Microorganismos con acción probiótica en alteraciones causadas por la exposición a xenobióticos obesógenos: Modulación e intervención en disbiosis de la microbiota

Zusammenfassung

The human intestinal microbiota comprises a diverse ecosystem of bacteria, viruses, fungi, parasites, and other microorganisms that play a crucial role in maintaining human health. This microbial community is vital for efficient digestion, nutrient absorption, defense against pathogens, and immune system modulation. Several factors can influence the composition of the microbiota, including the mode of birth, age, dietary patterns, exposure to environmental toxins, antibiotic usage, and lifestyle choices, such as physical activity. Perturbations in the microbiota, known as microbial dysbiosis, have been associated with the development of different pathologies, including obesity, malnutrition, inflammatory bowel diseases, neurological disorders, and certain types of cancer. Investigating the intricate relationship between the intestinal microbiota and these pathologies holds promise for preventive and therapeutic interventions by targeting the composition and functionality of the microbiota. Overweight and childhood obesity constitute a global health problem that begins at early ages and leads to comorbidities and other non-communicable diseases throughout life. The prevalence of childhood obesity is significantly higher in Western countries, specifically in Spain, where 39% of children are overweight and 16% are obese. This is a multifactorial disease where sedentary lifestyle, high-fat and high-carbohydrate diets, and cumulative exposure to obesogenic contaminants have a significant influence. Moreover, exposure to synthetic chemical substances resulting from industrialization has been linked to increased obesity rates. Bisphenol A (BPA) is one of the most studied endocrine disruptors, and its exposure during early life stages can have significant implications for the development of chronic diseases throughout life. The intestinal microbiota may play an important role in the response to BPA exposure, and studying it helps us understand the cause-and-effect relationship between the intestinal microbiota and diseases triggered by endocrine disruptors. In this doctoral thesis, the main objective is to determine the obesogenic effect of BPA in children through its impact on the gut microbiota, as well as the identification of microbial taxa with beneficial properties for the modulation of dysbiosis caused by endocrine disruptors. The research conducted has allowed for the first-time evaluation of changes in the maturation process of the intestinal microbiota following perinatal exposure to BPA and its possible association with obesity and neurodevelopment. A perinatal BPA exposure trial has been conducted in murine models, where the microbial composition of mothers during pregnancy, the potential synergistic effect of a high-fat diet on offspring microbial evolution, the development of obesity, and changes in neurodevelopment are determined. The combined influence of BPA exposure and a high-fat diet on compositional changes in the microbiota has been determined through 16S ribosomal RNA gene amplicon sequencing. It was found that in the offspring, both variables have a synergistic impact after weaning, but over time, while both variables still have a significant impact, they cease to be synergistic, and the diet's impact increases. The maturation process of the mice's intestinal microbiota was altered after perinatal exposure to BPA, with the genera Alistipes and Turicibacter identified as signature taxa present in groups exposed to BPA and BPA plus a high-fat diet, respectively. Additionally, the genera Alistipes and Anaerostipes, overrepresented in the perinatally BPA-exposed groups, positively correlate with the percentage of body fat. Through a directed BPA culturing assay, 106 fecal samples from children with normal weight, overweight, and obesity were exposed to different concentrations of BPA. In this way, species of the microbiota that exhibited higher abundance in an environment influenced by this endocrine disruptor (ED) were isolated and identified, and the potential resistance of the intestinal microbiota to this compound was described. A catalog of 333 BPA-tolerant bacteria was obtained, which showed taxonomic differences according to the study population. Furthermore, we determined the potential inference of the targeted culturomics assay results on the compositional dynamics of the intestinal microbiota in this population. Specific previously identified genera that tolerated high concentrations of BPA and either promoted or worsened microbial diversity were associated. Clostridium and Romboutsia showed positive correlations, while Intestinibacter, Escherichia-Shigella, Bifidobacterium, and Lactobacillus showed negative correlations with α-diversity. Analysis of the intestinal microbiota in the study groups through 16S ribosomal RNA gene sequencing revealed that the normal-weight group exhibited a more connected network of ASVs (amplicon sequence variants) than the overweight and obesity groups in a network analysis, potentially forming a microbiological community that is more resistant to external environmental factors. Lastly, we have described the bacterial isolate Bacillus sp. AM1, identified through the targeted culturomics assay. By sequencing its complete genome, we were able to identify genes encoding enzymes involved in potential BPA degradation pathways. Finally, together with another strain of the genus Paeniclostridium, also obtained from the targeted culturomics assay, their in vitro and in vivo anti-inflammatory properties were characterized using a murine model of colitis and BPA exposure. The bacteria Paeniclostridium sp. and Bacillus sp. AM1 were capable of reducing the secretion of pro-inflammatory cytokine IL-8 levels by HT-29 cells stimulated with TNF-α in in vitro assays. Additionally, in a murine model of colitis and BPA exposure, Paeniclostridium sp. and Bacillus sp. AM1 were able to limit tissue damage in the colon and reduce the levels of MCP-1 and LCN-2 proteins, whose elevated levels have been previously associated with high urinary levels of BPA in humans.