Effects of Intense Pulsed Light on the Biological Properties and Ultrastructure of Skin Dermal Fibroblasts: Potential Roles in Photoaging

Objectives: The aim of this study was to evaluate the effects of intense pulsed light (IPL) irradiation on skin fibroblasts in vitro, as well as to explore the biomolecular mechanisms and ultrastructure changes of the IPL effect. Background: IPL is frequently used to improve telangiectasias, lentigos, and skin texture. Clinical studies have demonstrated that IPL has significant photorejuvenation effects on photoaged skin. However, the biomolecular mechanisms underlying the photorejuvenation of IPL treatment remain largely unknown. Methods: Human skin fibroblasts cultured in vitro were irradiated with IPL via double pulses of 4 ms and 6 ms with a pulse interval of 20 ms and fluences of 18, 23, 28, and 33 J/cm 2 . Twenty-four hours after irradiation, cell viability, cell cycle distribution, mRNA and protein levels of procollagen (types I and III), and changes of ultrastructure were evaluated using methyl thiazole tetrazolium (MTT) assay, flow cytometry, real-time reverse transcriptase polymerase chain reaction (RT-PCR), enzyme-linked immunosorbent assays (ELISA), and transmission electron microscopy, respectively. Results: IPL irradiation resulted in the improvement of cell viability of skin fibroblasts in a dose-dependent manner. There were obvious changes in ultrastructure of fibroblasts, compared with the control group. The percentage of fibroblasts at the S and G 2 /M stage of the cell cycle was significantly higher, whereas the percentage at the G 0 /G 1 stage was lower. IPL irradiation increased the mRNA level of collagen I considerably, to 123%, 154%, 172%, and 141% of the control, and that of collagen III to 120%, 141%, 164%, and 132%. IPL irradiation was able to upregulate expression of collagen (types I and III) at the mRNA and protein level. Conclusions: The present study demonstrates that IPL irradiation imparts stimulatory effects on skin fibroblasts in vitro . This provides valuable evidence of the photorejuvenation effect of IPL in vivo .