title: Laser-induced inactivation of Plasmodium falciparum.
abstract: BACKGROUND
  Haemozoin crystals, produced by Plasmodium during its intra-erythrocytic asexual reproduction cycle, can generate UV light via the laser-induced, non-linear optical process of third harmonic generation (THG). In the current study the feasibility of using haemozoin, constitutively stored in the parasite's food vacuole, to kill the parasite by irradiation with a near IR laser was evaluated.
  
  
  METHODS
  Cultured Plasmodium parasites at different stages of development were irradiated with a pulsed NIR laser and the viability of parasites at each stage was evaluated from their corresponding growth curves using the continuous culture method. Additional testing for germicidal effects of haemozoin and NIR laser was performed by adding synthetic haemozoin crystals to Escherichia coli in suspension. Cell suspensions were then irradiated with the laser and small aliquots taken and spread on agar plates containing selective agents to determine cell viability (CFU).
  
  
  RESULTS
  Parasites in the late-trophozoites form as well as trophozoites in early-stage of DNA synthesis were found to be the most sensitive to the treatment with -4-log reduction in viability after six passes through the laser beam; followed by parasites in ring phase (-2-log reduction). A -1-log reduction in E. coli viability was obtained following a 60 min irradiation regimen of the bacteria in the presence of 1 μM synthetic haemozoin and a -2-log reduction in the presence of 10 μM haemozoin. Minimal (≤ 15%) cell kill was observed in the presence of 10 μM haemin.
  
  
  CONCLUSIONS
  Laser-induced third-harmonic generation by haemozoin can be used to inactivate Plasmodium. This result may have clinical implications for treating severe malaria symptoms by irradiating the patient's blood through the skin or through dialysis tubing with a NIR laser.
authors.affiliation: Department of Physics, University of Arkansas, Fayetteville, AR 72701, USA.
authors.forename: Danielle
authors.initials: D
authors.lastname: LeBlanc
authors.forename: Robert
authors.initials: R
authors.lastname: Story
authors.forename: Eitan
authors.initials: E
authors.lastname: Gross
mesh_terms: D002470:Cell Survival / Q000528:radiation effects; D015169:Colony Count, Microbial; D006420:Hemeproteins / Q000528:radiation effects*; D006801:Humans; D007834:Lasers; D010963:Plasmodium falciparum / Q000502:physiology* / Q000528:radiation effects*
chemical_list: D006420:Hemeproteins; C020753:hemozoin