Spin label study of erythrocyte deformability. Ca2+-induced loss of deformability and the effects of stomatocytogenic reagents on the deformability loss in human erythrocytes in shear flow

Effect of N-ethylmaleimide, chymotrypsin, and H₂O₂ on the viscoelasticity of human erythrocytes: experimental measurement and theoretical analysis

The physiological functions of erythrocytes depend critically on their morphology, deformability, and aggregation capability in response to external physical and chemical stimuli. The dynamic deformability can be described in terms of their viscoelasticity. We applied jumping optical tweezers to trap and stretch individual red blood cells (RBCs) to characterize its viscoelasticity in terms of the Young's modulus and viscosity by analyzing the experimental data of dynamic deformation using a 2-parameter Kelvin solid model. The effects of three chemical agents (N -ethylmaleimide, Chymotrypsin, and Hydrogen peroxide) on RBC's mechanical properties were studied by comparing the Young's modulus and viscosity of RBCs with and without these chemical treatments. Although the effects of each of these chemicals on the molecular structures of RBC may not be exclusive, based on the dominant effect of each chemical, we attempted to dissect the main contributions of different constituents of the RBC membrane to its viscosity and elasticity.

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.

Erythrocyte deformability of nonpregnant, pregnant, and fetal blood

Erythrocyte deformability is an important determinant of microcirculation, of oxygen transport and release to the tissue. In an attempt to clarify the rheological peculiarity during pregnancy, erythrocyte deformability was measured in 10 nonpregnant controls and 10 pairs of mothers and newborns. When the hematocrit of the erythrocyte suspension in dextran solution was adjusted to 35%, the deformability of fetal erythrocytes was significantly higher than maternal blood (P < 0.05), and it was almost similar to that of nonpregnant controls. Erythrocyte deformability was dependent on the hematocrit, and there was an optimal hematocrit value at which the deformability was maximal. The hematocrit, where the deformability was maximal, was a lower value (32-35%) in maternal blood, conversely, a higher value (47-50%) in cord blood than that (40-43%) in the nonpregnant. Despite decreased deformability of maternal erythrocytes, it may be compensated by reducing the hematocrit (hemodilution), preserving effective peripheral circulation including uteroplacental perfusion. On the other hand, the deformability of fetal erythrocytes may be higher in vivo at the hematocrit of 47-50% to supply oxygen to the fetal tissue even in a low oxygen condition.

The effect of flunarizine on erythrocyte suspension viscosity under conditions of extreme hypoxia, low pH, and lactate treatment

Flunarizine is a class IV calcium channel blocker which increases oxygen delivery to hypoxic regions in solid tumours, exerting a radiosensitising effect in vivo in animal tumour models. Precisely how the drug improves oxygenation is not well understood. We hypothesised that metabolic conditions present within solid tumours reduce red blood cell (RBC) deformability and that flunarizine exerts its in vivo effect by preventing this loss of RBC deformability. A microrheometer was used to compare the viscosity of rat and human RBC suspensions in conditions of hypoxia (pO2 < 10 mmHg), acidic environment (pH 6.8), and elevated lactate concentration (lactate 5 mMol l-1), without or with flunarizine at concentrations of 5, 10, and 50 mg l-1. The effects of flunarizine on RBC density and morphology were also recorded. Hypoxia, low pH, and lactate exposure together increased both human and rat RBC suspension viscosity. Flunarizine at concentrations of 5 and 10 mg l-1 prevented the increases in viscosity. The drug caused dose-dependent shifts toward lower cell density while inducing a characteristic cupped shape (stomatcytic morphology), suggesting a mechanism involving calmodulin inhibition. The results support the hypothesis that flunarizine improves tumour blood flow and oxygenation by enhancing flow properties of RBC's in solid tumours.

Changes of hemorheologic properties during normal human pregnancy

To investigate alterations of hemorheologic properties during pregnancy, we measured the hematocrit (Hct) and fibrinogen levels, blood viscosity, and erythrocyte deformability in 10 healthy nonpregnant women and in 10 women with uncomplicated pregnancies. The Hct decreased during pregnancy, while the plasma fibrinogen concentration was elevated. No significant changes in blood viscosity were observed throughout pregnancy. Erythrocyte deformability was significantly decreased in pregnancy when compared to the nonpregnant state, but returned to the nonpregnant level by the 7th postpartum day. These findings suggest that adequate microcirculation is maintained in the uteroplacental unit during gestation by hemodilution, which prevents an elevation of blood viscosity despite the increase in fibrinogen and the decrease of erythrocyte deformability. These changes are thus thought to be among the physiological maternal adaptations to fetal growth and development.

A flow EPR study of deformation and orientation characteristics of erythrocyte ghosts: effects of lysing and resealing conditions

The effects of various conditions in lysing and resealing the red cell membrane on the degree of ghost deformation and orientation in flow are investigated using the flow EPR and spin-label method. The relatively low deformability of the standard ghost, which is lysed and resealed, respectively, in hypotonic and isotonic NaCl-Tris buffer, is markedly enhanced by the presence of Mg-ATP, chlorpromazine, or Ca2+ ion during resealing. The effect is concentration dependent, and there is an optimal level for each treatment. Chlorpromazine and Ca2+ are also effective when added to the resealed ghosts. Mg2+ ion shows an opposite effect reducing the ghost deformability in flow at all concentrations. An isotonic lysis in NH4HCO3 solution with less osmotic stress substantially raises ghost deformability above that of the standard ghosts. These results are interpreted on the basis of a misalignment between the bilayer leaflets that is probably brought about during hypotonic lysis and its recovery to the nearly normal bilayer state by the agents used during or after resealing. The novel finding of deformability enhancing effect of calcium is assumed to be caused by the electrostatic expansion of the inner layer relative to the outer leaflet. The explanations are supported by the resealed ghost shapes observed before and after the treatments; shape recovery from the monoconcave spheroid toward biconcave discoid is observed in most cases concomitantly with improvements of flow characteristics.