Tetracycline up-regulates COX-2 expression and prostaglandin E2 production independent of its effect on nitric oxide.
(17/4158)
Tetracyclines (doxycycline and minocycline) augmented (one- to twofold) the PGE2 production in human osteoarthritis-affected cartilage (in the presence or absence of cytokines and endotoxin) in ex vivo conditions. Similarly, bovine chondrocytes stimulated with LPS showed (one- to fivefold) an increase in PGE2 accumulation in the presence of doxycycline. This effect was observed at drug concentrations that did not affect nitric oxide (NO) production. In murine macrophages (RAW 264.7) stimulated with LPS, tetracyclines inhibited NO release and increased PGE2 production. Tetracycline(s) and L-N-monomethylarginine (L-NMMA) (NO synthase inhibitor) showed an additive effect on inhibition of NO and PGE2 accumulation, thereby uncoupling the effects of tetracyclines on NO and PGE2 production. The enhancement of PGE2 production in RAW 264.7 cells by tetracyclines was accompanied by the accumulation of both cyclooxygenase (COX)-2 mRNA and cytosolic COX-2 protein. In contrast to tetracyclines, L-NMMA at low concentrations (< or = 100 microM) inhibited the spontaneous release of No in osteoarthritis-affected explants and LPS-stimulated macrophages but had no significant effect on the PGE2 production. At higher concentrations, L-NMMA (500 microM) inhibited NO release but augmented PGE2 production. This study indicates a novel mechanism of action of tetracyclines to augment the expression of COX-2 and PGE2 production, an effect that is independent of endogenous concentration of NO. (+info)
Endotoxin fails to induce IFN-gamma in endotoxin-tolerant mice: deficiencies in both IL-12 heterodimer production and IL-12 responsiveness.
(18/4158)
Mice exposed to sublethal endotoxemia develop short-term endotoxin tolerance, a state characterized by decreased monokine production and enhanced protection against endotoxic lethality. We confirmed that TNF-alpha production is markedly impaired in endotoxin-tolerant mice and additionally found 2- to 6-fold decreases in serum IFN-gamma in these animals following endotoxin challenge. The IFN-gamma deficiency of endotoxin tolerance correlated with 8-fold decreases in the bioactive p40/p35 heterodimeric form of IL-12. In contrast, total circulating IL-12 p40 was reduced by only 30-50%. Endotoxin-tolerant mice were less responsive to IL-12 than control mice, as evidenced by 3-fold lower levels of IFN-gamma inducible in vivo when rIL-12 was administered at the time of endotoxin challenge. Similarly, spleen cell cultures of endotoxin-tolerant mice produced 3-fold less IFN-gamma in the presence of optimal concentrations of both IL-12 and IL-18. Finally, levels of IL-12R beta 2 subunit mRNA and the percent composition of NK lymphocytes in the spleen were both decreased in endotoxin-tolerant mice relative to controls. We conclude that endotoxin-tolerant mice are profoundly impaired in their ability to produce IFN-gamma in response to endotoxin and that this is associated with acquired defects in both the production of circulating IL-12 heterodimer response and the response to IL-12 by NK cells. (+info)
Integrative model for binding of Bacillus thuringiensis toxins in susceptible and resistant larvae of the diamondback moth (Plutella xylostella).
(19/4158)
Insecticidal crystal proteins from Bacillus thuringiensis in sprays and transgenic crops are extremely useful for environmentally sound pest management, but their long-term efficacy is threatened by evolution of resistance by target pests. The diamondback moth (Plutella xylostella) is the first insect to evolve resistance to B. thuringiensis in open-field populations. The only known mechanism of resistance to B. thuringiensis in the diamondback moth is reduced binding of toxin to midgut binding sites. In the present work we analyzed competitive binding of B. thuringiensis toxins Cry1Aa, Cry1Ab, Cry1Ac, and Cry1F to brush border membrane vesicles from larval midguts in a susceptible strain and in resistant strains from the Philippines, Hawaii, and Pennsylvania. Based on the results, we propose a model for binding of B. thuringiensis crystal proteins in susceptible larvae with two binding sites for Cry1Aa, one of which is shared with Cry1Ab, Cry1Ac, and Cry1F. Our results show that the common binding site is altered in each of the three resistant strains. In the strain from the Philippines, the alteration reduced binding of Cry1Ab but did not affect binding of the other crystal proteins. In the resistant strains from Hawaii and Pennsylvania, the alteration affected binding of Cry1Aa, Cry1Ab, Cry1Ac, and Cry1F. Previously reported evidence that a single mutation can confer resistance to Cry1Ab, Cry1Ac, and Cry1F corresponds to expectations based on the binding model. However, the following two other observations do not: the mutation in the Philippines strain affected binding of only Cry1Ab, and one mutation was sufficient for resistance to Cry1Aa. The imperfect correspondence between the model and observations suggests that reduced binding is not the only mechanism of resistance in the diamondback moth and that some, but not all, patterns of resistance and cross-resistance can be predicted correctly from the results of competitive binding analyses of susceptible strains. (+info)
Effects of a new C5a receptor antagonist on C5a- and endotoxin-induced neutropenia in the rat.
(20/4158)
A new C5a receptor antagonist, the cyclic peptide Phe-[Orn-Pro-D-cyclohexylalanine-Trp-Arg], (F-[OPdChaWR]), was tested for its ability to antagonize the neutropenic effects of both C5a and endotoxin in rats. Human recombinant C5a (2 microg kg(-1) i.v.) caused rapid neutropenia, characterized by an 83% decrease in circulating polymorphonuclear leukocytes (PMNs) at 5 min. Administration of F-[OPdChaWR] (0.3-3 mg kg(-1) i.v.), did not affect the levels of circulating PMNs but, when given 10 min prior to C5a, it inhibited the C5a-induced neutropenia by up to 70%. Administration of E. Coli lipopolysaccharide (LPS, 1 mg kg(-1) i.v.) also caused neutropenia with an 88% decrease in circulating PMNs after 30 min. When rats were pretreated with F-[OPdChaWR] (0.3 - 10 mg kg(-1) i.v.) 10 min prior to LPS, there was a dose-dependent antagonism of the neutropenia caused by LPS, with up to 69% reversal of neutropenia observed 30 min after LPS administration. These findings suggest that C5a receptor antagonists may have therapeutic potential in the many diseases known to involve either endotoxin or C5a. (+info)
Changes in the fibrinolytic components of cultured human umbilical vein endothelial cells induced by endotoxin, tumor necrosis factor-alpha and interleukin-1alpha.
(21/4158)
BACKGROUND AND OBJECTIVE: Vascular fibrinolysis, a major natural defense mechanism against thrombosis, is a highly regulated process. The aim of this study was to evaluate the effect of endotoxin, tumor necrosis factor-alpha (TNFalpha) and interleukin-1alpha (IL-1alpha), on the fibrinolytic potential of cultured human umbilical vein endothelial cells (HUVEC). DESIGN AND METHODS: Samples of stimulated conditioned media were collected over a period of 24 hours to determine: plasminogen activator (PA) and plasminogen activator inhibitor (PAI) activity, PAI-1 mRNA, tissue-type plasminogen activator (t-PA) antigen and urokinase-type plasminogen activator (u-PA) antigen. RESULTS: Similar changes were observed after endotoxin and cytokine stimulation: there was a significant increase of PAI activity (p<0.01), starting at 6 hours, which remained 24 hours after stimulation. PAI-1 mRNA also showed an important rise with these agents, although cytokines induced an earlier and more intense inhibitor response (up to 6-fold increase). PA activity increased significantly at 6 hours (p<0.01) to drop at 24 hours and was mainly related to the presence of u-PA. INTERPRETATION AND CONCLUSIONS: We conclude that endotoxin,+TNFalpha and IL-1alpha induce profound alterations in the fibrinolytic potential of HUVEC, characterized by an initial rise of activators (u-PA) followed by a strong increase of PAI-1. These changes may be of pathophysiologic significance for thrombosis and inflammatory reactions. (+info)
Dose-related inflammatory effects of intravenous endotoxin in humans: evaluation of a new clinical lot of Escherichia coli O:113 endotoxin.
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The administration of reference endotoxin (Escherichia coli O:113, Lot EC-5) to humans has been an important means to study inflammation in vivo; however, the supply of Lot EC-5 is depleted. A new lot of reference endotoxin (Clinical Center reference endotoxin [CCRE]), derived from the original bulk material extracted from E. coli O:113, was processed. The effects of 0-, 1-, 2-, and 4-ng/kg doses of intravenous CCRE and EC-5 were studied in 20 male subjects. CCRE resulted in dose-related increases in symptoms, temperature (P=. 016), total leukocyte count (P=.014), tumor necrosis factor-alpha (P=.004), interleukin (IL)-1 receptor antagonist (P=.004), IL-6 (P=. 005), IL-8 (P=.011), cortisol (P<.05), and C-reactive protein (P=. 04). These responses were attenuated (all P<.012) in subjects given Lot EC-5 (4 ng/kg) in comparison with those in subjects given CCRE, showing that, over several years, EC-5 had lost potency. Thus, in healthy subjects, the magnitude of exposure to CCRE results in a graded dose response of major components of innate immunity. (+info)
Endotoxin interactions with lipopolysaccharide-responsive cells.
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Recent work has identified two proteins that work together to enable many cell types to respond to endotoxin. These two proteins, lipopolysaccharide (LPS) binding protein (LBP) and CD14, also participate in cellular internalization of endotoxin, which may occur independently of cellular activation. Current work with antibodies to LBP and CD14 as well as "knockout" mice in the context of LPS-initiated endotoxic shock suggests that inhibition of this pathway could be therapeutically useful. These observations point to the need to identify new molecules that mediate LPS-initiated transmembrane signaling and internalization of LPS-protein complexes. (+info)
Induction of prostaglandin release from macrophages by bacterial endotoxin.
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This review summarizes the role of the monocytic responses to lipopolysaccharide as it relates to periodontal disease severity. Data are presented which illustrate that the levels of prostaglandin E2 (PGE2) secreted by systemic peripheral blood monocytes in culture, in the presence of bacterial endotoxins, are highly correlated with the levels observed in the gingival crevicular fluid. Furthermore, the different periodontal diagnostic categories have varying levels of monocytic and crevicular fluid PGE2, in juxtaposition with clinical disease severity. These data are consistent with the concept that there is close synchrony between the systemic responsiveness of peripheral blood monocytes with regard to prostanoid synthesis and the local levels of mediator present within the gingival crevice. (+info)