Activation of a Plasmodium falciparum cdc2-related kinase by heterologous p25 and cyclin H. Functional characterization of a P. falciparum cyclin homologue

Several Plasmodium falciparum genes encoding cdc2-related protein kinases have been identified, but the modalities of their regulation remains largely unexplored. In the present study, we investigated the regulation in vitro of PfPK5, a putative homologue of Cdk1 (cdc2) in P. falciparum. We show that (i) PfPK5 is efficiently activated by heterologous (human) cyclin H and p25, a cyclin-like molecule that specifically activates human Cdk5; (ii) the activated enzyme can be inhibited by chemical Cdk inhibitors; (iii) Pfmrk, a putative P. falciparum homologue of the Cdk-activating kinase, does neither activate nor phosphorylate PfPK5; and (iv) PfPK5 is able to autophosphorylate in the presence of a cyclin. Taken together, these results suggest that the regulation of Plasmodium Cdks may differ in important aspects from that of their human counterparts. Furthermore, we cloned an open reading frame encoding a novel P. falciparum protein possessing maximal homology to cyclin H from various organisms, and we show that this protein, called Pfcyc-1, is able to activate recombinant PfPK5 in vitro with an efficiency similar to that of human cyclin H and p25. This work opens the way to the development of screening procedures aimed at identifying compounds that specifically target the parasite Cdks.

Blood compatibility of particulate carriers investigated by cell electrophoresis and particle electrophoresis: a preliminary report

Polyethylene glycol (PEG) and dextran were covalently coupled, or only adsorbed, to the surface of three kinds of inorganic particles in order to shield their surface and reduce their nonspecific binding to red blood cells. Surface modification as well as interaction of particles with red blood cells was followed up by particle electrophoresis. This allowed a quick evaluation of the efficiency of polymer coupling. Moreover, the nonspecific binding of particles to red blood cells was easily investigated with cell electrophoresis, showing the inhibitory effect of immobilized PEG-5000 or dextran. The electrophoretic mobility analysis presented here may be used for screening blood compatibility of particulate drug carriers and could be helpful in formulating long-living circulating particles.

Covalent binding of polyethylene glycol to the surface of red blood cells as detected and followed up by cell electrophoresis and rheological methods

Cyanuric chloride activated polyethylene glycol (PEG)-5000 was covalently coupled to murine and human red blood cells (pegylated RBC). Our purpose was to camouflage RBC receptors, which is necessary for parasite invasion, a process essential to sustain parasitemia. Cell electrophoretic mobility analysis (CEM) of pegylated RBC distinguished a new population of cells bearing characteristic CEM. Pegylation of RBC also modified their rheological properties, which were documented by evaluation of cell deformability (based on cell transit time through calibrated micropores) and cell aggregation (as measured by ultrasonic interferometry). Homologous transfusion of pegylated RBC into murine malaria-infected mice had no significant effect on the cerebral malaria death rate in Plasmodium berghei-infected mice, but it reduced the peripheral blood parasitemia by a factor 2 while in Plasmodium yoelii infected mice, the parasitemia was dramatically reduced by a factor of 4. These experiments demonstrate that transfusion of pegylated RBC may inhibit peripheral parasitemia. Cell electrophoresis appears to be a useful tool to allow in vivo detection and to investigate the fate of transfused pegylated RBC.

Detection of phosphatidylserine surface exposure on human erythrocytes using annexin V-ferrofluid

The asymmetric transbilayer distribution of phospholipids in the plasma membrane and the regulation of phosphatidylserine (PS) exposure at the cell surface of animal cells are of high physiological significance. It has been shown previously that annexin V is one of the most sensitive tools with which the presence of small amounts of PS on the outer surface of eukaryotic cells can be detected. We present here the covalent coupling of annexin V molecules to magnetic nanoparticles of maghemite. The resulting annexin V-ferrofluid is used in the magnetic separation of PS exposing cells, as illustrated for human erythrocytes modified in their phospholipid transbilayer asymmetry by the use of a calcium ionophore. Results on stored human erythrocytes and comparison with results obtained using iodinated and fluorescein-labeled annexin V are also presented.

Particle electrophoresis of micrometric-sized superparamagnetic particles designed for magnetic purification of cells

Measuring the electrophoretic mobility of superparamagnetic particles (0.5-4.5 microns mean size) was undertaken to probe the coupling of lectins and antibodies to their surface. Coupling was either noncovalent (antigen-antibody and biotin-streptavidin linkage) or covalent (tosyl-activated beads). The direct observation of the electrophoresis of single particles illuminated in dark field and processed by image analysis allowed the determination of their apparent electrophoretic mobility. Mobilities ranged from -0.5 micron s-1/CmV-1 to +1 micron s-1/CmV-1 when measured at 20 degrees C in 0.15 M NaCl and 30 mg/mL sorbitol, pH 7.4. The relative standard deviation was less than 0.1%. Surface immobilization of charged proteins onto the superparamagnetic beads shifted their electrophoretic mobility up to 200%; this was also quantitatively correlated with some specific properties (enzymatic activity, antigen-binding activity, lectin-binding activity). Although particle electrophoresis has mainly been reported for the study of surface adsorption phenomenon, it may be a versatile tool for controlling covalent modifications of particles designed for therapeutical targeting or chromatographic use and may also apply to a quantitative analysis of ligand-binding interactions.

Characterization of a subpopulation of mouse red blood cells as preferential target for malarial invasion

Cell electrophoresis was used to study a distinct subpopulation of murine red blood cells (RBC). These RBC are normally found in the spleen and bone marrow. They appear in the peripheral blood when mice are mildly bled or sucked by mosquitos. These cells have been characterized as having larger size, light density, lower electrophoretic mobility, and being more resistant to lysis with unsaturated fatty acids and in glycerol-containing medium than mature erythrocytes. All their features suggest that their differentiation status represents an intermediate stage between reticulocytes and adult RBC. In vitro Plasmodium invasion tests showed their increased sensitivity to invasion by the parasites. The extent of their spreading in the blood was found to be strain-dependent, being more pronounced in C57B1/6 mice, highly susceptible to developing cerebral malaria after infection with Plasmodium berghei, as compared to Balb/c, a nonsusceptible strain of mice.

Surface modification of superparamagnetic nanoparticles (Ferrofluid) studied with particle electrophoresis: application to the specific targeting of cells

Colloidal aqueous suspension of superparamagnetic nanoparticles (9 nm in diameter) composed of maghemite (gamma Fe2O3) and forming an ionic ferrofluid in aqueous solution are covalently coupled with lectins, enzymes or antibodies, using specific thiol chemistry. The surface charge modifications of nanoparticles, caused by ligand coupling, were monitored by measuring their electrophoretic mobilities using laser-Doppler velocimetry. Particle electrophoretic mobility (PEM) changes are shown to correlate well with the amount of ligand fixed on the particles, as probed by its biological activity. The PEM method provides a useful tool to optimize ligand immobilization at the surface of nanoparticles, and may be advantageous when biological activity measurements are not convenient.

Membrane modifications of red blood cells in Alzheimer's disease

Red blood cells (RBC) from 24 Alzheimer's disease (AD) patients, 18 age- and sex-matched nondemented (ND) patients, hospitalized in the same facility for orthopedic problems, and 18 healthy volunteers aged 30-52 years were studied in order to gain insight into the nature of RBC membrane modifications in AD. Significant differences were found between RBC from AD and ND patients or young controls respectively for annexin V-binding (45.5 +/- 18.0% vs 27.1 +/- 14.7 and 2.7 +/- 1.9, p = .003), fraction of glycerol resistant cells (30.8 +/- 11.1% vs 19.6 +/- 6.4 and 10.2 +/- 3.1, p = .026), cell electrophoretic mobility in polymer (1.028 +/- 0.022 microns sec-1 V-1 cm vs 1.046 +/- 0.022 and 1.053 +/- 0.021, p = .02) and only limited significance for the filterability (1.46 +/- 0.12 msec vs 1.58 +/- 0.11 and 1.54 +/- 0.11, p = 0.1). A logistic analysis, using simultaneously several features as independent variables, suggested the combined use of annexinV- binding, glycerol resistance, and cell filterability which allowed the assignment of 95% of patients from this cohort to the right group. A prospective analysis of a larger cohort is required for the estimation of the diagnostic value of this test battery. In addition, the high level of annexin binding is characteristic of a disruption of the phospholipid asymmetry in aged or damaged cells, while the high glycerol resistance combined with low electrophoretic mobility an rigidity characterize young RBC, thus indicating an enhanced turnover of RBC in Alzheimer's disease.

Effect of fatty acid treatment in cerebral malaria-susceptible and nonsusceptible strains of mice

Cerebral malaria-susceptible (C57BL/6) mice infected with Plasmodium berghei ANKA (PbA) developed low parasitemia and died from typical neurological symptoms between 8 to 10 days after infection. In contrast, nonsusceptible (BALB/c) mice developed high peripheral blood parasitemia and died 22-24 days later without neurological implications. Daily injections of fatty acids (FA) during the first 3 days after infection protected C57BL/6 mice from cerebral symptoms but had no effect on BALB/c mice. Thus, treated C57BL/6 mice developed hyperparasitemia and died 25 days after infection, like BALB/c mice. Red blood cells from C57BL/6 control mice were found to be more resistant to lysis by linoleic acid than those of BALB/c mice. Three days following infection with PbA, these differences disappeared. Treatment with FA prevented these changes. We concluded that the host's cells were altered soon after infection and that the nature and degree of alterations depended on the mouse strain, thus determining the eventual outcome of the infection. Likewise, the effects of FA might not be directed against the parasite but rather seem to act early after infection on these parasite-induced modifications of host cells.

Use of annexin V-ferrofluid to enumerate erythrocytes damaged in various pathologies or during storage in vitro

Recombinant human annexin V was bound covalently to 9 nm maghemite (gamma Fe2O3) nanoparticles, yielding annexin-ferrofluid (AnxFF), and used to separate annexin-bound red blood cells (RBC) in a magnetic field and estimate their percentage in various bloods. Annexin binding in normal human RBC increased proportionately with storage from 8% on day 2 to 42% on day 100. Enhanced AnxFF binding was associated with various pathologies. Thus, normal blood contained 10.7 +/- 5.9% AnxFF binding RBC; bloods with normal sedimentation rates (albeit with some disease necessitating analysis) contained 23.5 +/- 6.2%; those with high sedimentation rates contained 51.5 +/- 12.3%; sickle cell anaemia patients' blood contained 50.0 +/- 9.3%, and bloods from patients with other pathologies (deforming rheumatic disease, cancer necessitating chemotherapy, etc.) contained 58.6 +/- 7.6% AnxFF binding RBC. Enhanced Ca+2-dependent annexin binding reflects a loss of the asymmetric distribution of anionic phospholipids in plasma membranes which may constitute a signal for the destruction of the modified cells by the reticuloendothelial system. Once these preliminary results are confirmed, the determination of the fraction of AnxFF bound erythrocytes, following their magnetic separation, could prove a simple and rapid quality test for example in the context of blood transfusion.

Immunological study of acidic fibroblast growth factor (aFGF) distribution in the eye

During the last ten years, several groups, including the present authors, have detected growth factor activities in various ocular tissues, and the presence of a ubiquitous Eye-Derived Growth Factor (EDGF) has been described. More recently, isolation and characterization of this growth factor activity from the retina led to the identification of two molecules. These molecules were shown to be identical to other growth factors isolated from neuronal and non-neuronal tissues and are now designated as acidic and basic fibroblast growth factor (aFGF, bFGF). The biological function and the reason for the ubiquitous distribution of these factors remain unclear. Understanding may be improved by quantification of this distribution in various tissues during development. In the present study, specific polyclonal antibodies were raised against acidic FGF, aFGF was determined in various ocular tissues by enzyme immunoassay, and the localization of immunoreactive aFGF by immunohistological staining with fluorescent antibodies or with enzyme- or gold-labeled antibodies was studied. In almost all tissues tested aFGF was found; but the retina, cornea, and vitreous body contained the highest levels of aFGF per gram of tissue. In the retina, aFGF was associated primarily with the nerve fiber layer and the inner and outer segments of the photoreceptors, whereas corneal aFGF was detected in the cytoplasma of the basal layer of epithelial cells.

Cyclosporin enhances diabetes induced by low-dose streptozotocin treatment in mice

This study concerns the effect of a 12-day cyclosporin A (CsA) treatment (50 mg per kg per day) on "autoimmune" diabetes induced by 5 low doses (40 mg per kg per day) of streptozotocin (SZ). The SZ-treatment period was initiated 4 days after initial administration of CsA. In young (45-day) CD-1 male mice, CsA enhanced hyperglycemia, hypoinsulinemia and beta-cell destruction following a multiple low-dosage SZ. Moreover, CsA did not prevent development of insulitis induced concomitantly by SZ. Similarly, CsA enhanced the "toxic" diabetes produced by a single high dose (160 mg/kg) of SZ. Furthermore, in the absence of SZ, CsA alone induced glucose intolerance, associated with beta-cell degranulation and high pancreatic CsA content. The enhancement of SZ-induced diabetes by CsA may thus be due to toxicity of the immunosuppressive agent for pancreatic beta cells. This side effect is noteworthy because CsA is currently being used in the therapy of human insulin-dependent diabetes.