Laser light activation of a second-generation photosensitiser and its use as a potential photomodulatory agent in skin rejuvenation

Photodynamic rejuvenation therapy (PDRT) is a growing field in cosmetic dermatology. In this study, different sources of light (a yellow laser, a red laser and ultraviolet A (UVA) lamps) were used to activate a second-generation photosensitiser, hypericin. Uptake of hypericin was monitored over 24 h and efficacy of PDRT was assessed using cell viability and reactive oxygen species (ROS) quantification assays. In addition, we show for the first time, a quantifiable assay for ROS production in human dermal fibroblasts incubated with hypericin and exposed to yellow laser light or UVA lamps. Furthermore, we optimised a protocol with regard to hypericin concentration and irradiation parameters using the XTT cell viability kit. This study showed that this photosensitiser, hypericin, was taken up by the cells in a concentration-dependent manner over 24 h with cell saturation occurring after approximately 16 h. The uptake seemed to be localised to the cell cytoplasm with no hypericin appearing in the nucleus. The levels of ROS increased in the cell when irradiated with the yellow laser (561 nm) however, it did not increase further with the addition of hypericin. Hypericin and UVA showed a significant increase in the amount of ROS produced. The results also show that cell viability is not affected by low power light (2 mW) from the yellow laser irrespective of the dose used. However, an increase to 10 mW power with 5 J/cm² light dose, resulted in a significant drop (p < 0.05) in cell viability at both 0.5 (77.53 ± 9.67 %) and 1 μM (48.51 ± 13.27 %) hypericin concentrations. In contrast, a 20 % increase in cell viability was seen with 1 J/cm² and 20 mW and 0.25 μM hypericin. Overall, this study highlights an optimised protocol for hypericin-induced photorejuvenative therapy using laser light and proposes that parameters of 0.25 μM hypericin as a photosensitiser activated via a dosage of 1 J/cm² yellow laser light produces an effective in vitro outcome to be considered as an important contribution towards optimising PDRT.