In vitro cytotoxicity evaluation of graphene oxide from the peroxidase-like activity perspective

In this study, PEGylated graphene oxide (PEG-GO)-hemin composite structure was constructed. Hemin in the form of nanoscaled aggregates were immobilized on PEG-GO sheets by the π-π stacking super-molecular interaction. Via catalyzing the oxidation of chromogenic substrates, we elicited the obtained PEG-GO-Hemin composite sheets have much higher peroxidase-like activity compared to hemin or PEG-GO alone, which is due to the introduction of enzyme active center of hemin with high dispersity, the excellent affinity to organic substrate through π-π stacking and/or electrostatic adsorption and the rapid electron transfer capability of PEG-GO. Similarly, PEG-GO-Hemin was found to be able to catalyze the oxidation of low density lipoprotein (LDL) by H₂O₂, resulting in toxicity to porcine iliac endothelial cells (PIECs) in vitro. Furthermore, we also demonstrated that PEG-GO sheets showed enhanced peroxidase activity when met hemin containing proteins including hemoglobin and cytochrome c. High glucose level (HG) in human umbilical vein endothelial cells (HUVECs) can induce cytochrome c to release from the respiratory chain, thus applying PEG-GO under HG condition could cause a much higher peroxidase-like activity, resulting in the production of hydroxyl radical (OH) and cytochrome c radical (cytochrome c), which eventually enhance the apoptosis. These results suggest GO has potential hazard for biomedical applications in some pathophysiological conditions.