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Table 4 TiO2 and intestinal pathologiesa

From: Titanium dioxide particles from the diet: involvement in the genesis of inflammatory bowel diseases and colorectal cancer

Study

Test system

Exposure conditions: dose range and exposure time

Material

Dispersion procedure

Main conclusions

Inflammatory bowel disease

 Powell et al., 1996 [54]

Human GALT from donors with CD, UC, and colon carcinoma

n/a

n/a

n/a

Presence of particles in phagolysosomes of macophages from GALT (“pigmented” cells). Anatase TiO2 (100–200 nm), flakes of aluminosilicates with some Fe on the surface (< 100–400 nm), mixed silicates without aluminium (100–700 nm).

 Powell et al., 2000 [123]

Human intestinal biopsies from donors with CD, UC and healthy donors, EL4.NOB-1 murine lymphoma lymphoblasts, CTLL murine T cells

5 μg/mL TiO2 or 5 μg/mL TiO2, together with 1 ng/mL LPS and 4 mM CaCl2 or 1 ng/mL LPS

Anatase TiO2, 0.2 μm

Suspension in culture medium, or suspension together with LPS and CaCl2 (ion bridge) followed by ultrasonication

Increased secretion of IL-1 in cells and organ cultures stimulated with the mixture of TiO2 and LPS, not with TiO2 or LPS alone.

 Nogueira et al., 2012 [104]

Mice

Oral gavage, 100 mg/kg bw/day; 10 days

TiO2-NPs (66 nm, home-made) and MP-TiO2 (260 nm, Kronos 1171, food-grade)

Suspension in distilled water, sonicated (no indication of the method) immediately before administration

Increased levels of CD4+ T cells in duodenum, jejunum and ileum of animals exposed to TiO2. Increased levels of IL-12, IL-4, IL-23, TNF-α, IFN-γ and TGF-β (pro-inflammatory), suggesting a Th1-mediated inflammatory response. Hypertrophy and hyperplasia of the mucosal epithelium in the duodenum, jejunum and ileum. Effects of NPs and MPs are not significantly different.

 Ammendolia et al., 2014 [126]

Listeria monocytogenes (LM2 and LM9) biofilms and Caco-2 cells

0.8, 8 and 80 μg/mL TiO2 for 24 h and 48 h

commercial TiO2-NPs, anatase, 139 nm mean diameter

Probe sonication in bacterial medium for 45 min

Exposure of bacteria to TiO2-NPs, then exposure of Caco-2 cells to TiO2-exposed bacteria. No impact on bacterial cell survival. Increased biofilm production for LM2 with 0.8, 8 and 80 μg/mL TiO2 for 24 h and for LM9 with 80 μg/mL TiO2 for 24 or 48 h. Modification of the biofilm structure. Increased interaction of LM2 with Caco-2 cells when exposed to TiO2, reduced intracellular accumulation of LM2 and LM9, reduced multiplication of LM2 and LM9 in Caco-2 cells when exposed to TiO2.

 Hummel et al., 2014 [124]

Biopsies from children suspected to having IBD

n/a

n/a

n/a

Amount of pigment (defined in Powell et al., 2000 as agglomerates of mineral particles) in Peyer’s patches. The amount of pigment increased with the age of patients. Significantly less pigment in patients supposed to having CD as compared to healthy donors and patients suspected to having UC.

 Urrutia-Ortega et al., 2016 [96]

Mice, or mice with chemically-induced CAC (12.5 mg/kg body weight/ip AOM and 2% DSS)

Oral gavage, 5 mg/kg b.w./day, 5 days a week, 10 weeks

E171

Suspension in water, sonication for 30 min at 60 Hz. 300 nm in diameter (DLS)

Transient inflammation observed in the CAC group, more intense in the CAC + E171 group. Decreased interleukin expression (IL-2, TNF-α, INF-γ, IL-10) in the CAC + E171 group, compared to the E171 group. Migration of TNF-α from the cytoplasm to the nucleus of colorectal epithelial cells in E171 and CAC groups.

 Ruiz et al., 2016 [56]

Mice, wild-type or deficient in (NLRP)3, with chemically-induced colitis (DSS). In vitro: Caco-2, HT29 and other epithelial cells, THP-1 treated or not with siRNA for caspase-1, ASC and NLRP3. Bone marrow-derived macrophages (from mice). Human patients with IBD having active disease

In vivo: oral gavage, 50 or 500 mg TiO2/day/kg b.w. for 7 days (WT) or 500 mg TiO2/day/kg b.w. for 7 days (Nlrp3−/− mice). In vitro: exposure to 5, 20 or 100 μg/mL of TiO2 for 24 h.

In vivo: 30–50 nm, rutile. In vitro: TiO2 rutile (30–50 nm) and anatase with size ca 0.36 μm (food-grade)

Suspension in drinking water (in vivo); suspension in ultrapure water and sonication for 5 min (in vitro)

In mice: no sign of colitis in WT mice exposed to TiO2 with no pre-existing colitis. In mice with chemically-induced colitis: colitis symptoms are worsened in WT mice, not in Nlrp3−/− mice. In vitro: both TiO2 particles triggers NLRP3-ASC-caspase-1 assembly, caspase-1 cleavage and the release of NLRP3-associated IL-1β and IL-18. TiO2 induces intracellular ROS accumulation. In human volunteers with IBD: Higher TiO2 level in the bloodstream compared to healthy patients.

 Bettini et al., 2017 [20]

Rats or rats with chemically-induced carcinogenesis (DMH)

Oral gavage 10 mg/kg of b.w./day, 7 days; or exposure via the drinking water at 200 μg or 10 mg/kg of b.w./day for 100 days

E171 and NM105 (21 nm, anatase/rutile TiO2-NP)

Probe sonication for 16 min in water/BSA 0.05%

Disturbance in intestinal and systemic immune homeostasis, colon microinflammation after 100 days of treatment.

 Chen et al., 2017 [82]

Mice

Oral gavage, 2.5 mg/kg b.w./day, once a day for 7 days

TiO2-NPs, anatase (not food-grade)

suspension in water, sonication in a water bath at 12–15 °C for 15 min

No evidence of inflammation (only a few inflammatory cells observed), no pathological changes by H&E staining. Increase of IL-1β in the colon only (measurement of IL-1β, IL-6 and TNF-α in the colon and small intestine).

 Hong et al., 2017 [135]

Mice

Oral gavage, 1.25, 2.5, and 5 mg/kg b.w./day, once a day for 9 months

TiO2-NPs, anatase (not food-grade), 5–6 nm

Suspension in 0.5% w/v HPMC, ultrasonication for 45 min and mechanic vibration for 10 min

Inflammatory cell infiltration in the stomach. Increased protein expression of NF-κB, TNF-α, IL-lβ, IL-6, IL-8, COX-2, and PGE2 in the stomach, decreased protein expression of IκB.

 Dorier et al., 2019 [95]

Caco-2/HT29-MTX co-culture

Acute (6-48 h; 50 μg/mL) or repeated twice a week for 3 weeks; 10 and 50 μg/mL)

E171, A12 (inhouse synthesis, anatase, 12 nm), P25 (anatase/rutile, 21 nm)

Suspension in distilled water, sonication indirect cup-type sonicator in continuous sonication mode for 30 min at 52.8 W (80% amplitude)

No impact on cell differentiation. Inflammatory profile (chronic and acute), increased mucus secretion (chronic). Epithelial integrity unaltered, content of ABC family of xenobiotic efflux pumps modified (either increased or decreased depending on the particle: decreased with E171, increased with P25).

 Pinget et al., 2019 [83]

mice, drinking water

2, 10, 50 mg TiO2/kg b.w./day for 21 days

E171

Suspension in drinking water

Proliferation of macrophages in the colonic myeloid compartment of mice exposed at 10 or 50 mg/kg b.w./day, no impact on the population of neutrophiles, dendritic cells, total monocytes. Upregulation of IL-6, TNF-α and IL-10 in the colon.

 Blevins et al., 2019 [102]

Rats, exposure to TiO2 included in food pellets

40, 400 or 5000 pm in food pellets, 7 or 100 days

E171

n/a

No effect on immune parameters: percentage of dendritic, CD4+ T or Tregs in Peyer’s patches, in their periphery. No effect on cytokine release in the colon, jejunum and plasma.

cancer

 Urrutia-Ortega et al., 2016 [96]

Mice, or mice with chemically-induced CAC (12.5 mg/kg body weight/ip AOM and 2% DSS)

Oral gavage 5 mg/kg bw/5 days a week/10 weeks

E171

1 mg/ml in water, water and sonication for 30 min at 60 Hz

E171 in non-chemically-induced animals: no tumor formation but in the distal colon: slight vascularization, increase of crypts size and number, hyperplastic epithelium with slight dysplastic changes. CAC: purulent material and blood discharge; abnormal behavior; well differentiated adenocarcinomas in the distal region of the colon. E171 in CAC: exacerbated blood and purulent discharge and higher inflammation with rectal prolapse (vs CTL CAC animals) + abnormal behavior. Enhanced the tumor formation in distal colon; mildly differentiated adenocarcinoma. Increased fluorescence of markers of tumor progression. Decrease IL2, IL10, TNFα, INFγ. Kidney weight reduced. Both groups: decrease of goblet cells in the distal colon, higher in CAC + E171.

 Bettini et al., 2017 [20]

Rats or rats with chemically-induced carcinogenesis (DMH)

Oral gavage 10 mg/kg of BW/day, 7 days; or exposure via the drinking water at 200 μg or 10 mg/kg of BW/day for 100 days

E171

Probe sonication for 16 min in water/BSA 0.05%

Increased number of aberrant cryt foci per colon after 100 days of treatment with E171 at 10 mg/kg b.w./day, proving initiation of preneoplastic lesions. In DMH-induced rats, increased number of aberrant crypts per colon and of large aberrant crypt foci per colon after exposure for 100 days at 10 mg E171/kg b.w./day, proving promotion of carcinogenesis.

 Proquin et al., 2017 [129]

Mice

Oral gavage, 5 mg/kg b.w./day, 2, 7, 14 and 21 days (5 times per week)

E171

1 mg/ml in water, water and sonication for 30 min at 60 Hz

Analysis of the colon. Structure of crypts altered, hyperplastic epithelium. No effect on intestinal cell proliferation. Transcriptome analysis with pathways affected: olfactory/GPCR receptor family, cancer, oxidative stress, cell cycle, immune response, metabolism of proteins.

 Proquin et al., 2018 [130]

Mice with chemically-induced CAC (12.5 mg/kg body weight/ip AOM and 2% DSS)

Oral gavage, 5 mg/kg b.w./day, 2, 7, 14 and 21 days (5 times per week)

E171

1 mg/ml in water, water and sonication for 30 min at 60 Hz

Analysis of the colon. Transcriptome analysis with pathways affected: olfactory/GPCR receptor family, cancer, metabolism of xenobiotics, immune system, oxidative stress.

 Setyawati et al., 2018 [132]

SW480 cells, in vitro

100, 250 and 500 μM, 4 days

TiO2-NP, 21 nm (P25 Evonik)

Sonication (no detail) in 0.5% FBS DMEM

Epithelial to mesenchymal (EMT) transition: phenotypic change (fibroblastic elongated morphology, lost of cell-cell junctions, diffuse actin staining), modulation of levels of EMT marker proteins: alpha-SMA, VIM, E-cadherin. Cell mobility and invasive behavior increased. Decreased cell proliferation. Activation of the TGF-beta (not via Smad3, rather via MAPK) pathway, concommittant with ROS level elevation. Activation of the Wnt pahway.

 Blevins et al., 2019 [102]

Rats, exposure to TiO2 included in food pellets

40, 400 or 5000 pm in food pellets, 7 or 100 days

E171

n/a

No effect on histopathological observation: aberrant crypt foci, goblet cell number, colonic gland 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 atypical cell proliferation in the intestine.

 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

Increased number of adenomas in the colon. No difference in the volume of adenomas. No abnormal cell proliferation (as probed via the PCNA and Ki67 proliferation markers mRNA expression)

  1. aAbbreviations: AOM azoxymethane, ABC ATP-binding cassette, BSA bovine serum albumin, CAC colitis-associated cancer, CD Crohn’s disease, CTL control, DLS dynamic light scattering, DMH 1,2-dimethylhydrazine, DSS dextran sulfate sodium, GALT gut-associated lymphoid tissue, H&E hematoxylin and eosin, HPMC hydroxypropyl methyl cellulose, IBD inflammatory bowel disease, LPS lipopolysaccharide, PMA phorbol 12-myristate 13-acetate, UC ulcerative colitis