Analysis of the Characteristics and Cytotoxicity of Titanium Dioxide Nanomaterials Following Simulated In Vitro Digestion

Abstract

Several metallic nanomaterials (NMs), such as titanium dioxide nanomaterials (TiO₂), present beneficial properties with a broad range of innovative applications. The human population is exposed to TiO₂, particularly by ingestion, due to its increasing use as a food additive and inclusion in dietary supplements and food packaging materials. Whether this oral exposure may lead to adverse local or systemic outcomes has been the subject of research, but studies have generated contradictory results, reflecting differences in the physicochemical properties of the TiO₂ studied, effects of the surrounding matrix, and modifications during digestion. This work aimed to investigate the toxic effects of three different TiO₂ NMs (NM-103, NM-103 and NM-105) on the gastrointestinal tract cells, Caco-2 and HT29-MTX-E12, after the use of the standardized static INFOGEST 2.0 in vitro digestion method to mimic human digestion of TiO₂, contributing to hazard assessment. The results show that, for one of the digested TiO₂ NMs studied (NM-105), a more pronounced toxicity occurs after exposure of HT29-MTX-E12 intestinal cells, as compared to undigested NM, concomitantly with subtle changes in characteristics of the NM. Thus, the inclusion of the digestion simulation in the safety evaluation of ingested NMs through in vitro bioassays can better integrate the modifications that NMs suffer in the organism. It is expected that such an approach will reduce uncertainties in the hazard assessment of ingested NMs for human health.

Keywords: cytotoxicity; ingested titanium dioxide; nanomaterials; standardized in vitro digestion.

Figure 1

TiO₂ observed under electron microscopy, at a scale of 500 nm.

Figure 2

TiO₂ observed under electron microscopy, at a scale of 200 nm.

Figure 3

Representative elemental analysis spectra by TEM-EDS. Note: Ti corresponds to titanium and Cu identifies the copper element present in TEM grid.

Figure 4

Analysis of the cytotoxic effects in Caco-2 cells, 24 h after exposure to the undigested and digested (DIG) NMs: (A) NM-102, (B) NM-103 and (C) NM-105.

Figure 5

Analysis of the cytotoxic effects in HT29-MTX-E12 cells, 24 h after exposure to the undigested and digested (DIG) NMs: (A) NM-102, (B) NM-103 and (C) NM-105.