Cell cycle synchronization reveals greater G2/M-phase accumulation of lung epithelial cells exposed to titanium dioxide nanoparticles
2015
Medina-Reyes, Estefany I. | Bucio-López, Laura | Freyre-Fonseca, Verónica | Sánchez-Pérez, Yesennia | García-Cuéllar, Claudia M. | Morales-Bárcenas, Rocío | Pedraza-Chaverri, José | Chirino, Yolanda I.
Titanium dioxide has been classified in the 2B group as a possible human carcinogen by the International Agency for Research on Cancer, and amid concerns of its exposure, cell cycle alterations are an important one. However, several studies show inconclusive effects, mainly because it is difficult to compare cell cycle effects caused by TiO₂nanoparticle (NP) exposure between different shapes and sizes of NP, cell culture types, and time of exposure. In addition, cell cycle is frequently analyzed without cell cycle synchronization, which may also mask some effects. We hypothesized that synchronization after TiO₂NP exposure could reveal dissimilar cell cycle progression when compared with unsynchronized cell population. To test our hypothesis, we exposed lung epithelial cells to 1 and 10 μg/cm²TiO₂NPs for 7 days and one population was synchronized by serum starvation and inhibition of ribonucleotide reductase using hydroxyurea. Another cell population was exposed to TiO₂NPs under the same experimental conditions, but after treatments, cell cycle was analyzed without synchronization. Our results showed that TiO₂NP-exposed cells without synchronization had no changes in cell cycle distribution; however, cell population synchronized after 1 and 10 μg/cm²TiO₂NP treatment showed a 1.5-fold and 1.66-fold increase, respectively, in proliferation. Synchronized cells also reveal a faster capability of TiO₂NP-exposed cells to increase cell population in the G2/M phase in the following 9 h after synchronization. We conclude that synchronization discloses a greater percentage of cells in the G2/M phase and higher proliferation than TiO₂NP-synchronized cells.
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