ONE MECHANISM BEHIND LED PHOTOTHERAPY FOR WOUND HEALING AND SKIN REJUVENATION: KEY ROLE OF THE MAST CELL

Abstract

Light-emitting diodes (LEDs) have attracted a lot of attention in light-only skin rejuvenation and wound healing with an 830 nm/633 nm combination, but the mechanisms by which LED therapy speeds up the healing process and increases collagen synthesis remain unclear. One hypothesis, ex-amined in the present study, concerns the interaction between 830 nm near infrared light and the degranulation of dermal mast cells. The left forearm of 8 healthy male subjects was irradiated with an 830 nm LED array (20 min, 57 J/cm²) with the right as the unirradiated control. Biopsies were taken before and two days after irradiation and routinely prepared for transmission electron microscopy (TEM), and compared between baseline, irradiated and unirradiated tissue. The TEM in all postirradiated specimens, while clearly showing no damage to the irradiated tissue with all tissue components essentially morphologically normal, demonstrated a mild inflammatory response 48 hr after 830 nm irradiation with interstitial and perivascular oedema. A number of macrophages and leukocytes had been recruited into the irradiated tissue, and mast cells had increased in number and had either degranulated or were in the process of doing so. The unirradiated control tissue showed no such changes. The TEM findings in the present study showed a clearly-visible inflammatory response similar to the first phase of wound healing, a ‘quasi-wound’, but created athermally and atraumatically following a single treatment with 830 nm light, thereby kick-starting the inflammatory stage of the wound healing process which is recognized as absolutely necessary in achieving good subsequent collagen synthesis in the second phase of proliferation, followed by good remodeling in the third phase. Good results in skin rejuvenation, both ablative and non-ablative, have been well-linked to establishing the wound healing process. The 830 nm-mediated ‘quasi-wound’ may well be an essential element in light-only LED photorejuvenation.
Furthermore, the action of 830 nm on the inflammatory cells in actual wounds will significantly accelerate the wound healing process, controlling and peaking inflammation, and allowing proliferation to occur sooner and more efficiently.