Abstract
Titanium dioxide (TiO(2) ) is generally regarded as a nontoxic and nongenotoxic white mineral, which is mainly applied in the manufacture of paper, paint, plastic, sunscreen lotion and other products. Recently, TiO(2) nanoparticles (TiO(2) NPs) have been demonstrated to cause chronic inflammation and lung tumor formation in rats, which may be associated with the particle size of TiO(2) . Considering the important role of activator protein-1 (AP-1) in regulating multiple genes involved in the cell proliferation and inflammation and the induction of neoplastic transformation, we aimed to evaluate the potency of TiO(2) NPs (≤ 20 nm) on the activation of AP-1 signaling pathway and the generation of reactive oxygen species (ROS) in a mouse epidermal cell line, JB6 cells. MTT, electron spin resonance (ESR), AP-1 luciferase activity assay in vitro and in vivo, and Western blotting assay were used to clarify this problem. Our results indicated that TiO(2) NPs dose-dependently caused the hydroxyl radical (·OH) generation and sequentially increased the AP-1 activity in JB6 cells. Using AP-1-luciferase reporter transgenic mice models, an obvious increased AP-1 activity was detected in dermal tissue after exposure to TiO(2) NPs for 24 h. Interestingly, TiO(2) NPs increased the AP-1 activity via stimulating the expression of mitogen-activated protein kinases (MAPKs) family members, including extracellular signal-regulated protein kinases (ERKs), p38 kinase, and C-Jun N-terminal kinases (JNKs). Of note, the AP-1 activation induced by TiO(2) NPs could be blocked by specific inhibitors (SB203580, PD98059, and SP 600125, respectively) that inhibit ERKs and p38 kinase but not JNKs. These findings indicate that ROS generation is involved in TiO(2) NPs-induced AP-1 activation mediated by MAPKs signal pathway.