Cold stress protein RBM3 responds to temperature change in an ultra-sensitive manner in young neurons.

Extremely mild hypothermia to 36.0 °C is not thought to appreciably differ clinically from 37.0 °C. However, it is possible that 36.0 °C stimulates highly sensitive hypothermic signaling mechanism(s) and alters biochemistry. To the best of our knowledge, no such ultra-sensitive pathway/mechanisms have been described. Here we show that cold stress protein RNA binding motif 3 (RBM3) increases in neuron and astrocyte cultures maintained at 33 °C or 36 °C for 24 or 48 h, compared to 37 °C controls. Neurons cultured at 36 °C also had increased global protein synthesis (GPS). Finally, we found that melatonin or fibroblast growth factor 21 (FGF21) augmented RBM3 upregulation in young neurons cooled to 36 °C. Our results show that a 1 °C reduction in temperature can induce pleiotropic biochemical changes by upregulating GPS in neurons which may be mediated by RBM3 and that this process can be pharmacologically mimicked and enhanced with melatonin or FGF21.

Acute CSF interleukin-6 trajectories after TBI: associations with neuroinflammation, polytrauma, and outcome.

Traumatic brain injury (TBI) results in a significant inflammatory burden that perpetuates the production of inflammatory mediators and biomarkers. Interleukin-6 (IL-6) is a pro-inflammatory cytokine known to be elevated after trauma, and a major contributor to the inflammatory response following TBI. Previous studies have investigated associations between IL-6 and outcome following TBI, but to date, studies have been inconsistent in their conclusions. We hypothesized that cohort heterogeneity, temporal inflammatory profiles, and concurrent inflammatory marker associations are critical to characterize when targeting subpopulations for anti-inflammatory therapies. Toward this objective, we used serial cerebrospinal fluid (CSF) samples to generate temporal acute IL-6 trajectory (TRAJ) profiles in a prospective cohort of adults with severe TBI (n=114). We examined the impact of injury type on IL-6 profiles, and how IL-6 profiles impact sub-acute (2weeks-3months) serum inflammatory marker load and long-term global outcome 6-12months post-injury. There were two distinct acute CSF IL-6 profiles, a high and low TRAJ group. Individuals in the high TRAJ had increased odds of unfavorable Glasgow Outcome Scale (GOS) scores at 6months (adjusted OR=3.436, 95% CI: 1.259, 9.380). Individuals in the high TRAJ also had higher mean acute CSF inflammatory load compared to individuals in the low TRAJ (p⩽0.05). The two groups did not differ with respect acute serum profiles; however, individuals in the high CSF IL-6 TRAJ also had higher mean sub-acute serum IL-1ß and IL-6 levels compared with the low TRAJ group (p⩽0.05). Lastly, injury type (isolated TBI vs. TBI+polytrauma) was associated with IL-6 TRAJ group (χ(2)=5.31, p=0.02). Specifically, there was 70% concordance between those with TBI+polytrauma and the low TRAJ; in contrast, isolated TBI was similarly distributed between TRAJ groups. These data provide evidence that sustained, elevated levels of CSF IL-6 are associated with an increased inflammatory load, and these increases are associated with increased odds for unfavorable global outcomes in the first year following TBI. Future studies should explore additional factors contributing to IL-6 elevations, and therapies to mitigate its detrimental effects on outcome.

Variable neuroendocrine-immune dysfunction in individuals with unfavorable outcome after severe traumatic brain injury.

Bidirectional communication between the immune and neuroendocrine systems is not well understood in the context of traumatic brain injury (TBI). The purpose of this study was to characterize relationships between cerebrospinal fluid (CSF) cortisol and inflammation after TBI, and to determine how these relationships differ by outcome. CSF samples were collected from 91 subjects with severe TBI during days 0-6 post-injury, analyzed for cortisol and inflammatory markers, and compared to healthy controls (n=13 cortisol, n=11 inflammatory markers). Group-based trajectory analysis (TRAJ) delineated subpopulations with similar longitudinal CSF cortisol profiles (high vs. low cortisol). Glasgow Outcome Scale (GOS) scores at 6months served as the primary outcome measure reflecting global outcome. Inflammatory markers that displayed significant bivariate associations with both GOS and cortisol TRAJ (interleukin [IL]-6, IL-10, soluble Fas [sFas], soluble intracellular adhesion molecule [sICAM]-1, and tumor necrosis factor alpha [TNF]-α) were used to generate a cumulative inflammatory load score (ILS). Subsequent analysis revealed that cortisol TRAJ group membership mediated ILS effects on outcome (indirect effect estimate=-0.253, 95% CI (-0.481, -0.025), p=0.03). Correlational analysis between mean cortisol levels and ILS were examined separately within each cortisol TRAJ group and by outcome. Within the low cortisol TRAJ group, subjects with unfavorable 6-month outcome displayed a negative correlation between ILS and mean cortisol (r=-0.562, p=0.045). Conversely, subjects with unfavorable outcome in the high cortisol TRAJ group displayed a positive correlation between ILS and mean cortisol (r=0.391, p=0.006). Our results suggest that unfavorable outcome after TBI may result from dysfunctional neuroendocrine-immune communication wherein an adequate immune response is not mounted or, alternatively, neuroinflammation is prolonged. Importantly, the nature of neuroendocrine-immune dysfunction differs between cortisol TRAJ groups. These results present a novel biomarker-based index from which to discriminate outcome and emphasize the need for evaluating tailored treatments targeting inflammation early after injury.

Anthraquinone-2-sulfonic acid (AQ2S) is a novel neurotherapeutic agent.

Anthraquinone derivatives such as emodin have recently been shown to protect in models of beta amyloid ß (Aß) and tau aggregation-induced cell death. The mechanisms of action possibly involve preconditioning effects, anti-aggregation properties, and/or enhancing the phosphatidylinositol-3-kinase (PI3K)/AKT survival mechanism. We studied several natural (emodin, rhein, and aloin) and synthetic (AQ2S) anthraquinones, to screen for post-treatment therapeutic benefit in two models of neuronal death, namely hydrogen peroxide (H(2)O(2)) and staurosporine (STS)-induced injury. Treatment with emodin, rhein, or aloin failed to reduce H(2)O(2) injury. Moreover, consistent with emodin behaving like a mild toxin, it exacerbated oxidative injury at the highest concentration used (50 µM) in our post-treatment paradigm, and potently inhibited AKT. In contrast, AQ2S was neuroprotective. It reduced H(2)O(2) injury at 50 and 75 µM. In addition, AQ2S potently inhibited staurosporine (STS)-induced injury. The mechanisms of action involve caspase inhibition and AKT activation. However, blockade of AKT signaling with LY294002 failed to abolish AQ2S-mediated protection on the STS assay. This is the first study to report that AQ2S is a new neuroprotective compound and a novel caspase inhibitor.

Regional brain injury on conventional and diffusion weighted MRI is associated with outcome after pediatric cardiac arrest.

BACKGROUND: To assess regional brain injury on magnetic resonance imaging (MRI) after pediatric cardiac arrest (CA) and to associate regional injury with patient outcome and effects of hypothermia therapy for neuroprotection. METHODS: We performed a retrospective chart review with prospective imaging analysis. Children between 1 week and 17 years of age who had a brain MRI in the first 2 weeks after CA without other acute brain injury between 2002 and 2008 were included. Brain MRI (1.5 T General Electric, Milwaukee, WI, USA) images were analyzed by 2 blinded neuroradiologists with adjudication; images were visually graded. Brain lobes, basal ganglia, thalamus, brain stem, and cerebellum were analyzed using T1, T2, and diffusion-weighted images (DWI). RESULTS: We examined 28 subjects with median age 1.9 years (IQR 0.4-13.0) and 19 (68 %) males. Increased intensity on T2 in the basal ganglia and restricted diffusion in the brain lobes were associated with unfavorable outcome (all P < 0.05). Therapeutic hypothermia had no effect on regional brain injury. Repeat brain MRI was infrequently performed but demonstrated evolution of lesions. CONCLUSION: Children with lesions in the basal ganglia on conventional MRI and brain lobes on DWI within the first 2 weeks after CA represent a group with increased risk of poor outcome. These findings may be important for developing neuroprotective strategies based on regional brain injury and for evaluating response to therapy in interventional clinical trials.

Increased CSF concentrations of myelin basic protein after TBI in infants and children: absence of significant effect of therapeutic hypothermia.

BACKGROUND: The objectives of this study were to determine effects of severe traumatic brain injury (TBI) on cerebrospinal fluid (CSF) concentrations of myelin basic protein (MBP) and to assess relationships between clinical variables and CSF MBP concentrations. METHODS: We measured serial CSF MBP concentrations in children enrolled in a randomized controlled trial evaluating therapeutic hypothermia (TH) after severe pediatric TBI. Control CSF was obtained from children evaluated, but found not to be having CNS infection. Generalized estimating equation models and Wilcoxon Rank-Sum test were used for comparisons of MBP concentrations. RESULTS: There were 27 TBI cases and 57 controls. Overall mean (± SEM) TBI case MBP concentrations for 5 days after injury were markedly greater than controls (50.49 ± 6.97 vs. 0.11 ± 0.01 ng/ml, p < 0.01). Mean MBP concentrations were lower in TBI patients <1 year versus >1 year (9.18 ± 1.67 vs. 60.22 ± 8.26 ng/ml, p = 0.03), as well as in cases with abusive head trauma (AHT) versus non-abusive TBI (14.46 ± 3.15 vs. 61.17 ± 8.65 ng/ml, p = 0.03). TH did not affect MBP concentrations. CONCLUSIONS: Mean CSF MBP increases markedly after severe pediatric TBI, but is not affected by TH. Infancy and AHT are associated with low MBP concentrations, suggesting that age-dependent myelination influences MBP concentrations after injury. Given the magnitude of MBP increases, axonal injury likely represents an important therapeutic target in pediatric TBI.

Apoptotic interactions of cytochrome c: redox flirting with anionic phospholipids within and outside of mitochondria.

Since the (re)discovery of cytochrome c (cyt c) in the early 1920s and subsequent detailed characterization of its structure and function in mitochondrial electron transport, it took over 70 years to realize that cyt c plays a different, not less universal role in programmed cell death, apoptosis, by interacting with several proteins and forming apoptosomes. Recently, two additional essential functions of cyt c in apoptosis have been discovered that are carried out via its interactions with anionic phospholipids: a mitochondria specific phospholipid, cardiolipin (CL), and plasma membrane phosphatidylserine (PS). Execution of apoptotic program in cells is accompanied by substantial and early mitochondrial production of reactive oxygen species (ROS). Because antioxidant enhancements protect cells against apoptosis, ROS production was viewed not as a meaningless side effect of mitochondrial disintegration but rather playing some - as yet unidentified - role in apoptosis. This conundrum has been resolved by establishing that mitochondria contain a pool of cyt c, which interacts with CL and acts as a CL oxygenase. The oxygenase is activated during apoptosis, utilizes generated ROS and causes selective oxidation of CL. The oxidized CL is required for the release of pro-apoptotic factors from mitochondria into the cytosol. This redox mechanism of cyt c is realized earlier than its other well-recognized functions in the formation of apoptosomes and caspase activation. In the cytosol, released cyt c interacts with another anionic phospholipid, PS, and catalyzes its oxidation in a similar oxygenase reaction. Peroxidized PS facilitates its externalization essential for the recognition and clearance of apoptotic cells by macrophages. Redox catalysis of plasma membrane PS oxidation constitutes an important redox-dependent function of cyt c in apoptosis and phagocytosis. Thus, cyt c acts as an anionic phospholipid specific oxygenase activated and required for the execution of essential stages of apoptosis. This review is focused on newly discovered redox mechanisms of complexes of cyt c with anionic phospholipids and their role in apoptotic pathways in health and disease.

Conventional and functional proteomics using large format two-dimensional gel electrophoresis 24 hours after controlled cortical impact in postnatal day 17 rats.

Conventional and functional proteomics have significant potential to expand our understanding of traumatic brain injury (TBI) but have not yet been used. The purpose of the present study was to examine global hippocampal protein changes in postnatal day (PND) 17 immature rats 24 h after moderate controlled cortical impact (CCI). Silver nitrate stains or protein kinase B (PKB) phosphoprotein substrate antibodies were used to evaluate high abundance or PKB pathway signal transduction proteins representing conventional and functional proteomic approaches, respectively. Isoelectric focusing was performed over a nonlinear pH range of 3-10 with immobilized pH gradients (IPG strips) using supernatant from the most soluble cellular protein fraction of hippocampal tissue protein lysates from six paired sham and injured PND 17 rats. Approximately 1,500 proteins were found in each silver stained gel with 40% matching of proteins. Of these 600 proteins, 52% showed a twofold, 20% a fivefold, and 10% a 10-fold decrease or increase. Spot matching with existing protein databases revealed changes in important cytoskeletal and cell signalling proteins. PKB substrate protein phosphorylation was best seen in large format two-dimensional blots and known substrates of PKB such as glucose transporter proteins 3 and 4 and forkhead transcription factors, identified based upon molecular mass and charge, showed altered phosphorylation 24 h after injury. These results suggest that combined conventional and functional proteomic approaches are powerful, complementary and synergistic tools revealing multiple protein changes and posttranslational protein modifications that allow for more specific and comprehensive functional assessments after pediatric TBI.

The simple model versus the super model: translating experimental traumatic brain injury research to the bedside.

Despite considerable investigation in rodent models of traumatic brain injury (TBI), no novel therapy has been successfully translated from bench to bedside. Although well-described limitations of clinical trails may account for these failures, several modeling factors may also contribute to the lack of therapeutic translation from the laboratory to the clinic. Specifically, models of TBI may omit one or more critical, clinically relevant pathophysiologic features. In this invited review article, the impact of the limited incorporation of several important clinical pathophysiologic factors in TBI, namely secondary insults (i.e., hypotension and/or hypoxemia), coma, and aspects of standard neurointensive care monitoring and management strategies (i.e., intracranial pressure [ICP] monitoring and ICP-directed therapies, sedation, mechanical ventilation, and cardiovascular support) are discussed. Comparative studies in rodent and large animal models of TBI (which may, in some cases, represent super models) are also presented. We conclude that therapeutic breakthroughs will likely require a multidisciplinary approach, involving investigation in a range of models, including clinically relevant modifications of established animal models, along with development and application of new innovations in clinical trial design.

Histopathologic response of the immature rat to diffuse traumatic brain injury.

The purpose of this study was to characterize the histopathologic response of rats at postnatal day (PND) 17 following an impact-acceleration diffuse traumatic brain injury (TBI) using a 150-g/2-meter injury as previously described. This injury produces acute neurologic and physiologic derangements as well as enduring motor and Morris water maze (MWM) functional deficits. Histopathologic studies of perfusion-fixed brains were performed by gross examination and light microscopy using hematoxylin and eosin, Bielschowsky silver stain, and glial fibrillary acidic protein (GFAP) immunohistochemistry at 1, 3, 7, 28, and 90 day after injury. Gross pathologic examination revealed diffuse subarachnoid hemorrhage (SAH) at 1-3 days but minimal supratentorial intraparenchymal hemorrhage. Petechial hemorrhages were noted in ventral brainstem segments and in the cerebellum. After 1-3-day survivals, light microscopy revealed diffuse SAH and intraventricular hemorrhage (IVH), mild edema, significant axonal injury, reactive astrogliosis, and localized midline cerebellar hemorrhage. Axonal injury most commonly occurred in the long ascending and descending fiber tracts of the brainstem and occasionally in the forebrain, and was maximal at 3 days, but present until 7 days after injury. Reactive astrocytes were similarly found both in location and timing, but were also significantly identified in the hippocampus, white matter tracts, and corpus callosum. Typically, TBI produced significant diffuse SAH accompanied by cerebral and brainstem astrogliosis and axonal injury without obvious neuronal loss. Since this injury produces some pathologic changes with sustained functional deficits similar to TBI in infants and children, it should be useful for the further study of the pathophysiology and therapy of diffuse TBI and brainstem injury in the immature brain.

Intraperitoneal, but not enteric, adenosine administration improves survival after volume-controlled hemorrhagic shock in rats.

OBJECTIVE: To circumvent the potential adverse systemic side effects of adenosine, this study explored the potential benefit of intraperitoneal or enteric adenosine on survival and inflammatory responses after volume-controlled hemorrhagic shock. DESIGN: Prospective, randomized, and blinded. A three-phase, volume-controlled hemorrhagic shock model was used: hemorrhagic shock phase (120 mins), resuscitation phase (60 mins), and observation phase (72 hrs). Three groups were compared: controls, intraperitoneal adenosine, and enteric adenosine. SETTING: Animal research facility. SUBJECTS: Male Sprague-Dawley rats. INTERVENTIONS: Starting at 20 mins of hemorrhagic shock and continuing through the resuscitation phase, all three groups received both intraperitoneal lavage and repeated bolus injections into the ileum of vehicle (normal saline) or adenosine. In the intraperitoneal adenosine group (n = 10), adenosine solution (0.1 mM) was used for intraperitoneal lavage. In the enteric adenosine group (n = 10), adenosine (1.0 mM) was injected into the ileum. Blood cytokine concentrations and leukocyte infiltration in lungs and liver were studied in 12 separate rats (control and intraperitoneal adenosine, n = 6 each) with the same hemorrhagic shock model at resuscitation time 1 hr or 4 hrs. MEASUREMENTS AND MAIN RESULTS: Mean arterial pressure and heart rate were similar between the three groups during hemorrhagic shock and resuscitation. Potassium, lactate, and blood urea nitrogen concentrations were lower and arterial pH was higher in the intraperitoneal and enteric adenosine groups compared with the control group (both p <.05). Survival time to 72 hrs was longer in the intraperitoneal adenosine group than in the control group(p <.05). Neither plasma interleukin-1beta, interleukin-6, interleukin-10, and tumor necrosis factor-alpha concentrations nor leukocyte infiltration in the lungs and liver was different between the control and intraperitoneal adenosine groups. CONCLUSIONS: The administration of adenosine via the intraperitoneal route improves survival time after severe volume-controlled hemorrhagic shock in rats without worsening hypotension or bradycardia. This beneficial effect may not be attributable to effects of adenosine on the inflammatory response.

Increased adrenomedullin in cerebrospinal fluid after traumatic brain injury in infants and children.

Adrenomedullin is a recently discovered 52-amino acid peptide that is a potent vasodilator and is produced in the brain in experimental models of cerebral ischemia. Infusion of adrenomedullin increases regional cerebral blood flow and reduces infarct volume after vascular occlusion in rats, and thus may represent an endogenous neuroprotectant. Disturbances in cerebral blood flow (CBF), including hypoperfusion and hyperemia, frequently occur after severe traumatic brain injury (TBI) in infants and children. We hypothesized that cerebrospinal fluid (CSF) adrenomedullin concentration would be increased after severe TBI in infants and children, and that increases in adrenomedullin would be associated with alterations in CBF. We also investigated whether posttraumatic CSF adrenomedullin concentration was associated with relevant clinical variables (CBF, age, Glasgow Coma Scale [GCS] score, mechanism of injury, and outcome). Total adrenomedullin concentration was measured using a radioimmunometric assay. Sixty-six samples of ventricular CSF from 21 pediatric patients were collected during the first 10 days after severe TBI (GCS score < 8). Control CSF was obtained from children (n = 10) undergoing lumbar puncture without TBI or meningitis. Patients received standard neurointensive care, including CSF drainage. CBF was measured using Xenon computed tomography (CT) in 11 of 21 patients. Adrenomedullin concentration was markedly increased in CSF of infants and children after severe TBI vs control (median 4.5 versus 1.0 fmol/mL, p < 0.05). Sixty-two of 66 CSF samples (93.9%) from head-injured infants and children had a total adrenomedullin concentration that was greater than the median value for controls. Increases in CSF adrenomedullin were most commonly observed early after TBI. CBF was positively correlated with CSF adrenomedullin concentration (p < 0.001), but this relationship was not significant when controlling for the effect of time. CSF adrenomedullin was not significantly associated with other selected clinical variables. We conclude adrenomedullin is markedly increased in the CSF of infants and children early after severe TBI. We speculate that adrenomedullin participates in the regulation of CBF after severe TBI.

Detection of single- and double-strand DNA breaks after traumatic brain injury in rats: comparison of in situ labeling techniques using DNA polymerase I, the Klenow fragment of DNA polymerase I, and terminal deoxynucleotidyl transferase.

DNA damage is a common sequela of traumatic brain injury (TBI). Available techniques for the in situ identification of DNA damage include DNA polymerase I-mediated biotin-dATP nick-translation (PANT), the Klenow fragment of DNA polymerase I-mediated biotin-dATP nick-end labeling (Klenow), and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL). While TUNEL has been widely utilized to detect primarily double-strand DNA breaks, the use of PANT to detect primarily single-strand DNA breaks and Klenow to detect both single- and double-strand DNA breaks has not been reported after TBI. Accordingly, coronal brain sections from naive rats and rats at 0, 0.5, 1, 2, 6, 24, and 72 h (n = 3-5/group) after controlled cortical impact with imposed secondary insult were processed using the PANT, Klenow, and TUNEL methods. Cells with DNA breaks were detected by PANT in the ipsilateral hemisphere as early as 0.5 h after injury and were maximal at 6 h (cortex = 66.3+/-15.8, dentate gyrus 58.6+/-12.8, CA1 = 15.8+/-5.9, CA3 = 12.8+/-4.2 cells/x 400 field, mean +/- SEM, all p < 0.05 versus naive). Cells with DNA breaks were detected by Klenow as early as 30 min and were maximal at 24 h (cortex = 56.3+/-14.3, dentate gyrus 78.0+/-16.7, CA1 = 25.8+/-4.7, CA3 = 29.3+/-15.1 cells/x 400 field, all p < 0.05 versus naive). Cells with DNA breaks were not detected by TUNEL until 2 h and were maximal at 24 h (cortex = 47.7+/-21.4, dentate gyrus 63.0+/-11.9, CA1 = 5.6+/-5.4, CA3 = 6.9+/-3.7 cells/x 400 field, cortex and dentate gyrus p < 0.05 versus naive). Dual-label immunofluorescence revealed that PANT-positive cells were predominately neurons. These data demonstrate that TBI results in extensive DNA damage, which includes both single- and double-strand breaks in injured cortex and hippocampus. The presence of multiple types of DNA breaks implicate several pathways in the evolution of DNA damage after TBI.

Cerebral perfusion during anesthesia with fentanyl, isoflurane, or pentobarbital in normal rats studied by arterial spin-labeled MRI.

The influence of anesthetic agents on cerebral blood flow (CBF) was tested in normal rats. CBF is quantified with arterial spin-labeled MRI in rats anesthetized with either an opiate (fentanyl), a potent inhalation anesthetic agent (isoflurane), or a barbiturate (pentobarbital) using doses commonly employed in experimental paradigms. CBF values were found to be about 2.5-3 times lower in most regions analyzed during anesthesia with either fentanyl (with N(2)O/O(2)) or pentobarbital vs. isoflurane (with N(2)O/O(2)), in agreement with findings utilizing invasive measurement techniques. CBF was heterogeneous in rats anesthetized with isoflurane (with N(2)O/O(2)), but relatively homogeneous in rats anesthetized with either fentanyl (with N(2)O/O(2)) or pentobarbital, also in agreement with studies using other techniques. Magn Reson Med 46:202-206, 2001.

Cerebral resuscitation after traumatic brain injury and cardiopulmonary arrest in infants and children in the new millennium.

As outlined in Figure 1, it is likely that a series of interventions beginning in the field and continuing through the emergency department, ICU, rehabilitation center, and possibly beyond, will be needed to optimize clinical outcome after severe TBI or asphyxial CA in infants and children. Despite the many differences between these two important pediatric insults, it is likely that many of the therapies targeting neuronal death, in either condition, will need to be administered early after the insult, possibly at the injury scene. Even cerebral swelling, a pathophysiologic derangement routinely treated in the PICU, almost certainly is better prevented rather than treated. Finally, this review includes, for one of the first times, a brief discussion of additional horizons in the management of patients with severe brain injury, namely, manipulation of the injured circuitry and stimulation of regeneration. Further research is needed to define better the pathobiology of these two important conditions at the bedside, to understand the optimal application of contemporary therapies, and to develop and apply novel therapies. The tools necessary to carry out these studies are materializing, although the obstacles are great. This difficult but important challenge awaits further investigation by clinician-scientists in pediatric neurointensive care.

Assessment of the effect of 2-chloroadenosine in normal rat brain using spin-labeled MRI measurement of perfusion.

Adenosine analogs such as 2-chloroadenosine are potent cerebrovasodilators. Spin-labeled MRI was used to investigate the spatial distribution, dose-response, and timing of the effect of 2-chloroadenosine on cerebral blood flow (CBF) after intraparenchymal injection into rat brain. Sprague-Dawley rats (N = 10) were injected with 2-chloroadenosine at doses of 0.3, 6.0, or 12 nmoles, or saline vehicle (2-4 microL). CBF was serially quantified in a slice through the injection site in a circular (3.6 mm diameter) region of interest (ROI) around the injection and in ipsilateral hemispheric ROIs at approximately 90 min and approximately 180 min. Marked 3.77- and 3.93-fold increases in CBF (vs. vehicle) were seen in the circular ROI at approximately 90 min and approximately 180 min after 12-nmol injection, respectively. Similarly, 2.92- and 2.78-fold increases in hemispheric CBF were observed at approximately 90 min and approximately 180 min, respectively, after injection of 12 nmoles. Linear dose-response relationships were observed at both times after injection in both ROIs (all P < 0.01). Spin-labeling MRI assessment revealed that parenchymal injection of 2-chloroadenosine produces potent, dose-dependent, and sustained vasodilation over large areas of brain. This treatment and imaging paradigm should facilitate investigation of the effect of CBF promotion in models of traumatic and ischemic brain injury.

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

OBJECTIVE: Adenosine 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. DESIGN: Study of critically ill adults with severe traumatic brain injury. SETTING: Adult neurointensive care unit. PATIENTS: We prospectively defined periods of normal saturation and desaturation in six patients after severe traumatic brain injury. INTERVENTIONS: During 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 (r(2) =.32,.14,.31,.07, and.26, respectively, all p <.05, Pearson product moment correlation). CONCLUSION: The 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.