J. Clay Goodman

Presence of dendritic cells, MCP-1, and activated microglia/macrophages in amyotrophic lateral sclerosis spinal cord tissue

Dendritic cells are potent antigen‐presenting cells that initiate and amplify immune responses. To determine whether dendritic cells participate in inflammatory reactions in amyotrophic lateral sclerosis (ALS), we examined mRNA expression of dendritic cell surface markers in individual sporadic ALS (sALS), familial ALS (fALS), and nonneurological disease control (NNDC) spinal cord tissues using semiquantitative and real‐time reverse transcription polymerase chain reaction (RT‐PCR). Immature (DEC205, CD1a) and activated/mature (CD83, CD40) dendritic cell transcripts were significantly elevated in ALS tissues. The presence of immature and activated/mature dendritic cells (CD1a+ and CD83+) was confirmed immunohistochemically in ALS ventral horn and corticospinal tracts. Monocytic/macrophage/microglial transcripts (CD14, CD18, SR‐A, CD68) were increased in ALS spinal cord, and activated CD68+ cells were demonstrated in close proximity to motor neurons. mRNA expressions of the chemokine MCP‐1, which attracts monocytes and myeloid dendritic cells, and of the cytokine macrophage‐colony stimulating factor (M‐CSF) were increased in ALS tissues. The MCP‐1 protein was expressed in glia in ALS but not in control tissues and was increased in the CSF of ALS patients. Those patients who progressed most rapidly expressed significantly more dendritic transcripts than patients who progressed more slowly. These results support the involvement of immune/inflammatory responses in amplifying motor neuron degeneration in ALS.

Effect of Erythropoietin and Transfusion Threshold on Neurological Recovery After Traumatic Brain Injury: A Randomized Clinical Trial

IMPORTANCE There is limited information about the effect of erythropoietin or a high hemoglobin transfusion threshold after a traumatic brain injury. OBJECTIVE To compare the effects of erythropoietin and 2 hemoglobin transfusion thresholds (7 and 10 g/dL) on neurological recovery after traumatic brain injury. DESIGN, SETTING, AND PARTICIPANTS Randomized clinical trial of 200 patients (erythropoietin, n = 102; placebo, n = 98) with closed head injury who were unable to follow commands and were enrolled within 6 hours of injury at neurosurgical intensive care units in 2 US level I trauma centers between May 2006 and August 2012. The study used a factorial design to test whether erythropoietin would fail to improve favorable outcomes by 20% and whether a hemoglobin transfusion threshold of greater than 10 g/dL would increase favorable outcomes without increasing complications. Erythropoietin or placebo was initially dosed daily for 3 days and then weekly for 2 more weeks (n = 74) and then the 24- and 48-hour doses were stopped for the remainder of the patients (n = 126). There were 99 patients assigned to a hemoglobin transfusion threshold of 7 g/dL and 101 patients assigned to 10 g/dL. INTERVENTIONS Intravenous erythropoietin (500 IU/kg per dose) or saline. Transfusion threshold maintained with packed red blood cells. MAIN OUTCOMES AND MEASURES Glasgow Outcome Scale score dichotomized as favorable (good recovery and moderate disability) or unfavorable (severe disability, vegetative, or dead) at 6 months postinjury. RESULTS There was no interaction between erythropoietin and hemoglobin transfusion threshold. Compared with placebo (favorable outcome rate: 34/89 [38.2%; 95% CI, 28.1% to 49.1%]), both erythropoietin groups were futile (first dosing regimen: 17/35 [48.6%; 95% CI, 31.4% to 66.0%], P = .13; second dosing regimen: 17/57 [29.8%; 95% CI, 18.4% to 43.4%], P < .001). Favorable outcome rates were 37/87 (42.5%) for the hemoglobin transfusion threshold of 7 g/dL and 31/94 (33.0%) for 10 g/dL (95% CI for the difference, -0.06 to 0.25, P = .28). There was a higher incidence of thromboembolic events for the transfusion threshold of 10 g/dL (22/101 [21.8%] vs 8/99 [8.1%] for the threshold of 7 g/dL, odds ratio, 0.32 [95% CI, 0.12 to 0.79], P = .009). CONCLUSIONS AND RELEVANCE In patients with closed head injury, neither the administration of erythropoietin nor maintaining hemoglobin concentration of greater than 10 g/dL resulted in improved neurological outcome at 6 months. The transfusion threshold of 10 g/dL was associated with a higher incidence of adverse events. These findings do not support either approach in this setting. TRIAL REGISTRATION clinicaltrials.gov Identifier: NCT00313716.

Elevation of tumor necrosis factor in head injury

Tumor necrosis factor (TNF) is a cytokine which mediates protein wasting in pathological states by promoting the catabolism of visceral tissues and skeletal muscle. The role that TNF plays in nitrogen wasting following head injury was studied by measuring TNF in the serum of 21 patients with severe head injury. Parallel measurements of TNF and urinary nitrogen excretion were performed on days 1, 3, and 5 after head injury. TNF values after head injury ranged from 65 pg/ml to 7500 pg/ml, with a mean of 1147 pg/ml, compared to control values of serum TNF of less than 38 pg/ml. The mean daily urinary nitrogen loss was 13 g/day with a range of 2.8 to 27.6 g/day, and the mean nitrogen balance was -5.8 g with a range of +4.6 to -19.1 g. While both serum TNF levels and nitrogen loss were increased after head injury, the elevation of TNF did not correlate strongly with nitrogen wasting.

Patterns of Energy Substrates during Ischemia Measured in the Brain by Microdialysis

The purpose of this study was to examine the patterns of change in microdialysate concentrations of glucose, lactate, pyruvate, and glutamate in the brain during periods of hypoxia/ischemia identified by monitoring brain tissue pO2 (PbtO2). Of particular interest was a better understanding of what additional information could be obtained by the microdialysis parameters that was not available from the PbtO2. Fifty-seven patients admitted with severe traumatic brain injury who had placement of both a brain tissue pO2 (PbtO2) and microdialysis probe were studied. The microdialysis probe was perfused with Ringers solution at 0.3 microL/min and dialysate was collected at 1-h intervals. The concentration of glucose, pyruvate, lactate, and glutamate were measured in each dialysate sample. Changes in the microdialysis parameters were examined during episodes where the PbtO2 decreased to below 10 mm Hg. Ten episodes of tissue hypoxia/ischemia identified by a decrease in PbtO2 below 10 mm Hg were observed during the period of monitoring. The concentration of the dialysate glucose closely followed the PbtO2. The dialysate pyruvate concentration was more variable and in some patients transiently increased as the PbtO2 dropped below 10 mm Hg. The dialysate concentration of lactate was significantly increased as the PbtO2 decreased to less than 10 mm Hg. Dialysate glutamate was significantly elevated only when PbtO2 decreased to very low levels. Although changes in the PbtO2 provided the earliest sign of hypoxia/ischemia, the microdialysis assays provided additional information about the consequences that the reduced tissue pO2 has on brain metabolism, which may be helpful in managing these critically ill patients.

Spinal cord ischemia-induced elevation of amino acids: Extracellular measurement with microdialysis

Excitatory amino acids have been implicated in the production of calcium mediated neuronal death following central nervous system ischemia. We have used microdialysis to investigate changes in the extracellular concentrations of amino acids in the spinal cord after aortic occlusion in the rabbit. Glutamate, aspartate, glutamine, asparagine, glycine, taurine, valine, and leucine were measured in the micordialysis perfusate by high pressure liquid chromatography. The concentrations of glutamate, glycine, and taurine were significantly higher during ischemia and reperfusion than controls. Delayed elevations in the concentrations of asparagine and valine were also detected. The elevation of glutamate is consistent with the hypothesis that excitotoxins may mediate neuronal damage in the ischemic spinal cord. Increased extracellular concentrations of asparagine and valine may reflect preferential use of amino acids for energy metabolism under ischemic conditions. The significance of increased concentrations of inhibitory amino acid neurotransmitters is unclear.

Microdialysis: is it ready for prime time?

Purpose of reviewThis review highlights recent advances in cerebral microdialysis for investigational and clinical neurochemical monitoring in patients with critical neurological conditions. Recent findingsUse of microdialysis with other methods, including PET, electrophysiological monitoring and brain tissue oximetry in traumatic brain injury, subarachnoid hemorrhage with vasospasm, and infarction with refractory increased intracranial pressure have been reported. Potentially adverse neurochemical effects of nonconvulsive status epilepticus and cortical slow depolarization waves, both of which are increasingly recognized in traumatic brain injury and stroke patients, have been reported. The explosive growth in the use of cerebral oximetry with targeted management of brain tissue oxygen levels is leading to greater understanding of derangements of cerebral bioenergetics in the critically ill brain, but there remain unresolved basic issues. Understanding of the analytes that are measurable at the bedside – glucose, lactate, pyruvate, glutamate and glycerol – continues to evolve with glucose, lactate, pyruvate and the lactate–pyruvate ratio taking center stage. Analytes including inflammatory biomarkers such as cytokines and metabolites of nitric oxide are presently investigational, but hold promise for future application in advancing our understanding of basic pathophysiology, therapeutic target selection and prognostication. Growing consensus on indications for use of clinical microdialysis and advances in commercially available equipment continue to make microdialysis increasingly ‘ready for prime time.’ SummaryCerebral microdialysis is an established tool for neurochemical research in the ICU. This technique cannot be fruitfully used in isolation, but when combined with other monitoring methods provides unique insights into the biochemical and physiological derangements in the injured brain.

Interstitial brain adenosine and xanthine increase during jugular venous oxygen desaturations in humans after traumatic brain injury.

ObjectiveAdenosine decreases the cerebral metabolic rate for oxygen and increases cerebral blood flow, and it may play an important role in cerebrometabolic and cerebrovascular responses to hypoperfusion after traumatic brain injury. Jugular venous oxygen saturation is monitored after traumatic brain injury to assess brain oxygen extraction, and desaturations may reflect secondary brain insults. We hypothesized that brain interstitial adenosine and related purine metabolites would be increased during jugular venous oxygen saturation desaturations (<50%) and determined associations between the purines, lactate, and glucose to assess the role of adenosine during secondary insults in humans. DesignStudy of critically ill adults with severe traumatic brain injury. SettingAdult neurointensive care unit. PatientsWe prospectively defined periods of normal saturation and desaturation in six patients after severe traumatic brain injury. InterventionsDuring these periods, cerebral microdialysis samples of brain interstitial fluid were collected, and adenosine and purine metabolites were measured by high-pressure liquid chromatography. Measurements and Main Results Adenosine increased 3.1-fold and xanthine increased 2.5-fold during desaturation periods (both p < .05 vs. normal saturation period, signed rank). Adenosine, xanthine, hypoxanthine, and cyclic-adenosine monophosphate correlated with lactate over both study periods (r2 = .32, .14, .31, .07, and .26, respectively, all p < .05, Pearson product moment correlation). ConclusionThe marked increases in interstitial brain adenosine that occur during jugular venous oxygen desaturations suggest that adenosine may play an important role during periods of secondary insults after traumatic brain injury. The correlation of these metabolites with lactate further suggests that adenosine is increased during periods of enhanced glycolytic metabolism.

Evolution of Brain Tissue Injury after Evacuation of Acute Traumatic Subdural Hematomas

OBJECTIVE Acute traumatic subdural hematoma complicated by brain parenchymal injury is associated with a 60 to 90% mortality rate. Early surgical evacuation of the mass lesion is essential for a favorable outcome, but the severity of the underlying brain injury determines the outcome, even when surgery has been prompt. The purpose of this study was to analyze tissue biochemical patterns in the brain underlying an evacuated acute subdural hematoma to identify a characteristic pattern of changes that might indicate evolving brain injury. METHODS Prospectively collected data from 33 patients after surgical evacuation of acute subdural hematoma were analyzed. Both a brain tissue oxygen tension probe and an intracerebral microdialysis probe were placed in brain tissue exposed at surgery. On the basis of the postoperative clinical course, the patients were divided into three groups: patients with early intractable intracranial hypertension, patients with evolution of delayed traumatic injury (DTI), and patients with an uncomplicated course (the no-DTI group). RESULTS The overall mortality rate was 46%, with 100% mortality in the intracranial hypertension group (five patients). Mortality in the DTI group was 53% compared with only 9% in the no-DTI group (P = 0.002). There were no significant differences in the initial computed tomographic scan characteristics, such as thickness of the subdural hematoma or amount of midline shift, among the three groups. Physiological variables, as well as the microdialysate measures of brain biochemistry, were markedly different in the intracranial hypertension group compared with the other groups. Differences between the other two groups were more subtle but were significant. Significantly lower values of brain tissue oxygen tension (14 +/- 8 mm Hg versus 27 +/- 14 mm Hg) and higher dialysate values of lactate and pyruvate were documented in patients who developed a delayed injury compared with patients with uncomplicated courses (4.1 +/- 2.3 mmol/L versus 1.7 +/- 0.7 mmol/L for lactate, and 104 +/- 47 micromol/L versus 73 +/- 54 micromol/L for pyruvate at 24 h after injury). CONCLUSION Evolution of DTI in the area of brain underlying an evacuated subdural hematoma is associated with a significant increase in mortality. Postoperatively decreasing brain tissue oxygen tension and increasing dialysate concentrations of lactate and pyruvate in this area may warn of evolving brain injury and evoke further diagnostic and therapeutic activity.

The Role of Endothelial Nitric Oxide Synthase in the Cerebral Hemodynamics after Controlled Cortical Impact Injury in Mice

Traumatic brain injury causes a reduction in cerebral blood flow, which may cause additional damage to the brain. The purpose of this study was to examine the role of nitric oxide produced by endothelial nitric oxide synthase (eNOS) in these vascular effects of trauma. To accomplish this, cerebral hemodynamics were monitored in mice deficient in eNOS and wild-type control mice that underwent lateral controlled cortical impact injury followed by administration of either L-arginine, 300 mg/kg, or saline at 5 min after the impact injury. The eNOS deficient mice had a greater reduction in laser Doppler flow (LDF) in the contused brain tissue at the impact site after injury, despite maintaining a higher blood pressure. L-Arginine administration increased LDF post-injury only in the wild-type mice. L-Arginine administration also resulted in a reduction in contusion volume, from 2.4 +/- 1.5 to 1.1 +/- 1.2 mm(3) in wild-type mice. Contusion volume in the eNOS deficient mice was not significantly altered by L-arginine administration. These differences in cerebral hemodynamics between the eNOS-deficient and the wild-type mice suggest an important role for nitric oxide produced by eNOS in the preservation of cerebral blood flow in contused brain following traumatic injury, and in the improvement in cerebral blood flow with L-arginine administration.

Role of Nitric Oxide in Cerebral Blood Flow Abnormalities after Traumatic Brain Injury

Nitric oxide (NO) has important regulatory functions within the central nervous system. NO is oxidized in vivo to nitrate and nitrite (NOx). Measurement of these products gives an index of NO production. The purpose of this study was to examine the relation between the brain extracellular concentration of NO metabolites and cerebral blood flow (CBF) after severe traumatic brain injury. Using a chemiluminescence method, NOx concentrations were measured in 6,701 microdialysate samples obtained from 60 patients during the first 5 d after severe head injury. Regional and global values of CBF obtained by xenon-enhanced computed tomography were used for analyses. Dialysate NOx values were the highest within the first 24 h after brain trauma and gradually decreased over the 5 postinjury d (time effect, P < 0.001). Mean dialysate concentration of NOx was 15.5 ± 17.6 μmol/L (minimum 0.3, maximum 461 μmol/L) and 65% of samples were between 5 and 20 μmol/L. There was a significant relation between regional CBF and dialysate NOx levels (r2 = 0.316, P < 0.001). Dialysate NOx levels (9.5 ± 2.2 μmol/L) in patients with critical reduction of regional CBF (<18 mL · 100 g−1 · min−1) were significantly lower than in patients with normal CBF (18.6 ± 8.1 μmol/L; P < 0.001). This relation between the dialysate concentration of NOx and regional CBF suggests some role for NO in the abnormalities of CBF that occur after traumatic brain injury.