Cysteinyl leukotriene receptor-1 antagonists as modulators of innate immune cell function.

Cysteinyl leukotrienes (cysLTs) are produced predominantly by cells of the innate immune system, especially basophils, eosinophils, mast cells, and monocytes/macrophages. Notwithstanding potent bronchoconstrictor activity, cysLTs are also proinflammatory consequent to their autocrine and paracrine interactions with G-protein-coupled receptors expressed not only on the aforementioned cell types, but also on Th2 lymphocytes, as well as structural cells, and to a lesser extent neutrophils and CD8(+) cells. Recognition of the involvement of cysLTs in the immunopathogenesis of various types of acute and chronic inflammatory disorders, especially bronchial asthma, prompted the development of selective cysLT receptor-1 (cysLTR1) antagonists, specifically montelukast, pranlukast, and zafirlukast. More recently these agents have also been reported to possess secondary anti-inflammatory activities, distinct from cysLTR1 antagonism, which appear to be particularly effective in targeting neutrophils and monocytes/macrophages. Underlying mechanisms include interference with cyclic nucleotide phosphodiesterases, 5'-lipoxygenase, and the proinflammatory transcription factor, nuclear factor kappa B. These and other secondary anti-inflammatory mechanisms of the commonly used cysLTR1 antagonists are the major focus of the current review, which also includes a comparison of the anti-inflammatory effects of montelukast, pranlukast, and zafirlukast on human neutrophils in vitro, as well as an overview of both the current clinical applications of these agents and potential future applications based on preclinical and early clinical studies.

Interactive inhibitory effects of formoterol and montelukast on activated human neutrophils.

The research question addressed in the current study was: do formoterol (1 and 10 nM) and montelukast (2 µM) possess interactive inhibitory effects on activated human neutrophils, particularly in relation to alterations in cyclic AMP and cytosolic Ca²(+) fluxes? Isolated human blood neutrophils were activated with the chemoattractant N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP) (1 µM) in combination with cytochalasin B (CB; 3 µM). Fura-2-acetoxymethyl ester-based spectrofluorimetry, lucigenin-enhanced chemiluminescence, colorimetric and flow cytometric procedures were used to measure cytosolic Ca²(+) fluxes, production of superoxide, elastase release and beta-2 integrin (CR3) expression, respectively, while cyclic AMP and leukotriene (LT)B4 were assayed using competitive binding ELISA procedures. Activation of the cells with fMLP/CB resulted in abrupt and sustained increases in cytosolic Ca²(+), as well as release of elastase and production of superoxide and LTB4, and expression of CR3, all of which were attenuated by formoterol and montelukast individually, and especially by the combination of these agents. These anti-inflammatory effects of each agent, as well as the combination, were associated with significant increases in cyclic AMP. The findings of the current study may explain the efficacy of montelukast and formoterol when used in combination with inhaled corticosteroids in the treatment of severe asthma, possibly by controlling neutrophil-driven inflammation of the airways.

Leukotrienes C4 and D4 sensitize human neutrophils for hyperreactivity to chemoattractants.

OBJECTIVE AND DESIGN: To investigate the sensitizing effects of the cysteinyl leukotrienes (CysLTs) C(4) and D(4) on the proinflammatory responses of chemoattractant-activated human neutrophils in vitro. MATERIALS: Neutrophils were isolated from venous blood taken from healthy, adult, human volunteers. TREATMENT: Cells were exposed to LTC(4) and LTD(4) (50-300 nM) prior to activation with 1 microM of N-formyl-L-methionyl- L-leucyl-L-phenylalanine (fMLF). METHODS: A fura-2/AM-based spectrofluorimetric procedure, lucigenin-enhanced chemiluminescence (LECL), a colourimetric method and an ELISA procedure, were used to measure Ca(2+) mobilization, superoxide production, elastase and MMP-8 release respectively following activation of LTC(4)/ D(4)-primed neutrophils with fMLF. Superoxide generation was also measured in the presence and absence of the CysLT receptor 1 antagonist, montelukast (100 nM). RESULTS: Exposure of neutrophils to either LTC(4) or LTD(4) alone had modest effects on Ca(2+) mobilization, while superoxide generation and elastase release were unaffected. However, relative to the responses of neutrophils activated with fMLF in the absence of the CysLTs, pre-treatment of the cells with either LTC(4)or LTD(4) resulted in significant, augmentation of fMLF-activated elastase and MMP-8 release and superoxide generation, which was attenuated by montelukast. CONCLUSION: These previously undocumented sensitizing interactions of LTs C(4) and D(4) with neutrophils may contribute to the activation of these cells in acute and chronic inflammation of both atopic and non-atopic aetiology, while identifying a role for montelukast in regulating neutrophil reactivity.