Distribution of sialic acids on the red blood cell membrane in beta thalassaemia

Biomimetic-Membrane-Protected Plasmonic Nanostructures as Dual-Modality Contrast Agents for Correlated Surface-Enhanced Raman Scattering and Photoacoustic Detection of Hidden Tumor Lesions

Optical imaging and spectroscopic modalities are of considerable current interest for in vivo cancer detection and image-guided surgery, but the turbid or scattering nature of biomedical tissues has severely limited their abilities to detect buried or occluded tumor lesions. Here we report the development of a dual-modality plasmonic nanostructure based on colloidal gold nanostars (AuNSs) for simultaneous surface-enhanced Raman scattering (SERS) and photoacoustic (PA) detection of tumor phantoms embedded (hidden) in ex vivo animal tissues. By using red blood cell membranes as a naturally derived biomimetic coating, we show that this class of dual-modality contrast agents can provide both Raman spectroscopic and PA signals for the detection and differentiation of hidden solid tumors with greatly improved depths of tissue penetration. Compared to previous polymer-coated AuNSs, the biomimetic coatings are also able to minimize protein adsorption and cellular uptake when exposed to human plasma without compromising their SERS or PA signals. We further show that tumor-targeting peptides (such as cyclic RGD) can be noncovalently inserted for targeting the ανβ3-integrin receptors expressed on metastatic cancer cells and tracked via both SERS and PA imaging (PAI). Finally, we demonstrate image-guided resections of tumor-mimicking phantoms comprising metastatic tumor cells buried under layers of skin and fat tissues (6 mm in thickness). Specifically, PAI was used to determine the precise tumor location, while SERS spectroscopic signals were used for tumor identification and differentiation. This work opens the possibility of using these biomimetic dual-modality nanoparticles with superior signal and biological stability for intraoperative cancer detection and resection.

Clinical impact of glycans in platelet and megakaryocyte biology

Humans produce and remove 1011 platelets daily to maintain a steady-state platelet count. The tight regulation of platelet production and removal from the blood circulation prevents anomalies in both processes from resulting in reduced or increased platelet count, often associated with the risk of bleeding or overt thrombus formation, respectively. This review focuses on the role of glycans, also known as carbohydrates or oligosaccharides, including N- and O-glycans, proteoglycans, and glycosaminoglycans, in human and mouse platelet and megakaryocyte physiology. Based on recent clinical observations and mouse models, we focused on the pathologic aspects of glycan biosynthesis and degradation and their effects on platelet numbers and megakaryocyte function.

The erythrocyte membrane properties of beta thalassaemia heterozygotes and their consequences for Plasmodium falciparum invasion

Malaria parasites such as Plasmodium falciparum have exerted formidable selective pressures on the human genome. Of the human genetic variants associated with malaria protection, beta thalassaemia (a haemoglobinopathy) was the earliest to be associated with malaria prevalence. However, the malaria protective properties of beta thalassaemic erythrocytes remain unclear. Here we studied the mechanics and surface protein expression of beta thalassaemia heterozygous erythrocytes, measured their susceptibility to P. falciparum invasion, and calculated the energy required for merozoites to invade them. We found invasion-relevant differences in beta thalassaemic cells versus matched controls, specifically: elevated membrane tension, reduced bending modulus, and higher levels of expression of the major invasion receptor basigin. However, these differences acted in opposition to each other with respect to their likely impact on invasion, and overall we did not observe beta thalassaemic cells to have lower P. falciparum invasion efficiency for any of the strains tested.

New Insights into Hemolytic Anemias: Ultrastructural and Nanomechanical Investigation of Red Blood Cells Showed Early Morphological Changes

Several diseases are characterized by changes in the mechanical properties of erythrocytes. Hemolytic anemias are an example of these diseases. Among the hemolytic anemias, Sickle Cell Disease and Thalassemia are the most common, characterized by alterations in the structure of their hemoglobin. Sickle cell disease has a pathological origin in synthesizing abnormal hemoglobin, HbS. In contrast, thalassemia results in extinction or decreased synthesis of α and β hemoglobin chains. This work presents a detailed study of biophysical and ultrastructural early erythrocytes membrane alterations at the nanoscale using Atomic Force Microscopy (AFM). Cells from individuals with sickle cell anemia and thalassemia mutations were studied. The analysis methodology in the AFM was given by blood smear and exposure of the inner membrane for ghost analysis. A robust statistic was used with 65,536 force curves for each map, ten cells of each type, with three individuals for each sample group. The results showed significant differences in cell rigidity, adhesion, volume, and roughness at early morphological alterations, bringing new perspectives for understanding pathogenesis. The sickle cell trait (HbAS) results stand out. Significant alterations were observed in the membrane properties, bringing new perspectives for the knowledge of this mutation. This work presents ultrastructural and biomechanical signatures of sickle cell anemia and thalassemia genotypes, which may help determine a more accurate biophysical description and clinical prognosis for these diseases.

Characterization and statistical modeling of glycosylation changes in sickle cell disease

Sickle cell disease is an inherited genetic disorder that causes anemia, pain crises, organ infarction, and infections in 13 million people worldwide. Previous studies have revealed changes in sialic acid levels associated with red blood cell sickling and showed that stressed red blood cells bare surface-exposed clustered terminal mannose structures mediating hemolysis, but detailed glycan structures and anti-glycan antibodies in sickle cell disease remain understudied. Here, we compiled results obtained through lectin arrays, glycan arrays, and mass spectrometry to interrogate red blood cell glycoproteins and glycan-binding proteins found in the plasma of healthy individuals and patients with sickle cell disease and sickle cell trait. Lectin arrays and mass spectrometry revealed an increase in α2,6 sialylation and a decrease in α2,3 sialylation and blood group antigens displayed on red blood cells. Increased binding of proteins to immunogenic asialo and sialyl core 1, Lewis A, and Lewis Y structures was observed in plasma from patients with sickle cell disease, suggesting a heightened anti-glycan immune response. Data modeling affirmed glycan expression and plasma protein binding changes in sickle cell disease but additionally revealed further changes in ABO blood group expression. Our data provide detailed insights into glycan changes associated with sickle cell disease and refer glycans as potential therapeutic targets.

Multivariate analysis of mean Raman spectra of erythrocytes for a fast analysis of the biochemical signature of ageing

Ageing of red blood cells (RBC) is a physiological process, fundamental to ensure a proper blood homeostasis that, in vivo, balances the production of new cells and the removal of senescent erythrocytes. A detailed characterization at the cellular level of the progression of the ageing phenomenon can reveal biological, biophysical and biochemical fingerprints for diseases related to misbalances of the cell turnover and for blood pathologies. We applied Principal Components Analysis (PCA) to mean Raman spectra of single cells at different ageing times to rapidly highlight subtle spectral differences associated with conformational and biochemical modifications. Our results demonstrate a two-step ageing process characterized by a first phase in which proteins plays a relevant role, followed by a further cellular evolution driven by alterations in the membrane lipid contribution. Moreover, we used the same approach to directly analyse relevant spectral effects associated to reduction in Haemoglobin oxygenation level and membrane fluidity induced by the ageing. The method is robust and effective, allowing to classify easily the studied cells based on their age and morphology, and consequently to evaluate the biological quality of a blood sample.

RBC-Derived Optical Nanoparticles Remain Stable After a Freeze-Thaw Cycle

Nanosized carriers engineered from red blood cells (RBCs) provide a means for delivering various cargos, including drugs, biologics, and imaging agents. We have engineered nanosized particles from RBCs, doped with the near-infrared (NIR) fluorochrome, indocyanine green (ICG). An important issue related to clinical translation of RBC-derived nanocarriers, including these NIR nanoparticles, is their stability postfabrication. Freezing may provide a method for long-term storage of these and other RBC-derived nanoparticles. Herein, we have investigated the physical and optical stability of these particles in response to a single freeze-thaw cycle. Nanoparticles were frozen to -20 °C, stored frozen for up to 8 weeks, and then thawed at room temperature. Our results show that the hydrodynamic diameter, zeta potential, optical density, and NIR fluorescence emission of these nanoparticles are retained following the freeze-thaw cycle. The ability of these nanoparticles in NIR fluorescence imaging of ovarian cancer cells, as well as their biodistribution in reticuloendothelial organs of healthy Swiss Webster mice after the freeze-thaw cycle is similar to that for freshly prepared nanoparticles. These results indicate that a single cycle of freezing the RBC-derived nanoparticles to -20 °C followed by thawing at room temperature is an effective method to retain the physical and optical characteristics of the nanoparticles, and their interactions with biological systems without the need for use of cryoprotectants.

Loss of phospholipid membrane asymmetry and sialylated glycoconjugates from erythrocyte surface in haemoglobin E beta-thalassaemia

This study aimed to investigate any correlation between the extent of phosphatidylserine (PS) asymmetry and sialylated glycoconjugate levels with the faster clearance of circulating erythrocytes in haemoglobin E (HbE) beta-thalassaemia. Erythrocytes from peripheral blood samples of different HbEbeta-thalassaemia patients showed loss of PS asymmetry measured by annexin V binding using flow cytometry. Maximum PS exposure was found when HbE was 50-60% and HbF was <20% indicating a possible correlation with severity of the disease. Separation of erythrocytes into aged and younger cells showed higher loss of PS asymmetry in the younger erythrocytes of HbEbeta-thalassaemia patients when compared with normal blood, where PS asymmetry was lost only in the older cells. Sialylated glycoconjugate measurement using the lectins wheatgerm agglutinin and pokeweed mitogen showed loss of sialic acid and N-acetyl-D-glucosamine-bearing glycoproteins in the order normal<homozygous E<HbEbeta-thalassaemic upon ageing. A possible correlation was found between the loss of PS asymmetry with HbE level and the reduction of glycophorins from the cell surface, mediated by membrane vesiculation. A more facilitated vesiculation process in HbEbeta-thalassaemic erythrocytes could lead to faster shedding of glycophorin-containing microvesicles, leaving highly PS-exposed erythrocytes accessible to phagocytes.

Flow cytometric quantitation of red blood cell vesicles in thalassemia

BACKGROUND

Thalassemia is a hereditary hemolytic anemia caused by mutations in the globin gene complex. Circulatory disturbances including arterial and venous thrombosis have also been noted in these patients. Aggregability of abnormal RBC and the high level of membrane-derived microparticles stemming from activated platelets and other blood cells are thought to be responsible for the associated thrombotic risk. Destruction of RBC is also thought to be an important pathophysiological consequence, particularly through the formation of circulating vesicles. To our knowledge, there has been no attempt to quantitatively evaluate the number of RBC vesicles in thalassemia. This prompted us to study the level of RBC vesicles in the peripheral blood of thalassemia patients using quantitative flow cytometry.

METHODS

Whole blood from each subject was doubly stained for RBC and platelet or annexin V markers, together with the known density TruCount beads. RBC vesicles were gated according to their forward/side scatter and RBC marker. Percentage of RBC vesicles and their absolute number were analyzed by flow cytometry.

RESULTS

Our data indicated that RBC vesicles were annexin V-positive. The number of annexin V-positive events was higher than their intact RBCs. RBC vesicles were present in both normal and thalassemic blood samples, but the numbers of RBC vesicles were significantly higher in thalassemia. Both the percentage and the absolute number of RBC vesicles were especially marked in splenectomized subjects with beta-thalassemia/Hemoglobin E. When clinical and hematological indices were compared with RBC vesicles, there was an inverse relationship between the degree of severity in thalassemia patients and the number of RBC vesicles.

CONCLUSION

Flow cytometric quantitation of RBC vesicles is simple, reliable and may offer new insights in to study of the relationship between defective hemoglobin synthesis, RBC perturbation and pathophysiological complications in thalassemia.

Defective organization of the erythroid cell membrane in a novel case of congenital anemia

In the present paper, we demonstrate the erythroid cell membrane unique properties in a previously characterized case of hemoglobin-H disease, associated with congenital dyserythropoietic anemia type-I features. In order to explain the patient's cell membrane distortions and the high affinity for the various intracellular inclusions, we studied its composition and structure in comparison to other anemic and non-anemic cases. Red cells from peripheral blood were fractionated into cellular, membrane and protein extracts. Membrane attached immunocomplexes were separated and collected by immunoprecipitation. The subcellular fractions were analyzed by SDS-PAGE electrophoresis and immunoblotted against a variety of erythroid-specific antibodies. The protein composition of the membrane was characterized by immunogold electron microscopy. In the membrane of the CDA-associated case, we identified sialic acid and protein deficiencies, formation of protein crosslinkings, excesses of bound globin and immunoglobulins and aberrant peptides. In contrast to the typical hemoglobin-H disease, the ghost-bound globin exhibited preferential attachment to the skeletal proteins than the band 3 and the skeleton-bound globin consisted not only of beta- but also of alpha-globin chains. Another hallmark, probably associated with the CDA defect, was the participation of glycophorins in the membrane-bound immunocomplexes and the pathological clustering of the latter in the membrane. This study strongly suggests that the result of the combinatorial effects on the diseased membrane created a unique profile, quite distinct from the one observed in several typical hemoglobinopathies. Our observations shed light into critical membrane alterations leading to hemolysis in the novel CDA-associated disease and probably into the CDA-I or CDA-I-like diseases.

Sialidase in rabbit blood. Characterization of sialidase purified from rabbit erythrocyte membrane

Sialidase activities of rabbit blood cells and serum were measured. The leucocyte particulate fraction showed the highest specific activity of sialidase towards mixed gangliosides and sialyllactose, and the cytosolic fraction showed for fetuin. Predominant sialidase activity in the blood was detected in erythrocyte particulate fraction when mixed gangliosides were used as substrate. The sialidase for ganglioside was solubilized from the erythrocyte ghosts by using Triton X-100. The solubilized sialidase was purified 1886-fold by sequential chromatographies on DEAE-cellulose, EAH-Sepharose 4B, Octyl-Sepharose CL-4B, Sephadex G-100, concanavalin-A--Sepharose, N-(p-aminophenyl)oxamic acid-agarose and Heparin-Sepharose CL-6B. The optimum pH of purified sialidase was 4.5 for ganglioside mixture, and this enzyme exhibited M(r) = 48,000 by gel filtration. When the purified sialidase was subjected to SDS/PAGE, a major sialidase-active protein band at M(r) = 54,000 and another fainter inactive protein band with M(r) = 115,000 were observed. The purified enzyme was active towards oligosaccharides, gangliosides, fetuin glycopeptide and 4-methylumbelliferyl alpha-D-N-acetylneuraminic acid except for glycoproteins tested. Fe2+, Fe3+ and dithiothreitol significantly inhibited the enzyme activity, while Triton X-100 activated the enzyme. Inside-out vesicles and unsealed ghosts of rabbit erythrocyte showed the sialidase activity for mixed gangliosides but not for resealed ghosts or intact erythrocytes. These results indicate that the active site of this sialidase is oriented mainly on the inside of the erythrocyte membrane and not on the outside. Treatment of rabbit erythrocyte unsealed ghosts with phosphatidylinositol-specific phospholipase C liberated no sialidase activity toward mixed gangliosides from the ghosts.

Interaction of avidin-carrying red blood cells with nucleated cells

In vivo application of red blood cells (RBC) modified with avidin-biotin complex has been suggested recently for various purposes. However, avidin attachment to RBC alters their biocompatibility. Thus, it has been described that avidin-carrying biotinylated RBC were lysed by the complement. In the present work interaction between avidin-carrying RBC and nucleated cells has been examined. It was found that attachment of avidin, but not streptavidin, to RBC led to binding of avidin-carrying RBC to nucleated cells. Adhesiveness of nucleated cells for avidin-carrying RBC varied for different types of nucleated cells. The strongest adhesion was observed with human fibroblasts and rat Kupffer cells, while rat liver endothelial cells were practically non-adhesive for avidin-carrying RBC of corresponding species. In contrast with avidin (streptavidin)-induced lysis by the complement, avidin-induced adhesion was independent of temperature, the presence of divalent ions and mode of avidin attachment. Polyanions (dextran sulphate and heparin) efficiently inhibited the adhesion presumably due to interaction with the membrane-bound avidin. Polyanions to a much lesser extent inhibited lysis of avidin-carrying RBC, which might be a result of their interaction with the complement components. Polycations also blocked adhesion of avidin-carrying RBC to nucleated cells, presumably due to interaction with negatively charged cell-surface components. Therefore, attachment of avidin to RBC alters their biocompatibility, due to both high positive charge of avidin and the cross-linking of biotinylated membrane proteins.

Avidin attachment to biotinylated human neutrophils induces generation of superoxide anion

The influence of biotinylation and subsequent attachment of avidin on generation of superoxide anion by human neutrophils was studied. Biotinylation of human neutrophils with succinimide ester of biotin does not reduce superoxide generation in response to activation with phorbol myristate acetate (PMA) and formyl peptide (FMLP). Addition of avidin to biotinylated, but not native, leukocytes induces generation of superoxide anion. The kinetics and level of superoxide generation by biotinylated neutrophils in response to addition of avidin were quite similar to those in response to activation with FMLP. The avidin sugar moiety and charge were not involved in superoxide generation, since streptavidin was also active. Both avidin- and PMA-induced superoxide generation were independent of the extracellular calcium, while FMLP-induced superoxide generation was dependent on the presence of calcium in solution. Therefore, interaction of avidin with biotinylated components of the neutrophil membrane alters functional activity of this cell and might induce 'activation-like' reaction of leukocytes.

Decreased sialic acid content of erythrocytes in patients with aplastic anaemia

The sialic acid content of erythrocytes from patients with aplastic anaemia was determined and compared with those in patients with several haematological disorders and healthy individuals. The sialic acid was released enzymatically with Vibrio cholerae sialidase and quantitated by the thiobarbituric acid method (Aminoff, 1961). The sialic acid content of normal erythrocytes was 538 +/- 31 nmol/ml of packed erythrocytes. That of erythrocytes from patients with aplastic anaemia was 480 +/- 35 nmol/ml of packed erythrocytes, which was significantly lower than normal (P less than 0.01). In contrast, erythrocytes from patients with myeloproliferative disorders showed significantly (P less than 0.05) higher sialic acid contents (564 +/- 45 nmol/ml of packed erythrocytes). These results suggest that some membrane changes occur in erythrocytes in patients with these disorders.

Qualitative and quantitative analysis of erythrocyte surface membrane sialyl residues using affinity cytochemistry with special reference to diabetic patients

Erythrocyte surface membrane sialyl residues were investigated by means of affinity cytochemistry using the avidin-biotin complex technique. Mild oxidation with the periodate (MO)-biotin hydrazide (BHZ)-ferritin avidin conjugate (FAv) sequence revealed numerous ferritin particles on erythrocytes from healthy donors. The ferritin particles attached on the perpendicularly sectioned membrane were seen at an average distance of 10 to 12 nm from the outer dense leaflet of the cell membrane. Pretreatment with neuraminidase followed by the MO-BHZ-FAv sequence almost eliminated erythrocyte ferritin labeling. Erythrocytes from diabetic patients showed less dense ferritin labeling compared with those from healthy donors. Quantiative analysis of sialyl residues demonstrated a marked reduction in ferritin labeling of erythrocytes from diabetic patients which was significantly less (p less than 0.01) than that of erythrocytes from healthy donors. This observation supports previous biochemical data demonstrating lower levels of surface membrane negative charge and sialyl residues on erythrocytes from patients with diabetes mellitus.

Cell-type-related segregation of surface galactosyl-containing components at an early developmental stage in hemopoietic bone marrow cells in the rabbit

The avidin-biotin complex was used for the selective ultrastructural labeling of terminal cell surface galactosyl residues. Rabbit bone marrow cells were treated with the enzyme galactose oxidase in the presence of biotin hydrazide. Subsequent treatment with ferritin-avidin conjugates enabled the electron microscopic visualization of terminal membrane-based galactose and/or N-acetylgalactosamine on these cells. All stages of erythroid development were characterized by high levels of exposed cell surface galactose, whereas all leukoid cells in the same preparations were virtually unlabeled by the above method. Modulations in the distribution of these surface determinants during differentiation and maturation of rabbit erythroid cells were found to concur in inverse fashion with respect to that of terminal sialic acids. Neuraminidase treatment, before the above labeling procedure, resulted in the exposure of additional galactosyl residues on the surface of all bone marrow cell types. The results indicate that a galactose-bearing glycoconjugate(s) may comprise an erythroid-specific membrane constituent of rabbit bone marrow cells. The high density of galactose on the surface of even the earliest erythroid precursors may eventually enable the identification and isolation of a stem cell, which already contains the erythroid-specific galactoconjugate(s). The results suggest that variations in the spectrum of cell surface carbohydrates may serve as recognition signals in the complex set of intercellular interactions which occur during the development and maturation of the erythrocyte. The occurrence of similar but species-specific variations in the complement of surface heterosaccharides during erythroid development of humans and other mammals supports this contention.

Moving boundary electrophoresis and sialic acid content of normal and polycythaemic red blood cells

Moving boundary electrophoresis has been used for the assessment of the negative charge on erythrocyte membranes. The equipment is easy to construct and simpler to use than the microelectrophoresis technique. There is a direct relationship between the electrophoretic velocity measured by the moving boundary method and the sialic acid content of the red cell membrane. Polycythaemic erythrocytes have a higher electrophoretic mobility and higher sialic acid content than normals. Separation of the erythrocytes according to their densities shows that old polycythaemic erythrocytes have a higher electrophoretic mobility and sialic acid content than young normal ones. This suggests that the difference is not associated with a younger erythrocyte population in polycythaemia vera, but may represent a membrane change in the abnormal erythroid clone present in this disease.

Preparation, properties, and applications of carbohydrate conjugates of proteins and lipids

As a result of the growing awareness of the involvement of the oligosaccharide moieties of glycoproteins and glycolipids in cell surface recognition and binding phenomena, a wide variety of methods have been developed, many quite recently, for preparing glycoconjugates. The chemical methods used for the attachment of sugars and certain hydrophilic polymers (e.g., polyethylene glycol) are discussed, as are the effects of such modifications on various properties of the protein (immune response, thermal stability and resistance to proteolysis, clearance, and specific binding to cell surface receptors). Enzymatic approaches to glycoconjugate preparation are also considered, and several examples are given of the preparation of model glycolipids, useful in studying cell surface phenomena. In a final section, three areas are considered in which rapid advances seem likely to occur: improved methods for the preparation of glycoconjugates; direct modification of cell surface glycoconjugates; and modification for the purpose of studying location and environment of membrane glycoconjugates.

Sialic acid content of erythrocytes in normal individuals and patients with certain hematologic disorders

The sialic acid content of erythrocytes from healthy individuals of different blood types and of patients with known hematological disorders has been determined. The sialic acid was completely released enzymatically with sialidase and quantitated by the thiobarbituric acid method. The sialic acid content of erythrocytes was constant irrespective of ABO blood type, or anticoagulant used; viz, 0.85-0.92 mumoles/ml of packed erythrocytes or 46-53 X 10(6) sialyl residues per cell. Deviations from these normal values were obtained with erythrocytes from patients with a variety of hematological disorders. Patients with the following disorders have significantly (P less than 0.01) lower sialic acid values compared to erythrocytes from healthy individuals (given in the order of decreasing sialic acid content): sickle cell anemia, acute lymphocytic leukemia, chronic lymphocytic leukemia, acute myelomonocytic leukemia, non-Hodgkin lymphocytic lymphoma, chronic granulocytic leukemia, acute myelocytic leukemia, leukemia, and Hodgkin disease.

The erythrocyte membranes in beta-thalassemia. Lower sialic acid levels in glycophorin

The sialic acids content of glycophorin of thalassemic erythrocyte membranes is about 25% lower than in glycophorin of normal erythrocyte membranes. Glycophorin extracted from old thalassemic erythrocytes separated by density centrifugation, has about half the sialic acids content found in glycophorin extracted from young thalassemic erythrocytes. Possible sialidase activty was sought in the plasma and erythrocyte membranes of thalassemic erythrocytes. No increased sialidase activity was detected in the plasma of the patients as compared to that of normal donors. Thus, other sites for sialidase activity, or other possibilities have to be explored to account for the increased sialic acid hydrolysis of glycophorin of the thalassemic erythrocytes.

Phagocytosis of nucleated and mature beta thalassaemic red blood cells by mouse macrophages in vitro

Physiological or experimental decrease in sialic acid (SA) content on the red blood cell (RBC) membrane is believed to play an important role in the recognition of these cells by macrophages. Since there is a 20-30% decrease in the SA content on the membrane of thalassaemic RBC, the interaction between macrophages and these RBC was studied in vitro. Using mouse peritoneal macrophages, it was found that these macrophages 'recognize' and phagocytize thalassaemic RBC while RBC from normal donors are hardly phagocytized. The average level of phagocytosis of thalassaemic RBC from splenectomized patients was found to be 22-fold higher than that of RBC from normal donors. The phagocytized cells consisted of both mature and nucleated RBC. Mouse peritoneal macrophages seem to be a useful in vitro system for the study of the accelerated sequestration and shortened life span of thalassaemic RBC.

On the mode of liposome-cell interactions. Biotin-conjugated lipids as ultrastructural probes

An efficient method for labeling and visualizing phospholipids at the ultrastructural level is described. Biotin was coupled to the amines of appropriate phospholipids via the N-hydroxysuccinimide ester. The biotinylated lipid could be specifically labeled by ferritin-avidin conjugates and detected by transmission electron microscopy. The lipid derivatives were analyzed and evaluated in terms of their resemblance to the original lipid. Although differing in some aspects from the parent lipid molecules, the biotinyl derivatives still retain the basic characteristics of lipids vis-a-vis their orientation and position in the membrane bilayer. The latter property renders the biotinylated lipid qualitatively suitable for tracing the fate of the lipid component(s) of liposomes during their interaction with biological membranes of various cell types. Using this system, we propose that the extent and pattern of the liposome-cell interaction depends, at least in part, on the cell type employed. This observation may be due to intrinsic variations in cell surface structure and properties relative to those of the liposome.