Glycolysis and the significance of lactate in traumatic brain injury

In traumatic brain injury (TBI) patients, elevation of the brain extracellular lactate concentration and the lactate/pyruvate ratio are well-recognized, and are associated statistically with unfavorable clinical outcome. Brain extracellular lactate was conventionally regarded as a waste product of glucose, when glucose is metabolized via glycolysis (Embden-Meyerhof-Parnas pathway) to pyruvate, followed by conversion to lactate by the action of lactate dehydrogenase, and export of lactate into the extracellular fluid. In TBI, glycolytic lactate is ascribed to hypoxia or mitochondrial dysfunction, although the precise nature of the latter is incompletely understood. Seemingly in contrast to lactate's association with unfavorable outcome is a growing body of evidence that lactate can be beneficial. The idea that the brain can utilize lactate by feeding into the tricarboxylic acid (TCA) cycle of neurons, first published two decades ago, has become known as the astrocyte-neuron lactate shuttle hypothesis. Direct evidence of brain utilization of lactate was first obtained 5 years ago in a cerebral microdialysis study in TBI patients, where administration of 13C-labeled lactate via the microdialysis catheter and simultaneous collection of the emerging microdialysates, with 13C NMR analysis, revealed 13C labeling in glutamine consistent with lactate utilization via the TCA cycle. This suggests that where neurons are too damaged to utilize the lactate produced from glucose by astrocytes, i.e., uncoupling of neuronal and glial metabolism, high extracellular levels of lactate would accumulate, explaining the association between high lactate and poor outcome. Recently, an intravenous exogenous lactate supplementation study in TBI patients revealed evidence for a beneficial effect judged by surrogate endpoints. Here we review the current state of knowledge about glycolysis and lactate in TBI, how it can be measured in patients, and whether it can be modulated to achieve better clinical outcome.We gratefully acknowledge financial support as follows. Research support: the Medical Research Council (MRC, Grant Nos. G0600986 ID79068 and G1002277 ID98489) and the National Institute for Health Research Biomedical Research Centre (NIHR BRC) Cambridge (Neuroscience Theme; Brain Injury and Repair Theme). Authors' support: KLHC—NIHR BRC Cambridge (Neuroscience Theme; Brain Injury and Repair Theme); IJ—MRC (Grant no. G1002277 ID 98489) and NIHR BRC Cambridge; PJH—NIHR Research Professorship, Academy of Medical Sciences/Health Foundation Senior Surgical Scientist Fellowship, and the NIHR BRC CambridgeThis is the final published version. It first appeared at http://journal.frontiersin.org/article/10.3389/fnins.2015.00112/full#h8

Glucose metabolism following human traumatic brain injury: methods of assessment and pathophysiological findings.

The pathophysiology of traumatic brain (TBI) injury involves changes to glucose uptake into the brain and its subsequent metabolism. We review the methods used to study cerebral glucose metabolism with a focus on those used in clinical TBI studies. Arterio-venous measurements provide a global measure of glucose uptake into the brain. Microdialysis allows the in vivo sampling of brain extracellular fluid and is well suited to the longitudinal assessment of metabolism after TBI in the clinical setting. A recent novel development is the use of microdialysis to deliver glucose and other energy substrates labelled with carbon-13, which allows the metabolism of glucose and other substrates to be tracked. Positron emission tomography and magnetic resonance spectroscopy allow regional differences in metabolism to be assessed. We summarise the data published from these techniques and review their potential uses in the clinical setting.This is the final published version. It originally appeared at http://dx.doi.org/10.1007/s11011-014-9628-y

Principal component analysis of the cytokine and chemokine response to human traumatic brain injury.

There is a growing realisation that neuro-inflammation plays a fundamental role in the pathology of Traumatic Brain Injury (TBI). This has led to the search for biomarkers that reflect these underlying inflammatory processes using techniques such as cerebral microdialysis. The interpretation of such biomarker data has been limited by the statistical methods used. When analysing data of this sort the multiple putative interactions between mediators need to be considered as well as the timing of production and high degree of statistical co-variance in levels of these mediators. Here we present a cytokine and chemokine dataset from human brain following human traumatic brain injury and use principal component analysis and partial least squares discriminant analysis to demonstrate the pattern of production following TBI, distinct phases of the humoral inflammatory response and the differing patterns of response in brain and in peripheral blood. This technique has the added advantage of making no assumptions about the Relative Recovery (RR) of microdialysis derived parameters. Taken together these techniques can be used in complex microdialysis datasets to summarise the data succinctly and generate hypotheses for future study

Cerebral microdialysis in clinical studies of drugs: pharmacokinetic applications.

The ability to deliver drug molecules effectively across the blood-brain barrier into the brain is important in the development of central nervous system (CNS) therapies. Cerebral microdialysis is the only existing technique for sampling molecules from the brain extracellular fluid (ECF; also termed interstitial fluid), the compartment to which the astrocytes and neurones are directly exposed. Plasma levels of drugs are often poor predictors of CNS activity. While cerebrospinal fluid (CSF) levels of drugs are often used as evidence of delivery of drug to brain, the CSF is a different compartment to the ECF. The continuous nature of microdialysis sampling of the ECF is ideal for pharmacokinetic (PK) studies, and can give valuable PK information of variations with time in drug concentrations of brain ECF versus plasma. The microdialysis technique needs careful calibration for relative recovery (extraction efficiency) of the drug if absolute quantification is required. Besides the drug, other molecules can be analysed in the microdialysates for information on downstream targets and/or energy metabolism in the brain. Cerebral microdialysis is an invasive technique, so is only useable in patients requiring neurocritical care, neurosurgery or brain biopsy. Application of results to wider patient populations, and to those with different pathologies or degrees of pathology, obviously demands caution. Nevertheless, microdialysis data can provide valuable guidelines for designing CNS therapies, and play an important role in small phase II clinical trials. In this review, we focus on the role of cerebral microdialysis in recent clinical studies of antimicrobial agents, drugs for tumour therapy, neuroprotective agents and anticonvulsants

Matrix Metalloproteinase Expression in Contusional Traumatic Brain Injury: A Paired Microdialysis Study.

Matrix metalloproteinases (MMPs) are extracellular enzymes that have been implicated in the pathophysiology of blood-brain barrier (BBB) breakdown, contusion expansion, and vasogenic edema after traumatic brain injury (TBI). Specifically, in focal injury models, increased MMP-9 expression has been observed in pericontusional brain, and MMP-9 inhibitors reduce brain swelling and final lesion volume. The aim of this study was to examine whether there is a similarly localized increase of MMP concentrations in patients with contusional TBI. Paired microdialysis catheters were inserted into 12 patients with contusional TBI (with or without associated mass lesion) targeting pericontusional and radiologically normal brain defined on admission computed tomography scan. Microdialysate was pooled every 8 h and analyzed for MMP-1, -2, -7, -9, and -10 using a multiplex immunoassay. Concentrations of MMP-1, -2, and -10 were similar at both monitoring sites and did not show discernible temporal trends. Overall, there was a gradual increase in MMP-7 concentrations in both normal and injured brain over the monitoring period, although this was not consistent in every patient. MMP-9 concentrations were elevated in pericontusional, compared to normal, brain, with the maximal difference at the earliest monitoring times (i.e., <24 h postinjury). Repeated-measures analysis of variance showed that MMP-9 concentrations were significantly higher in pericontusional brain (p=0.03) and within the first 72 h of injury, compared with later in the monitoring period (p=0.04). No significant differences were found for the other MMPs assayed. MMP-9 concentrations are increased in pericontusional brain early post-TBI and may represent a potential therapeutic target to reduce hemorrhagic progression and vasogenic edema.M.R.G. was supported by a National Institute for Health Research (NIHR) Academic Clinical Fellowship, a Royal College of Surgeons/Philip King Research Fellowship, and a Beverley and Raymond Sackler Fellowship. A.H. was supported by a joint Medical Research Council/ Royal College of Surgeons of England Clinical Research Training Fellowship. K.L.H.C. is supported by the NIHR Biomedical Research Center, Cambridge (Neuroscience Theme; Brain Injury and Repair Theme). J.D.P. is supported by the Traumatic Brain Injury NIHR Health Technology Cooperative. D.K.M. is supported by an NIHR Senior Investigator Award. P.J.A.H. is supported by the Cambridge NIHR BRC and an NIHR Research Professorship.This is the final published version. It was first made available by Mary Ann Liebert at http://dx.doi.org/10.1089/neu.2014.376

Dextran 500 Improves Recovery of Inflammatory Markers: An In Vitro Microdialysis Study.

Cerebral microdialysis (CMD) is used in severe traumatic brain injury (TBI) in order to recover metabolites in brain extracellular fluid (ECF). To recover larger proteins and avoid fluid loss, albumin supplemented perfusion fluid (PF) has been utilized, but because of regulatory changes in the European Union, this is no longer practicable. The aim with this study was to see whether fluid, absolute (AR), and relative (RR) recovery for the novel carrier, Dextran 500, was better than conventional PF for a range of cytokines and chemokines. An in vitro setup mimicking conditions observed in the neurocritical care of TBI patients was used, utilizing 100-kDa molecular-weight cut-off CMD catheters inserted through a triple-lumen bolt cranial access device into an external solution with diluted cytokine standards in known concentrations for 48 h (divided into 6-h epochs). Samples were run on a 39-plex Luminex (Luminex Corporation, Austin, TX) assay to assess cytokine concentrations. We found that fluid recovery was inadequate in 50% of epochs with conventional PF, whereas Dextran PF overcame this limitation. The AR was higher in the Dextran PF samples for a majority of cytokines, and RR was significantly increased for macrophage colony-stimulating factor and transforming growth factor-alpha. In summary, Dextran PF improved fluid and cytokine recovery as compared to conventional PF and is a suitable alternative to albumin supplemented PF for protein microdialysis.The work was supported by funding for SGC and KLHC from the National Institute for Health Research Biomedical Research Centre, Cambridge (Neuroscience Theme; Brain Injury and Repair Theme). PJH is funded by a National Institute for Health Research (NIHR) Professorship, Academy of Medical Sciences/Health Foundation Senior Surgical Scientist Fellowship and the National Institute for Health Research Biomedical Research Centre, Cambridge. EPT has received salary support from Swedish Society for Medical Research. AH is supported by the Royal College of Surgeons of England and the National Institute for Health Research Biomedical Research Centre, Cambridge. The study consumables were purchased through the NIHR Research Professorship (Peter Hutchinson) and the Luminex 200 analyser was purchased with Medical Research Council (MRC) funding (G0600986 ID79068)

Mildly oxidised LDL induces more macrophage death than moderately oxidised LDL:roles of peroxidation, lipoprotein-associated phospholipase A2 and PPARgamma

AbstractDeath of macrophages and smooth muscle cells (SMC) can lead to progression of atherosclerosis. Mildly oxidised low-density lipoprotein (mildly-oxLDL) induced more overall death and apoptosis than moderately oxidised LDL, in human monocyte-macrophages (HMM). Mildly-oxLDL also induced more overall death in human SMC than did moderately-oxLDL. Mildly-oxLDL contained more hydroperoxides, but less oxysterol, malondialdehyde and negative charge than moderately-oxLDL. Specific inhibition of lipoprotein-associated phospholipase A2 (by SB222657) diminished death induction in HMM by both oxLDL types. Peroxisome proliferator-activated receptor γ (PPARγ) antagonist (GW9662) and agonist (ciglitazone) experiments suggested that non-hydrolysed, oxidised phospholipids in oxLDL activate PPARγ as a cellular defence mechanism. These results may be relevant to LDL oxidation within atherosclerotic plaques and may suggest strategies for combating atherosclerosis progression

Systemic inflammation alters the neuroinflammatory response: a prospective clinical trial in traumatic brain injury.

BACKGROUND: Neuroinflammation following traumatic brain injury (TBI) has been shown to be associated with secondary injury development; however, how systemic inflammatory mediators affect this is not fully understood. The aim of this study was to see how systemic inflammation affects markers of neuroinflammation, if this inflammatory response had a temporal correlation between compartments and how different compartments differ in cytokine composition. METHODS: TBI patients recruited to a previous randomised controlled trial studying the effects of the drug anakinra (Kineret®), a human recombinant interleukin-1 receptor antagonist (rhIL1ra), were used (n = 10 treatment arm, n = 10 control arm). Cytokine concentrations were measured in arterial and jugular venous samples twice a day, as well as in microdialysis-extracted brain extracellular fluid (ECF) following pooling every 6 h. C-reactive protein level (CRP), white blood cell count (WBC), temperature and confirmed systemic clinical infection were used as systemic markers of inflammation. Principal component analyses, linear mixed-effect models, cross-correlations and multiple factor analyses were used. RESULTS: Jugular and arterial blood held similar cytokine information content, but brain-ECF was markedly different. No clear arterial to jugular gradient could be seen. No substantial delayed temporal associations between blood and brain compartments were detected. The development of a systemic clinical infection resulted in a significant decrease of IL1-ra, G-CSF, PDGF-ABBB, MIP-1b and RANTES (p < 0.05, respectively) in brain-ECF, even if adjusting for injury severity and demographic factors, while an increase in several cytokines could be seen in arterial blood. CONCLUSIONS: Systemic inflammation, and infection in particular, alters cytokine levels with different patterns seen in brain and in blood. Cerebral inflammatory monitoring provides independent information from arterial and jugular samples, which both demonstrate similar information content. These findings could present potential new treatment options in severe TBI patients, but novel prospective trials are warranted to confirm these associations

Extracellular N-Acetylaspartate in Human Traumatic Brain Injury.

N-acetylaspartate (NAA) is an amino acid derivative primarily located in the neurons of the adult brain. The function of NAA is incompletely understood. Decrease in brain tissue NAA is presently considered symptomatic and a potential biomarker of acute and chronic neuropathological conditions. The aim of this study was to use microdialysis to investigate the behavior of extracellular NAA (eNAA) levels after traumatic brain injury (TBI). Sampling for this study was performed using cerebral microdialysis catheters (M Dialysis 71) perfused at 0.3 μL/min. Extracellular NAA was measured in microdialysates by high-performance liquid chromatography in 30 patients with severe TBI and for comparison, in radiographically "normal" areas of brain in six non-TBI neurosurgical patients. We established a detailed temporal eNAA profile in eight of the severe TBI patients. Microdialysate concentrations of glucose, lactate, pyruvate, glutamate, and glycerol were measured on an ISCUS clinical microdialysis analyzer. Here, we show that the temporal profile of microdialysate eNAA was characterized by highest levels in the earliest time-points post-injury, followed by a steady decline; beyond 70 h post-injury, average levels were 40% lower than those measured in non-TBI patients. There was a significant inverse correlation between concentrations of eNAA and pyruvate; eNAA showed significant positive correlations with glycerol and the lactate/pyruvate (L/P) ratio measured in microdialysates. The results of this on-going study suggest that changes in eNAA after TBI relate to the release of intracellular components, possibly due to neuronal death or injury, as well as to adverse brain energy metabolism.We gratefully acknowledge financial support as follows. Research support: the Medical Research Council (MRC, Grant Nos. G0600986 ID79068 and G1002277 ID98489) and the National Institute for Health Research Biomedical Research Centre (NIHR BRC) Cambridge (Neuroscience Theme; Brain Injury and Repair Theme). Authors’ support: R.J.S. - NIHR BRC (Neuroscience Theme; Brain Injury and Repair Theme); SV - NIHR BRC (Neuroscience Theme; Brain Injury and Repair Theme); I.J. – MRC (Grant no. G1002277 ID 98489) and NIHR BRC Cambridge; D.K.M. - NIHR Senior Investigator Award; P.J.H. – NIHR Research Professorship, Academy of Medical Sciences/Health Foundation Senior Surgical Scientist Fellowship; K.L.H.C. – NIHR BRC Cambridge (Neuroscience Theme; Brain Injury and Repair Theme).This is the final version of the article. It first appeared from Mary Ann Liebert via http://dx.doi.org/10.1089/neu.2015.395