# Novel Synthesis of Titanium Oxide Nanoparticles: Biological Activity and Acute Toxicity Study

Authors: Moaaz T. Hamed; Basant A. Bakr; Yahya H. Shahin; Bassma H. Elwakil; Marwa M. Abu-Serie; Faizah S. Aljohani; Adnan A. Bekhit
Journal: Bioinorganic Chemistry and Applications
 (2021)

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## Abstract

Titanium oxide nanoparticles (TiO2 NPs) have been attracting numerous research studies due to their activity; however, there is a growing concern about the corresponding toxicity. Here in the present study, titanium oxide nanoparticles were newly synthesized using propolis extract followed by antimicrobial activity, cytotoxicity assay using human cancer cell lines, and acute toxicity study. The physicochemical characterization of the newly synthesized TiO2 NPs had average size = 57.5 nm, PdI = 0.308, and zeta potential = −32.4 mV. Antimicrobial activity assessment proved the superior activity against Gram-positive compared to Gram-negative bacteria and yeast (lowest MIC values 8, 32, and 32, respectively). The newly synthesized TiO2 NPs showed a potent activity against the following human cancer cell lines: liver (HepG-2) (IC50 8.5 µg/mL), colon (Caco-2), and breast (MDA-MB 231) (IC50 11.0 and 18.7 µg/mL). In vivo acute toxicity study was conducted using low (10 mg/kg) and high (1000 mg/kg) doses of the synthesized TiO2 NPs in albino male rats. Biochemistry and histopathology of the liver, kidney, and brain proved the safety of the synthesized TiO2 NPs at low dose while at high dose, there was TiO2 NPs deposit in different vital organs except the cerebral tissue.


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## Body

## 1. Introduction

Nanoparticles (NPs) are organic or inorganic matters with size range of 1–100 nm. NPs can be synthesized through chemical, physical, and natural (green) methods [1]. In spite of the marvelous applications of inorganic nanoparticles, their induced nanotoxicity has a significant public concern [2]. Nanoparticles have several unique characteristics; the most important factor is the large surface area/mass that has a tremendous impact on the corresponding toxicity due to the presence of reactive atoms on the NPs surfaces [3]. Among inorganic nanoparticles, titanium oxide (TiO2) nanoparticles have been used in many applications such as textile, plastics, cosmetics industries, and food packaging [4]. Previously, TiO2 NPs have been synthesized using different physicochemical methods such as microemulsion, chemical precipitation, hydrothermal crystallization, and sol-gel methods [5]. Physicochemical methods require pressure, high temperature, and toxic chemicals which restrain their potential uses [6]. Therefore, eco-friendly approaches have been invented to produce NPs on larger scale with lesser toxicity [7]. Biological extracts are the most appropriate reducing agents in the green (eco-friendly) approach in view of the fact that they act not only as reducing agent but also in stabilizing the formed nanoparticle [8].In the light of the above, many researchers explored the potential synthesis of TiO2 NPs using green approaches. This was simply achieved through mixing TiO2 salt with the biological extract and then observing the color change that can be affirmed by spectroscopic analyses [4]. Among those potent biological extracts, propolis is a resinous mixture collected by honeybees from the plant exudates to use in hives’ construction and adaptation [9]. Propolis extract has a broad range of pharmacological activities like anti-inflammatory, antitumour, antioxidant, hepatoprotective, and antimicrobial properties based on its rich polyphenolic compounds [10]. Propolis extract is rich in flavonoids and phenolic compounds which could attribute in the reduction and biological synthesis of metal nanoparticles [11]. Hence, the novelty embedded in the present study is that Egyptian propolis extract was used to synthesize TiO2 NPs. The newly synthesized TiO2 NPs were characterized using TEM, FTIR, and DLS, and their antimicrobial activity and cytotoxicity (against human cancer cell lines) were evaluated. Furthermore, acute toxicity study was performed to ensure its safety and prove their potential biomedical applications.


## 2. Materials and Methods

### 2.1. Microorganisms

Different Gram-positive, Gram-negative, and yeast strains were tested, namely, methicillin-resistantStaphylococcus aureus (MRSA), Staphylococcus epidermidis, Candida albicans, Klebsiella pneumoniae, Pseudomonas aeruginosa, Listeria monocytogenes, Proteus vulgaris, and Acinetobacter baumannii. All the strains were kindly identified and provided by Surveillance Microbiology Department’s strain bank of Al-Shatby Pediatric Hospital, Alexandria.


### 2.2. Chemicals and Raw Material

The microbial culture media and titanium (IV) oxide (232033 anatase, 99.8% trace metals basis, CAS Number 1317-70-0) were purchased from Sigma-Aldrich (MO, USA). Reagents ofin vivo study were purchased from BASF Co. (Ludwigshafen, Germany). All the solvents (analytical grade) used in the present work were purchased from well-known suppliers.Propolis samples were collected during summer 2019, from Tanta (30.79611491◦N, 30.99517822◦E), Egypt. The samples were collected and kept in sterile brown glass containers until further use.


### 2.3. Propolis Extraction

Propolis was cut into pieces and then extracted (30%w/v) using maceration technique by 99% ethanol for 4 days in dark container with continuous stirring and then sonified for 1 h at 72°C [12].


### 2.4. GC/MS Analysis

2 mg of the dried propolis extract was mixed with 20µl pyridine and 30 µl N,0-bis(trimethylsilyl)trifluoroacetamide (BSTFA); then the mixture was heated for 20 min at 80°C. The heated mixture was diluted with pyridine (100 µl) and then analyzed by GC/MS (7890A/5975C Agilent, USA) [13]. Compounds identification was achieved through Wiley 138 and Nist 98 libraries including mass spectra [9].


### 2.5. Nanoparticles Synthesis

The newly synthesized TiO2 NPs were prepared according to Krishnasamy et al. [14] with modifications. In order to form TiO2 NPs, 10 ml of propolis extract (500 mg/ml) was added to 20 ml of 2 mM titanium oxide aqueous solution for 24 hrs with continuous stirring. Titanium oxide nanoparticles were centrifuged at 800 ×g for 30 min and then stored for further use.


### 2.6. Physicochemical Characterization of the Synthesized Nanoparticles

Dynamic light scattering (DLS) technique was used to evaluate the zeta potential, particle size (PS), and polydispersity index (PDI) of the synthesized nanoparticles using Malvern Zetasizer according to Elnaggar et al. [9]. FTIR spectrum of the synthesized nanoparticles was analyzed using Perkin-Elmer R79521 (USA) FTIR with 2 cm−1 resolution and wave number 4000 cm−1 to 450 cm−1 during 64 scans [15]. The shape, size, and ultrastructure of the synthesized TiO2 NPs were examined using TEM (JEM-100 CX, JOEL, USA) (resolution 3 nm at 30 kV) [15].


### 2.7. Antimicrobial Activity of the Synthesized TiO2 NPs

The synthesized TiO2 NPs were evaluated for antimicrobial activity against different microorganisms using the disc-diffusion method. Further antimicrobial activity was evaluated by microdilution method to estimate the minimum inhibitory concentration (MIC) for the synthesized TiO2 NPs [16]. All the tests were done in triplicate.


### 2.8. Cytotoxicity Assay Using Human Cancer Cell Lines

Cytotoxicity effect of the synthesized TiO2 NPs was assayed using three human cancer cell lines (colon, liver, and breast cell line). Colon cancer cell line (Caco-2) was cultured in DMEM (Lonza, USA) contained with 10% FBS while liver cancer cell line (HepG-2) and triple negative breast cancer cell line (MDA-MB 231) were cultured in RPMI-1640 (Lonza, USA) supplemented with 10% FBS. All cancer cells (4 × 103 cells/well) were seeded in sterile 96-well plates. After 24 hrs, serial concentrations of the tested nanoparticles (40, 20, 10, 5, and 2.5 μg/ml) were incubated with three cancer cell lines for 72 h at 37°C in 5% CO2 incubator. After the incubation period, cancer cell viability was assayed [17]. After 24 hrs, 20 μl of 5 mg/ml MTT (Sigma, USA) was added to each well and the plates were incubated at 37°C for 3 hrs. Then MTT solution was removed, 100 μl DMSO was added, and the absorbance of each well was measured with a microplate reader (BMG LabTech, Germany) at 570 nm for estimation the inhibition in cancer cell growth through 72 hrs of incubation with TiO2 NPs. The half-maximal inhibitory concentration (IC50) values were calculated using the GraphPad Instat software. Furthermore, cellular morphological changes before and after treatment with the synthesized TiO2 NPs were investigated using phase contrast inverted microscope with a digital camera (Olympus, Japan).


### 2.9. In Vivo Acute Toxicity Study

#### 2.9.1. Rats and Administrative Dose

The present study was done to evaluate thein vivo cytotoxic effect of the prepared TiO2 NPs. The Animal Care and Use Committee (ACUC), Faculty of Science, Alexandria University, approved the current acute toxicity study which was in accordance with the International Principles for Laboratory and Care of the European Community Directive of 1986, AU/04/20/01/28/9/02. Thirty male albino rats (Rattus norvegicus albinus), with average body weight of 390 ± 30 g (4 months old), were divided, 10 rats/group, and kept in a cage with regular 12 h light/12 h dark cycle under conventional conditions of temperature and humidity for 30 days in average temperature (25 ± 2°C) inside an adequately ventilated room with free access to food and water ad libitum [18]. The rats were divided according to the different nanoparticles doses as follows.Treated animals received intraperitoneal injections with different doses of TiO2 NPs every 24 hrs for two days, and control group received a dose of 0.9% sodium chloride.Group 1: served as control, rats received 0.15 ml sodium chlorideGroup 2: rats received 0.15 ml TiO2 NPs (10 mg/kg body weight)Group 3: rats received 0.15 ml TiO2 NPs (1000 mg/kg body weight)


#### 2.9.2. Experimental Protocol

Animal groups underwent anesthesia via intraperitoneal injection with ketamine hydrochloride (100 mg/kg) and xylazine (10 mg/kg). 48 hrs after injection, histopathological, blood biochemical, and bioaccumulation studies were evaluated. The survival rate of each group was monitored and recorded for 30 days. Sodium pentobarbital (40 mg/kg) was used at the end of the experiment to anesthetize the rats via intraperitoneal injection [18].


#### 2.9.3. Blood Biochemical Study

Different biochemical tests were done in order to evaluate the cytotoxic effect of the synthesized TiO2 NPs. Rats were weighed (n = 5) and blood was sampled through the retro-orbital plexus. Each blood sample was centrifuged (20 min at 4000g) to collect the sample serum. Liver functions (alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bilirubin, albumin, alkaline phosphatase, and gamma-glutamyl transferase (GGT)), kidney functions (uric acid, creatinine, and urea), total cholesterol (high- and low-density lipoproteins), glucose, and total protein tests were determined using an automated biochemical analyzer [19].


#### 2.9.4. Histopathological Study

(1) Light Microscopic Examination. The liver, kidney, and brain were excised and weighted immediately after sacrifice. Each tissue was washed with normal saline and then fixed with 10% formalin, and then each sample was dehydrated using ethanol. Tissue samples were embedded in paraffin, cut into 5 µm thick sections, and then deparaffinized and stained with Ehrlich’s hematoxylin and eosin (H & E) stain [20].(2) Fluorescence Microscopic Examination. Fluorescence microscopic evaluation was performed using confocal laser scanning microscope (LSM 700) to qualitatively detect the nanoparticles biodistribution in different tissues. Paraffin tissue sections were dehydrated in descending ethanol concentration and then embedded in distilled water. Triton X (0.1%) was added to each tissue sample for 10 minutes; then the samples were washed twice with PBS buffer. Tissue sections were stained with Hoechst stain for 10 minutes to visualize the cell nucleus. The tissue samples were washed in PBS, dehydrated in alcohol and xylol, and then examined (laser excitation wavelengths between 543 and 488 nm) [21, 22].


### 2.10. Statistical Analyses

Results were the mean of three trials and were expressed as means ± standard deviation. One-way analysis of variance (ANOVA) and Tukey’s test (p<0.05) were used to detect differences between the groups with the SPSS 13.0 statistical software. The means of the treatments were considered significant when 0.05>p>0.01.


## 2.1. Microorganisms

Different Gram-positive, Gram-negative, and yeast strains were tested, namely, methicillin-resistantStaphylococcus aureus (MRSA), Staphylococcus epidermidis, Candida albicans, Klebsiella pneumoniae, Pseudomonas aeruginosa, Listeria monocytogenes, Proteus vulgaris, and Acinetobacter baumannii. All the strains were kindly identified and provided by Surveillance Microbiology Department’s strain bank of Al-Shatby Pediatric Hospital, Alexandria.


## 2.2. Chemicals and Raw Material

The microbial culture media and titanium (IV) oxide (232033 anatase, 99.8% trace metals basis, CAS Number 1317-70-0) were purchased from Sigma-Aldrich (MO, USA). Reagents ofin vivo study were purchased from BASF Co. (Ludwigshafen, Germany). All the solvents (analytical grade) used in the present work were purchased from well-known suppliers.Propolis samples were collected during summer 2019, from Tanta (30.79611491◦N, 30.99517822◦E), Egypt. The samples were collected and kept in sterile brown glass containers until further use.


## 2.3. Propolis Extraction

Propolis was cut into pieces and then extracted (30%w/v) using maceration technique by 99% ethanol for 4 days in dark container with continuous stirring and then sonified for 1 h at 72°C [12].


## 2.4. GC/MS Analysis

2 mg of the dried propolis extract was mixed with 20µl pyridine and 30 µl N,0-bis(trimethylsilyl)trifluoroacetamide (BSTFA); then the mixture was heated for 20 min at 80°C. The heated mixture was diluted with pyridine (100 µl) and then analyzed by GC/MS (7890A/5975C Agilent, USA) [13]. Compounds identification was achieved through Wiley 138 and Nist 98 libraries including mass spectra [9].


## 2.5. Nanoparticles Synthesis

The newly synthesized TiO2 NPs were prepared according to Krishnasamy et al. [14] with modifications. In order to form TiO2 NPs, 10 ml of propolis extract (500 mg/ml) was added to 20 ml of 2 mM titanium oxide aqueous solution for 24 hrs with continuous stirring. Titanium oxide nanoparticles were centrifuged at 800 ×g for 30 min and then stored for further use.


## 2.6. Physicochemical Characterization of the Synthesized Nanoparticles

Dynamic light scattering (DLS) technique was used to evaluate the zeta potential, particle size (PS), and polydispersity index (PDI) of the synthesized nanoparticles using Malvern Zetasizer according to Elnaggar et al. [9]. FTIR spectrum of the synthesized nanoparticles was analyzed using Perkin-Elmer R79521 (USA) FTIR with 2 cm−1 resolution and wave number 4000 cm−1 to 450 cm−1 during 64 scans [15]. The shape, size, and ultrastructure of the synthesized TiO2 NPs were examined using TEM (JEM-100 CX, JOEL, USA) (resolution 3 nm at 30 kV) [15].


## 2.7. Antimicrobial Activity of the Synthesized TiO2 NPs

The synthesized TiO2 NPs were evaluated for antimicrobial activity against different microorganisms using the disc-diffusion method. Further antimicrobial activity was evaluated by microdilution method to estimate the minimum inhibitory concentration (MIC) for the synthesized TiO2 NPs [16]. All the tests were done in triplicate.


## 2.8. Cytotoxicity Assay Using Human Cancer Cell Lines

Cytotoxicity effect of the synthesized TiO2 NPs was assayed using three human cancer cell lines (colon, liver, and breast cell line). Colon cancer cell line (Caco-2) was cultured in DMEM (Lonza, USA) contained with 10% FBS while liver cancer cell line (HepG-2) and triple negative breast cancer cell line (MDA-MB 231) were cultured in RPMI-1640 (Lonza, USA) supplemented with 10% FBS. All cancer cells (4 × 103 cells/well) were seeded in sterile 96-well plates. After 24 hrs, serial concentrations of the tested nanoparticles (40, 20, 10, 5, and 2.5 μg/ml) were incubated with three cancer cell lines for 72 h at 37°C in 5% CO2 incubator. After the incubation period, cancer cell viability was assayed [17]. After 24 hrs, 20 μl of 5 mg/ml MTT (Sigma, USA) was added to each well and the plates were incubated at 37°C for 3 hrs. Then MTT solution was removed, 100 μl DMSO was added, and the absorbance of each well was measured with a microplate reader (BMG LabTech, Germany) at 570 nm for estimation the inhibition in cancer cell growth through 72 hrs of incubation with TiO2 NPs. The half-maximal inhibitory concentration (IC50) values were calculated using the GraphPad Instat software. Furthermore, cellular morphological changes before and after treatment with the synthesized TiO2 NPs were investigated using phase contrast inverted microscope with a digital camera (Olympus, Japan).


## 2.9. In Vivo Acute Toxicity Study

### 2.9.1. Rats and Administrative Dose

The present study was done to evaluate thein vivo cytotoxic effect of the prepared TiO2 NPs. The Animal Care and Use Committee (ACUC), Faculty of Science, Alexandria University, approved the current acute toxicity study which was in accordance with the International Principles for Laboratory and Care of the European Community Directive of 1986, AU/04/20/01/28/9/02. Thirty male albino rats (Rattus norvegicus albinus), with average body weight of 390 ± 30 g (4 months old), were divided, 10 rats/group, and kept in a cage with regular 12 h light/12 h dark cycle under conventional conditions of temperature and humidity for 30 days in average temperature (25 ± 2°C) inside an adequately ventilated room with free access to food and water ad libitum [18]. The rats were divided according to the different nanoparticles doses as follows.Treated animals received intraperitoneal injections with different doses of TiO2 NPs every 24 hrs for two days, and control group received a dose of 0.9% sodium chloride.Group 1: served as control, rats received 0.15 ml sodium chlorideGroup 2: rats received 0.15 ml TiO2 NPs (10 mg/kg body weight)Group 3: rats received 0.15 ml TiO2 NPs (1000 mg/kg body weight)


### 2.9.2. Experimental Protocol

Animal groups underwent anesthesia via intraperitoneal injection with ketamine hydrochloride (100 mg/kg) and xylazine (10 mg/kg). 48 hrs after injection, histopathological, blood biochemical, and bioaccumulation studies were evaluated. The survival rate of each group was monitored and recorded for 30 days. Sodium pentobarbital (40 mg/kg) was used at the end of the experiment to anesthetize the rats via intraperitoneal injection [18].


### 2.9.3. Blood Biochemical Study

Different biochemical tests were done in order to evaluate the cytotoxic effect of the synthesized TiO2 NPs. Rats were weighed (n = 5) and blood was sampled through the retro-orbital plexus. Each blood sample was centrifuged (20 min at 4000g) to collect the sample serum. Liver functions (alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bilirubin, albumin, alkaline phosphatase, and gamma-glutamyl transferase (GGT)), kidney functions (uric acid, creatinine, and urea), total cholesterol (high- and low-density lipoproteins), glucose, and total protein tests were determined using an automated biochemical analyzer [19].


### 2.9.4. Histopathological Study

(1) Light Microscopic Examination. The liver, kidney, and brain were excised and weighted immediately after sacrifice. Each tissue was washed with normal saline and then fixed with 10% formalin, and then each sample was dehydrated using ethanol. Tissue samples were embedded in paraffin, cut into 5 µm thick sections, and then deparaffinized and stained with Ehrlich’s hematoxylin and eosin (H & E) stain [20].(2) Fluorescence Microscopic Examination. Fluorescence microscopic evaluation was performed using confocal laser scanning microscope (LSM 700) to qualitatively detect the nanoparticles biodistribution in different tissues. Paraffin tissue sections were dehydrated in descending ethanol concentration and then embedded in distilled water. Triton X (0.1%) was added to each tissue sample for 10 minutes; then the samples were washed twice with PBS buffer. Tissue sections were stained with Hoechst stain for 10 minutes to visualize the cell nucleus. The tissue samples were washed in PBS, dehydrated in alcohol and xylol, and then examined (laser excitation wavelengths between 543 and 488 nm) [21, 22].


## 2.9.1. Rats and Administrative Dose

The present study was done to evaluate thein vivo cytotoxic effect of the prepared TiO2 NPs. The Animal Care and Use Committee (ACUC), Faculty of Science, Alexandria University, approved the current acute toxicity study which was in accordance with the International Principles for Laboratory and Care of the European Community Directive of 1986, AU/04/20/01/28/9/02. Thirty male albino rats (Rattus norvegicus albinus), with average body weight of 390 ± 30 g (4 months old), were divided, 10 rats/group, and kept in a cage with regular 12 h light/12 h dark cycle under conventional conditions of temperature and humidity for 30 days in average temperature (25 ± 2°C) inside an adequately ventilated room with free access to food and water ad libitum [18]. The rats were divided according to the different nanoparticles doses as follows.Treated animals received intraperitoneal injections with different doses of TiO2 NPs every 24 hrs for two days, and control group received a dose of 0.9% sodium chloride.Group 1: served as control, rats received 0.15 ml sodium chlorideGroup 2: rats received 0.15 ml TiO2 NPs (10 mg/kg body weight)Group 3: rats received 0.15 ml TiO2 NPs (1000 mg/kg body weight)


## 2.9.2. Experimental Protocol

Animal groups underwent anesthesia via intraperitoneal injection with ketamine hydrochloride (100 mg/kg) and xylazine (10 mg/kg). 48 hrs after injection, histopathological, blood biochemical, and bioaccumulation studies were evaluated. The survival rate of each group was monitored and recorded for 30 days. Sodium pentobarbital (40 mg/kg) was used at the end of the experiment to anesthetize the rats via intraperitoneal injection [18].


## 2.9.3. Blood Biochemical Study

Different biochemical tests were done in order to evaluate the cytotoxic effect of the synthesized TiO2 NPs. Rats were weighed (n = 5) and blood was sampled through the retro-orbital plexus. Each blood sample was centrifuged (20 min at 4000g) to collect the sample serum. Liver functions (alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bilirubin, albumin, alkaline phosphatase, and gamma-glutamyl transferase (GGT)), kidney functions (uric acid, creatinine, and urea), total cholesterol (high- and low-density lipoproteins), glucose, and total protein tests were determined using an automated biochemical analyzer [19].


## 2.9.4. Histopathological Study

(1) Light Microscopic Examination. The liver, kidney, and brain were excised and weighted immediately after sacrifice. Each tissue was washed with normal saline and then fixed with 10% formalin, and then each sample was dehydrated using ethanol. Tissue samples were embedded in paraffin, cut into 5 µm thick sections, and then deparaffinized and stained with Ehrlich’s hematoxylin and eosin (H & E) stain [20].(2) Fluorescence Microscopic Examination. Fluorescence microscopic evaluation was performed using confocal laser scanning microscope (LSM 700) to qualitatively detect the nanoparticles biodistribution in different tissues. Paraffin tissue sections were dehydrated in descending ethanol concentration and then embedded in distilled water. Triton X (0.1%) was added to each tissue sample for 10 minutes; then the samples were washed twice with PBS buffer. Tissue sections were stained with Hoechst stain for 10 minutes to visualize the cell nucleus. The tissue samples were washed in PBS, dehydrated in alcohol and xylol, and then examined (laser excitation wavelengths between 543 and 488 nm) [21, 22].


## 2.10. Statistical Analyses

Results were the mean of three trials and were expressed as means ± standard deviation. One-way analysis of variance (ANOVA) and Tukey’s test (p<0.05) were used to detect differences between the groups with the SPSS 13.0 statistical software. The means of the treatments were considered significant when 0.05>p>0.01.


## 3. Results

### 3.1. GC/MS Analysis of Propolis Sample

By comparing the acquisition time of the present work to the database, twelve compounds were identified. Hexadecanoic acid and ethyl ester followed by n-hexadecanoic acid and oleic acid were the most prevalent compounds in Tanta’s propolis sample (37.2, 23.4, and 18.04% respectively) (Table1 and Figure 1).Table 1
GC/MS analysis of Tanta’s propolis.
RTProbable compoundContent %14.671-[2-O-Benzoyl-3, 5-O-dibenzyl-alpha-d-ribosyl]-5, 6-dimethylbenzimide0.817.3, 34.7, 35.1, 36.2, 37.3, 39.7, 43.1Gibberellic acid7.625.63-Phenylthioacrylic acid0.626.4Hexadecanoic acid, ethyl ester1.0828.913,16-Octadecadiynoic acid, methyl ester1.8830.3Hexadecanoic acid, ethyl ester37.230.5n-Hexadecanoic acid23.434.4, 35.5Oleic acid18.0440.2Octadecane, 3-ethyl-5-(2-ethylbutyl)7.146.9Cinnamic acid2.3Figure 1
GC/MS chromatogram of Tanta propolis.


### 3.2. Physicochemical Characterization of TiO2 NPs

#### 3.2.1. Particle Size, PDI, and Zeta Potential

The physical and chemical characteristics of the newly synthesized TiO2 NPs (Table 2) revealed that the mean diameter, PDI value, and Z-potential were 57.3 nm, 0.308, and −32.4 mV, respectively, which indicated the homogenous size distribution with a very high stability.Table 2
Physicochemical characteristics of the synthesized TiO2 NPs.
SamplePdIZeta potential (mV)Z-average size (nm)TiO2 NPs0.308−32.457.30


#### 3.2.2. Fourier-Transform Infrared (FTIR) Spectroscopy

FTIR analysis provided information about the structural and functional groups in the compounds to establish a correlation between the structure of the prepared nanoparticles and the observed spectra. Figure2(a) shows that a broad band (at 3600–2700 cm−1) resembles an O-H stretching alcohol, N-H stretching aliphatic primary amine band at 3409 cm−1, sharp strong band (2921 cm−1) of C-H stretching alkane, strong bands of C = C stretching alkene, C = O stretching primary amide (1634–1605 cm−1 respectively), strong band at 1272 cm−1 of C-O stretching alkyl aryl ether, and strong band of C-O stretching ester (1167 cm−1). The aforementioned results may indicate that the main reducing and capping agents among the propolis extract compounds were 1-[2-O-benzoyl-3, 5-O-dibenzyl-alpha-d-ribosyl]-5, 6-dimethylbenzimide, hexadecanoic acid ethyl ester, 13,16-octadecadiynoic acid methyl ester, and octadecane, 3-ethyl-5-(2-ethylbutyl).Figure 2
Physicochemical characterization of TiO2 NPs. (a) Infrared and (b) transmission electron microscopy of TiO2 nanoparticles.
(a)(b)


#### 3.2.3. Transmission Electron Microscopic Examination (TEM)

TiO2 NPs were examined by transmission electron microscope to determine the nanoparticles shape and size. It was found that the newly synthesized titanium oxide nanoparticles have a cubic to rectangular shape with average size of 57.3 ± 4 nm (Figure 2(b)).


### 3.3. Determination of the Antimicrobial Activity

Data in Table3 reveals that the newly synthesized nanoparticles had higher antimicrobial activity against Gram-positive bacteria than yeast and Gram-negative bacteria, respectively. P. vulgaris was the most resistant strain among the tested microorganisms (inhibition zone diameter 7 mm and MIC value 128 µg/mL) while S. epidermidis was the most susceptible microorganism (inhibition zone diameter 35 mm and MIC value 8 µg/mL).Table 3
The antimicrobial activity of the synthesized TiO2 NPs.
Tested microorganismInhibition zone diameter (mm)MIC (µg/mL)Candida albicans2532MRSA3116S. epidermidis358K. pneumoniae1832Ps. aeruginosa1364Listeria monocytogenes1264P. vulgaris7128Acinetobacter baumannii1064


### 3.4. Growth Inhibition Potency on Human Cancer Cell Lines

As it was shown in Table4 and Figures 3 and 4, TiO2 NPs exhibited potent growth inhibitory effect against the tested human cancer cell lines. At 24 h of incubation with serial dilutions of TiO2 NPs for 72 h, the percentages of growth inhibition for each human cancer cell lines were estimated. It was found that TiO2 NPs inhibited the growth of three cancer cell lines as their concentrations increased. Also, the maximum inhibition of cancer cell proliferation reached at 72 h. Accordingly, cytotoxicity effect of TiO2 NPs on Caco-2, HepG-2, and MDA-MB 231 cells was dose- and time-dependent as it is shown in Figure 3. TiO2 NPs had low IC50 (11.01, 8.56, and 18.74 µg/ml) for inhibiting the proliferation of colon, liver, and breast cancer cells, respectively. The morphological collapse of TiO2 NPs-treated human cancer cells (Figure 3) supported their powerful anticancer activity.Table 4
IC50 (µg/ml) of the tested compounds against human cancer cells.
Tested NPsCaco-2HepG2MDA-MB 231TiO2 NPs11.013 ± 0.499a8.556 ± 0.158a18.736 ± 0.679aAll values are expressed as mean ± SEM. Different letters of the same column are significantly different atp<0.05.Figure 3
Cytotoxicity of TiO2 NPs on human cancer cells (Caco-2, MDA-MB 231, and HepG-2) after 24 h, 48 h, and 72 h incubation.Figure 4
Morphological alteration of TiO2 NPs-treated Caco-2, MDA-MB 231, and HepG-2 cells (using IC50 of TiO2 NPs) in comparison with the untreated control cells after 72 hrs.


### 3.5. Acute Toxicity Studies

#### 3.5.1. Biochemical Study

The biochemical study of different rat groups receiving normal saline (control group), 10 mg/kg of TiO2 NPs (Group 2), and 1000 mg/kg TiO2 NPs (Group 3) is presented in Table 5. It was revealed that Group 2 has no or minimum sign of toxicity while Group 3 had high level of hepatotoxicity which was accompanied by depression-like symptoms and loss of appetite. However, hypoglycemia was recorded in the treated groups in comparison with the control group. These results indicate that the TiO2 NPs toxicity is a dose-dependent effect.Table 5
Biochemical tests in blood serum of different rat groups.
Dose/testControl groupGroup 2 (received 10 mg/kg)Group 3 (received 1000 mg/kg)Urea (mg/dl)17.30 ± 0.956.63 ± 1.4718.40 ± 0.17Creatinine (mg/dl)0.80 ± 0.630.52 ± 0.470.98 ± 0.94Glucose (mg/dl)80.10 ± 0.1163.78 ± 0.0973.62 ± 0.04Cholesterol (md/dl)50.70 ± 0.03a15.95 ± 0.02a69.94 ± 0.06aTotal protein (mg/dl)5.90 ± 0.413.24 ± 0.084.61 ± 0.23Albumin (g/dl)4.20 ± 0.902.91 ± 1.733.52 ± 1.46Uric acid (g/dl)2.80 ± 0.37b2.09 ± 0.51b5.26 ± 0.48bBilirubin (mg/dl)0.50 ± 0.010.57 ± 0.010.59 ± 0.03Alk phos (U/L)131.00 ± 1.49C60.53 ± 1.73C274.52 ± 1.97CGGT (U/L)70.00 ± 0.77d68.71 ± 2.80d226.97 ± 1.32dALT (U/L)11.00 ± 0.21e24.64 ± 0.13e100.69 ± 0.61eAST (U/L)27.00 ± 0.92f140.26 ± 0.45f431.84 ± 0.28fAll values are expressed as mean ± SD. Different letters of the same column are significantly different atp<0.05.


#### 3.5.2. Histopathological Study

(1) Kidney. Light microscopic examination of renal sections of all control rats demonstrated well preserved and kept intact normal histological appearance of renal (Malpighian) corpuscles which were formed of glomerular capillaries and Bowman’s capsules with subcapsular space. Numerous proximal convoluted tubules had narrow lumina and were lined with simple truncated cubical (pyramidal) cells with basal spherical nuclei. Distal convoluted tubules had wide lumina. They were less numerous and were lined with simple cubical cells with central or apical spherical nuclei (Figure 5(a)). Histological pictures of Group 2 (10 mg/kg TiO2 NPs-treated rats) were similar to those of the control group, showing most of the renal glomeruli and tubules more or less normal, but few tubules revealed cytoplasmic vacuolations in their lining cells (Figure 5(b)). On the other hand, moderate glomerular congestion was demonstrated by the renal tissues of rats exposed to 1000 mg/kg (high dose) TiO2 NPs for 48 h; Bowman’s capsule swelling and dilatation and massive necrotic degeneration were demonstrated in the renal cells of the proximal convoluted tubules and renal tubules. The epithelial lining of the renal tubule cells showed cloudy swelling with karyorrhexis or/and karyolysis (Figure 5(c)). Confocal microscopy (Figure 6) of the control group showed almost invisible blue fluorescence color, marking cells nuclei. With increasing TiO2 NPs concentration, there was a gradual enhancement of the fluorescence signal in experimental groups. There was significant change in high-dose TiO2-treated group compared to low-dose treated group or control group.Figure 5
Light micrographs in kidney of (a) control group demonstrating normal histological architecture. Kidney of rats which received low-dose TiO2 NPs (b) demonstrating most of convoluted tubules were apparently normal (yellow star). Few tubules have cytoplasmic vacuolations in their lining cells (red star). The kidney of rats which received high-dose TiO2 NPs (c) demonstrating swelling and dilatation of Bowman’s capsule (black arrows), glomerular congestion or inflamed glomeruli (red arrows), nuclear alterations (thick black arrows), and necrotic renal tubules (yellow star). H & E staining 400x magnification.
(a)(b)(c)Figure 6
Confocal microscopy images of control renal cells (a), TiO2 low-dose treated renal cells (b), and TiO2 high-dose treated renal cells (c).
(a)(b)(c)(2) Liver. H & E-stained sections of liver of the control group revealed normal characteristic of hepatic architecture; the normal hepatic lobules appeared to be made up of intact hepatocytes arranged in cords radiating from the central vein. They were polyhedral in shape with granular acidophilic and slightly vacuolated cytoplasm and rounded vesicular, centrally located nuclei. In between the hepatic cords, the hepatic sinusoids appeared as narrow spaces lined with flattened endothelial cells and scattered irregular Kupffer cells with ovoid nuclei (Figure 7(a)). The histological sections of low dose treated group (Group 2) revealed more or less preserved hepatic architecture. The hepatocytes are arranged in cords radiating from central veins with rounded vesicular, centrally located nuclei and separated by blood sinusoids. Some dilatation of central vein is still detected (Figure 7(b)). Histopathological examination of the liver from high-dose (Group 3) treated animals revealed various cellular and lobular abnormalities. Some hepatocytes were ballooned and vacuolated cytoplasm with nuclear changes; others appeared with early signs of apoptosis as hazy vacuolated cytoplasm and indistinct cell boundaries. These nuclear changes include nuclear division, nuclear eccentricity, pyknosis, necrosis, and karyorrhexis. The central vein is dilated, congested, and surrounded by mononuclear cellular infiltration. Most of the blood sinusoids are markedly dilated and congested (Figure 7(c)). Our investigations showed that TiO2 nanoparticle deposition was increased in livers of rats given high dose relative to other groups (Figures 8(a)–8(c)). Also, deposition was observed in nuclei compared to low-dose treated group that showed no nuclei deposition with mild TiO2 deposition in liver tissues.Figure 7
Photomicrograph of section of liver of control group (a) showing tightly packed cords of polygonal hepatocytes with rounded vesicular nuclei (black arrow), central vein (C) showing intact endothelial cells with flattened nuclei. Scattered irregular Kupffer cells with ovoid nuclei (red arrow). Low-dose treated group (b) showing mild affection of the hepatic lobule with preserved hepatic architecture. Hepatocytes arranged in cords radiating from dilated central vein and separated by blood sinusoids. However, high-dose treated group albino rat (c1) showed shrunken cells with hypereosinophilic cytoplasm and fragmented nuclei (black arrows) dilatation and cellular infiltration around the portal vessels and dilation and congestion in blood sinusoids (S), hepatocytes with vacuolar degeneration (red arrow) (c2). H & E staining 400x magnification.Figure 8
Confocal microscopy images of control hepatocytes (a), TiO2 low-dose treated hepatocytes (b), and TiO2 high-dose treated hepatocytes (c).
(a)(b)(c)(3) Brain. Pathological changes in the cerebrum and hippocampus of experimental rats were examined under light microscopy. H & E staining results showed no obvious damage or inflammation in brain cerebral cortex. Cerebral examination of all experimental rats revealed normal neurons structure with central large vesicular nuclei, containing one or more nucleoli, and peripheral distribution of Nissl granules which was illustrated by histological pictures (Figures 9(a)–9(c) and 10(a)–10(c)). Confocal microscopy was used to confirm the ability of TiO2 nanoparticles to cross the blood-brain barrier and reach the cerebral brain tissue by fluorescence images obtained by the IVIS Lumina XR system (Figures 11(a)–11(c)). Experimental groups showed almost invisible blue fluorescence color, illustrating that, with increasing TiO2 concentration, there was no significant change in both TiO2-treated groups compared to the control group. Moreover, no observable hippocampal histopathological changes were observed in control and low-dose treated group. Most of histopathological changes were observed in groups that received high TiO2 dose (Group 3). This treated group showed thickness decrease of pyramidal cell layer, with increased hippocampal neuronal necrosis with dilated blood vessel (Figure 9(c)).Figure 9
Photomicrograph of hippocampus of different experimental groups: control group (a) and low TiO2 dose group (b), illustrating normal hippocampal with its characteristic three layers, polymorphic 3, pyramidal 2, and molecular 1. High TiO2 dose group (c), illustrating neuronal necrosis (black arrows), dilated blood vessel (∗), molecular layer (ML), and glial cells (red arrows). H & E staining 400x magnification.
(a)(b)(c)Figure 10
Photomicrograph of cerebral cortex of experimental rat groups showing control normal neurons (a), TiO2 low-dose treated neurons (b), and TiO2 high-dose treated neurons (c). H & E staining 400x magnification.
(a)(b)(c)Figure 11
Confocal microscopy images of control cerebral cells (a), TiO2 low-dose treated cerebral cells (b), and TiO2 high-dose treated cerebral cells (c).
(a)(b)(c)


## 3.1. GC/MS Analysis of Propolis Sample

By comparing the acquisition time of the present work to the database, twelve compounds were identified. Hexadecanoic acid and ethyl ester followed by n-hexadecanoic acid and oleic acid were the most prevalent compounds in Tanta’s propolis sample (37.2, 23.4, and 18.04% respectively) (Table1 and Figure 1).Table 1
GC/MS analysis of Tanta’s propolis.
RTProbable compoundContent %14.671-[2-O-Benzoyl-3, 5-O-dibenzyl-alpha-d-ribosyl]-5, 6-dimethylbenzimide0.817.3, 34.7, 35.1, 36.2, 37.3, 39.7, 43.1Gibberellic acid7.625.63-Phenylthioacrylic acid0.626.4Hexadecanoic acid, ethyl ester1.0828.913,16-Octadecadiynoic acid, methyl ester1.8830.3Hexadecanoic acid, ethyl ester37.230.5n-Hexadecanoic acid23.434.4, 35.5Oleic acid18.0440.2Octadecane, 3-ethyl-5-(2-ethylbutyl)7.146.9Cinnamic acid2.3Figure 1
GC/MS chromatogram of Tanta propolis.


## 3.2. Physicochemical Characterization of TiO2 NPs

### 3.2.1. Particle Size, PDI, and Zeta Potential

The physical and chemical characteristics of the newly synthesized TiO2 NPs (Table 2) revealed that the mean diameter, PDI value, and Z-potential were 57.3 nm, 0.308, and −32.4 mV, respectively, which indicated the homogenous size distribution with a very high stability.Table 2
Physicochemical characteristics of the synthesized TiO2 NPs.
SamplePdIZeta potential (mV)Z-average size (nm)TiO2 NPs0.308−32.457.30


### 3.2.2. Fourier-Transform Infrared (FTIR) Spectroscopy

FTIR analysis provided information about the structural and functional groups in the compounds to establish a correlation between the structure of the prepared nanoparticles and the observed spectra. Figure2(a) shows that a broad band (at 3600–2700 cm−1) resembles an O-H stretching alcohol, N-H stretching aliphatic primary amine band at 3409 cm−1, sharp strong band (2921 cm−1) of C-H stretching alkane, strong bands of C = C stretching alkene, C = O stretching primary amide (1634–1605 cm−1 respectively), strong band at 1272 cm−1 of C-O stretching alkyl aryl ether, and strong band of C-O stretching ester (1167 cm−1). The aforementioned results may indicate that the main reducing and capping agents among the propolis extract compounds were 1-[2-O-benzoyl-3, 5-O-dibenzyl-alpha-d-ribosyl]-5, 6-dimethylbenzimide, hexadecanoic acid ethyl ester, 13,16-octadecadiynoic acid methyl ester, and octadecane, 3-ethyl-5-(2-ethylbutyl).Figure 2
Physicochemical characterization of TiO2 NPs. (a) Infrared and (b) transmission electron microscopy of TiO2 nanoparticles.
(a)(b)


### 3.2.3. Transmission Electron Microscopic Examination (TEM)

TiO2 NPs were examined by transmission electron microscope to determine the nanoparticles shape and size. It was found that the newly synthesized titanium oxide nanoparticles have a cubic to rectangular shape with average size of 57.3 ± 4 nm (Figure 2(b)).


## 3.2.1. Particle Size, PDI, and Zeta Potential

The physical and chemical characteristics of the newly synthesized TiO2 NPs (Table 2) revealed that the mean diameter, PDI value, and Z-potential were 57.3 nm, 0.308, and −32.4 mV, respectively, which indicated the homogenous size distribution with a very high stability.Table 2
Physicochemical characteristics of the synthesized TiO2 NPs.
SamplePdIZeta potential (mV)Z-average size (nm)TiO2 NPs0.308−32.457.30


## 3.2.2. Fourier-Transform Infrared (FTIR) Spectroscopy

FTIR analysis provided information about the structural and functional groups in the compounds to establish a correlation between the structure of the prepared nanoparticles and the observed spectra. Figure2(a) shows that a broad band (at 3600–2700 cm−1) resembles an O-H stretching alcohol, N-H stretching aliphatic primary amine band at 3409 cm−1, sharp strong band (2921 cm−1) of C-H stretching alkane, strong bands of C = C stretching alkene, C = O stretching primary amide (1634–1605 cm−1 respectively), strong band at 1272 cm−1 of C-O stretching alkyl aryl ether, and strong band of C-O stretching ester (1167 cm−1). The aforementioned results may indicate that the main reducing and capping agents among the propolis extract compounds were 1-[2-O-benzoyl-3, 5-O-dibenzyl-alpha-d-ribosyl]-5, 6-dimethylbenzimide, hexadecanoic acid ethyl ester, 13,16-octadecadiynoic acid methyl ester, and octadecane, 3-ethyl-5-(2-ethylbutyl).Figure 2
Physicochemical characterization of TiO2 NPs. (a) Infrared and (b) transmission electron microscopy of TiO2 nanoparticles.
(a)(b)


## 3.2.3. Transmission Electron Microscopic Examination (TEM)

TiO2 NPs were examined by transmission electron microscope to determine the nanoparticles shape and size. It was found that the newly synthesized titanium oxide nanoparticles have a cubic to rectangular shape with average size of 57.3 ± 4 nm (Figure 2(b)).


## 3.3. Determination of the Antimicrobial Activity

Data in Table3 reveals that the newly synthesized nanoparticles had higher antimicrobial activity against Gram-positive bacteria than yeast and Gram-negative bacteria, respectively. P. vulgaris was the most resistant strain among the tested microorganisms (inhibition zone diameter 7 mm and MIC value 128 µg/mL) while S. epidermidis was the most susceptible microorganism (inhibition zone diameter 35 mm and MIC value 8 µg/mL).Table 3
The antimicrobial activity of the synthesized TiO2 NPs.
Tested microorganismInhibition zone diameter (mm)MIC (µg/mL)Candida albicans2532MRSA3116S. epidermidis358K. pneumoniae1832Ps. aeruginosa1364Listeria monocytogenes1264P. vulgaris7128Acinetobacter baumannii1064


## 3.4. Growth Inhibition Potency on Human Cancer Cell Lines

As it was shown in Table4 and Figures 3 and 4, TiO2 NPs exhibited potent growth inhibitory effect against the tested human cancer cell lines. At 24 h of incubation with serial dilutions of TiO2 NPs for 72 h, the percentages of growth inhibition for each human cancer cell lines were estimated. It was found that TiO2 NPs inhibited the growth of three cancer cell lines as their concentrations increased. Also, the maximum inhibition of cancer cell proliferation reached at 72 h. Accordingly, cytotoxicity effect of TiO2 NPs on Caco-2, HepG-2, and MDA-MB 231 cells was dose- and time-dependent as it is shown in Figure 3. TiO2 NPs had low IC50 (11.01, 8.56, and 18.74 µg/ml) for inhibiting the proliferation of colon, liver, and breast cancer cells, respectively. The morphological collapse of TiO2 NPs-treated human cancer cells (Figure 3) supported their powerful anticancer activity.Table 4
IC50 (µg/ml) of the tested compounds against human cancer cells.
Tested NPsCaco-2HepG2MDA-MB 231TiO2 NPs11.013 ± 0.499a8.556 ± 0.158a18.736 ± 0.679aAll values are expressed as mean ± SEM. Different letters of the same column are significantly different atp<0.05.Figure 3
Cytotoxicity of TiO2 NPs on human cancer cells (Caco-2, MDA-MB 231, and HepG-2) after 24 h, 48 h, and 72 h incubation.Figure 4
Morphological alteration of TiO2 NPs-treated Caco-2, MDA-MB 231, and HepG-2 cells (using IC50 of TiO2 NPs) in comparison with the untreated control cells after 72 hrs.


## 3.5. Acute Toxicity Studies

### 3.5.1. Biochemical Study

The biochemical study of different rat groups receiving normal saline (control group), 10 mg/kg of TiO2 NPs (Group 2), and 1000 mg/kg TiO2 NPs (Group 3) is presented in Table 5. It was revealed that Group 2 has no or minimum sign of toxicity while Group 3 had high level of hepatotoxicity which was accompanied by depression-like symptoms and loss of appetite. However, hypoglycemia was recorded in the treated groups in comparison with the control group. These results indicate that the TiO2 NPs toxicity is a dose-dependent effect.Table 5
Biochemical tests in blood serum of different rat groups.
Dose/testControl groupGroup 2 (received 10 mg/kg)Group 3 (received 1000 mg/kg)Urea (mg/dl)17.30 ± 0.956.63 ± 1.4718.40 ± 0.17Creatinine (mg/dl)0.80 ± 0.630.52 ± 0.470.98 ± 0.94Glucose (mg/dl)80.10 ± 0.1163.78 ± 0.0973.62 ± 0.04Cholesterol (md/dl)50.70 ± 0.03a15.95 ± 0.02a69.94 ± 0.06aTotal protein (mg/dl)5.90 ± 0.413.24 ± 0.084.61 ± 0.23Albumin (g/dl)4.20 ± 0.902.91 ± 1.733.52 ± 1.46Uric acid (g/dl)2.80 ± 0.37b2.09 ± 0.51b5.26 ± 0.48bBilirubin (mg/dl)0.50 ± 0.010.57 ± 0.010.59 ± 0.03Alk phos (U/L)131.00 ± 1.49C60.53 ± 1.73C274.52 ± 1.97CGGT (U/L)70.00 ± 0.77d68.71 ± 2.80d226.97 ± 1.32dALT (U/L)11.00 ± 0.21e24.64 ± 0.13e100.69 ± 0.61eAST (U/L)27.00 ± 0.92f140.26 ± 0.45f431.84 ± 0.28fAll values are expressed as mean ± SD. Different letters of the same column are significantly different atp<0.05.


### 3.5.2. Histopathological Study

(1) Kidney. Light microscopic examination of renal sections of all control rats demonstrated well preserved and kept intact normal histological appearance of renal (Malpighian) corpuscles which were formed of glomerular capillaries and Bowman’s capsules with subcapsular space. Numerous proximal convoluted tubules had narrow lumina and were lined with simple truncated cubical (pyramidal) cells with basal spherical nuclei. Distal convoluted tubules had wide lumina. They were less numerous and were lined with simple cubical cells with central or apical spherical nuclei (Figure 5(a)). Histological pictures of Group 2 (10 mg/kg TiO2 NPs-treated rats) were similar to those of the control group, showing most of the renal glomeruli and tubules more or less normal, but few tubules revealed cytoplasmic vacuolations in their lining cells (Figure 5(b)). On the other hand, moderate glomerular congestion was demonstrated by the renal tissues of rats exposed to 1000 mg/kg (high dose) TiO2 NPs for 48 h; Bowman’s capsule swelling and dilatation and massive necrotic degeneration were demonstrated in the renal cells of the proximal convoluted tubules and renal tubules. The epithelial lining of the renal tubule cells showed cloudy swelling with karyorrhexis or/and karyolysis (Figure 5(c)). Confocal microscopy (Figure 6) of the control group showed almost invisible blue fluorescence color, marking cells nuclei. With increasing TiO2 NPs concentration, there was a gradual enhancement of the fluorescence signal in experimental groups. There was significant change in high-dose TiO2-treated group compared to low-dose treated group or control group.Figure 5
Light micrographs in kidney of (a) control group demonstrating normal histological architecture. Kidney of rats which received low-dose TiO2 NPs (b) demonstrating most of convoluted tubules were apparently normal (yellow star). Few tubules have cytoplasmic vacuolations in their lining cells (red star). The kidney of rats which received high-dose TiO2 NPs (c) demonstrating swelling and dilatation of Bowman’s capsule (black arrows), glomerular congestion or inflamed glomeruli (red arrows), nuclear alterations (thick black arrows), and necrotic renal tubules (yellow star). H & E staining 400x magnification.
(a)(b)(c)Figure 6
Confocal microscopy images of control renal cells (a), TiO2 low-dose treated renal cells (b), and TiO2 high-dose treated renal cells (c).
(a)(b)(c)(2) Liver. H & E-stained sections of liver of the control group revealed normal characteristic of hepatic architecture; the normal hepatic lobules appeared to be made up of intact hepatocytes arranged in cords radiating from the central vein. They were polyhedral in shape with granular acidophilic and slightly vacuolated cytoplasm and rounded vesicular, centrally located nuclei. In between the hepatic cords, the hepatic sinusoids appeared as narrow spaces lined with flattened endothelial cells and scattered irregular Kupffer cells with ovoid nuclei (Figure 7(a)). The histological sections of low dose treated group (Group 2) revealed more or less preserved hepatic architecture. The hepatocytes are arranged in cords radiating from central veins with rounded vesicular, centrally located nuclei and separated by blood sinusoids. Some dilatation of central vein is still detected (Figure 7(b)). Histopathological examination of the liver from high-dose (Group 3) treated animals revealed various cellular and lobular abnormalities. Some hepatocytes were ballooned and vacuolated cytoplasm with nuclear changes; others appeared with early signs of apoptosis as hazy vacuolated cytoplasm and indistinct cell boundaries. These nuclear changes include nuclear division, nuclear eccentricity, pyknosis, necrosis, and karyorrhexis. The central vein is dilated, congested, and surrounded by mononuclear cellular infiltration. Most of the blood sinusoids are markedly dilated and congested (Figure 7(c)). Our investigations showed that TiO2 nanoparticle deposition was increased in livers of rats given high dose relative to other groups (Figures 8(a)–8(c)). Also, deposition was observed in nuclei compared to low-dose treated group that showed no nuclei deposition with mild TiO2 deposition in liver tissues.Figure 7
Photomicrograph of section of liver of control group (a) showing tightly packed cords of polygonal hepatocytes with rounded vesicular nuclei (black arrow), central vein (C) showing intact endothelial cells with flattened nuclei. Scattered irregular Kupffer cells with ovoid nuclei (red arrow). Low-dose treated group (b) showing mild affection of the hepatic lobule with preserved hepatic architecture. Hepatocytes arranged in cords radiating from dilated central vein and separated by blood sinusoids. However, high-dose treated group albino rat (c1) showed shrunken cells with hypereosinophilic cytoplasm and fragmented nuclei (black arrows) dilatation and cellular infiltration around the portal vessels and dilation and congestion in blood sinusoids (S), hepatocytes with vacuolar degeneration (red arrow) (c2). H & E staining 400x magnification.Figure 8
Confocal microscopy images of control hepatocytes (a), TiO2 low-dose treated hepatocytes (b), and TiO2 high-dose treated hepatocytes (c).
(a)(b)(c)(3) Brain. Pathological changes in the cerebrum and hippocampus of experimental rats were examined under light microscopy. H & E staining results showed no obvious damage or inflammation in brain cerebral cortex. Cerebral examination of all experimental rats revealed normal neurons structure with central large vesicular nuclei, containing one or more nucleoli, and peripheral distribution of Nissl granules which was illustrated by histological pictures (Figures 9(a)–9(c) and 10(a)–10(c)). Confocal microscopy was used to confirm the ability of TiO2 nanoparticles to cross the blood-brain barrier and reach the cerebral brain tissue by fluorescence images obtained by the IVIS Lumina XR system (Figures 11(a)–11(c)). Experimental groups showed almost invisible blue fluorescence color, illustrating that, with increasing TiO2 concentration, there was no significant change in both TiO2-treated groups compared to the control group. Moreover, no observable hippocampal histopathological changes were observed in control and low-dose treated group. Most of histopathological changes were observed in groups that received high TiO2 dose (Group 3). This treated group showed thickness decrease of pyramidal cell layer, with increased hippocampal neuronal necrosis with dilated blood vessel (Figure 9(c)).Figure 9
Photomicrograph of hippocampus of different experimental groups: control group (a) and low TiO2 dose group (b), illustrating normal hippocampal with its characteristic three layers, polymorphic 3, pyramidal 2, and molecular 1. High TiO2 dose group (c), illustrating neuronal necrosis (black arrows), dilated blood vessel (∗), molecular layer (ML), and glial cells (red arrows). H & E staining 400x magnification.
(a)(b)(c)Figure 10
Photomicrograph of cerebral cortex of experimental rat groups showing control normal neurons (a), TiO2 low-dose treated neurons (b), and TiO2 high-dose treated neurons (c). H & E staining 400x magnification.
(a)(b)(c)Figure 11
Confocal microscopy images of control cerebral cells (a), TiO2 low-dose treated cerebral cells (b), and TiO2 high-dose treated cerebral cells (c).
(a)(b)(c)


## 3.5.1. Biochemical Study

The biochemical study of different rat groups receiving normal saline (control group), 10 mg/kg of TiO2 NPs (Group 2), and 1000 mg/kg TiO2 NPs (Group 3) is presented in Table 5. It was revealed that Group 2 has no or minimum sign of toxicity while Group 3 had high level of hepatotoxicity which was accompanied by depression-like symptoms and loss of appetite. However, hypoglycemia was recorded in the treated groups in comparison with the control group. These results indicate that the TiO2 NPs toxicity is a dose-dependent effect.Table 5
Biochemical tests in blood serum of different rat groups.
Dose/testControl groupGroup 2 (received 10 mg/kg)Group 3 (received 1000 mg/kg)Urea (mg/dl)17.30 ± 0.956.63 ± 1.4718.40 ± 0.17Creatinine (mg/dl)0.80 ± 0.630.52 ± 0.470.98 ± 0.94Glucose (mg/dl)80.10 ± 0.1163.78 ± 0.0973.62 ± 0.04Cholesterol (md/dl)50.70 ± 0.03a15.95 ± 0.02a69.94 ± 0.06aTotal protein (mg/dl)5.90 ± 0.413.24 ± 0.084.61 ± 0.23Albumin (g/dl)4.20 ± 0.902.91 ± 1.733.52 ± 1.46Uric acid (g/dl)2.80 ± 0.37b2.09 ± 0.51b5.26 ± 0.48bBilirubin (mg/dl)0.50 ± 0.010.57 ± 0.010.59 ± 0.03Alk phos (U/L)131.00 ± 1.49C60.53 ± 1.73C274.52 ± 1.97CGGT (U/L)70.00 ± 0.77d68.71 ± 2.80d226.97 ± 1.32dALT (U/L)11.00 ± 0.21e24.64 ± 0.13e100.69 ± 0.61eAST (U/L)27.00 ± 0.92f140.26 ± 0.45f431.84 ± 0.28fAll values are expressed as mean ± SD. Different letters of the same column are significantly different atp<0.05.


## 3.5.2. Histopathological Study

(1) Kidney. Light microscopic examination of renal sections of all control rats demonstrated well preserved and kept intact normal histological appearance of renal (Malpighian) corpuscles which were formed of glomerular capillaries and Bowman’s capsules with subcapsular space. Numerous proximal convoluted tubules had narrow lumina and were lined with simple truncated cubical (pyramidal) cells with basal spherical nuclei. Distal convoluted tubules had wide lumina. They were less numerous and were lined with simple cubical cells with central or apical spherical nuclei (Figure 5(a)). Histological pictures of Group 2 (10 mg/kg TiO2 NPs-treated rats) were similar to those of the control group, showing most of the renal glomeruli and tubules more or less normal, but few tubules revealed cytoplasmic vacuolations in their lining cells (Figure 5(b)). On the other hand, moderate glomerular congestion was demonstrated by the renal tissues of rats exposed to 1000 mg/kg (high dose) TiO2 NPs for 48 h; Bowman’s capsule swelling and dilatation and massive necrotic degeneration were demonstrated in the renal cells of the proximal convoluted tubules and renal tubules. The epithelial lining of the renal tubule cells showed cloudy swelling with karyorrhexis or/and karyolysis (Figure 5(c)). Confocal microscopy (Figure 6) of the control group showed almost invisible blue fluorescence color, marking cells nuclei. With increasing TiO2 NPs concentration, there was a gradual enhancement of the fluorescence signal in experimental groups. There was significant change in high-dose TiO2-treated group compared to low-dose treated group or control group.Figure 5
Light micrographs in kidney of (a) control group demonstrating normal histological architecture. Kidney of rats which received low-dose TiO2 NPs (b) demonstrating most of convoluted tubules were apparently normal (yellow star). Few tubules have cytoplasmic vacuolations in their lining cells (red star). The kidney of rats which received high-dose TiO2 NPs (c) demonstrating swelling and dilatation of Bowman’s capsule (black arrows), glomerular congestion or inflamed glomeruli (red arrows), nuclear alterations (thick black arrows), and necrotic renal tubules (yellow star). H & E staining 400x magnification.
(a)(b)(c)Figure 6
Confocal microscopy images of control renal cells (a), TiO2 low-dose treated renal cells (b), and TiO2 high-dose treated renal cells (c).
(a)(b)(c)(2) Liver. H & E-stained sections of liver of the control group revealed normal characteristic of hepatic architecture; the normal hepatic lobules appeared to be made up of intact hepatocytes arranged in cords radiating from the central vein. They were polyhedral in shape with granular acidophilic and slightly vacuolated cytoplasm and rounded vesicular, centrally located nuclei. In between the hepatic cords, the hepatic sinusoids appeared as narrow spaces lined with flattened endothelial cells and scattered irregular Kupffer cells with ovoid nuclei (Figure 7(a)). The histological sections of low dose treated group (Group 2) revealed more or less preserved hepatic architecture. The hepatocytes are arranged in cords radiating from central veins with rounded vesicular, centrally located nuclei and separated by blood sinusoids. Some dilatation of central vein is still detected (Figure 7(b)). Histopathological examination of the liver from high-dose (Group 3) treated animals revealed various cellular and lobular abnormalities. Some hepatocytes were ballooned and vacuolated cytoplasm with nuclear changes; others appeared with early signs of apoptosis as hazy vacuolated cytoplasm and indistinct cell boundaries. These nuclear changes include nuclear division, nuclear eccentricity, pyknosis, necrosis, and karyorrhexis. The central vein is dilated, congested, and surrounded by mononuclear cellular infiltration. Most of the blood sinusoids are markedly dilated and congested (Figure 7(c)). Our investigations showed that TiO2 nanoparticle deposition was increased in livers of rats given high dose relative to other groups (Figures 8(a)–8(c)). Also, deposition was observed in nuclei compared to low-dose treated group that showed no nuclei deposition with mild TiO2 deposition in liver tissues.Figure 7
Photomicrograph of section of liver of control group (a) showing tightly packed cords of polygonal hepatocytes with rounded vesicular nuclei (black arrow), central vein (C) showing intact endothelial cells with flattened nuclei. Scattered irregular Kupffer cells with ovoid nuclei (red arrow). Low-dose treated group (b) showing mild affection of the hepatic lobule with preserved hepatic architecture. Hepatocytes arranged in cords radiating from dilated central vein and separated by blood sinusoids. However, high-dose treated group albino rat (c1) showed shrunken cells with hypereosinophilic cytoplasm and fragmented nuclei (black arrows) dilatation and cellular infiltration around the portal vessels and dilation and congestion in blood sinusoids (S), hepatocytes with vacuolar degeneration (red arrow) (c2). H & E staining 400x magnification.Figure 8
Confocal microscopy images of control hepatocytes (a), TiO2 low-dose treated hepatocytes (b), and TiO2 high-dose treated hepatocytes (c).
(a)(b)(c)(3) Brain. Pathological changes in the cerebrum and hippocampus of experimental rats were examined under light microscopy. H & E staining results showed no obvious damage or inflammation in brain cerebral cortex. Cerebral examination of all experimental rats revealed normal neurons structure with central large vesicular nuclei, containing one or more nucleoli, and peripheral distribution of Nissl granules which was illustrated by histological pictures (Figures 9(a)–9(c) and 10(a)–10(c)). Confocal microscopy was used to confirm the ability of TiO2 nanoparticles to cross the blood-brain barrier and reach the cerebral brain tissue by fluorescence images obtained by the IVIS Lumina XR system (Figures 11(a)–11(c)). Experimental groups showed almost invisible blue fluorescence color, illustrating that, with increasing TiO2 concentration, there was no significant change in both TiO2-treated groups compared to the control group. Moreover, no observable hippocampal histopathological changes were observed in control and low-dose treated group. Most of histopathological changes were observed in groups that received high TiO2 dose (Group 3). This treated group showed thickness decrease of pyramidal cell layer, with increased hippocampal neuronal necrosis with dilated blood vessel (Figure 9(c)).Figure 9
Photomicrograph of hippocampus of different experimental groups: control group (a) and low TiO2 dose group (b), illustrating normal hippocampal with its characteristic three layers, polymorphic 3, pyramidal 2, and molecular 1. High TiO2 dose group (c), illustrating neuronal necrosis (black arrows), dilated blood vessel (∗), molecular layer (ML), and glial cells (red arrows). H & E staining 400x magnification.
(a)(b)(c)Figure 10
Photomicrograph of cerebral cortex of experimental rat groups showing control normal neurons (a), TiO2 low-dose treated neurons (b), and TiO2 high-dose treated neurons (c). H & E staining 400x magnification.
(a)(b)(c)Figure 11
Confocal microscopy images of control cerebral cells (a), TiO2 low-dose treated cerebral cells (b), and TiO2 high-dose treated cerebral cells (c).
(a)(b)(c)


## 4. Discussion

It is well known that TiO2 NPs have several applications (as in paint pigment and additives, paper, ceramics, plastics, foods, also diagnostic or therapeutic tools and water, air, and soil decontamination); hence in the present manuscript, Egyptian propolis extract was used in the novel synthesis of TiO2 NPs and then the antimicrobial activity and growth inhibitory effect against human cancer cell lines were evaluated and an acute toxicity study was performed to indicate the nanoparticles safety and the potential dose for biomedical applications. It was revealed that the synthesized nanoparticles had a significant antimicrobial activity against various microbes with superior activity against Gram-positive bacteria (MIC values ranged from 8 to 16 µg/mL). TiO2 NPs is gaining enormous attention due to its chemical stability and toxicity and above all the wide spectrum activity (effective against Gram-positive and Gram-negative bacteria) [23]. The main bactericidal mechanism of TiO2 NPs may possibly be explained by the ROS generation which leads to microorganisms’ degradation through several oxidation processes [23]. Pigeot-Rémy et al. [24] revealed that the antibacterial effect of TiO2 NPs was accomplished through a mechanical damage of the bacterial cell by damaging the bacterial outer membrane, while Foster et al. [25] stated that TiO2 NPs had a wide range of antimicrobial activity including Gram-positive and Gram-negative bacteria, yeast, fungi (filamentous and unicellular), protozoa, algae, and viruses.The cytotoxic effect of the newly synthesized TiO2 NPs was investigated through different cancer cell lines, namely, colon, liver, and breast cancer cell line. Significantly low IC50 was recorded against liver and colon cancer cell lines (8.56 and 11.01 µg/ml, respectively). Gandamalla et al. [26] tested the dose- and size-dependent cytotoxicity of titanium nanoparticles on human epithelial lung and colon cells. They revealed that titanium nanoparticles with size diameters 18, 30, and 87 nm with a dose range 0.1–100 mg/mL showed the minimum IC50 values 21.80 and 24.83 mg/ml upon using 18 nm titanium nanoparticles. It was concluded that the relationship between the titanium nanoparticles and the anticancer activity was an inversely proportional relationship. DeLoid et al. [27] illustrated the correlation between the nanoparticles toxicity and their physicochemical properties. The smaller nanoparticles size had a higher toxicity compared to the larger size nanoparticles due to the smaller size, larger surface area, and hydrodynamic diameter [27].In another avenue, the World Health Organization [28] stated the LD50 of TiO2 NPs in rats was more than 12.000 mg/kg body weight. Hence, in the present study, we explored the toxicity of TiO2 NPs at different concentrations. Rats have been widely utilized in this study of TiO2 NPs toxicity evaluation. This was mainly due to their availability and low cost [29]. The gastrointestinal tract is considered as important mean by which TiO2 NPs can enter the body. This can include the intake of foods or drugs containing nanoparticles. TiO2 NPs that enter the body via the gastrointestinal tract are absorbed by the lymphoid tissue of the small and large intestines and subsequently enter the blood circulation, are transferred to the mesentery, and reach the body organs, especially those with abundant reticuloendothelial systems, such as the liver. Finally, TiO2 NPs are excreted by urine [30] so it has influence on kidney. Because nanoparticles have high surface activity, they have a good ability to pass through organs. TiO2 NPs can be transported into various organs in the body through the blood and lymphatic circulatory systems. Moreover, TiO2 NPs can cross the blood-brain barrier, causing cavitation in hippocampal inflammation [31]. In the current study, to evaluate cytotoxicity of TiO2 NPs, we studied the biochemical in addition to the histopathological changes in liver, kidney, and brain tissues as scan for other biological effects of high (1000 mg/kg) and low dose (10 mg/kg) of TiO2 NPs.Younes et al. [18] tested the subacute toxicity using 20 mg/kg body weight of TiO2 NPs (20–30 nm diameter) and revealed that the increasing level of AST and ALT indicated the organs injury. The intraperitoneal injection induced increased level of AST and ALT and caused some histopathological changes of liver such as prominent vasodilatation, vacuolization, and congestion due to the titanium nanoparticles accumulation in liver. Liu et al. [32] observed higher coefficients not only of the liver but also of the kidney and spleen of mice. Our study exhibited hepatocytes swelling which may be a sign of hydropic degeneration of cells that received high dose TiO2 NPs compared to those of low dose and control. Similar results were reported by Wang et al. [31] who subjected 30 mice to a single dose of 5 g/kg TiO2 NPs with various sizes (25 and 80 nm), and an elevated ALT/AST ratio (regardless of the nanoparticles size) was revealed. In the same study, brain lesions and vacuoles in the hippocampus neurons were detected. On the other hand, in the kidney, proteinic liquids filled the renal tubule and renal glomerulus swellings were observed while in the liver, hydropic degeneration around the central vein plus spotty necrosis of hepatocyte was detected. It was explained by the long-time retention of the nanoparticles due to their small size which resulted in liver and kidney damage. The highly cytoplasmic acidophilia of these cells is demonstrated in this study such as the rupture of lysosomes which leads to amorphous eosinophilic cytoplasm as it is an initial sign of hepatocytes necrosis before shrinking and dissolution of nuclei [33]. In the present study, upon using a high dose of TiO2 NPs (1000 mg/kg), an inflammatory mononuclear cellular infiltration around the portal area was demonstrated. These results were in accordance with the results of Giray et al. [34] who suggested that TiO2 NPs could interact with proteins and enzymes of the hepatic interstitial tissue interfering with the antioxidant defense mechanism and leading to reactive oxygen species (ROS) generation which in turn may imitate an inflammatory response.Al-Rasheed et al. [35] found that TiO2 NPs administration to rats produced histopathological variations and abnormalities in the renal tissue in the form of congested dilated glomerular capillaries, flattening of the epithelial lining of some tubules, and exfoliation and pyknosis of some tubular cells with apparent luminal dilatation and intratubular cell debris. In the present study, occasional moderate glomerular congestion was demonstrated by the renal tissues of rats exposed to high dose TiO2 NPs (Figure 7(c)). This alteration was not observed in the kidneys of rats which received low dose TiO2 NPs (group II). It was reported that the renal glomerular basement membrane is fragile and sensitive to toxic effects of NPs [20] that can cause glomerulonephritis leading to renal failure due to glomerular damage characterized by protein leakage into urine. Some renal cells in the lining epithelia of the proximal convoluted tubule of NPs-treated rats demonstrated karyorrhexis or/and karyolysis (Figure 7(c)). This may indicate oxidative stress induced by TiO2 NPs exposure. Karyorrhexis and karyolysis are destructive fragmentation and complete dissolution of the chromatin matter of a necrotic or dying cell as confirmed by the previous studies done by Al-Doaiss et al. [20]. However, the analysis of brain sections after exposure to TiO2 NPs revealed no pathological changes of neurons in cerebral cortex and cerebellum, but the pyramidal cell soma was enlarged and elongated. Guo et al. [36] investigated the acute toxicity of two TiO2 NPs doses (200 and 500 mg/kg body weight by intraperitoneal injection) and a significant increase in ALT, AST/ALT, and urea nitrogen while using 500 mg/kg treatment which indicate that the liver and kidney injury were dose dependent. In the same year, Chen et al. [37] tracked the TiO2 NPs deposition in liver, kidney, and lung in adult male mice injected with 324, 648, 972, 1296, 1944, or 2592 mg/kg of the tested nanoparticles. In the high dose group (2592 mg/kg body weight) various signs of liver and kidney damage were observed, namely, proteinic liquids in renal tubules, swelling of renal glomerulus, hydropic degeneration, hepatic fibrosis, hepatocellular necrosis, and apoptosis. Liu et al. [38] intraperitoneally injected mice with TiO2 NPs of 5, 10, 50, 100, and 150 mg/kg body weight and revealed that a serious damage to the kidney, liver, and myocardium along with altered blood sugar and lipid levels was detected. Shakeel et al. [39] concluded that LD50 of intraperitoneally injected TiO2 NPs in mice was 150 mg/kg body weight.


## 5. Conclusion

TiO2 NPs could be a promising candidate as antimicrobial and anticancer agent. However, the results of fluorescence confocal microscopy at two representative concentrations confirmed that NPs were readily internalized and accumulated inside the cells. As expected, the level of internalization varied from one cell type to another, likely due to the intrinsic endocytic properties of each cell type. Independently of the differences in the NPs uptake between various cell types, the influence of surface coating on the internalization can be clearly observed in different organs. Low dose TiO2 NPs (10 mg/kg) were only poorly internalized by almost all of the cells types, whereas high dose TiO2 NPs (1000 mg/kg) highly increased the level of internalization in all examined cells except cerebral tissue. In another avenue the acute and subacute toxicity of various TiO2 NPs concentrations should be evaluated before applying the synthesized nanoparticles in biomedical applications.



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