Indocyanine green: Intracellular uptake and phototherapeutic effects in vitro

Indocyanine green (ICG; absorption peak in human plasma 805 nm) was investigated for ICG-mediated phototherapy in vitro. The cellular uptake of ICG (1 mu M-50 mu M) 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 mu M-50 mu M 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 mu M yielded a cell killing effect in combination with irradiation depending significantly on ICC concentration and Light dose. Cell viability for dark control and cells incubated with 50 mu M 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 mu M 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.