Pharmacological screening of tabernaemontana divaricate - a promising natural source for cytotoxic and antioxidant agents

Tabernaemontana divaricata is a medicinal plant belonging to the Apocynaceae family. Native to South and Southeast Asia, it is widely cultivated as an ornamental shrub due to its attractive white, pinwheel-like flowers. In Sinhalese, it is called “Wathusudda”. The leaves of this plant have traditionally been used for medicinal purposes, particularly in the treatment of inflammation and pain. Recently, a few studies have investigated the antioxidant, anti-inflammatory, and anticancer properties of related species within the same family. Therefore, this study aimed to evaluate the bioactivity of T. divaricata, with a particular focus on its potential cytotoxic effects. The leaves of T. divaricata were subjected to ethanol extraction before analysis. Total phenolic content (TPC) was determined using the Folin Ciocalteu method, while antioxidant activity was evaluated via DPPH (1,1 diphenyl-1-picrylhydrazyl) and ABTS (2,2′-azinobis-3-ethylbenzothiazoline-6 sulfonic acid) free radical scavenging assays in vitro. Anti-inflammatory activity was assessed through the human red blood cell (HRBC) membrane stabilization assay and the protein denaturation assay. Cytotoxicity was analyzed using the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] assay against the HeLa (cervical cancer) cell line. The extract exhibited a TPC of 114.32 ± 5.76 mg GAE/g, while the flavonoid content was 21.66 ± 1.68 mg QE/g. The leaf extract demonstrated high antioxidant activity, with an IC₅₀ = 0.01 mg/mL in the DPPH assay (standard ascorbic acid IC₅₀ < 0.06 mg/mL). However, in the ABTS assay, the extract showed a higher IC₅₀ value of 0.7 mg/mL (standard ascorbic acid IC₅₀ = 0.06 mg/mL). In anti-inflammatory assays, the leaf extract exhibited better activity in the HRBC assay (IC₅₀ = 0.1 mg/mL) (standard ibuprofen IC₅₀ < 0.06 mg/mL) compared to the protein denaturation assay (IC₅₀ > 1 mg/mL) (standard ibuprofen IC₅₀ < 0.06 mg/mL). Cytotoxicity evaluation revealed that the leaf extract inhibited 98.82% of HeLa cell viability at a concentration of 1 mg/mL, with an IC₅₀ value of 0.1 mg/mL. T. divaricata possesses considerable therapeutic potential, particularly as a natural source of antioxidant and anticancer agents, warranting further mechanistic and in vivo investigations.