Protective effects of a human 18-kilodalton cationic antimicrobial protein (CAP18)-derived peptide against murine endotoxemia

The Correlation of Antibacterial Peptides Concentration in Umbilical Cord Blood and Early Onset Sepsis in Preterm Infants

Umbilical cord blood from singleton preterm infants was collected during delivery, and the concentration of LL37 was measured. C-reactive protein (CRP), white blood cell count (WBC), platelets (PLT), and mean platelet volume (MPV) were determined within 3 days after birth. The differences in LL37, CRP, WBC, PLT, and MPV levels between the two groups were compared. Pearson correlation method was used to analyze the correlation between these factors. The early individual value of each detected index for early onset sepsis was analyzed by ROC curve. The level of LL37 in umbilical cord blood of sepsis group was significantly higher than those in the control group (383.85 ± 46.71 vs. 252.37 ± 83.30 ng/ml). Meanwhile, the levels of CRP, WBC, and MPV in the sepsis group were significantly higher than those in the control group (CRP:5.73 ± 4.19 vs. 2.50 ± 2.77 mg/L; WBC: 13.47 ± 12.35 vs. 6.83 ± 3.55 × 109/L; MPV: 11.20 ± 1.11 vs. 8.90 ± 0.68 fL), the level of PLT was significantly lower than those in the control group (PLT: 161.00 ± 38.51 vs. 241.50 ± 49.85 × 109/L) (P < 0.05). Pearson correlation analysis showed that the expression of LL37 was negatively correlated with PLT level (r = -0.9347, P < 0.0001), and positively correlated with MPV level (r = 0.9463, P < 0.0001). ROC curve analysis showed that the area under curve of LL37 for diagnosis of early onset sepsis was 0.875, the prediction probability was 0.7, the sensitivity was 90.0% and the specificity was 80.0%.

Enantioselective Synthesis and Application of Small and Environmentally Sensitive Fluorescent Amino Acids for Probing Biological Interactions

Environmentally sensitive fluorescent amino acids (FlAAs) have been used extensively to probe biological interactions. However, most of these amino acids are large and do not resemble amino acid side chains. Here, we report the enantioselective synthesis of two small and environmentally sensitive fluorescent amino acids bearing 7-dialkylaminocoumarin side chains by alkylation of a Ni(II) glycine Schiff base complex. These amino acids exhibit a large increase in fluorescence as environment polarity decreases. One of these FLAAs was incorporated into a highly active analog of the cyclic lipopeptide antibiotic paenibacterin by Fmoc solid-phase peptide synthesis via a new and very efficient route. This peptide was used to probe the interaction of the antibiotic with model liposomes, lipopolysaccharides, and live bacteria.

Role of biometals in activation of immune cum inflammatory response in ovine ageing eye: a potential model for understanding human geriatric eye diseases

The present study was designed to evaluate the age-related changes in biometal and antimicrobial peptide (cathelicidin) concentration and their role in oxidative cum pro-inflammatory cascade in an ovine animal model. Clinically healthy ovine (n = 126) were grouped as Group I (n = 55, age = up to 3 years), Group II (n = 52, age = above 3-below 6 years) and Group III (n = 19, age = 6 years above). Samples (aqueous humour and lens of the eye) were collected stored at - 80 °C till further analysis. In aqueous humour, the concentration of zinc (p < 0.001 in group III), copper (p < 0.05 in group II and p < 0.001 group III) and iron (p < 0.05 in group III) were significantly increased compared to group I. While as the concentration of magnesium were significantly decreased in group II (p < 0.001) and group III (p < 0.05) compared to group I. Similarly in eye lens the level of copper remained uniform as no significant change was observed across different age groups, while as significantly elevated levels of iron were observed in group III (p < 0.001) compared to group I. whereas, levels of lens Zinc (p < 0.05 in group II) and magnesium (p < 0.05 in group III and p < 0.001 in group II) were significantly decreased compared to group I. Age-dependent increase in levels of oxidation products which include advanced oxidation protein products (AOPP) in aqueous humour and lenses of group II and group III (p < 0.001) and MDA in aqueous humour of group III (p < 0.05) were found compared to levels recorded in group I. In contrast, levels of antioxidants which include lens vitamin C in group II and group III (p < 0.01) and lens superoxide dismutase (SOD) in group III (p < 0.001) were significantly increased compared to group I. Levels of pro-inflammatory cytokines in aqueous humour revealed significantly (p < 0.001) age-dependent increase in IL-1, IL-6 and TNF-α elevated in group III, and group II as compared to group I, However, cathelicidin level in aqueous humour of group III and group II were significantly (p < 0.001) lower as compared to groups I. Furthermore,the present study observed significant (p < 0.05) metal-metal positive interaction between copper levels in lens with levels of (iron and magnesium) in aqueous humour, levels of Zn in lens with levels of Zn in aqueous humour, levels of Mg in lens with levels of (Cu, Zn and Mg) in aqueous humour. In addition,the present study reports significantly negative interaction between levels of lens Fe with levels of lens magnesium level, aqueous humour magnesium level and levels of copper in aqueous humour. A significantly positive correlation was observed between oxidative markers and pro-inflammatory cytokine levels, while a significant negative correlation was observed between antioxidant defence markers and pro-inflammatory cytokine. These results suggest the essential role of age-related changes in biometal levels, oxidative stress and pro-inflammatory cytokines. These changes might help understand age-related changes in pathogenesis and effective targeting of pathogenetic pathways in ocular diseases.

Broad-Spectrum Robust Direct Bactericidal Activity of Fish IFNφ1 Reveals an Antimicrobial Peptide-like Function for Type I IFNs in Vertebrates

Type I IFNs (IFN-Is) play pivotal roles in host defense against viral infections but remain enigmatic against bacterial pathogens. In this study, we recombinantly expressed and purified intact grass carp (Ctenopharyngodon idella) IFNφ1 (gcIFNφ1), a teleost IFN-I. gcIFNφ1 widely powerfully directly kills both Gram-negative and Gram-positive bacteria in a dose-dependent manner. gcIFNφ1 binds to LPS or peptidoglycan and provokes bacterial membrane depolarization and disruption, resulting in bacterial death. Furthermore, gcIFNφ1 can efficiently protect zebrafish against Aeromonas hydrophila infection and significantly reduce the bacterial loads in tissues by an infection model. In addition, we wonder whether antibacterial IFN-I members exist in other vertebrates. The amino acid compositions of representative IFN-Is with strong positive charges from Pisces, Amphibia, reptiles, Aves, and Mammalia demonstrate high similarities with those of 2237 reported cationic antimicrobial peptides in antimicrobial peptide database. Recombinant intact representative IFN-I members from the nonmammalian sect exhibit potent broad-spectrum robust bactericidal activity through bacterial membrane depolarization; in contrast, the bactericidal activity is very weak from mammalian IFN-Is. The findings display a broad-spectrum potent direct antimicrobial function for IFN-Is, to our knowledge previously unknown. The results highlight that IFN-Is are important and robust in host defense against bacterial pathogens, and unify direct antibacterial and indirect antiviral bifunction in nonmammalian jawed vertebrates.

Murine and Human Cathelicidins Contribute Differently to Hallmarks of Mastitis Induced by Pathogenic Prototheca bovis Algae

Prototheca bovis (formerly P. zopfii genotype-II) is an opportunistic, achlorophyllous alga that causes mastitis in cows and skin disease in cats and dogs, as well as cutaneous lesions in both immunocompetent and immunosuppressed humans. Antifungal medications are commonly ineffective. This study aimed to investigate innate immune responses contributed by cathelicidins to P. bovis in the mammary gland using a mastitis model in mice deficient in the sole murine cathelicidin (Camp). We determined P. bovis caused acute mastitis in mice and induced Camp gene transcription. Whereas, Camp ^-/- and Camp ^+/+ littermates had similar local algae burden, Camp ^+/+ mice produced more pro-inflammatory cytokines, TNF-α, and Cxcl-1. Likewise, Camp ^+/+ bone marrow-derived macrophages were more responsive to P. bovis, producing more TNF-α and Cxcl-1. Human cathelicidin (LL-37) exhibited a different effect against P. bovis; it had direct algicidal activity against P. bovis and lowered TNF-α, Cxcl-1, and IL-1β production in both cultured murine macrophages and mammary epithelial cells exposed to the pathogenic algae. In conclusion, cathelicidins were involved in protothecosis pathogenesis, with unique roles among the diverse peptide family. Whereas, endogenous cathelicidin (Camp) was key in mammary gland innate defense against P. bovis, human LL-37 had algicidal and immunomodulatory functions.

Regulation of the Immune Balance During Allogeneic Hematopoietic Stem Cell Transplantation by Vitamin D

One of the most promising therapeutic approaches for numerous hematological malignancies represents the allogeneic hematopoietic stem cell transplantation (allo-HSCT). One major complication is the development of the life-threatening graft-vs.-host disease (GvHD) which limits beneficial effects of graft-vs.-leukemia (GvL) responses during allo-HSCT. Strengthening GvL effects without induction of severe GvHD is essential to decrease the relapse rate after allo-HSCT. An interesting player in this context is vitamin D₃ since it has modulatory capacity in both preventing GvHD and boosting GvL responses. Current studies claim that vitamin D₃ induces an immunosuppressive environment by dendritic cell (DC)-dependent generation of regulatory T cells (Tregs). Since vitamin D₃ is known to support the antimicrobial defense by re-establishing the physical barrier as well as releasing defensins and antimicrobial peptides, it might also improve graft-vs.-infection (GvI) effects in patients. Beyond that, alloreactive T cells might be attenuated by vitamin D₃-mediated inhibition of proliferation and activation. Despite the inhibitory effects of vitamin D₃ on T cells, anti-tumor responses of GvL might be reinforced by vitamin D₃-triggered phagocytic activity and antibody-based immunotherapy. Therefore, vitamin D₃ treatment does not only lead to a shift from a pro-inflammatory toward a tolerogenic state but also promotes tumoricidal activity of immune cells. In this review we focus on vitamin D₃ and its immunomodulatory effects by enhancing anti-tumor activity while alleviating harmful allogeneic responses in order to restore the immune balance.

Pathological Role and Diagnostic Value of Endogenous Host Defense Peptides in Adult and Neonatal Sepsis: A Systematic Review

BACKGROUND

Sepsis is a systemic host response to an infection leading to organ failure. This is associated with dynamic expression of endogenous host defense peptides. Dysregulation of these peptides is associated with septic morbidity and mortality.

METHODS

We performed a systematic search of articles indexed in PubMed, ISI Web of Knowledge, EmBase, and Scopus database from inception to October 2016. Both preclinical and clinical studies investigating the role of host defense peptides in pathogenesis and as biomarkers for sepsis were included.

RESULTS

Of the available literature, cathelicidin, defensin, and hepcidin are among the best-characterized peptides. These regulate immune response, and crosstalk with pyroptosis and coagulation cascades. The applicability of these peptides as septic biomarkers has been investigated in vitro and in vivo studies. However, numerous studies were based on endotoxemia without an infection, jeopardizing interpretation of the outcomes. Cathelicidin and defensin were frequently reported in adult sepsis while hepcidin in neonatal sepsis. The expression level of these peptides is significantly associated with septic condition. Most of the studies employed a cross-sectional design, precluding the establishment of a temporal relationship between candidate peptide biomarkers and sepsis.

CONCLUSIONS

Innate defense peptides have been insufficiently evaluated as either diagnostic or prognostic biomarkers. In the future, evaluation of host defense peptides as septic biomarkers may employ a longitudinal design and consider a panel of multiple peptides.

Antimicrobial Peptides Secreted From Human Cryopreserved Viable Amniotic Membrane Contribute to its Antibacterial Activity

Chronic wounds remain a large problem in the field of medicine and are often associated with risk of infection and amputation. Recently, a commercially available human cryopreserved viable amniotic membrane (hCVAM) has been shown to effectively promote wound closure and reduce wound-related infections. A sprevious study indicates that hCVAM can inhibit the growth of bacteria associated with chronic wounds. In the present study, we investigated the mechanism of hCVAM antimicrobial activity. Our data demonstrate that antimicrobial activities against common pathogens in chronic wounds such as P.aeruginosa, S.aureus and Methicillin-resistant S.aureus (MRSA) are mediated via the secretion of soluble factors by viable cells in hCVAM and that these factors are proteins in nature. Further, we show that genes for antimicrobial peptides (AMPs) including human beta-defensins (HBDs) are expressed by hCVAM and that expression levels positively correlate with antimicrobial activity of hCVAM. At the protein level, our data indicate that HBD2 and HBD3 are secreted by hCVAM and directly contribute to its activity against P. aeruginosa. These data provide evidence that soluble factors including AMPs are hCVAM antimicrobial agents and are consistent with a role for AMPs in mediating antimicrobial properties of the membrane.

Positive Rates and Factors Associated with Abnormal Lung Function of Greenhouse Workers in China: A Cross-Sectional Study

Since the number of greenhouse workers are increasing in China, this observational cross-sectional study was designed to evaluate lung function and discuss the potential risk factors, to provide evidence in the surveillance of greenhouse workers' health. 678 greenhouse workers in Gansu Province, China were enrolled. A questionnaire which included demographic and occupational information was used. Vital capacity (VC), forced vital capacity (FVC), forced expiratory volume in 1 s (FEV₁), and FEV₁:FVC ratios (FEV₁/FVC), maximal expiratory flow after 50% of the FVC has not been exhaled (MEF₅₀), maximal expiratory flow after 25% of the FVC has not been exhaled (MEF₂₅) and maximal mid-expiratory flow curve (MMEF) were measured as lung function indicators. The mean values and standard deviations (SDs) of VC% predicted, FVC% predicted, FEV₁% predicted and FEV₁/FVC ratio were 106.07 ± 13.36, 107.60 ± 13.95, 97.19 ± 14.80 and 89.76 ± 10.78 respectively. The positive rates of above four and abnormal lung ventilation function were 2.9%, 2.8%, 11.2%, 4.6% and 6.5% respectively. Gender, age, BMI and number of greenhouses owned were influence factors of lung ventilation function (p < 0.05). The mean values and SDs of MEF₅₀% predicted, MEF₂₅% predicted and MMEF% predicted were 69.63 ± 24.95, 54.04 ± 24.94 and 66.81 ± 24.53. The positive rates of above three and abnormal small airway function were 45.0%, 72.1%, 47.2% and 49.4% respectively. Age, education and number of greenhouses owned were influence factors for small airway function (p < 0.05). Working in a greenhouse might influence lung function of the workers. Small airway function indicators could be used as priority indicators for the surveillance of greenhouse workers' health.

Review: D-Galactosamine lethality model: scope and limitations

D-Galactosamine (D-galN) is well established as sensitizing mice and other animals to the lethal effects of TNF, specifically, and by several orders of magnitude. Protection by anti-TNF neutralizing antibody is complete, as is (metabolically-based) protection by uridine. Sensitization occurs regardless of the origin of the released TNF, whether it is released from macrophages and/or T-cells. The same is true for the challenging agent which leads to the release of TNF, whether it is endotoxin, a superantigen, lipoprotein, bacterial DNA, or bacteria, either killed or proliferating. Most studies have utilized endotoxin as the challenging agent, and more than 70 agents have been reported to confer protection against LPS and/or TNF challenge in the model. The model has provided new insight regarding modes of protection, including from dexamethasone, which protects against challenge from LPS but not from challenge by TNF. The D-galN lethality model has also been used to test for synergistic behavior between different bacterial components, and to test for lethality when only small amounts of the challenging agent are available (lipid A chemistry).

Invited review: Mechanisms of endotoxin neutralization by synthetic cationic compounds

A basic challenge in the treatment of septic patients in critical care units is the release of bacterial pathogenicity factors such as lipopolysaccharide (LPS, endotoxin) from the cell envelope of Gram-negative bacteria due to killing by antibiotics. LPS aggregates may interact with serum and membrane proteins such as LBP (lipopolysaccharide-binding protein) and CD14 leading to the observed strong reaction of the immune system. Thus, an effective treatment of patients infected by Gram-negative bacteria must comprise beside bacterial killing the neutralization of endotoxins. Here, data are summarized for synthetic compounds indicating the stepwise development to very effective LPS-neutralizing agents. These data include synthetic peptides, based on the endotoxin-binding domains of natural binding proteins such as lactoferrin, Limulus anti-LPS factor, NK-lysin, and cathelicidins or based on LPS sequestering polyamines. Many of these compounds could be shown to act not only in vitro, but also in vivo (e.g . in animal models of sepsis), and might be useful in future clinical trials and in sepsis therapy.

Anti-endotoxin properties of cationic host defence peptides and proteins

The innate immune system of mammals contains a series of peptides with overall positive charge and an amphipathic structure which have a variety of important properties in host defences. Although these are often termed cationic antimicrobial peptides, they have numerous roles in innate defences in all complex species of life and thus we prefer to refer to them as host defence peptides. These roles include: (i) an ability to kill micro-organisms directly, ranging from bacteria to viruses, fungi, parasites and helminths; (ii) an adjuvant activity in the adaptive response; and (iii) a multiplicity of roles in modulating innate immunity, including an apparent ability to stimulate protective innate immunity while suppressing harmful inflammatory/septic responses. This latter property may be one of the more important activities of these peptides in vivo. Innate immunity is thought to be triggered by the interaction of conserved bacterial components with particular receptors including Toll-like receptors (TLRs) on host cells. However, the initiation of the innate immune response through this route may trigger a pro-inflammatory cascade that is the principle cause of harmful conditions such as sepsis. Since we are exposed to potentially dangerous pathogens on a daily basis, the host response must contain certain checks and balances. We propose that host defence peptides have a role in feed-back modulation of inflammation under normal (low-pathogen exposure) conditions. This review surveys the available information regarding the antiendotoxic/anti-inflammatory properties of host defence peptides, and will address whether this potential might be exploited for therapeutic benefit in sepsis.

Guar gum as a new antimicrobial peptide delivery system against diabetic foot ulcers Staphylococcus aureus isolates

Diabetic patients frequently develop diabetic foot ulcers (DFUs), particularly those patients vulnerable to Staphylococcus aureus opportunistic infections. It is urgent to find new treatments for bacterial infections. The antimicrobial peptide (AMP) nisin is a potential candidate, mainly due to its broad spectrum of action against pathogens. Considering that AMP can be degraded or inactivated before reaching its target at therapeutic concentrations, it is mandatory to establish effective AMP delivery systems, with the natural polysaccharide guar gum being one of the most promising. We analysed the antimicrobial potential of nisin against 23 S. aureus DFU biofilm-producing isolates. Minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), minimum biofilm inhibitory concentration (MBIC) and minimum biofilm eradication concentration (MBEC) were determined for nisin diluted in HCl and incorporated in guar gum gel. Statistical analysis was performed using the Wilcoxon matched-pair test. Nisin was effective against all isolates, including some multidrug-resistant clinical isolates, independent of whether it is incorporated in guar gum. While differences among MIC, MBC and MBIC values were observed for HCl- and guar gum- nisin, no significant differences were found between MBEC values. Inhibitory activity of both systems seems to differ only twofold, which does not compromise guar gum gel efficiency as a delivery system. Our results highlight the potential of nisin as a substitute for or complementary therapy to current antibiotics used for treating DFU infections, which is extremely relevant considering the increase in multidrug-resistant bacteria dissemination. The guar gum gel represents an alternative, practical and safe delivery system for AMPs, allowing the development of novel topical therapies as treatments for bacterial skin infections.

In Vivo, In Vitro, and In Silico Characterization of Peptoids as Antimicrobial Agents

Bacterial resistance to conventional antibiotics is a global threat that has spurred the development of antimicrobial peptides (AMPs) and their mimetics as novel anti-infective agents. While the bioavailability of AMPs is often reduced due to protease activity, the non-natural structure of AMP mimetics renders them robust to proteolytic degradation, thus offering a distinct advantage for their clinical application. We explore the therapeutic potential of N-substituted glycines, or peptoids, as AMP mimics using a multi-faceted approach that includes in silico, in vitro, and in vivo techniques. We report a new QSAR model that we developed based on 27 diverse peptoid sequences, which accurately correlates antimicrobial peptoid structure with antimicrobial activity. We have identified a number of peptoids that have potent, broad-spectrum in vitro activity against multi-drug resistant bacterial strains. Lastly, using a murine model of invasive S. aureus infection, we demonstrate that one of the best candidate peptoids at 4 mg/kg significantly reduces with a two-log order the bacterial counts compared with saline-treated controls. Taken together, our results demonstrate the promising therapeutic potential of peptoids as antimicrobial agents.

The antimicrobial peptide cathelicidin modulates Clostridium difficile-associated colitis and toxin A-mediated enteritis in mice

BACKGROUND

Clostridium difficile mediates intestinal inflammation by releasing toxin A (TxA), a potent enterotoxin. Cathelicidins (Camp as gene name, LL-37 peptide in humans and mCRAMP peptide in mice) are antibacterial peptides that also posses anti-inflammatory properties.

OBJECTIVES

To determine the role of cathelicidins in models of Clostridium difficile infection and TxA-mediated ileal inflammation and cultured human primary monocytes.

DESIGN

Wild-type (WT) and mCRAMP-deficient (Camp(-/-)) mice were treated with an antibiotic mixture and infected orally with C difficile. Some mice were intracolonically given mCRAMP daily for 3 days. Ileal loops were also prepared in WT mice and treated with either saline or TxA and incubated for 4 h, while some TxA-treated loops were injected with mCRAMP.

RESULTS

Intracolonic mCRAMP administration to C difficile-infected WT mice showed significantly reduced colonic histology damage, apoptosis, tissue myeloperoxidase (MPO) and tumour necrosis factor (TNF)α levels. Ileal mCRAMP treatment also significantly reduced histology damage, tissue apoptosis, MPO and TNFα levels in TxA-exposed ileal loops. WT and Camp(-/-) mice exhibited similar intestinal responses in both models, implying that C difficile/TxA-induced endogenous cathelicidin may be insufficient to modulate C difficile/TxA-mediated intestinal inflammation. Both LL-37 and mCRAMP also significantly reduced TxA-induced TNFα secretion via inhibition of NF-κB phosphorylation. Endogenous cathelicidin failed to control C difficile and/or toxin A-mediated inflammation and even intestinal cathelicidin expression was increased in humans and mice.

CONCLUSION

Exogenous cathelicidin modulates C difficile colitis by inhibiting TxA-associated intestinal inflammation. Cathelicidin administration may be a new anti-inflammatory treatment for C difficile toxin-associated disease.

Defense peptides secreted by helminth pathogens: antimicrobial and/or immunomodulator molecules?

Host defense peptides (HDPs) are an evolutionarily conserved component of the innate immune response found in all living species. They possess antimicrobial activities against a broad range of organisms including bacteria, fungi, eukaryotic parasites, and viruses. HDPs also have the ability to enhance immune responses by acting as immunomodulators. We discovered a new family of HDPs derived from pathogenic helminth (worms) that cause enormous disease in animals and humans worldwide. The discovery of these peptides was based on their similar biochemical and functional characteristics to the human defense peptide LL-37. We propose that these new peptides modulate the immune response via molecular mimicry of mammalian HDPs thus providing a mechanism behind the anti-inflammatory properties of helminth infections.

A helminth cathelicidin-like protein suppresses antigen processing and presentation in macrophages via inhibition of lysosomal vATPase

We previously reported the identification of a novel family of immunomodulatory proteins, termed helminth defense molecules (HDMs), that are secreted by medically important trematode parasites. Since HDMs share biochemical, structural, and functional characteristics with mammalian cathelicidin-like host defense peptides (HDPs), we proposed that HDMs modulate the immune response via molecular mimicry of host molecules. In the present study, we report the mechanism by which HDMs influence the function of macrophages. We show that the HDM secreted by Fasciola hepatica (FhHDM-1) binds to macrophage plasma membrane lipid rafts via selective interaction with phospholipids and/or cholesterol before being internalized by endocytosis. Following internalization, FhHDM-1 is rapidly processed by lysosomal cathepsin L to release a short C-terminal peptide (containing a conserved amphipathic helix that is a key to HDM function), which then prevents the acidification of the endolysosomal compartments by inhibiting vacuolar ATPase activity. The resulting endolysosomal alkalization impedes macrophage antigen processing and prevents the transport of peptides to the cell surface in conjunction with MHC class II for presentation to CD4(+) T cells. Thus, we have elucidated a novel mechanism by which helminth pathogens alter innate immune cell function to assist their survival in the host.

Regulation of antimicrobial peptide gene expression by nutrients and by-products of microbial metabolism

BACKGROUND

Antimicrobial peptides (AMPs) are synthesized and secreted by immune and epithelial cells that are constantly exposed to environmental microbes. AMPs are essential for barrier defense, and deficiencies lead to increased susceptibility to infection. In addition to their ability to disrupt the integrity of bacterial, viral and fungal membranes, AMPs bind lipopolysaccharides, act as chemoattractants for immune cells and bind to cellular receptors and modulate the expression of cytokines and chemokines. These additional biological activities may explain the role of AMPs in inflammatory diseases and cancer. Modulating the endogenous expression of AMPs offers potential therapeutic treatments for infection and disease.

METHODS

The present review examines the published data from both in vitro and in vivo studies reporting the effects of nutrients and by-products of microbial metabolism on the expression of antimicrobial peptide genes in order to highlight an emerging appreciation for the role of dietary compounds in modulating the innate immune response.

RESULTS

Vitamins A and D, dietary histone deacetylases and by-products of intestinal microbial metabolism (butyrate and secondary bile acids) have been found to regulate the expression of AMPs in humans. Vitamin D deficiency correlates with increased susceptibility to infection, and supplementation studies indicate an improvement in defense against infection. Animal and human clinical studies with butyrate indicate that increasing expression of AMPs in the colon protects against infection.

CONCLUSION

These findings suggest that diet and/or consumption of nutritional supplements may be used to improve and/or modulate immune function. In addition, by-products of gut microbe metabolism could be important for communicating with intestinal epithelial and immune cells, thus affecting the expression of AMPs. This interaction may help establish a mucosal barrier to prevent invasion of the intestinal epithelium by either mutualistic or pathogenic microorganisms.

The neonatal immune system: immunomodulation of infections in early life

The innate and adaptive immune responses in neonates are usually functionally impaired when compared with their adult counterparts. The qualitative and quantitative differences in the neonatal immune response put them at risk for the development of bacterial and viral infections, resulting in increased mortality. Newborns often exhibit decreased production of Th1-polarizing cytokines and are biased toward Th2-type responses. Studies aimed at understanding the plasticity of the immune response in the neonatal and early infant periods or that seek to improve neonatal innate immune function with adjuvants or special formulations are crucial for preventing the infectious disease burden in this susceptible group. Considerable studies focused on identifying potential immunomodulatory therapies have been performed in murine models. This article highlights the strategies used in the emerging field of immunomodulation in bacterial and viral pathogens, focusing on preclinical studies carried out in animal models with particular emphasis on neonatal-specific immune deficits.

Prokaryotic selectivity and LPS-neutralizing activity of short antimicrobial peptides designed from the human antimicrobial peptide LL-37

To develop novel antimicrobial peptides (AMPs) with shorter lengths, improved prokaryotic selectivity and retained lipolysaccharide (LPS)-neutralizing activity compared to human cathelicidin AMP, LL-37, a series of amino acid-substituted analogs based on IG-19 (residues 13-31 of LL-37) were synthesized. Among the IG-19 analogs, the analog a4 showed the highest prokaryotic selectivity, but much lower LPS-neutralizing activity compared to parental LL-37. The analogs, a5, a6, a7 and a8 with higher hydrophobicity displayed LPS-neutralizing activity comparable to that of LL-37, but much lesser prokaryotic selectivity. These results indicate that the proper hydrophobicity of the peptides is crucial to exert the amalgamated property of LPS-neutralizing activity and prokaryotic selectivity. Furthermore, to increase LPS-neutralizing activity of the analog a4 without a remarkable decrease in prokaryotic selectivity, we synthesized Trp-substituted analogs (a4-W1 and a4-W2), in which Phe(5) or Phe(15) of a4 is replaced by Trp. Despite their same prokaryotic selectivity, a4-W2 displayed much higher LPS-neutralizing activity compared to a4-W1. When compared with parental LL-37, a4-W2 showed retained LPS-neutralizing activity and 2.8-fold enhanced prokaryotic selectivity. These results suggest that the effective site for Trp-substitution when designing novel AMPs with higher LPS-neutralizing activity, without a remarkable reduction in prokaryotic selectivity, is the amphipathic interface between the end of the hydrophilic side and the start of the hydrophobic side rather than the central position of the hydrophobic side in their α-helical wheel projection. Taken together, the analog a4-W2 can serve as a promising template for the development of therapeutic agents for the treatment of endotoxic shock and bacterial infection.

A family of helminth molecules that modulate innate cell responses via molecular mimicry of host antimicrobial peptides

Over the last decade a significant number of studies have highlighted the central role of host antimicrobial (or defence) peptides in modulating the response of innate immune cells to pathogen-associated ligands. In humans, the most widely studied antimicrobial peptide is LL-37, a 37-residue peptide containing an amphipathic helix that is released via proteolytic cleavage of the precursor protein CAP18. Owing to its ability to protect against lethal endotoxaemia and clinically-relevant bacterial infections, LL-37 and its derivatives are seen as attractive candidates for anti-sepsis therapies. We have identified a novel family of molecules secreted by parasitic helminths (helminth defence molecules; HDMs) that exhibit similar biochemical and functional characteristics to human defence peptides, particularly CAP18. The HDM secreted by Fasciola hepatica (FhHDM-1) adopts a predominantly α-helical structure in solution. Processing of FhHDM-1 by F. hepatica cathepsin L1 releases a 34-residue C-terminal fragment containing a conserved amphipathic helix. This is analogous to the proteolytic processing of CAP18 to release LL-37, which modulates innate cell activation by classical toll-like receptor (TLR) ligands such as lipopolysaccharide (LPS). We show that full-length recombinant FhHDM-1 and a peptide analogue of the amphipathic C-terminus bind directly to LPS in a concentration-dependent manner, reducing its interaction with both LPS-binding protein (LBP) and the surface of macrophages. Furthermore, FhHDM-1 and the amphipathic C-terminal peptide protect mice against LPS-induced inflammation by significantly reducing the release of inflammatory mediators from macrophages. We propose that HDMs, by mimicking the function of host defence peptides, represent a novel family of innate cell modulators with therapeutic potential in anti-sepsis treatments and prevention of inflammation.

Spotlight on Human LL-37, an Immunomodulatory Peptide with Promising Cell-Penetrating Properties

Cationic antimicrobial peptides are major components of innate immunity and help control the initial steps of the infectious process. They are expressed not only by immunocytes, but also by epithelial cells. They share an amphipathic secondary structure with a polar cationic site, which explains their tropism for prokaryote membranes and their hydrophobic site contributing to the destructuration of these membranes. LL-37 is the only cationic antimicrobial peptide derived from human cathelicidin. LL-37 can also cross the plasma membrane of eukaryotic cells, probably through special domains of this membrane called lipid rafts. This transfer could be beneficial in the context of vaccination: the activation of intracellular toll-like receptors by a complex formed between CpG oligonucleotides and LL-37 could conceivably play a major role in the building of a cellular immunity involving NK cells.

The antimicrobial peptide cathelicidin enhances activation of lung epithelial cells by LPS

Epithelial cells (ECs) are usually hyporesponsive to various microbial products. Detection of lipopolysaccharide (LPS), the major component of gram-negative bacteria, is impeded, at least in part, by intracellular sequestration of its receptor, Toll-like receptor-4 (TLR4). In this study, using human bronchial ECs (hBECs) as a model of mucosal epithelium, we tested the hypothesis that the human LPS-binding, membrane-active cationic host defense peptide cathelicidin LL-37 augments epithelial response to LPS by facilitating its delivery to TLR4-containing intracellular compartments. We found that LL-37 significantly increases uptake of LPS by ECs with subsequent targeting to cholera toxin subunit B-labeled structures and lysosomes. This uptake is peptide specific, dose and time dependent, and involves the endocytotic machinery, functional lipid rafts, and epidermal growth factor receptor signaling. Cathelicidin-dependent LPS internalization resulted in significant increased release of the inflammatory cytokines IL-6 and IL-8. This indicates that, in ECs, this peptide may replace LPS-binding protein functions. In polarized ECs, the effect of LL-37 was restricted to the basolateral compartment of the epithelial membrane, suggesting that LL-37-mediated activation of ECs by LPS may be relevant to disease conditions associated with damage to the epithelial barrier. In summary, our study identified a novel role of LL-37 in host-microbe interactions as a host factor that licenses mucosal ECs to respond to LPS.

The antimicrobial peptide LL-37 modulates the inflammatory and host defense response of human neutrophils

The human cathelicidin antimicrobial peptide acts as an effector molecule of the innate immune system with direct antimicrobial and immunomodulatory effects. The aim of this study was to test whether the cathelicidin LL-37 modulates the response of neutrophils to microbial stimulation. Human neutrophils were exposed to LPS, Staphylococcus aureus and Pseudomonas aeruginosa subsequent to incubation with LL-37 and cytokine release was measured by ELISA. The incubation with LL-37 significantly decreased the release of proinflammatory cytokines from stimulated human neutrophils. ROS production of neutrophils was determined by a luminometric and a flow cytometry method. The peptide induced the production of ROS and the engulfment of bacteria into neutrophils. Peritoneal mouse neutrophils isolated from CRAMP-deficient and WT animals were treated with LPS and TNF-alpha in the supernatant was measured by ELISA. Antimicrobial activity of neutrophils was detected by incubating neutrophils isolated from CRAMP-knockout and WT mice with bacteria. Neutrophils from CRAMP-deficient mice released significantly more TNF-alpha after bacterial stimulation and showed decreased antimicrobial activity as compared to cells from WT animals. In conclusion, LL-37 modulates the response of neutrophils to bacterial activation. Cathelicidin controls the release of inflammatory mediators while increasing antimicrobial activity of neutrophils.

Antimicrobial peptides: general overview and clinical implications in human health and disease

Antimicrobial peptides (AMPs) are evolutionarily conserved molecules involved in the defense mechanisms of a wide range of organisms. Produced in bacteria, insects, plants and vertebrates, AMPs protect against a broad array of infectious agents. In mammals these peptides protect against bacteria, viruses, fungi, and certain parasites. Recently, novel biologic effects of AMPs have been documented such as endotoxin neutralization, chemotactic and immunomodulating activities, induction of angiogenesis and wound repair. Thus these ancestral molecules are crucial components of the innate immune system and attractive candidates for novel therapeutic approaches. This review focuses on cathelicin and defensins, the most documented human AMPs, and discusses their antimicrobial activity and pleiotropic immunomodulating effects on inflammatory and infectious diseases.

Structure-function relationship of the human antimicrobial peptide LL-37 and LL-37 fragments in the modulation of TLR responses

Cathelicidins are effector molecules of the innate host defense system that establish an antimicrobial barrier at epithelial interfaces. The human cathelicidin LL-37, in addition to its antimicrobial activity, also exhibits immunomodulatory effects, such as inhibition of pro-inflammatory responses to bacterial LPS in human monocytic cells. In this report, we demonstrate that LL-37 almost completely prevents the pro-inflammatory cytokine release by human peripheral blood mononuclear cells (PBMCs) following stimulation with Toll-like receptor (TLR)4 and TLR2/1 agonists while leaving TLR2/6, TLR5, TLR7 and TLR8 responses unchanged. Modulation of the TLR response by LL-37 occurred at least partly through the MAP kinase pathway via inhibition of p38 phosphorylation. By using an LL-37 library with overlapping sequences, we identified the mid-region of LL-37, comprising amino acids 13-31, as the active domain for the modulation of TLR responses. The mechanism of immunomodulation of LL-37 and LL-37 fragments is lipopoly-saccharide binding. Correlations between the capacity of LL-37 fragments to modulate TLR responses and their physico-chemical properties revealed that cationicity and hydrophobicity are essential for the modulation of LL-37-mediated TLR responses.

Treating chronic wound infections with genetically modified free flaps

BACKGROUND

The success of antimicrobial therapy has been impaired by the emergence of resistant bacterial strains. Antimicrobial peptides are ubiquitous proteins that are part of the innate immune system and are successful against such antibiotic-resistant microorganisms. The authors have previously demonstrated the feasibility of protein delivery via microvascular free flap gene therapy and here they examine this approach for recalcitrant infections.

METHODS

The authors investigated the production of the human cathelicidin antimicrobial peptide-LL37, delivered by ex vivo transduction of the rodent superficial inferior epigastric free flap with Ad/CMV-LL37. The vascular permeabilizing agent vascular endothelial growth factor (VEGF) was co-administered during ex vivo transduction with adenoviral vectors in an attempt to augment transduction efficiency. A rodent model of chronic wound/foreign body infection seeded with bioluminescent Staphylococcus aureus was used to assess the biological efficacy of delivering therapeutic antimicrobial genes using this technology.

RESULTS

The authors were successful in demonstrating significant LL37 expression, which persisted for 14 days after ex vivo transduction with Ad/CMV-LL37. Transduction efficiency was significantly improved with the co-administration of 5 micrograms of VEGF during transduction without significantly increasing systemic dissemination of adenovirus or systemic toxicity. They were able to demonstrate in the rodent model of chronic wound/foreign body infections a significant reduction in bacterial loads from infected catheters following transduction with Ad/CMV-LL37 and increased bacterial clearance.

CONCLUSION

This study demonstrates for the first time that microbicidal gene therapy via microvascular free flaps is able to clear chronic infections such as occurs with osteomyelitis resulting from trauma or an infected foreign body [corrected]

Alterations in vitamin D status and anti-microbial peptide levels in patients in the intensive care unit with sepsis

Background

Vitamin D insufficiency is common in hospitalized patients. Recent evidence suggests that vitamin D may enhance the innate immune response by induction of cathelicidin (LL-37), an endogenous antimicrobial peptide produced by macrophages and neutrophils. Thus, the relationship between vitamin D status and LL-37 production may be of importance for host immunity, but little data is available on this subject, especially in the setting of human sepsis syndrome and other critical illness.

Methods

Plasma concentrations of 25-hydroxyvitamin D (25(OH)D), vitamin D binding protein (DBP) and LL-37 in critically ill adult subjects admitted to intensive care units (ICUs) with sepsis and without sepsis were compared to healthy controls.

Results

Critically ill subjects had significantly lower plasma 25(OH)D concentrations compared to healthy controls. Mean plasma LL-37 levels were significantly lower in critically ill subjects compared to healthy controls. Vitamin D binding protein levels in plasma were significantly lower in critically ill subjects with sepsis compared to critically ill subjects without sepsis. There was a significant positive association between circulating 25(OH)D and LL-37 levels.

Conclusion

This study demonstrates an association between critical illness and lower 25(OH)D and DBP levels in critically ill patients as compared to healthy controls. It also establishes a positive association between vitamin D status and plasma LL-37, which suggests that systemic LL-37 levels may be regulated by vitamin D status. Optimal vitamin D status may be important for innate immunity especially in the setting of sepsis. Further invention studies to examine this association are warranted.

The host defense peptide LL-37 selectively permeabilizes apoptotic leukocytes

LL-37 is a cationic host defense peptide that is highly expressed during acute inflammation and that kills bacteria by poorly defined mechanisms, resulting in permeabilization of microbial membranes. High concentrations of LL-37 have also been reported to have cytotoxic effects against eukaryotic cells, but the peptide is clearly capable of differentiating between membranes with different compositions (eukaryotic versus bacterial membranes). Eukaryotic cells such as leukocytes change their membrane composition during apoptotic cell death, when they are turned into nonfunctional but structurally intact entities. We tested whether LL-37 exerted specific activity on apoptotic cells and found that the peptide selectively permeabilized the membranes of apoptotic human leukocytes, leaving viable cells unaffected. This activity was seemingly analogous to the direct microbicidal effect of LL-37, in that it was rapid, independent of known surface receptors and/or active cell signaling, and inhibitable by serum components such as high-density lipoprotein. A similar selective permeabilization of apoptotic cells was recorded for both NK cells and neutrophils. In the latter cell type, LL-37 permeabilized both the plasma and granule membranes, resulting in the release of both lactate dehydrogenase and myeloperoxidase. Apoptosis is a way for inflammatory cells to die silently and minimize collateral tissue damage by retaining tissue-damaging and proinflammatory substances within intact membranes. Permeabilization of apoptotic leukocytes by LL-37, accompanied by the leakage of cytoplasmic as well as intragranular molecules, may thus shift the balance between pro- and anti-inflammatory signals and in this way be of importance for the termination of acute inflammation.

Pulmonary defense and the human cathelicidin hCAP-18/LL-37

Antimicrobial peptides form an important component of the innate immune system. The cathelicidin family, a key member of the antimicrobial peptide defenses, has been highly conserved throughout evolution. Though widespread in mammals, there is currently only one identified human example, hCAP-18/LL-37. The cathelicidins have been found to have multiple functions, in addition to their known antimicrobial and lipopolysaccharide-neutralizing effects. As a result, they profoundly affect both innate and adaptive immunity. Currently, antimicrobial peptides are being evaluated as therapeutic drugs in disease states as diverse as oral mucositis, cystic fibrosis, and septic shock. One such peptide, the cathelicidin hCAP-18/LL-37, is reviewed in detail in the context of its role in lung physiology and defense.

Structure-function analyses involving palindromic analogs of tritrypticin suggest autonomy of anti-endotoxin and antibacterial activities

Neutralization of invading pathogens by gene-encoded peptide antibiotics has been suggested to manifest in a variety of different modes. Some of these modes require internalization of the peptide through a pathway that involves LPS-mediated uptake of the peptide antibiotics. Many proline/tryptophan-rich cationic peptides for which this mode has been invoked do, indeed, show LPS (endotoxin) binding. If the mechanism of antibiotic action involves the LPS-mediated pathway, a positive correlation ought to manifest between the binding to LPS, its neutralization, and the bacterial killing. No such correlation was evident based on our studies involving minimal active analogs of tritrypticin. The anti-endotoxin activities of these analogs appear not to relate directly to their antibiotic potential. The two palindromic analogs of tritrypticin, NT7 (RRFPWWW) and CT7 (WWWPFRR), showed comparable antibacterial activities. However, while NT7 exhibited anti-endotoxin activity, CT7 did not. The LPS binding of two tritrypticin analogs correlated with their corresponding structures, but the antibacterial activities did not. Further structure-function analysis indicated specific structural implications of the antibacterial activity at the molecular level. Studies involving designed analogs of NT7 incorporating either rigid or flexible linkers between the specifically distanced hydrophobic and cationic clusters modulate the LPS binding. On the other hand, not knowing the target receptor for antibacterial activity is a drawback since the precise epitope for antibacterial activity is not definable. It is apparent that the anti-endotoxin and antibacterial activities represent two independent functions of tritrypticin, consistent with the emerging multifunctionality in the nature of cathelicidins.

Antibacterial cathelicidin peptide CAP11 suppresses the anandamide production from lipopolysaccharide-stimulated mononuclear phagocytes

The action of antibacterial cathelicidin peptide CAP11 on the anandamide production from mononuclear phagocytes was examined. Lipopolysaccharide (LPS)-stimulation induced the anandamide production from macrophage-like RAW264.7, accompanied with the enhanced anandamide-synthesizing enzyme activity; however, the anandamide-degrading enzyme activity was not changed by LPS-stimulation. Importantly, CAP11 suppressed the LPS-induced anandamide production and the increase of anandamide-synthesizing enzyme activity. Furthermore, CAP11 abrogated the LPS-binding to CD14-positive RAW264.7. These observations indicate that CAP11 inhibits the binding of LPS to CD14-positive mononuclear phagocytes, thereby suppressing the anandamide synthesizing enzyme activity and the anandamide production from the cells.

Determination of the antibacterial and lipopolysaccharide-neutralizing regions of guinea pig neutrophil cathelicidin peptide CAP11

Previously, we revealed that a cationic antibacterial polypeptide of 11 kDa (CAP11), a member of the cathelicidins isolated from guinea pig neutrophils, exhibits not only potent antibacterial activity but also lipopolysaccharide (LPS)-neutralizing activity. In this study, to determine the biologically active regions of CAP11, we isolated or synthesized the partial peptides of CAP11 and evaluated their antibacterial and LPS-neutralizing activities. Although CAP11 has a unique homodimeric structure with a disulfide bridge, the biological activities of dimeric and monomeric forms of CAP11 were almost the same. Moreover, the G(1)-E(33) peptide of CAP11 showed the same activities as CAP11, whereas the C-terminal region (Y(34) to I(43)) possessed no biological activities. In addition, the three 18-mer peptides (G(1)-R(18), T(9)-K(26), and L(16)-E(33)) with overlapping sequences were synthesized, and their activities were determined. The three 18-mer peptides retained the antibacterial activities, and G(1)-R(18) was the most potent. In contrast, the LPS-neutralizing activities of these peptides were markedly reduced. Together, these observations indicate that the active region with antibacterial activity is localized at G(1) to R(18) of CAP11, whereas longer sequences (such as G(1) to E(33)) would be required for the expression of LPS-neutralizing activity. Furthermore, the C-terminal region (Y(34) to I(43)) and a disulfide bridge are not essential for the antibacterial and LPS-neutralizing activities of CAP11.

Immunomodulatory properties of defensins and cathelicidins

Host defence peptides are a conserved component of the innate immune response in all complex life forms. In humans, the major classes of host defence peptides include the α- and β-defensins and the cathelicidin, hCAP-18/LL-37. These peptides are expressed in the granules of neutrophils and by a wide variety of tissue types. They have many roles in the immune response including both indirect and direct antimicrobial activity, the ability to act as chemokines as well as induce chemokine production leading to recruitment of leukocytes to the site of infection, the promotion of wound healing and an ability to modulate adaptive immunity. It appears that many of these properties are mediated though direct interaction of peptides with the cells of the innate immune response including monocytes, dendritic cells, T cells and epithelial cells. The importance of these peptides in immune responses has been demonstrated since animals defective in the expression of certain host defence peptides showgreater susceptibility to bacterial infections. In the very few instances in which human patients have been demonstrated to have defective host defence peptide expression, these individuals suffer from frequent infections. Although studies of the immunomodulatory properties of these peptides are in their infancy, there is a growing body of evidence suggesting that the immunomodulatory properties of these small, naturally occurring molecules might be harnessed for development as novel therapeutic agents.

Bovine and human cathelicidin cationic host defense peptides similarly suppress transcriptional responses to bacterial lipopolysaccharide

Genomic approaches can be exploited to expose the complexities and conservation of biological systems such as the immune network across various mammalian species. In this study, temporal transcriptional expression profiles were analyzed in human and bovine monocytic cells in response to the TLR-4 agonist, LPS, in the presence or absence of their respective host defense peptides. The cathelicidin peptides, human LL-37 and bovine myeloid antimicrobial peptide-27 (BMAP-27), are homologs, yet they have diverged notably in terms of sequence similarity. In spite of their low sequence similarities, both of these cathelicidin peptides demonstrated potent, antiendotoxin activity in monocytic cells at low, physiologically relevant concentrations. Microarray studies indicated that 10 ng/ml LPS led to the up-regulation of 125 genes in human monocytes, 106 of which were suppressed in the presence of 5 mug/ml of the human peptide LL-37. To confirm and extend these data, temporal transcriptional responses to LPS were assessed in the presence or absence of the species-specific host defense peptides by quantitative real-time PCR. The transcriptional trends of 20 LPS-induced genes were analyzed in bovine and human monocytic cells. These studies demonstrated conserved trends of gene responses in that both peptides were able to profoundly suppress many LPS-induced genes. Consistent with this, the human and bovine peptides suppressed LPS-induced translocation of NF-kappaB subunits p50 and p65 into the nucleus of monocytic cells. However, there were also distinct differences in responses to LPS and the peptides; for example, treatment with 5 mug/ml BMAP-27 alone tended to influence gene expression (RELA, TNF-alpha-induced protein 2, MAPK phosphatase 1/dual specificity phosphatase 1, IkappaBkappaB, NFkappaBIL1, TNF receptor-associated factor 2) to a greater extent than did the same amount of human LL-37. We hypothesize that the immunomodulatory effects of the species-specific host defense peptides play a critical role in regulating inflammation and represent an evolutionarily conserved mechanism for maintaining homeostasis, although the sequence divergence of these peptides is substantial.

A CD14 domain with lipopolysaccharide-binding and -neutralizing activity

The interaction of lipopolysaccharide with CD14 plays a key role in signaling that activates an early defense against pathogens but also contributes to the development of sepsis and septic shock. Here we have mapped the entire 356-amino-acid protein with synthetic 20-amino-acid peptides and have identified a new lipopolysaccharide-binding domain with a strong LPS-neutralizing activity. Moreover, analysis of the structure-activity relationship of this peptide, which corresponds to amino acids 81-100 of human CD14, revealed that leucines 87, 91, and 94 are essential for these activities. The functional relevance of these residues was confirmed by cellular expression of mutant CD14 proteins that are no longer able to bind LPS. Furthermore, the peptide provided a basis for the generation of highly soluble analogues with stronger lipopolysaccharide-neutralizing activity.

An antimicrobial cathelicidin peptide, human CAP18/LL-37, suppresses neutrophil apoptosis via the activation of formyl-peptide receptor-like 1 and P2X7

Peptide antibiotics possess the potent antimicrobial activities against invading microorganisms and contribute to the innate host defense. An antibacterial cathelicidin, human cationic antibacterial protein of 18 kDa/LL-37, not only exhibits potent bactericidal activities against Gram-negative and Gram-positive bacteria, but also functions as a chemoattractant for immune cells, including neutrophils. During bacterial infections, the life span of neutrophils is regulated by various pathogen- and host-derived substances. In this study, to further evaluate the role of LL-37 in innate immunity, we investigated the action of LL-37 on neutrophil apoptosis. Neutrophil apoptosis was assessed using human blood neutrophils based on the morphological changes. Of note, LL-37 dose dependently (0.01-5 microg/ml) suppressed neutrophil apoptosis, accompanied with the phosphorylation of ERK-1/2, expression of Bcl-x(L) (an antiapoptotic protein), and inhibition of caspase 3 activity. Interestingly, LL-37-induced suppression of neutrophil apoptosis was attenuated by the antagonists for formyl-peptide receptor-like 1 (FPRL1) and P2X7 nucleotide receptor. Of importance, the agonists for FPRL1 and P2X7 apparently suppressed neutrophil apoptosis. Collectively, these observations indicate that LL-37 cannot only kill bacteria, but also modulate (suppress) neutrophil apoptosis via the activation of FPRL1 and P2X7 in bacterial infections. Suppression of neutrophil apoptosis results in the prolongation of their life span, and may be advantageous for host defense against bacterial invasion.

Modulation of the TLR-mediated inflammatory response by the endogenous human host defense peptide LL-37

The sole human cathelicidin peptide, LL-37, has been demonstrated to protect animals against endotoxemia/sepsis. Low, physiological concentrations of LL-37 (< or =1 microg/ml) were able to modulate inflammatory responses by inhibiting the release of the proinflammatory cytokine TNF-alpha in LPS-stimulated human monocytic cells. Microarray studies established a temporal transcriptional profile and identified differentially expressed genes in LPS-stimulated monocytes in the presence or absence of LL-37. LL-37 significantly inhibited the expression of specific proinflammatory genes up-regulated by NF-kappaB in the presence of LPS, including NFkappaB1 (p105/p50) and TNF-alpha-induced protein 2 (TNFAIP2). In contrast, LL-37 did not significantly inhibit LPS-induced genes that antagonize inflammation, such as TNF-alpha-induced protein 3 (TNFAIP3) and the NF-kappaB inhibitor, NFkappaBIA, or certain chemokine genes that are classically considered proinflammatory. Nuclear translocation, in LPS-treated cells, of the NF-kappaB subunits p50 and p65 was reduced > or =50% in the presence of LL-37, demonstrating that the peptide altered gene expression in part by acting directly on the TLR-to-NF-kappaB pathway. LL-37 almost completely prevented the release of TNF-alpha and other cytokines by human PBMC following stimulation with LPS and other TLR2/4 and TLR9 agonists, but not with cytokines TNF-alpha or IL-1beta. Biochemical and inhibitor studies were consistent with a model whereby LL-37 modulated the inflammatory response to LPS/endotoxin and other agonists of TLR by a complex mechanism involving multiple points of intervention. We propose that the natural human host defense peptide LL-37 plays roles in the delicate balancing of inflammatory responses in homeostasis as well as in combating sepsis induced by certain TLR agonists.

Expression and purification of a recombinant LL-37 from Escherichia coli

Human cathelicidin-derived LL-37 is a 37-residue cationic, amphipathic alpha-helical peptide. It is an active component of mammalian innate immunity. LL-37 has several biological functions including a broad spectrum of antimicrobial activities and LPS-neutralizing activity. In order to determine the high-resolution three-dimensional structure of LL-37 using NMR spectroscopy, it is important to obtain the peptide with isotopic labels such as (15)N, (13)C and/or (2)H. Since it is less expensive to obtain such a peptide biologically, in this study, we report for the first time a method to express in E. coli and purify LL-37 using Glutathione S-transferase (GST) fusion system. LL-37 gene was inserted into vector pGEX-4T3 and expressed as a GST-LL-37 fusion protein in BL21(DE3) strain. The recombinant GST-LL-37 protein was purified with a yield of 8 mg/l by affinity chromatography and analyzed its biochemical and spectroscopic properties. Factor Xa was used to cleave a 4.5-kDa LL-37 from the GST-LL-37 fusion protein and the peptide was purified using a reverse-phase HPLC on a Vydac C(18) column with a final yield of 0.3 mg/l. The protein purified using reverse-phase HPLC was confirmed to be LL-37 by the analyses of Western blot and MALDI-TOF-Mass spectrometry. E. coli cells harboring the expression vector pGEX-4T3-LL-37 were grown in the presence of the (15)N-labeled M9 minimal medium and culture conditions were optimized to obtain uniform (15)N enrichment in the constitutively expressed LL-37 peptide. These results suggest that our production method will be useful in obtaining a large quantity of recombinant LL-37 peptide for NMR studies.

Human cathelicidin antimicrobial peptide (CAMP) gene is a direct target of the vitamin D receptor and is strongly up-regulated in myeloid cells by 1,25-dihydroxyvitamin D3

The innate immune system of mammals provides a rapid response to repel assaults from numerous infectious agents including bacteria, viruses, fungi, and parasites. A major component of this system is a diverse combination of cationic antimicrobial peptides that include the alpha- and beta-defensins and cathelicidins. In this study, we show that 1,25-dihydroxyvitamin D3 and three of its analogs induced expression of the human cathelicidin antimicrobial peptide (CAMP) gene. This induction was observed in acute myeloid leukemia (AML), immortalized keratinocyte, and colon cancer cell lines, as well as normal human bone marrow (BM) -derived macrophages and fresh BM cells from two normal individuals and one AML patient. The induction occurred via a consensus vitamin D response element (VDRE) in the CAMP promoter that was bound by the vitamin D receptor (VDR). Induction of CAMP in murine cells was not observed and expression of CAMP mRNA in murine VDR-deficient bone marrow was similar to wild-type levels. Comparison of mammalian genomes revealed evolutionary conservation of the VDRE in a short interspersed nuclear element or SINE in the CAMP promoter of primates that was absent in the mouse, rat, and canine genomes. Our findings reveal a novel activity of 1,25-dihydroxyvitamin D3 and the VDR in regulation of primate innate immunity.

Protective effects of antimicrobial peptides derived from the beetle Allomyrina dichotoma defensin on endotoxic shock in mice

Synthetic peptides, Arg-Leu-Tyr-Leu-Arg-Ile-Gly-Arg-Arg-NH2 (peptide A) and Arg-Leu-Arg-Leu-Arg-Ile-Gly-Arg-Arg-NH2 (peptide B), derived from the beetle Allomyrina dichotoma defensin, have not only antimicrobial activities but also anti-inflammatory effects by inhibiting tumour necrosis factor-alpha(TNF-alpha) production. In the present study, we evaluated the lipopolysaccharide (LPS)-binding activities and the protective effects of these peptides on LPS-induced lethal shock in d-galactosamine (GalN)-sensitized mice. These peptides were shown to bind to erythrocytes coated with LPS and the binding activity of peptide A to LPS was significantly higher than those of peptide B and polymyxin B. Mice were injected intraperitoneally with peptide A or B at doses of 25, 50, 100 and 150 mg/kg before an injection of Salmonella abortusequi LPS (5 microg/kg) and GalN (1 g/kg) (LPS+GalN). All of wild-type mice died within 24 h after challenged with LPS+GalN. All of TNF-alpha-deficient mice challenged with LPS+GalN survived. An injection of peptide A immediately after challenge with LPS+GalN resulted in significantly improved survival rates in a dose dependent manner. Peptide B showed only minor protection. The levels of TNF-alpha in the ameliorated mice by peptide A were significantly lower than those of challenge control, suggesting a suppressive effect of peptide A on TNF-alpha production. Furthermore, peptide A-treated mice showed significantly lower levels of asparate aminotransferase and alanine aminotransferase when compared to challenge control. Concordantly, hemorrhage and necrosis in the liver of peptide A-treated mice were less apparent than those of untreated control mice. These results suggest that peptide A has a protective effect on LPS-induced mortality in this mouse model.

Mouse cathelin-related antimicrobial peptide chemoattracts leukocytes using formyl peptide receptor-like 1/mouse formyl peptide receptor-like 2 as the receptor and acts as an immune adjuvant

Mammalian antimicrobial proteins, such as defensins and cathelicidin, have stimulating effects on host leukocytes. Cathelin-related antimicrobial peptide (CRAMP), the orthologue of human cathelicidin/LL-37, is the sole identified murine cathelicidin. CRAMP has been shown to have both antimicrobial and angiogenic activities. However, whether CRAMP, like human cathelicidin/LL-37, also exhibits a direct effect on the migration and function of leukocytes is not known. We have observed that CRAMP, like LL-37, was chemotactic for human monocytes, neutrophils, macrophages, and mouse peripheral blood leukocytes. CRAMP also induced calcium mobilization and the activation of MAPK in monocytes. CRAMP-induced calcium flux in monocytes was desensitized by MMK-1, an agonistic ligand specific for formyl peptide receptor-like-1 (FPRL1), and vice versa, suggesting the use of FPRL1 by CRAMP as a receptor. Furthermore, CRAMP induced the chemotaxis of human embryonic kidney 293 cells transfected with either FPRL1 or mouse formyl peptide receptor-2, the mouse homologue of FPRL1, but not by untransfected parental human embryonic kidney 293 cells, confirming the use of FPRL1/mouse formyl peptide receptor-2 by CRAMP. Injection of CRAMP into mouse air pouches resulted in the recruitment predominantly of neutrophils and monocytes, indicating that CRAMP acts as a chemotactic factor in vivo. Finally, simultaneous administration of OVA with CRAMP to mice promoted both humoral and cellular Ag-specific immune responses. Thus, CRAMP functions as both a chemoattractant for phagocytic leukocytes and an enhancer of adaptive immune response.

Reduction in the bactericidal activity of selected cathelicidin peptides by bovine calf serum or exogenous endotoxin

Synthetic cathelicidin peptides exhibit enhanced antimicrobial action and avid binding to LPS, thereby detoxifying the action of endotoxin released from degrading bacteria. A series of cathelicidin antimicrobial peptide (CAP) and sheep myeloid antimicrobial peptide (SMAP) congeners were examined to determine whether LPS-binding could predict other beneficial characteristics of the peptides. The peptides were challenged in complex media with bovine calf serum or LPS, and their ability to kill the Gram negative pathogens Klebsiella pneumoniae (ATCC 43816) or Pseudomonas aeruginosa (PA103) was then assessed. LPS-binding efficiency was not correlated with antimicrobial activity in complex media. Additionally, LPS- and serum-binding may interfere with the antimicrobial activity of peptides in complex media.