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Biocompatibility studies on glass ionomer cements by primary cultures of human osteoblasts.

Glass ionomer cements (GICs) are materials largely employed in the dental field that have been considered recently as cements in orthopaedic surgery for their proven osteogenic features. The aim of this study was to compare the response of cultured human osteoblastic cells to a number of commercial glass ionomer cements in order to provide indications useful for the further development of formulations that have potential for use as cements or implants in repair and replacement of bone tissue. The GICs tested were: Ketac-Fil Aplicap, lonocem lonocap 1,0, GC Fuji II, GC Fuji II LC and Vitremer 3M. Several features such as plating efficiency, adhesion and morphology of the cells were studied, as well as the only specific biochemical parameter of osteoblastic phenotype, namely osteocalcin production. In addition, the colonisation of materials by osteoblastic cells was verified by means of scanning electron microscopy. Altogether, the results obtained indicate that four of the five glass ionomer cements tested are biocompatible, showing vital cells adhering to the materials, proliferating and expressing the biochemical markers of osteoblastic phenotype, whereas Vitremer 3M, although currently employed in the dental field, exhibits a great cytotoxicity toward the cells. The adverse reaction of this GIC can be attributed to the leaching of at least two components of the polyacidic phase evidenced by protonic magnetic resonance analysis (PMR), namely 2-hydroxyethylmethacrylate (HEMA), and an unidentified acidic species. The addition of pure HEMA at the same concentrations found by means of PMR to cultures of osteoblastic cells resulted in a complete cell death. Our results also show that in vitro methods employing primary cultures of human cells specific to the implant sites of prostheses are appropriate and suitable tools for evaluating biocompatibility of materials. Furthermore, this kind of approach can provide indications useful in the design of novel materials as well as in improving the characteristics of the formulations already available.

Behaviour of human osteoblasts cultured on bioactive glass coatings

Two new formulations of bioactive glasses were used as coatings on titanium alloy (TiAl6V4) implants for prosthetic applications in the orthopaedic field. The biocompatibility of these bioglasses, as well as their osteoconductive properties, were assessed by employing primary cultures of human osteoblasts. A nonbioactive glass, the titanium alloy and polystyrene surface were used as controls. The results obtained demonstrated that the two bioglasses elicited a rapid and strong proliferative response by osteoblasts, which spread, formed a close layer and then expressed the specific osteoblastic marker i.e. osteocalcin. In comparison, cells grew on the nonbioactive glass to a much minor extent, similar to that of polystyrene control, showing individual cellular elements not forming a compact sheet, but expressed levels of osteocalcin clearly higher than both the polystyrene control and the two bioglasses. Finally, a very low proliferative rate of osteoblasts and the synthesis of hardly detectable osteocalcin amounts were observed with the titanium alloy. In conclusion, our studies indicate that the new bioactive glasses are effective in stimulating osteoblast growth and differentiation.

Biochemical Characterization of p16INK4- and p18-containing Complexes in Human Cell Lines

The regulation of the D-type cyclin-dependent kinase (CDK4 and CDK6) activity appears to be the key step in the progression of eukaryotic cells through the G1 cell cycle phase. One of the mechanisms involved in this process is the binding of some small proteic inhibitors, with a molecular mass ranging between 14 and 20 kDa, to these CDKs. We have evaluated the amount of two such inhibitors, namely p16INK4 and p18, in normal and transformed cells, as well as the biochemical features of the macromolecular complexes containing these proteins. The results obtained indicated that (i) p18 gene expression, unlike p16INK4 gene, is not regulated by pRb status, (ii) no evident relationship exists between the expression of p16INK4 and p18 genes, (iii) significant amounts of the two proteins are not bound to CDKs but occur as free molecules, (iv) each inhibitor forms a complex with the CDK protein with a 1:1 stoichiometry, and (v) a competition exists between cyclin D and the inhibitor protein toward the CDK protein resulting in the absence of detectable cellular free kinase. Moreover, employing the human native partially purified p16INK4 or the pure recombinant protein, we have been able to demonstrate in vitro the dissociation of CDK4-cyclin D1 complex and the formation of CDK4-p16INK4 bimolecular complex. Our findings suggest that during the cell division cycle the members of the p16INK4 protein family and cyclin Ds compete for binding to CDK4/CDK6 and that their quantitative ratio is essential for G1 → S transition.

Raloxifene induces cell death and inhibits proliferation through multiple signaling pathways in prostate cancer cells expressing different levels of estrogen receptorα and β

Raloxifene (RAL), a selective estrogen receptor (ER) modulator (SERM) seems to induce apoptosis in both androgen‐dependent and ‐independent prostate cell (PC) lines via activation of ERβ and an antagonistic effect on ERα. In this study, we evaluated the effects of RAL on epithelial PC growth using the two following in vitro models: the androgen‐dependent cell line EPN which expressed both ERs; and a stabilized epithelial cell line derived from a prostate cancer specimen (CPEC), which expressed low levels of ERβ and lacked ERα. In EPN cells, there was an increase in the pre‐G1 apoptotic peak and a reduction in the S phase of the cell cycle with G0/G1 arrest after E2 or RAL treatment; bcl‐2 mRNA and Bcl‐2 protein levels were significantly reduced, while activated caspase‐3 and Par‐4 levels increased significantly after either E2 or RAL treatment; in addition, c‐myc transcript was inhibited after 10−6 M RAL treatment. A dose‐dependent increase of metallothionein II gene RNA level was also induced by RAL in EPN. In CPEC, there was only a weak apoptotic peak associated with caspase‐3 activation and Par‐4 increase after either E2 or RAL treatment; while c‐myc transcript level increased. RAL induced a rapid but transient phosphorylation of ERK 1/2 in EPN cells but generated a sustained effect in CPEC. These findings suggest that RAL effects on PC growth control in vitro are cell‐specific, depending on ERβ or ERβ/ERα relative expression levels. Moreover, this study demonstrated that RAL affected both transcriptional regulation and non‐genomic signals, which resulted in the modulation of multiple signaling pathways of apoptosis and of cell cycle progression. J. Cell. Physiol. 226: 1334–1339, 2011.

Reduced expression of transforming growth factor-beta receptor type III in high stage neuroblastomas

Transforming growth factor beta (TGF-β) is a powerful inhibitor of cell proliferation and a potent inducer of differentiation. Resistance to TGF-β action is a characteristic of many malignancies and has been attributed to alterations of TGF-β receptors as well as disturbance of downstream transduction pathways. To analyse the TGF-β response in neuroblastoma, the expression of TGF-β1 and TGF-β type I, II and III receptor genes was investigated in 61 cancer samples by means of reverse transcription polymerase chain reaction. The specimens analysed belong to different stages, namely nine samples of stage 1, ten of stage 2, nine of stage 3 and 28 of stage 4. Moreover, five samples were of stage 4S, which represents a tumour form undergoing spontaneous regression. The results obtained show that TGF-β1 and TGF-β type I and II receptor genes appear to be almost equally expressed in neuroblastomas of all stages. Conversely, TGF-β type III receptor gene expression, which is required for an efficacious TGF-β binding and function, is strongly reduced exclusively in neuroblastomas of stages 3 and 4. These findings were directly confirmed by immunohistochemical analyses of ten neuroblastoma specimens. Our results suggest the occurrence of an altered TGF-β response in advanced neuroblastomas which might be an important mechanism for escaping growth control and for developing invasiveness. Moreover, our findings allow the proposal of a novel mechanism, namely down-regulation of TGF-β type III receptor gene expression, to avoid TGF-β inhibitory activity.

Cell division cycle control in embryonal and alveolar rhabdomyosarcomas

In this study, we investigated the mRNA level of several genes involved in cell cycle regulation in alveolar (ARMS) and embryonal rhabdomyosarcomas (ERMS). p21(Cip1), Cyclin D1, Cyclin D2, Cyclin D3, CDK2, and CDK4 were evaluated by RT-PCR. All (13 out of 13) ERMS expressed the p21(Cip1) gene compared with only 40% (4 out of 10) of the ARMS. Moreover, the amount of p21(Cip1) mRNA was noticeably higher in the ERMS samples than in the positive ARMS specimens. p27(Kip1) protein were analysed by immunohistochemical and immunoblotting. A noticeable difference was observed, in that ERMS had higher amounts of the cell cycle inhibitor compared with the ARMS. Finally, treatment of two rhabdomyosarcoma cell lines, RH-30 and RD, with butyrate, resulted in complete growth inhibition and in the upregulation of the p21(Cip1) and p27(Kip1) levels. Our results demonstrate that ERMS have a much higher level of p27(Kip1) and p21(Cip1) than the alveolar types, explaining, at least in part, the distinct features and outcomes (i.e. a poor prognosis of the alveolar type) of the two forms of this childhood solid cancer. Moreover, the data on butyrate-treated cell lines suggest that the two genes are potential novel therapeutic targets for the treatment of rhabdomyosarcomas.

New established melanoma cell lines: genetic and biochemical characterization of cell division cycle

Background Cancer might be envisaged as the result of a genetic process causing the unregulated proliferation of a given cell as well as its inability to undergo differentiation and/or apoptosis. Alterations of genes regulating cell division cycle appear to play a key role in the development of human cancer.

Alteration of cell division cycle regulation in human cancers: The role of CDKN2A gene

Cancer might be thought of as a disease characterized by a deregulated cellular growth. Thus, it is not surprising that some of the molecular components of cell division cycle machinery are altered in human tumors. The cell cycle of all post-embryonic eukaryotic cells (including malignant cells) is divided into four phases, namely: G1 phase (period prior to DNA synthesis), S phase (period of DNA synthesis), G2 phase (period between DNA synthesis and mitosis) and M phase (mitosis). Collectively, G1, S and G2 are called interphase, the cell cycle period distinct from division of the nucleus (mitosis) and cytoplasm (cytokinesis) (Pardee, 1989; Desai et al., 1992). The length of the S, G2 and M phases is remarkably similar in many different cells, while the greatest variation is seen in the length of G1. At some point late in G1, called restriction or R point, a cell becomes committed to traverse the remainder of the cell cycle. Thus, variations in cell cycle time are mostly due to variations in the length of G1 up to the R point (Pardee, 1989; Desai et al., 1992).