Intracellular
adenosine monophosphate (
AMP) is indispensable for cellular metabolic processes, and it is interconverted to
ADP and/or
ATP or activates
AMP-activated protein kinase (AMPK). However, the specific biological function of extracellular
AMP has not been identified. We evaluated the effect of extracellular
AMP using in vivo and in vitro models of
endotoxemia. We found that
AMP inhibited
inflammation and neutrophil activation in
lipopolysaccharide (LPS)-induced endotoxemic mice. The effects of extracellular
AMP were abolished by an
adenosine 1 receptor (A1R) antagonist but were not influenced by inhibiting the conversion of
AMP to
adenosine (
ADO), indicating that
AMP inhibited
inflammation by directly activating A1R. In addition, in vitro experiments using LPS-stimulated mouse neutrophils showed that
AMP inhibited LPS-induced
reactive oxygen species (ROS) production, degranulation, and
cytokine production, while the effects were reversed by an A1R antagonist. Further research showed that
AMP regulated LPS-stimulated neutrophil functions by inhibiting the
p38 MAPK pathway. These findings were also confirmed in primary neutrophils derived from healthy human blood. Moreover, we collected serum samples from septic patients. We found that
AMP levels were increased compared with those of healthy volunteers and that
AMP levels were negatively correlated with disease severity. Together, these data provide evidence that extracellular
AMP acts on A1R to suppress
endotoxemia-induced
inflammation by inhibiting neutrophil overactivation and that the
p38 MAPK signaling pathway is involved.