Evaluation of the Bioactive Potential of <i>Cassia fistula</i> Stem Bark Exhibiting Antioxidant, Antimicrobial, Anti-inflammatory, and Cytotoxic Activities

Cassia fistula is a medicinal plant known for its wide range of traditional applications. The present study evaluated the bioactive potential of C. fistula stem bark (CFSB) extracts through antioxidant, antimicrobial, anti-inflammatory, and cytotoxic assays. Sequential extraction with n-hexane (CF-1), chloroform (CF-2), ethyl acetate (CF-3), and methanol (CF-4) was performed to yield distinct crude fractions. Antioxidant properties, total phenolic content (TPC), total flavonoid content (TFC), total antioxidant capacity (TAC), cytotoxic potential, antimicrobial, and in vitro anti-inflammatory activities of the extracts were determined. The CF-3 displayed significant antioxidant activity (IC50 = 8.45 µg/mL), close to standard ascorbic acid (IC50 = 6.54 µg/mL), aligning with TAC results. Also, it demonstrated higher TPC and TFC values, emphasizing its robust antioxidant potential. Cytotoxicity analysis revealed moderate activity in the CF-1 (LC50 = 30.70 µg/mL) compared to vincristine sulfate (LC50 = 3.50 µg/mL). The antimicrobial assay showed that CF-2 and CF-3 exhibited mild to moderate inhibition against Gram-positive bacteria (Bacillus megaterium and Staphylococcus aureus) and the CF-3 was also active against Gram-negative bacteria (Salmonella typhi, and Escherichia coli), but CF-2 was inactive against these strains. Mild antifungal activity against Aspergillus niger was observed for CF-2 and CF-3, while all extracts were inactive against Aspergillus flavus. In vitro protein denaturation studies demonstrated moderate anti-inflammatory activity by CF-4, comparable to diclofenac sodium. These findings suggest that different extracts of CFSB hold promise sources of bioactive compounds with antioxidant, antimicrobial, and anti-inflammatory potential. Further studies may facilitate the isolation of these compounds for potential therapeutic applications.