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Improved Anaplerotic Metabolism Following Sodium Pyruvate, Ethyl Pyruvate or Glucose Supplementation after Experimental Traumatic Brain Injury1Radiology, Loma Linda University, Loma Linda, CA, United States, 2Neurosurgery, David Geffen School of Medicine at UCLA
Synopsis
Traumatic brain injury initiates a cascade of events including increased oxidative stress that contributes to the period of generalized metabolic depression. Previously, sodium and ethyl pyruvate and glucose supplementation were shown to reduce cell death and improve recovery following experimental TBI. In this study we used 13C NMR spectroscopy to determine if sodium pyruvate, ethyl pyruvate or glucose supplementation influences the activity of metabolic pathways associated with the intracellular redox state and oxidative metabolism. Our findings show improvements in astrocyte anaplerotic metabolism following all fuel treatments. Only animals treated with sodium pyruvate showed improved oxidative metabolism in neurons. None of the fuel treatments reduced the amount of glucose metabolized via the pentose phosphate pathway. The restoration of astrocyte metabolism by these fuels may partially underlie their abilities to improve cerebral glucose utilization and to reduce neuronal loss following experimental TBI.
Introduction
Previous studies have shown that traumatic brain injury (TBI) initiates ionic and neurotransmitter perturbations and increases oxidative stress that results in an initial increase in the cerebral metabolic rate for glucose (CMRglc), followed by a generalized metabolic depression associated with reduced ATP production (1-5). Sodium pyruvate (SP), ethyl pyruvate (EP), and glucose (GLC) have been shown to reduce cell death and attenuate injury-induced depression in glucose metabolism following experimental TBI (6,7). The purpose of this study is to determine if supplementation with these fuels is sufficient to meet increased metabolic demands following injury by influencing the activity of metabolic pathways associated with the intracellular redox state and oxidative metabolism. We hypothesized that in the period of metabolic depression after a controlled cortical impact (CCI) injury, supplementation with these fuels would increase oxidative metabolism and decrease metabolism through the pentose phosphate pathway (PPP) owing to a decreased need for reducing equivalents as a result of improved redox state.Methods
Thirty three male rats (300-350g) underwent a moderate-severe CCI with an additional 8 rats receiving anesthesia only (Sham). CCI-injured animals received an i.p. injection of 8% normal saline (CCI-SAL; n=8), sodium pyruvate (CCI-SP; 1000 mg/kg, n=8), ethyl pyruvate (CCI-EP; 40 mg/kg, n=9), or glucose (CCI-GLC; n=8) at 0, 1, 3, 6 and 23 hours post-injury. At 24 hours post-injury animals were infused, via femoral vein catheter, with [1, 2 13C2] glucose for 60 minutes. Following the infusion, animals were anesthetized and euthanized by a focused microwave beam and extracts of the left (injury) and right cortex and hippocampus underwent chloroform/methanol extraction and prepared for NMR. Proton decoupled 13C NMR spectra were obtained on a Bruker Avance 500 MHz spectrometer using a 45° flip angle, 10 KHz spectral width, 2 sec acquisition time, 3 sec relaxation delay, and 18 000 acquisitions. All peaks were integrated and the amount of 13C in each metabolite isotopomer was quantified using sodium 3-(trimethylsilyl) propionate (TSP) as an internal reference. All values are reported as mean ± SD and a one-way ANOVA was used to test for an overall difference with a post-hoc Bonferrroni comparison to determine individual group differences.Results
Compared to Shams, animals in the CCI-SAL group showed reduced 13C labeling of all glutamate and glutamine isotopomers (p < 0.05; Fig. 1). The CCI-SP group showed an increase in glutamate and glutamine C4 and C2 doublet labeling similar to sham-levels, indicating improvements in oxidative and anaplerotic metabolism via pyruvate dehydrogenase (PDH) and pyruvate carboxylase (PC), respectively. In contrast, the CCI-EP group showed an increase in glutamate and glutamine C2 doublet labeling, similar to sham-levels, indicating improved anaplerosis via PC. The CCI-GLC group showed decreased labeling of all glutamate isotopomers, compared to controls (p < 0.05), but an increase in glutamine C4 and C2 doublet labeling, that indicates improvements in astrocyte metabolism.Discussion
The doses of SP, EP and GLC examined in this study all enhanced glycolysis but differentially affected neuronal or astrocyte metabolism after CCI injury. The restoration of glutamate and glutamine isotopomer labeling via PC in all fuel groups indicates that astrocyte metabolism was improved. In contrast, only SP supplementation improves oxidative metabolism in neurons following CCI injury. These findings may explain, in part, the mechanisms responsible for the beneficial effects of SP, EP and GLC supplementation following experimental TBI.Acknowledgements
Supported by the UCLA Brain Injury Research Center and P01NS058489 from the National Institute of Neurological Disorders and Stroke (NINDS).References
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