Endogenous lipid mediators in the resolution of airway inflammation

Oxidative lipidomics of γ-radiation-induced lung injury: mass spectrometric characterization of cardiolipin and phosphatidylserine peroxidation

Oxidative damage plays a significant role in the pathogenesis of γ-radiation-induced lung injury. Endothelium is a preferred target for early radiation-induced damage and apoptosis. Given the newly discovered role of oxidized phospholipids in apoptotic signaling, we performed oxidative lipidomics analysis of phospholipids in irradiated mouse lungs and cultured mouse lung endothelial cells. C57BL/6NHsd female mice were subjected to total-body irradiation (10 Gy, 15 Gy) and euthanized 24 h thereafter. Mouse lung endothelial cells were analyzed 48 h after γ irradiation (15 Gy). We found that radiation-induced apoptosis in vivo and in vitro was accompanied by non-random oxidation of phospholipids. Cardiolipin and phosphatidylserine were the major oxidized phospholipids, while more abundant phospholipids (phosphatidylcholine, phosphatidylethanolamine) remained non-oxidized. Electrospray ionization mass spectrometry analysis revealed the formation of cardiolipin and phosphatidylserine oxygenated molecular species in the irradiated lung and cells. Analysis of fatty acids after hydrolysis of cardiolipin and phosphatidylserine by phospholipase A(2) revealed the presence of mono-hydroperoxy and/or mono-hydroxy/mono-epoxy, mono-hydroperoxy/mono-oxo molecular species of linoleic acid. We speculate that cyt c-driven oxidations of cardiolipin and phosphatidylserine associated with the execution of apoptosis in pulmonary endothelial cells are important contributors to endothelium dysfunction in γ-radiation-induced lung injury.

Polyunsaturated fatty acids. Immunomodulators in older adults

The immune system tends to become less efficient as people age, and nutrition plays a significant role in older adults' immune responses. In particular, dietary fatty acids are precursors to important immune system components. Certain fatty acids, predominantly those that are polyunsaturated, also tend to decrease the risk of certain neurological diseases in older adults. This article describes the impact of dietary polyunsaturated fatty acids (PUFA) on older adults' immune system and discusses the roles of age and immune status with regard to PUFA supplements.

Lovastatin decreases acute mucosal inflammation via 15-epi-lipoxin A4

The widespread use of statins for hypercholesterolemia has uncovered pleiotropic anti-inflammatory properties that were unexpected based on the drugs' original design; yet, mechanisms for these protective actions remain uncertain. In this study lovastatin triggered biosynthesis of the anti-inflammatory and pro-resolving mediator 15-epi-lipoxin A(4) (15-epi-LXA(4)). During interactions between human neutrophils and airway epithelial cells, the statin-induced increase in 15-epi-LXA(4) was associated with increased 14,15-epoxyeicosatrienoic acid (14,15-EET) generation. When added to activated neutrophils, 14,15-EET enhanced 15-epi-LXA(4) biosynthesis. In a murine model of airway mucosal injury and inflammation, lovastatin increased 15-epi-LXA(4) formation in vivo and markedly decreased acute lung inflammation. Administration of 15-epi-LXA(4) also inhibited lung inflammation in an additive manner with lovastatin. Together, these results indicate that statin-triggered 15-epi-LXA(4) generation during human leukocyte-airway epithelial cell interactions is an endogenous mechanism for statin-mediated tissue protection at mucosal surfaces that may also be relevant in the statins' ability to stimulate the resolution of inflammation.

Resolution of inflammation in murine autoimmune arthritis is disrupted by cyclooxygenase-2 inhibition and restored by prostaglandin E2-mediated lipoxin A4 production

Acute inflammation follows defined phases of induction, inflammation and resolution, and resolution occurs by an active process that requires cyclooxygenase-2 (COX-2) activity. This study aims to address whether this paradigm extends to recognized model of chronic inflammation. We demonstrated that murine collagen-induced arthritis follows a similar sequential course. Interestingly, COX-2 and its metabolite, the presumably proinflammatory PGE(2), are present in the joints during resolution, and blocking COX-2 activity and PGE(2) production within this period perpetuated, instead of attenuated, inflammation. Repletion with PGE(2) analogs restored homeostasis, and this function is mediated by the proresolving lipoxygenase metabolite, lipoxin A(4), a potent stop signal. Thus, the study provided in vivo evidence for a natural, endogenous link between the cyclooxygenase-lipoxygenase pathways and showed that PGE(2) serves as a feedback inhibitor essential for limiting chronic inflammation in autoimmune arthritis. These findings may explain the enigma regarding why COX-2 inhibitors are palliative rather than curative in humans, because blocking resolution may mitigate the benefit of preventing induction.

Oxidative lipidomics of hyperoxic acute lung injury: mass spectrometric characterization of cardiolipin and phosphatidylserine peroxidation

Reactive oxygen species have been shown to play a significant role in hyperoxia-induced acute lung injury, in part, by inducing apoptosis of pulmonary endothelium. However, the signaling roles of phospholipid oxidation products in pulmonary endothelial apoptosis have not been studied. Using an oxidative lipidomics approach, we identified individual molecular species of phospholipids involved in the apoptosis-associated peroxidation process in a hyperoxic lung. C57BL/6 mice were killed 72 h after exposure to hyperoxia (100% oxygen). We found that hyperoxia-induced apoptosis (documented by activation of caspase-3 and -7 and histochemical terminal deoxynucleotidyl transferase dUTP-mediated nick-end labeling staining of pulmonary endothelium) was accompanied by nonrandom oxidation of pulmonary lipids. Two anionic phospholipids, mitochondria-specific cardiolipin (CL) and extramitochondrial phosphatidylserine (PS), were the two major oxidized phospholipids in hyperoxic lung. Using electrospray ionization mass spectrometry, we identified several oxygenation products in CL and PS. Quantitative assessments revealed a significant decrease of CL and PS molecular species containing C(18:2), C(20:4), C(22:5), and C(22:6) fatty acids. Similarly, exposure of mouse pulmonary endothelial cells (MLEC) to hyperoxia (95% oxygen; 72 h) resulted in activation of caspase-3 and -7 and significantly decreased the content of CL molecular species containing C(18:2) and C(20:4) as well as PS molecular species containing C(22:5) and C(22:6). Oxygenated molecular species were found in the same two anionic phospholipids, CL and PS, in MLEC exposed to hyperoxia. Treatment of MLEC with a mitochondria-targeted radical scavenger, a conjugate of hemi-gramicidin S with nitroxide, XJB-5-131, resulted in significantly lower oxidation of both CL and PS and a decrease in hyperoxia-induced changes in caspase-3 and -7 activation. We speculate that cytochrome c driven oxidation of CL and PS is associated with the signaling role of these oxygenated species participating in the execution of apoptosis and clearance of pulmonary endothelial cells, thus contributing to hyperoxic lung injury.

Toddler formula supplemented with docosahexaenoic acid (DHA) improves DHA status and respiratory health in a randomized, double-blind, controlled trial of US children less than 3 years of age

Studies of docosahexaenoic acid (DHA) intake and status in US toddlers are lacking. One national survey found low DHA intakes. The objectives of this double-blind, randomized study were to (a) determine usual DHA intakes, (b) measure the effect of consuming formulas with DHA on red blood cell (RBC) and plasma DHA and (c) record adverse events in US children between 18 and 36 months of age. Children aged 18-36 months were provided 237-ml formula with 0, 43, or 130 mg DHA per day for 60 days. Blood was obtained at 0 and 60 days and 24-hour dietary recalls at 0, 30 and 60 days. Usual median daily DHA intake was 13.3 mg. RBC DHA increased in a dose-dependent manner with increasing DHA intake (p<0.05). Toddlers consuming the formula with 130 mg DHA per day have fewer adverse events (p=0.007) and a lower incidence of respiratory illness (p=0.024), compared to the formula without DHA. US toddlers have low DHA intake and status. Modest increases in DHA intake in toddlers might improve development, including respiratory health.

Lipoxin A4 generation is decreased in aspirin-sensitive patients in lysine-aspirin nasal challenge in vivo model

BACKGROUND

Lipoxins represent a group of lipoxygenase derived eicosanoids which, in contrast to leukotrienes, are potent anti-inflammatory mediators. The aim of our study was to determine lipoxin A(4) (LXA(4)) and leukotriene C(4) (LTC(4)) levels in nasal lavages after intranasal challenge with aspirin in aspirin intolerant (AIA) in comparison to aspirin tolerant (ATA) asthmatics and after allergen challenge in patients suffering from allergic rhinitis.

METHODS

Twelve AIA, 8 ATA and 20 allergic patients were challenged with placebo, 16 mg of lysine-aspirin (Lys-ASA) or allergen (grasses). Nasal lavages were collected and eicosanoids' levels were determined using ELISA.

RESULTS

Clinically positive Lys-ASA challenge in AIA resulted in influx of leukocytes (eosinophils and basophils) to nasal secretions and increase of LTC(4) to 106.82 pg/ml (P < 0.05 vs baseline (26.58 pg/ml)) on first hour after the challenge. We did not observe any differences in LTC(4) level before and after ASA challenge in ATA. In AIA group the mean level of LXA(4) was 43 +/- 21.5 pg/ml after placebo and decreased in 2 h after Lys-ASA challenge (29 +/- 17 pg/ml, P = 0.015). We found an increase in LXA(4) in ATA after ASA provocation as compared to placebo (33 +/- 16 pg/ml vs 52 +/- 31 pg/ml, P = 0.046). In atopic patients baseline level of LXA(4) was 33.49 +/- 16.95 pg/ml with no difference after the clinically positive allergen challenge (36.22 +/- 13.26 pg/ml, P = 0.23).

CONCLUSIONS

Results of our study confirm that AIA have diminished LXs' biosynthesis capacities in vivo after ASA challenge. Taking into consideration anti-inflammatory properties of lipoxins this phenomenon may be partially responsible for the development of chronic inflammation in AIA patients.

Interleukin-13-induced MUC5AC is regulated by 15-lipoxygenase 1 pathway in human bronchial epithelial cells

RATIONALE

15-Lipoxygenase-1 (15LO1) and MUC5AC are highly expressed in asthmatic epithelial cells. IL-13 is known to induce 15LO1 and MUC5AC in human airway epithelial cells in vitro. Whether 15LO1 and/or its product 15-HETE modulate MUC5AC expression is unknown.

OBJECTIVES

To determine the expression of 15LO1 in freshly harvested epithelial cells from subjects with asthma and normal control subjects and to determine whether IL-13-induced 15LO1 expression and activation regulate MUC5AC expression in human bronchial epithelial cells in vitro.

METHODS

Human airway epithelial cells from subjects with asthma and normal subjects were evaluated ex vivo for 15LO1 and MUC5AC expression. The impact of 15LO1 on MUC5AC expression in vitro was analyzed by inhibiting 15LO1 through pharmacologic (PD146176) and siRNA approaches in human bronchial epithelial cells cultured under air-liquid interface. We analyzed 15 hydroxyeicosatetraenoic acid (15-HETE) by liquid chromatography/UV/mass spectrometry. MUC5AC and 15LO1 were analyzed by real-time RT-PCR, immunofluoresence, and Western blot.

MEASUREMENTS AND MAIN RESULTS

Epithelial 15LO1 expression increased with asthma severity (P < 0.0001). 15LO1 significantly correlated with MUC5AC ex vivo and in vitro. IL-13 increased 15LO1 expression and stimulated formation of two molecular species of 15-HETE esterified to phosphotidylethanolamine (15-HETE-PE). Inhibition of 15LO1 suppressed 15-HETE-PE and decreased MUC5AC expression in the presence of IL-13 stimulation. The addition of exogenous 15-HETE partially restored MUC5AC expression.

CONCLUSIONS

Epithelial 15LO1 expression increases with increasing asthma severity. IL-13 induction of 15-HETE-PE enhances MUC5AC expression in human airway epithelial cells. High levels of 15LO1 activity could contribute to the increases of MUC5AC observed in asthma.

Effect of fish oil-derived omega-3 polyunsaturated Fatty Acid supplementation on exercise-induced bronchoconstriction and immune function in athletes

Exercise-induced bronchoconstriction (EIB) is a condition in which vigorous physical activity triggers acute airway obstruction in asthmatic and nonasthmatic individuals with hyperresponsive airways. Studies have shown that inflammatory mediators and contraction of airway smooth muscle are central components in the pathogenesis of EIB, and it has long been recognized that leukotrienes and prostaglandins play an important role in the EIB response. Clinical responses to current therapy, such as leukotriene modifiers and corticosteroids are heterogeneous, and even with optimal treatment there is a substantial burden of unaddressed disease. While daily medications such as leukotriene modifiers provide only modest protection against symptoms, prolonged use of several medications can result in reduced effectiveness or tachyphylaxis. Although the treatment of EIB almost exclusively involves pharmacotherapy, there is now convincing evidence that dietary modification has the potential to reduce the severity of this condition. Omega-3 polyunsaturated fatty acids, such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in fish oils, compete with arachidonic acid as substrates for the formation of proinflammatory mediators, such as leukotrienes, prostaglandins, and cytokines. Studies have shown that 3 weeks of fish oil supplementation, rich in EPA and DHA, reduces exercise-induced airway narrowing, airway inflammation, and bronchodilator use in elite athletes and asthmatic individuals with EIB. Based on the evidence to date, fish oil supplementation may represent a potentially beneficial treatment intervention for athletes and asthmatic individuals with EIB. From this, it follows that physicians should pay more attention to what their asthma/EIB patients eat, and incorporate dietary assessment and nutritional counseling in their everyday practice.

KEYWORDS

omega-3; polyunsaturated fatty acid; fish oil; exercise-induced bronchoconstriction.

Chronic inflammation in asthma: a contest of persistence vs resolution

Recent investigations have highlighted that endogenous anti-inflammatory mediators and immune regulating mechanisms are important for the resolution of inflammatory processes. A disruption of these mechanisms can be causally related not only to the initiation of unnecessary inflammation, but also to the persistence of several chronic inflammatory diseases. In asthma, chronic Th-2 driven eosinophilic inflammation of the airways is one of the central abnormalities. To date, elucidating the role of the different pro-inflammatory mediators involved in orchestrating the inflammatory processes in asthma has been the subject of intense research in both humans and animal models. However, the counter-regulatory mechanisms that co-determine the outcome in the contest of resolution vs persistence of the eosinophilic airway inflammation remain poorly understood. These are currently being investigated in animal models of chronic asthma. Elucidating these mechanisms is of relevance, since it can give rise to a new therapeutic approach in the treatment of chronic airway inflammation in asthmatics. This novel concept of treatment involves the stimulation of endogenous anti-inflammatory pathways, rather than solely antagonising the various pro-inflammatory mediators. Here, we review and discuss the current knowledge about these endogenous anti-inflammatory mediators in clinical and experimental asthma.