In vitro expression of osteoblastic markers in cells isolated from normal fetal and postnatal human bone and from bone of patients with osteogenesis imperfecta

Role of adult mesenchymal stem cells in bone tissue engineering applications: current status and future prospects

Mesenchymal stem cells (MSCs) have been demonstrated as an attractive cell source for tissue-engineering applications because of their ability to be easily isolated and expanded from adult bone marrow aspirates and their versatility for pluripotent differentiation into mesenchymal tissues. This review highlights advances and progress in bone reconstruction techniques for both the repair of site-specific bone defects and the attenuation of musculoskeletal disease symptoms associated with osteoporosis and osteogenesis imperfecta. Despite the enormous potential benefits of MSCs within these approaches, conventional tissue culture methods limit the clinical utility of these cells because of the gradual loss of both their proliferative and differentiation potential during ex vivo expansion. Novel strategies to overcome these limitations are discussed including cultivation in the presence of basic fibroblastic growth factor 2, induction of ectopotic telomerase expression, and ex vivo expansion on various collagenous biomaterials. In addition, this review also outlines mechanistic theories on the potential role of MSC-extracellular matrix interactions in mediating the retention of MSC proliferative and differentiation capacity after ex vivo expansion on collagenous biomaterials.

Enzyme histochemical localisation of alkaline phosphatase activity in osteogenesis imperfecta bone and growth plate: A preliminary study

At the ultrastructural level alkaline phosphatase has been studied in calcifying cartilage but not in bone. The aim of this study was to assess if there is an osteoblast dysfunction in Osteogenesis Imperfecta (OI) with respect to alkaline phosphatase activity. Specimens from three OI type II foetal femoral bones, two OI type II growth plates, one normal foetal femoral bone and growth plate, one OI type III femoral bone specimen and one normal juvenile bone specimens were examined using modified lead nitrate method to identify alkaline phosphatase reactivity. The electron dense reaction product (indicative of the presence of alkaline phosphatase) was demonstrable on the cell membrane of the osteoblasts, as focal concentrations in the collagen osteoid and on the mineralisation front of normal bone. In normal bone the intensity of the reaction seemed to be stronger than in OI bone and appeared as a continuous black line along the osteoblast cell membranes. In OI bone the reaction product only appeared as a few electron dense beads along the osteoblast cell membrane. There appeared to be reduced and diffuse reaction product on OI osteoblasts, thus implying either a reduced level and/or altered activity of alkaline phosphatase and hence a dysfunction of osteoblasts. This confirms the findings of the previous report of the impaired activity of alkaline phosphatase in OI osteoblasts. Even in the OI growth plate, hypertrophic chondrocytes showed less intense reaction product than the chondrocytes in the normal growth plate. The normal human growth plates used in this study showed a similar pattern, but in the OI growth plate even the hypertrophic zone, where the alkaline phosphatase activity is reported to be high, showed less intense reaction product. Biochemical reports indicate that alkaline phosphatase levels are normal in cultured OI cell lines, yet ultrastructural histochemical observations reported here, show reduced enzyme localisation and this may suggest reduced amounts of protein or reduced activity at the tissue level.

The influence of bone allograft processing on osteoblast attachment and function

In order to assess the influence of eight different sterilisation and disinfection methods for bone allografts on adhesion, proliferation, and differentiation of human bone marrow stromal cells (BMSC), cells were grown in culture and then plated onto pieces of human bone allografts. Following processing methods were tested: autoclavation (AUT), low-temperature-plasma sterilisation of demineralised allografts (D-LTP), ethylene oxide sterilisation (EtO), fresh frozen bone (FFB), 80 degrees C-thermodisinfection (80 degrees C), gamma-irradiation (Gamma), chemical solvent disinfection (CSD), and Barrycidal-disinfection (BAR). The seeding efficiency was determined after one hour to detect the number of attached cells before mitosis started. The cell viability was determined after 3, 7, and 21 days. Tests to confirm the osteoblastic differentiation included histochemical alkaline phosphatase staining and RT-PCR for osteocalcin. Human BMSC showed greatest attachment affinities for D-LTP-, 80 degrees C-, and CSD-allografts, whereas less cells were found attached to AUT-, EtO-, FFB-, Gamma-, and BAR-probes. Cell viability assays at day 3 revealed highest proliferation rates within the FFB- and 80 degrees C-groups, whereas after 21 days most viable cells were found in D-LTP-, 80 degrees C-, CSD-, and Gamma-groups. BAR-treatment showed a considerably toxic effect and therefore was excluded from all further experiments. Highest AP-activity and gene expression of osteocalcin were detected in the D-LTP-group in comparison with all other groups. In summary, our results demonstrate that cell adhesion, final population, and function of BMSC are influenced by different disinfection and sterilisation methods. Therefore, processing-related alterations of BMSC-function may be important for the success of bone grafting. The experimental setup used in the present work may be useful for further optimisation of bone allograft processing.

Bioengineered human bone tissue using autogenous osteoblasts cultured on different biomatrices

Surgical treatment of critical-size posttraumatic bone defects is still a challenging problem, even in modern bone and joint surgery. Progress in cellular and molecular biology during the last decade now permits novel approaches in bone engineering. Recent conceptual and technical advances have enabled the use of mitotically expanded, bone-derived cells as a therapeutic approach for tissue repair. Using three different tissue carrier systems, we successfully cultivated human osteoblasts in a newly developed perfusion chamber. We studied cell proliferation and the expression of osteocalcin, osteopontin, bone morphogenetic protein-2A, alkaline phosphatase, and vascular endothelial growth factor as parameters for osteoblast function and viability. Adherence of highly enriched human osteoblasts had already started after 1 h and resulted in completely overgrown human bone pieces after 10 days. Expression analysis of bone-specific alkaline phosphatase indicated differentiating osteoblasts, whereas the high mRNA expression of osteocalcin and osteopontin revealed terminally differentiated osteoblasts and the process of mineralization. Additionally, gene expression was significantly higher when demineralized bone was used as biomatrix, compared to autoclaved bone and hydroxyapatite ceramics. We conclude that with our newly developed perfusion culture system, vital autogenous bone implants of clinically applicable size can be generated within 17 days in order to manage critical-size bone defects.

Isolation and characterization of osteoblast cultures from normal and osteopenic sheep for biomaterials evaluation

Being very useful in the analysis of bone cell differentiation and activity, osteoblast cultures are also used in the in vitro biocompatibility study of new materials. The aim of this work was to evaluate sheep osteoblast cultures derived from normal and ovariectomized animals, and then to assess the in vitro biomaterial behavior on these cultures, taking into account the quality of bone where orthopedic devices are clinically used. For this purpose, we characterized sheep osteoblast cultures, isolated from iliac crest bone of normal (NB osteoblast culture) and osteopenic after ovariectomy (OB osteoblast culture) sheep. Moreover, we studied cell behavior when cultured on different biomaterials (titanium and two biological glasses, RKKP and AP40). Cell characterization at baseline demonstrated that both cultures (NB and OB) showed normal osteoblastic behavior. On the contrary, osteoblasts derived from osteopenic bone and cultivated on AP40 for 6 days revealed a different behavior in terms of both cell morphology and metabolic activity. Statistical analysis (one-way analysis of variance and Scheffé's post hoc multiple-comparison tests) revealed significant differences in Ca level (p<0.0005), MTT test (p<0.0005) and OC production (p<0.05). These in vitro tests demonstrated that sheep osteoblast cultures can be useful when determining biocompatibility and osteointegration of orthopedic materials, and also when evaluating for the presence of osteoporosis.

In vitro pathological model of osteopenia to test orthopaedic biomaterials

The association of in vitro tests and in vivo bone implants, has significantly improved the characterization of biomaterials for orthopaedic devices before their clinical use. However, neither cell cultures nor most animals models used for these tests entirely reflect the clinical conditions in which biomaterials are implanted. Pathological animal models are considered to substantially improve our knowledge of osteointegration of biomaterials; for this reason researchers increasingly use aged, osteopenic or arthritic animals in their experimental tests. The development of "pathological cell cultures" would also be of great importance for the study of biomaterials. It would allow a complete material evaluation, beginning with a biocompatibility test to a more finalized and specific preclinical evaluation. The present study, looks at the possibility of using cell culture methodology for the improvement of in vitro biomaterials characterization in the case of osteopenia. Cultures derived from normal (NB-OST) rats were compared to those of osteopenic (OB-OST) rats, by testing the osteoblasts against common parameters of characterization. Moreover, the reaction of these cultures to two biological glasses of known in vivo behavior (both in normal and osteopenic bone) by means of parameters on biocompatibility and bone formation index, was evaluated. Our results showed that there was no evidence of differences between the NB-OST and OB-OST cultures. After 6 days of culturing, the bioglass that did not osteointegrate in osteopenic animals, did not induce cytotoxicity in NB-OST, but a significative reduction of viability and Osteocalcin level in OB-OST was observed. We think that these data should stimulate researchers to develop further tests in order to improve preliminary in vitro comprehension on biomaterials.

Characterization of human bone marrow stromal cells with respect to osteoblastic differentiation

Human bone marrow was harvested by means of iliac crest aspiration and cultured under conditions that promote an osteoblastic phenotype. Human bone marrow aspirates from 30 normal subjects, ages 8-80 years, with no systemic illness, yielded a mean of 92 +/- 65 x 10(6) nucleated cells per 2 ml of aspirate. The prevalence of potential osteoblastic progenitors was estimated by counting the number of alkaline phosphatase-positive colonies. This assay demonstrated a mean of 43 +/- 28 alkaline phosphatase-positive colonies per 10(6) nucleated cells, which was about one per 23,000 nucleated cells. The prevalence of these colonies was positively correlated with the concentration of nucleated cells in the original aspirate (p = 0.014) and was negatively correlated with donor age (p = 0.020). The population of alkaline phosphatase-positive colonies in this model sequentially exhibited markers of the osteoblastic phenotype; essentially all colonies (more than 99%) stained positively for alkaline phosphatase on day 9. Matrix mineralization, which was associated with the synthesis of bone sialoprotein, was demonstrated on day 17 with alizarin red S staining. On day 45, cells that were stimulated with 1,25-dihydroxyvitamin D3 synthesized and secreted osteocalcin at concentrations consistent with known osteoblastic cell lines. This model provides a useful method for the assay of progenitors of connective tissue from human subjects, examination of the effects of aging and selected disease states on this progenitor population, and investigation into the regulation of human osteoblastic differentiation.

1,25-dihydroxyvitamin D3-mediated transforming growth factor-beta release is impaired in cultured osteoblasts from patients with multiple pituitary hormone deficiencies

To evaluate the osteoblastic function in patients with multiple pituitary hormone deficiencies (M-PHD) and with isolated growth hormone deficiency (I-GHD), bone cells were cultured and the effects of 10(-8) M 1,25-dihydroxyvitamin D3 (1,25[OH]2D3) on parameters of cell proliferation, osteoblastic differentiation, and local paracrine regulation were measured. Three days of 1,25(OH)2D3 treatment increased alkaline phosphatase activity and osteocalcin release but inhibited [3H]thymidine incorporation in all cell cultures from patients as well as from controls. In addition, 1,25(OH)2D3 increased the release of both total and active transforming growth factor-beta (TGF-beta) in bone cells from controls by, respectively, 4.9- and 3.2-fold and in bone cells from I-GHD by 5.1- and 1.5-fold, respectively. However, in bone cells from M-PHD, the stimulation of total TGF-beta release was significantly lower (1.3-fold) than in control and I-GHD cells, and active TGF-beta release was not stimulated at all. One year of supplementation with human growth hormone did not improve this deficient TGF-beta release in bone cells from M-PHD. We conclude that cultured bone cells from I-GHD and M-PHD show a normal response to 1,25(OH)2D3 regarding cell proliferation and osteoblastic differentiation, which implicates a normal 1,25(OH)2D3-receptor function. In cells from controls and I-GHD, 1,25(OH)2D3 enhanced both total and active TGF-beta release. However, bone cells from M-PHD showed a deficient TGF-beta response to 1,25(OH)2D3. These results suggest that the regulation of TGF-beta production is a major paracrine factor involved in hypopituitarism.