The Purine Salvage Pathway and the Restoration of Cerebral ATP: Implications for Brain Slice Physiology and Brain Injury

Abstract

Brain slices have been the workhorse for many neuroscience labs since the pioneering work of Henry McIlwain in the 1950s. Their utility is undisputed and their acceptance as appropriate models for the central nervous system is widespread, if not universal. However, the skeleton in the closet is that ATP levels in brain slices are lower than those found in vivo, which may have important implications for cellular physiology and plasticity. Far from this being a disadvantage, the ATP-impoverished slice can serve as a useful and experimentally-tractable surrogate for the injured brain, which experiences similar depletion of cellular ATP. We have shown that the restoration of cellular ATP in brain slices to in vivo values is possible with a simple combination of d-ribose and adenine (RibAde), two substrates for ATP synthesis. Restoration of ATP in slices to physiological levels has implications for synaptic transmission and plasticity, whilst in the injured brain in vivo RibAde shows encouraging positive results. Given that ribose, adenine, and a third compound, allopurinol, are all separately in use in man, their combined application after acute brain injury, in accelerating ATP synthesis and increasing the reservoir of the neuroprotective metabolite, adenosine, may help reduce the morbidity associated with stroke and traumatic brain injury.

Metabolomics analysis of the hippocampus in a rat model of traumatic brain injury during the acute phase

“…Xanthosine was reported as a product of increased oxidative stress involving purine catabolism (Yao et al, 2010). Adenine originally accompanied myocardial ATP decreases during periods of anoxia or ischemia (Frenguelli, 2019;Coffman, Lewis, & Gregg, 1960). Hypoxanthine was found to broadly affect purines with respect to neuron induction of glutamate excitotoxicity (Jackson et al, 2017).…”

The combination of ribose and adenine promotes adenosine release and attenuates the intensity and frequency of epileptiform activity in hippocampal slices: Evidence for the rapid depletion of cellular ATP during electrographic seizures

“…However, under conditions of ATP depletion, most notably cerebral ischaemia, ATP is metabolized to compounds that are lost to the circulation, or, in the case of xanthine, beyond salvage (Weigand et al . ; Frenguelli ; Tian et al . ).…”

“…). This loss of salvageable substrates, together with injury‐induced mitochondrial dysfunction, and indeed potential ATP consumption by mitochondria, likely explains the profound and protracted depletion of cerebral ATP after various forms of injury (Frenguelli ).…”

“…Alternatively, we have proposed the use of ribose and adenine, either alone or in combination with a xanthine oxidase inhibitor, to improve outcome after brain injury (Frenguelli ). In a rodent model of ischaemic stroke, RibAde, when given intravenously for 6 hr during reperfusion, showed an encouraging trend to reduce brain lesion volume and accelerate recovery of function in the week after the period of cerebral ischaemia (Faller et al .…”

“…). This enhancement by allopurinol may reflect: reduced production of non‐salvageable xanthine allowing more hypoxanthine for salvage and ATP synthesis; reduction in the production of reactive oxygen species derived from hydrogen peroxide, or a direct anti‐oxidant action of allopurinol or its active metabolite oxypurinol (Juul and Ferriero ; Frenguelli ).…”