Light-induced decomposition of indocyanine green.
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.
Engel
Eva
E
Departments of Organic Chemistry, University of Regensburg, Regensburg, Germany.
Schraml
Rüdiger
R
Maisch
Tim
T
Kobuch
Karin
K
König
Burkhard
B
Szeimies
Rolf-Markus
RM
Hillenkamp
Jost
J
Bäumler
Wolfgang
W
Vasold
Rudolf
R
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
D004396:Coloring Agents; D026082:Singlet Oxygen; D019810:Sodium Azide; D014343:Trypan Blue; D007208:Indocyanine Green