To identify new components that regulate the inflammatory cascade during sepsis, we characterized the functions of myeloid-related protein-8 (Mrp8, S100A8) and myeloid-related protein-14 (Mrp14, S100A9), two abundant cytoplasmic proteins of phagocytes. We now demonstrate that mice lacking Mrp8-Mrp14 complexes are protected from endotoxin-induced lethal shock and Escherichia coli–induced abdominal sepsis. Both proteins are released during activation of phagocytes, and Mrp8-Mrp14 complexes amplify the endotoxin-triggered inflammatory responses of phagocytes. Mrp8 is the active component that induces intracellular translocation of myeloid differentiation primary response protein 88 and activation of interleukin-1 receptor–associated kinase-1 and nuclear factor-κB, resulting in elevated expression of tumor necrosis factor-α (TNF-α). Using phagocytes expressing a nonfunctional Toll-like receptor 4 (TLR4), HEK293 cells transfected with TLR4, CD14 and MD2, and by surface plasmon resonance studies in vitro, we demonstrate that Mrp8 specifically interacts with the TLR4-MD2 complex, thus representing an endogenous ligand of TLR4. Therefore Mrp8-Mrp14 complexes are new inflammatory components that amplify phagocyte activation during sepsis upstream of TNFα–dependent effects.

Mrp8 and Mrp14 are endogenous activators of Toll-like receptor 4, promoting lethal, endotoxin-induced shock

We report here that miR-155 and miR-125b play a role in innate immune response. LPS stimulation of mouse Raw 264.7 macrophages resulted in the up-regulation of miR-155 and down-regulation of miR-125b levels. The same changes also occurred when C57BL/6 mice were i.p. injected with LPS. Furthermore, the levels of miR-155 and miR-125b in Raw 264.7 cells displayed oscillatory changes in response to TNF-alpha. These changes were impaired by pretreating the cells with the proteasome inhibitor MG-132, suggesting that these two microRNAs (miRNAs) may be at least transiently under the direct control of NF-kappaB transcriptional activity. We show that miR-155 most probably directly targets transcript coding for several proteins involved in LPS signaling such as the Fas-associated death domain protein (FADD), IkappaB kinase epsilon (IKKepsilon), and the receptor (TNFR superfamily)-interacting serine-threonine kinase 1 (Ripk1) while enhancing TNF-alpha translation. In contrast, miR-125b targets the 3'-untranslated region of TNF-alpha transcripts; therefore, its down-regulation in response to LPS may be required for proper TNF-alpha production. Finally, Emu-miR-155 transgenic mice produced higher levels of TNF-alpha when exposed to LPS and were hypersensitive to LPS/d-galactosamine-induced septic shock. Altogether, our data suggest that the LPS/TNF-alpha-dependent regulation of miR-155 and miR-125b may be implicated in the response to endotoxin shock, thus offering new targets for drug design.

/pdf/modulation-of-mir-155-and-mir-125b-levels-following-4jpbbspoxo.pdf

Modulation of miR-155 and miR-125b Levels following Lipopolysaccharide/TNF-α Stimulation and Their Possible Roles in Regulating the Response to Endotoxin Shock

Tumour necrosis factor (TNF), jointly referring to TNF alpha and TNF beta, is a central mediator of immune and inflammatory responses; its activities are mediated by two distinct receptors, TNFR1 (p55) and TNFR2 (p75) (reviewed in refs 1-3). The cytoplasmic domains of the TNFRs are unrelated, suggesting that they link to different intracellular signalling pathways. Although most TNF responses have been assigned to one or the other of the TNF receptors (mostly TNFR1), there is no generally accepted model for the physiological role of the two receptor types. To investigate the role of TNFR1 in beneficial and detrimental activities of TNF, we generated TNFR1-deficient mice by gene targeting. We report here that mice homozygous for a disrupted Tnfr1 allele (Tnfr1(0)) are resistant to the lethal effect of low doses of lipopolysaccharide after sensitization with D-galactosamine, but remain sensitive to high doses of lipopolysaccharide. The increased susceptibility of Tnfr1(0)/Tnfr1(0) mutant mice to infection with the facultative intracellular bacterium Listeria monocytogenes indicates an essential role of TNF in nonspecific immunity.

Mice lacking the tumour necrosis factor receptor 1 are resistant to TNF-mediated toxicity but highly susceptible to infection by Listeria monocytogenes

The antioxidant action of medicinal herbs used in Ghana for treating various ailments was evaluated in vitro and in vivo. Five plants, Desmodium adscendens, Indigofera arrecta, Trema occidentalis, Caparis erythrocarpus, and Thonningia sanguinea were tested for their free radical scavenging action by their interaction with 1,1-diphenyl-2-picrylhydrazyl (DPPH). Of these five plants, only Thonningia sanguinea was found to scavenge the DPPH radical. Lipid peroxidation in liver microsomes induced by H2O2 was also inhibited by T. sanguinea. The hepatoprotective effect of T. sanguinea was studied on acute hepatitis induced in rats by a single dose of galactosamine (GalN, 400 mg/kg, IP) and in mice by carbon tetrachloride (CCl4, 25 microl/kg, IP). GalN induced hepatotoxicity in rats as evidenced by an increase in alanine aminotransferase (ALT) and glutathione (GSH) S-transferase activities in serum was significantly inhibited when T. sanguinea extract (5 ml/kg, IP) was given to rats 12 hr and 1 hr before GalN treatment. The activity of liver microsomal GSH S-transferase, which is known to be activated by oxidative stress, was increased by the GaIN treatment and this increase was blocked by T. sanguinea pretreatment. Similarly, T. sanguinea pretreatment also inhibited CCl4-induced hepatotoxicity in mice. These data indicate that T. sanguinea is a potent antioxidant and can offer protection against GalN- or CCl4-induced hepatotoxicity.

Free-radical scavenging action of medicinal herbs from Ghana: Thonningia sanguinea on experimentally-induced liver injuries.

Sepsis is a state of disrupted inflammatory homeostasis that is often initiated by infection. The development and progression of sepsis is multi-factorial, and affects the cardiovascular, immunological and endocrine systems of the body. The complexity of sepsis makes the clinical study of sepsis and sepsis therapeutics difficult. Animal models have been developed in an effort to create reproducible systems for studying sepsis pathogenesis and preliminary testing of potential therapeutic agents. However, demonstrated benefit from a therapeutic agent in animal models has rarely been translated into success in human clinical trials. This review summarizes the common animal sepsis models and highlights how results of recent human clinical trials might affect their use.

Animal Models of sepsis: setting the stage

Treatment of rabbits, rats, and mice with D-galactosamine increased their sensitivity to the lethal effects of lipopolysaccharide several thousand fold. The susceptibility of the animals was highest when the lipopolysaccharide was injected together with galactosamine and decreased successively when injection was carried out 1, 2, and 3 hr later. Sensitization was absent when the lipopolysaccharide was administered 1 hr before or 4 hr after galactosamine. The onset of lethality after treatment with galactosamine and lipopolysaccharide occurred faster than with lipopolysaccharide alone; usually all animals died 5-9 hr later. The galactosamine-induced sensitization to lipopolysaccharide could be reversed by uridine which is known to inhibit the early biochemical alterations induced by the amino sugar in the hepatocytes. Although galactosamine is known to exhibit hepatotoxic activity inducing ultimate necrosis of the hepatocytes, the data so far suggests that the sensitization to lipopolysaccharide is related only to the early metabolic effects of the hexosamine.

https://www.pnas.org/content/pnas/76/11/5939.full.pdf

Galactosamine-induced sensitization to the lethal effects of endotoxin.

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Galactosamine-induced sensitization to the lethal effects of endotoxin.