title: Effect of laser therapy on DNA damage.
abstract: OBJECTIVE
  Whereas the biostimulative effect on tissues using low intensity laser therapy for treating many diseases has been described, the photobiological basis and adverse effects are not well understood. The aim of this study, using experimental models, is to observe the combined effect of physical damage (laser) and a chemical agent (hydrogen peroxide) on Escherichia coli cultures and bacterial plasmids.
  
  
  METHODS
  Survival of E. coli AB1157 (wild type) and BW9091 (xth(-)) cultures were used as an experimental model to assess the effect of agents on DNA, also agarose gel electrophoretic profile of bacterial plasmids for studying single and double strand breaks in DNA exposed to laser irradiation and in DNA pre-exposed to laser and subsequently incubated with hydrogen peroxide.
  
  
  RESULTS
  Data indicate low intensity laser: (i) did not alter the survival of E. coli cultures, (ii) pre-exposure had a protective effect against lethal action of hydrogen peroxide on E. coli cultures, and (iii) did not alter the electrophoretic profile and action of hydrogen peroxide on plasmids. This suggests that low intensity therapeutic red laser doses at different emission modes induces sub-lethal effects on E. coli wild type and exonuclease III mutant cultures inducing protective mechanisms against lethal action of hydrogen peroxide. Laser action on bacterial plasmids is related to lesions other than single or double DNA strands breaks.
  
  
  CONCLUSIONS
  This study shows a protective effect or DNA repair mechanism induction by pre-exposure to low intensity red laser on the lethal action of oxidant agents and, therefore, laser therapy protocol should consider fluencies, wavelength and tissue conditions before beginning treatment.
authors.affiliation: Departamento de Ciências Fisiológicas, Instituto Biomédico, Universidade Federal do Estado do Rio de Janeiro, Rua Frei Caneca, 94, Rio de Janeiro 20211040, Brazil. adnfonseca@ig.com.br
authors.forename: Adenilson S
authors.initials: AS
authors.lastname: Fonseca
authors.forename: Thiago O
authors.initials: TO
authors.lastname: Moreira
authors.forename: Deise L
authors.initials: DL
authors.lastname: Paixão
authors.forename: Fernanda M
authors.initials: FM
authors.lastname: Farias
authors.forename: Oscar R
authors.initials: OR
authors.lastname: Guimarães
authors.forename: Severo
authors.initials: S
authors.lastname: de Paoli
authors.forename: Mauro
authors.initials: M
authors.lastname: Geller
authors.forename: Flavia
authors.initials: F
authors.lastname: de Paoli
mesh_terms: D004249:DNA Damage / Q000528:radiation effects*; D004260:DNA Repair / Q000528:radiation effects*; D004269:DNA, Bacterial / Q000528:radiation effects; D004587:Electrophoresis, Agar Gel; D004926:Escherichia coli / Q000187:drug effects* / Q000235:genetics*; D006861:Hydrogen Peroxide / Q000009:adverse effects; D053685:Laser Therapy; D016877:Oxidants / Q000009:adverse effects; D010957:Plasmids / Q000235:genetics
chemical_list: D004269:DNA, Bacterial; D016877:Oxidants; D006861:Hydrogen Peroxide