title: Methylene blue inhibits the asexual development of vivax malaria parasites from a region of increasing chloroquine resistance.
abstract: OBJECTIVE
  Methylene blue, once discarded due to its unsettling yet mild side effects, has now found a renewed place in the pharmacopoeia of modern medicine. The continued spread of drug-resistant Plasmodium vivax and Plasmodium falciparum has also led to a recent re-examination of methylene blue's potent antimalarial properties. Here we examine the ex vivo susceptibility profile of Plasmodium spp. isolates to methylene blue; the isolates were from a region on the Thai-Myanmar border where there are increasing rates of failure when treating vivax malaria with chloroquine.
  
  
  METHODS
  To do this we used a newly developed ex vivo susceptibility assay utilizing flow cytometry and a portable flow cytometer with a near-UV laser.
  
  
  RESULTS
  P. vivax (median methylene blue IC50 3.1 nM, IQR 1.7-4.3 nM) and P. falciparum (median methylene blue IC50 1.8 nM, IQR 1.6-2.3 nM) are susceptible to methylene blue treatment at physiologically relevant levels. Unfortunately, the addition of chloroquine to combination treatments with methylene blue significantly reduces the ex vivo effectiveness of this molecule.
  
  
  CONCLUSIONS
  Our data support further efforts to employ methylene blue as a safe, low-cost antimalarial to treat drug-resistant malaria.
authors.affiliation: Singapore Immunology Network (SIgN), Agency for Science Technology and Research, Biopolis, Singapore.
authors.forename: Rossarin
authors.initials: R
authors.lastname: Suwanarusk
authors.affiliation: Department of Microbiology, Yong Loo Lin School of Medicine, National University of Singapore, National University Health System, Singapore.
authors.forename: Bruce
authors.initials: B
authors.lastname: Russell
authors.affiliation: Singapore Immunology Network (SIgN), Agency for Science Technology and Research, Biopolis, Singapore.
authors.forename: Alice
authors.initials: A
authors.lastname: Ong
authors.affiliation: Shoklo Malaria Research Unit, Mae Sot, Tak Province, Thailand.
authors.forename: Kanlaya
authors.initials: K
authors.lastname: Sriprawat
authors.affiliation: Shoklo Malaria Research Unit, Mae Sot, Tak Province, Thailand.
authors.forename: Cindy S
authors.initials: CS
authors.lastname: Chu
authors.affiliation: Shoklo Malaria Research Unit, Mae Sot, Tak Province, Thailand.
authors.forename: Aung
authors.initials: A
authors.lastname: PyaePhyo
authors.affiliation: Singapore Immunology Network (SIgN), Agency for Science Technology and Research, Biopolis, Singapore Department of Microbiology, Yong Loo Lin School of Medicine, National University of Singapore, National University Health System, Singapore.
authors.forename: Benoit
authors.initials: B
authors.lastname: Malleret
authors.affiliation: Shoklo Malaria Research Unit, Mae Sot, Tak Province, Thailand Mahidol-Oxford University Research Unit, Bangkok, Thailand Centre for Tropical Medicine, University of Oxford, Churchill Hospital, Oxford, UK.
authors.forename: François
authors.initials: F
authors.lastname: Nosten
authors.affiliation: Singapore Immunology Network (SIgN), Agency for Science Technology and Research, Biopolis, Singapore renia_laurent@immunol.a-star.edu.sg.
authors.forename: Laurent
authors.initials: L
authors.lastname: Renia
mesh_terms: D000962:Antimalarials / Q000494:pharmacology*; D002470:Cell Survival / Q000187:drug effects; D002738:Chloroquine / Q000494:pharmacology*; D004351:Drug Resistance; D005434:Flow Cytometry; D006801:Humans; D020128:Inhibitory Concentration 50; D047569:Laser Scanning Cytometry; D016780:Malaria, Vivax / Q000469:parasitology*; D008751:Methylene Blue / Q000494:pharmacology*; D002052:Myanmar; D021261:Parasitic Sensitivity Tests; D010966:Plasmodium vivax / Q000187:drug effects* / Q000302:isolation & purification; D013785:Thailand
chemical_list: D000962:Antimalarials; D002738:Chloroquine; D008751:Methylene Blue
keywords: Plasmodium falciparum; Plasmodium vivax; drug sensitivity assays; drug susceptibility assays