Metabolism of Exogenous [2,4-13C]β-Hydroxybutyrate following Traumatic Brain Injury in 21-22-Day-Old Rats: An Ex Vivo NMR Study

Abstract

Traumatic brain injury (TBI) is the leading cause of morbidity in young children. Acute dysregulation of oxidative glucose metabolism within the first hours after injury is a hallmark of TBI. The developing brain relies on ketones as well as glucose for energy. Thus, the aim of this study was to determine the metabolism of ketones early after TBI injury in the developing brain. Following the controlled cortical impact injury model of TBI, 21–22-day-old rats were infused with [2,4-13C]β-hydroxybutyrate during the acute (4 h) period after injury. Using ex vivo 13C-NMR spectroscopy, we determined that 13C-β-hydroxybutyrate (13C-BHB) metabolism was increased in both the ipsilateral and contralateral sides of the brain after TBI. Incorporation of the label was significantly higher in glutamate than glutamine, indicating that 13C-BHB metabolism was higher in neurons than astrocytes in both sham and injured brains. Our results show that (i) ketone metabolism was significantly higher in both the ipsilateral and contralateral sides of the injured brain after TBI; (ii) ketones were extensively metabolized by both astrocytes and neurons, albeit higher in neurons; (iii) the pyruvate recycling pathway determined by incorporation of the label from the metabolism of 13C-BHB into lactate was upregulated in the immature brain after TBI.

Tracing the path of disruption: 13C isotope applications in traumatic brain injury‐induced metabolic dysfunction

“…Several additional tracers have been used in the setting of TBI 84,144,145 . As PDH may be directly inhibited by ROS, PDH dysfunction is one of the commonest causes of mitochondrial dysfunction and subsequent OXPHOS impairment in trauma 146 .…”

“…Several additional tracers have been used in the setting of TBI. 84 , 144 , 145 As PDH may be directly inhibited by ROS, PDH dysfunction is one of the commonest causes of mitochondrial dysfunction and subsequent OXPHOS impairment in trauma. 146 The ketone body β‐hydroxybutyrate (β‐HB) can be directly converted to acetyl‐CoA, independent of PDH activity, making labeled β‐HB suitable for assessing mitochondrial enzyme activities within the TCA cycle.…”

“…Administering exogenous ketones can help spare cytosolic NAD + pools, enhancing metabolic efficiency 82 . Importantly, ketone metabolism is significantly higher in both the ipsilateral and contralateral sides of the injured brain after TBI 84 . The energetically favorable mechanisms of ketone body metabolism under TBI conditions help alleviate cerebral energy deficits, 82 with increased cerebral uptake and oxidation of exogenous β‐hydroxybutyrate improving ATP levels following TBI 85 …”

Fundamental Neurochemistry Review: Microglial immunometabolism in traumatic brain injury

“…Pre‐clinical studies have investigated ketone bodies as alternative fuels for the injured brain, including interventions using BHB and varied nutritional supplements (Maalouf et al, 2009; McKenna et al, 2015; Prins, 2008). Perivascular MCT2, a transporter protein for BHB, is increased acutely after TBI (Prins & Giza, 2006), while 13 C‐labeled BHB tracing experiments demonstrate increased ketone bodies incorporation into the TCA cycle in the injured cortex of rats (Scafidi et al, 2022). These tracing studies indicate that the metabolic rate of the TCA cycle stimulated by BHB administration is unaltered following TBI, but that there is increased pyruvate recycling from malate during acute brain injury (Scafidi et al, 2022).…”

“…Perivascular MCT2, a transporter protein for BHB, is increased acutely after TBI (Prins & Giza, 2006), while 13 C‐labeled BHB tracing experiments demonstrate increased ketone bodies incorporation into the TCA cycle in the injured cortex of rats (Scafidi et al, 2022). These tracing studies indicate that the metabolic rate of the TCA cycle stimulated by BHB administration is unaltered following TBI, but that there is increased pyruvate recycling from malate during acute brain injury (Scafidi et al, 2022). This is consistent with the observed changes in TCA cycle and glucose metabolism acutely after TBI (Bernini et al, 2020; O'Connell et al, 2005; Singh et al, 2006), and allows ketone body metabolism to support oxidative phosphorylation and drive malate cytosolic NADPH production and NOX2 activity.…”