Short Leishmanicidal and Antibacterial Membrane-Active peptides from frog skin

Amphibian skin secretions represent one of the richest natural sources for antimicrobial peptides (AMPs), which are synthesized and stored within granules of holocrine-type serous glands and released upon stimulation[1]. In particular, temporins constitute a large family and are among the smallest amphipathic a-helical peptides (10-16 residues) found in nature to date, and with the lowest number of positively charged amino acids[2]. Interestingly, some of them do possess attractive and unique properties including: (i) a rapid membranolytic effect against a large spectrum of pathogens (bacteria, fungi and protozoa of Leishmania genus[3]; (ii) preservation of biological activity in serum and in physiological salt concentration; (iii) anti-endotoxin activity by inhibition of TNF-a release from lipopolysaccharide (LPS)-activated macrophages; (iv) synergistic effect, between them, against Gram-negative bacteria to overcome the microbial resistance imposed by the LPS protective layer. LPS is the major component of the outer membrane of Gram-negative bacteria and forms an efficient barrier against a variety of molecules, including AMPs. LPS also possesses inflammatory properties which can result in a fatal phenomenon known as septic shock. Therefore, the ability of a peptide to display both antimicrobial and anti-endotoxin activities makes it an attractive compound for therapeutic application. Our data have indicated that membrane permeation is the major target for the killing process of temporins and that the synergistic effect of temporins A+L and B+L in the antimicrobial activity is related to the ability of temporin L to prevent the oligomerization of A and B when in contact with LPS, thus allowing their traslocation across the bacterial cell wall into the target cytoplasmic membrane. We have also demonstrated that the same temporin combinations can synergize in the LPS detoxification with a molecular mechanism which is different from that controlling the synergistic effect in the antimicrobial activity against Gram-negative bacteria. However, the two types of synergism are highly dependent on the type of LPS. Another interesting small-sized and membrane-active AMP from frog skin is the 1-18 fragment of esculentin-1b from Rana esculenta. This peptide has been found to endow a potent and rapid bactericidal effect against multi-drug resistant nosocomial pathogens, especially those belonging to Gram-negative species. Overall, such studies should give a valuable contribution to assist in the future design and manufacturing of new peptide-based anti-infective and antisepsis drugs with a new mode of action. 1 Mangoni, M. L., et al.FASEB J. 2001; 15:1431-1432. 2 Simmaco M. et al. Eur. J. Biochem. 1996; 242:788-792 3 Mangoni, M. Let al. J. Biol. Chem. 2005; 280:984-990