Biomedical subjects

H J Meiselman

Publications and source records attributed to H J Meiselman.

At least 19 recordsLinked to original sources

PubMed2006

Hemorheological parameters as determinants of myocardial tissue hematocrit values.

It is well known that the hematocrit in microvessels with diameters smaller than 1000 microm is lower than either venous or arterial hematocrit, thereby resulting in significantly lower mean hematocrit values for vessels perfusing a given tissue (i.e., lower tissue hematocrit). The mechanisms that underlie this reduction of microvascular hematocrit include axial migration, plasma skimming and the Fahraeus Effect. It has been previously demonstrated in rats that a linear hematocrit gradient normally exists through the thickness of the left ventricular myocardium, and that this gradient is sensitive to alterations of the rheological properties of the circulating blood. The gradient is abolished if the RBC in the perfusate are rigid; fibrinogen infusions, and thus increases of both plasma viscosity and RBC aggregation, also affect this gradient. In a new series of studies, it has been observed that enhanced RBC aggregation affects the myocardial hematocrit gradient regardless of alterations of plasma viscosity. Although the exact mechanisms responsible for the myocardial hematocrit gradient, as well as its physiological significance, are not yet clearly known, it is possible to speculate that alterations in local hematocrit could adversely affect myocardial perfusion and function.

Animals↗

PubMed2005

An automated tube-type blood viscometer: validation studies.

The technical complexity of previous rheometers has tended to limit the availability of blood viscosity data obtained over a wide range of shear rates. However, an automated tube-type viscometer, the Rheolog, has been developed; it employs a disposable flow assembly and less than five minutes are required to obtain blood viscosity results over a shear rate range of 1-1500 s(-1). We have carried out validation studies of the Rheolog using normal human blood and have compared these results with those obtained by cone-plate and Couette viscometers; storage time and temperature effects were also evaluated. Replicate measurements indicated mean CV levels less than 5%, and were independent of hematocrit and shear rate. Rheolog blood viscosity data agreed closely with those from other viscometers: average Rheolog differences from mean cone-plate and Couette values were -0.3% at 28% hematocrit, -1.4% at 41% hematocrit (i.e., native), and 1.0% at 56% hematocrit. Storage at room temperature up to 8 hours and at 4 degrees C up to 4 days had minimal effects whereas notable changes were observed when stored for 3 hours at 37 degrees C. Our results indicate that, within the hematocrit and shear rate limits employed herein, the Rheolog provides rapid, accurate and reproducible blood viscosity data, and suggest its usefulness for both basic science and clinical studies.

Adult↗

PubMed2004

The hydrodynamic radii of macromolecules and their effect on red blood cell aggregation.

The effects of nonionic polymers on human red blood cell (RBC) aggregation were investigated. The hydrodynamic radius (Rh) of individual samples of dextran, polyvinylpyrrolidone, and polyoxyethylene over a range of molecular weights (1,500-2,000,000) were calculated from their intrinsic viscosities using the Einstein viscosity relation and directly measured by quasi-elastic light scattering, and the effect of each polymer sample on RBC aggregation was studied by nephelometry and low-shear viscometry. For all three polymers, despite their different structures, samples with Rh <4 nm were found to inhibit aggregation, whereas those with Rh >4 nm enhanced aggregation. Inhibition increased with Rh and was maximal at approximately 3 nm; above 4 nm the pro-aggregant effect increased with Rh. For comparison, the Rh of 12 plasma proteins were calculated from literature values of intrinsic viscosity or diffusion coefficient. Each protein known to promote RBC aggregation had Rh >4 nm, whereas those with Rh <4 nm either inhibited or had no effect on aggregation. These results suggest that the influence of a nonionic polymer or plasma protein on RBC aggregation is simply a consequence of its size in an aqueous environment, and that the specific type of macromolecule is of minor importance.

Blood Viscosity↗

PubMed2004

Conductometric study of shear-dependent processes in red cell suspensions. II. Transient cross-stream hematocrit distribution.

A novel experimental approach based on electrical properties of red blood cell (RBC) suspensions was applied to study the effects of the size and morphology of RBC aggregates on the transient cross-stream hematocrit distribution in suspensions flowing through a square cross-section flow channel. The information about the effective size of RBC aggregates and their morphology is extracted from the capacitance (C) and conductance (G) recorded during RBC aggregation, whereas a slower process of particle migration is manifested by delayed long-term changes in the conductance. Migration-induced changes in the conductance measured at low shear rates (< or =3.1 s(-1)) for suspensions of RBCs in a strongly aggregating medium reveal an increase to a maximum followed by a decrease to the stationary level. The ascending branch of G(t) curves reflects the aggregate migration in the direction of decreasing shear rate. A further RBC aggregation in the region of lower shear stresses leads to the formation of RBC networks and results in the transformation of the rheological behavior of suspensions from the thinning to the thickening. It is suggested that the descending branches of the G(t) curves recorded at low shear rates reflect an adjustment of the Hct distribution to a new state caused by a partial dispersion of RBC networks. For suspensions of non-aggregating RBCs it is found that depending on whether the shear rate is higher or lower compared with the prior value, individual RBCs migrate either toward the centerline of the flow or in the opposite direction.

Conductometry↗

PubMed2004

Influence of cell-specific factors on red blood cell aggregation.

The reversible aggregation of red blood cells (RBC) into linear and three-dimensional structures continues to be of basic science and clinical interest: RBC aggregation affects low shear blood viscosity and microvascular flow dynamics, and can be markedly enhanced in several clinical states. Until fairly recently, most research efforts were focused on relations between suspending medium composition (i.e., protein levels, polymer type and concentration) and aggregate formation. However, there is now an increasing amount of experimental evidence indicating that RBC cellular properties can markedly affect aggregation, with the term "RBC aggregability" coined to describe the cell's intrinsic tendency to aggregate. Variations of aggregability can be large, with some changes of aggregation substantially greater than those resulting from pathologic states. The present review provides a brief overview of this topic, and includes such areas as donor-to-donor variations, polymer-plasma correlations, effects of RBC age, effects of enzymatic treatment, and current developments related to the mechanisms involved in RBC aggregation.

Adult↗

PubMed2003

Decreased red blood cell aggregation subsequent to improved glycaemic control in Type 2 diabetes mellitus.

AIMS: Reports of rheological changes following intensification of metabolic control are limited and not concordant. The present study was designed to test the hypothesis that intensification of management of Type 2 diabetes (T2DM) with diet, exercise and insulin improves haemorheological behaviour by reducing red blood cell (RBC) aggregation. METHODS: Blood was sampled from 55 subjects before and following 14 +/- 3 weeks of intensified management. RBC aggregation was measured in vitro for cells in plasma or in an aggregating 70 kD dextran solution. Plasma viscosity and whole blood viscosity were also measured. RESULTS: During treatment, fasting glucose fell 27%, HbA1c fell 21%, and serum triglycerides and total cholesterol fell 28% and 12%, respectively (P < 0.0001 for each). The extent and strength of RBC aggregation in plasma fell by 10-13% (P < 0.002). Similar decreases of RBC aggregation were seen for cells suspended in dextran (P < 0.002). Plasma viscosity decreased by 3% (P < 0.02) and high shear blood viscosity by 6-7% (P < 0.0001). Changes of RBC aggregation in plasma and in dextran were significantly correlated, supporting a cellular rather than a plasmatic origin for these changes. However, there were no significant correlations between RBC aggregation changes and changes of fasting glucose, HbA1c, serum triglycerides, serum cholesterol, or plasma fibrinogen. CONCLUSIONS: Intensified metabolic control results in a reduction of RBC aggregation that appears to be intrinsic to RBC. Since increased RBC aggregation can impair microcirculatory flow, it is possible that haemorheological factors may contribute to the reduction of microvascular complications resulting from improved metabolic control in T2DM.

Adult↗

PubMed2001

Polyethylene glycol-coated red blood cells fail to bind glycophorin A-specific antibodies and are impervious to invasion by the Plasmodium falciparum malaria parasite.

This study was designed to assess the binding of glycophorin A-specific antibodies to polyethylene glycol (PEG)-modified red blood cells (RBCs) and evaluate their resistance to invasion by Plasmodium falciparum malaria parasites. RBCs were conjugated with a range of concentrations (0.05 to 7.5 mM) of activated PEG derivatives of either 3.35 or 18.5 kd molecular mass. The binding of glycophorin A-specific antibodies was assessed by hemagglutination and flow cytometry. PEG-modified RBCs were assessed for their ability to form rosettes around Chinese hamster ovary (CHO) cells transiently expressing the glycophorin A binding domain of EBA-175, a P falciparum ligand crucial to RBC invasion. PEG-RBCs were also tested for their ability to be invaded by the malaria parasite. RBCs coated with 3.35 and 18.5 kd PEG demonstrated a dose-dependent inhibition of glycophorin A-specific antibody binding, CHO cell rosetting, and P falciparum invasion. These results indicate that glycophorin A epitopes responsible for antibody and parasite binding are concealed by PEG coating, rendering these cells resistant to P falciparum invasion. These studies confirm the effectiveness of PEG modification for masking RBC-surface glycoproteins. This may provide a means to prevent alloimmunization in the setting of RBC transfusion and suggests a novel method to enhance the effectiveness of exchange transfusion for the treatment of cerebral malaria.

Animals↗

PubMed2001

A new, pluronic-based, bone hemostatic agent that does not impair osteogenesis.

OBJECTIVE: Intraoperative bone hemostasis can be accomplished using surgical beeswax (bone wax). However, bone wax locally interferes with osteogenesis, and its use is avoided when bone fusion is critical. We describe the use of a Pluronic copolymer blend as a biocompatible, absorbable, hemostatic agent. METHODS: A rat femur defect model and a femur gap nonunion model were used. For each surgical model, 24 rats were divided into three treatment groups, i.e., those receiving bone wax implants, Pluronic (90% Pluronic P85/10% Pluronic F88) implants, or no implants (control group). After 10, 21, or 42 days, animals were killed and femora were removed for radiographic analysis and hematoxylin and eosin staining. RESULTS: In the femur defect model, no differences were observed between the Pluronic-treated and control groups; hematoxylin and eosin staining demonstrated bone formation and osteocytes within the defect. In the femur gap nonunion model, no fusions occurred in any group. Development of an osseous callus at the gap site was observed for the control and Pluronic-treated groups. In both models, rats that received bone wax implants exhibited no osseous growth. CONCLUSION: The Pluronic blend exhibits handling properties similar to those of bone wax, readily achieves hemostasis, and does not inhibit bone regrowth. Pluronic compounds may serve as effective absorbable hemostatic agents for the treatment of bone bleeding in sites where fusion is critical. In addition, this copolymer blend may find use as a vehicle for the short-term release of pharmacological agents, which may further reduce the incidence of infections, reduce inflammation, and improve fusion rates.

Absorbable Implants↗

PubMed2001

Gel-filtration of sickle erythrocytes: separation based on cell deformability.

UNLABELLED: Filtration of red blood cells (RBC) through columns of pre-swollen agarose-based beads has been evaluated using cells from subjects with sickle cell disease. Elution profiles from these gels showed elution times close to normal controls for a large fraction of sickle erythrocytes and a prolonged elution time for a sub-population of these cells. Analysis of red blood cell deformability using a computerized micropore filtration system (CTA) indicated that the deformability of sickle red blood cells in the first fraction was similar to controls but that the last fraction contained a sub-population of rigid RBC. We thus conclude that sickle red blood cell separation in columns of agarose-based beads is based upon cell deformability. Gel filtration therefore appears to be an interesting tool for the study of red blood cells in a variety of disorders with sub-populations of rigid, abnormal cells, and seems especially suited for studies in various sickle cell diseases. KEYWORDS: Deformability, gel filtration, sickle cell disease, erythrocyte

Anemia, Sickle Cell↗

PubMed2001

Electrophoretic and aggregation behavior of bovine, horse and human red blood cells in plasma and in polymer solutions.

The electrophoretic mobility of native and glutaraldehyde-fixed bovine, human, and horse red blood cells (RBC) was investigated as a function of ionic strength (5-150 mM) and concentration of 464 kDa dextran (2 and 3 g/dl); RBC aggregation in autologous plasma and in dextran solutions was also measured. In agreement with previous observations, human and horse RBC form stable rouleaux whereas bovine RBC do not aggregate in either plasma or in dextran 464 kDa solutions. Electrophoretic measurements showed a species-dependent adsorption and depletion of dextran that can be theoretically evaluated. Adsorption of polymer is not a prerequisite for RBC aggregation (bovine RBC show the highest amount of adsorbed dextran yet do not aggregate). Aggregate formation thus occurs as long as the Gibbs free energy difference, given by the osmotic pressure difference between the bulk phase and the polymer-depleted region between two RBC, is larger than the steric and electrostatic repulsive energy contributed by the macromolecules present on the RBC surface. With increasing bulk-phase polymer concentration the depletion layer thickness decreases and the amount of adsorbed macromolecules increases, thereby resulting in an increase of the repulsive component of the interaction energy and decreased aggregation. We thus view electrophoretic measurements of RBC in various media as an important tool for understanding polymer behavior near the red cell surface and hence the mechanisms involved in RBC aggregation.

Adult↗

PubMed2001

Aggregation of human RBC in binary dextran-PEG polymer mixtures.

The present study was prompted by prior reports suggesting that small polymers can affect RBC aggregation induced by large macromolecules. Human RBC were washed and re-suspended in isotonic buffer solutions containing 72.5 kDa dextran (DEX 70, 2 g/dl) or 35.0 kDa poly(ethylene glycol) (PEG 35, 0.35 g/dl), then tested for aggregation in these solutions with and without various concentrations of smaller dextrans (10.5 and 18.1 kDa) or PEGs (3.35, 7.5 and 10.0 kDa). RBC aggregation was measured at stasis and at low shear using a photometric cone-plate system (Myrenne Aggregometer) and RBC electrophoretic mobility (EPM) in the various polymer solutions via an automated system (E4, HaSoTec GmbH). Our results indicate: (1) a heterogeneous effect with greater reduction of aggregation for small PEGs added to DEX 70 or for small dextrans added to PEG 35 than for small polymers of the same species; (2) for cells in DEX 70, aggregation decreased with increasing molecular mass and concentration of the small dextrans or PEGs; (3) for cells in PEG 35, small dextrans decreased aggregation with increasing molecular mass and concentration, whereas small PEGs had minimal effects with a minor influence of concentration and an inverse association between molecular mass and inhibition of aggregation. RBC EPM results indicated the expected polymer depletion for cells in DEX 70 or PEG 35, and that small PEGs yielded greater EPM values than small dextrans for cells in PEG 35 whereas the opposite was true for cells in DEX 70. Interpretation of our results in terms of the depletion model for RBC aggregations appears appropriate, and our findings are consistent with the assumption that inhibition of aggregation occurs because of an increase of small molecules in the depletion region. Our results thus suggest the merit of further studies of red blood cell aggregation in binary polymer systems.

Adult↗

PubMed2001

Modulation of red blood cell aggregation and blood viscosity by the covalent attachment of Pluronic copolymers.

Despite many years of research, the physiologic or possible pathologic significance of RBC aggregation remains to be clearly determined. As a new approach to address an old question, we have recently developed a technique to vary the aggregation tendency of RBCs in a predictable and reproducible fashion by the covalent attachment of nonionic polymers to the RBC membrane. A reactive derivative of each polymer of interest is prepared by substitution of the terminal hydroxyl group with a reactive moiety, dichlorotriazine (DT), which covalently bonds the polymer molecule to membrane proteins. Pluronics are block copolymers of particular interest as these copolymers can enhance or inhibit RBC aggregation. Pluronics exhibit a critical micellization temperature (CMT): a phase transition from predominantly single, fully hydrated copolymer chains to micelle-like structures. The CMT is a function of both copolymer molecular mass and concentration. This micellization property of Pluronics has been utilized to enhance or inhibit RBC aggregation and hence to vary low-shear blood viscosity. Pluronic-coated RBCs were prepared using reactive DT derivatives of a range of Pluronics (F68, F88, F98 and F108) and resuspended in autologous plasma at 40% hematocrit. Blood viscosity was measured at a range of shear rates (0.1-94.5 s(-1)) and at 25 and 37 degrees C using a Contraves LS-30 couette low shear viscometer. RBC aggregation and whole blood viscosity was modified in a predictable manner depending upon the CMT of the attached Pluronic and the measurement temperature: below the CMT, RBC aggregation was diminished; above the CMT it was enhanced. This technique provides a novel tool to probe some basic research questions. While certainly of value for in vitro mechanistic studies, perhaps the most interesting application may be for in vivo studies: typically, intravital experiments designed to examine the role of RBC aggregation in microvascular flow require perturbation of the suspending plasma to promote or reduce aggregation (e.g., by the addition of dextran). By binding specific Pluronics to the surface, we can produce RBCs that intrinsically have any desired degree of increased or decreased aggregation when suspended in normal plasma, thereby eliminating many potential artifacts for in vivo studies. The copolymer coating technique is simple and reproducible, and we believe it will prove to be a useful tool to help address some of the longstanding questions in the field of hemorheology.

Blood Viscosity↗

PubMed2001

Electrophoretic mobility of human red blood cells coated with poly(ethylene glycol).

Poly(ethylene glycol), abbreviated as PEG, was covalently attached to the surface of human red blood cells (RBC) and the effects of such coating on the regions near the cell's glycocalyx were explored by means of cell electrophoresis. RBC electrophoretic mobilities were measured, in polymer-free buffers of various ionic strengths, as functions of PEG molecular mass (3.35, 18.5, 35.0, 35.9 kDa), geometry, (linear or 8-arm branched) and polymer/RBC ratio during attachment. The results indicate marked decreases of the mobility (up to 85%) which were affected by polymer molecular mass and geometry. Since PEG is neutral and its covalent attachment only removes positively-charged amino groups on the cell membrane, such decreases of mobility likely reflect structural changes near and within the RBC glycocalyx. Experimental results were analyzed using an extended "hairy sphere" model to consider friction and thickness of the polymer layer. Calculated polymer layer thickness increased with molecular mass for linear PEGs and was less extended for a branched PEG of similar molecular mass. Friction within the polymer layer increased with polymer/RBC ratio and for the linear PEGs was inversely related to molecular mass; friction was greatest for the branched PEG. Our results are consistent with the effects of attached PEGs on RBC aggregation and surface antigenic site masking, and suggest the usefulness of electrophoretic mobility techniques for studies of bound neutral polymers.

Electrophoretic Mobility Shift Assay↗

PubMed2001

Red blood cell rheological alterations in a rat model of ischemia-reperfusion injury.

Red blood cell (RBC) deformability and aggregation characteristics were investigated in an experimental model of ischemia-reperfusion injury. Ischemia was produced in rat hind limb by occluding the femoral artery for 10 minutes, followed by reperfusion. Blood samples were obtained either following the ischemia or 15 minutes after reperfusion. RBC deformability measured by ektacytometry was found to be significantly impaired immediately after the end of ischemic period in the blood samples obtained from femoral vein of the ischemic limb, while there was no significant difference after 15 minutes of reperfusion. In contrast, RBC aggregability was found to be decreased only after the reperfusion period and this alteration was not only limited to the blood returning from the ischemic limb but was also observed in the samples obtained from non-ischemic, contralateral hind limb, indicating a systemic alteration. RBC electrophoresis studies suggested that the altered aggregability might be related to altered RBC surface properties including increased RBC surface charge density.

Analysis of Variance↗

PubMed2000

Ineffective erythropoiesis in beta-thalassemia major is due to apoptosis at the polychromatophilic normoblast stage.

Beta-thalassemia major is characterized by ineffective erythropoiesis, although it is difficult to define the dynamics of this process from the static information revealed by analysis of bone marrow (BM) aspirates. We aimed to study the kinetics of sequential erythroid differentiation in beta-thalassemia major. We isolated the progenitor cells (CD34(+) and CD34(+)CD38(-) cells) from BM of thalassemia major patients and studied in vitro erythropoiesis. This is the first report of an in vitro study in human beta-thalassemia major from purified BM CD34(+) progenitor cells, using erythroid culture conditions, which allow unilineage differentiation to mature enucleated red blood cells. In contrast to normal donors, a high proportion of BM CD34(+) and CD34(+)CD38(-) progenitors from beta-thalassemia major coexpressed the late erythroid lineage-specific protein glycophorin A and generated a higher proportion of erythroid colonies. However, despite the marked increase in erythroid clonogenicity of the progenitor population, erythroid cultures initiated from beta-thalassemia major BM CD34(+) cells expanded 10- to 20-fold less than from normal BM. There were less viable cells during differentiation, specifically after the polychromatophilic normoblast stage. There was a progressive increase in the apoptotic erythroid progeny with differentiation, and apoptosis occurred predominantly at the polychromatophilic normoblast stage. In thalassemia major, BM progenitor cells show increased erythroid clonogenicity, increased expression of late erythroid lineage-specific proteins, and accelerated erythroid differentiation. However, despite the apparent increased erythroid commitment, ineffective erythropoiesis occurs due to apoptosis at the polychromatophil stage. Identification of the differentiation stage at which apoptosis occurs will permit further studies of the underlying mechanisms and target therapeutic strategies to improve red cell production.

ADP-ribosyl Cyclase↗

PubMed2000

Erythropoietin-induced rheological changes of rat erythrocytes.

The effects of recombinant human erythropoietin (rhEPO) on red blood cell (RBC) rheological properties were investigated in rats. Rats received intramuscular injections of 150 U/kg/d rhEPO for 5 d, following which blood samples were obtained 1, 5 or 10 d later. RBC deformability was assessed by determining cell transit times through 5-microm micropores (CTA) and RBC shape recovery time constants via photometry, aggregation in plasma and dextran was measured by photometry and RBC electrophoretic mobility was determined in a cylindrical electrophoresis system. RBC aggregation was found to be significantly decreased on day 5 after rhEPO treatment (P < 0.05), yet was unchanged from control on days 1 and 10. Mean RBC micropore transit times remained unchanged, but the distributions of transit times were altered; compared with control, the 5th percentiles on both days 1 and 5 were decreased and the 95th percentile on day 1 was elevated. Electrophoretic mobility of RBCs in phosphate-buffered saline was significantly increased on day 5 after rhEPO treatment (P < 0.05), with mobility measurements in dextran 500 (MW = 500 kDa) solutions suggesting that the cells' surface properties related to the formation of a 'depletion layer' may be altered on day 1. These results indicate that the rheological behaviour of RBC as a consequence of rhEPO treatment are temporal and are affected by the presence of reticulocytes as well as by the average age of the circulating cells.

Animals↗

PubMed2000

Increased polymorphonuclear leucocyte rigidity in HIV infected individuals.

AIM: Individuals with human immunodeficiency virus (HIV) infection were evaluated for evidence of abnormal polymorphonuclear leucocyte (PMN) rigidity, which can alter capillary blood flow. METHODS: The transit time of individual PMN through 8 microm pores in a cell transit analyser was used as a measure of cell rigidity. PMN transit time was compared between HIV infected individuals (n=45) with and without CMV retinitis and HIV negative controls (n=17). RESULTS: Transit times were longer for PMN from HIV infected individuals than for PMN from controls (p<0.001). PMN from HIV infected individuals with CMV retinitis (n=13) had longer transit times than PMN from those without CMV retinitis (n=32, p<0.001). Transit times were longer in HIV infected individuals with lower CD4+ T lymphocyte counts (p<0.001). Regression analysis indicated that the relation between transit times and the presence of CMV retinitis could not be explained solely on the basis of low CD4+ T lymphocytes. In HIV infected individuals, mean transit time was not correlated with age, blood pressure, or serum creatinine, cholesterol, or triglycerides. CONCLUSIONS: HIV infected individuals appear to have increased PMN rigidity, a cellular change that might be involved in the pathogenesis of HIV related retinal microvasculopathy. PMN rigidity appears to be related to severity of immune dysfunction. PMN rigidity may remain high in patients with CMV retinitis after elevations of CD4+ T lymphocyte counts that result from potent antiretroviral therapy.

Adult↗

PubMed2000

The effect of low-molecular weight dextran on erythrocyte aggregation in normal and preeclamptic pregnancy.

Erythrocyte aggregation was determined by a novel method enabling the quantification of the aggregation process in whole blood. Blood samples of 47 healthy pregnant women and 39 preeclamptic patients were examined. Subjects within each group were matched for the gestational age. It was found that RBC aggregation increases with the gestational age in healthy pregnancy and further increases in preeclampsia. Addition of low-molecular weight dextran (MW = 9300) to blood samples of both healthy pregnant women and preeclamptic patients reduces RBC aggregation in a concentration-dependent manner. The obtained results indicate alterations in plasma composition as the primary factor for the increased RBC aggregation in both normal and pathological pregnancy. It is suggested that adsorption of low-molecular weight dextran on the RBC membrane reduces the surface concentration of plasma bridging molecules thereby reducing RBC aggregation toward normal.

Adsorption↗