HD006

Defensins protect human barriers from commensal and pathogenic microorganisms. Human α-defensin 6 (HD-6) is produced exclusively by small intestinal Paneth cells but, in contrast to other antimicrobial peptides (AMPs) for HD-6, no direct antibacterial killing activity has been detected so far. Herein, we systematically tested how environmental factors, like pH and reducing conditions, affect antimicrobial activity of different defensins against anaerobic bacteria of the human intestinal microbiota. Remarkably, by mimicking the intestinal milieu we detected for the first time antibacterial activity of HD-6. Activity was observed against anaerobic gut commensals but not against some pathogenic strains. Antibiotic activity was attributable to the reduced peptide and independent of free cysteines or a conserved histidine residue. Furthermore, the oxidoreductase thioredoxin, which is also expressed in Paneth cells, is able to reduce a truncated physiological variant of HD-6. Ultrastructural analyses revealed that reduced HD-6 causes disintegration of cytoplasmic structures and alterations in the bacterial cell envelope, while maintaining extracellular net-like structures. We conclude that HD-6 is an antimicrobial peptide. Our data suggest two distinct antimicrobial mechanisms by one peptide: HD-6 kills specific microbes depending on the local environmental conditions, whereas known microbial trapping by extracellular net structures is independent of the reducing milieu.

The aim of this study was to determine the effect of interaction between tegafur (FT) and epigallocatechin-3-gallate (EGCG) on the expression of α-defensins (HD-5: human α-defensin 5, HD-6: human α-defensin 6) by using a Caco-2 cell line as a model of human intestinal epithelial cells. This is the first study in which the effect of interaction of an oral anticancer drug and functional food on the innate immune system was examined. α-Defensins are abundant constituents of mouse and human paneth cells and play a role in the innate immune system in intestine. We detected HD-5 and HD-6 mRNA in Caco-2 cells and evaluated the effects of FT and EGCG on these mRNA levels. HD-5 and HD-6 mRNA levels were decreased by exposure to FT. Production of reactive oxygen species (ROS) was induced by exposure to FT as well as H2O2 exposure, and EGCG suppressed FT-induced production of ROS. Furthermore, FT-induced decrease in HD-5 and HD-6 mRNA levels was almost completely suppressed by EGCG. These results indicate that EGCG restored the decrease of α-defensins induced by FT at the transcriptional level in Caco-2 cells, suggesting that EGCG can be used as adjunctive therapy in chemotherapy.