Clinical experience with 118 brain tissue oxygen partial pressure catheter probes

Acute intracranial hemorrhage during the installation of the LICOX microdialysis system: A case report

Neuro-monitoring is widely employed for the evaluation of intubated patients in the intensive care unit with stroke, severe head trauma, subarachnoid hemorrhage and/or hepatic encephalopathy. The present study reports the case of a patient with acute intracranial hemorrhage following the insertion of neuromonitoring catheters, which required surgical management. The patient was a 14-year-old male who sustained a severe traumatic brain injury and underwent a right-sided hemicraniectomy. During the installation of the neuromonitoring catheters, an acute hemorrhage was noted with a rapidly elevating intracranial pressure. A craniotomy was performed to identify and coagulate the injured cortical vessel. As demonstrated herein, the thorough evaluation of the clotting profile of the patient, a meticulous surgical technique and obtaining a post-insertion computed tomography scan may minimize the risk of any neuromonitoring-associated hemorrhagic complications.

New Insights into the Role of Mild Hypoxia in Regulating Neural Stem Cell Characteristics

The proliferation of neural stem cells (NSCs) is precisely regulated by extracellular environmental factors. In situ hypoxia, one of the key factors involved in the regulation of NSC characteristics, has attracted increasing amounts of attention. Numerous studies have demonstrated that hypoxia can significantly promote the formation of neurospheres and the proliferation of NSCs in vitro and that intermittent hypoxia can promote the proliferation of endogenous NSCs in vivo. In this article, the effects of different concentrations of oxygen on NSC proliferation and differentiation both in vivo and in vitro are reviewed, and the potential applications of hypoxia-preconditioned NSCs, as well as research progress and challenges in the treatment of central nervous system diseases, are further summarized. Here, the critical role of oxygen in the neurogenesis of NSCs is emphasized, and insights into the use of hypoxia to regulate NSC characteristics are provided.

Complications of Intracranial Multimodal Monitoring for Neurocritical Care: A Systematic Review and Meta-Analysis

Intracranial multimodal monitoring (iMMM) is increasingly used for neurocritical care. However, concerns arise regarding iMMM invasiveness considering limited evidence in its clinical significance and safety profile. We conducted a synthesis of evidence regarding complications associated with iMMM to delineate its safety profile. We performed a systematic review and meta-analysis (PROSPERO Registration Number: CRD42021225951) according to the Preferred Reporting Items for Systematic Review and Meta-Analysis and Peer Review of Electronic Search Strategies guidelines to retrieve evidence from studies reporting iMMM use in humans that mention related complications. We assessed risk of bias using the Newcastle-Ottawa Scale and funnel plots. The primary outcomes were iMMM complications. The secondary outcomes were putative risk factors. Of the 366 screened articles, 60 met the initial criteria and were further assessed by full-text reading. We included 22 studies involving 1206 patients and 1434 iMMM placements. Most investigators used a bolt system (85.9%) and a three-lumen device (68.8%), mainly inserting iMMM into the most injured hemisphere (77.9%). A total of 54 postoperative intracranial hemorrhages (pooled rate of 4%; 95% confidence interval [CI] 0-10%; I2 86%, p < 0.01 [random-effects model]) was reported, along with 46 misplacements (pooled rate of 6%; 95% CI 1-12%; I2 78%, p < 0.01) and 16 central nervous system infections (pooled rate of 0.43%; 95% CI 0-2%; I2 64%, p < 0.01). We found 6 system breakings, 18 intracranial bone fragments, and 5 cases of pneumocephalus. Currently, iMMM systems present a similar safety profile as intracranial devices commonly used in neurocritical care. Long-term outcomes of prospective studies will complete the benefit-risk assessment of iMMM in neurocritical care. Consensus-based reporting guidelines on iMMM use are needed to bolster future collaborative efforts.

Biophysics in tumor growth and progression: from single mechano-sensitive molecules to mechanomedicine

Evidence from physical sciences in oncology increasingly suggests that the interplay between the biophysical tumor microenvironment and genetic regulation has significant impact on tumor progression. Especially, tumor cells and the associated stromal cells not only alter their own cytoskeleton and physical properties but also remodel the microenvironment with anomalous physical properties. Together, these altered mechano-omics of tumor tissues and their constituents fundamentally shift the mechanotransduction paradigms in tumorous and stromal cells and activate oncogenic signaling within the neoplastic niche to facilitate tumor progression. However, current findings on tumor biophysics are limited, scattered, and often contradictory in multiple contexts. Systematic understanding of how biophysical cues influence tumor pathophysiology is still lacking. This review discusses recent different schools of findings in tumor biophysics that have arisen from multi-scale mechanobiology and the cutting-edge technologies. These findings range from the molecular and cellular to the whole tissue level and feature functional crosstalk between mechanotransduction and oncogenic signaling. We highlight the potential of these anomalous physical alterations as new therapeutic targets for cancer mechanomedicine. This framework reconciles opposing opinions in the field, proposes new directions for future cancer research, and conceptualizes novel mechanomedicine landscape to overcome the inherent shortcomings of conventional cancer diagnosis and therapies.

The Role of Brain Tissue Oxygenation Monitoring in the Management of Subarachnoid Hemorrhage: A Scoping Review

Monitoring of brain tissue oxygenation (PbtO2) is an important component of multimodal monitoring in traumatic brain injury. Over recent years, use of PbtO2 monitoring has also increased in patients with poor-grade subarachnoid hemorrhage (SAH), particularly in those with delayed cerebral ischemia. The aim of this scoping review was to summarize the current state of the art regarding the use of this invasive neuromonitoring tool in patients with SAH. Our results showed that PbtO2 monitoring is a safe and reliable method to assess regional cerebral tissue oxygenation and that PbtO2 represents the oxygen available in the brain interstitial space for aerobic energy production (i.e., the product of cerebral blood flow and the arterio-venous oxygen tension difference). The PbtO2 probe should be placed in the area at risk of ischemia (i.e., in the vascular territory in which cerebral vasospasm is expected to occur). The most widely used PbtO2 threshold to define brain tissue hypoxia and initiate specific treatment is between 15 and 20 mm Hg. PbtO2 values can help identify the need for or the effects of various therapies, such as hyperventilation, hyperoxia, induced hypothermia, induced hypertension, red blood cell transfusion, osmotic therapy, and decompressive craniectomy. Finally, a low PbtO2 value is associated with a worse prognosis, and an increase of the PbtO2 value in response to treatment is a marker of good outcome.

Temporal Patterns in Brain Tissue and Systemic Oxygenation Associated with Mortality After Severe Traumatic Brain Injury in Children

BACKGROUND

Brain tissue hypoxia is an independent risk factor for unfavorable outcomes in traumatic brain injury (TBI); however, systemic hyperoxemia encountered in the prevention and/or response to brain tissue hypoxia may also impact risk of mortality. We aimed to identify temporal patterns of partial pressure of oxygen in brain tissue (PbtO2), partial pressure of arterial oxygen (PaO2), and PbtO2/PaO2 ratio associated with mortality in children with severe TBI.

METHODS

Data were extracted from the electronic medical record of a quaternary care children's hospital with a level I trauma center for patients ≤ 18 years old with severe TBI and the presence of PbtO2 and/or intracranial pressure monitors. Temporal analyses were performed for the first 5 days of hospitalization by using locally estimated scatterplot smoothing for less than 1,000 observations and generalized additive models with integrated smoothness estimation for more than 1,000 observations.

RESULTS

A total of 138 intracranial pressure-monitored patients with TBI (median 5.0 [1.9-12.8] years; 65% boys; admission Glasgow Coma Scale score 4 [3-7]; mortality 18%), 71 with PbtO2 monitors and 67 without PbtO2 monitors were included. Distinct patterns in PbtO2, PaO2, and PbtO2/PaO2 were evident between survivors and nonsurvivors over the first 5 days of hospitalization. Time-series analyses showed lower PbtO2 values on day 1 and days 3-5 and lower PbtO2/PaO2 ratios on days 1, 2, and 5 among patients who died. Analysis of receiver operating characteristics curves using Youden's index identified a PbtO2 of 30 mm Hg and a PbtO2/PaO2 ratio of 0.12 as the cut points for discriminating between survivors and nonsurvivors. Univariate logistic regression identified PbtO2 < 30 mm Hg, hyperoxemia (PaO2 ≥ 300 mm Hg), and PbtO2/PaO2 ratio < 0.12 to be independently associated with mortality.

CONCLUSIONS

Lower PbtO2, higher PaO2, and lower PbtO2/PaO2 ratio, consistent with impaired oxygen diffusion into brain tissue, were associated with mortality in this cohort of children with severe TBI. These results corroborate our prior work that suggests targeting a higher PbtO2 threshold than recommended in current guidelines and highlight the potential use of the PbtO2/PaO2 ratio in the management of severe pediatric TBI.

Autophagy Is Essential for Neural Stem Cell Proliferation Promoted by Hypoxia

Hypoxia as a microenvironment or niche stimulates proliferation of neural stem cells (NSCs). However, the underlying mechanisms remain elusive. Autophagy is a protective mechanism by which recycled cellular components and energy are rapidly supplied to the cell under stress. Whether autophagy mediates the proliferation of NSCs under hypoxia and how hypoxia induces autophagy remain unclear. Here, we report that hypoxia facilitates embryonic NSC proliferation through HIF-1/mTORC1 signaling pathway-mediated autophagy. Initially, we found that hypoxia greatly induced autophagy in NSCs, while inhibition of autophagy severely impeded the proliferation of NSCs in hypoxia conditions. Next, we demonstrated that the hypoxia core regulator HIF-1 was necessary and sufficient for autophagy induction in NSCs. Considering that mTORC1 is a key switch that suppresses autophagy, we subsequently analyzed the effect of HIF-1 on mTORC1 activity. Our results showed that the mTORC1 activity was negatively regulated by HIF-1. Finally, we provided evidence that HIF-1 regulated mTORC1 activity via its downstream target gene BNIP3. The increased expression of BNIP3 under hypoxia enhanced autophagy activity and proliferation of NSCs, which was mediated by repressing the activity of mTORC1. We further illustrated that BNIP3 can interact with Rheb, a canonical activator of mTORC1. Thus, we suppose that the interaction of BNIP3 with Rheb reduces the regulation of Rheb toward mTORC1 activity, which relieves the suppression of mTORC1 on autophagy, thereby promoting the rapid proliferation of NSCs. Altogether, this study identified a new HIF-1/BNIP3-Rheb/mTORC1 signaling axis, which regulates the NSC proliferation under hypoxia through induction of autophagy.

Optical 4D oxygen mapping of microperfused tissue models with tunable in vivo-like 3D oxygen microenvironments

Sufficient and controllable oxygen supply is essential for in vitro 3D cell and tissue culture at high cell densities, which calls for volumetric in situ oxygen analysis methods to quantitatively assess the oxygen distribution. This paper presents a general approach for accurate and precise non-contact 3D mapping of oxygen tension in high cell-density cultures via embedded commercially available oxygen microsensor beads read out by confocal phosphorescence lifetime microscopy (PLIM). Optimal acquisition conditions and data analysis procedures are established and implemented in a publicly available software package. The versatility of the established method is first demonstrated in model-assisted fluidic design of microperfused 3D printed hydrogel culture chips with the aim of full culture oxygenation, and subsequently for monitoring and maintenance of physiologically relevant spatial and temporal oxygen gradients in the 3D printed chips controlled by static or dynamic flow conditions during 3D culture.

Functional Repercussions of Hypoxia-Inducible Factor-2α in Idiopathic Pulmonary Fibrosis

Hypoxia and hypoxia-inducible factors (HIFs) are essential in regulating several cellular processes, such as survival, differentiation, and the cell cycle; this adaptation is orchestrated in a complex way. In this review, we focused on the impact of hypoxia in the physiopathology of idiopathic pulmonary fibrosis (IPF) related to lung development, regeneration, and repair. There is robust evidence that the responses of HIF-1α and -2α differ; HIF-1α participates mainly in the acute phase of the response to hypoxia, and HIF-2α in the chronic phase. The analysis of their structure and of different studies showed a high specificity according to the tissue and the process involved. We propose that hypoxia-inducible transcription factor 2a (HIF-2α) is part of the persistent aberrant regeneration associated with developing IPF.

Targeting HIF-1α by Natural and Synthetic Compounds: A Promising Approach for Anti-Cancer Therapeutics Development

Advancement in novel target detection using improved molecular cancer biology has opened up new avenues for promising anti-cancer drug development. In the past two decades, the mechanism of tumor hypoxia has become more understandable with the discovery of hypoxia-inducible factor-1α (HIF-1α). It is a major transcriptional regulator that coordinates the activity of various transcription factors and their downstream molecules involved in tumorigenesis. HIF-1α not only plays a crucial role in the adaptation of tumor cells to hypoxia but also regulates different biological processes, including cell proliferation, survival, cellular metabolism, angiogenesis, metastasis, cancer stem cell maintenance, and propagation. Therefore, HIF-1α overexpression is strongly associated with poor prognosis in patients with different solid cancers. Hence, pharmacological targeting of HIF-1α has been considered to be a novel cancer therapeutic strategy in recent years. In this review, we provide brief descriptions of natural and synthetic compounds as HIF-1α inhibitors that have the potential to accelerate anticancer drug discovery. This review also introduces the mode of action of these compounds for a better understanding of the chemical leads, which could be useful as cancer therapeutics in the future.

Hyperoxia Reprogrammes Microvascular Endothelial Cell Response to Hypoxia in an Organ-Specific Manner

Organ function relies on microvascular networks to maintain homeostatic equilibrium, which varies widely in different organs and during different physiological challenges. The endothelium role in this critical process can only be evaluated in physiologically relevant contexts. Comparing the responses to oxygen flux in primary murine microvascular EC (MVEC) obtained from brain and lung tissue reveals that supra-physiological oxygen tensions can compromise MVEC viability. Brain MVEC lose mitochondrial activity and undergo significant alterations in electron transport chain (ETC) composition when cultured under standard, non-physiological atmospheric oxygen levels. While glycolytic capacity of both lung and brain MVEC are unchanged by environmental oxygen, the ability to trigger a metabolic shift when oxygen levels drop is greatly compromised following exposure to hyperoxia. This is particularly striking in MVEC from the brain. This work demonstrates that the unique metabolism and function of organ-specific MVEC (1) can be reprogrammed by external oxygen, (2) that this reprogramming can compromise MVEC survival and, importantly, (3) that ex vivo modelling of endothelial function is significantly affected by culture conditions. It further demonstrates that physiological, metabolic and functional studies performed in non-physiological environments do not represent cell function in situ, and this has serious implications in the interpretation of cell-based pre-clinical models.

Effect of Hypoxia on the Function of the Human Serotonin1A Receptor

Cellular hypoxia causes numerous pathophysiological conditions associated with the disruption of oxygen homeostasis. Under oxygen-deficient conditions, cells adapt by controlling the cellular functions to facilitate the judicious use of available oxygen, such as cessation of cell growth and proliferation. In higher eukaryotes, the process of cholesterol biosynthesis is intimately coupled to the availability of oxygen, where the synthesis of one molecule of cholesterol requires 11 molecules of O₂. Cholesterol is an essential component of higher eukaryotic membranes and is crucial for the physiological functions of several membrane proteins and receptors. The serotonin_1A receptor, an important neurotransmitter G protein-coupled receptor associated with cognition and memory, has previously been shown to depend on cholesterol for its signaling and function. In this work, in order to explore the interdependence of oxygen levels, cholesterol biosynthesis, and the function of the serotonin_1A receptor, we developed a cellular hypoxia model to explore the function of the human serotonin_1A receptor heterologously expressed in Chinese hamster ovary cells. We observed cell cycle arrest at G1/S phase and the accumulation of lanosterol in cell membranes under hypoxic conditions, thereby validating our cellular model. Interestingly, we observed a significant reduction in ligand binding and disruption of downstream cAMP signaling of the serotonin_1A receptor under hypoxic conditions. To the best of our knowledge, our results represent the first report linking the function of the serotonin_1A receptor with hypoxia. From a broader perspective, these results contribute to our overall understanding of the molecular basis underlying neurological conditions often associated with hypoxia-induced brain dysfunction.

Correlation between brain tissue oxygen tension and regional cerebral oximetry in uninjured human brain under conditions of changing ventilation strategy

Controversy surrounds regional cerebral oximetry (rSO₂) because extracranial contamination and unmeasured changes in cerebral arterial:venous ratio confound readings. Correlation of rSO₂ with brain tissue oxygen (PbrO₂), a “gold standard” for cerebral oxygenation, could help resolve this controversy but PbrO₂ measurement is highly invasive. This was a prospective cohort study. The primary aim was to evaluate correlation between PbrO₂ and rSO₂ and the secondary aim was to investigate the relationship between changing ventilation regimens and measurement of PbrO₂ and rSO₂. Patients scheduled for elective removal of cerebral metastases were anesthetized with propofol and remifentanil, targeted to a BIS range 40–60. rSO₂ was measured using the INVOS 5100B monitor and PbrO₂ using the Licox brain monitoring system. The Licox probe was placed into an area of normal brain within the tumor excision corridor. FiO₂ and minute ventilation were sequentially adjusted to achieve two set points: (1) FiO₂ 0.3 and paCO₂ 30 mmHg, (2) FiO₂ 1.0 and paCO₂ 40 mmHg. PbrO₂ and rSO₂ were recorded at each. Nine participants were included in the final analysis, which showed a positive Spearman’s correlation (r = 0.50, p = 0.036) between PbrO₂ and rSO₂. From set point 1 to set point 2, PbrO₂ increased from median 6.0, IQR 4.0–11.3 to median 22.5, IQR 9.8–43.6, p = 0.015; rSO₂ increased from median 68.0, IQR 62.5–80.5 to median 83.0, IQR 74.0–90.0, p = 0.047. Correlation between PbrO₂ and rSO₂ is evident. Increasing FiO₂ and PaCO₂ results in significant increases in cerebral oxygenation measured by both monitors.

Designing Sensitivity: A Comparative Analysis of Microelectrode Topologies for Electrochemical Oxygen Sensing in Biomedical Applications

The monitoring of dissolved oxygen is a key parameter in many fields, namely the treatment and monitoring of various cerebral traumas. Leveraging existing manufacturing techniques, electrochemical sensors hold the potential for compact, simple, and scalable dissolved oxygen sensors. Past studies have focused on the general design of such sensors, but a comparative study on the impact of microelectrode geometries for cerebral applications has been forthcoming. We present here the results of a characterization study conducted across solid-state sensors with varying microelectrode geometries. The electrode structures were covered with a Nafion membrane and included variations of the classic interdigitated microelectrode array in addition to a circular microelectrode array variation. Voltage sweeps were conducted while monitoring the devices’ sensing current responses across a 50.3 mmHg change in dissolved oxygen within a deionized aqueous solution. Half of the devices were identified as ultramicroelectrode designs that presented a greater dependence on electrode spacing and topology. The ultramicroelectrode-style (UME) interdigitated electrode (IDE) topology presented the greatest signal response at 25.24 nA/mmHg, an approximate eight-fold improvement in sensitivity from a non-UME variation with a sensitivity of 2.98 nA/mmHg. The design presented a linear response from 8.3 mmHg to 58.6 mmHg with r² = 0.9743. The sensitivity improvement was attributed to the ultramicroelectrode structure’s amplifying diffusive feedback, which was enabled by the IDE topology and short electrode spacings.

Safety profile of an intracranial multimodal monitoring bolt system for neurocritical care: a single-center experience

BACKGROUND

Intracranial multimodality monitoring (iMMM) is increasingly used in acute brain-injured patients; however, safety and reliability remain major concerns to its routine implementation.

METHODS

We performed a retrospective study including all patients undergoing iMMM at a single European center between July 2016 and January 2020. Brain tissue oxygenation probe (PbtO₂), alone or in combination with a microdialysis catheter and/or an 8-contact depth EEG electrode, was inserted using a triple-lumen bolt system and targeting normal-appearing at-risk brain area on the injured side, whenever possible. Surgical complications, adverse events, and technical malfunctions, directly associated with iMMM, were collected. A blinded imaging review was performed by an independent radiologist.

RESULTS

One hundred thirteen patients with 123 iMMM insertions were included for a median monitoring time of 9 [3-14] days. Of those, 93 (76%) patients had only PbtO₂ probe insertion and 30 (24%) had also microdialysis and/or iEEG monitoring. SAH was the most frequent indication for iMMM (n = 60, 53%). At least one complication was observed in 67/123 (54%) iMMM placement, corresponding to 58/113 (51%) patients. Misplacement was observed in 16/123 (13%), resulting in a total of 6/16 (38%) malfunctioning PbtO₂ catheters. Intracranial hemorrhage was observed in 14 iMMM placements (11%), of which one required surgical drainage. Five placements were complicated by pneumocephalus and 4 with bone fragments; none of these requires additional surgery. No CNS infection related to iMMM was observed. Seven (6%) probes were accidentally dislodged and 2 probes (2%) were accidentally broken. Ten PbtO₂ probes (8%) presented a technical malfunction after a median of 9 [ranges: 2-24] days after initiation of monitoring and 4 of them were replaced.

CONCLUSIONS

In this study, a high occurrence of complications related to iMMM was observed, although most of them did not require specific interventions and did not result in malfunctioning monitoring.

Prognostic Value of Fluorine-19 MRI Oximetry Monitoring in cancer

Hypoxia is a key prognostic indicator in most solid tumors, as it is correlated to tumor angiogenesis, metastasis, recurrence, and response to therapy. Accurate measurement and mapping of tumor oxygenation profile and changes upon intervention could facilitate disease progression assessment and assist in treatment planning. Currently, no gold standard exists for non-invasive spatiotemporal measurement of hypoxia. Magnetic resonance imaging (MRI) represents an attractive option as it is a clinically available and non-ionizing imaging modality. Specifically, perfluorocarbon (PFC) beacons can be externally introduced into the tumor tissue and the linear dependence of their spin-lattice relaxation rate (R1) on the local partial pressure of oxygen (pO₂) exploited for real-time tissue oxygenation monitoring in vivo. In this review, we will focus on early studies and recent developments of fluorine-19 MRI and spectroscopy (MRS) for evaluation of tumor oximetry and response to therapy.

A Review of Monitoring Methods for Cerebral Blood Oxygen Saturation

In recent years, cerebral blood oxygen saturation has become a key indicator during the perioperative period. Cerebral blood oxygen saturation monitoring is conducive to the early diagnosis and treatment of cerebral ischemia and hypoxia. The present study discusses the three most extensively used clinical methods for cerebral blood oxygen saturation monitoring from different aspects: working principles, relevant parameters, current situations of research, commonly used equipment, and relative advantages of different methods. Furthermore, through comprehensive comparisons of the methods, we find that near-infrared spectroscopy (NIRS) technology has significant potentials and broad applications prospects in terms of cerebral oxygen saturation monitoring. Despite the current NIRS technology, the only bedside non-invasive cerebral oxygen saturation monitoring technology, still has many defects, it is more in line with the future development trend in the field of medical and health, and will become the main method gradually.

Management of intracranial hypertension following traumatic brain injury: a best clinical practice adoption proposal for intracranial pressure monitoring and decompressive craniectomy. Joint statements by the Traumatic Brain Injury Section of the Italian Society of Neurosurgery (SINch) and the Neuroanesthesia and Neurocritical Care Study Group of the Italian Society of Anesthesia, Analgesia, Resuscitation and Intensive Care (SIAARTI)

No robust evidence is provided by literature regarding the management of intracranial hypertension following severe traumatic brain injury (TBI). This is mostly due to the lack of prospective randomized controlled trials (RCTs), the presence of studies containing extreme heterogeneously collected populations and controversial considerations about chosen outcome. A scientific society should provide guidelines for care management and scientific support for those areas for which evidence-based medicine has not been identified. However, RCTs in severe TBI have failed to establish intervention effectiveness, arising the need to make greater use of tools such as Consensus Conferences between experts, which have the advantage of providing recommendations based on experience, on the analysis of updated literature data and on the direct comparison of different logistic realities. The Italian scientific societies should provide guidelines following the national laws ruling the best medical practice. However, many limitations do not allow the collection of data supporting high levels of evidence for intracranial pressure (ICP) monitoring and decompressive craniectomy (DC) in patients with severe TBI. This intersociety document proposes best practice guidelines for this subsetting of patients to be adopted on a national Italian level, along with joint statements from "TBI Section" of the Italian Society of Neurosurgery (SINch) endorsed by the Neuroanesthesia and Neurocritical Care Study Group of the Italian Society of Anesthesia, Analgesia, Resuscitation and Intensive Care (SIAARTI). Presented here is a recap of recommendations on management of ICP and DC supported a high level of available evidence and rate of agreement expressed by the assemblies during the more recent consensus conferences, where members of both groups have had a role of active participants and supporters. The listed recommendations have been sent to a panel of experts consisting of the 107 members of the "TBI Section" of the SINch and the 111 members of the Neuroanesthesia and Neurocritical Care Study Group of the SIAARTI. The aim of the survey was to test a preliminary evaluation of the grade of predictable future adherence of the recommendations following this intersociety proposal. The following recommendations are suggested as representing best clinical practice, nevertheless, adoption of local multidisciplinary protocols regarding thresholds of ICP values, drug therapies, hemostasis management and perioperative care of decompressed patients is strongly recommended to improve treatment efficiency, to increase the quality of data collection and to provide more powerful evidence with future studies. Thus, for this future perspective a rapid overview of the role of the multimodal neuromonitoring in the optimal severe TBI management is also provided in this document. It is reasonable to assume that the recommendations reported in this paper will in future be updated by new observations arising from future trials. They are not binding, and this document should be offered as a guidance for clinical practice through an intersociety agreement, taking in consideration the low level of evidence.

The Role of 2-Oxoglutarate Dependent Dioxygenases in Gliomas and Glioblastomas: A Review of Epigenetic Reprogramming and Hypoxic Response

Gliomas are a heterogeneous group of cancers that predominantly arise from glial cells in the brain, but may also arise from neural stem cells, encompassing low-grade glioma and high-grade glioblastoma. Whereas better diagnosis and new treatments have improved patient survival for many cancers, glioblastomas remain challenging with a highly unfavorable prognosis. This review discusses a super-family of enzymes, the 2-oxoglutarate dependent dioxygenase enzymes (2-OGDD) that control numerous processes including epigenetic modifications and oxygen sensing, and considers their many roles in the pathology of gliomas. We specifically describe in more detail the DNA and histone demethylases, and the hypoxia-inducible factor hydroxylases in the context of glioma, and discuss the substrate and cofactor requirements of the 2-OGDD enzymes. Better understanding of how these enzymes contribute to gliomas could lead to the development of new treatment strategies.

Mismatch between Tissue Partial Oxygen Pressure and Near-Infrared Spectroscopy Neuromonitoring of Tissue Respiration in Acute Brain Trauma: The Rationale for Implementing a Multimodal Monitoring Strategy

The brain tissue partial oxygen pressure (PbtO₂) and near-infrared spectroscopy (NIRS) neuromonitoring are frequently compared in the management of acute moderate and severe traumatic brain injury patients; however, the relationship between their respective output parameters flows from the complex pathogenesis of tissue respiration after brain trauma. NIRS neuromonitoring overcomes certain limitations related to the heterogeneity of the pathology across the brain that cannot be adequately addressed by local-sample invasive neuromonitoring (e.g., PbtO₂ neuromonitoring, microdialysis), and it allows clinicians to assess parameters that cannot otherwise be scanned. The anatomical co-registration of an NIRS signal with axial imaging (e.g., computerized tomography scan) enhances the optical signal, which can be changed by the anatomy of the lesions and the significance of the radiological assessment. These arguments led us to conclude that rather than aiming to substitute PbtO₂ with tissue saturation, multiple types of NIRS should be included via multimodal systemic- and neuro-monitoring, whose values then are incorporated into biosignatures linked to patient status and prognosis. Discussion on the abnormalities in tissue respiration due to brain trauma and how they affect the PbtO₂ and NIRS neuromonitoring is given.

Hypoxia and the phenomenon of immune exclusion

Over the last few years, cancer immunotherapy experienced tremendous developments and it is nowadays considered a promising strategy against many types of cancer. However, the exclusion of lymphocytes from the tumor nest is a common phenomenon that limits the efficiency of immunotherapy in solid tumors. Despite several mechanisms proposed during the years to explain the immune excluded phenotype, at present, there is no integrated understanding about the role played by different models of immune exclusion in human cancers. Hypoxia is a hallmark of most solid tumors and, being a multifaceted and complex condition, shapes in a unique way the tumor microenvironment, affecting gene transcription and chromatin remodeling. In this review, we speculate about an upstream role for hypoxia as a common biological determinant of immune exclusion in solid tumors. We also discuss the current state of ex vivo and in vivo imaging of hypoxic determinants in relation to T cell distribution that could mechanisms of immune exclusion and discover functional-morphological tumor features that could support clinical monitoring.

Oxygen regulation of TET enzymes

Hypoxia has a significant impact on many physiological and pathological processes. Over the recent years, its role in modulation of epigenetic remodelling has also become clearer. In cancer, low oxygen environments and aberrant epigenomes often go hand in hand, and changes in DNA methylation are now commonly recognised as potential outcome indicators. TET (ten-eleven translocation) family enzymes are alpha-ketoglutarate-, iron- and oxygen-dependent DNA demethylases and are key players in these processes. Although TETs have historically been considered tumour suppressors, recent studies suggest that their functions in cancer might not be straightforward. Recently, inhibition of TETs has been reported to have positive impact in cancer immunotherapy and vaccination studies. This underlines the current interest in developing targeted pharmaceutical inhibitors of these enzymes. Here, we will survey the complexity of TET roles in cancer, and its hypoxic modulation, as well as highlight the potential of these enzymes as therapeutic targets.

Scanning Tissue Oxygen Needle Probe

A new device designed to scan oxygen partial pressure along a line in a biological tissue is described in this paper. The probe is housed in a stainless-steel needle. As opposed to other devices for oxygen scanning in tissue, the new probe does not require mechanical translation of the needle in the tissue. The probe includes an active sensing area along the needle shaft that can be scanned optically by an internal optical fiber. This feature allows for repeated scans of tissue oxygen along a line without translating the needle with respect to the tissue, thus avoiding tissue damage associated with needle motion. First, we describe the design of the device including its sensing mechanism, mechanical design, optical configuration, and signal processing. We then move on to describe the results of the device characterization and testing. Finally, we conclude by discussing possible applications of the device in research and in clinical diagnoses and treatment monitoring.

Individualized Brain Tissue Oxygen-Monitoring Probe Placement Helps to Guide Therapy and Optimizes Outcome in Neurocritical Care

Background/Objective

In order to monitor tissue oxygenation in patients with acute neurological disorders, probes for measurement of brain tissue oxygen tension (ptO₂) are often placed non-specifically in a right frontal lobe location. To improve the value of ptO₂ monitoring, placement of the probe into a specific area of interest is desirable. We present a technique using CT-guidance to place the ptO₂ probe in a particular area of interest based on the individual patient’s pathology.

Methods

In this retrospective cohort study, we analyzed imaging and clinical data from all patients who underwent CT-guided ptO₂ probe placement at our institution between October 2017 and April 2019. Primary endpoint was successful placement of the probe in a particular area of interest rated by two independent reviewers. Secondary outcomes were complications from probe insertion, clinical consequences from ptO₂ measurements, clinical outcome according to the modified Rankin Scale (mRS) as well as development of ischemia on follow-up imaging. A historical control group was selected from patients who underwent conventional ptO₂ probe placement between January 2010 and October 2017.

Results

Eleven patients had 16 CT-guided probes inserted. In 15 (93.75%) probes, both raters agreed on the correct placement in the area of interest. Each probe triggered on average 0.48 diagnostic or therapeutic adjustments per day. Only one infarction within the vascular territory of a probe was found on follow-up imaging. Eight out of eleven patients (72.73%) reached a good outcome (mRS ≤ 3). In comparison, conventionally placed probes triggered less diagnostic and therapeutic adjustment per day (p = 0.007). Outcome was worse in the control group (p = 0.024).

Conclusion

CT-guided probe insertion is a reliable and easy technique to place a ptO₂ probe in a particular area of interest in patients with potentially reduced cerebral oxygen supply. By adjusting treatment aggressively according to this individualized monitoring data, clinical outcome may improve.

Discoveries for Long Non-Coding RNA Dynamics in Traumatic Brain Injury

Simple Summary

The biomedical studies of traumatic brain injury (TBI) can lead to insight for treatment clinically. However, TBIs are occurred by various risk factors and showing heterogeneity that make difficult to accurate diagnosis for initiation treatment of patients. Therefore, identification of biomarkers requires to prediction and therapeutics for TBI treatment. The canonical function of the long non-coding RNAs (lncRNAs) have been recently shown to promote transcription, post-transcription, and protein activity in many different conditions. Therefore, understanding the molecular mechanisms that are altered by the expression of lncRNAs will allow the design of novel therapeutic strategies. Here, we review the molecular process of lncRNA as new targets and approaches in TBIs treatment.

Abstract

In recent years, our understanding of long non-coding RNAs (lncRNAs) has been challenged with advances in genome sequencing and the widespread use of high-throughput analysis for identifying novel lncRNAs. Since then, the characterization of lncRNAs has contributed to the establishment of their molecular roles and functions in transcriptional regulation. Although genetic studies have so far explored the sequence-based primary function of lncRNAs that guides the expression of target genes, recent insights have shed light on the potential of lncRNAs for widening the identification of biomarkers from non-degenerative to neurodegenerative diseases. Therefore, further advances in the genetic characteristics of lncRNAs are expected to lead to diagnostic accuracy during disease progression. In this review, we summarized the latest studies of lncRNAs in TBI as a non-degenerative disease and discussed their potential limitations for clinical treatment.

Brain tissue oxygenation during transnasal endoscopic skull base procedures

PURPOSE

We aimed to study brain tissue oxygenation during the period of controlled reduction of arterial blood pressure - a maneuver often used in extended endoscopic skull base surgery for bloodless operative field.

METHODS

Intracranial pressure, arterial blood pressure and the resultant cerebral perfusion pressure were measured during extended endoscopic skull base surgery in 5 patients with diagnosed tumors of the skull base and arterial hypertension. Simultaneously, in those patients, we measured partial pressure of oxygen in the brain parenchyma (PbtO₂).

RESULTS

Values of PbtO₂ lower than 15 mm Hg (risk of brain ischemia) were observed in 3 patients for periods of 40 min, 110 min and 123 min, respectively. In 2 of these patients, no hypotension (mean arterial pressure <65 mm Hg) was necessary for bloodless operative field. Another 2 patients had PbtO₂ above 30 mm Hg at the time when their mean arterial pressure was below 65 mm Hg. The time course of PbtO₂ followed that of cerebral perfusion pressure with a time lag of 40-60 s in all patients.

CONCLUSION

Moderate reduction of arterial pressure, often used to obtain bloodless operative field during extended endoscopic skull base surgery, may in patients with the medical history of arterial hypertension be associated with critically low values of partial oxygen pressure in brain tissue.

Electrochemical Evaluation of a Multi-Site Clinical Depth Recording Electrode for Monitoring Cerebral Tissue Oxygen

The intracranial measurement of local cerebral tissue oxygen levels—PbtO₂—has become a useful tool for the critical care unit to investigate severe trauma and ischemia injury in patients. Our preliminary work in animal models supports the hypothesis that multi-site depth electrode recording of PbtO₂ may give surgeons and critical care providers needed information about brain viability and the capacity for better recovery. Here, we present a surface morphology characterization and an electrochemical evaluation of the analytical properties toward oxygen detection of an FDA-approved, commercially available, clinical grade depth recording electrode comprising 12 Pt recording contacts. We found that the surface of the recording sites is composed of a thin film of smooth Pt and that the electrochemical behavior evaluated by cyclic voltammetry in acidic and neutral electrolyte is typical of polycrystalline Pt surface. The smoothness of the Pt surface was further corroborated by determination of the electrochemical active surface, confirming a roughness factor of 0.9. At an optimal working potential of −0.6 V vs. Ag/AgCl, the sensor displayed suitable values of sensitivity and limit of detection for in vivo PbtO₂ measurements. Based on the reported catalytical properties of Pt toward the electroreduction reaction of O₂, we propose that these probes could be repurposed for multisite monitoring of PbtO₂ in vivo in the human brain.

Using Electroencephalography (EEG) Power Responses to Investigate the Effects of Ambient Oxygen Content, Safety Shoe Type, and Lifting Frequency on the Worker's Activities

Objective

The study assesses the changes in electroencephalography (EEG) power spectral density of individuals in hypoxia when wearing a different type of safety shoes under different lifting frequencies. It also assesses the EEG response behavior induced via the process of lifting loads related to these variables.

Methods

The study was conducted in two consecutive phases: training and acclimatization phase and experimental lifting phase. Ten male college students participated in this study. A four-way repeated measures design was used in this research with independent variables: ambient oxygen content (“15%, 18%, and 20%”), safety shoes type (“light-duty, medium-duty, and heavy-duty”), lifting frequency (“1 and 4 lifts/min”), and replication (“first and second”). And the dependent variables were alpha, theta, beta, gamma, θ/α, θ/β, α/β, β/α, (θ + α)/β, and (θ + α)/(α + β). The participant was allowed to determine his maximum acceptable weight of lift (MAWL) in fifteen minutes of lifting using psychophysically technique. Then, he continued lifting the MAWL for another five minutes, where all the data were collected.

Results

Results showed that the EEG responses at lower levels of the independent variables were significantly high than at higher levels; except for oxygen content, the EEG responses at lower levels were considerably lower than at a higher level. It also showed that an upsurge in the physical demand increased lifting frequency and replication and caused decreasing in alpha power, theta/beta, alpha/beta, (theta + alpha)/beta, (theta + alpha)/(alpha + beta) and increasing in the theta power and the gamma power. Furthermore, several interactions among independent variables had significant effects on the EEG responses.

Conclusion

The EEG implementation for the investigation of neural responses to physical demands allows for the possibility of newer nontraditional and faster methods of human performance monitoring. These methods provide effective and reliable results as compared to other traditional methods. This study will safeguard the physical capabilities and possible health risks of industrial workers. And the applications of these tasks can occur in almost all working environments (factories, warehouses, airports, building sites, farms, hospitals, offices, etc.) that are at high altitudes. It can include lifting boxes at a packaging line, handling construction materials, handling patients in hospitals, and cleaning.

Hypoxia Inducible Factors' Signaling in Pediatric High-Grade Gliomas: Role, Modelization and Innovative Targeted Approaches

The brain tumor microenvironment has recently become a major challenge in all pediatric cancers, but especially in brain tumors like high-grade gliomas. Hypoxia is one of the extrinsic tumor features that interacts with tumor cells, but also with the blood-brain barrier and all normal brain cells. It is the result of a dramatic proliferation and expansion of tumor cells that deprive the tissues of oxygen inflow. However, cancer cells, especially tumor stem cells, can endure extreme hypoxic conditions by rescheduling various genes' expression involved in cell proliferation, metabolism and angiogenesis and thus, promote tumor expansion, therapeutic resistance and metabolic adaptation. This cellular adaptation implies Hypoxia-Inducible Factors (HIF), namely HIF-1α and HIF-2α. In pediatric high-grade gliomas (pHGGs), several questions remained open on hypoxia-specific role in normal brain during gliomagenesis and pHGG progression, as well how to model it in preclinical studies and how it might be counteracted with targeted therapies. Therefore, this review aims to gather various data about this key extrinsic tumor factor in pHGGs.

Increased Brain Tissue Oxygen Monitoring Threshold to Improve Hospital Course in Traumatic Brain Injury Patients

Introduction

This article is a retrospective analysis of the neurosurgical census at our institution to determine an optimal threshold for brain tissue oxygenation (PbtO2). The use of brain tissue oxygen monitoring has been in place for approximately three decades but data suggesting optimal thresholds to improve outcomes have been lacking. Though there are multiple modalities to monitor cerebral oxygenation, the monitoring of brain tissue oxygen tension has been deemed the gold standard. Still, it is not clear exactly how reductions in PbtO2 should be treated or what appropriate thresholds to treat might be. The aim of our study was to determine if our threshold of 28 mmHg for a good functional outcome could be correlated to the Glasgow Coma Scale (GCS) and Glasgow Outcome Scale (GOS).

Methods

A retrospective analysis of the Arrowhead Regional Medical Center (ARMC) Neurosurgery Census was performed. Patients from 2017-2019 who had placement of Licox® cerebral oxygen monitoring sensors (Integra® Lifesciences, Plainsboro Township, New Jersey) were included in the analysis. Fifteen patients were consecutively identified, all of which presented with traumatic brain injury (TBI). Data on age, gender, days in the intensive care unit (ICU), days before discharge or end of medical care, admission GCS, hospital length of stay, GOS, maximum and minimum PbtO2 values for five days following insertion, minimum and maximum intracranial pressures (ICPs), and brain temperature were included for analysis. Patient data were separated into two groups; those with consistently higher PbtO2 scores (≥ 28 mmHg; n = 7) and those with inconsistent/lower PbtO2 scores (< 28 mmHg; n = 8). Standard student t-tests were used to find potential statistical differences between the groups (α = 0.05).

Results

There were seven patients in the consistently high PbtO2 category (≥ 28 mmHg) and eight patients in the inconsistent/low PbtO2 category (<28 mmHg). The average maximum and minimum PbtO2 for the group displaying worse outcomes (as defined by GCS/GOS) was 23.0 mmHg and 14 mmHg, respectively. Those with consistent Day 2 PbtO2 scores of ≥ 28 mmHg had significantly higher GCS scores at discharge/end of medical care (p < 0.05). Average GCS for the patient group with >28 mmHg PbtO2 averaged over Days 2-5 group was 11.4 (n=7). Average GCS for the <28 group was 7.0 (n=8). The GCS for the >28 group was 63% higher than found in the <28 group (p = 0.03). GOS scores were significantly higher in those with consistently higher PbtO2 (≥ 28) than those with lower PbtO2 scores (< 28). The averages were 3.5 in the higher PbtO2 group as compared to 2 in the lower PbtO2 group.

Conclusion

Along with ICP monitors and monitoring in the assessment of CPP, brain tissue oxygenation allows yet another metric by which to optimize treatment in TBI patients. At our institution, a PbtO2 level of ≥ 28 mmHg is targeted in order to facilitate a good functional outcome in TBI patients. Keeping patients at this level improves GCS and GOS at discharge/end of medical treatment.

Endothelial cells and organ function: applications and implications of understanding unique and reciprocal remodelling

The microvasculature is a heterogeneous, dynamic and versatile component of the systemic circulation, with a unique ability to locally self-regulate and to respond to organ demand and environmental stimuli. Endothelial cells from different organs display considerable variation, but it is currently unclear to what extent functional properties of organ-specific endothelial cells are intrinsic, acquired and/or reprogrammable. Vascular function is a fundamental pillar of homeostasis, and dysfunction results in systemic consequences for the organism. Additionally, vascular failure can occur downstream of organ disease or environmental stress, often driving an exacerbation of symptoms and pathologies originally independent of the local circulation. The understanding of the molecular mechanisms underlying endothelial physiology and metabolism holds the promise to inform and improve diagnosis, prognosis and treatment options for a myriad of conditions as unrelated as cancer, neurodegeneration or pulmonary hypertension, and likely everything in between, if we consider that also treatments for such conditions are primarily distributed via the bloodstream. However, studying endothelial function has its challenges: the origin, isolation, culture conditions and preconditioning stimuli make this an extremely variable cell type to study and difficult to source. Animal models exist but are neither trivial to generate, nor necessarily adequately translatable to human disease. In this article, we aim to illustrate the breadth of microvascular functions in different environments, highlighting current and pioneering studies that have advanced our insight into the importance of the integrity of this tissue, as well as the limitations posed by its heterogeneity and plasticity.

Approaches to Multimodality Monitoring in Pediatric Traumatic Brain Injury

Traumatic brain injury (TBI) is a leading cause of morbidity and mortality in children. Improved methods of monitoring real-time cerebral physiology are needed to better understand when secondary brain injury develops and what treatment strategies may alleviate or prevent such injury. In this review, we discuss emerging technologies that exist to better understand intracranial pressure (ICP), cerebral blood flow, metabolism, oxygenation and electrical activity. We also discuss approaches to integrating these data as part of a multimodality monitoring strategy to improve patient care.

Evaluation of a New Multiparameter Brain Probe for Simultaneous Measurement of Brain Tissue Oxygenation, Cerebral Blood Flow, Intracranial Pressure, and Brain Temperature in a Porcine Model

BACKGROUND

A novel multiparameter brain sensor (MPBS) allows the simultaneous measurement of brain tissue oxygenation (ptiO₂), cerebral blood flow (CBF), intracranial pressure (ICP), and brain temperature with a single catheter. This laboratory investigation evaluates the MPBS in an animal model in relation to established reference probes.

METHODS

The study group consisted of 17 juvenile male pigs. Four MPBS and four reference probes were implanted per pig and compared simultaneously. The measured parameters were challenged by standardized provocations such as hyperoxia, dobutamine, and norepinephrine application, hypercapnia and hypoxia in combination with and without a controlled cortical impact (CCI) injury. Mean values over 2 min were collected for predefined time points and were analyzed using Bland-Altman plots.

RESULTS

The protocol was successfully conducted in 15 pigs of which seven received CCI. ICP and ptiO₂ were significantly influenced by the provocations. Subtraction of MPBS from reference values revealed a mean difference (limits of agreement) of 3.7 (- 20.5 to 27.9) mm Hg, - 2.9 (- 7.9 to 2.1) mm Hg, and 5.1 (- 134.7 to 145.0) % for ptiO₂, ICP, and relative CBF, respectively.

CONCLUSIONS

The MPBS is a promising measurement tool for multiparameter neuromonitoring. The conducted study demonstrates the in vivo functionality of the probe. Comparison with standard probes revealed a deviation which is mostly analogous to other multiparameter devices. However, further evaluation of the device is necessary before it can reliably be used for clinical decision making.

The paradox of metabolism in quiescent stem cells

The shift between a proliferating and a nonproliferating state is associated with significant changes in metabolic needs. Proliferating cells tend to have higher metabolic rates, and their metabolic profiles facilitate biosynthesis, as compared to those of nondividing cells of the same sort. Recent studies have elucidated specific molecules that control metabolic changes while cells shift between proliferation and quiescence. Embryonic stem cells, which are rapidly proliferating, tend to have metabolic patterns that are similar to those of nonstem cells in a proliferative state. Moreover, although adult stem cells tend to be quiescent, their metabolic profiles have been reported in multiple organs to more closely resemble those of proliferating than those of nondividing cells in some respects. The findings raise questions about whether there are metabolic profiles that are required for stemness, and whether these profiles relate to the metabolic properties that may be required for quiescence. Here, we review the literature on how metabolism changes upon commitment to proliferation and compare the proliferating and nonproliferating metabolic states of differentiated cells and embryonic and adult stem cells.

Continuous non-invasive optical monitoring of cerebral blood flow and oxidative metabolism after acute brain injury

Rapid detection of ischemic conditions at the bedside can improve treatment of acute brain injury. In this observational study of 11 critically ill brain-injured adults, we employed a monitoring approach that interleaves time-resolved near-infrared spectroscopy (TR-NIRS) measurements of cerebral oxygen saturation and oxygen extraction fraction (OEF) with diffuse correlation spectroscopy (DCS) measurement of cerebral blood flow (CBF). Using this approach, we demonstrate the clinical promise of non-invasive, continuous optical monitoring of changes in CBF and cerebral metabolic rate of oxygen (CMRO₂). In addition, the optical CBF and CMRO₂ measures were compared to invasive brain tissue oxygen tension (PbtO₂), thermal diffusion flowmetry CBF, and cerebral microdialysis measures obtained concurrently. The optical CBF and CMRO₂ information successfully distinguished between ischemic, hypermetabolic, and hyperemic conditions that arose spontaneously during patient care. Moreover, CBF monitoring during pressor-induced changes of mean arterial blood pressure enabled assessment of cerebral autoregulation. In total, the findings suggest that this hybrid non-invasive neurometabolic optical monitor (NNOM) can facilitate clinical detection of adverse physiological changes in brain injured patients that are otherwise difficult to measure with conventional bedside monitoring techniques.

Adaptive Changes of Glioblastoma Cells Following Exposure to Hypoxic (1% Oxygen) Tumour Microenvironment

Glioblastoma multiforme is the most aggressive and malignant primary brain tumour, with a median survival rate of between 15 to 17 months. Heterogeneous regions occur in glioblastoma as a result of oxygen gradients which ranges from 0.1% to 10% in vivo. Emerging evidence suggests that tumour hypoxia leads to increased aggressiveness and chemo/radio resistance. Yet, few in vitro studies have been performed in hypoxia. Using three glioblastoma cell-lines (U87, U251, and SNB19), the adaptation of glioblastoma cells in a 1% (hypoxia) and 20% (normoxia) oxygen microenvironment on proliferation, metabolism, migration, neurosphere formation, CD133 and VEGF expression was investigated. Compared to cells maintained in normoxia (20% oxygen), glioblastoma cells adapted to 1% oxygen tension by reducing proliferation and enhancing metabolism. Both migratory tendency and neurosphere formation ability were greatly limited. In addition, hypoxic-mediated gene upregulation (CD133 and VEGF) was reversed when cells were removed from the hypoxic environment. Collectively, our results reveal that hypoxia plays a pivotal role in changing the behaviour of glioblastoma cells. We have also shown that genetic modulation can be reversed, supporting the concept of reversibility. Thus, understanding the degree of oxygen gradient in glioblastoma will be crucial in personalising treatment for glioblastoma patients.

Relevance of Oxygen Concentration in Stem Cell Culture for Regenerative Medicine

The key hallmark of stem cells is their ability to self-renew while keeping a differentiation potential. Intrinsic and extrinsic cell factors may contribute to a decline in these stem cell properties, and this is of the most importance when culturing them. One of these factors is oxygen concentration, which has been closely linked to the maintenance of stemness. The widely used environmental 21% O₂ concentration represents a hyperoxic non-physiological condition, which can impair stem cell behaviour by many mechanisms. The goal of this review is to understand these mechanisms underlying the oxygen signalling pathways and their negatively-associated consequences. This may provide a rationale for culturing stem cells under physiological oxygen concentration for stem cell therapy success, in the field of tissue engineering and regenerative medicine.

Defining Physiological Normoxia for Improved Translation of Cell Physiology to Animal Models and Humans

The extensive oxygen gradient between the air we breathe (Po₂ ~21 kPa) and its ultimate distribution within mitochondria (as low as ~0.5-1 kPa) is testament to the efforts expended in limiting its inherent toxicity. It has long been recognized that cell culture undertaken under room air conditions falls short of replicating this protection in vitro. Despite this, difficulty in accurately determining the appropriate O₂ levels in which to culture cells, coupled with a lack of the technology to replicate and maintain a physiological O₂ environment in vitro, has hindered addressing this issue thus far. In this review, we aim to address the current understanding of tissue Po₂ distribution in vivo and summarize the attempts made to replicate these conditions in vitro. The state-of-the-art techniques employed to accurately determine O₂ levels, as well as the issues associated with reproducing physiological O₂ levels in vitro, are also critically reviewed. We aim to provide the framework for researchers to undertake cell culture under O₂ levels relevant to specific tissues and organs. We envisage that this review will facilitate a paradigm shift, enabling translation of findings under physiological conditions in vitro to disease pathology and the design of novel therapeutics.

Multiparametric High-Resolution MRI as a Tool for Mapping of Hypoxic Level in Tumors

Hypoxia is a condition, common to most malignant tumors, where oxygen tension in the tissue is below the physiological level. Among consequences of tumor hypoxia is also altered cancer cell metabolism that contributes to cancer therapy resistance. Therefore, precise assessment of tumor hypoxia is important for monitoring the tumor treatment progression. In this study, we propose a simple model for prediction of hypoxic level in tumors based on multiparametric magnetic resonance imaging. The study was performed on B16F1 murine melanoma tumors ex vivo that were first magnetic resonance scanned and then analyzed for hypoxic level using hypoxia-inducable factor 1-alpha antibody staining. Each tumor was analyzed in identical sections and in identical regions of interest for pairs of hypoxic level and magnetic resonance values (apparent diffusion coefficient and T₂). This was followed by correlation analysis between hypoxic level and respective magnetic resonance values. A moderate correlation was found between hypoxic level and apparent diffusion coefficient (ρ = 0.56, P < .00001) and lower between hypoxic level and T₂ (ρ = 0.38, P < .00001). The data were analyzed further to obtain simple predictive models based on the multiple linear regression analysis of the measured hypoxic level (dependent variable) and apparent diffusion coefficient and T₂ (independent variables). Among the hypoxic level models, the most efficient was the 3-parameter model given by relation (HL = k_ADCADC + k_T2T₂ + b), where k_ADC = 26%/µm²/ms, k_T2 = 0.8%/ms, and b = −32%. The model can be used for calculation of the predicted hypoxic level map based on magnetic resonance–measured apparent diffusion coefficient and T₂ maps. Similar prediction models, based on tumor apparent diffusion coefficient and T₂ maps, can be done also for other tumor types in vivo and can therefore help in assessment of tumor treatment as well as to better understand the role of hypoxia in cancer progression.

Bioinspired Engineering of Organ-on-Chip Devices

The human body can be viewed as an organism consisting of a variety of cellular and non-cellular materials interacting in a highly ordered manner. Its complex and hierarchical nature inspires the multi-level recapitulation of the human body in order to gain insights into the inner workings of life. While traditional cell culture models have led to new insights into the cellular microenvironment and biological control in vivo, deeper understanding of biological systems and human pathophysiology requires the development of novel model systems that allow for analysis of complex internal and external interactions within the cellular microenvironment in a more relevant organ context. Engineering organ-on-chip systems offers an unprecedented opportunity to unravel the complex and hierarchical nature of human organs. In this chapter, we first highlight the advances in microfluidic platforms that enable engineering of the cellular microenvironment and the transition from cells-on-chips to organs-on-chips. Then, we introduce the key features of the emerging organs-on-chips and their proof-of-concept applications in biomedical research. We also discuss the challenges and future outlooks of this state-of-the-art technology.

Induction and Assessment of Hypoxia in Glioblastoma Cells In Vitro

To simulate and study the hypoxic microenvironment associated with intracerebral glioma in vivo, simple and reproducible methods are described and discussed for inducing hypoxia or chemical pseudohypoxia in glioma cell cultures and assessing their effects on the expression and nuclear translocation of hypoxia-inducible factor (HIF)-1α, a key transcriptional factor of oxygen homeostasis, by Western blot analysis and immunocytochemistry.

Hypoxia and connectivity in the developing vertebrate nervous system

The developing nervous system depends upon precise regulation of oxygen levels. Hypoxia, the condition of low oxygen concentration, can interrupt developmental sequences and cause a range of molecular, cellular and neuronal changes and injuries. The roles and effects of hypoxia on the central nervous system (CNS) are poorly characterized, even though hypoxia is simultaneously a normal component of development, a potentially abnormal environmental stressor in some settings, and a clinically important complication, for example of prematurity. Work over the past decade has revealed that hypoxia causes specific disruptions in the development of CNS connectivity, altering axon pathfinding and synapse development. The goals of this article are to review hypoxia's effects on the development of CNS connectivity, including its genetic and molecular mediators, and the changes it causes in CNS circuitry and function due to regulated as well as unintended mechanisms. The transcription factor HIF1α is the central mediator of the CNS response to hypoxia (as it is elsewhere in the body), but hypoxia also causes a dysregulation of gene expression. Animals appear to have evolved genetic and molecular responses to hypoxia that result in functional behavioral alterations to adapt to the changes in oxygen concentration during CNS development. Understanding the molecular pathways underlying both the normal and abnormal effects of hypoxia on CNS connectivity may reveal novel insights into common neurodevelopmental disorders. In addition, this Review explores the current gaps in knowledge, and suggests important areas for future studies.

Summary: The nervous system's exposure to hypoxia has developmental and clinical relevance. In this Review, the authors discuss the effects of hypoxia on the development of the CNS, and its long-term behavioral and neurodevelopmental consequences.

Resistance to Plasmodium falciparum in sickle cell trait erythrocytes is driven by oxygen-dependent growth inhibition

Sickle cell trait (AS) confers partial protection against lethal Plasmodium falciparum malaria. Multiple mechanisms for this have been proposed, with a recent focus on aberrant cytoadherence of parasite-infected red blood cells (RBCs). Here we investigate the mechanistic basis of AS protection through detailed temporal mapping. We find that parasites in AS RBCs maintained at low oxygen concentrations stall at a specific stage in the middle of intracellular growth before DNA replication. We demonstrate that polymerization of sickle hemoglobin (HbS) is responsible for this growth arrest of intraerythrocytic P. falciparum parasites, with normal hemoglobin digestion and growth restored in the presence of carbon monoxide, a gaseous antisickling agent. Modeling of growth inhibition and sequestration revealed that HbS polymerization-induced growth inhibition following cytoadherence is the critical driver of the reduced parasite densities observed in malaria infections of individuals with AS. We conclude that the protective effect of AS derives largely from effective sequestration of infected RBCs into the hypoxic microcirculation.

The future of non-invasive cerebral oximetry in neurosurgical procedures: A systematic review

Background:Cerebral hypoxia is one of the most important causes of secondary brain injury during neurosurgical procedures and in neurointensive care. In patients with brain injury, cerebrovascular reactivity may be impaired and a decrease in mean arterial pressure or cerebral perfusion pressure may lead to inadequate cerebral blood flow and secondary ischemia. There are several techniques available to measure brain oxygenation. In particular, near infrared spectroscopy (NIRS) is a non-invasive neuromonitoring technique and there has been a rapid expansion of clinical evidence that NIRS reduces perioperative neurologic complications.  Methods:This systematic review synthesizes prospective and retrospective cohort studies that investigate the benefit of using NIRS in prevention of perioperative neurologic complications. The methodological quality of these studies is appraised.Results:Seven studies were included in this systematic review. The methodological quality of each study was assessed. They had representative patient populations, clear selection criteria and clear descriptions of study designs. Reproducible study protocols with ethics board approval were present. Clinical results were described in sufficient detail and were applicable to patient undergoing neurosurgical procedures and in neurointensive care. Limitations included small sample sizes and lack of reference standard.Conclusions:This systematic review synthesizes the most current evidence of non-invasive, inexpensive, and continuous measurement of cerebral oxygenation by NIRS. Results gained from these studies are clinically useful and shed light on how this neuromonitoring technique is beneficial in preventing perioperative neurological complications.