Thymoquinone, the Main Constituent of Nigella sativa, Could Impact on Adenosine A2 Receptors in Ovalbumin-sensitized Guinea Pigs

Thymoquinone has demonstrated anti-asthmatic effects in many studies but its exact mechanism is not yet fully known. This investigation aims to demonstrate its prophylactic effect in the presence of selective A(2A) and A(2B) adenosine receptors (AR) antagonist; MRS1706 and ZM241365, in sensitized guinea pigs. The gene expression of A(2) AR in blood lymphocytes and lung tissue, lung pathological changes and blood cytokines were evaluated in seven groups. The experiments in blood lymphocytes and lung tissue showed that thymoquinone could increase A(2A)AR mRNA expression and decrease A(2B) AR mRNA expression significantly (P<0.001 to P<0.05); however sensitization had opposite effects. Administration of A(2A) receptor antagonist attenuated inflammation and A(2B) receptor antagonist could prevent asthma-induced inflammatory changes. Moreover, the administration of thymoquinone and A(2A)receptor antagonist together relieved inflammation. Gene expression of A(2B) receptor showed that thymoquinone administration has more influence on blood lymphocytes while administration of the selective A(2B) receptor antagonist was more effective in lung tissue. The results showed some of the therapeutic effects of thymoquinone in reducing asthma symptoms might be partially mediated through A(2) adenosine receptors.