Self-assembled Amphiphilic Cationic Peptides And Their Antimicrobial Activities

The increasing emergence of drug-resistant pathogenic microbes,especially multidrug-resistant bacteria poses a serious threat to public health as well as a great challenge to clinical therapy.Despite the prompt antibiotic treatment,the morbidity and mortality involved in microbial infectious diseases remains devastating due to the inability of conventional antibiotics to kill drug-resistant microbes.Therefore,it is urgent to exploit new alternative antimicrobial agents with strong antimicrobial activities and a lower tendency to develop drug resistance.Cationic peptides have recently attracted great attention as one of the most promising substitute for antibiotics because of their unique mechanism and ability to combat multidrug-resistant microbes.In this study,we have designed two amphiphilic cationic peptides PA-28(C16WILA2G3K9TAT)and PAR9NP2,which incorporated cationic cell penetrating peptide(CPP)TAT and NP2 respectively.The self-assembled nanostructures of the cationic peptides were observed using scanning electron microscopy(SEM)and further characterized by dynamic light scattering(DLS)assay and determination of critical micelle concentration(CMC).The self-assembly behaviors of the two peptides were simulated using dissipative particle dynamics(DPD)method.To investigate their antimicrobial activities,the minimum inhibitory concentration(MIC)and minimum bactericidal concentration(MBC)of the peptides were tested on a range of bacteria and fungi,including drug-resistant bacteria.Their preliminary modes of action on microbes were investigated by SEM,transmission electron microscopy(TEM)and electrolyte release assay.The invo anti-infective activities of the peptides were evaluated using Staphylococcus aureus-induced meningitis rats.In addition,the hemolysis toxicity of the two cationic peptides were determined on human red blood cells(hRBC).Both PA-28 and PAR9NP2 were able to self-assemble into nanoparticles in water solution.And the simulation results were consistent with the experiments.PA-28 was potent against both gram-positive and gram-negative bacteria,including drug-resistant bacteria methicillin-resistant Staphylococcus aureus(MRSA).PAR9NP2 also showed broad-spectrum antimicrobial activities against tested bacteria and fungi including MRSA.Especially,PAR9NP2 was more potent than antibiotic cephalexin against S.aureus,and PAR9NP2 was much powerful on both bacteria and fungi than the unassembled counterpart R9.The two cationic peptides combined with and further disintegrated negatively charged microbial membrane,resulting in leakage of microbial intracellular electrolytes and cell death.In vivo assay indicated the two peptides were able to cross the blood brain barrier(BBB)and kill the bacteria in infected brains of rats.In addition,the peptides showed relatively low hemolysis on hRBCs.Taken together,they could be potential antimicrobial agents for treating microbial infections.