1. Influence of lysine N(ε)-trimethylation and lipid composition on the membrane activity of the cecropin A-melittin hybrid peptide CA(1-7)M(2-9)
Maria J Feio, Margarida Bastos, David Andreu, Beatriz G De la Torre, Luis Rivas, Vitor Teixeira, Ana Coutinho J Phys Chem B . 2010 Dec 16;114(49):16198-208. doi: 10.1021/jp106915c.
Although many studies have pointed out the promising role of antimicrobial peptides (AMPs) as therapeutical agents, their translation into clinical research is being slow due to the limitations intrinsic to their peptide nature. A number of structural modifications to overcome this problem have been proposed, leading to enhanced AMP biological lifetimes and therapeutic index. In this work, the interaction between liposomes of different lipidic composition and a set of lysine N(ε)-trimethylated analogs of the cecropin A and melittin hybrid peptide, CA(1-7)M(2-9) [H-KWKLFKKIGAVLKVL-amide], was studied by differential scanning calorimetry (DSC) and fluorescence spectroscopy. The study was carried out using membrane models for mammalian erythrocytes (zwitterionic lipids) and for bacteria (mixture of zwitterionic and negatively charged lipids). The results show that trimethylated peptides interact strongly with negatively charged (bacterial cell model) but not with zwitterionic (erythrocyte model) liposomes. These results are in agreement with the reduction of cytotoxicity and ensuing improvement in therapeutic index vs parental CA(1-7)M(2-9) found in a related study. Moreover, the modified peptides act differently depending on the model membrane used, providing further evidence that the lipid membrane composition has important implications on AMP membrane activity.
2. Lysine N(epsilon)-trimethylation, a tool for improving the selectivity of antimicrobial peptides
Dolores Díaz, María Fernández-Reyes, Mariona Vallès-Miret, David Andreu, Ania Cabrales-Rico, Jesús Jiménez-Barbero, Luis Rivas, Beatriz G de la Torre J Med Chem . 2010 Aug 12;53(15):5587-96. doi: 10.1021/jm100261r.
The effects of lysine N(epsilon)-trimethylation at selected positions of the antimicrobial cecropin A-melittin hybrid peptide KWKLFKKIGAVLKVL-amide have been studied. All five monotrimethylated, four bis-trimethylated plus the per-trimethylated analogues have been synthesized and tested for antimicrobial activity on Leishmania parasites and on Gram-positive and -negative bacteria, as well as for hemolysis of sheep erythrocytes as a measure of cytotoxicity. The impact of trimethylation on the solution conformation of selected analogues has been evaluated by NMR, which indicates a slight decrease in the alpha-helical content of the modified peptides, particularly in the N-terminal region. Trimethylation also enhances the proteolytic stability of mono- and bis-trimethylated analogues by 2-3-fold. Although it tends to lower antimicrobial activity in absolute terms, trimethylation causes an even higher decrease in hemolytic activity and therefore results in improved selectivity for several analogues. The monotrimethylated analogue at position 6 shows the overall best selectivity against both the Leishmania donovani protozoan and Acinetobacter baumannii, a Gram-negative bacterium of increasing clinical concern.
3. In vitro activities of antibiotics and antimicrobial cationic peptides alone and in combination against methicillin-resistant Staphylococcus aureus biofilms
Emel Mataraci, Sibel Dosler Antimicrob Agents Chemother . 2012 Dec;56(12):6366-71. doi: 10.1128/AAC.01180-12.
Methicillin-resistant Staphylococcus aureus (MRSA) strains are most often found as hospital- and community-acquired infections. The danger of MRSA infections results from not only the emergence of multidrug resistance but also the occurrence of bacteria that form strong biofilms. We investigated the in vitro activities of antibiotics (daptomycin, linezolid, teichoplanine, azithromycin, and ciprofloxacin) and antimicrobial cationic peptides {AMPs; indolicidin, CAMA [cecropin (1-7)-melittin A (2-9) amide], and nisin} alone or in combination against MRSA ATCC 43300 biofilms. The MICs and minimum biofilm eradication concentrations (MBECs) were determined by the broth microdilution technique. Antibiotic and AMP combinations were assessed using the checkerboard technique. For MRSA planktonic cells, MICs of antibiotics and AMPs ranged between 0.125 and 512 and 8 and 16 mg/liter, respectively, and the MBEC values were between 512 and 5,120 and 640 mg/liter, respectively. With a fractional inhibitory concentration of ≤0.5 as the borderline, synergistic interactions against MRSA biofilms were frequent with almost all antibiotic-antibiotic and antibiotic-AMP combinations. Against planktonic cells, they generally had an additive effect. No antagonism was observed. All of the antibiotics, AMPs, and their combinations were able to inhibit the attachment of bacteria at 1/10 MIC and biofilm formation at 1× MIC. Biofilm-associated MRSA was not affected by therapeutically achievable concentrations of antimicrobial agents. Use of a combination of antimicrobial agents can provide a synergistic effect, which rapidly enhances antibiofilm activity and may help prevent or delay the emergence of resistance. AMPs seem to be good candidates for further investigations in the treatment of MRSA biofilms, alone or in combination with antibiotics.
