Although multiple biochemical pathways produce
adenosine, studies suggest that the 2',3'-cAMP-adenosine pathway (2',3'-cAMP→2'-
AMP/3'-AMP→adenosine) contributes to
adenosine production in some cells/tissues/organs. To determine whether the 2',3'-cAMP-adenosine pathway exists in vivo in the brain, we delivered to the brain (gray matter and white matter separately) via the inflow perfusate of a microdialysis probe either 2',3'-cAMP, 3',5'-cAMP,
2'-AMP, 3'-AMP, or 5'-AMP and measured the recovered metabolites in the microdialysis outflow perfusate with mass spectrometry. In both gray and white matter, 2',3'-cAMP increased
2'-AMP, 3'-AMP and
adenosine, and 3',5'-cAMP increased 5'-AMP and
adenosine. In both brain regions,
2'-AMP, 3-AMP and 5'-AMP were converted to
adenosine. Microdialysis experiments in 2',3'-cyclic nucleotide-3'-phosphodiesterase (
CNPase) wild-type mice demonstrated that
traumatic brain injury (controlled cortical impact model) activated the brain 2',3'-cAMP-adenosine pathway; similar experiments in
CNPase knockout mice indicated that
CNPase was involved in the metabolism of endogenous 2',3'-cAMP to
2'-AMP and to
adenosine. In CSF from
traumatic brain injury patients, 2',3'-cAMP was significantly increased in the initial 12 h after injury and strongly correlated with CSF levels of
2'-AMP, 3'-AMP,
adenosine and
inosine. We conclude that in vivo, 2',3'-cAMP is converted to 2'-
AMP/3'-
AMP, and these AMPs are metabolized to
adenosine. This pathway exists endogenously in both mice and humans.