Phytochemical Composition, Antioxidant and Antiproliferative Activities of African Basil (Ocimum gratissimum L.) Leaves

Aim: To determine the phytochemicals in Ocimum gratissimum leaves, their phenolic content, antioxidant potential and antiproliferative activity against human prostate (DU145), colon (CT26) and cervical (HeLa 229) cancer cells. Place and Duration of the Study: Leaves of O. gratissimum were collected from cultivated plants in Wakiso district of Uganda. The samples were analyzed at Directorate of Government Analytical Laboratory, Kampala (Uganda) and Kenya Medical Research Institute, Centre for Traditional Medicine and Drug Research, Nairobi (Kenya) between August 2019 and January 2020. Methodology: The leaves were separately extracted by maceration using hexane, dichloromethane, ethyl acetate and methanol. The methanolic extract was further fractionated and subjected to solid phase extraction. Antiproliferative assay was done using dimethylthiazol-2,5-diphenyl-tetrazolium bromide assay while total phenolic content and antioxidant activity were determined by Folin-Ciocalteu method and 2,2-diphenyl-1-picrylhydrazyl radical scavenging assay respectively. Compounds were identified by Fourier transform infrared spectroscopy and liquid chromatography-tandem mass spectrometry. Results: A total of 34 compounds were identified in the fractions. The highest mean total phenolic content was 401.07 ± 6.47 µg/ml for the methanolic extract which also had the highest antioxidant activity with minimum inhibitory concentration of 5.79 ± 0.13 mg/ml. There was a positive correlation between the antioxidant activity of the extracts and antiproliferative activity of the extracts on prostate and cervical cancer cell lines. The extracts exhibited the highest toxicity against prostate cancer cells and the least against cervical cancer cells. Conclusion: The results of this study support the traditional use of this plant in cancer therapy in Uganda. Further research should isolate pure anticancer compounds from this plant which could act as lead candidates in the development of anticancer drugs.