The Antimicrobial Peptide NK-2, the Core Region of Mammalian NK-Lysin, Kills Intraerythrocytic Plasmodium falciparum

Abstract

In a time of dramatically increasing resistance of microbes to all kinds of antibiotics, natural antimicrobial peptides and synthetic analogs thereof have emerged as compounds with potentially significant therapeutical applications against human pathogens. Only very few of these peptide antibiotics have been tested against protozoan pathogens that are a major cause of morbidity and mortality in large parts of the world. Here, we studied the effect of NK-2, a peptide representing the cationic core region of the lymphocytic effector protein NK-lysin, on the malaria parasite Plasmodium falciparum. Whereas noninfected red blood cells were hardly affected, human erythrocytes infected with the parasite were rapidly permeabilized by NK-2 in the micromolar range. Loss of plasma membrane asymmetry and concomitant exposure of phosphatidylserine upon infection appears to be the molecular basis for the observed target preference of NK-2, as can be demonstrated by annexin V binding. The peptide also affects the viability of the intracellular parasite, as evidenced by the drop in DNA content of cultured parasites. Accumulated evidence derived from permeabilization assays using parasites and liposomes as targets and from fluorescence microscopy of infected erythrocytes treated with fluorescently labeled NK-2 indicates that the positively charged peptide electrostatically interacts with the altered and negatively charged plasma membrane of the infected host cell and traverses this membrane as well as the parasitophorous vacuole membrane to reach its final target, the intracellular parasite. The apparent affinity for foreign membranes that resulted in the death of a eukaryotic parasite residing in human host cells makes NK-2 a promising template for novel anti-infectives.

Structural Determinants of Antimicrobial and Antiplasmodial Activity and Selectivity in Histidine-rich Amphipathic Cationic Peptides

“…The less potent of these are hemolytic at their active concentrations, although erythrocytes infected with P. falciparum appear often to be more susceptible to lysis than noninfected host cells (56 -58). More potent peptides, including acylated derivatives (58,59) and, in particular, peptide analogues (60), are active at concentrations far below that required for erythrocyte lysis, and such peptides have been shown to be localized at the parasite membrane within infected erythrocytes (56,59). In the present study, the antiplasmodial activity of, in particular, D-HALO-rev indicates that histidinerich peptides can be designed that can also enter P. falciparuminfected erythrocytes at sublytic concentrations and kill the parasite.…”

“…One major difference is that Plasmodium plasma membranes also have an extremely low cholesterol content (61). Furthermore, both exposure of phosphatidylserine at the external surface of the erythrocyte plasma membrane (40,56) and increased membrane fluidity and disorder, accompanying an increase in the proportion of unsaturated lipid acyl chains in the erythrocyte membrane phospholipids and a slight reduction of the cholesterol content (62)(63)(64)(65), have been demonstrated postinfection. In contrast, healthy erythrocyte membranes retain asymmetry, and phosphatidylserine is not presented at the external surface prior to a pathological stimulus (40).…”

Cationic Antimicrobial Peptides and Biogenic Silver Nanoparticles Kill Mycobacteria without Eliciting DNA Damage and Cytotoxicity in Mouse Macrophages

“…NK-2 is a peptide representing the cationic core region of the lymphocytic effector protein NK-lysin, which is found in NK cells and cytotoxic T cells (13). NK-2 has been found active against Gram-positive and Gram-negative bacteria, parasitic protozoa such as Trypanosoma cruzi (14) and Plasmodium falciparum (13) and the fungal pathogen Candida albicans (15). LL-37, an amphipathic ␣-helical peptide, is expressed in neutrophils, macrophages, monocytes, myeloid bone marrow cells, and epithelial cells.…”

In vitro antibacterial and antimalarial activity of dehydrophenylalanine-containing undecapeptides alone and in combination with drugs

“…In addition, the results also showed that haemolysis of parasitised RBCs was negligible even after 48 h of incubation with peptide in combination with CQ. Literature shows that there are a number of natural and engineered AMPs with antiplasmodial activity, such as cecropin, magainin, defensin, gomesin, lipodermaseptin derivatives and defensin derivative NK-2 [29,30]. However, most of them fall short of the requirements for an effective antiplasmodial molecule, primarily because they lose their effectiveness in the presence of serum proteins and simultaneously cause high haemolysis.…”