Butyrate ameliorates allergic airway inflammation by limiting eosinophil trafficking and survival.

BACKGROUND: Lung eosinophilia is a hallmark of asthma, and eosinophils are believed to play a crucial role in the pathogenesis of allergic inflammatory diseases. Short-chain fatty acids (SCFAs), such as acetate, propionate, and butyrate, are produced in high amounts in the gastrointestinal tract by commensal bacteria and can be absorbed into the bloodstream. Although there is recent evidence that SCFAs are beneficial in allergic asthma models, the effect on eosinophils has remained elusive. OBJECTIVE: The role of SCFAs was investigated in human eosinophil function and a mouse model of allergic asthma. METHODS: Eosinophils were purified from self-reported allergic or healthy donors. Migration, adhesion to the endothelium, and eosinophil survival were studied in vitro. Ca2+ flux, apoptosis, mitochondrial membrane potential, and expression of surface markers were determined by using flow cytometry and in part by using real-time PCR. Allergic airway inflammation was assessed in vivo in an ovalbumin-induced asthma model by using invasive spirometry. RESULTS: For the first time, we observed that SCFAs were able to attenuate human eosinophils at several functional levels, including (1) adhesion to the endothelium, (2) migration, and (3) survival. These effects were independent from GPR41 and GPR43 but were accompanied by histone acetylation and mimicked by trichostatin A, a pan-histone deacetylase inhibitor. In vivo butyrate ameliorated allergen-induced airway and lung eosinophilia, reduced type 2 cytokine levels in bronchial fluid, and improved airway hyperresponsiveness in mice. CONCLUSION: These in vitro and in vivo findings highlight the importance of SCFAs, especially butyrate as a promising therapeutic agent in allergic inflammatory diseases.

Activated prostaglandin D2 receptors on macrophages enhance neutrophil recruitment into the lung.

BACKGROUND: Prostaglandin (PG) D2 is an early-phase mediator in inflammation, but its action and the roles of the 2 D-type prostanoid receptors (DPs) DP1 and DP2 (also called chemoattractant receptor-homologous molecule expressed on T(H)2 cells) in regulating macrophages have not been elucidated to date. OBJECTIVE: We investigated the role of PGD2 receptors on primary human macrophages, as well as primary murine lung macrophages, and their ability to influence neutrophil action in vitro and in vivo. METHODS: In vitro studies, including migration, Ca(2+) flux, and cytokine secretion, were conducted with primary human monocyte-derived macrophages and neutrophils and freshly isolated murine alveolar and pulmonary interstitial macrophages. In vivo pulmonary inflammation was assessed in male BALB/c mice. RESULTS: Activation of DP1, DP2, or both receptors on human macrophages induced strong intracellular Ca(2+) flux, cytokine release, and migration of macrophages. In a murine model of LPS-induced pulmonary inflammation, activation of each PGD2 receptor resulted in aggravated airway neutrophilia, tissue myeloperoxidase activity, cytokine contents, and decreased lung compliance. Selective depletion of alveolar macrophages abolished the PGD2-enhanced inflammatory response. Activation of PGD2 receptors on human macrophages enhanced the migratory capacity and prolonged the survival of neutrophils in vitro. In human lung tissue specimens both DP1 and DP2 receptors were located on alveolar macrophages along with hematopoietic PGD synthase, the rate-limiting enzyme of PGD2 synthesis. CONCLUSION: For the first time, our results show that PGD2 markedly augments disease activity through its ability to enhance the proinflammatory actions of macrophages and subsequent neutrophil activation.

Cytokines and their association with insulin resistance in obese pregnant women with different levels of physical activity.

BACKGROUND: Cytokines contribute to insulin resistance in pregnancy, but the role of distinct cytokines is not fully understood. OBJECTIVES: To study whether cytokines produced by tissues other than skeletal muscle are associated with glucose and insulin metabolism activity in overweight and obese women and to study whether these associations can be modified by physical activity. METHODS: A longitudinal study with 44 overweight and obese pregnant women was conducted. Changes in cytokines levels (IFN-γ, IP-10, IL1-α, MIP1-α, adiponectin and leptin) and ICAM1 from early (15wk) to late (32wk) pregnancy were determined. Physical activity was measured objectively with accelerometers. In linear regression models, the associations between (changes in) cytokine levels and fasting glucose, fasting insulin and HOMA-IR were studied. RESULTS: Both IFN-γ and IP-10 levels increased from early to late pregnancy, and adiponectin levels decreased. IFN-γ and IP-10 were positively associated with fasting glucose, whereas IL-1α, ICAM1 and adiponectin were inversely associated with insulin and insulin resistance. The association of IL-1α with insulin and insulin resistance was only found in women with low levels of physical activity. CONCLUSIONS: IFN-γ, IP-10, IL1-α, ICAM1, and adiponectin may play a role in glucose and insulin metabolism in pregnancy. The relationship of IL-1α with insulin and insulin resistance might be moderated by levels of physical activity. Further studies are required to confirm the role of these cytokines in glucose and insulin metabolism in obese pregnant women.

Sedentary behavior in obese pregnant women is associated with inflammatory markers and lipid profile but not with glucose metabolism.

BACKGROUND: Sedentary behavior is an independent risk factor for the metabolic syndrome, but the role of sedentary behavior in the development of gestational diabetes is unclear. OBJECTIVES: This study tested the hypothesis that less sedentary behavior is related to better insulin sensitivity, lipid and cytokine profile in obese pregnant women. METHODS: A longitudinal observational study with 46 overweight and obese pregnant women was conducted. Sedentary behavior was measured objectively using accelerometers at 15, 24 and 32weeks of gestation, and at those time points fasting blood was taken as well. A 100g oral glucose tolerance test was performed at 24 and 32weeks. Levels of glucose, insulin, total cholesterol, HDL, LDL, triglycerides were measured, as well as cytokines. The relationship between sedentary behavior and metabolic outcomes was assessed using linear regression analysis. RESULTS: Women spent almost 60% of their time sitting throughout pregnancy. In cross-sectional analyses, an association of sedentary time at 24weeks was found with increased total cholesterol and HDL. More sedentary time was associated with lower IL-6 at 24weeks and with higher IL-10, TNF-α and leptin levels at 32weeks of pregnancy. Changes in sedentary time were not associated with changes in any of the metabolic outcomes. CONCLUSIONS: In conclusion, time spent sedentary in pregnancy was associated with lipid and cytokine profile. Whether decreasing sedentary time beneficially influences lipid profile and influences cytokine profiles of overweight and obese women needs to be assessed in future intervention studies.

Lipid Mediators of Allergic Disease: Pathways, Treatments, and Emerging Therapeutic Targets.

Bioactive lipids are critical regulators of inflammation. Over the last 75 years, these diverse compounds have emerged as clinically-relevant mediators of allergic disease pathophysiology. Animal and human studies have demonstrated the importance of lipid mediators in the development of asthma, allergic rhinitis, urticaria, anaphylaxis, atopic dermatitis, and food allergy. Lipids are critical participants in cell signaling events which influence key physiologic (bronchoconstriction) and immune phenomena (degranulation, chemotaxis, sensitization). Lipid-mediated cellular mechanisms including: (1) formation of structural support platforms (lipid rafts) for receptor signaling complexes, (2) activation of a diverse family of G-protein coupled receptors, and (3) mediating intracellular signaling cascades by acting as second messengers. Here, we review four classes of bioactive lipids (platelet activating factor, the leukotrienes, the prostanoids, and the sphingolipids) with special emphasis on lipid synthesis pathways and signaling, atopic disease pathology, and the ongoing development of atopy treatments targeting lipid mediator pathways.

DP1 receptor signaling prevents the onset of intrinsic apoptosis in eosinophils and functions as a transcriptional modulator.

Prostaglandin (PG) D2 is the ligand for the G-protein coupled receptors DP1 (D-type prostanoid receptor 1) and DP2 (also known as chemoattractant receptor homologous molecule, expressed on Th2 cells; CRTH2). Both, DP1 and DP2 are expressed on the cellular surface of eosinophils; although it has become quite clear that PGD2 induces eosinophil migration mainly via DP2 receptors, the role of DP1 in eosinophil responses has remained elusive. In this study, we addressed how DP1 receptor signaling complements the pro-inflammatory effects of DP2. We found that PGD2 prolongs the survival of eosinophils via a DP1 receptor-mediated mechanism that inhibits the onset of the intrinsic apoptotic cascade. The DP1 agonist BW245c prevented the activation of effector caspases in eosinophils and protected mitochondrial membranes from depolarization which-as a consequence-sustained viability of eosinophils. DP1 activation in eosinophils enhanced the expression of the anti-apoptotic gene BCL-XL , but also induced pro-inflammatory genes, such as VLA-4 and CCR3. In HEK293 cells that overexpress recombinant DP1 and/or DP2 receptors, activation of DP1, but not DP2, delayed cell death and stimulated proliferation, along with induction of serum response element (SRE), a regulator of anti-apoptotic, early-response genes. We conclude that DP1 receptors promote the survival via SRE induction and induction of pro-inflammatory genes. Therefore, targeting DP1 receptors, along with DP2, may contribute to anti-inflammatory therapy in eosinophilic diseases.

Prostaglandins and Their Receptors in Eosinophil Function and As Therapeutic Targets.

Of the known prostanoid receptors, human eosinophils express the prostaglandin D2 (PGD2) receptors DP1 [also D-type prostanoid (DP)] and DP2 (also chemoattractant receptor homologous molecule, expressed on Th2 cells), the prostaglandin E2 receptors EP2 and EP4, and the prostacyclin (PGI2) receptor IP. Prostanoids can bind to either one or multiple receptors, characteristically have a short half-life in vivo, and are quickly degraded into metabolites with altered affinity and specificity for a given receptor subtype. Prostanoid receptors signal mainly through G proteins and naturally activate signal transduction pathways according to the G protein subtype that they preferentially interact with. This can lead to the activation of sometimes opposing signaling pathways. In addition, prostanoid signaling is often cell-type specific and also the combination of expressed receptors can influence the outcome of the prostanoid impulse. Accordingly, it is assumed that eosinophils and their (patho-)physiological functions are governed by a sensitive prostanoid signaling network. In this review, we specifically focus on the functions of PGD2, PGE2, and PGI2 and their receptors on eosinophils. We discuss their significance in allergic and non-allergic diseases and summarize potential targets for drug intervention.

Human Placental Hofbauer Cells Maintain an Anti-inflammatory M2 Phenotype despite the Presence of Gestational Diabetes Mellitus.

BACKGROUND: Hofbauer cells (HBCs) are macrophages of the feto-placental unit. Despite the general view that these cells have an anti-inflammatory M2 phenotype, recent studies have claimed that pregnancy pathologies-e.g., gestational diabetes mellitus (GDM)-cause a switch from an M2 to an M1 pro-inflammatory phenotype in HBCs. The pilot-study presented here challenges this claim, showing that HBCs maintain anti-inflammatory properties in spite of the hyperglycemic, low-grade inflammatory environment of GDM. METHODS: HBCs were isolated from placentae of healthy women (N = 5) and women with GDM (N = 6) diagnosed in the second trimester. FACS was used to measure surface markers associated with either M1 or M2 phenotype on the cells. In addition, placental tissue sections were subjected to immune histochemical imaging to assess the phenotype within the tissue context. Supernatant from control and GDM HBCs was collected at defined time points and used in a multiplex ELISA-on-beads approach to assess secretion of cytokines, chemokines, and growth factors. The effect of HBC cell culture supernatant on placental endothelial activation was investigated. RESULTS: FACS and immune staining showed that, indeed, M2 markers, such as CD206 and CD209, are increased in HBCs isolated from GDM placentae. Also, the M1 marker CD86 was increased, but only by trend. Secretion of numerous cytokines, chemokines and growth factors was not changed; pro-inflammatory interleukin (IL)-1ß and IL-6 release form GDM HBC was increased but not significant. Exposure to GDM HBC supernatant did not induce cell adhesion molecules (VCAM-1, selectins, vascular endothelial-cadherin) in placental endothelial cells compared to supernatant from control HBCs, an induction of intracellular adhesion molecule 1 was observed however. CONCLUSION: Our study-although performed in a small set of patients-shows that placental macrophages maintain their anti-inflammatory, tissue remodeling M2 phenotype even in pregnancies affected by gestational diabetes. This consistent phenotype might be important for propagation of maternal tolerance toward the fetus and for protection of the fetus from a low-grade inflammatory environment.

Adhesion of eosinophils to endothelial cells or substrates under flow conditions.

Recruitment of eosinophils into the lung tissue is a critical event in allergic inflammatory reactions. Extravasation of eosinophils from the bloodstream is a highly dynamic multistep process that involves capture, rolling, activation, firm adhesion, and transendothelial and subendothelial migration of the cells. It is assumed that the rate-limiting step in this cascade is the capture and firm adhesion of cells to the endothelium. As such it is most critical to study endothelial-leukocyte interaction using assays which are capable of mimicking physiological flow conditions. Previously, various parallel flow chamber setups had been used for studying leukocyte adhesion to endothelial cells. Here we describe a highly reproducible technique for investigating eosinophil adhesion to endothelial cell layer or adhesion molecule/extracellular matrix protein coating in biochips by using a semiautomated microfluidic platform and live-cell imaging. In detail, we show eosinophil adhesion to endothelial cells activated by tumour necrosis factor (TNF) alpha, and adhesion to fibronectin of eosinophils stimulated by prostaglandin (PG) D2.

Physical activity in overweight and obese pregnant women is associated with higher levels of proinflammatory cytokines and with reduced insulin response through interleukin-6.

OBJECTIVE Previously, we reported the positive association of moderate-to-vigorous physical activity (MVPA) with insulin sensitivity in overweight and obese pregnant women. We sought to assess whether these MVPA-induced changes in insulin sensitivity are mediated by changes in interleukin (IL)-6, IL-10, tumor necrosis factor (TNF)-α, and IL-1ß. RESEARCH DESIGN AND METHODS A prospective longitudinal study was conducted in 46 overweight and obese women at risk for gestational diabetes mellitus. Objective physical activity measurements and fasting blood samples were taken at 15, 24, and 32 weeks of pregnancy. At 24 and 32 weeks, a 100-g oral glucose test was performed in addition. Cytokines, C-reactive protein, and glucose and insulin levels were measured, and insulin sensitivity and first-phase insulin response were calculated. Relationships between the different parameters were assessed using linear regression models, adjusting for maternal age and BMI. RESULTS All cytokines were elevated in women with higher levels of MVPA at 15 weeks of gestation. Higher IL-6 was related to a lower first-phase insulin response (ß -810.5 [95% CI -1,524.5 to -96.5]; P = 0.03). TNF-α and IL-1ß had different effects in women with low MVPA (with low IL-6 levels) compared with more active women. CRP was not related to MVPA. CONCLUSIONS The association of MVPA with insulin sensitivity and first-phase insulin response may be (partly) mediated by IL-6, since this cytokine was related to reduced first-phase insulin response. The possible positive effects of the elevated cytokine profile in active obese pregnant women warrant further study.