Dysregulation along the gut microbiota-immune system axis after oral exposure to titanium dioxide nanoparticles: A possible environmental factor promoting obesity-related metabolic disorders.

Food additives are one major hallmark of ultra-processed food in the Western-diet, a food habit often associated with metabolic disorders. Among these additives, the whitener and opacifying agent titanium dioxide (TiO) raises public health issues due to the ability of TiO nanoparticles (NPs) to cross biological barriers and accumulate in different systemic organs like spleen, liver and pancreas. However before their systemic passage, the biocidal properties of TiO NPs may alter the composition and activity of the gut microbiota, which play a crucial role for the development and maintenance of immune functions. Once absorbed, TiO NPs may further interact with immune intestinal cells involved in gut microbiota regulation. Since obesity-related metabolic diseases such as diabetes are associated with alterations in the microbiota-immune system axis, this raises questions about the possible involvement of long-term exposure to food-grade TiO in the development or worsening of these diseases. The current purpose is to review the dysregulations along the gut microbiota-immune system axis after oral TiO exposure compared to those reported in obese or diabetic patients, and to highlight potential mechanisms by which foodborne TiO NPs may increase the susceptibility to develop obesity-related metabolic disorders.