Mansouri A, Lurie A A
Department of Medicine, Overton Brooks VAMC, Shreveport, Louisiana 71101-4295.
Am J Hematol. 1993 Jan;42(1):7-12. doi: 10.1002/ajh.2830420104.
The ferrous iron of hemoglobin is exposed continuously to high concentrations of oxygen and, thereby, is oxidized slowly to methemoglobin, a protein unable to carry oxygen. To restore hemoglobin function, methemoglobin (ferrihemoglobin) must be reduced to hemoglobin (ferrohemoglobin). Under physiological conditions, methemoglobin reduction is accomplished mainly by red cell NADH-cytochrome b5 reductase (NADH-methemoglobin reductase) so efficiently that there is insignificant amounts of methemoglobin in the circulating blood. However, should methemoglobin formation be increased--e.g., due to the presence of oxidant drugs, or an abnormal methemoglobin not amenable to reduction (hemoglobin M), or a deficiency in red cell cytochrome b5 reductase--methemoglobinemia will result. Most methemoglobinemias have no adverse clinical consequences and need not be treated. Under certain conditions, such as exposure to large amounts of oxidant or in young infants, rapid treatment is necessary. In hereditary cytochrome b5 deficiency, treatment is often directed at improving the poor cosmetic effect of persistent cyanosis with the minimum amount of drugs to give satisfactory clinical results.
血红蛋白中的亚铁离子持续暴露于高浓度氧气中，因此会缓慢氧化为高铁血红蛋白，这是一种无法携带氧气的蛋白质。为恢复血红蛋白功能，高铁血红蛋白（高铁血红素）必须还原为血红蛋白（亚铁血红蛋白）。在生理条件下，高铁血红蛋白的还原主要通过红细胞NADH - 细胞色素b5还原酶（NADH - 高铁血红蛋白还原酶）高效完成，以至于循环血液中的高铁血红蛋白含量极少。然而，如果高铁血红蛋白的形成增加，例如由于存在氧化药物、或存在无法还原的异常高铁血红蛋白（血红蛋白M）、或红细胞细胞色素b5还原酶缺乏，就会导致高铁血红蛋白血症。大多数高铁血红蛋白血症没有不良临床后果，无需治疗。在某些情况下，如接触大量氧化剂或在幼儿中，快速治疗是必要的。在遗传性细胞色素b5缺乏症中，治疗通常旨在用最少的药物改善持续性发绀的不良外观效果，以获得满意的临床结果。
