The effect of thymoquinone, the main constituent of Nigella sativa on tracheal responsiveness and white blood cell count in lung lavage of sensitized guinea pigs.

In previous studies, the relaxant, anticholinergic (functional antagonism) and antihistaminic, effects of Nigella sativa have been demonstrated on guinea pig tracheal chains. In the present study, the prophylactic effect of thymoquinone (one of the constituents of Nigella sativa) on tracheal responsiveness and white blood cell (WBC) count in lung lavage of sensitized guinea pigs was examined. Four groups of sensitized guinea pigs to ovalbumin (OA) were given drinking water alone (group S), drinking water containing low or high concentrations of thymoquinone (S + LTQ and S + HTQ groups) or inhaled fluticasone propionate (FP 250 microg) twice a day (positive control group) (n = 7, for all groups). Tracheal responses of control and four groups of sensitized animals to methacholine at an effective concentration causing 50 % of maximum response (EC(50) M) were measured. Tracheal responses to 0.1 % OA, relative to contraction induced by 10 microM methacholine were also examined. Total WBC and its differential count in lung lavage were also measured. The tracheal responsiveness to methacholine, OA and WBC of S guinea pigs was significantly higher than those of controls (p < 0.001 for all cases). Tracheal responsiveness in S + LTQ, S + HTQ, and FP groups to both methacholine (p < 0.05 to p < 0.001) and OA (p < 0.001 for all cases) was significantly decreased compared to that of the S group. Total WBC was also decreased in all experimental groups compared to that of the S group (p < 0.001 for all groups). There was an increase in eosinophils and a decrease in neutrophils, lymphocytes and monocytes in the S animals compared to the controls (p < 0.001 for all cases). Treatment with both concentrations of thymoquinone and FP variably improved differential WBC count changes compared to the S animals (nonsignificant to p < 0.001). The improvement in tracheal responsiveness, total WBC, eosinophils and lymphocytes changes in the S animals treated with both concentrations of TQ were significantly greater than those of FP (p < 0.05 to p < 0.001). These results showed a preventive effect of thymoquinone, one constituent of N. sativa, on tracheal responsiveness and inflammatory cells of lung lavage of sensitized guinea pigs which was comparable or even greater than that of the inhaled steroid.