Molecular Mechanisms Of Immune Function Impaired Of Mouse Spleen Following Exposure To Titanium Dioxide Nanoparticles

With the rapid development of nanotechnology many kinds of nanomaterials aremanufactured and used in our daily life. As new types of photo-catalyst, anti-ultravioletlight agents, and photoelectric effect agents, titanium dioxide nanoparticles (TiO2NPs)are used in a variety of consumer products, including: toothpastes, sunscreens,cosmetics, food products, paints and surface coatings, etc. TiO2NPs can enter thehuman body through various routes such as respiratory tract, digestive tract and skin,and then induced toxicity. However, there are few studies on the immune functionimpaired of mouse spleen caused by exposure to TiO2NPs worldwide, and themolecular mechanisms are still unclear. In view of these, we investigated molecularmechanisms of immune function impaired of mouse spleen after intragastricadministrations with dose-effect and time-effect of TiO2NP exposure. Our findings willprovide an important theoretical basis for evaluating the impairment of splenic immunefunction of nanomaterials on animals and human.The main results are listed as follows:(1) To understand the chronic spleen injury, CR mice were exposed to TiO2NPs byintragastric administrations with2.5,5, and10mg/kg body weigh for90consecutivedays. The findings showed that TiO2NP exposure resulted in the significant increase ofspleen indices, histopathological changes and splenocyte apoptosis in the spleen.Especially, in these TiO2NP-treated mice, immunoglobulin, blood cells, platelets,haemoglobin, lymphocyte subsets (such as CD3+, CD4+, CD8+, B cell, natural killer cell)of mice were significantly decreased. Furthermore, TiO2NP exposure can significantlyincrease the levels of NF-kB, TNF-α, MIF, IL-2/-4/-6/-8/-10/-18/-1, INF-r, Bax andCYP1A1, whereas decrease the levels of Bcl-2and HSP70expression. These findings suggest that long-term exposure to low dose of TiO2NP may result in spleen injury andreduction of immune capacity, TiO2NP-induced injury in the spleen may result fromalteration of inflammatory and apoptotic cytokines expression.(2) The purpose of this study was to determine whether the protein kinaseMAPKs/PI3-K/Akt signaling pathways and transcription factors are activated prior to orconcurrent with COX-2up-regulation in mouse spleen following exposure to10mg/kgBW of TiO2NPs by the intragastric route for1590days. The study clearly showed thatTiO2NPs was deposited in the spleen and resulted in reactive oxygen speciesproduction, time-dependent splenic infammation, and necrosis, coupled with increasesin COX-2and prostaglandin E2expression, respectively. Furthermore, TiO2NPselevated the expressions of ERK, AP-1, CRE, Akt, JNK2, MAPKs, PI3-K, c-Jun, andc-Fos in the spleen with increased exposure duration, respectively. These fndingssuggested that TiO2NP-induced COX-2expression may be mediated predominantlythrough the induction of AP-1and CRE and that AP-1/CRE induction occurred via theMAPKs/PI3-K/Akt signaling pathways in the spleen.(3) Mice were continuously exposed to2.5,5, or10TiO2NPs mg/kg BW for90days with itragastric administration to investigate the immunomodulatory mechanismsin the spleen. The findings showed that TiO2NP exposure resulted in significantincreases of spleen and thymus indices, and titanium accumulation, in turn led tohistopathological changes and splenocyte apoptosis. Furthermore, the exposure of TiO2NPs could significantly increase the levels of inflammatory cytokines(MIF, IL-13andIFN-γ); Chemokines (MIP-1α, MIP-2, Eotaxin, MCP-1and IP-10); Adherence factor(VCAM-1); immune effect-related molecules (CD69, MHC, NKG2D, NKp46,2B4,PTPK1and PTP), whereas markedly decrease the levels of repair and apoptosis oflymphocyte-related cytokines (bFGF, Fasl and GzmB). The altered expression of theseimmunomodulatory-related molecules of spleen has much to do with TiO2NPs-inducedchronic injury.(4) Mice were exposed to2.5,5, and10mg/kg BW TiO2NPs by intragastricadministration for120consecutive days, and their splenic injuries and gene-expressedprofile were investigated. The findings showed that with increased doses, TiO2NPexposure resulted in increased spleen indices, impairment of immune capacity whichmarked by significant decreases in hematological parameters, lymphocyte subsets andaccompanied with excessive generation of reactive oxygen species and peroxidation of lipid, protein and DNA, and severe macrophage infiltration as well as apoptosis in thespleen. Importantly, microarray data showed significant alterations in the expressions of1041genes involved in immune/inflammatory response, apoptosis, oxidative stress,response to stress, metabolic process, ion transport, signal transduction, cellproliferation/division, cytoskeleton and translation in the10mg/kg TiO2NP exposedspleen.