Abstract
BackgroundTitanium dioxide (TiO2) 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 TiO2 and intestinal mucus, by comparing food-grade E171 with NM-105 (Aeroxyde P25) OECD reference nanomaterial.ResultsWe 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 TiO2 particles at 364 nm resulted in fluorescence emission in the visible range, with a maximum at 510 nm. The penetration of E171 TiO2 into the mucoid area of HT29-MTX cells was visualized in situ. One hour after exposure, TiO2 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 TiO2 particles was attributed to this mucus patchy structure. We compared TiO2-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.ConclusionsFood-grade TiO2 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.
Highlights
Titanium dioxide (TiO2) particles are commonly used as a food additive (E171 in the European Union (EU)) for its whit‐ ening and opacifying properties
Physicochemical characterization of food‐grade (E171) vs. model (NM‐105) titanium dioxide (TiO2) The distribution of the hydrodynamic diameter after sonication for E171 and NM-105 TiO2 particles suspended in Milli-Q grade water was determined by Dynamic Light Scattering (DLS)
E171 had a mean hydrodynamic diameter of 255 nm and, under the same conditions, NM-105 exhibited a mean hydrodynamic diameter of 220 nm (Fig. 1A). This indicated that, in both cases, some agglomerates and/or aggregates remained in the suspension, given the primary TiO2 particle size measured by transmission electron microscopy, i.e., 22 ± 1 nm for NM-105 [29] and 118 ± 53 nm for our E171 batch [5]
Summary
Titanium dioxide (TiO2) particles are commonly used as a food additive (E171 in the EU) for its whit‐ ening and opacifying properties. Titanium dioxide (TiO2) is widely used as a white pigment and opacifying agent, due to its brightness and high refractive index. It accounts for 70% of the world’s pigment production, with 5000 metric tons produced per year, expected to rise to 60,000 metric tons by 2025. It is used in the food industry in an ultrafine form as a white coloring agent [referred to as food-grade additive E171 in the European Union (EU)] for confectionery, sauces, cakes, and pastries. More recent exposure estimates have ranged between 0.2 and 0.4 mg/kg bw/day in infants and the elderly, and 5.5 and 10.4 mg/kg bw/day in children, depending on the exposure scenario [7]
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