Titanium dioxide nanoparticles induce COX-2 expression through ROS generation in human periodontal ligament cells

Abstract

Titanium dioxide nanoparticles (TiO 2 -NPs) are used to improve the aesthetic of toothpaste. While TiO 2 -NPs have been used safely in toothpaste products for a long time, there haven't been studies to determine whether absorption of TiO 2 -NPs by the mucous membranes in the mouth induces pathogenic conditions. Here, we assessed whether TiO 2 -NPs induce cyclooxygenase-2 (COX-2) and investigated the molecular mechanisms underlying the pro-inflammatory effect of TiO 2 -NPs on human periodontal ligament (PDL) cells. Treatment of PDL cells with TiO 2 -NPs led to induction of both COX-2 mRNA and protein expression. TiO 2 -NPs stimulated the nuclear translocation of nuclear factor-kappaB (NF-κB) as well as its DNA binding by inducing phosphorylation and subsequent degradation of the inhibitory protein IκBα in PDL cells. TiO 2 -NPs treatment resulted in rapid activation of extracellular signal-regulated kinase (ERK)1/2 and Akt, which could be upstream of NF-κB. Treatment of PDL cells with both the MEK1/2 inhibitor U0126 and the PI3K inhibitor LY294002 strongly attenuated TiO 2 -NPs-induced activation of NF-κB, and also the expression of COX-2. PDL cells treated with TiO 2 -NPs exhibited increased accumulation of intracellular reactive oxygen species (ROS). Pretreatment of cells with ROS scavenger N-acetyl cysteine (NAC) abrogated the stimulatory effect of TiO 2 -NPs on p65, p50, and COX-2 expression. In conclusion, ROS, concomitantly overproduced by TiO 2 -NPs, induce COX-2 expression through activation of NF-κB signaling, which may contribute to the inflammatory effect of PDL cells.

Adverse Outcome Pathways Associated with the Ingestion of Titanium Dioxide Nanoparticles—A Systematic Review

“…Increased cytotoxicity may be associated with a similar trend in other endpoints as apoptosis [72,104], ROS [72,82], genotoxicity [104] or inflammation [121]. Nevertheless, this is not a general rule.…”

“…Most papers (47/72) revealed increased cytotoxicity upon NPs exposure, whereas 18 did not show any effect. A dose-dependent effect was indicated in 16/72 [72,82,104,109,113,[116][117][118][119][120][121][122][123][124][125][126]. Furthermore, Gandamalla et al [82] showed that not only TiO 2 -NPs dose, but also its size, could influence its potential toxicity.…”

Possible Adverse Effects of Food Additive E171 (Titanium Dioxide) Related to Particle Specific Human Toxicity, Including the Immune System

“…Table 3 shows an overview of recent publications summarizing the effects of TiO 2 nanoparticles and E171 on various cell models along the oro-gastrointestinal route, as well as cell types found in organs, following the systemic distribution of these particles. Some studies on TiO 2 showed the ability to decrease cell viability and induce the formation of ROS, while others do not detect such effects [16,57,58,[120][121][122][123][124][125][126][127][128][129][130][131]. In some cases, the increase in ROS was accompanied by elevated oxidative stress levels and lipid peroxidation, which may lead to the induction of DNA damage and micronuclei [16,123,127,129,130].…”

“…Other publications reported membrane permeabilization, lysosomal dysfunction, and the initiation of autophagic processes, including a decrease in phagocytic rate and index and changes in the gene expression for autophagy proteins 1A/1B-light-chain-3 (LC-3) and Beclin-I [128,132]. Additional alterations on gene expression related to inflammatory pathways including extracellular signaling regulated kinase (ERK 1/2), Akt, as well as tumor and inflammation-related proteins e.g., p53, BAX, Cytochrome-c, Apaf-1, COX-2, transcription factors such as NF-kB, Nuclear factor erythroid 2-related factor 2 (Nrf2) and caspase-3, 9 have been published and suggest the onset of a tumor-like phenotype [120,128,129,133]. The stimulation of inflammatory processes is indicated by increased production and release of pro-inflammatory cytokines such as TNF-α and IL-8 [58].…”

“…E171 ingestion and absorption led to a decreased T-cell population in Peyer's patches, which may result in local immunosuppression and pro-inflammatory conditions [14,103]. T-cell receptor suppression associated increase in COX-2 gene expression elevates the production and release of prostaglandin-2 and acts as another mediator for inflammation and GPCR stimulation [120]. Gene expression analysis in vitro and in vivo showed significant alterations in GPCR-family, olfactory receptors, and DNA repair.…”