Erythrocyte Clearance

Effects of weight loss on erythrocyte membrane composition and fluidity in overweight and moderately obese women

A previous study showed chemical and physical impairment of the erythrocyte membrane of overweight and moderately obese women. The present study investigated the effects of a low-calorie diet (800 kcal/day deficit for 8 weeks) on erythrocyte membrane properties in 70 overweight and moderately obese (body mass index, 25-33 kg/m(2)) normotensive, nondiabetic women. At the end of dietary intervention, 24.3% of women dropped out, 45.7% lost less than 5% of their initial weight (Group I) and only 30% of patients lost at least 5% of their initial body weight (Group II). Group I showed no significant changes in erythrocyte membrane composition and function. The erythrocyte membranes of Group II showed significant reductions in malondialdehyde, lipofuscin, cholesterol, sphingomyelin, palmitic acid and nervonic acid and an increase in di-homo-γ-linolenic acid, arachidonic acid and membrane fluidity. Moreover, Group II showed an improvement in total cholesterol, low-density lipoprotein cholesterol, glycemia and insulin resistance. These changes in erythrocyte membrane composition could reflect a virtuous cycle resulting from the reduction in insulin resistance associated with increased membrane fluidity that, in turn, results in a sequence of metabolic events that concur to further improve membrane fluidity.

Ion transport pathology in the mechanism of sickle cell dehydration

Polymers of deoxyhemoglobin S deform sickle cell anemia red blood cells into sickle shapes, leading to the formation of dense, dehydrated red blood cells with a markedly shortened life-span. Nearly four decades of intense research in many laboratories has led to a mechanistic understanding of the complex events leading from sickling-induced permeabilization of the red cell membrane to small cations, to the generation of the heterogeneity of age and hydration condition of circulating sickle cells. This review follows chronologically the major experimental findings and the evolution of guiding ideas for research in this field. Predictions derived from mathematical models of red cell and reticulocyte homeostasis led to the formulation of an alternative to prevailing gradualist views: a multitrack dehydration model based on interactive influences between the red cell anion exchanger and two K(+) transporters, the Gardos channel (hSK4, hIK1) and the K-Cl cotransporter (KCC), with differential effects dependent on red cell age and variability of KCC expression among reticulocytes. The experimental tests of the model predictions and the amply supportive results are discussed. The review concludes with a brief survey of the therapeutic strategies aimed at preventing sickle cell dehydration and with an analysis of the main open questions in the field.

Erythrocyte damage in mild and severe psoriasis

BACKGROUND

Psoriasis is a common chronic and recurrent inflammatory skin disorder. Oxygen metabolites and proteases released by activated inflammatory cells may induce oxidative and proteolytic damage to plasma constituents and red blood cells (RBCs). RBCs have a limited biosynthesis capacity and poor repair mechanisms.

OBJECTIVES

To study RBCs as a potential cumulative marker of oxidative and proteolytic stress in psoriasis, and as a marker of worsening of the disease.

METHODS

The study was performed in 70 patients with mild or severe psoriasis and in 40 control individuals. We evaluated total and differential leucocyte count and, as markers of leucocyte activation, plasma elastase and lactoferrin. Besides the basic RBC study (RBC count, haematocrit, haemoglobin concentration and haematimetric indices) we evaluated antioxidant defences (catalase, superoxide dismutase, glutathione peroxidase and selenium), osmotic fragility and reticulocyte count; in the RBC membrane we evaluated lipid peroxidation and susceptibility to lipid peroxidation, membrane fluidity, levels of cholesterol and phospholipids, membrane-bound haemoglobin, band 3 profile and levels of vitamin E; serum levels of bilirubin, total plasma antioxidant capacity, lipid profile and lipid peroxidation were also evaluated.

RESULTS

Psoriasis patients showed a rise in leucocytes, mainly neutrophils, which was associated with a rise in elastase and lactoferrin. Patients had a reduced RBC count, antioxidant defences and membrane fluidity, elevated membrane lipid peroxidation, membrane-bound haemoglobin, osmotic fragility and reticulocyte count, and a different band 3 profile. Most of these modifications were enhanced in severe psoriasis.

CONCLUSIONS

In summary, our data show that the RBCs are at a lower number in psoriasis patients, and present several changes denoting an enhanced damage and/or ageing process, which seem to be strongly connected with neutrophil activation, oxidative stress and worsening of psoriasis.

16alpha-bromoepiandrosterone, an antimalarial analogue of the hormone dehydroepiandrosterone, enhances phagocytosis of ring stage parasitized erythrocytes: a novel mechanism for antimalarial activity

Dehydroepiandrosterone (DHEA) and DHEA-sulfate (DHEA-S), which are the most abundant hormones secreted by the adrenal cortex and are present in plasma at approximately 6 micro M, as well as their analogue, 16alpha-bromoepiandrosterone (EPI), exerted antimalarial activities against two chloroquine-sensitive Plasmodium falciparum strains (Palo Alto, 50% inhibitory concentration [IC(50)] of EPI, 4.8 +/- 0.68 micro M; T996/86, IC(50) of EPI, 7.5 +/- 0.91 micro M, and IC(50) of DHEA-S, 19 +/- 2.6 micro M) and one mildly chloroquine-resistant strain (FCR-3, IC(50) of EPI, 6.5 +/- 1.01 micro M). Both EPI and DHEA/DHEA-S are potent inhibitors of glucose-6-phosphate dehydrogenase (G6PD), and G6PD deficiency is known to exert antimalaria protection via enhanced opsonization and phagocytosis of rings, the early forms of the parasite. Plasma-compatible antimalarial EPI concentrations did not inhibit G6PD activity and did not induce ring opsonization by immunoglobulin G and complement fragments, as observed in G6PD deficiency, but nevertheless remarkably stimulated ring phagocytosis. Plasma-compatible, low-micromolar concentrations of EPI induced exposure on the ring surface of phosphatidylserine, a signal for phagocytic removal independent of opsonization. We propose that enhanced ring phagocytosis due to exposure of negatively charged membrane phospholipids may explain the antimalarial activity of EPI.

Flow cytometric approach to the study of erythrophagocytosis: evidence for an alternative immunoglobulin-independent pathway in agammaglobulinemic mice

Neuraminidase treatment of red blood cells (RBCs) is believed to induce changes similar to RBC senescence, and leads to a rapid clearance of RBCs from the circulation in vivo. The objective of this study using immunodeficient SCID mice and the lipophilic fluorescent probe PKH-26 was to ascertain whether antibodies are required as the final signal allowing the phagocytosis of neuraminidase-treated murine RBCs. All of the methods we applied are based on flow cytometry analysis using fluorescent probes: fluoresceinyl isothiocyanate (FITC)-labeled lectins for membrane carbohydrate identification and PKH-26-labeled RBCs for in vitro phagocytosis and in vivo clearance studies. The results can be summarized as follows: (i) the rate of neuraminidase-induced desialylation of RBCs from normal and immunodeficient mice is identical as ascertained with FITC-labeled lectins (wheat germ agglutinin (WGA) and Ricinus communis agglutinin (RCA(120))); (ii) the rate of clearance of enzyme-treated RBCs from both types of mice is also similar, as is their localization in spleen, liver and lung; (iii) the rates of in vitro phagocytosis of untreated and neuraminidase-treated PKH-26-labeled RBCs from both species of mice are very similar in the presence of homologous sera. In the absence of serum or in the presence of heterologous sera, the rate of phagocytosis is markedly decreased but not totally abolished. These data suggest that neuraminidase-treated RBCs can be cleared via an alternative pathway that is antibody-independent. This pathway exists in immunocompetent mice but with a very low activity and is the only one active in immunodeficient mice. In accordance with results reported by Connor et al. [J. Biol. Chem. 269 (1994) 2399], it is possible that this antibody-independent mechanism is involved in the clearance of circulating senescent RBCs. Finally, the methods described here may also be of interest for the investigation of the mechanisms involved in the phagocytosis of apoptotic cells.

Acute haemolysis in childhood falciparum malaria

Acute haemolysis associated with clinical episodes of high-level Plasmodium falciparum parasitaemia was studied in 20 children from an holoendemic area (coastal Tanzania). The change in blood haemoglobin (Hb) concentration ranged from -46 to g/L during the 72-h observation period and was linearly related to maximum parasitaemia. Balance studies between loss of blood Hb, increase in plasma Hb and appearance of Hb in the urine indicated that extravascular clearance of red cells was the predominant mode of erythrocyte clearance. Most subjects, however, showed minor signs of intravascular haemolysis. The plasma Hb was << 1% of blood Hb and haemoglobinuria was detected in 14/20 children but the excretion of Hb in urine was < 0.5% of total Hb loss. Haemoglobinuria was, however, a marker of severe haemolysis, since the maximum blood Hb loss in children without haemoglobinuria was 10 g/L. Erythrocyte-bound opsonins known to induce erythrophagocytosis, i.e., complement C3c fragments and autologous IgG, were increased in all patients. In the patients with major haemolysis, the changes correlated to the haemolysis over time. Hence, a similar mechanism for predominantly extravascular erythrocyte clearance may be operative in acute malarial anaemia, normal erythrocyte senescence and other forms of acute haemolysis.

Alteration of alpha-spectrin ubiquitination due to age-dependent changes in the erythrocyte membrane

Mammalian red blood cell alpha-spectrin is ubiquitinated in vitro and in vivo [Corsi, D., Galluzzi, L., Crinelli, R., Magnani, M. (1995) J. Biol. Chem. 270, 8928-8935]. This process shows a cell age-dependent decrease, with senescent red blood cells having approximately one third of the amount of ubiquitinated alpha-spectrin found in young cells. In-vitro ubiquitination of alpha-spectrin was dependent on the source of the red cell membranes (those from older cells are less susceptible to ubiquitination than those from younger cells), on the source of ubiquitin-conjugating enzymes (those from older cells catalyze the process at a reduced rate compared to those from younger cells) and on the ubiquitin isopeptidase activity (which decreases during red cell ageing). However, once alpha-spectrin has been extracted from the membranes of young or old red blood cells, it is susceptible to ubiquitination to a similar extent regardless of source. This suggests that it is the membrane architecture, and not spectrin itself, that is responsible for the age-dependent decline in ubiquitination. Furthermore, spectrin oligomers, tetramers and dimers are also equally susceptible to ubiquitination. As spectrin ubiquitination occurs on domains alphaIII and alphaV of alpha-spectrin, and domain alphaV contains the nucleation site for the association of the alpha- and beta-spectrin chains, alterations in ubiquitination during red cell ageing could affect the stability and deformability of the erythrocyte membrane.

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.

Independent mechanisms for macrophage binding and macrophage phagocytosis of damaged erythrocytes. Evidence of receptor cooperativity

The binding and phagocytosis of oxidatively damaged red blood cells (OxRBCs) by mouse peritoneal macrophages can be inhibited by oxidatively modified LDL (OxLDL), implying some commonality at their receptor-binding domains. Studies from many different laboratories support the view that OxRBC binding is due to the disruption of plasma membrane phospholipid asymmetry and the subsequent exposure of phosphatidylserine (PS) on the outer membrane leaflet. Presumably, oxidation of LDL creates a surface structure on it in some way homologous to the PS-rich domain on OxRBCs. Apoptotic cells in some instances are also recognized because of PS exposure on the outer leaflet of the membrane, and apoptotic cells are a common feature of atherosclerotic lesions. In the present studies, the mechanisms of binding and internalization of cells recognized by virtue of their membrane PS were studied using OxRBCs or vanadate-treated erythrocytes (VaRBCs) as models. Disruption of phospholipid asymmetry with vanadate produced cells that were bound by macrophages in the same divalent cation-dependent manner as OxRBCs. However, whereas OxRBCs were rapidly phagocytosed, VaRBCs were not. Stimulation of mouse macrophages with phorbol myristate acetate resulted in a concentration-dependent induction of phagocytosis of bound VaRBCs, an effect that could be prevented by the protein kinase C inhibitor staurosporine. Because phagocytosis of OxRBCs occurred unassisted, we speculated that there must be additional membrane changes induced by oxidation (over and above the disruption of phospholipid asymmetry) that contribute to phagocytosis of OxRBCs, possibly resulting in the ligation of a distinct receptor that does not necessarily contribute to adherence. This proposal is supported by the finding that ligation of macrophage Fc gamma receptors by the anti-Fc gamma RII/RIII antibody 2.4G2 triggers the phagocytosis of bound VaRBCs. Phagocytosis is also triggered by subthreshold opsonization of VaRBC, i.e., by antibody concentrations that do not by themselves cause binding and phagocytosis of native RBCs. Finally, treatment with low concentrations of glutaraldehyde, which causes membrane protein cross-linking, promotes the phagocytosis of VaRBCs, but, at the low concentration used, has little or no effect on binding and phagocytosis of native RBCs. We suggest that the internalization of damaged cells, bound because of PS exposure, requires the cooperation of a PS-binding receptor with at least one additional receptor to trigger an intracellular signaling pathway to initiate phagocytosis.

Aminotransferase activities in mouse, Mus domesticus, erythrocytes separated according to age

Erythrocyte aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities are often used as indices of vitamin B-6 nutritional status; however, results using a mixed population of erythrocytes can be quite variable. Erythrocytes from two strains of mice (Mus domesticus), A/Ibg and DBA/Ibg, were separated according to age by centrifugation through discontinuous Percoll density gradients into three fractions: top (least dense, youngest), middle and bottom (most dense, oldest). A sufficient yield of age-fractionated erythrocytes was obtained from a single mouse for all of the enzyme measurements. The activities of AST, ALT and three age-marker enzymes, pyruvate kinase, acetylcholinesterase and hexokinase, were found to be significantly higher in the youngest cell fractions, and declined in the older, more dense fractions. A mice had significantly lower AST and ALT activities in the age separated fractions than did DBA mice. The measurement of enzyme activities in low density, young cells may be especially useful in studies involving conditions in which the proportion of young erythrocytes may be elevated with respect to the entire erythrocyte mass.

An indirect effect of an antibody on complement deposition and lysis of differently sensitized surrounding cells

Lysis of papain-treated group A and B erythrocytes by human complement was studied by an anti-A (BRIC. 131) and an anti-B (BRIC. 30) IgM monoclonal antibody in 51Cr release assays. The indirect effect of membrane-bound antibody, i.e. its influence on complement binding to sensitized surrounding cells, was examined in a cold target competition test in which sensitized, non-labelled cells are present along with sensitized labelled cells and complement. The mode by which anti-A antibodies indirectly suppressed lysis of sensitized B cells up to 20-fold was studied by following C1q and C3b binding. C1q binding to both types of erythrocytes was not altered in mixed populations of erythrocytes in the presence of both antibodies. Binding of C3b to a mixture of both cell types was, however, suppressed, when both antibodies were present. C3b deposition in mixed cell populations did not reach a significantly higher extent than deposited to one type of erythrocyte alone. This was consistent with the results from competitive lysis and suggests that the anti-A captured most C3b at high anti-A concentrations and deprived the similarly sensitized B erythrocytes of complement. We think that this phenomenon is not due to an uneven removal of complement regulatory proteins from A and B erythrocytes by papain. Instead, the phenomenon might be due to an inherent property of anti-A mAb to better produce nucleation sites for C3 convertases which, upon binding factor B, better compete for the limiting factor D. A mathematical analysis of cold target competition experiment (containing 2430 individual measurements) also shows that the distribution of complement between the competing A and B erythrocyte population is uneven, since it predicts that in any given antibody combination the majority of complement is bound to A erythrocytes. This is consistent with the measured average percentage of lysis.

Altered properties of erythrocytes in the aged

Erythrocytes in the aged have a decreased life span. The properties of the red blood cells of old individuals are compared to those of the cells of young individuals. In young individuals, removal of the normal erythrocyte at the end of its lifespan is determined by a signal(s) due to (1) modified phospholipids, (2) modified carbohydrate residues, and/or (3) modified proteins. Similar changes may occur in the erythrocytes of old individuals but at a greater rate. In particular, the enhanced degradation of band 3 protein by calpain may provide a senescence signal.

Inhibition of IgM antibody-mediated aggregation of Trypanosoma gambiense in the presence of complement

This paper deals with the immune reaction between Trypanosoma gambiense and monoclonal IgM mouse antibody at equivalence with or without rabbit complement. Antibody-mediated trypanosome clumps formed in the absence of complement, and were readily dissociated by complement to become free. In the presence of complement, on the other hand, T. gambiense were not aggregated by the antibody. Free parasites adhered readily to cultured peritoneal macrophages. Complement-mediated dissociation of the clumped trypanosomes in the equivalence area released a large number of previously bound surface antigens. These antigens were capable of binding again to fresh IgM antibody. Experimental results further indicated that the complement system caused a functional alteration, changing the multivalent nature of the IgM antibody in the immune complex into a univalent one. This phenomenon is of great advantage to the infected host in clearing pathogens in vivo, as it allows more antibodies to attach to trypanosomes and subsequently initiate complement activity.

Complement receptor 1 (CR1) expression in chronic myeloid leukemia

The complement receptor 1 (CR1), also called CD35, is a polymorphic glycoprotein which mediates a variety of neutrophil functions, including phagocytosis and, probably, tumor cell cytotoxicity. The role played by this molecule in chronic myeloid leukemia (CML) is not yet well understood. CML frequently shows a marked decrease of CR1 antigens on both the neutrophil population and myeloid precursors. This reduced expression appears to be related to disease activity, since patients at more advanced clinical stages, as well as those who develop blastic crisis, have been found to express the lowest levels of CR1 antigens. At the onset of the disease low CR1 expression on CML neutrophils seems to be associated with a higher risk of blastic transformation. Furthermore, CML neutrophils deficient in CR1 lack the ability to respond to PMA stimulation, suggesting a failure in CR1 granular storage. In patients lacking CR1, the number of receptors increased to normal levels following exposure of CML cells to therapeutic concentrations of recombinant alpha interferon. The role played by the CR1 molecule in sustaining neutrophil-mediated tumor cell cytotoxicity has yet to be definitively proved; studies performed by our group are relevant here, since complete suppression of tumor lysis following receptor neutralization by anti CR1 monoclonal antibodies was demonstrated in a large number of normal and CML individuals. In CML patients, the evidence of a direct relationship between lytic activity and antigen receptor levels seems to further support the involvement of CR1 molecules in tumor cell lysis, function.(ABSTRACT TRUNCATED AT 250 WORDS)