UVB photoprotection by thiourea and (thio)semicarbazone derivatives: cellular and molecular evidence

Ultraviolet B (UVB) radiation is a major environmental stressor that contributes to oxidative stress, inflammation, DNA damage, and ultimately an increased risk of skin carcinogenesis. The development of safer, multifaceted UV filters with improved photostability and bioprotective properties remains an important research priority. Here, alkyl chain-conjugated thiourea (I-XIX) and aryl-linked (thio)semicarbazone (XX-XXV) derivatives have been systematically assessed for their photoprotective potential against UVB-induced cellular damage.

The UV absorption properties, molar absorptivity, and photostability of the test compounds were assessed through spectroscopic studies. Cytotoxicity, effective concentrations, and bioprotective effects of the compounds were evaluated using in vitro cellular methods.

Several compounds exhibited robust UVB absorption with high molar absorptivity, particularly semicarbazone derivatives, while displaying minimal cytotoxicity to normal human dermal fibroblasts. Among the evaluated compounds, ten compounds were found to be more photostable than benzophenone (reference compound). Selected compounds significantly reduced UVB-induced intracellular reactive oxygen species and nitric oxide production, signifying effective attenuation of oxidative and nitrosative stress. In addition, compounds IV, XXI, and XXIII alleviated UVB-induced inflammatory cascades by diminishing Interleukin-1 beta (IL-1β) and Tumor Necrosis Factor alpha (TNF-α) levels. Therefore, these compounds also protected fibroblast morphology. Moreover, the same compounds protected from DNA damage by preventing UVB-induced genomic DNA fragmentation and formation of cyclobutane pyrimidine dimers. In particular, compound XXIII displayed selective UVB absorption, better photostability, low cytotoxicity, and moderate biological photoprotection (SPF 16).

Together, the results suggest that thiourea and (thio)semicarbazone derivatives, notably compound XXIII, represent promising photoprotective scaffolds requiring further formulation, in vivo, permeability, phototoxicity, and safety studies to validate their potential as UV-filtering agents.