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OBJECTIVE:Intestinal proteases carry out a variety of functions in the gastrointestinal (GI) tract. Studies have reported that elevated enteric proteases in patients with GI disease can alter intestinal physiology, however the origin (human vs. microbial) of elevated proteases in patients with GI disease is unclear. AIM:The aim of this study was to investigate the association between protease activity and the microbiota in human fecal samples. DESIGN:In order to capture a wide range of fecal protease (FP) activity stool samples were collected from 30 IBS patients and 24 healthy controls. The intestinal microbiota was characterized using 454 high throughput pyro-sequencing of the 16S rRNA gene. The composition and diversity of microbial communities were determined and compared using the Quantitative Insights Into Microbial Ecology (QIIME) pipeline. FP activity levels were determined using an ELISA-based method. FP activity was ranked and top and bottom quartiles (n=13 per quartile) were identified as having high and low FP activity, respectively. RESULTS:The overall diversity of the intestinal microbiota displayed significant clustering separation (p = 0.001) between samples with high vs. low FP activity. The Lactobacillales, Lachnospiraceae, and Streptococcaceae groups were positively associated with FP activity across the entire study population, whilst the Ruminococcaceae family and an unclassified Coriobacteriales family were negatively associated with FP activity. CONCLUSIONS:These data demonstrate significant associations between specific intestinal bacterial groups and fecal protease activity and provide a basis for further causative studies investigating the role of enteric microbes and GI diseases.

Over the past decade, attention has been paid to the role of visceral sensitivity in the pathophysiology of functional bowel disorders, especially irritable bowel syndrome, and visceral hypersensitivity is the most widely accepted mechanism responsible for both motor alterations and abdominal pain. Inflammatory mediators sensitize primary afferents, especially C-fibre polymodal nociceptors, favouring the recruitment of silent nociceptors that give rise to secondary spinal sensitization. After local tissue injury, the release of chemical mediators such as potassium ions, ATP, bradykinin and prostaglandin E2 directly activate nerve endings and indirectly trigger the release of algesic mediators such as histamine, 5-hydroxytryptamine and nerve growth factor from other cells, which, in turn, stimulate proximal afferent nerve endings and silent nociceptors. Among the intermediary structures activated by inflammatory mediators and susceptible to the release of proalgesic substances, mast cells and platelets play a crucial role; however, immunocytes such as macrophages and neutrophils or sympathetic nerve terminals are also candidates. Moreover, events likely to activate synthesis of mediators by mast cells, such as stress and septic shock, also trigger colonic hypersensitivity. Prolonged visceral hyperalgesia may also depend on spinal sensitization. Anumber of substances are candidates to play a role at the spinal cord level in mediating painful and nonpainful sensations. Among them, substance P, dynorphins and glutamate play a pivotal role in postsynaptic sensitization, particularly during and after gut inflammation. Finally, despite the complexity of the relationship between inflammatory mediators and gut hypersensitivity, numerous results strongly suggest that alteration neuroimmune communications at the gut level may trigger a series of events that give rise to chronic changes in visceral sensitivity.