Biomedical subjects

D Heymann

Publications and source records attributed to D Heymann.

At least 37 records · Page 2Linked to original sources

PubMed1999

Cellular mechanisms of calcium phosphate ceramic degradation.

Calcium phosphate (CaP) ceramics are widely used for bone substitution in orthopedic, maxillofacial and dental surgery. Many environmental factors are involved in the gradual degradation of calcium phosphate ceramic after implantation, including physiocochemical processes (dissolution-precipitation) and the effects of various cell types. Several of these cell types degrade ceramics by phagocytotic mechanisms (fibroblasts, osteoblasts, monocytes/macrophages) or by an acidic mechanism with a proton pump to reduce the pH of the microenvironment and resorb these synthetic substrates (osteoclasts). Various mesenchymal cells located at the implantation sites can induce the solubilization of CaP ceramics. Crystal-cell contacts were required to induce such crystal dissolution. Mesenchymal cells such as fibroblastic cells are also actively involved in the ceramic degradation process. In this context, CaP crystals underwent dissolution into the phagosome. If osteoclasts resorb CaP ceramics similarly to the natural bone, they possess a phagocytic capability. This phagocytosis mechanism consisted of three steps: crystal phagocytosis, disappearance of the endophagosome envelope membrane and fragmentation of phagocytosed crystals within the cytoplasm. Similar phenomenons have been observed during the phagocytic mechanism induced by monocytes/macrophages. The cellular mechanisms of CaP ceramic degradation are modulated by various parameters, such as the properties of the ceramic itself, the implantation sites and the presence of various proteins (cytokines, hormones, vitamins, ions, etc.). The cells involved in these mechanisms could intervene directly or indirectly through their cytokine/growth factor secretions and their sensitivity to the same molecules. This article reviews recent knowledge on the cellular mechanisms of calcium phosphate ceramic degradation.

Animals↗

PubMed1999

[Physiopathology of tumor-induced osteolysis].

Osteolysis, the most common expression of bone tumor, can cause pain, pathological fracture, epidural spinal cord compression and hypercalcemia. Multinucleated osteoclast-like cells, the main agents in bone resorption, are numerous in benign giant cell tumor of bone and can be recruited and activated by various carcinoma cell lines in vitro in animal models. Polykarion macrophages are also able to resorb bone matrix in a favourable tumoral environment. Direct bone resorption by tumor cells has recently been described in vitro and in vivo in animals. The presence of diffusible substances such as hormones, cytokines and growth factors creates a favourable microenvironment for stimulation of osteoclast-like cells and polykarion macrophages functional ability to resorb bone matrix. These mediators act within a complex but still unelucidated network involving high cell production (tumor cells, normal and reactional stroma as well as hematopoietic cells) and many targets (tumor production (tumor cells, normal and reactional stroma as well as hematopoietic cells) and many targets (tumor cells, monocyte/macrophage lineage cells, and osteoclast-like cells). The presence in the same environment of all these stimulating factors for tumor cell growth and resorbing ability could explain the vicious circle of tumoral and osteolytic progression. A better understanding of the complex mechanism of tumor induced osteolysis is essential for improving the conventional surgical approach to this pathology.

Animals↗

PubMed1998

Effects of leukemia inhibitory factor and oncostatin M on bone mineral formed in in vitro rat bone-marrow stromal cell culture: physicochemical aspects.

Leukemia inhibitory factor (LIF) and oncostatin M (OSM), two pleiotropic cytokines involved in bone remodeling, have both anabolic and catabolic activities. This study analyzed the effects of LIF and OSM on the physicochemical characteristics of mineral phases formed in a rat bone-marrow stromal cell culture model. Stromal cells were cultured for three weeks in the presence of 10(-8) M dexamethasone, 50 microgram/mL ascorbic acid and 10 mM Na beta-glycerophosphate with or without 10 ng/ml LIF or OSM. Subsequently, the physicochemical characteristics of the mineralization nodules formed were analyzed by energy dispersive X ray microanalysis (EDX) and Fourier transform-infrared (FT-IR) and FT-Raman spectroscopy. EDX and FT-IR spectroscopy revealed the influence of LIF and OSM on the physicochemical characteristics of mineral phases. FT-Raman spectroscopy showed modifications of the main vibrational modes of the organic matrix. These alterations induced by growth factors could help define new strategies for the prevention and treatment of skeletal disorders.

Animals↗

PubMed1998

Growth hormone-loaded macroporous calcium phosphate ceramic: in vitro biopharmaceutical characterization and preliminary in vivo study.

Calcium phosphate ceramics recently have been used for administering therapeutic agents in bone. The present work investigated the efficacy of macroporous biphasic calcium phosphate (MBCP) implants as a matrix for local delivery of human growth hormone (hGH). An initial study showed that the release of 5 microg of hGH loaded onto MBCP cylinders was rapid during the first 48 h and sustained for a total of 11 days. The biological integrity of hGH (88.2%) was checked using a specific bioassay (cellular proliferation of hGH-sensitive Nb2 cells) in comparison with a radioimmunoassay to calculate the proportion of bioactive hGH released. MBCP cylinders then were loaded with 1, 10, and 100 microg of hGH and implanted into rabbit femurs (n = 16) to determine hGH effects on bone ingrowth and ceramic resorption, as evaluated by scanning electron microscopy and image analysis. Results indicated that hGH increased bone ingrowth and ceramic resorption significantly in comparison with contralateral and control implants. Biochemical parameters monitored in rabbit plasma showed that hGH did not produce detectable systemic effects. Thus the use of MBCP appears to be effective for local delivery of hGH and for increasing bone ingrowth.

Absorption↗

PubMed1998

Growth hormone stimulates the degradation of calcium phosphate biomaterial by human monocytes macrophages in vitro.

This study investigated the effects of human growth hormone (hGH) on the monocyte/macrophage lineage, the first cell population involved in degradation of calcium phosphate ceramic after in vivo implantation. Monocytes isolated from human blood were cultured on biphasic calcium pellets (200 mg) for 8 days in the presence of lipopolysaccharides (LPS, 0.5 microgram/mL), hGH (10 and 50 ng/mL), or an association of LPS with hGH (10 and 50 ng/mL). Unlike LPS, hGH significantly decreased (about 25%) the total number of lacunae formed by monocytes. However, hGH induced the formation of lacunae with a greater surface area (about a 90% increase) as compared to the control. Finally, intense upmodulation (about a 250% increase) of lacuna surface area was observed in the presence of both soluble factors, suggesting that hGH and LPS act synergistically. In view of the development of a drug delivery system for hGH bone release, this study shows that hGH not only stimulates bone cells implicated in the synthesis of the extracellular matrix but also those involved in the early degradation of calcium phosphate biomaterial.

Biocompatible Materials↗

PubMed1998

Polymyxin B inhibits biphasic calcium phosphate degradation induced by lipopolysaccharide-activated human monocytes/macrophages.

Numerous cell types, such as monocytes and osteoclasts, are involved in calcified matrix degradation. In this context, calcium-phosphate ceramics present similar degradation processes in vivo and in vitro to those found in a natural calcified substrate. As the monocyte/macrophage lineage is among the first cells to appear in ceramic implantation sites, it is a key protagonist in inflammatory reaction and biodegradation mechanisms. This study investigated the ability of human monocytes/macrophages activated by various agents [lipopolysaccharides (LPS), polymyxin B (PMB)] to degrade biphasic calcium-phosphate ceramics. PMB sulfate is a bacteriostatic antibiotic that modulates LPS-induced cell activities in vivo and in vitro. Degradation pits (about 10 microns) produced on the pellet surface by these monocytes were discrete, with well defined margins. LPS increased the degradation of calcium-phosphate ceramic (number of lacunae, mean pellet surface area degraded) in a dose-dependent manner whereas polymyxin B downmodulated it significantly. The addition of 2 micrograms/mL of polymyxin B reduced the number of degradation lacunae and the extent of degraded surface area induced by 0.1 microgram/mL LPS by 87% and 64%, respectively. Thus this cell culture system can be very useful in the study of cellular degradation of biomaterials and of the influence of therapeutic agents that may modulate these cell activities.

Calcium Phosphates↗

PubMed1998

Oncostatin M stimulates macrophage-polykaryon formation in long-term human bone-marrow cultures.

Though oncostatin M (OSM) is a potent mediator of the inflammatory reaction, its role in inflammation and bone resorption is still unclear. A long-term bone-marrow culture system is usually developed to allow the formation of multinucleated cells (MNC) and was used here to define the effects of human recombinant OSM on human MNC formation. OSM significantly upregulated (1.9- to 5.6-fold) the number of MNC in these cultures in a dose- and time-dependent manner. Cell nucleation and tartrate-resistant acid phosphatase activity were also increased. MNC did not display osteoclast characteristics, such as response to calcitonin and failure to resorb dentin surface. However, they expressed a non-specific alpha-naphthyl acetate esterase as well as macrophage differentiation antigens (CD11b, CD13 and CD33) and were able to perform phagocytosis. Similar effects were observed after addition of 1 alpha, 25-dihydroxyvitamin D3. Moreover, in these culture conditions, human bone-marrow mononuclear cells were capable of low-grade resorption in the presence of bone-marrow stromal cells. This low-grade resorption was significantly inhibited by addition of 25 ng/ml OSM. Our data demonstrate for the first time that human recombinant OSM significantly stimulates the formation of MNC and could be involved in the inflammatory process via macrophage-polykaryon formation from human bone marrow.

Acid Phosphatase↗

PubMed1998

Increased levels of leukaemia inhibitory factor (LIF) in urine and tissue culture supernatant from human primary bone tumours.

Fifty-five adult patients with primary bone tumour, 27 benign and 28 malignant tumours, were assayed for leukaemia inhibitory factor (LIF) in urine and serum samples. Supernatant was obtained from primary tumour tissue cultures in 24 cases (14 benign, 10 malignant tumours). LIF was found in 11 urine samples (16.7%, 1 benign and 10 malignant tumours). In 23 urine samples from patients with malignant bone tumour tested before any treatment, LIF was detectable in eight cases (34.7%). High LIF levels were found in all supernatants from malignant tumour cultures and in supernatant from 12 of the 14 benign tumours cultured. LIF was never detected in control urine samples or supernatants from normal cancelous bone cultures. These first in vivo data concerning LIF in primary bone tumours raise the question as to the cellular origin of this multifunctional cytokine and its potential role in solid bone tumours and bone tumour resorption.

Adolescent↗

PubMed1998

Cytokines, growth factors and osteoclasts.

Osteoclasts, the main protagonists involved in bone resorption mechanisms, are generally considered to be of haematopoietic origin, although the exact nature of the primary osteoclastic stem cells is still unknown. In vitro cellular models developed to study the different events of osteoclastic differentiation have revealed that not only several cell types (osteoblasts, monocytes, lymphocytes, etc.) but also many soluble factors (cytokines, hormones, vitamins, ions, etc.) and extracellular matrix elements (osteopontin, osteocalcin, etc.) are involved in osteoclastic differentiation and activation. This article provides an exhaustive review of recent knowledge on the origin of the osteoclast and the main substances involved in the osteoclastogenesis and activation of these cells.

Animals↗

PubMed1998

Growth hormone stimulates multinucleated cell formation in long-term bone marrow cultures.

Although the effects of growth hormone on bone metabolism are well-documented, their role in the regulation of immune responses such as the inflammatory process has not been thoroughly explored. This study investigated the formation of multinucleated cells (MNC) in long-term human bone marrow cultures. Experiments using 1 and 100 ng/ml of human recombinant growth hormone (hGH) and 10(-7) M of 1,25 dihydroxyvitamin D3 (VD3) showed that hGH increased the total number and nucleation of MNC. The effects of hGH were generally greater than those observed with VD3. Cytological and immunological characterization of MNC revealed several macrophage polykaryon features. MNC did not respond to calcitonin in a cyclic adenosine monophosphate assay and failed to resorb dentin slices. These results demonstrate that MNC formed in the presence of hGH and VD3 present an essentially macrophage polykaryon phenotype. In this context, growth hormone may be involved in the inflammatory process through upmodulation of macrophage polykaryon formation.

Acid Phosphatase↗

PubMed1998

Transmission FT-IR microspectroscopy of mineral phases in calcified tissues.

Fourier-transform infrared microspectroscopy (FT-IRM) was used to study bone mineralization processes in an in vivo model and in enamel in osteogenesis imperfecta. Finally, the ability of FT-IRM to map new bone formed in implanted macroporous calcium phosphate biomaterial from sections was reported for the first time. FT-IRM allowed the correlation of the microstructure of bone formation in the in vivo model with modifications in carbonate and phosphate environments of the mineral phases during maturation. FR-IRM analysis on enamel sections revealed changes in the mineral environment of carbonate and phosphate ions and probably in the size of enamel crystals. These modifications contributed to the fragility of enamel in osteogenesis imperfecta. The infrared functional group imaging of a part of implanted biomaterial and the bone ingrowth provided the visualization of chemical modifications occurring in biomaterial implants at 20 microns spatial resolution. The use of FT-IRM, in conjunction with appropriate sampling methods and data analysis should provide further insight into the molecular structure of mineral phases of calcified tissues and help to elucidate mineralization processes, skeletal disorders and properties of the biomaterials used as bone substitute.

Animals↗

PubMed1998

Growth hormone stimulatory effects on osteoclastic resorption are partly mediated by insulin-like growth factor I: an in vitro study.

This study investigated the possible role in vitro of insulin-like growth factor I (IGF-I) as a mediator of the effects of growth hormone (GH) on osteoclastic resorption in an unfractioned rabbit bone cell model. After 4 days of rabbit bone cell culture, human GH (hGH) (50 ng/mL) and human IGF-I (hIGF-I) (50 ng/mL) significantly increased the formation of osteoclast-like cells with a lower level than parathyroid hormone (50 ng/mL) or VD3 (10(-8) mol/L). As well as parathyroid hormone and 1-alpha,25-dihydroxyvitamin D3, addition of hGH (1, 10, and 50 ng/mL) and hIGF-I (1, 10, and 50 ng/mL) stimulated the resorption activity of osteoclasts in terms of the percentage of dentin slice surface resorbed, number of lacunae per surface unit, and mean area of lacunae as compared to the control. When neutralizing antiserum against hIGF-I (4 micrograms/mL) was added at the start of culture, the stimulatory effects of hIGF-I and hGH on osteoclastic resorption activity were totally abolished. These results indicate that the effects of GH stimulation on osteoclastic resorption in vitro are mediated via local IGF-I secretion by stromal cells such as osteoblasts. As IGF-I receptors have recently been reported on rabbit osteoclasts, a direct action of IGF-I on mature osteoclasts could be envisaged. Further experiments will be required to determine the real level of IGF-I implicated in the stimulation of bone osteoclastic resorption.

Acid Phosphatase↗

PubMed1998

Leukemia inhibitory factor and oncostatin M influence the mineral phases formed in a murine heterotopic calcification model: a Fourier transform-infrared microspectroscopic study.

The study of bone mineralization processes is of considerable interest in understanding bone diseases and developing new therapies for skeletal disorders, particularly since bone homeostasis requires numerous cell types and a large cytokine network. Cell culture models of mineralization have often been used to study the cellular mechanisms of mineralization, but few data have been reported concerning the influence of extracellular matrix components and cytokines on the physicochemical properties of mineral. The purpose of this study was to analyze the effects of two cytokines, leukemia inhibitory factor (LIF) and oncostatin M (OSM), involved in bone metabolism on the physicochemical properties of bone mineral formed in a murine in vivo mineralization model. Murine bone marrow cells implanted under the kidney capsule in the presence or absence of cytokines led to heterotopic ossicle formation. A scanning electron microscopic microprobe revealed that heterotopic calcification had a lower (approximately 20%) Ca/P ratio after cytokine treatment as compared with the control without cytokine. Transmission electron microscopic analysis of cytokine-treated ossicles showed numerous areas with low mineral density, whereas electron diffraction pattern revealed an apatitic phase. These areas were not observed in the absence of cytokine. Moreover, Fourier transform-infrared microspectroscopy showed at the molecular level that the presence of either cytokine induced many microscopic areas in which short-range order organization, such as incorporation of carbonate and crystallinity/maturity of ossicle mineral, were modified. LIF and OSM influenced mineral phase formation in the present model and may thus be key protagonists in bone mineral development and skeletal diseases.

Animals↗

PubMed1998

Human growth hormone locally released in bone sites by calcium-phosphate biomaterial stimulates ceramic bone substitution without systemic effects: a rabbit study.

Calcium-phosphate bone replacement biomaterial has been used as a drug carrier for therapeutic agents. This study investigated the efficacy of local administration of human growth hormone (hGH) by macroporous biphasic calcium phosphate (MBCP) implants in improving the bone substitution qualities of ceramics. hGH release from MBCP implants loaded with 1 microg of hGH was rapid during the first 48 h and then sustained for a total of 9 days. Immunolocalization of hGH in vitro and in vivo by transmission electron microscopy showed its presence inside the material, indicating that it was able to penetrate within the porosity of the ceramic during the adsorption process. MBCP cylinders (6 x 6 mm) were loaded with 0.1, 1, and 10 microg of hGH and implanted into rabbit femurs (n = 40). The effects of locally released hGH on bone ingrowth and ceramic resorption were evaluated by scanning electron microscopy and image analysis. The results indicated that hGH increased bone ingrowth (+65%) and ceramic resorption (+140%) significantly in comparison with control implants and that the increase was dose dependent. Biochemical parameters monitored in rabbit plasma and urine, as well as the absence of any significant difference between contralateral implants and the control, indicated that hGH did not produce detectable systemic effects. Thus, the use of MBCP appears to be effective for local delivery of hGH, resulting in improved bone substitution.

Animals↗

PubMed1998

Heterotopic implantation of mouse bone-marrow cells: an in vivo model allowing analysis of mineral phases during mineralization processes.

Heterotopic calcification induced after implantation of bone-marrow cells under the murine kidney capsule was used to study the mineral phases occurring during the mineralization process. Ossicles were found to contain numerous osteoblastic cells that produced an organic matrix closely associated with active hematopoietic tissue. During implantation of bone marrow, needle-shaped microcrystals were progressively deposited on collagen fibers. The mineral formed in the heterotopic calcification consisted mainly of calcium phosphate. The distribution and density of the microcrystals were heterogeneous after 6 weeks of implantation but became homogeneous and well-crystallized after 10 weeks. The Fourier transform infrared microspectroscopy provided important spatial data on the nature of the mineral formed and the changes in the mineral environment. Similarities were noted between young bone (bone callus) and 6-week heterotopic ossicles, and between adult bone and 10- or 12-week heterotopic ossicles. The study demonstrated that murine heterotopic calcification under the renal capsule can be a very useful model for studying bone apatite formation during the mineralization process.

Animals↗

PubMed1998

Commentary: Emerging and other communicable diseases.

There is an increasing need for integrated, sustainable; and cost-effective approaches to the management of infectious diseases. For example, an emerging disease in one country may already be endemic in another country but nearing elimination in a third. A coordinated approach by WHO towards infectious diseases is therefore needed that will facilitate more effective support of on-going efforts for the prevention and control of endemic diseases, intensify efforts against those diseases targeted for eradication and elimination, and result in better preparedness and response to new and re-emerging diseases. In order to meet these challenges, WHO has created a new Programme on Communicable Diseases (CDS), which will replace the former Division of Emerging and other Communicable Diseases (EMC). The new Programme will better integrate surveillance, prevention, control, and research over the whole spectrum of communicable diseases. CDS will function as focal point for global data and information exchange on infectious diseases, and inter alia, will reinforce laboratory-based surveillance of bacterial, viral, and zoonotic diseases to ensure early detection of threats to international public health. Changes in susceptibility to infectious disease, increased opportunities for infection, and the ability of microbes to adapt rapidly will continue to challenge WHO to improve prevention and control of infectious diseases in the future by establishing strong partnerships with both the private and public sectors.

Communicable Disease Control↗

PubMed1997

Osteoclastic resorption of biphasic calcium phosphate ceramic in vitro.

Neonatal rabbit bone cells were cultured for 1 and 4 days on biphasic calcium phosphate ceramic specimens to study the osteoclastic resorption of the ceramic. Scanning electron microscopic studies after removal of stromal cells with pronase E and EDTA revealed many osteoclast-associated lacunae on the ceramic surface. The degraded crystals inside the lacunae appeared to have been dissolved by acids. Cellular degradation of the ceramic was clearly due to the extracellular process characteristic of osteoclastic resorption.

Animals↗

PubMed1997

LPS increases biomaterial degradation by human monocytes in vitro.

Different cell lines are involved during an immunological reaction, principally lymphocytes and monocytes. Monocyte/macrophage cells, which are among the first to appear in wound-healing and infection sites, are largely implicated in phagocytosis and could be involved in calcium-phosphate degradation. Their role in these processes may relate to cytokine secretions and/or their sensitivity to certain cytokines. We tested the behavior of human monocytes placed on the surface of biphasic calcium-phosphate (BCP) tablets in the presence of two lipopolysaccharide (LPS) concentrations. After short-term culture (48 h), cytokine release (IL-1beta, IL-6) was measured by ELISA, and morphological cell events and biomaterial degradation were observed in scanning electron microscopy. BCP surface pits were noted near cells stimulated by 0.5 microg/mL LPS but were not apparent with 10 microg/mL LPS. The number of lacunae on BCP was increased after LPS treatment of human monocytes. An upmodulation of IL-1beta and IL-6 (in culture medium) released by LPS-activated human monocytes was observed, indicating good cell stimulation. This study demonstrates that LPS-activated human monocytes can degrade the surface of calcium-phosphate ceramic and confirms the role of human monocytes in biomaterial degradation.

Biocompatible Materials↗