Effect of Titanium dioxide dietary particles on host-gut microbiota interactions: role of aryl hydrocarbon receptor and impact on the development of metabolic disorders and colon cancer. – TitADiet

TitADiet uses laboratory mice fed with diets supplemented or not with the food additive E171 at human exposure doses. The protocols used follow Efsa's recommendations on the minimum exposure time (90 days) to be useful in assessing the health risk for humans, in particular the incorporation of the additive into pellets for realistic exposure conditions in the general population. After several months of exposure to the different diets and doses, the impacts on the intestinal microbiota, the gut barrier function and the metabolism are studied in mice by a combination of targeted or high-throughput molecular approaches (metagenomics, transcriptomics, metabolomics) in the both sexes. In addition, fecal transfer and antibiotic therapy approaches as well as the use of mice deficient for genes of interest will allow us to determine the role of the intestinal microbiota in the potentially deleterious effects of E171.

Our preliminary results show that chronic oral exposure to the additive E171 since gestation or in adult mice alters the composition as well as the ability of the gut microbiota to produce protective molecules for the host. These effects are observed only in males exposed to E171 and are accompanied by a low grade intestinal inflammation and a glucose intolerance. Moreover, exposure to E171 in males worsens the deleterious metabolic effects of high fat diet when exposure to the additive begins during gestation. No effect on the gut microbiota and metabolism was observed in females exposed to E171 since the in utero life. Only a decrease of the pro and anti-inflammatory response was observed in the gut of females treated with the E171. These results report a sexual dimorphism effects of chronic exposure to E171 at the intestinal and metabolic level and show the deleterious potential on glucose metabolism when exposure to the additive begins during gestation and continues until adulthood.

The perspectives of the project are to determine the role of the intestinal microbiota in the intestinal and metabolic effects of the E171 by using fecal transfer and antibiotic therapy approaches as well as mice deficient for genes of interest. As the intestinal microbiota and its interaction with the intestinal immune system are often neglected in toxicology, our approach will provide new data for health authorities (ANSES, Efsa) on the consequences of food contaminants poorly absorbed by the intestine (in this case common inorganic additives) impacting the homeostasis of the microbiota as well as on the risk of perinatal exposure to these agents compared to adults.

A conference presenting our preliminary results has been selected for the annual congress of the « Société Française de Nutrition (SFN) » during the « Journées Francophones de Nutrition » (JFN, Lille) on November 12, 2021.

Manufactured mineral particles are abundant in daily life products (e.g., cosmetics, textiles, building materials), including foodstuffs. Among them, Titanium dioxide (TiO2) is a common food additive used as whitening and brightening agent in confectionary, processed food, white sauces and icing. TiO2 is also used as antimicrobial agent in packaging in contact with food. In Europe, the use of food-grade TiO2 (referred as E171) is authorized without establishment of an acceptable daily intake. The European Food Safety Authority (EFSA) has estimated the daily exposure levels to food-grade TiO2 ranging from 0.9 to 10.4 mg/kg body weight (bw)/day in children, and 0.3 to 6.8 mg/kg bw/day in adults. Given a high-consumption level, evaluation of the consequences of chronic oral exposure to TiO2 particles has become a major public health issue. Growing concerns were related to their mixed composition of micro- and nanosized particulate matter, due to TiO2 nanoparticles displaying toxicity on intestinal cells, including oxidative stress, genotoxicity, and inflammation. However, the oral route is still poorly studied for TiO2 toxicity, and health authorities conclude the need to develop exposure studies to assess the health risks of food additives containing nanomaterials, mainly with the E171. From animal and in vitro studies, there is evidence that the food-grade TiO2 is able to interact with bacteria from the intestinal microbiota before crossing through the gut epithelial barrier and interacting with local immune cells, setting various deleterious effects for the host. Of importance to the current project, the gut microbiota plays a crucial role in several vital functions such as digestive, metabolic and immune functions, but is often neglected in food toxicology. As microbiota alteration (i.e., dysbiosis) is a critical factor in gastrointestinal and metabolic diseases such as colorectal cancer (CRC), obesity and inflammatory bowel diseases (IBD), sustained gut dysbiosis in response to daily ingestion of TiO2 particles through the diet could contribute to the susceptibility to these diseases.
In Western countries, the prevalence of obesity and CRC has risen in parallel, suggesting shared lifestyle-related risk factors. Among these factors, chronic ingestion of inorganic particulate matter from food additives has been proposed. We recently observed that chronic exposure to food-grade TiO2 induced micro-inflammation in the rat colon, and initiated as well as promoted the expansion of colonic pre-neoplastic lesions. Interestingly, our preliminary results in mice orally exposed to the same TiO2 sample for 60 days, or in rats for 100 days, pointed out an impaired capacity of the gut microbiota to metabolize tryptophan into aryl hydrocarbon receptor (AhR) ligands as well as a decreased intestinal AhR signaling pathways. AhR is a ligand-activated nuclear factor that plays key roles in modulating the immune response as well as intestinal and metabolic functions, and displays an intestinal tumor suppressor role. Importantly, our previous data clearly showed that impaired production of AhR ligands by the gut microbiota is involved in metabolic disorders and IBD pathogenesis, both are risk factors for CRC. Altogether, this suggests that imbalanced host-microbiota interactions in these diseases could be partially mediated by a defect of AhR-ligand production by the gut microbiota, which could be induce by chronic exposure to TiO2.
In this context, the aim of this project is to investigate the potential link between chronic oral exposure to TiO2 (E171) and the occurrence and/or the aggravation of metabolic disorders and CRC, by assessing the impact of TiO2 on AhR ligand production by the microbiota and its consequences on gut barrier function, immune response, metabolic homeostasis and initiation of colonic pre-neoplastic lesions.