The lipid biology of sepsis Amunugama, Kaushalya; Pike, Daniel P.; Ford, David A.
Journal of lipid research,
01/2021, Volume:
62
Journal Article
Peer reviewed
Open access
Sepsis, defined as the dysregulated immune response to an infection leading to organ dysfunction, is one of the leading causes of mortality around the globe. Despite the significant progress in ...delineating the underlying mechanisms of sepsis pathogenesis, there are currently no effective treatments or specific diagnostic biomarkers in the clinical setting. The perturbation of cell signaling mechanisms, inadequate inflammation resolution, and energy imbalance, all of which are altered during sepsis, are also known to lead to defective lipid metabolism. The use of lipids as biomarkers with high specificity and sensitivity may aid in early diagnosis and guide clinical decision making. In addition, identifying the link between specific lipid signatures and their role in sepsis pathology may lead to novel therapeutics. In this review, we discuss the recent evidence on dysregulated lipid metabolism both in experimental and human sepsis focused on bioactive lipids, fatty acids, and cholesterol as well as the enzymes regulating their levels during sepsis. We highlight not only their potential roles in sepsis pathogenesis but also the possibility of using these respective lipid compounds as diagnostic and prognostic biomarkers of sepsis.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Neutrophils are the most abundant white blood cells recruited to the sites of infection and inflammation. During neutrophil activation, myeloperoxidase (MPO) is released and converts hydrogen ...peroxide to hypochlorous acid (HOCl). HOCl reacts with plasmalogen phospholipids to liberate 2-chlorofatty aldehyde (2-ClFALD), which is metabolized to 2-chlorofatty acid (2-ClFA). 2-ClFA and 2-ClFALD are linked with inflammatory diseases and induce endothelial dysfunction, neutrophil extracellular trap formation (NETosis) and neutrophil chemotaxis. Here we examine the neutrophil-derived chlorolipid production in the presence of pathogenic
strain CFT073 and non-pathogenic
strain JM109. Neutrophils cocultured with CFT073
strain and JM109
strain resulted in 2-ClFALD production. 2-ClFA was elevated only in CFT073 coculture. NETosis is more prevalent in CFT073 cocultures with neutrophils compared to JM109 cocultures. 2-ClFA and 2-ClFALD were both shown to have significant bactericidal activity, which is more severe in JM109
. 2-ClFALD metabolic capacity was 1000-fold greater in neutrophils compared to either strain of
. MPO inhibition reduced chlorolipid production as well as bacterial killing capacity. These findings indicate the chlorolipid profile is different in response to these two different strains of
bacteria.
Dysregulated lipid metabolism is common in infection and inflammation and is a part of the complex milieu underlying the pathophysiological sequelae of disease. Sepsis is a major cause of mortality ...and morbidity in the world and is characterized by an exaggerated host response to an infection. Metabolic changes, including alterations in lipid metabolism, likely are important in sepsis pathophysiology. Here, we designed an
cell culture model using endothelial cells,
, and neutrophils to mimic sepsis in a simplified cell model. Lipid alterations were studied in the presence of the pathogenic
strain CFT073 and non-pathogenic
strain JM109. We employed untargeted lipidomics to first identify lipid changes and then targeted lipidomics to confirm changes. Both unique and shared lipid signatures were identified in cocultures with these
strains. In the absence of neutrophils, the CFT073 strain elicited alterations in lysophosphatidylcholine and diglyceride molecular species during coculture while both strains led to increases in phosphatidylglycerols. Lipid alterations in these cocultures changed with the addition of neutrophils. In the presence of neutrophils with
and endothelial cells, triglyceride increases were a unique response to the CFT073 strain while phosphatidylglycerol and diglyceride increases occurred in response to both strains. Phosphatidylethanolamine also increased in neutrophils,
and endothelial cells cocultures, and this response was greater in the presence of the CFT073 strain. We further evaluated changes in phosphatidylethanolamine in a rat model of sepsis, which showed multiple plasma phosphatidylethanolamine molecular species were elevated shortly after the induction of sepsis. Collectively, these findings demonstrate unique lipid responses by co-cultures of
with endothelial cells which are dependent on the
strain as well as the presence of neutrophils. Furthermore, increases in phosphatidylethanolamine levels in CFT073 urosepsis
, endothelial cell, neutrophil cocultures were similarly observed in the plasma of septic rats.
Plasmalogens are a class of phospholipids containing vinyl ether linked aliphatic groups at the sn-1 position. Plasmalogens are known to contain 16- and 18-carbon aliphatic groups at the sn-1 ...position. Here, we reveal that the human neutrophil plasmenylethanolamine pool uniquely includes molecular species with very long carbon chain (VLC) aliphatic groups, including 20-, 22- and 24-carbon vinyl ether linked aliphatic groups at the sn-1 position. We identified these novel VLC plasmalogen species by electrospray ionization mass spectrometry methods. VLC plasmalogens were only found in the neutrophil plasmenylethanolamine pool. During neutrophil activation, VLC plasmenylethanolamines undergo myeloperoxidase-dependent oxidation to produce VLC 2-chlorofatty aldehyde and its oxidation product, 2-chlorofatty acid (2-ClFA). Furthermore, plasma concentrations of VLC 2-ClFA are elevated in human sepsis. These studies demonstrate for the first time VLC plasmenylethanolamine molecular species, their myeloperoxidase-mediated chlorolipid products and the presence of these chlorolipids in human sepsis.
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•Novel very long chain (VLC) plasmenylethanolamine molecular species are discovered in human neutrophils.•VLC plasmenylethanolamines undergo myeloperoxidase dependent oxidation to produce new VLC chlorinated lipids.•VLC 2-chlorofatty acids are elevated in human sepsis.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Neutrophils play vital roles in host defense against infections and acute inflammation. They are the major type of white blood cells first to arrive at the site of infection. Neutrophils are equipped ...with three major microorganism‐killing mechanisms: phagocytosis, release of antibacterial enzymes, and formation of neutrophil extracellular traps (NET). During neutrophil activation, the primary granules release myeloperoxidase (MPO), which is a major antibacterial enzyme. MPO catalyzes hydrogen peroxide and chloride to produce hypochlorous acid (HOCl). HOCl has a significant role as an antimicrobial agent and can also have deleterious effects on host cells. Previous studies have shown that HOCl targets vinyl ether bond at the sn‐1 position of plasmalogen phospholipids to liberate 2‐chlorofatty aldehyde (2‐ClFALD). 2‐ClFALD further gets oxidized to 2‐chlorofatty acids (2‐ClFA). 2‐ClFALD and 2‐ClFA are linked with inflammatory diseases such as endotoxemia, sepsis and atherosclerosis. The roles of 2‐ClFALD and 2‐ClFA have been explored in endothelial dysfunction, endoplasmic reticulum stress, apoptosis in monocytes, neutrophil chemotaxis and as a mediator of NET formation. Here we tested the hypothesis that the neutrophils are activated by bacterial stimuli to produce 2‐ClFALD and 2‐ClFA and the production may vary with the bacterial strain. We co‐cultured human neutrophils with CFT073 and JM109, pathogenic and non‐pathogenic E.coli strains, respectively. 2‐ClFALD production was significantly increased when neutrophils were incubated with either E.coli strains compared to control neutrophils. Interestingly, 2‐ClFA was only increased in CFT073 co‐culture. We have also observed that neutrophils killed more JM109 cells compared to CFT073 cells. However, CFT073 induced more NET formation suggesting the higher 2‐ClFA might be mediating NET formation. Furthermore, JM109 was more susceptible to killing by 2‐ClFALD and 2‐ClFA indicating their potential role in bactericidal activity. 2‐ClFA and 2‐ClFALD production was significantly reduced in neutrophil and E.coli co‐cultures by the addition of amino triazole (ATZ), an MPO inhibitor, and glutathione (GSH) that makes GSH‐FALD adduct as a 2‐ClFALD scavenger. ATZ treatment also reduced bacterial killing ability suggesting that MPO is an essential component of neutrophil antibacterial mechanisms. In contrast, GSH supplementation increased bacterial killing capacity. Taken together, these findings suggest that specific bacterial strains play a significant role in neutrophil derived chlorinated lipid production, which may also differentiate their susceptibility to neutrophil killing.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Abstract only Sepsis is a life‐threatening organ dysfunction caused by a dysregulated host response to an infection. When pathogens disseminate into the systemic blood circulation from a localized ...infection, the body initiates a complex series of immune and biochemical reactions. Neutrophils are the main leukocytes that are recruited to an infection site to eliminate bacteria. In sepsis, systemic neutrophil activation is also evident. One of the main pathologies of sepsis is the damage of the endothelial cell integrity by immune stimuli leading to leaky blood vessels. Although numerous research has been conducted on sepsis, the characteristic heterogeneity of sepsis has challenged the identification of specific biomarkers and treatments. We have designed an in vitro co‐culture model of endothelial cells, human neutrophils and, E.coli to identify lipid biomarkers of sepsis. The three cell types in the model allow us to dissect lipidome of individual cell systems under a cell culture sepsis‐like state. EA.hy926 cells were initially incubated with urosepsis E.Coli strain CFT073 and further incubated after adding neutrophils. We compared the lipidome of co‐culture samples with non‐co‐culture samples to identify altered lipid profiles. In addition, we have performed similar experiments with non‐pathogenic JM109 E.Coli strain. We first used an untargeted lipidomics platform with high‐resolution mass spectrometry in both positive and negative ion modes. Potential lipid biomarkers identified in untargeted lipidomics were furthered confirmed by a targeted lipidomics approach using shotgun lipidomics. In CFT073 co‐cultures, lipids were changed mainly in 4 lipid classes; phosphatidylcholine (PC), phosphatidylethanolamine (PE), lysophosphatidylcholine and triglycerides. Minor changes were observed in sphingomyelin, phosphatidylserine and phosphatidylglycerol classes. Several of the changes in molecular species in each lipid class included significant increases in PE 32:1, PE 34:1, PE 32:2, PC 36:0, PC 40:8 and PC 32:0. Lipid profiles were also altered in non‐pathogenic JM109 co‐cultures. Interestingly, there are marked species variations depending on E.coli strain used in co‐cultures such as PC 32:1, PC 36:1 are only elevated in CFT073 co‐cultures. Collectively, our studies demonstrate that lipid profiles are altered during inflammation initiated by bacterial exposure and subsequent neutrophil activation. We have also shown that pathogenicity of bacteria may lead to distinct alterations in lipidomes. These studies represent initial insights into the complex lipidomic alterations during host‐pathogen interactions and may provide new targets to examine as biomarkers and mediators during in vivo sepsis. Support or Funding Information R01 GM115553, R01 GM129508, U01 ES026458, U01 ES027697, U01 ES028182
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
•We developed a theoretical model for understanding the complex relationship between energy expenditure and longevity.•Model considers energy tradeoffs between life history traits and efficiency of ...energy utilization.•Model is supported by a broad variety of empirical studies.
The relationship between energy expenditure and longevity has been a central theme in aging studies. Empirical studies have yielded controversial results, which cannot be reconciled by existing theories. In this paper, we present a simple theoretical model based on first principles of energy conservation and allometric scaling laws. The model takes into considerations the energy tradeoffs between life history traits and the efficiency of the energy utilization, and offers quantitative and qualitative explanations for a set of seemingly contradictory empirical results. We show that oxidative metabolism can affect cellular damage and longevity in different ways in animals with different life histories and under different experimental conditions. Qualitative data and the linearity between energy expenditure, cellular damage, and lifespan assumed in previous studies are not sufficient to understand the complexity of the relationships. Our model provides a theoretical framework for quantitative analyses and predictions. The model is supported by a variety of empirical studies, including studies on the cellular damage profile during ontogeny; the intra- and inter-specific correlations between body mass, metabolic rate, and lifespan; and the effects on lifespan of (1) diet restriction and genetic modification of growth hormone, (2) the cold and exercise stresses, and (3) manipulations of antioxidant.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
We develop a theoretical model from an energetic viewpoint for unraveling the entangled effects of metabolic and biosynthetic rates on oxidative cellular damage accumulation during animal's growth, ...and test the model by experiments in hornworms. The theoretical consideration suggests that most of the cellular damages caused by the oxidative metabolism can be repaired by the efficient maintenance mechanisms, if the energy required by repair is unlimited. However, during growth a considerable amount of energy is allocated to the biosynthesis, which entails tradeoffs with the requirements of repair. Thus, the model predicts that cellular damage is more influenced by the biosynthetic rate than the metabolic rate. To test the prediction, we induced broad variations in metabolic and biosynthetic rates in hornworms, and assayed the lipid peroxidation and protein carbonyl. We found that the increase in the cellular damage was mainly caused by the increase in biosynthetic rate, and the variations in metabolic rate had negligible effect. The oxidative stress hypothesis of aging suggests that high metabolism leads to high cellular damage and short lifespan. However, some empirical studies showed that varying biosynthetic rate, rather than metabolic rate, changes animal's lifespan. The conflicts between the empirical evidence and the hypothesis are reconciled by this study.
•A model unravels the effects of metabolic and biosynthetic rates on cellular damage.•The model predicts biosynthesis has greater influences on damage than metabolism does.•Lipid peroxidation and protein carbonyl assays on hornworms verify the prediction.•Cellular damage is mainly caused by the increase in biosynthetic rate.•The variations in metabolic rate has less significant effect on cellular damage.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Growing animals must alter their energy budget in the face of environmental changes and prioritize the energy allocation to metabolism for life-sustaining requirements and energy deposition in new ...biomass growth. We hypothesize that when food availability is low, larvae of holometabolic insects with a short development stage (relative to the low food availability period) prioritize biomass growth at the expense of metabolism. Driven by this hypothesis, we develop a simple theoretical model, based on conservation of energy and allometric scaling laws, for understanding the dynamic energy budget of growing larvae under food restriction. We test the hypothesis by manipulative experiments on fifth instar hornworms at three temperatures. At each temperature, food restriction increases the scaling power of growth rate but decreases that of metabolic rate, as predicted by the hypothesis. During the fifth instar, the energy budgets of larvae change dynamically. The free-feeding larvae slightly decrease the energy allocated to growth as body mass increases and increase the energy allocated to life sustaining. The opposite trends were observed in food restricted larvae, indicating the predicted prioritization in the energy budget under food restriction. We compare the energy budgets of a few endothermic and ectothermic species and discuss how different life histories lead to the differences in the energy budgets under food restriction.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Sepsis is a dysregulated immune response to an infection. A complex series of reactions between host cells and bacteria result in microcirculatory dysfunction leading to multiple organ failure. ...Neutrophils play a major role in anti-microbial mechanisms to eliminate infections. During sepsis, neutrophil activities are dysregulated contributing to collateral damage to host tissues. In this dissertation, neutrophil-derived lipids were studied to get a better understanding of their roles in sepsis. Neutrophil-derived chlorinated lipid production was examined during bacterial exposure. Neutrophils exposed to a pathogenic bacteria strain induced neutrophils to produce higher chlorinated lipids compared to a non-pathogenic bacteria strain exposure. Higher chlorinated lipid levels in these bacteria-neutrophil cocultures were associated with neutrophil extracellular trap formation. This dissertation also provides data on the identification of novel very long chain plasmalogen species unique to the neutrophil ethanolamine glycerophospholipid pool. The very long chain plasmalogen species consist of 24 and 22 carbon length aliphatic chains that get oxidized to respective very long chain chlorinated lipids. These very long chain chlorinated lipids are also identified in sepsis plasma indicating their roles as potential biomarkers of sepsis and possible inflammatory mediators. Finally, an in vitro cell model was developed that mimics in vivo sepsis conditions to study the lipidomic alterations. Untargeted and targeted lipidomics approaches were taken to study the lipids under pathogenic and non-pathogenic bacteria exposure on endothelial cells with neutrophil presence. The altered lipid profile consists of diglycerides, triglycerides, phosphatidylglycerol, and phosphatidylethanolamine species. The pathogenic bacteria induced more lipid changes while causing endothelial cell death and higher bacterial cocolonization on endothelial cells. The altered lipids are linked with anti- and pro-inflammatory effects during inflammation. Collectively, this dissertation provides key insights into the lipidomics of host-pathogen interactions in sepsis.
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