Human CAP18: a novel antimicrobial lipopolysaccharide-binding protein

In vitro studies on the antimicrobial peptide human beta-defensin 9 (HBD9): signalling pathways and pathogen-related response (an American Ophthalmological Society thesis)

PURPOSE

Human β-defensins (HBDs) are an important part of the innate immune host defense at the ocular surface. Unlike other defensins, expression of HBD9 at the ocular surface is reduced during microbial infection, but activation of toll-like receptor 2 (TLR2) in corneal epithelial cells has been shown to up-regulate HBD9. Our purpose was to test the hypothesis that TLR2 has a key role in the signalling pathway(s) involved in the overexpression or underexpression of HBD9, and accordingly, different pathogens would induce a different expression pattern of HBD9.

METHODS

The in vitro RNAi silencing method and response to dexamethasone were used to determine key molecules involved in signalling pathways of HBD9 in immortalized human corneal epithelial cells. The techniques included cell culture with exposure to specific transcription factor inhibitors and bacteria, RNA extraction and cDNA synthesis, quantitative real-time polymerase chain reaction, and immunohistology.

RESULTS

This study demonstrates that TLR2 induces HBD9 mRNA and protein expression in a time- and dose-dependent manner. Transforming growth factor-β-activated kinase 1 (TAK1) plays a central role in HBD9 induction by TLR2, and transcription factors c-JUN and activating transcription factor 2 are also involved. Dexamethasone reduces TLR2-mediated up-regulation of HBD9 mRNA and protein levels in mitogen-activated protein kinase phosphatase 1 (MKP1)-dependent and c-JUN-independent manner. HBD9 expression differs with gram-negative and gram-positive bacteria.

CONCLUSIONS

TLR2-mediated MKPs and nuclear factor-κB signalling pathways are involved in HBD9 expression. TAK-1 is a key molecule. These molecules can be potentially targeted to modulate HBD9 expression. Differential expression of HBD9 with different bacteria could be related to differences in pathogen-associated molecular patterns of these organisms.

Cationic peptides neutralize Ox-LDL, prevent its uptake by macrophages, and attenuate inflammatory response

OBJECTIVE

Apolipoprotein A1 (ApoA1) and apolipoprotein E (ApoE) mimetic peptides have attracted attention due to their ability to reduce atherosclerosis and exhibit antioxidant, anti-inflammatory, and hypolipidemic properties. In this study, we tested whether three distinct and unrelated cationic peptides would inhibit the oxidation of lipoproteins and whether they would counteract and neutralize the negatively charged modified lipoproteins, inhibit their uptake and inflammation by macrophages.

METHODS AND RESULTS

5F-mimetic peptide of ApoA1, LL27 derived from the anti-microbial peptide hCAP, and a human glycodelin derived peptide were commercially synthesized. We noted that these three distinct cationic lysine-rich peptides, two of which were unrelated to any known apolipoproteins, inhibited copper-mediated oxidation of lipoproteins and reduced lipid peroxides in a lysine dependent manner. The peptides also retarded the electrophoretic mobility of previously oxidized LDL and acetylated LDL by virtue of their net positive charge. Pre-incubation of peptides with modified lipoproteins reduced the uptake of the latter by macrophages, thus preventing the formation of foam cells. The cationic peptides inhibited oxidized LDL (Ox-LDL)-induced inflammatory response both in vitro and in vivo.

CONCLUSION

Based on these results, we suggest that in addition to the well known mimetic peptides, other suitable cationic peptides may be of use for controlling Ox-LDL mediated inflammation and atherosclerotic progression.

Sphingolipids and antimicrobial peptides: function and roles in atopic dermatitis

Inflammatory skin diseases such as atopic dermatitis (AD) and rosacea were complicated by barrier abrogation and deficiency in innate immunity. The first defender of epidermal innate immune response is the antimicrobial peptides (AMPs) that exhibit a broad-spectrum antimicrobial activity against multiple pathogens, including Gram-positive and Gram-negative bacteria, viruses, and fungi. The deficiency of these AMPs in the skin of AD fails to protect our body against virulent pathogen infections. In contrast to AD where there is a suppression of AMPs, rosacea is characterized by overexpression of cathelicidin antimicrobial peptide (CAMP), the products of which result in chronic epidermal inflammation. In this regard, AMP generation that is controlled by a key ceramide metabolite S1P-dependent mechanism could be considered as alternate therapeutic approaches to treat these skin disorders, i.e., Increased S1P levels strongly stimulated the CAMP expression which elevated the antimicrobial activity against multiple pathogens resulting the improved AD patient skin.

LL-37-derived peptides eradicate multidrug-resistant Staphylococcus aureus from thermally wounded human skin equivalents

Burn wound infections are often difficult to treat due to the presence of multidrug-resistant bacterial strains and biofilms. Currently, mupirocin is used to eradicate methicillin-resistant Staphylococcus aureus (MRSA) from colonized persons; however, mupirocin resistance is also emerging. Since we consider antimicrobial peptides to be promising candidates for the development of novel anti-infective agents, we studied the antibacterial activities of a set of synthetic peptides against different strains of S. aureus, including mupirocin-resistant MRSA strains. The peptides were derived from P60.4Ac, a peptide based on the human cathelicidin LL-37. The results showed that peptide 10 (P10) was the only peptide more efficient than P60.4Ac, which is better than LL-37, in killing MRSA strain LUH14616. All three peptides displayed good antibiofilm activities. However, both P10 and P60.4Ac were more efficient than LL-37 in eliminating biofilm-associated bacteria. No toxic effects of these three peptides on human epidermal models were detected, as observed morphologically and by staining for mitochondrial activity. In addition, P60.4Ac and P10, but not LL-37, eradicated MRSA LUH14616 and the mupirocin-resistant MRSA strain LUH15051 from thermally wounded human skin equivalents (HSE). Interestingly, P60.4Ac and P10, but not mupirocin, eradicated LUH15051 from the HSEs. None of the peptides affected the excretion of interleukin 8 (IL-8) by thermally wounded HSEs upon MRSA exposure. In conclusion, the synthetic peptides P60.4Ac and P10 appear to be attractive candidates for the development of novel local therapies to treat patients with burn wounds infected with multidrug-resistant bacteria.

Human antimicrobial peptides and proteins

As the key components of innate immunity, human host defense antimicrobial peptides and proteins (AMPs) play a critical role in warding off invading microbial pathogens. In addition, AMPs can possess other biological functions such as apoptosis, wound healing, and immune modulation. This article provides an overview on the identification, activity, 3D structure, and mechanism of action of human AMPs selected from the antimicrobial peptide database. Over 100 such peptides have been identified from a variety of tissues and epithelial surfaces, including skin, eyes, ears, mouths, gut, immune, nervous and urinary systems. These peptides vary from 10 to 150 amino acids with a net charge between -3 and +20 and a hydrophobic content below 60%. The sequence diversity enables human AMPs to adopt various 3D structures and to attack pathogens by different mechanisms. While α-defensin HD-6 can self-assemble on the bacterial surface into nanonets to entangle bacteria, both HNP-1 and β-defensin hBD-3 are able to block cell wall biosynthesis by binding to lipid II. Lysozyme is well-characterized to cleave bacterial cell wall polysaccharides but can also kill bacteria by a non-catalytic mechanism. The two hydrophobic domains in the long amphipathic α-helix of human cathelicidin LL-37 lays the basis for binding and disrupting the curved anionic bacterial membrane surfaces by forming pores or via the carpet model. Furthermore, dermcidin may serve as ion channel by forming a long helix-bundle structure. In addition, the C-type lectin RegIIIα can initially recognize bacterial peptidoglycans followed by pore formation in the membrane. Finally, histatin 5 and GAPDH(2-32) can enter microbial cells to exert their effects. It appears that granulysin enters cells and kills intracellular pathogens with the aid of pore-forming perforin. This arsenal of human defense proteins not only keeps us healthy but also inspires the development of a new generation of personalized medicine to combat drug-resistant superbugs, fungi, viruses, parasites, or cancer. Alternatively, multiple factors (e.g., albumin, arginine, butyrate, calcium, cyclic AMP, isoleucine, short-chain fatty acids, UV B light, vitamin D, and zinc) are able to induce the expression of antimicrobial peptides, opening new avenues to the development of anti-infectious drugs.

High-quality 3D structures shine light on antibacterial, anti-biofilm and antiviral activities of human cathelicidin LL-37 and its fragments

Host defense antimicrobial peptides are key components of human innate immunity that plays an indispensible role in human health. While there are multiple copies of cathelicidin genes in horses, cattle, pigs, and sheep, only one cathelicidin gene is found in humans. Interestingly, this single cathelicidin gene can be processed into different forms of antimicrobial peptides. LL-37, the most commonly studied form, is not only antimicrobial but also possesses other functional roles such as chemotaxis, apoptosis, wound healing, immune modulation, and cancer metastasis. This article reviews recent advances made in structural and biophysical studies of human LL-37 and its fragments, which serve as a basis to understand their antibacterial, anti-biofilm and antiviral activities. High-quality structures were made possible by using improved 2D NMR methods for peptide fragments and 3D NMR spectroscopy for intact LL-37. The two hydrophobic domains in the long amphipathic helix (residues 2-31) of LL-37 separated by a hydrophilic residue serine 9 explain its cooperative binding to bacterial lipopolysaccharides (LPS). Both aromatic rings (F5, F6, F17, and F27) and interfacial basic amino acids of LL-37 directly interact with anionic phosphatidylglycerols (PG). Although the peptide sequences reported in the literature vary slightly, there is a consensus that the central helix of LL-37 is essential for disrupting superbugs (e.g., MRSA), bacterial biofilms, and viruses such as human immunodeficiency virus 1 (HIV-1) and respiratory syncytial virus (RSV). In the central helix, the central arginine R23 is of particular importance in binding to bacterial membranes or DNA. Mapping the functional roles of the cationic amino acids of the major antimicrobial region of LL-37 provides a basis for designing antimicrobial peptides with desired properties. This article is part of a Special Issue entitled: Interfacially Active Peptides and Proteins. Guest Editors: William C. Wimley and Kalina Hristova.

Little peptide, big effects: the role of LL-37 in inflammation and autoimmune disease

The innate immune system utilizes many approaches for defense against invading microorganisms, including complement-mediated lysis, engulfment, formation of neutrophil extracellular traps, and release of antimicrobial peptides. Although classically thought to be driven by adaptive immunity, the development of autoimmune diseases such as rheumatoid arthritis and systemic lupus erythematosus is increasingly associated with dysregulated innate immune pathways. An emerging theme within this literature is the contribution of antimicrobial peptides to the development of autoimmune disorders. This is best exemplified in atopic dermatitis and psoriasis where the defensins and the single human cathelicidin, LL-37, may contribute to disease. Furthermore, in the past few years, a role for LL-37 has emerged in the pathogenesis of systemic lupus erythematosus, rheumatoid arthritis, atherosclerosis, and possibly other diseases. In this review, we discuss the role of LL-37 and its murine ortholog, mCRAMP, in the modulation of immune and inflammatory pathways and their effects on autoimmune and inflammatory diseases.

Pulmonary vaccine delivery

This review will discuss developments in the field of pulmonary vaccine delivery. The possibilities of adopting aerosol-generation technology and specific pharmaceutical formulations for the purpose of pulmonary immunization are described. Aerosol-generation systems might offer advantages with respect to vaccine stability and antigenicity. Adjuvants and their inclusion in vaccine-delivery systems are described. Other formulation components, such as surfactants, particulate systems and dispersion of the aerosols are detailed in this paper. The noninvasive, relatively safe and low-cost nature of pulmonary delivery may provide great benefits to the public health vaccination campaign.

Antimicrobial peptides

The rapid increase in drug-resistant infections has presented a serious challenge to antimicrobial therapies. The failure of the most potent antibiotics to kill “superbugs” emphasizes the urgent need to develop other control agents. Here we review the history and new development of antimicrobial peptides (AMPs), a growing class of natural and synthetic peptides with a wide spectrum of targets including viruses, bacteria, fungi, and parasites. We summarize the major types of AMPs, their modes of action, and the common mechanisms of AMP resistance. In addition, we discuss the principles for designing effective AMPs and the potential of using AMPs to control biofilms (multicellular structures of bacteria embedded in extracellular matrixes) and persister cells (dormant phenotypic variants of bacterial cells that are highly tolerant to antibiotics).

Short KR-12 analogs designed from human cathelicidin LL-37 possessing both antimicrobial and antiendotoxic activities without mammalian cell toxicity

KR-12 (residues 18-29 of LL-37) was known to be the smallest peptide of human cathelicidin LL-37 possessing antimicrobial activity. In order to optimize α-helical short antimicrobial peptides having both antimicrobial and antiendotoxic activities without mammalian cell toxicity, we designed and synthesized a series of KR-12 analogs. Highest hydrophobic analogs KR-12-a5 and KR-12-a6 displayed greater inhibition of lipopolysaccharide (LPS)-stimulated tumor necrosis factor-α production and higher LPS-binding activity. We have observed that antimicrobial activity is independent of charge, but LPS neutralization requires a balance of hydrophobicity and net positive charge. Among KR-12 analogs, KR-12-a2, KR-12-a3 and KR-12-a4 showed much higher cell specificity for bacteria over erythrocytes and retained antiendotoxic activity, relative to parental LL-37. KR-12-a5 displayed the strongest antiendotoxic activity but almost similar cell specificity as compared with LL-37. Also, these KR-12 analogs (KR-12-a2, KR-12-a3, KR-12-a4 and KR-12-a5) exhibited potent antimicrobial activity (minimal inhibitory concentration: 4 μM) against methicillin-resistant Staphylococcus aureus. Taken together, these KR-12 analogs have the potential for future development as a novel class of antimicrobial and anti-inflammatory therapeutic agents.

Antibiotics in the clinical pipeline in 2013

The continued emergence of multi-drug-resistant bacteria is a major public health concern. The identification and development of new antibiotics, especially those with new modes of action, is imperative to help treat these infections. This review lists the 22 new antibiotics launched since 2000 and details the two first-in-class antibiotics, fidaxomicin (1) and bedaquiline (2), launched in 2011 and 2012, respectively. The development status, mode of action, spectra of activity, historical discovery and origin of the drug pharmacophore (natural product, natural product derived, synthetic or protein/mammalian peptide) of the 49 compounds and 6 β-lactamase/β-lactam combinations in active clinical development are discussed, as well as compounds that have been discontinued from clinical development since 2011. New antibacterial pharmacophore templates are also reviewed and analyzed.

The antimicrobial peptide LL37 promotes bone regeneration in a rat calvarial bone defect

LL37, an antimicrobial peptide, exhibits multiple bio-functions in various types of cells, including migration, cytokine production, apoptosis, and angiogenesis. Neovascularization and the subsequent recruitment of stem cells are essential for tissue engineering therapy, including bone regeneration. We hypothesized that LL37 can facilitate successful bone regeneration. To prove this hypothesis, the present study tested the effects of LL37 on bone formation in a rat calvarial bone defect model. Synthesized LL37 markedly induced newly formed bone. Interestingly, morphologically fibroblastic cells were observed in animals treated with LL37 on day 7, the early stage of tissue regeneration, which were positive for STRO-1, a marker of mesenchymal stem cells (MSCs), and accumulated in the bone defect area where cells positive for CD34, a marker of endothelial cells, were also localized. In addition, LL37 stimulated tube formation by endothelial cells and the proliferation of MSCs in vitro. These findings demonstrated for the first time that LL37 can regulate angiogenesis and the recruitment of stem cells to promote bone regeneration.

Cathelicidin-like helminth defence molecules (HDMs): absence of cytotoxic, anti-microbial and anti-protozoan activities imply a specific adaptation to immune modulation

Host defence peptides (HDPs) are expressed throughout the animal and plant kingdoms. They have multifunctional roles in the defence against infectious agents of mammals, possessing both bactericidal and immune-modulatory activities. We have identified a novel family of molecules secreted by helminth parasites (helminth defence molecules; HDMs) that exhibit similar structural and biochemical characteristics to the HDPs. Here, we have analyzed the functional activities of four HDMs derived from Schistosoma mansoni and Fasciola hepatica and compared them to human, mouse, bovine and sheep HDPs. Unlike the mammalian HDPs the helminth-derived HDMs show no antimicrobial activity and are non-cytotoxic to mammalian cells (macrophages and red blood cells). However, both the mammalian- and helminth-derived peptides suppress the activation of macrophages by microbial stimuli and alter the response of B cells to cytokine stimulation. Therefore, we hypothesise that HDMs represent a novel family of HDPs that evolved to regulate the immune responses of their mammalian hosts by retaining potent immune modulatory properties without causing deleterious cytotoxic effects.

In mammals, secreted host defence peptides (HDPs) protect against a wide range of infectious pathogens. They also perform a range of immune modulatory functions which regulate the immune response to pathogens, ensuring that the protective inflammatory response is not exacerbated and that post-infection repair mechanisms are initiated. We identified a novel family of molecules secreted by medically-important helminth pathogens (termed helminth defence molecules; HDMs) that exhibit striking structural and biochemical similarities to the HDPs. To further investigate the extent of this similarity, we have performed a comparative functional study between several well characterized, anti-microbial, mammalian HDPs and a series of parasite-derived peptides. The parasite HDMs displayed immune modulatory properties that were similar to their HDP homologs in mammals, but possessed no antimicrobial or cytotoxic activity. We propose that HDMs of these helminth pathogens underwent specific adaptation, losing their anti-microbial activity but retaining their ability to regulate the immune responses of their mammalian hosts. This absence of cytotoxicity and retention of immune-modulatory activity offers an opportunity to design novel immunotherapeutics derived from the HDMs which could be used to combat destructive inflammatory responses associated with microbial infection and immune-related disorders.

Recent advances in the field of antimicrobial peptides in inflammatory diseases

Antimicrobial peptides are cationic molecules, which participate in multiple aspects of the immune response including the control of inflammatory diseases, characteristic that make these molecules attractive as therapeutic tools. These peptides are produced in bacteria, insects, plants and vertebrates, and are classified together due to their capacity to directly inhibit the growth of microorganisms, and to regulate the immune response by inducing the secretion of chemokines and cytokines. Various families of antimicrobial peptides have been identified including the cathelicidins and defensins, the most investigated human antimicrobial peptides. This review will cover the main biological functions of antimicrobial and cell-penetrating peptides in inflammation, and describe the importance and utility of antimicrobial peptides as therapeutics for inflammatory diseases.

Identification of cell-penetrating peptides that are bactericidal to Neisseria meningitidis and prevent inflammatory responses upon infection

Meningococcal disease is characterized by a fast progression and a high mortality rate. Cell-penetrating peptides (CPPs), developed as vectors for cargo delivery into eukaryotic cells, share structural features with antimicrobial peptides. A screen identified two CPPs, transportan-10 (TP10) and model amphipathic peptide (MAP), with bactericidal action against Neisseria meningitidis. Both peptides were active in human whole blood at micromolar concentrations, while hemolysis remained negligible. Additionally, TP10 exhibited significant antibacterial activity in vivo. Uptake of SYTOX green into live meningococci was observed within minutes after TP10 treatment, suggesting that TP10 may act by membrane permeabilization. Apart from its bactericidal activity, TP10 suppressed inflammatory cytokine release from macrophages infected with N. meningitidis as well as from macrophages stimulated with enterobacterial and meningococcal lipopolysaccharide (LPS). Finally, incubation with TP10 reduced the binding of LPS to macrophages. This novel endotoxin-inhibiting property of TP10, together with its antimicrobial activity in vivo, indicates the possibility to design peptide-based therapies for infectious diseases.

Rational design of engineered cationic antimicrobial peptides consisting exclusively of arginine and tryptophan, and their activity against multidrug-resistant pathogens

The emergence of multidrug-resistant (MDR) pathogens underscores the need for new antimicrobial agents to overcome the resistance mechanisms of these organisms. Cationic antimicrobial peptides (CAPs) provide a potential source of new antimicrobial therapeutics. We previously characterized a lytic base unit (LBU) series of engineered CAPs (eCAPs) of 12 to 48 residues demonstrating maximum antibacterial selectivity at 24 residues. Further, Trp substitution in LBU sequences increased activity against both P. aeruginosa and S. aureus under challenging conditions (e.g., saline, divalent cations, and serum). Based on these findings, we hypothesized that the optimal length and, therefore, the cost for maximum eCAP activity under physiologically relevant conditions could be significantly reduced using only Arg and Trp arranged to form idealized amphipathic helices. Hence, we developed a novel peptide series, composed only of Arg and Trp, in a sequence predicted and verified by circular dichroism to fold into optimized amphipathic helices. The most effective antimicrobial activity was achieved at 12 residues in length (WR12) against a panel of both Gram-negative and Gram-positive clinical isolates, including extensively drug-resistant strains, in saline and broth culture and at various pH values. The results demonstrate that the rational design of CAPs can lead to a significant reduction in the length and the number of amino acids used in peptide design to achieve optimal potency and selectivity against specific pathogens.

Structural and functional analysis of the pro-domain of human cathelicidin, LL-37

Cathelicidins form a family of small host defense peptides distinct from another class of cationic antimicrobial peptides, the defensins. They are expressed as large precursor molecules with a highly conserved pro-domain known as the cathelin-like domain (CLD). CLDs have high degrees of sequence homology to cathelin, a protein isolated from pig leukocytes and belonging to the cystatin family of cysteine protease inhibitors. In this report, we describe for the first time the X-ray crystal structure of the human CLD (hCLD) of the sole human cathelicidin, LL-37. The structure of the hCLD, determined at 1.93 Å resolution, shows the cystatin-like fold and is highly similar to the structure of the CLD of the pig cathelicidin, protegrin-3. We assayed the in vitro antibacterial activities of the hCLD, LL-37, and the precursor form, pro-cathelicidin (also known as hCAP18), and we found that the unprocessed protein inhibited the growth of Gram-negative bacteria with efficiencies comparable to that of the mature peptide, LL-37. In addition, the antibacterial activity of LL-37 was not inhibited by the hCLD intermolecularly, because exogenously added hCLD had no effect on the bactericidal activity of the mature peptide. The hCLD itself lacked antimicrobial function and did not inhibit the cysteine protease, cathepsin L. Our results contrast with previous reports of hCLD activity. A comparative structural analysis between the hCLD and the cysteine protease inhibitor stefin A showed why the hCLD is unable to function as an inhibitor of cysteine proteases. In this respect, the cystatin scaffold represents an ancestral structural platform from which proteins evolved divergently, with some losing inhibitory functions.

The antimicrobial peptide LL-37 alters human osteoblast Ca2+ handling and induces Ca2+-independent apoptosis

The human antimicrobial peptide cathelicidin LL-37 has, besides its antimicrobial properties, also been shown to regulate apoptosis in a cell type-specific manner. Mechanisms involved in LL-37-regulated apoptotic signaling are not identified. Here, we show that LL-37 reduces the human osteoblast-like MG63 cell number and cell viability in the micromolar concentration range with an IC50 value of about 5 µM. Treatment with 4 µM LL-37 increased the number of annexin V-positive cells and stimulated activation of caspase 3 showing that LL-37 promotes apoptosis. Treatment with 4 µM LL-37 caused an acute and sustained rise in intracellular Ca(2+) concentration assessed by laser-scanning confocal microscopy of Fluo-4-AM-loaded MG63 cells. LL-37 increased Ca(2+) also in the presence of the respective L- and T-type voltage-sensitive Ca(2+) channel blockers nifedipine and NiCl2. LL-37 had no effect on Ca(2+) in cells incubated with Ca(2+)-free solution. LL-37 (4 and 8 µM) reduced the MG63 cell number both in the presence and absence of Ca(2+) in the medium. In conclusion, LL-37 reduces the osteoblast cell number by promoting apoptosis, and furthermore, LL-37 stimulates Ca(2+) inflow via a mechanism independent of voltage-sensitive Ca(2+) channels. Interestingly, LL-37-induced lowering of the cell number seems to be mediated via a mechanism independent of Ca(2+).

Defensin production by human limbo-corneal fibroblasts infected with mycobacteria

Epithelial cells of the cornea and the conjunctiva constitutively produce antimicrobial peptides; however, the production of defensins by other cell types located around the eye has not been investigated. We analyzed the production of beta-defensins (hBD) and cathelicidin LL-37 during the infection of primary limbo-corneal fibroblasts with M. tuberculosis (MTB), M. abscessus (MAB), and M. smegmatis (MSM). The intracellular survival of each mycobacterium, the production of cytokines and the changes on the distribution of the actin filaments during the infection were also analyzed. Fibroblasts produce basal levels of hBD1 and LL-37 and under PMA stimulation they produce hBD2, hBD3 and overexpress hBD1 and LL-37. MAB induced the highest levels of hBD1 and LL-37 and intermediate levels of IL-6; however, MAB was not eliminated. In addition, MAB induced the greatest change to the distribution of the actin filaments. MTB also produced changes in the structure of the cytoskeleton and induced low levels of hBD1 and IL-6, and intermediate levels of LL-37. The balance of these molecules induced by MTB appeared to contribute to the non-replicative state observed in the limbo-corneal cells. MSM induced the lowest levels of hBD1 and LL-37 but the highest levels of IL-6; MSM was eliminated. The results suggest that mycobacterial infections regulate the production of antimicrobial peptides and cytokines, which in conjunction can contribute to the control of the bacilli.

Ultrashort cationic lipopeptides and lipopeptoids selectively induce cytokine production in macrophages

A series of ultrashort lipopeptides and lipopeptoids were tested for their ability to induce cytokine production in macrophages. Fourteen compounds were found to strongly induce production of chemokines Groα and IL-8, with a structural bias that was absent from previous antibacterial activity investigations. Compounds based on LysGlyLys and NLysGlyNLys sequences did not induce cytokine production, whereas those based on LysLysLys and NLysNLysNLys were active only when linked to a lipid tail at least sixteen carbons long. Three lipopeptides induced high levels of IL-8 production, above that of equivalent concentrations of cathelicidin LL-37, while no compound induced production of the pro-inflammatory cytokine TNF-α at or below 100 µM. Two compounds, peptoids C16OH-NLysNLysNLys and C16OH-NHarNHarNHar, were selective for IL-8 production and did not induce TNF-α or IL-1β. These compounds may prove beneficial for in vivo treatment of infectious disease, with improved bioavailability over LL-37 due to their protease-resistant scaffold.

Effect of antimicrobial peptides derived from human cathelicidin LL-37 on Entamoeba histolytica trophozoites

The human cathelicidin hCAP18/LL-37 is an antimicrobial protein consisting of a conserved N-terminal prosequence called the cathelin-like domain and a C-terminal peptide called LL-37. This peptide contains 37 amino acid residues, and several truncated variants obtained from natural sources or by chemical synthesis differ in their capability to damage Gram positive and Gram negative bacteria as well as Candida albicans. KR-12 is the shortest peptide (12 amino acids) of LL-37 that has conserved antibacterial activity. In addition to LL-37, other active cathelicidin-derived peptides have been reported; for instance, the peptides KR-20, a 20-aa derivative of LL-37, and KS-30, a 30-aa derivative of LL-37, have been found in human sweat. Both peptides exhibit an overall increased antibacterial and antifungal activity when compared with LL-37. We investigated the effect of LL-37 and three peptides derived from this antimicrobial molecule, KR-12, KR-20 and KS-30, on the integrity of Entamoeba histolytica trophozoites. The four peptides showed effects on E. histolytica integrity and viability in the concentration range of 10-50 μM. The peptides KR-12, KR-20, KS-30 and LL-37 differed in their capability to damage the parasite integrity, with KR-20 being the most effective and with KR-12 and LL-37 being less active. These results demonstrate the ability of antimicrobial peptides derived from human cathelicidin to damage Entamoeba trophozoites. Moreover, it was shown that the integrity of the peptides is altered in the presence of an ameba soluble fraction with cysteine protease activity.

Human cathelicidin LL-37 prevents bacterial biofilm formation

Human pathogens often colonize their host by the formation of biofilms. These surface-attached aggregates of bacteria are characterized by a self-produced extracellular matrix, which makes them highly resistant towards antibiotic treatment. Their abilities to adhere to abiotic surfaces (e.g., catheters and other medical devices) also makes bacterial biofilm formation a challenge in modern medicine. Antimicrobial peptides have lately been introduced as a potential class of drug molecules for combating severe hospital-acquired infections. One of these peptides, human cathelicidin LL-37, has recently been demonstrated to bridge innate and adaptive host defence, in addition to facilitating a robust antibiofilm effect at sub-inhibitory concentrations. In this review we will discuss the evidence, potential and challenges for LL-37 as a candidate molecule for therapeutic use.

Human beta-defensin DEFB126 is capable of inhibiting LPS-mediated inflammation

β-Defensins are cationic, antimicrobial peptides that participate in antimicrobial defense as well as the regulation of innate and adaptive immunity. Human β-defensin 126 (DEFB126) is a multifunctional glycoprotein consisting of a conserved β-defensin core and a unique long glycosylated peptide tail. The long glycosylated peptide tail has been proven to be critical for efficient transport of sperm in the female reproductive tract, preventing their immune recognition, and efficient delivery of capacitated sperm to the site of fertilization. However, the functions of the conserved β-defensin core remain to be fully elucidated. In the present work, the conserved β-defensin core of the DEFB126 was expressed to explore its potential antimicrobial and anti-inflammatory activities. The DEFB126 core peptide exhibited both high potency for binding and neutralizing lipopolysaccharide (LPS) in vitro, and potent anti-inflammatory ability by down-regulating the mRNA expression of pro-inflammatory cytokines including IL-α, IL-1β, IL-6 and TNF-α in a murine macrophage cell line RAW264.7. The treatment with the DEFB126 core peptide also led to correspondingly decreased secretion of IL-6 and TNF-α. The blockade of LPS-induced p42/44 and p38 MAPK signal pathway might contribute to the anti-inflammation effects of the DEFB126 core peptide. Furthermore, fluorescence-labeled DEFB126 could enter RAW 264.7 cells and reduce the production of LPS-stimulated inflammatory factors, implying that DEFB126 might also participate in intracellular regulation beyond its direct LPS neutralization. In summary, our results demonstrate that the DEFB 126 core peptide has critical functions in parallel to its C-terminal tail by showing LPS-binding activity, anti-inflammatory effects and intracellular regulatory function.

A comprehensive summary of LL-37, the factotum human cathelicidin peptide

Cathelicidins are a group of antimicrobial peptides. Since their discovery, it has become clear that they are an exceptional class of peptides, with some members having pleiotropic effects. Not only do they possess an antibacterial, antifungal and antiviral function, they also show a chemotactic and immunostimulatory/-modulatory effect. Moreover, they are capable of inducing wound healing, angiogenesis and modulating apoptosis. Recent insights even indicate for a role of these peptides in cancer. This review provides a comprehensive summary of the most recent and relevant insights concerning the human cathelicidin LL-37.

Antibacterial activity of the human host defence peptide LL-37 and selected synthetic cationic lipids against bacteria associated with oral and upper respiratory tract infections

OBJECTIVES

We aim to develop antibacterial peptide mimics resistant to protease degradation, with broad-spectrum activity at sites of infection.

METHODS

The bactericidal activities of LL-37, ceragenins CSA-13, CSA-90 and CSA-92 and the spermine-conjugated dexamethasone derivative D2S were evaluated using MIC and MBC measurements. Gingival fibroblast counting, interleukin-8 (IL-8) and lactate dehydrogenase (LDH) release from keratinocytes (HaCat) were used to determine effects on cell growth, pro-inflammatory response and toxicity.

RESULTS

All tested cationic lipids showed stronger bactericidal activity than LL-37. Incubation of Staphylococcus aureus with half the MIC of LL-37 led to the appearance of bacteria resistant to its bactericidal effects, but identical incubations with CSA-13 or D2S did not produce resistant bacteria. Cathelicidin LL-37 significantly increased the total number of gingival fibroblasts, but ceragenins and D2S did not alter gingival fibroblast growth. Cationic lipids showed no toxicity to HaCat cells at concentrations resulting in bacterial killing.

CONCLUSIONS

These data suggest that cationic lipids such as ceragenins warrant further testing as potential novel antibacterial agents.

Linear bactenecin analogs with cell selectivity and anti-endotoxic activity

Bactenecin (Bac) is a 12-residue disulfide-linked antimicrobial peptide isolated from the granules of bovine neutrophils. In this study, to develop novel linear Bac analogs with cell selectivity and anti-endotoxic activity, we designed and synthesized a series of linear Bac analogs with amino acid substitution in Cys3,11 and/or Val6,7 of Bac. Among Bac analogs, some analogs (Bac-W, Bac-KW, Bac-L, Bac-KL, Bac-LW, and Bac-KLW) with higher hydrophobicity showed the amalgamated property of cell selectivity and anti-endotoxic activity. Furthermore, Bac-W, Bac-KW, Bac-LW, and Bac-KLW showed serum stability comparable with that of disulfide-bonded Bac. Therefore, these Bac analogs (Bac-W, Bac-KW, Bac-LW, and Bac-KLW) can serve as promising antibiotics for the development of therapeutic agents for treatment against endotoxic shock and bacterial infection. In addition, our results suggest that a little increase in hydrophobicity may be responsible for the decreased cell selectivity of the multiple Arg-containing peptides (Bac-W, Bac-L, and Bac-LW) over the multiple Lys-containing peptides (Bac-KW, Bac-KL, and Bac-KLW).

Positive correlation between circulating cathelicidin antimicrobial peptide (hCAP18/LL-37) and 25-hydroxyvitamin D levels in healthy adults

Background

Transcription of the cathelicidin antimicrobial peptide (CAMP) gene is induced by binding of the bioactive form of vitamin D, 1,25-dihydroxyvitamin D, to the vitamin D receptor. Significant levels of the protein hCAP18/LL-37 are found in the blood and may protect against infection and/or sepsis. We hypothesized that serum vitamin D levels may modulate the circulating levels of hCAP18. Only three studies have shown a positive correlation between circulating 25-hydroxyvitamin D and hCAP18 levels. Here we provide additional evidence for such a correlation in healthy, middle-aged adults.

Findings

Serum levels of 25-hydroxyvitamin D [25(OH)D] and plasma levels of hCAP18 were determined in 19 healthy middle-aged (mean of 50.1 years) adult men and women. Plasma hCAP18 concentrations correlated with serum 25(OH)D concentrations in subjects with 25(OH)D levels ≤ 32 ng/ml (r = 0.81, p < 0.005) but not in subjects with concentrations > 32 ng/ml (r = 0.19, p = 0.63).

Conclusions

We conclude that plasma hCAP18 levels correlate with serum 25(OH)D levels in subjects with concentrations of 25(OH)D ≤ 32 ng/ml as opposed to those with concentrations > 32 ng/ml and that vitamin D status may regulate systemic levels of hCAP18/LL-37.

Dimerization of a cell-penetrating peptide leads to enhanced cellular uptake and drug delivery

Over the past 20 years, cell-penetrating peptides (CPPs) have gained tremendous interest due to their ability to deliver a variety of therapeutically active molecules that would otherwise be unable to cross the cellular membrane due to their size or hydrophilicity. Recently, we reported on the identification of a novel CPP, sC18, which is derived from the C-terminus of the 18 kDa cationic antimicrobial protein. Furthermore, we demonstrated successful application of sC18 for the delivery of functionalized cyclopentadienyl manganese tricarbonyl (cymantrene) complexes to tumor cell lines, inducing high cellular toxicity. In order to increase the potential of the organometallic complexes to kill tumor cells, we were looking for a way to enhance cellular uptake. Therefore, we designed a branched dimeric variant of sC18, (sC18)(2), which was shown to have a dramatically improved capacity to internalize into various cell lines, even primary cells, using flow cytometry and fluorescence microscopy. Cell viability assays indicated increased cytotoxicity of the dimer presumably caused by membrane leakage; however, this effect turned out to be dependent on the specific cell type. Finally, we could show that conjugation of a functionalized cymantrene with (sC18)(2) leads to significant reduction of its IC(50) value in tumor cells compared to the respective sC18 conjugate, proving that dimerization is a useful method to increase the drug-delivery potential of a cell-penetrating peptide.

The effect of human antibacterial peptide LL-37 in the pathogenesis of chronic obstructive pulmonary disease

BACKGROUND

Previous research has shown that innate immune system was more important than the acquired immune system in the pathogenesis of COPD. LL-37 is the only human cathelicidin identified so far. As an integral part of the innate immune system, besides antibacterial activity, its chemotactic activity, damage repairing, influencing apoptosis and its cytotoxicity are attracting people's attention. The aim of the present study was to evaluate role of LL-37 in the pathogenesis of COPD.

METHODS

ELISA and immunohistochemistry were applied to investigate the expression of LL-37 in induced sputum and lung tissue of COPD patients. Bronchial epithelial cell (BEP2D) and alveolar epithelial cell (A549) were treated with LL-37 synthesis polypeptide in vitro to assess the role of LL-37 in inflammation and apoptosis.

RESULTS

We found that increased induced sputum levels of LL-37 in COPD patients were associated with airflow limitation, health status and exercise tolerance and the expressing intensity of LL-37 in both airway district and pulmonary alveoli area in COPD group significantly increased compared with control group. Through stimulation by CSE and LPS, the expression of LL-37 was increased in bronchial epithelial cell and alveolar epithelial cell. LL-37 synthesis polypeptide can promote the releasing of inflammatory factor IL-8 and induce apoptosis of bronchial epithelial cell and alveolar epithelial cell.

CONCLUSION

This study suggested that LL-37 may play important role in the pathogenesis of COPD and may be a possible novel therapeutic target in COPD.

Antimicrobial peptide LL37 promotes vascular endothelial growth factor-A expression in human periodontal ligament cells

BACKGROUND AND OBJECTIVE

LL37, originally found in the innate immune system, is a robust antimicrobial peptide. LL37 exhibits multiple bio-functions in various cell types, such as migration, cytokine production, apoptosis, and angiogenesis besides its antimicrobial activity Periodontal ligament (PL) cells play a pivotal role in periodontal tissue regeneration. Based on these findings, we hypothesized that LL37 can regulate PL cell function to promote regeneration of periodontal tissue. To prove this hypothesis, we investigated the effect of LL37 on the potent angiogenic inducer vascular endothelial growth factor (VEGF) expression in cultures of human PL (HPL) cells because neovascularization is indispensable for the progress of tissue regeneration. Moreover, we investigated the signaling cascade associated with LL37-induced VEGF expression.

MATERIAL AND METHOD

HPL cells were treated with synthesized LL37 in the presence or absence of PD98059, a MEK-ERK inhibitor, or PDTC, an NF-κB inhibitor. VEGF expression levels were assessed by real-time polymerase chain reaction analysis and an enzyme-linked immunoassay. Phosphorylation levels of ERK1/2 or NF-κB p65 were determined by Western blotting.

RESULTS

LL37 upregulated VEGF-A expression at the mRNA and protein levels in HPL cells, while VEGF-B mRNA expression was not affected. Both ERK and NF-κB inhibitors clearly abrogated the increase in VEGF-A levels induced by LL37 in HPL cells. Importantly, LL37 increased phosphorylated levels of ERK1/2 and NF-κB p65 in HPL cells.

CONCLUSION

LL37 induces VEGF-A production in HPL cells via ERK and NF-κB signaling cascades, which may result in angiogenesis, thereby contributing to periodontal regeneration.

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.

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.

Cathelicidin-related antimicrobial peptide is required for effective lung mucosal immunity in Gram-negative bacterial pneumonia

Cathelicidins are a family of endogenous antimicrobial peptides that exert diverse immune functions, including both direct bacterial killing and immunomodulatory effects. In this study, we examined the contribution of the murine cathelicidin, cathelicidin-related antimicrobial peptide (CRAMP), to innate mucosal immunity in a mouse model of Gram-negative pneumonia. CRAMP expression is induced in the lung in response to infection with Klebsiella pneumoniae. Mice deficient in the gene encoding CRAMP (Cnlp(-/-)) demonstrate impaired lung bacterial clearance, increased bacterial dissemination, and reduced survival in response to intratracheal K. pneumoniae administration. Neutrophil influx into the alveolar space during K. pneumoniae infection was delayed early but increased by 48 h in CRAMP-deficient mice, which was associated with enhanced expression of inflammatory cytokines and increased lung injury. Bone marrow chimera experiments indicated that CRAMP derived from bone marrow cells rather than structural cells was responsible for antimicrobial effects in the lung. Additionally, CRAMP exerted bactericidal activity against K. pneumoniae in vitro. Similar defects in lung bacterial clearance and delayed early neutrophil influx were observed in CRAMP-deficient mice infected with Pseudomonas aeruginosa, although this did not result in increased bacterial dissemination, increased lung injury, or changes in lethality. Taken together, our findings demonstrate that CRAMP is an important contributor to effective host mucosal immunity in the lung in response to Gram-negative bacterial pneumonia.

Modulation of neutrophil apoptosis by antimicrobial peptides

Peptide antibiotics possess the potent antimicrobial activities against invading microorganisms and contribute to the innate host defense. Human antimicrobial peptides, α-defensins (human neutrophil peptides, HNPs), human β-defensins (hBDs), and cathelicidin (LL-37) not only exhibit potent bactericidal activities against Gram-negative and Gram-positive bacteria, but also function as immunomodulatory molecules by inducing cytokine and chemokine production, and inflammatory and immune cell activation. Neutrophil is a critical effector cell in host defense against microbial infection, and its lifespan is regulated by various pathogen- and host-derived substances. Here, we provided the evidence that HNP-1, hBD-3, and LL-37 cannot only destroy bacteria but also potently modulate (suppress) neutrophil apoptosis, accompanied with the phosphorylation of ERK-1/-2, the downregulation of tBid (an proapoptotic protein) and upregulation of Bcl-x_L (an antiapoptotic protein), and the inhibition of mitochondrial membrane potential change and caspase 3 activity, possibly via the actions on the distinct receptors, the P2Y₆ nucleotide receptor, the chemokine receptor CCR6, and the low-affinity formyl-peptide receptor FPRL1/the nucleotide receptor P2X₇, respectively. Suppression of neutrophil apoptosis results in the prolongation of their lifespan and may be advantageous for the host defense against bacterial invasion.

Specificity of antimicrobial peptide LL-37 to neutralize periodontopathogenic lipopolysaccharide activity in human oral fibroblasts

BACKGROUND

The antimicrobial peptide LL-37 is known to have a potent lipopolysaccharide (LPS)-neutralizing activity in various cell types. Because of observed heterogeneity within periodontopathogenic LPS, the authors hypothesized that LL-37 had specificity to neutralize such LPS activity. The present study, therefore, aims to investigate the LPS-neutralizing activity of LL-37 to various periodontopathogenic LPS in interleukin-8 (IL-8) production after challenging them in human oral fibroblasts.

METHODS

Human periodontal ligament fibroblasts (PDLF) and gingival fibroblasts (GF) were cultured from biopsies of periodontal ligament and gingival tissues. After cell confluence in 24-well plates, LPS (10 μg/mL) from Porphyromonas gingivalis, Prevotella intermedia, Fusobacterium nucleatum, and Aggregatibacter actinomycetemcomitans were added with or without LL-37 (10 μg/mL). After 18 hours, the supernatant was collected and analyzed in IL-8 production by enzyme-linked immunosorbent assay.

RESULTS

All periodontopathogenic LPS statistically significantly induced IL-8 production in both PDLF and GF (P <0.01). After neutralization with LL-37, both PDLF and GF showed a statistically significant reduction in IL-8 production compared with LPS-treated groups without LL-37 (P <0.01), and the percentage of reduction in IL-8 production in PDLF appeared to be higher than in GF. In addition, the percentage of reduction in IL-8 production varied considerably according to each periodontopathogenic LPS.

CONCLUSIONS

The antimicrobial peptide LL-37 had an ability to suppress periodontopathogenic LPS-induced IL-8 production in both PDLF and GF. Its LPS-neutralizing activity revealed specificity to periodontopathogenic LPS and seemed to be dependent on the heterogeneity within LPS between different genera.

Doxycycline indirectly inhibits proteolytic activation of tryptic kallikrein-related peptidases and activation of cathelicidin

The increased abundance and activity of cathelicidin and kallikrein 5 (KLK5), a predominant trypsin-like serine protease (TLSP) in the stratum corneum, have been implicated in the pathogenesis of rosacea, a disorder treated by the use of low-dose doxycycline. Here we hypothesized that doxycycline can inhibit activation of tryptic KLKs through an indirect mechanism by inhibition of matrix metalloproteinases (MMPs) in keratinocytes. The capacity of doxycycline to directly inhibit enzyme activity was measured in surface collections of human facial skin and extracts of cultured keratinocytes by fluorescence polarization assay against fluorogenic substrates specific for MMPs or TLSPs. Doxycycline did inhibit MMP activity but did not directly inhibit serine protease activity against a fluorogenic substrate specific for TLSPs. However, when doxycycline or other MMP inhibitors were added to live keratinocytes during the production of tryptic KLKs, this treatment indirectly resulted in decreased TLSP activity. Furthermore, doxycycline under these conditions inhibited the generation of the cathelicidin peptide LL-37 from its precursor protein hCAP18, a process dependent on KLK activity. These results demonstrate that doxycycline can prevent cathelicidin activation, and suggest a previously unknown mechanism of action for doxycycline through inhibiting generation of active cathelicidin peptides.

Natural antimicrobial peptides as promising anti-HIV candidates

Human immunodeficiency virus type 1 (HIV-1) infection remains to be one of the major global health problems. It is thus necessary to identify novel therapeutic molecules to combat HIV-1. Natural antimicrobial peptides (AMPs) have been recognized as promising templates for developing topical microbicides. This review systematically discusses over 80 anti-HIV peptides annotated in the antimicrobial peptide database (http://aps.unmc.edu/AP). Such peptides have been discovered from bacteria, plants, and animals. Examples include gramicidin and bacteriocins from bacteria, cyclotides from plants, melittins and cecropins from insects, piscidins from fish, ascaphins, caerins, dermaseptins, esculentins, and maximins from amphibians, and cathelicidins and defensins from vertebrates. These peptides appear to work by different mechanisms and could block viral entry in multiple ways. As additional advantages, such anti-HIV peptides may possess other desired features such as antibacterial, antiparasital, spermicidal, and anticancer activity. With continued optimization of peptide stability, production, formulation and delivery methods, it is anticipated that some of these compounds may eventually become new anti-HIV drugs.

Antimicrobial peptides: key components of the innate immune system

Life-threatening infectious diseases are on their way to cause a worldwide crisis, as treating them effectively is becoming increasingly difficult due to the emergence of antibiotic resistant strains. Antimicrobial peptides (AMPs) form an ancient type of innate immunity found universally in all living organisms, providing a principal first-line of defense against the invading pathogens. The unique diverse function and architecture of AMPs has attracted considerable attention by scientists, both in terms of understanding the basic biology of the innate immune system, and as a tool in the design of molecular templates for new anti-infective drugs. AMPs are gene-encoded short (<100 amino acids), amphipathic molecules with hydrophobic and cationic amino acids arranged spatially, which exhibit broad spectrum antimicrobial activity. AMPs have been the subject of natural evolution, as have the microbes, for hundreds of millions of years. Despite this long history of co-evolution, AMPs have not lost their ability to kill or inhibit the microbes totally, nor have the microbes learnt to avoid the lethal punch of AMPs. AMPs therefore have potential to provide an important breakthrough and form the basis for a new class of antibiotics. In this review, we would like to give an overview of cationic antimicrobial peptides, origin, structure, functions, and mode of action of AMPs, which are highly expressed and found in humans, as well as a brief discussion about widely abundant, well characterized AMPs in mammals, in addition to pharmaceutical aspects and the additional functions of AMPs.

Antimicrobial peptides in periodontal innate defense

The development of oral biofilms and the host response to biofilm bacteria and their toxins are important factors in the development of periodontal disease. An early component of the host response is the secretion of antimicrobial proteins and peptides (AMPs) by salivary glands, oral epithelial cells and neutrophils. Over 45 AMPs have been identified in the oral cavity. All are found in saliva and several are also present in gingival crevicular fluid. Of these, 13 are up regulated in periodontal disease while 11 are downregulated. However, the concentrations of most AMPs found in oral fluids are below the effective in vitro concentrations, suggesting that local concentrations must be higher for effect or that additional biological functions are important in the oral cavity. Thus, in addition to direct antibacterial activity (e.g. bactericidal activity, bacterial agglutination), AMPs may affect the course of periodontal disease by inactivating bacterial or host proteases (e.g. secretory leukoprotease inhibitor) or bind bacterial toxins, including lipopolysaccharides (e.g. LL-37). Several AMPs (e.g. defensins) also act as immune system alarmins, i.e. endogenous mediators that recruit and activate antigen-presenting cells to enhance innate and adaptive immune responses. The differential regulation of AMP expression in periodontal disease suggests that AMP panels, including up- and downregulated proteins, can be used in oral fluid diagnosis of periodontal disease and to monitor treatment outcome.

The antimicrobial peptide LL-37 is anti-inflammatory and proapoptotic in human periodontal ligament cells

BACKGROUND AND OBJECTIVE

The antimicrobial peptide LL-37 is expressed in periodontal tissue, and variations in LL-37 levels have been associated with periodontal disease. The effects of LL-37 on periodontal ligament cell function have not been described before. Here, we assess anti-inflammatory properties of LL-37 and investigate the effects of LL-37 on cell differentiation, cell proliferation and apoptosis in human periodontal ligament cells.

MATERIAL AND METHODS

Periodontal ligament cells were obtained from teeth extracted for orthodontic reasons. Cytokine (interleukin-6) and chemokine (monocyte chemoattractant protein-1) expression was determined by quantitative PCR, cell differentiation by alkaline phosphatase activity, cell proliferation by counting cells in a Bürker chamber, DNA synthesis by incorporation of radiolabeled thymidine and apoptosis by cell morphology and activated caspase 3 quantities.

RESULTS

Treatment with 0.1 and 1 μm of LL-37 totally reversed lipopolysaccharide-induced monocyte chemoattractant protein-1 expression and suppressed lipopolysaccharide-induced interleukin-6 expression by 50-70%. LL-37 had no effect on alkaline phosphatase activity. Incubation with 8 μm LL-37 strongly reduced cell number. DNA synthesis was attenuated by about 90% in response to 8 μm LL-37, confirming its antiproliferative effect. Cell morphology was altered in an apoptosis-like fashion in cells treated with 8 μm LL-37. Furthermore, the quantity of activated caspase 3 was increased in cells treated with 1 and 8 μm of LL-37, suggesting apoptosis.

CONCLUSION

LL-37 strongly attenuates lipopolysaccharide-induced cytokine and chemokine expression and, in high concentrations, reduces cell proliferation through inhibition of DNA synthesis and by promoting apoptosis in human periodontal ligament cells.

Antimicrobial peptide killing of African trypanosomes

The diseases caused by trypanosomes are medically and economically devastating to the population of Sub-Saharan Africa. Parasites of the genus Trypanosoma infect both humans, causing African sleeping sickness, and livestock, causing Nagana. The development of effective treatment strategies has suffered from severe side effects of approved drugs, resistance and major difficulties in delivering drugs. Antimicrobial peptides (AMPs) are ubiquitous components of immune defence and are being rigorously pursued as novel sources of new therapeutics for a variety of pathogens. Here, we review the role of AMPs in the innate immune response of the tsetse fly to African trypanosomes, catalogue trypanocidal AMPs from diverse organisms and highlight the susceptibility of bloodstream form African trypanosomes to killing by unconventional toxic peptides.