Complementary DNA sequence of rabbit CAP18--a unique lipopolysaccharide binding protein

Regulatory Roles of Antimicrobial Peptides in the Nervous System: Implications for Neuronal Aging

Antimicrobial peptides (AMPs) are classically known as important effector molecules in innate immunity across all multicellular organisms. However, emerging evidence begins to suggest multifunctional properties of AMPs beyond their antimicrobial activity, surprisingly including their roles in regulating neuronal function, such as sleep and memory formation. Aging, which is fundamental to neurodegeneration in both physiological and disease conditions, interestingly affects the expression pattern of many AMPs in an infection-independent manner. While it remains unclear whether these are coincidental events, or a mechanistic relationship exists, previous studies have suggested a close link between AMPs and a few key proteins involved in neurodegenerative diseases. This review discusses recent literature and advances in understanding the crosstalk between AMPs and the nervous system at both molecular and functional levels, with the aim to explore how AMPs may relate to neuronal vulnerability in aging.

Emerging Advances of Nanotechnology in Drug and Vaccine Delivery against Viral Associated Respiratory Infectious Diseases (VARID)

Viral-associated respiratory infectious diseases are one of the most prominent subsets of respiratory failures, known as viral respiratory infections (VRI). VRIs are proceeded by an infection caused by viruses infecting the respiratory system. For the past 100 years, viral associated respiratory epidemics have been the most common cause of infectious disease worldwide. Due to several drawbacks of the current anti-viral treatments, such as drug resistance generation and non-targeting of viral proteins, the development of novel nanotherapeutic or nano-vaccine strategies can be considered essential. Due to their specific physical and biological properties, nanoparticles hold promising opportunities for both anti-viral treatments and vaccines against viral infections. Besides the specific physiological properties of the respiratory system, there is a significant demand for utilizing nano-designs in the production of vaccines or antiviral agents for airway-localized administration. SARS-CoV-2, as an immediate example of respiratory viruses, is an enveloped, positive-sense, single-stranded RNA virus belonging to the coronaviridae family. COVID-19 can lead to acute respiratory distress syndrome, similarly to other members of the coronaviridae. Hence, reviewing the current and past emerging nanotechnology-based medications on similar respiratory viral diseases can identify pathways towards generating novel SARS-CoV-2 nanotherapeutics and/or nano-vaccines.

Immunomodulatory Expression of Cathelicidins Peptides in Pulp Inflammation and Regeneration: An Update

The role of inflammatory mediators in dental pulp is unique. The local environment of pulp responds to any changes in the physiology that are highly fundamental, like odontoblast cell differentiation and other secretory activity. The aim of this review is to assess the role of cathelicidins based on their capacity to heal wounds, their immunomodulatory potential, and their ability to stimulate cytokine production and stimulate immune-inflammatory response in pulp and periapex. Accessible electronic databases were searched to find studies reporting the role of cathelicidins in pulpal inflammation and regeneration published between September 2010 and September 2020. The search was performed using the following databases: Medline, Scopus, Web of Science, SciELO and PubMed. The electronic search was performed using the combination of keywords "cathelicidins" and "dental pulp inflammation". On the basis of previous studies, it can be inferred that LL-37 plays an important role in odontoblastic cell differentiation and stimulation of antimicrobial peptides. Furthermore, based on these outcomes, it can be concluded that LL-37 plays an important role in reparative dentin formation and provides signaling for defense by activating the innate immune system.

Targeting Cancer Heterogeneity with Immune Responses Driven by Oncolytic Peptides

Accumulating preclinical and clinical evidence indicates that high degrees of heterogeneity among malignant cells constitute a considerable obstacle to the success of cancer therapy. This calls for the development of approaches that operate - or enable established treatments to operate - despite such intratumoral heterogeneity (ITH). In this context, oncolytic peptides stand out as promising therapeutic tools based on their ability to drive immunogenic cell death associated with robust anticancer immune responses independently of ITH. We review the main molecular and immunological pathways engaged by oncolytic peptides, and discuss potential approaches to combine these agents with modern immunotherapeutics in support of superior tumor-targeting immunity and efficacy in patients with cancer.

The absence of murine cathelicidin-related antimicrobial peptide impacts host responses enhancing Salmonella enterica serovar Typhimurium infection

BACKGROUND

Cathelicidins are a class of antimicrobial peptide, and the murine cathelicidin-related antimicrobial peptide (mCRAMP) has been demonstrated in vitro to impair Salmonella enterica serovar Typhimurium proliferation. However, the impact of mCRAMP on host responses and the microbiota following S. Typhimurium infection has not been determined. In this study mCRAMP^-/- and mCRAMP^+/+ mice (± streptomycin) were orally inoculated with S. enterica serovar Typhimurium DT104 (SA +), and impacts on the host and enteric bacterial communities were temporally evaluated.

RESULTS

Higher densities of the pathogen were observed in cecal digesta and associated with mucosa in SA+/mCRAMP^-/- mice that were pretreated (ST+) and not pretreated (ST-) with streptomycin at 24 h post-inoculation (hpi). Both SA+/ST+/mCRAMP^-/- and SA+/ST-/mCRAMP^-/- mice were more susceptible to infection exhibiting greater histopathologic changes (e.g. epithelial injury, leukocyte infiltration, goblet cell loss) at 48 hpi. Correspondingly, immune responses in SA+/ST+/mCRAMP^-/- and SA+/ST-/mCRAMP^-/- mice were affected (e.g. Ifnγ, Kc, Inos, Il1β, RegIIIγ). Systemic dissemination of the pathogen was characterized by metabolomics, and the liver metabolome was affected to a greater degree in SA+/ST+/mCRAMP^-/- and SA+/ST-/mCRAMP^-/- mice (e.g. taurine, cadaverine). Treatment-specific changes to the structure of the enteric microbiota were associated with infection and mCRAMP deficiency, with a higher abundance of Enterobacteriaceae and Veillonellaceae observed in infected null mice. The microbiota of mice that were administered the antibiotic and infected with Salmonella was dominated by Proteobacteria.

CONCLUSION

The study findings showed that the absence of mCRAMP modulated both host responses and the enteric microbiota enhancing local and systemic infection by Salmonella Typhimurium.

Metabolic acidosis stimulates the production of the antimicrobial peptide cathelicidin in rabbit urine

Intercalated cells of the collecting duct (CD) are critical for acid-base homeostasis and innate immune defense of the kidney. Little is known about the impact of acidosis on innate immune defense in the distal nephron. Urinary tract infections are mainly due to Escherichia coli and are an important risk factor for development of chronic kidney disease. While the effect of urinary pH on growth of E. coli is well established, in this study, we demonstrate that acidosis increases urine antimicrobial activity due, at least in part, to induction of cathelicidin expression within the CD. Acidosis was induced in rabbits by adding NH4Cl to the drinking water and reducing food intake over 3 days or by casein supplementation. Microdissected CDs were examined for cathelicidin mRNA expression and antimicrobial activity, and cathelicidin protein levels in rabbit urine were measured. Cathelicidin expression in CD cells was detected in kidney sections. CDs from acidotic rabbits expressed three times more cathelicidin mRNA than those isolated from normal rabbits. Urine from acidotic rabbits had significantly more antimicrobial activity (vs. E. coli) than normal urine, and most of this increased activity was blocked by cathelicidin antibody. The antibody had little effect on antimicrobial activity of normal urine. Urine from acidotic rabbits had at least twice the amount of cathelicidin protein as did normal urine. We conclude that metabolic acidosis not only stimulates CD acid secretion but also induces expression of cathelicidin and, thereby, enhances innate immune defense against urinary tract infections via induction of antimicrobial peptide expression.

Innate immune response to lipooligosaccharide: pivotal regulator of the pathobiology of invasive Neisseria meningitidis infections

Infections due to Neisseria meningitidis afflict more than one million people worldwide annually and cause death or disability in many survivors. The clinical course of invasive infections has been well studied, but our understanding of the cause of differences in patient outcomes has been limited because these are dependent on multiple factors including the response of the host, characteristics of the bacteria and interactions between the host and the bacteria. The meningococcus is a highly inflammatory organism, and the lipooligosaccharide (LOS) on the outer membrane is the most potent inflammatory molecule it expresses due to the interactions of the lipid A moiety of LOS with receptors of the innate immune system. We previously reported that increased phosphorylation of hexaacylated neisserial lipid A is correlated with greater inflammatory potential. Here we postulate that variability in lipid A phosphorylation can tip the balance of innate immune responses towards homeostatic tolerance or proinflammatory signaling that affects adaptive immune responses, causing disease with meningitis only, or septicemia with or without meningitis, respectively. Furthermore, we propose that studies of the relationship between bacterial virulence and gene expression should consider whether genetic variation could affect properties of biosynthetic enzymes resulting in LOS structural differences that alter disease pathobiology.

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.

Localization and developmental expression of two chicken host defense peptides: cathelicidin-2 and avian β-defensin 9

In the first weeks of life young chickens are highly susceptible to infectious diseases due to immaturity of the immune system. Little is known about the expression of host defense peptides (HDPs) during this period. In this study we examined the expression pattern of two chicken HDPs, the cathelicidin CATH-2 and the β-defensin AvBD9 by immunohistochemistry in a set of organs from embryonic day 12 until four weeks posthatch. AvBD9 was predominantly found in enteroendocrine cells throughout the intestine, the first report of in vivo HDP expression in this cell type, and showed stable expression levels during development. CATH-2 was exclusively found in heterophils which decreased after hatch in most of the examined organs including spleen, bursa and small intestine. In the lung CATH-2 expression was biphasic and peaked at the first day posthatch. In short, CATH-2 and AvBD9 appear to be expressed in cell types strategically located to respond to infectious stimuli, suggesting these peptides play a role in embryonic and early posthatch defense.

Unique features of human cathelicidin LL-37

Cathelicidins are antimicrobial peptides produced by humans and animals in response to various pathogenic microbes. This review intends to provide a brief overview of the expression, structure, properties and function of human cathelicidin LL-37 which may be a therapeutic agent against a variety of bacterial and viral diseases, cancers, and hard-to-heal wounds. Cathelicidins act as a primary defense against bacteria and other pathogens in the case of inflammation. They are able to kill bacteria and fungi, inhibit and destroy bacterial biofilms, and possess antiviral and antiparasitics properties. They can also play a role in angiogenesis, wound healing, and the regulation of apoptosis. The host defense peptide LL-37 has emerged as a novel modulator of tumor growth and metastasis in carcinogenesis of various types of cancers. LL-37 is an antimicrobial peptide able of inducing various effects. It acts as an anti- and pro- inflammatory factor. Cathelicidins are able to directly and selectively destroy membranes of various microbes and cancer cells, but they do not attack normal cells. The role of cathelicidins in cancer is double-sided. They play an important role in killing cancer cells and may provide a new possibility for the development of cancer therapeutics. However, they also can participate in carcinogenesis. Due to its activity spectrum LL-37 could be applied in pharmacotherapy. Cathelicidin peptides could serve as a template for the development of modern anti-microbial and anti-viral drugs. LL-37 is an excellent candidate to develop into therapeutics for infected wounds.

Cathelicidin (LL-37) and human β2-defensin levels of children with post-infectious bronchiolitis obliterans

INTRODUCTION

The antimicrobial peptides (AMPs) human β-defensins and cathelicidin (LL-37) are key factors in innate and adaptive immune responses of the respiratory tract and play an important role in many respiratory diseases. No data are available in the literature about the levels of these AMPs in paediatric patients with post-infectious bronchiolitis obliterans (BO). This study aimed to determine human β-defensin 2 (hBD2) and LL-37 levels and compare between post-infectious BO patients and the control group.

METHOD

The patients diagnosed with post-infectious BO between September 2012 and 2013 and age- and-gender matched healthy controls were enrolled in this multi-center study. Serum hBD2 and LL37 levels were determined with the enzyme-linked immunosorbent assay method.

RESULTS

Sixty-three post-infectious BO patients and 65 healthy children (median age 73 ± 55 and 78.74 ± 36.32 months, respectively) were enrolled in the study. The mean of hBD2 levels in patients and the control group were 1.06 ± 0.24 and 0.67 ± 0.72 ng/mL, respectively (P < 0.001). The mean of LL-37 levels in patients and the control group were 72.13 ± 29.06 and 50.10 ± 21.98 ng/mL, respectively (P < 0.001). No correlation was found between these AMPs levels and chronological age, age at the time of diagnosis, gender, Z-scores of weight and length, hospitalization numbers, the disease history before diagnosis and 25-OH D vitamin levels.

CONCLUSION

This is the first study to demonstrate the higher levels of serum hBD2 and LL-37 levels in paediatric post-infectious BO patients. These AMPs may have important roles in the immune systems and pathogenesis of these patients.

Human antimicrobial peptide LL-37 induces glial-mediated neuroinflammation

LL-37 is the sole cathelicidin-derived antimicrobial peptide found in humans. It becomes active upon C-terminal cleavage of its inactive precursor hCAP18. In addition to antimicrobial action, it also functions as an innate immune system stimulant in many tissues of the body. Here we report that hCAP18 and LL-37 are expressed in all organs of the human body that were studied with the highest basic levels being expressed in the GI tract and the brain. Its expression and functional role in the central nerve system (CNS) has not previously been reported. We found increased expression of LL-37 in IFNγ-stimulated human astrocytes and their surrogate U373 cells, as well as in LPS/IFNγ-stimulated human microglia and their surrogate monocyte-derived THP-1 cells. We found that treatment of microglia, astrocytes, THP-1 cells and U373 cells with LL-37 induced secretion of the inflammatory cytokines IL-1β and IL-6; the chemokines IL-8 and CCL-2, and other materials toxic to human neuroblastoma SH-SY5Y cells. The mechanism of LL-37 stimulation involves activation of intracellular proinflammatory pathways involving phospho-P38 MAP kinase and phospho-NFκB proteins. We blocked the inflammatory stimulant action of LL-37 by removing it with an anti-LL-37 antibody. The inflammatory effect was also prevented by treatment with inhibitors of PKC, PI3K and MEK-1/2 as well as with the intracellular Ca(2+)-chelator, BAPTA-AM. This indicates involvement of these intracellular pathways. Our data suggest that LL-37, in addition to its established roles, may play a role in the chronic neuroinflammation which is observed in neurodegenerative diseases such as Alzheimer's and Parkinson's disease.

Novel imidazolium salt--peptide conjugates and their antimicrobial activity

Our study presents innovative research dealing with the synthesis and biological evaluation of conjugates out of antimicrobial peptides (AMPs) and imidazolium cations that are derived from ionic liquids. AMPs are considered as promising alternatives to common antibiotics due to their different activity mechanisms. Antibacterial effects have also been described for ionic liquids bearing imidazolium cations . Besides single coupling of carboxy-functionalized imidazolium cations to the peptide N-terminal we also developed conjugates bearing multiple copies of imidazolium cations. The combination of both compounds resulted in synergistic effects that were most pronounced when more imidazolium cations were attached to the peptides. In addition, antibacterial activity even in drug-resistant bacterial strains could be observed. Moreover, the novel compounds showed good selectivity only against bacterial cells, an observation that was further proven by lipid interaction studies using giant unilamellar vesicles.

Complexity of antimicrobial peptide regulation during pathogen-host interactions

Antimicrobial peptides (AMPs) are a key component of the immune system and are expressed by a large variety of organisms. AMPs are capable of eliminating a broad range of micro-organisms, illustrated by murine models where lack of AMP expression resulted in enhanced susceptibility to infection. Despite the importance of AMPs in immune defences, it is not clear whether a change in AMP expression is pathogen-specific or reflects a general response to groups of pathogens. Furthermore, it is unclear how the evoked change in AMP expression affects the host. To fully exploit the therapeutic potential of AMPs - by direct application of peptides or by using AMP-inducers - it is crucial to gain an insight into the complexity involved in pathogen-mediated regulation of AMP expression. This review summarises current knowledge on how AMP expression is affected by pathogens. In addition, the relevance and specificity of these changes in AMPs during infection will be discussed.

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.

Antiviral potential of cathelicidins

ABSTRACT: The global burden of morbidity and mortality arising from viral infections is high; however, the development of effective therapeutics has been slow. As our understanding of innate immunity has expanded over recent years, knowledge of natural host defenses against viral infections has started to offer potential for novel therapeutic strategies. An area of current research interest is in understanding the roles played by naturally occurring cationic host defense peptides, such as the cathelicidins, in these innate antiviral host defenses across different species. This research also has the potential to inform the design of novel synthetic antiviral peptide analogs and/or provide rationale for therapies aimed at boosting the natural production of these peptides. In this review, we will discuss our knowledge of the antiviral activities of cathelicidins, an important family of cationic host defense peptides, and consider the implications for novel antiviral therapeutic approaches.

Structural and functional characterization of CATH_BRALE, the defense molecule in the ancient salmonoid, Brachymystax lenok

Thick-lipped lenok, Brachymystax lenok is one of the ancient fish species in China and northeast Asia countries. Due to the overfishing, the population of lenok has been declined significantly. Cathelicidins are innate immune effectors that possess both bactericidal activities and immunomodulatory functions. This report identifies and characterizes the salmonoid cathelicidin (CATH_BRALE) from this ancient fish. It consists of open reading frame (ORF) of 886 bp encoding the putative peptide of 199 amino acids. Sequence alignment with other representative salmonid cathelicidins displayed two distinctive features of current lenok cathelicidin: high level of arginine, resulting in high positive charge and glycine residues, which is significantly different from most acknowledged types of cathelicidins; and the six-aminoacid tandem repeated sequence of RPGGGS detected in a variable number of copies among fish cathelicidins, suggesting the existence of a genetically unstable region similar to that found in some mammalian cathelicidins. Expression of CATH_BRALE is predominantly found in gill, with lower levels in the gastrointestinal tract and spleen. The homology modeled structure of CATH_BRALE exhibits structural features of antiparallel b-sheets flanked by a-helices that are representative of small cationic cathelicidin family peptides. CATH_BRALE possesses much stronger antimicrobial activity against gram-negative bacteria than that of the human ortholog, LL-37. The growth of two typical fish bacterial pathogens, gram-negative bacterium of Aeromonas salmonicida and Aeromonas hydrophila was substantially inhibited by synthetic CATH_BRALE, with both MICs as low as 9.38 mM.

The human cathelicidin LL-37 inhibits influenza A viruses through a mechanism distinct from that of surfactant protein D or defensins

LL-37, the only human cathelicidin, is a cationic antimicrobial peptide with antibacterial and antifungal activity. LL-37 is released from neutrophil granules and produced by epithelial cells. It has been implicated in host defence against influenza A virus (IAV) in recent studies. We now demonstrate dose-related neutralizing activity of LL-37 against several seasonal and mouse-adapted IAV strains. The ability of LL-37 to inhibit these IAV strains resulted mainly from direct effects on the virus, since pre-incubation of virus with LL-37 was needed for optimal inhibition. LL-37 bound high-density lipoprotein (HDL), and pre-incubation of LL-37 with human serum or HDL reduced its antiviral activity. LL-37 did not inhibit viral association with epithelial cells as assessed by quantitative RT-PCR or confocal microscopy. This finding contrasted with results obtained with surfactant protein D (SP-D). Unlike collectins or human neutrophil defensins (HNPs), LL-37 did not induce viral aggregation under electron microscopy. In the electron microscopy studies, LL-37 appeared to cause disruption of viral membranes. LL-37 had additive antiviral activity when combined with other innate inhibitors like SP-D, surfactant protein A and HNPs. Unlike HNPs, LL-37 did not bind SP-D significantly. These findings indicate that LL-37 contributes to host defence against IAV through a mechanism distinct from that of SP-D and HNPs.

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.

Role of host-defence peptides in eye diseases

The eye and its associated tissues including the lacrimal system and lids have evolved several defence mechanisms to prevent microbial invasion. Included among this armory are several host-defence peptides. These multifunctional molecules are being studied not only for their endogenous antimicrobial properties but also for their potential therapeutic effects. Here the current knowledge of host-defence peptide expression in the eye will be summarised. The role of these peptides in eye disease will be discussed with the primary focus being on infectious keratitis, inflammatory conditions including dry eye and wound healing. Finally the potential of using host-defence peptides and their mimetics/derivatives for the treatment and prevention of eye diseases is addressed.

Acute involution in the tammar wallaby: identification of genes and putative novel milk proteins implicated in mammary gland function

Marsupials provide a suitable alternative model to studying mammary gland involution. They have evolved a different reproductive strategy from eutherians, giving birth to an altricial young and secreting milk that changes in composition during lactation. In this study, we used a marsupial-specific EST microarray to identify 47 up-regulated genes during mammary gland involution in the tammar wallaby (Macropus eugenii). These include the pro-apoptotic tumour necrosis factor receptor superfamily 21 (TNFRSF21) gene, whose expression in the mammary gland has not previously been reported. Genes encoding putative novel milk proteins which may protect the mammary gland from infection were also found to be up-regulated, such as amiloride binding protein 1 (ABP1), complement component 1QB (C1QB), complement component 4A (C4A) and colony stimulating factor 2 receptor β (CSF2Rβ). Our results show that the marsupial reproductive strategy was successfully exploited to identify genes and putative novel milk proteins implicated in mammary gland involution.

Peptide-based treatment of sepsis

Sepsis (blood poisoning) is a severe infectious disease with high mortality, and no effective therapy is actually known. In the case of Gram-negative bacteria, endotoxins (lipopolysaccharides) are known to be responsible for the strong inflammation reaction leading to the systemic infection. Peptides based on endotoxin-binding domains of human or animal proteins represent a promising approach in sepsis research. Although so far no medicament is available, the progress in recent years might lead to a breakthrough in this field. In this review, recent investigations are summarised, which may lead to an understanding of the mechanisms of action of peptides to suppress the inflammation reaction in vitro and in vivo (animal models) and thus may allow the development of effective anti-septic drugs.

The human cathelicidin hCAP18/LL-37: a multifunctional peptide involved in mycobacterial infections

Antimicrobial peptides are predominantly small cationic polypeptides that are classified together on the basis of these molecules to directly kill or inhibit the growth of microorganisms including mycobacteria, and to activate mechanisms of cellular and adaptive immunity. Various families of antimicrobial peptides have been identified, including the cathelicidins. The cathelicidin family is characterised by a conserved N-terminal cathelin domain and a variable C-terminal antimicrobial domain that can be released from the precursor protein after cleavage by proteinases. LL-37 is the C-terminal part of the only human cathelicidin identified to date called human cationic antimicrobial protein (hCAP18), which is mainly expressed by neutrophils and epithelial cells. The cathelicidin hCAP18/LL-37 is a multifunctional molecule that may mediate various host responses, including bactericidal action, chemotaxis, epithelial cell activation, angiogenesis, epithelial wound repair and activation of chemokine secretion. The antimicrobial peptide LL-37 is produced from human cells during infection of mycobacteria and exerts a microbicidal effect. The discussion will (1) describe recent work on the antimicrobial and immunomodulatory functions of the cathelicidin hCAP18/LL-37, (2) highlight the effectiveness of the cathelicidin hCAP18/LL-37 as a potent component in antimycobacterial immune responses and (3) summarise current progress in the understanding of the therapeutic application of hCAP18/LL-37 and its derivates antimicrobial peptides in mycobacterial infection.

Review: Defensins and cathelicidins in lung immunity

Defensins were first identified in 1985 and are now recognized as part of a large family of antimicrobial peptides, divided into three categories: alpha-, beta-, and -defensins. These defensin classes differ in structure, sites of expression and biological activities. Human alpha-defensins include peptides that are expressed primarily in neutrophils, whereas human beta-defensins are widely expressed in epithelial cells, including those lining the respiratory tract. Defensins were first studied for their broad spectrum activity against bacteria, fungi and viruses; however, it is now clear that they also recruit inflammatory cells and promote innate and adaptive immune responses. Recent evidence shows that defensins have anti-inflammatory effects as well. Hence, defensins can participate in all phases of an immune response in the lung, including initial killing of pathogens and mounting - and resolution -- of an immune or inflammatory response. The cathelicidin, LL-37, is an antimicrobial peptide produced by neutrophils and respiratory epithelial cells that has similar roles in lung immunity as the defensins. A major challenge for the coming years will be to sort out the relative contributions of defensins and LL-37 to overall immune responses in the lung and to determine which of their many in vitro activities are most important for lung immunity.

Antimicrobial peptides human beta-defensins and cathelicidin LL-37 induce the secretion of a pruritogenic cytokine IL-31 by human mast cells

In addition to their microbiocidal properties, human beta-defensins (hBDs) and cathelicidin LL-37 stimulate a number of mammalian cell activities, including migration, proliferation, and cytokine/chemokine production. Because hBDs and LL-37 cause mast cells to release pruritogens such as histamine and PGs, we hypothesized that these peptides would stimulate the secretion of a novel pruritogenic mediator IL-31, predominantly produced by T cells. hBDs and LL-37 enhanced IL-31 gene expression and IL-31 protein production and release in the human mast cell line LAD2, as well as in peripheral blood-derived cultured mast cells, suggesting that mast cells are another source of IL-31. Moreover, the expression of IL-31 was elevated in psoriatic skin mast cells, and hBD-2-4 and LL-37, but not hBD-1, enhanced its expression in vivo in rat skin mast cells. hBDs and LL-37 also induced the release of other pruritogenic mediators, including IL-2, IL-4, IL-6, GM-CSF, nerve growth factor, PGE(2), and leukotriene C(4), and increased mRNA expression of substance P. hBD- and LL-37-mediated IL-31 production/release was markedly reduced by pertussis toxin and wortmannin, inhibitors of G-protein and PI3K, respectively. As evidenced by the inhibitory effects of MAPK-specific inhibitors, hBD-2-4 and LL-37 activated the phosphorylation of MAPKs p38, ERK, and JNK that were required for IL-31 production and release. The ability of hBDs and LL-37 to stimulate the production and release of IL-31 by human mast cells provides a novel mechanism by which skin-derived antimicrobial peptides/proteins may contribute to inflammatory reactions and suggests a central role of these peptides in the pathogenesis of skin disorders.

Fusion of a Short HA2-Derived Peptide Sequence to Cell-Penetrating Peptides Improves Cytosolic Uptake, but Enhances Cytotoxic Activity

Cell-penetrating peptides (CPP) have become a widely used tool for efficient cargo delivery into cells. However, one limiting fact is their uptake by endocytosis causing the enclosure of the CPP-cargo construct within endosomes. One often used method to enhance the outflow into the cytosol is the fusion of endosome-disruptive peptide or protein sequences to CPP. But, until now, no studies exist investigating the effects of the fusion peptide to the cellular distribution, structural arrangements and cytotoxic behaviour of the CPP. In this study, we attached a short modified sequence of hemagglutinin subunit HA2 to different CPP and analysed the biologic activity of the new designed peptides. Interestingly, we observed an increased cytosolic distribution but also highly toxic activities in the micromolar range against several cell lines. Structural analysis revealed that attachment of the fusion peptide had profound implications on the whole conformation of the peptide, which might be responsible for membrane interaction and endosome disruption.

The role of antimicrobial peptides at the ocular surface

Antimicrobial peptides (AMPs) such as defensins and cathelicidins are small peptides with broad-spectrum activity against bacteria, fungi and viruses. In addition, several AMPs modulate mammalian cell behaviours including migration, proliferation and cytokine production. This review describes findings from recent studies showing the presence of various AMPs at the human ocular surface and discusses their mechanism of antimicrobial action and potential non-microbicidal roles. Corneal and conjunctival epithelial cells produce beta-defensins and the cathelicidin LL-37, whereas neutrophils, infiltrating in response to a specific stimulus, supply additional LL-37 as well as alpha-defensins. In vitro studies suggest that LL-37 and human beta-defensin-3 are the most likely to have significant independent antimicrobial activity, while other AMPs may act synergistically to help protect the ocular surface from invading pathogens. Current evidence also supports a role for some AMPs in modulating wound healing responses. Although yet to be brought to fruition, AMPs hold significant potential as therapeutic agents for the prophylaxis and treatment of infection, promotion of wound healing and immune modulation.

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.

A member of the cathelicidin family of antimicrobial peptides is produced in the upper airway of the chinchilla and its mRNA expression is altered by common viral and bacterial co-pathogens of otitis media

Cationic antimicrobial peptides (AMPs), a component of the innate immune system, play a major role in defense of mucosal surfaces against a wide spectrum of microorganisms such as viral and bacterial co-pathogens of the polymicrobial disease otitis media (OM). To further understand the role of AMPs in OM, we cloned a cDNA encoding a cathelicidin homolog (cCRAMP) from upper respiratory tract (URT) mucosae of the chinchilla, the predominant host used to model experimental OM. Recombinant cCRAMP exhibited alpha-helical secondary structure and killed the three main bacterial pathogens of OM. In situ hybridization showed cCRAMP mRNA production in epithelium of the chinchilla Eustachian tube and RT-PCR was used to amplify cCRAMP mRNA from several other tissues of the chinchilla URT. Quantitative RT-PCR analysis of chinchilla middle ear epithelial cells (CMEEs) incubated with either viral (influenza A virus, adenovirus, or RSV) or bacterial (nontypeable H. influenzae, M. catarrhalis, or S. pneumoniae) pathogens associated with OM demonstrated distinct microbe-specific patterns of altered expression. Collectively, these data showed that viruses and bacteria modulate AMP messages in the URT, which likely contributes to the disease course of OM.

Host antimicrobial defence peptides in human disease

Antimicrobial peptides or host defence peptides are endogenous peptide antibiotics, which have been confirmed as an essential part of the immune system. Apart from direct killing of bacteria, a role for the peptides in antiviral and immunomodulatory functions has recently been claimed. In this chapter we have focused on the host contact with microbes, where these host defence peptides are key players. The interplay with commensals and pathogens in relation to antimicrobial peptide expression is discussed, with specific emphasis on the respiratory and the alimentary systems. A possible novel difference in epithelial interactions between commensals and pathogens is considered in relation to disease.

Two cathelicidin genes are present in both rainbow trout (Oncorhynchus mykiss) and atlantic salmon (Salmo salar)

Further to the previous finding of the rainbow trout rtCATH_1 gene, this paper describes three more cathelicidin genes found in salmonids: two in Atlantic salmon, named asCATH_1 and asCATH_2, and one in rainbow trout, named rtCATH_2. All the three new salmonid cathelicidin genes share the common characteristics of mammalian cathelicidin genes, such as consisting of four exons and possessing a highly conserved preproregion and four invariant cysteines clustered in the C-terminal region of the cathelin-like domain. The asCATH_1 gene is homologous to the rainbow trout rtCATH_1 gene, in that it possesses three repeat motifs of TGGGGGTGGC in exon IV and two cysteine residues in the predicted mature peptide, while the asCATH_2 gene and rtCATH_2 gene are homologues of each other, with 96% nucleotide identity. Salmonid cathelicidins possess the same elastase-sensitive residue, threonine, as hagfish cathelicidins and the rabbit CAP18 molecule. The cleavage site of the four salmonid cathelicidins is within a conserved amino acid motif of QKIRTRR, which is at the beginning of the sequence encoded by exon IV. Two 36-residue peptides corresponding to the core part of rtCATH_1 and rtCATH_2 were chemically synthesized and shown to exhibit potent antimicrobial activity. rtCATH_2 was expressed constitutively in gill, head kidney, intestine, skin and spleen, while the expression of rtCATH_1 was inducible in gill, head kidney, and spleen after bacterial challenge. Four cathelicidin genes have now been characterized in salmonids and two were identified in hagfish, confirming that cathelicidin genes evolved early and are likely present in all vertebrates.

Inhibition of early steps in the lentiviral replication cycle by cathelicidin host defense peptides

Background

The antibacterial activity of host defense peptides (HDP) is largely mediated by permeabilization of bacterial membranes. The lipid membrane of enveloped viruses might also be a target of antimicrobial peptides. Therefore, we screened a panel of naturally occurring HDPs representing different classes for inhibition of early, Env-independent steps in the HIV replication cycle. A lentiviral vector-based screening assay was used to determine the inhibitory effect of HDPs on early steps in the replication cycle and on cell metabolism.

Results

Human LL37 and porcine Protegrin-1 specifically reduced lentiviral vector infectivity, whereas the reduction of luciferase activities observed at high concentrations of the other HDPs is primarily due to modulation of cellular activity and/ or cytotoxicity rather than antiviral activity. A retroviral vector was inhibited by LL37 and Protegrin-1 to similar extent, while no specific inhibition of adenoviral vector mediated gene transfer was observed. Specific inhibitory effects of Protegrin-1 were confirmed for wild type HIV-1.

Conclusion

Although Protegrin-1 apparently inhibits an early step in the HIV-replication cycle, cytotoxic effects might limit its use as an antiviral agent unless the specificity for the virus can be improved.

Inner field compensation as a tool for the characterization of asymmetric membranes and Peptide-membrane interactions

Symmetric and asymmetric planar lipid bilayers prepared according to the Montal-Mueller method are a powerful tool to characterize peptide-membrane interactions. Several electrical properties of lipid bilayers such as membrane current, membrane capacitance, and the inner membrane potential differences and their changes can be deduced. The time-resolved determination of peptide-induced changes in membrane capacitance and inner membrane potential difference are of high importance for the characterization of peptide-membrane interactions. Intercalation and accumulation of peptides lead to changes in membrane capacitance, and membrane interaction of charged peptides induces changes in the charge distribution within the membrane and with that to changes in the membrane potential profile. In this study, we establish time-resolved measurements of the capacitance minimization potential DeltaPsi on various asymmetric planar lipid bilayers using the inner field compensation method. The results are compared to the respective ones of inner membrane potential differences DeltaPhi determined from ion carrier transport measurements. Finally, the time courses of membrane capacitances and of DeltaPsi have been used to characterize the interaction of cathelicidins with reconstituted lipid matrices of various Gram-negative bacteria.

Cathelicidins, multifunctional peptides of the innate immunity

Cathelicidins comprise a family of mammalian proteins containing a C-terminal cationic antimicrobial domain that becomes active after being freed from the N-terminal cathelin portion of the holoprotein. Many other members of this family have been identified since the first cathelicidin sequences were reported 10 years ago. The mature peptides generally show a wide spectrum of antimicrobial activity and, more recently, some of them have also been found to exert other biological activities. The human cathelicidin peptide LL-37 is chemotactic for neutrophils, monocytes, mast cells, and T cells; induces degranulation of mast cells; alters transcriptional responses in macrophages; stimulates wound vascularization and re-epithelialization of healing skin. The porcine PR-39 has also been involved in a variety of processes, including promotion of wound repair, induction of angiogenesis, neutrophils chemotaxis, and inhibition of the phagocyte NADPH oxidase activity, whereas the bovine BMAP-28 induces apoptosis in transformed cell lines and activated lymphocytes and may thus help with clearance of unwanted cells at inflammation sites. These multiple actions provide evidence for active participation of cathelicidin peptides in the regulation of the antimicrobial host defenses.

Endotoxin-neutralizing effects of histidine-rich peptides

Inflammatory responses of human peripheral blood monocytes to the Gram-negative endotoxin lipopolysaccharide (LPS) are enhanced by structurally diverse substances, such as anionic polysaccharides or cationic polypeptides. Only a few substances are known to effectively blunt LPS-induced monocyte activation. We now show that synthetic poly-L-histidine (Hn) binds to LPS and abrogates the release of the proinflammatory cytokine interleukin-8 (IL-8) in LPS-stimulated human whole blood. LPS-induced stimulation of monocytes was strictly pH-dependent with only minor amounts of IL-8 secreted in acidic blood. Maximum levels of IL-8 secretion occurred at a strongly basic pH. Hn inhibition of the release of IL-8 from LPS-stimulated monocytes was observed under acidic, neutral and physiological conditions. With increasing alkalosis, the effectiveness of Hn was gradually lost, suggesting that protonated, but not deprotonated, Hn was effective in inhibiting LPS-induced monocyte responses. Histidine-rich protein 2 from the malaria parasite, Plasmodium falciparum, inhibited the ability of LPS to evoke an inflammatory response in CD14-transfected THP-1 cells. Further, a short synthetic peptide derived from human histidine- and proline-rich glycoprotein also exhibited LPS-inhibitory effects in CD14 transfectants. Taken together, these observations demonstrate the capacity of histidine-rich peptides, irrespective of their origin, to neutralize LPS-induced proinflammatory host responses.

Hagfish intestinal antimicrobial peptides are ancient cathelicidins

Three potent broad-spectrum antimicrobial peptides (HFIAP-1, -2, and -3) isolated from intestinal tissues of Myxine glutinosa (Atlantic hagfish) are identified as ancient members of the cathelicidin family of antimicrobial peptides, hitherto known only from mammals. In situ hybridization reveals that HFIAPs are produced in nests of myeloid cells within the loose connective tissue of the gut wall, a tissue reminiscent of both gut-associated lymphoid tissue (GALT) and vertebrate spleen. We suggest that this tissue organization provides local defense of the hagfish gastrointestinal tract via innate immunity and possibly served as the architectural plan upon which the adaptive immune system evolved.

Mammalian antibiotic peptides

The increasing development of bacterial resistance to traditional antibiotics has reached alarming levels, thus creating a strong need to develop new antimicrobial agents. These new antibiotics should possess novel mechanisms of action and different cellular targets compared with existing antimicrobials. Recent discoveries and isolations of so-called animal antibiotics, mostly small cationic peptides, which represent a potent branch of natural immunity, offered the possibility to acquire new and effective antibiotics of this provenance. To this date, more than 500 antibiotic peptides have been distinguished and defined. Their antimicrobial properties present new opportunities for their use as antibiotics or for construction of their more effective derivatives, but much research is still required to pave the way to their practical use. This is a survey of substances forming an armamentarium of natural immunity of mammals.

Receptors, mediators, and mechanisms involved in bacterial sepsis and septic shock

Bacterial sepsis and septic shock result from the overproduction of inflammatory mediators as a consequence of the interaction of the immune system with bacteria and bacterial wall constituents in the body. Bacterial cell wall constituents such as lipopolysaccharide, peptidoglycans, and lipoteichoic acid are particularly responsible for the deleterious effects of bacteria. These constituents interact in the body with a large number of proteins and receptors, and this interaction determines the eventual inflammatory effect of the compounds. Within the circulation bacterial constituents interact with proteins such as plasma lipoproteins and lipopolysaccharide binding protein. The interaction of the bacterial constituents with receptors on the surface of mononuclear cells is mainly responsible for the induction of proinflammatory mediators by the bacterial constituents. The role of individual receptors such as the toll-like receptors and CD14 in the induction of proinflammatory cytokines and adhesion molecules is discussed in detail. In addition, the roles of a number of other receptors that bind bacterial compounds such as scavenger receptors and their modulating role in inflammation are described. Finally, the therapies for the treatment of bacterial sepsis and septic shock are discussed in relation to the action of the aforementioned receptors and proteins.

Antimicrobial activity and stability to proteolysis of small linear cationic peptides with D-amino acid substitutions

Antimicrobial peptides contribute to innate host defense against a number of bacteria and fungal pathogens. Some of antimicrobial synthetic peptides were systemically administered in vivo; however, effective protection has so far not been obtained because the effective dose of peptides in vivo seems to be very high, often close to the toxic level against the host. Alternatively, peptides administered in vivo may be degraded by certain proteases present in serum. In this study, D-amino acids were substituted for the L-amino acids of antimicrobial peptides to circumvent these problems. Initially a peptide (L-peptide) rich in five arginine residues and consisting of an 11-amino acid peptide (residues 32-42) of human granulysin was synthesized. Subsequently, the L-amino acids of the 11-amino acid peptide were replaced partially (D-peptide) or wholly (AD-peptide) with D-amino acids. Activity and stability to proteolysis, in particular, in the serum of antimicrobial peptides with D-amino acid substitutions were examined. Peptides with D-amino acid substitutions were found to lyse bacteria as efficiently as their all-L-amino acid parent, L-peptide. In addition, the peptide composed of L-amino acids was susceptible to trypsin, whereas peptides containing D-amino acid substitutions were highly stable to trypsin treatment. Similarly, the peptide consisting of L-amino acids alone was also susceptible to fetal calf serum (FCS), however, protease inhibitors restored the lowered antimicrobial activity of the FCS-incubated peptide. Thus, D-amino acid substitutions can make antimicrobial peptides resistant to proteolysis, suggesting that the antimicrobial peptides consisting of D-amino acids are potential candidates for clinical therapeutic use.

Conformation-dependent antibiotic activity of tritrpticin, a cathelicidin-derived antimicrobial peptide

Tritrpticin, a Trp-rich cationic antimicrobial peptide with a unique amino acid sequence (VRRFPWWWPFLRR), is found in porcine cathelicidin cDNA. Tritrpticin has a broad spectrum of antibacterial and antifungal activities and hemolytic activity comparable to that of indolicidin. To investigate the mechanism of the bacterial killing action of tritrpticin and to identify structural features important for bacterial cell selectivity, we designed several tritrpticin analogs with amino acid substitutions of the Pro and Trp residues. Circular dichroism studies revealed that the substitution of Pro-->Ala (TPA) or Trp-->Phe (TWF) leads to significant conformational changes in SDS micelles, converting the beta-turn to alpha-helix or to poly-L-proline II helix, respectively. Compared to tritrpticin, TPA retained most of its antimicrobial activity, but showed enhanced hemolytic and membrane-disrupting activities. In contrast, TWF showed a 2-4-fold increase in antimicrobial activity against Gram-negative bacteria, but a marked decrease in both hemolytic and membrane-disrupting activities. Taken together, our findings suggest that compared with the beta-turn and alpha-helical structures, the poly-L-proline II helix is crucial for effective bacterial cell selectivity in tritrpticin and its analogs.

Activity of novispirin G10 against Pseudomonas aeruginosa in vitro and in infected burns

The emergence of multidrug-resistant microbes has serious implications for managing infection and sepsis and has stimulated efforts to develop alternative treatments, such as antimicrobial peptides. The objective of this study was to test a designer peptide, novispirin G10, against multidrug-resistant microorganisms. By two-stage radial diffusion assays, its activity against such organisms compared favorably with that of standard antibiotics and other antimicrobial peptides. It killed bacteria very rapidly, was nonhemolytic, and was relatively noncytotoxic. The peptide induced an immediate, massive efflux of potassium from Pseudomonas aeruginosa, suggesting that it altered the permeability of its inner membrane. The presence of human serum reduced but did not eliminate its activity. We tested the in vivo activity of novispirin G10 in rats with an infected, partial-thickness burn that covered 20% of their total body surface area. The burned area was seeded with 10(6) CFU of a Silvadene-resistant P. aeruginosa strain, and 24 h later a single treatment with 0, 1, 3, or 6 mg of synthetic novispirin G10 (n = 16 at each concentration) per kg was given intradermally. Significant bacterial killing (P < 0.0001) was evident within 4 h in each peptide group compared to controls receiving vehicle. Antimicrobial peptides such as novispirin G10 may provide a useful alternative or adjunct to standard antibiotic agents in treating burns or other wound infections.

Cathelicidins: microbicidal activity, mechanisms of action, and roles in innate immunity

Antimicrobial peptides are important host-defense molecules of innate immunity. Cathelicidins are a diverse family of potent, rapidly acting and broadly effective antimicrobial peptides, which are produced by a variety of cells. This review examines the classification, antimicrobial spectrum, mechanism of action, and regulation of cathelicidins.

Host defense functions of proteolytically processed and parent (unprocessed) cathelicidins of rabbit granulocytes

Members of the cathelicidin family are present in all mammals studied. Generally, these proteins contain a conserved N-terminal domain and a structurally and functionally divergent C-terminal region that expresses antibacterial or other activities when proteolytically released. Rabbit granulocytes produce CAP18, a cathelicidin that conforms to this structural and functional organization, and also 15-kDa protein isoforms (p15s) that share several key structural features with other cathelicidins but apparently do not undergo processing with release of an active peptide. To further define the importance of proteolysis in the antibacterial activities of these proteins, we have purified from granulocytes proCAP18, its C-terminal peptide (CAP18p), and two p15 isoforms to apparent homogeneity. Of these four polypeptides, only CAP18p was independently cytotoxic to encapsulated Escherichia coli (90% inhibitory concentration, approximately 600 nM) but it was approximately 50-fold less potent on a molar basis than the bactericidal/permeability-increasing protein (BPI). However, all four cathelicidin species, notably including proCAP18, exhibited antibacterial synergy with BPI, and the p15s also displayed synergy with CAP18p in the absence of BPI. Subnanomolar concentrations of proCAP18 blocked lipopolysaccharide-induced chemiluminescence of human leukocytes, showing a molar potency more than 100-fold greater than that of CAP18p ( approximately 20 nM) or BPI ( approximately 50 nM). Thus, while independent bactericidal activity of cathelicidins requires processing, other host-defense functions do not and are more potently expressed by the unprocessed protein than by the C-terminal peptide.

SMAP-29 has two LPS-binding sites and a central hinge

The CD spectra of SMAP-29, an antimicrobial peptide from sheep, showed disordered structure in aqueous buffers, and significant helicity in membrane-like environments, including SDS micelles, lipopolysaccharide (LPS) dispersions, and trifluoroethanol buffer systems. A structure determined by NMR in 40% perdeuterated trifluoroethanol indicated that residues 8-17 were helical, residues 18-19 formed a hinge, and residues 20-28 formed an ordered, hydrophobic segment. SMAP-29 was flexible in 40% trifluoroethanol, forming two sets of conformers that differed in the relative orientation of the N-terminal domain. We used a chromogenic Limulus assay to determine the EC50 of the peptide (the concentration that bound 50% of the added LPS). Studies with full-length and truncated SMAP-29 molecules revealed that each end of the holopeptide contained an LPS-binding domain. The higher affinity LPS-binding domain was situated in the flexible N-terminal portion. LPS binding to full-length SMAP-29 showed positive cooperativity, so the EC50 of the peptide (2.6 microm) was considerably lower than that of the individual LPS-binding domains. LPS-binding studies with a mixture of truncated peptides revealed that this cooperativity was primarily intramolecular (i.e. involving the N- and C-terminal LPS-binding sites of the same peptide molecule). CAP-18[106 -142], an antimicrobial cathelicidin peptide of rabbits, resembled SMAP-29 in that it contained N- and C-terminal LPS-binding domains, had an EC50 of 2.5 microm, and bound LPS with positive cooperativity. We conclude that the presence of multiple binding sites that function cooperatively allow peptides such as SMAP-29 and CAP-18 to bind LPS with high affinity.

Biologically active proteins from natural product extracts

The term "biologically active proteins" is almost redundant. All proteins produced by living creatures are, by their very nature, biologically active to some extent in their homologous species. In this review, a subset of these proteins will be discussed that are biologically active in heterologous systems. The isolation and characterization of novel proteins from natural product extracts including those derived from microorganisms, plants, insects, terrestrial vertebrates, and marine organisms will be reviewed and grouped into several distinct classes based on their biological activity and their structure.

Cathelicidin peptides inhibit multiply antibiotic-resistant pathogens from patients with cystic fibrosis

Endogenous peptide antibiotics are under investigation as inhaled therapeutic agents for cystic fibrosis (CF) lung disease. The bactericidal activities of five cathelicidin peptides (LL37 [human], CAP18 [rabbit], mCRAMP [mouse], rCRAMP [rat], and SMAP29 [sheep]), three novel alpha-helical peptides derived from SMAP29 and termed ovispirins (OV-1, OV-2, and OV-3), and two derivatives of CAP18 were tested by broth microdilution assays. Their MICs were determined for multiply antibiotic-resistant Pseudomonas aeruginosa (n = 24), Burkholderia cepacia (n = 5), Achromobacter xylosoxidans (n = 5), and Stenotrophomonas maltophilia (n = 5) strains isolated from CF patients. SMAP29 was most active and inhibited mucoid and nonmucoid P. aeruginosa strains (MIC, 0.06 to 8 microg/ml). OV-1, OV-2, and OV-3 were nearly as active (MIC, 0.03 to 16 microg/ml), but CAP18 (MIC, 1.0 to 32 microg/ml), CAP18-18 (MIC, 1.0 to >32 microg/ml), and CAP18-22 (MIC, 0.5 to 32 microg/ml) had variable activities. LL37, mCRAMP, and rCRAMP were least active against the clinical isolates studied (MIC, 1.0 to >32 microg/ml). Peptides had modest activities against S. maltophilia and A. xylosoxidans (MIC range, 1.0 to > 32 microg/ml), but none inhibited B. cepacia. However, CF sputum inhibited the activity of SMAP29 substantially. The effects of peptides on bacterial cell membranes and eukaryotic cells were examined by scanning electron microscopy and by measuring transepithelial cell resistance, respectively. SMAP29 caused the appearance of bacterial membrane blebs within 1 min, killed P. aeruginosa within 1 h, and caused a dose-dependent, reversible decrease in transepithelial resistance within 5 h. The tested cathelicidin-derived peptides represent a novel class of antimicrobial agents and warrant further development as prophylactic or therapeutic agents for CF lung disease.

Human cathelicidin, hCAP-18, is processed to the antimicrobial peptide LL-37 by extracellular cleavage with proteinase 3

Cathelicidins are a family of antimicrobial proteins found in the peroxidase-negative granules of neutrophils. The known biologic functions reside in the C-terminus, which must be cleaved from the holoprotein to become active. Bovine and porcine cathelicidins are cleaved by elastase from the azurophil granules to yield the active antimicrobial peptides. The aim of this study was to identify the physiological setting for cleavage of the only human cathelicidin, hCAP-18, to liberate the antibacterial and cytotoxic peptide LL-37 and to identify the protease responsible for this cleavage. Immunoelectron microscopy demonstrated that both hCAP-18 and azurophil granule proteins were present in the phagolysosome. Immunoblotting revealed no detectable cleavage of hCAP-18 in cells after phagocytosis. In contrast, hCAP-18 was cleaved to generate LL-37 in exocytosed material. Of the 3 known serine proteases from azurophil granules, proteinase 3 was solely responsible for cleavage of hCAP-18 after exocytosis. This is the first detailed study describing the generation of a human antimicrobial peptide from a promicrobicidal protein, and it demonstrates that the generation of active antimicrobial peptides from common proproteins occurs differently in related species. (Blood. 2001;97:3951-3959)