Antimicrobial peptides (AMPs) are usually small molecule peptides, which display broad-spectrum antimicrobial activity, high efficiency, and stability. For the multiple-antibiotic-resistant strains, AMPs play a significant role in the development of novel antibiotics because of their broad-spectrum antimicrobial activities and specific antimicrobial mechanism. Besides broad-spectrum antibacterial activity, AMPs also have anti-inflammatory activity. The neutralization of lipopolysaccharides (LPS) plays a key role in anti-inflammatory action of AMPs. On the one hand, AMPs can readily penetrate the cell wall barrier by neutralizing LPS to remove Gram-negative bacteria that can lead to infection. On the contrary, AMPs can also inhibit the production of biological inflammatory cytokines to reduce the inflammatory response through neutralizing circulating LPS. In addition, AMPs also modulate the host immune system by chemotaxis of leukocytes, to promote immune cell proliferation, epithelialization, and angiogenesis and thus play a protective role. This review summarizes some recent researches about anti-inflammatory AMPs, with a focus on the interaction of AMPs and LPS on the past decade.

Aims: To understand the effects of Trp residues in linear antimicrobial peptides with a-helical conformations on cell permeation ability and membrane transduction efficacy. Methods and Results: A series of L-K6 analogues were designed and synthesized by replacing Ile or Leu with Trp at different positions on the hydrophobic face of L-K6. The antimicrobial and haemolytic activity and secondary structure of the designed Trp-containing peptides were assessed. In addition, the role of Trp in membrane disruption for these designed peptides was investigated. I1W, I4W and L5W demonstrated stronger activity than the other peptides against both Gram-positive and Gram-negative bacteria. All of the tested peptides preferentially interacted with negatively charged vesicles composed of phosphatidylglycerol (PG)/cardiolipin (CL) or PG/CL/phosphatidylethanolamine, and, to a lesser extent, with zwitterionic vesicles. I1W, I4W and L5W caused calcein release at 2Á5 lmol l À1 . Conclusions:The position of Trp, rather than the number of Trp residues, in these peptides was an important factor in the antimicrobial activity. Trp residues were deeply inserted into negatively charged membranes but were largely exposed in aqueous buffer solution.Significance and Impact of the Study: These Trp-containing peptides may represent good candidates for new antibiotic agents and for use in new therapeutic approaches.

Dental caries and periodontitis are common bacterial mouth infections. As a potentially attractive substitute for conventional antibiotics, antimicrobial peptides have been widely tested and used for controlling bacterial infections. In this study, we tested the efficacy of the peptides from the skin secretions of Rana chensinensis for killing several major cariogenic and periodontic pathogens as well as Candida albicans. L-K6, a temporin-1CEb analog, exhibited high antimicrobial activity against the tested oral pathogens and was able to inhibit Streptococcus mutans biofilm formation and reduce 1-day-old S. mutans biofilms with a minimum biofilm inhibitory concentration and reducing concentration of 3.13 and 6.25 μM, respectively. The results of confocal laser scanning microscopy demonstrated that the peptide significantly reduced cell viability within oral biofilms. Furthermore, as little as 5 μM L-K6 significantly inhibited lipopolysaccharide (LPS)- and interleukin-1β-induced productions of interleukin-8 and tumor necrosis factor-α from THP-1 monocytic cells. This anti-inflammatory activity is associated with the binding of L-K6 to LPS and neutralizing LPS-induced proinflammatory responses in THP-1 cells, as well as dissociating LPS aggregates. Our results suggest that L-K6 may have potential clinical applications in treating dental caries by killing S. mutans within dental plaque and acting as anti-inflammatory agents in infected tissues.

Cell surface binding and internalization are critical for the specific targeting and biofunctions of some cationic antimicrobial peptides (CAPs) with anticancer activities. However, the detailed cellular process for CAPs interacting with cancer cells and the exact molecular basis for their anticancer effects are still far from being fully understood. In the present study, we examined the cell surface binding, uptaking and anti-cancer activity of L-K6, a lysine/leucine-rich CAP, in human MCF-7 breast cancer cells. We found that L-K6 preferentially interact with MCF-7 cells. This tumor-targeting property of L-K6 might be partially due to its interactions with the surface exposed and negatively charged phosphatidylserine. Subsequently, L-K6 could internalize into MCF-7 cells mainly through a clathrin-independent macropinocytosis, without significant cell surface disruption. Finally, the internalized L-K6 induced a dramatic nuclear damage and MCF-7 cell death, without significant cytoskeleton disruption and mitochondrial impairment. This cytotoxicity of L-K6 against MCF-7 cancer cells could be further confirmed by using a mouse xenograft model. In summary, all these findings outlined the cellular process and cytotoxicity of L-K6 in MCF-7 cancer cells, and might help understand the complicated interactions between CAPs and cancer cells.

Recent advances in the search for novel anticancer agents have indicated that the positively charged antimicrobial peptides have emerged as promising agents offering several advantages over the conventional anticancer drugs. As a naturally occurring, cationic, α-helical antimicrobial peptide, temproin-1CEa has been proved to exhibit a potent anticancer effect and a moderate hemolytic activity. In order to reduce the hemolytic activity of temporin-1CEa and improve its anticancer potency towards a range of human breast cancer cells, in the present study, six analogs of temporin-1CEa were rationally designed and synthesized. The amphipathicity levels and α-helical structural patterns of peptides were reserved, while their cationic property and hydrophobicity were changed. The results of MTT and hemolysis assay indicated that the analog peptides displayed an improved anticancer activity and showed an overall optimized therapeutic index. The hydrophobicity of peptides was positively correlated with their hemolytic and antitumor activities. Moreover, the data suggest a strategy of increasing the cationicity while maintaining the moderate hydrophobicity of naturally occurring amphipathic α-helical peptides to generate analogs with improved cytotoxicity against tumor cells but decreased activity against non-neoplastic cells such as human erythrocytes. This work highlights the potential for rational design and synthesis of improved antimicrobial peptides that have the capability to be used therapeutically for treatment of cancers.

No abstract

Tryptophan (Trp) residues reportedly exhibit a strong membrane-disruptive activity, and this property endows Trp-containing antimicrobial peptides (AMPs) with a unique ability to interact with the surface of bacterial cell membranes, possibly improving antimicrobial properties. In this study, we investigated the influence of Trp residues engineered to have a distinct preference for the interface region of lipid bilayers on antimicrobial activity. We designed two Trp-substituted AMPs (I1WL5W and I4WL5W) by replacing Ile or Leu residues with two Trp residues at different positions in the L-K6 peptide, and determined their antimicrobial activity and mechanism of membrane action. Both I1WL5W and I4WL5W exhibited significantly higher antimicrobial activity and lower cytotoxicity against Gram-negative and Gram-positive bacteria compared with L-K6. The Trp-substituted peptides had a disordered structure in aqueous solution and adopted an α-helical structure in solutions of 50% trifluoroethanol/water and 30 mM SDS. I1WL5W and I4WL5W caused a significant leakage of calcein from liposomes containing membranes that mimicked those of Escherichia coli and Staphylococcus aureus. Scanning electron microscopy analysis suggested that I1WL5W and I4WL5W killed bacteria by disrupting bacterial cell membranes. Furthermore, fluorescence and quenching data from a variety of liposomes, which mimic different cell membranes, indicated that the Trp-substituted peptides could insert into the lipid bilayers and induce blue shifts in the emission spectra of the Trp residues. I1WL5W and I4WL5W were also less susceptible to acrylamide or KI quenchers. The current work may be important for designing novel Trp-containing peptides exhibiting strong antimicrobial abilities by penetrating bacterial membranes.

Inorganic selenite can be transformed into organic forms and bind to proteins and polysaccharides in Se-enriched submerged Ganoderma lucidum cultures. In the present study, a novel Se-containing polysaccharide, SeGLP-2B-1, was purified from the Se-enriched mycelia of G. lucidum and the antiproliferative activities against six human cancer cell lines were investigated. The Se content of SeGLP-2B-1 was 186.7 microg/g, which was 150-fold larger than that of the regular polysaccharide GLP-2B-1 (1.3 microg/g). SeGLP-2B-1 (1.06 x 10(6) Da) was composed of glucose, rhamnose, xylose, and galactose with a molar ratio of 1.000:0.652:0.443:0.227. SeGLP-2B-1 exhibited an approximately 10-fold stronger antiproliferative activity against six human cancer cell lines as compared to GLP-2B-1. Thus, Se is believed to play an important role in increasing the antiproliferative property of SeGLP-2B-1. These findings indicate that SeGLP-2B-1 may serve as a dietary Se supplement.