Effects of sphingoid bases derived from brewer's yeast in PPAR activation. (A and B) Sphingoid base fraction from brewer's yeast was extracted, treated with o-phthalaldehyde, and analyzed by reversed-phase HPLC. The areas of PHS and DHS were quantified. (C) NIH/3T3 cells were transfected as described for Figure 2A. Cells were stimulated with the indicated concentration of yeast-derived sphingoid base fraction. Cells were also treated with authentic PHS, DHS or the mixture of PHS and DHS. (D) Transfected cells were cultured with phytoceramide or dihydroceramide (1 or 10 μM) for 24 h. Luciferase activity was presented as a fold induction relative to that of the control. All results are shown as means ± S.D. (n = 3). *P < 0.05, **P < 0.01, ***P < 0.001, significantly different from the level of vehicle control.