Rabbit erythrocytes were covalently labeled with biotin and then infused into the donor animial. Up to 60 days after infusion, the biotinylated cells were selectively isolated by their affinity for avidin. These aged erythrocytes, which are within 10 days of death, were analyzed for several biochemical parameters. The 2,3-bisphosphoglycerate and glutathione levels of these cells were constant with age; however, the adenosine 5'-triphosphate concentrations increased approximately 75% as the cells approached the end of their life span. The activities of several glycolytic enzymes did not change with age.The mechanisms of erythrocyte senescence are poorly understood (1). Clearly, erythrocytes have a well-defined life span; however, the study of the aging processes in these cells has been hindered by the inability to definitively isolate senescent erythrocytes. A myriad of publications have reported age-related differences in various biochemical parameters of erythrocytes (for a review, see ref. 1). However, the majority of these are based on the separation of cells over density gradients with the underlying assumption that the most dense fractions represent the old cells, an assumption that has been questioned (2,3).Two methods that are independent of the physical separation techniques outlined above have been reported for the isolation of senescent erythroctyes. Allison and Burn (4) transfused blood group 0 erythrocytes into normal blood group A individuals. At subsequent time points, the 0 cells were recovered after agglutination of the host A erythrocytes. Unfortunately, the technique was hindered by technical difficulties. More recently, Ganzoni et al. (5) Preparation of Young Erythrocyte Cohorts. In some experiments, young erythrocyte populations were used for biotinylation and replacement into donor rabbits. The advantage of using a young cohort of cells is that a larger percentage of the cells will still be circulating 50-60 days after replacement and therefore will allow recovery of greater numbers of senescent cells. Two procedures were used to produce young cell populations-phenylhydrazine treatment and repeated phlebotomy. Phenylhydrazine hydrochloride (25 mg) was subcutaneously injected into a rabbit on days 0, 2, and 3. On day 13, 50 ml of blood was collected in heparin for biotinylation. The reticulocyte count for these preparations averaged more than 50% on day 8. For the repeated phlebotomy procedure, 50-60 ml of blood was drawn from the rabbit on day 0, 2, and 4. The sample for biotinylation was taken on day 14. To protect against iron deficiency during repeated phlebotomy, each rabbit received 50 mg of iron-dextran intramuscularly on days -7, -5, -3, 0, 2, and 4.
Preparation and Infusion of Biotinylated Erythrocytes.Rabbit erythrocytes were washed, labeled with ['4C]cyanate, treated with NHS-biotin, and infused into the donor rabbit exactly as described (7). The average level of biotinylation was approximately 25,000 biotin molecules per erythrocyte.Avidin-Coated Polystyrene Beads. The av...