Influence of chemotype on the chemical composition, antioxidant activity and in vitro cytotoxicity of Ageratum conyzoides essential oil

Ageratum conyzoides is a medicinal plant characterized by marked chemical variability in its essential oils, which may directly influence biological activity. This study compared the chemical composition, antioxidant activity, cytotoxicity, and selectivity of two essential oil chemotypes of A. conyzoides bearing purple flowers (PFs) and white flowers (WFs). The oils were obtained by hydrodistillation and characterized by GC–MS analysis. Antioxidant capacity was evaluated using DPPH and ABTS radical scavenging assays, with results expressed as IC₅₀ and Trolox equivalent antioxidant capacity (TEAC). Cytotoxicity was assessed in RAW 264.7 macrophages, VERO epithelial cells, and L929 fibroblasts using the MTT assay, and selectivity indices were calculated to integrate antioxidant potency with cytotoxicity data. The PFs chemotype was rich in sesquiterpene hydrocarbons (34.52%) and oxygenated sesquiterpenes (27.56%), whereas WFs was dominated by the chromene precocene I (69.62%). PFs exhibited significantly lower IC₅₀ values for DPPH (128.63 µg/mL) and ABTS (132.47 µg/mL) compared to WFs (303.63 and 308.47 µg/mL, respectively), indicating greater antioxidant potency. Both chemotypes showed low cytotoxicity, with CC₅₀ values exceeding 400 µg/mL. The selectivity index was higher for PFs (SI > 3.0) than for WFs (SI > 1.3), suggesting a more favorable balance between biological activity and cellular safety. These findings demonstrate that antioxidant performance in A. conyzoides essential oils is chemotype-dependent and highlight the importance of chemical characterization prior to biological or industrial application.