The effect of intrinsic and extrinsic influences on skin ageing within associated demographics

Abstract

The skin ages because of intrinsic and extrinsic influences, resulting in damage to mitochondrial DNA (mtDNA). Intrinsic ageing occurs chronologically and cannot be controlled; however, extrinsic skin ageing results from exposure to environmental factors such as ultraviolet radiation (UVR). Although only reported in a small number of publications, previous studies have used a skin swab technique to detect differences in mtDNA damage as a result of UVR exposure. Limited repair mechanisms make mtDNA an effective biomarker of ageing, pioneered predominantly by the Birch-Machin laboratory. A plasmid containing a mitochondrial region of interest was developed to improve normalisation methodology for mtDNA damage comparison. A VISIA® Skin Analysis system was also used to investigate UV spot variation, which was used alongside the swab technique to determine whether differences in mtDNA damage following recent UVR exposure and lifestyle factors can be detected using a skin swab, including a large seasonal study (n=87). Although forskolin and caffeine are natural compounds frequently used in the cosmetic industry, their combined effect has not been investigated; therefore, their protective effects against complete solar light in human dermal neonatal fibroblasts (HDFn) was investigated using cell viability assays. We built upon previous research involving the skin swab by investigating differences in mtDNA damage between individuals. Results did not show a consistent increase in damage immediately following high intensity UVR exposure and significant correlations were not observed with sun exposure and protection behaviours. A seasonal study showed the greatest level of mtDNA damage in spring, in comparison to summer and autumn and a significant positive corelation was seen between protection behaviours and mtDNA damage in swabs collected from the left cheek in summer (p=0.02). UV spot %Area increased during summer and decreased during winter, and trends were observed with age and skin type. A trending correlation was observed between mtDNA damage and UV spots in samples collected from the right side of the face in spring (p=0.09). A combination of caffeine and forskolin was found to have protective effects against 4.32 standard erythemal dose (SED) complete solar light. Although mtDNA damage observed did not reflect perceived recent UVR exposure under our experimental study protocol, facial imaging analysis showed some correlations; however, further studies are necessary. Future studies would employ an objective measure of sunscreen use which would enable a clearer conclusion. Facial imaging analysis could not only prove

effective at measuring damage, but could also be useful in the screening of protective skincare compounds such as forskolin and caffeine.