Shrimp (Penaeus monodon) anti-lipopolysaccharide factor reduces the lethality of Pseudomonas aeruginosa sepsis in mice

Host Defense Proteins and Peptides with Lipopolysaccharide-Binding Activity from Marine Invertebrates and Their Therapeutic Potential in Gram-Negative Sepsis

Sepsis is a life-threatening complication of an infectious process that results from the excessive and uncontrolled activation of the host's pro-inflammatory immune response to a pathogen. Lipopolysaccharide (LPS), also known as endotoxin, which is a major component of Gram-negative bacteria's outer membrane, plays a key role in the development of Gram-negative sepsis and septic shock in humans. To date, no specific and effective drug against sepsis has been developed. This review summarizes data on LPS-binding proteins from marine invertebrates (ILBPs) that inhibit LPS toxic effects and are of interest as potential drugs for sepsis treatment. The structure, physicochemical properties, antimicrobial, and LPS-binding/neutralizing activity of these proteins and their synthetic analogs are considered in detail. Problems that arise during clinical trials of potential anti-endotoxic drugs are discussed.

A Novel Antimicrobial Peptide Sparanegtin Identified in Scylla paramamosain Showing Antimicrobial Activity and Immunoprotective Role In Vitro and Vivo

The abuse of antibiotics in aquaculture and livestock no doubt has exacerbated the increase in antibiotic-resistant bacteria, which imposes serious threats to animal and human health. The exploration of substitutes for antibiotics from marine animals has become a promising area of research, and antimicrobial peptides (AMPs) are worth investigating and considering as potential alternatives to antibiotics. In the study, we identified a novel AMP gene from the mud crab Scylla paramamosain and named it Sparanegtin. Sparanegtin transcripts were most abundant in the testis of male crabs and significantly expressed with the challenge of lipopolysaccharide (LPS) or Vibrio alginolyticus. The recombinant Sparanegtin (rSparanegtin) was expressed in Escherichia coli and purified. rSparanegtin exhibited activity against Gram-positive and Gram-negative bacteria and had potent binding affinity with several polysaccharides. In addition, rSparanegtin exerted damaging activity on the cell walls and surfaces of P. aeruginosa with rougher and fragmented appearance. Interestingly, although rSparanegtin did not show activity against V. alginolyticus in vitro, it played an immunoprotective role in S. paramamosain and exerted an immunomodulatory effect by modulating several immune-related genes against V. alginolyticus infection through significantly reducing the bacterial load in the gills and hepatopancreas and increasing the survival rate of crabs.

Anti-lipopolysaccharide Factor from Crucifix Crab Charybdis feriatus, Cf-ALF2: Molecular Cloning and Functional Characterization of the Recombinant Peptide

Antilipopolysaccharide factors (ALFs) are important effectors of innate immunity in crustaceans with broad spectrum antimicrobial activity. Present study deals with the molecular and functional characterization of a 98-amino acid ALF isoform from, crucifix crab, Charybdis feriatus termed as Cf-ALF2. The ALF isoform Cf-ALF2 exhibits characteristic features of an AMP including a cationic net charge of + 9 and a total hydrophobic ratio of 34%. Recombinant peptide rCf-ALF2 showed remarkable antimicrobial activity against Gram-negative and Gram-positive bacteria especially against Staphylococcus aureus (minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of 5 µM) and Escherichia coli (MIC 10 µM and MBC 20 µM). Using scanning electron microscopy, bacterial membrane blebbing, disruption, and cell content leakage were observed in peptide treated E. coli. The recombinant peptide was found to be non-hemolytic and non-cytotoxic in NCI-H460 cell line at the highest tested concentration (20 µM). Thus, this study identified a novel isoform of ALF from C. feriatus and revealed the potent antimicrobial property of the recombinant peptide Cf-ALF2 and the future prospects of using the peptide for therapeutic applications in the future.

Antibacterial Activity of Rationally Designed Antimicrobial Peptides

Many infectious diseases are still prevalent in the world's populations since no effective treatments are available to eradicate them. The reasons may either be the antibiotic resistance towards the available therapeutic molecules or the slow rate of producing adequate therapeutic regimens to tackle the rapid growth of new infectious diseases, as well as the toxicity of current treatment regimens. Due to these reasons, there is a need to seek and develop novel therapeutic regimens to reduce the rapid scale of bacterial infections. Antimicrobial Peptides (AMPs) are components of the first line of defense for prokaryotes and eukaryotes and have a wide range of activities against Gram-negative and Gram-positive bacteria, fungi, cancer cells, and protozoa, as well as viruses. In this study, peptides which were initially identified for their HIV inhibitory activity were further screened for antibacterial activity through determination of their kinetics as well as their cytotoxicity. From the results obtained, the MICs of two AMPs (Molecule 3 and Molecule 7) were 12.5 μg/ml for K. pneumoniae (ATCC 700603) and 6.25 μg/ml for P. aeruginosa (ATCC 22108). The two AMPs killed these bacteria rapidly in vitro, preventing bacterial growth within few hours of treatment. Furthermore, the cytotoxic activity of these two peptides was significantly low, even at an AMP concentration of 100 μg/ml. These results revealed that Molecule 3 and 7 have great potential as antibacterial drugs or could serve as lead compounds in the design of therapeutic regimens for the treatment of antibiotic-resistant bacteria.

The Immune Activity of PT-Peptide Derived from Anti-Lipopolysaccharide Factor of the Swimming Crab Portunus trituberculatus Is Enhanced when Encapsulated in Milk-Derived Extracellular Vesicles

PT-peptide is derived from the anti-lipopolysaccharide factor of the swimming crab Portunus trituberculatus. The peptide, consisting of 34 amino acids, contains a lipopolysaccharide binding domain. In this study, we investigated the effect of PT-peptide encapsulated in raw milk-derived extracellular vesicles (EVs), designated as EVs-PT peptide, on immune regulation. The results showed that raw milk-derived EVs efficaciously delivered the PT-peptide into monocytes and elevated immune activity, including reactive oxygen species level, superoxide anion production, and phagocytosis. PT-peptide and EVs-PT peptide also elevated the secretion of cytokines, such as interferon-γ, interleukin-6, and tumor necrosis factor-α in human monocytic THP-1 cells. These results suggest that the PT-peptide could be developed as an immune stimulator.

Regulation of antilipopolysaccharide factors, ALFPm3 and ALFPm6, in Penaeus monodon

ALFPm6, a member of antimicrobial peptide in the antilipopolysaccharide factor (ALF) family from Penaeus monodon, plays important roles in shrimp immunity against pathogens. However, its antimicrobial activity and underlying mechanism have not been reported. The synthetic cyclic ALFPm6#29–52 peptide (cALFPm6#29–52) corresponding to the ALFPm6 LPS-binding domain can agglutinate and exhibited bacterial killing activity toward a Gram-negative bacterium, Escherichia coli 363 and Gram-positive bacteria, Bacillus megaterium, Aerococcus viridans, and Micrococcus luteus, with MIC values of 25–50 μM. Specifically, ALFPm6 and ALFPm3, the most abundant ALF isoforms, are different in terms of gene expression patterns upon pathogen infections. Herein, the regulation of ALFPm3 and ALFPm6 gene expression was studied. The 5′-upstream and promoter sequences were identified and the putative transcription factor (TF)-binding sites were predicted. The narrow down assay indicated that the ALFPm3 promoter and partial promoter of the ALFPm6 active regions were located at nucleotide positions (−814/+302) and (−282/+85), respectively. Mutagenesis of selected TF-binding sites revealed that Rel/NF-κB (−280/−270) of ALFPm3 and C/EBPβ (−88/−78) and Sp1 (−249/−238) sites of ALFPm6 were the activator-binding sites. Knockdown of the PmMyD88 and PmRelish genes in V. harveyi-infected shrimp suggested that the ALFPm3 gene was regulated by Toll and IMD pathways, while the ALFPm6 gene was regulated by the Toll pathway.

Newly identified PcToll4 regulates antimicrobial peptide expression in intestine of red swamp crayfish Procambarus clarkii

Tolls or Toll-like receptors (TLRs) have an essential role in initiating innate immune responses against pathogens. In this study, a novel Toll gene, PcToll4, was first identified from the intestinal transcriptome of the freshwater crayfish, Procambarus clarkii. The PcToll4 cDNA is 4849bp long with a 3036bp open reading frame that encodes a 1011-amino acid protein. PcToll4 contains a signal peptide, 13 LRR domains, 3 LRR TYP domains, 2 LRR CT domains, an LRR NT domain, a transmembrane region, and a TIR domain. Quantitative RT-PCR analysis revealed that PcToll4 mRNA was detected in all tested tissues, and the expression of PcToll4 in the intestine was significantly upregulated after white spot syndrome virus (WSSV) challenge. Overexpression of PcToll4 in Drosophila Schneider 2 (S2) cells activates the antimicrobial peptides (AMPs) of Drosophila, including metchnikowin, drosomycin, attacin A, and shrimp Penaeidin-4. Results of RNA interference by siRNA also showed that PcToll4 regulates the expressions of 5 anti-lipopolysaccharide factors (ALFs) in the intestine of crayfish. Our findings suggest that PcToll4 is important for the innate immune responses of P. clarkii because this gene regulates the expressions of AMPs against WSSV.

Antimicrobial and Antitumor Activities of Novel Peptides Derived from the Lipopolysaccharide- and β-1,3-Glucan Binding Protein of the Pacific Abalone Haliotis discus hannai

Antimicrobial peptides are a pivotal component of the invertebrate innate immune system. In this study, we identified a lipopolysaccharide- and β-1,3-glucan-binding protein (LGBP) gene from the pacific abalone Haliotis discus hannai (HDH), which is involved in the pattern recognition mechanism and plays avital role in the defense mechanism of invertebrates immune system. The HDH-LGBP cDNA consisted of a 1263-bp open reading frame (ORF) encoding a polypeptide of 420 amino acids, with a 20-amino-acid signal sequence. The molecular mass of the protein portion was 45.5 kDa, and the predicted isoelectric point of the mature protein was 4.93. Characteristic potential polysaccharide binding motif, glucanase motif, and β-glucan recognition motif were identified in the LGBP of HDH. We used its polysaccharide-binding motif sequence to design two novel antimicrobial peptide analogs (HDH-LGBP-A1 and HDH-LGBP-A2). By substituting a positively charged amino acid and amidation at the C-terminus, the pI and net charge of the HDH-LGBP increased, and the proteins formed an α-helical structure. The HDH-LGBP analogs exhibited antibacterial and antifungal activity, with minimal effective concentrations ranging from 0.008 to 2.2 μg/mL. Additionally, both were toxic against human cervix (HeLa), lung (A549), and colon (HCT 116) carcinoma cell lines but not much on human umbilical vein cell (HUVEC). Fluorescence-activated cell sorter (FACS) analysis showed that HDH-LGBP analogs disturb the cancer cell membrane and cause apoptotic cell death. These results suggest the use of HDH-LGBP analogs as multifunctional drugs.

Enhanced Control of Bladder-Associated Tumors Using Shrimp Anti-Lipopolysaccharide Factor (SALF) Antimicrobial Peptide as a Cancer Vaccine Adjuvant in Mice

Shrimp anti-lipopolysaccharide factor (SALF) is an antimicrobial peptide with reported anticancer activities, such as suppression of tumor progression. In this study, we prepared a potential cancer vaccine comprised of SALF in conjunction with the cell lysate of inactivated murine bladder carcinoma cells (MBT-2), and evaluated its efficacy in a mouse tumor model. Our study shows that SALF added to cell culture media inhibits growth progression of MBT-2, and that SALF together with inactivated MBT-2 lysate elevates the level of inflammasome activity, and modulates the levels of IL-1β, MCP-1, IL-6, IL-12, and TNF-α in mouse macrophages. Immunization of 7, 14, and 21 day-old mice with the vaccine prevented growth of MBT-2 cell-mediated tumors. The vaccine was found to enhance expression of T-cell, cytotoxic T cells, and NK cells in the immunized mice groups. Recruitment of macrophages, T-helper cells, and NK cells was enhanced, but levels of VEGF were decreased in immunized mice. This report provides empirical evidence that our SALF as vaccine adjuvant enhances antitumor immunity in mice.

Functional diversity of anti-lipopolysaccharide factor isoforms in shrimp and their characters related to antiviral activity

Anti-lipopolysaccharide factor (ALF) is a small protein with broad-spectrum antimicrobial activity, which has potential application in the disease control. Previously, we isolated seven ALF isoforms from the Chinese shrimp Fenneropenaeuschinensis. In the present study, their distributions in tissues of shrimp were analyzed and the data showed that different isoforms had different expression profiles, which suggested that they might have different functions. Then, the functions of different isoforms were studied by analyzing the antibacterial and antiviral activities of the functional domain of ALFs, the LPS-binding domain (LBD), which were synthesized by chemical methods. Different ALFs showed distinct antibacterial and antiviral activities, which were consistent with their diverse tissue distribution patterns. Sequence analysis on the LBD domain of different isoforms revealed that an identical lysine residue site was specifically conserved in peptides with anti-WSSV activity. In order to confirm whether this lysine residue is critical to the antiviral activity of the peptide, new peptides were synthesized by changing residues at this site. Changing the lysine residue at the specific site to other amino acid residue, the antiviral activity of the peptide apparently decreased. While replacing other residue with a lysine residue at this site in LBD peptide without anti-WSSV activity, the peptide will obtain the antiviral activity to WSSV. These results not only showed us a comprehensive understanding on the function of ALFs from F. chinensis, but also provided clues for the development of ALFs as potential therapeutic drugs to WSSV.

Characterization of a novel anti-lipopolysaccharide factor isoform (SpALF5) in mud crab, Scylla paramamosain

Anti-lipopolysaccharide factors (ALFs), the potential antimicrobial peptides that bind and neutralize lipopolysaccharide (LPS), are common effectors of innate immunity in crustaceans. In this study, a novel isoform of ALFs (SpALF5) was isolated from the hemocytes of mud crab Scylla paramamosain. The full-length 975bp SpALF5 contains a 375bp open reading frame (ORF) encoding 125 amino acids. Although SpALF5 exhibits a low degree of nucleotide homology with other reported ALFs, it contains the conserved amino acid sequence with a signal peptide and a LPS-binding domain including two conservative cysteine residues. The genomic organization of SpALF5 consists of four exons and three introns, with each intron containing one or more tandem repeats. Unlike most of ALFs mainly distributed in crab hemocytes, SpALF5 transcript was predominantly observed in the brain, muscle and skin, while barely detected in the hemocytes in our study. In situ hybridization assay also showed that SpALF5 mRNA was localized in brain, muscle and skin tissues of mud crab. Further, SpALF5 transcript was significantly up-regulated after challenge with LPS, polyinosinic polycytidylic acid (PolyI:C) (with the except of that in brain), Vibrio parahemolyticus or white spot syndrome virus (WSSV). The recombinant SpALF5 protein showed a varying degree of binding activity towards bacteria and fungus. Moreover, in vitro, the recombinant SpALF5 revealed a strong antimicrobial activity against Gram-negative bacteria (V. parahemolyticus, Vibrio alginolyticus, Escherichia coli, Aeromonas hydrophila) and fungus (Sacchromyces cerevisiae), but could only inhibited the growth of some Gram-positive bacteria like Staphylococcus aureus. The results suggest that SpALF5 is a potent immune protector and plays an important role in immune defense against invading pathogens in S. paramamosain.

Characterization and function analysis of an anti-lipopolysaccharide factor (ALF) from the Chinese shrimp Fenneropenaeus chinensis

Anti-lipopolysaccharide factor (ALF) is one of the widely-studied antimicrobial peptides (AMPs) with broad-spectrum antibacterial activity and antiviral property. Previous studies show the existence of multiform of ALFs in crustacean which are important for immunity of the animals. In the present study, we characterized one isoform of ALF from the Chinese shrimp Fenneropenaeus chinensis (FcALF2). Tissue distribution analysis revealed that FcALF2 showed the highest expression level in the lymphoid organ (Oka) of the shrimp. The expression level of FcALF2 in shrimp was significantly up-regulated when they were injected with Micrococcus lysodeikticus and Vibrio anguillarum. A peptide corresponding to the LPS-binding domain of FcALF2 (FcALF2-LBD) was synthesized to analyze its antimicrobial activities. Data demonstrated that FcALF2-LBD possessed strong antibacterial activity against Gram-positive bacteria Micrococcus luteus and M.lysodeikticus with MIC ranges of 2-4 μM and 1-2 μM respectively and significant inhibition activity against white spot syndrome virus (WSSV). The antibacterial activities of the sequence modified peptides (FcALF2-LBDb, FcALF2-LBDv) were apparently enhanced and broadened after the amount of basic amino acids was increased in the synthetic LPS-binding domain. These data provide more insights into understanding the function of LPS-binding domain of ALF and the role of ALF in shrimp immunity.

Modification of a synthetic LPS-binding domain of anti-lipopolysaccharide factor from shrimp reveals strong structure-activity relationship in their antimicrobial characteristics

Anti-lipopolysaccharide factor (ALF) is a small protein with broad-spectrum antimicrobial activities and certain antiviral property. Its putative lipopolysaccharide (LPS) binding domain was deduced to be important for its activities. However, there is still no report revealing how the structure of the LPS-binding domain affects its biological function until now. In the present study, we designed and synthesized a peptide corresponding to the LPS-binding domain of ALF from the Chinese shrimp (designated as FcALF-LBDc) and its structure-modified isoforms in order to analyze the relationship between its structure and antimicrobial activities. Results showed that FcALF-LBDc exhibited apparent antibacterial activities against both Gram-negative bacteria Escherichia coli and Vibrio anguillarum and Gram-positive bacteria Micrococcus luteus and Micrococcus lysodeikticus with MIC ranges of 32-64, 2-4, 1-2, and 32-64μM, respectively. The disulfide loop and the basic amino acids in the LPS-binding domain (LBD) of ALF played key roles in its antibacterial activities. In addition, FcALF-LBDc could reduce the propagation of white spot syndrome virus (WSSV) in vivo, and its lysine residue is indispensable for its antiviral property. This is the first attempt to testify the effects of the sequence features of the LPS-binding domain on its antimicrobial activities.

Truncated antimicrobial peptides from marine organisms retain anticancer activity and antibacterial activity against multidrug-resistant Staphylococcus aureus

Antimicrobial peptides (AMPs) were recently determined to be potential candidates for treating drug-resistant bacterial infections. The aim of this study was to develop shorter AMP fragments that combine maximal bactericidal effect with minimal synthesis cost. We first synthesized a series of truncated forms of AMPs (anti-lipopolysaccharide factor from shrimp, epinecidin from grouper, and pardaxin from Pardachirus marmoratus). The minimum inhibitory concentrations (MICs) of modified AMPs against ten bacterial species were determined. We also examined the synergy between peptide and non-peptide antibiotics. In addition, we measured the inhibitory rate of cancer cells treated with AMPs by MTS assay. We found that two modified antibacterial peptides (epinecidin-8 and pardaxin-6) had a broad range of action against both gram-positive and gram-negative bacteria. Furthermore, epinecidin and pardaxin were demonstrated to have high antibacterial and anticancer activities, and both AMPs resulted in a significant synergistic improvement in the potencies of streptomycin and kanamycin against methicillin-resistant Staphylococcus aureus. Neither AMP induced significant hemolysis at their MICs. In addition, both AMPs inhibited human epithelial carcinoma (HeLa) and fibrosarcoma (HT-1080) cell growth. The functions of these truncated AMPs were similar to those of their full-length equivalents. In conclusion, we have successfully identified shorter, inexpensive fragments with maximal bactericidal activity. This study also provides an excellent basis for the investigation of potential synergies between peptide and non-peptide antibiotics, for a broad range of antimicrobial and anticancer activities.

Bacterial cell wall compounds as promising targets of antimicrobial agents I. Antimicrobial peptides and lipopolyamines

The first barrier that an antimicrobial agent must overcome when interacting with its target is the microbial cell wall. In the case of Gram-negative bacteria, additional to the cytoplasmic membrane and the peptidoglycan layer, an outer membrane (OM) is the outermost barrier. The OM has an asymmetric distribution of the lipids with phospholipids and lipopolysaccharide (LPS) located in the inner and outer leaflets, respectively. In contrast, Gram-positive bacteria lack OM and possess a much thicker peptidoglycan layer compared to their Gram-negative counterparts. An additional class of amphiphiles exists in Gram-positives, the lipoteichoic acids (LTA), which may represent important structural components. These long molecules cross-bridge the entire cell envelope with their lipid component inserting into the outer leaflet of the cytoplasmic membrane and the teichoic acid portion penetrating into the peptidoglycan layer. Furthermore, both classes of bacteria have other important amphiphiles, such as lipoproteins, whose importance has become evident only recently. It is not known yet whether any of these amphiphilic components are able to stimulate the immune system under physiological conditions as constituents of intact bacteria. However, all of them have a very high pro-inflammatory activity when released from the cell. Such a release may take place through the interaction with the immune system, or with antibiotics (particularly with those targeting cell wall components), or simply by the bacterial division. Therefore, a given antimicrobial agent must ideally have a double character, namely, it must overcome the bacterial cell wall barrier, without inducing the liberation of the pro-inflammatory amphiphiles. Here, new data are presented which describe the development and use of membrane-active antimicrobial agents, in particular antimicrobial peptides (AMPs) and lipopolyamines. In this way, essential progress was achieved, in particular with respect to the inhibition of deleterious consequences of bacterial infections such as severe sepsis and septic shock.

The antimicrobial peptide, epinecidin-1, mediates secretion of cytokines in the immune response to bacterial infection in mice

Epinecidin-1, an antimicrobial peptide which encodes 21 amino acids, was isolated from a marine grouper (Epinephelus coioides). In this study, we investigated its immunomodulatory functions in mice co-injected with Pseudomonas aeruginosa. In vivo results showed that the synthetic epinecidin-1 peptide induced significant secretion of immunoglobulin G1 (IgG1) in mice co-injected with P. aeruginosa. Moreover, after injection of 40, 100, 200, or 500 μg epinecidin-1/mouse, we detected IgM, IgG, IgG1, and IgG2a in mice treated for 1, 2, 3, 7, 14, 21, and 28 days. Results showed that there were no significant differences in IgM, IgG, or IgG2a between mice injected with epinecidin-1 alone. IgG1 increased to a peak at 24 h, 7 days, and 28 days after an epinecidin-1 (40 μg/mouse) injection. Injection of 500 μg epinecidin-1/mouse increased IgG1 to peaks at 2 and 3 days; injection of 100 μg epinecidin-1/mouse increased IgG1 to a peak at 21 days. This supports epinecidin-1 being able to activate the Th2 cell response (enhance IgG1 production) against P. aeruginosa infection. Treatment with different concentrations of epinecidin-1 in mice elevated plasma interleukin (IL)-10 to initial peaks at 24 and 48 h, and it showed a second peak at 16 days. In RAW264.7 cells, treatment with epinecidin-1 alone did not produce significant changes in tumor necrosis factor (TNF)-α protein secretion at 1, 6, or 24h after treatment with 3.75, 7.5, or 15 μg/ml epinecidin-1 compared to the lipopolysaccharide group.

Cationic antimicrobial peptides in penaeid shrimp

Penaeid shrimp aquaculture has been consistently affected worldwide by devastating diseases that cause a severe loss in production. To fight a variety of harmful microbes in the surrounding environment, particularly at high densities (of which intensive farming represents an extreme example), shrimps have evolved and use a diverse array of antimicrobial peptides (AMPs) as part of an important first-line response of the host defense system. Cationic AMPs in penaeid shrimps composed of penaeidins, crustins, and anti-lipopolysaccharide factors are comprised of multiple classes or isoforms and possess antibacterial and antifungal activities against different strains of bacteria and fungi. Shrimp AMPs are primarily expressed in circulating hemocytes, which is the main site of the immune response, and hemocytes expressing AMPs probably migrate to infection sites to fight against pathogen invasion. Indeed, most AMPs are produced as early as the nauplii developmental stage to protect shrimp larvae from infections. In this review, we discuss the sequence diversity, expression, gene structure, and antimicrobial activities of cationic AMPs in penaeid shrimps. The information available on antimicrobial activities indicates that these shrimp AMPs have potential therapeutic applications in the control of disease problems in aquaculture.

Peptide-based treatment of sepsis

Sepsis (blood poisoning) is a severe infectious disease with high mortality, and no effective therapy is actually known. In the case of Gram-negative bacteria, endotoxins (lipopolysaccharides) are known to be responsible for the strong inflammation reaction leading to the systemic infection. Peptides based on endotoxin-binding domains of human or animal proteins represent a promising approach in sepsis research. Although so far no medicament is available, the progress in recent years might lead to a breakthrough in this field. In this review, recent investigations are summarised, which may lead to an understanding of the mechanisms of action of peptides to suppress the inflammation reaction in vitro and in vivo (animal models) and thus may allow the development of effective anti-septic drugs.

Cationic antimicrobial peptides in penaeid shrimp

Penaeid shrimp aquaculture has been consistently affected worldwide by devastating diseases that cause a severe loss in production. To fight a variety of harmful microbes in the surrounding environment, particularly at high densities (of which intensive farming represents an extreme example), shrimps have evolved and use a diverse array of antimicrobial peptides (AMPs) as part of an important first-line response of the host defense system. Cationic AMPs in penaeid shrimps composed of penaeidins, crustins, and anti-lipopolysaccharide factors are comprised of multiple classes or isoforms and possess antibacterial and antifungal activities against different strains of bacteria and fungi. Shrimp AMPs are primarily expressed in circulating hemocytes, which is the main site of the immune response, and hemocytes expressing AMPs probably migrate to infection sites to fight against pathogen invasion. Indeed, most AMPs are produced as early as the nauplii developmental stage to protect shrimp larvae from infections. In this review, we discuss the sequence diversity, expression, gene structure, and antimicrobial activities of cationic AMPs in penaeid shrimps. The information available on antimicrobial activities indicates that these shrimp AMPs have potential therapeutic applications in the control of disease problems in aquaculture.

Antimicrobial peptide of an anti-lipopolysaccharide factor modulates of the inflammatory response in RAW264.7 cells

In this study, to clarify the protective mechanism of a peptide from shrimp anti-lipopolysaccharide (LPS) factor (SALF) against endotoxin shock, we evaluated the effects of the SALF and LPS on the production and release of tumor necrosis factor (TNF)-alphain vitro using the RAW264.7 murine macrophage cell line. Stimulation by LPS induced the production of inflammatory cytokines, and the SALF was able to modulate TNF-alpha production in LPS-stimulated RAW264.7 cells. Microarray studies revealed a transcriptional profile which was assessed in the presence or absence of the SALF by a quantitative real-time polymerase chain reaction. Pretreatment with the SALF significantly downregulated the expression of nuclear factor (NF)-kappaB in the presence of LPS. In contrast, pretreatment with the SALF significantly elevated the expressions of Anp32a, CLU, and SLPI, which are considered to be immune-related genes in the presence of LPS. Inhibitor studies suggested that the SALF's modulation of LPS-induced TNF-alpha production involved a complex mechanism with mitogen-activated protein kinase kinase, calcium, and protein kinase C. The data from this study, which imply that the SALF can suppress TNF-alpha production, suggest a role for the SALF in the defense mechanism which can potentially be applied to mammals for endotoxin treatment.

Anti-lipopolysaccharide factors in the American lobster Homarus americanus: molecular characterization and transcriptional response to Vibrio fluvialis challenge

Two partial mRNA sequences predicted to encode anti-lipopolysaccharide factors (ALFs) were identified among expressed sequence tags generated from the American lobster Homarus americanus and complete cDNA sequences were obtained from library clones. Comparison of the translated amino acid sequences to those publicly available confirmed similarity to arthropod anti-lipopolysaccharide factors. Both protein sequences, designated ALFHa-1 and ALFHa-2, contained an N-terminal signal peptide and two half-cysteines participating in a disulfide bridge, features conserved in other ALFs. Predicted secondary structures were similar to that described for the ALF from the horseshoe crab Limulus polyphemus. As part of an exploratory study of immunity in H. americanus, lobsters were injected with the bacterium Vibrio fluvialis and gill, hematopoietic, and hepatopancreas tissues were sampled for analysis of gene expression of ALFHa-1 and ALFHa-2 by quantitative PCR. The relative abundance of ALFHa-2 mRNA was not significantly affected by Vibrio injection in any of the three tissues tested. In contrast, ALFHa-1 mRNA levels in gills were increased by the treatment some 17-fold. Our results support a molecularly specific regulation of antimicrobial proteins in response to bacterial infection in H. americanus.

Shrimp anti-lipopolysaccharide factor peptide enhances the antitumor activity of cisplatin in vitro and inhibits HeLa cells growth in nude mice

The antitumor activity of the shrimp anti-lipopolysaccharide factor (SALF), an antimicrobial peptide, was not previously examined. In this study, a synthetic SALF was tested for antitumor activity using HeLa cells as the study model. We show that the SALF inhibited the proliferation of HeLa cells and reduced colony formation in a soft agar assay. An enhanced effect was observed when the SALF and cisplatin were used in combination, which caused significant inhibition of HeLa cells. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that the SALF altered the membrane structure similar to what a lytic peptide does. A flow cytometric analysis, qRT-PCR, and Western blotting showed that the SALF induced apoptosis, activated caspases-6, -7, and -9, and downregulated Bcl-2 and nuclear factor (NF)-kappaB suggesting that the SALF induces apoptosis through the death receptor/NF-kappaB signaling pathway. An in vivo analysis revealed that the SALF displayed significant tumor suppressive activity in mice with tumor xenografts. Overall, these results indicated that the SALF possesses the potential to be a novel therapeutic agent for treating cervical cancer.

Antiviral activity by fish antimicrobial peptides of epinecidin-1 and hepcidin 1-5 against nervous necrosis virus in medaka

The nervous necrosis virus (NNV)-medaka infection model was used in this study for analysis of NNV infection and treatment of NNV with the antimicrobial peptides (AMPs) of epinecidin-1 and hepcidin 1-5 at the organismal level. Our results showed that co-treatment of AMPs with the virus was effective in promoting a significant increase in medaka survival. Re-challenge with the virus also showed high survival suggesting that these two AMPs enhanced fish survival. However, pretreatment or post-treatment with AMPs showed that both of these AMPs increased medaka survival and suggested that AMPs can be used as drugs to rescue infected medaka. The data presented here indicate that epinecidin-1 and hepcidin 1-5 have in vivo antivirus activity against the NNV, and hepcidin 1-5 functions like a lytic peptide after an in vitro assay. Infection after pretreatment, co-treatment, and post-treatment with epinecidin-1 or hepcidin 1-5 was verified by RT-PCR which showed both peptides can downregulate NNV and interferon gene expressions. In addition, our results suggest that epinecidin-1 or hepcidin 1-5 may prove to be an effective chemotherapeutic agent for aquaculture in the future.

Antimicrobial peptides of an anti-lipopolysaccharide factor, epinecidin-1, and hepcidin reduce the lethality of Riemerella anatipestifer sepsis in ducks

Antimicrobial peptides (AMPs) are effective against a wide range of microbes, but still no research results have reported their use in duck disease therapy. Riemerella anatipestifer (RA) is a Gram-negative bacterium which infects ducks and causes very significant economic losses. The minimum inhibitory concentrations (MICs) of epinecidin-1 for the tested RA strains ranged 6.25-50microg/ml, those of the SALF55-76 cyclic peptide ranged 12.5-25microg/ml, those of the SALF55-76 linear peptide ranged 6.25-25microg/ml, those of hepcidin TH1-5 ranged 25-400microg/ml, and those of hepcidin TH2-3 ranged 100-400microg/ml. The antimicrobial activities of these peptides were confirmed by transmission electron microscopy which showed that RA disruption of the outer membrane brought about cell death. In addition, pretreatment, co-treatment, and post-treatment with peptides were all effective in promoting a significant decrease in duck mortality and decreasing the number of infectious bacteria. A quantitative RT-PCR was performed to survey levels of gene expressions of Mn superoxide dismutase in the brain, lipoprotein lipase in the liver, and H5 histone in the spleen induced in response to bacterial infection and an injection of the AMPs in experiments with the duck, Cairina moschata. Our results indicated that the rescue of ducks by the peptides and the behavior of the peptides, which was like an enhancer in immunology, may involve regulation of the expressions of these genes. Collectively, these peptides reduced the mortality in ducks during bacterial challenge, suggesting that AMPs have the potential to serve as therapeutic drugs for use against bacterial infectious diseases in ducks.

Expression of immune-related genes in one phase of embryonic development of freshwater crayfish, Pacifastacus leniusculus

Crayfish do not have larval stage as other crustacean such as penaeid shrimp they spawn their eggs until hatching and what hatches out from the eggs are miniature crayfish known as juveniles. In order to address the question whether immune genes are initially expressed during the embryo development in the egg stage, the expression of some immune-related genes: prophenoloxidase (proPO), peroxinectin, hemocyanin, anti-lipopolysaccharide factor (ALF), plcrustin, astakine-1, 2 and transglutaminase (TGase) were determined in the middle phase of crayfish embryo development. Furthermore, immune challenge was used to determine the immune response of eggs by immersing them in a solution of the highly pathogenic bacterium Aeromonas hydrophila. Semi-quantitative RT-PCR analysis showed that all tested genes are present except proPO in this phase of crayfish embryo development and none of the genes tested changed their expression following immersion in A. hydrophila. The proPO transcript has been reported from hemocytes in crustaceans and it plays crucial roles in crustacean immune response. This may indicate that the development of immune-competent hemocytes in this stage of crayfish embryo is not completed and the egg shell as such plays an important role as a shield in protecting the embryo from bacteria and maybe also other pathogens.

Antiviral immunity in crustaceans

Viral diseases of shrimp have caused negative effects on the economy in several countries in Asia, South America and America, where they have numerous shrimp culture industries. The studies on the immunity of shrimp and other crustaceans have mainly focused on general aspects of immunity and as a consequence little is known about the antiviral responses in crustaceans. The aim of this review is to update recent knowledge of innate immunity against viral infections in crustaceans. Several antiviral molecules have been isolated and characterized recently from decapods. Characterization and identification of these molecules might provide a promising strategy for protection and treatment of these viral diseases. In addition dsRNA-induced antiviral immunity is also included.

In vitro activities of three synthetic peptides derived from epinecidin-1 and an anti-lipopolysaccharide factor against Propionibacterium acnes, Candida albicans, and Trichomonas vaginalis

The synthetic epinecidin-1(22-42) peptide was derived from positions 22-42 of Epinephelus coioides epinecidin-1. The synthetic SALF(55-76) cyclic peptide (csSALF(55-76)) and SALF(55-76) linear peptide (lsSALF(55-76)) contained sequences from positions 55 to 76 of the Penaeus monodon anti-lipopolysaccharide factor (ALF), respectively. We studied the in vitro activities of epinecidin-1(22-42), csSALF(55-76), and lsSALF(55-76) against Propionibacterium acnes, Candida albicans, and Trichomonas vaginalis. The minimum inhibitory concentrations (MICs) of epinecidin-1(22-42) for the test pathogen strains ranged 12.5-200 microg/ml, those of csSALF(55-76) ranged 100-200 microg/ml, and those of lsSALF(55-76) ranged 25-200 microg/ml. epinecidin-1(22-42) exhibited cytotoxicity towards P. acnes, C. albicans, and T. vaginalis (one strain of which was a metronidazole-resistant strain, while the other strain was not), suggesting that epinecidin-1 functions like a lytic peptide. Similar cytotoxicity was identified against T. vaginalis treated with the csSALF(55-76) and lsSALF(55-76) peptides. The antimicrobial activities of these peptides were confirmed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), a viable cell count assay, and flow cytometric analysis. TEM and SEM examinations of T. vaginalis treated with these three peptides showed that severe swelling preceded cell death and breakage of the outer membrane, and the intracellular inclusion was found to have effluxed extracellularly. This phenomenon was also found with epinecidin-1(22-42) treatment of P. acnes and C. albicans. Our results suggest that the epinecidin-1(22-42), csSALF(55-76), and lsSALF(55-76) peptides may be good candidates for treating trichomoniasis, and epinecidin-1(22-42) may have potential as a drug supporting therapy for acne and candidiasis.

Stable expression in a Chinese hamster ovary (CHO) cell line of bioactive recombinant chelonianin, which plays an important role in protecting fish against pathogenic infection

Chelonianin, originally isolated from the shrimp (Penaeus monodon), exhibits antimicrobial effects in vitro and in vivo and is used to treat infectious fish diseases. Herein, we report that the recombinant chelonianin protein fused to a fluorescent protein (rcf protein) was expressed from a stably transfected Chinese hamster ovary (CHO) cells. The in vitro experiments showed that the rcf protein exhibited antimicrobial activity against several bacteria, while the recombinant fluorescent protein alone did not. In addition, pretreatment and post-treatment with the rcf protein were both effective in promoting a significant decrease in fish mortality and decreasing the number of infectious bacteria. We utilized the quantitative reverse-transcriptase polymerase chain reaction technique to survey the levels of gene expressions of tumor necrosis factor-alpha (TNF-alpha) and nitric oxide synthase 1 induced in response to bacterial infection in experiments with tilapia (Oreochromis mossambicus). Our results indicated that the rescue of fish treated with the rcf protein may involve regulation of TNF-alpha expression. Collectively, chelonianin inhibited the production of an inflammatory mediator and reduced mortality in fish during bacterial challenge, suggesting that it has potential as a therapeutic or prophylactic drug for use against bacterial infectious diseases.

Organization and promoter analysis of the grouper (Epinephelus coioides) epinecidin-1 gene

Epinecidin-1, an antimicrobial peptide documented in some fish, is an essential component of the innate immune response in fish, but little is known about its gene regulation. To better understand the molecular mechanism controlling transcription of the epinecidin-1 gene, we cloned and sequenced the genes and promoter regions of three epinecidin-1 peptides from the grouper (Epinephelus coioides). These genes have the potential to encode three putative epinecidin-1 peptides with either a short or a long 5'-untranslated region (UTR). These epinecidin-1 genes, numbered 124-1 (gene structure: 5 exons), 124-2 (gene structure: 5 exons), and 961 (gene structure: 4 exons), have 3' UTR sequences that dramatically differ by being located on different exons in clones 124 and 961. To address the roles of lipopolysaccharide (LPS) and poly(I):poly(C) in regulating epinecidin-1 expression, serial deletions were prepared in the promoter region of two clones that contained three genes. Different fragments of the epinecidin-1 5'-flanking region were transfected into U937 (human histiocytic lymphoma) and ZFL (zebrafish liver) cells and then treated with 0, 1, 10, and 100 mug/mL LPS or poly(I):poly(C). The results showed that after treatment with 10 mug/mL LPS, high promoter activity was observed in the 0.6-kb promoter fragment (of clone 961). Promoter deletions showed that hepatocyte nuclear factor (HNF)-1 was required for a maximal response of epinecidin-1 961 promoter activity after LPS treatment in ZFL cells. Morphological studies of transgenic zebrafish indicated that the 2-kb epinecidin-1 124-1 promoter-driven GFP transcripts appeared in the eye and skin as confirmed by immunohistochemical staining. These results indicate that the 2-kb epinecidin-1 124-1 promoter is active in a tissue-specific manner.

Localization of anti-lipopolysaccharide factor (ALFPm3) in tissues of the black tiger shrimp, Penaeus monodon, and characterization of its binding properties

Anti-lipopolysaccharide factor (ALF) is an antimicrobial peptide originally identified from horseshoe crabs and recently found in several shrimp species. ALFPm3, the most abundant isoform in the black tiger shrimp, Penaeus monodon, has been shown to possess a broad spectrum of antimicrobial activity against Gram-negative and Gram-positive bacteria, and filamentous fungi. In this study, a potential role for ALFPm3 in the shrimp innate immunity was revealed by examining the distribution of the protein in shrimp tissues in response to Vibrio harveyi challenge. Immunohistochemistry using anti-ALFPm3 antibody showed that the ALFPm3 protein is primarily localized in hemocytes and the positive cells observed at the injection site and in the cephalothorax are infiltrating hemocytes that migrate into shrimp tissues after bacterial injection. A rapid increase in the number of hemocytes producing ALFPm3 observed in V. harveyi-injected shrimp suggests a likely important function of the protein in defense against invading pathogens. ALFPm3 was shown to be able to bind to Gram-negative and Gram-positive bacterial cells and their major cell wall components, lipopolysaccharide (LPS) and lipoteichoic acid (LTA), respectively. The results suggested that ALFPm3 performs its antibacterial activity by binding to component(s) of the bacterial cell wall.