Spontaneous endocytosis in human neonatal and adult red blood cells: comparison to drug-induced endocytosis and to receptor-mediated endocytosis

Intra-erythrocytic vacuoles in asplenic patients: elusive genesis and original clearance of unique organelles

The spleen plays a dual role of immune response and the filtration of red blood cells (RBC), the latter function being performed within the unique microcirculatory architecture of the red pulp. The red pulp filters and eliminates senescent and pathological RBC and can expell intra-erythrocytic rigid bodies through the so-called pitting mechanism. The loss of splenic function increases the risk of infections, thromboembolism, and hematological malignancies. However, current diagnostic tests such as quantification of Howell-Jolly Bodies and splenic scintigraphy lack sensitivity or are logistically demanding. Although not widely available in medical practice, the quantification of RBC containing vacuoles, i.e., pocked RBC, is a highly sensitive and specific marker for hyposplenism. The peripheral blood of hypo/asplenic individuals contains up to 80% RBC with vacuoles, whereas these pocked RBC account for less than 4% of RBC in healthy subjects. Despite their value as a spleen function test, intraerythrocytic vacuoles have received relatively limited attention so far, and little is known about their origin, content, and clearance. We provide an overview of the current knowledge regarding possible origins and mechanisms of elimination, as well as the potential function of these unique and original organelles observed in otherwise "empty" mature RBC. We highlight the need for further research on pocked RBC, particularly regarding their potential function and specific markers for easy counting and sorting, which are prerequisites for functional studies and wider application in medical practice.

Role of Spectrin in Endocytosis

Cytoskeletal spectrin is found in (non)erythroid cells. Eukaryotic endocytosis takes place for internalizing cargos from extracellular milieu. The role of spectrin in endocytosis still remains poorly understood. Here, I summarize current knowledge of spectrin function, spectrin-based cytoskeleton and endocytosis of erythrocytes, and highlight how spectrin contributes to endocytosis and working models in different types of cells. From an evolutionary viewpoint, I discuss spectrin and endocytosis in a range of organisms, particularly in plants and yeast where spectrin is absent. Together, the role of spectrin in endocytosis is related to its post-translational modification, movement/rearrangement, elimination (by proteases) and meshwork fencing.

Receptor-Dependent Endocytosis Mediates α-Synuclein Oligomer Transport Into Red Blood Cells

Detection of oligomeric α-synuclein (o-α-Syn) in red blood cells (RBCs) has been shown to be promising in diagnosing Parkinson’s disease and other synucleinopathies. However, if RBC o-α-Syn derive from plasma and can reflect changes of plasma o-α-Syn remains unclear. In this study, synthetic o-α-Syn was intravenously injected into mice and dynamic changes in plasma and RBC o-α-Syn levels were investigated. Injection of o-α-Syn induced a temporary increase in plasma o-α-Syn levels, which then decreased to a relatively stable level. In contrast, levels of RBC o-α-Syn increased steadily and significantly. Besides, α-Syn-immunoreactive particles were observed in RBCs of the injected mice, suggesting that RBCs can actively take up and enrich o-α-Syn from plasma. Moreover, incubation of o-α-Syn with isolated RBCs at concentrations lower than those of endogenous o-α-Syn led to a time- and concentration-dependent o-α-Syn elevation in RBCs, which was impaired by lowering the temperature and treatment with proteinase K. The o-α-Syn accumulation in RBCs was also inhibited by specific inhibitors of receptor-dependent endocytosis, including dynamin- and clathrin-dependent endocytosis. The above results suggest that plasma o-α-Syn can be actively transported into RBCs via receptor-dependent endocytic pathways.

Targeting protein translation, RNA splicing, and degradation by morpholino-based conjugates in Plasmodium falciparum

Identification and genetic validation of new targets from available genome sequences are critical steps toward the development of new potent and selective antimalarials. However, no methods are currently available for large-scale functional analysis of the Plasmodium falciparum genome. Here we present evidence for successful use of morpholino oligomers (MO) to mediate degradation of target mRNAs or to inhibit RNA splicing or translation of several genes of P. falciparum involved in chloroquine transport, apicoplast biogenesis, and phospholipid biosynthesis. Consistent with their role in the parasite life cycle, down-regulation of these essential genes resulted in inhibition of parasite development. We show that a MO conjugate that targets the chloroquine-resistant transporter PfCRT is effective against chloroquine-sensitive and -resistant parasites, causes enlarged digestive vacuoles, and renders chloroquine-resistant strains more sensitive to chloroquine. Similarly, we show that a MO conjugate that targets the PfDXR involved in apicoplast biogenesis inhibits parasite growth and that this defect can be rescued by addition of isopentenyl pyrophosphate. MO-based gene regulation is a viable alternative approach to functional analysis of the P. falciparum genome.

Drug delivery carriers on the fringes: natural red blood cells versus synthetic multilayered capsules

Red blood cells (RBC) and synthetic multilayered nanocarriers may appear as distant 'extremes' of the continuum of diverse drug delivery systems. The former are natural, old and simple, whereas the latter are artificial, novel and sophisticated. However, juxtaposition of features of these types of carriers, offered in a review article published in this issue, is instructive. Such an analysis helps to define both their distinctions and similarities (structural, functional, technological, specific areas of utility), and illustrates perspectives of their translation into the practice. Thus, synthetic multilayered carriers (which, in some embodiments, use elements of design inspired by RBC) represent an attractive research object offering high degree of control of their features. These carriers may find utility for intracellular delivery, controlled release of multiple cargoes and imaging. On the other hand, RBC provide arguably the most attractive carriers for sustained intravascular delivery of variety of drugs including biotherapeutics, either encapsulated into the inner RBC volume or coupled to RBC surface. The discussion of specific medical utility of these carriers and comparative analysis of the factors that may affect their translation (including complexity, costs, market value and therapeutic benefit/risk ratio) is timely and likely to intensify in the near future.

Conjugation to the cell-penetrating peptide TAT potentiates the photodynamic effect of carboxytetramethylrhodamine

Background

Cell-penetrating peptides (CPPs) can transport macromolecular cargos into live cells. However, the cellular delivery efficiency of these reagents is often suboptimal because CPP-cargo conjugates typically remain trapped inside endosomes. Interestingly, irradiation of fluorescently labeled CPPs with light increases the release of the peptide and its cargos into the cytosol. However, the mechanism of this phenomenon is not clear. Here we investigate the molecular basis of the photo-induced endosomolytic activity of the prototypical CPPs TAT labeled to the fluorophore 5(6)-carboxytetramethylrhodamine (TMR).

Methodology/Principal Findings

We report that TMR-TAT acts as a photosensitizer that can destroy membranes. TMR-TAT escapes from endosomes after exposure to moderate light doses. However, this is also accompanied by loss of plasma membrane integrity, membrane blebbing, and cell-death. In addition, the peptide causes the destruction of cells when applied extracellularly and also triggers the photohemolysis of red blood cells. These photolytic and photocytotoxic effects were inhibited by hydrophobic singlet oxygen quenchers but not by hydrophilic quenchers.

Conclusions/Significance

Together, these results suggest that TAT can convert an innocuous fluorophore such as TMR into a potent photolytic agent. This effect involves the targeting of the fluorophore to cellular membranes and the production of singlet oxygen within the hydrophobic environment of the membranes. Our findings may be relevant for the design of reagents with photo-induced endosomolytic activity. The photocytotoxicity exhibited by TMR-TAT also suggests that CPP-chromophore conjugates could aid the development of novel Photodynamic Therapy agents.

Bilirubin toxicity to human erythrocytes: a review

Neonatal jaundice, a physiologic condition reflecting the interplay between developmentally modulated changes in bilirubin production and metabolism, affects virtually all newborn infants. Usually, it is an entirely benign process that is resolved at the end of the first week of life without treatment or sequelae. However, in a small percentage of neonates, unconjugated hyperbilirubinemia can pose a neurotoxic risk especially in the presence of aggravating conditions such as a diminished albumin binding capacity and/or affinity, acidosis, displacing drugs and prematurity. Although neuronal cells are considered the main target for unconjugated bilirubin (UCB) toxicity, circulating cells are also affected during neonatal hyperbilirubinemia. Moreover, the UCB ability to cause hemolysis shall further aggravate neonatal jaundice through a vicious circle. In this review, we summarize the most relevant data obtained by our group regarding UCB toxicity and the role of some risk factors for kernicterus. In order to improve the risk assessment of neurotoxicity it is essential to understand the underlying mechanisms of UCB pathophysiology.

Drug-induced transmembrane lipid scrambling in erythrocytes and in liposomes requires the presence of polyanionic phospholipids

The asymmetric transmembrane distribution of phospholipids between the two bilayer halves of erythrocyte can be modified upon addition of cationic amphiphilic drugs, such as chlorpromazine or verapamil. We studied this phenomenon in erythrocytes and in lipid vesicles using spin-labelled analogues of the endogenous phospholipids. The extent of the rapid disappearance of the analogues from the erythrocyte outer leaflet depended on the concentration of the drug. Up to 40% of spin-labelled sphingomyelin moved to the inner erythrocyte leaflet in 10 min in the presence of 1.5 mm chlorpromazine. Verapamil or vinblastine gave similar results. On the other hand, the inside-outside movement of the aminophospholipid analogues was less evident, and did not exceed 10%. This apparent discrepancy between inward and outward movements could result from the formation of an endovesicle which is known to occur upon drug addition at high concentration. A fraction of lipids would be trapped in the intravesicular leaflet, corresponding to the cell outer leaflet, and be inaccessible both from the cytoplasm and the extracellular medium. In cells submitted to a metabolic depletion of cellular ATP the intensity of the scrambling induced by the amphipaths was drastically lowered. We attribute this effect to the important reduction of the membrane content in phosphatidylinositol-4,5-bisphosphate (PIP2). The involvement of the latter lipid in triggering scrambling was partly confirmed by experiments carried out with artificial membranes. Indeed, in large unilamellar vesicles PIP2 is required in order to obtain a rapid redistribution of phospholipids between the two leaflets upon addition of drugs. However, the extent of phospholipid redistribution was limited to 15-20%. This redistribution was also induced when the vesicle membrane contained di-anionic phospholipids (phosphatidylinositol-4-monophosphate or diphosphatidylglycerol), but did not occur when it contained mono-anionic phospholipids (phosphatidylserine or phosphatidylinositol). Some drugs such as methochlorpromazine, active in artificial membranes, were ineffective in erythrocyte membranes, probably because they could not cross the membrane and reach PIP2 molecules at the cytoplasmic leaflet.

Effect of pyrexia in the formation of intraerythrocytic inclusion bodies and vacuoles in haemolytic crisis of haemoglobin H disease

Clinical aspects and in vivo formation of inclusion bodies and vacuoles in red cells of patients with haemoglobin H disease were studied and compared during steady state and after pyrexia of acute infections. During period of pyrexia, there were haemolytic crises with significant drops of the steady-state haemoglobin levels of 8.6 +/- 0.9 g/dl to 5.6 +/- 1.7 g/dl. The phenomenon was observed with splenic enlargement and significant increase of inclusion body formation. The findings suggested that inclusion body formation in red cells during pyrexia of acute infections played an important role in haemolytic crisis of haemoglobin H disease, probably by causing these cells to be sequestered and destroyed in the spleen.

Effect of chlorpromazine on kinetics of injected monoclonal antibody in MoAb-induced glomerular injury

The effect of chlorpromazine, one of several calmodulin antagonists that inhibit cytoskeletal movement, on the local kinetics of injected proteinuria-inducing MoAb 5-1-6 was examined to test the hypothesis that proteinuria is inhibited if the antigen recognized by MoAb 5-1-6 or injected MoAb remains on the surface of epithelial foot processes. MoAb 5-1-6 was injected into both chlorpromazine-treated (5 mg/100 g body weight) and untreated rats. As a positive control for the chlorpromazine treatment, anti-Fx1A serum was also injected into other chlorpromazine-treated and untreated rats. Chlorpromazine inhibited neither the change in localization of injected MoAb 5-1-6 nor proteinuria, although it showed an inhibitory effect on redistribution of immune complex and the fixation of complement in passive Heymann glomerulonephritis induced by injection of anti-Fx1A serum. We conclude that the kinetics of bound MoAb 5-1-6 are regulated by a system different from that operating in passive Heymann glomerulonephritis.