Five different piscidins from Nile tilapia, Oreochromis niloticus: analysis of their expressions and biological functions

Lack of Acute Toxicity and Mutagenicity from Recombinant Epinephelus lanceolatus Piscidin Expressed in Pichia pastoris

The antimicrobial peptide (AMP) piscidin was identified from Epinephelus lanceolatus and demonstrated to possess antimicrobial and immune-related functions. Supplementation of feed with recombinant Epinephelus lanceolatus piscidin (rEP)-expressing yeast pellets may minimize the excessive use of antibiotics and control pathogens in aquaculture or animal husbandry. However, before implementing rEP as a supplement, it is necessary to understand whether it harbors any toxicity. Since toxicological information on the topic is scarce, the present investigation was carried out to test whether rEP exhibits allergenic and/or toxic effects. In an oral acute toxicity test (OECD 425), Sprague Dawley (SD) rats were administered rEP dissolved in reverse osmosis water, yielding an LD₅₀ > 5000 mg/kg (no observed animal death). The compound was therefore classified as non-toxic by oral administration. In an acute respiratory toxicity test (OECD 403), heads and noses of SD rats were exposed to liquid aerosol for 4 h (the highest concentration that could be administered without causing any animal death), and a lethal concentration (LC₅₀) > 0.88 mg/L was obtained. The mass medium aerodynamics diameter (MMAD) of rEP aerosol particles was 8.18 μm and mass medium aerodynamics diameter (GSD) was 3.04, which meant that 25.90% could enter the airway (<4 μm) of a rat, and 58.06% (<10 μm) could be inhaled by humans. An ocular irritation test (OECD 405) with rEP powder was performed on New Zealand White (NZW) rabbits. Signs of irritation included conjunctival swelling and diffuse flushing 1 h after administration. The signs were less apparent after 24 h and disappeared after 72 h. The classification assigned to the powder was mild eye irritation. Skin sensitization was performed for a local lymphoproliferative test (OECD 442B) using BALB/c mice, with the highest soluble concentration of the rEP considered to be 100% test substance; formulations were diluted to 50% and 25%, and bromodeoxyuridine (BrdU) incorporation was used to measure the degree of lymphocyte proliferation. The stimulation indexes (SIs) were 1.06 (100%), 0.44 (50%), and 0.77 (25%), all of which were less than the cutoff value for a positive sensitization result (1.6). Negative response was also seen in the bacterial reverse mutation test (OECD 471), and no chromosomal effects on Chinese hamster ovary (CHO)-K1 cells were observed (OECD 487). Based on these six toxicity tests, rEP showed neither acute toxic effects in experimental animals nor mutagenicity. Thus, rEP can be considered safe for use in subsequent research on its application as a feed additive for poultry, cattle, or aquatic animals.

TP3, an antimicrobial peptide, inhibits infiltration and motility of glioblastoma cells via modulating the tumor microenvironment

Glioblastoma multiforme (GBM) is a cancer of the central nervous system with limited therapeutic outcomes. Infiltrating cancer cells are the contributing factor to high GBM malignancy. The intracranial brain cancer cell infiltration is a complex cascade involving adhesion, migration, and invasion. An arsenal of natural products has been under exploration to overcome GBM malignancy. This study applied the antimicrobial peptide tilapia piscidin 3 (TP3) to GBM8401, U87MG, and T98G cells. The cellular assays and microscopic observations showed that TP3 significantly attenuated cell adhesion, migration, and invasion. A live‐cell video clip showed the inhibition of filopodia protrusions and cell attachment. Probing at the molecular levels showed that the proteolytic activities (from secretion), the mRNA and protein expression levels of matrix metalloproteinases‐2 and ‐9 were attenuated. This result strongly evidenced that both invasion and metastasis were inhibited, although metastatic GBM is rare. Furthermore, the protein expression levels of cell‐mobilization regulators focal adhesion kinase and paxillin were decreased. Similar effects were observed in small GTPase (RAS), phosphorylated protein kinase B (AKT) and MAP kinases such as extracellular signal‐regulated kinases (ERK), JNK, and p38. Overall, TP3 showed promising activities to prevent cell infiltration and metastasis through modulating the tumor microenvironment balance, suggesting that TP3 merits further development for use in GBM treatments.

Defense involvement of piscidin from striped murrel Channa striatus and its peptides CsRG12 and CsLC11 involvement in an antimicrobial and antibiofilm activity

In this study, we have evaluated bioinformatics characterization and antimicrobial role of two piscidin (Pi) peptide identified from the established transcriptome of striped murrel Channa striatus (Cs). The identified CsPi cDNA contains 256 nucleotides encode a protein with 70 amino acids in length which has two antimicrobial peptides and named CsRG12 and CsLC11. The gene expression analysis with various immune stimulants indicated an induced expression pattern of CsPi. Antibiogram showed that CsRG12 and CsLC11 was active against Staphylococcus aureus ATCC 33592, a major multi-drug resistant (MDR) bacterial pathogen and Bacillus cereus ATCC 2106. The minimum inhibitory concentration (MIC) and antibiofilm assays were conducted to observe the activity of pathogenic bacteria with these derived antimicrobial peptides. Flow cytometry analysis noticed that the CsRG12 and CsLC11 disrupt the membrane formation of S. aureus and B. cereus, which was further assured by scanning electron microscopic (SEM) images that bleb formation leads to disruption around the bacterial membrane. Overall, it is reported that CsPi is involved in innate immunity as the gene expression plays a remarkable role in up and down regulation during infection. In addition, the involvement of peptides in antibiofilm formation and bacterial membrane disruption support its immune character. This study leads to a possibility for the development of therapeutics in aquaculture biotechnology.

Transcriptome analysis identifies immune-related genes and antimicrobial peptides in Siamese fighting fish (Betta splendens)

Siamese fighting fish (Betta splendens) is one of the most widely cultivated ornamental fish in global trade. However, transcriptomic data, which can reveal valuable genetic data for disease control and prevention, are extremely limited for this species. In this study, whole-body transcriptome sequencing of juvenile betta fish generated 4.457 GB of clean data and a total of 71,775 unigenes using the Illumina HiSeq4000 platform. These unigenes were functionally classified using 7 functional databases, yielding 45,316 NR (63.14%), 47,287 NT (65.88%), 39,105 Swiss-Prot (54.48%), 16,492 COG (22.98%), 37,694 KEGG (52.52%), 4,506 GO (6.28%), and 35,374 Interpro (49.28%) annotated unigenes. Furthermore, we also detected 13,834 SSRs distributed on 10,636 unigenes and 49,589 predicted CDSs. Based on KEGG analysis, five innate immune pathways (997 unigenes) were reported, including the NOD-like receptor signaling pathway, complement and coagulation cascades, toll-like receptor signaling pathway, RIG-I-like receptor signaling pathway and cytosolic DNA-sensing pathway. Moreover, four antimicrobial peptide (AMP) families (hepcidin, piscidin, LEAP-2, and defensins) from the betta fish transcriptome were also identified. Additionally, cDNA and genomic DNA of two β-defensins was successfully isolated from four betta fish species. RT-PCR analysis showed that BsBD1 transcripts were most abundant in the muscle and kidney and BsBD2 transcripts were most abundant in the gill. The genomic organization showed that the BD1 and BD2 genes consisted of three exons and two introns according to the GT-AG rule. Most importantly, this is the first report of the betta fish whole-body transcriptome obtained by high-throughput sequencing. Our transcriptomic data and the discovery of betta fish AMPs should promote a better understanding of molecular immunology for disease prevention for further ornamental fish aquaculture.

Dietary supplementation of recombinant antimicrobial peptide Epinephelus lanceolatus piscidin improves growth performance and immune response in Gallus gallus domesticus

Supplementing chicken feed with antibiotics can improve survival and prevent disease outbreaks. However, overuse of antibiotics may promote the development of antibiotic-resistant bacteria. Recently, antimicrobial peptides have been proposed as alternatives to antibiotics in animal husbandry. Here, we evaluate the effects of antimicrobial peptide, Epinephelus lanceolatus piscidin (EP), in Gallus gallus domesticus. The gene encoding EP was isolated, sequenced, codon-optimized and cloned into a Pichia pastoris recombinant protein expression system. The expressed recombinant EP (rEP) was then used as a dietary supplement for G. g. domesticus; overall health, growth performance and immunity were assessed. Supernatant from rEP-expressing yeast showed in vitro antimicrobial activity against Gram-positive and Gram-negative bacteria, according to an inhibition-zone diameter (mm) assay. Moreover, the antimicrobial peptide function of rEP was temperature independent. The fermentation broth yielded a spray-dried powder formulation containing 262.9 μg EP/g powder, and LC-MS/MS (tandem MS) analysis confirmed that rEP had a molecular weight of 4279 Da, as expected for the 34-amino acid peptide; the DNA sequence of the expression vector was also validated. We then evaluated rEP as a feed additive for G. g. domesticus. Treatment groups included control, basal diet and rEP at different doses (0.75, 1.5, 3.0, 6.0 and 12%). Compared to control, rEP supplementation increased G. g. domesticus weight gain, feed efficiency, IL-10 and IFN-γ production. Our results suggest that crude rEP could provide an alternative to traditional antibiotic feed additives for G. g. domesticus, serving to enhance growth and health of the animals.

Novel Chimeric Multiepitope Vaccine for Streptococcosis Disease in Nile Tilapia (Oreochromis niloticus Linn.)

Streptococcus agalactiae is a causative agent of streptococcosis disease in various fish species, including Nile tilapia (Oreochromis niloticus Linn.). Vaccination is an effective disease prevention and control method, but limitations remain for protecting against catastrophic mortality of fish infected with different strains of streptococci. Immunoproteomics analysis of S. agalactiae was used to identify antigenic proteins and construct a chimeric multiepitope vaccine. Epitopes from five antigenic proteins were shuffled in five helices of a flavodoxin backbone, and in silico analysis predicted a suitable RNA and protein structure for protein expression. 45F2 and 42E2 were identified as the best candidates for a chimeric multiepitope vaccine. Recombinant plasmids were constructed to produce a recombinant protein vaccine and DNA vaccine system. Overexpressed proteins were determined to be 30 kDa and 25 kDa in the E. coli and TK1 systems, respectively. The efficacy of the chimeric multiepitope construct as a recombinant protein vaccine and DNA vaccine was evaluated in Nile tilapia, followed by S. agalactiae challenge at 1 × 107 CFU/mL. Relative percentage survival (RPS) and cumulative mortality were recorded at approximately 57-76% and 17-30%, respectively. These chimeric multiepitope vaccines should be applied in streptococcosis disease control and developed into a multivalent vaccine to control multiple diseases.

Development and Challenges of Antimicrobial Peptides for Therapeutic Applications

More than 3000 antimicrobial peptides (AMPs) have been discovered, seven of which have been approved by the U.S. Food and Drug Administration (FDA). Now commercialized, these seven peptides have mostly been utilized for topical medications, though some have been injected into the body to treat severe bacterial infections. To understand the translational potential for AMPs, we analyzed FDA-approved drugs in the FDA drug database. We examined their physicochemical properties, secondary structures, and mechanisms of action, and compared them with the peptides in the AMP database. All FDA-approved AMPs were discovered in Gram-positive soil bacteria, and 98% of known AMPs also come from natural sources (skin secretions of frogs and toxins from different species). However, AMPs can have undesirable properties as drugs, including instability and toxicity. Thus, the design and construction of effective AMPs require an understanding of the mechanisms of known peptides and their effects on the human body. This review provides an overview to guide the development of AMPs that can potentially be used as antimicrobial drugs.

Impact of Tilapia hepcidin 2-3 dietary supplementation on the gut microbiota profile and immunomodulation in the grouper (Epinephelus lanceolatus)

Hepcidin regulates iron homeostasis and host-defense mechanisms, while the hepcidin-like protein, Tilapia hepcidin (TH)2-3, functions as an antimicrobial peptide (AMP). Since AMP dietary supplements may be used as alternatives to antibiotics in livestock, we tested the effects of recombinant (r)TH2-3 as a dietary supplement in grouper aquaculture. rTH2-3 was produced by a Pichia pastoris expression system and exhibited thermostability and broad-spectrum antimicrobial activity. The feed conversion ratio and feed efficiency were determined in Epinephelus lanceolatus (grouper) fed with rTH2-3-supplemented diet for 28 days. In addition, grouper showed enhanced superoxide dismutase (SOD) activity after rTH2-3 feeding compared to regular-diet-fed fish. Gut microbiota analysis revealed that microbial diversity was enhanced by feeding grouper with 1% rTH2-3. After challenging grouper with Vibrio alginolyticus, differential regulation of immune-related genes in the liver and spleen was observed between the TH2-3 and regular-diet groups, including for genes associated with antimicrobial and pro-inflammatory functions, complement components, and major histocompatibility complex (Mhc). These findings suggest that overall immunity was improved. Thus, our results suggest long-term supplementation with rTH2-3 may be beneficial for aquacultured grouper. The beneficial effects of the supplement are likely based on changes in the commensal microbial community as well as immunomodulation.

Multiomics analyses reveal that NOD-like signaling pathway plays an important role against Streptococcus agalactiae in the spleen of tilapia

Streptococcus aglactiae(GBS) infection in tilapia is a serious global disease that causes significant production loss. Here, we studied the role of GBS in the spleen and the spleen's response against the pathogen through dual RNA-seq and proteome technology. Animals were divided into three groups: control, virulent treated (HN016), and attenuated treated (YM001). Spleen samples were collected and analysis when a disease outbreak. Dual RNA-seq result showed the virulence factor genes of GBS, included CAMP factor, PGK, OCT, enolase, scpB, Sip, bca, were upregulation. downregulation of GapA, cylE, OCT, scpB, C5AP, rlmB, hly, FBP, in HN016 and YM001. But for proteomic, OCT and bca were downregulation, the others were upregulation. For host transcriptome KEGG analysis showed, the NOD-like receptor signaling pathway (NLRs) and TOLL-like receptor signaling pathway (TLRs) were upreguoation in HN016 infected fish than the control fish; But for proteome KEGG, only the NLRS was up, the TLRS was not change. Compared with YM001 infected fishes, for transcriptome, NLRs and TLRs in infected HN016 fishes were significance rise (p < 0.01); for proteome, the NLRs was up (p < 0.05), but TLRs was no change.Analysis of pathogen-host interaction showed that the peptidoglycan (PNG), CD2, LCK, and host's Zap70 were involved in the regulation of NLRs; PNG, LCK, and ZAP70 were involved in the regulation of TRLs. Conclusion: the virulent strain HN016 and attenuated strainYM001 differed in the quantity of virulence factors. In tilapia's innate immune system, NLRs was the main defense factors, but bacteria avoided the host defense through TLRs.

Epinecidin-1, an Antimicrobial Peptide Derived From Grouper (Epinephelus coioides): Pharmacological Activities and Applications

Epinecidin-1 is an antimicrobial peptide derived from the orange-spotted grouper (Epinephelus coioides). The mature epinecidin-1 peptide is predicted to have an amphipathic α-helical structure and a non-helical hydrophilic domain at the C-terminal RRRH. The majority of work studying the potential pharmacological activities of epinecidin-1, utilize synthesized epinecidin-1 (Epi-1), which is made up of 21 amino acids, from the amino acid sequence of 22-42 residues of Epi-1-GFIFHIIKGLFHAGKMIHGLV. The synthetized Epi-1 peptide has been demonstrated to possess diverse pharmacological activities, including antimicrobial, immunomodulatory, anticancer, and wound healing properties. It has also been utilized in different clinical and agricultural fields, including topical applications in wound healing therapy as well as the enhancement of fish immunity in aquaculture. Hence, the present work aims to consolidate the current knowledge and findings on the characteristics and pharmacological properties of epinecidin-1 and its potential applications.

Oligomerization and insertion of antimicrobial peptide TP4 on bacterial membrane and membrane-mimicking surfactant sarkosyl

Antimicrobial peptides (AMPs) are important components of the host innate defense mechanism against invading microorganisms. Although AMPs are known to act on bacterial membranes and increase membrane permeability, the action mechanism of most AMPs still remains unclear. In this report, we found that the TP4 peptides from Nile tilapia anchored on E. coli cells and enabled them permeable to SYTOX Green in few minutes after TP4 addition. TP4 peptides existed in small dots either on live or glutaraldehyde-fixed cells. TP4 peptides were driven into oligomers either in soluble or insoluble form by a membrane-mimicking anionic surfactant, sarkosyl, depending on the concentrations employed. The binding forces among TP4 components were mediated through hydrophobic interaction. The soluble oligomers were negatively charged on surface, while the insoluble oligomers could be fused with each other or piled on existing particles to form larger particles with diameters 0.1 to 20 μm by hydrophobic interactions. Interestingly, the morphology and solubility of TP4 particles changed with the concentration of exogenous sarkosyl or trifluoroethanol. The TP4 peptides were assembled into oligomers on or in bacterial membrane. This study provides direct evidence and a model for the oligomerization and insertion of AMPs into bacterial membrane before entering into cytosol.

A review on the application of Bacillus as probiotics in aquaculture

Probiotics use in aquaculture has gained attention as microbial candidates to maintain the health and the well-being of many aquaculture animals. Among the many microbial candidates, probiotic Bacillus has sporulation capacity that makes them survive harsh environmental conditions, are non-pathogenic and non-toxic when fed to fish, and can produce antimicrobial substances making them more suitable candidates compared to other probiotics. In this review, we discussed the necessity of using the probiotic Bacillus in sustainable aquaculture as a good alternative to improve feed utilization, stress response, immune response and disease resistance, maintenance of tissue integrity, and as well improvement of water quality for sustainable aquaculture. Therefore the findings of current researches about the effects of Bacillus application to improve the culture of aquatic animals for future research and development of Bacillus application in aquaculture have been summarised.

The putative mature peptide of piscidin-1 modulates global transcriptional profile and proliferation of splenic lymphocytes in orange-spotted grouper (Epinephelus coioides)

Piscidins are important components in protecting microbial infections in teleost. The present study purified and identified a truncated peptide, whose sequence was very close to that of putative mature peptide of epinecidin-1 (piscidin-1) in orange-spotted grouper (Epinephelus coioides), Epi-1 (also named as short form of ecPis-1, ecPis-1S). The immunomodulatory effects of ecPis-1S on splenic lymphocytes of orange-spotted grouper were explored in vitro. The transcriptome study was carried out by De novo transcriptome sequencing (RNA-Seq) in splenic lymphocytes of orange-spotted grouper. Regarding the profiles of gene expressions, 2994 genes were up-regulated and 2679 genes were down-regulated in the splenic lymphocytes stimulated by ecPis-1S. In the case of differential expression genes, 330 genes were involved in immune related pathways. Among them, 34 genes were involved in T cell receptor signaling pathway, 31 genes in natural killer cell mediated cytotoxicity and 23 genes in leukocyte transendothelial migration, respectively. Immune-related genes selected for qRT-PCR verification, such as interleukin-1β (il-1b), tumor necrosis factor α (tnfa), T cell antigen receptor (tcr), major histocompatibility complex class I (mhc I), and mhc II were significantly up-regulated by ecPis-1S (p < 0.05). ecPis-1S could significantly enhance the proliferation of splenic lymphocytes of orange-spotted grouper in vitro (p < 0.05). In addition, the result of qRT-PCR revealed that ecPis-1S also significantly up-regulated cell cycle-related genes, including cyclin A (cyca), cyclin-dependent kinase 2 (cdk2), cdk4, cell division cycle protein 6 (cdc6), and transforming growth factor β (tgfb) (p < 0.05), which suggested that ecPis-1S promoted the proliferation of lymphocytes by activating cell division cycle. In conclusion, the results indicated that the mature peptide of piscidin-1 in orange-spotted grouper could act as immune modulator and play an important role in regulation of the immune response in fish.

Oral vaccination of tilapia against Streptococcus agalactiae using Bacillus subtilis spores expressing Sip

Streptococcus agalactiae infections are becoming an increasing problem in aquaculture because of significant morbidity and mortality, which restricts the healthy development of tilapia aquaculture. To seek safe and effective prevention measures, a Bacillus subtilis GC5 surface displayed vaccine was prepared and applied orally in tilapia. The study first showed that recombinant spores can engraft in the tilapia intestine. Then, the effect of protection and the immune responses were evaluated. The results of ELISA showed that Sip-specific antibody in the sera of GC5-Sip-immunized fish can be detected after the first oral administration when compared to the phosphate buffer saline (PBS) control group, and the levels of specific IgM gradually strengthened with boosting, so does the specific antibody against bacteria, proving that humoral immunity was induced. Quantitative real-time PCR (qRT-PCR) results showed that the immune-related gene expression of the gut and spleen exhibited a different rising trend in the GC5-Sip group, revealing that innate immune response and local as well as systemic cellular immunity were induced. The outcome of fish immunized with GC5-Sip spores provided a relative percent survival (RPS) of 41.7% against S. agalactiae and GC5 group had an RPS of 24.2%, indicating that GC5-Sip was safe and effective in protecting tilapia against bacterial infection. Our study demonstrated that the oral administration of B. subtilis spores expressing Sip could cause an effective immune response and offer good resistance to bacterial infection. Our work may lead to the development of new ideas for immunoprophylaxis against S. agalactiae infection.

Antimicrobial Peptide TP4 Induces ROS-Mediated Necrosis by Triggering Mitochondrial Dysfunction in Wild-Type and Mutant p53 Glioblastoma Cells

Antimicrobial peptide tilapia piscidin 4 (TP4) from Oreochromis niloticus exhibits potent bactericidal and anti-tumorigenic effects. In a variety of cancers, the mutation status of p53 is a decisive factor for therapeutic sensitivity. Therefore, we investigated the impact of p53 status on TP4-induced cytotoxicity in glioblastoma cell lines and the molecular mechanisms that govern cytotoxic effects. Both U87MG (wild-type/WT p53) and U251 (mutant p53) glioblastoma cell lines were sensitive to TP4-induced cytotoxicity. The necrosis inhibitors Necrostatin-1 and GSK’872 attenuated TP4-induced cytotoxicity, and TP4 treatment induced the release of cyclophilin A, a biomarker of necrosis. Moreover, TP4 induced mitochondrial hyperpolarization and dysfunction, which preceded the elevation of intracellular reactive oxygen species, DNA damage, and necrotic cell death in both U87MG and U251 glioblastoma cells. p38 was also activated by TP4, but did not contribute to cytotoxicity. SB202190, a specific p38 inhibitor, enhanced TP4-induced oxidative stress, mitochondrial dysfunction, and cytotoxicity, suggesting a protective role of p38. Furthermore, TP4-induced cytotoxicity, oxidative stress, phosphorylation of p38, and DNA damage were all attenuated by the mitochondrial-targeted reactive oxygen species (ROS) scavenger MitoTEMPO, or the reactive oxygen species scavenger N-acetyl-L-cysteine. Based on these data, we conclude that TP4 induces necrosis in both WT and mutant p53 glioblastoma cells through a mitochondrial ROS-dependent pathway.

Review of antimicrobial peptides with anti-Helicobacter pylori activity

BACKGROUND

The emergence of antibiotic-resistant Helicobacter pylori strains in recent years has increased the need for finding an alternative in the post-antibiotic era. One of the fields being considered for this purpose is antimicrobial peptides. The aim of this review was to provide an obvious scheme from the studied anti-H. pylori peptides and to investigate their common features.

METHOD

First, all of the antimicrobial peptides with their anti-H. pylori effects have been proved up to September 2018 were selected and their information including structure, mechanism of action, and function was reviewed. To achieve this, three databases of PubMed, Scopus, and Web of science were used.

RESULTS

A total of 9 groups containing 22 antimicrobial peptides were found with demonstrated anti-H. pylori effects. The nine groups included pexiganan, tilapia piscidins, epinecidin-1, cathelicidins, defensins, bicarinalin, odorranain-HP, PGLa-AM1, and bacteriocins. Most of the antimicrobial peptides, not all, had common features such as the ability to kill antibiotic-resistant strains, having α-helical structure, being cationic, with high positive charge and isoelectric point.

CONCLUSION

Antimicrobial peptides with anti-H. pylori effects have the potential to replace the antibiotics, especially in the post-antibiotic era, if a rapid and low-cost production method would be found.

Nile Tilapia Derived TP4 Shows Broad Cytotoxicity Toward to Non-Small-Cell Lung Cancer Cells

Non-small cell lung cancer (NSCLC) is among the leading causes of human mortality due to a lack of effective treatments. Conventional chemotherapies affect healthy cells and cause multidrug resistance, while tumors may eventually develop resistance to less-toxic targeted therapies. Thus, the need to develop novel therapies for NSCLC is urgent. Here, we show that Nile tilapia-derived Tilapia piscidin (TP) 4 is cytotoxic to a panel of NSCLC cells with different genetic profiles. We observed that TP4 triggers NSCLC cell death through the necrosis and combining TP4 with potent Epidermal growth factor receptor (EGFR)- tyrosine kinase inhibitors (TKI)s, Erlotinib, and Gefitinib, improved drug responses in EGFR-mutated NSCLC cells, but not in EGFR-wild-type NSCLC cells. This work provides novel insights into potential NSCLC treatments, which may utilize antimicrobial peptide TP4 as monotherapy or in combination with EGFR-TKIs.

Identification and Characterization of Novel Antimicrobial Peptide from Hippocampus comes by In Silico and Experimental Studies

Antimicrobial peptides (AMPs) have attracted attentions as a novel antimicrobial agent because of their unique activity against microbes. In the present study, we described a new, previously unreported AMP, moronecidin-like peptide, from Hippocampus comes and compared its antimicrobial activity with moronecidin from hybrid striped bass. Antibacterial assay indicated that gram-positive bacteria were more sensitive to moronecidin and moronecidin-like compared with gram-negative bacteria. Furthermore, both AMPs were found to exhibit effective antifungal activity. Comparative analysis of the antimicrobial activity revealed that moronecidin-like peptide has higher activity against Acinetobacter baumannii and Staphylococcus epidermidis relative to moronecidin. Both moronecidin-like and moronecidin peptides retained their antibacterial activity in physiological pH and salt concentration. The time-killing assay showed that the AMPs completely killed A. baumannii and S. epidermidis isolates after 1 and 5 h at five- and tenfold above their corresponding MICs, respectively. Anti-biofilm assay demonstrated that peptides were able to inhibit 50% of biofilm formation at sub-MIC of 1/8 MIC. Furthermore, moronecidin-like significantly inhibited biofilm formation more than moronecidin at 1/16 MIC. Collectively, our results revealed that antimicrobial and anti-biofilm activities of moronecidin-like are comparable to moronecidin. In addition, the hemolytic and cytotoxic activities of moronecidin-like were lower than those of moronecidin, suggesting it as a potential novel therapeutic agent, and a template to design new therapeutic AMPs.

Nile Tilapia Derived Antimicrobial Peptide TP4 Exerts Antineoplastic Activity Through Microtubule Disruption

Some antimicrobial peptides (AMPs) exhibit anti-cancer activity, acting on cancer cells either by causing membrane lysis or via intracellular effects. While intracellular penetration of AMPs has been shown to cause cancer cell death, the mechanisms of toxicity remain largely unknown. Here we show that a tilapia-derived AMP, Tilapia piscidin (TP) 4, penetrates intracellularly and targets the microtubule network. A pull-down assay identified α-Tubulin as a major interaction partner for TP4, and molecular docking analysis suggested that Phe1, Ile16, and Arg23 on TP4 are required for the interaction. TP4 treatment in A549 cells was found to disrupt the microtubule network in cells, and mutation of the essential TP4 residues prevented microtubule depolymerization in vitro. Importantly, the TP4 mutants also showed decreased cytotoxicity in A549 cells, suggesting that microtubule disruption is a major mechanistic component of TP4-mediated death in lung carcinoma cells.

Copper regulates the interactions of antimicrobial piscidin peptides from fish mast cells with formyl peptide receptors and heparin

Phagocytic cells in fish secrete antimicrobial peptides (AMPs) such as piscidins, glycosaminoglycans such as heparin, and copper ions as first-line immune defenses. Recently, we established that Cu²⁺ coordination by piscidins 1 (P1) and 3 (P3) enhances their antibacterial activity against membranes and DNA. Interestingly, we noted that physicochemical similarities exist between both piscidins and other AMPs that interact with heparin and induce immune-cell chemotaxis through formyl peptide receptors (FPRs) involved in innate immunity. Thus, we postulated that P1 and P3 interact with heparin and FPRs but that these interactions distinctively depend on Cu²⁺ Here, we investigate the interactome potentiated by piscidins, heparin, FPR, and Cu²⁺ Utilizing FPR-transfected cells and neutrophils, we demonstrate that both piscidins exclusively use FPR1 and FPR2 to induce chemotaxis and that Cu²⁺ reduces their chemotaxis induction. P1 is more effective at activating FPR1 than P3 and other known AMP ligands. Furthermore, the expression of Fpr2 on the surface of neutrophils is down-regulated by both peptides. Copper conjugation of the peptides does not further increase down-regulation, suggesting that the conformational changes induced by the metal translate into reduced FPR efficacy without altering the binding affinity. Using surface plasmon resonance, we show that piscidin-heparin interactions are Cu²⁺-dependent and reduced at the acidic pH of phagosomes. Although heparin decreases the antimicrobial activity of P3-Cu²⁺, it does not affect bacterial killing by P1-Cu²⁺ Copper's effects on modulating the micromolar-range interactions of both piscidins with FPR and heparin suggest that the interactome of these distinct immune agents plays an important role in innate immunity. The interactions between diverse host-defense molecules uncovered here may help inform the design of novel therapeutics to treat immune-related diseases.

Antimicrobial Metallopeptides

Antimicrobial peptides are short amphipathic peptides that are produced by the innate immune system in order to protect a host from pathogens. They have been shown to have broad-spectrum antimicrobial activity toward Gram-positive and Gram-negative bacteria, as well as antifungal, antiprotozoan, and antiviral activity. These peptides are able to exert their activity through a variety of mechanisms that include inhibiting DNA and RNA replication, inhibiting protein synthesis, permeabilizing the cell membrane, disrupting proton and ion transmembrane gradients, and inhibiting cell wall biosynthesis. Certain antimicrobial peptides are able to utilize metals to modulate their activity through structural changes upon metal binding, metal sequestration, and redox chemistry. This work aims to provide a review of the current literature regarding the influence of metals on the activity of antimicrobial metallopeptides and their uses in drug delivery and the treatment of implant-associated infections.

Molecular mechanisms of an antimicrobial peptide piscidin (Lc-pis) in a parasitic protozoan, Cryptocaryon irritans

Background

Cryptocaryon irritans is an obligate parasitic ciliate protozoan that can infect various commercially important mariculture fish species and cause high lethality and economic loss. Current methods of controlling this parasite with chemicals or antibiotics are widely considered to be environmentally harmful. Piscidins with broad spectrum antibacterial, antifungal and antiviral activities were found to have potent activity against C. irritans. Little, however, has been understood about the killing mechanisms of piscidins in parasites.

Results

In total, 57.12, 50.44, 55.86 and 47.87 million raw reads were generated from untreated theront and trophont, and piscidin (Lc-pis) treated theront and trophont libraries, respectively. After de novo assembly, 966,609 unigenes were generated with an average length of 420 bp: among these, 618,629 unigenes showed identity with sequences in one or more databases, with some showing to be significantly manipulated by Lc-pis treatment. The species classification showed that more than 25.8% unigenes from trophonts were homologous to the large yellow croaker (Larimichthys crocea) and less than 3.8% unigenes from theronts were matched. The homologous unigenes demonstrated that the tissue from host could exist in trophonts and might be transported to parasite via vesicular transports. Our analysis showed that regulatory transcripts were involved in vesicular trafficking. Among transcripts induced by Lc-pis, most genes up-regulated in treated and untreated theronts were involved in cell migration and apoptosis related pathways. Few transcripts were found to be down-regulated in treated and untreated trophonts related to cell structure and migration after treatment.

Conclusions

This is the first transcriptome analysis of C. irritans exposed to Lc-pis, which enhanced the genomic resources and provided novel insights into molecular mechanisms of ciliates treated by cationic antimicrobial peptide. Our comprehensive transcriptome analysis can facilitate the identification of potential drug targets and vaccines candidates for controlling this devastating fish pathogen.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4565-5) contains supplementary material, which is available to authorized users.

Transgenic expression of tilapia piscidin 3 (TP3) in zebrafish confers resistance to Streptococcus agalactiae

To study the biological role of tilapia piscidin 3 (TP3) in Streptococcus agalactiae infection in vivo, TP3/DsRed overexpressing transgenic zebrafish were generated. Under normal growth conditions, TP3/DsRed transgenic zebrafish exhibited an orange-red body color, without any other obvious abnormalities. However, when compared to wild type fish, TP3/DsRed transgenic zebrafish were resistant to S. agalactiae infection. After infection, the TP3 overexpressing fish exhibited higher expression of Toll-like receptor 4a (TLR4a), interleukin (IL)-10, IL-22, and C3b. Furthermore, TP3/DsRed transgenic zebrafish exhibited reduced induction of proinflammatory cytokines, including TNFα, IL-1β, IL-21, MyD88, and nuclear factor (NF)-κB. Taken together, our data show that TP3 overexpression in zebrafish can effectively suppress proinflammatory responses and enhance production of C3b. Together, these actions are conducive to the resolution of inflammation and bacterial clearance. We further postulate that TP3 may exert its anti-inflammatory effects by enhancing TLR4a-mediated negative regulation of NF-κB.

Antimicrobial peptides within the Yellowtail Kingfish (Seriola lalandi)

A number of Seriola species are currently farmed or being investigated as future aquaculture species in countries around the world. However they face a number of issues and limitations which will need to be overcome to ensure future stability and growth, one of which are disease outbreaks. Despite this, very little has been done to understand the immune system of Seriola species and very few immune genes have been characterised. Antimicrobial peptides (AMP) are naturally occurring low molecular weight polypeptides that play a major role in an organism's immune system and act effectively as a first line of defence. This investigation isolates the full length cDNA sequences of two AMP's, piscidin and hepcidin from the yellowtail kingfish (Seriola lalandi). The full-length cDNA of the piscidin gene encodes a 65 amino acid prepropeptide, containing a 25-residue peptide, predicted to form an amphipathic helix-loop-helix structure. Phylogenetic analysis using fish piscidin sequences, showed that this AMP is only found in bony fish within the Acanthomorpha clade and that a possible three groups within the piscidin family exists, with S. lalandi belonging to a particular group. The full-length cDNA of the hepcidin gene encodes a 90 amino acid preprohepcidin, which contains a typical RX(R/K)R motif for cleavage of the mature peptide which comprises of eight conserved cysteine residues. Phylogenetic analysis of known vertebrate hepcidin antimicrobial peptide (HAMP) sequences, shows sequences from the Neoteleostei clade of bony fish form two very separate groups, HAMP1 and HAMP2, with the S. lalandi hepcidin gene grouped with the HAMP1 sequences. HAMP2 sequences are found to have multiple copies within fish and genome analysis showed very clearly that these two groups of genes are located on separate regions on the genome, with the multiple HAMP2 copies formed from tandem gene duplications. Lastly, using qPCR the expression of the S. lalandi piscidin gene within healthy fish was highest within, spleen and gills and lowest in liver, whereas hepcidin was highest in the liver with little or no expression in the spleen and gills.

Targeting FOSB with a cationic antimicrobial peptide, TP4, for treatment of triple-negative breast cancer

Triple-negative breast cancer (TNBC) currently lacks a suitable therapeutic candidate and is thus difficult to treat. Here, we report that a cationic antimicrobial peptide (CAP), tilapia piscidin 4 (TP4), which was derived from Nile tilapia (Oreochromis niloticus), is selectively toxic to TNBC. TP4 acts by inducing an AP-1 protein called FOSB, the expression of which is negatively associated with the pathological grade of TNBC. We show that TP4 is bound to the mitochondria where it disrupts calcium homeostasis and activates FOSB. FOSB overexpression results in TNBC cell death, whereas inhibition of calcium signaling eliminates FOSB induction and blocks TP4-induced TNBC cell death. Both TP4 and anthracyclines strongly induced FOSB, particularly in TNBC, indicating that FOSB may be suitable as a biomarker of drug responses. This study thus provides a novel therapeutic approach toward TNBC through FOSB induction.

Recent updates of marine antimicrobial peptides

Antimicrobial peptides are group of proteins showing broad-spectrum antimicrobial activity that have been known to be powerful agents against a variety of pathogens. This class of compounds contributed to solving the microbial resistance dilemma that limited the use of many potent antimicrobial agents. The marine environment is known to be one of the richest sources for antimicrobial peptides, yet this environment is not fully explored. Hence, the scientific research attention should be directed toward the marine ecosystem as enormous amount of useful discoveries could be brought to the forefront. In the current article, the marine antimicrobial peptides reported from mid 2012 to 2017 have been reviewed.

MSP-4, an Antimicrobial Peptide, Induces Apoptosis via Activation of Extrinsic Fas/FasL- and Intrinsic Mitochondria-Mediated Pathways in One Osteosarcoma Cell Line

Osteosarcoma (OS) is a common malignant bone cancer. The relatively high density of a person's bone structure means low permeability for drugs, and so finding drugs that can be more effective is important and should not be delayed. MSPs are marine antimicrobial peptides (AMP) and natural compounds extracted from Nile tilapia (Oreochromis niloticus). MSP-4 is a part of the AMPs series, with the advantage of having a molecular weight of about 2.7-kDa and anticancer effects, although the responsible anticancer mechanism is not very clear. The goal of this study is to determine the workings of the mechanism associated with apoptosis resulting from MSP-4 in osteosarcoma MG63 cells. The study showed that MSP-4 significantly induced apoptosis in MG63 cells, with Western blot indicating that MSP-4 induced this apoptosis through an intrinsic pathway and an extrinsic pathway. Thus, a pretreatment system with a particular inhibitor of Z-IETD-FMK (caspase-8 inhibitor) and Z-LEHD-FMK (caspase-9 inhibitor) significantly attenuated the cleavage of caspase-3 and prevented apoptosis. These observations indicate that low concentrations of MSP-4 can help induce the apoptosis of MG63 through a Fas/FasL- and mitochondria-mediated pathway and suggest a potentially innovative alternative to the treatment of human osteosarcoma.

Identification of a moronecidin-like antimicrobial peptide in the venomous fish Pterois volitans: Functional and structural study of pteroicidin-α

The present study characterizes for the first time an antimicrobial peptide in lionfish (Pterois volitans), a venomous fish. Using a peptidomic approach, we identified a mature piscidin in lionfish and called it pteroicidin-α. We detected an amidated form (pteroicidin-α- CONH₂) and a non-amidated form (pteroicidin-α-COOH), and then performed their functional and structural study. Interestingly, the two peptides displayed different antibacterial and hemolytic activity levels. Pteroicidin-α-CONH₂ was bactericidal on human pathogens like Staphylococcus aureus or Escherichia coli, as well as on the fish pathogen Aeromonas salmonicida, while pteroicidin-α-COOH only inhibited their growth. Furthermore, the two peptides induced hemolysis of red blood cells from different vertebrates, namely humans, sea bass and lesser-spotted dogfish. Hemolysis occurred with low concentrations of pteroicidin-α-CONH₂, indicating greater toxicity of the amidated form. Circular dichroism analysis showed that both peptides adopted a helical conformation, yet with a greater α-helix content in pteroicidin-α-CONH₂. Overall, these results suggest that amidation strongly influences pteroicidin-α by modifying its structure and its physico-chemical characteristics and by increasing its hemolytic activity.

Fish antimicrobial peptides (AMP's) as essential and promising molecular therapeutic agents: A review

Antimicrobial peptides (AMPs) are generally considered as an essential component of innate immunity, thereby providing the first line of defense against wide range of pathogens. In addition, they can also kill the pathogens which are generally resistant to number of antibiotics, thereby providing the avenues for the development of future therapeutic agents. Fishes are constantly challenged by variety of pathogens which not only shows detrimental effect on their health but also increases risk of becoming resistant to conventional antibiotics. As fishes rely more on innate immunity, AMPs can serve as a potential defensive weapons in fishes for combating emerging devastating diseases. Generally, AMPs show multidimensional properties like rapid diffusion to the site of infection, recruitment of other immune cells to infected tissues and vigorous potential to rapidly neutralize broad range of pathogens (bacterial, fungal and viral). AMPs also exhibit diverse biological effect like endotoxin neutralization, immunomodulation and induction of angiogenesis in mammals. Due to these properties AMPs have become one of the most promising therapeutic agents to be studied. Till date, many AMPs have been isolated from the fishes but not fully characterized at molecular level. This review provides an overview of the structures, functions, and putative mechanisms of major families of fish AMPs. Further, we also highlighted how fish AMPs can be used as a novel therapeutic tool which is the theme of future research in drug development.

Insight into the interactions, residue snorkeling, and membrane disordering potency of a single antimicrobial peptide into different lipid bilayers

Pardaxin, with a bend-helix-bend-helix structure, is a membrane-active antimicrobial peptide that its membrane activity depends on the lipid bilayer composition. Herein, all-atom molecular dynamics (MD) simulations were performed to provide further molecular insight into the interactions, structural dynamics, orientation behavior, and cationic residues snorkeling of pardaxin in the DMPC, DPPC, POPC, POPG, POPG/POPE (3:1), and POPG/POPE (1:3) lipid bilayers. The results showed that the C-terminal helix of the peptide was maintained in all six types of the model-bilayers and pardaxin was tilted into the DMPC, DPPC, and POPG/POPE mixed bilayers more than the POPC and POPG bilayers. As well as, the structure of zwitterionic membranes was more affected by the peptide than the anionic bilayers. Taken together, the study demonstrated that the cationic residues of pardaxin snorkeled toward the interface of lipid bilayers and all phenylalanine residues of the peptide played important roles in the peptide-membrane interactions. We hope that this work will provide a better understanding of the interactions of antimicrobial peptides with the membranes.

Transcriptome analysis of hybrid tilapia (Oreochromis spp.) with Streptococcus agalactiae infection identifies Toll-like receptor pathway-mediated induction of NADPH oxidase complex and piscidins as primary immune-related responses

Streptococcus agalactiae infection is one of the most significant bacterial diseases in tilapia aquaculture. Identification of immune-related genes associated with Streptococcus agalactiae infection may provide a basis for breeding selection or therapeutics to augment disease resistance. Therefore, we utilized transcriptome profiling to study the host response in tilapia following Streptococcus agalactiae infection. Based on GO and KEGG enrichment analyses, we found that differentially expressed genes are widely involved in immune-related pathways, including the induction of antimicrobial peptides. Moreover, the main components of two immune-related pathways (Toll-like receptor signaling and leukocyte transendothelial migration) and four environmental information processing pathways (TNF, PI3K-Akt, Jak-STAT and MAPK) were identified. Finally, a time-course expression profile for several of the identified transcripts including tilapia piscidin 3 (TP3), tilapia piscidin 4 (TP4), TLR2, TLR5, MyD88, TRAF6, p38, and interleukin components was performed by qRT-PCR. Collectively, these results provide a starting point to study molecular mechanisms of tilapia immune response to Streptococcus agalactiae infection and may be applied as a basis for developing disease resistant strains by breeding selection.

Hydrophobic residues are critical for the helix-forming, hemolytic and bactericidal activities of amphipathic antimicrobial peptide TP4

Antimicrobial peptides are important components of the host innate defense mechanism against invading pathogens, especially for drug-resistant bacteria. In addition to bactericidal activity, the 25 residue peptide TP4 isolated from Nile tilapia also stimulates cell proliferation and regulates the innate immune system in mice. In this report, TP4 hyperpolarized and depolarized the membrane potential of Pseudomonas aeruginosa at sub-lethal and lethal concentrations. It also inhibited and eradicated biofilm formation. The in vitro binding of TP4 to bacterial outer membrane target protein, OprI, was markedly enhanced by a membrane-like surfactant sarkosyl and lipopolysaccharide, which converted TP4 into an α-helix. The solution structure of TP4 in dodecylphosphocholine was solved by NMR analyses. It contained a typical α-helix at residues Phe10-Arg22 and a distorted helical segment at Ile6-Phe10, as well as a hydrophobic core at the N-terminus and a cationic patch at the C-terminus. Residues Ile16, Leu19 and Ile20 in the hydrophobic face of the main helix were critical for the integrity of amphipathic structure, other hydrophobic residues played important roles in hemolytic and bactericidal activities. A model for the assembly of helical TP4 embedded in sarkosyl vesicle is proposed. This study may provide valuable insight for engineering AMPs to have potent bactericidal activity but low hemolytic activity.

Study of the Antimicrobial Activity of Tilapia Piscidin 3 (TP3) and TP4 and Their Effects on Immune Functions in Hybrid Tilapia (Oreochromis spp.)

To address the growing concern over antibiotic-resistant microbial infections in aquatic animals, we tested several promising alternative agents that have emerged as new drug candidates. Specifically, the tilapia piscidins are a group of peptides that possess antimicrobial, wound-healing, and antitumor functions. In this study, we focused on tilapia piscidin 3 (TP3) and TP4, which are peptides derived from Oreochromis niloticus, and investigated their inhibition of acute bacterial infections by infecting hybrid tilapia (Oreochromis spp.) with Vibrio vulnificus and evaluating the protective effects of pre-treating, co-treating, and post-treating fish with TP3 and TP4. In vivo experiments showed that co-treatment with V. vulnificus and TP3 (20 μg/fish) or TP4 (20 μg/fish) achieved 95.3% and 88.9% survival rates, respectively, after seven days. When we co-injected TP3 or TP4 and V. vulnificus into tilapia and then re-challenged the fish with V. vulnificus after 28 days, the tilapia exhibited survival rates of 35.6% and 42.2%, respectively. Pre-treatment with TP3 (30 μg/fish) or TP4 (20 μg/fish) for 30 minutes prior to V. vulnificus infection resulted in high survival rates of 28.9% and 37.8%, respectively, while post-treatment with TP3 (20 μg/fish or 30 μg/fish) or TP4 (20 μg/fish) 30 minutes after V. vulnificus infection yielded high survival rates of 33.3% and 48.9%. In summary, pre-treating, co-treating, and post-treating fish with TP3 or TP4 all effectively decreased the number of V. vulnificus bacteria and promoted significantly lower mortality rates in tilapia. The minimum inhibitory concentrations (MICs) of TP3 and TP4 that were effective for treating fish infected with V. vulnificus were 7.8 and 62.5 μg/ml, respectively, whereas the MICs of kanamycin and ampicillin were 31.2 and 3.91 μg/ml. The antimicrobial activity of these peptides was confirmed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM), both of which showed that V. vulnificus disrupted the outer membranes of cells, resulting in the loss of cell shape and integrity. We examined whether TP3 and TP4 increased the membrane permeability of V. vulnificus by measuring the fluorescence resulting from the uptake of 1-N-phenyl-naphthylamine (NPN). Treating fish with TP3 and TP4 under different pH and temperature conditions did not significantly increase MIC values, suggesting that temperature and the acid-base environment do not affect AMP function. In addition, the qPCR results showed that TP3 and TP4 influence the expression of immune-responsive genes, including interleukin (IL)-1β, IL-6, and IL-8. In this study, we demonstrate that TP3 and TP4 show potential for development as drugs to combat fish bacterial infections in aquaculture.

Molecular characterization and functional analysis of a piscidin gene in large yellow croaker (Larimichthys crocea)

The piscidin family, which includes potent antimicrobial peptides with broad-spectrum activity, plays an important role in the innate immune system of fish. In this study, we cloned piscidin-5-like type 3 (Lcpis5lt3) in large yellow croaker (Larimichthys crocea). Multiple alignments with other known piscidins revealed amino acid conservation throughout the fish, especially at the signal peptide (22 amino acids). The phylogenetic tree confirmed that Lcpis5lt3 and large yellow croaker piscidin-5-like proteins were grouped together to form a branch. Quantitative real-time PCR revealed that Lcpis5lt3 was expressed in a wide range of tissues, including the brain, muscle, gill, head kidney, intestine, kidney, liver, and spleen. The highest mRNA expression level of Lcpis5lt3 was found in the spleen. After Vibrio alginolyticus infection, mRNA expression was rapidly upregulated in the liver, head kidney, gill, kidney, and intestine at 4, 8, 12, and 24 h post infection (hpi), whereas there were no significant changes in the spleen. The antimicrobial spectrum showed that the synthetic mature peptide of Lcpis5lt3 exhibited different activity in vitro against various bacteria, such as Aeromonas hydrophila, V. anguillarum, V. alginolyticus, V. parahaemolyticus, Staphylococcus aureus, and Listeria monocytogenes. In addition, survival rates from the in vivo assay indicated that the synthetic peptide of Lcpis5lt3 increased the survival rate of large yellow croaker after V. alginolyticus challenge, resulting in a decline in bacterial burden and mRNA expression levels of interleukin-1β, interleukin-10, and tumor necrosis factor-α. These data suggest that Lcpis5lt3 plays an important role in innate immunity in large yellow croaker and might represent a potential therapeutic agent against pathogen invasion.

A Diverse Family of Host-Defense Peptides (Piscidins) Exhibit Specialized Anti-Bacterial and Anti-Protozoal Activities in Fishes

Conventional antibiotics and other chemical-based drugs are currently one of the most common methods used to control disease-related mortality in animal agriculture. Use of the innate immune system to decrease disease related mortalities is a novel alternative to conventional drugs. One component of the innate immune system is the host-defense peptides, also known as antimicrobial peptides. Host-defense peptides are typically small, amphipathic, α-helical peptides with a broad-spectrum of action against viral, bacterial, fungal, and/or protozoal pathogens. Piscidins are host-defense peptides first discovered in the hybrid striped bass (white bass, Morone chrysops, x striped bass, M. saxatilis). In this paper we identify four new piscidin isoforms in the hybrid striped bass and describe their tissue distributions. We also determine the progenitor species of origin of each piscidin (orthology) and propose a revised nomenclature for this newly described piscidin family based on a three class system. The Class I piscidins (22 amino acids in length; striped bass and white bass piscidin 1 and piscidin 3) show broad-spectrum activity against bacteria and ciliated protozoans, while the Class III piscidins (55 amino acids in length; striped bass and white bass piscidin 6 and striped bass piscidin 7) primarily show anti-protozoal activity. The Class II piscidins (44-46 amino acids in length; striped bass and white bass piscidin 4 and white bass piscidin 5) have a level of activity against bacteria and protozoans intermediate to Classes I and III. Knowledge of piscidin function and activity may help in the future development of disease-resistant lines of striped bass and white bass that could be used to produce superior hybrids for aquaculture.

Marine Antimicrobial Peptides: Nature Provides Templates for the Design of Novel Compounds against Pathogenic Bacteria

The discovery of antibiotics for the treatment of bacterial infections brought the idea that bacteria would no longer endanger human health. However, bacterial diseases still represent a worldwide treat. The ability of microorganisms to develop resistance, together with the indiscriminate use of antibiotics, is mainly responsible for this situation; thus, resistance has compelled the scientific community to search for novel therapeutics. In this scenario, antimicrobial peptides (AMPs) provide a promising strategy against a wide array of pathogenic microorganisms, being able to act directly as antimicrobial agents but also being important regulators of the innate immune system. This review is an attempt to explore marine AMPs as a rich source of molecules with antimicrobial activity. In fact, the sea is poorly explored in terms of AMPs, but it represents a resource with plentiful antibacterial agents performing their role in a harsh environment. For the application of AMPs in the medical field limitations correlated to their peptide nature, their inactivation by environmental pH, presence of salts, proteases, or other components have to be solved. Thus, these peptides may act as templates for the design of more potent and less toxic compounds.

Use of tilapia piscidin 3 (TP3) to protect against MRSA infection in mice with skin injuries

Antimicrobial peptides (AMPs), represent promising agents for new therapeutic approaches of infected wound treatment, on account of their antimicrobial and wound closure activities, and low potential for inducing resistance. However, therapeutic applications of these AMPs are limited by their toxicity and low stability in vivo. Previously, we reported that the 23 amino-acid designer peptide TP3 possessed antimicrobial activities. Here, we analyzed the wound closure activities of TP3 both and in vivo. TP3 at doses of up to 40 μg/ml did not affect the viability of baby hamster kidney cells. Furthermore, TP3 was found to be highly effective at combating peritonitis and wound infection caused by MRSA in mouse models, without inducing adverse behavioral effects or liver or kidney toxicity. TP3 treatment increased survival by 100% at 8 days after infection, and accelerated the progression of proliferation, remodeling, and maturation of infected wounds. Taken together, our results indicate that TP3 enhances the rate of survival of mice infected with the bacterial pathogen MRSA through both antimicrobial and immunomodulatory effects. Overall, these results suggest that TP3 may be suitable for development as a novel topical agent for treatment of infected wounds.

Efficacy of the antimicrobial peptide TP4 against Helicobacter pylori infection: in vitro membrane perturbation via micellization and in vivo suppression of host immune responses in a mouse model

Helicobacter pylori infection is marked by a strong association with various gastric diseases, including gastritis, ulcers, and gastric cancer. Antibiotic treatment regimens have low success rates due to the rapid occurrence of resistant H. pylori strains, necessitating the development of novel anti-H. pylori strategies. Here, we investigated the therapeutic potential of a novel peptide, Tilapia Piscidin 4 (TP4), against multidrug resistant gastric pathogen H. pylori, based on its in vitro and in vivo efficacy.TP4 inhibited the growth of both antibiotic-sensitive and -resistant H. pylori (CagA+, VacA+) via membrane micelle formation, which led to membrane depolarization and extravasation of cellular constituents. During colonization of gastric tissue, H. pylori infection maintains high T regulatory subsets and a low Th17/Treg ratio, and results in expression of both pro- and anti-inflammatory cytokines. Treatment with TP4 suppressed Treg subset populations and pro- and anti- inflammatory cytokines. TP4 restored the Th17/Treg balance, which resulted in early clearance of H. pylori density and recovery of gastric morphology. Toxicity studies demonstrated that TP4 treatment has no adverse effects in mice or rabbits. The results of this study indicate that TP4 may be an effective and safe monotherapeutic agent for the treatment of multidrug resistant H. pylori infections.

Electrotransfer of the tilapia piscidin 3 and tilapia piscidin 4 genes into skeletal muscle enhances the antibacterial and immunomodulatory functions of Oreochromis niloticus

Tilapia piscidin 3 (TP3) and tilapia piscidin 4 (TP4) are antimicrobial peptides recently isolated from Oreochromis niloticus. We previously showed that synthetic TP3 and TP4 possessed antimicrobial activities. Here, we analyzed the bactericidal abilities and immunomodulatory properties of these AMPs following the electroporation of pCMV-GFP-TP3 or pCMV-GFP-TP4 plasmid into tilapia (O. niloticus) muscle and subsequent infection with Vibrio vulnificus or Streptococcus agalactiae. Prior overexpression of TP3 or TP4 in tilapia muscle tissues efficiently reduced bacterial numbers at 24 and 48 h after V. vulnificus infection and reduced bacterial numbers at 24 h after S. agalactiae infection compared to numbers in controls expressing pCMV-GFP (EGFP). Electroporation of pCMV-EGFP-TP3 (TP3) or pCMV-EGFP-TP4 (TP4) significantly increased expression of several immune-related genes in muscle (IL-1β (12 h, TP3), IL-8 (12 h, TP3), TGFβ (3 h, TP4), and IκB (48 h, TP3, TP4)) and decreased the expression of TLR5 (12 h and 24 h, TP3) after V. vulnificus infection. Following S. agalactiae infection, expression of the following genes was significantly decreased in muscle: IL-1β (12 h, TP3), IL-8 (12 h, TP3, TP4), TLR5 (3 h-24 h, TP3, TP4), TGFβ (3 h, TP4; 24 h, TP3, TP4), and IκB (3 h, TP3). These data suggest that TP3 and TP4 exert antimicrobial effects after overexpression in the O. niloticus muscle, and also play important roles in the regulation of immune-related gene expression.

Central Role of the Copper-Binding Motif in the Complex Mechanism of Action of Ixosin: Enhancing Oxidative Damage and Promoting Synergy with Ixosin B

Ticks transmit multiple pathogens to different hosts without compromising their health. Their ability to evade microbial infections is largely a result of their effective innate immune response including various antimicrobial peptides. Therefore, a deep understanding of how ticks (and other arthropod vectors) control microbial loads could lead to the design of broad-spectrum antimicrobial agents. In this paper we study the role of the amino-terminal copper and nickel (ATCUN)-binding sequence in the peptide ixosin, isolated from the salivary glands of the hard tick Ixodes sinensis. Our results indicate that the ATCUN motif is not essential to the potency of ixosin, but is indispensable to its oxidative mechanism of action. Specifically, the ATCUN motif promotes dioxygen- and copper-dependent lipid (per)oxidation of bacterial membranes in a temporal fashion coinciding with the onset of bacterial death. Microscopy and studies on model membranes indicate that the oxidized phospholipids are utilized as potential targets of ixosin B (another tick salivary gland peptide) involving its delocalization to the bacterial membrane, thus resulting in a synergistic effect. Our proposed mechanism of action highlights the centrality of the ATCUN motif to ixosin's mechanism of action and demonstrates a novel way in which (tick) antimicrobial peptides (AMPs) utilize metal ions in its activity. This study suggests that ticks employ a variety of effectors to generate an amplified immune response, possibly justifying its vector competence.

Molecular, genomic, and expressional delineation of a piscidin from rock bream (Oplegnathus fasciatus) with evidence for the potent antimicrobial activities of Of-Pis1 peptide

The piscidin family comprises a group of antimicrobial peptides (AMPs) that are vital components of teleost innate immunity. Piscidins protect the host from pathogens, through multifaceted roles as immunomodulators and anti-infective peptides. The present study reports the identification, and characterization of a putative piscidin homolog, Of-Pis1, from rock bream (Oplegnathus fasciatus). A combined genomic and transcriptomic approach revealed that the Of-Pis1 gene comprises 1396 nucleotides (nt), four exons, and three introns. The cDNA with the 213 nt open reading frame encoded a 70-amino acid preprotein consisting of a signal peptide, a mature peptide, and a prodomain. Predicted mature Of-Pis1 was assumed to be a membrane-active AMP, based on the prediction of an amphipathic α-helical conformation with a net charge of +4. In addition, Of-Pis1 demonstrated significant similarities with other piscidin family members in terms of gene structure, sequence homology, and evolutionary relationship. Examination by quantitative real-time PCR (qPCR) of basal transcription of Of-Pis1 in the tissues of naïve rock bream, revealed predominant transcript levels in the gills, followed by the spleen, intestine, skin, and head kidney. In gill tissues, the temporally induced mRNA expression of Of-Pis1, upon in vivo injection trials with lipopolysaccharide (LPS); polyinosinic:polycytidylic acid (poly I:C); and pathogens, including Edwardsiella tarda, Streptococcus iniae, and rock bream iridovirus (RBIV), was weak. In contrast, in vivo flagellin administration led to a robust upregulation of Of-Pis1 in different tissues. Antimicrobial potency was determined by employing recombinant (rOf-Pis1), and synthetic (pOf-Pis1) peptides, in in vitro assays. Recombinant overexpression inhibited the growth of bacteria expressing the rOf-Pis1 protein in a growth delay assay. The broad antimicrobial spectrum of pOf-Pis1 was evidenced by its potent activity against an array of microbes, including bacteria, fungi, and parasitic species. In addition, pOf-Pis1 showed no significant hemolytic toxicity against human erythrocytes. Collectively, the data presented in the current study improve our understanding of the piscidin AMP family, and the contribution of Of-Pis1 to the rock bream immunity.

Antimicrobial Peptides as Mediators of Innate Immunity in Teleosts

Antimicrobial peptides (AMPs) have been identified throughout the metazoa suggesting their evolutionarily conserved nature and their presence in teleosts is no exception. AMPs are short (18–46 amino acids), usually cationic, amphipathic peptides. While AMPs are diverse in amino acid sequence, with no two AMPs being identical, they collectively appear to have conserved functions in the innate immunity of animals towards the pathogens they encounter in their environment. Fish AMPs are upregulated in response to pathogens and appear to have direct broad-spectrum antimicrobial activity towards both human and fish pathogens. However, an emerging role for AMPs as immunomodulatory molecules has become apparent—the ability of AMPs to activate the innate immune system sheds light onto the multifaceted capacity of these small peptides to combat pathogens through direct and indirect means. Herein, this review focuses on the role of teleost AMPs as modulators of the innate immune system and their regulation in response to pathogens or other exogenous molecules. The capacity to regulate AMP expression by exogenous factors may prove useful in modulating AMP expression in fish to prevent disease, particularly in aquaculture settings where crowded conditions and environmental stress pre-dispose these fish to infection.

Tilapia Piscidin 4 (TP4) Stimulates Cell Proliferation and Wound Closure in MRSA-Infected Wounds in Mice

Antimicrobial peptides (AMPs) are endogenous antibiotics that directly affect microorganisms, and also have a variety of receptor-mediated functions. One such AMP, Tilapia piscidin 4 (TP4), was isolated from Nile tilapia (Oreochromis niloticus); TP4 has antibacterial effects and regulates the innate immune system. The aim of the present study was to characterize the role of TP4 in the regulation of wound closure in mice and proliferation of a keratinocyte cell line (HaCaT) and fibroblast cell line (Hs-68). In vitro, TP4 stimulated cell proliferation and activated collagen I, collagen III, and keratinocyte growth factor (KGF) gene expression in Hs-68 cells, which induces keratin production by HaCaT cells. This effect was detectable at TP4 concentrations of 6.25 µg/mL in both cell lines. In vivo, TP4 was found to be highly effective at combating peritonitis and wound infection caused by MRSA in mouse models, without inducing adverse behavioral effects or liver or kidney toxicity. Taken together, our results indicate that TP4 enhances the survival rate of mice infected with the bacterial pathogen MRSA through both antimicrobial and wound closure activities mediated by epidermal growth factor (EGF), transforming growth factor (TGF), and vascular endothelial growth factor (VEGF). The peptide is likely involved in antibacterial processes and regulation of tissue homeostasis in infected wounds in mice. Overall, these results suggest that TP4 may be suitable for development as a novel topical agent for wound dressing.

The longevity of the antimicrobial response in rainbow trout (Oncorhynchus mykiss) fed a peptidoglycan (PG) supplemented diet

This study builds upon previous work studying antimicrobial peptide (AMP) gene expression in rainbow trout (Oncorhynchus mykiss) fed a peptidoglycan (PG) enriched diet. The aims here were 1) to evaluate how long AMP expression is elevated in skin with continuous feeding of fish with the PG enriched diet for 21 or 28 days, and 2) to assess the impact of stopping PG feeding at day 14 when sampled at day 21 or 28. The rainbow trout were divided into 6 groups, with two fed a control commercial diet for the duration of the experiment and the other four given the same diet enriched with 10 mg PG/Kg for 14 days (PG 1-14) or continuously (PG continuous), the former reverting back to the commercial diet at day 14. No mortalities occurred during the study and there were no significant differences in growth among the fish in the different diet groups. The expression of six AMP genes was studied by real-time PCR in the skin, since these genes were shown to be induced in response to the PG enriched diets in a previous experiment. We show that continuous PG treatment for 21 or 28 days maintained high levels of AMP expression, although in general the levels decreased with time on the diets. Withdrawal of the PG diets at day 14 resulted in a fall in expression level especially apparent with omCATH-1, omCATH-2 and omLEAP-2a, but with omDB-3 and omDB-4 remaining at elevated levels (x10) in comparison to fish given a control diet. These results confirm that orally administered PG clearly enhances the trout innate immune system and could be used as a means to boost fish defences. Future studies should be conducted to verify the impact on survival after pathogen challenge in trout fed PG enriched diets under these regimes.

Piscidin is highly active against carbapenem-resistant Acinetobacter baumannii and NDM-1-producing Klebsiella pneumonia in a systemic Septicaemia infection mouse model

This study was designed to investigate the antimicrobial activity of two synthetic antimicrobial peptides from an aquatic organism, tilapia piscidin 3 (TP3) and tilapia piscidin 4 (TP4), in vitro and in a murine sepsis model, as compared with ampicillin, tigecycline, and imipenem. Mice were infected with (NDM-1)-producing K. pneumonia and multi-drug resistant Acinetobacter baumannii, and subsequently treated with TP3, TP4, or antibiotics for different periods of time (up to 168 h). Mouse survival and bacterial colony forming units (CFU) in various organs were measured after each treatment. Toxicity was determined based on observation of behavior and measurement of biochemical parameters. TP3 and TP4 exhibited strong activity against K. pneumonia and A. baumannii in vitro. Administration of TP3 (150 μg/mouse) or TP4 (50 μg/mouse) 30 min after infection with K. pneumonia or A. baumannii significantly increased survival in mice. TP4 was more effective than tigecycline at reducing CFU counts in several organs. TP3 and TP4 were shown to be non-toxic, and did not affect mouse behavior. TP3 and TP4 are able at potentiate anti-Acinetobacter baumannii or anti-Klebsiella pneumonia drug activity, reduce bacterial load, and prevent drug resistance, indicating their potential for use in combating multidrug-resistant bacteria.

Preliminary study on expression of antimicrobial peptides in European sea bass (Dicentrarchus labrax) following in vivo infection with Vibrio anguillarum. A time course experiment

Antimicrobial polypeptides (AMPPs) are humoral components of the vertebrates and invertebrates innate immune system. Their potent broad spectrum antimicrobial activities have drawn the attention of the scientific community to their potential use not only as an alternative to antibiotics but also as functional targets for immunostimulants in order to enhance the host immunity. Fish synthesize a great number of these peptides but in European sea bass, an important fish species in the Mediterranean aquaculture, only a few AMPPs have been studied and these surveys have highlighted their functional role as predictive markers of stressful conditions. Many aspects concerning AMPP mode of action in the host during bacterial infections are still unknown. In this work a 72 h time course experiment, performed on juvenile sea bass intraperitoneally (i.p.) injected with a sub-lethal dose of Vibrio anguillarum, was aimed to investigate the mRNA expression of four specific AMPP genes and interleukin-1β (IL-1β) in skin, gills, spleen, and head kidney. AMPP genes were: dicentracin (DIC), histone-like protein 1 (HLP-1), histone-like protein 2 (HLP-2) and hemoglobin-like protein (Hb-LP). The delta-delta C(T) method in real-time RT-PCR allowed to gain more knowledge about temporal dynamics, preferential sites of expression as well as immunological and physiological role of these molecular markers. DIC was significantly up-regulated mainly in head kidney at 1.5-3 h post-infection (p.i.). HLP-1 showed an extended-time overexpression in gills and a significant up-regulation in spleen. HLP-2 was interestingly overexpressed in gills at 24 h p.i., while Hb-LP showed a significant up-regulation in skin for all the 72 h trial as well as lower but always significant values either in gills or in spleen. Different was the response of IL-1β that showed a dramatic up-regulation in spleen and head kidney at 8 h p.i. whilst in gills it displayed a severe inhibition. During this survey the i.p. stimulus surely conditioned the AMPP expression in skin and gills, especially as regards the DIC that as piscidin-related gene has an important defensive role in the mucosal tissues. However, two unconventional AMPP genes such as HLP-2 and Hb-LP, strictly related to the physiological mechanisms of fish, were less affected in terms of expression by the route of infection, being more evident in peripheral loci. These findings might suggest them as potential markers to be analyzed within plans of health survey in fish farms.

Zebrafish fed on recombinant Artemia expressing epinecidin-1 exhibit increased survival and altered expression of immunomodulatory genes upon Vibrio vulnificus infection

Artemia has been used extensively in aquaculture as fodder for larval fish, shrimp, and shellfish. Epinecidin-1, an antimicrobial peptide, was isolated from grouper (Epinephelus coioides) in 2005. Epinecidin-1 has been previously reported to possess antimicrobial activity against several Gram-positive and Gram-negative bacterial species, including Staphylococcus coagulase, Pseudomonas aeruginosa, Streptococcus pyogenes, and Vibrio vulnificus. In this study, we used electroporation to introduce plasmid DNA encoding a green fluorescent protein (EGFP)-epinecidin-1 fusion protein under the control of the cytomegalovirus (CMV) promoter into decapsulated Artemia cysts. Optimization of various properties (including cyst weight (0.2 g), plasmid concentration (50 μg/100 μl), and pulse voltage (150 V), length (10 ms), and number (2)) resulted in a hatching rate of 41.15%, a transfection efficiency of 49.81%, and a fluorescence intensity (A.U.) of 47.46. The expression of EGFP-epinecidin-1 was first detected by quantitative RT-PCR at 120 h post-electroporation, and protein was identified by Western blot at the same time. Furthermore, the EGFP-epinecidin-1 protein inhibited V. vulnificus (204) growth, as demonstrated by zone of inhibition studies. Zebrafish fed on transgenic Artemia expressing CMV-gfp-epi combined with commercial fodder were more resistant to infection by V. vulnificus (204): survival rate was enhanced by over 70% at 7, 14, and 21 days post-infection, and bacterial numbers in the liver and intestine were reduced. In addition, feeding of transgenic Artemia to zebrafish affected the immunomodulatory response to V. vulnificus (204) infection; expression of immune-responsive genes, including hepcidin and defbl2, was altered, as shown by qPCR. These findings suggest that feeding transgenic Artemia expressing CMV-gfp-epi to larval fish has antimicrobial effects, without the drawbacks of introducing drug residues or inducing bacterial drug resistance.

Epinecidin-1 has immunomodulatory effects, facilitating its therapeutic use in a mouse model of Pseudomonas aeruginosa sepsis

Antimicrobial peptides (AMPs) are garnering attention as possible alternatives to antibiotics. Here, we describe the antimicrobial properties of epinecidin-1 against a multidrug-resistant clinical isolate of P. aeruginosa (P. aeruginosa R) and a P. aeruginosa strain from ATCC (P. aeruginosa ATCC 19660) in vivo. The MICs of epinecidin-1 against P. aeruginosa R and P. aeruginosa ATCC 19660 were determined and compared with those of imipenem. Epinecidin-1 was found to be highly effective at combating peritonitis infection caused by P. aeruginosa R or P. aeruginosa ATCC 19660 in mouse models, without inducing adverse behavioral effects or liver or kidney toxicity. Taken together, our results indicate that epinecidin-1 enhances the rate of survival of mice infected with the bacterial pathogen P. aeruginosa through both antimicrobial and immunomodulatory effects.

Antimicrobial peptides from fish

Antimicrobial peptides (AMPs) are found widely distributed through Nature, and participate in the innate host defense of each species. Fish are a great source of these peptides, as they express all of the major classes of AMPs, including defensins, cathelicidins, hepcidins, histone-derived peptides, and a fish-specific class of the cecropin family, called piscidins. As with other species, the fish peptides exhibit broad-spectrum antimicrobial activity, killing both fish and human pathogens. They are also immunomodulatory, and their genes are highly responsive to microbes and innate immuno-stimulatory molecules. Recent research has demonstrated that some of the unique properties of fish peptides, including their ability to act even in very high salt concentrations, make them good potential targets for development as therapeutic antimicrobials. Further, the stimulation of their gene expression by exogenous factors could be useful in preventing pathogenic microbes in aquaculture.