Antimicrobial peptides in intestinal inflammation, infection and cancer.

Antimicrobial peptides (AMPs) form a significant part of innate immunity. AMP expression is often altered in response to colonic infection, inflammation and cancer. Over the last two decades, the roles of antimicrobial peptides have been discovered and explored. Certain AMPs such as alpha defensin HD 5-6 and beta defensin HBD1 are constitutively expressed while others including defensin HBD2-4 and bactericidal/permeability increasing protein (BPI) are associated with Inflammatory Bowel Disease (IBD). Cathelicidin expression is decreased in colon cancer tumors. Gene expression of several AMPs (beta defensin HBD2-4 and cathelicidin) is induced in response to invasion by gut microbes. Cathelicidin can modulate colitis while other AMPs such as lactoferrin and hepcidin can serve as biomarkers of IBD disease activity and/or colon cancer. Several endogenous host-based AMPs (cathelicidin, elafin and SLPI) may be delivered intravenously or intracolonically in vivo. Novel AMPs (synthetic or artificial non-human peptides) with potent antimicrobial, antiinflammatory or anti-tumoral property have been developed but the application of AMPs for therapeutic purposes is still at an early stage of development. This report details the latest development of AMP-related research with emphasis on innate immunity and pathophysiology of colitis, intestinal infection and cancer.