Ultraviolet radiation (UV) is one of the most dangerous environmental stressors for skin causing oxidative stress and inflammation, which lead to photoaging or even carcinogenesis. Oxidative stress induced by UVB radiation leads to reduction of the epidermal barrier and disruption of intercellular communication, which combined with DNA mutations, may lead to epidermal exfoliation and the development of skin diseases, including psoriasis and even non-melanoma skin cancers.

The mechanisms by which UVB radiation causes such drastic changes of keratinocytes have been studied for many years. There is no doubt that UVB radiation induced oxidative stress leads to lipid membrane damage, changes in the structure and expression of proteins, as well as DNA modifications. As a result, many signalling pathways are activated including NRF2/AP-1-based gene expression; NFκB/TNFα pro-inflammatory signalization; enzymatic lipid metabolism, with increases eicosanoids generation and endocannabinoid system stimulation; growth factors synthesis; mitochondria-dependent apoptosis, phagocytosis induction, and activation of metalloproteinases. Most of these processes are dependent on the phosphorylation of specific factors, catalysed mainly by kinases. Therefore, various medicinal remedies aim to prevent the harmful effects of UVB or support the recovery of the damaged cells. The aim of this study was to evaluate the effects of the bioactive phytocannabinoid - cannabigerol (CBG) together with 3-O-ethyl ascorbic acid (EAA), a stable, lipophilic derivative of the antioxidant vitamin C, on UVB radiation-induced changes in kinase-dependent signalling pathways in cultured human keratinocytes.

CBG is a non-psychotropic phytocannabinoid with antioxidant and anti-inflammatory properties achieved through the activation of cannabinoid receptors (CB1/2), leading to the modulation of the expression of pro-inflammatory cytokines (TNF-α, interleukins (IL-1β, IL-6, IL-10), interferon-γ, prostaglandin E2), but it can also increase the expression of superoxide dismutase by interacting with the PPARγ receptor. CBG is much more lipophilic than EAA, which is a derivative of ascorbic acid with an additional ethyl group. Hence, its greater stability and stronger antioxidant properties. In addition to its ability to direct the scavenging of free radicals, EAA is a compound that readily inhibits ROS production and activates the cytoprotective transcription factor - Nrf2.

In our study proteomic analysis revealed a strong effect of CBG and EAA on unirradiated and UVB-irradiated keratinocytes even after 24 hours. These changes mainly resulted in an increased expression and phosphorylation of the most important kinases of cellular metabolism, such as ERK1/2, IKK, MAP3K7, MAPK14, RIPK2 and NLK. The CBG and EAA used together after UVB radiation of keratinocytes abolished the effects of the applied radiation, restoring the kinase profile to that observed for unirradiated control cells. Moreover, the increase in lipid peroxidation induced by UVB radiation promoted protein modifications by the bioactive lipid peroxidation product 4-hydroxynonenal (4-HNE). Such protein modifications lead to changes in their conformation and activity. However, CBG and EAA reduced the UVB-induced level of 4-HNE-protein adducts, especially for AKT, Camkk1, cJun, ERK1, IKKα, MAPK11 and PERK.

The results and their detailed description have been published at https://doi.org/10.1038/s41598-024-78859-5