Study | Test system | Exposure conditions: dose range and exposure time | Material | Dispersion procedure | Main conclusions |
---|---|---|---|---|---|
Faust et al., 2014 [89] | Caco-2BBe1 cells, differentiated | Exposure using microgravity bioreactor (“floating” epithelia) for 24 h | E171 (anatase from XRD, 122 nm from TEM, “E171”) and E171 extracted from gum (141 nm, TEM, “gum E171”) | Probe sonication > 2 min, then dilution in exposure medium, then probe sonication > 2 min | Disruption of the brush border independently of particle sedimentation (in a microgravity reactor, or in inverted epithelium configuration): fewer microvilli, limp, less erected, at 350 ng/mL and 3.5 μg/mL of gum E171 or E171. |
Brun et al., 2014 [52] | In vitro: differentiated Caco-2 and co-culture of Caco-2/HT29-MTX; ex vivo: Ussing chamber; in vivo: mice, oral gavage | In vitro: 50 μg/mL for 6 h, 24 h or 48 h; ex vivo: 50 μg/mL for 2 h; in vivo: 12.5 mg/kg b.w., sacrifice after 6 h | anatase (12 nm, TEM) | Probe sonication 30 min in water | In vitro: no impact on TEER value, paracellular and transcellular transport properties, activity of the P-gP. Upregulation of mRNA levels of proteins involved in tight and adherens junctions. In vivo and ex vivo: increased paracellular permeability after exposure to TiO2-NPs, downregulatio of mRNA expression of junction proteins (TJP1, TJP2, OCLN) in the ileum of mice exposed in vivo. |
Dorier et al., 2015 [91] | Caco-2 cells, differentiated | 50 μg/mL for 6 h, 24 h or 48 h | Anatase (12 nm, TEM) and rutile (20 nm, TEM) | Early and transient modulation of mRNA expression of ABC transporter genes, late modulation of mRNA expression of some SLC transporter genes. At 48 h significant increase of ABC transporter protein level (significant decrease at 4 h). | |
Guo et al., 2017 [92] | Co-culture of Caco-2/ HT29-MTX cells | 106, 108 and 1010 particles/cm2 (low, medium, high concentration), for 4 h (acute) or 5 days (chronic) | TiO2-NPs, 20–40 nm from TEM | Suspension in water, mixing, no sonication | Chronic exposure decreased TEER value at the three doses (not acute), enlargement of the gaps between cells, as shown via OCLN protein immunostaining. Decreased Fe, Zn and fatty acid transport transport. mRNA expression of nutrient transporters affected. |
Li et al., 2018 [61] | Mice (10 mice per group), oral gavage | 100 mg/kg b.w./day, once a day for 28 days | Anatase (20 nm, DLS) and rutile (16 nm, DLS) | Suspension in distilled water, no sonication | Longer intestinal villi in the colon (mild effect) and disturbed arrangement of villus epithelial cells when exposed to rutile but not anatase. |
Jensen et al., 2019 [134] | Rats, oral gavage once a week during 10 weeks | 50 μg/kg b.w./week (low dose) and 500 μg/kg b.w./week (high dose) | E171 (anatase, sizes: 135 nm, 305 nm and 900 nm from TEM) | Indirect cup-type sonication (high energy) in 2% FBS, 16 min | Decreased mRNA expression of TJP1 in the colon mucosa at the high dose. |
Dorier et al., 2019 [95] | Differentiated Caco-2 and co-culture of Caco-2/HT29-MTX | Repeated exposure (twice a week for 21 days); 10 and 50 μg/mL | E171 (anatase, 119 nm), A12 (anatase, 12 nm), NM105 (anatase/rutile, 21 nm) | Indirect cup-type sonication (high energy) in water, 30 min | No perturbation of the in vitro epithelial barrier development over the 21 days of exposure: TEER, mRNA expression of junction proteins and markers of microvilli differentiation unaffected. Decreased (E171) or decreased (NM105) levels of ABC transporters when repeated exposure. |
Pinget et al., 2019 [133] | Mice, drinking water | 2, 10, 50 mg TiO2/kg b.w./day for 21 days | E171 | Suspension in drinking water | No impact on Tjp1 expression, suggesting no impact on intestinal permeability. Expression of Defb3, encoding beta-defensin 3, increased; granzyme B, cathelin-related antimicrobial peptide, regenerating islet-derived protein 3 gamma and p-lysozyme not significantly modulated. Reduction of colonic crypt length at 50 mg/kg b.w./day, no impact on colon length. |
Talamini et al., 2019 [21] | Mice, TiO2 dripped into the mouse’s mouth | ~ 2 mg/kg b.w./day 3 days/week for 3 weeks | E171 | Suspension in water, no sonication, dripped into the mouth | No overt structural or morphological alteration in the stomach and intestine, no disruption of crypt structure, no atypical cell proliferation. |
Medina-Reyes et al., 2020 [88] | Mice with either high fat diet (HFD) or regular diet (RD) | 5 mg/kg b.w. for 16 weeks | E171 | Suspension in drinking water | Decreased colon crypt length, as compared to the respective control (HFD or RD). |
Zhang et al., 2021 [90] | Mice | 1% w/w TiO2 for 1, 3 or 6 months | TiO2 incorporated in food pellets | Increased villi height/crypt depth ratios at 1 and 3 months; increased expression of ZO-1 and occludin at 1 month; spare microvilli in small intestine at 6 months. No change in intestinal permeability. |