Phytochemical Analysis and Biological Activities of Flavonoids and Anthraquinones from <i>Cassia alata</i> (Linnaeus) Roxburgh and Their Implications for Atopic Dermatitis Management

To study <i>Cassia alata</i> (CA) (Linnaeus) Roxburgh’s effectiveness towards atopic dermatitis (AD), CA leaf extracts were prepared using three methanol-based extraction solvent systems. Bioactive constituents were characterized and quantified via high-performance liquid chromatography with diode array detection. Antioxidant properties and antimicrobial activities against <i>Staphylococcus aureus</i>, a major AD exacerbation factor, were assessed. Four polyphenols (two flavonoids, two anthraquinones) beneficial in AD control were detected (rhein > aloe-emodin > astragalin > kaempferol). The 75% <i>v</i>/<i>v</i> MeOH/water extract had the most polyphenols and the best antioxidant profile (total phenolic content, total flavonoid content, 2,2-diphenyl-1-picrylhydrazyl-hydrate radical scavenging activity, ascorbic acid equivalent antioxidant capacity), with excellent <i>S. aureus</i> inhibition (minimum inhibitory concentration = 0.625 mg/mL; minimum bactericidal concentration = 1.25 mg/mL). Hence, it was selected for the in vitro examination of cytotoxicity and wound healing activity towards human epidermal keratinocyte cells using a 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2h-tetrazolium bromide (MTT) assay and wound scratch assay. The extract showed no cytotoxicity (IC₅₀ > 100 µg/mL) without significant reduction in cell viability up to 200 µg/mL compared to the vehicle control. An amount of 50 μg/mL extract concentration showed the best wound-healing activity (<i>p</i> < 0.05), with a cell migration rate of 5.89 ± 0.80 µm/h over 96 h post-treatment. Such antioxidant, antimicrobial, and wound-healing activities suggest CA and its polyphenols to be promising natural, long-term AD remedies for skin health.