Anticancer activity of Nigella sativa (black seed) and its relationship with the thermal processing and quinone composition of the seed

Abstract

The traditional preparation process of Nigella sativa (NS) oil starts with roasting of the seeds, an allegedly unnecessary step that was never skipped. The aims of this study were to investigate the role and boundaries of thermal processing of NS seeds in the preparation of therapeutic extracts and to elucidate the underlying mechanism. NS extracts obtained by various seed thermal processing methods were investigated in vitro for their antiproliferative activity in mouse colon carcinoma (MC38) cells and for their thymoquinone content. The effect of the different methods of thermal processing on the ability of the obtained NS oil to inhibit the nuclear factor kappa B (NF-κB) pathway was then investigated in Hodgkin's lymphoma (L428) cells. The different thermal processing protocols yielded three distinct patterns: heating the NS seeds to 50°C, 100°C, or 150°C produced oil with a strong ability to inhibit tumor cell growth; no heating or heating to 25°C had a mild antiproliferative effect; and heating to 200°C or 250°C had no effect. Similar patterns were obtained for the thymoquinone content of the corresponding oils, which showed an excellent correlation with the antiproliferative data. It is proposed that there is an oxidative transition mechanism between quinones after controlled thermal processing of the seeds. While NS oil from heated seeds delayed the expression of NF-κB transcription, non-heated seeds resulted in only 50% inhibition. The data indicate that controlled thermal processing of NS seeds (at 50°C-150°C) produces significantly higher anticancer activity associated with a higher thymoquinone oil content, and inhibits the NF-κB signaling pathway.

Keywords: NF-κB; Nigella sativa; antiproliferative effect; thermal processing; thymoquinone.

Figure 1

Effect of Nigella sativa oil extracted from non-heated seeds versus seeds heated to 50°C on growth rate of non-cancerous fibroblasts versus a mouse colon carcinoma (MC38) cell line. Data are presented as the mean ± standard deviation (n=4).

Figure 2

Effect of Nigella sativa oil extracted from seeds after different thermal processing protocols (no heating, 25°C, 50°C, 100°C, 150°C, 200°C, and 250°C for 10 minutes) on growth rate of mouse colon carcinoma (MC38) cells following 24, 48, or 72 hours of incubation. Data are presented as the mean ± standard deviation (n=4).

Figure 3

Effect of the different thermal processing protocols used for Nigella sativa seeds (no heating, 25°C, 50°C, 100°C, 150°C, 200°C, and 250°C for 10 minutes) on the TQ content of the corresponding oil. Data are presented as the mean ± standard deviation (n=4). Abbreviation: TQ, thymoquinone.

Figure 4

Correlation between effect of Nigella sativa oil on tumor cell growth rate and oil TQ content for the different thermal processing protocols used for the Nigella sativa seeds (no heating, 25°C, 50°C, 100°C, 150°C, 200°C, and 250°C for 10 minutes). Data are presented as the mean ± standard deviation (n=4). Abbreviation: TQ, thymoquinone.

Figure 5

Effect of Nigella sativa oil from heated (50°C) versus non-heated seeds on the NF-κB signaling pathway in Hodgkin’s lymphoma (L428) cells expressing the NF-κB luciferase reporter gene. Extract of NUP was used as positive control, and medium without additives as negative control. Data are presented as the mean ± standard deviation (n=3). Abbreviations: NUP, Nuphar Lutea plant; NF-κB, nuclear factor kappa B.

Figure 6

Hypothesized mechanism of transition between quinones by an oxidation process after controlled heating of Nigella sativa seeds.