Combination of HBO and Memantine in Focal Cerebral Ischemia: Is There a Synergistic Effect?

Hyperbaric oxygen therapy for the treatment of hypoxic/ischemic injury upon perinatal asphyxia-are we there yet?

Birth asphyxia and its main sequel, hypoxic-ischemic encephalopathy, are one of the leading causes of children's deaths worldwide and can potentially worsen the quality of life in subsequent years. Despite extensive research efforts, efficient therapy against the consequences of hypoxia-ischemia occurring in the perinatal period of life is still lacking. The use of hyperbaric oxygen, improving such vital consequences of birth asphyxia as lowered partial oxygen pressure in tissue, apoptosis of neuronal cells, and impaired angiogenesis, is a promising approach. This review focused on the selected aspects of mainly experimental hyperbaric oxygen therapy. The therapeutic window for the treatment of perinatal asphyxia is very narrow, but administering hyperbaric oxygen within those days improves outcomes. Several miRNAs (e.g., mir-107) mediate the therapeutic effect of hyperbaric oxygen by modulating the Wnt pathway, inhibiting apoptosis, increasing angiogenesis, or inducing neural stem cells. Combining hyperbaric oxygen therapy with drugs, such as memantine or ephedrine, produced promising results. A separate aspect is the use of preconditioning with hyperbaric oxygen. Overall, preliminary clinical trials with hyperbaric oxygen therapy used in perinatal asphyxia give auspicious results.

Targeting organic cation transporters at the blood-brain barrier to treat ischemic stroke in rats

Drug discovery and development for stroke is challenging as evidenced by few drugs that have advanced beyond a Phase III clinical trial. Memantine is a N-methyl-d-aspartate (NMDA) receptor antagonist that has been shown to be neuroprotective in various preclinical studies. We have identified an endogenous BBB uptake transport system for memantine: organic cation transporters 1 and 2 (Oct1/Oct2). Our goal was to evaluate Oct1/Oct2 as a required BBB mechanism for memantine neuroprotective effects. Male Sprague-Dawley rats (200-250 g) were subjected to middle cerebral artery occlusion (MCAO) for 90 min followed by reperfusion. Memantine (5 mg/kg, i.v.) was administered 2 h following intraluminal suture removal. Specificity of Oct-mediated transport was evaluated using cimetidine (15 mg/kg, i.v.), a competitive Oct1/Oct2 inhibitor. At 2 h post-MCAO, [³H]memantine uptake was increased in ischemic brain tissue. Cimetidine inhibited blood-to-brain uptake of [³H]memantine, which confirmed involvement of an Oct-mediated transport mechanism. Memantine reduced post-MCAO infarction and brain edema progression as well as improved neurological outcomes during post-stroke recovery. All positive effects of memantine were attenuated by co-administration of cimetidine, which demonstrates that Oct1/Oct2 transport is required for memantine to exert neuroprotective effects in ischemic stroke. Furthermore, Oct1/Oct2-mediated transport was shown to be the dominant mechanism for memantine brain uptake in the MCAO model despite a concurrent increase in paracellular "leak." These novel and translational findings provide mechanistic evidence for the critical role of BBB transporters in CNS delivery of stroke therapeutics, information that can help such drugs advance in clinical trials.

Polygalasaponin F protects hippocampal neurons against glutamate-induced cytotoxicity

Excess extracellular glutamate leads to excitotoxicity, which induces neuronal death through the overactivation of N-methyl-D-aspartate receptors (NMDARs). Excitotoxicity is thought to be closely related to various acute and chronic neurological disorders, such as stroke and Alzheimer’s disease. Polygalasaponin F (PGSF) is a triterpenoid saponin monomer that can be isolated from Polygala japonica, and has been reported to protect cells against apoptosis. To investigate the mechanisms underlying the neuroprotective effects of PGSF against glutamate-induced cytotoxicity, PGSF-pretreated hippocampal neurons were exposed to glutamate for 24 hours. The results demonstrated that PGSF inhibited glutamate-induced hippocampal neuron death in a concentration-dependent manner and reduced glutamate-induced Ca²⁺ overload in the cultured neurons. In addition, PGSF partially blocked the excess activity of NMDARs, inhibited both the downregulation of NMDAR subunit NR2A expression and the upregulation of NMDAR subunit NR2B expression, and upregulated the expression of phosphorylated cyclic adenosine monophosphate-responsive element-binding protein and brain-derived neurotrophic factor. These findings suggest that PGSF protects cultured hippocampal neurons against glutamate-induced cytotoxicity by regulating NMDARs. The study was approved by the Institutional Animal Care Committee of Nanchang University (approval No. 2017-0006) on December 29, 2017.

Plasma Levels of Occludin and Claudin-5 in Acute Stroke Are Correlated with the Type and Location of Stroke but Not with the Neurological State of Patients-Preliminary Data

The blood–brain barrier is the structure (BBB), which isolates the central nervous system from the external environmental. During a stroke, the BBB gets damaged, which is accompanied by changes in the concentrations and distributions of claudin-5, occludin, ZO-1, and other building blocks of the BBB. The aim of this study was to assess the concentrations of selected components of the BBB—occludin, claudin-5, and zonulin (ZO-1)—and to define a potential relationship between the concentrations of these three substances and the type of stroke, the location and extent of the infarct focus, the neurological/functional status in the acute phase of the disease, and the patient’s clinical profile. Methods: In this prospective study, we qualified patients with first-in-life stroke. All patients were analyzed according to: the presence of comorbidities, type of stroke (OCSP), treatment type in the first day of hospitalization, hemorrhagic transformation of infarct focus (ECASS), neurological status on the first day of stroke (NIHSS), functional status (mRS) on the ninth day of disease. In all patients, the plasma concentrations of claudin-5, occludin, and ZO-1 on the first day of stroke were examined and next, the mean concentrations were analyzed and compared between subgroups created on the basis of demographical and clinical features. Results: The mean concentration of occludin was significantly higher in patients with partial anterior cerebral infarct (PACI) compared to patients with posterior cerebral infarct (POCI; 1.03 vs. 0.66 ng/mL; p = 0.009) and in patients with location of ischemic stroke in the carotid artery supply compared with in the vertebrobasilar supply (respectively: 1.036 vs. 0.660 ng/mL; p = 0.009). The mean concentration of claudin 5 was significantly higher in patients with PACI compared to patients with POCI (0.37 vs. 0.21 ng/mL; p = 0.011) and in patients with location of ischemic stroke in the carotid artery supply in comparison with vertebrobasilar supply (respectively: 0.373 vs. 0.249 ng/mL; p = 0.011). The differences in mean occludin and claudin 5 concentrations between female and male were statistically not significant, similarly between patients < 65 years and older. A significantly higher mean concentration of zonulin was observed in patients > 65 years of age compared to younger patients (0.59 vs. 0.48 ng/mL; p = 0.010) and in patients with arterial hypertension compared to patients without the disease (0.63 ng/mL vs. 0.26 ng/mL; p = 0.026). There were no statistically significant relationships between the concentration of occludin, claudin 5, and zonulin and the neurological status according to the NIHSS on the first day of stroke. Conclusions: The location of stroke in the anterior part of the brain’s blood supply is associated with high blood levels of occludin and claudin 5 in the acute phase of stroke. The blood concentration of occludin is significantly lower in lacunar stroke comparing to this in non-lacunar stroke. Old age and arterial hypertension correlate positively with the concentration of zonulin 1 in acute stroke. There is no relationship between the blood levels of occludin, claudin 5, and zonulin 1 on the first day of stroke and the neurological and functional status in the acute phase of the disease.

Hyperbaric Oxygen Treatment Improves Intestinal Barrier Function After Spinal Cord Injury in Rats

Intestinal barrier dysfunction is often observed clinically after spinal cord injury (SCI) and seriously affects long-term quality of life. Hyperbaric oxygen (HBO) treatment has been proved to promote barrier function recovery after injury, but the influence of HBO on intestinal barrier function following SCI is unclear. We aimed to investigate the effect and mechanisms of HBO treatment on intestinal barrier function by measuring the level of tight junction (TJ) proteins and the Ras homolog (Rho)/Rho-associated coiled-coil forming protein kinase (ROCK) signaling pathway. SCI model was established in rats, and the animals were randomly assigned into three groups: sham-operation group (SH), SCI group and SCI+HBO group. In the SCI+HBO group, the rats inhaled 100% O₂ for 1 h at 2.0 atmospheres absolute pressure (ATA) once per day after surgery. Neurological function and intestinal permeability were assessed after surgery, and the jejunum tissue was excised for histological and intestinal barrier function evaluations. The protein levels of TJ and the Rho/ROCK signaling pathway were also measured. The results showed that in the SCI group, intestinal mucosal injury score, intestinal permeability, and levels of Rho and ROCK1 were higher, and TJ proteins occludin and ZO-1 were lower than those in the SH group (P < 0.01). HBO treatment significantly inhibited the expression of Rho and ROCK1, increased occludin and ZO-1 expression, decreased intestinal permeability, and alleviated intestinal mucosal injury as compared with the SCI group (P < 0.05, P < 0.01). The SCI+HBO group showed higher Basso-Beattie-Bresnahan (BBB) scores relative to the SCI group on postoperative days 7 and 14 (P < 0.01). There was a significant negative correlation between BBB score and intestinal mucosal injury score in rats after HBO treatment (P < 0.05). We concluded from this study that HBO treatment promoted the expression of TJ proteins possibly through inhibiting Rho/ROCK signaling pathway, which protected the intestinal barrier function and improved the intestinal permeability after SCI in rats.

The effects of hyperbaric oxygen therapy on the brain with middle cerebral artery occlusion

Middle cerebral artery occlusion (MCAO) causes focal cerebral hypoperfusion, resulting in cerebral ischemia or ischemic stroke. The main therapeutic approach is to restore an adequate blood flow to the brain via the process of reperfusion. However, rapid reperfusion can itself aggravate brain damage; this adverse effect is known as ischemic/reperfusion (I/R) injury. The pathological conditions that occur after cerebral ischemia and cerebral I/R are microvascular injury, blood-brain barrier dysfunction, post-ischemic inflammation, increased oxidative stress/reactive oxygen species, and a reduction in neuronal survival, leading to brain infarction. Animal and clinical studies on hyperbaric oxygen therapy (HBOT) have recently been carried out, and there is evidence of positive effects on neurological outcomes after cerebral ischemia. However, some evidence has shown that HBOT may not affect the functional recovery after ischemic injury. This review describes the current evidence, both in vivo and clinical data, regarding the potential benefits of HBOT after MCAO and cerebral I/R injury. The contrary data are also discussed to verify the effectiveness of HBOT in stroke outcomes.

Acute and chronic effects of single dose memantine after controlled cortical impact injury in adult rats

BACKGROUND

Altered glutamatergic neurotransmission after traumatic brain injury (TBI) contributes to excitotoxic cell damage and death. Prevention or suppression of such changes is a desirable goal for treatment of TBI. Memantine (3,5-dimethyl-1-adamantanamine), an uncompetitive NMDA receptor antagonist with voltage-dependent open channel blocking kinetics, was reported to be neuroprotective in preclinical models of excitotoxicity, brain ischemia, and in TBI when administered prophylactically, immediately, or within minutes after injury.

METHODS

The current study examined effects of memantine administered by single intraperitoneal injection to adult male rats at a more clinically relevant delay of one hour after moderate-severe controlled cortical impact (CCI) injury or sham surgery. Histopathology was assessed on days 1, 7, 21, and 90, vestibulomotor function (beam balance and beam walk) was assessed on days 1-5 and 71-75, and spatial memory (Morris water maze test, MWM) was assessed on days 14-21 and 83-90 after CCI injury or sham surgery.

RESULTS

When administered at 10 mg/kg, but not 2.5 or 5 mg/kg, memantine preserved cortical tissue and reduced neuronal degeneration 1 day after injury, and attenuated loss of synaptophysin immunoreactivity in the hippocampus 7 days after injury. No effects of 10 mg/kg memantine were observed on histopathology at 21 and 90 days after CCI injury or sham surgery, or on vestibulomotor function and spatial memory acquisition assessed during any of the testing periods. However, 10 mg/kg memantine resulted in trends for improved search strategy in the MWM memory retention probe trial.

CONCLUSIONS

Administration of memantine at a clinically-relevant delay after moderate-severe CCI injury has beneficial effects on acute outcomes, while more significant improvement on subacute and chronic outcomes may require repeated drug administration or its combination with another therapy.

The Effects of Memantine on Glutamic Receptor-Associated Nitrosative Stress in a Traumatic Brain Injury Rat Model

BACKGROUND

The main aim of this study is to elucidate whether the neuroprotective effect of memantine, a noncompetitive N-methyl-d-aspartate receptor 2B (NR2B) antagonist, affects neuronal nitrosative stress, apoptosis, and NR2B expression and improves functional outcomes.

METHODS

Immediately after the onset of fluid percussion traumatic brain injury (TBI), anesthetized male Sprague-Dawley rats were divided into sham-operated, TBI + vehicle, and TBI + memantine groups. TBI rats were treated with a memantine intraperitoneal injection dose of 20 mg/kg intraperitoneally and then 1 mg/kg every 12 hours intraperitoneally for 6 doses. The motor function, proprioception, infarction volume, and neuronal apoptosis were then measured. Immunofluorescence was used to evaluate astrogliosis, microgliosis, nitrosative stress, and NR2A and NR2B expression in cortical cells. All the parameters were assessed 72 hours after TBI.

RESULTS

Compared with the sham-operated controls, the TBI-induced motor and proprioception deficits, and increased infraction volume after TBI were significantly attenuated by memantine therapy. The TBI-induced neuronal apoptosis, astrogliosis, and microgliosis, the numbers of neuronal NO synthase and 3-nitro-l-tyrosine expression in neurons, and inducible NO synthase expression in microglia and astrocyte cells in the ischemic cortex after TBI were significantly improved by memantine therapy. Simultaneously, without affecting the NR2A expression in neuronal cells, the NR2B expression significantly decreased after memantine therapy, as evaluated by an immunofluorescence stain.

CONCLUSIONS

Intraperitoneal injection of memantine in the acute stage may ameliorate TBI in rats by affecting NR2B expression and decreasing neuronal apoptosis and nitrosative stress in the injured cortex. These effects might represent 1 mechanism by which functional recovery occurred.

Differential gene expression profiles between two subtypes of ischemic stroke with blood stasis syndromes

Ischemic stroke is a cerebrovascular thrombotic disease with high morbidity and mortality. Qi deficiency blood stasis (QDBS) and Yin deficiency blood stasis (YDBS) are the two major subtypes of ischemic stroke according to the theories of traditional Chinese medicine. This study was conducted to distinguish these two syndromes at transcriptomics level and explore the underlying mechanisms. Male rats were randomly divided into three groups: sham group, QDBS/MCAO group and YDBS/MCAO group. Morphological changes were assessed after 24 h of reperfusion. Microarray analysis with circulating mRNA was then performed to identify differential gene expression profile, gene ontology and pathway enrichment analyses were carried out to predict the gene function, gene co-expression and pathway networks were constructed to identify the hub biomarkers, which were further validated by western blotting and Tunel staining analysis. Three subsets of dysregulated genes were acquired, including 445 QDBS-specific genes, 490 YDBS-specific genes and 1676 blood stasis common genes. Our work reveals for the first time that T cell receptor, MAPK and apoptosis pathway were identified as the hub pathways based on the pathway networks, while Nfκb1, Egfr and Casp3 were recognized as the hub genes by co-expression networks. This research helps contribute to a clearer understanding of the pathological characteristics of ischemic stroke with QDBS and YDBS syndrome, the proposed biomarkers might provide insight into the accurate diagnose and proper treatment for ischemic stroke with blood stasis syndrome.

Combining hypobaric hypoxia or hyperbaric oxygen postconditioning with memantine reduces neuroprotection in 7-day-old rat hypoxia-ischemia

BACKGROUND

Perinatal hypoxia-ischemia causes brain injury in neonates, but a fully successful treatment to prevent changes in the brain has yet to be developed. The aim of this study was to evaluate the effect of combining memantine treatment with HBO (2.5 ATA) or HH (0.47 ATA) on neonatal hypoxia-ischemia brain injury.

METHODS

7-day old rats were subjected to hypoxia-ischemia (H-I) and treated with combination of memantine and HBO or HH. The brain damage was evaluated by examination of infarct area and the number of apoptotic cells in CA1 region of hippocampus. Additionally, the level of reactive oxygen species (ROS) was measured.

RESULTS

Memantine, HBO or HH postconditioning applied at short time (1-6h) after H-I, and repeated for two subsequent days, resulted in significant neuroprotection. The reduction in ipsilateral hemisphere weight deficit and in the size of infarct area was observed 14days after H-I. A reduction in apoptosis and ROS level was also observed. Combining memantine with HBO or HH resulted in a loss of neuroprotection.

CONCLUSIONS

Our results show that, combining HBO or HH postconditioning with memantine produce no additive increase in the neuroprotective effect. On the contrary, combining the treatments resulted in lower neuroprotection in comparison to the effects of memantine, HBO or HH alone.

Memantine mediates neuroprotection via regulating neurovascular unit in a mouse model of focal cerebral ischemia

AIMS

Memantine is a low-moderate affinity and uncompetitive N-methyl-d-aspartate receptor (NMDAR) antagonist, which is also a potential neuroprotectant in acute ischemic stroke for its particular action profiles. The present study was to reveal the mechanisms involved in the neuroprotection of memantine.

MAIN METHODS

We used a mouse model of permanent focal cerebral ischemia via middle cerebral artery occlusion to verify our hypothesis. 2,3,5-Triphenyltetrazolium chloride staining was used to compare infarct size. The amount of astrocytes and the somal volume of the microglia cell body were analyzed by immunohistochemistry and stereological estimates. Western blotting was used to determine the protein expressions.

KEY FINDINGS

Memantine prevented cerebral ischemia-induced brain infarct and neuronal injury, and reduced oxygen-glucose deprivation-induced cortical neuronal apoptosis. Moreover, memantine reduced the amount of the damaged astrocytes and over activated microglia after 24h of ischemia. In the early phase of ischemia, higher production of MMP-9 was observed, and thereby collagen IV was dramatically disrupted. Meanwhile, the post-synaptic density protein 95(PSD-95) was also severely cleavaged. Memantine decreased MMP-9 secretion, prevented the degradation of collagen IV in mouse brain. PSD-95 cleavage was also inhibited by memantine.

SIGNIFICANCE

These results suggested that memantine exerted neuroprotection effects in acute ischemic brain damage, partially via improving the functions of neurovascular unit. Taking all these findings together, we consider that memantine might be a promising protective agent against ischemic stroke.

Phenotype-dependent alteration of pathways and networks reveals a pure synergistic mechanism for compounds treating mouse cerebral ischemia

AIM

Our previous studies have showed that ursodeoxycholic acid (UA) and jasminoidin (JA) effectively reduce cerebral infarct volume in mice. In this study we explored the pure synergistic mechanism of these compounds in treatment of mouse cerebral ischemia, which was defined as synergistic actions specific for phenotype variations after excluding interference from ineffective compounds.

METHODS

Mice with focal cerebral ischemia were treated with UA, JA or a combination JA and UA (JU). Concha margaritifera (CM) was taken as ineffective compound. Cerebral infarct volume of the mice was determined, and the hippocampi were taken for microarray analysis. Particular signaling pathways and biological functions were enriched based on differentially expressed genes, and corresponding networks were constructed through Ingenuity Pathway Analysis.

RESULTS

In phenotype analysis, UA, JA, and JU significantly reduced the ischemic infarct volume with JU being superior to UA or JA alone, while CM was ineffective. As a result, 4 pathways enriched in CM were excluded. Core pathways in the phenotype-positive groups (UA or JA) were involved in neuronal homeostasis and neuropathology. JU-contributing pathways included all UA-contributing and the majority (71.7%) of JA-contributing pathways, and 10 new core pathways whose effects included inflammatory immunity, apoptosis and nervous system development. The functions of JU group included all functions of JA group, the majority (93.1%) of UA-contributing functions, and 3 new core functions, which focused on physiological system development and function.

CONCLUSION

The pure synergism between UA and JA underlies 10 new core pathways and 3 new core functions, which are involved in inflammation, immune responses, apoptosis and nervous system development.

Poststroke depression as a factor adversely affecting the level of oxidative damage to plasma proteins during a brain stroke

Poststroke depression, the second most serious psychosomatic complication after brain stroke, leads to delay of the rehabilitation process and is associated with an increased disability and cognitive impairment along with increase in term mortality. Research into the biochemical changes in depression is still insufficiently described. The aim of our study was therefore to evaluate the possible association between plasma protein oxidative/nitrative damages and the development of poststroke depression. We evaluated oxidative/nitrative modifications of specific proteins by measurement of 3-nitrotyrosine and carbonyl groups levels using ELISA test. Additionally, we checked differences in proteins thiol groups by spectrophotometric assay based on reaction between DTNB and thiols. We also evaluated catalase activity in erythrocytes measured as ability to decompose H₂O₂. Correlation analysis was performed using Spearman's rank. We observed significant (P < 0.001) differences in all oxidative/nitrative stress parameters in brain stroke patients compared to healthy group. Our research shows that oxidative damage of proteins is correlated with the degree of poststroke depression, while nitrative changes do not show any relationship. We demonstrate a positive correlation between the concentration of carbonyl groups and the Geriatric Depression Scale and a negative correlation between the degree of depression and the concentration of -SH groups or catalase activity.