Can Nigella sativa oil control inflammation in human pre-adipocytes?

Objectives: The fixed oil obtained from the seeds of Nigella sativa L. (NS), also known as black cumin, is frequently used in the Mediterranean area for its therapeutic properties. Pertaining literature suggests that its anti-inflammatory, anti-oxidant and anticancer activities is due to thymoquinone (TQ), a main component of this oil, the bioactivity of which has been investigated mainly in cancer models. Besides TQ, NS oil is rich of components (including vitamins, amino acids, fatty acids, sterols, micro elements, etc.) that can contribute to its biological activity. We therefore aimed at evaluating TQ concentration in a Nigella sativa oil extracted from seeds of cultivar produced in the Marche region of Italy, and at determining if its content, antioxidant properties and biological activity decay during storage. Cytotoxicity and anti-inflammatory properties of NS oil were tested in an in vitro model of low-grade inflammation of Simpson-Golabi- Behmel syndrome (SGBS) human pre-adipocytes to assess if this oil, or equal concentration of synthetic thymoquinone, could affect the production of pro-inflammatory cytokines. Methods: Fresh extracted oil (FEO) and old extracted oil (OEO) were evaluated for their content in TQ by gas chromatography coupled to flame ionization detection (GC-FID). Total Antioxidant Activity (TAA), Oxygen Radical Absorbance Capacity (ORAC), Luminol-amplified- and lucigenin-amplified-chemiluminescence of FEO, OEO, TQ and medium from SGBS incubation (MI) were analyzed for their scavenger capacity by spectrophotometric and chemiluminescent assays. SGBS and monocytic leukemia (THP1) cell lines where cultured as previously described by Wabitsch and collaborators (Keuper et al., 2011). Cytotoxicity of NS extracts (FEO, OEO) and solutions equivalent in terms synthetic tymoquinone concentration (syntFEO) were tested by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay for 24 h. Inflammation was induced in SGBS cells by conditioning their culture medium with 15% of supernatant obtained after THP1 differentiation with phorbol 12-myristate 13-acetate (PMA) for 48 h (Keuper et al., 2011). SGBS inflamed cells were treated with FEO, OEO, syntFEO, solved in DMSO for 24 h. Cytokine production was assessed using Multi-Analyte ELISArray Kits (Quiagen). Results: the content of TQ in the NS oil from the Marche region cultivar was higher compared with other NS oils produced in the middle East and in other Mediterranean regions. The FEO contains33% more TQ than OEO, showing that storage affects its overall quality. FEO and OEO showed similar cytotoxicity, but in both cases lower than that of pure TQ. Pro-inflammatory cytokines (e.g. IL-1alfa, IL-1beta, IL-6, IL-8 and GM-CSF) were differently modulated by NS oils. Conclusions: NS oil produced in the Italian Marche region has a good content in TQ and a lower cytotoxicity than pure TQ. Its capacity to counterbalance proinflammatory cytokine production can be ascribed to the antioxidant properties of the other oil components.