Development of a new zirconia-toughened alumina: promising mechanical properties and absence of in vitro carcinogenicity.

High purity alumina as well as zirconia ceramics have been widely used as orthopaedic implant biomaterials and dental devices displaying optimal, but sometimes exclusive, mechanical properties. In order to combine the advantages of alumina and zirconia ceramic materials different types of composites have been developed in which either zirconia is dispersed in an alumina matrix or vice versa. Orthopaedic and dental implant biomaterials are expected to be in contact with living tissues for a long period of time and their long term toxicity must be carefully evaluated. In this study we report the development of a high performance chromia-doped zirconia toughened alumina (ZTA) material which displays promising mechanical properties in terms of hardness, strength and fracture toughness that make it suitable for prosthesis even for small joints. The long-term biocompatibility of this material was also evaluated, mainly in terms of DNA damage, mutagenicity and cancerogenetic potential in mammalian cells. The results obtained suggest that this new ZTA material does not display any longterm carcinogenic effect and it is suitable for biomedical applications from a cancerogenetic point of view. In conclusion, we report the development of a new chromia-doped ZTA material with interesting properties, both from a mechanical and a biocompatibility point of view which warrant further studies on its suitability as a candidate biomaterial for orthopaedic implants and dental devices.

Differential toxic effects of methyl tertiary butyl ether and tert-butanol on rat fibroblasts in vitro.

Methyl tertiary butyl ether (MTBE) is the most widely used motor vehicle fuel oxygenate since it reduces harmful emissions due to gasoline combustion. However, the significant increase in its use in recent years has raised new questions related to its potential toxicity. In fact, although available data are somehow conflicting, there is evidence that MTBE is a toxic substance that may have harmful effects on both animals and humans and an unresolved problem is the role played by MTBE metabolites, especially tertiary butyl alcohol (TBA), in determining toxic effects due to MTBE exposure. In this study, the toxic effects of MTBE have been analyzed on a normal diploid rat fibroblast cell line (Rat-1) and compared to the effects of TBA. The results obtained suggest that both MTBE and TBA inhibit cell growth in vitro but with different mechanisms in terms of effects on the cell cycle progression and on the modulation of cell cycle regulatory proteins. In fact, MTBE caused an accumulation of cells in the S-phase of the cell cycle, whereas TBA caused an accumulation in the G0/G1-phase with different effects on the expression of cyclin D1, p27Kip1, and p53. Moreover, both MTBE and TBA were also shown to induce DNA damage, as assessed in terms of oxidative DNA damage and nuclear DNA fragmentation, that appeared to be susceptible of repair by the cell DNA-repair machinery. In conclusion, these findings suggest that both MTBE and TBA can exert, by acting through different molecular mechanisms, important biological effects on fibroblasts in vitro. Further studies are warranted to shed light on the mechanisms responsible for the observed effects and on their potential significance for the in-vivo exposure.

Increased expression of cyclin E is associated with an increased resistance to doxorubicin in rat fibroblasts.

Cell cycle progression in eukaryotic cells is regulated by a family of cyclin-dependent kinases (CDKs). Cyclin E is a regulatory subunit of CDK2 and drives cells from G1 to S phase. Increased expression of cyclin E is a frequent event in human malignancies and has been associated with poor prognosis in various cancers. In this study, we evaluated the effects of cyclin E-overexpression on the sensitivity of rat fibroblasts to anticancer drugs. Cyclin E-overexpressing cells were less sensitive to doxorubicin-induced inhibition of cell growth but not to other antineoplastic drugs, such as paclitaxel, vincristine, etoposide and methotrexate. Cyclin E-overexpressing fibroblasts also displayed a reduction in ROS levels and a significantly lower increase following doxorubicin treatment compared with vector control cells. The expression of manganese superoxide dismutase (MnSOD) and its activity were increased (about 1.3-fold) in cyclin E-overexpressing derivatives compared with control cells. These results suggest that cyclin E overexpression might reduce tumour cells sensitivity to doxorubicin by affecting the expression of MnSOD and that determination of cyclin E expression levels might help to select patients to be treated with an anthracycline-based antineoplastic therapy.