Thymoquinone, the main constituent of Nigella sativa, affects adenosine receptors in asthmatic guinea pigs

Abstract

<em>Objective(s): </em>For determining the mechanism of anti-asthmatic effect of thymoquinone, this investigation evaluated the effect of thymoquinone in the presence of selective A_2Aand A_2Badenosine receptor antagonists (ZM241385 and MRS1706, respectively). <br/><em>Materials and Methods: </em>Seventy guinea pigs were randomly divided to 7 groups; control (C), sensitized with ovalbumin (S), sensitized groups pretreated with thymoquinone (S+TQ), ZM241385 (S+Anta A_2A), MRS1706 (S+Anta A_2B), thymoquinone and antagonists (S+Anta A_2A+TQ and S+Anta A_2B+TQ). Thymoquinone and each of these antagonists with 3 mg/kg dose were injected i.p. on 10^th day of sensitization protocol. Tracheal responsiveness (TR) to methacholine and ovalbumin (OA), and total and differential cell count in lung lavage fluid (LLF) in different groups were measured. <br/><em>Results: </em>Increased EC₅₀ and LLF neutrophil count and decreased TR to methacholine and OA, LLF eosinophil and basophil counts were observed in S+TQ group compared to S group (<em>P</em>P<0.05). Significant decrease in EC₅₀(<em>P</em><0.01), LLF neutrophil, lymphocyte and monocyte count (<em>P</em>P<0.01), LLF total WBC (<em>P</em><0.01) and eosinophil count (<em>P</em><0.001) were observed in S+A_2A group compared to S+TQ group. There was significant increase in LLF eosinophil and monocyte counts in S+Anta A_2Bgroup compared with S+TQ group (<em>P</em>2A group, there was significant increase in LLF eosinophil (<em>P</em><0.001) and significant decrease in LLF neutrophil (<em>P</em><0.01) and monocyte (<em>P</em><0.001) counts compared with S+TQ group. <br/><em>Conclusion: </em>Thymoquinone affects adenosine receptors, which suggest that some of its anti-inflammatory effects may be mediated by these receptors.