Effect of TGF-ß1 on eosinophils to induce cysteinyl leukotriene E4 production in aspirin-exacerbated respiratory disease.

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-ß1) in association with cysteinyl leukotriene E4 (LTE4) production, leading to eosinophil degranulation. To evaluate levels of serum TGF-ß1, 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-ß1 and urinary LTE4. The function of TGF-ß1 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-ß1 were significantly higher in AERD patients than in ATA patients or HCs (P = .001; respectively). Moreover, levels of serum TGF-ß1 and urinary LTE4 had a positive correlation (r = 0.273, P = .037). In the presence of TGF-ß1, 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-ß1, significantly induced eosinophilia with increased LTE4 production in the lung tissues were noted. These findings suggest that higher levels of TGF-ß1 in AERD patients may contribute to LTE4 production via enhancing LTC4S expression which induces eosinophil degranulation, accelerating airway inflammation.

Urinary leukotriene and Bcl I polymorphism of glucocorticoid receptor gene in preschoolers with recurrent wheezing and high risk of asthma.

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.

Identification of GPR99 protein as a potential third cysteinyl leukotriene receptor with a preference for leukotriene E4 ligand.

The cysteinyl leukotrienes (cys-LTs), leukotriene C4 (LTC4), a conjugation product of glutathione and eicosatetraenoic acid, and its metabolites, LTD4 and LTE4, are lipid mediators of smooth muscle constriction and inflammation in asthma. LTD4 is the most potent ligand for the type 1 cys-LT receptor (CysLT1R), and LTC4 and LTD4 have similar lesser potency for CysLT2R, whereas LTE4 has little potency for either receptor. Cysltr1/Cysltr2(-/-) mice, lacking the two defined receptors, exhibited a comparable dose-dependent vascular leak to intradermal injection of LTC4 or LTD4 and an augmented response to LTE4 as compared with WT mice. As LTE4 retains a cysteine residue and might provide recognition via a dicarboxylic acid structure, we screened cDNAs within the P2Y nucleotide receptor family containing CysLTRs and dicarboxylic acid receptors with trans-activator reporter gene assays. GPR99, previously described as an oxoglutarate receptor (Oxgr1), showed both a functional and a binding response to LTE4 in these transfectants. We generated Gpr99(-/-) and Gpr99/Cysltr1/Cysltr2(-/-) mice for comparison with WT and Cysltr1/Cysltr2(-/-) mice. Strikingly, GPR99 deficiency in the Cysltr1/Cysltr2(-/-) mice virtually eliminated the vascular leak in response to the cys-LT ligands, indicating GPR99 as a potential CysLT3R active in the Cysltr1/Cysltr2(-/-) mice. Importantly, the Gpr99(-/-) mice showed a dose-dependent loss of LTE4-mediated vascular permeability, but not to LTC4 or LTD4, revealing a preference of GPR99 for LTE4 even when CysLT1R is present. As LTE4 is the predominant cys-LT species in inflamed tissues, GPR99 may provide a new therapeutic target.