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Indocyanine green: intracellular uptake and phototherapeutic effects in vitro
S Fickweiler1, R M Szeimies, W Bäumler
1Department of Dermatology, University of Regensburg, Germany.
Insights
Indocyanine green (ICG) phototherapy effectively kills skin cells (keratinocytes) when activated by an 805 nm laser. This cell-killing effect, dependent on ICG concentration and light dose, was reduced by sodium azide, suggesting a photodynamic reaction mechanism.
Area of Science:
- Biomedical Engineering
- Photomedicine
- Dermatology
Background:
- Indocyanine green (ICG) is a near-infrared fluorescent dye used in medical imaging.
- Phototherapy utilizes light to treat diseases, and ICG's properties make it a candidate for photodynamic therapy.
Purpose of the Study:
- To investigate the efficacy of ICG-mediated phototherapy in vitro.
- To determine the dose-dependent phototoxic effects of ICG on HaCaT keratinocytes.
- To explore the mechanism of ICG-induced cell death.
Main Methods:
- HaCaT keratinocytes were incubated with varying concentrations of ICG (1-50 microM) for 24 hours.
- Cells were irradiated with an 805 nm diode laser at different energy densities (0-48 J cm-2).
- Cell viability was assessed, and the effect of sodium azide (a reactive oxygen species quencher) was evaluated.
Main Results:
- ICG uptake increased with concentration, reaching 12.1 +/- 1.3 nmol per 10(6) cells.
- Irradiation of ICG-treated cells significantly reduced viability in a dose-dependent manner.
- Sodium azide significantly inhibited ICG-induced cell killing, indicating a role for reactive oxygen species.
Conclusions:
- Photoactivation of ICG with an 805 nm laser effectively induces cell death in keratinocytes.
- The cell-killing mechanism appears to involve a photodynamic reaction.
- ICG-mediated phototherapy shows potential for applications in skin conditions.
Abstract:
Indocyanine green (ICG; absorption peak in human plasma 805 nm) was investigated for ICG-mediated phototherapy in vitro. The cellular uptake of ICG (1 microM-50 microM) into HaCaT keratinocytes after an incubation period of 24 h increased up to an intracellular ICG concentration of 12.1 +/- 1.3 nmol per 10(6) cells. To examine dose dependent phototoxic effects in vitro, keratinocytes were incubated with 0 microM-50 microM ICG for 24 h and irradiated by a diode laser (805 nm) with different energy densities (0, 12, 24, 48 J cm-2). All applied ICG concentrations except for 5 microM yielded a cell killing effect in combination with irradiation depending significantly on ICG concentration and light dose. Cell viability for dark control and cells incubated with 50 microM ICG and irradiated with 48 J cm-2 was 0.82 +/- 0.15 and 0.07 +/- 0.02, respectively. Sodium azide (100 mM), a quencher of reactive oxygen species, inhibited significantly the cell killing using 50 microM ICG and 24 J cm-2. Taken together, photoactivation of ICG by irradiation with a diode laser was shown to induce effectively cell killing of HaCaT keratinocytes. Moreover, this effect was inhibited by sodium azide, thus irradiation of ICG might induce a photodynamic reaction.