Toxicity of orally administered food-grade titanium dioxide nanoparticles

Abstract

Background The International Agency for Research on Cancer classified as a Group B carcinogen inhaled titanium dioxide (TiO 2 ) nanoparticles, and France banned the application of TiO 2 nanoparticles as a food additive based on the insufficient oral toxicity data. However, there still remains controversial due to the insufficient evidence for its safety. Here, we explored the toxicity of food-grade TiO 2 nanoparticles (hereafter, E171) in vivo and in vitro . Methods We investigated the subchronic toxic responses of E171 (0, 10, 100, and 1,000 mg/kg) under the Good Laboratory Practice (GLP) system and tried to elucidate the possible toxic mechanism using AGS cells, a human stomach epithelial cell line. Results There were no dose-related changes in the Organization for Economic Co-operation and Development test guideline-related endpoints. Meanwhile, E171 deeply penetrated cells lining the stomach tissues of rats administered the maximum dose, and blood IgM (male and female) and GM-CSF (female) levels were significantly lower in the E171-treated rats than in the control rats. Colonic SOD-1 (male and female) and SOD-2 (female) protein levels decreased with increasing Ti accumulation. When exposed to AGS cells for 24 h, E171 (40 μg/mL) located in the perinuclear region. The E171 treatment affected expression of ER stress-related proteins but did not induce cell death up to the used maximum concentration (40 μg/mL). A gene profile analysis also showed that immune response-related microRNAs were most strongly affected by E171 exposure. Conclusion Considering the potential toxicity observed in vivo and in vitro test, we concluded that the NOAEL of E171 for 90-days repeated oral administrations is less than 1,000 mg/kg for both male and female rats. Additionally, E171 may attenuate host's defense function against foreign bodies by decreasing antioxidant capacity, thus we propose that chronic toxicity studies on E171 are required to warrant the safety for use in the food industry.

Safety assessment of titanium dioxide (E171) as a food additive

“…In mice, no adverse effects associated with general toxicity were observed up to 1,000 mg E 171/kg bw per day, the highest dose tested, for dosing durations up to 90 days (Han et al., 2020a, scoring 2 for NSC). Also in rats, no adverse effects associated with general toxicity were observed in the EOGRT study with E 171 (Documentation provided to EFSA No 1) (scoring 4 for NSC) at doses up to 1,000 mg/kg bw per day (Section 4.2).…”

“…In the Han et al. (2020a) 90‐day study, effects on GM‐CSF and IgM and were observed following exposure to E 171, however the Panel noted the lack of a dose response, the magnitude of the effect was small that did not allow a firm conclusion given the natural variability in the parameters measured. It should be noted that in three single dose level studies with E 171 inflammatory effects were noted at lower doses, i.e.…”

“…In mice, no adverse effects were observed up to 1,000 mg E 171/kg bw per day, the highest dose tested, in a 90‐day study (Han et al., 2020a; scoring 2 for NSC). In rats, toxicity studies with TiO 2 NPs or TiO 2 containing a fraction of nanoparticles, having different duration (14–90 days), no adverse effects were observed up to the highest dose tested (100 mg/kg bw per day, Vasantharaja et al.…”

“…The Panel considered that the results indicated no effects of E 171 on SCFA production and mucus barrier in the gut at the highest dose tested of 10 mg/kg bw per day. Han et al (2020a) (scoring 2 for NSC) examined the effects of E 171 (0, 10, 100 or 1,000 mg/kg bw per day) for 90 days in rats. Although some changes were reported by the authors (6-10% higher feed intake of high-dose males, an 8% decrease in relative lymphocyte count in low-and high-dose males, respectively), overall, the Panel considered that gavage administration of E 171 at doses up to 1,000 mg/kg bw per day to rats for up to 90 days did not induce any adverse effects on clinical appearance, survival, body weight, feed intake, haematology, clinical chemistry, urinalysis, organ weights, or gross and microscopical pathology.…”

“…The Panel noted the absence of additional endpoints indicative of evidence for liver injury and the fact that these reported changes can variably occur as a background pathology in murine liver. In the rat, no signs of systemic toxicity were seen after gavage administration for 90 days at doses up amounting to 1,000 mg E 171/kg bw per day; the study had limitations for assessing the toxicological effects of the fraction of nanoparticles (Han et al., 2020a). E 171 did not affect caecal microbial production of SCFA in the caecum or mucus barrier in small and large intestine after 60 days of exposure via gavage at the highest dose tested of 10 mg/kg bw per day (Talbot et al., 2018).…”