title: Low-level laser irradiation (InGaAlP-660 nm) increases fibroblast cell proliferation and reduces cell death in a dose-dependent manner.
abstract: OBJECTIVE
  Impaired cell metabolism and increased cell death in fibroblast cells are physiological features of chronic tendinopathy. Although several studies have shown that low-level laser therapy (LLLT) at certain parameters has a biostimulatory effect on fibroblast cells, it remains uncertain if LLLT effects depend on the physiological state.
  
  
  METHODS
  High-metabolic immortal cell culture and primary human keloid fibroblast cell culture were used in this study. Trypan blue exclusion and the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test were used to determine cell viability and proliferation. Propidium iodide stain was used for cell-cycle analysis by flow cytometry. Laser irradiation was performed daily on three consecutive days with a GaAlAs 660-nm laser (mean output: 50 mW, spot size 2 mm(2), power density =2.5 W/cm(2)) and a typical LLLT dose and a high LLLT dose (irradiation times: 60 or 420 s; fluences:150 or 1050 J/cm(2); energy delivered: 3 or 21 J).
  
  
  RESULTS
  Primary fibroblast cell culture from human keloids irradiated with 3 J showed significant proliferation by the trypan blue exclusion test (p < 0.05), whereas the 3T3 cell culture showed no difference using this method. Propidium iodide staining flow cytometry data showed a significant decrease in the percentage of cells being in proliferative phases of the cell cycle (S/g(2)/M) when irradiated with 21 J in both cell types (hypodiploid cells increased).
  
  
  CONCLUSIONS
  Our data support the hypothesis that the physiological state of the cells affects the LLLT results, and that high-metabolic rate and short- cell-cycle 3T3 cells are not responsive to LLLT. In conclusion, LLLT with a dose of 3 J reduced cell death significantly, but did not stimulate cell cycle. A LLLT dose of 21 J had negative effects on the cells, as it increased cell death and inhibited cell proliferation.
authors.affiliation: Biological Sciences and Health Center, Cruzeiro do Sul University, São Paulo, Brazil. luciofrigo@uol.com.br
authors.forename: Lucio
authors.initials: L
authors.lastname: Frigo
authors.forename: Giovani M
authors.initials: GM
authors.lastname: Fávero
authors.forename: Haroldo J Campos
authors.initials: HJ
authors.lastname: Lima
authors.forename: Durvanei Augusto
authors.initials: DA
authors.lastname: Maria
authors.forename: Jan M
authors.initials: JM
authors.lastname: Bjordal
authors.forename: Jon
authors.initials: J
authors.lastname: Joensen
authors.forename: Vegard V
authors.initials: VV
authors.lastname: Iversen
authors.forename: Rodrigo Labat
authors.initials: RL
authors.lastname: Marcos
authors.forename: Nivaldo Antônio
authors.initials: NA
authors.lastname: Parizzoto
authors.forename: Rodrigo Alvaro Brandão
authors.initials: RA
authors.lastname: Lopes-Martins
mesh_terms: D016475:3T3 Cells; D000818:Animals; D016923:Cell Death / Q000528:radiation effects; D049109:Cell Proliferation / Q000528:radiation effects*; D002470:Cell Survival; D004307:Dose-Response Relationship, Radiation; D005347:Fibroblasts / Q000502:physiology*; D005434:Flow Cytometry; D006801:Humans; D007627:Keloid / Q000473:pathology; D028022:Low-Level Light Therapy; D051379:Mice