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Cysteinyl leukotriene (cysLT) overproduction and eosinophil activation are hallmarks of aspirin-exacerbated respiratory disease (AERD). However, pathogenic mechanisms of AERD remain to be clarified. Here, we aimed to find the significance of transforming growth factor beta 1 (TGF-β1) in association with cysteinyl leukotriene E4 (LTE4) production, leading to eosinophil degranulation. To evaluate levels of serum TGF-β1, first cohort enrolled AERD (n = 336), ATA (n = 442) patients and healthy control subjects (HCs, n = 253). In addition, second cohort recruited AERD (n = 34) and ATA (n = 25) patients to investigate a relation between levels of serum TGF-β1 and urinary LTE4. The function of TGF-β1 in LTE4 production was further demonstrated by ex vivo (human peripheral eosinophils) or in vivo (BALB/c mice) experiment. As a result, the levels of serum TGF-β1 were significantly higher in AERD patients than in ATA patients or HCs (P = .001; respectively). Moreover, levels of serum TGF-β1 and urinary LTE4 had a positive correlation (r = 0.273, P = .037). In the presence of TGF-β1, leukotriene C4 synthase (LTC4S) expression was enhanced in peripheral eosinophils to produce LTE4, which sequentially induced eosinophil degranulation via the p38 pathway. When mice were treated with TGF-β1, significantly induced eosinophilia with increased LTE4 production in the lung tissues were noted. These findings suggest that higher levels of TGF-β1 in AERD patients may contribute to LTE4 production via enhancing LTC4S expression which induces eosinophil degranulation, accelerating airway inflammation., Competing Interests: The authors declare that this is an investigator-initiated study therefore Dong-A ST Co. and MD Healthcare Inc. have no issues that lead to conflicts of interests in this study. This does not alter our adherence to PLOS ONE policies on sharing data and materials.

Background/aim: It is claimed that aberrant immune response has a more important role than the cytopathic effect of the virus in the morbidity and mortality of the coronavirus disease 2019 (COVID-19). We aimed to investigate the possible roles of tumor necrosis factor-like weak inducer of apoptosis (TWEAK)/Fn14 pathway and leukotrienes (LT) in uncontrolled immune response that occurs in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)., Materials and Methods: This study included 25 asymptomatic patients and 35 patients with lung involvement who were diagnosed with COVID-19 as well as 22 healthy volunteers. Lung involvement was determined using computed-tomography. Serum TWEAK, LTE4, and prostaglandin F2α (PGF2α) levels were determined., Results: Compared with the healthy control group, TWEAK, LTE4, and PGF2α levels were higher in the group of SARS-CoV-2 infection without lung involvement. In the group of SARS-CoV-2 infection with lung involvement, age, fibrinogen, sedimentation, C-reactive protein and ferritin, TWEAK, LTE4, and PGF2α levels were higher, and lymphocyte levels were lower compared with the asymptomatic group., Conclusions: In the study, TWEAK and LTE4 levels increased in cases with COVID-19. These results support that TWEAK/Fn14 pathway and LT may involved in the pathology of aberrant immune response against SARS-CoV-2. Inhibition of each of these pathways may be a potential target in the treatment of COVID-19., Competing Interests: All authors declare that they have no conflicts of interests., (This work is licensed under a Creative Commons Attribution 4.0 International License.)

Low basal endogenous concentrations (<20 pg/mL) of the 5-lipoxygenase (5-LO) pathway biomarker leukotriene E 4 (LTE 4 ) in human plasma present a significant analytical challenge. Analytical methods including liquid chromatography-mass spectrometry and enzyme linked immunosorbent assays have been used to quantify plasma LTE 4 in the past but have not provided consistent data in the lower pg/mL-range. With our new method, a detection limit (<1 pg/mL plasma) significantly below basal levels of LTE 4 was achieved by combining large volume sample purification and enrichment by anion-exchange mixed mode solid phase extraction (SPE) with large volume injection followed by chromatographic separation by ultra performance liquid chromatography (UPLC) and quantification by highly sensitive negative-ion electrospray tandem mass spectrometry (MS/MS). The method was reproducible, accurate and linear between 1 and 120 pg/mL plasma LTE 4 . The method was used to perform an analysis of plasma samples collected from healthy volunteers in a Phase 1 study with the FLAP (5-lipoxygenase activating protein) inhibitor AZD5718. Basal endogenous LTE 4 levels of 5.1 ± 2.7 pg/mL were observed in healthy volunteers (n = 34). In subjects that had been administered a single oral dose of AZD5718, significant suppression (>80%) of plasma LTE 4 level was observed, providing pharmacological evidence that endogenous 5-LO pathway activity could be assessed., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Platelets modulate asthma pathogenesis by forming the platelet-eosinophil aggregation (PEA), which facilitates the activation of eosinophils. Platelets exhibit the purinergic receptor (P2Y12R), which responds to cysteinyl leukotriene E4 (LTE 4 ). We have suggested that the combination of an antiplatelet drug (clopidogrel, [Clo]) and montelukast (Mon) would synergistically suppress asthma. BALB/c mice were intraperitoneally sensitized with ovalbumin (OVA) on days 0 and 14 and subsequently challenged on days 28-30 and 42-44. Mice were administered with Clo (10 mg/kg), Mon (10 mg/kg) or both drugs (Clo/Mon) orally 30 minutes before the OVA (1%) challenge on days 42-44. Mice were assayed for airway hyper-responsiveness (AHR) to methacholine and airway inflammation. Clopidogrel and montelukast attenuated the increased AHR; the combined treatment was more effective than a single treatment for total and eosinophil counts (all P < 0.05). Levels of interleukin (IL)-4, IL-5, IL-13, platelet factor 4, eosinophil peroxidase and LTE 4 increased in the bronchoalveolar lavage fluid of asthmatic mice, but these levels decreased in mice treated with Clo/Mon (all P < 0.05). Goblet cell hyperplasia decreased in response to Clo/Mon. Mouse platelets and eosinophils were isolated and co-cultured for an in vitro assay with 10 µmol/L adenosine diphosphate (ADP), LTE 4 (200 nmol/L), Mon (1 µmol/L), Clo (1 µmol/L) and Clo/Mon (1 µmol/L). Flow cytometry revealed that the increased formation of the PEA (%) was fully mediated by ADP and partly mediated by LTE 4 . Clo/Mon reduced ADP-induced PEA formation and P-selectin expression (P < 0.05). In conclusion, Clo/Mon synergistically relieved asthma by inhibiting ADP-mediated PEA formation., (© 2019 The Authors. Journal of Cellular and Molecular Medicine published by John Wiley & Sons Ltd and Foundation for Cellular and Molecular Medicine.)

Background: Clinical presentation of nonsteroidal anti-inflammatory drugs exacerbated respiratory disease (NERD) is found to be heterogeneous. This study classified phenotypic clusters to determine NERD subtypes., Methods: We performed two-step cluster analysis using urticaria, chronic rhinosinusitis (CRS), and atopy, in a NERD cohort comprising 302 patients. Asthma exacerbation was defined as receiving at least one burst of intravenous steroid treatment and/or at least two bursts of oral steroid use (≥ 45 mg/3 days) per year. The possession rate of anti-asthmatic medications was estimated during the follow-up period., Results: There were four subtypes: subtype 1 (NERD with CRS/atopy and no urticaria), subtype 2 (NERD with CRS and no urticaria/atopy), subtype 3 (NERD without CRS/urticaria), and subtype 4 (NERD with urticaria). Significant differences were found between the four subtypes in the female proportion, baseline FEV1%, serum total IgE level, and sputum/peripheral eosinophil count. A higher frequency of asthma exacerbations was noted in subtype 1 compared to subtype 3. The possession rates of medium- to high-dose inhaled corticosteroids/long-acting beta 2 -agonists showed significant differences among the four subtypes. Metabolomic analysis showed that the four subtypes of NERD had a higher serum leukotriene E4 (LTE4) level than those with aspirin-tolerant asthma. The patients with subtypes 1 and 3 had a higher urine LTE4 level than those with subtype 2., Conclusion: We found four distinct subtypes with different clinical/biochemical findings and asthma exacerbations in a NERD cohort. These findings suggest that stratified strategies by applying subtype classification may help achieve better outcomes in the management of NERD., (© 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Background: Urinary leukotriene (LTE4) is an important marker of airway inflammation presence. A relationship between single nucleotide polymorphism in the glucocorticoid receptor (GCR) gene promoter (Bcl I polymorphism), development of asthma and sensitivity to glucocorticoids has been hypothesised., Objective: To explore the possible association between the Bcl I polymorphism and baseline levels of urinary LTE4 in preschoolers with recurrent wheezing episodes. We prospectively enrolled and classified 86 preschoolers based on the risk of developing asthma (by the Asthma Predictive Index [API])., Methods: At admission standardised questionnaires for demographics and respiratory illness characteristics were completed. The Bcl I polymorphism of the GCR was determined by a PCR-RFLP assay from blood samples, and urinary leukotriene was assessed from urine samples by an enzyme immunoassay., Results: We enrolled 86 preschoolers (46 with positive API and 40 with negative API). There were no statistical differences in demographic, respiratory illnesses and wheezing episodes characteristics between both groups. Also, the prevalence of Bcl I polymorphism was similar between positive vs. negative API groups (34.8% vs. 38.9% for homozygote GG, 56.5% vs. 52.8% for heterozygote GC, 8.7% vs. 8.3% for homozygote CC, respectively, p=0.94). However, urinary LTE4 (median [IQR]) was higher in preschoolers with positive than negative API (7.18 [5.57-8.96pg/ml] vs. 6.42 [3.96-8.07pg/ml], p=0.02, respectively)., Conclusions: In our population, wheezing preschoolers with positive API exhibit higher levels of urinary LTE4 than those with negative API; but there were no differences in Bcl I polymorphism of the GCR., (Copyright © 2015 SEICAP. Published by Elsevier Espana. All rights reserved.)

Background: Allergic rhinitis (AR) is a chronic inflammatory disease of the nasal airways.Many therapies do not have immediate effects,even which have side-effects.However,the effects of Xingbi gel for the treatment of AR was investigated., Objective: We investigated the effects of Xingbi gel on serum levels of leukotriene E4 (LTE4) and immunoglobulin E (IgE), as well as eosinophil counts in the nasal mucosa using a guinea pig model of allergic rhinitis (AR)., Methods: In addition to a healthy control group without AR, guinea pigs with AR were randomly divided into untreated AR control group, low-dose Xingbi gel (0.2483 g/mL) group, high-dose Xingbi gel (0.4966 g/mL) group, and budesonide group., Results: Compared to the healthy controls, untreated AR guinea pigs had significantly higher ethology scores, serum LTE4 and IgE levels, and nasal mucosa eosinophil counts (p <0.01). Treatments with low-dose Xingbi gel, high-dose Xingbi gel, and budesonide significantly reduced the ethology scores, serum LTE4 and IgE levels, and nasal mucosa eosinophil counts as compared to untreated AR model guinea pigs (p <0.01)., Conclusion: Xingbi gel alleviates AR in part through inhibiting LTE4 and IgE production and reducing eosinophilia in the nasal mucosa.

Background: Arachidonic acid metabolites are implicated in the pathogenesis of asthma although only limited information is available on the impact of current smoking history on these metabolites. The aim of the study was to examine the effect of smoking status on urinary, sputum, and plasma eicosanoid concentrations and relevant enzyme transcripts in asthma., Methods: In 108 smokers and never smokers with asthma and 45 healthy controls [smokers and never smokers], we measured urinary tetranor prostaglandin (PG)D2 (PGDM) and leukotriene (LT)E4 , induced sputum fluid LTB4 , LTE4 , PGD2 , and PGE2 , plasma secretory phospholipase A2 (sPLA2 ), and 11β prostaglandin F2α (11βPGF2α ), and, in a subgroup with severe asthma, airway leukocyte and epithelial cell mRNA expression levels of arachidonic acid metabolic enzymes., Results: Smokers with asthma had higher urinary LTE4 ; 83 (59, 130) vs 59 (40, 90) pg/mg creatinine, P = 0.008, and PGDM; 60 (35, 100) vs 41 (28, 59) ng/mg creatinine, P = 0.012 concentrations, respectively, and lower sputum PGE2 concentrations 80 (46, 157) vs 192 (91, 301) pg/ml, P = 0.001 than never smokers with asthma. Sputum LTB4 (P = 0.013), and plasma 11βPGF2α (P = 0.032), concentrations, respectively, were increased in smokers with asthma compared with healthy smokers. Asthma-specific and smoking-related increases (>1.5-fold expression) in arachidonate 15-lipoxygenase and gamma-glutamyltransferase transcripts were demonstrated., Conclusions: Several arachidonic acid metabolites and enzyme transcripts involving both lipoxygenase and cyclooxygenase pathways are increased in smokers with asthma and differ from never smokers with asthma. Possibly targeting specific lipoxygenase and cyclooxygenase pathways that are activated by asthma and cigarette smoking may optimize therapeutic responses., (© 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Aim: To assess the pharmacokinetics, pharmacodynamics, safety and tolerability of the 5-lipoxygenase-activating protein inhibitor, GSK2190915, after oral dosing in two independent phase I studies, one in Western European and one in Japanese subjects, utilizing different formulations., Method: Western European subjects received single (50-1000 mg) or multiple (10-450 mg) oral doses of GSK2190915 or placebo in a dose-escalating manner. Japanese subjects received three of four GSK2190915 doses (10-200 mg) plus placebo once in a four period crossover design. Blood samples were collected for GSK2190915 concentrations and blood and urine were collected to measure leukotriene B₄ and leukotriene E₄, respectively, as pharmacodynamic markers of drug activity., Results: There was no clear difference in adverse events between placebo and active drug-treated subjects in either study. Maximum plasma concentrations of GSK2190915 and area under the curve increased in a dose-related manner and mean half-life values ranged from 16-34 h. Dose-dependent inhibition of blood leukotriene B₄ production was observed and near complete inhibition of urinary leukotriene E₄ excretion was shown at all doses except the lowest dose. The EC₅₀ values for inhibition of LTB₄ were 85 nM and 89 nM in the Western European and Japanese studies, respectively., Conclusion: GSK2190915 is well-tolerated with pharmacokinetics and pharmacodynamics in Western European and Japanese subjects that support once daily dosing for 24 h inhibition of leukotrienes. Doses of ≥50 mg show near complete inhibition of urinary leukotriene E₄ at 24 h post-dose, whereas doses of ≥150 mg are required for 24 h inhibition of blood LTB₄., (© 2012 GlaxoSmithKline. British Journal of Clinical Pharmacology © 2012 The British Pharmacological Society.)

Background: The aim of this study was to investigate the influence of exercise training on oxidative stress and markers of lung inflammation in children with asthma., Methods: Thirty children aged 8-13 years diagnosed with asthma were enrolled in the study as well as 13 healthy children. One group received only pharmacological treatment and the other group was also enrolled in an exercise programme. Venous blood and 24-hour urine samples were obtained from the children enrolled in the study at the beginning and end of the study. Leukotriene E4 and creatinine levels were measured in the urine and matrix metallopeptidase (MMP-9), endothelin-1(ET-1), malnodialdehyde (MDA), IgE and specific IgE levels were measured in blood samples., Results: Leukotriene E4, MDA and MMP9 levels decreased significantly with treatment in both groups (p < 0.001). However, ET-1 levels decreased significant only in the exercise group (26.5 ± 3.6 vs 21.3 ± 2.4 pg/ml respectively, p = 0.001). Moreover, ET-1 levels were found to be significantly lower in the exercise group compared to the only pharmacotherapy group (24.2 ± 3.1 vs 21.3 ± 2.4 pg/ml, p=0.007)., Conclusions: Positive influences of exercise training in children with asthma may be mediated by decrease in ET-1 levels., (Copyright © 2010 SEICAP. Published by Elsevier Espana. All rights reserved.)

Leukotrienes (LTs) are involved in the pathogenesis of lung fibrosis and were increased in exhaled breath condensate (EBC) of the patients with pneumoconiosis. However the possible influence of extra-pulmonary disorders on the EBC markers is not known. Therefore in parallel with EBC, LTs' levels in the plasma and urine were measured in patients with pneumoconiosis (45 × asbestos exposure, 37 × silica exposure) and in 27 controls. Individual LTs B4, C4, D4 and E4 were measured by liquid chromatography - electrospray ionization - tandem mass spectrometry (LC-ESI-MS/MS). In EBC, LT D4 and LT E4 were increased in both groups of patients (p<0.001 and p<0.05), comparing with the controls. Both LT B4 and cysteinyl LTs were elevated in asbestos-exposed subjects (p<0.05). Asbestosis with more severe radiological signs (s1/s2-t3/u2) and lung functions impairment has shown higher cysteinyl LTs and LT C4 in the EBC (p<0.05) than mild asbestosis (s1/s0-s1/s1). In addition, in the subjects with asbestosis, cysteinyl LTs in EBC correlated with TLC (-0.313, p<0.05) and TLCO/Hb (-0.307, p<0.05), and LT C4 with TLC (-0.358, p<0.05). In pneumoconioses, EBC appears the most useful from the 3 fluids studied.

The pathogenesis of Henoch-Schönlein purpura (HSP) is not clearly understood. It remains unclear how changes of lipoxin A(4) (LXA(4)) that acts as a "braking signal" in inflammatory process occur in patients with HSP. In this study, we determined the temporal changes of blood and urinary LXA(4), Leukotriene (LT)B(4) and urinary LTE(4) in 49 children with HSP. Inverse temporal changes between gradually increased blood and urinary LXA(4) and gradually decreased blood and urinary LTB(4) and urinary LTE(4) were found in patients with HSP. Furthermore, both 15-S-hydroxyeicosatetraenoic acid and LXA(4) inhibited the LTB(4)-induced chemotaxis of leukocytes and release of LTB(4) from leukocytes obtained from the patients in the active phase of HSP. In 22 children with HSP nephritis, concordant with the gradually increased severity of mesangial proliferation and proteinuria, the glomerular expressions of 15-lipoxygenase and the levels of urinary LXA(4) gradually decreased and the glomerular expressions of LTC(4) synthase and the urinary LTE(4) and LTB(4) gradually increased. The levels of blood and urinary LXA(4) in patients with HSP nephritis were lower than those in patients with purpura alone in early resolution of HSP. The levels of blood and urinary LTB(4) and urinary LTE(4) in the patients with HSP nephritis were higher than those in patients with purpura alone in early resolution of HSP. There was positive correlation between blood LTB(4) and serum C-reactive protein in 49 children with HSP. These data suggest that LTs may play a proinflammatory and profibrotic role in the pathogenesis of HSP, and insufficiency of LXA(4) may be responsible for the patients with HSP whose illness become more serious.

In this study, prospectively, we aimed to determine the effects of the different treatment alternatives on the oxidant system and inflammatory and clinic determinants during the stable period of 1 month following an asthmatic attack. Thirty-one patients (22 female, nine male) were randomly divided into three groups following the stabilization of an acute asthma attack. The control group that is an additional group to the three patient groups consisted of 10 healthy volunteers (five female, five male). The following protocols were used for 4 weeks: Group I: short-acting inhaler beta2 mimetic as required (treatment A)+800 mug inhaler budesonide (treatment B)+leukotriene receptor antagonist; Group II: treatment A and B; Group III: treatment A and B+vitamin E. The serum levels before and after treatment of eosinophilic cationic protein (ECP), leukotriene E4 (LTE(4)), and malondialdehyde (MDA) were determined. The values before and after treatment were statistically compared both with each other and control values. Pretreatment ECP, LTE(4), and MDA levels for the three groups were significantly higher compared with post-treatment levels (P<0.05 to P<0.001) and the control levels (P<0.01 to P<0.001). However, when post-treatment levels were compared with those of the control group, no significant differences were found (P>0.05). Lack of significant variation was observed when the pre- and post-treatment differences in the three groups were compared for each one of ECP, LTE(4), and MDA levels (P>0.05). Leukotriene receptor antagonist or antioxidant agents added to standard asthma treatment did not make a significant contribution on ECP, LTE(4), and MDA levels and respiratory parameters such as spirometric function tests. Etiologic factors and/or the possible changes in different pathogenetic ways of the inflammation process may have been responsible for nonsignificant intertreatment difference in the biomarker levels. The result confirms that suppressing the inflammation in asthma enables the entire inflammatory pathologic process to be controlled.

To evaluate the levels of leukotrienes (LTs), interleukin-2 (IL-2), interleukin-4 (IL-4), interferon-gamma (IFN-gamma) in patients with eczema and observe the effects inversed by mizolastine. Serum LTB4, LTC4, IL-2, IL-4, IFN-gamma and urinary LTE4 levels were detected by enzyme-linked immunosorbent assay (ELISA) and LTB4, LTC4, LTE4 concentrations of cutis tissue were measured by reverse-phase high-pressure liquid chromatography (RP-HPLC) in 10 eczema patients and 10 healthy volunteers. Eczema patients received mizolastine 10 mg once a day for 5 days, respectively, for comparison between before and after treatment. The above markers were assayed again after treatment. Serum LTB4, LTC4, IL-2, IFN-gamma and urinary LTE4 and skin tissue LTB4, LTC4, LTE4 levels in patients are higher than those in healthy volunteers significantly (P < 0.05). But serum IL-4 level did not show significant difference between patients and normal controls (P > 0.05). Mizolastine significantly reduced serum LTB4 and IFN-gamma levels as well as skin lesion LTB4, LTC4, LTE4 concentrations. LTs are involved in the pathogenesis of eczema. Mizolastine clearly reduces LTs levels in skin lesion.

To further establish the role of oxidative stress in the pathogenesis of acute bronchial asthma, we investigated the effects of platelet-activating factor (PAF) challenge on systemic oxidant-antioxidant balance in 12 asthmatic patients (age, 25+/-3[SEM] yr; FEV1, 95+/-10% predicted), using a double blinded, controlled with Lyso-PAF (L-PAF), cross-over design. Respiratory system resistance (Rrs), arterial blood gases, peripheral blood neutrophils and oxidant-antioxidant balance, including thiobarbituric acid (TBA)-malondialdehyde (MDA) adducts, protein sulphydryls and Trolox equivalent antioxidant capacity (TEAC), were assessed at baseline and 5, 15 and 45 min after PAF and L-PAF (18 microg each) bronchoprovocation. Urinary leukotriene E4 (uLTE4) elimination was measured 120 min after challenge. Compared with baseline, as expected, PAF increased significantly Rrs and AaPO2 and decreased PaO2 and peripheral blood neutrophils along with a rebound neutrophilia and increased uLTE4. By contrast, markers of systemic oxidative stress remained unaltered throughout the study. Unlike PAF, L-PAF-induced changes were negligible. We conclude that there is no systemic oxidant-antioxidant imbalance during acute bronchoconstriction induced by PAF in these patients with mild asthma.

A correlation between arsenic and cardiovascular disease (CVD) has been established through epidemiological studies, although the mechanisms are unknown. Using a mouse model that develops atherosclerotic lesions on a normal chow diet, we have confirmed a connection between long-term arsenic intake and CVD. Our results reveal a significant increase in the degree of atherosclerotic plaque stenosis within the innominate artery of ApoE-/-/LDLr-/- mice treated with 10 ppm sodium arsenite (133 microM) in drinking water for 18 weeks compared to controls. Immunohistochemistry shows nitrotyrosine formation, a marker of reactive nitrogen species generation, is significantly higher within the atherosclerotic plaque of arsenic-treated mice. In addition, there is a significant increase in the 5-lipoxygenase (5-LO) product, leukotriene E4 (LTE4), in the serum of arsenic-treated mice. This is supported by induction of the 5-LO protein and subsequent increases in LTE4 synthesis in bovine aortic endothelial cells. This increase in LTE4 is partially inhibited by inhibitors of nitric oxide synthase, suggesting a link between reactive nitrogen species and arsenic-induced inflammation. Furthermore, there is a significant increase in prostacyclin (PGI2) in the serum of arsenic-treated mice. We conclude that changes in specific inflammatory mediators such as LTE4 and PGI2 are related to arsenic-induced atherosclerosis. In addition, amplified synthesis of reactive species such as peroxynitrite results in increased protein nitration in response to arsenic exposure. This finding is consistent with the pathology seen in human atherosclerotic plaques.

Unlabelled: The purpose of this study was to investigate plasma and urinary levels of leukotriene (LT) and the changes in pulmonary function induced by strenuous exercise in highly trained cyclists (HT) with mild exercised-induced hypoxemia (EIH)., Method: Nine HT and five untrained subjects (UT) performed a 30-min exercise at 78% of their VO2peak. Leukotriene E4 (LTE4) was assayed in plasma and urine. Pulmonary function tests and pulmonary diffusion capacity (DLCO) were examined before and after exercising. Ear arterialized blood gases were assessed at rest and during exercise., Results: The mean drop in partial oxygen pressure was 15 mmHg in HT during exercise; and the DLCO decreased by 7.5% following exercise. No significant changes were found in forced vital capacity or forced expiratory flows. LTE4 levels increased significantly in HT following exercise: urinary LTE4 was 42.9 +/- 6.3 ng.mmol-1 creatinine at rest and 66.3 +/- 11.9 ng.mmol-1 creatinine 2 hrs after exercise, and plasma LTE4 rose from 528 +/- 91 pg.mL-1 at rest to 897 +/- 123 pg.mL-1 after exercise. By contrast, urinary LTE4 level was unchanged in the UT group. Among the HT group, there was no significant correlation between urinary LTE4 changes and PO2, air flow rates, or DLCO changes., Conclusion: These results suggest that strenuous exercise induces an increase of LTE4 release in highly trained cyclists with mild EIH. These changes in LTE4 levels were not related to significant impairment of lung function.

Background: Exhaled nitric oxide (eNO) is a noninvasive test that measures airway inflammation. Insufficient information is available concerning correlations between eNO and biologic, physiologic, and clinical characteristics of asthma in children currently not taking controller medications., Objective: The aim of this study was to find correlations between eNO and other characteristics of children with mild to moderate asthma currently not taking medications., Methods: Children aged 6 to 17 years with mild to moderate persistent asthma, taking only albuterol as needed, were characterized during 2 visits 1 week apart before being randomly assigned into a clinical trial. At the screening visit, online measurements of eNO, spirometry before and after bronchodilator, and biomarkers of peripheral blood eosinophils, serum eosinophil cationic protein, total serum IgE, and urinary leukotriene E4 were obtained. During a week characterization period before randomization, symptoms were recorded on a diary and peak expiratory flows were measured twice daily using an electronic device. At the randomization visit, eNO was repeated followed by a methacholine challenge and aeroallergen skin testing. Correlations and rank regression analyses between eNO and clinical characteristics, pulmonary function, and biomarkers were evaluated., Results: eNO was significantly correlated with peripheral blood eosinophils (r =.51, P <.0001), IgE (r =.48, P <.0001), and serum eosinophil cationic protein (r =.31, P =.0003) but not with urinary leukotriene E4 (r =.16, P =.08). A moderate correlation was found between eNO and the number of positive aeroallergen skin tests (r =.45, P <.0001). eNO did not correlate with FEV1% predicted but was weakly correlated with FEV1/forced vital capacity (r = -.19, P =.032), bronchodilator response (r =.20, P =.023), and FEV1 PC20 methacholine (r = -.31, P =.0005). No significant correlations were found between eNO and clinical characteristics or morning or evening peak expiratory flow measurements. The rank regression analysis demonstrated that 5 variables accounted for an R square of.52 (eosinophils [P <.0001], IgE [P =.0023], age [P <.0001], months of inhaled corticosteroid use in the year before study entry [P =.01], and FEV1 PC20 [P =.0061])., Conclusions: These findings suggest that eNO provides information about the asthmatic state consistent with information from other markers of inflammation. It is a noninvasive technique that could be used in decisional management of children with asthma.

We examined whether lung inflammatory mediators are increased during exercise and whether pharmacological blockade can prevent exercise-induced arterial hypoxemia (EIAH) in young athletes. Seventeen healthy athletes (9 men, 8 women; age 23 +/- 3 yr) with varying degrees of EIAH completed maximal incremental treadmill exercise tests after administration of fexofenadine, zileuton, and nedocromil sodium or placebo in a randomized double-blind crossover study. Lung function, arterial blood gases, and inflammatory metabolites in plasma, urine, and induced sputum were assessed. Drug administration did not improve EIAH or gas exchange during exercise. At maximal exercise, oxygen saturation fell to 91.4 +/- 2.6% (drug trial) and 91.9 +/- 2.1% (placebo trial) and alveolar-arterial oxygen difference widened to 28.1 +/- 6.3 Torr (drug trial) and 29.3 +/- 5.7 Torr (placebo trial). Oxygen consumption, ventilation, and other exercise variables were similarly unaffected by drug treatment. Although plasma histamine increased with exercise, values did not differ between trials, and urinary leukotriene E(4) and 11beta-prostaglandin F(2alpha) levels were unchanged after exercise. Postexercise sputum revealed no significant changes in markers of inflammation. These results demonstrate that EIAH in young athletes is not attenuated with acute administration of drugs targeting histamine and bioactive lipids. We conclude that airway inflammation is of insufficient magnitude to cause impairments in gas exchange and does not appear to be linked to EIAH in healthy young athletes.

Leukotrienes (LTs) are cell-membrane derived lipid inflammatory mediators, synthesized and eliminated by the liver. LTs have effects on liver cells in some pathological conditions. In this study, we measured plasma endogenous and liberated leukotriene (LT) concentration in peripheral blood leukocytes stimulated in vitro by the calcium ionophore (CaA23187) and platelet-activating factor (PAF). Production of LTs was measured in type A (n=37) and type B (n=10) acute hepatitis patients and control subjects (n=10). LTs levels were measured by high performance liquid chromatography (HPLC) and radioimmunoassay (RIA). The concentration of LTB4 measured in plasma and stimulated peripheral blood leukocyte supernatants of children with hepatitis A infection was found to be statistically elevated and in positive correlation with serum alanine aminotransferase (ALT) levels. In plasma samples of hepatitis B patients, LTC4 and LTE4 were measured in significantly elevated concentrations. These results suggest that LTB4 may be a critical mediator of hepatitis A virus-induced hepatocellular injury.

The effects of (-)-nicotine (0.0005-500 microM), (+)-nicotine (0.0005-50 microM) and (-)-cotinine (0.0005-500 microM) on arachidonic acid metabolism were investigated in Ca2+ ionophore A23187 (calcimycin)-stimulated human whole blood in vitro. (-)-Nicotine and (-)-cotinine stimulated prostaglandin E2 but inhibited thromboxane B2 synthesis, as has been observed previously in A23187-stimulated polymorphonuclear leukocytes and platelet-rich plasma [Saareks, V., Riutta, A., Mucha, I., Alanko, J., Vapaatalo, H., 1993. Nicotine and cotinine modulate eicosanoid production in human leukocytes and platelet rich plasma. Eur. J. Pharmacol., 248, 345-349.]. (+)-Nicotine also stimulated prostaglandin E2 but inhibited thromboxane B2 synthesis. High concentrations of (-)-nicotine and (-)-cotinine and even nanomolar concentrations of (+)-nicotine inhibited leukotriene E4 synthesis. These results indicate that (-)-nicotine and (-)-cotinine stimulate cyclooxygenase but inhibit thromboxane synthase and 5-lipoxygenase in whole blood in vitro. (+)-Nicotine is capable of affecting in the same direction as well.

A reversed-phase high-performance liquid chromatographic method with gradient elution for the separation of the mediator substances histamine and the leukotrienes C4 (LTC4), D4 (LTD4), and E4 (LTE4) is described. The detection occurs fluorimetrically after automated precolumn derivatization with o-phthaldialdehyde. All components are chromatographically separable. Because of the different excitation and emission wavelengths, only the most important biological active mediators histamine and LTC4 are determinable in one parallel chromatographic run. The method is examined by linearity and precision tests and is applicable to biological sample matrices like cell supernatants of human basophils enriched by Percoll-density gradient centrifugation and stimulated for mediator release by anti-IgE. The established method is suitable to separate the mediators from other matrix components. The determination limit for histamine is 55.0 micrograms/L and that for LTC4 16.0 micrograms/L, referring to the reference solutions. Therefore, a fast, economical method for the common determination of the most important mediators histamine and LTC4 is established. This method is also suitable for high sample amounts in routine medical analysis.

Estrogens have a beneficial effect on atherosclerosis and osteoporosis after menopause, but their exact mechanism of action is still unknown. The aim of the present study was to investigate the effects of estradiol and its metabolites catechol estrogens on arachidonic acid metabolism in vitro. Estradiol had no effect on arachidonic acid metabolism up to 33 microM in A23187-stimulated human whole blood. All catechol estrogens (2-hydroxyestradiol, 2-hydroxyestrone, 4-hydroxyestradiol and 4-hydroxyestrone) had similar kinds of actions on arachidonic acid metabolism, being over ten times more potent inhibitors of leukotriene synthesis (IC50 values 0.044-0.16 microM) than thromboxane (IC50 values 0.99-2.1 microM) and prostaglandin E2 synthesis (IC50 values 0.84-5.5 microM). It is suggested that some of the protective actions of estrogens--e.g., on atherosclerosis and osteoporosis--may be related to the inhibition of leukotriene synthesis by catechol estrogens.

Decompression-induced venous bubble formation has been linked to increased neutrophil counts, endothelial cell injury, release of vasoactive eicosanoids, and increased vascular membrane permeability. These actions may account for inflammatory responses and edema formation. Increasing the intracellular cAMP has been shown to decrease eicosanoid production and edema formation in various models of lung injury. Reduction of decompression-induced inflammatory responses was evaluated in decompressed rats pretreated with saline (controls) or dibutyryl cAMP (DBcAMP, an analog of cAMP). After pretreatment, rats were exposed to either 616 kPa for 120 min or 683 kPa for 60 min. The observed increases in extravascular lung water ratios (pulmonary edema), bronchoalveolar lavage, and pleural protein in the saline control group (683 kPa) were not evident with DBcAMP treatment. DBcAMP pretreatment effects were also seen with the white blood cell counts and the percent of neutrophils in the bronchoalveolar lavage. Urinary levels of thromboxane B2, 11-dehydrothromboxane B2, and leukotriene E4 were significantly increased with the 683 kPa saline control decompression exposure. DBcAMP reduced the decompression-induced leukotriene E4 production in the urine. Plasma levels of thromboxane B2, 11-dehydrothromboxane B2, and leukotriene E4 were increased with the 683-kPa exposure groups. DBcAMP treatment did not affect these changes. The 11-dehydrothromboxane B2 and leukotriene E4 levels in the bronchoalveolar lavage were increased with the 683 kPa exposure and were reduced with the DBcAMP treatment. Our results indicate that DBcAMP has the capability to reduce eicosanoid production and limit membrane permeability and subsequent edema formation in rats experiencing decompression sickness.

Cysteinyl leukotrienes (C-LTs) are local inflammatory mediators involved in bronchial asthma. Seventeen asthmatic patients (FEV1 ranging from 41 to 99.8% of predicted values) and 11 healthy subjects were studied. The clinical severity of asthma was assessed by the Aas score. Plasma C-LTs were measured by enzyme immunoassay (EIA) after sample purification by solid-phase extraction (SPE), to investigate whether differences may exist between asthmatic and control subjects and whether leukotriene E4 (LTE4) levels were related to the severity of disease. LT measurements showed that 87.6 +/- 1.2% was recovered as LTE4 and 9.4 +/- 1.3% as LTC4. In asthmatic subjects, LTE4 plasma levels were found to be significantly higher than those in the control group (1.073 +/- 0.133 and 0.53 +/- 0.19 ng/ml of plasma, respectively; P < 0.002). Moreover, there was a significant correlation between LTE4 plasma levels and the Aas clinical score (P < 0.005). These data suggest that plasma LTE4 levels might be used to assess the severity of asthma.

We investigated the relationship between circulating leukotriene E4 (LTE4) and chronic obstructive pulmonary disease (COPD) by measuring plasma levels of leukotriene E4 in patients with COPD and 10 normal controls. We also investigated the relationship between LTE4 levels and FEV1 and PaO2. Leukotriene E4 was measured by high performance liquid chromatography (HPLC) and radioimmunoassay. The mean leukotriene E4 level in patients with COPD during remission, during acute exacerbation before and after prednisolone treatment were 16.8[4.02], 41.7[21.9], and 19.5[3.78] pg/ml (mean[SD]), respectively. In contrast, the mean leukotriene E4 level of 10 normal controls was 11.8[4.49] pg/ml. Thus, the mean LTE4 level during an acute exacerbation of COPD was significantly lower in patients after prednisolone treatment than in patients before prednisolone treatment. The mean LTE4 level in patients after prednisolone treatment did not significantly differ from that in patients during remission and in normal controls (Scheffe F-test, P < 0.05) (Fig. 1). Mean FEV1 (% predict) values were 51.4[9.02] (mean[SD]), 38.0[4.82], and 44.2[4.48] on the three occasions, respectively; corresponding mean PaO2 values (mmHg) were 84.0[5.01] (mean[SD]), 61.3[1.66], and 80.6[5.30], respectively. Leukotriene E4 levels were significantly correlated with PaO2 and relatively with FEV1 in the patients during acute exacerbation before prednisolone treatment. Thus, we suggest that leukotriene E4 levels in arterial blood reflect the severity of COPD lung and oral prednisolone reduces the plasma levels of leukotriene E4 in patients with COPD.

Leukotrienes may mediate bronchoconstriction in asthma. Cysteinyl leukotriene production rises in vivo after allergen challenge, but few reports describe leukotriene concentrations in clinical asthma or in children. Using high performance liquid chromatography/radioimmunoassay, plasma and urinary leukotrienes in asthmatic children (aged 5-10 years) were measured during an acute exacerbation (peak expiratory flow (PEF) < 65%, n = 10) and one month later (PEF 74-169%, n = 9), and in non-atopic normal children (aged 1.3-13.2 years). In the asthmatics, geometric mean (95% confidence interval) plasma leukotriene B4 (LTB4) was 746 pg/ml (398 to 1403) acutely and 1026 pg/ml (662 to 1593) in remission, compared with 369 pg/ml (167 to 728) in the normal children (n = 14). Plasma cysteinyl leukotrienes were low or undetectable, but urinary leukotriene E4 (LTE4) was higher in the asthmatics during an acute episode (210 pmol/mmol creatinine, 101 to 454) and at follow up (179 pmol/mmol, 110 to 293), compared with the normal children (98 pmol/mmol, 81 to 118, n = 41). This persistent increase in plasma LTB4 and urinary LTE4 concentrations one month after a severe asthmatic episode suggests leukotriene production is related to chronic inflammation rather than to acute bronchoconstriction.

N-Acetyl-leukotriene E4 has been identified as an endogenous, biologically less active cysteinyl leukotriene metabolite in rodents and humans. To evaluate the ratio of hepatobiliary to renal elimination of leukotrienes noninvasively by positron emission tomography (PET), we synthesized N-[11C]acetyl-leukotriene E4 by chemical N-acetylation of leukotriene E4. After the intravenous injection of N-[11C]acetyl-leukotriene E4 in normal rats and monkey, uptake by the liver and subsequent excretion into bile were largely responsible for its rapid elimination from blood. In the Cynomolgus monkey, renal excretion of the leukotriene into urine was of additional quantitative importance. Kinetic modeling indicated a mean transit time through the liver of 17 minutes and 34 minutes in rat and monkey, respectively; the corresponding hepatic excretion half-times amounted to 8.5 minutes and 16 minutes. In a mutant rat strain deficient in the hepatobiliary excretion of cysteinyl leukotrienes across the canalicular membrane, the apparent mean liver transit time was 54 minutes, and the hepatic excretion half-time was 29 minutes, indicating prolonged organ storage and metabolism. After transport from the liver back into the circulating blood of omega-oxidized and beta-oxidized metabolites of N-[11C]acetyl-leukotriene E4, renal excretion compensated for the impairment of hepatobiliary elimination in the transport mutant. Metabolite analyses in urine after intravenous injection of N-[3H]acetyl-leukotriene E4 indicated the extensive inactivation of N-acetyl-leukotriene E4 by beta-oxidation from the omega-end in the mutants. A similar shift from hepatobiliary to renal cysteinyl leukotriene elimination was monitored in rats with cholestasis due to bile duct obstruction.(ABSTRACT TRUNCATED AT 250 WORDS)

Sulfidopeptide leukotrienes E4 (LTE4) and B4 (LTB4) were simultaneously extracted from rabbit whole blood with acetonitrile. LTC4 and LTD4 were converted to LTE4 by gamma-glutamyl transpeptidase and leucine-amino peptidase before extraction. LTE4 was extracted from urine with C18 Sep-Pak cartridges. The compounds were resolved and quantitated by reversed-phase high-performance liquid chromatography (HPLC) with a diode-array detector; in selected cases the collected fractions were assayed for LTB4 and LTE4 by specific enzyme immunoassay (EIA). The correlation factor of the measured increase in LTE4 concentrations and addition of incremental amounts of LTC4 to blood was r = 0.998; slope of 1.05 +/- 0.01 (mean +/- S.D.). Concentrations of LTE4 measured by HPLC correlated with those obtained with EIA (r = 0.996; slope = 0.98 +/- 0.03 and r = 0.991; slope = 0.97 +/- 0.04 in blood and urine, respectively). For blood LTB4 the correlation of HPLC versus EIA was r = 0.990; slope = 1.12 +/- 0.04. The method described is accurate and reproducible, allowing measurement of both LTB4 and LTE4 in whole blood after a single extraction procedure. Simultaneous measurement of these metabolites after specific stimulation or in pathological conditions is recommended for in vivo investigations of LTs production.

Background: The cysteinyl leukotrienes may play a central part in the mechanisms of aspirin-sensitive asthma. Previous work has shown that individuals with aspirin-sensitive asthma have high basal urinary LTE4 levels which increase further upon aspirin ingestion, and that sulphidopeptide leukotriene receptor antagonists attenuate aspirin-induced airflow obstruction. If the cysteinyl leukotrienes cause aspirin-induced asthmatic reactions, inhibition of the 5-lipoxygenase pathway should prevent aspirin-induced bronchospasm. This hypothesis has been tested with ZD2138, a specific non-redox 5-lipoxygenase inhibitor., Methods: Seven subjects (four men) with aspirin-sensitive asthma with baseline FEV1 values > 67% were studied. ZD2138 (350 mg) or placebo was given on two separate occasions two weeks apart in a randomised double blind fashion. A single dose of aspirin was administered four hours after dosing and FEV1 was measured for six hours. Inhibition of the 5-lipoxygenase pathway by ZD2138 was assessed by measurements of urinary LTE4 levels and ex vivo calcium ionophore stimulated LTB4 generation in whole blood, before administration of drug or placebo and at regular time intervals after dosing and aspirin administration., Results: ZD2138 protected against the aspirin-induced reduction in FEV1 with a 20.3 (4.9)% fall in FEV1 following placebo compared with 4.9 (2.9)% following ZD2138. This was associated with 72% inhibition of ex vivo LTB4 generation in whole blood at 12 hours and a 74% inhibition of the rise in urinary LTE4 excretion at six hours after aspirin ingestion., Conclusions: In aspirin-sensitive asthma the 5-lipoxygenase inhibitor ZD2138 inhibits the fall in FEV1 induced by aspirin and this is associated with substantial inhibition of 5-lipoxygenase.

To investigate the relationship between circulating leukotriene E4 and bronchial asthma, we tried to measure the concentration of leukotriene E4 during the clinical course of bronchial asthma with or without oral prednisolone treatment. Additionally, we investigated the relationship between the LTE4 levels and FEV1 (percent predicted) and PaCO2 (mm Hg) concomitantly. Two milliliters of blood were drawn from the femoral artery of eight patients on three occasions: (1) during remission; (2) during an attack treated without prednisolone; and (3) during an attack treated with prednisolone. Leukotriene E4 was detected by high-pressure liquid chromatography and radioimmunoassay. In eight asthmatic patients, mean (SD) leukotriene E4 levels on the three occasions were 11.8 (2.61), 48.4 (18.2), and 32.6 (8.28) pg/ml, respectively. In contrast, the mean leukotriene E4 level of ten normal control subjects was 11.8 (4.49) pg/ml. Leukotriene E4 levels differed significantly between remission and attack treated without prednisolone, and between attacks treated with and without prednisolone. Mean FEV1 values were 85.5 (3.07), 50.5 (9.58), and 65.9 (7.44) on the three occasions, respectively; corresponding mean PaCO2 values were 31.7 (2.74), 55.5 (5.81), 48.9 (2.56), respectively. Leukotriene E4 was significantly correlated with FEV1 and relatively with PaCO2 during an attack without prednisolone. We suggest that leukotriene E4 levels in arterial blood reflect the severity of asthmatic attacks and orally administered prednisolone may affect the leukotriene E4 levels.

To assess the contribution of the leukotrienes, LTC4, D4, E4 and B4 during bronchial asthma attacks, simultaneous determination was made of their levels in venous blood. 25 patients with bronchial asthma (15 atopic types, 10 non-atopic types) participated in this study and 4 normal controls were used. Samples were obtained using heparinized syringe from the patients before treatment. A radioimmunoassay was conducted to measure LTs after purification with a Sep-pak column and separation by HPLC. In normal subjects, the levels were less than the minimal detectable amounts. LTC4, D4, E4 and B4 during asthmatic attacks were 100 +/- 179, 88 +/- 116, 479 +/- 291, and 55 +/- 73 (Mean +/- SD) pg/ml respectively (n = 27). Peptide LTs in remission were below minimal detectable levels. LTD4 in patients with moderate attacks was significantly (p < 0.05) higher than in those with mild attacks. Peptide LTs in moderate attack exceeded those in mild attacks, although not to a statistically significant degree. No significant differences in LT during attacks could be detected in atopic or non-atopic type patients. LTs would thus appear importantly involved in asthmatic attacks in atopic and non-atopic type patients, although other chemical mediators may give rise to airway inflammation.

Sickle cell (HbSS) disease is associated with rheological and inflammatory stresses within the microcirculation. In order to determine the role of leukotrienes in the inflammatory processes in HbSS patients, we analysed plasma and urine levels of leukotrienes (LT); LTB4, LTC4, LTD4, and LTE4 as indicators of their in vivo metabolism. Plasma and urine level samples of 15 HbSS patients in steady-state and age-matched healthy, homozygous (HbAA) controls were extracted for leukotrienes and quantitated by HPLC. Control plasma level of leukotrienes (mean +/- SEM, ng ml-1) were: LTB4, 8.95 +/- 0.26; LTC4, 7.24 +/- 0.21; LTD4, 11.42 +/- 0.40; and LTE4, 14.51 +/- 0.50. Corresponding values for HbSS patients were: LTB4, 6.15 +/- 0.42; LTC4, 13.61 +/- 1.45; LTD4, 6.44 +/- 0.51 and LTE4, 4.97 +/- 0.37. The differences were significant at P < 0.05. Urine levels (mean +/- SEM, ng mmol-1 creatinine), for controls were: LTB4, 10.60 +/- 0.35; LTC4, 360.0 +/- 9.82. Values for HbSS urine were: LTB4, 27.50 +/- 3.33; LTC4, 356.0 +/- 17.87; LTD4, 69.90 +/- 14.51. LTD4 was not detected in control urine. These results suggest that sickle cell patients may exhibit impaired ability to catabolize LTC4 in plasma during steady state conditions. This altered metabolism may contribute to the persistent stress of the microcirculation, and is probably related to the abnormal microvascular rheology of sickle blood cells.

We have recently demonstrated that contact activation of the intrinsic coagulation cascade in vitro is accompanied not only by thromboxane (TX) B2 generation but also by the formation of 5-lipoxygenase-derived cysteinyl-leukotrienes (LT). In our present study we have investigated the effects of the vascular wall on the eicosanoid formation by whole human blood. Incubation of whole human blood in clamped segments of autologous umbilical veins incubated in oxygenated Tyrode solution led to a time-dependent generation of cysteinyl-LT and TXB2 in the blood samples. A clear dissociation in the time-dependent production profiles was observed with cysteinyl-LT practically reaching a plateau phase at 60 min while TXB2 levels increased up to 90 min. In blood samples incubated in glass tubes for 60 min TXB2 production was about 13 times higher and cysteinyl-LT formation only about half as much as in the umbilical vein segments indicating a differential stimulation of both the cyclooxygenase and 5-lipoxygenase pathway of arachidonic acid metabolism in these experiments. By reverse phase HPLC the immunoreactive cysteinyl-LT were identified as a mixture of LTC4, LTD4 and LTE4. Since the data were suggestive of intravascular cysteinyl-LT formation in thrombotic vessels, thrombus specimens from patients with acute deep vein thrombosis of the lower limb were analysed for these compounds by combined reverse phase HPLC and specific radioimmunoassay.(ABSTRACT TRUNCATED AT 250 WORDS)

In man, the therapeutic effectiveness of specific inhibitors of leukotriene (LT) biosynthesis against allergen-induced bronchoconstriction appears to be related to the in vivo biochemical efficacy of these compounds, as measured by inhibition of whole blood LTB4 generation (upon A23187 stimulus) and, particularly, urinary LTE4 excretion. Accordingly, we have assessed the ability of two clinically documented LT biosynthesis inhibitors, zileuton and MK-886, and the structurally novel 5-lipoxygenase activating protein antagonist, MK-0591, to inhibit the production of these inflammatory arachidonic acid metabolites in laboratory dogs. Zileuton (2 mg/kg) was extremely bioavailable in dogs (> 10 microM plasma concentrations), and inhibited the A23187-induced ex vivo production of LTB4 by venous blood by > 90%, in concordance with its potency in canine blood in vitro (IC50 = 1.1 microM). Despite this degree of inhibition in whole blood, urinary LTE4 excretion was reduced by only 52%, a profile of activity similar to that seen in clinical studies. MK-886 was less well absorbed, with plasma concentrations of 3 microM being achieved only at 25 mg/kg. These levels resulted in < 45% inhibition of LTB4 production, but a significant (p < 0.05) 47% inhibition of urinary LTE4 excretion. MK-0591 was similarly bioavailable (compared with MK-886), but 10-fold more active in vivo as a 2 mg/kg dose resulted in 41-62% inhibition of urinary LTE4 excretion (p < 0.05 vs controls; n = 4, 28). Significant inhibition of ex vivo LTB4 synthesis was also observed at this dose (49%), in accord with peak plasma concentrations of 0.5 microM and an in vitro potency of 0.2-0.4 microM (IC50) in whole blood from these animals. At higher dose (10 mg/kg), MK-0591 inhibited LTE4 excretion by 69%, with 88% inhibition of the LT biosynthetic capacity of whole blood. These data demonstrate that the biochemical efficacy of structurally diverse leukotriene biosynthesis inhibitors can be assessed in vivo in normal laboratory dogs. Such measurements, combined with bioavailability data from other species, may be useful for predicting biochemical activity in man.