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Hymenaea genus has been used in folk medicine in Brazil, but few studies investigated its toxicity profile. Thus, the aim of this study was to determine toxicological parameters of Hymenaea courbaril stem bark hydroalcoholic extract by utilizing three cell lines including murine macrophages (RAW 264.7), mouse fibroblast cells (L929) and human lung fibroblast (MRC-5), as well as Salmonella/ microsome assay, and in vivo Caenorhabditis elegans model. The predominant detected phytoconstituents in the extract were coumarins, flavonoids, phenolics, tannins and saponins and by HPLC analysis, astilbin (AST) was found to be the main component. The DPPH assay demonstrated that H. courbaril hydroalcoholic extract exhibited potent antioxidant activity, with an IC 50 of 3.12 μg/ml. The extract at concentrations of 400 and 800 μg/ml decreased cell viability 48 hr after treatment in L929 and MRC-5 cell lines. In the Raw 264.7 strain, just the highest concentration (800 μg/ml) lowered cell viability within 48 hr following exposure. The concentration of 100 μg/ml did not markedly affect cell viability in the trypan blue assay. In the alkaline comet assay the extract was found to be non-genotoxic. In the Ames test, the extract exhibited low mutagenic potential without metabolic activation, since only the highest concentrations produced an effect. H. courbaril extract only affected the survival of C. elegans at concentrations of 800 and 1600 μl/ml. These findings demonstrate that H. courbaril extract appears to exert low toxicity as evidenced in vitro and mutagenicity assays; however, the biological relevance of the response of C. elegans survival to safety assessments needs further studies.

Humans live in symbiosis with a diverse community of microorganisms, which has evolved to carry out many specific tasks that benefit the host, including protection against invading pathogens. Within the chemical diversity of the gastrointestinal tract, small molecules likely constitute chemical cues for the communication between the microbiota and pathogens. Therefore, we sought to investigate if molecules produced by the human gut microbiota show biological activity against the human pathogen Vibrio cholerae . To probe the effects of the gut metabolome on V. cholerae , we investigated its response to small-molecule extracts from human feces, from a complex bacterial community cultivated in vitro , and from culture supernatants of Enterocloster citroniae, Bacteroides thetaiotaomicron , and Bacteroides vulgatus . Using RNA sequencing, we determined the impact of the human gut metabolome on V. cholerae global gene expression. Among the genes downregulated in the presence of the fecal extract, the most overrepresented functional category was cell motility, which accounted for 39% of repressed genes. Repression of V. cholerae motility by the fecal extract was confirmed phenotypically, and E. citroniae extracts reproduced this phenotype. A complex in vitro microbial community led to increased motility, as did extracts from B. vulgatus , a species present in this community. Accordingly, mucin penetration was also repressed by fecal and E. citroniae extracts, suggesting that the phenotypes observed may have implications for host colonization. Together with previous studies, this work shows that small molecules from the gut metabolome may have a widespread, significant impact on microbe-microbe interactions established in the gut environment.

Yersinia pestis protein Pla is a plasmid-coded outer membrane protein with aspartic-protease activity. Pla exhibits a plasminogen (Plg) activator activity (PAA) that promotes the cleavage of Plg to the active serine-protease form called plasmin. Exactly how Pla activates Plg into plasmin remains unclear. To investigate this event, we performed the interactions between the predicted Plg and Pla protein structures by rigid-body docking with the HEX program and evaluated the complex stability by molecular dynamics (MD) using the GROMACS package programs. The predicted docked complex of Plg-Pla shows the same interaction site predicted by experimental site-direct mutagenesis in other studies. After a total of 8 ns of MD simulation, we observed the relaxation of the beta-barrel structure of Pla and the progressive approximation and stabilization between the cleavage site of Plg into the extracellular loops of Pla, followed by the increase in the number of H bonds. We also report here the aminoacids that participate in the active site and the sub sites of interaction. The total understanding of these interactions can be an important tool for drug design against bacterial proteases.