UVA1 is skin deep: molecular and clinical implications

Abstract

Long wavelength UVA1 (340-400 nm) is the main component of terrestrial UVR and is increasingly used in skin phototherapy. Its damage to critical biomolecules such as DNA has been widely attributed to its ability to generate reactive oxygen species (ROS) via other chromophores. However recent studies in vitro and in vivo have shown that UVA1 has a specific ability to generate cyclobutane pyrimidine dimers (CPD), especially thymine dimers (T<>T), and that this is probably due to direct absorption of UVR. The CPD has been implicated in many aspects of skin cancer. Measuring UVB-induced CPD in the epidermis and dermis in vivo shows that, as expected, the skin attenuates UVB. In contrast, our data show that this is not the case with UVA1: in fact there is more damage with increased skin depth. This suggests that the basal layer, which contains keratinocyte stem cells and melanocytes, is more vulnerable to the carcinogenic effects of UVA1 than would be predicted by mouse models. These data support the continuing trend for better UVA1 protection by sunscreens.

Dermal Damage Promoted by Repeated Low-Level UV-A1 Exposure Despite Tanning Response in Human Skin

“…3, 19, 20 Additionally, we speculate that one of the chromophores that mediate this induction is DNA. 5, 9 …”

“…5–7 Thus, compared with UVB irradiation, skin is exposed to more UVA irradiation, both daily and cumulatively over a lifetime. 5, 8 Furthermore, UVA irradiation penetrates deeper into the dermis than UVB irradiation and, therefore, potentially causes more widespread alterations in the dermis. 5 …”

“…5, 8 Furthermore, UVA irradiation penetrates deeper into the dermis than UVB irradiation and, therefore, potentially causes more widespread alterations in the dermis. 5 …”

Diversity of Biological Effects Induced by Longwave UVA Rays (UVA1) in Reconstructed Skin

“…In addition, it is important to note that the intensity of UVA1 rays exhibits low variation with increased latitude, indicating that loads of UVA1 throughout the year outside of the tropics are lower but more uniform throughout the year [4]. Indeed, in more temperate latitudes UVA irradiance is less affected by seasons than UVB irradiance leading in mid-winter in North Europe to erythemal exposure equally achieved by UVB and UVA [5], [6].…”

Has too much blame been placed on tanning beds for the rise in melanoma diagnosis?

“…The tanning industry has used this feature to promote the image of safe indoor tanning, but there is little evidence that modern tanning beds are any less carcinogenic than older models that emitted higher levels of UVB [15] . Rather, recent studies suggest that radiation in the UVA region also plays a large role in photocarcinogenesis and cyclobutane pyrimidine dimer formation, as well as being the major driver of photoaging [6, [16][17][18] . Whereas UVB radiation acts directly on DNA, the effects of UVA on the skin are mostly indirectly mediated through the generation of reactive oxygen species [19][20][21] .…”