u-75302 and Pulmonary-Eosinophilia

Basic and clinical studies suggest that hypothalamic-pituitary-adrenal (HPA) axis is the neuroendocrine-immune pathway that functionally regulates the chronic inflammatory disease including asthma. Our previous studies showed corresponding changes of cytokines and leukotriene B4 (LTB4) between brain and lung tissues in antigen-challenged asthmatic rats. Here, we investigated how the increased LTB4 level in brain interacts with HPA axis in regulating antigen-induced asthmatic response in sensitized rats.. Ovalbumin-sensitized rats were challenged by inhalation of antigen. Rats received vehicle, LTB4 or U75302 (a selective LTB4 BLT1 receptor inhibitor) was given via intracerebroventricular injection (i.c.v) 30 min before challenge. Lung resistance (RL) and dynamic lung compliance (Cdyn) were measured before and after antigen challenge. Inflammatory response in lung tissue was assessed 24 h after challenge. Expression of CRH mRNA and protein in hypothalamus were evaluated by RT-PCR and Western Blot, and plasma levels of adrenocorticotropic hormone (ACTH) and corticosterone (CORT) were measured using the ELISA kits.. Antigen challenge decreased pulmonary function and induced airway inflammation, evoked HPA axis response in sensitized rats. Administration of LTB4 via i.c.v markedly attenuated airway contraction and inflammation. Meanwhile, LTB4 via i.c.v markedly increased CORT and ACTH level in plasma before antigen challenge, and followed by further increases in CORT and ACTH levels in plasma after antigen challenge in sensitized rats. Expression of CRH mRNA and protein in hypothalamus were also significantly increased by LTB4 via i.c.v in sensitized rats after antigen challenge. These effect were completely blocked by pre-treatment with BLT1 receptor antagonist U75302 (10 ng), but not by BLT2 antagonist LY255283.. LTB4 administered via i.c.v down-regulates the airway contraction response and inflammation through activation of the HPA axis via its BLT1 receptor. This study expands our concept of the regulatory role of intracranial inflammatory mediators in inflammatory diseases including asthma. The favourable effects of LTB4 on the HPA axis may help to explain the phenomenon of self-relief after an asthmatic attack.

Topics: Adrenocorticotropic Hormone; Airway Resistance; Animals; Asthma; Blotting, Western; Corticotropin-Releasing Hormone; Disease Models, Animal; Enzyme-Linked Immunosorbent Assay; Fatty Alcohols; Female; Glycols; Hypothalamo-Hypophyseal System; Hypothalamus; Inflammation Mediators; Injections, Intraventricular; Leukotriene B4; Lung; Lung Compliance; Male; Ovalbumin; Pituitary-Adrenal System; Pulmonary Eosinophilia; Rats; Rats, Sprague-Dawley; Receptors, Leukotriene B4; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger

The effects of representatives of three classes of compounds were investigated on antigen-induced bronchopulmonary eosinophilia in sensitized Brown-Norway rats. Rats were sensitized by 3 weekly inhalation provocations with aerosols of ovalbumin. Twenty-four hours after a fourth weekly antigen provocation, cell populations were enumerated following bronchoalveolar lavage (BAL) in animals treated with test compounds or the appropriate vehicle. A marked eosinophil-rich influx of inflammatory cells into the bronchial lumen followed the antigen provocation in sensitized animals. Dose-related inhibitions of antigen-induced lung eosinophilia were demonstrated with: 1) glucocorticoids, given po (methylprednisolone acetate, U-8210) or by inhalation (methylprednisolone suleptanate, U-67590A); 2)the non-glucocorticoid 21-amino steroid, U-75412E, and 3) the leukotriene B4 antagonist, U-75302. The steroids methylprednisolone and U-75412E were tested for glucocorticoid activity using phorbol ester-differentiated U937 (human macrophage) cells. Methylprednisolone but not U-75412E produced a dose-dependent inhibition of lipopolysaccharide-stimulated thromboxane synthesis by the U937 cells. Leukotriene B4 antagonists and the novel 21-aminosteroid, U-75412E, which lacks glucorticoid activity, provide leads for the development of compounds which inhibit the chronic airway inflammation associated with asthma in man.

Topics: Administration, Oral; Animals; Bronchoalveolar Lavage Fluid; Fatty Alcohols; Glucocorticoids; Glycols; Leukotriene B4; Male; Methylprednisolone; Pulmonary Eosinophilia; Rats; Steroids

The selective leukotriene B4 (LTB4) antagonist, U-75302, 6-(6-(3-hydroxy-1E,5Z-undecadien-1-yl)-2-pyridinyl)-1,5-hexa nediol) was examined for its ability to inhibit the "late-phase" bronchopulmonary eosinophilia that occurs 6 to 24 h after inhalation of specific antigen in sensitized guinea pigs. Groups of 6 male guinea pigs, sensitized with ovalbumin, were pretreated with U-75302, 1.0, 10.0, or 30.0 mg/kg, or vehicle 1 h before and 7 h after antigen inhalation. Twenty-four hours after antigen provocation, the lungs were lavaged for the enumeration of inflammatory cell populations. Doses of U-75302 (1.0, 10.0 and 30.0 mg/kg) administered orally produced 12.2%, (p greater than 0.05), 43.2% (p less than 0.05), and 61.1% (p less than 0.05) inhibition, respectively, of the antigen-induced influx of eosinophils into the bronchial lumen. Neutrophil populations were not significantly affected by treatment with U-75302. In a separate study, we compared the histopathological changes that occurred following antigen challenge in U-75302-treated or vehicle-treated guinea pigs. Vehicle-treated, sensitized animals exhibited marked changes in the airway at 8 min, 6 h, and 24 h after antigen challenge. U-75302 treatment produced a significant reduction in eosinophil adherence to peribronchial/peribronchiolar capillaries followed by a dramatic and specific reduction of peribronchial eosinophil infiltration (81% reduction at 6 h and 79% reduction at 24 h). Neutrophil migration appeared unaffected. These data implicate LTB4 as a mediator of antigen-induced bronchopulmonary eosinophilia in the guinea pig.

Topics: Animals; Antigens; Bronchoalveolar Lavage Fluid; Eosinophils; Fatty Alcohols; Glycols; Guinea Pigs; Immunization; Leukocytes; Leukotriene B4; Lung; Male; Neutrophils; Ovalbumin; Pulmonary Eosinophilia