PSI inhibits the TNF-α-induced increase in 7α-OH-DHEA. Human rheumatoid arthritis (RA) fibroblast-like synoviocytes (FLS; SCRO.14.SF, 1 × 105 cells/well; passages 10–12) were preincubated in the presence or absence (-) of the PSI inhibitor for 1 hour. Thereafter, the cells were incubated with (solid bars) or without (open bars) tumour necrosis factor (TNF)-α for another 24 hours with 1.5 × 10-8 mol/l 3H-DHEA, as described in Materials and methods. Data are expressed as mean ± standard error of the mean and are representative of four independent experiments. *P < 0.0005. 7α-OH-DHEA = 7α-hydroxy-dehydroepiandrosterone.