['Montelukast is a potent cysteinyl leukotriene-1 receptor antagonist possessing some anti-inflammatory effects although the molecular mechanism of these anti-inflammatory effects is unknown. In this study, we aimed to investigate the effect of montelukast on nuclear factor (NF)-kappaB-associated histone acetylation activity in phorbol myristate acetate (PMA)-differentiated U937 cells.', 'We examined the inhibitory effects of montelukast on TNF-alpha-induced IL-8 production in PMA-differentiated U-937 cells. U-937 cells were exposed to PMA (50 ng/mL) for 48 h to allow differentiation to macrophages. Macrophages were then exposed to TNF-alpha (10 ng/mL) in the presence or absence of montelukast (0.01-10 microm) for 24 h. After this time, the concentration of IL-8 in the culture supernatant was measured by sandwich-type ELISA kit. The effect of signalling pathways on TNF-alpha-induced IL-8 release was examined pharmacologically using selective NF-kappaB/IKK2 (AS602868, 3 microm), (PD98059, 10 microm) and p38 mitogen activated protein kinase (MAPK) (SB203580, 1 microm) inhibitors. NF-kappaB DNA binding activity was measured by a DNA-binding ELISA-based assay. NF-kappaB-p65-associated histone acetyltransferase (HAT) activity was measured by immunoprecipitation linked to commercial fluorescent HAT.', 'TNF-alpha-induced IL-8 release was suppressed by an NF-kappaB inhibitor but not by MEK or p38 MAPK inhibitors. Montelukast induced a concentration-dependent inhibition of TNF-alpha-induced IL-8 release and mRNA expression that reached a plateau at 0.1 microm without affecting cell viability. Montelukast did not affect NF-kappaB p65 activation as measured by DNA binding but suppressed NF-kappaB p65-associated HAT activity.'] Does montelukast inhibit tumour necrosis factor-alpha-mediated interleukin-8 expression through inhibition of nuclear factor-kappaB p65-associated histone acetyltransferase activity?