Cysteinyl leukotriene D4 (LTD4) promotes airway epithelial cell inflammation and remodelling

OBJECTIVE

Cysteinyl leukotrienes (CysLTs), a group of inflammatory lipid mediators, are found elevated in obese-asthmatic patients. Leukotriene D4 (LTD4), a representative CysLT, is implicated in promoting lung inflammation and remodelling in allergic asthma, but its role in non-allergic asthma, especially in obese-asthmatic patients, is not known. Here, using primary human small airway epithelial cells (SAECs) we have investigated the mechanism of LTD4-induced inflammation and remodelling and assessed high proneness of obese mice to develop asthma upon challenge with allergen ovalbumin (OVA).

METHODS

Primary human small airway epithelial cells (SAECs) were stimulated with different concentrations of LTD4 for different time intervals and various inflammatory markers were measured through cytokine array, membrane-based ELISA and Western blotting. An air-liquid interface (ALI) model of SAECs was used to study the effects of LTD4-induced remodelling in SAECs using Western blotting, H&E staining and PAS staining. Further, OVA-based murine model was used to examine the propensity of high-fat diet (HFD)-fed obese mice to develop asthma symptoms by studying the infiltration of inflammatory cells (assessed by bronchioalveolar lavage (BAL) cytology) and airway remodelling (assessed by histopathology) upon allergen exposure.

RESULTS

The human primary small airway epithelial cells (SAECs) treated with LTD4 showed significant alterations in the levels of inflammatory markers such as GM-CSF, TNF-α, IL-1β, EGF and eotaxin in dose- and time-dependent manner. Further, LTD4 enhanced the activation of inflammasomes as evidenced by increased levels of NALP3, cleaved caspase-1 and IL-1β. LTD4 also enhanced inflammation by increasing the expression of COX-2 in SAECs. The airway remodelling markers Vimentin and Muc5AC were found elevated in ALI culture of SAECs when stimulated with LTD4, as it also increased TGF-β levels and activation of Smad2/3 phosphorylation in SAECs. Last, sensitization and challenge of HFD-fed obese mice with OVA showed increased infiltration of inflammatory cells in BAL and enhanced levels of remodeling phenotypes like loss of cilia, mucus cell metaplasia and collagen deposition in mice lung tissues.

CONCLUSION

The results suggest that LTD4 could induce inflammatory response in human airway epithelial cell by activating NALP3 inflammasome. LTD4 could further promote airway epithelial cells' remodelling through TGF-β/smad2/3-mediated pathway. Our in vivo results suggested that obesity predisposed the OVA challenged mice to develop lung inflammation and remodelling akin to asthma-like phenotypes during obesity.

Expression of functional cysteinyl leukotriene receptors by human basophils

BACKGROUND

Synthesis of leukotriene (LT) C 4 by basophils and mast cells is an important component of IgE-mediated inflammation, resulting in increased levels of the cysteinyl leukotrienes (cysLTs) LTC 4 , LTD 4 , and LTE 4 . Receptors for cysLTs are expressed on a variety of peripheral blood leukocytes, but of interest, they are also expressed on cells that synthesize LTC 4 , such as eosinophils and mast cells.

OBJECTIVE

We examined human basophils for expression and function of cysLT receptor type 1 (cysLT1) and cysLT receptor type 2 (cysLT2).

METHODS

Basophils were purified from human blood and analyzed by means of RT-PCR, Western blotting, and flow cytometry for receptor expression. Basophils were also examined for functional responses to LTD 4 , including cytosolic calcium flux, histamine release, viability, and chemotaxis.

RESULTS

We found that basophils express mRNA for cysLT1 and cysLT2. CysLT1 and cysLT2 were also detectable by means of flow cytometry, but only cysLT2 was detectable by means of Western blotting with available antibodies. Increases in cytosolic calcium induced by LTD 4 -stimulated basophils were inhibited by the cysLT1 receptor antagonist zafirlukast, confirming the presence of functional cysLT1 receptors on basophils. There was no significant effect of LTD 4 on histamine release; however, LTD 4 decreased CD95 (Fas) expression on basophils in several-day cultures.

CONCLUSIONS

We have demonstrated that basophils express the cysLT receptors cysLT1 and cysLT2, and some functional responses to LTD 4 can be observed.

Cysteinyl leukotrienes are secretagogues in atrophic coeliac and in normal duodenal mucosa of children

OBJECTIVE

The pathophysiology of intestinal inflammation and diarrhoea is complex and involves the arachidonic acid cascade. Prostaglandins induce chloride secretion in healthy subjects and in patients with coeliac disease. Leukotrienes (LTs) are also known inflammatory mediators which have been shown to stimulate ion secretion in ileum and colon of rats and rabbits. The aim of this study was to determine the effects of leukotrienes C(4) (LTC(4)) and D(4) (LTD(4)) in normal and atrophic intestinal mucosa in children.

MATERIAL AND METHODS

Routine paediatric intestinal biopsies were obtained from 109 children. Sixty-seven control biopsies and 42 biopsies from children with different stages of coeliac disease were mounted in a modified Ussing chamber. Potential difference (Pd) was measured continuously and tissue resistance (R(t)) and the generated current (I(m)) were calculated.

RESULTS

In morphologically normal mucosa of duodenum, LTC(4) and LTD(4) increased Pd and I(m) in a dose-dependent manner. The increase was more pronounced in the distal than in the proximal part, similar to the response to prostaglandin E(2). The induced current was chloride-mediated, since replacement of Cl(-) with SO(4)(2-) in the bathing solution eliminated the response to the LTs. The LTC(4)-induced secretion was significantly decreased in atrophic mucosa, but the response was partially restored after preincubation with the cyclooxygenase inhibitor indomethacin.

CONCLUSIONS

The results showed that LTC(4) and LTD(4) are secretagogues in the duodenal mucosa from healthy children by inducing a net chloride secretion. Restoration of the response in coeliac disease by cyclooxygenase inhibition suggests interactions between the different pathways of the arachidonic cascade in the intestinal mucosa.

Antigen specific quantification of sulfidoleukotrienes in patients allergic to Betalactam antibiotics

BACKGROUND

After in vitro allergen-specific stimulation, basophils become activated and release sulfidoleukotrienes LTC4, LTD4 and LTE4. This can be detected by means of the CAST assay. We assessed the positivity criteria and the reliability of antigen-specific sulfidoleukotriene production (CAST) in the in vitro diagnosis of betalactam (BL) allergic patients.

MATERIAL AND METHODS

We studied a sample of 67 patients (age 48.94 +/- 15.76 years) who had presented with anaphylaxis or urticaria-angioedema within the first 60 minutes after administration of Amoxicillin (54/67), Penicillin G (7/67), Cefuroxime (5/67) or Cefazoline (1/67). All of them had a positive skin test to at least one of the antigenic determinants of Penicillin. As control group 30 adults with negative skin tests who tolerated BL were included. All of them underwent skin tests, oral provocation tests, specific IgE (CAP-FEIA, Pharmacia) and CAST.

RESULTS

Positivity criteria were established by means of ROC curves: a sLT release induced by Betalactams of at least 100 pg/ml and greater than or equal to 3 times the basal value. The overall sensitivity of CAST is 47.7% and specificity 83.3%. Sensitivity of specific IgE is 37.8% and specificity 83.3%.

CONCLUSIONS

We have established validated positivity criteria for the CAST technique in patients allergic to Betalactams. This technique is a useful in vitro diagnostic method in patients with IgE-mediated allergy to Betalactam antibiotics.

Leukotriene D4-induced adhesion of Caco-2 cells is mediated by prostaglandin E2 and upregulation of α2β1-integrin

Cell-cell and extracellular matrix adhesions play important roles in the progression of cancer. We investigated the involvement of the inflammatory mediator leukotriene D4 (LTD4) in the regulation of cell-matrix adhesion of colon cancer (Caco-2) cells. We observed that LTD4 acted via its CysLT1 receptor in these cells to induce increased adhesion to collagen I. LTD4 also enhanced the activation and expression of alpha2beta1-integrins on the cell surface, which we found to be responsible for mediating the increased adhesion to collagen I. LTD4 simultaneously augmented expression of the prostaglandin-generating enzyme cyclooxygenase-2 (COX-2) and increased prostaglandin E2 (PGE2) production in Caco-2 cells. The adhesive capacity of the Caco-2 cells was reduced by specific inhibition of COX-2 and was subsequently restored by PGE2, but not by LTD4. A selective PGE2 receptor antagonist abolished the increased adhesion and the augmented alpha2beta1-integrin expression induced by both PGE2 and LTD4. Summarizing, the inflammatory mediator LTD4 regulates the adhesive properties and migration of the Caco-2 cell line by upregulating COX-2 and stimulating PGE2-induced expression of alpha2beta1-integrins. This suggests that inflammatory mediators such as LTD4 can be involved in the dissemination and survival of colon cancer cells.

Kinins are involved in the development of allergic nasal hyperresponsiveness in guinea pigs

We evaluated roles of kinins in allergen-induced nasal blockage and sneezing, and development of nasal hyperresponsiveness to leukotriene D4 in a Japanese cedar pollen-induced allergic rhinitis model of guinea pigs. Sensitised guinea pigs were repeatedly challenged by pollen inhalation once every week. Neither a bradykinin B1 receptor antagonist, des-Arg9-[Leu8]bradykinin nor a bradykinin B2 receptor antagonist, icatibant suppressed allergen-induced sneezing and nasal blockage. However, development of nasal hyperresponsiveness to leukotriene D4 was significantly suppressed by them. The amount of bradykinin in nasal cavity lavage fluid was immediately increased after the challenge. In non-sensitised animals, hyperresponsiveness to leukotriene D4 was developed by a bradykinin B2 receptor agonist, bradykinin, but not by a bradykinin B1 receptor agonist, des-Arg10-kallidin, while in the sensitised-challenged animal, both agonists developed hyperresponsiveness. In conclusion, the nasal hyperresponsiveness appeared to be induced by kinins produced in response to the antigen challenge through activation of not only bradykinin B2 but also B1 receptors.

[Leukotrienes as inflammation mediators]

Leukotrienes are biologically active metabolites derived from arachidonic acid playing an important role in inflammatory responses. There are two main groups of leukotrienes: dihydroxyleukotrienes (LTB4) and cysteinyl-leukotrienes (LTC4, LTD4, LTE4). By activating specific G-protein coupled receptors, leukotrienes take part in immune responses, like activation and chemotaxis of leukocytes. Several studies have shown that leukotrienes may play a significant role in pathomechanisms of inflammatory diseases of human airways, skin, digestive tract and heart.

Disruption of gamma-glutamyl leukotrienase results in disruption of leukotriene D(4) synthesis in vivo and attenuation of the acute inflammatory response

To study the function of gamma-glutamyl leukotrienase (GGL), a newly identified member of the gamma-glutamyl transpeptidase (GGT) family, we generated null mutations in GGL (GGL(tm1)) and in both GGL and GGT (GGL(tm1)-GGT(tm1)) by a serial targeting strategy using embryonic stem cells. Mice homozygous for GGL(tm1) show no obvious phenotypic changes. Mice deficient in both GGT and GGL have a phenotype similar to the GGT-deficient mice, but approximately 70% of these mice die before 4 weeks of age, at least 2 months earlier than mice deficient only in GGT. These double-mutant mice are unable to cleave leukotriene C(4) (LTC(4)) to LTD(4), indicating that this conversion is completely dependent on the two enzymes, and in some organs (spleen and uterus) deletion of GGL alone abolished more than 90% of this activity. In an experimental model of peritonitis, GGL alone is responsible for the generation of peritoneal LTD(4). Further, during the development of peritonitis, GGL-deficient mice show an attenuation in neutrophil recruitment but not of plasma protein influx. These findings demonstrate an important role for GGL in the inflammatory response and suggest that LTC(4) and LTD(4) have distinctly different functions in the inflammatory process.

Antigen-induced airway inflammation and hyper-responsiveness does not enhance airway responses to a subsequent antigen challenge in rats

Brown-Norway (BN) rats develop airway hyper-responsiveness and lung eosinophilia 18-24 h after ovalbumin (OA) challenge. We hypothesized therefore that allergen-induced airway inflammation would further enhance airway responses to a subsequent antigen challenge. Animals were sensitized to both OA and bovine serum albumin (BSA) and, 14 days later, challenged by aerosols with both antigens 24 h apart. Measurements of pulmonary resistance (RL) were made for 8 h after the second antigen challenge and bronchoalveolar lavage (BAL) was performed. Animals were divided into three groups and received two challenges as follows: saline-BSA (n=9), OA-saline (n=8) and OA-BSA (n=10). Sensitization was confirmed by measurements of specific OA-IgE and BSA-IgE. Early responses [determined as the highest value of RL within the first 30 min after the challenge] were absent in all study groups. The late responses [determined from the area under the RL versus time curve from 120 to 480 min after the challenge] were significantly greater in animals challenged with BSA (15.16+/-3.86) compared to saline (3.76+/-4.09; P<0.05). However previous exposure to OA did not further increase the late response in animals subsequently challenged with BSA (20.11+/-3.67) despite enhanced airway responsiveness to LTD4 at this time point. BAL eosinophils and lymphocytes were significantly increased following BSA challenge in previously OA-challenged animals, compared to numbers retrieved from animals previously exposed to saline (P<0.05). These data indicate that previous exposure to OA did not further increase the LR to a second antigen challenge despite substantial increases in airway inflammatory cells and airway hyper-responsiveness to LTD4.

Persistent airway eosinophilia after leukotriene (LT) D4 administration in the guinea pig: modulation by the LTD4 receptor antagonist, pranlukast, or an interleukin-5 monoclonal antibody

Aerosolized cysteinyl leukotrienes (CysLTs) elicit migration of eosinophils into guinea pig lungs and the airways of patients with asthma. The present studies were designed to analyze the concentration-response relationship, time course, and pharmacologic and histologic characteristics of leukotriene D4 (LTD4)-induced eosinophil influx into the airways of conscious guinea pigs. Animals were exposed to aerosols of 0.3 to 30 microg/ml LTD4 for 1 min, during which specific airway conductance (sGaw) was monitored. Bronchoalveolar lavages (BALs) of guinea pig airways were conducted at selected times from 4 h to 4 wk after LTD4 challenge. LTD4 produced maximal decreases in sGaw (70 to 90% reduction) at all concentrations tested and concentration-related increases in eosinophil levels in BALs, assessed 24 h after challenge. Increased numbers of eosinophils in the bronchial epithelium and subepithelium were confirmed histologically. Significant eosinophilia was maintained for up to 4 wk postchallenge. Pretreatment with the LTD4 receptor antagonist, pranlukast (ONO-1078, SB 205312) (20 mg/kg, intragastrically), significantly inhibited both the bronchoconstriction and the eosinophilia at 24 h, whereas the cyclooxygenase inhibitor, meclofenamic acid (5 mg/kg, intragastrically), had no effect on either parameter. Histologic observations were consistent with BAL results. Pretreatment with the rat anti-mouse antibody to interleukin-5 (IL-5), TRFK-5 (10-300 microg, intraperitoneally), produced dose-related inhibition of LTD4-induced eosinophilia, measured in 24 h or 3 wk BAL, but did not affect the acute bronchoconstriction. These results indicate that LTD4 elicits airway eosinophil influx in guinea pigs which persists as long as 4 wk after a single exposure, and provide the first evidence that IL-5 may have a role in LTD4-induced airways inflammation. This and other previously reported proinflammatory effects of LTD4 may contribute significantly to its overall influential role in the pathophysiology of asthma, and may underlie the therapeutic benefit of CysLT receptor antagonists, such as pranlukast, in this disorder.

Antagonism of leukotriene responses in human airways by BAY x7195

Contractions induced by leukotriene and anti-IgE (sheep antiserum to human IgE) were antagonized by pretreatment of human airways with the cysteinyl leukotriene receptor antagonist BAY x7195 ((4S)-[4-carboxyphenylthio]-7-[4-(4-phenoxybutoxy)-phenyl]-h ept-5-(z)- enoic acid). However, this receptor antagonist did not inhibit either leukotriene D4- or leukotriene C4-induced contractions in human pulmonary veins. The pA2 value for BAY x7195 in human airways against leukotriene D4 was 7.83 +/- 0.16 with a slope of 1.07 +/- 0.15 (means +/- S.E.M; n = 11). The IC50 value for BAY x7195 in human airways contracted with anti-IgE was 0.31 +/- 0.08 microM (n = 11). These results were comparable to those obtained with ICI 204,219 (4-(5-cyclopentyl-oxycarbonylamino-1-methylindol-3-ylmeth yl)-3-methoxy-N-otolyl - sulfonylbenzamide). These data demonstrate that BAY x7195 is a potent selective leukotriene receptor antagonist which may block allergic reactions in the lung.

Inhibition by a novel peptide leukotriene receptor antagonist ONO-1078 of airway wall thickening and airway hyperresponsiveness to histamine induced by leukotriene C4 or leukotriene D4 in guinea-pigs

We studied the effect of intravenous administration of leukotriene (LT) C4 or LTD4 on airway responsiveness to histamine and airway wall thickening in guinea-pigs. Guinea-pigs were killed and the lungs were fixed in formalin. Slides from paraffin-embedded section of the lungs were stained and the airways that were cut in transverse section were measured by tracing enlarged images using a digitizer. Moreover, airway resistance (Raw) was determined by a pulmonary mechanics analyser and we calculated two indices, an index of airway wall thickening and the one of airway hyperresponsiveness to histamine, from changes of baseline-Raw and peak-Raw following intravenous administration of histamine before and after the intravenous administration of LTC4 or LTD4. The infusion of LTC4 or LTD4 induced an increase of the relative thickness of the airway wall in peripheral bronchi demonstrable by the histological examination. In analysis of airway function, intravenous administration of LTC4 or LTD4 induced airway hyperresponsiveness to histamine with airway wall thickening. The LTC4 and LTD4 receptor antagonist ONO-1078 inhibited these effects of LTC4 and LTD4, suggesting LTC4 and LTD4 may induce airway wall thickening and airway hyperresponsiveness through LTC4 and LTD4 receptors in the airways.

In vitro allergic bronchoconstriction in the brown Norway rat

The ovalbumin (OA)-sensitized Brown Norway rat (BN) demonstrates early-response (ER) and late-response (LR) allergic bronchoconstriction. To determine whether these responses could be replicated in vitro, we studied lung explants from 8-wk-old male BN rats (wt: 239 +/- 28 g), of which 19 were sensitized to OA (test) and 16 served as controls. Two weeks after sensitization, the animals' lungs were removed, filled with a 1% (wt/vol) agarose-containing solution at 37 degrees C, and cooled to 4 degrees C. Transverse slices (0.5 to 1.0 mm thick) were cut and cultured overnight. Airways were visualized with an inverted microscope and baseline images were obtained with a video camera. To study the ER, 40 airways from 15 test rats and 29 airways from 10 control rats were challenged with 2 micrograms OA and imaged each minute for 10 min. To study the LR, 40 airways from 12 test rats and 44 airways from 12 control rats were challenged with 2 micrograms OA and imaged each hour for 8 h. The maximal response (MR) for each airway was defined as the percent of airway closure. The ER and LR were both defined as an MR > or = mean + 2 SD of the controls. An ER occurred in 38 of 40 test and 2 of 29 control airways (mean MR: 42 +/- 24% versus 4 +/- 3%, p < 0.001), and was completely blocked by methysergide pretreatment in 13 airways.(ABSTRACT TRUNCATED AT 250 WORDS)

Simplified sulfidoleukotriene ELISA using LTD4-conjugated phosphatase for the study of allergen-induced leukotriene generation by isolated mononuclear cells and diluted whole blood

By using leukotriene D4 (LTD4)-labeled alkaline phosphatase (LTD4-AP) and a mouse monoclonal anti-sulfidoleukotriene (sLT) antibody (1A-LDR1), we developed a solid-phase competition ELISA for sLTs. The detection limit of this assay was 6.3 +/- 1.2 pg sLT/100 microliters (mean +/- SEM; n = 10). Intraassay variations at 15, 50 and 150 pg sLT/well (9.8, 13.5 and 12.3%, respectively), the corresponding interassay variations (32.1, 11.9 and 18.8%, respectively) and the good correlation with a commercial radioimmunoassay (r = 0.97; n = 43) confirmed the validity of this ELISA. Furthermore, the assay had a low background and gave a 70-90% recovery of LTD4 added to medium containing up to 10% serum. In contrast to another sLT ELISA using the same antibody but based on competition with solid-phase LTE4-BSA, our assay is about 7-fold more sensitive. It also requires about 40 times less leukotriene for conjugate production than the previous method for the same number of determinations. The assay allows measurement of sLTs generated by small numbers of basophils present in isolated mononuclear cells or diluted whole blood in response to allergen, and allows simple and rapid determination of basophil reactivity to suspected allergens.