Molecular Mechanisms Of Kidney Injury Following Exposure To Titanium Dioxide Nanoparticles In Mice

Because of the unique characteristics of photocatalysis, anticorrosion and highstability of titanium dioxide nanoparticles (TiO2NPs), they have been widely used invarious areas such as cosmetics, paints, air purification, waste water treatment,sterilization and food additive, etc. Therefore，it is unavoidable for TiO2NPs to enter theenvironment and then enter the body through different routes to induce the potentialtoxicity. So the potential toxicity of TiO2NPs has become an urgent concern. Recently,numerous studies have been reported that TiO2NPs could lead to nephrotoxicity.However, the molecular mechanisms of nephrotoxicity are remained unclear. In view ofthis, we investigated the toxicological effects and related molecular mechanisms ofnephrotoxicity in mice after intragastric administrations with various doses of TiO2NPsuspensions for long-term. This study would provide an important theoretical basis forthe establish the evaluation system and standards of safe exposure for nanoparticles andsecurity applications of TiO2NPs．The main results are listed as follows:（1）TiO2NPs were shown to cause inflammatory in mice, however, the molecularmechanisms by which TiO2NPs exert theirs toxicity remains unclear. In an effort toexamine molecular mechanisms of infammation of the mouse kidney caused byintragastric administrations of TiO2NPs (2.5,5, and10mg/kg body weight) for90consecutive days, we assessed the expression levels of tumor necrosis factor-α,macrophage migration inhibitory factor, interleukin-2, interleukin-4, interleukin-6,interleukin-8, interleukin-10, interleukin-18, interleukin-1β, cross-reaction protein,transforming growth factor-β, interferon-γ, CYP1A1, heat shock protein70andhistopathological changes of kidney. The results showed that TiO2NPs wereaccumulated in the kidney, resulting in nephric inflammation, cell necrosis and dysfunction. The real-time quantitative RT-PCR and ELISA showed that TiO2NPs cansignifcantly increase the mRNA and protein expression of NF–κB, TNF–α, MIF, IL–2,IL-4, IL-6, IL-8, IL-10, IL-18, IL-1β, CRP, TGF-β, INF-γ and CYP1A1, however,significantly decrease the mRNA and protein expression of HSP70. These findingsimplied that TiO2NPs-induced nephric injury of mice might be associated withalteration of inflammatory cytokine expression and reduction of detoxification of TiO2NPs.（2）In order to further understand the molecular mechanisms induced by TiO2NPs, mice were exposed to2.5,5and10mg/kg by intragastric administrations of TiO2NPs for6consecutive months, we analysis biochemical parameters, histopathologicalchanges, various oxidative stress parameters, total GSH level and the oxidative andinflammatory pathway-related gene expression levels in mouse kidney. The findingsshowed that mice exhibited accumulation of reactive oxygen species and peroxidationof lipid, protein and DNA in the kidney, coupled with renal dysfunction, glutathionedepletion, inflammatory cell infiltration, fatty degeneration, and apoptosis. TiO2NPsdepressed expression of Nrf2and its target gene products, including heme oxygenase1,glutamate–cysteine ligase catalytic subunit and glutathione S-transferase, meanwhile,increased expression of oxidative and inflammatory pathways-related gene products likeNOX4, cyclooxygenase-2, and nuclear factor-κB. It implied that chronic TiO2NPexposure contributes to the pathogenesis of oxidative stress and inflammation in thekidney.(3) Numerous studies have demonstrated that TiO2NPs accumulated in the kidneyand caused corresponding damage. However, very little is known about the molecularmechanisms of multiple genes working together underlying this type of kidney injury inmice. Mice were exposed to2.5,5and10mg/kg TiO2NPs by intragastricadministration for90consecutive days, and their growth, element distribution, andoxidative stress in the kidney as well as kidney gene expression profile wereinvestigated using whole-genome microarray analysis technique. Our findings suggested that TiO2NPs resulted in significant reduction of renal glomerulus number,apoptosis, infiltration of inflammatory cells, tissue necrosis or disorganization of renaltubules, coupled with decreased body weight, increased kidney indices and unbalance ofelement distribution in mouse kidney tissue. Furthermore, microarray analysis showedsignificant alterations in the expression of1246genes in the10mg/kg TiO2NP-exposedkidney. Of the genes altered,1006genes were associated with immune/inflammatoryresponses, apoptosis, biological processes, oxidative stress, ion transport, metabolicprocesses, the cell cycle, signal transduction, cell component, transcription, translationand cell differentiation, respectively. Specifically, the vital up-regulation of Bcl6, Cfiand Cfd caused immune/inflammatory responses, the significant alterations ofCyp4a12a, Cyp4a12b, Cyp24a1, and Akric18expression resulted in severe oxidativestress, and great suppression of Axud1, Birc5, Ccl19, Ccl21and E2F1expression led torenal cell apoptosis. Axud1, Bcl6, Cf1, Cfd, Cyp4a12a, Cyp4a12b, Cyp24a1, Birc5,Ccl19, Ccl21and E2F1may be potential biomarkers of kidney toxicity caused by TiO2NP exposure.