Molecular characterization of the liver-expressed antimicrobial peptide 2 (LEAP-2) in a teleost fish, Plecoglossus altivelis: Antimicrobial activity and molecular mechanism

Skin transcriptome of lenok trout (Brachymystax lenok) provides new insight on lectin genes and immune response mechanisms to Aeromonas salmonicida infection

Brachymystax lenok is an economically valuable cold-water fish species that has shown lower morbidity during pathogen outbreaks compared to other cold-water species. To elucidate the innate immune mechanisms in B. lenok in response to Aeromonas salmonicida infection, the transcriptome sequencing of the skin was performed. A total of 297,142 unigenes were generated, with 64.21 % (190,809) successfully annotated. Differential expression analysis identified 9238 differentially expressed genes (DEGs), with significant enrichment in immune-related pathways, including NOD-like receptor, C-type lectin receptor, and Toll-like receptor signalling pathways. These pathways may play crucial role in pathogen recognition, immune activation, inflammation, and the induction of adaptive immune responses in B. lenok. Further analysis revealed significant upregulation of pro-inflammatory cytokines, complement system components, and antimicrobial peptides such as hepcidin and cathelicidin, highlighting their pivotal roles in B. lenok's immune defense. Moreover, a notable finding was the dynamic expression of various lectin families, including C-type lectins, plectins, galectin-3, and β-galactoside-binding lectins, which are involved in pathogen recognition, immune modulation, and cell signalling. Lectins may also contribute to resistance mechanisms by affecting bacterial membrane permeability, disrupting vital metabolic processes, and enhancing synergy with antimicrobial peptides. In the pathological experiments, histological examination correlated the upregulation of inflammatory mediators and complement components with tissue damage, immune cell infiltration, and lesion development, further supporting the involvement of these genes in the immune response. These results will enrich the information in understanding the immune response in B. lenok, and provide basic data for the following proteomics and functional assays that can verify the protein-level activity of these immune-related genes and clarify their specific roles in host defense and resistance mechanisms. This comprehensive transcriptome analysis provides insights into the immune response mechanisms of B. lenok, with particular emphasis on the role of lectins in pathogen recognition and resistance. These findings offer a foundation for further research on immune mechanisms in fish and the development of therapeutic strategies to mitigate infections in aquaculture.

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.

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.

Oral administration of LEAP2 enhances immunity against Edwardsiella tarda through regulation of gut bacterial community and metabolite in mudskipper

The liver-expressed antimicrobial peptide 2 (LEAP2) is gaining recognition for its immune regulatory functions beyond direct antimicrobial activity. In this study, we investigated the role of mudskipper (Boleophthalmus pectinirostris) LEAP2 (BpLEAP2) in enhancing the survival, gut health, and immune resilience against Edwardsiella tarda infection. Pre-oral delivery of BpLEAP2 significantly improved survival rates and mitigated infection-induced damage to the gut, as evidenced by preserved villus length and goblet cell count. Analysis of gut microbial communities using 16S rRNA sequencing revealed that pre-oral delivery of BpLEAP2 increased microbial diversity, evenness, and the abundance of beneficial genera such as Pseudoalteromonas and Shewanella, while reducing pathogenic genera like Pseudorhodobacter. Metabolomic profiling showed that BpLEAP2 altered the gut metabolite composition, significantly increasing levels of bile acids and amino acids, which are known to support gut health and immune responses. Correlation analysis demonstrated strong positive associations between BpLEAP2-induced microbial shifts and increased metabolites involved in amino acid metabolism. These findings suggest that BpLEAP2 promotes intestinal homeostasis by modulating gut microbiota composition and enhancing beneficial metabolite production, ultimately improving gut barrier integrity and conferring resistance against E. tarda infection. This study highlights the potential application of BpLEAP2 in enhancing disease resilience in aquaculture species, offering a promising strategy for sustainable aquaculture practices.

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.

Antibacterial activity of recombinant liver-expressed antimicrobial peptide-2 derived from olive flounder, Paralichthys olivaceus

Liver-expressed antimicrobial peptide-2 (LEAP-2) is a cysteine-rich peptide that plays a crucial role in the innate immune system of fish. To investigate the molecular function of LEAP-2 from olive flounder, Paralichthys olivaceus, we cloned the gene encoding LEAP-2 using PCR and expressed it in Escherichia coli. Analysis of LEAP-2 expression revealed predominant transcripts in the liver and lower levels in the intestine of olive flounder, whereas their expression levels in the liver and head kidney increased, during the initial stage of infection with the aquapathogenic bacterium Edwardsiella piscicida. Recombinant LEAP-2 (rOfLEAP-2) purified from E. coli exhibited antimicrobial activity, as demonstrated by the ultrasensitive radial diffusion assay, against both Gram-positive (Bacillus subtilis, Streptococcus parauberis, and Lactococcus garvieae) and Gram-negative (Vibrio harveyi and E. coli) bacteria, with minimum inhibitory concentrations ranging from 25 to 100 μg/mL depending on the species tested. The antibacterial activity of rOfLEAP-2 was attributed to its ability to disrupt bacterial membranes, validated by the N-phenylnaphthalen-1-amine uptake assays and scanning electron microscope analysis against E. coli, V. harveyi, B. subtilis, and L. garvieae treated with rOfLEAP-2. Furthermore, a synergistic enhancement of antibacterial activity was observed when rOfLEAP-2 was combined with ampicillin or synthetic LEAP-1 peptide, suggesting a distinct mechanism of action from those of other antimicrobial agents. These findings provide evidence for the antibacterial efficacy of LEAP-2 from olive flounder, highlighting its potential therapeutic application against pathogenic bacteria.

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.

New insights into the antimicrobial mechanism of LEAP2 mutant zebrafish under Aeromonas hydrophila infection using transcriptome analysis

Liver-expressed antimicrobial peptide 2 (LEAP2) is a blood-derived antimicrobial peptide expressed predominantly in the liver. Although LEAP2 has been reported to exert antimicrobial effects in various fish species, its antimicrobial mechanism is not entirely understood. Zebrafish is an intensively developing animal model for studying bacterial diseases. In this study, we used zebrafish to identify the role of LEAP2 in bacterial infection. We found that knockout of LEAP2 in zebrafish led to a higher bacterial burden and mortality. To further investigate the effect of LEAP2 mutation on the immune system, we conducted a comparative transcriptome analysis of zebrafish with a mutant of LEAP2. Based on gene ontologies (GO) enrichment, LEAP2 mutant zebrafish revealed that, compared to wild-type zebrafish, robust responses to bacteria, inflammatory factors, and disrupt immune homeostasis and induct hyperinflammation. Furthermore, based on Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, six immune pathways were identified: Phagosome, NOD-like receptor, ferroptosis, Cytokine-cytokine receptor, Toll-like receptor, and FOXO signalling pathways. Interestingly, besides the liver, muscle, intestine, and eggs are also significantly enriched to the ferroptosis pathway, as revealed using quantitative polymerase chain reaction (qPCR), further confirmed that the effect of LEAP2 mutations on inflammatory factors and ferroptosis-related genes. Most importantly, this is the first report of the zebrafish LEAP2 mutant transcriptome obtained using high-throughput sequencing. Our study employed comparative transcriptome analysis to reveal the inflammatory response and ferroptosis-signalling pathway as a novel potential mechanism of LEAP2 antibacterial activity, laying the foundation for future studies of LEAP2 immune functions.

Quercetin alleviates DEHP exposure-induced pyroptosis and cytokine expression changes in grass carp L8824 cell line by inhibiting ROS/MAPK/NF-κB pathway

Bis(2-ethylhexyl) phthalate (DEHP) is not only a widely used plasticizer but also a common endocrine disruptor that frequently lingers in water, posing a threat to the health of aquatic organisms. Quercetin (Que) is a common flavonol found in the plant kingdom known for its antioxidant, anti-inflammatory, and immunomodulatory effects. However, it is still unclear whether DEHP can cause pyroptosis and affect the expression of cytokines of grass carp L8824 cells and whether Que has antagonistic effect in this process. In our study, grass carp L8824 cells were treated into four groups after 24 h, namely NC group, DEHP group (1000 μM DEHP), Que group (5 μM Que), and DEHP + Que group (1000 μM DEHP + 5 μM Que). Our results indicate a significant increase in the level of ROS in L8824 cells after exposure to DEHP. DEHP upregulated oxidative stress markers (H2O2 and MDA) and downregulated antioxidant markers (CAT, GSH, SOD, and T-AOC). DEHP also upregulated MAPK and NF-κB signal pathway-related proteins and mRNA expressions (p-p38, p-JNK, p-EPK, and p65). As for cell pyroptosis and its related pathways, DEHP upregulated pyroptosis-related protein and mRNA expressions (GSDMD, IL-1β, NLRP3, Caspase-1, LDH, pro-IL-18, IL-18, and ASC). Finally, DEHP can up-regulated cytokines (IL-6 and TNF-α) expression, down-regulated cytokines (IL-2 and IFN-γ) expression, and antimicrobial peptides (β-defensin, LEAP2, and HEPC). The co-treatment of L8824 cells with DEHP and Que inhibited the activation of the ROS/MAPK/NF-κB axis, alleviated pyroptosis, and restored expression of immune-related indicators. Finally, NAC was applied to reverse intervention of oxidative stress. In summary, Que inhibited DEHP-induced pyroptosis and the influence on cytokine and antimicrobial peptide expression in L8824 cells by regulating the ROS/MAPK/NF-κB pathway. Our results demonstrate the threat to fish health from DEHP exposure and confirmed the harm of DEHP to the aquatic ecological environment and the detoxification effect of Que to DEHP, which provides a theoretical basis for environmental toxicology.

Genome-Wide Identification of Trachinotus ovatus Antimicrobial Peptides and Their Immune Response against Two Pathogen Challenges

Golden pompano, Trachinotus ovatus, as a highly nutritious commercially valuable marine fish, has become one of the preferred species for many fish farmers due to its rapid growth, wide adaptability, and ease of feeding and management. However, with the expansion of aquaculture scale, bacterial and parasitic diseases have also become major threats to the golden pompano industry. This study, based on comparative genomics, shows the possibility of preferential evolution of freshwater fish over marine fish by analyzing the phylogenetic relationships and divergence times of 14 marine fish and freshwater fish. Furthermore, we identified antimicrobial peptide genes from 14 species at the genomic level and found that the number of putative antimicrobial peptides may be related to species evolution. Subsequently, we classified the 341 identified AMPs from golden pompano into 38 categories based on the classification provided by the APD3. Among them, TCP represented the highest proportion, accounting for 23.2% of the total, followed by scolopendin, lectin, chemokine, BPTI, and histone-derived peptides. At the same time, the distribution of AMPs in chromosomes varied with type, and covariance analysis showed the frequency of its repeat events. Enrichment analysis and PPI indicated that AMP was mainly concentrated in pathways associated with disease immunity. In addition, our transcriptomic data measured the expression of putative AMPs of golden pompano in 12 normal tissues, as well as in the liver, spleen, and kidney infected with Streptococcus agalactiae and skin infected with Cryptocaryon irritans. As the infection with S. agalactiae and C. irritans progressed, we observed tissue specificity in the number and types of responsive AMPs. Positive selection of AMP genes may participate in the immune response through the MAPK signaling pathway. The genome-wide identification of antimicrobial peptides in the golden pompano provided a complete database of potential AMPs that can contribute to further understanding the immune mechanisms in pathogens. AMPs were expected to replace traditional antibiotics and be developed into targeted drugs against specific bacterial and parasitic pathogens for more precise and effective treatment to improve aquaculture production.

Alteration of synergistic immune response in gut-liver axis of white crucian carp (Carassius cuvieri) after gut infection with Aeromonas hydrophila

Aeromonas hydrophila can pose a great threat to the survival of farmed fish. In current study, we investigated the pathological characteristics and immune response in gut-liver axis of white crucian carp (WCC) upon gut infection. WCC anally intubated with A. hydrophila exerted a tissue deformation in damaged midgut with elevated levels of goblet cells along with a significant decrease in tight junction proteins and villi length-to-width ratios. In addition, immune-related gene expressions and antioxidant properties increased dramatically in gut-liver axis of WCC following gut infection with A. hydrophila. These results highlighted the immune modulation and redox alteration in gut-liver axis of WCC in response to gut infection.

Molecular characterization and antimicrobial activity of NK-lysin in black scraper (Thamnaconus modestus)

NK-lysin (NKL) is a positively charged antimicrobial peptide with broad-spectrum bactericidal activities. In this study, the cDNA sequence of NKL (TmNKL) from black scraper (Thamnaconus modestus) was cloned, which encodes a predicted polypeptide of 150 amino acids that contains a surfactant protein B domain with three disulfide bonds. Phylogenetically, TmNKL was most closely related to its teleost counterpart from tiger puffer (Takifugu rubripes). Expression analysis demonstrated that TmNKL transcripts were constitutively expressed in all tested tissues, with the highest expression levels in the gills. Its expression was significantly upregulated in the gills, head kidney, and spleen after infection with Vibrio parahaemolyticus. A linear peptide (TmNKLP40L) and a disulfide-type peptide (TmNKLP40O) were further synthesized and results showed that disulfide bonds are not essential for bactericidal activities of TmNKL, and that both forms of TmNKL exhibited potent bactericidal activities against 4 gram- negative bacteria, including V. parahaemolyticus, V. alginolyticus, Edwardsiella tarda, and V. harveyi. Observed antimicrobial activities are likely due to the effects of TmNKLP40L and TmNKLP40O treatment on disrupting the integrity of both inner and outer membrane of V. parahaemolyticus, resulting in hydrolysis of bacterial genomic DNA. Damaged cell membranes and leakage of intracellular contents were further confirmed using scanning and transmission microscopy. Moreover, administration of 1.0 μg/g TmNKLP40L or TmNKLP40O significantly decreased bacterial load in tissues and thus, pronouncedly enhanced the survival of V. parahaemolyticus-infected fish. Overall, our results demonstrated that TmNKL is a potent innate effector and provides protective effects against bacterial infection.

Tannin alleviates glyphosate exposure-induced apoptosis, necrosis and immune dysfunction in hepatic L8824 cell line by inhibiting ROS/PTEN/PI3K/AKT pathway

Glyphosate can cause tissue damage such as liver and kidney in mammals. Tannin has anti-inflammatory, antibacterial and anti-inflammatory properties. However, the effect of glyphosate on the growth of L8824 cell line and the effect of tannin on antagonism of glyphosate through the ROS/PTEN/PI3K/AKT axis are unclear. In this study, L8824 cells were treated with glyphosate (50 μg/mL) and/or tannin (4.5 μM) for 24 h to establish a model. The results showed that glyphosate exposure increased ROS and MDA levels, decreased CAT and SOD activities. PTEN was activated and the PI3K/AKT signaling pathway was inhibited. The P53/Bcl-2/Bax/CytC/Caspase3 and RIPK1/RIPK3/MLKL pathways were also activated. In addition, the cytokines and antimicrobial peptides LEAP-2, TNF-α and IL-1β were increased while β-defensin, Hepcidin, IL-2 and IFN-γ were decreased. The use of tannin reduced the adverse effects of glyphosate exposure on L8824 cells significantly. In conclusion, tannin can trigger oxidative stress via PTEN/PI3K/AKT pathway to cause apoptosis, necroptosis and immune dysfunction of L8824 cells.

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.

Comparative study on antibacterial characteristics of the multiple liver expressed antimicrobial peptides (LEAPs) in teleost fish

Antimicrobial peptides are important components of the host innate immune system, forming the first line of defense against infectious microorganisms. Among them, liver-expressed antimicrobial peptides (LEAPs) are a family of antimicrobial peptides that widely exist in vertebrates. LEAPs include two types, named LEAP-1 and LEAP-2, and many teleost fish have two or more LEAP-2s. In this study, LEAP-2C from rainbow trout and grass carp were discovered, both of which are composed of 3 exons and 2 introns. The antibacterial functions of the multiple LEAPs were systematically compared in rainbow trout and grass carp. The gene expression pattern revealed that rainbow trout and grass carp LEAP-1, LEAP-2A, LEAP-2B and/or LEAP-2C were differentially expressed in various tissues/organs, mainly in liver. After bacterial infection, the expression levels of LEAP-1, LEAP-2A, LEAP-2B and/or LEAP-2C in the liver and gut of rainbow trout and grass carp increased to varying degrees. Moreover, the antibacterial assay and bacterial membrane permeability assay showed that rainbow trout and grass carp LEAP-1, LEAP-2A, LEAP-2B and LEAP-2C all have antibacterial activities against a variety of Gram-positive and Gram-negative bacteria with varying levels through membrane rupture. Furthermore, cell transfection assay showed that only rainbow trout LEAP-1, but not LEAP-2, can lead to the internalization of ferroportin, the only iron exporter on cell surface, indicating that only LEAP-1 possess iron metabolism regulation activity in teleost fish. Taken together, this study systematically compared the antibacterial function of LEAPs in teleost fish and the results suggest that multiple LEAPs can enhance the immunity of teleost fish through different expression patterns and different antibacterial activities to various bacteria.

Brevinin-2PN, an antimicrobial peptide identified from dark-spotted frog (Pelophylax nigromaculatus), exhibits wound-healing activity

Brevinins exhibit a wide range of structural features and strong biological activities. Brevinin-2, derived from several amphibians, has shown antimicrobial activities. However, little is known about the wound-healing activity of brevinin-2. In this study, brevinin-2 cDNA was identified from the skin transcriptome of the dark-spotted frog (Pelophylax nigromaculatus) and it comprises a signal peptide, a propeptide, and a mature peptide. Sequence alignment with brevinin-2 derived from other amphibians showed variability of the mature peptide, and the presence of a C-terminal cyclic heptapeptide domain (Cys-Lys-Xaa4-Cys) in the mature peptide. Dark-spotted frog brevinin-2 belonged to the brevinin-2 cluster and was closely related to brevinin-2HB1 from Pelophylax hubeiensis. Synthetic dark-spotted frog brevinin-2 mature peptide (brevinin-2PN) exhibited antibacterial activity against several pathogens by destroying cell membrane integrity and hydrolysis of genomic DNA. Brevinin-2PN exhibited significant wound-healing activity by accelerating the healing of human skin fibroblast cell scratches, influencing cell migration, and stimulating gene expression of growth factors.

Role of the ghrelin system in alcohol use disorder and alcohol-associated liver disease: A narrative review

Unhealthy alcohol consumption is a global health problem. Adverse individual, public health, and socioeconomic consequences are attributable to harmful alcohol use. Epidemiological studies have shown that alcohol use disorder (AUD) and alcohol-associated liver disease (ALD) are the top two pathologies among alcohol-related diseases. Consistent with the major role that the liver plays in alcohol metabolism, uncontrolled drinking may cause significant damage to the liver. This damage is initiated by excessive fat accumulation in the liver, which can further progress to advanced liver disease. The only effective therapeutic strategies currently available for ALD are alcohol abstinence or liver transplantation. Any molecule with dual-pronged effects at the central and peripheral organs controlling addictive behaviors and associated metabolic pathways are a potentially important therapeutic target for treating AUD and ALD. Ghrelin, a hormone primarily derived from the stomach, has such properties, and regulates both behavioral and metabolic functions. In this review, we highlight recent advances in understanding the peripheral and central functions of the ghrelin system and its role in AUD and ALD pathogenesis. We first discuss the correlation between blood ghrelin concentrations and alcohol use or abstinence. Next, we discuss the role of ghrelin in alcohol-seeking behaviors and finally its role in the development of fatty liver by metabolic regulations and organ crosstalk. We propose that a better understanding of the ghrelin system could open an innovative avenue for improved treatments for AUD and associated medical consequences, including ALD.

The antibacterial activity of a novel NK-lysin homolog and its molecular characterization and expression in the striped catfish, Pangasianodon hypophthalmus

Aeromonas hydrophila was a common bacterial pathogen in aquaculture resulting in considerable losses to the striped catfish aquaculture industry. As an emergent antimicrobial peptide (AMP), NK-lysin (NKL) had activity against various microorganisms. However, the antibacterial activity of NKL from striped catfish (Pangasianodon hypophthalmus) both in vitro and vivo remains unclear. In this study, the cDNA sequence of P. hypophthalmus NK-lysin gene (PhNK-lysin) was cloned and characterized. The amino acid sequence of PhNK-lysin contains a signal peptide sequence of 17 amino acid (aa) residues and a mature peptide composed of 130 aa. The saposin B domain of mature peptide comprised six conserved cysteines forming three putative disulfide bonds. Phylogenetic analysis revealed that the PhNK-lysin was most closely related to that of the channel catfish (Ictalurus punctatus) NK-lysin. The transcriptional levels of the PhNK-lysin were significantly upregulated in response to A. hydrophila infection in various tissues including heart, liver, spleen, head kidney, trunk kidney and gill. The synthetic PhNK-lysin-derived peptide consisting of 38aa showed antibacterial activity against Vibrio harveii, Aeromonas hydrophila and Escherichia coli. The MIC for V. harveii, A. hydrophila and E. coli were 15.625 μM, 250 μM and 31.25 μM respectively. Besides, the synthetic PhNK-lysin decreased the bacterial load of liver and trunk kidney in vivo as well as increased the survival rate of A. hydrophila infected striped catfish. Hence, these data suggest that PhNK-lysin had antimicrobial effect and protects the host from pathogenic infection.

A novel ferritin L (FerL) in hybrid crucian carp could participate in host defense against Aeromonas hydrophila infection and diminish inflammatory signals

FerL, a multifunctional iron-storage polypeptide, not only exhibited a regulatory role in iron metabolism, but also participated in the regulation of fish immunity. In this study, ORF sequence of WR-FerL was 522 bp, encoding 173 amino acid residues. Tissue-specific analysis revealed that the highest expression of WR-FerL was detected in spleen. A. hydrophila challenge and LPS stimulation could sharply enhance WR-FerL mRNA expression in tissues and fish cells, respectively. Purified WR-FerL fusion peptide exhibited in vitro binding activity to A. hydrophila and endotoxin, limited bacterial dissemination to tissues as well as attenuated A. hydrophila-induced production of pro-inflammatory cytokines. Moreover, WR-FerL overexpression could abrogate NF-κB and TNFα promoter activity in fish cells. These results indicated that WR-FerL could play an important role in host defense against A. hydrophila infection.

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.

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.

Molecular characterization of cathelicidin in tiger frog (Hoplobatrachus rugulosus): Antimicrobial activity and immunomodulatory activity

Cathelicidins are an important antimicrobial peptide family and are expressed in many different vertebrates. They play an important role in the innate immune system of the host. However, amphibian cathelicidins are poorly understood. In this study, the cDNA of the cathelicidin gene was obtained from the skin transcriptome of tiger frog (Hoplobatrachus rugulosus). The predicted amino acid sequence of tiger frog cathelicidin (HR-CATH) comprises a signal peptide, a cathelin domain, and a mature peptide. The HR-CATH amino acid sequence alignment with other frog cathelicidins showed that the functional mature peptide is highly variable in amphibians, whereas the cathelin domain is conserved. A phylogenetic tree analysis showed that HR-CATH is most closely related to cathelicidin-NV from Nanorana ventripunctata. HR-CATH was chemically synthesized and its in vitro activity was determined. It had high antibacterial activity against Vibrio parahaemolyticus, Staphylococcus aureus, and the pathogenic bacterium Aeromonas hydrophila. HR-CATH damaged the cell membrane integrity of A. hydrophila according to a lactate dehydrogenase release assay and was able to hydrolyze the genomic DNA from A. hydrophila in a dose-dependent manner. Furthermore, in RAW264.7 cells (mouse leukemic monocyte/macrophage cell line), HR-CATH induced chemotaxis and enhanced respiratory burst. Our study shows that amphibian cathelicidin has antimicrobial activity and an immunomodulatory effect on immune cells.

A novel NK-lysin in hybrid crucian carp can exhibit cytotoxic activity in fish cells and confer protection against Aeromonas hydrophila infection in comparison with Carassius cuvieri and Carassius auratus red var

NK-lysin, an effector of natural killer (NK) cells and cytotoxic T lymphocytes (CTLs), not only exhibits cytotoxic effect in fish cells, but also participates in the immune defense against pathogenic infection. In this study, ORF sequences of RCC-NK-lysin, WCC-NK-lysin and WR-NK-lysin were 369 bp. Tissue-specific analysis revealed that the highest expressions of RCC-NK-lysin and WCC-NK-lysin were observed in gill, while the peaked level of WR-NK-lysin mRNA was observed in spleen. A. hydrophila infection sharply increased RCC-NK-lysin, WCC-NK-lysin and WR-NK-lysin mRNA expression in liver, trunk kidney and spleen. In addition, elevated levels of NK-lysin mRNA were observed in cultured fin cell lines of red crucian carp (RCC), white crucian carp (WCC) and their hybrid offspring (WR) after Lipopolysaccharide (LPS) challenge. RCC-NK-lysin, WCC-NK-lysin and WR-NK-lysin exerted regulatory roles in inducing ROS generation, modulating mitochondrial membrane potential, decreasing fish cell viability and antagonizing survival signalings, respectively. RCC/WCC/WR-NK-lysin-overexpressing fish could up-regulate expressions of inflammatory cytokines and decrease bacterial loads in spleen. These results indicated that NK-lysin in hybrid fish contained close sequence similarity to those of its parents, possessing the capacities of cytotoxicity and immune defense against bacterial infection.

Effects of dietary silkrose of Antheraea yamamai on gene expression profiling and disease resistance to Edwardsiella tarda in Japanese medaka (Oryzias latipes)

We previously identified a novel acidic polysaccharide, silkrose-AY, from the Japanese oak silkmoth (Antheraea yamamai), which can activate an innate immune response in mouse macrophage cells. However, innate immune responses stimulated by silkrose-AY in teleosts remain unclear. Here, we show the influence of dietary silkrose-AY in medaka (Oryzias latipes), a teleost model, in response to Edwardsiella tarda infection. Dietary silkrose-AY significantly improved the survival of fish and decreased the number of bacteria in their kidneys after the fish were artificially infected with E. tarda by immersion. We also performed a microarray analysis of the intestine, which serves as a primary barrier against microbial infection, to understand the profiles of differentially expressed genes (DEGs) evoked by silkrose-AY. The dietary silkrose-AY group showed differential expression of 2930 genes when compared with the control group prior to E. tarda infection. Gene ontology and pathway analysis of the DEGs highlighted several putative genes involved in pathogen attachment/recognition, the complement and coagulation cascade, antimicrobial peptides/enzymes, opsonization/phagocytosis, and epithelial junctional modification. Our findings thus provide fundamental information to help understand the molecular mechanism of bacterial protection offered by insect-derived immunostimulatory polysaccharides in teleosts.

LEAP2 has antagonized the ghrelin receptor GHSR1a since its emergence in ancient fish

Recent studies have demonstrated that liver-expressed antimicrobial peptide 2 (LEAP2) antagonizes the ghrelin receptor GHSR1a in mammals. However, its antagonistic function in lower vertebrates has not yet been tested. LEAP2 orthologs have been identified from a variety of fish species; however, previous studies all focused on their antimicrobial activity. To test whether LEAP2 functions as a GHSR1a antagonist in the lowest vertebrates, we studied the antagonism of a fish LEAP2 from Latimeria chalumnae, an extant coelacanth that is one of the closest living fish relatives of tetrapods. Using binding assays, we demonstrated that the coelacanth LEAP2 and ghrelin bound to the coelacanth GHSR1a with IC₅₀ values in the nanomolar range. Using activation assays, we demonstrated that the coelacanth ghrelin activated the coelacanth GHSR1a with an EC₅₀ value in the nanomolar range, and this activation effect was efficiently antagonized by a nanomolar range of the coelacanth LEAP2. In addition, we also showed that the human LEAP2 and ghrelin were as effective as their coelacanth orthologs towards the coelacanth GHSR1a; however, the coelacanth peptides had moderately lower activity towards the human GHSR1a. Thus, LEAP2 serves as an endogenous antagonist of the ghrelin receptor GHSR1a in coelacanth and the ghrelin-LEAP2-GHSR1a system has evolved slowly since its emergence in ancient fish.

MOSPD2 is a receptor mediating the LEAP-2 effect on monocytes/macrophages in a teleost, Boleophthalmus pectinirostris

Liver-expressed antimicrobial peptide 2 (LEAP-2) is a cationic peptide that plays an important role in a host's innate immune system. We previously demonstrated that mudskipper ( Boleophthalmus pectinirostris) LEAP-2 (BpLEAP-2) induces chemotaxis and activation of monocytes/ macrophages (MO/MФ). However, the molecular mechanism by which BpLEAP-2 regulates MO/MΦ remains unclear. In this study, we used yeast two-hybrid cDNA library screening to identify mudskipper protein(s) that interacted with BpLEAP-2, and characterized a sequence encoding motile sperm domain-containing protein 2 (BpMOSPD2). The interaction between BpLEAP-2 and BpMOSPD2 was subsequently confirmed by co-immunoprecipitation (Co-IP). Sequence analyses revealed that the predicted BpMOSPD2 contained an N-terminal extracellular portion composed of a CRAL-TRIO domain and a motile sperm domain, a C-terminal transmembrane domain, and a short cytoplasmic tail. Phylogenetic tree analysis indicated that BpMOSPD2 grouped tightly with fish MOSPD2 homologs and was most closely related to that of the Nile tilapia ( Oreochromis niloticus). The recombinant BpMOSPD2 was produced by prokaryotic expression and the corresponding antibody was prepared for protein concentration determination. RNA interference was used to knockdown BpMOSPD2 expression in the mudskipper MO/MФ, and the knockdown efficiency was confirmed by quantitative real-time polymerase chain reaction (qRT-PCR) and western blotting. Knockdown of BpMOSPD2 significantly inhibited BpLEAP-2-induced chemotaxis of mudskipper MO/MФ and BpLEAP-2-induced bacterial killing activity. Furthermore, knockdown of BpMOSPD2 inhibited the effect of BpLEAP-2 on mRNA expression levels of BpIL-10, BpTNFα, BpIL-1β, and BpTGFβ in MO/MФ. In general, BpMOSPD2 directly interacted with BpLEAP-2, and mediated the effects of BpLEAP-2 on chemotaxis and activation of mudskipper MO/MФ. This is the first identification of MOSPD2 as a receptor for LEAP-2.

Anti-infective Effects of a Fish-Derived Antimicrobial Peptide Against Drug-Resistant Bacteria and Its Synergistic Effects With Antibiotic

Antimicrobial peptides (AMPs) play pivotal roles in protecting against microbial infection in fish. However, AMPs from topmouth culter (Erythroculter ilishaeformis) are rarely known. In our study, we isolated an AMP from the head kidney of topmouth culter, which belonged to liver-expressed antimicrobial peptide 2 (LEAP-2) family. Topmouth culter LEAP-2 showed inhibitory effects on aquatic bacterial growth, including antibiotic-resistant bacteria, with minimal inhibitory concentration values ranging from 18.75 to 150 μg/ml. It was lethal for Aeromonas hydrophila (resistant to ampicillin), and took less than 60 min to kill A. hydrophila at a concentration of 5 × MIC. Scanning electron microscope (SEM) and SYTOX Green uptake assay indicated that it impaired the integrity of bacterial membrane by eliciting pore formation, thereby increasing the permeabilization of bacterial membrane. In addition, it showed none inducible drug resistance to aquatic bacteria. Interestingly, it efficiently delayed ampicillin-induced drug resistance in Vibrio parahaemolyticus (sensitive to ampicillin) and sensitized ampicillin-resistant bacteria to ampicillin. The chequerboard assay indicated that topmouth culter LEAP-2 generated synergistic effects with ampicillin, indicating the combinational usage potential of topmouth culter LEAP-2 with antibiotics. As expected, topmouth culter LEAP-2 significantly alleviated ampicillin-resistant A. hydrophila infection in vivo, and enhanced the therapeutic efficacy of ampicillin against A. hydrophila in vivo. Our findings provide a fish innate immune system-derived peptide candidate for the substitute of antibiotics and highlight its potential for application in antibiotic-resistant bacterial infection in aquaculture industry.

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.

NKL-24: A novel antimicrobial peptide derived from zebrafish NK-lysin that inhibits bacterial growth and enhances resistance against Vibrio parahaemolyticus infection in Yesso scallop, Patinopecten yessoensis

The extensive use of antibiotics in aquaculture has resulted in the prevalence of antibiotic-resistant bacteria and, consequently, new antibacterial strategies or drugs with clear modes of action are urgently needed. Antimicrobial peptides (AMPs) are currently widely considered as alternatives to antibiotics in the treatment of infections in aquatic animals. In this study, we aimed to evaluate the effects of NKL-24, a truncated peptide derived from zebrafish NK-lysin, against Yesso scallop (Patinopecten yessoensis) pathogen, Vibrio parahaemolyticus. The results showed that NKL-24 had a potent antibacterial effect against V. parahaemolyticus via a membrane active cell-killing mechanism. The in vitro study showed that sub-lethal levels of NKL-24 obviously reduced bacterial swimming ability and downregulated the transcription of the selected genes associated with V. parahaemolyticus virulence. Studies on NKL-24 biosafety in hemocytes and in Yesso scallop have shown no adverse effects from this peptide. Bacteria challenge test results demonstrated that NKL-24 significantly decreased the mortality and inhibited bacterial growth in the scallop infected with V. parahaemolyticus, while further in vivo examination revealed that NKL-24 could enhance non-specific immune parameters. Moreover, NKL-24 was capable of modulating a series of V. parahaemolyticus-responsive genes in the scallop. These results suggest the protective action of NKL-24 against V. parahaemolyticus and the potential of this peptide as a promising candidate for aquaculture applications.

Characterization and functional analysis of liver-expressed antimicrobial peptide-2 (LEAP-2) from golden pompano Trachinotus ovatus (Linnaeus 1758)

The liver-expressed antimicrobial peptide-2 (LEAP-2) is an important component of the innate immune defense system and plays an important role in resisting the invasion of pathogenic microorganisms. In this study, LEAP-2 from golden pompano (Trachinotus ovatus) was characterized and its expression in response to Photobacterium damselae was investigated. The full-length LEAP-2 cDNA was 1758 bp, which comprised a 5'-UTR of 250 bp, an ORF of 321 bp, and a 3'-UTR of 1187 bp, encoding 106 amino acids. LEAP-2 consisted of a conserved saposin B domain and four conserved cysteines that formed two pairs of disulphide bonds. The genomic organization of LEAP-2 was also determined and shown to consisted of three introns and two exons. The predicted promoter region of ToLEAP-2 contained several putative transcription factor binding sites. Quantitative real-time (qRT-PCR) analysis indicated that LEAP-2 was ubiquitously expressed in all examined tissues, with higher mRNA levels observed in the muscle, liver, spleen, and kidney. After P. damselae stimulation, the expression level of LEAP-2 mRNA was significantly upregulated in various tissues of golden pompano. In addition, SDS-PAGE showed that the molecular mass of recombinant LEAP-2 expressed in pET-32a was approximately 23 kDa. The purified recombinant protein showed antibacterial activity against Gram-positive and Gram-negative bacteria. Luciferase reporters were constructed for five deletion fragments of different lengths from the promoter region (-1575 bp to +251 bp), and the results showed that L3 (-659 bp to +251 bp) presented the highest activity, and it was therefore defined as the core region of the LEAP-2 promoter. The seven predicted transcription factor binding sites were deleted by using PCR technology, and the results showed that the mutation of the USF transcription factor binding site caused the activity to significantly decrease. The results indicate that golden pompano LEAP-2 potentially exhibits antimicrobial effects in fish innate immunity.

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

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

The effects of quercetin on immunity, antioxidant indices, and disease resistance in zebrafish (Danio rerio)

The main purpose of this study was to evaluate the immunity, antioxidant indices, and disease resistance of quercetin in zebrafish (Danio rerio). A total of 630 fish were assigned to 21 tanks with 30 fish/tank, and they were exposed to 0, 0.01, 0.1, 1, 10, 100, and 1000 μg/L quercetin, respectively, for 56 days. Results indicated that the immune indices including acid phosphatase (ACP), myeloperoxidase (MPO), lysozyme activities, and Complement 3 (C3), C4, IgM contents were significantly higher in 1 μg/L quercetin group than these parameters in the control group (P < 0.05). TNF-α and IL-8 mRNA expressions significantly decreased as the levels of quercetin increased up to 1 μg/L and increased thereafter (P < 0.05). 1 and 10 μg/L quercetin groups showed significantly lower TNF-α and IL-8 mRNA levels than the quercetin-free group. Transforming growth factor-β and IL-10 mRNA levels showed an obviously opposite trend with TNF-α expression. The SOD, GPX, CAT, T-AOC activities, and SOD and GPX gene expression in the liver were enhanced with increasing quercetin up to 1 μg/L, and decreased thereafter. MDA contents were affected by quercetin, in which 1 and 10 μg/L quercetin had a significantly lower level than that of the control group (P < 0.05). Defensin and Leap-II mRNA expression in the liver were the highest for fish exposed to 1 μg/L quercetin. The fish that exposed to 1 μg/L quercetin also showed a significantly higher survival rate than these of fish exposed to 0, 0.01, and 1000 μg/L quercetin (P < 0.05). In conclusion, the optimal level of quercetin promotes immunostimulant properties, antioxidant indices, and disease resistance of zebrafish.

Antibacterial and immunoregulatory activity of a novel hepcidin homologue in diploid hybrid fish (Carassius auratus cuvieri ♀ × Carassius auratus red var ♂)

Hepcidin, a multifunctional hormone oligopeptide, not only exhibits a regulatory role in iron metabolism, but also participates in the regulation of teleostean immunity. In this study, ORF sequence of WR-hepcidin was 258 bp and encoded 85 amino acid residues. Tissue-specific analysis revealed that the highest expression of WR-hepcidin was observed in liver. Aeromonas hydrophila challenge can sharply increased WR-hepcidin mRNA expression in liver, trunk kidney and spleen. The purified WR-hepcidin fusion peptide can directly bind to A. hydrophila and Streptococcus agalactiae, reduce the relative bacterial activity, limit bacterial growth and attenuate their dissemination to tissues in vivo. In addition, the treatment of WR-hepcidin fusion protein can diminish the production of pro-inflammatory cytokines. These results indicated that WR-hepcidin can play a negative regulatory role in bacteria-stimulated pro-inflammatory cytokines production and MyD88-IRAK4 activation.

The host defense peptide β-defensin confers protection against Vibrio anguillarum in ayu, Plecoglossus altivelis

β-defensin is a cationic host defense peptide actively participating in host innate immune response against pathogens. In teleost fish, β-defensin exhibits a diversity in genotypes and functions. Herein, a β-defensin homolog (PaBD) was identified from ayu, Plecoglossus altivelis, showing multiple tissues' upregulation against Vibrio anguillarum challenge. In vivo experiments revealed that intraperitoneal injection of chemically synthesized mature PaBD (mPaBD) increased the survival rate of V. anguillarum-infected ayu, accompanied by reduced bacterial load and decreased tissue mRNA levels of tumor necrosis factor α (PaTNF-α) and interleukin 1β (PaIL-1β). However, in vitro, mPaBD showed weak bactericidal activity against V. anguillarum. Interestingly, mPaBD enhanced phagocytosis, intracellular bacterial killing, and respiratory burst of ayu monocytes/macrophages (MO/MΦ). Moreover, it inhibited mRNA levels of PaIL-1β and PaTNF-α in MO/MФ upon V. anguillarum infection. In conclusion, PaBD protects ayu against V. anguillarum challenge not only through its direct antibacterial ability, but also through its immunomodulation in MO/MΦ.

A novel LEAP-2 in diploid hybrid fish (Carassius auratus cuvieri ♀ × Carassius auratus red var. ♂) confers protection against bacteria-stimulated inflammatory response

LEAP-2, a multifunctional peptide, not only exhibits a regulatory role in pathogenic infection, but also participates in the regulation of teleostean immunity. In this study, ORF sequence of WR-LEAP-2 was 240 bp and encoded 79 amino acid residues. Tissue-specific analysis revealed that the highest expression of WR-LEAP-2 was observed in liver. Aeromonas hydrophila challenge can sharply increase WR-LEAP-2 mRNA expression in liver, kidney and spleen. The purified WR-LEAP-2 peptide can directly bind to A. hydrophila and S. agalactiae, reduce the relative bacterial activity and limit bacterial growth in vitro. In addition, the treatment of WR-LEAP-2 can restrict bacterial dissemination in vivo and reduce production of pro-inflammatory cytokines. These results indicated that WR-LEAP-2 can confer protection against A. hydrophila- or S. agalactiae-stimulated MyD88-dependent pro-inflammatory cytokines activation.

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.

Antimicrobial activity and mechanisms of multiple antimicrobial peptides isolated from rockfish Sebastiscus marmoratus

Pathogenic disease is a major factor affecting the aquaculture of the rockfish Sebastiscus marmoratus, an important commercial species inhabiting the nearshore waters of the Western Pacific Ocean. Antimicrobial peptides (AMPs), as critical components of innate immunity, have been considered as promising antibiotic substitutes. The aims of this study were 1) to identify major AMPs in the rockfish, 2) to assess their antimicrobial activity and 3) to evaluate their potential therapeutic application. Six AMPs were identified, Hepcidin 1, liver-expressed antimicrobial peptide 2 (LEAP-2), Piscidin, Moronecidin, NK-lysin and β-defensin through analysis of the liver transcriptome of S. marmoratus. The transcriptional expression profiles of these AMPs were investigated by real-time quantitative PCR (RT-qPCR). These AMPs showed tissue-specific distribution patterns, and S. marmoratus displays a time-, dose- and tissue-dependent expression of AMPs in response to lipopolysaccharide (LPS) challenge. While the synthetic peptides of LEAP-2 and Moronecidin exerted broad-spectrum antimicrobial activity against important aquatic pathogens in vitro by directly disrupting microbial membrane, and no cytotoxicity against murine hepatic cells was observed at the effective concentrations from 5 μM to 40 μM. The existence of multiple AMPs and their distinct tissue distribution patterns and inducible expression patterns suggests a sophisticated, highly redundant, and multilevel network of antimicrobial defensive mechanisms of S. marmoratus. Therefore, S. marmoratus-derived AMPs appear to be potential therapeutic applications against pathogen infections in aquaculture.

Molecular characterization of the NK-lysin in a teleost fish, Boleophthalmus pectinirostris: Antimicrobial activity and immunomodulatory activity on monocytes/macrophages

NK-lysin (NKL) is a cationic host defense peptide that plays an important role in host immune responses against various pathogens. However, the immunomodulatory activity of NKL in fishes is rarely investigated. In this study, we characterized a cDNA sequence encoding an NK-lysin homolog (BpNKL) from the fish, mudskipper (Boleophthalmus pectinirostris). Sequence analysis revealed that BpNKL is most closely related to tiger puffer (Takifugu rubripes) NKL. BpNKL transcript was detected in all the tested tissues, with the highest level in the gill, followed by the spleen and kidney. Upon Edwardsiella tarda infection, the mRNA expression of BpNKL in the mudskipper was significantly upregulated in the spleen, kidney, and gill. A shortened peptide derived from BpNKL, BpNKLP40, was then chemically synthesized and its biological functions were investigated. BpNKLP40 exhibited a direct antibacterial activity against some Gram-negative bacteria, including E. tarda, Vibrio parahaemolyticus, Vibrio alginolyticus, and Vibrio harveyi, and induced hydrolysis of E. tarda genomic DNA. Intraperitoneal injection of 1.0 μg/g BpNKLP40 significantly improved the survival of mudskipper following E. tarda infection and reduced the bacterial burden in tissues and blood. Moreover, 1.0 μg/ml BpNKLP40 treatment had an enhanced effect on the intracellular killing of E. tarda by monocytes/macrophages (MO/MФ) as well as on the mRNA expression of pro-inflammatory cytokines in MO/MФ. In conclusion, our study reveals that BpNKL plays a role against E. tarda infection in the mudskipper by not only directly killing bacteria but also through an immunomodulatory activity on MO/MФ.

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.

Mudskipper (Boleophthalmus pectinirostris) Hepcidin-1 and Hepcidin-2 Present Different Gene Expression Profile and Antibacterial Activity and Possess Distinct Protective Effect against Edwardsiella tarda Infection

Hepcidins are small cysteine-rich antimicrobial peptides that play an important role in fish immunity against pathogens. Most fish species have two or more hepcidin homologs that have distinct functions. This study investigated the immune functions of mudskipper (Boleophthalmus pectinirostris) hepcidin-1 (BpHep-1) and hepcidin-2 (BpHep-2) in vitro and in vivo. Upon infection with Edwardsiella tarda, the expression of BpHep-1 and BpHep-2 mRNA in immune tissues was significantly upregulated, but the expression profiles were different. Chemically synthesized BpHep-1 and BpHep-2 mature peptides exhibited selective antibacterial activity against various bacterial species, and BpHep-2 exhibited a stronger antibacterial activity and broader spectrum than BpHep-1. BpHep-1 and BpHep-2 both inhibited the growth of E. tarda in vitro, with the latter being more effective than the former. In addition, both peptides induced hydrolysis of purified bacterial genomic DNA (gDNA) or gDNA in live bacteria. In vivo, an intraperitoneal injection of 1.0 μg/g BpHep-2 significantly improved the survival rate of mudskippers against E. tarda infection compared with 0.1 μg/g BpHep-2 or 0.1 and 1.0 μg/g BpHep-1. Similarly, only BpHep-2 treatment effectively reduced the tissue bacterial load in E. tarda-infected mudskippers. Furthermore, treatment with 1.0 or 10.0 μg/ml BpHep-2 promoted the phagocytic and bactericidal activities of mudskipper monocytes/macrophages (MO/MФ). However, only the highest dose (10.0 μg/ml) of BpHep-1 enhanced phagocytosis, and BpHep-1 exerted no obvious effects on bactericidal activity. In conclusion, BpHep-2 is a stronger bactericide than BpHep-1 in mudskippers, and acts not only by directly killing bacteria but also through an immunomodulatory function on MO/MФ.

An in vitro and in silico study on the antioxidant and cell culture-based study on the chemoprotective activities of fish muscle protein hydrolysates obtained from European seabass and gilthead seabream

European seabass (Dicentrarchus labrax, Linnaeus, 1758) (L) and gilthead seabream (Sparus aurata, Linnaeus, 1758) (C) muscles were hydrolysated by Alcalase (L_alc, C_alc) and Chymotrypsin (L_ch, C_ch) then hydrolysates were examined and their peptide profiles obtained. A total of 765, 794, 132 and 232 peptides were identified in C_alc, L_alc, C_ch and L_ch, respectively. Although, L_ch and C_ch were expected to have more antioxidant capacity because of their peptide profiles, Alcalase hydrolysates observed in vitro, were slightly higher (TEAC assay for C_alc: 848.11 ± 60.78 μmol TE/g protein). Maximum inhibition of oxidative stress was determined for L_alc (12.8% ± 4.5%) in MDCK1 cell lines. Highest proliferative capacity observed for C_alc (147.0% ± 3.1%) at MTT assay in MDCK1 cell culture. L_ch showed the highest chemopreventive effect with a 40-60% decrease for human colon adenocarcinoma cell line HT-29. This research points out the importance of aquatic sources as raw materials for peptide researches.

Excavating differentially expressed antimicrobial peptides from transcriptome of Larimichthys crocea liver in response to Cryptocaryon irritans

Larimichthys crocea, the special marine economy fish, owns the largest annual yield for a single species in China. One of the most significant factors affecting large yellow croaker culture is the diseases, especially the threat of marine white spot disease which caused by a protozoan Cryptocaryon irritans. Antimicrobial peptides (AMPs) have been demonstrated to be active against bacterium, fungi and parasites, showing their potential usefulness in aquaculture as substitutes for antibiotics. Many researches have been carried out about the AMPs concentrating on the activity resist on C. irritans, and piscidin-like of L. crocea owning widely antibacterial spectrum and strong activity against C. irritans was screened in our team. In the paper, taking advantage of the large yellow croaker hepatic comparison transcriptome in response to C. irritans at 3d post infection, seven kinds of AMPs have been excavated from the differently expressed genes, including LEAP2 like, LEAP-2A, hepcidin, hepcidin-like, piscidin-5-like, piscidin-5-like type 4 and bactericidal permeability increasing protein (BPI). Hepcidin, hepcidin-like, piscidin-5-like, piscidin-5-like type4 and BPI were up-regulated to protect large yellow croaker from being damaged by C. irritans infection; while LEAP2 like and LEAP-2A were down-regulated, they might be as a negative-feedback regulation factor or some other regulatory mechanisms to adjust the immune response in the process of C. irritans infection. The differential expression changes were verified with quantitative real-time PCR (qRT-PCR) to illustrate the reliability of the sequenced data. Hearteningly, piscidin-5-like type 4 was a novel type which was high similar to other piscidin-5-like types. Interestingly, the infection may well cause alternative splicing of LEAP-2A mRNA, which was a surprised phenomenon and finding after C. irritans infection, but more further study was needed to be conducted. Therefore, the data showed that these AMPs were involved in the immune response to the C. irritans infection. In all, these results implied that the immune response of AMPs to C. irritans infection was a complex and sophisticated regulatory process.

Recent updates of marine antimicrobial peptides

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

High-Throughput Identification of Antimicrobial Peptides from Amphibious Mudskippers

Widespread existence of antimicrobial peptides (AMPs) has been reported in various animals with comprehensive biological activities, which is consistent with the important roles of AMPs as the first line of host defense system. However, no big-data-based analysis on AMPs from any fish species is available. In this study, we identified 507 AMP transcripts on the basis of our previously reported genomes and transcriptomes of two representative amphibious mudskippers, Boleophthalmus pectinirostris (BP) and Periophthalmus magnuspinnatus (PM). The former is predominantly aquatic with less time out of water, while the latter is primarily terrestrial with extended periods of time on land. Within these identified AMPs, 449 sequences are novel; 15 were reported in BP previously; 48 are identically overlapped between BP and PM; 94 were validated by mass spectrometry. Moreover, most AMPs presented differential tissue transcription patterns in the two mudskippers. Interestingly, we discovered two AMPs, hemoglobin β1 and amylin, with high inhibitions on Micrococcus luteus. In conclusion, our high-throughput screening strategy based on genomic and transcriptomic data opens an efficient pathway to discover new antimicrobial peptides for ongoing development of marine drugs.

Antimicrobial peptides (AMPs): The quintessential 'offense and defense' molecules are more than antimicrobials

Antimicrobial peptides (AMPs) are cationic amphiphilic molecules with α-helix or β-sheet linear motifs and linear or cyclic configurations. For their role in 'defense and offense', they are present in all living organisms. AMPs are named so, as they inhibit a wide array of microbes by membrane pore formation and subsequent perturbation of mitochondrial membrane ionic balance. However, their functional repertoire is expanding with validated roles in cytotoxicity, wound healing, angiogenesis, apoptosis, and chemotaxis [1]. A number of endogenous AMPs have been characterized in human body such as defensins, cathelicidins, histatins etc. They mediate critical functions, but when homeostasis is broken, they turn hostile and initiate inflammatory diseases. This review discusses the sources of therapeutic AMPs; auto-immunity risks of endogenous AMPs, and their dermatological applications; normally overlooked risks of the peptides; and scopes ahead. This holistic work is expected to be a valuable reference for further research in this field.

Molecular characterization and functional analysis of the hepcidin gene from roughskin sculpin (Trachidermus fasciatus)

Hepcidin is a kind of cysteine-rich antimicrobial peptide that plays a vital role in host innate immune activity and iron regulation. Here, we report the molecular characterization and functional analysis of a novel hamp1 hepcidin isoforms Tf-Hep from roughskin sculpin, Trachidermus fasciatus. A cDNA fragment of 988 bp with an ORF of 273 bp was obtained. The coding sequence encodes for a signal peptide of 24 amino acids coupled with a prodomain of 40 amino acids and a mature peptide of 26 amino acids. Tissue distribution analysis indicated that Tf-Hep was most abundant in the liver. It could be significantly induced post lipopolysaccharide (LPS) challenge and heavy metal exposure. The mature peptide was expressed as a 6.061 kDa fusion protein in Pichia pastoris GS115. The active purified recombinant protein (rTf-Hep) exhibited a wide spectrum of potent antimicrobial activity in vitro against 4 Gram-negative bacteria Escherichia coli, Vibrio Anguillarum, Klebsiella pneumoniae, and Pseudomonas aeruginosa and 4 Gram-positive bacteria Staphylococcus aureus, Bacillus subtilis, Bacillus thuringiensis, and Bacillus megaterium with minimum inhibitory concentrations (MICs) of 5-80 μg/ml (0.825-13.2 μM). It also displayed high affinity to polysaccharides on bacteria surface including LPS, lipoteichoic acid (LTA) and peptidoglycan (PGN). We further revealed that rTf-hep was capable of agglutinating 6 of the 8 bacteria. All these results suggest that rTf-hep may be both an antibacterial effector and a pattern recognition molecule in fish immune defense. The in vivo bacterial treatment results demonstrated that rTf-Hep could significantly improve the survival rate of fish infected with V. anguillarum. Taken together, these data indicate an important role for Tf-hep in the innate immunity of Trachidermus fasciatus and suggest its potential application in aquaculture for increasing fish resistance to disease.

Occurrence, removal, and risk assessment of antibiotics in 12 wastewater treatment plants from Dalian, China

In this study, the occurrence and removal efficiencies of 31 antibiotics, including 11 sulfonamides (SAs), five fluoroquinolones (FQs), four macrolides (MLs), four tetracyclines (TCs), three chloramphenicols (CAPs), and four other antibiotics (Others), were investigated in 12 municipal wastewater treatment plants (WWTPs) in Dalian, China. A total of 29 antibiotics were detected in wastewater samples with the concentration ranging from 63.6 to 5404.6 ng/L. FQs and SAs were the most abundant antibiotic classes in most wastewater samples, accounting for 42.2 and 23.9% of total antibiotic concentrations, respectively, followed by TCs (16.0%) and MLs (14.8%). Sulfamethoxazole, erythromycin, clarithromycin, azithromycin, ofloxacin, and norfloxacin were the most frequently detected antibiotics; of these, the concentration of ofloxacin was the highest in most of influent (average concentration = 609.8 ng/L) and effluent (average concentration = 253.4 ng/L) samples. The removal efficiencies varied among WWTPs in the range of -189.9% (clarithromycin) to 100% (enoxacin, doxycycline, etc), and more than 50% of antibiotics could not be efficiently removed with the removal efficiency less than 65%. An environmental risk assessment was also performed in the WWTP effluents by calculating the risk quotient (RQ), and high RQ values (>1) indicated erythromycin and clarithromycin might cause the ecological risk on organisms in surrounding water near discharge point of WWTPs in this area, which warrants further attention.