Biomedical subjects

D K Kaul

Publications and source records attributed to D K Kaul.

At least 19 recordsLinked to original sources

PubMed2001

Ameliorating effects of fluorocarbon emulsion on sickle red blood cell-induced obstruction in an ex vivo vasculature.

In sickle cell (SS) vaso-occlusion, the culminating event is blockage of blood vessels by sickled red blood cells (SS RBCs). As shown in animal models, SS RBC-induced vaso-occlusion is often partial, allowing for a residual flow, hence oxygen delivery to partially occluded vessels could reduce vaso-occlusion. The efficacy of an oxygenated perflubron-based fluorocarbon emulsion (PFE) was tested for its anti-vaso-occlusive effects in the ex vivo mesocecum vasculature of the rat. Microvascular obstruction was induced by the infusion of deoxygenated SS RBCs into ex vivo preparations with or without pretreatment with platelet-activating factor (PAF). PAF induced enhanced SS RBC-endothelium interactions, leading to greater vaso-occlusion. Microvascular blockage resulted in increased peripheral resistance units (PRU). Deoxygenated SS RBCs caused a persistent 1.5-fold PRU increase in untreated preparations and approximately a 2-fold PRU increase in PAF-treated preparations. The greater PRU in PAF-treated preparations was caused by widespread adhesion and postcapillary blockage. Oxygenated PFE, but not deoxygenated PFE, resulted in PRU decreases to baseline values in both groups of experiments (with or without PAF). The PRU decrease caused by oxygenated PFE infusion was caused by unsickling of SS RBCs in partially occluded vessels, with no antiadhesive effect on already adherent SS RBCs as assessed by intravital microscopy. PFE had no effect on vascular tone. The efficacy of PFE appears to result from its greater capacity to dissolve oxygen (10-fold higher than plasma). The dislodgement of trapped SS RBCs and an increase in wall shear rates will help reverse the partial obstruction. Thus, oxygenated PFE is capable of reducing SS RBC-induced vaso-occlusion, and further development of this approach is advisable.

Adult↗

PubMed2001

Evaluation of serologic disease markers in a population-based cohort of patients with ulcerative colitis and Crohn's disease.

BACKGROUND: The sensitivity of assays for antineutrophil cytoplasmic antibody (ANCA), anti-Saccharomyces cerevisiae antibody (ASCA), and antipancreatic antibody (PAB) in different laboratories is unknown. Likewise, the sensitivity and diagnostic usefulness of these assays in patients with inflammatory bowel disease (IBD) in the community is unknown. METHODS: An incidence cohort of 290 patients with IBD were offered participation in the study. Blood was obtained from 162 patients (56%) (83 with ulcerative colitis, 79 with Crohn's disease) who agreed to participate. ANCA was determined in five laboratories. ASCA in two laboratories, and PAB in one laboratory. RESULTS: In ulcerative colitis, the sensitivity of ANCA determined in five laboratories varied widely, ranging from 0-63%. In Crohn's disease, the sensitivity of ASCA determined in two laboratories did not vary significantly, ranging from 39-44%; and the sensitivity of PAB determined in one laboratory was 15%. The optimal diagnostic usefulness was obtained from one laboratory where the positive predictive values of a positive ANCA assay combined with a negative ASCA assay for ulcerative colitis, and a negative ANCA combined with a positive ASCA for Crohn's disease, were 75% and 86%, respectively. CONCLUSIONS: In patients with IBD, the sensitivity of ANCA varied widely in different laboratories, whereas the prevalence of ASCA was similar. The positive predictive values of the ANCA assay combined with the ASCA assay for ulcerative colitis and Crohn's disease are high enough to be clinically useful.

Adolescent↗

PubMed2000

Monoclonal antibodies to alphaVbeta3 (7E3 and LM609) inhibit sickle red blood cell-endothelium interactions induced by platelet-activating factor.

Abnormal interaction of sickle red blood cells (SS RBC) with the vascular endothelium has been implicated as a factor in the initiation of vasoocclusion in sickle cell anemia. Both von Willebrand factor (vWf) and thrombospondin (TSP) play important roles in mediating SS RBC-endothelium interaction and can bind to the endothelium via alphaVbeta3 receptors. We have used monoclonal antibodies (MoAb) directed against alphaVbeta3 and alphaIIbbeta3 (GPIIb/IIIa) integrins to dissect the role of these integrins in SS RBC adhesion. The murine MoAb 7E3 inhibits both alphaVbeta3 and alphaIIbbeta3 (GPIIb/IIIa), whereas MoAb LM609 selectively inhibits alphaVbeta3, and MoAb 10E5 binds only to alphaIIbbeta3. In this study, we have tested the capacity of these MoAbs to block platelet-activating factor (PAF)-induced SS RBC adhesion in the ex vivo mesocecum vasculature of the rat. Infusion of washed SS RBC in preparations treated with PAF (200 pg/mL), with or without a control antibody, resulted in extensive adhesion of these cells in venules, accompanied by frequent postcapillary blockage and increased peripheral resistance units (PRU). PAF also caused increased endothelial surface and interendothelial expression of endothelial vWf. Importantly, pretreatment ofthe vasculature with either MoAb 7E3 F(ab')(2) or LM609, but not 10E5 F(ab')(2), after PAF almost completely inhibited SS RBC adhesion in postcapillary venules, the sites of maximal adhesion and frequent blockage. The inhibition of adhesion with 7E3 or LM609 was accompanied by smaller increases in PRU and shorter pressure-flow recovery times. Thus, blockade of alphaVbeta3 may constitute a potential therapeutic approach to prevent SS RBC-endothelium interactions under flow conditions. (Blood. 2000;95:368-374)

Abciximab↗

PubMed2000

Impaired nitric oxide-mediated vasodilation in transgenic sickle mouse.

Transgenic sickle mice expressing human beta(S)- and beta(S-Antilles)-globins show intravascular sickling, red blood cell adhesion, and attenuated arteriolar constriction in response to oxygen. We hypothesize that these abnormalities and the likely endothelial damage, also reported in sickle cell anemia, alter nitric oxide (NO)-mediated microvascular responses and hemodynamics in this mouse model. Transgenic mice showed a lower mean arterial pressure (MAP) compared with control groups (90 +/- 7 vs. 113 +/- 8 mmHg, P < 0.00001), accompanied by increased endothelial nitric oxide synthase (eNOS) expression. N(G)-nitro-L-arginine methyl ester (L-NAME), a nonselective inhibitor of NOS, caused an approximately 30% increase in MAP and approximately 40% decrease in the diameters of cremaster muscle arterioles (branching orders: A2 and A3) in both control and transgenic mice, confirming NOS activity; these changes were reversible after L-arginine administration. Aminoguanidine, an inhibitor of inducible NOS, had no effect. Transgenic mice showed a decreased (P < 0.02-0.01) arteriolar dilation in response to NO-mediated vasodilators, i.e., ACh and sodium nitroprusside (SNP). Indomethacin did not alter the responses to ACh and SNP. Forskolin, a cAMP-activating agent, caused a comparable dilation of A2 and A3 vessels ( approximately 44 and 70%) in both groups of mice. Thus in transgenic mice, an increased eNOS/NO activity results in lower blood pressure and diminished arteriolar responses to NO-mediated vasodilators. Although the increased NOS/NO activity may compensate for flow abnormalities, it may also cause pathophysiological alterations in vascular tone.

Anemia, Sickle Cell↗

PubMed2000

Hypoxia/reoxygenation causes inflammatory response in transgenic sickle mice but not in normal mice.

In sickle cell anemia, the initiation, progression, and resolution of a vasoocclusive episode may present features of ischemia-reperfusion injury, with recurrent episodes of ischemia/hypoxia and reoxygenation promoting inflammation. Here, we have tested the hypothesis that hypoxia/reoxygenation triggers inflammation in the transgenic sickle mouse. In these mice, even at ambient air, peripheral leukocyte counts are elevated by 1.7-fold and neutrophil counts by almost 3-fold. Two hours of hypoxia, followed by reoxygenation, induced a greater than normal rolling flux and adhesion of leukocytes in these mice, but no leukocyte extravasation. When 3 hours of hypoxia was followed by reoxygenation, sickle mice, but not normal mice, showed a distinct inflammatory response characterized by an increased number of adherent and emigrated leukocytes. Because these events, which are exaggerated in sickle mice, are not seen in response to hypoxia alone, we conclude that they represent a form of reperfusion injury. Studies using an H(2)O(2)-sensitive probe revealed clear evidence of oxidant production in vascular endothelial cells after hypoxia/reoxygenation in sickle mice. Infusion of an anti-P-selectin antibody, but not an anti-E-selectin antibody, completely inhibited this inflammatory response and significantly increased wall shear rates. These findings suggest that leukocyte-endothelium interaction contribute to vasoocclusive events in the sickle mice and perhaps in human sickle disease.

Anemia, Sickle Cell↗

PubMed1999

Anionic polysaccharides inhibit adhesion of sickle erythrocytes to the vascular endothelium and result in improved hemodynamic behavior.

The abnormal adherence of sickle red blood cells (SS RBC) to vascular endothelium may play an important role in vasoocclusion in sickle cell anemia. Thrombospondin (TSP), unusually large molecular weight forms of von Willebrand factor, and laminin are known to enhance adhesion of SS RBC. Also, these endothelial proteins bind to sulfated glycolipids and this binding is inhibited by anionic polysaccharides. Reversible sickling may expose normally cryptic membrane sulfatides that could mediate this adhesive interaction. In this study, we have investigated the effect of anionic polysaccharides, in the presence or absence of TSP, on SS RBC adhesion to the endothelium, using cultured human umbilical vein endothelial cells (HUVEC) (for the adhesion assay) and the ex vivo mesocecum of the rat (for hemodynamic evaluation). The baseline adhesion (ie, without added TSP) of SS RBC to HUVEC was most effectively inhibited by high molecular weight dextran sulfate (HDS), whereas low molecular weight dextran sulfate (LDS) and the glycosaminoglycan chondroitin sulfate A (CSA) also had significant inhibitory effects. Heparin was mildly effective whereas other glycosaminoglycans (chondroitin sulfates B and C, heparan sulfate, and fucoidan) were ineffective. Similarly, HDS and CSA resulted in an improved hemodynamic behavior of SS RBC. Soluble TSP caused significant increases in SS RBC adhesion and in the peripheral resistance. Both HDS and CSA prevented TSP-enhanced adhesion and hemodynamic abnormalities. Thus, anionic polysaccharides can inhibit SS RBC-endothelium interaction in the presence or absence of soluble TSP. These agents may interact with RBC membrane component(s) and prevent TSP-mediated adhesion of SS RBC to the endothelium.

Adult↗

PubMed1999

Rate of deoxygenation modulates rheologic behavior of sickle red blood cells at a given mean corpuscular hemoglobin concentration.

Although the mean corpuscular hemoglobin concentration (MCHC) plays a dominant role in the rheologic behavior of deoxygenated density-defined sickle red blood cells (SS RBCs), previous studies have not explored the relationship between the rate of deoxygenation and the bulk viscosity of SS RBCs at a given MCHC. In the present study, we have subjected density-defined SS classes (i.e., medium-density SS4 and dense SS5 discocytes) to varying deoxygenation rates. This approach has allowed us to minimize the effects of SS RBC heterogeneity and investigate the effect of deoxygenation rates at a given MCHC. The results show that the percentages of granular cells, classic sickle cells and holly leaf forms in deoxygenated samples are significantly influenced by the rate of deoxygenation and the MCHC of a given discocyte subpopulation. Increasing the deoxygenation rate using high K+ medium (pH 6.8), results in a greater percentage of granular cells in SS4 suspensions, accompanied by a pronounced increase in the bulk viscosity of these cells compared with gradually deoxygenated samples (mainly classic sickle cells and holly leaf forms). The effect of MCHC becomes apparent when SS5 dense cells are subjected to varying deoxygenation rates. At a given deoxygenation rate, SS5 dense discocytes show a greater increase in the percentage of granular cells than that observed for SS4 RBCs. Also, at a given deoxygenation rate, SS5 suspensions exhibit a higher viscosity than SS4 suspensions with fast deoxygenation resulting in maximal increase in viscosity. Although MCHC is the main determinant of SS RBC rheologic behavior, these studies demonstrate for the first time that at a given MCHC, the rate of deoxygenation (hence HbS polymerization rates) further modulates the rheologic behavior of SS RBCs. Thus, both MCHC and the deoxygenation rate may contribute to microcirculatory flow behavior of SS RBCs.

Anemia, Sickle Cell↗

PubMed1998

Microvascular hemodynamics and in vivo evidence for the role of intercellular adhesion molecule-1 in the sequestration of infected red blood cells in a mouse model of lethal malaria.

The cytoadherence of infected red blood cells (IRBCs) to the vascular endothelium is the major cause of IRBC sequestration and vessel blockage in the cerebral form of human malaria. Among the rodent models of malaria, Plasmodium yoelii 17XL-infected mice show many similarities with the human cerebral malaria caused by P. falciparum. In both, the sequestration of IRBCs in the brain vessels is secondary to the cytoadherence of IRBCs to the vascular endothelium. Similar to P. falciparum infection in the human but in contrast to P. berghei ANKA infection in mice, P. yoelii 17XL results in little, if any, accumulation of monocytes in the brain. In vivo microcirculatory studies reported here were designed to further understand the hemodynamic aspects and mechanisms underlying cytoadherence of IRBCs in the P. yoelii model using the easily accessible cremaster muscle vasculature. The results show significant decreases in arteriovenous red blood cell velocities (Vrbc) and wall shear rates in the microcirculation of P. yoelii-infected mice, with a maximal decrease occurring in small-diameter postcapillary venules, the main sites of cytoadherence. This reflects contributions from IRBC cytoadherence as well as from increased rigidity of parasitized red blood cells. No cytoadherence is observed in arterioles of the infected mice despite decreased wall shear rates, indicating that endothelial receptors for cytoadherence are restricted to venules. Infusion of a monoclonal antibody (MAb) against the intercellular adhesion molecule-1 (ICAM-1) resulted in significant increases in both arteriolar and venular Vrbc and wall shear rates, accompanied by detachment of adhered IRBCs at some venular sites. The peripheral blood smears taken after the MAb infusion showed a distinct increase in the percentage of schizonts, again indicating detachment and/or prevention of cytoadherence. An MAb against the vascular cell adhesion molecule-1 (VCAM-1) as well as an irrelevant control antibody had no effect on these parameters. These results provide the first in vivo microcirculatory evidence indicating involvement of ICAM-1, but not of VCAM-1, in the sequestration of IRBCs in a rodent model of cerebral malaria.

Animals↗

PubMed1997

A first evaluation of the natural high molecular weight polymeric Lumbricus terrestris hemoglobin as an oxygen carrier.

Lumbricus terrestris hemoglobin (LtHb), an unusually stable Hb (MW approximately 4x10(6) Da) with respect to dissociation and oxidation, circulates extracellularly in the earthworm and at neutral pH exhibits oxygen affinity and cooperativity similar to that of human HbA. Results suggest that LtHb may serve as a model for a high molecular weight extracellular oxygen carrier. Mice and a rat model partially exchanged with LtHb showed no apparent behavioral and physical changes. 31P NMR spectroscopy of perfused guinea pig hearts, used to assess phosphocreatine levels as an indication of the ability of LtHb to serve as an oxygen carrier to the heart, demonstrated that LtHb provides oxygen to the tissue and maintains the energy metabolism significantly better than the control non-Hb perfusion media. One day after infusion, video enhanced microscopy imaging of the mice cremaster muscle vasculature reveals temporal adhesion of leukocytes to the endothelial walls with temporal infiltration of leukocytes to the surrounding tissue, correlated with dosage. Exchanged mice rechallenged with LtHb show no overt allergic response or death. Further evaluation of this natural extracellular Hb as a potential polymeric Hb blood substitute/perfusion agent is warranted.

Animals↗

PubMed1996

The pathophysiology of vascular obstruction in the sickle syndromes.

Vasocclusive events in the sickle-cell syndromes have multiple determinants: first and foremost is the capacity of red cells to undergo intracellular polymerization of deoxy HbS. However, the impact of the sicklable red cell is not limited to mechanical obstruction of the microcirculation, but also results in other and sometimes unexpected consequences. For example, red-cell destruction leads to large numbers of young red cells with enhanced vascular adhesion and increased K:Cl cotransport expression, in addition to an elevated percent of erythrocytic HbF. These pleiotropic effects, that is, multiple phenotypic effects from a single gene, can be further modulated by the action of epistatic effects, that is, the action of other genes besides beta(S). The interaction of epistatic and pleiotropic effects leads to the interindividual phenotypic variations characteristic of sickle-cell disease. Further understanding of pleiotropic effects (i.e. mechanism of red-cell adhesion, production of vasoactive substances by damaged endothelium, etc.), will uncover new epistatic effects. At the end, we will be able to define not only the genotype, but also the phenotypic severity. This review covers the present knowledge of the red-cell and non-red-cell determinants of vasocclusion, and proposes models to explain the acute painful crises that commonly afflict these patients.

Anemia, Sickle Cell↗

PubMed1996

Compromised microcirculation in acute murine Trypanosoma cruzi infection.

Microvascular compromise has been 1 of many factors implicated in the etiology of the cardiomyopathy associated with Chagas' disease. To further assess the effect of Trypanosoma cruzi infection on the microcirculation, we examined the cremaster microvascular model in CD-1 male mice infected with the Brazil strain at 20-25 days postinfection. There was a significant decrease in red cell velocity (Vrbc) in first and third-order arterioles and venules, which was reversed by verapamil treatment. Video recordings revealed a marked inflammatory response that was confirmed by transmission electron microscopy. A marked inflammatory response was not seen in verapamil-treated infected mice. Segmental vasospasm and dilatation was evident in the microvascular bed of infected mice. This was not seen in control or verapamil-treated mice. This model provides a readily accessible method to observe directly the effects of T. cruzi infection on the microcirculatory flow in vivo. In addition, it confirms and extends our previous observations regarding T. cruzi-associated microvascular spasm and underscores a role for verapamil, a calcium-channel blocker, in the amelioration of the Chagas' disease.

Acute Disease↗

PubMed1995

In vivo demonstration of red cell-endothelial interaction, sickling and altered microvascular response to oxygen in the sickle transgenic mouse.

Intravascular sickling, red cell-endothelium interaction, and altered microvascular responses have been suggested to contribute to the pathophysiology of human sickle cell disease, but have never been demonstrated under in vivo flow. To address this issue, we have examined a transgenic mouse line, alphaHbetaSbetaS-Antilles [betaMDD] which has a combined high (78%) expression of beta S and beta S-Antilles globins. In vivo microcirculatory studies using the cremaster muscle preparation showed adhesion of red cells, restricted to postcapillary venules, in transgenic mice but not in control mice. Electron microscopy revealed distinct contacts between the red cell membrane and the endothelium surface. Some red cells exhibiting sickling were regularly observed in the venular flow. Infusion of transgenic mouse red cells into the ex vivo mesocecum vasculature also showed adhesion of mouse red cells exclusively in venules. Under resting conditions (pO2, 15-20 mmHg), there were no differences in the cremaster microvascular diameters of control and transgenic mice; however, transgenic mice showed a drastic reduction in microvascular red cell velocities (Vrbc) with maximal Vrbc decrease (> 60%) occurring in venules, the sites of red cell adhesion and sickling. Local, transient hyperoxia (pO2, 150 mmHg) resulted in striking differences between control and transgenic mice. In controls, oxygen caused a 69% arteriolar constriction, accompanied by 75% reduction in Vrbc. In contrast, in transgenic mice, hyperoxia resulted in only 8% decrease in the arteriolar diameter and in 68% increase in VrBC; the latter is probably due to an improved flow behavior of red cells as a consequence of unsickling. In summary, the high expression of human sickle hemoglobin in the mouse results not only in intravascular sickling but also red cell-endothelium interaction. The altered microvascular response to oxygen could be secondary to blood rheological changes, although possible intrinsic differences in the endothelial cell/vascular smooth muscle function in the transgenic mouse may also contribute. These sickle transgenic mice could serve as a useful model to investigate vasoocclusive mechanisms, as well as to test potential therapies.

Anemia, Sickle Cell↗

PubMed1994

Adhesion of sickle cells to vascular endothelium is critically dependent on changes in density and shape of the cells.

Experiments were performed to explore whether adhesion differences among different density sickle (SS) cells are mainly caused by deformability characteristics attendant to density variations, which could affect their surface contacts with the endothelium, or caused by any changes in their membrane surface (eg, receptors). Also, what is the contribution of morphologic attributes of SS cells in adhesive and obstructive events? To resolve these issues, controlled modifications of cell density were performed using Nystatin and sucrose. This allowed elevation of the mean corpuscular hemoglobin concentration (MCHC) of light-density SS2 discocytes to that of SS4 native dense cells, as well as its normalization in both native and artificially dehydrated cells. Hemodynamic and adhesive characteristics of these individual SS cell populations and their defined mixtures were investigated in the ex vivo mesocecum vasculature. Dehydrated (high MCHC) SS2 discocytes, alone or with SS2 control cells, caused a higher peripheral resistance but no persistent microvascular blockage. Nevertheless, dehydrated SS2 discocytes resulted in a significantly decreased adhesion in venules (adhesion sites). Rehydration of these high MCHC discocytes completely restored their adhesivity, similar to that of SS2 control cells. In contrast, irreversibly sickled cell (ISC)-rich SS4 dense cell class (dense discocytes and 66% to 72% ISCs) was less adherent than dehydrated SS2 discocytes, but caused a persistent blockage of small diameter postcapillary venules when infused with SS2 control or dehydrated discocytes. In the areas of adhesion, SS4 dense discocytes outnumbered ISCs by 4 to 1, demonstrating that ISCs, because of their shape characteristics, are minimally adherent but play a distinct role in postcapillary obstruction. When MCHC (density) of SS4 cells was decreased by rehydration, it resulted in an almost complete reversal of their hemodynamic and adhesive behavior, confirming a profound influence of cell density. These findings demonstrate for the first time that, under shear flow, adhesion of different density SS cells to the endothelium is dependent on the inverse of cell density rather than any changes in their adhesion potential. Finally, the trapping of ISC-rich native dense cells, but not of dehydrated discocytes, in the areas of adhesion shows a distinct contribution of ISC in adhesion-initiated vasoocclusion.

Adult↗

PubMed1994

Cerebral malaria in mice: demonstration of cytoadherence of infected red blood cells and microrheologic correlates.

To understand the microcirculatory events during cerebral malaria, we have studied the lethal strain of rodent Plasmodia, Plasmodium yoelii 17XL, originally described by Yoeli and Hargreaves in 1974. The virulence of P. yoelii 17XL is caused by intravascular sequestration of infected red blood cells (IRBCs), especially in the brain vessels and capillaries. This mouse model resembles human P. falciparum infection more closely than P. berghei ANKA infection since it shows little, if any, inflammation of the brain. In vivo microcirculatory studies on cytoadherence of IRBCs were performed using the cremaster muscle preparation, which is an easily accessible vasculature for intravital observations. Ex vivo assay of cytoadherence was carried out in the artificially perfused mesocecum preparation of the rat. The results in either preparation demonstrated cytoadherence of IRBCs that was restricted to postcapillary venules. Furthermore, the in vivo measurements showed the prevalence of cytoadherence in small-diameter (< 40 microns) venules in accordance with the local wall shear rates. The parasitized animals demonstrated significantly reduced red blood cell velocities and wall shear rates in the small-diameter postcapillary venules of the cremaster. The relationship between cytoadherence and venular wall shear rates was also reflected in the inverse correlation between the number of adhered cells and the venular diameter in the ex vivo mesocecum preparation. In the ex vivo preparation, cytoadherence of IRBCs was accompanied by a higher peripheral resistance. Transmission electron microscopy of the cremaster muscle and brain tissues showed a tight association of IRBCs with the endothelium of small venules. These observations demonstrate that cytoadherence of P. yoelii 17XL-infected mouse red blood cells is very similar to that of P. falciparum-infected cells. Thus, this model should allow a detailed analysis of the molecular mechanisms involved in the generation of cerebral malaria by cytoadherence of the infected red blood cells to the vascular endothelium.

Animals↗

PubMed1993

Sickle erythrocyte-endothelial interactions in microcirculation: the role of von Willebrand factor and implications for vasoocclusion.

To determine the role of von Willebrand factor (vWF) in adhesion of sickle (SS) erythrocytes in microvascular flow conditions, we have perfused the ex vivo mesocecum vasculature of the rat with desmopressin, an analogue of vasopressin that causes the release of endothelial vWF. Analysis of vWF in the venous effluent of the isolated vasculature showed mainly the presence of extra-large molecular weight forms characteristic of endothelial vWF, which in the presence of desmopressin showed an average increase of 54%. Also, desmopressin induced a significant increase in adhesion of washed oxygenated (oxy) unseparated SS erythrocytes, accompanied by a persistent microvascular obstruction and a pronounced increase in the peripheral resistance (PRU). In contrast, infusion of SS deformable discocytes (SS2) in desmopressin-perfused vasculature resulted in a significant adhesion but not in persistent vasoocclusion, showing that SS2 discocytes alone are not sufficient for microvascular obstruction. Furthermore, SS4 erythrocytes (dense discocytes and irreversibly sickled erythrocytes) caused a persistent microvascular blockage and a significantly higher PRU than SS2 discocytes. However, the increase in PRU for SS4 erythrocytes following desmopressin treatment was 50% less compared with a corresponding increase for SS2 discocytes over the control values, which showed a smaller effect of desmopressin on the hemodynamic behavior of SS4 dense erythrocytes. Incubation of desmopressin-treated vasculature with anti-vWF antibodies resulted in a pronounced decrease in adhesion and significantly improved hemodynamic behavior of SS cells. Also, in untreated vasculature, similarly incubated with anti-vWF antibodies, there was almost complete inhibition of adhesion. Under the described perfusion conditions, antibodies to fibronectin and thrombospondin, as well as incubation of SS erythrocytes with anti-vWF antibodies did not affect adhesion. These results are compatible with a model for SS vasoocclusion in which extra-large vWF-mediated adhesion of deformable SS erythrocytes is the first step followed by an accelerated entrapment of dense SS erythrocytes.

Adult↗

PubMed1993

Sickle cell vasoocclusion: many issues and some answers.

The pathophysiology of sickle (SS) cell vasoocclusion is derived from the presence of hemoglobin S (HbS) which forms polymeric fibers in the deoxygenated state. Nevertheless, phenotypic expression of sickle cell disease (i.e., clinical severity) shows marked individual variations and is influenced by genetic modifiers such as epistatic effects of linked and unlinked genes. Furthermore, the polymerization of HbS is central but not the only event, and is more likely a consequence of disruptions of the steady state of flow. The available evidence indicates that the vasoocclusive crisis is a microcirculatory event in which multiple factors could be involved. We present a model of vasoocclusion as a two step process in which adhesion of deformable cells occurs first, followed by obstruction induced by less deformable SS cells. This review discusses, in addition, rheologic and microcirculatory behavior of SS erythrocytes and the interacting role of vascular factors, red cell heterogeneity, deoxygenation rates, and red cell-endothelial interactions in the pathophysiology of SS cell vasoocclusion.

Anemia, Sickle Cell↗

PubMed1991

Rosetting of Plasmodium falciparum-infected red blood cells with uninfected red blood cells enhances microvascular obstruction under flow conditions.

The occurrence of rosetting of Plasmodium falciparum-infected human red blood cells (IRBC) with uninfected red blood cells (RBC) and its potential pathophysiologic consequences were investigated under flow conditions using the perfused rat mesocecum vasculature. Perfusion experiments were performed using two knobby (K+) lines of P falciparum, ie, rosetting positive (K+R+) and rosetting negative (K+R-). The infusion of K+R+ IRBC resulted in higher peripheral resistance (PRU) than K+R- IRBC (P less than .0012). Video microscopy showed that under conditions of flow, in addition to cytoadherence of K+R+ IRBC to the venular endothelium, rosette formation was also restricted to venules, especially in the areas of slow flow. Rosettes were absent in arterioles and were presumably dissociated by higher wall shear rates. The presence of rosettes in the venules must therefore reflect their rapid reformation after disruption. Cytoadherence of K+R+ IRBC was characterized by formation of focal clusters along the venular wall. In addition, large aggregates of RBC were frequently observed at venular junctions, probably as a result of interaction between flowing rosettes, free IRBC, and uninfected RBC. In contrast, the infusion of K+R+ IRBC resulted in diffuse cytoadherence of these cells exclusively to the venular endothelium but not in rosetting or large aggregate formation. The cytoadherence of K+R+ IRBC showed strong inverse correlation with the venular diameter (r = -.856, P less than .00001). Incubation of K+R+ IRBC with heparin and with monoclonal antibodies to glycoprotein IV/CD36 abolished the rosette formation and resulted in decreased PRU and microvascular blockage. These findings demonstrate that rosetting of K+R+ IRBC with uninfected RBC enhances vasocclusion, suggesting an important in vivo role for rosetting in the microvascular sequestration of P falciparum-infected RBC.

Animals↗

PubMed1991

Rate of deoxygenation and rheologic behavior of blood in sickle cell anemia.

To understand the relationship between deoxygenation rate, rheologic behavior, and red blood cell (RBC) morphologic characteristics of blood in sickle (SS) cell anemia, washed oxy SS RBC suspensions (hematocrit, 40%) were subjected to relatively fast and gradual deoxygenation procedures. Relatively fast deoxygenation resulted in 50% decline in percent hemoglobin oxygen saturation (%HbO2) within 1 minute. The SS suspensions following relatively fast deoxygenation showed two distinct phases in viscosity profiles. First, there was a sharp increase in individual viscosities to a peak value at 7 minutes of deoxygenation. Second, prolonged deoxygenation resulted in a 27% to 37% decrease in individual viscosities at 30 minutes as compared with the respective peak values at 7 minutes. Most of the viscosity increase (ie, about fourfold) occurred within the first 3 minutes of relatively fast deoxygenation. Scanning electron microscopy and differential morphologic analysis of deoxy cells showed that at 7 minutes a majority of cells had a granular appearance that was characterized by a bumpy irregular surface and the presence of small spicule-like projections. Prolonged deoxygenation resulted in the appearance of a large percentage of elongated cells that were unlike typical sickle cells. Transmission electron microscopy showed that the elongated shape resulted from the alignment of HbS polymers into long projections. In contrast, gradual deoxygenation over a period of 30 minutes resulted in a progressive increase in viscosity and in the formation of typical sickle shapes and holly leaf cells. The results show that at matching %HbO2, the SS suspensions containing mainly granular shaped cells after 7 minutes of relatively fast deoxygenation are as viscous as the gradually deoxygenated suspensions that contain classic sickle shapes and holly leaf forms, while the suspensions having a large percentage of elongated cells (30 minutes after relatively fast deoxygenation) are the least viscous. The two distinct time-dependent viscosity phases observed after relatively fast deoxygenation probably result from differences in the RBC shape characteristics reflecting physical attributes of the polymer, which could affect cell orientation in the viscometric flow.

Anemia, Sickle Cell↗