Assessment of TiO2 Nanoparticle Impact on Surface Morphology of Chinese Hamster Ovary Cells

The process of nanoparticles entering the cells of living organisms is an important step in understanding the influence of nanoparticles on biological processes. The interaction of nanoparticles with the cell membrane is the first step in the penetration of nanoparticles into cells; however, the penetration mechanism is not yet fully understood. This work reported the study of the interaction between TiO2 nanoparticles (TiO2-NPs) and Chinese hamster ovary (CHO) cells using an in vitro model. The characterization of crystalline phases of TiO2 NPs was evaluated by transmission electron microscopy (TEM), X-ray diffraction (XRD) spectrum, and atomic force microscopy (AFM). Interaction of these TiO2 nanoparticles (TiO2- NPs) with the CHO cell membrane was investigated using atomic force microscopy (AFM) and Raman spectroscopy. The XRD analysis result showed that the structure of the TiO2 particles was in the rutile phase with a crystallite size of 60 nm, while the AFM result showed that the particle size distribution had two peaks with 12.1 nm and 60.5 nm. The TEM analysis confirmed the rutile phase of TiO2 powder. Our study showed that exposure of CHO cells to TiO2-NPs caused morphological changes in the cell membranes and influenced the viability of cells. The TiO2-NPs impacted the cell membrane surface; images obtained by AFM revealed an 'ultra structure' with increased roughness and pits on the surface of the membrane. The depth of the pits varied in the range of 40-80 nm. The maximal depth of the pits after the treatment with TiO2-NPs was 100% higher than the control values. It is assumed that these pits were caveolae participating in the endocytosis of TiO2-NPs. The research results suggest that the higher maximal depth of the pits after the exposure of TiO2-NPs was determined by the interaction of these TiO2-NPs with the cell's plasma membrane. Moreover, some of pits may have been due to plasma membrane damage (hole) caused by the interaction of TiO2-NPs with membrane constituents. The analysis of AFM images demonstrated that the membrane roughness was increased with exposure time of the cells to TiO2-NPs dose. The average roughness after the treatment for 60 min with TiO2-NPs increased from 40 nm to 78 nm. The investigation of the membrane by Raman spectroscopy enabled us to conclude that TiO2-NPs interacted with cell proteins, modified their conformation, and potentially influenced the structural damage of the plasma membrane.