An examination of the age-related patterns of decay of the hexokinases of human red cells

Mitochondrial Dysfunction in Age-Related Metabolic Disorders

Aging is a natural biological process in living organisms characterized by receding bioenergetics. Mitochondria are crucial for cellular bioenergetics and thus an important contributor to age-related energetics deterioration. In addition, mitochondria play a major role in calcium signaling, redox homeostasis, and thermogenesis making this organelle a major cellular component that dictates the fate of a cell. To maintain its quantity and quality, mitochondria undergo multiple processes such as fission, fusion, and mitophagy to eliminate or replace damaged mitochondria. While this bioenergetics machinery is properly protected, the functional decline associated with age and age-related metabolic diseases is mostly a result of failure in such protective mechanisms. In addition, metabolic by-products like reactive oxygen species also aid in this destructive pathway. Mitochondrial dysfunction has always been thought to be associated with diseases. Moreover, studies in recent years have pointed out that aging contributes to the decay of mitochondrial health by promoting imbalances in key mitochondrial-regulated pathways. Hence, it is crucial to understand the nexus of mitochondrial dysfunction in age-related diseases. This review focuses on various aspects of basic mitochondrial biology and its status in aging and age-related metabolic diseases.

Relationship between Erythrocyte Hexokinase in Cancer Patients and Red Cell Age

A study of hexokinase isozymic pattern and age dependence of the enzyme was carried out on erythrocytes of 4 patients with adenocarcinoma of the gastrointestinal tract. On the basis of our results, we think that the increase in hexokinase activity previously reported and the increase in both subtypes (Ia and Ib) of the enzyme herein described are not due to a mean younger red cell population caused by secondary anemia, which is frequently present in cancer patients.

High resolution of multiple forms of rabbit reticulocyte hexokinase type I by hydrophobic interaction chromatography

Hydrophobic interaction chromatography (HIC) has been employed extensively in the separation of proteins by elution using a descending salt gradient, with and without the use of detergents or denaturing agents. In this study, a new hydrophobic interaction chromatographic support, Toyopearl Phenyl 650 S, was investigated in order to examine the distribution of multiple forms of rabbit reticulocyte hexokinase type I. These distinct forms of the enzyme, designated hexokinase Ia, Ia* and Ib, show similar kinetic and physical properties, similar molecular masses (ca. 100,000) and a different intracellular distribution. The results obtained using Toyopearl Phenyl 650 S of 20-50-microns particle diameter show that this HIC support allows very high resolution, comparable to that obtainable with HIC-HPLC columns but with the advantage of charging a higher amount of starting material even with a high protein concentration. These characteristics render Toyopearl Phenyl 650 S suitable for analytical and preparative purposes. Further, in the separation of multiple forms of rabbit reticulocyte hexokinase, the HIC method was shown to be superior to RP-HPLC, making possible the efficient separation of proteins with high molecular mass and their recovery in active forms. The Toyopearl Phenyl 650 S column was also shown to be more efficient than the ion-exchange chromatographic media previously used, allowing a quicker analysis of the multiple forms of rabbit reticulocyte hexokinase under different biological conditions.

Mechanism of red blood cell aging: relationship of cell density and cell age

The human red cell has a life span of 120 days. The mechanism that determines cell removal from the circulation with such precision remains unknown. Most studies of red cell aging have been based on analysis of cells of progressively increasing age separated by density. The relationship between red cell age and density has been recently challenged, and the hypothesis has been put forward that cell death is not the result of a progressive deterioration of essential cell constituents. This theory was based on preliminary observations in transient erythroblastopenia of childhood, which could not later be confirmed. When the relationship between cell aging and increasing density is critically reviewed, it appears to be based on firm experimental evidence, confirmed by in vivo demonstration of decreasing survival of cells of increasing age. Analysis of studies using buoyant density gradients reveals that this technique can easily distinguish the single exponential slope of decline for those cell components that change progressively throughout the red cell life span from the biphasic decline of those that decrease drastically at the reticulocyte-mature red cell transition. The view that the aging of the red cell and its removal from the circulation result from a progressive series of events during the 120 days of its life span appears to be the most consistent with the available data. Density separation, validated by much experimental evidence, remains a most useful technique for the study of the mechanism of aging of the red cell.

High resolution of multiple forms of red blood cell enzymes using a Toyopearl DEAE 650 S

We have investigated a new anion exchange chromatographic support (Toyopearl DEAE 650 S) which simultaneously allows easily to remove hemoglobin from hemolysates and to obtain a very high resolution of enzymes present in multiple forms. The results obtained are better than those obtainable using an anion-exchange HPLC column. The data obtained at analytical level suggest a wider use of this new matrix also for preparative purposes without significant changes in the resolution.

The levels of adenine nucleotides and pyridine coenzymes in red blood cells from the newborn, determined simultaneously by HPLC

The concentrations of ATP, ADP, AMP; NADP and NADPH; NAD and NADH were determined in erythrocytes from healthy newborns and compared with those obtained in healthy adults. No significant differences were found for the adenine nucleotide concentrations, but NADH levels were reduced in newborn erythrocytes, with a consequent increase in the NAD/NADH ratio. Moreover, in newborn erythrocytes increased levels of NADP were observed, with a consequent increase in the NADP/NADPH ratio and a decrease in the NAD/NADP ratio. These results indicate the need to use reference values of the ratios NAD/NADH, NADP/NADPH and NAD/NADP from healthy newborns in the study of syndromes affecting the metabolism of erythrocytes in the newborn.

On the diagnosis of erythrocyte enzyme defects in the presence of high reticulocyte counts

The separation of red blood cells into reticulocytes and young and old erythrocytes enables investigations of fractions with different contents of reticulocytes. Activities of hexokinase, glucose phosphate isomerase, phosphofructokinase, pyruvate kinase and glucose-6-phosphate dehydrogenase showed a linear relationship to reticulocyte counts. The dependence of these enzyme activities on the age of the red blood cells exhibited a strong decline from the reticulocyte to the young erythrocyte stage followed by only little further loss of activity, thus leading to a biphasic decay of enzyme activities. By linear regression analysis enzyme activities in erythrocytes (AE) and reticulocytes (AR) could be evaluated. The activity of a given enzyme in the reticulocyte exceeded that of the erythrocyte; the quotient AR/AE represents the decline of enzyme activity from the reticulocyte to the erythrocyte stage. This value AR/AE is 16.7 for pyruvate kinase and 9.4 for hexokinase and thus considerably higher than that for the other enzymes investigated (glucose phosphate isomerase: 2.9, phosphofructokinase: 4.3, glucose-6-phosphate dehydrogenase: 4.5). In patients suffering from erythrocyte enzymopathies, the AR/AE for pyruvate kinase was 16.2 and thus almost identical to the normal enzyme. Calibration curves where the enzyme activity is plotted versus the fraction of reticulocytes enable the determination of normal activity of a given erythrocyte enzyme depending on the content of reticulocytes in red blood cell suspensions. Thus an unambiguous diagnosis of enzyme defects irrespective of reticulocyte counts becomes possible.

Adenine and pyridine nucleotides during rabbit reticulocyte maturation and cell aging

In this paper we have used a new method which allows the simultaneous extraction and HPLC determination of ATP, ADP, AMP, NADP, NADPH, NAD and NADH to evaluate the changes in concentration of these compounds during maturation of rabbit reticulocytes and cell aging. The results show a significant increase of ATP concentration, higher ATP/ADP, ATP/AMP ratios and lower NADP+/NADPH, NAD+/NADH ratios in rabbit reticulocytes when compared to mature cells. Similar results were also obtained when the whole red blood cell population was separated into fractions of increasing mean age on discontinuous gradients of Percoll-BSA. These metabolic modifications are discussed in relation to the age-dependent metabolic decline of the erythrocyte.

Purification and physical properties of hexokinase from human erythrocytes

A bulk purification is described for hexokinase (ATP:D-hexose 6-phosphotransferase, EC 2.7.1.1) from human erythrocytes. Following a 110,000-fold purification from 40 litres of blood, 5 mg protein with a specific activity of 22 units/mg were obtained. On application of various separation techniques, the enzyme activity co-migrated with the main protein component. The physical properties, such as the relative molecular mass of 108,000 and sedimentation coefficient of 5.5 S, are similar to those of the enzyme from human heart. In particular, there is a correspondence in the conformational response to glucose 6-phosphate as shown by an association of the enzyme promoted by this metabolite.

Erythrocyte Rh antigens increase with red cell age

Certain blood group antigens may play a role in the removal of senescent red cells from the circulation. In order to elucidate this hypothesis, we have investigated the effect of red cell aging on Rh blood group antigens. Red cells from volunteer donors were separated into subpopulations of uniformly defined densities on discontinuous Stractan density gradients. The number of the five major Rh antigen sites of each fraction was determined both by enzyme-linked immunosorbent assay (ELISA) and by hemagglutination-scoring technique. All Rh antigens tested increased with cell age (p less than 0.01). The data indicate that there is a positive correlation between red cell age and the Rh blood group antigen site number.

Characteristics of hexokinase, pyruvate kinase, and glucose-6-phosphate dehydrogenase during adult and neonatal reticulocyte maturation

Erythrocytes from adults and newborn infants (at term and premature) were separated by Percoll density gradient centrifugation into four fractions of increasing density. Glycolytic enzymes, especially the age-dependent ones, hexokinase (EC 2.7.1.1, HK), pyruvate kinase (EC 2.7.1.40, PK), and glucose-6-phosphate dehydrogenase (EC 1.1.1.49, G6PD) were studied during reticulocyte maturation and further red cell senescence. Analysis of the fraction with lowest density showed an almost linear and steep decline of HK, PK, and G6PD activity with a decreasing number of reticulocytes. In the next three fractions of increasing density, the activity decline was far less. These data are therefore illustrative for a biphasic activity decay pattern of HK, PK, and G6PD during both adult and neonatal red cell aging. The strong decline in HK activity could not be ascribed to the disappearance of a particulate (mitochondrial) bound fraction of the enzyme during reticulocyte maturation. All hexokinase activity in human reticulocytes was found to be cytosolic in contrast with rabbit reticulocytes in which 70% of HK activity was particulate.

Age dependent behaviour of red cell glycolytic enzymes in haematological disorders

The age dependent behaviour of 11, mainly glycolytic, red blood cell enzymes in 26 patients with various haematological disorders has been investigated after separation of red blood cells by discontinuous density gradient centrifugation. The frequency of enzyme deficiencies in the old cells of these patients was significantly increased in comparison with the unseparated cells, 29 and 13 deficiencies, respectively. Particularly hexokinase activity, although normal or even increased in unseparated cells, was found deficient in old cells in seven cases. In addition, an increased number of phosphofructokinase deficiencies was observed in the patients' old cells (eight cases) as compared to the unseparated cells (three cases). However, the red blood cells of the majority of these patients were found to contain increased enzyme activities, irrespective of cell age. Enzyme activities in the youngest cell population did not correlate with the reticulocyte count. Cases of high pyruvate kinase and hexokinase activities were studied for kinetical, electrophoretical and immunological properties of the respective enzymes, but no abnormalities could be demonstrated, indicating an increased synthesis of these enzymes.

Molecular aspects of erythroenzymopathies associated with hereditary hemolytic anemia

Since the discovery of glucose 6-phosphate dehydrogenase (G6PD) and of pyruvate kinase deficiencies, erythroenzymopathies associated with hereditary hemolytic anemia have been extensively investigated. Kinetic and electrophoretic studies have shown that most, if not all, erythroenzymopathies are caused by the production of a mutant enzyme. Except for a few enzymes that are abundant in blood and tissues, it is difficult to obtain enough sample to study the functional and structural abnormalities of mutant enzymes associated with genetic disorders in man. The primary structures of only two normal red cell enzymes which can cause hereditary hemolytic anemia, phosphoglycerate kinase (PGK) and adenylate kinase, have been determined. Single amino acid substitutions of PGK variants have been found, and the identification of the exact molecular abnormalities of such variants has helped us to understand the accompanying functional abnormality. Gene cloning makes possible the identification of the DNA sequence that codes for enzyme proteins. Recently, human complementary DNA (cDNA) for aldolase, PGK, G6PD, and adenosine deaminase (ADA) have been isolated, and the nucleotide sequences for PGK and ADA determined. In the near future, human cDNA sequencing should permit identification of the gene alteration that gives rise to the mutant enzymes.

Characteristics of enzymes of erythrocytes from newborn infants and adults: activity, thermostability, and electrophoretic profile as a function of cell age

THe level of enzyme activity, the enzyme thermostability profile, and the isozyme electrophoretic pattern were determined in young and old erythrocytes from newborn infants and adults and in samples from adult individuals with increased reticulocyte counts. Cord blood samples had higher levels of enzymatic activity for 12 of the 14 enzymes measured, adenylate kinase and phosphoglucomutase being the exceptions. The largest differences in activity between newborns and adults were for glutamic oxaloacetic transaminase, hexokinase, glucose 6-phosphate dehydrogenase, and glutathione reductase, while glutamic oxaloacetic transaminase and pyruvate kinase showed the largest differences between young and old cells. The levels of activity of glutathione reductase, adenylate kinase, phosphoglucomutase, lactate dehydrogenase, phosphoglycerokinase, and glucose phosphate isomerase in cord blood samples suggest the regulation of expression of these enzymes is different in fetal erythrocytes than in erythrocytes from an adult. Differences in the thermostability profile of enzymes from cells from different sources and/or of different ages were noted for 5 of 9 enzymes. No unique electrophoretically identifiable fetal isozymes were observed, although differences in isozyme distribution and staining intensity associated with cell source and/or cell age were noted for many of the 23 enzymes examined. Many of these differences in enzyme characteristics have the potential to be confused with genetic alterations in enzyme structure and function.

Hexokinase "New Hyde Park": a low activity erythrocyte isozyme in a Chinese kindred

Chronic hemolytic anemia in a 7-year-old Chinese boy was found to be associated with decreased activity of erythrocyte hexokinase (approximately 20% of appropriate control values). Alterations in kinetics, stability, pH optimum, or electrophoretic patterns could not be demonstrated with proband hexokinase, but subtle differences between maternal and paternal hexokinase characteristics suggested that two separate mutant isozymes were involved and that the proband was heterozygous for each. Comparisons with previously reported cases of hexokinase deficiency demonstrate the broad genetic heterogeneity that characterizes this disorder.

Non-spherocytic haemolytic anaemia in mother and son associated with hexokinase deficiency

The case history, laboratory findings and properties of the enzyme in a patient with hexokinase deficiency are reported. The mother had a haemolytic disorder of similar severity. In these cases the expression of the disease in both mother and son suggests a dominant mode of inheritance. This family further illustrates the necessity of taking the reticulocyte level into account when interpreting red cell enzyme levels.

Red cell magnesium as a function of cell age

The variation in the magnesium content of human red cells as a function of cell age has been measured by atomic absorption spectrophotometry. The cell population was split into different age fractions using discontinuous density gradient centrifugation, since it is known that cell density increases with age. A mathematical model relating predicted cell age to cell density has been developed which allows the quantification of the observed fall-off in magnesium content with cell age. This model suggests that cells lose magnesium monoexponentially with age, the half-life being approximately 100 days. A previously proposed hypothesis that magnesium could enter the cells only at erythropoiesis and then decay monoexponentially predicted a half-life of 22.4 days and is therefore seen to be an oversimplification of magnesium kinetics in the red cell. The relevance of the present findings to pathologic conditions with abnormal red cell magnesium concentrations is discussed.

Decay pattern of rabbit erythrocyte hexokinase in cell aging

As previously reported, during rabbit red blood cell aging glucose phosphorylating activities show several modifications. In the first period of the red cell life span the predominant form is similar to hexokinase II, while in the mature erythrocyte the predominant glucose phosphorylating activity resembles hexokinase I. In the oldest cells glucose phosphorylating activity has a low affinity (high Km) for glucose. In this paper the modifications of hexokinase in cell aging have been studied in vivo in a young erythrocyte population synchronized by actinomycin D, and in vitro in red cells separated in fractions according to different ages. Since protein synthesis is lacking in the mature red cell, we are inclined to explain the presence of low-affinity hexokinase activity in the oldest erythrocytes as an age-dependent transformation of a primary hexokinase.

A comparative study of the age-related patterns of decay of some nucleoside monophosphate kinases in human red cells

The nucleoside monophosphate kinases, adenylate kinase (AK), guanylate kinase (GUK), and uridine monophosphate kinase (UMPK), were studied electrophoretically and quantitatively in density gradient fractions of human red cells from normal adults which contain red cells of differing mean age. The enzymes were found to differ both in their rates and patterns of decay and in secondary isozyme formation during the life of the red cell in the circulation. AK showed no appreciable enzyme decay and slight genetation of secondary isozymes; UMPK showed a rapid monophasic decline and no secondary isozyme formation; GUK showed intermediate overall loss of activity with a biphasic pattern of decay and marked secondary isozyme formation. A comparative study of the two common phenotypes of UMPK (UMPK 1 and UMPK 2-1) and of AK (AK 1 and AK 2-1) was made. The UMPK 2 isozyme showed a more rapid decay than the UMPK 1 isozyme, whereas no difference was observed between the AK 1 and AK 2 isozymes.

Relationship between glucose phosphorylating activities and erythrocyte age

Glucose phosphorylating activity of human erythrocytes quickly decreases during cell ageing; the electrophoretic pattern suggests that this fast decrease is due mainly to the isozyme II. We have shown that in the young cells only hexokinase I and II are responsible for the glucose phosphorylation, while in the old cells another glucose phosphorylating activity, more evident at high glucose concentration, is also present. The appearance of this activity during cell ageing could be interpreted as a post-translational modification of the native hexokinase.

An examination of the age-related patterns of decay of acid phosphatase (ACP1) in human red cells from individuals of different phenotypes

A study has been made of the decay of acid phosphatase (ACP1) in the human red cell using red cell fractions of different mean ages prepared by density gradient centrifugation. Red cells from acid phosphatase type A and type B individuals were used in the study. Acid phosphatase activity of the red cell fractions was determined by two different assay methods. The results obtained were comparable and have been combined. Acid phosphatase type A and type B showed a biphasic decay pattern with a rapid early loss of activity, followed by a more gradual rate of decline. Type A appeared to decay more rapidly than type B in both decay phases. It is proposed that differences in stability between type A and type B in vivo may explain the observed differences in activity between the enzyme types. There was no evidence for the generation of secondary isozymes by acid phosphatase type A or type B during red cell aging.

In vivo and in vitro variations of human erythrocyte glutathione peroxidase activity as result of cells ageing, selenium availability and peroxide activation

Cases showing erythrocyte glutathione peroxidase (GSH-Px) defects have been previously described. Our experiments demonstrate that a number of non genetic factors may influence the GSH-Px activity in human erythrocytes. Selenium administration in vivo was followed in four subjects by elevation in erythrocyte GSH-Px activity ranging from 30% to 1400%. Selenium operates mainly in the bone marrow erythroblasts by facilitating the synthesis of active GSH-Px molecules; experiments in vivo demonstrate that, in the youngest erythrocytes, selenium can raise the enzyme activity, but by a different mechanism. The reticulocyte GSH-Px activity appears to depend on selenium availability and may vary over a wide range. In some normal and iron deficient subjects the GSH-Px activity in the youngest erythrocyte fraction was equal or lower than that previously found in whole erythrocytes of patients affected by haemolytic anaemia. During erythrocyte life, GSH-Px activity may either diminish or increase, and these variations are inversely related to the initial GSH-Px activity in youngest cells. In vitro experiments with the addition of acetyl-phynyl-hydrazine strongly suggest that elevation of GSH-Px activity may be due to allosteric enzyme activation by activated oxygen.

Post-synthetic changes in creatine kinase isozymes (EC 2.7.3.2)

1. An in vivo change from creatine kinase MM3 into MM2 and finally into MM1 was described earlier in sera of patients during a post-myocardial infarction period. The same change takes place in vitro. 2. Parallel to this change, a turn-over from the MB2 isozyme into the MB1 form can be detected in vitro. 3. Immediately after the mixing of various extracts from heart tissue and other muscles with a serum with low creatine kinase activity, only MM3 and MB2 can be detected. MM1, MM2 and MB1 are not present in muscle cells. From these three observations it can be concluded that the phenomenon of the three MM and two MB isozymes is postsynthetic (i.e. epigenetic). Furthermore evidence is presented that the change from MM3 into MM1 is brought about by a thermolabile substance. This factor transforms one of the two M2 chains, present in the MM3 form, into a M1 chain. This results in the MM2 isozyme. Later on the second M2 chain is also transformed, resulting in the MM1 isozyme. The same mechanism is proposed for the observed change in MB pattern.

Properties of human erythrocyte hexokinase related to cell age

The kinetic, electrophoretic and immunological properties of hexokinase from human erythrocytes have been studied in relation to cell age. No differences in kinetic behaviour between hexokinase partly purified from reticulocytes, 10% youngest cells, normal red cell population or from 10% oldest cells were observed. The stability of the enzyme preparations showed little differences; hexokinase from the 10% youngest cells was the most labile enzyme, followed respectively by the enzyme from reticulocytes, normal red cell population and the 10% oldest cells. The electrophoretic pattern of erythrocyte hexokinase changed during senescence. The hexokinase activity located in the second band from the anode is shifted to the third with increasing cell age. The molecular specific acitivity of the enzyme from the 10% youngest cells, the normal red cell population and the 10% oldest cells remains the same, while the molecular specific activity of hexokinase from reticulocytes was much lower.