The effect of in-vivo ageing of the human erythrocyte on the proteins of the plasma membrane. A comparison with metabolic depletion and blood bank storage

Electrical impedance alterations of red blood cells during storage

The electrical impedance of blood is determined mainly by the resistance of the plasma (Rp), resistance of the red cell interior fluid (Ri), and capacitance of the cell membranes (Cm). These parameters were measured on 10 stored blood samples consecutively during 4 or 5 weeks of storage at 4 degrees C, once every week. Compared to the values of fresh samples, a statistically significant decrease in Rp was found mainly during the first week of storage, Ri did not decrease significantly until after 3 weeks, whereas Cm decreased progressively with time. These alterations can be explained by known red cell lesions during storage. The results indicate that electrical impedance measurements might be useful for monitoring red cell ageing and assessing the quality of stored red blood cells.

Isolation and partial characterization of antibody- and globin-enriched complexes from membranes of dense human erythrocytes

In previous studies we have described a process whereby an erythrocyte in biochemical distress can initiate its own removal by macrophages of the reticuloendothelial system. This process involves the clustering of the integral membrane protein band 3 by denatured haemoglobin and the subsequent recognition of the exofacial poles of clustered band 3 and associated proteins by autologous antibodies. To determine whether this clearance pathway might mediate normal cell turnover, the fraction of normal erythrocytes containing the 0.5% densest cells, which are known to be destined for immediate removal, was isolated and characterized biochemically. This densest fraction was found to contain 6 times more membrane-bound globin (haemichromes) and 10 times more surface-bound autologous IgG than the other fractions containing cells of lower density. To determine whether the autologous IgG was physically associated with the haemichrome-stabilized membrane protein clusters, a procedure was developed for isolation and characterization of the microscopic aggregates. The isolated aggregates were found to contain a disulphide-cross-linked mixture of several membrane proteins, predominantly haemichromes, spectrin and band 3. Although the aggregates constituted only 0.09% of the total membrane protein, they still contained approximately 55% of the total cell-surface IgG. Since in control studies anti-(blood group A) antibodies, which are distributed randomly over the surface of type A cells, could not be recovered in the aggregate, we conclude that the autologous cell-surface IgGs were physically associated with the membrane protein clusters when they were co-isolated with them in our procedure. Thus the 640-fold enrichment of autologous IgG in the aggregates compared with regions of the membrane devoid of tightly clustered protein suggests that sites of integral protein clustering either are non-specifically sticky to IgG or are viewed as foreign or 'non-self' by the immune system and aggressively opsonized with IgG.

The effects of pentoxifylline on rat erythrocytes of different age

Age-separated rat erythrocytes were exposed to pentoxifylline, a dimethylxanthine derivative which increases erythrocyte deformability. A comparison of drug-induced effects in young and old erythrocytes yielded age-specific alterations in: (1) accumulation of intracellular Ca2+; (2) membrane protein phosphorylation; (3) ATP concentrations; and (4) membrane associated protein kinase activity. The effect of Ca2+ accumulation and membrane protein phosphorylation appears to be biphasic. Low drug concentrations (0.5-2.5 mM) reduced intracellular Ca2+ and increased membrane protein phosphorylation, whereas higher concentrations (4.0-5.0 mM) increased Ca2+ levels and reduced membrane protein phosphorylation. Young cells exhibited increased ATP levels over the whole range of pentoxifylline tested; however, older erythrocytes demonstrated higher ATP levels at 5.0 mM drug only. Membrane-associated protein kinase activity was enhanced 10% in young erythrocytes at 1.0 mM pentoxifylline and decreased to 30% of control values at 4.0 and 5.0 mM drug. Protein kinase of old erythrocytes exhibited gradual inhibition over the entire drug concentration range. In general, younger erythrocytes appear to be more responsive to pentoxifylline exposure. Based on these studies, it appears that the ageing of the erythrocyte and loss of deformability in vivo may be a consequence of increased Ca2+ entry into the cell.

[Activity of the glutathione redox system in human erythrocytes at various ages]

Human erythrocytes were separated into three groups according to their density and age by centrifugation in a continuous Percoll gradient. The specific activities of glucose-6-phosphate dehydrogenase, catalase, glutathione peroxidase, glutathione reductases as well as the glutathione and selenium content were highest in the youngest cell and uniformly decreased by about 20-30% in the eldest group. The age-dependence of superoxide dismutase was much more pronounced. The malondialdehyde content taken as an estimate for lipid peroxidation showed an inverse age dependence and increased by 35% in the eldest cell population. Red blood cells from 10 anemic patients exhibited less glutathione and also less malondialdehyde, while GSH-peroxidase and GSSG-reductase contents were higher. The parameters showed similar age profiles as in healthy subjects. The findings support the concept of lipid peroxidation as one of the causal events in red cell aging, but do not allow to deduce the involvement of a single enzyme related to the glutathione redox cycle in this process.