Novel Peptides from Skins of Amphibians Showed Broad-Spectrum Antimicrobial Activities

An esculentin-1 homolog from a dark-spotted frog (Pelophylax nigromaculatus) possesses antibacterial and immunoregulatory properties

BACKGROUND

Esculentin-1, initially discovered in the skin secretions of pool frogs (Pelophylax lessonae), has demonstrated broad-spectrum antimicrobial activity; however, its immunomodulatory properties have received little attention.

RESULTS

In the present study, esculentin-1 cDNA was identified by analysing the skin transcriptome of the dark-spotted frog (Pelophylax nigromaculatus). Esculentin-1 from this species (esculentin-1PN) encompasses a signal peptide, an acidic spacer peptide, and a mature peptide. Sequence alignments with other amphibian esculentins-1 demonstrated conservation of the peptide, and phylogenetic tree analysis revealed its closest genetic affinity to esculentin-1P, derived from the Fukien gold-striped pond frog (Pelophylax fukienensis). Esculentin-1PN transcripts were observed in various tissues, with the skin exhibiting the highest mRNA levels. Synthetic esculentin-1PN demonstrated antibacterial activity against various pathogens, and esculentin-1PN exhibited bactericidal activity by disrupting cell membrane integrity and hydrolyzing genomic DNA. Esculentin-1PN did not stimulate chemotaxis in RAW264.7, a murine leukemic monocyte/macrophage cell line. However, it amplified the respiratory burst and augmented the pro-inflammatory cytokine gene (TNF-α and IL-1β) expression in RAW264.7 cells.

CONCLUSIONS

This novel finding highlights the immunomodulatory activity of esculentin-1PN on immune cells.

Immunohistochemical Characterization of Langerhans Cells in the Skin of Three Amphibian Species

The amphibian taxon includes three orders that present different morphological characteristics: Anura, Caudata, and Apoda. Their skin has a crucial role: it acts as an immune organ constituting a physical, chemical, immunological, and microbiological barrier to pathogen insult and conducts essential physiological processes. Amphibians have developed specialized features to protect the vulnerable skin barrier, including a glandular network beneath the skin surface that can produce antimicrobial and toxic substances, thus contributing to the defense against pathogens and predators. This study aims to characterize Langerhans cells in the skin of Lithobates catesbeianus (order: Anura; Shaw, 1802), Amphiuma means (order: Caudata; Garden, 1821), and Typhlonectes natans (order: Apoda; Fischer, 1880) with the following antibodies: Langerin/CD207 (c-type lectin), Major Histocompatibility Complex (MHC)II, and Toll-like receptor (TLR)2 (expressed by different types of DCs). Our results showed Langerhans cells positive for Langerin CD/207 in the epidermis of the three species; moreover, some antigen-presenting cells (APCs) in the connective tissue expressed TLR2 and MHCII. The distribution of the Langerhans cells is very similar in the three amphibians examined, despite their different habitats. A greater knowledge of the amphibian immune system could be useful to better understand the phylogeny of vertebrates and to safeguard amphibians from population declines. Furthermore, the similarities between amphibians' and human skin concerning immunological features may be useful in both biology and translational medicine.

Heterologous expression of the novel dimeric antimicrobial peptide LIG in Pichia pastoris

The antimicrobial peptide (AMP) LI is a fusion product of antimicrobial peptide LL37 produced by human neutrophils and Indolicidin secreted by bovine neutrophils. LI retained the antimicrobial activity of the parental peptides and showed high cell selectivity. In this study, the flexible linker Gly-Ser-Gly (G-S-G) was used to ligate LI into dimeric LIG, and constructed the Pichia pastoris (P. pastoris) expression vector pPIC9K-6×His-3×FLAG-LIG. The total protein expression of P. pastoris GS115 reached the highest level (189.6 mg/L) after 96 h induction with 3 % methanol at the initial pH value of 7.0. Finally, 5.9 mg/L of recombinant LIG (rLIG) was obtained after enterokinase digestion and purification. The rLIG had high antimicrobial activity and low hemolytic activity. Compared with monomer LI, GSG linked dimeric LIG, which had no significant change in antimicrobial activity and had good salt ions stability. In this study, the dimeric antimicrobial peptide LIG was successfully expressed, which provided a new idea for the expression of AMPs in the P. pastoris expression system, and had important significance for the application of AMPs.

Antimicrobial peptides for novel antiviral strategies in the current post-COVID-19 pandemic

The recent pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has highlighted how urgent and necessary the discovery of new antiviral compounds is for novel therapeutic approaches. Among the various classes of molecules with antiviral activity, antimicrobial peptides (AMPs) of innate immunity are among the most promising ones, mainly due to their different mechanisms of action against viruses and additional biological properties. In this review, the main physicochemical characteristics of AMPs are described, with particular interest toward peptides derived from amphibian skin. Living in aquatic and terrestrial environments, amphibians are one of the richest sources of AMPs with different primary and secondary structures. Besides describing the various antiviral activities of these peptides and the underlying mechanism, this review aims at emphasizing the high potential of these small molecules for the development of new antiviral agents that likely reduce the selection of resistant strains.

Peptide NCTX15 derived from spider toxin gland effectively relieves hyperuricemia in mice

Hyperuricemia is a clinical disease characterized by a continuous increase in uric acid (UA) due to purine metabolism disorder. As current drug treatments are limited, it is imperative to explore new drugs that offer better safety and efficacy. In this study, Nephila clavata toxin gland homogenates were isolated and purified by exclusion chromatography and high-performance liquid chromatography, resulting in the identification and isolation of a short peptide (NCTX15) with the sequence 'QSGHTFK'. Analysis showed that NCTX15 exhibited no cytotoxicity in mouse macrophages or toxic and hemolytic activity in mice. Notably, NCTX15 inhibited UA production by down-regulating urate transporter 1 and glucose transporter 9 and up-regulating organic anion transporter 1, thus promoting UA excretion. In addition, NCTX15 alleviated the inflammatory response and renal injury by inhibiting the expression of inflammatory factors interleukin-6, interleukin-1β, tumor necrosis factor alpha, NLR family, pyrin domain-containing 3, and pyroptosis-related factor gasdermin D. These results indicate that NCTX15 displayed urate-lowering, anti-inflammatory, and analgesic effects. As the first urate-reducing short peptide isolated from a spider toxin gland homogenate, NCTX15 exhibits considerable potential as a novel drug molecule for anti-gout and hyperuricemia treatment.

Interaction of Uperin Peptides with Model Membranes: Molecular Dynamics Study

The interaction of antimicrobial and amyloid peptides with cell membranes is a critical step in their activities. Peptides of the uperin family obtained from the skin secretion of Australian amphibians demonstrate antimicrobial and amyloidogenic properties. All-atomic molecular dynamics and an umbrella sampling approach were used to study the interaction of uperins with model bacterial membrane. Two stable configurations of peptides were found. In the bound state, the peptides in helical form were located right under the head group region in parallel orientation with respect to the bilayer surface. Stable transmembrane configuration was observed for wild-type uperin and its alanine mutant in both alpha-helical and extended unstructured forms. The potential of mean force characterized the process of peptide binding from water to the lipid bilayer and its insertion into the membrane, and revealed that the transition of uperins from the bound state to the transmembrane position was accompanied by the rotation of peptides and passes through the energy barrier of 4-5 kcal/mol. Uperins have a weak effect on membrane properties.

Purification and Biological Properties of Raniseptins-3 and -6, Two Antimicrobial Peptides from Boana raniceps (Cope, 1862) Skin Secretion

The number of multidrug-resistant pathogenic microorganisms has been growing in recent years, most of which is due to the inappropriate use of the commercial antibiotics that are currently available. The dissemination of antimicrobial resistance represents a serious global public health problem. Thus, it is necessary to search for and develop new drugs that can act as antimicrobial agents. Antimicrobial peptides are a promising alternative for the development of new therapeutic drugs. Anurans' skin glands are a rich source of broad-spectrum antimicrobial compounds and hylids, a large and diverse family of tree frogs, are known as an important source of antimicrobial peptides. In the present study, two novel antimicrobial peptides, named Raniseptins-3 and -6, were isolated from Boana raniceps skin secretion and their structural and biological properties were evaluated. Raniseptins-3 and -6 are cationic, rich in hydrophobic residues, and adopt an α-helix conformation in the presence of SDS (35 mM). Both peptides are active against Gram-negative bacteria and Gram-positive pathogens, with low hemolytic activity at therapeutic concentrations. No activity was observed for yeasts, but the peptides are highly cytotoxic against B16F10 murine melanoma cells and NIH3T3 mouse fibroblast cells. None of the tested compounds showed improvement trends in the MTT and LDH parameters of MHV-3 infected cells at the concentrations tested.

The dual antimicrobial and immunomodulatory roles of host defense peptides and their applications in animal production

Host defense peptides (HDPs) are small molecules with broad-spectrum antimicrobial activities against infectious bacteria, viruses, and fungi. Increasing evidence suggests that HDPs can also indirectly protect hosts by modulating their immune responses. Due to these dual roles, HDPs have been considered one of the most promising antibiotic substitutes to improve growth performance, intestinal health, and immunity in farm animals. This review describes the antimicrobial and immunomodulatory roles of host defense peptides and their recent applications in animal production.

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.

Anurans against SARS-CoV-2: A review of the potential antiviral action of anurans cutaneous peptides

At the end of 2019, in China, clinical signs and symptoms of unknown etiology have been reported in several patients whose sample sequencing revealed pneumonia caused by the SARS-CoV-2 virus. COVID-19 is a disease triggered by this virus, and in 2020, the World Health Organization declared it a pandemic. Since then, efforts have been made to find effective therapeutic agents against this disease. Identifying novel natural antiviral drugs can be an alternative to treatment. For this reason, antimicrobial peptides secreted by anurans' skin have gained attention for showing a promissory antiviral effect. Hence, this review aimed to elucidate how and which peptides secreted by anurans' skin can be considered therapeutic agents to treat or prevent human viral infectious diseases. Through a literature review, we attempted to identify potential antiviral frogs' peptides to combat COVID-19. As a result, the Magainin-1 and -2 peptides, from the Magainin family, the Dermaseptin-S9, from the Dermaseptin family, and Caerin 1.6 and 1.10, from the Caerin family, are molecules that already showed antiviral effects against SARS-CoV-2 in silico. In addition to these peptides, this review suggests that future studies should use other families that already have antiviral action against other viruses, such as Brevinins, Maculatins, Esculentins, Temporins, and Urumins. To apply these peptides as therapeutic agents, experimental studies with peptides already tested in silico and new studies with other families not tested yet should be considered.

Spectroscopic study of antimicrobial peptides: Structure and functional activity

Amphibians are a natural source of a large number of peptides with a wide range of functional activities. Here, a complex of spectroscopic methods including NMR-, FTIR-, CD-, and UV-spectroscopy was applied to characterize the structure and functional activity of megin-1, a peptide isolated from amphibian skin. The three-dimensional structure of two forms of the peptide was determined using solution NMR spectroscopy. Thermodynamic characteristics of the process of peptide transformation from linear to cyclic form were obtained. Antibacterial and antimycotic properties of the peptide, as well as its protease inhibitory activities, were analyzed.

Antimicrobial peptides as a feed additive alternative to animal production, food safety and public health implications: An overview

In the last few years, feed additives have been used in animal nutrition to improve nutrient utilization, health parameters and animal performance. However, the use of antibiotics as feed additives has allowed the occurrence of antimicrobial resistance (AMR), which can bring as a consequence, an increase in the morbidity and mortality of diseases that were previously treatable with antibiotics. In this context, antimicrobial peptides (AMP) have appeared as a promising strategy because they have multiple biological activities and represent a powerful strategy to prevent the development of resistant microorganisms. Despite the small number of studies applied in vivo, AMP appear as a potent alternative to the use of antibiotics in animal nutrition, due to an increase in feed efficiency and the prevention/treatment of some animal diseases. This review discusses the problems associated with antimicrobial resistance and the use of AMP as a strong candidate to replace conventional antibiotics, mainly in the animal industry.

Antimicrobial Peptide Brevinin-1RL1 from Frog Skin Secretion Induces Apoptosis and Necrosis of Tumor Cells

Cancer has always been one of the most common malignant diseases in the world. Therefore, there is an urgent need to find potent agents with selective antitumor activity against cancer cells. It has been reported that antimicrobial peptides (AMPs) can selectively target tumor cells. In this study, we focused on the anti-tumor activity and mechanism of Brevivin-1RL1, a cationic α-helical AMP isolated from frog Rana limnocharis skin secretions. We found that Brevivin-1RL1 preferentially inhibits tumor cells rather than non-tumor cells with slight hemolytic activity. Cell viability assay demonstrated the intermolecular disulfide bridge contributes to the inhibitory activity of the peptide as the antitumor activity was abolished when the disulfide bridge reduced. Further mechanism studies revealed that both necrosis and apoptosis are involved in Brevivin-1RL1 mediated tumor cells death. Moreover, Brevivin-1RL1 induced extrinsic and mitochondria intrinsic apoptosis is caspases dependent, as the pan-caspase inhibitor z-VAD-FMK rescued Brevinin-1RL1 induced tumor cell proliferative inhibition. Immunohistology staining showed Brevivin-1RL1 mainly aggregated on the surface of the tumor cells. These results together suggested that Brevivin-1RL1 preferentially converges on the cancer cells to trigger necrosis and caspase-dependent apoptosis and Brevivin-1RL1 could be considered as a pharmacological candidate for further development as anti-cancer agent.

A recombinant fungal defensin-like peptide-P2 combats Streptococcus dysgalactiae and biofilms

Streptococcus dysgalactiae, considered one of the main pathogens that causes bovine mastitis, is a serious threat to humans and animals. However, the excessive use of antibiotics and the characteristic of S. dysgalactiae forming biofilms in mastitic teat canal have serious clinical implications. In this study, in vivo and in vitro multiple mechanisms of action of P2, a mutant of fungal defensin plectasin, against S. dysgalactiae were systematically and comprehensively investigated for the first time. P2 showed potent antibacterial activity against S. dysgalactiae (minimum inhibitory concentration, MIC = 0.23-0.46 μM) and rapid bactericidal action by 3.0 lg units reduction in 2-4 h. No resistant mutants appeared after 30-d serial passage of S. dysgalactiae in the presence of P2. The results of electron microscopy and flow cytometer showed that P2 induced membrane damage of S. dysgalactiae, causing the leakage of cellular content and eventually cell death. Besides, P2 effectively inhibited early biofilm formation, eradicated mature biofilms, and killed 99.9% persisters which were resistant to 100 × MIC vancomycin; and confocal laser scanning microscopy (CLSM) also revealed the potent antibacterial and antibiofilm activity of P2 (the thickness of biofilm reduced from 18.82 to 7.94 μm). The in vivo therapeutic effect of P2 in mouse mastitis model showed that it decreased the number of mammary bacteria and alleviated breast inflammation by regulating cytokines and inhibiting bacterial proliferation, which were superior to vancomycin. These data indicated that P2 maybe a potential candidate peptide for mastitis treatment of S. dysgalactiae infections. KEY POINTS: •P2 showed potential in vitro antibacterial characteristics towards S. dysgalactiae. •P2 eradicated biofilms, killed persisters, and induced cell death of S. dysgalactiae. •P2 could effectively protect mice from S. dysgalactiae infection in gland.

Peptide OM-LV20 exerts neuroprotective effects against cerebral ischemia/reperfusion injury in rats

Ischemia/reperfusion (I/R) is a common injury leading to ischemic stroke. At present, I/R treatment remains limited, highlighting the urgent need for the discovery and development of new protective drugs for brain injury. Here, we investigated the neuroprotective effects of short peptide OM-LV20 previously identified from amphibian against I/R rats. Results showed that intraperitoneal administration of OM-LV20 (20 ng/kg) significantly reduced infarct area formation, improved behavioral abnormalities, and protected cortical and hippocampal neurons against death caused by I/R. Moreover, the underlying molecular mechanism was involved with the regulation of the MAPK and BDNF/AKT signaling pathways, as well as the levels of cyclic adenosine monophosphate, pituitary adenylate cyclase-activating polypeptide receptor, and tryptophan hydroxylase 1. To the best of our knowledge, this research was the first report to describe the neuroprotective effects of an amphibian skin secretion-derived peptide in I/R rats and highlighted OM-LV20 as a promising drug candidate for the development of novel anti-stroke therapies.

The Potential of Frog Skin Peptides for Anti-Infective Therapies: The Case of Esculentin-1a(1-21)NH2

Antimicrobial Peptides (AMPs) are the key effectors of the innate immunity and represent promising molecules for the development of new antibacterial drugs. However, to achieve this goal, some problems need to be overcome: (i) the cytotoxic effects at high concentrations; (ii) the poor biostability and (iii) the difficulty in reaching the target site. Frog skin is one of the richest natural storehouses of AMPs, and over the years, many peptides have been isolated from it, characterized and classified into several families encompassing temporins, brevinins, nigrocins and esculentins. In this review, we summarized how the isolation/characterization of peptides belonging to the esculentin-1 family drove us to the design of an analogue, i.e. esculentin-1a(1-21)NH2, with a powerful antimicrobial action and immunomodulatory properties. The peptide had a wide spectrum of activity, especially against the opportunistic Gram-negative bacterium Pseudomonas aeruginosa. We described the structural features and the in vitro/in vivo biological characterization of this peptide as well as the strategies used to improve its biological properties. Among them: (i) the design of a diastereomer carrying Damino acids in order to reduce the peptide's cytotoxicity and improve its half-life; (ii) the covalent conjugation of the peptide to gold nanoparticles or its encapsulation into poly(lactide- co-glycolide) nanoparticles; and (iii) the peptide immobilization to biomedical devices (such as silicon hydrogel contact lenses) to obtain an antibacterial surface able to reduce microbial growth and attachment. Summing up the best results obtained so far, this review traces all the steps that led these frog-skin AMPs to the direction of peptide-based drugs for clinical use.

A novel peptide from the skin of amphibian Rana limnocharis with potency to promote skin wound repair

In clinical trials, the healing of wounds remains a substantial physiological and financial incumbrance on patients. Therefore, the development of new drugs that can accelerate wound healing is vital. Based on genomic methods, we identified a new peptide (RL-RL10) with the amino acid sequence 'RLFKCWKKDS' from the skin of an amphibian frog species (Rana limnocharis). RL-RL10 promoted wound healing of human keratinocytes (HaCaT) in a concentration-dependent manner. RL-RL10 also had an effect on the migration and proliferation of HaCaT cells and promoted healing of a full-thickness wound in mice in a dose-dependent manner. In conclusion, we discovered RL-RL10 that promoted healing activity of cellular and animal wounds, thus providing a new peptide template for the development of novel wound-repairing drugs.

Accelerated Wound Healing Induced by a Novel Amphibian Peptide (OA-FF10)

BACKGROUND

Despite the continued development of modern medicine, chronic wounds are still a critical issue in clinical treatment, placing a great physiological, psychological, and financial burden on patients. Researchers have investigated many methods to solve this problem, with bioactive peptides gaining increasing attention due to their considerable advantages and diverse functions, as well as low cost, simple storage, and easy transportation.

METHODS

In this research, a novel peptide (named OA-FF10) was identified from the skin secretions of the odorous frog species Odorrana andersonii. The sequence of mature OA-FF10 was "FFTTSCRSGC", which was produced by the post-translational processing of a 61-residue prepropeptide.

RESULTS

Similar to most frog peptides, OA-FF10 showed an intramolecular disulfide bridge at the C-terminus. OA-FF10 demonstrated no antibacterial, antioxidant, hemolytic, or acute toxic activity, but promoted wound healing and proliferation of human keratinocytes (HaCaT) both time- and dose-dependently. Furthermore, while OA-FF10 had no effect on wound healing of Human Skin Fibroblasts (HSF), it did accelerate healing in a full-thickness skin-wound mouse model.

CONCLUSION

Our research revealed the strong wound-healing activity of OA-FF10 in vivo and in vitro, thus providing a new candidate for the development of novel wound-healing drugs.

Structure and mode of action of a novel antibacterial peptide from the blood of Andrias davidianus

Andrias davidianus is widely recognized in traditional medicine as a cure-all to treat a plethora of ailments. In a previous study, a novel antibacterial peptide named andricin B was isolated from A. davidianus blood. In this study, we investigated andricin B structure and its mode of action. Circular dichroism spectra suggested that andricin B adopts a random coil state in aqueous solution and a more rigid conformation in the presence of bacteria. Moreover propidium iodide/fluorescein diacetate double staining indicated that bacteria treated with andricin B were not immediately eliminated. Rather, there is a gradual bacterial death, followed by a sublethal stage. Scanning electronic microscope imaging indicates that andricin B might form pores on cell membranes, leading to the release of cytoplasmic contents. These results were consistent with flow cytometry analysis. Furthermore, Fourier transform infrared spectroscopy suggests that andricin B induces changes in the chemical properties in the areas surrounding these "pores" on the cell membranes. SIGNIFICANCE AND IMPACT OF THE STUDY: The results of this study suggested the new perspectives about the mode of action of antimicrobial peptide (AMP) active against sensitive bacteria. The AMP was able to be in a random coiled state in aqueous solution but to change to a more rigid one in the presence of sensitive bacteria. Exposure to AMP might not lead to immediate death of treated bacteria, rather bacteria concentration decreased gradually flattening at a sublethal stage. These findings will help people to understand better how the AMPs activate against sensitive bacteria.

A short peptide potentially promotes the healing of skin wound

Skin wound, a common form of skin damage in daily life, remains a serious challenge in clinical treatment. Bioactive peptides with high efficiency have been considered as potential therapeutic candidates for wound healing. In this report, a novel short linear peptide, with mature peptide sequence of 'GLLSGINAEWPC' and no obvious similarity with other known bioactive peptides, was identified by genomic method from the skin of odorous frog, Odorrana andersonii Our results suggested that OA-GL12 (OA: abbreviation of species (O. andersonii), GL: two initial amino acids, 12: peptide length) obviously accelerated the scratch-healing of keratinocytes and human fibroblasts in a time- and concentration-dependent manner. Meanwhile, OA-GL12 showed significant effect in promoting the wound healing on the full-thickness skin wound model. Inflammatory assay results demonstrated that OA-GL12 induced the secretion of tumor necrosis factor (TNF) and transforming growth factor β1 (TGF-β1) on murine macrophage cell line (RAW264.7), which might explain the powerful accelerating capacity of wound healing. Moreover, results also indicated that epidermal growth factor receptor (EGFR) was involved in the mechanisms underlying the scratch-healing promoting activity of OA-GL12. In addition, OA-GL12 showed obvious free radical scavenging activity. Results supported that OA-GL12 did not exert risk in acute toxicity, hemolytic activity, and direct antibacterial activity. The remarkable effect of OA-GL12 on promoting wound healing verified in this research made it potential to be a novel template for the development of wound healing-promoting agents.

Brevinin-2 Drug Family—New Applied Peptide Candidates Against Methicillin-Resistant Staphylococcus aureus and Their Effects on Lys-7 Expression of Innate Immune Pathway DAF-2/DAF-16 in Caenorhabditis elegans

The issue of Staphylococcus aureus (MRSA) developing a resistance to drugs such as methicillin has long been the focus for new drug development. In recent years, antimicrobial peptides, such as small molecular peptides with broad-spectrum antibacterial activity and special antibacterial mechanism, have shown a strong medicinal potential. In particular, the Brevinin-2 family has been shown to have a significant inhibitory effect against gram-positive bacteria (G+). In this study, we researched the influence of MRSA on the behavior and survival rate of nematodes. We established an assay of Caenorhabditis elegans–MRSA antimicrobial peptides to screen for new potent anti-infective peptides against MRSA. From the Brevinin-2 family, 13 peptides that had shown strong effects on G+ were screened for their ability to prolong the lifespan of infected worms. Real-time Polymerase Chain Reaction (PCR) tests were used to evaluate the effect on the innate immune pathway dauer formation defective (DAF)-2/DAF-16 of C. elegans. The assay successfully screened and filtered out four of the 13 peptides that significantly improved the survival rate of MRSA-infected worms. The result of real-time PCR indicated that the mRNA and protein expression levels of lys-7 were consistently upregulated by being treated with four of the Brevinin-2 family. The Brevinin-2 family peptides, including Brevinin-2, Brevinin-2-OA3, Brevinin-2ISb, and Brevinin-2TSa, also played an active role in the DAF-2/DAF-16 pathway in C. elegans. We successfully demonstrated the utility of anti-infective peptides that prolong the survival rate of the MRSA-infected host and discovered the relationship between antibacterial peptides and the innate immune system of C. elegans. We demonstrated the antimicrobial effects of Brevinin-2 family peptides, indicating their potential for use as new drug candidates against MRSA infections.

OA-GL21, a novel bioactive peptide from Odorrana andersonii, accelerated the healing of skin wounds

Nowadays, the number of chronic trauma cases caused by a variety of factors such as the world's population-ageing and chronic diseases is increasing steadily, and thus effective treatment for chronic wounds has become a severe clinical challenge, which also burdens the patient both physically and financially. Therefore, it is urgent to develop new drugs to accelerate the healing of wounds. Bioactive peptides, which are relatively low cost, easy to produce, store and transport, have become an excellent choice. In this research, we identified a novel peptide OA-GL21, with an amino acid sequence of 'GLLSGHYGRVVSTQSGHYGRG', from the skin secretions of Odorrana andersonii Our results showed that OA-GL21 exerted the ability to promote wound healing of human keratinocytes (HaCaT) and human fibroblasts in a dose- and time-denpendent manner. However, OA-GL21 had no significant effect on the proliferation of these two cells. Significantly, OA-GL21 showed obvious ability to promote wound healing in the full-thickness skin wound model in dose- and scar-free manners. Further studies showed that OA-GL21 had no direct antibacterial, hemolytic, and acute toxic activity; it had weak antioxidant activities but high stability. In conclusion, this research proved the promoting effects of OA-GL21 on cellular and animal wounds, and thus provided a new peptide template for the development of wound-repairing drugs.

Cathelicidin-OA1, a novel antioxidant peptide identified from an amphibian, accelerates skin wound healing

Cathelicidins play pivotal roles in host defense. The discovery of novel cathelicidins is important research; however, despite the identification of many cathelicidins in vertebrates, few have been reported in amphibians. Here we identified a novel cathelicidin (named cathelicidin-OA1) from the skin of an amphibian species, Odorrana andersonii. Produced by posttranslational processing of a 198-residue prepropeptide, cathelicidin-OA1 presented an amino acid sequence of 'IGRDPTWSHLAASCLKCIFDDLPKTHN' and a molecular mass of 3038.5 Da. Functional analysis showed that, unlike other cathelicidins, cathelicidin-OA1 demonstrated no direct microbe-killing, acute toxicity and hemolytic activity, but did exhibit antioxidant activity. Importantly, cathelicidin-OA1 accelerated wound healing against human keratinocytes (HaCaT) and skin fibroblasts (HSF) in both time- and dose-dependent manners. Notably, cathelicidin-OA1 also showed wound-healing promotion in a mouse model with full-thickness skin wounds, accelerating re-epithelialization and granulation tissue formation by enhancing the recruitment of macrophages to the wound site, inducing HaCaT cell proliferation and HSF cell migration. This is the first cathelicidin identified from an amphibian that shows potent wound-healing activity. These results will help in the development of new types of wound-healing agents and in our understanding of the biological functions of cathelicidins.

Antimicrobial peptides sourced from post-butter processing waste yak milk protein hydrolysates

Yak butter is one of the most important foods for the Tibetan people. Of note, its production yields waste yak milk as a by-product. In this work, waste yak milk protein hydrolysates made via Pepsin hydrolysis were shown to have antimicrobial activity. Furthermore, an innovative method of magnetic liposome adsorption combined with reversed-phase high performance liquid chromatography (RP-HPLC) was developed to screen for and purify the antimicrobial peptides. Two antimicrobial peptides were obtained and their amino acid sequences were determined by N-sequencing, namely Arg-Val-Met-Phe-Lys-Trp-Ala and Lys-Val-Ile-Ser-Met-Ile. The antimicrobial activity spectra of Arg-Val-Met-Phe-Lys-Trp-Ala included Bacillus subtilis, Staphylcoccus aureus, Listeria innocua, Escherichia coli, Enterobacter cloacae and Salmonella paratyphi, while the Lys-Val-Ile-Ser-Met-Ile peptide shows not only bacterial growth inhibition but also of fungi. Haemolytic testing suggested that these two antimicrobial peptides could be considered to have no haemolytic effect at their minimum inhibitory concentrations (MICs).

Selectively screen the antibacterial peptide from the hydrolysates of highland barley

Highland barley is one of the most important industrial crops in Tibetan plateau. Previous research indicated that highland barley has many medical functions. In this work, the antibacterial abilities of highland barley were investigated. The protein solutions hydrolyzed by trypsin for 4 h exhibited the highest antibacterial activity. An antibacterial peptide, barleycin, was screened and purified by magnetic liposome extraction combining with the protein profiles of reversed-phase high-performance liquid chromatography (RP-HPLC). Structure, characterization, and safety evaluation of barleycin were further investigated. Amino acids sequence was determined as Lys-Ile-Ile-Ile-Pro-Pro-Leu-Phe-His by N-sequencing. Circular dichroism spectra indicated the a-helix conformation of barleycin. The activity spectrum included Bacillus subtilis, Staphylcoccus aureus, Listeria innocua and Escherichia coli and the MICs were from 4 to 16 μg/mL. Safety evaluations with cytotoxicity and hemolytic suggested this antibacterial peptide could be considered as safe at MICs. Finally, mode of action of barleycin on sensitive cells was primarily studied. The results suggested the damage of cell membrane.

OM-LV20, a novel peptide from odorous frog skin, accelerates wound healing in vitro and in vivo

The healing of chronic wounds remains a considerable challenge in clinical trials and imposes severe financial and physiological burdens on patients. Many works are being tried to find ideal clinical promoting wound healing biomaterials. Small bioactive peptides with low cost and easy production, store and transfer become excellent candidates. Here, we identified a novel peptide (named OM-LV20) from skin secretions of odorous frog Odorrana margaretae. The peptide had an amino acid sequence of "LVGKLLKGAVGDVCGLLPIC," contained an intramolecular disulfide bridge at the C-terminus, and was produced by post-translational processing of a 71-residue prepropeptide. Our results showed that OM-LV20 had no direct microbe-killing effects, hemolytic activity, or acute toxicity, but did exhibit weak antioxidant activity. OM-LV20 promoted wound healing against human keratinocytes (HaCaT) and human skin fibroblasts (HSF) in both time- and dose-dependent manners. In addition, it induced the proliferation of HaCaT but not HSF cells. Of note, OM-LV20 showed strong wound healing-promoting activity in a mice model of full-thickness skin wound. Our research indicates the cellular and animal level wound healing potential of OM-LV20, and thus provides a novel bioactive peptide template for the development of wound healing agents and medicine.

Promising Approaches to Optimize the Biological Properties of the Antimicrobial Peptide Esculentin-1a(1-21)NH2: Amino Acids Substitution and Conjugation to Nanoparticles

Antimicrobial peptides (AMPs) represent an interesting class of molecules with expanding biological properties which make them a viable alternative for the development of future antibiotic drugs. However, for this purpose, some limitations must be overcome: (i) the poor biostability due to enzymatic degradation; (ii) the cytotoxicity at concentrations slightly higher than the therapeutic dosages; and (iii) the inefficient delivery to the target site at effective concentrations. Recently, a derivative of the frog skin AMP esculentin-1a, named esculentin-1a(1–21)NH₂, [Esc(1–21): GIFSKLAGKKIKNLLISGLKG-NH₂] has been found to have a potent activity against the Gram-negative bacterium Pseudomonas aeruginosa; a slightly weaker activity against Gram-positive bacteria and interesting immunomodulatory properties. With the aim to optimize the antimicrobial features of Esc(1–21) and to circumvent the limitations described above, two different approaches were followed: (i) substitutions by non-coded amino acids, i.e., α-aminoisobutyric acid or d-amino acids; and (ii) peptide conjugation to gold nanoparticles. In this mini-review, we summarized the structural and functional properties of the resulting Esc(1–21)-derived compounds. Overall, our data may assist researchers in the rational design and optimization of AMPs for the development of future drugs to fight the worldwide problem of antibiotic resistance.

Centipede venom peptide SsmTX-I with two intramolecular disulfide bonds shows analgesic activities in animal models

Pain is a major symptom of many diseases and results in enormous pressures on human body or society. Currently, clinically used analgesic drugs, including opioids and nonsteroidal anti-inflammatory drugs, have adverse reactions, and thus, the development of new types of analgesic drug candidates is urgently needed. Animal venom peptides have proven to have potential as new types of analgesic medicine. In this research, we describe the isolation and characterization of an analgesic peptide from the crude venom of centipede, Scolopendra subspinipes mutilans. The amino acid sequence of this peptide was identical with SsmTX-I that was previously reported as a specific Kv2.1 ion channel blocker. Our results revealed that SsmTX-I was produced by posttranslational processing of a 73-residue prepropeptide. The intramolecular disulfide bridge motifs of SsmTX-I was Cys1-Cys3 and Cys2-Cys4. Functional assay revealed that SsmTX-I showed potential analgesic activities in formalin-induced paw licking, thermal pain, and acetic acid-induced abdominal writhing mice models. Our research provides the first report of cDNA sequences, disulfide motif, successful synthesis, and analgesic potential of SsmTX-I for the development of pain-killing drugs. It indicates that centipede peptide toxins could be a treasure trove for the search of novel analgesic drug candidates. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.

Antimicrobial Peptides as Potential Alternatives to Antibiotics in Food Animal Industry

Over the last decade, the rapid emergence of multidrug-resistant pathogens has become a global concern, which has prompted the search for alternative antibacterial agents for use in food animals. Antimicrobial peptides (AMPs), produced by bacteria, insects, amphibians and mammals, as well as by chemical synthesis, are possible candidates for the design of new antimicrobial agents because of their natural antimicrobial properties and a low propensity for development of resistance by microorganisms. This manuscript reviews the current knowledge of the basic biology of AMPs and their applications in non-ruminant nutrition. Antimicrobial peptides not only have broad-spectrum activity against bacteria, fungi, and viruses but also have the ability to bypass the common resistance mechanisms that are placing standard antibiotics in jeopardy. In addition, AMPs have beneficial effects on growth performance, nutrient digestibility, intestinal morphology and gut microbiota in pigs and broilers. Therefore, AMPs have good potential as suitable alternatives to conventional antibiotics used in swine and poultry industries.