Cell age-dependent changes in deformability and calcium accumulation of human erythrocytes

Effect of Cell Age and Membrane Rigidity on Red Blood Cell Shape in Capillary Flow

Blood flow in the microcirculatory system is crucially affected by intrinsic red blood cell (RBC) properties, such as their deformability. In the smallest vessels of this network, RBCs adapt their shapes to the flow conditions. Although it is known that the age of RBCs modifies their physical properties, such as increased cytosol viscosity and altered viscoelastic membrane properties, the evolution of their shape-adapting abilities during senescence remains unclear. In this study, we investigated the effect of RBC properties on the microcapillary in vitro flow behavior and their characteristic shapes in microfluidic channels. For this, we fractioned RBCs from healthy donors according to their age. Moreover, the membranes of fresh RBCs were chemically rigidified using diamide to study the effect of isolated graded-membrane rigidity. Our results show that a fraction of stable, asymmetric, off-centered slipper-like cells at high velocities decreases with increasing age or diamide concentration. However, while old cells form an enhanced number of stable symmetric croissants at the channel centerline, this shape class is suppressed for purely rigidified cells with diamide. Our study provides further knowledge about the distinct effects of age-related changes of intrinsic cell properties on the single-cell flow behavior of RBCs in confined flows due to inter-cellular age-related cell heterogeneity.

Impact of small fractions of abnormal erythrocytes on blood rheology

Red blood cell (RBC) populations are inherently heterogeneous, given mature RBC lack the transcriptional machinery to re-synthesize proteins affected during in vivo aging. Clearance of older, less functional cells thus aids in maintaining consistent hemorheological properties. Scenarios occur, however, where portions of mechanically impaired RBC are re-introduced into blood (e.g., damaged from circulatory support, blood transfusion) and may alter whole blood fluid behavior. Given such perturbations are associated with poor clinical outcomes, determining the tolerable level of abnormal RBC in blood is valuable. Thus, the current study aimed to define the critical threshold of blood fluid properties to re-infused physically-impaired RBC. Cell mechanics of RBC were impaired through membrane cross-linking (glutaraldehyde) or intracellular oxidation (phenazine methosulfate). Mechanically impaired RBC were progressively re-introduced into the native cell population. Negative alterations of cellular deformability and high shear blood viscosity were observed following additions of only 1-5% rigidified RBC. Low-shear blood viscosity was conversely decreased following addition of glutaraldehyde-treated cells; high-resolution microscopy of these mixed cell populations revealed decreased capacity to form reversible aggregates and decreased aggregate size. Mixed RBC populations, when exposed to supraphysiological shear, presented with compounded mechanical impairment. Collectively, key determinants of blood flow behavior are sensitive to mechanical perturbations in RBC, even when only 1-5% of the cell population is affected. Given this fraction is well-below the volume of rigidified RBC introduced during circulatory support or transfusion practice, it is plausible that some adverse events following surgery and/or transfusion may be related to impaired blood fluidity.

Calcium/protein kinase C signaling mechanisms in shear-induced mechanical responses of red blood cells

Red blood cell (RBC) deformability has vital importance for microcirculation in the body, as RBCs travel in narrow capillaries under shear stress. Deformability can be defined as a remarkable cell ability to change shape in response to an external force which allows the cell to pass through the narrowest blood capillaries. Previous studies showed that RBC deformability could be regulated by Ca²⁺/protein kinase C (PKC) signaling mechanisms due to the phosphorylative changes in RBC membrane proteins by kinases and phosphatases. We investigated the roles of Ca²⁺/PKC signaling pathway on RBC mechanical responses and impaired RBC deformability under continuous shear stress (SS). A protein kinase C inhibitor Chelerythrine, a tyrosine phosphatase inhibitor Calpeptin, and a calcium channel blocker Verapamil were applied into human blood samples in 1 micromolar concentration. Samples with drugs were treated with or without 3 mM Ca²⁺. A shear stress at 5 Pa level was applied to each sample continuously for 300 s. RBC deformability was measured by a laser-assisted optical rotational cell analyzer (LORRCA) and was calculated as the change in elongation index (EI) of RBC upon a range of shear stress (SS, 0.3-50 Pa). RBC mechanical stress responses were evaluated before and after continuous SS through the parameterization of EI-SS curves. The drug administrations did not produce any significant alterations in RBC mechanical responses when they were applied alone. However, the application of the drugs together with Ca²⁺ substantially increased RBC deformability compared to calcium alone. Verapamil significantly improved Ca²⁺-induced impairments of deformability both before and after 5 Pa SS exposure (p < 0.0001). Calpeptin and Chelerythrine significantly ameliorated impaired deformability only after continuous SS (p < 0.05). Shear-induced improvements of deformability were conserved by the drug administrations although shear-induced deformability was impaired when the drugs were applied with calcium. The blocking of Ca²⁺ channel by Verapamil improved impaired RBC mechanical responses independent of the SS effect. The inhibition of tyrosine phosphatase and protein kinase C by Calpeptin and Chelerythrine, respectively, exhibited ameliorating effects on calcium-impaired deformability with the contribution of shear stress. The modulation of Ca²⁺/PKC signaling pathway could regulate the mechanical stress responses of RBCs when cells are under continuous SS exposure. Shear-induced improvements in the mechanical properties of RBCs by this signaling mechanism could facilitate RBC flow in the microcirculation of pathophysiological disorders, wherein Ca²⁺ homeostasis is disturbed and RBC deformability is reduced.

Production of erythrocyte microparticles in a sub-hemolytic environment

Microparticles are produced by various cells due to a number of different stimuli in the circulatory system. Shear stress has been shown to injure red blood cells resulting in hemolysis or non-reversible sub-hemolytic damage. We hypothesized that, in the sub-hemolytic shear range, there exist sufficient mechanical stimuli for red blood cells to respond with production of microparticles. Red blood cells isolated from blood of healthy volunteers were exposed to high shear stress in a microfluidic channel to mimic mechanical trauma similar to that occurring in ventricular assist devices. Utilizing flow cytometry techniques, both an increase of shear rate and exposure time showed higher concentrations of red blood cell microparticles. Controlled shear rate exposure shows that red blood cell microparticle concentration may be indicative of sub-hemolytic damage to red blood cells. In addition, properties of these red blood cell microparticles produced by shear suggest that mechanical trauma may underlie some complications for cardiovascular patients.

Calcium dynamically alters erythrocyte mechanical response to shear

Red blood cells (RBC) are constantly exposed to varying mechanical forces while traversing the cardiovascular system. Upon exposure to mechanical stimuli (e.g., shear stress), calcium enters the cell and prompts potassium-efflux. Efflux of potassium is accompanied by a loss of intracellular fluid; thus, the volume of RBC decreases proportionately (i.e., 'Gárdos effect'). The mechanical properties of the cell are subsequently impacted due to complex interactions between cytosolic viscosity (dependent on cell hydration), the surface-area-to-volume ratio, and other molecular processes. The dynamic effects of calcium on RBC mechanics are yet to be elucidated, although accumulating evidence suggests a vital role. The present study thus examined the effects of calcium on contemporary biomechanical properties of RBC in conjunction with high-precision geometrical analyses with exposure to shear. Mechanical stimulation of RBC was performed using a co-axial Couette shearing system to deform the cell membrane; intracellular signaling events were observed via fluorescent imaging. Calcium was introduced into RBC using ionophore A23187. Increased intracellular calcium significantly impaired RBC deformability; these impairments were mediated by a calcium-induced reduction of cell volume through the Gárdos channel. Extracellular calcium in the absence of the ionophore only had an effect under shear, not at stasis. Under low shear, the presence of extracellular calcium induced progressive lysis of a sub-population of RBC; all remaining RBC exhibited exceptional capacity to deform, implying preferential removal of potentially aged cells. Collectively, we provide evidence of the mechanism by which calcium acutely regulates RBC mechanical properties.

Active modulation of human erythrocyte mechanics

The classic view of the red blood cell (RBC) presents a biologically inert cell that upon maturation has limited capacity to alter its physical properties. This view developed largely because of the absence of translational machinery and inability to synthesize or repair proteins in circulating RBC. Recent developments have challenged this perspective, in light of observations supporting the importance of posttranslational modifications and greater understanding of ion movement in these cells, that each regulate a myriad of cellular properties. There is thus now sufficient evidence to induce a step change in understanding of RBC: rather than passively responding to the surrounding environment, these cells have the capacity to actively regulate their physical properties and thus alter flow behavior of blood. Specific evidence supports that the physical and rheological properties of RBC are subject to active modulation, primarily by the second-messenger molecules nitric oxide (NO) and calcium-ions (Ca²⁺). Furthermore, an isoform of nitric oxide synthase is expressed in RBC (RBC-NOS), which has been recently demonstrated to have an active role in regulating the physical properties of RBC. Mechanical stimulation of the cell membrane activates RBC-NOS, leading to NO generation, which has several intracellular effects, including the S-nitrosylation of integral membrane components. Intracellular concentration of Ca²⁺ is increased upon mechanical stimulation via the recently identified mechanosensitive cation channel piezo1. Increased intracellular Ca²⁺ modifies the physical properties of RBC by regulating cell volume and potentially altering several important intracellular proteins. A synthesis of recent advances in understanding of molecular processes within RBC thus challenges the classic view of these cells and rather indicates a highly active cell with self-regulated mechanical properties.

Intracellular Ca2+ Concentration and Phosphatidylserine Exposure in Healthy Human Erythrocytes in Dependence on in vivo Cell Age

After about 120 days of circulation in the blood stream, erythrocytes are cleared by macrophages in the spleen and the liver. The “eat me” signal of this event is thought to be the translocation of phosphatidylserine from the inner to the outer membrane leaflet due to activation of the scramblase, while the flippase is inactivated. Both processes are triggered by an increased intracellular Ca²⁺ concentration. Although this is not the only mechanism involved in erythrocyte clearance, in this minireview, we focus on the following questions: Is the intracellular-free Ca²⁺ concentration and hence phosphatidylserine exposure dependent on the erythrocyte age, i.e. is the Ca²⁺ concentration, progressively raising during the erythrocyte aging in vivo? Can putative differences in intracellular Ca²⁺ and exposure of phosphatidylserine to the outer membrane leaflet be measured in age separated cell populations? Literature research revealed less than dozen of such publications with vastly contradicting results for the Ca²⁺ concentrations but consistency for a lack of change for the phosphatidylserine exposure. Additionally, we performed reanalysis of published data resulting in an ostensive illustration of the situation described above. Relating these results to erythrocyte physiology and biochemistry, we can conclude that the variation of the intracellular free Ca²⁺ concentration is limited with 10 μM as the upper level of the concentration. Furthermore, we propose the hypothesis that variations in measured Ca²⁺ concentrations may to a large extent depend on the experimental conditions applied but reflect a putatively changed Ca²⁺ susceptibility of erythrocytes in dependence of in vivo cell age.

A Flow Induced Autoimmune Response and Accelerated Senescence of Red Blood Cells in Cardiovascular Devices

Red blood cells (RBCs) passing through heart pumps, prosthetic heart valves and other cardiovascular devices undergo early senescence attributed to non-physiologic forces. We hypothesized that mechanical trauma accelerates aging by deformation of membrane proteins to cause binding of naturally occurring IgG. RBCs isolated from blood of healthy volunteers were exposed to high shear stress in a viscometer or microfluidics channel to mimic mechanical trauma and then incubated with autologous plasma. Increased binding of IgG was observed indicating forces caused conformational changes in a membrane protein exposing an epitope(s), probably the senescent cell antigen of band 3. The binding of immunoglobulin suggests it plays a role in the premature sequestration and phagocytosis of RBCs in the spleen. Measurement of IgG holds promise as a marker foreshadowing complications in cardiovascular patients and as a means to improve the design of medical devices in which RBCs are susceptible to sublethal trauma.

Epoetin beta pegol for treatment of anemia ameliorates deterioration of erythrocyte quality associated with chronic kidney disease

Background

Epoetin beta pegol (continuous erythropoietin receptor activator; C.E.R.A.) is currently widely used for the treatment of anemia associated with chronic kidney disease (CKD). Therapeutic control of anemia is assessed by monitoring haemoglobin (Hb) levels. However, certain qualitative aspects of erythrocytes are also impaired in CKD, including loss of deformability and shortened life-span. Therefore, monitoring Hb alone could potentially fail to reveal pathological changes in erythrocytes. Focusing on erythrocyte quality in CKD may lead to more effective anemia therapy with C.E.R.A.

Methods

A CKD rat model was induced by uninephrectomy followed by anti-Thy1.1 antibody injection. From 5 weeks after the operation, C.E.R.A. (0.6 μg/kg) or vehicle was administered every 2 weeks. Erythrocyte deformability was quantified with ektacytometry and erythrocyte turnover was estimated by biotin labeling. Intracellular calcium level was assessed by Fluo-3/AM.

Results

Erythrocyte deformability progressively declined in CKD rats. Furthermore, erythrocyte turnover in the circulation drastically accelerated in CKD rats. With administration of C.E.R.A. at a dose sufficient to adequately control Hb, deterioration of erythrocyte deformability and turnover in CKD rats were significantly improved. Intracellular calcium, which plays a pivotal role in the mediation of erythrocyte quality, was significantly increased in CKD and was normalized by C.E.R.A. treatment.

Conclusion

C.E.R.A. treatment exerted a favorable effect not only on anemia but also on the improvement of erythrocyte quality. C.E.R.A. administered for the treatment of CKD-associated anemia may confer therapeutic benefits on erythrocytes.

The Action of Red Cell Calcium Ions on Human Erythrophagocytosis in Vitro

In the present work we have studied in vitro the effect of increasing red cell Ca²⁺ ions on human erythrophagocytosis by peripheral monocyte-derived autologous macrophages. In addition, the relative contribution to phagocytosis of phosphatidylserine exposure, autologous IgG binding, complement deposition and Gárdos channel activity was also investigated. Monocytes were obtained after ficoll-hypaque fractionation and induced to transform by adherence to glass coverslips, for 24 h at 37°C in a RPMI medium, containing 10% fetal calf serum. Red blood cells (RBC) were loaded with Ca²⁺ using 10 μM A23187 and 1 mM Ca-EGTA buffers, in the absence of Mg²⁺. Ca²⁺-loaded cells were transferred to above coverslips and incubated for 2 h at 37°C under various experimental conditions, after which phagocytosis was assessed by light microscopy. Confirming earlier findings, phagocytosis depended on internal Ca²⁺. Accordingly; it was linearly raised from about 2–15% by increasing the free Ca²⁺ content of the loading solution from 0.5 to 20 μM, respectively. Such a linear increase was virtually doubled by the presence of 40% autologous serum. At 7 μM Ca²⁺, the phagocytosis degree attained with serum was practically equal to that obtained with either 2 mg/ml affinity-purified IgG or 40% IgG-depleted serum. However, phagocytosis was reduced to levels found with Ca²⁺ alone when IgG-depleted serum was inactivated by heat, implying an involvement of complement. On the other hand, phagocytosis in the absence of serum was markedly reduced by preincubating macrophages with phosphatidylserine-containing liposomes. In contrast, a similar incubation in the presence of serum affected it partially whereas employing liposomes made only of phosphatidylcholine essentially had no effect. Significantly, the Gárdos channel inhibitors clotrimazole (2 μM) and TRAM-34 (100 nM) fully blocked serum-dependent phagocytosis. These findings show that a raised internal Ca²⁺ promotes erythrophagocytosis by independently triggering phosphatidylserine externalization, complement deposition and IgG binding. Serum appeared to stimulate phagocytosis in a way dependent on Gárdos activity. It seems likely that Ca²⁺ promoted IgG-binding to erythrocytes via Gárdos channel activation. This can be an important signal for clearance of senescent human erythrocytes under physiological conditions.

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.

Rheological properties of young and aged erythrocytes in chronic venous disease patients with varicose veins

We hypothesize that heterogeneity in RBC rheology can be attributed not only to the aging process but also to various disease states. The present study aims at investigating the rheological properties of young and old RBC in chronic venous disease (CVD) patients. RBC were separated on the basis of their density. RBC rheology was assessed with Laser Optical Rotational Cell Analyzer. For medium and high shear stress elongation index (EI) of young RBC from CVD patients was significantly higher than of young cells from controls. The same was observed for the old cells. Threshold shear rate (THR) of young RBC from CVD patients was significantly higher than of young cells from controls indicating a decreased tendency towards the formation of aggregates and of their stability in CVD patients. The same situation was observed for the old cells. To sum up, the present study demonstrated that heterogeneity in RBC rheology is both affected by age and CVD. Additionally, CVD-induced changes in RBC rheology occur to different degrees among the subpopulations of young and old RBC. CVD patients subpopulations of RBC had higher deformability and increased tendency towards aggregates formation and of their stability when compared to appropriate subpopulations of controls.

Oxidative stress and rheologic properties of stored red blood cells before and after transfusion to surgical patients

BACKGROUND

The loss of structural and functional integrity of red blood cells (RBCs) during storage, collectively referred to as "storage lesion," has been implicated in reduced oxygen delivery after transfusion. RBCs are highly susceptible to oxidative damage from generation of reactive oxygen species by autoxidation of hemoglobin. Therefore, we examined whether increased oxidative stress (OS) in stored RBCs is associated with impaired cell membrane deformability before or after transfusion.

STUDY DESIGN AND METHODS

Thirty-four patients undergoing multilevel spine fusion surgery were enrolled. OS in RBCs was assessed by the presence of fluorescent heme degradation products and methemoglobin, which were measured with fluorimetric and spectrophotometric methods, respectively. Deformability and aggregation were determined by ektacytometry in stored RBCs, autologous salvaged RBCs, and posttransfusion blood samples.

RESULTS

OS in stored RBCs was significantly increased with longer storage (R = 0.54, p = 0.032) and significantly higher than that in fresh RBCs (9.1 ± 1.3 fluorescent arbitrary units vs. 7.7 ± 0.9 fluorescent arbitrary units, p < 0.001). Deformability decreased (R = -0.60, p = 0.009) with increasing storage duration. OS was elevated (p < 0.05) and deformability was decreased (p < 0.05) in postoperative blood from patients who had undergone moderate (≥4 RBC units) but not minimal or no transfusion. Neither the decrease in deformability of RBCs nor the aggregation changes were correlated with OS.

CONCLUSIONS

Although stored RBCs show signs of increased OS and loss of cell membrane deformability, these changes were not directly correlated and were only evident after moderate but not lower dose transfusion in postoperative surgical patients. These findings suggest that factors other than OS may contribute to impaired rheology with stored RBCs in the clinical setting.

Quantitation of malaria parasite-erythrocyte cell-cell interactions using optical tweezers

Erythrocyte invasion by Plasmodium falciparum merozoites is an essential step for parasite survival and hence the pathogenesis of malaria. Invasion has been studied intensively, but our cellular understanding has been limited by the fact that it occurs very rapidly: invasion is generally complete within 1 min, and shortly thereafter the merozoites, at least in in vitro culture, lose their invasive capacity. The rapid nature of the process, and hence the narrow time window in which measurements can be taken, have limited the tools available to quantitate invasion. Here we employ optical tweezers to study individual invasion events for what we believe is the first time, showing that newly released P. falciparum merozoites, delivered via optical tweezers to a target erythrocyte, retain their ability to invade. Even spent merozoites, which had lost the ability to invade, retain the ability to adhere to erythrocytes, and furthermore can still induce transient local membrane deformations in the erythrocyte membrane. We use this technology to measure the strength of the adhesive force between merozoites and erythrocytes, and to probe the cellular mode of action of known invasion inhibitory treatments. These data add to our understanding of the erythrocyte-merozoite interactions that occur during invasion, and demonstrate the power of optical tweezers technologies in unraveling the blood-stage biology of malaria.

Numerical analysis of a red blood cell flowing through a thin micropore

Red blood cell (RBC) deformability plays a key role in microcirculation, especially in vessels that have diameters even smaller than the nominal cell size. In this study, we numerically investigate the dynamics of an RBC in a thin micropore. The RBC is modeled as a capsule with a thin hyperelastic membrane. In a numerical simulation, we employ a boundary element method for fluid mechanics and a finite element method for membrane mechanics. The resulting RBC deformation towards the flow direction is suppressed considerably by increased cytoplasm viscosity, whereas the gap between the cell membrane and solid wall becomes smaller with higher cytoplasm viscosity. We also measure the transit time of the RBC and find that nondimensional transit time increases nonlinearly with respect to the viscosity ratio, whereas it is invariant to the capillary number. In conclusion, cytoplasmic viscosity plays a key role in the dynamics of an RBC in a thin pore. The results of this study will be useful for designing a microfluidic device to measure cytoplasmic viscosity.

Numerical and experimental study on the development of electric sensor as for measurement of red blood cell deformability in microchannels

A microsensor that can continuously measure the deformability of a single red blood cell (RBC) in its microchannels using microelectrodes is described in this paper. The time series of the electric resistance is measured using an AC current vs. voltage method as the RBC passes between counter-electrode-type micro-membrane sensors attached to the bottom wall of the microchannel. The RBC is deformed by the shear flow created in the microchannel; the degree of deformation depends on the elastic modulus of the RBC. The resistance distribution, which is unique to the shape of the RBC, is analyzed to obtain the deformability of each cell. First, a numerical simulation of the electric field around the electrodes and RBC is carried out to evaluate the influences of the RBC height position, channel height, distance between the electrodes, electrode width, and RBC shape on the sensor sensitivity. Then, a microsensor was designed and fabricated on the basis of the numerical results. Resistance measurement was carried out using samples of normal RBCs and rigidified (Ca(2+)-A23186 treated) RBCs. Visualization measurement of the cells' behavior was carried out using a high-speed camera, and the results were compared with those obtained above to evaluate the performance of the sensor.

Effects of pre-storage leukoreduction on stored red blood cells signaling: a time-course evaluation from shape to proteome

The introduction of pre-storage leukoreduction in the preparation of standard RBCs intended for transfusion provided significant improvement in the quality of labile products and their post transfusion viability and effects, although the literature data are controversial. To elucidate the issue of the probable leukoreduction effects on RBCs storage lesion, we evaluated various storage quality measures in RBCs stored in either leukoreduced (L) or non-leukoreduced (N) units, with emphasis to senescence and oxidative stress associated modifications. Our data suggest that the residual leukocytes/platelets of the labile products represent a stressful storage factor, countering the structural and functional integrity of stored RBCs. Hemolysis, irreversible echinocytosis, microvesiculation, removal signaling, ROS/calcium accumulation, band 3-related senescence modifications, membrane proteome stress biomarkers as well as emergence of a senescence phenotype in young RBCs that is disproportionate to their age, are all encountered more or mostly in N-RBCs compared to the L-RBCs, either for a part or for the whole of the storage period. The partial, yet significant, alleviation of so many storage-related manifestations in the L-RBCs compared to the N-RBCs, is presented for the first time and provides a rational mechanistic interpretation of the improved storage quality and transfusions observed by the introduction of pre-storage leukoreduction. This article is part of a Special Issue entitled: Integrated omics.

Age-dependent acoustic and microelastic properties of red blood cells determined by vector contrast acoustic microscopy

Variations of the mechanical properties of red blood cells that occur during their life span have long been an intriguing task for investigations. The research presented is based on noninvasive monitoring of red blood cells of different ages performed by scanning acoustic microscopy with magnitude and phase contrast. The characteristic signature of fixed cells from groups of three different ages fractionated according to mass density is obtained from the acoustic microscope images, with the data represented in polar graphs. The analysis of these data enables the determination of averaged values for the velocities of ultrasound propagating in the cells from the different groups ranging from (1,681 ± 16) m s(-1) in the youngest to (1,986 ± 20) m s(-1) in the oldest group. The determined bulk modulus varies with age from (3.04 ± 0.05) GPa to (4.34 ± 0.08) GPa. An approach to determine for an age-mixed population of red blood cells, collected from a healthy person, the age of the individual cells and the age dependence of the cell parameters including density, velocity, and attenuation of longitudinal polarized ultrasonic waves traveling in the cells is demonstrated.

Evaluation of Red Blood Cell Deformability and Uterine Blood Flow in Pregnant Women with Preeclampsia or IUGR and Reduced Uterine Blood Flow Following the Intravenous Application of Magnesium

OBJECTIVE

Red blood cells (RBC) deformability is one of the factors determining microcirculation. In preeclampsia (PE) and some cases of intrauterine growth restriction (IUGR), RBC deformability and, consequently, microcirculation appear to be impaired. Magnesium sulfate is administered to reduce the risk of seizures in PE. The aim of our study was to detect the effect of 24-hour intravenous (IV) magnesium on RBC deformability and on uterine artery blood flow in pregnant patients with preeclampsia or IUGR and pathologic uterine blood flow.

METHODS

Magnesium IV (1 g/h) was administered to 25 pregnant women with reduced uterine blood flow for a period of at least 24 hours. The RBC deformability was measured by uterine artery Doppler. Measurements were taken before the start of magnesium therapy and 24 h later. Magnesium plasma levels were measured at the same time.

RESULTS

High plasma levels of magnesium improve RBC deformability from E = 0.109 (SD +/- 0.023) to E = 0.115 (SD +/- 0.021) after 24 h IV magnesium (p = 0.043). There is no correlation of E to the plasma magnesium level either before or after 24 h magnesium treatment. Blood volume flow in the uterine arteries increased significantly from 5.09 mL/s (SD +/- 3.03) to 10.02 mL/s (SD +/- 5.86) after 24 h magnesium (p = 0.0002). The differences in the resistance index do not significantly differ from 0 (p = 0.46).

CONCLUSION

A high IV dosage of magnesium over a period of 24 hours dilates the uterine arteries of pregnant women with PE and/or IUGR, reduces uterine blood flow and improves the deformability of RBC. Both parameters enhance the oxygen supply to the fetus, a clinical parameter in these pregnancies. Thus magnesium might not only be effective as phrophylaxis against seizures but also in cases of IUGR with a reduced uterine blood flow. The clinically observed beneficial effect of magnesium in PE could be due to the improved blood supply for the fetus.

Effects of menopause and hormone therapy on erythrocyte deformability

OBJECTIVE

The climacteric disturbance seen among perimenopausal women often includes symptoms related to poor microcirculation. This hemorheological condition plays an important role in the hemodynamism of microcirculation. Specifically, erythrocyte deformability is considered to be one of the most significant factors in determining this hemorheological condition.

METHODS

The present study investigated the level of erythrocyte deformability in four groups of women: namely, 10 healthy premenopausal women (PRE group), 25 postmenopausal women (POST group), 20 postmenopausal women on estrogen therapy (ET group) who received conjugated equine estrogens 0.625 mg/day, and 20 postmenopausal women on estrogen plus progestogen therapy (EPT group) who received conjugated equine estrogens 0.625 mg/day plus medroxyprogesterone acetate 2.5 mg/day. The erythrocyte deformability score (EDS), measured by the Micro Channel Array Flow Analyzer, was determined as an index of erythrocyte deformability.

RESULTS

The mean EDS for the POST group was significantly higher (mean +/- SE, 1.02 +/- 0.04) (P < 0.01) than that for the PRE group (0.78 +/- 0.05). The mean EDS for the ET group (0.88 +/- 0.03) was significantly lower than that for the POST group and close to that of the PRE group. There was no difference in the EDS values between the ET group and the EPT group (0.87 +/- 0.03).

CONCLUSIONS

These results indicate that erythrocyte deformability may worsen with the decrease in the estrogen level because of the onset of menopause, and also suggest that ET and EPT may allow it to recover.

Effect of Magnesium on Red Blood Cell Deformability in Pregnancy

OBJECTIVE

Red blood cell (RBC) deformability is an important factor in determining movement of red blood cells through the microcirculation. In preeclampsia and some cases of intrauterine growth restriction (IUGR), RBC deformability and microcirculation are reduced. Magnesium is administered to reduce the risk of seizures. The aim of this study was first to detect the effect of intravenous magnesium application (2 g/h) on the deformability of RBCs in pregnancies with normal RBC deformability, receiving magnesium as tocolytic agent. The second aim was to examine the effect of calcium-antagonists (magnesium, nifedipin) on the deformability of RBC of preeclamptic patients in vitro.

METHODS

Part 1: magnesium (2 g/h), fenoterol (270 microg/h)+verapamil (0.2 mg/h) or placebo (NaCl 0.9%) was administered intravenously to pregnant women with premature contractions to test the tocolytic effect. RBC-deformability was measured by laser diffractoscopy in all three groups. Blood samples were taken before, after 1 h and after 24 h of administration. Magnesium-plasma-levels were measured. Part 2: Blood samples from patients with preeclampsia were incubated in vitro with magnesium (2 mmol), nifedipine (0.25 mg/ml), or placebo (NaCl 0.9%). RBC deformability was measured before and 15 min, 1 h, 2 h, 6 h, and 10 h after start of the incubation.

RESULTS

Part 1: The initial RBC-deformability was the same in all groups (E=0.232+/-0.017 in NaCl, 0.232+/-0.023 in fenoterol+verapamil, 0.232+/-0.019 in magnesium). After 1 h of administration, RBC-deformability was significantly greater with magnesium (0.254+/-0.020) and Fenoterol+Verapamil (0.238+/-0.02) compared to placebo (0.231+/-0.015). After 24 h the effect on RBC deformability in the fenoterol+verapamil-group was gone (0.234+/-0.021 compared to 0.234+/-0.016 in placebo), while in the IV-magnesium-group RBC-deformability remained increased (E=0.241+/-0.019). Statistical analysis of the influence of magnesium-plasma-levels showed the maximum effect at concentrations of 1.95-2.15 mmol/l. Part 2: RBC-deformability in preeclampsia was reduced as predicted by previous studies (0.120+0.0086 versus 0.232 in normal pregnancy). In vitro incubation with magnesium enhanced RBC-deformability in preeclampsia. Even after 15 min, a statistically significant effect was seen (0.127+/-0.0091 versus 0.121+/-0.0091 in placebo). Maximum effect was reached after 6 h of incubation (0.159+/-0.0093 versus 0.133+/-0.0091). Incubation with Nifedipine also enhanced RBC deformability [0.127+/-0.0091 after 15 min, 0.149+/-0.010 after 6 h (maximum effect)], but the effect was less pronounced than with magnesium.

CONCLUSION

Intravenous magnesium therapy over a 24-hour period increases RBC-deformability even in pregnancies with normal RBC-deformability. In vitro measurements show an increase of RBC-deformability in preeclampsia in response to magnesium, which could offer additional therapeutic benefit for the treatment of reduced blood flow seen in most cases of preeclampsia.

Active caspases-8 and -3 in circulating human erythrocytes purified on immobilized annexin-V: a cytometric demonstration

Human red blood cells (RBCs) have a normal life span of 120 days in vivo and might be primed in vitro to die in response to apoptotic stimuli through a caspase-independent pathway. It is well known that, in vivo, aging RBCs externalize phosphatidylserine residues but is unknown whether these cells express active caspases at this stage. We isolated RBCs expressing phosphatidylserine on their surface from human blood by applying an original method of affinity chromatography using annexin-V fixed on gelatin or on magnetic beads. The isolated RBCs were then analyzed by flow cytometry for morphological changes (dot-plot forward scatter versus side scatter), phosphatidylserine externalization (annexin-V test), cell viability (calcein-AM test), and caspase activities using fluorescent substrates specific for caspases-3 and -8. In addition, cells were systematically visualized using phase contrast, fluorescence, and confocal microscopy. We found that the population of RBCs fixed on annexin-V is a mixture of discocytes and shrunken cells. This annexin-V-positive population showed a dramatic loss of viability based on esterase activity determination (calcein-AM test). Moreover, we demonstrated that circulating RBCs express both active caspases-8 and -3 in half of the annexin-V-positive cells. All of these results were confirmed by phase contrast, fluorescence, and confocal microscopy. Our results demonstrate active caspases in RBC isolated from blood suggesting that caspases may participate in the regulation of in vivo RBC half-life. This finding open the door to fruitful investigations in the field of RBC pathology.

Oxygen-dependent ion transport in erythrocytes

The present contribution reviews current knowledge of apparently oxygen-dependent ion transport in erythrocytes and presents modern hypotheses on their regulatory mechanisms and physiological roles. In addition to molecular oxygen as such, reactive oxygen species, nitric oxide, carbon monoxide, regional variations of cellular ATP and hydrogen sulphide may play a role in the regulation of transport, provided that they are affected by oxygen tension. It appears that the transporter molecules themselves do not have direct oxygen sensors. Thus, the oxygen level must be sensed elsewhere, and the effect transduced to the transporter. The possible pathways involved in the regulation of transport, including haemoglobin as a sensor, and phosphorylation/dephosphorylation reactions both in the transporter and its upstream effectors, are discussed.

Calcium-dependent human erythrocyte cytoskeleton stability analysis through atomic force microscopy

Erythrocytes affected by age and diseases such as sickle cell anemia, hypertension, diabetes, etc., exhibit abnormally high intracellular Ca2+ ion levels, and appear to have altered cytoskeleton properties. It has been proposed that extra binding of Ca2+ to membrane-associated calmodulin attenuates the spectrin-ankyrin-Band 3 tether of the cytoskeleton to the cytoplasmic membrane and might change the cytoskeleton structure. Due to the close apposition of the network, direct observation of such a structural change in vivo is restricted. In this study, atomic force microscopy and quantitative image analysis were applied to investigate the structural change of young healthy erythrocyte cytoskeletons upon extra Ca2+ binding to the cytoplasmic membrane in vitro. The results show that extra Ca2+ binding increased the cytoskeleton rigidity and prevented spectrin aggregation during sample preparation. The cytoskeleton morphology observed in Ca2+ -incubated healthy young cell were similar to the glutaraldehyde-fixed healthy young cells.

Red blood cell rheology in sepsis

Changes in red blood cell (RBC) function can contribute to alterations in microcirculatory blood flow and cellular dysoxia in sepsis. Decreases in RBC and neutrophil deformability impair the passage of these cells through the microcirculation. While the role of leukocytes has been the focus of many studies in sepsis, the role of erythrocyte rheological alterations in this syndrome has only recently been investigated. RBC rheology can be influenced by many factors, including alterations in intracellular calcium and adenosine triphosphate (ATP) concentrations, the effects of nitric oxide, a decrease in some RBC membrane components such as sialic acid, and an increase in others such as 2,3 diphosphoglycerate. Other factors include interactions with white blood cells and their products (reactive oxygen species), or the effects of temperature variations. Understanding the mechanisms of altered RBC rheology in sepsis, and the effects on blood flow and oxygen transport, may lead to improved patient management and reductions in morbidity and mortality.

Reduced red blood cell deformability, an indicator for high fetal or maternal risk, is found in preeclampsia and IUGR

OBJECTIVE

Red blood cell (RBC) deformability is one of the factors determining microcirculation. In preeclampsia (PE) and some cases of intrauterine growth restriction (IUGR), microcirculation appears to be reduced. The aim of the study is to examine whether there are differences in RBC deformability in uncomplicated pregnancy when compared to pregnancies complicated by PE and/or IUGR.

MATERIAL AND METHODS

RBC deformability of 87 pregnant women with initially normal pregnancies was evaluated with the laser diffractoscope. RBC deformability was measured beginning in week 16 of gestation up to 5 days after delivery. Thirty-seven women had an uncomplicated pregnancy. In addition, RBC deformability of 10 nonpregnant women was measured on days 5 and 22 of their menstrual cycle. RBC deformability of women with preeclampsia (PE, N=15), intrauterine growth restriction (IUGR, N=17), or PE plus IUGR (N=17) was measured weekly, beginning with the onset of clinical symptoms, up to 5 days after delivery.

RESULTS

In early uncomplicated pregnancies, RBC deformability does not differ from the nonpregnant state. At week 30 of gestation, there is a slight decrease in RBC deformability followed by a return back to the values of nonpregnant women after delivery. Women with PE and/or IUGR show reduced RBC deformability. This is most pronounced in cases with severe fetal or maternal complications. After delivery, RBC deformability also returns to nonpregnancy values within 5 days.

CONCLUSION

Reduced RBC deformability may contribute to a reduced microcirculation in PE and IUGR. Increasing RBC deformability therapeutically in these cases could offer new options for the treatment of decreased uterine and fetal perfusion and their sequelae.

Purification and characterization of a cytosolic, 42-kDa and Ca2+-dependent phospholipase A2 from bovine red blood cells: its involvement in Ca2+-dependent release of arachidonic acid from mammalian red blood cells

It has become evident that a Ca(2+)-dependent release of arachidonic acid (AA) and subsequent formation of bioactive lipid mediators such as prostaglandins and leukotrienes in red blood cells (RBCs) can modify physiological functions of neighboring RBCs and platelets. Here we identified a novel type of cytosolic PLA(2) in bovine and human RBCs and purified it to apparent homogeneity with a 14,000-fold purification. The purified enzyme, termed rPLA(2), has a molecular mass of 42 kDa and reveals biochemical properties similar to group IV cPLA(2), but shows different profiles from cPLA(2) in several column chromatographies. Moreover, rPLA(2) did not react with any of anti-cPLA(2) and anti-sPLA(2) antibodies and was identified as an unknown protein in matrix-assisted laser desorption/ionization time-of-flight mass spectrometric analysis. Divalent metal ions tested exhibited similar effects between rPLA(2) and cPLA(2), whereas mercurials inhibited cPLA(2) but had no effect on rPLA(2). Antibody against the 42-kDa protein not only precipitated the rPLA(2) activity, but also reacted with the 42-kDa protein from bovine and human RBCs in immunoblot analysis. The 42-kDa protein band was selectively detected in murine fetal liver cells known as a type of progenitor cells of RBCs. It was found that EA4, a derivative of quinone newly developed as an inhibitor for rPLA(2), inhibited a Ca(2+) ionophore-induced AA release from human and bovine RBCs, indicating that this enzyme is responsible for the Ca(2+)-dependent AA release from mammalian RBCs. Finally, erythroid progenitor cell assay utilizing diaminobenzidine staining of hemoglobinized fetal liver cells showed that rPLA(2) detectable in erythroid cells was down-regulated when differentiated to non-erythroid cells. Together, our results suggest that the 42-kDa rPLA(2) identified as a novel form of Ca(2+)-dependent PLA(2) may play an important role in hemostasis, thrombosis, and/or erythropoiesis through the Ca(2+)-dependent release of AA.

Osmotic resistance of high-density erythrocytes in transglutaminase 2-deficient mice

Transglutaminase 2 (TGase 2) is a Ca(2+)-dependent enzyme responsible for the posttransttranslational modification of proteins by transamidation of specific polypeptide-bound glutamine residues. Elevating the intracellular concentration of Ca(2+)-ions in human erythrocytes leads to the formation of cytoskeletal and cytoplasmic protein polymers. The Ca(2+)-dependent TGase 2-dependent cross-linking activity has been proposed for its involvement in erythrocyte aging, by inducing irreversible modification of their cell shape and deformability. Accordingly, we found that high-density ("old") TGase 2(minus sign/minus sign) red blood cells (RBCs) were more resistant to osmotic stress-induced hemolysis than those from wild type mice. In addition, elevating the intracellular concentration of Ca(2+) by treatment of total RBCs with ionophore A23187 resulted in enhanced resistance of TGase 2-deficient erythrocytes compared to their normal counterpart. These findings indicate that TGase 2 may have a role in regulating structural flexibility of RBCs, possibly affecting their life span in physiopathological conditions, such as erythrocyte senescence, which are accompanied by increases in intracellular Ca(2+) concentration.

Human mature red blood cells express caspase-3 and caspase-8, but are devoid of mitochondrial regulators of apoptosis

Although proteases of the caspase family are essential mediators of apoptosis in nucleated cells, in anucleate cells their presence and potential functions are almost completely unknown. Human erythrocytes are a major cell population that does not contain a cell nucleus or other organelles. However, during senescence they undergo certain morphological alterations resembling apoptosis. In the present study, we found that mature erythrocytes contain considerable amounts of caspase-3 and -8, whereas essential components of the mitochondrial apoptotic cascade such as caspase-9, Apaf-1 and cytochrome c were missing. Strikingly, although caspases of erythrocytes were functionally active in vitro, they failed to become activated in intact erythrocytes either during prolonged storage or in response to various proapoptotic stimuli. Following an increase of cytosolic calcium, instead the cysteine protease calpain but not caspases became activated and mediated fodrin cleavage and other morphological alterations such as cell shrinkage. Our results therefore suggest that erythrocytes do not have a functional death system. In addition, because of the presence of procaspases and the absence of a cell nucleus and mitochondria erythrocytes may be an attractive system to dissect the role of certain apoptosis-regulatory pathways.

Role of iron in the interaction of red blood cells with methylglyoxal. Modification of L-arginine by methylglyoxal is catalyzed by iron redox cycling

Diabetes mellitus is characterized by increased methylglyoxal (MG) production. The aim of the present study was to investigate the role of iron in the cellular and molecular effects of MG. A red blood cell (RBC) model and L-arginine were used to study the effects of MG in the absence and presence of iron. Intracellular free radical formation and calcium concentration were measured using dichlorofluorescein and Fura-2-AM, respectively. Effects of MG were compared to the effect of ferrous iron. Reaction of L-arginine with MG was investigated by electron spin resonance (ESR) spectroscopy and by a spectrophotometric method. MG caused an iron dependent oxidative stress in RBCs and an elevation of the intracellular calcium concentration due to formation of reactive oxygen species. Results of co-incubation of MG with ferrous iron in the RBC model suggested an interaction of MG and iron; one interaction was a reduction of ferric iron by MG. A role of iron in the MG-L-arginine reaction was also verified by ESR spectroscopy and by spectrophotometry. Ferric iron increased free radical formation as detected by ESR in the MG-L-arginine reaction; however, ferrous iron decreased it. The reaction of MG with L-arginine yielded a brown product as detected spectrophotometrically and this reaction was catalyzed at a lower rate with ferric iron but at a higher rate with ferrous iron. These data suggest that MG causes oxidative stress in cells, which is due at least in part to ferric iron reduction by MG and to the modification of amino acids e.g. L-arginine by MG, which is catalyzed by iron redox cycling.

Temperature transition of human hemoglobin at body temperature: effects of calcium

We studied the effects of calcium ion concentration on the temperature dependence of rheological behavior of human red blood cells (RBCs) and concentrated hemoglobin solutions. Our previous study (G. M. Artmann, C. Kelemen, D. Porst, G. Büldt, and S. Chien, 1998, Biophys. J., 75:3179-3183) showed a critical temperature (Tc) of 36.4 +/- 0.3 degrees C at which the RBCs underwent a transition from non-passage to passage through 1.3 microm micropipettes in response to an aspiration pressure of -2.3 kPa. An increase in intracellular Ca2+ concentration by using the ionophore A23187 reduced the passability of intact RBCs through small micropipettes above T(c); the micropipette diameter needed for >90% passage increased to 1.7 microm. Viscometry of concentrated hemoglobin solutions (45 and 50 g/dl) showed a sudden viscosity transition at 36 +/- 1 degrees C (Tc(eta)) at all calcium concentrations investigated. Below Tc(eta), the viscosity value of the concentrated hemoglobin solution at 1.8 mM Ca(2+) was higher than that at other concentrations (0.2 microM, 9 mM, and 18 mM). Above Tc(eta), the viscosity was almost Ca2+ independent. At 1.8 mM Ca2+ and 36 +/- 1 degrees C, the activation energy calculated from the viscometry data showed a strong dependence on the hemoglobin concentration. We propose that the transition of rheological behavior is attributable to a high-to-low viscosity transition mediated by a partial release of the hemoglobin-bound water.

Nisoldipine improves the impaired erythrocyte deformability correlating with elevated intracellular free calcium-ion concentration and poor glycaemic control in NIDDM

AIMS

To explore the mechanisms underlying the impaired erythrocyte deformability (RBC-df) in diabetic patients, the relationship between erythrocyte intracellular free calcium-ion concentration ([Ca2+]i) and RBC-df, and the effects of Ca2+-channel blocker on [Ca2+]i and RBC-df were evaluated.

METHODS

Forty-eight patients with NIDDM and 24 control subjects were enrolled in this study. [Ca2+]i was determined using fura-2, and RBC-df by filtration method expressed as Deformability Index (DI). Erythrocytes were treated with nisoldipine to evaluate the effects of a Ca2+-channel blocker.

RESULTS

[Ca2+]i was significantly higher (82.6 (78.0-87.2) vs 76.6 (74.3-81.2) nmol lRBC-1, P<0.001), and DI was significantly lower (0. 14 (0.09-0.28) vs 0.22 (0.16-0.28), P<0.01) in NIDDM than in controls. There was a significant correlation between HbA1c and [Ca2+]i (r=0.38, P<0.01), between HbA1c and DI (r=-0.51, P<0.01), and between [Ca2+]i and DI (r=-0.42, P<0.01). Stepwise multiple regression analysis revealed HbA1c and [Ca2+]i as independent determinants for the impaired RBC-df. Nisoldipine treatment in vitro significantly decreased [Ca2+]i, and significantly improved RBC-df.

CONCLUSIONS

These data indicate that the impaired RBC-df in NIDDM may at least partly be attributed to the elevated [Ca2+]i and poor glycaemic control. In addition, favorable effects of a Ca2+-channel blocker on both [Ca2+]i and RBC-df have been demonstrated.

Effects of Ca2+ on erythrocyte membrane skeleton-bound phosphofructokinase, ATP levels, and hemolysis

Erythrocyte Ca2+ overload is known to occur in several different disease states, and to affect the erythrocyte membrane deformability. We show here that an increase in intracellular Ca2+ concentration in erythrocytes, induced by ionomycin, caused a reduction in ATP levels. Concomitant to the fall in ATP, a marked activation of phosphofructokinase (PFK) (EC 2.7.1.11), the rate-limiting enzyme in glycolysis, in the membrane skeleton fraction occurred. The increase in the membrane skeleton-bound PFK activity was most probably mediated by Ca2+, as direct addition of Ca2+ to the membrane skeleton fraction from the erythrocyte induced an enhancement of the bound PFK activity. Time-response curves revealed that erythrocyte hemolysis did not occur during the first 30 min of incubation with ionomycin, when the membrane skeleton-bound PFK was activated. Longer incubation time resulted in solubilization of the membrane skeleton-bound PFK and a concomitant hemolysis of the erythrocytes. These results suggest that the Ca2+-induced activation of membrane skeleton-bound PFK, and thereby glycolysis, the sole source of energy in erythrocytes, may be a defense mechanism to surmount the damage induced by high Ca2+ levels.

Erythrocyte disaggregation shear stress, sialic acid, and cell aging in humans

Erythrocyte aggregation, which plays an important role in the physiological behavior of blood fluidity, was found to be enhanced in hypertension and hypercholesterolemia. While the role of macromolecule bridging force has been widely described, cellular factors related to membrane sialic acid content, which might contribute to the negative charge of cell surface causing the repulsion of erythrocytes, have been less studied. Cell age-dependent changes in membrane sialic acid content (in micromoles per gram of integral membrane protein) were investigated in 24 normotensive and 24 hypertensive matched subjects, each divided into 2 identical subgroups according to a cutoff of 6.2 mmol/L serum cholesterol. A progressive and significant (P<0.001) decrease in membrane sialic acid content associated with an increase (P<0.001) of disaggregation shear rate threshold (laser reflectometry in the presence of dextran) were observed with increased erythrocyte density (erythrocytes fractionated by density using ultracentrifugation) in both normotensive and hypertensive groups regardless of the cholesterol level. However, disaggregation shear rate threshold was significantly higher and sialic acid content was lower (P<0.001) in both hypertensive and normotensive subjects with hypercholesterolemia compared with either normotensive or hypertensive subjects with low cholesterol, respectively. A high membrane sialic acid content variance, beginning in the younger erythrocytes, was due mainly to triglyceride and LDL cholesterol levels (R2=0.49 for low, R2=0.43 for middle, and R2=0.54 for high densities, ie, young, mean, and senescent erythrocytes, respectively). We conclude that an early decrease in erythrocyte sialic acid content may influence the rheological properties of blood by increasing the adhesive energy of erythrocyte aggregates.

Differences in Ca2+ pumping activity between sub-populations of human red cells

It has been shown recently that the free Ca2+ content of human red cells rises during ageing in vivo. With the aim of determining the mechanisms involved in such a change, we have investigated some aspects of Ca2+ homeostasis. Both the initial rate of Ca2+ influx and some kinetic parameters of the Ca2+ pump of human red cells were studied in light and dense sub-populations obtained through stringent, self-formed Percoll gradients. At 37 degrees C and pH 7.4, no differences in Ca2+ entry were found. By contrast, either at pH 7.0 or 7.4, the maximal Ca2+ extrusion rate of the approximately 10% heaviest cells was one-half of the corresponding lighter ones. The results demonstrate that the elevated free Ca2+ concentration distinctive of senescent cells, arises from a reduction in Ca2+ extrusion capacity during ageing. The possible physiological significance of this finding is discussed.

Ionic calcium content of light dense human red cells separated by Percoll density gradients

In this paper we have compared the adequacy of two methods using Percoll density gradients to separate light and dense erythrocytes from fresh human blood. After measuring the distribution of some classical age-markers such as haemoglobin, potassium and creatine contents, it was found that preformed gradients generated more stringent conditions for age-related density separations. Employing such gradients the free Ca2+ content of above sub-populations was assessed with Fura-2, under conditions where the viscosity effect was abolished. In five experiments, the free Ca2+ content (mean value +/- 1 S.D.) was 8.4 +/- 2.82 nM and 31.2 +/- 13.0 nM for the 7-10% lightest and densest cells, respectively. These results are discussed in connection to red cell senescence.

Blood viscosity in chronically hypoxic rats: an effect independent of packed cell volume

We compared apparent blood viscosity, measured with a cone-plate viscometer, in normoxic and chronically hypoxic rats. All comparisons were made at equal packed cell volume (PCV) and shear rate conditions. Apparent viscosity of whole blood from the hypoxic rats was significantly lower than that from normoxic littermates and was similar to that of young rats. Apparent viscosity of red cells from hypoxic rats suspended in phosphate buffered saline remained lower than that from the normoxic rats. When blood cells from the hypoxic rats were suspended in plasma from normoxic rats, apparent viscosity was lower than when blood cells from normoxic animals were suspended in plasma from hypoxic rats. The lower viscosity of the blood from hypoxic rats appears to be associated with characteristics present in newly generated red cells. The reduced apparent viscosity of blood in hypoxic rats may partially compensate for the increase in PCV, at least during the early stages of hypoxia.

Leukocyte modulation inhibits endotoxin-induced disruption of intracellular calcium homeostasis

OBJECTIVE

Sepsis is associated with disruption of intracellular calcium homeostasis. The specific mechanisms responsible for these changes remain unclear. This study attempts to modify endotoxin-induced alterations in erythrocyte intracellular calcium dynamics through modulation of the activated leukocyte and its products.

METHODS

Paired anticoagulated whole-blood specimens were obtained from healthy adult volunteers (n = 30). Specimens were incubated with 2 micrograms/mL endotoxin [lipopolysaccharide (LPS)] or saline control in the presence and absence of the white blood cell. Studies were repeated in specimens pretreated with allopurinol, superoxide dismutase, and pentoxifylline (PTX). After incubation, erythrocytes were separated, washed, and loaded with the fluorescent calcium chelator, FURA-2. Free cytosolic calcium concentration was determined on 10(6) cells using fluorescent spectroscopy. Values were computer-calculated every 1.8 seconds for 1 minute, and mean results were used for analysis. Differences were evaluated by analysis of variance.

RESULTS

The LPS resulted in a significant increase in intracellular calcium concentration (LPS 70.95 nM vs. control 44.04 nM). This increase was dependent on the presence of the white blood cell and could not be induced in its absence (control 30.15 --> LPS 32.78). Pretreatment inhibited these endotoxin-induced alterations: allopurinol, 50.49 nM; superoxide dismutase, 49.12 nM; and PTX, 40.23 nM (p < 0.01).

CONCLUSIONS

Endotoxin induces a significant increase in intracellular calcium concentration. This alteration seems to be mediated by activated neutrophils and can be ameliorated by both leukocyte modulation (PTX) and free radical scavengers.

Effect of sepsis on erythrocyte intracellular calcium homeostasis

OBJECTIVES

To examine erythrocyte intracellular calcium dynamics in clinical sepsis and experimental endotoxemia.

DESIGN

Prospective, multiexperimental study utilizing in vitro manipulation and evaluation of human erythrocytes.

SETTING

University research laboratory.

PATIENTS

Healthy, elective surgical patients, "septic" surgical patients, and normal volunteers.

INTERVENTIONS

For all experimental studies, whole blood specimens were incubated with 2 micrograms/mL of Escherichia coli endotoxin (experimental) or an equivalent volume of phosphate buffered saline (control). Incubations were performed in specimens pretreated with 0.4 mM of verapamil and/or 50 mM of dantrolene. Incubations were performed in the presence and absence of extracellular calcium. Incubations were also performed utilizing pre- and posttreatment with 1 mM of adenosine 5'-triphosphate (ATP) and/or 30 mM of adenosine.

MEASUREMENTS AND MAIN RESULTS

Free cytosolic calcium concentration was determined by fluorescent spectroscopy, utilizing the calcium chelator, FURA-2AM. Sepsis was associated with a significant increase in erythrocyte intracellular calcium concentration as compared with nonseptic controls (96.26 vs. 45.38 nM; p < .001). Similar changes could be induced by endotoxin incubation of whole blood (84.52 vs. 40.45 nM; p < .001). This endotoxin-induced increase was independent of extracellular calcium concentration and was only partially ameliorated by calcium-channel blockade. Inhibition of intracellular calcium release was ineffective in altering the endotoxin-induced increase in the erythrocyte intracellular calcium value. In contrast, pretreatment with either adenosine or ATP minimized these increases. Posttreatment with ATP, but not adenosine, allowed partial reversal of this endotoxin-induced increase in intracellular calcium.

CONCLUSIONS

Sepsis induces alterations of erythrocyte intracellular calcium homeostasis. A significant increase in free cytosolic concentrations of intracellular calcium is characteristic of this altered homeostasis. These changes are reproducible by the incubation of whole blood with endotoxin. This increase in cytosolic calcium concentration appears to be independent of extracellular calcium concentration, transmembrane calcium channels, and/or intracellular calcium stores. It can, however, be modulated through provision of high-energy phosphates and/or their precursors to the cell itself.

Exercise, training and red blood cell turnover

Endurance training can lead to what has been termed 'sports anaemia'. Although under normal conditions, red blood cells (RBCs) have a lifespan of about 120 days, the rate of aging may increase during intensive training. However, RBC deficiency is rare in athletes, and sports anaemia is probably due to an expanded plasma volume. Cycling, running and swimming have been shown to cause RBC damage. While most investigators measure indices of haemolysis (for example, plasma haemoglobin or haptoglobin), RBC removal is normally an extravascular process that does not involve haemolysis. Attention is now turning to cellular indices (such as antioxidant depletion, or protein or lipid damage) that may be more indicative of exercise-induced damage. RBCs are vulnerable to oxidative damage because of their continuous exposure to oxygen and their high concentrations of polyunsaturated fatty acids and haem iron. As oxidative stress may be proportional to oxygen uptake, it is not surprising that antioxidants in muscle, liver and RBCs can be depleted during exercise. Oxidative damage to RBCs can also perturb ionic homeostasis and facilitate cellular dehydration. These changes impair RBC deformability which can, in turn, impede the passage of RBCs through the microcirculation. This may lead to hypoxia in working muscle during single episodes of exercise and possibly an increased rate of RBC destruction with long term exercise. Providing RBC destruction does not exceed the rate of RBC production, no detrimental effect to athletic performance should occur. An increased rate of RBC turnover may be advantageous because young cells are more efficient in transporting oxygen. Because most techniques examine the RBC population as a whole, more sophisticated methods which analyse cells individually are required to determine the mechanisms involved in exercise-induced damage of RBCs.

Glutathione regeneration in calcium-loaded erythrocytes: a possible relationship among calcium accumulation, ATP decrement and oxidative damage

Glutathione (GSH) regeneration was studied in rabbit erythrocytes which were loaded with calcium using ionophore A23187. Calcium-loading induced by A23187 and various concentrations of CaCl2 caused a dose-dependent depression in red cell GSH regeneration. The lowered GSH regeneration was mainly due to reduction of ATP level. In an experiment using haemolysate, the effect of calcium per se was negligible, while magnesium strongly affected GSH regeneration by controlling the rate of hexokinase reaction. These results indicate a possibility that cation perturbation, metabolic decay and oxidative damage are all interrelated in the erythrocyte aging process.

The effect of endotoxin on neonatal erythrocyte intracellular calcium concentration

Erythrocyte membrane deformability is dependent on the maintenance of "normal" intracellular calcium (Ca) levels. Red cell flexibility is known to be altered in the septic neonate. In turn, this adversely affects viscosity and compromises flow in the microcirculation. It has been suggested that this may play a role in the mesenteric hypoperfusion associated with necrotizing enterocolitis. This study was designed to determine the effect of endotoxin on erythrocyte Ca homeostasis in the neonate. Paired specimens were obtained from the umbilical cord of 10 healthy neonates. The samples were incubated with either buffered saline (control) or 2 micrograms/mL of Escherichia coli endotoxin (LPS). Erythrocytes were then isolated, washed, and loaded with the fluorescent Ca chelator, FURA-2. The free cytosolic Ca concentration was determined by spectroscopic analysis of the ratio of fluorescent intensities at 340 nm and 380 nm. Results were obtained every 1.8 seconds for 1 minute, and the mean value was used for analysis. In 10 additional neonates, the white blood cells were removed before incubation in saline and LPS, and the erythrocytes were evaluated as described above. Differences were analyzed statistically by the paired t test. In the presence of white blood cells, endotoxin resulted in a significant increase in free cytosolic Ca concentration (LPS, 42.602 +/- 5.166 nmol; control, 31.661 +/- 4.002 nmol; P < .02). However, no significant difference were detected when cells were incubated in the absence of white blood cells (LPS, 32.374 +/- 2.479 nmol; control, 34.021 +/- 2.549 nmol). Endotoxin induces a significant increase in neonatal free cytosolic Ca concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Erythrocyte Ca2+ handling in the spontaneously hypertensive rat, effect of vanadate ions

Cytosolic Ca2+ concentration ([Ca2+]i) and 45Ca2+ influx were investigated in erythrocytes from conscious spontaneously hypertensive rats (SHR) and their normotensive controls Wistar-Kyoto (WKY). [Ca2+]i was evaluated with fura-2 and intra- and extra-cellular calibration parameters were compared. Irrespective of the calibration parameters used, erythrocyte [Ca2+]i was always significantly higher in SHR than in WKY and Wistar rats (by 25 and 40%, p < 0.01 and 0.001). A rise of the external Ca2+ concentration from 1 to 2 mmol/l increased less [Ca2+]i in SHR than in WKY erythrocytes (17 vs 37%, p < 0.01). SHR erythrocytes incorporated more 45Ca2+ than those from WKY, with an initial rate of 45Ca2+ uptake higher by 57% than that of WKY erythrocytes (p < 0.05). Vanadate ions, after corrections of their quenching effect on red cell and fura-2 fluorescence signals, increased [Ca2+]i by 19% in WKY erythrocytes (p = 0.05), but did not modify the SHR values. They also increased 45Ca2+ accumulation and the initial rate of 45Ca2+ influx in WKY erythrocytes only (p < 0.01). This study indicates that, when compared to WKY rats, erythrocytes from SHR are characterized by higher [Ca2+]i values, higher initial rate of Ca2+ influx and low sensitivity to vanadate ions.

Antioxidant systems and erythrocyte life-span in mammals

1. Erythrocyte antioxidant systems--superoxide dismutase (SOD), catalase (CAT), reduced glutathione (GSH), glutathione peroxidase (GSH-Px), glutathione S-transferase (GST) and glutathione reductase (GR)--were discussed in relation to life-spans in some mammalian species. 2. The erythrocyte life-span of different mammals was found to be correlated with the levels of SOD, GSH-Px and GSH. 3. Data reviewed indicates that the erythrocyte life-span of each species is governed by both the oxygen radical formation and the efficiency of intrinsic antioxidant systems.

Effect of propane-1,2-diol ingestion on carbohydrate metabolism in female rat erythrocytes

This study was undertaken to assess the effect of propane-1,2-diol(PD) ingestion on carbohydrate metabolism in female rat erythrocytes. For this purpose, two different groups of adult albino female rats were treated orally with PD at two different dose levels of 73 and 294 mg 100 g-1 body wt. The blood samples drawn from the retro-orbital sinus prior to the treatment served as the controls, whereas the treated samples were collected at peak periods (1/2 and 2 h) 2 and 7 days after the treatment. A single dose of PD was found to elevate levels of blood glucose, lactate, pyruvate and the lactate/pyruvate ratio at the peak periods (P < 0.001) and after 2 days (P < 0.001) in both the groups. A significant (P < 0.05) increase in the contents of erythrocyte 2,3-diphosphoglycerate (2,3-DPG) was observed only at the peak periods. All these parameters returned to their base level after 7 days of treatment. The activities of hexokinase (HK), 2,3-diphosphoglycerate phosphatase (2,3-DPG Pase), lactate dehydrogenase (LDH), glucose-6-phosphate dehydrogenase (G-6-PD), 6-phosphogluconate dehydrogenase (6-PGD) and aldehyde reductase II (AR II) declined markedly, whereas those of pyruvate kinase (PK) and aldose reductase increased as a result of PD ingestion. The changes in the activities of 2,3-DPG Pase and LDH were persistent up to 8 days post-treatment. The [14C]glucose flux through glycolysis and the hexose monophosphate shunt pathway in erythrocytes was found to be lowered (P < 0.001) in response to PD treatment.(ABSTRACT TRUNCATED AT 250 WORDS)