Alteration of platelet-activating factor-induced signal transduction in macrophages by n-3 fatty acids

Innate immunity signaling pathways: links between immunonutrition and responses to sepsis

Septic infections in patients treated in intensive care units show the highest mortality rates. Despite advances in treatment methods, there is still no therapy available to efficiently reduce the excessive inflammatory response, which can increase the risk of multiple organ failure. One of the ways to discover new, more efficient treatment methods involves regulating the mechanisms of inflammatory response to a massive infection. Toll-like receptors (TLRs) that recognize pathogen-associated molecular patterns play a significant role in innate antibacterial and inflammatory responses. The regulatory impact of immunonutrition on TLR expression in septic patients seems to be a promising research direction. This paper presents the main mechanisms for the innate immune response to lipopolysaccharide, based on the research results for both TLR-dependent and independent signaling pathways. Special emphasis was put on the research results for the TLR-dependent immune response and the anti-bacterial/anti-inflammatory response after applying immunonutrition with increased concentrations of glutamine and unsaturated fatty acids.

Parenteral nutrition with fish oil modulates cytokine response in patients with sepsis

Infusion of fish oil-based (n-3) lipids may influence leukocyte function and plasma lipids in critical care patients. Twenty-one patients with sepsis requiring parenteral nutrition were randomized to receive an n-3 lipid emulsion rich in eicosapentaenoic acid and docosahexaenoic acid or a conventional (n-6) lipid emulsion (index fatty acid: arachidonic acid) for 5 days. The impact on plasma-free fatty acids, mononuclear leukocyte cytokine generation, and membrane fatty acid composition was examined. Cytokine synthesis by isolated mononuclear leukocyte was elicited by endotoxin. Before the onset of lipid infusion therapy, plasma-free fatty acid concentrations were greatly increased in septic patients, with arachidonic acid by far surpassing eicosapentaenoic acid and docosahexaenoic acid, a feature maintained during conventional lipid infusion. Within 2 days of fish oil infusion, free n-3 fatty acids increased, and the n-3/n-6 ratio was reversed, with rapid incorporation of n-3 fatty acids into mononuclear leukocyte membranes. Generation of proinflammatory cytokines by mononuclear leukocytes was markedly amplified during n-6 and was suppressed during n-3 lipid application. After termination of lipid administration, free n-3 fatty acid concentrations and mononuclear leukocyte cytokine synthesis returned to preinfusion values. Use of lipid infusions might allow us to combine intravenous alimentation with differential impact on inflammatory events and immunologic functions in patients with sepsis.

Phosphoinositide fatty acids regulate phosphatidylinositol 5-kinase, phospholipase C and protein kinase C activities

PtdIns(4,5)P(2) generally results from phosphorylation of PtdIns(4)P by the phosphatidylinositol 5-kinase (PtdIns5-K). Its hydrolysis by phospholipase C (PLC) yields inositol 1,4,5-trisphosphate and diacylglycerol, which stimulates protein kinase C (PKC). We show that epithelial cells of the cockroach rectum contain three different inositol lipids: PtdIns(4,5)P(2), PtdIns(4)P, and PtdIns. They are composed of six major fatty acids: palmitic (16:0) stearic (18:0), oleic (18:1n--9), linoleic (18:2n--6), linolenic (18:3n--3), and arachidonic (20:4n-6) acids. The fatty acid preference of each of the above enzymes was evaluated by incorporating different fatty acids in pairs into membrane lipids. Incorporation of 16:0 plus 18:1n--9 provoked an increase in PtdIns(4,5)P2-PLC activity and a decrease in PtdIns5-K activity. In contrast, incorporation of 16:0 plus 18:3n--3 led to a potentiation of PtdIns5-K activity and a decrease in PtdIns(4,5)P(2)-PLC activity. Furthermore, PLC and PtdIns5-K acted preferentially on substrates containing 18:3n--3, and 18:3n--3-containing diacylglycerol specifically potentiated PKC activity. Thus, we propose that the fatty acids that make up the phosphoinositides function as intracellular modulators of the activity of certain enzymes.

Rationales for treating IgA nephropathies

An outline is given of the pathophysiology of IgA nephropathy (IgA) in order to emphasize the role of eicosanoids, angiotensin II, and reactive oxygen species. ACE inhibitors and early corticosteroid usage are prime therapies. Tonsillectomy is to be considered, certainly for individual cases. It is logical that other components of a cocktail could be (i) thromboxane antagonists, (ii) leukotriene antagonists, or (iii) PAF antagonist. In theory there should be benefit from antioxidants. Fish oils have not come up to expectation. PDGF aptamers look promising for the prevention of mesangial cell proliferation. Heparins are not used in the way that they could be. Various other agents could help reduce decline.

Differential kinetics for induction of interleukin-6 mRNA expression in murine peritoneal macrophages: evidence for calcium-dependent and independent-signalling pathways

It is presently unclear what role elevations in intracellular calcium concentration ([Ca2+]i) play in the control of monokine secretion, or whether such alterations underlie the ability of physiologic stimuli to induce production of these important signalling molecules. To address these issues, we have performed experiments in murine peritoneal macrophages to determine whether lipopolysaccharide (LPS) or interferon gamma (IFN-gamma) initiate production of the proinflammatory monokine interleukin 6 (IL-6) concomitant with elevations in [Ca2+]i and with kinetics similar to that seen with known Ca2+ mobilizing agents. Alterations in [Ca2+]i after treatment with LPS, IFN-gamma, platelet activating factor (PAF), or thapsigargin were measured by fluorimetric methods. These effects were compared with the ability of each to induce IL-6 mRNA expression as measured by semiquantitative reverse-transcribed polymerase chain reactions. We report that neither LPS nor IFN-gamma elicited detectable elevations in [Ca2+]i but that both up-regulated expression of IL-6 mRNA expression within 60 min. In contrast, experiments using either thapsigargin or PAF showed rapid and dramatic elevations in [Ca2+]i with marked increases in IL-6 mRNA expression, as quickly as 15 min after initial exposure. Elevations in mRNA encoding IL-6 by thapsigargin and PAF were found to occur in a dose-dependent manner, mirroring their ability to elicit elevations in [Ca2+]i. These data demonstrate that LPS and IFN-gamma induce IL-6 message expression by means of Ca2+-independent signalling pathways. Furthermore, Ca2+-mobilizing agents that evoke monokine message expression do so far more rapidly than do LPS or IFN-gamma. Taken in concert, these data are consistent with the hypothesis that multiple signalling pathways exist by which production of proinflammatory monokines are initiated.

Lipids and the immune response

The effects of fatty acids on immune responses have been studied since the early 1970s, but much controversy still remains. The present review examines recent studies in both animals and in humans, and highlights some new and exciting ideas concerning the mechanism by which fatty acids may affect immune responses in both normal and pathological situations, an area which is likely to progress rapidly over the next few years.