Syk Kinase Inhibitors Synergize with Artemisinins by Enhancing Oxidative Stress in Plasmodium falciparum-Parasitized Erythrocytes

Plasmodium falciparum exploits CD44 as a coreceptor for erythrocyte invasion

The malaria parasite Plasmodium falciparum invades and replicates asexually within human erythrocytes. CD44 expressed on erythrocytes was previously identified as an important host factor for P falciparum infection through a forward genetic screen, but little is known about its regulation or function in these cells, nor how it may be used by the parasite. We found that CD44 can be efficiently deleted from primary human hematopoietic stem cells using CRISPR/Cas9 genome editing, and that the efficiency of ex vivo erythropoiesis to enucleated cultured red blood cells (cRBCs) is not affected by lack of CD44. However, the rate of P falciparum invasion was reduced in CD44-null cRBCs relative to isogenic wild-type control cells, validating CD44 as an important host factor for this parasite. We identified 2 P falciparum invasion ligands as binding partners for CD44, erythrocyte binding antigen 175 (EBA-175) and EBA-140 and demonstrated that their ability to bind to human erythrocytes relies primarily on their canonical receptors, glycophorin A and glycophorin C, respectively. We further show that EBA-175 induces phosphorylation of erythrocyte cytoskeletal proteins in a CD44-dependent manner. Our findings support a model in which P falciparum exploits CD44 as a coreceptor during invasion of human erythrocytes, stimulating CD44-dependent phosphorylation of host cytoskeletal proteins that alter host cell deformability and facilitate parasite entry.

Investigation of new ferrocenyl-artesunate derivatives as antiparasitics

Artesunate (Ars) is a semisynthetic antimalarial drug and is a part of the artemisinin-based combination therapy arsenal employed for malaria treatment. The drug functions mainly by activation of its endoperoxide bridge leading to increased oxidative stress in malaria parasites. The purpose of this study was to ascertain the antiparasitic effects of combining ferrocene and Arsvia short or long chain ester or amide linkages (C1-C4). The compounds were evaluated for growth inhibition activity on the apicomplexan parasites, Plasmodium falciparum (P. falciparum) and Toxoplasma gondii (T. gondii). All the complexes demonstrated good activity against T. gondii with IC50 values in the low micromolar range (0.28-1.2 μM) and good to excellent antimalarial activity against a chloroquine sensitive strain of P. falciparum (NF54). Further investigations on T. gondii revealed that the likely mode of action (MoA) is through the generation of reactive oxygen species. Additionally, immunofluorescence microscopy suggested a novel change in the morphology of the parasite by complex C3, an artesunate-ferrocenyl ethyl amide complex. The complexes were not cytotoxic or showed low cytotoxicity to two normal cell lines tested.

Molecular Hybridization as a Strategy for Developing Artemisinin-Derived Anticancer Candidates

Artemisinin is a natural compound extracted from Artemisia species belonging to the Asteraceae family. Currently, artemisinin and its derivatives are considered among the most significant small-molecule antimalarial drugs. Artemisinin and its derivatives have also been shown to possess selective anticancer properties, however, there are several limitations and gaps in knowledge that retard their repurposing as effective anticancer agents. Hybridization resulting from a covalent combination of artemisinin with one or more active pharmacophores has emerged as a promising approach to overcome several issues. The variety of hybridization partners allows improvement in artemisinin activity by tuning the ability of conjugated artemisinin to interact with various molecule targets involved in multiple biological pathways. This review highlights the current scenario of artemisinin-derived hybrids with potential anticancer activity. The synthetic approaches to achieve the corresponding hybrids and the structure-activity relationships are discussed to facilitate further rational design of more effective candidates.

Plasmodium falciparum exploits CD44 as a co-receptor for erythrocyte invasion

The malaria parasite Plasmodium falciparum invades and replicates asexually within human erythrocytes. CD44 expressed on erythrocytes was previously identified as an important host factor for P. falciparum infection through a forward genetic screen, but little is known about its regulation or function in these cells, nor how it may be utilized by the parasite. We found that CD44 can be efficiently deleted from primary human hematopoietic stem cells using CRISPR/Cas9 genome editing, and that the efficiency of ex-vivo erythropoiesis to enucleated cultured red blood cells (cRBCs) is not impacted by lack of CD44. However, the rate of P. falciparum invasion was substantially reduced in CD44-null cRBCs relative to isogenic wild-type (WT) control cells, validating CD44 as an important host factor for this parasite. We identified two P. falciparum invasion ligands as binding partners for CD44, Erythrocyte Binding Antigen-175 (EBA-175) and EBA-140, and demonstrated that their ability to bind to human erythrocytes relies primarily on their canonical receptors-glycophorin A and glycophorin C, respectively. We further show that EBA-175 induces phosphorylation of erythrocyte cytoskeletal proteins in a CD44-dependent manner. Our findings support a model where P. falciparum exploits CD44 as a co-receptor during invasion of human erythrocytes, stimulating CD44-dependent phosphorylation of host cytoskeletal proteins that alter host cell deformability and facilitate parasite entry.

Aging Injury Impairs Structural Properties and Cell Signaling in Human Red Blood Cells; Açaì Berry Is a Keystone

Red blood cell (RBC) deformability is the ability of cells to modulate their shape to ensure transit through narrow capillaries of the microcirculation. A loss of deformability can occur in several pathological conditions, during natural RBC aging through an increase in membrane protein phosphorylation, and/or through the structural rearrangements of cytoskeletal proteins due to oxidative conditions, with a key role played by band 3. Due to the close relationship between aging and oxidative stress, flavonoid-rich foods are good candidates to counteract age-related alterations. This study aims to verify the beneficial role of Açaì extract in a d-Galactose (d-Gal)-induced model of aging in human RBCs. To this end, band 3 phosphorylation and structural rearrangements in membrane cytoskeleton-associated proteins, namely spectrin, ankyrin, and/or protein 4.1, are analyzed in RBCs treated with 100 mM d-Gal for 24 h, with or without pre-incubation with 10 μg/mL Açaì extract for 1 h. Furthermore, RBC deformability is also measured. Tyrosine phosphorylation of band 3, membrane cytoskeleton-associated proteins, and RBC deformability (elongation index) are analyzed using western blotting analysis, FACScan flow cytometry, and ektacytometry, respectively. The present data show that: (i) Açaì berry extract restores the increase in band 3 tyrosine phosphorylation and Syk kinase levels after exposure to 100 mM d-Gal treatment; and (ii) Açaì berry extract partially restores alterations in the distribution of spectrin, ankyrin, and protein 4.1. Interestingly, the significant decrease in membrane RBC deformability associated with d-Gal treatment is alleviated by pre-treatment with Açaì extract. These findings further contribute to clarify mechanisms of natural aging in human RBCs, and propose flavonoid substances as potential natural antioxidants for the treatment and/or prevention of oxidative-stress-related disease risk.

Artemisinin Loaded Cerium-Doped Nanopowders Improved In Vitro the Biomineralization in Human Periodontal Ligament Cells

BACKGROUND

A promising strategy to enhance bone regeneration is the use of bioactive materials doped with metallic ions with therapeutic effects and their combination with active substances and/or drugs. The aim of the present study was to investigate the osteogenic capacity of human periodontal ligament cells (hPDLCs) in culture with artemisinin (ART)-loaded Ce-doped calcium silicate nanopowders (NPs); Methods: Mesoporous silica, calcium-doped and calcium/cerium-doped silicate NPs were synthesized via a surfactant-assisted cooperative self-assembly process. Human periodontal ligament cells (hPDLCs) were isolated and tested for their osteogenic differentiation in the presence of ART-loaded and unloaded NPs through alkaline phosphatase (ALP) activity and Alizarine red S staining, while their antioxidant capacity was also evaluated; Results: ART promoted further the osteogenic differentiation of hPDLCs in the presence of Ce-doped NPs. Higher amounts of Ce in the ART-loaded NPs inversely affected the mineral deposition process by the hPDLCs. ART and Ce in the NPs have a synergistic role controlling the redox status and reducing ROS production from the hPDLCs; Conclusions: By monitoring the Ce amount and ART concentration, mesoporous NPs with optimum properties can be developed towards bone tissue regeneration demonstrating also potential application in periodontal tissue regeneration strategies.

Non-coding RNAs in malaria infection

Malaria is one of the most severe infectious diseases affecting humans and it is caused by protozoan pathogens of the species Plasmodium (spp.). The malaria parasite Plasmodium is characterized by a complex, multistage life cycle that requires tight gene regulation which allows for host invasion and defense against host immune responses. Unfortunately, the mechanisms regulating gene expression during Plasmodium infection remain largely elusive, though several lines of evidence implicate a major involvement of non-coding RNAs (ncRNAs). The ncRNAs have been found to play a key role in regulating transcriptional and post-transcriptional events in a broad range of organisms including Plasmodium. In Plasmodium ncRNAs have been shown to regulate key events in the multistage life cycle and virulence ability. Here we review recent progress involving ncRNAs (microRNAs, long non-coding RNAs, and circular RNAs) and their role as regulators of gene expression during Plasmodium infection in human hosts with focus on the possibility of using these molecules as biomarkers for monitoring disease status. We also discuss the surprising function of ncRNAs in mediating the complex interplay between parasite and human host and future perspectives of the field. This article is categorized under: RNA in Disease and Development > RNA in Disease.

Carnosic Acid and Carnosol Display Antioxidant and Anti-Prion Properties in In Vitro and Cell-Free Models of Prion Diseases

Prion diseases are transmissible encephalopathies associated with the conversion of the physiological form of the prion protein (PrP^C) to the disease-associated (PrP^Sc). Despite intense research, no therapeutic or prophylactic agent is available. The catechol-type diterpene Carnosic acid (CA) and its metabolite Carnosol (CS) from Rosmarinus officinalis have well-documented anti-oxidative and neuroprotective effects. Since oxidative stress plays an important role in the pathogenesis of prion diseases, we investigated the potential beneficial role of CA and CS in a cellular model of prion diseases (N2a22L cells) and in a cell-free prion amplification assay (RT-QuIC). The antioxidant effects of the compounds were confirmed when N2a22L were incubated with CA or CS. Furthermore, CA and CS reduced the accumulation of the disease-associated form of PrP, detected by Western Blotting, in N2a22L cells. This effect was validated in RT-QuIC assays, indicating that it is not associated with the antioxidant effects of CA and CS. Importantly, cell-free assays revealed that these natural products not only prevent the formation of PrP aggregates but can also disrupt already formed aggregates. Our results indicate that CA and CS have pleiotropic effects against prion diseases and could evolve into useful prophylactic and/or therapeutic agents against prion and other neurodegenerative diseases.

A new isothiocyanate-based Golgi-targeting fluorescent probe for Cys and its bioimaging applications during the Golgi stress response

When the cell environment changes or is stimulated, the Golgi apparatus will respond to the corresponding stress, through the opening of related pathways, the expression of corresponding substances can be promoted or inhibited to achieve the purpose of controlling cell redox homeostasis and reducing cytotoxicity. Intuitive analysis of the changes in the content of various substances in the process of stress has important guiding value for the further study of stress response, drug evaluation and clinical diagnosis. Therefore, for the Cys overexpressed during the oxidative stress of the Golgi apparatus, we developed a specific and sensitive fluorescent probe (Gol-NCS) to visually monitor the biologically important Cys in real time. The probe has low cytotoxicity and shows great potential in cell and zebrafish imaging, it can detect the changes of endogenous and exogenous cysteine. It is important to explore the synthetic pathway of Cys during Golgi stress by using the Golgi targeting performance of the probe Gol-NCS. It is confirmed by fluorescence imaging for the first time that the activity of CSE enzyme plays a decisive role in the formation of Cys. Therefore, probe Gol-NCS with excellent photochemical properties is expected to provide help for the research on the involvement of Cys in Golgi stress.

Slipknot or Crystallographic Error: A Computational Analysis of the Plasmodium falciparum DHFR Structural Folds

The presence of protein structures with atypical folds in the Protein Data Bank (PDB) is rare and may result from naturally occurring knots or crystallographic errors. Proper characterisation of such folds is imperative to understanding the basis of naturally existing knots and correcting crystallographic errors. If left uncorrected, such errors can frustrate downstream experiments that depend on the structures containing them. An atypical fold has been identified in P. falciparum dihydrofolate reductase (PfDHFR) between residues 20–51 (loop 1) and residues 191–205 (loop 2). This enzyme is key to drug discovery efforts in the parasite, necessitating a thorough characterisation of these folds. Using multiple sequence alignments (MSA), a unique insert was identified in loop 1 that exacerbates the appearance of the atypical fold-giving it a slipknot-like topology. However, PfDHFR has not been deposited in the knotted proteins database, and processing its structure failed to identify any knots within its folds. The application of protein homology modelling and molecular dynamics simulations on the DHFR domain of P. falciparum and those of two other organisms (E. coli and M. tuberculosis) that were used as molecular replacement templates in solving the PfDHFR structure revealed plausible unentangled or open conformations of these loops. These results will serve as guides for crystallographic experiments to provide further insights into the atypical folds identified.

In Vitro and In Silico Antimalarial Evaluation of FM-AZ, a New Artemisinin Derivative

Artemisinin-based Combination Therapies (ACTs) are currently the frontline treatment against Plasmodium falciparum malaria, but parasite resistance to artemisinin (ART) and its derivatives, core components of ACTs, is spreading in the Mekong countries. In this study, we report the synthesis of several novel artemisinin derivatives and evaluate their in vitro and in silico capacity to counteract Plasmodium falciparum artemisinin resistance. Furthermore, recognizing that the malaria parasite devotes considerable resources to minimizing the oxidative stress that it creates during its rapid consumption of hemoglobin and the release of heme, we sought to explore whether further augmentation of this oxidative toxicity might constitute an important addition to artemisinins. The present report demonstrates, in vitro, that FM-AZ, a newly synthesized artemisinin derivative, has a lower IC₅₀ than artemisinin in P. falciparum and a rapid action in killing the parasites. The docking studies for important parasite protein targets, PfATP6 and PfHDP, complemented the in vitro results, explaining the superior IC₅₀ values of FM-AZ in comparison with ART obtained for the ART-resistant strain. However, cross-resistance between FM-AZ and artemisinins was evidenced in vitro.

Impact of Drug Pressure versus Limited Access to Drug in Malaria Control: The Dilemma

Malaria burden has severe impact on the world. Several arsenals, including the use of antimalarials, are in place to curb the malaria burden. However, the application of these antimalarials has two extremes, limited access to drug and drug pressure, which may have similar impact on malaria control, leading to treatment failure through divergent mechanisms. Limited access to drugs ensures that patients do not get the right doses of the antimalarials in order to have an effective plasma concentration to kill the malaria parasites, which leads to treatment failure and overall reduction in malaria control via increased transmission rate. On the other hand, drug pressure can lead to the selection of drug resistance phenotypes in a subpopulation of the malaria parasites as they mutate in order to adapt. This also leads to a reduction in malaria control. Addressing these extremes in antimalarial application can be essential in maintaining the relevance of the conventional antimalarials in winning the war against malaria.

Can repurposing drugs play a role in malaria control?

Innovative drug treatments for malaria, optimally with novel targets, are needed to combat the threat of parasite drug resistance. As drug development efforts continue, there may be a role for a host-targeting, repurposed cancer drug administered together with an artemisinin combination therapy that was shown to improve the speed of recovery from a malaria infection.

Sol-Gel Synthesis and Characterization of YSZ Nanofillers for Dental Cements at Different Temperatures

BACKGROUND

Yttria-stabilized zirconia nanoparticles can be applied as fillers to improve the mechanical and antibacterial properties of luting cement. The aim of this study was to synthesize yttria-stabilized zirconia nanoparticles by the sol-gel method and to investigate their composition, structure, morphology and biological properties.

METHODS

Nanopowders of ZrO₂ 7 wt% Y₂O₃ (nY-ZrO) were synthesized by the sol-gel method and were sintered at three different temperatures: 800, 1000 and 1200 °C, and their composition, size and morphology were investigated. The biocompatibility was investigated with human gingival fibroblasts (hGFs), while reactive oxygen species (ROS) production was evaluated through fluorescence analysis.

RESULTS

All synthesized materials were composed of tetragonal zirconia, while nanopowders sintered at 800 °C and 1000 °C additionally contained 5 and 20 wt% of the cubic phase. By increasing the calcination temperature, the crystalline size of the nanoparticles increased from 12.1 nm for nY-ZrO800 to 47.2 nm for nY-ZrO1200. Nano-sized particles with good dispersion and low agglomeration were received. Cell culture studies with human gingival fibroblasts verified the nanopowders' biocompatibility and their ROS scavenging activity.

CONCLUSIONS

the obtained sol-gel derived nanopowders showed suitable properties to be potentially used as nanofillers for dental luting cement.

Human Serum Extracellular Vesicle Proteomic Profile Depends on the Enrichment Method Employed

The proteomic profiling of serum samples supposes a challenge due to the large abundance of a few blood proteins in comparison with other circulating proteins coming from different tissues and cells. Although the sensitivity of protein detection has increased enormously in the last years, specific strategies are still required to enrich less abundant proteins and get rid of abundant proteins such as albumin, lipoproteins, and immunoglobulins. One of the alternatives that has become more promising is to characterize circulating extracellular vesicles from serum samples that have great interest in biomedicine. In the present work, we enriched the extracellular vesicles fraction from human serum by applying different techniques, including ultracentrifugation, size-exclusion chromatography, and two commercial precipitation methods based on different mechanisms of action. To improve the performance and efficacy of the techniques to promote purity of the preparations, we have employed a small volume of serum samples (<100 mL). The comparative proteomic profiling of the enriched preparations shows that ultracentrifugation procedure yielded a larger and completely different set of proteins than other techniques, including mitochondrial and ribosome related proteins. The results showed that size exclusion chromatography carries over lipoprotein associated proteins, while a polymer-based precipitation kit has more affinity for proteins associated with granules of platelets. The precipitation kit that targets glycosylation molecules enriches differentially protein harboring glycosylation sites, including immunoglobulins and proteins of the membrane attack complex.

Imatinib augments standard malaria combination therapy without added toxicity

To egress from its erythrocyte host, the malaria parasite, Plasmodium falciparum, must destabilize the erythrocyte membrane by activating an erythrocyte tyrosine kinase. Because imatinib inhibits erythrocyte tyrosine kinases and because imatinib has a good safety profile, we elected to determine whether coadministration of imatinib with standard of care (SOC) might be both well tolerated and therapeutically efficacious in malaria patients. Patients with uncomplicated P. falciparum malaria from a region in Vietnam where one third of patients experience delayed parasite clearance (DPC; continued parasitemia after 3 d of therapy) were treated for 3 d with either the region’s SOC (40 mg dihydroartemisinin + 320 mg piperaquine/d) or imatinib (400 mg/d) + SOC. Imatinib + SOC–treated participants exhibited no increase in number or severity of adverse events, a significantly accelerated decline in parasite density and pyrexia, and no DPC. Surprisingly, these improvements were most pronounced in patients with the highest parasite density, where serious complications and death are most frequent. Imatinib therefore appears to improve SOC therapy, with no obvious drug-related toxicities.

The newly discovered role of endocytosis in artemisinin resistance

Artemisinin and its derivatives (ART) are the cornerstone of malaria treatment as part of artemisinin combination therapy (ACT). However, reduced susceptibility to artemisinin as well as its partner drugs threatens the usefulness of ACTs. Single point mutations in the parasite protein Kelch13 (K13) are necessary and sufficient for the reduced sensitivity of malaria parasites to ART but several alternative mechanisms for this resistance have been proposed. Recent work found that K13 is involved in the endocytosis of host cell cytosol and indicated that this is the process responsible for resistance in parasites with mutated K13. These studies also identified a series of further proteins that act together with K13 in the same pathway, including previously suspected resistance proteins such as UBP1 and AP-2μ. Here, we give a brief overview of artemisinin resistance, present the recent evidence of the role of endocytosis in ART resistance and discuss previous hypotheses in light of this new evidence. We also give an outlook on how the new insights might affect future research.

Cellular Oxidative Stress

Oxidative stress on a cellular level affects the function of tissues and organs and eventually of the whole body [...].

Parasite and Host Erythrocyte Kinomics of Plasmodium Infection

Malaria remains a heavy public health and socioeconomic burden in tropical and subtropical regions. Increasing resistance against front-line treatments implies that novel targets for antimalarial intervention are urgently required. Protein kinases of both the parasites and their host cells possess strong potential in this respect. We present an overview of the updated kinome of Plasmodium falciparum, the species that is the largest contributor to malaria mortality, and of current knowledge pertaining to the function of parasite-encoded protein kinases during the parasite's life cycle. Furthermore, we detail recent advances in drug initiatives targeting Plasmodium kinases and outline the potential of protein kinases in the context of the growing field of host-directed therapies, which is currently being explored as a novel way to combat parasite drug resistance.

Identification of tyrosine kinase inhibitors that halt Plasmodium falciparum parasitemia

Although current malaria therapies inhibit pathways encoded in the parasite’s genome, we have looked for anti-malaria drugs that can target an erythrocyte component because development of drug resistance might be suppressed if the parasite cannot mutate the drug’s target. In search for such erythrocyte targets, we noted that human erythrocytes express tyrosine kinases, whereas the Plasmodium falciparum genome encodes no obvious tyrosine kinases. We therefore screened a library of tyrosine kinase inhibitors from Eli Lilly and Co. in a search for inhibitors with possible antimalarial activity. We report that although most tyrosine kinase inhibitors exerted no effect on parasite survival, a subset of tyrosine kinase inhibitors displayed potent anti-malarial activity. Moreover, all inhibitors found to block tyrosine phosphorylation of band 3 specifically suppressed P. falciparum survival at the parasite egress stage of its intra-erythrocyte life cycle. Conversely, tyrosine kinase inhibitors that failed to block band 3 tyrosine phosphorylation but still terminated the parasitemia were observed to halt parasite proliferation at other stages of the parasite’s life cycle. Taken together these results suggest that certain erythrocyte tyrosine kinases may be important to P. falciparum maturation and that inhibitors that block these kinases may contribute to novel therapies for P. falciparum malaria.

Syk Inhibitors: New Computational Insights into Their Intraerythrocytic Action in Plasmodium falciparum Malaria

Resistance to antimalarial drugs has spread rapidly over the past few decades. The WHO recommends artemisinin-based combination therapies for the treatment of uncomplicated malaria, but unfortunately these approaches are losing their efficacy in large areas of Southeast Asia. In 2016, artemisinin resistance was confirmed in 5 countries of the Greater Mekong subregion. We focused our study on Syk inhibitors as antimalarial drugs. The Syk protein is present in human erythrocytes, and the membrane of protein band 3 is its major target following activation by oxidant stress. Tyr phosphorylation of band 3 occurs during P. falciparum growth, leading to the release of microparticles containing hemicromes and structural weakening of the host cell membrane, simplifying merozoite reinfection. Syk inhibitors block these events by interacting with the Syk protein’s catalytic site. We performed in vitro proteomics and in silico studies and compared the results. In vitro studies were based on treatment of the parasite’s cellular cultures with different concentrations of Syk inhibitors, while proteomics studies were focused on the Tyr phosphorylation of band 3 by Syk protein with the same concentrations of drugs. In silico studies were based on different molecular modeling approaches in order to analyze and optimize the ligand–protein interactions and obtain the highest efficacy in vitro. In the presence of Syk inhibitors, we observed a marked decrease of band 3 Tyr phosphorylation according to the increase of the drug’s concentration. Our studies could be useful for the structural optimization of these compounds and for the design of novel Syk inhibitors in the future.