Immunotoxicity of titanium dioxide nanoparticles via simultaneous induction of apoptosis and multiple toll-like receptors signaling through ROS-dependent SAPK/JNK and p38 MAPK activation

Background: Titanium dioxide nanoparticles (TiO ₂ NPs) represent a scientific breakthrough in the areas of biological and medicinal applications. Interaction of TiO ₂ NPs with components of innate immune system remains elusive. Aim: This study explored in vitro immunotoxicity of murine macrophage RAW 264.7 to TiO ₂ NPs (20 nm, negative charge) and its underlying molecular mechanism by way of immunoredox profiling. Materials and methods: In this study, chemically synthesized BSA-functionalized TiO ₂ NPs (20 nm, negative charge) were characterized and immunotoxicity was investigated on RAW 264.7 cells. Results: We found that reactive oxygen species levels significantly increased with increasing nitric oxide production, whereas depleting endogenous antioxidant super oxide dismutase as well as nuclear factor erythroid 2-related factor 2 (Nrf2) protein levels. Furthermore, NPs exposure increased the expression of apoptotic factors such as BAX, BIM, and PUMA with disruption of mitochondrial membrane potential (Δψ _m ) that lead to decrease in immunocytes. Molecular immune profiling revealed the activation of multiple toll-like receptors (TLRs) 4/9/12/13 simultaneously with the phosphorylation of p-p38MAPK and p-SAPK/c-Jun N-terminal kinase (JNK) compared to untreated control. Conclusion: Collectively, this study shows that the molecular nature of TiO ₂ ^SA20(-) NP-induced immunotoxicity in RAW 264.7 macrophage is simultaneous induction of immunocyte apoptosis and multiple TLRs signaling through oxidative stress-dependent SAPK/JNK and p38 mitogen-associated protein kinase activation. This is the first study to address newer molecular mechanism of TiO ₂ ^SA20(-) NP-induced immunotoxicity.