Interaction of the red cell membrane skeleton with the membrane

Erythrocyte damage and leukocyte activation in ischemic stroke

BACKGROUND

The traditional lipid risk factors can only predict some of the cardiovascular events. Our work has focused on new potential biological markers of risk, namely leukocyte activation and erythrocyte membrane damage, in ischemic stroke cases.

METHODS

Besides the traditional lipid profile, we evaluated the plasma levels of elastase and lactoferrin as markers of leukocyte activation, and membrane band 3 protein profile and membrane bound hemoglobin as markers of erythrocyte damage. Total and differential leukocyte counts and erythrocyte counts, hematocrit and hemoglobin concentrations were also evaluated. The lipid study included the evaluation of triglycerides, total cholesterol, high-density lipoprotein cholesterol (HDLc), low-density lipoprotein cholesterol (LDLc), apolipoprotein AI (Apo AI) and B (Apo B), and lipoprotein (a) (Lp(a)). The work was performed in a control group (n=29) with no history of cardiovascular events, presenting normal hematological and lipid values, and in a pathologic group (n=21) of ischemic stroke cases diagnosed by computed tomographic imaging.

RESULTS

We found that ischemic stroke was associated with significantly higher values of leukocytes, which seem to be activated, as shown by significant higher levels of elastase and lactoferrin. This activation seems to impose erythrocyte damage, as suggested by a significant increase in membrane bound hemoglobin and by a different band 3 profile.

CONCLUSIONS

Our data suggest that plasma levels of elastase and lactoferrin, together with levels of erythrocyte membrane bound hemoglobin and band 3 profile, could be used as powerful new markers of risk for cardiovascular events.

Erythrocyte membrane band 3 profile imposed by cellular aging, by activated neutrophils and by neutrophilic elastase

The aim of this study was to evaluate in vitro the modifications in the profile of erythrocyte membrane protein band 3 (monomer, aggregates and fragments) imposed by cellular aging, by activated neutrophils (AN) and by neutrophilic elastase. The modifications imposed by cellular aging were evaluated in fractions of less dense and dense red blood cells (RBCs). To evaluate the changes imposed by AN, suspensions of RBCs and AN were used, in a ratio similar to or higher than that described elsewhere for individuals post-myocardial infarction (Santos-Silva A et al. Atherosclerosis 1995; 116:199-209). Neutrophilic elastase was used at increased concentrations. We found that the modifications imposed upon band 3 profile by AN and neutrophilic elastase were significantly correlated with AN and elastase concentration, and were similar to those presented by cellular aging. We propose band 3 profile as a useful cumulative marker of oxidative and/or proteolytic stress conditions, namely those arising from normal RBC aging or from an accelerated aging process imposed by stressful situations, such as inflammatory diseases.

Restriction by ankyrin of band 3 rotational mobility in human erythrocyte membranes and reconstituted lipid vesicles

Rotational diffusion of eosin-5-maleimide-labeled band 3 was measured in erythrocyte membranes at pH 9.4-10.4. Band 3 was found to be more mobile in this pH range than at pH 7.5. Similar results were obtained with spectrin-actin-depleted membranes, where it was further shown that ankyrin is the only detectable protein released from the membrane at pH 10. Further experiments were performed at pH 7.5 to investigate the effects of rebinding purified ankyrin and/or band 4.1 to ghosts stripped of skeletal proteins. Ankyrin was found to reduce band 3 rotational mobility, but band 4.1 had no effect. A fluorescence binding assay revealed that fluorescein isothiocyanate-labeled ankyrin had similar binding parameters to those reported previously using 125I labeling. Finally, the rotational mobility of purified band 3 reconstituted into lipid bilayers was determined before and after ankyrin binding. The results of these reconstitution experiments were globally analyzed, assuming the existence of two populations of band 3 with different correlation times. The faster correlation time is consistent with that expected for either dimers or compact tetramers of band 3. Ankyrin binding reduces the proportion of band 3 contributing to the faster component. This result demonstrates that ankyrin promotes the association of band 3 into more slowly rotating complexes independently of any other components of the erythrocyte membrane. It has been reported that ankyrin contains two binding sites for band 3 [Michaely, P., & Bennett, V. (1995) J. Biol. Chem. 270, 22050-22057]. The results of the present study are thus explained by the ability of ankyrin to cross-link band 3 into larger diameter complexes. Cross-linking by ankyrin in part accounts for the slow components in the anisotropy decays of band 3 in the erythrocyte membrane. Other factors which probably influence band 3 aggregation include the membrane "fluidity" and protein concentration.

A role for erythrocyte band 3 degradation by the parasite gp76 serine protease in the formation of the parasitophorous vacuole during invasion of erythrocytes by Plasmodium falciparum

A purified Plasmodium falciparum serine protease (gp76) implicated in erythrocyte invasion, degrades human erythrocyte band 3 and glycophorin A. Inhibition studies using synthetic peptides derived from the presumed band 3 enzymatic cleavage sites and the observed uptake of fluorescent phospholipids following gp76 treatment, suggest that band 3 degradation by this serine protease participates in the formation of the parasitophorous vacuole by restructuring the red cell cytoskeleton. These results provide a rationale for the elaboration of specific inhibitors to block red cell invasion by malaria parasites.

Loss of rotational mobility of band 3 proteins in human erythrocyte membranes induced by antibodies to glycophorin A

The effect of antibodies to glycophorin A on the rotational diffusion of band 3 in human erythrocyte membranes was investigated by transient dichrosim. Three antibodies that recognize different epitopes on the exofacial domain of glycophorin A all strongly reduce the rotational mobility of band 3. The effect is at most only weakly dependent on the distance of the epitope from the membrane surface. The degree of immobilization obtained with two of the antibodies, BRIC14 and R18, is very similar to that produced by antibodies to band 3 itself. Similar results were obtained with membranes stripped of skeletal proteins. Fab fragments and an antibody to glycophorin C had no effect on band 3 rotational mobility. These results rule out a mechanism whereby band 3 rotational immobilization results from enhanced interactions with the membrane skeleton that are mediated by a conformational change in glycophorin A. Rather, they strongly indicate that the antibodies to glycophorin A cross-link existing band 3-glycophorin A complexes that have lifetimes that are long compared with the millisecond time scale of the transient dichroism measurements.