(+)-Usnic Acid as a Promising Candidate for a Safe and Stable Topical Photoprotective Agent

Abstract

The study aimed to examine whether usnic acid—a lichen compound with UV-absorbing properties—can be considered as a prospective photoprotective agent in cosmetic products. Moreover, a comparison of two usnic acid enantiomers was performed to preselect the more effective compound. To meet this aim, an in vitro model was created, comprising the determination of skin-penetrating properties via skin-PAMPA assay, safety assessment to normal human skin cells (keratinocytes, melanocytes, fibroblasts), and examination of photostability and photoprotective properties. Both enantiomers revealed comparable good skin-penetrating properties. Left-handed usnic acid was slightly more toxic to keratinocytes (IC50 80.82 and 40.12 µg/mL, after 48 and 72 h, respectively) than its right-handed counterpart. The latter enantiomer, in a cosmetic formulation, was characterized by good photoprotective properties and photostability, comparable to the UV filter octocrylene. Perhaps most interestingly, (+)-usnic acid combined with octocrylene in one formulation revealed enhanced photoprotection and photostability. Thus, the strategy can be considered for the potential use of (+)-usnic acid as a UV filter in cosmetic products. Moreover, the proposed model may be useful for the evaluation of candidates for UV filters.

A Comparative Survey of Anti-Melanoma and Anti-Inflammatory Potential of Usnic Acid Enantiomers—A Comprehensive In Vitro Approach

“…The highest inhibition of proliferation was noted for HTB140 cells (Figure 2A) and the effect was especially apparent after 72 h of incubation (IC50 19.9 µg/mL and 31.1 µg/mL for (+)-and (−)-usnic acid, respectively). Also, the most significant differences 0.43 Pharmaceuticals 2021, 14,945 For HTB140 cells, a strong antagonism was observed for (+)-usnic acid with doxorubicin, with the tendency to change into additive after longer incub while the effect for (−)-usnic acid changed from synergistic (24 h) through ad finally antagonistic (48 h). Thus, even though each cell line responded differe combination of usnic acid enantiomers with doxorubicin, our results indicate th of the drug may be reduced.…”

“…Pharmaceuticals 2021, 14,945 For HTB140 cells, a strong antagonism was observed for (+)-usnic acid with doxorubicin, with the tendency to change into additive after longer incuba while the effect for (−)-usnic acid changed from synergistic (24 h) through ad finally antagonistic (48 h). Thus, even though each cell line responded differe combination of usnic acid enantiomers with doxorubicin, our results indicate th of the drug may be reduced.…”

“…It seems, therefore, that topical application of usnic acid could be a better option for its future use. In our previous work, we proved the high safety of both enantiomers to different normal skin cells and also indicated their good permeability through the skin barrier [ 14 ], which is essential for effectiveness when used topically. These results prompted us to widen our research and to examine the potential of both usnic acid enantiomers in skin cancer.…”

Antimelanoma Potential of Cladonia mitis Acetone Extracts – Comparative in Vitro Studies in Relation to Usnic Acid Content

“…Following the prospective results obtained for usnic acid in our previous studies on normal and cancer skin cells, [12,14] we decided to determine the cytotoxic potential of Cladonia mitis acetone extracts and to compare it with the impact of usnic acid alone. In the present study we used 19 Cladonia mitis samples, collected along the North‐South European transect, in which the usnic acid content was determined in our previous work [10] .…”

Toxicity of Usnic Acid: A Narrative Review

“…Surprisingly, (+)-UA in combination with octocrylene showed enhanced photoprotective properties and improved photostability. The authors concluded that (+)-UA can be used in cosmetic products as a UV filter [ 63 ].…”