Genotoxicity evaluation of food additive titanium dioxide using a battery of standard in vivo tests

From literature to predictive modeling: Insights and machine learning applications from in vitro comet assays related to the genotoxicity of titanium dioxide nanomaterials

The genotoxicity of titanium dioxide nanomaterials (TiO2 NMs) remains a debated topic in the scientific community. In this study, we applied the read-across concept based on machine learning (ML) algorithms to predict the genotoxic potential of TiO₂ NMs. Key objectives included: (i) compiling a systematic dataset capturing DNA damage percentage from in vitro comet assays, (ii) creating a homogenized dataset integrating physicochemical properties, exposure conditions, and experimental details, (iii) training ML models for prediction, (iv) evaluating model performance, and (v) identifying the features that contribute the most to predictive accuracy. The dataset was divided into three parts: the Entire dataset (all features), the Physicochemical dataset, and the Experimental design dataset. Extra Trees Regressor and XGB Regressor demonstrated high predictive accuracy, achieving R2 values of 0.906 and 0.788 for the P-chem and Experimental dataset, respectively. Exposure concentration, cold lysis conditions, and electrophoresis parameters emerged as key predictors of DNA damage, alongside contributions from NM properties. These findings highlight the intricate interplay between NM properties and experimental conditions in genotoxicity assessments. By providing a FAIR dataset, this study facilitates future research, allowing for the integration of additional variables and quality criteria to enhance the modeling approach. This work reinforces the value of nano-informatics in nanosafety and serves as a footing for advancing data-driven hazard assessment methodologies, positioning ML-enabled read-across strategies as a valuable tool for regulatory nanosafety framework.

Effects of the Interactions Between Food Additive Titanium Dioxide and Matrices on Genotoxicity

Titanium dioxide (TiO2), a white color food additive, is widely used in bakery products, candies, chewing gums, soups, and creamers. Concerns about its potential genotoxicity have recently emerged, particularly following the European Union's ban on its usage as a food additive due to its genotoxicity potential. Conflicting in vitro and in vivo results regarding its genotoxicity highlight the need for further in-depth investigation. Moreover, food additives can interact with food components or biological matrices, potentially altering their biological responses and genotoxicity. In this study, we evaluated the interactions between two different sizes of additive TiO2 particles and food or biological matrices, including albumin, fetal bovine serum (FBS), and glucose. The results showed that the hydrodynamic diameters of TiO2 increased upon interaction with albumin or FBS, but not with glucose. The presence of albumin or FBS reduced TiO2-induced cytotoxicity, oxidative stress, in vitro intestinal transport, and ex vivo intestinal absorption to untreated control levels, regardless of particle size. While TiO2 caused DNA damage in intestinal Caco-2 cells, the interactions with albumin or FBS significantly reduced the DNA damage to levels comparable to untreated controls. The DNA damage was closely related to oxidative stress caused by TiO2. These findings suggest that the interaction of TiO2 with albumin or FBS, resulting in increased hydrodynamic diameters, mitigates its cytotoxicity, oxidative stress, intestinal transport, and genotoxicity. Further investigation is required to fully understand the potential genotoxicity of TiO2 in food contexts.

Updated assessment of the genotoxic potential of titanium dioxide based on reviews of in vitro comet, mode of action and cellular uptake studies, and recent publications

In 2021 the European Food Safety Authority (EFSA) concluded that "A concern for genotoxicity of TiO2 particles that may be present in E 171 could therefore not be ruled out.". A detailed review of the genotoxicity of titanium dioxide (TiO2) was subsequently published by Kirkland et al. (2022) using a comprehensive weight of evidence (WoE) approach in which test systems and endpoints were allocated different levels of relevance. At that time only 34 publications met the reliability and quality criteria for being most relevant in the evaluation of genotoxicity, and based on these it was concluded that the existing evidence did not support a direct DNA damaging mechanism for TiO2. Recently a number of regulatory opinions have been published, in which papers were cited that described in vitro DNA damage (mainly comet), mode of action, and cellular uptake studies that were not discussed in Kirkland et al. (2022). Furthermore, a number of additional papers have been published recently or have been identified from the regulatory opinions as a result of using extended search criteria. A total of 70 publications not previously reviewed in Kirkland et al. (2022) have been reviewed here, and again show that the published data on the genotoxicity of TiO2 are inconsistent, often of poor quality, and in some cases difficult to interpret. The cellular uptake studies show some evidence of cytoplasmic uptake, particularly in cells treated in vitro, but there is no convincing evidence of nuclear uptake. In terms of genotoxicity, the conclusions of Kirkland et al. (2022) that existing evidence does not support a direct DNA damaging mechanism for titanium dioxide (including nano forms), and that the main mechanism leading to TiO2 genotoxicity is most likely indirect damage to DNA through generation of reactive oxygen species (ROS), are still valid.

Gastrointestinal tract exposure to particles and DNA damage in animals: A review of studies before, during and after the peak of nanotoxicology

Humans ingest particles and fibers on daily basis. Non-digestible carbohydrates are beneficial to health and food additives are considered safe. However, titanium dioxide (E171) has been banned in the European Union because the European Food Safety Authority no longer considers it non-genotoxic. Ingestion of microplastics and nanoplastics are novel exposures; their potential hazardous effects to humans have been under the radar for many years. In this review, we have assessed the association between oral exposure to man-made particles/fibers and genotoxicity in gastrointestinal tract cells and secondary tissues. We identified a total of 137 studies on oral exposure to particles and fibers. This was reduced to 49 papers with sufficient quality and relevance, including exposures to asbestos, diesel exhaust particles, titanium dioxide, silver nanoparticles, zinc oxide, synthetic amorphous silica and certain other nanomaterials. Nineteen studies show positive results, 25 studies show null results, and 5 papers show equivocal results on genotoxicity. Recent studies seem to show null effects, whereas there is a higher proportion of positive genotoxicity results in early studies. Genotoxic effects seem to cluster in studies on diesel exhaust particles and titanium dioxide, whereas studies on silver nanoparticles, zinc oxide and synthetic amorphous silica seem to show mainly null effects. The most widely used genotoxic tests are the alkaline comet assay and micronucleus assay. There are relatively few results on genotoxicity using reliable measurements of oxidatively damaged DNA, DNA double strand breaks (γH2AX assay) and mutations. In general, evidence suggest that oral exposure to particles and fibers is associated with genotoxicity in animals.