Reproducible method for assessing the effects of blue light using in vitro human skin tissues.

Introduction: High-intensity visible light (HEV), also referred to as blue light, has a wavelength of 400-500 nm and accounts for approximately one-third of the visible light. Blue light is also emitted from electronic devices and artificial indoor lighting. Studies have shown that exposure of human skin cells to light emitted from electronic devices, even as short as 1 h, can cause an increase in reactive oxygen species (ROS), apoptosis and necrosis. Despite comprising a significant portion of the light spectrum, the effects of HEV light have not been studied as extensively. This is in part due to a lack of suitable in vitro testing methods. This work was conducted in order to develop a reproducible testing method for assessing the effects of blue light on the skin.

Methods: Testing was performed using a full thickness, 3D in vitro skin tissue model. Different exposure protocols were tested to (1) determine the biological effects of blue light on the skin and (2) to identify an appropriate exposure for routine testing of cosmetic materials that may protect the skin from blue light damage. Gene expression and protein biomarkers were measured using qPCR, ELISA and immunohistochemical (IHC) methods.

Results: Our work demonstrates that daily exposure to blue light produced dose-and-time-dependent changes in biomarkers associated with skin damage. Exposure to blue light for 6 h for 5 consecutive days (total intensity of 30 J/cm ) increased the expression of genes that regulate inflammation and oxidative stress pathways and decreased the expression of genes that maintain skin barrier and tissue integrity. Exposure to blue light significantly increased protein biomarkers associated with ageing, inflammation and tissue damage. IHC staining confirmed changes in collagen, filaggrin and NQO1 protein expression. Treatment with ascorbic acid inhibited the effects of blue light, demonstrating a role in protection from blue light.

Conclusion: Our results showed that consistent blue light exposure produced skin damage via alterations in biological pathways that are associated with skin ageing. This work provides a new, reproducible in vitro testing method for assessing the effects of blue light on human skin using gene expression, protein ELISA and IHC staining.