Effect of the cysteinyl-leukotrienes on the production of eosinophils in culture of bone marrow: direct actions, mediation of the actions of the indometacina and the aspirin, and regulation of the reply to the PGE2.
Cysteinyl-Leukotrienes (CysLT) are important mediators of asthma, which induce bronchoconstriction, mucus secretion and a variety of regulatory effects on the infiltrating leukocyte populations, especially eosinophils. Increased CysLT production resulting from the shunting of arachidonic acid towards the 5-lipoxygenase (5-LO) pathway in the absence of active cyclooxygenase (COX) is a one mechanism proposed to explain the fisiopatology of Aspirin-sensitive, or aspirin-induced, asthma (AIA). Because the COX inhibitors, aspirin and indomethacin, increase Interleucin-5-dependent eosinophilopoiesis in murine bone-marrow culture, we evaluated the participation of CysLT in the mechanism of action of both agents in this model. Liquid bone-marrow cultures were established from BALB/c, C57BL/6 and CysLT1R deficient mice (in both the BALB/c and C57BL/6 genetic background) in the presence of interleucin-5, for 7 days. CysLTs (LTC4, LTD4 and LTE4) increased eosinophil production (maximum effect at 10-7-10-8M). Their effects were comparable, in number as well as morphology of the eosinophils, to those of aspirin (10-8M) and indomethacin (10-7M). The 5-lipoxygenase activating protein (FLAP) inhibitor, MK-886, blocked the effects of both aspirin and indomethacin, but not those of the CysLT. On the other hand, the competitive antagonists of the CysLT receptor type 1 (CysLT1R), MK-571 and Montelukast, blocked the effects of LTD4, indomethacin and aspirin. All three agents were capable of protecting developing eosinophils from the apoptosis-inducing actions of prostaglandin E2 (PGE2). Bone-marrow from CysLT1R deficient mice did not respond to LTD4, indomethacin or aspirin. The ability of COX inhibitors to protect developing eosinophils from the effects of a preformed COX derivative (PGE2) further indicates that these drugs act by promoting CysLT production rather than preventing synthesis of PGE2. Furthermore, this cytoprotective effect is abolished if bone-marrow is incubated with COX inhibitors in association with FLAP or CysLT1R inhibitors, or with LTD4 in association with CysLT1R inhibitors. Taken together, these findings suggest that, in the presence of COX inhibitors, CysLT are formed which promote eosinophilopoiesis by acting on high affinity CysLT1R. CysLT equally mediate the cytoprotective effects of COX inhibitors. The mechanism of action of COX inhibitors on murine eosinophilopoiesis is, therefore, similar in its essential features to the shunting mechanism, one of mechanisms involved with fisiopatology of AIA.
Advisor:Pedro Paulo Xavier Elsas; Maria Ignez Capella Gaspar Elsas
School:Faculdades Oswaldo Cruz
Source Type:Master's Thesis
Date of Publication:05/31/2007