Binding of Plasmodium falciparum to CD36 can be shielded by the glycocalyx

Abstract Background Plasmodium falciparum-infected erythrocytes sequester in the microcirculation due to interaction between surface-expressed parasite proteins and endothelial receptors. Endothelial cells are covered in a carbohydrate-rich glycocalyx that shields against undesired leukocyte adhesion. It was investigated if the cellular glycocalyx affects the binding of P. falciparum-infected erythrocytes to CD36 in vitro. Methods Glycocalyx growth was followed in vitro by using azido sugars and cationized ferritin detecting O-glycoproteins and negatively charged proteoglycans, respectively. P. falciparum (clone FCR3/IT) was selected on Chinese hamster ovary (CHO) cells transfected with human CD36. Cytoadhesion to CHO CD36 at 1–4 days after seeding was quantified by using a static binding assay. Results The glycocalyx thickness of CHO cells increased during 4 days in culture as assessed by metabolic labelling of glycans with azido sugars and with electron microscopy studying the binding of cationized ferritin to cell surfaces. The functional importance of this process was addressed in binding assays by using CHO cells transfected with CD36. In parallel with the maturation of the glycocalyx, antibody-binding to CD36 was inhibited, despite stable expression of CD36. P. falciparum selected for CD36-binding recognized CD36 on CHO cells on the first day in culture, but the binding was lost after 2–4 days. Conclusion The endothelial glycocalyx affects parasite cytoadhesion in vitro, an effect that has previously been ignored. The previously reported loss of glycocalyx during experimental malaria may play an important role in the pathogenesis of malaria complications by allowing the close interaction between infected erythrocytes and endothelial receptors

Investigating dye performance and crosstalk in fluorescence enabled bioimaging using a model system

Detailed imaging of biological structures, often smaller than the diffraction limit, is possible in fluorescence microscopy due to the molecular size and photophysical properties of fluorescent probes. Advances in hardware and multiple providers of high-end bioimaging makes comparing images between studies and between research groups very difficult. Therefore, we suggest a model system to benchmark instrumentation, methods and staining procedures. The system we introduce is based on doped zeolites in stained polyvinyl alcohol (PVA) films: a highly accessible model system which has the properties needed to act as a benchmark in bioimaging experiments. Rather than comparing molecular probes and imaging methods in complicated biological systems, we demonstrate that the model system can emulate this complexity and can be used to probe the effect of concentration, brightness, and cross-talk of fluorophores on the detected fluorescence signal. The described model system comprises of lanthanide (III) ion doped Linde Type A zeolites dispersed in a PVA film stained with fluorophores. We tested: F18, MitoTracker Red and ATTO647N. This model system allowed comparing performance of the fluorophores in experimental conditions. Importantly, we here report considerable cross-talk of the dyes when exchanging excitation and emission settings. Additionally, bleaching was quantified. The proposed model makes it possible to test and benchmark staining procedures before these dyes are applied to more complex biological systems

Glucagon-like peptide-1 analogue, liraglutide, in experimental cerebral malaria: implications for the role of oxidative stress in cerebral malaria

BACKGROUND: Cerebral malaria from Plasmodium falciparum infection is major cause of death in the tropics. The pathogenesis of the disease is complex and the contribution of reactive oxygen and nitrogen species (ROS/RNS) in the brain is incompletely understood. Insulinotropic glucagon-like peptide-1 (GLP-1) mimetics have potent neuroprotective effects in animal models of neuropathology associated with ROS/RNS dysfunction. This study investigates the effect of the GLP-1 analogue, liraglutide against the clinical outcome of experimental cerebral malaria (ECM) and Plasmodium falciparum growth. Furthermore the role of oxidative stress on ECM pathogenesis is evaluated. METHODS: ECM was induced in Plasmodium berghei ANKA-infected C57Bl/6j mice. Infected Balb/c (non-cerebral malaria) and uninfected C57Bl/6j mice were included as controls. Mice were treated twice-daily with vehicle or liraglutide (200 μg/kg). ROS/RNS were quantified with in vivo imaging and further analyzed ex vivo. Brains were assayed for cAMP, activation of cAMP response element binding protein (CREB) and nitrate/nitrite. Plasmodium falciparum was cultivated in vitro with increasing doses of liraglutide and growth and metabolism were quantified. RESULTS: The development and progression of ECM was not affected by liraglutide. Indeed, although ROS/RNS were increased in peripheral organs, ROS/RNS generation was not present in the brain. Interestingly, CREB was activated in the ECM brain and may protect against ROS/RNS stress. Parasite growth was not adversely affected by liraglutide in mice or in P. falciparum cultures indicating safety should not be a concern in type-II diabetics in endemic regions. CONCLUSIONS: Despite the breadth of models where GLP-1 is neuroprotective, ECM was not affected by liraglutide providing important insight into the pathogenesis of ECM. Furthermore, ECM does not induce excess ROS/RNS in the brain potentially associated with activation of the CREB system

Systemic and cerebral vascular endothelial growth factor levels increase in murine cerebral malaria along with increased Calpain and caspase activity and can be reduced by erythropoietin treatment

The pathogenesis of cerebral malaria (CM) includes compromised microvascular perfusion, increased inflammation, cytoadhesion, and endothelial activation. These events cause blood–brain barrier disruption and neuropathology and associations with the vascular endothelial growth factor (VEGF) signaling pathway have been shown. We studied this pathway in mice infected with Plasmodium berghei ANKA causing murine CM with or without the use of erythropoietin (EPO) as adjunct therapy. ELISA and western blotting was used for quantification of VEGF and relevant proteins in brain and plasma. CM increased levels of VEGF in brain and plasma and decreased plasma levels of soluble VEGF receptor 2. EPO treatment normalized VEGF receptor 2 levels and reduced brain VEGF levels. Hypoxia-inducible factor (HIF)-1α was significantly upregulated whereas cerebral HIF-2α and EPO levels remained unchanged. Furthermore, we noticed increased caspase-3 and calpain activity in terminally ill mice, as measured by protease-specific cleavage of α-spectrin and p35. In conclusion, we detected increased cerebral and systemic VEGF as well as HIF-1α, which in the brain were reduced to normal in EPO-treated mice. Also caspase and calpain activity was reduced markedly in EPO-treated mice

Creating infinite contrast in fluorescence microscopy by using lanthanide centered emission

The popularity of fluorescence microscopy arises from the inherent mode of action, where the fluorescence emission from probes is used to visualize selected features on a presumed dark background. However, the background is rarely truly dark, and image processing and analysis is needed to enhance the fluorescent signal that is ascribed to the selected feature. The image acquisition is facilitated by using considerable illumination, bright probes at a relatively high concentration in order to make the fluorescent signal significantly more intense than the background signal. Here, we present two methods for completely removing the background signal in spectrally resolved fluorescence microscopy. The methodology is applicable for all probes with narrow and well-defined emission bands (Full width half-maximum < 20 nm). Here, we use two lanthanide based probes exploiting the narrow emission lines of europium(III) and terbium(III) ions. We used a model system with zeolites doped with lanthanides immobilized in a polymer stained with several fluorescent dyes regularly used in bioimaging. After smoothing the spectral data recorded in each pixel, they are differentiated. Method I is based on the direct sum of the gradient, while method II resolves the fluorescent signal by subtracting a background calculated via the gradient. Both methods improve signal-to-background ratio significantly and we suggest that spectral imaging of lanthanide-centered emission can be used as a tool to obtain absolute contrast in bioimaging