Montelukast inhibition of resting and GM-CSF-stimulated eosinophil adhesion to VCAM-1 under flow conditions appears independent of cysLT(1)R antagonism

Montelukast (MLK) is a cysteinyl leukotriene receptor-1 (cysLT(1)R) antagonist with inhibitory effects on eosinophils, key proinflammatory cells in asthma. We assessed the effect of MLK on resting and GM-CSF-stimulated eosinophil adhesion to recombinant human (rh) VCAM-1 at different flow rates using our novel microflow system. At 1 or 2 dyn cm(-2), shear-stress unstimulated eosinophils tethered immediately to rhV-CAM-1, "rolled" along part of the channel until they tethered, or rolled without tethering. At flow rates greater than 2 dyn cm(-2), adherent eosinophils began to be displaced from rhVCAM-1. MLK (10 nM and 100 nM) gave partial (similar to 40%) but significant (P < 0.05) inhibition of unstimulated eosinophil adhesion to rhVCAM-1 at 1 or 2 dyn cm(-2) shear stress. Once adhered, unstimulated eosinophils did not exhibit morphological changes, and GM-CSF-stimulated eosinophil adhesion under flow was characterized by greater cell flattening with significant (P < 0.05) inhibition of adherent cell numbers by 100 nM MLK observed. This effect appeared specific for MLK, as the analog (E)-3-[[[ 3-[2-(7-chloro-2-quinolinyl) ethenyl]phenyl]-[[3dimethylamino)- 3-oxopropyl]thio]methyl]thio]propanoic acid, sodium salt, had no significant effect on eosinophil adhesion to VCAM-1. The possibility that LTC4, released from unstimulated or GM-CSF-treated eosinophils, contributed to their adhesion to VCAM-1 was excluded as the LT biosynthesis inhibitor 3-[1-(p-Chlorobenzyl)-5(isopropyl)-3-t-butylthioindol-2-yl]-2,2-dimethylpropanoic acid had no inhibitory effect, and exogenously added LTC4 did not enhance eosinophil adhesion. In contrast, LTD4 enhanced eosinophil adhesion to VCAM-1, an effect blocked by MLK (10 and 100 nM). These findings demonstrate that MLK-mediated inhibition of unstimulated and GM-CSF-stimulated eosinophil adhesion to VCAM-1 under shear-stress conditions appears independent of cysLT(1)R antagonism.