Hemoglobin precipitation by hemopexin is prevented by haptoglobin. Viable cultures were treated for 24 hours with FITC-conjugated Hb (3 μM) alone (A,B), with unlabeled Hpx 1 mg/ml (C,D), or with Hb+Hpx plus 100 μM ascorbate (Asc, E,F) or 1 mg/ml haptoglobin (Hp, G,H). Bars represent mean fluorescence intensity in cultures treated as above or with deferoxamine (DFO) 100 μM or ferrostatin-1 (FS) 10 μM. *p < 0.05, ***p < 0.001 versus Hb+Hpx condition, n = 6 cultures/condition for sham, Hb and Hb+Hpx, 4 cultures/condition for +DFO, +Asc and +FS, and 5 cultures/condition for +Hp.