Contribution of neutrophils to lipopolysaccharide-induced tumor necrosis factor production and mortality in a carrageenan-pretreated mouse model

Bupivacaine???s Action on the Carrageenan-Induced Inflammatory Response in Mice: Cytokine Production by Leukocytes After Ex-Vivo Stimulation

We aimed to study the effect of bupivacaine on the systemic response elicited by intraplantar injection of carrageenan. To that purpose, we studied the effects of carrageenan, bupivacaine, or both on the production of tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, and IL-10 by whole blood cultured in the presence of lipopolysaccharide (LPS) and of heat-killed Staphylococcus Aureus Cowan (SAC). Mice received a hindpaw injection of carrageenan with or without encapsulated IM bupivacaine given contralaterally. Whole blood was sampled 15 h later and cultured for 24 h with LPS or SAC. The amounts of TNF-alpha, IL-1beta, and IL-10 in the supernatants were measured. In the presence of LPS or SAC, proinflammatory cytokine (TNF-alpha and IL-1beta) production was increased after carrageenan. Bupivacaine prevented this inflammatory response: 992 +/- 102 versus 2146 +/- 338 versus 919 +/- 116 pg/mL for TNF-alpha (bupivacaine + carrageenan versus carrageenan versus control after LPS stimulation). This effect of bupivacaine was less after SAC stimulation. Moreover, IL-10 was not involved in the inhibition of proinflammatory cytokine production observed after treatment by bupivacaine alone. These experiments show that carrageenan-induced hindpaw inflammation modifies the blood cell reactivity to LPS and SAC and that bupivacaine regulates the systemic response elicited by carrageenan. Furthermore, IL-10 does not seem to be a factor of the antiinflammatory response induced by bupivacaine. The precise mechanism underlying this effect of bupivacaine remains to be clarified.

PI3K-Akt pathway suppresses coagulation and inflammation in endotoxemic mice

OBJECTIVE

In endotoxemia, lipopolysaccharide (LPS) induces a systemic inflammatory response and intravascular coagulation. Monocytes orchestrate the innate immune response to LPS by expressing a variety of pro-inflammatory cytokines, such as tumor necrosis factor-alpha (TNF-alpha), and the procoagulant molecule, tissue factor (TF). In this study, we analyzed the role of the phosphoinositide 3-kinase (PI3K)-Akt pathway in the activation of coagulation and the innate immune response in a mouse model of endotoxemia.

METHODS AND RESULTS

Wortmannin and LY294002 were used to inhibit the PI3K-Akt pathway. We found that wortmannin inhibited LPS-induced Akt phosphorylation in blood cells. Inhibition of the PI3K-Akt pathway significantly increased TF mRNA expression in blood cells, TF antigen, and thrombin-antithrombin III levels in the plasma, and fibrin deposition in the liver of endotoxemic mice. Inhibition of the PI3K-Akt pathway also strongly enhanced LPS-induced cytokine expression and the levels of soluble E-selectin in the plasma, suggesting enhanced activation of both monocytes and endothelial cells. Wortmannin treatment also increased the number of macrophages in the liver and kidney of endotoxemic mice. Finally, wortmannin and LY294002 dramatically reduced the survival time of endotoxemic mice.

CONCLUSIONS

These data suggest that the PI3K-Akt pathway suppresses LPS-induced inflammation and coagulation in endotoxemic mice.

Therapeutic effects of lysophosphatidylcholine in experimental sepsis

Sepsis represents a major cause of death in intensive care units. Here we show that administration of lysophosphatidylcholine (LPC), an endogenous lysophospholipid, protected mice against lethality after cecal ligation and puncture (CLP) or intraperitoneal injection of Escherichia coli. In vivo treatment with LPC markedly enhanced clearance of intraperitoneal bacteria and blocked CLP-induced deactivation of neutrophils. In vitro, LPC increased bactericidal activity of neutrophils, but not macrophages, by enhancing H(2)O(2) production in neutrophils that ingested E. coli. Incubation with an antibody to the LPC receptor, G2A, inhibited LPC-induced protection from CLP lethality and inhibited the effects of LPC in neutrophils. G2A-specific antibody also blocked the inhibitory effects of LPC on certain actions of lipopolysaccharides (LPS), including lethality and the release of tumor necrosis factor-alpha (TNF-alpha) from neutrophils. These results suggest that LPC can effectively prevent and treat sepsis and microbial infections.

Endotoxins stimulate neutrophil adhesion followed by synthesis and release of platelet-activating factor in microparticles

Lipopolysaccharides and triacyl-cysteine-modified proteins of Gram-negative and positive organisms are potent endotoxins. Animal models show that the receptor for platelet-activating factor (PAF) is responsible for many of the deleterious effects of endotoxin, where regulated, localized PAF production localizes the inflammatory response. In contrast, biologically active analogs of PAF (PAF-like lipids) are generated by oxidative attack on phospholipids by chemical reactions that are unregulated and unlocalized. The identity and distribution of the PAF receptor ligand in endotoxemia is unknown. We found human polymorphonuclear leukocytes (PMNs) were a significant source of PAF receptor agonists after stimulation by either class of endotoxin. Production of PAF receptor agonists required that the PMN adhere to a surface, and adhesion (and therefore accumulation of PAF-like bioactivity) in response to endotoxic stimulation was delayed for several minutes. PAF-like oxidized phospholipids were found by mass spectroscopy, but biosynthetic PAF accounted for most of the phospholipid agonists arising from endotoxic stimulation. A significant portion of the PAF made by PMNs was secreted, in contrast to its near complete retention by other inflammatory cells. Endotoxic stimulation induced a respiratory burst with the production of superoxide and the formation and shedding of microparticles. Free and microparticle-bound PAF appeared in the media, and blocking microvesiculation with calpeptin blocked PAF release. The released material activated platelets, and platelets co-aggregated with endotoxin-stimulated PMNs. Adherent PMNs therefore behave differently than suspended cells and are a significant source of free PAF after endotoxin exposure. Leukocytes can couple endotoxic challenge to the widespread circulatory and inflammatory effects of endotoxin.

Regulation by C5a of neutrophil activation during sepsis

In sepsis, there is evidence that excessive C5a generation leads to compromised innate immune functions, being associated with poor outcome. We now report that in vitro exposure of neutrophils to C5a causes increased levels of IkappaBalpha, decreased NF-kappaB-dependent gene transcription of TNFalpha, and decreased lipopolysaccharide (LPS)-induced TNFalpha production. Similar findings were obtained with neutrophils from cecal ligation/puncture (CLP)-induced septic rats. Such changes were reversed by antibody-induced in vivo blockade of C5a. In contrast, in vitro exposure of alveolar macrophages to C5a and LPS resulted in enhanced production of TNFalpha and no increase in IkappaBalpha. These data suggest that CLP-induced sepsis causes a C5a-dependent dysfunction of neutrophils, which is characterized by altered signaling associated with NF-kappaB activation.

Changes in the response of neutrophils to endotoxin priming following major abdominal surgery

Endotoxin (ETX) primes polymorphonuclear cells (PMNs) for the subsequent release of reactive oxygen species (ROS) in response to various stimulants such as phorbol myristate acetate (PMA). Although PMNs contribute to oxidative stress after stimulation by standard stimulants and after priming by many humoral factors, it is unknown whether the PMNs from patients at different postoperative times exhibit the same response to the same standard stimulant. We examined the response of PMA-induced production of ROS from PMNs at various intervals after major abdominal surgery in response to ETX priming. This study was a prospective clinical and laboratory study conducted over a 7-day period that involved 25 patients who were referred for elective major abdominal surgery (8 for gastric cancer, 9 for colonic cancer, 8 for rectal cancer). Blood was sampled on the day before operation and on postoperative days (PODs) 1, 3, and 7. For each sample we measured luminol-dependent chemiluminescence (CL), the time to peak counts (Tmax) of PMNs stimulated by PMA, and the serum ETX level. We studied the correlation between CL and ETX in samples from PODs 1 and 3. We also studied the CL of PMNs on PODs 1 and 3 preincubated (primed) with various concentrations of ETX (0, 20, 40, 60, and 100 pg/ml). We found that CL decreased on POD 1 compared with the preoperative level (p <0.05) because of the decreased Tmax. The level of CL per 1 ml of whole blood, however, was higher on PODs 1 and 3 than preoperatively. During this time, leukocytosis should compensate for the impaired production of ROS by an individual PMN. The serum ETX level was increased on POD 1 (p <0.05). There was a negative correlation between CL and ETX on POD 1 (correlation coefficient ?0.62, p < 0.01) and a positive correlation on POD 3 (0.61, p <0.01). CL on POD 3 was accelerated by ETX priming, but the CL on POD 1 was depressed by the priming using a low concentration of ETX. The mode of the response of PMNs to ETX priming differed between PODs 1 and 3. On POD 1 the responses of PMNs to environmental stimulants is suppressed, but by POD 3 these responses had increased.