Determination of disulphide bridges in PG-2, an antimicrobial peptide from porcine leukocytes

Growth hormone receptor knockout to reduce the size of donor pigs for preclinical xenotransplantation studies

BACKGROUND

Many genetically multi-modified donor lines for xenotransplantation have a background of domestic pigs with rapid body and organ growth. The intrinsic growth potential of porcine xeno-organs may impair their long-term function after orthotopic transplantation in non-human primate models. Since growth hormone is a major stimulator of postnatal growth, we deleted its receptor (GHR-KO) to reduce the size of donor pigs in one step.

METHODS

Heart weight and proteome profile of myocardium were investigated in GHR-KO and control pigs. GHR-KO mutations were introduced using CRISPR/Cas9 in an α1,3-galactosyltransferase (GGTA1)-deficient background expressing the human cluster of differentiation (hCD46) and human thrombomodulin (hTHBD) to generate quadruple-modified (4GM) pigs.

RESULTS

At age 6 months, GHR-KO pigs had a 61% reduced body weight and a 63% reduced heart weight compared with controls. The mean minimal diameter of cardiomyocytes was 28% reduced. A holistic proteome study of myocardium samples from the two groups did not reveal prominent differences. Two 4GM founder sows had low serum insulin-like growth factor 1 (IGF1) levels (24 ± 1 ng/mL) and reached body weights of 70.3 and 73.4 kg at 9 months. Control pigs with IGF1 levels of 228 ± 24 ng/mL reached this weight range three months earlier. The 4GM sows showed normal sexual development and were mated with genetically multi-modified boars. Offspring revealed the expected Mendelian transmission of the genetic modifications and consistent expression of the transgenes.

CONCLUSION

GHR-KO donor pigs can be used at an age beyond the steepest phase of their growth curve, potentially reducing the problem of xeno-organ overgrowth in preclinical studies.

Structures of β-hairpin antimicrobial protegrin peptides in lipopolysaccharide membranes: mechanism of gram selectivity obtained from solid-state nuclear magnetic resonance

The structural basis for the gram selectivity of two disulfide-bonded β-hairpin antimicrobial peptides (AMPs) is investigated using solid-state nuclear magnetic resonance (NMR) spectroscopy. The hexa-arginine PG-1 exhibits potent activities against both gram-positive and gram-negative bacteria, while a mutant of PG-1 with only three cationic residues maintains gram-positive activity but is 30-fold less active against gram-negative bacteria. We determined the topological structure and lipid interactions of these two peptides in a lipopolysaccharide (LPS)-rich membrane that mimics the outer membrane of gram-negative bacteria and in the POPE/POPG membrane, which mimics the membrane of gram-positive bacteria. (31)P NMR line shapes indicate that both peptides cause less orientational disorder in the LPS-rich membrane than in the POPE/POPG membrane. (13)C chemical shifts and (13)C-(1)H dipolar couplings show that both peptides maintain their β-hairpin conformation in these membranes and are largely immobilized, but the mutant exhibits noticeable intermediate-time scale motion in the LPS membrane at physiological temperature, suggesting shallow insertion. Indeed, (1)H spin diffusion from lipid chains to the peptides shows that PG-1 fully inserts into the LPS-rich membrane whereas the mutant does not. The (13)C-(31)P distances between the most hydrophobically embedded Arg of PG-1 and the lipid (31)P are significantly longer in the LPS membrane than in the POPE/POPG membrane, indicating that PG-1 does not cause toroidal pore defects in the LPS membrane, in contrast to its behavior in the POPE/POPG membrane. Taken together, these data indicate that PG-1 causes transmembrane pores of the barrel-stave type in the LPS membrane, thus allowing further translocation of the peptide into the inner membrane of gram-negative bacteria to kill the cells. In comparison, the less cationic mutant cannot fully cross the LPS membrane because of weaker electrostatic attractions, thus causing weaker antimicrobial activities. Therefore, strong electrostatic attraction between the peptide and the membrane surface, ensured by having a sufficient number of Arg residues, is essential for potent antimicrobial activities against gram-negative bacteria. The data provide a rational basis for controlling gram selectivity of AMPs by adjusting the charge densities.

Arasin 1, a proline-arginine-rich antimicrobial peptide isolated from the spider crab, Hyas araneus

Antimicrobial peptides (AMPs) are considered to play an important role as host-defense molecules in both vertebrates and invertebrates. This work was undertaken to characterize AMPs from hemocyte extracts of the small spider crab, Hyas araneus. A novel proline-arginine-rich AMP of 37 amino acids was isolated and characterized. The peptide, named arasin 1, has a chimeric structure with an N-terminal domain rich in proline and arginine and a C-terminal domain containing two disulfide linkages. The peptide precursor of 64 amino acids, deduced from a cDNA library, contained a hydrophobic pre-region of 25 amino acids, directly followed by the mature peptide. C-terminally, this precursor had two additional amino acids, which seem to be cleaved off post-translationally. Synthetic arasin 1 showed antibacterial activity. A putative isoform of arasin 1, named arasin 2, was found at the genetic level, and both transcripts were shown by real-time RT-PCR to be expressed mainly in hemocytes.

De novo designed cyclic cationic peptides as inhibitors of plant pathogenic bacteria

Head-to-tail cyclic peptides of 4-10 residues consisting of alternating hydrophilic (Lys) and hydrophobic (Leu and Phe) amino acids were synthesized and tested against the economically important plant pathogenic bacteria Erwinia amylovora, Xanthomonas vesicatoria and Pseudomonas syringae. The antibacterial activity, evaluated as the minimal inhibitory concentration (MIC), the cytotoxicity against human red blood cells and stability towards protease degradation were determined. The influence of cyclization, ring size, and replacement of l-Phe with d-Phe on antibacterial and hemolytic activities was studied and correlated with the degree of structuring and hydrophobicity. Our results showed that linear peptides were inactive against the three bacteria tested. Cyclic peptides were active only toward X. vesicatoria and P. syringae, being c(KLKLKFKLKQ) (BPC10L) the most active peptide with MIC values of 6.25 and 12.5 microM, respectively. The improved antibacterial activity of cyclic peptides compared to their linear counterparts was associated to an increase of the hydrophobicity, represented as RP-HPLC retention time (t(R)), and secondary structure content which are related to an enhanced amphipathicity. A decrease of antibacterial and hemolytic activities was observed when a d-Phe was introduced into the cyclic sequences, which was attributed to their low amphipathicity as shown by their low secondary structure content and low t(R). The small size, simple structure, bactericidal effect, and stability to protease degradation of the best peptides make them potential candidates for the development of effective antibacterial agents for use in plant protection.

Antimicrobial peptides as microbicidal contraceptives: prophecies for prophylactics--a mini review

The global increase in human immunodeficiency virus/acquired immune deficiency syndrome (HIV/AIDS) and sexually transmitted infections (STIs) has led to the introduction of barrier methods, such as condoms. However, drawbacks associated with condoms, such as men being reluctant to use them and women being unable to negotiate their use, have led to the search for better and acceptable alternatives, namely the microbicides. These are gel formulations that, when used prior to sexual intercourse, protect against the transmission of HIV and other STIs. However, after observing the side-effects of nonoxynol-9, a component of the microbicidal formulations available on the market, the focus has shifted to natural available compounds demonstrating the preferred protective effects. Antimicrobial peptides (AMPs) are one such group of compounds present in a wide range of organisms from bacteria to humans. The existing 750 or so, low-molecular-weight, cationic charged peptides are classified into five major groups based on their three-dimensional structure obtained by nuclear magnetic resonance studies. The hypothesized mode of action seems to be the interaction of the positively charged peptides with the negatively charged phospholipids present on the surface of the cell membrane. Various studies have demonstrated the effect of several AMPs, namely, defensins, protegrins, cathelicidins, cecropins, polyphemusins, magainins and melittins, against various STI-causing pathogens and HIV/herpes simplex virus, both in vitro and in vivo. The contraceptive efficacies of magainin and nisin in vitro and in vivo are worth mentioning. We believe these peptides are suitable candidates in the development of newer mechanism-based microbicides in future.

CysMap and CysJoin: Database and tools for protein disulphides localisation

We have developed a computer program able to make user-customised databases derived from the public PIR non-redundant reference protein database. When the database of interest has been created, the user will generate the map of all the possible linear peptides containing one and two cysteines for each protein and combine them to calculate the mass of all the possible clusters of linear peptides linked by a disulphide bridge with a cysteine pair. It is also possible to create selected maps corresponding to peptides formed by the action of specific proteases. In this way, mass spectrometric data obtained from the hydrolysis of proteins of unknown sequence can be related to that contained in the database for quick disulphide assignment and protein identification. To confirm signal attribution, the program will also furnish the expected mass of cluster peptides after performing a cycle of Edman degradation. The utility of the program is discussed and examples of application are given.

Can we predict biological activity of antimicrobial peptides from their interactions with model phospholipid membranes?

Cationic antibacterial peptides are produced in all living organisms and possess either selective activity toward a certain type of cell or microorganism, or a broad spectrum of activity toward several types of cells including prokaryotic and mammalian cells. In order to exert their activity, peptides first interact with and traverse an outer barrier, e.g., mainly LPS and peptidoglycan in bacteria or a glycocalix layer and matrix proteins in mammalian cells. Only then, can the peptides bind and insert into the cytoplasmic membrane. The mode of action of many antibacterial peptides is believed to be the disruption of the lipidic plasma membrane. Therefore, model phospholipid membranes have been used to study the mode of action of antimicrobial peptides. These studies have demonstrated that peptides that act preferentially on bacteria are also able to interact with and permeate efficiently anionic phospholipids, whereas peptides that lyse mammalian cells bind and permeate efficiently both acidic and zwitterionic phospholipids membranes, mimicking the plasma membranes of these cells. It is now becoming increasingly clear that selective activity of these peptides against different cells depends also on other parameters that characterize both the peptide and the target cell. With respect to the peptide's properties, these include the volume of the molecule, its structure, and its oligomeric state in solution and in membranes. Regarding the target membrane, these include the structure, length, and complexity of the hydrophilic polysaccharide found in its outer layer. These parameters affect the ability of the peptides to diffuse through the cell's outer barrier and to reach its cytoplasmic plasma membrane.

Improved brain uptake and pharmacological activity of dalargin using a peptide-vector-mediated strategy

The blood-brain barrier restricts the passage of substances into the brain. Neuropeptides, such as enkephalins, cannot be delivered into the brain when given systemically because of this barrier. Therefore, there is a need to develop efficient transport systems to deliver these drugs to the brain. Recently, we have demonstrated that conjugation of doxorubicin or penicillin to peptide vectors significantly enhances their brain uptake. In this study, we have conjugated the enkephalin analog dalargin with two different peptide vectors, SynB1 and SynB3, to improve its brain delivery and its pharmacological effect. We show by in situ brain perfusion that vectorization markedly enhances the brain uptake of dalargin. We also show using the hot-plate model that this enhancement in brain uptake results in a significant improvement in the observed antinociceptive effect of dalargin. These results support the usefulness of peptide-mediated strategies for improving the availability and efficacy of central nervous system drugs.

Drug delivery to brain via the blood-brain barrier

1. Many neurodegenerative diseases, cancer and infections of the brain become more prevalent as populations become older. Despite major advances in neuroscience, the blood-brain barrier (BBB) ensures that many potential therapeutic cannot reach the central nervous system (CNS). The BBB is formed by the complex tight junctions between the endothelial cells of the brain capillaries and their low endocytic activity. This results in the capillary wall that behaves as a continuous lipid bilayer and prevents the passage of polar and lipid-insoluble substances. It is, therefore, the major obstacle to drugs that may combat diseases affecting the CNS. 2. Several strategies for delivering drugs to the CNS have been developed. These enhance the capacity of therapeutic molecules to cross the BBB by modifying the drug itself, or by coupling it to a vector for receptor-mediated or adsorption-mediated transcytosis. 3. The current challenge is to develop drug-delivery systems that ensure that drugs cross the BBB in a safe and effective manner. This review focuses on the strategies developed to enhance drug delivery across the BBB.

Optimization of microbial specificity in cyclic peptides by modulation of hydrophobicity within a defined structural framework

In the present study we have utilized the structural framework of the analog GS14K4 (cyclo(VKLd-KVd-YPL KVKLd-YP, where d denotes a d-amino acid)), to examine the role of hydrophobicity in microbial activity and specificity. The hydrophobicity of GS14K4 was systematically altered by residue replacements in the hydrophobic sites of the molecule to produce a series of analogs that were either less or more hydrophobic than the parent compound. Circular dichroism spectroscopy and reversed-phase high performance liquid chromatography analysis showed that the molecules were structurally similar and only differed in overall hydrophobicity. The hydrophobicity of GS14K4 was found to be the midpoint for hemolytic activity, with more hydrophobic analogs exhibiting increased hemolytic activity and less hydrophobic analogs showing decreased hemolytic activity. For antimicrobial activity there were differences between the hydrophobicity requirements against Gram-positive and Gram-negative microorganisms. The hydrophobicity of GS14K4 was sufficient for maximum activity against Gram-negative microorganisms and yeast, with no further increases in activity occurring with increasing hydrophobicity. With Gram-positive microorganisms significant increases in activity with increasing hydrophobicity were seen in three of the six microorganisms tested. A therapeutic index (calculated as a measure of specificity of the peptides for the microorganisms over human erythrocytes) served to define the boundaries of a therapeutic window within which lay the optimum peptide hydrophobicity for each microorganism. The therapeutic window was found to be at a lower hydrophobicity level for Gram-negative microorganisms than for Gram-positive microorganisms, although the limits were more variable for the latter. Our results show that the balance between activity and specificity in the present cyclic peptides can be optimized for each microorganism by systematic modulation of hydrophobicity.

Vector-mediated drug delivery to the brain

As a consequence of the growing ageing population, many neurodegenerative diseases, cancer and infections of the brain will become more prevalent. Despite major advances in neuroscience, many potential therapeutic agents are denied access to the central nervous system (CNS) because of the existence of the blood-brain barrier (BBB). This barrier is formed by the endothelial cells of the brain capillaries and its primary characteristic is the impermeability of the capillary wall due to the presence of complex tight junctions and a low endocytic activity. The BBB behaves as a continuous lipid bilayer and prevents the passage of polar and lipid-insoluble substances. The BBB is, therefore, the major obstacle to drugs that are potentially useful for combating diseases affecting the CNS. Extensive efforts have been made to develop CNS drug delivery strategies in order to enhance delivery of therapeutic molecules across the BBB. The current challenge is to develop drug-delivery strategies that will allow the passage of therapeutic drugs through the BBB in a safe and effective manner. This review focuses specifically on the strategies developed to enhance drug delivery across the BBB with an emphasis on the vector-mediated strategy.

Identification of Proteus mirabilis mutants with increased sensitivity to antimicrobial peptides

Antimicrobial peptides (APs) are important components of the innate defenses of animals, plants, and microorganisms. However, some bacterial pathogens are resistant to the action of APs. For example, Proteus mirabilis is highly resistant to the action of APs, such as polymyxin B (PM), protegrin, and the synthetic protegrin analog IB-367. To better understand this resistance, a transposon mutagenesis approach was used to generate P. mirabilis mutants sensitive to APs. Four unique PM-sensitive mutants of P. mirabilis were identified (these mutants were >2 to >128 times more sensitive than the wild type). Two of these mutants were also sensitive to IB-367 (16 and 128 times more sensitive than the wild type). Lipopolysaccharide (LPS) profiles of the PM- and protegrin-sensitive mutants demonstrated marked differences in both the lipid A and O-antigen regions, while the PM-sensitive mutants appeared to have alterations of either lipid A or O antigen. Matrix-assisted laser desorption ionization-time of flight mass spectrometry analysis of the wild-type and PM-sensitive mutant lipid A showed species with one or two aminoarabinose groups, while lipid A from the PM- and protegrin-sensitive mutants was devoid of aminoarabinose. When the mutants were streaked on an agar-containing medium, the swarming motility of the PM- and protegrin-sensitive mutants was completely inhibited and the swarming motility of the mutants sensitive to only PM was markedly decreased. DNA sequence analysis of the mutagenized loci revealed similarities to an O-acetyltransferase (PM and protegrin sensitive) and ATP synthase and sap loci (PM sensitive). These data further support the role of LPS modifications as an elaborate mechanism in the resistance of certain bacterial species to APs and suggest that LPS surface charge alterations may play a role in P. mirabilis swarming motility.

Doxorubicin-peptide conjugates overcome multidrug resistance

A well-known mechanism leading to the emergence of multidrug-resistant tumor cells is the overexpression of P-glycoprotein (P-gp), which is capable of lowering intracellular drug concentrations. To overcome this problem, we tested the capability of two peptide vectors that are able to cross cellular membranes to deliver doxorubicin in P-gp-expressing cells. The antitumor effect of peptide-conjugated doxorubicin was tested in human erythroleukemic (K562/ ADR) resistant cells. The conjugate showed potent dose-dependent inhibition of cell growth against K562/ADR cells as compared with doxorubicin alone. Doxorubicin exhibited IC50 concentrations of 65 microM in the resistant cells, whereas vectorized doxorubicin was more effective with IC50 concentrations of 3 microM. After treatment of the resistant cells with verapamil, the intracellular levels of doxorubicin were markedly increased and consequent cytotoxicity was improved. In contrast, treatment of resistant cells with verapamil did not cause any further enhancement in the cell uptake nor in the cytotoxic effect of the conjugated doxorubicin, indicating that the conjugate bypasses the P-gp. Finally, we show by the in situ brain perfusion method in P-gp-deficient and competent mice that vectorized doxorubicin bypasses the P-gp present at the luminal site of the blood-brain barrier. These results indicate that vectorization of doxorubicin with peptide vectors is effective in overcoming multidrug resistance.

Development of protegrins for the treatment and prevention of oral mucositis: structure-activity relationships of synthetic protegrin analogues

Protegrin antimicrobial peptides possess activity against gram-positive and gram-negative bacteria and yeasts. An extensive structure-activity relationship (SAR) study was conducted on several hundred protegrin analogues to gain understanding of the relationship between the primary and secondary structure of the protegrins and their antimicrobial activities, and to identify a protegrin analogue for clinical development. Native sequence protegrins are cationic, amphiphilic peptides that are characterized by the presence of a beta-sheet structure that is maintained by two disulfide bridges. The presence of the beta-sheet is key to the stability of the protegrin structure; linearized analogues or analogues that have amino acid substitutions that eliminate hydrogen bonding across the beta-sheet have reduced activity, especially in the presence of physiological concentrations of NaCl. Also, maintaining amphiphilicity of the beta-sheet is key; analogues with substitutions of polar amino acids in the hydrophobic face have reduced activity. Analogues with reduced positive charge tend to be less active, an observation that is more marked for gram-negative than gram-positive bacteria, and may implicate binding to lipopolysaccharide as a key mechanistic step in the killing of gram-negative bacteria. A very large number of amino acid substitutions are tolerated by the protegrin structure, implying that overall structural features such as amphiphilicity, charge, and shape are more important to activity than the presence of specific amino acids. This lack of importance of specific stereochemistry is supported by the fact that completely D-amino acid substituted protegrins are fully potent. Based on the SAR studies, and on the microbiological data from an animal model, one protegrin analogue, IB-367, was selected for clinical development as a topical agent to prevent the oral mucositis associated with cancer therapy.

Membranolytic selectivity of cystine-stabilized cyclic protegrins

To correlate conformational rigidity with membranolytic selectivity of antimicrobial activity and cytotoxicity, we prepared six cyclic analogs of protegrin-1 (PG-1), an 18-residue cationic peptide with a broad-spectrum antimicrobial activity. These cyclic protegrins bear end-to-end peptide bonds together with varying numbers (zero to three) of cross-strand disulfide constraints. The most constrained analog is a cyclic tricystine protegrin (ccPG 3) containing three evenly spaced, parallel disulfide bonds. Antimicrobial assays against 10 organisms in low- and high-salt conditions showed that these cyclic protegrins were broadly active with different antimicrobial profiles against Gram-positive and Gram-negative bacteria, fungi and one tested virus, HIV-1. Compared to PG-1, the cyclic tricystine ccPG 3 displayed approximately a 10-fold decrease in hemolytic activity against human cells and 6- to 30-fold improvement of membranolytic selectivity against six of the 10 tested organisms. In contrast, [DeltaSS]cPG 8, a cyclic protegrin with no disulfide bond, and [DeltaCys6,15]cPG 5, a cyclic mimic of PG-1 with one disulfide bond, exhibited activity spectra, potency, and cytotoxicity similar to PG-1. Circular dichroism showed that cyclic protegrins containing with one to three cystine bonds displayed some degree of beta-strand structures in water/trifluoroethanol or phosphate-buffered solutions. Collectively, our results indicate that cyclic structures are useful in the design of antimicrobial peptides and that an increase in the conformational rigidity of protegrins may confer membranolytic selectivity that dissociates antimicrobial activity from hemolytic activity.

Interaction of antimicrobial peptides with biological and model membranes: structural and charge requirements for activity

Species right across the evolutionary scale from insects to mammals use peptides as part of their host-defense system to counter microbial infection. The primary structures of a large number of these host-defense peptides have been determined. While there is no primary structure homology, the peptides are characterized by a preponderance of cationic and hydrophobic amino acids. The secondary structures of many of the host-defense peptides have been determined by a variety of techniques. The acyclic peptides tend to adopt helical conformation, especially in media of low dielectric constant, whereas peptides with more than one disulfide bridge adopt beta-structures. Detailed investigations have indicated that a majority of these host-defense peptides exert their action by permeabilizing microbial membranes. In this review, we discuss structural and charge requirements for the interaction of endogenous antimicrobial peptides and short peptides that have been derived from them, with membranes.

Lipid-induced conformation and lipid-binding properties of cytolytic and antimicrobial peptides: determination and biological specificity

While antimicrobial and cytolytic peptides exert their effects on cells largely by interacting with the lipid bilayers of their membranes, the influence of the cell membrane lipid composition on the specificity of these peptides towards a given organism is not yet understood. The lack of experimental model systems that mimic the complexity of natural cell membranes has hampered efforts to establish a direct correlation between the induced conformation of these peptides upon binding to cell membranes and their biological specificities. Nevertheless, studies using model membranes reconstituted from lipids and a few membrane-associated proteins, combined with spectroscopic techniques (i.e. circular dichroism, fluorescence spectroscopy, Fourier transform infra red spectroscopy, etc.), have provided information on specific structure-function relationships of peptide-membrane interactions at the molecular level. Reversed phase-high performance chromatography (RP-HPLC) and surface plasmon resonance (SPR) are emerging techniques for the study of the dynamics of the interactions between cytolytic and antimicrobial peptides and lipid surfaces. Thus, the immobilization of lipid moieties onto RP-HPLC sorbent now allows the investigation of peptide conformational transition upon interaction with membrane surfaces, while SPR allows the observation of the time course of peptide binding to membrane surfaces. Such studies have clearly demonstrated the complexity of peptide-membrane interactions in terms of the mutual changes in peptide binding, conformation, orientation, and lipid organization, and have, to a certain extent, allowed correlations to be drawn between peptide conformational properties and lytic activity.

Consequences of introducing a disulfide bond into an antibacterial and hemolytic peptide

The effect of introducing a disulfide bridge between the N- and C-terminal ends on the structure and biological activities of the 13-residue linear peptide PKLLKTFLSKWIG(SPFK), which has both antibacterial and hemolytic activity, have been investigated. The terminal amino acids P and G in SPFK were replaced by cysteines to form a disulfide bridge. The linear peptides C(Acm)KLLKTFLSKWIC(Acm) and C(Acm) KLLKTFLSKWIC(Acm)-amide, where Acm is acetamidomethyl group, showed antibacterial activity but did not possess hemolytic activity unlike SPFK. Introduction of an S-S bridge resulted in enhanced hemolytic activity compared with SPFK. The hemolytic activity was particularly pronounced in the cyclic peptide CKLLKTFLSKWIC-amide. Circular dichroism studies indicate that the cyclic peptides tend to adopt distorted helical structures. The cyclic peptides also have a greater affinity for lipid vesicles, which could be the reason for the effective perturbation of the erythrocyte membrane.

Effect of local application of the antimicrobial peptide IB-367 on the incidence and severity of oral mucositis in hamsters

OBJECTIVE

The purpose of this animal study was to determine whether IB-367, an antimicrobial peptide, is able to ameliorate oral mucositis by reducing microflora densities on the mucosal surfaces of the mouth.

STUDY DESIGN

Oral mucositis was induced in hamsters by intraperitoneal injection of 5-fluorouracil followed by superficial abrasion of the buccal mucosa. A test formulation was applied topically to the buccal mucosa 5 or 6 times per day starting 6 to 8 hours before abrasion.

RESULTS

Mucositis scores were significantly lower (P < .05) in hamsters given formulations containing 0.5 or 2.0 mg/mL of IB-367 than in placebo-treated controls. Treatment with IB-367 produced a more than 100-fold reduction in oral microflora densities. In a second experiment, treatment of hamsters with a formulation containing IB-367 at 0.12, 0.5 or 2.0 mg/mL resulted in a dose-dependent reduction in mucositis severity.

CONCLUSION

The results indicate that reduction of local microflora densities through use of IB-367 may improve clinical outcomes in patients at risk for the development of oral mucositis.

Beta-sheet antibiotic peptides as potential dental therapeutics

Small, cysteine-rich, beta-sheet peptide antibiotics are found throughout the Animalia. Though broad spectrum in potential, they may exert selective antimicrobial effects under certain conditions. We have explored the antimicrobial properties of two families of beta-sheet peptide antibiotics, defensins and protegrins, against periodontopathic bacteria. The rabbit defensin NP-1 was active against facultative Gram-negative bacteria associated with early onset periodontitis, including Actinobacillus actinomycetemcomitans and the Capnocytophaga spp. Porcine protegrins showed even greater activity against those organisms, as well as against anaerobic bacteria associated with adult periodontitis, including Porphyromonas gingivalis Prevotella intermedia and Fusobacterium nucleatum. Based on these observations, we believe that protegrin-like beta-sheet peptide antibiotics may be useful dental therapeutics.

Killing of Fusobacterium nucleatum, Porphyromonas gingivalis and Prevotella intermedia by protegrins

Protegrins are broad spectrum antibiotic peptides isolated from porcine leukocytes. In this study, we (i) examine the sensitivity of Gram-negative, anaerobic periodontal pathogens to synthetic protegrins; (ii) determine the relative potencies of protegrin congeners against these bacteria; and (iii) compare the potency of protegrins with other antibiotic peptides, including magainin MSI-78, tachyplesin I, cecropin P1, human defensins HNP-1-3, and clavanin A. Synthetic L- and D-enantiomers of protegrin 1 (PG-1 and D-PG-1, respectively), and L-enantiomers of protegrins 2, 3 and 5 (PG-2, PG-3 and PG-5) were tested against Fusobacterium nucleatum, and black-pigmented organisms including Porphyromonas gingivalis and Prevotella intermedia. Strains of both F. nucleatum and the black-pigmented organisms were sensitive to PG-1, and exhibited mean ED99 of 2.2-2.3 micrograms/ml and 3.4-9.9 micrograms/ml, respectively. The D-form was statistically more potent than the L-form against these oral anaerobes, and although this difference in potency is unlikely to be of decisive therapeutic significance, the D-form may be of value given ability to resist microbial and host-derived proteases. PG-1 was more potent than magainin, tachyplesin, cecropin, defensins and clavanin under test conditions. Hypertonic salt concentrations and heat-inactivated serum were found to be inhibitory to the bactericidal activity of PG-1. PG-1 was found to induce morphologic alterations in the ultrastructural appearance of F. nucleatum consistent with damage to the bacterial membranes. We conclude that protegrins may be useful antimicrobial agents in therapy against Gram-negative anaerobic bacteria believed to be involved in chronic, adult forms of periodontal infections.

Oligomerization of protegrin-1 in the presence of DPC micelles. A proton high-resolution NMR study

Protegrins are members of a family of five Cys-rich naturally occurring cationic antimicrobial peptides. The NMR solution structure of protegrin-1 (PG-1) has been previously determined as a monomeric beta-hairpin both in water and in dimethylsulfoxide solution. Protegrins are bactericidal peptides but their mechanism of action is still unknown. In order to investigate the structural basis of their cytotoxicity, we studied the effect of lipid micelles on the structure of PG-1. The NMR study reported in the present work indicates that PG-1 adopts a dimeric structure when it binds to dodecylphosphocholine micelles. Moreover, the amide proton exchange study suggests the possibility of an association between several dimers.

Sensitivity of periodontal pathogens to the bactericidal activity of synthetic protegrins, antibiotic peptides derived from porcine leukocytes

Protegrins, small peptides (1900 to 2160 daltons) isolated from porcine leukocytes, are bactericidal against a broad range of medical pathogens in vitro under conditions which reflect the extracellular milieu. The purpose of this study was to determine whether Gram-negative, facultative periodontal pathogens were sensitive to the protegrins. Synthetic L- and D-enantiomers of protegrin 1 (PG-1 and D-PG-1, respectively), and L-enantiomers of protegrins 2, 3, and 5 (PG-2, PG-3, and PG-5) were tested against Actinobacillus actinomycetemcomitans (three strains) and Capnocytophaga spp. (three strains). Strains of both A. actinomycetemcomitans and Capnocytophaga spp. were sensitive to PG-1, and exhibited ED99 (dose at which 99% killing was observed after 1 hr at 37 degrees C) of 0.5 to 3 microg/mL and 4 to 19 microg/mL, respectively. The D-form and the L-form were equally effective. Serum (above 5% v/v) inhibited the bactericidal effects of 10 microg/mL PG-1, but the inhibitory effect was overcome by concentrations of PG-1 at 100 microg/mL. Different patterns of sensitivity were observed when the effects of PG-1, D-PG-1, PG-2, PG-3, and PG-5 were compared against A. actinomycetemcomitans and the Capnocytophaga. We conclude that protegrins may be useful antimicrobial agents in therapy against periodontal infections.

Protegrin-1: a broad-spectrum, rapidly microbicidal peptide with in vivo activity

Protegrin-1 (PG-1) is a cysteine-rich, 18-residue beta-sheet peptide isolated from porcine leukocytes with antimicrobial activity against a broad range of microorganisms. The MICs of PG-1 against representative gram-positive and gram-negative bacteria ranged from 0.12 to 2 microg/ml. At these levels, PG-1 was rapidly bactericidal in vitro, reducing the number of viable CFU of either methicillin-resistant Staphylococcus aureus (MRSA) or Pseudomonas aeruginosa by more than three log units in less than 15 min. Resistance to PG-1 did not develop after 11 subculturings of P. aeruginosa or 18 subcultures of MRSA in Mueller-Hinton broth containing PG-1 at one-half the MIC. Under similar conditions of serial passage, the MICs of norfloxacin and gentamicin against P. aeruginosa increased 10 and 190 times, respectively. Similarly, the MIC of norfloxacin against MRSA increased 85 times. Immunocompetent mice inoculated intraperitoneally (i.p.) with P. aeruginosa or S. aureus exhibited 93 to 100% mortality in the vehicle control group compared with 0 to 27% mortality in animals that received a single i.p. injection of PG-1 (0.5 mg/kg of body weight). Mice inoculated with S. aureus by intravenous (i.v.) injection and dosed 0 to 60 min later with a single i.v. injection of PG-1 (5 mg/kg) had a mortality of 7 to 33%, compared to a mortality of 73 to 93% in the vehicle controls. In leukopenic mice inoculated i.v. with vancomycin-resistant Enterococcus faecium, mortality was 87% in the vehicle control group and 33% in animals that received a single i.v. injection of PG-1 (2.5 mg/kg). Taken together, these data indicate that PG-1 has potential for use as an antimicrobial agent in the treatment of local or systemic infections caused by clinically relevant pathogens.

Protegrin structure and activity against Neisseria gonorrhoeae

Protegrin 1 (PG-1) is a broad-spectrum antimicrobial peptide that contains 18 amino acid residues (RG GRLCYCRRRFCVCVGR) and has two intramolecular cystine disulfide bonds. To determine the minimal structure responsible for protegrin-mediated activity against Neisseria gonorrhoeae, we synthesized 15 protegrin variants and tested them against two well-characterized gonococcal strains. The MICs of PG-1 were 0.61 microM (1.31 microg/ml) for the serum-sensitive strain F 62 and 0.98 microM (2.11 microg/ml) for the serum-resistant strain FA 19. Six amino acid residues (Arg1, Gly2, Gly3, Arg4, Gly17, and Arg18) and either disulfide bond could be deleted from PG-1 without impairing its potency against strain F 62. In contrast, only Gly17 and Arg18 could be removed without decreasing its activity against FA 19. Protegrin congener 64a (PC-64a; LTYCRRRFCVTV), a variant of PG-1 with 12 amino acid residues and one disulfide bond, displayed MICs of 0.45 microM (0.68 microg/ml) for strain F 62 and 1.37 microM (2.07 microg/ml) for strain FA 19, which approximated those of intact PG-1. Serum-sensitive sac-1+ and sac-3+ transformants of N. gonorrhoeae FA 19 and two FA 19 derivatives with truncated lipooligosaccharide structures were more susceptible to PG-1 and variants with altered disulfide structures. These data suggest that structurally simpler protegrin variants, such as PC-64a, could be used as topical microbicides for N. gonorrhoeae. They also suggest that the cystine-stabilized antiparallel beta-sheet formed by PG-1 residues 5 to 16 is principally responsible for its activity against gonococci.

Endogenous vertebrate antibiotics. Defensins, protegrins, and other cysteine-rich antimicrobial peptides

Although newly recognized, endogenous cystine-stabilized beta-sheet antimicrobial peptides have ancient origins. These peptides can arm circulating phagocytes and cells of the gastrointestinal, respiratory, and genitourinary tracts to resist invasion by bacteria, mycobacteria, fungi, and enveloped viruses. Defensins and protegrin-like peptides are likely to play a considerable role in innate immunity and may provide molecular templates that can be used to generate novel antibiotics for topical and systemic use.

Intramolecular disulfide bonds enhance the antimicrobial and lytic activities of protegrins at physiological sodium chloride concentrations

Protegrins are 2-kDa antimicrobial peptides that contain 16-18 amino acid residues and two intramolecular disulfide bonds. We studied the contribution of these disulfide bonds to the bactericidal activity of protegrins in physiological concentrations of NaCl by comparing protegrin PG-1 with variants that lacked one or both cysteine disulfides. Whereas the bactericidal and liposome-lytic properties of protegrin PG-1 were enhanced by adding 100 mM NaCl to the phosphate-buffered medium, NaCl addition strongly inhibited the effects of its linearized, disulfide-free variant, [A6, A8, A13, A15]protegrin-1. Whereas protegrin PG-1 manifested beta-sheet structure by CD (circular dichroism) and ATR-FTIR (attenuated-total-reflectance-Fourier-transform-infrared) spectroscopy in buffer or membrane-mimetic environments, [A6, A8, A13, A15]protegrin-1 manifested disordered structure in phosphate buffer and alpha-helical characteristics in membrane-mimetic environments. Both single-disulfide protegrin variants, [A8, A13]protegrin-1 and [A6, A15]protegrin-1, assumed beta-sheet conformations with liposomes that simulated bacterial membranes, and both retained substantial bactericidal activity when 100 mM NaCl was present. These findings demonstrate that the intramolecular disulfide bonds of protegrins are required for their antiparallel beta-sheet conformation in membrane-mimetic environments and for their potent antimicrobial activity in media containing NaCl concentrations comparable to those found in serum and extracellular fluids.

Solution structure of protegrin-1, a broad-spectrum antimicrobial peptide from porcine leukocytes

BACKGROUND

The protegrins are a family of arginine- and cysteine-rich cationic peptides found in porcine leukocytes that exhibit a broad range of antimicrobial and antiviral activities. They are composed of 16-18 amino-acid residues including four cysteines, which form two disulfide linkages. To begin to understand the mechanism of action of these peptides, we set out to determine the structure of protegrin-1 (PG-1).

RESULTS

We used two-dimensional homonuclear nuclear magnetic resonance spectroscopy to study the conformation of both natural and synthetic PG-1 under several conditions. A refined three-dimensional structure of synthetic PG-1 is presented.

CONCLUSIONS

Both synthetic and natural protegrin-1 form a well-defined structure in solution composed primarily of a two-stranded antiparallel beta sheet, with strands connected by a beta turn. The structure of PG-1 suggests ways in which the peptide may interact with itself or other molecules to form the membrane pores and the large membrane-associated assemblages observed in protegrin-treated, gram-negative bacteria.

Synthesis and solution structure of the antimicrobial peptide protegrin-1

Protegrins are members of a family of five Cys-rich, cationic antimicrobial peptides recently isolated from porcine cells. We have synthesised an 18-amino-acid peptide that corresponds to protegrin-1. After Cys oxidation, the peptide has bactericidal activity against gram-positive and gram-negative bacteria, similar to that described for the natural peptide. The solution structure of protegrin-1 was investigated by means of 1H-NMR spectroscopy in water and in (CD3)2SO, with distance-geometry and simulated-annealing calculations. The C6-C15 and C8-C13 disulfide pattern was determined on the basis of NMR-derived constraints. These two parallel disulfide bridges stabilised a beta-sheet structure which comprised two antiparallel strands (residues 5-9 and 12-16) linked by a distorted beta-turn (residues 9-12). The N-terminus and C-terminus were essentially disordered. The distribution of hydrophobic and hydrophilic residues at the peptide surface was found to be a structural feature shared with tachyplesin-1, a related peptide which displays cytolytic activity, and, to a lesser extent, with mammalian defensins. These findings led us to assume that the distribution pattern could be required for the cytolytic activity of these peptides.

Susceptibility of Neisseria gonorrhoeae to protegrins

We developed a sensitive and quantitative radial diffusion method to ascertain the susceptibility of six strains of Neisseria gonorrhoeae to antimicrobial peptides derived from mammalian leukocytes. The test organisms included the well-characterized serum-resistant FA19 and serum-sensitive F62 strains plus four antibiotic-resistant clinical isolates. Although each N. gonorrhoeae strain was resistant to human neutrophil defensins, all six were exquisitely sensitive to protegrins, a family of small beta-sheet antimicrobial peptides recently identified in porcine leukocytes. Protegrin-treated N. gonorrhoeae became vacuolated and had striking membrane changes when viewed by transmission and scanning electron microscopy. Because low concentrations of protegrins can also inactivate Chlamydia trachomatis and human immunodeficiency virus, they show promise for development as topical agents to avert sexually transmitted diseases.

Change in membrane permeability induced by protegrin 1: implication of disulphide bridges for pore formation

Protegrin 1 (PG-1) is a naturally occurring cationic antimicrobial peptide that is 18 residues long, has an aminated carboxy terminus and contains two disulphide bridges. Here, we investigated the antimicrobial activity of PG-1 and three linear analogues. Then, the membrane permeabilisation induced by these peptides was studied upon Xenopus laevis oocytes by electrophysiological methods. From the results obtained, we concluded that protegrin is able to form anion channels. Moreover, it seems clear that the presence of disulphide bridges is a prerequisite for the pore formation at the membrane level and not for the antimicrobial activity.

Susceptibility of Chlamydia trachomatis to protegrins and defensins

We compared the susceptibilities of Chlamydia trachomatis elementary bodies (EBs) to human defensin HNP-2 and porcine protegrin PG-1, cysteine-rich beta-sheet antimicrobial peptides produced by mammalian leukocytes. Although both peptides protected McCoy cell monolayers from infection by chlamydial EBs, protegrins were especially potent. Protegrin-mediated inactivation of chlamydiae occurred rapidly, was relatively independent of the presence of serum, and was effective against serovars L2, D, and H. Protegrin-treated EBs showed striking morphological changes, with obvious damage to their limiting membranes and loss of their cytoplasmic contents and nucleoid. Their effectiveness against chlamydial EBs and other sexually transmitted pathogens combined with their relative lack of cytotoxicity suggests that protegrins and related molecules could serve as prototypes for topical agents to prevent sexually transmitted chlamydial infection.