Juliane Ott

Acute Lung Injury Is Reduced in fat-1 Mice Endogenously Synthesizing n-3 Fatty Acids

RATIONALE Acute lung injury (ALI) remains an important cause of mortality in intensive care units. Inflammation is controlled by cytokines and eicosanoids derived from the n-6 fatty acid (FA) arachidonic acid (AA). The n-3 FA eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) and mediators derived from EPA and DHA possess reduced inflammatory potency. OBJECTIVES To determine whether the ability of fat-1 mice to endogenously convert n-6 to n-3 FA, and thus generate an increased ratio of n-3 to n-6 FA, impacts experimental ALI. METHODS We investigated ALI induced by intratracheal instillation of endotoxin in fat-1 and wild-type (WT) mice, assessing leukocyte numbers, protein concentration, and prostaglandin and cytokine levels in bronchoalveolar lavage fluid, as well as free FA in plasma, and lung ventilator compliance. Body temperature and motor activity of mice--markers of sickness behavior--were also recorded. MEASUREMENTS AND MAIN RESULTS In ALI, fat-1 mice exhibited significantly reduced leukocyte invasion, protein leakage, and macrophage inflammatory protein-2 and thromboxane B(2) levels in lavage fluid compared with WT mice. Free AA levels were increased in the plasma of WT mice in response to endotoxin, whereas EPA and DHA were increased in the fat-1 group. Ventilator compliance was significantly improved in fat-1 mice. Body temperature and motor activity were decreased in ALI. fat-1 Mice recovered body temperature and motor activity faster. CONCLUSIONS fat-1 Mice exhibited reduced features of ALI and sickness behavior. Increasing the availability of n-3 FA may thus be beneficial in critically ill patients with ALI.

Lipids in critical care medicine

While enteral nutrition is the basis for the critically ill, parenteral nutrition is often used when a sufficient enteral nutrition is not or not fully achievable. Lipids are a mainstay of caloric supply in both cases as they combine the provision of building blocks for the membranes and are precursors for function molecules including lipid mediators bearing the ability to influence immunity. Pro-inflammatory lipid mediators as prostaglandins and leukotrienes are generated from arachidonic acid (AA), a key member of the n-6 polyunsaturated fatty acids (PUFA). In contrast, lipid mediators derived from the n-3 fatty acids eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA) may exhibit less inflammatory properties compared to their AA-derived counterparts. Furthermore, intercellular mediators as resolvins and protectins are generated from n-3 fatty acids. They induce the resolution of inflammation, hence the name resolution phase interaction product-resolvin. Modulating the amount of PUFA and the n-6/n-3 ratio were investigated as means to change the inflammatory response and improve the outcome of patients. Experimental data showed that n-3 fatty acids may improve acute lung injury and sepsis in animal models. Studies in patients undergoing major surgery with application of n-3 fatty acids demonstrated beneficial effects in terms of reduction of length of stay and infectious complications. Clinical data hints that this concept may also improve outcome in critically ill patients. Additionally, experimental and clinical data suggest that a reduction in n-6 PUFA may change the immune response. In conclusion, modulating the amount of PUFA, the n-6/n-3 ratio and the composition of lipid emulsions may prove to be a useful means to improve the outcome of critically ill patients.

Immunomodulation by n-3- versus n-6-rich lipid emulsions in murine acute lung injury - role of platelet-activating factor receptor

Objective:Cytokines, platelet-activating factor (PAF), and eicosanoids control local and systemic inflammation. Conventional soybean oil-based lipid emulsions used for parenteral nutrition may aggravate the leukocyte inflammatory response or adhesion to the vessel wall. Fish oil-based lipid emulsions, in contrast, may exert an anti-inflammatory effect. Design:We investigated the impact of lipid emulsions on leukocyte invasion, protein leakage, and cytokines in two murine models of acute inflammation. Setting:Research laboratory of a university hospital. Subjects:Wild-type mice and PAF-receptor knockout mice. Interventions:Mice received an infusion of normal saline, fish oil- or soybean oil-based lipid emulsions before lipopolysaccharide challenge. Measurements and Main Results:Preinfusion with soybean oil resulted in increased leukocyte invasion, myeloperoxidase activity, and protein leakage and exaggerated release of tumor necrosis factor (TNF)-&agr; as well as macrophage inflammatory protein (MIP)-2 into the alveolar space after intratracheal lipopolysaccharide challenge. In contrast, preinfusion with fish oil reduced leukocyte invasion, myeloperoxidase activity, protein leakage, and TNF-&agr; as well as MIP-2 generation. Corresponding profiles were found in plasma following intraperitoneal lipopolysaccharide application: Soybean oil increased but fish oil decreased the TNF-&agr; and MIP-2 formation. When PAF-receptor-deficient mice were challenged with lipopolysaccharide, leukocyte invasion, lung tissue myeloperoxidase, cytokine generation, and alveolar protein leakage corresponded to those observed in wild-type animals. Fish oil and soybean oil lost their diverging effects on leukocyte transmigration, myeloperoxidase activity, leakage response, and cytokine generation in these knockout mice. Similarly, the differential impact of both lipid emulsions on these lipopolysaccharide-provoked changes was suppressed after pretreating animals with a PAF-receptor antagonist. Conclusions:Fish oil- vs. soybean oil-based lipid infusions exert anti- vs. proinflammatory effects in murine models of acute inflammation. The PAF/PAF-receptor-linked signaling appears to be a prerequisite for this differential profile.

Peroxisome proliferator-activated receptor-α reduces inflammation and vascular leakage in a murine model of acute lung injury

Acute lung injury (ALI) still represents a major cause of morbidity and mortality in intensive care units. Beneficial effects have been described after activation of the peroxisome proliferator-activated receptor (PPAR)-α by fibrates such as WY 14,643 (WY) in inflammatory models. In the present study, the impact of WY was investigated in a model of endotoxin (lipopolysaccharide; LPS)-induced ALI in mice. Intratracheal LPS challenge dose-dependently resulted in leukocyte invasion, protein leakage and release of tumour necrosis factor-α as well as macrophage inflammatory protein-2, prostaglandin E2 and thromboxane B2 into the alveolar space after 8 and 24 h. Lung ventilator compliance was reduced at both time-points. In isolated perfused mouse lungs, platelet-activating factor (PAF) induced an acute increase in pulmonary artery pressure (Ppa) and in capillary filtration coefficient (Kfc). WY significantly improved all features of ALI in vivo and blunted the increase in Kfc in isolated perfused mice lungs. In mice with genetic deletion of PPAR-α, all characteristics of ALI, Ppa, and Kfc were not significantly different from wild-type mice but WY failed to improve ALI and PAF-induced increase in Kfc. Activation of peroxisome proliferator-activated receptor-α by WY 14,643 reduced acute lung injury and vascular leakage. Fibrates may possess beneficial effects in acute pulmonary diseases beyond their lipid-lowering capability.

Immunomodulation by fish-oil containing lipid emulsions in murine acute respiratory distress syndrome

IntroductionAcute respiratory distress syndrome (ARDS) is a major cause of mortality in intensive care units. Patients with ARDS often require parenteral nutrition with lipid emulsions as essential components. Besides being an energy supply, these lipid emulsions might display differential modulatory effects on lung integrity and inflammation.MethodsIn a pre-emptive strategy, we investigated the impact of three different intravenously infused lipid emulsions on lung morphology, leukocyte invasion, protein leakage and cytokines in a murine model of ARDS. Mice received an infusion of normal saline solution, a pure long-chain triglycerides (LCT) emulsion, a medium-chain triglycerides (MCT) containing mixed emulsion (LCT/MCT), or a fish oil (FO) containing mixed emulsion (LCT/MCT/FO) before lipopolysaccharide (LPS) challenge.ResultsMice pre-infused with fish oil-containing lipid emulsion showed decreased leukocyte invasion, protein leakage, myeloperoxidase activity, and cytokine production in their alveolar space after LPS challenge compared to mice receiving LCT or LCT/MCT. In line with these findings, lung morphology assessed by histological staining after LPS-induced lung injury improved faster in the LCT/MCT/FO group. Concerning the above mentioned parameters, no significant difference was observed between mice infused with LCT or the combination of LCT and MCT.ConclusionFish oil-containing lipid emulsions might exert anti-inflammatory and pro-resolving effects in the murine model of acute lung injury. Partial replacement of n-6 fatty acids with n-3 fatty acids may thus be of benefit for critically ill patients at risk for ARDS which require parenteral nutrition.

Induction of lymphocyte apoptosis in a murine model of acute lung injury--modulation by lipid emulsions.

Acute lung injury (ALI) and sepsis are the major causes of mortality in intensive care units. Lymphocytes apoptosis is a hallmark feature of late detrimental sepsis. Parenteral nutrition in critically ill patients is based on lipid emulsions, but the impact of ALI and lipid emulsions on lymphocytes has not been defined. The effects of intravenously infused conventional soybean oil (SO)-based and new olive oil (OO)-based emulsions on splenic and blood lymphocytes were investigated in a murine model of endotoxin-induced ALI. After LPS challenge and infusion of lipid emulsions, apoptosis of lymphocytes and lung injury were assessed by flow cytometry, Western blot, and histology. Induction of ALI led to a time-dependent decline in splenic and circulating lymphocyte numbers and an increase in apoptosis, with engagement of the extrinsic apoptotic pathway. Both SO- and OO-based emulsions promoted the apoptosis of splenic lymphocytes before induction of ALI. The OO-based emulsions exhibited lower proapoptotic activity than did SO-based emulsions, an observation paralleled by the induction of survival factors. Induction of ALI increased the mortality of mice receiving SO-based emulsions compared with OO-based emulsions and normal saline. Splenic lymphocyte apoptosis is apparent in murine ALI, which may be linked to detrimental outcome. Infusion of lipid emulsions per se provoked splenic lymphocyte apoptosis. Infusion of SO-based emulsions further augmented the apoptosis of splenic and circulating lymphocytes in ALI and led to increased mortality in mice. These findings may be of relevance for patients experiencing ALI that require parenteral nutrition.

Immunomodulation by lipid emulsions in pulmonary inflammation: a randomized controlled trial

IntroductionAcute respiratory distress syndrome (ARDS) is a major cause of mortality in intensive care units. As there is rising evidence about immuno-modulatory effects of lipid emulsions required for parenteral nutrition of ARDS patients, we sought to investigate whether infusion of conventional soybean oil (SO)-based or fish oil (FO)-based lipid emulsions rich in either n-6 or n-3 fatty acids, respectively, may influence subsequent pulmonary inflammation.MethodsIn a randomized controlled, single-blinded pilot study, forty-two volunteers received SO, FO, or normal saline for two days. Thereafter, volunteers inhaled pre-defined doses of lipopolysaccharide (LPS) followed by bronchoalveolar lavage (BAL) 8 or 24 h later. In the murine model of LPS-induced lung injury a possible involvement of resolvin E1 (RvE1) receptor ChemR23 was investigated. Wild-type and ChemR23 knockout mice were infused with both lipid emulsions and challenged with LPS intratracheally.ResultsIn volunteers receiving lipid emulsions, the fatty acid profile in the plasma and in isolated neutrophils and monocytes was significantly changed. Adhesion of isolated monocytes to endothelial cells was enhanced after infusion of SO and reduced by FO, however, no difference of infusion on an array of surface adhesion molecules was detected. In neutrophils and monocytes, LPS-elicited generation of pro-inflammatory cytokines increased in the SO and decreased in the FO group. LPS inhalation in volunteers evoked an increase in neutrophils in BAL fluids, which decreased faster in the FO group. While TNF-α in the BAL was increased in the SO group, IL-8 decreased faster in the FO group. In the murine model of lung injury, effects of FO similar to the volunteer group observed in wild-type mice were abrogated in ChemR23 knockout mice.ConclusionsAfter infusion of conventional lipid emulsions, leukocytes exhibited increased adhesive and pro-inflammatory features. In contrast, FO-based lipid emulsions reduced monocyte adhesion, decreased pro-inflammatory cytokines, and neutrophil recruitment into the alveolar space possibly mediated by ChemR23-signaling. Lipid emulsions thus exert differential effects in human volunteers and mice in vivo.Trial registrationDRKS00006131 at the German Clinical Trial Registry, 2014/05/14