Titolo della tesi: The impact of an animal protein-based diet on murine glioma model
Glioblastoma (GB) is the most aggressive primary brain tumor in adults, characterized by high proliferation, therapy resistance, and limited survival (Koshy et al., 2012). Increasing evidence highlights the role of the gut-brain axis and microbial metabolites, such as hydrogen sulfide (H2S), in modulating central nervous system (CNS) tumor progression (Silver et al., 2021). H2S is endogenously produced but also derives from microbial fermentation of sulfur-containing amino acids, particularly in diets rich in red meat (Teigen et al., 2023). This study explored the impact of an animal protein diet on glioma progression in a murine othotopic model and investigated the involvement of gut-derived H2S in shaping tumor behavior.
Mice fed a red meat-derived protein diet displayed a distinct gut microbial composition enriched in sulfate-reducing bacteria, with significantly elevated fecal H2S levels. Notably, glioma-bearing mice receiving this diet showed reduced tumor volume and decreased cell proliferation, as revealed by Ki67 staining, compared to control mice fed an animal-derived protein diet. Importantly, this was not accompanied by changes in body weight or gut morphology, suggesting a microbiota-driven systemic effect.
In-depth analysis of the tumor microenvironment via confocal immunofluorescence revealed a significant shift in the morphology of tumor-associated microglia/macrophages (TAMs). Iba1+ cells in the red meat diet group exhibited a rounder, less ramified morphology, quantified through form factor analysis and plot profile mapping. This shape shift is indicative of an activated, pro-inflammatory phenotype, which is frequently associated with anti-tumor responses. In contrast, mice on the animal-derived protein diet showed Iba1+ cells with a more branched and complex morphology, typical of a resting or tumor-supportive state. To validate the functional role of H2S, in vitro exposure of GL261 glioma cells to sodium hydrosulfide (NaHS, an H2S donor) led to reduced cell viability and proliferation, and induced a similar morphological rounding in both primary BV2 microglial cells, consistent with an activated state.
Conversely, inhibition of microbial H2S biosynthesis with aminooxyacetic acid (AOAA) abolished the protective effects of the red meat diet in vivo, restoring tumor volume and reversing TAM morphology toward a less activated state. Moreover, blocking TRPV1 receptors—known to mediate vagus nerve activation by H2S—through capsazepine treatment, abolished the antitumor effect, indicating a possible role for neuronal/neuroimmune signaling. In conclusion, these findings suggest that moderate red meat intake modulates the gut microbiota and enhances microbial H2S production, which may exert anti-tumor effects by reshaping the glioma microenvironment through vagal TRPV1 signaling. These results open new perspectives on the gut-brain-tumor axis and highlight the potential role of diet-based interventions in GB therapy.