Page - (000236) - in Biomedical Chemistry: Current Trends and Developments

Insects are widely distributed and developed in various ecological niches and serve as vectors of many parasitic diseases in humans and animals, suggesting outstanding strategies for defending against pathogens such as microorganisms by overcoming and adapting to different environmental conditions (Lowenberger, 2001). After infection, the parasites are presented to the host immune system and induce the production of defence compounds such as proteins and peptides. Several of these humoral response peptides exert antibacterial, antifungal, or antiviral properties (Bulet, 1999) and are known as small cationic peptides, host defense peptides or antimicrobial peptides (AMPs) (Bell, 2011). AMPs mostly contain 15−45 amino acid residues and are generally cationic at physiological pH, often with an amphipathic character and encoded by separated genes. They form the first line of host defence against pathogenic infections and are a key component of the ancient innate immune system. AMPs have been identified in various species ranging from bacteria and frogs to mammals, including humans. In insects, AMPs are synthesized in the fat body, blood cells (hemocytes) or epithelia and are released into the hemolymph, the insect blood. In vertebrates, AMPs are present in amphibian skin secretions (Simmaco, 1999) and epithelia (Ganz & Weiss, 1997; Bals, 1998). In mammals, they were also observed in lymphocytes (Agerberth, 2000) and leukocytes (Sorensen, 1997). Because of their broad activity against microbes and expression triggered by various infections, AMPs are currently intensely examined as potential antiparasitic compounds (Vale, 2014). In 2004, the antimicrobial peptide database (APD, http://aps.unmc.edu/AP/main.php) reported a significant number of AMPs that have been discovered at both the gene and protein levels (Wang Z & Wang G, 2003). The APD was later updated and expanded to allow users to search peptide families (bacteriocins, cyclotides, or defensins), peptide sources (fish, frogs or chicken), post-translationally modified peptides (amidation, oxidation, lipidation, glycosylation or D- amino acids), and peptide binding targets (membranes, proteins, DNA/RNA, LPS or sugars) (Wang, 2009).