Immunomodulatory peptides-A promising source for novel functional food production and drug discovery

Immunomodulatory peptides are a complex class of bioactive peptides that encompasses substances with different mechanisms of action. Immunomodulatory peptides could also be used in vaccines as adjuvants which would be extremely desirable, especially in response to pandemics. Thus, immunomodulatory peptides in food of plant origin could be regarded both as valuable suplements of novel functional food preparation and/or as precursors or possible active ingredients for drugs design for treatment variety of conditions arising from impaired function of immune system. Given variety of mechanisms, different tests are required to assess effects of immunomodulatory peptides. Some of those effects show good correlation with in vivo results but others, less so. Certain plant peptides, such as defensins, show both immunomodulatory and antimicrobial effect, which makes them interesting candidates for preparation of functional food and feed, as well as templates for design of synthetic peptides.

Potent bactericidal activity of reduced cryptdin-4 derived from its hydrophobicity and mediated by bacterial membrane disruption

Defensin is a cysteine-rich antimicrobial peptide with three disulphide bonds under normal oxidative conditions. Cryptdin-4 (Crp4) is a defensin secreted by Paneth cells in the small intestine of mice, and only reduced Crp4 (Crp4_red) shows activity against enteric commensal bacteria, although both oxidised Crp4 (Crp4_ox) and Crp4_red can kill non-commensal bacteria. To investigate the molecular factors that affect the potent antimicrobial activity of Crp4_red, the bactericidal activities of Crp4_ox and Crp4_red, Crp4 with all Cys residues substituted with Ser peptide (6C/S-Crp4), and Crp4 with all thiol groups modified by N-ethylmaleimide (NEM-Crp4) were assessed. All peptides showed bactericidal activity against non-commensal bacteria, whereas Crp4_red and NEM-Crp4 showed bactericidal activity against commensal bacteria. These potent peptides exhibited high hydrophobicity, which was strongly correlated with membrane insertion. Intriguingly, Crp4_ox formed electrostatic interactions with the membrane surface of bacteria, even without exerting bactericidal activity. Moreover, the bactericidal activity of both oxidised and reduced forms of Crp4 was abolished by inhibition of electrostatic interactions; this finding suggests that Crp4_red targets bacterial membranes. Finally, a liposome leakage assay against lipids extracted from commensal bacteria demonstrated a correlation with bactericidal activity. These results suggest that the potent bactericidal activity of Crp4_red is derived from its hydrophobicity, and the bactericidal mechanism involves disruption of the bacterial membrane. Findings from this study provide a better understanding of the bactericidal mechanism of both Crp4_ox and Crp4_red.

Differential activity on trypanosomatid parasites of a novel recombinant defensin type 1 from the insect Triatoma (Meccus) pallidipennis

Defensins are one of the major families of antimicrobial peptides (AMPs) that are widely distributed in insects. In Triatomines (Hemiptera: Reduviidae) vectors of Trypanosoma cruzi the causative agent of Chagas disease, two large groups of defensin isoforms have been described: type 1 and type 4. The aim of this study was to analyze the trypanocidal activity of a type 1 recombinant defensin (rDef1.3) identified in Triatoma (Meccus) pallidipennis, an endemic specie from México. The trypanocidal activity of this defensin was evaluated in vitro, against the parasites T. cruzi, T. rangeli, and two species of Leishmania (L. mexicana and L. major) both causative agents of cutaneous leishmaniasis. Our data demonstrated that the defensin was active against all the parasites although in different degrees. The defensin altered the morphology, reduced the viability and inhibited the growth of T.cruzi. When tested against T. rangeli (a parasite that infects a variety of mammalian species), stronger morphological effects where observed. Surprisingly the greatest effects were observed against the two Leishmania species, of which L. major was the parasite most affected with 50% of dead cells or with damaged membranes, in addition of a reduction in its proliferative capacity in culture. These results suggest that rDef1.3 has an important antimicrobial effect against trypanosomatids which cause some of the more important neglected tropical diseases transmitted by insect vectors.

Bioinformatic analysis and antiviral effect of Periplaneta americana defensins

Due to the lack of an adaptive immune system, insects rely on innate immune mechanisms to fight against pathogenic infections. Two major innate immune pathways, Toll and IMD, orchestrate anti-pathogen responses by regulating the expression of antimicrobial peptide (AMP) genes. Although the antifungal or antibacterial function of AMPs has been well characterized, the antiviral role of AMPs in insects remains largely unclear. Periplaneta americana (P. americana), or the American cockroach, is used in traditional Chinese medicine as an antiviral agent; however, the underlying mechanism of action of P. americana extracts is unclear. Our previous study showed that the P. americana genome encodes multiple antimicrobial peptide genes. Based on these data, we predicted five novel P. americana defensins (PaDefensins) and analyzed their primary structure, secondary structure, and physicochemical properties. The putative antiviral, antifungal, antibacterial, and anticancer activities suggested that PaDefensin5 is a desirable therapeutic candidate against viral diseases. As the first experimental evidence of the antiviral effects of insect defensins, we also showed the antiviral effect of PaDefensin5 in Drosophila Kc cells and Drosophila embryos in vivo . In conclusion, results of both in silico predictions and subsequent antiviral experiments suggested PaDefensin5 a promising antiviral drug.

Are Host Defense Peptides and Their Derivatives Ready to be Part of the Treatment of the Next Coronavirus Pandemic?

The term host defense peptides arose at the beginning to refer to those peptides that are part of the host’s immunity. Because of their broad antimicrobial capacity and immunomodulatory activity, nowadays, they emerge as a hope to combat resistant multi-drug microorganisms and emerging viruses, such as the case of coronaviruses. Since the beginning of this century, coronaviruses have been part of different outbreaks and a pandemic, and they will be surely part of the next pandemics, this review analyses whether these peptides and their derivatives are ready to be part of the treatment of the next coronavirus pandemic.

Identification and expression analysis of the β-defensin genes in the goat small intestine

Defensins represent a family of cysteine-rich peptides that have broad-spectrum antimicrobial activities and serve as a typical kind of effector molecule in the immunity. Ruminant species have a large number of β-defensins in the absence of α- and θ-defensins. It is well-known that the genomes of sheep and cattle harbor at least 43 and 57 β-defensin genes, respectively. However, the repertoire of the goat β-defensin gene family has not been fully elucidated. In this study, we identified a total of 50 β-defensins from the goat genome, including 48 functional genes and 2 pseudogenes. Cross-species genomic and evolutionary analyses showed that all of the β-defensins in goat chromosomes 8, 13 and 23 present one-to-one orthologous relationships to their sheep and cattle counterparts, whereas some β-defensin genes in goat chromosome 27 are goat-specific. Moreover, we observed that some duplicated genes in goat chromosome 27 may be derived from gene copy number variation, and the annotation of sheep and cattle β-defensins appears to be incomplete in the genome. Importantly, real-time PCR analysis showed that 17 β-defensins are expressed in the small intestine with abundant cBD1s expression. These findings significant increased our knowledge of ruminant β-defensin and provided useful information for genetic studies, as well as providing a foundation for future research exploring the role of defensins in the immune response.

Activity of Anti-Microbial Peptides (AMPs) against Leishmania and Other Parasites: An Overview

Anti-microbial peptides (AMPs), small biologically active molecules, produced by different organisms through their innate immune system, have become a considerable subject of interest in the request of novel therapeutics. Most of these peptides are cationic-amphipathic, exhibiting two main mechanisms of action, direct lysis and by modulating the immunity. The most commonly reported activity of AMPs is their anti-bacterial effects, although other effects, such as anti-fungal, anti-viral, and anti-parasitic, as well as anti-tumor mechanisms of action have also been described. Their anti-parasitic effect against leishmaniasis has been studied. Leishmaniasis is a neglected tropical disease. Currently among parasitic diseases, it is the second most threating illness after malaria. Clinical treatments, mainly antimonial derivatives, are related to drug resistance and some undesirable effects. Therefore, the development of new therapeutic agents has become a priority, and AMPs constitute a promising alternative. In this work, we describe the principal families of AMPs (melittin, cecropin, cathelicidin, defensin, magainin, temporin, dermaseptin, eumenitin, and histatin) exhibiting a potential anti-leishmanial activity, as well as their effectiveness against other microorganisms.

Preliminary investigations on the pathogenesis-related protein expression profile of the medicinal herb Macleaya cordata and anti-bacterial properties of recombinant proteins

The plant pathogenesis-related (PR) proteins play a crucial role in the defense of plants against pathogens and orchestrate the innate immune system of plants. In this paper, a non-normalized cDNA library of the leaf was constructed to obtain a comprehensive view of PR proteins of Macleaya cordata. Specifically, 511 expressed sequence tags (ESTs) were generated using Sanger sequencing. All ESTs were assembled into 364 non-redundancy sequences, including 78 clusters and 286 singlets. The PR protein expression profile of the medicinal herb M. cordata has been investigated and is represented by defensin, lipid-transfer protein, (S)-norcoclaurine synthase, and major allergen protein, suggesting that the herb contains rich active proteins against pathogens. Furthermore, two defensins were selected for recombinant expression in yeast, and the antimicrobial activities were explored. Since they both present a broad antimicrobial spectrum, they are of particular importance for agricultural and medicinal applications. Our study describes defensins in Papaveraceae for the first time and provides novel insights into the effective components. In addition to the alkaloids, PR proteins (such as defensins, lipid transfer proteins, (S) - norcoclaurine synthase, major allergen protein, and Class IV chitinases) are involved in the antibacterial and anti-inflammatory activities of M. cordata.

Paneth Cell Alertness to Pathogens Maintained by Vitamin D Receptors

BACKGROUND AND AIMS

Vitamin D exerts a regulatory role over mucosal immunity via the vitamin D receptor (VDR). Although Paneth cells and their products are known to regulate the commensal and pathogenic microbiota, the role that VDRs in Paneth cells play in these responses is unknown.

METHODS

We identified the decreased intestinal VDR significantly correlated with reduction of an inflammatory bowel disease risk gene ATG16L1 and Paneth cell lysozymes in patients with Crohn's disease. We generated Paneth cell-specific VDR knockout (VDR^ΔPC) mice to investigate the molecular mechanisms.

RESULTS

Lysozymes in the Paneth cells were significantly decreased in the VDR^ΔPC mice. Isolated VDR^ΔPC Paneth cells exhibited weakened inhibition of pathogenic bacterial growth and displayed reduced autophagic responses. VDR^ΔPC mice had significantly higher inflammation after Salmonella infections. VDR^ΔPC mice also showed high susceptibility to small intestinal injury induced by indomethacin, a nonsteroidal anti-inflammatory drug. Co-housing of VDR^ΔPC and VDR^lox mice made the VDR^ΔPC less vulnerable to dextran sulfate sodium colitis, suggesting the transmission of protective bacterial from the VDR^lox mice. Thus, a lack of VDR in Paneth cells leads to impaired antibacterial activities and consequently increased inflammatory responses. Genetically and environmentally regulated VDRs in the Paneth cells may set the threshold for the development of chronic inflammation, as observed in inflammatory bowel diseases.

CONCLUSIONS

We provide new insights into the tissue-specific functions of VDRs in maintaining Paneth cell alertness to pathogens in intestinal disorders. Targeting the VDR affects multiple downstream events within Paneth cells that inhibit intestinal inflammation and establish host defense against enteropathogens.

A novel defensin-like peptide contributing to antimicrobial and antioxidant capacity of the tick Dermacentor silvarum (Acari: Ixodidae)

Defensins are the most diverse groups of antimicrobial peptides in invertebrate animals. In ticks, defensins show great potential as targets for tick control, and display future prospect for therapeutic drug development. In the present study, a novel defensin-like gene (Ds-defensin) contributing to the antimicrobial and antioxidant capacity of the tick Dermacentor silvarum was characterized. The full-length of the Ds-defensin gene was 382 bp, which displayed tissue-specific expression and was highly abundant in the salivary glands and carcasses of the adults. It encodes a 71-amino acid defensin-like protein, and the protein precursor is characterized by a 22-amino acid signal peptide and a 34-amino acid mature peptide. The peptide displayed potent activity against most of the tested gram-positive bacteria, including Staphylococcus aureus, S. carnosus and Nocardia asteroides, and one tested gram-negative bacterium, Psychrobacter faecalis. Scanning electron microscopy revealed that the cell wall and surface of treated bacteria became rough and gradually formed pores after a 30-min exposure to the Ds-defensin peptide. Additionally, the peptide also showed significant antioxidant capacity. The above results implied that the defensin-like peptide may play an important role in tick defense and the interaction with microorganisms.

Bitter taste receptor agonists regulate epithelial two-pore potassium channels via cAMP signaling

Background

Epithelial solitary chemosensory cell (tuft cell) bitter taste signal transduction occurs through G protein coupled receptors and calcium-dependent signaling pathways. Type II taste cells, which utilize the same bitter taste signal transduction pathways, may also utilize cyclic adenosine monophosphate (cAMP) as an independent signaling messenger in addition to calcium.

Methods

In this work we utilized specific pharmacologic inhibitors to interrogate the short circuit current (Isc) of polarized nasal epithelial cells mounted in Ussing chambers to assess the electrophysiologic changes associated with bitter agonist (denatonium) treatment. We also assessed release of human β-defensin-2 from polarized nasal epithelial cultures following treatment with denatonium benzoate and/or potassium channel inhibitors.

Results

We demonstrate that the bitter taste receptor agonist, denatonium, decreases human respiratory epithelial two-pore potassium (K2P) current in polarized nasal epithelial cells mounted in Ussing chambers. Our data further suggest that this occurs via a cAMP-dependent signaling pathway. We also demonstrate that this decrease in potassium current lowers the threshold for denatonium to stimulate human β-defensin-2 release.

Conclusions

These data thus demonstrate that, in addition to taste transducing calcium-dependent signaling, bitter taste receptor agonists can also activate cAMP-dependent respiratory epithelial signaling pathways to modulate K2P currents. Bitter-agonist regulation of potassium currents may therefore serve as a means of rapid regional epithelial signaling, and further study of these pathways may provide new insights into regulation of mucosal ionic composition and innate mechanisms of epithelial defense.

A rhamnose-binding lectin from Rhodnius prolixus and the impact of its silencing on gut bacterial microbiota and Trypanosoma cruzi

Lectins are ubiquitous proteins involved in the immune defenses of different organisms and mainly responsible for non-self-recognition and agglutination reactions. This work describes molecular and biological characterization of a rhamnose-binding lectin (RBL) from Rhodnius prolixus, which possesses a 21 amino acid signal peptide and a mature protein of 34.6 kDa. The in-silico analysis of the primary and secondary structures of RpLec revealed a lectin domain fully conserved among previous insects studied. The three-dimensional homology model of RpLec was similar to other RBL-lectins. Docking predictions with the monosaccharides showed rhamnose and galactose-binding sites comparable to Latrophilin-1 and N-Acetylgalactosamine-binding in a different site. The effects of RpLec gene silencing on levels of infecting Trypanosoma cruzi Dm 28c and intestinal bacterial populations in the R. prolixus midgut were studied by injecting RpLec dsRNA into the R. prolixus hemocoel. Whereas T. cruzi numbers remained unchanged compared with the controls, numbers of bacteria increased significantly. The silencing also induced the up regulation of the R. prolixus defC (defensin) expression gene. These results with RpLec reveal the potential importance of this little studied molecule in the insect vector immune response and homeostasis of the gut bacterial microbiota.

Molecular characterization and evaluation of the antibacterial activity of a plant defensin peptide derived from a gene of oat (Avena sativa L.)

Plant defensins are a group of small disulfide-rich cationic peptides that exhibit a broad spectrum of antimicrobial activities. In the present study, an antibacterial plant defensin peptide was successfully identified and characterized from the transcriptome of the oat (Avena sativa L.), and called AsDef1. The complete nucleotide sequence of AsDef1 was determined (321 bp) and found to contain an open reading frame (ORF) encoding a peptide of 77 aa with a putative 22 aa signal peptide sequence that addresses the mature defensin to the apoplast. Further in silico analyses revealed that the structure of the identified defensin (AsDef1) consists of the Knot1 functional domain with eight conserved cysteine residues and four disulfide bonds. The highest expression of AsDef1 was observed in the developing seeds of the A. sativa plant. AsDef1 also showed antibacterial activity against both Gram-positive and Gram-negative bacteria. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values ranged from 0.15625 μM to 0.625 μM. In this study, we identified and characterized an antibacterial defensin from A. sativa for the first time. The findings of the present study offer insights that can be used in producing pathogen-resistant transgenic plants and in developing potential antibacterial agents in the future using AsDef1 from A. sativa.

Salivary peptide human neutrophil defensin1-3 and its relationship with early childhood caries

BACKGROUND

This study aimed to evaluate the relationship of the level of salivary peptides human neutrophil defensin (HNP) 1-3 in children with and without early childhood caries (ECC).

MATERIALS AND METHODS

This in vitro study was conducted among 86 children of age 3-6 years who were divided into two groups: Group 1 - children with ECC (n = 43) and Group 2 - children without ECC (n = 43). Saliva samples were collected, and salivary peptide HNP1-3 levels were analyzed using enzyme-linked immunosorbent assay. The data collected were subjected to appropriate statistical analysis. Independent sample t-test was used to compare the mean salivary peptide levels of HNP1-3 in children with and without ECC. One-way ANOVA was used for intragroup comparison of the mean peptide levels between the ages. P < 0.05 was considered statistically significant.

RESULTS

The mean age of the children in Group 1 and Group 2 was 5.12 ± 0.851 and 4.88 ± 0.879 years, respectively. A statistically significant decrease was seen in salivary peptide HNP1-3 levels in children with ECC (1.44 ng/ml) when compared to children without ECC (6.04 ng/ml) with P < 0.001. There were no statistically significant differences in the gender- and age-based comparisons.

CONCLUSION

A decrease in salivary peptide HNP1-3 levels might be a biological factor for predisposition to ECC and hence can be used as a predictive and a preventive tool in caries prevention.

Glycoproteomic analysis identifies cryptdin-related sequence 1 as O-glycosylated protein modified with α1,2-fucose in the small intestine

The modification of galactose with α1,2-fucose is involved in symbiosis with intestinal bacteria and elimination of pathogenic bacteria. It is postulated that α1,2-fucosylated mucin secreted from goblet cells is involved in defending an organism against infections, but the detailed molecular mechanisms are yet to be elucidated. It was previously reported that Paneth cells of the small intestine were positive for UEA-1 lectin staining. However, glycoproteins in Paneth cells carrying α1,2-fucose have not yet been identified. Glycoproteomic analysis of ileal lysates identified 3212 O-linked and 2962 N-linked glycopeptides. In particular, cryptdin-related sequence 1 (CRS1) expressed in Paneth cells was found to be α1,2-fucosylated. Unlike other antimicrobial α-defensin proteins, CRS1 contains unique Thr residues, which are modified with O-glycans, with 3HexNAc2Hex1Fuc1NeuAc being the main glycoform. Identification of α1,2-fucose on the O-glycans of CRS1 expressed in Paneth cells will pave the way for a mechanistic understanding of α1,2-fucose-dependent symbiosis with intestinal bacteria and elimination of pathogenic bacteria in the intestine.

Utilization of a recombinant defensin from Maize (Zea mays L.) as a potential antimicrobial peptide

The search for effective and bioactive antimicrobial molecules to  encounter the medical need for new antibiotics is an encouraging area of research. Plant defensins are small cationic, cysteine-rich peptides with a stabilized tertiary structure by disulfide-bridges and characterized by a wide range of biological functions. The heterologous expression of Egyptian maize defensin (MzDef) in Escherichia coli and subsequent purification by glutathione affinity chromatography yielded 2 mg/L of recombinant defensin peptide. The glutathione-S-transferase (GST)-tagged MzDef of approximately 30 kDa in size (26 KDa GST +  ~ 4 KDa MzDef peptide) was immunodetected with anti-GST antibodies. The GST-tag was successfully cleaved from the MzDef peptide by thrombin, and the removal was validated by the Tris-Tricine gel electrophoresis. The MzDef induced strong growth inhibition of Rhizoctonia solani, Fusarium verticillioides, and Aspergillus niger by 94.23%, 93.34%, and 86.25%, respectively, whereas relatively weak growth inhibitory activity of 35.42% against Fusarium solani was recorded. Moreover, strong antibacterial activities were demonstrated against E. coli and Bacillus cereus and the moderate activities against Salmonella enterica and Staphylococcus aureus at all tested concentrations (0.1, 0.2, 0.4, 0.8, 1.6, and 3.2 µM). Furthermore, the in vitro MTT assay exhibited promising anticancer activity against all tested cell lines (hepatocellular carcinoma, mammary gland breast cancer, and colorectal carcinoma colon cancer) with IC50 values ranging from 14.85 to 29.85 µg/mL. These results suggest that the recombinant peptide MzDef may serve as a potential alternative antimicrobial and anticancer agent to be used in medicinal application.

Antimicrobial peptide gene expression in medication-related osteonecrosis of the jaw

Bisphosphonates and denosumab are commonly used antiresorptive therapies in patients with bone metastasis and osteoporosis. Medication-related osteonecrosis of the jaw (MRONJ) is a serious side effect of these drugs, and infection has been recognized as a contributing factor. Current therapeutic options for MRONJ show limited effectiveness, therefore necessitating novel treatment strategies. Bisphosphonates have recently been reported to induce the expression of antimicrobial peptides (AMPs), an inherent component of the immune system. Therefore, the aim of the present study was to investigate and compare the influence of the anti-RANKL antibody denosumab and bisphosphonates on the gene expression of selected AMPs: human α-defensin-1, human α-defensin-3, human β-defensin-1, and human β-defensin-3. Bone specimens were collected from patients with MRONJ who had been treated with bisphosphonates (n = 6) or denosumab (n = 6), and from healthy subjects (n = 6) with no history of treatment with bone metabolism-influencing drugs. Reverse transcription-quantitative polymerase chain reaction was used to quantify the expression levels of selected AMPs. Samples from patients treated with denosumab showed significantly higher mRNA expression of human α-defensin-3 and human β-defensin-3 than those from healthy subjects. This finding is similar to previously described upregulated expression of human defensins in patients with MRONJ after bisphosphonates treatment. This suggests that the elevated expression of defensins may be at least a part of the mechanism underlying the pathogenesis of osteonecrosis induced by antiresorptive therapies, which can serve as a new target for potential treatment of MRONJ.

Plant Antimicrobial Peptides: State of the Art, In Silico Prediction and Perspectives in the Omics Era

Even before the perception or interaction with pathogens, plants rely on constitutively guardian molecules, often specific to tissue or stage, with further expression after contact with the pathogen. These guardians include small molecules as antimicrobial peptides (AMPs), generally cysteine-rich, functioning to prevent pathogen establishment. Some of these AMPs are shared among eukaryotes (eg, defensins and cyclotides), others are plant specific (eg, snakins), while some are specific to certain plant families (such as heveins). When compared with other organisms, plants tend to present a higher amount of AMP isoforms due to gene duplications or polyploidy, an occurrence possibly also associated with the sessile habit of plants, which prevents them from evading biotic and environmental stresses. Therefore, plants arise as a rich resource for new AMPs. As these molecules are difficult to retrieve from databases using simple sequence alignments, a description of their characteristics and in silico (bioinformatics) approaches used to retrieve them is provided, considering resources and databases available. The possibilities and applications based on tools versus database approaches are considerable and have been so far underestimated.

Antimicrobial peptides from Capsicum chinense fruits: agronomic alternatives against phytopathogenic fungi

In recent years, the antimicrobial activity of peptides isolated from a wide variety of organs from plant species has been reported. However, a few studies have investigated the potential of antimicrobial peptides (AMPs) found in fruits, especially Capsicum chinense (pepper). The present study aimed to purify and characterize peptides from Capsicum chinense fruits and evaluate their inhibitory activities against different phytopathogenic fungi and also analyze the possible mechanisms of action involved in microbial inhibition. After fruit protein extraction and high-performance liquid chromatography (HPLC), different fractions were obtained, named F1 to F10. Peptides in the F4 and F5 fractions were sequenced and revealed similarity with the plant antimicrobial peptides like non-specific lipid transfer proteins and defensin-like peptide. The F4 and F5 fractions presented strong antimicrobial activity against the fungus Fusarium solani and Fusarium oxysporum, causing toxic effects on these fungi, leading to membrane permeabilization, endogenous reactive oxygen species increase, activation of metacaspase and loss of mitochondrial function.

Antibacterial activities and mechanisms of action of a defensin from manila clam Ruditapes philippinarum

Defensins represent an evolutionary ancient family of antimicrobial peptides, which played an undeniably important role in host defense. In the present study, a defensin isoform was identified and characterized from manila clam Ruditapes philippinarum (designed as Rpdef1α). Multiple alignments and phylogenetic analysis suggested that Rpdef1α belonged to the defensin family. Quantitative RT-PCR and immunohistochemical analysis revealed that Rpdef1α transcripts and the encoding peptide were dominantly expressed in the tissues of gills and mantle. After Vibrio anguillarum challenge, the Rpdef1α transcripts were significantly up-regulated in gills of clams. In addition, rRpdef1α not only showed broad-spectrum antimicrobial activities towards Vibrio species, but also inhibited the formation of bacterial biofilms. Knockdown of Rpdef1α transcripts caused significant increase in the cumulative mortality of manila clams post V. anguillarum challenge. Membrane integrity, scanning electron microscopy analysis and electrochemical assay indicated that rRpdef1α was capable of causing bacterial membrane permeabilization and then resulted in cell death. Moreover, phagocytosis and chemotactic ability of hemocytes could be significantly enhanced after incubation with rRpdef1α. Overall, these results suggested that Rpdef1α could act as both antibacterial agent and opsonin to defend against the invading microorganisms in manila clam R. philippinarum.

A Novel Approach on Leukodepletion Filters: Investigation of Synergistic Anticancer Effect of Purified α-Defensins and Nisin

Purpose: There are number of reports available regarding defensins activity against mammalian cells besides their antimicrobial and immune regulatory activities. This study aims to investigate anticancer and apoptosis activity of the purified defensins from leukodepletion filters alone or in synergism with bacterial peptide, nisin, on prostate and colorectal cancer. Methods: Leucoflex LCR-5 filters were backflushed by an optimized elution system. Isolated granulocytes were sonicated and the supernatant treated before further purification by high performance liquid chromatography (HPLC). SDS-PAGE and western blot testing verified the fraction. Cell culture on PC-3 (human prostate adenocarcinoma), and HCT-116 (human colorectal carcinoma) were conducted following by MTT assays in addition to annexin flow cytometry for sole and synergistic effects with peptide nisin. Results: Viable and active neutrophils could recover, and α-defensins were extracted and purified. Combinations of an optimal dose of α-defensins and nisin showed a remarkable synergistic effect on cancer cell lines (over 90% and 70% for PC-3 and HCT-116, respectively). Conclusion: It also observed that less than 40% of both cells could survive after co-treatment with optimal dose. Also, apoptosis was increased after treatment by these peptides together. Annexin Vpositive populations significantly increased in percentage in comparison with control.

Crystal structure of rice defensin OsAFP1 and molecular insight into lipid-binding

Defensins are antibacterial peptides that function in the innate immune system. OsAFP1, a defensin identified from Oryza sativa (rice), exhibits antimicrobial activity against rice pathogens. Intriguingly, OsAFP1 was also shown to demonstrate potent antifungal activity against the human pathogenic fungus Candida albicans by inducing apoptosis in target cells, suggesting that OsAFP1 represents a potential new antibiotic candidate; however, further analyses, particularly at the structural level, are required to elucidate the mechanistic underpinnings of OsAFP1 antifungal activity. Here, we determined the three-dimensional structure of OsAFP1 using X-ray crystallography. OsAFP1 features the cysteine-stabilized αβ structure highly conserved in plant defensins and presents a dimeric structure that appears necessary for antifungal activity. Superimposition of the OsAFP1 structure with that of Nicotiana alata NaD1 complexed with phosphatidic acid indicated that the target molecule is likely trapped between the S2-S3 loops of each OsAFP1 dimer. In lipid-binding analyses performed using nitrocellulose membranes immobilized with various membrane lipid components, OsAFP1 was found to bind to phosphatidylinositols (PIPs) harboring phosphate groups, particularly PI(3)P. These results indicate that OsAFP1 exerts antifungal activity by binding to PI(3)P contained in the C. albicans cell membrane, thereby applying cellular stress and inducing apoptosis. Furthermore, the OsAFP1 structure and site-specific-mutation analyses revealed that Arg1, His2, Leu4, Arg9, and Phe10 play critical roles in OsAFP1 dimer formation. Thus, our study provides novel insights into the antifungal mechanism of OsAFP1.

Impact of sublethal exposure to synthetic and natural acaricides on honey bee (Apis mellifera) memory and expression of genes related to memory

Acaricides are used by beekeepers in honey bee (Apis mellifera L.) colonies to control parasitic mites, but may also have adverse effects to honey bees. In this study, five commonly used acaricides were tested for their sublethal effects on memory and expression of neural-related genes in honey bees. Memory measured with the proboscis extension reflex (PER) assay was significantly reduced by topical treatment of bees with a single LD₀₅ dose of formic acid at 2 and 24 h post treatment (hpt). However, tau-fluvalinate, amitraz, coumaphos, and formic acid, but not thymol, resulted in memory loss at 48 hpt. The LD₀₅ doses of the acraricides did not affect expression of neuroligin-1, related to memory, or expression of major royal jelly protein-1, related to both memory and development, although expression of both genes was affected at LD₅₀ doses. The LD₀₅ doses of thymol, formic acid, amitraz and coumaphos increased defensin-1 expression, which is related to both memory and immunity. The effect of thymol, however, may have been due to its impact on the immune response rather than memory. This study demonstrates that acaricides vary in their effects on bee's memory, and that the widely used acaricide, formic acid, is particularly damaging.

Ion channel modulation by scorpion hemolymph and its defensin ingredients highlights origin of neurotoxins in telson formed in Paleozoic scorpions

An increasing number of scorpion fossils indicate that the venomous telson developed from the sharp telson in sea scorpions into the extant scorpion-like telson in aquatic scorpions in the Paleozoic Era and then further evolved into the fetal venom system. This hypothesis led us to evaluate the inhibition of scorpion venom-sensitive potassium channels by hemolymph from the scorpion Mesobuthus martensii. Scorpion hemolymph diluted 1:10 inhibited Kv1.1, Kv1.2, Kv1.3 and SK3 potassium channel currents by 76.4%, 90.2%, 85.8%, and 52.8%, respectively. These discoveries encouraged us to investigate the functional similarity between the more ancient defensin ingredients in hemolymph and the evolved neurotoxins in the venom. In addition to the expression of the representative defensin BmKDfsin3 and BmKDfsin5 in both venomous and non-venomous tissues, NMR analysis revealed structural similarities between scorpion defensin and neurotoxin. Functional experiments further indicated that scorpion defensin used the same mechanism as classical neurotoxin to block the neurotoxin-sensitive Kv1.1, Kv1.2, Kv1.3 and SK3 channels. These findings emphasize the likelihood that scorpion defensins evolved into neurotoxins that were adapted to the emergence of the scorpion telson from the sharp telson of sea scorpions into the extant scorpion-like telson in aquatic scorpions in the Paleozoic Era.

CgSOCS6 negatively regulates the expression of CgIL17s and CgDefh1 in the pacific oyster Crassostrea gigas

As a family of negatively feedback regulating factors, the suppressor of cytokine signaling (SOCS) can depress cytokine signal transduction, and eventually modulate growth, development, differentiation, and immune response. In the present study, a SOCS homologue (designated as CgSOCS6) was identified from oyster Crassostrea gigas. The open reading frame of CgSOCS6 cDNA was of 1167 bp encoding a peptide of 388 amino acid residues with a central Src homology 2 (SH2) domain, a conserved C-terminal SOCS box, and a nucleus localization sequence (NLS) in its N-terminus. The deduced amino acid sequence of CgSOCS6 shared 37.9-45.5% similarity with other SOCS6/7 family members. In the unrooted phylogenetic tree, CgSOCS6 was clustered with EsSOCS6 from Chinese mitten crab Eriocheir sinensis and assigned into the SOCS6/7 group. The mRNA transcripts of CgSOCS6 were constitutively distributed in all the tested tissues, with the highest level in hemocytes. After lipopolysaccharide (LPS) stimulation, the mRNA expression of CgSOCS6 in hemocytes was significantly up-regulated to the highest level at 6 h (8.48-fold compared to the control group, p < 0.01), and then kept at a relatively higher level from 12 h to 72 h. CgSOCS6 protein could be translocated into the hemocyte nucleus after LPS stimulation. The mRNA expressions of interleukin 17-4 (CgIL17-4), CgIL17-5, and defensin (CgDefh1) in the hemocytes of CgSOCS6-knockdown oysters increased significantly (2.55-fold, 2.68-fold, 4.68-fold of that in EGFP-RNAi oysters, p < 0.05, p < 0.05, p < 0.001, respectively) after LPS stimulation. These findings suggested that CgSOCS6 was involved in the oyster immune response by regulating the expressions of CgIL17-4, CgIL17-5, and CgDefh1.