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Kulkeaw K. Progress and challenges in the use of fluorescence-based flow cytometric assays for anti-malarial drug susceptibility tests. Malar J 2021; 20:57. [PMID: 33478496 PMCID: PMC7818911 DOI: 10.1186/s12936-021-03591-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2020] [Accepted: 01/13/2021] [Indexed: 01/27/2023] Open
Abstract
Drug-resistant Plasmodium is a frequent global threat in malaria eradication programmes, highlighting the need for new anti-malarial drugs and efficient detection of treatment failure. Plasmodium falciparum culture is essential in drug discovery and resistance surveillance. Microscopy of Giemsa-stained erythrocytes is common for determining anti-malarial effects on the intraerythrocytic development of cultured Plasmodium parasites. Giemsa-based microscopy use is conventional but laborious, and its accuracy depends largely on examiner skill. Given the availability of nucleic acid-binding fluorescent dyes and advances in flow cytometry, the use of various fluorochromes has been frequently attempted for the enumeration of parasitaemia and discrimination of P. falciparum growth in drug susceptibility assays. However, fluorochromes do not meet the requirements of being fast, simple, reliable and sensitive. Thus, this review revisits the utility of fluorochromes, notes previously reported hindrances, and highlights the challenges and opportunities for using fluorochromes in flow cytometer-based drug susceptibility tests. It aims to improve drug discovery and support a resistance surveillance system, an essential feature in combatting malaria.
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Affiliation(s)
- Kasem Kulkeaw
- Department of Parasitology, Faculty of Medicine Siriraj Hospital, Mahidol University, 2, Wanglang Road, Bangkoknoi, 10700, Bangkok, Thailand.
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2
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Linzke M, Yan SLR, Tárnok A, Ulrich H, Groves MR, Wrenger C. Live and Let Dye: Visualizing the Cellular Compartments of the Malaria Parasite Plasmodium falciparum. Cytometry A 2019; 97:694-705. [PMID: 31738009 DOI: 10.1002/cyto.a.23927] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2019] [Revised: 10/03/2019] [Accepted: 10/24/2019] [Indexed: 12/15/2022]
Abstract
Malaria remains one of the deadliest diseases worldwide and it is caused by the protozoan parasite Plasmodium spp. Parasite visualization is an important tool for the correct detection of malarial cases but also to understand its biology. Advances in visualization techniques promote new insights into the complex life cycle and biology of Plasmodium parasites. Live cell imaging by fluorescence microscopy or flow cytometry are the foundation of the visualization technique for malaria research. In this review, we present an overview of possibilities in live cell imaging of the malaria parasite. We discuss some of the state-of-the-art techniques to visualize organelles and processes of the parasite and discuss limitation and advantages of each technique. © 2019 International Society for Advancement of Cytometry.
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Affiliation(s)
- Marleen Linzke
- Unit for Drug Discovery, Department of Parasitology, Institute of Biomedical Sciences, University of São Paulo, Avenida Professor Lineu Prestes 1374, São Paulo, São Paulo, 05508-000, Brazil
| | - Sun Liu Rei Yan
- Unit for Drug Discovery, Department of Parasitology, Institute of Biomedical Sciences, University of São Paulo, Avenida Professor Lineu Prestes 1374, São Paulo, São Paulo, 05508-000, Brazil
| | - Attila Tárnok
- Institute for Medical Informatics, Statistics and Epidemiology, Medical Faculty, University Leipzig, D-04107, Härtelstraße 16-18, Leipzig, Germany
| | - Henning Ulrich
- Department of Biochemistry, Institute of Chemistry, University of São Paulo, Avenida Professor Lineu Prestes 748, São Paulo, São Paulo, 05508-900, Brazil
| | - Matthew R Groves
- Structural Biology Unit, Department of Pharmacy, Faculty of Science and Engineering, University of Groningen, 9713AV, Antonius Deusinglaan 1, AV Groningen, The Netherlands
| | - Carsten Wrenger
- Unit for Drug Discovery, Department of Parasitology, Institute of Biomedical Sciences, University of São Paulo, Avenida Professor Lineu Prestes 1374, São Paulo, São Paulo, 05508-000, Brazil
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3
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Zhang L, Sevinsky CJ, Davis BM, Vertes A. Single-Cell Mass Spectrometry of Subpopulations Selected by Fluorescence Microscopy. Anal Chem 2018; 90:4626-4634. [DOI: 10.1021/acs.analchem.7b05126] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Affiliation(s)
- Linwen Zhang
- Department of Chemistry, The George Washington University, Washington, District of Columbia 20052, United States
| | | | - Brian M. Davis
- GE Global Research, Niskayuna, New York 12309, United States
| | - Akos Vertes
- Department of Chemistry, The George Washington University, Washington, District of Columbia 20052, United States
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Wirjanata G, Handayuni I, Prayoga P, Apriyanti D, Chalfein F, Sebayang BF, Kho S, Noviyanti R, Kenangalem E, Campo B, Poespoprodjo JR, Price RN, Marfurt J. Quantification of Plasmodium ex vivo drug susceptibility by flow cytometry. Malar J 2015; 14:417. [PMID: 26498665 PMCID: PMC4619360 DOI: 10.1186/s12936-015-0940-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2015] [Accepted: 10/11/2015] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The emergence and spread of multidrug-resistant Plasmodium falciparum and Plasmodium vivax highlights the need for objective measures of ex vivo drug susceptibility. Flow cytometry (FC) has potential to provide a robust and rapid quantification of ex vivo parasite growth. METHODS Field isolates from Papua, Indonesia, underwent ex vivo drug susceptibility testing against chloroquine, amodiaquine, piperaquine, mefloquine, and artesunate. A single nucleic acid stain (i.e., hydroethidine (HE) for P. falciparum and SYBR Green I (SG) for P. vivax) was used to quantify infected red blood cells by FC-based signal detection. Data derived by FC were compared to standard quantification by light microscopy (LM). A subset of isolates was used to compare single and double staining techniques. RESULTS In total, 57 P. falciparum and 23 P. vivax field isolates were collected for ex vivo drug susceptibility testing. Reliable paired data between LM and FC was obtained for 88 % (295/334) of these assays. The median difference of derived IC50 values varied from -5.4 to 6.1 nM, associated with 0.83-1.23 fold change in IC50 values between LM and FC. In 15 assays (5.1 %), the derived difference of IC50 estimates was beyond the 95 % limits of agreement; in eleven assays (3.7 %), this was attributable to low parasite growth (final schizont count < 40 %), and in four assays (1.4 %) due to low initial parasitaemia at the start of assay (<2000 µl(-1)). In a subset of seven samples, LM, single and double staining FC techniques generated similar IC50 values. CONCLUSIONS A single staining FC-based assay using a portable cytometer provides a simple, fast and versatile platform for field surveillance of ex vivo drug susceptibility in clinical P. falciparum and P. vivax isolates.
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Affiliation(s)
- Grennady Wirjanata
- Global and Tropical Health Division, Menzies School of Health Research, Charles Darwin University, PO Box 41096, Casuarina, 0811, Darwin, Australia. .,Papuan Health and Community Development Foundation (PHCDF), Timika, Papua, Indonesia.
| | - Irene Handayuni
- Global and Tropical Health Division, Menzies School of Health Research, Charles Darwin University, PO Box 41096, Casuarina, 0811, Darwin, Australia.
| | - Pak Prayoga
- Papuan Health and Community Development Foundation (PHCDF), Timika, Papua, Indonesia.
| | - Dwi Apriyanti
- Eijkman Institute for Molecular Biology, Jl. Diponegoro 69, Jakarta, 10430, Indonesia.
| | - Ferryanto Chalfein
- Papuan Health and Community Development Foundation (PHCDF), Timika, Papua, Indonesia.
| | - Boni F Sebayang
- Eijkman Institute for Molecular Biology, Jl. Diponegoro 69, Jakarta, 10430, Indonesia.
| | - Steven Kho
- Global and Tropical Health Division, Menzies School of Health Research, Charles Darwin University, PO Box 41096, Casuarina, 0811, Darwin, Australia.
| | - Rintis Noviyanti
- Eijkman Institute for Molecular Biology, Jl. Diponegoro 69, Jakarta, 10430, Indonesia.
| | - Enny Kenangalem
- Papuan Health and Community Development Foundation (PHCDF), Timika, Papua, Indonesia. .,District Health Authority, Timika, Papua, Indonesia.
| | - Brice Campo
- Medicines for Malaria Venture (MMV), 20 rte de Pré-Bois, PO Box 1826, 1215, Geneva 15, Switzerland.
| | - Jeanne Rini Poespoprodjo
- Papuan Health and Community Development Foundation (PHCDF), Timika, Papua, Indonesia. .,District Health Authority, Timika, Papua, Indonesia. .,Department of Paediatrics, Faculty of Medicine, Gadjah Mada University, Yogyakarta, Indonesia.
| | - Ric N Price
- Global and Tropical Health Division, Menzies School of Health Research, Charles Darwin University, PO Box 41096, Casuarina, 0811, Darwin, Australia. .,Nuffield Department of Clinical Medicine, Centre for Tropical Medicine and Global Health, University of Oxford, Oxford, UK.
| | - Jutta Marfurt
- Global and Tropical Health Division, Menzies School of Health Research, Charles Darwin University, PO Box 41096, Casuarina, 0811, Darwin, Australia.
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Varela ML, Razakandrainibe R, Aldebert D, Barale JC, Jambou R. Cytometric measurement of in vitro inhibition of Plasmodium falciparum field isolates by drugs: a new approach for re-invasion inhibition study. Malar J 2014; 13:110. [PMID: 24649924 PMCID: PMC3973617 DOI: 10.1186/1475-2875-13-110] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2013] [Accepted: 03/10/2014] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND A flow cytometric method is proposed to study in vitro drug sensitivity of Plasmodium falciparum. Standard [(3)H]-hypoxanthine incorporation assay gives only information on inhibition of maturation by drugs. This method is usable on field isolates and provides data on both inhibition of maturation and re-invasion. METHODS The method is based on the staining of parasites with hydroethidine (HE) and thiazole orange (TO) which allow differential identification of early, trophozoite and late stage of the parasite by flow cytometry. Late stages of the parasites are obtained by incubation in culture for 24 hours. Reinvasion is followed by culturing parasitized red blood cells for 24 h more. RESULTS Compared to the standard [(3)H]-hypoxanthine incorporation assay, it gave similar results as expressed by 50% inhibitory concentrations for chloroquine of laboratory strains and "field" isolates. The effect of quinine on the schizont-ring transition was also explored using this method. First data on the inhibition of re-invasion induced by quinine are presented for both P. falciparum-cultured strains and field isolates. DISCUSSION This method is simple to use event for field isolate study. It is suitable to analyse effect of drugs on steps of the parasite life cycle different for the maturation one. Using this method quinine was found to have a inhibitory effect on re-invasion of red cells by Plasmodium.
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Affiliation(s)
| | | | | | | | - Ronan Jambou
- Unité d'immunologie Institut Pasteur de Madagascar, Antananarivo BP1274, Madagascar.
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Shapiro HM, Apte SH, Chojnowski GM, Hänscheid T, Rebelo M, Grimberg BT. Cytometry in malaria--a practical replacement for microscopy? ACTA ACUST UNITED AC 2014; Chapter 11:11.20.1-11.20.23. [PMID: 23835802 DOI: 10.1002/0471142956.cy1120s65] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Malaria, caused by protozoan Plasmodium parasites, kills ~800,000 people each year. Exact figures are uncertain because presumptive diagnoses are often made without identifying parasites in patients' blood either by microscopy, using Giemsa's century-old stain, or by simpler tests that are ultimately dependent on microscopy for quality control. Microscopy itself relies on trained observers' ability to detect subtle morphological features of parasitized red blood cells, only a few of which may be present on a slide. Quantitative and objective flow cytometric measurements of cellular constituents such as DNA, RNA, and the malaria pigment hemozoin are now useful in research in malaria biology and pharmacology, and can provide more reliable identification of parasite species and developmental stages and better detection of low-density parasitemia than could microscopy. The same measurements can now be implemented in much smaller, simpler, cheaper imaging cytometers, potentially providing a more accurate and precise diagnostic modality.
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Defining the timing of action of antimalarial drugs against Plasmodium falciparum. Antimicrob Agents Chemother 2013; 57:1455-67. [PMID: 23318799 DOI: 10.1128/aac.01881-12] [Citation(s) in RCA: 101] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Most current antimalarials for treatment of clinical Plasmodium falciparum malaria fall into two broad drug families and target the food vacuole of the trophozoite stage. No antimalarials have been shown to target the brief extracellular merozoite form of blood-stage malaria. We studied a panel of 12 drugs, 10 of which have been used extensively clinically, for their invasion, schizont rupture, and growth-inhibitory activity using high-throughput flow cytometry and new approaches for the study of merozoite invasion and early intraerythrocytic development. Not surprisingly, given reported mechanisms of action, none of the drugs inhibited merozoite invasion in vitro. Pretreatment of erythrocytes with drugs suggested that halofantrine, lumefantrine, piperaquine, amodiaquine, and mefloquine diffuse into and remain within the erythrocyte and inhibit downstream growth of parasites. Studying the inhibitory activity of the drugs on intraerythrocytic development, schizont rupture, and reinvasion enabled several different inhibitory phenotypes to be defined. All drugs inhibited parasite replication when added at ring stages, but only artesunate, artemisinin, cycloheximide, and trichostatin A appeared to have substantial activity against ring stages, whereas the other drugs acted later during intraerythrocytic development. When drugs were added to late schizonts, only artemisinin, cycloheximide, and trichostatin A were able to inhibit rupture and subsequent replication. Flow cytometry proved valuable for in vitro assays of antimalarial activity, with the free merozoite population acting as a clear marker for parasite growth inhibition. These studies have important implications for further understanding the mechanisms of action of antimalarials, studying and evaluating drug resistance, and developing new antimalarials.
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Boyle MJ, Wilson DW, Beeson JG. New approaches to studying Plasmodium falciparum merozoite invasion and insights into invasion biology. Int J Parasitol 2012; 43:1-10. [PMID: 23220090 DOI: 10.1016/j.ijpara.2012.11.002] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2012] [Revised: 10/30/2012] [Accepted: 11/03/2012] [Indexed: 10/27/2022]
Abstract
Merozoite invasion of human red blood cells by Plasmodium falciparum is essential for blood stage asexual replication and the development of malaria disease. Despite this, many of the processes involved in invasion are poorly understood. Recent advances have been made in methods to isolate viable merozoites for studies of invasion. The application of these approaches is providing new insights into the kinetics of invasion and merozoite survival, as well as proteins and interactions involved in invasion, and will facilitate the development and testing of anti-merozoite vaccines and the identification of invasion-inhibitory compounds with potential for drug development. This review discusses these recent advances and considers potential avenues for future research.
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Affiliation(s)
- Michelle J Boyle
- The Burnet Institute for Medical Research and Public Health, Melbourne, Victoria, Australia
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The walking dead: Is hydroethidine a suitable viability dye for intra-erythrocytic Plasmodium falciparum? Parasitol Int 2012; 61:731-4. [DOI: 10.1016/j.parint.2012.07.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2012] [Revised: 07/04/2012] [Accepted: 07/09/2012] [Indexed: 11/22/2022]
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10
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Jogdand PS, Singh SK, Christiansen M, Dziegiel MH, Singh S, Theisen M. Flow cytometric readout based on Mitotracker Red CMXRos staining of live asexual blood stage malarial parasites reliably assesses antibody dependent cellular inhibition. Malar J 2012; 11:235. [PMID: 22818754 PMCID: PMC3418546 DOI: 10.1186/1475-2875-11-235] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2012] [Accepted: 07/20/2012] [Indexed: 11/10/2022] Open
Abstract
Background Functional in vitro assays could provide insights into the efficacy of malaria vaccine candidates. For estimating the anti-parasite effect induced by a vaccine candidate, an accurate determination of live parasite count is an essential component of most in vitro bioassays. Although traditionally parasites are counted microscopically, a faster, more accurate and less subjective method for counting parasites is desirable. In this study mitochondrial dye (Mitotracker Red CMXRos) was used for obtaining reliable live parasite counts through flow cytometry. Methods Both asynchronous and tightly synchronized asexual blood stage cultures of Plasmodium falciparum were stained with CMXRos and subjected to detection by flow cytometry and fluorescence microscopy. The parasite counts obtained by flow cytometry were compared to standard microscopic counts obtained through examination of Giemsa-stained thin smears. A comparison of the ability of CMXRos to stain live and compromised parasites (induced by either medium starvation or by anti-malarial drug treatment) was carried out. Finally, parasite counts obtained by CMXRos staining through flow cytometry were used to determine specific growth inhibition index (SGI) in an antibody-dependent cellular inhibition (ADCI) assay. Results Mitotracker Red CMXRos can reliably detect live intra-erythrocytic stages of P. falciparum. Comparison between staining of live with compromised parasites shows that CMXRos predominantly stains live parasites with functional mitochondria. Parasite counts obtained by CMXRos staining and flow cytometry were highly reproducible and can reliably determine the ability of IgG from hyper-immune individuals to inhibit parasite growth in presence of monocytes in ADCI assay. Further, a dose-dependent parasite growth inhibitory effect could be detected for both total IgG purified from hyper-immune sera and affinity purified IgGs against the N-terminal non-repeat region of GLURP in ADCI assays coupled with determination of parasite counts through CMXRos staining and flow cytometry. Conclusions A flow cytometry method based on CMXRos staining for detection of live parasite populations has been optimized. This is a rapid and sensitive method with high inter-assay reproducibility which can reliably determine the anti-parasite effect mediated by antibodies in functional in vitro assays such as ADCI assay.
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Affiliation(s)
- Prajakta S Jogdand
- Centre for Medical Parasitology at Department of International Health, Immunology and Microbiology, University of Copenhagen, Copenhagen, Denmark
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Somsak V, Srichairatanakool S, Yuthavong Y, Kamchonwongpaisan S, Uthaipibull C. Flow cytometric enumeration of Plasmodium berghei-infected red blood cells stained with SYBR Green I. Acta Trop 2012; 122:113-8. [PMID: 22222185 DOI: 10.1016/j.actatropica.2011.12.010] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2011] [Revised: 12/19/2011] [Accepted: 12/21/2011] [Indexed: 01/21/2023]
Abstract
High-throughput methods for evaluation of in vivo efficacy of candidate compounds against Plasmodium parasites are necessary during the antimalarial drug development process. It is essential that enumeration of parasitemia in the infected blood from experimental host animals is accurate and reliable. Flow cytometric enumeration of parasitized cells stained with fluorescent dye is a rapid alternative method to conventional microscopic counting. In this study, a protocol for flow cytometric enumeration of rodent malaria parasite Plasmodium berghei-infected red blood cells (RBC) stained with SYBR Green I was developed. The optimal concentration of SYBR Green I used to stain infected RBC was 4× for 30 min. This SYBR Green I staining protocol in combination with the bi-dimensional FL-1(530)/FL-3(620) detection method accurately detects parasitemia above 0.02%. The dye is stable during the prolonged incubation period necessary for accurate enumeration of parasitemia, with no loss of fluorescent signal over a period of hours. This protocol was validated in an antimalarial assay and the result was comparable to that obtained from conventional microscopic counting. The SYBR Green I flow cytometric protocol is thus a rapid and precise tool for high-throughput in vivo antimalarial drug screening.
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Affiliation(s)
- Voravuth Somsak
- National Center for Genetic Engineering and Biotechnology, National Science and Technology Development Agency, 113 Thailand Science Park, Pathumthani 12120, Thailand
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Bang G, Prieur E, Roussilhon C, Druilhe P. Pre-clinical assessment of novel multivalent MSP3 malaria vaccine constructs. PLoS One 2011; 6:e28165. [PMID: 22145028 PMCID: PMC3228738 DOI: 10.1371/journal.pone.0028165] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2011] [Accepted: 11/02/2011] [Indexed: 11/18/2022] Open
Abstract
Background MSP3 has been shown to induce protection against malaria in African children. The characterization of a family of Plasmodium falciparum merozoite surface protein 3 (MSP3) antigens sharing a similar structural organization, simultaneously expressed on the merozoite surface and targeted by a cross-reactive network of protective antibodies, is intriguing and offers new perspectives for the development of subunit vaccines against malaria. Methods Eight recombinant polyproteins containing carefully selected regions of this family covalently linked in different combinations were all efficiently produced in Escherichia coli. The polyproteins consisted of one monovalent, one bivalent, one trivalent, two tetravalents, one hexavalent construct, and two tetravalents incorporating coiled-coil repeats regions from LSA3 and p27 vaccine candidates. Results All eight polyproteins induced a strong and homogeneous antibody response in mice of three distinct genotypes, with a dominance of cytophilic IgG subclasses, lasting up to six months after the last immunization. Vaccine-induced antibodies exerted a strong monocyte-mediated in vitro inhibition of P. falciparum growth. Naturally acquired antibodies from individuals living in an endemic area of Senegal recognized the polyproteins with a reactivity mainly constituted of cytophilic IgG subclasses. Conclusions Combination of genetically conserved and antigenically related MSP3 proteins provides promising subunit vaccine constructs, with improved features as compared to the first generation construct employed in clinical trials (MSP3-LSP). These multivalent MSP3 vaccine constructs expand the epitope display of MSP3 family proteins, and lead to the efficient induction of a wider range of antibody subclasses, even in genetically different mice. These findings are promising for future immunization of genetically diverse human populations.
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MESH Headings
- Adolescent
- Animals
- Antibodies, Protozoan/immunology
- Antibodies, Protozoan/metabolism
- Antibody Formation/immunology
- Antigens, Protozoan/genetics
- Antigens, Protozoan/immunology
- Blotting, Western
- Child
- Child, Preschool
- Cross Reactions
- Drug Evaluation, Preclinical
- Enzyme-Linked Immunosorbent Assay
- Female
- Flow Cytometry
- Fluorescent Antibody Technique
- Humans
- Immunization
- Immunoglobulin G/immunology
- Infant
- Malaria Vaccines/genetics
- Malaria Vaccines/immunology
- Malaria Vaccines/therapeutic use
- Malaria, Falciparum/immunology
- Malaria, Falciparum/parasitology
- Malaria, Falciparum/prevention & control
- Mice
- Mice, Inbred BALB C
- Mice, Inbred C57BL
- Plasmodium falciparum/genetics
- Plasmodium falciparum/immunology
- Protozoan Proteins/genetics
- Protozoan Proteins/immunology
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Affiliation(s)
- Gilles Bang
- Malaria Vaccine Development Laboratory, Institut Pasteur, and Vac4all initiative, Paris, France
| | - Eric Prieur
- Malaria Vaccine Development Laboratory, Institut Pasteur, and Vac4all initiative, Paris, France
| | - Christian Roussilhon
- Malaria Vaccine Development Laboratory, Institut Pasteur, and Vac4all initiative, Paris, France
| | - Pierre Druilhe
- Malaria Vaccine Development Laboratory, Institut Pasteur, and Vac4all initiative, Paris, France
- * E-mail:
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A rapid and robust tri-color flow cytometry assay for monitoring malaria parasite development. Sci Rep 2011; 1:118. [PMID: 22355635 PMCID: PMC3216599 DOI: 10.1038/srep00118] [Citation(s) in RCA: 147] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2011] [Accepted: 10/03/2011] [Indexed: 11/08/2022] Open
Abstract
Microscopic examination of Giemsa-stained thin blood smears remains the gold standard method used to quantify and stage malaria parasites. However, this technique is tedious, and requires trained microscopists. We have developed a fast and simple flow cytometry method to quantify and stage, various malaria parasites in red blood cells in whole blood or in vitro cultured Plasmodium falciparum. The parasites were stained with dihydroethidium and Hoechst 33342 or SYBR Green I and leukocytes were identified with an antibody against CD45. Depending on the DNA stains used, samples were analyzed using different models of flow cytometers. This protocol, which does not require any washing steps, allows infected red blood cells to be distinguished from leukocytes, as well as allowing non-infected reticulocytes and normocytes to be identified. It also allows assessing the proportion of parasites at different developmental stages. Lastly, we demonstrate how this technique can be applied to antimalarial drug testing.
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A phase 1 trial of MSP2-C1, a blood-stage malaria vaccine containing 2 isoforms of MSP2 formulated with Montanide® ISA 720. PLoS One 2011; 6:e24413. [PMID: 21949716 PMCID: PMC3176224 DOI: 10.1371/journal.pone.0024413] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2011] [Accepted: 08/10/2011] [Indexed: 11/19/2022] Open
Abstract
Background In a previous Phase 1/2b malaria vaccine trial testing the 3D7 isoform of the malaria vaccine candidate Merozoite surface protein 2 (MSP2), parasite densities in children were reduced by 62%. However, breakthrough parasitemias were disproportionately of the alternate dimorphic form of MSP2, the FC27 genotype. We therefore undertook a dose-escalating, double-blinded, placebo-controlled Phase 1 trial in healthy, malaria-naïve adults of MSP2-C1, a vaccine containing recombinant forms of the two families of msp2 alleles, 3D7 and FC27 (EcMSP2-3D7 and EcMSP2-FC27), formulated in equal amounts with Montanide® ISA 720 as a water-in-oil emulsion. Methodology/Principal Findings The trial was designed to include three dose cohorts (10, 40, and 80 µg), each with twelve subjects receiving the vaccine and three control subjects receiving Montanide® ISA 720 adjuvant emulsion alone, in a schedule of three doses at 12-week intervals. Due to unexpected local reactogenicity and concern regarding vaccine stability, the trial was terminated after the second immunisation of the cohort receiving the 40 µg dose; no subjects received the 80 µg dose. Immunization induced significant IgG responses to both isoforms of MSP2 in the 10 µg and 40 µg dose cohorts, with antibody levels by ELISA higher in the 40 µg cohort. Vaccine-induced antibodies recognised native protein by Western blots of parasite protein extracts and by immunofluorescence microscopy. Although the induced anti-MSP2 antibodies did not directly inhibit parasite growth in vitro, IgG from the majority of individuals tested caused significant antibody-dependent cellular inhibition (ADCI) of parasite growth. Conclusions/Significance As the majority of subjects vaccinated with MSP2-C1 developed an antibody responses to both forms of MSP2, and that these antibodies mediated ADCI provide further support for MSP2 as a malaria vaccine candidate. However, in view of the reactogenicity of this formulation, further clinical development of MSP2-C1 will require formulation of MSP2 in an alternative adjuvant. Trial Registration Australian New Zealand Clinical Trials Registry 12607000552482
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Schuck DC, Ribeiro RY, Nery AA, Ulrich H, Garcia CRS. Flow cytometry as a tool for analyzing changes in Plasmodium falciparum cell cycle following treatment with indol compounds. Cytometry A 2011; 79:959-64. [PMID: 22015733 DOI: 10.1002/cyto.a.21136] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2011] [Revised: 07/28/2011] [Accepted: 08/04/2011] [Indexed: 11/09/2022]
Abstract
Melatonin and its derivatives modulate the Plasmodium falciparum and Plasmodium chabaudi cell cycle. Flow cytometry was employed together with the nucleic acid dye YOYO-1 allowing precise discrimination between mono- and multinucleated forms of P. falciparum-infected red blood cell. The use of YOYO-1 permitted excellent discrimination between uninfected and infected red blood cells as well as between early and late parasite stages. Fluorescence intensities of schizont-stage parasites were about 10-fold greater than those of ring-trophozoite form parasites. Melatonin and related indolic compounds including serotonin, N-acetyl-serotonin and tryptamine induced an increase in the percentage of multinucleated forms compared to non-treated control cultures. YOYO-1 staining of infected erythrocyte and subsequent flow cytometry analysis provides a powerful tool in malaria research for screening of bioactive compounds.
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Affiliation(s)
- Desirée Cigaran Schuck
- Departamento de Parasitologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, Brazil
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Grimberg BT. Methodology and application of flow cytometry for investigation of human malaria parasites. J Immunol Methods 2011; 367:1-16. [PMID: 21296083 DOI: 10.1016/j.jim.2011.01.015] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2010] [Revised: 12/29/2010] [Accepted: 01/27/2011] [Indexed: 02/03/2023]
Abstract
Historically, examinations of the inhibition of malaria parasite growth/invasion, whether using drugs or antibodies, have relied on the use of microscopy or radioactive hypoxanthine uptake. These are considered gold standards for measuring the effectiveness of antimalarial treatments, however, these methods have well known shortcomings. With the advent of flow cytometry coupled with the use of fluorescent DNA stains allowed for increased speed, reproducibility, and qualitative estimates of the effectiveness of antibodies and drugs to limit malaria parasite growth which addresses the challenges of traditional techniques. Because materials and machines available to research facilities are so varied, different methods have been developed to investigate malaria parasites by flow cytometry. This review is intended to serve as a reference guide for advanced users and importantly, as a primer for new users, to support expanded use and improvements to malaria flow cytometry, particularly in endemic countries.
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Affiliation(s)
- Brian T Grimberg
- Center for Global Health and Diseases, Case Western Reserve, University, Wolstein Research Building, 4-134 Cleveland, OH 44106-7286, United States.
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Systematic genetic analysis of the Plasmodium falciparum MSP7-like family reveals differences in protein expression, location, and importance in asexual growth of the blood-stage parasite. EUKARYOTIC CELL 2010; 9:1064-74. [PMID: 20472690 DOI: 10.1128/ec.00048-10] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Proteins located on Plasmodium falciparum merozoites, the invasive form of the parasite's asexual blood stage, are of considerable interest in vaccine research. Merozoite surface protein 7 (MSP7) forms a complex with MSP1 and is encoded by a member of a multigene family located on chromosome 13. The family codes for MSP7 and five MSP7-related proteins (MSRPs). In the present study, we have investigated the expression and the effect of msrp gene deletion at the asexual blood stage. In addition to msp7, msrp2, msrp3, and msrp5 are transcribed, and mRNA was easily detected by hybridization analysis, whereas mRNA for msrp1 and msrp4 could be detected only by reverse transcription (RT)-PCR. Notwithstanding evidence of transcription, antibodies to recombinant MSRPs failed to detect specific proteins, except for antibodies to MSRP2. Sequential proteolytic cleavages of MSRP2 resulted in 28- and 25-kDa forms. However, MSRP2 was absent from merozoites; the 25-kDa MSRP2 protein (MSRP2(25)) was soluble and secreted upon merozoite egress. The msrp genes were deleted by targeted disruption in the 3D7 line, leading to ablation of full-length transcripts. MSRP deletion mutants had no detectable phenotype, with growth and invasion characteristics comparable to those of the parental parasite; only the deletion of MSP7 led to a detectable growth phenotype. Thus, within this family some of the genes are transcribed at a significant level in asexual blood stages, but the corresponding proteins may or may not be detectable. Interactions of the expressed proteins with the merozoite also differ. These results highlight the potential for unexpected differences of protein expression levels within gene families.
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Zielonka J, Kalyanaraman B. Hydroethidine- and MitoSOX-derived red fluorescence is not a reliable indicator of intracellular superoxide formation: another inconvenient truth. Free Radic Biol Med 2010; 48:983-1001. [PMID: 20116425 PMCID: PMC3587154 DOI: 10.1016/j.freeradbiomed.2010.01.028] [Citation(s) in RCA: 393] [Impact Index Per Article: 28.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/12/2009] [Revised: 01/20/2010] [Accepted: 01/21/2010] [Indexed: 12/15/2022]
Abstract
Hydroethidine (HE; or dihydroethidium) is the most popular fluorogenic probe used for detecting intracellular superoxide radical anion. The reaction between superoxide and HE generates a highly specific red fluorescent product, 2-hydroxyethidium (2-OH-E(+)). In biological systems, another red fluorescent product, ethidium, is also formed, usually at a much higher concentration than 2-OH-E(+). In this article, we review the methods to selectively detect the superoxide-specific product (2-OH-E(+)) and the factors affecting its levels in cellular and biological systems. The most important conclusion of this review is that it is nearly impossible to assess the intracellular levels of the superoxide-specific product, 2-OH-E(+), using confocal microscopy or other fluorescence-based microscopic assays and that it is essential to measure by HPLC the intracellular HE and other oxidation products of HE, in addition to 2-OH-E(+), to fully understand the origin of red fluorescence. The chemical reactivity of mitochondria-targeted hydroethidine (Mito-HE, MitoSOX red) with superoxide is similar to the reactivity of HE with superoxide, and therefore, all of the limitations attributed to the HE assay are applicable to Mito-HE (or MitoSOX) as well.
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Affiliation(s)
- Jacek Zielonka
- Department of Biophysics and Free Radical Research Center, Medical College of Wisconsin, Milwaukee, WI 53226, USA.
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Chevalley S, Coste A, Lopez A, Pipy B, Valentin A. Flow cytometry for the evaluation of anti-plasmodial activity of drugs on Plasmodium falciparum gametocytes. Malar J 2010; 9:49. [PMID: 20149239 PMCID: PMC2830217 DOI: 10.1186/1475-2875-9-49] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2009] [Accepted: 02/11/2010] [Indexed: 11/29/2022] Open
Abstract
Background The activity of promising anti-malarial drugs against Plasmodium gametocytes is hard to evaluate even in vitro. This is because visual examination of stained smears, which is commonly used, is not totally convenient. In the current study, flow cytometry has been used to study the effect of established anti-malarial drugs against sexual stages obtained from W2 strain of Plasmodium falciparum. Gametocytes were treated for 48 h with different drug concentrations and the gametocytaemia was then determined by flow cytometry and compared with visual estimation by microscopy. Results and conclusions Initially gametocytaemia was evaluated either using light microscopy or flow cytometry. A direct correlation (r2 = 0.9986) was obtained. Two distinct peaks were observed on cytometry histograms and were attributed to gametocyte populations. The activities of established anti-malarial compounds were then measured by flow cytometry and the results were equivalent to those obtained using light microscopy. Primaquine and artemisinin had IC50 of 17.6 μM and 1.0 μM, respectively. Gametocyte sex was apparently distinguishable by flow cytometry as evaluated after induction of exflagellation by xanthurenic acid. These data form the basis of further studies for developing new methods in drug discovery to decrease malaria transmission.
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Affiliation(s)
- Séverine Chevalley
- Université de Toulouse-3, LPSNPR (Laboratoire Pharmacochimie des Substances Naturelles et Pharmacophores Redox), Toulouse, France
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Jiménez-Díaz MB, Mulet T, Gómez V, Viera S, Alvarez A, Garuti H, Vázquez Y, Fernández A, Ibáñez J, Jiménez M, Gargallo-Viola D, Angulo-Barturen I. Quantitative measurement of Plasmodium-infected erythrocytes in murine models of malaria by flow cytometry using bidimensional assessment of SYTO-16 fluorescence. Cytometry A 2009; 75:225-35. [PMID: 18785271 DOI: 10.1002/cyto.a.20647] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Flow cytometry is a powerful tool for measuring parasitemias in murine malaria models used to test new antimalarials. Measurement of the emission of the nonpermeable nucleic acid dye YOYO-1 (at 530 and 585 nm after excitation at 488 nm) allowed the unambiguous detection of low parasitemias (> or =0.01%) but required prolonged fixation and permeabilization of the sample. Thus, we tested whether this issue could be overcome by use of the cell-permeant dye SYTO-16 with this same bidimensional method. Blood samples from CD1 mice infected with Plasmodium yoelii, Plasmodium vinckei, or Plasmodium chabaudi or from NOD(scidbeta2m-/-) engrafted with human erythrocytes and infected with P. falciparum were stained with SYTO-16 in the presence or absence of TER-119 mAb (for engrafted mice) in 96-well plate format and acquired in Trucount tubes. Bidimensional analysis with SYTO-16 was quantitatively equivalent to YOYO-1. Moreover, by combining SYTO-16 with the use of TER-119-PE antimouse erythrocyte mAb and Trucount tubes, the measurement of the concentration of P. falciparum-infected erythrocytes over a range of five orders of magnitude was achieved. Bidimensional analysis using SYTO-16 can be used to accurately measure the concentration of Plasmodium spp.-infected erythrocytes in mice without complex sample preparation.
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Soulard V, Roland J, Gorgette O, Barbier E, Cazenave PA, Pied S. An early burst of IFN-gamma induced by the pre-erythrocytic stage favours Plasmodium yoelii parasitaemia in B6 mice. Malar J 2009; 8:128. [PMID: 19508725 PMCID: PMC2699347 DOI: 10.1186/1475-2875-8-128] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2009] [Accepted: 06/09/2009] [Indexed: 01/20/2023] Open
Abstract
BACKGROUND In murine models of malaria, an early proinflammatory response has been associated with the resolution of blood-stage infection. To dissect the protective immune mechanism that allow the control of parasitaemia, the early immune response of C57BL/6 mice induced during a non-lethal plasmodial infection was analysed. METHODS Mice were infected with Plasmodium yoelii 265BY sporozoites, the natural invasive form of the parasite, in order to complete its full life cycle. The concentrations of three proinflammatory cytokines in the sera of mice were determined by ELISA at different time points of infection. The contribution of the liver and the spleen to this cytokinic response was evaluated and the cytokine-producing lymphocytes were identified by flow cytometry. The physiological relevance of these results was tested by monitoring parasitaemia in genetically deficient C57BL/6 mice or wild-type mice treated with anti-cytokine neutralizing antibody. Finally, the cytokinic response in sera of mice infected with parasitized-RBCs was analysed. RESULTS The early immune response of C57BL/6 mice to sporozoite-induced malaria is characterized by a peak of IFN-gamma in the serum at day 5 of infection and splenic CD4 T lymphocytes are the major producer of this cytokine at this time point. Somewhat unexpected, the parasitaemia is significantly lower in P. yoelii-infected mice in the absence of IFN-gamma. More precisely, at early time points of infection, IFN-gamma favours parasitaemia, whereas helping to clear efficiently the blood-stage parasites at later time points. Interestingly, the early IFN-gamma burst is induced by the pre-erythrocytic stage. CONCLUSION These results challenge the current view regarding the role of IFN-gamma on the control of parasite growth since they show that IFN-gamma is not an essential mediator of protection in P. yoelii-infected C57BL/6 mice. Moreover, the mice parasitaemia is more efficiently controlled in the absence of an early IFN-gamma production, suggesting that this cytokine promotes parasite's growth. Finally, this early burst of IFN-gamma is induced by the pre-erythrocytic stage, showing the impact of this stage on the immune response taking place during the subsequent erythrocytic stage.
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Affiliation(s)
- Valérie Soulard
- Unité d'Immunophysiopathologie Infectieuse, Centre National de la Recherche Scientifique (CNRS) URA 1961, Université Paris VI, Institut Pasteur, Paris, France.
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22
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The use of fluorescence enhancement to improve the microscopic diagnosis of falciparum malaria. Malar J 2007; 6:89. [PMID: 17617912 PMCID: PMC1950880 DOI: 10.1186/1475-2875-6-89] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2007] [Accepted: 07/06/2007] [Indexed: 12/01/2022] Open
Abstract
Background Giemsa staining of thick blood smears remains the "gold standard" for detecting malaria. However, this method is not very good for diagnosing low-level infections. A method for the simultaneous staining of Plasmodium-parasitized culture and blood smears for both bright field and fluorescence was developed and its ability to improve detection efficiency tested. Methods A total of 22 nucleic acid-specific fluorescent dyes were tested for their ability to provide easily observable staining of Plasmodium falciparum-parasitized red blood cells following Giemsa staining. Results Of the 14 dyes that demonstrated intense fluorescence staining, only SYBR Green 1, YOYO-1 and ethidum homodimer-2 could be detected using fluorescent microscopy, when cells were first stained with Giemsa. Giemsa staining was not effective when applied after the fluorescent dyes. SYBR Green 1 provided the best staining in the presence of Giemsa, as a very high percentage of the parasitized cells were simultaneously stained. When blood films were screened using fluorescence microscopy the parasites were more readily detectable due to the sharp contrast between the dark background and the specific, bright fluorescence produced by the parasites. Conclusion The dual staining method reported here allows fluorescence staining, which enhances the reader's ability to detect parasites under low parasitaemia conditions, coupled with the ability to examine the same cell under bright field conditions to detect the characteristic morphology of Plasmodium species that is observed with Giemsa staining.
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Daher W, Biot C, Fandeur T, Jouin H, Pelinski L, Viscogliosi E, Fraisse L, Pradines B, Brocard J, Khalife J, Dive D. Assessment of Plasmodium falciparum resistance to ferroquine (SSR97193) in field isolates and in W2 strain under pressure. Malar J 2006; 5:11. [PMID: 16464254 PMCID: PMC1395321 DOI: 10.1186/1475-2875-5-11] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2005] [Accepted: 02/07/2006] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Ferroquine (FQ), or SSR97193, is a novel antimalarial drug currently in phase I clinical trials. FQ is a unique organometallic compound designed to overcome the chloroquine (CQ) resistance problem. FQ revealed to be equally active on CQ-sensitive and CQ-resistant Plasmodium falciparum laboratory strains and field isolates. FQ is also curative on rodent malaria parasites. As FQ will be tested in patients, the potential for resistance to this drug was evaluated. METHODS The relationship between CQ-resistant transporter gene genotype and susceptibility to FQ were studied in 33 Cambodian P. falciparum field isolates previously studied for their in vitro response to CQ. In parallel, the ability of the CQ-resistant strain W2, to become resistant to FQ under drug pressure was assessed. RESULTS The IC50 values for FQ in field isolates were found to be unrelated to mutations occurring in the P. falciparum chloroquine resistance transporter (PfCRT) or to the level of expression of the corresponding mRNA. In vitro, under a drug pressure of 100 nM of FQ, transient survival was observed in only one of two experiments. CONCLUSION Field isolates studies and experimental drug pressure experiments showed that FQ overcomes CQ resistance, which reinforces the potential of this compound as a new antimalarial drug.
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Affiliation(s)
- Wassim Daher
- Inserm U547, Institut Pasteur, 1 rue du Pr Calmette, B.P. 245, 59019 Lille, France
| | - Christophe Biot
- Unité de Catalyse et Chimie du Solide – UMR CNRS 8181 Synthèse Organométallique et Catalyse, Ecole Nationale Supérieure de Chimie de Lille, 59652 Villeneuve d'Ascq cedex, France
| | - Thierry Fandeur
- UMR Université-INRA d'Immunologie Parasitaire, Faculté des Sciences Pharmaceutiques, 31, avenue Monge, Parc Grandmont, 37200 Tours, France
| | - Helene Jouin
- Inserm U547, Institut Pasteur, 1 rue du Pr Calmette, B.P. 245, 59019 Lille, France
- Immunologie Moléculaire des Parasites, Institut Pasteur, 25 rue du Dr Roux, 75724 Paris cedex 15, France
| | - Lydie Pelinski
- Unité de Catalyse et Chimie du Solide – UMR CNRS 8181 Synthèse Organométallique et Catalyse, Ecole Nationale Supérieure de Chimie de Lille, 59652 Villeneuve d'Ascq cedex, France
| | - Eric Viscogliosi
- Inserm U547, Institut Pasteur, 1 rue du Pr Calmette, B.P. 245, 59019 Lille, France
| | - Laurent Fraisse
- Sanofi-Aventis Recherche, Discovery Department, 31000 Toulouse Cedex, France
| | - Bruno Pradines
- Institut de Médecine Tropicale du Service de Santé des Armées, Unité de Parasitologie, Bd Charles Livon, Parc le Pharo, BP 46, 13998 Marseille Armées, France
| | - Jacques Brocard
- Unité de Catalyse et Chimie du Solide – UMR CNRS 8181 Synthèse Organométallique et Catalyse, Ecole Nationale Supérieure de Chimie de Lille, 59652 Villeneuve d'Ascq cedex, France
| | - Jamal Khalife
- Inserm U547, Institut Pasteur, 1 rue du Pr Calmette, B.P. 245, 59019 Lille, France
| | - Daniel Dive
- Inserm U547, Institut Pasteur, 1 rue du Pr Calmette, B.P. 245, 59019 Lille, France
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Jiménez-Díaz MB, Rullas J, Mulet T, Fernández L, Bravo C, Gargallo-Viola D, Angulo-Barturen I. Improvement of detection specificity of Plasmodium-infected murine erythrocytes by flow cytometry using autofluorescence and YOYO-1. Cytometry A 2005; 67:27-36. [PMID: 16082714 DOI: 10.1002/cyto.a.20169] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
BACKGROUND Microscopic analysis of blood smears is currently the most frequently used method to measure parasitemias in experiments of drug efficacy in murine models of malaria. However, it is subjective and labour intensive, which preclude its utilization in large-scale evaluation programs. Flow cytometry is an alternative method, but due to the limited specificity achieved with the currently available techniques, it has not been widely used in murine models of malaria during preclinical evaluation. We describe a new flow cytometric method based on the differences of autofluorescence and DNA content measured after staining with YOYO-1 that are observed in infected erythrocytes compared with noninfected erythrocytes. METHODS Samples of blood from Plasmodium yoelii-infected animals were fixed with glutaraldehyde, incubated with RNAase, and stained with YOYO-1 in 96-well plate format. After acquisition, erythrocytes gated in logarithmic side/scatter plots were analyzed in bidimensional FL-2/YOYO-1 plots in comparison with unidimensional YOYO-1 analysis. RESULTS The infected erythrocytes showed a characteristic pattern of staining different from that of noninfected erythrocytes. In routine evaluation, the limit of sensitivity was 0.01% and the measurements of parasitemia were linear at parasitemias above 0.1%. Interestingly, using this approach, infected reticulocytes could be differentiated from infected normocytes. CONCLUSIONS The method described is robust, increases the specificity and sensitivity of detection in routine testing, and is especially well suited for detection of low parasitemias in murine models of malaria.
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