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

To study Cassia alata (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 Staphylococcus aureus, 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% v/v 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 S. aureus 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 (p < 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.