Photothermal and photochemical effects of laser light absorption by indocyanine green (ICG)

Indocyanine Green (ICG) is clinically used as a fluorescent dye for imaging purposes. Its rapid circulation kinetics and minimal toxicity has prompted investigation into ICG's utility as a photosentitizer for therapeutic applications. Traditionally, optically mediated tumor therapy has focused on photodynamic therapy, which employs a photochemical mechanism resulting from the absorption of low intensity CW laser light by localized photosensitizers such as Photofrin II, Benzoporphyrin Derivative (BPD), ICG. Treatment of cutaneous vascular malformations such as port-wine stains, on the other hand, is based on a photothermal mechanism resulting from the absorption of high intensity pulsed laser light by hemoglobin. In this study, we compared the effectiveness of combining photochemical and photothermal mechanisms during application of ICG in conjunction with laser irradiation with the intention that the combined approach may lead to a reduction in the threshold dose of pulsed laser light required to treat hypervascular malformations. The blood vessels in rabbit ears were used as an in vivo model for targeted vasculature. Irradiation of the ears with IR light (λ=785 nm, Δτ = 3 min, Io = 120 mW) was used to elicit photochemical damage, while photothermal damage was brought about using pulses from a ruby laser (λ=694 nm, τ = 3 ms) with different fluences. For the combined modality, photochemical damage was induced first and followed by photothermal irradiation. This modality was compared with photothermal irradiation alone. The effectiveness of each irradiation scheme was assessed using histopathological analysis. We present preliminary data that suggests that pretreatment with photodynamic therapy before photothermal coagulation results in more severe vascular damage with lower photothermal fluence levels. The results of this study provide the foundation work for further exploration of the therapeutic potentials of photochemical and photothermal effects during application of ICG in conjunction with laser irradiation.

[1]  Christoph Abels,et al.  Indocyanine green (ICG) and laser irradiation induce photooxidation , 2000, Archives of Dermatological Research.

[2]  Lanigan.  Port‐wine stains unresponsive to pulsed dye laser: explanations and solutions , 1998, The British journal of dermatology.

[3]  Lihong V. Wang,et al.  Optimum pulse duration and radiant exposure for vascular laser therapy of dark port-wine skin: a theoretical study. , 2003, Applied optics.

[4]  M Landthaler,et al.  Photo-oxidative killing of human colonic cancer cells using indocyanine green and infrared light , 1999, British Journal of Cancer.

[5]  H. Barr,et al.  Clinical Aspects of Photodynamic Therapy , 2002, Science progress.

[6]  U Hohenleutner,et al.  Epidermal damage and limited coagulation depth with the flashlamp-pumped pulsed dye laser: a histochemical study. , 1995, The Journal of investigative dermatology.

[7]  M Landthaler,et al.  Indocyanine green: intracellular uptake and phototherapeutic effects in vitro. , 1997, Journal of photochemistry and photobiology. B, Biology.

[8]  W. Hall,et al.  Selective Photothermolysis : Precise Microsurgery by Selective Absorption of Pulsed Radiation , 2005 .

[9]  M C Oz,et al.  Changes in type I collagen following laser welding , 1992, Lasers in surgery and medicine.

[10]  M. Reed,et al.  The History of Photodetection and Photodynamic Therapy¶ , 2001, Photochemistry and photobiology.

[11]  Vishal Saxena,et al.  Degradation kinetics of indocyanine green in aqueous solution. , 2003, Journal of pharmaceutical sciences.

[12]  James W Tunnell,et al.  Effects of cryogen spray cooling and high radiant exposures on selective vascular injury during laser irradiation of human skin. , 2003, Archives of dermatology.

[13]  K. Bartels,et al.  Photothermal effects on murine mammary tumors using indocyanine green and an 808-nm diode laser: an in vivo efficacy study. , 1996, Cancer letters.

[14]  Christoph Abels,et al.  Absorption and Fluorescence Spectroscopic Investigation of Indocyanine Green , 1996 .

[15]  Patrycja Nowak-Sliwinska,et al.  Indocyanine green as a prospective sensitizer for photodynamic therapy of melanomas. , 2002, Acta biochimica Polonica.

[16]  G. Kwant,et al.  Light-absorbing properties, stability, and spectral stabilization of indocyanine green. , 1976, Journal of applied physiology.

[17]  H. Chan,et al.  Laser treatment of congenital facial port‐wine stains: Long‐term efficacy and complication in Chinese patients , 2002, Lasers in surgery and medicine.

[18]  Quing Zhu,et al.  Emission and absorption properties of indocyanine green in Intralipid solution. , 2004, Journal of biomedical optics.

[19]  Sol Kimel,et al.  Combined photodynamic and photothermal induced injury enhances damage to in vivo model blood vessels , 2004, Lasers in Surgery and Medicine.

[20]  M. Landthaler,et al.  Indocyanine green and laser light for the treatment of AIDS-associated cutaneous Kaposi's sarcoma. , 1998, British Journal of Cancer.

[21]  Valery V Tuchin,et al.  A pilot study of ICG laser therapy of acne vulgaris: Photodynamic and photothermolysis treatment , 2003, Lasers in surgery and medicine.