Escaping the Phagocytic Oxidative Burst: The Role of SODB in the Survival of Pseudomonas aeruginosa Within Macrophages

Reactive oxygen species (ROS) are small oxygen-derived molecules that are used to control infections by phagocytic cells. In macrophages, the oxidative burst produced by the NOX2 NADPH-oxidase is essential to eradicate engulfed pathogens by both oxidative and non-oxidative killing. Indeed, while the superoxide anion (O2-) produced by NOX2, and the other ROS derived from its transformation, can directly target pathogens, ROS also contribute to activation of non-oxidative microbicidal effectors. The response of pathogens to the phagocytic oxidative burst includes the expression of different enzymes that target ROS to reduce their toxicity. Superoxide dismutases (SODs) are the primary scavengers of O2-, which is transformed into H2O2. In the Gram-negative Salmonella typhimurium, periplasmic SODCI has a major role in bacterial resistance to NOX-mediated oxidative stress. In Pseudomonas aeruginosa, the two periplasmic SODs, SODB, and SODM, appear to contribute to bacterial virulence in small-animal models. Furthermore, NOX2 oxidative stress is essential to restrict P. aeruginosa survival in macrophages early after infection. Here, we focused on the role of P. aeruginosa SODs in the counteracting of the lethal effects of the macrophage oxidative burst. Through this study of the survival of sod mutants in macrophages and the measurement of ROS in infected macrophages, we have identified a dual, antagonistic, role for SODB in P. aeruginosa survival. Indeed, the survival of the sodB mutants, but not of the sodM mutants, was greater than that of the wild-type (WT) bacteria early after infection, and sodB-infected macrophages showed higher levels of O2- and lower levels of H2O2. This suggests that SODB contributes to the production of lethal doses of H2O2 within the phagosome. However, later on following infection, the sodB mutants survived less that the WT bacteria, which highlights the pro-survival role of SODB. We have explained this defensive role through an investigation of the activation of autophagy, which was greater in the sodB-infected macrophages

Involvement of Phospholipids in the Mechanism of Insulin Action in HEPG2 Cells

Summary The mechanism of action by which insulin increases phosphatidic acid (PA) and diacylglycerol (DAG) levels was investigated in cultured hepatoma cells (HEPG2). Insulin stimulated phosphatidylcholine (PC) and phosphatidylinositol (PI) degradation through the activation of specific phospholipases C (PLC). The DAG increase appears to be biphasic. The early DAG production seems to be due to PI breakdown, probably through phosphatidyl-inositol-3-kinase (PI3K) involvement, whereas the delayed DAG increase is derived directly from the PC-PLC activity. The absence of phospholipase D (PLD) involvement was confirmed by the lack of PC-derived phosphatidylethanol production. Experiments performed in the presence of R59022, an inhibitor of DAG-kinase, indicated that PA release is the result of the DAG-kinase activity on the DAG produced in the early phase of insulin action

Proliferative effect of ammodytin L from the venom of Vipera ammodytes on 208F rat fibroblasts in culture

Ammodytin L, purified from the venom of Vipera ammodytes, triggers a rapid and dramatic lytic process in myotubes in vitro, as well as in differentiated muscle cells in vivo, through a mechanism that is not well understood. Despite its great sequence similarity to phospholipase A2, it is devoid of any enzyme activity. Data on artificial membranes demonstrating a direct interaction between this toxin and the hydrophobic core of the lipid bilayer suggest that the toxin also acts on the lipid microenvironment in cell membranes. Recent experiments on living cells do not confirm this hypothesis, and a more intricate mechanism is proposed. In vitro, ammodytin L has necrotic effects only in well-differentiated myogenic cells, whereas other cell types such as platelets, red blood cells and lymphocytes show neither morphological nor functional alterations. In this work we demonstrate that rat 208F fibroblasts in culture after ammodytin L challenge increase [3H]thymidine incorporation, indicating that this toxin has a myogenic effect. Moreover, ammodytin L increases intracellular Ca2+ by acting on intracellular stores probably by activating a phosphatidylinositol-specific phospholipase C. Preincubation of the cells with ammodytin L did not prevent the massive Ca2+ release evoked by bradykinin, a phenomenon observed when fibroblasts were incubated with both thapsigargin and ionomycin. Heparin, an agent that inhibits the necrotic effect of the myotoxin in myotubes, also reduces the effect of ammodytin L on DNA synthesis. Heparin inhibits only the late sustained increase in intracellular Ca2+ induced by the toxin

Thyroid hormone inhibition in L6 myoblasts of IGF-I-mediated glucose uptake and proliferation: New roles for integrin αvβ3

Thyroid hormones L-thyroxine (T4) and 3,3′,5-triiodo-L-thyronine (Se