Oxidation and haem loss kinetics of poly(ethylene glycol)-conjugated haemoglobin (MP4):: dissociation between in vitro and in vivo oxidation rates
Oxidation and haem loss kinetics of poly(ethylene glycol)-conjugated haemoglobin (MP4):: dissociation between in vitro and in vivo oxidation rates
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DOI：
10.1042/bj20060809
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发表时间：
2006-11-01
影响因子：
4.1
通讯作者：
Winslow, Robert M.
中科院分区：
文献类型：
--
作者：
Vandegriff, Kim D.;Malavalli, Ashok;Winslow, Robert M.
以血红蛋白为基础的氧载体可以将亚铁血红蛋白氧化成无功能的铁形式，并增加血红素的损失率。最近开发的一种与马来酰亚胺活化的聚乙二醇偶联的人血红蛋白，称为MP4，具有独特的物理化学性质（增加分子半径，高氧亲和力和低协同性），并且缺乏大多数无细胞血红蛋白溶液所观察到的典型高血压反应。在室温（20-22℃）和37℃时，体外MP4的自氧化率均高于未修饰的SFHb（无基质血红蛋白）（P < 0.001）。这似乎归因于SFHb中残留的过氧化氢酶活性，而不是MP4。相比之下，MP4和SFHb对黄嘌呤-黄嘌呤氧化酶体系产生的活性氧具有相同的氧化敏感性。一旦完全氧化为甲基血红蛋白，MP4中体外血红素的损失率比SFHb在快期高5倍，我们将其归因于亚基，而慢期（即从a链中失去血红素）两种血红蛋白的损失率相似。在大鼠和人体内输血后，MP4甲基血红蛋白的形成比其体外一级自氧化率预测的要慢，并且在血浆中没有明显的MP4甲基血红蛋白积累，然后从循环中消失。这些结果表明，在体外观察到的MP4氧化和血红素损失特征提供了关于聚乙二醇偶联对血红蛋白分子稳定性影响的信息，但不符合MP4在体内的氧化行为。
Haemoglobin-based oxygen carriers can undergo oxidation of ferrous haemoglobin into a non-functional ferric form with enhanced rates of haem loss. A recently developed human haemoglobin conjugated to maleimide-activated poly(ethylene glycol), termed MP4, has unique physicochemical properties (increased molecular radius, high oxygen affinity and low cooperativity) and lacks the typical hypertensive response observed with most cell-free haemoglobin solutions. The rate of in vitro MP4 autoxidation is higher compared with the rate for unmodified SFHb (stroma-free haemoglobin), both at room temperature (20-22 degrees C) and at 37 degrees C (P < 0.001). This appears to be attributable to residual catalase activity in SFHb but not MP4. In contrast, MP4 and SFHb showed the same susceptibility to oxidation by reactive oxygen species generated by a xanthine-xanthine oxidase system. Once fully oxidized to methaemoglobin, the rate of in vitro haem loss was five times higher in MP4 compared with SFHb in the fast phase, which we assign to the subunits, whereas the slow phase (i.e. haem loss from a chains) showed similar rates for the two haemoglobins. Formation of MP4 methaemoglobin in vivo following transfusion in rats and humans was slower than predicted by its first-order in vitro autoxidation rate, and there was no appreciable accumulation of MP4 methaemoglobin in plasma before disappearing from the circulation. These results show that MP4 oxidation and haem loss characteristics observed in vitro provide information regarding the effect of poly(ethylene glycol) conjugation on the stability of the haemoglobin molecule, but do not correspond to the oxidation behaviour of MP4 in vivo.