The Role of Adenosine during the Period of Delayed Cerebral Swelling after Severe Traumatic Brain Injury in Humans

Abstract

Cerebrovascular failure with an increase in cerebral blood volume or hyperemia contributes delayed cerebral swelling after severe traumatic brain injury (TBI) in humans. One mediator that could be involved in this process is adenosine, which stimulates a concurrent reduction in cerebral metabolic rate and an increase in cerebral blood flow (CBF). We hypothesized that during the delayed phase after TBI in humans; 1) CSF adenosine concentration is associated with uncoupling of CBF and CMRO2, and 2) adenosine formation is driven by mediator-stimulated cAMP production in injured brain. We serially measured CBF and AVDO2, and CSF adenosine, lactate and cAMP after severe TBI in 13 humans. After 6-18 h, global CBF was increased and AVDO2 was reduced vs all other time periods, defining the uncoupling phase as the period between 18 h and 5 days. CSF adenosine concentration was negatively associated with AVDO2 and strongly associated with death (both p < 0.05), CSF lactate peaked during the initial 18 h, but remained increased for 5 days. CSF cAMP concentration was not increased (vs normal). The association between CSF adenosine concentration and death, and the correlation between uncoupling of CBF and oxidative metabolism and CSF adenosine concentration support our first hypothesis. In contrast, the low levels of cAMP in CSF observed in these patients, but persistently increased CSF lactate, refute our second hypothesis. We speculate that hyperglycolysis or occult ischemic foci are possible sources of ATP breakdown and adenosine formation, and that adenosine is playing a neuroprotective role.