Temporins Exert a Potent Leishmanicidal Activity at the Promastigote and Amastigote Stages

Leishmaniasis includes a wide variety of clinical symptoms caused by infection with different species of the genus Leishmania, a human protozoan parasite with a worldwide incidence of 12-14 million people affected. The Leishmania parasite has two major stages, differing widely in their antigenic pattern, metabolism, and plasma membrane composition, (i) the flagellated promastigote, in the midgut of the insect vector and (ii) the mammalian intracellular non-flagellated amastigote. Similar to other pathogens, parasites become resistant to most of the first-line drugs. Therefore, there is an urgent need to develop antiparasitic agents with new modes of action. Gene-encoded antimicrobial peptides (AMPs) are promising candidates, but so far only a few of them have shown anti-protozoan activities, mainly on the promastigote stage. Here we show that temporins A and B, 13-amino acid AMPs secreted from the skin of the European red frog Rana temporaria, display anti-Leishmania activity at micromolar concentrations, with no cytolytic activity against human erythrocytes. To the best of our knowledge, temporins represent the shortest natural peptides having the highest leishmanicidal activity, the lowest number of positively charged amino acids (a single lysine/arginine) and maintaining biological function in physiological salt concentration as well as in serum. A series of biophysical studies with intact parasite reveal that their lethal mechanism involves plasma membrane permeation. The unique properties of temporins, as well as their membranolytic effect, which should make it difficult for the pathogen to develop resistance, suggest them as potential candidates for the future design of antiparasitic drugs with a new mode of action.