Chemical and biological studies of Lobelia flaccida (C. Presl) A.DC leaf: A medicinal plant used by traditional healers in Eastern Cape, South Africa

Purpose: To investigate the phytochemical constituents, acute toxicity and biological activities of Lobelia herb (dried leaf of Lobelia flaccida; family: Campanulaceae), a popular medicinal agent used to manage pain and epilepsy among other indications in Eastern Cape Region of South Africa. Methods: Essential oil (EO) obtained from the dried leaf was analysed with gas chromatography-mas spectroscopy GC/MS while an infusion extract of the herb was obtained by soaking in hot boiled water (100°C) for 24 h, filtered and the filtrate dried in vacuo. Phytochemical screening of the infusion extract was performed to detect the presence of secondary plant metabolites and relative abundance of some of the metabolites. The aqueous extract was evaluated for oral (p.o.) acute toxicity (LD50) using the Lorke’s method [30];, thereafter the extract was tested for anti-inflammatory activity on carrageenaninduced rat paw oedema at 250 and 500 mg/kg, p.o., normal saline and aspirin (100 mg/kg, p.o.) used as negative and positive controls respectively. Finally, the extract at 500 and 1000 mg/kg, p.o. was tested for anticonvulsant activity on pentylene tetrazol (85 mg/kg, intraperitoneally)-induced convulsion model in mice, normal saline and diazepam (1 mg/kg, i.p.) served as negative and positive control groups respectively. Results: EO yield was 0.022 % w/w and the two major compounds identified were acetophenone (26.37 %) and caryophyllene (17.35 %). Phytochemical screening showed high concentration of alkaloids, saponins and flavonoids among other constituents. LD50 of the aqueous extract was ≥ 5000 mg/kg per oral while the aqueous extract exhibited significant (p < 0.01) anti-inflammatory activity on carrageenan-induced rat paw oedema comparable to aspirin but insignificant anticonvulsant activity on pentylene tetrazol-induced convulsion when compared with diazepam. Conclusion: Lobelia herb is non-toxic, and possesses significant anti-inflammatory and mild anticonvulsant activities. It is suggested that the essential oil of this herb should be screened for pharmacological activities.