Lysophospholipids in Lung Inflammatory Diseases

Discovery of a Novel Orally Active, Selective LPA Receptor Type 1 Antagonist, 4-(4-(2-Isopropylphenyl)-4-((2-methoxy-4-methylphenyl)carbamoyl)piperidin-1-yl)-4-oxobutanoic Acid, with a Distinct Molecular Scaffold

Lysophosphatidic acid receptor 1 (LPAR1) antagonists show promise as potentially novel antifibrotic treatments. In a human LPAR1 β-arrestin recruitment-based high-throughput screening campaign, we identified urea 19 as a hit with a LPAR1 IC50 value of 5.0 μM. Hit-to-lead activities revealed that one of the urea nitrogen atoms can be replaced by carbon and establish the corresponding phenylacetic amide as a lead structure for further optimization. Medicinal chemistry efforts led to the discovery of piperidine 18 as a potent and selective LPAR1 antagonist with oral activity in a mouse model of LPA-induced skin vascular leakage. The molecular scaffold of 18 shares no obvious structural similarity with any other LPAR1 antagonist disclosed so far.

Understanding the modulations of glycero-lysophospholipids in an elastase-induced murine emphysema model

BACKGROUND

Increasing evidence indicates that bioactive lipid mediators are involved in chronic obstructive pulmonary disease (COPD) pathogenesis. Recently, glycero-lysophospholipids, such as lysophosphatidic acid (LysoPA) and lysophosphatidylserine (LysoPS), have been recognized as significant inflammation-related lipid mediators. However, their association with COPD remains unclear.

METHODS

We used an elastase-induced murine emphysema model to analyze the levels of lysophospholipids and diacyl-phospholipids in the lungs. Additionally, we assessed the expression of LysoPS-related genes and published data on smokers.

RESULTS

In the early phase of an elastase-induced murine emphysema model, the levels of LysoPS and its precursor (phosphatidylserine [PS]) were significantly reduced, without significant modulations in other glycero-lysophospholipids. Additionally, there was an upregulation in the expression of lysoPS receptors, specifically GPR34, observed in the lungs of a cigarette smoke-exposed mouse model and the alveolar macrophages of human smokers. Elastase stimulation induces GPR34 expression in a human macrophage cell line in vitro.

CONCLUSIONS

Elastase-induced lung emphysema affects the LysoPS/PS-GPR34 axis, and cigarette smoking or elastase upregulates GPR34 expression in alveolar macrophages. This novel association may serve as a potential pharmacological target for COPD treatment.

Involvement of Lysophospholipids in Pulmonary Vascular Functions and Diseases

Extracellular lysophospholipids (lysophosphatidic acid, lysophosphatidylcholine, sphingosine 1-phosphate, etc.), which are synthesized from phospholipids in the cell membrane, act as lipid mediators, and mediate various cellular responses in constituent cells in the respiratory system, such as contraction, proliferation, migration, and cytoskeletal organization. In addition to these effects, the expression of the adhesion molecules is enhanced by these extracellular lysophospholipids in pulmonary endothelial cells. These effects are exerted via specific G protein-coupled receptors. Rho, Ras, and phospholipase C (PLC) have been proven to be their signaling pathways, related to Ca2+ signaling due to Ca2+ dynamics and Ca2+ sensitization. Therefore, lysophospholipids probably induce pulmonary vascular remodeling through phenotype changes in smooth muscle cells, endothelial cells, and fibroblasts, likely resulting in acute respiratory distress syndrome due to vascular leak, pulmonary hypertension, and pulmonary fibrosis. Moreover, lysophospholipids induce the recruitment of inflammatory cells to the lungs via the enhancement of adhesion molecules in endothelial cells, potentially leading to the development of asthma. These results demonstrate that lysophospholipids may be novel therapeutic targets not only for injury, fibrosis, and hypertension in the lung, but also for asthma. In this review, we discuss the mechanisms of the effects of lysophospholipids on the respiratory system, and the possibility of precision medicine targeting lysophospholipids as treatable traits of these diseases.

A targeted metabolomics approach for sepsis-induced ARDS and its subphenotypes

BACKGROUND

Acute respiratory distress syndrome (ARDS) is etiologically and clinically a heterogeneous disease. Its diagnostic characteristics and subtype classification, and the application of these features to treatment, have been of considerable interest. Metabolomics is becoming important for identifying ARDS biology and distinguishing its subtypes. This study aimed to identify metabolites that could distinguish sepsis-induced ARDS patients from non-ARDS controls, using a targeted metabolomics approach, and to identify whether sepsis-induced direct and sepsis-induced indirect ARDS are metabolically distinct groups, and if so, confirm their metabolites and associated pathways.

METHODS

This study retrospectively analyzed 54 samples of ARDS patients from a sepsis registry that was prospectively collected from March 2011 to February 2018, along with 30 non-ARDS controls. The cohort was divided into direct and indirect ARDS. Metabolite concentrations of five analyte classes (energy metabolism, free fatty acids, amino acids, phospholipids, sphingolipids) were measured using liquid chromatography-tandem mass spectrometry and gas chromatography-mass spectrometry by targeted metabolomics.

RESULTS

In total, 186 metabolites were detected. Among them, 102 metabolites could differentiate sepsis-induced ARDS patients from the non-ARDS controls, while 14 metabolites could discriminate sepsis-induced ARDS subphenotypes. Using partial least-squares discriminant analysis, we showed that sepsis-induced ARDS patients were metabolically distinct from the non-ARDS controls. The main distinguishing metabolites were lysophosphatidylethanolamine (lysoPE) plasmalogen, PE plasmalogens, and phosphatidylcholines (PCs). Sepsis-induced direct and indirect ARDS were also metabolically distinct subgroups, with differences in lysoPCs. Glycerophospholipid and sphingolipid metabolism were the most significant metabolic pathways involved in sepsis-induced ARDS biology and in sepsis-induced direct/indirect ARDS, respectively.

CONCLUSION

Our study demonstrated a marked difference in metabolic patterns between sepsis-induced ARDS patients and non-ARDS controls, and between sepsis-induced direct and indirect ARDS subpheonotypes. The identified metabolites and pathways can provide clues relevant to the diagnosis and treatment of individuals with ARDS.

Deciphering the role of platelets in severe allergy by an integrative omics approach

BACKGROUND

Mechanisms causing the onset and perpetuation of inflammation in severe allergic patients remain unknown. Our previous studies suggested that severe allergic inflammation is linked to platelet dysfunction.

METHODS

Platelet-rich plasma (PRP) and platelet-poor plasma (PPP) samples were obtained by platelet-apheresis from severe (n = 7) and mild (n = 10) allergic patients and nonallergic subjects (n = 9) to perform platelet lipidomics by liquid chromatography coupled to mass spectrometry (LC-MS) and RNA-seq analysis. Significant metabolites and transcripts were used to identify compromised biological pathways in the severe phenotype. Platelet and inflammation-related proteins were quantified by Luminex.

RESULTS

Platelets from severe allergic patients were characterized by high levels of ceramides, phosphoinositols, phosphocholines, and sphingomyelins. In contrast, they showed a decrease in eicosanoid precursor levels. Biological pathway analysis performed with the significant lipids revealed the alteration of phospholipases, calcium-dependent events, and linolenic metabolism. RNAseq confirmed mRNA overexpression of genes related to platelet activation and arachidonic acid metabolism in the severe phenotypes. Pathway analysis indicated the alteration of NOD, MAPK, TLR, TNF, and IL-17 pathways in the severe phenotype. P-Selectin and IL-17AF proteins were increased in the severe phenotype.

CONCLUSIONS

This study demonstrates that platelet lipid, mRNA, and protein content is different according to allergy severity. These findings suggest that platelet load is a potential source of biomarkers and a new chance for therapeutic targets in severe inflammatory pathologies.

Metabolomics Profiling of Vitamin D Status in Relation to Dyslipidemia

Vitamin D deficiency is a global disorder associated with several chronic illnesses including dyslipidemia and metabolic syndrome. The impact of this association with both dyslipidemia and vitamin D deficiency on metabolomics profile is not yet fully understood. This study analyses the metabolomics and lipidomic signatures in relation to vitamin D status and dyslipidemia. Metabolomics data were collected from Qatar Biobank database and categorized into four groups based on vitamin D and dyslipidemia status. Metabolomics multivariate analysis was performed using the orthogonal partial least square discriminate analysis (OPLS-DA) whilst linear models were used to assess the per-metabolite association with each of the four dyslipidemia/vitamin D combination groups. Our results indicate a high prevalence of vitamin D deficiency among the younger age group, while dyslipidemia was more prominent in the older group. A significant alteration of metabolomics profile was observed among the dyslipidemic and vitamin D deficient individuals in comparison with control groups. These modifications reflected changes in some key pathways including ceramides, diacylglycerols, hemosylceramides, lysophospholipids, phosphatidylcholines, phosphatidylethanol amines, and sphingomyelins. Vitamin D deficiency and dyslipidemia have a deep impact on sphingomyelins profile. The modifications were noted at the level of ceramides and are likely to propagate through downstream pathways.

Tetramethylpyrazine Alleviates Tight Junction Disruption of Bronchial Mucosal Epithelial Cells Caused by Interleukin-17 via Inhibiting Nuclear Factor-κB-p65/Tumor Necrosis Factor-α Signaling Pathway

Bronchial mucosal epithelial dysregulation and barrier disruption are involved in the initiation and development of acute lung injury (ALI). Some inflammatory cytokines such as tumor necrosis factor-α (TNF-α) and interleukin-17 (IL-17) contribute to the pathological changes of ALI. However, the roles and relationship between TNF-α and IL-17 during the disruption of bronchial epithelial tight junction remain unclear. Tetramethylpyrazine (TMP) is confirmed to have beneficial functions in hemostasis, inflammation, and cell growth. Here, we demonstrated the protective effects of TMP on bronchial mucosal epithelial injury induced by IL-17. We showed that IL-17 stimulation in vitro markedly reduced occludin and zonula occludens-1 (ZO-1) expression in bronchial mucosal epithelial cells via the nuclear factor-κB-p65/TNF-α signaling pathway, including NF-κB-p65-triggered TNF-α gene transcription and expression. TMP obviously rescued IL-17-induced occludin and ZO-1 downregulation. Mechanically, TMP substantially suppressed NF-κB-p65 activation and NF-κB-p65-induced TNF-α production in bronchial mucosal epithelial cells caused by IL-17. Taken together, this study indicates that TMP has a protective effect on bronchial mucosal epithelial cell injury due to IL-17 induction by inhibiting the NF-κB-p65/TNF-α signaling pathway.

LPA and Autotaxin: Potential Drug Targets in Asthma?

Lysophosphatidic acid (LPA) is a versatile lysolipid, and activates a variety of signaling cascades in many cell types. Extracellular LPA is produced from lysophosphatidylcholine (LPC) by the enzyme autotaxin (ATX), and binds to a family of G-protein coupled receptors on its target cells. Research by many groups continues to support the idea that LPA, and the ATX-LPA axis, have important roles in asthma and allergic airway inflammation. In vitro studies have shown that LPA activates many cell types implicated in airway inflammation, including eosinophils, mast cells, dendritic cells, lymphocytes, airway epithelial cells, and airway smooth muscle cells. In animal models ATX and LPA receptor antagonists have been shown to attenuate allergic airway inflammation and hyperreactivity, cardinal features of asthma in humans. ATX and LPA antagonists are currently under active development to treat lung fibrosis, cancer, and other conditions. If compounds with acceptable safety profiles can be identified, then it seems likely that they will be useful in inflammatory lung diseases like asthma.