Method for Investigation of Photobiological Effects of Light on Human Skin Cells Mediated by Low Doses of Light

Highlighting nuances of blue light phototherapy: Mechanisms and safety considerations

“…Therefore, the reported "adverse" effects on skin hydration and elasticity could be attributed to a suboptimal experimental study design. Clinical treatment protocols with blue light and also recently developed protocols for ex vivo and in vitro studies all need to pay careful attention to the selection of irradiance, light dose and thermal management [71,81,82] to avoid undesired effects due to heating. This review of the clinical studies, where assessment of pigmentary change was conducted in intact skin, not in isolated cultured melanocytes in 2D assays, shows that application of blue light (400-495 nm) in vivo causes a clinical hyperpigmentation, detected by both noninvasive optical methods, and confirmed histologically [87][88][89].…”

“…Therefore, the reported “adverse” effects on skin hydration and elasticity could be attributed to a suboptimal experimental study design. Clinical treatment protocols with blue light and also recently developed protocols for ex vivo and in vitro studies all need to pay careful attention to the selection of irradiance, light dose and thermal management [71, 81, 82] to avoid undesired effects due to heating.…”

“…Thus, much caution is needed when reviewing data purporting to link blue light irradiation effects on photodamage of DNA, fibrillin, elastin, collagen, induction of apoptosis, alterations in proteins, including MMPs, and so forth in human skin cells [79]. While in vitro cell culture data may identify fundamental mechanisms of light interaction with cutaneous cells [8,[80][81][82] and clearly are attractive for researchers eager to avoid the complexity of running clinical studies on living human subjects, there is growing concern in biomedicine as to whether cell culture models can ever accurately reflect multilayered processes in real living humans [83]. Thus, great care is needed when interpreting blue light data obtained from in vitro cell models as well as extrapolating those readouts to physiologically relevant (i.e., real-world) clinical settings for example, skin aging and other visual manifestations.…”

“…In the first instance, the design of research studies involving light interaction with cells and tissues requires an in‐depth understanding of relevant parameters (physical, optical, biological, and chemical conditions), which need to be fulfilled to enable photobiological effects to be accurately interpreted [82]. It may surprise many readers, but an overarching systematic approach and well‐defined protocols are often lacking for many of the published in vitro studies of human skin cells [39, 82]. Second, the interpretation and extrapolation of in vitro cell‐based data at an in vivo organ and whole body level require very careful consideration.…”