Search PubMed⌕ Search

Biomedical subjects

D K Kaul

Publications and source records attributed to D K Kaul.

At least 37 records · Page 2Linked to original sources
PubMed1991

Sickle cell vaso-occlusion.

A polymerizable cell is a requirement for sickle cell vaso-occlusion, but other factors clearly modulate the course of the disease. Hemolysis produces a young red cell population that is capable of adhesion and may result in polymer formation in cells that would otherwise have remained deformable during transit through the microcirculation owing to prolonged delay time for polymerization. In addition, a young red cell population will have a higher activity of K:Cl cotransport, which is capable of rapidly dehydrating cells under acid conditions, thus promoting a vicious circle of hemolysis and adhesion. Transient occlusion may stimulate the release of vasoactive substances, which may lead to involvement of a larger area. In the past, research aimed at reducing the incidence of painful crisis was primarily focused on antisickling agents. Currently, hydroxyurea, which increases the level of fetal hemoglobin, which may be described as a natural antisickling agent, is undergoing clinical trials. Future research may involve agents that inhibit sickle cell adhesion, K:Cl cotransport, or vasoactive substances.

Anemia, Sickle Cell↗
PubMed1990

Desmopressin induces adhesion of normal human erythrocytes to the endothelial surface of a perfused microvascular preparation.

The interaction of red blood cells (RBCs) with vascular endothelium under flow conditions was investigated using the perfused rat mesocecum. Under videomicroscopy, normal human erythrocytes were found to adhere to the venular endothelium of desmopressin-treated microvasculature. Transmission electron microscopy showed that the erythrocytes were attached to the endothelial cells at discrete electron-dense sites. Compared with control preparations in which the microvasculature was perfused with Ringer's-albumin solution alone, more than a 10-fold increase in radioactivity was retained in the desmopressin-treated microvasculature when technetium (99mTc)-labeled erythrocytes were infused into the vasculature. This erythrocyte adherence was accompanied by a higher increment in vascular resistance during the passage of RBCs through the microcirculation, and by a delay in the recovery toward baseline. The erythrocyte adherence in desmopressin-treated microvasculature was completely abolished with antibodies to von Willebrand factor (vWF). Desmopressin infusion in rats resulted in elevated vWF antigen levels and the appearance of extra-large molecular weight forms of vWF in plasma. These findings suggest that normal erythrocytes adhere to desmopressin-conditioned microvascular endothelium and that endothelial cell-derived vWF is involved in the erythrocyte-endothelium interaction.

Animals↗
PubMed1989

Modeling sickle cell vasoocclusion in the rat leg: quantification of trapped sickle cells and correlation with 31P metabolic and 1H magnetic resonance imaging changes.

We have developed an animal model to elucidate the acute effects of perfusion abnormalities on muscle metabolism induced by different density-defined classes of erythrocytes isolated from sickle cell anemia patients. Technetium-99m (99mTc)-labeled, saline-washed normal (AA), homozygous sickle (SS), or high-density SS (SS4) erythrocytes were injected into the femoral artery of the rat and quantitative 99mTc imaging, 31P magnetic resonance spectroscopy by surface coil at 2 teslas, and 1H magnetic resonance imaging at 0.15 tesla were performed. Between 5 and 25 microliters of SS4 cells was trapped in the microcirculation of the thigh (or 1-6 x 10(7) cells per cubic centimeter of tissue). In contrast, fewer SS discocytes (SS2) or AA cells were trapped (an equivalent packed cell volume of less than 6.7 microliters and 0.3 microliters, respectively). After injection of SS4 cells an initial increase in inorganic phosphate was observed in the region of the thigh served by the femoral artery, intracellular pH decreased, and subsequently the proton relaxation time T1 reached a broad maximum at 18-28 hr. When T1 obtained at this time was plotted against the volume of cells trapped, an increase of T1 over the control value of 411 +/- 48 msec was found that was proportional to the number of cells trapped. We conclude that the densest SS cells are most effective at producing vasoocclusion. The extent of the change detected by 1H magnetic resonance imaging is dependent on the amount of cells trapped in the microcirculation and the magnitude of the initial increase of inorganic phosphate.

Anemia, Sickle Cell↗
PubMed1989

Microvascular sites and characteristics of sickle cell adhesion to vascular endothelium in shear flow conditions: pathophysiological implications.

To understand the role of sickle cell adherence to the vascular endothelium in the pathophysiology of sickle cell anemia (SS) vasoocclusion, we have carried out a microcirculatory study utilizing the ex vivo mesocecum vasculature of the rat. A single bolus of washed oxy-normal (AA) erythrocytes or oxy-SS cells (unseparated or density-defined SS cell classes) was infused. Hemodynamic monitoring and intravital microscopic observations of the microvascular flow revealed higher peripheral resistance for SS erythrocytes and adherence of these cells exclusively to the venular endothelium but rare or no adherence of AA cells. The extent of adhesion was inversely correlated with venular diameters (r = -0.812; P less than 0.00001). The adhesion of SS erythrocytes is density-class dependent: reticulocytes and young discocytes (SS1) greater than discocytes (SS2) greater than irreversible sickle cells and unsicklable dense discocytes (SS4). Selective secondary trapping of SS4 (dense cells) is found in postcapillary venules where deformable SS cells are preferentially adhered. We conclude that in the oxygenated condition, vasoocclusion can be induced by two events: (i) random precapillary obstruction by a small number of SS4 cells; (ii) increased adhesion of SS1 and SS2 cells in the immediate postcapillary venules. A combination of precapillary obstruction, adhesion in postcapillary venules, and secondary trapping of dense cells may induce local hypoxia, increased polymerization of hemoglobin S, and rigidity of SS erythrocytes, thereby extending obstruction to nearby vessels.

Adult↗
PubMed1989

Pentoxifylline (Trental) has no significant effect on laboratory parameters in sickle cell disease.

The possible effect of pentoxifylline (Trental) in sickle celle disease was tested in 2 clinical trials: a controlled double-blinded intravenous study involving patients hospitalized with painful crises and an ublinded 5-month oral study in steady state patients. In the intravenous trial 29 painful episodes were treated in 16 patients. Complete blood counts, serum chemistries, red cell density gradients, intracellular pH, p50, whole blood viscosity, plasma viscosity and red cell distribution widths were monitored daily during the hospital admission. We confirmed the decrease of dense red cells during crisis and found, in addition, the related significant decrease in whole blood p50. There were no major differences in any of these parameters when pentoxifylline was compared to placebo for each individual day. When the data was examined over time, minor differences emerged. The red cell distribution width, the number of cells in density fraction SS2 (discocytes) and the plasma viscosity were all slightly higher over time in the pentoxifylline group than in the control group. In the oral group 23 patients were monitored for the same parameters on seven visits during a five month period. Administration of oral pentoxifylline produced no changes from baseline for all parameters examined except for a statistically significant, but minor, increase in plasma viscosity demonstrable for these patients during one visit only. We conclude that pentoxifylline has little effect on laboratory parameters in sickle cell disease.

Administration, Oral↗
PubMed1988

Thrombospondin mediates the cytoadherence of Plasmodium falciparum-infected red cells to vascular endothelium in shear flow conditions.

Cerebral malaria is thought to involve specific attachment of Plasmodium falciparum-infected knobby red cells to venular endothelium. The nature of surface ligands on host endothelial cells that may mediate cytoadherence is poorly understood. We have investigated the effects of soluble thrombospondin, rabbit antiserum raised against thrombospondin, and human immune serum on cytoadherence of parasitized erythrocytes in ex vivo mesocecum vasculature. Preincubation of infected red cells with soluble thrombospondin or human immune serum inhibits binding of infected red cells to rat venular endothelium. Infusion of the microcirculatory preparation with rabbit antithrombospondin antibodies before perfusion of parasitized erythrocytes also resulted in decreased cytoadherence. In addition, incubation of infected cells with human immune sera obtained from malaria patients significantly inhibited the observed cytoadherence. Our results indicate that thrombospondin mediates binding of infected red cells to venular endothelium and may thus be involved in the pathogenesis of cerebral malaria.

Animals↗
PubMed1987

Survival rates and properties of sickle cell anemia red cells treated with nitrogen mustard.

A machine for the extracorporeal delivery of covalent anti-sickling agents has been described by Babb and coworkers and this therapeutic modality has been found feasible by others. We report here, further evaluation of nitrogen mustard (HN2), for possible use in the extracorporeal therapy of sickle cell anemia. Heparinized aliquots of whole blood from three patients with sickle cell disease were treated extra-corporeally with HN2 (0.65 mg/ml); the excess HN2 was neutralized with thiosulfate, and the blood was returned to the donor after labelling with 51Cr. HN2 produced an average 51Cr T1/2 which was 160% of control values. Fractionation of labelled red cells into different densities (ages) revealed that the main effect of HN2 was on the younger cell population which was characterized by a 51Cr T1/2 increase of 300% over the untreated blood. Further, "in vitro" studies were conducted to establish the effects on the SS red cells that could be expected from the treatment with HN2 at the concentrations used. Solubility determination (Csat) of deoxy hemoglobin S gels demonstrated that HN2 markedly inhibited the polymerization of HbS, was significantly more effective than potassium cyanate, and is among the most potent anti-sickling agents thus far reported. The viscosity of deoxygenated sickle red cells in a cone plate viscometer was markedly reduced by HN2, and hemodynamic studies using the microvasculature of an isolated rat mesoappendix demonstrated a reduction of peripheral resistance and an increase in flow rate when deoxygenated sickle cells pre-treated with HN2 were tested. At the highest concentration of HN2 (2 mg/ml), the peripheral resistance and the flow rates of deoxygenated cells attained levels found with oxygenated sickle blood. O2 affinity was partially corrected in the HN2 treated HbSS red cells. -SH reactivity of the red cell membrane was not affected by HN2. Among the added advantages of HN2 for extra-corporeal use is its rapid reaction rate, the lack of significant change of the O2 equilibrium at the concentration tested and the fact that the unreacted compound can be readily detected and neutralized. For these reasons HN2 is well suited for extra-corporeal treatment of sickle cell anemia for those patients with a severe form of the disease.

Anemia, Sickle Cell↗
PubMed1986

Vaso-occlusion by sickle cells: evidence for selective trapping of dense red cells.

We have characterized the type of red cells from sickle cell patients that were trapped in the course of sickle-cell vaso-occlusion. In addition, the perfusion conditions (arterial perfusion pressure [Pa] and oxygen tension [PO2]) leading to experimentally induced vaso-occlusion in the artificially perfused, innervated mesocecum microvascular preparation were determined. Microvascular obstruction was induced by decrease in Pa; the lower the Pa, the greater the peripheral resistance as well as the extent of obstruction. The cells involved in the obstruction were recovered by vasodilation (secondary to denervation) and increase in Pa. Densitometric analysis of density gradient-separated infused and trapped cells was supplemented with morphological analysis to ascertain the involvement of density classes as well as morphological types seen in oxy and deoxy sickle blood. The trapping phenomenon was sensitive to PO2. Percentage of densest gradient classes, ie, fraction 3 (F3; mainly dense unsicklable SS discocytes [USDs]) and fraction 4 (F4; irreversibly sickled cells [ISCs] and the densest discocytes), showed a significant increase in trapping when perfusion was switched from oxy to deoxy perfusate. Morphological analysis revealed that unsicklable SS discocytes are more effectively trapped when deoxygenated. The deoxygenation of infused cells did not further change the percentage of ISCs trapped, suggesting that ISCs are equally capable of sequestration in the oxy and the deoxy states. The venous effluent showed a selective and significant depletion of dense cells (F4) and ISC counts at all Pa. We conclude that the progressive obstruction of the microcirculation by sickle cells involves selective sequestration of the densest classes of cells and that this mechanism might explain their partial disappearance during painful sickle cell crisis.

Anemia, Sickle Cell↗
PubMed1985

Membrane knobs are required for the microcirculatory obstruction induced by Plasmodium falciparum-infected erythrocytes.

We have studied the pathophysiology of the vascular obstruction induced by Plasmodium falciparum-parasitized erythrocytes with the use of an ex vivo microcirculatory preparation perfused with red cells infected with knobless and knobby clones of the FCR-3 strain. We find that parasitized erythrocyte membrane knobs are indispensable for the generation of the circulatory obstruction. Uninfected erythrocytes incubated in culture and erythrocytes infected with early or late forms of the knobless clones or the early forms of the knobby clone all failed to obstruct the microcirculation, although exhibiting various effects on bulk viscosity and peripheral resistance during flow. In contrast, late forms of the knobby clone produced significantly higher peripheral resistance during flow and significant obstruction as detected by changes in time of pressure flow recovery as well as by direct videorecorded microscopic observation. Optical and electron microscopy showed that the adherence of parasitized cells to the endothelium was limited to the venules and involved the knobs in junctions. In addition, we were able to follow the sequence of events during obstruction: initial red-cell adherence to the venular endothelium (sometimes only transitory) followed by progressive recruitment at the venule surface, finally leading to total obstruction that involved parasitized and nonparasitized erythrocytes. Sometimes, retrograde aggregation would extend the obstruction to the capillaries or even precapillary arterioles. These results show that knobs are necessary and sufficient to produce vascular obstruction and that other factors (spleen, immunological, etc.) can only have a modulating role. These results also exclude the possibility that the exclusive adherence to venules is the consequence of "plasma factors" found in the malaric patients.

Blood Viscosity↗
PubMed1983

Pressure effects on the flow behavior of sickle (HbSS) red cells in isolated (ex-vivo) microvascular system.

The effect of varying arterial perfusion pressure (Pa) on flow behavior of human normal (HbAA) and sickle (HbSS) erythrocytes was evaluated in isolated rat mesoappendix vasculature. Red cell velocity (Vrbc) and wall shear rate in single arterioles (i.d. 20.4 +/- 4.5 Microns means and SD) were determined and total peripheral vascular resistance (PRU) calculated. The vasculature initially perfused with Ringer's solution was then perfused with red cells suspended (HCT 2%) in the same medium. At Pa of 100 mm Hg, oxy HbSS cells resulted in higher (50%) PRU and lower Vrbc (7.1 +/- 2.2 mm/sec) and wall shear rates (1800 +/- 490 sec-1) than those recorded with HbAA cells which show a more rapid microvascular passage, i.e., Vrbc (14.4 +/- 2.8 mm/sec) and wall shear rates (3810 +/- 360 sec-1). At the same Pa, partial deoxygenation (PO2 40 mm Hg) of HbSS cells caused marked (300%) increase in PRU, and decrease in Vrbc (3.2 +/- 0.9 mm/sec), and wall shear rates (820 +/- 440 sec-1). During stepwise decrement of Pa (100-30 mm Hg), PRU for oxy HbSS cells remains elevated but the overall trend is similar to that for HbAA cells and Ringer's perfusion. At Pa of 30 mm Hg, oxy HbSS cells caused some microvascular obstruction. In contrast, with decrement in Pa below 80 mm Hg partially deoxy HbSS cells resulted in progressive increase in PRU and drastic decrease in Vrbc, coupled with progressive capillary obstruction and stasis. An increased propensity of these cells to cause irreversible vasoocclusion is demonstrated when low-pressure conditions prevail.

Adult↗
PubMed1983

Erythrocytes in sickle cell anemia are heterogeneous in their rheological and hemodynamic characteristics.

To understand the contribution to the pathophysiology of sickle cell anemia of the different erythrocyte density types present in the blood of these patients, we have studied the viscosimetric and hemodynamic characteristics of four major classes of hemoglobin SS erythrocytes. We have isolated reticulocytes, discocytes, dense discocytes, and irreversibly sickled cells (fractions I-IV) on Percoll-Renografin density gradients. Bulk viscosity was studied in a coneplate viscosimeter and the hemodynamic studies were performed on the isolated, artificially perfused mesoappendix vasculature of the rat (Baez preparation). Bulk viscosity measurements at shear rates of 230 S-1 demonstrate that when the cells are oxygenated, fraction I (reticulocyte rich) has a higher viscosity than expected from its low intracellular hemoglobin concentration. The rest of the fractions exhibit moderate increases in bulk viscosity pari-passu with the corresponding increases in density (mean corpuscular hemoglobin concentration). When deoxygenated, all cell fractions nearly doubled their bulk viscosity and the deoxy-oxy differences remained constant. The Baez preparation renders a different picture: oxygenated fractions behave as predicted by the viscosimetric data, but, when deoxygenated, cell fractions exhibit dramatically increased peripheral resistance and the deoxy-oxy difference are directly proportional to cell density, thus, the largest increases were observed for fractions III and IV. The differences between the rheological and the hemodynamic measurements are most probably due to the different sensitivity of the two methods to the extent of intracellular polymerization. These results also demonstrate that the hitherto unrecognized fraction III cells (very dense discocytes that change shape very little on deoxygenation) are as detrimental to the microcirculation as the irreversibly sickled cell-rich fraction IV. They may, however, induce obstruction by a different mechanism. As the extent to which these fractions are populated by erythrocytes varies considerably from patient to patient, the distribution function of cell densities in each sickle cell anemia patient might have consequences for the type of pathophysiological events occurring in their microcirculation.

Adult↗
PubMed1982

SC erythrocytes have an abnormally high intracellular hemoglobin concentration. Pathophysiological consequences.

We have examined 20 SC patients on Percoll-Stractan continuous density gradients and find that they have an elevated mean corpuscular hemoglobin concentration (MCHC). Reduction of the MCHC to normal values results in amelioration of four physiologically important blood abnormalities: decreased oxygen affinity, viscosity of deoxygenated erythrocyte suspensions, rate of sickling, and deoxygenation induced K+ efflux. These observations suggest that the rehydration of SC cells to normal values should be considered a potential approach in the therapeutic manipulation of this disease.

Anemia, Sickle Cell↗