Cytotoxicity and apoptosis induction of copper oxide-reduced graphene oxide nanocomposites in normal rat kidney cells

Copper oxide-reduced graphene oxide nanocomposites (CuO-rGO NCs) have received great attention from researchers due to their exceptional physicochemical properties that cannot be achieved by a single composition. CuO-rGO NCs have the potential to be used in diverse fields including agriculture, cosmetic, textile, the food industry, and biomedicine. The growing application and production of CuO-rGO NCs raises the concern of their effects on human and the environmental health. Knowledge on the toxicological response of CuO-rGO NCs in biological systems is scarce. This study was aimed to explore the cytotoxicity and apoptosis response of CuO-rGO NCs in normal rat kidney cells (NRR52E). CuO-rGO NCs was synthesized by a simple hydrothermal method using copper nitrate and graphene oxide (GO) as precursors. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and energy dispersive X-ray spectroscopy (EDS) confirmed the preparation of CuO-rGO NCs with high crystallinity, polygonal shape, smooth surface morphology. Besides, CuO nanoparticles were tightly anchored on rGO nanosheets. Biological results showed that CuO-rGO NCs induce a dose-dependent cytotoxicity in NRK52E cells evident by cell viability reduction and irregular cellular morphology. Fluorescent microscopic examination of 2,7-dichlorofluorescin probe showed that CuO-rGO NCs generate intracellular reactive oxygen species (ROS) in NRK52E cells. Acridine orange/ethidium bromide dual staining depicted that number of orange-red stained cells (apoptotic cells) increases with increasing concentration of CuO-rGO NCs. The 4′, 6-diamidino-2-phenylindole (DAPI) fluorescent staining exhibited that CuO-rGO NCs induce chromosomal condensation while normal-shaped nuclei were observed in the control cells. In cell cycle analysis, cells exposed to CuO-rGO NCs demonstrated significantly higher accumulation of apoptotic cells in subG1 phase. Altogether, we observed that CuO-rGO NCs induce cytotoxicity, ROS generation, and apoptosis in NRK52E cells. This preliminary study warrants future research to evaluate the potential mechanisms of CuO-rGO NCs toxicity at molecular level.