Relative potencies of various fibrates and 25-HC in the inhibition of the human CYP7A1 gene promoter in cells co-expressing LXRα and PPARα. The human CYP7A1 gene promoter–reporter gene chimera (hCYP7A1.CAT) (1 µg) was introduced into McArdle RH7777 cells along with PPARα (0.5 µg), LXRα (0.5 µg) or RXR (0.5 µg) expression plasmids, as indicated. The transfected cells were subsequently incubated for 24 h with WY 14,643, clofibrate, bezafibrate, gemfibrozil, 25-HC or vehicle (0.1% dimethyl sulfoxide for PPARα activators and 0.1% ethanol for 25-HC) in medium containing 5% lipoprotein-deficient serum.