Bacterial Endotoxin (bacterial + endotoxin)

Distribution by Scientific Domains

Selected Abstracts

Unphosphorylated STAT3 modulates alpha7 nicotinic receptor signaling and cytokine production in sepsis

Geber Peña
Abstract The role of STAT3 in infectious diseases remains undetermined, in part because unphosphorylated STAT3 has been considered an inactive protein. Here, we report that unphosphorylated STAT3 contributes to cholinergic anti-inflammation, prevents systemic inflammation, and improves survival in sepsis. Bacterial endotoxin induced STAT3 tyrosine phosphorylation in macrophages. Both alpha7 nicotinic receptor (alpha7nAChR) activation and inhibition of JAK2 blunt STAT3 phosphorylation. Inhibition of STAT3 phosphorylation mimicked the alpha7nAChR signaling, inhibiting NF-,B and cytokine production in macrophages. Transfection of macrophages with the dominant-negative mutant STAT3F, to prevent its tyrosine phosphorylation, reduced TNF production but did not prevent the alpha7nAChR signaling. However, inhibition of STAT3 protein expression enhanced cytokine production and abrogated alpha7nAChR signaling. Alpha7nAChR controls TNF production in macrophages through a mechanism that requires STAT3 protein expression, but not its tyrosine phosphorylation. In vivo, inhibition of STAT3 tyrosine phosphorylation by stattic prevented systemic inflammation and improved survival in experimental sepsis. Stattic also prevented the production of late mediators of sepsis and improved survival in established sepsis. These results reveal the immunological implications of tyrosine-unphosphorylated STAT3 in infectious diseases. [source]

Increased lipopolysaccharide binding protein in cirrhotic patients with marked immune and hemodynamic derangement

HEPATOLOGY, Issue 1 2003
Agustín Albillos
Intestinal bacterial overgrowth and translocation, both common in cirrhosis with ascites, may lead to the activation of monocytes and lymphocytes, increased levels of proinflammatory cytokines, and enhanced synthesis of nitric oxide present in cirrhosis. Bacterial endotoxin promotes the synthesis of lipopolysaccharide (LPS)-binding protein (LBP), and forms a LPS-LBP complex that binds to CD14. This study was designed to evaluate LBP levels and their correlation to the immune response and the hemodynamic status in cirrhotic patients. Plasma LBP, endotoxin, soluble CD14 (sCD14), cytokines, renin, nitrites, and systemic vascular resistance were determined before and 4 weeks after norfloxacin or placebo in 102 cirrhotic patients and 30 controls. LBP was elevated in 42% of ascitic cirrhotic patients (15.7 ± 0.7 versus 6.06 ± 0.5 ,g/mL, P < .01). In 60% of high LBP patients, endotoxin was within normal range. Among ascitic patients, those with high LBP showed greater (P < .05) levels of sCD14, tumor necrosis factor , (TNF-,), interleukin 6 (IL-6), nitrites + nitrates (NOx)/creatinine, and renin, and lower vascular resistance. In the cirrhotic patients with high LBP, norfloxacin normalized (P < .01) LBP (from 16.6 ± 0.5 to 5.82 ± 0.8 , g/mL) and sCD14; reduced the level of cytokines, NOx/creatinine, and renin; and increased vascular resistance; but lacked effect in patients with normal LBP. Portal pressure was unchanged after norfloxacin in another group of 18 cirrhotic patients with high and 19 with normal LBP. In conclusion, the subset of ascitic cirrhotic patients with marked immune and hemodynamic derangement is identified by increased LBP levels. Amelioration of these abnormalities by norfloxacin suggests the involvement of enteric bacteria or their products in the triggering of the process. [source]

Effect of different irrigation solutions and calcium hydroxide on bacterial LPS

J. M. G. Tanomaru
Abstract Aim, To evaluate the effect of biomechanical preparation with different irrigating solutions and calcium hydroxide dressing in dog root canals containing bacterial endotoxin (lipopolysaccharides; LPS). Methodology, One hundred and forty premolar roots from seven dogs were filled with Escherichia coli LPS for 10 days (three roots were lost during histological processing). The following irrigating solutions were used for biomechanical preparation: 1% (group I, n = 20), 2.5% (group II, n = 19) and 5% sodium hypochlorite (group III, n = 19), 2% chlorhexidine digluconate (group IV, n = 20) and physiological saline solution (group V, n = 19). In group VI (n = 20), the LPS solution was maintained in the root canal during the entire experiment and in group VII (n = 20), after biomechanical preparation with saline solution, the root canals were filled with a calcium hydroxide dressing (Calen; control). After 60 days, the animals were sacrificed and the following parameters of periapical disease were evaluated: (a) inflammatory infiltrate, (b) periodontal ligament thickness, (c) cementum resorption and (d) bone resorption. Scores were given and data were analysed statistically with the Kruskal,Wallis and Dunn tests (P < 0.05). Results, Histopathological evaluation showed that groups I,VI had more inflammatory infiltrate, greater periodontal ligament thickening and greater cementum and bone resorption (P < 0.05) compared to group VII, which received the calcium hydroxide intracanal dressing. Conclusions, Biomechanical preparation with the irrigating solutions did not inactivate the effects of the endotoxin but the calcium hydroxide intracanal dressing did appear to inactivate the effects induced by the endotoxin in vivo. [source]

Inhibition by Lipopolysaccharide of Naloxone-Induced Luteinising Hormone Secretion Is Accompanied by Increases in Corticotropin-Releasing Factor Immunoreactivity in Hypothalamic Paraventricular Neurones in Female Rats

D. He
Abstract We have recently reported that lipopolysaccharide (LPS), a bacterial endotoxin, inhibits steroid-induced as well as naloxone-induced luteinising hormone (LH) secretion in ovariectomised oestrogen-primed rats. In the present study, we examined whether corticotropin-releasing factor (CRF) may be involved in the LPS-induced inhibition of LH secretion. Unanaesthetised rats were treated with an intravenous (i.v.) injection of LPS (10 µg) or saline, followed by an i.v. injection of naloxone (20 mg/kg). After sequential blood samples were collected for determination of serum LH concentrations, the brains were fixed and CRF-immunoreactivity was examined histochemically. In control rats receiving saline injections, only a small number of CRF-immunoreactive (ir) cells were found in the parvocellular portion of the hypothalamic paraventricular nucleus (PVN), and naloxone significantly increased serum LH concentrations within 10 min. By contrast, in LPS-treated rats, the number of CRF-ir cells was significantly greater than that in control rats, and the effect of naloxone was completely abolished. In a separate experiment, an intracerebroventricular injection of 5 µg CRF inhibited naloxone-induced LH release, mimicking the effect of LPS. These results suggest that LPS stimulates production of CRF in PVN neurones, which in turn inhibits LH secretion without opioidergic mediation. [source]

Selenium attenuates pro-inflammatory gene expression in macrophages

Hema Vunta
Abstract Selenium (Se) is an important element required for the optimal functioning of the immune system. Particularly in macrophages, which play a pivotal role in immune regulation, Se acts as a major antioxidant in the form of selenoproteins to mitigate the cytotoxic effects of reactive oxygen species. Here we describe the role of Se as an anti-inflammatory agent and its effect on the macrophage signal transduction pathways elicited by bacterial endotoxin, LPS. Our studies demonstrate that supplementation of Se to macrophages (Se-deficient) leads to a significant decrease in the LPS-induced expression of two important pro-inflammatory genes, cyclooxygenase-2 (COX-2) and tumor necrosis factor-, (TNF-,) via the inhibition of MAP kinase pathways. Furthermore, Se-deficiency in mice exacerbated the LPS-mediated infiltration of macrophages into the lungs suggesting that Se status is a crucial host factor that regulates inflammation. In summary, our results indicate that Se plays an important role as an anti-inflammatory agent by tightly regulating the expression of pro-inflammatory genes in immune cells. [source]

Release of ATP in the central nervous system during systemic inflammation: real-time measurement in the hypothalamus of conscious rabbits

Alexander V. Gourine
Receptors for extracellular ATP (both ionotropic and metabotropic) are widely expressed in the CNS both in neurones and glia. ATP can modulate neuronal activity in many parts of the brain and contributes to the central nervous control of several physiological functions. Here we show that during the systemic inflammatory response the extracellular concentrations of ATP increase in the anterior hypothalamus and this has a profound effect on the development of the thermoregulatory febrile response. In conscious rabbits we measured ATP release in real time with novel amperometric biosensors and monitored a marked increase in the concentration of ATP (4.0 ± 0.7 ,m) in the anterior hypothalamus in response to intravenous injection of bacterial endotoxin , lipopolysaccharide (LPS). No ATP release was observed in the posterior hypothalamus. The release of ATP coincided with the development of the initial phase of the febrile response, starting 18 ± 2 min and reaching its peak 45 ± 2 min after LPS injection. Application of the ATP receptor antagonists pyridoxal-5,-phosphate-6-azophenyl-2,,4,-disulphonic acid, Brilliant Blue G or periodate oxidized ATP dialdehyde to the site of ATP release in the anterior hypothalamus markedly augmented and prolonged the febrile response. These data indicate that during the development of the systemic inflammation, ATP is released in the anterior hypothalamus to limit the magnitude and duration of fever. This release may also have a profound effect on the hypothalamic control of other physiological functions in which ATP and related purines have been implicated to play modulatory roles, such as food intake, hormone secretion, cardiovascular activity and sleep. [source]

REVIEW ARTICLE: Immunopathogenesis of Pelvic Endometriosis: Role of Hepatocyte Growth Factor, Macrophages and Ovarian Steroids

Khaleque Newaz Khan
Endometriosis, a chronic disease characterized by endometrial tissue located outside the uterine cavity is associated with chronic pelvic pain and infertility. However, an in-depth understanding of the pathophysiology of endometriosis is still elusive. It is generally believed that besides ovarian steroid hormones, the growth of endometriosis can be regulated by innate immune system in pelvic microenvironment by their interaction with endometrial cells and immune cells. We conducted a series of studies in perspectives of pelvic inflammation that is triggered primarily by bacterial endotoxin (lipopolysacccharide) and is mediated by toll-like receptor 4 and showed their involvement in the development of pelvic endometriosis. As a cellular component of innate immune system, macrophages were found to play a central role in inducing pelvic inflammatory reaction. We further report here that peritoneal macrophages retain receptors encoding for estrogen and progesterone and ovarian steroids also participate in producing an inflammatory response in pelvic cavity and are involved in the growth of endometriosis either alone or in combination with hepatocyte growth factor (HGF). As a pleiotropic growth factor, HGF retains multifunctional role in endometriosis. We describe here the individual and step-wise role of HGF, macrophages and ovarian steroid hormones and their orchestrated involvement in the immunopathogenesis of pelvic endometriosis. [source]

Biophysical characterization of the interaction of high-density lipoprotein (HDL) with endotoxins

FEBS JOURNAL, Issue 23 2002
Klaus Brandenburg
The interaction of bacterial endotoxins [lipopolysaccharide (LPS) and the ,endotoxic principle' lipid A], with high-density lipoprotein (HDL) from serum was investigated with a variety of physical techniques and biological assays. HDL exhibited an increase in the gel to liquid crystalline phase transition temperature Tc and a rigidification of the acyl chains of the endotoxins as measured by Fourier-transform infrared spectroscopy and differential scanning calorimetry. The functional groups of the endotoxins interacting with HDL are the phosphates and the diglucosamine backbone. The finding of phosphates as target groups is in accordance to measurements of the electrophoretic mobility showing that the zeta potential decreases from ,50 to ,60 mV to ,20 mV at binding saturation. The importance of the sugar backbone as further target structure is in accordance with the remaining negative potential and competition experiments with polymyxin B (PMB) and phase transition data of the system PMB/dephosphorylated LPS. Furthermore, endotoxin binding to HDL influences the secondary structure of the latter manifesting in a change from a mixed ,-helical/,-sheet structure to a predominantly ,-helical structure. The aggregate structure of the lipid A moiety of the endotoxins as determined by small-angle X-ray scattering shows a change of a unilamellar/inverted cubic into a multilamellar structure in the presence of HDL. Fluorescence resonance energy transfer data indicate an intercalation of pure HDL, and of [LPS],[HDL] complexes into phospholipid liposomes. Furthermore, HDL may enhance the lipopolysaccharide-binding protein-induced intercalation of LPS into phospholipid liposomes. Parallel to these observations, the LPS-induced cytokine production of human mononuclear cells and the reactivity in the Limulus test are strongly reduced by the addition of HDL. These data allow to develop a model of the [endotoxin]/[HDL] interaction. [source]

Interpretation of biological activity data of bacterial endotoxins by simple molecular models of mechanism of action

FEBS JOURNAL, Issue 3 2000
Vladimir Frecer
Lipid A moiety has been identified as the bioactive component of bacterial endotoxins (lipopolysaccharides). However, the molecular mechanism of biological activity of lipid A is still not fully understood. This paper contributes to understanding of the molecular mechanism of action of bacterial endotoxins by comparing molecular modelling results for two possible mechanisms with the underlying experimental data. Mechanisms of action involving specific binding of lipid A to a protein receptor as well as nonspecific intercalation into phospholipid membrane of a host cell were modelled and analysed. As the cellular receptor for endotoxin has not been identified, a model of a peptidic pseudoreceptor was proposed, based on molecular structure, symmetry of the lipid A moiety and the observed character of endotoxin-binding sites in proteins. We have studied the monomeric form of lipid A from Escherichia coli and its seven synthetic analogues with varying numbers of phosphate groups and correlated them with known biological activities determined by the Limulus assay. Gibbs free energies associated with the interaction of lipid A with the pseudoreceptor model and intercalation into phospholipid membrane calculated by molecular mechanics and molecular dynamics methods were used to compare the two possible mechanisms of action. The results suggest that specific binding of lipid A analogues to the peptidic pseudoreceptor carrying an amphipathic cationic binding pattern BHPHB (B, basic; H, hydrophobic; P, polar residue, respectively) is energetically more favourable than intercalation into the phospholipid membrane. In addition, binding affinities of lipid A analogues to the best minimum binding sequence KFSFK of the pseudoreceptor correlated with the experimental Limulus activity parameter. This correlation enabled us to rationalize the observed relationship between the number and position of the phosphate groups in the lipid A moiety and its biological activity in terms of specific ligand,receptor interactions. If lipid A,receptor interaction involves formation of phosphate-ammonium ion-pair(s) with cationic amino-acid residues, the specific mechanism of action was fully consistent with the underlying experimental data. As a consequence, recognition of lipid A variants by an amphipathic binding sequence BHPHB of a host-cell protein receptor might represent the initial and/or rate-determining molecular event of the mechanism of action of lipid A (or endotoxin). The insight into the molecular mechanism of action and the structure of the lipid A-binding pattern have potential implications for rational drug design strategies of endotoxin-neutralizing agents or binding factors. [source]

Towards a rational development of anti-endotoxin agents: novel approaches to sequestration of bacterial endotoxins with small molecules

Sunil A. David
Abstract Endotoxins, or lipopolysaccharides (LPS), present on the surface of Gram-negative bacteria, play a key role in the pathogenesis of septic shock, a common clinical problem and a leading cause of mortality in critically ill patients, for which no specific therapeutic modalities are available at the present time. The toxic moiety of LPS is a glycolipid called ,lipid A', which is composed of a bisphosphorylated diglucosamine backbone bearing up to seven acyl chains in ester and amide linkages. Lipid A is structurally highly conserved in Gram-negative bacteria, and is therefore an attractive target for developing anti-endotoxin molecules designed to sequester, and thereby neutralize, the deleterious effects of endotoxins. The anionic and amphipathic nature of lipid A enables the interaction of a wide variety of cationic amphiphiles with the toxin. This review describes the systematic evaluation of several structural classes of cationic amphiphiles, both peptides and non-peptidic small molecules, in the broader context of recent efforts aimed at developing novel anti-endotoxin strategies. The derivation of a pharmacophore for LPS recognition has led to the identification of novel, nontoxic, structurally simple small molecules, the lipopolyamines. The lipopolyamines bind and neutralize LPS in in vitro experiments as well as in animal models of endotoxicity, and thus present novel and exciting leads for rational, structure-based development of LPS-sequestering agents of potential clinical value. Copyright © 2001 John Wiley & Sons, Ltd. [source]