Diversity, evolution and medical applications of insect antimicrobial peptides

Immune modulation by dexketoprofen trometamol, a selective eicosanoid biosynthesis inhibitor of cellular immune response and phenoloxidase reaction in response to viral infection in Pimpla turionellae adults

Nodulation is the first immune defence mechanism related to melanisation in response to microbial infections in insects. Adult parasitoid insects have been hypothesised to produce nodules with melanisation in response to viral infections and, eicosanoids, to mediate nodulation reactions and phenoloxidase (PO) activation in this type of infections. To test this hypothesis, endoparasitoid Pimpla turionellae adults were first inoculated with a novel generation nonsteroidal anti-inflammatory drug (NSAID) dexketoprofen trometamol (DT) (5 μg/adult), which is a selective cyclooxygenase-1 (COX-1) inhibitor. These adults were then immediately injected with intrahaemocoelic injection of Bovine herpes simplex virus-1 (BHSV-1) as a model insect-virus interaction. Additionally, adults were fed on artificial diet with increasing concentrations of DT (0.001, 0.01, or 0.1 g/100 ml diet) per os prior to intrahaemocoelic injection of BHSV-1 (2 × 103 PFU/adult) and nodulation and PO activity were recorded at 2 h post inoculation (PI). BHSV-1-treated newly emerged adults fed with inhibitors showed low levels of nodulation and increased PO enzyme activity. DT-treated Pimpla adults produced significantly fewer nodules (approximately nine nodules/adult), whereas viral infection provoked nodules (approximately 33 nodules/adult) in comparison with needle (vehicle)-treated controls (approximately five nodules/adult). Increasing dietary dexketoprofen trometamol concentrations decreased nodulation (by 12-fold at the highest concentration) and increased PO reactions (by approximately 3-fold at the highest concentration) to BHSV-1 injection. Compared with control adults, adults orally fed on the lowest DT concentration (0.001 %) significantly increased PO activity (1.22 ± 0.23-2.74 ± 0.31 unit/min/mg protein) while nodules significantly decreased (43.19 ± 4.26-17.84 ± 2.19) in response to virus infections. These findings suggest that eicosanoid biosynthesis, at least in the context of prostaglandins (PGs) formed by COX-1, mediates nodulation reactions and PO activation in response to viral infection in adults of this endoparasitoid. This is the first demonstration that the immune response of P. turionellae adults to viral pathogens is modulated by DT, which initiates haemolymph PO activation.

Linc20486 promotes BmCPV replication through inhibiting the transcription of AGO2 and Dicers

The silkworm holds pivotal economic importance, serving not only as a primary source of silk but also as a prominent model organism in scientific research. Nonetheless, silkworm farming remains vulnerable to diverse factors, with viral infections posing the gravest threat to the sericulture industry. Among these, the Bombyx mori cytoplasmic polyhedrosis virus (BmCPV), a member of the Reoviridae family and the cytoplasmic polyhedrosis virus genus, emerges as a significant pathogen in silkworm production. BmCPV infection primarily induces midgut sepsis in silkworms, spreads rapidly, and can inflict substantial economic losses on sericulture production. Presently, effective strategies for preventing and treating BmCPV infections are lacking. Long non-coding RNA (lncRNA) constitutes a class of RNA molecules with transcripts exceeding 200 nt, playing a crucial role in mediating the interplay between pathogens and host cells. Investigation through high-throughput technology has unveiled that BmCPV infection markedly upregulates the expression of Linc20486. This observation suggests potential involvement of Linc20486 in regulating virus replication. Indeed, as anticipated, knockdown of Linc20486 in cells profoundly impedes BmCPV replication, whereas overexpression significantly enhances virus propagation. To probe into the mechanism underlying Linc20486's impact on virus replication, its effects on autophagy, innate immunity, and RNAi-related pathways were scrutinized. The findings revealed that Linc20486 exerts significant influence on the expression of RNAi pathway-related genes, such as Dicer1, Dicer2 and AGO2. This discovery holds promise for unveiling novel avenues to comprehend and combat BmCPV infections in silkworms.

Necrophages and necrophiles: a review of their antibacterial defenses and biotechnological potential

With antibiotic resistance on the rise, there is an urgent need for new antibacterial drugs and products to treat or prevent infection. Many such products in current use, for example human and veterinary antibiotics and antimicrobial food preservatives, were discovered and developed from nature. Natural selection acts on all living organisms and the presence of bacterial competitors or pathogens in an environment can favor the evolution of antibacterial adaptations. In this review, we ask if vultures, blow flies and other carrion users might be a good starting point for antibacterial discovery based on the selection pressure they are under from bacterial disease. Dietary details are catalogued for over 600 of these species, bacterial pathogens associated with the diets are described, and an overview of the antibacterial defenses contributing to disease protection is given. Biotechnological applications for these defenses are then discussed, together with challenges facing developers and possible solutions. Examples include use of (a) the antimicrobial peptide (AMP) gene sarcotoxin IA to improve crop resistance to bacterial disease, (b) peptide antibiotics such as serrawettin W2 as antibacterial drug leads, (c) lectins for targeted drug delivery, (d) bioconversion-generated chitin as an antibacterial biomaterial, (e) bacteriocins as antibacterial food preservatives and (f) mutualistic microbiota bacteria as alternatives to antibiotics in animal feed. We show that carrion users encounter a diverse range of bacterial pathogens through their diets and interactions, have evolved many antibacterial defenses, and are a promising source of genes, molecules, and microbes for medical, agricultural, and food industry product development.

Effect of Bioactive Peptides on Gut Microbiota and Their Relations to Human Health

Bioactive peptides derived from both exogenous and endogenous origins have been studied extensively to use their beneficial effects in humans and animals. Bioactive peptides exhibit beneficial bodily functions and contribute to a healthy gastrointestinal system by influencing barrier functions, immune responses, and gut microbiota. Gut microbiota is a diverse microbial community that significantly influences the overall well-being and homeostasis of the body. Factors such as diet, age, lifestyle, medication, and environmental circumstances can affect the composition and diversity of the gut microbiota. The disturbances or imbalances in the gut microbiota have been associated with various health problems. The interplays between bioactive peptides and gut microbiota are not fully understood, but bioactive peptides hold promise as modulators of the gut microbiota to promote gut health. Almost all the bioactive research on human health, including the development of therapeutics and nutritional interventions, uses cell culture, even though their direct biofunctional activities can only occur when absorbed in the intestine and into the blood system. This review focuses on the current understanding of bioactive peptides in gut microbiota and their impact and mechanisms on gut and human health. The novelty of this review lies in its comprehensive analysis of the multifaceted interactions between bioactive peptides and gut microbiota, integrating knowledge from diverse disciplines between microbiology and nutrition. By elucidating the underlying mechanisms and identifying current research gaps, this review offers an outlook on the potential of bioactive peptides in promoting gut health and shaping future therapeutic and nutritional interventions.

Immunometabolic crosstalk in Aedes fluviatilis and Wolbachia pipientis symbiosis

Wolbachia pipientis is a maternally transmitted symbiotic bacterium that mainly colonizes arthropods, potentially affecting different aspects of the host's physiology, e.g., reproduction, immunity, and metabolism. It has been shown that Wolbachia modulates glycogen metabolism in mosquito Aedes fluviatilis (Ae. fluviatilis). Glycogen synthesis is controlled by the enzyme GSK3, which is also involved in immune responses in both vertebrate and invertebrate organisms. Here we investigated the mechanisms behind immune changes mediated by glycogen synthase kinase β (GSK3β) in the symbiosis between Ae. fluviatilis and W. pipientis using a GSK3β inhibitor or RNAi-mediated gene silencing. GSK3β inhibition or knockdown increased glycogen content and Wolbachia population, together with a reduction in Relish2 and gambicin transcripts. Furthermore, knockdown of Relish2 or Caspar revealed that the immunodeficiency pathway acts to control Wolbachia numbers in the host. In conclusion, we describe for the first time the involvement of GSK3β in Ae. fluviatilis immune response, acting to control the Wolbachia endosymbiotic population.

Peptides with Antimicrobial Activity in the Saliva of the Malaria Vector Anopheles coluzzii

Mosquito saliva plays a crucial physiological role in both sugar and blood feeding by helping sugar digestion and exerting antihemostatic functions. During meal acquisition, mosquitoes are exposed to the internalization of external microbes. Since mosquitoes reingest significant amounts of saliva during feeding, we hypothesized that salivary antimicrobial components may participate in the protection of mouthparts, the crop, and the gut by inhibiting bacterial growth. To identify novel potential antimicrobials from mosquito saliva, we selected 11 candidates from Anopheles coluzzii salivary transcriptomic datasets and obtained them either using a cell-free transcription/translation expression system or, when feasible, via chemical synthesis. Hyp6.2 and hyp13, which were predicted to be produced as propeptides and cleaved in shorter mature forms, showed the most interesting results in bacterial growth inhibition assays. Hyp6.2 (putative mature form, 35 amino acid residues) significantly inhibited the growth of Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli and Serratia marcescens) bacteria. Hyp13 (short form, 19 amino acid residues) dose-dependently inhibited E. coli and S. marcescens growth, inducing membrane disruption in both Gram-positive and Gram-negative bacteria as indicated with scanning electron microscopy. In conclusion, we identified two A. coluzzii salivary peptides inhibiting Gram-positive and Gram-negative bacteria growth and possibly contributing to the protection of mosquito mouthparts and digestive tracts from microbial infection during and/or after feeding.

When the microbiome shapes the host: immune evolution implications for infectious disease

The microbiome includes both 'mutualist' and 'pathogen' microbes, regulated by the same innate immune architecture. A major question has therefore been: how do hosts prevent pathogenic infections while maintaining beneficial microbes? One idea suggests hosts can selectively activate innate immunity upon pathogenic infection, but not mutualist colonization. Another idea posits that hosts can selectively attack pathogens, but not mutualists. Here I review evolutionary principles of microbe recognition and immune activation, and reflect on newly observed immune effector-microbe specificity perhaps supporting the latter idea. Recent work in Drosophila has found a surprising importance for single antimicrobial peptides in combatting specific ecologically relevant microbes. The developing picture suggests these effectors have evolved for this purpose. Other defence responses like reactive oxygen species bursts can also be uniquely effective against specific microbes. Signals in other model systems including nematodes, Hydra, oysters, and mammals, suggest that effector-microbe specificity may be a fundamental principle of host-pathogen interactions. I propose this effector-microbe specificity stems from weaknesses of the microbes themselves: if microbes have intrinsic weaknesses, hosts can evolve effectors that exploit those weaknesses. I define this host-microbe relationship as 'the Achilles principle of immune evolution'. Incorporating this view helps interpret why some host-microbe interactions develop in a coevolutionary framework (e.g. Red Queen dynamics), or as a one-sided evolutionary response. This clarification should be valuable to better understand the principles behind host susceptibilities to infectious diseases. This article is part of the theme issue 'Sculpting the microbiome: how host factors determine and respond to microbial colonization'.

Insect Antimicrobial Peptides as Guardians of Immunity and Beyond: A Review

Antimicrobial peptides (AMPs), as immune effectors synthesized by a variety of organisms, not only constitute a robust defense mechanism against a broad spectrum of pathogens in the host but also show promising applications as effective antimicrobial agents. Notably, insects are significant reservoirs of natural AMPs. However, the complex array of variations in types, quantities, antimicrobial activities, and production pathways of AMPs, as well as evolution of AMPs across insect species, presents a significant challenge for immunity system understanding and AMP applications. This review covers insect AMP discoveries, classification, common properties, and mechanisms of action. Additionally, the types, quantities, and activities of immune-related AMPs in each model insect are also summarized. We conducted the first comprehensive investigation into the diversity, distribution, and evolution of 20 types of AMPs in model insects, employing phylogenetic analysis to describe their evolutionary relationships and shed light on conserved and distinctive AMP families. Furthermore, we summarize the regulatory pathways of AMP production through classical signaling pathways and additional pathways associated with Nitric Oxide, insulin-like signaling, and hormones. This review advances our understanding of AMPs as guardians in insect immunity systems and unlocks a gateway to insect AMP resources, facilitating the use of AMPs to address food safety concerns.

Molecular characterization and antimicrobial activity of cecropin family in Hermetia illucens

Antimicrobial peptides are potential alternatives to traditional antibiotics in the face of increasing bacterial resistance. Insects possess many antimicrobial peptides and have become a valuable source of novel and highly effective antimicrobial peptides. Hermetia illucens as a resource insect, for example, has the highest number of antimicrobial peptides of any dipteran. However, most antimicrobial peptides, especially cecropin, have not been comprehensively identified and have not been evaluated for their antimicrobial ability. In this study, we analyzed the localization and gene structure of 33 cecropin molecules in the H. illucens genome and evaluated their activity against common human pathogens. The results showed that 32 cecropin molecules were concentrated on 1 chromosome, most with 2 exons. More importantly, most of the cecropins had a good antibacterial effect against Gram-negative bacteria, and were not hemolytic. The minimum inhibitory concentration (MIC) of the cecropin designated H3 against E. coli was 4 μg/mL. The toxicity, killing time kinetics, and anti-biofilm activity of H3 were further investigated and confirmed its antimicrobial ability. Overall, H3 is a potential candidate for the development of new antimicrobials to treat severe infections caused by Gram-negative pathogens such as E. coli.

Single Deletion Unmasks Hidden Anti-Gram-Negative Bacterial Activity of an Insect Defensin-Derived Peptide

Insect defensins are a large family of antimicrobial peptides primarily active against Gram-positive bacteria. Here, we explore their hidden anti-Gram-negative bacterial potential via a nature-guided strategy inspired by natural deletion variants of Drosophila defensins. Referring to these variants, we deleted the equivalent region of an insect defensin with the first cysteine-containing N-terminus, and the last three cysteine-containing C-terminal regions remained. This 15-mer peptide exhibits low solubility and specifically targets Gram-positive bacteria. Further deletion of alanine-9 remarkably improves its solubility, unmasks its hidden anti-Gram-negative bacterial activity, and alters its states in different environments. Intriguingly, compared with the oxidized form, the 14-mer reduced peptide shows increased activity on Gram-positive and Gram-negative bacteria through a membrane-disruptive mechanism. The broad-spectrum activity and tolerance to high-salt environments and human serum, together with no toxicity to mammalian or human cells, make it a promising candidate for the design of new peptide antibiotics against Gram-negative bacterial infections.

Diversity and Mechanisms of Action of Plant, Animal, and Human Antimicrobial Peptides

Antimicrobial peptides (AMPs) are usually made up of fewer than 100 amino acid residues. They are found in many living organisms and are an important factor in those organisms' innate immune systems. AMPs can be extracted from various living sources, including bacteria, plants, animals, and even humans. They are usually cationic peptides with an amphiphilic structure, which allows them to easily bind and interact with the cellular membranes of viruses, bacteria, fungi, and other pathogens. They can act against both Gram-negative and Gram-positive pathogens and have various modes of action against them. Some attack the pathogens' membranes, while others target their intracellular organelles, as well as their nucleic acids, proteins, and metabolic pathways. A crucial area of AMP use is related to their ability to help with emerging antibiotic resistance: some AMPs are active against resistant strains and are susceptible to peptide engineering. This review considers AMPs from three key sources-plants, animals, and humans-as well as their modes of action and some AMP sequences.

Insights into midgut cell types and their crucial role in antiviral immunity in the lepidopteran model Bombyx mori

The midgut, a vital component of the digestive system in arthropods, serves as an interface between ingested food and the insect's physiology, playing a pivotal role in nutrient absorption and immune defense mechanisms. Distinct cell types, including columnar, enteroendocrine, goblet and regenerative cells, comprise the midgut in insects and contribute to its robust immune response. Enterocytes/columnar cells, the primary absorptive cells, facilitate the immune response through enzyme secretions, while regenerative cells play a crucial role in maintaining midgut integrity by continuously replenishing damaged cells and maintaining the continuity of the immune defense. The peritrophic membrane is vital to the insect's innate immunity, shielding the midgut from pathogens and abrasive food particles. Midgut juice, a mixture of digestive enzymes and antimicrobial factors, further contributes to the insect's immune defense, helping the insect to combat invading pathogens and regulate the midgut microbial community. The cutting-edge single-cell transcriptomics also unveiled previously unrecognized subpopulations within the insect midgut cells and elucidated the striking similarities between the gastrointestinal tracts of insects and higher mammals. Understanding the intricate interplay between midgut cell types provides valuable insights into insect immunity. This review provides a solid foundation for unraveling the complex roles of the midgut, not only in digestion but also in immunity. Moreover, this review will discuss the novel immune strategies led by the midgut employed by insects to combat invading pathogens, ultimately contributing to the broader understanding of insect physiology and defense mechanisms.

In Vitro Assessment of the Anti-Proliferative and Anti-Viability Effects of Salivary Gland Extracts from Hyalomma ticks (Acari: Ixodidae) on Human Colorectal Cancer Cells

Background

The saliva and salivary glands of ticks possess a wide range of immuno-pharmacologically active molecules that effectively modulate the activity of enzymes, antibodies, and amines that have a role in different biological processes. Derived components from saliva and salivary glands of hard ticks Ixodidae have been characterized as potential natural sources for discovering promising anti-cancer drug candidates.

Methods

The anti-cancer activity of salivary gland extracts (SGEs) from Hyalomma anatolicum, Hyalomma dromedarii, Hyalomma marginatum, and Hyalomma schulzei was assessed. MTT assays and flow cytometry were done on the HT-29 colorectal cancer cell line to evaluate the anti-viability and proliferative inhibition.

Results

Based on the MTT assay results, the SGEs from Hy. dromedarii had the highest and lowest substantial anti-viability effects on the HT-29 cancer cell and human foreskin fibroblast (HFF) normal cell, respectively. The cytometric assessment revealed a significant increase in the apoptosis and necrosis ratio of the HT-29 cancer cells after treatment with Hy. dromedarii SGEs.

Conclusion

The results demonstrated that Hy. dromedarii SGEs have significant anti-proliferative, anti-viability, and apoptotic potential. The result of this study suggests that Hy. dromedarii SGEs is an appropriate candidate for further investigations to identify and purify the mechanisms and molecules involved in the anti-cancer activity of the SGEs.

Screening and Functional Analyses of Novel Cecropins from Insect Transcriptome

Antibiotic resistance is a significant and growing threat to global public health. However, antimicrobial peptides (AMPs) have shown promise as they exhibit a broad spectrum of antibacterial activities with low potential for resistance development. Insects, which inhabit a wide range of environments and are incredibly diverse, remain largely unexplored as a source of novel AMPs. To address this, we conducted a screening of the representative transcriptomes from the 1000 Insect Transcriptome Evolution (1KITE) dataset, focusing on the homologous reference genes of Cecropins, the first identified AMPs in insects known for its high efficiency. Our analysis identified 108 Cecropin genes from 105 insect transcriptomes, covering all major hexapod lineages. We validated the gene sequences and synthesized mature peptides for three identified Cecropin genes. Through minimal inhibition concentration and agar diffusion assays, we confirmed that these peptides exhibited antimicrobial activities against Gram-negative bacteria. Similar to the known Cecropin, the three Cecropins adopted an alpha-helical conformation in membrane-like environments, efficiently disrupting bacterial membranes through permeabilization. Importantly, none of the three Cecropins demonstrated cytotoxicity in erythrocyte hemolysis tests, suggesting their safety in real-world applications. Overall, this newly developed methodology provides a high-throughput bioinformatic pipeline for the discovery of AMP, taking advantage of the expanding genomic resources available for diverse organisms.

Antimicrobial Peptides: The Production of Novel Peptide-Based Therapeutics in Plant Systems

The increased prevalence of antibiotic resistance is alarming and has a significant impact on the economies of emerging and underdeveloped nations. The redundancy of antibiotic discovery platforms (ADPs) and injudicious use of conventional antibiotics has severely impacted millions, across the globe. Potent antimicrobials from biological sources have been extensively explored as a ray of hope to counter the growing menace of antibiotic resistance in the population. Antimicrobial peptides (AMPs) are gaining momentum as powerful antimicrobial therapies to combat drug-resistant bacterial strains. The tremendous therapeutic potential of natural and synthesized AMPs as novel and potent antimicrobials is highlighted by their unique mode of action, as exemplified by multiple research initiatives. Recent advances and developments in antimicrobial discovery and research have increased our understanding of the structure, characteristics, and function of AMPs; nevertheless, knowledge gaps still need to be addressed before these therapeutic options can be fully exploited. This thematic article provides a comprehensive insight into the potential of AMPs as potent arsenals to counter drug-resistant pathogens, a historical overview and recent advances, and their efficient production in plants, defining novel upcoming trends in drug discovery and research. The advances in synthetic biology and plant-based expression systems for AMP production have defined new paradigms in the efficient production of potent antimicrobials in plant systems, a prospective approach to countering drug-resistant pathogens.

Insect-pathogen crosstalk and the cellular-molecular mechanisms of insect immunity: uncovering the underlying signaling pathways and immune regulatory function of non-coding RNAs

Multicellular organisms are constantly subjected to pathogens that might be harmful. Although insects lack an adaptive immune system, they possess highly effective anti-infective mechanisms. Bacterial phagocytosis and parasite encapsulation are some forms of cellular responses. Insects often defend themselves against infections through a humoral response. This phenomenon includes the secretion of antimicrobial peptides into the hemolymph. Specific receptors for detecting infection are required for the recognition of foreign pathogens such as the proteins that recognize glucans and peptidoglycans, together referred to as PGRPs and βGRPs. Activation of these receptors leads to the stimulation of signaling pathways which further activates the genes encoding for antimicrobial peptides. Some instances of such pathways are the JAK-STAT, Imd, and Toll. The host immune response that frequently accompanies infections has, however, been circumvented by diseases, which may have assisted insects evolve their own complicated immune systems. The role of ncRNAs in insect immunology has been discussed in several notable studies and reviews. This paper examines the most recent research on the immune regulatory function of ncRNAs during insect-pathogen crosstalk, including insect- and pathogen-encoded miRNAs and lncRNAs, and provides an overview of the important insect signaling pathways and effector mechanisms activated by diverse pathogen invaders.

The Effects of Diet on the Immune Responses of the Oriental Armyworm Mythimna separata

Nutrients can greatly affect host immune defenses against infection. Possessing a simple immune system, insects have been widely used as models to address the relationships between nutrition and immunity. The effects of high versus low protein-to-carbohydrate ratio (P:C) diets on insect immune responses vary in different studies. To reveal the dietary manipulation of immune responses in the polyphagous agricultural pest oriental armyworm, we examined immune gene expression, phenoloxidase (PO) activity, and phagocytosis to investigate the immune traits of bacteria-challenged oriental armyworms, which were fed different P:C ratio diets. We found the oriental armyworms that were fed a 35:7 (P:C) diet showed higher phenoloxidase (PO) activity and stronger melanization, and those reared on a 28:14 (P:C) diet showed higher antimicrobial activity. However, different P:C diets had no apparent effect on the hemocyte number and phagocytosis. These results overall indicate that high P:C diets differently optimize humoral immune defense responses in oriental armyworms, i.e., PO-mediated melanization and antimicrobial peptide synthesis in response to bacteria challenge.

The genetic basis of variation in immune defense against Lysinibacillus fusiformis infection in Drosophila melanogaster

The genetic causes of phenotypic variation often differ depending on the population examined, particularly if the populations were founded by relatively small numbers of genotypes. Similarly, the genetic causes of phenotypic variation among similar traits (resistance to different xenobiotic compounds or pathogens) may also be completely different or only partially overlapping. Differences in genetic causes for variation in the same trait among populations suggests context dependence for how selection acts on those traits. Similarities in the genetic causes of variation for different traits, on the other hand, suggests pleiotropy which would also influence how natural selection shapes variation in a trait. We characterized immune defense against a natural Drosophila pathogen, the Gram-positive bacterium Lysinibacillus fusiformis, in three different populations and found almost no overlap in the genetic architecture of variation in survival post infection. However, when comparing our results to a similar experiment with the fungal pathogen, B. bassiana, we found a convincing shared QTL peak for both pathogens. This peak contains the Bomanin cluster of Drosophila immune effectors. Loss of function mutants and RNAi knockdown experiments confirms a role of some of these genes in immune defense against both pathogens. This suggests that natural selection may act on the entire cluster of Bomanin genes (and the linked region under the QTL) or specific peptides for specific pathogens.

Antimicrobial Peptides in Infectious Diseases and Beyond-A Narrative Review

Despite recent medical research and clinical practice developments, the development of antimicrobial resistance (AMR) significantly limits therapeutics for infectious diseases. Thus, novel treatments for infectious diseases, especially in this era of increasing AMR, are urgently needed. There is ongoing research on non-classical therapies for infectious diseases utilizing alternative antimicrobial mechanisms to fight pathogens, such as bacteriophages or antimicrobial peptides (AMPs). AMPs are evolutionarily conserved molecules naturally produced by several organisms, such as plants, insects, marine organisms, and mammals, aiming to protect the host by fighting pathogenic microorganisms. There is ongoing research regarding developing AMPs for clinical use in infectious diseases. Moreover, AMPs have several other non-medical applications in the food industry, such as preservatives, animal husbandry, plant protection, and aquaculture. This review focuses on AMPs, their origins, biology, structure, mechanisms of action, non-medical applications, and clinical applications in infectious diseases.

Antimicrobial peptide moricin induces ROS mediated caspase-dependent apoptosis in human triple-negative breast cancer via suppression of notch pathway

BACKGROUND

Breast cancer is the world's most prevalent cancer among women. Microorganisms have been the richest source of antibiotics as well as anticancer drugs. Moricin peptides have shown antibacterial properties; however, the anticancer potential and mechanistic insights into moricin peptide-induced cancer cell death have not yet been explored.

METHODS

An investigation through in silico analysis, analytical methods (Reverse Phase-High Performance Liquid Chromatography (RP-HPLC), mass spectroscopy (MS), circular dichroism (CD), and in vitro studies, has been carried out to delineate the mechanism(s) of moricin-induced cancer cell death. An in-silico analysis was performed to predict the anticancer potential of moricin in cancer cells using Anti CP and ACP servers based on a support vector machine (SVM). Molecular docking was performed to predict the binding interaction between moricin and peptide-related cancer signaling pathway(s) through the HawkDOCK web server. Further, in vitro anticancer activity of moricin was performed against MDA-MB-231 cells.

RESULTS

In silico observation revealed that moricin is a potential anticancer peptide, and protein-protein docking showed a strong binding interaction between moricin and signaling proteins. CD showed a predominant helical structure of moricin, and the MS result determined the observed molecular weight of moricin is 4544 Da. An in vitro study showed that moricin exposure to MDA-MB-231 cells caused dose dependent inhibition of cell viability with a high generation of reactive oxygen species (ROS). Molecular study revealed that moricin exposure caused downregulation in the expression of Notch-1, NF-ƙB and Bcl2 proteins while upregulating p53, Bax, caspase 3, and caspase 9, which results in caspase-dependent cell death in MDA-MB-231 cells.

CONCLUSIONS

In conclusion, this study reveals the anticancer potential and underlying mechanism of moricin peptide-induced cell death in triple negative cancer cells, which could be used in the development of an anticancer drug.

Insect Antimicrobial Peptides: Advancements, Enhancements and New Challenges

Several insects are known as vectors of a wide range of animal and human pathogens causing various diseases. However, they are also a source of different substances, such as the Antimicrobial Peptides (AMPs), which can be employed in the development of natural bioactive compounds for medical, veterinary and agricultural applications. It is well known that AMP activity, in contrast to most classical antibiotics, does not lead to the development of natural bacterial resistance, or at least the frequency of resistance is considered to be low. Therefore, there is a strong interest in assessing the efficacy of the various peptides known to date, identifying new compounds and evaluating possible solutions in order to increase their production. Moreover, implementing AMP modulation in insect rearing could preserve insect health in large-scale production. This review describes the current knowledge on insect AMPs, presenting the validated ones for the different insect orders. A brief description of their mechanism of action is reported with focus on proposed applications. The possible effects of insect diet on AMP translation and synthesis have been discussed.

Diversity of Antimicrobial Peptides in Silkworm

Antimicrobial resistance is a phenomenon that the present-day world is witnessing that poses a serious threat to global health. The decline in the development of novel therapeutics over the last couple of decades has exacerbated the situation further. In this scenario, the pursuit of new alternative therapeutics to commonly used antibiotics has gained predominance amongst researchers across the world. Antimicrobial peptides (AMPs) from natural sources have drawn significant interest in the recent years as promising pharmacological substitutes over the conventional antibiotics. The most notable advantage of AMPs is that microorganisms cannot develop resistance to them. Insects represent one of the potential sources of AMPs, which are synthesized as part of an innate immune defence against invading pathogens. AMPs from different insects have been extensively studied, and silkworm is one of them. Diverse classes of AMPs (including attacins, cecropins, defensins, enbocins, gloverins, lebocins and moricins) were identified from silkworm that exhibit antimicrobial property against bacteria, fungi and viruses, indicating their potential therapeutic benefits. This review briefs about the immune responses of silkworm to invading pathogens, the isolation of AMPs from silkworms, AMPs reported in silkworms and their activity against various microorganisms.

Heterologous Expression and Bioactivity Determination of Monochamus alternatus Antibacterial Peptide Gene in Komagataella phaffii (Pichia pastoris)

Insects have evolved to form a variety of complex natural compounds to prevent pathogen infection in the process of a long-term attack and defense game with various pathogens in nature. Antimicrobial Peptides (AMPs) are important effector molecules of the insect immune response to the pathogen invasion involved in bacteria, fungi, viruses and nematodes. The discovery and creation of new nematicides from these natural compounds is a key path to pest control. A total of 11 AMPs from Monochamus alternatus were classified into 3 categories, including Attacin, Cecropin and Defensin. Four AMP genes were successfully expressed by Komagataella phaffii KM71. The bioassay results showed that the exogenous expressed AMPs represented antimicrobial activity against Serratia (G−), Bacillus thuringiensis (G+) and Beauveria bassiana and high nematicide activity against Bursaphelenchus xylophilus. All four purified AMPs’ protein against B. xylophilus reached LC50 at 3 h (LC50 = 0.19 mg·mL−1 of MaltAtt-1, LC50 = 0.20 mg·mL−1 of MaltAtt-2 and MaltCec-2, LC50 = 0.25 mg·mL−1 of MaltDef-1). Furthermore, the AMPs could cause significant reduction of the thrashing frequency and egg hatching rate, and the deformation or fracture of the body wall of B. xylophilus. Therefore, this study is a foundation for further study of insect biological control and provides a theoretical basis for the research and development of new insecticidal pesticides.

Diversity of the Antimicrobial Peptide Genes in Collembola

Multidrug-resistant bacteria are a current health crisis threatening the world's population, and scientists are looking for new drugs to combat them. Antimicrobial peptides (AMPs), which are part of the organism's innate immune system, are a promising new drug class as they can disrupt bacterial cell membranes. This study explored antimicrobial peptide genes in collembola, a non-insect hexapod lineage that has survived in microbe-rich habitats for millions of years, and their antimicrobial peptides have not been thoroughly investigated. We used in silico analysis (homology-based gene identification, physicochemical and antimicrobial property prediction) to identify AMP genes from the genomes and transcriptomes of five collembola representing three main suborders: Entomobryomorpha (Orchesella cincta, Sinella curviseta), Poduromorpha (Holacanthella duospinosa, Anurida maritima), and Symphypleona (Sminthurus viridis). We identified 45 genes belonging to five AMP families, including (a) cysteine-rich peptides: diapausin, defensin, and Alo; (b) linear α-helical peptide without cysteine: cecropin; (c) glycine-rich peptide: diptericin. Frequent gene gains and losses were observed in their evolution. Based on the functions of their orthologs in insects, these AMPs potentially have broad activity against bacteria, fungi, and viruses. This study provides candidate collembolan AMPs for further functional analysis that could lead to medicinal use.

Multiple mosquito AMPs are needed to potentiate their antifungal effect against entomopathogenic fungi

Mosquito resistance to microbial infections, including fungal entomopathogens that are selected for mosquito control, depend on a range of antimicrobial effectors, among them antimicrobial peptides (AMPs). These short peptides, along the antimicrobial effector lysozyme, act by disrupting the microbial cell membrane or by interfering with microbial physiological processes. While the induction of AMPs and lysozyme during fungal entomopathogenic infections have been reported, their contribution to the mosquito antifungal response has not been evaluated. In this study, we assessed the induction of Ae. aegypti AMPs and lysozyme genes at two points of infection and against distinct entomopathogenic fungi. Our results indicate that fungal infection elicits the expression of cecropin, defensin, diptericin, holotricin, and lysozyme, but do not affect those of attacin or gambicin. We further evaluated the role of these antimicrobial effectors via RNAi-based depletion of select AMPs during challenges with two entomopathogenic fungi. Our results reveal that AMPs and lysozyme are critical to the antifungal response, acting in concert, rather than individually, to potentiate their antimicrobial effect against entomopathogenic fungi. This study further contributes to a better understanding of the mechanisms that confer resistance to entomopathogenic fungi in an important mosquito vector.

Sublethal toxicity, transgenerational effects, and transcriptome expression of the neonicotinoid pesticide cycloxaprid on demographic fitness of Coccinella septempunctata

Evaluating side effects of new neonicotinoids in terms of sublethal doses and transcriptome expression is a crucial but challenging part of integrated pest management (IPM) approaches. To this end, a study of lethal and sublethal effects on Coccinella septempunctata larvae was conducted, and an age-stage, two-sex life table procedure was performed to investigate life-table parameters. Cycloxaprid (CYC) was shown to have adverse effects on survival, development, total longevity, reproductive capacity, and predation ability in C. septempunctata. In addition, demographic growth parameters of the F1 generation such as net reproductive rate, and the intrinsic and finite rates of increase were significantly decreased under sublethal dosage LR₃₀ (1.91 g ai/hm²). These results demonstrated that the population growth of C. septempunctata was impacted by a sublethal dosage of CYC. For transcriptome expression, 544 up- and 338 down-regulated significantly differentially expressed genes (DEGs), were observed between LR₃₀ treatment and control groups. Moreover, pathways related to metabolism of retinol, carcinogenesis, biosynthesis of steroid hormone, P450 metabolism, and metabolism of xenobiotics were identified in KEGG pathway analysis. Ten DEGs were chosen and confirmed with quantitative real-time PCR analysis. Based on these findings, CYC should be considered as a component of IPM strategies in the field.

Emerging Evidence on Tenebrio molitor Immunity: A Focus on Gene Expression Involved in Microbial Infection for Host-Pathogen Interaction Studies

In recent years, the scientific community's interest in T. molitor as an insect model to investigate immunity and host-pathogen interactions has considerably increased. The reasons for this growing interest could be explained by the peculiar features of this beetle, which offers various advantages compared to other invertebrates models commonly used in laboratory studies. Thus, this review aimed at providing a broad view of the T. molitor immune system in light of the new scientific evidence on the developmental/tissue-specific gene expression studies related to microbial infection. In addition to the well-known cellular component and humoral response process, several studies investigating the factors associated with T. molitor immune response or deepening of those already known have been reported. However, various aspects remain still less understood, namely the possible crosstalk between the immune deficiency protein and Toll pathways and the role exerted by T. molitor apolipoprotein III in the expression of the antimicrobial peptides. Therefore, further research is required for T. molitor to be recommended as an alternative insect model for pathogen-host interaction and immunity studies.

In Silico Identification of Potential Insect Peptides against Biofilm-Producing Staphylococcus aureus

Biofilm-producing Staphylococcus aureus (SA) strains are frequently found in medical environments, from surgical/ wound sites, medical devices. These biofilms reduce the efficacy of applied antibiotics during the treatment of several infections, such as cystic fibrosis, endocarditis, or urinary tract infections. Thus, the development of potential therapeutic agents to destroy the extra protective biofilm layers or to inhibit the biofilm-producing enzymes is urgently needed. Advanced and cost-effective bioinformatics tools are advantageous in locating and speeding up the selection of antibiofilm candidates. Based on the potential drug characteristics, we have selected one-hundred thirty-three antibacterial peptides derived from insects to assess for their antibiofilm potency via molecular docking against five putative biofilm formation and regulated target enzymes: the staphylococcal accessory regulator A or SarA (PDB ID: 2FRH), 4,4'-diapophytoene synthase or CrtM (PDB ID: 2ZCQ), clumping factor A or ClfA (PDB ID: 1N67) and serine-aspartate repeat protein C or SdrC (PDB ID: 6LXH) and sortase A or SrtA (PDB ID: 1T2W) of SA bacterium. In this study, molecular docking was performed using HPEPDOCK and HDOCK servers, and molecular interactions were examined using BIOVIA Discovery Studio Visualizer-2019. The docking score (kcal/mol) range of five promising antibiofilm peptides against five targets was recorded as follows: diptericin A (-215.52 to -303.31), defensin (-201.11 to -301.92), imcroporin (-212.08 to -287.64), mucroporin (-228.72 to -286.76), apidaecin II (-203.90 to -280.20). Among these five, imcroporin and mucroporin were 13 % each, while defensin contained only 1 % of positive net charged residues (Arg+Lys) projected through ProtParam and NetWheels tools. Similarly, imcroporin, mucroporin and apidaecin II were 50 %, while defensin carried 21.05 % of hydrophobic residues predicted by the tool PEPTIDE. 2.0. Most of the peptides exhibited potential characteristics to inhibit S. aureus-biofilm formation via disrupting the cell membrane and cytoplasmic integrity. In summary, the proposed hypothesis can be considered a cost-effective platform for selecting the most promising bioactive drug candidates within a limited timeframe with a greater chance of success in experimental and clinical studies.

A new antimicrobial peptide, Pentatomicin, from the stinkbug Plautia stali

Antimicrobial peptides (AMPs) play crucial roles in the innate immunity of diverse organisms, which exhibit remarkable diversity in size, structural property and antimicrobial spectrum. Here, we describe a new AMP, named Pentatomicin, from the stinkbug Plautia stali (Hemiptera: Pentatomidae). Orthologous nucleotide sequences of Pentatomicin were present in stinkbugs and beetles but not in other insect groups. Notably, orthologous sequences were also detected from a horseshoe crab, cyanobacteria and proteobacteria, suggesting the possibility of inter-domain horizontal gene transfers of Pentatomicin and allied protein genes. The recombinant protein of Pentatomicin was effective against an array of Gram-positive bacteria but not against Gram-negative bacteria. Upon septic shock, the expression of Pentatomicin drastically increased in a manner similar to other AMPs. On the other hand, unlike other AMPs, mock and saline injections increased the expression of Pentatomicin. RNAi-mediated downregulation of Imd pathway genes (Imd and Relish) and Toll pathway genes (MyD88 and Dorsal) revealed that the expression of Pentatomicin is under the control of Toll pathway. Being consistent with in vitro effectiveness of the recombinant protein, adult insects injected with dsRNA of Pentatomicin exhibited higher vulnerability to Gram-positive Staphylococcus aureus than to Gram-negative Escherichia coli. We discovered high levels of Pentatomicin expression in eggs, which is atypical of other AMPs and suggestive of its biological functioning in eggs. Contrary to the expectation, however, RNAi-mediated downregulation of Pentatomicin did not affect normal embryonic development of P. stali. Moreover, the downregulation of Pentatomicin in eggs did not affect vertical symbiont transmission to the offspring even under heavily contaminated conditions, which refuted our expectation that the antimicrobial activity of Pentatomicin may contribute to egg surface-mediated symbiont transmission by suppressing microbial contaminants.

Antimicrobial peptides: features, applications and the potential use against covid-19

BACKGROUND

Antimicrobial peptides (AMPs) are a diverse class of molecules that represent a vital part of innate immunity. AMPs are evolutionarily conserved molecules that exhibit structural and functional diversity. They provide a possible solution to the antibiotic-resistance crisis.

MAIN TEXT

These small cationic peptides can target bacteria, fungi, and viruses, as well as cancer cells. Their unique action mechanisms, rare antibiotic-resistant variants, broad-spectrum activity, low toxicity, and high specificity encourage pharmaceutical industries to conduct clinical trials to develop them as therapeutic drugs. The rapid development of computer-assisted strategies accelerated the identification of AMPs. The Antimicrobial Peptide Database (APD) so far contains 3324 AMPs from different sources. In addition to their applications in different fields, some AMPs demonstrated the potential to combat COVID-19, and hinder viral infectivity in diverse ways.

CONCLUSIONS

This review provides a brief history of AMPs and their features, including classification, evolution, sources and mechanisms of action, biosynthesis pathway, and identification techniques. Furthermore, their different applications, challenges to clinical applications, and their potential use against COVID-19 are presented.

Characterization of Recombinant Antimicrobial Peptide BMGlv2 Heterologously Expressed in Trichoderma reesei

Antimicrobial peptides (AMPs) serve as alternative candidates for antibiotics and have attracted the attention of a wide range of industries for various purposes, including the prevention and treatment of piglet diarrhea in the swine industry. Escherichia coli, Salmonella, and Clostridium perfringens are the most common pathogens causing piglet diarrhea. In this study, the antimicrobial peptide gloverin2 (BMGlv2), derived from Bombyx mandarina, was explored to determine the efficient prevention effect on bacterial piglet diarrhea. BMGlv2 was heterologously expressed in Trichoderma reesei Tu6, and its antimicrobial properties against the three bacteria were characterized. The results showed that the minimum inhibitory concentrations of the peptide against E. coli ATCC 25922, S. derby ATCC 13076, and C. perfringens CVCC 2032 were 43.75, 43.75, and 21.86 μg/mL, respectively. The antimicrobial activity of BMGlv2 was not severely affected by high temperature, salt ions, and digestive enzymes. It had low hemolytic activity against rabbit red blood cells, indicating its safety for use as a feed additive. Furthermore, the measurements of the leakage of bacterial cell contents and scanning electron microscopy of C. perfringens CVCC 2032 indicated that BMGlv2 exerted antimicrobial activity by destroying the cell membrane. Overall, this study showed the heterologous expression of the antimicrobial peptide BMGlv2 in T. reesei and verified its antimicrobial properties against three common pathogenic bacteria associated with piglet diarrhea, which can provide a reference for the applications of AMPs as an alternative product in industrial agriculture.

Profiling hymenopteran venom toxins: Protein families, structural landscape, biological activities, and pharmacological benefits

Hymenopterans are an untapped source of venom secretions. Their recent proteo-transcriptomic studies have revealed an extraordinary pool of toxins that participate in various biological processes, including pain, paralysis, allergic reactions, and antimicrobial activities. Comprehensive and clade-specific campaigns to collect hymenopteran venoms are therefore needed. We consider that data-driven bioprospecting may help prioritise sampling and alleviate associated costs. This work established the current protein landscape from hymenopteran venoms to evaluate possible sample bias by studying their origins, sequence diversity, known structures, and biological functions. We collected all 282 reported hymenopteran toxins (peptides and proteins) from the UniProt database that we clustered into 21 protein families from the three studied clades - wasps, bees, and ants. We identified 119 biological targets of hymenopteran toxins ranging from pathogen membranes to eukaryotic proteases, ion channels and protein receptors. Our systematic study further extended to hymenopteran toxins' therapeutic and biotechnological values, where we revealed promising applications in crop pests, human infections, autoimmune diseases, and neurodegenerative disorders.

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The hymenopteran toxin diversity includes 21 protein families from 81 species.

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Some toxins are shared across wasps, bees and ants, others are clade-specific.

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Their venoms contain membrane-active peptides, neurotoxins, allergens and enzymes.

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Hymenopteran toxins have been tested against a total of 119 biological targets.

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Hymenopteran toxins were predominantly evaluated as anti-infective agents.

Evolving and assembling to pierce through: Evolutionary and structural aspects of antimicrobial peptides

The burgeoning menace of antimicrobial resistance across the globe has necessitated investigations into other chemotherapeutic strategies to combat infections. Antimicrobial peptides, or host defense peptides, are a set of promising therapeutic candidates in this regard. Most of them cause membrane permeabilization and are a key component of the innate immune response to pathogenic invasion. It has also been reported that peptide self-assembly is a driving factor governing the microbicidal activity of these peptide candidates. While efforts have been made to develop novel synthetic peptides against various microbes, many clinical trials of such peptides have failed due to toxicity and hemolytic activity to the host. A function-guided rational peptide engineering, based on evolutionary principles, physicochemical properties and activity determinants of AMP activity, is expected to help in targeting specific microbes. Furthermore, it is important to develop a unified understanding of the evolution of AMPs in order to fully appreciate their importance in host defense. This review seeks to explore the evolution of AMPs and the physicochemical determinants of AMP activity. The specific interactions driving AMP self-assembly have also been reviewed, emphasizing implications of this self-assembly on microbicidal and immunomodulatory activity.

Modern venomics-Current insights, novel methods, and future perspectives in biological and applied animal venom research

Venoms have evolved >100 times in all major animal groups, and their components, known as toxins, have been fine-tuned over millions of years into highly effective biochemical weapons. There are many outstanding questions on the evolution of toxin arsenals, such as how venom genes originate, how venom contributes to the fitness of venomous species, and which modifications at the genomic, transcriptomic, and protein level drive their evolution. These questions have received particularly little attention outside of snakes, cone snails, spiders, and scorpions. Venom compounds have further become a source of inspiration for translational research using their diverse bioactivities for various applications. We highlight here recent advances and new strategies in modern venomics and discuss how recent technological innovations and multi-omic methods dramatically improve research on venomous animals. The study of genomes and their modifications through CRISPR and knockdown technologies will increase our understanding of how toxins evolve and which functions they have in the different ontogenetic stages during the development of venomous animals. Mass spectrometry imaging combined with spatial transcriptomics, in situ hybridization techniques, and modern computer tomography gives us further insights into the spatial distribution of toxins in the venom system and the function of the venom apparatus. All these evolutionary and biological insights contribute to more efficiently identify venom compounds, which can then be synthesized or produced in adapted expression systems to test their bioactivity. Finally, we critically discuss recent agrochemical, pharmaceutical, therapeutic, and diagnostic (so-called translational) aspects of venoms from which humans benefit.

Advances in the Immune Regulatory Role of Non-Coding RNAs (miRNAs and lncRNAs) in Insect-Pathogen Interactions

Insects are by far the most abundant and diverse living organisms on earth and are frequently prone to microbial attacks. In other to counteract and overcome microbial invasions, insects have in an evolutionary way conserved and developed immune defense mechanisms such as Toll, immune deficiency (Imd), and JAK/STAT signaling pathways leading to the expression of antimicrobial peptides. These pathways have accessory immune effector mechanisms, such as phagocytosis, encapsulation, melanization, nodulation, RNA interference (RNAi), lysis, autophagy, and apoptosis. However, pathogens evolved strategies that circumvent host immune response following infections, which may have helped insects further sophisticate their immune response mechanisms. The involvement of ncRNAs in insect immunity is undeniable, and several excellent studies or reviews have investigated and described their roles in various insects. However, the functional analyses of ncRNAs in insects upon pathogen attacks are not exhaustive as novel ncRNAs are being increasingly discovered in those organisms. This article gives an overview of the main insect signaling pathways and effector mechanisms activated by pathogen invaders and summarizes the latest findings of the immune modulation role of both insect- and pathogen-encoded ncRNAs, especially miRNAs and lncRNAs during insect–pathogen crosstalk.

Antimicrobial Mechanisms and Clinical Application Prospects of Antimicrobial Peptides

Antimicrobial peptides are a type of small-molecule peptide that widely exist in nature and are components of the innate immunity of almost all living things. They play an important role in resisting foreign invading microorganisms. Antimicrobial peptides have a wide range of antibacterial activities against bacteria, fungi, viruses and other microorganisms. They are active against traditional antibiotic-resistant strains and do not easily induce the development of drug resistance. Therefore, they have become a hot spot of medical research and are expected to become a new substitute for fighting microbial infection and represent a new method for treating drug-resistant bacteria. This review briefly introduces the source and structural characteristics of antimicrobial peptides and describes those that have been used against common clinical microorganisms (bacteria, fungi, viruses, and especially coronaviruses), focusing on their antimicrobial mechanism of action and clinical application prospects.

In Vitro Evaluation of Antimicrobial Peptides from the Black Soldier Fly (Hermetia Illucens) against a Selection of Human Pathogens

Antimicrobial peptides (AMPs) are being explored as alternatives to traditional antibiotics to combat the rising antimicrobial resistance. Insects have proven to be a valuable source of new, potent AMPs with large structural diversity. For example, the black soldier fly has one of the largest AMP repertoires ever recorded in insects. Currently, however, this AMP collection has not yet undergone antimicrobial evaluation or in-depth in vitro characterization. This study evaluated the activity of a library of 36 black soldier fly AMPs against a panel of human pathogens (Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Candida albicans, and Aspergillus fumigatus) and a human cell line (MRC5-SV2). The activity profile of two cecropins (Hill-Cec1 and Hill-Cec10) with potent Gram-negative activity, was further explored by characterizing their hemolysis, time-to-kill kinetics, membrane-permeabilization properties, and anti-biofilm activity. Hill-Cec1 and Hill-Cec10 also showed high activity against other bacterial species, including Klebsiella pneumoniae and multi-drug resistant P. aeruginosa. Both AMPs are bactericidal and have a rapid onset of action with membrane-permeabilizing effects. Hill-Cec1 and Hill-Cec10 were also able to prevent P. aeruginosa biofilm formation, but no relevant effect was seen on biofilm eradication. Overall, Hill-Cec1 and Hill-Cec10 are promising leads for new antimicrobial development to treat critical infections caused by Gram-negative pathogens such as P. aeruginosa.

IMPORTANCE With the ever growing antimicrobial resistance, finding new candidates for antimicrobial drug development is indispensable. Antimicrobial peptides have steadily gained attention as alternatives for conventional antibiotics, due to some highly desirable characteristics, such as their low propensity for resistance development. With this article, we aim to upgrade the knowledge on the activity of black soldier fly antimicrobial peptides and their potential as future therapeutics. To achieve this, we have evaluated for the first time a library of 36 synthetically produced peptides from the black soldier fly against a range of human pathogens and a human cell line. Two selected peptides have undergone additional testing to characterize their antimicrobial profile against P. aeruginosa, a clinically important Gram-negative pathogen with a high established resistance. Overall, this research has contributed to the search for new peptide drug leads to combat the rising antimicrobial resistance.

Adaptively evolved human oral actinomyces-sourced defensins show therapeutic potential

The development of eukaryote‐derived antimicrobial peptides as systemically administered drugs has proven a challenging task. Here, we report the first human oral actinomyces‐sourced defensin—actinomycesin—that shows promise for systemic therapy. Actinomycesin and its homologs are only present in actinobacteria and myxobacteria, and share similarity with a group of ancient invertebrate‐type defensins reported in fungi and invertebrates. Signatures of natural selection were detected in defensins from the actinomyces colonized in human oral cavity and ruminant rumen and dental plaque, highlighting their role in adaptation to complex multispecies bacterial communities. Consistently, actinomycesin exhibited potent antibacterial activity against oral bacteria and clinical isolates of Staphylococcus and synergized with two classes of human salivary antibacterial factors. Actinomycesin specifically inhibited bacterial peptidoglycan synthesis and displayed weak immunomodulatory activity and low toxicity on human and mammalian cells and ion channels in the heart and central nervous system. Actinomycesin was highly efficient in mice infected with Streptococcus pneumoniae and mice with MRSA‐induced experimental peritoneal infection. This work identifies human oral bacteria as a new source of systemic anti‐infective drugs.

Seminal fluid proteins induce transcriptome changes in the Aedes aegypti female lower reproductive tract

BACKGROUND

Mating induces behavioral and physiological changes in the arbovirus vector Aedes aegypti, including stimulation of egg development and oviposition, increased survival, and reluctance to re-mate with subsequent males. Transferred seminal fluid proteins and peptides derived from the male accessory glands induce these changes, though the mechanism by which they do this is not known.

RESULTS

To determine transcriptome changes induced by seminal proteins, we injected extract from male accessory glands and seminal vesicles (MAG extract) into females and examined female lower reproductive tract (LRT) transcriptomes 24 h later, relative to non-injected controls. MAG extract induced 87 transcript-level changes, 31 of which were also seen in a previous study of the LRT 24 h after a natural mating, including 15 genes with transcript-level changes similarly observed in the spermathecae of mated females. The differentially-regulated genes are involved in diverse molecular processes, including immunity, proteolysis, neuronal function, transcription control, or contain predicted small-molecule binding and transport domains.

CONCLUSIONS

Our results reveal that seminal fluid proteins, specifically, can induce gene expression responses after mating and identify gene targets to further investigate for roles in post-mating responses and potential use in vector control.

Effects of chitin from Daphnia similis and its derivative, chitosan on the immune response and disease resistance of white shrimp, Litopenaeus vannamei

Daphnia similis chitin and its derivative chitosan were prepared as immunostimulants to boost the immune response and determine the ability to control infectious disease caused by Vibrio alginolyticus in white shrimp, Litopenaeus vannamei. Three experimental diets supplemented with 0% chitin or chitosan (control) and 0.4% chitin or 0.4% chitosan were fed to shrimp for 56 days. Dietary inclusion of 0.4% chitosan accelerated shrimp growth compared to chitin and control. The survival and disease resistance of shrimp increased significantly when fed chitin and chitosan diets, after pathogenic injection, as indicated by the up-regulated immune responses in respiratory burst (RB), superoxide dismutase (SOD), and phagocytic activity (PA). There were no significant differences in the total haemocyte count (THC), phenoloxidase (PO)activity, and lysozyme (LYZ) activity among the groups. No significant differences were observed for prophenoloxidase system-related gene expressions among groups. However, shrimp fed chitin, and chitosan expressed significantly higher levels of antimicrobial proteins (penaeidin 3a, crustin, and anti-lipopolysaccharide factor 2) in the haemocytes than in control. The gene expressions of catalase and heat shock protein 70 increased in the hepatopancreas of shrimp fed chitosan diet compared to the chitin and control diet. The O-linked N-acetylglucosamine transferase (ogt) was significantly higher in the haemocytes of shrimp fed chitosan and chitin than the control, but ogt was only significantly higher in the hepatopancreas of shrimp fed chitosan. Dietary chitin and chitosan also showed positive effects on the transcription of peritrophin-like protein. These findings suggest that both chitin and chitosan from D. similis are efficacious at boosting the immunity of shrimp by preventing and controlling infectious diseases caused by Vibrio and have great potential to be used as a feasible immunostimulant that significantly contributes to the circular economy.

Diversity of insect antimicrobial peptides and proteins - A functional perspective: A review

The innate immune response of insects provides a robust line of defense against pathogenic microbes and eukaryotic parasites. It consists of two types of overlapping immune responses, named humoral and cellular, which share protective molecules and regulatory mechanisms that closely coordinate to prevent the spread and replication of pathogens within the compromised insect hemocoel. The major feature of the humoral part of the insect immune system involves the production and secretion of antimicrobial peptides from the fat body, which is considered analogous to adipose tissue and liver in vertebrates. Previous research has identified and characterized the nature of antimicrobial peptides that are directed against various targets during the different stages of infection. Here we review this information focusing mostly on the diversity and mode of action of these host defense components, and their critical contribution to maintaining host homeostasis. Extending this knowledge is paramount for understanding the evolution of innate immune function and the physiological balance required to provide sufficient protection to the host against external enemies while avoiding overactivation signaling events that would severely undermine physiological stability.

Construction of a Tandem Repeat Peptide Sequence with Pepsin Cutting Sites to Produce Recombinant α-Melanocyte-Stimulating Hormone

The production of α-melanocyte-stimulating hormone (α-MSH), a peptide hormone composed of 13 amino acids, is attempted by recombinant expression using E. coli as the host. To achieve this aim, a synthetic gene containing eight tandem repeats of msh gene (8msh) was designed for ribosomal synthesis of 8 α-MSH. The merit of the strategy is to diminish the peptide toxicity against the host cell and to achieve a higher production yield. Pepsin cleavage sites are introduced between the peptides for enzymatic proteolysis to obtain the monomeric peptide of α-MSH. The constructed plasmid was transformed into different strains of E. coli hosts, and E. coli XL1-Blue with gene 8msh revealed the highest yield of 8 α-MSH. Although 8 α-MSH was fractionalized in the insoluble pellets after cell lysis, pepsin cleavage was able to produce soluble α-MSH peptide, as analyzed and confirmed by mass spectrometry and peptide activity assays. The production of α-MSH was quantified using HPLC with a yield of 42.9 mg/L of LB culture. This study demonstrates the feasibility of producing α-MSH using recombinant expression of tandem repeat gene. The production procedure involves minimal post-treatment and processing and can be scaled up for industrial application.

Application of Capillary and Free-Flow Zone Electrophoresis for Analysis and Purification of Antimicrobial β-Alanyl-Tyrosine from Hemolymph of Fleshfly Neobellieria bullata

The problem of a growing resistance of bacteria and other microorganisms to conventional antibiotics gave rise to a search for new potent antimicrobial agents. Insect antimicrobial peptides (AMPs) seem to be promising novel potential anti-infective therapeutics. The dipeptide β-alanyl-tyrosine (β-Ala-Tyr) is one of the endogenous insect toxins exhibiting antibacterial activity against both Gram-negative and Gram-positive bacteria. Prior to testing its other antimicrobial activities, it has to be prepared in a pure form. In this study, we have developed a capillary zone electrophoresis (CZE) method for analysis of β-Ala-Tyr isolated from the extract of the hemolymph of larvae of the fleshfly Neobellieria bullata by reversed-phase high-performance liquid chromatography (RP-HPLC). Based on our previously described correlation between CZE and free-flow zone electrophoresis (FFZE), analytical CZE separation of β-Ala-Tyr and its admixtures have been converted into preparative purification of β-Ala-Tyr by FFZE with preparative capacity of 45.5 mg per hour. The high purity degree of the β-Ala-Tyr obtained by FFZE fractionation was confirmed by its subsequent CZE analysis.

Taxonomic bias in AMP prediction of invertebrate peptides

Invertebrate antimicrobial peptides (AMPs) are at the forefront in the search for agents of therapeutic utility against multi-resistant microbial pathogens, and in recent years substantial advances took place in the in silico prediction of antimicrobial function of amino acid sequences. A yet neglected aspect is taxonomic bias in the performance of these tools. Owing to differences in the prediction algorithms and used training data sets between tools, and phylogenetic differences in sequence diversity, physicochemical properties and evolved biological functions of AMPs between taxa, notable discrepancies may exist in performance between the currently available prediction tools. Here we tested if there is taxonomic bias in the prediction power in 10 tools with a total of 20 prediction algorithms in 19 invertebrate taxa, using a data set containing 1525 AMP and 3050 non-AMP sequences. We found that most of the tools exhibited considerable variation in performance between tested invertebrate groups. Based on the per-taxa performances and on the variation in performances across taxa we provide guidance in choosing the best-performing prediction tool for all assessed taxa, by listing the highest scoring tool for each of them.

Black soldier fly larvae in broiler diets improve broiler performance and modulate the immune system

Non-conventional feed ingredients are receiving more interest in their ability to increase farming efficiency, sustainability and animal performance. The objective of this study was to determine the optimal rate of inclusion level of the full-fat black soldier fly larvae (BSFL) in broiler diets and to evaluate their impact on performance, nutrient digestibility, and the immune system (blood cells and intraepithelial lymphocytes). A total of 400 male day-old Ross 308 broilers were randomly assigned to 5 treatment groups with 8 replicates each. Five inclusion levels of full-fat BSFL were investigated across starter (0, 2.5%, 5%, 7.5% and 10%), grower and finisher diets (0, 5%, 10%, 15% and 20%). All diets were formulated based on digestible amino acid values according to the Aviagen (2016) recommendations. A polynomial regression at different degrees was performed to analyse broiler performance parameters (body weight, body weight gain, feed intake, and feed conversion ratio), nutrient digestibility, and blood cell count. Intraepithelial lymphocyte population data was analysed performing univariate linear regression. During the entire experimental period (from 2 to 42 d), BSFL inclusion levels decreased the feed conversion ratio by 10% in broilers that received 20% BSFL in their diets (P < 0.05). Lymphocytes and white blood cell count decreased linearly by 47.7% and 35.9%, respectively, with up to 20% BSFL inclusion (P < 0.001). A 4-fold decrease in CD3+ T lymphocytes and a 9.7-fold decrease of CD3+CD8+ intestinal cytotoxic T lymphocytes occurred in broilers fed 20% BSFL compared to the control group. These findings suggest that the inclusion of BSFL can improve broiler performance and potentially reduce immune response energy expenditure in birds fed 20% BSFL for 42 d.

Increasing Anthonomus grandis susceptibility to Metarhizium anisopliae through RNAi-induced AgraRelish knockdown: a perspective to combine biocontrol and biotechnology

BACKGROUND

The hemolymph and insect gut together have an essential role in the immune defense against microorganisms, including the production of antimicrobial peptides (AMP). AMPs are mainly induced by two specific signaling pathways, Toll and immune deficiency (IMD). Here, we characterize the expression profile of four genes from both pathways and describe the importance of AgraRelish in the immune defense of Anthonomus grandis against the entomopathogenic fungus Metarhizium anisopliae by RNA interference (RNAi).

RESULTS

To characterize the pathway that is activated early during the A. grandis-M. anisopliae interaction, we assessed the expression profiles of AgraMyD88 and AgraDorsal (Toll pathway), AgraIMD and AgraRelish (IMD pathway), and several AMP genes. Interestingly, we found that IMD pathway genes are upregulated early, and Toll pathway genes are upregulated just 3 days after inoculation (DAI). Furthermore, nine AMPs were upregulated 24 h after fungus inoculation, including attacins, cecropins, coleoptericins, and defensins. AgraRelish knockdown resulted in a reduction in median lethal time (LT₅₀ ) for M. anisopliae-treated insects of around 2 days compared to control treatments. In addition, AgraRelish remained knocked down at 3 DAI. Finally, we identified that AgraRelish knockdown increased fungal loads at 2 DAI compared to control treatments, possibly indicating a faster infection.

CONCLUSIONS

Our data indicate the influence of the IMD pathway on the antifungal response in A. grandis. Combining biocontrol and RNAi could significantly improve cotton boll weevil management. Hence, AgraRelish is a potential target for the development of biotechnological tools aimed at improving the efficacy of M. anisopliae against A. grandis.

Current understanding of immune priming phenomena in insects

It may seem that the most important issues related to insect immunity have already been described. However, novel phenomena observed in recent years shed new light on the understanding of the immune response in insects.The adaptive abilities of insects helped them to populate all ecological land niches.One important adaptive ability of insects that facilitates their success is the plasticity of their immune system. Although they only have innate immune mechanisms, insects can increase their resistance after the first encounter with the pathogen. In recent years, this phenomenon,namedimmunepriming, has become a "hot topic" in immunobiology.Priming can occur within or across generations. In the first case, the resistance of a given individual can increase after surviving a previous infection. Transstadial immune priming occurs when infection takes place at one of the initial developmental stages and increased resistance is observed at the pupal or imago stages. Priming across generations (transgenerationalimmune priming, TGIP) relies on the increased resistance of the offspring when one or both parents are infected during their lifetime.Despite the attention that immune priming has received, basic questions remain to be answered, such as regulation of immune priming at the molecular level. Research indicates that pathogen recognition receptors (PRRs) can be involved in the priming phenomenon. Recent studies have highlighted the special role of microRNAs and epigenetics, which can influence expression of genes that can be transmitted through generations although they are not encoded in the nucleotide sequence. Considerable amounts of research are required to fully understand the mechanisms that regulate priming phenomena. The aim of our work is to analyse thoroughly the most important information on immune priming in insects and help raise pertinent questions such that a greater understanding of this phenomenon can be obtained in the future.

Potent Activity of Hybrid Arthropod Antimicrobial Peptides Linked by Glycine Spacers

Arthropod antimicrobial peptides (AMPs) offer a promising source of new leads to address the declining number of novel antibiotics and the increasing prevalence of multidrug-resistant bacterial pathogens. AMPs with potent activity against Gram-negative bacteria and distinct modes of action have been identified in insects and scorpions, allowing the discovery of AMP combinations with additive and/or synergistic effects. Here, we tested the synergistic activity of two AMPs, from the dung beetle Copris tripartitus (CopA3) and the scorpion Heterometrus petersii (Hp1090), against two strains of Escherichia coli. We also tested the antibacterial activity of two hybrid peptides generated by joining CopA3 and Hp1090 with linkers comprising two (InSco2) or six (InSco6) glycine residues. We found that CopA3 and Hp1090 acted synergistically against both bacterial strains, and the hybrid peptide InSco2 showed more potent bactericidal activity than the parental AMPs or InSco6. Molecular dynamics simulations revealed that the short linker stabilizes an N-terminal 3₁₀-helix in the hybrid peptide InSco2. This secondary structure forms from a coil region that interacts with phosphatidylethanolamine in the membrane bilayer model. The highest concentration of the hybrid peptides used in this study was associated with stronger hemolytic activity than equivalent concentrations of the parental AMPs. As observed for CopA3, the increasing concentration of InSco2 was also cytotoxic to BHK-21 cells. We conclude that AMP hybrids linked by glycine spacers display potent antibacterial activity and that the cytotoxic activity can be modulated by adjusting the nature of the linker peptide, thus offering a strategy to produce hybrid peptides as safe replacements or adjuncts for conventional antibiotic therapy.