الفهرس 
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Abstract
Titanium dioxide nanoparticles (TiO2NPs) are among the most produced in the world. They have been widely applied in numerous products including pigments, paints, paper, plastics, toothpaste, food colorants, nutritional supplements and cosmetics that may raising the potential health risk problems. Studies on the toxicity of TiO2 NPs have shown that they could lead to toxic effects on human and environment.
The aim of this study was to evaluate the effects of oral administration of two different doses of Titanium dioxide nanoparticles (TiO2 NPS) on submandibular salivary gland of adult male albino rats by histological and immunohistochemical evaluation.
Material and methods:
A total number of 50 adult male albino rats (weighing about ±200-250) were used and were classified into four main groups: group 1(control group), group 2 was divided into 2 subgroups: Subgroup (2A) was received TiO2 NPs a daily dose of 10 mg/kg/day for 14 days and subgroup (2B) was received TiO2 NPs a daily dose of 50 mg/kg/day for 14 days, group 3was divided into 2 subgroups: Subgroup (3A) was received TiO2 NPs a daily dose of 10 mg/kg/day for one month and subgroup( 3B) was received TiO2 NPs a daily dose of 50 mg/kg/day for one month & group IV (recovery group) was received TiO2 NPs a daily dose of 10 mg/kg/day for one month & was allowed for one month of recovery after TiO2 NPs withdrawal. All animals were sacrificed, SMSGs were dissected, specimens were prepared and sections were examined histologically by H&E and Masson’s trichrome stain and immunohistochemically by anti-proliferating cell nuclear antigen (PCNA), caspase-3 and Alpha Smooth Muscle Actin (α-SMA). Image analysis was performed in which PCNA, caspase-3 and α-SMA immunoreactivity was measured as area fraction and then statistical analysis was carried out by using Kruskal-Wallis and Mann Whitney test for analysis of data.
Results:
Hematoxylin and Eosin Stain Results: Revealed progressive atrophy and degenerative changes in acini, striated ducts & granular convoluted tubules (GCTs). Compared to group Me, group 2 showed acinar and ductal vacuolization, loss of the acinar architecture, apoptotic nuclei and discontinuity of the epithelial lining with retained coagulum in the granular convoluted tubules (GCTs). These changes were found to be exaggerated in-group 3 accompanied by ductal destruction and completely loss of gland architecture. In contrast, mild recovery of the size of serous acini was observed in group4 (Recovery Group).
Masson’s trichrome Stain Results: Masson’s trichrome sections of SMSG of the current study revealed a dramatically increasing of the amount of blue-stained collagen fibers from group II to group III in compared to control group. The collagen fibers in recovery group exhibited degree of hyaline degeneration.
PCNA Immunohistochemical Results: Immunologically there was a statistically high significant increase in PCNA positive nuclear immunoreaction.
Caspase-3 Immunohistochemical Results: Immunohistochemical results revealed a high significant increase in caspase-3 cytoplasmic immunoreaction.
Alpha-SMA Immunohistochemical Results: Immunohistochemical results revealed a statistically high significant increase in α-SMA positive cytoplasmic immunoreaction of myoepithelial cells at the periphery of serous acini, striated ducts and granular convoluted ducts from group II to group IV.
Image Analysis Results: There was an increase of the mean labeling index of PCNA, caspase-3 and α-SMA area fraction from group 2 to group 4 (recovery group). It was found that the duration of exposure and the dose of TiO2 NPs were the significant predictors that affected PCNA, caspase-3 and α-SMA level. There was persistence of changes triggered by TiO2 NPs.
Conclusion: TiO2 NPs could produce apparent histological alterations and toxicity in SMSG structure of male albino rat at the level of histological and immunohistochemical examinations. These changes were both time and dose dependent. In addition, these changes were persistent, which did not regress after one month following cessation of TiO2 NPs intake only some serous acini exhibited mild recovery of their size.
Recommendation: It is recommended to reduce the use of TiO2 NPs as an additive in food and toothpaste and increase knowledge and ongoing study to find protective measures and cures for diseases associated with nanoparticles exposure. Further studies are requisite to evaluate the effect of withdrawal of TiO2NPs for a longer period of observation and estimate the required time for fully improvement of this toxicity.