Deformation factor: an extracellular protein synthesized by Bartonella bacilliformis that deforms erythrocyte membranes.
(65/352)
Bartonella bacilliformis, a hemotropic bacterium and the causative agent of the human disease bartonellosis, when incubated in a tryptone-based medium produces an extracellular factor, termed deformation factor (DF), which induces extensive indentations and trenches in trypsinized erythrocyte membranes. The factor is stable during storage at 4 degrees C. It can be inactivated by proteases or brief heating to 70 to 80 degrees C, can be precipitated by ammonium sulfate, is nondialyzable, and is retained by membranes with a 30,000-molecular-weight cutoff. These properties suggest that DF is probably a protein. Incubation of erythrocytes with phospholipase D renders them resistant to deformation by DF. (+info)
A common type of the spectrin alpha I 46-50a-kD peptide abnormality in hereditary elliptocytosis and pyropoikilocytosis is associated with a mutation distant from the proteolytic cleavage site. Evidence for the functional importance of the triple helical model of spectrin.
(66/352)
We studied nine individuals from five unrelated families with alpha I/46-50a hereditary elliptocytosis (HE) or hereditary pyropoikilocytosis (HPP), including one of the original HHP probands first reported by Zarkowsky and colleagues (1975. Br. J. Haematol. 29:537-543). Biochemical analysis of erythrocyte membrane proteins from these patients revealed, as a common abnormality, the presence of the alpha I/46-50a peptide after limited tryptic digestion of spectrin. The polymerase chain reaction was utilized to study the structure of the DNA encoding the alpha I domain of spectrin in the affected individuals. The DNA sequence of the alpha-spectrin gene encoding the region of the alpha-spectrin chain surrounding the abnormal proteolytic cleavage site was normal. We identified a point mutation causing the replacement of a highly conserved leucine residue by proline at position 207 in the alpha-spectrin chain, a site 51 residues to the amino-terminal side of the abnormal proteolytic cleavage site. Analysis of the proposed triple helical model of spectrin repeats reveals that the mutation occurs in helix 2 at a position directly opposite the abnormal proteolytic cleavage site in helix 3, making this the first report of a mutation occurring in helix 2 of a repeat in the alpha I domain of spectrin. These results add to the molecular heterogeneity of mutations associated with HE/HPP and provide further support for the proposed triple helical model of spectrin. Disruption of this proposed alpha-helical structure by helix-breaking proline substitutions may result in a functionally defective spectrin chain. (+info)
Is the surface area of the red cell membrane skeleton locally conserved?
(67/352)
The incompressibility of the lipid bilayer keeps the total surface area of the red cell membrane constant. Local conservation of membrane surface area requires that each surface element of the membrane skeleton keeps its area when its aspect ratio is changed. A change in area would require a flow of lipids past the intrinsic proteins to which the skeleton is anchored. in fast red cell deformations, there is no time for such a flow. Consequently, the bilayer provides for local area conservation. In quasistatic deformations, the extent of local change in surface area is the smaller the larger the isotropic modulus of the skeleton in relation to the shear modulus. Estimates indicate: (a) the velocity of relative flow between lipid and intrinsic proteins is proportional to the gradient in normal tension within the skeleton and inversely proportional to the viscosity of the bilayer; (b) lateral diffusion of lipids is much slower than this flow; (c) membrane tanktreading at frequencies prevailing in vivo as well as the release of a membrane tongue from a micropipette are fast deformations; and (d) the slow phase in micropipette aspiration may be dominated by a local change in skeleton surface. (+info)
Globin-chain specificity of oxidation-induced changes in red blood cell membrane properties.
(68/352)
We have previously shown that excess unpaired alpha- and beta-globin chains in severe alpha- and beta-thalassemia interacting with the membrane skeleton induce different changes in membrane properties of red blood cells (RBCs) in these two phenotypes. We suggest that these differences in membrane material behavior may reflect the specificity of the membrane damage induced by alpha- and beta-globin chains. To further explore this hypothesis, we sought in vitro models that induce similar membrane alterations in normal RBCs. We found that treatment of normal RBCs with phenylhydrazine produced rigid and mechanically unstable membranes in conjunction with selective association of oxidized alpha-globin chains with the membrane skeleton, features characteristic of RBCs in severe beta-thalassemia. Methylhydrazine, in contrast, induced selective association of oxidized beta-globin chains with the membrane skeleton and produced rigid but hyperstable membranes, features that mimicked those of RBCs in severe alpha-thalassemia. These findings suggest that consequences of oxidation induced by globin chains are quite specific in that those agents that cause alpha-globin chain accumulation at the membrane produce rigid but mechanically unstable membranes, whereas membrane accumulation of beta-globin chains results in rigid but mechanically stable membranes. These in vitro experiments lend further support to the hypothesis that membrane-associated alpha- and beta-chains induce oxidative damage to highly specific different skeletal components and that the specificity of this skeletal damage accounts for the differences in material membrane properties of these oxidatively attacked RBCs and perhaps of alpha- and beta-thalassemic RBCs as well. (+info)
Pancreatic duct ligation reduces lung injury following trauma and hemorrhagic shock.
(69/352)
OBJECTIVE: To determine whether pancreatic digestive enzymes released into the ischemic gut during an episode of T/HS are involved in the generation of distant organ injury. This hypothesis was tested by examining the effect of PDL on T/HS-induced intestinal injury, lung injury, and RBC deformability. SUMMARY BACKGROUND DATA: The effect of pancreatic duct ligation (PDL) on distant organ injury following trauma/hemorrhagic shock (T/HS) was examined. PDL before T/HS decreases lung and red blood cell (RBC) injury and exerts a limited protective effect on the gut. Pancreatic proteases in the ischemic gut appear to be involved in gut-induced lung and RBC injury. Based on recent work, it appears that proinflammatory and/or toxic factors, which are generated by the ischemic intestine, play an important role in the pathogenesis of multiple organ failure. The process by which these toxic factors are generated remains unknown. Previous experimental work has clearly documented that intraluminal inhibition of pancreatic proteases decreases the degree of T/HS-induced lung injury and neutrophil activation. One possible explanation for this observation is that the toxic factors present in intestinal lymph are byproducts of interactions between pancreatic proteases and the ischemic gut. METHODS: Male Sprague-Dawley rats were subjected to a laparotomy (trauma) and 90 minutes of sham (T/SS) or T/HS with or without PDL. At 3 and 24 hours following resuscitation, animals were killed and samples of gut, lung, and blood were collected for analysis. Lung permeability, pulmonary myeloperoxidase levels, and bronchoalveolar fluid protein content were used to quantitate lung injury. Intestinal injury was determined by histologic analysis of terminal ileum (% villi injured). To assess RBC injury, RBC deformability was measured, as the RBC elongation index (RBC-EI), using a LORCA device. RESULTS: At 3 and 24 hours following resuscitation, PDL prevented shock-induced increases in lung permeability to both Evans blue dye and protein in addition to preventing an increase in pulmonary myeloperoxidase levels. T/HS-induced impairments in RBC deformability were significantly reduced at both time points in the PDL + T/HS group, but deformability did not return to T/SS levels. PDL did reduce the magnitude of ileal injury at 3 hours after T/HS, but the protective effect was lost at 24 hours after T/HS. CONCLUSIONS: PDL prior to T/HS decreases lung injury and improves RBC deformability but exerts a limited protective effect on the gut. Thus, the presence of pancreatic digestive enzymes in the ischemic gut appears to be involved in gut-induced lung and RBC injury. (+info)
Effect of antioxidant vitamin treatment on the time course of hematological and hemorheological alterations after an exhausting exercise episode in human subjects.
(70/352)
This study examined the effects of a 2-mo antioxidant vitamin treatment on acute hematological and hemorheological alterations induced by exhausting exercise; both sedentary and trained individuals were employed. Eighteen young male, human subjects (9 sedentary, 9 trained by regular exercise) participated in the study and performed an initial maximal aerobic cycle ergometer exercise with frequent blood sampling over a 24-h period and analysis of hematological and hemorheological parameters. All subjects were treated with an antioxidant vitamin A, C, and E regimen, supplemented orally for 2 mo, and then subjected to a second exercise test and blood sampling at the end of this period. In the sedentary group during the first testing period (before vitamin treatment), white blood cell counts and granulocyte percentages were increased at 2 h after the exercise test and remained elevated for 4-12 h. Red blood cell (RBC) deformability and aggregation were also altered by exercise in the sedentary group before vitamin treatment. However, none of these parameters in the sedentary group were altered by exercise after the 2-mo period of antioxidant vitamin treatment. With the exception of a transient rise in granulocyte percentage, these parameters were also not affected in the trained subjects before the vitamin treatment. Significant increases of RBC lipid peroxidation observed 12 h after the exercise test in both sedentary and trained subjects were also totally prevented by vitamin treatment. Our results indicate that antioxidant vitamin treatment is effective in preventing the inflammation-like response and coincident adverse hemorheological changes after an episode of exhausting exercise, and suggest that such changes may be related to exercise-induced death events. (+info)
Deformability measurements on individual sickle cells using a new system with pO2 and temperature control.
(71/352)
Although the rheologic behavior of sickle erythrocytes (SS cells) is highly dependent on oxygen tension (pO2) and temperature, very little data exist regarding the effects of deoxygenation and reoxygenation on the rheology of "individual" SS cells at body temperature. We have devised and assessed a new experiment system, in which micropipette aspiration can be performed on individual cells in a constant-temperature chamber that has ports for changing media with different pO2 (effected in 30 to 120 seconds) and sensing probes for monitoring pO2 and temperature. This system enabled us to simultaneously alter and monitor pO2 at 37 +/- 0.5 degrees C, and to monitor and study a single cell under microscopic observation. The static rigidity (E) and dynamic rigidity (eta) of individual SS cells were determined by repeated aspirations of the same cell under various pO2. With stepwise reductions in pO2, E and eta showed no significant changes before sickling, but once sickled, their values markedly increased by 10(2)- to 10(3)-fold concomitantly with morphologic alteration of the cell. Thus, the deformability of a single SS cell behaves in an "all or none" manner at a critical pO2, and earlier studies on the effect of deoxygenation on the rheology of SS cell suspensions probably reflect the overall behavior of SS cells with widely distributed critical pO2. (+info)
Red blood cell changes during the evolution of the sickle cell painful crisis.
(72/352)
A longitudinal study of the red blood cell (RBC) deformability, percent of dense erythrocytes, and hematologic parameters has been conducted during 117 painful crises affecting 36 patients with sickle cell anemia between January, 1985 and December, 1990. RBC deformability was determined by osmotic gradient ektacytometry and the percentage of dense cells was quantitated by centrifugation on a discontinuous Stractan density gradient. The data indicate that the painful crisis is a process that follows a bimodal form of evolution. The first phase of the painful crisis is characterized by increase in the severity of pain, increase in the number of dense cells, and a decrease in RBC deformability. In some patients the changes in dense cells and RBC deformability are evident 1 to 3 days before the onset of pain. In addition, the hemoglobin level decreases and the reticulocyte count increases during this initial phase. The second phase of the crisis is characterized by reduction in pain intensity, decrease in the number of dense cells, and increase in RBC deformability to values higher than those seen in the steady state. Moreover, the improvement in RBC deformability and the decrease in the number of dense cells at the end of a crisis seem to constitute new risk factors that may incite a recurrence of the crisis within 1 month in about 50% of painful episodes. The pathophysiologic events responsible for this bimodal behavior of RBCs during painful episodes may represent the appearance of factors that induce (1) preferential trapping of deformable cells in the microcirculation during the first phase of the crisis, followed by a decrease of dense cells and the appearance of new deformable RBCs released from the bone marrow during the second phase of the crisis; or (2) variable sickling of all circulating RBCs during the first phase followed by disappearance of dense RBCs and their replenishment by deformable cells during the second phase. (+info)