Effects Of Different Sized Nano-titanium Dioxide Particles On The Oxidative Stress And DNA Damage In Rats After Intratracheal Administration

Objective: Because of the unique electrical, thermal and opticalperformance, nanomaterials be widely used in many fields of pharmaceutical,chemical, computer, semiconductor, optical, environmental protection andcosmetics. Nano-titanium dioxide （Nano-TiO₂） is a sort of nanomaterials, asthe new photocatalysts are widely used in the degradation of environmentalpollutants. Process of production and use of nano-titanium dioxide into theenvironment, might be potential risk to the environment and organisms;Therefore, the study of nanomaterials on the body to produce health damage,and to explore its possible mechanism has a very important significance. Inthis paper, by the method of non-exposed tracheal injection, and simulatedabsorption pathway explore the different particle size of nano-titaniumdioxide,to induced oxidative stress and DNA damage, and provide referencedata for toxicological evaluation and safety applications of Nano-TiO₂.Methods:136healthy male Wistar rats were randomly divided into three groups of12. Experimental group were exposed to non-exposed tracheal injection,andwere given50nm and120nmTiO₂dose of2g/kg weight, the control groupreceived an equal volume of distilled water. Observed one week killed theanimals and detective the corresponding items.2Determination of Ti content of rats: microwave digestion and ICP-MSassay Ti content in rat liver, kidneys, lungs, and cortex tissues.3The histopathologic observation: Make histology of the liver, kidney,lung and hippocampus.Observe pathological changes of the light microscopeNano-TiO₂exposed organs.4Determination of DNA damage: using single-cell gel electrophoresis assay （SCGE）,and detect rat liver,kidney,lung,cortex, hippocampus cells OTMvalues change.5Determination of cellular oxidative damage indicators: detective thechange of rat liver, kidney, lung, cortex and hippocampus MDA content andSOD, GSH-Px activity.6Determination of level of intracellular reactive oxygen species（DCFH-DA） as a fluorescent probe, using flow cytometry to detect ratliver,kidney,lung,cortex, hippocampus. Intracellular of organization levels ofreactive oxygen species （ROS）.7Determination GADD45α gene mRNA expression: using polymerasechain reaction （PCR） method for detective changes of rat liver, kidney, lung,cortex, hippocampus cells DNA damage inducible protein45α （GADD45α）genethe mRNA expression level.Results:1Nano-TiO₂on the general condition of the ratsAll groups survived. At the first and second day, all groups showedreduce water drink and food intake and less activity. On the third day,all thegroups returned to normal, the rest no abnormal changes. The weight of ratsincrease normally.There are no significant difference in the exposure groupand control group.2Nano-TiO₂on Ti content of rat tissuesNano-titanium dioxide exposure in rat liver, kidney, lung, cerebral cortextissue Ti content were significantly increased （P <0.05）. After50nmTiO₂exposure, the Ti content in the cortical tissue was significantly higher than120nm TiO₂group （P <0.05）. Despite the Ti content of the liver, kidney, lungtissue are elevated, but no statistically significant.3Nano-TiO₂on pathological changes in ratsAfter Nano-titanium dioxide exposure, the rat liver, kidney, lung, andhippocampus were varying degrees of pathological changes. Treated rats livertissue cell disorder, edema, increased cell volume, cytoplasmic vacuolization,and inflammatory cells in some areas flocks necrosis; kidney tubular edema, renal capsule increases, and necrosis, glomerular atrophy, the gap increaseschanges; lung tissue appears to thickening of the alveolar septa, connectivetissue increased, and fibrous tissue proliferation; hippocampal tissue nucleicontraction deformation, irregular shapes, heterochromatin and euchromatintriangle eosinophils increased changes. Degree of pathological changes of theabove-mentioned organizations, in50nmTiO₂exposure group compared120nmTiO₂exposure group.4Nano-TiO₂on DNA damage in ratsCompared with the control group, the rat liver, the kidneys,the lungs,thecortex and the hippocampus cells of treatment group OTM significantlyincreased （P <0.05）. The group of50nmTiO₂, kidney, hippocampus cells OTMvalue significantly higher than the120nm TiO₂exposure group （P <0.05）;liver, cortical cells OTM values increased, but no statistically significant.5Nano-TiO₂on the level of oxidative stress in rats5.1Nano-TiO₂intracellular ROS levels in rat tissuesCompared with the control group,rat liver,kidney,lung,cortex andhippocampus cells of treatment groups average ROS level was significantlyincreased （P <0.05）.50nmTiO₂after exposure, kidney, hippocampal cells ROSlevels significantly higher than120nm TiO₂exposure group （P <0.05）; liver,Despite the increase in ROS level of the cortical cells, but no statisticallysignificant.5.2Nano-TiO₂rat tissue MDA content and SOD, GSH-Px activityCompared with the control group, the MDA content in rat liver wassignificantly increased SOD, GSH-Px activity of treatment groups weresignificantly lower （P <0.05）.50nmTiO₂exposure, MDA content wassignificantly higher than120nm TiO₂exposure group （P <0.05）, SOD,GSH-Px activity declined, but no statistically significant.Compared with the control group, the MDA content in the rat kidneysignificantly increased SOD, GSH-Px activity of treatment groups weresignificantly lower （P <0.05）.50nmTiO₂exposure, GSH-Px activity wassignificantly below120nm TiO₂exposure group （P <0.05）, SOD activity decreased, but no statistically significant, and no significant change in MDAcontent.Compared with the control group, the MDA content in rat lung tissue wassignificantly higher SOD, GSH-Px activity of treatment groups weresignificantly lower （P <0.05）. On the treatment group of50nm TiO₂, MDAcontent was significantly increase higher than120nm TiO₂treantmentexposure group （P <0.05）, SOD, GSH-Px activity declined, but no statisticallysignificant.Compared with the control group, the MDA content in rat corticalsignificantly increased SOD, GSH-Px activity of treatment groups wassignificantly lower （P <0.05）.50nmTiO₂exposure group compared120nmTiO₂exposure group change was not statistically significant.Hippocampal MDA content was significantly higher compared with thecontrol group, SOD, GSH-Px activity were significantly lower （P <0.05）.50nmTiO₂exposure, MDA content was significantly higher than120nm TiO₂exposure group （P <0.05）, SOD, GSH-Px activity declined, but no statisticallysignificant.6Nano-TiO₂impact on the the rat tissues GADD45α gene mRNAexpression levelsCompared with the control group, the rat liver, kidney, lung, cortical andhippocampal cells of treatment groups GADD45α gene mRNA expressionlevels were significantly increased （P <0.05）. There were no significantdifferences between the50nm TiO₂treatment group to120nm TiO₂treatmentgroup.Conclusions:1After Nano-TiO₂exposured, Ti element can distribute in the variousorgans including liver, kidney, lung and brain of the rat, and make varyingdegrees of pathological changes to the organs above.2After Nano-TiO₂exposured, Ti can cause DNA damage, oxidativestress and GADD45α mRNA over expression.3With Nano-TiO₂particle size decreases, the damaging effects of rats is increased, but the relationship between the Nano-TiO₂particle size and itsdamaging effects need to be further in-depth study.