Cytotoxicity and autophagy induction by graphene quantum dots with different functional groups

Craphene quantum dots (CQDs) possess great potential in various applications due to their superior physicochemical properties and wide array of available surface modifications. However, the toxicity of GQDs has not been systematically assessed, thus hindered their further development; especially, the risk of surface modifications of GQDs is largely unknown. In this study, we employed a lung carcinoma A549 cells as the model to investigate the cytotoxicity and autophagy induction of three types GQDs, including cGQDs COOH-CQDs), hGQDs (OH-GQDs), and aGQDs (NH2-GQDs). The results showed hGQDs was the most toxic, as significant cell death was induced at the concentration of 100 mu g/mL, determining by WST-1 assay as well as Annexin-V-FITC/PI apoptosis analysis, whereas cGQDs and aGQDs were non-cytotoxic within the measured concentration. Autophagy detection was performed by TEM examination, LC3 fluorescence tracking, and Westernblot. Both aGQDs and hGQDs induced cellular autophagy to various degrees except for cGQDs. Further analysis on autophagy pathways indicated all GQDs significantly activated p-p38MAPK; p-ERK1/2 was inhibited by aGQDs and hGQDs but activated by cGQDs. p-JNK was inhibited by aGQDs and cGQDs, while activated by hGQDs. Simultaneously, Akt was activated by hGQDs but inhibited by aGQDs. Inhibition of autophagy by 3-MA significantly increased the cytotoxicity of CQDs, suggesting that autophagy played a protective role against the toxicity of GQDs. In conclusion, cGQDs showed excellent biocompatibility and may be considered for biological applications. Autophagy induction may be included in the health risk assessment of GQDs as it reflects the stress status which may eventually lead to diseases. (C) 2018 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.