Recognition of lipopolysaccharide pattern by TLR4 complexes

Lipopolysaccharide (LPS) is a major component of the outer membrane of Gram-negative bacteria. Minute amounts of LPS released from infecting pathogens can initiate potent innate immune responses that prime the immune system against further infection. However, when the LPS response is not properly controlled it can lead to fatal septic shock syndrome. The common structural pattern of LPS in diverse bacterial species is recognized by a cascade of LPS receptors and accessory proteins, LPS binding protein (LBP), CD14 and the Toll-like receptor4 (TLR4)-MD-2 complex. The structures of these proteins account for how our immune system differentiates LPS molecules from structurally similar host molecules. They also provide insights useful for discovery of anti-sepsis drugs. In this review, we summarize these structures and describe the structural basis of LPS recognition by LPS receptors and accessory proteins.

The effects of Porphyromonas gingivalis LPS and Actinobacillus actinomycetemcomitans LPS on human dendritic cells in vitro, and in a mouse model in vivo.

Interaction between different bacterial plaque pathogens and dendritic cells may induce different types of T helper (Th) cell response, which is critical in the pathogenesis of periodontitis. In this study we investigated the effects of lipopolysaccharide (LPS) from Porphyromonas gingivalis and Actinobacillus actinomycetemcomitans on human monocyte-derived dendritic cells (Mo-DCs) with respect to co-stimulatory molecule expression, cytokine production and Th cell differentiation. Unlike Escherichia coli and A. actinomycetemcomitans LPS, P. gingivalis LPS induced only low levels of CD40, CD80, HLA-DR and CD83 expression on Mo-DCs. LPS from both bacteria induced considerably lower TNF-alpha and IL-10 than did E. coli LPS. LPS from all three bacteria induced only negligible IL-12 production. In a human mixed-leukocyte reaction, and in an ovalbumin-specific T cell response assay in mice, both types of LPS suppressed IFN-gamma production. In conclusion, stimulation by P. gingivalis LPS and A. actinomycetemcomitans LPS appears to bias Mo-DCs towards Th2 production.

Avances en el desarrollo de terapias neutralizantes en la sepsis / Advances in the development of neutralizing therapies for sepsis

El lipopolisacarido bacteriano (LPS), tambien denominado endotoxina, es el constituyente mayoritario de la membrana externa de bacterias Gram negativas. Esta molecula es liberada de la bacteria a la circulacion exhibiendo una amplia variedad de efectos toxicos y pro-inflamatorios, los cuales estan asociados al lipido A y a su vez estan relacionados a la patogenesis de la sepsis. Muchos de los fenomenos fisiologicos producidos por el LPS resultan de la capacidad de esta molecula de activar las celulas del sistema inmune del huesped, entre ellas monocitos, macrofagos y leucocitos polimorfonucleares. Este proceso produce una inflamacion local, proceso beneficioso para el huesped. Sin embargo, si la cantidad de LPS liberado excede cierta concentracion critica umbral, la exacerbada liberacion de citoquinas inflamatorias como Factor de Necrosis Tumoral (TNF-alfa) e interleuquinas (IL) resulta en sepsis grave, lo que hace necesario encontrar nuevas opciones terapeuticas capaces de neutralizar la endotoxina circulante. En este articulo se presenta una revision actualizada de los resultados experimentales obtenidos in vivo e in vitro empleando proteinas y peptidos sinteticos con la finalidad de neutralizar el LPS, y las perspectivas que en este area ofrece el uso de lipoproteinas, en particular la apolipoproteina A-I y formas mutantes o peptidos derivados de esta proteina.

Lipopolisaccharide (LPS), also called endotoxin, is the major component of the external membrane in Gram negative bacteria. This molecule is released to circulation by the bacteria, producing a large variety of toxic and pro-inflammatory effects which are associated with lipid A as well as with sepsis pathogenesis. Many physiological henomena produced by LPS arise from this molecule's capacity to activate cells in the host immune system such as monocytes, macrophages and polymorphonuclear leukocytes. This process leads to a local inflammation, and it is beneficial for the host. However, if the amount of LPS released exceeds the critical concentration thresholdan augmented release of inflammatory cytokines as TNF-alfa, and interleukines (IL) produce a severe sepsis. This fact led us to find therapeutical alternatives able to neutralize circulating endotoxin. This work is focused on the experimental results obtained in vivo and in vitro using synthetic proteins and peptides in order to neutralizeLPS, and on future perpectives in this research area that offer the use of lipoprotein and in particular apolipoprotein A-I and mutants or peptides derived from this protein.

Generation of Nitric Oxide in the Opossum Lower Esophageal Sphincter during Physiological Experimentation

Lipopolysaccharide (LPS), given in vivo, modulates opossum esophageal motor functions by inducing the inducible nitric oxide synthase (iNOS), which increases nitric oxide (NO) production. Superoxide, a NO scavenger, is generated during this endotoxemia. Superoxide is cleared by superoxide dismutase (SOD) and catalase (CAT) to protect the physiological function of NO. This study examined whether lower esophageal sphincter (LES) motility, NO release, and iNOS and nitrotyrosine accumulation in the LES are affected by LPS in vitro. Muscle strips from the opossum LES were placed in tissue baths containing oxygenated Krebs buffer. NO release was measured with a chemiluminescence NOx analyzer, and Western blots were performed to analyze iNOS and nitrotyrosine production. The percent change in resting LES tone after a 6-hour exposure to LPS was significantly increased compared to pretreatment values. The percent LES relaxation upon electrical stimulation was significantly decreased in the control group at 6 hours, indicating that the LPS treatment had an effect. The NO concentration in the tissue bath of LPS-treated muscle without nerve stimulation was significantly less than that of LPS treatment combined with SOD/CAT or SOD/CAT alone. iNOS and nitrotyrosine were detectable and increased over time in the LES muscle of both the control and LPS-treated groups. Antioxidant enzymes may play a role in regulating NO-mediated neuromuscular functions in the LES.

Effect of cholesterol and 7-beta hydroxycholesterol on glutathione status and nitric oxide production in murine peritoneal macrophages.

Present study was conducted to observe the effect of cholesterol and oxidized cholesterol (7beta-hydroxycholesterol,7beta-OH) on the nitric oxide (NO) production and the redox ratio by lipopolysaccharide-stimulated macrophages. Dose-dependent decrease in NO levels was seen with both cholesterol and 7beta-OH at different incubation intervals (6,12,18,24 hr) and concentrations (2.5,5,7.5microg/ml). On comparison, a significant decrease in the NO was observed at 24 hr interval in 7beta-OH exposed cells with all respective concentrations of cholesterol. Incubation with 7beta-OH also resulted in significant increase in levels of oxidized glutathione (GSSG) and decrease in reduced glutathione (GSH), while cholesterol showed no effect on GSSG levels. Moreover, GSH levels were lowered only at highest concentration (7.5microg/ml), and at longer incubation intervals (18,24 hr) with cholesterol exposure. This altered the redox status in both cholesterol/7beta-OH treated macrophages. Increased redox ratio and decreased NO levels indicated increased oxidative stress and decreased vasodilation by 7beta-OH compared to cholesterol.

Extract of gum resins of Boswellia serrata L. inhibits lipopolysaccharide induced nitric oxide production in rat macrophages along with hypolipidemic property.

Boswellia serrata, Linn F (Burseraceae) is commonly used in Indian system of medicine (Ayurvedic) as an anti-inflammatory, analgesic, anti-arthritic and anti-proliferative agent. This study was planned to investigate the water-soluble fraction of the oleoresin gum of Boswellia serrata (BS extract) on lipopolysaccharide (LPS) induced nitric oxide (NO) production by macrophages under in vivo and in vitro conditions. In the previous condition, rats were fed on atherogenic diet (2.5% cholesterol, 1% cholic acid, 15.7 % saturated fat) along with the BS extract for 90 days. Blood was collected for lipid profile and toxicological safety parameters. Peritoneal macrophages were isolated and cultured to see the LPS induced NO production. Under in vivo experiment, BS extract significantly reduced serum total cholesterol (38-48 %), increased serum high-density lipoprotein- cholesterol (HDL-cholesterol, 22-30%). Under in vitro experiments with thioglycolate activated macrophages, it inhibited LPS induced (NO) production with IC 50 value at 662 ng /ml. Further, this fraction, in the dose of 15 mg/100 g body wt for 90 days, did not show any increase in serum glutamate-pyruvate transaminase (SGPT) and blood urea, in normal control animals. However, it significantly reversed the raised SGPT and blood urea in the atherogenic diet-fed animals. Transverse section of liver and kidney also supported its protective effect. Thus it may be concluded that water extract of Boswellia serrata possesses strong hypocholesterolemic property along with increase in serum HDL. It inhibits the LPS induced NO production by the activated rat peritoneal macrophages and show hepato-protective and reno-protective property.

Immunologic reactivity of a lipopolysaccharide-protein complex of type A Pasteurella multocida in mice

The immunologic reactivity of a lipopolysaccharide (LPS)-protein complex isolated from a potassium thiocyanate extract of a Pasteurella multocida (capsular type A and somatic type 3) strain was evaluated in mice. The LPS-protein complex provided 100% protection in mice against a challenge with the homologous strain. However, when the complex was fractionated into LPS and protein moieties by phenol-water treatment, both components lacked immunogenicity. The complex and extracted components were mitogenic for mouse B lymphocytes with the protein moiety the most active. Although immune serum against the LPS-protein complex protected mice against challenge thereby indicating a role for humoral immunity, the LPS-protein complex of P. multocida was also found to induce cell-mediated immunity. This cell-mediated immunity was demonstrated in mice immunized with the complex by: (1). mitogenic responses of T lymphocytes, (2). induction of delayed type hypersensitivity reaction in the hind footpads, and (3). enhanced resistance to challenge infection with Salmonella enteritidis.

Chemical characterization of the lipopolysaccharides from enteropathogenic Escherichia coli O142 and O158.

Lipopolysaccharides (LPS) from two enteropathogenic strains of E. coli O142 and O158 were isolated by hot phenol-water extraction procedure. Polyacrylamide gel electrophoretic pattern of the LPS showed the typical ladder like pattern of smooth type of LPS. The LPS of E. coli O158 was found to contain L-rhamnose, D-glucose and N-acetyl-D-galactosamine as major constituents together with D-galactose, N-acetyl-D-glucosamine, L-glycero-D-manno-heptose and 2-keto-3-deoxy-D-manno-octulosonic acid (KDO) whereas LPS from E. coli O142 contained L-rhamnose, N-acetyl-D-glucosamine and N-acetyl-D-galactosamine as major constituents together with D-glucose, D-galactose, N-acetyl-D-glucosamine, L-glycero-D-mannoheptose and 2-keto-3-deoxy-D-manno-octulosonic acid (KDO). LPS was degraded by mild acid hydrolysis to yield a degraded polysaccharide fraction and an insoluble lipid-A fraction. The main fatty acids of the lipid-A fraction of the LPS were C12:O, C14:O, and 3-OH C14:O for O158 strain whereas E. coli O142 lipid-A consisted of C12:O, C14:O, 3-OH C14:O, and C16:O. The degraded polysaccharide fraction on gel permeation chromatography gave a high moleculer weight O-chain fraction and a core oligosaccharide and a fraction containing degraded sugars. The chemical composition of LPS and its fragmented products are reported in this communication.

Effect of gamma irradiation on chemical and biological properties of lipopolysaccharide from Salmonella typhimurium.

Lipopolysaccharide (LPS) from S. typhimurium on exposure to gamma-radiation resulted in decrease in toxicity and was less mitogenic, Silver stained profiles of irradiated LPS on polyacrylamide gels revealed complete loss of its heteropolysaccharides which was confirmed further by analysing lipid A and LPS from Salmonella minnesota Re mutants on SDS-PAGE. Glucosamine and 2-keto 3-deoxy-octonate(Kdo) contents were significantly decreased on treatment. Lipid A obtained by removal of heteropolysaccharides from LPS was less toxic on exposure to gamma radiations.

El lipopolisacárido bacteriano: una potente endotoxina con múltiples actividades biológicas, recientes avances en estructura, genética y bioquímica / Lipopolysaccharides, bacterial: an potent endotoxin with multiples biological activities

Los lipopolisacáridos (LPS) constituyen el antígeno O y la endotoxina de las bacterias Gram-negativas. Están localizados en la membrana externa de la envoltura celular bacteriana y juegan un papel muy importante en la patogénesis de las infecciones bacterianas, así como en la interacción con el hospedero y su sistema de defensa. Básicamente el LPS se compone de una porción lipídica muy conservada entre las especies, denominada lípido A, inmersa en la cara externa de la membrana externa de la bacteria, y una porción hidrofílica compuesta por azúcares que presenta una gran variabilidad estructural. El lípido A es responsable de las propiedades patofisiológicas de las endotoxinas. El polisacárido O, que es la porción mas externa, le confiere a la bacteria su especificidad serológica. El oligosacárido nuclear o core une el polisacárido O al líquido A. En general, los genes responsables de la síntesis del LPS están organizados ya sea en grupos de genes contiguos como en la síntesis del núcleo y el polisacárido O, o bien, dispersos alrededor del cromosoma bacteriano como en el caso del lípido A. La mayoría de los pasos de la vía biosintética del LPS han sido elucidados al menos en las enterobacterias. Tanto las interacciones moleculares de enzimas y sistratos durante la síntesis comoe el transporte del LPS hasta la membrana externa bacteriana son aspectos de constante investigación hoy en día, debido a las implicaciones en la biología de estos microorganismos y en el potencial uso farmacológico de análogos o antagonistas de LPS en la terapéutica del choque endotóxico. Esta revisión pretende actualizar los aspectos relevantes de la estructura, bioquímica y genética de esta importante molécula bacteriana

Comparison of outer membrane protein and lipopolysaccharide profiles of enterotoxigenic Escherichia coli strains isolet in Säo Paulo, Brazil

The outer membrane protein (OMP) and lipopolysaccharide (LPS) patterns of 12 strains of serogroups of enterotoxigenic E. coli frequntly isolated in Säo Paulo city werte determined by fractionation techniques and by sodium dodecyl sulfate-plyacrylamide gel electrophoresis (SDS-PAGE). Five O6, three O78 and four O128 serogroup isolates of different serotypes (flagellar antigens) and virulence factors (toxins and colonization factor antigens) showed a high degree of variability in their OMP pattern and at least nine groups could be identified. The analysis of LPS aptterns by SDS-PAGE showed a homogenous profile for the O6 strains and some minor differences for the O128 and 078 strains. The oresented data indicate that analysis of OMP and LPS by SDS-PAGE may further improve the discriminating ability of extensively used serological techniques or the detection of virulence factors and could be a useful tool in epidemiological studies of enterotoxigenic E. coli (ETEC) strains from this area

Production of monoclonal antibodies to lipoarabinomannan-B and use in the detection of mycobacterial antigens in sputum

Tuberculosis has traditionally been confirmed by AFB staining or culturing Mycobacterium tuberculosis from clinical specimens. However, because of the low sensitivity of the sputum smear examination and of the delayed report in culturing, the conventional methods for detection of M. tuberculosis have not been always satisfactory. In an attempt to develop an alternate tool, this study was initiated to produce monoclonal antibodies (MAb) to lipoarabinomannan B (LAM-B) antigen and to use the antibodies in detecting mycobacteria. In this study, five monoclonal antibodies specific to LAM-B were produced; LAM701 (IgG3), LAM138 (IgM), LAM204 (IgM), LAM302 (IgM), and LAM604 (IgM). A sandwich enzyme-linked immunosorbent assay (ELISA) was developed for detecting LAM-B and other mycobacterial antigens using the monoclonal antibodies. With the MAb LAM701, the minimal detectable concentration was 1.0 ng/ml for LAM-B, and 1.0 microgram/ml for M. tuberculosis whole cells, respectively. When 14 clinical specimens proven to contain AFB by smear staining or culture were examined, ten (71.4%) were positive by the sandwich ELISA; in contrast, sputum smear examination gave positive results in only six (42.9%) specimens. Meanwhile, none of 25 specimens with no evidence of AFB were positive by the sandwich ELISA using the MAb LAM701. Although further evaluations are required, this study suggests that the monoclonal antibodies to LAM-B may be useful in detecting mycobacteria from clinical specimens.