Neuroprotective effects of therapeutic hypercapnia on spatial memory and sensorimotor impairment via anti-apoptotic mechanisms after focal cerebral ischemia/reperfusion

Relationship between Hypoxia and Hypercapnia Tolerance and Life Expectancy

The review discusses the potential relationship between hypoxia resistance and longevity, the influence of carbon dioxide on the mechanisms of aging of the mammalian organism, and intermittent hypercapnic-hypoxic effects on the signaling pathways of aging mechanisms. In the article, we focused on the potential mechanisms of the gero-protective efficacy of carbon dioxide when combined with hypoxia. The review summarizes the possible influence of intermittent hypoxia and hypercapnia on aging processes in the nervous system. We considered the perspective variants of the application of hypercapnic-hypoxic influences for achieving active longevity and the prospects for the possibilities of developing hypercapnic-hypoxic training methods.

Molecular Mechanisms of Neuroprotection after the Intermittent Exposures of Hypercapnic Hypoxia

The review introduces the stages of formation and experimental confirmation of the hypothesis regarding the mutual potentiation of neuroprotective effects of hypoxia and hypercapnia during their combined influence (hypercapnic hypoxia). The main focus is on the mechanisms and signaling pathways involved in the formation of ischemic tolerance in the brain during intermittent hypercapnic hypoxia. Importantly, the combined effect of hypoxia and hypercapnia exerts a more pronounced neuroprotective effect compared to their separate application. Some signaling systems are associated with the predominance of the hypoxic stimulus (HIF-1α, A1 receptors), while others (NF-κB, antioxidant activity, inhibition of apoptosis, maintenance of selective blood-brain barrier permeability) are mainly modulated by hypercapnia. Most of the molecular and cellular mechanisms involved in the formation of brain tolerance to ischemia are due to the contribution of both excess carbon dioxide and oxygen deficiency (ATP-dependent potassium channels, chaperones, endoplasmic reticulum stress, mitochondrial metabolism reprogramming). Overall, experimental studies indicate the dominance of hypercapnia in the neuroprotective effect of its combined action with hypoxia. Recent clinical studies have demonstrated the effectiveness of hypercapnic-hypoxic training in the treatment of childhood cerebral palsy and diabetic polyneuropathy in children. Combining hypercapnic hypoxia with pharmacological modulators of neuro/cardio/cytoprotection signaling pathways is likely to be promising for translating experimental research into clinical medicine.

Ultrastructural Changes in Hippocampal Region CA1 Neurons After Exposure to Permissive Hypercapnia and/or Normobaric Hypoxia

Isolated exposure to intermittent hypoxia and permissive hypercapnia activates signaling mechanisms that induce ultrastructural changes in mitochondria and endoplasmic reticulum, accompanied by the development of maximal ischemic tolerance in neurons under the combined influence of these factors. However, there are a lack of data on the combined impact of these factors on the ultrastructure of neuronal organelles. The present study aims to comparatively assess the ultrastructural changes in neurons following isolated and combined exposure to hypoxia and hypercapnia, as well as to correlate these changes with the neuroprotective potential previously observed for these factors. Following a 15-session course of 30-min exposures to permissive hypercapnia (PCO2 ≈ 50 mmHg) and/or normobaric hypoxia (PO2 ≈ 150 mmHg), morphometric assessment was conducted to evaluate the extent of ultrastructural changes in hippocampal neurons (mitochondria, perinuclear space, and granular endoplasmic reticulum). It was found that in hippocampal neurons from the CA1 region, permissive hypercapnia resulted in increased mitochondrial size, expansion of membranous compartments of the granular endoplasmic reticulum, and perinuclear space. Normobaric hypoxia affected only mitochondrial size, while hypercapnic hypoxia specifically widened the perinuclear space. These ultrastructural changes objectively reflect varying degrees of the influence of hypoxia and hypercapnia on organelles responsible for energy metabolism, anti-apoptotic, and synthetic functions of neurons. This confirms the effect of potentiation of their neuroprotective effects under combined exposure and highlights the dominant role of the hypercapnic component in this mechanism.

Carbon dioxide and MAPK signalling: towards therapy for inflammation

Inflammation, although necessary to fight infections, becomes a threat when it exceeds the capability of the immune system to control it. In addition, inflammation is a cause and/or symptom of many different disorders, including metabolic, neurodegenerative, autoimmune and cardiovascular diseases. Comorbidities and advanced age are typical predictors of more severe cases of seasonal viral infection, with COVID-19 a clear example. The primary importance of mitogen-activated protein kinases (MAPKs) in the course of COVID-19 is evident in the mechanisms by which cells are infected with SARS-CoV-2; the cytokine storm that profoundly worsens a patient's condition; the pathogenesis of diseases, such as diabetes, obesity, and hypertension, that contribute to a worsened prognosis; and post-COVID-19 complications, such as brain fog and thrombosis. An increasing number of reports have revealed that MAPKs are regulated by carbon dioxide (CO2); hence, we reviewed the literature to identify associations between CO2 and MAPKs and possible therapeutic benefits resulting from the elevation of CO2 levels. CO2 regulates key processes leading to and resulting from inflammation, and the therapeutic effects of CO2 (or bicarbonate, HCO3-) have been documented in all of the abovementioned comorbidities and complications of COVID-19 in which MAPKs play roles. The overlapping MAPK and CO2 signalling pathways in the contexts of allergy, apoptosis and cell survival, pulmonary oedema (alveolar fluid resorption), and mechanical ventilation-induced responses in lungs and related to mitochondria are also discussed. Video Abstract.

Stellate ganglion block potentially ameliorates postoperative cognitive decline in aged rats by regulating the neuroendocrine response to stress

Background

Postoperative cognitive dysfunction (POCD) is a common postoperative complication in elderly patients. The strong stress response causing by surgical trauma can induce POCD. We hypothesized that stellate ganglion block (SGB) can provide the neuroprotection to POCD by regulating the neuroendocrine response.

Methods

Sprague-Dawley male rats, 18-20 months old and weighing 550-650 g were assigned into four groups: sham surgery group (Sham), sham surgery + saline group (Sham + NS), surgery group (Surgery), and surgery + SGB group (Surgery + SGB). The change of body weight, heart rate variability analysis, behavior testing, neuronal damage, inflammatory response, neuroendocrine hormone level were evaluated by their corresponding methods.

Results

The results showed that SGB can reduce the number of both types of errors in the postoperative eight-arm maze assay, attenuate neural structural damage, inhibit neuroapoptosis, suppress inflammatory responses, increase the release of neurotrophic factors, accelerate postoperative weight recovery, and promote postoperative recovery in rats. Most importantly, SGB reduced the level of neuroendocrine hormone of TH, Cyp11b1, CRH, and SGB also activated dorsal motor nucleus of vagus (detected by c-fos immunohistochemistry).

Conclusions

Our findings indicated that SGB could be a neuroprotective therapy for the cognitive dysfunction induced by exploratory laparotomy model of POCD, which might be attributable for balancing the autonomic nervous system, regulating hypothalamic-pituitary-adrenal (HPA) axis system.

Understanding the Therapeutic Approaches for Neuroprotection

The term "neurodegenerative disorders" refers to a group of illnesses in which deterioration of nerve structure and function is a prominent feature. Cognitive capacities such as memory and decision-making deteriorate as a result of neuronal damage. The primary difficulty that remains is safeguarding neurons since they do not proliferate or regenerate spontaneously and are therefore not substituted by the body after they have been damaged. Millions of individuals throughout the world suffer from neurodegenerative diseases. Various pathways lead to neurodegeneration, including endoplasmic reticulum stress, calcium ion overload, mitochondrial dysfunction, reactive oxygen species generation, and apoptosis. Although different treatments and therapies are available for neuroprotection after a brain injury or damage, the obstacles are inextricably connected. Several studies have revealed the pathogenic effects of hypothermia, different breathed gases, stem cell treatments, mitochondrial transplantation, multi-pharmacological therapy, and other therapies that have improved neurological recovery and survival outcomes after brain damage. The present review highlights the use of therapeutic approaches that can be targeted to develop and understand significant therapies for treating neurodegenerative diseases.

Potential Therapeutic Effects of Mi-Jian-Chang-Pu Decoction on Neurochemical and Metabolic Changes of Cerebral Ischemia-Reperfusion Injury in Rats

As a traditional Chinese medicine formula, Mi-Jian-Chang-Pu decoction (MJCPD) has been successfully used in patients with language dysfunction and hemiplegia after ischemic stroke (IS). Given the excellent protective effects of MJCPD against nerve damage caused by IS in clinical settings, the present investigation mainly focused on its underlying mechanism on ischemia-reperfusion (IR) injury. Firstly, by applying the MCAO-induced cerebral IR injury rats, the efficacy of MJCPD on IS was estimated using the neurological deficit score, TTC, HE, and IHC staining, and neurochemical measurements. Secondly, an UHPLC-QTOF-MS/MS-based nontargeted metabolomics was developed to elucidate the characteristic metabolites. MJCPD groups showed significant improvements in the neurological score, infarction volume, and histomorphology, and the changes of GSH, GSSG, GSH-PX, GSSG/GSH, LDH, L-LA, IL-6, TNF-α, and VEGF-c were also reversed to normal levels after the intervention compared to the MCAO model group. Metabolomics profiling identified 21 different metabolites in the model group vs. the sham group, 10 of which were significantly recovered after treatment of MJCPD, and those 10 metabolites were all related to the oxidative stress process including glucose, fatty acid, amino acid, glutamine, and phospholipid metabolisms. Therefore, MJCPD might protect against IS by inhibiting oxidative stress during IR.

Recent advances in the neuroprotective effects of medical gases

Central nervous system injuries are a leading cause of death and disability worldwide. Although the exact pathophysiological mechanisms of various brain injuries vary, central nervous system injuries often result in an inflammatory response, and subsequently lead to brain damage. This suggests that neuroprotection may be necessany in the treatment of multiple disease models. The use of medical gases as neuroprotective agents has gained great attention in the medical field. Medical gases include common gases, such as oxygen, hydrogen and carbon dioxide; hydrogen sulphide and nitric oxide that have been considered toxic; volatile anesthetic gases, such as isoflurane and sevoflurane; and inert gases like helium, argon, and xenon. The neuroprotection from these medical gases has been investigated in experimental animal models of various types of brain injuries, such as traumatic brain injury, stroke, subarachnoid hemorrhage, cerebral ischemic/reperfusion injury, and neurodegenerative diseases. Nevertheless, the transition into the clinical practice is still lagging. This delay could be attributed to the contradictory paradigms and the conflicting results that have been obtained from experimental models, as well as the presence of inconsistent reports regarding their safety. In this review, we summarize the potential mechanisms underlying the neuroprotective effects of medical gases and discuss possible candidates that could improve the outcomes of brain injury.

Optimizing functional outcome endpoints for stroke recovery studies

Novel therapeutic intervention that aims to enhance the endogenous recovery potential of the brain during the subacute phase of stroke has produced promising results. The paradigm shift in treatment approaches presents new challenges to preclinical and clinical researchers alike, especially in the functional endpoints domain. Shortcomings of the "neuroprotection" era of stroke research are yet to be fully addressed. Proportional recovery observed in clinics, and potentially in animal models, requires a thorough reevaluation of the methods used to assess recovery. To this end, this review aims to give a detailed evaluation of functional outcome measures used in clinics and preclinical studies. Impairments observed in clinics and animal models will be discussed from a functional testing perspective. Approaches needed to bridge the gap between clinical and preclinical research, along with potential means to measure the moving target recovery, will be discussed. Concepts such as true recovery of function and compensation and methods that are suitable for distinguishing the two are examined. Often-neglected outcomes of stroke, such as emotional disturbances, are discussed to draw attention to the need for further research in this area.

Hypercapnia increases brain viscoelasticity

Brain function, the brain's metabolic activity, cerebral blood flow (CBF), and intracranial pressure are intimately linked within the tightly autoregulated regime of intracranial physiology in which the role of tissue viscoelasticity remains elusive. We applied multifrequency magnetic resonance elastography (MRE) paired with CBF measurements in 14 healthy subjects exposed to 5-min carbon dioxide-enriched breathing air to induce cerebral vasodilatation by hypercapnia. Stiffness and viscosity as quantified by the magnitude and phase angle of the complex shear modulus, |G*| and ϕ, as well as CBF of the whole brain and 25 gray matter sub-regions were analyzed prior to, during, and after hypercapnia. In all subjects, whole-brain stiffness and viscosity increased due to hypercapnia by 3.3 ± 1.9% and 2.0 ± 1.1% which was accompanied by a CBF increase of 36 ± 15%. Post-hypercapnia, |G*| and ϕ reduced to normal values while CBF decreased by 13 ± 15% below baseline. Hypercapnia-induced viscosity changes correlated with CBF changes, whereas stiffness changes did not. The MRE-measured viscosity changes correlated with blood viscosity changes predicted by the Fåhræus-Lindqvist model and microvessel diameter changes from the literature. Our results suggest that brain viscoelastic properties are influenced by microvessel blood flow and blood viscosity: vasodilatation and increased blood viscosity due to hypercapnia result in an increase in MRE values related to viscosity.

Evaluation of the effects of the green nanoparticles zinc oxide on monosodium glutamate-induced toxicity in the brain of rats

Background

Monosodium glutamate (MSG) is used extensively as a food additive in the diets of many countries around the world.

Aim of the study

Our aim was to determine the effects of green zinc oxide nanoparticles on MSG-induced oxidative damage, neurotransmitter changes, and histopathological alternation in the cerebral cortexes of rats.

Methods

MSG was administered orally at two doses of 6 and 17.5 mg/kg body weight. The higher dose was associated with a significant decline in the activities of superoxide dismutase, catalase, and glutathione peroxidase, as well as the levels of brain-derived neurotrophic factor (BDNF) and glutathione (GSH) in the cerebral cortex of rats.

Results

The administration of zinc oxide nanoparticles/green tea extract (ZnO NPs/GTE) to 17.5 mg/kg MSG-treated rats was associated with significant improvements in all parameters previously shown to be altered by MSG. The higher dose of MSG induced significant histopathological variation in brain tissue. Co-treatment of rats with ZnO NPs/GTE and MSG-HD inhibited the reduction of neurotransmitters and acetylcholinesterase by MSG.

Conclusions

ZnO NPs/GTE have the potential to protect against oxidative stress and neuronal necrosis induced by MSG-HD. ZnO NPs/GTE conferred a greater benefit than the control treatment or ZnO NPs or GTE administered separately.

Calcitriol alleviates global cerebral ischemia-induced cognitive impairment by reducing apoptosis regulated by VDR/ERK signaling pathway in rat hippocampus

BACKGROUND

Vitamin D (VD) has important neuroprotective functions in the central nervous system. However, further exploration is still needed in the neuroprotective effects of VD monomer therapy on global cerebral ischemia (GCI) and its potential molecular mechanism.

OBJECTIVE

To investigate whether calcitriol, a biologically active metabolite of VD, could alleviate cognitive impairment induced by GCI via reducing cell apoptosis and activating the extracellular signal-regulated kinase (ERK) signaling pathway.

METHODS

A total of 145 adult male Sprague Dawley rats were randomly divided into five groups: Sham group (n = 45), GCI group (n = 45), calcitriol treatment group (GCI + calcitriol, n = 45), PD98059 treatment group (n = 5) and vehicle group (n = 5). Morris water maze test was used for evaluating spatial learning and memory functions. Neurological Severity Score and wet-dry weight method were applied to detect neurological deficits and brain water content, respectively. Hematoxylin and eosin staining, transmission electron microscopy, and terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick end-labeling staining were performed for evaluating the changes of hippocampal CA1 neurons. Immunocytochemistry, immunofluorescence chemistry, and western blot analysis were performed for evaluating the changes of related proteins.

RESULTS

Calcitriol significantly ameliorated the spatial learning and memory impairments, improved neurological function, attenuated brain edema, and improved the morphological defects in the CA1 area of the hippocampus. Besides, calcitriol reduced GCI-induced cell apoptosis and reversed the up-regulation of pro-apoptotic proteins (Caspase-3 and Bax) and the down-regulation of anti-apoptotic protein (Bcl-2). Furthermore, calcitriol also increased the expression of VD receptors (VDR) and activated the ERK signaling pathway. Moreover, the p-ERK1/2 inhibitor PD98059 reversed the effect of calcitriol on the expression of apoptosis-related proteins.

CONCLUSIONS

Calcitriol may have a protective effect against GCI-induced cognitive impairments via inhibition of apoptotic cascade by activating the VDR/ERK signaling pathway.

ESE1 expression correlates with neuronal apoptosis in the hippocampus after cerebral ischemia/reperfusion injury

Epithelial-specific ETS-1 (ESE1), a member of the ETS transcription factor family, is widely expressed in multiple tissues and performs various functions in inflammation. During neuroinflammation, ESE1 promotes neuronal apoptosis; however, the expression and biological functions of ESE1 remain unclear after cerebral ischemia/reperfusion. We performed in vivo and in vitro experiments to explore the role of ESE1 in cerebral ischemic injury. A modified four vessel occlusion method was used in adult Sprague-Dawley rats. At 6, 12, 24, 48, and 72 hours after model induction, the hippocampus was collected for analysis. Western blot assays and immunohistochemistry showed that the expression of ESE1, phosphorylated p65 and active caspase-3 was significantly up-regulated after ischemia. Double immunofluorescence staining indicated that ESE1 and NeuN were mostly co-located in the hippocampus after ischemia. Furthermore, ESE1 was also co-expressed with active caspase-3. PC12 cells were stimulated with cobalt chloride (CoCl₂) to establish a chemical hypoxia model. After ESE1 knockdown by siRNA for 6 hours, cell viability was detected by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide assays. The levels of ESE1, phosphorylated p65 and active caspase-3 were also remarkably increased in PC12 cells after CoCl₂ stimulation. After ESE1 knockdown, PC12 cell viability was increased after hypoxia. siRNA knockdown of ESE1 decreased the level of p-p65 and active caspase-3 after CoCl₂ stimulation. These data reveal that ESE1 levels are elevated in the hippocampus after cerebral ischemia/reperfusion injury. This may play a role in neuronal apoptosis via activation of the nuclear factor-κB pathway.

Pediatric acute respiratory distress syndrome - current views

Acute respiratory distress syndrome (ARDS) mainly involves acute respiratory failure. In addition to this affected patients feel progressive arterial hypoxemia, dyspnea, and a marked increase in the work of breathing. The only clinical solution for the above pathological state is ventilation. Mechanical ventilation is necessary to support life in ARDs but it itself worsen lung injury and the term is known clinically as ‘ventilation induced lung injury’ (VILI). At the cellular level, respiratory epithelial cells are subjected to cyclic stretch, i.e. repeated cycles of positive and negative strain, during normal tidal ventilation. In aerated areas of diseased lungs, or even normal lungs subjected to injurious positive pressure mechanical ventilation, the cells are at risk of being over distended, and worsening injury by disrupting the alveolar epithelial barrier. Further, hypercapnic acidosis (HCA) in itself confers protection from stretch injury, potentially via a mechanisms involving inhibition of nuclear factor κB (NF-κB), a transcription factor central to inflammation, injury and repair. Mesenchymal stem cells are the latest in the field and are being investigated as a possible therapy for ARDS.

Upregulation of Cdh1 signaling in the hippocampus attenuates brain damage after transient global cerebral ischemia in rats

Cerebral ischemia is a major cause of brain dysfunction. The E3 ubiquitin ligase anaphase-promoting complex and its coactivator Cdh1 have been reported to be involved in the regulation of neuronal survival, differentiation, axonal growth and synaptic development in the central nervous system. However, its role in the ischemic brain and the underlying mechanisms remain poorly understood. The present study aimed to investigate the effects of Cdh1 overexpression on the ischemic rat brain by direct intra-hippocampal injection of lentivirus-delivered Cdh1 before transient global cerebral ischemia reperfusion. Spatial memory acquisition and retention were assessed using a Morris water maze task. Neuronal damage, glial activation, oxidative stress and the synaptic ultrastructure were also examined. The results indicated that a recombinant Cdh1-encoding lentiviral vector can upregulate the expression of Cdh1 in the rat hippocampus. Cdh1 overexpression increased the survival rates of rats, reversed the abnormal accumulation of cyclin B1, alleviated neuronal death, inhibited glial activation, mitigated oxidative stress, modulated synaptic plasticity and improved neurological deficits caused by ischemia. Our study indicates that targeting the Cdh1 signaling pathway in the hippocampus may provide a promising therapeutic strategy for the clinical treatment of transient global cerebral ischemia.

Methylprednisolone sodium succinate reduces BBB disruption and inflammation in a model mouse of intracranial haemorrhage

Inflammation and disruption of the blood-brain barrier (BBB) cause oedema and secondary brain injury after intracranial haemorrhage (ICH), which is closely related to patient prognosis. Methylprednisolone sodium succinate (MPSS), a well-known immunosuppressive agent, is widely applied in many diseases to inhibit inflammation. In this study, we investigated the effect of MPSS on inflammation and disruption of the BBB in a model mouse of ICH. ICH was induced by injecting collagenase into the right striatum of male C57/BL mice. Permeability of BBB was measured with Evans Blue assay and brain oedema was detected by measurement of brain water content. Expressions of NF-κB, TLR4, occludin, ZO-1, IL-1β, TNF-α, Bax, and Bcl-2 were determined by Western Blot. Neutrophils, microglia were measured by immunohistochemistry staining, neuronal apoptosis was measured by TUNEL and NeuN co-stained. Administration of MPSS post-ICH significantly reduced permeability of the BBB and brain oedema and upregulated expression of ZO-1 and Occludin. MPSS inhibited inflammatory responses, including reducing proinflammatory cytokines (IL-1β, TNF-α), suppressing infiltration of neutrophils and activation of microglia. This was accompanied by attenuated activation of the TLR4/NF-κB signalling pathway. In addition, MPSS reduced neuronal apoptosis through increasing Bcl-2 expression and reducing Bax expression. MPSS suppressed inflammatory responses, attenuated disruption of the BBB and reduced neuronal apoptosis, contributing to reduction of secondary brain injury after ICH. These results suggest that MPSS may be a potential therapy for ICH.

Neuroprotective effects of human umbilical cord-derived mesenchymal stromal cells combined with nimodipine against radiation-induced brain injury through inhibition of apoptosis

BACKGROUND AIMS

Mesenchymal stromal cells (MSCs) possess the ability to repair brain injuries. Additionally, nimodipine is a neuroprotective agent that increases cerebral blood flow and may help with the homing of MSCs to the injury site. Here we investigate the effectiveness of a combined human umbilical cord-derived MSCs and nimodipine therapy in radiation-induced brain injury (RIBI).

METHODS

Female mice received whole brain irradiation (WBI) and were treated with saline, nimodipine, hUC-MSCs, or hUC-MSCs combined with nimodipine. Body weight was measured weekly. An open field test for locomotor activity and a step-down avoidance test for learning and memory function were conducted at week 4 and week 12 post-WBI. The histological damage was evaluated by hematoxylin and eosin staining and glial fibrillary acidic protein immunohistochemistry. Quantitative polymerase chain reaction and Western blotting were used to detect apoptosis-related mediators (p53, Bax and Bcl-2).

RESULTS

In mice receiving the hUC-MSCs or the combined treatment, their body weight recovered, their locomotor and cognitive ability improved, and the percentage of necrotic neurons and astrocytes was reduced. The combined therapy was significantly (P < 0.05) more effective than hUC-MSCs alone; these mice showed decreased expression of pro-apoptotic indicators (p53, Bax) and increased expression of an anti-apoptotic indicator (Bcl-2), which may protect brain cells.

CONCLUSIONS

We demonstrated that hUC-MSCs therapy helps recover body weight loss and behavior dysfunction in a mice model of RIBI. Moreover, the effectiveness of the combined hUC-MSCs and nimodipine therapy is due to apoptosis inhibition and enhancing homing of MSCs to the injured brain.

Relationship between PCO2 and unfavorable outcome in infants with moderate-to-severe hypoxic ischemic encephalopathy

BACKGROUND

Abnormal PCO2 is common in infants with hypoxic ischemic encephalopathy (HIE). The objective was to determine whether hypocapnia was independently associated with unfavorable outcome (death or severe neurodevelopmental disability at 18 mo) in infants with moderate-to-severe HIE.

METHODS

This was a post hoc analysis of the CoolCap Study in which infants were randomized to head cooling or standard care. Blood gases were measured at prespecified times after randomization. PCO2 and follow-up data were available for 196 of 234 infants. Analyses were performed to investigate the relationship between hypocapnia in the first 72 h after randomization and unfavorable outcome.

RESULTS

After adjusting for pH, amplitude-integrated electroencephalogram background and seizures, birth weight, Apgar score at 5 min, cooling status, and Sarnat stage, PCO2 was inversely associated with unfavorable outcome (P < 0.001). The probability of unfavorable outcome was 0.20 ± 0.1 (point estimate ± SE), 0.53 ± 0.23 and 0.89 ± 0.16 for a PCO2 of 40, 30, and 20 mm Hg respectively and was greater in infants with severe HIE than with moderate HIE.

CONCLUSIONS

Hypocapnia in infants with moderate-to-severe HIE was independently associated with unfavorable outcome. Future studies of controlled normocapnia will be important.

Effects of Acute Systemic Hypoxia and Hypercapnia on Brain Damage in a Rat Model of Hypoxia-Ischemia

Therapeutic hypercapnia has the potential for neuroprotection after global cerebral ischemia. Here we further investigated the effects of different degrees of acute systemic hypoxia in combination with hypercapnia on brain damage in a rat model of hypoxia and ischemia. Adult wistar rats underwent unilateral common carotid artery (CCA) ligation for 60 min followed by ventilation with normoxic or systemic hypoxic gas containing 11%O2,13%O2,15%O2 and 18%O2 (targeted to PaO2 30-39 mmHg, 40-49 mmHg, 50-59 mmHg, and 60-69 mmHg, respectively) or systemic hypoxic gas containing 8% carbon dioxide (targeted to PaCO2 60-80 mmHg) for 180 min. The mean artery pressure (MAP), blood gas, and cerebral blood flow (CBF) were evaluated. The cortical vascular permeability and brain edema were examined. The ipsilateral cortex damage and the percentage of hippocampal apoptotic neurons were evaluated by Nissl staining and terminal deoxynucleotidyl transferase-mediated 2'-deoxyuridine 5'-triphosphate-biotin nick end labeling (TUNEL) assay as well as flow cytometry, respectively. Immunofluorescence and western blotting were performed to determine aquaporin-4 (AQP4) expression. In rats treated with severe hypoxia (PaO2 < 50 mmHg), hypercapnia augmented the decline of MAP with cortical CBF and damaged blood-brain barrier permeability (p < 0.05). In contrast, in rats treated with mild to moderate hypoxia (PaO2 > 50 mmHg), hypercapnia protected against these pathophysiological changes. Moreover, hypercapnia treatment significantly reduced brain damage in the ischemic ipsilateral cortex and decreased the percentage of apoptotic neurons in the hippocampus after the CCA ligated rats were exposed to mild or moderate hypoxemia (PaO2 > 50 mmHg); especially under mild hypoxemia (PaO2 > 60 mmHg), hypercapnia significantly attenuated the expression of AQP4 protein with brain edema (p < 0.05). Hypercapnia exerts beneficial effects under mild to moderate hypoxemia and augments detrimental effects under severe hypoxemia on brain damage in a rat model of hypoxia-ischemia.

Suppressing Receptor-Interacting Protein 140: a New Sight for Salidroside to Treat Cerebral Ischemia

The purpose of the current study was to detect the effect of salidroside (Sal) on cerebral ischemia and explore its potential mechanism. Middle cerebral artery occlusion (MCAO) was performed to investigate the effects of Sal on cerebral ischemia. The rats were randomly divided into five groups: sham group, vehicle group, clopidogrel (7.5 mg/kg) group, Sal (20 mg/kg) group, and Sal (40 mg/kg) group. SH-SY5Y cells were exposed to ischemia-reperfusion (I/R) injury to verify the protective effect of Sal in vitro. We also built the stable receptor-interacting protein 140 (RIP140)-overexpressing SH-SY5Y cells. The results showed that Sal significantly reduces brain infarct size and cerebral edema. Sal could effectively decrease the levels of interleukin-6 (IL-6), interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α) in serum of the MCAO rats and supernatant of I/R-induced SH-SY5Y cells. Immunohistochemical and Western blot results demonstrated that Sal inhibited RIP140-mediated inflammation and apoptosis in the MCAO rats and SH-SY5Y cells. In addition, we further confirmed that RIP140/NF-κB signaling plays a crucial role by evaluating the protein expression in RIP140-overexpressing SH-SY5Y cells. Our findings suggested that Sal could be used as an effective neuroprotective agent for cerebral ischemia due to its significant effect on preventing neuronal cell injury after cerebral ischemia both in vivo and in vitro by the inhibitions of RIP140-mediated inflammation and apoptosis.

Hypercapnia: clinical relevance and mechanisms of action

PURPOSE OF REVIEW

Multiple clinical and laboratory studies have been conducted to illustrate the effects of hypercapnia in a range of injuries, and to understand the mechanisms underlying these effects. The aim of this review is to highlight and interpret information obtained from these recent reports and discuss how they may inform the clinical context.

RECENT FINDINGS

In the last decade, several important articles have addressed key elements of how carbon dioxide interacts in critical illness states. Among them the most important insights relate to how hypercapnia affects critical illness and include the effects and mechanisms of carbon dioxide in pulmonary hypertension, infection, inflammation, diaphragm dysfunction, and cerebral ischemia. In addition, we discuss molecular insights that apply to multiple aspects of critical illness.

SUMMARY

Experiments involving hypercapnia have covered a wide range of illness models with varying degrees of success. It is becoming evident that deliberate hypercapnia in the clinical setting should seldom be used, except wherever necessitated to avoid ventilator-associated lung injury. A more complete understanding of the molecular mechanisms must be established.