Plasma ceramide and lysophosphatidylcholine inversely correlate with mortality in sepsis patients

Alterations of plasma lysophosphatidylcholine species in obesity and weight loss

Background

Obesity and related diseases of the metabolic syndrome contribute to the major health problems in industrialized countries. Alterations in the metabolism of lipid classes and lipid species may significantly be involved in these metabolic overload diseases. However, little is known about specific lipid species in this syndrome and existing data are contradictive.

Methods

In this study, we quantified plasma lipid species by electrospray ionization tandem mass spectrometry (ESI-MS/MS) in obese subjects before and after 3 month weight loss as well as in a control group.

Results

The comparison of obese subjects with control subjects before weight loss revealed significantly lower lysophosphatidylcholine (LPC) concentrations in obesity. LPC concentrations did not significantly increase during the observed period in the weight loss group. Analysis of LPC species revealed a decrease of most species in obesity and negative correlations with C-reactive protein (CRP) and body mass index (BMI). Correlating BMI ratio before and after weight loss with the ratio of total LPC and individual LPC species revealed significant negative relationships of LPC ratios with BMI ratio.

Conclusions

Our findings contribute to the contradictive discussion of the role of LPC in obesity and related chronic inflammation strongly supporting pre-existing data in the literature that show a decrease of LPC species in plasma of obese and a potentially anti-inflammatory role in these subjects.

Oxidized lipids and lysophosphatidylcholine induce the chemotaxis, up-regulate the expression of CCR9 and CXCR4 and abrogate the release of IL-6 in human monocytes

Lipids through regulation of chronic inflammation play key roles in the development of various diseases. Here, we report that a mixed population of human primary monocytes migrated towards LPC, as well as oxidized linoleic acid isoforms 9-S-HODE, 9-R-HODE and 13-R-HODE. Incubation with 9-R-HODE, 13-R-HODE and LPC resulted in increased expression of CXCR4, the receptor for SDF-1α/CXCL12, correlated with increased monocyte migration towards SDF-1α/CXCL12. Further, we report increased expression of CCR9, the receptor for TECK/CCL25, after stimulation with these lipids. Upon examining the migratory response towards TECK/CCL25, it was observed that an increase in CCR9 expression upon pre-treatment with 9-S-HODE, 9-R-HODE, 13-R-HODE and LPC resulted in increased migration of monocytes expressing CCR9. Only LPC but not any other lipid examined increased the influx of intracellular Ca²⁺ in monocytes. Finally, 9-S-HODE, 9-R-HODE, 13-R-HODE, or LPC inhibited the release of IL-6 from monocytes suggesting that these lipids may play important role in controlling inflammatory responses.

Integrative "omic" analysis of experimental bacteremia identifies a metabolic signature that distinguishes human sepsis from systemic inflammatory response syndromes

RATIONALE

Sepsis is a leading cause of morbidity and mortality. Currently, early diagnosis and the progression of the disease are difficult to make. The integration of metabolomic and transcriptomic data in a primate model of sepsis may provide a novel molecular signature of clinical sepsis.

OBJECTIVES

To develop a biomarker panel to characterize sepsis in primates and ascertain its relevance to early diagnosis and progression of human sepsis.

METHODS

Intravenous inoculation of Macaca fascicularis with Escherichia coli produced mild to severe sepsis, lung injury, and death. Plasma samples were obtained before and after 1, 3, and 5 days of E. coli challenge and at the time of killing. At necropsy, blood, lung, kidney, and spleen samples were collected. An integrative analysis of the metabolomic and transcriptomic datasets was performed to identify a panel of sepsis biomarkers.

MEASUREMENTS AND MAIN RESULTS

The extent of E. coli invasion, respiratory distress, lethargy, and mortality was dependent on the bacterial dose. Metabolomic and transcriptomic changes characterized severe infections and death, and indicated impaired mitochondrial, peroxisomal, and liver functions. Analysis of the pulmonary transcriptome and plasma metabolome suggested impaired fatty acid catabolism regulated by peroxisome-proliferator activated receptor signaling. A representative four-metabolite model effectively diagnosed sepsis in primates (area under the curve, 0.966) and in two human sepsis cohorts (area under the curve, 0.78 and 0.82).

CONCLUSIONS

A model of sepsis based on reciprocal metabolomic and transcriptomic data was developed in primates and validated in two human patient cohorts. It is anticipated that the identified parameters will facilitate early diagnosis and management of sepsis.

Impact of serial measurements of lysophosphatidylcholine on 28-day mortality prediction in patients admitted to the intensive care unit with severe sepsis or septic shock

PURPOSE

The purpose of this study is to investigate the effect of serial lysophosphatidylcholine (LPC) measurement on 28-day mortality prediction in patients with severe sepsis or septic shock admitted to the medical intensive care unit (ICU).

METHODS

This is a prospective observational study of 74 ICU patients in a tertiary hospital. Serum LPC, white blood cell, C-reactive protein, and procalcitonin (PCT) levels were measured at baseline (day 1 of enrollment) and day 7. The LPC concentrations were compared with inflammatory markers using their absolute levels and relative changes.

RESULTS

The LPC concentration on day 7 was significantly lower in nonsurvivors than in survivors (68.45 ± 42.36 μmol/L and 99.76 ± 73.65 μmol/L; P = .04). A decreased LPC concentration on day 7 to its baseline as well as a sustained high concentration of PCT on day 7 at more than 50% of its baseline value was useful for predicting the 28-day mortality. Prognostic utility was substantially improved when combined LPC and PCT criteria were applied to 28-day mortality outcome predictions. Furthermore, LPC concentrations increased over time in patients with appropriate antibiotics but not in those with inappropriate antibiotics.

CONCLUSIONS

Serial measurements of LPC help in the prediction of 28-day mortality in ICU patients with severe sepsis or septic shock.

Sphingolipids in human synovial fluid--a lipidomic study

Articular synovial fluid (SF) is a complex mixture of components that regulate nutrition, communication, shock absorption, and lubrication. Alterations in its composition can be pathogenic. This lipidomic investigation aims to quantify the composition of sphingolipids (sphingomyelins, ceramides, and hexosyl- and dihexosylceramides) and minor glycerophospholipid species, including (lyso)phosphatidic acid, (lyso)phosphatidylglycerol, and bis(monoacylglycero)phosphate species, in the SF of knee joints from unaffected controls and from patients with early (eOA) and late (lOA) stages of osteoarthritis (OA), and rheumatoid arthritis (RA).

SF without cells and cellular debris from 9 postmortem donors (control), 18 RA, 17 eOA, and 13 lOA patients were extracted to measure lipid species using electrospray ionization tandem mass spectrometry - directly or coupled with hydrophilic interaction liquid chromatography.

We provide a novel, detailed overview of sphingolipid and minor glycerophospholipid species in human SF. A total of 41, 48, and 50 lipid species were significantly increased in eOA, lOA, and RA SF, respectively when compared with normal SF.

The level of 21 lipid species differed in eOA SF versus SF from lOA, an observation that can be used to develop biomarkers. Sphingolipids can alter synovial inflammation and the repair responses of damaged joints. Thus, our lipidomic study provides the foundation for studying the biosynthesis and function of lipid species in health and most prevalent joint diseases.

Dietary fat sources differentially modulate intestinal barrier and hepatic inflammation in alcohol-induced liver injury in rats

Endotoxemia is a causal factor in the development of alcoholic liver injury. The present study aimed at determining the interactions of ethanol with different fat sources at the gut-liver axis. Male Sprague-Dawley rats were pair fed control or ethanol liquid diet for 8 wk. The liquid diets were based on a modified Lieber-DeCarli formula, with 30% total calories derived from corn oil (rich in polyunsaturated fatty acids). To test the effects of saturated fats, corn oil in the ethanol diet was replaced by either cocoa butter (CB, rich in long-chain saturated fatty acids) or medium-chain triglycerides (MCT, exclusively medium-chain saturated fatty acids). Ethanol feeding increased hepatic lipid accumulation and inflammatory cell infiltration and perturbed hepatic and serum metabolite profiles. Ethanol feeding with CB or MCT alleviated ethanol-induced liver injury and attenuated ethanol-induced metabolic perturbation. Both CB and MCT also normalized ethanol-induced hepatic macrophage activation, cytokine expression, and neutrophil infiltration. Ethanol feeding elevated serum endotoxin level, which was normalized by MCT but not CB. In accordance, ethanol-induced downregulations of intestinal occludin and zonula occludens-1 were normalized by MCT but not CB. However, CB normalized ethanol-increased hepatic endotoxin level in association with upregulation of an endotoxin detoxifying enzyme, argininosuccinate synthase 1 (ASS1). Knockdown ASS1 in H4IIEC3 cells resulted in impaired endotoxin clearance and upregulated cytokine expression. These data demonstrate that the protection of saturated fats against alcohol-induced liver injury occur via different actions at the gut-liver axis and are chain length dependent.

Evaluation of the role of secretory sphingomyelinase and bioactive sphingolipids as biomarkers in hemophagocytic lymphohistiocytosis

Hemophagocytic lymphohistiocytosis (HLH) is a rare systemic inflammatory syndrome that results from unrestrained immune cell activation. Despite significant advances in the understanding of the pathophysiology of HLH, interventions remain limited for this often-fatal condition. Secretory sphingomyelinase (S-SMase) is a pro-inflammatory lipid hydrolase that is upregulated in several inflammatory conditions, including HLH. S-SMase promotes the formation of ceramide, a bioactive lipid implicated in several human disease states. However, the role of the S-SMase/ceramide pathway in HLH remains unexplored. To further evaluate the role of S-SMase upregulation in HLH, we tested the serum of patients with HLH (n = 16; primary = 3, secondary = 13) and healthy control patients (n = 25) for serum S-SMase activity with tandem sphingolipid metabolomic profiling. Patients with HLH exhibited elevated levels of serum S-SMase activity, with concomitant elevations in several ceramide species and sphingosine, while levels of sphingosine-1-phosphate were significantly decreased. Importantly, the ratio of C16 -ceramide:sphingosine was uniquely elevated in HLH patients that died despite appropriate treatment, but remained low in HLH patients that survived, suggesting that this ratio may be of prognostic significance. Together, these results demonstrate upregulation of the S-SMase/ceramide pathway in HLH, and suggest that the balance of ceramide and sphingosine determine clinical outcomes in HLH. .

Sphingolipids in acute lung injury

Acute lung injury is a life-threatening disease that is characterized by pulmonary inflammation, loss of barrier functions, and hypoxemia. Sphingolipids are critically involved in the disease process that they can both expedite and extenuate: They expedite inflammation by promoting chemotaxis (neutral sphingomyelinase), increased endothelial permeability (acid sphingomyelinase, S1P3-receptors), increased epithelial permeability (S1P2- and S1P3-receptors), and delaying neutrophil apoptosis (neutral sphingomyelinase, S1P1-receptors). They extenuate inflammation by attenuating chemotaxis (S1P) and by stabilizing the endothelial and the epithelial barrier (S1P1-receptor). This chapter discusses the multiple roles and therapeutic options that sphingolipids offer with respect to acute lung injury.

An integrated clinico-metabolomic model improves prediction of death in sepsis

Sepsis is a common cause of death, but outcomes in individual patients are difficult to predict. Elucidating the molecular processes that differ between sepsis patients who survive and those who die may permit more appropriate treatments to be deployed. We examined the clinical features and the plasma metabolome and proteome of patients with and without community-acquired sepsis, upon their arrival at hospital emergency departments and 24 hours later. The metabolomes and proteomes of patients at hospital admittance who would ultimately die differed markedly from those of patients who would survive. The different profiles of proteins and metabolites clustered into the following groups: fatty acid transport and β-oxidation, gluconeogenesis, and the citric acid cycle. They differed consistently among several sets of patients, and diverged more as death approached. In contrast, the metabolomes and proteomes of surviving patients with mild sepsis did not differ from survivors with severe sepsis or septic shock. An algorithm derived from clinical features together with measurements of five metabolites predicted patient survival. This algorithm may help to guide the treatment of individual patients with sepsis.

Lysophosphatidylcholine, oxidized low-density lipoprotein and cardiovascular disease in Korean hemodialysis patients: analysis at 5 years of follow-up

Although oxidized low-density lipoprotein (LDL) and lysophosphatidylcholine (LPC) have been proposed as important mediators of the atherosclerosis, the long-term contribution to the risk of cardiovascular disease (CVD) in hemodialysis patients has not been evaluated. This study investigated the relation between oxidized LDL and LPC levels with long term risk of CVD. Plasma oxidized LDL and LPC levels were determined in 69 Korean hemodialysis patients as a prospective observational study for 5 yr. During the observation period, 18 cardiovascular events (26.1%) occurred including 6 deaths among the hemodialysis patients. The low LPC level group (≤ 254 µM/L, median value) had much more increased risk of CVD compared to the high LPC level group (> 254 µM/L) (P = 0.01). However, serum levels of oxidized LDL were not significantly different between groups with and without CVD. In adjusted Cox analysis, previous CVD, (hazard ratio [HR], 5.68; 95% confidence interval [CI], 1.94-16.63, P = 0.002) and low LPC level (HR, 3.45; 95% CI, 1.04-11.42, P = 0.04) were significant independent risk factors for development of CVD. It is suggested that low LPC, but not oxidized LDL, is associated with increased risk of CVD among a group of Korean hemodialysis patients.

A metabolomic investigation of the effects of vitamin E supplementation in humans

Background

Vitamin E is a nutrient with both antioxidant and non-antioxidant activities and has been shown to modulate the function of a number of cell types in vitro and in human studies. However studies have also shown vitamin E to have detrimental interactions and therefore it is important to establish the extent to which this nutrient influences metabolism. Metabolomics can potentially identify nutrient-metabolism interactions and therefore the aim of this study was to use a non-targeted metabolomic approach to identify changes to the plasma metabolome following vitamin E supplementation in humans.

Methods

A relatively homogenous healthy adult male population (n = 10) provided a fasting blood sample immediately before and after a 4-week vitamin E supplementation regime (400 mg/d of RRR-α-tocopheryl acetate)) on top of their habitual diet. Plasma samples were analysed for vitamin E and clinical markers. Plasma underwent non-targeted metabolite profiling using liquid chromatography/mass spectroscopy and data was processed using multivariate statistical analysis.

Results

Plasma vitamin E concentrations were significantly increased following supplementation (p < 0.001). A partial least squares-discriminant analysis (PLS-DA) model was able to discriminate between samples taken pre and post vitamin E supplementation (goodness of fit R²Y = 0.82, predictive ability Q² = 0.50). Variable influence on projection and PLS-DA loadings highlighted a number of discriminating ions that were confirmed as discriminatory through pairwise analysis. From database searches and comparison with standards these metabolites included a number of lysophosphatidylcholine species (16:0, 18:0, 18:1, 18:2, 20:3 and 22:6) that were increased in intensity post supplementation by varying degrees from 4% to 29% with the greatest changes found for lysoPC 22:6 and 20:3.

Conclusions

Although a small scale study, these results potentially indicate that vitamin E supplementation influences phospholipid metabolism and induces lysoPC generation; a general pro-inflammatory response. Moreover the study identifies novel areas of vitamin E interactions and highlights the potential of metabolomics for elucidating interactions between nutrients and metabolic pathways in nutritional research.

Hyperresponsiveness of mice deficient in plasma-secreted sphingomyelinase reveals its pivotal role in early phase of host response

Plasma secretion of acid sphingomyelinase is a hallmark of cellular stress response resulting in the formation of membrane embedded ceramide-enriched lipid rafts and the reorganization of receptor complexes. Consistently, decompartmentalization of ceramide formation from inert sphingomyelin has been associated with signaling events and regulation of the cellular phenotype. Herein, we addressed the question of whether the secretion of acid sphingomyelinase is involved in host response during sepsis. We found an exaggerated clinical course in mice genetically deficient in acid sphingomyelinase characterized by an increased bacterial burden, an increased phagocytotic activity, and a more pronounced cytokine storm. Moreover, on a functional level, leukocyte-endothelial interaction was found diminished in sphingomyelinase-deficient animals corresponding to a distinct leukocytes’ phenotype with respect to rolling and sticking as well as expression of cellular surface proteins. We conclude that hydrolysis of membrane-embedded sphingomyelin, triggered by circulating sphingomyelinase, plays a pivotal role in the first line of defense against invading microorganisms. This function might be essential during the early phase of infection leading to an adaptive response of remote cells and tissues.

Mechanisms involved in cellular ceramide homeostasis

Sphingolipids are ubiquitous and critical components of biological membranes. Their biosynthesis starts with soluble precursors in the endoplasmic reticulum and culminates in the Golgi complex and plasma membrane. Ceramides are important intermediates in the biosynthesis of sphingolipids, such as sphingomyelin, and their overload in the membranes is injurious to cells. The major product of ceramide metabolism is sphingomyelin. We observed that sphingomyelin synthase (SMS) 1 or SMS2 deficiencies significantly decreased plasma and liver sphingomyelin levels. However, SMS2 but not SMS1 deficiency increased plasma ceramides. Surprisingly, SMS1 deficiency significantly increased glucosylceramide and ganglioside GM3, but SMS2 deficiency did not. To explain these unexpected findings about modest to no significant changes in ceramides and increases in other sphingolipids after the ablation of SMS1, we hypothesize that cells have evolved several organelle specific mechanisms to maintain ceramide homeostasis. First, ceramides in the endoplasmic reticulum membranes are controlled by its export to Golgi by protein mediated transfer. Second, in the Golgi, ceramide levels are modulated by their enzymatic conversion to different sphingolipids such as sphingomyelin, and glucosylceramides. Additionally, these sphingolipids can become part of triglyceride-rich apolipoprotein B-containing lipoproteins and be secreted. Third, in the plasma membrane ceramide levels are maintained by ceramide/sphingomyelin cycle, delivery to lysosomes, and efflux to extracellular plasma acceptors. All these pathways might have evolved to ensure steady cellular ceramide levels.

Biomarkers of inflammation, immunosuppression and stress with active disease are revealed by metabolomic profiling of tuberculosis patients

Although tuberculosis (TB) causes more deaths than any other pathogen, most infected individuals harbor the pathogen without signs of disease. We explored the metabolome of >400 small molecules in serum of uninfected individuals, latently infected healthy individuals and patients with active TB. We identified changes in amino acid, lipid and nucleotide metabolism pathways, providing evidence for anti-inflammatory metabolomic changes in TB. Metabolic profiles indicate increased activity of indoleamine 2,3 dioxygenase 1 (IDO1), decreased phospholipase activity, increased abundance of adenosine metabolism products, as well as indicators of fibrotic lesions in active disease as compared to latent infection. Consistent with our predictions, we experimentally demonstrate TB-induced IDO1 activity. Furthermore, we demonstrate a link between metabolic profiles and cytokine signaling. Finally, we show that 20 metabolites are sufficient for robust discrimination of TB patients from healthy individuals. Our results provide specific insights into the biology of TB and pave the way for the rational development of metabolic biomarkers for TB.

Role of sphingomyelinase in infectious diseases caused by Bacillus cereus

Bacillus cereus (B. cereus) is a pathogen in opportunistic infections. Here we show that Bacillus cereus sphingomyelinase (Bc-SMase) is a virulence factor for septicemia. Clinical isolates produced large amounts of Bc-SMase, grew in vivo, and caused death among mice, but ATCC strains isolated from soil did not. A transformant of the ATCC strain carrying a recombinant plasmid containing the Bc-SMase gene grew in vivo, but that with the gene for E53A, which has little enzymatic activity, did not. Administration of an anti-Bc-SMase antibody and immunization against Bc-SMase prevented death caused by the clinical isolates, showing that Bc-SMase plays an important role in the diseases caused by B. cereus. Treatment of mouse macrophages with Bc-SMase resulted in a reduction in the generation of H₂O₂ and phagocytosis of macrophages induced by peptidoglycan (PGN), but no effect on the release of TNF-α and little release of LDH under our experimental conditions. Confocal laser microscopy showed that the treatment of mouse macrophages with Bc-SMase resulted in the formation of ceramide-rich domains. A photobleaching analysis suggested that the cells treated with Bc-SMase exhibited a reduction in membrane fluidity. The results suggest that Bc-SMase is essential for the hydrolysis of SM in membranes, leading to a reduction in phagocytosis.

Metabolomic analysis as biomarker to study steroid hormone administration in sepsis

Sepsis is a life-threatening disease requiring rapid diagnosis and treatment. Steroid hormones (e.g., estradiol, dehydroepiandosterone) have been suggested to reduce the hyper-inflammatory response of the immune system and to improve outcome in sepsis. We hypothesize that the impact of steroid hormones on the metabolic profile (metabolomic fingerprint) can be used to study and guide steroid hormone administration in sepsis. Potential biomarker candidates are sphingomyelines and phosphatidylcholines.

Targeted metabolomics for discrimination of systemic inflammatory disorders in critically ill patients

The occurrence of systemic inflammatory response syndrome (SIRS) remains a major problem in intensive care units with high morbidity and mortality. The differentiation between noninfectious and infectious etiologies of this disorder is challenging in routine clinical practice. Many biomarkers have been suggested for this purpose; however, sensitivity and specificity even of high-ranking biomarkers remain insufficient. Recently, metabolic profiling has attracted interest for biomarker discovery. The objective of this study was to identify metabolic biomarkers for differentiation of SIRS/sepsis. A total of 186 meta-bolites comprising six analyte classes were determined in 143 patients (74 SIRS, 69 sepsis) by LC-MS/MS. Two markers (C10:1 and PCaaC32:0) revealed significantly higher concentrations in sepsis. A classification model comprising these markers resulted in 80% and 70% correct classifications in a training set and a test set, respectively.This study demonstrates that acylcarnitines and glycerophosphatidylcholines may be helpful for differentiation of infectious from noninfectious systemic inflammation due to their significantly higher concentration in sepsis patients. Considering the well known pathophysiological relevance of lipid induction by bacterial components, metabolites as identified in this study are promising biomarker candidates in the differential diagnosis of SIRS and sepsis.

Involvement of ceramide in cell death responses in the pulmonary circulation

Ceramides are signaling sphingolipids involved in cellular homeostasis but also in pathological processes such as unwanted apoptosis, growth arrest, oxidative stress, or senescence. Several enzymatic pathways are responsible for the synthesis of ceramides, which can be activated in response to exogenous stimuli such as cytokines, radiation, or oxidative stress. Endothelial cells are particularly rich in acid sphingomyelinases, which can be rapidly activated to produce ceramides, both intracellular and at the plasma membrane. In addition, neutral sphingomyelinases, the de novo pathway and the ceramide recycling pathway, may generate excessive ceramides involved in endothelial cell responses. When up-regulated, ceramides trigger signaling pathways that culminate in endothelial cell death, which in murine lungs has been linked to the development of emphysema-like disease. Furthermore, ceramides may be released paracellularly where they are believed to exert paracrine activities. Such effects, along with ceramides released by inflammatory mediators, may contribute to lung inflammation and pulmonary edema, because ceramide-challenged pulmonary endothelial cells exhibit decreased barrier function, independent of apoptosis. Reestablishing the sphingolipid homeostasis, either by modulating ceramide synthesis or by opposing its biological effects through augmentation of the prosurvival sphingosine-1 phosphate, may alleviate acute or chronic pulmonary conditions characterized by vascular endothelial cell death or dysfunction.

Analysis of sphingolipids in extracted human plasma using liquid chromatography electrospray ionization tandem mass spectrometry

We have developed an analytical method used to quantify sphingolipids, including deoxysphingoid bases, in lipid extracts prepared from human plasma. In total, 39 analytes were identified and analyzed in a single chromatographic run in less than 5 min. The new method is 4-8 times faster and more sensitive than previously published methods. We also describe a simple sample preparation method that allows medium-throughput screening of human plasma samples. Mass spectrometric analyses were performed online using liquid chromatography electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) in the positive multiple reaction monitoring mode. Samples were extracted using a one-phase extraction method (methanol-dichloromethane) with appropriate internal standards. Sphingolipid analytes were linear over a wide range of concentrations, from 0.01 to 50 ng/ml, with a high correlation coefficient (r2 = 0.999). We successfully applied this method to analyze the levels of sphingolipid metabolites in healthy human plasma. The ceramide, dihydroceramide, hexosylceramide, and GM3 levels observed in females were slightly higher than those observed in males.

Phospholipids and insulin resistance in psychosis: a lipidomics study of twin pairs discordant for schizophrenia

BACKGROUND

Several theories have been proposed to conceptualize the pathological processes inherent to schizophrenia. The 'prostaglandin deficiency' hypothesis postulates that defective enzyme systems converting essential fatty acids to prostaglandins lead to diminished levels of prostaglandins, which in turn affect synaptic transmission.

METHODS

Here we sought to determine the lipidomic profiles associated with schizophrenia in twin pairs discordant for schizophrenia as well as unaffected twin pairs. The study included serum samples from 19 twin pairs discordant for schizophrenia (mean age 51 ± 10 years; 7 monozygotic pairs; 13 female pairs) and 34 age and gender matched healthy twins as controls. Neurocognitive assessment data and gray matter density measurements taken from high-resolution magnetic resonance images were also obtained. A lipidomics platform using ultra performance liquid chromatography coupled to time-of-flight mass spectrometry was applied for the analysis of serum samples.

RESULTS

In comparison to their healthy co-twins, the patients had elevated triglycerides and were more insulin resistant. They had diminished lysophosphatidylcholine levels, which associated with decreased cognitive speed.

CONCLUSIONS

Our findings may be of pathophysiological relevance since lysophosphatidylcholines, byproducts of phospholipase A2-catalyzed phospholipid hydrolysis, are preferred carriers of polyunsaturated fatty acids across the blood-brain barrier. Furthermore, diminishment of lysophosphatidylcholines suggests that subjects at risk of schizophrenia may be more susceptible to infections. Their association with cognitive speed supports the view that altered neurotransmission in schizophrenia may be in part mediated by reactive lipids such as prostaglandins.

Clinical significance of enzymatic lysophosphatidylcholine (LPC) assay data in patients with sepsis

Lysophosphatidylcholine (LPC) has been suggested to serve as a useful prognostic marker for sepsis. However, existing LPC assays are complicated, time-consuming, and of limited application in real clinical situations. Thus, we investigated the serum LPC levels in sepsis patients using an enzymatic assay and analyzed the correlations between the serum LPC concentration and clinical characteristics. We prospectively collected blood samples from suspected sepsis patients, commencing on day 1 of sepsis. We analyzed all samples using an enzymatic assay. Additionally, we analyzed the serum LPC concentrations in a control group of 21 healthy blood donors. A total of 105 patients who fulfilled the sepsis criteria were included. The mean serum LPC concentration was 43.49 ± 33.09 μmol/L in sepsis patients, which was much lower than that of 21 healthy controls (234.68 ± 30.33 μmol/L, p<0.001). Bacteremic sepsis was associated with a lower serum LPC concentration than non-bacteremic sepsis (34.8 ± 26.85 vs. 49.05 ± 35.63 μmol/L, p<0.05). No difference in serum LPC concentration was evident between survivors and non-survivors. The serum LPC concentration tended to decrease with the severity of sepsis. The day 1 serum LPC concentration was decreased in patients with sepsis, especially when bacteremia was present. However, the serum LPC level did not correlate with disease severity and did not predict mortality from sepsis.

Blood sphingolipids in homeostasis and pathobiology

Sphingolipids have emerged as key signaling molecules involved in the regulation of a variety of cellular functions including cell growth and differentiation, proliferation and apoptotic cell death. Sphingolipids in blood constitute part of the circulating lipoprotein particles (HDL, LDL and VLDL), carried by serum albumin and also present in blood cells and platelets. Recent lipidomic and proteomic studies of plasma lipoproteins have provided intriguing data concerning the protein and lipid composition of lipoproteins in the context of disease. Sphingolipids have been implicated in several diseases such as cancer, obesity, atherosclerosis and sphingolipidoses; however, efforts addressing blood sphingolipidomics are still limited. The development of methods to determine levels of circulating bioactive sphingolipids in humans and validation of these methods to be a routine clinical laboratory test could be a pioneering approach to diagnose disease in the population. This approach would probably evolve to be analogous in implication to determining "good" and "bad" cholesterol and triglyceride levels in lipoprotein classes.

Quantification of bioactive sphingo- and glycerophospholipid species by electrospray ionization tandem mass spectrometry in blood

Bioactive glycerophospho- and sphingolipids species are involved in the regulation of numerous biological processes and implicated in the pathophysiology of various diseases. Here we review electrospray ionization tandem mass spectrometric (ESI-MS/MS) methods for the analysis of these bioactive lipid species in blood including lysophosphatidic acid (LPA), lysophosphatidylcholine (LPC), bis(monoacylglycero)phosphate (BMP), ceramide (Cer), sphingosine-1-phosphate (S1P) and sphingosylphosphorylcholine (SPC). Beside direct tandem mass spectrometric and liquid chromatography coupled approaches, we present an overview of concentrations of these bioactive lipids in plasma. The analytical strategies are discussed together with aspects of sample preparation, quantification and sample stability.

Lysophosphatidylcholine: A Novel Modulator of Trypanosoma cruzi Transmission

Lysophosphatidylcholine is a bioactive lipid that regulates a large number of cellular processes and is especially present during the deposition and infiltration of inflammatory cells and deposition of atheromatous plaque. Such molecule is also present in saliva and feces of the hematophagous organism Rhodnius prolixus, a triatominae bug vector of Chagas disease. We have recently demonstrated that LPC is a modulator of Trypanosoma cruzi transmission. It acts as a powerful chemoattractant for inflammatory cells at the site of the insect bite, which will provide a concentrated population of cells available for parasite infection. Also, LPC increases macrophage intracellular calcium concentrations that ultimately enhance parasite invasion. Finally, LPC inhibits NO production by macrophages stimulated by live T. cruzi, and thus interferes with the immune system of the vertebrate host. In the present paper, we discuss the main signaling mechanisms that are likely used by such molecule and their eventual use as targets to block parasite transmission and the pathogenesis of Chagas disease.

Lipid profiling of lipoproteins by electrospray ionization tandem mass spectrometry

Lipoproteins are of fundamental importance for the lipid transport and cardiovascular disease. The function and metabolism of lipoproteins is intimately linked to the biophysical properties of their surface lipids. Although a number of disease associations were found for lipid species in plasma, only a few studies reported lipid profiles of lipoproteins. Here, we provide an overview of techniques for lipoprotein separation, methods for lipid species analysis based on electrospray ionization tandem mass spectrometry (ESI-MS/MS) as well as data from recent lipidomic studies on lipoprotein fractions. We also discuss the different analytical strategies and how lipid profiling can expand our understanding of the biology and structures of lipoproteins.

Lung-derived soluble mediators are pathogenic in ventilator-induced lung injury

Ventilator-induced lung injury (VILI) due to high tidal volume (V(T)) is associated with increased levels of circulating factors that may contribute to, or be markers of, injury. This study investigated if exclusively lung-derived circulating factors produced during high V(T) ventilation can cause or worsen VILI. In isolated perfused mouse lungs, recirculation of perfusate worsened injury (compliance impairment, microvascular permeability, edema) induced by high V(T). Perfusate collected from lungs ventilated with high V(T) and used to perfuse lungs ventilated with low V(T) caused similar compliance impairment and permeability and caused a dose-dependent decrease in transepithelial electrical resistance (TER) across rat distal lung epithelial monolayers. Circulating soluble factors derived from the isolated lung thus contributed to VILI and had deleterious effects on the lung epithelial barrier. These data demonstrate transferability of an injury initially caused exclusively by mechanical ventilation and provides novel evidence for the biotrauma hypothesis in VILI. Mediators of the TER decrease were heat-sensitive, transferable via Folch extraction, and (following ultrafiltration, 3 kDa) comprised both smaller and larger molecules. Although several classes of candidate mediators, including protein cytokines (e.g., tumor necrosis factor-α, interleukin-6, macrophage inflammation protein-1α) and lipids (e.g., eicosanoids, ceramides, sphingolipids), have been implicated in VILI, only prostanoids accumulated in the perfusate in a pattern consistent with a pathogenic role, yet cyclooxygenase inhibition did not protect against injury. Although no single class of factor appears solely responsible for the decrease in barrier function, the current data implicate lipid-soluble protein-bound molecules as not just markers but pathogenic mediators in VILI.

Identification and characterization of acyl-protein thioesterase 1/lysophospholipase I as a ghrelin deacylation/lysophospholipid hydrolyzing enzyme in fetal bovine serum and conditioned medium

Ghrelin contains an octanoic acid at the third residue serine, and the presence of octanoic acid on ghrelin is critical to its physiological functions. The precise mechanism for the deacylation of ghrelin in circulation remains to be clarified, although the level of deacylated ghrelin (des-acyl ghrelin) is higher than that of acylated ghrelin in serum. In this study, rapid identification of ghrelin deacylation activity was achieved by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and a ghrelin deacylation enzyme was purified 1515-fold from fetal bovine serum. Chromatographic separation showed a 24-kDa band on SDS-PAGE corresponding to ghrelin deacylation activity, and the protein band was identified as acyl-protein thioesterase 1 (APT1)/lysophospholipase I. A ghrelin deacylation enzyme in medium from HepG2 cells was also purified and identified as APT1. Although it lacks a secretion signal sequence, APT1 may be released by cells expressing APT1, mainly from liver in vivo. APT1 was originally purified as a cytosolic lysophospholipid hydrolyzing enzyme (lysophospholipase I), and recombinant APT1 exhibited deacylation activity as well as lysophospholipase activity in vitro. APT1 is released at high levels from RAW264.7 macrophage-like cells into the culture medium after stimulation with lipopolysaccharide (LPS), and LPS suppresses APT1 mRNA and protein expressions in these cells. More potent ghrelin deacylase activities were detected in sera from LPS-treated rats than in control sera. These results suggested that the serum activity of APT1 may play an important role in determination of the concentration of des-acyl ghrelin in circulation, especially under septic inflammation.

Direct profiling of phospholipids and lysophospholipids in rat brain sections after ischemic stroke

Stroke, a deleterious cerebrovascular event, is caused by a critical reduction in the blood flow to the brain parenchyma that leads to brain injury and loss of brain functions. The inflammatory responses following ischemia often aggravate the neurological damage. Several pro-inflammatory mediators released after stroke are closely related to the metabolism of phospholipids. In this study we directly profiled the changes in phospholipids in the infarcted rat cerebral cortex 24 hours after middle cerebral artery occlusion (MCAO) using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Several phosphatidylcholine (PC) species and sphingomyelin (SM) were significantly decreased after infarction. The cationization pattern of the remaining PCs showed a prominent shift from a mostly potassiated or protonated form to a predominantly sodiated pattern. Stroke also elevated the lysophosphatidylcholines (LPCs) and heme in tissue. The isobaric pairs in PC and LPC classes were resolved by masses through their respective alkali metal adducts in the presence of CsCl. The major fatty acyl LPC species were also structurally confirmed by MALDI-MS/MS. Overall, the results described the changes in PC and LPC species in the infarcted rat cortex. The elevated tissue levels of LPCs and heme signify the ongoing pathological lipid breakdown and the state of parenchymal inflammation. The elevated LPC level in tissue suggests a means of intervention through lysophospholipid metabolism that could potentially benefit the management of stroke and other acute neurological injuries.

Blood sphingolipidomics in healthy humans: impact of sample collection methodology

We used a HPLC-MS/MS methodology for determination of a basic metabolomic profile (18:1,18:0 sphingoid backbone, C(14)-C(26) N-acyl part) of "normal" sphingolipid levels in human serum and plasma. Blood was collected from healthy males and nonpregnant females under fasting and nonfasting conditions with and without anticoagulants. Sphingolipids analyzed included sphingoid bases, sphingosine and dihydrosphingosine, their 1-phosphates (S1P and dhS1P), molecular species (C(n)-) of ceramide (Cer), sphingomyelin (SM), hexosylceramide (HexCer), lactosylceramide (LacCer), and Cer 1-phosphate (Cer1P). SM, LacCer, HexCer, Cer, and Cer1P constituted 87.7, 5.8, 3.4, 2.8, and 0.15% of total sphingolipids, respectively. The abundant circulating SM was C(16)-SM (64.0 µM), and it increased with fasting (100 µM). The abundant LacCer was C(16)-LacCer (10.0 µM) and the abundant HexCer was C(24)-HexCer (2.5 µM). The abundant Cer, C(24)-Cer (4.0 µM), was not influenced by fasting; however, levels of C(16)-C(20) Cers were decreased in response to fasting. S1P levels were higher in serum than plasma (0.68 µM vs. 0.32 µM). We also determined levels of sphingoid bases and SM species in isolated lipoprotein classes. HDL(3) was the major carrier of S1P, dhS1P, and Sph, and LDL was the major carrier of Cer and dhSph. Per particle, VLDL contained the highest levels of SM, Cer, and S1P. HPLC-MS/MS should provide a tool for clinical testing of circulating bioactive sphingolipids in human blood.

Do soluble mediators cause ventilator-induced lung injury and multi-organ failure?

BACKGROUND

Significant advances in the management of patients with acute respiratory distress syndrome have been few in the recent past despite considerable efforts in clinical testing and experimental work. The biotrauma hypothesis of ventilator-associated lung injury (VALI), suggesting that mechanical ventilation induces the release of injurious mediators from the lung, implies that pharmaceutical interventions targeting these circulating pathogenic mediators would be clinically beneficial. Among the commonly reported classes of ventilation-associated mediators are cytokines, coagulation factors, hormones (e.g., angiotensin-II), lipid-derived mediators and oxidants, yet proof of their pathogenicity is lacking.

DISCUSSION

This review discusses evidence surrounding the roles of these mediators in VALI and describes how definitive proof could be provided based on Koch's postulates, using an isolated perfused lung model. According to this experimental concept, candidate mediators would fulfill certain criteria, including increased accumulation in perfusate during injurious ventilation and induction of injury during non-injurious ventilation. Accumulation of mediators in the perfusate would facilitate isolation and characterization by standard biochemical means, from broad determination of physical and chemical properties to precise identification of individual molecules (e.g., by modern "omic" approaches such as mass spectrometry). Finally, confirmation by exogenous administration of mediators or antagonists can assess effects on injury and its mechanisms such as cell permeability or cytotoxicity.

CONCLUSIONS

Adaptation of Koch's postulates to the biotrauma hypothesis of VALI could provide important insights. Translation of the acquired knowledge into clinical testing is challenged by the heterogeneity of the patient population (e.g., etiology, co-morbidity, genetics or concomitant therapy) and the specificity and efficacy of the therapeutic intervention on the cellular/molecular level.

Synthesis of lysophospholipids

New synthetic methods for the preparation of biologically active phospholipids and lysophospholipids (LPLs) are very important in solving problems of membrane-chemistry and biochemistry. Traditionally considered just as second-messenger molecules regulating intracellular signalling pathways, LPLs have recently shown to be involved in many physiological and pathological processes such as inflammation, reproduction, angiogenesis, tumorogenesis, atherosclerosis and nervous system regulation. Elucidation of the mechanistic details involved in the enzymological, cell-biological and membrane-biophysical roles of LPLs relies obviously on the availability of structurally diverse compounds. A variety of chemical and enzymatic routes have been reported in the literature for the synthesis of LPLs: the enzymatic transformation of natural glycerophospholipids (GPLs) using regiospecific enzymes such as phospholipases A1 (PLA1), A2 (PLA2) phospholipase D (PLD) and different lipases, the coupling of enzymatic processes with chemical transformations, the complete chemical synthesis of LPLs starting from glycerol or derivatives. In this review, chemo-enzymatic procedures leading to 1- and 2-LPLs will be described.

Altered sphingolipid metabolism induced by tumor hypoxia - new vistas in glycolipid tumor markers

Uncontrolled growth of malignant cells produces hypoxic regions in locally advanced tumors. Recently we showed that tumor hypoxia-induced transcription of multiple genes involved in glycan synthesis, leading to expression of useful glycolipid tumor markers, such as gangliosides having N-glycolyl sialic acid. Our subsequent studies indicated that the ceramide portion of glycolipids, as well as their glycan moiety, was also significantly affected by hypoxia. Tumor hypoxia-induced marked accumulation of sphinganine (dihydrosphingosine) long-chain base, and significant reduction of unsaturated very long-chain fatty acids in the ceramide moiety. Mass-spectrometry, which yields information on both glycan- and ceramide moieties, is expected to be clinically useful in detecting such distinct molecular species of cancer-associated glycolipids having combined alteration in both glycan- and ceramide moieties.

An extremely simple method for extraction of lysophospholipids and phospholipids from blood samples

Lipids, lysophospholipids and phospholipids in particular, have been shown to be biomarkers and potential therapeutic targets for human diseases. While many extraction and analytical methods have been developed for quantitative analyses of these molecules, most of them are laborious and time-consuming, with associated issues of poor reproducibility. This becomes one of the critical bottle-necks to move lipid markers to clinics. In the current work, we have developed an extremely simple method for lysophospholipids and phospholipids extraction from human plasma or serum samples, which only utilizes a single methanol (MeOH) solvent and involves a single step of centrifugation. This method has been subjected to strict validation by comparing it with classical lipid extraction methods. This simple method will be extremely useful for the lipidomic, diseases marker, and lipid biochemistry fields not only for its potential wide applications associated with its simplicity and reproducibility, but also for its impact in moving lipid markers into clinics through high-throughput processing.

Response and recovery in the plasma metabolome tracks the acute LCMV-induced immune response

Lymphocytic choriomeningitis virus (LCMV) infection of mice is noncytopathic, producing well-characterized changes reflecting the host immune response. Untargeted metabolomics using mass spectrometry identified endogenous small molecule changes in blood from mice inoculated with LCMV, sampled at days 1, 3, 7, and 14 post infection. These time points correspond to well characterized events during acute LCMV infection and the immune response. Diverse pathways were altered, including TCA cycle intermediates, gamma-glutamyl dipeptides, lysophosphatidyl cholines, and fatty acids. The kynurenine pathway was activated, surprising because it is stimulated by IFN-gamma, which LCMV suppresses, thus, suggesting alternative activators. In contrast, biopterin/neopterin, another IFN-gamma stimulated pathway, was not activated. Many metabolites followed "response and recovery" kinetics, decreasing after infection to a minimum at days 3-7, and returning to normal by day 14. The TCA pathway followed this pattern, including citrate, cis-aconitate and alpha-ketoglutarate, intriguing because succinate has been shown to mediate cellular immunity. This response and recovery dynamic tracks the immune response, including the rise and fall of natural killer cell populations, serum TNF receptor concentration, and viral clearance. Metabolomics can provide target pathways for molecular diagnostics or therapeutics of viral infection and immunity.

Measurement of endogenous lysophosphatidic acid by ESI-MS/MS in plasma samples requires pre-separation of lysophosphatidylcholine

The levels of lysophosphatidic acid (LPA) or lysophosphatidylcholine (LPC) in plasma have been shown to be markers for several human diseases, including cancers. Here we show that the presence of LPC or other lysophospholipids (LPLs) in lipids extracted from biological samples affects accurate measurement of endogenous LPA in biological samples. We report for the first time the artificial conversion of LPC and lysophosphatidylserine (LPS) to LPA at the ion source of electrospray ionization tandem mass spectrometry (ESI-MS/MS). To avoid the interference of LPC with the quantification of LPA, a method based on high-performance liquid chromatography (HPLC) separation of LPA from LPC has been developed.

TNF-alpha-induced up-regulation of pro-inflammatory cytokines is reduced by phosphatidylcholine in intestinal epithelial cells

Background

Phosphatidylcholine (PC) is a major lipid of the gastrointestinal mucus layer. We recently showed that mucus from patients suffering from ulcerative colitis has low levels of PC. Clinical studies reveal that the therapeutic addition of PC to the colonic mucus using slow release preparations is beneficial. The positive role of PC in this disease is still unclear; however, we have recently shown that PC has an intrinsic anti-inflammatory property. It could be demonstrated that the exogenous application of PC inhibits membrane-dependent actin assembly and TNF-α-induced nuclear NF-κB activation. We investigate here in more detail the hypothesis that the exogenous application of PC has anti-inflammatory properties.

Methods

PC species with different fatty acid side chains were applied to differentiated and non-differentiated Caco-2 cells treated with TNF-α to induce a pro-inflammatory response. We analysed TNF-α-induced NF-κB-activation via the transient expression of a NF-κB-luciferase reporter system. Pro-inflammatory gene transcription was detected with the help of a quantitative real time (RT)-PCR analysis. We assessed the binding of TNF-α to its receptor by FACS and analysed lipid rafts by isolating detergent resistant membranes (DRMs).

Results

The exogenous addition of all PC species tested significantly inhibited TNF-α-induced pro-inflammatory signalling. The expression levels of IL-8, ICAM-1, IP-10, MCP-1, TNF-α and MMP-1 were significantly reduced after PC pre-treatment for at least two hours. The effect was comparable to the inhibition of NF-kB by the NF-kB inhibitor SN 50 and was not due to a reduced binding of TNF-α to its receptor or a decreased surface expression of TNF-α receptors. PC was also effective when applied to the apical side of polarised Caco-2 cultures if cells were stimulated from the basolateral side. PC treatment changed the compartmentation of the TNF-α-receptors 1 and 2 to DRMs.

Conclusion

PC induces a prolonged inhibition of TNF-α-induced pro-inflammatory signalling. This inhibition may be caused by a shift of the TNF-α receptors at the surface to lipid rafts. Our results may offer a potential molecular explanation for the positive role of PC seen in clinical studies for the treatment of ulcerative colitis.

Peptidoglycan induces cyclooxygenase-2 expression in macrophages by activating the neutral sphingomyelinase-ceramide pathway

The sphingomyelin signal transduction pathway is known to play a role in mediating the action of various cytokines. Herein, we examined the role of neutral sphingomyelinase (nSMase)/ceramide in peptidoglycan (PGN)-induced NF-kappaB activation and cyclooxygenase-2 (COX-2) expression in macrophages. PGN-induced COX-2 expression was attenuated by an nSMase inhibitor (3-O-methyl-sphingomyeline, 3-OMS) and ceramidase, but not by an acidic SMase inhibitor (imipramine). C2-ceramide, bacterial SMase (which mimics cellular SMase activity), and a ceramidase inhibitor (N-oleoyl-ethanolamine) individually had no effect on COX-2 expression; however, they markedly enhanced PGN-induced COX-2 expression. PGN activated nSMase, but not acidic SMase, resulting in increased ceramide generation. PGN-induced nSMase activation and ceramide formation were inhibited by 3-OMS, but not by imipramine. PGN-induced COX-2 expression was inhibited by a p38 MAPK inhibitor (SB 203580) and dominant negative mutants of MAPK kinase (MKK) 3, MKK6, and p38 MAPKalpha. 3-OMS selectively inhibited PGN-induced p38 MAPK and MKK3/6 activation, but not JNK or ERK1/2. C2-ceramide, bacterial SMase, and N-oleoyl-ethanolamine all induced p38 MAPK or MKK3/6 activation. The PGN-mediated increases in kappaB-luciferase activity were also inhibited by 3-OMS and the p38 MAPKalphaDN, but not by imipramine. Furthermore, C2-ceramide caused an increase in kappaB-luciferase activity. Our data demonstrate for the first time that PGN activates the nSMase/ceramide pathway to induce MKK3/6/p38 MAPK activation, which in turn initiates NF-kappaB activation and ultimately induces COX-2 expression in macrophages. The nSMase/ceramide pathway is required but might not be sufficient for COX-2 expression induced by PGN.

Metabolism and atherogenic disease association of lysophosphatidylcholine

Lysophosphatidylcholine (LPC) is a major plasma lipid that has been recognized as an important cell signalling molecule produced under physiological conditions by the action of phospholipase A(2) on phosphatidylcholine. LPC transports glycerophospholipid components such as fatty acids, phosphatidylglycerol and choline between tissues. LPC is a ligand for specific G protein-coupled signalling receptors and activates several second messengers. LPC is also a major phospholipid component of oxidized low-density lipoproteins (Ox-LDL) and is implicated as a critical factor in the atherogenic activity of Ox-LDL. Hence, LPC plays an important role in atherosclerosis and acute and chronic inflammation. In this review we focus in some detail on LPC function, biochemical pathways, sources and signal-transduction system. Moreover, we outline the detection of LPC by mass spectrometry which is currently the best method for accurate and simultaneous analysis of each individual LPC species and reveal the pathophysiological implication of LPC which makes it an interesting target for biomarker and drug development regarding atherosclerosis and cardiovascular disorders.

Oral phosphatidylcholine pretreatment decreases ischemia-reperfusion-induced methane generation and the inflammatory response in the small intestine

We have shown that phosphatidylcholine (PC) metabolites may have a function in counteracting the production of reactive oxygen species (ROS), and that this mechanism can lead to the generation of methane from choline. The aims were to establish whether the dietary administration of PC can protect the reperfused small bowel mucosa by its acting as an anti-inflammatory agent and to investigate this possibility in association with in vivo methane generation. Group 1 (n = 5) of anesthetized dogs served as sham-operated controls, whereas in groups 2 (n = 6) and 3 (n = 6), complete small intestinal ischemia was induced by occluding the superior mesenteric artery for 60 min. Groups 1 and 2 were fed with normal laboratory chow for 1 week before the experiments, whereas the animals in group 3 received a special diet containing 1% soybean PC. The intramucosal pH and the difference of the arterial and local PCO2 (PCO2 gap) were detected by indirect tonometry. Intestinal superoxide production and myeloperoxidase (MPO) activity (a marker of tissue leukocyte infiltration) were ascertained on ileal biopsy samples 180 min after reperfusion. The content of methane in the exhaled air was determined by gas chromatography. I/R was characterized by significant tissue acidosis with ROS generation and elevated MPO activity. These changes were accompanied by increased methane production in the exhaled air during reoxygenation. The PC-enriched diet prevented the decrease in intramucosal pH, diminished the intestinal superoxide generation and the MPO activity, and significantly decreased the exhaled methane concentration. The increased dietary uptake of PC exerts an anti-inflammatory influence in the gastrointestinal tract. Exhaled methane is linked to abnormal ROS generation; a decreased methane production is associated with significantly reduced inflammatory activation during I/R.

Experimental therapeutic strategies for severe sepsis: mediators and mechanisms

Severe sepsis is the leading cause of mortality in intensive care units. The limited ability of current therapies to reduce sepsis mortality rates has fueled research efforts for the development of novel treatment strategies. Through the close collaboration between clinicians and scientists, progress can be seen in the struggle to develop effective therapeutic approaches for the treatment of sepsis and other immune and inflammatory disorders. Indeed, significant advances in intensive care, such as lung protective mechanical ventilation, improved antibiotics, and superior monitoring of systemic perfusion, are improving patient survival. Nonetheless, specific strategies that target the pathophysiological disorders in sepsis patients are essential to further improve clinical outcomes. This article reviews current clinical management approaches and experimental interventions that target pleiotropic or late-acting inflammatory mediators like caspases, C5a, MIF, and HMGB1, or the body's endogenous inflammatory control mechanisms such as the cholinergic anti-inflammatory pathway. These inflammatory mediators and anti-inflammatory mechanisms, respectively, show significant potential for the development of new experimental therapies for the treatment of severe sepsis and other infectious and inflammatory disorders.

Changes of the plasma metabolome during an oral glucose tolerance test: is there more than glucose to look at?

The oral glucose tolerance test (oGTT) is a common tool to provoke a metabolic challenge for scientific purposes, as well as for diagnostic reasons, to monitor the kinetics of glucose and insulin. Here, we aimed to follow the variety of physiological changes of the whole metabolic pattern in plasma during an oGTT in healthy subjects in a nontargeted reversed-phase ultra performance liquid chromatography coupled to electrospray ionization quadrupole time of flight mass spectrometric metabolomics approach. We detected 11,500 metabolite ion masses/individual. Applying multivariate data analysis, four major groups of metabolites have been detected as the most discriminating oGTT biomarkers: free fatty acids (FFA), acylcarnitines, bile acids, and lysophosphatidylcholines. We found in detail 1) a strong decrease of all saturated and monounsaturated FFA studied during the oGTT; 2) a significant faster decline of palmitoleate (C16:1) and oleate (C18:1) FFA levels than their saturated counterparts; 3) a strong relative increase of polyunsaturated fatty acids in the fatty acid pattern at 120 min; and 4) a clear decrease in plasma C10:0, C12:0, and C14:1 acylcarnitine levels. These data reflect the switch from beta-oxidation to glycolysis and fat storage during the oGTT. Moreover, the bile acids glycocholic acid, glycochenodeoxycholic acid, and glycodeoxycholic acid were highly discriminative, showing a biphasic kinetic with a maximum of a 4.5- to 6-fold increase at 30 min after glucose ingestion, a significant decrease over the next 60 min followed by an increase until the end of the oGTT. Lysophosphatidylcholines were also increased significantly. The findings of our metabolomics study reveal detailed insights in the complex physiological regulation of the metabolism during an oGTT offering novel perspectives of this widely used procedure.

Plasma ceramides are elevated in obese subjects with type 2 diabetes and correlate with the severity of insulin resistance

OBJECTIVE

To quantitate plasma ceramide subspecies concentrations in obese subjects with type 2 diabetes and relate these plasma levels to the severity of insulin resistance. Ceramides are a putative mediator of insulin resistance and lipotoxicity, and accumulation of ceramides within tissues in obese and diabetic subjects has been well described.

RESEARCH DESIGN AND METHODS

We analyzed fasting plasma ceramide subspecies by quantitative tandem mass spectrometry in 13 obese type 2 diabetic patients and 14 lean healthy control subjects. Results were related to insulin sensitivity measured with the hyperinsulinemic-euglycemic clamp technique and with plasma tumor necrosis factor-alpha (TNF-alpha) levels, a marker of inflammation. Ceramide species (C18:1, 18:0, 20:0, 24:1, and 24:0) were quantified using electrospray ionization tandem mass spectrometry after separation with high-performance liquid chromatography.

RESULTS

Insulin sensitivity (mg x kg(-1) x min(-1)) was lower in type 2 diabetic patients (4.90 +/- 0.3) versus control subjects (9.6 +/- 0.4) (P < 0.0001). Type 2 diabetic subjects had higher (P < 0.05) concentrations of C18:0, C20:0, C24:1, and total ceramide. Insulin sensitivity was inversely correlated with C18:0, C20:0, C24:1, C24:0, and total ceramide (all P < 0.01). Plasma TNF-alpha concentration was increased (P < 0.05) in type 2 diabetic subjects and correlated with increased C18:1 and C18:0 ceramide subspecies.

CONCLUSIONS

Plasma ceramide levels are elevated in type 2 diabetic subjects and may contribute to insulin resistance through activation of inflammatory mediators, such as TNF-alpha.