Insights into electrochemical decomposition mechanism of lipopolysaccharide using TiO2 nanotubes arrays electrode

Electrochemical decomposition of lipopolysaccharide (LPS) was firstly investigated over titania nanotubes (TNTs) arrays electrode. The TNTs layer of this electrode consisted of numerous tubular structures which arranged tightly, and the average diameter of each nanotube is 100 ± 5 nm. The degradation of LPS and polysaccharides followed pseudo-first-order kinetics. The optimal LPS removal ratio was nearly 80 %. The endotoxin toxicity of LPS steadily decreased during the electrolysis process. The acute toxicity of the intermediates increased suddenly at the beginning of electrochemical degradation process (< 5 min), then maintained high inhibition ratio (> 95 %) for about 150 min, and decreased significantly (< 10 %) after electrolysis for 240 min. After 20 min of electrolysis, LPS with molecular weight of 116,854 Da was transformed into small molecular compounds with molecular weights of 59,312 - 12,209 Da. Possible degradation and detoxification mechanisms of LPS including electric-field-force-driving accumulation, adsorption and direct electron transfer on TNTs arrays electrode, and •OH oxidation were proposed. This study underscores that electrochemical technique can be applied to eliminate and decrease the toxicity of LPS from contaminated water.

Bacterial endotoxin (lipopolysaccharide) stimulates the rate of iron oxidation

Bacterial endotoxin (lipopolysaccharide) has affinity for a number of cations, including iron. Previous investigations have demonstrated that lipopolysaccharide can affect the oxidation rate of iron; heme-bound ferrous iron in hemoglobin is oxidized to ferric iron when hemoglobin binds lipopolysaccharide. In the present study, we directly examined the interaction between lipopolysaccharide and iron. Lipopolysaccharide caused a concentration-dependent increase in the rate of iron oxidation, with up to a 23-fold increase in oxidation in the presence of 200 µg/ml Escherichia coli lipopolysaccharide. This effect was seen both with several carbohydrate-rich smooth lipopolysaccharides and also with carbohydrate-poor rough lipopolysaccharide. Extensively deacylated rough lipopolysaccharide had no effect, suggesting a role of the fatty acid components of lipopolysaccharide in this process. Purified lipid A produced inconsistent results: some preparations stimulated iron oxidation and others did not. A series of sugars, starches and a preparation of purified O-chain polysaccharide (the carbohydrate portion of the lipopolysaccharide macromolecule) had no effect on the rate of iron oxidation, whereas phospholipid-enriched brain tissue extracts (similar to the lipid A component of lipopolysaccharide) stimulated oxidation. We conclude that the lipid moiety of bacterial lipopolysaccharide is responsible for the stimulation of iron oxidation. This process may contribute to the ability of lipopolysaccharide to cause oxidation of heme-bound iron in hemoglobin.

Effects of pig hemoglobin binding on some physical and biological properties of Actinobacillus pleuropneumoniae lipopolysaccharides

Binding of pig hemoglobin (Hb) to Actinobacillus pleuropneumoniae lipopolysaccharide (LPS), either extracted or present at the surface of whole cells, was studied. After a short incubation period, pig Hb seemed to cover the bacterial cell surface and enhanced the cells' contrast when examined by transmission electron microscopy (TEM). Energy-dispersive X-ray spectroscopy analysis showed that the amount of elemental iron detected was increased when cells of A. pleuropneumoniae were incubated with pig Hb. Coating with pig Hb, however, did not interfere with the accessibility of O- and capsular antigens to antibodies on the bacterial cell surface. Binding of pig Hb and polymyxin B to lipid A of A. pleuropneumoniae was confirmed with a fluorescent probe (dansylcadaverine) displacement assay. The binding of pig Hb to extracted LPS resulted in a disaggregation of LPS as observed by TEM after negative staining. Additional evidence for a direct physical interaction between pig Hb and A. pleuropneumoniae LPS was demonstrated by a shift in the sedimentation velocity of LPS-Hb complexes determined by sucrose gradient centrifugation. Pig Hb binding to extracted LPS or to bacterial cells resulted in a significant decrease of chromogenic Limulus amebocyte lysate activation. Finally, the capacity of extracted LPS to induce NO2-in the presence of pig Hb was tested by using cell line J774 and determined by the Greiss' reaction. LPS alone induced, as expected, NO2- production, whereas the presence of pig Hb significantly reduced NO2-production by murine macrophages. Taken together, our results indicate that binding of pig Hb affected some physical and biological properties of A. pleuropneumoniae LPS.

Morphology, size distribution, and aggregate structure of lipopolysaccharide and lipid A dispersions from enterobacterial origin

Lipopolysaccharides (LPSs) from Gram-negative bacteria are strong elicitors of the human immune systems. There is strong evidence that aggregates and not monomers of LPS play a decisive role at least in the initial stages of cell activation of immune cells such as mononuclear cells. In previous reports, it was shown that the biologically most active part of enterobacterial LPS, hexa-acyl bisphosphorylated lipid A, adopts a particular supramolecular conformation, a cubic aggregate structure. However, little is known about the size and morphology of these aggregates, regarding the fact that LPS may have strong variations in the length of the saccharide chains (various rough mutant and smooth-form LPS). Thus, in the present paper, several techniques for the determination of details of the aggregate morphology such as freeze-fracture and cryo-electron microscopy, analytical ultracentrifugation, laser backscattering analysis, and small-angle X-ray scattering were applied for various endotoxin (lipid A and different LPS) preparations. The data show a variety of different morphologies not only for different endotoxins but also when comparing different applied techniques. The data are interpreted with respect to the suitability of the single techniques, in particular on the basis of available literature data.

Structural investigations into the interaction of hemoglobin and part structures with bacterial endotoxins

An understanding of details of the interaction mechanisms of bacterial endotoxins (lipopolysaccharide, LPS) with the oxygen transport protein hemoglobin is still lacking, despite its high biological relevance. Here, a biophysical investigation into the endotoxin:hemoglobin interaction is presented which comprises the use of various rough mutant LPS as well as free lipid A; in addition to the complete hemoglobin molecule from fetal sheep extract, also the partial structure alpha-chain and the heme-free sample are studied. The investigations comprise the determination of the gel-to-liquid crystalline phase behaviour of the acyl chains of LPS, the ultrastructure (type of aggregate structure and morphology) of the endotoxins, and the incorporation of the hemoglobins into artificial immune cell membranes and into LPS. Our data suggest a model for the interaction between Hb and LPS in which hemoglobins do not react strongly with the hydrophilic or with the hydrophobic moiety of LPS, but with the complete endotoxin aggregate. Hb is able to incorporate into LPS with the longitudinal direction parallel to the lipid A double-layer. Although this does not lead to a strong disturbance of the LPS acyl chain packing, the change of the curvature leads to a slightly conical molecular shape with a change of the three-dimensional arrangement from unilamellar into cubic LPS aggregates. Our previous results show that cubic LPS structures exhibit strong endotoxic activity. The property of Hb on the physical state of LPS described here may explain the observation of an increase in LPS-mediating endotoxicity due to the action of Hb.

CE to monitor endotoxins by protein complexation

A new CE method for fast and efficient analysis of bacterial endotoxins (lipopolysaccharides) is described. It is based on the strong interaction between proteins and endotoxins. The UV absorption of the protein component in the complex is used for the detection. The electrophoretic mobility of the complex hemoglobin/endotoxin can be employed for qualitative analysis of the endotoxin. For instance, the structural differences between "smooth" and "rough" lipopolysaccharides from Salmonella minnesota (wild-type), Salmonella minnesota R595 and Shigella sonnei R562H are reflected in the electrophoretic mobilities of their hemoglobin complex.

Forming and immunological properties of some lipopolysaccharide–chitosan complexes

The complex formation of lipopolysaccharide (LPS) with chitosan (Ch) was demonstrated using sedimentation velocity analysis in the analytical ultracentrifuge, centrifugation in glycerol gradient and isopicnic centrifugation in cesium chloride. An addition of Ch to the Escherichia coli and Yersinia pseudotuberculosis LPS solutions was found to result in formation of the stable LPS-Ch complexes. The interaction is a complicated process and depends on time and reaction temperature, as well as on the molecular weight of chitosan. A stable LPS-Ch complex could be formed only after preliminary incubation of the initial components at an elevated temperature (37 degrees C). It should be noted that process of LPS complexation with Ch is accompanied by additional dissociating of LPS. The complex formation was shown to be a result not only of ionic binding, but also of other types of interactions. The interaction of Ch with LPS was shown to modulate significantly the biological activity of LPS. The LPS-Ch complex (1:5 w/w) was shown to possess much lower toxicity in a comparison with the parent LPS at injection to mice in the similar concentration. The LPS-Ch complex was shown to maintain an ability to induce of IL-8 and TNF, but induction of IL-8 and TNF biosynthesis by the LPS-Ch complex was lower than that by the parent LPS. The complex LPS-Ch, similarly to the parent LPS, was found stimulated the formation of the IL-8 in the dose-dependent manner in the human embryonal kidney cells (HEK 293 cells) transfected with TLR4 in combination with MD2.

Cross-linked hemoglobin converts endotoxically inactive pentaacyl endotoxins into a physiologically active conformation

The interaction of purified alpha alpha cross-linked hemoglobin (alpha alpha Hb) with a pentaacylated mutant lipopolysaccharide (pLPS) and the corresponding lipid A (pLA) was studied biophysically and the effects correlated with data from biological assays, i.e. cytokine induction (tumor necrosis factor-alpha) in human mononuclear cells and the Limulus amebocyte lysate assay. Fourier transform infrared spectroscopic and Zeta-Sizer experiments indicated an electrostatic as well as a non-electrostatic binding of alpha alpha Hb to the hydrophilic and to the hydrophobic moieties of the endotoxins with an increase of the inclination angle of the pLA backbone, with respect to the membrane surface, from 25 degrees to more than 50 degrees. Small angle synchrotron radiation x-ray diffraction measurements indicated a reorientation of the lipid A aggregates from a multilamellar into a cubic structure as a result of alpha alpha Hb interaction. Thus, in the absence of alpha alpha Hb, the molecular shape of the pentaacyl samples was cylindrical with a moderate inclination of the diglucosamine backbone, whereas, in the presence of the protein, the shape was conical, and the inclination angle was high. The cytokine-inducing capability in human mononuclear cells, negligible for the pure pentaacylated compounds, increased markedly in the presence of alpha alpha Hb in a concentration-dependent manner. In the Limulus assay, the pentaacylated samples were active a priori, and their activity was enhanced following binding to alpha alphaHb, at least at the highest protein concentrations. The data can be understood in the light of a reaggregation of the endotoxins because of alpha alpha Hb binding, with the endotoxin backbones then readily accessible for serum and membrane proteins. By using fluorescence resonance energy transfer spectroscopy, an uptake of the endotoxin-Hb complex into phospholipid liposomes was observed, which provides a basis for cell activation.