Figure 8. Heme scavenging attenuates ER stress.

Immunoblot analysis showed that the incubation of the human bronchial epithelial cells with hemin (a form of heme, 25 μM), increased the ER stress markers ATF4 and CHOP (n = 3) (A) at 6 and 24 hours after hemin challenge. In addition, male C57BL/6 mice were exposed to air or Br₂ gas (400 ppm, 30 minutes) and then returned to room air. Some Br₂-exposed mice were given an intraperitoneal injection of purified human hemopexin (Hx) (4 μg/g BW) 1 hour after Br₂ exposure. All air-exposed mice and some Br₂-exposed mice received saline injection as an appropriate control. Hx attenuated plasma total heme levels in Br₂-exposed mice (n = 9–24) (B). Immunoblotting showed that Hx lowered Br₂-induced ER stress markers, ATF4 (n = 10) (C) and CHOP (n = 11–15) (D), in mouse lungs 14 days after Br₂ exposure. Similarly, immunohistochemical staining of lung sections showed an increased accumulation of ATF4 and CHOP (n = 4–5) (E) (arrows showing brown stain) lining bronchioles and in the lung parenchyma in Br₂-exposed mice 14 days after exposure. Hx lowered ATF4 and CHOP levels. Values are mean ± SEM. All animals were males. Scale bars are 200 µm. For A, *P < 0.05 versus air + saline, ^†P < 0.05 versus Br₂ + saline (1 day after), and ^‡P < 0.05 versus Br₂ + saline (14 days after); for B and C, ^†P < 0.05 versus Br₂ + saline (14 days after) by 1-way ANOVA followed by Tukey’s post hoc test.