Acute UV response of early erythema and late edema in SKH1 mice.

Abstract

In human skin, erythema assessed 24 h after ultraviolet (UV) exposure is a non-invasive method for determining the acute UV response. Although erythema is often reported in murine models as a measure of acute UV response, the most informative timepoint after UV exposure is unclear because of variability in mouse strain, sex, and light source. Our current work addresses this critical gap by elucidating the development of erythema and edema over time after acute UV irradiation with solar-simulator UV (SSUV) or UVB light in female or male SKH1 mice. Cutaneous erythema was assessed with ImageJ on digital photographs, and edema was assessed using optically guided high-frequency ultrasound (OG-HFUS) to measure skin thickness and a visual edema scale up to 72 h after UV exposure. Erythema was observed between 4 and 10 h in both female and male mice at most doses of SSUV or UVB irradiation. Erythema induced by irradiation doses of 200, 300, 400 mJ/cmpeaked earlier at the 4-6 h timepoint with SSUV irradiation compared to the same doses of UVB that peaked at the 6-8 h timepoint. At 24 h, edema-induced blanching of the skin masked the erythema, resulting in the highest-dose area having a lower erythema index than non-irradiated areas. Edema was dose-dependent (with SSUV exposure) and peaked between 24 and 48 h using both the OG-HFUS and visual edema scale. Erythema measurement at 4-8 h after UV is optimal for assessing the acute UV response in the SKH1 mouse model at lower irradiation doses. Whereas edema measured at 24-48 h after UV exposure is a sex-neutral and reliable universal measure of acute UV response in SKH1 mouse skin at high UV irradiation doses.