. The combination of dbcAMP and ionomycin showed a synergistic effect, and fully reproduced PTH effect. In conclusion, PTH signal transduction for control of cell proliferation and bone resorption is mediated mainly by cAMP. Activation of the Ca2+/PKC message system is nevertheless necessary to express a full hormonal response in both cell and organ culture systems.

Animals↗
PubMed1989

An acidic fibroblast growth factor stimulates DNA synthesis, inhibits collagen and alkaline phosphatase synthesis and induces resorption in bone.

We have examined the effects of an acidic fibroblast growth factor (aFGF) on bone cell growth and differentiation and on osteoclastic resorption using rat fetus organ cultured calvariae and long bones, respectively. Low concentrations of this aFGF stimulated DNA synthesis (1.28 ng/ml) and inhibited collagen formation (1.28 ng/ml) and alkaline phosphatase activity (0.64 ng/ml) in the isolated calvariae. The inhibition of collagen synthesis was independent of the aFGF's mitogenic effect, and was evident in periosteum-containing and periosteum-free bones, pointing to osteoblasts as the aFGF-responsive cells. Our preparation of aFGF enhanced resorption in the long bones by a calcitonin-inhibitable mechanism. PGE2 release accompanied and indomethacin prevented the enhancement of resorption. By contrast, indomethacin did not block the stimulation of DNA and collagen synthesis caused by our aFGF. These results indicate that our aFGF exerts a PGE2-independent effect on DNA synthesis and collagen synthesis and a PGE2-dependent effect on resorption in bone tissue in vitro.

Alkaline Phosphatase↗
PubMed1989

Monokines produced by macrophages stimulate the growth of osteoblasts.

We have previously reported that the J774A.1 macrophage-like tumor cell line produces two potent monokines which stimulate the growth of osteoblasts and chondrocytes. These growth factors, which have an affinity for heparin-agarose, have been termed HEP I (a 30 Kd PDGF-like molecule) and HEP II (an approximately 20 Kd molecule), respectively, based on their elution profile. Unlike HEP I, HEP II does not stimulate the growth of fibroblasts. Extensive biological and chromatographic studies disclosed that HEP II appears to be a unique bone cell mitogen unlike any known growth factor, including the FGFs, IL-1s, and TNFs, EGF, IGF-I and -II, TGF-beta, beta 2 microglobulin, G-CSF, CSF-1 and GM-CSF. To characterize more fully the effects of the macrophage-derived monokines on osteoblast growth and function, clones were derived from calvaria explant cultures. Two clones, SDFRC-2.05 and SDFRC-3, were developed and found to exhibit osteoblastic characteristics, including high levels of alkaline phosphatase, synthesis of type I but not type III collagen, and an increased intracellular cAMP production in response to PTH. The SDFRC-3 cells exhibited a polygonal morphology like that of the explant-derived cells while SDFRC-2.05 cells exhibited a more fibroblastic morphology. When tested on the explant cultures and clones, HEP I and HEP II were found to stimulate DNA synthesis and increase protein per culture, but decreased alkaline phosphatase activity. Clone SDFRC-3 was found to be more responsive to HEP II than clone SDFRC-2.05. Both monokines were found to be more potent mitogens for bone cells than TGF-beta. HEP II, but not HEP I or TGF-beta, induced a transformation of bone cells from a polygonal to a fibroblastic morphology, suggesting the induction of migration prior to proliferation. Thus, macrophages may be responsible not only for bone repair but also for ensuring the linkage of bone formation to resorption during physiological remodeling.

Animals↗
PubMed1988

Bone-resorbing agents promote and interferon-gamma inhibits bone cell collagenase production.

Parathyroid hormone, prostaglandin E2, 1 alpha,25-dihydroxyvitamin D3, interleukin-1, tumor necrosis factor alpha, and epidermal growth factor, all known stimulators of bone resorption, markedly enhanced collagenase secretion by rat fetus osteoblastlike cells in primary culture as judged by enzyme-linked immunosorbent assay. Untreated cells contained no immunostainable or extractable collagenase. Collagenase was detected in the treated cells and media only after 1-3 h of treatment, and there was no increment in collagenase activity when cells were treated in the presence of actinomycin D or cycloheximide. Cells secreted collagenase in a latent form and also elaborated collagenase inhibitor; chromatographic separation of collagenase from collagenase inhibitor and subsequent activation of the collagenase with trypsin yielded the active species in stimulated but not in unstimulated cells. The ability of individual prostanoids, among seven tested, to promote collagenase production correlated positively with their reported capacity to promote bone resorption. Interferon-gamma (IFN-gamma), a known resorption inhibitor, blocked the increment in collagenase production caused by all agents tested. These results indicate a close linkage between stimulation of bone resorption and collagenase production by osteoblastlike cells. Various resorption stimulators, including some not previously tested for effects on collagenase, augment the de novo synthesis and secretion of collagenase and act by an IFN-gamma-inhibitable mechanism.

Animals↗
PubMed1988

Characterization of a (Ca2+ + Mg2+)-ATPase system in the osteoblast plasma membrane.

A high affinity, calmodulin-sensitive (Ca2 + Mg2+)-ATPase was demonstrated in the plasma membrane preparation of three different osteosarcoma cell lines previously demonstrated to respond to parathyroid hormone with an increase in cytosolic calcium and a decrease in pH. The maximal velocity of the enzyme activity in the membrane preparations ranged from 0.83 to 2.42 nmol Pi released per min per mg protein with half-saturation constants of 26 nM of free Ca. The enzyme activity was not affected by Na+, K+, ouabain and azide, and exhibited an absolute requirement for Mg2+ ions. These results suggest a possible role for a membrane Ca2 + Mg2+-ATPase in initiating and perpetuating the ionic control of osteoblastic function.

Animals↗
PubMed1987

J774A.1 macrophage cell line produces PDGF-like and non-PDGF-like growth factors for bone cells.

In light of evidence that macrophages participate in the local regulation of bone remodeling, we have examined the production of peptide stimulators of bone cell growth and specialization by the J774A.1 macrophage cell line. Cultured J774A.1 cells secrete growth-promoting activities which have an affinity for heparin. The first partially purified material, termed HEP I, appears to contain platelet-derived growth factor (PDGF)-like activity. It has a molecular weight of about 30,000 daltons, inhibits the binding of labeled PDGF to its receptors, reacts with polyclonal anti-human PDGF antibody, and exhibits mitogenic activity for osteoblasts, which is partially blocked by anti-PDGF antisera. Like PDGF, HEP I is active in a wide variety of mesenchyme-derived cells, including osteoblasts, chondrocytes, smooth muscle cells, fibroblasts, 3T3 cells and NRK cells. The J774A.1 cells contain mRNA, which hybridizes to a v-sis DNA probe, suggesting that they express the c-sis gene, which contains the code for a PDGF-like protein. The second factor, HEP II, has an approximate molecular weight of 20,000 daltons and possesses substantial mitogenic activity for osteoblasts, chondrocytes, and smooth muscle cells, but is not mitogenic for fibroblasts, 3T3 cells, and NRK cells. HEP II appears to be a unique bone cell mitogen, which is distinct from the growth factors presently known. Neither HEP I nor HEP II contained interleukin 1, a macrophage product known to promote bone resorption and perhaps the growth and activity of osteoblasts.

Animals↗
PubMed1986

Prostaglandins change cell shape and increase intercellular gap junctions in osteoblasts cultured from rat fetal calvaria.

Mounting experimental evidence indicates that osteoblasts may be cellular intermediaries in the local activation of bone remodeling. To elucidate the role of these cells in activation, we examined the effects of prostaglandins (PGs), known resorption stimulators, on cell shape and intercellular junctional relationships in osteoblasts cultured from rat fetal calvaria. Exposure to PGE2 and PGE1, promoters of bone resorption, rapidly (within 20 min) converted the osteoblasts from a flattened to a stellate shape (shape change), and markedly increased the appearance of intercellular (gap) junctions within 10 min. Both effects were directly related to the prostaglandin concentration, as little as 1 nM being effective. PGE1, but not PGB1, PGF1 alpha, PGD2, and PGF2 alpha, mimicked the substantial effect of PGE2 on shape change. Shape change and gap junction formation appear to arise independently. PTH, an inducer of shape change, did not affect the number of gap junctions appreciably. Colchicine, a microtubule polymerization inhibitor, and trifluoperazine, an inhibitor of calmodulin action, blunted PGE2-mediated shape change but not the effect of PGE2 on gap junctions. Shape change and gap junction formation may be important events in local activation, shape changes in surface osteoblasts serving to expose bone surfaces which are chemotactic for osteoclasts and gap junctions propagating locally initiated activation messages.

Animals↗
PubMed1985

(Ca2+ + Mg2+)-ATPase activity in plasma membrane of circulating mononuclear cells. Lack of a direct effect of vitamin D.

The in vivo effect of vitamin D on (Ca2+ + Mg2+)-ATPase activity was examined in a plasma membrane fraction of rat circulating mononuclear cells (MPM). Although there was no significant difference in the ATPase activities in red blood cell ghosts, (Ca2+ + Mg2+)-ATPase activity in MPM was significantly higher (p less than 0.05) in long-term vitamin D3-replete rats (100 IU/day for 6 months) than that in vitamin D-deplete rats (for 6 months). In rats maintained on vitamin D-deficient diets for 5-7 weeks, in vivo administration of either vitamin D3, 2,000 IU orally, 5 days prior to killing or 1,25-dihydroxyvitamin D3, 2.4 nmol, intraperitoneally, 24 h prior to killing failed to show any significant effect on (Ca2+ + Mg2+)-ATPase activity in MPM. (Ca2+ + Mg2+)-ATPase activity in MPM from rats maintained on vitamin D-deficient diet with high calcium content (1.8%) was significantly higher (p less than 0.05) than that from rats maintained on vitamin D-deficient diet with low calcium content (0.3%). Moreover, in vitro addition of vitamin D3 metabolites did not show any effect on (Ca2+ + Mg2+)-ATPase activity in MPM. These data suggest that decreased (Ca2+ + Mg2+)-ATPase activity in MPM from long-term vitamin D-deplete rats resulted from an adaptation to low extracellular calcium rather than vitamin D depletion.

Animals↗
PubMed1985

Fetal rat chondrocytes sequentially elaborate separate growth- and differentiation-promoting peptides during their development in vitro.

Chondrocytes isolated from the calvaria of rat fetuses proliferate and form cartilage when cultured in a chemically defined, serum-free medium, suggesting that they may elaborate self-regulatory factors. Conditioned media obtained from these chondrocytes stimulated DNA synthesis and proliferation when added to separate cultures of chondrocytes and the closely related osteoblast-like cells, but were not very effective in skin fibroblasts isolated from the same fetuses, as judged by [3H]thymidine incorporation and cell proliferation. Chondrocyte-conditioned medium also promoted chondrocyte differentiation, augmenting 35SO4 incorporation, and the accumulation of type II collagen and cartilage-specific proteoglycan. Stimulation of growth and differentiation appears to be attributable to separate activities, released into the medium sequentially by the cultured chondrocytes during their proliferation and maturation phases. Media obtained from growing chondrocytes stimulated growth, but had little effect on 35SO4 incorporation. Media obtained from mature cultures promoted growth as well as 35SO4 incorporation. The mitogenic and sulfation activities were trypsin inhibitable, but exhibited different solubility characteristics and striking differences in their patterns of elution from gel filtration columns. These results suggest that chondrocytes elaborate autostimulatory peptides, the biological activities of which mirror, at least in part, the developmental stage of the donor cells.

Animals↗
PubMed1985

Macrophages release a peptide stimulator of osteoblast growth.

Cells of the monocyte-macrophage series play multiple roles in bone resorption; they appear to act as osteoclast precursors and are known to elaborate several substances which promote osteoclast activity. Because bone formation is closely linked (coupled) to resorption under physiological conditions, we explored the possibility that macrophages also elaborate a stimulator of bone formation. Our results indicate that rat resident peritoneal and bone marrow macrophages elaborate a potent stimulator of DNA synthesis and growth in osteoblasts (as well as chondrocytes) cultured from the calvaria of rat fetuses. Growth factor activity resides mainly in a 43 000-dalton heat-stable protein, though a lower molecular weight peptide (Mr approximately 10 000) also contained growth-promoting activity. In contrast to osteoblasts and chondrocytes, skin fibroblasts prepared from the same rat fetuses exhibited only a minimal response to the macrophage-derived factor, though they responded briskly to epidermal and fibroblast growth factors. These findings are consistent with the thesis that macrophages direct both phases of remodeling, resorption and formation, and therefore may be responsible for coupling these events.

Animals↗
PubMed1984

Adriamycin inhibits PTH-mediated but not PGE2-mediated stimulation of cyclic AMP formation in isolated bone cells.

We have examined the effect of adriamycin, an anthracycline antibiotic which modifies plasma membrane functions, on the cyclic AMP response to PTH and PGE2 in isolated osteoblastlike cells. Adriamycin blunted the increment in bone cell cyclic AMP caused by exposure to PTH. This effect appeared rapidly (within 3 min after bone cells were exposed to adriamycin) and disappeared soon after exposure of adriamycin-treated cells to adriamycin-free incubation medium. Inhibition was evident over the entire time course of PTH action, at low as well as high PTH concentrations, and was one-half maximal at 31 microM adriamycin. It could not be attributed to alterations in cyclic AMP exodus, degradation or interference with the cyclic AMP assay, nor to impaired cell viability. Adriamycin also reduced the stimulatory effect of PTH on adenylate cyclase activity in a crude plasma membrane preparation. By contrast, adriamycin failed to modify the effects of PGE2 on cyclic AMP generation in intact bone cells, and on adenylate cyclase activity in broken cells. Moreover, concentrations of adriamycin that blunted the effect of PTH on adenylate cyclase activity did not inhibit the stimulatory effects of sodium fluoride or of GppNHp. These results suggest that adriamycin selectively alters the interaction between PTH and its receptor or impairs the transmission of information from hormone-receptor complex to adenylate cyclase (or both), perhaps by binding to specific lipid domains in the plasma membrane. Structural analogues of adriamycin, which vary in their lipophilic properties, also varied in their capacity to perturb the cyclic AMP response.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenylyl Cyclases↗
PubMed1984

Macrophage-derived growth factor for osteoblast-like cells and chondrocytes.

Rat resident peritoneal macrophages in primary culture were found to elaborate a mitogenic factor (or factors) for rat osteoblast-like cells and chondrocytes but not for skin fibroblasts. Growth-promoting activity appeared in the incubation medium within the first 20 hr of macrophage culture and was released in amounts that paralleled the number of macrophages per culture. After their proliferative response, as judged by increases in DNA synthesis and cell number, the osteoblast-like cells became enriched in alkaline phosphatase, an index of osteoblast specialization. The macrophage-derived activity was nondialyzable and heat-stable, and it was eliminated by exposure to trypsin. Inhibition of prostaglandin cyclooxygenase failed to modify its generation. Partial purification (Amicon filter concentration, gel filtration) disclosed principal peaks of activity corresponding to Mr of 43,000 and 10,000. The crude conditioned medium and the Mr 43,000-peak, but not the low-molecular-weight peak, exhibited interleukin 1 activity, as judged by the ability to stimulate the proliferation of mouse thymic lymphocytes. The macrophage-derived growth factor described herein may participate in bone remodeling and repair and in primary bone and cartilage growth.

Animals↗
PubMed1983

A high affinity, calmodulin-responsive (Ca2+ + Mg2+)-ATPase in isolated bone cells.

Although acute alterations in Ca2+ fluxes may mediate the skeletal responses to certain humoral agents, the processes subserving those fluxes are not well understood. We have sought evidence for Ca2+-dependent ATPase activity in isolated osteoblast-like cells maintained in primary culture. Two Ca2+-dependent ATPase components were found in a plasma membrane fraction: a high affinity component (half-saturation constant for Ca2+ of 280 nM, Vmax of 13.5 nmol/mg per min) and a low affinity component, which was in reality a divalent cation ATPase, since Mg2+ could replace Ca2+ without loss of activity. The high affinity component exhibited a pH optimum of 7.2 and required Mg2+ for full activity. It was unaffected by potassium or sodium chloride, ouabain or sodium azide, but was inhibited by lanthanum and by the calmodulin antagonist trifluoperazine. This component was prevalent in a subcellular fraction which was also enriched in 5'-nucleotidase and adenylate cyclase activities, suggesting the plasma membrane as its principal location. Osteosarcoma cells, known to resemble osteoblasts in their biological characteristics and responses to bone-seeking hormones, contained similar ATPase activities. Inclusion of purified calmodulin in the assay system caused small non-reproducible increases in the Ca2+-dependent ATPase activity of EGTA-washed membranes. Marked, consistent calmodulin stimulation was demonstrated in membranes exposed previously to trifluoperazine and then washed in trifluoperazine-free buffer. These results indicate the presence of a high affinity, calmodulin-sensitive Ca2+-dependent ATPase in osteoblast-like bone cells. As one determinant of Ca2+ fluxes in bone cells, this enzyme may participate in the hormonal regulation of bone cell function.

Animals↗