Isolation of thymoquinone from Nigella sativa L. and Thymus vulgaris L., and its anti-proliferative effect on HeLa cancer cell lines

Purpose : To isolate thymoquinone (TQ) from Nigella sativa L. and Thymus vulgaris L., and investigate its anti-proliferative effect on HeLa cancer cells. Method : Pulverized dried samples of N. sativa seed (100 g) and aerial parts of T. vulgaris (1000 g) were subjected to Soxhlet extraction using methanol and n-hexane combined in different proportions. Thymoquinone (TQ) was then isolated from the extracts using high performance liquid chromatography (HPLC). The isolated TQ was further subjected to Fourier Transform Infrared (FTIR) spectroscopy to identify its functional groups. The anti-proliferative effect of TQ on HeLa cancer cells was evaluated using 3-[4, 5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide (MTT) assay. Results : Extract yield from N. sativa was significantly higher than from T. vulgaris, and also increased with increase in the proportion of methanol in the extraction solvent (p < 0.05). Methanol and n-hexane (4:1, v:v) yielded the highest amount of oil, with yields of 15.8 and 9.7 ml/25 g dry weight (d.wt.) from N. sativa and T. vulgaris, respectively. The results obtained from HPLC showed that the concentration of TQ isolated from N. sativa (388.61 μg/ml) was significantly higher than that from T. vulgaris (357.03 μg/ml, p < 0.05). The anti-proliferative effects of TQ standard and TQ isolated from N. sativa on HeLa cancer cells were dose-dependent, and was highest at the lowest concentration. The number of viable cells significantly decreased with increase in TQ concentration (p < 0.01). TQ from N. sativa significantly reduced the number of viable cells even at the lowest concentration when compared to TQ standard (p < 0.05). Cell death was significantly higher in TQ-treated groups than in untreated cancer cells. Conclusion : The results obtained in this study show that N. sativa is a potential source of TQ, with the yield enhanced by modifying the extraction procedure or solvent used. Furthermore, TQ isolated from N. sativa exerts a dose-dependent anti-proliferative effect on HeLa cancer cells. Keywords : Thymoquinone, Nigella sativa, Thymus vulgaris, Anti-proliferative effect