Polyunsaturated lysophosphatidic acid as a potential asthma biomarker

Farfarae Flos Mitigates Cigarette Smoking-Induced Lung Inflammation by Regulating the Lysophosphatidylcholine Biosynthesis and Tryptophan Metabolism

An increased risk of developing respiratory diseases has been linked to exposure to cigarette smoking (CS). The flower buds of Tussilago farfara L., also known as Farfarae Flos (FF), can be used for the treatment of cough, bronchitis, and asthmatic disorders in China. In the present study, we used lung and fecal metabolomics, as well as the intestinal flora analysis, aimed to investigate the protective effect of FF against the CS exposure induced lung inflammation on mice. The results showed that FF administration could relieve the lung inflammation as demonstrated by lung index, interleukin-6 (IL-6), and interleukin-1β (IL-1β) levels, as well as the pulmonary pathological change. The lung metabolomics coupled with molecular docking showed that FF could alleviate lung inflammation by regulating lysophosphatidylcholine biosynthesis through the caffeoyl quinic acids distributed in the lung tissue. In addition, fecal metabolome coupled with 16S rRNA gene sequencing showed that FF could regulate the tryptophan metabolism by regulating the intestinal flora disorders. This study provided new insights of FF to relieve CS-induced pulmonary inflammation with the multimechanism.

Severe Allergy as a Chronic Inflammatory Condition From a Systems Biology Perspective

Persistent and unresolved inflammation is a common underlying factor observed in several and seemingly unrelated human diseases, including cardiovascular and neurodegenerative diseases. Particularly, in atopic conditions, acute inflammatory responses such as those triggered by insect venom, food or drug allergies possess also a life-threatening potential. However, respiratory allergies predominantly exhibit late immune responses associated with chronic inflammation, that can eventually progress into a severe phenotype displaying similar features as those observed in other chronic inflammatory diseases, as is the case of uncontrolled severe asthma. This review aims to explore the different facets and systems involved in chronic allergic inflammation, including processes such as tissue remodelling and immune cell dysregulation, as well as genetic, metabolic and microbiota alterations, which are common to other inflammatory conditions. Our goal here was to deepen on the understanding of an entangled disease as is chronic allergic inflammation and expose potential avenues for the development of better diagnostic and intervention strategies.

The Role of Lysophospholipid Metabolites LPC and LPA in the Pathogenesis of Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is a heterogeneous lung condition characterized by persistent respiratory symptoms and airflow limitation. While there are some available treatment options, the effectiveness of treatment varies depending on individual differences and the phenotypes of the disease. Therefore, exploring or identifying potential therapeutic targets for COPD is urgently needed. In recent years, there has been growing evidence showing that lysophospholipids, namely lysophosphatidylcholine (LPC) and lysophosphatidic acid (LPA), can play a significant role in the pathogenesis of COPD. Exploring the metabolism of lysophospholipids holds promise for understanding the underlying mechanism of COPD development and developing novel strategies for COPD treatment. This review primarily concentrates on the involvement and signaling pathways of LPC and LPA in the development and progression of COPD. Furthermore, we reviewed their associations with clinical manifestations, phenotypes, and prognosis within the COPD context and discussed the potential of the pivotal signaling molecules as viable therapeutic targets for COPD treatment.

Emerging Roles of Lysophosphatidic Acid in Macrophages and Inflammatory Diseases

Lysophosphatidic acid (LPA) is a bioactive phospholipid that regulates physiological and pathological processes in numerous cell biological functions, including cell migration, apoptosis, and proliferation. Macrophages are found in most human tissues and have multiple physiological and pathological functions. There is growing evidence that LPA signaling plays a significant role in the physiological function of macrophages and accelerates the development of diseases caused by macrophage dysfunction and inflammation, such as inflammation-related diseases, cancer, atherosclerosis, and fibrosis. In this review, we summarize the roles of LPA in macrophages, analyze numerous macrophage- and inflammation-associated diseases triggered by LPA, and discuss LPA-targeting therapeutic strategies.

Stratification of asthma by lipidomic profiling of induced sputum supernatant

BACKGROUND

Asthma is a chronic respiratory disease with significant heterogeneity in its clinical presentation and pathobiology. There is need for improved understanding of respiratory lipid metabolism in asthma patients and its relation to observable clinical features.

OBJECTIVE

We performed a comprehensive, prospective, cross-sectional analysis of the lipid composition of induced sputum supernatant obtained from asthma patients with a range of disease severities, as well as from healthy controls.

METHODS

Induced sputum supernatant was collected from 211 adults with asthma and 41 healthy individuals enrolled onto the U-BIOPRED (Unbiased Biomarkers for the Prediction of Respiratory Disease Outcomes) study. Sputum lipidomes were characterized by semiquantitative shotgun mass spectrometry and clustered using topologic data analysis to identify lipid phenotypes.

RESULTS

Shotgun lipidomics of induced sputum supernatant revealed a spectrum of 9 molecular phenotypes, highlighting not just significant differences between the sputum lipidomes of asthma patients and healthy controls, but also within the asthma patient population. Matching clinical, pathobiologic, proteomic, and transcriptomic data helped inform the underlying disease processes. Sputum lipid phenotypes with higher levels of nonendogenous, cell-derived lipids were associated with significantly worse asthma severity, worse lung function, and elevated granulocyte counts.

CONCLUSION

We propose a novel mechanism of increased lipid loading in the epithelial lining fluid of asthma patients resulting from the secretion of extracellular vesicles by granulocytic inflammatory cells, which could reduce the ability of pulmonary surfactant to lower surface tension in asthmatic small airways, as well as compromise its role as an immune regulator.

Cellular and Molecular Control of Lipid Metabolism in Idiopathic Pulmonary Fibrosis: Clinical Application of the Lysophosphatidic Acid Pathway

Idiopathic pulmonary fibrosis (IPF) is a representative disease that causes fibrosis of the lungs. Its pathogenesis is thought to be characterized by sustained injury to alveolar epithelial cells and the resultant abnormal tissue repair, but it has not been fully elucidated. IPF is currently difficult to cure and is known to follow a chronic progressive course, with the patient's survival period estimated at about three years. The disease occasionally exacerbates acutely, leading to a fatal outcome. In recent years, it has become evident that lipid metabolism is involved in the fibrosis of lungs, and various reports have been made at the cellular level as well as at the organic level. The balance among eicosanoids, sphingolipids, and lipid composition has been reported to be involved in fibrosis, with particularly close attention being paid to a bioactive lipid "lysophosphatidic acid (LPA)" and its pathway. LPA signals are found in a wide variety of cells, including alveolar epithelial cells, vascular endothelial cells, and fibroblasts, and have been reported to intensify pulmonary fibrosis via LPA receptors. For instance, in alveolar epithelial cells, LPA signals reportedly induce mitochondrial dysfunction, leading to epithelial damage, or induce the transcription of profibrotic cytokines. Based on these mechanisms, LPA receptor inhibitors and the metabolic enzymes involved in LPA formation are now considered targets for developing novel means of IPF treatment. Advances in basic research on the relationships between fibrosis and lipid metabolism are opening the path to new therapies targeting lipid metabolism in the treatment of IPF.

Sex-Biased Control of Inflammation and Metabolism by a Mitochondrial Nod-Like Receptor

Mitochondria regulate steroid hormone synthesis, and in turn sex hormones regulate mitochondrial function for maintaining cellular homeostasis and controlling inflammation. This crosstalk can explain sex differences observed in several pathologies such as in metabolic or inflammatory disorders. Nod-like receptor X1 (NLRX1) is a mitochondria-associated innate receptor that could modulate metabolic functions and attenuates inflammatory responses. Here, we showed that in an infectious model with the human protozoan parasite, Leishmania guyanensis, NLRX1 attenuated inflammation in females but not in male mice. Analysis of infected female and male bone marrow derived macrophages showed both sex- and genotype-specific differences in both inflammatory and metabolic profiles with increased type I interferon production, mitochondrial respiration, and glycolytic rate in Nlrx1-deficient female BMDMs in comparison to wild-type cells, while no differences were observed between males. Transcriptomics of female and male BMDMs revealed an altered steroid hormone signaling in Nlrx1-deficient cells, and a “masculinization” of Nlrx1-deficient female BMDMs. Thus, our findings suggest that NLRX1 prevents uncontrolled inflammation and metabolism in females and therefore may contribute to the sex differences observed in infectious and inflammatory diseases.

Dual-Directional Regulation of Belamcanda chinensis Extract on Ovalbumin-Induced Asthma in Guinea Pigs of Different Sexes Based on Serum Metabolomics

To explore the potential biomarkers and metabolic pathways underlying the anti-asthma effects of Belamcanda chinensis extract, this study established an ovalbumin-induced allergic bronchial asthma model in guinea pigs. Sixty guinea pigs were randomly divided into the blank control group, model control group, Belamcanda chinensis extract groups (0.8 g/kg, 1.2 g/kg, 1.6 g/kg, respectively), and dexamethasone acetate tablet group (0.5 mg/kg). Starting on the 22nd day, the drugs were administered by gavage for seven consecutive days. Serum and bronchoalveolar lavage fluid (BALF) were collected. The levels of IL-4 and IgE in the serum and IFN-γ and TNF-α in the BALF were detected by ELISA. UPLC-MS was combined with multivariate statistical analyses, including partial least squares discriminant analysis (PLS-DA), and differential metabolites between groups were identified. Metabolic pathway analysis was performed by querying the KEGG (Kyoto Encyclopedia of Genes and Genomes) online database. Female and male guinea pigs were analyzed. The results showed that compared with the model group, the IgE and IL-4 serum levels were significantly decreased in the 1.6 g/kg group, and the IFN-γ level in the BALF was significantly increased. The TNF-α level was significantly decreased in the 1.2 g/kg and 1.6 g/kg groups. There were 39 common differential metabolites among females and males, and 37 differential metabolites showed opposite regulatory trends in the serum of guinea pigs with asthma and after treatment, mainly involving 17 metabolic pathways, such as pantothenate and CoA biosynthesis, the arachidonic acid mechanism, and glycerophospholipid metabolism. Belamcanda chinensis extract improved OVA-induced asthma, as determined based on immune mechanisms, inflammation, nerve metabolism, and energy metabolism. The serum levels of metabolites produced by the model animals exhibited distinct sex-specific differences, and the treatment effect of Belamcanda chinensis extract also showed sex-specific differences and bidirectional regulation.

Phospholipase A1 Member A Activates Fibroblast-like Synoviocytes through the Autotaxin-Lysophosphatidic Acid Receptor Axis

Lysophosphatidylserine (lysoPS) is known to regulate immune cell functions. Phospholipase A1 member A (PLA1A) can generate this bioactive lipid through hydrolysis of sn-1 fatty acids on phosphatidylserine (PS). PLA1A has been associated with cancer metastasis, asthma, as well as acute coronary syndrome. However, the functions of PLA1A in the development of systemic autoimmune rheumatic diseases remain elusive. To investigate the possible implication of PLA1A during rheumatic diseases, we monitored PLA1A in synovial fluids from patients with rheumatoid arthritis and plasma of early-diagnosed arthritis (EA) patients and clinically stable systemic lupus erythematosus (SLE) patients. We used human primary fibroblast-like synoviocytes (FLSs) to evaluate the PLA1A-induced biological responses. Our results highlighted that the plasma concentrations of PLA1A in EA and SLE patients were elevated compared to healthy donors. High concentrations of PLA1A were also detected in synovial fluids from rheumatoid arthritis patients compared to those from osteoarthritis (OA) and gout patients. The origin of PLA1A in FLSs and the arthritic joints remained unknown, as healthy human primary FLSs does not express the PLA1A transcript. Besides, the addition of recombinant PLA1A stimulated cultured human primary FLSs to secrete IL-8. Preincubation with heparin, autotaxin (ATX) inhibitor HA130 or lysophosphatidic acid (LPA) receptor antagonist Ki16425 reduced PLA1A-induced-secretion of IL-8. Our data suggested that FLS-associated PLA1A cleaves membrane-exposed PS into lysoPS, which is subsequently converted to LPA by ATX. Since primary FLSs do not express any lysoPS receptors, the data suggested PLA1A-mediated pro-inflammatory responses through the ATX-LPA receptor signaling axis.

Risk of hospitalised falls and hip fractures in working age adults receiving mental health care

OBJECTIVE

This retrospective cohort study investigates risks of hospitalised fall or hip fractures in working age adults receiving mental health care in South London.

METHODS

Patients aged 18 to 64, who received a first mental illness diagnosis between 2008 and 2016 were included. Primary outcome was hospitalised falls, secondary outcome was hip fractures. Age- and gender-standardised incidence rates and incidence rate ratios (IRRs) compared to local general population were calculated. Multivariate Cox proportionate hazard models were used to investigate which mental health diagnoses were most at risk.

RESULTS

In 50,885 patients incidence rates were 8.3 and 0.8 per 1,000 person-years for falls and hip fractures respectively. Comparing mental health patients to the general population, age-and-gender-adjusted IRR for falls was 3.6 (95% CI: 3.3-4.0) and for hip fractures 7.5 (95% CI: 5.2-10.4). The falls IRR was highest for borderline personality and bipolar disorder and lowest for schizophreniform and anxiety disorder. After adjusting for multiple confounders in the sample of mental health service users, borderline personality disorder yielded a higher and anxiety disorder a lower falls risk.

CONCLUSION

Working age adults using mental health services have almost four times the incidence of hospitalised falls compared to general population. Targeted interventions are warranted.

Huanglong Antitussive Granule Relieves Acute Asthma Through Regulating Pulmonary Lipid Homeostasis

Background: Asthma is a respiratory disease with chronic airway inflammatory, and individuals with asthma exacerbations is one of the most frequent causes of hospitalization. Huanglong antitussive granule (HL Granule), a Chinese proprietary herbal medicine, has been proved to be effective in the clinical treatment of pulmonary disease. This study is devoted to the pharmacodynamics of HL Granule in acute asthma and the possible mechanism from the perspective of lipidomics. Methods: Mice were divided into four groups, control group, acute asthma model group, HL Granule treatment and montelukast sodium treatment group. Acute asthma was induced by ovalbumin (OVA). Histopathology, pulmonary function and enzyme linked immunosorbent assay (ELISA) were used to validated model and effect of HL Granule. Lipids were detected by ultra-high-performance liquid chromatography coupled to hybrid Quadrupole-Exactive Orbitrap mass spectrometry (UHPLC-Q-Exactive Orbitrap MS) and identified by MS-DAIL and built-in Lipidblast database. Differentially expressed lipids recalled in HL Granule treatment group were extracted for heatmap, enrichment analysis and correlation analysis. Results: HL Granule was effective in decreasing airway hyperresponsiveness (AHR), airway inflammatory and the levels of IL-4 and IL-5. A total of 304 and 167 lipids were identified in positive and negative ion mode, respectively. Among these, 104 and 73 lipids were reserved in HL Granule group (FDR < 0.05), including acylcarnitine (ACar), fatty acid (FA), lysophosphatidylcholine (LPC), phosphatidylcholine (PC), lysophosphatidylethanolamine (LPE), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), phosphatidylinositol (PI), phosphatidylserine (PS), diglyceride (DG), triglyceride (TG), sphingomyelin (SM) and ceramide (Cer). Furthermore, 118 and 273 correlations among 47 and 96 lipids in the positive and negative were observed, with ether-linked phosphatidylethanolamine (PEe) and phosphatidylcholine (PCe) (FDR < 0.001, Spearman correlation coefficient r ² > 0.75). Conclusion: HL Granule might improve pulmonary lipid homeostasis and could be used as an alternative or supplementary therapy in clinical for the treatment of asthma.

Emerging Role of Phospholipase-Derived Cleavage Products in Regulating Eosinophil Activity: Focus on Lysophospholipids, Polyunsaturated Fatty Acids and Eicosanoids

Eosinophils are important effector cells involved in allergic inflammation. When stimulated, eosinophils release a variety of mediators initiating, propagating, and maintaining local inflammation. Both, the activity and concentration of secreted and cytosolic phospholipases (PLAs) are increased in allergic inflammation, promoting the cleavage of phospholipids and thus the production of reactive lipid mediators. Eosinophils express high levels of secreted phospholipase A2 compared to other leukocytes, indicating their direct involvement in the production of lipid mediators during allergic inflammation. On the other side, eosinophils have also been recognized as crucial mediators with regulatory and homeostatic roles in local immunity and repair. Thus, targeting the complex network of lipid mediators offer a unique opportunity to target the over-activation and 'pro-inflammatory' phenotype of eosinophils without compromising the survival and functions of tissue-resident and homeostatic eosinophils. Here we provide a comprehensive overview of the critical role of phospholipase-derived lipid mediators in modulating eosinophil activity in health and disease. We focus on lysophospholipids, polyunsaturated fatty acids, and eicosanoids with exciting new perspectives for future drug development.

Lysophospholipids in Lung Inflammatory Diseases

The lysophospholipids (LPLs) belong to a group of bioactive lipids that play pivotal roles in several physiological and pathological processes. LPLs are derivatives of phospholipids and consist of a single hydrophobic fatty acid chain, a hydrophilic head, and a phosphate group with or without a large molecule attached. Among the LPLs, lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) are the simplest, and have been shown to be involved in lung inflammatory symptoms and diseases such as acute lung injury, asthma, and chronic obstructive pulmonary diseases. G protein-coupled receptors (GPCRs) mediate LPA and S1P signaling. In this chapter, we will discuss on the role of LPA, S1P, their metabolizing enzymes, inhibitors or agonists of their receptors, and their GPCR-mediated signaling in lung inflammatory symptoms and diseases, focusing specially on acute respiratory distress syndrome, asthma, and chronic obstructive pulmonary disease.

Role of lysophosphatidic acid and its receptors in health and disease: novel therapeutic strategies

Lysophosphatidic acid (LPA) is an abundant bioactive phospholipid, with multiple functions both in development and in pathological conditions. Here, we review the literature about the differential signaling of LPA through its specific receptors, which makes this lipid a versatile signaling molecule. This differential signaling is important for understanding how this molecule can have such diverse effects during central nervous system development and angiogenesis; and also, how it can act as a powerful mediator of pathological conditions, such as neuropathic pain, neurodegenerative diseases, and cancer progression. Ultimately, we review the preclinical and clinical uses of Autotaxin, LPA, and its receptors as therapeutic targets, approaching the most recent data of promising molecules modulating both LPA production and signaling. This review aims to summarize the most update knowledge about the mechanisms of LPA production and signaling in order to understand its biological functions in the central nervous system both in health and disease.

"Modeling-Prediction" Strategy for Deep Profiling of Lysophosphatidic Acids by Liquid Chromatography-Mass Spectrometry: Exploration Biomarkers of Breast Cancer

Lysophosphatidic acids (LPAs) are important bioactive phospholipids consisting of various species involved in a wide array of physiological and pathological processes. However, LPAs were rarely identified in untargeted lipidomics studies because of the incompatibility with analytical methods. Moreover, in targeted studies, the coverages of LPAs remained unsatisfactorily low due to the limitation of reference standards. Herein, a "modeling-prediction" workflow for deep profiling of LPAs by liquid chromatography-mass spectrometry was developed. Multiple linear regression models of qualitative and quantitative parameters were established according to features of fatty acyl tails of the commercial standards to predict the corresponding parameters for unknown LPAs. Then 72 multiple reaction monitoring (MRM) transitions were monitored simultaneously and species of LPA 14:0, LPA 16:1, LPA 18:3, LPA 20:3 and LPA 20:5 were firstly characterized and quantified in plasma. Finally, the workflow was applied to explore the changes of LPAs in plasma of breast cancer patients compared with healthy volunteers. Multi-LPAs indexes with strong diagnostic ability for breast cancer were identified successfully using Student's t- test, orthogona partial least-squares discrimination analysis (OPLS-DA) and logistic regression- receiver operating characteristic (ROC) curve analysis. The proposed workflow with high sensitivity, high accuracy, high coverage and reliable identification would be a powerful complement to untargeted lipidomics and shed a light on the analysis of other lipids.

Antibodies Against Lysophosphatidic Acid Protect Against Blast-Induced Ocular Injuries

Exposure to blast overpressure waves is implicated as the major cause of ocular injuries and resultant visual dysfunction in veterans involved in recent combat operations. No effective therapeutic strategies have been developed so far for blast-induced ocular dysfunction. Lysophosphatidic acid (LPA) is a bioactive phospholipid generated by activated platelets, astrocytes, choroidal plexus cells, and microglia and is reported to play major roles in stimulating inflammatory processes. The levels of LPA in the cerebrospinal fluid have been reported to increase acutely in patients with traumatic brain injury (TBI) as well as in a controlled cortical impact (CCI) TBI model in mice. In the present study, we have evaluated the efficacy of a single intravenous administration of a monoclonal LPA antibody (25 mg/kg) given at 1 h post-blast for protection against injuries to the retina and associated ocular dysfunctions. Our results show that a single 19 psi blast exposure significantly increased the levels of several species of LPA in blood plasma at 1 and 4 h post-blast. The anti-LPA antibody treatment significantly decreased glial cell activation and preserved neuronal cell morphology in the retina on day 8 after blast exposure. Optokinetic measurements indicated that anti-LPA antibody treatment significantly improved visual acuity in both eyes on days 2 and 6 post-blast exposure. Anti-LPA antibody treatment significantly increased rod photoreceptor and bipolar neuronal cell signaling in both eyes on day 7 post-blast exposure. These results suggest that blast exposure triggers release of LPAs, which play a major role promoting blast-induced ocular injuries, and that a single early administration of anti-LPA antibodies provides significant protection.

Metabolic response of blood vessels to TNFα

TNFα signaling in the vascular endothelium elicits multiple inflammatory responses that drive vascular destabilization and leakage. Bioactive lipids are main drivers of these processes. In vitro mechanistic studies of bioactive lipids have been largely based on two-dimensional endothelial cell cultures that, due to lack of laminar flow and the growth of the cells on non-compliant stiff substrates, often display a pro-inflammatory phenotype. This complicates the assessment of inflammatory processes. Three-dimensional microvessels-on-a-chip models provide a unique opportunity to generate endothelial microvessels in a more physiological environment. Using an optimized targeted liquid chromatography–tandem mass spectrometry measurements of a panel of pro- and anti-inflammatory bioactive lipids, we measure the profile changes upon administration of TNFα. We demonstrate that bioactive lipid profiles can be readily detected from three-dimensional microvessels-on-a-chip and display a more dynamic, less inflammatory response to TNFα, that resembles more the human situation, compared to classical two-dimensional endothelial cell cultures.

In a range of conditions called autoimmune diseases, the immune system attacks the body rather than foreign elements. This can cause inflammation that is harmful for many organs. In particular, immune cells can produce excessive amounts of a chemical messenger called tumor necrosis factor alpha (TNFα for short), which can lead to the release of fatty molecules that damage blood vessels.

This process is normally studied in blood vessels cells that are grown on a dish, without any blood movement. However, in this rigid 2D environment, the cells become ‘stressed’ and show higher levels of inflammation than in the body. This makes it difficult to assess the exact role that TNFα plays in disease.

A new technology is addressing this issue by enabling scientist to culture blood vessels cells in dishes coated with gelatin. This allows the cells to organize themselves in 3D, creating tiny blood vessels in which fluids can flow. However, it was unclear whether these ‘microvessels-on-a-chip’ were better models to study the role of TNFα compared to cells grown on a plate.

Here, Junaid et al. compared the levels of inflammation in blood vessels cells grown in the two environments, showing that cells are less inflamed when they are cultured in 3D. In addition, when the artificial 3D-blood vessels were exposed to TNFα, they responded more like real blood vessels than the 2D models. Finally, experiments showed that it was possible to monitor the release of fatty molecules in this environment. Together, this work suggests that microvessels-on-a-chip are better models to study how TNFα harms blood vessels.

Next, systems and protocols could be develop to allow automated mass drug testing in microvessels-on-a-chip. This would help scientists to quickly screen thousands of drugs and find candidates that can protect blood vessels from TNFα.

Lipid Mediators Regulate Pulmonary Fibrosis: Potential Mechanisms and Signaling Pathways

Idiopathic pulmonary fibrosis (IPF) is a progressive lung disease of unknown etiology characterized by distorted distal lung architecture, inflammation, and fibrosis. The molecular mechanisms involved in the pathophysiology of IPF are incompletely defined. Several lung cell types including alveolar epithelial cells, fibroblasts, monocyte-derived macrophages, and endothelial cells have been implicated in the development and progression of fibrosis. Regardless of the cell types involved, changes in gene expression, disrupted glycolysis, and mitochondrial oxidation, dysregulated protein folding, and altered phospholipid and sphingolipid metabolism result in activation of myofibroblast, deposition of extracellular matrix proteins, remodeling of lung architecture and fibrosis. Lipid mediators derived from phospholipids, sphingolipids, and polyunsaturated fatty acids play an important role in the pathogenesis of pulmonary fibrosis and have been described to exhibit pro- and anti-fibrotic effects in IPF and in preclinical animal models of lung fibrosis. This review describes the current understanding of the role and signaling pathways of prostanoids, lysophospholipids, and sphingolipids and their metabolizing enzymes in the development of lung fibrosis. Further, several of the lipid mediators and enzymes involved in their metabolism are therapeutic targets for drug development to treat IPF.

Signalling by lysophosphatidate and its health implications

Extracellular lysophosphatidate (LPA) signalling is regulated by the balance of LPA formation by autotaxin (ATX) versus LPA degradation by lipid phosphate phosphatases (LPP) and by the relative expressions of six G-protein-coupled LPA receptors. These receptors increase cell proliferation, migration, survival and angiogenesis. Acute inflammation produced by tissue damage stimulates ATX production and LPA signalling as a component of wound healing. If inflammation does not resolve, LPA signalling becomes maladaptive in conditions including arthritis, neurologic pain, obesity and cancers. Furthermore, LPA signalling through LPA1 receptors promotes fibrosis in skin, liver, kidneys and lungs. LPA also promotes the spread of tumours to other organs (metastasis) and the pro-survival properties of LPA explain why LPA counteracts the effects of chemotherapeutic agents and radiotherapy. ATX is secreted in response to radiation-induced DNA damage during cancer treatments and this together with increased LPA1 receptor expression leads to radiation-induced fibrosis. The anti-inflammatory agent, dexamethasone, decreases levels of inflammatory cytokines/chemokines. This is linked to a coordinated decrease in the production of ATX and LPA1/2 receptors and increased LPA degradation through LPP1. These effects explain why dexamethasone attenuates radiation-induced fibrosis. Increased LPA signalling is also associated with cardiovascular disease including atherosclerosis and deranged LPA signalling is associated with pregnancy complications including preeclampsia and intrahepatic cholestasis of pregnancy. LPA contributes to chronic inflammation because it stimulates the secretion of inflammatory cytokines/chemokines, which increase further ATX production and LPA signalling. Attenuating maladaptive LPA signalling provides a novel means of treating inflammatory diseases that underlie so many important medical conditions.

The roles of autotaxin/lysophosphatidic acid in immune regulation and asthma

Lysophosphatidic acid (LPA) species are present in almost all organ systems and play diverse roles through its receptors. Asthma is an airway disease characterized by chronic allergic inflammation where various innate and adaptive immune cells participate in establishing Th2 immune response. Here, we will review the contribution of LPA and its receptors to the functions of immune cells that play a key role in establishing allergic airway inflammation and aggravation of allergic asthma.

Effects of diet and hyperlipidemia on levels and distribution of circulating lysophosphatidic acid

Lysophosphatidic acids (LPAs) are bioactive radyl hydrocarbon-substituted derivatives of glycerol 3-phosphate. LPA metabolism and signaling are implicated in heritable risk of coronary artery disease. Genetic and pharmacological inhibition of these processes attenuate experimental atherosclerosis. LPA accumulates in atheromas, which may be a consequence of association with LDLs. The source, regulation, and biological activity of LDL-associated LPA are unknown. We examined the effects of experimental hyperlipidemia on the levels and distribution of circulating LPA in mice. The majority of plasma LPA was associated with albumin in plasma from wild-type mice fed normal chow. LDL-associated LPA was increased in plasma from high-fat Western diet-fed mice that are genetically prone to hyperlipidemia (LDL receptor knockout or activated proprotein convertase subtilisin/kexin type 9-overexpressing C57Bl6). Adipose-specific deficiency of the ENPP2 gene encoding the LPA-generating secreted lysophospholipase D, autotaxin (ATX), attenuated these Western diet-dependent increases in LPA. ATX-dependent increases in LDL-associated LPA were observed in isolated incubated plasma. ATX acted directly on LDL-associated lysophospholipid substrates in vitro. LDL from all human subjects examined contained LPA and was decreased by lipid-lowering drug therapies. Human and mouse plasma therefore contains a diet-sensitive LDL-associated LPA pool that might contribute to the cardiovascular disease-promoting effects of LPA.

Development of a Rapid Ultra High-Performance Liquid Chromatography/Tandem Mass Spectrometry Method for the Analysis of sn-1 and sn-2 Lysophosphatidic Acid Regioisomers in Mouse Plasma

Lysophosphatidic acids (lysoPtdOH) are involved in several physiological processes including cell proliferation, inflammation, and glucose metabolism. However, measuring lysoPtdOH is challenging due to inadequate extraction techniques, poor chromatographic resolution, or the inability to discriminate between sn-1 and sn-2 regioisomers. In the present work, we developed a high-throughput (10 min run times) ultra-high-performance liquid chromatography-tandem mass spectrometry method capable of discriminating lysoPtdOH species by their fatty acyl composition and sn-localization on glycerol backbones. We quantitated sn-1/sn-2 regioisomeric pairs of lysoPtdOH with 16:0, 18:0, 18:1, 18:2, 20:4, and 22:6 fatty acyl chains using 50 μL of mouse plasma. The method presented here can be expanded to profile more lysoPtdOH species, and has the potential to be used in clinical settings to quickly screen lysoPtdOH profiles. Finally, the ability to discriminate between sn-1 and sn-2 isomers can provide insights regarding the metabolic origins and fates of specific lysoPtdOH molecules.

Evaluation of lipid markers in surfactant obtained from asthmatic horses exposed to hay

OBJECTIVE To evaluate the lipidomic profile of surfactant obtained from horses with asthma at various clinical stages and to compare results with findings for healthy horses exposed to the same conditions. SAMPLE Surfactant samples obtained from 6 horses with severe asthma and 7 healthy horses. PROCEDURES Clinical evaluation of horses and surfactant analysis were performed. Samples obtained from horses with severe asthma and healthy horses before (baseline), during, and after exposure to hay were analyzed. Crude surfactant pellets were dried prior to dissolution in a solution of isopropanol:methanol:chloroform (4:2:1) containing 7.5mM ammonium acetate. Shotgun lipidomics were performed by use of high-resolution data acquisition on an ion-trap mass spectrometer. Findings were analyzed by use of an ANOVA with a Tukey-Kramer post hoc test. RESULTS Results of lipidomic analysis were evaluated to detect significant differences between groups of horses and among exposure statuses within groups of horses. Significantly increased amounts of cyclic phosphatidic acid (cPA) and diacylglycerol (DAG) were detected in surfactant from severely asthmatic horses during exposure to hay, compared with baseline and postexposure concentrations. Concentrations of cPA and DAG did not change significantly in healthy horses regardless of exposure status. CONCLUSIONS AND CLINICAL RELEVANCE cPA 16:0 and DAG 36:2 were 2 novel lipid mediators identified in surfactant obtained from asthmatic horses with clinical disease. These molecules were likely biomarkers of sustained inflammation. Further studies are needed to evaluate a possible correlation with disease severity and potential alterations in the plasma lipidomic profile of horses with asthma.

High-resolution atmospheric-pressure MALDI mass spectrometry imaging workflow for lipidomic analysis of late fetal mouse lungs

Mass spectrometry imaging (MSI) provides label-free, non-targeted molecular and spatial information of the biomolecules within tissue. Lipids play important roles in lung biology, e.g. as surfactant, preventing alveolar collapse during normal and forced respiration. Lipidomic characterization of late fetal mouse lungs at day 19 of gestation (E19) has not been performed yet. In this study we employed high-resolution atmospheric pressure scanning microprobe matrix-assisted laser desorption/ionization MSI for the lipidomic analysis of E19 mouse lungs. Molecular species of different lipid classes were imaged in E19 lung sections at high spatial and mass resolution in positive- and negative-ion mode. Lipid species were characterized based on accurate mass and on-tissue tandem mass spectrometry. In addition, a dedicated sample preparation protocol, homogenous deposition of matrices on tissue surfaces and data processing parameters were optimized for the comparison of signal intensities of lipids between different tissue sections of E19 lungs of wild type and Pex11β-knockout mice. Our study provides lipid information of E19 mouse lungs, optimized experimental and data processing strategies for the direct comparison of signal intensities of metabolites (lipids) among the tissue sections from MSI experiments. To best of our knowledge, this is the first MSI and lipidomic study of E19 mouse lungs.

Lysophosphatidic acid LPA1 and LPA3 receptors play roles in the maintenance of late tissue plasminogen activator-induced central poststroke pain in mice

We developed a mouse model for central post-stroke pain (CPSP), a centrally-originated neuropathic pain (NeuP). In this mode, mice were first injected with Rose Bengal, followed by photo-irradiation of left middle cerebral artery (MCA) to generate thrombosis. Although the MCA thrombosis was soon dissolved, the reduced blood flow remained for more than 24 h due to subsequent occlusion of microvessels. This photochemically induced thrombosis (PIT) model showed a hypersensitivity to the electrical stimulation of both sides of paw, but did not show any abnormal pain in popular thermal or mechanical nociception tests. When tissue-type plasminogen activator (tPA) was injected 6 h after the PIT stress, tPA-dependent hypersensitivity to the electrical paw stimulation and stable thermal and mechanical hyperalgesia on both sides for more than 17 or 18 days after the PIT treatment. These hyperalgesic effects were abolished in lysophosphatidic acid receptor 1 (LPA1)- and lysophosphatidic acid receptor 3 (LPA3)-deficient mice. When Ki-16425, an LPA1 and LPA3 antagonist was treated twice daily for 6 days consecutively, the thermal and mechanical hyperalgesia at day 17 and 18 were significantly reversed. The liquid chromatography-mass spectrometry (LC-MS/MS) analysis revealed that there is a significant increase in several species of LPA molecules in somatosensory S-I and medial dorsal thalamus (MD), but not in striatum or ventroposterior thalamus. All these results suggest that LPA1 and LPA3 signaling play key roles in the development and maintenance of CPSP.

Coming of Age for Autotaxin and Lysophosphatidate Signaling: Clinical Applications for Preventing, Detecting and Targeting Tumor-Promoting Inflammation

A quarter-century after the discovery of autotaxin in cell culture, the autotaxin-lysophosphatidate (LPA)-lipid phosphate phosphatase axis is now a promising clinical target for treating chronic inflammatory conditions, mitigating fibrosis progression, and improving the efficacy of existing cancer chemotherapies and radiotherapy. Nearly half of the literature on this axis has been published during the last five years. In cancer biology, LPA signaling is increasingly being recognized as a central mediator of the progression of chronic inflammation in the establishment of a tumor microenvironment which promotes cancer growth, immune evasion, metastasis, and treatment resistance. In this review, we will summarize recent advances made in understanding LPA signaling with respect to chronic inflammation and cancer. We will also provide perspectives on the applications of inhibitors of LPA signaling in preventing cancer initiation, as adjuncts extending the efficacy of current cancer treatments by blocking inflammation caused by either the cancer or the cancer therapy itself, and by disruption of the tumor microenvironment. Overall, LPA, a simple molecule that mediates a plethora of biological effects, can be targeted at its levels of production by autotaxin, LPA receptors or through LPA degradation by lipid phosphate phosphatases. Drugs for these applications will soon be entering clinical practice.

Serum metabolic profiling identified a distinct metabolic signature in patients with idiopathic pulmonary fibrosis - a potential biomarker role for LysoPC

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a lethal lung disease of unknown etiology. Patients present loss of lung function, dyspnea and dry cough. Diagnosis requires compatible radiologic imaging and, in undetermined cases, invasive procedures such as bronchoscopy and surgical lung biopsy. The pathophysiological mechanisms of IPF are not completely understood. Lung injury with abnormal alveolar epithelial repair is thought to be a major cause for activation of profibrotic pathways in IPF. Metabolic signatures might indicate pathological pathways involved in disease development and progression. Reliable serum biomarker would help to improve both diagnostic approach and monitoring of drug effects.

METHOD

The global metabolic profiles measured by ultra high-performance liquid chromatography coupled to high-resolution mass spectrometry (UHPLC-HRMS) of ten stable IPF patients were compared to the ones of ten healthy participants. The results were validated in an additional study of eleven IPF patients and ten healthy controls.

RESULTS

We discovered 10 discriminative metabolic features using multivariate and univariate statistical analysis. Among them, we identified one metabolite at a retention time of 9.59 min that was two times more abundant in the serum of IPF patients compared to healthy participants. Based on its ion pattern, a lysophosphatidylcholine (LysoPC) was proposed. LysoPC is a precursor of lysophosphatidic acid (LPA) - a known mediator for lung fibrosis with its pathway currently being evaluated as new therapeutic drug target for IPF and other fibrotic diseases.

CONCLUSIONS

We identified a LysoPC by UHPLC-HRMS as potential biomarker in serum of patients with IPF. Further validation studies in a larger cohort are necessary to determine its role in IPF.

TRIAL REGISTRATION

Serum samples from IPF patients have been obtained within the clinical trial NCT02173145 at baseline and from the idiopathic interstitial pneumonia (IIP) cohort study. The study was approved by the Swiss Ethics Committee, Bern (KEK 002/14 and 246/15 or PB_2016-01524).

Metabolomics analysis identifies sex-associated metabotypes of oxidative stress and the autotaxin-lysoPA axis in COPD

Chronic obstructive pulmonary disease (COPD) is a heterogeneous disease and a leading cause of mortality and morbidity worldwide. The aim of this study was to investigate the sex dependency of circulating metabolic profiles in COPD.

Serum from healthy never-smokers (healthy), smokers with normal lung function (smokers), and smokers with COPD (COPD; Global Initiative for Chronic Obstructive Lung Disease stages I–II/A–B) from the Karolinska COSMIC cohort (n=116) was analysed using our nontargeted liquid chromatography–high resolution mass spectrometry metabolomics platform.

Pathway analyses revealed that several altered metabolites are involved in oxidative stress. Supervised multivariate modelling showed significant classification of smokers from COPD (p=2.8×10⁻⁷). Sex stratification indicated that the separation was driven by females (p=2.4×10⁻⁷) relative to males (p=4.0×10⁻⁴). Significantly altered metabolites were confirmed quantitatively using targeted metabolomics. Multivariate modelling of targeted metabolomics data confirmed enhanced metabolic dysregulation in females with COPD (p=3.0×10⁻³) relative to males (p=0.10). The autotaxin products lysoPA (16:0) and lysoPA (18:2) correlated with lung function (forced expiratory volume in 1 s) in males with COPD (r=0.86; p<0.0001), but not females (r=0.44; p=0.15), potentially related to observed dysregulation of the miR-29 family in the lung.

These findings highlight the role of oxidative stress in COPD, and suggest that sex-enhanced dysregulation in oxidative stress, and potentially the autotaxin–lysoPA axis, are associated with disease mechanisms and/or prevalence.

Oxidative stress and the autotaxin–lysoPA axis evidence sex-associated metabotypes in the serum of COPD patientshttp://ow.ly/kAeE309MpdI

Adult Lysophosphatidic Acid Receptor 1-Deficient Rats with Hyperoxia-Induced Neonatal Chronic Lung Disease Are Protected against Lipopolysaccharide-Induced Acute Lung Injury

Aim: Survivors of neonatal chronic lung disease or bronchopulmonary dysplasia (BPD) suffer from compromised lung function and are at high risk for developing lung injury by multiple insults later in life. Because neonatal lysophosphatidic acid receptor-1 (LPAR1)-deficient rats are protected against hyperoxia-induced lung injury, we hypothesize that LPAR1-deficiency may protect adult survivors of BPD from a second hit response against lipopolysaccharides (LPS)-induced lung injury.

Methods: Directly after birth, Wistar control and LPAR1-deficient rat pups were exposed to hyperoxia (90%) for 8 days followed by recovery in room air. After 7 weeks, male rats received either LPS (2 mg kg⁻¹) or 0.9% NaCl by intraperitoneal injection. Alveolar development and lung inflammation were investigated by morphometric analysis, IL-6 production, and mRNA expression of cytokines, chemokines, coagulation factors, and an indicator of oxidative stress.

Results: LPAR1-deficient and control rats developed hyperoxia-induced neonatal emphysema, which persisted into adulthood, as demonstrated by alveolar enlargement and decreased vessel density. LPAR1-deficiency protected against LPS-induced lung injury. Adult controls with BPD exhibited an exacerbated response toward LPS with an increased expression of pro-inflammatory mRNAs, whereas LPAR1-deficient rats with BPD were less sensitive to this “second hit” with a decreased pulmonary influx of macrophages and neutrophils, interleukin-6 (IL-6) production, and mRNA expression of IL-6, monocyte chemoattractant protein-1, cytokine-induced neutrophil chemoattractant 1, plasminogen activator inhibitor-1, and tissue factor.

Conclusion: LPAR1-deficient rats have increased hyperoxia-induced BPD survival rates and, despite the presence of neonatal emphysema, are less sensitive to an aggravated “second hit” than Wistar controls with BPD. Intervening in LPA-LPAR1-dependent signaling may not only have therapeutic potential for neonatal chronic lung disease, but may also protect adult survivors of BPD from sequelae later in life.

Measurement of Lysophosphatidic Acid and Sphingosine-1-Phosphate by Liquid Chromatography-Coupled Electrospray Ionization Tandem Mass Spectrometry

Lysophosphatidic acids and sphingosine-1-phosphate are bioactive lipids that regulate diverse cellular and physiological processes through actions that are largely mediated by cell surface receptors. The roles played by these lipids in multiple disease processes make the enzymes and receptors involved in their synthesis, inactivation, and signaling attractive targets for pharmacological therapies. In this chapter we describe methods for sensitive accurate quantitation of LPA and S1P levels in biological fluids using liquid chromatography-coupled electrospray ionization tandem mass spectrometry.

Cyclooxygenase-2 Mediated Oxidation of 2-Arachidonoyl-Lysophospholipids Identifies Unknown Lipid Signaling Pathways

Eicosanoid lipids play important roles in cellular signaling as second messengers in inflammation, immune response, vascular tone, and the CNS. Biosynthesis of eicosanoid lipids proceeds via hydrolysis of esterified arachidonic acid from phospholipids followed by oxidation of the released arachidonic acid by a variety of enzymes including cyclooxygenases (COX). Herein, we demonstrate the remarkable ability of COX-2, but not COX-1, to directly oxidize 2-arachidonoyl-lysolipids, resulting in the generation of previously unknown classes of eicosanoid-lysolipids, and provide evidence that intracellular lipases can release eicosanoids from their eicosanoid-lysolipid precursors. Importantly, genetic ablation of a phospholipase, iPLA₂γ, significantly reduced the amounts of these eicosanoid-lysolipids in murine hepatic tissue and fibroblasts. Furthermore, calcium stimulation of wild-type murine lung fibroblasts produced robust increases in these eicosanoid-lysolipids, which were markedly attenuated in iPLA₂γ^-/- fibroblasts. Collectively, these results identify an iPLA₂γ-initiated pathway generating new classes of lipid metabolites with potential signaling functions resulting from the direct COX-2 catalyzed oxidation of 2-arachidonoyl-lysolipids.

The incidence and risk of osteoporosis in patients with anxiety disorder: A Population-based retrospective cohort study

The purpose of this study was to investigate the relationship between anxiety disorder (AD) and the subsequent development of osteoporosis.We conducted a population-based retrospective cohort analysis according to the data in the Longitudinal Health Insurance Database 2000 of Taiwan. We included 7098 patients in both the AD and no-anxiety cohort who were matched according to age and sex between January 1, 2000, and December 31, 2013. The incidence rate and the risk ratios (RRs) of subsequent new-onset osteoporosis were calculated for both cohorts. We used Cox proportional hazards models to assess the effect of AD. The Kaplan-Meier method was applied to estimate the cumulative osteoporosis incidence curves.The AD cohort consisted of 7098 patients, and the comparison cohort comprised the same matched control patients without anxiety. The risk of osteoporosis was higher in the AD cohort than in the comparison cohort. In addition, the incidence of newly diagnosed osteoporosis remained significantly increased in all of the stratified follow-up durations (0-1, 1-5, 5-10, ≥10years). Patients with AD were 1.79 times more likely to get osteoporosis than those without AD. We also observed a significant increase in osteoporotic risk in AD patients who are comorbid with hypertension, diabetes mellitus, and chronic liver disease.The incidence of osteoporosis in Taiwan is associated with an a priori AD history. The risk ratios are the highest for osteoporosis within 1 year of AD diagnosis, but the risk remains statistically significant for >1 year. Clinicians should pay particular attention to osteoporotic comorbidities in AD patients.