Cytotoxicity and antigenicity of antimicrobial synthesized peptides derived from the beetle Allomyrina dichotoma defensin in mice

The draft genome sequence of the Japanese rhinoceros beetle Trypoxylus dichotomus septentrionalis towards an understanding of horn formation

The Japanese rhinoceros beetle Trypoxylus dichotomus is a giant beetle with distinctive exaggerated horns present on the head and prothoracic regions of the male. T. dichotomus has been used as a research model in various fields such as evolutionary developmental biology, ecology, ethology, biomimetics, and drug discovery. In this study, de novo assembly of 615 Mb, representing 80% of the genome estimated by flow cytometry, was obtained using the 10 × Chromium platform. The scaffold N50 length of the genome assembly was 8.02 Mb, with repetitive elements predicted to comprise 49.5% of the assembly. In total, 23,987 protein-coding genes were predicted in the genome. In addition, de novo assembly of the mitochondrial genome yielded a contig of 20,217 bp. We also analyzed the transcriptome by generating 16 RNA-seq libraries from a variety of tissues of both sexes and developmental stages, which allowed us to identify 13 co-expressed gene modules. We focused on the genes related to horn formation and obtained new insights into the evolution of the gene repertoire and sexual dimorphism as exemplified by the sex-specific splicing pattern of the doublesex gene. This genomic information will be an excellent resource for further functional and evolutionary analyses, including the evolutionary origin and genetic regulation of beetle horns and the molecular mechanisms underlying sexual dimorphism.

Design of a Helical-Stabilized, Cyclic, and Nontoxic Analogue of the Peptide Cm-p5 with Improved Antifungal Activity

Following the information obtained by a rational design study, a cyclic and helical-stabilized analogue of the peptide Cm-p5 was synthetized. The cyclic monomer showed an increased activity in vitro against Candida albicans and Candida parapsilosis, compared to Cm-p5. Initially, 14 mutants of Cm-p5 were synthesized following a rational design to improve the antifungal activity and pharmacological properties. Antimicrobial testing showed that the activity was lost in each of these 14 analogues, suggesting, as a main conclusion, that a Glu-His salt bridge could stabilize Cm-p5 helical conformation during the interaction with the plasma membrane. A derivative, obtained by substitution of Glu and His for Cys, was synthesized and oxidized with the generation of a cyclic monomer with improved antifungal activity. In addition, two dimers were generated during the oxidation procedure, a parallel and antiparallel one. The dimers showed a helical secondary structure in water, whereas the cyclic monomer only showed this conformation in SDS. Molecular dynamic simulations confirmed the helical stabilizations for all of them, therefore indicating the possible essential role of the Glu-His salt bridge. In addition, the antiparallel dimer showed a moderate activity against Pseudomonas aeruginosa and a significant activity against Listeria monocytogenes. Neither the cyclic monomer nor the dimers were toxic against macrophages or THP-1 human cells. Due to its increased capacity for fungal control compared to fluconazole, its low cytotoxicity, together with a stabilized α-helix and disulfide bridges, that may advance its metabolic stability, and in vivo activity, the new cyclic Cm-p5 monomer represents a potential systemic antifungal therapeutic candidate.

Effective control of Salmonella infections by employing combinations of recombinant antimicrobial human β-defensins hBD-1 and hBD-2

We successfully produced two human β-defensins (hBD-1 and hBD-2) in bacteria as functional peptides and tested their antibacterial activities against Salmonella enterica serovar Typhi, Escherichia coli, and Staphylococcus aureus employing both spectroscopic and viable CFU count methods. Purified peptides showed approximately 50% inhibition of the bacterial population when used individually and up to 90% when used in combination. The 50% lethal doses (LD50) of hBD-1 against S. Typhi, E. coli, and S. aureus were 0.36, 0.40, and 0.69 μg/μl, respectively, while those for hBD-2 against the same bacteria were 0.38, 0.36, and 0.66 μg/μl, respectively. Moreover, we observed that bacterium-derived antimicrobial peptides were also effective in increasing survival time and decreasing bacterial loads in the peritoneal fluid, liver, and spleen of a mouse intraperitoneally infected with S. Typhi. The 1:1 hBD-1/hBD-2 combination showed maximum effectiveness in challenging the Salmonella infection in vitro and in vivo. We also observed less tissue damage and sepsis formation in the livers of infected mice after treatment with hBD-1 and hBD-2 peptides individually or in combination. Based on these findings, we conclude that bacterium-derived recombinant β-defensins (hBD-1 and hBD-2) are promising antimicrobial peptide (AMP)-based substances for the development of new therapeutics against typhoid fever.

In vitro bactericidal activity of human beta-defensin 2 against nosocomial strains

Human beta-defensin 2 (hBD-2) is a 41-amino acid cationic peptide of the innate immune system that serves as antimicrobial molecule. We determined the bactericidal activity of synthetic hBD-2 against nosocomial strains belonging to eight different bacterial species and exhibiting various antimicrobial resistance phenotypes. The native disulfide connectivity was found essential for the bactericidal activity of hBD-2, while sodium chloride concentration was reversely associated with its potency. hBD-2 exhibited high bactericidal activity against Acinetobacter baumannii, Pseudomonas aeruginosa, Enterococcus faecalis, Enterococcus faecium and Staphylococcus aureus clinical strains. Characteristically, A. baumannii strains that exhibited multi-drug resistant (MDR) phenotypes were susceptible to lower concentrations of hBD-2 (vLD(90)=3.25-4.5 microg/ml) in comparison with non-MDR (wild-type) A. baumannii strains (vLD(90)=3.90-9.35 microg/ml). Bactericidal activity of hBD-2 was less pronounced against Escherichia coli, Klebsiella pneumoniae and Proteus mirabilis strains but was significantly enhanced against strains of these species that exhibited resistance to several beta-lactam antibiotics. These observations give indications that the natural hBD-2 has a potential therapeutic role against bacterial pathogens and particularly against those exhibiting MDR phenotypes.

Characteristics of novel insect defensin-based membrane-disrupting trypanocidal peptides

Synthetic D- and L-amino acid type cationic 9-mer peptides (all sequences were synthesized as D- or L-amino acids) derived from the active sites of insect defensins were tested for their ability to modify the growth of blood-stream form African trypanosomes in vitro. One of them, the D-type peptide A (RLYLRIGRR-NH(2)), irreversibly suppressed proliferation of the Trypanosoma brucei brucei GUTat3.1 parasite. The presence of negatively charged phosphatidylserine on the surface of the parasites was demonstrated, suggesting electrostatic interaction between the peptide and the phospholipids. Furthermore, this peptide was found to alter trypanosome membrane-potentials significantly, an effect apparently due to the removal of the parasite's plasma membrane. The potential toxic effects of D-peptide A on mammalian cells was assessed using human brain microvascular endothelial cells. Only minor effects were found when the endothelial cells were exposed for 16 h to peptide concentrations of less than 200 microM. These findings suggest that insect defensin-based peptides represent a potentially new class of membrane-disrupting trypanocidal drugs.

Selective cancer cell cytotoxicity of enantiomeric 9-mer peptides derived from beetle defensins depends on negatively charged phosphatidylserine on the cell surface

Four enantiomeric 9-mer peptides named d-peptide A, B, C and D were designed and synthesized on the basis of 43-mer insect defensins from two beetles. The d-9-mer peptides maintained bacterial membrane disruptive activity similar to the original peptides and also showed various extents of growth inhibitory activity against different cancer cell lines. Of these peptides, d-peptide B exhibited the highest selective cancer cell cytotoxicity against the mouse myeloma cell line, P3-X63-Ag8.653. Flow cytometric and scanning electron microscopic analysis revealed d-peptide B disrupts mouse myeloma membrane construction, whereas no cytotoxic effect on normal leukocytes was observed. Moreover, a strong correlation between negatively charged phosphatidylserine (PS) density in cancer cell membrane surface and sensitivity to d-9-mer peptides were observed in various cancer cell lines. These results suggest that d-9-mer peptides have negative charge-dependent selective cancer cell cytotoxicity targeting PS in the cancer cell membrane. In addition, synergic growth inhibitory activity against mouse myeloma was observed in combinations of d-peptide B and dexamethasone. These results suggest d-9-mer peptides are promising candidates for novel anticancer drugs.

Synthetic nonamer peptides derived from insect defensin mediate the killing of African trypanosomes in axenic culture

Synthetic antimicrobial 9-mer peptides (designated as peptides A and B) designed on the basis of insect defensins and their effects on the growth of African trypanosomes were examined using two isolates of Trypanosoma congolense, IL1180 and IL3338, and two isolates of Trypanosoma brucei brucei, ILTat1.1and GUTat 3.1, under axenic culture conditions. Both peptides inhibited the growth of all bloodstream form (BSF) trypanosomes at 200-400 microg/mL in the complete growth medium, with peptide A being more potent than peptide B. In addition, these peptides exhibited efficient killing at 5-20 microg/mL on BSF trypanosomes suspended in phosphate-buffered saline, whereas procyclic insect forms in the same medium were more refractory to the killing. Electron microscopy revealed that the peptides induced severe defects in the cell membrane integrity of the parasites. The insect defensin-based peptides up to either 200 or 400 microg/mL showed no cell killing or growth inhibition on NIH3T3 murine fibroblasts. The results suggest that the design of suitable synthetic insect defensin-based 9-mer peptides might provide potential novel trypanocidal drugs.