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. 2020 Dec 28;22(1):207. doi: 10.3390/ijms22010207

Table 3.

Overview of in vitro and ex vivo studies assessing molecular biological effects, cytotoxicity, genotoxicity and gene expression changes following TiO2 exposure to relevant cellular model system Abbreviations: ROS = reactive oxygen species, OS = oxidative stress, ER = endoplasmic reticulum, * various NP mixtures/sizes (see original publication), ** µg/cm2, *** ppm).

Reference Material Ø Primary Size (nm) Hydrodynamic Diameter (nm) Zeta-Potential (mV) Cell Type Duration (h) Conc. (µg/mL) Observation
Teubl 2015 [57] NM-103 rutile dimethicone coated
NM-104 rutile glycerol coated		 NM-103: 20
NM-104: 20		 In PBS
NM-103: 1819 ± 61.56
NM-104: 1539 ± 489
In artificial saliva
NM-103: 3061 ± 134.4
NM-104: 2597 ± 426		 In PBS
NM-103: −25.2 ± 8.2
NM-104: −21 ± 4.3
Inartificial saliva
NM-103: −9.5 ± 3.7
NM-104: −9.1 ± 3.3		 Human buccal epithelial TR146 4 1–200

  • NM-103, NM-104 did not penetrate into mitochondria (LSM)

  • No decrease in cell viability (MTS)

  • ↑ of mitochondrial activity/viability

  • NM-104 decreased mitochondrial membrane potential, resulting in ↑ROS
Teuble 2015 [56] NM-100 anatase
NM-101 anatase
NM-105 80% anatase, 20% rutile		 NM-100: 148 ± 45/34 ± 15
NM-101: 28 ± 8
NM-105: 36 ± 10		 In PBS (d0.5)
NM-100: 1346 ± 76
NM-101: 627 ± 5
NM-105: 868 ± 16
In artificial saliva (d0.5)
NM-100: 2850 ± 482
NM-101: 1095 ± 28
NM-105: 1183 ± 74		 In PBS (d0.5)
NM-100: −10.3 ± 8.2
NM-101: −28.7 ± 4.3
NM-105: −24.0 ± 3.4
Inartificial saliva (d0.5)
NM-100: −12.0 ± 5.7
NM-101: −8.46 ± 4.8
NM-105: −11.7 ± 5.6		 Human buccal epithelial TR146 4, 24 1–200

  • No effect on cell viability (MTS)

  • No effects membrane integrity (LDH)

  • Small variances in mitochondrial activity

  • ↑ ROS formation for NM-101/-105
Kim 2019 [120] TiO2 NPs anatase 99%anatase 15 n/a n/a Periodontal Ligament cells 0.5, 1, 3, 8, 24, 48 2.5–50

  • Activation of ERK 1/2, Akt, NF-kB signaling

  • ↑ COX-2 gene expression

  • ↑ intracellular ROS formation
Gerloff 2012 [121] TiO2 NPs * (anatase/rutile) 4–215 * Was assessed * Was assessed * Caco-2 4, 24 20, 80 **

  • Low ↓ cell viability

  • ↓ metabolic activity

  • No effects on ROS formation, DNA damage, GSH levels
Botelho 2014 [133] E171
80% anatase, 20% rutile		 21 In milli-Q water or RPMI supplemented with 10% FBS, or 2% BSA in PBS
420.7		 In milli-Q water or RPMI supplemented with 10% FBS, or 2% BSA in PBS
−27.8		 AGS human gastric epithelial 3, 6, 24 20–150

  • Tumor like phenotype

  • ↑ cell proliferation

  • ↑ OS, genotoxicity

  • ↓ apoptotic cells
Dorier 2015 [123] TiO2 NPs
A12
R20		 A12: 12
R20: 20		 In water
A12: 132 ± 1
R20: >1000
In exposure medium
A12: 320
R20: >1000		 In water
A12: −20,0 ± 0.6
R20: −19.5 ± 0.9
In exposure medium
A12: −10.8 ± 0.6
R20: −11.7 ± 0.8		 Caco-2 6, 24, 48 50

  • ↑ ROS formation

  • Impairment of redox repair system, without effects on cell viability, DNA damage
Dorier 2017 [122] A12
E171 *
P25 (anatase/rutile)		 A12: 12 ± 3
P25: 24 ± 6
E171: 118 ± 53 *		 In water
A12: 85 ± 2.9
E171 *: 415.6 ± 69.5
P25: 157.6 ± 1.0
In cell culture medium
A12: 447.9 ± 0.3
E171 *: 739.3 ± 355.3
P25: 439.9 ± 6.7		 In cell culture medium
A12: −10.8 ± 0.6
E171 *: −19 ± 0.7
P25: −11.2 ± 0.8		 Caco-2/HT29-MTX (co-culture) 6, 48,
3 weeks		 0–200

  • ↑ ROS formation

  • ↓ gene expression CAT, SOD, GR

  • ↑ OS after 48h exposure correlating with intracellular accumulation of TiO2

  • No ER stress
Proquin 2017 [16] E171
TiO2 MPs
TiO2 NPs
99.5% anatase		 E171: 50–250
TiO2 MPs: 535
TiO2 NPs: 10–25		 In DMEM 0.05% BSA
E171: 669.62 ± 30.13
TiO2 MPs: 1385.83 ± 38.85
TiO2 NPs: > 1000
HBSS
E171: > 1000
TiO2 MPs: > 1000
TiO2 NPs: > 1000
McCoy + 10% FBS at 1 mg/mL
E171: 316 ± 282.4		 In DMEM 0.05% BSA
E171: −12.97 ± 0.29
TiO2 MPs: −14.10 ±0.56
TiO2 NPs: −13.12 ± 0.44
HBSS
E171: −4.39 ± 0.12
TiO2 MPs: −5.62 ± 0.9
TiO2 NPs: −6.08 ± 0.09
McCoy +10% FBS at 1 mg/mL
E171: −12.56 ± 8.3		 Caco-2, HCT116 24 0.001–1000

  • ↑ ROS formation after MP exposure

  • E171, MPs and NPs induced SS-DNA breaks

  • E171 induced chromosome damage (MN)

  • Overall low cytotoxicity
Popp 2018 [132] TiO2 NPs
NanoAmor, mkNano
MKN-TiO2-A100 (purity > 98%)		 NanoAmor:15
mkNano: 50
MKN-TiO2-A100: 100		 In DMEM at 25 µg/mL
NanoAmor: ~300
mkNano: ~800
MKN-TiO2-A100: ~500		 In DMEM at 25 µg/mL
NanoAmor: ~−15
mkNano: ~−12
MKN-TiO2-A100: ~−12		 HeLa 24, 48, 72 0–500

  • lysosomal dysfunction and membrane permeabilization

  • induction of lysosomal autophagy mediated by TFEB

  • ↑ autophagic efflux
Pedata 2019 [58] TiO2 NPs P25 P25: 21 Not assessed Not assessed Caco-2 (differentiated) 4, 24, 48 42, 84

  • ↓ barrier integrity → disruption of TJs

  • ↓ cell viability

  • ↑production of TNF-⍺, IL-8
Dorier 2019 [124] E171
A12
NM-105		 E171: 118 ± 53
A12: 12 ± 3
NM-105: 24 ± 6		 In ultrapure sterile water at 10 mg/mL
E171:415 ± 69
A12: 85 ± 3
NM-105: 158 ± 1
In DMEM + 10% FBS
E171:739 ± 355
A12: 448 ± 1
NM-105: 440 ± 7		 In ultrapure sterile water at 10 mg/mL
E171: −19 ± 1
A12: −11 ± 1
NM-105: −11 ± 1		 Caco-2/HT29-MTX (co-culture) 6, 24, 48 0–200

  • ↑ ROS formation

  • ↓ cell viability

  • No oxidative DNA damages

  • Modulation of GSH level, ↓ SOD
Cao 2019 [125] E171 E171: 113.4 ± 37.2 Not assessed Not assessed Caco-2/HT29-MTX (co-culture), + Raji B 6, 24 10, 150 ***

  • ↑ ROS formation

  • ↓ cell viability

  • ↓ TEER, barrier integrity → ↑ translocation of boscalid, inducing more adverse effects formation
Li 2020 [126] TiO2 NPs 25 Not assessed Not assessed HCT116, NCM4660 24 2, 30

  • Small ↓ cell viability

  • ↑ OS

  • changes in gene expression of microRNA including apoptosis, ↑ cell proliferation, metabolism
Ghosh 2013 [127] TiO2 NPs 100 In PBS
6180.73		 Not assessed Human lymphocyte, human erythrocytes 3 25, 50, 100

  • ↓ cell viability

  • No effect on cell membrane integrity

  • ↑ DNA damage, apoptosis

  • Erythrocytes showed morphological changes
Dai 2019 [128] TiO2 NPs
rutile		 30–50
50–100		 Not assessed Not assessed RAW 264.7 24 50, 100, 200, 300, 400

  • ↓ cell viability

  • ↓ phagocytotic rate, phagocytotic index

  • Gene expression changes in mRNA for LC-3, Beclin-I
Brzicova 2019 [131] TiO2 NPs 20–60 * Was assessed* Was assessed * THP-1 24 32, 128, 256

  • Small ↓ cell viability

  • Ability to reduce cell viability directly relate to NP size
Shukla 2013 [129] TiO2 NPs
Anatase (purity 99.7%)		 30–70 * In Milli-Q water
192.5 ± 2.00
In CMEM
124.9 ± 3.20		 In Milli-Q water
−11.4 ± 0.25
In CMEM
−17.6 ± 0.48		 HepG2 6, 24, 48 1, 10, 20, 40, 80

  • ↑ oxidative DNA damage, micronuclei

  • ↑ ROS formation, changes in GSH levels, lipid peroxidation

  • ↑ activity of p53, BAX, cytochrome-c, Apaf1, caspase-3, caspase-9
Shi 2015 [130] TiO2 NPs
Anatase
(purity 99.7%)		 10–25 DMEM + 1% FCS
366.5 ± 30		 DMEM + 1% FCS
−26.93 ± 0.43		 HepG2 24 0.1, 1, 10

  • ↑ DNA damage

  • ↑ Nrf2 mRNA and protein expression

  • ↑ ROS, lipid peroxidation