Lipopolysaccharide neutralization by a novel peptide derived from phosvitin

Enhancing the activity of β-lactamase inhibitory protein-II with cell-penetrating peptide against KPC-2-carrying Klebsiella pneumoniae

Carbapenem-resistant Enterobacterales (CRE) is considered a paramount threat due to its rapid spread and high mortality rate. Klebsiella pneumoniae carbapenemases (KPCs), specifically KPC-2, are prevalent enzymes responsible for carbapenem resistance in many countries. While combinations of antibiotics are commonly used, they must be tailored to match the remaining susceptibility of the infecting strains. Therefore, there is a need to develop the β-lactamase inhibitor to effectively address this issue. β-lactamase inhibitor protein (BLIP) and its variants, BLIP-I and BLIP-II, have demonstrated the ability to inhibit class A β-lactamases. In particular, BLIP-II shows strong binding to the KPC-2 carbapenemase, making it a potential candidate for inhibition. To improve the intracellular penetration of BLIP-II, a cell-penetrating peptide (CPP) was employed. In this study, a KRK-rich peptide was introduced at either the N-terminal or C-terminal region of tBLIP-II, excluding the signal sequence of the BLIP-II protein. tBLIP-II, tBLIP-II-CPP, and CPP-BLIP-II were successfully expressed, and the chimeric proteins retained inhibitory activity compared to tBLIP-II alone. It is apparent that homology modeling demonstrated neither the poly-histidine tag nor the CPP interfered with the essential interaction residues of tBLIP-II. Interestingly, BLIP-II-CPP exhibited the highest inhibitory activity, reducing the minimal inhibitory concentration (MIC) of meropenem by 8 folds. Moreover, the combination of tBLIP-CPP with meropenem significantly decreased the viable bacterial cell count compared to the combination of tBLIP-II with meropenem or meropenem alone. These findings suggest that tBLIP-CPP is a promising candidate for restoring carbapenem susceptibility against CRE and provides a valuable therapeutic option for infections caused by CRE.

Synergistic effect of two antimicrobial peptides, BP203 and MAP-0403 J-2 with conventional antibiotics against colistin-resistant Escherichia coli and Klebsiella pneumoniae clinical isolates

Drug-resistant Enterobacterales infections are a great health concern due to the lack of effective treatments. Consequently, finding novel antimicrobials or combining therapies becomes a crucial approach in addressing this problem. BP203 and MAP-0403 J-2, novel antimicrobial peptides, have exhibited effectiveness against Gram-negative bacteria. In this study, we assessed the in vitro antibacterial activity of BP203 and MAP-0403 J-2, along with their synergistic interaction with conventional antibiotics including colistin, rifampicin, chloramphenicol, ceftazidime, meropenem, and ciprofloxacin against colistin-resistant Escherichia coli and Klebsiella pneumoniae clinical isolates. The minimal inhibitory concentrations (MIC) of BP203 and MAP-0403 J-2 against tested E. coli isolates were 2-16 and 8-32 μg/mL, respectively. However, for the majority of K. pneumoniae isolates, the MIC of BP203 and MAP-0403 J-2 were >128 μg/mL. Notably, our results demonstrated a synergistic effect when combining BP203 with rifampicin, meropenem, or chloramphenicol, primarily observed in most K. pneumoniae isolates. In contrast, no synergism was evident between BP203 and colistin, chloramphenicol, ceftazidime, rifampicin, or ciprofloxacin when tested against all E. coli isolates. Furthermore, synergistic effects between MAP-0403 J-2 and rifampicin, ceftazidime or colistin were observed against the majority of E. coli isolates. Similarly, the combined effect of MAP-0403 J-2 with rifampicin or chloramphenicol was synergistic in the majority of K. pneumoniae isolates. Importantly, these peptides displayed the stability at high temperatures, across a wide range of pH values, in specific serum concentrations and under physiological salt conditions. Both peptides also showed no significant hemolysis and cytotoxicity against mammalian cells. Our findings suggested that BP203 and MAP-0403 J-2 are promising candidates against colistin-resistant E. coli. Meanwhile, the synergism of these peptides and certain antibiotics could be of great therapeutic value as antimicrobial drugs against infections caused by colistin-resistant E. coli and K. pneumoniae.

Yeast Expressed Hybrid Peptide CLP Abridged Pro-Inflammatory Cytokine Levels by Endotoxin Neutralization

The aim of this study was to apply a strategy to express a recombinant CLP peptide and explore its application as a product derived from natural compounds. The amphiphilic CLP peptide was hybridized from three parent peptides (CM4, LL37, and TP5) and was considered to have potent endotoxin-neutralizing activity with minimal cytotoxic and hemolytic activity. To achieve high secretion expression, an expression vector of pPICZαA-HSA-CLP was constructed by the golden gate cloning strategy before being transformed into Pichia pastoris and integrated into the genome. The recombinant CLP was purified through the Ni-NTA affinity chromatography and analyzed by SDS-PAGE and mass spectrometry. The Limulus amebocyte lysate (LAL) test exhibited that the hybrid peptide CLP inhibited lipopolysaccharides (LPS) in a dose-dependent manner and was significantly (p < 0.05) more efficient compared to the parent peptides. In addition, it essentially diminished (p < 0.05) the levels of nitric oxide and pro-inflammatory cytokines (including TNF-α, IL6, and IL-1β) in LPS-induced mouse RAW264.7 macrophages. As an attendant to the control and the parental peptide LL37, the number of LPS-induced apoptotic cells was diminished compared to the control parental peptide LL37 (p < 0.05) with the treatment of CLP. Consequently, we concluded that the hybrid peptide CLP might be used as a therapeutic agent.

Functionalized core-shell nanogel scavenger for immune modulation therapy in sepsis

Sepsis is a complex, life-threatening hyperinflammatory syndrome associated with organ failure and high mortality due to lack of effective treatment options. Here we report a core-shell hydrogel nanoparticle with the core functionalized with telodendrimer (TD) nanotrap (NT) to control hyperinflammation in sepsis. The combination of multi-valent charged and hydrophobic moieties in TD enables effective binding with biomolecules in NT. The higher crosslinking in the shell structure of nanogel excludes the abundant large serum proteins and allows for size-selectivity in scavenging the medium-sized septic molecules (10-30 kDa), e.g., lipopolysaccharides (LPS, a potent endotoxin in sepsis), thus reducing cytokine production. At the same time, the core-shell TD NT nanogel captures the over-flowing proinflammatory cytokines effectively both in vitro and in vivo from biological fluids to further control hyperinflammation. Intraperitoneal injection of core-shell TD NT nanogel effectively attenuates NF-κB activation and cytokine production in LPS-induced septic mouse models. These results indicate the potential applications of the injectable TD NT core-shell nanogel to attenuate local or systemic inflammation.

Identification of zebrafish PLEKHF2 presents in egg/embryos as an antibacterial protein

PLEKHF2 proteins are widespread in animals, but their functions and mechanisms remain poorly defined. Here we clearly demonstrate that PLEKHF2 is a newly identified present abundantly in the eggs/embryos of zebrafish. We also show that recombinant PLEKHF2 acts as a pattern recognition receptor capable of identifying the bacterial signature molecule PGN, LPS, and LTA, binding the bacteria, and functions as an antibacterial effector directly killing the bacteria. In brief, these results indicate that PLEKHF2 is an antibacterial protein, a novel role assigned to PLEKHF2 proteins.

Biotechnological Innovations and Therapeutic Application of Pediococcus and Lactic Acid Bacteria: The Next-Generation Microorganism

Lactic acid bacteria represent a worthwhile organism within the microbial consortium for the food sector, health, and biotechnological applications. They tend to offer high stability to environmental conditions, with an indicated increase in product yield, alongside their moderate antimicrobial activity. Lack of endotoxins and inclusion bodies, extracellular secretion, and surface display with other unique properties, are all winning attributes of these Gram-positive lactic acid bacteria, of which, Pediococcus is progressively becoming an attractive and promising host, as the next-generation probiotic comparable with other well-known model systems. Here, we presented the biotechnological developments in Pediococcal bacteriocin expression system, contemporary variegated models of Pediococcus and lactic acid bacteria strains as microbial cell factory, most recent applications as possible live delivery vector for use as therapeutics, as well as upsurging challenges and future perspective. With the radical introduction of artificial intelligence and neural network in Synthetic Biology, the microbial usage of lactic acid bacteria as an alternative eco-friendly strain, with safe use properties compared with the already known conventional strains is expected to see an increase in various food and biotechnological applications in years to come as it offers better hope of safety, accuracy, and higher efficiency.

Identification of ribosomal protein L30 as an uncharacterized antimicrobial protein

Several ribosomal proteins have been shown to adopt for an antimicrobial function as antimicrobial proteins (AMPs). However, information as such is rather limited and their mode of action remains ill-defined. Here we demonstrated that amphioxus RPL30, BjRPL30, was a previously uncharacterized AMP, which was not only capable of binding Gram-negative and Gram-positive bacteria via interaction with LPS, LTA and PGN but also capable of killing the bacteria. We also showed that the residues positioned at 2-46 formed the core region for the antimicrobial activity of BjRPL30. Notably, both the hydrophobic ratio and net charge as well as 3D structures of the residues corresponding to BjRPL30_2-27 and BjRPL30_23-46 from both eukaryotic and prokaryotic RPL30 proteins were closely similar to those of BjRPL30_2-27 and BjRPL30_23-46, suggesting the antibacterial activity of RPL30 was highly conserved. This was further corroborated by the fact that the synthesized counterparts human RPL_5-30 and RPL_26-49 also had antibacterial activity. We show that the recombinant protein BjRPL30 executes antimicrobial function in vitro by a kind of membranolytic action including interaction with bacterial membrane through LPS, LTA and PGN as well as induction of membrane depolarization. Finally, we found that neither BjRPL30 nor its truncated form BjRPL30_2-27 and BjRPL30_23-46 had hemolytic activity towards human red blood cells, making them promising lead molecules for the design of novel AMPs against bacteria. Altogether, these indicated that RPL30 is a member of AMP which has ancient origin and is highly conserve throughout evolution.

Potent intracellular antibacterial activity of a marine peptide-N6NH2 and its D-enantiomer against multidrug-resistant Aeromonas veronii

Aeromonas veronii can cause a variety of diseases such as sepsis in humans and animals. However, there has been no effective way to eradicate A. veronii. In this study, the intracellular antibacterial activities of the C-terminal aminated marine peptide N6 (N6NH₂) and its D-enantiomer (DN6NH₂) against A. veronii were investigated in macrophages and in mice, respectively. The result showed that DN6NH₂ with the minimum inhibitory concentration (MIC) of 1.62 μM is more resistant to cathepsin B than N6NH₂ (3.23 μM). The penetration percentages of the cells treated with 4-200 μg/mL fluorescein isothiocyanate (FITC)-DN6NH₂ were 52.5-99.6%, higher than those of FITC-N6NH₂ (27.0-99.1%). Both N6NH₂ and DN6NH₂ entered macrophages by macropinocytosis and an energy-dependent manner. DN6NH₂ reduced intracellular A. veronii by 34.57%, superior to N6NH₂ (19.52%). After treatment with 100 μg/mL DN6NH₂, the levels of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and IL-1β were reduced by 53.45%, 58.54%, and 44.62%, respectively, lower than those of N6NH₂ (15.65%, 12.88%, and 14.10%, respectively); DN6NH₂ increased the IL-10 level (42.94%), higher than N6NH₂ (7.67%). In the mice peritonitis model, 5 μmol/kg DN6NH₂ reduced intracellular A. veronii colonization by 73.22%, which was superior to N6NH₂ (32.45%) or ciprofloxacin (45.67%). This suggests that DN6NH₂ may be used as the candidate for treating intracellular multidrug-resistant (MDR) A. veronii. KEY POINTS: • DN6NH₂ improved intracellular antibacterial activity against MDR A. veronii. • DN6NH₂ entered macrophages by micropinocytosis and enhanced the internalization rates. • DN6NH₂ effectively protected the mice from infection with A. veronii.

An update on endotoxin neutralization strategies in Gram-negative bacterial infections

INTRODUCTION

Gram-negative bacterial infections represent still a severe problem of human health care, regarding the increase in multi-resistance against classical antibiotics and the lack of newly developed antimicrobials. For the fight against these germs, anti-infective agents must overcome and/or bind to the Gram-negative outer membrane consisting of a lipopolysaccharide (LPS, endotoxin) outer leaflet and an inner leaflet from phospholipids, with additional peripheral or integral membrane proteins (OMP's).

AREAS COVERED

The current article reviews data of existing therapeutic options and summarizes newer approaches for targeting and neutralizing endotoxins, ranging from in vitro over in vivo animal data to clinical applications by using databases such as Medline.

EXPERT OPINION

Conventional antibiotic treatment of the bacteria leads to their killing, but not necessary LPS neutralization, which may be a severe problem in particular for the systemic pathway. This is the reason why there is an increasing number of therapeutic approaches, which - besides combating whole bacteria - at the same time try to neutralize endotoxin within or outside the bacterial cells mainly responsible for the high inflammation induction in Gram-negative species.

Preserved antibacterial activity of ribosomal protein S15 during evolution

Conventional role of ribosomal proteins is ribosome assembly and protein translation, but some ribosomal proteins also show antimicrobial peptide (AMP) activity, though their mode of action remains ill-defined. Here we demonstrated for the first time that amphioxus RPS15, BjRPS15, was a previously uncharacterized AMP, which was not only capable of identifying Gram-negative and -positive bacteria via interaction with LPS and LTA but also capable of killing the bacteria. We also showed that both the sequence and 3D structure of RPS15 and its prokaryotic homologs were highly conserved, suggesting its antibacterial activity is universal across widely separated taxa. Actually this was supported by the facts that the residues positioned at 45-67 formed the core region for the antimicrobial activity of BjRPS15, and its prokaryotic counterparts, including Nitrospirae RPS19_33-55, Aquificae RPS19_33-55 and P. syringae RPS19_50-72, similarly displayed antibacterial activities. BjRPS15 functioned by both interaction with bacterial surface via LPS and LTA and membrane depolarization as well as induction of intracellular ROS. Moreover, we showed that RPS15 existed extracellularly in amphioxus, shrimp, zebrafish and mice, hinting it may play a critical role in systematic immunity in different animals. In addition, we found that neither BjRPS15 nor its truncated form BjRPS15_45-67 were toxic to mammalian cells, making them promising lead molecules for the design of novel AMPs against bacteria. Collectively, these indicate that RPS15 is a new member of AMP with ancient origin and high conservation throughout evolution.

A nanotrap improves survival in severe sepsis by attenuating hyperinflammation

Targeting single mediators has failed to reduce the mortality of sepsis. We developed a telodendrimer (TD) nanotrap (NT) to capture various biomolecules via multivalent, hybrid and synergistic interactions. Here, we report that the immobilization of TD-NTs in size-exclusive hydrogel resins simultaneously adsorbs septic molecules, e.g. lipopolysaccharides (LPS), cytokines and damage- or pathogen-associated molecular patterns (DAMPs/PAMPs) from blood with high efficiency (92-99%). Distinct surface charges displayed on the majority of pro-inflammatory cytokines (negative) and anti-inflammatory cytokines (positive) allow for the selective capture via TD NTs with different charge moieties. The efficacy of NT therapies in murine sepsis is both time-dependent and charge-dependent. The combination of the optimized NT therapy with a moderate antibiotic treatment results in a 100% survival in severe septic mice by controlling both infection and hyperinflammation, whereas survival are only 50-60% with the individual therapies. Cytokine analysis, inflammatory gene activation and tissue histopathology strongly support the survival benefits of treatments.

Anticancer and immunomodulatory activity of egg proteins and peptides: a review

Eggs are widely recognized as a highly nutritious food source that offer specific health benefits for humans. Eggs contain all of the proteins, lipids, vitamins, minerals, and growth factors necessary for embryonic development. In particular, egg white and yolk proteins are considered functional food substances because they possess biological activities such as antimicrobial, antioxidant, metal-chelating, antihypertensive, anticancer, and immunomodulatory activities. Peptides produced via processes such as enzymatic hydrolysis, fermentation by microorganisms, and some chemical and physical treatments of egg proteins have been shown to enhance the functional properties and solubility of these peptides. Peptide activity is strongly related to amino acid sequence, composition, and length. At present, cancer remains among the leading causes of mortality worldwide, and therefore research aimed at developing new treatments for cancer immunotherapy is of great interest. The present review focuses primarily on the anticancer and immunomodulatory activities of egg proteins and their peptides and provides some insight into their underlying mechanisms of action. A number of egg proteins and peptides have been reported to induce apoptosis in cancer cells, protect against DNA damage, decrease the invasion ability of cancer cells, and exhibit cytotoxic and antimutagenic activity in various cancer cell lines. Furthermore, egg proteins and peptides can stimulate or suppress pro- or anti-inflammatory cytokines, as well as affect the production of inflammatory mediators in a variety of cell lines. In addition, the composition of eggs and the processes of egg proteins and peptides production will be discussed.

Effects of yolkin on the immune response of mice and its plausible mechanism of action

Yolkin is a product of proteolytic degradation of vitellogenin, a protein contained in eggs' yolk, with already described procognitive properties. Here, we investigated effects of yolkin on the humoral and cellular immune response in mice, phenotype of cells from lymphoid organs and function of innate immunity cells. In vitro studies included effects of yolkin on mitogen-induced thymocyte proliferation, percentage of CD19 cells in bone marrow cells culture, expression of signaling molecules in Jurkat cells, interleukin 2 receptor (IL-2R) subunits in WEHI 231 cells and susceptibility of these cells to anti-Ig-induced cell death. The results showed that repeatable i.p. injections of yolkin stimulated the humoral immune response to sheep red blood cells (SRBC) irrespective of the time of the treatment. On the other hand, yolkin inhibited contact sensitivity to oxazolone. Treatment of mice with yolkin diminished the percentage of double positive cells and increasing the content of single positive CD4+ and CD8+ cells in the thymus. At the same time an increase of percentage of CD19 + B cells in the spleen and mesenteric lymph nodes was observed. In addition, the protein, given i.p., diminished ex vivo ability to synthesize nitric oxide by resident, peritoneal macrophages, stimulated with lipopolisaccharide (LPS). In vitro studies showed that yolkin increased CD19+ cell content in bone marrow cell population. The protein also enhanced proliferation of thymocytes to concanavalin A and stimulated expression of MAP kinases in Jurkat cells. In WEHI 231 B cell line yolkin caused a loss of IL-2R gamma chain expression, correlated with an increased resistance of these cells to proapoptotic action of anti-Ig antibodies. In conclusion, this is a first demonstration of immunotropic properties of yolkin in in vitro and in vivo tests. The results provide evidence for induction of maturation and stimulatory signals in immature T and B cells by the protein, suggesting its potential role in the development of an embryo's immune system.

Identification and functional characterization of amphioxus Miple, ancestral type of vertebrate midkine/pleiotrophin homologues

Midkine (MK) and pleiotrophin (PTN) are the only two members of heparin-binding growth factor family. MK/PTN homologues found from Drosophila to humans are shown to have antibacterial activities and their antibacterial domains are conserved during evolution. However, little is known about MK/PTN homologue in the basal chordate amphioxus, and overall, information regarding MK/PTN homologues is rather limited in invertebrates. In this study, we identified a single MK/PTN homologue in Branchiostoma japonicum, termed BjMiple, which has a novel domain structure of PTN-PTNr1-PTNr2, and represents the ancestral form of vertebrate MK/PTN family proteins. BjMiple was expressed mainly in the ovary in a tissue-dependent fashion, and its expression was remarkably up-regulated following challenge with bacteria or their signature molecules LPS and LTA, suggesting its involvement in antibacterial responses. Functional assays revealed that BjMiple had strong antimicrobial activity, capable of killing a panel of Gram-negative and Gram-positive bacteria via a membranolytic mechanism, including interaction with bacterial membrane via LPS and LTA, membrane depolarization and high intracellular levels of ROS. Importantly, strong antibacterial activity was localized in PTN_42-61 and PTNr1_42-66. Additionally, BjMiple and its derived peptides PTN_42-61 and PTNr1_42-66 were not cytotoxic to human RBCs and mammalian cells. Taken together, our study suggests that amphioxus Miple is the ancestral type of vertebrate MK/PTN family homologues, and can play important roles as innate peptide antibiotics, which renders it a promising template for the design of novel peptide antibiotics against multi-drug resistant bacteria.

Identification and bioactivity analysis of a newly identified defensin from the oyster Magallana gigas

The relatively conserved sequences of signal peptides and proregions that antimicrobial peptides (AMPs) contain have been successfully used to search for and identify novel AMPs from databases within the same lineages of fish and amphibians and across different animal classes. If such an approach is applicable to invertebrate species such as oyster has not yet been tested so far. In this study, we found a cDNA from the digestive gland of the oyster Magallana gigas, designated Mgdefdg, which contains two exons interspaced by one intron. Mgdefdg coded for a protein with features characteristic of defensins. The mature peptide had the cysteine-stabilized α-helix/β-sheet motif (CSαβ) and the consensus pattern C-X_5-6-C-X₃-C-X_4-6-C-X_3-4-C-X_7-8-C-X-C-X₂-C forming potential disulfide linkages C1-C5, C2-C6, C3-C7 and C4-C8 in the predicted tertiary structure. Functional assays revealed that recombinant mature MgDefdg (rmMgDefdg) was able to kill the Gram-negative bacterium Aeromonas hydrophila and the Gram-positive bacterium Staphylococcus aureus, and to induce bacterial membrane/cytoplasmic damage. ELISA showed that rmMgDefdg had high affinity to both A. hydrophila and S. aureus as well as the microbe-associated molecular pattern molecules LPS and LTA. Moreover, rmMgDefdg was capable of causing bacterial membrane permeabilization and depolarization, and intracellular ROS increase. Additionally, rmMgDefdg was not cytotoxic to human red blood cells and murine RAW264.7 cells. Taken together, our results indicate that MgDefdg is a previously uncharacterized defensin with membrane selectivity towards bacterial cells. It also shows that the use of conserved sequences of signal peptides of defensins can be an effective tool to identify potential defensins across different animal genera in invertebrates.

Augmentation of the antibacterial activities of Pt5-derived antimicrobial peptides (AMPs) by amino acid substitutions: Design of novel AMPs against MDR bacteria

The ever-growing concerns on multi-drug resistant (MDR) bacteria lead to urgent demands for novel antibiotics including antimicrobial peptides (AMPs). Pt5, a peptide consisting of the C-terminal 55 residues of zebrafish phosvitin, has been shown to function as an antibacterial agent. Here we used Pt5 as a template to design new AMPs by shortening the sequence and substituting with tryptophan (W) and lysine (K) at selected positions. Among the resultant Pt5-derived peptides, Pt5-1c showed the strongest antimicrobial activity against both Gram-negative and Gram-positive bacteria, including MDR bacteia, with the minimum inhibitory concentrations (MICs) ranging from 1.2 μM to 4.8 μM. Electron microscopic examination showed that Pt5-1c was able to kill the bacteria directly. ELISA revealed that Pt5-1c possessed high affinity to lipopolysaccharide (LPS), lipoteichoic acid (LTA) and peptidoglycan (PGN). Importantly, Pt5-1c was able to disrupt the bacterial membrane by a combined action of membrane depolarization and permeabilization, with little cytotoxicity to mammalian cells. Taken together, these findings suggest that Pt5-1c has considerable potential for future development as novel peptide antibiotics against MDR bacteria.

Recent Advances in Antibacterial and Antiendotoxic Peptides or Proteins from Marine Resources

Infectious diseases caused by Gram-negative bacteria and sepsis induced by lipopolysaccharide (LPS) pose a major threat to humans and animals and cause millions of deaths each year. Marine organisms are a valuable resource library of bioactive products with huge medicinal potential. Among them, antibacterial and antiendotoxic peptides or proteins, which are composed of metabolically tolerable residues, are present in many marine species, including marine vertebrates, invertebrates and microorganisms. A lot of studies have reported that these marine peptides and proteins or their derivatives exhibit potent antibacterial activity and antiendotoxic activity in vitro and in vivo. However, their categories, heterologous expression in microorganisms, physicochemical factors affecting peptide or protein interactions with bacterial LPS and LPS-neutralizing mechanism are not well known. In this review, we highlight the characteristics and anti-infective activity of bifunctional peptides or proteins from marine resources as well as the challenges and strategies for further study.

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.

Zebrafish phosvitin-derived peptide Pt5 inhibits melanogenesis via cAMP pathway

Zebrafish phosvitin-derived peptide Pt5, consisting of the C-terminal 55 residues of phosvitin, has been shown to have an antimicrobial-immunomodulatory activity comparable to phosvitin. Here, we showed clearly that Pt5 had the capacity to inhibit tyrosinase (TYR) activity and melanin biosynthesis, and this inhibition was independent of cell proliferation and cytotoxic effects. Incubation of fluorescein isothiocyanate (FITC)-labeled Pt5 with B16F10 melanoma cells revealed that Pt5 was localized in the cytoplasm of the cells. In addition, Pt5 inhibited the expression of TYR, tyrosinase-related protein-1 (TRP-1), tyrosinase-related protein-2 (TRP-2), and microphthalmia-associated transcription factor (MITF) in B16F10 melanoma cells and reduced the intracellular cyclic adenosine monophosphate (cAMP) concentration in the cells, but it did not affect the cellular contents of pERK1/2 and β-catenin, suggesting that Pt5 regulates melanin biosynthesis via cAMP signaling pathway rather than Wnt and MAPK pathways. Collectively, these data indicate that Pt5 has the potential to be used as a melanogenesis inhibitor in medical and cosmetic industry, a novel role ever reported.

Killing of Staphylococcus aureus and Salmonella enteritidis and neutralization of lipopolysaccharide by 17-residue bovine lactoferricins: improved activity of Trp/Ala-containing molecules

Bovine lactoferricin (LfcinB) has potent antibacterial, antifungal and antiparasitic activities but is also hemolytic. Our objective was to identify LfcinB17-31 derivatives with reduced hemolysis and improved antimicrobial activity via substituting Cys3, Arg4, Gln7, Met10, and Gly14 with more hydrophobic residues. Two peptides, Lfcin4 and Lfcin5, showed higher activity against Staphylococcus aureus and Salmonella enteritidis and lower hemolytic activity than the parent peptide LfcinB17-31. These peptides permeabilized the outer and inner membranes of S. enteritidis; however, Lfcin5 did not permeabilize the inner membrane of S. aureus. Gel retardation and circular dichroism spectra showed that Lfcin4 and Lfcin5 bound to bacterial genomic DNA. Lfcin4 inhibited DNA, RNA and protein synthesis. Both peptides induced the peeling of membranes and the lysis of S. enteritidis. At doses of 10 and 15 mg/kg, Lfcin4 and Lfcin5 reduced the bacterial counts in infected thigh muscles by 0.03‒0.10 and 0.05‒0.63 log₁₀ CFU/g of tissue, respectively, within 10 h. Lfcin4 and Lfcin5 enhanced the survival rate of endotoxemic mice; reduced serum IL-6, IL-1β and TNF-α levels; and protected mice from lipopolysaccharide-induced lung injury. These data suggest that Lfcin4 and Lfcin5 may be antimicrobial and anti-endotoxin peptides that could serve as the basis for the development of dual-function agents.

Identification of Ly2 members as antimicrobial peptides from zebrafish Danio rerio

The emergence of multidrug-resistant (MDR) microbes caused by overuse of antibiotics leads to urgent demands for novel antibiotics exploration. Our recent data showed that Ly2.1–3 (a novel lymphocyte antigen 6 (Ly6) gene cluster) were proteins with cationic nature and rich in cysteine content, that are characteristic of antimicrobial peptides (AMPs) and their expression were all significantly up-regulated after challenge with lipopolysaccharide (LPS). These strongly suggested that Ly2.1–3 are potential AMPs, but firm evidence are lacking. Here, we clearly showed that the recombinant proteins of Ly2.1–3 were capable of killing Gram-negative bacteria Aeromonas hydrophila and Escherichia coli, while they had little bactericidal activity against the Gram-positive bacteria Staphylococcus aureus and Bacillus subtilis. We also showed that recombinant proteins Ly2.1–3 (rLy2.1–3) were able to bind to the Gram-negative bacteria A. hydrophila, E. coli and the microbial signature molecule LPS, but not to the Gram-positive bacteria S. aureus and B. subtilis as well as the microbial signature molecule LTA. Moreover, the Scatchard analysis revealed that rLy2.1–3 could specifically bind to LPS. Finally, we found that Ly2.1–3 were not cytotoxic to mammalian cells. All these together indicate that Ly2.1–3 can function as AMPs.

Combined Systems Approaches Reveal a Multistage Mode of Action of a Marine Antimicrobial Peptide against Pathogenic Escherichia coli and Its Protective Effect against Bacterial Peritonitis and Endotoxemia

A marine arenicin-3 derivative, N4, displayed potent antibacterial activity against Gram-negative bacteria, but its antibacterial mode of action remains elusive. The mechanism of action of N4 against pathogenic Escherichia coli was first researched by combined cytological and transcriptomic techniques in this study. The N4 peptide permeabilized the outer membrane within 1 min, disrupted the plasma membrane after 0.5 h, and localized in the cytoplasm within 5 min. Gel retardation and circular dichroism (CD) spectrum analyses demonstrated that N4 bound specifically to DNA and disrupted the DNA conformation from the B type to the C type. N4 inhibited 21.1% of the DNA and 20.6% of the RNA synthesis within 15 min. Several hallmarks of apoptosis-like cell death were exhibited by N4-induced E. coli, such as cell cycle arrest in the replication (R) and division(D) phases, reactive oxygen species production, depolarization of the plasma membrane potential, and chromatin condensation within 0.5 h. Deformed cell morphology, disappearance of the plasma membrane, leakage of the contents, and ghost cell formation were demonstrated by transmission electron microscopy, and nearly 100% of the bacteria were killed by N4. A total of 428 to 663 differentially expressed genes are involved in the response to N4, which are associated mainly with membrane biogenesis (53.9% to 56.7%) and DNA binding (13.3% to 14.9%). N4-protected mice that were lethally challenged with lipopolysaccharide (LPS) exhibited reduced levels of interleukin-6 (IL-6), IL-1β, and tumor necrosis factor alpha (TNF-α) in serum and protected the lungs from LPS-induced injury. These data facilitate an enhanced understanding of the mechanisms of marine antimicrobial peptides (AMPs) against Gram-negative bacteria and provide guidelines in developing and applying novel multitarget AMPs in the field of unlimited marine resources as therapeutics.

Antibacterial activity and modes of action of phosvitin-derived peptide Pt5e against clinical multi-drug resistance bacteria

Pt5e, a mutant peptide derived from the C-terminal 55 residues of zebrafish phosvitin, has been suggested to be a novel antibacterial peptide. However, if it is applicable to clinical MDR bacteria remains to be tested. In this study, high-purity Pt5e was first expressed and purified by fusion with cationic elastin-like polypeptide. Pt5e was then shown to be capable of effectively killing all the five clinical MDR bacteria tested. Pt5e kill the MDR bacteria at several levels, including inserting into the bacterial membranes, causing the membrane depolarization and permeabilization, and inducing the intracellular apoptosis/necrosis. All these data suggest that Pt5e is a promising therapeutic potential as an antibiotics against clinical MDR bacteria.

Identification and functional characterization of an uncharacterized antimicrobial peptide from a ciliate Paramecium caudatum

The global ever-growing concerns about multi-drug resistant (MDR) microbes leads to urgent demands for exploration of new antibiotics including antimicrobial peptides (AMPs). Here we demonstrated that a cDNA from Ciliata Paramecium caudatum, designated Pcamp1, coded for a protein with features characteristic of AMPs, which is not homologous to any AMPs currently known. Both the C-terminal 91 amino acid residues of PcAMP1, cPcAMP1, expressed in Escherichia coli and the C-terminal 26 amino acid residues (predicted mature AMP), cPcAMP1/26, synthesized, underwent a coil-to-helix transition in the presence of TFE, SDS or DPC. Functional assays revealed that cPcAMP1 and cPcAMP1/26 were both able to kill Aeromonas hydrophila and Staphylococcus aureus. ELISA showed that cPcAMP1 and cPcAMP1/26 were able to bind to microbe-associated molecular pattern molecules LPS and LTA, which was further corroborated by the observations that cPcAMP1 could deposit onto the bacterial membranes. Importantly, both cPcAMP1 and cPcAMP1/26 were able to induce bacterial membrane permeabilization and depolarization, and to increase intracellular ROS levels. Additionally, cPcAMP1 and cPcAMP1/26 were not cytotoxic to mammalian cells. Taken together, our results show that PcAMP1 is a potential AMP with a membrane selectivity towards bacterial cells, which renders it a promising template for the design of novel peptide antibiotics against MDR microbes. It also shows that use of signal conserved sequence of AMPs can be an effective tool to identify potential AMPs across different animal classes.

Identification of a novel antimicrobial peptide from amphioxus Branchiostoma japonicum by in silico and functional analyses

The emergence of multi-drug resistant (MDR) microbes leads to urgent demands for novel antibiotics exploration. We demonstrated a cDNA from amphioxus Branchiostoma japonicum, designated Bjamp1, encoded a protein with features typical of antimicrobial peptides (AMPs), which is not homologous to any AMPs currently discovered. It was found that Bjamp1 was expressed in distinct tissues, and its expression was remarkably up-regulated following challenge with LPS and LTA. Moreover, the synthesized putative mature AMP, mBjAMP1, underwent a coil-to-helix transition in the presence of TFE or SDS, agreeing well with the expectation that BjAMP1 was a potential AMP. Functional assays showed that mBjAMP1 inhibited the growth of all the bacteria tested, and induced membrane/cytoplasmic damage. ELISA indicated that mBjAMP1 was a pattern recognition molecule capable of identifying LPS and LTA. Importantly, mBjAMP1 disrupted the bacterial membranes by a membranolytic mechanism. Additionally, mBjAMP1 was non-cytotoxic to mammalian cells. Collectively, these data indicate that mBjAMP1 is a new AMP with a high bacterial membrane selectivity, rendering it a promising template for the design of novel peptide antibiotics against MDR microbes. It also shows for the first time that use of signal conserved sequence of AMPs is effective identifying potential AMPs across different animal classes.

Effect of Regular Exercise on Inflammation Induced by Drug-resistant Staphylococcus aureus 3089 in ICR mice

Obesity is often associated with irregular dietary habits and reduced physical activity. Regular exercise induces a metabolic response that includes increased expression of various cytokines, signaling proteins and hormones, and reduced adipocyte size. In this study, mice performed a swimming exercise for 10 min/day, 5 days/week for 3 weeks. We then investigated the effect of this exercise regimen on inflammation induced by infection with drug-resistant Staphylococcus aureus strain 3089 (DRSA). In humans, DRSA causes dermatitis and pneumonitis. Similarly, DRSA induced inflammatory pneumonitis in both no-exercise (No-EX) and swim-trained (SW-EX) ICR mice. Regular exercise increased levels of the pro-inflammatory cytokines TNF-α and IL-1β and nitric oxide in both serum and whole lung tissue in SW-EX, as compared to No-EX control mice. Moreover, levels of the antimicrobial peptide cathelicidin were significantly increased in visceral adipose tissue and whole lung tissue in the SW-EX group, and this was accompanied by a reduction in the size of visceral adipocytes. In addition, levels of the inflammation marker peroxisome proliferator-activated receptor gamma coactivator-1 (PGC-1) were not increased in the lung tissue of SW-EX mice. These findings suggest that in these model mice, regular exercise strengthens immune system responses, potentially preventing or mitigating infectious disease.

Immune-Relevant and Antioxidant Activities of Vitellogenin and Yolk Proteins in Fish

Vitellogenin (Vtg), the major egg yolk precursor protein, is traditionally thought to provide protein- and lipid-rich nutrients for developing embryos and larvae. However, the roles of Vtg as well as its derived yolk proteins lipovitellin (Lv) and phosvitin (Pv) extend beyond nutritional functions. Accumulating data have demonstrated that Vtg, Lv and Pv participate in host innate immune defense with multifaceted functions. They can all act as multivalent pattern recognition receptors capable of identifying invading microbes. Vtg and Pv can also act as immune effectors capable of killing bacteria and virus. Moreover, Vtg and Lv are shown to possess phagocytosis-promoting activity as opsonins. In addition to these immune-relevant functions, Vtg and Pv are found to have antioxidant activity, which is able to protect the host from oxidant stress. These non-nutritional functions clearly deepen our understanding of the physiological roles of the molecules, and at the same time, provide a sound basis for potential application of the molecules in human health.

Immune-Relevant and Antioxidant Activities of Vitellogenin and Yolk Proteins in Fish

Vitellogenin (Vtg), the major egg yolk precursor protein, is traditionally thought to provide protein- and lipid-rich nutrients for developing embryos and larvae. However, the roles of Vtg as well as its derived yolk proteins lipovitellin (Lv) and phosvitin (Pv) extend beyond nutritional functions. Accumulating data have demonstrated that Vtg, Lv and Pv participate in host innate immune defense with multifaceted functions. They can all act as multivalent pattern recognition receptors capable of identifying invading microbes. Vtg and Pv can also act as immune effectors capable of killing bacteria and virus. Moreover, Vtg and Lv are shown to possess phagocytosis-promoting activity as opsonins. In addition to these immune-relevant functions, Vtg and Pv are found to have antioxidant activity, which is able to protect the host from oxidant stress. These non-nutritional functions clearly deepen our understanding of the physiological roles of the molecules, and at the same time, provide a sound basis for potential application of the molecules in human health.

Zebrafish phosvitin is an antioxidant with non-cytotoxic activity

Antioxidants, or anti-oxidant agents, have attracted a great deal of attention in recent years because of their roles in prevention of chronic diseases and utilization as preservatives in food and cosmetics. In this study, we clearly demonstrated that zebrafish recombinant phosvitin (rPv) is an antioxidant agent capable of inhibiting the oxidation of the linoleic acid, and scavenging the 2,2-diphenyl-1-picrylhydrazyl radical. We also showed that zebrafish rPv is a cellular antioxidant capable of protecting radical-mediated oxidation of cellular biomolecules. Importantly, zebrafish rPv is non-cytotoxic to murine macrophage RAW264.7 cells. It is the first report that showed the antioxidant activities of Pv in fishes, suggesting that zebrafish Pv can be an important antioxidant, which can be used as preservatives in food and cosmetics and even as supplementary mediator in different diseased states.

Molecular cloning, expression, purification and characterization of vitellogenin in scallop Patinopecten yessoensis with special emphasis on its antibacterial activity

Vitellogenin (Vg), the major precursor of the egg-yolk proteins, has been found to play an immune role in fish and protochordate amphioxus, however, no study on the immune function of Vg in invertebrates has ever been studied before. In this study, the complete cDNA of Vg was identified from the scallop Patinopecten yessoensis (termed PyVg). The cDNA contained an open reading frame (ORF) of 6888 bp, encoding a polypeptide of 2295 amino acid protein, which had an N-terminal signal peptide followed by the mature Vg. The mature Vg had the domains Vitellogenin_N, domain of unknown function 1943 (DUF1943) and von Willebrand factor type D domain (VWD) as well as the consensus cleavage site (R-X-R/K-R) and conserved motif (KTIGNAG). Tissue distribution assay revealed that PyVg transcripts were predominantly present in the ovary and hepatopancreas, and its expression profile in ovary well reflected the annual cycle of vitellogenesis. Interestingly, bacterial challenge caused a significant change in PyVg expression, hinting an involvement of PyVg in the acute phase response in P. yessoensis. Consistently, recombinant DUF1943 and VWD domains both could interact with LTA and LPS on bacterial wall, and purified native PyVg displayed a broad-spectrum antibacterial activity against both Gram-negative (Escherichia coli and Vibrio anguillarum) and Gram-positive bacteria (Staphylococcus aureus). Overall, these data indicate that Vg is a pattern recognition molecule with bacterial growth-inhibiting activity in the scallop.

Characterization and bioactivity of hepcidin-2 in zebrafish: dependence of antibacterial activity upon disulfide bridges

Hepcidin is an antimicrobial peptide and iron-regulatory molecule with highly conserved disulfide bridges among vertebrates, but structural insights into the function in fish remains largely missing. We demonstrate here that recombinant hepcidin-2 from zebrafish is capable of inhibiting the growth of the Gram-negative bacteria Escherichia coli and Vibrio anguillarum, and the Gram-positive bacteria Staphylococcus aureus and Bacillus subtilis with minimum inhibitory concentrations (MICs) of 18, 15, 13 and 9μM, respectively. We also show by TEM examination that recombinant hepcidin-2 is directly cidal to the cells of E. coli and S. aureus. Moreover, we find that hepcidin-2 displays affinity to LPS, LTA and PGN. All these data indicate that hepcidin-2 is both a pattern recognition molecule, capable of identifying LPS, LTA and PGN, and an antibacterial effector, capable of inhibiting the growth of bacteria. The data also show that the antibacterial activity of hepcidin-2 depends upon the disulfide bridges.