In Vitro Age Dependent Response to TiO₂ Particles on Macrophages

Titanium is one of the most used metallic biomaterials in oral implantology. Still, at the material-tissue interface titanium dioxide (TiO₂) could trigger an inflammatory response. The magnitude of the biological response depends not only on TiO₂ physicochemical properties (shape, size, concentration, etc.) but, on the individual characteristics (sex, genetics, age, etc). Lately, macrophages as pivotal members of the host immune system and their responses to biomaterials have attracted wide concern in biomedicine. Objective: To evaluate the inflammatory and cytotoxic effect of TiO₂ micro and nanoparticles on culture macrophages from young and aged animals. Methods: Alveolar Macrophages(AM)obtained by bronchoalveolar lavage from young(Y) and senescent(S)(3 & 18 month old respectively) Wistar rats, were cultured in RPMI-1640 with 10% FCS and exposed to 2.5-100µg/ml of (micro[M] and nano[N]) TiO₂ particles. After 24 hours culture, the following functional parameters were assessed: nitric oxide (NO) generation by Griess reaction; proinflammatory (TNFa,IL-6) and antiinflammatory(IL-10)cytokine release by ELISA and cell death by light microscopy and flow cytometry. Results: In Y&S-AM independent of particle size, NO metabolism tended to increase in a dose dependent manner (e.g.:Y-AM Control:5.54±1.3vs TiO₂[N-10µg/ml]: 10.47±0.91; [N-100µg/ml]:13.63±2.4; S-AM:Control:3.64±1.3vs TiO₂[N-10µg/ml]:9.36±2.8; [N-100µg/ml]:16.67±3.6). No differences were found for IL-6 release on S-AM exposed to TiO₂ (M&N), however a marked increase was found for MTiO₂ on Y-AM. On the contrary, M&N TiO₂ particles caused a significant and dose dependent TNFa increase on S-AM cultures while on Y-AM only [100µg/ml] NTiO₂ provoked a significant increase on its expression. IL-10 significantly increased only for the highest concentration used on S-AM irrespective of the grain size and, throughout the whole range of doses for M&N TiO₂ on Y-AM. DNA strand brake and capase-3 results showed that the main cytotoxic mechanism was via apoptosis. Conclusions: TiO₂ particle-biological responses on macrophages rely on size, concentration and are age dependent. PICT2008-1116ANPCyT, UBACyT20020100200157 and CONICET-PIP11220090100117.