Assessment of the effect of solvent polarity on Nigella sativa extracts of different origin

Context: Nigella sativa (black cumin) has gained attention for its therapeutic potential in natural medicine. Among its components, thymoquinone and thymol have gained attention for their antitumor and therapeutic potential. Aims: To identify the most effective solvent for extracting active compounds from N. sativa and to compare the yield of cytotoxic phytochemicals across different seed origins. Methods: Twelve extracts were obtained using Soxhlet extraction by combining seeds from four geographic origins with three solvents of varying polarity (n-hexane, methanol, chloroform). Thymoquinone and thymol concentrations were quantified. Cytotoxic activity was assessed using the MTT assay on MCF-7 (breast cancer), HCT-116 (colon cancer), and HFF-1 (normal fibroblast) cell lines. Results: The extraction yield followed the solvent polarity order: chloroform > methanol > n-hexane. The methanol extract from Sudanese seeds yielded the highest concentration of thymoquinone, while the hexane extract from Indian seeds exhibited the highest thymol content. All extracts, irrespective of seed origin and solvent used, reduced MCF-7 cell viability in a concentration-dependent manner. In HCT-116 cells, the methanol extract of Saudi origin demonstrated the most pronounced cytotoxic effect. Notably, cytotoxicity was also observed in the normal HFF-1 cell line. Conclusions: The observed cytotoxic effects were not directly correlated with thymoquinone or thymol concentrations. These findings suggest that other bioactive constituents may contribute to the cytotoxicity observed. Further investigations are warranted to isolate and characterize additional phytochemicals from N. sativa that may play a more significant role in selective tumor cell cytotoxicity.