Abstract
Increasing evidence regarding positive effects of exposure to sunlight has led to suggestions that current advice may be overly weighted in favour of avoidance. UV-A has been reported to lower blood pressure, possibly through nitric oxide (NO) production in skin. Here, we set out to investigate effects of UV-A and solar-simulated radiation on the potential source of dermal NO, the effective doses and wavelengths, the responsiveness of different human skin cells, the magnitude of inter-individual differences and the potential influence of age. We utilised isogenic keratinocytes, microvascular endothelial cells, melanocytes and fibroblasts isolated from 36 human skins ranging from neonates to 86 years old. We show that keratinocytes and microvascular endothelial cells show greatest NO release following biologically relevant doses of UV-A. This was consistent across multiple neonatal donors and the effect is maintained in adult keratinocytes. Our observations are consistent with a bi-phasic mechanism by which UV-A can trigger vasodilatory effects. Analyses of NO-production spectra adds further evidence that nitrites in skin cells are the source of UV-mediated NO release. These potentially positive effects of ultraviolet radiation lend support for objective assessment of environmental influence on human health and the idea of “healthy sun exposure”.
Highlights
In spite of the well-known detrimental effects of over-exposure to sunlight and ultraviolet (UV) radiation, devising public health advice in this regard is not straightforward as exposure to sunlight brings benefits to health
To determine first-hand how these UV radiations affect primary human skin cells, we exposed primary human foreskin keratinocytes (FSKs) to UV-A or UV-B with 9 J/cm[2] and 0.09 J/cm[2] respectively. These doses were selected on the basis that sunlight at noon on a clear summer’s day in the UK would give a dose of 9 J/cm[2] of UV-A in approximately 35 minutes[30, 31]
The results revealed that FSKs and microvascular endothelial cells (FSECs) generated the greatest relative increases in Nitric oxide (NO) while melanocytes (FSMs) and fibroblasts (FSFs) show smaller increases (Fig. 3)
Summary
In spite of the well-known detrimental effects of over-exposure to sunlight and ultraviolet (UV) radiation, devising public health advice in this regard is not straightforward as exposure to sunlight brings benefits to health. It has been demonstrated that exposure to UV can result in an increase in the level of iNOS in the skin 8–10 hours post-exposure[17, 25] This is one way by which UV can increase NO in cells, it is not the sole means; studies have reported NO released so rapidly following exposure that this cannot be accounted for by increased synthesis of NOS enzymes[5]. The amount of NO released immediately following exposure was sufficient to reduce blood pressure[8, 16, 20] This strongly suggests that UV can induce a non-enzymatic mechanism to augment NO at physiologically relevant levels[20]. UV-A cannot be considered intrinsically ‘safe’, but its safety must be considered on balance of the risk to benefit ratio
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
