Astaxanthin as a Natural Photoprotective Agent: In Vitro and In Silico Approach to Explore a Multi-Targeted Compound

Ultraviolet B radiation is a major cause of skin aging, cellular senescence, and inflammaging, mediated by the excessive production of reactive oxygen species (ROS) and induction of apoptosis. This study evaluated the photo-protective effects of astaxanthin, one of the strongest natural antioxidants, in UVB-treated keratinocytes. The antioxidant capacity of astaxanthin was evaluated using ABTS, DPPH, and NBT/riboflavin/SOD assays. HaCaT cells were exposed to 30 mJ/cm2 of UVB radiation. Photoprotective effects and accumulated ROS were evaluated in UVB-irradiated HaCaT cells by MTT and DCFH-DA assays. Nitric oxide levels were quantified using the Griess reagent. Apoptosis was assessed by dual staining using acridine orange/ethidium bromide, lysosomal integrity by acridine orange uptake, and cell migration by scratch assay. Cell adhesion was assessed on ECM-coated Nunc plates. Finally, we formulated a 0.5% astaxanthin-enriched cream. Astaxanthin mitigated UVB-induced damage by reducing intracellular ROS levels by 3.7-fold, decreasing nitric oxide production to 29.8 ± 7.7% at the highest concentration, and maintaining lysosomal integrity. The carotenoid significantly enhanced cell viability, increasing it from 60.64 ± 8.3% in UV-treated cells to 102.1 ± 3.22% at 40 µM. Moreover, treated cells showed a significant reduction (p < 0.001) in the apoptotic rate (37.7 ± 3.1 vs. 87.7 ± 3.8 in UVB-irradiated cells, as evidenced by reduced chromatin condensation and nuclear fragmentation. Astaxanthin also enhanced tissue repair, as evidenced by increased cell migration and adhesion to several extracellular matrix (ECM) proteins (poly-L-lysine, laminin, fibrinogen, vitronectin and collagen I). In silico molecular docking predicted strong binding affinities between astaxanthin and key cellular targets, including JAK2 (−9.9 kcal/mol, highest affinity), STAT3, FAK, COX-2, NF-k-B, MMP2, and MMP9. The formulated cream demonstrated an in vitro SPF of 7.2 ± 2.5. Astaxanthin acts as a multifunctional photoprotective compound, providing a strong rationale for its incorporation into cosmetic and dermatological formulations, as further supported by the successful formulation and in vitro SPF estimation of an astaxanthin-enriched cream.