Sepsis and septic shock is a continuing problem in the United States with an estimated 200,000 deaths annually. Septic shock occurs when conserved pathogen-derived mediators are released and initiate a systemic activation of the innate immune system. Widespread activation of innate immune system cells results in the release of several proinflammatory mediators including: IL-1, IL-6, IL-12, nitric oxide, leukotrienes, and TNF?. Systemic release of these proinflammatory molecules can cause disseminated intravascular coagulation, hypotension, tachycardia, fever, multi-organ failure, and eventual cardiovascular collapse. While a number of strategies have been developed for the treatment of septic shock, few have proven efficacious in clinical trials. Recent evidence suggests that adenosine receptor agonists might be useful in the treatment of septic shock. Adenosine interacts with a family of four seven transmembrane spanning G-protein coupled receptors designated A1, A2A, A2B, and A3. These receptors exhibit differential tissue expression and couple to different G-proteins. Activation of the A2A and A3 receptor subtypes has been linked to a diminished inflammatory response to lipopolysaccharide, a cell wall component of Gram-negative bacteria. The goal of this study was to pharmacologically characterize the A2A and A3 receptor subtypes in the human monocytic cell line Mono Mac 6. Radioligand binding assays were used to demonstrate expression of each of these receptors on Mono Mac 6 cells. In addition, activation of the A2A receptor was shown to inhibit TNF? secretion induced by lipopolysaccharide and peptidoglycan a major component of the Gram-positive cell wall. A3 receptor agonists were found to inhibit LPS-induced TNF? production, however this effect was not mediated by the A3 receptor. The effect of adenosine receptor activation on signaling pathways activated by LPS was also examined. LPS-induced activation of the MAP kinases was unaffected by an A2A receptor agonist, however ERK activation was substantially inhibited by an A3 receptor agonist. Neither A2A nor A3 agonists modulated NF?B DNA binding. NF?Bdependent activation of a luciferase reporter construct was inhibited by the A2A receptor agonist.
