Division of Molecular and Translational Biomedicine, USA; Pulmonary Injury and Repair Center, USA; Department of Anesthesiology and Perioperative Medicine, School of Medicine, University of Alabama at Birmingham, Birmingham, AL, 35205-3703, USA.
Division of Molecular and Translational Biomedicine, USA; Department of Anesthesiology and Perioperative Medicine, School of Medicine, University of Alabama at Birmingham, Birmingham, AL, 35205-3703, USA.
Redox Biol. 2020 Sep;36:101592. doi: 10.1016/j.redox.2020.101592. Epub 2020 Jun 1.
We previously reported that the highly reactive cell-free heme (CFH) is increased in the plasma of patients with chronic lung injury and causes pulmonary edema in animal model of acute respiratory distress syndrome (ARDS) post inhalation of halogen gas. However, the mechanisms by which CFH causes pulmonary edema are unclear. Herein we report for the first time that CFH and chlorinated lipids (formed by the interaction of halogen gas, Cl, with plasmalogens) are increased in the plasma of patients exposed to Cl gas. Ex vivo incubation of red blood cells (RBC) with halogenated lipids caused oxidative damage to RBC cytoskeletal protein spectrin, resulting in hemolysis and release of CFH. Patch clamp and short circuit current measurements revealed that CFH inhibited the activity of amiloride-sensitive epithelial Na channel (ENaC) and cation sodium (Na) channels in mouse alveolar cells and trans-epithelial Na transport across human airway cells with EC of 125 nM and 500 nM, respectively. Molecular modeling identified 22 putative heme-docking sites on ENaC (energy of binding range: 86-1563 kJ/mol) with at least 2 sites within its narrow transmembrane pore, potentially capable of blocking Na transport across the channel. A single intramuscular injection of the heme-scavenging protein, hemopexin (4 μg/kg body weight), one hour post halogen gas exposure, decreased plasma CFH and improved lung ENaC activity in mice. In conclusion, results suggested that CFH mediated inhibition of ENaC activity may be responsible for pulmonary edema post inhalation injury.
我们之前曾报道过，在患有慢性肺损伤的患者的血浆中，高反应性的无细胞血红素（CFH）增加，并在吸入卤素气体后的急性呼吸窘迫综合征（ARDS）动物模型中引起肺水肿。然而，CFH 引起肺水肿的机制尚不清楚。在此，我们首次报道，在接触 Cl 气体的患者的血浆中，CFH 和氯化脂质（由卤素气体 Cl 与溶血磷脂相互作用形成）增加。体外孵育红细胞（RBC）与氯化脂质会导致 RBC 细胞骨架蛋白血影蛋白发生氧化损伤，从而导致溶血和 CFH 的释放。膜片钳和短路电流测量表明，CFH 抑制了肺泡细胞中阿米洛利敏感的上皮钠通道（ENaC）和阳离子钠（Na）通道的活性，以及人气道细胞中的跨上皮钠转运，其 EC50 分别为 125 nM 和 500 nM。分子建模确定了 ENaC 上 22 个潜在的血红素结合位点（结合能范围：86-1563 kJ/mol），其中至少有 2 个位于其狭窄的跨膜孔内，有可能阻止 Na 通过通道的转运。卤素气体暴露后 1 小时，单次肌肉注射血红素清除蛋白，血影蛋白（4μg/kg 体重），可降低血浆 CFH 并改善小鼠的肺 ENaC 活性。总之，结果表明，CFH 介导的 ENaC 活性抑制可能是吸入性损伤后肺水肿的原因。
