E. coli hemolysin-induced lipid mediator metabolism in alveolar macrophages: impact of eicosapentaenoic acid

Impact of Bacterial Toxins in the Lungs

Bacterial toxins play a key role in the pathogenesis of lung disease. Based on their structural and functional properties, they employ various strategies to modulate lung barrier function and to impair host defense in order to promote infection. Although in general, these toxins target common cellular signaling pathways and host compartments, toxin- and cell-specific effects have also been reported. Toxins can affect resident pulmonary cells involved in alveolar fluid clearance (AFC) and barrier function through impairing vectorial Na⁺ transport and through cytoskeletal collapse, as such, destroying cell-cell adhesions. The resulting loss of alveolar-capillary barrier integrity and fluid clearance capacity will induce capillary leak and foster edema formation, which will in turn impair gas exchange and endanger the survival of the host. Toxins modulate or neutralize protective host cell mechanisms of both the innate and adaptive immunity response during chronic infection. In particular, toxins can either recruit or kill central players of the lung's innate immune responses to pathogenic attacks, i.e., alveolar macrophages (AMs) and neutrophils. Pulmonary disorders resulting from these toxin actions include, e.g., acute lung injury (ALI), the acute respiratory syndrome (ARDS), and severe pneumonia. When acute infection converts to persistence, i.e., colonization and chronic infection, lung diseases, such as bronchitis, chronic obstructive pulmonary disease (COPD), and cystic fibrosis (CF) can arise. The aim of this review is to discuss the impact of bacterial toxins in the lungs and the resulting outcomes for pathogenesis, their roles in promoting bacterial dissemination, and bacterial survival in disease progression.

A Matter of Fat

Acute respiratory disease syndrome (ARDS) is a common complication of critical illness, associated with significant morbidity, prolonged intensive care unit (ICU) and hospital stay, and increased mortality. Inflammation plays a central role in ARDS, with inflammatory eicosanoid mediators produced from the ω-6 fatty acid arachidonic acid, such as leukotriene B4, being involved. The ω-3 fatty acids found in fish oil exert anti-inflammatory effects, including decreasing production of inflammatory eicosanoids from arachidonic acid. The ω-3 fatty acids are effective in models relevant to ARDS. Several randomized controlled trials of enteral formulas rich in ω-3 fatty acids, often in combination with other bioactive substances, have been conducted in patients with ARDS. Four of these trials reported marked clinical benefits, 2 reported no effect, and 1 reported a negative impact. A systematic review and meta-analysis of these 7 trials identified no overall effect on ventilator-free days or on ICU-free days. There was a small reduction in ICU length of stay and no overall effect on mortality. However, the authors formally identified that trials that used high fat in both treatment and control groups showed a significant reduction in mortality, while trials that used a high, or higher, fat treatment and a low-fat control group showed a trend toward an increase in mortality. It is concluded that differences in outcome reported among these studies largely relate to the relative fat contents of the treatment and control formulas. Further, it is concluded that high-fat enteral formulas should not be used in this patient group.

Hydroxyeicosapentaenoic acids from the Pacific krill show high ligand activities for PPARs

PPARs regulate the expression of genes for energy metabolism in a ligand-dependent manner. PPARs can influence fatty acid oxidation, the level of circulating triglycerides, glucose uptake and insulin sensitivity. Here, we demonstrate that 5-hydroxyeicosapentaenoic acid (HEPE), 8-HEPE, 9-HEPE, 12-HEPE and 18-HEPE (hydroxylation products of EPA) obtained from methanol extracts of Pacific krill (Euphausia pacifica) can act as PPAR ligands. Two of these products, 8-HEPE and 9-HEPE, enhanced the transcription levels of GAL4-PPARs to a significantly greater extent than 5-HEPE, 12-HEPE, 18-HEPE, EPA, and EPA ethyl-ester. 8-HEPE also activated significantly higher transcription of GAL4-PPARα, GAL4-PPARγ, and GAL4-PPARδ than EPA at concentrations greater than 4, 64, and 64 μM, respectively. We also demonstrated that 8-HEPE increased the expression levels of genes regulated by PPARs in FaO, 3T3-F442A, and C2C12 cells. Furthermore, 8-HEPE enhanced adipogenesis and glucose uptake. By contrast, at the same concentrations, EPA showed weak or little effect, indicating that 8-HEPE was the more potent inducer of physiological effects.

Fish oil supplementation alters levels of lipid mediators of inflammation in microenvironment of acute human wounds

Chronic wounds often result from prolonged inflammation involving excessive polymorphonuclear leukocyte activity. Studies show that the ω-3 polyunsaturated fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) found in fish oils generate bioactive lipid mediators that reduce inflammation and polymorphonuclear leukocyte recruitment in numerous inflammatory disease models. This study's purpose was to test the hypotheses that boosting plasma levels of EPA and DHA with oral supplementation would alter lipid mediator levels in acute wound microenvironments and reduce polymorphonuclear leukocyte levels. Eighteen individuals were randomized to 28 days of either EPA+DHA supplementation (Active Group) or placebo. After 28 days, the Active Group had significantly higher plasma levels of EPA (p<0.001) and DHA (p<0.001) than the Placebo Group and significantly lower wound fluid levels of two 15-lipoxygenase products of ω-6 polyunsaturated fatty acids (9-hydroxyoctadecadienoic acid [p=0.033] and 15-hydroxyeicosatrienoic acid [p=0.006]), at 24 hours postwounding. The Active Group also had lower mean levels of myeloperoxidase, a leukocyte marker, at 12 hours and significantly more reepithelialization on Day 5 postwounding. We suggest that lipid mediator profiles can be manipulated by altering polyunsaturated fatty acid intake to create a wound microenvironment more conducive to healing.

Pneumolysin-mediated activation of NFkappaB in human neutrophils is antagonized by docosahexaenoic acid

This study was designed to investigate the relationship between influx of extracellular Ca(2+), activation of NFkappaB and synthesis of interleukin-8 (IL-8) following exposure of human neutrophils to subcytolytic concentrations (8.37 and 41.75 ng/ml) of the pneumococcal toxin, pneumolysin, as well as the potential of the omega-3 polyunsaturated fatty acid, docosahexaenoic acid, to antagonize these events. Activation and translocation of NFkappaB were measured using a radiometric electrophoretic mobility shift assay, while influx of extracellular Ca(2+) and synthesis of IL-8 were determined using a radioassay and an ELISA procedure, respectively. Exposure of neutrophils to pneumolysin was accompanied by influx of Ca(2+), activation of NFkappaB, and synthesis of IL-8, all of which were eliminated by inclusion of the Ca(2+)-chelating agent, EGTA (10 m m), in the cell-suspending medium, as well as by pretreatment of the cells with docosahexaenoic acid (5 and 10 microg/ml). The antagonistic effects of docosahexaenoic acid on these pro-inflammatory interactions of pneumolysin with neutrophils were not attributable to inactivation of the toxin, and required the continuous presence of the fatty acid. These observations demonstrate that activation of NFkappaB and synthesis of IL-8, following exposure of neutrophils to pneumolysin are dependent on toxin-mediated influx of Ca(2+) and that these potentially harmful activities of the toxin are antagonized by docosahexaenoic acid.

Mediator generation and signaling events in alveolar epithelial cells attacked by S. aureus alpha-toxin

Staphylococcus aureus alpha-toxin is a pore-forming bacterial exotoxin that has been implicated as a significant virulence factor in human staphylococcal diseases. In primary cultures of rat pneumocyte type II cells and the human A549 alveolar epithelial cell line, purified alpha-toxin provoked rapid-onset phosphatidylinositol (PtdIns) hydrolysis as well as liberation of nitric oxide and the prostanoids PGE(2), PGI(2), and thromboxane A(2). In addition, sustained upregulation of proinflammatory interleukin (IL)-8 mRNA expression and protein secretion occurred. "Priming" with low-dose IL-1beta markedly enhanced the IL-8 response to alpha-toxin, which was then accompanied by IL-6 appearance. The cytokine response was blocked by the intracellular Ca(2+)-chelating reagent 1,2-bis(2-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid, the protein kinase C inhibitor bis-indolyl maleimide I, as well as two independent inhibitors of nuclear factor-kappaB activation, pyrrolidine dithiocarbamate and caffeic acid phenethyl ester. We conclude that alveolar epithelial cells are highly reactive target cells of staphylococcal alpha-toxin. alpha-Toxin pore-associated transmembrane Ca(2+) flux and PtdIns hydrolysis-related signaling with downstream activation of protein kinase C and nuclear translocation of nuclear factor-kappaB are suggested to represent important underlying mechanisms. Such reactivity of the alveolar epithelial cells may be relevant for pathogenic sequelae in staphylococcal lung disease.