In the last decades, the indiscriminate use of conventional antibiotics has generated high rates of microbial resistance. This situation has increased the need for obtaining new antimicrobial compounds against infectious diseases. Among these, antimicrobial peptides (AMPs) constitute a promising alternative as therapeutic agents against various pathogenic microbes. These therapeutic agents can be isolated from different organisms, being widespread in nature and synthesized by microorganisms, plants and animals (both invertebrates and vertebrates). Additionally, AMPs are usually produced by a non-specific innate immune response. These peptides are involved in the inhibition of cell growth and in the killing of several microorganisms, such as bacteria, fungi, enveloped viruses, protozoans and other parasites. They have many interesting properties as potential antibiotics, such as relatively small sizes (below 25-30 kDa), amphipathic structures, cationic nature, and offer low probability for the generation of microbial resistance. In recent years, many novel AMPs, with very promising therapeutic properties, have been discovered. These peptides have been the base for the production of chemical analogs, which have been designed, chemically synthesized and tested in vitro for their antimicrobial activity. This review is focused on antibacterial (against Gram (-) and Gram (+) bacteria) and antifungal peptides, discussing action mode of AMPs, and recent advances in the study of the molecular basis of their anti-microbial activity. Finally, we emphasize on their current pharmacological development, future directions and applications of AMPs as promising antibiotics of therapeutic use for microbial infections.

Bovine trypsin immobilized on glyoxyl agarose and submitted to different inactivation conditions produce different conformations.

Nanocarrier systems are currently being developed for peptide, protein and gene delivery to protect them in the blood circulation and in the gastrointestinal tract. Polylactic acid (PLA) and poly(lactic-co-glycolic) acid (PLGA) nanoparticles loaded with a new antimicrobial GIBIM-P5S9K peptide were obtained by the double emulsion solvent extraction/evaporation method. PLA- and PLGA-NPs were spherical with sizes between 300 and 400 nm for PLA and 200 and 300 nm for PLGA and 20 mV. The peptide-loading efficiency of PLA-NP and PLGA-NPs was 75% and 55%, respectively. PLA- and PLGA-NPs released around 50% of this peptide over 8 h. In 10% human sera the size of peptide loaded PLA- and PLGA-NPs increased between 25.2% and 39.3%, the PDI changed from 3.2 to 5.1 and the surface charge from −7.15 to 14.6 mV. Both peptide loaded PLA- and PLGA-NPs at 0.5 μ M peptide concentration inhibited the growth of Escherichia coli O157:H7 ( E . coli O157:H7 ), methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas. aeruginosa (P. aeruginosa) . In contrast, free peptide inhibited at 10 μ M but did not inhibit at 0.5 and 1 μ M. These PLA- and PLGA-NPs presented <10% hemolysis indicating that they are hemocompatible and promising for delivery and protection system of GIBIM-P5S9K peptide.

Lactoferrampin 265–284 (LFampin 265–284) is a peptide consisting of residues 265–284 of N1‐domain of bovine Lactoferrin (LF). This peptide has several cationic groups in the C‐terminal lobe, exhibiting an antibacterial activity against a wide range of microorganisms. However, LFampin 265–284 exhibits low antimicrobial activity against the O157:H7 enterohaemorrhagic Escherichia coli (EHEC O157:H7) when compared with Lactoferrin chimera and Lactoferricin. Here, we have designed three analogues of LFampin 265–284 based on the distribution of cationic groups, hydrophobicity, size, and sequence. Analogues were synthesized by solid phase chemistry using Fmoc methodology obtaining peptides with 95% purity. All peptides maintain the ability to adopt helical conformations (checked by circular dichroism spectra and molecular simulations). Some of these analogues exhibited a significant increase in antimicrobial activity by counting colony forming units against EHEC O157:H7 compared to native LFampin 265–284, with MIC of 10 and 40 µM for 264G‐D265K and 264G‐D265K/S272R, respectively. The incorporation of a GKLI sequence in the N‐terminal lobe increased dramatically its antibacterial activity, an effect which has been attributed to the addition of cationic groups in the N‐terminal side that may stabilize the helical conformation of the new designed peptides. © 2013 Wiley Periodicals, Inc. Biopolymers 101: 319–328, 2014.