Oxygen therapy reduces secondary hemorrhage after thrombolysis in thromboembolic cerebral ischemia

The Effect of Inhaled Oxygen on Postpartum Hemorrhage: A Systematic Review and Meta-Analysis

Background

Postpartum Hemorrhage (PPH) is a significant problem that can increase the risk of maternal mortality. Previous studies investigated the effect of Inhaled Oxygen (IO) on PPH. They found some conflicting results. Thus, the current systematic review and meta-analysis aimed to determine the effect of IO on PPH.

Materials and Methods

Randomized trials were searched according to the PRISMA framework until the end of November 2022 in Web of Science, PubMed, Scopus, and Cochrane Library databases. Statistical analyses were performed in the STATA v. 14 software. I2 statistic was applied to assess heterogeneity between studies. The random effect model, sample size, and mean and standard deviation of each group were applied to report the pooled effect size. Version 2 of the Cochrane risk-of-bias tool for randomized trials (RoB 2) was used to evaluate the risk of bias in the included studies. Finally, five articles were included in the meta-analysis. Two and three studies reported the mean of bleeding after vaginal delivery during one- and two-hours oxygen therapy, respectively.

Results

Results showed that IO significantly reduced bleeding by 38.91 mL in the intervention group compared to routine care (WMD: -38.91, 95%CI: -60.18 to -17.64) after vaginal delivery. In addition, IO during one (WMD: -38.42, 95%CI: -71.62 to -5.22) and two (WMD: -41.93, 95%CI: -60.15 to - 23.71) hours significantly decreased bleeding in the intervention.

Conclusion

According to the present study, IO can significantly reduce PPH in the intervention group compared to routine care. However, more rigorously randomized clinical trials are required to decide better about this issue.

Early hyperbaric oxygen therapy through regulating the HIF-1α signaling pathway attenuates Neuroinflammation and behavioral deficits in a mouse model of Sepsis-associated encephalopathy

BACKGROUND

Sepsis-associated encephalopathy (SAE) presents a significant clinical challenge, associated with increased mortality and healthcare expenses. Hyperbaric oxygen therapy (HBOT), involving inhaling pure or highly concentrated oxygen under pressures exceeding one atmosphere, has demonstrated neuroprotective effects in various conditions. However, the precise mechanisms underlying its protective actions against sepsis-associated brain injury remain unclear. This study aimed to determine whether HBOT protects against SAE and to elucidate the impact of the hypoxia-inducible factor-1α (HIF-1α) signaling pathway on SAE.

METHODS

The experiment consisted of two parts. In the first part, C57BL/6 J male mice were divided into five groups using a random number table method: control group, sham surgery group, sepsis group, HBOT + sepsis group, and HBOT + sham surgery group. In the subsequent part, C57BL/6 J male mice were divided into four groups: sepsis group, HBOT + sepsis group, HIF-1α + HBOT + sepsis group, and HIF-1α + sepsis group. Sepsis was induced via cecal ligation and puncture (CLP). Hyperbaric oxygen therapy was administered at 1 h and 4 h post-CLP. After 24 h, blood and hippocampal tissue were collected for cytokine measurements. HIF-1α, TNF-α, IL-1β, and IL-6 expression were assessed via ELISA and western blotting. Microglial expression was determined by immunofluorescence. Blood-brain barrier permeability was quantified using Evans Blue. Barnes maze and fear conditioning were conducted 14 days post-CLP to evaluate learning and memory.

RESULTS

Our findings reveal that CLP-induced hippocampus-dependent cognitive deficits coincided with elevated HIF-1α and increased TNF-α, IL-1β, and IL-6 levels in both blood and hippocampus. Observable activation of microglial cells in the hippocampus and increased blood-brain barrier (BBB) permeability were also evident. HBOT mitigated HIF-1α, TNF-α, IL-1β, and IL-6 levels, attenuated microglial activation in the hippocampus, and significantly improved learning and memory deficits in CLP-exposed mice. Additionally, these outcomes were corroborated by injecting a lentivirus that overexpressed HIF-1α into the hippocampal region of the mice.

CONCLUSION

HIF-1α escalation induced peripheral and central inflammatory factors, promoting microglial activation, BBB impairment, and cognitive dysfunction. However, HBOT ameliorated these effects by reducing HIF-1α levels in Sepsis-Associated Encephalopathy.

Hemorrhagic Transformation After Tissue Plasminogen Activator Treatment in Acute Ischemic Stroke

Hemorrhagic transformation (HT) is a common complication after thrombolysis with recombinant tissue-type plasminogen activator (rt-PA) in ischemic stroke. In this article, recent research progress of HT in vivo and in vitro studies was reviewed. We have discussed new potential mechanisms and possible experimental models of HT development, as well as possible biomarkers and treatment methods. Meanwhile, we compared and analyzed rodent models, large animal models and in vitro BBB models of HT, and the limitations of these models were discussed. The molecular mechanism of HT was investigated in terms of BBB disruption, rt-PA neurotoxicity and the effect of neuroinflammation, matrix metalloproteinases, reactive oxygen species. The clinical features to predict HT were represented including blood biomarkers and clinical factors. Recent progress in neuroprotective strategies to improve HT after stroke treated with rt-PA is outlined. Further efforts need to be made to reduce the risk of HT after rt-PA therapy and improve the clinical prognosis of patients with ischemic stroke.

Reaction of the Hippocampal Microglia to Hyperbaric Oxygen

We studied the reaction of rat hippocampal microgliocytes to hyperbaric oxygen at a pressure of 5 ata (absolute atmosphere). Immunohistochemical analysis with selective macrophage marker CD68 (ED1) and microglial marker Iba-1 allowed separate analysis of these two cell populations. It was shown that macrophages do not significantly contribute to reactive changes in the total pool of Iba-1⁺ hippocampal cells induced by hyperbaric oxygen.

Responses of matrix metalloproteinases to hyperbaric oxygen treatment: changing for good or ill?

Background: Hyperbaric oxygen (HBO₂) is currently emerging as a promising therapeutic option for diseases involving impaired tissue repair and remodeling. In this regard, HBO₂ has been shown to modulate signaling pathways responsible for matrix metalloproteinases (MMPs) regulation, which makes the MMPs interesting targets for investigation. However, the understanding regarding how HBO₂ treatment affects the expression and activity of the MMP family members in different tissues and diseases needs to be clarified. The precise roles of MMPs in the physiopathology of various tissue repair disorders also remain unclear. Because of potential off-target systemic effects of the HBO₂ on MMPs, researchers and physicians should carefully consider whether their patients could be affected adversely by HBO₂ exposure. Aims: This narrative review provides an overview of MMP biology (structure, function, and regulation) and summarizes available data showing how MMPs respond to HBO₂ in different tissues and pathologies, also highlighting possible mechanisms.

A review on the neuroprotective effects of hyperbaric oxygen therapy

Hyperbaric oxygen therapy, intermittent breathing of 100% oxygen at a pressure upper than sea level, has been shown to be some of the neuroprotective effects and used therapeutically in a wide range of neurological disorders. This review summarizes current knowledge about the neuroprotective effects of hyperbaric oxygen therapy with their molecular mechanisms in different models of neurological disorders.

Angiogenesis and Blood-Brain Barrier Permeability in Vascular Remodeling after Stroke

Angiogenesis, the growth of new blood vessels, is a natural defense mechanism helping to restore oxygen and nutrient supply to the affected brain tissue following an ischemic stroke. By stimulating vessel growth, angiogenesis may stabilize brain perfusion, thereby promoting neuronal survival, brain plasticity, and neurologic recovery. However, therapeutic angiogenesis after stroke faces challenges: new angiogenesis-induced vessels have a higher than normal permeability, and treatment to promote angiogenesis may exacerbate outcomes in stroke patients. The development of therapies requires elucidation of the precise cellular and molecular basis of the disease. Microenvironment homeostasis of the central nervous system is essential for its normal function and is maintained by the blood-brain barrier (BBB). Tight junction proteins (TJP) form the tight junction (TJ) between vascular endothelial cells (ECs) and play a key role in regulating the BBB permeability. We demonstrated that after stroke, new angiogenesis-induced vessels in peri-infarct areas have abnormally high BBB permeability due to a lack of major TJPs in ECs. Therefore, promoting TJ formation and BBB integrity in the new vessels coupled with speedy angiogenesis will provide a promising and safer treatment strategy for improving recovery from stroke. Pericyte is a central neurovascular unite component in vascular barriergenesis and are vital to BBB integrity. We found that pericytes also play a key role in stroke-induced angiogenesis and TJ formation in the newly formed vessels. Based on these findings, in this article, we focus on regulation aspects of the BBB functions and describe cellular and molecular special features of TJ formation with an emphasis on role of pericytes in BBB integrity during angiogenesis after stroke.

Occludin degradation makes brain microvascular endothelial cells more vulnerable to reperfusion injury in vitro

Intracerebral hemorrhage is the most dangerous complication in tPA thrombolytic therapy for ischemic stroke, which occurs as a consequence of endothelial cell death at the blood-brain barrier (BBB) during thrombolytic reperfusion. We have previously shown that cerebral ischemia-induced rapid occludin degradation and BBB disruption. Here we demonstrated an important role of occludin degradation in facilitating the evolution of ischemic endothelial cells toward death. Cultured brain microvascular endothelial cells (bEnd.3 cells) were exposed to oxygen-glucose deprivation (OGD) or incubated with occludin siRNA or occludin AAV to achieve an occludin deficiency or over-expression status before exposing to reoxygenation (R) or TNF-α treatment. Cell death was assessed by measuring lactate dehydrogenase release, TUNEL staining, and flow cytometry analysis. Inhibition of OGD-induced occludin degradation with SB-3CT or over-expression of occludin with occludin AAV both significantly attenuated OGD/R-induced apoptosis and pyroptosis in bEnd.3 cells. Consistently, knockdown of occludin with siRNA potentiated TNF-α-induced apoptosis, supporting an important role of occludin integrity in endothelial cell survival. Similar results were observed for pyroptosis, in which occludin knockdown with siRNA led to a significant augmentation of cytokines secretion, inflammasome activation, and pyroptosis occurrence in TNF-α-treated bEnd.3 cells. Lastly, up-regulation of c-Yes, PI3K/AKT, and ERK concurrently occurred with occludin degradation after OGD/R or TNF-α treatment, and the level of these proteins were further increased when inhibition of occludin degradation or over-expression of occludin. These data indicate that occludin degradation inflicted during ischemia makes BBB endothelial cells more vulnerable to reperfusion-associated stress stimuli.

Endothelial Targets in Stroke: Translating Animal Models to Human

Cerebral ischemia (stroke) induces injury to the cerebral endothelium that may contribute to parenchymal injury and worsen outcome. This review focuses on current preclinical studies examining how to prevent ischemia-induced endothelial dysfunction. It particularly focuses on targets at the endothelium itself. Those include endothelial tight junctions, transcytosis, endothelial cell death, and adhesion molecule expression. It also examines how such studies are being translated to the clinic, especially as adjunct therapies for preventing intracerebral hemorrhage during reperfusion of the ischemic brain. Identification of endothelial targets may prove valuable in a search for combination therapies that would specifically protect different cell types in ischemia.

Protecting the ischaemic penumbra as an adjunct to thrombectomy for acute stroke

After ischaemic stroke, brain damage can be curtailed by rescuing the 'ischaemic penumbra' - that is, the severely hypoperfused, at-risk but not yet infarcted tissue. Current evidence-based treatments involve restoration of blood flow so as to salvage the penumbra before it evolves into irreversibly damaged tissue, termed the 'core'. Intravenous thrombolysis (IVT) can salvage the penumbra if given within 4.5 h after stroke onset; however, the early recanalization rate is only ~30%. Direct removal of the occluding clot by mechanical thrombectomy considerably improves outcomes over IVT alone, but despite early recanalization in > 80% of cases, ~50% of patients who receive this treatment do not enjoy functional independence, usually because the core is already too large at the time of recanalization. Novel therapies aiming to 'freeze' the penumbra - that is, prevent core growth until recanalization is complete - hold potential as adjuncts to mechanical thrombectomy. This Review focuses on nonpharmacological approaches that aim to restore the physiological balance between oxygen delivery to and oxygen demand of the penumbra. Particular emphasis is placed on normobaric oxygen therapy, hypothermia and sensory stimulation. Preclinical evidence and early pilot clinical trials are critically reviewed, and future directions, including clinical translation and trial design issues, are discussed.

T Cells Prevent Hemorrhagic Transformation in Ischemic Stroke by P-Selectin Binding

Objective- Hemorrhagic transformation is a serious complication of ischemic stroke after recanalization therapies. This study aims to identify mechanisms underlying hemorrhagic transformation after cerebral ischemia/reperfusion. Approach and Results- We used wild-type mice and Selplg^-/- and Fut7^-/- mice defective in P-selectin binding and lymphopenic Rag2^-/- mice. We induced 30-minute or 45-minute ischemia by intraluminal occlusion of the middle cerebral artery and assessed hemorrhagic transformation at 48 hours with a hemorrhage grading score, histological means, brain hemoglobin content, or magnetic resonance imaging. We depleted platelets and adoptively transferred T cells of the different genotypes to lymphopenic mice. Interactions of T cells with platelets in blood were studied by flow cytometry and image stream technology. We show that platelet depletion increased the bleeding risk only after large infarcts. Lymphopenia predisposed to hemorrhagic transformation after severe stroke, and adoptive transfer of T cells prevented hemorrhagic transformation in lymphopenic mice. CD4⁺ memory T cells were the subset of T cells binding P-selectin and platelets through functional P-selectin glycoprotein ligand-1. Mice defective in P-selectin binding had a higher hemorrhagic score than wild-type mice. Adoptive transfer of T cells defective in P-selectin binding into lymphopenic mice did not prevent hemorrhagic transformation. Conclusions- The study identifies lymphopenia as a previously unrecognized risk factor for secondary hemorrhagic transformation in mice after severe ischemic stroke. T cells prevent hemorrhagic transformation by their capacity to bind platelets through P-selectin. The results highlight the role of T cells in bridging immunity and hemostasis in ischemic stroke.

Thrombus Permeability on Dynamic CTA Predicts Good Outcome after Reperfusion Therapy

BACKGROUND AND PURPOSE

Thrombus permeability assessed on conventional CTA is associated with neurologic outcome in patients with acute ischemic stroke. We aimed to investigate whether dynamic CTA can improve the accuracy of thrombus permeability assessment and its predictive value for outcome.

MATERIALS AND METHODS

We reviewed consecutive patients with acute ischemic stroke who had occlusion of the M1 segment of the middle artery cerebral artery and underwent pretreatment perfusion CT. Thrombus permeability, determined by thrombus attenuation increase (TAI), was assessed on 26-phase dynamic CTA derived from perfusion CT. TAI_max was defined as the maximum TAI among phases; TAI_peak, as TAI of peak arterial phase; TAI_con, as TAI on phase 13. Good outcome was defined as a 3-month mRS score of ≤2.

RESULTS

One hundred four patients were enrolled in the final analysis. The median TAI_max, TAI_peak, and TAI_con were 30.1 HU (interquartile range, 13.0-50.2 HU), 9.5 HU (interquartile range, -1.6-28.7 HU), and 6.6 HU (interquartile range, -5.1-24.4 HU), respectively. Multivariable regression analyses showed that TAI_max (OR = 1.027; 95% CI, 1.007-1.048; P = .008), TAI_peak (OR = 1.029; 95% CI, 1.005-1.054; P = .020), and TAI_con (OR = 1.026; 95% CI, 1.002-1.051; P = .037) were independently associated with good outcome. The areas under the ROC curve of TAI_max, TAI_peak, and TAI_con in predicting good outcome were 0.734, 0.701, and 0.658, respectively.

CONCLUSIONS

Thrombus permeability assessed on dynamic CTA could be a better predictor of outcome after reperfusion therapy than that assessed on conventional single-phase CTA.

Pretreatment with rivaroxaban attenuates stroke severity in rats by a dual antithrombotic and anti-inflammatory mechanism

Stroke outcome is more favourable in patients receiving oral anticoagulants compared with non-anticoagulated patients. The reasons for this “stroke-attenuating” property of oral anticoagulants are largely unknown. This study examined whether prestroke anticoagulation with rivaroxaban, a novel direct factor Xa inhibitor, influences stroke severity, thrombin-mediated intracerebral thrombus formation and pro-inflammatory processes in a rat model of brain ischaemia/reperfusion injury. Male Wistar rats were anticoagulated with rivaroxaban and subjected to 90 minutes of transient middle cerebral artery occlusion. Infarct size, functional outcome and the occurrence of intracranial haemorrhage (ICH) were assessed until day 7. Thrombin generation was determined by measuring the amount of thrombin/antithrombin complex. Intracerebral thrombus formation was evaluated by histology and Western blot. CD68-immunoreactivity and the expression of cytokines and adhesion molecules were investigated to assess postischaemic inflammation. The integrity of the blood–brain barrier was analysed using fluorescein isothiocyanate-dextran. Rats pretreated with rivaroxaban developed significantly smaller strokes and less severe functional deficits compared with controls. Although rivaroxaban strongly reduced thrombin-mediated thrombus formation, this was not accompanied by an increased risk of ICH. In addition, rivaroxaban dampened the inflammatory response in the ischaemic brain by downregulating ICAM-1 expression and the activation of CD68+-immune cells. In contrast, rivaroxaban had no effect on the integrity of the blood–brain barrier after stroke. Here, we identified reduced thrombo-inflammation as a major determinant of the stroke-protective property of rivaroxaban in rats. Further studies are needed to assess the therapeutic potential of novel oral anticoagulants in the acute phase after a stroke.

β2-Adrenergic Receptor-Mediated HIF-1α Upregulation Mediates Blood Brain Barrier Damage in Acute Cerebral Ischemia

Disruption of the blood brain barrier (BBB) within the thrombolytic time window is an antecedent event to intracerebral hemorrhage in ischemic stroke. Our recent studies showed that 2-h cerebral ischemia induced BBB damage in non-infarcted area and secreted matrix metalloproteinase-2 (MMP-2) accounted for this disruption. However, the factors that affect MMP-2 secretion and regulate BBB damage remains unknown. Since hypoxia-inducible factor-1 alpha (HIF-1α) was discovered as a mater regulator in hypoxia, we sought to investigate the roles of HIF-1α in BBB damage as well as the factors regulating HIF-1α expression in the ischemic brain. in vivo rat middle cerebral artery occlusion (MCAO) and in vitro oxygen glucose deprivation (OGD) models were used to mimic ischemia. Pretreatment with HIF-1α inhibitor YC-1 significantly inhibited 2-h MCAO-induced BBB damage, which was accompanied by suppressed occludin degradation and vascular endothelial growth factor (VEGF) mRNA upregulation. Interestingly, β2-adrenergic receptor (β2-AR) antagonist ICI 118551 attenuated ischemia-induced BBB damage by regulating HIF-1α expression. Double immunostaining showed that HIF-1α was upregulated in ischemic neurons but not in astrocytes andendothelial cells. Of note, HIF-1α inhibition with inhibitor YC-1 or siRNA significantly prevented OGD-induced VEGF upregulation as well as the secretion of VEGF and MMP-2 in neurons. More importantly, blocking β2-AR with ICI 118551 suppressedHIF-1α upregulation in ischemic neurons and attenuated occludin degradation induced by the conditioned media of OGD-treatedneurons. Taken together, blockade of β2-AR-mediated HIF-1α upregulation mediates BBB damage during acute cerebral ischemia. These findings provide new mechanistic understanding of early BBB damage in ischemic stroke and may help reduce thrombolysis-related hemorrhagic complications.

Hyperbaric Oxygen Reduces Infarction Volume and Hemorrhagic Transformation Through ATP/NAD+/Sirt1 Pathway in Hyperglycemic Middle Cerebral Artery Occlusion Rats

BACKGROUND AND PURPOSE

Energy depletion is a critical factor leading to cell death and brain dysfunction after ischemic stroke. In this study, we investigated whether energy depletion is involved in hyperglycemia-induced hemorrhagic transformation after ischemic stroke and determined the pathway underlying the beneficial effects of hyperbaric oxygen (HBO).

METHODS

After 2-hour middle cerebral artery occlusion, hyperglycemia was induced by injecting 50% dextrose (6 mL/kg) intraperitoneally at the onset of reperfusion. Immediately after it, rats were exposed to HBO at 2 atmospheres absolutes for 1 hour. ATP synthase inhibitor oligomycin A, nicotinamide phosphoribosyl transferase inhibitor FK866, or silent mating type information regulation 2 homolog 1 siRNA was administrated for interventions. Infarct volume, hemorrhagic volume, and neurobehavioral deficits were recorded; the level of blood glucose, ATP, and nicotinamide adenine dinucleotide and the activity of nicotinamide phosphoribosyl transferase were monitored; the expression of silent mating type information regulation 2 homolog 1, acetylated p53, acetylated nuclear factor-κB, and cleaved caspase 3 were detected by Western blots; and the activity of matrix metalloproteinase-9 was assayed by zymography.

RESULTS

Hyperglycemia deteriorated energy metabolism and reduced the level of ATP and nicotinamide adenine dinucleotide and exaggerated hemorrhagic transformation, blood-brain barrier disruption, and neurological deficits after middle cerebral artery occlusion. HBO treatment increased the levels of the ATP and nicotinamide adenine dinucleotide and consequently increased silent mating type information regulation 2 homolog 1, resulting in attenuation of hemorrhagic transformation, brain infarction, as well as improvement of neurological function in hyperglycemic middle cerebral artery occlusion rats.

CONCLUSIONS

HBO induced activation of ATP/nicotinamide adenine dinucleotide/silent mating type information regulation 2 homolog 1 pathway and protected blood-brain barrier in hyperglycemic middle cerebral artery occlusion rats. HBO might be promising approach for treatment of acute ischemic stroke patients, especially patients with diabetes mellitus or treated with r-tPA (recombinant tissue-type plasminogen activator).

Co-administration of tissue plasminogen activator and hyperbaric oxygen in ischemic stroke: a continued promise for neuroprotection

Intravenous recombinant tissue-type plasminogen activator (r-tPA, alteplase) remains the recommended therapy for acute ischemic stroke. However, several factors are limiting its practical use. It makes it urgent for us to search more efficient strategies that can save the ischemic neurons, and safely extend the time window, while in the mean time reducing the detrimental effects for stroke thrombolysis. Hyperbaric oxygen therapy (HBOT) is considered to be potentially neuroprotective. Co-administration of r-tPA and HBOT has already been proved to be effective, safe and feasible in myocardial infarction. In this article, we would like to review whether HBOT has any beneficial effects on r-tPA thrombolysis. If there is, what is the underlying possible mechanisms and how to optimize for maximal effects?

Blood Occludin Level as a Potential Biomarker for Early Blood Brain Barrier Damage Following Ischemic Stroke

Concern about intracerebral hemorrhage (ICH) is the primary reason for withholding tPA therapy from patients with ischemic stroke. Early blood brain barrier (BBB) damage is the major risk factor for fatal post-thrombolysis ICH, but rapidly assessing BBB damage before tPA administration is highly challenging. We recently reported that ischemia induced rapid degradation of tight junction protein occludin in cerebromicrovessels. The present study investigates whether the cleaved occludin is released into the blood stream and how blood occludin levels correlate to the extent of BBB damage using a rat model of ischemic stroke. Cerebral ischemia induced a time-dependent increase of blood occludin with a sharp increase at 4.5-hour post-ischemia onset, which concurrently occurred with the loss of occludin from ischemic cerebral microvessels and a massive BBB leakage at 4.5-hour post-ischemia. Two major occludin fragments were identified in the blood during cerebral ischemia. Furthermore, blood occludin levels remained significantly higher than its basal level within the first 24 hours after ischemia onset. Our findings demonstrate that blood occludin levels correlate well with the extent of BBB damage and thus may serve as a clinically relevant biomarker for evaluating the risk of ICH before tPA administration.

Effects of normobaric versus hyperbaric oxygen on cell injury induced by oxygen and glucose deprivation in acute brain slices

Normobaric oxygen (NBO) and hyperbaric oxygen (HBO) are emerging as a possible co-treatment of acute ischemic stroke. Both have been shown to reduce infarct volume, to improve neurologic outcome, to promote endogenous tissue plasminogen activator-induced thrombolysis and cerebral blood flow, and to improve tissue oxygenation through oxygen diffusion in the ischemic areas, thereby questioning the interest of HBO compared to NBO. In the present study, in order to investigate and compare the oxygen diffusion effects of NBO and HBO on acute ischemic stroke independently of their effects at the vascular level, we used acute brain slices exposed to oxygen and glucose deprivation, an ex vivo model of brain ischemia that allows investigating the acute effects of NBO (partial pressure of oxygen (pO₂) = 1 atmospheres absolute (ATA) = 0.1 MPa) and HBO (pO₂ = 2.5 ATA = 0.25 MPa) through tissue oxygenation on ischemia-induced cell injury as measured by the release of lactate dehydrogenase. We found that HBO, but not NBO, reduced oxygen and glucose deprivation-induced cell injury, indicating that passive tissue oxygenation (i.e. without vascular support) of the brain parenchyma requires oxygen partial pressure higher than 1 ATA.

Hyperbaric oxygen increases tissue-plasminogen activator-induced thrombolysis in vitro, and reduces ischemic brain damage and edema in rats subjected to thromboembolic brain ischemia

Recent data have shown that normobaric oxygen (NBO) increases the catalytic and thrombolytic efficiency of recombinant tissue plasminogen activator (rtPA) in vitro, and is as efficient as rtPA at restoring cerebral blood flow in rats subjected to thromboembolic brain ischemia. Therefore, in the present study, we studied the effects of hyperbaric oxygen (HBO) (i) on rtPA-induced thrombolysis in vitro and (ii) in rats subjected to thromboembolic middle cerebral artery occlusion-induced brain ischemia. HBO increases rtPA-induced thrombolysis in vitro to a greater extent than NBO; in addition, HBO treatment of 5-minute duration, but not of 25-minute duration, reduces brain damage and edema in vivo. In line with the facilitating effect of NBO on cerebral blood flow, our findings suggest that 5-minute HBO could have provided neuroprotection by promoting thrombolysis. The lack of effect of HBO exposure of longer duration is discussed.

Hyperbaric oxygen therapy in experimental and clinical stroke

Stroke, which is defined as a neurologic deficit caused by sudden impaired blood supply, has been considered as a common cause of death and disability for decades. The World Health Organization has declared that almost every 5 seconds a new stroke occurs, placing immense socioeconomic burdens. However, the effective and available treatment strategies are still limited. Additionally, the most effective therapy, such as thrombolysis and stenting for ischemic stroke, generally requires a narrow therapeutic time window after the event. A large majority of patients cannot be admitted to hospital and receive these effective treatments for reperfusion timely. Hyperbaric oxygen therapy (HBOT) has been frequently applied and investigated in stroke since 1960s. Numerous basic and clinical studies have shown the beneficial efficacy for neurological outcome after stroke, and meanwhile many underlying mechanisms associated with neuroprotection have been illustrated, such as cerebral oxygenation promotion and metabolic improvement, blood-brain barrier protection, anti-inflammation and cerebral edema, intracranial pressure modulation, decreased oxidative-stress and apoptosis, increased vascular and neural regeneration. However, HBOT in human stroke is still not sufficiently evidence-based, due to the insufficient randomized double-blind controlled clinical studies. To date, there are no uniform criteria for the dose and session duration of HBOT in different strokes. Furthermore, the additional effect of HBOT combined with drugs and other treatment strategies are being investigated recently. Therefore, more experimental and clinical research is imperative to identify the mechanisms more clearly and to explore the best protocol of HBOT in stroke treatment.

Effects of stroke severity and treatment duration in normobaric hyperoxia treatment of ischemic stroke

In order to improve clinical trial design and translation of normobaric oxygen (NBO) treatment of ischemic stroke, NBO treatment parameters need to be better understood. This study investigated NBO treatment efficacy at two different stroke severities and two NBO treatment durations in rats. For the 60-min middle cerebral artery occlusion (MCAO), NBO treatment for 25 min and 150 min were studied. For the 90-min MCAO, NBO treatment for 55 min and 150 min were studied. Cerebral blood flow (CBF), apparent diffusion coefficients (ADC) and T2 MRI were acquired during occlusion prior to treatment, after reperfusion, and 48h after MCAO. The effects of NBO treatment on lesion volumes, and CBF, ADC and T2 of ischemic core, perfusion-diffusion mismatch and normal tissue were analyzed longitudinally. The major findings were: i) NBO treatment was effective in both groups of stroke severities, salvaging similar percentage of initial abnormal ADC tissue, and ii) NBO treatments continued after reperfusion were more beneficial than NBO treatment during occlusion alone for both MCAO groups. These findings underscore the importance of the effects of NBO duration and stroke severity on treatment outcomes.

Normobaric hyperoxia markedly reduces brain damage and sensorimotor deficits following brief focal ischaemia

'True' transient ischaemic attacks are characterized not only clinically, but also radiologically by a lack of corresponding changes on magnetic resonance imaging. During a transient ischaemic attack it is assumed that the affected tissue is penumbral but rescued by early spontaneous reperfusion. There is, however, evidence from rodent studies that even brief focal ischaemia not resulting in tissue infarction can cause extensive selective neuronal loss associated with long-lasting sensorimotor impairment but normal magnetic resonance imaging. Selective neuronal loss might therefore contribute to the increasingly recognized cognitive impairment occurring in patients with transient ischaemic attacks. It is therefore relevant to consider treatments to reduce brain damage occurring with transient ischaemic attacks. As penumbral neurons are threatened by markedly constrained oxygen delivery, improving the latter by increasing arterial O2 content would seem logical. Despite only small increases in arterial O2 content, normobaric oxygen therapy experimentally induces significant increases in penumbral O2 pressure and by such may maintain the penumbra alive until reperfusion. Nevertheless, the effects of normobaric oxygen therapy on infarct volume in rodent models have been conflicting, although duration of occlusion appeared an important factor. Likewise, in the single randomized trial published to date, early-administered normobaric oxygen therapy had no significant effect on clinical outcome despite reduced diffusion-weighted imaging lesion growth during therapy. Here we tested the hypothesis that normobaric oxygen therapy prevents both selective neuronal loss and sensorimotor deficits in a rodent model mimicking true transient ischaemic attack. Normobaric oxygen therapy was applied from the onset and until completion of 15 min distal middle cerebral artery occlusion in spontaneously hypertensive rats, a strain representative of the transient ischaemic attack-prone population. Whereas normoxic controls showed normal magnetic resonance imaging but extensive cortical selective neuronal loss associated with microglial activation (present both at Day 14 in vivo and at Day 28 post-mortem) and marked and long-lasting sensorimotor deficits, normobaric oxygen therapy completely prevented sensorimotor deficit (P < 0.02) and near-completely Day 28 selective neuronal loss (P < 0.005). Microglial activation was substantially reduced at Day 14 and completely prevented at Day 28 (P = 0.002). Our findings document that normobaric oxygen therapy administered during ischaemia nearly completely prevents the neuronal death, microglial inflammation and sensorimotor impairment that characterize this rodent true transient ischaemic attack model. Taken together with the available literature, normobaric oxygen therapy appears a promising therapy for short-lasting ischaemia, and is attractive clinically as it could be started at home in at-risk patients or in the ambulance in subjects suspected of transient ischaemic attack/early stroke. It may also be a straightforward adjunct to reperfusion therapies, and help prevent subtle brain damage potentially contributing to long-term cognitive and sensorimotor impairment in at-risk populations.

Therapeutic effect of tPA in ischemic stroke is enhanced by its combination with normobaric oxygen and hypothermia or ethanol

BACKGROUND AND PURPOSE

Our lab has previously elucidated the neuroprotective effects of normobaric oxygen (NBO) and ethanol (EtOH) in ischemic stroke. The present study further evaluated the effect of EtOH or hypothermia (Hypo) in the presence of low concentration of NBO and determined whether EtOH can substitute hypothermia in a more clinically relevant autologous embolus rat stroke model in which reperfusion was established by tissue-type plasminogen activator (t-PA).

METHODS

At 1h of middle cerebral artery occlusion (MCAO) by an autologous embolus, rats received t-PA. In addition, at the same time, ischemic animals were treated with either EtOH (1.0 g/kg) or hypothermia (33°C for 3h) in combination with NBO (60% for 3h). Extent of neuroprotection was assessed by apoptotic cell death measured by ELISA and Western immunoblotting analysis for pro- (AIF, activated Caspase-3, Bax) and anti-apoptotic (Bcl-2) protein expression at 3 and 24h of reperfusion induced by t-PA administration.

RESULTS

Compared to ischemic rats treated only with t-PA, animals with NBO, hypothermia or EtOH had significantly reduced apoptotic cell death by 32.5%, 43.1% and 36.0% respectively. Furthermore, combination therapy that included NBO+EtOH or NBO+Hypo with t-PA exhibited a much larger decline (p<0.01) in the cell death by 71.1% and 73.6%, respectively. Similarly, NBO+EtOH or NBO+Hypo treatment in addition to t-PA enhanced beneficial effects on both pro- and anti-apoptotic protein expressions as compared to other options.

CONCLUSIONS

Neuroprotection after stroke can be enhanced by combination treatment with either EtOH or hypothermia in the presence of t-PA and 60% NBO. Because the effects produced by EtOH and hypothermia are comparable, their mechanism of action may be not only similar but also could be interchangeable in future clinical trials.

Effects of high-pressure oxygen therapy on brain tissue water content and AQP4 expression in rabbits with cerebral hemorrhage

To investigate the effects of different atmosphere absolutes (ATA) of high-pressure oxygen (HPO) on brain tissue water content and Aquaporin-4 (AQP4) expression in rabbits with cerebral hemorrhage. 180 New Zealand white rabbits were selected and randomly divided into normal group (n = 30), control group (n = 30) and cerebral hemorrhage group (n = 120), and cerebral hemorrhage group was divided into group A, B, C and D with 30 rabbits in each group. The groups received 1.0, 1.8, 2.0 and 2.2 ATA of HPO treatments, respectively. Ten rabbits in each group were killed at first, third and fifth day to detect the brain tissue water content and change of AQP4 expression. In cerebral hemorrhage group, brain tissue water content and AQP4 expression after model establishment were first increased, then decreased and reached the maximum on third day (p < 0.05). Brain tissue water content and AQP4 expression in control group and cerebral hemorrhage group were significantly higher than normal group at different time points (p < 0.05). In contrast, brain tissue water content and AQP4 expression in group C were significantly lower than in group A, group B, group D and control group (p < 0.05). In control group, AQP4-positive cells significantly increased after model establishment, which reached maximum on third day, and positive cells in group C were significantly less than in group A, group B and group D. We also found that AQP4 expression were positively correlated with brain tissue water content (r = 0.719, p < 0.05) demonstrated by significantly increased AQP4 expression along with increased brain tissue water content. In conclusion, HPO can decrease AQP4 expression in brain tissue of rabbits with cerebral hemorrhage to suppress the progression of brain edema and promote repairing of injured tissue. 2.0 ATA HPO exerts best effects, which provides an experimental basis for ATA selection of HPO in treating cerebral hemorrhage.

Docosahexaenoic acid attenuates hyperglycemia-enhanced hemorrhagic transformation after transient focal cerebral ischemia in rats

Hemorrhagic transformation (HT) is a feared complication of cerebral ischemic infarction, especially following the use of thrombolytic therapy. In this study, we examined whether docosahexaenoic acid (DHA; 22:6n-3), an omega-3 essential fatty acid family member, can protect the brain from injury and whether DHA can decrease the risk of HT enhanced by hyperglycemia after focal ischemic injury. Male Sprague-Dawley rats were injected with 50% dextrose (6ml/kg intraperitoneally) to induce hyperglycemia 10min before 1.5h of filament middle cerebral artery occlusion (MCAO) was performed. Treatment with DHA (10mg/kg) 5min before reperfusion reduced HT and further improved the 7-day neurological outcome. It also reduced infarct volume, which is consistent with the restricted DWI and T2WI hyperintensive area. Reduced Evans Blue extravasation and increased expression of collagen IV indicated the improved integrity of the blood-brain barrier (BBB) in DHA-treated rats. Moreover, DHA reduced the expression of the intercellular adhesion molecule-1 (ICAM-1) in the ischemic injured brain. Therefore, we conclude that DHA attenuated hyperglycemia-enhanced HT and improved neurological function by preserving the integrity of BBB and reducing inflammation.

Matrix metalloproteinases as therapeutic targets for stroke

Matrix metalloproteinases (MMPs) are important in injury and recovery in ischemic injury. They are proteolytic enzymes that degrade all components of the extracellular matrix (ECM). They are secreted in a latent form, protecting the cell from damage, but once activated induce injury prior to rapid inactivation by four tissue inhibitors to metalloproteinases (TIMPs). Normally the constitutive enzymes, MMP-2 and membrane type MMP (MMP-14), are activated in a spatially specific manner and act close to the site of activation, while the inducible enzymes, MMP-3 and MMP-9, become active through the action of free radicals and other enzymes during neuroinflammation. Because of the complex nature of the interactions with tissues during development, injury and repair, the MMPs have multiple roles, participating in the injury process in the early stages and contributing to recovery during the later stages. This dual role complicates the planning of treatment strategies. This article is part of a Special Issue entitled SI: Cell Interactions In Stroke.

Endothelial dysfunction abrogates the efficacy of normobaric hyperoxia in stroke

Hyperoxia has been uniformly efficacious in experimental focal cerebral ischemia. However, pilot clinical trials have showed mixed results slowing its translation in patient care. To explain the discordance between experimental and clinical outcomes, we tested the impact of endothelial dysfunction, exceedingly common in stroke patients but under-represented in experimental studies, on the neuroprotective efficacy of normobaric hyperoxia. We used hyperlipidemic apolipoprotein E knock-out and endothelial nitric oxide synthase knock-out mice as models of endothelial dysfunction, and examined the effects of normobaric hyperoxia on tissue perfusion and oxygenation using high-resolution combined laser speckle and multispectral reflectance imaging during distal middle cerebral artery occlusion. In normal wild-type mice, normobaric hyperoxia rapidly and significantly improved tissue perfusion and oxygenation, suppressed peri-infarct depolarizations, reduced infarct volumes, and improved neurological function. In contrast, normobaric hyperoxia worsened perfusion in ischemic brain and failed to reduce infarct volumes or improve neurological function in mice with endothelial dysfunction. These data suggest that the beneficial effects of hyperoxia on ischemic tissue oxygenation, perfusion, and outcome are critically dependent on endothelial nitric oxide synthase function. Therefore, vascular risk factors associated with endothelial dysfunction may predict normobaric hyperoxia nonresponders in ischemic stroke. These data may have implications for myocardial and systemic circulation as well.

Hyperbaric oxygen therapy in acute ischemic stroke: a review

Stroke, also known as cerebrovascular disease, is a common and serious neurological disease, which is also the fourth leading cause of death in the United States so far. Hyperbaric medicine, as an emerging interdisciplinary subject, has been applied in the treatment of cerebral vascular diseases since the 1960s. Now it is widely used to treat a variety of clinical disorders, especially hypoxia-induced disorders. However, owing to the complex mechanisms of hyperbaric oxygen (HBO) treatment, the therapeutic time window and the undefined dose as well as some common clinical side effects (such as middle ear barotrauma), the widespread promotion and application of HBO was hindered, slowing down the hyperbaric medicine development. In August 2013, the US Food and Drug Administration declared artery occlusion as one of the 13 specific indications for HBO therapy. This provides opportunities, to some extent, for the further development of hyperbaric medicine. Currently, the mechanisms of HBO therapy for ischemic stroke are still not very clear. This review focuses on the potential mechanisms of HBO therapy in acute ischemic stroke as well as the time window.

Ischemic neurons activate astrocytes to disrupt endothelial barrier via increasing VEGF expression

Blood-brain barrier (BBB) disruption occurring within the first few hours of ischemic stroke onset is closely associated with hemorrhagic transformation following thrombolytic therapy. However, the mechanism of this acute BBB disruption remains unclear. In the neurovascular unit, neurons do not have direct contact with the endothelial barrier; however, they are highly sensitive and vulnerable to ischemic injury, and may act as the initiator for disrupting BBB when cerebral ischemia occurs. Herein, we employed oxygen-glucose deprivation (OGD) and an in vitro BBB system consisting of brain microvascular cells and astrocytes to test this hypothesis. Neurons (CATH.a cells) were exposed to OGD for 3-h before co-culturing with endothelial monolayer (bEnd 3 cells), or endothelial cells plus astrocytes (C8-D1A cells). Incubation of OGD-treated neurons with endothelial monolayer alone did not increase endothelial permeability. However, when astrocytes were present, the endothelial permeability was significantly increased, which was accompanied by loss of occludin and claudin-5 proteins as well as increased vascular endothelial growth factor (VEGF) secretion into the conditioned medium. Importantly, all these changes were abolished when VEGF was knocked down in astrocytes by siRNA. Our findings suggest that ischemic neurons activate astrocytes to increase VEGF production, which in turn induces endothelial barrier disruption.

Anticoagulation with dabigatran does not increase secondary intracerebral haemorrhage after thrombolysis in experimental cerebral ischaemia

Dabigatran etexilate (DE) has recently been introduced for stroke prevention in atrial fibrillation, but management of acute ischaemic stroke during therapy with DE is a challenge. Thrombolysis is contraindicated because of a presumed increased risk of intracerebral haemorrhagic complications. We studied in different ischaemia models whether DE increases secondary haemorrhage after thrombolysis. C57BL/6 mice were anticoagulated with high-dose DE or warfarin. After 2 hour (h) or 3 h transient filament MCAO, rt-PA was injected. At 24 h after MCAO, secondary haemorrhage was quantified using a macroscopic haemorrhage score and haemoglobin spectrophotometry. Post-ischaemic blood-brain-barrier (BBB) damage was assessed using Evans blue. To increase the validity of findings, the duration of anticoagulation was prolonged in mice (5 x DE over 2 days), and the effect of DE after thrombolysis was also examined in thromboembolic MCAO in rats.Pretreatment with warfarin resulted in significantly more secondary haemorrhage (mean haemorrhage score 2.6 ± 0.2) compared to non-anticoagulated animals (1.7 ± 0.3) and DE (9 mg/kg, 1.6 ± 0.3) in 2 h ischaemia. Also after a 3 h period of ischaemia, haemorrhage was more severe in animals anticoagulated with warfarin compared to 9 mg/kg DE and non-anticoagulated control. Prolonged or enteral dabigatran pretreatment led to identical results. Also, thrombolysis after thromboembolic MCAO in rats did not induce more severe bleeding in DE-treated animals. Mice pretreated with warfarin had higher BBB permeability and increased activation of matrix-metalloproteinase 9. In conclusion, DE does not increase the risk of secondary haemorrhage after thrombolysis in various rodent models of ischaemia and reperfusion. The implications of this finding for stroke patients have to be determined in the clinical setting.

Method parameters' impact on mortality and variability in rat stroke experiments: a meta-analysis

Background

Even though more than 600 stroke treatments have been shown effective in preclinical studies, clinically proven treatment alternatives for cerebral infarction remain scarce. Amongst the reasons for the discrepancy may be methodological shortcomings, such as high mortality and outcome variability, in the preclinical studies. A common approach in animal stroke experiments is that A) focal cerebral ischemia is inflicted, B) some type of treatment is administered and C) the infarct sizes are assessed. However, within this paradigm, the researcher has to make numerous methodological decisions, including choosing rat strain and type of surgical procedure. Even though a few studies have attempted to address the questions experimentally, a lack of consensus regarding the optimal methodology remains.

Methods

We therefore meta-analyzed data from 502 control groups described in 346 articles to find out how rat strain, procedure for causing focal cerebral ischemia and the type of filament coating affected mortality and infarct size variability.

Results

The Wistar strain and intraluminal filament procedure using a silicone coated filament was found optimal in lowering infarct size variability. The direct and endothelin methods rendered lower mortality rate, whereas the embolus method increased it compared to the filament method.

Conclusions

The current article provides means for researchers to adjust their middle cerebral artery occlusion (MCAo) protocols to minimize infarct size variability and mortality.

Serum leptin levels decrease after permanent MCAo in the rat and remain unaffected by delayed hyperbaric oxygen therapy

Hyperbaric oxygen therapy (HBOT), referring to the medical use of oxygen at a level higher than atmospheric pressure, exerts neuroprotective effects after ischemic stroke via various mechanisms. It has been demonstrated that HBOT modulates the synthesis and degradation of hormones. Leptin, an adipose derived hormone, has been found to confer neuroprotection following experimental stroke. However, it is not known whether HBOT alters leptin concentrations after permanent middle cerebral artery occlusion (pMCAo) in the rat. In this present study, we aimed to investigate the effect of HBOT on the serum concentration of leptin in rats subjected to pMCAo. HBOT was initiated 48 hrs after experimental pMCAo, at 2.5 atmospheres absolutes with 100% oxygen, 1 hr a day for 10 consecutive days. Body weight, neurobehavioral deficits and infarct size were evaluated. Blood was collected on day 1 and day 16 following HBOT. Serum leptin concentrations were measured with ELISA. Delayed HBOT reduced infarct size and improved neurobehavioral scores. Decreased serum levels of leptin were found in treated and untreated pMCAo animals, compared to the sham group on day 1 (P > 0.05) and day 16 (P < 0.05). However, no statistical significance was found between HBOT and the air group. We concluded that the neuroprotective effects of delayed HBOT in pMCAo rats were unlikely to be exerted through changes in the serum concentration of leptin.

Normobaric hyperoxia combined with minocycline provides greater neuroprotection than either alone in transient focal cerebral ischemia

Normobaric hyperoxia (NBO), which maintains penumbral oxygenation, reduces brain injury during cerebral ischemia, and minocycline, a tetracycline derivative, reduces reperfusion injury, including inflammation, apoptosis and matrix metalloproteinases (MMPs) activation. Since they have different mechanisms of action, we hypothesized that combining them would provide greater neuroprotection. To test the hypothesis, we evaluated the neuroprotective effects of the combination of NBO with minocycline. Male Sprague-Dawley rats were exposed to NBO (95% O(2)) or normoxia (21% O(2)) during 90-min filament occlusion of the middle cerebral artery, followed by 48 h of reperfusion. Minocycline (3 mg/kg) or vehicle was intravenously administered to rats 15 min after reperfusion onset. Treatment with NBO and minocycline alone resulted in 36% and 30% reductions in infarction volume, respectively. When the two treatments were combined, there was a 68% reduction in infarction volume. The combination therapy also significantly reduced hemispheric swelling, which was absent with monotherapy. In agreement with its greater neuro- and vasoprotection, the combination therapy showed greater inhibitory effects on MMP-2/9 induction, occludin degradation, caspase-3 and -9 activation and apoptosis inducing factor (AIF) induction in ischemic brain tissue. Our results show that NBO plus minocycline effectively reduces brain injury in transient focal cerebral ischemia with protection due to inhibition on MMP-2/9-mediated occludin degradation and attenuation of caspase-dependent and independent apoptotic pathways.

Delayed hyperbaric oxygen therapy induces cell proliferation through stabilization of cAMP responsive element binding protein in the rat model of MCAo-induced ischemic brain injury

Treatments that could extend the therapeutic window of opportunity for stroke patients are urgently needed. Early administration of hyperbaric oxygen therapy (HBOT) has been proven neuroprotective in the middle cerebral artery occlusion (MCAo) in rodents. Our aim was to determine: 1) whether delayed HBOT after permanent MCAo (pMCAo) can still convey neuroprotection and restorative cell proliferation, and 2) whether these beneficial effects rely on HBO-induced activation of protein phosphatase-1γ (PP1-γ) leading to a decreased phosphorylation and ubiquitination of CREB and hence its stabilization. The experiments were performed in one hundred thirty-two male Sprague-Dawley rats with the body weight ranging from 240 to 270 g. Permanent MCAo was induced with the intraluminal filament occluding the right middle cerebral artery (MCA). In the first experiment, HBOT (2.5 ATA, 1h daily for 10 days) was started 48 h after pMCAo. Neurobehavioral deficits and infarct size as well as cyclic AMP response element-binding protein (CREB) expression and BrdU-DAB staining in the hippocampus and the peri-infarct region were evaluated on day 14 and day 28 post-MCAo. In the second experiment, HBOT (2.5 ATA, 1h) was started 3h after pMCAo. The effects of CREB siRNA or PP1-γ siRNA on HBO-induced infarct size alterations and target protein expression were studied. HBOT started with 48 h delay reduced infarct size, ameliorated neurobehavioral deficits and increased protein expression of CREB, resulting in increased cell proliferations in the hippocampus and peri-infarct region, on day 14 and day 28 post-MCAo. In the acute experiment pMCAo resulted in cerebral infarction and functional deterioration and reduced brain expression of PP1-γ, which led to increased phosphorylation and ubiquitination of CREB 24h after MCAo. However HBOT administered 3h after ischemia reversed these molecular events and resulted in CREB stabilization, infarct size reduction and neurobehavioral improvement. Gene silencing with CREB siRNA or PP1-γ siRNA reduced acute beneficial effects of HBO. In conclusion, delayed daily HBOT presented as potent neuroprotectant in pMCAo rats, increased CREB expression and signaling activity, and bolstered regenerative type cell proliferation in the injured brain. As shown in the acute experiment these effects of HBO were likely to be mediated by reducing ubiquitin-dependent CREB degradation owing to HBO-induced activation of PP1γ.

Standards and pitfalls of focal ischemia models in spontaneously hypertensive rats: with a systematic review of recent articles

We reviewed the early development of various focal ischemia models in spontaneously hypertensive rats (SHR), and summarized recent reports on this topic. Among 6 focal ischemia models established in divergent substrains of SHR, distal middle cerebral artery occlusion is the most frequently used and relevant method of focal ischemia in the light of penumbra concept. We performed an online PubMed search (2001–2010), and identified 118 original articles with focal ischemia in SHR. Physiological parameters such as age, body weight, and even blood pressure were often neglected in the literature: the information regarding the physiological parameters of SHR is critical, and should be provided within the methodology section of all articles related to stroke models in SHR. Although the quality of recent studies on neuroprotective strategy is improving, the mechanisms underlying the protection should be more clearly recognized so as to facilitate the translation from animal studies to human stroke. To overcome the genetic heterogeneity in substrains of SHR, new approaches, such as a huge repository of genetic markers in rat strains and the congenic strategy, are currently in progress.

Spatio-temporal course of macrophage-like cell accumulation after experimental embolic stroke depending on treatment with tissue plasminogen activator and its combination with hyperbaric oxygenation

Inflammation following ischaemic stroke attracts high priority in current research, particularly using human-like models and long-term observation periods considering translational aspects. The present study aimed on the spatio-temporal course of macrophage-like cell accumulation after experimental thromboembolic stroke and addressed microglial and astroglial reactions in the ischaemic border zone. Further, effects of tissue plasminogen activator (tPA) as currently best treatment for stroke and the potentially neuroprotective co-administration of hyperbaric oxygen (HBO) were investigated. Rats underwent middle cerebral artery occlusion and were assigned to control, tPA or tPA+HBO. Twenty-four hours, 7, 14 and 28 days were determined as observation time points. The accumulation of macrophage-like cells was semiquantitatively assessed by CD68 staining in the ischaemic area and ischaemic border zone, and linked to the clinical course. CD11b, ionized calcium binding adaptor molecule 1 (Iba), glial fibrillary acidic protein (GFAP) and Neuronal Nuclei (NeuN) were applied to reveal delayed glial and neuronal alterations. In all groups, the accumulation of macrophage-like cells increased distinctly from 24 hours to 7 days post ischaemia. tPA+HBO tended to decrease macrophage-like cell accumulation at day 14 and 28. Overall, a trend towards an association of increased accumulation and pronounced reduction of the neurological deficit was found. Concerning delayed inflammatory reactions, an activation of microglia and astrocytes with co-occurring neuronal loss was observed on day 28. Thereby, astrogliosis was found circularly in contrast to microglial activation directly in the ischaemic area. This study supports previous data on long-lasting inflammatory processes following experimental stroke, and additionally provides region-specific details on glial reactions. The tendency towards a decreasing macrophage-like cell accumulation after tPA+HBO needs to be discussed critically since neuroprotective properties were recently ascribed to long-term inflammatory processes.

Spatio-temporal course of macrophage-like cell accumulation after experimental embolic stroke depending on treatment with tissue plasminogen activator and its combination with hyperbaric oxygenation

Inflammation following ischaemic stroke attracts high priority in current research, particularly using human-like models and long-term observation periods considering translational aspects. The present study aimed on the spatio-temporal course of macrophage-like cell accumulation after experimental thromboembolic stroke and addressed microglial and astroglial reactions in the ischaemic border zone. Further, effects of tissue plasminogen activator (tPA) as currently best treatment for stroke and the potentially neuroprotective co-administration of hyperbaric oxygen (HBO) were investigated. Rats underwent middle cerebral artery occlusion and were assigned to control, tPA or tPA+HBO. Twenty-four hours, 7, 14 and 28 days were determined as observation time points. The accumulation of macrophage-like cells was semiquantitatively assessed by CD68 staining in the ischaemic area and ischaemic border zone, and linked to the clinical course. CD11b, ionized calcium binding adaptor molecule 1 (Iba), glial fibrillary acidic protein (GFAP) and Neuronal Nuclei (NeuN) were applied to reveal delayed glial and neuronal alterations. In all groups, the accumulation of macrophage-like cells increased distinctly from 24 hours to 7 days post ischaemia. tPA+HBO tended to decrease macrophage-like cell accumulation at day 14 and 28. Overall, a trend towards an association of increased accumulation and pronounced reduction of the neurological deficit was found. Concerning delayed inflammatory reactions, an activation of microglia and astrocytes with co-occurring neuronal loss was observed on day 28. Thereby, astrogliosis was found circularly in contrast to microglial activation directly in the ischaemic area. This study supports previous data on long-lasting inflammatory processes following experimental stroke, and additionally provides region-specific details on glial reactions. The tendency towards a decreasing macrophage-like cell accumulation after tPA+HBO needs to be discussed critically since neuroprotective properties were recently ascribed to long-term inflammatory processes.

Matrix metalloproteinase-2-mediated occludin degradation and caveolin-1-mediated claudin-5 redistribution contribute to blood-brain barrier damage in early ischemic stroke stage

Blood-brain barrier (BBB) disruption occurs early enough to be within the thrombolytic time window, and this early ischemic BBB damage is closely associated with hemorrhagic transformation and thus emerging as a promising target for reducing the hemorrhagic complications of thrombolytic stroke therapy. However, the mechanisms underlying early ischemic BBB damage remain poorly understood. Here, we investigated the early molecular events of ischemic BBB damage using in vitro oxygen-glucose deprivation (OGD) and in vivo rat middle cerebral artery occlusion (MCAO) models. Exposure of bEND3 monolayer to OGD for 2 h significantly increased its permeability to FITC-labeled dextran and promoted the secretion of metalloproteinase-2 and -9 (MMP-2/9) and cytosolic translocation of caveolin-1 (Cav-1). This same OGD treatment also led to rapid degradation of tight junction protein occludin and dissociation of claudin-5 from the cytoskeleton, which contributed to OGD-induced endothelial barrier disruption. Using selective MMP-2/9 inhibitor SB-3CT (2-[[(4-phenoxyphenyl)sulfonyl]methyl]-thiirane) or their neutralizing antibodies or Cav-1 siRNA, we found that MMP-2 was the major enzyme mediating OGD-induced occludin degradation, while Cav-1 was responsible for claudin-5 redistribution. The interaction between Cav-1 and claudin-5 was further confirmed by coimmunoprecipitation. Consistent with these in vitro findings, we observed fluorescence tracer extravasation, increased gelatinolytic activity, and elevated interstitial MMP-2 levels in ischemic subcortical tissue after 2 h MCAO. Moreover, occludin protein loss and claudin-5 redistribution were detected in ischemic cerebromicrovessels. These data indicate that cerebral ischemia initiates two rapid parallel processes, MMP-2-mediated occludin degradation and Cav-1-mediated claudin-5 redistribution, to cause BBB disruption at early stroke stages relevant to acute thrombolysis.

Prothrombolytic action of normobaric oxygen given alone or in combination with recombinant tissue-plasminogen activator in a rat model of thromboembolic stroke

The potential benefit of 100 vol% normobaric oxygen (NBO) for the treatment of acute ischemic stroke patients is still a matter of debate. To advance this critical question, we studied the effects of intraischemic normobaric oxygen alone or in combination with recombinant tissue-plasminogen activator (rtPA) on cerebral blood flow and ischemic brain damage and swelling in a clinically relevant rat model of thromboembolic stroke. We show that NBO provides neuroprotection by achieving cerebral blood flow restoration equivalent to 0.9 mg/kg rtPA through probable direct interaction and facilitation of the fibrinolytic properties of endogenous tPA. In contrast, combined NBO and rtPA has no neuroprotective effect on ischemic brain damage despite producing cerebral blood flow restoration. These results 1) by providing a new mechanism of action of NBO highlight together with previous findings the way by which intraischemic NBO shows beneficial action; 2) suggest that NBO could be an efficient primary care therapeutic intervention for patients eligible for rtPA therapy; 3) indicate that NBO could be an interesting alternative for patients not eligible for rtPA therapy; and 4) caution the use of NBO in combination with rtPA in acute stroke patients.

Hyperbaric oxygen therapy: can it prevent irradiation-induced necrosis?

Radiosurgery is an important non-invasive procedure for the treatment of tumors and vascular malformations. However, in addition to killing target tissues, cranial irradiation induces damage to adjacent healthy tissues leading to neurological deterioration in both pediatric and adult patients, which is poorly understood and insufficiently treatable. To minimize irradiation damage to healthy tissue, not the optimal therapeutic irradiation dose required to eliminate the target lesion is used but lower doses. Although the success rate of irradiation surgery is about 95%, 5% of patients suffer problems, most commonly neurological, that are thought to be a direct consequence of irradiation-induced inflammation. Although no direct correlation has been demonstrated, the appearance and disappearance of inflammation that develops following irradiation commonly parallel the appearance and disappearance of neurological side effects that are associated with the neurological function of the irradiated brain regions. These observations have led to the hypothesis that brain inflammation is causally related to the observed neurological side effects. Studies indicate that hyperbaric oxygen therapy (HBOT) applied after the appearance of irradiation-induced neurological side effects reduces the incidence and severity of those side effects. This may result from HBOT reducing inflammation, promoting angiogenesis, and influencing other cellular functions thereby suppressing events that cause the neurological side effects. However, it would be significantly better for the patient if rather than waiting for neurological side effects to become manifest they could be avoided. This review examines irradiation-induced neurological side effects, methods that minimize or resolve those side effects, and concludes with a discussion of whether HBOT applied following irradiation, but before manifestation of neurological side effects may prevent or reduce the appearance of irradiation-induced neurological side effects.