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Biomedical subjects

D Lerche

Publications and source records attributed to D Lerche.

At least 55 records · Page 3Linked to original sources
PubMed1987

Topo-optical investigations of human erythrocyte glycocalyx conformational changes induced by dextran.

Cell surface properties are involved in the aggregation process of red blood cells. Using the topo-optical toluidine blue reaction, conformational changes of the glycocalyx (main component glycophorin A) were found when red blood cells were incubated and fixed in the presence of dextran. Relative differences in optical path as a measure of red blood cell membrane anisotropy decreased in relation to dextran concentration during fixation. These conformational changes could not be detected by electrophoretic measurements. When incubating, fixing and staining red blood cells in the presence of dextran, anisotropy decreased only at low dextran concentrations and increased at rising dextran concentrations. This biphasic course of differences in optical path seems to be due to different effects of dextran superimposing upon each other: a disturbing influence on the spatial order of sialic acid carrying oligosaccharide side chains due to H-bond interaction, and an increase in the size of dye aggregates and suppression of the thermal motion of macromolecules at higher dextran concentrations.

Dextrans↗
PubMed1987

Electrostatic free energy and spontaneous curvature of spherical charged layered membrane.

A biophysical model for the equilibrium curvature of a composite membrane element is derived taking into account the mechanical bilayer properties and the adjacent charged protein layers. The minimum of the total free energy density with respect to the curvature of such a membrane curved was estimated from the sum of the electrostatic free energy density of the charges of the membrane and the elastic surface energy density due to bending the lipid bilayer membrane. It was shown that the equilibrium curvature, i.e. the spontaneous curvature, of such a charged composite sandwich-like membrane depends inversely on the bending stiffness of the lipid membrane itself and directly on the charge amount inside and outside the membrane to the second power. Furthermore the geometric and electrostatic structure of the protein layers and the physico-chemical environment conditions are involved. Corresponding to the model developed a "standard RBC" membrane element has a negative spontaneous curvature, accounting for a discocyte RBC shape. The shape change from a discocyte to a more stomatocytic shape (increase in the negative spontaneous curvature) after reducing the charges in the glycocalyx is also explained within this model.

Biophysical Phenomena↗
PubMed1987

Fission and refusion of red blood cells using a micropipette technique.

In micropipette experiments with small capillaries and moderate high pressure difference (approximately 1000 Pa) cell fragmentation (fission) of human red blood cells without hemolysis was observed by TV-system for a large number of fresh red blood cells of different donors. After separation, the fragment moves away from the residual cell. In seven cases this process was evaluated quantitatively and was shown that the rate of the fragment was constant in time. Two mechanisms for this phenomenon are discussed. In particular cases a spontaneous re-fusion with the residual cell body in the capillary can be observed. In our opinion probably protein-depleted membrane surfaces arise and membrane fusion is possible simply by mechanical contact without additional electric fields and/or fusion agents.

Cell Separation↗
PubMed1987

Deformability investigations of erythrocytes stored at different temperatures.

The deformability changes of erythrocytes stored at different temperatures were characterized by a filtration procedure. The filterability index (FI) of erythrocytes cryopreserved at either -196 degrees C or -28 degrees C increased (deformability decreased) by about 9% and 40% respectively. For comparison with the cryopreserves the filterability of erythrocytes stored in liquid state at +4 degrees C were investigated. The filterability changes are discussed in comparison with the changes of MCHC during storage.

Blood Preservation↗
PubMed1987

Deformability characterization of erythrocytes stored in different resuspension media.

The deformability changes of erythrocytes during 35 days of storage in different resuspension media were characterized by a filtration procedure. The filterability of erythrocytes stored in CDS-AG medium decreased drastically, whereas the filterability of erythrocytes stored in SAGM and SAGS medium decreased only slightly. The MCHC change of stored erythrocytes were discussed in relation to filterability effects.

Blood Preservation↗
PubMed1987

Deformability of human red blood cells stored for different periods at subzero temperatures.

Deformability changes of human red blood cells (RBC) stored for different periods at +4 degrees C, -28 degrees C and -196 degrees C were characterized by a filtration procedure. The filterability index (FI) of RBC stored at -196 degrees C increased (deformability decreased) by about 8%, whereas FI of RBC, liquid stored at +4 degrees C as whole blood, increased by about 25%. In contrast to both the FI of RBC cryopreserved at -28 degrees C for different periods showed an increase of about 40% after 62 days and seemed to be constant for some further months (up to 240 days). A further FI increase was measured after 485 days. Mean cellular hemoglobin concentration changes during storage are excluded to be the cause for deformability loss in this case. An estimation illustrates the osmotic effect of the residual glycerol content after routine deglycerolization procedure and the differences of osmotic and ionic strength effects on RBC deformability in stored blood.

Blood Preservation↗
PubMed1987

Investigations on the deformability of human red blood cells stored in different preservative solutions: influence of changed medium composition.

In continuation of a former paper (W. Kucera, G. Wegner, D. Lerche: Biomed. Biochim. Acta 44, 1459 to 1467, 1985) the deformability changes of human red blood cells (RBC) during 35 days of storage in different resuspension media of changed composition were characterized by a filtration procedure. The filterability of RBC stored in CDS-AG medium (high sucrose content) decreased drastically (increase of the filterability index to more than the 6-fold). This deformability loss is caused by an increase of the internal viscosity (at least 4-fold) due to shrinkage of red blood cells by more than 20% as an effect of low ionic strength. In contrast, the filterability loss of RBC stored in SAGM medium was slight. The cell volume showed a slight increase with unchanged mean cellular hemoglobin concentration. By changing the composition of CDS-AG medium by reduction of the sucrose content from 234 mM to 30 mM and addition of 150 mM NaCl (SAGS medium) the drastic deformability loss was avoided. From the viewpoint of deformability this SAGS medium is comparable to the internationally accepted SAGM resuspension medium.

Blood Preservation↗
PubMed1987

Membrane elastic shear modulus of red blood cells with glucose-6-phosphate dehydrogenase and pyruvatekinase enzymopathies.

The membrane elastic shear modulus mu determined by a micropipette technique was found to be elevated by 25% to 200% for red blood cells (RBC) from 7 patients with glucose-6-phosphate dehydrogenase (G-6-PD) and 9 patients with pyruvate-kinase (PK) enzymopathies above the mean value for normal controls. All patients exhibit chronic nonspherocytic hemolytic anemias. A negative linear correlation (r = -0.72) between mu and the number of reticulocytes was obtained in G-6-PD deficiencies. In contrast, a positive correlation (r = 0.88) was found for red blood cells of patients with PK deficiency. A mechanically induced swelling of RBC was observed for some deficient cells. The results are discussed in the framework of structural alterations of the RBC membrane due to the disturbed pentose-phosphate pathway and the diminished ATP supply through glycolysis, respectively.

Elasticity↗
PubMed1986

[Deformability of stored erythrocytes as a criteria for their in vivo survival rate].

The loss of deformability observed in erythrocytes stored as whole blood for 36 days (ACD-AG) or as buffy-coat free erythrocyte concentrate (EK) was characterized by measuring their filterability. During the first 3 weeks the index of filterability for ACD-AG erythrocytes increased only slightly and rose to about 140% of its initial value on the 36th day. In contrast, a heavy loss of deformability (increase of the filterability index to more than 600%) was detected for erythrocytes from EK, which, from a rheological point of view, is apt to raise doubts of using this stored blood. An incubation of 1 hour at 37 degrees C in fresh plasma did not result in improving the deformability. A cell volume loss of more than 20% connected with an increase of the inner viscosity to more than 400% was found to be the cause of this decrease of deformability. These rheological differences are also reflected in the 24 hours in vivo survival rate (SR), if the "early loss" of damaged erythrocytes immediately after transfusion is taken into account. Whereas the SR values of 80% for whole blood erythrocytes do not change significantly, the SR values for EK values can be found to reach 54% approximately.

Blood Transfusion↗
PubMed1986

[Influence of heat-induced changes in the mechanical properties of the membrane on the filterability of human erythrocytes].

The influence of heat induced changes of mechanical membrane properties of human erythrocytes on their filterability was investigated. A 10-minute incubation at 47, 48 and 48.4 degrees C, respectively, leads to an increase of elastic membrane shear modulus (up to 130%, 240%, 260%) and membrane viscosity (up to 220%, 380%, 480%). In comparison to these effects the filterability determined by cellulose filters was diminished relatively slightly (increase of filterability index up to 110%, 130%, 170%), with the mean erythrocyte volume remaining unchanged. Taking into account former investigations it is concluded that the used filtration technique is less sensitive with respect to changes of the elastic and viscous membrane properties compared with changes of cytoplasmic viscosity of the cells.

Blood Viscosity↗
PubMed1985

Cell surface alterations during blood-storage characterized by artificial aggregation of washed red blood cells.

Aggregation measurement of washed human erythrocytes (RBC) were carried out in a NaCl-PBS solution under laminar shear conditions. Artificial aggregation of fresh and stored erythrocytes was caused by decreased pH and reduced ionic strength and characterized by collision efficiency alpha. Generally, the collision efficiency alpha of stored erythrocytes rises with the increased storage time. Such an aggregation technique might be useful to detect and quantify changes of the membrane and/or the surface structure due to aging and/or storage.

Blood Preservation↗
PubMed1985

Investigations on the deformability of human red blood cells stored in different preservative solutions.

Deformability changes of red blood cells stored either as whole blood or as different resuspensions in sucrose-free or sucrose-containing media were characterized by measuring red cell filterability during 36 days of storage. For whole blood and SAG-resuspensions only a slight increase of the filterability index was observed during the first 3 weeks; after 36 days it was elevated 1.4-fold (whole blood) and 1.8-fold (SAG-resuspension). In contrast, a strong deformability loss (increase of the filterability index to more than the 6-fold) was observed for red blood cells stored in sucrose-containing CDS-AG medium. This deformability loss is caused by an increase of the internal viscosity (at least 4-fold) due to the shrinkage of red blood cells by more than 20%. After incubation for 1 h in fresh plasma no changes of filterability could be found. The in vivo behavior of such rigid cells is discussed with regard to references about the posttransfusion survival.

Blood Preservation↗
PubMed1984

Moderate heat treatment of only red blood cells (RBC) slows down the rate of RBC-RBC aggregation in plasma.

Rouleau formation by back scattered light and flow behaviour by viscometry of heat-treated (48.4, 48.8 and 49.5 degrees C) and normal (37 degrees C) human red blood cells (RBC) were investigated. Washed RBC were treated in PBS and afterwards resuspended in their own plasma. It was found that the time behaviour of the fibrinogen mediated weak RBC-RBC interaction is influenced (decreased) already at an incubating temperature of 48.4 degrees C. Kinetic measurements are more sensitive than a static aggregation characterization. Beside the decreased deformability of the RBC also a heat-altered structure of the RBC-glycocalyx and the aggregating energy of the macromolecules have to be considered.

Blood Viscosity↗