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(Investigative Ophthalmology and Visual Science. 2008;49:1777-1783.)
© 2008 by The Association for Research in Vision and Ophthalmology, Inc.
DOI:  10.1167/iovs.07-0911
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Light-Induced Decomposition of Indocyanine Green

Eva Engel,1 Rüdiger Schraml,1 Tim Maisch,2 Karin Kobuch,3 Burkhard König,1 Rolf-Markus Szeimies,1 Jost Hillenkamp,4 Wolfgang Bäumler,2 and Rudolf Vasold1

1From the Departments of Organic Chemistry, 2Dermatology, and 3Ophthalmology, University of Regensburg, Regensburg, Germany; and the 4Department of Ophthalmology, University Hospital Schleswig-Holstein, Campus Kiel, Germany.

PURPOSE. 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.






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