The Aging Process of Human Neonatal Erythrocytes

Abstract

ABSTRACT. The red blood cell population of the human newborn is more heterogeneous than that of adults. TO characterize this heterogeneity, red cells were separated on Stractan gradients into populations according to their density and, therefore, generally according to their age. Lipid content, phospholipid asymmetry, osmotic fragility, and deformability were measured. With increasing density, osmotic resistance and deformability decreased to a greater extent in the neonatal than the adult red cell. There was a marked loss of surface area throughout the life span of the neonatal red cell which was not accompanied by a parallel loss of membrane lipid. This apparent discrepancy could be explained at least in part by internalization of membrane lipid as a result of endocytosis, a process shown to be present in even the densest neonatal red cells. creased life span. Another property of neonatal cells which may potentially have adverse rheological consequences is their loss of more than one-quarter of their surface area as they age in circulation (3-5). We have suggested that this property may be linked to the enhanced propensity of such cells to internalize plasma membrane through the process of endocytosis (5-7). In the current report, we further explore this possibility. To do so, we used the technique of Stractan density gradient centrifugation to prepare populations of buoyant (presumably young) and dense (3, 8, 9) (presumably old) neonatal red cells. The amount of cell lipid was measured in each density fraction and the degree to which the loss in surface area was accompanied by loss of membrane lipid determined. Changes in phospholipid composition (10, 11) or asymmetry (12) were also sought. As an independent index of cell surface area (13), we measured red cell deformability in the ektacytometer (14). Our findings demonstrate that although the densest ("oldest") neonatal red cells have lost considerable surface area, they have not lost the expected equivalent quantities of membrane lipid, implying that at least some of the lipid must have been internalized rather than released into the plasma. MATERIALS AND METHODS CHV, critical hemolytic volume - Materials. Stractan was purchased from St. Regis Lumber Co., DI, deformability indexLibby, MT and prepared as previously described (5, 9). Cellulose PC, phosphatidylcholine (Sigmacell-50), a-cellulose, cholesterol standard solution (CH-I), PE, phosphatidylethanofamine and bee venom phospholipase A2 were purchased from Sigma PS, phosphatidylserine Chemical Co., St. Louis, MO. Sphingomyelinase C was prepared PI, phosphatidylinositol as previously described (12). SM, sphingomyelinBlood collection and density separation. Venous blood was DI,,,, maximum deformability collected from adult volunteers and cord blood was drawn from the placental vessels immediately upon delivery according to a protocol approved by the Stanford Medical Committee for the Protection of Human Subjects in Research. EDTA was used as The shortened life span of neonatal red cells relative to that of...

Oxidative Stress in Newborn Erythrocytes

“…The light layer contained younger cells, as indicated by the higher reticulocyte counts and GOT ( Table 2). The separation yielded mean corpuscular Hb concentration values higher than those in the parallel layers of adult cells; this is in accordance with the data reported by Matovcik et al (17), using Stractan gradient. The heavy layer was enriched with HbF (80% compared with 58% in the light layer).…”

“…Similar maintenance of GSH levels in the most dense population has been recently reported by Lane et al (19). Osmotic fragility increased in the old cells, in accordance with the data of Matovcik et al (17) (data not shown).…”

“…The heavy layer contained 20% more HbF than the light one, proving that the former was enriched with old cells. This layer was also osmotically more fragile than the light layer and whole blood, as has been demonstrated with other gradient separations (17). We did not find any significant difference between light and heavy layers in oxidized Hb and GSH levels, nor were significant differences found after exposure to PHZ.…”

Cellular Dehydration and Immunoglobulin Binding in Senescent Neonatal Erythrocytes

“…Two potentially lethal defects have now been identified in subpopulations of neonatal erythrocytes enriched for senescent cells. The first defect is a significant decrease in cell deformability that is primarily due to a marked loss of surface area (10). The second defect is the presence of bound immunoglobulin on the cell surface.…”

“…Recently, Matovcik et al (10) studied density-separated red cells and showed that the aging process of human neonatal erythrocytes is associated with a more rapid loss of membrane surface area than is the case with adult red cells. The loss of surface area was demonstrated to have a significant detrimental effect on cell deformability.…”