Ultrasound-Assisted Recovery and Biological Evaluation of an Astaxanthin-Containing Extract from Chara corallina

Oxidative stress and chronic inflammation are major contributors to skin photoaging, highlighting the need for natural antioxidants with multifunctional bioactivities. This study developed an ultrasound-assisted extraction (UAE) strategy to recover an astaxanthin-rich extract from the underutilized freshwater macroalga Chara corallina and evaluated its antioxidant, anti-inflammatory, and anti-photoaging properties. Different solvent systems were evaluated for extraction efficiency, and astaxanthin-equivalent recovery was quantified by high-performance liquid chromatography with photodiode array detection (HPLC–PDA). Antioxidant activity was evaluated using the DPPH radical scavenging assay, whereas biological activities were assessed in human dermal fibroblasts and RAW264.7 macrophages using cell viability assays, quantitative real-time PCR, and extracellular matrix-related enzyme inhibition assays. The selected solvent system (48% ethanol in ethyl acetate) provided the highest astaxanthin-equivalent recovery (0.2598 ± 0.0086% w/w). The selected CCE exhibited DPPH radical-scavenging activity, modulated antioxidant- and inflammation-associated gene expression, increased COL1A2 mRNA expression, and inhibited collagenase, elastase, and hyaluronidase within the evaluated concentration range. HPLC–PDA analysis revealed a chromatographic component with retention-time and UV–visible spectral characteristics corresponding to those of an authentic astaxanthin reference standard; however, comprehensive structural and phytochemical characterization was not performed. Because CCE is a chemically complex extract, the observed biological responses cannot be attributed exclusively to astaxanthin. Overall, these findings provide an initial basis for further investigation of C. corallina as an underexplored freshwater source of carotenoid-containing bioactive extracts rather than establishing it as a commercially competitive source of natural astaxanthin.