A46 FECAL β-DEFENSIN LEVELS AS A RELIABLE BIOMARKER OF INTESTINAL DYSBIOSIS

Dysbiosis is defined as alterations or instability in gut microbial composition resulting in altered host function. It is triggered by many environmental factors and has been implicated in the pathogenesis of the Irritable Bowel Syndrome (IBS). Recent focus on the putative role of intestinal microbiome generating low grade inflammation and immune activation in IBS has increased the need for a marker of dysbiosis. β-defensins (β-def) are inducible antimicrobial peptides secreted by diverse cell types in response to pathogen encounter or pro-inflammatory cytokines. Studies in IBS patients show that dysbiosis results in skewing of innate mucosal immunity toward a proinflammatory response (increased β-def levels) in the absence of macroscopic signs of inflammation. Our lab recently demonstrated that colonizing germ-free mice with IBS microbiota results in IBS-like changes in gut function and increase in colonic β-def expression in recipient mice. To investigate whether fecal β-def levels constitute a reliable biomarker of dysbiosis. We induced dysbiosis using different protocols including single antibiotic (Neomycin), an antibiotic cocktail (ABC) or a high-fat/high-sugar diet (HF/HSD). Mice (n=20) were divided into 3 groups and all received 1 week of treatment, preceded and followed by 1-week long baseline and recovery periods. The single antibiotic was administered to C57/BL6 ASF mice, the ABC was given to C57/BL6 SPF mice and another group of C57/BL6 SPF mice received HF/HSD. Stool samples were collected every day for 16S rRNA gene profiling, qPCR analysis of total bacterial load and fecal β-def levels analysis by an ELISA. SPF mice receiving the ABC showed a significant decrease in β-def levels (p<0.0001). Similar differences in β-def levels were observed in ABC treated females. Changes in microbial composition (Bacteroidetes, Firmicutes, Proteobacteria, Tenericutes, TM7) in ABC treated mice significantly correlated with β-def levels. In ASF mice, neomycin administration led to significant changes in β-def levels and alpha- diversity. Unlike ASF males, females showed a significant correlation between changes in microbial composition (Bacteroidetes and Verrucomicrobia) and β-def levels. The HF/HSD transiently altered the microbial richness (baseline vs. treatment: p=0.042; treatment vs. recovery: p=0.045) and diversity (baseline vs. treatment: p=0.009; treatment vs. recovery: p=0.021) but no significant correlations were found between β-def levels and microbial composition. There were significant differences between β-def levels in ASF and SPF treated mice. Our results suggest that innate immune activation is differentially affected in ASF and SPF mice depending on the microbial complexity of the microbiota. These findings indicate that fecal β-defensins are a putative biomarker for dysbiosis and warrant further investigation. CIHR