Zerez C R, Lachant N A, Tanaka K R
Department of Medicine, Harbor-UCLA Medical Center, Torrance 90502.
Blood. 1990 Sep 1;76(5):1008-14.
We have examined aspects of methemoglobin (metHb) reduction in sickle and in thalassemic red blood cells (RBCs). NADH metHb reductase activity in sickle and thalassemic RBCs was significantly increased compared with normal RBCs. Because in vitro enzyme activity does not necessarily represent in vivo activity, we measured the rate of metHb reduction in intact RBCs. Intact thalassemic RBCs demonstrated a significantly increased rate of metHb reduction compared with normal RBCs. In contrast, intact sickle RBCs had a rate of metHb reduction that was similar to normal RBCs and significantly decreased relative to high reticulocyte RBCs of equivalent cell age. To determine the mechanism for the relative impairment of metHb reduction in sickle RBCs, we measured intraerythrocytic NADH, a cofactor in the metHb reduction reaction. Thalassemic RBCs had a significantly increased NADH content relative to normal RBCs. In contrast, sickle RBCs did not have an increase in NADH content. Furthermore, incubating normal RBCs under conditions that increase the NADH content resulted in an increased rate of metHb reduction. In contrast, conditions that decrease the NADH content in normal RBC resulted in a decreased rate of metHb reduction. These data and other results suggest that metHb reduction in intact RBCs is dependent on NADH content, and that the impaired metHb reduction rate in sickle RBCs may be a result of a lack of increase in NADH content. The dependence of metHb reduction on RBC NADH content and the ability to manipulate NADH content in vitro suggest a new strategy for decreasing oxidant damage to sickle RBCs in vivo.
我们研究了镰状红细胞和地中海贫血红细胞中高铁血红蛋白（metHb）还原的相关方面。与正常红细胞相比，镰状红细胞和地中海贫血红细胞中的NADH高铁血红蛋白还原酶活性显著增加。由于体外酶活性不一定代表体内活性，我们测量了完整红细胞中高铁血红蛋白的还原速率。与正常红细胞相比，完整的地中海贫血红细胞表现出高铁血红蛋白还原速率显著增加。相比之下，完整的镰状红细胞的高铁血红蛋白还原速率与正常红细胞相似，且相对于同等细胞年龄的高网织红细胞显著降低。为了确定镰状红细胞中高铁血红蛋白还原相对受损的机制，我们测量了细胞内NADH，它是高铁血红蛋白还原反应中的一种辅助因子。相对于正常红细胞，地中海贫血红细胞的NADH含量显著增加。相比之下，镰状红细胞的NADH含量没有增加。此外，在增加NADH含量的条件下孵育正常红细胞会导致高铁血红蛋白还原速率增加。相反，降低正常红细胞中NADH含量的条件会导致高铁血红蛋白还原速率降低。这些数据和其他结果表明，完整红细胞中的高铁血红蛋白还原依赖于NADH含量，并且镰状红细胞中高铁血红蛋白还原速率受损可能是由于NADH含量没有增加所致。高铁血红蛋白还原对红细胞NADH含量的依赖性以及在体外操纵NADH含量的能力提示了一种在体内减少镰状红细胞氧化损伤的新策略。
