Studies of factors regulating the ageing of human erythrocytes--I. The role of pH and of divalent cations

Studies of factors regulating the ageing of human erythrocytes--V. The role of vesiculation in the loss of membrane-bound sialic acid

1. Erythrocytes aged in vitro in protein-free media with and without leukocytes, release glycopeptides and vesicles. 2. Addition of soybean trypsin inhibitor (SbTI) blocks almost completely the release of glycopeptides but not the vesiculation. 3. Vesicles appear as a heterogeneous population with a diameter of 125 +/- 20 nm and with a lower content of N-acetylneuraminic acid (NAN) than ghosts of the original erythrocytes. 4. The NAN:phosphorus and NAN:cholesterol ratios in the vesicles are lower than in intact membranes. 5. The results indicate a redistribution of membrane components during in vitro erythrocyte incubation and the major importance of sialopeptides release in comparison with vesiculation.

Aging of the erythrocyte. XVII. Binding of autologous immunoglobulin G

Increased amounts of autologous immunoglobulin (Ig) G were found on older bovine erythrocytes employing 125I-labelled Protein A, 125I-labelled anti(bovine IgG) antibodies and hemolysis in the presence of anti(bovine IgG) antibodies + complement. In vitro, desialylation, proteolysis and action of an O2-. source but not glycosylation induced binding of extraneous IgG to the erythrocytes.

[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.

Cyclic changes of sialidase in human cervical mucus

1. Sialidase activity is detectable in whole cervical mucus of normal women throughout the menstrual cycle and presents cyclic variations toward endogenous and exogenous substrates. 2. The level of sialic acid bound to the mucus increases progressively till mid-cycle and declines in the post-ovulatory phase. 3. The sialidase of the mucus probably derives from different sources and its role remains speculative.

Studies of factors regulating the ageing of human erythrocytes--III. Metabolism and fate of erythrocytic vesicles

1. Ageing erythrocytes release vesicles the metabolism of which is unknown. 2. Human and rat erythrocytic vesicles labelled with 51Cr and injected into rats, disappear very rapidly from the circulation with half-lives from 2 to 8 min. 3. Their lifetime resembles that of liposomes encapsulating [51Cr]haemoglobin (Hb) and in both cases, liver and spleen take up considerable amounts of radioactivity. 4. These results indicate, for the first time, that vesicles released from erythrocytes are cleared at very fast rates from the circulation and suggest that this may be the reason for the absence of vesicles in the plasma in vivo.

Studies of factors regulating the ageing of human erythrocytes. II. Metabolic depletion of erythrocytes is not accompanied by a decrease of their sialic acid content during blood bank storage

Erythrocytes from human blood stored at 5 degrees C in anticoagulant-preservative solutions are considered, after a period from 21 to 24 days, unsuitable for transfusion. The nonviability of the cells appears due to metabolic impairment accompanied by a change of the biophysical properties of the cell but surprisingly not to a decrease of sialic acid of the membrane. The absence of proteolysis can be attributed to calcium chelation and to the stable levels of plasma protease inhibitors throughout the storage period. In fact, when erythrocytes are incubated for several days at 5 degrees C in protein-free media, release of sialopeptides from the membrane increases slowly and steadily, particularly if the medium is without glucose and adenine but contains divalent cations. Moreover, this phenomenon is strikingly amplified when incubation in protein-free media is carried out at 37 degrees C and once the ATP level has fallen below 5% of its initial value.