Glutathione homeostasis in Sickle Cell Disease

纯合子镰状细胞病（HbSS）的特征是溶血性增加， “镰刀形”红细胞比率。此外，HbSS患者还 内源性抗氧化剂的红细胞浓度较低 谷胱甘肽（GSH），这表明他们有受损的抗氧化能力。它 已经提出，超氧化物自由基的产生是通过 血红素，铁原子和释放血红素基团，导致过氧化的 红细胞脂质膜，这有助于镰状化过程。但是，在这方面， 抗氧化能力实际受损的程度，机制 潜在的这种损害，以及与氧化损伤和 HbSS体内镰状化的程度尚未确定。研究 提出的解决了以下假设：i）HbSS受试者具有较低的 红细胞GSH浓度高于对照组，因为它们合成 GSH以较慢的速度。ii）GSH合成的较慢速率是由于减少了 甘氨酸和半胱氨酸的可利用性，因为 这两种氨基酸。iii）用以下物质补充HbSS受试者的饮食： 半胱氨酸、甘氨酸或半胱氨酸加甘氨酸均可刺激GSH合成 从而补充GSH库 尺寸iv）HbSS受试者的较高氧化负荷与以下直接相关： GSH的合成和可用性降低，从而刺激GSH 合成速率将导致氧化应激降低。使用生化 和稳定同位素示踪方法，这些假设将在32 HbSS受试者和8例年龄、性别和日常生活习惯匹配的对照受试者 饮食摄入量实验方案将确定1） 红细胞GSH、半胱氨酸和甘氨酸的合成率，2）全身 蛋白质分解率，3）脂质过氧化氢的血浆浓度， 4)红细胞对氧化应激抵抗力 几周的饮食补充。获得的数据将提供洞察力， 氧化能力与镰状化之间的关系以及饮食是否 干预可以改善HbSS受试者的代谢状态。

Homozygous sickle cell disease (HbSS) is characterized by increased hemolytic rate of "sickle shaped" erythrocytes. In addition, individuals with HbSS also have lower erythrocyte concentrations of the endogenously produced antioxidant glutathione (GSH), suggesting that they have impaired antioxidant capacity. It has been proposed that the generation of superoxide free radical by hemichromes, iron atoms and released haem groups, leads to peroxidation of the erythrocyte lipid membrane, which contributes to the sickling process. However, the extent to which antioxidant capacity is actually impaired, the mechanism(s) underlying such an impairment, and the relationships to oxidant damage and to the degree of in vivo sickling in HbSS have not been determined. The research proposed addresses the following hypotheses: i) HbSS subjects have lower erythrocyte GSH concentrations than control subjects because they synthesize GSH at a slower rate. ii) The slower rate of GSH synthesis is due to reduced availability of glycine and cysteine because of slower de novo synthesis of these two amino acids. iii) Supplementing the diets of the HbSS subjects with either cysteine, glycine, or cysteine plus glycine will stimulate GSH synthesis to a higher rate than its rate of consumption thereby replenishing the GSH pool size. iv) The higher oxidative load of the HbSS subject is directly related to the decreased synthesis and availability of GSH, hence stimulation of GSH synthesis rate will result in a decreased oxidative stress. Using biochemical and stable isotope tracer methods, these hypotheses will be tested in 32 subjects with HbSS and 8 control subjects matched for age, gender and usual dietary intakes. The experimental protocol will determine differences in 1) the rates of synthesis of erythrocyte GSH, cysteine and glycine, 2) whole body protein breakdown rate, 3) the plasma concentrations of lipid hydroperoxides, 4) the resistance of erythrocyte to oxidative stress at baseline and after a 4 weeks of dietary supplementation. The data obtained will provide insight into the relationship between oxidant capacity and sickling and whether dietary intervention can improve the metabolic status of subjects with HbSS.