title: Light-induced decomposition of indocyanine green.
abstract: OBJECTIVE
  To investigate the light-induced decomposition of indocyanine green (ICG) and to test the cytotoxicity of light-induced ICG decomposition products.
  
  
  METHODS
  ICG in solution was irradiated with laser light, solar light, or surgical endolight. The light-induced decomposition of ICG was analyzed by high-performance liquid chromatography (HPLC) and mass spectrometry. Porcine retinal pigment epithelial (RPE) cells were incubated with the light-induced decomposition products of ICG, and cell viability was measured by trypan blue exclusion assay.
  
  
  RESULTS
  Independent of the light source used, singlet oxygen (photodynamic type 2 reaction) is generated by ICG leading to dioxetanes by [2+2]-cycloaddition of singlet oxygen. These dioxetanes thermally decompose into several carbonyl compounds. The decomposition products were identified by mass spectrometry. The decomposition of ICG was inhibited by adding sodium azide, a quencher of singlet oxygen. Incubation with ICG decomposition products significantly reduced the viability of RPE cells in contrast to control cells.
  
  
  CONCLUSIONS
  ICG is decomposed by light within a self-sensitized photo oxidation. The decomposition products reduce the viability of RPE cells in vitro. The toxic effects of decomposed ICG should be further investigated under in vivo conditions.
authors.affiliation: Departments of Organic Chemistry, University of Regensburg, Regensburg, Germany.
authors.forename: Eva
authors.initials: E
authors.lastname: Engel
authors.forename: Rüdiger
authors.initials: R
authors.lastname: Schraml
authors.forename: Tim
authors.initials: T
authors.lastname: Maisch
authors.forename: Karin
authors.initials: K
authors.lastname: Kobuch
authors.forename: Burkhard
authors.initials: B
authors.lastname: König
authors.forename: Rolf-Markus
authors.initials: RM
authors.lastname: Szeimies
authors.forename: Jost
authors.initials: J
authors.lastname: Hillenkamp
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Bäumler
authors.forename: Rudolf
authors.initials: R
authors.lastname: Vasold
mesh_terms: D000818:Animals; D002470:Cell Survival / Q000187:drug effects; D002851:Chromatography, High Pressure Liquid; D004396:Coloring Agents / Q000378:metabolism / Q000528:radiation effects* / Q000633:toxicity; D007208:Indocyanine Green / Q000378:metabolism / Q000528:radiation effects* / Q000633:toxicity; D007834:Lasers; D008027:Light; D013058:Mass Spectrometry; D010084:Oxidation-Reduction; D010778:Photochemotherapy; D010857:Pigment Epithelium of Eye / Q000187:drug effects / Q000473:pathology; D026082:Singlet Oxygen / Q000378:metabolism; D019810:Sodium Azide / Q000494:pharmacology; D013472:Sunlight; D013552:Swine; D014343:Trypan Blue
chemical_list: D004396:Coloring Agents; D026082:Singlet Oxygen; D019810:Sodium Azide; D014343:Trypan Blue; D007208:Indocyanine Green