Clinical relevance of lipid mediators in asthma

Dietary oxidized oil influences the levels of type 2 T-helper cell-related antibody and inflammatory mediators in mice

The aim of this present study was to investigate the effect of amount and degree of oxidation of dietary oil on type 2 T-helper cell (TH)-related immune responses. Four groups of BALB/c mice were fed either 50 g soyabean oil/kg (50-S), 50 g oxidized oil/kg (50-O), 150 g soyabean oil/kg (150-S) or 150 g oxidized oil/kg (150-O). After 14 weeks consuming the experimental diets, the mice were immunized with ovalbumin (OVA) plus Al and antigen-specific immunoglobulin (Ig)E, IgG1 and IgG2a, inflammatory mediators such as prostaglandin (PG) E2 and leukotriene (LT)B4 were determined. Higher hepatic microsomal cytochrome P450 was noted in mice fed 150 g oxidized oil/kg compared with those of other groups. OVA-specific IgG1 and IgE were higher in mice fed 150 g oxidized oil/kg compared with those of the other groups. The data suggested the interleukin (IL)-4: interferon (IFN)-γ ratio was higher in mice fed 50 g dietary oxidized oil/kg compared with that of the 50-S group. The IL-5:IFN-γ ratios were higher in the 150-S and 150-O groups than in the 50-S and 50-O groups. PGE2 and LTB4 produced by macrophages stimulated by lipopolysaccharide were highest in mice in the 150 g oxidized oil/kg group. The data suggested that an increased intake of oxidized oil might exert an unfavourable effect on the TH2 response involved in allergic disease.

Inhaled leukotriene E(4), but not leukotriene D(4), increased airway inflammatory cells in subjects with atopic asthma

Allergen-induced late airway responses are associated with increased numbers of airway eosinophils and basophils. The purpose of this study was to compare and contrast the effects of inhaled cysteinyl leukotrienes LTD(4) and LTE(4), which are released during allergen- induced airway responses, and allergen, on airway inflammatory cells. Fifteen subjects with atopic, mild asthma inhaled diluent, LTD(4), LTE(4), and allergen. Spirometry was performed for 7 h, and sputum inflammatory cells were measured before, 7 h, and 24 h after challenges. The maximum early percent fall in FEV(1) was 23.6 +/- 1.4%, 21.6 +/- 2.3%, 29.3 +/- 2.4%, and 4.0 +/- 1.1% after LTD(4), LTE(4), allergen, and diluent, respectively. Only inhaled LTE(4) and allergen significantly increased sputum eosinophils at 7 h and 24 h, and sputum basophils at 7 h. Six additional subjects underwent airway biopsies 4 h after inhalation. There were significantly more eosinophils in the lamina propria after inhalation of LTE(4) compared with LTD(4) and diluent (p < 0.05). These results suggest cysteinyl leukotrienes play a role in eosinophil migration into the airways in allergic asthma, and for the same degree of bronchoconstriction, inhaled LTE(4) causes more tissue and airway eosinophilia than LTD(4).

Exercise-induced bronchoconstriction does not cause eosinophilic airway inflammation or airway hyperresponsiveness in subjects with asthma

The cysteinyl leukotrienes (LT) C(4), D(4), and E(4) may partially mediate eosinophilic airway inflammation in patients with asthma. High- intensity exercise by patients with asthma can result in exercise- induced bronchoconstriction, partly due to leukotriene production, but it is still debated whether this causes airway inflammation. Ten subjects completed a randomized, controlled study to examine the effects of exercise-induced bronchoconstriction on airway inflammatory cells. Subjects completed exercise challenge and methacholine challenge in random order separated by 1 wk. Spirometry was measured for 2 h after challenges, and airway responsiveness was measured the day before and 24 h after each challenge. Blood and sputum samples were obtained before, and 2, 4, 7, and 24 h after each challenge for measurement of inflammatory cells. Nine of the subjects inhaled allergen at least 3 wk before or 1 wk after the study. Sputum samples were collected before, 7 h, and 24 h after challenge. The maximum percentage fall in FEV(1) was 21.3 +/- 1.5% after exercise, 29.9 +/- 1.5% after methacholine, and 28.9+/-2.7% after allergen. Exercise had no effect on airway responsiveness or inflammatory cells measured in blood or sputum, unlike allergen inhalation, which resulted in significant airway hyperresponsiveness and increases in sputum eosinophils (p < 0.05). This study demonstrates that exercise-induced bronchoconstriction does not cause eosinophilic airway inflammation in subjects with asthma who develop airway inflammation with the same degree of allergen-induced bronchoconstriction. We conclude that exercise-induced bronchoconstriction does not cause airway inflammation or airway hyperresponsiveness.

Effect of inhaled leukotriene D4 on airway eosinophilia and airway hyperresponsiveness in asthmatic subjects

Inhaled cysteinyl leukotrienes may cause recruitment of eosinophils into asthmatic airways. We compared the effects of inhaled leukotriene D4 (LTD4), methacholine, and allergen on airway eosinophils in 10 nonsmoking, atopic, mildly asthmatic subjects in a double-blind, diluent-controlled, randomized crossover study. Concentrations of LTD4, methacholine, and allergen resulting in a 30% decrease in FEV1, and diluent controls (ethanol and saline), were inhaled with at least 7 d between challenges. Spirometry was conducted for 4 h after inhalation challenge, and airway hyperresponsiveness (AHR) to methacholine was measured before and 24 h after challenge. Sputum was induced before and 4 h, 7 h, and 24 h after challenge. The maximum decrease in FEV1 was 31.4 +/- 1.8% with LTD4, 39.4 +/- 2.8% with methacholine, and 30.1 +/- 3.4% with allergen. AHR to methacholine, at the provocative concentration causing a 20% decrease in FEV1 (PC20), was enhanced 24 h after allergen challenge, but remained unchanged 24 h after LTD4 and methacholine (p > 0.05). The percentage of eosinophils in sputum was increased after inhalation of allergen at 7 h and 24 h (p = 0.003), but not after LTD4 or methacholine (p = 0.70). We demonstrated that neither inhalation of LTD4 nor of methacholine at concentrations causing submaximal bronchoconstriction increases the number of sputum eosinophils in the airways of mildly asthmatic subjects. However, LTD4 may still be an important cofactor for eosinophil recruitment in asthma.

Leukotriene D4- and prostaglandin F2 alpha-induced airflow obstruction and airway plasma exudation in guinea-pig: role of thromboxane and its receptor

1. We studied the effects of a thromboxane A2 receptor (TP receptor) antagonist, ICI-192,605 (0.5 mg kg-1, i.v.) and a selective thromboxane (Tx) synthetase inhibitor, OKY-046 (30 mg kg-1, i.v.), on airway responses induced by leukotriene D4 (LTD4; 0.2 nmol) or prostaglandin F2 alpha (PGF2 alpha; 20 nmol) instilled via the airways route to anaesthetized guinea-pigs. For a comparison, airway responses to a TxA2-mimetic, U-46619 (0.02 nmol) were also studied. We measured both lung resistance (RL) to monitor airflow obstruction, and extravasation of Evans Blue dye to quantify airway plasma exudation. 2. Instilled LTD4 into the tracheal lumen induced an immediate peak and subsequently persistent increase in RL and produced a large amount of extravasation of Evans Blue dye at all airway levels. Both ICI-192,605 and OKY-046 significantly attenuated the persistent increase in RL following the immediate response and reduced LTD4-induced extravasation of Evans Blue dye in the trachea and proximal intrapulmonary airway. Instilled LTD4 produced significant increases in immunoreactive TxB2 in bronchoalveolar lavage fluid obtained 1.5 min after instillation of LTD4. 3. Instilled PGF2 alpha into the tracheal lumen induced an immediate increase in RL which peaked at approximately 15 s. We also observed a delayed sustained increase in RL, reaching a second peak at approximately 4 min. PGF2 alpha produced small but significant increases in the amount of Evans Blue dye at all airway levels. As with PGF2 alpha, instillation of U-46619 produced a biphasic increase in RL and extravasation of Evans Blue dye. The potency of PGF2a, in inducing these airway responses was about 1000 times less than U-46619. ICI-192,605 abolished both the immediate and the delayed increase in RL after PGF2a, and also blocked PGF2a,-induced extravasation of Evans Blue dye. However, OKY-046 had no inhibitory effects on these responses.4. We conclude that airflow obstruction and airway plasma exudation induced by instilled LTD4 is, in part, mediated via TxA2 generation and subsequent activation of TP-receptors. On the other hand,instilled PGF2a, while inducing similar responses, does so primarily by direct activation of TP receptors,rather than via TxA2 generation.