Jejunal villus absorption and paracellular tight junction permeability are major routes for early intestinal uptake of food-grade TiO2 particles: an in vivo and ex vivo study in mice

Abstract

Background: Food-grade TiO₂ (E171 in the EU) is widely used as a coloring agent in foodstuffs, including sweets. Chronic dietary exposure raises concerns for human health due to proinflammatory properties and the ability to induce and promote preneoplastic lesions in the rodent gut. Characterization of intestinal TiO₂ uptake is essential for assessing the health risk in humans. We studied in vivo the gut absorption kinetics of TiO₂ in fasted mice orally given a single dose (40 mg/kg) to assess the ability of intestinal apical surfaces to absorb particles when available without entrapment in the bolus. The epithelial translocation pathways were also identified ex vivo using intestinal loops in anesthetized mice.

Results: The absorption of TiO₂ particles was analyzed in gut tissues by laser-reflective confocal microscopy and ICP-MS at 4 and 8 h following oral administration. A bimodal pattern was detected in the small intestine: TiO₂ absorption peaked at 4 h in jejunal and ileal villi before returning to basal levels at 8 h, while being undetectable at 4 h but significantly present at 8 h in the jejunal Peyer's patches (PP). Lower absorption occurred in the colon, while TiO₂ particles were clearly detectable by confocal microscopy in the blood at 4 and 8 h after treatment. Ex vivo, jejunal loops were exposed to the food additive in the presence and absence of pharmacological inhibitors of paracellular tight junction (TJ) permeability or of transcellular (endocytic) passage. Thirty minutes after E171 addition, TiO₂ absorption by the jejunal villi was decreased by 66% (p < 0.001 vs. control) in the presence of the paracellular permeability blocker triaminopyrimidine; the other inhibitors had no significant effect. Substantial absorption through a goblet cell (GC)-associated pathway, insensitive to TJ blockade, was also detected.

Conclusions: After a single E171 dose in mice, early intestinal uptake of TiO₂ particles mainly occurred through the villi of the small intestine, which, in contrast to the PP, represent the main absorption surface in the small intestine. A GC-associated passage and passive diffusion through paracellular TJ spaces between enterocytes appeared to be major absorption routes for transepithelial uptake of dietary TiO₂.

Keywords: Food additive; Intestinal absorption; Nanoparticles; Titanium dioxide.