Effects of stimulation of adenosine A_2A receptors on lipopolysaccharide-induced production of reactive oxygen species by equine neutrophils

Objective - To assess the anti-inflammatory effects of an adenosine analogue on lipopolysaccharide (LPS)-stimulated equine neutrophils. Sample Population - Neutrophils obtained from 10 healthy horses. Procedures - An adenosine analogue (5′-N-ethylcarboxamidoadenosine [NECA]) was tested for its ability to inhibit production of reactive oxygen species (ROS) in LPS-stimulated equine neutrophils. Selective adenosine receptor antagonists were used to identify the receptor subtype responsible for effects. To assess the mechanism of action of NECA, cAMP concentrations were measured, and effects of dibutyryl cAMP (a stable analogue of cAMP) and rolipram (a type 4 phosphodiesterase inhibitor) were investigated. Results - NECA elicited concentration-dependent inhibition of ROS production that was inhibited by ZM241385, a selective adenosine A_2A receptor antagonist; this effect of NECA was not affected by the adenosine A_2B receptor antagonist MRS1706. Also, ZM241385 blocked NECA-induced increases in cAMP concentrations, whereas MRS1706 did not alter this effect of NECA. Rolipram potentiated NECA-induced inhibition of ROS production, and dibutyryl cAMP also inhibited ROS production. Conclusions and Clinical Relevance - Activation of adenosine A_2A receptors inhibited ROS production by LPS-stimulated equine neutrophils in a cAMP-dependent manner. These results suggest that stable adenosine A_2A receptor agonists may be developed as suitable anti-inflammatory drugs in horses.