Actual Isothermal Effects of Water‐Filtered Infrared A‐Irradiation

Abstract

In this study, the athermal effects of water-filtered infrared A (wIRA)-irradiation (780-1400 nm) on human dermal fibroblasts were investigated. For this purpose, cells were exposed to wIRA-irradiation (178 mW cm(-2) for 1 h), while a sophisticated experimental setup prevented warming of the samples exceeding 0.1°C. The investigated parameters were the formation of reactive oxygen species (ROS), mitochondrial membrane potential and superoxide release, protein oxidation, proliferation rate, as well as intracellular Ca(2+) -release in single cells, most of them quantified via fluorescence microscopy and fluorimetric techniques. The existence of actual athermal wIRA-effects is still intensively discussed, since their detection requires a careful experimental setup and both efficient and powerful temperature regulation of the exposed samples. Here, we can definitively show that some of the supposed athermal wIRA-effects may be rather artifacts, since wIRA did not reveal any impact on the above mentioned parameters-as long as the temperature of the exposed cells was carefully maintained. Though, we were able to identify an athermal DNA-protective wIRA-effect, since the induced DNA damage (quantified via 8-Oxo-G-formation) was significantly decreased after a subsequent UVB-exposure. These results suggest that many of the supposed athermal wIRA-effects can be induced by pure warming of the samples, independent from any wIRA-irradiation.

High‐energy visible light at ambient doses and intensities induces oxidative stress of skin—Protective effects of the antioxidant and Nrf2 inducer Licochalcone A in vitro and in vivo

“…A, Setup for the irradiation of cultured cells under sunscreen protection. During irradiation, culture plates were covered by PMMA plates without or with sunscreen SPF 50+/ UVA‐PF 40 containing LicA applied. To mimic penetration of antioxidant into the skin, some cultures were incubated with LicA prior to irradiation .…”

“…During irradiation, culture plates were covered by PMMA plates without or with sunscreen SPF 50+/ UVA‐PF 40 containing LicA applied. To mimic penetration of antioxidant into the skin, some cultures were incubated with LicA prior to irradiation . B, ROS formation after VIS irradiation with SPF 50+/ UVA‐PF 40 sunscreen protection and with or without LicA.…”

“…Such findings further support recent recommendations to extend sun protection “beyond UV radiation” . However, our experiments show that the relevance of nonthermal IR at intensities representing natural solar radiation is neglectible with respect to ROS formation in cultured human fibroblasts, as corroborated by others …”

“…It is well established that cellular damage, in particular by UVA, is mediated through the generation of reactive oxygen species (ROS) in sun‐exposed skin. At the opposite end of the solar spectrum, investigations on the effects of infrared (IR) light have resulted in conflicting effects and conclusions ; physiological doses are mostly deemed non‐hazardous and even may be beneficial . The intermediate visible spectrum (VIS 400‐760 nm) was long regarded harmless although more than 50% of solar radiation reaching the surface of the earth is visible light with the global spectral irradiance at a latitude of 45°N at solar noon peaking at around 500 nm .…”

Development of an in vitro Test Procedure to Determine the Direct Infrared A Protection of Sunscreens and Non-Cosmetic Samples

“…Moreover there are studies that negate the aforementioned negative effects of IRA radiation on human skin [6,12,13]. Some studies even showed a benefit of IRA radiation for human skin, as it may lower the UVB cytotoxicity [14,15]. Accordingly, there is a necessity for a definite assessment of the harmfulness of IRA radiation and therewith the need for IRA protection for human skin.…”