Exploring Ga³⁺ metal complexes of a tryptophan metabolite in microbiota exposed to ionizing radiation

In the human body, bacteria coexist symbiotically under normal conditions. However, radiation can disrupt this balance, causing microbiota dysbiosis. This is particularly observed in cancer patients undergoing radiation therapy. Recent research highlights microbiota-derived metabolites as critical signalling molecules or metabolic precursors, with shown radioprotective effects. Among these, 8-hydroxyquinoline-2-carboxylic acid (8-HQA), a tryptophan metabolite from the kynurenic acid pathway, has been studied for its chelation properties and radioprotective effects. Previous studies indicated the potential of 8-HQA for the complexation of cations, such as Ga³⁺, to affect the bacterial metabolism. These results lead us to a deeper evaluation of the possible action on 8-HQA and its Ga³⁺ metal complexes on microbiota exposed to ionizing radiation. Inactivation kinetics studies by ionizing radiation of individual and co-culture bacterial isolates from human microbiota were performed. The preliminary results indicated a radioprotective effect of Ga³⁺/8-HQA complex on Actinomyces viscosus and a potential preservation effect against gut microbiota species. Co-culture experiment provided a new perspective, revealing a potential symbiotic effect among oral cavity bacteria with increased survival rates under certain conditions compared to individual assays. This study further advances the assessment of the radioresistance of human microbiota bacteria in a tryptophan metabolite and its Ga³⁺ complexes, contributing to a better understanding of bacterial inactivation patterns in the context of radiotherapy.