Fig. 6.

Effects of sulfa drugs on chemical redox cycling and the formation of BH2 and BH4 in PC12 cells. (A) Effects of sulfasalazine on menadione-generated H₂O₂ in cell lysates of PC12 cells. (B) Effects of different sulfa drugs on menadione-generated H₂O₂ in lysates of PC12 cells. H₂O₂ formation during chemical redox cycling was assayed using 100 μg/ml of a cell lysate prepared from PC12 cells. Assays contained 100 μM NADPH and 200 μM menadione. Control assays were run in the absence of cell lysates and sulfa drugs. (C) Effects of sulfathiazole on the formation of BH2 and BH4 in PC12 cell lysates. Lysates were incubated for 2 hours in the presence [upper and middle panels; high-performance liquid chromatography (HPLC) tracings] and absence (lower HPLC tracing) of 100 μM sepiapterin plus 200 μM NADPH. The middle HPLC tracing was from cell lysates that also contained 100 μM sulfathiazole. (D) Effects of sulfathiazole on BH2 and BH4 formation in intact PC12 cells. Cells were treated for 2 hours in the presence (upper and middle HPLC tracings) and absence (lower HPLC tracing) of 100 μM sepiapterin. In the middle HPLC tracing, cells were treated with 100 μM sulfathiazole 2 hours before the addition of sepiapterin and when sepiapterin was present. BH2 and BH4 formation were measured using HPLC with fluorescence detection.