N-Alkyl derivatives of diosgenyl 2-amino-2-deoxy-β-D-glucopyranoside; synthesis and antimicrobial activity

Diosgenyl 2-amino-2-deoxy-β-D-glucopyranoside is a synthetic saponin exhibiting attractive pharmacological properties. Different pathways tested by us to obtain this glycoside are summarized here. Moreover, the synthesis of N-alkyl and N,N-dialkyl derivatives of the glucopyranoside is presented. Evaluation of antibacterial and antifungal activities of these derivatives indicates that they have no inhibitory activity against Gram-negative bacteria, whereas many of the tested N-alkyl saponins were found to inhibit the growth of Gram-positive bacteria and human pathogenic fungi.

Self-assembly and interactions of short antimicrobial cationic lipopeptides with membrane lipids: ITC, FTIR and molecular dynamics studies

In this work, the self-organization and the behavior of the surfactant-like peptides in the presence of biological membrane models were studied. The studies were focused on synthetic palmitic acid-containing lipopeptides, C16-KK-NH2 (I), C16-KGK-NH2 (II) and C16-KKKK-NH2 (III). The self-assembly was explored by molecular dynamics simulations using a coarse-grained force field. The critical micellar concentration was estimated by the surface tension measurements. The thermodynamics of the peptides binding to the anionic and zwitterionic lipids were established using isothermal titration calorimetry (ITC). The influence of the peptides on the lipid acyl chain ordering was determined using FTIR spectroscopy. The compounds studied show surface-active properties with a distinct CMC over the millimolar range. An increase in the steric and electrostatic repulsion between polar head groups shifts the CMC toward higher values and reduces the aggregation number. An analysis of the peptide-membrane binding revealed a unique interplay between the initial electrostatic and the subsequent hydrophobic interactions enabling the lipopeptides to interact with the lipid bilayer. In the case of C16-KKKK-NH2 (III), compensation of the electrostatic and hydrophobic interactions upon binding to the anionic membrane has been suggested and consequently no overall binding effects were noticed in ITC thermograms and FTIR spectra.

Biological and surface-active properties of double-chain cationic amino acid-based surfactants

Cationic amino acid-based surfactants were synthesized via solid phase peptide synthesis and terminal acylation of their α and ε positions with saturated fatty acids. Five new lipopeptides, N-α-acyl-N-ε-acyl lysine analogues, were obtained. Minimum inhibitory concentration and minimum bactericidal (fungicidal) concentration were determined on reference strains of bacteria and fungi to evaluate the antimicrobial activity of the lipopeptides. Toxicity to eukaryotic cells was examined via determination of the haemolytic activities. The surface-active properties of these compounds were evaluated by measuring the surface tension and formation of micelles as a function of concentration in aqueous solution. The cationic surfactants demonstrated diverse antibacterial activities dependent on the length of the fatty acid chain. Gram-negative bacteria and fungi showed a higher resistance than Gram-positive bacterial strains. It was found that the haemolytic activities were also chain length-dependent values. The surface-active properties showed a linear correlation between the alkyl chain length and the critical micelle concentration.

Antimicrobial peptides as potential tool to fight bacterial biofilm

Recently, the topic of biofilm has met a huge interest of researchers owing to a significant role played by this microbial life form in severe infections. These well organised three-dimensional microbial communities are characterized by a strong resistance to antimicrobials. Biofilms significantly contribute to morbidity and mortality as related infections are very difficult to treat due to their tendency to relapse after the withdrawal of antibiotics. According to the literature, antimicrobial peptides (AMPs) have a high potential as future antibiofilm agents. AMPs can influence various stages of biofilm formation and exhibit antimicrobial activity against a broad spectrum of microorganisms including multi-drug resistant strains. The purpose of the present study was to determine the activity of antimicrobial peptides against biofilms formed by a variety of bacterial strains. To do this, the following antimicrobial peptides were synthesized: Citropin 1.1, Lipopeptides Palm-KK-NH2 and Palm-RR-NH2, Omiganan, Pexiganan and Temporin A. Antimicrobial activity of the compounds and conventional antibiotics was determined for planktonic cells and biofilms formed by reference strains of Gram-positive (Staphylococcus aureus, S. epidermidis, Streptococcus pneumoniae, Streptococcus pyogenes) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa, Proteus mirabilis) bacteria. AMPs exhibited a strong antibacterial activity against Gram-positive strains, while Gram-negative bacteria were less susceptible. Antimicrobial activity of the tested peptides against biofilms formed by Gram-positive organisms was significantly stronger as compared to that of conventional antimicrobials.

Synthetic amphibian peptides and short amino-acids derivatives against planktonic cells and mature biofilm of Providencia stuartii clinical strains

Over the last decade, the growing number of multidrug resistant strains limits the use of many of the currently available chemotherapeutic agents. Furthermore, bacterial biofilm, due to its complex structure, constitutes an effective barrier to conventional antibiotics. The in vitro activities of naturally occurring peptide (Citropin 1.1), chemically engineered analogue (Pexiganan), newly-designed, short amino-acid derivatives (Pal-KK-NH2, Pal-KKK-NH2, Pal-RRR-NH2) and six clinically used antimicrobial agents (Gatifloxacin, Ampicilin, Cefotaxime, Ceftriaxone, Cefuroxime and Cefalexin) were investigated against planktonic cells and mature biofilm of multidrug-resistant Providencia stuartii strains, isolated from urological catheters. The MICs, MBCs values were determined by broth microdilution technique. Inhibition of biofilm formation by antimicrobial agents as well as biofilm susceptibility assay were tested using a surrogate model based on the Crystal Violet method. The antimicrobial activity of amino-acids derivatives and synthetic peptides was compared to that of clinically used antibiotics. For planktonic cells, MICs of peptides and antibiotics ranged between 1 and 256 μg/ml and 256 and ≥ 2048 μg/ml, respectively. The MBCs values of Pexiganan, Citropin 1.1 and amino-acids derivatives were between 16 and 256 μg/ml, 64 and 256 μg/ml and 16 and 512 μg/ml, respectively. For clinically used antibiotics the MBCs values were above 2048 μg/ml. All of the tested peptides and amino-acids derivatives, showed inhibitory activity against P. stuartii biofilm formation, in relation to their concentrations. Pexiganan and Citropin 1.1 in concentration range 32 and 256 μg/ml caused both strong and complete suppression of biofilm formation. None of the antibiotics caused complete inhibition of biofilm formation process. The biofilm susceptibility assay verified the extremely poor antibiofilm activity of conventional antibiotics compared to synthetic peptides. The obtained results showed that synthetic peptides are generally more potent and effective than clinically used antibiotics.

Antimicrobial activity of untypical lipid compounds in the cuticular and internal lipids of four fly species

AIMS

This article describes the qualitative and quantitative analyses of untypical compounds in the cuticular and internal lipids of four dipteran species. For isolated compounds, antimicrobial activity against 18 reference strains of bacteria and fungi was determined.

METHODS AND RESULTS

In this study, gas chromatography (GC) combined with mass spectrometry (GC-MS) was used to analyse the surface and internal compounds of four fly species. Seven untypical compounds from both pre-imaginal and imaginal stages of examined insects were identified. Azelaic acid (AA) was the most abundant, while phenylacetic and phenylpropionic acids occurred in lower concentration. Minor quantities of sebacic acid, 2-methyl-2-hydroxybutanoic acid, tocopherol acetate and trace amounts of 2,4-decadienal were also detected. Tocopherol acetate was found only in cuticular lipids of Musca domestica larvae. Each compound was tested against several species of fungi and bacteria by determining minimal inhibitory concentration (MIC). Human pathogenic fungi were also investigated. Phenylpropionic acid showed the greatest antifungal activity. Bacterial strains were insensitive to the presence of identified compounds, apart from 2,4-decadienal which strongly inhibited bacterial growth.

CONCLUSIONS

This is the first time that the chemical composition and the antimicrobial activity of untypical compounds in the cuticular and internal lipids of four fly species has been analysed.

SIGNIFICANCE AND IMPACT OF THE STUDY

Determination of untypical compounds and their antimicrobial activity can effectively contribute to the knowledge concerning insect defence mechanisms.

Safety profile of antimicrobial peptides: camel, citropin, protegrin, temporin a and lipopeptide on HaCaT keratinocytes

Antimicrobial peptides (AMPs) are an essential part of the innate immunity of the skin and mucosal surfaces. They have a broad spectrum of antimicrobial activity: antibacterial, antifungal, antiviral as well as antiprotozoal. Numerous studies using AMPs as potential agents against different microbes has been performed during the last two decades. Here we investigated antistaphylococcal activity and safety of following AMPs: camel, citropin, protegrin, temporin A and lipopeptide Palm-KK-NH2. The susceptibility of the strains of Staphylococcus aureus isolated from the patients with erythrodermia to conventional antibiotics and AMPs was determined by the broth dilution method. The cytotoxicity assay was performed on HaCaT keratinocytes. Tested peptides turned out to be very effective against all clinical isolates, including strains resistant to conventional antibiotics. The majority of the examined peptides as well as conventional antimicrobials do not exert any toxic effect on HaCaT cells in minimal inhibitory concentration. Peptides are very promising agents for the topical treatment of staphylococcal skin infections. The most promising seem to be citropin 1.1 and temporin A, as they were toxic only in two highest concentration (50 and 100 microg/mL), with relatively low MIC values.

Free fatty acids in the cuticular and internal lipids of Calliphora vomitoria and their antimicrobial activity

The cuticular and internal lipid composition in Calliphora vomitoria larvae, pupae, and male and female adults was studied. The free fatty acid (FA) compositions of the lipids were chemically characterized using gas chromatography (GC) and gas chromatography-electron impact mass spectrometry (GC-MS). Analyses of cuticular extracts from larvae, pupae, and male and female adults revealed that the carbon numbers of the acids ranged from C7:0 to C22:0, from C8:0 to C24:0, from C7:0 to C24:0 and from C7:0 to C22:0 respectively. The internal lipids of C. vomitoria larvae, pupae, male and female adults contained FAs ranging from C8:0 to C20:0, from C9:0 to C22:0, from C8:0 to C24:0 and from C9:0 to C22:0 respectively. Nine FAs with odd-numbered carbon chains from C7:0 to C21:0 were identified in the cuticular lipids of the larvae. The internal lipids of C. vomitoria larvae contained 8 odd-numbered FAs ranging from C9:0 to C19:0. Eight odd-numbered FAs from C9:0 to C21:0 were identified in the cuticular and internal lipids of pupae, while nine such FAs were found in the cuticular lipids of male and female adults. The internal lipids of adult males and females respectively contained nine and seven odd-numbered FAs, while both larvae and pupae contained eight such compounds. Eight unsaturated FAs were identified in the cuticular lipids of larvae, adult males and females and also in the internal lipids of females. Seven unsaturated FAs were identified in the cuticular lipids of pupae. The internal lipids of larvae, pupae and males contained 10, 11 and 12 unsaturated FAs respectively. Developmental changes were found both in the amounts of extracted cuticular and internal FAs and in their profiles. Four cuticular FAs (C7:0, C9:0, C10:0 and C15:1), identified as being male-specific, were either absent in the female cuticle or present there only in trace amounts. Cuticular and internal extracts obtained from larvae, pupae, adult males and females were tested for their potential antimicrobial activity. The minimal inhibitory concentrations of extracts against reference strains of bacteria and fungi were determined. Antimicrobial activity was the strongest against Gram-positive bacteria; Gram-negative bacteria, on the other hand, turned out to be resistant to all the lipids tested. Overall, the activities of the internal lipids were stronger. All the lipid extracts were equally effective against all the fungal strains examined. In contrast, crude extracts containing both cuticular and internal lipids displayed no antifungal activity against the entomopathogenic fungus Conidiobolus coronatus, which efficiently killed adult flies, but not larvae or pupae.

Composition and antimicrobial activity of fatty acids detected in the hygroscopic secretion collected from the secretory setae of larvae of the biting midge Forcipomyia nigra (Diptera: Ceratopogonidae)

The hygroscopic secretion produced by the secretory setae of terrestrial larvae of the biting midge Forcipomyia nigra (Winnertz) was analysed using gas chromatography coupled with mass spectrometry (GC-MS). The viscous secretion is stored at the top of each seta and absorbs water from moist air. GC-MS analyses (four independent tests) showed that the secretion contained 12 free fatty acids, the most abundant of which were oleic (18:1), palmitic (16:0), palmitoleic (16:1) and linoleic (18:2). Other acids identified were valeric (5:0), enanthic (7:0), caprylic (8:0), pelargonic (9:0), capric (10:0), lauric (12:0), myristic (14:0) and stearic (18:0). Two other compounds, glycerol and pyroglutamic acid, were also found. The antibacterial activity of the fatty acids and pyroglutamic acid was tested using the agar disc diffusion method and targeted Gram positive (Bacillus cereus, Bacillus subtilis, Enterococcus faecalis) and Gram negative bacterial strains (Citrobacter freundii, Pseudomonas aeruginosa, Pseudomonas fluorescens). The antifungal activity was tested by determining minimal inhibitory concentration (MIC) of examined compounds. Fatty acids were tested against enthomopathogenic fungi (Paecilomyces lilacinus, Paecilomyces fumosoroseus, Lecanicillium lecanii, Metarhizium anisopliae, Beauveria bassiana (Tve-N39), Beauveria bassiana (Dv-1/07)). The most effective acids against bacterial and fungal growth were C(9:0), C(10:0) and C(16:1), whereas C(14:0), C(16:0,) C(18:0) and C(18:1) demonstrated rather poor antifungal activity and did not inhibit the growth of bacteria. The antimicrobial assay investigated mixtures of fatty and pyroglutamic acids (corresponding to the results of each GC-MS test): they were found to be active against almost all the bacteria except P. fluorescens and also demonstrated certain fungistatic activity against enthomopathogenic fungi. The hygroscopic secretion facilitates cuticular respiration and plays an important role in the antimicrobial protection of F. nigra larvae living in moist terrestrial habitats.

Synthesis, biological activity and conformational analysis of head-to-tail cyclic analogues of LL37 and histatin 5

LL37 and histatin 5 are antimicrobial peptides. LL37 exhibits killing activity against a broad spectrum of pathogens, whereas histatin 5 is primarily an antifungal agent. Head-to-tail cyclization of histatin 5 did not affect its antimicrobial and haemolytic activity. The cyclic LL37 exhibits identical antifungal and haemolytic activity as does LL37. Its antimicrobial activity varied in one dilution depending on the kind of bacteria. The structure of cyclic peptides was studied by circular dichroism spectroscopy. Both peptides undergo a conformational change leading to stabilisation of their α-helical structure in the presence of negatively charged sodium dodecyl sulfate micelles. However, with cyclic histatin 5, the presence of Zn(2+) ions is also necessary to fuse the peptide to the micelle. The specific action of the Zn(2+) ions is attributed to the presence of a zinc-binding motif, His-Glu-X-X-His. It has been speculated that this zinc complexing may be related to the well-established anticandidal activity. In the case of cyclic LL37, also the presence of a zwitterionic dodecylphosphocholine micelle induces formation of the helical structure. A microwave-assisted procedure for the cleavage of a peptide from the 2-chlorotrityl chloride resin was, for the first time, successfully used to obtain protected peptide fragments that can be applied to the preparation of head-to-tail cyclopeptides or to condensation of peptidic fragments.

Antimicrobial activity of alcohols from Musca domestica

Information on the stimulatory and inhibitory effects of cuticular alcohols on growth and virulence of insecticidal fungi is unavailable. Therefore, we set out to describe the content of cuticular and internal alcohols in the body of housefly larvae, pupae, males and females. The total cuticular alcohols in larvae, males and females of Musca domestica were detected in comparable amounts (4.59, 3.95 and 4.03 μg g(-1) insect body, respectively), but occurred in smaller quantities in pupae (2.16 μg g(-1)). The major free alcohol in M. domestica larvae was C(12:0) (70.4%). Internal alcohols of M. domestica larvae were not found. Among cuticular pupae alcohols, C(12:0) (31.0%) was the most abundant. In the internal lipids of pupae, only five alcohols were identified in trace amounts. The most abundant alcohol in males was C(24:0) (57.5%). The percentage content of cuticular C(24:0) in males and females (57.5 and 36.5%, respectively) was significantly higher than that of cuticular lipids in larvae and pupae (0.9 and 5.6%, respectively). Only two alcohols were present in the internal lipids of males in trace amounts (C(18:0) and C(20:0)). The most abundant cuticular alcohols in females were C(24:0) (36.5%) and C(12:0) (26.8%); only two alcohols (C(18:0) and C(20:0)) were detected in comparable amounts in internal lipids (3.61±0.32 and 5.01±0.42 μg g(-1), respectively). For isolated alcohols, antimicrobial activity against 10 reference strains of bacteria and fungi was determined. Individual alcohols showed approximately equal activity against fungal strains. C(14:0) was effective against gram-positive bacteria, whereas gram-negative bacteria were resistant to all tested alcohols. Mixtures of alcohols found in cuticular lipids of larvae, pupae, males and females of M. domestica generally presented higher antimicrobial activity than individual alcohols. In contrast, crude extracts containing both cuticular and internal lipids showed no antifungal activity against the entomopathogenic fungus Conidiobolus coronatus, which efficiently kills adult house flies.

Urea biosensors and their application in hemodialysis--perspective of EnFET application

Parameters such as blood urea nitrogen concentration, normalized protein catabolic rate and Kt/V that are utilized for urea concentration measurements in blood and dialysate for the optimization of the hemodialysis process are reviewed in the paper. Basic methods of urea concentration measurement are described. Urea biosensors of the EnFET type based on the pH-sensitive Si3N4 gate FET and pNH4-sensitive FET with a Siloprene membrane containing nonactine, both of our own construction, are presented. Application of these biosensors for urea concentration measurement in blood and dialysate is described. An experimental microdialysis system with urease in detector solution and a pH-ISFET detector are described. A comparison of two dialysis procedures, with a commercial dialysate an initial of pH 5.6 and with pH kept lowered during the dialysis process applied to rats, is given.