Aging of the erythrocyte. VII. On the possible causes of inactivation of red cell enzymes

Understanding quasi-apoptosis of the most numerous enucleated components of blood needs detailed molecular autopsy

Erythrocytes are the most numerous cells in human body and their function of oxygen transport is pivotal to human physiology. However, being enucleated, they are often referred to as a sac of molecules and their cellularity is challenged. Interestingly, their programmed death stands a testimony to their cell-hood. They are capable of self-execution after a defined life span by both cell-specific mechanism and that resembling the cytoplasmic events in apoptosis of nucleated cells. Since the execution process lacks the nuclear and mitochondrial events in apoptosis, it has been referred to as quasi-apoptosis or eryptosis. Several studies on molecular mechanisms underlying death of erythrocytes have been reported. The data has generated a non-cohesive sketch of the process. The lacunae in the present knowledge need to be filled to gain deeper insight into the mechanism of physiological ageing and death of erythrocytes, as well as the effect of age of organism on RBCs survival. This would entail how the most numerous cells in the human body die and enable a better understanding of signaling mechanisms of their senescence and premature eryptosis observed in individuals of advanced age.

Mechanisms tagging senescent red blood cells for clearance in healthy humans

This review focuses on the analysis and evaluation of the diverse senescence markers suggested to prime red blood cells (RBC) for clearance in humans. These tags develop in the course of biochemical and structural alterations accompanying RBC aging, as the decrease of activities of multiple enzymes, the gradual accumulation of oxidative damage, the loss of membrane in form of microvesicles, the redistribution of ions and alterations in cell volume, density, and deformability. The actual tags represent the penultimate galactosyl residues, revealed by desialylation of glycophorins, or the aggregates of the anion exchanger (band 3 protein) to which anti-galactose antibodies bind in the first and anti-band 3 naturally occurring antibodies (NAbs) in the second case. While anti-band 3 NAbs bind to the carbohydrate-free portion of band 3 aggregates in healthy humans, induced anti-lactoferrin antibodies bind to the carbohydrate-containing portion of band 3 and along with anti-band 3 NAbs may accelerated clearance of senescent RBC in patients with anti-neutrophil cytoplasmic antibodies (ANCA). Exoplasmically accessible phosphatidylserine (PS) and the alterations in the interplay between CD47 on RBC and its receptor on macrophages, signal regulatory protein alpha (SIRPalpha protein), were also reported to induce erythrocyte clearance. We discuss the relevance of each mechanism and analyze the strength of the data.

Irreversible inactivation of glutathione peroxidase 1 and reversible inactivation of peroxiredoxin II by H2O2 in red blood cells

Catalase, glutathione peroxidase1 (GPx1), and peroxiredoxin (Prx) II are the principal enzymes responsible for peroxide elimination in RBC. We have now evaluated the relative roles of these enzymes by studying inactivation of GPx1 and Prx II in human RBCs. Mass spectrometry revealed that treatment of GPx1 with H(2)O(2) converts the selenocysteine residue at its active site to dehydroalanine (DHA). We developed a blot method for detection of DHA-containing proteins, with which we observed that the amount of DHA-containing GPx1 increases with increasing RBC density, which is correlated with increasing RBC age. Given that the conversion of selenocysteine to DHA is irreversible, the content of DHA-GPx1 in each RBC likely reflects total oxidative stress experienced by the cell during its lifetime. Prx II is inactivated by occasional hyperoxidation of its catalytic cysteine to cysteine sulfinic acid during catalysis. We believe that the activity of sulfiredoxin in RBCs is sufficient to counteract the hyperoxidation of Prx II that occurs in the presence of the basal level of H(2)O(2) flux resulting from hemoglobin autoxidation. If the H(2)O(2) flux is increased above the basal level, however, the sulfinic Prx II begins to accumulate. In the presence of an increased H(2)O(2) flux, inhibition of catalase accelerated the accumulation of sulfinic Prx II, indicative of the protective role of catalase.

The effects of superoxide dismutase knockout on the oxidative stress parameters and survival of mouse erythrocytes

The erythrocytes of 12-month old Sod1^−/− mice showed an increased level of reactive oxygen species (ROS), as estimated by the degree of dihydroethidine and dihydrorhodamine oxidation, and the increased level of Heinz bodies. No indices of severe oxidative stress were found in the red blood cells and blood plasma of Sod1^−/− mice as judged from the lack of significant changes in the levels of erythrocyte and plasma glutathione, plasma protein thiol and carbonyl groups and thiobarbituric-acid reactive substances in the blood plasma. However, a decreased erythrocyte lifespan, increased reticulocyte count and splenomegaly were noted, indicating the importance of superoxide dismutase for maintaining erythrocyte viability. The levels of erythrocyte ROS and Heinz bodies and the reticulocyte count were indistinguishable in Sod1^+/+ and Sod1^+/− mice, suggesting that a superoxide dismutase activity decrease to half of its normal value may be sufficient to secure the protective effects of the enzyme.

Influence of splenectomy on the properties of erythrocytes with hemoglobin Volga disease

Hemoglobin Volga is a rare unstable hemoglobin in which there is a replacement of an internal alanine residue, beta 27 (B9), by an aspartate. From a clinical point of view it is characterized by a moderately severe Heinz body hemolytic anemia. A possible clue to the cause of the hemolysis is the increased vulnerability to oxidation of Hb Volga, with increased free radical turnover and consequent damage to the red cell membrane. Splenectomy performed on carriers of Hb Volga may have a positive outcome leading to improvements in both the clinical condition of the patient and hematological variables such as hemoglobin concentration and bilirubin concentration. With the aim of defining a more complete biochemical picture of the beneficial effect of splenectomy in this disease, we have evaluated some enzymic activities of the red cells of a young patient with Hb Volga disease, before and after splenectomy. In particular, we have investigated the activity of superoxide dismutase (superoxide: superoxide oxidoreductase), glutathione peroxidase (GSH peroxidase, glutathione: hydrogen-peroxidase oxidoreductase) and catalase (hydrogen-peroxide: hydrogen-peroxide oxidoreductase) that catalyze reactions relevant to the steady-state concentration of potentially toxic oxygen derivatives such as O2- and H2O2. Besides, we have carried out experiments on the erythrocytic membrane to evaluate eventual changes on the chemical (i.e. peroxidation) and physico-chemical (i.e. fluidity) properties following surgery.

S-adenosylhomocysteine hydrolase and adenosine deaminase activities in human red cell ageing

The enzyme activities of S-adenosylhomocysteine hydrolase, adenosine deaminase and pyruvate kinase were determined in normal human erythrocytes subpopulations of different ages separated by centrifugation on a discontinuous Percoll:NaCl density gradient. The levels of S-adenosylhomocysteine hydrolase activity were found to undergo a sharp decrease with red cell ageing. Adenosine deaminase activities were, however, less critically dependent on erythrocyte age.

Effect of the level of ATP and of the state of spectrin on osmotic properties of bovine erythrocytes

The effect of the intracellular level of ATP and of the state of spectrin on the critical cell volume of bovine erythrocyte was studied. The state of spectrin was changed by thermal denaturation, which for the bovine red cell took place at similar temperature as for the human erythrocyte. The increase of the ATP level and the spectrin denaturation increased the critical cell volume, while metabolic starvation decreased it. The changes of the ATP level did not influence the critical volume after the denaturation of spectrin. The results suggest that the ATP-dependent effect on the critical cell volume was caused by an alteration of the membrane extensibility due to the change of the membrane skeleton-lipid bilayer interaction(s).

Glutathione-linked enzyme activities in red cell aging

The enzyme activities of glucose-6-phosphate dehydrogenase (G6PD), 6-phospho-gluconate dehydrogenase (6PGD), glutathione peroxidase (GSH-Px) and glutathione reductase (GR) were measured in normal human red cells separated centrifugally in a discontinuous density gradient of Percoll. Activities of G6PD, GSH-Px and GR decreased with red cell aging.

The decline of catalytic enzyme activity concentration of in vivo ageing erythrocytes of the man, the dog and the rat. Approach to a quantitative diagnostic enzymology, IV. Communication

Human, dog and rat erythrocytes were separated by centrifugation on a discontinuous buffered Percoll gradient into fractions of progressively increasing mean cell age to measure the in vivo decline in catalytic activity of eleven enzymes during the erythrocyte lifespan. Erythrocyte enzymes decline exponentially at different rates and also differ between the species. The maximal and minimal catalytic activities (erythrocyte catalytic activity at the beginning and at the end of the appropriate erythrocyte life-span for a given species) and the intracellular half-life of enzymes estimated. To test the hypothesis that circulating erythrocytes make a significant contribution to the normal catalytic activity in plasma it was assumed as a working hypothesis that the measured loss of catalytic activity in ageing erythrocytes is equivalent to the amount of the enzymes released in catalytically active form into plasma. This contribution was calculated.

Aging of the erythrocyte--XVII. Changes in the properties of superoxide dismutase

1. An increase in the sensitivity of superoxide dismutase (SOD) to the action of diethyldithio-carbamate and cyanide was observed in red cell fractions of greater age. 2. It suggests that SOD inactivation during erythrocyte aging is not an "all or none" process but involves transition(s) between enzyme forms of different properties. 3. An increase in the ratio of less mobile to the more mobile SOD bands was observed by polyacrylamide-gel-electrophoresis in older erythrocytes.

Decreased deformability in aging erythrocytes

Deformability of bovine erythrocytes separated according to density (and age) was estimated by a modified Teitel's filterability test, the centrifugational test of Sirs, and viscosity measurements of cell suspensions. Both youngest and oldest erythrocytes were found to be less deformable than middle-aged cells, a result speaking against any chief role for deformability in the recognition of senescent erythrocytes and their removal from the circulation.

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.