Solar broadband UV irradiation is commonly regarded as a major causative reason for cutaneous photoaging. The pro-aging molecular pathways and cellular targets affected by UVA+UVB light in human skin have been extensively investigated. Notwithstanding growing knowledge in mechanisms of photoaging, research and development of clinically efficient, nontoxic, and sustainable topical preparations providing full physical, chemical, and biological photoprotection still remain a great challenge for pharmaceutical and cosmetic industries. In this study, we are proposing a panel of the in vitro methods for preselection of natural photoprotective substances with high photostability and low phototoxicity able of absorbing a broadband UVA+UVB irradiation (physical sunscreen), reducing UV-related overproduction of free radicals and loss of endogenous antioxidants (chemical protection), and attenuating UV-induced cytotoxicity and immune and metabolic responses (biological protection) in primary human epidermal keratinocytes and immortalized human keratinocyte cultures. Our data showed that secondary metabolites biosynthesized in plant cells in response to UV irradiation, such as phenylpropanoids and their glycosylated metabolites, aglycons and glycosylated flavonoids, and leontopodic acids, hold the best promise for complete natural topical prevention of photoaging and rejuvenation of photoaged skin. Meristem plant cell cultures elicited by solar simulating UV could be the most environmentally sustainable biotechnological source of polyphenols with combined photoprotective and antiaging properties.

The effect of plant polyphenolic compounds (PPs) on the viability of human keratinocytes exposed to ultraviolet (UV) radiation of range C (UVС) and the number of single-stranded DNA breaks in the nuclei of these cells was studied. The experimental data obtained indicate that, along with the cytoprotective effect, the addition of silybin and acacetin immediately after the UVC exposure leads to a significant decrease in the number of single-stranded DNA breaks in the nuclei of HaCaT keratinocytes 2 and 5 h after exposure. It was concluded that PPs are able to reduce the destructive effect of UV radiation on skin cells, reducing the number of genetic damage.

In this study it was investigated the responses of cultured human cells – keratinocytes and fibroblasts to physiological doses of ultraviolet radiation (UVR) applied with or without plant polyphenolic compounds: rutin, quercetin, taxofolin, silybin and baikalein. Experimental data obtained in this work indicate the presence of synergism in the action of physiological doses of UVR and plant polyphenolic compounds on inflammatory signaling pathways in keratinocytes and fibroblasts. It is concluded that the identified synergies can contribute to the adaptation of the skin to subsequent exposure to UVR, and thus be one of the photoprotective mechanisms of the plant polyphenolic compounds.