Redox cycling of DBBF-Hb induces apoptosis.

Cells were incubated with (A) FBS-free medium alone or medium containing (B) 2 mU/mL GOX, (C) 50 μM DBBF-Hb, or (D) DBBF-Hb and GOX. After 18 hours, adherent and nonadherent cells were pooled and analyzed for PS externalization using the annexin V–PI assay (see “Materials and methods”). Each panel shows a typical flow cytometric plot of 10 000 cells per sample from a representative experiment. Early apoptotic cells (annexin V+, PI−) are shown in the lower right quadrant (R2), and late apoptotic–plasma membrane-damaged cells (annexin V +, PI+) are shown in the upper right quadrant (R3).