title: Long-term safety of low-level laser therapy at different power densities and single or multiple applications to the bone marrow in mice.
abstract: OBJECTIVE
  The purpose of this study was to determine the long-term safety effect of low-level laser therapy (LLLT) to the bone marrow (BM) in mice.
  
  
  BACKGROUND
  LLLT has been shown to have a photobiostimulatory effect on various cellular processes and on stem cells. It was recently shown that applying LLLT to BM in rats post-myocardial infarction caused a marked reduction of scar tissue formation in the heart.
  
  
  METHODS
  Eighty-three mice were divided into five groups: control sham-treated and laser-treated at measured density of either 4, 10, 18, or 40 mW/cm(2) at the BM level. The laser was applied to the exposed flat medial part of the tibia 8 mm from the knee joint for 100 sec. Mice were monitored for 8 months and then killed, and histopathology was performed on various organs.
  
  
  RESULTS
  No histological differences were observed in the liver, kidneys, brain or BM of the laser-treated mice as compared with the sham-treated, control mice. Moreover, no neoplasmic response in the tissues was observed in the laser-treated groups as compared with the control, sham-treated mice. There were no significant histopathological differences among the same organs under different laser treatment regimes in response to the BM-derived mesenchymal stem cell proliferation following LLLT to the BM.
  
  
  CONCLUSIONS
  LLLT applied multiple times either at the optimal dose (which induces photobiostimulation of stem cells in the BM), or at a higher dose (such as five times the optimal dose), does not cause histopathological changes or neoplasmic response in various organs in mice, as examined over a period of 8 months.
authors.affiliation: Department of Zoology, The George S. Wise Faculty of Life Sciences, Tel-Aviv University Tel-Aviv, Israel.
authors.forename: Hana
authors.initials: H
authors.lastname: Tuby
authors.forename: Einat
authors.initials: E
authors.lastname: Hertzberg
authors.forename: Lidya
authors.initials: L
authors.lastname: Maltz
authors.forename: Uri
authors.initials: U
authors.lastname: Oron
mesh_terms: D000818:Animals; D001853:Bone Marrow / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D007668:Kidney / Q000528:radiation effects; D008099:Liver / Q000528:radiation effects; D028022:Low-Level Light Therapy; D059630:Mesenchymal Stem Cells / Q000528:radiation effects; D051379:Mice; D008813:Mice, Inbred ICR; D013234:Stem Cells / Q000528:radiation effects