The effect of the MAPK inhibitors PD98059 or SB203580 on TNF-α-induced Cyp7b activity. (a) Fibroblast-like synoviocytes (FLS; SCRO.14.SF, passages 8–12) were incubated for 1 hour in the presence or absence (-) of the mitogen-activated protein kinase (MAPK) kinase (MEK)1 inhibitor PD98059 (PD) or the p38 inhibitor SB203580 (SB). Thereafter, cells were incubated in the presence or absence of 0.5 ng/ml tumour necrosis factor (TNF)-α plus 1.5 × 10-8 mol/l [3H]-dehydroepiandrosterone (DHEA) for 24 hours and processed using high-performance liquid chromatography. The amount of 7α-hydroxy-dehydroepiandrosterone (7α-OH-DHEA) is expressed as the percentage [3H]-7α-OH-DHEA of the total amount of [3H]-label measured. Results are expressed as the mean ± standard error of the mean of triplicate sample. Data are representative of three independent experiments. *P < 0.05 versus TNF-α (Student's t-test). (b) The data from panel a (three independent experiments) are combined for the highest inhibitor concentrations. PD98059 and SB23580 were dissolved in methanol (MeOH) and dimethylsulfoxide (DMSO), respectively, and used as controls. *P < 0.05 (Student's t-test). Cyp7b = cytochrome p450 enzyme 7b.