The increasing demand from consumers for greener and safer cosmetic products has driven the search for bio-based materials and nanomaterials as sustainable and eco-friendly alternatives. Traditional cosmetic ingredients can sometimes raise environmental and safety concerns, prompting the exploration of renewable resources. In this context, agro-derived lignin, a significant byproduct of paper manufacturing with known UV radiation absorption properties and antioxidant capabilities, and cellulose nanofibers (CNFs), derived from industrial waste with universal ligand characteristics and potential for stable dispersions, have emerged as promising candidates for cosmetic formulations. This study addresses the critical need to evaluate the phototoxicity and photoprotection mechanisms of specific kraft lignin fractions (LE and R1) and kraft-bleached pulp CNF to ascertain their safety and efficacy for cosmetic applications using an in vitro model of human skin cells.
This study utilized the HaCaT cell line (immortalized human keratinocytes) to assess the phototoxicity and photoprotection of two kraft lignin fractions (LE and R1) and kraft-bleached pulp CNF. Phototoxicity was evaluated by exposing cells pre-treated with the test substances to UVA radiation (4 J/cm²) and measuring cell viability using MTT and neutral red uptake (NRU) assays. Photoprotection was assessed by measuring the reduction in UVA (10 J/cm²)-induced reactive oxygen species (ROS) production using a DCF-DA probe and fluorescence measurements. Different concentrations of the test substances were used in both assays, and the photoirritant factor (PIF) was calculated for lignin when feasible.
Key Findings:
•Both lignin fractions, LE and R1, exhibited concentration-dependent increases in phototoxicity under UVA irradiation, as evidenced by decreased cell viability in MTT and NRU assays.
•CNF showed no phototoxic effects on HaCaT cells under the tested conditions (0.97 to 125 µg/mL).
•At higher concentrations (0.97 to 125 µg/mL), LE presented PIF values of 9.99 (MTT) and 8.73 (NRU), classifying it as phototoxic, while R1 showed PIF values of 6.36 (MTT) and 5.59 (NRU), also indicating phototoxic potential.
•LE, R1, and CNF all significantly reduced the production of ROS induced by UVA irradiation at all tested concentrations (3.9, 7.81, and 15.2 µg/mL for lignin; 31.25, 62.5, and 125 µg/mL for CNF), suggesting photoprotective properties.
This research provides novel data on the phototoxic potential of specific kraft lignin fractions, demonstrating a concentration-dependent phototoxic effect in HaCaT cells under UVA irradiation, which is a critical safety parameter for topical applications. While CNF displayed no phototoxicity, the study highlights that higher concentrations of kraft lignin fractions can pose a phototoxic risk. Importantly, the findings also underscore the photoprotective capabilities of both kraft lignin and CNF, evidenced by their significant reduction of UV-induced ROS production. The novelty of this work lies in its specific evaluation of the phototoxicity of these particular kraft lignin fractions and the comparative assessment with kraft-bleached pulp CNF. The future implications of this research are significant for the development of renewable and sustainable cosmetic formulations, suggesting that while both materials hold promise, the concentration of lignin must be carefully considered to ensure product safety, paving the way for further research into optimizing their use in cosmetics
Link to the study: https://www.mdpi.com/2079-9284/12/2/61
