The Bioactive Properties of Syringomycin E-Rhamnolipid Mixtures and Syringopeptins

The need for new antimicrobial agents has become important in the last decade due to emerging resistance to a number of conventional antimicrobial agents. New approaches and sources are needed to generate novel and effective antimicrobials. For example, synergistic combinations between two or more agents may lead to new antimicrobial therapies. Furthermore, the increase in health problems caused by the exposure to agricultural crop pesticides and synthetic fungicides and the emerging development of organic farming has increased the necessity to develop natural products than can be used safely in controlling crop diseases. In this work, I present the first studies on the bioactive properties, particularly fungicidal activities, of mixtures of SRE and rhamnolipids. The in vitro results clearly showed strong synergism between SRE and rhamnolipids against phytopathogenic fungi and yeast. However, no activity was observed against bacteria. The hemolytic activities and cytotoxicities of SRE and SYRA were dose dependent. SRE acts on yeast and plant plasma membranes to cause numerous cellular effects. The effects are consistent with SRE\u27s ability to form ion-conducting voltage sensitive channels in membrane bilayers. In addition, studies with yeast have revealed that sphingolipids and sterols modulate the fungicidal activity of SRE. Saccharomyces cerevisiae sphingolipid and sterol biosynthetic mutants were used to investigate the mechanism of action of SYRA against fungi. These results suggest that similar to SRE, SYRA antifungal action is promoted by sphingolipids and sterols of the plasma membrane and involves pore formation. I further explored the antimicrobial spectrum of syringopeptin SP25A and show that it specifically inhibits Gram-positive bacteria and yeast. I also investigated its mechanism of action against yeast and bacteria. The results revealed the role for D-alanylation of teichoic acids in modulating the susceptibility of B. subtilis to SP25A and other syringopeptins. This is consistent with the charged nature of the cyclic peptide portions of the syringopeptins, and it provides an explanation for SP25A\u27s higher degree of specificity for Gram-positive bacteria. In addition and similar to SRE, SP25A antifungal action is promoted by sphingolipids and sterols of the plasma membrane and involves pore formation. Overall, the research shows that SRE and rhamnolipids are synergistically active against yeast and fungi and that the syringopeptins have antimicrobial activities against yeast and Gram-positive bacteria. Insights into the mechanisms of action of the SRE and rhamnolipid mixtures and the syringopeptins and their potential as novel antimicrobial agents are revealed

Polymerized Hemin as An Electrocatalytic Platform for Peroxynitrite\u27s Oxidation and Detection

Peroxynitrite (ONOO−) constitutes a major cytotoxic agent, implicated in a host of pathophysiological conditions, thereby stimulating a tremendous interest in evaluating its role as an oxidant in vivo. Some of the detection methods for peroxynitrite include oxidation of fluorescent probes, EPR spectroscopy, chemiluminescence, immunohistochemistry, and probe nitration; however, these are more difficult to apply for real-time quantification due to their inherent complexity. The electrochemical detection of peroxynitrite is a simpler and more convenient technique, but the best of our knowledge there are only few papers to date studying its electrochemical signature, or reporting amperometric microsensors for peroxynitrite. Recently, we have reported the use of layered composite films of poly(3,4-ethylenedioxythiophene) (PEDOT) and hemin (iron protoporphyrin IX) as a platform for amperometric measurement of peroxynitrite. The main goal herein is to investigate the intrinsic catalytic role of hemin electropolymerized thin films on carbon electrodes in oxidative detection of peroxynitrite. The electrocatalytic oxidation of peroxynitrite is characterized by cyclic voltammetry. The catalytic current increased as a function of peroxynitrite\u27s concentration, with a peak potential shifting positively with peroxynitrite\u27s concentration. The catalytic efficiency decreased as the scan rate increased, and the peak potential of the catalytic oxidation was found to depend on pH. We show that optimized hemin-functionalized carbon electrodes can be used as simple platforms for peroxinitrite detection and quantification. We report dose–response amperometry as an electroanalytical determination of this analyte on hemin films and we contrast the intrinsic hemin catalytic role with its performance in the case of the PEDOT–hemin as a composite matrix. Finally, we include some work extending the use of simple hemin films for peroxynitrite determination on carbon microfiber electrodes in a flow system

Fonctionnement et salinité de la nappe de l'oasis de Fatnassa : arguments géochimiques

International audienceLes sols et les eaux de la nappe du périmètre oasien de Fatnassa Nord (114 hectares) sont menacés par un risque de salinisation en raison d'une salinité élevée des eaux d'irrigation et de la position superficielle de la nappe. Un réseau de 27 piézomètres a été installé depuis 2001 pour le suivi de la profondeur, de la salinité et de la composition chimique de la nappe. La composition chimique de la nappe apparaît principalement liée à la concentration des eaux d'irrigation et à la précipitation de gypse et de calcite, et secondairement aux variations de la pression partielle en CO2 influençant la teneur en carbonate et le pH. Ces processus ont été simulés avec le modèle IRRICHEM. Les ions chlorure n'interviennent pas dans les mécanismes géochimiques et ont été retenus comme indicateur du facteur de concentration des eaux de la nappe par rapport aux eaux d'irrigation. Le facteur de concentration des eaux de la nappe varie d'un facteur 1,7 à 7,7 par rapport aux eaux d'irrigation (médiane de 4,41) tandis que le facteur de concentration des eaux de drainage est de 3,41. On n'observe aucune tendance évolutive significative de la salinité de la nappe qui est supposée avoir atteint un état stationnaire résultant d'un équilibre entre les apports de sels par l'irrigation et les sorties de sels sous l'effet conjugué du système de drainage enterré et des écoulements naturels. La fraction de lessivage apparente est estimée de 13 à 60 % pour une valeur médiane de 23 %. Des axes naturels d'écoulement sont mis en évidence et contribueraient majoritairement au lessivage des sels alors la fraction de lessivage induite par le réseau de drainage enterré ne dépassent pas 10 %. Les valeurs élevées de la salinité sont observées en relation avec une position élevée de la nappe en raison d'un drainage déficient dans les zones basses à proximité du chott El Jerid. Les enjeux d'une gestion durable des ressources en eau et en sol sur le périmètre de Fatnassa sont enfin discutés sur la base de ces résultats

Manganese Oxide/Hemin-Functionalized Graphene as a Platform for Peroxynitrite Sensing

Peroxynitrite (ONOO−, PON) is a powerful oxidizing agent generated in vivo by the diffusion-limited reaction of nitric oxide (NO) and superoxide (O2˙−) radicals. Under oxidative stress, cumulated peroxynitrite levels are associated with chronic inflammatory disorders and other pathophysiological conditions. The accurate detection of peroxynitrite in biological systems is important, not only to understand the genesis and development of diseases, but also to explore and design potential therapeutics. Herein, a manganese oxide/hemin-modified graphene interface is explored as a platform for peroxynitrite amperometric detection. Hemin-functionalized reduced graphene oxide was further modified with manganese oxide nanoparticles to provide a composite material with catalytic activity toward the electrochemical oxidation of peroxynitrite. The morphology of the composite material was characterized using scanning electron microscopy, energy dispersive X-ray analysis, X-ray photoelectron spectroscopy, and UV-Vis absorption measurements. We investigated the electrocatalytic oxidation of peroxynitrite on graphite electrodes modified with the composite material using cyclic voltammetry and amperometry. The results showed that the incorporation of manganese oxide nanoparticles into graphene/hemin material enhances the catalytic detection of peroxynitrite compared to graphene/hemin alone

Nitric Oxide Synthase Encapsulation in Liposomes: A Potential Delivery Platform to (Nitric Oxide)-Deficient Targets

Nitric oxide (NO) is a freely diffusible, gaseous free radical, associated with many physiological and pathological processes: such as neuronal signaling, immune response and inflammatory response. In mammalian organisms, NO is produced from L-arginine in an NADPH-dependent reaction catalyzed by a family of nitric oxide synthase (NOS) enzymes. Typically, large NO fluctuations in biological systems under/over a critical limit is associated with problems that range from transient dysfunctions to severe chronic disease states. In this regard, we explore the development of a potential delivery and release method of nitric oxide to NO-deficient sites using liposomes as vehicles. Liposomes have already been used as effective nano-carriers. In this short communication, we report on the preparation and characterization of liposomes carrying a recombinant NOS enzyme. We report on the efficacy of using liposomes to carry NOS enzymes, and on the extent of preservation of native NOS structure and function. In addition to the characterization of liposome stability and recovery of enzymatic activity after encapsulation in liposomes, we also measured the NO production upon NOS stimulation. The NO release was monitored with a nitric oxide ultrasensitive electrochemical microsensor placed near NOS-carrying liposomes. This method of NOS-carrying liposomes shows the promise of potential development as a platform for targeted NO-delivery

Fungicidal Activities and Mechanisms of Action of Pseudomonas syringae pv. syringae Lipodepsipeptide Syringopeptins 22A and 25A

The plant-associated bacterium Pseudomonas syringae pv. syringae simultaneously produces two classes of metabolites: the small cyclic lipodepsinonapeptides such as the syringomycins and the larger cyclic lipodepsipeptide syringopeptins SP22 or SP25. The syringomycins inhibit a broad spectrum of fungi (but particularly yeasts) by lipid-dependent membrane interaction. The syringopeptins are phytotoxic and inhibitory to Gram-positive bacteria. In this study, the fungicidal activities of two major syringopeptins, SP22A and SP25A, and their mechanisms of action were investigated and compared to those of syringomycin E. SP22A and SP25A were observed to inhibit the fungal yeasts Saccharomyces cerevisiae and Candida albicans although less effectively than syringomycin E. S. cerevisiae mutants defective in ergosterol and sphingolipid biosyntheses were less susceptible to SP22A and SP25A but the relative inhibitory capabilities of SRE vs. SP22A and SP25A were maintained. Similar differences were observed for capabilities to cause cellular K+ and Ca2+ fluxes in S. cerevisiae. Interestingly, in phospholipid bilayers the syringopeptins are found to induce larger macroscopic ionic conductances than syringomycin E but form single channels with similar properties. These findings suggest that the syringopeptins target the yeast plasma membrane, and, like syringomycin E, employ a lipid-dependent channel-forming mechanism of action. The differing degrees of growth inhibition by these lipodepsipeptides may be explained by differences in their hydrophobicities. The more hydrophobic SP22A and SP25A might interact more strongly with the yeast cell wall that would create a selective barrier for their incorporation into the plasma membrane

Synthetic Melanin Films as Potential Interfaces for Peroxynitrite Detection and Quantification

Peroxynitrite (PON) is a highly reactive oxygen-nitrogen species that facilitates both oxidation and nitration reactions. Early reports have revealed the deleterious effects of PON on DNA, proteins, and lipids. Recent studies have suggested that melanin can act as an antioxidative therapy to scavenge the reactive oxygen-nitrogen species (RO-NS) including PON. Melanin is a natural pigment that has many physiological functions involving the neutralization of highly oxidative species. In this project, the interaction between PON and synthetic melanin has been studied. In addition, the electrochemical characteristics of the polymerized 5,6-dihydroxy indole (DHI) as a model of synthetic melanin were examined using cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM). The ultraviolet-visible (UV-Vis) spectroscopy showed a significant difference in the absorbance of PON alone and in the presence of melanin films. Finally, we report on the possibility of using the DHI-melanin film as a platform for the quantitative detection of PON in solutions

Elevation of serum soluble E-selectin and VCAM-1 in severe asthma.

OBJECTIVE: To investigate the significance of circulating adhesion molecules associated with leucocyte-endothelial cell interactions in asthma, serum levels of soluble E (sE)-selectin, soluble P (sP)-selectin, soluble L (sL)-selectin, and soluble vascular cell adhesion molecule-1 (sVCAM-1) were measured in mild, moderate and severe asthma. METHOD: Serum levels of sE-selectin, sP-selectin, sL-selectin, and sVCAM-1 were measured in 32 women with asthma and 30 healthy donors using an enzyme-linked immunosorbent assay method. Twenty patients were suffering from severe asthma, and 12 from mild/moderate asthma. RESULTS: Serum sE-selectin and sVCAM-1 levels from patients with asthma were significantly higher than those observed in healthy donors (p < 0.01). The levels of sP-selectin were the same as those of controls. The level of sE-selectin exhibited an important increase in the severe asthmatic patients compared with mild/moderate asthma (p < 0.01). The sVCAM-1 level was increased in severe asthma when compared with healthy controls. There was no correlation between the levels of soluble selectins and the age of the patients. A significant correlation was found between sE-selectin and sVCAM-1 levels. CONCLUSION: These data indicate that circulating soluble forms of the selectins may have different kinetics during the clinical course of asthma, suggesting that they may reflect different inflammatory pathways in severe asthma. Both sVCAM-1 and sE-selectin may be useful immunological markers for monitoring disease activity in asthma

Structure, bonding and morphology of hydrothermally synthesised xonotlite

The authors have systematically investigated the role of synthesis conditions upon the structure and morphology of xonotlite. Starting with a mechanochemically prepared, semicrystalline phase with Ca/Si=1, the authors have prepared a series of xonotlite samples hydrothermally, at temperatures between 200 and 250 degrees C. Analysis in each case was by X-ray photoelectron spectroscopy, environmental scanning electron microscopy and X-ray diffraction. The authors’ use of a much lower water/solid ratio has indirectly confirmed the ‘through solution’ mechanism of xonotlite formation, where silicate dissolution is a key precursor of xonotlite formation. Concerning the role of temperature, too low a temperature (~200 degrees C) fails to yield xonotlite or leads to increased number of structural defects in the silicate chains of xonotlite and too high a temperature (>250 degrees C) leads to degradation of the xonotlite structure, through leaching of interchain calcium. Synthesis duration meanwhile leads to increased silicate polymerisation due to diminishing of the defects in the silicate chains and more perfect crystal morphologies