Investigation into the effects of infrared,visible and ultraviolet wavelengths of the solar spectrum on human skin cell damage

Abstract

Ultraviolet light is known to cause skin damage and photoaging, and chronic exposure can lead to skin cancer. The effects of visible light and infrared light on the skin are less well understood, though some believe they contribute to oxidative stress and photoaging. Understanding the mechanisms of photodamage is important for the development of sunscreens to effectively prevent photodamage and maintain skin health. The objective of this study was to optimise experimental conditions for assaying the irradiation of visible and infrared light on human skin cells in vitro, and determining the effects of these wavelengths on reactive oxygen species (ROS) production and gene expression. Temperature control during infrared irradiations is critical to understanding the effect of light on chromophores rather than through heating. Without adequate temperature control, tissue culture plates could exceed 60°C, resulting in greater than 90% cell death. Careful consideration of medium conditions is crucial for ensuring results are not due to unexpected interactions of light with medium components. The presence of riboflavin, a component of almost all commercially available cell culture medium, reduced viability in cells irradiated with blue light by 45%. When adequately controlled, it was found that 2 hours of infrared at solar intensity or a 10- hour equivalent dose at 9 x peak solar intensity did not affect ROS as measured with flow cytometry, and RNA sequencing showed few changes to gene expression with less than 10 differentially expressed genes. A dose of visible light equivalent to one hour of peak solar visible light did not induce a ROS signal measurable after irradiation. However, it was found to affect extracellular matrix genes MMP1 and MMP3 to similar extents to a 2.16 standard erythemal dose of UV and induce ferritin expression where the UV dose did not, indicating a possible effect on photoaging and oxidative stress. In summary, this thesis demonstrates that infrared light has little effect through absorption of chromophores, but visible light may affect fibroblast extracellular matrix regulation and iron homeostasis.