title: Non-damaging retinal phototherapy: dynamic range of heat shock protein expression.
abstract: OBJECTIVE
  Subthreshold retinal phototherapy demonstrated clinical efficacy for the treatment of diabetic macular edema without visible signs of retinal damage. To assess the range of cellular responses to sublethal hyperthermia, expression of the gene encoding a 70 kDa heat shock protein (HSP70) was evaluated after laser irradiation using a transgenic reporter mouse.
  
  
  METHODS
  One hundred millisecond, 532 nm laser exposures with 400 μm beam diameter were applied to the retina surrounding the optic nerve in 32 mice. Transcription from the HSP70 promoter was assessed relative to the control eye using a bioluminescence assay at 7 hours after laser application. The retinal pigmented epithelium (RPE) viability threshold was determined with a fluorescence assay. A computational model was developed to estimate temperature and the extent of cell damage.
  
  
  RESULTS
  A significant increase in HSP70 transcription was found at exposures over 20 mW, half the threshold power for RPE cell death. Computational modeling estimated peak temperature T = 49°C at HSP70 expression threshold. At RPE viability threshold, T = 57°C. Similar temperatures and damage indices were calculated for clinical subvisible retinal treatment parameters.
  
  
  CONCLUSIONS
  Beneficial effects of laser therapy have been previously shown to extend beyond those resulting from destruction of tissue. One hundred millisecond laser exposures at approximately half the threshold power of RPE damage induced transcription of HSP70, an indication of cellular response to sublethal thermal stress. A computational model of retinal hyperthermia can guide further optimization of laser parameters for nondamaging phototherapy.
authors.affiliation: Hansen Experimental Physics Laboratory, Stanford University, Stanford, California, USA. csramek@stanford.edu
authors.forename: Christopher
authors.initials: C
authors.lastname: Sramek
authors.forename: Mark
authors.initials: M
authors.lastname: Mackanos
authors.forename: Ryan
authors.initials: R
authors.lastname: Spitler
authors.forename: Loh-Shan
authors.initials: LS
authors.lastname: Leung
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Nomoto
authors.forename: Christopher H
authors.initials: CH
authors.lastname: Contag
authors.forename: Daniel
authors.initials: D
authors.lastname: Palanker
mesh_terms: D000818:Animals; D002470:Cell Survival; D003198:Computer Simulation; D020342:Finite Element Analysis; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation / Q000502:physiology*; D017930:Genes, Reporter; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics*; D017075:Laser Coagulation / Q000009:adverse effects*; D053844:Lasers, Solid-State / Q000009:adverse effects*; D008163:Luminescent Measurements; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D023421:Models, Animal; D012160:Retina / Q000293:injuries* / Q000378:metabolism; D055213:Retinal Pigment Epithelium / Q000378:metabolism
chemical_list: D018840:HSP70 Heat-Shock Proteins