Intragastric exposure to titanium dioxide nanoparticles induced nephrotoxicity in mice, assessed by physiological and gene expression modifications

Abstract

Background: Numerous studies have demonstrated that titanium dioxide nanoparticles (TiO2 NPs) induced nephrotoxicity in animals. However, the nephrotoxic multiple molecular mechanisms are not clearly understood.

Methods: Mice were exposed to 2.5, 5 and 10 mg/kg TiO2 NPs by intragastric administration for 90 consecutive days, and their growth, element distribution, and oxidative stress in kidney as well as kidney gene expression profile were investigated using whole-genome microarray analysis technique.

Results: Our findings suggest that TiO2 NPs resulted in significant reduction of renal glomerulus number, apoptosis, infiltration of inflammatory cells, tissue necrosis or disorganization of renal tubules, coupled with decreased body weight, increased kidney indices, unbalance of element distribution, production of reactive oxygen species and peroxidation of lipid, protein and DNA in mouse kidney tissue. Furthermore, microarray analysis showed significant alterations in the expression of 1, 246 genes in the 10 mg/kg TiO2 NPs-exposed kidney. Of the genes altered, 1006 genes were associated with immune/inflammatory responses, apoptosis, biological processes, oxidative stress, ion transport, metabolic processes, the cell cycle, signal transduction, cell component, transcription, translation and cell differentiation, respectively. Specifically, the vital up-regulation of Bcl6, Cfi and Cfd caused immune/ inflammatory responses, the significant alterations of Axud1, Cyp4a12a, Cyp4a12b, Cyp4a14, and Cyp2d9 expression resulted in severe oxidative stress, and great suppression of Birc5, Crap2, and Tfrc expression led to renal cell apoptosis.

Conclusions: Axud1, Bcl6, Cf1, Cfd, Cyp4a12a, Cyp4a12b, Cyp2d9, Birc5, Crap2, and Tfrc may be potential biomarkers of kidney toxicity caused by TiO2 NPs exposure.

Figure 1

The (101) X-ray diffraction peak of anatase TiO₂ NPs. The average grain size was about 5 nm by calculation of Scherrer’s equation.

Figure 2

Transmission electron microscope image of anatase TiO₂ NPs particles. (a) TiO₂ NPs powder; (b) TiO₂ NPs suspended in HPMC solvent after incubation for 12 h; (c) TiO₂ NPs suspended in HPMC solvent after incubation for 24 h. TEM images showed that the sizes of the TiO₂ NPs powder or suspended in HPMC solvent for 12 h, 24 h were distributed from 5 to 6 nm, respectively.

Figure 3

Hydrodynamic diameter distribution of TiO₂ NPs in HPMC solvent using DLS characterization. (a) Incubation for 12 h; (b) Incubation for 24 h.

Figure 4

Histopathological observation of kidney caused by intragastric administration of TiO₂ NPs for 90 consecutive days. (a) Control, (b) 2.5 mg/kg TiO₂ NPs, (c) 5 mg/kg TiO₂ NPs, (d) 10 mg/kg TiO₂ NPs. Yellow arrows indicate apoptosis or vacuolization, green arrows indicate cell abscission, fatty degeneration or cell necrosis, green virtual circle indicates infiltration of inflammatory cells, blue arrows indicate tissue necrosis or disorganization of renal tubules. Yellow virtual circle indicates TiO₂ NPs aggregation. Arrow A spot is a representative cell that not engulfed the TiO₂ NPs, while arrow B spot denotes a representative cell that loaded with TiO₂ NPs. The right panels show the corresponding Raman spectra identifying the specific peaks at about 148 cm^-1.

Figure 5

Ultrastructure of kidney in male mice caused by intragastric administration of TiO₂ NPs for 90 consecutive days. (a) Control, (b) 2.5 mg/kg TiO₂ NPs, (c) 5 mg/kg TiO₂ NPs, (d) 10 mg/kg TiO₂ NPs. Yellow arrows indicate nucleus shrinkage, chromatin marginalization, green arrows indicate mitochondria swelling, and red arrows show presence of TiO₂ NPs. Arrow A spot is a representative cell that not engulfed the TiO₂ NPs, while arrow B spot denotes a representative cell that loaded with TiO₂ NPs. The right panels show the corresponding Raman spectra identifying the specific peaks at about 148 cm^-1.

Figure 6

Functional categorization of 1246 genes. Genes were functionally classified based on the ontology-driven clustering approach of PANTHER.