A Limulus antilipopolysaccharide factor-derived peptide exhibits a new immunological activity with potential applicability in infectious diseases

Anti-inflammatory activities of arthropod peptides: a systematic review

Peptides obtained from different animal species have gained importance recently due to research that aims to develop biopharmaceuticals with therapeutic potential. In this sense, arthropod venoms have drawn attention, not only because of their toxicity but mainly for the search for molecules with various bioactivities, including anti-inflammatory activity. The purpose of the present study is to gather data available in the literature on new peptides derived from arthropod species with anti-inflammatory potential. This systematic review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. Studies on peptides from arthropods that display anti-inflammatory activity were retrieved from PubMed, Scopus, Web of Science, and Google Scholar databases. The bibliographic research started in 2020 and searched papers without a limit on the publication date. The articles were analyzed using a search string containing the following terms: "Peptides" and "Anti-inflammatory", in combinations such as "Ant", "Bee", "Wasp", "Crab", "Shrimp", "Scorpion", "Spider", "Tick" and "Centipedes". Besides, a search was carried out in the databases with the terms: "Peptides", "Antitumor", or "Anticancer", and "Arthropods". Articles that met the inclusion and exclusion criteria totalized 171, and these served for data extraction. Additionally, the present review included anti-inflammatory peptides with anticancer properties. Peptides with confirmed anti-inflammatory activity were from insects (ants, bees, and wasps), crustaceans (shrimp and crabs), arachnids (scorpions, spiders, and ticks), and centipedes. These arthropod peptides act mainly by decreasing pro-inflammatory cytokines as analyzed in vitro and in vivo. Some showed significant antineoplastic activity, working in essential cellular pathways against malignant neoplasms.

Evaluation of Cell-Penetrating Peptides as Mucosal Immune Enhancers for Nasal Vaccination

Cell-penetrating peptides (CPPs) have been evaluated as enhancers in drug delivery, their addition in medical formulations favors drug absorption allowing obtaining the pharmacological effect with lower doses. In vaccine formulations their inclusion has been also explored with interesting results. Currently mucosal vaccination constitutes a promising alternative with the main advantage of inducing both systemic and mucosal immune responses, which are crucial for control tumors and infections at mucosal tissues. In the present work the nasal immune-enhancing effect of four CPPs was evaluated in Balb/c mice. Animals were intranasally immunized with CPP and the recombinant hepatitis B surface protein (HBsAg) as model antigen. The antibody response in sera and mucosal tissue was measured by ELISA. The IFN-γ secretion response at spleen was also evaluated by ELISPOT and ELISA. Among the CPPs studied one novel peptide stand out by its ability to potentiate the humoral and cellular immune response against the co-administered antigen. Considering that the use of mucosal routes is a promising strategy in vaccination, which are gaining special relevance nowadays in the development of novel candidates against SARS-CoV-2 and other potential emerging respiratory virus, the searching and development of safe mucosal adjuvants constitute a current need.

A first-in-class, first-in-human, phase I trial of CIGB-552, a synthetic peptide targeting COMMD1 to inhibit the oncogenic activity of NF-κB in patients with advanced solid tumors

CIGB-552 is a synthetic peptide that interacts with COMMD1 and upregulates its protein levels. The objectives of this phase I study were safety, pharmacokinetic profile, evaluation of the lymphocytes CD4+ and CD8+ and preliminary activity in patients with advanced tumors. A 3 + 3 dose-escalation design with seven dose levels was implemented. Patients were included until a grade 3 related adverse event occurred and the maximum tolerated dose was reached. The patients received subcutaneous administration of CIGB-552 three times per week for 2 weeks. Single-dose plasma pharmacokinetics was characterized at two dose levels, and tumor responses were classified by RECIST 1.1. Twenty-four patients received CIGB-552. Dose-limiting toxicity was associated with a transient grade 3 pruritic maculopapular rash at a dose of 7.0 mg. The maximum tolerated dose was defined as 4.7 mg. Ten patients were assessable for immunological status. Seven patients had significant changes in the ratio CD4/CD8 in response to CIGB-552 treatment; three patients did not modify the immunological status. Stable disease was observed in five patients, including two metastatic soft sarcomas. We conclude that CIGB-552 at dose 4.7 mg was well tolerated with no significant adverse events and appeared to provide some clinical benefits.

Innate immune responses against viral pathogens in Macrobrachium

Some members of genus Macrobrachium are important economically prawns and valuable objects for studying the innate immune defense mechanism of crustaceans. Studies have focused on immune responses against bacterial and fungal infections and have expanded to include antiviral immunity over the past two decades. Similar to all living organisms, prawns are exposed to viruses, including white spot syndrome virus, Macrobrachium rosenbergii nodavirus, and Decapod iridescent virus 1 and develop effective defense mechanisms. Here, we review current understanding of the antiviral host defense in two species of Macrobrachium. The main antiviral defense of Macrobrachium is the activation of intracellular signaling cascades, leading to the activation of cellular responses (apoptosis) and humoral responses (immune-related signaling pathways, antimicrobial and antiviral peptides, lectins, and prophenoloxidase-activating system).

The Role of Endogenous Antimicrobial Peptides in Modulating Innate Immunity of the Ocular Surface in Dry Eye Diseases

The ocular surface has the challenging responsibility of maintaining a clear moist refractive surface while protecting the eye from exogenous pathogens and the environment. Homeostasis of the ocular surface, including its innate immune components, is altered in ocular surface disease states. In this review, we focus on antimicrobial peptides and the role they play in the immune response of the ocular surface during healthy states and dry eye diseases. Antimicrobial peptides are of special interest to the study of the ocular surface because of their various roles that include microbial threat neutralization, wound healing, and immune modulation. This review explores current literature on antimicrobial peptides in ocular surface diseases and discusses their therapeutic potential in ocular surface diseases and dry eye.

The Anticancer Peptide CIGB-552 Exerts Anti-Inflammatory and Anti-Angiogenic Effects through COMMD1

CIGB-552 is a synthetic anti-tumor peptide capable of reducing tumor size and increasing the lifespan of tumor-bearing mice. Part of its anti-cancer effects consists of inducing apoptosis, modulating NF-kB signaling pathway, and the angiogenesis process. Although one of its major mediators, the COMMD1 protein, has been identified, the mechanism by which CIGB-552 exerts such effects remains elusive. In the present study, we show the role of COMMD1 in CIGB-552 mechanism of action by generating the COMMD1 knock-out from the human lung cancer cell line NCI-H460. A microarray was performed to analyze both wild-type and KO cell lines with regard to CIGB-552 treatment. Additionally, different signaling pathways were studied in both cell lines to validate the results. Furthermore, the interaction between CIGB-552 and COMMD1 was analyzed by confocal microscopy. By signaling pathway analysis we found that genes involved in cell proliferation and apoptosis, oncogenic transformation, angiogenesis and inflammatory response are potentially regulated by the treatment with CIGB-552. We then demonstrated that CIGB-552 is capable of modulating NF-kB in both 2D and 3D cell culture models. Finally, we show that the ability of CIGB-552 to negatively modulate NF-kB and HIF-1 pathways is impaired in the COMMD1 knock-out NCI-H460 cell line, confirming that COMMD1 is essential for the peptide mechanism of action.

Anti-lipopolysaccharide Factor from Crucifix Crab Charybdis feriatus, Cf-ALF2: Molecular Cloning and Functional Characterization of the Recombinant Peptide

Antilipopolysaccharide factors (ALFs) are important effectors of innate immunity in crustaceans with broad spectrum antimicrobial activity. Present study deals with the molecular and functional characterization of a 98-amino acid ALF isoform from, crucifix crab, Charybdis feriatus termed as Cf-ALF2. The ALF isoform Cf-ALF2 exhibits characteristic features of an AMP including a cationic net charge of + 9 and a total hydrophobic ratio of 34%. Recombinant peptide rCf-ALF2 showed remarkable antimicrobial activity against Gram-negative and Gram-positive bacteria especially against Staphylococcus aureus (minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of 5 µM) and Escherichia coli (MIC 10 µM and MBC 20 µM). Using scanning electron microscopy, bacterial membrane blebbing, disruption, and cell content leakage were observed in peptide treated E. coli. The recombinant peptide was found to be non-hemolytic and non-cytotoxic in NCI-H460 cell line at the highest tested concentration (20 µM). Thus, this study identified a novel isoform of ALF from C. feriatus and revealed the potent antimicrobial property of the recombinant peptide Cf-ALF2 and the future prospects of using the peptide for therapeutic applications in the future.

Current strategies against persistent human papillomavirus infection (Review)

Human papillomavirus (HPV) is the most common sexually transmitted infection, exhibiting a tropism for the epidermis and mucosae. The link between persistent HPV infection and malignancies involving the anogenital tract as well as the head and neck has been well‑established, and it is estimated that HPV‑related cancers involving various anatomical sites account for 4.5% of all human cancers. Current prophylactic vaccines against HPV have enabled the prevention of associated malignancies. However, the sizeable population base of current infection in whom prophylactic vaccines are not applicable, certain high‑risk HPV types not included in vaccines, and the vast susceptible population in developing countries who do not have access to the costly prophylactic vaccines, put forward an imperative need for effective therapies targeting persistent infection. In this article, the life cycle of HPV, the mechanisms facilitating HPV evasion of recognition and clearance by the host immune system, and the promising therapeutic strategies currently under investigation, particularly antiviral drugs and therapeutic vaccines, are reviewed.

Immunotherapy of gynecological cancers

Oncology treatments have evolved from intuitive, via empiric, to the present precision medicine, with the integration of molecular targeted therapies in our treatment arsenal. The use of the patients' powerful immune system has long been contemplated and recently led to the integration of immunotherapy to overturn the well-documented inhibitory effects of the tumor on the immune system and restore it to a state of activity against the cancer. Recent favorable results have shown the value and effectiveness of immunotherapy against gynecological cancers. In particular, the checkpoint inhibitors, targeting the programmed death-1 (PD-1) pathway, have shown durable clinical responses with manageable toxicity. Several phase II and III clinical trials testing the association of different regimen of chemotherapy and immunotherapy are ongoing in gynecological cancers, and important results are expected. In this chapter, we outline the main principles of immunotherapy for gynecological cancers and summarize the current strategies used in clinical trials.

Molecular and functional analyses of novel anti-lipopolysaccharide factors in giant river prawn (Macrobrachium rosenbergii, De Man) and their expression responses under pathogen and temperature exposure

Anti-lipopolysaccharide factor (ALF) is an immune-related protein that is crucially involved in immune defense mechanisms against invading pathogens in crustaceans. In the current study, three different ALFs of giant river prawn (Mr-ALF3, Mr-ALF8 and Mr-ALF9) were discovered. Based on sequence analysis, Mr-ALF3 and Mr-ALF9 were identified as new members of ALFs in crustaceans (groups F and G, respectively). Structurally, each newly identified Mr-ALF contained three α-helices packed against a four-stranded β-sheet bearing the LPS-binding motif, which usually binds to the cell wall components of bacteria. Tissue expression analysis using quantitative real-time RT-PCR (qRT-PCR) demonstrated that Mr-ALF3 was expressed in most tissues, and the highest expression was in the heart and hemocytes. The Mr-ALF8 gene was highly expressed in the heart, hemocytes, midgut, hepatopacreas and hindgut, respectively, while the Mr-ALF9 gene was modestly expressed in the heart and hemocytes, respectively. The transcriptional responses of the Mr-ALFs to Aeromonas hydrophila and hot/cold temperatures were investigated by qRT-PCR in the gills, hepatopancreas and hemocytes. We found that all Mr-ALFs were clearly suppressed in all tested tissues when the experimental prawns were exposed to extreme temperatures (25 and 35 °C). Moreover, the expression levels of these genes were significantly induced in all examined tissues by 2 different concentrations of A. hydrophila (1 × 10⁶ and 1 × 10⁹ CFU/ml), particularly 12 and 96 h after the injection. Finally, binding activity analysis of LPS-motif peptides of each Mr-ALF revealed that the LPS peptide of Mr-ALF3 exhibited the strongest adhesion to two pathogenic Gram-negative bacteria, A. hydrophila and Vibrio harveyi, and the non-pathogenic Gram-positive Bacillus megaterium. The results also showed that the Mr-ALF8 and Mr-ALF9 peptides had mild antimicrobial effects against similar tested bacteria. Based on information obtained in this study, novel ALF genes were clearly identified. Analyses of their responses under pathogenic and temperature stresses demonstrated the binding and antimicrobial activities of these ALFs and the consequent physiological effects, indicating their crucial functional roles in the prawn immune system.

Therapeutic vaccines for high-risk HPV-associated diseases

Cancer is the second leading cause of death worldwide, and it is estimated that Human papillomavirus (HPV) related cancers account for 5% of all human cancers. Current HPV vaccines are extremely effective at preventing infection and neoplastic disease; however, they are prophylactic and do not clear established infections. Therapeutic vaccines which trigger cell-mediated immune responses for the treatment of established infections and malignancies are therefore required. The E6 and E7 early genes are ideal targets for vaccine therapy due to their role in disruption of the cell cycle and their constitutive expression in premalignant and malignant tissues. Several strategies have been investigated for the development of therapeutic vaccines, including live-vector, nucleic acid, peptide, protein-based and cell-based vaccines as well as combinatorial approaches, with several vaccine candidates progressing to clinical trials. With the current understanding of the HPV life cycle, molecular mechanisms of infection, carcinogenesis, tumour biology, the tumour microenvironment and immune response mechanisms, an approved HPV therapeutic vaccine seems to be a goal not far from being achieved. In this article, the status of therapeutic HPV vaccines in clinical trials are reviewed, and the potential for plant-based vaccine production platforms described.

Expression optimization of a cell membrane-penetrating human papillomavirus type 16 therapeutic vaccine candidate in Nicotiana benthamiana

High-risk human papillomaviruses (hr-HPVs) cause cervical cancer, the fourth most common cancer in women worldwide. A HPV-16 candidate therapeutic vaccine, LALF32-51-E7, was developed by fusing a modified E7 protein to a bacterial cell-penetrating peptide (LALF): this elicited both tumour protection and regression in pre-clinical immunization studies. In the current study, we investigated the potential for producing LALF32-51-E7 in a plant expression system by evaluating the effect of subcellular localization and usage of different expression vectors and gene silencing suppressors. The highest expression levels of LALF32-51-E7 were obtained by using a self-replicating plant expression vector and chloroplast targeting, which increased its accumulation by 27-fold compared to cytoplasmic localization. The production and extraction of LALF32-51-E7 was scaled-up and purification optimized by affinity chromatography. If further developed, this platform could potentially allow for the production of a more affordable therapeutic vaccine for HPV-16. This would be extremely relevant in the context of developing countries, where cervical cancer and other HPV-related malignancies are most prevalent, and where the population have limited or no access to preventative vaccines due to their typical high costs.

Shrimp anti-lipopolysaccharide factor (SALF), an antimicrobial peptide, inhibits proinflammatory cytokine expressions through the MAPK and NF-κB pathways in LPS-induced HeLa cells

Recently, an antimicrobial peptide (AMP), the shrimp anti-lipopolysaccharide factor (SALF), was shown to act against vaginal pathogens as demonstrated by a minimum inhibitory concentration (MIC) assay and suggested that the SALF might play a protective role in orchestrating various defensive responses. The demonstration of a protective role of the SALF in cervical cancer epithelial cells (HeLa cells) led us to investigate the anti-inflammatory effects of the SALF by determining its inhibitory effects on proinflammatory markers in LPS-stimulated cervical cancer HeLa cells. The SALF was shown to inhibit the production of inflammatory cytokines including tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, IL-1α, and monocyte chemoattractant protein (MCP)-1 according to an ELISA analysis. The SALF also suppressed mRNA levels of il-6, il-8, il-1α, and mcp-1 according to an RT-PCR. We also found that the SALF might regulate vaginal epithelial cell immune responses through the MAPK and NF-κB pathways. These findings suggest that the SALF is a potential drug candidate for treating chronic inflammatory diseases, such as urethritis, vaginitis, cervicitis, and pelvic inflammatory diseases.

Host defense peptides: an alternative as antiinfective and immunomodulatory therapeutics

Host defense peptides are conserved components of innate immune response present among all classes of life. These peptides are potent, broad spectrum antimicrobial agents with potential as novel therapeutic compounds. Also, the ability of host defense peptides to modulate immunity is an emerging therapeutic concept since its selective modulation is a novel antiinfective strategy. Their mechanisms of action and the fundamental differences between pathogens and host cells surfaces mostly lead to a not widely extended microbial resistance and to a lower toxicity toward host cells. Biological libraries and rational design are novel tools for developing such molecules with promising applications as therapeutic drugs.

Bacterial cell wall compounds as promising targets of antimicrobial agents I. Antimicrobial peptides and lipopolyamines

The first barrier that an antimicrobial agent must overcome when interacting with its target is the microbial cell wall. In the case of Gram-negative bacteria, additional to the cytoplasmic membrane and the peptidoglycan layer, an outer membrane (OM) is the outermost barrier. The OM has an asymmetric distribution of the lipids with phospholipids and lipopolysaccharide (LPS) located in the inner and outer leaflets, respectively. In contrast, Gram-positive bacteria lack OM and possess a much thicker peptidoglycan layer compared to their Gram-negative counterparts. An additional class of amphiphiles exists in Gram-positives, the lipoteichoic acids (LTA), which may represent important structural components. These long molecules cross-bridge the entire cell envelope with their lipid component inserting into the outer leaflet of the cytoplasmic membrane and the teichoic acid portion penetrating into the peptidoglycan layer. Furthermore, both classes of bacteria have other important amphiphiles, such as lipoproteins, whose importance has become evident only recently. It is not known yet whether any of these amphiphilic components are able to stimulate the immune system under physiological conditions as constituents of intact bacteria. However, all of them have a very high pro-inflammatory activity when released from the cell. Such a release may take place through the interaction with the immune system, or with antibiotics (particularly with those targeting cell wall components), or simply by the bacterial division. Therefore, a given antimicrobial agent must ideally have a double character, namely, it must overcome the bacterial cell wall barrier, without inducing the liberation of the pro-inflammatory amphiphiles. Here, new data are presented which describe the development and use of membrane-active antimicrobial agents, in particular antimicrobial peptides (AMPs) and lipopolyamines. In this way, essential progress was achieved, in particular with respect to the inhibition of deleterious consequences of bacterial infections such as severe sepsis and septic shock.

Cyclic Limulus anti-lipopolysaccharide (LPS) factor-derived peptide CLP-19 antagonizes LPS function by blocking binding to LPS binding protein

Inflammation and septic shock due to endotoxins from Gram-negative bacteria infection continue to pose significant challenges to human healthcare. It is, therefore, necessary to develop therapeutic strategies targeting endotoxins, such as lipopolysaccharide (LPS), to prevent their potentially systemic effects. Pathogenesis due to Gram-negative bacteria involves LPS binding to the host LPS-binding protein (LBP), causing detrimental downstream signaling cascades. Our previous study showed that CLP-19, a synthetic peptide derived from the Limulus anti-LPS factor (LALF), could effectively neutralize LPS toxicity; however, the detailed mechanisms underlying this anti-LPS effect remained unexplained. Thus, we carried out investigations to determine how the CLP-19 neutralizes LPS toxicity. CLP-19 was found to block LPS binding to LBP in a dose-dependent manner, as evidenced by competitive enzyme-linked immunosorbent assay (ELISA). In peripheral blood mononuclear cells, CLP-19 blocked LPS-induced phosphorylation of mitogen activated protein kinase (MAPK) signaling proteins p38, extracellular signal-regulating kinase (ERK)1/2 and c-Jun N-terminal kinase (JNK)1/2. Furthermore, CLP-19 potency in LPS antagonism in vitro and in vivo was directly associated with its ability to block the LPS-LBP interaction. Taken together, the results suggested that CLP-19's inhibitory effect on LPS-LBP binding and on the subsequent MAPK pathway signaling may be responsible for its anti-LPS mechanism. This peptide appears to represent a potential therapeutic agent for clinical treatment of sepsis.

A novel fusion protein-based vaccine comprising a cell penetrating and immunostimulatory peptide linked to human papillomavirus (HPV) type 16 E7 antigen generates potent immunologic and anti-tumor responses in mice

The ultimate success of cancer vaccination is dependent upon the generation of tumor-specific CTLs. In this study, we designed and evaluated a novel fusion protein comprising a cell penetrating and immunostimulatory peptide corresponding to residues 32-51 of the Limulus polyphemus protein (LALF(32-51)) linked to human papillomavirus (HPV) 16 E7 antigen (LALF(32-51)-E7). We demonstrated that LALF(32-51) penetrates the cell membrane and delivers E7 into cells. In a preclinical model of HPV16-induced cervical carcinoma we showed that vaccination with adjuvant-free LALF(32-51)-E7 fusion protein significantly improves the presentation of E7-derived peptides to T-cells in vitro and induces suppression of tumor growth.

Antimicrobial peptide of an anti-lipopolysaccharide factor modulates of the inflammatory response in RAW264.7 cells

In this study, to clarify the protective mechanism of a peptide from shrimp anti-lipopolysaccharide (LPS) factor (SALF) against endotoxin shock, we evaluated the effects of the SALF and LPS on the production and release of tumor necrosis factor (TNF)-alphain vitro using the RAW264.7 murine macrophage cell line. Stimulation by LPS induced the production of inflammatory cytokines, and the SALF was able to modulate TNF-alpha production in LPS-stimulated RAW264.7 cells. Microarray studies revealed a transcriptional profile which was assessed in the presence or absence of the SALF by a quantitative real-time polymerase chain reaction. Pretreatment with the SALF significantly downregulated the expression of nuclear factor (NF)-kappaB in the presence of LPS. In contrast, pretreatment with the SALF significantly elevated the expressions of Anp32a, CLU, and SLPI, which are considered to be immune-related genes in the presence of LPS. Inhibitor studies suggested that the SALF's modulation of LPS-induced TNF-alpha production involved a complex mechanism with mitogen-activated protein kinase kinase, calcium, and protein kinase C. The data from this study, which imply that the SALF can suppress TNF-alpha production, suggest a role for the SALF in the defense mechanism which can potentially be applied to mammals for endotoxin treatment.

Conventional and unconventional antimicrobials from fish, marine invertebrates and micro-algae

All eukaryotic organisms, single-celled or multi-cellular, produce a diverse array of natural anti-infective agents that, in addition to conventional antimicrobial peptides, also include proteins and other molecules often not regarded as part of the innate defences. Examples range from histones, fatty acids, and other structural components of cells to pigments and regulatory proteins. These probably represent very ancient defence factors that have been re-used in new ways during evolution. This review discusses the nature, biological role in host protection and potential biotechnological uses of some of these compounds, focusing on those from fish, marine invertebrates and marine micro-algae.

Identification, cloning, characterization and recombinant expression of an anti-lipopolysaccharide factor from the hemocytes of Indian mud crab, Scylla serrata

Anti-lipopolysaccharide factors (ALF) are a group of small basic proteins which are released into the hemolymph as a result of rapid degranulation of hemocytes in response to bacterial lipopolysaccharide (LPS). In the present study, using a combined approach of degenerate and RACE PCR, the gene coding for Scylla serrata anti-lipopolysaccharide factor (SsALF) was cloned and characterized. The full-length SsALF cDNA sequence consists of 607 bp and encodes a polypeptide of 97 amino acids, constituting a molecular mass of 11172 Da with an estimated pI of 10.01. The SsALF protein showed upto 92% similarity with ALF from Scylla paramamosain and about 33-53% amino acid sequence identity with other known ALF sequences. SsALF protein sequence demonstrated the presence of two highly conserved cysteine residues and putative LPS binding domain. An in vivo expression study showed that SsALF mRNA was expressed predominantly in hemocytes, heart and muscle of healthy mud crabs. The recombinant form of SsALF protein (rSsALF) was expressed with a Histag, in Escherichia coli, using the pTriEx-4 Ek/LIC vector. The purified rSsALF protein demonstrated antimicrobial activity against both Gram-positive and Gram-negative bacteria. The recombinant protein was able to significantly neutralize LPS-induced expression on SsALF in vivo as demonstrated by real-time PCR. rSsALF was able to permeabilize artificial phospholipid membranes as demonstrated by calcein enclosed liposome model. These studies strongly suggest that SsALF is one among the important antimicrobial factors produced in the crab during a microbial invasion.

Localization of anti-lipopolysaccharide factor (ALFPm3) in tissues of the black tiger shrimp, Penaeus monodon, and characterization of its binding properties

Anti-lipopolysaccharide factor (ALF) is an antimicrobial peptide originally identified from horseshoe crabs and recently found in several shrimp species. ALFPm3, the most abundant isoform in the black tiger shrimp, Penaeus monodon, has been shown to possess a broad spectrum of antimicrobial activity against Gram-negative and Gram-positive bacteria, and filamentous fungi. In this study, a potential role for ALFPm3 in the shrimp innate immunity was revealed by examining the distribution of the protein in shrimp tissues in response to Vibrio harveyi challenge. Immunohistochemistry using anti-ALFPm3 antibody showed that the ALFPm3 protein is primarily localized in hemocytes and the positive cells observed at the injection site and in the cephalothorax are infiltrating hemocytes that migrate into shrimp tissues after bacterial injection. A rapid increase in the number of hemocytes producing ALFPm3 observed in V. harveyi-injected shrimp suggests a likely important function of the protein in defense against invading pathogens. ALFPm3 was shown to be able to bind to Gram-negative and Gram-positive bacterial cells and their major cell wall components, lipopolysaccharide (LPS) and lipoteichoic acid (LTA), respectively. The results suggested that ALFPm3 performs its antibacterial activity by binding to component(s) of the bacterial cell wall.

A synthetic cyclic peptide derived from Limulus anti-lipopolysaccharide factor neutralizes endotoxin in vitro and in vivo

Endotoxin, also known as lipopolysaccharide (LPS), is the major mediator of septic shock due to Gram-negative bacterial infections. Recently, much attention has been focused on cationic peptides which possess the potential to detoxify LPS. Limulus anti-LPS factor (LALF), a protein found in the horseshoe crab (Limulus polyphemus), has been proved with striking anti-LPS effects. We synthesized a cyclic peptide (CLP-19), and then investigated its bioactivity both in vitro and in vivo. The ability of CLP-19 to neutralize LPS in vitro was tested using a Limulus amebocyte lysate (LAL) assay and the LPS-binding affinity was measured with an affinity biosensor method. The synthetic peptide LALF31-52 (residues 31 to 52 of LALF) was used as the positive control peptide in this study. It was found that CLP-19 exhibited the significant activity to antagonize LPS without observable cytotoxicity effect on mouse macrophages. CLP-19 directly bound to LPS, and neutralized it in a dose-dependent manner in the LAL assay. Moreover, CLP-19 also showed the remarkable ability to protect mice from lethal LPS attack and to inhibit the LPS-induced tumor necrosis factor alpha (TNF-alpha) release by decreasing serum LPS in vivo. Our work suggests that this peptide is worthy of further investigation as a potential anti-LPS agent in the treatment of septic shock.

Mechanism of interaction of optimized Limulus-derived cyclic peptides with endotoxins: thermodynamic, biophysical and microbiological analysis

On the basis of formerly investigated peptides corresponding to the endotoxin-binding domain from LALF [Limulus anti-LPS (lipopolysaccharide) factor], a protein from Limulus polyphemus, we have designed and synthesized peptides of different lengths with the aim of obtaining potential therapeutic agents against septic shock syndrome. For an understanding of the mechanisms of action, we performed a detailed physicochemical and biophysical analysis of the interaction of rough mutant LPS with these peptides by applying FTIR (Fourier-transform infrared) spectroscopy, SAXS (small-angle X-ray scattering), calorimetric techniques [DSC (differential scanning calorimetry) and ITC (isothermal titration calorimetry)] and FFTEM (freeze-fracture transmission electron microscopy). Also, the action of the peptides on bacteria of different origin in microbial assays was investigated. Using FTIR and DSC, our results indicated a strong fluidization of the lipid A acyl chains due to peptide binding, with a decrease in the endothermic melting enthalpy change of the acyl chains down to a complete disappearance in the 1:0.5 to 1:2 [LPS]:[peptide] molar ratio range. Via ITC, it was deduced that the binding is a clearly exothermic process which becomes saturated at a 1:0.5 to 1:2 [LPS]:[peptide] molar ratio range. The results obtained with SAXS indicated a drastic change of the aggregate structures of LPS into a multilamellar stack, which was visualized in electron micrographs as hundreds of lamellar layers. This can be directly correlated with the inhibition of the LPS-induced production of tumour necrosis factor alpha in human mononuclear cells, but not with the action of the peptides on bacteria.

Shrimp (Penaeus monodon) anti-lipopolysaccharide factor reduces the lethality of Pseudomonas aeruginosa sepsis in mice

We investigated the efficacy of amino acids 55-76 of the synthetic shrimp anti-lipopolysaccharide factor peptide (SALF(55-76) cyclic peptide), the C-terminal part of the shrimp anti-lipopolysaccharide factor. This study was conducted to elucidate the effects of the antiseptic action of this peptide. The SALF(55-76) cyclic peptide was tested against bacterial clinical isolates and showed broad-spectrum antimicrobial activity. Transmission electron microscopic (TEM) examination of SALF(55-76) cyclic peptide-treated Pseudomonas aeruginosa showed that severe swelling preceded cell death and breakage of the outer membrane; the intracellular inclusion was found to have effluxed extracellularly. When mice were treated with the SALF(55-76) cyclic peptide before bacterial challenge with P. aeruginosa, the peptide highly protected mice against death by sepsis. The P. aeruginosa recovered from SALF(55-76) cyclic peptide-treated mice after 4 h exhibited reduced bacterial growth similar to that recovered from vancomycin-treated mice. In addition, the syntheses of inflammatory cytokines, such as interleukin (IL)-2, IL-4, IL-10, IL-12, IL-13, interferon-gamma, and tumor necrosis factor [TNF]-alpha, were significantly upregulated 4 h after SALF(55-76) cyclic peptide treatment except for IL-4 in the liver. The expressions of Toll-like receptor 4 (Tlr4), Irf3, myd88, and Tram, were considerably elevated, but only Tlr4 existed in the spleen 4 h after SALF(55-76) cyclic peptide treatment. The prophylactic administration of SALF(55-76) cyclic peptide was begun the TNF-alpha response in comparison to untreated mice by an ELISA analysis. Due to its multifunctional properties, the SALF(55-76) cyclic peptide may become an important prophylaxis against and therapy for bacterial infectious diseases, as well as for septic shock.

Host defence peptides from invertebrates – emerging antimicrobial strategies

Cationic antimicrobial (host defence) peptides are found as potent components of the innate immune system of all invertebrates in which they have been investigated. They vary substantially in their amino acid sequences, secondary structures, inducibility, potency and antimicrobial activity spectra. This enormous diversity is providing templates for the design and development of both antibiotic peptides and peptides that selectively modulate innate immunity to increase protection against infections and sepsis.

Cationic host defense (antimicrobial) peptides

Members of the cationic host defense (antimicrobial) peptide family are widely distributed in nature, existing in organisms from insects to plants to mammals and non-mammalian vertebrates. Although many demonstrate direct antimicrobial activity against bacteria, fungi, eukaryotic parasites and/or viruses, it has been established that cationic peptides have a key modulatory role in the innate immune response. More recent evidence suggests that host defense peptides are effective adjuvants, are synergistic with other immune effectors, polarize the adaptive response, and support wound healing. In addition, the mechanisms of action are being unraveled, which support more effective implementation of derivatives of these endogenous peptides as therapeutic agents.

Cyclic antimicrobial peptides based on Limulus anti-lipopolysaccharide factor for neutralization of lipopolysaccharide

Bacterial endotoxin (lipopolysaccharide, LPS) is responsible for the septic shock syndrome. As potential therapeutic agents cyclic cationic antimicrobial peptides of different length, based on the Limulus anti-lipopolysaccharide factor (LALF), were synthesized, and their interaction with LPS was characterized physico-chemically and related to results in biological assays. All peptides inhibited the LPS-induced cytokine production in human mononuclear cells and the Limulus amebocyte lysate in a concentration-dependent way, with the peptide comprising the complete LPS-binding loop of the LALF (cLALF22) being the most effective. The peptides were neither cytotoxic nor hemolytic, except a slight effect of cLALF22. The peptides were able to displace Ca(2+) cations from a LPS monolayer, with cLALF22 being again most effective in accordance with results from isothermal titration calorimetry, in which saturation of binding was observed at an equimolar [cLALF22]:[LPS] ratio, and at a ratio 2-2.5 for the other peptides. For cLALF22, zeta (xi) potential experiments exhibited a complete compensation of the negative charges of LPS, whereas for the other peptides a residual negative potential of -20 to -40mV was found. X-ray diffraction experiments showed that the mixed unilamellar/cubic inverted aggregate structure of the lipid A part of LPS was converted into a multilamellar one. The gel to liquid crystalline phase transition of the acyl chains of LPS was changed upon cLALF22 binding, leading to a clear fluidization, which was not observed or only to a lesser degree for the other peptides. The affinity of the peptides for LPS led to a reduced binding of lipopolysaccharide-binding protein (LBP) to target membranes and hence to an inhibition of cytokine induction in human mononuclear cells.

A Limulus anti-LPS factor-derived peptide modulates cytokine gene expression and promotes resolution of bacterial acute infection in mice

Sepsis in experimental animals and humans has been associated with perturbed immune response. A major event contributing to the decrease in immune functions in septic disorders seems to be the inadequate balance of cytokines mediating the interactions between the innate and adaptive immune systems. We previously observed that a cyclic peptide derived from the Limulus anti-LPS factor (LALF), which partially protect mice from endotoxic shock lethality, has the ability to modulate cytokine secretion in vitro. We herein examined the effects of the LALF(31-52) peptide in an experimental model of Gram-negative peritoneal sepsis and analyzed the cytokine gene expression in the spleen and liver of peptide-treated mice. The prophylactic administration of LALF(31-52) abrogated the systemic TNF-alpha response, reduced organ damage and increased the survival of infected mice. Histological examination of spleen and liver in peptide-treated mice showed prevention of tissue damage induced by the high dose of Pseudomonas aeruginosa. This treatment modulates the cytokine gene expression in these tissues, stimulating IL-2, IL-12 and IL-13 mRNA synthesis, while IL-4 and IL-10 mRNA expression was not modified. This cytokine profile induced by the LALF-derived peptide seems to be favorable for host resistance against Gram-negative bacteria acute infection. In addition, peptide treatment was effective after the initiation of the systemic inflammatory response, promoting a significant increase in mice survival. These results further demonstrate the immunomodulatory potential of LALF(31-52) and are relevant for the design of prophylactic and therapeutic strategies for acute bacteria infection and sepsis, especially for preventing or ameliorating host immunity defects in these disorders.