Structure-activity relationship of human liver-expressed antimicrobial peptide 2

Transcriptomic functional characterization of recombinant adeno-associated virus producing cell line adapted to suspension-growth

Recombinant adeno-associated virus (rAAV) is a widely used delivery vehicle in gene therapy. A scalable production technology is essential for its wide clinical applications. We have taken a synthetic biology approach to generate HEK293-based cell lines which harbor integrated genetic elements encoding essential AAV and adenoviral helper components and can be induced to produce rAAV. Through cycles of cell line enhancement, a high rAAV productivity could be achieved. The cell lines, like their parental HEK293, grew adherently. For scalable production, cell cultivation in suspension is highly desirable. A producer cell line GX6B was adapted to suspension growth in serum-free medium (named GX6Bs). However, it had substantially reduced virus titer. Returning GX6Bs cells to adherent culture conditions using adherent medium and cultured stationarily brought the productivity back to close to the level of adherent GX6B. A survey of the transcriptome revealed that induction and rAAV production elicited a wide range of cellular changes in various functional classes, including host immune defense response and nucleosome organization. The response was more subdued in suspension-growing GX6Bs. Upon reverting to adherent growth, the cellular transcriptome change regained its vigor to be more similar to that seen in GX6B. The GX6Bs maintained in suspension serum-free conditions were then reverted to the adherent culture medium but under an agitated culture environment to keep suspension growth for rAAV production. The productivity returned to within 25%-50% of GX6B. This work demonstrated the feasibility of the suspension culture of synthetic cell lines for the expansion and production of rAAV.

Molecular characterization of an antimicrobial peptide LEAP-2 in Onychostoma macrolepis: Expression pattern, antimicrobial ability and immunomodulation function

Antimicrobial peptides (AMPs) as the host's antimicrobial source are promising candidates for the development of novel antibacterial agents. Our study identified and analyzed the LEAP-2 gene from the cavefish - Onychostoma macrolepis (OmLEAP-2), and antimicrobial activity of OmLEAP-2 was assessed through both in vivo and in vitro experiments. The OmLEAP-2 encodes 92 amino acids with a hydrophobic surface (LAMMPWY) and two disulfide bonds. Following A. hydrophila infection, OmLEAP-2 expression was up-regulated in the liver, spleen and intestine in Onychostoma macrolepis. Recombinant OmLEAP-2 protein exhibited dose-dependent antimicrobial activity against both Gram-negative and Gram-positive bacteria, particularly A. hydrophila and A. veronii. OmLEAP-2 overexpression not only reduced bacterial load and increased survival rate, but also suppressed expression of TNF-α and IL-1β in A. hydrophila-infected Onychostoma macrolepis. Furthermore, OmLEAP-2 regulated iron metabolism by increasing liver iron levels, altering serum iron content, and modulating iron-related genes (fpn1 and hepcidin) expression. Collectively, these findings demonstrate that OmLEAP-2 exhibits broad-spectrum antibacterial activity against aquatic pathogens and shows potential as a therapeutic peptide for treating bacterial disease.

Ghrelin-LEAP2 interactions along the stomach-liver axis

Ghrelin produced in the stomach promotes food intake and GH secretion, and acts as an anabolic peptide during starvation. Ghrelin binds to the growth hormone secretagogue receptor, a G protein-coupled receptor (GPCR), whose high-resolution complex structures have been determined in the apo state and when bound to an antagonist. Anamorelin, a low-molecular-weight ghrelin agonist, has been launched in Japan for the treatment of cancer cachexia, and its therapeutic potential has attracted attention due to the various biological activities of ghrelin. In 2019, liver-expressed antimicrobial peptide (LEAP2), initially discovered as an antimicrobial peptide produced in the liver, was identified to be upregulated in the stomach of diet-induced obese mice after vertical sleeve gastrectomy. LEAP2 binds to the GHSR and antagonizes ghrelin's activities. The serum concentrations of human LEAP2 are positively correlated with body mass index, body fat accumulation, and fasting serum concentrations of glucose and triglyceride. Serum LEAP2 elevated and ghrelin reduced in obesity. Ghrelin and LEAP2 regulate body weight, food intake, and GH and blood glucose concentrations, and other physiological phenomena through their interactions with the same receptor, GHSR.

Identification and characterisation of LEAP2 from Chinese spiny frogs (Quasipaa spinosa) with antimicrobial and macrophage activation properties

BACKGROUND

The liver-expressed antimicrobial peptide 2 (LEAP2) family is an important group of antimicrobial peptides (AMPs) involved in vertebrate defence against bacterial infections. However, research on LEAP2 in amphibians is still in its infancy.

RESULTS

This study aimed to explore the role of LEAP2 in the Chinese spiny frog (Quasipaa spinosa). The cDNA of the LEAP2 gene (QsLEAP2) was cloned from a Chinese spiny frog. The QsLEAP2 protein comprises a signal peptide, a prodomain, and a mature peptide. Sequence analysis indicated that QsLEAP2 is a member of the amphibian LEAP2 cluster and closely related to the LEAP2 of the African clawed frog (Xenopus laevis). Expression of QsLEAP2 was detected in various tissues, with the liver exhibiting the highest expression. Following infection with Aeromonas hydrophila, QsLEAP2 expression was significantly upregulated in the spleen, lungs, kidneys, liver, and gut. The synthetic mature peptide QsLEAP2 exhibited selective antimicrobial activity against several bacterial strains in vitro. It disrupted bacterial membrane integrity and hydrolysed bacterial genomic DNA, exhibiting bactericidal effects on specific bacterial species. Furthermore, QsLEAP2 induced chemotaxis in RAW264.7 murine leukemic monocytes/macrophages, enhancing their phagocytic activity and respiratory bursts. Docking simulations revealed an interaction between QsLEAP2 and QsMOSPD2.

CONCLUSIONS

These findings provide new insights into the role of LEAP2 in the amphibian immune system.

Peptide with Dual Roles in Immune and Metabolic Regulation: Liver-Expressed Antimicrobial Peptide-2 (LEAP-2)

Liver-expressed antimicrobial peptide 2 (LEAP-2) was originally discovered as an antimicrobial peptide that plays a vital role in the host innate immune system of various vertebrates. Recent research discovered LEAP-2 as an endogenous antagonist and inverse agonist of the GHSR1a receptor. By acting as a competitive antagonist to ghrelin, LEAP-2 influences energy balance and metabolic processes via the ghrelin-GHSR1a signaling pathway. LEAP-2 alone or the LEAP-2/ghrelin molar ratio showed potential as therapeutic targets for obesity, diabetes, and metabolic disorders. This review explores the recent advances of LEAP-2 in immune modulation and energy regulation, highlighting its potential in treating the above diseases.

Host defense peptides in crocodilians - A comprehensive review

Amphibians and reptiles, like all animals, are prone to periodic infections. However, crocodilians stand out for their remarkable ability to remain generally healthy and infection-free despite frequent exposure to a wide variety of microorganisms in their habitats and often sustaining significant injuries. These animals have evolved highly active immune mechanisms that provide rapid and effective defense. This is evidenced by the superior hemolytic capacity of their plasma compared to that of other organisms. To date, several host defense peptides (HDPs) have been identified in crocodilians, including cathelicidins, beta-defensins, hepcidins, leucrocins, hemocidins, and omwaprins. These peptides exhibit potent and broad-spectrum antimicrobial, antibiofilm, antifungal, and anticancer activities. Due to the relatively low but diverse evolutionary rate of crocodilians, the HDPs found in this species offer valuable insights into proteins and mechanisms of action that are highly conserved across many animals related to immune defense. The potential applications of HDPs in modern medicine represent a promising strategy for developing new therapeutic agents. Their novelty and the vast variability with which peptide sequences can be designed and modified expand the field of application for HDPs almost infinitely. This review addresses the urgent need for innovative and more effective drugs to combat the rise of antimicrobialresistant infections and evaluates the potential of crocodilian HDPs. It presents recent advances in the identification of crocodilian HDPs, particularly antimicrobial peptides (AMPs), including previously underexplored topics such as the sequential and structural conformation of different peptide types in crocodilians and the use of bioinformatics tools to enhance native peptides.

Structure-activity relationships of the intramolecular disulphide bonds in LEAP2, an antimicrobial peptide from Acrossocheilus fasciatus

BACKGROUND

The liver-expressed antimicrobial peptide 2 (LEAP2) plays a pivotal role in the host's immune response against pathogenic microorganisms. Numerous such antimicrobial peptides have recently been shown to mitigate infection risk in fish, and studying those harboured by the economically important fish Acrossocheilus fasciatus is imperative for enhancing its immune responses against pathogenic microorganisms. In this study, we cloned and sequenced LEAP2 cDNA from A. fasciatus to examine its expression in immune tissues and investigate the structure-activity relationships of its intramolecular disulphide bonds.

RESULTS

The predicted amino acid sequence of A. fasciatus LEAP2 was found to include a signal peptide, pro-domain, and mature peptide. Sequence analysis indicated that A. fasciatus LEAP2 is a member of the fish LEAP2A cluster and is closely related to Cyprinus carpio LEAP2A. A. fasciatus LEAP2 transcripts were expressed in various tissues, with the head kidney exhibiting the highest mRNA levels. Upon exposure to Aeromonas hydrophila infection, LEAP2 expression was significantly upregulated in the liver, head kidney, and spleen. A mature peptide of A. fasciatus LEAP2, consisting of two disulphide bonds (Af-LEAP2-cys), and a linear form of the LEAP2 mature peptide (Af-LEAP2) were chemically synthesised. The circular dichroism spectroscopy result shows differences between the secondary structures of Af-LEAP2 and Af-LEAP2-cys, with a lower proportion of alpha helix and a higher proportion of random coil in Af-LEAP2. Af-LEAP2 exhibited potent antimicrobial activity against most tested bacteria, including Acinetobacter guillouiae, Pseudomonas aeruginosa, Staphylococcus saprophyticus, and Staphylococcus warneri. In contrast, Af-LEAP2-cys demonstrated weak or no antibacterial activity against the tested bacteria. Af-LEAP2 had a disruptive effect on bacterial cell membrane integrity, whereas Af-LEAP2-cys did not exhibit this effect. Additionally, neither Af-LEAP2 nor Af-LEAP2-cys displayed any observable ability to hydrolyse the genomic DNA of P. aeruginosa.

CONCLUSIONS

Our study provides clear evidence that linear LEAP2 exhibits better antibacterial activity than oxidised LEAP2, thereby confirming, for the first time, this phenomenon in fish.

Molecular characterization, antibacterial and immunoregulatory activities of liver-expressed antimicrobial peptide 2 in black rockfish, Sebastes schlegelii

LEAP2 (liver expression antimicrobial peptide 2), is an antimicrobial peptide widely found in vertebrates and mainly expressed in liver. LEAP2 plays a vital role in host innate immunity. In teleosts, a number of LEAP2 homologs have been reported, but their in vivo effects on host defense are still limited. In this study, a LEAP2 homolog (SsLEAP2) was identified from black rockfish, Sebastes schlegelii, and its structure, expression as well as biological functions were analyzed. The results showed that the open reading frame of SsLEAP2 is 300 bp, with a 5'- untranslated region (UTR) of 375 bp and a 3' - UTR of 238 bp. The deduced amino acid sequence of SsLEAP2 shares the highest overall identity (96.97%) with LEAP2 of Sebastes umbrosus. SsLEAP2 possesses conserved LEAP2 features, including a signal peptide sequence, a prodomain and a mature peptide, in which four well-conserved cysteines formed two intrachain disulphide domain. The expression of SsLEAP2 was highest in liver and could be induced by experimental infection with Listonella anguillarum, Edwardsiealla piscicida and Rock bream iridovirus C1 (RBIV-C1). Recombinant SsLEAP2 (rSsLEAP2) purified from Escherichia coli was able to bind with various Gram-positive and Gram-negative bacteria. Further analysis showed that rSsLEAP2 could enhance the respiratory burst activity, and induce the expression of immune genes including interleukin 1-β (IL-1β) and serum amyloid A (SAA) in macrophages; additionally, rSsLEAP2 could also promote the proliferation and chemotactic of peripheral blood lymphocytes (PBLs). In vivo experiments indicated that overexpression of SsLEAP2 could inhibit bacterial infection, and increase the expression level of immune genes including IL-1β, tumor necrosis factor ligand superfamily member 13B (TNF13B) and haptoglobin (HP); conversely, knock down of SsLEAP2 promoted bacterial infection and decreased the expression level of above genes. Taken together, these results suggest that SsLEAP2 is a novel LEAP2 homolog that possesses apparent antibacterial activity and immunoregulatory property, thus plays a critical role in host defense against pathogens invasion.

Identification of antibacterial activity of liver-expressed antimicrobial peptide 2 (LEAP2) from primitive vertebrate lamprey

Liver-expressed antimicrobial peptide 2 (LEAP2) is a member of the antimicrobial peptides family and plays a key role in the innate immune system of organisms. LEAP2 orthologs have been identified from a variety of fish species, however, its function in primitive vertebrates has not been clarified. In this study, we cloned and identified Lc-LEAP2 from the primitive jawless vertebrate lamprey (Lethenteron camtschaticum) which includes a 25 amino acids signal peptide and a mature peptide of 47 amino acids. Although sequence similarity was low compared to other species, the mature Lc-LEAP2 possesses four conserved cysteine residues, forming a core structure with two disulfide bonds between the cysteine residues in the relative 1-3 (Cys 58 and Cys 69) and 2-4 (Cys 64 and Cys 74) positions. Lc-LEAP2 was most abundantly expressed in the muscle, supraneural body and buccal gland of lamprey, and was significantly upregulated during LPS and Poly I:C stimulations. The mature peptide was synthesized and characterized for its antibacterial activity against different bacteria. Lc-LEAP2 possessed inhibition of a wide range of bacteria with a dose-dependence, disrupting the integrity of bacterial cell membranes and binding to bacterial genomic DNA, although its inhibitory function is weak compared to that of higher vertebrates. These data suggest that Lc-LEAP2 plays an important role in the innate immunity of lamprey and is of great value in improving resistance to pathogens. In addition, the antimicrobial mechanism of LEAP2 has been highly conserved since its emergence in primitive vertebrates.

Identification of antibacterial activity of LEAP2 from Antarctic icefish Chionodraco hamatus

Liver-expressed antimicrobial peptide 2 (LEAP2) is a small peptide, which is consisted of signal peptide, pro-peptide and the bioactive mature peptide. Mature LEAP2 is an antibacterial peptide with four highly conserved cysteines forming two intramolecular disulfide bonds. Chionodraco hamatus, an Antarctic notothenioid fish that lives in the coldest water, has white blood unlike most fish of the world. In this study, the LEAP2 coding sequence was cloned from C. hamatus, including a 29 amino acids signal peptide and mature peptide of 46 amino acids. High levels of LEAP2 mRNA were detected in the skin and liver. Mature peptide was obtained by chemical synthesis in vitro, displayed selective antimicrobial activities against Escherichia coli, Aeromonas hydrophila, Staphylococcus aureus and Streptococcus agalactiae. Liver-expressed antimicrobial peptide 2 showed bactericidal activity by destroying the cell membrane integrity and robustly combined with bacterial genomic DNA. In addition, overexpression of the Tol-LEAP2-EGFP in zebrafish larva showed stronger antimicrobial activity in C. hamatus than in zebrafish, accompanied by lower bacterial load and expression of pro-inflammatory factors. This is the first demonstration of the antimicrobial activity of LEAP2 from C. hamatus, which is of useful value in improving resistance to pathogens.

Host defence peptide LEAP2 contributes to antimicrobial activity in a mustache toad (Leptobrachium liui)

BACKGROUND

The liver-expressed antimicrobial peptide 2 (LEAP2) is essential in host immunity against harmful pathogens and is only known to act as an extracellular modulator to regulate embryonic development in amphibians. However, there is a dearth of information on the antimicrobial function of amphibian LEAP2. Hence, a LEAP2 homologue from Leptobrachium liui was identified, characterized, and chemically synthesized, and its antibacterial activities and mechanisms were determined.

RESULTS

In this study, LEAP2 gene (Ll-LEAP2) cDNA was cloned and sequenced from the Chong'an Moustache Toad (Leptobrachium liui). The predicted amino acid sequence of Ll-LEAP2 comprises a signal peptide, a mature peptide, and a prodomain. From sequence analysis, it was revealed that Ll-LEAP2 belongs to the cluster of amphibian LEAP2 and displays high similarity to the Tropical Clawed Frog (Xenopus tropicalis)'s LEAP2. Our study revealed that LEAP2 protein was found in different tissues, with the highest concentration in the kidney and liver of L. liui; and Ll-LEAP2 mRNA transcripts were expressed in various tissues with the kidney having the highest mRNA expression level. As a result of Aeromonas hydrophila infection, Ll-LEAP2 underwent a noticeable up-regulation in the skin while it was down-regulated in the intestines. The chemically synthesized Ll-LEAP2 mature peptide was selective in its antimicrobial activity against several in vitro bacteria including both gram-positive and negative bacteria. Additionally, Ll-LEAP2 can kill specific bacteria by disrupting bacterial membrane and hydrolyzing bacterial gDNA.

CONCLUSIONS

This study is the first report on the antibacterial activity and mechanism of amphibian LEAP2. With more to uncover, the immunomodulatory functions and wound-healing activities of Ll-LEAP2 holds great potential for future research.

Molecular cloning and analysis of the ghrelin/GHSR system in Xenopus tropicalis

Ghrelin is a gut-derived peptide with several physiological functions, including feeding, gastrointestinal motility, and hormonal secretion. Recently, a host defense peptide, liver-expressed antimicrobial peptide-2 (LEAP2), was reported as an endogenous antagonist of growth hormone secretagogue receptor (GHS-R). The physiological relevance of the molecular LEAP2-GHS-R interaction in mammals has been explored; however, studies on non-mammals are limited. Here, we report the identification and functional characterization of ghrelin and its related molecules in Western clawed frog (Xenopus tropicalis), a known model organism. We first identified cDNA encoding X. tropicalis ghrelin and GHS-R. RT-qPCR revealed that ghrelin mRNA expression was most abundant in the stomach. GHS-R mRNA was widely distributed in the brain and peripheral tissues, and a relatively strong signal was observed in the stomach and intestine. In addition, LEAP2 was mainly expressed in intestinal tissues at higher levels than in the liver. In functional analysis, X. tropicalis ghrelin and human ghrelin induced intracellular Ca²⁺ mobilization with EC₅₀ values in the low nanomolar range in CHO-K1 cells expressing X. tropicalis GHS-R. Furthermore, ghrelin-induced GHS-R activation was antagonized with IC₅₀ values in the nanomolar range by heterologous human LEAP2. We also validated the expression of ghrelin and feeding-related factors under fasting conditions. After 2 days of fasting, no changes in ghrelin mRNA levels were observed in the stomach, but GHS-R mRNA levels were significantly increased, associated with significant downregulation of nucb2. In addition, LEAP2 upregulation was observed in the duodenum. These results provide the first evidence that LEAP2 functions as an antagonist of GHS-R in the anuran amphibian X. tropicalis. It has also been suggested that the ghrelin/GHS-R/LEAP2 system may be involved in energy homeostasis in X. tropicalis.

From "Hunger Hormone" to "It's Complicated": Ghrelin Beyond Feeding Control

Discovered as a peptide involved in releasing growth hormone, ghrelin was initially characterized as the "hunger hormone." However, emerging research indicates that ghrelin appears to play an important part in relaying information regarding nutrient availability and value and adjusting physiological and motivational processes accordingly. These functions make ghrelin an interesting therapeutic candidate for metabolic and neuropsychiatric diseases involving disrupted nutrition that can further potentiate the rewarding effect of maladaptive behaviors.

Three of a Kind: Control of the Expression of Liver-Expressed Antimicrobial Peptide 2 (LEAP2) by the Endocannabinoidome and the Gut Microbiome

The endocannabinoidome (expanded endocannabinoid system, eCBome)-gut microbiome (mBIome) axis plays a fundamental role in the control of energy intake and processing. The liver-expressed antimicrobial peptide 2 (LEAP2) is a recently identified molecule acting as an antagonist of the ghrelin receptor and hence a potential effector of energy metabolism, also at the level of the gastrointestinal system. Here we investigated the role of the eCBome-gut mBIome axis in the control of the expression of LEAP2 in the liver and, particularly, the intestine. We confirm that the small intestine is a strong contributor to the circulating levels of LEAP2 in mice, and show that: (1) intestinal Leap2 expression is profoundly altered in the liver and small intestine of 13 week-old germ-free (GF) male mice, which also exhibit strong alterations in eCBome signaling; fecal microbiota transfer (FMT) from conventionally raised to GF mice completely restored normal Leap2 expression after 7 days from this procedure; in 13 week-old female GF mice no significant change was observed; (2) Leap2 expression in organoids prepared from the mouse duodenum is elevated by the endocannabinoid noladin ether, whereas in human Caco-2/15 epithelial intestinal cells it is elevated by PPARγ activation by rosiglitazone; (3) Leap2 expression is elevated in the ileum of mice with either high-fat diet—or genetic leptin signaling deficiency—(i.e., ob/ob and db/db mice) induced obesity. Based on these results, we propose that LEAP2 originating from the small intestine may represent a player in eCBome- and/or gut mBIome-mediated effects on food intake and energy metabolism.

Marine Transcriptomics Analysis for the Identification of New Antimicrobial Peptides

Antimicrobial peptides (AMPs) participate in the immune system to avoid infection, are present in all living organisms and can be used as drugs. Fish express numerous AMP families including defensins, cathelicidins, liver-expressed antimicrobial peptides (LEAPs), histone-derived peptides, and piscidins (a fish-specific AMP family). The present study demonstrates for the first time the occurrence of several AMPs in lionfish (Pterois volitans). Using the lionfish transcriptome, we identified four transcript sequences encoding cysteine-rich AMPs and two new transcripts encoding piscidin-like peptides. These AMPs are described for the first time in a species of the Scorpaenidae family. A functional approach on new pteroicidins was carried out to determine antimicrobial sequences and potential uses, with a view to using some of these AMPs for human health or in aquaculture.

Molecular characterization and antibacterial immunity functional analysis of liver-expressed antimicrobial peptide 2 (LEAP-2) gene in golden pompano (Trachinotus ovatus)

Liver-expressed antimicrobial peptide-2 (LEAP-2) is a member of the antimicrobial peptides family. Research has demonstrated that LEAP-2 contains a number of cations and plays a key role in the innate immune system of organism. In this study, we cloned and identified TroLEAP-2, from the golden pompano (Trachinotus ovatus), and analyzed its functions in vivo and in vitro. Results showed that TroLEAP-2 contains a 321 bp open reading frame (ORF) that encodes 106 putative amino acids with a molecular weight of 11.65 kDa. The mature TroLEAP-2 peptide possesses four conserved cysteine residues, which can form a core structure with two disulfide bonds between the cysteine residues in the relative 1-3 (Cys 77 and Cys 88) and 2-4 (Cys 83 and Cys 93) positions. It has a high amino acid sequence similarity (38.68%-83.02%) with the liver-expressed antimicrobial peptide -2 of other teleosts. Phylogenetic analysis showed that TroLEAP-2 clustered with the LEAP-2 of Paralichthys olivaceus and Miichthy milluy. TroLEAP-2 was most abundantly expressed in the liver, spleen, and kidney, and was significantly upregulated during Edwardsiella tarda and Streptococcus agalactiae infection. Purified recombinant TroLEAP-2 (rTroLEAP-2) could significantly inhibit the in vitro growth of E. tarda and S. agalactiae. Overexpression of TroLEAP-2 in vivo was shown to significantly reduce E. tarda and S. agalactiae colonization of tissues, whereas its knockdown resulted in an increase of bacteria in fish tissues. We also saw that TroLEAP-2 overexpression significantly improved macrophage activation in vivo. Moreover, TroLEAP-2 can induce the expression of nonspecific immune-related genes. These results showed that it might play a significant role in the innate immune system of golden pompano. In conclusion, our results indicate that TroLEAP-2 plays an important role in antibacterial immunity and provides a new avenue for protection against pathogenic infections in golden pompano.

Subfunctionalization and evolution of liver-expressed antimicrobial peptide 2 (LEAP2) isoform genes in Siberian sturgeon (Acipenser baerii), a primitive chondrostean fish species

Two liver-expressed antimicrobial peptide 2 (LEAP2) isoforms were characterized in a primitive chondrostean sturgeon species, Acipenser baerii (Acipenseriformes). A. baerii LEAP2 isoforms represented essentially common structures shared by their vertebrate orthologs at both genomic (i.e., tripartite organization) and peptide (two conserved disulfide bonds) levels. A. baerii LEAP2 isoforms (designed LEAP2AB and LEAP2C, respectively) phylogenetically occupy the most basal position in the actinopterygian lineage and represent an intermediate character between teleostean and tetrapodian LEAP2s in the sequence alignment. Molecular phylogenetic analysis including LEAP2s from extant primitive fish species indicated that the evolutionary origin of ancestral LEAP2 in vertebrate groups should date back to earlier than the actinopterygian-sarcopterygian split. Gene expression assays under both basal and stimulated conditions suggested that A. baerii LEAP2 isoforms have undergone substantial subfunctionalization in tissue distribution pattern, developmental/ontogenetic expression, and immune responses. LEAP2AB showed a predominant liver expression, while LEAP2C exhibited the highest level of expression in the intestine. LEAP2C was a more dominantly expressed isoform during embryonic development and prelarval ontogeny. The LEAP2AB isoform is more closely associated with innate immune response to microbial invasion, compared with LEAP2C, as evidenced by results from LPS, poly(I:C) and Aeromonas hydrophila challenges. Synthetic mature peptides of LEAP2AB displayed a more potent antimicrobial activity than did LEAP2C. Data from this study could be useful not only to provide deeper insights into the evolutionary mechanism of LEAP2 in the actinopterygian lineage but also to better understand the innate immunity of this commercially important chondrostean species.

Host defense peptide LEAP-2 contributes to monocyte/macrophage polarization in barbel steed (Hemibarbus labeo)

The liver-expressed antimicrobial peptide 2 (LEAP-2) plays a vital role in host immunity against pathogenic organisms. In the present study, cDNA of the LEAP-2 gene was cloned and sequenced from the barbel steed (Hemibarbus labeo). The predicted amino acid sequence of the barbel steed LEAP-2 comprises a signal peptide and a prodomain, which is followed by the mature peptide. Sequence analysis revealed that barbel steed LEAP-2 belongs to the fish LEAP-2A cluster and that it is closely related to zebrafish LEAP-2A. We found that barbel steed LEAP-2 transcripts were expressed in a wide range of tissues, with the highest mRNA levels detected in the liver. In response to lipopolysaccharide (LPS) treatment, LEAP-2 was significantly upregulated in the liver, head kidney, spleen, gill, and mid intestine. A chemically synthesized LEAP-2 mature peptide exhibited selective antimicrobial activity against several bacteria in vitro. Moreover, LEAP-2, alone or in combination with LPS or phorbol 12-myristate 13-acetate, strongly induced a pro-inflammatory reaction in barbel steed monocytes/macrophages (MO/MФ), involving the induction of iNOS activity, respiratory burst, and the pro-inflammatory cytokines IFN-γ, TNF-α, and IL-1β. Collectively, the results of this study indicate the importance of fish LEAP-2 in the M1-type polarization of MO/MΦ.

Identification of duck liver-expressed antimicrobial peptide 2 and characterization of its bactericidal activity

Objective

This study was conducted to identify duck liver-expressed antimicrobial peptide 2 (LEAP-2) and demonstrate its antimicrobial activity against various pathogens.

Methods

Tissue samples were collected from 6 to 8-week-old Pekin ducks (Anas platyrhynchos domesticus), total RNA was extracted, and cDNA was synthesized. To confirm the duck LEAP-2 transcript expression levels, quantitative real-time polymerase chain reaction was conducted. Two kinds of peptides (a linear peptide and a disulfide-type peptide) were synthesized to compare the antimicrobial activity. Then, antimicrobial activity assay and fluorescence microscopic analysis were conducted to demonstrate duck LEAP-2 bactericidal activity.

Results

The duck LEAP-2 peptide sequence showed high identity with those of other avian species (>85%), as well as more than 55% of identity with mammalian sequences. LEAP-2 mRNA was highly expressed in the liver with duodenum next, and then followed by lung, spleen, bursa and jejunum and was the lowest in the muscle. Both of LEAP-2 peptides efficiently killed bacteria, although the disulfide-type LEAP-2 showed more powerful bactericidal activity. Also, gram-positive bacteria was more susceptible to duck LEAP-2 than gram-negative bacteria. Using microscopy, we confirmed that LEAP-2 peptides could kill bacteria by disrupting the bacterial cell envelope.

Conclusion

Duck LEAP-2 showed its antimicrobial activity against both gram-positive and gram-negative bacteria. Disulfide bonds were important for the powerful killing effect by disrupting the bacterial cell envelope. Therefore, duck LEAP-2 can be used for effective antibiotics alternatives.

Comparative expression of host defense peptides in turkey poults

Host defense peptides (HDPs) are a large group of small, positively charged peptides that play an important role in innate immunity, particularly at early ages when other components of the immune system have not fully developed. There are 3 classes of avian HDPs: avian beta defensins (AvBDs), cathelicidins (Cath), and liver-expressed antimicrobial peptide 2 (LEAP-2). The objective was to compare expression of HDP mRNAs in male turkey poults at day of hatch (d 0), d 7, d 14, d 21 and d 28 from the thymus, spleen, bursa, duodenum, jejunum, and ileum. The expression of AvBD1, AvBD2, AvBD8, AvBD9, AvBD10, AvBD13, Cath2, Cath3, and LEAP-2 mRNA was measured using qPCR (n = 6 birds/tissue/age). Data were analyzed by one-way ANOVA and Tukey's test, and significance considered at P < 0.05. AvBDs and Caths exhibited greater expression in immune organs (thymus, spleen, and bursa) than intestinal tissues. In the thymus, expression of all AvBDs examined, except AvBD8, showed an increase from d 0 to d 21. In the spleen, AvBD1 and AvBD2 exhibited reduced expression from d 0 to d 7 and low expression thereafter. In the intestine, AVBD1, AVBD8, and AvBD13 increased expression from d 0 to d 28 in the duodenum, while AvBD10 showed the greatest expression at d 0 that declined to d 7 and stayed low thereafter in the duodenum, jejunum, and ileum. Cath2 and Cath3 demonstrated the highest expression in the spleen, which was greatest at d 0 then declined to d 7 through d 28. Conversely, LEAP-2 showed greater expression in the intestinal tissues than in the immune organs. LEAP-2 expression was upregulated from d 0 to d 7 and then remained elevated from d 7 through d 14 in the duodenum. In the jejunum, LEAP-2 increased from d 0 to d 21 and d 28. Understanding the differential expression of HDPs could reveal the innate immune status of turkey poults, and may subsequently allow improvement of their health through appropriate mitigation strategies.

Vitamin A deficiency suppresses fish immune function with differences in different intestinal segments: the role of transcriptional factorNF-κBandp38 mitogen-activated protein kinasesignalling pathways

The present study investigated the effects of dietary vitamin A on immune function in the proximal intestine (PI), mid intestine (MI) and distal intestine (DI) of young grass carp (Ctenopharyngodon idella). Fish were fed graded levels of dietary vitamin A for 10 weeks, and then a challenge test using an injection ofAeromonas hydrophilawas conducted for 14 d. The results showed that, compared with the optimum vitamin A level, vitamin A deficiency significantly decreased fish growth performance, increased enteritis morbidity, decreased intestinal innate humoral immune response and aggravated intestinal inflammation. However, liver-expressed antimicrobial peptide 2A/B mRNA in the DI andIL-6,IL-17D,IL-10, transforming growth factor (TGF)-β1andTGF-β2mRNA in the PI were not affected by vitamin A levels. Meanwhile, vitamin A deficiency disturbed inflammatory cytokines in the PI, MI and DI, which might be partly linked to p38 mitogen-activated protein kinase (p38MAPK) signalling andNF-κBcanonical signalling pathway (IκB kinaseβ(IKKβ),IKKγ, inhibitor ofκBα,NF-κB p65andc-Rel) rather thanNF-κBnon-canonical signalling pathway (NF-κB p52andIKKα). However, the signalling moleculesNF-κB p65andp38MAPKdid not participate in regulating cytokines in the PI. These results suggested that vitamin A deficiency decreased fish growth and impaired intestinal immune function, and that different immune responses in the PI, MI and DI were mediated partly byNF-κBcanonical signalling andp38MAPKsignalling pathways. On the basis of percentage of weight gain, to protect fish against enteritis morbidity and acid phosphatase activity, the optimum dietary vitamin A levels were estimated to be 0·664, 0·707 and 0·722 mg /kg, respectively.

The protection effect of LEAP-2 on the mudskipper (Boleophthalmus pectinirostris) against Edwardsiella tarda infection is associated with its immunomodulatory activity on monocytes/macrophages

Liver-expressed antimicrobial peptide 2 (LEAP-2) is a cationic peptide that plays an important role in the host's innate immune system. However, the mechanism by which LEAP-2 modulates/regulates the host defense against pathogens remains largely unknown. In this study, we identified a cDNA sequence encoding LEAP-2 homolog (BpLEAP-2) in the mudskipper, Boleophthalmus pectinirostris. Sequence analysis revealed that BpLEAP-2 belonged to the fish LEAP-2A cluster and that it was closely related to ayu LEAP-2. BpLEAP-2 mRNA was detected in a wide range of tissues, with the highest level of transcripts found in the liver. Upon infection with Edwardsiella tarda, BpLEAP-2 mRNA expression was significantly increased in the liver, kidney, spleen, and gill, but decreased in the intestine. Chemically synthesized BpLEAP-2 mature peptide did not exhibit antibacterial activity against E. tarda in vitro. Intraperitoneal injection of BpLEAP-2 (1.0 or 10.0 μg/g) resulted in significantly improved survival rate and reduced tissue bacterial load in E. tarda-infected mudskippers. In E. tarda-infected fish, BpLEAP-2 (0.1, 1.0, or 10.0 μg/g) eliminated E. tarda-induced tissue mRNA expression of BpTNF-α and BpIL-1β. In monocytes/macrophages (MO/MФ), BpLEAP-2 (1.0 or 10.0 μg/ml) induced chemotaxis, enhanced respiratory burst, and inhibited E. tarda-induced mRNA expression of BpTNF-α and BpIL-1β. At a concentration of 10.0 μg/ml, BpLEAP-2 also significantly enhanced the bacterial killing efficiency of MO/MФ. No significant effect was seen in the phagocytic activity of MO/MФ upon treatment with BpLEAP-2. Our study provides evidence, for the first time, that LEAP-2 exhibited immunomodulatory effects on immune cells, and protected the host from pathogenic infections independent of direct bacterial killing function.

Overexpression of Leap2 impairs Xenopus embryonic development and modulates FGF and activin signals

Besides its widely described function in the innate immune response, no other clear physiological function has been attributed so far to the Liver-Expressed-Antimicrobial-Peptide 2 (LEAP2). We used the Xenopus embryo model to investigate potentially new functions for this peptide. We identified the amphibian leap2 gene which is highly related to its mammalian orthologues at both structural and sequence levels. The gene is expressed in the embryo mostly in the endoderm-derived tissues. Accordingly it is induced in pluripotent animal cap cells by FGF, activin or a combination of vegT/β-catenin. Modulating leap2 expression level by gain-of-function strategy impaired normal embryonic development. When overexpressed in pluripotent embryonic cells derived from blastula animal cap explant, leap2 stimulated FGF while it reduced the activin response. Finally, we demonstrate that LEAP2 blocks FGF-induced migration of HUman Vascular Endothelial Cells (HUVEC). Altogether these findings suggest a model in which LEAP2 could act at the extracellular level as a modulator of FGF and activin signals, thus opening new avenues to explore it in relation with cellular processes such as cell differentiation and migration.

Antimicrobial activity of trout hepcidin

Hepcidin is an antimicrobial peptide and a hormone produced mostly the liver. It is a cysteine-rich peptide with a highly conserved β-sheet structure. Recently, we described the hepcidin expression in liver of rainbow trout and its inducibility by iron overloading and lipopolysaccharide (LPS). Thus, in this work, we focused in analyzing the importance of the peptide conformation associated to its oxidative state in the antimicrobial activity. This peptide showed a α-helix conformation in reduced state and the characteristic β-sheet conformation in the oxidized state. Antimicrobial activity assays showed that the oxidized peptide is more effective than the reduced peptide against Escherichia coli and the important salmon fish pathogen Piscirickettsia salmonis. In addition, confocal analysis of P. salmonis culture exposed to trout hepcidin coupled with rhodamine revealed the intracellular location of this peptide and Sytox permeation assay showed that membrane disruption is not the mechanism of its antimicrobial action. Moreover, a conserved ATCUN motif was detected in the N-terminus of this peptide. This sequence has been described as a small metal-binding site that has been implicated in DNA cleavage. In this work we proved that this peptide is able to induce DNA hydrolysis in the presence of ascorbate and CuCl2. When the same experiments were carried out using a variant with truncated N-terminus no DNA hydrolysis was observed. Our results suggest that correct folding of hepcidin is required for its antimicrobial activity and most likely the metal-binding site (ATCUN motif) present in its N-terminus is involved in the oxidative damage to macromolecules.

LEAP-2, LL-37 and RNase7 in tonsillar tissue: downregulated expression in seasonal allergic rhinitis

In the upper airway, the production of antimicrobial peptides (AMPs) protects against bacteria, viruses and fungi. Previous investigations have revealed downregulated expression of AMPs in different manifestations of allergic disease. In this study, we examined the expression of LL-37, Ribonuclease7 (RNase7) and Liver-expressed antimicrobial peptide 2 (LEAP-2) in tonsillar tissue and studied a possible relation to seasonal allergic rhinitis (SAR). Tonsils, obtained from patients with SAR and nonallergic controls, were examined for the occurrence of LL-37, RNase7 and LEAP-2 with real-time RT-PCR and immunohistochemistry. Tonsillar mononuclear cells were cultured in presence or absence of LEAP-2 or LL-37 and analyzed for cytokine levels using ELISA. mRNA and protein for LL-37, RNase 7 and LEAP-2 were found in all tonsils. Immunohistochemistry revealed prominent staining for LL-37 and RNase7 in the tonsillar epithelium, whereas a moderate staining was seen with LEAP-2. Real-time RT-PCR showed a downregulation of RNase7 and LEAP-2 in the allergic as compared to the nonallergic group. Mononuclear cells cultured in presence of LEAP-2 or LL-37 demonstrated reduced levels of IL-10. The present study demonstrates the presence and function of LEAP-2, LL-37 and RNase7 in tonsils. Moreover, a downregulation of LEAP-2 and RNase7 is seen in SAR patients, indicating that allergic individuals may be more susceptible to respiratory tract infections due to an impaired antimicrobial defense.

Antimicrobial peptides in reptiles

Reptiles are among the oldest known amniotes and are highly diverse in their morphology and ecological niches. These animals have an evolutionarily ancient innate-immune system that is of great interest to scientists trying to identify new and useful antimicrobial peptides. Significant work in the last decade in the fields of biochemistry, proteomics and genomics has begun to reveal the complexity of reptilian antimicrobial peptides. Here, the current knowledge about antimicrobial peptides in reptiles is reviewed, with specific examples in each of the four orders: Testudines (turtles and tortosises), Sphenodontia (tuataras), Squamata (snakes and lizards), and Crocodilia (crocodilans). Examples are presented of the major classes of antimicrobial peptides expressed by reptiles including defensins, cathelicidins, liver-expressed peptides (hepcidin and LEAP-2), lysozyme, crotamine, and others. Some of these peptides have been identified and tested for their antibacterial or antiviral activity; others are only predicted as possible genes from genomic sequencing. Bioinformatic analysis of the reptile genomes is presented, revealing many predicted candidate antimicrobial peptides genes across this diverse class. The study of how these ancient creatures use antimicrobial peptides within their innate immune systems may reveal new understandings of our mammalian innate immune system and may also provide new and powerful antimicrobial peptides as scaffolds for potential therapeutic development.

Molecular characterization and functional analysis of two distinct liver-expressed antimicrobial peptide 2 (LEAP-2) genes in large yellow croaker (Larimichthys crocea)

Liver-expressed antimicrobial peptide 2 (LEAP-2) plays a vital role in the host innate immune system. In the present study, two LEAP-2 genes (LcLEAP-2A and LcLEAP-2C) from large yellow croaker (Larimichthys crocea) were cloned, both of which consist of 3 exons and 2 introns. The LcLEAP-2A transcripts were expressed in a wide range of tissues, with the highest mRNA levels found in the liver and intestine, while LcLEAP-2C transcripts showed obvious lower mRNA levels in all tested tissues compared to LcLEAP-2A. Upon infection by Vibrio alginolyticus, LcLEAP-2A transcripts were significantly up-regulated in liver, trunk kidney, spleen, head kidney, and gill, but down-regulated in intestine. In addition, significant up-regulation of LcLEAP-2C transcripts were also detected in all tissues tested, including intestine. The LcLEAP-2A and LcLEAP-2C mature peptides were chemically synthesized and found to exhibit selective antimicrobial activity in vitro against various species of bacteria. LcLEAP-2C, but not LcLEAP-2A, had antimicrobial activity against V. alginolyticus. Moreover, LcLEAP-2C treatment at low concentrations was evaluated and found to improve survival rate in V. alginolyticus-infected large yellow croaker, resulting in a decrease in bacterial load and expression of inflammatory cytokines. These results suggest that LcLEAP-2 isoforms play an important role in innate immunity by killing bacteria and inhibiting early inflammatory response in large yellow croaker.

Avian host defense peptides

Host defense peptides (HDPs) are important effector molecules of the innate immune system of vertebrates. These antimicrobial peptides are also present in invertebrates, plants and fungi. HDPs display broad-spectrum antimicrobial activities and fulfill an important role in the first line of defense of many organisms. It is becoming increasingly clear that in the animal kingdom the functions of HDPs are not confined to direct antimicrobial actions. Research in mammals has indicated that HDPs have many immunomodulatory functions and are also involved in other physiological processes ranging from development to wound healing. During the past five years our knowledge about avian HDPs has increased considerably. This review addresses our current knowledge on the evolution, regulation and biological functions of HDPs of birds.

Immune activation in HIV/HCV-infected patients is associated with low-level expression of liver expressed antimicrobial peptide-2 (LEAP-2)

BACKGROUND

Immune activation is one of the main features of HIV/Hepatitis C virus (HCV) infections and has been linked to the disturbance of the gut-associated lymphoid tissue (GALT). In chronic HIV infection, loss of GALT integrity results in translocation of microbial products and chronic immune activation. We explored the relationship between bacterial translocation and specific colonic proteins, including liver expressed antimicrobial peptide (LEAP 2) which may play a role in modulating the bacterial translocation process.

METHODS

A total of 40 subjects (10 HIV/HCV, 10 HIV, 10 HCV-infected patients and 10 controls) were enrolled and underwent serum and colonic tissue sampling. The levels of immune activation were evaluated by measuring plasma sCD27, and the levels of selected proinflammatory, Th2 and regulatory cytokines in both the plasma and supernatant of CD3-stimulated intraepithelial lymphocytes. We also evaluated LEAP-2 expression in the colon biopsies using Affymetrix Human Gene 1.0 ST (HuGene) and fluorescent immunohistochemistry.

RESULTS

Increased levels of sCD27 were observed in HIV/HCV coinfected (p=0.03) and HIV monoinfected (p=0.04) patients compared with controls consistent with the presence of immune activation. The chip array identified LEAP-2 expression as a key marker associated with immune activation. LEAP-2 expression in HIV, HCV and HIV/HCV-infected patients was significantly lower compared with controls, and was significantly negatively correlated (p=0.03, r=-0.44) with sCD27.

CONCLUSIONS

Our data suggests that HCV and HIV infections are associated with decreased expression of LEAP-2 in colonic tissue. This may represent a key mechanism for enhanced microbial translocation and immune activation in HIV/HCV-infected patients.

Antimicrobial peptide trichokonin VI-induced alterations in the morphological and nanomechanical properties of Bacillus subtilis

Antimicrobial peptides are promising alternative antimicrobial agents compared to conventional antibiotics. Understanding the mode of action is important for their further application. We examined the interaction between trichokonin VI, a peptaibol isolated from Trichoderma pseudokoningii, and Bacillus subtilis, a representative Gram-positive bacterium. Trichokonin VI was effective against B. subtilis with a minimal inhibitory concentration of 25 µM. Trichokonin VI exhibited a concentration- and time-dependent effect against B. subtilis, which was studied using atomic force microscopy. The cell wall of B. subtilis collapsed and the roughness increased upon treatment with trichokonin VI. Nanoindentation experiments revealed a progressive decrease in the stiffness of the cells. Furthermore, the membrane permeabilization effect of trichokonin VI on B. subtilis was monitored, and the results suggest that the leakage of intracellular materials is a possible mechanism of action for trichokonin VI, which led to alterations in the morphological and nanomechanical properties of B. subtilis.

Importance of the disulfide bridges in the antibacterial activity of human hepcidin

Hepcidin was first identified as an antimicrobial peptide present in human serum and urine. It was later demonstrated that hepcidin is the long sought hormone that regulates iron homeostasis in mammals. The native peptide of 25 amino acids (Hepc25) contains four disulfide bridges that maintain a β-hairpin motif. The aim of the present study was to assess whether the intramolecular disulfide bridges are necessary for Hepc25 antimicrobial activity. We show that a synthetic peptide corresponding to human Hepc25, and which contains the four disulfide bridges, has an antibacterial activity against several strains of Gram-positive and Gram-negative bacteria. On the contrary, a synthetic peptide where all cysteines were replaced by alanines (Hepc25-Ala) had no detectable activity against the same strains of bacteria. In a further step, the mode of action of Hepc25 on Escherichia coli was studied. SYTOX Green uptake was used to assess bacterial membrane integrity. No permeabilization of the membrane was observed with Hepc25, indicating that this peptide does not kill bacteria by destroying their membranes. Gel retardation assay showed that the Hepc25 binds to DNA with high efficiency, and that this binding ability is dependent on the presence of the intramolecular disulfide bridges. Reduction of Hepc25 or replacement of the eight cysteines by alanine residues led to peptides that were no longer able to bind DNA in the in vitro assay. Altogether, these results demonstrate that Hepc25 should adopt a three-dimensional structure stabilized by the intramolecular disulfide bridges in order to have antibacterial activity.

Selectivity for and destruction of Salmonella typhimurium via a membrane damage mechanism of a cell-penetrating peptide ppTG20 analogue

P7, an analogue of the cell-penetrating peptide (CPP) ppTG20, was derived by replacing Phe and Trp with Arg based on the structure-activity relationships of CPPs and antimicrobial peptides (AMPs). P7 showed antimicrobial activity against Salmonella typhimurium at 4 μM and possessed broad antimicrobial activity greater than its parent peptide. P7 displayed good selectivity, with low haemolysis below its minimum inhibitory concentration range, but displayed cytotoxic activity against the HT29 and MDA-MB231 mammalian cell lines. Studies of calcein leakage from egg yolk L-α-phosphatidylcholine/egg yolk L-α-phosphatidyl-DL-glycerol (EYPC/EYPG) (bacterial membrane mimic) and EYPC/cholesterol (eukaryotic membrane mimic) vesicles also demonstrated that P7 exhibited high selectivity and caused pore formation in the bacterial membrane. Circular dichroism experiments suggested that the conformation of P7 underwent transitions from a random coil in sodium phosphate buffer to an α-helical conformation in bacterial model membranes. P7 induced influx of the membrane fluorescent probe 1-N-phenylnaphthylamine (NPN) and the nucleic acid fluorescent probe SYTOX(®) Green by increasing live S. typhimurium cell outer membrane and plasma membrane permeability, respectively. P7 also induced ion channel formation in the cell plasma membrane causing leakage of potassium ions. Flow cytometric analysis demonstrated that S. typhimurium cell membrane integrity was destroyed following incubation with P7. These results indicated that P7 exhibited good bacterial selectivity and exerted its antibacterial activity by a membrane damage mechanism. Furthermore, these results suggested that CPPs may represent a source of templates for AMP design.

The oligo-acyl lysyl antimicrobial peptide C₁₂K-2β₁₂ exhibits a dual mechanism of action and demonstrates strong in vivo efficacy against Helicobacter pylori

Helicobacter pylori has developed antimicrobial resistance to virtually all current antibiotics. Thus, there is a pressing need to develop new anti-H. pylori therapies. We recently described a novel oligo-acyl-lysyl (OAK) antimicrobial peptidomimetic, C(12)K-2β(12), that shows potent in vitro bactericidal activity against H. pylori. Herein, we define the mechanism of action and evaluate the in vivo efficacy of C(12)K-2β(12) against H. pylori after experimental infection of Mongolian gerbils. We demonstrate using a 1-N-phenylnaphthylamine (fluorescent probe) uptake assay and electron microscopy that C(12)K-2β(12) rapidly permeabilizes the bacterial membrane and creates pores that cause bacterial cell lysis. Furthermore, using nucleic acid binding assays, Western blots, and confocal microscopy, we show that C(12)K-2β(12) can cross the bacterial membranes into the cytoplasm and tightly bind to bacterial DNA, RNA, and proteins, a property that may result in inhibition of enzymatic activities and macromolecule synthesis. To define the in vivo efficacy of C(12)K-2β(12), H. pylori-infected gerbils were orogastrically treated with increasing doses and concentrations of C(12)K-2β(12) 1 day or 1 week postinfection. The efficacy of C(12)K-2β(12) was strongest in animals that received the largest number of doses at the highest concentration, indicating dose-dependent activity of the peptide (P < 0.001 by analysis of variance [ANOVA]) regardless of the timing of the treatment with C(12)K-2β(12). Overall, our results demonstrate a dual mode of action of C(12)K-2β(12) against the H. pylori membrane and cytoplasmic components. Moreover, and consistent with the previously reported in vitro efficacy, C(12)K-2β(12) shows significant in vivo efficacy against H. pylori when used as monotherapy. Therefore, OAK peptides may be a valuable resource for therapeutic treatment of H. pylori infection.

Antimicrobial activity of human hepcidin 20 and 25 against clinically relevant bacterial strains: effect of copper and acidic pH

Hepcidin 25 (hep-25) is a peptide primarily produced by human liver with a central role in iron homeostasis. Its isoform, hepcidin 20 (hep-20), has an unknown function and lacks the first five aminoacids of the amino-terminal portion. This sequence is crucial for iron regulation by hep-25 and contains a molecular motif able to bind metals. Aim of this study, was to evaluate the antibacterial properties of both peptides in vitro, against a wide range of bacterial clinical isolates and in different experimental conditions. Although both peptides were found to be bactericidal against a variety of clinical isolates with different antibiotic resistance profiles, hep-20 was active at lower concentrations than hep-25, in most of the cases. Killing kinetics, carried on in sodium-phosphate buffer at pH 7.4, demonstrated that bactericidal activity occurred not earlier than 30-90 min of incubation. Bactericidal activity of hep-25 was slightly enhanced in the presence of copper, while the same metal did not affect the activity of hep-20. Interestingly, bactericidal activity of both hepcidins was highly enhanced at acidic pH. Acidic pH (pH 5.0 and 6.6) not only reduced the microbicidal concentrations of hepcidins, but also shortened the killing times of both peptides, as compared to pH 7.4. Combining hep-20 and hep-25 at pH 5.0 a bactericidal effect could be obtained at very low concentrations of both peptides. These results render hepcidins interesting for the design of new drugs for the treatment of infections occurring in body districts with physiologic acidic pH.

Expression of chicken LEAP-2 in the reproductive organs and embryos and in response to Salmonella enterica infection

In recent years host antimicrobial peptides and proteins have been recognised as key mediators of the innate immune response in many vertebrate species, providing the first line of defense against potential pathogens. In chickens a number of cationic antimicrobial peptides have been recently identified. However, although these peptides have been studied extensively in the avian gastrointestinal tract, little is known about their function in the chicken reproductive organs and embryos. Chicken Liver Expressed Antimicrobial Peptide-2 (cLEAP-2) has been previously reported to function in protecting birds against microbial attack. The aim of this study was to investigate the expression of cLEAP-2 gene in the chicken reproductive organs, as well as in chicken embryos during embryonic development, and to determine whether cLEAP-2 expression in the chicken reproductive organs was constitutive or induced as a response to Salmonella enteritidis infection. RNA was extracted from ovary, oviduct, testis and epididymis of sexually mature healthy and Salmonella infected birds, as well as from chicken embryos until day ten of embryonic development. Expression analysis data revealed that cLEAP-2 was expressed in the chicken ovary, testis and epididymis as well as in embryos during early embryonic development. Quantitative real-time PCR analysis revealed that cLEAP-2 expression was constitutive in the chicken epididymis, but was significantly up regulated in the chicken gonads, following Salmonella infection. In addition, expression of cLEAP-2 during chicken embryogenesis appeared to be developmentally regulated. These data provide evidence to suggest a key role of cLEAP-2 in the protection of the chicken reproductive organs and the developing embryos from Salmonella colonization.