Food-grade TiO(2) is trapped by intestinal mucus in vitro but does not impair mucin O-glycosylation and short-chain fatty acid synthesis in vivo: implications for gut barrier protection

BACKGROUND: Titanium dioxide (TiO(2)) particles are commonly used as a food additive (E171 in the EU) for its whitening and opacifying properties. However, the risk of gut barrier disruption is an increasing concern because of the presence of a nano-sized fraction. Food-grade E171 may interact with mucus, a gut barrier protagonist still poorly explored in food nanotoxicology. To test this hypothesis, a comprehensive approach was performed to evaluate in vitro and in vivo interactions between TiO(2) and intestinal mucus, by comparing food-grade E171 with NM-105 (Aeroxyde P25) OECD reference nanomaterial. RESULTS: We tested E171-trapping properties of mucus in vitro using HT29-MTX intestinal epithelial cells. Time-lapse confocal laser scanning microscopy was performed without labeling to avoid modification of the particle surface. Near-UV irradiation of E171 TiO(2) particles at 364 nm resulted in fluorescence emission in the visible range, with a maximum at 510 nm. The penetration of E171 TiO(2) into the mucoid area of HT29-MTX cells was visualized in situ. One hour after exposure, TiO(2) particles accumulated inside “patchy” regions 20 µm above the substratum. The structure of mucus produced by HT29-MTX cells was characterized by MUC5AC immunofluorescence staining. The mucus layer was thin and organized into regular “islands” located approximately 20 µm above the substratum. The region-specific trapping of food-grade TiO(2) particles was attributed to this mucus patchy structure. We compared TiO(2)-mediated effects in vivo in rats after acute or sub-chronic oral daily administration of food-grade E171 and NM-105 at relevant exposure levels for humans. Cecal short-chain fatty acid profiles and gut mucin O-glycosylation patterns remained unchanged, irrespective of treatment. CONCLUSIONS: Food-grade TiO(2) is trapped by intestinal mucus in vitro but does not affect mucin O-glycosylation and short-chain fatty acid synthesis in vivo, suggesting the absence of a mucus barrier impairment under “healthy gut” conditions. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12951-018-0379-5) contains supplementary material, which is available to authorized users.