Potential of Spirulina-derived phycocyanin as a functional food ingredient for protection against UVB-induced skin oxidative stress

Phycocyanin (PC) is a natural blue pigment–protein derived from Spirulina and has received considerable attention as a food-derived bioactive compound because of its antioxidant and health-promoting properties. This study investigated the potential of Spirulina-derived PC as a functional food ingredient for supporting skin health by evaluating its inhibitory effects on skin aging-related enzymes and its protective effects against ultraviolet B (UVB)-induced oxidative stress in human keratinocytes. The inhibitory activities of PC against elastase and collagenase were evaluated using in vitro enzyme assays. HaCaT keratinocytes were pretreated with PC and subsequently exposed to UVB radiation. Intracellular Reactive Oxygen Species (ROS) accumulation was assessed using a fluorescence-based assay. The effects of PC on Mitogen-Activated Protein Kinase (MAPK) signaling were evaluated by western blot analysis, while the mRNA expression levels of nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) were determined by quantitative real-time PCR. PC inhibited both elastase and collagenase activities in a concentration-dependent manner. In UVB-stimulated HaCaT cells, PC pretreatment reduced intracellular ROS accumulation and attenuated UVB-induced activation of MAPK signaling. Furthermore, PC upregulated the mRNA expression of Nrf2 and HO-1, suggesting that antioxidant defense-related responses may contribute to its protective activity. Collectively, these findings indicate that Spirulina-derived PC may alleviate UVB-induced oxidative stress by reducing intracellular ROS accumulation, modulating MAPK signaling, and regulating antioxidant-related gene expression. Our findings suggest that Spirulina-derived PC enhances cellular antioxidant defense responses against UVB-induced oxidative stress in HaCaT keratinocytes, highlighting its potential as a functional food ingredient for supporting skin health. Further in vivo studies are required to establish the efficacy and bioavailability of PC for functional food and cosmetic applications.