Toxic Effects of Synthesized Bismuth Oxide/Reduced Graphene Oxide (Bi2O3/RGO) Nanocomposites in Two Distinct Mammalian Cell Lines: Role Oxidative Stress and Apoptosis

Abstract

Background: Researchers have shown substantial interest in bismuth oxide/reduced graphene oxide (Bi₂O₃/RGO) nanocomposites due to their superior features that are not achievable by each material alone. The growing applications and manufacturing of Bi₂O₃/RGO nanocomposites have raised concerns regarding their potential human health risks. This work was designed to explore the possible toxicity mechanisms of Bi₂O₃/RGO nanocomposites in two distinct mammalian cell lines, normal rat kidney cells (NRK52E) and human liver cancer cells (HepG2).

Methods: Bi₂O₃/RGO nanocomposites were prepared by a simple hydrothermal technique. X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and dynamic light scattering (DLS) were used to characterize the synthesized nanocomposites. The cytotoxicity of Bi₂O₃/RGO nanocomposites in NRK52E and HepG2 cells was examined by MTT cell viability assay. Reactive oxygen species (ROS) and glutathione (GSH) were measured as the biomarkers of oxidative stress. The apoptosis study was carried out by measuring several parameters, including cell cycle and caspase-3.

Results: High-quality Bi₂O₃/RGO nanocomposites of ≈33-38 nm size without impurities, where crystalline Bi₂O₃ particles are evenly attached to the RGO sheets. Bi₂O₃/RGO nanocomposites exhibit cytotoxic effects on NRK52E and HepG2 cells, which were dose- and time-dependent. Interestingly, NRK52E exhibited marginally higher vulnerability to Bi₂O₃/RGO nanocomposites compared to HepG2. Bi₂O₃/RGO nanocomposites also cause a dose-dependent increase in ROS production and a decrease in GSH levels. Exposing NRK52E and HepG2 cells to Bi₂O₃/RGO nanocomposites results in activation of the caspase-3 enzyme and chromosomal condensation. The apoptotic response of Bi₂O₃/RGO nanocomposites against both types of cells was further confirmed by AO-EB dual staining and altered cell cycle.

Conclusion: This study demonstrated that the toxicity of Bi₂O₃/RGO nanocomposites in both NRK52E and HepG2 cells is attributed to their ability to produce ROS, leading to apoptosis and cell cycle arrest as a consequence of oxidative stress.

Keywords: Bi2O3/RGO nanocomposites; Caspase-3; HepG2; NRK52E; ROS; apoptosis; health effects.