The role of neuroglobin in the neuroprotection of limb ischemic preconditioning in rats

Remote but not Distant: a Review on Experimental Models and Clinical Trials in Remote Ischemic Conditioning as Potential Therapy in Ischemic Stroke

Stroke is one of the main causes of neurological disability worldwide and the second cause of death in people over 65 years old, resulting in great economic and social burden. Ischemic stroke accounts for 85% of total cases, and the approved therapies are based on re-establishment of blood flow, and do not directly target brain parenchyma. Thus, novel therapies are urgently needed. In this review, limb remote ischemic conditioning (RIC) is revised and discussed as a potential therapy against ischemic stroke. The review targets both (i) fundamental research based on experimental models and (ii) clinical research based on clinical trials and human interventional studies with healthy volunteers. Moreover, it also presents two approaches concerning RIC mechanisms in stroke: (i) description of the underlying cerebral cellular and molecular mechanisms triggered by limb RIC that promote neuroprotection against stroke induced damage and (ii) the identification of signaling factors involved in inter-organ communication following RIC procedure. Limb to brain remote signaling can occur via circulating biochemical factors, immune cells, and/or stimulation of autonomic nervous system. In this review, these three hypotheses are explored in both humans and experimental models. Finally, the challenges involved in translating experimentally generated scientific knowledge to a clinical setting are also discussed.

Neuroglobin alleviates arsenic-induced neuronal damage

People who drink water contaminated with arsenic for a long time develop neuritis, cerebellar symptoms, and deficits in memory and intellectual function. Arsenic induces oxidative stress and promotes apoptosis through multiple signalling pathways in nerve cells. Neuroglobin (Ngb), as a key mediator, is considered to be protective against oxidative stress. In this study, we aimed to study the effects of Ngb knockdown in arsenite-treated rat neurons on levels of apoptosis markers and reactive oxygen species and serum Ngb levels of subjects from arsenic-endemic regions in China. We discovered that arsenic-induced apoptosis and reactive oxygen species production were enhanced in Ngb-knocked-down rat neurons. Silencing of Ngb aggravated the arsenic-induced decrease in the rate of Bcl-2/Bax and the levels of Bcl-2 protein following arsenite treatment. The results also showed that serum Ngb levels were independently negatively correlated with arsenic concentration in drinking water. Furthermore, the serum Ngb levels of four groups (245 individuals) according to different degree exposure to arsenic were 815.18 ± 89.52, 1247.97 ± 117.18, 774.79 ± 91.55, and 482.72 ± 49.30 pg/mL, respectively. Taken together, it can be deduced that Ngb has protective effects against arsenic-induced apoptosis by eliminating reactive oxygen species.

The Neuroprotective Effect of Hemin and the Related Mechanism in Sevoflurane Exposed Neonatal Rats

Background

Many studies have reported that sevoflurane can increase neuronal apoptosis and result in cognitive deficits in rodents. Although neurotoxicity may be associated with mitochondrial dysfunction and oxidative stress, the exact mechanism remains unclear. In order to evaluate potential treatment therapies, we studied the effects of hemin on neurotoxicity of neonatal rat sevoflurane exposure.

Methods

Postnatal day (P) seven rats were assigned randomly to four groups; (1) group C: non-anesthesia, (2) group H: intraperitoneal hemin (50 mg kg^-1) treatment on days 5 and 6, (3) group S: 3% sevoflurane exposure for 4 h, and (4) group SH: hemin treatment + sevoflurane exposure. The expression of neuroglobin in neonatal hippocampus was determined by western blot and immunohistochemistry. Neuroglobin was localized by immunofluorescence. Western blot for the expression of cleaved caspase-3 and TUNEL were used to detect neonatal hippocampal apoptosis, and cytochrome c was used to evaluate mitochondrial function. Drp-1 and Mfn-2 immunoblotting were used to assess mitochondrial dynamics. The Morris water maze test was performed to detect cognitive function in the rats on P30.

Results

Exposure to sevoflurane increased the expression of cleaved caspase-3, cytochrome c, and Drp1 in the neonatal hippocampus and resulted in cognitive deficiency but decreased expression of Mfn2. Hemin reduced apoptosis, improved mitochondrial dynamics and ameliorated the cognitive impairment caused by sevoflurane exposure.

Conclusion

Hemin reduced neuronal apoptosis, improved mitochondrial dynamics and protected against cognitive deficits induced by sevoflurane in neonatal rats. This neuroprotective effect may be achieved by increasing the expression of neuroglobin.

Effect of Shenmai injection on cognitive function after cardiopulmonary bypass in cardiac surgical patients: a randomized controlled trial

BACKGROUND

Postoperative cognitive dysfunction (POCD) is a common complication after cardiac surgery that influences the clinical outcomes and quality of life of patients. This study aimed to evaluate the effects of Shenmai injection (SMI) on POCD of patients who underwent cardiac valve replacement under cardiopulmonary bypass (CPB).

METHODS

This prospective, randomized, controlled trial was conducted from September 2014 to January 2017. Eighty-eight patients receiving cardiac valve replacement under CPB were randomized into the control (C) or the SMI (S) group. SMI (0.6 mL/kg) was administered intravenously from the time of anesthesia induction to the beginning of CPB. Cognitive function was assessed at 3 days before surgery and 3 days, 7 days, and 1 month after surgery using the Beijing version of the Montreal Cognitive Assessment (MoCA-BJ) score. The serum levels of neuroglobin (Ngb), hypoxia-inducible factor-1α (HIF-1α), and neuron-specific enolase (NSE) were measured at 30 min after induction (T₀), immediately after the endonasal temperature rewarmed to 36 °C (T₁), and 1 h (T₂), 6 h (T₃), 24 h (T₄), 48 h (T₅), and 72 h (T₆) after CPB.

RESULTS

Compared with the baseline values at T₀, the serum Ngb levels in group C were significantly decreased at T_1-2 and then increased at T_3-6, while the levels in group S were decreased at T_1-2 and increased at T_4-6, compared to group C (p < 0.05). The serum HIF-1α levels at T_1-4 and the serum NSE levels at T_1-6 were significantly increased in both groups (p < 0.05). The serum levels of Ngb at T₃, HIF-1α at T_1-3, and NSE at T_3-4,6 were lower in group S, compared to group C (p < 0.01). The MoCA-BJ scores were decreased at 3 and 7 days after surgery in both groups, and the MoCA-BJ scores in group S were higher than those in group C at 3 and 7 days after surgery (p < 0.01).

CONCLUSION

Cognitive function is impaired postoperatively in patients who have undergone cardiac valve replacement under CPB. In addition, treatment with the traditional Chinese medicine SMI decreases the serum levels of Ngb, HIF-1α, and NSE as well as attenuates cognitive dysfunction.

TRIAL REGISTRATION

This trial was registered with Clinicaltrials.gov as ChiCTR-TRC-14004373 on March 11, 2014.

Rat hippocampal CA3 neuronal injury induced by limb ischemia/reperfusion: A possible restorative effect of alpha lipoic acid

Limb ischemia reperfusion (I/R) injury is associated with serious local and systemic effects. Reperfusion may augment tissue injury in excess of that produced by ischemia alone. The hippocampus has been reported to be vulnerable to I/R injury. Alpha lipoic acid (ALA) is an endogenous antioxidant with a powerful antioxidative, anti-inflammatory, and antiapoptotic properties. We studied the probable restorative effect of ALA on limb I/R-induced structural damage of rat hippocampus. Forty adult male albino rats were divided equally into four groups: group I (sham); group II (I/R-1 day) has undergone bilateral femoral arteries occlusion (3 h), then reperfusion for 1 day; group III (I/R-7 days) has undergone reperfusion for seven days; group IV (I/R-ALA) has undergone I/R as group III and received an intraperitoneal injection of ALA (100 mg/kg) for 7 days. I/R groups revealed degenerative changes in the pyramidal neuronal perikarya of CA3 field in the form of dark-stained cytoplasm, dilated RER cisternae, mitochondrial alterations, and dense bodies' accumulation. Their dendrites showed disorganized microtubules. Astrogliosis is featured by an increased number and increased immunoreactivity of astrocytes for glial fibrillary acid protein. Morphometric data revealed significant reduction of light neurons, surface area of neurons, and thickness of the CA3 layer. Most blood capillaries exhibited narrow lumen and irregular basal lamina. ALA ameliorated the neuronal damage. Pyramidal neurons revealed preservation of normal structure. Significant increase in the thickness of pyramidal layer in CA3 field and surface area and number of light neurons was observed but astrogliosis persisted. Limb I/R had a deleterious remote effect on the hippocampus aggravated with longer period of reperfusion. This work may encourage the use of ALA in the critical clinical settings with I/R injury.

Neuroglobin mediates neuroprotection of hypoxic postconditioning against transient global cerebral ischemia in rats through preserving the activity of Na+/K+ ATPases

Hypoxic postconditioning (HPC) is an innovative neuroprotective strategy with cytoprotective effects on the hippocampal neurons against transient global cerebral ischemia (tGCI) in adult rats. However, its molecular mechanisms have not yet been adequately elucidated. Neuroglobin (Ngb) is an endogenous neuroprotectant with hypoxia-inducible property, and its role in experimental stroke has been increasingly attractive. Hence, the purpose of this study is to explore the involvement of Ngb in HPC-mediated neuroprotection and to further investigate its underlying molecular mechanism. We found that HPC increased Ngb expression in CA1 subregion after tGCI. Also, the inhibition of Ngb expression with Ngb antisense oligodeoxynucleotide (AS-ODNs) eliminated the neuroprotective effect mediated by HPC, whereas overexpression of Ngb ameliorated neuronal damage in CA1 after tGCI, indicating that HPC conferred neuroprotective effects via upregulation of Ngb. We further showed that HPC increased the membranous level of Na⁺/K⁺ ATPases β1 subunit (Atp1b1) in CA1 after tGCI. Furthermore, we demonstrated that Ngb upregulation in CA1 after HPC maintained the membranous level of Atp1b1 through Ngb-Atp1b1 interaction and reduced the glutathionylation of membranous Atp1b1 via suppression of reactive oxygen species (ROS), ultimately preserving the activity of NKA. Taken together, these data indicate that Ngb is involved in the neuroprotection of HPC against tGCI via maintenance of NKA activity in the hippocampal CA1.

Neuroimmune-Driven Neuropathic Pain Establishment: A Focus on Gender Differences

The role of neuroinflammatory cells in the establishment of neuropathic pain has been investigated in depth in the last few years. In particular, microglia have been shown to be key players in the induction of tactile allodynia, as they release proinflammatory molecules that, in turn, sensitize nociceptive neurons within the spinal cord. However, the role of peripheral immune cells such as macrophages, infiltrating monocytes, mast cells, and T-cells has been highlighted in the last few studies, even though the data are still conflicting and need to be clarified. Intriguingly, the central (microglia) and peripheral (T-cell)-adaptive immune cells that orchestrate maladaptive process-driven neuropathic pain seem to be involved in a gender-dependent manner. In this review, we highlight the role of the microglia and peripheral immune cells in chronic degenerative disease associated with neuro-immune-inflammatory processes.

Chronic intermittent hybobaric hypoxia protects against cerebral ischemia via modulation of mitoKATP

OBJECTIVE

Providing adequate protection against cerebral ischemia remains an unrealized goal. The present study was aimed at testing whether chronic intermittent hypobaric hypoxia (CIHH) would have protective effects against cerebral ischemia and investigating the potential role of mitochondrial membrane ATP-sensitive potassium channel (mitoK_ATP) in this effect.

METHODS

Ischemia was induced in rats by occlusion of bilateral common carotid arteries for 8min on day 2 after bilateral vertebral arteries were permanently electrocauterized and CIHH was simulated in a hypoxic chamber. Learning and memory impairments were analyzed using the Morris water maze. The delay neuronal death (DND) in the hippocampus CA1 was observed by thionine staining. The expression of the two subunits of mitoK_ATP, SUR1 and Kir 6.2, and the concentration of cytochrome c (Cyt c) were observed by Western blotting. The mitochondrial membrane potential (Δym) was determined by flow cytometry. Morphological changes of the mitochondria were investigated by electron microscopy. The antagonist of mitoK_ATP, 5-hydroxydecanoate (5-HD), was used to demonstrate the involvement of mitoK_ATP.

RESULTS

CIHH pretreatment ameliorated the learning and memory impairments produced by ischemia, concomitant with reduced DND in the hippocampus CA1 area. Expression levels of SUR1 and Kir6.2 both increased for at least one week after CIHH pretreatment. Levels of the two subunits were higher in the CIHH pretreatment combined with ischemia group than the ischemia only group at 2 d and 7 d after ischemia. Furthermore, the concentration of Cyt c was decreased in mitochondria and increased in the cytoplasm after ischemia which was prevented by CIHH. The decrease of Δψm and the destruction of mitochondrial ultrastructure were both rescued by CIHH pretreatment. The above protective effects of CIHH were blocked by 5-HD intraperitoneal injection 30min before ischemia.

CONCLUSION

CIHH pretreatment can reduce cerebral ischemic injury, which is mediated by upregulating the expression and activity of mitoK_ATP.

Neuroglobin – recent developments

Neuroglobin (Ngb), a monomeric hexacoordinated heme protein of 17 kDa, was identified in 2000 in the nervous system. Accumulative evidence has proved that Ngb is an endogenous neuroprotective molecule against ischemic/hypoxic insults and oxidative stresses, and in most ischemic conditions, Ngb is up-regulated. The underlying mechanisms, however, are not fully clarified. Here we review the recent experimental findings, mainly focusing on the mechanisms of Ngb’s protection and induction during ischemic/hypoxic conditions, the roles of Ngb in astrocytes and tumors, as well as Ngb’s function in neurite outgrowth.

Neuroglobin expression and oxidant/antioxidant balance after graded traumatic brain injury in the rat

Neuroglobin is a neuron-specific hexacoordinated globin capable of binding various ligands, including O2, NO, and CO, the biological function of which is still uncertain. Various studies seem to indicate that neuroglobin is a neuroprotective agent when overexpressed, acting as a potent inhibitor of oxidative and nitrosative stress. In this study, we evaluated the pathophysiological response of the neuroglobin gene and protein expression in the cerebral tissue of rats sustaining traumatic brain injury of differing severity, while simultaneously measuring the oxidant/antioxidant balance. Two levels of trauma (mild and severe) were induced in anesthetized animals using the weight-drop model of diffuse axonal injury. Rats were then sacrificed at 6, 12, 24, 48, and 120 h after traumatic brain injury, and the gene and protein expression of neuroglobin and the concentrations of malondialdehyde (as a parameter representative of reactive oxygen species-mediated damage), nitrite + nitrate (indicative of NO metabolism), ascorbate, and glutathione (GSH) were determined in the brain tissue. Results indicated that mild traumatic brain injury, although causing a reversible increase in oxidative/nitrosative stress (increase in malondialdehyde and nitrite + nitrate) and an imbalance in antioxidants (decrease in ascorbate and GSH), did not induce any change in neuroglobin. Conversely, severe traumatic brain injury caused an over nine- and a fivefold increase in neuroglobin gene and protein expression, respectively, as well as a remarkable increase in oxidative/nitrosative stress and depletion of antioxidants. The results of this study, showing a lack of effect in mild traumatic brain injury as well as asynchronous time course changes in neuroglobin expression, oxidative/nitrosative stress, and antioxidants in severe traumatic brain injury, do not seem to support the role of neuroglobin as an endogenous neuroprotective antioxidant agent, at least under pathophysiological conditions.

Neuroglobin involvement in the course of arsenic toxicity in rat cerebellar granule neurons

Exposure to arsenic in drinking water results in a widespread environmental problem in the world, and the brain is a major target. Neuroglobin is a vertebrate heme protein regarded as playing neuroprotective role in hypoxia or oxidative stress. In this study, we investigated the toxic effects of sodium arsenite (NaAsO2) on primary cultured rat cerebellar granule neurons (CGNs) and detected neuroglobin (Ngb) expression in rat CGNs exposed to NaAsO2. Our results show that apoptosis was obviously induced by NaAsO2 treatment in rat CGNs by annexin V-fluorescein isothiocyanate assay. Intracellular reactive oxygen species generation increased significantly in the cells exposed to NaAsO2, and the apoptotic effects could be partially reversed by antioxidant N-acetyl-L-cysteine. Ngb protein and mRNA expression were significantly downregulated in rat CGNs shortly after NaAsO2 exposure and then upregulated after a longer time of exposure. Furthermore, mRNA expression changed more than protein expression and the toxic effect of NaAsO2 on Ngb expression is dose dependent. Higher Ngb expression was also detected in rat cerebellum, but not in other parts (cerebrum, hippocampus, and midbrain) of the brain exposed to NaAsO2 for 16 weeks. Taken together, cytotoxic effects of NaAsO2 on rat CGNs is induced at least partly by oxidative stress and Ngb may influence the course of arsenic toxicity in rat CGNs and rat cerebellum.

Neuroglobin involvement in visual pathways through the optic nerve

Neuroglobin is a member of the globin superfamily proposed to be only expressed in neurons and involved in neuronal protection from hypoxia or oxidative stress. A significant fraction of the protein localizes within the mitochondria and is directly associated with mitochondrial metabolism and integrity. The retina is the site of the highest concentration for neuroglobin and has been reported to be up to 100-fold higher than in the brain. Since neuroglobin was especially abundant in retinal ganglion cell layer, we investigated its abundance in optic nerves. Remarkably in optic nerves, neuroglobin is observed, as expected, in retinal ganglion cell axon profiles but also astrocyte processes, in physiological conditions, possess high levels of the protein. Neuroglobin mRNA and protein levels are ~10-fold higher in optic nerves than in retinas, indicating an important accumulation of neuroglobin in these support cells. Additionally, neuroglobin levels increase in Müller cells during reactive gliosis in response to eye injury. This suggests the pivotal role of neuroglobin in retinal glia involved in neuronal support and/or healing. This article is part of a Special Issue entitled: Oxygen Binding and Sensing Proteins.