Neocytolysis: Quantification, characterization, and mechanisms of the destruction of newly formed erythrocytes upon return from high altitude

在高海拔缺氧环境中形成的红细胞似乎在回到正常缺氧状态后的几天内优先被破坏，以减少循环红细胞的数量。这个过程被称为“新细胞溶解”。对人类登山运动员的实验研究证据不足，但最近有证据表明小鼠有新细胞溶解作用。新细胞溶解似乎在停用促红细胞生成素后发生。然而，在人类身上缺乏直接的实验证据。新细胞溶解具有重要的临床意义，因为它可能对接受促红细胞生成素治疗肾性贫血的患者的预后产生不利影响。新细胞溶解也可以解释运动员在低氧环境中训练后提高表现的不同结果，运动员选择低氧环境来增加氧运输能力。这项研究的主要目的是证明新细胞溶解确实发生在人类身上。因此，受试者将在高海拔（3450m）缺氧环境中暴露3周，以诱导产生足够数量的新红细胞，使其能够被检测到，同时也能使其进入循环后的破坏率和总体寿命得以延长。新形成红细胞的数量将通过使用一氧化碳再呼吸技术的指示剂稀释来测量。新形成的红细胞将分别通过摄入15N-甘氨酸（海拔前）和13C-2-甘氨酸（海拔后）进行年龄队列标记，其中循环中新形成的细胞数量将通过从全血中分离的血红素中15N/14N和13C/12C的比值进行检测。此外，将确定溶血标志物。该项目的其他目标是：澄清在缺氧环境中形成的红细胞与在常压环境中形成的红细胞在功能上的差异，并在此基础上确定可能解释其过早破坏易感性的机制。这些实验将包括氧化应激参数的测量，红细胞Ca2+稳态可能参与细胞裂解。这些测量将在新分离的网织红细胞和红细胞以及在体外培养和研究的红细胞干细胞上进行。

Erythrocytes formed during exposure to hypoxia at high altitude seem to be destroyed preferentially within a few days upon return to normoxia in order to reduce the number of circulating erythrocytes. This process has been termed “neocytolysis”. Experimental evidence from studies on human mountaineers is weak, but there is recent evidence for neocytolysis on mice. Neocytolysis seems to occur upon withdrawal of erythropoietin. However, direct experimental proof in humans is lacking. Neocytolysis is of significant clinical interest because it might adversely affect the outcome of patients receiving erythropoietin to treat renal anemia. Neocytolysis might also explain the variable results on improved performance of athletes after training in hypoxic environments, which athletes choose to increase oxygen transport capacity.It is the primary goal of this study to prove that neocytolysis actually occurs in humans. Therefore, subjects will be exposed to hypoxia at high altitude (3450m) for 3 weeks to induce production of sufficient amounts of new erythrocytes allowing their detection, but also their rate of destruction after entering circulation and their overall life-span. The amount of newly formed erythrocytes will be measured by indicator dilution using a carbon-monoxide rebreathing technique. Age-cohort labeling of newly formed erythrocytes will be performed by intake of 15N-glycine (pre-altitude) and 13C-2-glycine (post altitude), respectively, where the amount of newly formed cells in circulation will be detected from the ratio of 15N/14N and 13C/12C, measured by mass spectroscopy in heme isolated from whole blood. Furthermore, markers of hemolysis will be determined. Additional goals of this project are: clarifying differences in function of erythrocytes that had been formed in hypoxia relative to those formed in a normoxic environment, and, based on this, to define mechanisms that might explain their susceptibility for premature destruction. Those experiments will include measurements of parameters indicating oxidative stress, erythrocyte Ca2+-homeostasis that might be involved in cell lysis. Such measurements will be performed on freshly isolated reticulocytes and erythrocytes, as well as on erythroid stem cells cultured and studied in vitro.