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Anti-inflammatory effect of the alcoholic extracts of N. sativa seeds and its callus on mix glial cells of rat with regard to their thymoquinone (TQ) content was investigated. Callus induction was achieved for explants of young leaf, stem, petiole, and root of N. sativa on solid Murashige and Skoog (MS) medium containing 2,4-D (1 mg/l) and kinetin (2.15 mg/l). TQ content of the alcoholic extracts was measured by HPLC. Total phenols were determined using Folin-Ciocalteu method and antioxidant power was estimated using FRAP tests. The mix glial cells, inflamed by lipopolysaccharide, were subjected to anti-inflammatory studies in the presence of various amounts of TQ and the alcoholic extracts. Viability of the cells and nitric oxide production were measured by MTT and Griess reagent, respectively. The leaf callus obtained the highest growth rate (115.4 mg/day) on MS medium containing 2,4-D (0.22 mg/l) and kinetin (2.15 mg/l). Analyses confirmed that TQ content of the callus of leaf was 12 times higher than that measured in the seeds extract. However, it decreased as the calli aged. Decrease in the TQ content of the callus was accompanied with an increase in its phenolic content and antioxidant ability. Studies on the inflamed rat mix glial cells revealed significant reduction in the nitric oxide production in the presence of 0.2 to 1.6 mg/ml of callus extract and 1.25 to 20 μl/ml of the seed extracts. However, the extent of the effects is modified assumingly due to the presence of the other existing substances in the extracts.

Three new n-alkyl dithiocarbamate compounds, as sodium salts, C4H9NHCS2Na (I), C6H13NHCS2Na (II) and C8H17NHCS2Na (III), were synthesized and examined for inhibition of both cresolase and catecholase activities of mushroom tyrosinase (MT) from a commercial source of Agaricus bisporus in 10 mM phosphate buffer pH 6.8, at 293K using UV spectrophotometry. Caffeic acid and p-coumaric acid were used as natural substrates for the enzyme for the catecholase and cresolase reactions, respectively. Lineweaver-Burk plots showed different patterns of mixed and competitive inhibition for catecholase and cresolase reactions, respectively. These new synthetic compounds can be classified as potent inhibitors of MT due to Ki values of 0.8, 1.0 and 1.8 microM for cresolase inhibitory activity, and also 9.4, 14.5 and 28.1 microM for catecholase inhibitory activity for I, II and III, respectively. They showed a greater potency in the inhibitory effect towards the cresolase activity of MT. Both substrate and inhibitor can be bound to the enzyme with negative cooperativity between the binding sites (alpha > 1) and this negative cooperativity increases with increasing length of the aliphatic tail in these compounds. The inhibition mechanism is presumably related to the chelating of the binuclear coppers at the active site and the different Ki values may be related to different interaction of the aliphatic chains of I, II and III with the hydrophobic pocket in the active site of the enzyme.

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