Continuousin vitroexposure of intestinal epithelial cells to E171 food additive causes oxidative stress, inducing oxidation of DNA bases but no endoplasmic reticulum stress

Abstract

The whitening and opacifying properties of titanium dioxide (TiO) are commonly exploited when it is used as a food additive (E171). However, the safety of this additive can be questioned as TiO nanoparticles (TiO-NPs) have been classed at potentially toxic. This study aimed to shed some light on the mechanisms behind the potential toxicity of E171 on epithelial intestinal cells, using two in vitro models: (i) a monoculture of differentiated Caco-2 cells and (ii) a coculture of Caco-2 with HT29-MTX mucus-secreting cells. Cells were exposed to E171 and two different types of TiO-NPs, either acutely (6-48 h) or repeatedly (three times a week for 3 weeks). Our results confirm that E171 damaged these cells, and that the main mechanism of toxicity was oxidation effects. Responses of the two models to E171 were similar, with a moderate, but significant, accumulation of reactive oxygen species, and concomitant downregulation of the expression of the antioxidant enzymes catalase, superoxide dismutase and glutathione reductase. Oxidative damage to DNA was detected in exposed cells, proving that E171 effectively induces oxidative stress; however, no endoplasmic reticulum stress was detected. E171 effects were less intense after acute exposure compared to repeated exposure, which correlated with higher Ti accumulation. The effects were also more intense in cells exposed to E171 than in cells exposed to TiO-NPs. Taken together, these data show that E171 induces only moderate toxicity in epithelial intestinal cells, via oxidation.

TiO2 Nanoparticles and Commensal Bacteria Alter Mucus Layer Thickness and Composition in a Gastrointestinal Tract Model

“…Through experimental studies, researchers have reported that the translocation and accumulation of TiO 2 in the mucus layer were facilitated by the different factors such as exposure time and particle concentration. [8,57] It has also been shown that TiO 2 NPs permeate the mucus layer and penetrate into the epithelial tissues in ex vivo studies performed on porcine buccal mucosa. [19] The findings in this study are significant because they shed light on the effects of acute exposure to TiO 2 NPs and the implications on overall intestinal health.…”

“…in U.S. adults. [4,7,8] However, these estimations have been refined recently and the range of exposure was reported to be between 5.5 and 10.4 mg kg −1 b.w. in children depending on the exposure scenario.…”

“…in children depending on the exposure scenario. [8] Referred to as food grade nanoparticle in Europe, E171 can contain ≈43% of TiO 2 NPs, and has been found to be absorbed in the gastrointestinal (GI) tract at low levels. [6,8,9] Models of the GI tract have been used as a means to understand the potential toxic or functional effects of exposure to NPs as a food additive.…”

“…[8] Referred to as food grade nanoparticle in Europe, E171 can contain ≈43% of TiO 2 NPs, and has been found to be absorbed in the gastrointestinal (GI) tract at low levels. [6,8,9] Models of the GI tract have been used as a means to understand the potential toxic or functional effects of exposure to NPs as a food additive. [1,5,6,10] The small size of NPs allows them to cross cellular barriers and can lead to free radical formation in tissues and oxidative damage to the cells that line the GI tract or the mucus layer.…”

The food additive E171 and titanium dioxide nanoparticles indirectly alter the homeostasis of human intestinal epithelial cells in vitro

“…2 However, recent reports indicate that it can contain up to 55% of nanoparticles. [3][4][5][6] Due to its multiple uses, nano-or micro-sized TiO 2 can be ingested by the population both when consuming food and when inhaling contaminated air, followed by mucociliary clearance and swallowing. 7 Human oral exposure to TiO 2 is estimated to range between 0.2 and 0.4 mg per kg of body weight (b.w.)…”