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Neuraxial access is necessary for an array of procedures in anaesthesia, interventional pain medicine and neurosurgery. The commonly used anatomical landmark technique is challenging and requires practical experience.We aimed to evaluate the technical feasibility of an augmented reality-guided approach for neuraxial access and tested the hypothesis that its use would improve success as the primary outcome. As secondary outcomes, we measured accuracy and the procedural duration compared with the classical landmark approach.A randomised phantom-based study.The three-dimensional image of a thoracolumbar phantom spine model with the surrounding soft tissue was created with a neurosurgical planning workstation and ideal trajectories to the epidural space on the levels T10-L1 were planned using a paramedian approach. Both the three-dimensional holographic image of the spine and the trajectories were transferred to an augmented reality-headset. Four probands (two anaesthesiologists, one neuroradiologist and one stereotactic neurosurgeon) performed 20 attempts, 10 each of either conventional landmark or augmented reality-guided epidural punctures, where anatomical level, side and sequence of modality were all randomised.Accuracy was assessed by measuring Euclidean distance and lateral deviation from the predefined target point. Success of epidural puncture on the first attempt was compared between the conventional and the augmented reality-guided approaches.Success was achieved in 82.5% of the attempts using augmented reality technique, compared with 40% with the conventional approach [ P = 0.0002, odds ratio (OR) for success: 7.07]. Euclidean distance (6.1 vs. 12 mm, P 0.0001) and lateral deviation (3.7 vs. 9.2 mm, P 0.0001) were significantly smaller using augmented reality. Augmented reality-guided puncture was significantly faster than with the conventional landmark approach (52.5 vs. 67.5 s, P = 0.0015).Augmented reality guidance significantly improved the accuracy and success in an experimental phantom model of epidural puncture. With further technical development, augmented reality guidance might prove helpful in anatomically challenging neuraxial procedures.

Background Red blood cell-induced cerebral inflammation and toxicity has been shown to be attenuated by induction of the heme-catalyzing enzyme, hemoxygenase-1 (HO-1), in animal models of subarachnoid hemorrhage (SAH). Although inflammatory mechanisms leading to secondary neuronal injury in SAH are becoming increasingly well understood, markers of cerebral inflammation have so far not been implemented in clinical prediction models of SAH. Methods In this biomarker observational study, HO-1 messenger ribonucleic acid (mRNA) expression levels were determined in cerebrospinal fluid (CSF) and blood of 66 patients with aneurysmal SAH on days 1, 7, and 14 after the SAH event. HO-1 mRNA expression was determined via real time polymerase chain reaction (PCR), and relative expression changes were quantified in comparison with expression levels in nonhemorrhagic control CSF. Subarachnoid blood burden, as well as presence of vasospasm and delayed cerebral ischemia (DCI), were recorded. Short and long-term clinical outcomes were assessed using the Modified Rankin Scale at discharge and 1 year after the SAH event. Results CSF HO-1 expression levels showed a significant increase over the 14-day observation period (p F = 22.53) and correlated with intracranial hematoma burden (ρ = 0.349, p = 0.025). In multivariate analyses, CSF HO-1 expression levels did not reach significance as independent predictors of outcome. Vasospasm on computed tomographic angiography was associated with lower CSF HO-1 expression levels on day 7 after SAH (n = 53, p = 0.010), whereas patients with DCI showed higher CSF HO-1 expression levels on day 14 after SAH (n = 21, p = 0.009). Conclusions HO-1 expression in CSF in patients with SAH follows a distinct temporal induction pattern and is dependent on intracranial hematoma burden. CSF HO-1 expression was unable to predict functional outcome. Associations of early low HO-1 expression with vasospasm and late elevated HO-1 expression with DCI may point to detrimental effects of late HO-1 induction, warranting the need for further investigation in a larger study population.

We previously found that argon exerts its neuroprotective effect in part by inhibition of the toll-like receptors (TLR) 2 and 4. The downstream transcription factors signal transducer and activator of transcription 3 (STAT3) and nuclear factor kappa B (NF-κB) are also affected by argon and may play a role in neuroprotection. It also has been demonstrated that argon treatment could mitigate brain damage, reduce excessive microglial activation, and subsequently attenuate brain inflammation. Despite intensive research, the further exact mechanism remains unclear. In this study, human neuroblastoma cells were damaged in vitro with rotenone over a period of 4 hours (to mimic cerebral ischemia and reperfusion damage), followed by a 2-hour post-conditioning with argon (75%). In a separate in vivo experiment, retinal ischemia/reperfusion injury was induced in rats by increasing intraocular pressure for 1 hour. Upon reperfusion, argon was administered by inhalation for 2 hours. Argon reduced the binding of the transcription factors signal transducer and activator of transcription 3, nuclear factor kappa B, activator protein 1, and nuclear factor erythroid 2-related factor 2, which are involved in regulation of neuronal damage. Flow cytometry analysis showed that argon downregulated the Fas ligand. Some transcription factors were regulated by toll-like receptors; therefore, their effects could be eliminated, at least in part, by the TLR2 and TLR4 inhibitor oxidized phospholipid 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (OxPAPC). Argon treatment reduced microglial activation after retinal ischemia/reperfusion injury. Subsequent quantitative polymerase chain reaction analysis revealed a reduction in the pro-inflammatory cytokines interleukin (IL-1α), IL-1β, IL-6, tumor necrosis factor α, and inducible nitric oxide synthase. Our results suggest that argon reduced the extent of inflammation in retinal neurons after ischemia/reperfusion injury by suppression of transcription factors crucial for microglial activation. Argon has no known side effects or narcotic properties; therefore, therapeutic use of this noble gas appears ideal for treatment of patients with neuronal damage in retinal ischemia/reperfusion injury. The animal experiments were approved by the Commission for Animal Care of the University of Freiburg (approval No. 35-9185.81/G14-122) on October 19, 2012.

OBJECTIVES Neurologic damage following cardiac arrest remains a major burden for modern resuscitation medicine. Cardiopulmonary resuscitation with extracorporeal circulatory support holds the potential to reduce morbidity and mortality. Furthermore, the endogenous gasotransmitter carbon monoxide attracts attention in reducing cerebral injury. We hypothesize that extracorporeal resuscitation with additional carbon monoxide application reduces neurologic damage. DESIGN Randomized, controlled animal study. SETTING University research laboratory. SUBJECTS Landrace-hybrid pigs. INTERVENTIONS In a porcine model, carbon monoxide was added using a novel extracorporeal releasing system after resuscitation from cardiac arrest. MEASUREMENTS AND MAIN RESULTS As markers of cerebral function, neuromonitoring modalities (somatosensory-evoked potentials, cerebral oximetry, and transcranial Doppler ultrasound) were used. Histopathologic damage and molecular markers (caspase-3 activity and heme oxygenase-1 expression) were analyzed. Cerebral oximetry showed fast rise in regional oxygen saturation after carbon monoxide treatment at 0.5 hours compared with extracorporeal resuscitation alone (regional cerebral oxygen saturation, 73% ± 3% vs 52% ± 8%; p < 0.05). Median nerve somatosensory-evoked potentials showed improved activity upon carbon monoxide treatment, whereas post-cardiac arrest cerebral perfusion differences were diminished. Histopathologic damage scores were reduced compared with customary resuscitation strategies (hippocampus: sham, 0.4 ± 0.2; cardiopulmonary resuscitation, 1.7 ± 0.4; extracorporeal cardiopulmonary resuscitation, 2.3 ± 0.2; extracorporeal cardiopulmonary resuscitation with carbon monoxide application [CO-E-CPR], 0.9 ± 0.3; p < 0.05). Furthermore, ionized calcium-binding adaptor molecule 1 staining revealed reduced damage patterns upon carbon monoxide treatment. Caspase-3 activity (cardiopulmonary resuscitation, 426 ± 169 pg/mL; extracorporeal cardiopulmonary resuscitation, 240 ± 61 pg/mL; CO-E-CPR, 89 ± 26 pg/mL; p < 0.05) and heme oxygenase-1 (sham, 1 ± 0.1; cardiopulmonary resuscitation, 2.5 ± 0.4; extracorporeal cardiopulmonary resuscitation, 2.4 ± 0.2; CO-E-CPR, 1.4 ± 0.2; p < 0.05) expression were reduced after carbon monoxide exposure. CONCLUSIONS Carbon monoxide application during extracorporeal resuscitation reduces injury patterns in neuromonitoring and decreases histopathologic cerebral damage by reducing apoptosis. This may lay the basis for further clinical translation of this highly salutary substance.

PurposeSix-19% of critically ill COVID-19 patients display circulating auto-antibodies against type I interferons (IFN-AABs). Here, we establish a clinically applicable strategy for early identification of IFN-AAB-positive patients for potential subsequent clinical interventions.MethodsWe analysed sera of 430 COVID-19 patients with severe and critical disease from four hospitals for presence of IFN-AABs by ELISA. Binding specificity and neutralizing activity were evaluated via competition assay and virus-infection-based neutralization assay. We defined clinical parameters associated with IFN-AAB positivity. In a subgroup of critically ill patients, we analyzed effects of therapeutic plasma exchange (TPE) on the levels of IFN-AABs, SARS-CoV-2 antibodies and clinical outcome.ResultsThe prevalence of neutralizing AABs to IFN-α and IFN-ω in COVID-19 patients was 4.2% (18/430), while being undetectable in an uninfected control cohort. Neutralizing IFN-AABs were detectable exclusively in critically affected, predominantly male (83%) patients (7.6% IFN-α and 4.6% IFN-ω in 207 patients with critical COVID-19). IFN-AABs were present early post-symptom onset and at the peak of disease. Fever and oxygen requirement at hospital admission co-presented with neutralizing IFN-AAB positivity. IFN-AABs were associated with higher mortality (92.3% versus 19.1 % in patients without IFN-AABs). TPE reduced levels of IFN-AABs in three of five patients and may increase survival of IFN-AAB-positive patients compared to those not undergoing TPE.ConclusionIFN-AABs may serve as early biomarker for development of severe COVID-19. We propose to implement routine screening of hospitalized COVID-19 patients according to our algorithm for rapid identification of patients with IFN-AABs who most likely benefit from specific therapies.

Despite recent advances in cancer immunotherapy, its efficacy in Glioblastoma (GBM) is limited due to poor understanding of molecular states and cellular plasticity of immune cells within the tumor microenvironment. Here, we combined spatial and single-cell transcriptomics of 47.284 immune cells, to map the potential cellular interactions leading to the immunosuppressive microenvironment and dysfunction of T cells. Computational approach identified a subset of IL10 releasing HMOX1+ myeloid cells which activates transcriptional programs towards a dysfunctional state in T cells, and was found to be localized within mesenchymal dominated subregions of the tumor. These findings were further validated by a human ex-vivo neocortical GBM model (n=6) coupled with patient derived peripheral T-cells. Finally, the dysfunctional transformation of T cells was shown to be rescued by JAK/STAT inhibition in both our model and in-vivo. We strongly believe that our findings would be the stepping stone towards successful development of immunotherapeutic approaches in GBM.

SummaryThe diversity of molecular states and cellular plasticity of immune cells in the glioblastoma environment is still poorly understood. Here, we performed scRNA sequencing of the immune compartment and mapped potential cellular interactions leading to an immunosuppressive microenvironment and dysfunction of T cells. Through inferring the dynamic adaptation during T cell activation, we identified three different terminal states with unique transcriptional programs. Modeling of driver genes for terminal T cell fate identified IL-10 signaling alterations in a subpopulation of HAVCR2(+) T cells. To explore in depth cellular interactions, we established an in-silico model by the integration of spatial transcriptomic and scRNA-sequencing, and identified a subset of HMOX1+ myeloid cells defined by IL10 release leading to T cell exhaustion. We found a spatial overlap between HMOX(+) myeloid and HAVCR2(+) T cells, suggesting that myeloid-lymphoid interaction causes immunosuppression present in tumor regions with enriched mesenchymal gene expression. Using human neocortical GBM model, coupled with patient-derived T cells, we confirmed that the functional interaction between myeloid and lymphoid cells, leads to a dysfunctional state of T cells. This IL-10 driven T cell exhaustion was found to be rescued by JAK/STAT inhibition. A comprehensive understanding of the cellular states and plasticity of lymphoid cells in GBM will aid towards successful immunotherapeutic approaches.

Microglial erythrophagocytosis is crucial in injury response to hemorrhagic stroke. We hypothesized that regulation of microglial erythrophagocytosis via HO-1/CO depends on a pathway involving reactive oxygen species (ROS) and CD36 surface-expression. The microglial BV-2 cell line and primary microglia (PMG) were incubated +/-blood and +/-CO-exposure. PMG isolated from tissue-specific HO-1-deficient (LyzM-Cre-Hmox1 fl/fl ) and CD36 -/- mice or siRNA against AMPK (AMP-activated protein kinase) were used to test our hypothesis. In a murine subarachnoid hemorrhage (SAH) model, we compared neuronal injury in wild-type and CD36 -/- mice. Readouts included vasospasm, microglia activation, neuronal apoptosis, and spatial memory. We observed increased microglial HO-1-expression after blood-exposure. A burst in ROS-production was seen after CO-exposure, which led to increased amounts of phosphorylated AMPK with subsequently enhanced CD36 surface-expression. Naive PMG from LyzM-Cre-Hmox1 fl/fl mice showed reduced ROS-production and CD36 surface-expression and failed to respond to CO with increased CD36 surface-expression. Lack of HO-1 and CD36 resulted in reduced erythrophagocytosis that could not be rescued with CO. Erythrophagocytosis was enhanced in BV-2 cells in the presence of exogenous CO, which was abolished in cells treated with siRNA to AMPK. CD36 -/- mice subjected to SAH showed enhanced neuronal cell death, which resulted in impaired spatial memory function. We demonstrate that microglial phagocytic function partly depends on a pathway involving HO-1 with changes in ROS-production, phosphorylated AMPK, and surface expression of CD36. CD36 was identified as a crucial component in blood clearance after hemorrhage that ultimately determines neuronal outcome. These results demand further investigations studying the potential neuroprotective properties of CO.

Background: Perioperative damage of neuronal tissue due to insufficient cerebral circulation as a result of hypotension or stroke, lead to permanent destruction and functional impairment via apoptotic and inflammatory pathways. Recently, the noble gas argon has been shown to exert neuroprotective effects. Despite intensive research, the exact mechanism remains unclear. Methods: In-vitro, after injury of human neuroblastoma cells with rotenone over a period of four hours, postconditioning with argon 75 Vol% was performed for 2. In-vivo, retinal ischemia reperfusion injury in the rat was induced by increasing intraocular pressure for 1 hour (h). Upon reperfusion, argon was administered by inhalation for 2 h. Results: In summary, argon reduced binding activity of transcription factors involved in regulation of neuronal damage such as STAT3 (Signal transducer and activator of transcription 3), NF-kB (Nuclear factor `kappa-light-chain-enhancer´ of activated B-cells), AP-1 (Activator protein 1) and Nrf-2 (Nuclear factor erythroid 2-related factor 2). Flow cytometry analysis showed that argon down-regulated the Fas-Ligand. Since some of these transcription factors were regulated via toll-like receptors (TLR), their effects could be eliminated - at least in part - by OxPAPC (TLR2 and -4 inhibitor). Argon was able to reduce the quantity and the activity of neuronal microglia after ischemia-reperfusion injury. Consecutively, qPCR (quantitative Polymerase chain reaction) showed a reduction of the pro-inflammatory cytokines IL-1α (Interleukin-1α), IL-1ß (Interleukin-1ß), IL-6 (Interleukin 6), TNFα (Tumor necrosis factor alpha) and iNOS (inducible Nitric oxide synthase). Conclusion: Argon reduced the extent of inflammation after neuronal injury by suppression of transcription factors crucial for microglia activation. The therapeutic use of the noble gas would be ideal for treating in the context of neuronal damage due to the lack of known side effects and narcotic properties with preservation of neurological assessability. Although preclinical studies are promising, further investigations are required before argon can be approved for use in patients.

Inflammation plays a central role in the pathophysiology of many diseases. The inducible enzyme heme oxygenase-1 (HO-1) protects cells against inflammation and can be induced by electrophilic compounds like the chalcones (1,3-diphenylprop-2-enones) from the class of α,β-unsaturated carbonyl compounds. We hypothesized that the synthetic chalcone E-α-(p-methoxyphenyl)-2',3,4,4'-tetramethoxychalcone (E-α-p-OMe-C6H4-TMC) exerts anti-inflammatory effects in RAW264.7, Jurkat lymphocytes and HK-2 cells via HO-1 induction. RAW264.7 cells were treated with lipopolysaccharide prior to E-α-p-OMe-C6H4-TMC treatment. Subsequently, HO-1 protein induction and activity were analyzed, as well as expression of pro- and anti-inflammatory mediators, transcription factors and mitogen-activated protein kinases to evaluate the possible molecular mechanism. These results were confirmed in human cell lines (Jurkat T-lymphocytes and HK-2 epithelial cells). We found that the E-α-p-OMe-C6H4-TMC exerts significant anti-inflammatory effects in a dose dependent manner, showing no toxic effects in LPS-treated RAW264.7 macrophages. E-α-p-OMe-C6H4-TMC induced HO-1 and SOD-1 protein expression and HO-1 enzyme activity, reduced the upregulation of COX-2 and iNOS, while inducing the translocation of Nrf2. NF-κB activity was attenuated following E-α-p-OMe-C6H4-TMC treatment accompanied by the downregulation of proinflammatory cytokines IL-1β, IL-6 and MCP-1. Pretreatment with E-α-p-OMe-C6H4-TMC revealed significant changes in phosphorylation of ERK and p38, but not JNK. These anti-inflammatory effects of E-α-p-OMe-C6H4-TMC were approved in Jurkat and HK-2 cells, furthermore revealing a downregulation of IL-8 and IL-10. In conclusion, it is tempting to speculate about E-α-p-OMe-C6H4-TMC as a new and non-toxic agent, inducing HO-1 in cells. This opens up new opportunities regarding the development of therapeutic agents using beneficial effects of HO-1 and its products.

BACKGROUND: General anesthesia in patients with or at risk for neuronal injury remains challenging due to the controversial influence of volatile anesthetics on neuronal damage. We hypothesized that isoflurane, sevoflurane, and desflurane would exert variable degrees of neurotoxicity in vitro and in vivo via activation of the p75 neurotrophin receptor (p75 NTR ). METHODS: SH-SY5Y cells were exposed to oxygen–glucose deprivation (OGD, 16 hours), preceded or followed by incubation with isoflurane, sevoflurane, or desflurane (1.2 minimal alveolar concentration, 2 hours). Neuronal cell death was analyzed by flow cytometry (mitochondrial membrane potential, Annexin V/propidium iodide [AV/Pi]) and quantification of lactate dehydrogenase release. We analyzed NF-κB activity by DNA-binding ELISA and luciferase assay. The role of p75 NTR was studied using the p75 NTR -blocking peptide TAT-pep5 and siRNA knockdown. The effect of isoflurane ±p75 NTR inhibition on retinal ischemia-reperfusion injury (IRI) in adult Sprague-Dawley rats was assessed by analyzing retinal ganglion cell (RGC) density. RESULTS: Isoflurane but not sevoflurane or desflurane postexposure aggravated OGD-induced neuronal cell death (AV/Pi positive cells: OGD 41.1% [39.0/43.3] versus OGD + isoflurane 48.5% [46.4/63.4], P = 0.001). Isoflurane significantly increased NF-κB DNA-binding and transcriptional activity of NF-κB (relative Luminescence Units: OGD 500 [499/637] versus OGD + isoflurane 1478 [1363/1643], P = 0.001). Pharmacological inhibition or siRNA knockdown of p75 NTR counteracted the aggravating effects of isoflurane. Isoflurane increased RGC damage in vivo (IRI 1479 RGC/mm 2 [1311/1697] versus IRI + isoflurane 1170 [1093/1211], P = 0.03), which was counteracted by p75 NTR -inhibition via TAT-pep5 (P = 0.02). CONCLUSIONS: Isoflurane but not sevoflurane or desflurane postexposure aggravates neurotoxicity in preinjured neurons via activation of p75 NTR and NF-κB. These findings may have implications for the choice of volatile anesthetic being used in patients with or at risk for neuronal injury, specifically in patients with a stroke or history of stroke and in surgical procedures in which neuronal injury is likely to occur, such as cardiac surgery and neurovascular interventions. (Anesth Analg 2014;119:1429–41)

Background and Purpose— Subarachnoid hemorrhage (SAH) is associated with a temporal pattern of stroke incidence. We hypothesized that natural oscillations in gene expression controlling circadian rhythm affect the severity of neuronal injury. We moreover predict that heme oxygenase-1 (HO-1/ Hmox1 ) and its product carbon monoxide (CO) contribute to the restoration of rhythm and neuroprotection. Methods— Murine SAH model was used where blood was injected at various time points of the circadian cycle. Readouts included circadian clock gene expression, locomotor activity, vasospasm, neuroinflammatory markers, and apoptosis. In addition, cerebrospinal fluid and peripheral blood leukocytes from SAH patients and controls were analyzed for clock gene expression. Results— Significant elevations in the clock genes Per-1 , Per-2 , and NPAS-2 were observed in the hippocampus, cortex, and suprachiasmatic nucleus in mice subjected to SAH at zeitgeber time (ZT) 12 when compared with ZT2. Clock gene expression amplitude correlated with basal expression of HO-1, which was also significantly greater at ZT12. SAH animals showed a significant reduction in cerebral vasospasm, neuronal apoptosis, and microglial activation at ZT12 compared with ZT2. In animals with myeloid-specific HO-1 deletion ( Lyz-Cre-Hmox1 fl/fl ), Per-1, Per-2 , and NPAS-2 expression was reduced in the suprachiasmatic nucleus, which correlated with increased injury. Treatment with low-dose CO rescued Lyz-Cre-Hmox1 fl/fl mice, restored Per-1, Per-2 , and NPAS-2 expression, and reduced neuronal apoptosis. Conclusions— Clock gene expression regulates, in part, the severity of SAH and requires myeloid HO-1 activity to clear the erythrocyte burden and inhibit neuronal apoptosis. Exposure to CO rescues the loss of HO-1 and thus merits further investigation in patients with SAH.

We report a repositioning maneuver of a dislocated Avalon Elite dual lumen catheter during ongoing veno-venous ECMO support. The inferior tip of the catheter dislocated into a liver vein, which was accompanied by a dramatic decrease in pump flow. After standard repositioning maneuvers under transthoracic echocardiographic guidance had failed, a special guiding sheath was inserted into the main lumen through a Y-connector with a valve. Over this valve, a stiff wire could be placed into the inferior vena cava to help guiding the catheter back into the correct position.

Propofol, midazolam and ketamine are widely used in today's anaesthesia practice. Both neuroprotective and neurotoxic effects have been attributed to all three agents.To establish whether propofol, midazolam and ketamine in the same neuronal injury model exert neuroprotective effects on injured neurones in vitro and in vivo by modulation of the Toll-like receptor 4-nuclear factor kappa-light-chain-enhancer of activated B cells (TLR-4-NF-κB) pathway.Cell-based laboratory (n = 6 repetitions per experiment) and animal (n = 6 per group) studies using a neuronal cell line (SH-SY5Y cells) and adult Sprague-Dawley rats.Cells were exposed to oxygen-glucose deprivation before or after treatment using escalating, clinically relevant doses of propofol, midazolam and ketamine. In animals, retinal ischaemia (60 min) was induced followed by reperfusion and randomised treatment with saline or propofol.Neuronal cell death was determined using flow-cytometry (mitochondrial membrane potential) and lactate dehydrogenase (LDH) release. Nuclear factor NF-κB and hypoxia-inducible factor 1 α-activity were analysed by DNA-binding ELISA, expression of NF-κB-dependent genes and TLR-4 by luciferase-assay and flow-cytometry, respectively. In animals, retinal ganglion cell density, caspase-3 activation and gene expression (TLR-4, NF-κB) were used to determine in vivo effects of propofol. Results were compared using ANOVA (Analysis of Variance) and t test. A P value less than 0.05 was considered statistically significant.Post-treatment with clinically relevant concentrations of propofol (1 to 10 μg ml) preserved the mitochondrial membrane potential in oxygen-glucose deprivation-injured cells by 54% and reduced LDH release by 21%. Propofol diminished TLR-4 surface expression and preserved the DNA-binding activity of the protective hypoxia-inducible factor 1 α transcription factor. DNA-binding and transcriptional NF-κB-activity were inhibited by propofol. Neuronal protection and inhibition of TLR-4-NF-κB signalling were not consistently seen with midazolam or ketamine. In vivo, propofol treatment preserved rat retinal ganglion cell densities (cells mm, saline 1504 ± 251 vs propofol 2088 ± 144, P = 0.0001), which was accompanied by reduced neuronal caspase-3, TLR-4 and NF-κB expression.Propofol, but neither midazolam nor ketamine, provides neuroprotection to injured neuronal cells via inhibition of TLR-4-NF-κB-dependent signalling.

Subarachnoid hemorrhage (SAH) carries a 50% mortality rate. The extravasated erythrocytes that surround the brain contain heme, which, when released from damaged red blood cells, functions as a potent danger molecule that induces sterile tissue injury and organ dysfunction. Free heme is metabolized by heme oxygenase (HO), resulting in the generation of carbon monoxide (CO), a bioactive gas with potent immunomodulatory capabilities. Here, using a murine model of SAH, we demonstrated that expression of the inducible HO isoform (HO-1, encoded by Hmox1) in microglia is necessary to attenuate neuronal cell death, vasospasm, impaired cognitive function, and clearance of cerebral blood burden. Initiation of CO inhalation after SAH rescued the absence of microglial HO-1 and reduced injury by enhancing erythrophagocytosis. Evaluation of correlative human data revealed that patients with SAH have markedly higher HO-1 activity in cerebrospinal fluid (CSF) compared with that in patients with unruptured cerebral aneurysms. Furthermore, cisternal hematoma volume correlated with HO-1 activity and cytokine expression in the CSF of these patients. Collectively, we found that microglial HO-1 and the generation of CO are essential for effective elimination of blood and heme after SAH that otherwise leads to neuronal injury and cognitive dysfunction. Administration of CO may have potential as a therapeutic modality in patients with ruptured cerebral aneurysms.

PHYSIOLOGY OF CARBON MONOXIDE The longstanding perception of the gas carbon monoxide (CO) as an odorless and colorless “silent killer” began to attract the attention of the public with the arrival of the industrial age in the beginning of the twentieth century (Douglas et al., 1912). In fact, carbon monoxide has been present in all societies since the discovery of fire, yet it was John Haldane in the early part of the twentieth century that declared CO a lethal poison based on his investigations of mine disasters. American Indians knew that in addition to warmth, gathering around a fire brought calming and tranquil effects, something we now attribute to neuroactive properties of the gas. Poisonings from exhaust certainly continue to pose significant problems, as it did in the coal mine explosions, but it remains unclear why the>500 other molecules that emerge from combustion, many of which are carcinogens, are largely ignored, yet pose just as great a risk as CO. It was not until the late 1960’s that endogenous production of CO was discovered as a result of the catabolism of heme (Sjostrand, 1949; Coburn et al., 1963), suggesting a physiological role for this simple, diatomic gas. Decades after these findings were reported, investigators noted that levels of CO were significantly elevated in the exhaled breath of hospitalized patients (Vos et al., 2009; Cheng et al., 2010; James et al., 2010; Zhang et al., 2010). The illnesses were wide-ranging, yet it was clear that CO levels would decrease as the pathology resolved. How then can it be explained that CO is toxic if the body generates it physiologically and even more puzzling, generates more when in a compromised state? The answer may lie in the ancient organelle known as the mitochondria, an evolutionary endosymbiont originating from proteobacteria whose singular responsibility is to generate energy for the cell. It relies principally on the presence of gases in the elegant transfer of electrons among the oxidases contained within its membranes. The targets for CO are ostensibly clear. CO binds rapidly and with high affinity to heme-containing proteins such as hemoglobin, the mitochondria oxidases or the enzymes necessary for reactive oxygen species generation. CO competes with oxygen transport and cellular respiration and it is perhaps in this primitive symbiotic organelle, among the numerous hemoprotein complexes competing with the other bioactive gases including nitric oxide, oxygen, hydrogen sulfide and carbon dioxide that CO integrates itself and impacts cellular physiology. The body of evidence supporting a physiological role for CO is immense and continues to move forward as CO is being evaluated in ongoing clinical trials (www.clinicaltrials. gov, Identifier: NCT 01727167, 00094406, 00122694, 01214187, 01050712, 01050933, 01523548, and 00531856). The endogenous generation of CO as described by Tenhunen et al. (1968) occurs through the enzymatic degradation of heme by the heme oxygenases, enzymes present in all cells that convert heme into biliverdin, iron and CO. Like CO, it has become undeniably clear that each catalytic product has important physiological functions beyond serving as byproducts. Two isoforms of heme oxygenase exist: heme oxygenase 1 (Hmox-1), which is expressed ubiquitously and is highly inducible by an array of stimuli, and the constitutive heme oxygenase-2 (Hmox-2) isoform, predominantly expressed in neurons, the testes, and the vasculature. Induction of HO1 has proven to be a strong cytoprotectant while deficiency in HO-1 leads to aggravated disease states, even in humans (Poss and Tonegawa, 1997; Otterbein et al., 1999; Park et al., 2007; Tsuchihashi et al., 2007; Chen et al., 2009; Wang et al., 2009, 2012; Yin et al., 2010; Ferenbach et al., 2011; Ogawa et al., 2011; Zhang et al., 2012).

Eine Subarachnoidalblutung (SAB) geht trotz Verbesserung bei Diagnose und Behandlung immer noch mit einer hohen Sterblichkeit einher. Und auch wenn sie uberlebt wird, resultieren haufig deutliche funktionelle und kognitive Einschrankungen. Kann ein neuer therapeutischer Ansatz – die Gabe von Kohlenmonoxid – hier helfen? Mediziner aus Freiburg und Harvard haben das experimentell und bei Patienten untersucht.